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| Illustration 1 | g00739666 |
The secondary steering pump is located on the rear of the transfer case. (1) Secondary steering pump (2) Signal line (3) Pump Control Valve | |
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| Illustration 2 | g00734460 |
Secondary steering pump (3) Pump control valve (4) Passage from the pump control valve (5) Actuator piston (6) Spring (7) Outlet opening (8) Drive shaft (9) Inlet opening (10) Barrel (11) Piston (12) Swashplate | |
The secondary steering pump will supplement the hydraulic and steering pump when the machine is moving forward. If the engine fails the secondary steering pump will provide a constant flow of oil while the machine is moving forward.
Note: The secondary steering pump will not supply oil to the steering system when the machine is moving in reverse.
The secondary steering pump has nine pistons (11). When the machine moves forward, the upper transfer gear rotates and turns drive shaft (8). When drive shaft (8) turns, barrel (10), and pistons (11) turn. The piston ends connect to the slippers. Swashplate (12) does not rotate. There is a bearing journal on each side of swashplate (12). The two bearing journals are inside bearings which allow movement of swashplate (12). Oil flow through the passages in the pistons and slippers lubricates the internal components of the pump.
When the machine is moving in a forward direction and swashplate (12) is at the maximum angle, drive shaft (8) and barrel (10) turn moving the pistons in and out of barrel (10). As pistons (11) move out of barrel (10), pistons (11) create a vacuum at inlet opening (9). The pressure in the hydraulic tank pushes the oil into the inlet opening. The oil passes through the inlet opening into the piston bore in barrel (10). As barrel (10) continues to turn, pistons (11) move forward as the slippers rotate up the angle of swashplate (12). Pistons (11) push the oil from the piston bore through the pump outlet opening (7) and into the steering system.
The angle of swashplate (12) controls the amount of oil flow that is produced by the pump. The swashplate angle is varied in order to satisfy the setting of the pressure and flow compensator (1) .
Pump Control Valve
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| Illustration 3 | g01034972 |
Positions of the pressure and flow compensator spools with greater swashplate angle. (2) Signal line (4) Passage to the pump control valve (13) Pressure compensator spool (14) Cavity (15) Return oil passage (16) Blocked oil passage (17) Passage from the pump outlet (18) Flow compensator spool (AA) High pressure oil (BB) Tank oil (CC) Signal oil | |
Pump control valve (1) senses pump pressure from pump outlet (7) through passage (17). Pump control valve (1) also senses signal pressure on the opposite side of the block (orifice) through passage (2). The difference between the two pressures is known as the margin pressure. Refer to Testing and Adjusting, "Pump Control Valve (Secondary Steering) - Test and Adjust" for the margin pressure of the secondary steering system.
When the tractor is moving in a forward direction pump outlet pressure exerts force on spool (13). When system pressure exceeds the cutoff pressure, spool (13) moves to the left. Refer to Testing and Adjusting, "Pump Control Valve (Secondary Steering System) - Test and Adjust" for the cutoff pressure of the secondary steering system. The oil flow from pump outlet (7) through passage (17) is delivered to actuator piston (5) through passage (4). This will overcome the force of spring (6). The angle of swashplate (12) will decrease. The decreased swashplate angle will decrease the flow of oil from the pump in order to limit the pressure.
At the same time, oil under pressure from pump outlet (7) through passage (17) exerts force on spool (18). Signal oil from the opposite side of the block (orifice) flows through line (2) and into cavity (14). The signal pressure and the spring in cavity (14) exert force on spool (18). When signal oil pressure plus the spring force is greater than the pump pressure that is acting on the opposite end of the spool, the spool will move to the right. Oil that is behind actuator piston (5) will now flow out of passage (4), around spools (13) and (18), and into return line (16). The angle of swashplate (12) will increase. The increased swashplate angle will increase the output flow from the secondary steering pump until the pump outlet pressure equals the signal pressure plus the force of the spring.
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| Illustration 4 | g01034977 |
Positions of the pressure and flow compensator spools with reduced swashplate angle. (2) Signal line (4) Passage to the pump control valve (13) Pressure compensator spool (14) Cavity (15) Return oil passage (16) Blocked oil passage (17) Passage from the pump outlet (18) Flow compensator spool (AA) High pressure oil (BB) Tank oil (CC) Signal oil | |
When oil under pressure from the pump outlet exceeds the signal pressure and the spring force, spool (18) moves to the left. The oil flow from outlet (7) of the secondary steering pump is now delivered through passage (4) to actuator piston (5). This will overcome the force of spring (6). The angle of swashplate (12) will decrease. This will decrease the outlet flow from the secondary steering pump. The outlet flow decreases until the combined force of the spring in cavity (14) and the signal pressure exceed pump outlet pressure. Spool (18) will move right. The oil that is behind actuator piston (5) will flow around spools (13 ) and (18) and into return line (15). The force of spring (6) is now greater than the force behind actuator piston (5). The angle of swashplate (12) will increase. This will increase the output flow from the secondary steering pump. The continuous movement of spool (18) is known as metering. Metering keeps the pressure equal on both sides of spool valve (18).