DCT Shift Control for Power-On Upshift SAG
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Solution Overview
Problem
In vehicles with dual clutch transmission (DCT), the gear ratio change during power-on upshift leads to a deterioration in the acceleration feeling experienced by the driver, known as 'SAG feeling', which affects the transmission and commerciality of the vehicle.
Innovation Solution
A shift control method for DCT vehicles that involves an initiation determination step to assess power-on upshift, a handover step where the release-side clutch is gradually released and engine torque is increased to a corrected torque considering gear ratio differences, and a synchronization step where the engine torque is reduced to synchronize engine speed with the engagement-side clutch speed, thereby minimizing the torque difference and enhancing acceleration feeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a power-on upshift is performed in a DCT vehicle, then the gear ratio changes from large to small to enable vehicle acceleration, but the torque transmitted to the drive wheel is lowered causing deterioration of acceleration feeling (SAG feeling)
Solution Approach 1:
The controller increases engine torque in advance during the torque phase before the actual gear shift occurs. This preliminary torque increase compensates for the upcoming torque reduction, ensuring continuous acceleration feeling. The engine torque is increased to a corrected engine torque that considers the gear ratio difference between current and target gears.
Solution Approach 2:
The controller dynamically adjusts engine torque parameters during the shift process. By changing the engine torque from basic engine torque to corrected engine torque (which accounts for gear ratio differences), the system maintains adequate torque transmission to the drive wheel throughout the gear transition, preventing SAG feeling.
2Ease of operation
If the release-side clutch is gradually released during the torque phase, then the handover from current gear to target gear is achieved, but the engine speed needs to be synchronized with the engagement-side clutch speed requiring torque adjustment
Solution Approach 1:
The controller dynamically adjusts engagement-side clutch torque based on real-time conditions during the handover process. The engagement-side clutch torque is determined considering both the corrected engine torque and vehicle speed, allowing flexible adaptation to maintain smooth power transmission while achieving gear synchronization.
Solution Approach 2:
The controller uses feedback from the torque phase completion state to adjust engine torque during the synchronization phase. The engine torque is reduced while considering the torque difference between corrected engine torque and engagement-side clutch torque at handover completion, ensuring smooth synchronization without power interruption.
Data Source
AI summary
A shift control method for a vehicle with a double clutch transmission (DCT) is configured such that when a power-on upshift is initiated, during a target time for a controller to perform a torque phase, a release-side clutch is gradually released, an engine torque is gradually increased to a basic engine torque or more, and an engagement-side clutch torque is increased according to an increase in the engine torque and a vehicle speed; and when the release-side clutch is completely released, the controller reduces the engine torque while gradually reducing the engagement-side clutch torque to be equal to the basic engine torque, to perform an inertia phase such that an engine speed is synchronized with an engagement-side clutch speed.