Vehicle Transmission Fail-Safe Control for Clutch Abnormality
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Solution Overview
Problem
Existing vehicle power transmission systems face challenges in decelerating vehicles safely while preventing engine stalling, particularly when shifting into neutral at high speeds, which can increase braking distance, or stalling during deceleration if shifted too late.
Innovation Solution
A vehicle power transmission system that includes a transmission with multiple gear stages, a clutch actuator, shift actuator, travelling state detection sensor, and a control device that shifts the selected gear stage into a lower gear ratio and then neutral before the vehicle stops, using sensors to detect abnormal clutch actuator conditions and vehicle state, and includes a slipper mechanism to reduce pressing force between friction and clutch plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transmission is shifted into neutral immediately when clutch actuator failure is detected, then the engine stalling is prevented, but the braking distance increases and the vehicle cannot move while at rest
Solution Approach 1:
The control device performs preliminary actions by sequentially downshifting through lower gear stages before finally shifting to neutral. This staged approach prepares the transmission system gradually, allowing engine braking to assist deceleration throughout the process, rather than abruptly shifting to neutral which would eliminate engine braking support and increase braking distance.
Solution Approach 2:
The fail-safe operation is segmented into multiple discrete steps: detecting clutch actuator failure, sequentially downshifting through intermediate gear stages, and finally shifting to neutral. This segmentation allows the system to maintain engine braking assistance during deceleration while progressively preparing for the eventual neutral state, preventing both engine stalling and excessive braking distance.
2Speed
If the transmission is shifted into neutral late during deceleration, then the braking distance is reduced, but the engine may stall
Solution Approach 1:
The control device performs preliminary downshifting actions through lower gear stages before the vehicle comes to a complete stop. By anticipating the need for neutral engagement and preparing the transmission in advance through staged downshifts, the system maintains engine braking support during deceleration while ensuring the engine remains connected to the drivetrain until the appropriate moment, preventing stalling.
Solution Approach 2:
The control device continuously monitors vehicle speed and deceleration state to determine the optimal timing for each downshift and final neutral engagement. This feedback mechanism allows the system to adjust the timing of gear stage changes based on actual vehicle conditions, ensuring that neutral is engaged at the precise moment that prevents engine stalling while minimizing braking distance.
3Reliability
If the clutch actuator is switched off immediately upon detecting abnormality, then the engine stalling is prevented, but the vehicle cannot move while at rest
Solution Approach 1:
The control device performs preliminary gear stage downshifts while maintaining clutch engagement before finally switching off the clutch actuator and shifting to neutral. This preliminary action sequence allows the vehicle to remain movable during the transition, and by the time the clutch is fully disengaged and the vehicle is at rest, the transmission is already in neutral, enabling easy movement when needed.
4Device complexity
If the transmission shifts directly to neutral without downshifting, then the fail-safe operation is simplified, but sudden engine braking and shift shocks occur
Solution Approach 1:
The control device segments the fail-safe operation into multiple controlled downshift steps through lower gear stages before final neutral engagement. This segmentation transforms a single abrupt shift into a series of gradual transitions, distributing the engine braking effect across multiple stages and eliminating sudden shocks to the drivetrain and vehicle body, while the control logic remains relatively simple.
Solution Approach 2:
The control device applies beforehand cushioning by introducing intermediate gear stages between the current gear and neutral. These intermediate stages act as cushions that absorb and distribute the mechanical shock and engine braking force, preventing sudden impacts to the transmission system and vehicle body while maintaining a straightforward control sequence.
Data Source
AI summary
A vehicle power transmission system includes: a transmission; a shift actuator; a clutch; a clutch actuator for mutually switching between the transmission and the shutting off of a driving force at the clutch; and a control device being configured to, when having detected that the vehicle is in the travelling state and that the clutch actuator is abnormal by use of the travelling state detection sensor and the CA abnormality detection sensor, control the operation of the shift actuator and cause the selected gear stage in the transmission to be shifted into neutral before the vehicle comes to a stop while shifting the selected gear stage in the transmission into a gear stage having a lower gear ratio.