With the advent of technology man has always asked for better systems to lower his efforts in doing things. The same story goes for Transmissions. Manual transmission served the purpose very well. However, soon the customer demands became higher and he wanted a system that could change gears on its own. No one wanted the clutch anymore!! Well atleast not the folks who always tended to over the engine by downshifting too early or lead the vehicle to stall by upshifting too early. This lead designers to come up with a system in which the clutch pedal could be totally eliminated. There were lot of solutions and some have been described here. Unfortunately, i dont know the order of their evolution but guess that that is not really all that interesting...
Lets take the case of the simple Hero puch or the TVS 50.....Can we call it an automatic transmission....?
Not really...however to some extent yes.
How does based on throttle the vehicle start moving?
This is because of a clutch that engages as the RPM increases. Such a clutch is called Centrifugal Clutch. Normally the clutch is disengaged. Which means that no power from the engine will be fed to the chain drive. However as the RPM increases a certain threshold the clutch engages. With the clutch engaging the power is transferred to the wheels. This is a very basic of how we can eliminate the manual clutch ( our initial aim ....). As it is clear that the centrifugal clutch will wear out with time and that means RPM points at which the power will get transferred to you chain drive will vary with time. The second disadvantage is that this method cannot transfer huge amount of torque from the engine shaft to the output shaft. I am not really using the term Transmission shaft because this is not a "Transmisison" in classical sense.
What are the other methods?
How about Kinetic Honda that has been ruling the roads since i was a kid?
Well a Kinetic Honda uses a different mechanism. It uses what is known as a belt drive...( atleast that is what i was told. I am not 100% sure!!). This is fed to a Stepped pulley or Coned Pulley. This coned pulley will be able to provided different Pulley Ratios based on which point of the pulley is used to Tap the output. A the most broad end of the pulley the Torque transmission will be less and a the thinnest end of the pulley the Torque transmission maximum. Centrifugal clutch is still used here.
Does that mean CVT ( The stuff we talk ed about...Continuous Variable Transmission) is a cheap and dirty technology?
No absolutely not. Like any other technology based on how much complexity is added one can make the system very sophisticated. The commonly used CVT's in bikes like Honda Activa, Honda Dio, Kinetec etc are fairly simple. However, some really complicated stuff from Audi can be found here and remember the core is still same....a coned pulley...
After taking care of these two aspects...i.e. some kind of autoclutch and a automatically shifting gearbox the other biggest challenge was to ensure that high amounts of torques are transmitted through the shafts. When you talk of cars like Mercedes, BMW's and high end Maybach's Torque can touch much more than 100 Nm's. 12 cylinders V's could not be "Auto-Transmitted" using a simple or complicated CVT...
Something new was needed...and that will be apart of the next blog ofcourse :P
Lets take the case of the simple Hero puch or the TVS 50.....Can we call it an automatic transmission....?
Not really...however to some extent yes.
How does based on throttle the vehicle start moving?
This is because of a clutch that engages as the RPM increases. Such a clutch is called Centrifugal Clutch. Normally the clutch is disengaged. Which means that no power from the engine will be fed to the chain drive. However as the RPM increases a certain threshold the clutch engages. With the clutch engaging the power is transferred to the wheels. This is a very basic of how we can eliminate the manual clutch ( our initial aim ....). As it is clear that the centrifugal clutch will wear out with time and that means RPM points at which the power will get transferred to you chain drive will vary with time. The second disadvantage is that this method cannot transfer huge amount of torque from the engine shaft to the output shaft. I am not really using the term Transmission shaft because this is not a "Transmisison" in classical sense.
What are the other methods?
How about Kinetic Honda that has been ruling the roads since i was a kid?
Well a Kinetic Honda uses a different mechanism. It uses what is known as a belt drive...( atleast that is what i was told. I am not 100% sure!!). This is fed to a Stepped pulley or Coned Pulley. This coned pulley will be able to provided different Pulley Ratios based on which point of the pulley is used to Tap the output. A the most broad end of the pulley the Torque transmission will be less and a the thinnest end of the pulley the Torque transmission maximum. Centrifugal clutch is still used here.
Does that mean CVT ( The stuff we talk ed about...Continuous Variable Transmission) is a cheap and dirty technology?
No absolutely not. Like any other technology based on how much complexity is added one can make the system very sophisticated. The commonly used CVT's in bikes like Honda Activa, Honda Dio, Kinetec etc are fairly simple. However, some really complicated stuff from Audi can be found here and remember the core is still same....a coned pulley...
After taking care of these two aspects...i.e. some kind of autoclutch and a automatically shifting gearbox the other biggest challenge was to ensure that high amounts of torques are transmitted through the shafts. When you talk of cars like Mercedes, BMW's and high end Maybach's Torque can touch much more than 100 Nm's. 12 cylinders V's could not be "Auto-Transmitted" using a simple or complicated CVT...
Something new was needed...and that will be apart of the next blog ofcourse :P
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