Four-Wheel-Drive Control Apparatus Wheel Speed Correction
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Solution Overview
Problem
Existing four-wheel-drive vehicle control systems struggle to accurately calculate correction coefficients for wheel diameters, leading to inaccurate slip ratio calculations and inappropriate timing for vehicle behavior stabilization control, especially on low-friction surfaces where rear wheels slip due to differing final gear ratios.
Innovation Solution
A control apparatus that detects the coupling torque information to determine when the vehicle is not in a four-wheel-drive state, allowing for accurate calculation of correction coefficients based on wheel diameters, and adjusts wheel speeds to reduce the influence of diameter differences, enabling precise vehicle behavior stabilization control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the final gear ratio on the rear wheel side is set to be smaller than that on the front wheel side to increase rear wheel rotation speeds, then the rear wheels can rotate faster to improve four-wheel-drive performance, but the rear wheels will slip on low-friction surfaces even when wheel diameters are identical, leading to inaccurate slip ratio calculations
Solution Approach 1:
The system dynamically changes the parameter (correction coefficient) based on detected wheel speeds and gear ratio information. When rear wheel speed exceeds front wheel speed by a predetermined threshold (indicating slipping due to gear ratio difference rather than wheel diameter difference), the correction coefficient is adjusted to account for this expected speed difference, thereby maintaining accurate slip ratio calculations despite the inherent speed differential caused by different final gear ratios
Solution Approach 2:
The control device introduces an intermediary correction coefficient that mediates between the raw wheel speed measurements and the final slip ratio calculation. This correction coefficient compensates for the systematic speed difference caused by the different final gear ratios, allowing the slip ratio calculation to accurately reflect actual wheel slipping conditions rather than being confounded by the intentional speed differential
2Device complexity
If correction coefficients are calculated based on wheel rotation speeds without considering the difference in final gear ratios, then the calculation process remains simple, but the correction coefficients become inaccurate when rear wheels slip due to gear ratio differences, leading to inappropriate vehicle behavior stabilization control timing
Solution Approach 1:
The control device performs preliminary action by calculating and storing the expected speed difference between front and rear wheels based on the known final gear ratio difference before slip ratio calculation. This pre-calculated reference value is then used to adjust the correction coefficient, allowing the system to account for gear ratio effects without adding complex real-time calculations during slip detection
Solution Approach 2:
The system implements dynamics by making the correction coefficient adaptive rather than fixed. The correction coefficient is dynamically adjusted based on the detected relationship between front and rear wheel speeds and the known gear ratio difference. This dynamic adjustment allows the system to distinguish between speed differences caused by wheel diameter variations and those caused by intentional gear ratio differences, maintaining accuracy without excessive complexity
Data Source
AI summary
Provided is a control apparatus for a four-wheel-drive vehicle configured to, when a degree of transmission of a driving force to a side of rear wheels is smaller than a predetermined degree, calculate a correction value for a wheel speed based on a rotation-related value, and calculate a wheel speed through use of the rotation-related value and the correction value.