Heat Management, Basic Function - GF07.10-D-9900A
Engine All (Light transporter)
Overview
This document contains information on:
- General
- Function requirements
- Function
General
Heat management essentially controls and regulates the following systems:
- Engine cooling
- Transmission cooling (for automatic transmissions)
- Charge air cooling
- Vehicle interior heating
The combustion engine control unit regulates the coolant temperature, the exhaust gas temperature and the fuel pressure of the engine. The following advantages arise from this:
- Rapid reaching of the optimal operating temperature
- Reduction of the exhaust emissions
- Fuel savings
- Improved heating comfort
- Component protection for a high engine load
To control the heat management, the combustion engine control unit reads e.g. the following signals:
- Engine oil temperature sensor
- Charge air temperature
- Intake air temperature
- Boost pressure
- Coolant temperature
- Temperature sensor upstream of diesel particulate filter (DPF) or gasoline particulate filter (OPF)
- DPF or OPF differential pressure sensor
- Accelerator pedal position
- Fuel temperature
- Engine speed
- Temperature in combustion engine control unit
The combustion engine control unit also evaluates the following variables:
- Status of the air conditioning system for rotational speed and torque adjustment
- Vehicle speed
- Wheel speed
- Transmission oil temperature (for automatic transmissions)
- Outside temperature
Function requirements
- Circuit 87M (Engine management ON)
- Engine in operation
Function
Heat management is controlled by the combustion engine control unit and the powertrain control unit. The combustion engine control unit regulates and controls liquid cooling in the engine. The powertrain control unit controls and regulates air cooling of the engine, as well as the components that are to be cooled by the low and medium-temperature circuits.
The thermal management function encompasses the following subfunctions:
- Coolant thermostat heating
- Fan control
- Overheating protection
- Heating system switch-off
- Air flap control
Coolant thermostat heating
The temperature of the coolant can be controlled variably by heated coolant thermostats. The coolant thermostats contain heating elements that are actuated as required by the combustion engine control unit using a ground signal.
Fan control
The powertrain control unit actuates the fan motor directly. The combustion engine control unit sends the specified fan speed to the powertrain control unit. If the powertrain control unit does not receive a valid fan request, the fan motor is actuated at maximum rpm. In the case of a fault in the signal line (loss of frequency) by the powertrain control unit, the fan motor switches itself to the maximum rpm (fan emergency mode).
The climate control unit sends the status of the air conditioning system and the fan request to the electronic ignition lock control unit and the powertrain control unit.
Delayed fan switch off:
If the coolant temperature, the temperature of the combustion engine control unit or a heat input integral calculated from engine load, coolant temperature, vehicle speed and outside temperature exceeds a specified threshold value, the fan motor continues to run for up to 5 min after ignition OFF. If the battery voltage drops down a lot, the delayed fan switch off is suppressed.
The delayed fan switch off is not broken off by "ignition ON". When starting the engine in delayed fan switch off the fan regulation for normal operation is suppressed until the delayed fan switch off is completed.
Overheating protection
In a case of thermal overload the overheating protection protects the catalytic converters against engine damage and overheating damage.
To do so, the combustion engine control unit reads in the signals from the coolant temperature sensor and the engine oil temperature sensor.
The following action is initiated to prevent overheating of the engine:
- map-dependent ignition angle setting in the direction "retarded", depending on engine load and engine speed
- map-dependent reduction of the injection quantity
- Regulation of the injection period through actuation of:
- Quantity control valve
- Fuel injectors
- Reduced opening of the throttle valve actuator, depending on the engine load and engine speed
- Actuation of the coolant thermostat heating element by the combustion engine control unit
Heating system switch-off
To heat the combustion engine more quickly, the combustion engine control unit switches off the coolant circuit of the heating system by means of the heating system shutoff valve.
Air flap control
The air flowing through the engine compartment is routed via an air duct (passive duct) at the hood in a targeted manner into the area between the cylinder banks in order to then flow into the component parts positioned there (exhaust gas turbocharger, catalytic converters and soot particle filter).
In certain operating conditions, the air duct must be sealed via the air flap in order to prevent recirculation of the radiator exhaust air via the air duct, e.g. during engine fan operation at low vehicle speeds. The air flap releases or closes the cross section. The air flap is actuated via the engine cooling air flap actuator motor. The powertrain control unit controls the engine cooling air flap actuator motor.
| Function schematics | |||
| Function schematic for heat management | Engine 654 in model 907 | PE20.00-D-2502TSH | |
| Additional basic functions | |||
| Charge air cooling, basic function | GF09.41-D-1000A | ||
| Engine cooling, basic function | GF20.00-D-1002A | ||
| Control units | |||
| Combustion engine control unit, basic function | GF07.08-D-9890A | ||
| Powertrain control unit, basic function | GF54.21-D-9894A |