Hybrid Powertrain Motor Torque Control for Overrunning Synchronization
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Solution Overview
Problem
Hybrid vehicles face challenges in efficiently managing motor torque during overrunning transmission states, particularly when starting the engine, due to limitations in torque control strategies that affect synchronization time and responsiveness.
Innovation Solution
A controller is programmed to limit motor torque below its rated value when the disconnect clutch is disengaged and the speed difference between input and output shafts is below a threshold, and to permit higher torque when the speed difference exceeds the threshold, allowing faster synchronization and reducing engine start time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If torque is limited to buffer-limit value when disconnect clutch is disengaged, then battery state of charge is maintained, but synchronization time increases and responsiveness deteriorates
Solution Approach 1:
The system dynamically adjusts the torque limit based on real-time operating conditions. When the disconnect clutch is disengaged and speed difference is below threshold, torque is limited to buffer-limit value to maintain battery charge. When speed difference exceeds threshold, the torque limit is increased to enable faster synchronization, resolving the contradiction between energy conservation and time efficiency
Solution Approach 2:
The controller changes the torque parameter from buffer-limit value to a higher value based on the speed difference condition. This parameter change allows the system to prioritize synchronization speed when needed while maintaining energy conservation during normal operation
2Reliability
If torque is limited to buffer-limit value during engine start, then engine start reliability is improved, but engine start time increases
Solution Approach 1:
The system dynamically adjusts torque delivery during the engine start process. Initially, torque is limited to buffer-limit value to ensure reliable engine starting. When the speed difference between input and output shafts exceeds the threshold during the start process, the torque limit is increased to reduce synchronization time and shorten overall engine start duration
3Speed
If higher torque is commanded to reduce speed difference, then synchronization speed increases, but risk of torque hole increases
Solution Approach 1:
The controller acts as an intermediary that mediates between the demand for high synchronization speed and the risk of torque hole. It selectively applies higher torque commands only when the speed difference exceeds the threshold, using this intermediate condition to balance the competing requirements of speed and reliability
Data Source
AI summary
A hybrid vehicle includes an engine, an electric machine, a disconnect clutch configured to selectively couple the engine to the electric machine, a transmission having an input shaft operably coupled to the electric machine and an output shaft operably coupled to a driveline, and a controller programmed to, in response to (i) the disconnect clutch being disengaged and (ii) a speed difference between the input and output shafts being less than a threshold, limit torque commanded to the electric machine to a value that is less than a rated torque of the electric machine regardless of driver-demand torque, and further programmed to, in response to (i) the disconnect clutch being disengaged, (ii) a request to start the engine, and (iii) the speed difference exceeding the threshold, permit a torque command to the electric machine that exceeds the value to reduce the speed difference between the input and output shafts.