Η Mercedes-Benz έδωσε τις αναλυτικές λεπτομέρειες για τους κινητήρες που θα φορά η νέα A-Class η οποία θα ξεκινήσει να πωλείται από τον Σεπτέμβριο. Από πλευράς βενζινοκινητήρων υπάρχει ένας 1.600αρης και ένας 2.0-λιτρος τετρακύλινδρος κινητήρας, με τον 1.600αρη να διαθέτει το νέο σύστημα CAMTRONIC το οποίο ρυθμίζει τη βύθιση των βαλβίδων εισαγωγής που περιορίζει την ποσότητα του φρέσκου αέρα ώστε να μειώνει την κατανάλωση.
Στην έκδοση A180 ο 1.595 κ.εκ κινητήρα αποδίδει 122 άλογα με 200 Nm ροπής με μέση κατανάλωση 5.5 λίτρα/100 χλμ και 128 γρ/χλμ εκπομπές CO2. Τα 0-100 χλμ/ώρα τα κάνει σε 9.2 δευτ (9.1 με το 7G-DCT διπλού συμπλέκτη) με τελική ταχύτητα 202 χλμ/ώρα.
Η έκδοση A200 φορά τον ίδιο κινητήρα απόδοσης 156 ίππων με 250 Nm ροπής. Τα 0-100 χλμ/ώρα τα κάνει σε 8.4 δευτ (8.3 με το 7G-DCT διπλού συμπλέκτη) με τελική ταχύτητα 224 χλμ/ώρα. Έχει μέση κατανάλωση 5.5 λίτρα/100 χλμ και 129 γρ/χλμ εκπομπές CO2.
Στην κορυφή των βενζινοκινητήρων υπάρχει ο 2.0-λιτρος (1.991 κ.εκ) στις εκδόσεις A 250 BlueEFFICIENCY και Α 250 Sport, που αποδίδει 211 άλογα με 350 Nm ροπής. Συνδυάζεται αποκλειστικά με το αυτόματο 7G-DCT κιβώτιο διπλού συμπλέκτη, με τα 0-100 χλμ/ώρα να τα κάνει σε 6.6 δευτ με τελική ταχύτητα 240 χλμ/ώρα. Έχει μέση κατανάλωση 6.1 λίτρα/100 χλμ και 143 γρ/χλμ εκπομπές CO2.
Από πλευράς πετρελαιοκινητήρων, η έκδοση A 180 CDI φορά τον 1.500αρη (1.461 κ.εκ) κινητήρα απόδοσης 109 ίππων με 260 Nm ροπής με μέση κατανάλωση 3.8 λίτρα/100 χλμ και 98 γρ/χλμ εκπομπές CO2
Η έκδοση A 200 CDI φορά τον 1.800αρη (1.796 κ.εκ) κινητήρα απόδοσης 136 ίππων με 300 Nm ροπής με μέση κατανάλωση 4.1 λίτρα/100 χλμ και 111 γρ/χλμ εκπομπές CO2 και τέλος η A 220 CDI φορά τον 2.2-λίτρων κινητήρα απόδοσης 170 ίππων με 350 Nm ροπής.
Όλοι οι κινητήρες διαθέτουν το σύστημα ECO Start/Stop είτε συνδυάζονται με το 6-τάχυτο μηχανικό είτε με το 7G-DCT διπλού συμπλέκτη. Περισσότερες λεπτομέρειες μπορείς να βρεις στο δελτίο τύπου που ακολουθεί.
The development of the Mercedes-Benz A-Class: The drive system
High output, low consumption
Stuttgart. The beating heart of a new generation: the new Mercedes-Benz A-Class will create a sensation. Before deliveries to the European dealers commence in September 2012, Mercedes-Benz is providing a series of insights into major development aspects on the way to the market launch. This one concerns the powertrain.
A wide choice of petrol and diesel engines meets every power requirement and reaches new heights in terms of efficiency and environmental compatibility: the A 180 CDI will be the very first Mercedes-Benz to emit only 98 g of CO2 per kilometre. Moreover, the A 220 CDI is the first Mercedes to meet the Euro-6 emission standard which only comes into force in 2015. All engines of the new A-Class feature the ECO start/stop function as standard. The engines can be combined with the new six-speed manual transmission or optionally with the 7G-DCT dual clutch automatic transmission, which ideally combines comfort and sportiness.
Up to 26 percent lower fuel consumption compared to comparable preceding models, accompanied by a considerable power increase: these are the salient features of the engine range for the new A-Class. Diesels: the new basic engine in the OM 607 series develops 80 kW (109 hp), delivers 260 Nm to the crankshaft and with a manual transmission consumes 3.8 litres per 100 km, corresponding to 98 g of CO2/km. This is a 22-percent improvement over the only 60 kW (82 hp) preceding model, the A 160 CDI, which consumed 4.9 litres. The new top diesel, the A 220 CDI, is no less than 25 percent better than its predecessor: it develops an output of 125 kW (170 hp) and 350 Nm of torque, and in combination with the 7G-DCT automatic dual clutch transmission it consumes only 4.3 litres/100 km (provisional figure). The figures for the preceding A 200 CDI were 103 kW (140 hp), 5.7 litres, 149 g of CO2.
A comparison between the new and previous A 200 demonstrates what has been achieved with the petrol engines: with 115 kW (156 hp) and 250 Nm of torque, the new engine delivers superior performance but consumes only 5.5 litres/100 km (129g CO2/km), which is 26 percent less than its predecessor (100 kW, 185 Nm, 7.4 l/100 km, 174 g CO2). Even the new top model with 7G-DCT, 155 kW (211 hp) and 350 Nm is considerably more efficient with a consumption of 6.1 litres and CO2 emissions of 143 g.
The completely new engines and transmissions are not the only decisive factors in this exemplary efficiency. Thanks to the modular system, the optimal transmission configurations could also be chosen. The overall package also includes progressive aerodynamics with a Cd figure of only 0.27, together with a number of other improvements.
“The new four-cylinder models from Mercedes-Benz occupy a peak position by virtue of their performance, high efficiency and very low emissions. They impress with their smooth, superior power delivery and offer customers refinement at the highest level,” says Professor Thomas Weber, the member of the Daimler AG Executive Board responsible for corporate research and development at Mercedes-Benz Cars.
Economy right across the board
Downsizing for the entry-level engines and downspeeding for the more powerful units – that is the Mercedes-Benz strategy for the diesel engines in the new A-Class. The wide range meets every performance requirement, and demonstrates the potential residing in the diesel engine: for the first time – with the A 180 CDI – a Mercedes-Benz will emit just 98 g of CO2 per kilometre. As a further highlight, the A 220 CDI already meets the Euro-6 emission standard only coming into effect from 2015.
The diesel engines also boast extreme efficiency and environmental friendliness, thanks to state-of-the-art injection technology and turbocharging. The A 180 CDI kicks off at 80 kW (109 hp) and offers maximum torque of up to 250 Nm (dual clutch transmission) or 260 Nm (6-speed manual transmission). In the A 200 CDI the maximum power output stands at 100 kW (136 hp), accompanied by maximum torque of 300 Nm. The A 220 CDI has a displacement of 2.2 litres and generates 125 kW (170 hp) with 350 Nm of torque, giving the performance of the A-Class a decidedly sporty touch.
From the S-Class to the A-Class: the diesel engines of the OM 651 series
Since its world premiere in 2008 the direct-injection diesel engine known as the OM 651 has been setting standards in terms of performance and torque characteristics, economy, emissions and smooth running. It is in more widespread use than any other Mercedes-Benz diesel engine and serves as a model of efficiency and power right up to the S-Class. For transverse installation the belt drive for the ancillary units, the installed position of the turbocharger and the air ducting have been modified.
No less than three versions are used in the new A-Class:
- Dynamic to drive, extremely efficient and outstandingly clean, the A 220 CDI is only available in combination with the 7G-DCT dual clutch transmission. The 125 kW (170 hp) top diesel is equipped with a weight-optimised crankshaft with individual bearing covers bolted from below and four counterweights, enabling it to tip the scales at around six kilograms less than a longitudinally installed OM 651 of the same displacement. The single-stage turbocharger has larger dimensions than that in the 80 and 100 kW variants. The A 200 CDI has multiple exhaust gas recirculation (see “Under the microscope”) to reduce nitrogen oxide emissions. It already meets the Euro-6 emission standard coming into force from 2015. With 112 g of CO2 per kilometre (provisional figure) the A 220 CDI sets new standards in its segment. With a displacement of 2.2 litres the engine is comparatively large, and therefore already agile at low rpm. “Downspeeding” is the term used by the engine specialists at Mercedes-Benz to describe this combination of a large displacement and low engine speeds. As a result it has been possible to make the ECONOMY mode of the 7G-DCT transmission decidedly economical and comfortable. If the driver selects “S”, gearshifts are performed much faster and the ratio spread uses the rpm reserves of the engine for dynamic performance. The performance of the A 220 CDI – which is available in BlueEFFICIENCY and Sport versions – is at sports car level with 7.8 seconds from zero to 100 km/h and a top speed of 227 km/h.
- The 1.8-litre engine variant is used in the A 180 CDI with the 7G-DCT dual clutch transmission and the A 200 CDI. The displacement was reduced by shortening the stroke (83 mm instead of 99 mm). The significantly longer connecting rods ensure lower transverse friction, and the two Lanchester balancer shafts are also of low-friction design. The single-stage turbocharger was optimised for efficiency and features adjustable vanes. With a distance between cylinders of 94 millimetres and cylindrical gears driving the camshafts, transverse installation and the necessary length restriction were part of the design specification from the very start.
To realise the start/stop function, the belt drive is decoupled from the crankshaft in all three engines.
Other common features include:
- Common rail technology with a rail pressure increased to 1800 bar. The maximum ignition pressure of 180 bar also contributes to the high power output and a muscular torque curve.
- The oil injection nozzles and the water pump are activated only when required, in order to save energy and fuel. The controlled oil pump additionally reduces oil flow and thus fuel consumption.
- The engine block is made of cast iron, the cylinder head of aluminium.
- A two-piece water jacket in the cylinder head provides for optimum cooling in the area of the combustion chamber plate. This enables an ignition pressure of 200 bar and a high specific power output.
- The cast iron barrels have undergone considerably finer honing than on the predecessor, also contributing to the reduction in fuel consumption.
- To compensate for the second-order forces which are inherent to four-cylinder in-line engines there are two Lanchester balancer shafts at the bottom of the engine block running in low-friction roller bearings rather than conventional plain bearings.
- The two-mass flywheel has been specifically designed for high engine torque at low engine speeds in order to isolate the crankshaft’s vibration stimuli, thereby contributing to the engine’s excellent smooth running.
Replete with Mercedes-Benz know-how: the OM 607
For the A 180 CDI with manual transmission Mercedes-Benz has had recourse to its cooperation with Renault to achieve fuel economy advantages from a compact, lightweight, low-friction engine which has been rigorously downsized. The common-rail four-cylinder with a rail pressure of 1600 bar is currently in its sixth generation, with more than 1.3 million units produced each year. This 1.5-litre engine with low-pressure EGR generates 80 kW (109 hp). With 98 g of CO2 per kilometre, it is among the most environmentally friendly diesels in the compact car segment. The turbocharger features variable turbine geometry (VTG).
This engine with the in-house designation OM 607 weighs around 30 kilograms less than an OM 651. Numerous components are specific to Mercedes-Benz, for example the OM 607 has the engine mountings of the M 270 petrol engine, as well as a special two-mass flywheel. The starter flanged onto the transmission, the alternator and the refrigerant compressor also come from the Mercedes modular system, and are driven by a belt with six grooves.
Like all Mercedes engines, the OM 607 was required to absolve the extensive engine test programme involving bench-testing and endurance runs. The application effort devoted to the OM 607 by Mercedes-Benz was very considerable. In a joint project team of Mercedes and Renault personnel the engine was especially improved with respect to NVH and driveability. Coordination work also went into the ECO start/stop function included as standard. This Mercedes-specific feature also operates at temperatures down to minus 10 degrees Celsius, for example, and can therefore make a more frequent contribution to fuel economy.
Overview of technical data for the A-Class with diesel engine
|Model||A 180 CDI*||A 180 CDI **||A 200 CDI***||A 220 CDI**|
|Rated output||[kW/hp] at [rpm]||80/109 4000||80/109 3200-4600||100/136 3600-4400||125/170 3600-4000|
|Rated torque||[Nm] at [rpm]||260 1750-2500||250 1400-2800||300 1600-3000||350 1600-3200|
|Fuel consumption, combined||[l/100 km]||3.8||4.1||4.3 (4.1)||n/a|
|CO2 emissions, combined||[g/km]||98||109||111 (109)||n/a|
* manual transmission, ** 7G-DCT dual clutch transmission, *** figures for 7G-DCT dual clutch transmission in brackets
Under the microscope: dual exhaust gas recirculation
Even lower combustion residues
To reduce nitrogen oxide (NOx) emissions even further, the OM 651 engine of the A 220 CDI is equipped with what is known as multiple exhaust gas recirculation (EGR). In addition to high-pressure EGR, where hot exhaust gases are taken from the manifold and reintroduced on the fresh air side, downstream of the intercooler, exhaust gases are diverted at a lower pressure level. This low-pressure EGR diverts the filtered exhaust gases downstream of the diesel particulate filter, cools them and uses a valve to return them to the fresh air flow upstream of the turbocharger.
NOx generation is primarily influenced by the oxygen concentration in the combustion chamber (= proportion of exhaust gases). A further increase in EGR rates using classic high-pressure EGR has the inherent disadvantage of charging losses and further throttling to achieve the necessary scavenging gradient. This leads to disadvantages with respect to particulate emissions and fuel consumption. Low-pressure EGR solves these problems, as it does not reduce the drive energy of the turbocharger while at the same time considerably reducing the throttling requirement of a high-pressure EGR system.
The petrol engines
Powerful, responsive and super-clean
Mercedes-Benz has systematically transferred the BlueDIRECT technology of the V6 and V8 engines in the Mercedes-Benz luxury class. The BlueDIRECT four-cylinder petrol engines for the new A-Class combine great responsiveness and exemplary power delivery with outstanding efficiency and the best emission figures in this class. The world-first CAMTRONIC, an innovative valve lift adjustment feature, makes a major contribution to this. There is a choice of 1.6 or 2-litre variants of the new four-cylinder engine family for the A-Class, covering a power range from 90 kW (122 hp) and 200 Nm to 155 kW (211 hp) and 350 Nm.
Thanks to BlueDIRECT and highly precise piezo-injection, the new engines are already expected to meet the Euro-6 emission standard for petrol engines coming into force from 2015. Even the much more stringent diesel particulate limit in the Euro-6 standard is already bettered with no additional exhaust aftertreatment. This was a major motivation for introducing BlueDIRECT into this segment as well. This means that the completely newly developed generation of four-cylinder petrol engines is ideally prepared for the future.
The basis for all three petrol engine variants in the new A-Class is the all-aluminium M 270 engine with two chain-driven overhead camshafts and four-valve technology. This power unit is extremely versatile, and will also be gradually introduced into larger model series. In this way it also contributes to a sustained reduction in production costs. The four-cylinder can be installed transversely (M 270) or longitudinally (M 274), and combined with front, rear or 4MATIC all-wheel drive, and also with a manual, automatic torque converter or dual clutch transmission.
The BlueDIRECT family has grown: three new petrol engines
The M270 engine is available in three power classes in the new A-Class. As the A 180 BlueEFFICIENCY with a displacement of 1595 cc it develops 90 kW (122 hp) and a maximum torque of 200 newton metres over a wide engine speed range from 1250 to 4000 rpm. With the basic engine and the 6-speed manual or seven-speed dual clutch transmission (figures in brackets) the A-Class accelerates from zero to 100 km/h in 9.2 seconds (9.1 seconds), and has a top speed of up to 202 km/h (202 km/h). The fuel consumption and CO2 emission figures of 5.5 l/100 km (5.4 l/100 km, both NEDC combined) resp. 128 g/km (127 g/km) are so low that they possibly set a new record.
The A 200 BlueEFFICIENCY with the same displacement of 1595 cc develops 115 kW (156 hp) and a maximum torque of 250 Nm, which is likewise available from 1250 to 4000 rpm. It sprints from zero to 100 km/h in 8.4 seconds (8.3 seconds) and has a top speed of 224 km/h (224 km/h), but is happy with an average 5.5 l/100 km of fuel (5.4 l/100 km), corresponding to CO2 emissions of 129 g/km (127 g/km).
The new, top engine variant with 1991 cc is available as the A 250 BlueEFFICIENCY or A 250 Sport. In both cases the engine develops 155 kW (211 hp) and a maximum torque of 350 Nm from 1200 to 4000 rpm. Performance is at sports car level, with acceleration from zero to 100 km/h in 6.6 seconds and a top speed of 240 km/h. Nonetheless it has the best fuel consumption in this class at 6.1 l/100 km, and CO2 emissions of 143 g/km (A 250 BlueEFFICIENCY).
All engine variants are designed for customer-friendly operation with E10 premium petrol (95 RON).
Overview of technical data for the A-Class with petrol engine
|Model||A 180*||A 200*||A 250**|
|Rated output||[kW/hp] at [rpm]||90/122 5000||115/156 5000||155/211 5500|
|Rated torque||[Nm] at [rpm]||200 1250-4000||250 1250-4000||350 1200-4000|
|Fuel consumption, combined||[l/100 km]||5.5 (5.4)||5.5 (5.4)||6.1|
|CO2 emissions, combined||[g/km]||128 (127)||129 (127)||143|
*figures for 7G-DCT dual clutch transmission in brackets, ** only available with dual clutch transmission
Engine technology from the S-Class for the A-Class
The technology package in the new four-cylinder petrol engines includes a number of new developments which were introduced in 2010 with the ultra-modern BlueDIRECT V6 and V8 engines for the Mercedes-Benz S-Class, and are now available in the compact class for the first time.
The combustion process is based on third-generation Mercedes-Benz direct injection with highly precise, multiple piezo injection technology. In 2006 Mercedes-Benz was the first car manufacturer to introduce direct injection with spray-guided combustion into series production.
Piezo injectors for very low particulate emissions below the Euro-6 limits
Newly developed piezo injectors allow up to five injections per power stroke. In the warm-up phase this enables particulate emissions to be reduced by more than 90 percent. The overall result is that all emission figures including particulates are now already below the limits set by the Euro-6 emission standard, which only comes into force from 2015.
Compared with conventional multi-hole solenoid valves, piezo injectors have numerous advantages in petrol engines. The fuel vaporises up to four times as fast, the jet of fuel penetrates less deeply into the combustion chamber and the injectors are able to deliver minute quantities of fuel extremely precisely. All this prevents fuel from being deposited on the combustion chamber walls, resulting in significantly reduced particulate emissions. Moreover, multiple injections allow operating strategies for maximum fuel efficiency while improving cold-start characteristics.
The crystalline structure of the piezo-ceramic changes in microseconds under an electric voltage, and with a precision of just a few thousandths of a millimetre. The central component of a piezo-electric injector is the piezo-stack, which directly controls the metering needle. With a response time of just 0.1 milliseconds, the fuel injection can be very sensitively and precisely adjusted to the current load and engine speed, with a beneficial effect on emissions, fuel consumption and combustion noise.
Multi-spark ignition for optimal efficiency
The third-generation direct injection system also features “rapid multi-spark ignition” (MSI). Following the first spark discharge and a brief combustion period, the coil is recharged rapidly and a further spark is discharged. The MSI system enables up to four sparks to be discharged in rapid succession within one millisecond, creating a plasma with a larger spatial expansion than conventional ignition.
The rapid multi-spark ignition can be actuated to vary both the timing of the sparks and the combustion period to suit the relevant operating point. This provides scope for the best possible centre of combustion and improved residual gas compatibility. This in turn reduces fuel consumption. Fuel savings of up to 4 percent are possible alone by the use of piezo-electric injection technology in combination with multi-spark ignition, depending on the driving cycle.
CAMTRONIC: up to ten percent lower fuel consumption
A trailblazing innovation known as CAMTRONIC is celebrating its debut in the 1.6-litre engine. For the first time in a turbocharged direct-injection engine, a load management system with an earlier intake cut-off and intake valve lift adjustment has been realised. This reduces the throttle losses under partial load, lowering fuel consumption. In the New European Driving Cycle (NEDC), fuel consumption is reduced by three to four percent compared to the M 270 without CAMTRONIC. In day-to-day driving, which typically has a high proportion of partial load operation, the potential saving is even greater, with fuel savings of up to ten percent in certain operating ranges. This world first was developed completely in-house by the Mercedes-Benz Technology Center in Stuttgart and the Daimler engine plant in Berlin.
No turbo-lag thanks to scavenging
Above all, Mercedes-Benz engineers were able to obtain a high output from a small displacement by the use of a turbocharger. This forces the intake air into the combustion chambers at a pressure of up to 1.9 bar, with the turbine vanes rotating at up to 230,000 rpm. The charger has been designed to deliver high torque even at low engine speeds. A newly developed manifold turbocharger module is integrated and positioned in front of the engine for the best possible cooling. Separate exhaust ducting from the cylinders to the turbocharger and the high exhaust temperature of up to 1050 degrees Celsius make optimal use of the exhaust gas energy, producing a high output and outstanding responsiveness.
By using a combination of direct injection and variable adjustment of the intake and exhaust camshafts, the developers were also able to exploit the advantages of so-called scavenging: partly overlapping the opening times of the intake and exhaust valves causes some of the cold intake air to flush the hot exhaust gas from the cylinder into the exhaust manifold, which considerably improves charging compared to conventional operation.
Especially at low engine speeds, and thanks to the increased mass flow in the exhaust tract, the turbocharger also responds much more rapidly – this completely avoids any “turbo-lag” or delay when moving off. The direct injection system ensures that the fresh gas is not yet mixed with fuel when it enters the cylinder, as would be the case in engines with manifold injection. There are therefore no undesirable scavenging losses, i.e. unburned fuel flushed into the exhaust manifold.
Torque levels like a diesel
As a result the new 1.6-litre four-cylinder in the A-Class already delivers its maximum torque at 1250 rpm, maintaining it to 4000 rpm. The 2.0-litre even does a little better: its maximum torque of 350 Nm is already available from 1200 rpm, which means that for low-end torque it leads the field for four-cylinder engines.
In combination with the new 7G-DCT transmission, whose control unit communicates with the engine management system, the new four-cylinder responds to the accelerator very readily. At cruising speed a higher ratio can be chosen, which further improves fuel consumption and noise level. The turbocharged engines also maintain their exemplary fuel consumption under high loads, as the outstanding cooling system only makes a richer mixture necessary at speeds above 200 km/h. A two-piece water jacket with optimised cross-flow cooling and fine, only three-millimetre wide cooling ducts between the spark plugs and injectors bring the coolant to the right places.
Thermal management shortens the warm-up phase
A new thermal management system has also been developed: in cold state, a switchable water pump with flow-optimised ball valve ensures that no coolant flows through the engine, providing for swift heating-up of the combustion chambers after starting up the engine. The thermostat is electronically controlled and the coolant temperatures are adjusted according to driving style and ambient conditions. The thermostat itself is also a flow-optimised ball valve. In the interest of high efficiency, the volumetric flow of the oil pump is also controlled as in the V engines.
Controlled oil pump with two pressure stages
The variable vane-type oil pump operates with two pressure stages, depending on the characteristic map. At low engine speeds and loads the pump runs at a low pressure of two bar. At this time the oil-spray nozzles for piston cooling are switched off. The high-pressure stage is activated at the upper load and engine speed levels. Thanks to this control concept, depending on engine load and engine speed the lubrication and cooling points of the engine can be supplied with significantly lower drive energy than would be possible with an uncontrolled pump.
New coolant ducting and 3-phase thermal management
The coolant ducting in the cylinder head is also completely new. The water mantle is of two-piece construction to improve flow. This leads to specific increases in flow speeds and heat dissipation at certain points, accompanied by a rigorous reduction in pressure losses throughout the coolant circuit. This has made it possible to reduce the power output of the water pump despite an increased engine output.
As it warms up, the flow of coolant is regulated by a 3-phase thermal management system so that it rapidly reaches normal operating temperature. Initially the coolant remains at rest in the engine. It then circulates in the engine circuit, but without the radiator. When a temperature of 105 degrees Celsius has been reached in normal operation (87 degrees Celsius under high load), the vehicle’s radiator is included in the circuit.
ECO start/stop function with direct-start
The start/stop system included as standard in all models operates with starter-supported direct-start. This means that when the engine is switched off, the attitude of the crankshaft is registered by a new crankshaft sensor so that the engine control unit knows the positions of the individual cylinders. On restarting, it can then select the cylinder that is in the most suitable position for first ignition. After the starter has briefly turned over the engine, reliable injection, ignition and combustion is immediately possible in the ideally positioned cylinder.
First use of Lanchester balancer shifts with antifriction bearings in a petrol engine
The secondary inertia forces inherently occurring in a four-cylinder in-line engine are compensated by two Lanchester balancer shafts in the bottom of the engine block. Mercedes-Benz is the first automobile manufacturer to use antifriction bearings to balance masses: imbalances are compensated by cylinder roller bearings, with axial forces from the gearing taken up by a ball bearing. This arrangement not only improves driving comfort, but also helps to lower fuel consumption thanks to considerably less friction. In view of the more favourable connecting rod configuration, the 1.6-litre version requires no Lanchester dynamic balancing.
Particular attention was also paid to reduced friction. This was primarily achieved by a reduction in flow through the oil and water pumps, low-friction pistons, piston rings and cylinder walls, plus the new thermal management system and chain drive.
The engine and transmission are mounted at four points by an engine mounting, a transmission mounting and two pendulum supports. These are specially configured for the needs of the high-torque engine variants with a view to maximum noise comfort. The hydraulic damping integrated into the transmission mounting also contributes decisively to the excellent driving comfort.
Using the camshaft to accelerate
Mercedes-Benz is the first automobile manufacturer to equip the 1.6-litre version of the M 270 engine with CAMTRONIC intake valve lift adjustment. The system operates mechanically, but is served by an electronically controlled actuator. The intake camshaft is made up of several components: two hollow-drilled sub-shafts of equal size are mounted on the carrier shaft. Mercedes-Benz engineers refer to these as “cam-pieces”, of which the first controls the intake valves of cylinders 1 and 2, and the second those of cylinders 3 and 4. The cams themselves are masterpieces of the caster’s art: they take the form of a double-cam with two curved surfaces. The surface operating the valves via roller-type rocker arms is only half as wide as on a conventional cam, therefore the space requirement is the same.
When the steeper half of the cam is active, the valve lift is increased and the valves remain open for longer. Switching to the flatter half of the cam shortens the valve lift and the valves close sooner.
“Accelerating” with the camshaft
Load control with the smaller valve lift is realised using various components. At very low engine torque the load control is conventional, using the position of the throttle flap, at medium torque levels using the position of the intake camshaft and at high torque levels using the charging level of the turbocharger.
As the torque increases the valve lift is switched to the larger level, load control once again being conventional via the throttle flap or, in the charged operating range, via the charging level of the turbocharger. In popular terms one might also say that the new Mercedes-Benz A-Class also accelerates with its camshaft.
Mercedes-Benz development engineers took numerous measures to ensure the most efficient combustion even with the smaller valve lift. Owing to the smaller valve lift and early intake valve closure, the turbulence in the combustion chamber is reduced at the spark plug. This turbulence decisively influences the combustion speed and full combustion of the fuel/air mixture. To compensate this apparent disadvantage, the turbulence is increased in the lower partial load range by using a multiple injection strategy with injection ignition, while multi-spark ignition ensures reliable combustion.
The switchover from the smaller to the larger valve lift goes unnoticed by the driver. As cylinders 1 and 2 as well as 3 and 4 are coupled in pairs with one cam-piece each, it is possible to adjust the valve lift of all four cylinders within one camshaft revolution using just one double actuator. A correspondingly large effort was required to develop the synchronisation for the switching process and ensure the long-term durability of the components.
The variable, hydraulic vane-type camshaft adjusters on the intake and exhaust sides have a wide adjustment range of 40 degrees with reference to the crankshaft. This new development excels by virtue of its significantly smaller dimensions. The installation space along the engine’s longitudinal and vertical axes can therefore be made very compact.
Under the microscope: engine test benches
Trial by ordeal
Before the new engines were allowed onto the roads for practical endurance trials, they had already absolved a series of tortures on the engine test benches of the test facility in Untertürkheim. 24 of the very latest engine test benches are installed on each floor of this imposing three-storey building. These 72 test benches are in operation by day and night, on 365 days of the year.
The test-benches can be used to simulate a wide variety of road and load cycle situations to reflect every conceivable operating profiles, e.g. hot and cold-starting, stop-and-go traffic and long-distance operation under a wide variety of conditions. Even steep mountain gradients can be simulated in the laboratory: a pivoting test rig is e.g. used to tilt the engine by up to 40 degrees to examine the effects on the oil circuit.
At various development stages the engines are subjected to accelerated stress tests. “This simulates stresses that no customer can achieve,” says Thomas Uhr, who is responsible for the workshops at the Mercedes-Benz development centre and for powertrain testing. The test-bench programmes have a duration of 500 to 2400 hours, with large proportions under full load and partial load. Thermal characteristics and component durability are tested under full load conditions, however particularly low loads can also be a real torture for an engine in the form of e.g. engine oil sludging. Other tests include heavy stresses such as cooling the coolant from 110° C to approx. 25° C within a max. of 60 seconds, and running the engine up to its rated speed under full load when the coolant is cold. Thomas Uhr: “We test our engines more intensively than any other manufacturer.”
The new OM 607 diesel engine absolved more than 25,000 hours on the test-benches, for example, before it received approval for use in the A-Class.
The energy generated by the test engines is recovered as fully as possible. The engine testing facility in Untertürkheim is certificated as a combined heating and power plant: only active equipment is used to monitor and measure engine power. This power is not used to propel a vehicle as in normal use, but rather converted into electrical energy and fed into the plant’s power network.
In addition to long-term durability, fuel consumption, emissions and driveability in conjunction with the transmission are the major development goals. This requires enormously painstaking dynamometer tests followed by practical trials on the roads.
The 7G-DCT dual clutch transmission
Dynamic and efficient
Drawing on over 50 years of experience in the development and production of automatic transmissions, Mercedes-Benz ventured into new technical territory with the 7G-DCT dual clutch transmission: the new system is an automated three-shaft manual transmission consisting of two subtransmissions, each with its own clutch. Both actuation of the clutches and gear shifting take place fully automatically and without any interruption in tractive power. This allows a particularly comfortable but nevertheless dynamic mode of driving.
Thanks to its seven gears it offers an exceptionally large spread of up to 7.99. This means that a very short transmission ratio is available when moving off on an uphill slope with a high payload, for example, while during cruising the engine speed can be lowered considerably. The efficiency of this transmission leads to a nine percent improvement in fuel consumption compared to the CVT employed in the A-Class to date, and betters the consumption with a manual transmission.
At a length of 367 millimetres and a weight of 86 kilograms, the 7G-DCT is more compact and lighter than the transmissions in this torque class which have been available on the market to date. The clutches take the form of oil-cooled multi-disc clutches. The specially developed hydraulic fluid is actively cooled, thus ensuring correct functioning of the transmission even under extreme conditions, despite the comparatively low filling level of six litres. Excess engine heat can also be transferred to the transmission, which improves its efficiency.
For the first time on this type of unit, the transmission is supplied with oil by two oil pumps – one mechanical and one electric. The electric pump maintains the oil pressure when the engine is switched off via the start/stop function. This means that the transmission is immediately operational when the engine is restarted and the vehicle can move off again without any delay. In addition, the electric pump is able to support the mechanical pump when peak loads apply, enabling a more compact and efficient design for the mechanical pump.
Another new feature is electric activation of the hydraulics for the parking lock, which is locked by mechanical means. This “park by wire” function enables the transmission selector lever to be positioned as desired: it is located in the form of a steering column lever on the right behind the steering wheel in the A-Class. In combination with the electric parking brake, additional space has thus been created in the centre console for additional stowage facilities.
Three gearshift modes are available to the driver:
- ECONOMY: In this mode, the transmission performs gearshifts fully automatically and particularly comfortably. The gears are selected with due regard to a particularly economical style of driving at low revs.
- SPORT: The transmission performs gearshifts fully automatically. The shift and response times are shorter, with gearshifts at higher engine speeds.
- MANUAL: In this mode, the driver operates the transmission manually via shift paddles behind the steering wheel. The engine speeds at which the gears are shifted can therefore be freely chosen.
In ECO or Sport mode, the driver is still able to intervene manually in the gear-shifting process via the shift paddles. The transmission reverts to the selected automatic mode after the paddles have remained inactive for twelve seconds, or after a longer delay when driving downhill or on winding roads.
A key factor contributing to the overall efficiency and dynamism of the A-Class is the closely coordinated operation of the transmissions and engines. A continuous exchange of data between the control units ensures that the engines run at the ideal operating point at all times. The 7G-DCT transmission is manufactured at Daimler’s Stuttgart-Hedelfingen plant.
The six-speed manual transmission
Comfortable manual gearshifts
The new six-speed manual transmission was developed in parallel with 7G-DCT. They share a number of common parts and are both produced in Gaggenau and Rastatt.
The three-shaft transmission is also very compact (length 345 mm) and light (dry weight 46 kg) and incorporates a number of special features for particularly pleasant gearshifting. An integrated magnet on the gearshift shaft is detected by a Hall sensor. The idle position is identified in this way, making the start/stop function possible. The signal for reverse gear activates the reversing lights.
The large spread of 6.7 allows a reduction in engine speed while at the same time ensuring that sufficient tractive power is available when moving off with a fully laden A-Class and trailer up to a gross weight of 3.4 tonnes. The clutch is operated hydraulically and the gears are actuated via cables.
The overhead camshaft with third and fourth gears and the reverse gear do not run in the oil bath. This reduces drag torque, thus facilitating gear shifting at low temperatures in particular. The three-cone synchronisation of the first two gears serves the same purpose, while the following gears are provided with two-cone synchronisation. The weight-optimised cast aluminium shift forks are installed on anti-friction bearings on the shift rods, in order to reduce the shift forces.