Cooling System: Description and Operation
Engine Cooling
Engine cooling
A turbocharged engine with direct fuel injection makes strong demands on the engine cooling. This is why an additional coolant pump is used for the exhaust turbocharger.
Brief component description
The following components are described for engine cooling:
Electric fan
The fan is 2-stage. There is a separate relay for each fan setting. The two relays are in the engine compartment distribution box.
On the electric fan, a resistor is fitted in the supply lead for stage 1. This reduces the voltage supply of the electric fan in stage 1. In stage 2. the vehicle voltage is fed directly at the electric motor of the electric fan.
The electric fan is controlled by the engine control unit via a pulse-width-modulated signal (evaluation by electronic circuitry in the fan). The engine control unit controls the various radiator fan speeds by means of a pulse-width modulated signal (between 7% and 93%). Pulse duty factors less than 7% and greater than 93% do not trigger activation but rather they are used for fault recognition purposes. The speed of the radiator fan is dependent on the coolant temperature at the coolant outlet (radiator) and the pressure in the air conditioning system. When the cars driving speed increases, the speed of the radiator fan decreases.
Map thermostat and coolant temperature sensor
There is a heating element in the map thermostat. The map thermostat opens and closes, regulated by a characteristic map.
The opening temperature is 105 °C. The mapped thermostat ensures that within its control range a constant coolant temperature is maintained at the engine intake. In driving conditions with low load, the map thermostat sets a high coolant temperature (favorable for consumption). At full load or high engine speed, the coolant temperature is lowered to approx. 85 °C to protect the components.
The coolant temperature sensor is located in the thermostat housing.
The coolant temperature sensor converts the temperature of the coolant - and thus of the engine oil - into an electrical variable (resistance). The coolant temperature is the measured variable for the following calculations, for example: Fuel injection rate and nominal idle speed.
A temperature-dependent electrical resistor is used for temperature sensing. The circuit contains a voltage divider where the resistance can be measured depending on the temperature. A temperature is converted using a characteristic curve specific to the sensor.
Friction-gear servodrive
The coolant pump is driven with a friction gear. The friction-gear servodrive can be enabled (European version). It is switched via an electrical contact.
The back of the belt on the belt pulley of the crankshaft drives the friction gear. The friction gear drives the coolant pump. This means that no second belt drive is necessary. The friction-gear servodrive means that the engine is very short and compact.
The switch-on conditions and switch-off conditions depend on:
- Engine temperature
- Ambient temperature
- Rotational speed
- Load
Turbocharger coolant pump
The high temperatures mean that the exhaust turbocharger is not only connected to the oil supply but is also integrated in the cooling circuit of the engine.
The engine has an additional coolant pump. The DME control unit switches on the turbocharger coolant pump after stopping the engine, whereby the process is map-controlled. This protects the exhaust turbocharger from thermal overload. The turbocharger coolant pump also cools the exhaust turbocharger at high oil temperatures.
The accumulated heat from the exhaust turbocharger is drawn off via the turbocharger coolant pump, thus counteracting coking of the oil in the bearing positions.
System functions
The following system functions are described for the engine cooling:
Engine cooling
The cooling system consists of coolant cooling and a circuit for engine oil cooling. The branch that leads to the engine oil cooler also cools the exhaust turbocharger.
Overview:
The map thermostat opens and closes, regulated by a characteristic map. This regulating operation can be split into 3 operating ranges:
- Engine cold, map thermostat closed:
The coolant only flows in the engine (short circuit). The cooling circuit is closed. The thermostat is not activated.
- Engine hot, map thermostat open:
The entire volume of coolant flows via the radiator. This results in maximum use of the available cooling power. The thermostat is not activated.
- Control range of the map thermostat:
Part of the coolant flows through the radiator. The map thermostat opens as of 105 °C and maintains a constant coolant temperature. In this operating range, the map thermostat can now be used to influence the coolant temperature specifically. This enables the setting of a higher coolant temperature in the partial load range of the engine. At higher operating temperatures in the part-load range, friction is reduced. This in turn leads to reduced consumption and pollutant emissions. During full load operation, certain disadvantages are associated with higher operating temperatures (ignition advance reduction due to knock). For this reason, during full load operation, the map thermostat is used to specifically set a coolant temperature of 85 °C.
Notes for Service department
General notes
NOTICE: Vehicles without air-conditioning compressor, without belt tensioner.
On vehicles without an air-conditioning compressor, there is no belt tensioner.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.