Automated Vehicle Brake Pressure Control at Low Speed
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Solution Overview
Problem
Wheel-speed sensors have a slow update rate at very slow vehicle speeds, making it difficult for automated vehicles to accurately control brake pressure for a smooth stop as the vehicle approaches zero speed.
Innovation Solution
A brake control system that includes a motion detector to determine vehicle speed relative to a stationary feature, such as a road surface or lane marking, and a controller to regulate brake pressure based on this speed when the vehicle is moving below a certain threshold, improving brake control at slow speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If wheel-speed sensors are used to determine vehicle speed for brake control, then brake pressure control can be automated, but at very slow vehicle speeds the sensor update rate becomes too slow to enable smooth braking
Solution Approach 1:
The system segments the speed measurement function by using different sensors for different speed ranges: wheel-speed sensors for higher speeds and motion detectors for very slow speeds. This allows each sensor to operate in its optimal range, resolving the contradiction between automated brake control and slow-speed sensor performance.
Solution Approach 2:
The motion detector acts as an intermediary device that provides accurate speed information at slow speeds when the primary wheel-speed sensor becomes ineffective. This intermediary measurement system enables smooth automated braking across the entire speed range.
2Speed
If brake pressure is reduced too quickly at slow speeds, then the vehicle can stop faster, but this causes jerking and reduces ride comfort
Solution Approach 1:
The brake pressure control is made dynamic and adaptive based on real-time speed measurements. The controller continuously adjusts brake pressure according to the current speed, applying more pressure at higher speeds and progressively reducing it at lower speeds to prevent jerking while maintaining stopping efficiency.
Solution Approach 2:
The system changes the brake pressure parameter dynamically based on speed thresholds. When speed exceeds a threshold, higher brake pressure is applied; when speed drops below the threshold, brake pressure is reduced to prevent discomfort, enabling both fast stopping and ride comfort.
3Length of stationary object
If high brake pressure is applied at very slow speeds, then stopping distance is reduced, but this causes jerking and potential wheel lockup
Solution Approach 1:
The brake pressure parameter is changed based on speed conditions. At very slow speeds below the threshold, the controller reduces brake pressure to prevent wheel lockup and jerking, while still maintaining sufficient pressure to achieve short stopping distances. This adaptive parameter adjustment resolves the contradiction between stopping distance and braking smoothness.
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
Enables smoother automated braking by accurately determining vehicle speed and adjusting brake pressure, reducing the risk of jerking and improving safety at speeds below 5 kph.
Implementation Method 1
The motion-detector detects relative-movement of a host-vehicle by measuring a Doppler-shift of a frequency of a signal
Data Source
AI summary
A brake control system for operating brakes of an automated vehicle at slow speed includes a motion-detector and a controller. The motion-detector detects relative-movement of a host-vehicle relative to a stationary-feature located apart from the host-vehicle. The controller is configured to operate brakes of the host-vehicle. The controller determines a vehicle-speed of the host-vehicle based on the relative-movement when the vehicle-speed is less than a speed-threshold, and regulates brake-pressure of the brakes based on the vehicle-speed.