Partial Clutch Prefill for Vehicle Coast Downshift
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Solution Overview
Problem
Vehicle transmissions face inefficiencies during coast downshift conditions due to the conventional practice of fully engaging clutches only during the downshift event, which can lead to increased fluid pump demand and slower downshift processes.
Innovation Solution
A controller algorithm prefills clutches to a staging pressure prior to the downshift event by generating pressure commands based on predefined coast conditions, using a look-up table that considers turbine speed and transmission fluid temperature, allowing for earlier engagement of oncoming clutches and reducing fluid demand during the downshift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If clutches are fully engaged only during the downshift event, then the hydraulic system operates in a conventional manner, but the downshift process becomes slower and fluid pump demand increases
Solution Approach 1:
The patent applies preliminary action by pre-filling the clutch with hydraulic fluid to a staging pressure before the downshift event occurs. This advance preparation ensures that when the downshift is commanded, the clutch is already partially pressurized and ready for rapid engagement, eliminating the delay associated with fluid delivery during the shift event itself.
Solution Approach 2:
The patent segments the clutch engagement process into distinct phases: a pre-fill phase where the clutch is pressurized to a staging pressure before the downshift, and an engagement phase where the clutch is fully pressurized during the actual shift. This segmentation allows the hydraulic system to prepare the clutch in advance rather than delivering all fluid demand simultaneously during the downshift event.
2Loss of time
If clutches are pre-filled to staging pressure before downshift, then downshift responsiveness improves, but hydraulic system complexity increases
Solution Approach 1:
The patent implements dynamics by making the clutch pre-fill status a variable state that changes based on operating conditions. The controller monitors whether the clutch is pre-filled and adjusts the downshift command accordingly, creating a dynamic control system that adapts to the current hydraulic state of the clutch rather than using a fixed engagement procedure.
Solution Approach 2:
The patent employs feedback by having the controller track the pre-fill status of the clutch and use this information to determine when to execute the downshift command. The system receives feedback about the hydraulic pressure state and uses this feedback to timing the shift event optimally, ensuring the clutch is ready for engagement without requiring overly complex predictive modeling.
3Productivity
If clutch pre-fill is implemented, then transmission efficiency improves, but control algorithm complexity increases
Solution Approach 1:
The patent applies self-service by having the hydraulic system automatically manage its own pre-fill status without requiring complex external control. The system monitors its own pressure states and timing, and the controller uses straightforward logic to determine when pre-fill has occurred and when to execute the downshift, rather than requiring sophisticated algorithms to predict or control the hydraulic behavior.
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 downshift events with reduced hydraulic system load, improving transmission efficiency and responsiveness by partially engaging clutches before the coast downshift, thus optimizing gear transitions.
Implementation Method 1
Each of the oncoming clutches includes a biasing member (e.g., a return spring) having a return spring pressure (PR) such that the oncoming clutch is fully engaged when the return spring pressure (PR) is applied
Implementation Method 2
A pressure command is generated to at least partially pressurize at least one of the oncoming clutches to the staging pressure (PS)
Data Source
AI summary
A vehicle transmission includes a plurality of oncoming clutches that are hydraulically-actuated. A controller is operatively connected to the plurality of oncoming clutches. An algorithm stored on and executable by the controller causes the controller to determine if at least one predefined coast condition is met and identify the plurality of oncoming clutches configured to be engageable during a downshift event from an initial gear ratio to respective other gear ratios. The initial gear ratio is greater than each of the respective other gear ratios. The algorithm causes the controller to generate a first pressure command to at least partially pressurize a first one of the oncoming clutches to a first staging pressure (PS1) if the at least one predefined coast condition is met prior to the downshift event. The first staging pressure (PS1) is defined as a first return spring pressure (PR1) minus a first variable correction factor (CF1).