The new CLK-Class (W209): Engines & Transmissions

Engines and transmissions: seven of the best

Six of seven powerplants new to the CLK line-up

Fuel consumption reduced by an average of six percent

New top-of-the-range CLK 500 with V8 engine developing 306 hp

Launch of new 4-cylinder engine generation with TWINPULSE system

Fuel consumption reduced by up to 16 percent thanks to direct petrol injection

Premiere for five-cylinder CDI engine in the CLK-Class

V8 powerplant in the CLK 55 AMG with output boosted by 15kW/20 hp

A whole host of new developments lie beneath the bonnet of the new CLK-Class, in particular many innovations that herald major technical advances. For instance, six of the seven powerplants available for the Coupé are new to this Mercedes model series: the powerful five-litre V8 engine from the S-Class, the state-of-the-art V6 powerplant with 2.6-litre displacement, the torquey five-cylinder CDI engine and the powerful eight-cylinder AMG engine. Not to mention the newly developed four-cylinder powerplant that is one of the first direct petrol injection engines in the world to feature the unique TWINPULSE system, including a compressor supercharger and Lanchester balancer among other things. This new engine line-up delivers substantially lower fuel consumption and exemplary emissions performance whilst ensuring vastly enhanced driving pleasure, agility and power delivery -- in every displacement class. The numbers back this up:

Fuel consumption in the CLK models is, on average, six percent lower than in the preceding models.

All petrol models already comply with the strict EU-4 emission standard due to come into force in the year 2005 and the US-American standards for "Ultralow Emission Vehicles" (ULEV). The CDI engine meets the requirements of the EU-3 standard.

The seven CLK engines have power outputs ranging from 120 kW/163 hp to 270 kW/367 hp (preceding models: 120 kW/163 hp to 255 kW/347 hp).

Maximum engine torque ranges from 240 to 510 Newtonmetres (predecessor models: 230 to 510 Newtonmetres).

New V8 CLK 500 model with power to match a thoroughbred sports car

The new eight-cylinder model in the CLK-Class line-up is called the CLK 500. In this guise, the new Coupé delivers driving dynamics and performance on a par with thoroughbred sports cars such as the SL 500 or top-of-the-range Coupés such as the CL 500. One look at the figures confirms this: the CLK 500 takes a mere 6.0 seconds to accelerate from 0 to 100 km/h and, thanks to its exemplary torque characteristics, completes the sprint from 60 to 120 km/h in just 6.2 seconds -- class-leading figures in this coupé segment. A quick dab of the accelerator is all it takes to feel the sheer power beneath the bonnet of the new top-of-the-range CLK model: even at a speed just above idle, the V8 powerplant plants 344 Newtonmetres of torque onto the road -– an impressive 75 % of maximum torque. Furthermore, at 2240 rpm, there are a massive 428 Newtonmetres available -- 93 percent of the maximum torque of 460 Newtonmetres, which the engine provides from 2700 rpm and maintains until 4250 rpm. At launch, the eight-cylinder engine will be available with five-speed automatic transmission as standard.

Two powerful six-cylinder models with 2.6 and 3.2-litre displacement

Mercedes-Benz has extended the six-cylinder line-up for the new CLK-Class by adding the tried-and-tested 2.6-litre V6 engine which develops 125 kW/170 hp and provides a maximum torque of 240 Newtonmetres at 4500 rpm.

The CLK 320 remains unchanged in the line-up. And with good reason: the powerful V6 powerplant (160 kW/218 hp), which Mercedes-Benz offers with five-speed automatic transmission as standard, is particularly well-suited to the new Mercedes Coupé, since it delivers equally impressive performance during either sporty driving with high power output or more serene and relaxed driving at lower engine speeds. With 310 Newtonmetres of torque on tap from just 3000 rpm, the six-cylinder engine offers the very best of both worlds.

New four-cylinder engine with the option of direct petrol injection

Mercedes-Benz will again show the way forward, this time in the field of four-cylinder technology, when a new generation of engines is launched in mid-2002. The newly developed engines highlight the shape of things to come in all the major areas of development: fuel consumption, torque characteristics, power delivery, lightweight design and refinement.

There is a choice of two versions of this sophisticated engine for the CLK-Class, both featuring the unique TWINPULSE system. This technology package contains a host of innovations, designed to ensure sheer driving pleasure and low fuel consumption: mechanical supercharger, intercooler, four valves per cylinder, double overhead camshafts with variable valve timing, Lanchester balancer shafts, adaptive drive system, aluminium construction and optional direct petrol injection. The options:

Four-cylinder engine developing 120 kW/163 hp with electronically controlled fuel injection in the intake ports for the CLK 200 KOMPRESSOR.

Direct-injection petrol engine developing 125 kW/170 hp -- the first latest-generation Mercedes powerplant featuring this new technology and the world's first engine of its kind, which combines leading-edge, direct-injection technology with a compressor supercharger and counter-balancer. Mercedes models incorporating this sophisticated engine technology will be recognisable by the CGI badge on the rear, which stands for (Stratified) Charged Gasoline Injection.

One look at the performance and fuel consumption figures reveals that both four-cylinder engines have everything it takes to deliver superb economy and a dynamic driving experience:

The new CLK 200 KOMPRESSOR accelerates from 0 to 100 km/h in 9.3 seconds, going on to reach a top speed of 230 km/h, making it 7 km/h faster than the equally powerful predecessor model. Fuel consumption has been reduced to 8.6 litres per 100 kilometres (NEDC combined), 0.8 litres less than in the previous CLK 200 KOMPRESSOR.

The four-cylinder newcomer also delivers when it comes to pulling power and flexibility: the maximum torque of 240 Newtonmetres is available from 3500 rpm. And accelerating from 60 to 120 km/h (in fifth gear) takes the new CLK 200 KOMPRESSOR a mere 15.8 seconds.

To put it another way, mechanical supercharging and sophisticated engine technology enable the newly developed engine to combine the pulling power and refinement of a six-cylinder engine with the economy of a four-cylinder engine.

Direct injection petrol engine consuming 16 percent less fuel

The CLK 200 CGI is even more impressive at underlining the qualities of the new generation of Mercedes engines. Offering similar levels of performance -- 0 to 100 km/h in 9.2 seconds and a top speed of 231 km/h -- fuel consumption in the direct petrol injection engine is around eight percent lower than in its counterpart with port injection. In concrete terms: the new CLK 200 CGI consumes a mere 7.9 litres of sulphur-free Super Plus per 100 kilometres (NEDC combined). This represents a fuel saving of around 16 percent, compared to the predecessor model, despite the higher engine output.

Over 75 percent of the torque is available from just 1500 rpm. And the four-cylinder engine develops its maximum torque of 250 Newtonmetres from 3000 rpm. What is more, it maintains this impressive level up to 4500 rpm.

Lean-burn operation under partial load and emission control with storage catalytic converter

Mercedes-Benz has a long tradition in the field of direct petrol injection. As early as the mid-fifties, the Stuttgart manufacturer unveiled this technology in the 300 SL, the legendary "Gullwing". This classic sports car was the first series-produced automobile to receive a four-stroke engine with direct injection -- a sensational development that significantly boosted the six-cylinder powerplant's output.

Nowadays further development of this particular injection technology focuses on two different aspects: fuel consumption and exhaust emissions. Major advances in the fields of emission control and engine management have resulted in a solution to a familiar technical problem: producing an engine that is sufficiently lean-burning to provide the desired fuel consumption whilst using catalytic converters that usually require a "stoichiometric" air/fuel mixture (14.6 : 1). The solution in question is a newly developed NOx storage catalytic converter which absorbs the nitrogen oxides during the lean-burn cycle and then re-releases them in brief regeneration phases, so that they react with other constituents of the exhaust gas to form harmless nitrogen.

Thanks to this technology, which Mercedes-Benz combines with exhaust gas recirculation and secondary air injection in the new direct-injection petrol engine, the CLK 200 CGI is able to comfortably comply with the future EU-4 emissions standard. Up to 35 percent of the exhaust gases can be recirculated, depending on the engine operating characteristics, thus bringing about a substantial reduction in nitrogen oxide emissions. Another new innovation comes in the form of the "linear" oxygen sensor which becomes active immediately when the engine is started from cold and supplies information about the exhaust gas composition. This information is then processed by the engine computer, for the purpose of warm-up control among other things. It enables the catalytic converter to reach operating temperature in considerably less time. In addition, a newly developed, electronically networked NOx sensor with digital control is used, to ensure optimum control of the NOx storage catalytic converter.

Direct injection at a pressure of up to 120 bar

In the direct-injection system, the air and fuel are not mixed until they reach the combustion chambers. With the help of an injector, the fuel is injected into the cylinders at an angle of 42 degrees and, depending on the engine operating characteristics, at a pressure of between 50 and 120 bar. Here the fuel droplets and the air particles form a mixture which flows to the spark plugs via specially shaped recesses in the pistons. By way of comparison, the fuel pressure in a four-cylinder engine incorporating conventional injection technology is approximately 3.8 bar.

The CGI engine has two separate intake ports with flow characteristics that have been developed using sophisticated processes. These ports ensure optimum swirl in the mixture, thus making combustion fast and as complete as possible. In each case, one of these intake ports also has an adjustable swirl flap. The high-pressure fuel pump is driven by the intake camshaft. A pressure regulator controlled by the engine computer regulates the pressure in the fuel line (rail) which is directly connected to the injectors. The regulator receives signals from a pressure sensor.

Under partial load, at a mean pressure of four to five bar and at low engine speeds, the four-cylinder engine is "lean-burning". In other words, with the throttle wider open and with a high level of excess air. Engineers talk about "stratified charging": the fuel is injected into the air compressed by the piston at a relatively late stage. Outside of this range, the direct-injection engine is operated with the usual air/fuel mixture for engines with catalytic converters (lambda 1).

Aluminium cylinder head with variable valve timing

Made from high-strength aluminium alloy, the cylinder head in both versions of the new Mercedes engine has 16 valves and double overhead camshafts. Unlike in the previous four-cylinder engine in the CLK-Class, both camshafts are adjustable and have variable valve timing. A newly developed vane-type adjuster with integrated control valve ensures optimum valve timing at all times. This has a positive effect on torque characteristics under full load as well as on fuel consumption and exhaust emissions. The valves are controlled by means of cam followers with roller mechanism and have hydraulic valve lifters.

Highly efficient, low-noise compressor

The Mercedes developers have reengineered the compressor – which ensures exemplary bottom-end torque characteristics in both engine versions – by reducing the clearance between the rotors and the supercharger housing and by using a new coating for the rotors. The result is an even higher rate of air flow and even better efficiency than in the mechanical supercharger used in previous Mercedes four-cylinder engines. Special wide-band silencers are installed on the intake side and pressure side.

After being compressed, the air exits the compressor and flows through an intercooler, thus reaching the optimum temperature and density for the combustion process. The standard version and the CGI version of the new engine have different plastic intake pipe arrangements: in the direct-injection version, they separate into two lines per cylinder before actually entering the cylinder head. In each case, one of these pipes has an electrically adjustable swirl flap which further promotes air swirl.

Electronic control unit on the air cleaner housing

The round air cleaner attached to the intake pipe has the advantage of being able to provide a relatively large filter area in the smallest of spaces. In addition, the electronic control unit – equipped with two powerful processors – is located on the side of the air cleaner housing. The two processors share the complex tasks: one is responsible for the real-time processes, such as calculation of the ignition and injection pulses, whilst the other deals with time-synchronised tasks, such as lambda control or determining the ignition timing and the injection quantity. The control unit is integrated in the electronic network of the new CLK-Class via CAN databus (Controller Area Network) and swaps data with other microcomputers. The hot-film air flow sensor, incorporating reengineered functions, is positioned directly behind the air cleaner housing.

As is the case in all state-of-the-art petrol engines from Mercedes-Benz, the new four-cylinder generation uses electronic monitoring for components that simply have to function correctly in order to ensure low emissions. By way of example, this on-board diagnostic system permanently monitors catalytic converter efficiency and the ignition system as well as checking the purge valve electrics and the oxygen sensor. The "Check Engine" display on the CLK-Class instrument cluster lights up if a fault occurs in one of these systems. Meanwhile, details of any malfunctions are stored so that service engineers can detect the problem immediately and remedy the fault.

Refinement similar to a six-cylinder engine thanks to newly developed counter-balancer

Alongside exemplary power delivery, low fuel consumption and low exhaust emissions, the new Mercedes four-cylinder engine has a further advantage, namely refinement and acoustics similar to a six-cylinder engine. This is primarily down to the newly developed Lanchester balancer which consists of two forged shafts supported in multiple bearings. The shafts rotate in opposite directions at twice the crankshaft speed and, in so doing, counter-balance the inertia forces caused by the motion of the pistons, for example, which tend to cause irritating vibration.

The size, weight and arrangement of the counter-balance shafts have been perfectly harmonised to neutralise the vibratory forces in the four-cylinder engine. This technology thus substantially reduces noise emissions and vibrations and vastly enhances ride comfort.

The aluminium housing that contains the bearing-mounted balancer shafts is located in the oil sump and bolted to the crankcase from below. The drive is provided by a newly developed silent chain with low masses. The crankcase also contains the engine oil pump which is driven by one of the two shafts by means of a gear pair.

The crankcase is made from diecast aluminium (previous engine: cast iron) and is a major component in the lightweight design concept at the heart of the new four-cylinder engine. To put this into figures, the engine only weighs around 167 kilograms, making it some 18 kilograms or almost ten percent lighter than the preceding model.

Driving dynamics tailored to driver requirements

Mercedes-Benz also offers a newly developed system in the four, six and eight-cylinder CLK-Class models, which recognises individual driving styles and adapts the drive characteristics of the engine accordingly, thus further adding to the scintillating, dynamic driving experience. For those that fancy themselves as racing drivers, the ECU does its best to please, providing superlative accelerator response. If, on the other hand, the computer detects a driver looking for comfort rather than speed, it adapts the ECU control characteristics, harmonising the engine settings to suit this particular style of driving.

To ensure there is no doubt when detecting the driving style or the driver's requirements, the system monitors the pedal movements extremely closely and records every instance of acceleration before adapting the pedal characteristics. This is a continual step-by-step process which ensures that the driving characteristics never contradict the driver's expectations. In the case of a sporty driving style, the pedal characteristics change so that, although pedal travel may remain the same, the throttle valve is opened further than would usually be the case. The engine therefore reacts more instantaneously to driver input and is quicker to provide maximum acceleration. If a more comfort-oriented driving style is detected, the ECU sets flatter pedal characteristics. In this instance, although the pedal travel remains the same, the throttle valve opens more slowly than usual and acceleration is smoother.

Assuming the CLK 500 is being driven at 120 km/h in third gear, for example, and the ECU has detected a sporty driving style, the accelerator pedal only needs to be pressed halfway to the floor to obtain an effective acceleration of over 80 percent. If the driving style is more comfort-oriented, this degree of acceleration potential is not obtained until the accelerator has been pressed approximately 75 percent to the floor.

CDI diesel engine with fuel consumption of just 6.7 litres per 100 km

The CLK 270 CDI is the first state-of-the-art direct diesel injection engine Mercedes-Benz has offered its customers in the coupé segment. What really makes it stand out, alongside the high torque, is the extremely low fuel consumption. In terms of acceleration and top speed, the new CDI Coupé is therefore on a par with the V6 CLK 240 model.

The superb torque characteristics ensure that the five-cylinder engine always reacts instantaneously to driver input, accelerating immediately. For instance, the maximum torque of 400 Newtonmetres is available from just 1800 rpm and is kept constant until 2600 rpm. With so much bottom-end torque, the CLK 270 CDI accelerates from 0 to 100 km/h in just 9.2 seconds and from 60 to 120 km/h (in fifth gear) in a mere 12.6 seconds. The direct injection diesel engine's power curve reaches its summit – 125 kW/170 hp – at 4200 rpm.

However, the five-cylinder model delivers low fuel consumption of just 6.7 litres per 100 kilometres (NEDC combined), an astonishing figure given the impressive performance figures.

As is the case with all diesel engines in the Mercedes-Benz passenger car line-up, the new five-cylinder version is crammed with technical refinements:

The common-rail injection system keeps the injection pressure of up to 1350 bar constant in the common fuel rail, upstream of the cylinders, at all times. And it meters the injection quantity according to requirements, depending on the engine load and speed.

The intake system operates using a hot-film air flow sensor that enables accurate analysis of the air intake. This is important for ensuring precise control of the exhaust gas recirculation and, therefore, a reduction in nitrogen oxide emissions.

The engine ECU controls all the processes within the sophisticated CDI engine and, thanks to a databus network, also uses information provided by other control units.

The intercooler cools the intake air, thus enabling the engine to deal with greater quantities of air, for high torque and power output.

The four valves per cylinder allow the injector nozzles to be positioned centrally so that the fuel can be evenly dispersed in all directions within the combustion chamber. This makes combustion more complete than is the case in engines with two valves per cylinder, leading to lower exhaust emissions.

The VNT turbocharger ensures a fast build-up of charge pressure at low revs thanks to variable turbine geometry. This noticeable benefits of this are improved cylinder charging and, consequently, higher torque.

Facts and figures: engine and performance data for the new CLK-Class

The new CLK-Class will be available with a choice of seven engines with power outputs ranging from 120 kW/163 hp to 270 kW/367 hp. Six of these powerplants have been newly developed or further improved.

	CLK 270 CDI	CLK 200 KOM-PRESSOR	CLK 200 CGI	CLK 240	CLK 320	CLK 500	CLK 55 AMG
Cylinders/valves per cyl.	In-line 5/4	In-line 4/4	In-line 4/4	V6/3	V6/3	V8/3	V8/3
Displacement cc	2685	1796	1796	2597	3199	4966	5439
Output kW/hp	125/170	120/163	125/170	125/170	160/218	225/306	270/367
Torque Nm at rpm	400 1800-2600	240 3000-4000	250 3000-4500	240 4500	310 3000-4600	460 2700-4000	510/ 4000
Consumption*l/100 km	6.7	8.6	7.9	10.8	10.4	11.5	12.8
0– 100 km/h s	9.2	9.3	9.2	9.2	7.9	6.0	5.2
Top speed km/h	230	230	231	236	244	250	250

Provisional figures for models with six-speed transmission. *NEDC combined consumption

New CLK 55 AMG: 0 to100 km/h in 5.2 seconds

At the heart of the new high-performance CLK 55 AMG Coupé is a further improved V8 powerplant with 5439-cc displacement, developing 15 kW/20 hp more than its successful predecessor model. The eight-cylinder engine provides 510 Newtonmetres of pulling power from just 4000 rpm, impressive figures for a naturally aspirated engine. This enables the two-door model to accelerate from 0 to 100 km/h in just 5.2 seconds, making it exactly 0.2 seconds faster than the previous CLK 55 AMG. The top speed is electronically limited to 250 km/h -- although the speedometer dial in the flagship sports model goes up to 320 km/h, giving an indication of the potential power harnessed beneath the bonnet.

Prominent features of the V8 engine from Mercedes-AMG include the use of forged-aluminium pistons and specially developed oil jets for cooling the pistons. Optimum cylinder charging is assured thanks to a twin-pipe intake train, specially formed camshafts and a sports-tuned variable intake manifold, which provide the eight-cylinder engine with all it needs to deliver exemplary torque characteristics. The exhaust system consists of two firewall and four underfloor catalytic converters as well as specially designed silencer systems which minimise exhaust gas backpressure.

Three transmission versions available

Standard equipment in the CLK 200 KOMPRESSOR, CLK 200 CGI, CLK 240 and CLK 270 CDI models includes the sophisticated six-speed manual transmission which is ideally suited to the car's agile character thanks to its short shift travel. The Mercedes engineers have configured 6th gear as a real "driver's gear" in which the Coupé reaches its top speed.

For an especially dynamic driving experience, these models are also available with the option of SEQUENTRONIC. Here the driver merely has to nudge the shift lever, without pressing the clutch pedal, to change gear automatically and with the utmost speed and precision. Electric pulses transfer the driver input to a microcomputer which, in turn, controls a special hydraulic system for engaging the desired gear.

Components that do not feature on the SEQUENTRONIC spec list include the mechanical connections that usually link the shift lever to the six-speed transmission. In contrast to the previous six-speed manual transmission, the new system has an "add-on" unit attached to the transmission housing, containing all the auxiliary components with the exception of the control unit: the hydraulic unit connected with the main shift rail, the central release mechanism required for clutch operation, the power supply comprising electric motor and hydraulic pump, a special oil tank, the accumulator module required in order to maintain the constant system pressure and the sensors which check all movements of the shifter shaft and ascertain which gear is engaged.

To operate the SEQUENTRONIC, the driver simply has to nudge the shift lever forwards or backwards: nudging the lever towards the "+" symbol causes the hydraulic system to disengage the clutch and, via the main shift rail, engage a higher gear. During this process, the ECU takes into account the engine speed, engine torque, wheel speeds and a series of further parameters that are necessary in order to ensure precise gear changing. The system then engages the next-highest gear with lightning speed. The SEQUENTRONIC therefore fulfils the driver's shift requests in the correct order every time. In other words, the system is sequential, shifting and engaging the gears one after the other, be it for upshifts or downshifts.

Moving the shift lever in "+" or "—" direction and holding it there causes the SEQUENTRONIC to automatically shift up or down one or several gears, in order to select the optimum ratio for the current situation.

On the road, the system is quick to translate driver input into action. Furthermore, the driver no longer needs to monitor the engine speeds during automated gear changes as this is done by the SEQUENTRONIC which automatically kicks in if the engine speed exceeds or falls below certain limits. What is more, the transmission status can be checked at any time, since a display in the instrument cluster always indicates the currently engaged gear.

The new transmission has a further function that is of benefit when driving in town, in stop-and-go traffic and for many other situations encountered on the road: Autoshift mode. If the driver nudges the shift lever fully to the left – towards the "A" symbol – the SEQUENTRONIC assumes control, relying on numerous sensor signals to automatically change up and down through the six gears. By using intelligent technology, the new SEQUENTRONIC combines the benefits of a six-speed manual transmission with those of an automatic transmission. In addition, the innovative system increases driving pleasure as it is so easy to use and offers a choice of either fast and precise manual shifts or automatic gear changes.

Five-speed automatic transmission with new converter lockup mechanism

For drivers who demand even greater comfort and convenience, Mercedes-Benz offers the option of an electronically controlled five-speed automatic transmission with Touchshift for the CLK-Class. This is fitted as standard in the CLK 320 and CLK 500 models.

With its modified control set-up, the Touchshift feature gives the driver even more options for engaging the ideal gear for the situation in hand. Holding the selector lever in the "--" position tells the transmission to keep moving down the ratios until the one that can best slow or accelerate the Coupé is found. When driving downhill, the driver thus has the convenient option of shifting down to obtain the best possible engine braking effect. The same is true when accelerating, since the ratio from which the vehicle derives optimum performance can be engaged. Manual shifts down into the optimum gear are monitored by the transmission ECU so as to prevent the permitted engine speed limits from being exceeded. The Mercedes engineers have extended the operating time during which the torque converter lockup clutch is engaged, both to further improve vehicle agility when moving off and to reduce fuel consumption. Torque converter lockup is now possible in any gear – even first gear – whereas, before, it could only be engaged in third, fourth and fifth. Torque converter lockup reduces the slip that usually occurs between the pump and the turbine wheel. This increases efficiency and reduces fuel consumption.

Formula 1-style gearshift on the steering wheel

Another special technical feature enhances the sporty driving experience in the new CLK 55 AMG: a five-speed automatic transmission with steering wheel gearshift and SPEEDSHIFT function. This means that – as in the top-of-the-range SL 55 AMG sports car – the driver can opt for a Formula-1-style gearshift with two selector switches located behind the top two steering wheel spokes. To enable the system, the driver must first activate manual transmission mode by pressing the program select button on the automatic selector lever. The selector switch on the right of the steering wheel is used for upshifts whilst the one on the left is for downshifts. The transmission only intervenes of its own accord and changes gear if the maximum permitted engine speed is exceeded. A display in the instrument cluster tells the driver which transmission mode is active and which gear is selected.

The additional SPEEDSHIFT function combines the advantages of a five-speed automatic transmission with the dynamism of a manual transmission. Notable technical features include active downshifting: once deceleration reaches a certain level, the transmission automatically shifts down and engages the correct gear, for example if a sporty driver brakes before entering a bend. Similarly, when cornering at speed, the transmission reliably retains the engaged gear once lateral acceleration reaches a certain level, thus ensuring unbridled driving pleasure whilst preventing any power-off effects.

Furthermore, to shift down before overtaking, the driver of the new CLK 55 AMG merely has to move the Touchshift lever to the left and briefly hold it there. The transmission control unit then selects the optimum gear for powerful acceleration, depending on the road speed and the engine map.