DCT Shift Control for Rough Terrain Torque Handover
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Solution Overview
Problem
Dual clutch transmission (DCT) vehicles face challenges in achieving smooth and reliable shift control during power-off downshifting on rough terrain due to the lack of a torque converter to absorb shifting shocks, requiring precise clutch control which is difficult to maintain on uneven road conditions.
Innovation Solution
A shift control method that determines if the vehicle has entered rough terrain by analyzing the input shaft speed change rate, calculates a target transfer torque for the engaging clutch based on pre-determined speed change rates, and gradually increases and then maintains this torque until a specific slip rate is reached, reducing shifting shock and improving clutch endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DCT uses dry clutches for precise gear shifting, then shifting precision is improved, but shifting shock increases and clutch endurance deteriorates
Solution Approach 1:
The system detects rough terrain conditions in advance and pre-adjusts the transfer torque of the dry clutch before gear shifting occurs. This preliminary torque adjustment ensures smoother engagement and reduces shock during the shifting process, resolving the contradiction between precise shifting and shock reduction.
2Speed
If DCT performs power-off downshifting on rough terrain, then vehicle responsiveness is improved, but shift control reliability deteriorates due to unreliable input shaft speed data
Solution Approach 1:
The system introduces an intermediary mechanism that detects rough terrain conditions and uses this information to mediate the gear shifting process. When rough terrain is detected, the system adjusts transfer torque based on pre-stored speed change rates rather than relying solely on real-time input shaft speed data, thereby maintaining shift control reliability despite unreliable sensor data.
Solution Approach 2:
The system pre-stores speed change rates for different gear stages before entering rough terrain. This preliminary preparation allows the control system to execute reliable power-off downshifting even when real-time speed data becomes unreliable due to terrain-induced vibrations and noise.
3Productivity
If DCT increases transfer torque quickly during shifting, then shifting speed is improved, but shifting shock increases and comfort deteriorates
Solution Approach 1:
The system dynamically adjusts the transfer torque increase rate based on detected road conditions. On rough terrain, the torque increase is moderated to reduce shock, while on smooth roads, faster torque application is permitted to maintain quick shifting. This dynamic adaptation resolves the contradiction between shifting speed and comfort.
Data Source
AI summary
A shift control method in a vehicle having a dual clutch transmission may include determining whether or not power-off downshifting is started and whether or not torque handover is started, determining whether or not the vehicle has entered a rough terrain, calculating and storing a speed change rate of an engaging input shaft right before the vehicle enters the rough terrain, calculating a target transfer torque of an engaging clutch, and gradually increasing a transfer torque of the engaging clutch by an amount until arriving at the target transfer torque of the engaging clutch, controlling the target transfer torque of the engaging clutch to be maintained until a slip rate arrives at a reference value, and completing the power-off downshifting by gradually reducing the transfer torque of the engaging clutch by the amount of torque that the engaging clutch was gradually increased.