CVT Hydraulic Pressure Control During Kickdown
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Solution Overview
Problem
In continuously variable transmissions, the actual hydraulic pressure overshoots and undershoots the target pressure during rapid increases due to kickdown, leading to belt slipping due to insufficient oil flow balance and delayed feedback in drain regulator valves.
Innovation Solution
Implementing a control strategy that increases the target line and secondary pressures to a second target pressure higher than the first target pressure during kickdown, suppressing the activity of the line and secondary pressure regulator valves to prevent overshooting and undershooting, and maintaining the pressures at this level for a predetermined time to prevent belt slipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the target hydraulic pressure is rapidly increased during kickdown, then the belt clipping force is improved, but the actual hydraulic pressure overshoots and undershoots the target pressure causing belt slipping
Solution Approach 1:
The control device increases the target line pressure to a first target pressure before the kickdown is fully completed, in advance of when the maximum belt clipping force is required. This preliminary pressure increase prevents the hydraulic pressure from overshooting during the kickdown process, as the pressure is already at the appropriate level when the kickdown completes, thereby maintaining reliable belt clipping force without oscillation
Solution Approach 2:
The control device dynamically adjusts the target line pressure based on the kickdown state and engine rotational speed. During kickdown, the target pressure is set to a higher first target pressure, and after kickdown completes, it transitions to a lower second target pressure. This dynamic adjustment matches the hydraulic pressure profile to the actual operational requirements, preventing both overshooting and undershooting while maintaining adequate belt clipping force throughout the transition
2Speed
If the drain port is closed to increase hydraulic pressure, then the line pressure increases rapidly, but the feedback circuit causes the drain port to remain open delaying pressure increase and causing undershooting
Solution Approach 1:
The control device preliminarily increases the target line pressure before the kickdown completes, anticipating the need for high pressure. This prevents the situation where the drain port would need to close rapidly during kickdown, as the pressure is already building appropriately in advance, eliminating the delay caused by the feedback circuit's response time
Solution Approach 2:
The control device uses feedback from the kickdown state detection to adjust the target line pressure. When kickdown is detected, the feedback loop sets the target pressure to the higher first target pressure, which overrides the normal feedback control that would otherwise cause the drain port to remain open too long. This feedback-based adjustment synchronizes the pressure control with the actual operational needs, preventing both overshooting and undershooting
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This strategy effectively prevents belt slipping by maintaining adequate belt clipping force, ensuring the hydraulic pressures remain within the target range, thereby enhancing transmission efficiency and preventing fuel efficiency deterioration.
Implementation Method 1
an oil pump, and a line pressure regulator valve that reduces a discharge pressure of the oil pump to regulate a line pressure
Implementation Method 2
a spool on whose edges a signal pressure corresponding to a target line pressure and the line pressure are acted and which opens and closes a drain port in accordance with a stroke, and a spring that biases the spool
Implementation Method 3
control a regulated hydraulic pressure to a hydraulic pressure corresponding to the signal pressure (target hydraulic pressure) by a feedback circuit that causes the regulated hydraulic pressure to act on the spool
Data Source
AI summary
A transmission controller determines whether a shift is a kickdown, and when the shift is determined as the kickdown, the target line pressure is increased to a first target pressure corresponding to an input torque to a continuously variable transmission increased by the kickdown; the transmission controller then determines whether the line pressure has reached the first target pressure, and if determined that the line pressure has reached the first target pressure, the target line pressure is increased to a second target pressure higher than the first target pressure.