Mercedes-Benz New Twin-Pulse Four-cylinder Gasoline Engines

Stuttgart, Germany, February 2002

With the launch of its new engine generation in mid-2002, Mercedes-Benz will once again show the way forward, this time in the field of four-cylinder technology. The state-of-the-art engines, which will initially be installed in the C-Class and subsequently in other Mercedes model series, highlight the shape of things to come in all the major areas of development: fuel consumption, torque characteristics, power delivery, lightweight design and refinement.

The sophisticated 1.8-litre engine is available in four guises, all featuring the unique TWINPULSE system which combines numerous technologies – including a compressor supercharger, intercooler, four valves per cylinder, variable valve timing, Lanchester balancer and adaptive drive system – to minimise fuel consumption and maximise driving pleasure and refinement.

Direct-injection engine developing 170 hp with a fuel consumption of just 7.8 litres per 100 km

The new four-cylinder engines from Mercedes have power outputs ranging from 105 kW/143 hp to 141 kW/192 hp. From the end of 2002, Mercedes-Benz will also offer a direct-injection petrol engine developing 125 kW/170 PS for the first time. This is the first engine of its kind in the world to combine 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. CGI stands for (Stratified) Charged Gasoline Injection.

The new engine develops more power, yet it consumes over 19 percent less fuel than the equivalent C-Class predecessor model. The figures speak for themselves: fuel consumption in the C 200 CGI is a mere 7.8 litres per 100 kilometres (sulphur-free Super Plus, NEDC combined consumption).

Over 75 percent of the torque is available from just 1500 rpm, and the direct-injection engine develops its maximum torque of 250 Newtonmetres from 3000 rpm. What's more, it maintains this impressive torque up to 4500 rpm.

TWINPULSE for enhanced dynamism and lower fuel consumption

Comparisons with the preceding models reveal that Mercedes' three new four-cylinder engines with conventional fuel injection also have everything it takes to deliver superb economy and a dynamic driving experience: the new C 180 KOMPRESSOR accelerates from 0 to 100 km/h in 9.7 seconds, going on to reach a top speed of 222 km/h, making it 1.3 seconds quicker and 12 km/h faster than the previous C 180 Saloon. Fuel consumption has been reduced by a full litre to 8.4 litres per 100 kilometres (NEDC combined consumption), a saving of more than ten percent. And the four-cylinder newcomer also delivers when it comes to pulling power and flexibility: the maximum torque of 220 Newtonmetres is some 15 percent higher than in the predecessor model (190 Nm) and available from just 2500 rpm.

Meanwhile the new C 200 KOMPRESSOR consumes over eleven percent less fuel than its predecessor. Its four-cylinder engine develops a maximum torque of 240 Newtonmetres at 3000 rpm (predecessor model: 230 Newtonmetres).

In terms of power output and torque, the C 230 KOMPRESSOR (141 kW/192 hp, 260 Newtonmetres) is the star of the new four-cylinder engine line-up. This version, which Mercedes-Benz will install in the C-Class Sports Coupé, delivers a fuel saving of 0.7 litres per 100 kilometres compared to its predecessor.

High thermal efficiency and exemplary torque curve

The Mercedes engineers have ensured that the new four-cylinder engines deliver exemplary fuel consumption, primarily by shifting the operating points to engine speed ranges that offer optimum thermodynamic efficiency. In addition, reducing the displacement to 1.8 litres results in lower friction losses and improved thermodynamics, all of which has a positive effect on the fuel economy. However, the four-cylinder C-Class models have lost none of their exemplary agility and dynamism. This is largely thanks to the compressor supercharger installed in all the new-generation powerplants, which helps the engine to provide impressive torque from idle. This, in turn, extends the overall ratio by up to 13 percent. As a result, the new engines largely run with the throttle wider open, making them particularly economical. This is the TWINPULSE effect: even higher performance and even lower fuel consumption.

The TWINPULSE system enables the compressor supercharger and the Lanchester balancer – a combination that is unique in the world – to resolve a further conflict of aims that arises when developing four-cylinder engines: the balancer shafts counter-balance the vibrations which would normally occur, thus ensuring a level of refinement that is exemplary in this displacement class.

In other words, mechanical supercharging and sophisticated engine technology enable the new Mercedes engines to combine the tractive power and the low-noise characteristics of a six-cylinder engine with the economy of a four-cylinder engine.

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

As well as being renowned for its compressor technology, 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 powerpack'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 normally 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 C 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. This regulator receives signals from a special 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 refer to what is known as "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 all versions of the new Mercedes engine has 16 valves and double overhead camshafts. Unlike in the previous Mercedes four-cylinder engine, 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 favourable effect on torque characteristics under full load as well as on fuel consumption and exhaust emissions. The valves are controlled by means of cam follower with roller mechanism and have a maintenance-free hydraulic valve lifter.

Highly efficient, low-noise compressor

The Mercedes developers have reengineered the compressor – which ensures exemplary bottom-end torque characteristics in all new Mercedes four-cylinder engines – 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. In this new generation of engines, the standard version and CGI version have different plastic pipe arrangements: in the direct-injection version, they are separated into two separate 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 in 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 vehicle's electronic system 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 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 on a par with 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 engines have a further advantage, namely refinement and acoustics that are on a par with a six-cylinder engine. This is primarily down to the newly developed Lanchester balancer which consists of two forged shafts supported in multiple bearings, located below the crank mechanism. 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 balancer shafts have been perfectly harmonised to neutralise the vibratory forces in the four-cylinder engine. This technology thus substantially reduces noise emissions and vibrations. In other words, it 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. 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. Made of diecast aluminium (previous engine: cast iron), the crankcase is one of the major components in the lightweight design concept at the heart of the new four-cylinder engine. Again the figures speak for themselves: the engine weighs just 167 kilograms, making it much lighter than its predecessor. The actual weight saving equates to 18 kilograms or almost ten percent.

Driving dynamics tailored to driver requirements

Mercedes-Benz also offers a newly developed system 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 four-cylinder 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 more “gentle”.