10125Progressive dual rate fixed cantilever spring Fig 1084e

This interesting layout has the front end of the main leaf spring attached by a shackle pin to the fixed hanger. The main blade rear tip contacts the out end of a quarter-elliptic spring, which is clamped and mounted to the rear spring hanger. When the axle is unloaded the effective spring length consists of both the half- and quarter-elliptic main leaf spans so that the combined spring lengths provides a relative low first phase spring rate.

As the axle is steadily loaded both the half- and quarter-elliptic main leaves deflect and flatten out so that their interface contact area progressively moves forwards until full length contact is obtained. When all the leaves are aligned the effective spring span is much shorter, thereby considerably increasing the operating spring rate. This spring suspension concept has been adopted for the rear spring on some tractor units.

10.12.6 Dual rate kink swing shackle spring

Support for the semi-elliptic spring is initially achieved in the conventional manner; the front end of the spring is pinned directly to the front spring hanger and indirectly via the swinging shackle plates to the rear spring hanger. The spring shackle plates have a right angled abutment kink formed on the spring side of the plates.

In the unladen state the cambered (bowed) spring leaves flex as the wheel rolls over humps and dips, causing the span of the spring to continuously extend and contract. Thus the swinging shackle plates will accommodate this movement. As the axle becomes laden, the cambered spring leaves straighten out until eventually the kink abutment on the shackle plates contact the upper face of the main blade slightly in from the spring eye. Any further load increase will kink the main leaf, thereby shortening the effective spring span and resulting in the stiffening of the spring to restrict excessive vertical deflection. A kink swing shackle which provides two stages of spring stiffness is suitable for vans and light commercial vehicles.

10.12.7 Progressive dual rate swing contilever springs (Fig. 10.84(g))

This dual rate spring has a quarter-elliptic spring pack clamped to the spring shackle plates. In the unloaded condition the half-elliptic main leaf and the auxiliary main leaf tips contact each other. With a rise in axle load, the main half-elliptic leaf loses its positive camber and flattens out. At the same time the spring shackle plates swing outward. This results in both main spring leaves tending to roll together thereby progressively shortening the effective spring leaf span. Instead of providing a sudden reduction in spring span, a progressive shortening and stiffening of the spring occurs. Vans and light commercial vehicles have incorporated this unusual design of dual rate springing in the past, but the complicated combined swing shackle plate and spring makes this a rather expensive way of extending the spring rate from unladen to fully laden conditions.

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