Terrain-Adaptive Creep Torque Control for Stable Low-Speed Driving
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Solution Overview
Problem
Automatic transmissions in vehicles experience variations in creep speed due to uncontrolled torque converter operation, particularly on gradients or irregular surfaces, and can generate excessive torque on low-friction surfaces, leading to wheel slip and surface polishing.
Innovation Solution
A control system that determines a terrain mode and adjusts the relationship between torque and speed to maintain a target creep speed by controlling drive torque, using electronic processors and memory devices to manage torque and speed based on terrain conditions, optionally employing braking torque to counteract excessive drive torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a torque converter is used to enable creep motion from rest, then the vehicle can accelerate to creep speed without accelerator input, but the creep speed varies on gradients or irregular surfaces and excessive torque may exceed available surface friction on low friction surfaces
Solution Approach 1:
The control system dynamically adjusts the drive torque parameter based on detected terrain conditions (gradient, surface friction, road load) to maintain consistent creep speed. The controller modifies torque converter operation parameters in response to changing environmental conditions, transforming a fixed-characteristic system into an adaptive one that resolves the contradiction between enabling creep motion and maintaining speed consistency.
2Speed
If maximum torque is generated by the torque converter when moving away from rest, then acceleration capability is improved, but wheel slip occurs on low friction surfaces such as wet grass or ice
Solution Approach 1:
The control system implements feedback by continuously monitoring wheel speed, terrain conditions, and torque application. When wheel slip is detected or predicted based on surface friction characteristics, the controller reduces drive torque to prevent further slip. This closed-loop control resolves the contradiction by allowing high torque application only when conditions permit, preventing wheel slip on low friction surfaces while maintaining acceleration capability when appropriate.
Solution Approach 2:
The system dynamically adjusts torque converter operation based on real-time terrain assessment. Rather than applying fixed maximum torque, the controller continuously adapts torque application to match available surface friction and road load conditions. This dynamic adjustment enables optimal acceleration while preventing wheel slip, resolving the contradiction between acceleration capability and slip prevention.
3Device complexity
If the torque converter operates without control to provide creep, then the system complexity is reduced, but the driver experiences variation of creep speed and the torque may exceed available surface friction
Solution Approach 1:
The control system acts as an intermediary between the driver's creep mode selection and the torque converter operation. Rather than directly controlling the torque converter, the controller assesses terrain conditions and modulates torque application accordingly. This intermediary layer adds minimal complexity while significantly improving creep speed consistency and preventing wheel slip, resolving the contradiction between system simplicity and control reliability.
Data Source
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AI summary
Aspects of the present invention relate to a control system for a vehicle. The control system comprises one or more controllers, and is configured to select a relationship between torque and speed based, at least in part, on a determined terrain mode. The control system is further configured to control a drive torque of the vehicle in accordance with the selected relationship between torque and speed when the vehicle is operating in a creep control mode. The vehicle may be a hybrid or electric vehicle and the terrain mode may be determined from a Terrain Response ™ switch input or automatically determined.