Here are two common methods for controlling the speed of a hydraulic motor:
1. Displacement Control:
- Method: This method controls the speed of the hydraulic motor by regulating the flow of hydraulic fluid entering the motor. The flow rate is directly proportional to the motor speed.
- Components:
- Variable Displacement Pump: A pump that can adjust its displacement volume to vary the flow output. By adjusting the pump’s displacement, the flow rate delivered to the motor can be precisely controlled.
- Control Valve: A valve used to regulate the flow path and pressure of the hydraulic fluid. This valve might be a simple flow control valve or a more sophisticated servo valve for precise control.
- Operation:
- Adjusting the variable displacement pump or the control valve setting changes the flow rate of the hydraulic fluid entering the motor.
- Increasing the flow rate results in a higher motor speed, while decreasing the flow rate leads to a slower motor speed.
- This method offers good control over the motor speed and can be very efficient, as minimal energy is wasted through throttling.
2. Pressure Relief Control (Throttle Control):
- Method: This method controls the speed of the hydraulic motor by regulating the pressure drop across the motor. A portion of the hydraulic fluid bypasses the motor, and the speed is indirectly controlled by varying the amount of bypass flow.
- Components:
- Fixed Displacement Pump: A pump that delivers a constant flow rate regardless of the pressure or load on the system.
- Pressure Relief Valve: A valve that regulates the system pressure by bypassing excess flow back to the reservoir. By adjusting the pressure setting of the valve, the pressure drop across the motor can be controlled.
- Operation:
- The fixed displacement pump continuously delivers a constant flow of hydraulic fluid.
- Adjusting the pressure relief valve setting changes the amount of fluid that bypasses the motor and returns to the reservoir.
- Increasing the bypass flow reduces the pressure drop across the motor, resulting in a slower motor speed. Conversely, decreasing the bypass flow increases the pressure drop, leading to a higher motor speed.
- Considerations:
- This method is simpler to implement but less efficient than displacement control. Energy is wasted by throttling the flow through the pressure relief valve, which can generate heat.
- Pressure relief control might not be suitable for applications requiring high precision speed control due to its indirect control method.
The choice between displacement control and pressure relief control depends on the specific application requirements. Displacement control offers better efficiency and precise speed control, while pressure relief control is simpler to implement but less efficient.