Mercedes-Benz OM 457 diesel engine

Daimler
OM 457
Production period:	since 2003
Manufacturer:	Daimler
How it works:	diesel
Engine Type:	Line six-cylinder
displacement:	11,967 cm 3
Fuel supply:	Pump-line-nozzle
Engine charging:	Turbocharger withintercooler
Power:	185 - 335 kW
Dimensions:	1065 kg
Previous model:	none
Successor:	OM 47x series

The OM 457 is a water-cooled four - stroke diesel engine with pump-line-nozzle injection. It was developed for the drive of vehicles. It can be installed longitudinally or transversely. The displacement of 11,967 cm³ results from a bore of 128 mm together with 155 mm stroke. The ignition sequence of the engine is 1 - 5 - 3 - 6 - 2 - 4, the crankshaft rotation is counterclockwise. The OM 457 is available in several variants for the emission standards Euro III to Euro V  in the power levels 185 - 335 kW.

The cylinder block and the crankcase are made of cast iron , the seven-bearing crankshaft is forged and has bolted counterweights. From the pistons, the power is transmitted to the crankshaft via forged  connecting rods . The engine has single-cylinder heads made of cast iron, which are screwed on with stud bolts. The engine crankcase incorporates coolant, fuel, and oil ports, as well as oil coolers, pump-injector units, and oil spray nozzles. The oil sump of the engine is made of aluminum alloy and holds 27 liters. It must contain at least 16 liters for proper operation, the volume of the oil filter is not included.

The OM 457 has a side down , seven-bearing camshaft. It is driven by a flywheel from the flywheel. The spur gear of the camshaft has a gear that drives the air compressor and the power steering pump. At the end of the camshaft sits a gear that drives the fuel pump. The camshaft per cylinder has one inlet and one exhaust cam, as well as another cam, which operates the unit injector.

The camshaft actuates two suspended intake and exhaust valves (OHV) per cylinder via tappets , bumpers and rocker arms . The inlet valves are connected via a horizontal crosshead (valve bridge), the same applies to the exhaust valves. On the middle of these trusses act at 45 ° angle to arranged rocker arms. Unlike a four-valve system with two overhead camshafts (DOHC), intake and exhaust valves are controlled by the same camshaft and there are only two cams for four valves.

The pistons are graphite coated from an aluminum alloy and below the piston rings. They have a height of 140 mm at the mentioned diameter of 128 mm. The mass of the pistons is 2470 g. The pistons have three piston rings. The piston ring is a chromium-ceramic coated trapezoidal ring made of gray cast iron. The second piston ring is conical and chrome-plated, the third piston ring is made of cast iron with bevelled edge and ring spring. Within the piston runs a cooling channel, which is fed by cooling oil. The combustion chamber in the piston (the piston recess) is divided and holds 93.6 cc. The piston crowns are cooled by oil spray nozzles in the crankcase, the piston pins have a diameter of 52 mm.

The fuel is injected through six- or seven-hole nozzles  with up to 1800 bar  in the cylinder, which are connected via relatively short high-pressure lines with pump-line-nozzle units. Unlike a common railSystem, each cylinder has its own high-pressure pump with its own high-pressure circuit. The pump-nozzle units are located next to the cylinders and are actuated directly by the underlying camshaft. The amount of fuel is controlled by solenoid valves from the controller. The required fuel first flows from the fuel tank into the fuel cooler, which is attached to the crankcase. From there, the fuel runs into the fuel pump, which pumps the fuel into the fuel filter. The fuel filter is heated and is equipped with a water separator for countries with poor fuel quality (primarily Eastern Europe). From the fuel filter, the fuel flows into the pump-nozzle units. Excess fuel is first fed via a leakage line to a pressure control valve, which returns the fuel to the fuel pump. From the fuel filter leakage line, excess fuel flows back into the tank. As fuels diesel fuels can afterEN 590 or EN 14214 . 

The cooling system has a water cooler and holds 15 liters, which is circulated by a pump with 7.7 liters per second at nominal engine speed. From a temperature of 83 ° C, the thermostat opens the valve from the motor water circuit to the water cooler, from 95 ° C it is fully open. The maximum water temperature should be 100 ° C. In addition to the radiator, the engine also has a fan, which is offered in two variants. The first variant has an oil-hydraulic coupling whose power transmission depends on the viscosity of the oil. As the engine temperature increases, the viscosity of the oil changes, causing the fan to spin faster. A disadvantage of this variant is the inertia. The second variant has an electromagnetic clutch that can control the fan speed more precisely. At least every three years, the coolant in the engine to be replaced.

The engine is charged by a turbocharger from BorgWarner with fixed vanes. The charge air is cooled by a charge air cooler before it reaches the intake tract. The exhaust gas is cleaned under the Euro 5 emission standard with SCR catalytic converter and AdBlue.  The air compressor for the compressed air system delivers 890 liters per minute with 12 bar system pressure and rated motor power. The electrical system operates at 24 volts and is powered by up to two V-ribbed belt alternators . To start the engine is a starter with 7 kW power.