by Adrian-Liviu Dorofte

The new Mercedes-Benz CLA-Class: Engines and Transmissions

VIII. The petrol engines: Powerful, responsive and super-clean

Mercedes-Benz has systematically transferred the BlueDIRECT technology from the V6 and V8 engines of the Mercedes-Benz luxury class. The BlueDIRECT four-cylinder petrol engines for the new CLA-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 CLA-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 already meet the Euro 6 emissions 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.
Extremely versatile

The basis for all three petrol engine variants in the new CLA-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 ECO start/stop function is always featured as standard.

The BlueDIRECT family has grown: three new petrol engines

The M 270 engine is available in three output levels in the new CLA-Class. As the CLA 180 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 transmission the new CLA-Class accelerates from zero to 100 km/h in 9.3 seconds and has a top speed of up to 210 km/h. The fuel consumption and CO2 emission figures of 5.4 l/100 km, NEDC, combined, and 126 g/km, respectively, are so low that they possibly set a new record.

Thanks to extensive aerodynamic optimisation measures (see the corresponding section), the CLA 180 BlueEFFICIENCY Edition, whose premiere is to be in June, betters even these figures: with 5.0 litres/100 km and 118 g CO2/km, it is among the most frugal cars in its class.

The CLA 200 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 8.6 seconds and has a top speed of 230, but is happy with an average 5.5 l/100 km of fuel, meaning CO2 emissions of 127 g/km.

The CLA 250 is powered by the top engine variant with a displacement of 1991 cc. 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 6.7 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 142 g/km.

All engine variants are designed for customer-friendly operation with E10 premium petrol (95 RON).

Overview of technical data for the CLA-Class with petrol engine

IX. The diesel engines: From the S-Class to the CLA-Class

The CLA 220 CDI combines sporty handling with exemplary efficiency and already complies with the Euro 6 exhaust gas standard, which will only become mandatory from 2015. The ECO start/stop function is featured as standard. The CLA 200 CDI is due to follow in September.

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 is an exemplary 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.

Dynamic in its handling, extremely efficient and of exemplary cleanliness: the CLA 220 CDI, available exclusively in combination with the 7G-DCT dual clutch transmission. The 125 kW (170 hp) top diesel with a displacement of 2.2 litres and a peak torque of 350 Nm, features a weight-optimised crankshaft and, with its individual bearing covers bolted from below and four counterweights, weighs around six kilograms less than an OM 651 of the same displacement, in the longitudinal-installation variant. The CLA 220 CDI is equipped with a multi-path exhaust gas recirculation system which reduces the nitrogen oxide emission levels.

Already today it meets the Euro 6 exhaust gas standard which will be compulsory from 2015. With 109 g CO2 per km and a combined fuel consumption of 4.2 litres per 100 km, the CLA 220 CDI sets new standards in its segment with 8.2 seconds for the standard sprint and a top speed of 230 km/h, its performance is of sports car level.

At 2.2 litres, the engine is relatively large-displacement, which makes it agile already at low speeds. Mercedes-Benz engine experts call this combination of large-displacement engine and low engine speeds "downspeeding". This made it possible for the ECONOMY gearshift program of the 7G‑DCT transmission to be 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 CLA 200 CDI can be ordered from 8 April 2013, the first vehicles will be delivered to customers from September 2013. Its top output is 100 kW (136 hp), its maximum torque, 300 Nm. The displacement was reduced to 1.8 litres 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 also have a low-friction design. The single-stage turbocharger has been 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 short length required were part of the design specification from the very start.

Overview of technical data for the CLA-Class with diesel engine

X. The transmissions: Shifting comfort combined with efficiency

The 7G-DCT dual clutch transmission and the six-speed manual transmission enable a driving style that is both comfortable and dynamic. Both transmissions are extremely compact and share a series of components with each other.

The 7G-DCT dual clutch transmission is extremely compact, extremely variable with regard to adaptation of the engine speed thanks to seven gears, incorporates an electric oil pump for start/stop capability, shifts gear without any interruptions in tractive power and combines the comfort of an automatic with the efficiency of a manual transmission. The CLA 250 and the CLA 220 CDI are equipped as standard with the 7G-DCT transmission, it is also optionally available for the CLA 200, CLA 180 (from June) and the CLA 200 CDI (from September).

The manual transmission, designed along similarly compact lines as a three-shaft transmission, is a close relative of the DCT. Extremely easy gear shifting, low shift forces, low internal friction and a low weight are among its most important characteristics.

The 7G-DCT dual clutch transmission: dynamic and efficient

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.

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 in 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 CLA-Class. In combination with the electric parking brake, additional space has thus been created in the centre console for additional stowage facilities.

Three gearshift programs 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. The gear selected is displayed in the instrument cluster and a shift recommendation is made for a fuel-saving driving style.

A key factor contributing to the overall efficiency and dynamism of the CLA-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: convenient manual gear-shifting

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 CLA-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.

Credits: Daimler AG

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