Quick Note: Mercedes Brings Nine-Speed Automatic to E-Class
July 22, 2013 11:34 AM
comment(s) - last by
it will gain a combined fuel economy of 53.3 MPG from 51.4 MPG
Mercedes is updating its
with a new nine-speed automatic.
Last weekend, Mercedes-Benz’s German language website configurator revealed that the nine-speed automatic -- known as 9G-Tronic -- will now be standard on the rear-wheel-drive E350 BlueTec. It will replace the seven-speed 7G-Tronic automatic gearbox, which will now be standard equipment on the E220 BlueEfficiency Edition.
While bringing the 9G-Tronic along won't change the E350 BlueTec’s ability to hit 0-62 MPH in 6.6 seconds, it will gain a combined fuel economy [European rating] of 53.3 MPG (from 51.4 MPG with the 7G-Tronic). This is due to a boost in city MPG from 40.9 to 44.1.
The 9G-Tronic also brings reduced average CO2 emissions from 144g/km to 138g/km.
Back in May, Mercedes said it was aiming for
45 MPG highway
on the new 2014 E250 Bluetec 4Matic diesel sedan. Its 2.1-liter, 4-cylinder turbodiesel engine uses twin sequential turbochargers for 195 HP and 369 lb-ft of torque.
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RE: Are 9 Gears Really Necessary?
7/23/2013 11:28:57 AM
The 9 gears are necessary to keep the engine at its most efficient rpm for the given task at any particular time. Not necessarily low rpm. And with direct injection and today's control systems, your fuel usage is directly related to calculated demands and has only a passing relation to engine rpm as one more variable that goes into the calculation. If this is a European only vehicle, I would be surprised if stratified charge is not part of the efficiency attempts in the control system.
Complexity perhaps, but inefficient I highly doubt. With a claimed 16% efficiency gain over a equivalent 6 speed auto I would at least call it sufficiently efficient for the application.
RE: Are 9 Gears Really Necessary?
7/23/2013 4:42:50 PM
If you are speaking in respect to having the extra gear ratios I would agree - 9 gears is more efficient than 6 for keeping an engine within its most efficient rpm range for the load it is under. BUT the actual mechanical operation of any hydraulic automatic transmission is horribly inefficient. The parasitic losses from driving the hydraulics and the slippage of the torque converter are horrible. Lockup converters help, but you still get major frictional losses and heat from the large number of clutches and bands needed to control the sun, ring and planet gears in planetary gear transmissions.
Think about it for a minute. A 4-speed (3 plus overdrive & reverse) automatic transmission has a total of 2 bands and 4 clutches. For purpose of figuring losses, think of a band as another clutch. Each clutch in the driveline introduces frictional power losses. So 6 clutches in total for a simple 4 speed tranny.
Now just imagine the complexity and inefficiency of 9 speeds. Add another band and clutch for each new planetary gearset.
If car makers really need to go turn to stratospheric numbers of speeds, they really should think about moving away from the common slushbox that has been around since the 1950s. There are better ways of incorporating high numbers of gears without incurring all the parasitic and frictional losses.
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