How it works: CVT box
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How it works: CVT box

It has long been known that the transmission in a car allows you to evenly distribute the torque that the power unit generates. This is necessary for smooth or dynamic acceleration of the vehicle. The driver engages a certain range of engine rpm, preventing it from going into a higher mode.

As for the manual transmission, about its device and how to keep it for longer, we have already said. And this seems to be a hackneyed topic. Let's talk about cvt: what kind of mechanism it is, its work and whether it is worth taking a car with a similar transmission.

What is a CVT box

This is a kind of automatic transmission. It belongs to the category of continuously variable transmissions. Its peculiarity lies in the fact that the variator provides a smooth change in gear ratios in such a small range that cannot be achieved in mechanics.

How it works: CVT box

It is equipped with cars operating under the control of an electronic control unit. This device evenly distributes the loads coming from the engine in accordance with the resistance that is applied to the drive wheels of the vehicle.

Gear shifting is carried out smoothly - the driver sometimes does not even notice how the operating mode of the mechanism changes. This improves ride comfort.

Principal device

The design of the mechanism is rather complicated, which is why its production is materially costly. In addition, due to the complexity of the design, the continuously variable transmission is not able to provide an even distribution of loads in certain types of engines.

How it works: CVT box

The key difference between a continuously variable transmission and a mechanical analogue is that it lacks a clutch. Today, variators are constantly being modernized, and there are already several fundamentally different modifications. However, the main elements of the box are:

  • The main transmission mechanism is a torque converter. This is a unit that takes on the torque that the engine generates and transmits it to the executing elements;
  • The primary gear pulley (connected to the hydraulic clutch) and the secondary gear pulley (transfers forces to the chassis of the car);
  • The transmission of forces is carried out through a belt, and in some cases, a chain;How it works: CVT box
  • Electronics controls changing the operating modes of mechanisms;
  • A separate unit that is activated when reverse gear is engaged;
  • The shaft on which the transmission pulley and main gear are fixed;
  • Most versions also have a differential.

It should be noted that these elements do not provide an understanding of how the gearbox works. It all depends on the modification of the device, which will be discussed a little later, but now we will consider on what principle the mechanism functions.

How it works

There are three main types of transmissions that are used in transport and have a principle of operation similar to cvt:

  • Power transmission. In this case, the device is used only for narrow-profile transport. The motor drives the dynamo of the generator, which generates the necessary energy for the transmission. An example of such a gearbox is BelAZ;
  • Transmission from torque converter. This type of gear is very smooth. The hydraulic clutch is spun up by a pump, which supplies oil under high pressure, depending on the engine speed. This mechanism is at the heart of all modern automatic transmissions;How it works: CVT box
  • Hydrostatic type transmission. Old technology, but still used in some transport. The principle of such a box - the internal combustion engine drives the oil pump, which supplies pressure to the hydraulic motors connected to the drive wheels. An example of such a transport is some models of combines.

As for the variators, although they work on a somewhat similar principle, there are still significant differences. The design of the classic variator includes a fluid coupling, which is unwound by the power unit of the machine. Only the transmission of torque to the driven shaft of the box is carried out using an intermediate element. Most often, manufacturers of such transmissions use a durable belt in the mechanism. However, there is also a chain transmission.

The gear ratio is changed by changing the diameter of the drive and driven pulleys. When the driver selects the appropriate driving mode on the transmission selector, the control unit records the data from the wheels and engine components. Based on these data, the electronics at the right moment shifts the walls of the active pulleys, due to which their central diameter increases (such a feature of the device of these parts). The gear ratio increases and the wheels start to turn faster.

How it works: CVT box

When reverse gear is engaged, the mechanism does not work in reverse mode, but activates an additional device. In most cases, this is a planetary gearbox.

Accelerating dynamics of the variator

Compared to a classic automatic transmission, the CVT will feel sluggish from the start, as if the driver is slowly pressing the gas pedal. The machine will be sharper at the start. In this case, during the transition to the next gear, the car will twitch. But if we talk about the distance, then with the same engines and dimensions of the car, the variator has more advantages.

The reason is that when shifting from gear to gear, the machine loses traction. The variator, during operation, changes the gear ratio more smoothly, due to which there is no gap in the transmission of thrust. In this case, the motor operates at the speed at which the maximum torque is transmitted. The machine, on the other hand, often captures less traction engine speeds, which is why the overall dynamics of the car suffers.

CVTs of the old release (until 2007, and some modifications until 2010) changed the gear ratios when the engine speed increased almost to the maximum. With the introduction of individual control units for the transmission, this drawback was eliminated. The new generation of CVTs adapt to the sport mode, and when you press the accelerator sharply, it immediately switches to changing gear ratios at the most efficient engine speeds.

At the same time, traction is maintained throughout the entire change in gear ratios of the box. Or until the driver stops depressing the accelerator pedal. Thus, the dynamics of the car is directly affected by the force of pressing the gas pedal.

Emulation of a manual box on a CVT

Under manual shifting in the variator is meant the installation of a gearshift lever for forced increase / decrease in the gear ratio of the transmission. If we talk about classic machines, then when you move the handle towards "+" or "-", the control unit gives a command to change the gear.

How it works: CVT box

Since CVTs do not have a stepwise transition from gear to gear, this process is somewhat different. Even if the electronics show the gear indicated by the driver on the dashboard, the electronic control unit of a modern CVT will still ensure that the tachometer needle does not enter the red zone (it will not allow the engine to operate at maximum speed). The same will happen if the driver instructs the electronics to keep the gear ratio at low revs - the transmission will not allow the engine to stall due to critically low revs.

If we talk about the dynamics of the car, then in manual mode on the machine, the driver will be able to improve the acceleration of the vehicle by adjusting the shift to another gear, but in the case of the CVT, this will not improve the acceleration of the car. The reason is that the “manual mode” also uses the less efficient engine speed zones for acceleration.

The presence of this option in modern CVTs is just a marketing ploy for those motorists who like to “control” the process of using torque. For the most efficient dynamics in the case of a variator, it is better to use automatic mode (position on the selector "D").

Features of the movement of a car with such a transmission

Consider the features of the movement of a car on a CVT-type transmission. The owner of such a car must remember:

  1. With a variator, it will not work to slip at the start. The reason is that the electronics constantly controls the most efficient gear ratio in accordance with the engine speed and load on it.
  2. The variator will help the driver on which road at the time of launch. Due to the smooth increase in traction, the wheels will not slip if the driver does not calculate the effort on the gas pedal.
  3. When overtaking a car with a CVT, you will need to press the gas harder not at the time of the maneuver, as on a mechanic or automatic, but immediately before that, since the transmission works with a slight delay.
  4. On the variator, it is more difficult to master a controlled skid due to the same “belated” reaction of the box to pressing the gas. If on the mechanics for skidding it is necessary to sharply press the gas after turning the steering wheel, then in the case of the variator this must be done directly when the steering wheel is turned.
  5. Since this type of transmission constantly selects the optimal gear ratio in accordance with the engine speed, this results in an ideal combination between traction and low fuel consumption. This system allows the motor to work in such a mode, as if the car is driving on a flat highway outside the city. If the car is equipped with cruise control, the fuel economy will be more noticeable.

Types and principle of operation of the variator on a car

Modern cars equipped with a CVT can get one of two types of transmission:

  • V-belt;
  • Toroid.

Their differences are in the design features, although the principle of operation remains the same. Let's consider these types of drive separately.

V-belt

Most cars with a CVT get this type of gearbox. Often in such transmissions one belt drive is used (sometimes there are modifications with two gears). This mechanism uses two pulleys with wedge-shaped rings. A belt with an identical wedge-shaped profile is put on them. Initially, manufacturers used reinforced rubber. Modern transmissions use steel counterparts.

How it works: CVT box

Each pulley (located on the drive and driven shafts) has outwardly inclined walls with an angle of inclination relative to the shaft axis of 70 degrees. In the process of changing the gear ratio, the walls of the pulleys move or diverge, due to which the diameter of the pulley changes. The walls of the pulleys are driven by springs, centrifugal force or servos.

This part of the unit in V-belt variators is the most vulnerable, since it is most exposed to the load. For this reason, modern transmissions of this type use steel structures with plates of complex shape.

Among the wedge-shaped drives, there are variators equipped with a chain. The number of links in it is large, due to which it fits snugly against the walls of the pulley. This type of variator is characterized by high efficiency compared to other analogues, but due to the high friction force, it is required to use the most durable material, which makes the chain for such a variator very expensive.

Toroidal

These are more complex designs. Such CVTs are more often equipped with rear-wheel drive cars with a powerful power unit. For the most efficient transmission of torque at high speed, a reduction planetary gearbox is used, which transmits thrust directly. In front-wheel drive vehicles, such a variator is connected to the main gear and differential.

How it works: CVT box

The design of the toroidal variator also has two disks, only their axes coincide. In cross section, these discs look like isosceles triangles (have a spherical shape). Rollers are installed between the side parts of these disks, which change their position by compressing the working disks.

When the drive disc presses the roller against the driven one, more torque is transmitted and the driven disc rotates faster. When the force is reduced, the driven disk rotates more slowly.

Types of V-belt variators

After the advent of the variator type transmission, they began to develop in the field of increasing its efficiency. Thanks to this, today car owners are offered the most running modification, which has shown itself to be the most effective among analogues - V-belt variators.

Each manufacturer calls this modification of gearboxes differently. For example, Ford has Transmatic, Ecotronic or Durashift. Toyota is equipping its cars with a similar transmission, only under the name Multidrive. Nissan cars also have a V-belt variator, but the name is Xtronic or Hyper. An analogue to all the mentioned variators is Autotronic, which is found in many Mercedes models.

In such variators, the main elements remain identical, only the principle of coupling between the motor and the main gear is slightly different. Most budget models use CVTs such as Xtronic, Multidrive and others. At the heart of these modifications is the torque converter.

How it works: CVT box

There are more expensive options:

  • Electronic clutch based on electromagnetic action of mechanisms. These variators are called Hyper;
  • Another automatic clutch option is the Transmatic. It uses the centrifugal force of the hydraulic fluid;
  • If the name of the transmission contains the prefix Multi, then often in such modifications several wet clutch discs are used.

When a new car is purchased, and its technical documentation indicates that the transmission is CVT, this does not always mean the presence of a torque converter. But in most cases, the box will be equipped with just this mechanism.

Advantages and disadvantages of CVT

Each type of transmission has its own adherents, so in most cases, according to one, some function is considered an advantage, and the other - on the contrary, a disadvantage. If we consider reliability, then the variator box does not need any special maintenance - just change the oil on time and operate in accordance with the manufacturer's recommendations.

Here are some more benefits:

  • Transport has a smooth dynamics when changing gear ratios, which makes it as comfortable to drive as possible;
  • To quickly pick up speed, you just need to drown the gas pedal;
  • The driver does not hesitate to change gears - an especially convenient feature for beginners;
  • With a working mechanism, it will work silently;
  • The power take-off of the motor is in the optimal range, which does not allow the motor to overload or go to maximum speed;
  • If the mechanics shift up a gear early, the motor experiences an increased load. To compensate for this, the throttle valve opens more, and more fuel enters the cylinders, but in this mode it burns less efficiently. As a result, more unburned substances enter the exhaust system. If the car has catalyst, then the remnants will burn out in it, which will significantly reduce the working resource of the part.
How it works: CVT box

Cars equipped with a variator also have several significant disadvantages:

  • If the wheels slip, the box may not properly distribute the loads. For example, this often happens on ice;
  • He does not like high revs, so the driver must be careful at what moment the transmission no longer increases the gear ratio;
  • Natural wear of active pulleys;
  • The schedule for changing the lubricant in the mechanism is strictly limited - depending on the manufacturer's recommendations, this period can be 20 thousand, and maybe 30 000 km;
  • The variator is easier to break than the manual transmission;
  • It is very expensive to repair due to the fact that only a specialist who will take a decent fee for his services can do the job correctly.

Major faults

CVT breakdown is a real problem for a motorist. However, with due adherence to the manufacturer's recommendations, it works quite stably. Here's what can fail in it:

  • The connecting body through which the forces are transmitted from the driving pulley to the driven pulley. In some cases it is a belt, in others it is a chain;
  • Electronic malfunction - loss of contact, failure of sensors;
  • Mechanical breakdown of the fluid coupling;
  • Failure of the selector elements;
  • Breakage of the oil pump pressure reducing valve;
  • Errors in the control unit. This problem is easily identified as a result of a complete vehicle diagnostics at the stand.
How it works: CVT box

As for the electronics, the computer will immediately show what the fault is. But with mechanical breakdowns, diagnostics becomes more complicated. Here's what might indicate a problem with the variator:

  • Unstable movement of the car, accompanied by jerks;
  • When neutral speed is selected, the car continues to move;
  • Difficult or impossible manual gear shifting (if such an option is present in the transmission).

Causes of CVT breakdown

Any mechanism sooner or later fails due to the natural wear and tear of its parts. The same applies to the variator. Although this type of box is considered quite hardy, motorists are still faced with its malfunctions.

A key factor affecting the life of the unit is the timely maintenance of the transmission. The scheduled maintenance schedule is specified by the vehicle manufacturer. It is also necessary to take into account the recommendations for operating this type of transmission. The list of correct maintenance of the variator includes:

  • Timely replacement of transmission oil and all gearbox consumables;
  • Timely repair or replacement of failed parts of the box;
  • Correct driving style (it is not recommended to use drifting on the CVT, sports driving with frequent acceleration and sudden stops, dynamic driving on an unheated box).
How it works: CVT box

Other causes of variator failures are natural wear or defects during the production of parts or the entire unit. The second is very rare, and this applies more to budget car models.

Most often, the variator fails due to the use of bad oil. In the operation of such a transmission, a key role is assigned to the quality of the lubricant, so the car owner needs to take the transmission fluid replacement procedure seriously.

If an old-style variator is installed in the car, then often the oil in it needs to be changed every 30-50 thousand kilometers. If the vehicle uses a more modern transmission, then an oil change may be required after 60-80 thousand km. Moreover, it is the mileage that affects this interval, and not the hours, as is the case with internal combustion engines.

Operation of the variator

The CVT box is capricious, but if you adapt to it, it will last a long time. Here's what you need to know for a motorist whose vehicle is driven by such a transmission:

  • The box does not like aggressive driving. Rather, the "retirement" style or measured movement with moderate acceleration is suitable for her;
  • The transmission of this type does not withstand high revs, so if the driver has a habit of "immersing" on the highway at a long distance, it is better to stop at the mechanics. At least it's cheaper to repair it;
  • On the variator, you must not start abruptly and allow the drive wheels to slip;
  • This transmission is not suitable for a utility vehicle that often carries heavy loads or tows a trailer.
How it works: CVT box

When a car with cvt gets into the mud and gets stuck, you shouldn't try to drive out on your own. It is better to use the help of strangers, as in this case it is impossible to avoid wheel slip.

Which is better: a variator or an automatic machine?

If you compare these two types of boxes, then you should immediately pay attention to the fact that the automatic analogue is on the market much more than the variator. For this reason, a sufficient number of mechanics are already versed in the device and the intricacies of the automatic transmission. But with variators, the situation is much worse - it is much more difficult to find a real specialist.

Here are some more benefits of an automatic transmission:

  • It is arranged easier than cvt, and there are plenty of spare parts in car dealerships;
  • As for driving, the box works on the principle of mechanics - the gears are clear, but the ECU is responsible for switching them;
  • Working fluid for a machine is cheaper than for a variator. You can even save money by buying a cheaper option, since there is a wide variety of oils for automatic machines on the market;
  • The electronics selects the optimal rpm at which you can shift an overdrive;
  • The machine breaks less often than the variator, especially with regard to electronics failures. This is due to the fact that the control unit controls only a quarter of the transmission operation. The mechanics do the rest;
  • The machine has a much larger working resource. If the driver carefully operates the unit (changes the oil in a timely manner and avoids constant aggressive driving), then the mechanism will last at least 400 thousand, and will not need major repairs.
How it works: CVT box

However, despite its advantages, the machine also has several tangible drawbacks:

  • The efficiency of the transmission is lower, since most of the torque is spent on unwinding the torque converter;
  • Gear shifting is not so smooth - the driver still feels when the car has changed to another gear;
  • The acceleration of the car does not have such a quality indicator as that of the variator - there the speed is smoothly picked up;
  • The machines have the largest oil container. Normal mechanics require about three liters of lubricant, a variator - up to eight, but an automatic machine - about 10 liters.

If objectively compared, then these shortcomings are more than covered by the endurance and reliability of such units. However, it all depends on what the owner expects of his car.

So, a car equipped with a variator box is designed for quiet urban movement. With such a transmission, the driver can feel like driving a land yacht rather than a sports car pilot.

In conclusion, how to determine where which box is:

How to choose a car, which box is better: automatic, variator, robot, mechanics

How to check the variator when buying a car in the secondary market

When buying a car in the secondary market, you should check the performance of all key systems and assemblies of the vehicle. Particular attention should be paid to the variator if such a transmission is used in the car. The reason is that this unit is expensive to repair.

Here's what you need to pay attention to when buying such a car.

Car mileage

This parameter is directly related to the condition of the gearbox. Of course, unscrupulous sellers deliberately twist the mileage on the odometer, but the newer the car, the more difficult it is to completely eliminate all traces of this operation.

In CVTs on cars manufactured since 2007 or 2010 (depending on the model), individual control units for the transmission are installed. Some errors recorded by the main control unit may also be displayed in the transmission ECU.

Oil condition

In addition to the car's mileage, transmission oil will also tell you about the condition of the variator. Here's what to consider when looking at lubricants when inspecting a vehicle:

Mount

To make sure that the transmission has not been repaired, the machine must be raised on a lift or driven into a pit, and the mounting bolts should be checked for damage to the edges. If there are scuffs, chips or serifs, then the unit was disassembled, and the seller must tell you what was repaired in the box.

How it works: CVT box

If the seller denies that repairs were carried out, and the unit was clearly disassembled, the purchase of such a car should be abandoned. When told what work was carried out, the seller will have to take his word for it.

History of the car

This kind of verification can be performed if the seller is the first owner of the car. When the car has changed several owners, it is almost impossible to check the history of the car. The parameters that relate to the past car include:

  1. Checking the VIN number;
  2. If the car was serviced exclusively by an authorized dealer, then all work will be reflected in the report. At the same time, it is impossible to check whether the transmission was repaired in garage service stations;
  3. When buying an imported vehicle from abroad, it is necessary to check the customs documents (mileage and other technical condition of the car).

Such a check will provide additional indirect information about the state of the variator.

Check in motion

It is mandatory to check the performance of the variator. This is done during a test drive in different modes in order to listen or observe the nature of the transmission. Such a check is the most informative in terms of the state of the variator.

A serviceable transmission provides the smoothest vehicle dynamics without jerks and noticeable step changes in the gear ratio. Otherwise, jerks and shocks indicate damage to the variator drive belt.

CVT sound

The sound can also determine the condition of the car's transmission. For example, a serviceable variator at idle speed of the internal combustion engine is not audible at all. While driving, the sound of the box can be heard, but with poor sound insulation of the body.

Clicks, hum, whistle, harsh noise and other sounds are not typical for a working variator. Since it is extremely difficult for an inexperienced motorist to determine a transmission malfunction by sound, it is better to invite a specialist to inspect the car, especially those who understand the operation of the CVT gearbox.

Related videos

Here are five factors that will help extend the life of the variator:

Questions and answers:

What is worse variator or automatic machine? If we start from the dynamism and smoothness of the acceleration, then the variator has more advantages over automatic transmissions.

What's wrong with a variator on a car? The variator is sensitive to the mass of the car (the greater the weight of the car, the greater the load on the variator parts), sharp and monotonous loads and high torque.

Why is the CVT bad? Such a box is afraid of slipping of the driving wheels, the set of speed and the operation of the motor are too monotonous due to the smoothness of the change in the gear ratio. It's expensive to maintain.

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