Abstract
Heavy forklifts that are widely used in ports and stations have large gravitational potential energy at the lowering of the boom. As concerning the large rated power level, the engine is still the main power source for the heavy forklifts. With the increasingly stringent emissions regulations, the electric heavy forklift becomes an important choice. The structure and the working mode of an electric heavy forklift are introduced. Additionally the schematic of double hydraulic motor-generators is adopted to regenerate the potential energy when the boom is descending. The judge rule of the working mode and control strategy are analyzed. A test rig of a prototype electric heavy forklift is established. Control mode discrimination of potential energy regeneration, the control performance and the influence factors on regeneration efficiency are tested based on the test rig. The experimental results show that the discrimination method of the working mode of the proposed double hydraulic motor-generators with a potential energy regeneration system for potential energy is feasible. The descending of the lifting cylinder is consistent with the handle. The forklift can obtain the good following ability. Although the lifting cylinder descends at low velocity, the velocity is stable and the fluctuation of the rodless chamber pressure is within 0.1 MPa. With the increase of the load mass and descending velocity, the regeneration efficiency increases accordingly. The maximum efficiency is up to 74%. Hence, the proposed potential energy regeneration system is feasible and potential energy regeneration system does not affect the control performance of the boom.
Highlights
Non-road mobile construction machinery powered by a traditional internal combustion engine has problems such as low efficiency, bad emission and high pollution, which have a great impact on source utilization and global climate
The common characteristics about the electric heavy forklifts (EHFs) can be summarized as below: due to the large mass associated with the boom, when actuators go down, the gravitational potential energy and inertial energy that are dissipated into heat in the control valves are not easy to be regenerated in conventional heavy forklift
The potential energy recovery efficiency is defined as the percentage of the charged electric quantity of the battery and the potential energy of the load and door rack in one descending process, descending process of the forklifts
Summary
Non-road mobile construction machinery powered by a traditional internal combustion engine has problems such as low efficiency, bad emission and high pollution, which have a great impact on source utilization and global climate. The test results showed that the lifting, walking, steering and tilting accounted for 41%, 44%, 12% and 3% of the total energy consumption, respectively [12]. 2011, the efficiency of the electric motor (EM), hydraulic pump and valves were analyzed [14]. In the year 2013, the potential energy regeneration scheme of direct servo motor control technology was proposed. The same year, the PERS of the electric forklift with a lithium battery was built, and the regeneration efficiency of the system at a different velocity was analyzed [16]. Controlled the valve group to drive the hydraulic motor to make EM generate electric energy when the boom is descending, and stored the recovered energy into the battery of the forklift. A double hydraulic motor-generators (HMGs) with PERS to regenerate the potential energy when the boom descending is proposed.
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