SYSTEM / Control System Speed Sensing Control Purpose: Controls the pump flow rate in response to engine speed changes due to variations in load so that the engine output can be utilized more efficiently. (Engine stall is prevented when the machine operates under adverse conditions such as operating at high alti- tude.) Operation: 1. The target engine operating speed is set by con- trolling the engine control dial. 2. MC calculates the difference in speed between the target engine speed and the actual engine speed input from ECM. Then, MC sends signals to the pump control solenoid valve. 3.
The pump control solenoid valve delivers pilot pressure oil in response to the received signals to the pump regulator and controls the pump deliv- ery flow rate. 4. If the engine load increases and the actual engine speed becomes slower than the target engine speed, the pump swash angle is reduced so that pump flow rate will be reduced. Therefore, the engine load is reduced and engine stall is pre- vented. 5. If the actual engine speed becomes faster than the target engine speed, the pump swash angle is increased so that pump flow rate will increase. Therefore, the engine output can be utilized more efficiently.
Q HP Mode Increase Decrease Basic Torque T111-05-02-004 Pressure P Pump P-Q Curve Q Flow Rate P/E Mode NOTE: As for the actual engine speed, ECM cal- culates the signals from crank speed sen- sor and cam angle sensor and sends to MC. Decrease Basic Torque T166-02-01-014 Pressure P T2-2-24