VEHICLE WHEEL SUSPENSION UNIT

Abstract: A road vehicle suspension unit particularly suited for the front wheels of a front wheel drive vehicle has an outer subframe (1) consisting of a double-wishbone structure (2,4) which supports the road wheel (7) and is mounted on a rigid inner subframe (10) so as to accommodate vertical road wheel movement, which is strongly opposed by a spring or damper device (8). The inner subframe is mounted on the vehicle chassis or body by forward (21,22) and rear (24) resilient mountings such that horizontal wheel movement also is strongly opposed but with provision for some rearward movement of the wheel by turning of the subframe about an axis through the forward mounting.

Description: The invention relates to a suspension unit for a vehicle according to the preamble of claim 1. Such a suspension unit is known from FR-A-990 802. A variety of wheel suspension units and systems have been developed for road vehicles, all with the general object of providing a smooth quiet ride for the vehicle regardless of variable road conditions. The present invention is concerned with the provision of a vehicle wheel suspension unit, for use in road vehicles, which is capable of providing optimum wheel location as well as the capacity to accommodate road impacts to a degree appropriate to a normal passenger vehicle. The invention according to claim 1 provides a vehicle wheel suspension unit comprising inner and outer subframes, each subframe having a wheel location function and being capable of reacting suspension forces. A suspension unit of the invention is preferably arranged to oppose forces in all directions other than a preferred direction rather stiffly. Thus, the unit can be arranged to oppose forces tending to turn it rearwardly about a forward generally vertical axis less strongly than forces acting in other directions. A suspension unit of the invention can thus comprise an outer subframe carrying the wheel axle, the outer subframe having the form of a double wishbone linkage with spring and damper means which may be conventional, the inner ends of the linkage being pivotally connected to an inner subframe which is connected in turn to the vehicle chassis for limited relative compliance with forces received by way of the outer subframe. The inner subframe can be capable of limited pivotation about a substantially vertical axis located forwardly on the subframe, as by means of forward and rear resilient bushes of which the rear bush preferentially allows the limited pivotation. In this arrangement, the shocks developed when the wheel runs into a pot-hole for example are absorbed by movement of the wheel rearwardly. The subframes are constructed to be capable of articulation in a manner retaining optimum wheel geometry control whilst reducing input to the vehicle chassis of loads, and noise and vibration. The movements of the two subframes can be restrained mechanically, or the unit can instead be incorporated into an active suspension system. The invention is further described below, by way of example, with reference to the accompanying drawing, the single figure of which is a schematic partial perspective view of a suspension unit embodying the invention, looking rearwardly and outwardly from the vehicle body. The illustrated suspension unit is intended for a vehicle such as a passenger road vehicle, and is particularly suited to suspension of a front wheel in a front wheel drive vehicle. The unit comprises an outer subframe 1 having upper and lower pairs 2 and 4 of wishbone members joined at their apices to upper and lower ends of an upright member 5 from which extends an axle 6 for a road wheel 7. A spring or damping means 8 extends between the outer subframe 1 and the vehicle frame or chassis 9 so that the subframe serves to locate the vehicle wheel, whilst being able to react suspension forces. The spring or damping means 8 may be passive or active, that is, part of an active suspension system, preferably of the kind disclosed in EP-A-0 114 757. The subframe 1 constituted by the members 2, 4 and 5 is carried by a second or inner subframe 10 which is compliantly mounted on the vehicle chassis 9. The subframe 10 comprises a channel-shaped lower member 11 of which the centre web is presented outwardly and mounts a forward pair 12 and a rear pair 14 of apertured flanges, in which the inner ends of the lower wishbone member 4 are journalled about a generally horizontal axis extending lengthwise of the vehicle. Extending upwardly from the member 11 in a triangular configuration are forward and rear upper subframe members 16,17 from which extend forward and rear stub shafts 19,20 on which the inner ends of the upper wishbone member 2 are journalled, again about a horizontal longitudinally extending axis. The length of the subframe member 17 exceeds that of the member 16, so the upper ends of the members join at a position nearly above flanges 12. The inner subframe 10 is carried by the vehicle chassis 9 by lower and upper forward resilient mountings 21 and 22 and by a lower rear resilient mounting 24. The resilient mounting 21 is received within the lower subframe member 11 and comprises a rigid outer sleeve 25 secured to the chassis 9, a mounting bolt 26 extending through the sleeve and secured to the subframe member, and a resilient bush 26, for example of rubber, between the bolt and the sleeve. The mountings 22 and 24 are of similar construction. The mountings 21 and 24 have their axes vertical and are located in the subframe member 11 in the regions of the flanges 12 and 14 respectively. The resilient mounting 22 is located at the apex formed by the two upper frame members 16,17 and has its axis horizontal. The lower rear mounting 24 provides compliance for movement of the inner subframe 10 about the axis of the forward mounting 22 which is directional, being greater in respect of inward movement of the rear end of the subframe 10 than for outward movement. The mounting 24 includes for this purpose a resilient bush 30 with inner and outer axially extending slots 31 and 32 of which the former is radially narrower than the latter and is located further outwardly. Preferably, the outer subframe 1 stiffly opposed vertically acting forces and the resilient mountings 21 and 22 are very stiff, to oppose forces acting transversely to the upright member 5. The mounting 21 may be fitted with snubber means permitting movement of the order of 1 mm only. Rotation about the mounting 21, allowing rearward movement of the wheel 7, is however accommodated relatively readily. The inner subframe 10 is thus also capable of reacting suspension forces, its articulation being restrained for optimum wheel geometry control. The restraint imposed on the outer subframe 1 by the spring or damping means 8 is of course capable of accommodating the movements of the inner subframe 10. The invention according to the claims can be embodied in a variety of ways other than as specifically described and shown.

Claims: A suspension unit for a vehicle comprising: an inner subframe (10), an outer subframe (1) connected to the inner subframe (10) and having first mounting means (6) provided thereon for mounting a vehicle wheel (7) and linkage means (2,4) allowing vertical motion of a mounted wheel (7) relative to the inner subframe (10), first (21,22) and second (24) resilient mounting means provided on the inner subframe (10) for mounting the inner subframe (10) to the vehicle body, said first resilient mounting means (21,22) defining a vertical pivot axis for the suspension unit when mounted to the body and said second resilient mounting means (24) being spaced from the vertical pivot axis and being deformable to allow pivoting of the inner subframe (10) relative to the vehicle body, characterised in that the inner subframe (10) extends lengthwise of the vehicle body when mounted thereto. A suspension unit as claimed in Claim 1 wherein the outer subframe (1) is connected to the inner subframe (10) such that all points of connection are either forward or rearward of the second resilient mounting means (24) and are on the same side of the second resilient mounting means (24) as the first mounting means (21,22). A suspension unit as claimed in either Claim 1 or Claim 2 wherein the first resilient mounting means (21,22) comprises first (22) and second (21) vertically spaced apart resilient mounts, the first resilient mount (22) located above the highest point of connection of the outer subframe (1) to the inner subframe (10) and the second resilient mount (21) located level with the lowest point of connection of the outer subframe (1) to the inner subframe (10). A suspension unit as claimed in any of the preceding claims wherein the outer subframe (1) comprises two vertically spaced apart wishbones (2,4) joined by an upright member (5) for carrying the wheel (7), the wishbones (2,4) each having two points of connection to the inner subframe (10) with the points of connection of the first wishbone lying on a first axis which is parallel to the wheel (7) in its straight ahead position and the points of connection of the second wishbone lying on a second axis which is parallel to the wheel (7) in its straight ahead position. A suspension unit as claimed in any one of the preceding claims wherein the second mounting means (24) resist rotation of inner subframe (10) corresponding to forward motion of the vehicle wheel (7) more strongly than rotation of the inner subframe corresponding to rearward motion of the vehicle wheel (7). A suspension unit as claimed in any one of the preceding claims wherein the inner subframe (10) is of generally upright triangular configuration and the first mounting means comprise upper and lower mounting means (21,22) located in the region of a forward corner and the apex of the inner subframe and the second mounting means (24) is located in the region of the rear corner thereof. A suspension unit as claimed in Claim 6 wherein each mounting means comprises a resilient sleeve between an inner bolt and an outer eye, and the axes of the lower mounting means (21,24) extend generally vertically and that of the upper means extends generally horizontally. A suspension unit as claimed in any one of the preceding claims wherein the outer subframe (1) comprises upper and lower wishbone structures (3,4) joined at the outer ends thereof by an upright member (5) carrying the wheel axle and wherein the inner subframe (10) comprises a lower member (11) and upper forward and rear members (16,17) in a generally upright triangular configuration, the lower wishbone structure (4) being carried by the lower member (11), and the upper wishbone structure (3) being carried by the upper members (16,17).

Inventors: BOOEN, JEREMY JONATHAN, MILES, JOHN
Applicants: GROUP LOTUS PLC
Application year: 1988
Main classification: B60G7
IPC codes: B60G3, B60G7, B60G21