With the development of the electric vehicle market, the braking energy recovery system has received extensive attention, and the driving ability can be improved through the braking energy recovery system.
The energy of deceleration and braking of traditional internal combustion engine vehicles is converted into heat energy through the braking system for release. In electric vehicles and hybrid vehicles, this wasted energy can be converted into electrical energy through braking energy recovery technology, stored in the battery, and further converted into driving energy. The braking energy recovery system includes a generator, a battery, and an intelligent battery management system that match the model and is coordinated with the mechanical braking system to achieve vehicle braking.
Brake energy recovery system concept:
The braking system with braking energy recovery was developed for vehicles with three-phase current drives. Depending on the motor speed, the temperature of the high-voltage battery, and the charge level, the three-phase current drive can decelerate the vehicle in alternator mode. These factors fluctuate in electrical deceleration and may require hydraulic compensation. The alternation between electrical and hydraulic deceleration is called hybrid braking.
The power and control electronics of the electric drive supply the generated energy to the high-voltage battery. When braking while driving, the braking system utilizes the decelerating electromotive force of the three-phase current drive to increase the cruising range of the electric drive.
The braking system includes:
Tandem master cylinder, wheel brakes, electromechanical brake booster, ESC/ABS, brake system accumulator, three-phase current drive. The electromechanical brake booster increases the brake pedal force applied by the driver.
The composition and working principle of eBKV:
The driver operates the brake pedal. The push rod transmits the pedal actuation force and transmits it through the piston rod to the tandem brake master cylinder. Move the fader to the left by a specific numerical amount. This value is sent to the brake booster control unit via the brake pedal position sensor. At the same time, the electromechanical brake booster receives the position information of the electric motor. This information comes from the engine (electric motor) position sensor of the brake booster (installed in the electric motor/transmission unit). The brake booster control unit in the electromechanical brake booster calculates the required increased braking force based on the driver's braking request and motor position information. At the same time, the reinforcement sleeve that drives the pinion shaft axially is moved to the left to support the braking force applied by the driver. The braking force can be amplified by 6 times.
The composition and working principle of the accumulator:
The brake system accumulator stores brake fluid when needed and direct it back into the brake system. Its purpose is to reduce brake pressure. If the brake booster control unit detects insufficient alternator deceleration, the brake fluid is pressurized from the accumulator back into the brake system. A corresponding signal is sent from the brake booster control unit to the control unit of the pressure accumulator. If the alternator decelerates sufficiently, the brake pressure on the wheel brakes is reduced. This is achieved by the flow of brake fluid into the accumulator, and the brake accumulator electric motor for energy recovery then pushes the piston back.
The working process of hybrid braking:
- Deceleration request:
The driver depresses the brake pedal to slow the vehicle and bring it to a complete stop. The driver's braking request is communicated via the brake booster control unit using the brake pedal position.
- Friction deceleration:
The driver's request to decelerate increases the pressure in the hydraulic brake system to reduce vehicle speed.
- Energy recovery deceleration:
- Support for regenerative deceleration: The brake boost control unit receives information from the power and control electronics of the electric drive that the three-phase current drive is capable of supporting the hydraulic braking system. This happens when the vehicle is moving at high speed. Depending on the available alternator braking torque, the brake pressure will not increase or it will decrease. As the vehicle speed decreases, the braking torque of the alternator increases. The brake pressure on the wheels is then reduced according to the available alternator braking torque. For this purpose, the brake system accumulator draws in brake fluid, which reduces the pressure in the hydraulic brake system. This means that only the braking torque of the alternator can be used for deceleration for a certain period.
- Insufficient support of three-phase current drive device: If the braking torque of the alternator decreases during deceleration, the brake booster control unit sends a signal to the control unit of the brake system accumulator. The accumulator then returns the stored brake fluid to the brake system, increasing the pressure in the hydraulic brake system. This occurs when the vehicle brakes and comes to a complete stop. The alternator torque is reduced when the vehicle speed is below 10 km/h. At this time, the vehicle is braked by hydraulic pressure.
- Function backup mechanism:
- When the eBKV has a component failure (such as the controller, booster motor, sensor, etc.), resulting in no brake booster, the eBKV will light up a yellow or red brake warning light in the vehicle combination instrument. If the ESC is still working normally and the driver brakes at this time, the ESC will activate the HBV function to assist the driver with the brake pedal.
- When the eBKV and ESC have functional failures at the same time, and there is no brake booster, the eBKV will, like a traditional vacuum booster, ensure that the mechanical device can still meet the 0.25g deceleration of the whole vehicle under the 500N pedal force required by the national standard.