FixVault
Home › Mercedes Benz › 2021 › GLB250 Base › Repair and Diagnosis › Engine Mechanical › Mechanical › Complete Engine - 247 Chassis › Basic Knowledge › Combustion Engine Mechanical Components, Basic Function - GF01.00-P-9900A

Combustion Engine Mechanical Components, Basic Function - GF01.00-P-9900A

Engine all (4xWD) 

Engine all (CAR) 

Overview 

This document contains information on:

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 

G14574394Courtesy of MERCEDES-BENZ USA

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.

Cylinder liners made of cast iron are installed on engine model designations M 260 and M 264 as well as M 270, M 274 and M 278. 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 and in the inside area including for supporting the entire crank assembly.

Essential components of the crank assembly are:

The tribological designs of the cylinder barrels, i.e. taking friction, wear and lubrication into account, as well as the entire crank assembly, are fundamental for 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 mixture formation, combustion and the transfer of heat from the combustion chamber to the engine 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 when the engine is started and ring flutter is prevented at high engine speeds.

The crank assembly is installed in the crankcase. The crankcase essentially has the following tasks:

The crankcase is equipped with further attachment points for add-on components and creates an oil- and water-tight machine and coolant chamber.

Example illustration of valve train 

G14574395Courtesy of MERCEDES-BENZ USA

Valve assembly 

The valve train defines when and for how long fresh air is sucked in as well as when and for how 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:

The valve assembly essentially comprises the following components:

The camshaft and intake and exhaust valves are controlled via a timing chain or a toothed belt through the crankshaft. The cams of the camshaft open the intake and exhaust valves via the transfer organs, e.g. end-pivot rocker arm, against the spring force of the valve springs. 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.

IMPORTANT The speed ratio of the crankshaft to camshaft is 2: 1.

Belt drive 

The purpose of the belt drive is to transfer the rotational movement of the crankshaft to ancillaries, such as the alternator, the water pump or the refrigerant compressor, and drive them.

The belt drive essentially comprises the following components:

Engine lubrication 

The engine lubrication is used to supply all areas in the engine that require lubrication and cooling, such as the 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:

The engine lubrication system has the following tasks:

  Additional basic functions     
  Crankcase, basic function   GF01.40-P-1000A 
  Valve train, basic function   GF05.30-P-1000A
  Belt drive, basic function   GF13.21-P-1001A
  Engine lubrication, basic function   GF18.00-P-1003A
About FixVault