Electronically Controlled Cooling
The aim of developing an electronically controlled cooling system was to be able to set the operating temperature of the engine to a specified value based on the load state. An optimal operating temperature is set according to “maps” stored in the Motronic Engine Control Module J220 by heating the thermostat electrically and adjusting the radiator fan settings. Cooling can thus be adapted to the engine’s overall performance and load state.
The advantages of adapting the coolant
temperature to the current operating state
of the engine are:
Changes to the conventional cooling
minimal design modifications.
thermostat are combined to form a single
thermostat on the cylinder head.
contains the maps of the electronically
controlled cooling system
The Coolant Temperature Level
Engine performance is dependent on
proper engine cooling.
In the electronically controlled cooling
system, the coolant temperatures range
from 203°F to 230°F (95°C to 110°C)
in the part-throttle range and from
185°F to 203°F (85°C to 95°C) in the
range improve efficiency, which in turn
reduces fuel consumption and pollutants
in the exhaust gases.
range increase power output. The
inducted air is heated to a lesser degree,
Coolant Thermostat Housing with
Map Controlled Engine Cooling
The Functional Components
wax thermocouple (Map Controlled
Engine Cooling Thermostat F265).
closing the coolant ducts.
The Map Controlled Engine Cooling Thermostat F265 in the coolant distributor housing is always immersed in coolant. The wax thermocouple regulates the thermostat opening temperature unheated as before, but is rated for a different opening temperature. The coolant temperature causes the wax to liquefy and expand, producing a lifting movement of the lifting pin. This normally happens in accordance with the new coolant temperature profile of 230°F (110°C) at the engine cylinder head outlet, without the application of voltage to the heating resistor integrated into the wax thermocouple. When voltage is applied to the heating resistor, it heats the wax thermocouple above the temperature of the surrounding coolant. The adjustment of the lifting pin stroke is then determined not only by the coolant temperature, but also as specified by the map stored in the Motronic Engine Control Module J220.
The Coolant Temperature
Activation of the Map Controlled Engine Cooling Thermostat F265 is regulated by maps to distribute the coolant flow volume between the large and small cooling circuits. The relevant temperature set points are stored in these maps. The pre-control pulse duty factor information is stored in a map. This map is required to determine the coolant temperature set point when the vehicle is at rest with the engine running. The information required for this purpose is obtained by comparing the actual temperature and the specified temperature as factors of engine speed. A temperature constant between 185°F and 230°F (85°C and 110°C) can then be set for the Map Controlled Engine Cooling Thermostat F265 based on engine speed and coolant temperature. In the specified coolant temperature 1 map the temperature setting is calculated from the engine load (determined by measured intake air mass) and engine speed. The specified coolant temperature 2 setting is calculated from temperature set points that are stored based on road speed and intake air temperature in a second map. By comparing maps 1 and 2, the lower value is used by the Motronic Engine Control Module J220 as the set point and the Map Controlled Engine Cooling Thermostat F265 is set accordingly. The Map Controlled Engine Cooling Thermostat F265 is not activated until a temperature threshold has been exceeded and the coolant temperature is just below the set point.
Engine Coolant Temperature (ECT)
Sensor G62 and Engine Coolant
Temperature (ECT) Sensor
(On Radiator) G83
These sensors both operate as negative temperature coefficient (NTC) sensors. The coolant temperature set points are stored in the Motronic Engine Control Module J220 in the form of maps. The actual coolant temperature values are registered at two different points in the cooling circuit and indicated to the Motronic Engine Control Module J220 in the form of a voltage signal.
the cylinder head coolant outlet by
Engine Coolant Temperature (ECT)
Sensor G62 located in the upper level of
the coolant distributor housing.
the radiator by Engine Coolant
Temperature (ECT) Sensor (On Radiator)
G83 before the radiator coolant outlet.
Comparison of the specified temperatures
stored in the maps with the coolant actual
value 1 temperature gives the pulse-widthmodulated
signal for the application of
voltage to the heating resistor in the Map
Controlled Engine Cooling Thermostat F265.
Comparison of the coolant actual values
1 and 2 is the basis for activation of
the electric Coolant Fan V7 and Coolant
Fan -2- V177.
Effects of Failure
If Engine Coolant Temperature (ECT) Sensor G62 fails, a defined substitute value of 203°F (95°C) is used for coolant temperature control and the first fan speed stays activated. If Engine Coolant Temperature (ECT) Sensor (On Radiator) G83 fails, the control function remains active and the first fan speed stays activated. If a certain temperature threshold is exceeded, the second fan speed is activated. If both sensors fail, maximum voltage is applied to the heating resistor in the Map Controlled Engine Cooling Thermostat F265 and the second fan speed stays activated.
Map Controlled Engine
Cooling Thermostat F265
The Map Controlled Engine Cooling Thermostat F265 is the coolant control actuator. A standard expansion-element thermostat without the benefit of electric heating is designed to regulate engine outlet coolant at a specific temperature. The Map Controlled Engine Cooling Thermostat F265 sets the coolant temperature at a designdefined point in much the same way, but the defined set point can be changed to meet the cooling needs of the engine using the available control maps. A heating resistor is integrated into the wax thermocouple expansion element of the Map Controlled Engine Cooling Thermostat F265. Without the application of voltage to the heating resistor, the surrounding coolant temperature causes the wax in the expansion element to liquefy and expand at 230°F (110°C). With an application of voltage, the heating resistor heats the wax above the temperature of the surrounding coolant. The heating wax expands causing the lifting pin to extend in accordance with the map. The positions of the coolant thermostat large and small valve discs are mechanically adjusted by the movement of the lifting pin.Thermostat heating resistor heating is controlled by the Motronic Engine Control Module J220 in accordance with the map by a pulse-width-modulated (PWM) signal. The extent of heating varies depending on pulse width and time.
Effects of Failure
If there is no operating voltage present:
means of the wax thermocouple
Coolant Fan V7 and
Coolant Fan -2- V177
The full-throttle low coolant temperature
mode makes heavy demands on the
To increase its cooling capacity, the
Motronic Engine Control Module J220 can
initiate one of two speed settings for
Coolant Fan V7 and Coolant Fan -2- V177.
Fan control is based on the difference
between the coolant temperatures
measured at the engine outlet and at the
The Motronic Engine Control Module J220
stores the control conditions for the fans in
Both maps are similar to the one shown here, and both are dependent on engine load (intake air mass) and engine speed (rpm). There are three fan operating modes:
Run-on of Coolant Fan V7 and Coolant Fan -2- V177 after the engine is turned off is time and temperature dependent.
Effects of Failure
If a fault occurs in the circuit for the first fan output stage, the second stage is activated. If a fault occurs in the circuit for second fan output stage, the Map Controlled Engine Cooling Thermostat F265 is fully energized as a safety precaution.
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