Torque Converter Impeller Clutch for NVH Reduction
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Solution Overview
Problem
Rolling start/stop systems in vehicles with automatic transmissions and conventional torque converters result in objectionable noise, vibration, and harshness (NVH) due to the engine remaining connected to the drivetrain, which affects fuel economy and drivability.
Innovation Solution
Implementing an impeller disconnect clutch in the torque converter, controlled by a vehicle controller to disengage and reengage the impeller from the engine based on brake pressure and vehicle speed thresholds, allowing for seamless engine stop and start operations without continuous drivetrain engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the engine remains connected to the drivetrain during rolling auto stop, then the engine can quickly restart when power is needed, but this results in objectionable noise, vibration, and harshness (NVH)
Solution Approach 1:
The torque converter is segmented into two independent connections: the impeller clutch connects the impeller to the engine, while the bypass clutch connects the impeller to the turbine. This segmentation allows the engine to be disconnected from the drivetrain during auto stop while maintaining the ability to quickly reengage, resolving the contradiction between quick restart capability and NVH reduction.
2Object-affected harmful factors
If the transmission is shifted into neutral to mitigate NVH during engine stop, then NVH is reduced, but this requires rapid reengagement when power is demanded which may result in a shift bump
Solution Approach 1:
The impeller clutch acts as an intermediary mechanism between the engine and the drivetrain. By engaging or disengaging this clutch, the system can smoothly connect or disconnect the engine from the drivetrain without requiring a neutral shift, thereby avoiding shift bumps while still reducing NVH during engine stop.
3Use of energy by moving object
If the engine is stopped during rolling auto stop to improve fuel economy, then fuel consumption is reduced, but engine drag during deceleration increases
Solution Approach 1:
The impeller clutch is dynamically controlled based on operating conditions. During deceleration when brake pressure exceeds a threshold and vehicle speed is above a threshold, the clutch disengages to eliminate engine drag. When vehicle speed drops below a threshold, the clutch reengages to allow the engine to drive the vehicle, optimizing the balance between fuel economy and propulsion needs.
4Use of energy by moving object
If the impeller clutch is disengaged during rolling auto stop, then engine drag is reduced and fuel economy improves, but the complexity of the torque converter system increases
Solution Approach 1:
The impeller clutch integrates multiple functions into a single component: it disconnects the engine from the drivetrain during auto stop to reduce drag and improve fuel economy, while also enabling smooth reengagement without shift bumps. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in system complexity.
Data Source
AI summary
A system and method for operating an automatic start/stop system in a motor vehicle having an internal combustion engine, an automatic transmission and a torque converter with an impeller disconnect clutch is disclosed. A controller may implement an engine start/stop system by, at appropriate times, stopping engine by halting fuel and restarting engine when propulsion is needed. During an engine start/stop event, the engine is automatically shut down and the impeller clutch of the torque converter may be disengaged to decouple the impeller and the engine to provide for fuel and emissions savings.