9-Speed Automatic from "ZF"

[Laurentiu]

ZF has developed the world's first 9-speed automatic transmission for vehicles equipped with a transversely mounted engine. It will be built in a new, state-of-the-art manufacturing facility near Greenville, South Carolina.

"Already a leader in technically advanced, fuel-saving multi-speed transmissions for rear-drive vehicles, ZF's new 9-speed enables significant fuel economy improvements and delivers excellent performance characteristics for front-wheel-drive vehicles," said Hans-Georg Harter, ZF's President and CEO.

Groundbreaking for the new South Carolina factory takes place next month. Production and application details will be released later.

Fuel economy and increased performance

Compared to conventional 6-speed automatic transmissions for front-drive platforms, ZF's new 9-speed automatic transmission enhances driving performance and fuel economy. An advanced shock absorber system in the torque converter, for example, allows rapid lock up of the converter clutch, enabling greater fuel economy and lower carbon dioxide emissions.

Similar to ZF's 8-speed automatic transmission used in rear-drive platforms, the new 9-speed delivers extremely short response and shifting times that are below the threshold of perception. That means double shifts and direct multiple gearshifts occur without the driver or passenger noticing.

Sophisticated electronic controls select the right gear for the driving conditions, eliminating unnecessary "stepping" or constant shifting. In this regard, the 9-speed carries the same precise, sporty attributes found in ZF's transmissions for rear-drive vehicles, including excellent shift characteristics, immediate response to input and exceptional smoothness.

[gone-ot]

...a geared semi-equivalent version of an CVT?

...physically, think of about a flat-surfaced equivalent of a circle.

[Allch Chcar]

If it can be price competitive with the CVT it might gain some acceptance.
And it doesn't have to be variable ratio it just needs a better ratio spread and feel more connected to beat out the CVT. CVT's are pretty inefficient(72%), but they allow a wider ratio spread than most multi geared transmissions. You get a gearbox transmission and there is room to improve the performance over a CVT.

[user removed]

Originally Posted by Allch Chcar

If it can be price competitive with the CVT it might gain some acceptance.
And it doesn't have to be variable ratio it just needs a better ratio spread and feel more connected to beat out the CVT. CVT's are pretty inefficient(72%), but they allow a wider ratio spread than most multi geared transmissions. You get a gearbox transmission and there is room to improve the performance over a CVT.

CanadianDriver » Technology » Auto Tech: Nissan’s CVT transaxle

According to this article the CVT Nissan uses in my Altima approaches 97% efficiency, virtually identical to a manual transmission. The 97% figure is at the bottom of the first page.

I feels like a direct mechanical connection, and the torque converter locks up at 18 KPH, when you accelerate gently.

regards
Mech

[Allch Chcar]

Originally Posted by Old Mechanic

CanadianDriver » Technology » Auto Tech: Nissan’s CVT transaxle

According to this article the CVT Nissan uses in my Altima approaches 97% efficiency, virtually identical to a manual transmission. The 97% figure is at the bottom of the first page.

I feels like a direct mechanical connection, and the torque converter locks up at 18 KPH, when you accelerate gently.

regards
Mech

Theoretically.
"Under optimal force conditions the pulleys of the variator should exceed 97%
efficiency, although additional losses exist associated with events within the belt itself.."
But not in practice .

Source:
CVT Efficiency Thesis

In reality multi-gear Manual transmissions tend to be 85-90% efficient while Automatics with torque converters tend to be around 75-80%.

I've noticed more and more CVTs getting torque converters to improve low speed performance but that reduces efficiency. Torque converter Lockup doesn't eliminate the efficiency loss completely though, I think?

[user removed]

That was an excellent link, the paper was written in 2001. Current Nissan CVTs are 10% more efficient than manuals under identical testing scenarios, so significant improvements have been made.

The Murano with 245 HP has a CVT than can handle torque loads several times greater than the tested unit in the thesis, also the Murano is rated to tow 3500 pounds for a total gross vehicle load of about 8500 pounds.

I did not read the whole thesis but the conclusions were certainly studied by Nissan since the first CVT equipped Murano sold in the US was 2003. They also use a special fluid that has properties specifically for the CVT and no other transmission type.

Also of course when you consider the trans axle itself your total efficiency cost is the complete drive train compared to a separate transmission and differential.

It would be very interesting to see an identical thesis that used the current production Nissan unit in a side by side direct comparison to the Rover unit in the original thesis.

It looks like Nissan addressed the issues that the original testing revealed as major causes of losses.

Fluid type
Pulley deformation
Operating temperature
CPU control sophistication
Pressure pump design
Pulley diameter to prevent drive segment deflection
Elimination of the multi disc clutch with a torque converter with very aggressive lockup characteristics, which has the additional benefit of elimination of friction material contamination of the fluid.

My personal opinion is that adding more gearing to the traditional automatic design is a band aid cure, but that is only my opinion, and the cost of repairs and replacements is already prohibitive.

I like the CVT because it can, when combined with electronic throttle control and high speed data processing capabilities, compete well with a manual. While not quite as efficient, the control strategies allow higher BSFC operational states.

Of course my real belief is in the in wheel hydraulic IVT design that I worked on for many years and got a patent finally, since it has an inherent high efficiency regenerative capability and steady speed P&G capability.

That allows all hypermiling strategies to be incorporated into the vehicle so even drivers who have no concept of efficient driving will see significantly higher mileage, while the hypermiler would see even greater mileage through intelligent operation.

regards
Mech

[arcosine]

CVTs rely on traction, therefore have higher resistance since the traction belt force is not modulated for load. Involute gears, on the other hand transmit force between teeth.

[PaleMelanesian]

Even a 5-speed car can be very efficient, if it's geared right. Most are not. I'd think that's an easier engineering challenge than adding more and more gears.

[Allch Chcar]

Originally Posted by PaleMelanesian

Even a 5-speed car can be very efficient, if it's geared right. Most are not. I'd think that's an easier engineering challenge than adding more and more gears.

Well you need a low gear for starting out and an overdrive for fuel economy. That gives you just 3 gears for acceleration and vehicles now need to cover a range between 15mph-80mph. 6spd trannies are a big part of the reason that the new Mustang/Camaro V6 get 30mpg EPA scores! Double overdrive FTW.

[user removed]

Originally Posted by arcosine

CVTs rely on traction, therefore have higher resistance since the traction belt force is not modulated for load. Involute gears, on the other hand transmit force between teeth.

Why would you think the traction belt force would not be modulated for load? I was actually surprised at how low a pressure was needed in the linked document to maintain sufficient tension on the belt. I think in one case it was 6 atmospheres or about 90 psi, not much more than some oil pumps.

The fluid Nissan uses has some unique properties that act like a bunch of microscopic rubber balls when subjected to the shear forces of the 400 segments in the push belt.

I can tell you one thing in my personal experience. When my car is on cruise control it feels like a direct mechanical connection, and the RPMs do not change when going uphill or downhill on the rather shallow grades here. Instantaneous fuel consumption can vary from 15 to over 60 MPG (gauge limit) but the RPM is rock steady and it feels like a direct connection.

The ratio range is 600%. That's the equivalent of 2000 RPM at 60 mph or 2000 rpm at 10 mph, without considering the torque converter, which under light loads locks up at 12 MPH or about 3 car lengths from a dead stop under normal acceleration.

regards
Mech