Title of Invention	A MECHANICAL SERVO LINKAGE FOR AGRICULTURAL TRACTOR'S HYDRAULIC CONTROL SYSTEM
Abstract	1. A mechanical servo linkage for tractor s iiydraulic control system performing raising and lowering of a position control mechianism and a draft control lesbianism corresponding feedback control mechanisms characterized in the position control mechanism and the draft control mechanism interfaced with a main lever 7; a position cam 6 contoured for attaching to and detaching from main lever 7, and a draft cam 26 also contoured for attaching to and detaching from main lever 7. 2, A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism, the said position control mechanism comprising:- - a housing 34; - a concentric hollow shaft 20 supported in housing 34; - a horizontal shaft 3 supported in the concentric hollow shaft 20; - a position control lever 1 fixed onto shaft 3, operable between first position and second position wherein first position is top position and second position is down position, where the shift from first to second position is clockwise; - a position crank 4 fixed with threaded grub screw onto shaft 3, operable by position control lever 1 for corresponding clock wise and anti-clock wise rotary motion; - a roller 5 disposed in the slot formed on position crank 4 and operable with crank 4; - a cam 6 comprising contour in first portion operable by roller 5 movement in the first contour portion for corresponding clockwise and anti-clockwise rotary motion. - a main lever 7 operable by cam 6 for corresponding rotary motion along its pivot screw 15 which screw is fixedly screwed in housing 34; - a spring arbor assembly 10 coupled to the main lever 7 at its first end through a revolute joint; - a front lever 11 coupled to the spring arbor assembly 10 at the second end of the spring arbor assembly 10 with a revolute joint for corresponding reverse rotary motion along Its pivot screw 12, which screw 12 is fixedly screwed onto housing 34; - a push rod 13 threaded onto front lever 11 for corresponding forward and backward displacement; - a valve lifter 14 coupled to the push rod 13 operable by the push rod for corresponding inward and outward motion; - a crank 16 comprising a first portion operable by the valve lifter 14 for corresponding rotary clockwise and anti-clockwise motion; - a hydraulic shaft 33 connected fixedly by means of splines to the crank 16 for corresponding motion; - a set of lift arm 17 rigidly fixed on hydraulic shaft 33 by means of splines, also correspondingly rotate in the same direction as crank 16, thereby performing the corresponding raising and lowing of the hitch.

Title of Invention

A MECHANICAL SERVO LINKAGE FOR AGRICULTURAL TRACTOR'S HYDRAULIC CONTROL SYSTEM

Abstract

1. A mechanical servo linkage for tractor s iiydraulic control system performing raising and lowering of a position control mechianism and a draft control lesbianism corresponding feedback control mechanisms characterized in the position control mechanism and the draft control mechanism interfaced with a main lever 7; a position cam 6 contoured for attaching to and detaching from main lever 7, and a draft cam 26 also contoured for attaching to and detaching from main lever 7. 2, A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism, the said position control mechanism comprising:- - a housing 34; - a concentric hollow shaft 20 supported in housing 34; - a horizontal shaft 3 supported in the concentric hollow shaft 20; - a position control lever 1 fixed onto shaft 3, operable between first position and second position wherein first position is top position and second position is down position, where the shift from first to second position is clockwise; - a position crank 4 fixed with threaded grub screw onto shaft 3, operable by position control lever 1 for corresponding clock wise and anti-clock wise rotary motion; - a roller 5 disposed in the slot formed on position crank 4 and operable with crank 4; - a cam 6 comprising contour in first portion operable by roller 5 movement in the first contour portion for corresponding clockwise and anti-clockwise rotary motion. - a main lever 7 operable by cam 6 for corresponding rotary motion along its pivot screw 15 which screw is fixedly screwed in housing 34; - a spring arbor assembly 10 coupled to the main lever 7 at its first end through a revolute joint; - a front lever 11 coupled to the spring arbor assembly 10 at the second end of the spring arbor assembly 10 with a revolute joint for corresponding reverse rotary motion along Its pivot screw 12, which screw 12 is fixedly screwed onto housing 34; - a push rod 13 threaded onto front lever 11 for corresponding forward and backward displacement; - a valve lifter 14 coupled to the push rod 13 operable by the push rod for corresponding inward and outward motion; - a crank 16 comprising a first portion operable by the valve lifter 14 for corresponding rotary clockwise and anti-clockwise motion; - a hydraulic shaft 33 connected fixedly by means of splines to the crank 16 for corresponding motion; - a set of lift arm 17 rigidly fixed on hydraulic shaft 33 by means of splines, also correspondingly rotate in the same direction as crank 16, thereby performing the corresponding raising and lowing of the hitch.

Full Text	FIELD OF INVENTION: The present invention relates to an agricultural tractor and more particularly relates to an improved mechanical servo linkage for agricultural tractor's hydraulic control system performing rising and of hitch with position control mechanism and draft control mechanism with corresponding feedback control mechanism BACKGROUND OF THE INVENTION The present invention relates to a mechanical servo linkage for agricultural tractor's hydraulic control system. This servo linkage working in closed loop with a hydraulic distributor, a hydraulic actuator and with input from hand operated levers, can control the position of hitch linkage within a given range and can automatically regulate the working depth of an implement. The servo linkage can also control the position of an auxiliary implement. Various types of mechanical servo linkages for agricultural tractor's hydraulic control system are known. Typical mechanical servo linkages consist of two external hand operated levers for input to the mechanism, internal position and draft control mechanism and a draft sensing unit mounted external to the hydraulic control system housing. A typical internal linkage consists of a cam mounted on hydraulic shaft to incorporate feedback in the system, heavy springs to limit the displacement signal to hydraulic distributor and complex links to complete the input to hydraulic distributor. Conventional internal linkages also have two parallel linkages, one each for position control and draft control mechanism, which give displacement or input to the hydraulic disthbutor. The parallel linkages working in tandem form a summation junction for the mechanism. Draft sensing unit, typically consists of a draft sensing device, which can be a cantilever type sponge plate, or a helical hot coiled long spring, or a torsion bar; a top link bracket which has slots to receive the top link of hitch linkage; and finally an arrangement to hold above together. A drawback of a conventional mechanical servo linkage of aforesaid type, is coarser control of working depth of the hitch-mounted implement. This can be attributed to high hysteresis and friction losses due to stiff springs and motion loss due to play at joints of the complex mechanism. Another drawback of the conventional linkage is the need to remember settings of hand levers by tractor operator in case levers are moved temporarily to another location, which ultimately results in disturbed settings of hand lever. This condition occurs when implement is lifted temporarily while tractor takes a turn in the field. To improve on above mentioned drawbacks of a conventional servo mechanical linkage and incorporate new features, either a complex mechanical linkage occupying large amount of space or an expensive electronic interface may be required. Prior Art search/Reference cited: 1. Specification No. 78256 .Accepted on 10'^ May, 1963-, Government of India: The patent office, 214, Lower circular road, Calcutta. "Improvements Relating to Tractor Hydraulics Control Systems" by Massey-Ferguson Ltd. SUMMARY OF INVENTION The aim of the present invention is to overcome aforesaid disadvantages by means Df improvements in mechanical servo linkage, which is simple in design, has less lumber of parts and is easy to manufacture. 3y combining improved mechanical servo linkage with conventional linkages the present invention provides a wide variety of control mechanism. In present invention t is possible to have "pure position control", "automatic pure draft control", "automatic nixed-mode position and draft control", "float control" and "quick lift control" of the itch linkage. With improved mechanical servo linkage it is possible to achieve very fine positioning of the hitch linkage of the order of 350 steps, which in a conventional linkage can be up to 200 steps only. The linkage in present invention can also regulate the draft signal with 10% accuracy at higher draft forces and with 25 % accuracy at lower draft forces, making the agricultural tractor suitable for sandy soil. A known conventional linkage can give maximum accuracy of 33%) only. Also, as opposed to a minimum value of 150kgf of horizontal top link draft force for a conventional linkage, the linkage in present invention can sense a minimum horizontal top link draft force of 10Okgf. A quick lift control mechanism is also incorporated in the present invention. With the help of this feature the tractor operator can quickly raise or lower the hitch linkage without disturbing the settings of hand operated levers. In order to achieve the objective mentioned above, the invention discloses an improved mechanical servo linkage, which composes of, a forged position crank and cam with machined profiles, as forged lever main and draft cam, parts of draft sensing unit which includes a pair of helical cold coiled draft springs, pair of bar stock machined cups and holders, a top link bracket, and finally a quick lift mechanism which consists of thumb operated levers. BRIEF DESCRIPTION ON THE DRAWINGS With reference to the drawings, the preferred embodiment of the present invention is illustrated as follows. Fig.l is a fragmentary section through the center of the housing of tractor showing control mechanism for position control mode, Fig.2 is a fragmentary section through the center of the housing of tractor showing control mechanism for draft control mode. Fig-3 is a perspective view of the mechanism for quick lift control in exploded state. Fig.4 is a perspective view of assembly of draft spring 32 and related parts in partly sectioned and partly exploded state. Fig. 5 is a perspective view showing assembly of lever main 7, position cam 6 and position crank 4 in exploded state, DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in detail with reference to the illustrated preferred embodiments. In the present invention, the mechanical servo linkage has three hand levers and a pair of button type levers, mounted alongside a stationary quadrant 18. "Position control", is selected using position control hand lever 1. "Automatic pure and mixed-mode draft control" and "float control" are selected using combinations of different settings of position control hand lever 1, draft control hand lever 2 and finger-tip hand lever 44. Quick lift control is performed using lever 40 housed in casing 42 which is held on to quadrant 18 by means of an interface 43, Fig.3, In fig.l, control mechanism is shown for position control. The position control range is between limit positions shown by position control hand lever 1 in full and dotted lines. The full-lines position represents the fully lowered position of the hitch, whereas dotted line position is the transport position of the hitch i.e. when hitch is at its maximum raised position. In between position of position control hand lever 1 on the quadrant 18 corresponds to only one position of the hitch. Position control hand lever 1 is fixed to a horizontal shaft 3 supported in a concentric hollow shaft 20, fig. 2, which is supported in housing 34. Both shaft 3 and hollow shaft 20 extend into the housing 34. On the other end of shaft 3 which is inside housing 34, position crank 4 is fixed by means of a grub screw 47 which goes through the threading in position crank 4 and into the dimple made in the shaft 3. On clockwise rotation of position control hand lever 1 from full-line position to any position on the quadrant 18, position crank 4 also rotates in clockwise direction. Roller 5, which is free to move up down inside the slot given in position crank 4, climbs up the incline plane on position cam 6 pressing against lever main 7. As a result lever main 7 rotates in clockwise direction about its pivot, special screw 15, which is screwed inside the housing 34. This motion is passed to spring-arbor assembly 10, whose one end forms a revolute joint with a pin on the leg of lever main 7. Other end of spring-arbor assembly 10 forming a revolute joint with front lever 11, gives anti-clockwise rotation to front lever 11, which is pivoted on special screw 12 screwed inside the housing 34, Push rod 13 threaded on front lever 11 pushes valve lifter 14 of distributor assembly 19 inside and into lift position of spool valve of distributor assembly 19- Oil from pump goes inside hydraulic actuator moving piston outwards and rotating crank 16 in anti-clockwise direction through connecting rod. Hydraulic shaft 33 rigidly connected to crank 16 and lift arms 17 rigidly connected to hydraulic shaft 33, both by means of splines, also rotate in anti¬clockwise direction performing raising of the hitch. Stopping action of the hitch occurs when spool valve of distributor assembly 19 is brought to neutral condition. This action is performed through a feedback lever 8 pivoted on pin 9, which is connected to crank 16, While in raise mode of hitch, when crank 16 is rotating in anti-clockwise direction, feedback lever 8 moves downwards while at other end pushing position cam 6 to rotate in clockwise direction. On arm of position cam 6 a pin is welded, which receives one end of feedback lever 8, to form a revolute joint. At one stage, roller 5 wedged between position cam 6 and lever main 7 will start climbing down the inclined plane of the position cam 6. To close the gap thus created between lever main 7 and roller 5, lever main 7 will rotate in anti-dock wise direction. This happens under the action of spring of spool valve of distributor assembly 19, which pushes the valve lifter 14 outwards and making front lever 11 rotate in clockwise direction and lever main 7 in anti-clockwise direction. This would continue until spool valve of distributor assembly 19 comes back to neutral position, Reverse of above will happen if position control hand lever 1 is rotated anti-clockwise from any position on quadrant 18 towards its full-line position. Rotation of position control hand lever 1 from one extreme position to another can produce a large amount of linear travel of valve lifter 14 and thus spool valve of distributor assembly 19. Since valve lifter 14 of distributor assembly 19 has only a limited travel of few millimeters it is required that major part of angular movement of position control hand lever 1 be absorbed and rest transmitted to the valve lifter 14. As shown in fig. 1 and fig. 5, position cam 6 has been given a typical geometry consisting of an inclined plane merging with a circular surface. The circular surface is almost concentric to the arc given in lever main 7 on its topside. Roller 5 will push lever main 7 only till the end of incline plane of position cam 6. As soon as roller 5 reaches the circular surface of position cam 6 further push to lever main 7 does not occur. To accomplish above, a conventional mechanical linkage employs a heavy spring, which compresses when force acting on it increases due to excess motion given by hand levers. However, as described above, in the present invention, this is accomplished by use of position cam 6. In this way use of heavy springs is avoided, which has resulted in reduced force in the linkage members lowering overall fhction and has given increased accuracy simultaneously. Refer fig. 5 for geometric details of position cam 6. As described above, it is noteworthy that in present linkage, feedback from crank 16 is not by means of any dedicated cam mounted on hydraulic shaft 33, but it is through a four bar mechanism formed by position cam 6, feedback link 8 and crank 16. This mechanism is superior to one having a cam mounted on hydraulic shaft 33, as it reduces complicated cam geometries and simultaneously ensures accuracy of the control. In fig.2, control mechanism is shown for draft control. Draft control is divided into four zones viz. "dead zone", "draft zone", "neutral zone" and "lift zone". Draft control hand lever 2 shown in full-line is in draft range and the one shown in dotted lines is at lift point. On quadrant 18, towards right side of lift point is so called "lift zone" and at left end of the quadrant 18 is "dead zone" of draft control, fig. 2. Draft control hand lever 2 is fixed to hollow shaft 20. On the other end of hollow shaft 20 an across flat is given on which lever draft 35 is mounted. It is fixed there by means of a grub screw 47 which goes through the threading in lever draft 35 and presses against the surface of hollow shaft 20. From left end of quadrant 18, clockwise rotation of draft control hand lever 2, also rotates the hollow shaft 20 and in same direction. Lever draft 35 being an integral part of hollow shaft 20 rotates in the same direction. As shown in fig.3, coupler 21 pivoted at one end to lever draft 35 is pushed downwards by this action. At other end of coupler 21 a roller 22 is attached, which riding on lever main 7 is also pushed towards draft cam 26. Opposite happens if the draft control hand lever 2 is moved anti-clockwise. Starting from left end position on quadrant 18, draft control hand lever 2 needs to cover some distance so that linkage starts sensing the external draft force through top link bracket 30. This distance is called "dead zone". This zone is required to get good float control operation. Moving draft control hand lever 2 further on the quadrant 18 brings draft control hand lever 2 into "draft range". This position of draft control hand lever 2 is shown by full lines, fig-2. The value of draft to be sensed decreases when draft control hand lever 2 is moved towards right end of quadrant 18. This is due to the reduction in the gap between draft roller 22 and draft cam 26. As shown in fig. 2 and fig. 3, draft roller 22 is also guided by a sliding lever 23, which has one end pivoted with draft roller 22 and the slotted end guided at pin guide 24. Pin guide 24 is rigidly connected to sliding lever 23. This arrangement gives support to draft roller 22 and prevents it from dislocating while assembly. Also, with this arrangement sliding lever 23 will not move when linkage receives draft signal, thereby further reducing friction loss when compared to known conventional linkage. To work in pure draft control mode assume that hitch linkage is lowered to its least height by keeping position control hand lever 1 at its extreme left position on quadrant 18 and draft control hand lever 2 is kept in draft range. The implement cutting the soil would maintain its level until the ground reaction on the implement approaches the value set by draft control hand lever 2. At this point, top link of hitch linkage pivoted to top link bracket 30 in one of the holes, will exert a compressive force on the top link bracket 30 against the force of two draft spring 32 which are of helical coil type. Clockwise rotation of top link bracket 30 will happen. Extension link 55 rigidly connected to top link bracket 30 at its bottom, will move forward by a distance equal to the compression of the draft spring 32. Feedback rod 28 forms two revolute joints, one with extension link 55 and another with the pin of h-link 25. Other end of h-link 25 is rigidly connected to shaft 27, which goes inside housing 34 and is supported in a hollow screw 47, the hollow screw being mounted on housing 34 from outside. Due to this arrangement forward motion of feedback rod 28 will result in rotation of both h-link 25 and shaft 27 in clockwise direction. Inside the housing 34, draft cam 26 which is rigidly connected to the shaft 27 with a dowel pin will also rotate in clockwise direction. If the forward motion of feedback rod 28 is enough such that the draft cam 26 presses the roller 22 against lever main 7, lever main 7 will rotate in clockwise direction. This will rotate the front lever 11 in anti-clockwise direction via spring-arbor assembly 10, Valve lifter 14 is then pushed inside by push rod 13 making spool valve of distributor assembly 19 to move in lift position, raising the lift arms 17. Opposite will happen once the force exerted by the top link on top link bracket 30 decreases {draft decreases). Lift arms 17 will again come down to the initial state. Opposite of above will happen when draft force on top link bracket 30 through top link is tensile, i.e. when top link bracket 30 is pulled. The range of draft force sensed by linkage is equal both in compressive and tensile loading. In addition to serving as a motion transmitting device, draft cam 26 has to serve another purpose also. The draft force on top link bracket 30 is fluctuating one and it is not unusual for it to reach a value, which can produce maximum compression of draft spring 32. Since, all this displacement should not get transmitted to spool valve of distributor assembly 19 due to limited travel of spool valve, excess travel must be absorbed by the linkage as is done in case of position control. In this case, draft cam 26 transmits only a limited amount of displacement to lever main 7. This is achieved by giving a radius profile in draft cam 26, vt/hich is concentric to the arc in lever main. Due to this geometry, roller 22 being pushed by draft cam 26 transmits motion to lever main 7 til! it doesn't come under the two concentric arcs. Again, use of heavy spring is avoided to absorb this extra displacement, thereby simplifying the design and reducing hysteresis losses in the system. In fig.2 and fig. 4 it is shown that draft spring 32 is placed between cup 31 and holder 49, and is also guided by holder 49. Cup 31 is guided in the bore of housing 34 and bore of flange 54. Holder is placed against the vi/all of housing 34 and flange 54 is held on to housing 34 by means of screws. A bolt 50 passes through holder 49, draft spring 32 and cup 31 to lock these parts together with top link bracket 30. A nut 53 is screwed on to bolt 50 against clamping surface of top link bracket 30 and head of bolt 50 butting against step in holder 49. Also, to prevent loosening of nut due to frequent application and release of load on top link bracket 30, a lock pin 52 along with shims 51 is inserted in bolt 50. As shown in fig.4, a pair of above described arrangement is used to complete the mechanism. When Cup 31 slides linearly into the bore of the housing 34 due to a compressive draft force on top link bracket 30, it results into compression of draft spring 32, since holder 49 is held stationary against the wall of housing 34. A tensile force on top link bracket 30 will rotate top link bracket 30 in anti-clockwise direction, pulling nut 53 and bolt 50 along with it. This will result in movement of holder 49 away from housing. In that case collar of cup 31 butting against flange 54 will not allow cup 31 to come out. Draft spring 32 will compress. Above arrangement is configured to be assembled in a small space. Two helical coiled draft springs 32, which are cold coiled, are designed so as to replace one longer spring found in known present systems, which would otherwise occupy more space and need to undergo expensive hot coiling process. Also, in this arrangement, cup 31 and holder 49 have been optimized so as to give sufficient to guide to draft spring 32 and reduce hysteresis due to rubbing action. Collar of cup 31 has easy to manufacture profile, which also ensures proper guide and minimizes friction with mating part. Also, the arrangement does not require any shims to adjust pre- compression of draft spring 32 because tolerances on parts limit the value in acceptable range. In fig. 2, shown by dotted lines, if draft control hand lever 2 is kept near lift point {starting from left hand side) on the quadrant 18, roller 22 will come in contact with draft cam 26. On further clockwise rotation of draft control hand lever 2, roller 22 pushing against draft cam 26 will make lever main 7 to rotate in clockwise direction, This forces the spring-arbor assembly 10 and causes front lever 11 to rotate in anti¬clockwise direction. Valve lifter 14 is moved inside pushing spool valve of distributor assembly 19 into delivery position, thus raising the lift arms 17, thereby generating neutral and lift zone. In position control system wherein lift arms 17 come to stop due to feedback mechanism composed of crank 16, pin 9 and feedback lever 8, fig. 1. However, when draft control hand lever 2 is kept in lift zone, roller 22 wedged between draft cam 26 and lever main 7, does not allow lever main 7 to come to its initial position under the action of spring of spool valve of distributor assembly 19. A separate safety provision called "auto-thp mechanism", is made to stop lifting action of lift arms 17. In this case, lift arms 17 will come to stop only when the piston which is moving out from the hydraulic actuator, comes in contact with the autotrip lever 45, fig. 2. Autotrip lever 45 forms a simple four-bar mechanism with front lever 11 and autotrip support 46, which is pivoted at other end on the special screw 15 and placed beside lever main 7. Force exerted by the piston will cause autotrip lever 45 to rotate front lever 11 in anti-clockwise direction against the action of spring of spring-arbor assembly 10. This action will release contact between push rod 13 and valve lifter 14, letting spool valve of distributor assembly 19 to come outwards to the neutral position, thus halting rotation of lift arms 17, Spring of spring-arbor assembly 10 compresses only when auto-trip mechanism functions. Compression of this spring is so adjusted such that under normal working of linkage mechanism it will not compress and will transmit all the motion to valve lifter 14. Operation in mixed-mode position and draft control is done by first moving the position control hand lever 1 until the maximum working depth of the implement has been attained. Then determine the desired minimum working depth by operating draft control hand lever 2 by keeping it in draft zone. In mixed-mode control, setting of position control hand lever 1 along with lever main 7, roller 5 (fig.1), position cam 6 and valve lifter 14 prevent the spool valve to enter the lowering position. Now the implement cannot sink even if the draft acting on the implement diminishes. If the draft increases to the limit set by the draft control hand lever 2, the implement will be raised. Implement will come down back to its initial position {set by the position control hand lever 1) when draft acting at implement decreases- In the described linkage, Lever main 7 sen/es as a summation junction. Mixed-mode draft control is possible because of lever main 7, which creates an interface between position and draft control mechanism. In conventional linkage, in place of lever main 7, two separate links are used to complete the linkage, making it a complex linkage and reducing Its accuracy. Fig. 5 shows the detailed geometry and features of lever main 7. In addition to above, lever main 7 has a provision to receive a press fitted pin guide 24. the purpose of which is to give guide to sliding lever 23 as shown in fig. 3. As shown in fig. 5, Lever main 7 also holds a dowel pin, which is meant to limit the travel of position crank 4 and prevent it from falling down while assembling. Lever main 7 has additional provision on its front leg to fix pins at different locations. This will enable variation of mechanical advantage given by lever main 7 for different tractor models. To assist the tractor operator working in draft control mode, a third hand lever called finger tip hand lever 44 is mounted alongside draft control hand lever 2 and has no connection with internal control mechanism. Usually same position is set for both draft control hand lever 2 and finger tip hand lever 44. While operating the tractor it may be required that draft control hand lever 2 be temporarily taken from its set position in draft zone to lift zone and then brought back to its initial position. In that case, finger tip hand lever 44 stays at initial position of draft control hand lever 2 and serves as a memory lever for the operator. Fig.3 shows quick lift control mechanism, which is an 'actuation cum release' mechanism for lifting implement. Pressing a lever 40 Vi/ith thumb raises lift arms 17 to transport height and pulling release lever 41 brings lift arms 17 back to initial position. These levers are housed in a casing 42, which is held on to quadrant 18 by means of an interface 43. Unlike the draft and position control hand levers, used for precise control of the hitch linkage quick lift mechanism instantly triggers the spool of distributor assembly 19 to lift position, moving hitch to the transport height {irrespective of hand lever settings). Pivoting on special screw 48, lever 40 when pressed from topside, will push link 38 against the force of two extension springs 39. This will make link 38 rotate about shaft of lever-shaft assembly 37, whose shaft is connected by means of a dowel pin to link 38 and is supported in the housing 34. On the other end of fever-shaft assembly 37, which is inside housing 34, the lever part will push pin guide 24, which is rigidly connected to lever main 7, This action will make lever main 7 rotate. This action will lead to spool valve of distributor assembly 19 to move to lift condition and raise the lift arms 17 till the actuation of auto-trip mechanism. Lever 40 when pressed gets locked with release lever 41, with the help of two extension springs 39. Then it is not necessary to keep pressing lever 40 in order to raise lift arms 17. One extension spring 39 ensures contact between lever 40 and link 38. Other extension spring 39 ensures contact between lever 40 and release lever 41 and also brings lever 40 back to its initial condition, Lowering of lift arms 17 will happen when release lever 41 of quick lift control mechanism, is actuated. In that case it will release lever 40, thus releasing force on lever main 7, which brings spool valve of distributor assembly 19 to lowering position. In quick lift mechanism, lever 40, release lever 41 and casing 42 are specially profiled for ease of operation by thumb. 38 is a hollow pipe, which simplifies the design and interface with other parts in the mechanism. Operation in float control is performed by keeping both position and draft control hand levers at extreme left end of quadrant 18- With this setting of mechanism, implement will only follow the contour of the ground. No draft sensing will happen. Thus, the embodiment of the apparatus in accordance with the present invention has been described in detail and it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the features of the present invention. WE CLAIM :- 1. A mechanical servo linkage for tractor s iiydraulic control system performing raising and lowering of a position control mechianism and a draft control lesbianism corresponding feedback control mechanisms characterized in the position control mechanism and the draft control mechanism interfaced with a main lever 7; a position cam 6 contoured for attaching to and detaching from main lever 7, and a draft cam 26 also contoured for attaching to and detaching from main lever 7. 2, A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism, the said position control mechanism comprising:- - a housing 34; - a concentric hollow shaft 20 supported in housing 34; - a horizontal shaft 3 supported in the concentric hollow shaft 20; - a position control lever 1 fixed onto shaft 3, operable between first position and second position wherein first position is top position and second position is down position, where the shift from first to second position is clockwise; - a position crank 4 fixed with threaded grub screw onto shaft 3, operable by position control lever 1 for corresponding clock wise and anti-clock wise rotary motion; - a roller 5 disposed in the slot formed on position crank 4 and operable with crank 4; - a cam 6 comprising contour in first portion operable by roller 5 movement in the first contour portion for corresponding clockwise and anti-clockwise rotary motion. - a main lever 7 operable by cam 6 for corresponding rotary motion along its pivot screw 15 which screw is fixedly screwed in housing 34; - a spring arbor assembly 10 coupled to the main lever 7 at its first end through a revolute joint; - a front lever 11 coupled to the spring arbor assembly 10 at the second end of the spring arbor assembly 10 with a revolute joint for corresponding reverse rotary motion along Its pivot screw 12, which screw 12 is fixedly screwed onto housing 34; - a push rod 13 threaded onto front lever 11 for corresponding forward and backward displacement; - a valve lifter 14 coupled to the push rod 13 operable by the push rod for corresponding inward and outward motion; - a crank 16 comprising a first portion operable by the valve lifter 14 for corresponding rotary clockwise and anti-clockwise motion; - a hydraulic shaft 33 connected fixedly by means of splines to the crank 16 for corresponding motion; - a set of lift arm 17 rigidly fixed on hydraulic shaft 33 by means of splines, also correspondingly rotate in the same direction as crank 16, thereby performing the corresponding raising and lowing of the hitch. 3. A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism, as claimed in claim 1 characterized in the feedback mechanism of the position control mechanism comprising:- - a feedback lever 8 operable by second portion of crank 16 to operate cam 6 further with roller 5 movement in the contour of second portion of cam 6 thereby rendering main lever 7 inoperable by cam 6; - a spring action of the spool valve of distributor assembly 19 further operable on valve lifter 14 for its outward movement thereby resulting in spool valve distributor assembly 19 moving to lower the lift arms 17, 4. A mechanical steno linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism, the draft control mechanism for performing draft raising and lowering of the hitch, the said draft control mechanism comprising:- - a concentric hollow shaft 20; - a draft hand lever 2 fixed to shaft 20 operable between first top position and second down position where the shift from first to second position is clockwise; - a draft lever 35 fixed on the other end of shaft 20 across a flat, rotating along the shaft 20 in same direction; - a coupler 21 pivoted at one end of draft lever 35; - a sliding lever having a slotted end guided with a pin guide 24; - a draft roller 22 attached at its one end to the other end of the coupler and at its other end pivoted with draft roller 22, adapted to ride correspondingly on main lever 7 thereby performing the corresponding raising and lowering of the hitch. 5. A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism, as claimed in claim 1 characterized in the feedback mechanism of draft control mechanism comprising:- - a housing 34; - a top link pivoted on hitch linkage with a top link bracket 30; - a pair of draft spring 32 (helical coil type) exert compressive force on top link bracket 30, when valve set by draft control hand lever 2 is arrived at predetermined level, thereby rotating the top link bracket 30 in clockwise direction; - a extension link 55 rigidly connected to top link bracket 30 at its bottom movable forward by a distance equal to the compression of the draft spring 32. - a feedback rod 28 forming a revolute joint with extension link 55 at its one end. - a H link 25 forming at one end a revolute joint with the second end of the feedback rod 28. - a shaft 27 onto which the second end of H link 25 is rigidly fixed, the shaft 27 being supported in screw 47 & screw 47 is supported in housing 34; - a draft cam 26 supported on shaft 27 with a dowel pin having a radius profile concentric to the arc of main lever such that roller 22 pushed by draft cam 26 transmits motion to main lever 7 such that the poniard motion of feedback rod 28 will rotate in the same direction correspondingly rotating the roller 22 riding on the main lever 7 thereby 17 rotating the main lever 7 in same direction until it does not come under the two concentric arcs at which point renders the main lever 7 inoperable by cam 6 resulting in spool valve distributor assembly 19 moving to lower the lift arms 17. 6. A feedback mechanism of the draft control mechanism claimed in claim 5 characterized in the feedback mechanism of the draft control mechanism including a draft control memory mechanism comprising of a finger tip hand lever 44 mounted along side draft control hand lever 2 with the same position setting as of hand lever 2, wherein the finger tip lever 44 remains in the initial position of draft control hand lever 2 when the draft control hand lever 2 temporarily moves away from a set position, thereby serving as a memory lever for the draft control operation. 7. A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism with corresponding feedback control mechanisms as claimed in claim 1 having a quick lift control mechanism comprising:- - a press type lever 40 adapted to raise lift arm 17 and - a press type lever 41 adapted to lower lift arm 17, characterized in both lever housed in casing 42, - lever 40 pivoted on specific screw 48; - a push link 38 operable pushed by lever 40 against force of two extension springs 39 making the link 38 rotate about lever-shaft assembly 37; wherein the shaft end is coupled to link 38 with a dowel pin and supported in the housing 34; wherein the lever end is disposed within housing 34 thereby pushing the pin guide 24 rigidly connected to main lever 7, thereby rotating the main lever 7 and resulting in spool valve of the distributor assembly moving to raise the lift arm 17; - characterized in the lever 41 adapted to release lever 40, thereby releasing the force on main lever 7, resulting in spool valve of distributor assembly 19 moving to lower the lift arm 17. A mechanical linkage for tractor's hydraulic control system with a position control mechanism having a cam 6 as claimed in claim 1 and 2, christened in the cam 6 having the first contour in first portion and the second contour in the second portion. The position control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 2, characterized in position crank 4 and position lever 1 to move the roller 5 along the first portion with first contour of the cam 6 so as to move cam 6 towards the main lever 7. 10. The feedback mechanism of the position control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 3, charactenzed in feedback lever 8 and crank 16 to move roller 5 along the second portion with second contour of cam 6 so as to move cam 6 away from the main lever 7. 11. A mechanical servo linkage for tractor's hydraulic control system with a position control mechanism having a cam 6 as claimed in claim 1 and 2, charactenzed in the profile of cam 6 having a first inclined plane portion and a second portion with circular consenting arc surface in line with main lever 7. 12. The draft control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 4, characterized in draft lever 35 and coupler 21 to rotate roller 22 ending on the main lever 7 so as to couple with the draft cam 26. 13. The feedback mechanism of draft control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 5, characterized in feedback rod 28 and shaft 27 to rotate draft cam 26 to couple with roller 22 riding on the main lever 7. 14. The feedback mechanism of draft control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 5, characterized in the draft song 32 placed between a cup 31 and a holder 49 with the cup 31 disposed in the base of housing 34 and bore of flange 54, which flange is screwed to housing 34 and the holder 49 placed against the wall of housing 34, a locking bolt 50 passing through the holder 49, draft spring 32 and the cup 31, thereby locking with the top link bracket 30, a nut 53 screwed onto bolt 50 against clamping surface of top link bracket 30 and the head of bolt 50 butting against the step in holder 49, a lock pin 52 with shim 51 inserted in bolt 50 to prevent loosening of nut 53-

Full Text

FIELD OF INVENTION:
The present invention relates to an agricultural tractor and more particularly relates to an improved mechanical servo linkage for agricultural tractor's hydraulic control system performing rising and of hitch with position control mechanism and draft control mechanism with corresponding feedback control mechanism
BACKGROUND OF THE INVENTION
The present invention relates to a mechanical servo linkage for agricultural tractor's hydraulic control system. This servo linkage working in closed loop with a hydraulic distributor, a hydraulic actuator and with input from hand operated levers, can control the position of hitch linkage within a given range and can automatically regulate the working depth of an implement. The servo linkage can also control the position of an auxiliary implement.
Various types of mechanical servo linkages for agricultural tractor's hydraulic control system are known. Typical mechanical servo linkages consist of two external hand operated levers for input to the mechanism, internal position and draft control mechanism and a draft sensing unit mounted external to the hydraulic control system housing. A typical internal linkage consists of a cam mounted on hydraulic shaft to incorporate feedback in the system, heavy springs to limit the displacement signal to hydraulic distributor and complex links to complete the input to hydraulic distributor.
Conventional internal linkages also have two parallel linkages, one each for position control and draft control mechanism, which give displacement or input to the hydraulic disthbutor. The parallel linkages working in tandem form a summation junction for the mechanism.
Draft sensing unit, typically consists of a draft sensing device, which can be a cantilever type sponge plate, or a helical hot coiled long spring, or a torsion bar; a top link bracket which has slots to receive the top link of hitch linkage; and finally an arrangement to hold above together.

A drawback of a conventional mechanical servo linkage of aforesaid type, is coarser control of working depth of the hitch-mounted implement. This can be attributed to high hysteresis and friction losses due to stiff springs and motion loss due to play at joints of the complex mechanism.
Another drawback of the conventional linkage is the need to remember settings of hand levers by tractor operator in case levers are moved temporarily to another location, which ultimately results in disturbed settings of hand lever. This condition occurs when implement is lifted temporarily while tractor takes a turn in the field.
To improve on above mentioned drawbacks of a conventional servo mechanical linkage and incorporate new features, either a complex mechanical linkage occupying large amount of space or an expensive electronic interface may be required.
Prior Art search/Reference cited:
1. Specification No. 78256 .Accepted on 10'^ May, 1963-, Government of India: The patent office, 214, Lower circular road, Calcutta.
"Improvements Relating to Tractor Hydraulics Control Systems" by Massey-Ferguson Ltd.
SUMMARY OF INVENTION
The aim of the present invention is to overcome aforesaid disadvantages by means Df improvements in mechanical servo linkage, which is simple in design, has less lumber of parts and is easy to manufacture.
3y combining improved mechanical servo linkage with conventional linkages the present invention provides a wide variety of control mechanism. In present invention t is possible to have "pure position control", "automatic pure draft control", "automatic nixed-mode position and draft control", "float control" and "quick lift control" of the itch linkage.

With improved mechanical servo linkage it is possible to achieve very fine positioning of the hitch linkage of the order of 350 steps, which in a conventional linkage can be up to 200 steps only.
The linkage in present invention can also regulate the draft signal with 10% accuracy at higher draft forces and with 25 % accuracy at lower draft forces, making the agricultural tractor suitable for sandy soil. A known conventional linkage can give maximum accuracy of 33%) only. Also, as opposed to a minimum value of 150kgf of horizontal top link draft force for a conventional linkage, the linkage in present invention can sense a minimum horizontal top link draft force of 10Okgf.
A quick lift control mechanism is also incorporated in the present invention. With the help of this feature the tractor operator can quickly raise or lower the hitch linkage without disturbing the settings of hand operated levers.
In order to achieve the objective mentioned above, the invention discloses an improved mechanical servo linkage, which composes of, a forged position crank and cam with machined profiles, as forged lever main and draft cam, parts of draft sensing unit which includes a pair of helical cold coiled draft springs, pair of bar stock machined cups and holders, a top link bracket, and finally a quick lift mechanism which consists of thumb operated levers.
BRIEF DESCRIPTION ON THE DRAWINGS
With reference to the drawings, the preferred embodiment of the present invention is illustrated as follows.
Fig.l is a fragmentary section through the center of the housing of tractor showing control mechanism for position control mode,
Fig.2 is a fragmentary section through the center of the housing of tractor showing control mechanism for draft control mode.
Fig-3 is a perspective view of the mechanism for quick lift control in exploded state.

Fig.4 is a perspective view of assembly of draft spring 32 and related parts in partly sectioned and partly exploded state.
Fig. 5 is a perspective view showing assembly of lever main 7, position cam 6 and position crank 4 in exploded state,
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below in detail with reference to the illustrated preferred embodiments.
In the present invention, the mechanical servo linkage has three hand levers and a pair of button type levers, mounted alongside a stationary quadrant 18. "Position control", is selected using position control hand lever 1. "Automatic pure and mixed-mode draft control" and "float control" are selected using combinations of different settings of position control hand lever 1, draft control hand lever 2 and finger-tip hand lever 44. Quick lift control is performed using lever 40 housed in casing 42 which is held on to quadrant 18 by means of an interface 43, Fig.3,
In fig.l, control mechanism is shown for position control. The position control range is between limit positions shown by position control hand lever 1 in full and dotted lines. The full-lines position represents the fully lowered position of the hitch, whereas dotted line position is the transport position of the hitch i.e. when hitch is at its maximum raised position. In between position of position control hand lever 1 on the quadrant 18 corresponds to only one position of the hitch.
Position control hand lever 1 is fixed to a horizontal shaft 3 supported in a concentric hollow shaft 20, fig. 2, which is supported in housing 34. Both shaft 3 and hollow shaft 20 extend into the housing 34. On the other end of shaft 3 which is inside housing 34, position crank 4 is fixed by means of a grub screw 47 which goes through the threading in position crank 4 and into the dimple made in the shaft 3.

On clockwise rotation of position control hand lever 1 from full-line position to any position on the quadrant 18, position crank 4 also rotates in clockwise direction. Roller 5, which is free to move up down inside the slot given in position crank 4, climbs up the incline plane on position cam 6 pressing against lever main 7. As a result lever main 7 rotates in clockwise direction about its pivot, special screw 15, which is screwed inside the housing 34. This motion is passed to spring-arbor assembly 10, whose one end forms a revolute joint with a pin on the leg of lever main 7. Other end of spring-arbor assembly 10 forming a revolute joint with front lever 11, gives anti-clockwise rotation to front lever 11, which is pivoted on special screw 12 screwed inside the housing 34, Push rod 13 threaded on front lever 11 pushes valve lifter 14 of distributor assembly 19 inside and into lift position of spool valve of distributor assembly 19- Oil from pump goes inside hydraulic actuator moving piston outwards and rotating crank 16 in anti-clockwise direction through connecting rod. Hydraulic shaft 33 rigidly connected to crank 16 and lift arms 17 rigidly connected to hydraulic shaft 33, both by means of splines, also rotate in anti¬clockwise direction performing raising of the hitch.
Stopping action of the hitch occurs when spool valve of distributor assembly 19 is brought to neutral condition. This action is performed through a feedback lever 8 pivoted on pin 9, which is connected to crank 16, While in raise mode of hitch, when crank 16 is rotating in anti-clockwise direction, feedback lever 8 moves downwards while at other end pushing position cam 6 to rotate in clockwise direction. On arm of position cam 6 a pin is welded, which receives one end of feedback lever 8, to form a revolute joint.
At one stage, roller 5 wedged between position cam 6 and lever main 7 will start climbing down the inclined plane of the position cam 6. To close the gap thus created between lever main 7 and roller 5, lever main 7 will rotate in anti-dock wise direction. This happens under the action of spring of spool valve of distributor assembly 19, which pushes the valve lifter 14 outwards and making front lever 11 rotate in clockwise direction and lever main 7 in anti-clockwise direction. This would continue until spool valve of distributor assembly 19 comes back to neutral position,

Reverse of above will happen if position control hand lever 1 is rotated anti-clockwise from any position on quadrant 18 towards its full-line position.
Rotation of position control hand lever 1 from one extreme position to another can produce a large amount of linear travel of valve lifter 14 and thus spool valve of distributor assembly 19. Since valve lifter 14 of distributor assembly 19 has only a limited travel of few millimeters it is required that major part of angular movement of position control hand lever 1 be absorbed and rest transmitted to the valve lifter 14.
As shown in fig. 1 and fig. 5, position cam 6 has been given a typical geometry consisting of an inclined plane merging with a circular surface. The circular surface is almost concentric to the arc given in lever main 7 on its topside. Roller 5 will push lever main 7 only till the end of incline plane of position cam 6. As soon as roller 5 reaches the circular surface of position cam 6 further push to lever main 7 does not occur. To accomplish above, a conventional mechanical linkage employs a heavy spring, which compresses when force acting on it increases due to excess motion given by hand levers. However, as described above, in the present invention, this is accomplished by use of position cam 6. In this way use of heavy springs is avoided, which has resulted in reduced force in the linkage members lowering overall fhction and has given increased accuracy simultaneously. Refer fig. 5 for geometric details of position cam 6.
As described above, it is noteworthy that in present linkage, feedback from crank 16 is not by means of any dedicated cam mounted on hydraulic shaft 33, but it is through a four bar mechanism formed by position cam 6, feedback link 8 and crank 16. This mechanism is superior to one having a cam mounted on hydraulic shaft 33, as it reduces complicated cam geometries and simultaneously ensures accuracy of the control.
In fig.2, control mechanism is shown for draft control. Draft control is divided into four zones viz. "dead zone", "draft zone", "neutral zone" and "lift zone". Draft control hand lever 2 shown in full-line is in draft range and the one shown in dotted lines is at lift point. On quadrant 18, towards right side of lift point is so called "lift zone" and at left end of the quadrant 18 is "dead zone" of draft control, fig. 2.

Draft control hand lever 2 is fixed to hollow shaft 20. On the other end of hollow shaft 20 an across flat is given on which lever draft 35 is mounted. It is fixed there by means of a grub screw 47 which goes through the threading in lever draft 35 and presses against the surface of hollow shaft 20.
From left end of quadrant 18, clockwise rotation of draft control hand lever 2, also rotates the hollow shaft 20 and in same direction. Lever draft 35 being an integral part of hollow shaft 20 rotates in the same direction. As shown in fig.3, coupler 21 pivoted at one end to lever draft 35 is pushed downwards by this action. At other end of coupler 21 a roller 22 is attached, which riding on lever main 7 is also pushed towards draft cam 26. Opposite happens if the draft control hand lever 2 is moved anti-clockwise.
Starting from left end position on quadrant 18, draft control hand lever 2 needs to cover some distance so that linkage starts sensing the external draft force through top link bracket 30. This distance is called "dead zone". This zone is required to get good float control operation.
Moving draft control hand lever 2 further on the quadrant 18 brings draft control hand lever 2 into "draft range". This position of draft control hand lever 2 is shown by full lines, fig-2. The value of draft to be sensed decreases when draft control hand lever 2 is moved towards right end of quadrant 18. This is due to the reduction in the gap between draft roller 22 and draft cam 26.
As shown in fig. 2 and fig. 3, draft roller 22 is also guided by a sliding lever 23, which has one end pivoted with draft roller 22 and the slotted end guided at pin guide 24. Pin guide 24 is rigidly connected to sliding lever 23. This arrangement gives support to draft roller 22 and prevents it from dislocating while assembly. Also, with this arrangement sliding lever 23 will not move when linkage receives draft signal, thereby further reducing friction loss when compared to known conventional linkage.
To work in pure draft control mode assume that hitch linkage is lowered to its least height by keeping position control hand lever 1 at its extreme left position on

quadrant 18 and draft control hand lever 2 is kept in draft range. The implement cutting the soil would maintain its level until the ground reaction on the implement approaches the value set by draft control hand lever 2. At this point, top link of hitch linkage pivoted to top link bracket 30 in one of the holes, will exert a compressive force on the top link bracket 30 against the force of two draft spring 32 which are of helical coil type. Clockwise rotation of top link bracket 30 will happen. Extension link 55 rigidly connected to top link bracket 30 at its bottom, will move forward by a distance equal to the compression of the draft spring 32. Feedback rod 28 forms two revolute joints, one with extension link 55 and another with the pin of h-link 25. Other end of h-link 25 is rigidly connected to shaft 27, which goes inside housing 34 and is supported in a hollow screw 47, the hollow screw being mounted on housing 34 from outside. Due to this arrangement forward motion of feedback rod 28 will result in rotation of both h-link 25 and shaft 27 in clockwise direction.
Inside the housing 34, draft cam 26 which is rigidly connected to the shaft 27 with a dowel pin will also rotate in clockwise direction. If the forward motion of feedback rod 28 is enough such that the draft cam 26 presses the roller 22 against lever main 7, lever main 7 will rotate in clockwise direction. This will rotate the front lever 11 in anti-clockwise direction via spring-arbor assembly 10, Valve lifter 14 is then pushed inside by push rod 13 making spool valve of distributor assembly 19 to move in lift position, raising the lift arms 17. Opposite will happen once the force exerted by the top link on top link bracket 30 decreases {draft decreases). Lift arms 17 will again come down to the initial state.
Opposite of above will happen when draft force on top link bracket 30 through top link is tensile, i.e. when top link bracket 30 is pulled. The range of draft force sensed by linkage is equal both in compressive and tensile loading.
In addition to serving as a motion transmitting device, draft cam 26 has to serve another purpose also. The draft force on top link bracket 30 is fluctuating one and it is not unusual for it to reach a value, which can produce maximum compression of draft spring 32. Since, all this displacement should not get transmitted to spool valve of distributor assembly 19 due to limited travel of spool valve, excess travel must be absorbed by the linkage as is done in case of position control. In this case, draft cam

26 transmits only a limited amount of displacement to lever main 7. This is achieved by giving a radius profile in draft cam 26, vt/hich is concentric to the arc in lever main. Due to this geometry, roller 22 being pushed by draft cam 26 transmits motion to lever main 7 til! it doesn't come under the two concentric arcs. Again, use of heavy spring is avoided to absorb this extra displacement, thereby simplifying the design and reducing hysteresis losses in the system.
In fig.2 and fig. 4 it is shown that draft spring 32 is placed between cup 31 and holder 49, and is also guided by holder 49. Cup 31 is guided in the bore of housing 34 and bore of flange 54. Holder is placed against the vi/all of housing 34 and flange 54 is held on to housing 34 by means of screws. A bolt 50 passes through holder 49, draft spring 32 and cup 31 to lock these parts together with top link bracket 30. A nut 53 is screwed on to bolt 50 against clamping surface of top link bracket 30 and head of bolt 50 butting against step in holder 49. Also, to prevent loosening of nut due to frequent application and release of load on top link bracket 30, a lock pin 52 along with shims 51 is inserted in bolt 50. As shown in fig.4, a pair of above described arrangement is used to complete the mechanism.
When Cup 31 slides linearly into the bore of the housing 34 due to a compressive draft force on top link bracket 30, it results into compression of draft spring 32, since holder 49 is held stationary against the wall of housing 34. A tensile force on top link bracket 30 will rotate top link bracket 30 in anti-clockwise direction, pulling nut 53 and bolt 50 along with it. This will result in movement of holder 49 away from housing. In that case collar of cup 31 butting against flange 54 will not allow cup 31 to come out. Draft spring 32 will compress.
Above arrangement is configured to be assembled in a small space. Two helical coiled draft springs 32, which are cold coiled, are designed so as to replace one longer spring found in known present systems, which would otherwise occupy more space and need to undergo expensive hot coiling process. Also, in this arrangement, cup 31 and holder 49 have been optimized so as to give sufficient to guide to draft spring 32 and reduce hysteresis due to rubbing action. Collar of cup 31 has easy to manufacture profile, which also ensures proper guide and minimizes friction with mating part. Also, the arrangement does not require any shims to adjust pre-

compression of draft spring 32 because tolerances on parts limit the value in acceptable range.
In fig. 2, shown by dotted lines, if draft control hand lever 2 is kept near lift point {starting from left hand side) on the quadrant 18, roller 22 will come in contact with draft cam 26. On further clockwise rotation of draft control hand lever 2, roller 22 pushing against draft cam 26 will make lever main 7 to rotate in clockwise direction, This forces the spring-arbor assembly 10 and causes front lever 11 to rotate in anti¬clockwise direction. Valve lifter 14 is moved inside pushing spool valve of distributor assembly 19 into delivery position, thus raising the lift arms 17, thereby generating neutral and lift zone.
In position control system wherein lift arms 17 come to stop due to feedback mechanism composed of crank 16, pin 9 and feedback lever 8, fig. 1. However, when draft control hand lever 2 is kept in lift zone, roller 22 wedged between draft cam 26 and lever main 7, does not allow lever main 7 to come to its initial position under the action of spring of spool valve of distributor assembly 19. A separate safety provision called "auto-thp mechanism", is made to stop lifting action of lift arms 17.
In this case, lift arms 17 will come to stop only when the piston which is moving out from the hydraulic actuator, comes in contact with the autotrip lever 45, fig. 2. Autotrip lever 45 forms a simple four-bar mechanism with front lever 11 and autotrip support 46, which is pivoted at other end on the special screw 15 and placed beside lever main 7. Force exerted by the piston will cause autotrip lever 45 to rotate front lever 11 in anti-clockwise direction against the action of spring of spring-arbor assembly 10. This action will release contact between push rod 13 and valve lifter 14, letting spool valve of distributor assembly 19 to come outwards to the neutral position, thus halting rotation of lift arms 17,
Spring of spring-arbor assembly 10 compresses only when auto-trip mechanism functions. Compression of this spring is so adjusted such that under normal working of linkage mechanism it will not compress and will transmit all the motion to valve lifter 14.

Operation in mixed-mode position and draft control is done by first moving the position control hand lever 1 until the maximum working depth of the implement has been attained. Then determine the desired minimum working depth by operating draft control hand lever 2 by keeping it in draft zone.
In mixed-mode control, setting of position control hand lever 1 along with lever main 7, roller 5 (fig.1), position cam 6 and valve lifter 14 prevent the spool valve to enter the lowering position. Now the implement cannot sink even if the draft acting on the implement diminishes. If the draft increases to the limit set by the draft control hand lever 2, the implement will be raised. Implement will come down back to its initial position {set by the position control hand lever 1) when draft acting at implement decreases-
In the described linkage, Lever main 7 sen/es as a summation junction. Mixed-mode draft control is possible because of lever main 7, which creates an interface between position and draft control mechanism. In conventional linkage, in place of lever main 7, two separate links are used to complete the linkage, making it a complex linkage and reducing Its accuracy. Fig. 5 shows the detailed geometry and features of lever main 7.
In addition to above, lever main 7 has a provision to receive a press fitted pin guide 24. the purpose of which is to give guide to sliding lever 23 as shown in fig. 3. As shown in fig. 5, Lever main 7 also holds a dowel pin, which is meant to limit the travel of position crank 4 and prevent it from falling down while assembling. Lever main 7 has additional provision on its front leg to fix pins at different locations. This will enable variation of mechanical advantage given by lever main 7 for different tractor models.
To assist the tractor operator working in draft control mode, a third hand lever called finger tip hand lever 44 is mounted alongside draft control hand lever 2 and has no connection with internal control mechanism. Usually same position is set for both draft control hand lever 2 and finger tip hand lever 44. While operating the tractor it may be required that draft control hand lever 2 be temporarily taken from its set

position in draft zone to lift zone and then brought back to its initial position. In that case, finger tip hand lever 44 stays at initial position of draft control hand lever 2 and serves as a memory lever for the operator.
Fig.3 shows quick lift control mechanism, which is an 'actuation cum release' mechanism for lifting implement. Pressing a lever 40 Vi/ith thumb raises lift arms 17 to transport height and pulling release lever 41 brings lift arms 17 back to initial position. These levers are housed in a casing 42, which is held on to quadrant 18 by means of an interface 43.
Unlike the draft and position control hand levers, used for precise control of the hitch linkage quick lift mechanism instantly triggers the spool of distributor assembly 19 to lift position, moving hitch to the transport height {irrespective of hand lever settings). Pivoting on special screw 48, lever 40 when pressed from topside, will push link 38 against the force of two extension springs 39. This will make link 38 rotate about shaft of lever-shaft assembly 37, whose shaft is connected by means of a dowel pin to link 38 and is supported in the housing 34. On the other end of fever-shaft assembly 37, which is inside housing 34, the lever part will push pin guide 24, which is rigidly connected to lever main 7, This action will make lever main 7 rotate. This action will lead to spool valve of distributor assembly 19 to move to lift condition and raise the lift arms 17 till the actuation of auto-trip mechanism.
Lever 40 when pressed gets locked with release lever 41, with the help of two extension springs 39. Then it is not necessary to keep pressing lever 40 in order to raise lift arms 17. One extension spring 39 ensures contact between lever 40 and link 38. Other extension spring 39 ensures contact between lever 40 and release lever 41 and also brings lever 40 back to its initial condition,
Lowering of lift arms 17 will happen when release lever 41 of quick lift control mechanism, is actuated. In that case it will release lever 40, thus releasing force on lever main 7, which brings spool valve of distributor assembly 19 to lowering position.

In quick lift mechanism, lever 40, release lever 41 and casing 42 are specially profiled for ease of operation by thumb. 38 is a hollow pipe, which simplifies the design and interface with other parts in the mechanism.
Operation in float control is performed by keeping both position and draft control hand levers at extreme left end of quadrant 18- With this setting of mechanism, implement will only follow the contour of the ground. No draft sensing will happen.
Thus, the embodiment of the apparatus in accordance with the present invention has been described in detail and it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the features of the present invention.

WE CLAIM :-
1. A mechanical servo linkage for tractor s iiydraulic control system performing
raising and lowering of a position control mechianism and a draft control
lesbianism corresponding feedback control mechanisms characterized in the
position control mechanism and the draft control mechanism interfaced with a main
lever 7; a position cam 6 contoured for attaching to and detaching from main lever 7,
and a draft cam 26 also contoured for attaching to and detaching from main lever 7.
2, A mechanical servo linkage for tractor's hydraulic control system performing
raising and lowering of hitch with a position control mechanism and a draft control
mechanism, the said position control mechanism comprising:-
- a housing 34;
- a concentric hollow shaft 20 supported in housing 34;
- a horizontal shaft 3 supported in the concentric hollow shaft 20;
- a position control lever 1 fixed onto shaft 3, operable between first position and second position wherein first position is top position and second position is down position, where the shift from first to second position is clockwise;
- a position crank 4 fixed with threaded grub screw onto shaft 3, operable by position control lever 1 for corresponding clock wise and anti-clock wise rotary motion;
- a roller 5 disposed in the slot formed on position crank 4 and operable with crank 4;
- a cam 6 comprising contour in first portion operable by roller 5 movement in the first contour portion for corresponding clockwise and anti-clockwise rotary motion.
- a main lever 7 operable by cam 6 for corresponding rotary motion along
its pivot screw 15 which screw is fixedly screwed in housing 34;
- a spring arbor assembly 10 coupled to the main lever 7 at its first end through a revolute joint;
- a front lever 11 coupled to the spring arbor assembly 10 at the second end of the spring arbor assembly 10 with a revolute joint for corresponding

reverse rotary motion along Its pivot screw 12, which screw 12 is fixedly screwed onto housing 34;
- a push rod 13 threaded onto front lever 11 for corresponding forward and backward displacement;
- a valve lifter 14 coupled to the push rod 13 operable by the push rod for corresponding inward and outward motion;
- a crank 16 comprising a first portion operable by the valve lifter 14 for corresponding rotary clockwise and anti-clockwise motion;
- a hydraulic shaft 33 connected fixedly by means of splines to the crank 16 for corresponding motion;
- a set of lift arm 17 rigidly fixed on hydraulic shaft 33 by means of splines, also correspondingly rotate in the same direction as crank 16, thereby performing the corresponding raising and lowing of the hitch.
3. A mechanical servo linkage for tractor's hydraulic control system performing
raising and lowering of hitch with a position control mechanism and a draft control
mechanism, as claimed in claim 1 characterized in the feedback mechanism of the
position control mechanism comprising:-
- a feedback lever 8 operable by second portion of crank 16 to operate cam 6 further with roller 5 movement in the contour of second portion of cam 6 thereby rendering main lever 7 inoperable by cam 6;
- a spring action of the spool valve of distributor assembly 19 further operable on valve lifter 14 for its outward movement thereby resulting in spool valve distributor assembly 19 moving to lower the lift arms 17,
4. A mechanical steno linkage for tractor's hydraulic control system performing
raising and lowering of hitch with a position control mechanism and a draft control
mechanism, the draft control mechanism for performing draft raising and lowering of
the hitch, the said draft control mechanism comprising:-
- a concentric hollow shaft 20;
- a draft hand lever 2 fixed to shaft 20 operable between first top position and second down position where the shift from first to second position is clockwise;

- a draft lever 35 fixed on the other end of shaft 20 across a flat, rotating along the shaft 20 in same direction;
- a coupler 21 pivoted at one end of draft lever 35;
- a sliding lever having a slotted end guided with a pin guide 24;
- a draft roller 22 attached at its one end to the other end of the coupler and at its other end pivoted with draft roller 22, adapted to ride correspondingly on main lever 7 thereby performing the corresponding raising and lowering of the hitch.
5. A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism, as claimed in claim 1 characterized in the feedback mechanism of draft control mechanism comprising:-
- a housing 34;
- a top link pivoted on hitch linkage with a top link bracket 30;
- a pair of draft spring 32 (helical coil type) exert compressive force on top link bracket 30, when valve set by draft control hand lever 2 is arrived at predetermined level, thereby rotating the top link bracket 30 in clockwise direction;
- a extension link 55 rigidly connected to top link bracket 30 at its bottom movable forward by a distance equal to the compression of the draft spring 32.
- a feedback rod 28 forming a revolute joint with extension link 55 at its one end.
- a H link 25 forming at one end a revolute joint with the second end of the feedback rod 28.
- a shaft 27 onto which the second end of H link 25 is rigidly fixed, the shaft 27 being supported in screw 47 & screw 47 is supported in housing 34;
- a draft cam 26 supported on shaft 27 with a dowel pin having a radius profile concentric to the arc of main lever such that roller 22 pushed by draft cam 26 transmits motion to main lever 7 such that the poniard motion of feedback rod 28 will rotate in the same direction correspondingly rotating the roller 22 riding on the main lever 7 thereby
17

rotating the main lever 7 in same direction until it does not come under the two concentric arcs at which point renders the main lever 7 inoperable by cam 6 resulting in spool valve distributor assembly 19 moving to lower the lift arms 17.
6. A feedback mechanism of the draft control mechanism claimed in claim 5 characterized in the feedback mechanism of the draft control mechanism including a draft control memory mechanism comprising of a finger tip hand lever 44 mounted along side draft control hand lever 2 with the same position setting as of hand lever 2, wherein the finger tip lever 44 remains in the initial position of draft control hand lever 2 when the draft control hand lever 2 temporarily moves away from a set position, thereby serving as a memory lever for the draft control operation.
7. A mechanical servo linkage for tractor's hydraulic control system performing raising and lowering of hitch with a position control mechanism and a draft control mechanism with corresponding feedback control mechanisms as claimed in claim 1 having a quick lift control mechanism comprising:-

- a press type lever 40 adapted to raise lift arm 17 and
- a press type lever 41 adapted to lower lift arm 17, characterized in both lever housed in casing 42,
- lever 40 pivoted on specific screw 48;
- a push link 38 operable pushed by lever 40 against force of two
extension springs 39 making the link 38 rotate about lever-shaft
assembly 37;
wherein the shaft end is coupled to link 38 with a dowel pin and supported in the housing 34;
wherein the lever end is disposed within housing 34 thereby pushing the pin guide 24 rigidly connected to main lever 7, thereby rotating the main lever 7 and resulting in spool valve of the distributor assembly moving to raise the lift arm 17;
- characterized in the lever 41 adapted to release lever 40, thereby
releasing the force on main lever 7, resulting in spool valve of
distributor assembly 19 moving to lower the lift arm 17.

A mechanical linkage for tractor's hydraulic control system with a position control mechanism having a cam 6 as claimed in claim 1 and 2, christened in the cam 6 having the first contour in first portion and the second contour in the second portion.
The position control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 2, characterized in position crank 4 and position lever 1 to move the roller 5 along the first portion with first contour of the cam 6 so as to move cam 6 towards the main lever 7.
10. The feedback mechanism of the position control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 3, charactenzed in feedback lever 8 and crank 16 to move roller 5 along the second portion with second contour of cam 6 so as to move cam 6 away from the main lever 7.
11. A mechanical servo linkage for tractor's hydraulic control system with a position control mechanism having a cam 6 as claimed in claim 1 and 2, charactenzed in the profile of cam 6 having a first inclined plane portion and a second portion with circular consenting arc surface in line with main lever 7.
12. The draft control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 4, characterized in draft lever 35 and coupler 21 to rotate roller 22 ending on the main lever 7 so as to couple with the draft cam 26.
13. The feedback mechanism of draft control mechanism of the mechanical servo linkage for tractor's hydraulic control system as claimed in claim 1 and 5, characterized in feedback rod 28 and shaft 27 to rotate draft cam 26 to couple with roller 22 riding on the main lever 7.
14. The feedback mechanism of draft control mechanism of the mechanical servo
linkage for tractor's hydraulic control system as claimed in claim 1 and 5,
characterized in the draft song 32 placed between a cup 31 and a holder 49 with

the cup 31 disposed in the base of housing 34 and bore of flange 54, which flange is screwed to housing 34 and the holder 49 placed against the wall of housing 34, a locking bolt 50 passing through the holder 49, draft spring 32 and the cup 31, thereby locking with the top link bracket 30, a nut 53 screwed onto bolt 50 against clamping surface of top link bracket 30 and the head of bolt 50 butting against the step in holder 49, a lock pin 52 with shim 51 inserted in bolt 50 to prevent loosening of nut 53-

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=2wqw2wpzoQPCX2Z1LHi/IA==&loc=egcICQiyoj82NGgGrC5ChA==

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Patent Number

268582

Indian Patent Application Number

2079/CHE/2008

PG Journal Number

37/2015

Publication Date

11-Sep-2015

Grant Date

04-Sep-2015

Date of Filing

27-Aug-2008

Name of Patentee

TAFE MOTORS AND TRACTORS LIMITED

Applicant Address

Old No.35, New No.77, Nungambakkam High Road, Chennai -600034

Inventors:

#	Inventor's Name	Inventor's Address
1	ANIL SHARMA	TAFE MOTORS AND TRACTOR LTD, PLOT NO.1 SECTOR D, INDUSTRIAL AREA, MANDIDEEP 462 046 DISTRICT. RAISEN(NEAR BHOPAL)
2	PRADEEP MATHUR	TAFE MOTORS AND TRACTOR LTD, PLOT NO.1 SECTOR D, INDUSTRIAL AREA, MANDIDEEP 462 046 DISTRICT. RAISEN(NEAR BHOPAL)
3	RAJESH MALIK	TAFE MOTORS AND TRACTOR LTD, PLOT NO.1 SECTOR D, INDUSTRIAL AREA, MANDIDEEP 462 046 DISTRICT. RAISEN(NEAR BHOPAL)

PCT International Classification Number

A01B63/111

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA