Mechanical engineering | Vehicles » 7G Tronic, Seven Speeds for Improved Fuel Consumption and Driving Pleasure

7G-TRONIC: seven speeds for improved fuel consumption and driving pleasure • • • • Introduction autumn 2003 in the E-, S-, CL and SL-Classes New shift principle for faster acceleration Integrated electronics and state-of-the-art lightweight design Eleven million Mercedes automatic transmissions built since 1959 Starting in September 2003, Mercedes-Benz has equipped the E-, S-, CL- and SL-Classes with the new 7G-TRONIC automatic transmission. The 7G-TRONIC offers outstanding performance all round – as well as reducing fuel consumption significantly, it also performs gear changes more quickly and more smoothly than existing automatic transmissions. To meet their ambitious goals, the Mercedes engineers designed the worlds first ever volume-production passenger car transmission with seven forward speeds and two manually engaged reverse gears. The result underlines once again that MercedesBenz technology leads the way in the passenger car industry The new automatic transmission,

designed to handle a continuous torque of 700 newton metres, will be standard-fitted in place of the present five-speed automatic transmission in a number of Mercedes-Benz models – initially the E 500, S 430, S 500, CL 500 and SL 500 – starting in autumn 2003. The new 7G-TRONIC inaugurates the fifth generation of MercedesBenz automatic transmissions, thereby continuing a long tradition. Since 1959, Mercedes-Benz has built more than eleven million automatic transmissions – automatic transmissions are standard in the S-Class and are specified in around 88 per cent of E-Class models. In the C-Class, some 65 per cent of all Saloons, Estates and Sports Coupés are fitted with automatic transmission, and the trend is rising. Reduced fuel consumption and improved driving pleasure The new seven-speed automatic transmission incorporates a range of technical ad-vances which bring significant improvements on fuel consumption, comfort and driving pleasure: • • Fuel consumption: the new

7G-TRONIC reduces NEDC combined fuel consumption by up to 0.6 litres per 100 kilometres, or around five per cent, depending on model. Under everyday driving conditions, actual fuel savings of well over one litre per 100 km are possible. Refinement: Gears are engaged between 0.1 and 02 seconds sooner, making the torquey V8 engine even more responsive • to accelerator inputs. At the same time the transmission also operates more smoothly and more quietly. Driving pleasure: for the same engine, acceleration times from 0 to 62.5 mph are reduced by up to 03 seconds compared with the same Mercedes models fitted with the previous five-speed automatic transmission, while as much as 2.1 seconds can be shaved off the 37 to 74 mph time, which is particularly useful for speedy overtaking. Fuel consumption and performance figures in detail (models with previous five-speed automatic transmission in brackets): E 500 Fuel 25.2 consumpti (24. on mpg* 6) Accelerat 5.8 ion 0– (6.1 62.5 mph ) s

Accelerat 5.6 ion 37–74 (6.6 mph s ) S 430 S 500 CL 500 25.9 248 241 (24.6 (237 (237 ) ) ) 7.1 6.3 6.3 (7.3) (65) (65) SL 500 23.3 (22.2) 6.0 (6.1) 7.0 6.1 6.1 5.6 (9.1) (78) (78) (76) *NEDC combined consumption Optimal ratios for all driving situations The superior performance of the new automatic transmission is due to a number of different design modifications. Most important among these is the increase in the number of forward speeds, from five to seven. This increases the overall spread, yet at the same time the ratios are closer together than on the five-speed transmission. In this way optimal ratios are provided for virtually all driving situations. On the five-speed transmission the ratio of the highest to the lowest gear was 4.33, whereas the high/low ratio for the new seven-speed automatic transmission is 6.0 This gives the electronic control unit which triggers the gear changes even greater scope for maximising fuel economy and smoothness. One important benefit of this

is a significant reduction in average engine speeds. At 625 mph, for example, engine speeds are reduced by between 800 and 1000 rpm depending on operating conditions. The optimal rev-matching results in more fuelefficient, quieter operation The seven gear ratios at a glance: Seven-speed automatic transmission for E 500, S 430, S 500, CL 500 and SL 1st gear 2nd gear 3rd gear 4th gear 5th gear 6th gear 7th gear Reverse 1 and 2 500 4.377 2.859 1.921 1.368 1.000 0.820 0.728 gears -3.416/ -2231 The shift principle too has been significantly enhanced. When it is necessary to downshift quickly through several gears for speedy acceleration, for example in response to "kickdown", the new seven-speed automatic transmission resorts to a so-called "sliding multiple downshift", rather than performing gear changes one after the other. As the name implies, the individual gearshifts partially overlap. For example while the transmission is still changing down from seventh to

sixth gear, it will already be initiating the change from sixth to fifth, and before that operation in turn is completed, the transmission will already be starting to change from fifth to fourth. This speeds the overall process of shifting through the gears and at the same time results in greater smoothness, making the individual gear changes virtually imperceptible. The speedier gear changes produce a noticeable increase in agility. Gears are engaged between 0.1 and 02 seconds sooner than with the five-speed automatic, resulting in improved acceleration and tractive power. Multiple downshifts for fast "kickdown" acceleration The sliding multiple downshift principle is enhanced by dispensing with sequential gearshifts when appropriate. When fast downshifts are required, the 7G-TRONIC transmission will sometimes skip gears, for example changing down from seventh gear directly into fifth, and then from fifth into third. Thus in some driving situations, only two instead of the

previous four gear changes may be necessary for fast acceleration under kickdown. At the same time smoothness is also improved. The rapidly executed, "sliding" gear changes are virtually imperceptible, particularly in the higher gears. In subjective appraisals of smoothness, around 95 per cent of all gear changes went virtually unnoticed by the driver. Converter lockup engages even in first gear Like its predecessor, the new seven-speed automatic transmission is equipped with a torque converter lockup clutch. Under a wide range of operating conditions the lockup clutch, located in the hydrodynamic torque converter, almost completely eliminates slip between the pump and turbine. Whenever appropriate, it creates a virtually rigid connection between the engine and the transmission shaft, thus preventing power losses. On the new Mercedes-Benz 7G-TRONIC, converter lockup engages even in first gear, rather than only in the higher gears as on conventional automatic

transmissions. The lockup clutch engages with a degree of controlled slippage, which makes a further contribution to smoothness. Based on the intelligent principle pioneered by French engineer Ravigneaux In technical terms, the new seven-speed automatic transmission is a logical development of its predecessor, which has been giving excellent service for many years. The transmission developers at Mercedes-Benz decided to combine two simple planetary gear sets with a "Ravigneaux" gear set. Here the simple planetary gear set used before is replaced by two different planetary gear sets and sun gears operating in a single ring gear. This design, first developed by the Frenchman Paul Ravigneaux in the nineteen twenties, provides the basis for a transmission with seven forward speeds and two reverse speeds. At the same time the Stuttgart engineers have also changed the gear tooth geometry, resulting in a further reduction in power losses and noise. As before, the actuation elements

comprise hydraulically operated multiple-disc clutches and brakes – a design which is capable of handling much higher torque, of up to 700 newton metres – than other solutions. Despite its greater torque-carrying capacity and its two additional forward gears, the new transmission is only 41 millimetres longer than the previous version, while the diameter of the torque converter is actually 20 millimetres smaller than before. And despite the seven gears, there is virtually no difference in weight between the two transmissions – since for the first time the transmission housing is produced from magnesium, the 7G-TRONIC weighs in at just 81.5 kilograms excluding the control unit. Shift plate and control unit form a single unit Operation of the gearshift is the same in principle as for the previous five-speed transmission with Touchshift. Also familiar is the mode selector for "S" (= Standard) and "C" (= Comfort) programs. Program "C" features

second-gear start and lower-rpm upshifts. Future shift-by-wire technology is also catered for, with steering-wheel gear-shift buttons which allow gears to be selected quickly and conveniently. As far as the control unit is concerned, the engineers have once again trodden new paths. It is integrated with the shift plate, which contains the maze of hydraulic passages and tubes supplying the hydraulic fluid. This means fewer cables and further enhanced reliability. The electronic control unit is directly integrated in the oil sump, which allows it to directly measure, using sensors, three different rotational speeds within the transmission and to directly evaluate this information. The signals for the eight solenoids which are also integrated in the control unit are likewise transmitted very directly. The solenoids regulate the working pressure, the seven actuation elements and the torque converter lockup clutch. The fully integrated control system makes a further important

contribution to the exceptionally fast operation of the new transmission. Fast data exchange with other control units Further information is supplied to the control unit by sensors monitoring rolling resistance (uphill or downhill gradient, vehicle payload), atmospheric pressure (altitude), driver inputs and longitudinal and transverse vehicle acceleration. The transmission control unit uses this information to vary the shift points with reference to driver-specific and vehiclespecific requirements, and to calculate the required hydraulic pressures and the control signals for the torque converter lockup clutch. The transmission control unit is also linked, by databus, to the engine management system, which means that it has access at all times to all the signals and derived data currently being supplied by sensors and other control units. Conversely, as well as receiving information, the transmission control unit also transmits its own commands to the engine management system, for

example requesting a reduction in engine power while gears are being changed, or calling for shift point changes designed to speed catalytic converter warm-up. The control unit of the Mercedes-Benz seven-speed automatic transmission operates flexibly rather than just switching between a small number of stored shift programs as in the case of previous transmissions. This ensures optimal transmission control whatever the operating conditions and whatever the wishes of the driver. This in turn guarantees fuel-efficient operation, high standards of ride comfort and sporty, agile response