SYSTEM / Control System Engine Protection Control (HST Pump, HST Motor) Purpose: In order to prevent overrunning of the engine caused by HST brake, the engine protection control controls the HST motor displacement angle, and controls the engine speed to 2800 min-1. Operation: 1. When releasing the accelerator while traveling in fast speed, the HST brake is applied. The HST pump is forcibly rotated by the pressure oil in the HST circuit. 2. The HST pump and the engine are connected with the shaft. Therefore, the rotation of the HST pump is transmitted to the engine as well. The engine runs in fast speed. 3. The HST control unit detects the signal from the engine speed sensor. When the engine speed is -1 over 2800 min , the HST control unit controls so that the HST motor displacement angle should be reduced in stages.
4. This control releases the HST brake and prevents the engine from overrunning. NOTE: This control is available when the High-Low selector switch is set to the High mode. NOTE: This control is given priority over Overrunning Control (T2-1-8). Therefore, the machine may travel in fast speed.
Maximum Displacement Angle Displacement Angle before Control HST Motor Displacement Angle
Displacement Angle after Control
Minimum Displacement Angle
Machine Speed Speed after Control Speed before Control
T2-1-9
T4FC-02-01-019
