Shown with code M5Z (Engine version Euro VI) |
1 | Oil/coolant module |
1.1 | Coolant thermostat |
1.2 | Coolant pump |
2 | Cylinder liner |
3 | Cylinder head |
4 | Coolant manifold |
5 | Injection nozzle for regeneration of diesel particulate filter (only for code M5Z (Euro VI engine version)) |
6 | Exhaust gas recirculation cooler |
8 | Fuel cooler |
9 | Compressor |
12 | Fan |
14 | Coolant feed to AdBlue® heater |
KA | Coolant outlet to the cooler |
KE | Coolant inlet from the cooler |
W20.00-1073-76
General
The engines for the model series OM 470, 471 & 473 have a closed engine cooling system (pressurized system). This means that coolant in the engine cooling system, which is circulated by the coolant pump (1.2), absorbs the heat from the hot engine components and - once the engine has reached its operating temperature - it dissipates this through a cooler to the outside air.
Engine cooling circuit
The coolant pump (1.2) is belt driven. If the engine is running, and if it has not yet reached its operating temperature, then the coolant pump (1.2) circulates the coolant inside the engine. In the process, in vehicles with code M7T (coolant pump, regulated) the pump speed of the coolant pump (1.2) is constantly monitored by the engine management control unit (MCM) (A4) with the aid of the coolant pump speed sensor (B640) and adjusted as required through actuation of the switched water pump solenoid valve (Y644).
Because the coolant thermostat (1.1) is usually closed when the engine is cold, the coolant flows via the coolant short circuit duct into the oil/coolant module (1) and, from there, it is led past the closed coolant thermostat (1.1) and through the coolant pump (1.2) to the heat exchanger.
The engine oil is cooled via the heat exchanger when its temperature is above 115 °C (opening temperature of the oil thermostat), so that it does not exceed the temperature of 120 °C. The heat exchanger is fastened to the oil/coolant module (1), and projects into the crankcase.
In this way, the coolant gets into the crankcase and, therefore, reaches the cylinder liners (2). At the same time, part of the coolant is led to the fuel cooler (8) and to the compressor (9) and, via separate feed lines, to the exhaust gas recirculation cooler (6) and to the exhaust gas recirculation positioner (Y621).
From the fuel cooler (8) and from the compressor (9), the coolant comes directly back to the coolant pump (1.2).
The coolant delivered to the cylinder liner (2) flows further to the cylinder head (3).
The cylinder head (3) has a split coolant jacket. This means that the coolant, after flushing the cylinders, flows both on the inlet side and the outlet side in the cylinder head (3). In the cylinder head (3), the coolant first gets into the bottom cooling level where it flushes the fuel injectors and valve seat rings.
Finally, the coolant flows to the upper cooling level and cools the valve guides located there.
Afterward, the coolant is led outward into the coolant pipe manifold (4), into which the coolant from the exhaust gas recirculation cooler (6) and the coolant from the exhaust gas recirculation positioner (Y621) is also led.
From the coolant pipe manifold (4), the coolant, via the coolant short circuit duct and the still closed coolant thermostat (1.1), comes back into the oil/coolant module (1) and the coolant pump (1.2) until the operating temperature of the engine is reached.
When the engine operating temperature is reached, a flow through the cooler circuit is started by opening the coolant thermostat (1.1).
Depending on the position of the coolant thermostat (1.1), more or less coolant now flows through the vehicle cooler directly via the coolant short circuit line to the coolant pump (1.2). The temperature of the coolant in the coolant circuit is regulated in this way.
The fan (12) is used to increase the vehicle cooler's cooling output.
Meanwhile, the coolant temperature is constantly monitored via the outlet coolant (B606) and inlet coolant (B607) temperature sensors, both of which are connected to the engine management control unit (MCM) (A4).
The various pressures in the engine cooling system, which arise due to the temperature fluctuations, are balanced out via the coolant expansion reservoir, which is located either at the front behind the maintenance flap or at the rear on the crossmember of the cab suspension system depending on the vehicle equipment.
Heating circuit
The coolant for the heating circuit is taken from the coolant pipe manifold (4).
A shutoff valve is installed in front of the heater heat exchanger, through which the coolant flow through the heater circuit or the heater heat exchanger can be regulated.
For vehicles with code D6I(Residual heat utilization), the additional residual heat pump (M20) upstream of the heater shutoff valve (Y49) ensures that the coolant is circulated in the heater circuit when the engine is switched off. This in turn means that the engine's residual heat can be used for up to two hours.
The auxiliary heater installed in vehicles with code D6M (hot-water auxiliary heater, cab) or with code D6N (hot-water auxiliary heater, cab and engine) is integrated into the heating circuit with an additional bypass in such a way that the coolant circulates with the aid of the additional circulation pump only within the heating circuit and therefore does not have to be routed through the entire engine.
Connection of secondary water retarder - for vehicles with code B3H(Secondary water retarder)
The coolant for the secondary coolant-retarder is also taken from the coolant pipe manifold (4). Due to the fact that when the secondary water retarder is activated, a large volume of coolant is taken from the coolant circuit thereby causing the pressure in the cooling system to be greatly reduced, this is regulated by targeted injection of compressed air from the consumer circuit.
To do so, the drive control (CPC) control unit (A3) uses the coolant pressure control sensor (B87) to permanently monitor the pressure in the coolant expansion reservoir. Under a certain pressure and dependent on the coolant temperature, it actuates the coolant pressure solenoid valve control (Y53), which accordingly allows compressed air to pass through the consumer circuit in the coolant expansion reservoir.
Cooling of injection nozzle for regeneration of diesel particulate filter (DPF) – for vehicles with code M5Z (Euro VI engine version)
The coolant for cooling the injection nozzle is taken from the exhaust gas recirculation cooler (6), led through the nozzle unit for DPF regeneration, in which the injection nozzle is located, and fed back into the coolant pipe manifold (4).
AdBlue® heater
The coolant for the AdBlue® heating is also removed from the coolant pipe manifold (4). During actuation of the AdBlue® heating coolant solenoid valve (Y627), the coolant is led via the hose package to the AdBlue® container and, from there, is led back into the oil/coolant module (1).
Coolant circuit schematic | |||
Engine management (MCM) control unit, component description | A4 | ||
Auxiliary heater heater unit, component description | Vehicles with code D6M (hot-water auxiliary heater, cab) or code D6N (hot-water auxiliary heater, cab and engine) | ||
Auxiliary heater coolant circulation pump, component description | Vehicles with code D6M (hot-water auxiliary heater, cab) or with code D6N (hot-water auxiliary heater, cab and engine) | ||
Coolant pressure control sensor, component description | Vehicles with code B3H (secondary water retarder) | ||
Coolant outlet temperature sensor component description | B606 | ||
Coolant inlet temperature sensor, component description | B607 | ||
Residual heat pump, component description | Vehicles with code D6I (residual heat utilization) | ||
Heater shutoff valve, component description | Y49 | ||
Coolant pressure control solenoid valve, component description | Vehicles with code B3H (secondary water retarder) | ||
Component description for exhaust gas recirculation actuator | Y621 | ||
AdBlue heater coolant solenoid valve, component description | Y627 | ||
Component description for exhaust gas recirculation cooler | |||
Oil/coolant module, component description | |||
Coolant pump component description | Vehicles with code M7T (coolant pump, regulated) | ||
Oil-water heat exchanger component description | |||
Component description for the coolant thermostat | |||
Retarder, component description | Vehicles with code B3H (secondary water retarder) | ||
Nozzle unit for DPF regeneration, component description | Only on vehicles with CODE M5Z (engine version Euro VI) | ||
Heating system heat exchanger, component description |
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