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ZF to present new 9-speed automatic transmission for front-transverse drive; fuel savings up to 16% compared to 6-speeds

ZF 9HP.The 9 HP construction kit is designed for different starting elements, hybrid drive, a stop-start function, and all-wheel drive. Click to enlarge.

ZF Friedrichshafen AG will present a 9-speed automatic transmission for passenger cars with front-transverse drive at the International VDI Conference Transmissions in Vehicles 2011, 7 - 8 July 2011, Friedrichshafen, Germany. With its two model ranges, it covers a torque range between 280 and 480 Nm (207 and 354 lb-ft). The new 9-speed (9HP) can deliver fuel savings of up to 16% compared to today’s standard 6-speed automatic transmissions in front-transverse installations.

Thanks to its construction kit principle, the basic transmission can be supplemented in line with special requirements. Thus, different starting elements, hybrid and all-wheel drive applications can also be implemented cost-efficiently given the restricted installation space conditions.

The new 9-speed automatic transmission owes its fuel efficiency to its extremely high total spread of 9.84. Nevertheless, extremely small gear steps can be realized thanks to the nine speeds. This not only have a positive effect on driving comfort but, in addition, the engine always runs in the consumption-optimal speed range; in the ninth speed, there are only 1,900 revolutions per minute at 120 km/h instead of 2,600 in case of transmissions featuring 6 speeds.

ZF realized the high number of speeds of the 9HP with the help of four individual gearsets and six shifting elements. Placement of these additional components in the transmission was a major challenge, ZF said—in principle, the transmission installation space in front-transverse passenger cars is highly restricted by the vehicle’s width.

For this reason, the gearsets have not been allocated on the 9HP’s longitudinal axis but were intelligently nested in. This concept was supplemented by using hydraulically operated constant-mesh elements, since these can be integrated without a major impact on the overall transmission length and still enable high efficiency.

While multidisk shift elements in the open condition create drag torques, these losses are very low in dog clutches. This aspect is particularly important with regard to the multi-speed concept of the 9HP: Thus, enhanced efficiency generated by small transmission steps is not lost again via drag losses due to the rather complex design.

A torque converter is used in the 9HP as the standard starting element for smooth starting and maneuvering quality. Here, a multi-level torsion damper system minimizes hydraulic losses while, already at low speeds, facilitating quick bridging of the torque converter lock-up clutch. This is not only beneficiary for fuel consumption and comfort but also for driving dynamics. For an even more direct driving experience, ZF has designed all control components for shorter response and shift times, actually below the threshold of perception.

Direct multiple gearshifts are also possible with the 9HP and give the automatic transmission its sporty character. Thus, the transmission controls can be influenced by the OEM and the end customer: Shifting points and shifting dynamics are highly variable—from emphasis given to comfort and optimized fuel consumption up to extremely sporty. ATSYS, the shifting sequence control, contains all clutch controls, adaptation functions, and transmission protection functions while ASIS, the driving strategy, ensures that the optimal gear is selected for each driving situation.

With the 9HP, as a result of cost efficiency and installation space optimization reasons, ZF engineers did not use a fully-integrated mechatronics module for all sensors, actuators, and the electronic control unit (EGS). Instead, ZF develops and produces the EGS under its own aegis. It is installed separately from the now significantly smaller hydraulic control unit (HSG) on the upper side of the transmission housing. The EGS’s computing performance can be increased by another 30% when needed. Thus, the 9HP is also equipped for even more comprehensive software functions in the future. The EGS’s hardware layout has been designed in such a way that the different OEM requirements can be applied.

So that the new 9-speed automatic transmission can be installed in as many vehicle applications as possible, it has been prepared as a “construction kit”—e.g., an additional transfer case can be connected for the all-wheel drive operation. To this end, ZF developed an all-wheel drive that can be decoupled (AWD Disconnect). It actuates the rear axle drive only when needed and, thus, saves five percent fuel compared to the permanent all-wheel drive.

The 9-speed automatic transmission is, by default and without an additional oil pump, stop-start capable. Since, in the case of restarting, it is only one friction shift element that needs to be closed, response times are highly spontaneous. In addition, the 9HP is easy to hybridize. On the basis of an parallel hybrid architecture, the torque converter is then replaced by an electric motor. Finally, thanks to its open software and interface structure as well as the powerful electronic control unit, it will be possible to integrate the unit flexibly in different vehicle concepts. This diversity of the 9HP construction kit makes the transmission especially efficient for OEMs, ZF claims.

(A hat-tip to Ray!)



At first I was like "what the...." and then it occurred to me that this is actually a very potent package for manufacturers. I hope it sees wide acceptance, especially in its hybrid form.

In a couple of years, the headlines will read: "ZF releases 16 speed transmission"


Six, seven, eight, nine, sixteen, twenty six speeds seems to claim more and more fuel economy. Wouldn't an improved CVT (1001 speeds) beat them all?


Trucks sometimes have up to 16 speed transmissions. However some of these gears are "crawlers", so in practice it is seldom more than 14 (or 10-12) that can be used for normal driving. The power to weight ratio for a truck is far lower than for a car, so, in principle, a truck needs more gears than a car. Transmissions with more than 8-9 speeds will not give any further benefits in cars. Some energy is lost to friction in every gear change, so increasing the number of speeds over a certain limit will be contra productive. A CVT has an infinite number of speeds and is not plagued by torque converter losses. However, contemporary CVTs have rather high mechanical losses. It is also difficult to provide as big spread as the ZF transmission discussed here (9.84). Thus, a CVT is less competitive than first anticipated. Some development companies (e.g. Torotrak) claim that they can reduce the losses but we will not know for sure until they are ready for production.

Stan Peterson

Optimizing a transmission for an ICE for either Otto/Diesel or other cycle nuances is very well done. Transmission losses have become a target for Engineers seeking furhter fuel economy improvments. Furthermore they have anticipated and incorporated functionalities such as AWD, Stop-Start, and or parallel hybridization.

It is easy to see that future LDVs will have fuel economy that would have been unbelievable to Engineers of the 1970s, when auto fuel economy first became important.

The losses and narrow overall transmission ratios of CVTs, have led to disapointing performance and fuel economy. The market is choosing, and unless the CVT designers can make substantial improvements, the markets have chosen and moved beyond them.


CVTs are also often challenged to provide smooth controlled engagement from stand still (or creep), to close that annoying gap while in line at the stop light without that annoying collision with the car ahead.
I'd still like to own one before they vanish.


What about a hybrid transmission that has ~4 gears with a relatively wide spread and a CVT with a relatively narrow spread? I'd imagine that CVTs could be relatively efficient if they operate within a narrow range.


How about two-stage CVTs?


How about a $100, 2 speed "Power-Glide" with a lock-up torque converter that weighs 2/9ths of the 9 speed ZF?


TT: Do you want to go back to 15 mpg cars?


I do believe the Leaf has 1 one speed transmission.


Well designed EVs should not need a mechanical transmission, not even a one or two speed unit.


A well designed EV should not even need a differential once motor/controller prices come down. Imagine eliminating the cooling, engine, transmission, differential, catalytic converter, muffler, gas tank and the rest.


Imagine eliminating the drive shafts and CV joints as well. In-wheel motors seem to be not quite ready for prime time, but someday younger mechanics will wonder what a CV joint boot is.


These photos show the Tesla Roadster with two forward gears, they are dated 2006 however.


There is a nice picture of their motor that weighs only 70 pounds and propels the car 0 to 60 mph in about 4 seconds.


One could use IVT. It's an ultimate solution for ICE transmission.


People have used CV boots on a lot of cars for a long time. If you have them inspected periodically and replace when needed, they pose no problem.

The unsprung weight of wheel motors is there. Even with advanced suspension systems, increasing the weight on each wheel poses problems. I was merely pointing out the simplicity of EVs.


I call "no way" on the 16% increase in fuel economy.

Engines clearly have an operating "range" where BSFC (brake specific fuel consumption) is best. This "range" is not ultra narrow, and does not require and engine to be within 90RPM of "ideal" to achieve maximum fuel economy numbers. Remember that an engine still needs to produce significant power to move a vehicle of a certain size, weight and drag.

Sure, there are gains to be had. Some of them are reduced frictional losses and hydraulic losses. VW's DSG 6 speed matches the fuel efficiency of a manual transmission. It also does a great job of keeping the engine right at the bottom of the BSFC curve.

My guess is that there are diminishing gains to be had with all these extra gears. I can't imagine that this could, for example change my 06 VW TDI from 42MPG average to 48MPG. In fact, there simply is not enough energy in the fuel to achieve those numbers, with that PD engine.


VW reduced frictional losses in the new 7-speed DSG in comparison to the “old” 6-speed DSG. The ZF 9-speed gearbox has hydraulic losses that the "mechanical" DSG does not have. I have tested a car with the 7-speed DSG and frankly (without having tested the ZF 9-speed transmission); I cannot understand why a torque converter would be needed. Maybe a 9-speed DSG would be even better. The engineering company IAV recently published a paper on such a 9-speed transmission. They showed that the potential benefit of an ideal CVT/IVT without losses was only a few per cent compared to that 9-speed transmission.


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