Most of us love riding on bikes and some of us prefer to ride on a gearless bike due to various reasons. Many of us are aware about how transmission in a bike works but only few of us know how power is transmitted in a gearless vehicle and if you are interested to learn that, this is what that happens in the back ground.
When we talk about transmission in vehicles the first thing that strikes our mind is gears. In gearless bikes as the name itself suggests there are no gears in transmission. The gearless vehicle transmission involves CVT.
CVT stands for Continuously Variable Transmission. In this type of transmission we have infinite number of gear ratios between the maximum and minimum values. The maximum and minimum values are determined maximum and minimum pulley diameters which shall be discussed in below.
A CVT consists of following parts:
- Primary pulley
- Secondary pulley
- Belt
Here the word pulley literally doesn't mean a pulley. Each pulley consists of two sheaves one of which is stationary and the other moves far and close to stationary sheave which eventually changes the diameter of pulley on which the belt rotates. The sheaves are conical in shape.
The Primary pulley is also called Driver pulley which is connected to the crankshaft of the engine, the moving sheave in driver pulley is called variator. The Secondary pulley is also called Driven pulley is connected to output shaft. The belt is generally made of steel. Generally centrifugal clutches are used in CVT.
When ever we start our gearless bike engine the crankshaft rotates. At idle speed the clutch is not engaged and the vehicle is stationary, This is like a neutral position in case of bikes with gear transmission. When we rise the acceleration throttle as the clutch engages the vehicle will be in motion.
Once the vehicle is moving and when we want to increase the speed we rise the throttle high as a result the crankshaft rotates even faster and the variator connected to it also rotates at high rpm. The variator consists of weights in it, whenever speed increases the weights move outward due to centrifugal force. As a result of this the variator move closer to stationary sheave thus increasing the pulley diameter.
Because the belt length is fixed, When the diameter of driver pulley increases more length of belt is around it and as a result belt is pulled down to center of driven pulley and the movable sheave moves away from stationary sheave. But when we reduce the speed the movable sheave should return to it's position. This action is taken care by the contra spring present between clutch and movable sheave.
Goto 1:33
This video demostrates the live working of CVT.
To know each and every part involved it CVT or if you want to self service your gearless bike check this video.
So, this is the mechanism in background that drives a gearless bike.
Notify me about anything you want to know in the comments. Thanks and peace.
References
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