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| Illustration 1 | g01419427 |
(1) Pressure sensor (2) Pressure tap (3) Implement pump (4) Bias spring (5) Actuator (6) Super charger impeller (7) Implement ECM (8) Control spool (9) Coil assembly (A) Implement supply oil (B) Return oil (C) Pilot supply oil (D) Suction oil | |
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| Illustration 2 | g01443402 |
Pump compartment (10) Implement pump (180 cc (11.0 in3)) (11) Implement pump (250 cc (15.3 in3))(right) (12) Implement pump (250 cc (15.3 in3))(center) | |
Note: During normal operation, each of the three implement pumps operates in the manner that is described below. Differences in standby operation are noted within the text.
The implement pumps are variable displacement axial piston pumps that supply hydraulic oil to the main control valves. Each pump contains a swashplate that is driven by a single actuator (5). The small end of the actuator is connected to system pressure (A) from the discharge of the pump. The small end of the actuator also has bias spring (4) that assists in upstroking the pump during low discharge pressure. The large end of the actuator is connected to modulated pilot pressure that is controlled by control spool (8). The pilot pressure that is used to control the large end of the actuator is externally supplied. The pump displacement is controlled by a proportional current from the implement electronic control module (ECM) (7) to coil assembly (9) .
When a higher pump displacement is desired, the current that is supplied to coil assembly (9) is increased. This shifts control spool (8) upward. This drains a portion of the pilot pressure that is acting against the large end of actuator (5). The oil drains to the case drain of the pump. The force that is generated by pump discharge pressure (A) and bias spring (4) is now greater than the modulated pilot pressure and spring force on the large end of the actuator. Actuator (5) shifts downward. This increases the angle of the swashplate.
When a lower pump displacement is desired, the current that is supplied to coil assembly (9) is decreased. This shifts control spool (8) downward. This increases the pilot pressure that is acting against the large end of actuator (5) by closing the path to the case drain of the pump. The force that is generated by pump discharge pressure (A) and bias spring (4) is now less than the modulated pilot pressure and spring force on the large end of the actuator. Actuator (5) shifts upward. This decreases the angle of the swashplate.
When the implement system is in standby operation, two 250 cc (15.3 in3) pumps (11, 12) are controlled in order to provide the necessary flow that lubricates the rotating group. This lubrication also cools the rotating group. Adequate response from the pump is maintained and parasitic load on the engine is minimized. Standby control is active when no command is received from the tilt control lever or the lift control lever. During standby, a proportional current is sent to coil assembly (9). This current shifts control spool (8). This modulates the pilot pressure that is applied to the large end of actuator (5). Pump discharge pressure (A) is read by implement ECM (7) by using pressure sensor (1). Implement ECM (7) adjusts the proportional current in order to maintain a pump discharge pressure of 2500 kPa (360 psi).
When the implement system is in standby operation, the output of 180 cc (11.0 in3) pump (10) is set to the minimum. Standby control is active when no command is received from the tilt control lever or the lift control lever. During standby, no current is sent to coil assembly (9). This applies full pilot pressure to the large end of actuator (5). Actuator (5) is shifted fully upward. The angle of the swashplate and pump displacement are at the minimum.
When the implement system is in normal operating mode, the displacement of the pump is controlled in order to provide only the flow that is required in order to satisfy the requests that are received from the lift control lever and the tilt control lever. Implement ECM (7) reads the requests by using the tilt lever position sensor and the lift lever position sensor. Implement ECM (7) adjusts the proportional current that is sent to coil assembly (9) in order to provide the appropriate pump flow.
During engine start-up, implement ECM (7) commands maximum displacement of the pump in order to purge air from the hydraulic system. Also, the float valves are opened in order to reduce parasitic loads on the engine. Once the engine is running, the implement system enters standby mode.
Suction oil (D) is charged by super charger impeller (6). Also, the pump features internal flushing of the case. Charged oil flows from the inlet to the case. Due to the flushing feature, flow of case drain oil from the pump depends on oil temperature, pump speed, and the pressure differential between inlet pressure and case pressure. An increase in the pump speed, the oil temperature, or the pressure differential will increase the flow of case drain oil.