Electromechanical Wheel Brake Locking for Overheat-Free Braking Torque
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Solution Overview
Problem
In braking systems with electromechanically actuated wheel brakes, prolonged braking maneuvers with high clamping forces lead to overheating of the electric motors due to high motor currents, posing a risk of vehicle immobilization.
Innovation Solution
The method involves selectively mechanically locking electromechanical force actuators in an actuation position to maintain high braking torque without continuous energization, distributing the braking torque among wheel brakes to reduce heat generation, and using temperature and speed thresholds to determine when to lock the actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electric motor of the force actuator is continuously energized to maintain high clamping forces during prolonged braking maneuvers, then high braking torque is provided, but the electric motor overheats due to high motor currents
Solution Approach 1:
The patent applies periodic action by alternately activating different wheel brakes instead of continuously energizing a single force actuator. The control unit switches between left and right wheel brakes in periodic intervals, allowing each motor to rest and cool down while the other provides braking torque. This periodic switching resolves the contradiction by maintaining continuous braking torque while preventing continuous overheating of any single motor.
Solution Approach 2:
The patent segments the braking function by dividing it between multiple wheel brakes (left and right wheels). Instead of relying on a single force actuator that would overheat, the braking torque is distributed across multiple segmented units (different wheel brakes), each with its own motor. This segmentation allows the system to maintain high overall braking torque while individual motors can periodically rest and cool down.
2Temperature
If the force actuator is mechanically locked to reduce heat generation in the motor, then motor temperature is reduced, but the braking torque may become insufficient to fully implement the braking request
Solution Approach 1:
The patent merges the output of multiple force actuators (on different wheel brakes) to achieve the total required braking torque. When one actuator is locked and providing constant torque, another actuator is activated to provide additional torque. The combined torque from multiple actuators meets the total braking request while individual actuators operate at lower, cooler temperatures.
Solution Approach 2:
The patent applies partial action by having each individual force actuator provide only a portion of the total braking torque rather than all of it. Each actuator operates at a reduced load level that generates less heat, while the cumulative effect of multiple actuators provides the full required braking torque. This partial action approach prevents overheating while maintaining sufficient total braking capability.
3Temperature
If the wheel brakes are used to cool the brakes by alternating braking force application, then brake temperature is reduced, but the vehicle may experience instability or wheel lock-up
Solution Approach 1:
The patent employs feedback control by continuously monitoring wheel speed and comparing it to a reference value. The control unit adjusts the braking torque applied to each wheel based on this feedback, ensuring that braking forces are modulated to prevent wheel lock-up. This feedback mechanism allows the system to cool brakes through alternating application while maintaining vehicle stability by preventing excessive or uncontrolled braking forces.
Solution Approach 2:
The patent applies dynamics by continuously adjusting the braking torque in real-time based on current operating conditions. Rather than applying fixed braking forces, the system dynamically modulates the torque applied to each wheel, switching between brakes and adjusting magnitudes based on wheel speed feedback. This dynamic approach enables effective brake cooling while adapting to changing conditions to maintain stability and prevent lock-up.
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 approach prevents overheating of the force actuators, ensuring continuous high braking torque while minimizing the risk of wheel lock-up and vehicle immobilization.
Implementation Method 1
an electric motor, such as a brushless DC motor, may drive a hydraulic cylinder or a tandem master cylinder
Implementation Method 2
the friction surfaces of the wheel brakes would only absorb a small amount of heat due to the low speeds
Data Source
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AI summary
The invention relates to a method for operating a braking system of a vehicle (100), comprising electromechanically actuated wheel brakes (102, 104, 106, 108) and a control unit (118), the wheel brakes each having an electromechanical force actuator (120, 122, 124, 126) for applying a braking torque to a vehicle wheel (110, 112, 114, 116) associated with the wheel brake in question. The method comprises: capturing a braking request; determining a braking torque to be applied by the force actuators of the wheel brakes in order to implement the braking request; determining current temperatures of the wheel brakes and/or of components of the wheel brakes; determining a speed of the vehicle; if the determined temperature of at least one wheel brake and/or of the components of the wheel brake lies above a first limit value and the determined speed lies below a second limit value, activating the force actuator of at least one wheel brake to provide part of a braking torque corresponding to the braking request and mechanically locking the force actuator of the at least one wheel brake in an actuation position corresponding to the set braking torque, and activating the other wheel brakes to provide the braking torque remaining for the complete implementation of the braking request. The steps are carried out by means of the control unit.