Hybrid Vehicle Clutch Slip Control for Shift Shock Mitigation
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Solution Overview
Problem
During gear shifts in vehicles, especially when accelerating, a sudden torque bump can cause 'shift shock' due to the mismatch between engine speed reduction and transmission input, which is exacerbated in hybrid electric vehicles by the additional torque from electric motors.
Innovation Solution
A control strategy that uses a clutch to selectively slip when the estimated drive torque after a shift event exceeds the combined available regenerative torque and engine braking torque, reducing engine torque transmission and mitigating shift shock by modulating the clutch's slip based on input speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the clutch is locked during a gear shift, then torque transmission is efficient and power delivery is direct, but a sudden torque bump occurs causing shift shock
Solution Approach 1:
The controller predicts an upcoming shift event based on current operating conditions and proactively commands the clutch to slip before the shift occurs. This preliminary action prepares the drivetrain for the incoming torque bump, allowing the clutch to absorb the shock when it arrives rather than transmitting it directly to the transmission input, thereby reducing shift shock while maintaining overall power transmission efficiency
Solution Approach 2:
The clutch control system dynamically adjusts its state between locked and slipping conditions based on real-time predictions of shift events. The controller continuously monitors operating parameters and modulates clutch engagement accordingly, transitioning from a static locked state to a dynamic controlled-slip state when a shift is anticipated, optimizing both torque transmission and shock reduction
2Object-affected harmful factors
If the clutch slips to reduce torque transmission during a shift, then shift shock is reduced, but torque transmission efficiency decreases
Solution Approach 1:
The clutch is commanded to slip only in advance of predicted shift events rather than continuously, maintaining efficiency during normal operation. The controller uses shift prediction logic to determine when slipping is necessary, keeping the clutch locked during steady-state conditions to preserve torque transmission efficiency while temporarily allowing slip only when needed to mitigate upcoming shift shocks
Solution Approach 2:
The clutch slip is applied partially and temporarily only during the specific window before and during predicted shift events, rather than continuously. This partial action approach minimizes the impact on overall torque transmission efficiency while providing sufficient shock reduction during the critical shift period, achieving the necessary protection without excessive sacrifice of power transmission capability
3Stability of the object's composition
If the clutch is locked continuously, then driveline connection is stable, but torque bumps are transmitted causing disturbances during shifts
Solution Approach 1:
The clutch control system dynamically transitions between locked and slipping states based on predicted shift conditions. During normal operation, the clutch remains locked providing stable driveline connection. When a shift is predicted, the controller dynamically switches the clutch to a controlled-slip state to absorb torque bumps, then returns to locked state after the shift, maintaining stability while eliminating disturbances
Solution Approach 2:
The clutch acts as an intermediary element between the engine and transmission, capable of selectively decoupling them during predicted shift events. This intermediary function allows the clutch to isolate the transmission from engine torque bumps during shifts while maintaining the driveline connection during normal operation, reducing disturbances without sacrificing overall connection stability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces shift shock by managing torque transmission during gear shifts, ensuring a smoother transition and minimizing driveline disturbances, even in hybrid electric vehicles with higher input inertia.
Implementation Method 1
The at least one controller is programmed to slip the clutch when locked in response to a drive torque (that is estimated to be present upon completion of an anticipated shift event) exceeding a combination of available regenerative torque and engine braking torque
Data Source
AI summary
A hybrid electric vehicle includes an engine, an electric motor, a transmission gearbox, and a clutch selectively coupling the engine to the electric motor. Engine speed can drop dramatically when operating at high speeds during a scheduled shift event in the gearbox. To reduce the effects felt by the engine speed change, at least one controller is provided and programmed to slip the clutch when locked in response to a drive torque, estimated to be present upon completion of an anticipated shift event, exceeding available negative torque, such as regenerative torque and engine braking torque.