## ZF showcasing second-generation 8HP 8-speed transmission at NAIAS; additional 3% boost in fuel savings

##### 18 January 2015

At the North American International Auto Show (NAIAS) in Detroit, ZF is presenting its broad technology portfolio including the second generation of the 8HP 8-speed transmission. The new generation offers further developments ranging from lower drag torques and higher spread to an improved torsional vibration absorption.

Compared to the already highly energy-efficient first generation of the 8HP (earlier post), the second-generation unit achieves an additional three percent of fuel savings. The first generation of the eight speed 8HP saved up to 6% more fuel—and its stop-start variant up to 11% more—that the second-generation ZF 6-speed automatic transmission. With its flexible modular construction system, ZF’s 8HP covers a broad torque range between 300 and 1,000 N·m (221 to 738 lb-ft) and can be adapted to fit hybrid or all-wheel drive applications.

The transmission comprises 8 gears, four gear sets and five shift elements. ZF has further optimized the new transmission generation for the requirements of modern engine technology. In order to meet the forthcoming CO2 emission specifications without losses in terms of torque and performance, there are two central trends when it comes to combustion units: downsizing (which means turbocharged engines with fewer cylinders and less engine displacement); and downspeeding, which is the reduction of the engine speeds combined with a maximum torque that is applied at a very early stage.

The reduction of the speeds in particular demands transmissions with a higher spread; accordingly, ZF has increased it from 7.0 to 7.8 on the new 8HP by means of optimized gearsets.

This measure alone reduces the speed across all gears by 50 revolutions per minute on average and reduces fuel consumption by almost one percent.

—Dr. Jürgen Greiner, head of Passenger Car Transmission Development at ZF Friedrichshafen AG

Furthermore, the ZF developers have succeeded in once again reducing the internal transmission losses. This is primarily ensured by the new multidisk separation. Additional springs integrated into the multidisk packages of the shift elements ensure that the friction shift elements are almost fully opened and, consequently, cause less drag torque.

Compared to the first 8HP model range, we have reduced the power losses by more than two-thirds with the new generation.

—Dr. Greiner

Meanwhile, a further innovative function minimizes the creeping torques: A clutch is now fully opened during deceleration and when the vehicle is stationary; it is no longer necessary to brake against the drive, explained Greiner. Another positive effect is that the oil pump belonging to the ZF automatic transmission works with a system pressure that has been reduced from 5 to 3.5 bar and, as a result, requires less energy overall.

Furthermore, the objective was to take the changing vibration behavior of the increasingly economical yet, at the same time, more powerful downsizing units into account. Therefore, all 8HP automatic transmissions feature particularly advanced torsional vibration dampers.

These dampers eliminate the vibrations that occur on the engine side so that they are unable to move further along and into the driveline and the body. The newly developed torque converter contributes to downspeeding because the hydrodynamic transmission of power can be bridged even more quickly—this enables traveling with a closed lock-up clutch at an early stage and at an extremely low engine speed.

The tailored, fuel-efficient uncoupling of the transmission in connection with a temporary engine stop, the so-called coasting function, is now possible at speeds up to 160 km/h (99 mph). At the other end of the speed scale, ZF has further optimized the optional start/stop function of the 8HP: After the vehicle has come to a stop, it stops the engine without any discernible delay, instead of after 1.5 seconds as was previously the case.

ZF did not neglect dynamics; among other things, the new transmission control unit enables nested multiple downshifts which permits the 8HP to respond in an even more spontaneous and dynamic manner where necessary.

The new 8HP entered volume production at the start of July 2014 in the BMW 520d as the 8HP50 version that is designed for torques of up to 500 N·m. The 8HP75 will be part of the ZF portfolio for drives with even higher torque of up to 750 N·m.

Gradually, all further automotive manufacturers to whom ZF has already supplied the 8HP in more than 1,000 vehicle applications will utilize the latest generation of the 8-speed automatic transmission.

Is this better than Fiat-Chrysler 10 speed units?

Another very small incremental improvement in efficiency, 6% is quoted. So if we have a car that uses 20%, which is quite high as efficiency goes, of the potential energy in a gallon of gasoline and gets 30 mpg, a 6% increase would be .20 x .06 = .012 gain in efficiency, a one percent gain.
Or, 30 x .012 = .36, Or, about a third more mile per gallon.

Wonder what this wondrous mechanical engineering experiment cost and is it really worth bringing to market. Perhaps the money would be better spent on adding an electric motor/battery.

ZF has to keep current with its clients and those clients continue to specify and purchase something they understand.

Another recent example of this is to see how successful auto dealerships have been at handling the sales of electric cars. Not.

Of course it is one thing to have machines designed by those with Doctorates but out in the market the transmission repair shops don't have that luxury. For that reason it has been stated that the increasing sophistication of these devices has resulted in more than 50% of them being uneconomic to repair.

In other news, ZF believes their new buggy whip is more efficient, takes less effort from the driver and will get an extra 3% of effort from a team of two horses!

T2, most if not all transmissions (since 2000 at least) just get rebuilt at a remanufacturer, it cheaper to just swap for a rebuilt rather than split the case on most of them when it comes down to labor... It saves the technician a lot of headache and it saves the customer money. The remanufacturer is so much more efficient at repairing transmissions its silly not to go that route.(unless you have a very very cheap labor rate)

So I dont know where you pulled that 50% from. Transmissions while they have some complexities aren't just some magic box that no one knows what's going on inside. CVTs are a bit different, but slushboxes and automated manuals are very straight forward, again, like I said it has to do more with the labor than the transmissions complexity.

Agree with the 6% (relative to previous) corresponds to 1% (absolute). But you are applying the wrong percentage to the MPG, so it is 1.8 more MPG.

DavidJ:
OK, Apply it to a 6% increase in fuel savings directly from the tank, which I doubt; that's trifling for the complication and cost, especially when compared to electric motor assist.

Any efficiency boost now, is better than no boost at all. 1% improvement over 10s of thousands(even millions) of vehicles does add up. The sooner its implemented the more vehicle miles it effects....

Okay, I can totally appreciate an electric drive system, and I would love a battery car with the capabilities and range of my current car (could happen), but I don't know why people here are fussing over the addition of a planetary gear set into a technology that's been around for a long while.

The same thing can be said about complication and cost when it comes to EV's batteries. Most chemistries pose a fire risk, require thermal management, safety circuits, etcetera which all grow with the number of Kwh available to the vehicle. To electrify light duty trucks we may see 150Kwh+ battery packs.

If you look at the MTBF for a cell, and you take how many hours a vehicle is in service, then you multiply how many cells by the hours, then divide by the failure rate... you could see how scary a proposition it would be for certain long range EV's especially it is a larger vehicle. Yes, modularity and very good monitoring can reduce the downtime/effect, just something to think about,

I just don't see anything that jumps out and screams that this transmission is vastly more complicated or vastly more expensive than slush boxes of the past, sorry for the rant.

I probably overreacted, but I dream of a holistic approach in the near/mid term... one that includes PHEVs, and lots of them... even plug in FCVs.

Think of the longer gears, the engine off operation, getting to a destination without using fuel, AWD, regen-braking, overnight charging, hardly any engine maintenance on almost every vehicle... but none require an impressive yet to be released battery, nor are dependent on such a battery for its day to day operation. The volt is a great example. 60 miles electric capacity on a vehicle would easily reduce the operator's fuel consumption to zero most days of the year.

This transmission is compatible with hybrid drive lines (as the article states), so I'm not sure what your point is. Should ZF close-up shop just because you are enamored with electric drive? Should they ignore the 10s of millions of cars that are sold every year and concentrate on a market that is a thousand times smaller?

Harvey,

This transmission is designed for cars with longitudinal engines, such as the BMW 3 series mentioned in the article. The "Fiat-Chrysler 10 speed" is actually a ZF 9 speed and is designed for transversal engines. Both are very advanced transmission, but they are designed for different cars/trucks.

CheeseEater, you reminded me that
most, if not all transmissions (since 2000 at least) just get rebuilt at a remanufacturer, it cheaper to just swap for a rebuilt.

I agree that back in the day, repair of three-speeds used by those 350 cubic inch engines was indeed practicable. However, following the advent of five speed or more sophisticated transmissions with their electronic interface to the ECU it is no longer so. At least not unless significant proprietry technical resources are made available.

I would have to rebut that the more pricier rebuild may be the option for late model vehicles, but often or not, particularly outside of the warranty, it is increasingly becoming a deal breaker with older vehicles.

ZF provides complex mechanical solutions in a world that is intent on moving the complexity part into the electronics where the reliability improvement is a thousand fold. In this world only the simplest mechanics will exist.

On this note I predict that even Tesla will eventually eschew the differential final gear that is possibly giving them the occasional gear lash problem (from what I read) in favour of a slightly more robust twin motor drive.

In manufacturing you strive for repeatability and reproduceability. That these goals are more easily reached with electronic systems is probably an understatement.

Again, I want to stress there isn't much more to an 8speed in operation, concept, or repair than there is to an older 3 speed, it simply has more planetary gear sets and solenoids.

Cars, are increasingly aging on our roadways, people are putting more money into old cars keeping them on the road longer.

Also, to that point, cars are simply engineered better, most failures come from neglect or abuse now. (*and its becoming harder and harder to "neglect" them... with longer service intervals e.g. 10K mile oil changes, lifetime transmission fluid and filter, the biggest innovation/improvement was sealed transmissions(customers cannot add anything).

Dealerships and other small shops are feeling this hurt from cars getting better and better.

Yes, electronic drive systems and components are more reliable, but to what end? Late model cars can easily go 200K miles on an original transmission, or around 13 years.

If that were an EV application... what would the state of the battery be in at that time? 70% max capacity? 60%? 50%? When does utility become an issue?

There are other things that are expensive (routine maintenance) on all cars that could easily make the car too expensive to repair example: suspension. Mine was $1100 for just the rears. Cars are an investment, its unfortunate that they cost a lot, but its always about the opportunity cost. Do I repair a beater to drive for another 3-7 years before I buy a new car or do I go out and buy something new now? What's$3000 over another 5-13 years?

New cars are expensive, even the used car market in the US is very expensive considering mileage and age. Cars just hold their value longer now because they are better than in the past.

I will say, the most frustrating thing about repairing cars is intermittent electrical issues... "In this world only the simplest mechanics will exist." I don't think that will be the case. If you're good with a DVOM you can make great money as a mechanic.

Quick shops are taking over the simplest tasks: Tires, brakes, suspension, belts, and fluids. Even those tasks aren't 'that' simple, but nothing is very complicated on a car to a point as far as repairs are concerned... you just follow pin point tests... most repairs can be accurately diagnosed before any actual teardown of components. Transmission are also very neat in that regard, you can tell exactly what is wrong with it in most cases by the symptoms.

CE88 makes some very good points.

An 8 speed is repairable while most electronic things like radios, televisions etc. are disposed of when they fail.

When a ICE or EV car has electrical problems you usually must take it to a professional or, if it is older, live with the degradation - but you can fix the brakes, suspension, belts, radiator and low fluids yourself.

Electric/hybrid (as well as ICE) vehicles are getting MORE complex (while those that think this is due to a conspiracy are staying simple).

At 3.5% of the market EVs save little gas; they are indeed "a market that is a thousand times smaller."

And the decision of where the money is best invested should be made by those that have earned it.

The real reason for the demise of the local transmission shop is that modern transmissions are so reliable.

The old 3-speed Hydramatic/Torqueflite automatics needed regular band adjustments, and were more susceptible to failure from overheating and rough handling. Modern computer-controlled transmissions avoid these issue by design. They can not be made to shift inadvisedly (over-revs, that sort of thing), and they constantly monitor fluid temps and pressures. The only maintenance left is fluid changes, which can be handled by non-specialists.

There's very little money left in specializing in car transmissions, and that's why the occasional repair is done through replacement.

Thanks for the responses. You are obviously more adept mechanically than I. Perhaps I ought to have stopped by my local transmission shop for their take before I posted.

My life experience through aquaintances, who have kept older vehicles on the road, is that despite having immaculate interiors, no dings nor any signs of exterior rust at 150k kms will never be enough to prevent these vehicles from going to the crusher when their transmissions begin to fail. They just shrug and start searching for the next and newer CPO.

CE88 , you countered mechanical reliabilty by introducing the question of EV battery longevity. I have to agree that this is a sensitive matter over on the Tesla Motors forum.

There are a number of members on that website who are also owners of the Model S . Several of the latter group seem to be unaware that they are still in the early adopter phase for vehicles of that type, specifically the 300+Hp electric sedan. Regardless of that they persist in clocking up much more mileage than the average 1000 miles/month usually demanded from a typical gas car. One particular character increased his odometer reading by 17K miles in just four months !

Now we know that for the S85 (denotes the 85Kwh battery version) the complete powertrain warranty is eight years with unlimited mileage.

The problem is trying to get a fix on exactly what this warranty supports in terms of battery failure. Leaving aside the obvious pack total failure, how the battery pack warranty intends to deal with a pack whose charge retention is beginning to deteriorate needs to be answered. On this Tesla is somewhat vague.

There are of course a whole bunch who are quick to dive in and attest to their packs proficiency after 40K miles etc etc. Then there have been extreme cases that allow Tesla to extend some goodwill and do a full replacement. But there are now increasingly more cases where the company factors in the usage delivered and replaces the pack with one of similar wear. In some of these cases customers have turned around and demanded a pack which is capable of the original mileage at delivery on the grounds that so_and_so has reported that his battery is only a couple of miles down after a full year of use.

That of course is the problem. Perhaps so_and_so has a commute where he doesn't exceed 45mph whereas the other profligate owner likes to bury the needle so to speak. Of course the console display is merely a computer prediction based on best practice modelling and headwinds and low ambient temperatures will also eat into the rated miles as displayed on that console. For the future maybe they should consider the pack's Kwh storage - let the supercharger decide - at ownership change and leave the car and the rest of the powertrain out of the equation.

Finally mechanical transmisions are based on a mature technology with lots of history whereas battery packs are only on their second iteration. Time will tell.

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