The basic theory of general electricity has made it clear that Fleming's left-hand rule is the working principle of motor drive, while Fleming's right-hand rule is the principle of power generation. Due to the operation of the motor, the coil generates electromotive force in the direction that hinders the change of magnetic flux. This direction is opposite to the direction of current flow when rotating the motor. So people call it back electromotive force. The back electromotive force increases with the increase of rotating speed. Due to the increase of rotational speed, the flow resistance of the current that originally caused the motor to rotate increased, and finally reached a certain rotational speed, which could not be exceeded upward. Therefore, when braking, the current through the motor is cut off, and instead, the back electromotive force is generated. This is the principle of braking energy recovery, which makes the motor play the role of generator. This kind of motor is called "motor generator".
However, how to deal with foot braking when braking energy recovery braking is implemented. How to maintain the harmonious relationship between the stroke (or strength) of the brake pedal and the braking energy recovery system when the foot brakes. This is because the braking part, which plays the role of braking energy recovery, will reduce the braking force of foot braking.
Because for foot braking, considering the role of braking energy recovery, corresponding measures must be taken to reduce the braking force of foot braking. When the braking force decreases, the pedal force of the brake pedal should correspond to the pedal stroke.
What is important is that the function of the brake pedal still exists, just like ordinary vehicles, regardless of whether braking energy recovery occurs or not. Therefore, a device called stroke simulator has been developed.
1, Coordinated Control of Braking Energy Recovery and Hydraulic Braking for Toyota Hybrid Electric Vehicle
The braking energy recovery system of Toyota Hybrid Electric Vehicle consists of hydraulic brakes (including hydraulic sensors and hydraulic valves) of the original engine model, motors (which are used as generators during deceleration and braking, that is, converted into energy recovery power generation conditions), inverters and electronic control units (including power battery electronic control units, motor electronic control units and energy recovery electronic control units).
Toyota's energy recovery braking system is characterized by the coordinated control of braking energy recovery and hydraulic braking. The principle of coordinated braking is to ensure the braking stability and safety of vehicles under different road conditions and working conditions. At the same time, considering the regenerative braking ability of the power battery (controlled by the power battery electronic control unit), the coordinated control of wheel braking torque and motor energy recovery braking torque can be realized, and centralized control is implemented by the vehicle electronic control unit.
When the driver steps on the brake pedal, according to the brake pedal force, the hydraulic brake (hydraulic servo braking system) will enter the corresponding work in real time through the travel simulator and other components, and then the braking energy recovery system will also enter the working state. That is to say, if the electric control unit of the power battery judges that the power battery has the corresponding SOC recovery capability, the braking energy recovery braking force accounts for the corresponding part of the whole braking force. When the vehicle approaches a stop, the braking force of the braking energy recovery system becomes zero. The energy conversion rate of these two braking forces is equivalent to the ratio of the corresponding areas shown in figure 1 When the hydraulic braking area is small and the braking area of braking energy recovery is large, it means that the braking energy recovery is increased. Increasing the area of braking energy recovery is directly related to reducing fuel consumption. However, under the condition of constant hydraulic braking, only the increase of braking energy recovery rate is considered to increase braking force, which leads to the driver's uncomfortable feeling on the braking road surface. In order to solve this problem, an electronic brake by wire is developed. As shown in Figure 2, in the electronically controlled brake, the brake pedal is not directly connected with the wheel brake cylinder through the hydraulic pipeline, but sends corresponding instructions to the hydraulic energy supply source through the electronic control unit (ECU), so that the hydraulic pressure corresponding to the braking intensity recovered by the braking energy is transmitted to the corresponding wheel brake cylinder. Therefore, the sum of braking energy recovery braking and hydraulic braking reaches a braking force value corresponding to the stroke of the brake pedal, thereby improving the driver's road feeling during braking operation.
As can be seen from Figure 2, the braking energy recovery control is controlled by the foot brake pedal force signal, which enters the hydraulic mechanism of the hydraulic control part (including hydraulic pump motor and accumulator) through the input part of the brake master cylinder and the stroke simulator, and is transmitted to the wheel brake cylinder through the brake hydraulic adjustment. At the same time, if the system fails to stop, the hydraulic pressure will start urgently, and the electromagnetic switching valve will open, that is, it will be switched by the electromagnetic valve and transmitted to the wheel brake cylinder.
2. Control of braking energy recovery system of Honda's fourth generation IMA hybrid power system.
Honda's fourth-generation IMA hybrid system is applied to 20 10 Insight hybrid vehicle. Its braking energy recovery system adopts the integrated module form of actuator and electronic control unit, including IMA system motor control module, power battery monitoring module and motor drive module.
The working process of the braking energy recovery system is as follows:
When the IMA motor brakes and slows down slowly, the electric control unit of the hybrid electric vehicle sends corresponding instructions to make the motor turn into the generator regenerative power generation state, and the braking energy recovery control system charges the power battery in the form of electric energy. Its basic working process is: when braking, the brake pedal sensor makes the IMA electronic control unit activate the brake master cylinder servo device, and sends corresponding instructions through the power battery electronic control unit, energy recovery electronic control unit, motor electronic control unit and other electronic control units, so that the braking force between hydraulic mechanical braking and motor energy recovery is coordinated and balanced, and the best energy recovery is achieved. The fourth generation IMA system adopts variable braking energy distribution ratio, and the braking energy recovery capacity is improved by 70% compared with the previous generation.
IMA motor, power battery electronic control unit, energy recovery electronic control unit and motor electronic control unit all belong to "Intelligent Power Unit (IPU)" of Honda's fourth-generation IMA hybrid power system. It consists of PCU(Power Control Unit), high-performance Ni-MH battery and refrigeration system. PCU is the core part of IPU, which controls the motor to assist (i.e. enter the electric working state). PCU determines the auxiliary amount of electric energy and the energy recovery capacity of the battery according to the relevant operating parameters of the engine and the state of charge of the power battery by receiving the opening signal of the throttle sensor. The main components of PCU are battery monitoring module-battery state monitor BCM (battery state monitor), motor control module MCM (motor control module) and motor drive module MDM (motor drive module).
Throughout the existing practical different hybrid power systems, the braking energy recovery control is different in details. Generally, the combination of electronic hydraulic braking and braking energy recovery is adopted, which is also called electro-hydraulic braking servo control system.