What are the classifications of hybrid electric vehicles?

Hybrid vehicles have two or more power sources. According to the arrangement of different power sources, hybrid electric vehicles can be divided into series hybrid electric vehicles, parallel hybrid electric vehicles and hybrid hybrid electric vehicles. Kind of classification. There are typically two configurations in series and parallel (Figure 1). The main difference between the two is the connection between the power source and the wheels. The parallel configuration combines the advantages of the above two configurations. .

What are the classifications of hybrid electric vehicles?
Figure 1 Basic configuration of hybrid vehicles

1. Series hybrid electric vehicle
The schematic diagram of the assembly structure of the series hybrid vehicle drive system is shown in Figure 1 (a). In a series hybrid vehicle, the two components of the engine and the generator are usually integrated to form an APU. The engine drives the generator to generate electricity, and the generated electric energy is directly sent to the motor through the controller, and the motor generates a driving torque to drive the car. . The battery actually balances the output power of the engine-generator set and the input power of the motor: when the power generated by the generator is higher than the power required by the motor (the car is slowing down, driving at low speed, or short-term parking conditions), the controller controls The generator charges the battery; when the power generated by the generator is lower than the power required by the motor (car starting, acceleration, high-speed driving, and climbing conditions), the battery provides additional power to the motor.

Compared with the transmission forms of other types of hybrid vehicles (parallel, hybrid), the transmission form of series hybrid electric vehicles has its own characteristics.

(1) There is no direct mechanical connection between the engine, the electric motor, and the drive train, which makes the layout of the whole vehicle more free, and at the same time, the working state of the engine is not affected by the driving state of the car, and the engine can be kept stable, efficient, and stable. Working under low-emission operating conditions, the car has good fuel economy and low emissions.

(2) In a series hybrid vehicle, the electric energy generated by the engine driving the generator and the electric energy output by the battery pack together drive the electric motor to drive the car. Electric drive is the only driving mode, so the control technology is relatively simple.

(3) The drive mode of the series transmission determines that the power of the motor should be close to or equal to the maximum drive power required by the car, so the power of the motor is larger, and the appearance and mass are larger. Therefore, the tandem arrangement is not easy to realize in small and medium cars.

(4) In the energy conversion of thermal energy to electrical energy to mechanical energy in the engine-generator-motor system, the energy loss is relatively large. Therefore, the fuel economy of series hybrid vehicles is relatively poor compared with parallel hybrid vehicles.

(5) This transmission form is more suitable for vehicles running on highways in cities with complex road conditions. In urban areas with high environmental protection requirements, the car can also turn off the engine and enter a pure electric state when starting and driving at low speeds, so that the car can meet the zero emission requirements.

The direct source of the drive power of the series hybrid electric vehicle is the drive motor, and the engine-generator set and the battery pack are the sources of the drive motor power. The two can coordinate with each other and supplement their respective working states and working forms according to their different working characteristics. , To achieve the purpose of energy saving and emission reduction. Like hybrid vehicles in the form of parallel transmission, series hybrid vehicles can also solve the problem of high engine power in traditional cars (large horse-drawn trolleys), eliminate engine idling, and recover braking energy through the motor during braking. In addition, the series hybrid electric vehicle has a significant advantage: it can better control the area of ​​the engine, optimize the working area of ​​the engine, and make the engine always work in the high-efficiency and low-emission area, thereby improving the vehicle Improve fuel economy and reduce emissions. This is because there is no direct mechanical connection between the engine and the drive train of a series hybrid vehicle, but only electrical connections, and the working state of the engine can not be restricted by the driving state of the vehicle. This advantage is an important reason for the recognition of series hybrid electric vehicles.

2. Parallel hybrid electric vehicle
Parallel hybrid vehicles use two independent drive systems, an internal combustion engine and an electric motor, as shown in Figure 1(b). The internal combustion engine can drive the vehicle alone, the electric motor can also drive the vehicle alone, and the internal combustion engine and the electric motor can also drive the vehicle together. When the output power of the internal combustion engine is greater than the power required to drive the vehicle or regenerative braking, the motor works in the generator state, which will remove the excess The energy is converted into electrical energy and charged into the battery. Obviously, parallel hybrid vehicles can reduce vehicle exhaust emissions and fuel consumption.

The parallel structure can be simply understood as adding a set of electric drive system (motor and power battery) on the basis of an ordinary car. Both the engine and the motor can drive the wheels individually, or they can work at the same time to drive the vehicle together. When the power battery is insufficient , The engine can also drive the electric motor to reverse to charge the power battery.

There are generally three modes to choose from for power-carried models with parallel structure.
(1) Pure electric mode. The engine is turned off, and the battery powers the electric motor to drive the vehicle. This mode is mostly used for low-to-medium speed driving, and some models can also achieve high-speed cruising.
(2) Pure oil mode. The engine starts to drive the vehicle, and at the same time it can drive the electric motor to reverse and charge the power battery.
(3) Mixed mode. The engine and electric motor are started at the same time to drive the vehicle. This mode is mostly used for climbing, rapid acceleration and other high-load work situations.

Different from the series structure, the engine and the electric motor in the parallel structure can drive the car at the same time, and the power performance is more superior. Take BYD Qin as an example. Its 1.5T engine and electric motor have a combined power of 300hp (1hp=745.700W), but Qin is only a compact car of its own brand. Secondly, there are many drive modes of hybrid vehicles with parallel structure, which can adapt to a variety of working conditions. The engine can drive the car alone when running at medium and high speeds, without the need for secondary conversion of energy, so the overall fuel consumption is lower.

advantage:
(1) Since the mechanical energy of the engine can be directly output to the drive shaft of the car, there is no energy conversion in the middle. Compared with the series arrangement, the system efficiency is higher and the fuel consumption is less.
(2) The electric motor can be used as a generator at the same time. The system has only two power assemblies, the engine and the electric motor, and the quality of the whole vehicle is reduced and the cost is greatly reduced.
(3) As the power of the equipment is small, the additional equipment cost is also small.

Disadvantages: Due to the direct mechanical connection between the engine and the driving wheels of the vehicle, the operating conditions of the engine are inevitably affected by the specific driving conditions of the car. To maintain the engine working in the optimal working area, complex control systems and control strategies are required

3. Hybrid series (parallel/series) electric vehicles
The series-parallel device includes the characteristics of series and parallel, as shown in Figure 1(c). Its main derivative structure has two types: switch type and shunt type:
The switch type structure is shown in Figure 2. Through the coupling and disengagement of the clutch, the mutual switching between the series branch and the parallel branch is realized: the clutch is separated, which cuts off the mechanical connection between the engine and the electric motor and the driving wheel, and the system runs in series mode; the clutch is combined , The engine and the driving wheels are mechanically connected, and the system runs in parallel mode.

What are the classifications of hybrid electric vehicles?
Figure 2 Switch structure

The shunt structure is shown in Figure 3. Both the series branch and the parallel branch are always in working condition, and the planetary gear transmission is used for engine output between the series branch (from the engine to the generator) and the parallel branch (from the engine to the driving wheels). Reasonable distribution of energy. This structure can implement various controls on the series branch through the generator, and at the same time maintain the mechanical connection between the engine and the driving wheels through the parallel branch, and finally realize the speed control of the engine.

What are the classifications of hybrid electric vehicles?
Figure 3 Split structure

Adding a generator on the basis of parallel connection is a series connection, but it does not use a traditional gearbox, but instead uses a coupling unit called ECVT (electro continuously variable transmission) planetary gear structure, as shown in Figure 4. This technology has always been monopolized by Toyota, and some manufacturers use ordinary gearboxes in the hybrid structure, such as dual-clutch gearboxes, continuously variable gearboxes, etc., but the effect is far less than ECVT.

What are the classifications of hybrid electric vehicles?
Figure 4 Planetary row speed relationship

The hybrid structure can drive the generator to charge the power battery while the engine and the electric motor cooperate to drive the vehicle. It is no longer like a single electric motor in the parallel structure that needs to perform two roles, and theoretically it can realize the engine to drive the generator to generate electricity. , The mode of motor-driven vehicle, as shown in Figure 5. Therefore, the drive mode of the hybrid structure has four modes: pure electric mode, pure oil mode, hybrid mode, and charging mode.

What are the classifications of hybrid electric vehicles?
Figure 5 Schematic diagram of the hybrid structure

The structural advantages and use advantages of the hybrid series are closer to the parallel structure models, but the driving modes of the hybrid series are more abundant. On the basis of the parallel hybrid driving mode, the charging function is added, which means that the engine and electric motor are not used when the vehicle is fully driven. Worry about power consumption. And thanks to the addition of ECVT, the coordination of the electric motor and the engine is more tacit, it can adapt to more working conditions, and the fuel-saving effect is even better.