992G Wheel Loader and 854G Wheel Dozer Steering System Secondary Steering System - If Equipped Caterpillar


Secondary Steering System - If Equipped
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Illustration 1g01067888

Secondary Steering System Hydraulic Schematic

(1) Left steering cylinder. (2) Right steering cylinder. (3) Steering control valve. (4) Check valve. (5) Diverter valve. (6) Check valve. (7) Secondary steering relief valve. (8) Neutralizer check valves. (9) Steering pressure reducing valve. (10) Secondary steering pump. (11) Steering neutralizer valve for right turns. (12) Steering neutralizer valve for left turns. (13) Pilot valve (STIC steering). (14) Steering pilot check valve. (15) Steering pilot check valve. (16) Line to steering low oil pressure switch. (17) Piston pump (steering). (18) Selector and pressure control valve. (19) Hydraulic tank for the steering and brake systems. (A) Pressure port for the right steering cylinder. (B) Pressure port for the left steering cylinder. (C) Pressure port for the pilot circuit. (D) Pressure port for the steering pump.

The secondary steering system supplies the steering oil only if the following conditions exist. The primary steering pump fails, or the engine stops while the machine is still moving.

The main components of the secondary steering system include the following items: diverter valve (5), secondary steering relief valve (7), secondary steering pump (10) and hydraulic tank for the steering and brake systems (19) .

Note: Diverter valve (5) and secondary steering relief valve (7) are part of steering control valve (3) .

During normal machine operation, steering pump (17) draws oil from hydraulic tank (19). The pump then sends the oil through check valve (6). Check valve (6) is located in steering control valve (3). The oil then flows to pressure reducing valve (9), and steering cylinders (1) and (2).




Illustration 2g00118074

Location of the Secondary Steering Pump

(10) Secondary steering pump.

As the machine starts to move, oil begins to flow from secondary steering pump (10). Secondary steering pump (10) is a ground driven pump that is attached to the output transfer gears of the transmission. If the machine is moving forward or backward, the pump will provide oil flow.

With secondary steering pump (10) in operation, oil flows into diverter valve (5). If steering piston pump (17) maintains a steady pressure, that pressure remains greater than the pressure from secondary steering pump (10). This keeps check valve (4) against the valve seat. This also keeps the spool in diverter valve (5) in the DOWNWARD position.

With the spool in diverter valve (5) in the DOWNWARD position, the oil from secondary steering pump (10) flows back to hydraulic tank (19) .

When steering piston pump (17) does not maintain adequate system pressure, and if the machine is in motion, a spring on the bottom of the diverter valve spool forces the spool upward. The oil from secondary steering pump (10) now flows through diverter valve (5). The oil then flows through the check valve (4), and then to check valve (6) .

Because primary steering pump (17) has stopped working, or because the engine has stopped, the secondary steering oil forces check valve (6) to seat. This stops oil from the secondary steering pump (10) from flowing to steering piston pump (17) .

This forces the pressure oil to flow to pressure reducing valve (9), and to steering cylinder (1) and steering cylinder (2) .

Pressure reducing valve (9) changes the pressure of the secondary steering oil to pilot pressure. The pilot oil then flows through steering pilot check valve (14) and through pilot valve (STIC steering) (13). From pilot valve (13), the pilot oil flows through steering neutralizer valve (11) and steering neutralizer valve (12). The pilot oil then flows through neutralizer check valves (8). Then pilot oil flows to steering control valve (3) .

The pressure oil that flows to steering cylinder (1) and steering cylinder (2) is controlled by the manipulation of pilot valve (13) .

Selector and pressure control valve (18) senses the pressure from steering piston pump (17). If there is a loss of steering pressure from steering piston pump (17), the loss of pressure is detected by a pressure switch that is connected to line (16). The pressure switch sends a signal to the monitoring system in order to create a Warning Category 3 alarm.

A Warning Category 3 alerts the operator that engine shutdown should occur as soon as possible. This helps prevent injury to the operator or potential damage to the machine.

A Warning Category 3 causes both the action lamp and alert indicator to flash. The action alarm will also sound. A Warning Category 3 may cause a message to appear in the message area. In some cases, the universal gauge may show a relative value.

Do not operate the machine until the cause has been corrected.

Note: Pilot valve (13) will not provide the capacity for manual steering when the engine is stopped. When the engine is stopped, you can only steer the machine under two conditions. The secondary steering system must be installed, and the machine must be in motion.

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