Title of Invention	LIMITED SLIP DIFFERENTIAL AND ENGAGEMENT SENSING MECHANISM THEREFOR
Abstract	A differential having means (35) operable to limit rotation of an output guar (23) relative to gear case (11), and actuation means (55) for actuating the rotation limiting means, for an unactuated (FIG.1) to an actuated condition (FIG.4). The rotation limiting means includes a member (47), toward one axial end of the gear case and moveable between a first position, the unactuated condition of said rotation limiting means and a second position, the actuated condition. A sensor assembly is adjacent the one axial end of the gear case and includes a sensor element (71) and a wall-like member between the rotation limiting means and the actuation means. The wall-like member includes a non-ferromagnetic portion (73) between the sensor and the moveable member. Movement between the first and second positions results in a corresponding change in the electromagnetic flux (F) coupling the sensor element and the moveable member.

Title of Invention

LIMITED SLIP DIFFERENTIAL AND ENGAGEMENT SENSING MECHANISM THEREFOR

Abstract

A differential having means (35) operable to limit rotation of an output guar (23) relative to gear case (11), and actuation means (55) for actuating the rotation limiting means, for an unactuated (FIG.1) to an actuated condition (FIG.4). The rotation limiting means includes a member (47), toward one axial end of the gear case and moveable between a first position, the unactuated condition of said rotation limiting means and a second position, the actuated condition. A sensor assembly is adjacent the one axial end of the gear case and includes a sensor element (71) and a wall-like member between the rotation limiting means and the actuation means. The wall-like member includes a non-ferromagnetic portion (73) between the sensor and the moveable member. Movement between the first and second positions results in a corresponding change in the electromagnetic flux (F) coupling the sensor element and the moveable member.

Full Text	TITLE OF INVENTION [0001] Limited Slip Differential And Engagement Sensing Mechanism Therefor. EtACKGROUND OF THE DISCLOSURE [0002] The present invention relates to fraction modifying differentials, and more particularly, to such differentials of the type in which the differential action nay be retarded, and possibly even prevented ("locked"), in response to some sort of an input, for example, a mechanical input or an electrical input signal. [0003] Furthermore, the present invention relates to engagement sensing nechanisms and systems of the type which may be utilized to sense a change- of-state within a traction modifying differential, for example, a change between an unlocked condition and a locked condition. [0004] Traction modifying differentials of the type to which the present invention relates typically include a gear case defining a gear chamber, and disposed therein, a differential gear set including at least one input pinion gear, and a pair of output side gears, The present invention will be described in connection with a differential of the bevel gear type, although those skilled in the art will understand that the invention is not so limited, and could be utilized h connection with differentials having other gearing types, such as helical or planetary. Typically, a clutch pack is disposed between at least one of the side gears and an adjacent surface of the gear case, such that the clutch pack or locking mechanism is operable to limit relative rotation between the gear case and the one side gear. In most differentials of the type described, engaging the clutch pack or locking mechanism (to retard differentiation) is achieved by one of several different approaches. \|0005] In one approach, a "locking differential" of the type illustrated and described in U.S. Patent No, Re 28,004, assigned to the assignee of the present invention and incorporated herein by reference, the clutch pack is normally disengaged. When one of the wheels begins to spin out, relative to the other wheel, a speed sensitive mechanism senses the speed differential between the wheels, and by means of a cam and ramp mechanism, locks the . clutch pack solid. In the incorporated patent, the speed sensitive mechanism comprises a fly-weight mechanism, the output of which comprises the mechanical "input", in response to which the differential gearing is locked, [0006] U.S. Patent No. 5,019,021, also assigned to the assignee of the present invention and incorporated herein by reference, illustrates another approach to retarding differentiation. This patent illustrates and describes a " imited slip differential" in which the loading on the clutch pack may be varied in response to an external electrical input signal, thus varying the amount of slip within the clutch pack. Therefore, the amount of bias torque transmitted from c ne side gear to the other is also varied in response to changes in the external electric input signal. As is well known to those skilled in the art, in a limited slip differential, there is typically a certain amount of "slip" or speed differential, between the two side gears whenever the vehicle encounters (ess than optimum faction conditions. In the above-incorporated patent, the "input" to the differential is the electrical Input signal, but within the differential, there is smother "input" which is the axial movement of one of the plates of a ball ramp actuator, the axial movement of which varies the loading on the clutch pack in a Manner which is now generally well known to those skilled In the art. [0007] Finally, in U.S. Pat. No. 6,551,209, also assigned to the assignee of the present invention and incorporated herein by reference, there is illustrated a different approach to a "locking differential". In the above-incorporated patent, there is illustrated and described a locking differential in which there is no friction-type clutch pack, but instead, a mechanical locking arrangement. In the differential of the cited '209 patent, there is a ball ramp actuator which is able, in response to an electrical input signal, to move a series of pins into mating openings in the differential side gear, thus locking the side gear relative to the d fferential gear case. For purposes of the present invention, the movement of the pins, toward or away from the side gear, to achieve either a locked condition o" an unlocked condition, respectively, is also considered an "input" in regard to a means for limiting rotation of an output gear relative to a gear case in a differential. [0008] Thus, it may be seen, from a review of the above-described types of limited slip and locking differentials, that there are a number of different mechanisms known to those skilled in the art which are commonly used to limit (retard), or lock, the relative rotation between a differential gear case and one of the output side gears. However, it should be noted that most of the known, prior art limited slip and locking differential arrangements, and especially those which have been commercialized by the assignee of the present invention, have in common the presence of some sort of member which moves axiaily, in connection with the operation of the mechanism which achieves the slip limiting or locking function within the differentia). [D009] More recently, an increasing percentage of vehicles (especially passenger cars and light trucks) are incorporating some sort of stability, or traction, or safety system Into the drive train. Examples of such systems would include a traction control system (TCS), an anti-skid braking system (ABS), and am electronic stability program (ESP), it is quite common, and desirable, for such systems to include some sort of traction modifying device, and preferably, an electrically-actuated limited slip or locking differential. In order for these types of systems to operate most effectively and safely, it is important for the control logic of the system to receive some sort of feedback signal from the differential, whereby the control logic can know, at any given instant, whether ihe differential is in an actuated (locked) condition, or in an unactuated (unlocked) condition. \|0010] Unfortunately, sensing the occurrence of a locked condition (or an unlocked condition) in a locking differential, or sensing an Increasing clutch engagement (or a decreasing clutch engagement) in a limited slip differential involves sensing something such as the axial movement of a member within a differential gear case which, typically, is rotating within a stationary outer housing. One seemingly obvious way of mounting a sensor on a rotating differential case is to fix the sensor to the exterior of the case, and transmit the generated electrical signal from the differential to the vehicle microprocessor by means of slip rings, Unfortunately, such an arrangement is typically not feasible. For most differential Installations, nothing can be attached to the exterior of (the outer diameter of) the differential case (or extend radially cutward therefrom), because, in the axle assembly plant, it must be possible to slide the ring gear over the case outer diameter, and bolt the ring gear to the case flange. [3011] Another hindrance encountered by those skilled in the art, in attempting to develop arrangements for sensing the "change-of-state" in a limited slip or locking differentia! is the fact that the sensing system utilized needs to be able to survive and operate effectively in a fairly severe environment. For example, the sensing mechanism and the overall system need to be able to operate predictably over a broad temperature range (e.g., f"om about -40 degrees Celsius to about 190 degrees Celsius). Also the sensing mechanism must be able to operate while submersed in a petrochemical-based lubricant, without any adverse effect upon the accuracy of the sensing system "output" signal, indicating the current state of the differential. E3RIEF SUMMARY OF THE INVENTION [0012] Accordingly, it Is an object of "the present invention to provide an improved differential gear mechanism, and an improved sensing mechanism and assembly for use therein, which will overcome the above-described p'oblems of the prior art. [0013] It is a further object of the present invention to provide such an inproved differential gear mechanism and improved sensing system for use therein which achieves the above-stated object, but without any substantial redesign of the underlying differential mechanism, and with no substantial increase in the overall package size of the differential gear mechanism. [0014] It is a more specific object of the present invention to provide such an improved differential gear mechanism, and sensing system therefor, in which the occurrence of a change in the state of the differential can be sensed utilizing the axial movement, within the differential, of a member which is already a required part of the differential mechanism, rather than requiring some sort of additional "target" member. [0015] The above and other objects of the invention are accomplished by the provision of an improved differential gear mechanism including a gear case cefinlng an axis of rotation, and a gear chamber, differential gearing being cisposed In the gear chamber including at least one input gear and first and second output gears. The mechanism includes means operable to limit rotation cf the first output gear relative to the gear case, and actuation means for sctuating the rotation limiting means, the actuation means.being operable in response to an input, to move the rotation limiting means from an unactuated condition to an actuated condition. The rotation limiting means includes a member, disposed toward one axial end of the gear case and moveable in the direction of the axis of rotation between a first position corresponding to the unactuated condition of the rotation limiting means, and a second position corresponding to the actuated condition. [0016] The improved differential gear mechanism Is characterized by a siensor assembly being disposed adjacent the one axial end of the gear case and including a sensor element and a wall-like member disposed axially between the rotation limiting means and the actuation means. The wall-like member includes a non-ferromagnetic portion disposed axially between the sensor element and the moveable member, whereby movement of the moveable member between the first and the second positions results in a Corresponding change in the electromagnetic flux coupling the sensor element and the moveable member. [0017] In accordance with another aspect of the present invention, there Is provided a mechanism including a case defining an axis and a chamber, the mechanism including an actuation means for actuating the mechanism, the actuation means being operable in response to an input to move the mechanism from an unactuated condition to an actuated condition. The mechanism includes an axially moveable member disposed toward one axial end of the case and moveable in the direction of the axis between a first position corresponding to the unactuated condition of the mechanism, and a second position corresponding to the actuated condition, [0018] The improved mechanism is characterized by a sensor assembly being disposed adjacent the one axial end of the case and including a sensor element and a wall-like member disposed axially between the mechanism and the actuation means. The wall-like member includes a non-ferromagnetic portion disposed axially between the sensor element and the axially moveable nember, whereby movement of the axially moveable member between the first smd the second positions results in a corresponding change in the electromagnetic flux coupling the sensor element and the axially moveable member. The sensor element comprises an electromagnetic coil disposed adjacent the one axial end of the case and disposed generally concentrically about the axis. BRIEF DESCRIPTION OF THE DRAWINGS [0019] FIG. 1 is an axial cross-section of a locking differential made in accordance with the teachings of the present invention, in an unactuated, unlocked condition. [0020] FIG. 2 Is an enlarged, fragmentary, axial cross-section, similar to FIG. 1, but taken on a plane different than that of FIG. 1. [0021] FIG. 3 is a fragmentary, exploded, perspective view of a portion of the differential gear mechanism shown in FIGS. 1 and 2. [0022] FIG. 4 is an enlarged, fragmentary, somewhat schematic axial cross- ssction, similar to FIG. 2, illustrating one important aspect of the present invention. [0023] FIG. 5 is a graph of Voltage versus Time, illustrating an important relationship utilized, in one embodiment, by the sensing mechanism of the present invention, [0024] FIG. 6 is an electrical circuit schematic representing a portion of an embodiment of control circuitry which may be used with the engagement sensing mechanism of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0025] Referring now to the drawings, which are not intended to limit the invention, FIG. 1 is an axial cross-section of a slip-limiting differential, and more specifically, of a locking differential including the present invention. The specific construction and operation of differentials of the general type to which t'lis invention relates, and of the specific type illustrated in FIG. 1, may be better understood by reference to the above-incorporated patents. Specifically, the overall construction and function of the locking differential shown in FIG. 1 Is quite similar to that illustrated and described in above-incorporated U.S. Patent No. 5,551,209. [0026]' However, as has already been noted, the usefulness of the present invention is not restricted to only locking differentials, but could be also advantageous when used on limited slip differentials, at least on those including some sort of a member within the differential which moves axially within the differential case such that the movement of the member is representative of a change between a slipping condition and a slip-limiting condition. Furthermore, the use of the present invention is not restricted to any particular configuration o differential, except as is specifically noted in the appended claims. Finally, it should be noted that, in one aspect, the present invention comprises a sensing assembly and system which may be used effectively to sense the change of state of an associated mechanism which includes a member disposed therein, wherein movement of the member corresponds to a change in the operating state or condition of the associated mechanism. [0027] The differential gear mechanism (locking differential) shown in FIG. 1 includes a gear case 11 which defines therein a gear chamber, generally designated 13. In the subject embodiment, and by way of example only, the gear case 11 comprises a single, unitary gear case, and all parts within the differential are inserted through a "window" (not shown herein) in the gear case 11, as is well known to those skilled In the art. However, it should be understood that the present invention is not limited to any particular configuration of gear case 11, or any particular configuration of window, or even, to the presence of such a window. Torque input to the differential is typically by means of an input ring gear (not shown herein), which may be attached to a flange 15 (shown only fragmentarily herein) of the gear case 11 by any suitable means, such as a plurality of bolts (also not shown herein). [0028] Disposed within the gear chamber 13 is a differential gear set including a pair of input pinion gears 17 which are rotatably mounted on a pinion shaft 19. Typically, the pinion shaft 19 is secured relative to the gear case by any suitable means, such as a locking pin 21. The pinion gears 17 comprise the input gears of the differential gear set, and are in meshing engagement with a pair of side gears 23 and 25. The side gears 23 and 25 define sets of internal, straight splines 27 and 29, respectively, which are adapted to be In splined engagement with mating external splines of a pair of axle shafts (not shown). The gear case 11 includes annular hub portions 31 and 33 on which may be mounted a pair of bearing sets (not shown herein) which are used to provide rotational support for the differential mechanism relative to an outer differential housing (ai$o not shown herein). [0029] As is well known to those skilled in the art, during normal straight- ahead operation of the vehicle, no differentiation occurs between the left and right side gears 23 and 25, and therefore, the pinion gears 17 do not rotate relative to the pinion shaft 19. The gear case 11, the pinion gears 17, and the side gears 23 and 25 all rotate about an axis of rotation A (shown only in FIGS. 1 and 2) as a solid unit. [0030] It should be understood that the locking differential of the present invention may be operated in either of several modes. The differential may be operated manually, i.e., wherein the driver manually selects the locked mode, such that the differential operates in the locked mode almost immediately after the vehicle begins to move. Alternatively, the locking differential may operate in an "automatic mode" wherein, by way of example only, the vehicle nicroprocessor senses an operating condition, such as incipient wheel slip and transmits an appropriate electrical input signal ("input") to the locking differential, thus locking the side gear 25 relative to the gear case 11, to prevent siny further differentiation. [0031] in the case of the automatic mode of operation of the locking differential, it will be understood that under certain operating conditions, such us when the vehicle is turning or a slight difference In tire size exists, it is permissible for a certain amount of differentiating action to occur between the iside gears 23 and 25. However, in accordance with the present invention, the locking differential may or may not include a clutch pack, or any other similar mechanism which merely retards or limits differentiating action, but instead may provide a choice between only an unactuated condition as shown in FIG. 1 and an actuated, locked condition, not separately shown herein. [0032] Referring now to FIG. 2, in conjunction with FIG. 1, the locking differential of the present invention includes a rotation limiting mechanism, generally designated 35. The rotation limiting mechanism 35 may be better understood by reference to the above-incorporated U.S. Pat. No. 6,651,209. it snould be understood by those skilled in the differential art that, because the present invention is not limited to any particular structure or mode of operation of the rotation limiting mechanism 35, except as specifically otherwise noted in the appended claims, the mechanism 35 will be described only briefly herein, and only by way of background and example. The gear case 11 includes an end wall 37 which defines two arrays of bores. The first array of bores (shown in FIG. 1), comprises a plurality of pin bores 39 which extend axially through the entire axial extent of the end wall 37. Disposed within each of the pin bores 39 in an axially moveable, generally cylindrical pin member 41 (also referred to hereinafter, and in the appended claims, as a "lock member"). The second srray of bores (see FIG. 2) comprises a plurality of spring bores 43, which extend from the left end in FIG. 2 of the end wall 37 only partially through the eixial thickness of the end wall 37, such that within each spring bore 43 there is seated a coiled compression spring 45. [0033] The left end of each of the compression springs 45 is seated against sin inner ramp plate 47 (see also FIG. 3) of a ball ramp actuator, generally designated 49. The ball ramp actuator 49 also includes an outer ramp plate 51, and a plurality of cam members (balls) 53 are disposed between the inner ramp plate 47 and the outer ramp plate 51, in a manner now well known to those skilled in the art of ball ramp actuators. The ball ramp actuator 49 may be considered as part of the rotation limiting mechanism 35. [0034] Disposed axially outward of the gear case 11 (to the left In FIGS. 1 (and 2 from the ball ramp actuator 49) is an electromagnetic actuator, generally designated 55, which preferably comprises an annular electromagnetic coil 57 disposed radially outward from, and supported by, an annular support member 59. The support member 59 surrounds the larger diameter portion of the annular hub portion 31, such that the electromagnetic actuator 65 is stationary, (I.e., is fixed relative to an outer differential housing which is not shown herein), and the gear case 11 is free to rotate therein, and relative thereto. The electromagnetic actuator 55 is, in certain aspects, illustrated and described in greater detail in one or more of the above-incorporated patents. [0035] Actuation of the electromagnetic coil 57 occurs in response to an electrical input signal, transmitted to the coil 57 by means of a pair of electrical loads 61 (see FIG. 2), the reference numeral "61" to be used hereinafter to designate either the leads themselves, or the electrical input signal. [0036] Referring now primarily to FIGS. 2 and 3, disposed immediately adjacent the electromagnetic coil 57 is an annular drive plate 63 which is fixed, by any suitable means such as splines, to be non-rotatable relative to the outer ramp plate 51. The connection between the drive plate 63 and the outer ramp plate 51 will be described in greater detail subsequently, in connection with the cescription of the sensing mechanism of the present invention. Therefore, and es is now well known to those skilled in the art, and as is illustrated and c escribed in the above-incorporated patents, when the coil 57 is energized, the resulting flux path passes through the drive plate 63 and draws the plate into fictional engagement with adjacent friction surfaces on a coil housing 65, The coil housing 65 is preferably fixed to be non-rotatable relative to an outer differential housing, not shown herein, but represented in FIG. 2 by a "ground" symbol, designated 66. The result is to retard rotation of the annular drive plate 63 and therefore of the outer ramp plate 51, relative to the gear case 11. However, the inner ramp plate 47 is fixed to rotate with the gear case 11, such as by means of a plurality of ears 67 (see FIG. 3), and therefore, the ramping action results in rightward axial movement (in FIGS. II through 3) of the inner ramp plate 47, in apposition of the biasing force of the compression springs 45. Referring again primarily to FIG. 1, the "outer" face of the side gear 23 (i.e., the side facing the end wall 37), defines a plurality of openings 69, the openings 69 bsing arranged in an array which matches, or mates with, the array of pin bores 39. Therefore, with the arrays of pin bores 39 and openings 69 c rcurnferentially aligned (the position shown in FIG. 1), actuation of the electromagnetic coil 57 will move the Inner ramp plate 47 to the right in FIG. 1, and move the pin members 41 into engagement within the openings 69, thus locking the side gear 23 relative to the gear case 11 (the actuated or "locked" condition). [0037] Most of what has been described up to this point is already known, primarily from the above-incorporated patents. Referring now to all of the drawing figures in conjunction with each other, an important aspect of the present invention will be described. As stated previously, one of the objects of this invention is to be able to sense the occurrence of either the locked condition, or the unlocked condition (i.e., to be able to sense the change of state of a mechanism), utilizing the axial movement, within the mechanism, of a member which comprises part of the mechanism. [0038] In the subject embodiment, and by way of example only, the "axially moveable member" includes the inner ramp plate 47 of the ball ramp actuator ^•9. In accordance with one aspect of the invention, the inner ramp plate 47 itself serves as the "axially moveable member", for purposes of the appended claims, without the need for any added structure to serve as a target to be sensed by the sensing mechanism, which is to be described hereinafter. [0039] Referring now primarily to FIGS. 2, 3 and 4, the sensing mechanism of the present invention will be described. In accordance with a preferred embodiment of the invention, the coil housing 65 is of the '"two cavity11 type, (i-e., the coil housing 65 defines not only a cavity for the electromagnetic coil 57 (the "actuation" coil), but also provides a cavity within which is disposed a sensing coil 71), the function of which will be described subsequently. The sensing coil 71 may comprise simply an electromagnetic coil, or may comprise a magnetically-biased coil. In either case, the sensing coil 71 (also referred to hereinafter in the appended claims as a "sensor element") preferably provides a "proximity" sensing device, as that term is well understood in the sensing art. As is well known to those skilled in the art of electromagnetic actuation, the coil housing 65 comprises a ferromagnetic member, as does the annular drive plate 63 which comprises part of the electromagnetic "circuit" for purposes of actuation of the ball ramp actuator 49. The inner ramp plate 47 also preferably comprises a ferromagnetic member, for reasons which will become apparent subsequently. [0040] However, in accordance with an important saspect of the invention, the radially "inner" portion of the drive plate 63, immediately adjacent the sensing coll 71, is replaced by an annular window member 73, best seen in FIGS. 3 and A. The term "window" is used herein in regard to the member 73 primarily to explain that, for purposes of the present invention, the window member 73 is not ferromagnetic, and therefore, the electromagnetic circuit (or flux "path") is not "contained" within the window member 73, but instead, permits the flux lines F: (see FIG. 4) to pass through. By way of contrast, and as is well known in the electromagnetic arts, the flux lines resulting from actuation of the coil 57 would be contained within the drive plate 63, with lines of flux passing vertically therethrough. In the subject embodiment, and by way of example only, the nnnular window member 73 comprises an aluminum member, such that the window member 73 has the structural integrity and durability to transmit torque trom the annular drive plate 63 to the outer ramp plate 51. As is also well * known to those skilled in the art, the aluminum window member 73 will slightly increase the flux density, as compare to air. [0041] At the same time, and as may best be seen in FIG. 4, tine annular window member 73 is disposed axially between the sensing coil 71 and the nner ramp plate 47, the axially movable member in the subject embodiment. When a sensing current is imposed upon the sensing coil 71, the result is the e ectromagnetic flux path F, as shown in FIG. 4. The flux path F passes through the coll housing 65, around the sensing coll 71, passes through the window member 73, across an adjacent air gap, then through part of the inner ramp plate 47. As is known from the previous, brief description of the operation of the rotation-limiting mechanism 35 and the electromagnetic actuator 55, the Inner ramp plate 47 moves axially (see arrow in FIG. 4) between a first condition (FIG. 2), corresponding to the unactuated condition of the mechanism 35, and a second condition (position toward which inner ramp plate 47 is moving in FIG. 4), corresponding to the actuated condition of the mechanism 35. [0042] In accordance with an important aspect of trie invention, as the axial position of the inner ramp plate 47 changes, the magnetic flux path length changes, but is unaffected by the window member 73. The changes in the flux path length which result from the inner ramp plate 47 moving further from, or closer to, the sensing coil 71 result in either a decrease or an increase, respectively, in the flux density (or Inductance) of the flux path F. The changes in flux density (or inductance) may then be sensed, or monitored, by an external control circuitry which is capable of "converting" the sensed flux density (or inductance) into a value representative of the changes in the axial separation between the sensing coil 71 and the ramp plate 47. [0043] Referring now primarily to FIG. 5, there is a graph of Voltage versus Time, illustrating an important relationship utilized by one embodiment of the sensing mechanism of the present invention. In connection with the development of the invention, several different proximity-type sensing arrangements were investigated, including one known as pulse induction (PI) siensing. In a PI sensing arrangement, the sensing coil 71 is charged to a known current ("Constant current pulse" in FIG. 5). This known current produces a magnetic field which induces the magnetic flux path F shown in FIG, 4. This flux path F stores energy in the materials (Energy = % LI2). The -14- known coil current is then abruptly terminated, causing the magnetic flux path F to cease (decay) and energy to be dissipated. As the magnetic flux path F cianges, the change will cause eddy currents to flow in the inner ramp plate 47, but the eddy currents will decay slowly because of the internal resistance of the ferromagnetic ramp plate 47. [0044] As the above-described eddy currents flow in the ramp plate 47, the eddy currents also produce a magnetic field, which, in turn, induces a current back into the sensing coil 71, resulting in a back-EMF (electro-motive force). When the resulting voltage (from the back-EMF) is measured across the sensing coil 71, there is a negative voltage spike ("SPIKE" in FIG. 5), having an exponential decay rate or curve, as shown in FIG. 5. The decay rate of the regative spike is a function of the inductance, which, in turn, is directly related to the air gap distance from the sensing coil 71 to the inner ramp plate 47, However, it should be understood by those skilled in the sensing art that the present Invention is not limited to the above-described, or any other particular, sensing concept, except as specifically noted otherwise in the appended claims. [0045] A variety of sensing systems are available and well known and the present invention is not limited to pulse induction sensing. Tuned lank" oscillator circuits, whereby an inductor and capacitor form a tuned frequency oscillator, can be used as well to determine the distance by measuring the frequency of oscillation. As this concept can be used to look for any metal, it will not "see" thru the aluminum if the frequency is too high. It does include the tuned oscillator front end circuitry. Other known magnetic proximity sensors and LVDT arrangements could be implemented as well. It was found, in connection with the development of the present invention, that the pulse induction sensing was relatively simple and was effective when implemented in this particular environment. [0046] in view of the particular application for the present Invention, the above-described sensing concept comprises a preferred embodiment, partly because it was found to be effective under a broad range of operating temperatures (from about -40 degrees Celsius to about 190 degrees Celsius), and while immersed in various petrochemical-based lubricants (such as gear o Is). Neither the temperature variations nor the various oils appeared to have a negative effect upon the ability to accurately sense the change-of-state (axial movement) of the ramp plate 47. [0047] Referring now primarily to FIG. 6, there is illustrated a portion of an electrical control circuitry, generally designated 81, which may be used to implement the sensing concept illustrated and described in connection with FIG. 5. In the circuit shown in FIG. 6, a Pulse Train (shown as the Constant Current Pulse in FIG. 5) is an input to the control circuitry 81. The "Output" of the control circuit 81 is an analog signal 91 which is representative of the c istance of the inner ramp plate 47 from the sensing coil 71. [3048] The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims. what is claimed is: 1. A differential gear mechanism including a gear case (11) defining an axis of rotation (A), and a gear chamber (13); differential gearing disposed in said gear chamber including at least one input gear (17) and first (23) and second (25) output gears; means (35) operable to limit rotation of said first output gear (23) relative to said gear case (11), and actuation means (55) for actuating said rotation limiting means (35), said actuation means (55) being operable in response to an input (61), to move said rotation limiting means from an unactuated condition (FIG. 1) to an actuated condition (FIG. 4), said rotation limiting means (35) including a member (47), disposed toward one axial end of said gear case (11) and moveable in the direction of said axis of rotation (A) between a first position (FIG. 1) corresponding to said unactuated condition of said rotation limiting means (35), and a second position (FIG. 4) corresponding to said actuated condition, characterized by: (a) a sensor assembly being disposed adjacent said one axiai end of said gear case (11) and including a sensor element (71) and a wall-like member (63,73) disposed axially between said rotation limiting means (35) and said actuation means (55); (b) said wall-like member (63,73) including a non-ferromagnetic portion (73) disposed axially between said sensor element (71) and said moveable member (47), whereby movement of said moveable member between said first (FIG. 1) and said second (FIG. 4) positions results in a corresponding change in the electromagnetic flux (F) coupling said sensor element (71) and said moveable member (47). 2. A differential gear mechanism as claimed in claim 1, characterized by said means operable to limit rotation of said first output gear (23) relative to said gear case (11) includes a plurality of lock members (41) disposed within openings (39) defined by said one axial end (37) of said gear case (11), and axiaily rnoveable from an unlocked position (FIG. 1) to a locked position, in engagement with mating openings (69) defined by said first output gear (23). 3. A differential gear mechanism as claimed in claim 1, characterized by said actuation means (55) comprises a first electromagnetic coil (57) disposed adjacent said one axial end (37) of said gear case (11) and disposed generally concentrically about said axis of rotation (A). 4. A differential gear mechanism as claimed in claim 3, characterized by said wall-like member including a ferromagnetic portion (63) disposed axiaily between said first electromagnetic coil (57) and said rotation limiting means (35), said sensor element (71) being disposed radially inward from said first electromagnetic coil (57), 5. A differential gear mechanism as claimed in claim 4, characterized by said sensor element comprises a second electromagnetic coil (71) being disposed generally concentrically about said axis of rotation (A). (5. A differential gear mechanism as claimed In claim 5, characterized by said first (57) and second (71) electromagnetic coils being disposed within a common, ferromagnetic coil housing (65), said coil housing (65) being fixed relative to an outer differential housing (66). 7 A mechanism including a case (11) defining an axis (A) and a chamber; said mechanism Including an actuation means (55) for actuating the mechanism, the actuation means (55) being operable in response to an input (61) to move the mechanism from an unactuated condition (FIG, 1) to an actuated condition (FIG. 4); the mechanism including an axially moveable member (47) disposed toward one axial end (37) of the case (11) and moveable in the direction of the axis (A) between a first position (FIG. 1) corresponding to said unactuated condition of the mechanism, and a second position (FIG. 4) corresponding to said actuated condition, characterized by: (a) a sensor assembly being disposed adjacent said one axial end (37) of said case (11) and including a sensor element (71) and a walHike member (63,73) disposed axially between the mechanism and the actuation means (55); (b) said wall-like member (63,73) including a non-ferromagnetic portion (73) disposed axially between said sensor element (71) and said axially moveable member (47), whereby movement of said axially moveable member (47) between said first (FIG. 1) and said second (FIG, 4) positions results in a corresponding change in the electromagnetic flux (F) coupling said sensor element (71) and said axially moveable member (47); and (c) said sensor element comprises an electromagnetic coil (71) disposed adjacent said one axial end (37) of said case (11) and disposed generally concentrically about said axis (A). il A mechanism as claimed in claim 7, characterized by said actuation means (55) comprises a first electromagnetic coll (57) disposed adjacent said one axial end (37) of said case (11) and disposed generally concentrically about said axis (A), said sensor element comprising a second electromagnetic coil (71). 9. A mechanism as claimed in claim 8, characterized by said wall-like member including a ferromagnetic portion (63) disposed axially between said first electromagnetic coil (57) and said mechanism, said second electromagnetic coil (71) being disposed radially inward from said first electromagnetic coil (57). A differential having means (35) operable to limit rotation of an output guar (23) relative to gear case (11), and actuation means (55) for actuating the rotation limiting means, for an unactuated (FIG.1) to an actuated condition (FIG.4). The rotation limiting means includes a member (47), toward one axial end of the gear case and moveable between a first position, the unactuated condition of said rotation limiting means and a second position, the actuated condition. A sensor assembly is adjacent the one axial end of the gear case and includes a sensor element (71) and a wall-like member between the rotation limiting means and the actuation means. The wall-like member includes a non-ferromagnetic portion (73) between the sensor and the moveable member. Movement between the first and second positions results in a corresponding change in the electromagnetic flux (F) coupling the sensor element and the moveable member.

Full Text

TITLE OF INVENTION
[0001] Limited Slip Differential And Engagement Sensing Mechanism
Therefor.
EtACKGROUND OF THE DISCLOSURE
[0002] The present invention relates to fraction modifying differentials, and
more particularly, to such differentials of the type in which the differential action
nay be retarded, and possibly even prevented ("locked"), in response to some
sort of an input, for example, a mechanical input or an electrical input signal.
[0003] Furthermore, the present invention relates to engagement sensing
nechanisms and systems of the type which may be utilized to sense a change-
of-state within a traction modifying differential, for example, a change between
an unlocked condition and a locked condition.
[0004] Traction modifying differentials of the type to which the present
invention relates typically include a gear case defining a gear chamber, and
disposed therein, a differential gear set including at least one input pinion gear,
and a pair of output side gears, The present invention will be described in
connection with a differential of the bevel gear type, although those skilled in
the art will understand that the invention is not so limited, and could be utilized
h connection with differentials having other gearing types, such as helical or
planetary. Typically, a clutch pack is disposed between at least one of the side
gears and an adjacent surface of the gear case, such that the clutch pack or
locking mechanism is operable to limit relative rotation between the gear case
and the one side gear. In most differentials of the type described, engaging the
clutch pack or locking mechanism (to retard differentiation) is achieved by one
of several different approaches.
|0005] In one approach, a "locking differential" of the type illustrated and
described in U.S. Patent No, Re 28,004, assigned to the assignee of the

present invention and incorporated herein by reference, the clutch pack is
normally disengaged. When one of the wheels begins to spin out, relative to
the other wheel, a speed sensitive mechanism senses the speed differential
between the wheels, and by means of a cam and ramp mechanism, locks the
. clutch pack solid. In the incorporated patent, the speed sensitive mechanism
comprises a fly-weight mechanism, the output of which comprises the
mechanical "input", in response to which the differential gearing is locked,
[0006] U.S. Patent No. 5,019,021, also assigned to the assignee of the
present invention and incorporated herein by reference, illustrates another
approach to retarding differentiation. This patent illustrates and describes a
" imited slip differential" in which the loading on the clutch pack may be varied
in response to an external electrical input signal, thus varying the amount of slip
within the clutch pack. Therefore, the amount of bias torque transmitted from
c ne side gear to the other is also varied in response to changes in the external
electric input signal. As is well known to those skilled in the art, in a limited slip
differential, there is typically a certain amount of "slip" or speed differential,
between the two side gears whenever the vehicle encounters (ess than optimum
faction conditions. In the above-incorporated patent, the "input" to the
differential is the electrical Input signal, but within the differential, there is
smother "input" which is the axial movement of one of the plates of a ball ramp
actuator, the axial movement of which varies the loading on the clutch pack in a
Manner which is now generally well known to those skilled In the art.
[0007] Finally, in U.S. Pat. No. 6,551,209, also assigned to the assignee of
the present invention and incorporated herein by reference, there is illustrated a
different approach to a "locking differential". In the above-incorporated patent,
there is illustrated and described a locking differential in which there is no
friction-type clutch pack, but instead, a mechanical locking arrangement. In the
differential of the cited '209 patent, there is a ball ramp actuator which is able,
in response to an electrical input signal, to move a series of pins into mating

openings in the differential side gear, thus locking the side gear relative to the
d fferential gear case. For purposes of the present invention, the movement of
the pins, toward or away from the side gear, to achieve either a locked condition
o" an unlocked condition, respectively, is also considered an "input" in regard to
a means for limiting rotation of an output gear relative to a gear case in a
differential.
[0008] Thus, it may be seen, from a review of the above-described types of
limited slip and locking differentials, that there are a number of different
mechanisms known to those skilled in the art which are commonly used to limit
(retard), or lock, the relative rotation between a differential gear case and one
of the output side gears. However, it should be noted that most of the known,
prior art limited slip and locking differential arrangements, and especially those
which have been commercialized by the assignee of the present invention,
have in common the presence of some sort of member which moves axiaily, in
connection with the operation of the mechanism which achieves the slip limiting
or locking function within the differentia).
[D009] More recently, an increasing percentage of vehicles (especially
passenger cars and light trucks) are incorporating some sort of stability, or
traction, or safety system Into the drive train. Examples of such systems would
include a traction control system (TCS), an anti-skid braking system (ABS), and
am electronic stability program (ESP), it is quite common, and desirable, for
such systems to include some sort of traction modifying device, and preferably,
an electrically-actuated limited slip or locking differential. In order for these
types of systems to operate most effectively and safely, it is important for the
control logic of the system to receive some sort of feedback signal from the
differential, whereby the control logic can know, at any given instant, whether
ihe differential is in an actuated (locked) condition, or in an unactuated
(unlocked) condition.
|0010] Unfortunately, sensing the occurrence of a locked condition (or an

unlocked condition) in a locking differential, or sensing an Increasing clutch
engagement (or a decreasing clutch engagement) in a limited slip differential
involves sensing something such as the axial movement of a member within a
differential gear case which, typically, is rotating within a stationary outer
housing. One seemingly obvious way of mounting a sensor on a rotating
differential case is to fix the sensor to the exterior of the case, and transmit the
generated electrical signal from the differential to the vehicle microprocessor by
means of slip rings, Unfortunately, such an arrangement is typically not
feasible. For most differential Installations, nothing can be attached to the
exterior of (the outer diameter of) the differential case (or extend radially
cutward therefrom), because, in the axle assembly plant, it must be possible to
slide the ring gear over the case outer diameter, and bolt the ring gear to the
case flange.
[3011] Another hindrance encountered by those skilled in the art, in
attempting to develop arrangements for sensing the "change-of-state" in a
limited slip or locking differentia! is the fact that the sensing system utilized
needs to be able to survive and operate effectively in a fairly severe
environment. For example, the sensing mechanism and the overall system
need to be able to operate predictably over a broad temperature range (e.g.,
f"om about -40 degrees Celsius to about 190 degrees Celsius). Also the
sensing mechanism must be able to operate while submersed in a
petrochemical-based lubricant, without any adverse effect upon the accuracy of
the sensing system "output" signal, indicating the current state of the
differential.
E3RIEF SUMMARY OF THE INVENTION
[0012] Accordingly, it Is an object of "the present invention to provide an
improved differential gear mechanism, and an improved sensing mechanism
and assembly for use therein, which will overcome the above-described

p'oblems of the prior art.
[0013] It is a further object of the present invention to provide such an
inproved differential gear mechanism and improved sensing system for use
therein which achieves the above-stated object, but without any substantial
redesign of the underlying differential mechanism, and with no substantial
increase in the overall package size of the differential gear mechanism.
[0014] It is a more specific object of the present invention to provide such an
improved differential gear mechanism, and sensing system therefor, in which
the occurrence of a change in the state of the differential can be sensed
utilizing the axial movement, within the differential, of a member which is
already a required part of the differential mechanism, rather than requiring
some sort of additional "target" member.
[0015] The above and other objects of the invention are accomplished by the
provision of an improved differential gear mechanism including a gear case
cefinlng an axis of rotation, and a gear chamber, differential gearing being
cisposed In the gear chamber including at least one input gear and first and
second output gears. The mechanism includes means operable to limit rotation
cf the first output gear relative to the gear case, and actuation means for
sctuating the rotation limiting means, the actuation means.being operable in
response to an input, to move the rotation limiting means from an unactuated
condition to an actuated condition. The rotation limiting means includes a
member, disposed toward one axial end of the gear case and moveable in the
direction of the axis of rotation between a first position corresponding to the
unactuated condition of the rotation limiting means, and a second position
corresponding to the actuated condition.
[0016] The improved differential gear mechanism Is characterized by a
siensor assembly being disposed adjacent the one axial end of the gear case
and including a sensor element and a wall-like member disposed axially
between the rotation limiting means and the actuation means. The wall-like

member includes a non-ferromagnetic portion disposed axially between the
sensor element and the moveable member, whereby movement of the
moveable member between the first and the second positions results in a
Corresponding change in the electromagnetic flux coupling the sensor element
and the moveable member.
[0017] In accordance with another aspect of the present invention, there Is
provided a mechanism including a case defining an axis and a chamber, the
mechanism including an actuation means for actuating the mechanism, the
actuation means being operable in response to an input to move the
mechanism from an unactuated condition to an actuated condition. The
mechanism includes an axially moveable member disposed toward one axial
end of the case and moveable in the direction of the axis between a first
position corresponding to the unactuated condition of the mechanism, and a
second position corresponding to the actuated condition,
[0018] The improved mechanism is characterized by a sensor assembly
being disposed adjacent the one axial end of the case and including a sensor
element and a wall-like member disposed axially between the mechanism and
the actuation means. The wall-like member includes a non-ferromagnetic
portion disposed axially between the sensor element and the axially moveable
nember, whereby movement of the axially moveable member between the first
smd the second positions results in a corresponding change in the
electromagnetic flux coupling the sensor element and the axially moveable
member. The sensor element comprises an electromagnetic coil disposed
adjacent the one axial end of the case and disposed generally concentrically
about the axis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is an axial cross-section of a locking differential made in
accordance with the teachings of the present invention, in an unactuated,

unlocked condition.
[0020] FIG. 2 Is an enlarged, fragmentary, axial cross-section, similar to
FIG. 1, but taken on a plane different than that of FIG. 1.
[0021] FIG. 3 is a fragmentary, exploded, perspective view of a portion of the
differential gear mechanism shown in FIGS. 1 and 2.
[0022] FIG. 4 is an enlarged, fragmentary, somewhat schematic axial cross-
ssction, similar to FIG. 2, illustrating one important aspect of the present
invention.
[0023] FIG. 5 is a graph of Voltage versus Time, illustrating an important
relationship utilized, in one embodiment, by the sensing mechanism of the
present invention,
[0024] FIG. 6 is an electrical circuit schematic representing a portion of an
embodiment of control circuitry which may be used with the engagement
sensing mechanism of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] Referring now to the drawings, which are not intended to limit the
invention, FIG. 1 is an axial cross-section of a slip-limiting differential, and more
specifically, of a locking differential including the present invention. The
specific construction and operation of differentials of the general type to which
t'lis invention relates, and of the specific type illustrated in FIG. 1, may be better
understood by reference to the above-incorporated patents. Specifically, the
overall construction and function of the locking differential shown in FIG. 1 Is
quite similar to that illustrated and described in above-incorporated U.S. Patent
No. 5,551,209.
[0026]' However, as has already been noted, the usefulness of the present
invention is not restricted to only locking differentials, but could be also
advantageous when used on limited slip differentials, at least on those including
some sort of a member within the differential which moves axially within the

differential case such that the movement of the member is representative of a
change between a slipping condition and a slip-limiting condition. Furthermore,
the use of the present invention is not restricted to any particular configuration
o differential, except as is specifically noted in the appended claims. Finally, it
should be noted that, in one aspect, the present invention comprises a sensing
assembly and system which may be used effectively to sense the change of
state of an associated mechanism which includes a member disposed therein,
wherein movement of the member corresponds to a change in the operating
state or condition of the associated mechanism.
[0027] The differential gear mechanism (locking differential) shown in FIG. 1
includes a gear case 11 which defines therein a gear chamber, generally
designated 13. In the subject embodiment, and by way of example only, the
gear case 11 comprises a single, unitary gear case, and all parts within the
differential are inserted through a "window" (not shown herein) in the gear case
11, as is well known to those skilled In the art. However, it should be
understood that the present invention is not limited to any particular
configuration of gear case 11, or any particular configuration of window, or
even, to the presence of such a window. Torque input to the differential is
typically by means of an input ring gear (not shown herein), which may be
attached to a flange 15 (shown only fragmentarily herein) of the gear case 11
by any suitable means, such as a plurality of bolts (also not shown herein).
[0028] Disposed within the gear chamber 13 is a differential gear set
including a pair of input pinion gears 17 which are rotatably mounted on a
pinion shaft 19. Typically, the pinion shaft 19 is secured relative to the gear
case by any suitable means, such as a locking pin 21. The pinion gears 17
comprise the input gears of the differential gear set, and are in meshing
engagement with a pair of side gears 23 and 25. The side gears 23 and 25
define sets of internal, straight splines 27 and 29, respectively, which are
adapted to be In splined engagement with mating external splines of a pair of

axle shafts (not shown). The gear case 11 includes annular hub portions 31
and 33 on which may be mounted a pair of bearing sets (not shown herein)
which are used to provide rotational support for the differential mechanism
relative to an outer differential housing (ai$o not shown herein).
[0029] As is well known to those skilled in the art, during normal straight-
ahead operation of the vehicle, no differentiation occurs between the left and
right side gears 23 and 25, and therefore, the pinion gears 17 do not rotate
relative to the pinion shaft 19. The gear case 11, the pinion gears 17, and the
side gears 23 and 25 all rotate about an axis of rotation A (shown only in FIGS.
1 and 2) as a solid unit.
[0030] It should be understood that the locking differential of the present
invention may be operated in either of several modes. The differential may be
operated manually, i.e., wherein the driver manually selects the locked mode,
such that the differential operates in the locked mode almost immediately after
the vehicle begins to move. Alternatively, the locking differential may operate in
an "automatic mode" wherein, by way of example only, the vehicle
nicroprocessor senses an operating condition, such as incipient wheel slip and
transmits an appropriate electrical input signal ("input") to the locking
differential, thus locking the side gear 25 relative to the gear case 11, to prevent
siny further differentiation.
[0031] in the case of the automatic mode of operation of the locking
differential, it will be understood that under certain operating conditions, such
us when the vehicle is turning or a slight difference In tire size exists, it is
permissible for a certain amount of differentiating action to occur between the
iside gears 23 and 25. However, in accordance with the present invention, the
locking differential may or may not include a clutch pack, or any other similar
mechanism which merely retards or limits differentiating action, but instead may
provide a choice between only an unactuated condition as shown in FIG. 1 and
an actuated, locked condition, not separately shown herein.

[0032] Referring now to FIG. 2, in conjunction with FIG. 1, the locking
differential of the present invention includes a rotation limiting mechanism,
generally designated 35. The rotation limiting mechanism 35 may be better
understood by reference to the above-incorporated U.S. Pat. No. 6,651,209. it
snould be understood by those skilled in the differential art that, because the
present invention is not limited to any particular structure or mode of operation
of the rotation limiting mechanism 35, except as specifically otherwise noted in
the appended claims, the mechanism 35 will be described only briefly herein,
and only by way of background and example. The gear case 11 includes an
end wall 37 which defines two arrays of bores. The first array of bores (shown
in FIG. 1), comprises a plurality of pin bores 39 which extend axially through the
entire axial extent of the end wall 37. Disposed within each of the pin bores 39
in an axially moveable, generally cylindrical pin member 41 (also referred to
hereinafter, and in the appended claims, as a "lock member"). The second
srray of bores (see FIG. 2) comprises a plurality of spring bores 43, which
extend from the left end in FIG. 2 of the end wall 37 only partially through the
eixial thickness of the end wall 37, such that within each spring bore 43 there is
seated a coiled compression spring 45.
[0033] The left end of each of the compression springs 45 is seated against
sin inner ramp plate 47 (see also FIG. 3) of a ball ramp actuator, generally
designated 49. The ball ramp actuator 49 also includes an outer ramp plate 51,
and a plurality of cam members (balls) 53 are disposed between the inner ramp
plate 47 and the outer ramp plate 51, in a manner now well known to those
skilled in the art of ball ramp actuators. The ball ramp actuator 49 may be
considered as part of the rotation limiting mechanism 35.
[0034] Disposed axially outward of the gear case 11 (to the left In FIGS. 1
(and 2 from the ball ramp actuator 49) is an electromagnetic actuator, generally
designated 55, which preferably comprises an annular electromagnetic coil 57
disposed radially outward from, and supported by, an annular support member

59. The support member 59 surrounds the larger diameter portion of the
annular hub portion 31, such that the electromagnetic actuator 65 is stationary,
(I.e., is fixed relative to an outer differential housing which is not shown herein),
and the gear case 11 is free to rotate therein, and relative thereto. The
electromagnetic actuator 55 is, in certain aspects, illustrated and described in
greater detail in one or more of the above-incorporated patents.
[0035] Actuation of the electromagnetic coil 57 occurs in response to an
electrical input signal, transmitted to the coil 57 by means of a pair of electrical
loads 61 (see FIG. 2), the reference numeral "61" to be used hereinafter to
designate either the leads themselves, or the electrical input signal.
[0036] Referring now primarily to FIGS. 2 and 3, disposed immediately
adjacent the electromagnetic coil 57 is an annular drive plate 63 which is fixed,
by any suitable means such as splines, to be non-rotatable relative to the outer
ramp plate 51. The connection between the drive plate 63 and the outer ramp
plate 51 will be described in greater detail subsequently, in connection with the
cescription of the sensing mechanism of the present invention. Therefore, and
es is now well known to those skilled in the art, and as is illustrated and
c escribed in the above-incorporated patents, when the coil 57 is energized, the
resulting flux path passes through the drive plate 63 and draws the plate into
fictional engagement with adjacent friction surfaces on a coil housing 65, The
coil housing 65 is preferably fixed to be non-rotatable relative to an outer
differential housing, not shown herein, but represented in FIG. 2 by a "ground"
symbol, designated 66. The result is to retard rotation of the annular drive plate
63 and therefore of the outer ramp plate 51, relative to the gear case 11.
However, the inner ramp plate 47 is fixed to rotate with the gear case 11, such
as by means of a plurality of ears 67 (see FIG. 3), and therefore, the ramping
action results in rightward axial movement (in FIGS. II through 3) of the inner
ramp plate 47, in apposition of the biasing force of the compression springs 45.
Referring again primarily to FIG. 1, the "outer" face of the side gear 23 (i.e., the

side facing the end wall 37), defines a plurality of openings 69, the openings 69
bsing arranged in an array which matches, or mates with, the array of pin bores
39. Therefore, with the arrays of pin bores 39 and openings 69
c rcurnferentially aligned (the position shown in FIG. 1), actuation of the
electromagnetic coil 57 will move the Inner ramp plate 47 to the right in FIG. 1,
and move the pin members 41 into engagement within the openings 69, thus
locking the side gear 23 relative to the gear case 11 (the actuated or "locked"
condition).
[0037] Most of what has been described up to this point is already known,
primarily from the above-incorporated patents. Referring now to all of the
drawing figures in conjunction with each other, an important aspect of the
present invention will be described. As stated previously, one of the objects of
this invention is to be able to sense the occurrence of either the locked
condition, or the unlocked condition (i.e., to be able to sense the change of
state of a mechanism), utilizing the axial movement, within the mechanism, of a
member which comprises part of the mechanism.
[0038] In the subject embodiment, and by way of example only, the "axially
moveable member" includes the inner ramp plate 47 of the ball ramp actuator
^•9. In accordance with one aspect of the invention, the inner ramp plate 47
itself serves as the "axially moveable member", for purposes of the appended
claims, without the need for any added structure to serve as a target to be
sensed by the sensing mechanism, which is to be described hereinafter.
[0039] Referring now primarily to FIGS. 2, 3 and 4, the sensing mechanism
of the present invention will be described. In accordance with a preferred
embodiment of the invention, the coil housing 65 is of the '"two cavity11 type, (i-e.,
the coil housing 65 defines not only a cavity for the electromagnetic coil 57 (the
"actuation" coil), but also provides a cavity within which is disposed a sensing
coil 71), the function of which will be described subsequently. The sensing coil
71 may comprise simply an electromagnetic coil, or may comprise a

magnetically-biased coil. In either case, the sensing coil 71 (also referred to
hereinafter in the appended claims as a "sensor element") preferably provides a
"proximity" sensing device, as that term is well understood in the sensing art.
As is well known to those skilled in the art of electromagnetic actuation, the coil
housing 65 comprises a ferromagnetic member, as does the annular drive plate
63 which comprises part of the electromagnetic "circuit" for purposes of
actuation of the ball ramp actuator 49. The inner ramp plate 47 also preferably
comprises a ferromagnetic member, for reasons which will become apparent
subsequently.
[0040] However, in accordance with an important saspect of the invention, the
radially "inner" portion of the drive plate 63, immediately adjacent the sensing
coll 71, is replaced by an annular window member 73, best seen in FIGS. 3 and
A. The term "window" is used herein in regard to the member 73 primarily to
explain that, for purposes of the present invention, the window member 73 is
not ferromagnetic, and therefore, the electromagnetic circuit (or flux "path") is
not "contained" within the window member 73, but instead, permits the flux lines
F: (see FIG. 4) to pass through. By way of contrast, and as is well known in the
electromagnetic arts, the flux lines resulting from actuation of the coil 57 would
be contained within the drive plate 63, with lines of flux passing vertically
therethrough. In the subject embodiment, and by way of example only, the
nnnular window member 73 comprises an aluminum member, such that the
window member 73 has the structural integrity and durability to transmit torque
trom the annular drive plate 63 to the outer ramp plate 51. As is also well *
known to those skilled in the art, the aluminum window member 73 will slightly
increase the flux density, as compare to air.
[0041] At the same time, and as may best be seen in FIG. 4, tine annular
window member 73 is disposed axially between the sensing coil 71 and the
nner ramp plate 47, the axially movable member in the subject embodiment.
When a sensing current is imposed upon the sensing coil 71, the result is the

e ectromagnetic flux path F, as shown in FIG. 4. The flux path F passes
through the coll housing 65, around the sensing coll 71, passes through the
window member 73, across an adjacent air gap, then through part of the inner
ramp plate 47. As is known from the previous, brief description of the
operation of the rotation-limiting mechanism 35 and the electromagnetic
actuator 55, the Inner ramp plate 47 moves axially (see arrow in FIG. 4)
between a first condition (FIG. 2), corresponding to the unactuated condition of
the mechanism 35, and a second condition (position toward which inner ramp
plate 47 is moving in FIG. 4), corresponding to the actuated condition of the
mechanism 35.
[0042] In accordance with an important aspect of trie invention, as the axial
position of the inner ramp plate 47 changes, the magnetic flux path length
changes, but is unaffected by the window member 73. The changes in the flux
path length which result from the inner ramp plate 47 moving further from, or
closer to, the sensing coil 71 result in either a decrease or an increase,
respectively, in the flux density (or Inductance) of the flux path F. The changes
in flux density (or inductance) may then be sensed, or monitored, by an external
control circuitry which is capable of "converting" the sensed flux density (or
inductance) into a value representative of the changes in the axial separation
between the sensing coil 71 and the ramp plate 47.
[0043] Referring now primarily to FIG. 5, there is a graph of Voltage versus
Time, illustrating an important relationship utilized by one embodiment of the
sensing mechanism of the present invention. In connection with the
development of the invention, several different proximity-type sensing
arrangements were investigated, including one known as pulse induction (PI)
siensing. In a PI sensing arrangement, the sensing coil 71 is charged to a
known current ("Constant current pulse" in FIG. 5). This known current
produces a magnetic field which induces the magnetic flux path F shown in
FIG, 4. This flux path F stores energy in the materials (Energy = % LI2). The
-14-

known coil current is then abruptly terminated, causing the magnetic flux path F
to cease (decay) and energy to be dissipated. As the magnetic flux path F
cianges, the change will cause eddy currents to flow in the inner ramp plate 47,
but the eddy currents will decay slowly because of the internal resistance of the
ferromagnetic ramp plate 47.
[0044] As the above-described eddy currents flow in the ramp plate 47, the
eddy currents also produce a magnetic field, which, in turn, induces a current
back into the sensing coil 71, resulting in a back-EMF (electro-motive force).
When the resulting voltage (from the back-EMF) is measured across the
sensing coil 71, there is a negative voltage spike ("SPIKE" in FIG. 5), having an
exponential decay rate or curve, as shown in FIG. 5. The decay rate of the
regative spike is a function of the inductance, which, in turn, is directly related
to the air gap distance from the sensing coil 71 to the inner ramp plate 47,
However, it should be understood by those skilled in the sensing art that the
present Invention is not limited to the above-described, or any other particular,
sensing concept, except as specifically noted otherwise in the appended claims.
[0045] A variety of sensing systems are available and well known and the
present invention is not limited to pulse induction sensing. Tuned lank"
oscillator circuits, whereby an inductor and capacitor form a tuned frequency
oscillator, can be used as well to determine the distance by measuring the
frequency of oscillation. As this concept can be used to look for any metal, it
will not "see" thru the aluminum if the frequency is too high. It does include the
tuned oscillator front end circuitry. Other known magnetic proximity sensors
and LVDT arrangements could be implemented as well. It was found, in
connection with the development of the present invention, that the pulse
induction sensing was relatively simple and was effective when implemented in
this particular environment.
[0046] in view of the particular application for the present Invention, the

above-described sensing concept comprises a preferred embodiment, partly
because it was found to be effective under a broad range of operating
temperatures (from about -40 degrees Celsius to about 190 degrees Celsius),
and while immersed in various petrochemical-based lubricants (such as gear
o Is). Neither the temperature variations nor the various oils appeared to have
a negative effect upon the ability to accurately sense the change-of-state (axial
movement) of the ramp plate 47.
[0047] Referring now primarily to FIG. 6, there is illustrated a portion of an
electrical control circuitry, generally designated 81, which may be used to
implement the sensing concept illustrated and described in connection with
FIG. 5. In the circuit shown in FIG. 6, a Pulse Train (shown as the Constant
Current Pulse in FIG. 5) is an input to the control circuitry 81. The "Output" of
the control circuit 81 is an analog signal 91 which is representative of the
c istance of the inner ramp plate 47 from the sensing coil 71.
[3048] The invention has been described in great detail in the foregoing
specification, and it is believed that various alterations and modifications of the
invention will become apparent to those skilled in the art from a reading and
understanding of the specification. It is intended that all such alterations and
modifications are included in the invention, insofar as they come within the
scope of the appended claims.

what is claimed is:
1. A differential gear mechanism including a gear case (11) defining an axis
of rotation (A), and a gear chamber (13); differential gearing disposed in
said gear chamber including at least one input gear (17) and first (23)
and second (25) output gears; means (35) operable to limit rotation of
said first output gear (23) relative to said gear case (11), and actuation
means (55) for actuating said rotation limiting means (35), said actuation
means (55) being operable in response to an input (61), to move said
rotation limiting means from an unactuated condition (FIG. 1) to an
actuated condition (FIG. 4), said rotation limiting means (35) including a
member (47), disposed toward one axial end of said gear case (11) and
moveable in the direction of said axis of rotation (A) between a first
position (FIG. 1) corresponding to said unactuated condition of said
rotation limiting means (35), and a second position (FIG. 4)
corresponding to said actuated condition, characterized by:
(a) a sensor assembly being disposed adjacent said one axiai end of
said gear case (11) and including a sensor element (71) and a
wall-like member (63,73) disposed axially between said rotation
limiting means (35) and said actuation means (55);
(b) said wall-like member (63,73) including a non-ferromagnetic
portion (73) disposed axially between said sensor element (71)
and said moveable member (47), whereby movement of said
moveable member between said first (FIG. 1) and said second
(FIG. 4) positions results in a corresponding change in the
electromagnetic flux (F) coupling said sensor element (71) and
said moveable member (47).

2. A differential gear mechanism as claimed in claim 1, characterized by
said means operable to limit rotation of said first output gear (23) relative
to said gear case (11) includes a plurality of lock members (41) disposed
within openings (39) defined by said one axial end (37) of said gear case
(11), and axiaily rnoveable from an unlocked position (FIG. 1) to a locked
position, in engagement with mating openings (69) defined by said first
output gear (23).
3. A differential gear mechanism as claimed in claim 1, characterized by
said actuation means (55) comprises a first electromagnetic coil (57)
disposed adjacent said one axial end (37) of said gear case (11) and
disposed generally concentrically about said axis of rotation (A).
4. A differential gear mechanism as claimed in claim 3, characterized by
said wall-like member including a ferromagnetic portion (63) disposed
axiaily between said first electromagnetic coil (57) and said rotation
limiting means (35), said sensor element (71) being disposed radially
inward from said first electromagnetic coil (57),
5. A differential gear mechanism as claimed in claim 4, characterized by
said sensor element comprises a second electromagnetic coil (71) being
disposed generally concentrically about said axis of rotation (A).
(5. A differential gear mechanism as claimed In claim 5, characterized by
said first (57) and second (71) electromagnetic coils being disposed
within a common, ferromagnetic coil housing (65), said coil housing (65)
being fixed relative to an outer differential housing (66).

7 A mechanism including a case (11) defining an axis (A) and a chamber;
said mechanism Including an actuation means (55) for actuating the
mechanism, the actuation means (55) being operable in response to an
input (61) to move the mechanism from an unactuated condition (FIG, 1)
to an actuated condition (FIG. 4); the mechanism including an axially
moveable member (47) disposed toward one axial end (37) of the case
(11) and moveable in the direction of the axis (A) between a first position
(FIG. 1) corresponding to said unactuated condition of the mechanism,
and a second position (FIG. 4) corresponding to said actuated condition,
characterized by:
(a) a sensor assembly being disposed adjacent said one axial end
(37) of said case (11) and including a sensor element (71) and a
walHike member (63,73) disposed axially between the mechanism
and the actuation means (55);
(b) said wall-like member (63,73) including a non-ferromagnetic
portion (73) disposed axially between said sensor element (71)
and said axially moveable member (47), whereby movement of
said axially moveable member (47) between said first (FIG. 1) and
said second (FIG, 4) positions results in a corresponding change
in the electromagnetic flux (F) coupling said sensor element (71)
and said axially moveable member (47); and
(c) said sensor element comprises an electromagnetic coil (71)
disposed adjacent said one axial end (37) of said case (11) and
disposed generally concentrically about said axis (A).
il A mechanism as claimed in claim 7, characterized by said actuation
means (55) comprises a first electromagnetic coll (57) disposed adjacent
said one axial end (37) of said case (11) and disposed generally
concentrically about said axis (A), said sensor element comprising a

second electromagnetic coil (71).
9. A mechanism as claimed in claim 8, characterized by said wall-like
member including a ferromagnetic portion (63) disposed axially between
said first electromagnetic coil (57) and said mechanism, said second
electromagnetic coil (71) being disposed radially inward from said first
electromagnetic coil (57).

A differential having means (35) operable to limit
rotation of an output guar (23) relative to gear case
(11), and actuation means (55) for actuating the
rotation limiting means, for an unactuated (FIG.1) to
an actuated condition (FIG.4). The rotation limiting
means includes a member (47), toward one axial end of
the gear case and moveable between a first position,
the unactuated condition of said rotation limiting
means and a second position, the actuated condition. A
sensor assembly is adjacent the one axial end of the
gear case and includes a sensor element (71) and a
wall-like member between the rotation limiting means
and the actuation means. The wall-like member includes
a non-ferromagnetic portion (73) between the sensor
and the moveable member. Movement between the first and
second positions results in a corresponding change in
the electromagnetic flux (F) coupling the sensor
element and the moveable member.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=oFfQqNg3dJjvnmfuMoAclQ==&loc=wDBSZCsAt7zoiVrqcFJsRw==

« Previous Patent

Next Patent »

Patent Number

269707

Indian Patent Application Number

2380/KOLNP/2008

PG Journal Number

45/2015

Publication Date

06-Nov-2015

Grant Date

02-Nov-2015

Date of Filing

12-Jun-2008

Name of Patentee

EATON CORPORATION

Applicant Address

EATON CENTER 1111 SUPERIOR AVENUE, CLEVELAND, OHIO

Inventors:

#	Inventor's Name	Inventor's Address
1	NOFZINGER SCOTT, L.	5405 TEAL ROAD, PETERSBURG, MI 49270
2	HEATWOLE, GREGORY, L.	121 W. KENOSHA BOULEVARD, FT. WAYNE, IN 46807

PCT International Classification Number

F16H 48/20

PCT International Application Number

PCT/IB2006/003587

PCT International Filing date

2006-12-13

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/304,334	2005-12-15	U.S.A.