Transmission Shift Element Engagement for Park-to-Drive Transition
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Solution Overview
Problem
Automatic transmissions experience delays when transitioning from Park to Reverse or Drive modes, leading to inefficient engine speed increase without vehicle movement and potential jolts due to reaction torque, especially when the engine is running slowly or on hills.
Innovation Solution
The implementation of a method where shift elements are engaged to hold the output and turbine shafts against rotation in Park mode, and then transitioned to non-Park modes by disengaging the parking pawl and specific shift elements, with the controller sequencing their engagement to avoid temporary power flow and minimize delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shift elements are engaged to hold transmission components stationary in Park mode, then the vehicle remains stationary even on hills, but there is a delay when transitioning to Reverse or Drive modes causing inefficient engine speed increase and potential jolts
Solution Approach 1:
The patent applies preliminary action by pre-positioning the shift elements in specific engagement states before the Park-to-Reverse or Park-to-Drive transition is commanded. The controller pre-engages the appropriate shift element (first shift element for Reverse, second shift element for Drive) while maintaining the parking pawl engagement, so that when the transition is commanded, the shift element is already in position to immediately transmit torque, eliminating the delay.
Solution Approach 2:
The patent implements dynamics by making the shift element engagement state dynamic and adaptive based on the selected mode. The system transitions from a static Park state where all shift elements are disengaged to a dynamic state where the appropriate shift element is pre-engaged based on whether Reverse or Drive is selected, allowing the system to adapt its configuration for optimal performance in each mode.
2Productivity
If the parking pawl is disengaged early during transition, then the transmission can shift gears faster, but the vehicle may move unintentionally before the shift element is fully engaged
Solution Approach 1:
The controller performs preliminary action by pre-engaging the appropriate shift element (first or second shift element) while the parking pawl is still engaged. This ensures that when the parking pawl is disengaged, the shift element is already in position and can immediately transmit torque, preventing unintended vehicle movement while enabling fast gear shifting.
Solution Approach 2:
The shift element acts as an intermediary between the engine and the transmission output during the transition. By pre-engaging the shift element while the parking pawl is still engaged, the system creates a controlled power transmission path that prevents unintended vehicle movement while preparing for immediate torque transmission when the transition is complete.
3Speed
If multiple shift elements are engaged simultaneously, then the transmission can establish gear ratio faster, but temporary power flow paths may cause instability during engagement
Solution Approach 1:
The patent applies segmentation by dividing the shift element engagement process into distinct, sequential stages. The controller engages shift elements in a specific sequence (pre-engaging the appropriate shift element while maintaining others in their current state, then disengaging the parking pawl, and finally adjusting other shift elements as needed). This segmented approach prevents temporary power flow paths by ensuring only one shift element is in transition at any given time, maintaining power flow stability while still enabling fast gear ratio establishment.
Data Source
AI summary
While a transmission range selector is in a Park position, a controller engages multiple transmission shift elements to place the transmission in a tie-up state. In the tie-up state, both the transmission output shaft and the turbine shaft are held against rotation by the shift elements. To transition from Park to Drive, the controller releases one of the shift elements to place the transmission in a 1st gear state. To transition from Park to Reverse, the controller releases a different one of the shift elements to place the transmission in a reverse state. The controller may wait until the driver releases the brake pedal to release the shift element.