Mercedes-Benz OM 138 diesel engine
|Daimler Benz AG|
|Manufacturer:||Daimler Benz AG|
|How it works:||diesel|
|displacement:||2545 cm 3|
|Fuel supply:||indirect injection|
|Successor:||Mercedes-Benz OM 636|
The Mercedes-Benz OM 138 is from late 1935 to 1940 a diesel engine of Daimler-Benz AG and the first diesel engine, which was developed specifically for use in a passenger car. The first vehicle equipped with the OM 138 is the Mercedes-Benz W 138 . addition to the passenger car, the OM 138 was also used in the light commercial vehicles L 1100 and L 1500 including the bus model O 1500 The engine was offered as a boot drive under the name BOM 138th
Daimler-Benz AG built in 1928 the six-cylinder diesel engine OM 5 for trucks in series. With technical improvements, the speed could be increased, which allowed a takeover of the diesel engine in a car. The motivation for the step was the profitability . While the diesel engine OM 138 in the Mercedes-Benz W 138 liters of about 10 consumed to 100 km, the required spark-ignition engine of the related Mercedes-Benz W 21 13 liters. In addition, since diesel fuel was significantly cheaper than gasoline, the Mercedes-Benz W 138 with diesel engine prevailed, especially in the case of many-driving taxis.
Although the OM 138 was developed as a passenger car engine, of the total of about 5700 units built with 3752, about two-thirds of the engines built were used in commercial vehicle production. In the car model W 138, the OM 138 was installed only 1967 times. Although it began production of passenger car diesel engines at Daimler-Benz AG, there were still very few passenger cars with this drive in the overall automotive market. This changed only towards the end of the 1970s with the introduction of the EA 827 series of the Volkswagen Group.
The development of a diesel engine for passenger cars began at Mercedes-Benz in the autumn of 1933. First attempts were made with a 3.8-liter six-cylinder commercial vehicle engine that developed a rated output of 80 hp (59 kW). However, this engine caused in experimental car chassis to large vibrations, so that a less powerful engine was sought. Initially, all-new engines were developed, including the OM 134, a 30hp (22kW) water-cooled, single row, six-cylinder diesel engine and the OM 141, a 35hp (26kW) four-cylinder diesel engine. However, the tests with these engines were unsatisfactory, so that the concept of the commercial vehicle engine was used again to develop a suitable engine. This became the end of 1934 while maintaining bore and stroke by reducing the number of cylinders to only four more achieved. In 1935, the engine was finally brought to maturity, initial problems such as heavy exhaust and uneven engine running were resolved.The engine's designer was Albert Heeß ,who also developed the engines for the Silver Arrows .
The OM 138 is an uncharged in-line four-cylinder four-stroke diesel engine with prechamber 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, its rated power of 45 hp (33 kW) at a speed of 3000 min -1 as a car engine or 2800 min -1 than Truck engine reached.
The crankcase of the OM 138 consists of two parts, the lower part with the lower crankshaft bearing halves and the upper part with cylinder bank and camshaft .upper and lower parts are connected at the height of the horizontal center of the crankshaft with stud bolts. The lower part stiffened by transverse ribs is made of light metal , the gearbox flange is cast on it. The upper part is made of gray cast iron , it is sufficient from the crankshaft to the cylinder head . At the front of the engine a bulge is formed at the bottom of the crankcase upper part, in which the underlying camshaft runs; Thus, the camshaft can be driven without intermediate directly from the crankshaft. The cam shaft is five times stored and accessible through a lid in the bulge. Furthermore, brackets forstarter , alternator and injection pump are cast on the crankcase. The crankshaft and camshaft bearings are lubricated by an oil line drilled in the crankcase.
The pistons are made of light metal, have three compression rings and an oil scraper ring. They transfer the power to connecting rods with I-shaped tempered steelshafts , the bearing shells of the connecting rods are made of lead bronze and secured against twisting with a pin. For lubrication of the conrod bushes, an oil pipe is mounted in the shaft of the connecting rod. The five-bearing crankshaft is provided with counterweights on the crank webs to relieve the crankshaft bearings and has hardened journals. The connecting rods are hollow drilled. The bearing caps of the crankshaft are fastened with two stud bolts each. The flywheelis flanged to the crankshaft. On the opposite side, a vibration damper is attached to the crankcase .
The OM 138 has a one-piece cylinder head. The main component is the pre-chambers , which are inclined by about 45 ° to the combustion chamber and eccentrically led out of the cylinder head , into which the fuel is injected. Between main combustion chamber and antechamber is used for Mercedes-Benz pre-chamber diesel engines usual atomization. The injectors are located in the antechambers in the cylinder head and are easily accessible from the outside, the same applies to the glow plugs down obliquely to the antechambers. The one with an OHV engineusual bumpers for the valve train are performed on the OM 138 on the antechamber side through the cylinder head. The exhaust and intake passages face the bumpers with the intake passage housed in the upper 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 by four bolts on the cylinder head.
The camshaft in the crankcase is flange-shaped at its front to receive its drive wheel. Between the flange and the drive wheel another gear is mounted, which drives the injection pump. In the middle of the camshaft is a drive wheel for the oil pump of the engine. The hanging in the cylinder head valves with double valve springs, each cylinder an inlet and an outlet valve of the same size will be on mushroom tappet with coil springs for mass balancing, bumpers and rocker arm from the camshaftactuated. The rocker arms mounted in bronze bearings on the box are connected to the pressure circulation lubrication and are pressed laterally against the box with springs.The fuel is delivered by a Bosch In - Line Injection Pump Size A to the injectors, which is driven via the aforementioned gear from the camshaft via a crosshead clutch. The injection pump has a pneumatic regulator .
The oil pump is placed in the middle of the engine in the oil sump and flanged to the crankcase. It has a short suction tube with suction funnel and strainer to suck the oil out of the oil sump and then feed it through a gap filter to the main oil line. The control valve of the oil pump is easily accessible for adjusting the oil pressure. The water pump is installed in the cylinder head at the front of the engine. It is, as well as the alternator, by a V-belt driven, which is tightened by rotating the alternator. The fan is mounted on the shaft of the water pump.
|engine design||Four-cylinder engine|
|principle of operation||diesel|
|mixture preparation||indirect injection|
|valve control||OHV valve control , |
1 × inlet, 1 × outlet valve
|Bore × stroke||90 × 100 mm|
|Rated speed||Car engines: 3000 min -1 |
Truck engines: 2800 min -1
|Rated power at rated speed||45 hp (33 kW)|
|Torque at rated speed||Car Engines: 105 N · m (10.7 kp · m) |
Truck Engines: 112.9 N · m (11.5 kp · m)
|Medium working pressure||5.2 bar|
|compression ratio||20.5: 1|
|oil content||5 l|
|displacement power||13 kW / l|
|Fuel consumption||10-11 liters of diesel oil|