The Truth About Cars » zf The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Tue, 15 Jul 2014 13:00:42 +0000 en-US hourly 1 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars » zf Ur-Turn: Saturation Dive Into The ZF 9-Speed Tue, 25 Feb 2014 18:03:02 +0000 fig1

A TTAC reader is an engineer with a major powertrain company, and offered his extremely detailed analysis of the ZF 9-speed. Consider this an AP level course in powertrain engineering.

Before we dive right in to the 9-speed gearbox, let’s take a quick refresher on the basics of gears. The simplest gear set consists of 2 parallel gears mounted on 2 parallel shafts. Shown in Fig.1 is a gear set with a 20 tooth drive gear on the right and a 30 tooth driven gear on the left. For this gear set the speed of the driven gear is 1.5 times lower than the drive gear, and assuming no frictional losses anywhere, the torque on the driven gear is 1.5 times higher. This gear set has a ratio of 1.5:1. This type of a gear set is usually not favorable for packaging since it requires 2 parallel shafts, and there are largest separating forces that push the 2 gears apart which means that the bearings supporting the shafts have significant radial loads on them, in addition to an axial load if the gears are helical.


A simple planetary arrangement is shown in Fig.2 - this is the basis of most modern automatic transmissions. A simple planetary gear set has 3 members mounted on concentric shafts, the innermost gear is called a sun gear, the outermost gear is called the ring gear, and there are evenly spaced planetary pinions that mesh with both the sun gear and the ring gear. These pinions are free to spin around their own axes, and ride on the planetary carrier, which is the third concentric member. The radial forces in a planetary gear arrangement cancel out due to symmetry, and therefore the bearings supporting these shafts do not see much, if any radial loads. Since the 3 shafts are concentric, there are significant packaging advantages as well. This particular planetary arrangement has a 30 tooth sun gear, 72 tooth ring gear, and 21 tooth pinions. For this gear arrangement to go together, the difference between the number of teeth on the ring gear and the number of teeth on the sun gear has to be an even number, and the sum of teeth on the ring gear and the sun gear has to be divisible by the number of planetary pinions. In this case, the sum of the number of teeth on the ring gear and the sun gear is 102, which is divisible by the number of planets (3), hence this is a feasible gear arrangement.

Since there are 3 members in a planetary gear set, one member has to be grounded (i.e. forced to stand still) for there to be a ratio. There are 3 possible ground members (the sun gear, the ring gear, or the carrier), and 2 possible input and output combinations possible for each ground member, therefore this arrangement can provide 6 different speeds. If the number of teeth on the ring gear is denoted by R and the number of teeth on the sun gear is denoted by S

  1. If the ring gear is grounded by the use of a brake, the sun gear is the input and the carrier is the output, the
    ratio of this arrangement is S+R/S or 3.4, i.e. the carrier is rotating 3.4 times slower
    than the sun gear. Therefore in this configuration output is underdriven with respect to the input. If the carrier is
    the input, and the sun gear is the output, then the output is overdriven by the same ratio.
  2. If the sun gear is grounded, the ring gear is the input and the carrier is the output, the
    ratio of this arrangement is S+R/R or 1.417, i.e. the carrier is rotating 1.417 times
    slower than the ring gear. If the carrier is
    the input, and the ring gear is the output, then the output is overdriven by the same ratio.
  3. If the planetary carrier is grounded, the sun gear is the input and the ring gear is the
    output, the ratio of this arrangement is R/S or -2.1875, i.e. the ring gear is rotating
    2.1875 times slower than the sun gear and in the opposite direction. Therefore this arrangement
    provides a reverse underdrive gear. If the ring gear is the input and the sun gear is the output,
    this arrangement becomes a reverse overdrive, and who needs a reverse overdrive?

If 2 of the members are tied together, then the ratio of planetary becomes 1:1, as all members turn at the same speed. A single planetary gear with the right set of clutches and brakes to change the ground member, the input, and the output can provide 5 forward ratios and 2 reverse ratios with 9 shifting elements (6 clutches and 3 brakes). Of course it is not be possible to package the all 9 of the shifting
elements in a practical manner, and the 5 forward ratios are 3.4, 1.417, 1.0, 0.7, and 0.29 – not very useful even if it were possible to achieve them. In engineering literature, a stick diagram”is often used as short-hand to describe planetary gear sets, for the planetary shown in Fig.2 the stick diagram is shown in Fig.3.


Planetary gears can also carry a lot more torque in the same packaging envelope because the load is distributed between multiple gear meshes. Need more torque capacity than the 3 planet gears can provide? You can nearly double that by putting in 6 planets on the planetary carrier.

Now on to the ZF 9 speed – there is a high level presentation available from the ZF website. This presentation has some detailed CAD renders in it, but not a whole lot of detail on the exact function of the transmission. The 2 CAD renders are shown tell us that there are 4 planetary gear sets in this transmission.


Image converted using ifftoany

Image converted using ifftoany

From these CAD renders the patient among the B&B can see that the one ring gear visible in Fig.4 has 86 teeth, and the 4 planets have 22 teeth, which means the sun gear that is not fully visible in the view is a 42 tooth gear. Fig.6 shows the stick diagram representation of the ZF 9 speed transmission, with 4 planetary gear sets numbered 1 through 4 from left to right. If one were to spend 10 minutes gawking at the cut-away transmissions that ZF does bring to trade shows, the following gear specifications can be established quite easily

  1. Gear set 1 has a 42 tooth sun gear and a 110 tooth ring gear
  2. Gear set 2 has a 42 tooth sun gear and a 110 tooth ring gear
  3. Gear set 3 has a 91 tooth sun gear and a 133 tooth ring gear 1
  4. Gear set 4 has a 42 tooth sun gear and a 86 tooth ring gear


The input is the output shaft of the torque converter, which is not shown in Fig.6. The torque converter is obviously driven by the engine. The planetary carrier of gear set 1 is the output to the final drive of the transmission. The following elements are rigidly linked

  1. The 2 sun gears for gear sets 1 and 2 are connected together, in fact it is one wide gear
  2. The ring gear for gear set 1 is linked to the planetary carrier of gear set 2.
  3. The ring gear for gear set 2 is connected to the planetary carrier for gear set 3, which is also the
    planetary carrier for gear set 4
  4. The sun gear for gear set 3 is linked to the sun gear of gear set 4

Additionally, the 6 shifting elements work as follows

  1. Dog clutch A in connected state connects the sun gear of gear set 3 and the ring gear of gear set 4 to the
    input shaft
  2. Friction clutch B couples the sun gear of gear set 4 to the input shaft
  3. Friction brake C ties the sun gear of gear set 4 to ground, i.e. stops it from turning
  4. Friction brake D ties the ring gear of gear set 3 to ground
  5. Friction clutch E couples the planetary carrier of gear set 2 and the ring gear of gear set 1
    to the input shaft
  6. Dog brake F ties the sun gears of gear sets 1 and 2 to the ground

Now on to the gory calculations

First gear

First gear is achieved by engaging shift elements A, F, and D. In this configuration gear sets 1, 2, and 3 are used in series as underdrives, gear set 4 is just along for the ride. The sun gear of gear set 3 is connected to the input, and the ring gear is grounded, which leads to the carrier going slower than the input. The carrier is in turn connected to the ring gear of gear set 2, while the sun gear for gear set 2 is
grounded, causing the carrier of gear set 2 to be further under driven. Since the planetary carrier of gear set 2 is connected to the ring gear of gear set 1, and the sun gear of gear set 1 is connected to ground as well, the transmission output is underdriven even more. The overall ratio is


Second gear

An upshift to second gear is achieved by turning friction brake D off and engaging friction brake C, i.e. shift elements A, F, and C are engaged. Now gears sets 1, 2, and 4 are used as a cascaded series of underdrives. Operation of gears sets 1 and 2 is identical to the first gear, gear set 4 acts as an underdrive, while gear set 3 is along for the ride now. Gear set 4 acts as an underdrive because the transmission input is connected to the ring gear, the sun gear is held stationary by brake C, and the planetary carrier is the output. This leads to a ratio of


Third gear

The upshift to third hear is accomplished by releasing brake C and engaging clutch B. This operation causes both the ring gear and the sun gear of gear set 4 to be connected to the input, therefore the planetary carrier also turns at the same speed as the input. Since the planetary carrier of gear set 4 is connected to the ring gear of gear set 2, they both turn at the same speed, i.e. the input speed. The operation of gear sets 1 and 2 is unchanged, and they act as cascaded underdrives, yielding a gear ratio of


Fourth gear

By releasing clutch B and engaging clutch E, the transmission up shifts to 4th gear, i.e. shift elements A, F, and E are engaged. This action connects the ring gear of gear set 1 to the input, while the sun gear is connected to ground, setting up a straightforward underdrive ratio of


At this point, the 4 gear ratios have been achieved by leaving the 2 dog” elements engaged, and
cycling through the 4 friction elements – and the shifts between these gears are therefore expected
to feel normal”. At this point, the vehicle is going at 30-35 mph and the shift to gear 5 is coming
up, and things get a little interesting.

Fifth gear

To achieve fifth gear, dog brake F needs to be disengaged. This now leads to a brief torque interruption because as brake F is disengaged, the transmission is in Neutral and engaging the frictional element B prematurely would just lead to wear and tear on the transmission for no reason. At this point the transmission ECU and engine ECU are working in tandem to get this upshift done as quickly as possible. The ratio calculation is fairly trivial though, all 4 gear sets are turning at the speed of the input. Why? Because engaging elements A, B, and E means that

  • The ring gear and the sun gear of gear set 4 are connected to the input, i.e. the planetary carrier
    spins at the same speed as the input
  • Consequently, the sun gear and the planetary carrier for gear set 3 are spinning at the same
    speed as the input, i.e. the ring gear gears for gear sets 2 and 3 are turning at the same speed as
    the input
  • Through shift element E, the carrier of gear set 2 is turning at the same speed as the input,
    therefore the sun gear of gear set 2 (which is also the sun gear for gear set 1) is spinning at
    input speed
  • Since the ring gear and the sun gear of gear set 1 is turning at the same speed as the input,
    the planetary carrier which is the transmission output is turning at input speed

The ratio therefore is quite simply


Sixth gear

So far, things have been pretty simple but now the magic begins where planetary gear sets are going to act as mixer” modules, i.e. the input and output turn at different speeds, but the reacting or grounding member is also turning at some speed. The upshift to sixth gear is achieved by releasing clutch B and engaging brake C. This causes gear set 4 to act as an underdrive just like second gear, therefore ring gear of gear set 2 is turning at a speed which is approximately 1.5 times slower than the input speed. The difference between second gear and sixth gear is that brake F is disengaged andclutch E is engaged, which means that the common sun gear for gear sets 1 and 2 is spinning at approximately 1.85 times faster than the input. This sets up a kinematic state for gear set 1 where the ring gear is turning at the same speed as the input but the sun gear is turning at 1.85 times the speed of the input, therefore the carrier has to spin at approximately 1.25 times faster than the input speed – overdrive!. Since the B&B do not deal in approximations, the exact ratio is


Seventh gear

As sixth gear shows us, an underdriven ring gear of gear set 2 sets up an overdrive, seventh gear kicks it up a notch by underdriving the ring gear of gear set 2 even further. This is accomplished by releasing brake C and engaging brake D. The sun gear of gear set 3 through clutch A is connected to the input, while the ring gear is connected to the ground via brake D, which means that the carrier spins 2.46
times slower than the ring input, and the carrier is connected to ring gear of gear set 2. Therefore gear set 3 is in the same kinematic state as it is in first gear. This sets up a kinematic state for gear set 1 where the ring gear turns at the same speed as the input, but
the sun spins at a speed that is 2.85 times higher. Therefore at 2000 rpm engine speed, the sun gear of gear set 1 is spinning at 5700 rpm. A dog brake has essentially 0 parasitic losses, while a friction brake would have cost about a 0.2 horsepower drag. The ratio is


Eighth gear

Eighth gear is achieved by closing brakes C and D at the same time, while disconnecting clutch A. At this point in time, the torque levels are low enough that in my humble opinion only the most discerning driver would be able to feel the torque interruption. This causes gear sets 3 and 4 to stop turning entirely, therefore the ring gear of gear set 2 is grounded. This causes the sun gear for gear sets 1 and 2 to spin faster – 3.65 times the input speed and sets up another over drive ratio


Therefore at 2000 rpm engine the sun gear for gear sets 1 and 2 is turning at 7300 rpm. But we are
not done yet – things turn faster.

Ninth gear

If underdriving the ring gear of gear set 2 set up 2 overdrives, and grounding it set up another one, there is only one thing left to do, spin it backwards. Ninth gear does exactly that – by connecting clutch B and by the virtue of the fact that the ring gear for gear set 4 and the sun gear for gear set 3 are linked together, we have a very interesting kinematic state. Sun gear of gear set 4 spins at the input speed, the carrier for gear set 4 spins backwards at approximately half the input speed, and the ring gear turns backwards at 1.2 times the input speed. This means that the ring gear for gear set 2 is now spinning backwards at approximately half the input speed. The sun
gear of gear sets 1 and 2 is now turning at 4.95 times the input speed. If the car is going at 85 mph in the 4 cylinder engine variant at an engine speed of 2000 rpm, this little gear is going at any eye watering 9500 rpm. The use of a dog brake at F instead of a friction brake is saving 0.4 hp or about 0.4 miles per gallon, the ratio is


The interesting thing about the Ninth gear is that there are parts in the transmission spinning
backwards to send you forward.

Reverse gear

Reverse and 9th have the same kinematic states for gear sets 3 and 4, i.e. the ring gear for gear set 2 turns backwards at approximately half in the input speed. But gear sets 1 and 2 are switched over to an underdrive configuration which is identical to the configuration in First gear, i.e. brake F is engaged. The ratio is therefore



The only real kink when shifting up through the gears is that the 4 to 5 shift might have an objectionable torque interruption, but otherwise this transmission is going to be well behaved. Downshifting from say 7th to 5th is no problem as well, but a downshift from 8th or 9th to 5th is hard work for this design. As an example if the engine speed is 1700 rpm and a shift from 8th to 5th
is required (passing on 2 lane highways), clutch A has 1700 rpm of slip that needs to be reduced to 0 before it can be engaged. So as a first order of business brakes D needs to be disengaged (100 milliseconds), then engine ECU needs to blip the throttle” to increase speed to approximately 2350 rpm (another 400 milliseconds), then engine power needs to be cut and dog clutch A needs to be
engaged (another 100 milliseconds), and now you are in sixth after a half a second of no torque at all at the wheels, then another 200 milliseconds of low torque as the transmission finds fifth with a more conventional frictional clutch to frictional clutch shift and your engine speed is finally at the 2900 rpm.

From eighth gear to fourth gear is going to be even more of a contortion, with a torque interruption that is about a second long as the transmission ECU and the engine ECU do this delicate dance required to get both the dog shifting elements to engage. When you are looking to pass on a 2 lane road at 60 mph, a second can feel like an eternity, especially to a driver who has to use those paddle shifters to get into the right gear before executing the pass.

Gear spacing

Another issue that the reviewers (including our own Alex L. Dykes) tend to take note of is the wide spacing between first and second gears. Unfortunately this is a direct result of the transmission lay out. Gear set 3 is pushed to the limit with the ratio, trying to make first gear ratio any lower than 4.7 would make the planetary gear pinion speed unreasonably high. So the first gear ratio is more or less
a given. It would be possible to change the tooth count on gear set 4 to numerically increase the second gear ratio. As a thought experiment, we could change the sun gear of gear set 4 to 46 or 50 teeth instead of the 42 it has, the result?

Gear Ratios with S4 = 42 Ratios with S4 = 50 Ratios with S4=46
1st 4.700 4.700 4.700
2nd 2.842 3.020 2.931
3rd 1.909 1.909 1.909
4th 1.382 1.382 1.382
5th 1.000 1.000 1.000
6th 0.808 0.790 0.799
7th 0.699 0.699 0.699
8th 0.580 0.580 0.580
9th 0.479 0.454 0.467
Rev -3.805 -2.891 -3.308

So a 50 tooth sun gets better spacing between first and second, somewhat worse spacing between second and third, all other gears are largely unchanged, expect that reverse gets screwed up – it is perhaps not low enough for vehicles with off road ambitions. So perhaps a happier middle ground could have been a 46 tooth sun of gear set 4, that leads to a reverse of 3.308 with a second gear ratio of
2.9307. It also gives the transmission an overall ratio spread of 10.065, which sounds better for marketing purposes than the 9.81 that exists currently. This alternate reverse ratio is almost identical to the reverse in the ZF 8 speed RWD transmissions. So this 42 tooth sun gear is a bit of a head scratcher – perhaps keeping the tooth count at 42 saves some money because there is manufacturing tools can be shared between this sun gear and the sun gear for gear sets 1 and 2.


I give a Colbert Tip of the Hat” to the engineers at ZF for this design. It is obviously a clever design but one that could cause some drivability surprises to an average driver, though durability-wise, I see nothing that causes major concerns. Design and development of a transmission concept like this ranges from 20 million dollars
to 50 million dollars, so the ZF management had some serious cojones to OK this design, it is a risk that has paid off to an extent. I know of many a management teams that would have said no, but time will tell just how compact other 8/9/10 speed transmissions and just how good a decision this is..

Some CAD renders
available on line show a 78 tooth sun with 114 tooth ring gear, this is a kinematic
equivalent of 91 tooth sun gear and 133 tooth ring gear

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ZF’s 9-Speed 9HP Transmission Puts Dog Clutches On The Leash Sun, 09 Feb 2014 03:34:39 +0000 ZF 9HP Transmission, Picture Courtesy of Land RoverIn a week we will post our first full review of the all-new and all-controversial 2014 Jeep Cherokee. The new Jeep isn’t just raising eyebrows for the love-it or hate-it styling. Or the resurrection of the Cherokee badge. Or the constant delays in production. Or the transverse mounted engine. Or the lack of solid axles. None of that laundry list seems to cause as much discussion around the automotive water cooler than ZF’s 9HP 9-speed transmission. Click past the jump for a deep dive into the tranny with more speeds than my bicycle. If you don’t want to explore transmissions in detail, don’t click. You have been warned.

When Derek drove the Cherokee at a launch event he complained about the transmission. When I drove a pre-production model for a very brief hour and a half I was more perplexed than anything. I chalked it up to pre-production programming issues and the fact that the transmission has 50% more speeds than a 6-speed, so I expected 50% more shifting. A month later I was able to sample a different Cherokee with newer software and some of my shifting complaints had been solved but something still felt “wrong.” Now three months later a full production Cherokee landed in my hands and while the shift logic (when and why the transmission would shift up or down) was finally where I thought it should be, the shifts themselves felt different from what I am used to. The reason is all down to clutches, but let’s start at the beginning.

In general terms an engine is most efficient in a somewhat narrow band of RPMs. That exact band varies from engine to engine based on what the designers intended at the time. The longer you can keep the engine in this range of RPMs, the more efficient the car will be. Secondary to this is a desire for improved off-the-line performance, this necessitates ever-lower first gear ratios. The distance between the lowest and the tallest gear in a transmission is called the ratio spread. (You get it by dividing the lowest ratio by the tallest and that gives you a number that represents the delta between first and last.) GM’s venerable 4-speed 4L80 has a spread of 3.3 while their new 6-speed 6L80 has a spread of 6. The deeper first gear and taller 6th allow the 6L80 to deliver better performance and better fuel economy. The reason ZF’s 8-speed 8HP doesn’t have the same delta in performance over the average 6-speed as the 6-speed had over the 4-speed, is easy to explain. The 8HP’s ratio spread is 7, just 1 higher than a 6 speed while the 6-speeds had a 3 point advantage over the 4-speeds. Aisin’s new 8-speed transaxle in Volvo and Lexus models goes a small step further with a 7.59 spread. These can all be seen as progressive improvements. The 9HP is different. With a 4.7:1 first gear and a 0.48:1 ninth gear the overall spread is a whopping 9.8.


On closer inspection you’ll notice something interesting about the 9HP’s ratios. Fifth is the 1:1 ratio where the output shaft of the transmission is spinning at the same rate as the engine meaning there four overdrive ratios. In contrast both ZF and Aisin’s 8-speed transmissions have just two overdrive ratios with 6th gear being the direct-drive (1:1) ratio. As a result the 9HP’s lower gears are farther apart, especially first and second gear. When you look deeper at the numbers you’ll also notice that the 9HP is geared much taller at the top end with 7th gear being approximately equal to 8th in the Aisin or ZF 8-speed units. Many reviewers of the Cherokee noted they never experienced 9th gear during their test drive and I now know why. At 0.48:1 with the 3.2L V6 (3.251 final drive) you have to be going faster than 80 MPH to engage 9th because at 80 your engine loafs around at 1,460 RPM. (The 2.4L four-cylinder in the Cherokee Trailhawk would be going about 1,810 RPM at 80.) According to ZF this results in an impressive 12-16% improvement in fuel economy versus the same final drive ratio and their own 6-speed automatic and 11-15% when compared to their 8-speed.

OK, so the 9HP has plenty of gears, but why does it shift the way that it does? It’s all down to the clutches. While a traditional automatic uses friction clutches in the form of either band clutches or multi-plate friction clutches, the 9HP blends friction clutches and dog clutches in the same transmission case. Dog clutches are “interference” clutches more commonly found in manual transmissions and transfer cases. Friction clutches work by pressing two plates together. The friction between them allows the transfer of energy and it allows one plate to spin faster than the other or “slip.” Think of slipping the clutch in a manual car, it is the same action. Automatic transmissions use this clutch type to their advantage because changing gear doesn’t always require engine power to drop, the transmission simply disconnects one clutch as it engages another, they slip and engage and you’re in another gear. Dog clutches however are different. If you look at the illustration below you can see a dog clutch on the right. Power is transmitted by the tooth of one side pressing on the tooth of the other. This type of clutch cannot slip so it is either engaged or disengaged. This is the type of clutch used inside manual transmissions. When you move the shifter to a different gear, you are physically disengaging and engaging dog clutches. This style of clutch is used because it suffers little parasitic loss and it is simple and compact. The use of a dog clutch in an “automatic” transmission isn’t new, dual clutch robotized manuals use this style of clutch internally as well, but it is the key to understanding why the 9HP shifts the way it does.


Because dog clutches can’t slip, their engagement must be controlled and precise. Going back to the manual transmission example, this is why modern manual transmissions have “synchros” or synchromesh. A Synchro is a mechanism that aligns the dog teeth prior to engagement. Without them you get that distinct gear grinding noise. Synchros work well in a manual transmission because when you are changing gear you are disconnecting the engine with the clutch (a friction clutch), then engaging a dog clutch for your gear selection. Because one end of the transmission is “free” the synchro synchronizes the two sides and then allows the toothed gear to engage. There is a “pause” in power when a shift occurs. If you look at an acceleration chart of a car with a good manual driver and an automatic you will see pauses in acceleration in the manual while most autos just have “reductions” in acceleration. That’s down to the pause required to engage a dog clutch vs a friction clutch that slips and engages without much reduction in power.

Let’s digress for a moment and talk about the DSG. The reason dual clutch gearboxes exist is because of the dog clutch. As I said engaging a dog clutch takes time and precision. This is part of the reason single-clutch robotic manuals like the one in the Smart ForTwo and the RAM ProMaster (and other Euro sedans) have such exaggerated shifts. Double clutch gearboxes get around this by having two gears engaged at all times. DSG style gearboxes are really two manual transmissions in the same case. 1st gear is engaged via the first transmission and 2nd is engaged but not active on the second. Changing gears simply involves swapping (via a friction clutch) from transmission A to transmission B. Once that is accomplished, the transmission A disengages and engages the dog clutches to select the next gear. Going from 2nd to 3rd involves swapping back from transmission B to the already shifted transmission A.

Let’s put it all together now. To save space and increase efficiency, the 9HP uses two multi-plate clutch elements, two friction brakes and two electronically synchronized dog clutches. (The 8HP uses two brakes and three multi-plate clutches.) The way the gearsets are arranged inside the case, shifts from 1-2, 2-3, and 3-4 involve only the traditional friction brake and clutch elements. As you would expect, aside from 1st being fairly low and somewhat distant from 2nd, these shifts feel perfectly “normal.” Under hard acceleration there is a momentary reduction in engine torque (courtesy of the computer to reduce clutch wear) and the shift occurs quickly and smoothly. The shift from 4-5 however is different. The transmission has to disengage dog clutch “A” in addition to engaging a friction clutch. This shift takes slightly longer than the 3-4 shift and the car’s computer makes a drastic reduction in torque to prevent wear of the dog teeth. Shifts 5-6 and 6-7 again happen with the only the friction elements at which point we need to disconnect the final dog clutch for gears 8 and 9 so we get the same kind of torque reduction in those shifts. The result is a transmission that has two distinct “feels” to its shifts, one that has only a slight torque reduction (1-2, 2-3, 3-4, 5-6, 6-7, 8-9) and one that has a more “manual transmission” feel where torque is cut severely (4-5 and 7-8).

2014 Jeep Cherokee Instrument Cluster

Because of the positioning of the two dog clutches in the shift pattern, the torque reduction isn’t objectionable in upshifts. Hard acceleration from a stop didn’t involve 5th gear even in the 1/4 mile. However, once you let off the gas the transmission will shift upwards rapidly for fuel economy settling in 6th or 7th in the 60-65 MPH range and 8th in the 70-75 MPH range.

Downshifts are where the 9HP truly feels different. Because of the design, if you’re in 8th gear and want to pass, the transmission will often need to drop 4 or 5 gears to get to a suitable ratio. (Remember that 4th gear is the first ratio going back down the scale that is lower than 1:1.) To do this the transmission has to accomplish the harder task of engaging two dog clutches. To do this the transmission doesn’t use cone synchros like a manual (too bulky) it uses software. Engaging dog clutches requires a longer and yet more severe reduction in torque than the disengagement because the transmission has to align the clutch and then engage it. In most automatics when you floor the car you get an instant feeling of acceleration that improves as the transmission downshifts. Although there would be moments of power reduction (depending on the programming) during this time, the engine is always providing some force forward. The 9HP’s software on the other hand responds by cutting power initially, then diving as far down the gear-ladder as it can, engaging the dog clutches and then reinstating your throttle command. The result is a somewhat odd delay between the pedal on the floor and the car taking off like a bat out of hell. According to Volvo’s powertrain guys, this shift behavior is one of the main reasons they chose the Aisin 8-speed (shared with the Lexus RX F-Sport) over the ZF 9-speed used by Land Rover and Chrysler.

All of a sudden the “odd” shift feel made perfect sense. In the march toward ever-improving fuel economy the automotive public will continually be introduced to cars that feel different from the “good old days.” Electric power steering numbs the wheel-feel but steer-by-wire promises to artificiality resurrect it. Dual clutch robotized manuals have a particular feel that was accepted by performance enthusiasts but has been a source of complaint for Focus and Fiesta shoppers. For me, understanding why the transmission is doing what it is doing is key to my like or dislike of a car’s road manners. Once I understood what the Cherokee’s automatic was up to, I was able to focus on the rest of the car. What about you? Are you willing to “sacrifice” shift quality at the altar of fuel economy? Be sure to let me know.

Have an automotive technology question? Want to see a deep-dive on another powertrain component?

Let us know by using the contact form at the top of the page!

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Review: 2014 Dodge Durango Limited V8 (with Video) Thu, 16 Jan 2014 15:00:23 +0000 2014 Dodge Durango Exterior-002

Car shopping used to be so simple: you could buy a truck or a car. Then came the wagon, minivan, sport utility and the latest craze: the crossover. There’s just one problem with the crossover for me however: it’s not a crossover. With a name like that you’d assume that a modern crossover blended the lines between a truck/SUV with a car/minivan. The reality of course is that the modern three-row crossover is just a front-driving minivan that doesn’t handle as well or haul as much stuff. In this sea of transverse minivans in SUV clothing lies just one mass-market vehicle that I can honestly call a three-row crossover: the Dodge Durango. Instead of a car that’s been turned into an AWD minivan with a longer hood, the Dodge uses drivetrains out of the RAM 1500 combined with a car-like unibody. While rumors swirled that the Durango would be canceled in favor of a 7-seat Jeep, Dodge was working a substantial makeover for 2014.

Click here to view the embedded video.

So what is the Durango? Is it an SUV? Is it a crossover? In my mind, both. If a Grand Cherokee can be a unibody SUV and not a crossover, the Durango must be an SUV. But if a crossover is a hybrid between a car and a truck, then the Durango is one as well. While the first and second generation Durangos were body-on-frame SUVs based on the Dakota pickup, this Durango is a three-row Grand Cherokee, which is a two-row Jeep version of the three-row Mercedes ML which is quasi related to the Mercedes E-Class, which is quasi related to the Chrysler 300. Lost yet?


2014 brings few changes to the outside of the Durango. The design first released in 2011 still looks fresh to my eye but that could be because I don’t see many on the road. Up front we get a tweaked corporate grille and new lamps while out back we get “race track” inspired light pipes circling the rump. Aside from a lowered right height on certain models and new wheels, little has changed for the Durango’s slab-sided profile, which I think is one of the Dodge’s best features. No, I’m not talking about the plain-Jane acres of sheet metal, I’m talking about RWD proportions. Bucking the trend, this three-row sports a long (and tall) hood, blunt nose, short front overhang and high belt-line.

To create the Durango from the Grand Cherokee, Chrysler stretched the Jeep’s wheelbase by 5-inches to 119.8 inches and added three inches to the body. The result is four-inches longer than an Explorer but two inches shorter than the Traverse, Acadia and Enclave triplets. Thanks to the Durango’s short front overhand, the Dodge has the longest wheelbase by a long way, beating even the full-size Chevy Tahoe. Speaking of the body-on-frame competition, the Durango may have been a size too small in the past, but this generation is just 8/10ths of an inch shorter than that Tahoe.



Body-on-frame SUVs have a practicality problem when it comes to space efficiency. Because the frame sits between the body and the road, they tend to be taller than unibody crossovers despite having less interior volume. Like the rest of the crossover crowd, this allows the Durango to have a spacious interior with a comparatively low entry height. 2014 brings a raft of much-needed interior updates to the cabin including a new soft touch dashboard, Chrysler’s latest corporate steering wheel with shift paddles, revised climate controls, Chrysler’s latest uConnect 2 infotainment system and a standard 7-inch LCD instrument cluster. Like the other Chrysler products with this LCD, the screen is flanked by a traditional tachometer, fuel and temperature gauge. Oddly enough, the standard infotainment screen is a smallish (in comparison) 5-inches.

Front seat comfort proves excellent in the Durango which was something of a relief, as the last few Chrysler products I have driven had form and oddly shaped seat bottom cushions that make me feel as if I was “sitting on and not in the seat.” As with all three-row vehicles, the accommodations get less comfortable as you move toward the back. By default all Durango trims are 7-passenger vehicles with a three-across second row. For $895 Dodge will delete the middle seat and insert a pair of more comfortable captain’s chairs and a center console with cup holders and a storage compartment. The third row is a strictly two-person affair and, like most crossovers, is best left to children and your mother in law. Those who do find themselves in “the way back” will be comforted by above average headroom and soft touch plastic arm rests. With large exterior proportions you’d expect a big cargo hold like in the cavernous Traverse, alas the RWD layout that makes the Durango so unique renders the interior less practical. With more of the body used up for “hood,” we get just 17 cubes of space behind the third row. That’s three less than an Explorer, seven less than GM’s Lambda triplets and about the same as a Honda Pilot. On the bright side this is more than you will find in a Highlander or Sorento and shockingly enough, more than in the Tahoe as well.



uConnect 2 is the first major update to Chrysler’s 8.4-inch touchscreen system that launched in 2011 and the first version of this system the Durango has ever had. Based on a QNX UNIX operating system, the system features well polished graphics, snappy screen changes and a large, bright display. For the second edition of uConnect, Chrysler smoothed out the few rough edges in the first generation of this system and added a boat-load of trendy tech features you may or may not care about. In addition to improved voice commands for USB/iDevice control, uConnect 2 offers smartphone integration allowing you to stream audio from Pandora, iHeart Radio or Slacker Radio. You can have text messages read to you and dictate replies (if your phone supports it) and search for restaurants and businesses via Yelp. In addition to all the smartphone-tied features, uConnect 2 integrates a CDMA modem on the Sprint network into the unit for over-the-air software updates and access to the new “App Store” where you will be able to buy apps for your car. Since there’s a cell modem onboard, uConnect can be configured to act as a WiFi hot spot for your tablets and game devices as well. Keep in mind speeds are 3G, not Sprint’s WiMAX or LTE network.

Completing the information assault is SiriusXM’s assortment of satellite data services which include traffic, movie times, sports scores, fuel prices and weather reports. As with uConnect data services, there’s a fee associated after the first few months so keep that in mind. 2014 also brings uConnect Access which is Chrysler’s answer to GM’s OnStar providing 911 assistance, crash notification and vehicle health reports. Garmin’s navigation software is still available as a $500 add-on (standard on Summit) and it still looks like someone cut a hole in the screen and stuck a hand-held Garmin unit in the dash. The interface is easy to use but notably less snazzy than the rest of the system’s graphics. If the bevy of USB ports has you confused, you can rock your Cat Stevens CD by paying $190 for a single-slot disc player jammed into the center armrest.

2014 Dodge Durango 5.7L HEMI V8 Engine-001Drivetrain

Dodge shoppers will find two of the Grand Cherokee’s four engines under the hood. First up we have a 290HP/260lb-ft 3.6L V6 (295HP in certain trims) standard in all trims except the R/T. R/T models get a standard 360HP/390lb-ft 5.7L HEMI V8 which can be added to the other trims for $2,795. 2014 brings a beefed up cooling system and a number of minor tweaks in the name of fuel economy. Sadly Chrysler has decided to keep the V6 EcoDiesel engine and 6.4L SRT V8 Grand Cherokee only options, so if you hoped to sip diesel or burn rubber in your three row crossover, you’ll need to look elsewhere.

Both engines are mated to a ZF-designed 8-speed automatic. V6 models use the low torque variety made by Chrysler while V8 models use a heavy-duty 8HP70 made in a ZF factory. If you’re up to date on Euro inbreeding, you know this is the same transmission used by BMW, Audi, Jaguar, Land Rover and Rolls Royce. To say this is a step up from the vilified Mercedes 5-speed or the Chrysler 6 speed (the 65RFE featured some of the strangest ratio spacing ever) is putting it mildly. Fuel economy jumps 9% in the V6, 10% in the V8. No small feat in a 4,835lb SUV (as tested). All Durangos start out as rear wheel drive vehicles but you can add a two-speed four-wheel-drive system for $2,400. Although Dodge bills this as AWD, it is the same transfer case that Jeep calls 4×4 in Selec-Trac II equipped Grand Cherokees. Thanks to the heavy-duty drivetrain towing rings in at 6,200lbs for the V6 and 7,400lbs for the V8. Like the Jeeps the Durango has moved to more car-like 5-lug wheels which should widen after-market selection.

2014 Dodge Durango Exterior


The engineers took the refresh opportunity to tweak the Durango toward the sportier side of the segment with stiffer springs and beefier sway bars. While far from a night-and-day transformation, the difference is noticeable and appreciated out on the roads. While never harsh, it is obvious the Durango is tuned towards the firm side of this segment. Thanks to the long wheelbase the Durango feels well composed on the highway or on broken pavement.

With a nearly 50/50 weight balance, wide 265-width tires, and a lower center of gravity than a “traditional SUV”, the Durango is easily the handling and road feeling champion. That’s not to say the Durango is some sort of sports car in disguise, but when you compare a well balanced 360 horsepower rear wheel drive elephant to a slightly lighter but much less balanced front driving elephant on skinny rubber, it’s easy to see which is more exciting. Thanks to the Mercedes roots there’s even a whiff of feedback in the steering, more than you can say for the average crossover. Despite the long wheelbase and wide tires, the Durango still cuts a fairly respectable 37-foot turning circle.

Those statement may have you scratching your head if you recall what I said about Jeep on which the Durango is based, I must admit I scratched my head as well. Although the Dodge and the Jeep share suspension design elements and a limited number of components, the tuning is quite different. The Grand Cherokee Summit rides 3.1-inchs higher and was equipped with the off-road oriented air suspension.

2014 Dodge Durango Exterior-005

When it comes to performance, the new 8-speed automatic makes a night and day difference shaving a whopping 1.4 seconds off the 0-60 time versus the last V8 Durango we tested. The reason is all in the gear ratios. While the 545RFE and 65RFE transmissions suffered from some truly odd ratios, the ZF unit’s ratios are more evenly spread and dig deeper in the low gears. The result is a 6.0 second sprint to highway speeds which finally nips on the tails of the Explorer Sport which we’re told will do the same in 5.9-6.0 (TTAC hasn’t tested one yet). This proves what extra gears can do for you because the Explorer is 200lbs lighter and has a far more advantageous torque curve thanks to the twin turbos.

You can also thank the ZF transmission for the Durango’s robust towing numbers. V6 models are now rated for 6,200lbs while the V8 can haul up to 7,400lbs when properly equipped. That’s nearly 50% more than you can tow in any of the crossover competition and just 1,000 lbs shy of the average full-size body-on-frame hauler.

The transmission is also responsible for a whopping 20% increase in fuel economy. The last V8 Durango I tested eked out a combined 14.8 MPG over a week while the 2014 managed 18.0 MPG. While 18 MPG isn’t impressive in wider terms, it is 1/2 an MPG better than GM’s Lambda crossovers or the Ford Explorer on my commute cycle. The V6 yields improved fuel economy at the expense of thrust, but you should know that although the acceleration provided by the V6 is competitive with the V6 three-row competition, the 20 MPG average falls short of the new Highlander, Pathfinder and the rest of the FWD eco-minded competition.

After a week with the Durango I was no closer to answering the biggest question car buffs have: is this Dodge a crossover or an SUV? One thing is sure however, the Durango is likely the most fun you can have with 6 of your friends for under $50,000.


Chrysler provided the vehicle, insurance and one tank of gas for this review.

Specifications as tested:

0-30: 2.4

0-60: 6.0

1/4 Mile: 14.6 Seconds @ 96 MPH

Cabin noise at 50 MPH: 69dB @ 50 MPH

Average observed fuel economy: 18 MPG over 811 miles


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ZF and Levant Power Develop Regenerative Active Suspension Fri, 30 Aug 2013 19:13:09 +0000 ZF-Levant-regenerative-shock

ZF Friedrichshafen AG and Levant Power Corp., a Woburn, Massachusetts technology company spun off from MIT, have announced what they call the first fully active suspension system that includes a regenerative function that recovers energy from the motion of the suspension. The system is branded GenShock. Active suspensions are not new, General Motors experimented with an actively suspended ZR-1 Corvette when the automaker owned Lotus, which had worked with active suspensions before the technology was banned in Formula One. Going back even farther, there were the hydropneumatic Citroens and the last true Packards’ “torsion level” suspension. With road cars the goal in using such a system would be to combine good ride with good handling, soft sometimes and stiff sometimes, depending on the driving circumstances. Early tries at developing what chassis engineers call a “high bandwidth active suspension”, capable of dealing with those varying circumstances, have run into cost, complexity and power consumption issues. The GenShock system is claimed to be affordable, simple to integrate in existing suspension designs, and not only have modest power consumption but also be able to recover energy from the suspension.

The heart of the system is what Levant Power calls the Activalve TM, a device that combines electric and hydraulic motors (the companies are calling that an “electrohydraulic gear pump”) and can be adapting to standard mono, twin, and tri-tube damper configurations. Hydraulic fluid in the shock absorber is routed from the damper body through the valve, where the electric motor can be used to control the flow of fluid through the gear pump, or alternatively, the pump can be used to drive the electric motor as a generator, recovering electricity. The poorer the road quality, the more bumps there are, the more energy is recovered. Electronic controls adapt the damping characteristics to the driving situation, reducing body pitch and roll during cornering and braking. While the system adds a little bit of weight, compared to a passive suspension, it also eliminates the need to carry a jack, since the system is capable of raising or lowering each wheel independently.

Note that this is not a perpetual motion machine, like putting a wind generator on a car. It creates no new load on the powertrain, it merely recovers energy that would normally be turned into heat. ZF and Levant Power haven’t released any figures on just how much energy is recovered and whether that exceeds the power required to run the system. Like Innowatech‘s piezoelectric roadways, BMW’s Turbosteamer concept, or Purdue professor Xianfan Xu’s work recovering electricity from engine exhaust using large scale Peltier devices, the GenShock is harvesting energy that would otherwise go to waste.

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’41 Plymouth Hell Project Puzzle Piece Scored Via Craigslist: Corvette ZR-1 6-Speed! Fri, 19 Jul 2013 13:00:46 +0000 02 - ZF Transmission Purchase - Pictures courtesy of Murilee MartinThe 1941 Plymouth Special Deluxe sedan Junkyard Find that I bought from the Brain-Melting Colorado Junkyard last fall now has the body off the frame and is awaiting a Lexus SC400 suspension subframe swap. After much debate about what engine/transmission combo to use in this Hell Project (the plan is to build it to Pikes Peak International Hill Climb specs, while retaining a grimy-looking rat-roddish character), I decided to go with the GM Vortec 4200 aka LL8 L6 engine, with turbocharging added, and that meant that I’d need to find a manual transmission that can withstand at least 400 ft-lbs of torque. Since the Vortec 4200 never came with a manual transmission, and the pseudo-bolt-on Aisin-based 5-speed out of the Solstice and Colorado can’t take the sort of power I’m hoping to get (thus forcing me to go the machine-shop bellhousing-adapter/custome-flywheel route), I was looking for a Borg-Warner T-56 out of a fourth-gen GM F-body, or maybe a Tremec TKO out of a fourth-gen Mustang. Then, an ad for a ZF S6-40 6-speed showed up on Denver Craigslist, with a very reasonable asking price.
14 - ZF Transmission Purchase - Pictures courtesy of Murilee MartinKnown as the “Black Tag” ZF transmission, this rugged German 6-speed was used in C4 Corvette ZR-1s and is rated for up to 450 ft-lbs of torque. Thanks to its square-cut gear teeth, this transmission made more noise than many Corvette buyers could tolerate, and so GM went to a quieter gears and (if you believe the rants of detail-obsessed Corvette freaks) less strength for the 1994 model year.
03 - ZF Transmission Purchase - Pictures courtesy of Murilee MartinThe seller of this transmission had purchased it out of a wrecked ’93 ZR-1 for use in this beautiful ’57 Chevy project, which is getting an LS swap, but the ZF turned out to be too big to fit in the Chevy without major transmission-tunnel hackage.
06 - ZF Transmission Purchase - Pictures courtesy of Murilee MartinI brought along Rich, the guy I’ve hired to do the engineering and fabrication work on the ’41 Plymouth project, to check out this transmission and say yea or nay on the possibility of using the ZF. He’s the captain of the Index of Effluency-winning Rocket Surgery Racing Checker Marathon 24 Hours of LeMons team, and he managed to get a small-block Chevy engine to bolt up to a Ford Toploader transmission and then stick the resulting mess into the Checker using all manner of garage-expedient cheap technology The ZF transmission came with all the little bits and pieces that make a Frankensteinian swap like this a lot easier, including the shifter, clutch master/slave cylinders, bellhousing, flywheel, even a bag full of fasteners. Looks good!
08 - ZF Transmission Purchase - Pictures courtesy of Murilee MartinSo, into the hatch of my cargo-hauling, thief-magnet ’92 Civic with all the goodies.
07 - ZF Transmission Purchase - Pictures courtesy of Murilee MartinDid I mention that the transmission seller owns the nicest Jeepster Commando I’ve ever seen?
13 - ZF Transmission Purchase - Pictures courtesy of Murilee MartinI haven’t bought the Vortec 4200 yet (the plan is to buy a wrecked Trailblazer or Envoy donor vehicle, so I can get all the harnesses, computers, and maddening little bits needed for the planned swap), but we’ve got this block and pan to enable Rich to move forward on the necessary fabrication on the Plymouth’s frame.
IMG_3240For now, the Plymouth’s body sits on wood blocks in the yard, awaiting its modernized frame.

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GM, Ford Prepare To Downshift To 8th Gear Wed, 17 Apr 2013 11:30:11 +0000

GM and Ford will be working together to bring 9 and 10 speed transmissions to market. Reuters reports that the two companies will jointly develop the gearboxes for both front and rear-drive applications, and expect to use them in cars, trucks and SUVs.

Automotive News reports that GM will take responsibility for a transverse 9-speed gearbox, while Ford will handle the longitudinal 10-speed unit. Production is expected to begin in 2016, and that volumes for each transmission could exceed one million units annually by 2018.

TTAC’s own Alex Dykes outlined the way that OEMs share gearboxes from various parts suppliers. GM and Ford already source many transmissions from third party suppliers. Their new 9-speed design will face competition from ZF’s upcoming 9-speed unit (above), which is expected to be used in Honda products as well as Chrysler’s full line of transverse vehicles.

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Read between the lines: Volvo’s 8-speed automatic Wed, 10 Apr 2013 19:40:20 +0000

What do the Volvo XC60 and Lexus RX F-Sport have in common? Not much. Yet. Today’s vehicles aren’t just built on “modular” platforms, sharing parts with other vehicles from the same manufacturer, they are also “parts bin creations.” You’ll find the same power mirror switch in a Chevy, Jeep, Peugeot, Citroën, Lancia, Lincon and many more. That’s because car parts are like Lego pieces, made by a handful of car parts companies and designed to be everything for everyone. It’s cheaper for everyone to design one switch, one control module, one key fob and just alter some of the plastics and a connector to suit your new car design.

Parts sharing isn’t new of course, it’s been going on ever since “badge engineering” was invented in 1917, but this is different. Instead of one company buying parts from another, or GM tossing a new logo on an Oldsmobile to create a Buick, these parts are made by a third party, available for sale to anyone with the cash. Ever wonder how Fiskar and Tesla can create a unique vehicle so quickly? The universal parts bin is how.

Most car companies dive into the same interior parts bins time after time, rarely seeking new foraging grounds. This is why the Big Three seem to frequently share things like those window switches, seat controls, etc. Meanwhile the Europeans and Japanese tend to have their own circle of parts suppliers. It’s also why the Coda sedan looks so odd to Americans; Coda raided a Chinese market parts bin. When it comes to powertrains, geographic divisions drop because engines and transmissions are expensive to develop resulting in a smaller global pond to fish from.

The big boys in passenger car automatic transmission design are: ZF, GM, Aisin, Mercedes, Jatco and Hyundai. Why am I not including Chrysler and Honda? Chrysler is easy: they have chosen to license/tweak transmissions from ZF rather than developing their own. Ford can’t make up their mind co-developing a 6-speed transaxle with GM, then licensing ZF’s 6-speed RWD swapper. All indications seem to point to Ford licensing the 8-speed RWD box from ZF while splitting development costs with GM on new xx-speed transaxles for smaller cars. Honda doesn’t tend to sell its in-house transmissions to other companies and if the rumor mill is correct, Honda will be buying ZF’s 9-speed transaxle while they shift R&D dollars to CVT development.

What does that mean to you as a consumer? And why are we talking Volvo and Lexus? Because companies tend to stick with a transmission maker for the long haul. BMW has a history of buying GM and ZF. Luxury car companies (and now Ford and Chrysler) typically use ZF cog-swappers. Ford Europe and Renault are in bed with Jatco. Chrysler likes Hyundai’s FWD transaxles. Toyota, Lexus, Volvo, MINI, VW, Mitsubishi and Porsche order from Aisin’s transmission catalog. Consequently when a new Euro sedan comes out with ZF’s latest widget, you know that sooner-or-later every ZF customer have it. (There is usually a delay because companies will pay extra to have a period of exclusive access to new technology.)

When the 2013 Lexus RX 350 F-Sport dropped quietly last year at a Lexus event, I was excited and intrigued. Not by the refreshed RX, but by what;s under the hood: the first production 8-speed automatic transaxle. Since the RX is a Lexus, we know that the transmission was made by Aisin (Toyota doesn’t use anyone else). Logically it was only a matter of time until this tranny landed on the Aisin general catalog and today appears to be that day. As a footnote in Volvo’s press release about their new four-cylinder engine family is buried one line “Volvo will also introduce a new 8-speed automatic gearbox that contributes to a refined drive and excellent fuel economy.” I’ll bet dollars to doughnuts the new slushbox is the same 8-speed unit that’s in the RX F-Sport I’m driving this week. Next stop: 8-speed Mazda 6, VW Jetta, MINI Cooper.

If you’ve ever wondered why it took so long for the four speed automatic to be developed, while 5, 6, 7, 8 and 9 speed units have happened so rapidly, part of the answer is in this shift to communal parts-bin technology. While this means technology can develop more rapidly with more resources being applied to the same development project, it also means cars lack the uniqueness they once had. No longer can we sit around the card table drinking beer and arguing the eternal question: TorqueFlite vs Cruise-O-Matic vs Hydra-Matic.


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Jeep Cherokee Won’t Be The Only 9-Speed Soft Roader Thu, 28 Feb 2013 15:49:43 +0000

ZF’s 9-speed transmission seems to be gaining popularity with storied off-road name plates that are now marketing unibody vehicles better meant for the urban jungle. The Range Rover Evoque is the next recipient of the ZF 9-speed, which should help squeeze some more efficiency out of the Evoque’s boosted four-cylinder engine.

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ZF CEO: 9 Speeds Is Enough Wed, 07 Nov 2012 16:32:46 +0000 Click here to view the embedded video.

Wondering when the automatic gearbox arms race will end? 8 speeds? 9 speeds? Even 10 speed gearboxes have been thrown out as grist for the automotive rumor mill, but one exec apparently has the answer.

The CEO of ZF transmissions said that 9 speed gearboxes will be the zenith of transmissions – anything more will be too complex and heavy to produce any efficiency gains.

Stefan Sommer, ZF’s grand fromage told Automotive News Europe that 9 speeds is the “natural limit” for gearboxes, and anything beyond that invokes the law of diminishing returns. Chrysler is expected to be the first to adopt a 9-speed automatic, but don’t look for anything beyond that, says AN

Earlier this year, Julio Caspari, president of ZF’s North American operations, hinted that a “Can-you-top-this?” race to add gears may be driven by marketing considerations rather than fuel economy.

That’s because there is only an 11 percent gap between the most-efficient transmissions today and a theoretically perfect gearbox


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