According to the connection mode of the drive system, the hybrid hydraulic excavator can be divided into series type, parallel type and mixed type.
The series hybrid power system is directly driven by the engine to generate electricity. The generated electric energy is transmitted to the energy storage device through the control unit and stored in the form of DC power. Then, the energy storage device is transferred to the motor to the kinetic energy driven hydraulic pump, and finally the actuator is driven by the multi-channel reversing valve. The advantage of the series system is that the energy storage device balances the output power of the engine and the input power of the motor, so as to ensure the normal operation of the excavator. The engine and motor work independently, and it is easy to realize flexible structure layout. The disadvantage is that the energy output of the engine is done after the mechanical energy electrical energy mechanical energy conversion, which results in a large energy loss and a large installed power of the motor.
When the boom in the energy recovery system falls, the pump motor works in the motor state, which converts the hydraulic energy of the return oil into mechanical energy to participate in the pump drive. If the power recovered exceeds the pump demand, the excess mechanical energy is converted into electrical energy stored in the capacitance through the motor / generator (generator mode). The advantage of this method is that pump motor is used to shorten the energy recovery process, which requires higher requirements for system components and increases the complexity of control.
