Electronic parking brake system for new energy vehicles 2
System workflow
2.1. Manual workflow
The implementation of the EPB function can usually be divided into two categories: manual and automatic. The manual method is: when the driver steps on the brake pedal, the vehicle starts to slow down, and after the speed reaches 0, the driver presses the EPB button in the cockpit (the button with "P"), and after the ECU receives the valid key signal, it will send relevant instructions to the brake motor. At this time, the motor will start and pull the brake through the transmission mechanism to put the vehicle into the parking state. At this time, the indicator light on the dashboard will light up, indicating that the parking brake is enabled.
When the driver needs to release the function, he needs to press the EPB button with "P" again. At this time, the ECU will receive an instruction that the key signal is invalid. Then the ECU sends an instruction to the brake motor according to this key state signal. After receiving this instruction, the motor starts to rotate in the opposite direction, thereby releasing the brake to get the vehicle out of the parking state, and the indicator light on the dashboard goes out.
Compared with the traditional mechanical handbrake, this manual method simplifies the action of pulling and releasing the handbrake, converts it into an electrical signal, and the ECU performs the relevant control actions.
2.2. Automatic workflow
In the automation process of the EPB system, the application of sensor signals may vary from manufacturer to manufacturer based on strategy differences. One of the more comprehensive safety detection conditions is: when the control unit receives signals from sensors such as gyroscopes to determine that the vehicle is on a horizontal road, the ECU detects that the vehicle speed is 0 through the vehicle speed sensor signal, and then detects whether the driver has unfastened the seat belt based on the seat belt sensor signal. When the system detects that the seat belt is unfastened and the main cockpit door is opened (indicating that the driver is ready to get out of the vehicle), the ECU will automatically activate the parking brake function and send a start command to the brake motor of the rear wheel. After the motor starts, the brake will be pulled to put the vehicle into a parking state. At the same time, the parking indicator light on the dashboard lights up, indicating that the parking brake is enabled.
When the system detects that the driver has fastened the seat belt through the seat belt sensor, it determines the driver's intention based on the gear information and decides whether the parking brake function needs to be released based on whether the accelerator pedal is pressed. When all the above sensor signals are available, the ECU will automatically release the parking brake function. During the process, the motor rotates in the opposite direction to release the brake, and the indicator light on the dashboard goes out.
In the above manual and automatic workflows, first of all, the braking method of the terminal is usually the same, and the brake is pulled or released by the forward and reverse rotation of the motor to achieve the parking brake and release of the vehicle. The main difference is that in the manual mode, the ECU detects the validity of the key signal as the key instruction, while the automatic mode identifies whether the parking brake is needed by the comprehensive judgment of multi-sensor signals.
In the current automated workflow, it is not certain to use the seat belt signal as one of the judgment conditions for enabling and releasing the parking brake function. For example, in such a scenario: when the driver needs to move the vehicle temporarily, at this time, because he does not need to drive on the road, and the speed is usually low, the seat belt unfastened alarm will not be activated. Therefore, in this actual car use, for convenience, the driver usually does not wear a seat belt. In the face of such a scenario, the driver's operation process is: the remote control key activates the vehicle, then opens the door, after entering the car, starts the vehicle, puts the gear in, steps on the accelerator pedal, and the vehicle starts to run. When reaching the appropriate position, the driver steps on the brake pedal, the speed is reduced to 0, then turns off the engine, opens the door, and gets off. During this process, the seat belt does not move, but the parking brake can be activated and released normally.
Therefore, in actual strategies, whether to use the seat belt as a judgment condition for releasing and activating the parking brake is not fixed, but in order to enable drivers to develop good driving habits and provide driving safety, it is recommended to use whether the seat belt is fastened as one of the judgment conditions in the automated system.
