New-9 speed gearbox: The more the better ?

The new 9-speed automatic transmission
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Mercedes will replace on medium term the 7-speed automatic gearbox on the models with rear wheel drive, with a 9-speed automatic transmission which will be available also for the four-cylinder engines.

With a few months ahead of Range Rover, Mercedes presented the first 9-speed automatic gearbox in the world meant for the premium segment. The new gearbox, named 9G-Tronic, will replace on medium term the current automatic gearbox 7G-Tronic. The new transmission came out with E 350 BlueTec and it is available now on four versions of CLS facelift (meaning CLS 220 BlueTec, CLS 250 Blue Tec, CLS 350 BlueTec and CLS 500). Subsequently it will also be mounted on other versions of E-Class, C, S, ML and the next GLK.

The new gearbox is already being produces at Stuttgart in Germany and it will be made at the Mercedes plant in Sebes, Romania, starting 2016, the production in Romania will have to supplement the demand as the new gearbox is introduced on other models.

On medium term, new 9-speed automatic gearbox will replace actual 7-speed automatic gearbox on all Mercedes with rwd and will be available also for 4-cylinder engines

At the cornerstone of the new location for the 9-speed gearbox from Sebes, Romania, Markus Schaefer, member in the Administration Council at Mercedes-Benz cars, responsible for vehicle production planning and the suppliers declared “Sebes plant will supplement optimally the production of the new 9-speed gearbox, as a consequence of a growing demand for the automatic transmissions.” Furthermore, he stated that the new gearbox will be gradually introduced in all the Mercedes-Benz line-ups with rear-wheel drive and will be combined also with the four-cylinder engines.

What brings this new automatic gearbox and what are the benefits of the additional two gears? Nowadays, the automotive industry follows the motto “the more the better”.

The two extra gears offer a lower rev level at higher speeds: only 1350 rpm at 120 km/h and 2700 rpm at 250 km/h

The additional two gears provide a direct advantage at least from a certain point of view: the distance between the ratio between the first and the ninth gear is 9.15, which means that it is an important part regarding the efficiency. Thus, E 350 BlueTec can reach higher speeds at incredibly low revs. This translates for instance in driving at 120km/h while the rev counter shows only 1350 rpm and, furthermore, at E 350 BlueTec’s maximum speed of 250km/h is being reached an rev of only 2700 rpm. Through comparison, at the competitors like BMW and Audi, the distance between the ratio from the first and the 8th gear, respectively 7th gear is about 8 or 7, thus meaning that at maximum speed, the six-cylinders diesel engines from BMW and Audi are rotating at a higher revs with 500 or even 1000 rpm in the top gear of the transmission. Mercedes pledges for an official average fuel consumption extremely modest for E 350 BlueTech of only 5.3 l/100 km (138g/km CO2 emissions), with a minimum of 4.7 l/100 km for extra urban.

Not only the efficiency is the advantage of the large distance between the ratio  from the first and the ninth gear, but also the driving comfort. Theoretically, taking into consideration the huge torque of 620 Nm of the 3-liter diesel available from 1600rpm, the Mercedes engine would do honorable with only three or four gears, while the nine gears offer more refinement and driving comfort.

With a weight less than 100 kg, the new 9-speed gearbox is lighter than the actual 7-speed automatic gearbox

Despite the two additional gears and a maximum transferable torque of 1000 Nm, the new transmission does not take more space than the 7 gears one and, furthermore, it is lighter than the previous one, with a weight of less than 100 kg. The gear housing is composed of two components: the aluminum housing of the torque converter and the transmission housing made from magnesium alloy, while the sump is made of plastic. Even though there are two additional gears, the 9-speed transmission also has four semi-axle and six shift elements instead of five as found in the previous gearbox.

The main mechanical pump, considerably smaller than the previous one is located close to the main axle, it is chain driven and it is being operated by a auxiliary powered pump. Thus, the lubrication and the cooling are being actively controlled upon request, in order to adapt to the stop & start system. Due to the enhance of the hydraulic circuit from the torque converter, the transmission efficiency goes up till 92%, minimizing the loss in the transfer from the torque to the engine and to the transmission shaft.

Similar to the 7G-Tronic Plus, the gearbox provides the Economy, Sport and Manual modes and another Short-term M mode. This is enabled on the Eco and Sport modes only if the drivers engage a certain gear using the steering wheel-mounted paddle shifters and it remains active when manually changing the gears or if it maintains a sporty driving style. This is entirely different from the permanent Manual mode available in combination with the AMG Line package declutching it after a period of time.

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