Redundant Brake Holding Control for Autonomous Vehicle Rolling
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Solution Overview
Problem
Existing autonomous driving vehicles face challenges in stabilizing their position on gradients, particularly when rolling back or forward, due to issues with brake torque application delays, software errors, and occupant comfort concerns from rapid brake torque changes.
Innovation Solution
A redundant holding control system that activates primary, secondary, and electronic parking brakes, along with an engine brake, based on predetermined speed thresholds and vehicle status, while generating warning messages to balance safety and passenger comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the control system adds more pressure to the brake unit when the ADV starts to roll, then the braking torque increases to prevent rolling, but the command may not transfer successfully due to computing delays or software errors, and the braking torque may not be enough to protect against vehicle rolling
Solution Approach 1:
The system applies preliminary braking action by detecting rolling status early through sensors and activating the brake unit before the vehicle rolls significantly. The control system monitors vehicle status continuously and triggers braking when rolling is detected, preventing the need for delayed corrective actions.
Solution Approach 2:
The system implements beforehand cushioning by using multiple brake units (first and second brake units) that can be activated in sequence or simultaneously. The first brake unit provides initial braking, and the second brake unit provides additional braking support, ensuring sufficient braking torque is available even if one system experiences delays or failures.
2Speed
If the ramp-up rate of brake torque is increased to quickly stop vehicle rolling, then the braking response speed improves, but occupant or passenger comfort deteriorates due to sudden brake application
Solution Approach 1:
The braking action is segmented into multiple phases using different brake units. The first brake unit applies braking torque at a controlled rate for initial deceleration, while the second brake unit can apply additional torque as needed. This segmentation allows the system to achieve quick stopping while distributing the brake torque application to reduce sudden impacts on occupants.
Solution Approach 2:
The system dynamically adjusts the brake torque application rate based on vehicle status and rolling conditions. The control system monitors the rolling status and adjusts the ramp-up rate of brake torque in real-time, applying higher rates when rapid stopping is critical and lower rates when occupant comfort can be maintained while still preventing rolling.
3Device complexity
If the conventional braking system is used to hold the ADV on gradients, then the system complexity remains low, but the braking torque may not be enough to protect vehicle rolling due to system issues
Solution Approach 1:
The system merges multiple brake units (first brake unit and second brake unit) into a unified braking system. Both brake units can be activated simultaneously or in sequence to provide combined braking torque, ensuring sufficient force to hold the vehicle on gradients and prevent rolling even if one unit experiences issues.
Solution Approach 2:
The system changes the parameter of braking torque availability by introducing a second brake unit that can supplement the first brake unit. This increases the total braking torque capacity of the system, ensuring that the vehicle can be reliably held on steep gradients or prevented from rolling even if one braking system experiences partial failure or torque limitations.
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
Effectively stabilizes the vehicle on slopes by sequentially engaging brakes, reducing the risk of further rolling and minimizing crash damage, while considering passenger comfort through graduated brake application and warning levels.
Implementation Method 1
the brake unit may add the wheel pressure... If the ADV continues to slip over... the EPB may be activated... the secondary brake may be activated
Data Source
AI summary
Data is received from a plurality of sensors mounted on an ADV being held to a standstill. A status of the ADV including a rolling speed of the ADV is detected based on the data from the plurality of sensors. One of a primary brake or a secondary brake is activated, in response to detecting the status of the ADV being a first status including the rolling speed being higher than zero and lower than a first predetermined speed threshold. An electronic parking brake is activated, in response to detecting the status of the ADV being a second status including the rolling speed being higher than the first predetermined speed threshold and lower than a second predetermined speed threshold. An engine brake may be used to reduce the crash damage, and a warning message (e.g., Message-4) may be generated.