Advantages and disadvantages of multi-speed electric drive system for autonomous driving

The popularity of electric vehicles has made the multi-gear electric drive system an inevitable trend. The electric drive system shift bench test can not only promote the development of electric drive technology, but also help to better understand and utilize new energy, and contribute to the construction of a more environmentally friendly and efficient future travel mode.

The inevitability of electrification of drive systems

The inevitability of the electrification of the drive system mainly covers environmental protection needs, energy transformation, technological progress, economic benefits, policy promotion, etc. The development of the drive system electrification technology is conducive to the development of the vehicle towards the "new four modernizations" of electrification, intelligence, networking and sharing.

The working state of the electric drive system (see Figure 1) can be precisely controlled by the electronic control system, which not only helps to improve the driving performance of the car, but also facilitates the realization of advanced functions such as autonomous driving. In addition, from an economic perspective, the operating cost of electric vehicles is lower than that of traditional fuel vehicles. The electrification of the drive system can improve energy efficiency and reduce operating costs, thereby enhancing the market competitiveness of electric vehicles.

The trend of multi-speed development of electric drive system

The drive motor of an electric vehicle needs to have both high torque at start-up and high speed at maximum speed. If the electric drive system is a single-gear structure, the motor required to match it will be large in size and mass, and the cost will be high; and when the electric drive system is driving at high speed, the motor speed is too high, which may cause efficiency problems.

In order to reduce the size and weight of electric motors, reduce costs, optimize the driving performance of electric vehicles, improve the working efficiency of electric motors, and reduce energy consumption, the development of electric drive systems towards multi-speed has become an inevitable trend in the development of electric vehicle technology (see Figure 2).

The multi-speed electric drive system can better adapt to the driving needs of the car at different speeds. By changing the gear of the drive system, the high-efficiency area of ​​the electric motor can be better utilized, allowing the electric motor to operate in the best working state, thereby achieving a more efficient, economical and comfortable driving experience.

However, the development of multi-speed electric drive systems is not an easy task, and gear shifting technology is a great challenge. How to ensure smooth and fast gear shifting and efficient use of motor energy in the entire process is a problem that researchers must face. For this reason, the study of electric drive system gear shift bench tests has become an important research direction in this field.

Multi-speed electric drive system structure

The multi-speed electric drive system is a key component of electric vehicles, mainly consisting of an electric motor, a multi-speed reducer and a control system.

1) The electric motor is the core part of the electric drive axle system, responsible for converting electrical energy into mechanical energy to drive the car. In a multi-speed electric drive system, the electric motor needs to cooperate with the reducer to adapt to different driving conditions.

2) The multi-speed reducer is an important feature of the multi-speed electric drive system. It is mainly composed of a reducer, a shift motor, a shift actuator, and a shift fork. It is mainly responsible for changing the torque and speed output from the motor and transmitting them to the wheels. By adjusting the shift actuator through the shift motor and changing the gear of the reducer through the shift fork, the electric drive system can keep the motor in the best possible working state at different vehicle speeds.

3) The control system is the "brain" of the electric drive system, responsible for controlling the working state of the motor to achieve smooth and efficient operation of the car. The shift TCU collects information from various sensors and control systems to accurately control the timing and process of shifting to ensure smooth shifting and reduce energy loss.

The multi-speed electric drive system eliminates the main friction elements such as clutch and synchronizer, greatly simplifies the structure, and realizes the multi-operating condition driving of electric vehicles through the coordinated work of the above main components. Compared with the single-speed electric drive system, the multi-speed electric drive system can better adapt to different driving conditions and improve the driving performance and energy efficiency of electric vehicles (see Figure 3).

Figure 3 Schematic diagram of a certain model's shift mechanism

The multi-speed electric drive system uses the shift motor to drive the shift actuator to drive the coupling sleeve to switch between different gears to achieve gear shifting. This structure does not have a synchronizer, and the shifting process relies on the motor debugging to achieve the speed synchronization of the coupling sleeve and the coupling ring gear. This process requires precise control to ensure smooth and efficient gear shifting.

In actual operation, the shifting process of electric vehicles includes detection stage, decision stage, execution stage and stabilization stage.

First, the control system will continuously detect the working status of the motor and the driving conditions of the vehicle, such as the motor speed, torque, vehicle speed, acceleration, etc. When the motor speed or torque reaches the preset shift value, the control system will decide whether to shift gears. If a shift is required, the control system will calculate the best shift timing and the target output of the motor. Next, after the control system issues a shift command, the motor will adjust its torque and speed according to the command, and the reducer will also adjust the meshing state of the gears according to the command to achieve the shift. After the shift is completed, the control system will continue to monitor the status of the motor and reducer to ensure their stable operation. If an abnormality is found, the control system will make timely adjustments to ensure the normal driving of the vehicle.

The shifting process of an electric vehicle is shown in Figure 4.

Figure 4 Gear shifting process

During the entire shifting process, the precise coordination of various components achieves smooth and fast shifting. Compared with traditional mechanical shifting, this shifting method is smoother and there is almost no noticeable gear shifting, providing a better driving experience.

Advantages and disadvantages of multi-speed electric drive system

1. Advantages

The structure of the multi-speed electric drive system has significant advantages in the field of electric vehicles, especially commercial vehicles.

Firstly, it can automatically adjust the gear according to different driving conditions, so that the motor can run in the best working state, which helps to improve the working efficiency of the motor and thus reduce energy consumption.

Secondly, the multi-speed electric drive system can provide corresponding torque and speed under different driving conditions, achieving a smoother and more efficient driving experience, allowing electric vehicles to perform well in scenarios such as acceleration, climbing and high-speed driving.

In addition, since the multi-speed electric drive system can make the motor operate in the best working state, it reduces the possibility of the motor working in extreme conditions for a long time, thereby reducing the wear of the motor and extending its service life.

At the same time, the multi-speed electric drive system precisely adjusts the gear position to keep the electric motor in a high-efficiency operating range at all times, helping to reduce losses and increase driving range.

Finally, the gear shifting process of the multi-speed electric drive system is relatively smooth, which helps to improve driving comfort and makes the driver feel more relaxed and enjoyable during driving.

The multi-speed electric drive system helps optimize the configuration of the transmission system, improve the working efficiency, driving performance and comfort of electric vehicles, reduce energy consumption, extend the life of the motor, make the electric drive assembly lighter and more compact, and reduce costs. These advantages have led to the widespread attention and application of the multi-speed electric drive system in the field of electric vehicles.

2. Insufficient

Multi-speed electric drive systems have significant advantages, but also have disadvantages.

First of all, compared with the single-speed electric drive system, its structure is more complex, which not only increases the difficulty of design and manufacturing, but also puts higher requirements on maintenance.

Secondly, the complexity of the structure also increases the manufacturing cost.

In addition, the speed and torque regulation capabilities of the drive motor will affect the AMT's shifting time and may result in power interruption.

At the same time, the shift control strategy of the multi-speed electric drive system is more complex than that of the single-speed electric drive system, and more advanced algorithms are required to ensure the smoothness and efficiency of the shift, which also increases the difficulty of development and debugging. Due to the complexity of the structure and control strategy of the multi-speed electric drive system, there will be potential reliability issues, such as frequent shifting leading to premature wear of components, affecting the reliability of the entire vehicle.