Hybrid Electrical Vehicle (Hybrid Electrical Vehicle, abbreviated as HEV) refers to a vehicle equipped with two power sources at the same time-thermal power source (generated by a traditional gasoline engine or diesel engine) and electric power source (battery and electric motor). By using electric motors in hybrid vehicles, the power system can be flexibly adjusted in accordance with the actual operating conditions of the vehicle, while the engine is kept working in the area with the best overall performance, thereby reducing fuel consumption and emissions.
How hybrid vehicles work
The power system of a hybrid electric vehicle is mainly composed of a control system, a drive system, an auxiliary power system, and a battery pack.
Take a series hybrid electric vehicle as an example to introduce the working principle of a hybrid electric vehicle.
At the beginning of the vehicle driving, the battery is in a fully charged state, its energy output can meet the requirements of the vehicle, and the auxiliary power system does not need to work. When the battery power is less than 60%, the auxiliary power system starts: when the vehicle energy demand is large, the auxiliary power system and the battery pack provide energy for the drive system at the same time; when the vehicle energy demand is small, the auxiliary power system provides energy for the drive system At the same time, the battery pack is also charged. Due to the existence of the battery pack, the engine works in a relatively stable working condition and its emissions are improved.
Hybrid vehicles use smaller engines that can meet the needs of car cruises, and rely on electric motors or other auxiliary devices to provide additional power for acceleration and climbing. The result is improved overall efficiency without sacrificing performance. Hybrid vehicles are designed to recover braking energy. In a traditional car, when the driver steps on the brake, the energy that could be used to accelerate the car is thrown away as heat in vain. However, hybrid vehicles can recover most of this energy and store it temporarily for reuse during acceleration. When the driver wants maximum acceleration, the gasoline engine and the electric motor work in parallel to provide starting performance comparable to a powerful gasoline engine. In situations where the acceleration requirements are not too high, the hybrid vehicle can run on the electric motor alone, or on the gasoline engine alone, or a combination of the two to achieve maximum efficiency. For example, the gasoline engine is used when cruising on the highway. When driving at low speeds, it can be driven by the motor alone, without the assistance of a gasoline engine. Even when the engine is off, the electric power steering system can still maintain its control function, providing greater efficiency than traditional hydraulic systems.
Classification of hybrid systems
A. According to the connection mode of the hybrid drive, the hybrid power system is mainly divided into the following three categories:
One is a series hybrid system. The series hybrid power system generally uses the internal combustion engine to directly drive the generator to generate electricity. The generated electrical energy is transmitted to the battery through the control unit, and then transmitted from the battery to the motor to convert into kinetic energy, and finally the car is driven by the transmission mechanism. In this connection mode, the battery is like a reservoir, but the object of regulation is not water, but electricity. The battery adjusts between the energy produced by the generator and the energy required by the electric motor to ensure the normal operation of the vehicle. This kind of power system is widely used in urban buses, and rarely used in cars.
The second is a parallel hybrid power system. The parallel hybrid power system has two drive systems: the traditional internal combustion engine system and the electric motor drive system. The two systems can work in coordination at the same time, or they can work independently to drive the car. This system is suitable for a variety of different driving conditions, especially for complex road conditions. The connection method has a simple structure and low cost. Honda’s Accord and Civic use a parallel connection method.
The third is a series-parallel hybrid power system. The characteristic of the series hybrid power system is that the internal combustion engine system and the motor drive system each have a set of mechanical transmission mechanisms. The two sets of mechanisms are combined through a gear train or a planetary wheel structure to comprehensively adjust the speed between the internal combustion engine and the electric motor. relation. Compared with the parallel hybrid power system, the hybrid power system can adjust the power output of the internal combustion engine and the operation of the electric motor more flexibly according to the working conditions. This connection method is complicated in system and high in cost. Prius uses a hybrid connection method.
B. According to the proportion of the output power of the motor in the output power of the entire system in the hybrid power system, which is often referred to as the difference in the degree of mixing, the hybrid power system can also be divided into the following four categories:
One is the micro-hybrid system. The representative models are PSA’s hybrid version of C3 and Toyota’s hybrid version of Vitz. This hybrid power system adds a belt-driven starter motor (also known as Belt-alternator Starter Generator, referred to as the BSG system) on the starter motor (usually 12V) on the traditional internal combustion engine. The motor is a stop-start integrated motor, which is used to control the start and stop of the engine, thereby canceling the idle speed of the engine and reducing fuel consumption and emissions. Strictly speaking, a car with a micro-hybrid system is not a true hybrid car, because its electric motor does not provide continuous power for the car. In a micro-hybrid system, there are usually two voltages of the motor: 12v and 42v. Among them, 42v is mainly used in diesel hybrid power systems.
The second is a light hybrid system. The representative model is GM’s hybrid pickup truck. The hybrid power system uses an integrated starter motor (also known as Integrated Starter Generator, referred to as ISG system). Compared with the micro-hybrid system, the light-hybrid system can not only use the generator to control the start and stop of the engine, but also: (1) absorb part of the energy under deceleration and braking conditions; (2) During driving, the engine runs at a constant speed, and the energy produced by the engine can be adjusted between the driving demand of the wheels and the charging demand of the generator. The blending degree of light hybrid power system is generally below 20%.
The third is the hybrid system. Honda’s Hybrid Insight, Accord and Civic all belong to this system. The hybrid power system also uses the ISG system. Unlike mild hybrid systems, medium hybrid systems use high-voltage motors. In addition, the hybrid power system also adds a function: when the car is under acceleration or heavy load conditions, the electric motor can assist in driving the wheels, thereby supplementing the lack of power output of the engine itself, thereby better improving the performance of the vehicle. The mixing degree of this system is relatively high, which can reach about 30%. The current technology is mature and widely used.
Four is a complete hybrid system. Toyota’s Prius and future Estima are fully hybrid systems. The system uses a 272-650v high-voltage starter motor with a higher degree of mixing. Compared with the mid-hybrid system, the hybrid system of the complete hybrid system can reach or exceed 50%. The development of technology will make the complete hybrid system gradually become the main development direction of hybrid technology.
The various mixing methods above can reduce costs and emissions to a certain extent. In the past ten years, major automobile manufacturers have formed their own hybrid technology roads through continuous R&D investment, test summary, and commercial application, and their performance in the market is also unique.