GB2464939A

GB2464939A - Vehicle suspension system

Info

Publication number: GB2464939A
Application number: GB0819845A
Authority: GB
Inventors: Stuart Clark; Nick Dalton
Original assignee: Nissan Motor Manufacturing UK Ltd
Current assignee: Nissan Motor Manufacturing UK Ltd
Priority date: 2008-10-30
Filing date: 2008-10-30
Publication date: 2010-05-05
Also published as: GB0819845D0

Abstract

A suspension system for a vehicle having a vehicle body (40) and an axle (38) extending transversely across the vehicle between left- and right-side vehicle wheels (20l, 20r), includes a left-side mount (54l), typically in the form of a bush, for mounting the vehicle body (40) to a left-side of the axle, and a right-side mount (54r), typically in the form of a second bush, for mounting the vehicle body (40) to a right-side of the axle. Each of the left- and right-side mounts (54l, 54r) includes a first chamber (64l, 64r) for receiving fluid and a second chamber (66l, 66r) for receiving fluid. The vehicle suspension system further comprises hydraulic flow paths (68, 70) for allowing fluid transfer between chambers (64l, 64r, 66l, 66r) on opposite sides of the vehicle. Chambers (64l, 66l; 64r, 66r) within the same bush (54l, 54r) are substantially sealed from one another.

Description

Vehicle Suspension System

Field of the Invention

The invention relates to a vehicle suspension system including left-and right-side mounts for mounting on left-and right-sides, respectively, of an axle assembly of the vehicle to enable the axle assembly to be mounted to the vehicle body. In particular, the vehicle suspension system includes left-and right-side mounts for mounting on left-and right-sides, respectively, of a rear axle of the vehicle axle assembly.

Background to the Invention

It is known to provide a non-independent vehicle suspension system with elastomer bushes on the left-and right-sides of the rear axle assembly so as to provide the axle assembly with a degree of compliance in the event of a symmetric longitudinal load being applied through the vehicle wheels. Such longitudinal loads, or "shocks", occur due to the vehicle travelling over undulations in the road, speed breakers or bridge or road joints.

The use of bushes on the suspension system dampens the effects of such longitudinal shocks and therefore provides the vehicle passengers with an improved level of comfort.

However, to improve handling and stability of the vehicle, particularly when asymmetric longitudinal loads or side loads are applied to the vehicle, it is also desirable for the suspension system to have a high longitudinal stiffness to minimise compliance steer (i.e. low compliance). The two conflicting requirements of the suspension system therefore pose a compatibility problem for the vehicle designer.

To provide a degree of compromise between the requirement for high stiffness under some conditions and low stiffness under other conditions, it has been proposed to provide voids in the bushes which are moulded into the elastomer from which the bush is formed. However, a problem has been found with this system when the vehicle experiences a lateral cornering force. Because the bushes are mounted forward of the rear axle, and as the deflection of the rear axle of the vehicle is increased due to the inherent lack of stiffness of the bushes, the rear axle tends to steer the rear wheels counter to the steering direction.

It is also known to provide each of the left-and right-side bushes with two fluid-filled chambers in communication with one another via an orifice. The fluid is able to flow between the chambers, through the orifice, depending on the forces applied to the vehicle. The effect of the fluid transferring between the chambers is to provide a relatively high level of stiffness for some frequencies of impact force, but a lower level of stiffness for other frequencies. This type of system suffers from several disadvantages.

For example, it can pose service problems and is also prone to unforeseen modes of operation.

It is an object of the present invention to provide a vehicle suspension system for a vehicle which overcomes the drawbacks of known systems but which provides a compromise between the requirement for low suspension stiffness under symmetric longitudinal loads and high suspension stiffness under asymmetric longitudinal loads or cornering.

Summary of Invention

According to the invention, a suspension system for a vehicle having a vehicle body and an axle assembly comprising an axle extending transversely across the vehicle between left-and right-side vehicle wheels, comprises a left-side mount for mounting the vehicle body to a left-side of the axle, and a right-side mount for mounting the vehicle body to a right-side of the axle. Each of the left-and right-side mounts includes a first chamber for receiving fluid and a second chamber for receiving fluid. The vehicle suspension system further comprises means for allowing fluid transfer between chambers on opposite sides of the vehicle.

In one embodiment, the first and second chambers within the same mount are sealed from one another so that substantially no fluid can flow between them.

Each of the mounts is preferably oriented such that the first chamber is located further forward (along a front-to-rear, longitudinal axis of the vehicle) of the second chamber.

When the vehicle upon which the suspension system is installed is subjected to a symmetric longitudinal load through the left-and right wheels, fluid within the front chamber of the left-side mount is able to flow to the rear chamber of the right-side mount and fluid within the front chamber of the right-side mount is able to flow to the rear chamber of the left-side mount. This has the effect of reducing the stiffness of the suspension system so that the longitudinal load applied through the wheels is absorbed and the level of comfort for passengers of the vehicle is improved. Conversely, if the vehicle is subjected to cornering forces, as no fluid is able to flow between the front and rear chambers within the same mount, the suspension system adopts a relatively high stiffness so that handling and stability of the vehicle is improved. The invention therefore provides an adaptable vehicle suspension system which can adjust the stiffness of the system depending on the loads to which the vehicle is subjected. In this way passenger comfort can be maintained for longitudinal loads whilst still maintaining vehicle handling and stability upon cornering.

The first chamber of the left-side mount may be in fluid communication with the second chamber of the right-side mount through a first flow path, and the second chamber of the left-side mount may be in fluid communication with the first chamber of the right-side mount through a second flow path.

In one embodiment, at least one of the first or second flow paths is provided with valve means for controlling fluid flow between the chambers of the mounts on opposite sides of the vehicle which enables the system to be "tuned".

In one embodiment, each of the left-and right-side mounts includes an inner collar, an outer collar and a mount body defined therebetween, the first and second chambers being defined between the inner and outer collars within the mount body.

It is convenient to mount the outer collar of each of the left-and right-side mounts to the axle. The inner collar of each mount is conveniently mounted to the vehicle body.

Preferably, each of the fluid filled chambers of the left-and right-side mounts is arcuate in cross-section.

Preferably, the fluid received within the chambers of the mounts is a liquid.

The mounts conveniently include or take the form of mounting bushes.

According to a second aspect of the invention, there is provided a vehicle having a suspension system as set out in the first aspect of the invention. The vehicle may include one or more of the optional or preferred features of the vehicle suspension system, alone or in appropriate combination.

The invention has particular advantage when applied to a rear axle assembly including a rear axle extending transversely across the vehicle between left-and right-side vehicle wheels, wherein the rear axle carries a left-side suspension arm forward of the left-side wheel and a right-side suspension arm forward of the right-side wheel, the left-and right-side suspension arms carrying a respective one of the left-and right-side mounts.

Thus, one preferred embodiment of the second aspect of the invention relates to a vehicle having a vehicle body and a rear axle assembly including a rear axle extending transversely across the vehicle between left-and right-side vehicle wheels, wherein the rear axle carries a left-side suspension arm forward of the left-side wheel and a right-side suspension arm forward of the right-side wheel, the vehicle further comprising a vehicle suspension system including a left-side mount for mounting the vehicle body to the left- side suspension arm and a right-side mount for mounting the vehicle body to the right-side suspension arm, each of the left-and right-side mounts including a first chamber for receiving fluid and a second chamber for receiving fluid, and means for allowing fluid transfer between chambers on opposite sides of the vehicle, the first and second chamber of each of the left-and right-side mounts being sealed from one another so that substantially no fluid can pass between chambers within the same mount.

Brief Description of the Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings in which; Figures 1 is a schematic view of a vehicle suspension system, known in the prior art, under static conditions, Figure 2 is a section view of a mounting bush forming part of the vehicle suspension system in Figure 1, Figure 3 is a plan view of the vehicle suspension system in Figure 1 when subjected to a symmetrical longitudinal load applied through the rear wheels, Figure 4 is a plan view of the vehicle suspension system in Figure 1 when cornering to the left, Figure 5 is a plan view from the underside of a rear section of a vehicle fitted with the suspension system of an embodiment of the invention, Figure 6 is a left-side view of the rear axle assembly of the vehicle in Figure 5 to illustrate a longitudinal load applied to the rear vehicle wheels, Figure 7 is a plan view of a rear section of the vehicle suspension system of Figures 5 and 6 under static conditions, Figure 8 is a section view of a bush of the vehicle suspension system in Figures 5, 6 and Figure 9 is a plan view of the rear end of the vehicle suspension system in Figures 5, 6 and 7 when subjected to a longitudinal load through the rear vehicle wheels, and Figure 10 is a plan view of the rear end of the vehicle suspension system in Figures 5, 6 and 7 when subjected to a left-side cornering load.

Detailed Description of the Preferred Embodiments

In order to better understand the advantages of the invention, there now follows a more detailed description of a vehicle suspension system that is known in the prior art.

Figures 1 and 2 show a known vehicle suspension system under static conditions, including a front axle assembly 10 and a rear axle assembly 12. Front left-and right-side wheels 141, 14r are mounted on left-and right sides of the front axle assembly 10, respectively. The rear axle assembly 12 has a rear axle 16, also referred to as the twist beam, which extends transversely across the vehicle and longitudinal left-and right-side suspension arms 181, 18r. The rear axle assembly 12 supports rear left-and right-side wheels 201, 20r of the vehicle, respectively.

Each of the rear wheels 201, 20r is mounted towards the rear end of the respective left-or right-side suspension arm 181, 18r. A mounting bush 221, 22r is mounted at the front end of each side suspension arm 181, 18r so that the bushes are forward of the twist beam 16 along a longitudinal axis of the vehicle. The mounting bushes 221, 22r are identical to one another so only one will be described in detail here.

As shown in Figure 2, the mounting bush 22 is a generally annular component having an outer collar 24 defining a bush outer perimeter, an inner collar 26 defining a bush inner perimeter and a main body region 28. The main body region 28 is typically formed from an elastomer and the inner and outer collars are typically formed from a suitable metal (e.g. aluminium). The outer collar 24 may also be formed from plastic. The inner collar 26 is mounted to the vehicle body at a bush mounting point (not shown) and the outer collar of the bush is mounted to the respective left-or right-side suspension arm 181, 1 8r of the rear axle assembly 12 at the front end thereof. The main body region 28 of the bush 22 is provided with four void regions, two on the left side of the bush (regions 301, 321) and two on the right side (regions 30r, 32r), which allow the bush to be compressed and, thus, provide the bush with a degree of compliance.

When the vehicle is in motion, it is subjected to longitudinal and lateral (side) loads which are transmitted to the body of the vehicle through the rear vehicle wheels 201, 20r.

Referring to Figure 3, when the vehicle experiences a longitudinal load (as indicated by the arrows), the forces acting on each bush 221, 22r cause the voids 301, 30r to the front to be compressed and the voids 321, 32r to the rear to be expanded. The bushes 221, 22r therefore have relatively low stiffness which causes the bushes 221, 22r, and hence the suspension system, to absorb some of the longitudinal load transmitted through the vehicle wheels 201, 20r, thereby improving the comfort level of the passengers in the vehicle.

Referring to Figure 4, when the front wheels 141, 14r of the vehicle are steered to the left (as indicated by the central arrow), the rear axle assembly 12 is caused to twist about a vertical axis due to the lateral loads applied to the wheels 201, 20r rearward of the bush mounting points. The provision of the voids 301, 30r, 321, 32r in the mounting bushes 221, 22r increases the deflection of the twist beam 16, causing it to steer against the direction of steering. Thus, although passenger comfort is improved against longitudinal loading of the rear wheels 201, 20r due to the low stiffness of the mounting bushes 221, 22r, this causes the rear wheels 201, 20r to steer against the steering direction of the front wheels 141, 14r when the vehicle is cornering.

The inventors have now realised that what is required to satisfy the requirements of passenger comfort during longitudinal loading of the rear wheels and improved stability during cornering is for the suspension system to have a low stiffness under the former circumstances but a high stiffness under the latter.

Referring to Figure 5, an underbody 40 of a vehicle having a suspension system of the invention includes a vehicle floorpan 42 and a rear bumper beam 44. A high stiffness component in the form of a rear cross-member 46 forms a part of the vehicle floorpan 42 and extends laterally across the vehicle rearward of a vehicle fuel tank 48. Longitudinal members 501, 50r on the left-and right-sides of the vehicle, respectively, extend between the rear cross-member 46 and the rear bumper beam 44 to add further strength to the floorpan 42.

The vehicle body 40 is supported on a rear axle assembly 38 through a spring (52 -shown in Figure 6) and through left-and right-side mounting bushes 541, 54r, respectively, located on the left-and right-sides of the vehicle, respectively, as best seen in Figure 7. The vehicle includes a front axle assembly (not shown) of the type described previously for the known vehicle suspension system.

The rear axle assembly 38 includes a rear axle 16, or twist beam, and left-and right-side suspension arms 181, 18r upon which the rear left-and right-side wheels 201, 20r are supported, respectively, as described previously for the known vehicle suspension system. As the rear cross member 46 is a high-stiffness component, it provides suitably rigid mounting points for the left-and right-side mounting bushes 541, 54r. The bushes 541, 54r are also attached to the rear axle 16 via the suspension arms 181, 18r and, thus, form the intermediate mounting parts between the vehicle body 40 and the rear axle assembly 38.

Referring to Figure 8, each mounting bush 54 is of generally annular form and includes an outer collar 56 and an inner collar 60, both collars may be formed from a suitable metal. The outer collar 56 may alternatively be formed from a suitable plastic. The inner collar 60 defines an opening through the centre of the bush 54 and is that part of the bush that is mounted to the rear cross-member 46 of the vehicle body 40 via a separate mounting bracket (not shown). The size and shape of the inner collar and corresponding mounting bracket are configured to allow the inner collar 60 to be freely inserted into the mounting bracket to keep assembly time to a minimum. The bush 54 is secured to the mounting bracket using a pinch-bolt which, when correctly tightened, locally deforms the sides of the mounting bracket, effectively clamping the bush 54 within the bracket. This clamping prevents any relative movement of the inner collar 60 and the mounting bracket. In this way, any articulation of the suspension arms 181 and 18r of the rear axle assembly 38 relative to the vehicle are controlled by the compliance of the main body region 28 of the bush 54. The outer collar 56 of each bush is pressed into a respective one of the left-and right-side suspension arms 181, 1 8r of the rear axle assembly 38. The relative dimensions of the outer collar 56 and the corresponding receiving hole in the left-and right-side suspension arms 181, 18r is arranged to provide an interference fit. In this way, once the outer collar 56 is pressed into the suspension arm, there is no possibility for relative movement between the outer collar and suspension arm.

A main body 62 of the bush is defined between the inner and outer collars 60, 56 and is formed from an elastomer. The main body 62 is provided with first and second chambers 64, 66 which, in use, are located so that, when the bush 54 is mounted to the vehicle body 40, the first chamber 64 forms a front chamber of the bush and the second chamber 66 forms a rear chamber of the bush. Typically the chambers 64, 66 are filled with fluid (e.g. a glycol-based mixture). The front and rear chambers 64, 66 of each bush 54 are sealed from one another so that fluid within the front chamber 64 of one bush cannot flow into the rear chamber 66 of the same bush, and vice versa.

Referring again to Figure 7, the front chamber 641 of the left-side bush 541 is in fluid communication with the rear chamber 66r of the right-side bush 54r by means of a first hydraulic flow path 68. In a similar manner, the front chamber 64r of the right-side bush 54r is in fluid communication with the rear chamber 661 of the left-side bush 541 by means of a second hydraulic flow path 70. In other words, one end of the first hydraulic flow path 68 connects with the front chamber 641 of the left-side bush 541 and the other end connects with the rear chamber 66r of the right-side bush 54r, and one end of the second hydraulic flow path 70 connects with the rear chamber 661 of the left-side bush 541 and the other end connects with the front chamber 64r of the right-side bush 54r.

Operation of the vehicle suspension system under two different conditions will now be described with reference to Figures 9 and 10.

Referring to Figure 9, if the vehicle passes over an uneven road surface, a speed breaker or a bridge or road joint, the rear vehicle wheels 201, 20r experience a longitudinally directed impact load, as indicated by the arrows. This load is transmitted through the wheels 201, 20r, through the suspension arms 181, 18r of the rear axle assembly 38 and through the mounting bushes 541, 54r to the vehicle body.

The load applied to the rear side of the left-side mounting bush 541 causes fluid within its front chamber 641 to flow from the front chamber 641, through the first hydraulic flow path 68 and into the rear chamber 66r of the right-side bush 54r on the opposite side of the vehicle. Similarly, fluid within the front chamber 64r of the right-side bush 54r is caused to flow out of the front chamber 64r, through the second hydraulic flow path 70 and into the rear chamber 661 of the left-side bush 541. The effect of the transfer of fluid from one mounting bush 541, 54r to the other, and vice versa, is that the longitudinal impact load through the wheels 201, 20r is partially absorbed, reducing the longitudinal shock force' that is transmitted to the vehicle body 40 and, hence, improving the ride comfort of the passengers. The interference fits between the outer collar 56 and the rear axle assembly 38 and between the inner collar 60 and the bracket on the vehicle body 40 are sufficient for the rear axle assembly 38 to be returned to the "normal" position after impact.

The provision of the hydraulically connected chambers 641, 661, 64r, 66r in the left-and right-side bushes 541, 54r has a further advantage during vehicle cornering. Referring to Figure 10, if the front wheels of the vehicle are steered to the left, the rear wheels 201, 20r are caused to turn in the opposite direction (i.e. to the right -as indicated by the arrows) due to the loads which act on the rear wheels behind the bush mounting points (i.e. at the rear cross-member 46). Because the fluid within the chambers 641, 661, 64r, 66r of the mounting bushes 541, 54r is incompressible, and because the chambers within each mounting bush 541, 54r are isolated from one another, under such lateral loading no deflection of the rear axle 16 is possible and the bushes on each side maintain their static configuration. As no fluid flows between the left-and right-side bushes 541, 54r under lateral loads, steering of the rear axle 16 against the direction of steer of the front wheels is therefore reduced or avoided altogether and vehicle handling and stability is improved.

The present invention therefore provides an improvement over the known vehicle suspension system in Figures 1 to 4 as the conflicting requirements for low stiffness under longitudinal loads for reasons of comfort, and for high stiffness under lateral loads for reasons of stability, are satisfied without compromise.

It will be appreciated that the present invention is equally applicable to a front axle assembly of a vehicle, as opposed to a rear axle assembly, depending on the vehicle drive design. In addition, the system may also be used to mount a truck cab to a truck chassis to decouple vertical motions from roll motions.

In other embodiments (not shown), oscillation-control valves may be located within the first and second hydraulic flow paths 68, 70 to control the flow between the front and rear chambers of opposed bushes (i.e. between chamber 641 and 66r and between clambers 64r and 661, and vice versa). The use of valves provides the advantage that any resonance behaviour of the system under symmetric (i.e. dual-wheel) longitudinal loading, as a result of the high compliance of the mounting bushes 541, 54r, can be tuned out by valve control. The valve system enables the rate of fluid flow between bush chambers on opposite sides of the vehicle to be controlled so as to control vehicle oscillations.

In a still further embodiment (also not shown) fluid accumulators could be added to the system to give some controlled compliance under asymmetric/lateral load conditions. An active bush system is also envisaged in which a system of fluid accumulators, one or more pumps and valves enables fluid to be pumped from the front chamber of one bush to the rear chamber of the opposed bush, or vice versa.

Claims

Claims 1. A suspension system for a vehicle having a vehicle body (40, 46) and an axle (38) extending transversely across the vehicle between left-and right-side vehicle wheels (201, 20r), the vehicle suspension system comprising: a left-side mount (541) for mounting the vehicle body (40, 46) to a left-side of the axle (38), and a right-side mount (54r) for mounting the vehicle body (40, 46) to a right-side of the axle (38), wherein each of the left-and right-side mounts (541, 54r) includes a first chamber (641, 64r) for receiving fluid and a second chamber (661, 66r) for receiving fluid, the suspension system further comprising means (68, 70) for allowing fluid transfer between chambers (641, 64r, 661, 66r) of the mounts (541, 54r) on opposite sides of the vehicle, and wherein the first and second chambers (641, 661; 64r, 66r) within the same mount (541; 54r) are sealed from one another so that substantially no fluid can flow between them.
2. The suspension system as claimed in claim 1, wherein each of the mounts (541, 54r) is oriented such that the first chamber (641, 64r) is located forward of the second chamber (661, 66r).
3. The suspension system as claimed in claim 2, wherein the first chamber (641) of the left-side mount (541) is in fluid communication with the second chamber (66r) of the right-side mount (54r) through a first flow path (68), and the second chamber (661) of the left-side mount (541) is in fluid communication with the first chamber (64r) of the right-side mount (54r) through a second flow path (70).
4. The suspension system as claimed in claim 3, wherein at least one of the first or second flow paths (68, 70) is provided with valve means for controlling fluid flow between the chambers of the mounts (541, 54r) on opposite sides of the vehicle.
5. The suspension system as claimed in any of claims 1 to 4, wherein each of the left-and right-side mounts (541, 54r) includes an inner collar (60), an outer collar (56) and a mount body (62) defined therebetween, the first and second chambers (641, 64r; 661, 66r) being defined between the inner and outer collars (60, 56).
6. The suspension system as claimed in claim 6, wherein the inner collar (60) of each of the left-and right-side mounts (541, 54r) is mounted to the axle (38).
7. The suspension system as claimed in any of the preceding claims, for a rear axle assembly of a vehicle including a rear axle (38) extending transversely across the vehicle between left-and right-side vehicle wheels (201, 20r), wherein the rear axle (38) carries a left-side suspension arm (181) forward of the left-side wheel (201) and a right-side suspension arm (18r) forward of the right-side wheel (20r), wherein the left-and right-side mounts (541, 54r) are adapted for mounting on the left-and right-side suspension arms (181, 18r) respectively so that the rear axle assembly is mounted to the vehicle body (40) via the mounts (541, 54r).
8. The suspension system as claimed in any one of claims 1 to 7, wherein each of the fluid filled chambers (641, 64r, 661, 66r) is arcuate in cross-section.
9. The suspension system as claimed in any of claims 1 to 8, wherein the fluid is liquid.
10. The suspension system as claimed in any one of claims 1 to 9, wherein the mounts include bushes (641, 64r, 661, 66r).
11. A vehicle having a suspension system as claimed in any one of claims 1 to 10.