Cruise Control Downshift Limits for Low-Traction Vehicle Speed Hold
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Solution Overview
Problem
Existing vehicle speed control systems are ineffective in low traction conditions, such as off-road environments, where wheel locking can occur due to downshifts, and are often disabled in situations where continued progress is desirable, like in congested traffic or low-speed scenarios.
Innovation Solution
A system that estimates tractive force between wheels and the driving surface based on surface coefficient of friction, generating a gear shift limit signal to prevent downshifts if traction is below a threshold, and includes a mu-check operation to monitor wheel speed changes and adjust engine speed accordingly, allowing the vehicle to maintain target speed without wheel locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cruise control system operates in low-speed conditions, then the vehicle can maintain progress in congested traffic, but the system becomes ineffective and may cause wheel locking due to insufficient traction
Solution Approach 1:
The system dynamically changes the parameter of gear shift timing based on detected traction conditions. When low traction is detected (through wheel slip detection or traction control activation), the system modifies the gear shift map to prevent downshifts that would cause wheel locking, thereby maintaining reliable operation in low-speed congested traffic conditions
Solution Approach 2:
The gear shift map is made dynamic rather than fixed, allowing real-time adjustments based on driving conditions. The system transitions between different gear shift strategies depending on whether high or low traction conditions are detected, enabling adaptive operation across varying traffic and road conditions
2Speed
If the transmission controller performs downshifts to maintain target speed, then the vehicle can respond quickly to speed changes, but wheel locking occurs in low traction conditions
Solution Approach 1:
The system takes preliminary action by detecting traction conditions before a downshift is executed. When low traction is anticipated or detected, the system preemptively prevents the downshift that would cause wheel locking, rather than reacting after the harmful effect has already occurred
Solution Approach 2:
The control system acts as an intermediary between the transmission controller and the wheels, monitoring traction conditions and intervening to prevent harmful gear shifts. The system mediates between the need for quick speed response and the need to prevent wheel locking by selectively allowing or blocking downshift commands
3Reliability
If the cruise control system is disabled in low-speed conditions, then wheel locking is prevented, but the vehicle cannot maintain progress in congested traffic
Solution Approach 1:
The system provides universal speed control functionality that works across multiple driving conditions by integrating both high-speed and low-speed cruise control modes. The adaptive gear shift map enables the same cruise control system to function reliably in both highway and congested traffic conditions without requiring separate systems
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
The system reduces the likelihood of wheel locking during low traction conditions and enables continuous vehicle progress by preventing unnecessary downshifts, thereby enhancing safety and control in varied driving conditions.
Implementation Method 1
estimate an amount of tractive force that may be developed between each wheel and a driving surface in dependence on a signal (sfc_mu) having a value indicative of a surface coefficient of friction between each wheel and a driving surface
Data Source
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AI summary
Embodiments of the present invention provide a system comprising: a first controller configured in each of a predetermined plurality of states to generate a torque request signal in order to cause a vehicle to operate in accordance with a target speed value, the system being configured, when the first controller is one of said plurality of states to generate a gear shift limit signal to cause a change in an engine speed at which a transmission controller is permitted to cause a gear downshift, the gear shift limit signal being generated in dependence on at least one traction indicator signal indicative of an amount of estimated traction between the vehicle and a driving surface.