Lockup Clutch Release During Engine Braking
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Solution Overview
Problem
The disengagement of a lockup clutch in a powertrain during negative engine torque conditions can cause shocks or impulses to the vehicle operator due to the engine's braking action, as existing methods do not effectively manage the transition to minimize these sensations.
Innovation Solution
A method and system where the engine is commanded to a target torque value of zero or near zero during engine braking, and the lockup clutch is released only after a sufficient time has elapsed, allowing for a controlled disengagement by using a coordinated controller system to manage engine and transmission operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the lockup clutch is disengaged during negative engine torque conditions, then the lockup clutch can be released to improve powertrain efficiency, but the operator feels shocks or impulses due to engine braking action
Solution Approach 1:
The controller commands the engine to a target torque value of zero or near zero before releasing the lockup clutch. This preliminary torque adjustment prepares the engine to accept the sudden load change without creating harmful shocks or impulses during clutch disengagement.
Solution Approach 2:
The controller modifies the engine torque parameter by commanding it to a specific target value (zero or near zero) before clutch release. This parameter change ensures the engine is in the optimal state to minimize operator-perceived shocks during the transition.
2Ease of operation
If the engine is held at target torque value for sufficient time, then the lockup clutch can be released smoothly, but the disengagement process takes longer
Solution Approach 1:
The controller applies a partial hold time at the target torque value - sufficient to enable smooth clutch release but not excessively long. This balanced approach achieves smooth disengagement while minimizing the time penalty.
3Productivity
If the lockup clutch is engaged to reduce slip, then powertrain operating efficiency increases, but the operator may perceive the engagement and disengagement operations
Solution Approach 1:
Before clutch engagement, the controller ensures the engine is at the appropriate torque value. This preliminary preparation minimizes the likelihood of operator-perceived shocks or impulses during the engagement transition, while still achieving the efficiency benefits of reduced slip.
Solution Approach 2:
The controller manages engine torque parameters during engagement and disengagement transitions to keep the operator's perception of these operations to a minimum, while maintaining the efficiency benefits of lockup clutch operation.
Data Source
AI summary
A method of releasing a lockup clutch for a fluid coupling assembly disposed between an engine and an automatically shiftable transmission during a negative engine torque mode of operation is provided. The method includes the steps of: A) determining a current engine torque value prior to commanding the engine to ramp to a target engine torque value; B) commanding the engine to a target engine torque value wherein the target engine torque value is one of a zero and near zero value; C) holding the engine at the target engine torque value; and D) releasing or disengaging the lockup clutch when the engine is operating at the target engine torque value. A powertrain is also provided having a controller sufficiently configured to operate according to the method of the present invention.