GF07.10-P-1012OG Thermal Management, Function
GF07.10-P-1012OG Thermal Management, Function
ENGINES 642.8 in MODEL 204.0 /2 /9, 207.3 /4, 212.0 /2, 218.3
Function requirements for thermal management, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
Thermal management, general
The coolant temperature, exhaust temperature and fuel pressure of the engine are regulated by the thermal management system controlled by the CDI control unit (N3/9). 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:
- Left hot film mass air flow sensor (B2/6), engine load
- Left intake air temperature sensor (B2/6b1)
- Right hot film mass air flow sensor (B2/7)
- Right intake air temperature sensor (B2/7b1)
- Boost pressure sensor (B5/1), engine load
- Coolant temperature sensor (B11/4)
- Charge air temperature sensor (B17/8)
- Temperature sensor upstream of diesel particulate filter (B19/9) (with code (474) Particulate filter)
- DPF differential pressure sensor (B28/8) (with code (474) Particulate filter)
- DPF differential pressure sensor for OBD (B28/16) (with code (U42) BlueTEC (SCR) diesel exhaust treatment and code (494) USA version)
- Accelerator pedal sensor (B37), accelerator pedal operation (how fast and how far driver Model calm or sporty)
- Fuel temperature sensor (B50)
- Crankshaft Hall sensor (B70), engine speed
- Temperature sensor in CDI control unit
- Front SAM control unit with fuse and relay module (N10/1), outside temperature via the chassis CAN (CAN E)
- Automatic air conditioning control and operating unit (N22/7), outside air temperature and status of the air conditioning unit via the interior CAN (CAN B) and chassis CAN
- Electrically stability program control unit (N30/4) (except code (233) DISTRONIC PLUS) or Premium electrically stability program control unit (N30/7) (with code (233) DISTRONIC PLUS), vehicle speed via the chassis CAN
- Fully integrated transmission control controller unit (Y3/8) (vehicles with code (427) 7-speed automatic transmission), gear range via drive train CAN (CAN C)
The Electronic Stability Program control unit (N30/4) will be used as of 1.3.2011 (model 204.0/2) in 2 variants:
- Electronic Stability Program control unit, basis variant (except code (233) DISTRONIC PLUS)
- Electronic Stability Program control unit, Premium variant (except code (233) DISTRONIC PLUS)
Up to 28.2.2011 or 31.5.2011 (model 204.9) and as of 1.6.2011 only the basic variant of the ESP control unit is used.
Function sequence for thermal management
The thermal management system is described in the following steps:
^ Function sequence for post-start phase (for model 218)
^ Function sequence for heating the coolant thermostat
^ Function sequence for maximum heating combustion
^ Function sequence for fuel preheating system
^ Function sequence for fuel tank protection
^ Function sequence for fan control
^ Function sequence for radiator shutters (for model 204, 212, 218)
^ Function sequence for overheating protection
Function sequence for post-start phase (for model 218)
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 engine is warmed up quicker and this the exhaust emissions are reduced.
The coolant pump is switched off for a cold start for a maximum of 500 s if the following conditions are fulfilled:
- The limits stored in the CDI control unit for the intake air and coolant temperature as well as for the injected total fuel quantities are still not reached.
- No "heating" was requested by the automatic air conditioning control and operating unit (N22/7).
- The engine speed or injection quantity has not exceeded its established limit value.
Function sequence for heating the coolant thermostat
The CDI control unit actuates the coolant thermostat heating element (R48) (except code (U42) BlueTEC (SCR) diesel exhaust treatment and code (494) USA version) (based on a characteristics map), depending on the operating conditions, with the aid of a ground signal. The voltage is supplied through "circuit 87" by the CDI control unit. The heating causes the two-disk thermostat in the coolant thermostat to open which leads to a lowering of the coolant temperature. The orifice area of the two-disk thermostat is determined by the duty cycle of the electrical current.
The coolant thermostat heating element regulates the coolant temperature within the range of approx. 87°C to 102 °C. The limp home function ensures that the two-disk thermostat is completely opened above around 102°C, irrespective of actuation.
The two-disk thermostat can take the following positions:
- Short-circuit mode position; t less than 87°C; coolant flow in engine only, a flow through the passenger compartment heater is possible
- Mixed mode position; 87°C less than t less than 102°C; the two-disk thermostat opens, the coolant through flow begins
- Radiator mode position; t greater than 102°C; the two-disk thermostat is opened, full radiator through flow
The following benefits result from regulating the coolant temperature of the engine:
- Operating temperature is reached faster
- Reduction of emissions and improved heating comfort
Schematic representation
67 Coolant thermostat
A Short-circuit mode position
B Mixed mode position
C Radiator mode position
K To the radiator
M From the engine
W To the water pump
Function sequence for maximum heating combustion
With maximum heating combustion, more heat is introduced into the coolant by a new combustion strategy on the engine side.
The following function conditions must be met simultaneously:
- Accelerator pedal position reported by the accelerator pedal sensor is below 80% (partial throttle)
- No regeneration mode for the diesel particulate filter (DPF) (with code (474) Particulate filter)
- At least 90% heat output is requested by the automatic air conditioning control and operating unit
- Outside air temperature below 7°C (renewed cut-in takes place at 4°C), from the front SAM control unit with fuse and relay
- Coolant temperature from coolant temperature sensor is below 82°C (renewed cut-in takes place at 74°C)
During maximum heating combustion, a higher exhaust temperature is generated by means of two preinjections by the fuel injectors (Y76), for which a significantly greater amount of fuel is used, followed by a late main injection. This process, in combination with exhaust gas recirculation (EGR), causes more heat to be transferred to the coolant inside the engine, allowing for more rapid attainment of the optimum operating temperature and improved warming of the vehicle interior.
The CDI control unit regulates, stabilizes and increases the idle speed depending on operating conditions and engine loads if the accelerator pedal is not actuated.
Function sequence for fuel preheating system
Fuel preheating is achieved using the following regulation strategies:
^ Pressure regulating valve regulation
^ 2-regulator concept regulation
^ Quantity control valve regulation
Pressure regulating valve regulation
The rail pressure is regulated via the pressure regulating valve (Y74) during the starting procedure and for fuel heating. The quantity control valve (Y94) is controlled to open.
Pressure regulating valve regulation takes place under one of the following conditions:
- Up to 30 s after the engine starts in idle
- Up to a fuel temperature of 20°C
Pressure regulating valve regulation causes the cold fuel to be heated rapidly by the fuel being forced at high pressure through a narrow gap in the pressure regulating valve.
2-regulator concept regulation
The rail pressure is jointly regulated in idle and in deceleration mode by the pressure regulating valve and quantity control valve.
Quantity control valve regulation
Rail pressure regulation via the quantity control valve takes place from 30 s following engine start and from a fuel temperature of 20°C.
With the 2-regulator design and with regulation by the quantity control valve, the fuel is heated less than is the case with pressure regulating valve regulation.
Function sequence for fuel tank protection
Increasing the fuel pressure via the high-pressure pump from 4.5 bar up to 1600 bar also increases the temperature of the fuel. To protect the fuel tank from overheating, the CDI control unit reads in the fuel temperature sensor and thus monitors the temperature of the fuel delivered to the high-pressure pump.
If the temperature of the fuel delivered to the high-pressure pump rises above 90°C, the CDI control unit reduces the injection quantity and the rail pressure using the pressure regulating valve. This causes less fuel to be compressed.
The CDI control unit causes the excess fuel to return to the fuel tank via the quantity control valve. When the temperature of the fuel delivered to the high-pressure pump drops below 90°C, the tank protection function is deactivated by the CDI control unit.
Function sequence for fan control
The CDI control unit actuates the combustion engine and air conditioning fan motor with integrated control (M4/7). The specified fan speed is set by the CDI control unit by means of 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
A fault in the combustion engine and air conditioning fan motor with integrated control is transmitted to the CDI control unit by means of a PWM signal.
If there is a malfunction in the signal line (loss of frequency) from the CDI control unit, the combustion engine and air conditioning fan motor with integrated control switches automatically to the maximum rotational speed (fan emergency mode).
The automatic air conditioning control and operating unit transfers the status of the air conditioning via the interior and chassis CAN to the CDI control unit.
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.
Function sequence for radiator shutters (for model 204, 212, 218)
The radiator shutters are closed in order to lower the fuel consumption (by producing a lower aerodynamic drag). This also causes reduced engine compartment cooling and a dampening of engine noise emissions to the outside. The radiator shutters actuator (Y84) is actuated by the CDI control unit after engine start by means of a ground signal.
In this way the vacuum in the vacuum unit is built up and the radiator shutters closed by means of a linkage. The radiator shutters are opened when the coolant temperature reaches 106°C and closed again at 94°C.
Function sequence for overheating protection
The overheating protection protects against engine damage if there is a thermal overload. At a coolant temperature above 106°C the injection quantity is reduced based on the characteristic maps stored in the CDI control unit. Reduction occurs depending on the coolant temperature and oil temperature. To this end, the CDI control unit reads in the coolant temperature sensor, oil temperature sensor (B1) and the temperature sensor upstream of the turbocharger (B19/11) (turbocharger protection).
After evaluating the input signals, the CDI control unit regulates the fuel pressure in the rails via the quantity control valve and the pressure regulating valve, and controls the injection timing by actuating the fuel injectors.
If engine oil or coolant temperature is too high, a warning message is shown in the multifunction display (A1p13) on the instrument cluster (A1). For this purpose, the CDI control unit sends the appropriate signal over the chassis CAN to the instrument cluster.
