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Zeroshift Launches Second Generation of Automated Manual Transmission

19 April 2007

Zs1
The Zeroshift transmission offers better fuel economy than automatic transmissions while preserving ease of driving. Click to enlarge. Source: Zeroshift.

Zeroshift, Ltd. launched the second generation of its automated manual transmission (earlier post) at the SAE World Congress. The Zeroshift transmission allows a manual transmission to change gear in zero time, thereby offering potential fuel economy improvements from driveline efficiency and the best possible vehicle acceleration.

The Zeroshift concept is to remove the synchromesh components within a manual transmission and replace them with a ring drive system.

The latest version uses a new drive ring system, combined with other developments, to deliver reductions in cost, weight and packaging volume while improving durability, fuel economy, emissions and refinement.

The first generation Zeroshift was pneumatically operated and used six drive elements—specially contoured metal “bullets”—to engage and disengage the drive gears in a similar manner to dog clutches.

Zs2
A simplified rendering showing the rings and bullets (red and blue).

In the second generation system, these have been replaced by a pair of interlocking rings, each incorporating the three drive elements in a single forged component and operated by shift forks.

When shifting from neutral, ring one is engaged to take up drive while ring two is engaged within a few degrees of revolution to takeup backlash. The next shift is made with ring two taking up the drive and ring one taking the backlash. As ring two is unloaded during the change, it requires less than 1/20th the axial force required by a conventional synchromesh.

The control system, also developed and calibrated by Zeroshift, coordinates gearshift actuation, engine management and clutch operation to provide full control over the driveline during gearshifting.

Zeroshift improved the transmission’s refinement and durability through the design of the working surfaces. Shift forces also have been reduced from around 100N in the first generation system (compared to about 1,000N for a conventional AMT) to 40N. The low forces allow the components to be manufactured from proven light-weight materials.

The second-generation system uses simplified actuators with lighter rails and light weight shift forks. Total packaging volume is also reduced in this version of the AMT.

Compared to a manual transmission, Zeroshift calculates that its transmission can deliver 2% better fuel economy and 5% better acceleration. While the Zeroshift AMT would increase production cost over a manual transmission by about 25%, it is significantly less expensive to manufacture than a 6 speed AT, which, Zeroshift calculates, costs 70% more to manufacture than a manual transmission.

Resources:

  • Zeroshift. A Seamless Automated Manual Transmission (AMT) With No Torque Interrupt (SAE 2007-01-1307)

April 19, 2007 in Fuel Efficiency, Transmissions | Permalink | Comments (10) | TrackBack (0)

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Comments

In the fuel economy comparison chart, the DSG transmission is not mentioned.
I think the DSG can attain slightly better fuel economy than a conventional manual transmission; similar to the zeroshift.

Nice engineering and a good near-future adaptation to improve the efficiencies of manual transmissions. However, in the long-term-future, direct drive electric motors without transmissions will be the passenger car drive line of choice. Gears in drive lines produce friction losses and are to be avoided if possible.

Although there is no key, I'd have to guess that "DCT" is Dual Clutch Transmission. Regardless, I'm skeptical of the numbers they quote.

For the most part, Europeans never warmed to conventional ATs because they cost more, use more fuel and tend to reduce performance. DCTs offer a better trade-off and are a popular available option. Therefore, 25% over and above a manual for the Zeroshift sounds like a great deal IFF the implementation holds what the SAE paper claims.

In dense traffic, there are definite safety advantages to eliminating gear change actions. Moreover, if you interpret gas pedal angle as power demand and pair that with knowledge of the engine SFC map, the tranny's ECU can always choose the gear ratio at which the engine runs at its most economical, i.e. high load at low RPM. When you do need to accelerate, the kickdown sequence should be both fast and smooth. This obviously works best with a CVT but with enough discrete gears an AMT/DCT should deliver a good approximation.

For those who prefer to change gear manually on occasion, flappy paddles and/or a regular poke are possible with AMTs.

Jorge -

DCT = dual clutch transmission, the generic name for what VW calls DSG. There are two variants: the more efficient ones use dry clutches but are limited to 200-250Nm engine torque. The ones VW has in production change gears more smoothly and are rated for higher torque but they rely on wet clutches. These reduce fuel economy by the 3-4% indicated above.

Lad -

if you're suggesting that mechanical transmissions are about to be replaced by serial hybrids, I would have to disagree. Not only are such concept heavy and expensive, the combined losses of generator, power electronics and motor are on the order of 15%. Such concepts only make sense in tanks, open-cast mining trucks, perhaps city buses.

High load at low rpm would not work for fuel efficiency in most current (gasoline) vehicles. OEMs tend to be very conservative and go to open loop operation quite quickly when the load is greater AND they tend to make them over-rich at high load (even low rpm) for both open and closed fuel mapping. At least in the ECUs whose code I've been disassembling over the past few months.

Patrick -

I'm not sure which engines you are referring to. I was thinking of e.g. the new 1.6L inline 4 with GDI, Valvetronic variable valve lift and phase and optional turbocharger that recently came out of the BMW-PSA co-operation. Production capacity is over a million units a year, with 80% going into Peugeot/Citroen vehicles and 20% into the new Mini. BMW was able to improve fuel economy by 16% relative to the old Ford-sourced supercharged powerplant, yet the incremental manufacturing cost is on the order of just EUR 100.

The turbocharged variants in particular reach their maximum torque of 240Nm at just 1400-1700RPM, depending on the size of the turbo. This maximum is artificially imposed to keep the cranktrain and transmission light and, can be sustained through ~5000RPM.

Because of the improved scavenging possible with GDI, turbo lag is down to 100-150ms - a claim made by the engineering lead from BMW at a talk I attended earlier this week. That's virtually undetectable.

Having a lot of torque low down in the RPM range means you can use long gearing to deliver the power you need for cruising even at freeway speeds at perhaps 2/3 of the engine speed but 1.5 times the torque. That translates directly to lower internal friction losses, which are relatively high in part load.

To really push the envelope on fuel economy, you have to try and run at 80-90% of rated torque for a given speed. Most transmissions are not laid out that aggressively, for the reasons you indicate plus engine life expectancy plus a desire to avoid overly frequent kick-downs. However, all of the European car makers are heading in this direction for their gasoline engines because of the upcoming fleet average CO2 emissions limit of 120 g/km.


Lad, the electrical losses in a generator/battery/frequency-drive/AC-motor system are quite a bit greater than the gear-to-gear losses of a mechanical transmission. Any time you convert between energy forms, you are going to have losses. It's worth noting that the Toyota Prius has its gear train arranged so that at typical motorway speeds, most of the engine power is going through the gear-to-gear part of its "transmission" and only a fraction is going through the electrical route, only enough to achieve the simulation of a CVT. They wouldn't have done it that way if it were more efficient to go all-electric ...

This Zeroshift arrangement ought to be close to the same efficiency as VW's DSG. I suppose by using a different mechanical arrangement, it avoids stepping on BorgWarner's patents. It still needs a mechanical clutch for starting off from a standstill ...

snip

This Zeroshift arrangement ought to be close to the same efficiency as VW's DSG. I suppose by using a different mechanical arrangement, it avoids stepping on BorgWarner's patents. It still needs a mechanical clutch for starting off from a standstill ...

snip

Th zero shift will have no worse FC than a manual transmission (they say 2% improvement - reasonable)

DCT or DSG deifinetly has lower efficiency than a manual GB.

Ciao,

Mike

Can this still be shifted manually as well?

Rafael,

Yes GDI is a different animal altogether but all MFI/MPI (port fuel injection) engines that I have had a chance to pull down the code from their ECUs have fuel tables as I mentioned previously.

I have never disassembled the code from a BMW Valvetronic or any GDI engine. Rare to find either one in the US unless the car is very recent (7 series are not that common, and Audi/VW's FSI is nearly brand new.)

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