Brake Control System for Electric Vehicles
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Solution Overview
Problem
Conventional brake control systems for electrically driven vehicles experience variations in master cylinder pressure generation due to mechanical tolerances, leading to unpleasant brake feel and reduced regenerative energy recovery.
Innovation Solution
A brake control system that includes a master cylinder, wheel cylinders, a brake fluid pressure actuator, a regenerative brake force control unit, and a regenerative coordinate brake control unit, which sets a target brake characteristic based on the actual master cylinder pressure generating point to compensate for variations, ensuring a comfortable brake feel and secure regenerative energy recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a predetermined nominal point of brake pedal stroke is used to define driver demand deceleration, then the brake control system can be simplified, but mechanical tolerances cause variations in master cylinder pressure generation leading to unpleasant brake feel
Solution Approach 1:
The system detects the actual master cylinder pressure generation point and feeds this information back to adjust the driver demand deceleration characteristic map. This feedback mechanism compensates for variations caused by mechanical tolerances, ensuring consistent brake feel without requiring complex mechanical precision.
Solution Approach 2:
The system dynamically adjusts the driver demand deceleration characteristic map based on the detected actual master cylinder pressure generation point. By changing the parameter (deceleration characteristic) according to the detected variation, the system maintains optimal brake performance despite mechanical tolerances.
2Ease of operation
If the actual master cylinder pressure generation point is delayed compared to the designed point, then the brake feel deteriorates, but if the actual generation point is earlier than designed, then regenerative energy recovery is restricted
Solution Approach 1:
The system continuously monitors the actual master cylinder pressure generation point and adjusts the driver demand deceleration characteristic map in real-time. This feedback control ensures that when the generation point shifts, the system compensates appropriately to maintain both brake feel and maximize regenerative energy recovery.
Solution Approach 2:
The driver demand deceleration characteristic map is made dynamic rather than fixed. The system adapts the characteristic map based on the detected actual pressure generation point, allowing the brake control strategy to change dynamically to optimize both brake feel and energy recovery under different conditions.
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
The system achieves a comfortable brake feel and secure recovery of regenerative energy by compensating for variations in master cylinder pressure, maintaining appropriate brake target force and preventing suppression of brake force increases or decreases due to mechanical tolerances.
Implementation Method 1
a pump up pressure portion by a brake fluid pressure actuator for increasing the MC pressure
Implementation Method 2
the regenerative brake force control unit controls the amount of regenerative braking produced by the electric motor acting as a generator
Data Source
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AI summary
During regenerative coordinate braking control, a target brake force is defined by eliminating influences of brake system component tolerances to achieve a comfortable brake feel and secure regenerative energy. A brake control system includes a master cylinder, wheel cylinders, a VDC brake fluid pressure unit and a motor controller. In response to a brake pedal operation by a driver, a brake pedal stroke position is detected at which a pressure in a master cylinder actually begins to be generated. A target deceleration characteristic is adjusted from a theoretical characteristic so that the target deceleration equals a maximum value of an add-on brake force (i.e., the regenerative brake gap) at the detected brake pedal stroke position.