| Pure electric vehicles is the most industrialized and market-oriented vehicle series, which has the bright prospect in all the clean cars. It uses electromotor and power battery as a power-train. For its zero-emission, low-noise, high efficiency of energy use, and can effectively alleviate urban "heat island effect", has drawn worldwide attention, was known as the "green car". EV-Buses gradually becomes a main choice of city transport .The limited range of pure electric vehicle is its fatal weakness. In all the electric vehicles study, how to improve energy reserves technology and energy efficiency became two of the more important aspects. However, from the current technology development trends, there will be no major breakthrough in power battery energy storage technology in a short period of time. Therefore, in the process of electric vehicle industry how to improve the energy efficiency become a key issue, and regenerative braking is an important way to solve the problem. In driving cycles of city, the average speed of buses is not high, vehicle load changes significantly, the need for starting and braking is quite frequently, if the part of energy which is lost in the process of braking can be recycled, the range of electric vehicle will be greatly enhanced. The United States test results about the practical application of electric vehicle shows that regenerative braking can prolong the range of electric vehicle by 10% to 30%.Regenerative braking system of electric bus can not complete brake task independently in emergency braking, it must be matched with the traditional friction brake. In this paper, the brake system of modified electric bus is a kind of composite brake system, which was added by regenerative braking system on the basis of the original double-loop hydraulic brake system. Hydraulic brake system and regenerative braking system are independent and unity for each other. "Independent", it means that hydraulic brake system works as usual, is not limited by the regenerative braking system. When the regenerative braking system in a failure mode, the hydraulic brake system can bear the brake task alone, and maintain vehicle brake performance. Similarly, the regenerative braking control units regulate the braking torque according to the state of driving wheel."Unity", it means that the goal of the two brake system is harmony and unification, to ensure the vehicle's brake performance, stability and ride comfort.After installing the regenerative braking system, a new front, rear axle brake force distribution coefficientsβvalues should still meet the requirements of ECE braking regulations, which involved regenerative braking control strategy research. The performance of regenerative braking system is largely depend on the regenerative braking control strategy, so it is also a major issue to solve in this paper. After analyzing typical regenerative braking strategy, four major constraint conditions was summed up, and then carried out a detailed analysis and calculation.After making a detailed comparison about braking characteristics of original sample bus and modified electric bus, this paper put forward a regenerative braking control strategy for modified electric bus. When electromotor which connected with driving wheel worked as a generator, it can prevent rear-wheel from locking and can alleviate the front-wheel locking trends. This is a major innovation in this paper.In this paper, a scheme about the key technology of composite brake system of modified electric bus was designed. Because of the cancellation of internal combustion engine, the vacuum source was disappeared. Now, it is provided by the electric vacuum pump, which ensure the brake pedal force is as same as usual. At the same time, reasonable regenerative braking manipulator was designed, to ensure that the electrical regenerative braking control accurate and reliable. Finally, this paper analyzed the electrical regenerative braking energy recovery factors, and carry out a preliminary discussion on the focus and direction of the future work. |
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