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?