Vehicle Motion Model With Low-Speed Cornering Stiffness Derating
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Solution Overview
Problem
Dynamic vehicle motion models become less accurate at lower speeds due to inaccuracies in calculations involving tire forces, particularly with tire cornering stiffness values approaching zero.
Innovation Solution
Derating the tire cornering stiffness value used in the dynamic model when the vehicle approaches lower speeds, ensuring the value remains above zero to maintain model accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dynamic model utilizing tire cornering stiffness is used to predict vehicle motion, then prediction accuracy is improved at higher speeds, but prediction accuracy deteriorates at lower speeds (5 mph or less)
Solution Approach 1:
The patent applies dynamics by making the tire cornering stiffness parameter variable rather than constant. The system dynamically adjusts the cornering stiffness value based on the current vehicle speed, transitioning from a fixed parameter model to an adaptive model that responds to changing operating conditions. This resolves the contradiction by allowing the model to maintain accuracy across different speed ranges through real-time parameter adjustment.
Solution Approach 2:
The patent directly changes the parameter (tire cornering stiffness) based on the operating condition (vehicle speed). When speed drops below the threshold of 5 mph, the system modifies the cornering stiffness parameter to a derated value, which compensates for the model's inherent inaccuracies at low speeds. This parameter change approach allows the dynamic model to maintain prediction accuracy across the full speed range despite the theoretical limitations of using velocity-based calculations near zero.
2Reliability
If tire cornering stiffness value is maintained at nominal level, then model accuracy is preserved at higher speeds, but calculation accuracy deteriorates as velocity approaches zero
Solution Approach 1:
The patent changes the tire cornering stiffness parameter from a fixed nominal value to a speed-dependent variable. At low speeds (below 5 mph), the system derates the cornering stiffness parameter to a lower value, which prevents the calculation errors that would otherwise occur when velocity approaches zero. This parameter modification maintains both model reliability and calculation accuracy across all operating conditions.
Solution Approach 2:
The system preemptively adjusts the cornering stiffness parameter before calculation errors can occur. By detecting when vehicle speed drops below the threshold, the system proactively derates the parameter to prevent the inaccuracies that would result from using nominal values near zero velocity, rather than attempting to correct errors after they occur.
Data Source
AI summary
Systems and methods are provided for predicting a vehicle's motion. It is determined that speed of the vehicle is below a threshold speed. A derated tire cornering stiffness value that is less than a nominal cornering stiffness value is obtained. The vehicle's motion is predicted based on a dynamic model using the derated tire corning stiffness value.