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Hyrban front suspension
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1. General concept #

As for all components of the car, the primary target for the front suspension design was minimal weight, with good ride, handling and roadholding performance. The fuel cell stack is located at the front of the car so the front suspension assembly also had to be compact and not impinge on packaging space excessively (see Figure 1 to 4).

Figure 1
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Figure 1 is a bottom view, the front of the car is on the right and the rear on the left, showing both front and rear suspension packaging.

Figure 2
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Figure 3
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Figure 4
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2. Assembly design #

To achieve a lightweight and compact design with good ride and handling, a semi-leading arm configuration was used. The suspension is designed so that the anchor points of the suspension are as far back as possible on the chassis. The target was to have no mounting points ahead of the firewall. With the pick up points of the rear suspension pushed as far forward as possible, the distance between suspension pickup points is reduced, improving chassis torsional rigidity. A related but separate point is that it also avoids the necessity of providing rigid chassis members further forward, reducing structural weight. The steering rack and semi-leading arm pickups are located underneath an aluminium subframe with a mass of 1.475kg. This subframe was a separate component in order to simplify monocoque production and give flexibility for late design changes and modifications in development; in a production vehicle, these pickups would probably be mounted directly to the chassis, unless it is felt wise to have a separate sacrificial subframe to reduce the chance of monocoque damage in an accident.


Figure 5
figure5

Figure 5 is a view of the whole suspension system. Each semi-leading arm is a tubular steel assembly, resembling a pair of wishbones, connected to the wheel upright. However, unlike wishbones, both upper and lower arms are rigidly connected to each other at their inner ends, operating as a single swinging arm. Furthermore, both upper arms are rigidly connected to each other at the centre point, via a housing for a spherical joint that is carried on the subframe, so there is only a single inner pickup for both swinging arms (see figure 6). This pickup is braced by a vertical link to a mounting on the firewall.

Figure 6
figure6

With this configuration, the semi-leading arms act as anti-roll components and, as the three suspension pickups are not on a common axis, they also have a single natural rest position. They therefore provide a spring force in vertical travel, operating with the spring in bump and against the spring in droop. This arrangement is not suitable in production, as the suspension components cannot be replaced independently and there are potential fatigue problems around the centre joint. The leading angle is 17.5° to the transverse axis (see Figure 7), which has been determined to control camber change.

Figure 7
figure7

With such an arrangement, it is not possible to achieve absolute zero bump steer but in order to minimise it, a very short steering rack was used, allowing for the longest possible steering arms (see figure 8). As the car is very light, the steering does not need to be power assisted. With a short rack and no need for power assistance, the whole steering system is also very light.

Figure 8
figure8

The damper and spring had to be selected in accordance with the characteristics of the car. The overall mass of the car is 380kg and the unsprung mass is 16.2kg per corner, excluding contribution from the suspension links. To provide a comfortable and safe ride, the damper selected on the prototype is a adjustable Koni 26series, and the spring rate is 300lbf/in.
Figures 9 and 10 are back and side views of a corner assembly.

Figure 9
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Figure 10
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Discuss these designs#

2.1 Suspension and steering

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Picture 10.png 72.2 kB 1 15-Jan-2010 18:29 Nicolas Sergent
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Picture 2.png 197.1 kB 1 15-Jan-2010 18:27 Nicolas Sergent
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Picture 5.png 301.0 kB 1 15-Jan-2010 18:28 Nicolas Sergent
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Picture 8.png 48.9 kB 1 15-Jan-2010 18:28 Nicolas Sergent
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Picture_6.png 107.5 kB 1 19-Jan-2010 16:57 Nicolas Sergent
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