Vehicle Path Control Using Real-Time Understeer Gradient Updates
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Solution Overview
Problem
Autonomous or semi-autonomous vehicles face challenges in maintaining precise trajectory control during bends due to unaccounted changes in understeer gradient caused by factors like load distribution, which can lead to incorrect steering angles and vehicle decentering.
Innovation Solution
A method and device for real-time adjustment of understeer gradient by continuously determining and updating its value based on state variables, using a recursive least squares method and a 'bicycle' model to maintain the vehicle's trajectory in the center of the lane, accounting for changes in load distribution and other factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional control law with fixed understeer gradient is used, then the steering angle can be determined, but the vehicle trajectory becomes inaccurate when load distribution changes
Solution Approach 1:
The understeer gradient is transformed from a fixed parameter to a dynamic variable that is continuously updated based on real-time vehicle state measurements. The system adapts the understeer gradient value according to actual vehicle behavior during bends, allowing the control law to respond to load distribution changes and maintain accurate trajectory control.
Solution Approach 2:
The system implements feedback by measuring actual vehicle trajectory deviations and steering angles, then using this information to recursively update the understeer gradient value. The feedback loop continuously compares predicted versus actual vehicle behavior and adjusts the understeer gradient to minimize trajectory errors, ensuring adaptability to changing load conditions.
2Adaptability or versatility
If the understeer gradient is updated frequently during bends, then real-time adaptability improves, but trajectory control stability deteriorates due to sudden changes
Solution Approach 1:
The system performs preliminary updates of the understeer gradient during straight-line travel before the vehicle enters a bend. This preliminary action allows the understeer gradient to be optimized based on current load conditions without causing instability during the critical bending maneuver, as the update is completed before trajectory control becomes sensitive.
Solution Approach 2:
The understeer gradient is updated periodically at specific phases of vehicle operation (during straight travel between bends) rather than continuously during all maneuvers. This periodic update strategy maintains real-time adaptability to load changes while avoiding frequent updates during bends that would cause trajectory instability and occupant discomfort.
3Adaptability or versatility
If the understeer gradient is updated during straight line travel, then real-time adaptability improves, but the complexity of determining when to update increases
Solution Approach 1:
The update determination logic is extracted as a separate functional module that independently evaluates update conditions based on simple, easily measurable parameters such as vehicle speed, steering angle, and lateral acceleration. This modular extraction simplifies the overall system architecture and makes the update timing determination less complex by focusing on key discriminative features.
Solution Approach 2:
The system uses the vehicle's own operational parameters (speed, steering angle, acceleration) to automatically determine update timing without requiring external input or complex scheduling. The update mechanism serves itself by monitoring readily available sensor data and making autonomous decisions about when recalibration is appropriate, reducing system complexity.
Data Source
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AI summary
The invention relates to a method for controlling in real time the path of a motor vehicle travelling in a traffic lane, comprising steps of: - detecting a corner in the traffic lane, then, when the motor vehicle enters said corner, - determining a first quantity and a second quantity for a plurality of successive sampling increments, on the basis of state variables characteristic of the movement of the motor vehicle, - determining a first stored value and a second stored value, said first stored value being dependent on the first quantity determined in the current sampling increment and on first quantities determined for at least one of the preceding sampling increments, said second stored value being dependent on the second quantity determined in the current sampling increment and on second quantities determined for at least one of the preceding sampling increments, - saving in memory said first stored value and second stored value determined for each sampling increment, then, when the motor vehicle exits said corner: - determining a value of the understeer gradient depending on said first stored value and second stored value saved in memory, and - determining a command for the motor vehicle on the basis of the value of the understeer gradient thus determined.