W 140 (1991 to 1998)

Mercedes-Benz S-Class, W 140 series (1991 to 1998)

In March 1991 the new S-Class generation (W 140 series) made its debut at the Geneva Motor Show. The body design incorporated the typical traditional Mercedes-Benz stylistic elements and thus fitted unobtrusively into the homogenous design of the passenger car model series.

As had already been the case with the SL models in the R 129 series, with the new S-Class the distinctive trademark radiator grille was given a new stylistic interpretation while retaining the traditional basic shape. This variation on a classic theme was designated the “integrated radiator” and with its much narrower chrome frame the radiator shell was organically integrated into the engine lid. For the first time, the Mercedes star was positioned not on top of the radiator grille, but slightly to the rear on the engine hood. The overall aim of the design concept of the new S-Class generation was to achieve a high degree of aerodynamic quality while at the same time respecting a maximum of everyday practicality.

As with the predecessor models of the W 126 series and generations of Mercedes-Benz premium-class series before them, the normal version was also accompanied by a long-wheelbase variant, in which the additional 100 mm (3.9 in) served exclusively to increase legroom in the rear. As far as the engine was concerned, initially four units were available on the domestic market, of which only the 5.0-liter V8 four-valve M 119 was an old and familiar friend. As with the 500 E of the mid-range W 124 series, the engine used here was the so-called Einheitsdeckmotor (standard engine) – a crankcase for both the 4.2 and 5.0-litre assemblies – whose fully-electronic Bosch “LH Jetronic” injection system was controlled via a hot-wire air mass sensor.

The other three engines were newly developed: Like the 5.0-liter unit, the 4.2-liter four-valve V8 was based on the 4.2-liter two-valve engine, and the six-cylinder in-line engine with 3.2-liter displacement was based on the 3.0-liter four-valve unit introduced two years earlier. An interesting detail to note here is that the model designation of the 3.2-liter and 4.2-liter models did not reflect exactly the displacement as had always been the case in the past.  Instead, for the sake of homogeneity the designations 300 SE/SEL and 400 SE/SEL were chosen.

The twelve-cylinder

600 SEL at the 1991 Geneva Motor Show

The 6.0-liter V12 M 120 engine was an entirely new design, not just the first series-produced twelve-cylinder Mercedes-Benz passenger car, but also the most powerful Mercedes-Benz car engine of its day, with a rated power output of 300 kW (408 hp). With a peak torque of 580 Nm (428 lb-ft), it reached the 500 Nm mark at 1600/min. As with the six-cylinder and the two V8 engines, the twelve-cylinder was also equipped with four-valve technology, variable intake camshaft and an electronic injection system with hot-wire air mass sensor. With all engines a high priority was placed on minimizing exhaust emissions and reducing fuel consumption. The new fully electronic ignition system calculated the optimum ignition point from 300 ignition maps, tuned for each cylinder individually and to the knock limit in each case. The M 120 was the only twelve-cylinder engine worldwide to feature this cylinder-selective anti-knock control. This alone made possible the high compression ratio of 10:1, necessary for optimum use of fuel.

M 120 V12 engine of the 600 SE/SEL

Engine and drive management was also completely new. Here, all control modules communicated with one another via a common data channel, which meant that the control units were jointly active. This served for rapidly warming up the catalytic converters on cold-starting the engine, for example, as well as for acceleration skid control ASR and for the new engine friction torque control, which maintained handling stability during power-off situations on slippery road surfaces.

Interior of the 600 SEL

The V12 offered the world’s largest catalytic converter unit for passenger cars. With a seven-litre volume in order to avoid any excess fuel consumption on account of the catalytic converter, it ensured a high degree of long-term stability. Thanks to an innovative concept involving a double-walled and triple-insulated exhaust manifold, as well as double-walled pipes, the ceramic catalytic converters – embedded in insulating expandable matting – reached the optimum operating temperature in a very short time.

Environmental compatibility

In addition to optimizing and reducing exhaust emissions, the W 140 series also featured a number of other details that made it a pioneer for environmentally compatible automotive production. It heralded the age of the CFC-free (chlorofluorocarbons) car and set new standards in terms of recycling. The plastic components used were not only recyclable and clearly identifiable, they were also to a large extent manufactured using regranulated plastics. In 1992 the W 140 series won an environmental award from the US Environmental Protection Agency, the “Stratospheric Ozone Protection Award.”

Double wishbone suspension front axle

Apart from reducing fuel consumption and optimizing environmental compatibility, development of the W 140 series placed a special emphasis on raising comfort and safety to new levels of perfection. In this respect, the meticulous design and coordination of the running gear played a particular role. A newly developed double wishbone front axle, with the main point of load application mounted on a subframe, provided front suspension – a system designed to isolate the body from audible and perceptible vibrations.

Multi-link independent rear suspension

Rear suspension was derived from the multi-link independent suspension of the other passenger car series, although radically revised in terms of wheel location and modified in line with the special requirements of the S-Class. To take account of the significantly greater longitudinal and transverse forces, the link geometry was also redesigned. Of particular interest was the crossed design of the upper links, which allowed axle space to be kept to a minimum in spite of the long control arms.

Dashboard of the 600 SEL

In terms of active safety the S-Class saloons in the W 140 series were known for their exceptionally good straight-line stability even on uneven road surfaces, their low crosswind sensitivity, precise and responsive steering and handling which remained relatively unaffected by the size of payload. The brake system for the eight and twelve-cylinder models was a fundamental innovation. By distributing more braking power to the rear wheels, it was possible to improve the fade resistance of the brake system and reduce wear to the front wheel brakes.

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