Variable line-fluid pressure (VLP) transmissions

variable line pressure transmissionTransmissions with variable line-fluid pressure (VLP) frequently adjust their internal fluid pressure to reduce parasitic losses from the pump and hydraulic system, increasing gas mileage and lengthening the transmission lifespan.

VLP was phased in throughout the Chrysler four-speed automatics, both car and truck versions, in model-year 2006 (actual production started in late 2005). In the first year, rear wheel drive automatics connected to the 2.7 liter and 3.7 liter V6 engines gained it; in 2007, all Chrysler transmissions used it.

The first related patent Allpar could find was issued to DaimlerChrysler (Auburn Hills, indicating Chrysler Group development) — patent 6,471,613 was issued for a regulator valve system with a variable force solenoid.

The inventors, Valentin Botosan and Berthold Martin, wrote that the ideal was to maintain a lower transmission fluid pressure without letting the clutch slip, because it increases both gas mileage and the transmission’s lifespan. However, increased pressure is needed in low gears or under load, for better clutch-holding capability.

Choosing the desired line pressure was based on the output of input and output speed sensors, which combined provided an indication of clutch slip. The powertrain control module (engine computer) considered this information as well as the throttle angle and engine torque, so that under higher torque, higher throttle (indicating a forthcoming increase in torque), or clutch slip, pressure could be quickly raised.

In February 2006, Botosan and Martin filed another patent, this time for a revised hydraulic control system, still relying on a line pressure regulating valve activated by a solenoid.

Their initial work was refined over time, and June 2006, three other Chrysler engineers filed a patent for adaptive fluid pressure control. Weijia Cui, Gary K. Lowe, and Daniel H. Black set up a system which also considered transmission fluid temperature, engine speed, and battery voltage, so that fluid pressures would be set according to a table (open loop) or feedback (closed loop) depending on conditions. This refinement was most likely developed based on durability and driveability feedback.

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