Hill Hold Release Torque Control for Unintended Vehicle Motion
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Solution Overview
Problem
Vehicles in hill hold mode tend to move in unintended directions when released, due to the inability to effectively manage torque and friction forces.
Innovation Solution
A method involving a controller to adjust the pressure of a fluid to disengage a vehicle motion restraining device and adjust torque output from an electric machine based on the friction coefficient and slip of the device, ensuring controlled vehicle movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the vehicle uses a motion restraining device (brake/clutch) to maintain position during hill hold mode, then the vehicle can remain stationary on an incline, but upon release the vehicle tends to move in unintended directions due to unmanaged torque and friction forces
Solution Approach 1:
The electric machine applies preliminary torque before the motion restraining device is fully disengaged. The controller coordinates the release by first applying torque from the electric machine to counteract gravitational forces, then gradually reducing brake/clutch pressure, ensuring the vehicle moves in the intended direction rather than reversing or stalling
Solution Approach 2:
The controller dynamically adjusts multiple parameters during release: electric machine torque output, fluid pressure to the motion restraining device, and monitors slip conditions. By changing these parameters in a coordinated sequence, the system transitions smoothly from held position to controlled movement without unintended motion
2Reliability
If the vehicle applies brakes or locks transmission output shaft to maintain position, then the vehicle can hold position on incline, but releasing these mechanisms causes uncontrolled vehicle movement
Solution Approach 1:
The controller monitors slip conditions of the motion restraining device during release and uses this feedback to adjust electric machine torque in real-time. When slip is detected, the system responds by modulating torque output to maintain controlled movement, preventing both reverse motion and excessive forward acceleration
Solution Approach 2:
The electric machine provides a counteracting force to balance gravitational forces acting on the vehicle during release. By applying torque in the opposite direction of gravitational pull, the system prevents the vehicle from moving in unintended directions and achieves controlled forward motion
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
Reduces the likelihood of vehicles moving in unintended directions by compensating for gravitational forces during hill hold mode release, allowing for controlled forward motion and maintaining position.
Implementation Method 1
adjusting an amount of torque output via an electric machine
Implementation Method 2
lowering a pressure of a fluid to disengage a vehicle motion restraining device
Implementation Method 3
a friction coefficient of the vehicle motion restraining device
Data Source
AI summary
A method and system for releasing a vehicle from a hill hold mode is described. In one example, torque output of an electric machine is adjusted to reduce a possibility of the vehicle moving in an unintended direction prior to or during release of the vehicle from hill hold mode.