Automatic Transmission Downshift Torque Control via Third Clutch Modulation
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Solution Overview
Problem
During a coasting downshift event, existing transmission control systems struggle to match driver expectations for output torque and engine speed due to the influence of clutch torque capacity, leading to unexpected vehicle deceleration and engine speed changes.
Innovation Solution
The method involves reducing the torque capacity of the off-going clutch and increasing the oncoming clutch torque capacity during a torque transfer phase, with subsequent modulation of a third clutch's torque capacity based on output torque feedback, and adjusting engine torque based on input speed feedback to maintain desired torque and speed profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the torque capacity of the oncoming clutch is increased to match driver expectations for output torque, then the output torque behavior aligns with expectations, but the engine speed changes become more difficult to control
Solution Approach 1:
The patent segments the control of clutch torque capacity into two distinct phases: a torque transfer phase where the oncoming clutch torque capacity is increased to match driver expectations, followed by a modulation phase where a third clutch (torque converter bypass clutch) is used to control engine speed. This segmentation allows each clutch to be optimized for a specific control objective without the conflicting influences that would exist in a single-clutch system.
Solution Approach 2:
The patent introduces a third clutch (torque converter bypass clutch) as an intermediary device to mediate between the conflicting requirements of output torque control and engine speed control. This intermediary clutch allows the system to decouple the control functions, enabling the oncoming clutch to focus on output torque while the bypass clutch manages engine speed, thereby resolving the control complexity issue.
2Stability of the object's composition
If the torque capacity of the off-going clutch is reduced during the torque transfer phase, then the transition between speed ratios is smoother, but the control of output torque and engine speed becomes more challenging
Solution Approach 1:
The patent segments the clutch control into distinct phases with specific objectives. During the torque transfer phase, the off-going clutch torque capacity is reduced to ensure smooth transition, while the oncoming clutch torque capacity is increased to maintain output torque control. This segmentation allows each clutch's torque capacity to be independently optimized for its specific role in the transition process.
Solution Approach 2:
The patent employs feedback control where the controller monitors transmission output torque and engine speed, and adjusts the torque capacity of the clutches accordingly. The feedback mechanism allows the system to maintain desired output torque and engine speed profiles even as clutch torque capacities are modified during the transition, thereby preserving ease of operation despite the complex torque capacity adjustments.
3Device complexity
If a single clutch is used to control both output torque and engine speed, then the device complexity is reduced, but the control precision for both parameters deteriorates
Solution Approach 1:
The patent segments the control functions between multiple clutches: the oncoming clutch is responsible for output torque control, while the torque converter bypass clutch (third clutch) is responsible for engine speed control. This functional segmentation allows each clutch to be optimized for a specific control parameter, achieving high control precision for both output torque and engine speed without requiring an overly complex single-clutch system.
Solution Approach 2:
The patent dynamically changes the torque capacity parameters of multiple clutches during the downshift event. The controller adjusts the torque capacity of the oncoming clutch to control output torque, while simultaneously adjusting the torque capacity of the bypass clutch to control engine speed. This parameter change strategy allows precise control of multiple parameters through a coordinated multi-clutch system.
Data Source
AI summary
A method of controlling a transmission and engine during a coasting downshift is particularly suited to transmission arrangements exhibiting strong inertia coupling. During the inertia phase of the downshift, a third clutch such as a torque converter bypass clutch is modulated to control output torque. Simultaneously, engine torque is modulated to control engine speed. The resulting control scheme is only semi-coupled.