WO2019097211A1

WO2019097211A1 - Improved suspension strut

Info

Publication number: WO2019097211A1
Application number: PCT/GB2018/053258
Authority: WO
Inventors: Liam Bradley WIDDRINGTON; Andrew James KITTLEY; Philip Alner WILBY
Original assignee: Bae Systems Plc
Priority date: 2017-11-16
Filing date: 2018-11-12
Publication date: 2019-05-23
Also published as: GB2568484A; GB201718950D0

Abstract

A suspension strut (10) for a vehicle comprises: a first connector (12) for connecting to a first point on the vehicle; a second connector (14) for connecting to a second point on the vehicle; a piston (20); and a first chamber (22) on a first side of the piston (20), wherein the piston comprises a first cavity (202) on the first side of the piston (20), the first cavity (202) forming part of the first chamber (22), wherein displacement of the first point relative to the second point is resisted by a change in volume of the first chamber (22) due to movement of the piston.

Description

Improved Suspension Strut

The invention relates to a suspension strut and a vehicle.

A suspension strut for a vehicle can comprise a piston and a chamber containing a fluid. During displacement of the strut, the piston moves within the strut to vary the volume of the chamber, with expansion/compression of the fluid within the chamber resisting the displacement. Such suspension struts are vulnerable to loss of fluid pressure, which can result in bottom out of the piston during compression and damage to the strut.

According to a first aspect of the invention, there is provided a suspension strut for a vehicle, the suspension strut comprising: a first connector for connecting to a first point on the vehicle; a second connector for connecting to a second point on the vehicle; a piston; and a first chamber on a first side of the piston, wherein the piston comprises a first cavity on the first side of the piston, the first cavity forming part of the first chamber, wherein displacement of the first point relative to the second point is resisted by a change in volume of the first chamber due to movement of the piston.

The suspension strut is advantageous, as the first cavity increases an effective volume of the first chamber. This means that if the pressure in the first chamber falls, the effect on the performance of the strut, and the likelihood of bottom out of the piston is reduced.

Additionally, increasing the effective volume means that during relative compression between the first point and the second point, the pressure rise in the first chamber is reduced. This means that the maximum operating pressure of the strut is reduced, decreasing the stresses in the strut. This also means that the pre-charge pressure of the piston (i.e. the pressure in the first chamber before the vehicle is raised up to its operating height) can be increased without a corresponding increase in maximum operating pressure, allowing a heavier load to be carried by the vehicle.

In one example, the piston is a floating piston, and the suspension strut comprises a second chamber on a second side of the piston. In one example, the piston comprises a second cavity on the second side of the piston, the second cavity forming part of the second chamber. This is particularly advantageous where a damping assembly (as described below) is employed, as the damping assembly can locate within the second cavity during extension of the strut.

In one example, the first chamber comprises a first port allowing a first fluid to enter the first chamber during a pre-charging phase, the first port operable to be closed in use. In one example, the second chamber comprises a second port allowing second fluid to flow into the second chamber during a vehicle preparation phase, the second port operable to be closed in use. In one example, the first fluid is a gas and the second fluid is a liquid, such that the second chamber is operable to maintain a substantially constant volume in use.

In one example, the suspension strut further comprises a rod connected to the first point and a cylinder connected to the second point, wherein the first chamber and the piston are located within the rod, and the second chamber is located at least partially within the cylinder, the piston movable within the rod to effect movement of the rod relative to the cylinder and displacement of the first point relative to the second point.

In one example, the suspension strut further comprises a damper assembly adapted to provide a damping force as fluid flows through the damper assembly during relative compression between the first point and the second point.

In one example, the damper assembly comprises side wall and a damper aperture in the side wall, wherein the damper aperture is open throughout operation of the strut to allow fluid to flow through the damper assembly. Including such a damper aperture is advantageous, as it allows damping to be reduced during relative extension between the first point and the second point, resulting in a faster extension reaction. The reduction in damping is less significant during relative compression, as relative compression occurs much more quickly than relative extension.

In one example, the damper assembly comprises a damper valve openable by fluid flowing through the damper assembly during relative compression between the first point and the second point, the damper valve remaining closed as fluid flows through the damper assembly during relative extension between the first point and the second point. In one example, the damper valve comprises: a plate; a valve aperture; and a bias device, wherein the bias device biases the plate towards the valve aperture to close the valve aperture, and fluid flowing through the damper assembly during relative compression between the first point and the second point causes the plate to move away from the valve aperture to open the damper valve. The damper valve is particularly advantageous in combination with the damper aperture, as the aperture being in a side wall means that the full axial area of the damper assembly can be devoted to the damper valve. This increases the surface area of the damper valve, which allows the valve to open more easily with only a small differential pressure across the damper valve. In one example, the suspension strut further comprises second and third damper apertures in the side wall of the damper assembly, wherein the second and third damper apertures are open throughout operation of the strut to allow fluid to flow through the damper assembly.

In one example, the damper assembly is located within an end region of the rod, the damper assembly providing a damping force as fluid flows into the rod through the damper assembly during relative compression between the first point and the second point.

According to a second aspect of the invention, there is provided a vehicle comprising a suspension strut as described above.

In one example, the vehicle is a military vehicle for carrying a weapon.

For a better understanding of the invention reference is made, by way of example only, to the accompanying figures, in which:

FIG. 1 shows a sectional view of a suspension strut;

FIG. 2 shows a perspective view of a piston;

FIG. 3 shows a cut away perspective view of the piston;

FIG. 4 shows a perspective view of a damper assembly;

FIG. 5 shows a sectional view of the damper assembly;

FIG. 6 shows a first sectional view of the suspension stut during operation;

FIG. 7 shows a second sectional view of the suspension strut during operation;

FIG. 8 shows a third sectional view of the suspension strut during operation; and

FIG. 9 shows a fourth sectional view of the suspension strut during operation.

Referring to FIG. 1 there is shown a sectional view of a suspension strut 10. The suspension strut 10 comprises a first connector 12 for connecting to a first point on a vehicle (not shown) and a second connector 14 for connecting to second point on the vehicle. The first connector 12 and the second connector 14 are located at opposite end regions of the suspension strut 10.

The suspension strut 10 comprises a rod 16 connected to the first connector 12. The rod 16 is integrally formed with the first connector 12. The suspension strut 10 comprises a cylinder 18 connected to the second connector 18. The cylinder 18 is integrally formed with the second connector 14. The rod 16 and the cylinder 18 are coaxial, with the rod 16 located within and slidable relative to the cylinder 18. The rod 16 and the cylinder 18 are elongate. The rod 16 and the cylinder 18 are hollow. The rod 16 and the cylinder 18 are constructed from titanium.

The suspension strut 10 comprises a piston 20 (described in more detail below with respect to FIG. 2 and FIG. 3). The piston 20 is a floating piston. The piston 20 is located within and movable relative to the rod 16. The piston 20 seals the rod 16, thereby providing a boundary between a first chamber 22 and a second chamber 24.

The first chamber 22 is located entirely within the rod 16. The second chamber 24 is located at least partially within the cylinder 18. The second chamber 24 is located partially within the rod 16. The volume of second chamber 24 located in the rod 16 and the cylinder 18 varies throughout operation of the suspension strut 10, as described below with respect to FIG. 6 to FIG. 9.

The suspension strut 10 comprises a first port 26 in fluid communication with the first chamber 22. The first port 26 is closable by a charging valve (not shown), which closes to form a seal after pre-charging. The suspension strut comprises a second port 28 in fluid communication with the second chamber 24. The second port 28 is closable by a valve (not shown).

The suspension strut 10 comprises a seal 32, which provides a seal between the rod 16 and the cylinder 18. The seal 32 is fixed to the cylinder 18, and surrounds the rod 16, to prevent fluid from flowing out of the suspension strut 10 from the cylinder 18. The seal 32 remains in place on the cylinder 18 as during sliding of the rod 16 relative to the cylinder 18. The seal 32 is an excluder. In addition to the seal 32, further seals (not shown) are included on the rod 16 and/or cylinder 18.

The suspension strut 10 comprises a damper assembly 30 (described in more detail below with respect to FIG. 4 and FIG. 5). The damper assembly 30 is located inside the rod 16 in an end region of the rod 16. The damper assembly 30 is fixed in position in the rod 16. The damper assembly fully spans the rod’s diameter. Referring to FIG. 2 and FIG. 3, there are shown views of the piston 20. The piston 20 comprises a first cavity 202 on a first side of the piston 20. The piston 20 comprises a second cavity 204 on a second side of the piston 20.

As shown in FIG. 1 , the first cavity 202 is in fluid communication with and forms part of the first chamber 22. The presence of the first cavity 202 provides an increase in an effective volume of the first chamber 22. Similarly, the second cavity 204 is in fluid communication with and forms part of the second chamber 24. The presence of the second cavity 204 provides an increase in an effective volume of the second chamber 24.

The piston 20 comprises rounded edges on the first side and the second side of the piston 20. This prevents damage to the rod 16 and the damper assembly 30, as explained in more detail below with respect to FIG. 6 to 9.

The first cavity 202 is sized to provide a desired spring curve for the piston 20.

Referring to FIG. 4 and FIG. 5, there are shown views of the damper assembly 30. The damper assembly 30 comprises a damper valve 302. The damper valve 302 comprises a plate 304, a valve aperture 306 and a bias device 308 (i.e. a spring). The damper valve 302 comprises six valve apertures 306, each of which has a diameter of 9mm.

The damper assembly 30 has a top hat construction, such that the damper assembly 30 comprises a side wall 310. The side wall 310 extends along the strut in a substantially axial direction. Additionally, the side wall 310 extends fully around a circumference of the damper assembly.

The plate 304 is located on an axial face of the damper assembly 30. The plate 304 extends across a major portion of the diameter of the rod 16. The valve aperture 306 is also located on the axial face of the damper assembly 30. The bias device 308 biases the plate 304 towards the valve aperture 306, so that the plate 304 closes the valve aperture 306.

The damper assembly 30 comprises three damper apertures 312 (only one of which is shown in FIG. 4). The damper apertures 312 are located in the side wall 310. The damper apertures 312 extend through the side wall 310 in a substantially radial direction. The damper apertures 312 provide fluid communication between two sides of the damper assembly 30. This means that fluid can flow through the damper apertures 312 between the rod 16 and the cylinder 18. The operation of the suspension strut 10 is now explained with reference to FIG. 6 to FIG. 9. For clarity, many of the reference numerals are omitted from FIG. 6 to FIG. 9. However, it will be appreciated that the suspension strut 10 of FIG. 6 to FIG. 9 is the same suspension strut 10 as that shown in FIG. 1.

Referring to FIG. 6, there is shown a sectional view of the suspension strut 10 in a precharge phase. During the pre-charge phase, the first connector 12 is fixed relative to the second connector 14. A compressor is used to pass first fluid (which is a gas) into the first chamber 22 through the first port 26. This causes the piston 20 to slide along the rod 16, until the piston 20 reaches the damper assembly 30 and cannot move any further. Further first fluid is added until a desired pre-charge pressure is reached in the first chamber 22. The first port 26 is then closed, and remains closed during use. The first fluid is nitrogen.

Referring to FIG. 7, there is shown a sectional view of the suspension strut 10 in a static nominal ride height position on a vehicle. Following the pre-charge phase, the first connector 12 is fixed to the first point on the vehicle, and the second connector 14 is fixed to the second point on the vehicle. The first point is connected to a wheel of the vehicle, while the second point is connected to a body of the vehicle.

To reach the static nominal ride height position, second fluid (which is liquid) is pumped into the second chamber 24 through the second port 28, until the desired height of the vehicle is reached. During this process, the piston 20 moves within the rod 16, reducing the volume of the first chamber 22 and compressing the first fluid. This causes compression of the suspension strut, with displacement of the first point relative to the second point decreasing. Once the desired ride height is reached, the second port 28 is closed, and remains closed during use. The second fluid is an oil.

Referring to FIG. 8, there is shown a sectional view of the suspension strut 10 in a piston bottom out position. When the wheel travels over a bump, the suspension strut 10 compresses, and the displacement of the first point relative to the second point decreases, which causes the piston 20 to move within the rod 16 to decrease the volume of the first chamber 22. Compressed first fluid in the first chamber resists compression of the suspension strut 10.

During compression of the suspension strut 10, the volume of the second chamber 24 (which contains the second fluid, a liquid) remains approximately constant. Second fluid flows from the cylinder 18 into the rod 16, which causes the plate 304 to displace away from the valve aperture 306, overcoming the bias device. The second fluid then flows through the valve apertures 306, which provides a damping force to oppose the compression and the movement of the first point towards the second point.

At the position show in FIG. 8, the suspension strut has undergone significant compression (for example, due to the wheel travelling over a large bump) such that the piston 20 has reached a bottom out position, in which the piston 20 is in contact with the end of the rod. In this position, the entirety of the first chamber 22 is located within the first cavity 202 of the piston 20. This demonstrates an advantage of the first cavity 202, which is that when the piston 20 bottoms out, some volume remains available for first fluid, which means that the maximum operating pressure in the suspension strut 10 is much lower than in a strut without such a first cavity 202. Additionally, the rounded edge on the first side of the piston 20 helps avoid damage to the rod 16.

Referring to FIG. 9, there is shown a sectional view of the suspension strut 10 in a fully extended position. Such extension may occur during rebound from the wheel travelling over a bump when the vehicle is off the ground.

During extension of the suspension strut 10, the displacement of the first point relative to the second point increases, which causes the piston 20 to move within the rod 16 to increase the volume of the first chamber 22. The pressure in the first chamber 22 falls as the first fluid expands while the vehicle is off the ground, which resists the extension.

During extension of the suspension strut 10, the volume of the second chamber 24 (which contains the second fluid, a liquid) remains approximately constant. Second fluid flows from the rod 16 into the cylinder 18. However, since the second fluid flows in the same direction as that in which the bias device’s 308 bias acts, the plate 304 remains against the valve aperture 306, which causes the valve aperture 306 to remain closed. However, second fluid flows through the damper apertures 310.

At the position show in FIG. 9, the suspension strut has undergone significant extension (for example, due to rebound after the wheel travels over a large bump) such that the piston 20 has reached a fully extend position, in which the piston 20 is almost in contact with damper assembly 30. In this position, the damper assembly 30 is located within the second cavity 204, preventing impact between the damper assembly 30 and the piston 20.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1 . A suspension strut for a vehicle, the suspension strut comprising:

a first connector for connecting to a first point on the vehicle;

a second connector for connecting to a second point on the vehicle;

a piston; and

a first chamber on a first side of the piston,

wherein the piston comprises a first cavity on the first side of the piston, the first cavity forming part of the first chamber,

wherein displacement of the first point relative to the second point is resisted by a change in volume of the first chamber due to movement of the piston; wherein the suspension strut (10) further comprises a damper assembly (30) adapted to provide a damping force as fluid flows through the damper assembly (30) during relative compression between the first point and the second point;

wherein the damper assembly (30) comprises a side wall (310) and a damper aperture (312) in the side wall (310), wherein the damper aperture (312) is open throughout operation of the strut (10) to allow fluid to flow through the damper assembly (30).

2. A suspension strut according to claim 1 , wherein the piston is a floating piston, and the suspension strut comprises a second chamber on a second side of the piston.

3. A suspension strut according to claim 2, wherein the piston comprises a second cavity on the second side of the piston, the second cavity forming part of the second chamber.

4. A suspension strut according claim 2 or 3, wherein the first chamber comprises a first port allowing a first fluid to enter the first chamber during a pre-charging phase, the first port operable to be closed in use.

5. A suspension strut according to claim 4, wherein the second chamber comprises a second port allowing second fluid to flow into the second chamber during a vehicle preparation phase, the second port operable to be closed in use.

6. A suspension strut according to claim 5, wherein the first fluid is a gas and the second fluid is a liquid, such that the second chamber is operable to maintain a substantially constant volume in use.

7. A suspension strut according to any of claims 2 to 6, further comprising a rod connected to the first point and a cylinder connected to the second point, wherein the first chamber and the piston are located within the rod, and the second chamber is located at least partially within the cylinder, the piston movable within the rod to effect movement of the rod relative to the cylinder and displacement of the first point relative to the second point.

9. A suspension strut according to any preceding claim, wherein the damper assembly comprises a damper valve openable by fluid flowing through the damper assembly during relative compression between the first point and the second point, the damper valve remaining closed as fluid flows through the damper assembly during relative extension between the first point and the second point.

10. A suspension strut according to claim 10, wherein the damper valve comprises: a plate;

a valve aperture; and

a bias device,

wherein the bias device biases the plate towards the valve aperture to close the valve aperture, and fluid flowing through the damper assembly during relative compression between the first point and the second point causes the plate to move away from the valve aperture to open the damper valve. 11. A suspension strut according to any preceding claim, further comprising second and third damper apertures in the side wall of the damper assembly, wherein the second and third damper apertures are open throughout operation of the strut to allow fluid to flow through the damper assembly. 12. A suspension strut according to any of claims 8 to 12 when dependent on claim 7, wherein the damper assembly is located within an end region of the rod, the damper assembly providing a damping force as fluid flows into the rod through the damper assembly during relative compression between the first point and the second point. 13. A vehicle comprising a suspension strut according to any preceding claim.

14. A vehicle according to claim 13, wherein the vehicle is a military vehicle for carrying a weapon.