Brake Actuator Force Feedback Using Redundant Signal Estimation
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Solution Overview
Problem
Existing electro-mechanical brake actuators in electronic brake systems lack a reliable and safe force feedback mechanism, particularly in environments without compressed air, necessitating a solution that meets high safety integrity levels like ASIL D.
Innovation Solution
A force determination unit comprising a force acquisition unit and a force estimation unit, which provides redundant force signals to enhance safety, using filters and plausibility checks to determine a reliable force feedback signal, and incorporates sensors for stroke, motor position, temperature, and current to estimate actuating force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a force sensor is used to provide force feedback in an electro-mechanical brake actuator, then measurement precision is improved, but reliability deteriorates due to potential sensor failure and lack of redundancy
Solution Approach 1:
The system implements beforehand cushioning by creating a redundant force estimation mechanism that can compensate for force sensor failures. The force estimation unit uses motor current, position, and stroke data to calculate expected actuating force, providing a backup signal path that cushions against the harmful effect of sensor failure and maintains ASIL D safety integrity level
Solution Approach 2:
The system applies copying by creating a virtual copy of the force measurement through estimation. Instead of relying solely on the physical force sensor, the system generates an estimated force signal based on motor parameters and actuator state, providing a redundant copy of the force information that can be used if the original sensor fails
2Reliability
If redundant force signals are generated through force estimation, then reliability is improved, but device complexity increases
Solution Approach 1:
The force determination unit implements universality by making existing sensors serve multiple functions. The motor position sensor, stroke sensor, and current sensor used for basic actuator control are also utilized for force estimation, eliminating the need for additional dedicated sensors and reducing overall system complexity while improving reliability
Solution Approach 2:
The system applies self-service by having the actuator's own operational parameters (motor current, position, stroke) generate the force estimation without requiring external measurement devices. The actuator essentially measures its own force output through its operational state, reducing system complexity while providing redundant force information
3Reliability
If multiple force signals are processed and compared, then reliability is improved, but loss of time increases due to additional processing
Solution Approach 1:
The system implements preliminary action by continuously calculating the estimated force signal in parallel with normal actuator operation, so that when a force sensor failure occurs, the estimated signal is already available and validated. This pre-computation eliminates the time delay that would occur if force estimation were only performed after detecting a sensor failure
Data Source
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AI summary
The present invention relates to a force determination unit (40) for determining a force feedback representative of an actuating force of a brake actuator (20), comprising: a force acquisition unit (41) configured to provide an acquired force signal (411) as a signal representing a measured actuating force, and a force estimation unit (42) configured to provide an estimated force signal (421) as a signal representing an estimated actuating force.