Shift Control Device for Smooth CVT Mode Transition
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Solution Overview
Problem
Existing shift control devices for continuously variable transmissions face challenges in smoothly switching between stepless and stepped shift modes, leading to rapid engine rotation speed increases that can cause discomfort to vehicle occupants during mode transitions.
Innovation Solution
A shift control device that includes a shift controller, a minimum value detector, and an upper-limit-value setting unit, which switches from stepped to stepless shift mode by limiting engine rotational acceleration based on the accelerator-pedal operated amount, setting an upper limit value for rotational acceleration to prevent rapid engine speed increases during downshifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the shift mode is switched from stepped shift mode to stepless shift mode during accelerator pedal operation, then the transmission can provide better acceleration response, but the engine rotation speed increases rapidly causing discomfort to vehicle occupants
Solution Approach 1:
The system performs preliminary detection of the accelerator pedal operated amount before switching from stepped to stepless shift mode. By detecting the pedal position in advance and comparing it against threshold values, the control device determines whether the current operating conditions warrant mode switching, thereby preventing rapid engine speed increases that would cause discomfort while still enabling acceleration response when appropriate
Solution Approach 2:
The invention changes the control parameter from binary mode switching to continuous parameter-based control. By using the accelerator pedal operated amount as a continuous parameter and comparing it against threshold values, the system smoothly transitions between shift modes based on the degree of pedal depression, avoiding abrupt changes in engine rotation speed that cause occupant discomfort
2Measurement precision
If the transmission gear ratio is controlled in a stepwise fashion during stepped shift mode, then the engine rotation speed can be controlled more precisely, but the mode transition to stepless shift mode causes rapid engine speed increases
Solution Approach 1:
The accelerator pedal operated amount serves as an intermediary parameter that mediates between stepped and stepless shift modes. By using this intermediate parameter to determine mode transition conditions and control the transition process, the system maintains engine rotation speed stability while still enabling precise control characteristics of stepped mode when needed
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 shift controller that switches the shift mode to the stepless shift mode by executing shift control of the transmission if an accelerator-pedal operated amount falls below a switch threshold during the stepped shift mode, a minimum value detector that detects an operated-amount minimum value in a shift process of switching the shift mode to the stepless shift mode, and an upper-limit-value setting unit that sets an upper limit value for engine rotational acceleration based on a difference between the operated amount and the minimum value in the shift process. In the shift process, the shift controller limits the rotational acceleration to the upper limit value or lower by limiting a shift rate when the transmission is downshifted.