Double inclined rectangular sandwich mounting

(Fig. 1.18(h)) A pair of rectangular sandwich rubber blocks are supported on the slopes of a triangular pedestal. A bridging plate merges the resilience of the inclined rubber blocks so that they provide a combined shear and compressive distortion within the rubber. Under small deflection conditions the shear and compression is almost equal, but as the load and thus deflection increases, the proportion of compression over the shear loading predominates.

These mounts provide very good lateral stability without impairing vertical deflection flexibility and progressive stiffness control. When used for road wheel axle suspension mountings, they offer good insulation against road and other noises.

Flanged sleeve bobbin mounting with rebound control (Fig. 1.19(a and b)) These mountings have the rubber moulded partially around the outer flange sleeve and in between this sleeve and an inner tube. A central bolt attaches the inner tube to the body structure while the outer member is bolted on two sides to the subframe.

When loaded in the vertical downward direction, the rubber between the sleeve and tube walls will be in shear and the rubber on the outside of the flanged sleeve will be in compression.

There is very little relative sideway movement between the flanged sleeve and inner tube due to rubber distortion. An overload plate limits the downward deflection and rebound is controlled by the lower plate and the amount and shape of rubber trapped between it and the underside of the flanged sleeve. A reduction of rubber between the flanged sleeve and lower plate (Fig. 1.19(a)) reduces the rebound, but an increase in depth of rubber increases rebound (Fig. 1.19(b)). The load deflection characteristics are given for both mounts in Fig. 1.19c. These mountings are used extensively for body to subframe and cab to chassis mounting points.

Hydroelastic engine mountings (Figs 1.20(a c) and 1.21) A flanged steel pressing houses and supports an upper and lower rubber spring diaphragm. The space between both diaphragms is filled and sealed with fluid and is divided in two by a separator plate and small transfer holes interlink the fluid occupying these chambers (Fig. 1.20(a and b)). Under vertical vibratory conditions the fluid will be displaced from one chamber to the other through transfer holes. During downward deflection (Fig. 1.20(b)), both rubber diaphragms are subjected to a combined shear and compressive action and some of the fluid in the upper chamber will be pushed into the lower and back again by way of the transfer holes when the rubber rebounds (Fig. 1.20(a)). For low vertical vibratory frequencies, the movement of fluid between the chambers is unrestricted, but as the vibratory frequencies increase, the transfer holes offer increasing resistance to the flow of fluid and so slow down the up and down motion of the engine support arm. This damps and reduces the amplitude of mountings vertical vibratory movement over a number of cycles. A comparison of conventional rubber and hydroelastic damping resistance over the normal operating frequency range for engine mountings is shown in Fig. 1.20(c).

Instead of adopting a combined rubber mount with integral hydraulic damping, separate diagonally mounted telescopic dampers may be used in conjunction with inclined rubber mounts to reduce both vertical and horizontal vibration (Fig. 1.21).

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