Electric Vehicle Brake Control Differential Pressure Regulation
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Solution Overview
Problem
Conventional brake control devices for electric vehicles experience a reduction in braking force when the pump motor stops, leading to uncomfortable deceleration for the driver due to an insufficient pressure difference between the wheel cylinder and master cylinder pressures.
Innovation Solution
The brake control device incorporates a differential pressure regulating valve operation control mechanism that adjusts the pressure difference based on the rotation speed of the pump motor when it is stopped, maintaining the desired pressure difference by controlling the flow rate of brake fluid, thus compensating for the reduction in braking force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If feedforward control is used to determine the differential pressure regulating valve operation current based on VDC motor operation condition, then the control system is simple, but the pressure difference between wheel cylinder pressure and master cylinder pressure becomes lower than expected when the pump motor is stopped, causing insufficient braking force
Solution Approach 1:
The patent implements feedback control by using the rotation speed of the pump motor as feedback information to dynamically adjust the differential pressure regulating valve operation current. When the pump motor stops, the control unit detects the zero rotation speed and automatically adjusts the valve current to maintain the expected pressure difference, ensuring reliable braking force without requiring complex predictive models.
Solution Approach 2:
The system uses the pump motor's own rotation speed signal to automatically adjust the differential pressure regulating valve current. The control unit monitors the motor's operational state and self-adjusts the valve current accordingly, eliminating the need for external intervention or complex feedforward calculations while maintaining consistent braking performance.
2Use of energy by moving object
If the pump motor is stopped to save energy, then energy consumption is reduced, but the braking force decreases due to insufficient pressure difference
Solution Approach 1:
The patent changes the operational parameters of the differential pressure regulating valve based on the pump motor's state. When the motor stops, the valve current is increased to fully open the valve, allowing maximum brake fluid flow to maintain the pressure difference. This parameter adjustment ensures that energy savings from stopping the motor do not compromise braking force.
Solution Approach 2:
The system dynamically adjusts the differential pressure regulating valve current based on the real-time operational state of the pump motor. The control unit continuously monitors motor rotation speed and automatically modifies valve current accordingly, enabling the system to transition smoothly between motor-operated and motor-stopped states while maintaining consistent braking performance.
3Force
If the differential pressure regulating valve current is increased to maintain pressure difference when pump motor stops, then braking force is maintained, but the valve operation current control becomes more complex
Solution Approach 1:
The control unit uses feedback from the pump motor's rotation speed sensor to automatically determine the appropriate differential pressure regulating valve current. This feedback mechanism simplifies the control logic by using readily available motor state information, avoiding the need for complex pressure sensors or multiple feedback loops while maintaining reliable braking force.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures consistent deceleration and prevents the uncomfortable feeling caused by reduced braking force, improving the reliability and durability of the system by maintaining the desired pressure difference even when the pump motor is turned off.
Implementation Method 1
a brake fluid pressure actuator that includes a wheel cylinder that is installed to each of front and rear road wheels to apply each road wheel with a hydraulic braking force in accordance with a wheel cylinder pressure
Implementation Method 2
a differential pressure regulating valve that controls a pressure difference between the wheel cylinder pressure and the master cylinder pressure under operation of the pump motor
Implementation Method 3
a hydraulic pump that is installed between the master cylinder and the wheel cylinder and driven by a pump motor
Data Source
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AI summary
A brake control device of an electric vehicle comprises a master cylinder 13, wheel cylinders 4FL, 4FR, 4RL and 4RR, a VDC brake fluid pressure unit 2, a motor controller 8 and an integrated controller 9. The motor controller 8 controls a regenerative braking force produced by a vehicle driving electric motor 5. The integrated controller 9 achieves, upon braking operation, a driver-desired deceleration based on the sum of a base hydraulic pressure part produced by a master cylinder pressure and a regenerative part produced by the regenerative braking force and compensates an insufficient regenerative part with a pressure increased part produced by the VDC brake fluid pressure unit 2. In addition to this, at the time when the VDC motor 21 is stopped due to the regenerative cooperative brake control, a pressure difference control effected by M/C cut solenoid valves 25 and 26 which are differential pressure regulating valves is carried out based on a motor rotation speed of the VDC motor 21.