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Heat Management
The engine control unit of the N54 engine controls the coolant pump according to
requirements:
• Low output in connection with low cooling requirements and low outside
temperatures
• High output in connection with high cooling requirements and high outside
temperatures
The coolant pump may also be completely switched off under certain circumstances,
e.g. to allow the coolant to heat up rapidly during the warm-up phase. However, this only
occurs when no heating is required and the outside temperature is within the permitted
range.
The coolant pump also operates differently than conventional pumps when controlling
the engine temperature. To date, only the currently applied temperature could be
controlled by the thermostat.
The software in the engine control unit now features a calculation model that can take
into account the development of the cylinder head temperature based on load.
In addition to the characteristic map control of the thermostat, the heat management
system makes it possible to use various maps for the purpose of controlling the coolant
pump. For instance, the engine control unit can adapt the engine temperature to match
the current operating situation.
This means that four different temperature ranges can be implemented:
• 108°C ECO mode
• 104°C Normal mode
• 95°C High mode
• 90°C High + map-thermostat mode
The control system aims to set a higher cylinder-head temperature (108°C) if the engine
control unit determines ECO (economy) mode based on the engine performance.
The engine is operated with relatively low fuel consumption in this temperature range as
the internal friction is reduced.
An increase in temperature therefore favors slower fuel consumption in the low load
range. In HIGH and map-thermostat mode, the driver wishes to utilize the optimum
power development of the engine. The cylinder-head temperature is reduced to 90°C for
this purpose. This results in improved volumetric efficiency, thus increasing the engine
torque. The engine control unit can now set a certain temperature mode adapted to the
respective operating situation. Consequently, it is possible to influence fuel
consumption and power output by means of the cooling system.
The temperatures specified only ever represent a target value, the attainment of which is
dependent on many factors. These temperatures are first and foremost not attained
precisely.
The consumption-reducing and power increasing effects arise in each case in a
temperature spectrum. The function of the cooling system is to provide the optimal
cooling output according to the boundary conditions under which the engine is being
operated.
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