Good evening guys once again welcome back to my blog. In the last blog, I have written about Dual-clutch Transmission which combines features of an automatic transmission with the manual transmission and delivers a great on road performance. But the problems of dual clutch transmission are a big hindrance to its way of covering a major automobile these problems includes its size and cost. Dual clutch transmission is not cheaper at any rate if you compare it the manual or automatic that's one of the main reason you probably won't find it in your car. But since everything evolves and engineering always gave you surprises. So, the task before engineers and innovators was to design a compact and low-cost but equally good transmission which would combine the features of manual and automatic transmission. Then the solutions came to engineers in the form of Continuous Variable Transmission (Popularly known as CVT). So, let me begin this post about introducing you to this type of Transmission.
As far in the previous post, we have seen we always requires selecting some gear with some fixed gear ratio. What if, I had a choice to select an infinite number of gear ratio available to me? Yes, you read it to write an infinite number of the gear ratio. For those who are reading about transmission for the first time please refer to gear ratio from my previous post on Transmission basics. So, as I say infinite gear ratios let us find it out how it has been made possible by the engineers.
As far in the previous post, we have seen we always requires selecting some gear with some fixed gear ratio. What if, I had a choice to select an infinite number of gear ratio available to me? Yes, you read it to write an infinite number of the gear ratio. For those who are reading about transmission for the first time please refer to gear ratio from my previous post on Transmission basics. So, as I say infinite gear ratios let us find it out how it has been made possible by the engineers.
Actually, a CVT consist of a centrifugal clutch (maybe two), springs, two pulleys and a single belt which run over the pulley. One pulley (primary pulley) is coupled to engine output shaft coming from the flywheel and another pulley (secondary pulley) is coupled with the output shaft where power is required. As now let’s start the engine and see what happens, you would see primary pulley starts rotating at the given rpm as same as that of the engine but secondary pulley rotates with some slower speed due to initial gear ratio but no power is transmitted to the wheels. |
As soon as you accelerate what happens is the centrifugal clutch comes into the role. When the secondary clutch acquire a minimum amount of rpm as set by you or company it gets engaged and start transmitting power. Then, you go on accelerating, you would see the size of the belts at both end changes as the speed increase and we could achieve an infinite number of gear ratio with the desired velocity and acceleration. The next question arises how the size of both sides of belt changed? The answer lies behind is the simple physics of centrifugal forces. As body, start revolving it experiences a centripetal force given by
Force= mass*square of velocity/ radius
Mass and radius doesn’t changes but velocity in the CVT changes and is provided by the engine. So, by changing the velocity the force experienced by the clutch and spring is known and it is set to work similarly by moving the pulley to overcome the centripetal forces and thus achieving the desired ratio. I will write about it in more details in my next post “Tuning of CVT”.
Advantages
Since every coin has two faces, similarly anything could not be invented without any demerits. So, despite its advantage, CVT may be disadvantaged as:
Because of greater advantages, it is now widely used in automobile especially in scooters some of the examples are Honda Activa, TVS Jupiter, Suzuki Access 125, Vespa and much more. But CVT is not only limited to scooters it is also available in cars like Ford C-MAX hybrid, Toyota Corolla, Honda Accord etc.
I had attached some videos at the bottom if you wish you could probably have a look at them.
Thanks for reading the post. If you like my post please do share it and if you have any queries, complaints, suggestion or want me to write something just leave a message in the comment box. Till then stay tuned to my website http://vehicledynamics.weebly.com and http://vehicledynamics.quora.com
Force= mass*square of velocity/ radius
Mass and radius doesn’t changes but velocity in the CVT changes and is provided by the engine. So, by changing the velocity the force experienced by the clutch and spring is known and it is set to work similarly by moving the pulley to overcome the centripetal forces and thus achieving the desired ratio. I will write about it in more details in my next post “Tuning of CVT”.
Advantages
- Better fuel consumptions comparable to the manual transmission. So, it’s economic to drive a CVT as compared to automatic ones.
- Low power losses which mean more acceleration and torque reaches to you on wheels.
- Adapts to any road conditions whether it is stepping hill climb, muddy areas or just simply a plain road.
- One of the special features of CVT, it provided maximum torque at each and every instant of time.
Since every coin has two faces, similarly anything could not be invented without any demerits. So, despite its advantage, CVT may be disadvantaged as:
- The cost of CVT is low compared to automatic and dual-clutch transmission but higher than of manual.
- You may not enjoy the ride because the feel of manual the shifting of gears is fun.
Because of greater advantages, it is now widely used in automobile especially in scooters some of the examples are Honda Activa, TVS Jupiter, Suzuki Access 125, Vespa and much more. But CVT is not only limited to scooters it is also available in cars like Ford C-MAX hybrid, Toyota Corolla, Honda Accord etc.
I had attached some videos at the bottom if you wish you could probably have a look at them.
Thanks for reading the post. If you like my post please do share it and if you have any queries, complaints, suggestion or want me to write something just leave a message in the comment box. Till then stay tuned to my website http://vehicledynamics.weebly.com and http://vehicledynamics.quora.com