History of Hybrid Vehicles?

With the increasing scarcity of oil supply and the worsening of environmental pollution, electric vehicles, which are powered by electricity, have become the focus of attention in the industry due to their energy-saving and environmentally friendly advantages[1]. Since the 1980s, many developed countries have invested heavily in the research and development of electric vehicles, and China's "863 Program" has also clearly identified electric vehicles as a key research project. China's "863 Program" has also clearly put electric vehicles as a key research project. At present, China's electric vehicle R & D level and developed countries are basically in the same starting line, in some aspects even more than foreign countries [2]. 2005, China's first generation of hybrid commercial vehicles through the demonstration and acceptance [3].

France, Japan, the United States, Germany and so on have gone through the test and demonstration operation, developed a pure electric car with commercialization level, such as the French PSA company's logo P106 and Citro?n AX electric sedan, Japan's Toyota Motor Corporation's RAV-4EV electric sedan, the United States of America's General Motors Company's EV1 electric sedan and so on. China will also include the research and development of electric vehicles in the "Eighth Five-Year Plan" and "Ninth Five-Year Plan" national scientific and technological research projects, and in June 1996, Shantou, Guangdong Province, built a national electric vehicle test demonstration base. During the "Tenth Five-Year Plan" period, the Ministry of Science and Technology of the People's Republic of China included the electric vehicle project in the national "863" major special project. In addition to the funding of batteries, motors and their control systems, vehicle control systems, the project focused on funding the Beijing Municipality (led by the Beijing Institute of Technology) to carry out research and development and demonstration of purely electric buses. 14 purely electric buses with lead-acid batteries were formally approved by the National Development and Reform Commission (NDRC) to be put into commercial operation on the 121 routes of the Beijing Public Transportation Company Limited on June 21, 2005, and another project was funded by Tianjin Qingyuan Power Company Limited. Another project funded Tianjin Qingyuan Power Company (China Automotive Technology Research Center) to carry out research, development and demonstration operation of pure electric cars. Five of these pure electric cars were first exported to the United States in early 2005[4].

Although the electric car has many advantages, but it can not replace the traditional gas-powered model, and hybrid cars are currently the new clean power vehicles in the most industrialized and marketable prospects of the car, the direction of its development is a truly zero-emission, non-polluting, non-fuel-consuming fuel cell vehicles. Now hybrid vehicles in Europe and the United States and Japan have formed industrialization [3], while the domestic is still in the initial stage, not formed industrialization.

2. Classification and principle of hybrid technology

HybridElectric Vehicle (HEV) is a combination of electric drive and auxiliary power (APU), giving full play to the respective advantages of the two and the combination of the two to produce the advantages of the vehicle. The auxiliary power can be a prime mover that burns some kind of fuel, such as an internal combustion engine, a gas turbine, etc. or other power generator sets. According to the different ways of hybrid power system connection, hybrid vehicles can be divided into three main structural forms, namely series, parallel and hybrid, which have their own advantages.

2.1 Series connection

A schematic diagram of a series hybrid system is shown in Figure 1. The series structure is characterized by compounding in the form of electricity, where the engine directly drives a generator to supply power to the energy storage device and the traction motor, the electric motor is used to drive the wheels, and the energy storage device acts as a regulator between the engine output and the demand of the electric motor. The advantage is that the engine operates independently of vehicle speed and road conditions, and is suitable for frequent vehicle starts, accelerations and low-speed operation. The engine operates near the optimum operating point, avoiding idling and low-speed conditions, which increases efficiency and improves emission performance. However, in the conversion process of mechanical energy and electrical energy loss of efficiency, it is difficult to achieve the purpose of significantly reducing fuel consumption, is currently mainly used in urban buses, rarely seen in cars.

2.2 Parallel

The schematic diagram of the parallel hybrid system is shown in Figure 2. Parallel structure is characterized by the mechanical form of the compound, the engine is directly connected to the drive axle through the variable speed parallel hybrid system schematic device, the motor can be used as a motor or generator at the same time in order to balance the load on the engine, so that it can work in the high-efficiency region. However, due to the mechanical connection between the engine and the drive axle, the engine does not run at the optimal operating point in urban conditions, and the fuel economy of the vehicle is worse than in series.　

Among them, the speed compound device is similar to the differential, this form of structure is difficult to be used in practice, because this structure requires the engine and motor output torque is always kept equal; single-axis torque compound vehicle drive system in the mechanical power of the joint is realized in the output of the engine crankshaft, the transmission is a single-shaft input, the Honda Insight belongs to this form; dual-axis torque compound mechanical power of the joint is realized in the engine crankshaft output, transmission is a single-shaft input, Honda Insight belongs to this form; dual-axis torque Composite mechanical power is realized in the output shaft of the transmission, the engine and motor using different transmission systems, transmission for the double-ended input; Warsaw University of Technology designed hybrid system belongs to this form, this structure can also realize stepless speed, but can not realize the engine output torque and the motor output torque of the direct superposition.

In the traction composite system, the union of mechanical power is realized through the road at the drive wheels, with two sets of independent drive systems, which can realize all-wheel drive, and is mainly applicable to SUVs; Toyota's THS-C system belongs to this form.