Sunday, December 9, 2012

770G and 772G Off-Highway Truck: Rear Suspension (Cylinder)

The rear suspension cylinders are fastened between supports on the rear of the machine frame and to the rear axle housing. The suspension cylinder is a oil-pneumatic hydraulic cylinder. The rear suspension cylinders are located in line with the side rails of the frame. A support, which is fastened to the front side of the axle housing, is connected to the frame by a ball joint. The rear suspension cylinders provide the shock absorber action between the rear wheels and the machine frame. The rear suspension cylinders support the rear end of the machine which includes the load.

The main components of the suspension cylinder are a cylinder and a rod. The cylinder is fastened to the rear axle housing with a pin. The rod is fastened to the rear of the frame with a pin. As the wheel moves up or as the wheel moves down, the cylinder is free to move outside the rod. The rear axle housing moves with the wheel. The cylinder moves with the rear axle housing.

Cylinder Under Shock Load

Rear suspension cylinder operation
(1) Rod
(2) Chamber
(3) Cavity
(4) Drain ball check
(5) Orifices
(6) Cylinder
(AA) Nitrogen(LL) Oil

Orifices (5) and drain ball check (4) control the flow rate of the oil from chamber (2) to cavity (3) .

When a shock load is felt in the rear wheels, the rear axle housing will move up. This movement causes cylinder (6) to move up around rod (1). The movement of cylinder (6) compresses the nitrogen in chamber (2). Oil flows from chamber (2) to cavity (3) through orifices (5) and through drain ball check (4) .

The compression of the nitrogen in chamber (2) provides the shock absorber action. The suspension cylinder dampens the amount of shock load that is felt by the machine frame.

Cylinder Under Normal Loads

Rear suspension cylinder operation
(1) Rod
(2) Chamber
(3) Cavity
(4) Drain ball check
(5) Orifices
(6) Cylinder
(AA) Nitrogen(LL) Oil

As the shock load diminishes, the action of the suspension cylinder is reversed. The weight of the wheel and of the rear axle housing in addition to the pressure of the nitrogen in chamber (2) moves cylinder (6) down rod (1). As cylinder (6) moves down, the oil volume of cavity (3) decreases and the oil is put under pressure. The flow of oil closes drain ball check (4). The oil pressure in cavity (3) holds drain ball check (4) closed. At this time, oil can only drain to chamber (2) through orifices (5) .

As cylinder (6) moves down, the lower orifice is closed and the amount of oil that goes to chamber (2) is decreased. The other orifice is slowly closed off as cylinder (6) moves down. This again decreases the amount of oil that goes to chamber (2). By slowly decreasing the amount of oil that drains to chamber (2), the suspension cylinder reduces the speed of downward movement for cylinder (6). This reduces the shock load that is created when cylinder (6) reaches the bottom of rod (1) .