Mercedes-Benz launches medium-duty engine range14 March 2012

Mercedes-Benz has introduced a completely redesigned engine series for light and heavy-duty trucks, as well as buses and coaches.

The medium-duty four- and six-cylinder engines of the OM 93x series, offer displacements of either 5.1 or 7.7 litres, with power outputs ranging from 156bhp to 354bhp.

According to Mercedes-Benz, the new engines are designed with environmental compatibility, economic efficiency and performance in mind.

The new range is also the first commercial vehicle engine series where every engine meets the Euro 6 emissions standard right from the outset.

One of the many technical highlights is the first use, in series-production diesel engines, of an adjustable camshaft. The adjustment supports regeneration of the essential diesel particulate filter.

If regeneration is needed, the timing can be adjusted by up to 65 degrees to 'early': in this case the exhaust valves open and close earlier, so the exhaust gas released from the cylinder is hotter.

The adjustment is made hydraulically via a vane piston on the exhaust camshaft, acting on a signal from the ECU – with engine oil flowing into the vane piston, which turns to alter the position of the camshaft relative to its drive gear.

Other features include its crossflow cylinder head, with four valves per cylinder, and intake and outlet valves arranged in parallel pairs – an arrangement that keeps the intake and outlet ducts as short as possible and hence flow losses (and fuel consumption) to a minimum.

Also, the cylinder head and crankcase have been robustly joined. The former is formed from grey cast iron with lamellar graphite (GJL), developed by Mercedes-Benz in Mannheim, claimed to give exceptional strength and thermal properties. Meanwhile, the crankcase is attached via no fewer than six bolts per cylinder – which some might regard as over-engineering.

Meanwhile, the dual overhead camshafts harness another Mannheim speciality – hollow tube composite technology, with the cams shrink-fitted, making for a lightweight yet solid design, as used in the OM 471, launched last year.

Other key elements include the rigid crankshaft and crankcase – the latter using a supporting spar structure made out of the same material as the cylinder head. That's what enables the high combustion pressures, while at the same time reducing noise.

And so it goes on, with attention to detail, right down to the way the crankshaft drives the camshafts via a compact and rigid gear drive on the back of the engine. Gear wheels on the flywheel side of the engine help reduce noise, while also driving the unusually compact arrangement of auxiliary units and optional available live engine PTO, with up to 600 Nm of net torque.

Incidentally, injection pressure is up to 2400 bar, based on a common-rail design with an oil-lubricated, high-pressure pump and centrally-positioned injectors – and the unit enables up to five individual injections per cycle.

Oh, and there's also customised turbocharging for each output category. In the four-cylinder OM 934, pressure for output up to 177bhp comes from a single-stage exhaust gas turbocharger. Two-stage turbocharging is then used for the higher outputs. The six-cylinder OM 936 uses an asymmetric exhaust gas turbocharger with double-flow turbine for outputs up to 299bhp. Two-stage charging with twin turbochargers is used once again for the two output categories above this level.

Author
John Challen

Related Companies
Mercedes-Benz UK Ltd

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