Transmission Friction Element Hydraulic Boost Control
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Solution Overview
Problem
Existing hydraulic clutch systems face challenges in efficiently controlling fluid flow rates during the boost phase of friction element engagement, leading to potential over-stroking and prolonged shift times in transmission systems.
Innovation Solution
A method involving a controller that commands a first hydraulic boost pressure for a plurality of control loop cycles followed by a second, lower hydraulic boost pressure for a single control loop cycle at the end of the boost phase, allowing precise control of fluid flow to the friction element and reducing engagement time without over-stroking the piston.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high hydraulic boost pressure is commanded for multiple control loop cycles during the boost phase, then the engagement speed of the friction element is improved, but the risk of over-stroking the piston increases
Solution Approach 1:
The controller implements periodic action by commanding high boost pressure for a specific number of control loop cycles (N cycles) during the boost phase, then transitioning to a lower pressure. This periodic high-pressure application provides sufficient fluid flow to rapidly engage the friction element while the time-limited nature of the high pressure prevents excessive piston travel and over-stroking.
Solution Approach 2:
The system applies dynamics by varying the boost pressure level based on the engagement phase. The controller dynamically adjusts pressure from a high level during the initial N control loop cycles to a lower level subsequently, optimizing both engagement speed and piston protection throughout the engagement process.
2Loss of time
If a constant high hydraulic boost pressure is maintained during the boost phase, then the shift time is reduced, but the control precision deteriorates
Solution Approach 1:
The controller uses periodic action with a defined structure: high boost pressure is commanded for exactly N control loop cycles, then reduced. This structured periodic approach ensures the boost phase completes within an optimized time frame while maintaining precise control through the defined transition point, preventing both premature and delayed engagement.
Solution Approach 2:
The boost phase is segmented into distinct control periods: an initial phase of N control loop cycles with high pressure, followed by a subsequent phase with reduced pressure. This segmentation allows the system to achieve rapid engagement during the first segment while maintaining control precision through the structured transition to the second segment.
3Reliability
If the boost phase duration is extended to ensure complete friction element engagement, then the engagement reliability is improved, but the overall shift time increases
Solution Approach 1:
The system applies periodic action by commanding high boost pressure for a predetermined number of control loop cycles (N cycles) during the boost phase, then transitioning to a lower pressure. This time-limited high-pressure application ensures sufficient fluid flow to reliably engage the friction element while preventing excessive duration that would prolong the shift.
Solution Approach 2:
The controller changes the pressure parameter dynamically during the boost phase. By commanding a high boost pressure for N control loop cycles and then reducing it, the system optimizes the balance between achieving reliable engagement (sufficient pressure duration) and minimizing shift time (limited pressure duration), with the parameter change occurring at a precisely defined point.
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 enables faster engagement of friction elements, reducing shift times and improving vehicle acceleration while maintaining control precision, thus addressing the limitations of traditional constant pressure strategies.
Implementation Method 1
commanding fluid to the friction element at a first flow rate for a plurality of control loop cycles and subsequently commanding the fluid to the friction element at a second flow rate
Data Source
AI summary
A vehicle includes a transmission having a plurality of friction elements selectively engageable to establish power flow paths within the transmission. A controller of the vehicle is programmed to, during a boost phase of a shift, command a first hydraulic boost pressure for a plurality of control loop cycles to an oncoming one of the friction elements (oncoming friction element) and subsequently command a second hydraulic boost pressure less than the first hydraulic boost pressure for only a single control loop cycle that defines an end of the boost phase to the oncoming friction element.