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

Engine all (4xWD) 

Engine all (CAR) 

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 

Courtesy 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. 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 nozzles. The 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 pulleys Engine 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.

  Courtesy of MERCEDES-BENZ USA

  EXAMPLE ILLUSTRATION OF VALVE TRAIN M139
  
  

  	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