Thermal management, function

Function requirements for thermal management, general points

 Circuit 87M (engine control ON)

 Engine running

Thermal management, general

The coolant temperature of the engine is regulated by the controlled thermal management from ME-SFI [ME] control unit (N3/10). This has the following advantages:

- The optimum operating temperature is reached faster

- Reduction of the exhaust emissions

- Fuel savings (up to around 4%)

- Improved heating comfort

Thermal management is performed based on the following sensors and signals:

- Coolant temperature sensor (B11/4)

- Charge air temperature sensor upstream of throttle valve (B17/7)

- Charge air temperature sensor downstream of throttle valve (B17/9)

- Pressure sensor downstream of throttle valve (B28/7), engine load

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- Accelerator pedal sensor (B37), accelerator pedal operation (how fast and how far  driver Model calm or sporty)

- Crankshaft Hall sensor (B70) (with direction of rotation recognition), motor rpm

- SAM control unit (N10), outside air temperature via the interior CAN (CAN B) and chassis CAN (CAN E)

- Automatic air conditioning control and operating unit (N22/7), air conditioning system status over interior CAN and chassis CAN

- Electronic Stability Program control unit (N30/4) wheel speed via the chassis CAN

- Fully integrated transmission control unit for dual clutch transmission (Y3/14n4), status of transmission oil temperature via drive CAN (CAN C)

 Transmission oil cooling

The function of the following components is described in more detail partial function "Transmission cooling with transmission oil heat exchanger function":

- Transmission cooling coolant circulation pump relay (F58kO)

- Transmission cooling coolant circulation pump (M13/7)

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Function sequence for thermal management

The thermal management system is described in the following Operation steps:

 Function sequence for post-start phase

 Function sequence for coolant thermostat regulation

 Function sequence for overheating protection

 Function sequence for fan control

Function sequence for post-start phase

In the post start phase the coolant circulation is interrupted through switching off the coolant pump with the aid of a coolant pump switchover valve (Y133).

The coolant pump switchover valve is actuated by the ME-SFI [ME] control unit and applies a vacuum unit on the coolant pump with vacuum.

In this way a linkage is actuated which closes a ball rotary slide located in the coolant stream and therefore the coolant stream to the engine is blocked.

The engine warms up this more quickly due to the missing cooling and the exhaust emissions are reduced.

The coolant pump is switched off for a cold start if the following conditions are fulfilled:

- The coolant temperature is below 85°C.

- The limit value for the charge air temperature stored in the ME-SFI [ME] control unit is not reached yet.

- The engine speed has not exceeded an established limit value of 4000 rpm.

- No "heating" was requested by the automatic air conditioning control and operating unit.

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View of the coolant pump

1 Coolant pump housing

2 Coolant pump vacuum cell

3 Belt pulley

4 Ball rotary slide

The ME-SFI [ME] control unit ends actuation of the coolant pump switchover valve if the conditions for shutoff of the coolant pump is no longer fulfilled. The switchover valve is ventilated over the ventilation connection.

The vacuum unit opens the ball rotary slide through spring support and allows the coolant stream to the engine again. Therefore the coolant pump is switched off and the coolant circulation is re-established.

Function sequence for coolant thermostat regulation

Opening and closing of the ball rotary slide in the coolant thermostat occurs through stretching or contraction of the expanding wax element influenced by the temperature in a temperature range of about 98°C to 108°C.

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Furthermore opening and closing of the coolant thermostat can be performed variably and dependent on the requirements on the engine through actuation of the coolant thermostat heating element (R48).

To do this the ME-SFI [ME] control unit actuates the coolant thermostat heating element dependent on the characteristic field by means of a ground signal. The voltage is supplied through circuit 87 M2

The coolant thermostat can take the following positions:

 CLOSED

 Opening (mixed-fuel mode)

 Open (cooler operation mode)

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CLOSED

The ball rotary slide for the coolant thermostat is closed if the following conditions are fulfilled:

- Coolant temperature below about 98°C.

- Coolant thermostat heating element deenergized

- No full load requirement

In this position the coolant flows through the engine circuit and also the heater heat exchanger as required. The engine radiator is not integrated into the coolant circuit. The coolant is heated up more quickly this way.

Through more rapid heating up the engine reaches its operating temperature quicker which has a favourable effect on the fuel consumption and the emissions.

Opening (mixed-fuel mode)

The ball rotary slide begins to open if one of the following conditions is fulfilled:

- Reaching a coolant temperature of about 98°C for the first time after the start (no full load request)

- The coolant thermostat heating element is energized

Within a temperature range of the coolant of about 98°C to about
108°C or according to energization of the coolant thermostat heating element, the expanding wax element begins to expand and actuates the ball rotary slide. This frees up the connection to the engine radiator. The opening cross-section of the ball rotary slide is adapted according to the temperature of the expanding wax element or the coolant temperature. In this way the coolant stream to the engine radiator.

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View Coolant thermostat closed

48 Coolant thermostat housing

48a Expanding wax element

48b Ball rotary slide

R48 Coolant thermostat heating element

A from engine

B to engine radiator

C to heater heat exchanger

Open (cooler operation mode)

When exceeding a coolant temperature of about 108°C the ball rotary slide is completely opened and the coolant can flow unimpeded through the engine radiator.

For a coolant temperature >85°C and a full load request also opens the ball rotary slide completely through heating of the expanding wax element.



The expanding wax element is heated by the coolant thermostat heating element.

The coolant temperature is lowered under the following conditions to prevent critical temperature ranges from occurring:

- intake air temperature >38°C

- engine speed >3000 rpm

- engine load > 30%

The coolant temperature is lowered in the process dependent on the outside air temperature through heating of the expanding wax element. For an outside air temperature <12°C up to 90°C and for an outside air temperature >12°C up to 80°C

P20.10-2325-76

View Coolant thermostat opened

48 Coolant thermostat housing

48a Expanding wax element

48b Ball rotary slide

R48 Coolant thermostat heating element

A from engine

B to engine radiator

C to heater heat exchanger

Function sequence for overheating protection

In case of thermal overload, the overheating protection protects against engine damage and overheating damage to the catalytic converter.

The following measures are taken as overheating protection:

- Characteristic map-dependent ignition timing adjustment in the direction "retarded", dependent on the engine load and rotational speed, as of a coolant temperature from about 90°C and a charge air temperature of about 20°C

- Reduce opening of the throttle valve actuator (M16/6), dependent on the engine load and rotational speed

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- Shortening of the injection time of the fuel injectors (Y76) or shortening of the injection time of the gas injection valves gas (Y106) according to the lower air mass

- Actuation of the coolant thermostat heating element by the ME-SFI [ME] control unit for full opening of the ball rotary slide in the coolant thermostat



If the coolant temperature is too high, a warning message is shown in the multifunction display (A1p13) on the instrument cluster (A1). For this purpose, the ME-SFI [ME] control unit transmits the appropriate signal over the chassis CAN to the instrument cluster.

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Function sequence for fan control

The ME-SFI [ME] control unit actuates the fan motor (M4/7). The specified fan speed is set by the ME-SFI [ME] control unit with a pulse width modulated signal (PWM signal).

The duty cycle of the PWM signal is 10 to 90%.

This means, for example:

10% Fan motor "OFF"

20% Fan motor "ON", minimum rpm

90% Fan motor "ON", maximum rpm

If actuation is faulty, the air fan rotates at the maximum rotational speed (fan emergency mode). Its status is transmitted to the fan motor as a ground signal over the actuation line.

Delayed fan switch off

With "ignition OFF", the fan motor runs on for up to 5 min. if the coolant temperature or engine oil temperature (calculated from the temperature model) has exceeded the specified maximum values.

The PWM signal duty cycle is 40% maximum while the delayed fan switch-off is active. If the battery voltage drops too much during this time, delayed fan switch-off is stopped.

P20.10-2326-79

1 Radiator

2 Coolant expansion reservoir

3 Coolant/transmission oil cooler

4 Turbocharger

5 Coolant pump

6 Engine 270

7 Engine oil/coolant heat exchanger

A Coolant return for low-temperature cooling circuit

B Coolant return to engine

C Coolant feed

D Coolant circuit ventilation

8 Coolant thermostat

9 Heater heat exchanger

M13/5 Coolant circulation pump (with code (581) Comfort automatic air conditioning)

M13/7 Transmission oil cooling coolant circulation pump