GB1593258A

GB1593258A - Vehicle suspension systems

Info

Publication number: GB1593258A
Application number: GB4333376A
Authority: GB
Original assignee: National Research Development Corp UK; National Research Development Corp of India
Current assignee: National Research Development Corp UK; National Research Development Corp of India
Priority date: 1976-10-19
Filing date: 1976-10-19
Publication date: 1981-07-15
Also published as: DE2745768A1; FR2368649A1

Description

(54) IMPROVEMENTS IN AND RELATING TO VEHICLE SUSPENSION SYSTEMS (71) We, NATIONAL RESEARCH DEVELOPMENT CORPORATION, a British Corporation established by Statute, of Kingsgate House, 66 - 74 Victoria Street, London, S.W,1, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to vehicle suspension systems including hydraulic dampers for controlling relative movements between the sprung and unsprung masses of the vehicle.

In such systems, where damping is necessary to deal with relative movement between the sprung chassis and the unsprung axles of the road wheels, there is a need to cater for more than one set of conditions in use. Thus, were the suspension dampers to be set to control only the type of movement which obtains on a smooth highway, they would not be able to cope with the shock loads which are experienced on rougher roads; and, vice versa, were the suspension dampers suited to coping preferentially with the rougher road conditions, the quality of the ride which they gave on the smooth roads would suffer.

In smooth running conditions the tendency for relative movements between the road wheels with their associated unsprung parts of the wheel mounts and, through the suspension, the chassis, will be small and the wheels will be maintained in contact with the road surface without the necessity for more than a moderate restriction of flow of fluid in the damper, that is, minimum damping.

However, immediately the wheels encounter a rough road surface, different conditions apply. In the case of a hump in the road, a wheel and the unsprung mass will at first be accelerated in the upward direction but due to the inertia of the unsprung mass the wheel will continue to be maintained in contact with the road surface and a minimum of damping force is desirable to enable the wheel to rise over the hump. Towards the top of the hump, the upward motion of the wheel and associated mass will be subject to deceleration but again due to inertial effects the mass will tend to continue to move on upwards with the result that the wheel will tend to leave the road surface unless a substantial damping force is provided. Over the top of the hump, deceleration continues but the mass should be commencing to move downwards and a minimum of damping force is desirable to enable the suspension springs to maintain the wheel in contact with the road surface. Finally, towards the bottom of the hump, as the road surface levels out, the wheel mass will be subject to acceleration upwardly and due to the inertial effects the wheel load on the road surface will be augmented. To reduce this undesirable condition increased damping will again be required. It is in these changeable conditions in which the present invention may be used effectively to provide the desired damping of suspension movement. Attempts have been made to provide suspension dampers to meet the conditions by the use of inertiacontrolled valves arranged to control the movement of fluid in the dampers in dependence upon the type of ride being experienced. However, it appears that in such known systems the pressure difference across the valve has never yet been controlled in a "proportional" manner, that is to say so that the pressure difference bears a constant relationship to a relevant parameter such as the vertical acceleration of the unsprung mass of the vehicle. The present invention arises from appreciating the potential advantages of such proportional control.

The invention is defined by the claims at the end of this specification and will now be described, by way of example only, with reference to Figures 1 and 2 of the accompanying diagrammatic drawings. Each Figure indicates a section of a damper and rela tive fixation between the damper, a vehicle chassis and one of the wheel mounts of the vehicle.

In Figure 1, the body 1 of the damper 2 contains a cylinder 3 in which a piston 4 operates, the piston being connected through piston rod 5 to a hinge 6 on the chassis 7 of a motor vehicle. The body of the damper is hinged at 8 to the wheel mount 9, i.e. to the unsprung mass on which the wheel 10 is mounted. The spring suspension for the car is shown as spring 11.

Ducts 12 and 13 connect each end of the cylinder 3 to a common valve chamber 14, non-return valves 15 and 16 being provided respectively in each duct. The ends of the valve chamber 14 are formed as valve ports 17, 18 respectively, each port being connected to the opposite duct 12 or 13 through ducts 19 and 20, the latter ducts being provided with flow restrictors 21, 22 respectively. These restrictors may be fixed or variable orifices or may be combinations of fixed and/or variable orifices.

In the valve chamber 14, an inertial member 23 is mounted on a compensating spring 24 of low stiffness which renders the member 23 effectively weightless. Each end of the member 23 is formed to co-operate with the respective valve port 17 and 18 in controlling flow of fluid between the ends of cylinder 3 and the valve chamber 14. The body of the member 23 is shaped to provide free flow of fluid throughout the valve chamber.

It will be observed that the inertial member 23, in tending to remain static in space when the damper 2 is first moved, will tend to close the valve port 18 when the wheel is accelerated upwardly on reaching a hump in a roadway. By this relative movement between the member 23 and the damper body, the valve port 17 is left fully open and flow is not restricted except for the restrictor 21 from the lower part of the cylinder 3 and past the non-return valve 15 into the upper part of the cylinder as the piston tends to move downwards against the upward movement of the wheel mass. As has been explained above, there is little likelihood of the wheel leaving the road surface at this stage and there is no necessity for heavy damping.

However, as the top of the hump is approached the upward movement of the wheel mass will be subject to deceleration and with it the damper body. In consequence, the inertial member 23 moves to the other end of the cylinder and tends to close valve port 17 where thereupon restricts flow of fluid from the lower part of the cylinder 3 to tend to prevent continued relative movement of the piston downwardly, notwithstanding the comparatively free flow through the restrictor 21. As will be understood, the greater the deceleration forces the greater will be the pressure of the member 23 against the fluid flowing through the valve port 17 so that there will be proportional control of the fluid flow by this inertial member.

During the next phase of movement of the vehicle over the hump, the wheel mass will continue to decelerate but will now tend to move down the hump away from the chassis under the action of the suspension springs and as the valve member 23 is maintained against the valve port 17, this leaves valve port 18 fully open to permit unrestricted flow from the upper part of the cylinder through the valve chamber 14 and non-return valve 16 to the lower part of the cylinder; the movement of the piston is thus restricted only by the flow through the restrictor 22.

The wheel then is comparatively free to maintain contact with the road.

As the wheel approaches the bottom of the hump the wheel mass and damper are subjected to another acceleration towards the chassis and this causes the inertial member 23 to leave the valve port 17 and to commence to control the fluid flowing through valve port 18.

This control of fluid through the valve port 18 provides greater damping to cater for the continuing downward movement of the unsprung mass. The control of the flow in this latter phase is also proportional to the degree of acceleration.

It will be seen therefore that the damping provided by the system in accordance with the invention may meet the varied conditions which apply to progress over any type of road surface.

The damper shown in Figure 1 relies upon a ducting system contained in a body attached to the damper cylinder. Alternatively the valve ports, non-return valves and inertia member could be within or attached to the damper piston itself, and all contained with the damper cylinder. Such an alternative construction is illustrated in Figure 2 which shows a damper cylinder 30 containing a piston 31, the rod 32 of which is hinged at 33 to the wheel mount 34. The upper end of cylinder 30 is hinged at 35 to the chassis 36, and the chassis and wheel mount are also connected as usual by a spring suspension 37 in parallel with the damper.

The flat central areas of the upper and lower faces of piston 31 are formed with annular grooves 38 and 39 respectively, and passages 40 connect groove 38 to the lower face of the piston while similar passages 41 connect groove 39 to the upper face.

A resilient, annular shim 42 covers the mouth of groove 38, being held in place on the upper flat face of piston 31 by a washer 43 held down by the flange of a stud 44. This stud is taped to receive a second stud 45 having a shank 46 which fits within the cen tral hole 47 of an inertia member 48 so that that member can slide up and down the shank. A compensating spring 49 lies between member 48 and washer 43. At the other side of the piston another inertia member 51 is mounted to slide on a sleeve 52 which is threaded on rod 32 at 53. End face 54 of the sleeve anchors a shim 55 to the lower flat face of the piston and a compensating spring 56 separates member 51 from the bottom flange 57 of the sleeve.

If the vehicle is in motion and the vehicle wheel carried by mount 34 is moving out of a trough of the highway towards the next crest, piston 31 will tend to accelerate upwards within cylinder 30. The damper should allow this motion, and does so because while both the pressure of the fluid within the upper chamber 60 of the cylinder and the force of rim 61 of member 48 both tend to force shim 42 to close the mouth of channel 38, inertia member 51 lags as the piston rises and so allows the fluid pressure in channel 39 and passages 41 to lift resilient shim 55 from the mouth of channel 39, allowing fluid to pass relatively freely through passages 41 from chamber 60 to the lower cylinder chamber 62. As the wheel approaches closer to the crest, however, the vertical motion of the wheel will still be upward but the direction of its acceleration must change to downward, otherwise the wheel will tend to jump the crest instead of rolling over it. The construction shown in Figure 2 helps to achieve this change in direction because the member 51, sensing the change, rises so that its rim 63 meets shim 55 and causes the shim to close the mouth of channel 39 progressively more tightly as the magnitude of the downward acceleration of the wheel increases. Member 48 will now ride clear of shim 42, but the difference in pressure between chamber 60 and 62 will still cause that shim to hold the mouth of channel 38 tightly closed, so that passage of fluid from 60 to 62 is now progressively restricted and the sprung mass of the vehicle body that supports the damper is resisting too rapid a rise of the vehicle wheel.

When the wheel is travelling from a crest to the next trough the damper works similarly, shim 55 now shutting the mouth of channel 39 throughout and the necessary control being achieved by rim 61 of member 48, shim 42, channel 38 and passages 40.

If greater force is required to shut the mouths of channels 38, 39 than can be achieved by the direct contact of rims 61, 63 upon shims 42, 55, then of course levers or other force-multiplying devices may be interposed between them.

Other variations are, of course, countenanced within the scope of the invention, such as in the form of the valve ports and the inertial member. For example, as suggested in the last paragraph, the inertial member need not operate directly on the valve port itself. Needle or slide type valves may also be used.

In other alternative arrangement pistons or diaphragms may be provided to operate on the inertial member to give appropriate balance forces relating the pressure drop at the valve ports to acceleration. In yet another alternative arrangement the inertial member may be made effectively of negative mass by arranging for it to be buoyant in the hydraulic fluid of the damper, with appropriate rearrangement of the ducts.

WHAT WE CLAIM IS: 1. A vehicle suspension system comprising a hydraulic damper connecting the sprung and unsprung masses of the vehicle and including a fluid-filled circuit comprising a cylinder divided into two opposed chambers by a piston and at least one passage interconnecting those chambers, and in which at least one such passage is controlled by a valve comprising an inertial mass responsive in one direction to a force proprtional to the vertical acceleration of the unsprung mass and in the opposite direction to a force proportional to the pressure difference across the valve, whereby the damping effect of the damper contains a substantial term proportional to the vertical acceleration of the unsprung mass.

2. A vehicle suspension system according to Claim 1 in which the pressure difference across the valve is directly proportional to the vertical acceleration of the unsprung mass.

3. A vehicle suspension system according to Claim 1 in which the inertial mass operates a slide-type valve by which the size of the port of the valve is controlled.

4. A vehicle suspension system according to Claim 1 in which at least one piston or diaphragm, sensitive to the fluid pressure difference across the valve, operates upon the inertial mass to communicate the pressure difference force to it.

5. A vehicle suspension system according to Claim 1 in which the inertial mass confronts the port of the valve directly.

6. A vehicle suspension system according to Claim 1 in which at least one such passage also includes at least one metering orifice in series with the valve, further to control the rate of flow in the passage including the valve.

7. A vehicle suspension system according to Claim 6 including means to vary the flow resistance of at least one such metering orifice.

8. A vehicle suspension system according to any of the preceding claims in which the valve lies external to the cylinder.

9. A vehicle suspension system according to any one of Claims 1 to 7 in which the valve lies within the cylinder and at least two

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tral hole 47 of an inertia member 48 so that that member can slide up and down the shank. A compensating spring 49 lies between member 48 and washer 43. At the other side of the piston another inertia member 51 is mounted to slide on a sleeve 52 which is threaded on rod 32 at 53. End face 54 of the sleeve anchors a shim 55 to the lower flat face of the piston and a compensating spring 56 separates member 51 from the bottom flange 57 of the sleeve. If the vehicle is in motion and the vehicle wheel carried by mount 34 is moving out of a trough of the highway towards the next crest, piston 31 will tend to accelerate upwards within cylinder 30. The damper should allow this motion, and does so because while both the pressure of the fluid within the upper chamber 60 of the cylinder and the force of rim 61 of member 48 both tend to force shim 42 to close the mouth of channel 38, inertia member 51 lags as the piston rises and so allows the fluid pressure in channel 39 and passages 41 to lift resilient shim 55 from the mouth of channel 39, allowing fluid to pass relatively freely through passages 41 from chamber 60 to the lower cylinder chamber 62. As the wheel approaches closer to the crest, however, the vertical motion of the wheel will still be upward but the direction of its acceleration must change to downward, otherwise the wheel will tend to jump the crest instead of rolling over it. The construction shown in Figure 2 helps to achieve this change in direction because the member 51, sensing the change, rises so that its rim 63 meets shim 55 and causes the shim to close the mouth of channel 39 progressively more tightly as the magnitude of the downward acceleration of the wheel increases. Member 48 will now ride clear of shim 42, but the difference in pressure between chamber 60 and 62 will still cause that shim to hold the mouth of channel 38 tightly closed, so that passage of fluid from 60 to 62 is now progressively restricted and the sprung mass of the vehicle body that supports the damper is resisting too rapid a rise of the vehicle wheel. When the wheel is travelling from a crest to the next trough the damper works similarly, shim 55 now shutting the mouth of channel 39 throughout and the necessary control being achieved by rim 61 of member 48, shim 42, channel 38 and passages 40. If greater force is required to shut the mouths of channels 38, 39 than can be achieved by the direct contact of rims 61, 63 upon shims 42, 55, then of course levers or other force-multiplying devices may be interposed between them. Other variations are, of course, countenanced within the scope of the invention, such as in the form of the valve ports and the inertial member. For example, as suggested in the last paragraph, the inertial member need not operate directly on the valve port itself. Needle or slide type valves may also be used. In other alternative arrangement pistons or diaphragms may be provided to operate on the inertial member to give appropriate balance forces relating the pressure drop at the valve ports to acceleration. In yet another alternative arrangement the inertial member may be made effectively of negative mass by arranging for it to be buoyant in the hydraulic fluid of the damper, with appropriate rearrangement of the ducts. WHAT WE CLAIM IS:

1. A vehicle suspension system comprising a hydraulic damper connecting the sprung and unsprung masses of the vehicle and including a fluid-filled circuit comprising a cylinder divided into two opposed chambers by a piston and at least one passage interconnecting those chambers, and in which at least one such passage is controlled by a valve comprising an inertial mass responsive in one direction to a force proprtional to the vertical acceleration of the unsprung mass and in the opposite direction to a force proportional to the pressure difference across the valve, whereby the damping effect of the damper contains a substantial term proportional to the vertical acceleration of the unsprung mass.

interconnecting passages are formed within the body of the piston.

10. A vehicle suspension system according to Claim 9 in which the flow through each of two of such passages is controlled by separate valves which are responsive in opposite senses to the vertical acceleration of the unsprung mass.

11. A vehicle suspension system according to Claim 10 in which each valve comprises a flexible member, positioned so as to be capable of obstructing the mouth of such a passage and acted upon by an inertial mass.

12. A suspension system for the wheel axle of a vehicle, according to Claim 1 and substantially as described with reference to either Figure 1 or Figure 2 of the accompanying drawings.