Torque Converter Lockup Clutch Control for Downshift Quality
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Solution Overview
Problem
Existing vehicle drive train systems face issues with shift quality and ride comfort during speed-controlled downshifts due to incorrect actuation pressure of the torque converter lockup clutch, leading to inadequate damping or decoupling between the prime mover and driven end.
Innovation Solution
A method for operating a vehicle drive train that involves disengaging a shift element from the power flow, guiding the torque converter lockup clutch into a non-slip condition during engine override, and transitioning to continuous slip operation at synchronous speed, using a control unit to manage power transmission capacity and avoid hydrodynamic losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the torque converter lockup clutch is actuated with high pressure during downshift, then the coupling between impeller and turbine is strengthened, but the damping or decoupling function of the hydrodynamic torque converter is lost, adversely affecting shift quality and ride comfort
Solution Approach 1:
The patent applies dynamics by transitioning the torque converter lockup clutch from a static high-pressure engaged state to a dynamic controlled slip state during downshift. The clutch is actuated with reduced pressure to maintain partial slippage, enabling the hydrodynamic torque converter to provide necessary damping while still maintaining coupling. This dynamic pressure control allows the system to adapt between coupling reliability and shift quality based on operational phase.
Solution Approach 2:
The patent changes the actuating pressure parameter of the torque converter lockup clutch from high (engaged state) to reduced (slip state) during downshift operations. This parameter change enables the clutch to operate in a transitional slip mode rather than full engagement, preserving the hydrodynamic damping characteristics of the torque converter while maintaining sufficient coupling for controlled downshift execution.
2Loss of energy
If the torque converter lockup clutch is kept in non-slip condition during engine override, then power transmission efficiency is improved, but the ability to provide damping during speed changes is reduced
Solution Approach 1:
The patent applies periodic action by alternately switching the torque converter lockup clutch between slip state and non-slip state based on operational requirements. During engine override and speed transitions, the clutch operates in slip mode to provide damping. During steady-state operation, it transitions to non-slip mode to eliminate hydrodynamic losses. This periodic switching optimizes energy efficiency while maintaining adaptability across different operating conditions.
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 ensures high shift quality by accelerating rotational speeds, overcoming drag torques, and achieving desired decoupling, thereby improving shift quality and reducing power losses, allowing for efficient operation with minimal discontinuities in power transmission.
Implementation Method 1
a hydrodynamic torque converter (3) including an associated torque converter lockup clutch (4)
Implementation Method 2
The torque converter lockup clutch (4) is provided for coupling an impeller to a turbine wheel of the hydrodynamic torque converter (3)
Data Source
AI summary
A method for operating a vehicle drive train (1) includes, during a downshift, disengaging at least one shift element (A through F) from a power flow of the transmission (5), guiding a power transmission capacity of a torque converter lockup clutch (4) to a level at which the torque converter lockup clutch (4) is in a non-slip operating condition during a positive engine override when a rotational speed of a prime mover (2) is guided towards a synchronous speed of a demanded desired ratio, and guiding the power transmission capacity of the torque converter lockup clutch (4)—no later than a point in time of the downshift at which the rotational speed of the prime mover (2) is equal to the synchronous speed of the desired ratio—to a level at which the torque converter lockup clutch (4) is transferred into a continuous slip operation due to torque.