120M, 12M, 140, 140M, 150, 14M, 160M, 160 and 16M Motor Graders Secondary Steering System Introduction Caterpillar

The secondary steering system provides an emergency backup for the failure of the steering control valve and a failure of the steering pump. The secondary steering system operates under three modes:

• The secondary steering pilot valve is activated.

• The secondary steering pump is activated.

• The secondary steering pump is activated and the secondary steering pilot valve is activated.

The secondary steering system has the following main components:

• Electric drive pump

• Relief valve

• Control manifold

• Check valve

• Pressure sensor

• Hydraulic tank and filter

• Transmission/chassis electronic control module (ECM)

• Secondary steering pilot control valve

Electric Drive Pump

The electric drive pump is an electric motor that drives a gear pump. The gear pump provides oil flow to the control manifold.

Relief Valve

The relief valve in the secondary steering system is a safety valve. The relief valve will open preventing system oil pressure from rising too high. The open relief valve directs the excess flow of oil back to the hydraulic tank.

Control Manifold

When hydraulic pressure is lost in the primary steering system, the control manifold receives hydraulic oil from the secondary steering pump. The control manifold then directs the hydraulic oil to the steering control valve.

Check Valve

The check valves in the secondary steering system prevent oil from flowing backward through the system.

Pressure Sensor

The pressure sensor reads the steering system pressure. When the steering system pressure drops below a certain setting the ECM will signal the electric drive pump to start for the secondary steering.

Hydraulic Tank and Filter

The hydraulic tank supplies oil to the hydraulic system. The filter is remotely located next to the hydraulic tank. The filter screens return oil from the hydraulic system.

Transmission/Chassis Electronic Control Module (ECM)

The transmission/chassis ECM will perform the necessary electrical functions in order to activate the secondary steering system. The ECM receives an input signal from the implement control ECM 1 and the engine ECM. The ECM will then energize the electric drive pump when the input signal indicates a primary steering failure or an engine failure.

Secondary Steering Pilot Valve

When the primary steering control valve fails, the secondary steering pilot valve will direct oil to the main control valve spool.