Hybrid Motor Speed Control via Torque Converter Bypass Clutch
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Solution Overview
Problem
Hybrid-electric vehicles face challenges in accurately controlling torque delivery during transitions, such as engine start, due to inaccuracies in estimating the disconnect clutch capacity, leading to torque delivery errors and perceivable powertrain disturbances.
Innovation Solution
Implementing a controller that switches the electric motor from torque control to speed control, generating torque commands based on the error between measured and estimated speeds of the impeller, using a torque converter with a bypass clutch to manage torque transmission and prevent motor speed spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the electric motor operates in torque control mode, then the torque delivery is simple to control, but torque delivery accuracy deteriorates due to inaccuracies in estimating disconnect clutch capacity
Solution Approach 1:
The patent replaces mechanical torque control with speed control during transition periods. Instead of directly controlling torque through the disconnect clutch (mechanical approach), the system controls the electric motor speed and uses the torque converter's hydraulic characteristics to achieve smooth torque delivery. This substitution eliminates the need to accurately estimate disconnect clutch capacity during transitions.
Solution Approach 2:
The patent changes the control parameter from torque to speed during transition periods. By switching from torque control mode to speed control mode when the bypass clutch is engaged, the system leverages the torque converter's natural torque multiplication characteristics to achieve accurate torque delivery without requiring precise clutch capacity estimation.
2Measurement precision
If the motor switches from torque control to speed control, then torque delivery accuracy improves, but motor speed stability deteriorates due to potential speed spikes
Solution Approach 1:
The patent applies preliminary action by pre-charging the speed estimator before switching to speed control mode. The speed estimator is trained during the torque control phase, and this pre-established estimation is used to initialize the speed control transition, preventing speed spikes and ensuring smooth mode switching.
Solution Approach 2:
The patent implements feedback by continuously monitoring actual motor speed and comparing it with estimated speed. The speed estimator is updated based on the difference between measured and estimated speeds, creating a closed-loop control system that automatically corrects speed deviations and maintains stability during mode transitions.
3Adaptability or versatility
If the bypass clutch is open or slipping, then torque transmission flexibility improves, but powertrain disturbances increase due to torque delivery errors
Solution Approach 1:
The patent replaces direct mechanical torque transmission through the bypass clutch with hydraulic torque transmission through the torque converter. During the transition period when the bypass clutch is open or slipping, the torque converter's fluid coupling provides smooth torque transmission, eliminating the harsh disturbances that would result from mechanical slip.
Solution Approach 2:
The patent introduces the torque converter as an intermediary between the electric motor and the transmission during transition periods. The torque converter's hydraulic fluid acts as a mediator that smoothly transmits torque while accommodating the bypass clutch transition, thereby reducing powertrain disturbances and improving ride comfort.
Data Source
AI summary
A hybrid powertrain includes an engine having a crankshaft, and an electric motor having a rotor selectively coupled to the crankshaft via a disconnect clutch and configured to operate in torque control and in speed control. The powertrain further includes a transmission having a torque converter with an impeller fixed to the rotor, a turbine disposed on an input shaft of the transmission, and a bypass clutch configured to selectively transmit torque from the impeller to the turbine. A controller is configured to, in response to the motor switching from torque control to speed control, generate a torque command for the motor that defines a magnitude derived from an error between measured and estimated speeds of the impeller obtained during torque control to prevent a spike in motor speed when the motor switches from torque control to speed control.