Introduction
The Mercedes-Benz M260 and M264 are inline, four-cylinder petrol engines that are part of a modular engine family with:
- The OM654 four-cylinder diesel engine;
- The OM656 inline six-cylinder diesel engine;
- The M256 turbocharged inline six-cylinder petrol engine; and,
- The M176 biturbo V8 petrol engine.
While the M260 engine will be fitted transversely in front-wheel drive vehicles, the M264 engine will be fitted longitudinally for rear-wheel drive vehicles. Like the M256, the M260 and M264 engines have been designed for electrification and have both 48 and 12 volt electrical systems. High-output (‘Toptype’) versions of the M264 engines will produce up to 200 kW.
Production of the M260 and M264 engines will commence at Mercedes-Benz’s Untertürkeim plant in Baden-Württemberg in 2018. The M260 and M264 engines effectively replaced the M270 and M274 engines, respectively.
Crankcase
While Mercedes-Benz has not announced specifications of the M260 and M264 engine, the modular design with the M256 engine suggests that the aluminium crankcase will have 83.0 mm bores – spaced at 90 mm intervals – and a 90 mm stroke for a capacity of 2000 cc.
Within the cylinder bores, twin-wire arc spraying (TWAS) is used to apply a low-friction coating (‘Nanoslide’) that is based on an iron-carbon alloy. Since the Nanoslide coating results in a microporous surface for the cylinder walls, effective lubrication is achieved without the need for cast-iron cylinder liners. According to Mercedes-Benz, the Nanoslide coating reduces friction between the piston, piston rings and cylinder wall by up to 50 per cent and achieves a mass reduction of several kilograms.
To reduce vibrations, the M260 and M264 engines have plastic engine mounts.
Chain drive
The timing chain for the M260 engine is located on the flywheel side and acts directly on a sprocket attached to the crankshaft. As such, the primary chain drives the high-pressure fuel pump, the oil pump and the camshaft drive gear which, in turn, drives the exhaust camshaft; the exhaust camshaft then drives by the intake camshaft.
Cylinder head and Camtronic
The cylinder heads of the M260 and M264 engines are made of an aluminium-silicon alloy. Mounted in a separate camshaft bearing housing, the two overhead camshafts operate two intake valves and two exhaust valves per cylinder via roller cam followers. The valves are arranged in parallel to optimise the cross-section and strength of the combustion plate.
Previously introduced on the M270 engine (see video below), the ‘Camtronic’ system provides intake valve lift adjustment. For Camtronic, the intake camshaft has two hollow-drilled sub-shafts of equal size which are mounted on the carrier shaft. The first sub-shaft controls the intake valves of cylinders 1 and 2, and the second sub-shaft controls the valves of cylinders 3 and 4. As such, the intake camshaft takes the form of a double-cam with two curved surfaces. While Camtronic operates mechanically, it is served by an electronically-controlled double actuator which can adjust valve lift for all four cylinders within one camshaft revolution. When the steeper half of the cam is active, valve lift is increased and the valves remain open for longer. Switching to the flatter half of the cam, however, reduces valve lift and the valves close sooner.
In addition to variable intake valve lift, hydraulic vane-type camshaft adjusters on the intake and exhaust sides.For the M270 engine, the camshafts had an adjustment range of 40 degrees relative to the crankshaft.
Twin-scroll turbocharger
The M260 and M264 engines have a single twin-scroll turbocharger, while boost pressure is controlled via an electric wastegate actuator. In a twin-scroll turbocharger, the spiral housing of the turbine is divided by a flow separator into two parallel flow channels. In combination with a two-pipe exhaust manifold, this design enables the exhaust gases to be separately supplied to the turbine wheel to prevent interference between the individual cylinders during the charge cycle. As a result, twin-scroll turbochargers can produce high torque at low engine speeds with high specific output.
48 volt and 12 volt electrical systems
Like the M256, the M260 and M264 engines have been designed for electrification and, as such, have 48 volt and 12 volt electrical systems. Whereas the M256 engine has an Integrated Starter-Alternator (ISG), the M260 and M264 engines have a belt-driven starter-alternator (BSA) which combines the starter and alternator. Like a conventional alternator, the BSA is connected to the crankshaft by a belt drive. For the M260 and M264 engines, the 48 volt electrical system is used to power the BSA and the electric water pump.
For the M260 and M264 engines, the BSA provides the following fuel-saving hybrid functions –
- Boost: up to 10 kW of output to support the engine during acceleration at engine speeds up to 2500 rpm;
- Partial recuperation of kinetic energy during braking of up to 12.5 kW;
- Shifting of the load point: operation of the electric motor can enable the engine to be operated in a more favourable area of the engine map. Engine load can also be increased or decreased depending on the state of charge of the battery;
- iECO: extended stop/start with intelligent engine shut-off even at low speeds;
- A coasting function which can shut down the engine; and,
- ‘Easy start’: virtually imperceptible starting and acceleration of the engine since the 48 volt system brings the engine to idle speed smoothly; and,
Mercedes-Benz expects that all its passenger vehicles will be ‘electrified’ in the future. The 48 volt electrical system is a development in this progression and is initially introduced as a sub-system for functions inside the engine compartment. Since a 48 volt system requires only one quarter of the current of a 12 volt system for the same power output, the wiring can also be made thinner to reduce vehicle mass.
Direct injection
The M260 and M264 engines have direct injection in which piezo injectors spray fuel at high pressure into the four combustion chambers.
Exhaust and particulate filter
With the M256 and M176 engines, Mercedes-Benz claims to be the first manufacturer to ‘opt for the large-scale use of particulate filters for petrol engines’; the M260 and M264 engines will also be equipped with a particulate filter subsequent to their release.
For the Mercedes-Benz’s petrol engines, the particulate filter works in a similar way to the technology in diesel vehicles. Specifically, the exhaust gas stream passes through a particulate filter that has a honeycomb structure with alternately sealed inlet and outlet channels. As such, the exhaust gas is forced to flow through a porous filter wall which traps the soot. The filter can also be continuously regenerated under certain driving conditions. While Mercedes-Benz uses ceramic particulate filters of silicon carbide (SiC, also known as carborundum) in diesel vehicles, the particulate filter for petrol engines is based on cordierite, a magnesium iron aluminium cyclosilicate.
