Dynamic Control of the Coolant Temperature for a Reduction of Fuel Consumption and Hydrocarbon Emission

Conventional expansion-element thermostats allow a fixing of only one coolant temperature level. This results in significantly different temperatures of the components which are near the combustion chamber depending on the load and rpm state of the engine. The fuel consumption and the emission are increased.

Therefore a requirements-adapted cooling control is suggested. The main challenge for the development of such a system is to get an attractive proportion of cost and benefit. For the expense of the actuator the motor is dominant. For this reason a valve was chosen which integrates the regulation of the radiator circuit, the bypass and the heat exchanger circuit in one part. A control algorithm was developed which can be easily integrated in the engine management and is supplied from existing sensors.

Dynamic tests show that a sufficient fast regulation of the coolant temperature is possible with the realized system. Therefore higher coolant temperatures in part load range do not lead to excessive component temperature when sudden full load is required. Measurements on different engines prove that a fuel reduction of one to three percent is possible in the FTP 75-test cycle by an increased coolant temperature in part load range.

For modem engine the warm-up is decisive for the emissions in the test cycles. The realized system also allows to reduce the warm-up period of the coolant up to 50% with positive effects on fuel consumption and hydrocarbon emission.