Overview: Mercedes-Benz CL-class

To compare Mercedes’ new CL with the recently-launch Bentley Continental GT gives an interesting insight into the attitudes and psychologies of the two companies and, to a significant extent, their customers.

The Bentley, though smaller in overall length, is six per cent. heavier, produces 71 per cent. more CO2 and reaches 100km/h from rest a rather academic 0.3s before the Mercedes — which itself takes only 4.9s. The CL’s maximum speed is limited to 155mph — more than ample for any motorway in Europe that we have ever driven on — while Bentley allows its car to run on to a useless (but perhaps psychologically powerful) 198mph.

The Bentley isn’t all kerb weight and emotion, though. At least some of its extra mass goes into a very good four-wheel drive system; the Mercedes is driven by its rear wheels. And the Mercedes’ torque-to-weight ratio is inferior to the Bentley’s by 11 per cent., though the cost in fuel and emissions is substantial.

Although there are two CL models, the more powerful V12 variant will be available to special order only. We will concentrate on the one standard model, the V8-engined CL 500 Blue Efficiency.

The CL’s twin-turbo V8 has been completely redesigned for the new model. A glance at the comparison table shows the extent of the changes: next to its predecessor, the new engine has a smaller swept volume, produces more power and torque, and uses less fuel. One of the main reasons for the improvements is the introduction of a new spray-guided direct injection system which Mercedes-Benz describes as Blue Direct. Piezo injectors are used, with an injection pressure of 18kPa. Of particular note is the new engine’s multi-spark ignition régime, with up to four ignition sparks within one millisecond.

There is also a new Blue Efficiency package for the CL including — among other things — energy-efficient control of the alternator, in which the unit is switched on-load and off-load according to the demands on the engine and the on-board electrical systems; kinetic energy capture on overrun is a major feature. The fuel pump, air-conditioning compressor and power-assisted steering system are also on-demand items. The V8 itself features a stop-start system; low rolling-resistance tyres are specified.

The cooling system uses thermal management to accelerate the warm-up process by isolating the block and head from the rest of the cooling circuit until a predetermined operating temperature is reached.

Safety and driver-assistance systems

The CL features a number of camera- and radar-based assistance systems. These include the increasingly familiar active cruise control, which monitors the gap between the car and the vehicle in front, as well as systems to help the driver keep in lane and to provide warnings about any vehicles in the car’s blind spots.

Active Lane Keeping Assist is being introduced on the CL and S-class cars. If the car approaches close to a continuous lane marking line, the system actuates an electric motor in the steering wheel, causing the wheel it to vibrate briefly. If the Mercedes unintentionally crosses a continuous lane marking line to the right or left, the system intervenes by gently braking the wheels at the opposite side of the car, causing a mild swerve back into lane. This system uses the car’s Electronic Stability Program functions.

Active Lane-Keeping Assist uses information provided by a camera mounted on the inside of the windscreen. It identifies the contrast between the road surface and the lane marking lines. Additionally, it uses radar scans of the side of the roadway for crash barriers and other roadway edge markings. This car also evaluates the driver’s actions to determine whether a warning is appropriate: if the driver is using the indicators, if he accelerates hard just before overtaking or when accessing a motorway, or if he brakes hard or steers into a curve, then the system is not triggered.

Blind Spot Assist detects whether a change of lane would be dangerous. If so, the system warns the driver by displaying a red triangle in the glass of the exterior mirror. Close-range radar sensors monitor the area immediately to the side and to the rear of the car. If the driver disregards a warning and, for example, actuates the turn indicator, an audible warning also sounds. If the driver continues to ignore the warnings and comes dangerously close to a vehicle in the neighbouring lane, a corrective braking intervention by way of the car’s ESP system on the wheels of the opposite side of the car produce a swerve away from the other vehicle. If, despite this, an impact cannot be avoided, the active Blind Spot Assist system applies the brakes.

Adaptive Main Beam Assist is another standard item on the CL-class. This camera-based system can recognise oncoming vehicles or the tail-lights of vehicles ahead. The system then controls the headlamps to provide the best possible beam range without dazzling other road users. Mercedes also offers an infra-red pedestrian detection system called Night View Assist Plus: as soon as the system detects pedestrians on the road ahead, their image is highlighted on the dashboard display screen.

The images supplied by the windscreen camera are also used by the Speed Limit Assist system, which is an optional extra. It recognises speed limit signs in passing and shows the relevant speed limit in the central display and on the navigation system’s map display.

For the new-generation CL-class, Mercedes-Benz boasts of improvements to the long- and medium-range radar used by Brake Assist and Distronic Plus proximity cruise control.

Pre-Safe Brake is another radar-based system. If the driver fails to respond to the imminent danger of a rear-end collision — or to the warning signal of an assistance system — this system can intervene and brake the vehicle independently. If the driver fails to react even after automatic, partial braking action, the Pre-Safe system applies maximum braking pressure around 0.6 seconds before what it now recognises as an unavoidable collision impact. As we have commented elsewhere about these systems, it stops short of acting to prevent the collision.

Attention Assist is standard equipment on the CL. The system continuously evaluates around 70 different parameters to determine how alert the driver is and to provide a warning before the driver enters the microsleep phase. Observing the driver’s steering behaviour has proved to be a particularly strong indicator: drowsy drivers make minor steering errors which they often correct very rapidly in a characteristic way.

The CL’s Active Body Control incorporates a function to reduce the effect of a crosswind. It works by modifying the wheel load distribution by way of the spring struts within a few milliseconds, depending on crosswind direction and intensity, to the extent that it can largely compensate the effects of the crosswind. The Active Body Control suspension system also regulates roll, pitching and squatting movements by adjusting the damping rate at each wheel: clearly, the maximum roll angle at a given speed and a given curve radius is not reduced, but the rate of roll is, so roll angles are reduced during transient manoeuvres.

On final chassis function worth mentioning is Torque Vectoring Brakes. This brakes the inside rear wheel during brisk cornering, reducing understeer.

Chassis

Wheel location is by means of four links at the front and a multi-link arrangement at the rear. The rate of each damper is controlled electronically. Both front and rear brake discs are internally ventilated; the front items are also perforated. The parking brake is electrically-operated with drums at the rear.

Mercedes-Benz CL
500
Blue
Efficiency
600
Cylinders 8V 12V
Valves 4 3
Bore/stroke 92.9/86.0 82.0/87.0
Swept volume 4663cc
5461cc
5513cc
Compression
ratio
10.5:1 9.0:1
PS/rpm 435/5250
388/6000
517/5000
Nm/rpm 530/1800
530/2800
830/1900
Maximum speed 155 155
0-100km/h 4.9
5.5
4.6
Combined MPG
(l/100km)
29.7 (9.5)
23.0 (12.3)
20.4 (13.8)
CO2 g/km 224-232
288
322-328
Emissions EU5 EU5
Transmission A7 A5
Driven wheels Rear Rear
Fuel tank 90l 90l
Kerb mass * 1995 2110
PS/t 218 245
Nm/t 270 393
Length 5095 5095
Width 1871 1871
Height 1419 1419
Wheelbase 2955 2955
Track: front
Track: rear
1601
1607
1601
1607
* DIN. EU kerb mass = DIN + 75kg.
Figures in italics are for the outgoing model.
Mercedes-Benz
CL 500
Blue
Efficiency
Bentley
Continental
GT
Swept volume 4663cc 5998cc
PS/rpm 435/5250 575/6000
Nm/rpm 530/1800 700/1700
Maximum speed 155 198
0-100km/h 4.9 4.6
Combined MPG
(l/100km)
29.7
(9.5)
17.1
(16.5)
CO2 g/km 224 384
Driven wheels Rear All
Kerb mass * 1995 2320
PS/t 218 247
Nm/t 270 301
Length 5095 4806
Width 1871 1944
Height 1419 1404
Wheelbase 2955 2746
* DIN. EU kerb mass = DIN + 75kg.
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