A Study Into An Electric Vehicle Hydraulic Regenerative Braking System

To alleviate the energy crisis and reduce environmental pollution, and to realize low carbon economy sustainable development, one of the best ways is to use electric vehicles. Lithium battery has the good characteristics such as high specific energy density, high power density, more life cycle than lead-acid battery and other batteries, so it is the best power source to be act as the electric vehicle power source. When driven in the city, the electric vehicle has to accelerate and brake to decelerate frequently just for traffic jam and traffic lights. In speedup phase, high electric current is one of the main reasons to make the lithium battery broken prematurely. To use the battery much efficiency, it has important theoretical and engineering application value about studying pure electric hydraulic regenerative braking system.A study on the electric vehicle’s hydraulic energy store regenerative braking system is given in the paper. A patent application has granted authorization to the author of this paper. The electric vehicle’s hydraulic energy store regenerative braking system can absorb the electric vehicle’s kinetic energy when braking. When the electric vehicle start to accelerate, the accumulator with high liquid pressure release its liquid to drive the liquid motor, and the liquid motor drive the vehicle to a certain speed, then the electric motor can start to run at a high speed with very low current. When run with a low peak current, the lithium accumulator battery life cycle can be increased. What’s more, the vehicle can run longer when been charged once.A pattern is given on how to solve the hydraulic energy store system parameters and it is proved to be right by simulation. In this paper, one parallel connection hydraulic energy store system is studied. Vehicle dynamic modeling equation, liquid pump / motor modeling equation and a high pressure accumulator modeling equation are given. The high pressure accumulator’s voltage, liquid pump / motor displacement, liquid pipe diameter, low pressure accumulator’s voltage are figured out. By experimental verification, all parameters can meet the needs. By the ECE rule, Power consumption is simulated. In the no-load and full load, pure electric car with hydraulic regenerative braking system has less peak current time, lower average current, and can run longer.Again, in order to collect braking energy as much as possible, different driving conditions are given, simulation and verification are done. The four different driving conditions are slight braking, moderate braking, emergent braking and gliding. Different control strategies are given to each driving condition. By doing simulation and verification, the control strategy is right.A circuit is designed to test lead-acid battery and lithium battery, and experimental study on lead-acid battery and lithium battery working characteristics are done. It can be concluded that the lithium accumulator battery current and the voltage change trends are the same when the load is constant, and the lowest working voltage has no relationship with the load, and the released energy has no relation to the load. Some circuits are designed, and the circuits can measure single battery voltage accurately. The circuits can charge the lower electric power battery.Semi-physical simulation test-bed control system is designed, and Semi-physical simulation test of hydraulic regenerative braking system are studied. MC9S12XS128 single-chip microcomputer is used as the control system MCU. PM150CLA060 is used as driver module.Brushless DC motor controller is designed. Hall sensor is used to measure vehicle speed.Some circuits are designed to drive electromagnetic valves and magnetic clutch. A circuit is designed to measure high gas pressure.Some parameters such as braking energy recovery rate, braking energy release rate, braking energy regeneration rate are figured out. Running with the ECE cycle mode test, the vehicle can save electric energy obviously. By doing group test with traditional electric vehicle, the electric consumption per hundred kilometers and the average current value are driven. The test data can prove that the electric vehicle with the hydraulic energy store regenerative braking system can make the lithium accumulator battery peak working current lower, the lithium accumulator battery peak working current time shorter and average working current lower, and the vehicle can run much longer per time.