ISG Speed Hold for Smooth Hybrid Engine Restart
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Solution Overview
Problem
Restarting an engine in a hybrid vehicle after shutdown can be challenging due to driveline torque disturbances and noise, especially when using an integrated starter/generator (ISG) to maintain engine idle speed.
Innovation Solution
Inhibiting the stopping of the ISG rotation after an engine shutdown request is made, while the vehicle is stopped and the engine speed is above a threshold, allows the ISG to maintain a steady speed, enabling smoother engine restarts by closing the driveline disconnect clutch without torque disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the ISG is stopped after engine shutdown request, then energy consumption is reduced, but engine restarting consistency deteriorates and driveline torque disturbances increase
Solution Approach 1:
The patent applies dynamics by making the ISG operational state dynamic rather than static. The ISG maintains rotation during engine restart rather than being completely stopped, creating a dynamic transition state that allows smooth engine restarting while minimizing energy consumption. This resolves the contradiction by finding an optimal dynamic operating point between complete stop (low energy, poor restart consistency) and continuous operation (high energy, good restart consistency).
Solution Approach 2:
The patent changes the operational parameters of the ISG by maintaining its rotational speed within a specific range during engine shutdown and restart. Instead of binary stop/start control, the system adjusts the ISG speed parameter to maintain rotation above a threshold during restart, improving engine starting consistency while managing energy consumption through controlled parameter adjustment.
2Device complexity
If the ISG is stopped after engine shutdown request, then system simplicity is maintained, but driveline noise and vibration increase
Solution Approach 1:
The patent applies preliminary action by preparing the ISG to maintain rotation before the actual engine restart occurs. The control system anticipates the restart need and keeps the ISG rotating at an appropriate speed, so when restart is commanded, the driveline is already in a favorable state, preventing noise and vibration rather than correcting them afterward.
3Stability of the object's composition
If the ISG maintains steady speed during engine restart, then driveline torque disturbances are reduced, but energy consumption increases
Solution Approach 1:
The patent applies partial action by maintaining ISG rotation only to the extent necessary for smooth engine restarting, rather than continuous full operation. The ISG speed is maintained above a threshold during restart critical periods, providing sufficient torque stability, then allowed to decelerate when not needed, balancing energy consumption with driveline stability requirements.
Data Source
AI summary
Systems and methods for operating a hybrid vehicle are presented. In one example, an integrated starter/generator (ISG) is operated in a speed control mode after an engine stop request. The ISG is prevented from stopping while engine rotational speed is greater than a threshold engine rotational speed so that the engine may be restarted via the ISG.