Transmission Line Pressure Offset for Coordinated Shifts
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Solution Overview
Problem
In transmissions with both continuously variable and stepped mechanisms, coordinated shifts can lead to hydraulic pressure shortages and belt slip due to undershooting of actual line pressure when using existing techniques for setting target line pressures.
Innovation Solution
A transmission system with a continuously variable transmission mechanism and a stepped transmission mechanism in series, where the target line pressure is set to an offset value by adding a positive offset to one of the target primary or secondary pressures during coordinated shifts, ensuring the line pressure does not decrease and increase excessively, thus maintaining adequate hydraulic pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the target line pressure is set to the higher one of target primary pressure and target secondary pressure in a cross point region, then the control is simplified, but the actual line pressure may undershoot the target line pressure during coordinated shift causing hydraulic pressure shortage
Solution Approach 1:
The invention applies preliminary action by predicting the target line pressure at a future time point (second time point) that is later than the current time point, and using this predicted value as the target line pressure at the current time. This anticipatory approach prevents hydraulic pressure shortage by proactively adjusting the target pressure before the undershoot occurs during coordinated shift between stepped transmission and continuously variable transmission.
Solution Approach 2:
The invention implements feedback by using the detected actual line pressure and actual transmission fluid temperature to determine the target line pressure. The control unit continuously monitors the actual line pressure and adjusts the target value based on the comparison between actual and target pressures, ensuring the actual line pressure follows the target trajectory and preventing undershoot during coordinated shift operations.
2Speed
If the target line pressure increases after decreasing during coordinated shift, then the speed ratio control is responsive, but the actual line pressure undershoots causing belt slip at secondary pulley
Solution Approach 1:
The control unit predicts the target line pressure at a second time point that is later than the current first time point, and determines the target line pressure at the current time based on this predicted future value. This preliminary action prevents the target line pressure from increasing after decreasing, thereby avoiding actual line pressure undershoot and the resulting belt slip at the secondary pulley during coordinated shift.
Solution Approach 2:
The invention applies preliminary anti-action by counteracting the potential line pressure undershoot before it occurs. By using the predicted target line pressure from a future time point, the system preemptively prevents the harmful effect of pressure shortage that would otherwise occur during the coordinated shift when the continuously variable transmission speed ratio changes.
Data Source
AI summary
In a transmission, a controller sets a target line pressure to an offset target value, which is a value obtained by adding a positive offset amount to one of a target PRI pressure and a target SEC pressure, in a speed ratio range in which the offset target value is higher than the other at least during an inertia phase in a sub-transmission mechanism when a coordinated shift is carried out. At that time, the one of the target PRI pressure and the target SEC pressure is the target SEC pressure when a variator is downshifted by the coordinated shift while being the target PRI pressure when the variator is upshifted by the coordinated shift.