Engine Cooling
Engine Cooling
The coolant pump is driven by a friction disk. On the N12 engine, a wheel and disk actuating drive. This switches the coolant pump on or off. As a general principle, the coolant pump always runs. If required, the DME can switch off the coolant pump by activating the wheel and disk actuating drive. However, activating only takes place in the warm-up phase when no heat output is requested. The activation is stored in a characteristic map.
Brief description of components
The following components are described for engine cooling:
Electric Fan
The fan in the N12 is 1-stage.
Depending on requirements and the coolant temperature, the DME activates the electrical fan relay. The pressure sensor also influences activation of the air conditioning system.
The electrical fan relay is in the distribution box in the engine compartment.
Coolant-temperature sensor
The coolant temperature sensor records the coolant temperature in the engine cooling circuit. The coolant temperature is one of the measured variables e.g. for the following calculations: fuel injection rate and nominal idle speed.
The coolant-temperature sensor is supplied with ground by the DME. The second connection is connected to a voltage divider circuit in the DME.
The resistor has a negative temperature coefficient (NTC). NTC means that the resistance becomes smaller with increasing temperature.
The resistor is part of a voltage divider circuit that is supplied with 5 Volt by the DME. The electrical voltage at the resistor depends on the air temperature. A table that specifies the associated temperature for each voltage value is stored in the DME. This compensates for the non-linear relationship between electrical voltage and temperature. The resistance changed depending on the temperature from 167 k to 150 , which corresponds to a temperature of -40 °C to 130 °C.
The coolant-temperature sensor is located on the thermostat housing.
Characteristic map thermostat
There is a heating element in the map thermostat.
The map thermostat opens and closes as regulated by a characteristic map. The opening temperature is 105 °C. The map thermostat sets a constant coolant temperature within its control range at the engine inlet.
The map thermostat is supplied with 12 Volts vehicle voltage by the DME. It is activated by the DME on the earth side.
Input variables for the calculation:
- Engine speed
- Load
- Road speed
- Intake air temperature
- Coolant temperature
The DME uses the above input variables to calculate the optimal coolant temperature for each operating point. The optimal coolant temperature is influenced by specific supply to a heated thermostat as well as activation of the electric fan according to requirements.
Wheel and disk actuating drive
On the N12 engine, the coolant pump is driven for the first time by a friction disk. The back of the belt on the belt pulley of the crankshaft drives the frictional wheel. The friction disk drives the coolant pump. This has enabled elimination of a second belt drive.
The wheel and disk actuating drive means that the engine is very short and compact.
The lower lateral forces exerted on the coolant pump shaft mean that the entire housing of the coolant pump can be made of plastic. The fact that the housing is made of plastic has a positive influence on the flow characteristics and supply rate of the coolant pump.
The wheel and disk actuating drive is activated by the DME dependent on characteristic map. The integrated electric motor is supplied with 12 Volts vehicle voltage by the DME. If required, DME switches ground to the wheel and disk actuating drive. When activated, the coolant pump is decoupled from the drive.
System functions
The following system functions are described for the engine cooling:
Engine cooling
The map thermostat opens and closes, regulated by a characteristic map. This regulation can be divided 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 means that the maximum available cooling output is exploited.
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 part-load range of the engine. At higher operating temperatures in the part-load range, friction is reduced. This results in lower consumption and pollutant emissions. During full-load operation, higher operating temperatures involve disadvantages (retarding of the ignition due to knocking). 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 information
NOTE: Vehicles without A/C compressor without belt tensioner.
On vehicles without an A/C compressor, there is no belt tensioner.
No liability can be accepted for printing or other faults. Subject to changes of a technical nature