Ratios Galore: A Deep Look at ZF’s 9-speed Automatic

When is enough, enough? When it comes to transmissions, the available ratios from any trans maker are on a steady climb into two-digit territory. Take ZF’s newest for example: the 9HP. It’s a nine-speed transaxle for transverse applications sporting a 9.8 ratio spread (that’s good) and it promises 10-percent better fuel economy when compared to a six-speed slushbox. In a market that goes full frenzy by one-percent here and two-percent there, 10 can’t be ignored.

The trouble with engineering a transmission for a transverse application is packaging. The gearbox, along with the engine, has to fit between the shock towers. According to ZF, which announced it will initially supply the 9HP to the Jeep Cherokee and the Land Rover Range Rover Evoque with more customers to come, the maximum width for such a transmission is about 14.6 inches. It’s no surprise, then, that the 9HP is 14.4 inches wide. With four planetary gear sets and six shifting elements (brakes and clutches) that’s a very dense 14.4 inches.

Of those four planetary gearsets, two of them are nested. In this nested pair, the annulus, or ring gear, of the smaller planetary doubles as the sun gearbox  of the larger set. This arrangement trims some width from the four-gearset tranny.

Simply adding ratios to a transmission might not make it a tool for greater efficiency, however. More ratios require more shifting elements and these add weight, complexity, and drag to the transmission. This is why ZF implemented two dog clutches in the 9HP. The beauty of a dog clutch is there’s little-to-no parasitic loss when they aren’t engaged, whereas a conventional friction clutch zaps some efficiency, and they’re relatively compact.

Parallel shaft gearbox

The tricky part of the canine clutch is how, or rather when, to engage them. Synchromesh helps dog clutches within a manual transmission from grinding away and easing gear changes. ZF relies on computers to anticipate the precise moment both halves of each dog clutch are spinning the exact same speed, and engagement happens without the slightest crunch, as proven by our short sample in an Evoque test mule.

• Comparison Test: 2013 BMW X3 xDrive28i vs. 2013 Audi Q5 2.0T, 2013 Land Rover Range Rover Evoque
• First Drive: 2014 Jeep Grand Cherokee V-6 / V-8
• Instrumented Test: 2014 Jeep Grand Cherokee SRT

Internal efficiencies aren’t the only source for the claimed fuel-economy improvement, either; the nine ratios play a part, too. Internal-combustion engines are most efficient in a relatively small rpm range and the biggest ratio step is just 1.65, between first and second. Having many small ratio steps in hand allows any engine coupled to a 9HP to operate in that ideal rpm window more of the time.

Oh yeah, one of the best parts of the 9HP: it’s 100 percent American made. Every

WHAT'S HOT Trending styles Diamond Of The Week: 1.91 Carat

The Lowdown: 1.91 carat oval brilliant cut diamond with D color and SI1 clarity grade. This oval cut diamond features Excellent polish and Very good symmetry grades and is considered an Excellent cut oval diamond. The measurements on this particular diamond are 9.89 mm in length by 7.20 mm in width. While these are all the characteristics easily discerinible from the GIA report alone, we will go into depth on the characteristics of this engagement ring diamond to show some more detail. Watch the  video here of this oval cut diamond to get an idea of the bright white and fiery look this special oval cut has. A diamond with this quality and size combination is an amazing budget option for someone wanting a 2 carat diamond in the colorless range for a large, bright white look. 

In this post we will delve into detail on the various aspects of this special value diamond

drop earrings

The Color: At D color it simply cannot get any better than this! D is at the top of the Colorless range resulting in a perfectly white diamond. Oval diamonds specifically tend to show color saturation a lot easier than other diamond shapes. Check out this video showing the color changes from D, H, and I color oval diamonds.  Because ovals tend to show color very easily we recommend in most cases stearing clear of the J color range for this shape. Otherwise, the tint of yellow closer to the J color range can become too apparent. While we won't say D color is an absolutely necessity, there is no engagement ring denying the bright white appearance and the sheer rarity of a D color is extremely appealing and gives a very crisp clear appearance to this special diamond.

The Clarity: The Slightly Included clarity range is a tricky range because many of the diamonds will not be eye clean. However we sieve through to select the best SI clarity diamond options for our clients to maximize the beautiful face up look. Notice there are not an overwhelming amount of clouds or feathers which could result in a hazy look in the diamond. An SI1 clarity diamond with with well hidden imperfections is considered flawless to the naked eye meaning you can only view inclusions on close inspection/magnification.

The Shape: The shape of an oval diamond is one of the most important characteristics and unfortunately not a listed characteristic on the GIA report of the diamond. We love the rounded symmettrical look to this oval featuring perfectly curved edges that oval diamonds are famous for. Oval's can be cut in a variety of ways. A poorly cut oval might have a bulging mid-section like a marquise cut diamond resulting in a football shape diamond. Other ovals might have a more squarish appearance detracting from the soft graceful look the oval is so well known for. Since this is an unlisted characteristic this is where a video comes in and allows you to see the nuances and outline of each diamond.

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