The following tutorial describes basic operation of the constant mesh type gearbox which can be found on virtually all modern motorcycles.
The gearbox has 3 main components:
1. Input Shaft, which is driven by the engine through the clutch.
2. Output Shaft which is connected to the rear wheel through a chain and sprockets.
3. Selector Drum with forks.
The gears on both shafts (input and output shafts) are at constant mesh: that means that the gear teeth for all ratios are always engaged with each other at all times. Instead of sliding a gear out of engagement with another gear, the gear is disengaged by disconnecting it from the shaft that it is on. Only one gear ratio pair can be connected to the shafts at the same time and the selector drum through the forks choose which gears to be engaged at any moment.
When the rider shifts gears, he needs to pull the clutch to disengage the Input Shaft from the engine, press the gear lever which rotates the Selector Drum and engage the next gear UP or DOWN. Since the gear ratios on each gear are different when shifting gear-Down (5-4-3-2-1) it is very good (as everyone knows) to blip the throttle so the engine speed equalizes the next gear higher ratio with the rear wheel speed and the result is a smooth down shift. When shifting gears-UP(2-3-4-5-6) the principle is same with the only difference that the engine revolutions needs to drop in order to equalize engine speed, gear ratio and rear wheel speed. The advantage of UP shifting is that if you apply enough pressure to the gear lever when accelerating (this is called preload) and back off the throttle to equalize engine speed, gear ratio and rear wheel speed-the selector drum will react and engage the next gear, then you can continue accelerating without the use of a clutch.
Here comes the Quickshifter, since the reaction time of the gearbox mechanism is faster than a human reaction of backing off the throttle, the Quickshifter creates an engine interrupt impulse according to your gearbox reaction time to drop the engine revolutions after enough preload is applied to the gear lever and then you have a full throttle clutchless upshift. Preload is necessary so there is enough force for the selector drum to rotate and therefore disengage and engage the gears from the shaft they're on. This action still relies on the physical movement of your foot so when pressing the gear lever, the shift rod must travel to rotate fully the selector drum for complete engage. Here comes the Shift Sensor- when you press the gear lever, the shift sensor senses force and when the force reaches certain level-(also called preload) it initiates the engine interrupt impulse.
SP shift sensors are made in such a way that by pressing the gear lever it compresses physically the cell and when the force necessary to engage is reached it triggers engine interrupt impulse, engine speed drops and the selector drum start to rotate for engage, at this time the SP sensor mechanism extends rapidly and virtually shoots the gears resulting in faster (10-15ms shorter) response time compared to Strain Gauge sensors which relies entirely on the foot physical movement to rotate the selector drum since there is no moving parts and could be considered as a flat rod.
Another advantage of the SP shift sensors is that they protect the gearbox from missed gears by ensuring the selector drum will fully rotate each shift and will not stall in a mid-position between gears, also a fast response means less wear. An example is one of the words first OEM Quickshifter on BMW S1000RR to implement the same type Shift Sensor. A little truth revealed here, the strain gauges are not complex to build, it is just a way of measuring strain widely used for commercial applications, "actually you can find that your personal weighing scale is using strain gauge for giving you the number and also your local store digital scale is using strain gauge for weighing sale products."
In general, we are not saying who's bad and who's good, we are just explaining how things works and you can make an informed choice when you have the knowledge to do so, not blinded by the widely spread propaganda about the strain gauge technology.
Sr.Manager - R.Petrov