Gears can also achieve infinitely variable speed, do you believe? CVT also withstands a torque of 1000 N.m. Do you believe it? I am afraid many people think that this statement is a fantasy. And a new thing called the movable tooth CVT stepless gearbox (live tooth CVT, later abbreviated) can realize this seemingly unreliable transmission mode, and has applied for the United States, Germany, Invention patents of thirteen countries including Britain, France and Japan. Today we walked into a high-tech company called Viedi, located in Yizhuang, to take a look at what this little-known "weird guy" looks like.
Can "gear" achieve infinitely variable speed?
We are no stranger to the traditional CVT continuously variable transmission, which achieves stepless shifting mainly through two variable slot width main and driven ratchets and steel belts or chains. The main and driven ratchets can change the width of the V-groove by sliding, so that the radius of gyration of the steel strip or chain on the main and driven ratchets changes, and the ratio of the radius of gyration is what we call the transmission ratio, and the radius of gyration becomes The natural gear ratio has also changed, and since the change is continuous and there are no breakpoints, we call it a continuously variable shift. Generally, the gear transmission is not the case, even if there are more gears, there will be a break point in the transmission ratio, so the effect of stepless speed change cannot be achieved. Why can this new thing called the movable tooth CVT achieve infinitely variable gear through the gear? Let's continue reading.
Before introducing the mystery, we must first understand one of the most central concepts in this gearbox - "live teeth." We all know that the traditional gear transmission is the power transmission by the tooth surface of the two rigid gears, and the transmission mode of the movable tooth CVT is significantly different from our usual gear transmission.
First of all, it is not two gears in the traditional sense, but consists of a toothed drive chain and a part called a "toothed tooth unit". Secondly, its teeth are "one dead and one live", "dead teeth" refers to the teeth on the drive chain, its characteristics are just like the teeth on our general gear, hard and contoured; and "live teeth" refers to A very thin movable slide on the "toothed tooth unit". When it comes into contact with the "dead tooth", these slides will move due to the pressure, forming a cogging with the same "dead tooth" contour. "Swallow it."
Knowing what is a "live tooth", the next drive principle is very simple. The transmission of the movable tooth CVT is very similar to the traditional CVT at first glance. The components that realize the shifting are also similar to the CVT we usually see. It mainly consists of the main and driven ratchet, the transmission chain and the movable tooth unit. The main and driven ratchets are connected by a chain, and the surface is provided with a groove for accommodating the movable tooth unit, and the movable tooth unit is slidable along the groove, and the movable tooth portion on the surface is in contact with the transmission chain.
During the operation, the movable tooth unit on the ratchet rotates following the ratchet, and the transmission chain is only able to rotate with the tooth groove formed by the movable tooth unit, and can only rotate with it, thereby realizing the transmission of force. When the movable tooth unit is disengaged from the chain, the slide piece will be pulled to the position before compression under the action of centrifugal force to realize automatic reset. When the speed ratio needs to be changed during driving, the movable tooth CVT will change the width of the V-shaped groove by the ratcheting motion like the conventional CVT, and realize the continuous change of the transmission ratio. Article Tags: Gearbox Technology â—
Can the torque really reach 1000N.m?
Understand the transmission process, we will definitely ask, this transmission method does not look too much difference with the traditional CVT, what is the difference in the bone? We all know that the traditional CVT relies on the friction generated by the steel strip or chain on the main driven ratchet surface to achieve power transmission. This type of transmission is limited by the material and its own principle, and the friction generated is not infinite. This leads to a limited range of torque transmission that can be achieved by conventional CVT. If the torque is too large, the steel strip or chain will be insufficient due to friction. And slipping occurs.
At present, the maximum torque transmission that can be achieved by conventional CVT is no more than 450N.m. This kind of movable tooth CVT is not. Because it is based on the principle of gear transmission, it avoids the limitation of friction to the transmission torque. In theory, as long as the transmission chain and The meshing teeth are not damaged by excessive force and can be effectively driven. According to our understanding, the prototypes that are currently manufactured can deliver more than 1000 N.m of torque, which is not possible with traditional CVT.
In order to ensure that such a large torque will not cause damage to the shifting mechanism, the engineering staff is also painstaking. The first question is how the drive chain can not be pulled off under high torque, and it has undergone a period of repeated modification around this problem.
At the beginning of the development of this movable tooth CVT, it was not driven by a chain, but it was similar to a steel belt on a conventional CVT, and it was very similar. The steel strips of different sizes are put together by metal strips to form a "tooth belt", which is used for power transmission. In the high-torque experiment, the fate of this metal belt is extremely unfortunate. Because the metal belt itself has limited strength, it will not be able to withstand how long it will be cut off cleanly, and the metal piece interlaced on it is also made seven thousand. Eight down, which made the development stage once in trouble in the initial stage. After repeated trials, we finally chose the chain drive method we saw today.
However, the chain transmission method is not perfect. Anyone who rides a bicycle knows that the most vulnerable part of the chain is the connection between each section. This part is very fragile. It is very likely that the entire chain cannot be used due to the breakage of the connection point of a certain section. . At present, the chain used by the CVT is generally connected by a very thin pin at the connection point. This connection method is relatively expensive and is not very reliable under high torque conditions. Therefore, after undergoing numerous baptisms of failure, the engineers finally solved this problem by fixing the outermost chain of the chain to the fixed connection.
Although the problem of the chain has been solved, the task of withstanding high torque is not only the chain side, but the “live tooth†slide that we mentioned earlier is even more difficult in this respect. Since the slider is very thin, once it happens that only one piece of the sheet is stressed during operation, it is certain that the sheet is in jeopardy. However, the improvement in this area is much smoother and simpler than the chain, and the outermost sheet can be thickened. In theory, this sheet is also the key to high torque.
No hydraulic system, high transmission efficiency
In addition to increased torque, this live tooth CVT has a significant feature that the efficiency of transmitting power is much higher than that of conventional CVT gearboxes. This is because the CVT eliminates the hydraulic control used by conventional CVTs. system. The efficiency loss of CVT mainly comes from controlling hydraulic loss, lubrication and agitation loss, mechanical transmission loss, etc., and controlling hydraulic loss accounts for a large proportion. For example, in the case of the conventional CVT transmission, the loss of the pressing force caused by the slippage of the steel strip and the loss of the internal control oil passage are all in this category, and such energy consumption seriously restricts the improvement of the CVT efficiency.
The movable tooth CVT is driven by the gear principle, and does not need to use a large force to compress the ratchet in order to generate the friction required for the transmission. Therefore, the hydraulic system in the conventional CVT is eliminated, and only the motor is used to control the ratchet movement and change. The width of the V-shaped groove is sufficient. This change can greatly improve the transmission efficiency. The engineers involved in research and development revealed that the current transmission efficiency of the movable tooth CVT can reach 96%, which is close to the efficiency level of the manual transmission.
However, some people may be questioned here. Although the movable tooth CVT is not driven by friction, during operation, the chain will hold the live tooth unit and move the ratchet outward. In order to keep the ratchet from running, it still takes a lot of pressure to live it. This kind of questioning is absolutely reliable, and it is theoretically true, but the engineers told me that this kind of worry is superfluous because they solved the problem with a simple design.
We can divide the main and driven ratchets into four parts, each of which is divided into two halves by the drive chain. These four parts can be divided into two groups according to the diagonal line, the upper part of the active ratchet and the lower part of the driven ratchet are one group, and the rest are the other group. One of them is a fixed wheel that is integrated with the main and driven shafts, and the other is a movable wheel that is placed on the main and driven shafts. The change of the width of the V-shaped groove is realized by the movement of the movable wheel.
In the transmission, the chain squeezes the ratchet, and the fixed wheel that is integrated with the shaft must not be squeezed, so only the movable wheel is in danger of being squeezed. The engineer used a metal plate to connect the two movable wheels together to become a whole, so that the diagonally distributed movable wheels would cancel each other through the metal plates when subjected to the opposite pressing force. This is like a person standing in the middle of two cars, you push the left and right hands, the two cars will move to the left and right at the same time, but if you use the chain to connect the two cars together, then push the left and right cars from the middle, the car It won't move. At the same time, there is another advantage of connecting together, that is, only one control motor can control the V-shaped groove change of the main and driven ratchets, and when the width of one end becomes larger, the other end will inevitably become smaller.
In addition, the movable tooth CVT can also not use the hydraulic torque converter. The manual clutch with the pressure plate clutch can ensure the transmission system demand, so that the hydraulic loss generated by the hydraulic torque converter is also Can be eliminated. However, the engineers told me that in the future, they can still decide whether to use a hydraulic torque converter according to the needs of different models. This is not a difficult thing for the gearbox. Article Tags: Gearbox Technology â—
Will the cost be unacceptable?
The live tooth CVT without the hydraulic system is much less than the conventional CVT parts. According to engineering personnel, this CVT has only a hundred parts, which is nearly half less than the traditional CVT, and the machining accuracy of the ratchet surface is also reduced because it no longer relies on friction transmission. As a result, the cost will naturally be saved a lot. It is understood that the movable tooth CVT has a relatively large torque transmission, and its positioning is mainly for medium and heavy vehicles. Due to the use and market positioning of these vehicles, the cost control is much stricter than that of a family car. If the cost is too high, it may be high and low, and no one cares.
High speed drive is still difficult
Although this kind of movable tooth CVT has its own unique advantages in terms of torque, efficiency and cost, the engineers bluntly say that there are still some difficulties that have not been completely solved in the research and development. How to ensure that it can work effectively at high speed is a subject to be further studied.
The maximum speed that can be achieved by this type of movable tooth CVT is about 5000 rpm, and the engine speed of the conventional domestic car is generally higher than this value, which makes the current movable tooth CVT still to be improved in the field of higher speed engines. . The reason is mainly because the movable teeth of the gearbox are automatically reset by the action of centrifugal force when they are disengaged from the chain. This kind of motion will affect the torque transmission at high speed, causing pulsation and power transmission. Unstable phenomena, but researchers have developed a detailed design for this problem.
Actual test, the drive is smoother
Whether it is good or bad, you have to know it yourself. The engineering staff has already prepared an experimental prototype car. This is not unexpected. After all, this kind of thing that I have never seen before is not reliable. No one is sure, but after seeing the car, it still makes I was surprised that it was a Dongfeng warrior, this is a military car! After the explanation, I know that the reason why I chose this car is mainly because the car is equipped with a 6.5L diesel engine and the torque can reach 550N.m. This value is unattainable by the traditional CVT. It is more representative. Just go ahead.
However, during the test, I didn't drive, just try the experience. It's a bit of a pity, but it does have something to do. Due to financial problems, the high development cost of the electronic control system was temporarily unaffordable, so the gearbox mounted on the experimental vehicle was not equipped with this aspect, and the transmission could only be controlled by manual operation. For me who have never been in contact with it, I am afraid I don't know how to call it up.
When the vehicle just started, there was some jitter. The engineers told me that this was mainly because the clutch could only be adjusted manually, and then I pointed the button that controls the clutch. After the driving, the vehicle was smooth, and the discomfort caused by the change of the transmission ratio was not felt during the speed-increasing process. The transmission monitoring display also clearly marked the whole process of the speed ratio change, because there is no electronic control system. The aid, the test car just simulated 10 gears through a simple program, so that we have a more intuitive understanding of gear changes.
Under this manual control condition, the maximum speed of the whole process reached 50km/h, and the current transmission gearbox can reach a speed of 80km/h. The entire test was about 2km away, and the ride feels not much different from the traditional CVT gearbox.
In the process of communication, we also learned that engineers are still developing a continuously variable transmission with the principle of leverage. In general, the speed ratio change is achieved by changing the center point of the lever. However, due to the complexity of this gearbox structure and its immatureness, no more design details have been announced.
In general, this kind of continuously variable transmission called the movable tooth CVT theoretically realizes the idea of ​​gear stepless speed change. Its own characteristics of high torque and high efficiency are also worthy of our recognition, but its own existence. Some technical difficulties still make us difficult to predict whether this CVT can be approached by ordinary people, and how to transform it into products that can be industrially produced, and to ensure product consistency, is a problem that must be solved on the road of development. These problems will gradually be revealed as time goes by and research progresses. Whether or not it will succeed will be accepted by consumers, and we can only wait and see.
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