Thermal management, function - GF07.10-P-1012MMC

ENGINES 157.9 in MODEL 216.3, 221.0/1

ENGINES 278.9 in MODEL 216.3, 221.0/1

Function requirements for thermal management, general points

Circuit 87M (engine timing unit ON)
Engine running

Thermal management, general points

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 gas emissions
Fuel savings (up to around 4%)
Improved heat comfort.
Optimal main combustion point for a high load

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

Coolant temperature sensor (B11/4)
Intake air temperature sensor (B17)
Pressure sensor downstream of throttle valve actuator (B28/7), engine load
Accelerator pedal sensor (B37), accelerator pedal operation (how fast and how far driver type calm or sporty)
Oil sensor (oil level, temperature and quality) (B40) (for engine 157)
Crankshaft Hall sensor (B70), engine speed
Temperature sensor in the ME-SFI [ME] control unit
AAC control unit (N22/1), status of the A/C and outside air temperature via the interior CAN (CAN B) and chassis CAN (CAN E)
ESP control unit (N47-5), wheel speed via the chassis CAN
Electric controller unit (VGS) (Y3/8), status of the transmission oil temperature via the drive train CAN (CAN C)

Function sequence for thermal management

The thermal management system is described in the following steps:

Function sequence for heating system switch-off up to 05/2011
Function sequence for two-disk thermostat heating
Function sequence for fan control
Function sequence for overheating protection

Function sequence for heating system switch-off up to 05/2011

To heat up the engine more quickly, the ME-SFI control unit switches off the heating system coolant circuit by actuating the heating system shutoff valve (Y16/2).

Function sequence for two-disk thermostat heating

The coolant temperature in the engine can be varied by the two-disk heated thermostat. For this purpose, the two-disk thermostat contains the two-disk thermostat heating element (R48), which adjusts the thermostat disc positions as needed and actuated for this by the ME-SFI [ME] control unit by means of a ground signal.

The two-disk thermostat can be set to three positions:

Bypass mode
Mixed mode
Cooler mode

Two-disk thermostat positions

Fig 1: Engine Coolant Flow Diagram

Courtesy of MERCEDES-BENZ USA

Short-circuit operation position

Heating element de-energized Coolant temperature <100°C Heating element energized Coolant temperature <65°C

To optimize in-engine friction and thus save fuel, the coolant temperature can be raised to about 105°C in the partial-load range (heating element is de-energized).

The friction power is reduced by the higher engine oil temperature and mixture formation is improved by reducing the fuel condensation in the cylinder barrels.

Mixed fuel operation position

Heating element de-energized Coolant temperature 100 to 115°C Heating element energized Coolant temperature 65 to 100°C

Radiator operation position

Heating element de-energized Coolant temperature >115°C Heating element energized Coolant temperature >100°C

Heating the two-disk thermostat (heating element energized) causes it to open and the coolant passes through the engine radiator.

At full load, the two-disk thermostat can be opened very quickly. The coolant temperature can be lowered in the process to about 80°C whereby the best possible engine cooling and knock-free combustion is achieved.

When coolant temperature is over about 115°C, the two-disk thermostat is always fully open (limp-home function), whether the heating element is energized or not.

If coolant temperature is too high, a warning message is shown on the multifunction display (A1p13) of the instrument cluster (A1). To do this, the ME-SFI control unit sends the corresponding signal via the chassis CAN and central CAN (CAN F) to the instrument cluster.

Function sequence for fan control

The ME-SFI [ME] control unit actuates the engine and air conditioning electric suction fan with integrated control (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).

The AAC control unit sends the air conditioning status via the interior CAN and chassis CAN to the ME-SFI [ME] control unit.

Delayed fan switch off

The fan motor runs on for "ignition OFF" for up to 6 minutes if the coolant temperature or the temperature of the ME-SFI [ME] control unit has exceeded the prescribed maximum values or the heat input into the engine block before switching off the engine was very high. The PWM signal duty cycle is 40% maximum while the delayed fan switch-off is active.

If the on-board electrical system voltage drops too much during this time, delayed fan switch-off is stopped.

Function sequence for overheating protection

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

If the coolant or intake air temperature is too high, the ME-SFI [ME] control unit no longer fully opens the throttle valve actuator (M16/6), depending on engine speed and load. The ME-SFI [ME] control unit shortens the injection time of the fuel injectors (Y76).

The ME-SFI [ME] control unit also actuates the coolant thermostat heating element so that the two-disk thermostat is fully open and all the coolant is cooled by the engine radiator.

If engine oil or coolant temperature is too high, a warning message is shown on the multifunction display (A1p13) of the instrument cluster (A1). To do this, the ME-SFI control unit sends the corresponding signal via the chassis CAN and central CAN (CAN F) to the instrument cluster.

Electrical function schematic for thermal management	Model 216	PE07.10-P-2712-97CAH
Electrical function schematic for thermal management	Model 221	PE07.10-P-2712-97SAH
Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MMB