Hill Start Brake Control on Split-Mu Grades to Reduce Rollback
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Solution Overview
Problem
Vehicle rollback occurs during hill start assist operations due to insufficient propulsive torque and wheel slip on split-mu surfaces, where some tires lack traction, leading to disconcerting rollback and instability, especially with timid drivers, varying vehicle loads, and approaching traction limits.
Innovation Solution
A stability control system that detects wheel slip and backward movement post-hill start assist, identifies the undriven wheel with the highest coefficient of friction, and re-actuates its brake to reduce rollback, with braking force proportional to wheel speed, ensuring all brake pressure returns to zero when the vehicle is ready to move forward.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If brake pressure is released before wheel slip occurs to avoid sticky brakes, then ease of operation is improved, but vehicle rollback occurs due to insufficient propulsive torque
Solution Approach 1:
The system performs preliminary detection of wheel slip conditions and rollback tendencies before the driver completes the launch. The control module monitors wheel speeds and detects slip conditions, then proactively applies braking force to the wheel with highest coefficient of friction to prevent rollback before it significantly occurs, rather than waiting for the problem to manifest.
Solution Approach 2:
The system continuously monitors wheel speed sensors to detect wheel slip conditions and provides feedback to the electronic braking control module. Based on this feedback, the system dynamically adjusts brake application to the specific wheel showing slip or rollback tendency, creating a closed-loop control system that adapts to real-time conditions.
2Stability of the object's composition
If brake pressure is maintained to prevent rollback, then vehicle stability is improved, but sticky brakes sensation occurs reducing ease of operation
Solution Approach 1:
Instead of applying brake pressure to all wheels uniformly, the system identifies the specific wheel with the highest coefficient of friction through wheel speed monitoring and applies braking force locally to that single wheel. This localized braking approach prevents rollback while minimizing the sticky brakes sensation, as only the wheel most prone to slip receives braking intervention.
Solution Approach 2:
The braking system is segmented to operate independently on individual wheels rather than as a unified four-wheel brake system. The electronic braking control module can selectively apply brake pressure to one specific wheel based on detected slip conditions, allowing precise control that prevents rollback without creating uniform brake drag across all wheels.
3Reliability
If traction control applies cross-differential braking to find optimal propulsive torque, then reliability is improved, but significant rollback occurs during initial hill start phase
Solution Approach 1:
The system performs preliminary detection of wheel slip conditions and rollback tendencies before the driver completes the launch. The control module monitors wheel speeds and detects slip conditions, then proactively applies braking force to the wheel with highest coefficient of friction to prevent rollback before it significantly occurs, rather than waiting for the problem to manifest.
Solution Approach 2:
The system continuously monitors wheel speed sensors to detect wheel slip conditions and provides feedback to the electronic braking control module. Based on this feedback, the system dynamically adjusts brake application to the specific wheel showing slip or rollback tendency, creating a closed-loop control system that adapts to real-time conditions.
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 minimizes vehicle rollback by optimizing brake application on the wheel with the highest traction, enhancing stability and smooth transition from rollback to forward motion, even on split-mu surfaces.
Implementation Method 1
A plurality of wheel speed sensors measure each of the vehicle wheel speeds
Implementation Method 2
The electronic braking control module actuates the vehicle brake of the undriven wheel having the highest coefficient of friction at the tire/road surface interface
Data Source
AI summary
A stability control system of a vehicle utilizing an electronic control unit that minimizes rollback of a vehicle as a result of wheel slip immediately following a hill start assist operation. The electronic braking control module controls actuation and de-actuation of vehicle brakes on an inclined surface. Immediately following a hill start assist operation on the inclined surface after each wheel brake is de-actuated for allowing forward movement of the vehicle up the hill, a split-mu road surface condition is detected in response to sensing wheel slip for each of the wheels. The electronic control unit determines a respective undriven, or non-dominant driven, wheel having the highest coefficient of friction among the undriven, or less dominant driven wheels, as determined by the wheel speeds. The electronic braking control module actuates the vehicle brake of the undriven, or less dominant, driven wheels having the highest coefficient of friction relative to a tire/road surface interface for reducing rollback of the vehicle. The braking of the undriven, or less dominant, driven wheel is in addition to any standard stability control braking that may already be occurring.