Transmission Cold Shift Delay Mitigation via Torque Locking
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Solution Overview
Problem
Automatic transmissions experience significant delays when shifting out of park mode in cold environments due to hydraulic lag issues, leading to inefficiencies in gear engagement.
Innovation Solution
A method that measures the transmission's operating temperature and engages specific torque transmitting mechanisms, such as clutches and a selectable one-way clutch, to lock the first gear member of the planetary gear set to the ground, preventing input torque transfer to the park pawl and facilitating quicker shifting out of park mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the transmission operates in cold environments using conventional hydraulic control systems, then the transmission can maintain its standard hydraulic lag characteristics, but significant delays occur when shifting out of park mode due to hydraulic lag
Solution Approach 1:
The patent applies preliminary action by engaging specific torque transmitting mechanisms (fourth and fifth) before the actual shift operation is needed. When cold temperature is detected, these mechanisms are pre-engaged to lock the first gear member to ground, preventing torque transfer to the park pawl before the shift command is executed. This preparatory engagement eliminates the hydraulic lag delay that would otherwise occur during the shift operation.
2Productivity
If torque transmitting mechanisms are engaged to prevent torque transfer to the park pawl, then shift delays are reduced, but the complexity of the torque transmitting mechanism engagement increases
Solution Approach 1:
The patent applies local quality by selectively engaging specific torque transmitting mechanisms (fourth and fifth) rather than all mechanisms. The fourth torque transmitting mechanism locks the first gear member to ground, while the fifth mechanism provides additional locking support. This selective local engagement achieves the goal of preventing torque transfer to the park pawl and reducing shift delays without requiring engagement of all available torque transmitting mechanisms, thereby limiting the increase in system complexity.
3Reliability
If the first gear member is locked to ground to prevent torque transfer, then park pawl loading is prevented, but additional torque transmitting mechanisms must be engaged
Solution Approach 1:
The patent uses the fourth and fifth torque transmitting mechanisms as intermediary elements between the first gear member and the park pawl. By engaging these mechanisms to lock the first gear member to ground, torque transfer to the park pawl is prevented without directly modifying the park pawl itself. This intermediary approach protects the park pawl from loading while using existing transmission components, avoiding the need for additional specialized protection mechanisms.
Data Source
AI summary
A method of operating a motor vehicle transmission includes measuring an operating temperature of the transmission, the transmission having at least seven torque transmitting mechanisms and at least three planetary gear sets, each planetary gear set having three gear members; determining if the transmission is in a park mode; determining if the operating temperature is below a predetermined threshold; if the operating temperature is below the predetermined threshold and the transmission is the park mode, implementing a shift delay mitigation process that includes engaging a fourth torque transmitting mechanism and a firth torque transmitting mechanism of the at least seven torque transmitting mechanisms so that they are locked to a ground to prevent a first gear member of the first planetary gear set from moving, which, in turn, prevents an input torque being transferred to a park pawl.