Auto-calibrated Brake Control for Low-Speed Vehicle Precision
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Solution Overview
Problem
Existing vehicle control systems face challenges in achieving precise longitudinal control, particularly in low-speed operations like automatic hitching, due to the complex interplay of factors influencing brake torque command, vehicle deceleration, and speed, making it difficult to model and execute precise control algorithms.
Innovation Solution
A proposed scheme involves a 'practice run' to collect data on brake parameters at a steady low speed, which is then used to calibrate brake profiles for precise stopping, utilizing a combination of feedforward and feedback data to ensure accurate positioning within a few millimeters of the target, incorporating radar odometry for low-speed speed measurement and accounting for variations in brake torque command and applied torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional brake control systems are used for low-speed operations, then the system structure remains simple, but the longitudinal control precision deteriorates and cannot achieve sub-centimeter accuracy
Solution Approach 1:
The system performs a calibration maneuver before the actual hitching operation to determine brake parameters. During this preliminary phase, the vehicle executes a controlled stop from a known speed, and the system measures the relationship between brake torque commands and actual deceleration. These pre-determined parameters are then stored and applied during subsequent precision hitching operations, enabling accurate low-speed control without requiring complex real-time computation during the critical positioning phase.
Solution Approach 2:
The system implements a feedback mechanism where the actual vehicle deceleration and position are continuously monitored during the calibration and operation phases. The measured brake parameters from the calibration maneuver are used to adjust and refine the brake control commands during the actual hitching operation. This feedback loop allows the system to compensate for variations in brake performance and achieve precise longitudinal control at low speeds.
2Measurement precision
If brake parameters are calibrated through practice runs, then the stopping precision improves to sub-centimeter accuracy, but the calibration time and data collection requirements increase
Solution Approach 1:
The calibration process is executed as a preliminary one-time operation that determines brake parameters before normal hitching operations begin. During this initial calibration phase, the system collects data from brake torque commands and actual vehicle deceleration measurements to establish the brake response characteristics. Once calibrated, these parameters are reused for subsequent precision operations, avoiding the need for repeated calibration and minimizing time loss.
Solution Approach 2:
The system changes the operational parameters during calibration by executing controlled deceleration maneuvers at specific low speeds (e.g., 1-5 mph) to capture brake performance characteristics in the critical low-speed regime. The calibration process varies brake torque commands across a range of values to map the nonlinear brake response. This parameter variation during calibration enables the system to accurately predict brake behavior during precision hitching operations without requiring extensive calibration time.
3Manufacturing precision
If the vehicle speed is reduced to very low values for precise positioning, then the positioning accuracy improves, but the measurement of vehicle speed becomes more difficult and less reliable
Solution Approach 1:
The system uses an intermediary calibration process that indirectly determines vehicle speed and position information through brake parameter measurements. Instead of relying solely on direct speed sensor measurements at very low speeds (which may be unreliable), the system infers speed and position by measuring the relationship between brake torque commands and actual vehicle deceleration during the calibration maneuver. This intermediary measurement approach provides more reliable data for low-speed control than direct sensing alone.
Data Source
AI summary
Certain driver-assist features of a vehicle require incredibly precise longitudinal control of the vehicle. Achieving the precise control requires up-to-date knowledge of performance parameters of a brake system of the vehicle, which may vary extensively based on a wide set of influences outside the control of the brake system. The present disclosure proposes techniques to determine these parameters, for example, by stopping the vehicle early in maneuvering in order to study the brake performance, so that precise longitudinal control of the vehicle may be realized.