Mercedes-Benz OM 85 diesel engine
|rated capacity||kW||220||300 hp|
|Rated speed||min -1||1500|
|Idle speed||min -1||550|
|number of cylinders||12|
|mean piston speed||m / s||8.5|
|average working pressure||bar||5.9|
|firing||1-12-5-8-3-10-6-7-2-11-4-9||at full load|
The 12-cylinder four-stroke diesel engine Mercedes-Benz OM 85 was a high-speed diesel engine from Mercedes-Benz for installation in railcars and later trucks. The engine was used for the first time in 1934 and from 1938 referred to as MB 805 . It was installed in nine units in pre-war railcars and can be described as an evolution of the numerous six-cylinder four-stroke diesel engines of the two-axle Nebenbahntriebwagen. At its time of origin there were in the DR 137 025 to 027six-cylinder in-line engines with the same performance, the Mercedes-Benz OM 85 but had smaller piston diameter and a smaller stroke. As an uprated version of the engine was offered from 1937 as Mercedes-Benz OM 86 ( Mercedes-Benz MB 806 ).
Construction and components
The engine was a naturally aspirated engine and had prechamber injection of fuel. It was stored together with the main generator in a subframe, which was rigidly suspended in the machine bogie in three points. One of the first three railcars was tentatively fitted with rubber-supported support. The engine axle was tilted slightly forward so that the generator also found space under the car floor.
The engine case was in two parts, as in all pre-war engines; The lower part of the housing simultaneously exercised the function of the oil sump. The housing was made of silumin . The upper part of the housing was provided with wide supports, on which the engine and generator could be supported on the subframe. In the upper part of the housing, the cylinders were used, of which three each formed a casting mold. Also a casting formed three cylinder heads , they were screwed onto the crankcase. The twelve cylinders were arranged at an angle of 60 ° in V-shape. The cylinder liners were made of gray cast iron and pressed into the crankcase.
The cylinder head housed the spring closing inlet and outlet valves, the injection nozzle and the prechamber with the burner. On each side of the cylinder was a camshaft , which operated the hanging valves via rocker arms and roller tappets. The cylinder heads were sealed to the outside by a hood oil-tight.
The crankshaft of the engine was mounted seven times. The crank pins to the connecting rod and the crankshaft bearing were slidably mounted with ThermodurBearings (with steel support shell and thrown in bronze) executed. The crank pins of the crankshaft received the bearings of Hauptpleuel, to these the connecting rods of Nebenpleuel were forked screwed. The upper connecting rod bearings were normal bronze bearings. They were connected to the piston bodies by floating piston pins with light alloy mushrooms. The central main bearing of the crankshaft was designed as a flange bearing and was used to absorb the axial forces. The pins of the main and stroke bearings were drilled through for lubrication. At the ends of the crankshaft flywheel or a speed vibration damper were attached. Obviously, the crankshafts were not sufficiently dimensioned in the load, because in 1937 the equipment of reinforced shafts with counterweights.
The pistons were made of light metal, they had a trough-shaped recessed combustion chamber. Within the testing an alloy form had to be found, which had coped with the thermal load of the pre-chamber beam. In the end this was the alloy EC 124 with anodized piston bottom plate and a zone cast in the piston crown. This design withstood the stresses and was retained until the introduction of EC 124 forged pistons . In addition, a burner with a seven-hole nozzle was also taken over. Each piston had 5 sealing rings and one oil scraper ring .
Fuel system and engine control
The engine works on the prechamber principle of fuel injection. For each cylinder side, a separate diesel injection pump was used, manufactured by Bosch and mounted on the side of the motor housing. Both injection pumps were driven via a spray distributor from the crankshaft via transmission wheels. The injection phaser was used to advance the injection timing with increasing engine speed to achieve optimum combustion. Through pressure lines of the same length, the fuel from the injection pump to the injectors, which pushed him finely atomized into the antechamber.
The engine control was carried out on the basis of the speed control in five stages. The five load levels were between 1.050 min -1 and 1500 min -1 The controller was working with engine oil pressure. If the oil pressure was too low, the speed controller was reset to zero and the engine stopped.
The engine was started electrically via the main generator. Before starting, the antechambers had to be preheated with glow plugs.