Torque Converter Pressure Control for 8L Transmission Shudder
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Solution Overview
Problem
The 8L(xx) series automatic transmissions experience torque converter shudder due to insufficient converter clutch apply pressure, caused by delayed lockup apply pressure rise and insufficient clamping force, which is not effectively addressed by existing solutions.
Innovation Solution
Re-engineering the hydraulic circuitry with a flow corrected converter clutch control valve and anti-ballooning pressure relief damper assembly, including rescheduling valve sequencing and implementing a torque converter enable valve with non-oscillating pressure output, to enhance converter rear side pressure during switching events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the converter clutch apply pressure is increased to eliminate shudder, then the clamping force becomes sufficient, but the risk of converter ballooning and potential damage increases
Solution Approach 1:
The enable valve begins its regulation cycle before the converter control valve switches, pre-building pressure in the converter clutch apply circuit. This preliminary action ensures that when the clutch engages, sufficient clamping force is immediately available to prevent shudder, while the gradual pressure build-up prevents sudden pressure spikes that could cause ballooning
Solution Approach 2:
The system uses periodic PWM (Pulse Width Modulation) signals to control the enable valve, creating a regulated oscillating pressure output. This periodic action allows the pressure to build up in a controlled manner with built-in damping, preventing both insufficient clamping force and excessive pressure that could cause damage
2Speed
If the lockup apply pressure rise is accelerated to prevent shudder, then the responsiveness improves, but the pressure control stability may deteriorate
Solution Approach 1:
The enable valve starts its regulation cycle before the converter control valve switches, pre-building pressure in the apply circuit. This preliminary pressure build-up accelerates the overall response time while maintaining stability through controlled, gradual pressure increase rather than sudden spikes
Solution Approach 2:
The system uses PWM feedback control to regulate the enable valve, continuously monitoring and adjusting the pressure output. This feedback mechanism maintains pressure control stability while allowing rapid response, as the system can quickly adjust the duty cycle to achieve the desired pressure rise rate without overshooting
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 solution significantly reduces torque converter shudder by ensuring rapid and sufficient clamping force, even at cruising speeds, thereby improving transmission performance and preventing damage.
Implementation Method 1
The converter control valve controls direction of fluid fill into the torque converter. When filled from the front side FS, or engine side, of the damper plate and lockup clutch assembly CA, the clutch is held OFF of the lockup clutch surface
Implementation Method 2
the clutch is held OFF of the lockup clutch surface, inside the front cover, by continual charge at higher pressure than that in the rear side RS, with sufficient volume to maintain a constant flow of automatic transmission fluid (ATF) across the lockup clutch lining as a lubricant and coolant
Data Source
AI summary
Three operational defects in the 8L series transmission, individually or in combination, produce a shudder complaint and potentially damage the torque converter. An incorrectly ported torque converter control valve is corrected by increasing length of an undersized third land to prevent mixing of three adjacent flow channels and a loss of lockup apply pressure. Start time of a torque converter enable valve regulation cycle is rescheduled to avoid causing excessive rear side pressure drop and significantly shortening time required to pressure up apply side of a converter clutch. A lockup solenoid is replaced with an anti-ballooning assembly to better control pressure and avoid complete transmission failure.