Dynamic Temperature Model of an Automatic Transmission

Abstract

This report presents the development of a dynamic temperature model for an automatic transmission in a Volvo Cars passenger vehicle. The model should simulate the oil to cooler temperature and flow from the transmission. A mathematical approach to use lumped masses for different parts of the transmission was used. These lumped masses were the oil, moving parts and house. To tune the response of the lumped masses and heat transfer coefficients, temperature measurements were used. Some existing measurements at Volvo Cars were tested, but these measurements were not accurate enough. New improved measurements on a vehicle in a chassis dyno were then performed. A decision to do measurements on all eight gears were made since the power losses were different on every gear. However the torque converter was open on the first gear, and could not be closed, which led to the decision to only test the remaining gears since the first gear will only be used during short times during most driving scenarios. To verify the model, simple drive cycles were performed with temperature measurement in the same chassis dyno and on the same vehicle. The verification on the model shows that the model can simulate the behaviour of a transmission with an error of 2.5 °C during normal behaviour and 6.5 °C for a few minutes, when a sudden change in the temperature from the cooler have a large transient increase. Because of this, the model is considered to be fairly accurate. However, in order to make the model compatible with Volvo Cars existing simulation software, Vsim, a "cooler model" has to be created.