Thermal Management, Function - GF07.10-D-1012TSC

Engine 642.8 in model 907 

Block diagram 

Function requirements for thermal management, general points 

• Circuit 87 (Engine management ON)
• Engine running.

Thermal management, general 

Heat management as controlled by the CDI control unit (N3/28) regulates the engine's coolant temperature, exhaust gas temperature, and the fuel pressure. The following advantages arise from this:

• Rapid reaching of the optimal operating temperature
• Reduction of the exhaust emissions
• Fuel savings (up to 4 %)
• Improved heating comfort
• Component protection for a high engine load

Thermal management controlling is dependent on the following sensors and signals:

• Engine oil sensor (B40/8)
• Hot film MAF sensor (B2/14), engine load
• Boost pressure sensor (B5/8), engine load
• Coolant temperature sensor (B11/19)
• Charge air temperature sensor (B17/15)
• Temperature sensor upstream of diesel particulate filter (B19/19)
• DPF differential pressure sensor (B28/16)
• Fuel temperature sensor (B50/6)
• Crankshaft position sensor (B70/1), engine speed
• Accelerator pedal module (A68), accelerator pedal actuation (how fast and how far → driver type calm or sporty) via powertrain control unit (N127) and drive CAN (CAN C)
• SAM control unit (N10), outside temperature via interior CAN (CAN B), electronic ignition lock control unit (EZS) (N73/8), suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C)

• Control and operating unit for automatic air conditioning (N22/2), air conditioning system status via the air conditioning control LIN (LIN B8), SAM control unit, interior CAN, EZS control unit, suspension FlexRay, powertrain control unit, and drive CAN
• ESP® control unit (N30/4), wheel speed via suspension FlexRay, powertrain control unit, and drive CAN
• Fully integrated transmission control (VGS) electric controller unit (N1511) (with code G42 (7G-TRONIC PLUS)), drive range via drive CAN

Function sequence for thermal management 

The thermal management is described in the following points:

• Function sequence for 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 overheating protection

Function sequence for coolant thermostat 

The two-disk thermostat can take the following positions:

• Short-circuit operation position: T < 87 °C; coolant flow in engine only. Flow through the passenger compartment heating is possible.
• Mixed-fuel mode position; 87 °C < T < 102 °C; the two-disk thermostat opens, coolant starts to flow.
• Radiator mode position; T > 102 °C; two-disk thermostat is opened, full radiator flow-through

The following advantages result from regulating the refrigerant temperature of the engine:

• Operating temperature is reached faster
• Emissions reduced
• Improved heating comfort
• Component protection for engine high load

Schematic diagram 

Function sequence for maximum heating combustion 

With the maximum heating combustion more heat is introduced into the refrigerant by a new combustion strategy on the engine side.

The following function conditions must be met simultaneously:

• Accelerator pedal position as reported by the accelerator pedal sensor below 80 % (partial throttle).
• Diesel particulate filter (DPF) not in regeneration mode
• At least 90 % of the heat output is requested from the climate control unit.
• Outside temperature is less than 7 °C (cut-in takes place again at 4 °C from SAM control unit)
• The coolant temperature from the coolant temperature sensor is below 82 °C (renewed cut-in takes place at 74 °C).

During maximum heating combustion, a higher exhaust temperature is achieved by means of 2 preinjections from the fuel injectors (Y76) using a much greater fuel quantity, plus a retarded 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. To do this, the exhaust gas recirculation positioner (Y27/17) is actuated by the CDI control unit.

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-control concept regulation
• Quantity control valve regulation

Pressure regulating valve regulation 

The fuel pressure is regulated by the pressure regulating valve (Y74/6) during the starting procedure and for fuel heating. The quantity control valve is opened in a controlled manner.

Pressure regulating valve regulation takes place under one of the following conditions:

• Up to 30 seconds after engine start in neutral
• 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-control concept regulation 

The fuel pressure is jointly regulated in idle and in deceleration mode by the pressure regulating valve and quantity control valve.

Quantity control valve regulation  The fuel pressure is regulated via the quantity control valve (Y94/4) beginning 30 seconds after engine start and beginning with 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 through the high-pressure pump from 4.5 bar to 1800 bar increases the fuel's temperature.

To protect the fuel tank from overheating, the CDI control unit reads in values from the fuel temperature sensor and thus monitors the temperature of the fuel delivered to the high-pressure pump. If the temperature of the fuel increases to over 90 °C, the CDI control unit reduces the injection quantity and the fuel 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.

If the temperature of the fuel delivered to the high-pressure pump drops below 90 °C, the protection function is deactivated by the CDI control unit.

Function sequence for fan control 

The CDI control unit actuates the fan (A27/2). In doing this, the fan speed is steplessly specified by the CDI control unit.

Delayed fan switch off 

At "ignition OFF" the fan motor runs on for 5 minutes, when the coolant temperature, CDI control unit temperature or a thermal input integral calculated based on engine load, coolant temperature, vehicle speed and outside temperature (averaged over the last 6 minutes) exceeds specified threshold values.

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.

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 characteristics maps stored in the CDI control unit. Reduction occurs depending on the coolant temperature and oil temperature. To do this, the CDI control unit reads the signals from the coolant temperature sensor, the engine oil temperature sensor, and the temperature sensor upstream of the exhaust gas turbocharger (B16/11) (exhaust gas 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 period by actuating the fuel injectors.

If the engine oil or coolant temperature is too high, a warning message is shown in the instrument cluster (A1). To do this, the CDI control unit transmits an appropriate signal via the drive CAN, powertrain control unit, suspension FlexRay, EZS control unit, and user interface CAN (CAN HMI) to the instrument cluster.

Electrical function schematic for heat management	PE07.10-D-2712-97TSC
Overview of system components for common rail diesel injection (CDI)	GF07.16-D-9997TSC