Engineers? Please explain how this instant-shift transmission works

[kaisen]

Xtrac shows seamless gearchange alternative to dual clutch transmission




After two years secret development in motorsport competition, Xtrac unveiled an important new driveline technology this week in the form of an Instantaneous Gearchange System (IGS). It does exactly the same thing a dual clutch transmission achieves with less weight, cost, and complexity. The secret to Xtrac IGS is the integration of a ratchet and pawl mechanism between each gear hub and the main shaft so that two consecutive gear ratios can be selected and engaged simultaneously, but with only one set of gears driving.

Conventional gearboxes have always had some serious problems associated with needing to interrupt engine torque in order to change gear. Apart from increasing fuel usage, hydrocarbon and CO2 emissions, momentarily cutting power delivery to the rear wheels obviously also reduces performance.

Porsche was the first to develop an answer to this problem with its Doppelkupplungsgetriebe (dual clutch transmission - DCT) and the DCT is now in common usage in cars and has just been applied to motorcycles for the first time by Honda.

Size, weight and complexity are the main drawbacks of the DCT. Now motorsport transmission specialist Xtrac has applied its high performance engineering skills to design and develop a seamless gearchange known as IGS or Instantaneous Gearchange System. IGS is small, lightweight, and is now ready for commercial development in motorcycles, electric vehicles, cars, trucks and buses. IGS was unveiled this week in Berlin at the International CTI Symposium “Innovative Automotive Transmissions Hybrid & Electric Drives”.

The secret to Xtrac IGS is the integration of a ratchet and pawl mechanism between each gear hub and the main shaft so that two consecutive gear ratios can be selected and engaged simultaneously, but with only one set of gears driving.

“When introducing new technology to the automotive mainstream it’s important to have progressed beyond the initial research and development phase,” said Xtrac Technical Director Adrian Moore.

“Car makers like to see practical demonstrations to show that the technology actually works and is more than a concept. With our motorsport experience we have the advantage of two years of racing IGS with professional teams.”

IGS is protected by worldwide patents, and the company reports that initial development will focus on improving the efficiency of electric vehicle powertrains. Xtrac has considerable experience in the design and manufacture of transmission systems for experimental, prototype, pre-production and specialist low volume vehicles, and a study is already underway to implement IGS into a two-speed EV transmission with the aim of ensuring the optimum performance of the vehicle.

Xtrac is based in Berkshire, UK, with satellite motorsport operations in located at Indianapolis and North Carolina in the United States. Its gearboxes, differentials and driveline components are used in Formula One, IndyCar, Touring Car, Rallying, Rally Raid, GRAND-AM and Le Mans sportscar racing.

[doug_porsche]

trying to find the article I read in Racecar Engineering Mag on this.

See also www.zeroshift.com

The keys to the kingdom is in the paragraph
secret to Xtrac IGS is the integration of a ratchet and pawl mechanism between each gear hub and the main shaft so that two consecutive gear ratios can be selected and engaged simultaneously, but with only one set of gears driving.

If I remember correctly, and I probably dont, the sifter works on the ratcheting engagement as much as gear change. You engage both first and second at the same time.

The ratcheting for second gear is engaged so it is "freewheeling" if it is spinning slower than the input shaft. When you shift to second the ratcheting for second is switched to locked and the ratcheting for fist is engaged to freewheel if its going slower than the input shaft.

Sorry, cant find the article that explains it MUCH better.

[911pcars]

I've always theorized that the OEM's lock up their gearbox engineers in a padded cell while they design/engineer the latest 6 or 7 speed A/T, or in this case, the Instantaneous Gearchange System (IGS). While this looks simple in concept, the complexity, especially for A/T boxes, is on a high order.

Sherwood

[Brando]

Sounds like awesome tech, but how would this work in a manual trans? If you shift to 2nd, it would have to be able to instant-shift to 1st or 3rd; you've only got 1 shift-lever, right?

[Green 912]

the overdriven gear just spins on the shaft.

i wonder how downshifts are handled? no motor braking if the gears spin if back driven?

[Flieger]

A freewheel works alright on a bicycle but what about compression braking? It seems it would be like a slipper clutch on a motorcycle. And not to mention the heat and friciton of a freewheel running continuously, as if you were on the track.

What about the new Lamborghini (Audi) dual-shift rod system? It is supposed to be used on the Jota, I think, and maybe that carbon concept car. It basically uses more shift rods so that you can be disengaging second while engaging third, even though their sliders/synchros are separate.

F1 cars do something similar to this, but they do not have a rachet/freewheel. They just use electronics. It is scary to hear a gearbox engineer talk about them, because they say that VERY briefly, two gears are engaged at the same time. Not sure if this is a red herring or if it is literally true and there is just wind-up in the shaft between the two gears.

[Red88Carrera]

I believe this is the patent for the gearbox:

United States Patent: 7428854

You can view alot more images within the patent, and read about how it works.

[flatbutt]

so a ratchet and pawl for each gear? isn't that alot of metal subject to wear and tear?

[artplumber]

Originally Posted by flatbutt

so a ratchet and pawl for each gear? isn't that alot of metal subject to wear and tear?

Hope car has a flexible engine so when the thing malfunctions you can drive around in only one gear...

[Red88Carrera]

They're designed for motorsport competition. They probably get rebuilt after each race.

[doug_porsche]

Originally Posted by flatbutt

so a ratchet and pawl for each gear? isn't that alot of metal subject to wear and tear?

these were designed for F1 before the rules stipulating that the trans cant be rebuilt after each race.

I understand that this is not the design of choice now.

they also had problems shocking the drive-train when a shift happens.

[Zeke]

The way I read the description is that there are two gears/hubs for each different drive gear. It may not be that there are 12 hubs in a 6 speed, but that seems to be he gist of it. This would allow seamless shifting up and down if I understand the thing.

[RANDY P]

I hope it isn't all straight cut gears. It'll sound like a pissed off cat when it's running.


Probably run lots of TQ thru it tho. Blown tranny could be thing of the past

rjp

[Normy]

My sig-other has a VW CC with the DSG transmission, and this thing is slick! It shifts instantly and you can barely tell, other than the sound of the engine, that it has happened. This car, this CC? This thing is dangerous to your license, because it is so smooth and quiet. You go 35 mph in a 35 mph zone in this thing and it feels like you are doing 20, so you tend to speed. The 200 hp engine doesn't help matters. Her previous car was an Acura TSX with 205 hp; the CC would have that silly Honda for breakfast! The performance of these two cars is night and day, a testament to the great god "torque"!

N!

[artplumber]

Originally Posted by doug_porsche

these were designed for F1 before the rules stipulating that the trans cant be rebuilt after each race.

I understand that this is not the design of choice now.

they also had problems shocking the drive-train when a shift happens.

Makes sense. With some mechanism internal to the output shaft that forces pawls out to engage (at least judging by the drawing), the changeover would be anything but smooth at full throttle. That is the positive characteristic of any clutch based system (with or without temporarily decreasing throttle) - lets there be transition from 0 to full torque over a more reasonable interval. Second suddenly engaging the pawls must take a significant toll on those components over the life of the transimission.

[Red88Carrera]

This is how we change speeds on our machine instantaneously. This same design has been used on our machine since 1947. You can't really see exactly how it is done, but you can see the output shaft change speed instantly. Only 2 speeds though. We use a clutch and a sprag.

[Flieger]

Originally Posted by Normy

My sig-other has a VW CC with the DSG transmission, and this thing is slick! It shifts instantly and you can barely tell, other than the sound of the engine, that it has happened. This car, this CC? This thing is dangerous to your license, because it is so smooth and quiet. You go 35 mph in a 35 mph zone in this thing and it feels like you are doing 20, so you tend to speed. The 200 hp engine doesn't help matters. Her previous car was an Acura TSX with 205 hp; the CC would have that silly Honda for breakfast! The performance of these two cars is night and day, a testament to the great god "torque"!

N!

This is not the transmission we are talking about. The VW/Audi uses two clutches for a nice smooth shift that neither you nor the rest of the gears feel.

The gearbox asked about in this thread uses no clutches for shifting. It is basically just getting gears to mesh by being at the same speed as they are crashed together. It is just done very quickly, carefully, and with lots of hope. Even if it is not gears crashing, there is some sort of engagement pawl that must be instantaneously accelerated (a physical impossibility).

[Schumi]

Originally Posted by RANDY P

I hope it isn't all straight cut gears. It'll sound like a pissed off cat when it's running.


Probably run lots of TQ thru it tho. Blown tranny could be thing of the past

rjp

They are indeed straight cut.

This is a racing transmission.

Idea being that possibly one day it could be adapted for road use.

[Flieger]

So this is the setup F1 teams had been using recently? I did not think that a freewheel could stand the F1 levels of power and acceleration. Seems like a lot of friction and inertia to have a freewheel idling at 20000 rpm.

[Flieger]

Here is the last page of an article in Racecar Engineering: Racecar Engineering | See Inside Page 74 | November 2010 | Zinio Digital Magazines & Books



Not sure if it will get big enough for non-subscribers.

Michael Schumacher in his Benetton became stuck in 5th out of 6 gears in the 1994 Spanish Grand Prix. He came to the pits to swap steering wheels but that did not help. He did the standing start out of the pits, and went on with the race. Lap times went from 1:26.8 with all gears to 1:31.8 on his first out lap. Rev limiter at 16,000 rpm on the straights, lugging in the turns at 4,000 rpm.
Schumacher pressed on. By lap 38, he turned a 1:26.3 lap. He completed 42 laps with 5th gear only and finished second. Truly a triumph of driving skill from Schumacher and engineering from the motor designers.

Variable valve timing and lift can make extra gear ratios and power interruption just a waste of energy in the form of friction and exces weight.

It seems from F1 informants that an F1 gearbox weighs about 90 pounds. About 30 pounds should be the gear sets, so if 5/6ths of them were gone, that would be 25 pounds less weight. 10 kilos at Monaco at that time was worth .7 seconds a lap. 10 kilos at Suzuka at that time was worth 3 seconds a lap. Schumacher lost an average of 2 seconds a lap with only 5th gear. Imagine if he had two gears? Short third and short 6th?