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Category: Auto Tips

CVTs: Case Without Steps

2024

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Video: CVTs: Case Without Steps

Video: CVTs: Case Without Steps
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CVTs: Case Without Steps
CVTs: Case Without Steps
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The continuously variable transmission ensures constant engine operation at the peak of torque, and therefore - optimal acceleration dynamics. The variator does not break the power flow, thereby minimizing fuel consumption. Finally, working on the principle “the lower the engine torque, the longer the resource”, it would seem that the CVTs should completely displace the usual stepped gearboxes, at least in the initial segments A, B and C. But no, the pace of attack is not so impressive. Well, let's try to figure out why, and also answer another question: what problems might the owner of a car face with a new-fangled transmission.

CVT pro et contra

Современные вариаторы: pro et contra
Современные вариаторы: pro et contra

Modern CVTs: pro et contra Modern CVTs: pro et contra

V-belt transmission

The first production car equipped with a CVT appeared in the distant 1958. Model DAF 600 can rightfully be called a pioneer among cars with V-belt drive. In fact, the Variomatic transmission was a drive and driven pulleys connected by a V-belt. Change of torque is provided by cunning pulleys. The leader is designed in such a way that, depending on the speed of rotation, the lateral planes of the pulley are compressed and “squeeze” the V-belt to the outer radius. The driven pulley is designed according to the mirror principle: the greater the centrifugal force, the smaller the radius of rotation of the belt. Everything is simple and clear: it is very similar to the design of the gearbox of a racing bike. Almost without changes, such a transmission migrated to the Volvo 343. The Swedish car was equipped with it until 1980.

The main and perhaps the only serious problem of Variomatic was the limited resource of the V-belt. The question of the practicality of the variator remained open until the Van Dorn brothers patented a belt of composing plates. In addition to the fact that the multilayer construction itself turned out to be significantly more durable, its functional originality also spoke in favor of the type-setting belt. He did not pull the clutch, but pushed, so the variator's resource increased significantly. Today, Van Dorn's belt is actively used by brands such as MINI, Nissan, Honda in continuously variable transmissions of their cars.

Is the chain the head of everything?

A somewhat different resource problem was solved by Audi specialists. They connected the pulleys not with a belt, but with a chain, logically assuming that the latter would be more durable in any case. However, having coped with the task of transmission link strength, they posed a new question - thermal stability. The variator was desperately basking. Engineers puzzled over how to cool the contact points of the chain link axles with the pulley. It is clear that everything rested on the quality composition of both the circuit itself and the lubricant / coolant. For 10 years, Audi and ZF have been fighting for the future of their brainchild. Their efforts were rewarded: the Multitronic system, equipped with a chain transmission, has found serial application in the Audi A6 transmission.

Variable speed drive

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Note, however, that the method of transmitting torque Multitronic refers to V-belt variators. The operating principle of the Ingolstadt auto transmission remained the same as the DAF 600 more than half a century ago. Although, of course, the materials, workmanship, reliability and, of course, the cost of Multitronic is much higher.

Extroid

The principle of operation of the so-called toroidal variator by itself eliminates the intermediate link in the form of a belt or chain. The moment is transmitted by rollers located on the coaxial disks. The gear ratio of such a transmission is changed by changing the radius along which the clips are in contact with the rollers. Roughly speaking, the speed of a car equipped with a toroidal variator depends on the position of the contact rollers.

Such a mechanism is used in the Extroid continuously variable transmission installed, for example, on the Nissan Cedric. Note that at the beginning of the new millennium Extroid CVT earned the prize "Technology of the Year 1999–2000." In this case, the hydraulics help to change the gear ratio of the variator. At the direction of the electronic control unit, it shifts the roller clips vertically. The disc alignment broken as a result completes the job: the roller rotates independently.

It would seem a successful and practical design. However, there were some pitfalls. Due to the enormous pressure in the contact patch, the rollers were destroyed quite quickly. The toroidal variator was faced with the same problem as the V-belt, a limited service life. By the method of scientific and mathematical “poke”, the engineers had to find materials for the parts of the Extroid variator. In the end, the issue of reliability was resolved, and the resource of the toroidal transmission became comparable with the declared resource of a modern car. However, this did not fail to affect the cost of the variator, and ultimately the price of the Extroid transmission.

Better more often and more expensive

CVTs require the closest attention and respect. Keep this in mind all the time. Otherwise, the car can seriously hit the owner’s wallet. Here are some examples.

Honda Jazz Operational Regulations require changing the oil (CVT-F) in a continuously variable transmission every 45 thousand km. However, as practice shows, changing the oil in the variator should be carried out every 20 thousand km, especially if the car has to alternate a torn city rhythm with prolonged march-throws. Continuous highway driving warms up the CVT. As a result, the oil quickly loses its working properties, and the variator wears out. The cost of the new CVT is quite comparable to the price of a bit of jazz! By the way, the variator resource is somewhere around 100 thousand km. V-belt variator mounted on Honda HR-V is no exception. It is convenient, dynamic, sensitive to changes in speed and, of course, reliable … That's just not in comparison with the "mechanics". According to service statistics, the variator resource turned out to be two times lower; in addition, he eats two and a half times more transmission fluid. If 2 liters are poured into the manual gearbox, then almost five is put into the variator. Honda advises changing the fluid every 70 thousand km. Practice shows that it is desirable to reduce the interval to at least 30 thousand km. Price - $ 20 per liter of original fluid.

Nissan Murano with V-belt variator is one of the most frequent visitors to specialized service stations. Sometimes a continuously variable transmission does not even take care of 40 thousand kilometers. You can revive an unexpectedly unexpectedly variator that can serve somewhere for 150-200 thousand rubles. Of these, 100 thousand rubles. will have to pay for the original repair kit. Here, as they say, no options.

The quieter you go, the further you'll get

The torque converter or the starting clutch helps to move the car from its place to the variator. Due to the simplicity of design and cheapness, manufacturers most often use the latter. It should be remembered that sharp accelerations to the starting clutch are contraindicated. If, once again, pressing the gas, you felt a jerking and tapping, and the engine speed began to jump - this means the beginning of the end. Most often, first-generation MINI transmissions and Honda suffer from this. The clutch is inexpensive, and the variator itself can still serve. However, it is better not to tighten the clutch replacement. If the variator "stalled", write is gone. Frequent, but usually useless advice is to replace the fluid. Helps for quite a while. It is very difficult to find the variator in disassembly. And if you are lucky, it will cost you thousands and a half dollars, no less. The quality of the variator from disassembly is no one guarantees.

By the way, contrary to popular belief, in a pinch, you can tow a car with a CVT. True, no more than 40 km at a speed of 30 km / h, pouring an extra liter of liquid into the box. After such a trip, it is necessary to completely replace the fluid in the gearbox.

Grain of doubt

As a result, each operational advantage of a continuously variable transmission has its own operational fad. The continuous howl of an engine running at maximum torque, almost drove many drivers crazy. As a result, automobile companies, meeting customers, adjust the variator to the more familiar “acceleration - switching” mode. Which, naturally, eliminates the dynamic advantages of the variator. The continuously variable transmission guarantees higher operating costs. This is due to both reduced service intervals and the use of special products approved by the manufacturer. A significant minus for the Russian market is that a car with a CVT is a car of one (first) owner. The purchase of a CVT machine in the secondary market cannot be called a pig in a poke. According to the “korobochnik” metropolitan service centers, this is “hit in 90 percent of cases. As for the use of a continuously variable transmission on relatively low-power cars, for example, golf-class, then everything is not going smoothly …

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