Constant Control of Horsepower
Constant control of the horsepower is associated with the 1 to 9 setting of the engine speed dial. The flow of the pump is controlled by the power shift pressure when the engine speed dial is in the 1 through 9 position. The hydraulic output will be set according to the position of the engine speed dial. Even though the pump is delivering the maximum flow, the controller will correct the power shift pressure in order to maintain the maximum amount of flow. During the delivery of middle pressure and high pressure, the horsepower of the main pump is controlled in order to prevent high horsepower of the pump with lower engine horsepower. The controller receives feedback from the engine speed sensor. The power shift pressure is proportional to the target flow. The target flow is calculated from the setting of the engine speed and the pressure of the delivery pump pressure sensor. Thus, the power shift pressure will vary according to the position of the engine speed dial and the pressure of the delivery pump. The antistall feature for the engine is used in order to prevent the engine from stalling. The antistall feature will be activated, if the speed of the engine decreases 250 rpm below the position of the dial in comparison to the setting of the engine speed dial.
The power shift pressure is fixed for the positions of 1 through 9. The positions of 1 through 4 of the engine speed dial have a different power shift pressure for each setting. The engine speed dial will set the desired RPM, which will produce the desired flows. The positions of 5 through 9 of the engine speed dial have a common power shift pressure that is fixed. The positions 1 through 9 use engine speed, the position of the engine speed dial, and the pump pressure to set a fixed output. The output is fixed until a decrease of 250 RPM below the target RPM. At a RPM of 250 below the target RPM, the engine controller will adjust the power shift pressure in order to maintain engine RPM within 250 RPM of the target RPM.
Control Of An Underspeed Condition
The underspeed condition is associated with a position of 10 of the engine speed dial. The 10 position of the engine speed dial is used when a large amount of horsepower is required or a high travel speed is requested. In this case, it is necessary to utilize the underspeed feature when the engine is being operated at a maximum horsepower. The underspeed feature will maintain the speed of the engine at approximately maximum power. The controller reads the engine speed and the controller will adjust the power shift pressure in order to regulate the engine speed. The controller controls the power shift pressure in the underspeed condition. The engine maintains a speed of approximately 1950 rpm for the 312C, 2150 rpm for the 315C and 318C, and 1800 rpm for the 319C, 320C, 321C, 322C, 325C, and 330C in order to achieve the maximum horsepower. Therefore, when the engine speed is higher than the full load speed, the output of the pump will increase and the power shift pressure will decrease. Also, when the engine speed is lower than the target speed, the output of the pump will decrease and the power shift pressure will increase.
The horsepower of the engine may decrease under the following conditions:
- The engine becomes worn.
- The quality of the fuel is poor.
- The engine is operating at a high altitude.
The controller will decrease the output of the pump and the controller will increase the power shift pressure in order to reduce the load on the engine without reducing the engine speed. This condition occurs if the speed of the engine decreases below full load speed.