LABORATORY WORK No. 13
Topic: “Purpose, design and principle of operation of the gearbox”
Goal of the work: studying the purpose, design and operating principle of a manual gearbox.
General provisions
Gearbox classification
Manual Transmission- is a multi-stage helical gearbox, which provides for manual gear shifting.
Automated transmission- provides automatic (without direct participation of the driver) selection of the gear ratio corresponding to the current driving conditions, depending on many factors.
Robotic gearbox- is a manual gearbox in which the clutch release and gear shift functions are automated.
CVT gearbox- this is a mechanical unit designed to transmit engine power steplessly to the drive wheels.
By control method
1. With manual gear shift- the driver (operator) engages the gear.
· Direct action- only operator effort is used. Direct acting drives are mechanical And hydraulic.
· Servo drives- the force of the operator and the servo device is used, while the main part of the work is performed by the servo device, and the force of the operator is necessary to control the operation of the servo device. Depending on the source (converter) of energy, servos are divided into hydraulic, mechanical, electric, vacuum, mixed etc. In automobile and tank construction, hydraulic servo drives are most widespread .
2. Automatic- depending on external conditions (for example, rotation speed and load on the engine crankshaft), gears are switched by an automated gearbox control system without driver participation.
Purpose and principle of operation of the gearbox
The gearbox serves to change over a wide range of torque transmitted from the engine to the drive wheels of the car when starting and accelerating. In addition, the gearbox allows the vehicle to move in reverse and allows long-term separation of the engine and drive wheels, which is necessary when the engine is idling while driving or when the vehicle is parked.
Modern cars mainly use mechanical step transmissions with toothed gears. The number of forward gears is usually four or five, not counting reverse gears.
Gear shifting in them is carried out by moving gears, which mesh alternately with other gears, or by locking the gears on the shaft using synchronizers. Synchronizers equalize the rotation speed of the engaged gears and block one of them with the driven shaft. The movement of gears or synchronizers is controlled by the driver when the clutch is disengaged. Depending on the number of forward gears, gearboxes are three-speed, four-speed, etc.
Diagram of the operation of a manual transmission.
1 - input shaft; 2 - gear shift lever; 3 - gear shift mechanism; 4 - secondary shaft; 5 - drain plug; 6 - intermediate shaft; 7 - gearbox housing
The manual transmission consists of:
· crankcase,
· primary, secondary and intermediate shafts with gears,
additional shaft and reverse gear
· synchronizers,
· gear shift mechanism with locking and locking devices
· shift lever.
Carter contains all the main components and parts of the gearbox. It is attached to the clutch housing, which in turn is attached to the engine. Since during operation, the gearbox gears experience heavy loads, they must be well lubricated. Therefore, the crankcase is filled with half its volume with transmission oil (motor oil is used in some car models).
Gearbox shafts rotate in bearings installed in the crankcase and have sets of gears with different numbers of teeth.
Synchronizers necessary for smooth, silent and shock-free gear shifting by equalizing the angular speeds of the rotating gears.
Gear shift mechanism serves to change gears in the box and is controlled by the driver using a lever from inside the car. In this case, the locking device does not allow two gears to turn on at the same time, and the locking device keeps the gears from turning off spontaneously.
Reverse gear, that is, rotation of the secondary shaft of the gearbox in the other direction is ensured by an additional, fourth shaft with a reverse gear. An additional shaft is necessary in order to obtain an odd number of pairs of gears, then the torque changes its direction:
Torque transmission diagram when reverse gear is engaged
1 - input shaft; 2 - input shaft gear; 3 - intermediate shaft; 4 - gear and reverse gear shaft; 5 - secondary shaft
Design and purpose of the gearbox
Purpose
The gearbox (abbreviated as gearbox) is designed to change the torque in magnitude and direction and transmit it from the clutch (we will get acquainted with the clutch mechanism in the next section) to the drive wheels. In other words, with the help of a gearbox, at constant engine power, the traction force on the driving wheels of the car changes. The gearbox also allows you to engage reverse gear and for an unlimited time (unlike the clutch) disconnect the engine from the drive wheels. Cars can be equipped with a manual or automatic transmission. Note that a manual transmission is more common today; it was installed on all cars before the invention of the “automatic”, which appeared around the middle of the last century. box switching transmission shaft
Device
A manual transmission contains the following main elements: crankcase, input shaft, secondary shaft, intermediate shaft, gears, additional shaft, reverse gears, synchronizers, gear shift mechanism, locking device, locking device, gear shift lever. Note that the gearbox lever (abbreviated gearbox lever) is the only one of the listed elements that is accessible from the passenger compartment.
The gearbox housing is mounted on the clutch housing, which, in turn, is mounted on the engine crankcase. Half of the volume of the gearbox housing is occupied by transmission oil, which is used to lubricate gearbox parts. Changing the oil in the gearbox is rarely done; on many modern cars it is not necessary to change it (it is filled at the manufacturer and is designed for the entire life of the vehicle). This is due to the fact that in the gearbox, compared to the engine, the parts rotate much more slowly. Consequently, they do not wear out as intensively, and significantly less of their work products (metal filings, shavings, etc.) get into the oil. Therefore, the oil in the gearbox remains in a condition suitable for use longer.
The gearbox housing contains bearings on which the shafts rotate. These shafts have sets of gears with different numbers of teeth. To ensure that gears shift smoothly and silently, the gearbox uses synchronizers. The essence of their work is that they equalize the angular speeds of rotating gears.
The main unit of the gearbox is the gear shift mechanism, with the help of which, in fact, gear changes are carried out. This mechanism is controlled using a lever located in the cabin. Usually the gearshift lever is located between the front seats and at the same time in front of them, but it can be located, for example, on the steering column.
The locking device prevents two gears from being engaged simultaneously, and the locking device prevents the gears from switching off spontaneously.
Job
The basic principle of operation of a gearbox is based on the fact that different gears have different numbers of teeth. Let's assume that the crankshaft rotates at 3000 rpm and transmits this torque to the input shaft with a gear that meshes with another gear that is larger and has twice as many teeth. The shaft on which this second gear is mounted will rotate at half the speed, i.e. 1500 rpm. When using different combinations of meshing gears (mounted on different shafts), this principle allows different torques to be received and transmitted to the drive wheels. As a result, when the crankshaft rotates at a speed of 3000 rpm, the drive wheels, when the corresponding gears are engaged, can rotate, for example, at a speed of 1500 rpm or 2000 rpm, etc.
For reversing, the gearbox has the ability to engage reverse gear. In this case, the gearbox secondary shaft rotates in the opposite direction due to the use of an odd number of meshing gears (in this case, the direction of the torque is reversed). This “odd” gear is located on the additional gearbox shaft.
The driver of the car independently changes gears using a lever, depending on driving conditions, engine operating mode, its capabilities, as well as other factors. Modern passenger cars are most often equipped with a five-speed transmission: this means that the car has five gears for driving in the forward direction and one gear for driving in the rear direction.
Remember that the lower the gear, the stronger it is, but at the same time, the slower it is. Therefore, the strongest gears used for starting and driving at low speeds are first and reverse gears. When they are turned on, the motor easily rotates the drive wheels, but you will not be able to accelerate to high speed: the engine will “roar” loudly, but the car will not go faster than 10-20 km/h. Therefore, after starting to move and reaching the minimum speed, you need to switch to second gear - less powerful, but faster. Then you can reach a speed of 40-50 km/h to switch to third gear - even faster and less powerful, etc.
Speaking in dry technical language, the gearbox serves to change the torque transmitted from the engine crankshaft to the drive wheels, to move the car in reverse and to long-term disconnect the engine from the transmission while the car is parked and when it is moving by inertia (coasting).
Now, from the point of view of a beginner, let's figure it out - why do you need a gearbox on a car at all, and why do you need to change gears? Gear shifting is a necessity that arose due to the uneven torque characteristics of the internal combustion engine. Let's compare, for example, an internal combustion engine and an electric motor.
The main difference between a car and an electric traction motor from the point of view of interest to us is the traction characteristics, that is, how power and torque change depending on the speed.
The electric motor has quite a lot of torque at low speeds. As it spins up, the torque drops.
For a transport vehicle, this characteristic is most favorable: when starting and accelerating, when you have to overcome significant inertial forces, it is desirable to have as much torque as possible. And to maintain uniform motion, much less torque is needed. Note that the power of the electric motor at any speed can remain close to maximum and is used almost completely in all modes, that is, it is perfectly adapted to road operating conditions. With an internal combustion engine, everything is different: its power at low speeds is significantly reduced, and the amount of torque within the operating speed limits generally changes little.
The graph shows (Fig. A) that if the resistance to movement has increased and the engine speed begins to fall, then for the electric motor this is accompanied by a significant (several times) increase in torque; In a car engine, the torque first increases a little, and then decreases - the engine stalls.
As you can see, the traction characteristics of the internal combustion engine are completely unsatisfactory. But a power plant with such an engine is lightweight,
The efficiency and other qualities are still superior to the electric motor. Therefore, the designers had to come to terms with the shortcomings of the internal combustion engine and, to overcome them, install a gearbox on the car that changes the gear ratio
between the engine and the drive wheels and, accordingly, the torque on them. Figure B shows how, with the help of a stepped gearbox, the traction characteristic of an internal combustion engine tries to approach the ideal hyperbola.
What is it gear ratio? Let's go a little deeper into the mechanics. In a gear train consisting of two gears, one driving and the other driven, their relative sizes determine the rotation speed and torque. The ratio of the number of teeth of the driven gear to the number of teeth of the drive gear is called the gear ratio.
If the drive gear is smaller than the driven gear, then the rotation speed of the driven gear will be less, and the torque will be greater, and vice versa. That is, while gaining in strength, we lose in speed, and, on the contrary, while gaining in speed, we lose in strength. If in transmission
Several pairs of gears are involved, then the total gear ratio is obtained by multiplying the gear ratios of all pairs of gears involved in the transmission.
To obtain varying amounts of torque required for vehicle operation in different conditions, the gearbox has several pairs of gears with different gear ratios. If an intermediate gear is placed between the drive and driven gears, the driven gear will change the direction of rotation to the opposite (we get reverse gear).
Thus, any gearbox, be it manual, automatic or CVT, serves to ensure optimal engine operation in various driving conditions by changing the gear ratio.
In any gearbox there are higher and lower stages (gears).
When starting from a stop, accelerating, driving at low speeds and off-road, high torque is required, which is achieved at medium-high speeds, but there is no need to develop high speeds. To move in this mode, the lower stages of the gearbox (usually the first to third), which have the highest gear ratio, are used; in this case, even at high engine speeds the car will drive slowly.
For uniform movement at high speed, it is necessary to ensure a high rotation speed of the wheels, maintaining engine speed in the optimal range. For this purpose, higher gears (from fourth and higher) are used, which have significantly lower gear ratios compared to lower ones. In this case, the car will drive quite quickly at the same engine speed until the maximum operating speed of the engine is reached. However, in higher gears, the car cannot move at low speed, much less move away, since the engine will not be able to develop the torque necessary to move the car and will stall.
A gear with a gear ratio of 1 is called direct (usually fourth). If the gear ratio is less than one, such a gear is called accelerating (from fifth and above). The overdrive gear is engaged when the vehicle is moving in good road conditions, when a large traction force on the drive wheels is not required. By allowing the engine to operate at lower speeds, overdrive transmission helps reduce engine wear and save fuel.
The concept of gear ratio is associated with the expression “long box” and “short box”. We are talking about the difference in gear ratios of different gears - in a “long” box it is larger. Consider two cars that are identical in everything except gearboxes. The driver of a car with a “short” gearbox, maintaining high engine speeds, will accelerate faster and quickly reach maximum speed. A driver in a car with a “long” gearbox will accelerate longer, but to a higher speed. Thus, the choice of gearbox depends on the driver’s temperament. With a “short” gearbox, the car is more dynamic, but you have to shift more often. With the “long” one, it’s not so playful, but the speed range in one gear is larger, that is, you can get to the highest gear and ride it at a speed of fifty to more than a hundred, changing it only with the gas and brake. Fans of an aggressive “sporty” style will prefer a “short” box, calm people will prefer a long one.
Modern cars can be equipped with one of four types of gearbox – manual, automatic, robotic or CVT.
Automatic transmission– planetary gearbox with automatic shifting. A planetary gear consists of several gears, called planetary gears or pinions, rotating around a central (or sun) gear. The planetary gears are locked together using a carrier.
In addition, an additional external ring gear has internal mesh with the planetary gears. The satellites mounted on the carrier rotate around the central gear (like planets around the Sun), the outer gear rotates around the satellites. Different gear ratios are achieved by fixing different parts relative to each other. Modern gearboxes use multiple planetary gears to achieve a wide range of gear ratios.
The advantages of an automatic transmission include, first of all, ease of control and comfort. Automatic transmissions are capable of changing gears at full engine power, which is practically impossible in a manual transmission. The advantages of an “automatic” include a smooth ride during shifting, no rolling back when starting off, protection of the engine and transmission parts from overloads and breakdowns due to incorrect gear selection, and an increased service life.
Variable speed drive is a continuously variable transmission. Its main parts are two sliding pulleys and a belt connecting them, which has a trapezoidal cross-section. If the halves of the drive pulley are moved, they will push the belt outward - the radius of the pulley along which the belt operates will increase, therefore, the gear ratio will increase.
And if the halves of the driven pulley, on the contrary, are moved apart, then the belt will fall inward and will work along a smaller radius - the gear ratio will decrease. If both pulleys are in an intermediate position, the transmission will become direct. Instead of a belt, a chain or a belt made of metal plates can be used, but the principle does not change. To start the car, a conventional clutch or a small torque converter is used, which is blocked shortly after the start of movement. The pulley disks are controlled by an electronic system of servos, a control unit and sensors.
The main advantage of the variator is that the engine constantly operates in optimal mode. The indisputable advantages of a CVT (compared to an automatic transmission) are: efficiency, smoother running and dynamic acceleration. The CVT is simpler in design than a conventional automatic. However, compared to manual transmissions, CVTs have lower efficiency and dynamics.
The main disadvantage of the variator is its incompatibility with powerful engines due to the weakness and fragility of the belts. The use of continuously variable transmissions is also limited by the need for additional mechanisms for starting and reverse modes, high cost, expensive maintenance and repairs. Read more about the CVT variator.
Robotic The gearbox is a regular manual gearbox. A standard dry single-plate clutch is also used to transfer torque from the engine to the transmission. The difference is that the processes of engaging and disengaging the clutch and shifting gears are automated. Such a box makes driving easier, freeing you from the need to change gears manually and think about which gear to engage at the moment. The advantages of a robot box include light weight, low cost and efficiency.
This type of box also has several significant disadvantages. First of all, this concerns the smoothness of its operation, which leaves much to be desired. Gears are switched with a noticeable delay, and in the “gas to the floor” mode there are jerks and jerks when shifting. The manual mode does not help either, since the clutch is still controlled electronically. In terms of clarity of switching, the “robot” is inferior even to a simple “automatic”. In addition, the “robot” is characterized by a slight rollback when starting to move. This type of box is usually installed on inexpensive models.
More advanced is the robotic dual-clutch gearbox. In such a box, one clutch engages odd gears, and the other – even ones. While driving, torque is transmitted through one clutch, that is, the disc is closed. At the same time, the second clutch disc is open, but in the box itself the next gear is already engaged.
Which box is better?
As with any rhetorical question, there is no clear answer. Which type of checkpoint to choose is a personal matter, depending on the priorities of a particular person. Decide what is more important to you (price, dynamics, comfort) - and then choosing a gearbox will not be difficult for you!
A car's manual transmission is designed to change torque and transmit it from the engine to the wheels. It disconnects the engine from the drive wheels of the car. Let's explain what a manual gearbox consists of - how it works.
The mechanical “box” consists of:- crankcase;
- primary, secondary and intermediate shafts with gears;
- additional shaft and reverse gear;
- synchronizers;
- gear shift mechanism with locking and locking devices;
- shift lever.
Scheme of work: 1 - input shaft; 2 - shift lever; 3 - switching mechanism; 4 - secondary shaft; 5 - drain plug; 6 - intermediate shaft; 7 - crankcase.
The crankcase contains the main components of the transmission. It is attached to the clutch housing, which is mounted on the engine. Because During operation, the gears experience heavy loads; they must be well lubricated. Therefore, the crankcase is filled with half its volume with transmission oil.
The shafts rotate in bearings installed in the crankcase. They have sets of gears with different numbers of teeth.
Synchronizers are necessary for smooth, silent and shock-free gear shifting by equalizing the angular speeds of rotating gears.
Switching mechanism serves to change gears in the box and is controlled by the driver using a lever from inside the car. In this case, the locking device does not allow two gears to engage simultaneously, and the locking device keeps them from turning off spontaneously.
Gearbox Requirements
- Ensuring the best traction and fuel-economic properties
- high efficiency
- ease of control
- shock-free switching and quiet operation
- inability to engage two gears or reverse at the same time when moving forward
- reliable retention of gears in the engaged position
- simplicity of design and low cost, small size and weight
- ease of maintenance and repair
Ease of control depends on the gear shift method and the type of drive. Gears are switched using movable gears, gear couplings, synchronizers, friction or electromagnetic devices. For shockless shifting, synchronizers are installed, which complicate the design and also increase the size and weight of the transmission. Therefore, the most widespread are those in which higher gears are switched by synchronizers, and lower ones by gear couplings.
How do gears work?
Let's look at an example of how the torque (rpm) changes in different gears.
a) Gear ratio of one pair of gears
Let's take two gears and count the number of teeth. The first gear has 20 teeth, and the second 40. This means that with two revolutions of the first gear, the second will make only one revolution (gear ratio is 2).
b) Gear ratio of two gears
On the image b) The first gear (“A”) has 20 teeth, the second (“B”) has 40, the third (“C”) has 20, and the fourth (“D”) has 40. The rest is simple arithmetic. The input shaft and gear “A” rotate at 2000 rpm. Gear “B” rotates 2 times slower, i.e. it has 1000 rpm, and because gears “B” and “C” are fixed on the same shaft, then the third gear also makes 1000 rpm. Then gear “G” will rotate 2 times slower - 500 rpm. From the engine, 2000 rpm comes to the input shaft, and 500 rpm comes out. On the intermediate shaft at this time - 1000 rpm.
In this example, the gear ratio of the first pair of gears is two, and the second pair of gears is also two. The total gear ratio of this scheme is 2x2=4. That is, the number of revolutions on the secondary shaft decreases 4 times compared to the primary one. Please note that if we disengage gears “B” and “D”, the secondary shaft will not rotate. At the same time, the transmission of torque to the drive wheels of the car stops, which corresponds to neutral gear.
Reverse gear, i.e. rotation of the secondary shaft in the other direction, is provided by an additional fourth shaft with a reverse gear. An additional shaft is needed to get an odd number of pairs of gears, then the torque changes direction: 
Torque transmission diagram when reverse gear is engaged: 1 - input shaft; 2 - input shaft gear; 3 - intermediate shaft; 4 - gear and reverse gear shaft; 5 - secondary shaft.
Gear ratios
Since the “box” has a large set of gears, by engaging different pairs, we have the opportunity to change the overall gear ratio. Let's look at the gear ratios:| Transfers | VAZ 2105 | VAZ 2109 |
| I | 3,67 | 3,636 |
| II | 2,10 | 1,95 |
| III | 1,36 | 1,357 |
| IV | 1,00 | 0,941 |
| V | 0,82 | 0,784 |
| R(Reverse) | 3,53 | 3,53 |
Such numbers are obtained by dividing the number of teeth of one gear by the divisible number of teeth of the second and further along the chain. If the gear ratio is equal to one (1.00), then this means that the secondary shaft rotates at the same angular speed as the primary. The gear in which the speed of rotation of the shafts is equal is usually called - straight. As a rule, this is the fourth. The fifth (or highest) gear ratio is less than one. It is needed for driving on the highway with minimal engine speed.
First and reverse gears are the “strongest”. It is not difficult for the engine to turn the wheels, but in this case the car moves slowly. And when driving uphill in the “nimble” fifth and fourth gears, the engine does not have enough strength. Therefore, you have to switch to lower, but “strong” gears.
First gear is required to start moving so that the engine can move a heavy machine. Next, having increased the speed and made some reserve of inertia, you can switch to second gear, weaker but faster, then to third and so on. The usual driving mode is fourth (in the city) or fifth (on the highway) - they are the fastest and most economical.
What types of malfunctions occur?
They usually appear as a result of rough handling of the shift lever. If the driver constantly “pulls” the lever, i.e. transfers it from one gear to another with a quick, sharp movement - this will lead to repairs. If you handle the lever this way, the switching mechanism or synchronizers will definitely fail.The shift lever is moved with a calm, smooth movement, with micro-pauses in the neutral position so that the synchronizers are activated, protecting the gears from damage. If you handle it correctly and periodically change the oil in the “box,” it will not break until the end of its service life.
Operating noise, which depends mainly on the type of gears installed, is significantly reduced when straight-cut gears are replaced with helical ones. Proper operation also depends on timely maintenance.
Transmission is an important component in a car and is designed to transmit engine power to the drive wheels. In the process of transmitting power, in the form of torque, it is transformed (increased or decreased), changed in direction, etc. The second purpose of the gearbox is to cut off torque from the transmission, with the exception of a manual gearbox. In this type of gearbox, the torque is turned off using a separate unit - the clutch.
Let's consider below all the concepts of gearboxes, their main pros and cons, and prospects.
There are main types of gearboxes:
Manual transmission (manual transmission)
Automatic transmission (automatic transmission)
Robotic transmission (manual transmission)
Variable box (variator)
The manual transmission is controlled manually, this is an older type, but has proven itself very well, especially among drivers who like to feel the full power of their iron horse. The natural disadvantage of such gearboxes is low efficiency, due to friction of gear teeth and transmission oil resistance.
There are two main types of gearboxes used in passenger cars: mechanical and automatic (hydromechanical). The manual transmission is controlled by the driver, including the desired gear of his choice (depending on the vehicle's driving mode). In a hydromechanical gearbox, gears are switched automatically depending on the engine load (crankshaft speed).
Any principle of operation gearbox is based on a change in the rotation speed of the driven gear when the number of teeth of the drive gear changes. If the number of teeth on the drive gear decreases, the driven gear will rotate at a lower frequency, and if it increases, it will rotate at a higher frequency. At the same time, as the number of teeth on the drive gear decreases, the torque on the driven gear increases.
Typically, passenger car transmissions have four or five pairs of gears with different gear ratios. Depending on their number, the gearbox is called four- or five-speed. (Reverse gear is not included in this number, although it is required in any gearbox.) The gear ratio from the lowest (first) gear to the highest (fourth or fifth) gradually decreases. The fourth gear ratio in all gearboxes is usually equal to one. This type of transmission is called direct.
The first gear is intended for starting and moving the car at the lowest speed. When accelerating to 10... 15 km/h, you can switch to second gear, then at a speed of 30... 40 km/h - to third and, finally, at a speed of 60... 70 km/h - to fourth gear. The Operating Manual for a particular vehicle must indicate the maximum speed in each gear.
Shift up gears (from low to high) only sequentially. When slowing down and shifting down, some steps can be skipped if the vehicle speed allows. For example, after driving in a straight line at 60 km/h and slowing down to 20 km/h before turning a corner, you can shift from fourth to second gear.
Recently, five-speed gearboxes have become increasingly common. The fifth gear in them is an overdrive (the gear ratio is less than one, for example, 0.8, that is, the number of teeth of the driven gear is slightly less than the number of teeth of the drive gear). This transmission allows you to drive a car at a steady speed of over 80 km/h at a reduced crankshaft speed, for example on a flat straight highway, and the engine consumes less fuel.
In modern passenger car gearboxes, all pairs of gears are in constant mesh, and for durable and silent operation, the gear teeth are helical. The synchronizer allows the driver to silently engage the required gear.
The synchronizer includes a hub rigidly mounted on the secondary shaft, on the surface of which there are teeth. A gear coupling sliding along it is placed on the teeth of the hub. The design of the clutch allows, when it is engaged, to smoothly equalize the frequency of the engaged gear with the rotational speed of the driven shaft. The ring groove on the surface of the coupling serves for a fork, which is connected to the parts of the gear shift mechanism. The gears are freely placed on the secondary (driven) shaft. They are all manufactured as one unit with straight-toothed gear rings.
To engage 1st gear, move the rear clutch back until it connects with the ring gear of the largest gear on the driven shaft. In this case, the rotating force from the engine is transmitted to the secondary shaft through the gears.
To engage reverse gear, use the intermediate gear. When moving in reverse, rotation from the input shaft to the secondary shaft is transmitted through the intermediate shaft gear and the gear to the movable gear, which is moved all the way back along the shaft splines. In this case, the secondary shaft changes the direction of rotation to the opposite.
Automatic transmission is also known and used for a long time in the automotive industry. Switching speed levels occurs automatically, but the command to start moving or reversing requires a command from the driver. Like a manual transmission, an automatic transmission has low efficiency for the same reasons and due to the presence of planetary gears in the gearbox.
Of course, our ladies are fans of such boxes. Many simply do not know that there used to be a third pedal – the clutch. The American consumer can also be considered a lady; Americans very rarely buy cars with manual transmission.
As mentioned above, manual transmission is the best transmission option, and even a robotic gearbox is made on its basis, but with automatic control. The robot's control can even adapt to its driving style. The disadvantages are the same as those of mechanics, but there are many more advantages. By using two shafts, it was possible to increase efficiency, reduce overall dimensions, and increase the reliability of the box.
Automatic transmissions (AT) are found mainly on foreign (especially American) cars, and on domestic ones - on some Volga cars. The main difference between an automatic transmission and a manual transmission is the transmission of torque from the engine to the transmission through the pressure of the fluid flow in the torque converter (there is no clutch mechanism).
A torque converter is one of the types of hydrodynamic transmission. It consists of pump and turbine wheels and a reactor placed between them, filled with liquid. The pump wheel is rigidly connected to the flywheel and drive shaft and, when the engine is running, creates a powerful flow of fluid that rotates the turbine wheel. From the turbine wheel blades, liquid falls onto the reactor blades, resulting in a reactive force directed in the direction of rotation of the turbine wheel. Depending on the rotational speed of the engine crankshaft, the reactive force increases or decreases, and in the step mechanism (gearbox), connected to the torque converter by the driven shaft, automatic gear shifting is carried out - respectively, up or down (up or down).
The use of a torque converter allows you to move away smoothly and accelerate smoothly under load, continuously changing the speed of the vehicle.
A car with an automatic transmission is certainly easier to drive than a car with a manual transmission. However, such cars are usually more expensive, and repairing an automatic transmission in the event of a breakdown is more difficult.
To lubricate the parts of a manual transmission, gear oil is used, a certain volume of which is poured into the gearbox housing and final drive. Transmission oil reduces energy costs to overcome friction, reduces wear of parts, and prevents overheating and corrosion. In passenger cars, transmission oils of groups GL-4 and GL-5 (according to the international API classification) are used.
They correspond to domestic oils of groups TM-4 and TM-5. Transmission oils are divided into viscosity classes: 75W, 85W, 90 and 140 (according to SAE classification depending on the season) or 9; 12; 18 and 34 (according to domestic classification). The higher the number, the higher the viscosity. The indicated numbers are included in the designation of the oil brand. Imported all-season oil 85W-90 of group GL-5 corresponds to all-season oil TM-5-18. For some cars, the manufacturer recommends using motor oil of a certain viscosity in transmission units. A special fluid is used in torque converters of automatic transmissions. In addition to its quantity (level) and quality (compliance with a given automatic transmission model), the driver also needs to monitor its temperature during operation. The automatic transmission fluid cooling system is structurally combined with the engine cooling system, so a car with an automatic transmission cannot be towed with the engine not running for longer than a certain time: the fluid, without receiving sufficient cooling, will overheat, and automatic transmission parts may fail.
