Question

What are advantages and disadvantages of stepping transmission mechanism and variable transmission mechanism? Why don’t we use variable transmission mechanism on CNC machine?

Answer 1

Hello my dear student i hope you will understand the descriptions I mentioned below, if you have any doubts please feel free to ask me.please give me a thumbs up if you are satisfied.

CONTINUOUSLY VARIABLE TRANSMISSION

A CVT or Continuously Variable Transmission is an automatic, single speed, and gearless transmission that can shift through an infinite number of gear ratios. This ability to seamlessly shift through these different gears provides a number of benefits including extremely smooth shifts and exceptional fuel economy. However, it can also come with many disadvantages.

How It Works…

The CVT works similar to the way the transmission on a snowmobile works, in that there is a pulley system with cones at each pulley, all connected by a chain belt. The cone moves closer together or further apart to increase or decrease the diameter at which the belt operates. This is how the unit changes gear ratios and allows the unit to quickly “shift” into the necessary gear ratio to allow for either increased power and/or increased fuel economy when needed. The important thing to note is that although it is considered an automatic transmission it does not shift at all like a traditional gearbox.

CVT Transmission Pros and Cons

ADVANTAGES

Optimal Power Delivery: With this type of transmission, your car is always in the right gear. Unlike an automatic or even a manual unit, the CVT is programmed to keep the engine’s speed square in its optimal power band, rather than running the tachometer needle from idle to redline when a driver needs acceleration. This arguably provides better performance in some situations, especially when passing another vehicle.

Economy Advantages: A CVT is often more efficient than its traditional counterpart, at least in terms of fuel economy, by dint of always placing a vehicle’s engine speed at the right place at the right time. Cruising at a steady freeway speed, drivers of CVT-equipped cars will find their tachometers reading a very low number, which is great for efficiency.

Simpler Construction: The total number of mechanical parts in a CVT are lower compared to a typical planetary-gearset transmission. Devoid of the usual phalanx of gears and cogs, a CVT box uses a brace of adjustable conical pulleys connected by a steel chain or belt. Depending on the vehicle’s speed, the sides of each pulley move toward or away from each other, varying the drive ratio, passes the chain into a groove formed between the pulleys. This mechanical simplicity means things tend to go wrong less often.

Lighter Weight: Thanks to their innards, CVTs are often lighter and more compact than a conventional automatic transmission. Dropping weight from a car’s powertrain has several advantages, not the least of which is a bump in fuel economy.

Smooth Shifter: Anyone who’s awkwardly poked their left foot at a clutch pedal knows the embarrassment of roughly grabbing the next gear. Your passenger snaps about like a bobblehead, wondering why you’re driving like a pro-demolition derby driver. CVTs, thanks to not having any gears at all, move seamlessly from idle to peak power.

DISADVANTAGES

Sounds Like It’s Busted: CVTs have a natural disadvantage because some of them are programmed in such a way that makes consumers think they are broken or working improperly. A traditionally programmed CVT absent of any stepped gear feeling may cause a driver to unfairly misjudge its normal operating performance as a sign of unreliability.

Noisy Operation: Many drivers have complained about the CVT propensity to “hang” at a high rpm, causing the engine to rev wildly under acceleration. This is an inherent trait of all CVTs, even those programmed with simulated stepped gears. Extra noise is generally unwelcome in any car unless it is the rumble of a powerful engine.

Expensive Maintenance: Upkeep and running costs of a CVT tend to be quite low but actual repairs can be more expensive thanks to parts that are generally more expensive to replace.Finding a competent transmission specialist who knows their way around a CVT with the same confidence as a traditional manual or
automatic may also be a challenge.

Gearbox drive or stepped transmission mechanism

The gear drives have a very special and prominent place. This is the most preferred technology when you need to transmit considerable power over a short distance with a constant velocity ratio. The mechanism of gear drives is quite simple the teeth, which are cut on the blanks of the gear wheel, mesh with each other to transmit power. To avoid slipping, the projections on one disc mesh with the recesses on other disc in gear drives.

This technology uses different types of gears for power transmission. In fact, it can transmit power not only between parallel shafts, but also between non-parallel, co-planar, and intersecting etc. shafts.

ADVANTAGES

They are positive and non-slip drives

Large and constant velocity ratio of 60:1 can be obtained by using gear trains with minimum space

Gear drives are mechanically strong, allowing scopes for lifting higher loads

Longer service life compared to both belt and chain drives

They can transmit large power

Gear drives have high transmission efficiency

They can transmit motion over small centre distance of shafts

These drives are ideal for low, medium, high power transmission

Gears can transmit motion even between non-parallel intersecting shafts

These are the most compact compared to belt and chain drives

DISADVANTAGES:

Gear drives cannot be used for shafts with large center distances

They are not ideal for large velocities

These drives require regular lubrication and a more complicated process of applying it

Noise and vibrations are increased at a high speed

They are less economical compared to belt and chain drives

Using multiple gears increase the machine’s overall weight

They have no flexibility

Not suitable for transmitting motion over a large distance

Some part of the machine can get permanently damaged because of the toothed wheel of gears. This is more common in case of excessive loading

REASON FOR NOT USING CVT IN CNC

The main reason for avoiding of cvt drives in cnc machines that it cannot bear the high machining load.If the load increases the cvt belt will fail to transmit the power.

And also the cvt cannot be automated the speed cannot be maintained constantly because the variation in load takes place.

For a specified operation there should be a constant speed throughout the process it cannot be achieved using cvt.