Automatic Transmission Friction Element Engagement Timing Control
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Solution Overview
Problem
Automatic transmissions face challenges in achieving adequate relative timing between disengaging and engaging friction elements during speed changes, leading to uncomfortable phenomena like 'pull-in of output torque' and 'blow-up of engine speed', due to difficulties in accurately controlling the engagement timing of the engagement-side friction element.
Innovation Solution
A method and apparatus that involve a pre-charge step, an oil pressure holding step, and a pressure raising step to engage the engagement-side friction element, with a pre-charge period setting mechanism to adjust the timing difference between predicted and actual engagement, ensuring accurate relative timing between disengagement and engagement operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engagement-side friction element engaging operation is controlled to achieve adequate relative timing with disengagement, then the uncomfortable phenomena (pull-in of output torque, blow-up of engine speed) are reduced, but it is not easy to accurately control the engagement timing while avoiding longer speed change period
Solution Approach 1:
The patent applies preliminary action by performing a pre-charge operation before the main engagement control. The pre-charge fills the oil passage and pressure chamber with operating oil in advance, so that when engagement control starts, the friction element can engage smoothly without delay. This preliminary preparation resolves the timing control difficulty by ensuring the system is ready before the actual engagement begins.
Solution Approach 2:
The engagement process is segmented into distinct phases: pre-charge phase and engagement control phase. The pre-charge phase fills the oil passage and pressure chamber, while the engagement control phase raises pressure to fully engage the friction element. This segmentation allows each phase to be optimized independently, improving overall control accuracy without increasing overall complexity.
2Productivity
If the engagement control is started just after completion of pre-charge, then the speed change period is shortened, but a shock is likely to occur due to rapid engagement of the engagement-side friction element
Solution Approach 1:
The pre-charge operation serves as preliminary action that prepares the oil passage and pressure chamber before engagement control begins. By pre-filling these components with operating oil, the system eliminates delays during engagement while controlling the pressure rise rate to prevent shock. This allows rapid engagement without the harmful effects of sudden pressure spikes.
Solution Approach 2:
The pre-charge phase acts as a cushioning period that prepares the hydraulic system for the upcoming engagement. During pre-charge, the oil passage and pressure chamber are gradually filled, creating a buffer that prevents sudden pressure changes during the subsequent engagement control phase, thereby reducing engagement shock.
3Measurement precision
If the operating pressure is held approximately constant for a given period of time after pre-charge, then the engagement timing control is improved, but the speed change period becomes longer
Solution Approach 1:
The oil pressure holding period serves as a preparatory phase that stabilizes the system before engagement control begins. By holding pressure constant after pre-charge, the system ensures that the friction element is ready to engage at the precise intended moment, improving timing accuracy without requiring excessive holding time.
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 approach allows for a satisfactory speed change operation by adjusting the pre-charge period to minimize timing differences, thereby reducing the occurrence of uncomfortable phenomena such as output torque pull-in and engine speed blow-up, while maintaining a constant oil pressure holding period to prevent engagement shocks.
Implementation Method 1
a hydraulic actuator for driving each of the friction elements
Implementation Method 2
an oil pressure control valve for controlling an oil pressure against the hydraulic actuator
Data Source
AI summary
A method comprises a pre-charge step of pre-charging operating oil; a holding step of holding an operating pressure at an oil pressure less than an oil pressure during the pre-charge, for a given period of time; and a raising step of raising the operating pressure to cause an engagement-side friction element to be engaged. The method further comprises a setting step of setting a pre-charge period in the pre-charge step. The setting step includes predicting a timing at which the engagement-side friction element is to be engaged; actually measuring a timing at which the engagement-side friction element has been actually engaged; and setting the period of the pre-charge step to allow a difference between the timings to become smaller.