Electric Braking System Stiffness-Based Reference Position Detection
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Solution Overview
Problem
Existing electric braking systems face inaccuracies in determining the reference position where a brake pad contacts a brake disc due to ineffective displacement and zero-point drift in the power transmission mechanism, leading to errors in braking torque generation.
Innovation Solution
An electric braking system that includes braking operation amount acquisition, pressing force acquisition, and position acquisition means, with control means to compute a stiffness value and determine the reference position by storing candidate positions and forces based on changes in stiffness, and compensating for zero-point drift, ensuring accurate contact detection despite mechanical clearances and abrasion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reference position is determined based on the output of a press sensor or gradient of pressing force reduction, then the braking system can generate braking torque, but the determination accuracy is reduced due to ineffective displacement and zero-point drift in the power transmission mechanism
Solution Approach 1:
The patent replaces mechanical reference position detection methods (press sensor output, gradient calculation) with a stiffness-based detection method. By measuring the stiffness value (rate of change of pressing force with respect to motor rotation angle) and identifying the reference position where stiffness transitions from increasing to decreasing, the system eliminates errors from ineffective displacement and zero-point drift in the power transmission mechanism.
Solution Approach 2:
The patent changes the detection parameter from pressing force magnitude or its gradient to the stiffness value (second-order derivative). This parameter transformation allows the system to identify the reference position at the peak of the stiffness curve, where the transition from contact to non-contact state occurs, providing accurate detection despite mechanical clearances and abrasion in the transmission mechanism.
2Duration of action of stationary object
If mechanical clearances and abrasion are present in the power transmission mechanism, then the system can operate over time, but the reference position determination becomes inaccurate due to ineffective displacement
Solution Approach 1:
The patent implements a feedback mechanism where the stiffness value is continuously calculated based on the relationship between pressing force and motor rotation angle. The reference position is dynamically identified as the point where the stiffness value reaches its maximum and begins to decrease. This feedback-based detection adapts to changing mechanical conditions (clearances, abrasion) and maintains accurate reference position determination throughout the system's operational life.
Solution Approach 2:
The patent performs preliminary detection of the stiffness value characteristics during brake release. By analyzing the stiffness profile before actual braking operation, the system pre-identifies the reference position and compensates for any ineffective displacement in the power transmission mechanism, ensuring accurate braking torque generation from the start of operation.
Data Source
AI summary
When a braking operation amount is reduced, a stiffness value representing a ratio of variation in actual pressing force of a friction member to a variation in actual position of an electric motor are sequentially computed. The actual position when the stiffness value changes from being higher than or equal to a predetermined value to being lower than the predetermined value is stored as a candidate position. When a duration during which the stiffness value is lower than the predetermined value is shorter than a clearance corresponding value corresponding to a transmission member clearance in a state where the candidate position is stored, the candidate position is deleted. When the duration during which the stiffness value is lower than the predetermined value exceeds the clearance corresponding value, the stored candidate position is determined as a reference position at which the friction member and the rotary member begin contacting each other.