Lockup Clutch Control for Automatic Transmission Judder
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Solution Overview
Problem
Automatic transmission systems with torque converters and lockup clutches experience judder vibrations due to variations in frictional states between input and output elements, particularly during transitions to lockup states, leading to inefficient torque transmission and potential shock.
Innovation Solution
A control device for automatic transmissions that includes a torque converter with a lockup clutch, featuring a control system that adjusts the engagement state and transmission gear ratio based on vehicle travel state, rotation speed differences, and engine torque, prohibiting transmission gear ratio control during initial engagement to stabilize the rotation speed difference and adding torque transmission capacity when necessary to manage frictional variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lockup clutch is engaged from disengagement state, then the rotation speed difference is decreased and full engagement is achieved, but judder vibration is generated due to friction coefficient variation
Solution Approach 1:
The control device performs preliminary slip engagement control before full lockup clutch engagement. The slip engagement control gradually reduces the rotation speed difference between input and output elements while managing the frictional state transition, preventing sudden friction coefficient changes that cause judder vibration. This preliminary action prepares the clutch for smooth full engagement.
Solution Approach 2:
The control device dynamically adjusts the engagement control strategy based on the current state of the lockup clutch. During slip engagement, the control continuously monitors rotation speed difference and adjusts engagement pressure to maintain optimal frictional state, transitioning smoothly from slip to full engagement while minimizing vibration.
2Power
If the accelerator is depressed during slip engagement to increase engine torque, then the vehicle acceleration is improved, but the transmission torque capacity becomes deficient and judder vibration occurs
Solution Approach 1:
The control device monitors engine torque demand and rotation speed difference in real-time during slip engagement. When accelerator depression increases engine torque, the feedback control adjusts engagement pressure to maintain sufficient torque transmission capacity, preventing the deficiency that leads to judder vibration while still allowing vehicle acceleration.
Solution Approach 2:
The control device changes engagement pressure parameters dynamically based on engine torque conditions. When high torque is demanded during slip engagement, the control increases engagement pressure to maintain adequate torque transmission capacity, preventing the capacity deficiency that causes judder while enabling vehicle acceleration.
3Loss of time
If the lockup clutch is rapidly engaged to improve fuel consumption, then the response time is reduced, but the torque shock is increased
Solution Approach 1:
The control device performs preliminary slip engagement before full lockup clutch engagement. This preliminary slip phase gradually reduces the rotation speed difference and prepares the frictional interface, enabling subsequent full engagement to occur with minimal torque shock while maintaining relatively fast overall response time.
Solution Approach 2:
The slip engagement control acts as a cushioning phase before full lockup engagement. During this phase, the control manages the frictional state transition and rotation speed difference reduction, cushioning against the potential torque shock that would occur during sudden full engagement.
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
The control device effectively stabilizes the engagement process, reducing judder vibrations by managing frictional state variations and ensuring smooth lockup of the clutch, even during increased engine torque conditions, thereby improving transmission efficiency and reducing vibration.
Implementation Method 1
a torque converter 2 having a lockup clutch 20 disposed between an input element 11 and an output element 21
Implementation Method 2
a lockup clutch 20 disposed between an input element 11 and an output element 21 of the torque converter 2
Data Source
Figure 1
Figure 2(a)~2(e)
Figure 3(a)~3(h)
AI summary
When a torque converter (2) is being switched from a slip engagement state to a full engagement state as a result of an ON operation of an accelerator, during the execution of control that achieves the full engagement state after increasing the rotation of an internal combustion engine (1) in the slip engagement state while expanding the torque transmission capacity of a lockup clutch (20) by means of slip engagement, if it is determined that there has been a gain in the output torque of the internal combustion engine (1) when, within a prescribed period of time after the beginning of the control, the detected input/output differential rotation speed of the lockup clutch (20) is at or below a second prescribed value (ΔN2) that is smaller than a first prescribed value (ΔN1) after having increased to or above the first prescribed value, a prescribed capacity is added to the expanding torque transmission capacity of the lockup clutch (20). It is possible to avoid judder variation caused by the release of an accelerator pedal during a transition to a lockup state.