Title of Invention

RETRACTABLE SUSPENSION SYSTEM THROUGH CONTROLLED KINEMATICS

Abstract

A retractable suspension system for a multi axle vehicle comprising a straight link [7] for carrying a driven axle [2] at its front end; an angled link [8] for carrying a tag axle [3] at its rear end; the rear end of the straight link [7] being rotatably connected to the fulcrum point of the angled link [8]; a support bracket [10] for connecting the straight link [7] to a frame [1] of the vehicle; a removable locking link [9] for connecting the front end of the angled link [8] to the straight link [7] so as to lock the movement between the straight link [7] and the angled link [8]; a first locking pin 15[1] for engaging one end of the locking link [9] with the straight link [7]; a second locking pin 15[2] for engaging the other end of the locking link [9] with the front end of the angled link [8]; said locking link [9] comprising a first locking position 16[1] for locking the straight link [7] and the angled link [8] thereby the tag axle [3] is in normal condition and a second locking position 16[2] for locking the straight link [7] and the angled link [8] thereby the tag axle [3] is in lifted condition; a screw-jack unit for lifting and lowering the tag axle [3].

Full Text

RETRACTABLE SUSPENSION SYSTEM THROUGH CONTROLLED KINEMATICS FIELD OF THE INVENTION The present invention relates to a novel retractable suspension system for a vehicle. This is a mechanical suspension system that handles the retraction and the normal working conditions gracefully thereby working as a normal rugged suspension during its normal working condition and lifts the tag axle and holds it in the lifted position when necessary. BACKGROUND OF THE INVENTION Auxiliary axles [non-driven axles or tag axels] are sometimes added to the basic vehicle chassis to meet specialized hauling requirements, which can increase payload carrying capacity and / or facilitate compliance with local, state and federal road and bridge laws. When properly integrated into the vehicle, auxiliary axles can provide fleets owner and operators with financial and performance benefits in terms of reduced tire wear and improved fuel consumption. The tag axles can be lifted during periods of empty, or light, running. From a strictly economic sense, it is desirable to operate fully loaded as far as possible. But in reality, a certain amount of empty running is inevitable. For a Multi Axle Vehicle, the facility to lift and retain a non-driven axle clear off the ground when partially loaded can be economic in terms of both tire life and fuel consumption. Lifting of tag axles can also transfer weight temporarily to the drive axle for increased traction. Liftable Axle is designed to deploy, in a downward position, a portion of the load during normal highway operations, and to be retracted in order to relinquish contact with the ground for off-road operations or for highway operation in unloaded or light-load conditions when the weight bearing requirement is substantially less. US 3,285,261 and US 4,573,704 reports that under light load or no load conditions, the presence of additional axles, more than what is necessary, can lead to undesirable effects such as: 1. Higher Rolling Resistance 2. Losses in Fuel Economy 3. Engine Wear 4. Steering and Handling difficulties in some conditions 5. Losses in traction by the driven axle in some conditions The choice of having a liftable tag axle can deliver the following advantages as stated in US 4,300,787 and 5,549,322 : 1. Tire wear is reduced on the auxiliary axle while rolling resistance and fuel consumption are decreased in off-road operations and in lights loads or unloaded conditions. 2. Reduce tire scrub on the auxiliary axle during slow speed job site maneuvers, or when cornering a loaded vehicle. 3. Decreases the load imposed on the front axle of truck making steering loads lighter, while increasing the weight and traction on the driving wheels. 4. Shortening the wheel base to aid maneuverability. 5. Reduce suspension, axle bearing and brake maintenance with empty vehicles. 6. Minimize road or bridge tolls on an empty or partially loaded vehicle [toll collection is often based on the number of axles in contact with the ground] 7. Improve ride quality when the vehicle is running empty. Hydraulic and pneumatic lift mechanisms are available for lifting the tag axle. However, such mechanism is not attractive particularly from an Indian perspective for the following reasons: 1. The cost of fuel and economic conditions necessitate engine power to be less compared to those of American and European vehicles. This makes the Indian vehicles power-hungry thereby restricting the luxury of tapping power from the engine for operating auxiliary hydraulic and pneumatic devices. 2. Pneumatic and hydraulic devices are expensive to buy and to maintain. 3. Indian roads and weather conditions are challenging enough to add to the maintenance cost. In view of the above-mentioned limitations of sophisticated designs, there is a need to develop a robust yet simple retractable suspension system devoid of pneumatic or hydraulic power, and solely dependent on manual effort which can provide improved ride quality and easy maintenance. SUMMARY OF THE INVENTION In order to exploit the advantages of a liftable tag axle as explained in the previous section and ensure that the functionality of the suspension does not depend on hydraulic or pneumatic power, the object of the present invention is to provide a novel retractable suspension system. The suspension system of the present invention is a mechanical linkage based manual retractable suspension system using the concept of controlled kinematics, which implies addition or deletion of structural member[s] in the suspension systems, resulting in alteration of the kinematic state of the suspension mechanism. The concept of retractable suspension is applicable to vehicles, where the rear-most axle is non-driven, and on trailer application, where the trailer axles are non-driven. The present invention has been explained in terms of a multi-axle vehicle. The present invention provides a retractable suspension system for a multi axle vehicle comprising a straight link for carrying a driven axle at its front end; an angled link for carrying a tag axle at its rear end; the rear end of the straight link being rotatably connected to the fulcrum point of the angled link; a support bracket for connecting the straight link to a frame of the vehicle; a removable locking link for connecting the front end of the angled link to the straight link so as to lock the movement between the straight link and the angled link; a first locking pin for engaging one end of the locking link with the straight link; a second locking pin for engaging the other end of the locking link with the front end of the angled link; said locking link comprising a first locking position for locking the straight link and the angled link thereby the tag axle is in normal condition and a second locking position for locking the straight link and the angled link thereby the tag axle is in lifted condition; a screw-jack unit for lifting and lowering the tag axle. The tag axle, that is to be lifted, is carried by an angled link shaped like a boomerang and the driven axle in front of this tag axle is carried by a straight link. The angled link and the straight link are locked using a locking link. The locking link locks the whole setup by making a rigid triangular arrangement thereby creating kinematic inadmissibility. The purpose of load sharing by the two axles is taken care by this locked configuration. The driven axle is suspended using leaf springs. The other set of leaf springs is attached to the fulcrum point of angled link, which is rotably connected to the rear end of the straight link. During normal working conditions where both the axles are required on the ground to share the load, the triangular locking arrangement formed by the straight link, the angled link and the locking link holds the two axles at ground position. Now in times of retraction, the integral screw-jack unit is used to lift the tag axle. This is done after disengaging the locking link. After the axle has been lifted up, the locking link is engaged again and the screw-jack unit is relieved. Again, with the help of the locking link the whole linkage mechanism is locked, with the tag axle in lifted position. When the tag axle is to be brought down for normal working conditions, the screw-jack unit releases the tag axle after disengaging the locking link. The straight link and the angled link are locked, with both the axles on the ground. The screw-jack unit comes in use only when the tag axle is to be released or lifted up. When the vehicle is under operation, the locking link takes the dynamic load and the screw-jack unit is never subjected to any static or dynamic vehicle loads. BRIEF DESCRIPTION OF THE DRAWINGS The present invention is described with the help of the accompanying drawings in which: Figure 1 : shows a retractable suspension system of the present invention in normal position Figure 2 : shows exploded view of screw-jack unit, locking link and pins. Figure 3 : shows the retractable suspension system of the present invention in lifted position Figure 4 : shows isometric view of the retractable suspension system of the present invention Figure 5 : shows a ride comparison in normal and lifted position. DETAILED DESCRIPTION OF THE PREFERRED EMBOIMENTS OF THE INVENTION The Figure 1 shows the side view of the retractable suspension system of the present invention. The suspension system comprises a straight link [7] [load sharing link] which is connected to the base of two leaf springs [4, 5] at it ends. At the centre of the straight link [7], it is connected to a frame [1] of the vehicle through a first locking pin [15[1]] and a support bracket [10]. To the front end of the straight link [7], a driven axle [2] is connected through a bracket [20] as shown in figure 4. The suspension system further comprises an angled link [8] which holds a tag axle [3] through a bracket [21] at its rear end. The front end of the angled link [8] holds a second locking pin [15[2]]. The fulcrum for the angled link [8] is rotatably connected to the rear end of the straight link [7] where second rear leaf spring [5] is attached. The angle of the angled link [8] is calculated based on the distance of the tag axle [3] from the fulcrum and also the amount of force required on the angled link [8] to lift the whole tag axle [3] along with the tires. The straight link [7] and the angled link [8] are joined with a locking link [9] by making a triangular mechanism and thereby locking the whole system, hence when the locking link [9] is in place, the straight link [7] and the angled link [8] act as a single unit and this locked system has only one degree of freedom with respect to the frame, i.e. the first locking pin [15[1]] position. The locking link [9] includes a first locking position [16[1]] and a second locking position [16[2]]. The first locking position [16[l]]is for locking the straight link [7] and the angled link [8] in a normal position of the suspension system. The second locking position [16[2]] is for locking the straight link [7] and the angled link [8] in a lifted position of the suspension system. The locking link [9] makes the kinematic inadmissibility to the whole linkage system. This is the link that takes the static as well as the dynamic load of the system during vehicle operation. The connection of this locking link [9] with the frame [1] is via first locking pin [15[1]] supported by the support bracket [10] attached to the frame [1]. Figure 2 shows a screw jack unit which is used to lift the tag axle from the normal position to the lifted position as well as to bring the tag axle from the lifted position to the normal position. The screw-jack unit comprises a claw [11], a screw [12], a jack [13] and a nut [14]. The jack [13] can rotate about the first locking pin [15[1]]. The jack [13] is on the first locking pin [15[1]] and this has a revolute joint with respect to the frame [1]. There is a play [17] provided at the claw [11] and the screw [12] connection place, this is to accommodate slight offset in the second locking pin [15[2]] while working conditions. Recess is provided in the claw [11] shape to provide a stable configuration during lifting and pulling of the second locking pin [15[2]]. The shape of the claw [11] is designed to ensure that the second pin [15[2]] does not have a tendency to slip from the claw [11] when the screw-jack unit is in operation. The claw has initial clearance to accommodate the diameter of the second locking pin [15 [2]] and then a depression to prevent the second pin [15[2]] to slip off during operation of the screw-jack-unit During the locked positions of the straight link [7] and the angled link [8], the screw jack arrangement is left free, i.e. claw [11] is no longer in contact with the second locking pin [15[2]]. The screw-jack unit is kept free so that the threads of the screw [12] do not take the load coming on the locked linkage mechanism during vehicle operations. The figure 2 also shows the locking link [9] which comprises a first locking position 16[1] and a second locking position 16[2]. The locking link [9] locks the straight link [7] and the angled link [8] in its first locking position with the help of the second locking pin 15 [2] during the normal position. The straight link [7] and the angled link [8] are locked at the second locking position 16[2] of the locking link [9] with the help of the second locking pin 15 [2] during the lifted position. The locking link [9] is held in place with the help of nuts 19[1] and 19[2]. The first and the second locking positions 16[1] and 16[2] can be in the form of holes as shown in the figure 2. During operations when both the axles are required on the ground, the locking link [9] locks the straight link [7] and the angled link [8] as shown in Figure 1. The second locking pin [15 [2]] is held by the angled link [8] and the locking link [9] at the first locking position [16[1]]. During uneven road conditions, as extra upward displacement [compared to tag axle [3]] is input to driven axle [2], the locked linkage mechanism will have a tendency to rotate about the first locking pin [15[1]], thereby transferring extra downward force to the tag axle [3] [based on the leverage given during designing]. The first rear leaf spring [4] and the second rear leaf spring [5] together act as suspension for the dual axle system. During operations when the tag axle [3] is not required, the tag axle [3] needs to be lifted, leaving contact from the ground. The screw-jack arrangement is used to lift the tag-axle [3], which is subsequently placed in the lifted position using the locking link [9]. The angled link [8] and the locking link [9] are held in the second locking position 16[2] by the second locking pin 15[2]. For retraction of the tag axle [3], the locking link [9] is removed temporarily by removing the nuts [19[1, 2]]. The claw [11] arrangement of the screw-jack unit is positioned to hold the second locking pin [15[2]]. The nut [14] of the screw-jack unit is tightened such that the screw [12] starts traveling downward thereby rotating the angled link [8] in counter-clockwise direction and hence lifting the tag axle [3] upwards. Once the tag axle [3] has reached the lifted position, the locking link [9] is brought back and the second locking position [16[2]] of the locking link [9] goes into the second locking pin [15[2]], and the nuts [19[1, 2]] are placed back. The screw-jack unit is relieved and claw [11] leaves second locking pin [15[2]] and the screw-jack unit goes back to rest. With second locking pin [15[2]] in the second locking position [16[2]] of the locking link [9], the linkage mechanism again becomes locked and at this position the tag axle [3] is in lifted position [Ref: Figure 3]. The lift achieved [18] in this configuration can be seen in Figure 3. During lifted position, the load coming on the driven axle [2] is shared by both the leaf springs [4 and 5]. Again when the tag axle [3] is required on ground, the locking link [9] is removed after removing the nuts [19[1, 2]] and the screw-jack unit is fitted into the second locking pin [15[2]] and the nut [14] is rotated in opposite direction, thereby pushing the screw [12] upwards and hence the angled link [8] starts rotating in clockwise direction. When the tag axle [3] touches the ground, the first locking position [16[1]] of the locking link [9] holds the second locking pin [15[2]] and the screw-jack unit is relieved of the static load. The lifting and lowering of the tag axle can be activated by any known conventional means. The screw jack arrangement described herein is only a preferred arrangement. It is also possible to replace the screw jack arrangement with hydraulics and pneumatic mechanisms. The suspension system of the present invention is designed to raise the tag axle to the desired height above the ground and to effectively lower the tag axle into full engagement with the ground. The retractable suspension system of the present invention is completely manual and does not tap any sort of energy from the vehicle. The ride of the vehicle becomes softer during the lifted condition of the tag axle. The retractable suspension system will provide a better ride to the driver compared to a normal multi-axle vehicle with all the axles on ground during unladen condition of the vehicle. As explained above, as the angled link [8] is rotated about its fulcrum, using the screw-jack unit, the tag axle [3] gets lifted. When the tag axle [3] lifts off the ground, the second rear leaf spring [5] is pulled downwards, due to this the straight link [7] rotates in clockwise direction thereby pushing the first rear leaf spring [4] upwards and this creates a force in the first rear leaf spring [4] in downward direction, which is opposing the load coming on the driven axle [2], thereby decreasing the preload in the first rear leaf spring [4]. Due to reduced preload, the operating range changes to a softer ride condition during the lifted position as shown in Figure 5. Support Bracket [10] serves as a fulcrum point for the retraction mechanism. The support bracket [10] also acts as a mounting point for the shackle/ slipper [6[1]] of the first rear leaf spring [4] and the eye of the second rear leaf spring [5]. It is also a mounting point for the screw-jack unit and the locking link [9]. Additionally the support bracket [10] offers local reinforcement to the frame [1]. Normally leaf springs [4 and 5] are mounted on the axle, but here the second rear leaf spring [5] is not mounted on the tag axle [3]. The second rear leaf spring [5] is mounted on a dummy carrier that will act as a fulcrum for the angled link [8]. The suspension system of the present invention can be used for springs other than leaf springs. In the retractable suspension system of the present invention, when working with both the wheels on ground, the leaf springs [the suspension system] are not under loaded condition. The bushing at the first locking pin [15[1]] is going to take the load in flat road conditions. And the leaf springs come into existence only in uneven road conditions. In view of this, the number of leafs can be reduced. Further, there is a possibility of reducing the frame height. Retractable suspension system of the present invention can be applicable to driven axles also, provided a disengagement mechanism is there to disengage the drive.

Documents:

1013-che -2006 abstract.pdf

1013-che -2006 claims.pdf

1013-che -2006 complete description.pdf

1013-che -2006 correspondance -others.pdf

1013-che -2006 correspondance -po.pdf

1013-che -2006 drawings.pdf

1013-che -2006 form 1.pdf

1013-che -2006 form 3.pdf

1013-che-2006 abstract granted.pdf

1013-che-2006 claims granted.pdf

1013-CHE-2006 CORRESPONDENCE OTHERS.pdf

1013-CHE-2006 CORRESPONDENCE PO.pdf

1013-che-2006 description (complete) granted.pdf

1013-che-2006 drawings granted.pdf

1013-CHE-2006 FORM 1.pdf

1013-CHE-2006 FORM 18.pdf

1013-CHE-2006 FORM 9.pdf

1013-CHE-2006 POWER OF ATTORNEY.pdf