Engines for the new A-Class

Significant increase in output and torque with exemplary fuel consumption and comfort.......

More output, more torque and more driving pleasure – these were the development objectives for the engines in the new Mercedes-Benz A-Class, which will celebrate its world premiere at the end of June 2004 and appear in the showrooms of company-owned sales outlets and Mercedes-Benz dealerships in the autumn. The range of engines available for this innovative compact car will comprise seven four-cylinder units, including three newly developed direct-injection CDI diesels and a new, turbocharged 142 kW/193 hp petrol engine. Mercedes-Benz is also presenting its first continuously variable automatic transmission, which can be combined with any of the engines as an option. A new six-speed manual transmission is also celebrating its premiere.
Compared to the preceding series, the output of the petrol and diesel engines for the new A-Class has increased by up to 38 percent, while torque has improved by up to 46 percent. All the four-cylinder engines meet the stringent EU4 exhaust emission limits, and a particulate filter is available on request for the diesel units. Despite this higher performance the fuel consumption of the petrol engines has been significantly reduced.

The engines for the new A-Class are of a unique design which allows installation at an angle of up to 59 degrees behind the front axle. This makes the four-cylinder units important components in the intelligent safety concept: during a severe frontal collision they slide downwards to the rear without damaging the passenger cell.

The output range of the three newly developed CDI diesel engines extends from 60 kW/82 hp to 103 kW/140 hp. Major differences compared with the outgoing model include an increase in displacement from 1689 to 1991 cc, higher ignition pressures and second-generation common-rail fuel injection, which operates with dual pilot injection and a higher injection pressure (1600 bar). These and other measures lead to a significant increase in output and torque, a reduction in exhaust emissions and a noticeable improvement in noise comfort. The new A 160 CDI has a roughly nine percent greater output (60 kW/82 hp) and develops a 12.5 percent higher torque (180 Newton metres) than the previous model of the same name. The new 80 kW/109 hp diesel engine in the A 180 CDI has 14 percent more output than the power unit of the A 170 CDI and makes almost 39 percent more torque available between 1600 and 2600 rpm.

The flagship diesel model in the new A-Class is the A 200 CDI, which achieves new standards in terms of agility and driving pleasure. The direct-injection engine with a VNT turbocharger and an ignition pressure of 180 bar has an output of 103 kW/140 hp and develops a torque of 300 Newton metres over a wide engine speed range between 1600 and 3000 rpm. This guarantees rapid acceleration and brisk inter-mediate sprints. The fuel consumption of the CDI models in the new A-Class is at the same exemplary level as the previous series.

The optionally available particulate filter reduces particulate emissions by a further 99 percent. It regenerates without additives and remains effective over a high mileage.

Petrol engines: new A 200 TURBO with 142 kW/193 hp

Compared to the preceding model, the four-cylinder petrol engines for the new A-Class show an increase of up to 38 percent in output and up to 36 percent in torque. At the same time the fuel consumption, exhaust emissions and noise levels have been significantly reduced. With the A 200 TURBO the A-Class enters new realms in terms of performance: with 142 kW/193 hp this engine achieves a remarkable power-to-swept-volume ratio of approx. 70 Kilowatts per litre, making it one of the most powerful units in its displacement class. The maximum torque of 280 Newton metres remains constant throughout a wide engine speed range between 1800 and 4850 rpm. The turbocharger is a joint development by Mercedes engineers and their colleagues at DaimlerChrysler Research.

In each case the increased output and higher torque of the new A 150, A 170 and A 200 models are based on a 100 cc increase in displacement and the use of a variable intake manifold, which helps to improve pulling power at lower engine speeds.

By reducing friction losses in the piston, connecting rod and valve control system, as well as improving the mixture distribution within the combustion chambers, the specific fuel consumption of the spark-ignition engines has been even further lowered. Despite their higher performance the petrol models in the new A-Class will consume approx. ten percent less fuel that their predecessors as measured in the NEDC.

AUTOTRONIC: premiere of the first continuously variable automatic transmission by Mercedes

Mercedes-Benz is introducing a new era in transmission technology with the AUTOTRONIC automatic transmission. This operates on the principle of a continuously variable transmission, in which the ratios are changed by means of a variator pulley and a steel thrust belt. As a result the A-Class accelerates with no interruption of tractive power, and the engine reaches its maximum performance more quickly than with a conventional automatic transmission. The continuously variable AUTOTRONIC transmission also ensures a high level of ride and noise comfort.

AUTOTRONIC allows the driver to choose between two transmission programs. In the Comfort program the transmission keeps the engine speed at the lowest possible level, so that the A-Class accelerates more gently and consumes less fuel. In the Sport program AUTOTRONIC automatically recognises the individual driving style and adapts the shift strategy accordingly. A manual mode is also available in which the automatic transmission divides the ratio range into seven virtual stages. The driver shifts the gears up or down by briefly nudging the shift lever. The complete AUTOTRONIC unit has a length of only 330 millimetres, making it the world’s most compact continuously variable transmission.

Like AUTOTRONIC, the standard six-speed manual transmission of the A 180 CDI, A 200 CDI and A 200 TURBO is a new development. This unit is of compact aluminium construction and is particularly precise in operation. The tried-and-tested five-speed manual transmission is standard equipment for the other engine variants of the new A-Class. Mercedes engineers have made detailed improvements and configured this unit to suit the new engines.

©1998-2004 DaimlerChrysler. All rights reserved.

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Engines: Powerful presence

  • Diesel engines: three new power units with up to 140 hp of output

  • Petrol engines: increase in output to 142 kW/193 hp

Stuttgart, May 25, 2004

The A-Class by Mercedes-Benz is a very special automobile in every respect - innovative, intelligent and unique. In short: typically A-Class.

A glance beneath the bonnet confirms this: the four-cylinder engines of this compact car are of a unique construction which is specially configured for the A-Class and offers numerous advantages in an automobile of this size. The most important of these is occupant protection: the power unit is installed transversely behind the front axle and inclined forward at an angle of 59 degrees (diesel engines: 56 degrees). This installed position precisely matches the shape of the front bodyshell floor panel. During a severe frontal collision, the engine and transmission are able to slide downwards and to the rear against this panel without damaging the passenger cell. This means that the front end of the A-Class possesses the entire deformation potential provided by a system of robust structural members, absorbing the impact energy and reducing the loads acting on the vehicle occupants.

The second major advantage of the A-Class engines is their compact construction. Their transverse position, partly in front of and partly beneath the passenger compartment, is not only extremely safe but also saves space. It allows a shorter front end design, making a much larger area of the bodyshell available for the comfort of the occupants than conventional designs.

And finally, in addition to their unique, angled design and compact dimensions, the four-cylinder engines of the A-Class also have a great deal to offer in engineering terms. This applies more than ever before to the power units which Mercedes-Benz will use for the second generation of this successful compact car from autumn 2004.

More output, more torque, more driving pleasure – these were the development objectives for the new and improved engines, and these are achieved together with equally impressive progress in terms of environmental compatibility and comfort, as well as a further reduction in fuel consumption:

  • Compared to the preceding model, the increase in output generated by the petrol and diesel engines for the new A-Class is up to 38 percent. The output range extends from 60 kW/82 hp for the new A 160 CDI to 142 kW/193 hp for the future flagship model, the A 200 TURBO.
  • Compared to the previous A-Class, maximum torque has increased by up to 46 percent. The new A 200 CDI already develops its high torque of 300 Newton metres from 1600 rpm.

Versatility is another important advantage of the engine range for the Mercedes-Benz A-Class: instead of six there is now a choice of seven four-cylinder power units, which are combined with either a five or six-speed manual transmission depending on the torque level. The newly developed AUTOTRONIC continuously variable transmission is also available for all model variants on request.

The range of engines and transmissions for the A-Class at a glance:

A 160
CDI
*
A 180
CDI
A 200
CDI
A 150* A 170 A 200 A 200
TURBO
**
Displacement cc 1991 1991 1991 1498 1699 2034 2034
Output kW/hp

60/82

80/109 103/140 70/95 85/115 100/136 142/193
Man. transmission Five-speed Six-
speed
Six-
speed
Five-speed Five-speed Five-speed Six-
speed

*Available from end of 2004; **Available from mid-2005

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The diesel engines: torque is fun

The diesel engines for the new A-Class have been newly developed. Major differences versus the engines in the preceding model include an increase in displacement from 1689 to 1991 cc, higher ignition pressures, improved air ducting and second-generation common-rail fuel injection. These and other measures lead to a significant increase in output and torque, a reduction in exhaust emissions and a noticeable improvement in noise comfort. Take the A 160 CDI, for example: the new engine has an approx. nine percent higher output (60 kW/82 hp) and develops 12.5 percent more torque (180 Newton metres) than the previous A 160 CDI. The differences are even more striking for the A 180 CDI: the new 80 kW/109 hp diesel engine has 14 percent more output than the engine of the A 170 CDI, and makes almost 39 percent more torque available between 1600 and 2600 rpm: 250 Newton metres.

The flagship diesel model in the new A-Class is the A 200 CDI, which achieves new standards in terms of agility and driving pleasure. The direct-injection engine has an output of 103 kW/140 hp and develops 300 Newton metres of torque over a wide engine speed range between 1600 and 3000 rpm. This guarantees rapid acceleration and brisk intermediate sprints.

Key data of the diesel engines for the new A-Class:

A 160 CDI A 180 CDI A 200 CDI

Cylinders

4 4 4

Valves per cylinder

4 4 4

Displacement
cc

1991 1991 1991

Bore/Stroke

mm

83/92 83/92 83/92

Dist. between cylinders mm

90 90 90

Output
kW/hp

60/82at
4200 rpm
80/109at
4200 rpm
103/140at
4200 rpm

Max. torque
Nm

180at
1400-2600 rpm

250at
1600-2600 rpm

300at
1600-3000 rpm

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Fuel consumption lowered by a variable high-pressure pump

Despite this impressive performance increase, the fuel consumption remains at the same, exemplary level for which the Mercedes compact class is known. The specific fuel consumption of the diesel engines has now seen an improvement over the previous CDI engines of the C-Class to 205 g/kWh, which means that NEDC fuel consumption values of just five litres per 100 kilometres may be expected.

This result is largely thanks to the second-generation common-rail injection system, which allows even more precise control of the solenoid valves on the injectors and demand-related regulation of the high-pressure pump. In the first-generation CDI engines this pump always operated at maximum output, which required a high energy input at the expense of fuel consumption and also caused a large increase in fuel temperature. This conflict of aims has now been resolved with a newly developed high-pressure pump, which is demand-controlled by means of a vacuum throttle. Depending on the fuel pressure calculated by the engine management system, the delivery chambers of the pump are only partly filled and enable the delivery volume to be demand-related. This technology considerably reduces the energy input required by the pump, and therefore the fuel consumption.

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Three-phase fuel injection at up to 1600 bar

Another important feature of this second-generation common-rail technology is the newly developed seven-hole injection nozzle, which replaces the previous six-hole nozzle. The new injector makes it possible to reduce the hole diameter by around 20 percent, thereby reducing the flow rate. This means that the fuel is distributed more evenly in the cylinders, ignites more rapidly and burns more completely than before. The progress achieved thanks to this improved mixture formation is particularly noticeable when measuring the exhaust emissions.

The greater throttling effect of the smaller nozzle holes increases the injection time, however, which is particularly unfavourable when more performance is required. To compensate this effect the engineers at Mercedes have increased the injection pressure from the previous 1350 to 1600 bar, thereby shortening the injection time. As in all common-rail engines this high injection pressure is available at all times, i.e. also at low engine speeds.

The pilot-injection system has always been a special feature of common-rail engines by Mercedes-Benz. This ensures quieter combustion: a few milliseconds before the main injection process, a small quantity of diesel fuel flows into the cylinders, ignites and thereby pre-heats the combustion chambers. This creates more favourable conditions for the subsequent main injection: the fuel ignites more easily in the pre-heated cylinders, which means that the pressure and temperature no longer increase as suddenly as in an engine without pilot injection. This has a favourable effect on combustion noise.

In these second-generation CDI engines the engineers at Mercedes have perfected this principle by means of dual pre-injection. The highly-efficient solenoid valves in the new 1600-bar injectors permit even shorter time delays between pilot and main injection, and now small pilot quantities flow into the combustion chambers twice in succession within less than a millisecond, ensuring even better pre-heating. The result is audible, as combustion noise levels are once again significantly reduced.

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New electronic engine management system with a wide range of functions

The injection time, volume and pressure are regulated by a newly developed electronic control unit, which is integrated into the data bus network of the A-Class. The other tasks this unit performs in connection with the fuel injection process include idling and individual cylinder torque control, limiting the engine speed, deceleration fuel cut-off and control of the fuel pump. The micro-computer is also responsible for controlling the charge pressure of the turbocharger, exhaust gas recirculation and demand-related intake duct closure in the diesel engines. All the system components and their functions are monitored by an efficient diagnostic system.

The quick-start glow-plug system is yet another new feature. This enables the diesel engines to be started almost as quickly as their petrol counterparts.

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New A 200 CDI with 180-bar ignition pressure and a VNT turbocharger

The impressive increase in output and torque which clearly distinguishes the CDI engines of the new A-Class from those in the preceding model is not just the result of increasing the engine displacement by almost 18 percent. At the same time the Mercedes engineers improved the gas cycle in the cylinders and increased the ignition pressure from the previous 145 to 180 bar. As a result the new engines develop even more tractive power in the lower engine speed range. Specifically this means that in the A 180 CDI, 198 Newton metres no less than 79 percent of the maximum torque – is already available from 1300 rpm.

Even more impressive torque characteristics are shown by the new A 200 CDI, whose engine operates with an ignition pressure increased to 180 bar and distinguishes itself from the other diesel units for the new A-Class by featuring a VNT (Variable Nozzle Turbine) turbocharger. In a VNT charger the angle of the turbine vanes can be varied according to the engine operating parameters, enabling the greatest possible volume of exhaust gas to be used to compress the intake air and build up the charge pressure. At low engine speeds the vanes reduce the flow cross-section and the charge pressure increases, while the cross-section is increased at higher engine speeds to reduce the rotation speed of the turbocharger. The major advantages of this variable turbocharger control include better cylinder charging and therefore more torque.

In all the diesel engines for the A-Class, the air compressed by the turbocharger flows through an intercooler which has now been tripled in size, from where it enters a mixing chamber and meets the recirculated exhaust gases. The exhaust gases are fed directly from the exhaust manifold and flow through a water-cooled heat exchanger. They mix with the compressed fresh air, with an automatic intake air throttling system ensuring the most favourable ratio of charge air to recirculated exhaust gases. In the A 200 CDI the VNT turbocharger has the task of setting the optimal pressure conditions for exhaust gas recirculation.

The mixing chamber is part of a complex air distribution module. From here each cylinder is supplied with the air/exhaust gas mixture via two ducts. One of the two intake ducts can be shut off in keeping with the engine speed and engine load, thereby increasing the swirl rate of the mixture. At low engine speeds a system of variable swirl flaps is also in action. These further increase the air speed in the four spiral ducts of the cylinder head, thereby improving the output and torque under partial load.

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Well-proven technology for the crankcase and cylinder head

A crankcase of grey cast iron provides the solid basis for the new-generation diesel engines of the A-Class. In view of the compact engine dimensions, increased displacement and higher ignition pressure this well-proven material offers the most advantages. While maintaining the distance between cylinders, Mercedes engineers have increased the bore from 80 to 83 millimetres and the stroke from 84 to 92 millimetres. The forged connecting rods have been lengthened to 147.85 millimetres. The crankshaft is likewise of forged steel and features five bearings, eight counterweights and a vibration damper. The pistons, whose crowns have a special, dished profile, are equipped with cooling ducts into which oil is sprayed by pressure-controlled nozzles.

The cylinder head in the new diesel engines has two overhead camshafts, each of which controls two intake and two exhaust valves via roller-type rocker arms. The steel camshafts are produced using an internal high-pressure forming process developed by Mercedes-Benz, which ensures a very high level of precision: the cavities in the blanks are filled with a liquid and subsequently formed for a precise fit at a pressure of up to 2000 bar. A chain drives the camshaft on the intake side, which meshes with its counterpart on the exhaust side.

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Exhaust emissions below the EU4 limits, optional diesel particulate filter

The diesel models of the new A-Class have also made great strides where exhaust emissions are concerned. The newly developed diesel engines are so clean that they are able to meet the stringent exhaust limits of the EU4 guideline without a particulate filter system. Compared to the previous CDI units, gaseous emissions have been reduced by up to 56 percent while particulate emissions are now down to 0.025 grams per kilometre.

Sophisticated engine improvements and use of the latest common-rail technology are in large measure responsible for this. The new A-Class is also equipped with two oxidation-type catalytic converters, whose task is to reduce gaseous pollutants by combining them with oxygen (oxidation). In this way unburned hydrocarbons (HC) and carbon monoxide (CO) are converted to water (H2O) and carbon dioxide (CO2). One of these catalytic converters (volume 2.1 litres) is located immediately downstream of the turbocharger turbine, while the second with a volume of two litres is positioned in the underbody area. An oxygen sensor upstream of the catalytic converter close to the engine monitors the exhaust gas constituents.

Mercedes-Benz also offers an optional, maintenance-free particulate filter system, which reduces particulate emissions by a further 99 percent. The particulate filter (volume 2.5 litres) replaces the underbody catalytic converter and is connected to the upstream converter close to the engine by an air-gap-insulated exhaust duct. The particles retained on the walls of the filter ducts are burned off at an exhaust temperature above 600 degrees Celsius.

The particulate filter system developed by Mercedes-Benz regenerates itself without the use of additives and remains effective over a very high mileage, which distinguishes it from previously available processes of this kind. Dispensing with fuel additives, whose purpose is to help burn the soot particles trapped in the filter at low temperatures, has a positive effect on fuel consumption, durability and engine output. Studies have shown that fuel additives used to clean the filter remain in the filter ducts as non-regenerable ash, and can block these after a high mileage. This increases the exhaust counterpressure and therefore the fuel consumption, while the output of the diesel engines correspondingly reduced.

With this filter system, high mileages can be achieved by the diesel models in the new A-Class without any additional servicing. The exhaust temperature required for particulate regeneration is reached either at high engine speeds or by appropriate adaptation of various engine functions. These are controlled as a function of the exhaust pressure and temperature at the particulate filter. Variable, second-generation common-rail technology makes a major contribution in this respect, as it allows a brief post-injection of fuel depending on the operating status and filter condition. This specifically increases the exhaust temperature, burning off the particles trapped in the filter in a controlled manner.

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Petrol engines: up to 193 hp of output with turbocharging

Mercedes-Benz has improved the proven four-cylinder petrol engines for the A-Class in major respects, achieving remarkable progress in numerous aspects. Output has been increased by up to 38 percent compared to the preceding models, with torque improving by more than 36 percent, while the fuel consumption, exhaust emissions and noise are significantly reduced.

As before, there is a choice of four petrol engines. The increase in output and torque is mainly based on an approx. 100 cc larger displacement and the use of a variable intake manifold in models A 150, A 170 and A 200. This means that without complex four-valve technology, these engines have a volumetric efficiency of 47 to 50 Kilowatts per litre of swept volume, a remarkable achievement in this vehicle class, and develop a high torque even at low engine speeds. Take the A 200 as an example: this lively 100 kW/136 hp engine makes 156 Newton metres – 84 percent of its maximum torque – available at a mere 1500 rpm. The figures for the engine in the new A 200 TURBO are even more impressive. This 142 kW/193 hp unit achieves a ratio of approx. 70 Kilowatts per litre of displacement, and from 1800 rpm the driver can call upon a maximum torque of 280 Newton metres which remains constant throughout a wide engine speed range. This creates the ideal conditions for rapid acceleration and powerful intermediate sprints.

Key data of the petrol engines for the new A-Class at a glance:

A 150 A 170 A 200 A 200 TURBO

Cylinders

4 4 4 4

Valves per cylinder

2 2 2 2

Displacement
cc

1498 1699 2034 2034

Bore/stroke
mm

83/69.2 83/78.5 83/94 83/94

Dist. between cylinders
mm

90 90 90 90

Output
kW/hp

70/95
at 5500 rpm
85/115
at 5500 rpm
100/136
at 5750 rpm
142/193
at 4800 rpm

Max. torque
Nm

140
at 3500 rpm
155
at 3500 rpm
185
at 3500 rpm
280
at 1800 rpm

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Fuel consumption significantly reduced

With NEDC fuel consumption values between 6.9 and 7.9 litres per 100 kilometres (combined consumption), the petrol models in the Mercedes-Benz A-Class have always been among the most economical cars in their class. The new A-Class will consolidate this position even further. The specific fuel consumption of the spark-ignition engines has been lowered by reducing friction losses in the piston, connecting rod and valve control systems, as well as by further improvements to the mixture distribution in the combustion chambers. In practical terms this means that in the NEDC test, the petrol models in the new A-Class will consume less fuel than their predecessors despite a higher output.

The up-to-the-minute, lightweight power unit consists of an aluminium crankcase with grey cast iron cylinder liners. The pistons, sump, oil pump, rocker arms, engine mounting, timing case and other engine components are also of aluminium, while the intake manifold, air filter and cylinder head cover are made from plastic. Depending on the displacement, and thanks to this lightweight design, the petrol engines tip the scales at only 92 (A 150) to 117 kilograms (A 200 TURBO) and are therefore significantly lighter than other four-cylinder units in this displacement class. The power-to-weight ratio of the turbocharged engine is a remarkable 0.82 kilograms per Kilowatt.

The compact cylinder head features a swirl duct which creates high turbulence in the fuel/air mixture, thereby ensuring an optimal combustion process. The central location of the spark plugs serves the same purpose. Valve control is by a hollow camshaft of induction-hardened forged steel and low-friction rocker arms. A timing chain with a hydraulic tensioner and rubber-coated sprockets drives the camshaft. A hydraulic system automatically controls valve clearance compensation.

Mercedes engineers have also achieved the high thermal efficiency of the spark-ignition engines with a high compression ratio of 11.0 : 1. This made it necessary to divide the water jacket into two sections: the lower section has a high speed of flow in order to cool the very hot combustion chamber areas – especially the webs between the intake valves – and therefore make this high compression ratio possible in the first place. The upper section cools the engine’s valve control system. In addition the exhaust valves of the A 170, A 200 and A 200 TURBO are sodium-cooled.

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More torque by virtue of a newly developed variable intake manifold

Mercedes engineers have considerably improved the air supply to the engine by means of a variable intake manifold with long intake ducts. This consists of three plastic shells and features an electro-pneumatically controlled actuation wheel which opens or closes the ducts according to the load and engine speed. At low engine speeds the intake air flows to the cylinders via four long intake ducts to obtain a high torque yield. This creates pressure waves in the intake ducts which support the intake process. At high engine speeds the flaps close these intake ducts, so that the air takes a direct path to the combustion chambers via a short intake duct. The engine computer decides whether and when the actuation wheel opens or closes the ducts on the basis of stored characteristic maps which ensure optimal engine operation.

The turbocharged engine newly developed for the A-Class has no variable intake manifold. Instead the intake air flows from the air filter to the turbocharger, which is located in the exhaust manifold to save space. The flow of exhaust gases required to drive the charger turbine is controlled by a pneumatically regulated wastegate valve, depending on the current engine operating point. The compressed intake air flows from the turbocharger through an intercooler, which is in turn linked to the throttle valve actuator.

The outstanding torque characteristics of the 142 kW/192 hp engine confirm the high efficiency of the turbocharger, which was developed by Mercedes engineers together with their DaimlerChrysler Research colleagues. A special turbine geometry ensures excellent responsiveness even at low engine speeds, making possible the extremely wide torque plateau available between 1800 and 4850 rpm.

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Emission control with two catalytic converters

The petrol engines for the new A-Class meet the requirements of the EU4 standard. These low emission levels are firstly the result of good fuel combustion, which ensures a low level of untreated emissions. Secondly the efficient emission control system makes a major contribution: from the sheet steel exhaust manifold, whose material heats up rapidly after a cold start, the exhaust gases flow through four stainless steel ducts to a catalytic converter (volume 0.7 litres) which is located close to the engine and which features a control sensor and a diagnostic sensor. This converter is complemented by a downstream catalytic converter (volume 1.3 litres) on the underbody.

In the A 200 TURBO the exhaust manifold is air-gap-insulated, and is directly welded to the turbocharger housing.