Purpose of the device and principle of operation of the gearbox. Purpose and design of the gearbox. Shafts and gears
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 us 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)
Manual transmission controlled manually, it's more old look, 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 a corner, you can shift from fourth to second gear.
IN Lately Five-speed gearboxes are becoming more 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 rims.
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 best option boxes, 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 rotation 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 switching gears - up or down, respectively (high or low).
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 are used (according to international classification API).
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. The imported all-season oil 85W-90 of the GL-5 group corresponds to the 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.
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 gear sets with different number 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 work also depends on service on time.
Almost everyone who has dealt with a car or other type of wheeled vehicle knows well that in addition to the design of the vehicle, a gearbox is also used. The gearbox () is the second most important unit after the engine on different types Vehicle.
At the same time, there are several types of gearboxes, but the main task of these units on a car is to receive, convert and further transmit from the engine to the drive wheels of the car. Next, we will consider in detail the purpose of the gearbox and why a gearbox is needed in a car transmission device.
Read in this article
Why is a gearbox needed in a car?
So, the gearbox is considered the main element of a car's transmission. As already mentioned, its main purpose is to change the torque from the engine, as well as the speed and direction of movement of the car. The box also allows you to “disconnect” the engine from the transmission during gear changes.
It is thanks to the gearbox that the car is able to move forward and backward, movement can be carried out at different speeds, while the engine operates stably at different speeds and loads, and smooth gear shifting is achieved while driving.
To make it clear, the main task of the gearbox is the need to provide both the required dynamic performance of the vehicle and the fuel efficiency of the engine. This takes into account different conditions movements, load, speed, etc.
- Let's move on. The engine speed range is different from the wheel rotation range. Also, in relation to internal combustion engines, it is necessary to take into account the speed of maximum power and maximum torque.
So, to start and accelerate you need torque, while to drive at high speeds and overcome heavy loads you need power revolutions. At the same time, the peculiarity of the internal combustion engine is that the torque speed is “average” (3000-3500 rpm), while the engine reaches “power” speeds closer to the maximum values (5500-6000 thousand rpm).
In simple words, if the load on the engine is high and the speed is too low, the engine will not be able to produce enough power and will stall. If the speed is too high, and driving at high speed is not necessary, fuel consumption increases significantly. To achieve optimal balance, the box includes a change.
Thanks to this feature, you can confidently start from a standstill, move at low speed, reverse, etc. It is also possible to maintain engine speed in the optimal range in relation to constantly changing road conditions and loads.
For example, accelerating a car involves the need to overcome high values of resistance forces (overcoming increased friction and inertia forces). The presence of a gearbox makes it possible to start from a stop and accelerate to medium and high speeds, which involves a smooth or stepwise transition from low to higher gears (gear shifting).
As a result, the speed increases gradually, and the dynamic loads on the engine and transmission are greatly reduced. In this case, it is optimal to keep the speed precisely in the range of high engine torque values.
Taking into account the weight and characteristics of the vehicle, the installed engine, the intended purpose of the vehicle and a number of other characteristics and features, designers select the number of gears and gear ratios in the box, etc. (in the presence of).
Types of gearboxes: types of gearboxes
Having understood the purpose of the box, it should be noted that the gearboxes themselves can be stepped, continuously variable and combined. Let's look at these types of boxes in more detail. First of all, the most common type of transmission is the stepped transmission. In such gearboxes, the torque changes in steps. This type includes (mechanics) and (robot box).
- The manual transmission is a multi-stage cylindrical gearbox, which allows the driver to manually change gears. Manual transmissions come in four-speed, five-speed, six-speed, etc. The main advantage of such a box is considered to be reliability and simplicity, as well as complete control in all modes.
- A robotic gearbox (robotic gearbox) is still the same mechanics, but the functions of releasing the clutch and shifting gears are fully automated thanks to the use of separate actuators controlled by the box (for example, gearbox).
The most modern manual transmissions have and are distinguished by a complex design. At the same time, the double clutch makes the switching process fast and smooth, torque is transmitted without interrupting the power flow from the internal combustion engine to the wheels.
As a result, such a gearbox shifts faster than a professional driver or an experienced racing driver could do. A car with such a “robot” (for example,) is distinguished by fast acceleration, as well as maintaining optimal engine speed and at the same time high fuel efficiency. The disadvantage is considered to be the complexity of repairs, reduced service life, low maintainability and the high cost of individual spare parts and elements.
What is the difference between a “classic” automatic transmission with a torque converter and a robotic gearbox with one clutch and preselective robots such as DSG.
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 the gearbox is based on the fact that different gears have different number 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. Using different combinations meshing gears (installed 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 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.
The gearbox, or transmission in other words, transmits the rotational force - the so-called torque - from the car engine to the wheels. Moreover, depending on the driving conditions of the vehicle, it can transmit torque completely or partially.
A car going uphill should be in a lower gear than a car going down a flat highway. With a lower gear, more torque is transmitted to the wheels. And this is required when the car is moving slowly because it is hard. Higher gears are suitable for driving the car faster.
There are manual transmissions, but there are also automatic ones. To change gear in a manual transmission, the driver first presses the clutch pedal (picture on the left). In this case, the engine is disconnected from the gearbox. Then the driver moves the control lever to another gear and releases the clutch pedal. The engine is reconnected to the gearbox and can once again transfer its energy to the wheels. In an automatic transmission, the position of the gas (accelerator) pedal is correlated with the speed of the vehicle, and the gear is automatically changed if necessary.
Manual transmission control
The accompanying diagrams show how the control lever can be used to change from one gear to another. Depending on the gear installed, different shares of torque, passing through the gearbox (red lines with arrows), reach the wheels. Neutral gear. Engine energy is not transferred to the wheels.
Neutral gear. Engine energy is not transferred to the wheels.
First transfer. The largest gear on the drive shaft is connected to its pair on the driven shaft. The car moves slowly, but can overcome difficult sections of the road.
Second gear. The second pair of gears works together with the clutch mechanism. In this case, the vehicle speed is usually from 15 to 25 miles per hour.
Third gear. The third pair of gears works together with the clutch mechanism. The speed of the car is even greater, and the torque on the wheels is less.
Fourth gear. The input and output shafts are connected directly (direct transmission) - the vehicle speed is maximum and the torque is the lowest.
Reverse (5th gear in the picture) When reverse gear is engaged, its drive gear rotates the output (drive) shaft in the opposite direction.
Accelerator operation
The engine speed per minute depends on how much fuel flows from the carburetor into the cylinders. The movement of fuel is regulated by the carburetor throttle valve, and the operation of the throttle valve is controlled using the accelerator pedal, which is located on the floor in front of the driver.
When the driver presses the accelerator pedal with his foot, the throttle valve opens and more fuel flows into the engine. If the driver releases the accelerator pedal, the throttle closes and the amount of incoming fuel decreases. At the same time, both engine speed and vehicle speed decrease.
Automatic transmission
When an automatic transmission is used, the driver does not have a clutch pedal under his foot. Instead, a torque converter paired with a planetary gear (picture on the right and below) automatically disconnects the engine from the drive shaft when driving conditions require changing to another gear.
And after the gear has changed, the drive shaft is reconnected. As soon as the driver puts the control lever in the operating position, the automatic transmission mechanism itself will select the desired gear in accordance with the driving conditions of the car at the moment.
