Electronically Controlled Cooling
System Overview

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.

Advantages

The advantages of adapting the coolant temperature to the current operating state of the engine are:

Lower fuel consumption in the partthrottle
range.

Reduced raw CO and HC emissions.

Changes to the conventional cooling
circuit include:

Integration in the cooling circuit through
minimal design modifications.

The coolant distributor housing and
thermostat are combined to form a single
module.

There is no longer any need for a coolant
thermostat on the cylinder head.

Motronic Engine Control Module J220
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 full-throttle range.

Higher temperatures in the part-throttle
range improve efficiency, which in turn
reduces fuel consumption and pollutants
in the exhaust gases.

Lower temperatures in the full-throttle
range increase power output. The
inducted air is heated to a lesser degree,
boosting performance.

 

Coolant Thermostat Housing with
Map Controlled Engine Cooling
Thermostat F265

The Functional Components

 

An expansion-element thermostat with a
wax thermocouple (Map Controlled
Engine Cooling Thermostat F265).

Resistance heating in the wax
thermocouple.

Pressure springs for mechanically
closing the coolant ducts.

One large valve disc and one small
valve disc.

Function

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
Set Points

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.

Coolant actual value 1 is measured at
the cylinder head coolant outlet by
Engine Coolant Temperature (ECT)
Sensor G62 located in the upper level of
the coolant distributor housing.

Coolant actual value 2 is measured at
the radiator by Engine Coolant
Temperature (ECT) Sensor (On Radiator)
G83 before the radiator coolant outlet.

 

Signal Utilization

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:

Thermostat control takes place only by
means of the wax thermocouple
expansion element.

The first fan speed is continuously
activated.

 

Coolant Fan V7 and
Coolant Fan -2- V177

The full-throttle low coolant temperature mode makes heavy demands on the cooling system. 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 radiator outlet. The Motronic Engine Control Module J220 stores the control conditions for the fans in two maps:

Temperature difference for fan, first
speed.

Temperature difference for fan, second
speed.

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:

Off.

On, first speed.

On, second speed.

Run-On

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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