Engine coolant heat management function

P07.70-2148-79

1 to radiator

2 from engine

3 to engine

18 Oil/water heat exchanger

A1 Instrument cluster

B2/5 Hot film mass air flow sensor

B11/4 Coolant temperature sensor

B70 Crankshaft Hall sensor

A Full throttling

B Short-circuit mode position

C Mixed fuel mode position

D Maximum radiator operation position

M4/7 Engine and AC electric suction fan with integrated control

N3/10 ME-SFI [ME] control unit

N47-5 ESP control unit

Y16/2 Heating system shutoff valve

Y110 Three-disk thermostat valve

Y125 Low temperature cooling system shutoff valve

CAN Data bus

Heat management controls the coolant temperature of the engine. Advantages are

 The operating temperature is reached more rapidly

 Emissions reduced

 Fuel savings up to around 4%

 Improved heat comfort.

Heat management is dependent on the following input signals:

 Coolant temperature

 Engine load

 Engine speed

 Outside air temperature

 Intake air temperature

 Actuation of the suction fan

 Vehicle speed

 Driver type (quiet or sporty).

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Depending on the operating conditions, the ME-SFI [ME] control unit actuates the heater element in the three-disk thermostat depending on performance mapping via a ground signal. The voltage is supplied to the three disk thermostat via circuit 87. The coolant temperature is regulated between 80°C and 100°C via the duty cycle.



If the coolant temperature is too high, the coolant temperature warning lamp in the instrument cluster is actuated. To do this, the ME-SFI [ME] control units sends a CAN command to the instrument cluster.

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Full throttle position (A)

For a cold start the three-disk thermostat is not actuated and also for a switched off vehicle heating the coolant circuit is closed via the heating system shutoff valve and the low temperature cooling system shutoff valve. The standing coolant now warms up very quickly. Heat is sent from the engine oil via the heat exchanger at the front of the engine.

At a coolant temperature from around 70°C or from around 45°C (with outside temperature above around 12°C), switching from full throttle to short-circuit operation takes place. In addition, the closing disk opens due to pressure via the running coolant pump over around 3500 rpm.

Short-circuit operation position (B)

Short-circuit operation with the engine and heat exchanger can be throttled so that the heater responds more rapidly.

Mixed fuel operation position (C)

Temperature regulation with the three-disk thermostat is not enabled until the coolant temperature following start reaches around 98°C. At outside temperatures above around 12°C it is active immediately.

At partial load, the three-disk thermostat regulates at an increased coolant temperature of around 100°C.

To prevent critical temperatures, the increased coolant temperature range is reduced under the following conditions to around 90°C (with outside temperature below 12°C) or to around 80°C (with outside temperature over 12°C):

 Engine speed greater than 3000 rpm

 Engine load more than 30 %

 Intake air temperature more than around 38°C

 Sporty driver detected.

Maximum radiator operation position (D)

The three-disk thermostat is actuated constantly during radiator operation. Above around 110°C, the three-disk thermostat is always fully opened independently of actuation (emergency operation function).

P20.00-2325-79

Schematic diagram of engine cooling

1 Cap

2 Coolant expansion reservoir

3 Radiator

5 Coolant pump

7 Oil/water heat exchanger

8 Heater heat exchanger

12/1 Exhaust gas recirculation connecting pipe to intake manifold (cooled)

27 Fuel cooler

110/11 Low temperature radiator

A32 Heating systems recirculation unit

M13 Heating water circulation pump

M16/45 EGR [ARF] actuator motors

N3/10 ME-SFI [ME] control unit

Y16/2 Heating system shutoff valve

Y110 Three-disk thermostat valve

Y125 Low temperature cooling system shutoff valve

A Coolant return flow

B Coolant feed

C Vent line

S Heated windshield washer fluid reservoir

The cooling system is adapted as follows to the direct injection

:

 Coolant is led from the engine radiator to the low temperature cooling system shutoff valve from the coolant return.

 With an open shutoff valve part flows for cooling directly to the EGR [ARF] actuator motors and to the exhaust gas recirculation connecting pipe at rear on the intake manifold.

 The other part is further cooled in the low temperature radiator by the airstream and supplies the ME-SFI [ME] control unit and the fuel cooler.

The fuel cooler limits the fuel temperature to

approx. 70°C. The output stages for fuel injectors generate much heat in the ME-SFI [ME] control unit which must be dissipated.

The coolant in the low-temperature cooling system is carried around by the coolant pump and does not need extra purging.

Actuation of the low temperature cooling system shutoff valve is dependent on the following operating conditions:

 Fuel temperature

 Temperature in the ME-SFI [ME] control unit (integral temperature sensor)

 Exhaust gas recirculation rate.