Illustration 1 | g06611098 |
Offset Hydraulic System ZERO OFFSET (1) Check valve (2) Counterbalance valve (3) Steering cylinder (4) Shuttle valve (5) Steering control valve (6) Compensator spool (7) To side cutter (8) From side cutter (9) Steering pump (10) Warmup valve (11) Steering shunt valve (12) Steering manifold (13) Margin spool (14) Main relief valve (15) Shuttle valve (16) Shuttle valve (17) Compensator spool (18) Offset control valve (19) Offset cylinder (20) Shuttle valve (21) Counterbalance valve (22) Check valve |
The drum offset system and the steering system are both controlled by components contained within steering manifold (12). The steering system is controlled by steering control valve (5). The drum offset system uses the steering control valve and the offset control valve (18) to control the drum offset while maintaining a constant steering angle. The drum offset system and steering system operate independently.
Note: The term "ZERO OFFSET" in the following discussion of the drum offset system is representative of no command made for drum offset. In application, this schematic applies to any situation where drum offset is hydraulically in hold.
Note: The following discussion of the drum offset system assumes that the machine is not steering. Refer to "Steering System" for additional information about the components and controls of the steering system.
When the engine is running, steering pump (9) sends flow to port "P" of steering manifold (12). Supply oil passes through a filter and is directed to warm up valve (10), margin spool (13), and compensator spools (6) and (17). If differential pressure across the filter exceeds
When steering shunt valve (11) is energized, the steering system and drum offset system are enabled. When the shunt valve closes, all supply oil is directed to compensator spools (6) and (17) and warmup valve (10). When the parking brake is applied, the steering system and the drum offset system are disabled. In this condition, the shunt valve is de-energized and directs all oil flow to the hydraulic tank.
Margin spool (13) is a load-sensing valve that compares the hydraulic pressure supplied to steering manifold (12) with the highest pressure demand being placed on the steering system and the drum offset system. When the operator is not steering the machine or operating the drum offset system, steering control valve (5), and offset control valve (18) are de-energized. In this case, the demand pressure is at hydraulic tank pressure. When this happens, the margin spool shifts and directs the supply oil to the hydraulic tank.
If steering cylinder (3) or offset cylinder (19) experience a shock load, the check valve in the low-pressure side of the affected cylinder opens. This action allows oil to enter the low-pressure side of the hydraulic cylinder, preventing cylinder cavitation. Counterbalance valves (2) and (21) limit the maximum pressure in the cylinders to
Main relief valve (14) limits the maximum pressure in the steering system and the drum offset system to
Illustration 2 | g06611107 |
Offset Hydraulic System LEFT OFFSET (1) Check valve (2) Counterbalance valve (3) Steering cylinder (4) Shuttle valve (5) Steering control valve (6) Compensator spool (7) To side cutter (8) From side cutter (9) Steering pump (10) Warmup valve (11) Steering shunt valve (12) Steering manifold (13) Margin spool (14) Main relief valve (15) Shuttle valve (16) Shuttle valve (17) Compensator spool (18) Offset control valve (19) Offset cylinder (20) Shuttle valve (21) Counterbalance valve (22) Check valve |
When the operator presses the drum offset left switch, the machine ECM sends signals to the solenoids in steering control valve (5) and offset control valve (18). Each control valve has two solenoids. When the machine changes the drum offset, steering cylinder (3), and offset cylinder (19) extend or retract together. When both cylinders extend, the rear drum moves laterally to the right regarding the front drum. When both cylinders retract, the rear drum moves laterally to the left regarding the front drum. When neither solenoid on the steering control valve or the drum offset valve is energized, each control valve is spring-returned to the center position.
Note: In the schematic shown, the machine is moving the rear drum to the left of the front drum.
Compensator spool (17) senses the pressure on the inlet to offset control valve (18) and the highest pressure on the outlet of the offset control valve. Compensator spool (6) senses the pressure on the inlet to steering control valve (5) and the highest pressure on the outlet of the steering control valve. In both spools, the load sensing signal acts against the compensator spool with a spring. Both compensator spools control the flow of oil to maintain a constant pressure drop of
When the rear counterclockwise solenoid in offset control valve (18) is energized, the spool of the control valve will shift. This shift directs supply oil to the check valve at the rod end of offset cylinder (19). At the same time, the offset control valve directs supply oil to counterbalance valve (21) on the head end of the offset cylinder. This supply oil with the pressure created in the head end of the cylinder opens the relief valve to the hydraulic tank. When this happens, the offset cylinder retracts.
The front counterclockwise solenoid in steering control valve (5) is energized at the same time as the rear counterclockwise solenoid in offset control valve (18). The steering control valve operates in a similar manner to the offset control valve. In this case, steering cylinder (3) retracts.
Steering cylinder (3) and offset cylinder (19) retract at the same time to maintain a constant steering angle while the drum offset is being adjusted.
The load signal from the outlet of steering control valve (5) and the load signal from the outlet of offset control valve (18) are sent to shuttle valve (16). This shuttle valve sends the larger demand signal to shuttle valve (15), where it is compared to the demand signal from side cutter (8) (if equipped). The highest demand signal is sent to margin spool (13). This load-sensing signal pushes against the spring in the margin spool to close the margin spool. This action increases the system pressure to the level required to move the steering cylinder and the offset cylinder.