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A Class Technical Glossary |
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Friday, 11 June 2004 |
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Page 1 of 3 ASSYST
All A-Class engines are equipped as standard with the Active Service System ASSYST. This system records the conditions under which the vehicle is operated, and takes this into account when calculating servicing intervals. A microprocessor uses information provided by the sensors monitoring oil level, oil temperature, coolant temperature, engine speed, vehicle speed and engine load to compute the actual wear on the engine oil and to produce an engine servicing plan based on actual needs.
The central display in the instrument cluster shows the driver how much further he can drive until the next service. The Active Service System includes an oil level sensor which warns if the oil level is too high or too low, and displays the shortfall in litres. It also detects if the oil is topped up, in which case it extends the servicing interval accordingly.
Automatic child seat recognition
The front passenger seat of the Mercedes-Benz A-Class estate is equipped as standard with technology which automatically recognises special rear-facing child seats fitted with a transponder system. The electronic unit transmits a coded interrogation signal via two aerials in the seat upholstery, which receivers (transponders) in the base of the rear-facing child seat decode and then reply to with a response code. This code is relayed from the seat aerials to the airbag electronics which thus 'recognise' that such a child seat is installed. If this is the case, the microcomputer automatically prevents deployment of the front passenger airbag. The "Airbag Off" indicator lamp in the centre console lights up to confirm that the aerials and transponder have exchanged signals correctly.
Automatic clutch system
For drivers looking for easier gear-shifting, Mercedes-Benz has developed a low-cost alternative to the automatic transmission, the automatic clutch. A sensor system detects that the driver wishes to change gear and ascertains the gear currently engaged, while a microprocessor evaluates the sensor signals and sends a command to the electric motor to open the clutch by means of two hydraulic cylinders. When the gear change is complete, the clutch immediately closes again. The control system develops a precise feel for different types of driving style: it can distinguish between fast, sporty gear-changing and slow, gentler operation of the shift lever and it manages the clutch engagement accordingly.
Automatic transmission
The (optional) electronically controlled five-speed automatic transmission automatically adapts its shifting patterns to the particular driving situation and the individual requirements of the driver. Like all Mercedes-Benz automatic transmissions the A-Class transmission features a hydrodynamic torque converter and torque converter lock-up with computer-controlled constant slippage, for maximised fuel efficiency, dynamism and comfort. Torque converter lock-up engages even at low speeds, and continuous computer-controlled slip when lock-up is engaged minimises vibration and noise. To engage the different gear ranges, the electronic control actuates five electro-mechanical hydraulic valves which in turn actuate the multi-disc clutches and the torque-converter lock-up clutch. By means of a switch, one of two shift modes, "S" (standard) and "W" (winter) can be selected. Winter mode features second-gear start and lower-rpm upshifts.
Axles
The A-Class has a MacPherson front suspension system with coil springs, twin-tube shock absorbers and a stabiliser. One advantage of this system is its compact design. The Mercedes engineers have modified the patented design of US automotive engineer E.S. MacPherson on one important point: on the A-Class the stabiliser is not involved in the task of wheel location but is connected by linkage to the spring strut, while a triangular link is responsible for wheel location. This arrangement offers greater flexibility when tuning the suspension, resulting in improved elastokinematics and reduced road noise and tyre vibration. The axle components together with the rack-and-pinion steering, the engine and the transmission are mounted on an integral sub-frame which is bolted to the body at eight points. The rear suspension of the A-Class features trailing arms with coil springs, a stabiliser and single-tube gas pressure shock absorbers. It has been designed so that the axle components are accommodated under the load compartment floor and no interior space is sacrificed. The excellent dynamic characteristics of this rear axle are largely attributable to special additional links which control the elastic deformation of the trailing arms and thus reduce toe-in changes.
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