Dog Clutch Transmission Coasting Downshift NVH Control
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Solution Overview
Problem
Conventional automatic transmission systems preschedule coast downshifts, which can result in undesirable noise/vibration/harshness (NVH) and shift malfunctions, particularly in dog-clutch transmissions where torque increases are noticeable to the driver and may lead to false malfunction detections due to time-based diagnostic routines.
Innovation Solution
A control and diagnostic system that monitors accelerator pedal position, vehicle speed, and external shift requests to perform coast downshifts only when synchronized with torque generating device speed, disabling shift malfunction timers for dog-clutch operations and enabling them based on driver input or external requests, ensuring non-intrusive downshifts and accurate diagnostics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coast downshift is performed using positive torque from the torque generating device, then the downshift can be completed, but noise/vibration/harshness (NVH) is generated and perceived by the driver
Solution Approach 1:
The system changes the parameter of torque generating device speed by detecting whether it is increasing or decreasing. Based on this parameter change direction, the controller selectively applies different diagnostic approaches (timers vs. NVH thresholds) to resolve the contradiction between ensuring downshift completion and minimizing NVH perception.
2Reliability
If time-based shift malfunction diagnostic routines are used, then shift completion can be monitored, but false malfunction detections occur during coast downshifts
Solution Approach 1:
The diagnostic approach dynamically changes based on operating conditions. The system detects the direction of torque generating device speed change and adaptively selects between time-based diagnostic timers and NVH threshold-based diagnostics, preventing false malfunctions while maintaining accurate shift completion monitoring.
Solution Approach 2:
The system changes the diagnostic parameter from time-based to NVH-based depending on the operating condition. When torque generating device speed is decreasing (coast downshift), NVH thresholds are used instead of time-based timers, eliminating false detections while maintaining diagnostic accuracy.
3Device complexity
If coast downshift is performed without considering driver intent, then automatic transmission control is simplified, but driver dissatisfaction occurs due to undesirable shifts
Solution Approach 1:
The system uses feedback from NVH sensors to detect actual downshift occurrence and compares it with driver intent inferred from torque generating device speed trends. This feedback mechanism allows the system to distinguish between driver-initiated and coast downshifts, maintaining driver acceptance while managing control complexity.
Data Source
AI summary
Systems and methods for a vehicle automatic transmission comprising a dog clutch utilize a set of sensors configured to measure accelerator pedal position, torque generating device speed, and vehicle speed, and a controller configured to detect whether a coast downshift of the transmission to a desired gear ratio and involving the dog clutch is to be performed. In response to detecting that the coast downshift involving the dog clutch is to be performed, the controller determines whether the accelerator pedal has been depressed indicating a request for increased torque generating device speed/torque, when the accelerator pedal is depressed, performs a downshift of the transmission, while the accelerator pedal is not depressed, determines whether a synchronization point of the vehicle speed relative to the torque generating device speed has been reached and when the vehicle/torque generating device speed synchronization point has been reached, performs the downshift of the transmission.