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Zeroshift - Gearbox

The Only Gearbox The Future Really Needs

Dave Coleman
Dec 21, 2006
Photographer: James Tate
0601_sccp_01_z+gearbox+zeroshift Photo 1/1   |   Zeroshift - Gearbox

In any given quarter mile there is nearly a second of just sitting there coasting. On the average road course, maybe 2 or 3 seconds per lap of utterly failing to accelerate. In something like the Dakar rally, it could possibly be an entire week that's wasted.

That time, of course, is spent standing on the clutch and stirring the stick. Shifting gears the normal way is a colossal waste of time. A blazingly fast shift takes about a quarter of a second. Make eight upshifts per lap and you just blew 2 seconds. Do 30 laps and that's a minute of coasting that could have been spent accelerating.

Imagine this instead: You launch in first gear just like any other car (with a cloud of tire smoke and a dent in the firewall, of course), but when you get to redline, instead of jabbing the clutch and grabbing second, you keep your right foot planted, do absolutely nothing with your left, and slide the shifter into second gear. And with nothing but a clunk and a surge, you're in second gear. No lifting, no grinding, no break in the sweet thrust of acceleration.

That's pretty much possible now with the VW/Audi/Getrag DSG (Direct Shift Gearbox), only you push a button instead of actually touching a shifter. I explained how the revolutionary DSG works in "Technobabble" back in April 2004 and predicted that someday it would replace both the conventional manual and the dreaded slushbox.

I take that back.

Before DSG even gets its chance, the considerably less revolutionary (and therefore much cheaper to build) Zeroshift gearbox is gonna kick its complicated, dual-clutched ass back to Germany. Auf weidersehen.

The Zeroshift gearbox, being developed by a British startup company of the same name, is a shockingly simple modification of a good, old-fashioned dog box. Shockingly simple, that is, if you already know how a dog box works.

Here's how a dog box works:Say you've got your input shaft connected to the engine, and on that shaft you have two gears, first and second. Both gears ride on bearings around the input shaft, though, so as the input shaft spins, the gears don't necessarily spin at the same speed, or even at all.

Each of these gears has teeth around the outside (imagine that!) and three arc-shaped warts (called dogs) on the sides of the gear. (Really you can have as many as six or seven, but let's work with three.) Between those two gears sits the dog ring.

The dog ring has three arc-shaped slots on each side that match the dogs. There's just enough room between the gears that the dog ring can slide back and forth to engage the dogs of either gear or sit in the middle and not touch anything.

This matters because the dog ring is attached to the input shaft via splines, so the dog ring always spins with the input shaft. Slide the dog ring into the slots on first gear and first gear will be driven by the input shaft. Slide it into second, and suddenly second gear is the one being driven.

Feel smarter now?

There are a lot of important details about dog boxes that I won't bother to explain, but here are two that matter. First, the slots in the dog ring are much larger than the dogs themselves, so the dogs can fall into the slots even when they're going at a substantially different speed. When they do fall in, they'll slap into the end of the slot with a big clunk, but they'll go in.

The second important detail is that the face of each dog and the ends of each groove are both angled slightly so that when the dog is pushing on the end of the groove, the two kind of interlock. This makes it nearly impossible to pull a dog box out of gear while you're accelerating. You have to either step on the clutch or lift off the gas briefly to pull the dog away from the end of the groove.

Here's how the future will work:Most of the Zeroshift gearbox is a perfectly normal dog box, but instead of the dog ring, you have a ring that holds six little doodads that Zeroshift calls bullets.

Zeroshift's bullets work like the dogs and use a similar angled engagement to lock everything together under power. But, of course, there's a twist. Each bullet has this angled face on only one side. When the bullets slide over to engage the dog on a gear, each dog will be trapped between two bullets, each with the angled faces facing the dog.

By now you're confused enough to be looking at the diagram, so you've noticed that one bullet is red and the other is blue. The ring holding the bullets has been removed in this picture so you can actually see the bullets, but just like the dog ring in the old box, the bullet ring is splined to the input shaft and always turns with it. In this diagram, everything turns counterclockwise.

So, if you're accelerating and the bullets are around the first gear dogs, it's the blue bullets that push on the gear while the red ones just float along (figure 1), not quite touching the dog. Under engine braking, the wheels are effectively driving the engine, so inside the Zeroshift box, the dogs are pushing on the engine via the red bullets while the blue ones just hang out.

So far, we're still operating like a normal dog box, so let's shake things up.

The bullet ring slides the bullets into engagement with each gear via springs. If the bullets are free to move, they'll move with the ring. If they're interlocked with a dog because of that angled face, though, they'll stay engaged and the spring will just pull hopelessly on them.

We're gonna shift gears soon, I promise, but first, one other detail I failed to mention about the dog box: The gears are meshing with other gears. (That should have been obvious.)

Those other gears are on the countershaft, and unlike the input shaft, all the gears on the countershaft spin together as one. Now, let's make up some wildly simple gear ratios so you don't have to go buy a calculator. Let's say first gear is 2:1 and second gear is 1:1. If we're in first gear at 8000 rpm, the countershaft will be spinning at 4000 rpm because of that 2:1 gear ratio. Second gear will be sitting on the input shaft also spinning at 4000 rpm since it's meshing with the countershaft at that fanciful 1:1 ratio.

OK, we're gonna shift. Ready?

You're accelerating, as usual, so the blue bullets are pushing on first gear and are effectively stuck to it because of that whole interlocking face thing. The red bullets are just hanging out.

Yank that lever into second gear and the red bullets slide right over into second while the blue ones keep driving first gear (figure 2). Now, if the red bullets are going 8000 rpm and second gear is going 4000 rpm, it won't take long for the red bullets to slam into the second-gear dogs. Blammo, you're in second gear!

But what about the red bullets?

Funny thing, first gear is still going 8000 rpm, even though the bullet ring (and the engine) is suddenly going 4000 rpm, so first gear immediately outruns the blue bullets, releasing their interlocking grasp. At this point the blue bullets will pop over to second gear, either because of the spring pulling on them from the bullet ring or because the next first-gear dog has come swinging around and smacked it from behind (figure 3).

Which brings up another clever little detail about these Zeroshift bullets, they're angled on the other side so a dog hitting them from behind will push them away from the gear.

Wow, we just shifted from first to second gear at full throttle without lifting and with no interruption of power, and we did it with a nearly conventional dog box with some very clever dog rings. Step back for a minute, revel in the brilliant simplicity of this design. Have a beer. Take an aspirin.

Why you can't have one yetIs your head done throbbing yet? Let's think about why you don't have this gearbox in your car yet.1: They just thought of it a few years ago It's youth that's the only thing keeping Zeroshift from selling you this technology in a racing gearbox right now. There are bigger fish to fry than your racecar, though. The Zeroshift design has the potential to offer the same ambidextrous performance as the VW/Getrag DSG, putting real, usable manual shifting and seamless slushbox performance into one transmission. And without the DSG's more expensive multi-plate clutches and concentric input shafts, it should be much cheaper to build.

Ah, but making it civilized brings up problems two and three.

2: Shift shockThe gear ratios I made up were a little unrealistic, so the engine won't go from 8000 to 4000 rpm in an instant, but it probably will go from 8000 to 6000. Dumping 2000 rpm worth of engine inertia into the drivetrain in one sudden jolt will cause, well, a sudden jolt. No big deal if you're drag racing. Very big deal if you're trying to sell a car with this transmission to your Great Aunt Ethel.

Same thing happens when you downshift. Say you're trail braking into a corner at 6000 rpm and you bang down a gear. Instantly the engine has to be going 8000 rpm, and the power to spin it up has to come from the drive wheels. The car lurches, the drive tires bark in protest and you go spinning into the weeds.

So Zeroshift has to work on some way to smooth this shifting thing out. It could be some sort of slipper clutch. It could be some connection to the engine management that cuts power during upshifts or blips the throttle slightly during downshifts. Or something else entirely. They're smart, they'll figure it out.

3: Shifting the rest of the timeUpshifting under power works great and downshifting during engine braking works great, but what if you mash the gas first and then decide to downshift? This will happen with a manual if you're not planning well, and it's standard operating procedure on an automatic, which doesn't know you need to downshift until you mash the gas.

If you're in second gear at full throttle, the red bullets will be locked into second gear. Shift down to first and the blue bullets will try to grab the dogs, but they'll hit the back of the bullet, the side that's cut so it gets kicked away from the dog, and you'll stay in second gear.

Downshifting here will require a brief lift off the throttle to let the red bullet disengage second gear. Zeroshift could program the ECU to cut power for a fraction of a second to pull this off, but it isn't going to happen with the mechanical simplicity of the full-throttle upshift.

These things are but minor details that need to be worked out. Since revealing its brilliant idea, Zeroshift has found itself sitting on a mountain of investor cash and now employs a full staff of brilliant engineers striving to rid the world of slushboxes forever.

The dog ring sits between two adjacent gears and can slide over to engage the dogs of either one or can sit between them waiting to be useful. Here it's engaged in with the gear on the left.

The four dogs sticking out the side of the gear fit into the four slots on the dog ring. If I were king of the world, these slots would be called dog houses, but they aren't. Since the dog ring is splined to the input shaft (or it could be on the output shaft, but let's not confuse things too much) this dog-in-the-house arrangement locks the gear to the engine.

Notice how much bigger the houses are than the dogs. This way, if the gear is spinning a different speed than the dog ring, the dogs can still fall into the slots.

The three tabs on each gear are just like the dogs in a normal dog box. The blue and red things here are called bullets, but they do the same thing as the slots in a dog ring. This image has been simplified so your brain can handle it. In a real gearbox, there would be two bullets for every dog, there would be some sort of cage holding all the bullets and ensuring they spin with whatever shaft they're on, and finally, there would be springs encouraging the bullets to follow the cage when the shift fork yanks that cage toward the next gear.

Let's say the top gear is first and the bottom gear is second. In this position, the shaft is turning the bullets counterclockwise, so the blue bullet is pushing on first gear.

Here, the shifter has been moved, pulling the bullets toward the second gear. Since the blue bullet is interlocked with the last gear and only getting pulled on by a spring, it stays engaged. Meanwhile, the red bullet gets pulled into place between the dogs of the next gear.

Second gear is turning slower than first, so when the red bullet hits it, the bullets (and the whole engine) slow down. First gear, still going fast, pulls away from the bullets, setting the blue one free. Just like that, you're in second gear.

By Dave Coleman
94 Articles

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