Overview
This document contains information on:
General
Function
General
The combustion engine as piston engine is characterized by the oscillating piston movement and internal, cyclical combustion. Through the mechanical interaction of various modules, the piston engine compresses the fuel–air mix and transfers the combustion pressure to the crankshaft in the form of torque.
Example illustration of crank assembly M139 |
1 | Crankcase |
2 | Oil pan |
3 | Oil pan bottom section |
4 | Timing case |
5 | Balance shaft |
6 | Intermediate gear |
7 | Crankshaft |
8 | Connecting rod |
9 | Piston |
10.1 | Oil scraper ring |
10.2 | Taper-faced ring |
10.3 | Compression ring |
A | Cylinder barrel (NANOSLIDE® coating) |
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Function
Crankcase
The crankcase of the current Mercedes diesel and gasoline engines are made out of aluminum. The cylinder barrels are applied directly to the inside areas of the crankcase through the NANOSLIDE® coating procedure on many engine model designations. On the engine model designations M260 and M264 as well as M270, M274 and M278, cylinder liners made of cast iron are installed.
As a central component part of the engine housing, which usually consists of the following components: Crankcase, oil pan, and timing case, the crankcase fulfills important tasks. For example, absorbing interactive forces from combustion processes and oscillating piston movements as well as strong thermal loads. Mechanically, the crankcase is a carrier of many engine components on the outer walls in the inside area incl. supporting the entire crank assembly. Essential components of the crank assembly are:
Balance shaft with bearing shells
Intermediate gear
Crankshaft with top and bottom bearing shells
Connecting rod with bearing shells
Piston pin
Piston
Piston rings
The tribological designs of the cylinder barrels and the entire crank assembly are key to reducing friction losses and for the robustness of the engine. The combustion pressure acting directly on the pistons generates a linear movement. The resulting force acts on the crankshaft via the connecting rods, thus generating torque.
The pistons and their piston rings are subject to high mechanical and thermal loads. The geometry and surface quality of the pistons has a major influence on the mixture formation and combustion. It is also responsible for dissipating the heat from the combustion chamber to the oil and coolant. The piston rings are designed in different geometries according to their functions. The bottom-most ring, the oil scraper ring, removes engine oil from the cylinder barrel and, while doing so, proportions the film of oil, on which the upper piston rings slide during the stroke. The taper-faced ring, in which the center piston groove is assigned, controls the film of oil both for sufficient tribological conditions and its coat thickness. This must be very thin so that the oil loss due to evaporation is low. Additionally, the taper-faced ring seals against combustion gases and influences the blowby behavior of the engine through interaction with the movement of the bottom-most ring. The plain compression ring or compression ring seals the combustion chamber to the crankcase and diverts the combustion heat to the cooled cylinder barrel. As a result of the mechanical preload of this piston ring, sealing is ensured upon the engine start and ring flutter is prevented at high engine speeds.
The crank assembly is installed in the crankcase. The crankcase essentially has the following tasks:
Bearing of the crankshaft and balance shaft
Bearing for installed balance shaft
Force-transferring connection between the cylinder head and powertrain
Mount of cylinder barrels and cylinder liners
Integrated duct structures for cooling, lubrication, ventilation
Accommodating the ancillaries
The crankcase is equipped with further attachment points for add-on components and creates an oil- and water-tight machine and coolant chamber.
Valve assembly
The valve assembly defines when and for how long fresh air is sucked in as well as when and for long the combusted gases are discharged. The valve assembly and associated components are the main elements of the cylinder head.
The valve train describes the charge change of a combustion engine. The cylinder head has the following tasks:
Absorbing the compressive forces of the cylinder
Cooling areas close to the combustion chamber
Lubricating of the valve train
Terminating the combustion chamber at the top
Mounting the spark plugs and injection nozzlesThe valve assembly essentially comprises the following components:
Intake and outlet valves
Valve springs
End-pivot rocker arm
Intake and exhaust camshaft
Cylinder head
Timing chain (or toothed belt)The camshaft and intake and exhaust valves are controlled via the timing chain through the crankshaft. The cams of the camshaft open via the transfer organs, e.g. end-pivot rocker arm, against the spring force of the valve springs of the intake and exhaust valves. The spring force of the valve springs closes the valves again. One working cycle lasts four strokes, i.e two crankshaft rotations. The opening and closing of the valves occurs only once each time, with only one revolution of the camshaft. The camshaft runs at half the engine speed of the crankshaft.
The speed ratio of the crankshaft to camshaft is 2 : 1.
Belt drive
The belt drive has the task of transferring the rotational movement of the crankshaft to ancillaries, such as the alternator, the water pump, and refrigerant compressor, and driving these.
The belt drive essentially comprises the following components:
Poly-V-belt
Belt tensioner
Guide pulleysEngine lubrication
The engine lubrication is used to supply all areas in the engine that require lubrication and cooling, such as pistons, bearing shells, and end-pivot rocker arms, with lubricating oil. Thus, the oil pressure varies depending on the engine speed.
The engine lubrication system essentially comprises the following components:
Oil pump
Oil pan
Oil pump valve
Oil sensor
Oil filter module
Engine oil heat exchanger The engine lubrication system has the following tasks:
Lubrication to avoid loss of energy and wear as a result of any friction caused between component parts sliding against each other.
Cooling to protect engine parts because they cannot deliver heat directly to the coolant or cooled air.
Sealing for fine sealing between component parts that slide against each other (e.g. piston ring against cylinder wall).
Cleaning for dissipation or bonding of abrasion, deposits, and combustion residues in the engine oil.
Protect against corrosion.
Dampen engine noise because the lubricating film has a noise- and vibration-dampening effect.
Example illustration of valve train M139 |
7 | Crankshaft |
11 | Timing chain |
12 | Chain slide bar with hydraulic chain tensioner |
13 | Exhaust camshaft |
14 | Intake camshaft |
15 | Valve springs |
16 | Inlet valves |
17 | Exhaust valves |
18 | Spark plugs |
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Referenced documents
- gf0140p1000a Crankcase, basic function
- gf0530p1000a Valve train, basic function
- gf1321p1001a Belt drive, basic function
- gf1800p1003a Engine lubrication, basic function