Shift-by-wire fail control device limp-home mode
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Solution Overview
Problem
Conventional shift-by-wire automatic transmission systems fail to allow vehicles to travel from a stopped position under their own power when the shift-by-wire system fails, as they unconditionally stop engine operation, preventing movement to a repair shop or safe parking, even if the driver intends to travel safely.
Innovation Solution
A shifting apparatus and method that includes an actuator to direct the vehicle transmission into a travel range setting, a selector to choose a desired travel range, a transmission controller to move the actuator electronically, and a shift-by-wire fail detection system, which permits limited engine output if the system fails while in the desired travel range and inhibits travel if the system fails in an undesired range, using shut-off valves and throttle control to manage clutch and brake engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine operation is unconditionally stopped when shift-by-wire system fails, then safety is improved, but the vehicle cannot travel to repair shop or safe parking location
Solution Approach 1:
The patent applies local quality by differentiating the fail-safe response based on the specific range position of the manual valve. When the manual valve is in a travel range position (D or R), the system permits limited engine output to allow travel to a safe location. When in a non-travel position (P or N), the system stops engine operation. This localized differentiation resolves the contradiction by adapting the safety response to the specific operational context.
Solution Approach 2:
The patent implements dynamics by making the fail-safe control response changeable based on real-time system state. The control device dynamically adjusts between permitting limited output and stopping engine operation depending on whether the manual valve position corresponds to a travel range. This dynamic adaptation allows the system to maintain both safety and travel capability under different failure conditions.
2Volume of moving object
If the manual valve is moved by electronic control without mechanical link, then vehicle size is reduced, but fail-safe control becomes more complex
Solution Approach 1:
The patent uses an intermediary approach by introducing a control device that monitors the manual valve position and compares it with the detected selection operation. This intermediary control unit serves as a bridge between the electronic actuator and the fail-safe requirement, simplifying the overall system by centralizing the fail-safe logic in a dedicated monitoring component rather than distributing complexity throughout the system.
Solution Approach 2:
The patent implements feedback by having the control device continuously monitor the manual valve position and compare it with the intended selection operation from the range selection switch. When a discrepancy is detected indicating shift-by-wire system failure, the feedback triggers appropriate fail-safe control. This feedback mechanism provides a straightforward way to detect failures and respond appropriately without requiring complex predictive controls.
Data Source
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AI summary
A shifting apparatus includes an actuator to direct a travel range setting of a vehicle transmission, a selector to indicate a desired travel range setting, a transmission controller to move the actuator into the travel range setting in response to the desired travel range setting of the selector, and a restrictor to restrict an output of a drive motor if the vehicle transmission is in a travel range setting other than the desired travel range setting. A method to control a vehicle transmission includes detecting a travel range setting of the vehicle transmission, detecting a desired travel range setting of a selector, and entering a limp-home mode if the detected travel range setting is different from the desired travel range setting and a detected vehicle travel direction corresponding to the detected travel range setting is the same as a desired travel direction corresponding to the desired travel range setting.