When choosing a vehicle for many car owners, one of the main criteria is the type of transmission. One of the most perfect is a variator, reviews for which, design features, characteristics and other nuances are given below.
CVT Features
A feature of the variator, distinguishing it from other types of gearboxes - both manual and automatic - is the absence of fixed gears. For each such unit, the transmission force, or number, is in a certain range at a particular point in time and under certain conditions. This is possible due to the fact that the variator is based on a different principle than other gearboxes.
The principle of operation of the variator
The principle of operation of the variator is to transfer force from the drive shaft to the driven shaft by means of a belt drive. In modern cars, a chain or a metal belt acts as a belt drive, the drive shaft is the engine, and the driven shaft is the wheel. A smooth change in the gear ratio is ensured by a no less smooth change in the diameter of the driven and drive shaft. To ensure this process, special techniques are used. Every modern automaker has got some experience in this area: for example, according to reviews, the Mitsubishi CVT has the smoothest move.
All variators are divided into two main categories depending on the type of gear.
V-belt drive variators
V-belt transmission is based on a trapezoidal toothed belt, which for many automakers is represented by a belt of metal plates or a chain. The second component is two pulleys assembled from conical disks. The change in the value of torque and speed occurs due to a change in the diameter of the pulleys.
Principle of operation of a variator with V-belt drive
The drive pulley, after depressing the accelerator pedal, transmits rotation to the driven shaft from the engine. It is designed in such a way that under the influence of centrifugal forces with increasing speed, the cheeks of the discs are compressed, as a result of which the drive belt is pushed to the edge of the pulley from its center. In this case, the reverse process occurs on the driven shaft: the cheeks are unclenched, which leads to a shift of the belt to the center of the pulley. Thus, a smooth change in effort and gear ratio occurs. When you release the accelerator pedal, the reverse process is performed.
Toroidal variator
The principle of operation of the toroidal variator is somewhat different and proceeds from its design: the shafts in it are replaced by wheels with a spherical surface, between which the rollers are sandwiched. One of these wheels is driving, the second, respectively, is driven. A change in the friction force between the rollers and the wheels provokes a change in the gear ratio and the transmitted torque value. The gear ratio changes as a result of changing the position of the rollers in the transverse plane. The angular speed of the driving and driven wheels is the same, provided the horizontal location of the roller. A change in gear ratio occurs when the position of the rollers changes.
Toroidal variators are used extremely rarely, which is associated with complex manufacturing technologies and design solutions. The most popular in the automotive industry today are V-belt devices: they are used by many automakers - judging by the reviews, CVTs on the Nissan are of this type.
CVT oils
CVT oils are marked accordingly - CVT - and are very different from other transmission fluids. Such compositions not only lubricate rubbing surfaces, but also prevent slipping. Using a belt to transfer between the shafts of torque is possible only due to this property of oil. In the responses to the CVTs, it is noted that it is impossible to allow oil starvation in connection with this feature, otherwise you may encounter chain slippage along the working surfaces of the shafts, which will lead to their rapid wear.
CVT Benefits
Owners in reviews of CVTs note the following advantages:
- Smoothness of movement. The car accelerates without jerks, which are characteristic of other checkpoints. The ride is like driving on an electric lift or electric car.
- High efficiency. The transmission time of the useful power from the engine to the transmission is significantly reduced due to the high efficiency. In the reviews on the CVTs, an increase in the dynamics of the car during acceleration is noted, which is especially felt at speeds from 50-60 km / h and above.
- Fuel economy. Smooth set of speeds and the same smooth braking, coupled with high efficiency provide significant fuel economy.
- Environmental friendliness. Lower fuel consumption and, consequently, lower CO 2 emissions into the atmosphere make the car more environmentally friendly.
- Gentle operation. In the reviews of the variator, the owners note a reduced wear of the parts and an increase in their working life due to the fact that the operating conditions are selected by the electronics so that the device and engine work in a gentle mode.
CVT disadvantages
Despite the fact that the variator is considered to be a perfect gearbox, it also has its drawbacks:
- Installing such a device on cars with a powerful engine - more than 220 horsepower - is impossible. Many automobile concerns - Nissan, Toyota - note this in the reviews on CVTs and determine that too much effort is exerted on the CVT roller or its drive belt in powerful engines.
- Expensive gear oil. Owners of many foreign cars - for example, Nissan with a CVT - note in the reviews that the transmission oil is too expensive and the assembly itself is picky about the quality of the lubricant. For this reason, it is only necessary to purchase original oil from authorized dealers, which is several times more expensive than its budget counterparts.
- High probability of failure associated with a large number of sensors and electronics in the variator control system. Quite often, the Nissan X Trail CVTs suffer from this. In the reviews, the owners of such foreign cars note that with a minor breakdown, the variator switches to emergency mode or is completely turned off.
- The complexity of the repair work. The cost of repairing the variator is several times higher than that of automatic transmissions and manual transmissions, in addition, the repair is complicated by the search for car services specializing in such works. For example, the owners of the Nissan X Trail with a CVT in the reviews indicate that in the event of a gearbox breakdown, you will have to contact an authorized dealer.
- Other vehicles or trailers cannot be towed on a vehicle with a variator, just like a car with the engine and variator turned off. In the reviews of “Qashqai” with a CVT and other cars with a similar gearbox, car owners note that the only exception is the situation when the drive axle is hung out.
Summary
Despite all the shortcomings, CVTs today are the perfect type of transmission. In reviews of the Qashqai with a CVT and many other cars with this type of transmission, car owners appreciated all the advantages of using them. Manufacturers are constantly improving the design of variators, so we can say that in the next few years they will displace mechanical and automatic transmissions from automobile markets.
When buying and operating a car with a CVT, several nuances must be taken into account:
- This type of transmission does not accept an aggressive driving style.
- Long driving at extremely low or high speed on the variator is not recommended.
- Operation of the variator at low or high temperature is necessary in special conditions.
- You cannot tow a vehicle with a variator and the engine off. An exception is the situation in which towing is carried out with the drive axle suspended. In addition, it is also prohibited to tow other vehicles and trailers using a variator vehicle.
- Impact loads on the drive belt of the variator are contraindicated, therefore it is better to ride on smooth tracks.
- The drive belt and transmission oil must be replaced in a timely manner.
Before purchasing a car with a CVT, it is necessary to prepare in advance for the conditions of its operation, especially if the car owner previously used an automatic or mechanical transmission. The only requirement is timely servicing of the variator and regular replacement of consumables - transmission oil and drive belt.