Underdrive Accumulator Spring Tuning for 68RFE Clutch Pressure
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Solution Overview
Problem
The DODGE RAM 68RFE automatic transmission's hydraulic circuitry causes excessive pressure on the underdrive clutch in 5th and 6th gears, leading to potential damage and failure due to the underdrive clutch apply pressure exceeding the resilient force of the piston return spring when line pressure is below 139 psi.
Innovation Solution
Replacing the factory-installed high-rate underdrive accumulator spring with a shorter, stronger spring and adding a weaker, flat low-rate waved spring washer to reduce fluid pressure applied to the underdrive accumulator piston, allowing it to move in two stages and maintain pressure below the threshold necessary to overcome the piston return springs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If main line pressure is raised above 139 psi through internal mechanical means or external software manipulation, then the transmission can handle higher load conditions, but the underdrive clutch apply pressure exceeds the resilient force of the piston return spring causing clutch plate destruction and premature failure
Solution Approach 1:
A new intermediary component - a waved spring washer with lower spring rate - is introduced between the accumulator piston and the high-rate spring. This washer acts as a mediator that absorbs excess pressure and prevents it from being transmitted to the underdrive clutch, thereby protecting the clutch while allowing main line pressure to remain high for handling load conditions.
Solution Approach 2:
The patent changes the spring rate parameter of the accumulator spring by replacing the original high-rate spring with a combination of a shorter high-rate spring and a waved spring washer with lower spring rate. This parameter modification ensures that the accumulator apply pressure remains below the threshold that would damage the clutch plates.
2Reliability
If the underdrive clutch is cycled on every 1.7 seconds for 0.1 second to purge air when line pressure is below 139 psi, then air is kept purged from the clutch, but the clutch apply pressure remains insufficient to overcome the piston return spring and apply the clutch
Solution Approach 1:
The patent converts the previously harmful effect of insufficient clutch apply pressure into a beneficial feature. By modifying the accumulator spring combination, the system now maintains pressure below the damage threshold while still achieving sufficient clutch application when needed, transforming the pressure limitation from a defect into a protective characteristic.
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 modification prevents damage to the underdrive clutch by ensuring the fluid pressure applied does not exceed the resilient force of the piston return springs, even when main line pressure rises above 139 psi, thereby extending the clutch's lifespan and ensuring smooth operation.
Implementation Method 1
Replacing the factory-installed high-rate underdrive accumulator spring with a new and shorter high rate accumulator spring and a weaker, flat low rate waved spring washer operatively associated with the stronger, shorter higher rate underdrive accumulator spring for conjointly driving the underdrive accumulator piston
Data Source
AI summary
The hydraulic circuitry of a factory installed automatic automotive transmission is modified to replace an underdrive accumulator spring with a shorter spring and a separate lower rated spring washer operatively associated with the shorter replacement underdrive accumulator spring. The combined replacement spring and spring washer conjointly act on an underdrive accumulator piston to move it in two predetermined distances, in two separate continuous stages, namely, movement of the piston for a first predetermined distance is controlled by the spring washer, while movement of the piston for a second predetermined distance is controlled by the replacement spring. The spring washer has a lower spring rating than the replacement spring, so that less fluid pressure is required to move the piston the total distance traveled, resulting in less fluid pressure applied to an underdrive clutch than in the factory installed transmission. The spring ratings of the replacement spring and the spring washer are selected such that the total fluid pressure required to move the piston both the first and second predetermined distances is less than the fluid pressure required to overcome the resilient force of underdrive piston return springs acting on an underdrive apply piston so that a lower fluid pressure is applied to an underdrive clutch.