Front
Suspension
|
In horse carriages and in the first cars, steering was performed by the rotation of the whole axle around its pivot point on the chassis. But soon engineers realised that axle steering has great disadvantages at high speed and they began to design wheels that pivoted on the axle ends. Designers concluded that it would be better to spring the front wheels independently, so that when one wheel met an obstruction it did not affect the other wheel. Another disadvantage of these dependent systems was the amount of unsprung mass due to the presence of the heavy, unsprung front axle. |
Transverse
Leaf Springs (1898)
|
In 1898 R. Stephens invented the transverse leaf system (see Figure 6). It allowed the front wheels to move independently, but any vertical movement of the wheel consequently reduced the wheel track and tilted the wheel, which resulted in damaging the tyre tread. |
|
|
Figure
6: Transverse leaf system (1898)
Longitudinal
Leaf Springs (1921)
|
Therefore instead of using transverse leaf springs that would damage the tyres, engineers designed suspension systems with a longitudinal elliptic spring to allow the vertical motion (see Figure 7). Since 1921 this vertical post system has featured in a number of cars including the Lancia and Morgan. |
|
|
Figure
7: Longitudinal leaf system (1921)
Vertical
Movement Coil Suspension (1926)
|
In 1926 the vertical movement coil suspension appeared, thanks to the design of Guido Fornaca of Fiat (see Figure 8). The wheel spindles (purple) are supported by an upper (green) and lower (blue) 'A' shaped arm. It is a very basic lever system that allows the spindles to travel vertically up and down. When they do this, they also have a slight side-to-side motion caused by the arc that the levers scribe about their pivot points. This side-to-side motion is known as scrub. Unless the links are infinitely long the scrub motion is always present. The springs in Figure 8 are called 'coil over oil' because the shock absorbers (yellow) are inside the springs (red). |
|
|
Figure 8: Vertical
movement coil suspension (1926)
Double
Wishbone Suspension
|
The next great improvement in front suspension was the double wishbone also called 'knee-action' (see Figure 9). The name comes from the shape of the lower and upper arms. In this system the spindle is a highly complex construction, as are the wishbones themselves. The double wishbone suspension rapidly became one of the most favoured suspension types as it gave excellent road-holding capabilities without taking too much room under the car. |
|
|
Figure 9: Double
wishbone suspension
MacPherson
Strut Suspension (1947)
|
The real revolution in front suspension occurred in 1947 when Earle S. MacPherson created the MacPherson strut for General Motors (see Figure 10). Its new features were the use of a combination of the damper (blue) and the spring (red) as the pivot point for the wheel steering. This system has one of the best road-holding capabilities of all the passive suspensions for a very reasonable price, making it one of the most popular. The MacPherson strut has been used for years by many car manufacturers including all the Ford range and is still in use today. |
|
|
Figure 10: MacPherson
strut suspension (1947)
E-MAIL ME: en9apr@bath.ac.uk