Mercedes W176 A-Class 2012 –
Suspension: agility and refined sportiness
Refined sportiness means maximum agility combined with the sense of safety, unspoilt driving stability and high levels of ride comfort which are all typical of the brand.
The suspension of the new A-Class has a four-link rear axle, electromechanical power steering with assistance functions and ESP® with “Extended Traction Control” (XTC).
During development, the suspension experts made intensive use of simulations and the driving simulators at the Mercedes development centre in Sindelfingen as part of the so-called digital ride and handling test.
The preconditions for achieving dynamic handling are excellent in the A-Class. This is because compared with its predecessor the centre of gravity (24 mm lower) and seating position (174 mm lower) has been reduced significantly.
A new feature is the four-link rear axle: forces are absorbed by three control arms and one trailing arm per wheel.
This means that longitudinal and lateral dynamics are virtually independent of one another. Wheel carriers and spring links are made of aluminium to reduce the unsprung masses.
The goal was to achieve high lateral agility with high driving stability thanks to small sideslip angle on the rear axle.
Three chassis and suspension set-ups are available: the comfort suspension and optional sports suspension for sporty yet comfortable handling (in conjunction with the Dynamic Handling package or the AMG Sport equipment line).
In addition, the A 250 Sport has a sporty, “engineered by AMG” high-performance suspension.
Altogether this results in low dynamic rolling behaviour and low start-off pitch angle. Furthermore, the vehicle also has a reduced tendency to understeer in the higher lateral acceleration range: the driver is therefore able to control changes in direction with low steering input but high steering precision.
When accelerating out of bends taken at speed, the tendency to understeer is reduced even further by “Extended Traction Control” (XTC): with this function, ESP® provides support in the form of directional stability by generating a yaw moment on the front and rear wheels located on the inside of the bend.
Safety: setting the very highest standard
In an innovative move in the compact segment, the A-Class is equipped as standard with a radar-based collision warning system with adaptive Brake Assist, a combination which lowers the risk of rear-end collisions.
The COLLISION PREVENTION ASSIST system gives a visual and audible warning to alert a possibly distracted driver to identified obstacles, and prepares Brake Assist for the most precise braking response possible.
This is initiated as soon as the driver operates the brake pedal decisively.
“With the new A-Class, Mercedes-Benz is setting new standards in many disciplines, not least when it comes to the area of safety”, emphasizes Prof Dr Thomas Weber, Daimler Board Member responsible for Group Research and Head of Mercedes-Benz Cars Development.
“The new A-Class provides the highest standard of safety ever seen in this vehicle class.”
The democratisation of safety encompasses an array of assistance systems which have been adopted into the A-Class from the larger model series, or sometimes developed further in the A-Class. These include:
- Adaptive Highbeam Assist
- Blind Spot Assist and Lane Keeping Assist
- ATTENTION ASSIST (standard)
- Speed Limit Assist (speed limit sign recognition)
- Active Parking Assist with parking guidance
- Brake hold function
- Hill-Start Assist
- Reversing camera
- DISTRONIC PLUS
Premiere in the compact class: PRE-SAFE® available for the first time
The availability of the PRE-SAFE® anticipatory occupant protection system for the A-Class marks another first in this vehicle category. This represents a further step in the on-going democratisation of this innovation, which was premiered in the S-Class in 2002.
Core features of PRE-SAFE® are reversible belt tensioning, the closing of side windows and sliding sunroof in case of critical lateral dynamics and adjustment of the fully electric front passenger seat with memory function to an ideal position for maximum effectiveness of the restraint systems.
PRE-SAFE® is always activated in response to critical longitudinal and lateral dynamics and may also be triggered upon intervention by certain assistance functions.
Body: a strong basis and intelligent protection
The new A-Class has passed the brand’s rigorous programme of crash tests. This includes not only some 30 different impact configurations, which are laid down as requirements for safety ratings and international type approval, but also nine proprietary crash tests, such as the roof-drop test or the pole impact test, developed by the brand itself.
The ability of the new A-Class to satisfy requirements which go far beyond the statutory conditions in some cases is also demonstrated by an internal offset front collision test against a future luxury-segment saloon from Mercedes-Benz: despite the high impact speed and the fact that it is the smaller accident participant, the A-Class offers its occupants an intact passenger compartment and excellent chances of survival.
The scope of the restraint systems takes special account of the A-Class’s use as a family car. Great importance has been attached to the safety of the rear occupants.
Belt tensioners, belt-force limiters and belt height adjusters come as standard on the outer seats. Rear sidebags are optionally available.
The driver and front passenger are provided with new thorax-pelvisbags which are able to cover the pelvis and the entire upper part of the body. A windowbag is fitted as standard for head protection.
Comprehensive iPhone® integration
This seamless integration of the iPhone® into the vehicle, in conjunction with the new revolutionary user interface design, means that Mercedes-Benz is now able to offer the Facebook generation its natural home on four wheels in the guise of the new A-Class.
Along with Facebook, Twitter and so on, the “Drive Kit Plus for the iPhone®” (expected to be available as an accessory from September and as an optional extra from the first quarter of 2013), together with the Daimler app concept, brings further digital lifestyle services and content into the vehicle.
Highlights include advanced navigation software from Garmin, with internet-based real-time traffic information, online destination searches and 3D map display.
The Drive Kit Plus for the iPhone® can already be used with the Audio 20 CD. This features a twin tuner and mp3-capable CD player as well as a Bluetooth interface with hands-free function and audio streaming.
The colour display measures 14.7 cm diagonally. Thanks to a new “Cover Art” function, the title images of the music albums currently being played are shown if their details are stored in the audio file.
The Becker® MAP PILOT makes a low-cost 3D navigation function, which can also be retrofitted, available for the Audio 20 CD radio.
The navigation system boasts voice-controlled input of destinations and an intuitive user interface. Its advantages over aftermarket solutions include integrated operation via the central controls and the Audio 20 CD display, a concealed location in the glove compartment and updating via an internet portal.
The multimedia system COMAND Online now provides internet access via a web-enabled mobile phone, plus various Mercedes-Benz services on the move.
These include weather information and a special destination search via Google, as well as the option of downloading a route that has been previously configured on a PC using Google Maps and sent to the car.
A new feature is the “News” app which enables news on politics, finance and technology to be called up online in the vehicle. Information is displayed in such a way that it is clearly legible while on the move.
Continuing success: the Mercedes-Benz A-Class
The A-Class has been a bestseller for a number of generations. Since its market launch in 1997, it has blazed a trail for a new vehicle class with its unique design, becoming a driving force in the compact car segment.
The second generation alone, which was launched in 2005, sold more than a million examples worldwide.
The development of the 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 already meets 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 if 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.
The diesel engines
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
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 |
|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 |
|Fuel consumption, combined||[l/100 km]||5.5 (5.4)||5.5 (5.4)||6.1|
|CO2 emissions, |
|[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.