Continuously Variable Transmission

Continuously Variable Transmission

Continuously Variable Transmission (Transaxle), also known as CVT, is a type of automatic transmission that gives improved performance within its power and allows smoother driving and supports a better fuel economy. The following paper is based on my understanding of a CVT. There are several types of CVT engines; Variable-diameter pulley (VDP) or Reeves drive, Magnetic CVT (MCVT), Toroidal or Roller-based CVT (extroid CVT), Hydrostatic CVT and a Ratcheting CVT. In this essay we will refer to the VDP which is commonly used in our vehicles today. I will research the history, full operations and internal components to understand its advantages and disadvantages over other transmissions.

The History of CVT

Well improved and enhanced continuously variable transmissions were introduced in the late 1990s and early 2000s. Now recognised in our everyday vehicles, the CVT is found in a Honda, Ford, Nissan and much more. In the early stages of the CVT, there were complications due to limitations of technology and was then considered inappropriate to use with engines whose engine speed power was greater than 100. The CVT, in 1490, was first sketched by Leonardo DaVinci and was then used in the late 1950 by a Dutch automaker.

Leonardo DaVinci

What is a CVT?

As defined above in the introduction, a CVT is well enhanced than a “traditional” automatic. The CVT is a transmission that will change gear ratio without a person hearing or feeling it shift. The gear ratios will move from the lowest to the highest to determine the engine and car speed. This is an advantage when working with a CVT as it enables outstanding acceleration and breaking.

While using a CVT, the driving shaft will retain a consistent velocity to enable a variety of velocity outputs. This will support the engine to work to its highest quality of RPMs (revolutions per minute); to allow speed changes to occur. In the view of a driver, it is an advantage as the CVT does not require a clutch pedal however Simpson & May (2010) included that a few vehicles include a clutch to offer neutral stances on a motorcycle… which is useful when idling.

Internal Components and Full Operations

One of the components found in the CVT is called a final drive and reduction gears. Now this reduction gears system has two reduction gears which is called a driver and driven. This is also used to calculate the ratio of the moving gears. There is also a final drive gear inside the CVT and also the speedometer which is located on the differential case. All the gears are helical except for the reverse idler, which is made of cast harden medal. You will notice when you reverse in a manual transmission, you will hear the spur gears.

Another component inside the CVT is called the steel belt and pulley system. Now the pulley system consists of the input and output pulley otherwise known as the primary or secondary. The belt is slightly on an angle of 11 degrees which fits in the groove of the pulley. The pulley both input and output has a fixed half and sliding half. As the gears are widening and expanding in a narrow direction, the CVT enables for a smooth change in the gears. The pulley and belt system supports a successful outcome which allows CVT users to not feel the shifting or changes of the gears.

The belt consists of approximately 280 steel blocks which are held together by two laminated steel bands. Basically when pressure is put onto the output pulley (secondary), the steel blocks tighten together creating a tight grip and therefore forcing the pulley upwards.  Once the pull is created, the steel blocks will clam together and force the power into the bands, yet the bands will retain the friction needed to continue driving. Inside the internal components, as stated above in the final drive, there are common gears called helical and spurs. These are the most common gears used in a transmission. The helical enables good grip and works well whereas spurs causes friction against the shaft. A great example of the spur is when you hear the reversal in manual transmission.

The steel belt and pulley system is controlled by the ECU (electronic control unit) which is found inside the CVT. This will take into account the engine speed, engine torque also the position of the accelerator or where the brake pedal is at the moment. For example, a magnetic clutch will give drive between the engine and the transmission.

The electronic power clutch, in my understanding, has a small gap between the driver and driven gears which receives iron powder. This powder plays an important part as it enables magnetism within the drive to give power. This will be connected to the engine or the drive to enable power to be transmitted within it. Therefore more powder equal more power which gives more solidification nevertheless too much solidification will or can cause the clutch to lock up.

Most cars will be using the VDP. The pulleys within the VDP will be in reverse opposites of each other with a metal belt running between the pulleys. One pulley will be connected to drive and the other to engine (input and output shaft). Each half is capable of moving to allow a ratio of the gears to move upwards to offer further power.

Advantages and Disadvantages

The following advantages and disadvantages were found in our textbook “Automotive Mechanics” by Ed May & Les Simpson (Volume 1 and 2). Resources were also found in the textbook “Continuously Variable Transmission (CVT)” by Bruce D Anderson and John R Maten.

The advantages are as follows:

·         CVT changes the engine speed when required to ensure it is working at a high performance level

·         The torque also works at the highest level

·         Great fuel economy

·         Does not require a clutch pedal

·         Ensures smoother driving allowing the engine to increase to its fullest power

·         Quicker acceleration which is faster than a ‘normal’ automatic or manual transmission

According to research, the one disadvantage found is acceptance by the customers. As many customers will usually purchase a transmission which was either manual or automatic; they were not familiar to the unusual noises that arose from the engine when increasing the power. The noise coming from the hood when a CVT is in place, is a noise which sounds of a clutch that may have slipped off or a transmission which had slided therefore allowing the user to believe there was something incorrect occurring inside the hood of the car and problems may happen thereafter. The noise occurring is not what the customer believes is happening however is what is considered normal for a CVT transmission.

                                    

As shown above, the advantages of using a CVT are better than those of other transmissions. In this research, I’ve learnt that a traditional automatic or manual car when flooring will cause an impulsive force of power which causes the vehicle to stagger and stumble whereas the CVT enables efficient and swift boosts to the engine to work smoothly. According to Harris (2007), a few drivers have the impression that the car is running at a slower pace however Harris mentions that a CVT will normally out-accelerate an automatic or manual.

Conclusion

The history of Continuously Variable Transmission did not begin in such a great note; with it having limited technology and therefore restricting vehicles with less than 100 horsepower to use it. There were anxieties in regards to the noise that was generated by the CVT transmission and concerns over the reliability to whether or not it will endure long-term. Nevertheless advanced technology was later introduced enabling a robust CVT to be used in today’s vehicles. The VDP (Variable-Diameter Pulley) is the most common used CVT today and as it does not require a “given road speed directly to a given engine speed”, the CVT can differ within its engine speed to retrieve the highest power in addition  to increasing effective fuel economy. When choosing a car, both a CVT and a DSG transmission have a range of advantages and disadvantages, therefore when choosing a car it depends solely on the users’ personality and needs. In my opinion, I would choose a CVT as I prefer the quietness and the ability to drive smoothly.