Before supercharging technology was introduced into China, Japanese, Korean and self-owned cars all liked to put the logo of VVT-i, CVVT and DVVT on the front fender, which would arouse interest and ask what these letters mean. I'm afraid the sales will last for half an hour, making you want to take the car away with a bag of money!
In fact, VVT refers to variable valve timing, which may be easier to understand. The intake and exhaust of the engine are controlled by two corresponding valves. The technical term is called valves. When the valves are opened and closed, they are controlled by the camshaft, which works for the crankshaft, and it follows the crankshaft, but the workload is only half that of the crankshaft.
this mode of working closely following the crankshaft is not efficient, because you don't need to go to work early in the morning when the business is not busy, just like who goes to the barbecue stall during the day, isn't it a waste of time to ask you to set up a stall early in the morning? The camshaft that can control the valve is only a part-time worker after all. The crankshaft (boss) goes to work normally. Does the camshaft dare to be late? Even if you don't have a business valve, you can go to work normally. VVT will work 8 hours a day, and get off work early, and vice versa.
after this explanation, does it feel that VVT is not very smart either? We can imagine such a scene, the total number of customers entering the store in a day is not much, but there are customers very late, and the clerk shuts down because he only works for 8 hours, which leads to the loss of customers, and finally reduces the turnover. This is the true portrayal of the traditional variable valve timing operation mode.
although the engine with VVT technology has better power and more fuel economy, it is still worse than the ideal state. I thought that the internal combustion engine was coming to an end, and no one except Japanese manufacturers was willing to bet on gasoline engines. As a result, Hyundai went upstream last year and introduced CVVD technology.
what is p>CVVD? To put it simply, it is a technology that can make the valve work overtime. CVVD can make the valve work overtime whether the valve goes to work early or at night, so CVVD is called continuously variable adjustment of valve duration. So the question is, what benefits does this technology bring to the engine?
compared with CVVT, CVVD can shorten the valve opening time and improve the power performance by 4% in performance mode, and prolong the valve opening time and improve the fuel economy by 5% in economy mode. These data are very abstract. We took a photo from modern official website to explain the influence of the valve switch.
The principle of the engine is very similar to that of an injector. Air intake means that the piston handle of the injector is pulled down. If the top of the injector is blocked by hand in the process of pulling down, it will take a lot of effort to pull the piston handle. If the piston handle is pushed up, it will also take a lot of effort. This simple principle is the so-called pumping loss of the engine, except that the engine sucks gas and the injector sucks liquid.
In normal injection, the general logic is to inject as much medicine as possible, which can be indirectly understood as pushing up as much as the plunger handle of the syringe is pulled down. But after all, no one in the engine is so smart. No matter how much power is needed, the piston moves from top dead center to bottom dead center, and so on. If the valve is as brainless as the piston, it hurts each other, and it consumes oil anyway.
the p>CVVD operation mode is like this, with low speed and low load, and the valve keeps opening for a long time, so that the pumping loss is small during the downward suction and upward compression of the piston, thus reducing the fuel consumption. Driving at high speed and high load, the valve keeps opening for a short time, and more air is compressed to generate stronger power. The reason is as simple as that.
Everyone understands the truth. The problem is that the valve is controlled by the camshaft, and the camshaft works for the crankshaft. This fixed relationship makes it impossible for the valve to change its operation mode. If you have seen the engine valve timing system, you should know that the cam is directly fixed on the camshaft, and the cam speed is not controlled by itself at all, so it is impossible to extend the valve duration.
The idea of modern CVVD is to separate the camshaft from the cam, which is also a split structure from the previous integrated structure. There is an intermediary between the cam and the camshaft, that is, the eccentric actuator.
According to the structural drawing published by official website, the structure of CCVD camshaft is really different from the traditional camshaft, and what is more unique is that CCVD is also installed in the CVVD variable control unit.
From this structural drawing, we can more intuitively understand the special features of CCVD camshaft, and the most special feature on CCVD is the orange eccentric wheel in the drawing, which is the core part of CVVD and the most abstract structure.
The inside of this deflection wheel is actually a lever structure. When you see the official schematic diagram, it is estimated that you are all puzzled. In this figure, the yellow circle is connected to the camshaft, the orange circle is connected to the cam, and the orange and yellow circles are connected through the lever structure. This lever structure just achieves the eccentric effect.
The lever is used to connect two different rotating parts. This design was once applied to the driving wheel of the train, but the previous train was simply connected at two points, so the wheel speed remained the same. The connecting rod structure inside the modern CVVD eccentric wheel is 6-point connection, two of which are sliding connections.
The official specially made a dynamic diagram to help fans understand how the cam speed is out of sync with the camshaft. As can be seen from the dynamic diagram, the left, middle and right eccentric wheels have exactly the same structure, and they all have three connecting rods of purple, blue and orange. The uniqueness lies in that the three eccentric wheels rotate at the same speed, but the yellow cam on the left is the slowest and the one on the right is the fastest.
the orange connecting rod is slidably connected with both ends of the purple and blue connecting rods, while one end of the purple and blue connecting rods is connected with the cam, and the camshaft is fixed with the connecting point in the middle of the orange connecting rod. This lever mechanism separates the cam from the camshaft. Because the camshaft can't move, as long as the control mechanism of CVVD pushes the eccentric wheel left and right, the orange sliding connecting rod will be displaced at both ends of the purple and blue connecting rods, and the original angular velocity of the camshaft will be converted into the displacement of the orange lever and the angular velocity of the other two connecting rods.
A strange thing happened. The schematic diagram published by the government in front seems to be different from the CVVD structural plan published later. What about the orange lever?
After some tossing, we found the patent application drawing of CVVD, and the original purple lever is No.62 in the drawing, which is inserted in the camshaft. The blue lever is position 82b. 82a and 74 can just move horizontally, which becomes the orange sliding lever in concept.
The so-called lever is actually very compact, and as can be seen from the patent drawing, the camshaft transmits the angular velocity to the cams 72 and 71 through 88, 82a and 74. It turns out that the camshaft moves in a circular motion, but the circular motion of the camshaft is transformed into an elliptical motion through this lever mechanism, which finally reduces the cam synchronization speed.
when the CVVD control mechanism pushes the eccentric to the left and right, the position No.62 in the figure acts as the aforementioned blue lever. Since the position of the camshaft is fixed, when the eccentric moves to the right and left, the timing angle of the camshaft is also changed. Once the No.62 part moves to the left and right and fixes its position, the rotation of 82b is no longer a perfect circle but an ellipse, and 82b is just connected with the cam, which converts the angular velocity of the circular camshaft into the angular velocity of the elliptical cam.
when the angular velocity of the cam is not synchronized with the camshaft, it becomes the time when the valve opens, that is, the working hours and working hours.
just like Nissan VC-Turbo, the complicated linkage mechanism puts forward higher requirements for manufacturing technology, for example, when the engine speed is 6rpm, the cam speed is 3rpm. The control mechanisms of CCVD camshaft and CVVD are high-speed rotating parts.
in order to realize the continuous variable valve duration, the modern cam, camshaft, eccentric wheel and CVVD control mechanism are designed into multiple solid and hollow structures. The input shaft of dual-clutch gearbox is divided into two parts, while CVVD is divided into at least four parts.
So many solid and hollow parts are embedded together, which puts forward higher requirements for the lubrication system. Secondly, how to make the structure compact and reduce the friction loss is also a difficult problem. Obviously, modern times have solved these problems.
the first model equipped with CVVD engine is Hyundai sonata, which is called Smartstream? 1.6L? TGDI? Compared with the previous 1.6T power and fuel economy, CVVD engine has improved. However, CVVD has two versions in development, and the latest version is 1.5t. In 219, an industry conference announced the technical information in advance, which is the previous 1.6T? An upgraded version of CVVD (I heard about it, too).
domestic brand-new sonata? 27TGDi? The model is equipped with 1.5T? CVVD engine, the application information shows that the comprehensive fuel consumption of this car is only 5.6L What is the concept of this fuel consumption? You can compare the Accord 1.5T.
another model with the same engine is KIA K5 Kaiku? 1.5T, compared with overseas 1.6T? The maximum power of CVVD engine is 134KW and the peak torque is 265? N? M, domestic 1.5T? The CVVD engine is 125KW and the peak torque is 253N? m。
has the internal combustion engine really come to an end? I'm afraid no one can give an accurate answer, but with the unremitting efforts of internal combustion engine engineers, the performance of internal combustion engine is getting closer and closer to the ideal goal. If the emissions of internal combustion engine are greatly reduced in the future, it may still be irreplaceable!
This article comes from the author of Chejia, car home, and does not represent car home's standpoint.