MotoGP technique: The “Seamless” gearbox scrutinized (1/2)

Ducati does not have a monopoly on new technologies in MotoGP. In 2011, Honda introduced the so-called “seamless” gearbox on its MotoGP prototypes. And since then, all other manufacturers have adopted this technology. How is this gearbox different from a classic gearbox equipped with a shifter?

While a conventional gearbox disengages the gear used when changing gear, the so-called gearbox seamless pattern allows you to change gear without disengaging the gear in use and therefore avoid the short interruption of torque transmission at each gear change. More progressive gear changes in the boxes seamless pattern thus improve the stability of machines by eliminating jerks during acceleration and also provide better engine braking efficiency during deceleration.

“Classic” gearbox

In a conventional transmission, only one set of gears can be engaged at any given time. Because only one gear can be engaged at a time and the gears must slide along the shafts, there is a finite time for each gear change during which the motor cannot deliver power to the wheel. This is possible mechanically using the clutch, or thanks to a gear change switch integrated into the gearbox linkage which cuts the ignition of the engine for a programmed instant: this is the famous shifter.

If the clutch was not used or if the ignition was not switched off, the engine would accelerate sharply during this neutral, which could damage the gearbox in the long term. Even with a shifter, there is a variation in engine speed during the neutral period.

 

 

 

So, even with shifter, it is necessary to stop the movement of the engine transmission to allow the gearbox parts to engage and disengage. This pause, during which the clutch disengages and re-engages, causes a jolt which destabilizes the motorcycle and leads to a drop in efficiency: the motorcycle tilts forward, then the mass is transferred to the rear as soon as the gear is engaged. This is felt in the suspension, and contributes to premature tire wear.

Worse, if the driver is on the corner, accelerating out of the corner, this impulse continues in the form of a slight rocking fore and aft, which varies the loads on the two tires and thus reduces grip.

The “Seamless” box

The term seamless pattern is used because of the ability of this box to shift from one gear to another smoothly, without the usual pause that occurs when disengaging the clutch: it does not shift to neutral between disengagement of the first pair of gears and engagement of the next pair. Thus, there is no break in torque between the motor and the rear wheel when changing to a higher gear, and the gear change time is reduced to its minimum possible value (just enough time for the electronics to manage engine speed difference).

 

 

From a logical point of view, the concept is simple: two gears mesh at the same time, with a system which allows the transition from one report to the other. It works both upshift (first to sixth gear) and downshift (sixth to first). There is a mechanical device that disconnects one of the two gears as soon as the next gear begins to transmit torque. To give you an idea: the bike is in third, the rider presses the gear lever to shift to fourth, but in fact he only puts that specific gear in "preselected" mode. The engine stays in third, with fourth preselected, until a complex system of mechanisms commands it to shift to the next gear, which is fourth. When the gearbox transmits torque, third gear is automatically deactivated.

 

 

 

In the second part of this article, we will address the more technical explanation of how the box works. seamless pattern, then we will see what are the gains brought to the pilot, and finally, its cost!