Mercedes-Benz OM 138

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Daimler-Benz AG
OM 138

OM 138
OM 138
Production period: 1935-1940
Manufacturer: Daimler-Benz AG
Working principle: diesel
Motor design: R4
Valve control: OHV
Displacement: 2545 cm 3
Mixture preparation: Pre-chamber injection
Engine charging: no
Power: 33 kW
Dimensions: 300 kg
Previous model: none
Successor: Mercedes-Benz OM 636

The Mercedes-Benz OM 138 is from late 1935 to 1940 a total of 5719 times built four-cylinder - diesel engine of Daimler-Benz AG and the first diesel engine, which was developed specifically for use in a passenger car. The abbreviation "OM" means "Oel-Motor", i. H. an engine that runs on light oil / diesel and is still used today for the diesel engines of Daimler AG. The first vehicle to be equipped with the OM 138 is the Mercedes-Benz W 138 . In addition to the passenger car, the OM 138 was also used in the L 1100 and L 1500 light commercial vehicles, including the O 1500 bus model. The engine was offered as a boat drive under the designation BOM 138.

meaning

From 1928, Daimler-Benz AG built the six-cylinder OM 5 diesel engine in series for trucks . With technical improvements, the speed could be increased, which made it possible to adopt the diesel engine in a car. The motivation for the move was profitability . While the OM 138 diesel engine in the Mercedes-Benz W 138 consumed around 10 liters per 100 km, the gasoline engine in the related Mercedes-Benz W 21 required 13 liters. Since diesel fuel was also significantly cheaper than gasoline, the Mercedes-Benz W 138 with diesel engine prevailed, especially in frequent taxis.

Although the OM 138 was developed as a passenger car engine, of the total of around 5700 units built, 3752 made up around two-thirds of the engines that went into commercial vehicle production. The OM 138 was only installed in 1967 times in the W 138 car model. Although the production of passenger car diesel engines at Daimler-Benz AG began with him, there were still hardly any passenger cars with this drive on the overall automotive market. That changed only towards the end of the 1970s with the introduction of the EA 827 series from the Volkswagen group.

development

The W 138 was equipped with the OM 138 developed for this purpose.
Also equipped with the OM 138: The light trucks L 1100 and L 1500. However, the vehicle shown in the picture has a wood gas system and, accordingly, a gasoline engine.

The development of a diesel engine for passenger cars began at Mercedes-Benz in the autumn of 1933. The first attempts were made with a 3.8-liter six-cylinder commercial vehicle unit that developed a nominal output of 80 hp (59 kW). However, this engine caused excessive vibrations in test car chassis, so that a less powerful engine was sought. First, completely new engines were developed, including the OM 134, a water-cooled three-cylinder in-line diesel engine with 30 hp (22 kW) and the OM 141, a four-cylinder diesel engine with 35 hp (26 kW). However, the tests with these engines were not satisfactory, so that the concept of the commercial vehicle engine was used again to develop a suitable engine. While maintaining the bore and stroke, the end of 1934 was achieved by reducing the number of cylinders to just four. In 1935, the engine was finally ready for series production, initial problems such as excessive exhaust emissions and uneven engine running were resolved.

The engine designer was Albert Heeß , who also developed the engines for the Mercedes Silver Arrows .

technology

The OM 138 is a naturally aspirated inline four-cylinder four-stroke diesel engine with pre-chamber injection , pressure circulation lubrication , OHV valve control and water cooling. Its displacement is 2.54 liters. With a cylinder bore of 90 mm and a piston stroke of 100 mm, the engine is designed as a high-speed engine that delivers its rated output of 45 hp (33 kW) at a speed of 3000 min −1 as a car engine or 2800 min −1 as a truck engine reached.

Crankcase

The crankcase of the OM 138 consists of two parts, the lower part with the lower crankshaft bearing halves and the upper part with the cylinder bank and camshaft . The upper and lower part are connected with stud bolts at the level of the horizontal crankshaft center. The lower part, reinforced on the inside by transverse ribs, is made of light metal , the gear flange is cast onto it. The upper part is made of gray cast iron , it extends from the crankshaft to the cylinder head . On the front of the engine, a bulge is formed on the upper part of the crankcase, in which the lower camshaft runs; this means that the camshaft can be driven directly by the crankshaft without an intermediate gear. The camshaft has five bearings and is accessible through a cover in the bulge. Furthermore, brackets for the starter , alternator and injection pump are cast onto the crankcase. The crankshaft and camshaft bearings are lubricated by an oil line drilled into the crankcase.

Pistons and power transmission

The pistons are made of light metal, have three compression rings and an oil control ring. They transmit the force to connecting rods with an I-shaped shaft made of heat -treated steel , the bearing shells of the connecting rod are made of lead bronze and secured against twisting with a pin. An oil pipe is attached to the shaft of the connecting rod to lubricate the connecting rod bushings. The crankshaft with five bearings is provided with counterweights on the crank webs to relieve the crankshaft bearings and has hardened bearing journals. The connecting rod pins are bored hollow. The crankshaft bearing caps are each fastened with two studs. The flywheel is flanged to the crankshaft. A vibration damper is attached to the crankcase on the opposite side .

Cylinder head

The OM 138 has a one-piece cylinder head. The main components are the pre-chambers , which are inclined at approx. 45 ° to the combustion chamber and eccentrically out of the cylinder head , into which the fuel is injected. Between the main combustion chamber and the prechamber there is an atomization insert, which is common for Mercedes-Benz prechamber diesel engines. The injection nozzles are located in the prechambers in the cylinder head and are easily accessible from the outside, the same applies to the glow plugs at the bottom of the prechambers. The bumpers for the valve train, which are common in an OHV engine , are passed through the cylinder head on the OM 138 on the antechamber side. The exhaust and intake ports face the bumpers, with the intake port housed in the top surface of the cylinder head. The intake air enters the engine via the intake manifold in the longitudinally split cylinder head cover. The cylinder head cover is held on the cylinder head by four nuts.

Valve train and engine control

The front of the camshaft in the crankcase is flange-shaped to accommodate its drive wheel. Another gear is mounted between the flange and the drive wheel, which drives the injection pump. In the middle of the camshaft is a drive wheel for the engine's oil pump . The valves with double valve springs hanging in the cylinder head, one inlet and one outlet valve of the same size for each cylinder, are actuated by the camshaft via mushroom tappets with coil springs for mass balancing, push rods and rocker arms . The rocker arms, which are mounted on the bracket in bronze bearings, are connected to the pressure lubrication system and are pressed laterally against the bracket by springs. The fuel is of a Bosch - line injection pump size A conveyed to the injectors via said gear of the camshaft from an Oldham coupling is driven. The injection pump has a pneumatic regulator .

Lubrication and ancillary equipment

The oil pump is placed in the center of the engine in the oil pan and flanged to the crankcase. It has a short suction pipe with a suction funnel and sieve to suck the oil out of the oil pan and then to feed it through a slot filter to the main oil line. The control valve of the oil pump is easily accessible for setting the oil pressure. The water pump is built into the cylinder head on the face of the engine. Like the alternator, it is driven by a V- belt which is retensioned by swiveling the alternator. The fan wheel is mounted on the shaft of the water pump.

Technical specifications

Parameters OM 138
Engine design Four-cylinder in-line engine
Working principle diesel
Mixture preparation Pre-chamber injection
Valve control OHV valve control ,
1 × inlet, 1 × outlet valve
Bore × stroke 90 × 100 mm
Displacement 2545 cc
Rated speed Car engines: 3000 min -1
truck engines: 2800 min -1
Nominal power at nominal speed 45 hp (33 kW)
Torque at rated speed Car engines: 105 Nm (10.7 kp m)
Truck engines: 112.9 N m (11.5 kp m)
Medium work pressure 5.2 bar
Compression ratio 20.5: 1
Oil content 5 l
Dimensions 300 kg
Displacement 13 kW / l
Fuel consumption
(in the Mercedes-Benz W 138 ) 		10–11 l diesel oil / 100 km

literature

Individual evidence

  1. ↑ a b c d e Mercedes-Benz 260 D Pullman sedan. ( Memento from January 10, 2017 in the Internet Archive )
  2. ↑ Oswald, p. 139 and 231.
  3. ↑ a b February 1936: The diesel engine in passenger cars celebrates its premiere ( Memento from January 10, 2017 in the Internet Archive )
  4. ↑ BOM 138 boat engine
  5. ↑ 1927 - The pre-chamber diesel prevails ( Memento from January 10, 2017 in the Internet Archive )
  6. ↑ Diesel engines in Mercedes-Benz passenger cars - 1936 - Favorite of taxi operators ( Memento from January 10, 2017 in the Internet Archive )
  7. ↑ von Fersen, p. 38 u. 282
  8. ↑ Oswald, p. 275
  9. ↑ Diesel engines in Mercedes-Benz passenger cars - 1934 - four-cylinder diesel for passenger cars ( Memento from January 10, 2017 in the Internet Archive )
  10. ↑ Mercedes-Benz Veteranenclub eV - Type 260 ( Memento from January 10, 2017 in the Internet Archive )
  11. ↑ von Fersen, p. 274
  12. ↑ Landenberger, p. 46
  13. ↑ a b c Kremser, p. 126
  14. ↑ a b c d e f g h i j Kremser, p. 129
  15. ↑ a b c d Kremser, p. 128
  16. ↑ a b Kremser, p. 125
  17. ↑ a b Oswald, p. 231
  18. ↑ a b Kremser, p. 127
  19. ^ Kremser, p. 130

Remarks

  1. ↑ a b Oswald names 1082 copies for the L 1100 and 2670 copies for the L 1500, Daimler gives 1967 copies for the W 138.
  2. ↑ The O 1500 received its own model name, but had the same chassis as the L 1500.

Web links

Commons : OM 138  - collection of images, videos and audio files


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
This version was added to the list of articles worth reading on January 10, 2017 .