In short, the question is: How the EPC affects an automatic transmission?

I'm planning to build an automatic transmission controller module, TCM for 4F27E Ford transmission. So far I haven't found an aftermarket transmission controller that would work for this transmission, hence this project. For now I would like to raise a discussion about EPC. I will then write a control software for the TCM based on what I learn about EPC and other solenoids.

In an automatic transmission, EPC solenoid controls the pressure in the hydraulic circuits affecting the line pressure. There is a steady state pressure, that is the amount of pressure required to hold applied clutches and bands without slipping after the shift has completed and for steady use. The line pressure controls the shift, too low pressure will cause soft and long shifts; too high will cause harsh shift.

Great theory, but...

Question: does the line pressure affects the torque converter? The 4F27E (and similar) has a dedicated solenoid to control the torque converter clutch (TCC) but normally is an on-off solenoid, is it possible achieve the increase of speed with fairly constant RPM, commonly observed in automatic transmission, by varying the EPC? (or this is purely done by the torque converter characteristics?)

Continuing the question: as the theory says, high pressure causes harsh shift. Does the TCM need to action on the EPC to reduce the line pressure to the required level before gear shift?

More: The line pressure varies with the engine RPM (or more precisely, speed of input shaft connected to the hydraulic pump). Does that means the line pressure is function of RPM x EPC x temperature, or there are other variables?


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