GB2347397A - Suspension systems having greater roll resistance than cross articulation resistance - Google Patents

Abstract

Various suspension systems are disclosed in which vehicle pitch is controlled by controlling the resistance to fluid flow between interconnected hydraulic (or pneumatic) cylinders 42, 44 at the front and rear of the vehicle. Roll control is provided by mechanically interconnected torsion bars 20,22 so that vehicle roll is resisted more than cross articulation.

Description

Vehicle Suspensions The present invention relates to vehicle suspension systems, and in particular to such systems in which the resistance to vehicle roll and pitch and axle cross articulation can be controlled.

The present invention provides a suspension system for connecting two front wheels and two rear wheels to a vehicle body the system comprising: at least one front piston unit operating between the front wheels and the body, at least one rear piston unit operating between the rear wheels and the body, and a fluid interconnection which allows but resists fluid flow between the front and rear piston units thereby to control vehicle pitch; and front and rear torsion bars each connected between the wheels at a respective end of the vehicle and a second interconnection between the front and rear torsion bars arranged to provide greater resistance to vehicle roll than to cross articulation.

Preferably the system further comprises a beam axle between the two wheels at at least one end of the vehicle, said at least one piston unit at that end of the vehicle comprising a single piston unit operating on the centre of the beam axle.

Preferably said at least one piston unit at at least one end of the vehicle comprises a pair of interconnected piston units, each connecting a respective one of the wheels to the body. Each pair of piston units is preferably interconnected by a fluid interconnection which allows fluid to flow between said pair of piston units thereby facilitating their movement in opposite vertical directions, and from which the first interconnection leads to the other end of the vehicle.

The piston units may comprise air springs, in which case said interconnection or interconnections are conveniently formed as air interconnections allowing air to flow between the air springs.

Alternatively the piston units may each comprise a mechanical spring acting on a piston and the interconnection or interconnections be hydraulic interconnections allowing hydraulic fluid to flow between hydraulic chambers partly defined by the pistons.

Preferably the first interconnection includes a fluid accumulator which allows fluid to leave and enter it to accommodate vehicle bounce.

Each torsion bar may be connected to one of the wheels at its end of the vehicle by means of a crank member and the second interconnection be arranged to control rotation of the crank member relative to the torsion bar.

The second interconnection may be hydraulic and comprise a piston and cylinder assembly associated with each torsion bar, the cylinders being interconnected so that fluid can flow between them to allow cross articulation but the cylinders operate to tend to increase or decrease the volume of fluid in part of the interconnection under vehicle roll which is thereby resisted.

Preferably resilient means is provided in the interconnection to allow but resist the flow of fluid into or out of said volume thereby to allow but resist vehicle roll.

Alternatively each torsion bar may have a crank portion rigidly connected to it and extending away from its torsional axis the crank portion having one end rigidly connected to the axle of one of the wheels and the other end connected to the second interconnection wherein a part of the second interconnection is urged to move in opposite directions by said two other ends during vehicle roll, but is urged to move in the same direction by both said other ends during cross articulation such that the torsion bars will operate to provide more resistance to roll than to cross articulation.

Preferably the system further comprises a roll damper connected between said axle and said part of the second interconnection such that it provides more damping for roll than for cross articulation.

The second interconnection is preferably a hydraulic interconnection and said part of the second interconnection is preferably a piston, which may conveniently form part of the damper.

Preferably the piston comprises a cylinder in which a further piston is movable such that the cylinder and further piston form the damper.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic representation of a suspension system according to a first embodiment of the invention; Figures la and lb are enlargements of part of Figure 1; Figure 2 is a schematic representation of a suspension system according to a second embodiment of the invention; Figure 2a is an enlargement of part of Figure 2; Figures 3 and 4 are schematic views of different parts of a suspension system according to a third embodiment of the invention; and Figure 5 shows a hydraulic strut forming part of a fourth embodiment of the invention.

Referring to Figure 1, a vehicle has two front wheels 10a. lOb and two rear wheels 12a, 12b supported on front and rear beam axles 14,16. A vehicle body, not shown, is supported on the axles by four springs 18, one at each end of each axle.

A roll control system comprises a pair of front and rear torsion bars 20,22 each extending across the vehicle parallel to the respective axle. The right hand end of each bar 20,22 is bent round to form a horizontally extending crank portion 24 which is connected to the right hand end of the respective axle 14,16 by means of a vertical link 26. The left hand end of each bar 20,22 has a separate crank arm 28 extending perpendicularly from it, parallel to the crank portion 24. Each crank arm 28 is rotatably connected to the torsion bar 20,22 at one end so that it can rotate relative to the torsion bar 20,22 and is connected at the other end to the axle via a vertical link 30. A short control arm 32 is connected rigidly to the end of each torsion bar 20,22 near the crank arm 28 and has its upper end connected to the furthest end of the crank arm 28 by a hydraulic control strut 33. As shown in Figure la, each control strut comprises a cylinder 34 connected to the control arm 32 and divided into two chambers 36a, 36b by a piston 38 connected to the crank arm 28. Each of the chambers 36a, 36b is hydraulically connected to the corresponding chamber 36a, 36b on the other strut 33 by hydraulic lines 40a, 40b.

In operation, if the front and rear axles 14,16 rotate in opposite directions about the central longitudinal axis of the vehicle, i. e. in cross articulation, the crank arms 28 can rotate about the respective torsion bars 20,22, one upwards and one downwards (though in the same rotational direction, clockwise or anticlockwise) the pistons 38 moving along the cylinders 34 and hydraulic fluid flowing through the hydraulic lines 40a, 40b. The torsion bars 20,22 therefore provide no resistance to pure cross articulation apart from the damping effect of the hydraulic interconnection. In vehicle roll, i. e. when the front and rear axles 14,16 rotate in the same direction about the central longitudinal axis of the vehicle, the pistons 38 in the control struts 33 cannot move in the pistons 34 because they tend to compress the hydraulic fluid in one of the lines 40a, 40b and expand the fluid in the other. The crank arms 28 are therefore rotationally fast with the torsion bars 20,22 which operate as conventional one-piece anti-roll bars and resist wheel movement.

Clearly during normal operation the wheel movements will include components of roll and components of cross articulation. These components will be distinguished by the roll control system and only the roll components resisted by the torsion bars 20,22.

A pitch control system comprises front and rear pitch spring units 40,42 or rams each comprising a hydraulic cylinder 44 mounted on the vehicle body and a piston 46 slidable in the piston and connected to the centre of the respective beam axle 14,16. The working chambers of the two units 40,42 are each connected by a hydraulic line 43a, 43b to a respective side of a pitch control unit 48, shown in detail in Figure lb. This unit 48 comprises a cylinder 49 divided into two chambers 50a, 50b by a sliding piston 52. Coil springs 54a, 54b acting between the piston 52 and the ends of the cylinder 49 bias the piston towards the central position as shown in Figure lb but allow it to move towards either end of the cylinder 49 against a resilient force. Each of the chambers 50a, 50b is connected to the respective hydraulic line 43a, 43b through a port 55a, 55b in the end of the cylinder 49. Each of the hydraulic lines 43a, 43b has an accumulator 56a, 56b connected to it having a chamber into which fluid can flow from the line 43a, 43b against the force of a gas spring.

In operation, during pitch in which the front and rear axles 14,16 move in opposite directions relative to the vehicle body, the pistons in the pitch spring units 40,42 move in opposite directions and fluid flows through the hydraulic lines 43a, 43b. This flow is resisted by the springs 54a, 54b in the pitch control unit 48 which therefore define the pitch stiffness of the vehicle. In bounce, in which all four of the wheels 10a, lOb, 12a, 12b move simultaneously in the same vertical direction, the pistons in the pitch spring units 42,44 move in the same direction, either up or down. This does not result in any movement of the piston 52 in the pitch control unit 48, but causes fluid to flow into or out of the accumulators 56a, 56b. The bounce stiffness and the pitch stiffness of the vehicle are therefore controllable by control of the stiffness of the accumulator springs and the pitch control unit springs 54a, 54b respectively.

It will be appreciated that the pitch control units 42,44 could be simple hydraulic cylinders without including springs.

Referring to Figure 2, in a second embodiment of the invention the pitch control system and roll control systems are essentially the same as in the first embodiment and are given the same reference numerals. The only difference is that the anti-roll torsion bars 20,22 are made stiffer and the two hydraulic lines 40a, 40b between the roll control struts 33 are interconnected by roll control unit 58 which is exactly the same construction as the pitch control unit 48 and has each of its chambers connected to a respective one of the hydraulic lines 40a, 40b. This means that in pitch, the system operates as the first embodiment, but in roll the wheel movement is accommodated by twisting of the torsion bars 20,22 and by movement of fluid between the lines 40a, 40b against the resistance of the springs in the roll control unit 58. A hydraulic damper valve 60a, 60b is provided at each of the ports in the roll control unit 58 which provides damping for vehicle roll, but none, or much less, for cross articulation.

Referring to Figures 3 and 4, in a third embodiment of the invention the main load supporting springs comprise piston units in the form of two front gas springs 100a and two rear gas springs 100b each operating between the body and one end of the respective beam axle 102. The pitch control system is formed by interconnecting these gas springs as shown in Figure 3. The two front springs 100a are interconnected by a first pneumatic pipe 104a and the two rear springs 100b are interconnected by a second pneumatic pipe 104b, and these two pipes 104a, 104b are interconnected by a third pneumatic pipe 106 which includes a pneumatic pitch control unit 108. This is the equivalent of the hydraulic pitch control unit 48 in Figure 1 having a piston 110 dividing a cylinder 112 into two chambers 114a, 114b each of which is connected to a respective one of the pipes 104a, 104b, the piston being biased towards the centre of the cylinder by a pair of springs so as to allow by resist the flow of air from the front gas springs 100a to the rear gas springs 100b and back. The springs in the pitch control unit 108 therefore control the resistance of the system to vehicle pitch, but do not affect roll or cross articulation during which air will flow across the vehicle through the pipes 104a, 104b and not through the pitch control unit.

Referring to Figure 4, the roll control system is essentially symmetrical about the transverse centre line of the vehicle, only the front end being shown. A torsion bar 120 has its central torsion section 120a connected to the front axle 102 by brackets in which it can rotate, and its ends are bent through ninety degrees towards the rear of the vehicle to form crank portions 120b. On each side of the vehicle a rocker 122 is pivotably mounted on the vehicle body and has a first arm 124 extending forwards from its pivot with its free end 126 being located over the end of the crank portion 120b of the torsion bar 120 and a second arm 128 extending vertically downwards from the pivot. The ends of the first and second arms 124,128 are joined by a support strut 130 so that the rocker forms a rigid triangular structure. The end of the first rocker arm 124 is connected by a rigid vertical link 132 to the rear end of the torsion bar crank portion 120b, and by a damping strut 134 to the end of the transverse torsion section 120a. The end of the second rocker arm 128 is connected by a rigid longitudinal link 136 to the corresponding point on the rocker on the same side of the rear of the vehicle. At the rear of the vehicle the roll control linkages are the mirror image of those at the front, the torsion bar crank portions extending towards the front of the vehicle and the first rocker arms towards the rear.

During pure roll motion when both the wheels on one side of the vehicle will tend to move upwards relative to the body and those on the other side to move downwards, the rockers 122 will tend to rotate in opposite directions, one clockwise and one anti-clockwise. However this will be resisted by the longitudinal interconnecting links 136, so the rockers will remain essentially stationary.

Rotation of each axle 102 about its centre will therefore cause twisting of the torsion bar 120, which will therefore operate as a conventional anti-roll bar, and be damped by the dampers 134. During cross articulation, when the front and rear wheels on each side of the vehicle will move vertically in opposite directions, their respective rockers 122 can rotate in the same direction causing the longitudinal link 136 to move in the longitudinal direction. The ends 126 of the first rocker arms 124 therefore move vertically with the wheels, so neither the torsion bars 120 nor the dampers 134 resist the movement. The roll stiffness and roll damping can therefore be increased to the desired level by increasing the stiffness of the torsion bars 120 and the dampers 134 without restricting cross articulation.

With reference to Figure 5, if the mechanical interconnection of the rockers 122 and links 136 between the front and rear of the system of Figure 4 are replaced by hydraulic links comprising a hydraulic strut 138 having a piston 140 and cylinder 142, and hydraulic lines 144, then the roll damper can be integrated into the piston 140 as shown. Specifically, if the cylinder 142 is mounted on the vehicle body, the piston 140 is connected to the axle through the damper 146. The damper comprises a cylindrical damper housing 148 with a damper piston connected to the axle and slidable in the damper housing against a damping resistance. The damper housing 148 is a sliding fit in the cylinder 142 and thereby forms the cylinder 140. The hydraulic chamber 150 defined in the cylinder 142 above the damper housing 148 is hydraulically connected to the corresponding chamber in the strut on the same side of the vehicle at the opposite end. The torsion bar 152 is mounted on the axle as in Figure 4, but the end of its crank portion is connected to the damper housing 148 by a rigid link 154. During vehicle roll, when the two wheels on the same side of the vehicle will be moving vertically in the same direction the incompressibility of the hydraulic fluid will prevent movement of the damper housings 148 in the cylinders 142. The axle will therefore move relative to the damper housing against the resistance of the damper 146 and the torsion bar. Hydraulic accumulators 156 can be provided in the interconnection pipes 144 to provide further control over the roll stiffness. In cross articulation flow of fluid through the hydraulic interconnection 144 will allow the damper housings 148 at opposite ends of the vehicle to move in opposite directions. The wheels will therefore be able to move with them without resistance from the dampers or the torsion bar 152.

Whilst all of the embodiments described above include beam axles it will be appreciated that the roll and pitch control systems they include would operate, sometimes with some modification, with independent suspensions.

Claims (17)

1. CLAIMS 1. A suspension system for connecting two front wheels and two rear wheels to a vehicle body the system comprising: at least one front piston unit operating between the front wheels and the body, at least one rear piston unit operating between the rear wheels and the body, and a fluid interconnection which allows but resists fluid flow between the front and rear piston units thereby to control vehicle pitch; and front and rear torsion bars each connected between the wheels at a respective end of the vehicle and a second interconnection between the front and rear torsion bars arranged to provide greater resistance to vehicle roll than to cross articulation.
2. 2. A vehicle according to claim 1 comprising a beam axle between the two wheels at at least one end of the vehicle, said at least one piston unit at that end of the vehicle comprising a single piston unit operating on the centre of the beam axle.
3. 3. A vehicle according to claim 1 or claim 2 wherein said at least one piston unit at at least one end of the vehicle comprises a pair of interconnected piston units, each connecting a respective one of the wheels to the body.
4. 4. A vehicle according to claim 3 wherein said pair of piston units is interconnected by a fluid interconnection which allows fluid to flow between said pair of piston units thereby facilitating their movement in opposite vertical directions, and from which the first interconnection leads to the other end of the vehicle.
5. 5. A vehicle according to any foregoing claim wherein said piston units comprise air springs.
6. 6. A vehicle according to claim 5 wherein said interconnection or interconnections are air interconnections allowing air to flow between the air springs.
7. 7. A vehicle according to any one of claims 1 to 4 wherein the piston units each include a spring acting on a piston and the interconnection or interconnections are hydraulic interconnections allowing hydraulic fluid to flow between hydraulic chambers partly defined by the pistons.
8. 8. A system according to any foregoing claim wherein the first interconnection includes a fluid accumulator which allows fluid to leave and enter it to accommodate vehicle bounce.
9. 9. A system according to any foregoing claim wherein each torsion bar is connected to one of the wheels at its end of the vehicle by means of a crank member and the second interconnection is arranged to control rotation of the crank member relative to the torsion bar.
10. 10. A system according to claim 9 wherein the second interconnection is hydraulic and comprises a piston and cylinder assembly associated with each torsion bar, the cylinders being interconnected so that fluid can flow between them to allow cross articulation but the cylinders operate to tend to increase or decrease the volume of fluid in part of the interconnection under vehicle roll which is thereby resisted.
11. 11. A system according to claim 10 wherein resilient means is provided in the interconnection to allow but resist the flow of fluid into or out of said volume thereby to allow but resist vehicle roll.
12. 12. A system according to any of claims 1 to 8 wherein each torsion bar has a crank portion rigidly connected to it and extending away from its torsional axis the crank portion having one end rigidly connected to the axle of one of the wheels and the other end connected to the second interconnection wherein a part of the second interconnection is urged to move in opposite directions by said two other ends during vehicle roll, but is urged to move in the same direction by both said other ends during cross articulation such that the torsion bars will operate to provide more resistance to roll than to cross articulation.
13. 13. A system according to claim 12 further comprising a roll damper connected between said axle and said part of the second interconnection such that it provides more damping for roll than for cross articulation.
14. 14. A system according to claim 12 or claim 13 wherein the second interconnection is a hydraulic interconnection and said part of the second interconnection is a piston.
15. 15. A system according to claim 14 wherein the piston forms part of the damper.
16. 16. A system according to claim 15 wherein the piston comprises a cylinder in which a further piston is movable such that the cylinder and further piston form the damper.
17. 17. A vehicle suspension system substantially as hereinbefore described with reference to the accompanying drawings.