GB2160830A

GB2160830A - Vehicle suspension

Info

Publication number: GB2160830A
Application number: GB08415588A
Authority: GB
Inventors: David Frederick Spriggs
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1984-06-19
Filing date: 1984-06-19
Publication date: 1986-01-02
Also published as: GB8415588D0

Abstract

Double acting hydraulic cylinders 4 and 5 act as dampers by pumping fluid around the circuit when spool valve 13 is open i.e. when vehicle is steering in a straight line. On cornering steering cam 20 closes spool valve 13 and system acts as an anti-roll suspension. As the vehicle body attempts to roll towards the outside of the corner being negotiated, the inside spring takes control extending the inside piston and cylinder. Fluid is pumped from the inside annulus chamber to the outside piston chamber via a cross connection thus forcing the more heavily loaded outside spring and cylinder to extend thus counteracting the roll. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vehicle suspensions This invention relates to improvements in vehicle suspensions. In particular, though not exclusively, the present invention relates to suspension systems on vehicles comprising pivotally connected components.

Pivotally connected vehicles suffer the problem that when steering lock is applied there is a lateral transfer of weight from the axle centre. This generates an overturning moment which encourages the body of the vehicle to "roll" upon a corner being negotiated.

One prior known method which attempts to overcome the problem is to incorporate an anti-roll bar in the vehicle's suspension system. This has three major disadvantages: Firstly, the introduction of an anti-roll bar increases not only the overall roll stiffness but also the resistance to twist, axle to axle. In conditions where large changes of roadway cross gradient exist, this can result in excessively uneven wheel loadings and loss of wheel adhesion.

Secondly, the anti-roll bar still allows, to a reduced degree, the heaviest side of the vehicle to slump when steering lock is applied. This slump produces the opposite effect to the intended self centering action in the steering system and forces the use of non-reactive type mechanisms. Steering loads are also increased and any play in the various mechanical joints can lead to directional sta bility problems.

Thirdly, suitable anti-roll bars are difficult to manufacture (compared to a vertical spring of a similar duty) and are there fore more costly. The vertical space available for its installation and its vulnerability to physical damage from below means that its life expectancy could well be limited.

An object of the present invention is to overcome in part, the disadvantages of existing anti-roll means to produce an improved performance.

Accordingly a first aspect of the present invention provides a vehicle suspension incorporating an anti-roll system, said anti-roll system comprising a pair of double acting hydraulic cylinders mounted between the vehicle body and the axle inboard the wheels whose piston and annulus chambers, the piston chambers being uppermost, are cross connected.

Conveniently there is provided an hydraulic fluid reservoir with valve means to allow ingress of fluid to the system.

Conveniently there is provided a spool valve which controls the flow of hydraulic fluid allowing the system to operate as a conventional damping system or as an anti-roll system.

Conveniently the spool valve is controlled by a steering cam. Conveniently hydraulic anccumulators are connected to the piston chambers to offer some suspension resilience in the "anti-roll" mode.

A second aspect of the present invention provides a vehicle with resilient suspension when fitted with an anti-roll system according to the first aspect of the invention.

One embodiment of the present invention will now be described by way of example only with reference to the accompanying figure which shows a hydraulic circuit diagram of a vehicle suspension system according to the present invention.

The figure shows a vehicle axle 1 carrying a pair of road wheels 2 and 3. The axle is connected to the body of the vehicle (not shown) by a pair of biasing members, such a as springs (not shown) whose movement is damped by a pair of doubleacting hydraulic cylinders 4 and 5 pivotally mounted between the axle 1 and the body (not shown). The hydraulic cylinders 4 and 5 are arranged such that the cylinder body is attached to the vehicle body (not shown) and the hydraulic cylinders' pistons 6 and 7 are connected to the axle 1.

The hydraulic system further includes a spool valve 13 one-way valves 14 and 15, a pressure relief valve 16 and various pipework including lines 10, 11 and 12. The system also uses a cam on the steering 20.

Lines 10 and 11 go to an identical system of cross connected double acting hydraulic cylinders on the other axle of the vehicle (not shown). Line 12 goes to a hydraulic fluid reservoir which is maintained at a small super atmospheric pressure which pressure is regulated by pressure reiief valve 16.

In operation the system works as follows; in straight line operation the steering cam 20 allows spool valve 13 to sit open as shown on the diagram this allows movement of both pistons 6 and 7, the viscous drag of the hydraulic fluid along the lines providing the necessary damping action. The size of the spool valve and bore and length of the various connecting lines being chosen to provide suitable damping.

When a corner is negotiated the steering cam 20 closes the spool valve 13 isolating the circuit from the fluid reserviour (line 12). One way valves 14 and 15 ensure fluid cannot leave the system. As the vehicle starts to "roll" on a corner of the road springs on the most heavily loaded side attempt to compress while the springs on the more lightly loaded side extend. Due to the differing areas between piston and annulus the springs whose load is reducing take control and pump fluid from their annuli to the pistons on the more heavily loaded side, forcing the more heavily loaded springs to extend against the load rather than compress with it. Due to cylinder movement there is a net increase in the volume of the system which is made up from the fluid reservoir via either of one way valves 14 or 15. The connections 10 and 11 to the other axle allow the anti-roll torque to be maintained whilst providing no hydraulic restriction on relative twist between the axles.

The controlling spool valve (13) position can be mechanically determined by the steering system such that steering movements, other than minor course corrections, will automatically give the "anti-roll" mode.

This anti-roll system may, in principle, be applied to any vehicle using spring-and-damper suspension but will be found especially useful for vehicles that are pivotally steered when the spool valve is shut and the system is operating in the anti-roll mode the suspension becomes substantially rigid and lion resilient. This may be alleviated by the inclusion of hydraulic fluid accumulators in the piston chamber lines.

Claims

1. An anti-roll system for vehicles with resilient suspensions comprising a pair of double acting hydraulic cylinders mounted between the vehicle body and the axle inboard the wheels whose piston and annulus chambers, the piston chambers being uppermost, are cross connected.

2. An anti-roll system according to claim 1 wherein there is provided a hydraulic fluid reservoir with valve means to allow ingress of fluid to the system.

3. An anti-roll system according to claim 1 or 2 wherein there is provided a spool valve which controls the flow of hydraulic fluid allowing the system to operate as a conventional damping system or as an anti-roll system.

4. An anti-roll system according to claim 3 wherein the spool valve is controlled by a steering cam.

5. A vehicle substantially as described herein and substantially as shown in the accompanying drawing.

5. An anti-roll system according to any of the preceding claims wherein hydraulic accumulators are connected to the piston chambers.

6. An anti-roll system for vehicles with resilient suspensions substantially as hereinbefore described.

7. Any vehicle with a resilient suspension when fitted with an anti-roll system according to any of the preceding claims.

Amendments to the claims have been filed, and have the following effect: (a) Claims 1 -7 above have been deleted or textually amended.

(b) New or textually amended claims have been filed as follows:

1. A vehicle having pivotally connected body components, the vehicle being steered by pivotal movement of the connected components, resilient suspension means mounted between the body of one of the body components and a wheel carrying axle, and an anti-roll system comprising a pair of double acting piston and cylinder devices, each device having a piston chamber and an annulus chamber and each device being mounted between the body of said one body component and said wheel carrying axle, the piston and annulus chambers of the pair of devices being cross connected, the anti-roll system further comprising a supply of pressurised fluid for the piston and cylinder devices and flow control means for controlling the supply of pressurised fluid to the piston and cylinder devices, the flow control means including a flow control valve and a cam mounted for rotation when, in use, the vehicle is steered, rotation of the cam activating the flow control valve between its operational modes.

2. A vehicle as claimed in claim 1, in which the anti-roll system comprises a further pair of double acting piston and cylinder devices associated with a further wheel carrying axle.

3. A vehicle as claimed in claim 1 or 2, in which the flow control valve in one operational mode allows the system to operate as a conventional damping system and in another operational mode allows the system to operate as an anti- roll system.

4. A vehicle as claimed in claim 1, 2 or 3, in which hydraulic accumulators are connected to the piston chambers of the piston and cylinder devices.