Electric Motor Braking Control for Smooth Low-Speed Vehicle Stops
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Solution Overview
Problem
Existing methods for braking vehicles with electric drive motors face challenges in accurately controlling vehicle speed and position, particularly at low speeds, due to measurement inaccuracies and signal processing latencies, leading to potential vehicle acceleration in the wrong direction and uncomfortable maneuvers.
Innovation Solution
A method involving a two-phase braking process is implemented, where a target braking torque is set in the first phase, and a speed target trajectory is specified in the second phase, using a jerk value to determine the threshold speed, ensuring a linear deceleration to zero, with interference correction for external disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If wheel speed is used as the input variable for controlling vehicle speed, then the control system can operate with simple sensors, but measurement inaccuracies and signal processing latencies occur leading to imprecise speed control at low speeds
Solution Approach 1:
The patent introduces an intermediary calculation process that derives vehicle speed from wheel speed measurements through a computational model rather than direct sensing. This mediator (the speed calculation algorithm) processes the raw wheel speed data to produce a more accurate vehicle speed estimate, resolving the contradiction between simple sensing and precise measurement.
Solution Approach 2:
The patent replaces direct mechanical speed sensing with a computational approach. Instead of using complex mechanical sensors to directly measure vehicle speed, the system substitutes a calculation-based method that processes wheel speed data to determine vehicle speed, achieving higher precision without increasing hardware complexity.
2Productivity
If a torque is generated by the electric motor to decelerate the vehicle, then the vehicle can be brought to a stop, but reverse travel may be initiated directly after the stop due to control inaccuracies
Solution Approach 1:
The patent applies preliminary action by establishing a speed threshold before complete stopping occurs. The control system prepares for the stopping event by monitoring when vehicle speed approaches this predetermined threshold, allowing it to adjust the torque trajectory in advance to prevent overshoot and reverse travel, thereby ensuring reliable stopping position accuracy.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the calculated vehicle speed and adjusting the electric motor torque accordingly. The control system uses the feedback from the speed calculation to modify the torque trajectory in real-time, preventing the vehicle from accelerating in the wrong direction after stopping and ensuring accurate stopping position.
3Ease of operation
If a constant deceleration is applied during braking, then the braking process is simple to control, but the jerk (rate of change of acceleration) becomes large causing uncomfortable maneuvers
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant deceleration approach to a dynamic deceleration profile. The system continuously adjusts the deceleration rate based on the calculated vehicle speed, creating a time-varying braking profile that reduces jerk and improves passenger comfort while maintaining braking effectiveness.
Solution Approach 2:
The patent changes the deceleration parameter from a constant value to a variable that depends on vehicle speed. By making the deceleration parameter dynamic and speed-dependent, the system reduces the rate of change of acceleration (jerk) during braking, thereby eliminating passenger discomfort while preserving braking control effectiveness.
4Device complexity
If the vehicle speed is derived directly from wheel speed using incremental encoders, then the measurement system remains simple, but the speed signal becomes a volatile function unsuitable for low speed control
Solution Approach 1:
The patent replaces the direct mechanical encoding approach with a computational speed derivation method. Instead of relying on the volatile output of incremental encoders, the system substitutes a calculation-based speed determination that processes wheel speed data through a stable algorithm, producing a reliable speed signal suitable for low-speed control applications.
Solution Approach 2:
The patent introduces an intermediary computational layer between the wheel speed sensor and the control system. This mediator (the speed calculation algorithm) stabilizes the speed signal by processing the raw encoder data through a robust mathematical model, eliminating the volatility inherent in direct encoder readings while maintaining system simplicity.
Data Source
AI summary
The invention relates to a method of braking a vehicle (10) having an electric drive motor (14), wherein, in a first braking phase, a target value for a braking torque is specified to the electric drive motor (14), wherein a current speed of the vehicle (10) is sensed as the actual speed, wherein, when the actual speed reaches a threshold value (v0) for a vehicle speed, the specification of the target value for a braking torque is ended and a speed target trajectory (202) is specified in a second braking phase, wherein the speed target trajectory proceeds from the threshold value (v0) for the vehicle speed to a speed of zero, and wherein the threshold value (v0) for the vehicle speed is determined from a current deceleration of the vehicle (10) and a jerk value.