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.
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.
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.
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;
- 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;
- 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.
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.
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, in Ford worth Transmatic, Ecotronic or Durashift. The concern equips its cars with a similar transmission, only under the name Multidrive Toyota... By car Nissan there is also a V-belt variator, but its name is Xtronic or Hyper. An analogue to all the mentioned variators is Autotronic, which is installed in many models Mercedes.
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.
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.
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.
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.
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).
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.
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.
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: