IMPROVEMENTS IN VEHICLE SUSPENSIONS

Abstract: A lightweight goods vehicle has a chassis frame or subframe whose rear end can be lowered to the ground by de-pressurising the air in air suspension units (80) for the rear axle. The air suspension units (80) act between the chassis longitudinal members and the axle (74), and the axle is further controlled by modified leaf spring members (82A, 82B) which are articulated together at (86) and connected at their rear end by means of rear links or shackles (32) to the chassis member. The air bags (94) are preferably arranged in tandem to either side of the axle (74) and may be connected by a separate base plate (90) and saddle (92) to the axle (74) where the spring position is outboard of the chassis member position, or may be directly connected to the forward leaf spring part (82A) where the leaf spring positions underlie the chassis members.

Description: IMPROVEMENTS IN VEHICLE SUSPENSIONS The present invention relates to an improved suspension system for light commercial vehicles, i.e. vehicles of weight up to about 6 tons, and to vehicles fitted with the aforesaid suspension system. The suspension system gives improved ride and/or permits the rear end of the vehicle to approach closely to the ground when pressure in the suspension is removed so that, for example, in the case of a passenger or goods carrying vehicle a porter's trolley or wheelchair can be pushed directly into the vehicle. AMK Automotive Limited make a wheelchair-accessible vehicle based on the Renault Extra Van with a body extended at the rear and with a lowered floor to permit the carriage of a wheel chair or powered scooter. In such a vehicle, the axle has a central region which is located beneath the rotational axis of the rear wheels, the air suspension units and the positioning means being attached to the axle in the central region. An access ramp is provided to enable a wheelchair to enter through a back door of the vehicle, the ramp being stowed away after use. Devices are known by which the rear ends of certain vehicles may be made to approach the ground by lowering the suspension, but these suffer from the disadvantage of complexity in construction and a requirement for chassis modification and movement of components such as fuel tanks and exhausts . Patent specification GB-A-2218949 (Paccar lnc) discloses an air suspension system for a front axle of a vehicle. The air suspension is fitted between frame members of the vehicle and leaf springs of the suspension, the rear end of each leaf spring being connected by a pair of hinged links to the frame member. The range of available movement in this suspension is limited to that which is likely to be encountered during normal riding, and there is no facility to collapse the suspension to permit part of the vehicle to be lowered to the ground. An air suspension system which can be installed on a pick-up truck or other vehicle in a relatively short time using frame supports provided on the truck as it is manufactured is disclosed in US patent 5351986 (Hedenberg) . An air suspension system for each rear wheel of a van type vehicle is disclosed in international publication O85/01703 (Hedenberg), and is concerned with providing smooth travel in ambulances or other emergency vehicles, but does not provide a facility for lowering the rear of the vehicle to the ground. It is an object of the invention to provide a suspension system for vehicles that can provide improved ride quality and a lowering to ground facility. In one aspect the invention provides a lightweight road vehicle having a frame or sub-frame provided with chassis longitudinal members, a rear axle, air suspension units being located at the rear of the vehicle for transferring the vehicle load from the chassis longitudinal members to the axle, means connected between the longitudinal members and the rear axle to position the rear axle and to resist torsion between the rear axle and the vehicle chassis, means for preventing movement of the axle laterally with respect to the body, and means for switching the air suspension units between a pressurised travelling state and de-pressurised collapsed state, the collapsed state permitting the rear of the vehicle to approach the ground. The invention also provides a rear suspension for a vehicle comprising at each side of the vehicle an air spring unit having air springs disposed in tandem to either side of the axle, and leaf spring means providing location for an axle of the vehicle, said leaf spring means being articulated behind the axle so that it resists torsion of the axle and provides transverse location thereof but does not provide the principal load path from a vehicle chassis to the ground, and an air supply system having means for switching the air spring unit between a pressurised travelling state and a de- pressurised collapsed state. The vehicle may be rear wheel driven but is preferably front wheel driven and may be adapted to carry goods loaded and unloaded through a back door of the vehicle, or it may be adapted to carry wheelchair passengers loaded and unloaded through a back door of the vehicle. For carriage of light loads, or for light vehicles, the air suspension means comprises two air bags disposed one on each side of the body, but preferably comprises four air bags disposed two on each side of the body, one in advance of and one behind the vehicle axle with reference to the normal direction of travel of the vehicle. The air bags will normally be of the rolling lobe type. To permit relatively large internal space of the air bags and relatively large travel of the air bags from their working to their suspension lowered position, the axle may carry forwardly and rearwardly directed supports located generally below the axle, the air bags being sandwiched between the supports and the sub-frame or chassis longitudinal members . Alternatively, for fitting to vehicles where the leaf spring underlie respective chassis members, the lower ends of the air bags may be fastened to the leaf springs to the front and rear of the chassis . The standard vehicle as manufactured will normally be provided with points whose normal use is for attachment of semi-elliptical steel suspension springs, and when the suspension of this invention replaces the standard suspension the longitudinal positioning means and the lateral movement preventing means are preferably secured to said attachment points . The longitudinal positioning means may be leaf springs pivoted to hanger brackets attached to the chassis in advance of the axle which defines suspension front attachment points . The lateral movement preventing means may be members pivoted at their front ends to leaf springs for relative movement in a vertical plane and pivoted at the their rear end to suspension rear attachment points e.g. by further articulated linkages . The combination in a light goods vehicle as aforesaid of air suspension units with locating members derived by dividing the conventional semi-elliptical leaf springs of the vehicle into front and rear portions articulated together so as to retain their location functions while not providing load path to the ground and while having sufficient travel to enable the rear of the vehicle to be lowered towards the ground is believed to be new. For wheelchair access or the like, the vehicle is preferably arranged so that when pressure is removed from the rear suspension a floor at the rear end of the vehicle is close to the ground. The vehicle of the invention will carry ancillary components of the air suspension including a compressor, reservoir tank, ride height valve and other air circuit components which are conventional. For lowering of the rear of the vehicle to the ground a control valve is positioned between the ride height valve and the air springs of the suspension, and can be opened to release the pressure in the air springs and permit the rear of the vehicle to be lowered to the ground. This operation can be performed under manual control from the cab of the vehicle, or from a control switch provided at the rear of the vehicle and does not require the de-pressurising of the upstream components of the air suspension system. How the invention may be put into effect will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a front wheel drive van with its rear chassis components exposed; Figures 2 and 3 are side views of a front wheel drive van with the suspension in its working and lowered positions respectively; Figures 4, 5 and 6 are respectively views of a pick up truck, a road sweeping vehicle, and a trailer to which the present invention is applicable. Figures 7 and 8 are respectively a plan and a side view of a first embodiment of the suspension system of the invention, which is applicable to a vehicle in which the leaf springs are located outboard of the longitudinal chassis members of the vehicle, Figure 9 is a diagrammatic side view of an air bag unit forming part of the suspension system of Figures 7 and 8, and Figure 10 is a diagrammatic rear view of the suspension system; Figures 11 and 12 are perspective views of a second form of the suspension system, also for fitting to a vehicle where the leaf springs are located outboard of the chassis longitudinal members, Figure 11 showing the suspension system in its ride height state, and Figure 12 showing the suspension in its lowered state; Figures 13 and 14 are diagrammatic side views of a third form of the suspension system, which resembles that of Figures 11 and 12 except that the pivot between the forward and rear portions of the leaf spring has been relocated; Figure 15 is a sectional view of an air bag unit of Figures 13 and 14; Figure 16 is a sectional view of one of the pivots in the suspension system of Figures 13 and 14; Figure 17 shows a further form of the suspension system for a vehicle in which the leaf springs are located underneath the chassis longitudinal members; and Figure 18 is a diagram of an air circuit for a suspension system as aforesaid. In Figure 1, there is shown a truck body (10) having a front wheel drive and cab unit (12) at the rear of which is a chassis (14) formed of longitudinal members (16, 18) and cross members (20, 22 and 24). Leaf springs (26, 28) connect the chassis members (16, 18) to a rear axle (30), the connection at the rear ends of the springs (26, 28) being by means of pivoted links (32, 34). In this instance, the leaf springs (26, 28) are located underneath the chassis members (16, 18) but it is also commonplace to locate the leaf springs outboard of the longitudinal chassis members. Embodiments of the present invention provides an air suspension system which replaces the conventional leaf springs (26, 28) without requiring additional attachment points to the chassis members, and without requiring significant modification to the chassis members, and which permits the rear end of the chassis (14) to be lowered towards the ground when required for loading or discharge of the vehicles. Figures 2 and 3 show a goods or passenger carrying vehicle having a body (40) built onto the chassis structure shown in Figure 1, Figure 2 showing the body in its normal position, and Figure 3 showing the body in a lowered position which it is an object of this invention to provide. Figure 4 shows a pick up truck based on the same chassis structure as in Figure 1, but with tandem axles (45, 47) to accommodate the greater load to be carried. A load platform (49) is movable by means of an air suspension system according to the invention between a lowered position shown in solid lines and a running position shown in phantom. Figures 5 and 6 show alternative types of vehicle to which the invention may be applicable. Figure 5 shows a road sweeping vehicle (50) having a leaf spring (52) forming part of its rear suspension, which leaf spring may be fitted with an air suspension system according to the invention to enable brushes to be lowered towards or lifted from the ground. Figure 6 shows a tandem axle boat trailer (60) which may have an air bag and leaf spring suspension system according to the invention for lowering the rear end of the trailer towards the ground when de-pressurised and for lifting the rear end of the trailer from the ground when re-pressurised. Figures 7 to 10 show a two-twin tandem air bag suspension system which may be fitted to a front wheel drive panel van, for example a Renault T35 or a Renault Traffic, Citroen Relay, Peugeot Boxer or Fiat Tucato. Such vehicles have a rear sub-frame or chassis incorporating a pair of spaced longitudinal frame members (70) braced by cross members (72). It is usual to provide a tubular axle (14) of reverse portal type in which there is a central region (76) located at a vertical position below the wheel centers, and raised lateral regions (78) which carry bearings for the road wheels of the vehicle, and are located above the central region (16) as shown in Figure 8. Both the air bag suspension units (80) and modified leaf springs (82) are attached to the lowered central region (76) of the axle (74). The chassis members (70) have hanger brackets (84) to provide pivots for eyes at the forward ends of the leaf springs (82), which are located outboard of the chassis or sub-frame. These hanger brackets (84) and pivots are pre-existing in the sense that they are already fitted for a conventional suspension. The leaf springs (82) which are now divided into front and rear parts are formed at a location behind the axle (74) with a Metallastic type rubber and metal joint (86) of the cup and spike kind which resists sideways movement of the forward and rear parts of the spring (82), but allows articulation of the forward and rear parts in a vertical plane. The rear part of the spring (82) has nylon bearings instead of the rubber bushes of a conventional steel suspension so as to permit free movement of the rear part in a vertical plane. However, the rear end is pivoted to an otherwise conventional shackle (83) whose other end is pivoted to an otherwise conventional attachment point of the vehicle. With the above arrangement, the spring (82) is no longer active as a load-bearing member, but retains its function as a radius arm, continues to provide a reaction to the break torque, and by virtue of its resilience acts as anti-roll member resisting twist of the axle relative to the chassis or sub-frame. The spring (82) may be formed by modifying an existing steel suspension spring for the vehicle, or it may be purpose-built to provide desired anti-roll characteristics. The rear part of the spring (82) is not now essential for ride purposes, but is preferably retained as shown to improve transverse location. The leaf spring (82), could, of course, be replaced by purpose-built members which combine the function of radius rods and torsion members, and again the rear link portions of the springs could be purpose made and could be made of a material which is not springy. The suspension units (80) are attached to the axle (74) inboard of the clamp group for the springs (82), and in line with the chassis members (70). They comprise a base plate (90) and saddle (92) between which the axle (74) is clamped, the saddle being puddle-welded at the center line of the axle, and the base plate being welded to the saddle. Load from the chassis members (70) is transferred to the axle at each side of the vehicle by a pair of air bags (94) sandwiched between a plate underneath the chassis and forward and rear plate regions of the saddle. The air bags are bolted to the saddle assembly and have locating formations at their upper ends which fit with corresponding formations on the plate to locate the air bags in place, the plate (100, Fig 11) extending along the underside of the chassis members between one air bag and another thereby providing a distributed load to the chassis. Bump stops are provided in the air bags or springs (94). In an alternative construction the saddle (92) may be allowed limited angular movement relative to the axle (74) to permit the body to be lowered further. The use of a pair of air bags (94) in tandem as shown is advantageous because in many vehicles the space for installing an air suspension is limited. The two air bags (94) may be made relatively small in plan so that the protrude relatively slightly beyond the chassis longitudinals and can fit into the available space. The amount of suspension travel permitted by the above arrangement is limited in a downward direction only by the shock absorbers fitted to the vehicle and in the upward direction by the bump stop. The upward travel, by removing the air pressure in the system, should be sufficient to enable the rear of the vehicle to approach close the ground, thereby permitting access to the vehicle from a low step or from the ground. The travel may, for example, be about 1200 mm. In the case of a low floor vehicle, it may be arranged that the porter's trolleys or wheelchairs can be pushed direct into the vehicle from the ground. Figures 11 and 12 show the working components of a further form of suspension unit according to the invention in the working and dumped positions respectively. In these figures the forward and rear parts of the leaf springs are identified (82a and 82b respectively). Plates (100) span between the air bags (94) and fit underneath the chassis longitudinal members (70). The Metallastic joint (86) has now been replaced by a pivot pin (102) supported at a clearance from the forward spring portion (82a) by means of a U-bracket (104). A further pin (106) at the rear of the spring portion (82b) fits to a pivoted link (32 or 34) as previously described. Figures 13 and 14 which show a third form of the suspension unit in its ride height and in its collapsed position respectively are similar to Figures 11 and 12 except that the pins and brackets (102A and 104A) are now located on the underside of the leaf spring forward portions (82a) so that, as can be seen in Figure 14 there is no problem of abutment of the spring portions (82a, 82b) at the downward extremity of the suspension lowering. Figure 15 is a sectioned view of a suspension unit (80) showing the bump stops (109). Figure 16 shows in section a bracket (104) and pin (102) which passes through a steel sleeve (110) and half bushes (112) of plastics or elastomeric material. This connection arrangement permits articulation and can provide resistance to torsion. The remaining pins at the front and rear of the leaf springs are similar. The arrangement of the Figure 17 is for a vehicle like Figure 1 where the leaf springs are located immediately beneath the chassis longitudinal members. For this purpose the lower ends of the air bags (94) are fixed to the forward leaf spring portion (82a) to either side of the axle (74) as shown. Figure 18 shows a compressed air circuit for the air bags (94). Air from a filter (111) passes to a compressor (113) and one way valve (114) to a tank (116). A branch line (118) leads to a ride height valve (120) and thence via a solenoid valve (122) to the air bags (94). An LSV modulator (124) can be arranged to maintain pressure in the system according to vehicle load. Normally compressed air is supplied through the ride height valve (120) and solenoid valve (122) to the air bags (94) to maintain a constant ride height. However, on actuation of the solenoid valve (122) by a switch in the cab of the vehicle or adjacent a rear door of the vehicle, the downstream side of the valve (122) is opened to allow the compressed air in the air bags (94) to escape, lowering the rear of the vehicle towards the ground and permitting loading and unloading thereof . It will be apparent that various modifications can be made to the embodiments described above without departing from the invention.

Claims: CLAIMS 1. A road vehicle having a frame or sub-frame provided with chassis longitudinal members, a rear axle, air suspension units being located at the rear of the vehicle for transferring the vehicle load from the chassis longitudinal members to the axle, means connected between the longitudinal members and the rear axle to position the rear axle and to resist torsion between the rear axle and the vehicle chassis, means for preventing movement of the axle laterally with respect to the body, and means for switching the air suspension units between a pressurised travelling state and a de-pressurised collapsed state, the collapsed state permitting the rear of the vehicle to approach the ground. 2. The vehicle of claim 1, which is of weight about 1-6 tons . 3. The vehicle of claim 2, which is front wheel driven. 4. The vehicle of any preceding claim, which is a pick¬ up truck. 5. The vehicle of any of claims 1-3, which is a road cleaning vehicle. 6. The vehicle of any of claims 1-3, which is a load carrying trailer. 7. The vehicle of any of claims 1-3, which has a van or passenger vehicle body. 8. The vehicle of claim 7, which is adapted to carry goods loaded and unloaded through a back door of the vehicle. 9. The vehicle of claim 7, which is adapted to carry wheelchair passengers loaded and unloaded through a back door of the vehicle. 10. The vehicle of any preceding claim, wherein the axle has a central region which is located beneath the rotational axis of the rear wheels, the air suspension units and the positioning means being attached to the axle in the central region. 11. The vehicle of any preceding claim, wherein the air suspension means comprises two air bags disposed one on each side of the body. 12. The vehicle of any of claims 1-10, wherein the air suspension means comprises four air bags, disposed two on each side of the body, one in advance of and one behind the vehicle axle with reference to the normal direction of travel of the vehicle. 13. The vehicle of claim 12, wherein the axle carries forwardly and rearwardly directed supports at a vertical position generally below the axle, the air bags being sandwiched between the supports and the longitudinal members . 14. The vehicle of any preceding claim, whose frame or sub-frame has points whose normal use is for attachment of a semi-elliptical steel suspension, and the longitudinal positioning means and the lateral movement preventing means are secured to said attachment points. 15. The vehicle of claim 14, wherein the longitudinal positioning means is leaf springs pivoted to the chassis in advance of the axle at suspension front attachment points, and the lateral movement preventing means is members pivoted at their front end to the leaf springs for relative movement in a vertical plane and pivoted at their rear ends to the suspension rear attachment points. 16. The vehicle of claim 15, comprising rubber and metal joints which resists lateral movement but permit articulation of the leaf springs and the lateral movement prevention members . 17. The vehicle of claim 15, wherein the leaf springs are pivoted to the lateral movement prevention members by means of pins whose axes are directed transversely of the vehicle. 18. A vehicle according to any preceding claim arranged so that when pressure is removed from the air suspension, a floor at the rear end of the vehicle is close to the ground. 19. A rear suspension for a vehicle comprising at each side of the vehicle an air spring unit having air springs disposed in tandem to either side of an axle, and leaf spring means providing location for the axle, said leaf spring means being articulated behind the axle so that it resists torsion of the axle and provides transverse location thereof but does not provide the principal a load path from the chassis to the ground, and an air supply system having means for switching the air spring unit between a pressurised travelling state and a de- pressurised collapsed state. 20. The suspension of claim 19, wherein the articulation is by Metallastic joints. 21. The suspension of claim 19, wherein the articulation is by transverse pins . 22. The suspension of any preceding claim, further comprising hinged links at the rear of each leaf spring means for providing an articulated connection to a chassis member.

Inventors: GLAZIER MARK, MILLER ERIC JOHN, GLAZIER, MARK, MILLER, ERIC, JOHN
Applicants: AMK AUTOMOTIVE LIMITED, GLAZIER MARK, MILLER ERIC JOHN, GLAZIER, MARK, MILLER, ERIC, JOHN
Application year: 1997
Main classification: B60G11
IPC codes: B60G9, B60G11