A quickshifter (or quick shifter) is a device that allows clutchless gearshift on a manual transmission, and is commonly used on motorcycles. It increases safety and comfort of the vehicle since it eliminates the need of adjusting the clutch or throttle before and after gearshift. Since they eliminate the need of adjusting clutch and throttle during gearshift, they are quicker(usually shift in less than 50 millisecond) and also used as performance enhancement on motorcycles.
Almost all quickshifters work on the same basis, a sensor senses the gearshift action, a microcontroller (CPU) processes the data (and calculates the timing) and cuts off ignition momentarily, resulting in reduction of load at the transmission allowing the new gear to slip (and engage) into its place. However the method of sensing and reducing the load can vary.
Most gearshift sensors work by measuring the pressure change (push or pull) on the shift rod. However, some sensors measure the molecular strain in the shift rod to determine the gearshift process instead of using a pressure switch. The use of molecular strain gauge (sensor) is costly but more reliable (than push/pull sensor) and free from false readings due to vibrations since it has no moving parts.
These CPUs generally control the ignition and/or fuel supply to reduce load from transmission when needed. They can be either separate from ECU or a single unit(ECU performing quickshifting). They can provide near-perfect gearshift in tens of milliseconds.
The load from transmission is generally reduced by cutting off the ignition and/or fuel supply in the engine, or by disengaging the clutch. Since load is reduced from transmission precisely (if tuned correctly) by microcontroller, it does less damage to use the quickshifter than clutchless gearshift without a quickshifter on a manual transmission. This process is also called unloading.
The term bi-directional quickshifter means that the quickshifter works on both directions of gearshift - upshifts and downshifts. Most quickshifters are bidirectional, so the term quickshifter is usually alone sufficient.
However, exceptions are present such as 2016 Kawasaki Ninja ZX-10R and 2015 H2/R's "KQS" quickshifters which are "mono-directional" and only work on upshifts. Their primary aim is usually to achieve better acceleration by reducing the time interval between gearshifts during acceleration which results in continuous and smoother power delivery to the wheels.
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