CVT Shift Control Threshold Correction for Smooth Kick-Down
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Solution Overview
Problem
Existing shift control devices for continuously variable transmissions face challenges in smoothly transitioning from stepless to stepped shift modes, leading to repetitive upshifting that can cause discomfort to vehicle occupants, especially during kick-down control when engine rotation speed exceeds predetermined thresholds.
Innovation Solution
A shift control device that includes a mode setting unit, correction-value setting unit, and upshift controller to switch from stepless to stepped shift mode based on engine rotation speed, setting a correction value and shift threshold to control the transmission gear ratio effectively, thereby reducing repetitive upshifting and enhancing driving comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the shift mode is switched from stepless to stepped shift mode when engine rotation speed exceeds the switch threshold, then the transmission gear ratio can be controlled in a stepwise fashion for better acceleration, but repetitive upshifting occurs causing discomfort to vehicle occupants
Solution Approach 1:
The patent applies preliminary action by setting a correction value before the mode switching occurs. When the engine rotation speed exceeds the switch threshold, the correction value is calculated based on the excess speed, and this correction value is used to adjust the shift threshold beforehand. This preliminary adjustment prevents the repetitive upshifting issue from occurring in the first place, rather than correcting it after the problem arises.
Solution Approach 2:
The patent changes the shift threshold parameter dynamically by adding a correction value to the basic switch threshold. The correction value is determined based on how much the engine rotation speed exceeds the switch threshold. This parameter change allows the shift threshold to adapt to different operating conditions, preventing repetitive upshifting while maintaining good acceleration performance.
2Loss of energy
If the transmission gear ratio is controlled in a stepwise fashion during stepped shift mode, then powertrain efficiency can be improved, but engine noise increases due to frequent upshifting
Solution Approach 1:
The correction value is calculated in advance based on the engine rotation speed exceeding the switch threshold. This preliminary calculation ensures that the shift threshold is appropriately adjusted before the upshift operation, preventing unnecessary repetitive upshifting that would generate engine noise while still achieving the powertrain efficiency benefits of stepped shift mode.
Solution Approach 2:
The shift threshold parameter is dynamically adjusted by adding the correction value, which is proportional to the extent that engine rotation speed exceeds the switch threshold. This parameter change reduces frequent upshifting events, thereby reducing engine noise while maintaining the powertrain efficiency advantages of controlled stepped shift operation.
3Device complexity
If the shift threshold is set at the basic switch threshold without correction, then the control logic is simple, but the transmission gear ratio switching becomes unstable during kick-down control
Solution Approach 1:
The shift threshold is changed from a fixed basic value to a dynamic value that includes a correction component. The correction value is calculated based on the engine rotation speed exceeding the switch threshold, making the shift threshold adaptive to current operating conditions. This parameter change stabilizes the shift mode during kick-down control while adding only minimal computational complexity.
Solution Approach 2:
The correction value is determined based on feedback from the engine rotation speed measurement. When the engine rotation speed exceeds the switch threshold, the amount of excess speed provides feedback that is used to calculate the appropriate correction value. This feedback mechanism stabilizes the shift mode by adapting the shift threshold to actual operating conditions without requiring complex control logic.
Data Source
AI summary
A shift control device has stepless and stepped shift modes in which a transmission gear ratio of a continuously variable transmission is controlled in stepless and stepwise fashions, respectively, and includes a mode setting unit that switches the shift mode to the stepped shift mode if an engine rotation speed in the stepless shift mode exceeds a switch threshold, a correction-value setting unit that sets a correction value based on the engine rotation speed if the shift mode is to be switched to the stepped shift mode, a shift-threshold setting unit that sets a shift threshold by adding the correction value to the switch threshold if the shift mode is to be switched to the stepped shift mode, and an upshift controller that switches the transmission gear ratio toward a higher side when the engine rotation speed in the stepped shift mode reaches the shift threshold.