PRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No. 2020902674 titled “VEHICLE SUSPENSION SYSTEM” and fried on 30 July 2020, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present invention relates to a vehicle suspension system. In a particular form the present invention relates to an adjustable hydropneumatic vehicle suspension system.

BACKGROUND

[0003] A vehicle suspension system typically comprises a spring and a hydraulic damper. While in many examples the spring is in the form of a linearly wound coil spring, a leaf spring or a torsion bar, in another the spring is in the form of a hydropneumatic accumulator.

[0004] It is desirable for such a system to be capable of static ride height levelling, in which case, hydraulic actuators would be provided, allowing the vehicle to be lowered or raised to allow aerodynamic advantages, increased ground clearance, passenger / cargo loading, lowering total vehicle height for ensuring overhead clearance, or ride levelling responsive to variable loading.

[0005] It is also desirable that the suspension properties of a system are kept constant throughout all loading conditions and to have a natural frequency independent of the static spring load, by being able to vary the spring rate in applications where the suspension is subjected to different operating conditions.

[0006] It is against this background that the present disclosure has been developed.

SUMMARY

[0007] According to a first aspect, there is provided a vehicle suspension system comprising at least one hydraulic actuator hydraulically connected to an accumulator module acting as a hydropneumatic spring, the accumulator module comprising a first chamber filled with a hydraulic fluid and hydraulically connected to the actuator, and a hydraulic fluid supply, a second chamber filled with a gas and separated from the first chamber by a first divider, a third chamber in fluid communication with the second chamber, and a fourth chamber filled with a hydraulic fluid, separated from the third chamber by a second divider and hydraulically connected to the hydraulic fluid supply, wherein the position of the first and second dividers are able to be adjusted so as to increase or decrease the volume of the second and third chambers.

[0008] In one form, the hydraulic fluid supply comprises a hydraulic pump and a hydraulic tank.

[0009] In one form, the system further comprises a first and second control valve, for selectively connecting the first chamber to the hydraulic pump and hydraulic tank respectively, and a third and fourth control valve, for hydraulically connecting the fourth chamber to the hydraulic pump and hydraulic tank respectively.

[0010] In one form, the first, second, third and fourth control valves are configured to independently control the position of each dividing piston by controlling the volume of hydraulic fluid in the first and fourth chambers respectively.

[0011] In one form, the system further comprises a means for monitoring respective positions of the first and second dividing pistons.

[0012] In one form, the system further comprises a means for monitoring respective hydraulic pressures in the first and fourth chambers.

[0013] In one form, the accumulator module comprises a primary cylinder housing the first chamber, second chamber and first dividing piston, and a secondary cylinder housing the third chamber, fourth chamber and second dividing piston.

[0014] In one form, the first and second dividers are in the form of first and second dividing pistons which are slidably retained within the primary and secondary cylinders respectively and configured to move along the length of the cylinders so as to increase or decrease the volume of the second and third chambers respectively.

[0015] In one form, the primary and secondary cylinders are connected with an intermediate body.

[0016] In one form, gas pressure is balanced between the second and third chambers via at least one control valve.

[0017] In one form, an adjustable orifice valve is provided between the second and third chambers. [0018] In one form, a pressure relief valve configured to vent gas pressure from the second to third chamber is provided.

[0019] In one form, a check valve configured to permit free flow of gas from the third chamber to the second chamber is provided.

[0020] According to a second aspect, there is provided a method for controlling the ride height and natural frequency of a vehicle suspension system as described above, wherein the ride height and natural frequency of the suspension system are adjusted by varying the volume of hydraulic fluid in the first and fourth chambers.

[0021] In one form, the ride height and natural frequency of the system may be increased by supplying hydraulic fluid to the first chamber and withdrawing it from the fourth chamber.

[0022] In one form, the ride height of the system may be increased and the natural frequency of the system maintained by supplying hydraulic fluid to the first chamber.

[0023] In one form, the ride height of the system may be increased and the natural frequency of the system may be decreased by supplying hydraulic fluid to the first and fourth chambers respectively.

[0024] In one form, the ride height of the system may be maintained and the natural frequency of the system may be increased by supplying hydraulic fluid to the first chamber and withdrawing it from the fourth chamber.

[0025] In one form, the ride height of the system may be maintained and the natural frequency of the system may be decreased by withdrawing hydraulic fluid from the first chamber and supplying hydraulic fluid to the fourth chamber.

[0026] In one form, the ride height of the system may be decreased and the natural frequency of the system increased by withdrawing hydraulic fluid from the first chamber and the fourth chamber.

[0027] In one form, the ride height may be decreased and the natural frequency of the system maintained by withdrawing hydraulic fluid from the first chamber.

[0028] In one form, the ride height and the natural frequency of the system may be decreased by withdrawing hydraulic fluid from the first chamber and supplying it to the fourth chamber. [0029] According to a further aspect, there is provided an accumulator module for a vehicle suspension system, comprising a first chamber filled with a hydraulic fluid and configured to hydraulically connect to a hydraulic actuator, and a hydraulic fluid supply, a second chamber filled with a gas and separated from the first chamber by a first divider, a third chamber in fluid communication with the second chamber, and a fourth chamber filled with a hydraulic fluid, separated from the third chamber by a second divider and configured to hydraulically connect to the hydraulic fluid supply, wherein the position of the first and second dividing pistons are able to be adjusted so as to increase or decrease the volume of the second and third chambers.

BRIEF DESCRIPTION OF DRAWINGS

[0030] Embodiments of the present invention will be discussed with reference to the accompanying drawings wherein:

[0031] Figure 1 is a schematic of a vehicle suspension system, according to an embodiment;

[0032] Figure 2 is a perspective view of an accumulator module, according to an embodiment;

[0033] Figure 3 is a first end view of the accumulator module of Figure 2;

[0034] Figure 4 is a second end view of the accumulator module of Figure 2;

[0035] Figure 5 is a cross-sectional view of the accumulator module of Figure 2;

[0036] Figure 6 is a cross-sectional view of the accumulator module of Figure 3 with dividing pistons shown at full displacement; and

[0037] Figure 7 is a cross-sectional view of the accumulator module of Figure 3 with dividing pistons shown at zero displacement.

DESCRIPTION OF EMBODIMENTS

[0038] Referring now to Figure 1, there is shown a schematic of a vehicle suspension system 1, according to an embodiment. The system 1 comprises at least two hydraulic actuators in the form of damper units 2a, 2b hydraulically connected to an accumulator module 100. The accumulator module 100 acts as a hydropneumatic spring and comprises four chambers 101, 102, 103, 104 (as best shown in Figures 5 to 7) where the first chamber 101 is hydraulically connected to the damper units 2a, 2b, and a hydraulic fluid supply in the form of a hydraulic pump 3 and a hydraulic tank or reservoir 4, the second chamber 102 is separated from the first chamber 101 by a first divider in the form of a first dividing piston 105 and is in fluid communication with the third chamber 103, and the fourth chamber 104 is separated from the third chamber 103 by a second divider in the form of a second dividing piston 106 and is hydraulically connected to the hydraulic pump 3 and hydraulic tank 4.

[0039] In the embodiment shown the hydraulic actuators are in the form of damper units 2a, 2b, where it will be appreciated that supply of hydraulic fluid to each damper unit causes the overall length of the damper unit to increase (resulting in an increased ride height for the vehicle), and withdrawal of hydraulic fluid causes the overall length of the damper unit to decrease (resulting in a decreased ride height for the vehicle). It will be appreciated that any type of hydraulic actuator for use as part of a vehicle suspension system is to form part of the scope of this disclosure.

[0040] The second and third chambers 102, 103 are statically balanced and pre-charged with a gas, such as Nitrogen. The gas pressure is balanced between the second and third chambers 102, 103 via control valves 107, 108, 109. It will be appreciated that the first chamber, second chamber and first dividing piston act as a hydropneumatic spring, where compression of one or both damper units 2a, 2b causes displacement of hydraulic fluid causing the first dividing piston 105 to compress the gas in the second chamber 102. It will further be appreciated that the rate of pressure balancing between the second and third chamber 102, 103 controls the dynamic spring rate for the damper units 2a, 2b. An adjustable orifice valve 107 between the second and third chamber 102, 103 controls the rate of static pressure balancing between each chamber, and a pressure relief valve 108 configured to vent from the second chamber 102 to the third chamber 103 controls the dynamic pressure limit within the second chamber 102. A check valve 109 permits free flow of gas from the third chamber 103 to the second chamber 102, permitting quick re-balancing of pressure between the chambers in damper extension conditions. Furthermore, it will be appreciated, that by virtue of the above configuration it is the target gas volume of chamber 2 at ride height that determines the dynamic spring rate for the connected damper units 2a, 2b.

[0041] The first chamber 101 is connected to the hydraulic pump 3 via a first control valve 201, and is connected to the hydraulic tank 4 via a second control valve 202. The fourth chamber 104 is connected to the hydraulic pump 3 via a third control valve 203, and is connected to the hydraulic tank 4 via a fourth control valve 204.

[0042] Each of the control valves 201, 202, 203, 204 are in the form of a normally closed proportional 2/2 solenoid with spring return, where, in a first position (spring return) the control valve is closed, and in a second position (solenoid active), the valve is open. It will be appreciated that hydraulic fluid may be variably supplied to and withdrawn or vented from the first chamber 101 via the first control valve 202 and second control valve 203 respectively, and that hydraulic fluid may be variably supplied to and withdrawn from the fourth chamber 104 via the third control valve 203 and fourth control valve 204 respectively.

[0043] It will therefore be appreciated that by virtue of the four control valves 201, 202, 203, 204, that the system is capable of independent control of the position of each dividing piston 105, 106 by controlling the volume of hydraulic fluid in the first and fourth chambers 101, 104. The accumulator module 100 is able to monitor the respective positions of the first and second dividing pistons 105, 106 and therefore provide a control system with the respective volumes of the first, second, third and fourth chambers, 101, 102, 103, 104 using position sensors. The accumulator module 100 is also able to monitor the hydraulic fluid pressure in the first and fourth chambers 101, 104 using pressure sensors.

[0044] The accumulator module 100 may have all (or nearly all) of the hydraulic fluid withdrawn from the first and fourth chambers 101, 104, such that the gas in the second and third chambers 102, 103 is allowed to fully expand, displacing both of the dividing pistons 105, 106 to 0% positions corresponding to zero displacement as shown in Figure 7. Conversely, the system may fully fill (or nearly fully fill) the first and fourth chambers 101, 104, such that both the dividing pistons 105, 106 are displaced to 100% positions corresponding to full displacement, and the gas in the second and third chambers 102, 103 is fully compressed.

[0045] It will be appreciated that the ability to variably supply and/or withdraw hydraulic fluid to and from the first and fourth chambers 101, 104 means that the volume of gas in the second and third chambers 102, 103 is able to be adjusted in order to vary the spring rate and natural frequency of the system 1. It will also be appreciated that the variable supply and/or withdrawal of hydraulic fluid to and from the first chamber 101 allows for the ride height of the vehicle to be adjusted.

[0046] For a static sprung mass with no dynamic forces, a control strategy can be formulated for the control valves 201, 202, 203, 204 in order to infinitely adjust both the ride height and the spring rate of the system 1, as described below:

[0047] To increase the ride height and the natural frequency of the system 1, the first and fourth control valves 201, 204 are opened, supplying hydraulic fluid to the first chamber 101 and withdrawing it from the fourth chamber 104. This has the effect of reducing the volume of gas in the second chamber 102 (increasing the spring rate) and supplying fluid to the damper units 2a, 2b via the first chamber 101 (increasing the ride height). [0048] To increase the ride height and maintain the natural frequency of the system 1, the first control valve 201 is opened, supplying hydraulic fluid to the first chamber 101. This has the effect of maintaining the volume of gas in the second chamber 102 (maintaining the spring rate) and supplying fluid to the damper units 2a, 2b via the first chamber 101 (increasing the ride height).

[0049] To increase the ride height and decrease the natural frequency of the system 1, the first and third control valves are opened 201, 203, supplying hydraulic fluid to the first chamber 101 and the fourth chamber 104. This has the effect of increasing the volume of gas in the second chamber 102 (decreasing the spring rate) and supplying fluid to the damper units 2a, 2b via the first chamber 101 (increasing the ride height).

[0050] To maintain the ride height and increase the natural frequency of the system 1, the first and fourth control valves 201, 204 are opened, supplying hydraulic fluid to the first chamber 101 and withdrawing it from the fourth chamber 104. This has the effect of reducing the volume of gas in the second chamber 102 (increasing the spring rate) and supplying fluid to the damper units 2a, 2b via the first chamber 101 (to maintain the ride height).

[0051] To maintain the ride height and the natural frequency of the system, all of the valves remain closed.

[0052] To maintain the ride height and decrease the natural frequency of the system 1, the second and third control valves 202, 203 are opened, withdrawing hydraulic fluid from the first chamber 101 and supplying it to the fourth chamber 104. This has the effect of increasing the volume of gas in the second chamber 102 (decreasing the spring rate) and withdrawing fluid from the damper units 2a, 2b via the first chamber 101 (to maintain the ride height).

[0053] To decrease the ride height and increase the natural frequency of the system 1, the second and fourth control valves 202, 204 are opened, withdrawing hydraulic fluid from the first chamber 101 and the fourth chamber 104. This has the effect of decreasing the volume of gas in the second chamber 102 (increasing the spring rate) and withdrawing fluid from the damper 2a, 2b via the first chamber 101 (decreasing the ride height).

[0054] To decrease the ride height and maintain the natural frequency of the system 1, the second control valve 202 is opened, withdrawing hydraulic fluid from the first chamber 101. This has the effect of maintaining the volume of gas in the second chamber 102 (maintaining the spring rate) and withdrawing fluid from the damper units 2a, 2b via the first chamber 101 (decreasing the ride height). [0055] To decrease the ride height and natural frequency of the system 1, the second and third control valves 202, 203 are opened, withdrawing hydraulic fluid from the first chamber 101 and supplying it to the fourth chamber 104. This has the effect of increasing the volume of gas in the second chamber 102 (decreasing the spring rate) and withdrawing fluid from the damper units 2a, 2b via the first chamber 101 (decreasing the ride height).

[0056] In order to set the vehicle height and displacement piston locations, the following procedure is followed:

1. The second and fourth control valves 202, 204 are opened until all of the fluid from the first and fourth chambers 101, 104 has been withdrawn.

2. The first control valve 201 is opened until the first dividing piston 105 is moved to a 50% position against the load of the sprung mass of the vehicle.

3. The third control valve 203 is opened until the ride height of the vehicle starts to increase or the first dividing piston 105 begins to move. This increases the gas pressure as required to support the sprung mass.

4. The first control valve 201 is then opened again, adding hydraulic fluid between the damper units 2a, 2b and the first dividing piston 105 and increasing the ride height until the target ride height is achieved without effecting system pressure (both dividing pistons 105, 106 remaining fixed).

[0057] It will also be appreciated that the system 1 is capable of compensating for changes in suspension loading in order to maintain a target ride height and natural frequency, as described below.

[0058] When there is an increased load, the damper units 2a, 2b will compress and displace fluid causing the first dividing piston 105 to decrease the gas volume in the second chamber 102, resulting in reduced ride height and increased spring stiffness. In order to restore the ride height and spring stiffness, the third control valve 203 is opened, supplying hydraulic fluid to the fourth chamber 104. This has the effect of shifting the first dividing piston 105, increasing the volume of gas in the second chamber 102 (decreasing the spring rate until it returns to the target value) and supplying fluid to the damper units 2a, 2b via the first chamber 101 (increasing the ride height until it returns to its target value). [0059] Conversely, when there is a reduced load, the damper units 2a, 2b will extend causing the gas volume in the second chamber 102 to increase, resulting in increased ride height and reduced spring stiffness. In order to restore the ride height and spring stiffness, the fourth control valve 204 is opened, withdrawing hydraulic fluid from the fourth chamber 104. This has the effect of decreasing the volume of gas in the second chamber 102 (increasing the spring rate until it returns to the target value), shifting dividing piston 105 and withdrawing fluid from the damper units 2a, 2b via the first chamber 101 (decreasing the ride height until it returns to its target value).

[0060] The system also comprises a blocking system 200 operated by a hydraulic pilot, for locking the ride height and isolating the accumulator module 100 from the damper units 2a, 2b. This may be used in instances where suspension movement is not desirable - a frequent requirement for working machines.

For example, when loads are lifted from or removed from a vehicle, the change in suspended load will cause the suspension system to react with a change in position, complicating the exact positioning of the load. It is therefore desirable to be able to maintain the height of the vehicle for exact positioning of the load.

[0061] Referring now to Figures 2 to 7, where an embodiment of the accumulator module 100 is shown. It can be seen that the accumulator module 100 has an elongate body and comprises a primary cylinder 110 housing the first chamber 101, second chamber 102 and first dividing piston 105, and a secondary cylinder 120 housing the third chamber 103, fourth chamber 104 and second dividing piston 106. As best shown in Figure 5, it can be seen that the first and second dividing pistons are slidably retained within the primary and secondary cylinders 110, 120 respectively and configured to freely slide along concentric rods 111, 121 running along the lengths of the respective cylinders 110, 120. The accumulator module 100 is configured to accurately monitor or measure the position of the dividing pistons 105, 106 by virtue of sensor magnets 112, 122 mounted to each dividing piston and position sensors 161, 162 capable of accurately measuring the position of each magnet 112,122 and thus the position of each piston 105, 106 in each cylinder 110, 120.

[0062] The primary and secondary cylinders 110, 120 are connected with an intermediate body 130 which houses the orifice valve 107, pressure relief valve 108 and check valve 109 interconnecting the second and third chambers 102, 103. The intermediate body 130 also comprises a gassing valve 131 for pre-charging the second and third chambers 102, 103 and an electrical connection 132 for a piston position sensor for detecting the positions of the dividing pistons 105, 106. The primary cylinder 110 end of the accumulator module 100 houses the electrical and hydraulic connections 141, 142 for the blocking system. It also features hydraulic connections 143, 144 for the damper units 2a, 2b. While not described in this disclosure, the accumulator module also features a connection 145 for a roll control module, also capable of supplying or withdrawing hydraulic fluid to and from the first chamber 101 for roll stabilization. The secondary cylinder 120 end of the accumulator module 100 houses the electrical connections 151, 152, 153, 154 for the four control valves 201, 202, 203, 204 as well as the hydraulic connections 155, 156 to the hydraulic pump and tank 3, 4.

[0063] As shown in Figure 1, the vehicle suspension system is equipped with other sensors used to measure damper displacement (displacement sensors 165a, 165b), hydraulic pressure in the first chamber 101 (pressure sensor 163) and consequently the dampers 2a, 2b, hydraulic pressure in the fourth chamber (pressure sensor 164), and hydraulic fluid temperature in the first chamber 101 (temperature sensor 166) and consequently the dampers 2a, 2b. It will be appreciated that the system would be capable of calculating the load on the system by virtue of the pressure observed in the first chamber 101.

[0064] While in the embodiment shown, the system comprises four valves to connect the first and fourth chambers 101, 104 to the hydraulic pump and tank, it will be appreciated that the system could comprise of any quantity of valves to achieve the same effect of controlling fluid flow into and out of chambers 101 and 104.

[0065] While in the embodiment shown, the accumulator module 100 carries all of the electrical and hydraulic connections, the control valves and associated hydraulic interconnections on board, it will be appreciated that in an alternative embodiment, some or all these items could be located remotely from the accumulator module for instance, the control valves could be located on an external manifold, with a single connection to each of the hydraulic pump, tank and first and fourth chambers.

[0066] While the above disclosure has described an accumulator module in hydraulic connection with two damper units 2a, 2b, it will be appreciated that an alternative embodiment may comprise an accumulator module in hydraulic connection with any number of damper units. For instance, a vehicle may feature an accumulator module per damper unit.

[0067] While in the embodiment shown, the accumulator module comprises first and second dividers in the form of first and second dividing pistons, it will be appreciated that an alternate embodiment may comprise alternative means for dividing the chambers. For instance, in one form, the first and second, third and fourth chambers may be separated by a flexible diaphragm or bladder, as is known in the art.

[0068] Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprising” and “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0069] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0070] In some cases, a single embodiment may, for succinctness and/or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0071] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.