How sequential gearboxes work

Sequential gearbox is a transmission used on equipment such as an ATV or a motorcycle where the gears are shifted by using a toe to move a lever up and down. Even some racecars have transmissions with sequential gearboxes. These racecars are shifted with a hand control.

Transmissions using sequential gearboxes have a set of gear selection forks that move collars, which engage the gears. On an ATV, the gearshift lever is moved up and down with your foot and the transmission is moved from gear to gear. When the gearshift lever is moved, a ratcheting drum is rotated. This ratcheting drum has grooves cut into the side of it.

The grooves will direct the standard control rods when the drum is away from the transmission’s gears or the grooves move the gear selector fork when the drum is next to the gears. Moving the gear selector fork is the most common use of the grooves.

With this in mind, whenever the lever is moved up or down, the drum is rotated one increment. The rotation of the drum allows for movement of the rods or forks as determined by the grooves in the drum and the gears are then changed. The gear shifting sequence is required to be done in order, with no gears skipped, because of the rotation of the drum allowing the gears to change. The shifting order must be correct whether shifting the gears from a higher gear to a lower or from a lower gear to a higher gear.

There are distinct advantages to this type of transmission. These advantages are that it is quicker when shifting. The shift is consistent; it is the same motion for every gear. The location of the foot is consistent, meaning that the shift lever is always in the same place, ready for the next shift. And, the last advantage of this transmission is that there are no surprises. There is no chance of blowing up a transmission by is-shifting; the transmission must be shifted in sequence.

From neutral, first, or in some vehicles, second gear must be shifted to before advancing on to other gears except reverse. For reverse, the transmission is shifted straight from neutral to reverse. This type of system virtually eliminates shifting mistakes. The last advantage of this transmission is that it takes up less space, which can be important in a vehicle such as a racecar where there is limited room.

With a sequential shift approach, the drum is rotated manually or by electronically activated solenoids, pneumatics or hydraulics. A rotating cam located on the shift lever, which operates dogs, accomplishes sequential shifts. These dogs, found on two counter-rotating shafts, carry the gears. The final drive mechanism is geared by one shaft and the other shaft is geared to the clutch.

When the shift lever is moved, individual gears on one shaft intersect with matching gears on the other shaft. These two shafts are always geared together, with neutral being the exception, and spin at a speed almost at the next higher or lower gear ratio.

When the shift lever

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