Mercedes-Benz OM 85
The 12-cylinder four-stroke diesel engine Mercedes-Benz OM 85 was a high-speed diesel engine from Mercedes-Benz for installation in fast railcars of the Deutsche Reichsbahn . The engine was used for the first time in 1934 and was designated the MB 805 from 1938 . Nine copies of it were installed in railcars of the pre-war design and can be described as a further development of the numerous six-cylinder four-stroke diesel engines of the two-axle railcars. When it was first built, the DR 137 025 to 027 had six-cylinder in-line engines with the same output, but the Mercedes-Benz OM 85 had a smaller piston diameter and a smaller stroke. As a performance-enhanced version, the engine was offered as the Mercedes-Benz OM 86 ( Mercedes-Benz MB 806 ) from 1937 .
Structure and components
Basic structure
The engine was naturally aspirated and had pre-chamber injection of the fuel. It was stored together with the main generator in a subframe, which was rigidly suspended at three points in the machine bogie. One of the first three railcars was given a rubber-sprung support on a trial basis. The engine axis was inclined slightly forward so that the generator could also be placed under the car floor.
As with all engines from the pre-war era, the motor housing was in two parts; the lower part of the housing also performed the function of the oil pan. 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. The cylinders were inserted in the upper part of the housing, three of which formed a mold. Three cylinder heads also formed a mold and were screwed onto the crankcase. The twelve cylinders were arranged in a V-shape at an angle of 60 °. The cylinder liners were made of gray cast iron and pressed into the crankcase.
The spring-closing inlet and outlet valves, the injection nozzle and the prechamber with the burner were housed in the cylinder head . On each cylinder side there was a camshaft that operated the hanging valves via rocker arms and roller tappets. The cylinder heads were sealed oil-tight from the outside by a hood.
The engine's crankshaft had seven bearings. The crank pins for the connecting rods and the crankshaft bearings were designed with plain bearings with Thermodur bearings (with a support shell made of steel and cast bronze). The crank pins of the crankshaft held the slide bearings of the main connecting rods, to which the connecting rods of the secondary connecting rods were bolted in a fork shape. The upper connecting rod bearings were normal bronze bearings. They were connected to the piston bodies by floating piston pins with light metal mushrooms. The central main bearing of the crankshaft was designed as a flange bearing and was used to absorb the axial forces. The journals of the main and pin bearings were drilled through for lubrication. A flywheel and a speed vibration damper were attached to the ends of the crankshaft. Obviously, the crankshafts were not sufficiently dimensioned for the load, because in 1937 reinforced shafts were equipped with counterweights.
The pistons were made of light metal and had a trough-shaped, recessed combustion chamber. During the trial, an alloy form had to be found that could withstand the thermal load of the prechamber beam. In the end, this was the alloy EC 124 with an anodized piston head plate and a zone cast into the piston head. This design withstood the loads and was retained until forged pistons from EC 124 were introduced. In addition, a burner with a seven-hole nozzle was also taken over. Each piston had 5 sealing rings and an oil control ring .
Fuel system and engine control
The engine works on the prechamber principle of fuel injection. A separate diesel injection pump was used for each cylinder side ; they were manufactured by Bosch and mounted on the side of the engine housing. Both injection pumps were driven by the crankshaft via transmission gears via an injection distributor. The injection adjuster was used to advance the injection timing with increasing engine speed in order to achieve optimum combustion. The fuel passed through pressure lines of the same length from the injection pump to the injection nozzles, which, in a finely atomized form, forced it into the antechamber.
The motor 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 1,500 min −1. The controller worked with engine lubricating oil pressure. If the oil pressure was too low, the speed controller was set to zero and the engine was switched off.
The engine was started electrically via the main generator. Before starting, the antechambers had to be preheated with glow plugs.
Cooling, lubrication and air system
The engine was water-cooled. The lubrication was designed as pressure circulation lubrication . The oil was delivered by a double gear pump . A pump delivered the oil from the oil pan via the oil cooler into a 45 liter lubricating oil container located in the engine room. From here the oil was pumped to the lubrication points by the second pump. The cylinder liners and the piston were cooled by spray oil.
Each cylinder side had a common air intake device and a common water-cooled exhaust pipe. The two exhaust pipes were brought together and led the exhaust gases through a vertical exhaust pipe to the exhaust gas pot on the roof.
Technical specifications
| Parameter | unit | value | comment |
|---|---|---|---|
| rated capacity | kW | 220 | 300 hp |
| Rated speed | min -1 | 1,500 | |
| Idle speed | min -1 | 550 | |
| Number of cylinders | 12 | ||
| Cylinder diameter | mm | 138 | |
| Piston stroke | mm | 170 | |
| Stroke volume | l | 30.5 | |
| mean piston speed | m / s | 8.5 | |
| medium work pressure | bar | 5.9 | |
| Injection pressure | bar | 80 | |
| Firing order | 1-12-5-8-3-10-6-7-2-11-4-9 | at full load | |
| Compression ratio | 17th | ||
| Engine ground | kg | 1,835 | dry |
| Oil content | l | 40 | |
| Water content | l | 82 | |
| Procurement price | Reichsmark | 26,700 |
Vehicles equipped with the engine for delivery
The motor coaches of the series DR 137 055 to 057 and DR 137 111 to 116 as well as the series DR 137 236 were equipped.
Operating experience
The vehicles equipped with these engines had an average annual mileage of approx. 76,000 km before the Second World War .
literature
- Heinz R. Kurz: The railcars of the Reichsbahn types . EK-Verlag, Freiburg 1988, ISBN 3-88255-803-2
Individual evidence
- ↑ Heinz R. Kurz: The railcars of the Reichsbahn types . EK-Verlag, Freiburg 1988, ISBN 3-88255-803-2 , p. 251
| Timeline of the Daimler-Benz diesel engines up to 1945 | |||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Number of cylinders | design type | Displacement (l) | 1920s | 1930s | 1940s | ... | |||||||||||||||||||||||
| 0 | 1 | 2 | 3 | 4th | 5 | 6th | 7th | 8th | 9 | 0 | 1 | 2 | 3 | 4th | 5 | 6th | 7th | 8th | 9 | 0 | 1 | 2 | 3 | 4th | 5 | ||||
| 1 | Lying | 3.4 | OE engine | ||||||||||||||||||||||||||
| 4.2 | OE engine | ||||||||||||||||||||||||||||
| 2 | In-line engine | 5.7 | S6 engine | ||||||||||||||||||||||||||
| 4th | 2.6 | OM 138 | |||||||||||||||||||||||||||
| 3.8 | OM 59 | ||||||||||||||||||||||||||||
| 4.9 | OM 65 | ||||||||||||||||||||||||||||
| 8.8 | OB 2 | ||||||||||||||||||||||||||||
| 6th | 7.3 | OM 67 | |||||||||||||||||||||||||||
| 7.4 | OM 67 | ||||||||||||||||||||||||||||
| 8.6 | OM 5 | ||||||||||||||||||||||||||||
| 10.3 | OM 79 | ||||||||||||||||||||||||||||
| 11.3 | OM 57 | ||||||||||||||||||||||||||||
| 12.5 | |||||||||||||||||||||||||||||
| OM 54 | |||||||||||||||||||||||||||||
| 12 | Boxer engine | 30.2 | OM 807 | ||||||||||||||||||||||||||
| V engine | 30.5 | OM 85 | |||||||||||||||||||||||||||
| OM 86 | |||||||||||||||||||||||||||||
| Legend: | Benz engines | Daimler-Benz engines | |||||||||||||||||||||||||||