Characteristic MAP Cooling
Characteristic Map CoolingWater pump
The housing is made of die cast aluminum or plastic and is screw-mounted on the timing case cover. The dual temperature sensor for the coolant is installed in the water pump housing. This dual temperature sensor is located at the point where the coolant flows out of the engine.
Detail view of water pump with dual temperature sensor
Radiator
An engine oil cooler is additionally fitted for specific country variants.
Function of a conventional thermostat
The control of the engine cooling system with a conventional thermostat is determined by the
coolant temperature only. This control system can be subdivided into three operating ranges:
Thermostat closed: The coolant only flows in the engine. The radiator circuit is closed.
Thermostat open: The entire volume of coolant flows via the radiator. This ensures the
maximum cooling capacity available is utilized.
Thermostat control range: A part of the coolant volume flows via the radiator. The
thermostat sets a constant engine inlet temperature within the control range.
With the aid of the characteristic map thermostat, the coolant temperature can now be influenced
specifically within this operating range (thermostat control range).
In this way it is possible to set a higher coolant temperature in the partial load range of the
engine. Higher operating temperatures in the partial load range achieve improved combustion,
reflected in lower fuel consumption and pollutant emission.
However, higher operating temperatures in the full load range would involve specific
disadvantages (ignition timing (angle) reduction due to knocking). For this reason, lower coolant
temperatures are set specifically in the full load range with the aid of the characteristic map
thermostat.
With the aid of this thermostat it is possible to specifically increase the coolant temperature in the
partial load range. By increasing the coolant temperature under these engine operating
conditions, it is possible to reduce fuel consumption. This characteristic map thermostat is
controlled by the engine control module dependent on a characteristic map.
This characteristic map is determined by the following factors:
Engine load
Engine speed
Vehicle speed
Intake temperature
Coolant temperature
Design of the characteristic map thermostat
The characteristic map thermostat is an integral thermostat, i.e. the thermostat and thermostat
cover make up one unit.
The principle mechanical design of the characteristic map thermostat corresponds to that of a
conventional thermostat. However, a heating element is additionally integrated in the expansion
element (wax element).
Cross sectional view of the characteristic map thermostat
The cover of the characteristic map thermostat is made of an aluminum die casting. The electrical
connection for the heating element linked to the expansion element of the characteristic map
thermostat is integrated in the thermostat cover.
Characteristic map thermostat with electrical connection for heating element
Function of the characteristic map thermostat
The characteristic map thermostat is designed such that it opens (engine inlet) at a coolant
temperature at the thermostat of 103oC without intervention of the integrated heating system. Due
to the coolant heating up in the engine, a temperature of approx. 110 ° C is measured at the point
the coolant flows out of the engine (installation location of coolant temperature sensor for [1][2]DME
and instrument cluster gauge). This is the operating temperature of the engine, at which the
characteristic map thermostat begins to open without control intervention.
In the event of control intervention by the DME control module, power (12 V) is applied to the
heating element integrated in the thermostat. Heating the expansion element means that the
thermostat now opens at lower coolant temperatures than would be the case without the
additional heating function (thermostat control range: approx. 80oC - 103oC).
If the coolant temperature exceeds 113oC at the engine outlet, the heating of the characteristic
map thermostat is activated by the [1][2]DME irrespective of the other parameters.
Diagnosis
The line connection and the function of the characteristic map thermostat are monitored by the
diagnosis function in the DME control module. Any faults are stored in the fault code memory of
the DME control module.
Coolant temperature gauge
The indicator characteristics of the coolant temperature gauge in the instrument cluster have
been adapted to the higher temperature level of the engine due to the use of the characteristic
map thermostat.
The pointer of the coolant temperature gauge in the instrument cluster is located in the mid-position
at coolant temperatures of
75 ° C - 113 ° C
in center position.