CVT gearbox is both familiar and unfamiliar to most people. It is said that the familiarity is because it has a wide range of applications and is very close to our lives; and the unfamiliarity is because the types of CVT gearboxes are very diverse, and common CVTs are still familiar with it. There are many misunderstandings.
"Continuously Variable Transmission" is the full name of CVT, which translates to continuously variable transmission. In a broad sense, it can be called CVT gearbox as long as it conforms to the literal meaning. So in addition to the well-known two ratchets connected by steel belt or steel chain, there are other forms of CVT gearboxes.
first talked about an E-CVT that we are relatively familiar with. Honda iMMD and Toyota THS hybrid power systems use this set of gearboxes. "E" stands for electronic, replacing the mechanical structure with an electric motor to change the speed and torque of the engine. One thing to add here is that even hybrid models require a mechanism to adjust the engine speed and torque. Most hybrid vehicles other than Toyota and Honda need a set of gearboxes because their electric motors can only adjust the torque and cannot control the engine speed.
Rolling Ball/Rolling Ball CVT
After talking about the familiar ones, let's take a look at the unfamiliar ones. The first is the ball/ball CVT. This gearbox also does not have a ratchet and transmission belt. Its core component is multiple balls. We know that the linear velocity of a sphere whose surface is different from the axis of rotation is also different. The ball/ball CVT gearbox uses this principle. By changing the angle of the rotating shaft, the linear velocity of the input and output ends is changed, thereby realizing the functions of speed change and torque change. The language description of
may be a bit abstract. Let’s look at two pictures:
. The first one is a ball/ball CVT model, and the second one is a schematic diagram of power transmission and how to change speed. If it is not particularly clear, imagine this thing as the earth under our feet. If the input end is in Sanya, China in the northern hemisphere, and the output end is in the Strait of Magellan in the southern hemisphere, after one revolution, the distance of the person in Guangzhou must be greater than that of the person navigating in the Strait of Magellan. That is to say, a big gear is connected to a small gear, which is equivalent to the over-comparison of the AT gearbox.
On the contrary, if you need to amplify the torque to start or climb, you need to go north at the input end, such as to Mohe, Heilongjiang, and the output end close to the equator, such as in Lima, the capital of Peru. At this time, it becomes a situation where a small gear is connected to a large gear to achieve the purpose of speed reduction and torque increase. The biggest advantage of
ball/ball CVT lies in its simple structure and small size, which can be as big as the palm of your hand. So it is mainly used for scooters, but also many models of cars and ships. Of course, there are also big shortcomings, such as narrow speed range and lower torque tolerance, so it is only used for small machinery.
However, there are also companies trying to expand the ball/ball CVT function. I remember seeing planetary gearboxes at the auto show a few years ago. In fact, the planetary gear in the planetary gear set is replaced with a sphere. The principle is the same as the previous one, and the operation mode is the same as that of the planetary gear. Because this set of transmission mechanism is very small and exquisite, so it can be connected in series with a torque converter or a traditional gearbox. At that time, this ingenious design impressed me deeply.
Cone-ring CVT
Talking about ball/ball CVT gearboxes, let’s talk about a new thing "friction cone transmission", which is also a very large branch of continuously variable transmission, which has many evolved products. Related to automobiles is the cone ring transmission "cone ring transmission". Before introducing
, let’s briefly review the structure of traditional CVT gearboxes, because they are somewhat related to cone ring gearboxes.
Traditional CVT gearboxes have a V-shaped groove on both the driving and driven ratchets. The width of the groove is changed through the hydraulic system to achieve different speed ratios. The cone ring gearbox can be regarded as a simplified version of the CVT gearbox. The driving and driven ratchets are replaced by two cone wheels, and the steel belt is replaced by a steel ring.
This is a top view. The driving and driven bevel wheels are connected by a steel ring in the middle, and the steel ring can move between the two bevel wheels to achieve different speed ratios. Compared to traditional CVTGearbox, this gearshift mechanism is simpler and lighter, and the overall efficiency will be higher.
Speaking of efficiency, it just corrects a misunderstanding about CVT gearboxes. Many people think that the low transmission efficiency of CVT is caused by the slip between the ratchet wheel and the steel belt. This is a big misunderstanding. If there is a slip between the ratchet and the steel belt, it is not that the power response is slow and the accelerator does not go away, but the transmission starts the protection program, or the vehicle directly squats, which is a very serious problem.
Why do you say that the efficiency of the CVT gearbox is not high? I also said that changing the speed ratio is done by the hydraulic system, and this system consumes a lot of energy. Of course, this part of the energy comes from the engine, so it will There is power loss, which will reduce efficiency. The
cone ring gearbox does not require this hydraulic system, so the efficiency will be improved, and it also has the advantages of simple structure, low price, and smooth speed change. As for the shortcomings, it is similar to the ball/ball CVT, so the micro, small car and cone The ring gearbox is very good.
If you still don't know the working principle of cone-ring gearbox, you can recommend a video: https://www.bilibili.com/video/av65061553?p=1. Simple, intuitive, and very easy to understand.
CVT is not a "soft girl"
peculiar this kind of talk is over, let's talk about the traditional CVT gearbox again. I am quite fascinated by CVT gearboxes. Think about what a perfect state of "continuously variable" is.
First of all, this means that there is no power interruption during gear shifting. I remember reading car magazines very early on. A very important parameter for supercars is shift time. Only the CVT gearbox can reduce this parameter to 0.
Secondly, "continuously variable" changes the power output of the engine from a ladder to a slide, which means that the engine can always work in the most correct range. The reason why CVT saves fuel is the same. It can make the engine work in the highest thermal efficiency range to the maximum. It is a concept with Toyota and Honda's hybrid power. In addition, it is also very helpful for power output. CVT gearboxes can lock the speed at the maximum power point of the engine for twisting, which is also a skill that other gearboxes do not have.
has no power interruption and can lock the maximum power point output. Both of these points prove that CVT is also a good hand in sports. In the 1990s, the Williams team tried to put the CVT gearbox on the F1 car. The test driver "Cookhard" gave this kind of gearbox extremely high evaluation, so CVT is not a weak, weak and soft girl.
The reason why current performance cars and supercars do not use CVT is still a problem of efficiency. This is also the biggest weakness of CVT gearboxes. To solve this problem, it depends on whether there is any major breakthrough in material science.
The story about CVT is not over yet. Some people say that CVT was invented by the Italian painter Leonardo da Vinci. It can be said as an anecdote, but it is not the case if it is true. Da Vinci only proposed the concept of a continuously variable transmission system, which is quite different from today's CVT gearboxes. The modern ratchet steel belt CVT gearbox was designed by Hub vanDoorne in 1958.
To give an inappropriate example, Da Vinci just told a story about Chang'e and the moon, which is totally different from human exploration and moon landing.
This article comes from the author of Autohome and does not represent the viewpoint of Autohome.
