In the working process of hydraulic excavator, boom lifting action is frequent, and because of the high quality of working device, a large amount of potential energy will be released during the process of falling. Most of the energy is consumed in the main hydraulic valve orifice and converted into heat energy, which results in energy waste and system heating, and reduces the life of hydraulic components. Therefore, it is important to study the recovery and reuse of excavator boom, which is of great significance to prolong the excavator life and improve the energy utilization and reliability of excavator hydraulic system. At present, there are two kinds of recovery and reuse schemes of potential energy of excavator boom: electric type and hydraulic type.
1. Analysis of energy saving scheme of electric boom
The energy saving scheme of electric boom is based on the storage element of battery or super capacitor, and hydraulic motor generator as energy conversion element, which belongs to the hybrid power scheme of oil and electricity. The principle of the work is to recover the potential energy of boom and convert it into electric energy by hydraulic motor generator, and store it into battery or super capacitor to assist the engine to work outside. There are two ways to recover energy. One is that when the boom is lowered, the hydraulic oil without rod cavity of the mechanical arm cylinder drives the hydraulic motor to recover energy from the generator. The speed of boom lowering is regulated by the speed of generator. In order to improve the control of boom lowering, and to extend the energy recovery time and reduce the power of the components. The other is to convert the recoverable energy into electric energy in super capacitor during the boom lowering process. The rest is stored in hydraulic accumulator directly. When the lowering operation stops, the pressure oil of accumulator is released to drive the hydraulic motor generator unit, so as to realize the continuation of the recovery process. The installed power of hydraulic motor and generator can be reduced by more than 70% after adopting the accumulator hydraulic motor generator structure scheme, and the boom control performance can be achieved. Because of the problems of energy conversion, low power density, short battery life and high cost, the electric energy recovery system has restricted its further development and application in excavator.
2.Analysis of energy saving scheme of hydraulic boom
The principle of the work is that when the gravity potential energy of the system is recovered, the boom potential energy is recovered by variable pump / motor and stored in the hydraulic accumulator. When the system is used, the energy stored is released to assist the engine to work externally. When the boom is lowered, the variable displacement pump / motor is driven by the oil return without rod cavity of the hydraulic cylinder, and then the accumulator is filled by the crossover cylinder to realize the recovery of the potential energy of boom lowering. Based on the balanced drive scheme of accumulator auxiliary cylinder, the scheme is to add accumulator auxiliary cylinder device to the boom, and charge the potential energy of boom recovered when the boom is lowered to the auxiliary hydraulic cylinder when the boom rises to drive the boom to rise. It is a new energy recovery and reuse scheme.
