Vehicle suspension system

An independent suspension system for a vehicle has at each side of an axle of the vehicle upper and lower control arms each connected by articulating joints between a vehicle body and a wheel carrier such as a wheel hub to mount the wheel on the vehicle body. A compression spring is connected at each end by articulating joints between the vehicle body and one of the control arms. The compression spring is connected to the control arm such that the center of rotation of the articulating joint is below a line joining the centers of rotation of the articulating joints at opposite ends of the control arm.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, and initially to FIG. 1 thereof, there is illustrated one side of a prior art double control arm independent suspension system 1 , the other side of the system, which is located at an opposite side of the vehicle, being similar. The suspension system 1 has an upper control arm 2 connecting to a vehicle body 12 at an articulating joint 5 and to a wheel carrier 13 at an articulating joint 6 . A lower control arm 3 connects to the vehicle body 12 at an articulating joint 7 and to the wheel carrier 13 at an articulating joint 8 . A coil spring 4 has one end connected to the vehicle body 12 at an articulating joint 9 and the other end of the spring 4 is connected to the lower control arm 3 at an articulating joint 10 . It will be appreciated however, that the spring 4 could in fact be connected instead to the upper control arm 2 rather than the lower control arm 3 . The wheel carrier 13 may be a wheel hub carrying a wheel 14 which is shown in broken outline in the drawings. Referring now to FIG. 2 , there is shown an independent suspension system of the described for the prior art suspension system shown in FIG. 1 are assigned the same reference numerals. It will be noted that a distinguishing feature of the present invention is that the articulation joint 10 between the spring 4 and the lower control arm 3 is below the line X joining the bearing or articulation joint centres 7 and 8 . Given the same spring and given that the distance between articulating points 7 and 10 are identical in both suspension systems of FIG. 1 and FIG. 2 , the spring characteristic referred to the wheel will be identical in both cases because at each position of the suspension linkage, both the length of the spring 4 and the angle &agr; between the spring line of actions through points 9 and 10 and the line joining points 7 and 10 are the same. However, it will be noted that the mounting point 9 where the top of the spring 4 articulates on the vehicle body 12 is located at a lower level and further from the vehicle centreline in FIG. 2 than in FIG. 1 . The construction of the invention permits a more favourable location of the top of the spring 4 because the spring centreline is rotated outward through the angle &bgr; 1&plus; &bgr; 2, where &bgr; 1 is the angle between the line joining articulation points 7 and 10 and the line X joining points 7 and 8 in FIG. 2 , and &bgr; 2 is the corresponding angle in FIG. 1 . A bump stop 22 , shown in broken outline in FIG. 2 , may be mounted on tie vehicle body 12 to engage the upper control arm 2 as the coil spring 4 is compressed. It is frequently desirable to have a progressively increasing effective suspension stiffness at the wheel as the suspension moves towards the bump position. In order to accomplish this with a linear spring characteristic, it is necessary that the angle &agr; increase towards 90° as the suspension approaches the bump position so that the spring force has maximum leverage on the control arm at this position. It Will be appreciated that the invention makes it easier to achieve this while avoiding the intrusion of the spring on useful space closer to the vehicle centreline. The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the appended claims.