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 the gearbox gears experience heavy loads during operation, 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
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 in different types of vehicles.
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
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 driving conditions, load, speed, etc.
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 for 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).
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 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.
When beginners get behind the wheel of a car, at the stage of learning to drive, they have problems with the gearbox, or rather, with the need for constant shifts. Many have thought more than once that without this “poker” the car would be more ideal. But, unfortunately, without it the car would not be able to operate efficiently. This is due to the characteristics of the internal combustion engine. Let's find out the purpose of its types, structure and principle of operation.
If you open the reference books, it says that this mechanism is used to change the torque generated by the internal combustion engine. The gearbox also serves to temporarily cut off torque from the engine and for reversing.
Now let’s look at the purpose from the point of view of people who are far from the design and theory of the car. It is also worth understanding why you need to change the gearbox stages every time you drive.
The need to constantly change gears is directly related to the characteristics of internal combustion engines. Unlike electric units, the torque of an internal combustion engine has an uneven characteristic.
The main difference between electric motors and internal combustion engines is the thrust characteristics. This characteristic describes how power and torque change depending on the speed. In the case of electric motors, the torque is available immediately, and as the speed increases, the torque will fall.
This characteristic is more suitable for a car - at the moment of starting movement and during acceleration, when you need to make a lot of effort to overcome inertia, it is better to have a large torque. In order to move further evenly, much less effort is required. The power of electric motors in any rotor speed range is close to maximum, and in any mode it is realized and used almost completely. Therefore, electric motors are more suitable for use as a vehicle propulsion system. In an internal combustion engine, everything is a little different. When the crankshaft speed is low, the power is also low. The torque remains virtually unchanged.
If the resistance to movement increases and the speed begins to decrease, the electric motor will increase the torque. In the case of an internal combustion engine, the torque will increase only slightly and then decrease.
The traction performance of an internal combustion engine is considered completely unsatisfactory. But even now, in terms of efficiency, overall dimensions, and other qualities, they are significantly superior to modern electric power units. Based on these considerations, engineers accepted the shortcoming of the internal combustion engine and created a gearbox to solve this problem. Its purpose is to change the gear ratio between the crankshaft and the drive pair of wheels. As a result, maximum torque is available in a narrow range of optimal speeds, but in different gears. This makes the engine run more efficiently.
To better understand the purpose of a gearbox in a car, you should remember the school physics course and some sections of mechanics.
In gear-based transmission systems, where two gears operate, the diameter and number of teeth will determine the speed and torque. The ratio of the number of teeth on the driven gear to the number of teeth on the drive gear is the gear ratio. When the drive gear has a smaller diameter than the driven one, the speed at the latter will be lower, and the torque, on the contrary, will be higher.
While there is a gain in strength, there will be a loss in speed. And having gained in speed, we will notice a loss in strength. If there are several gears in the transmission mechanism, then the gear ratio is determined by multiplying the numbers of each pair of gears. The purpose of the gearbox is precisely to change gear ratios.
To obtain the different torque that is needed to drive a car in different road conditions, the gearbox has several pairs of gears. They come with different gear ratios. If you install an intermediate gear in a pair of drive and driven gears, the latter will rotate in the opposite direction - this is reverse gear.
Any type of car gearbox is necessary so that the internal combustion engine can operate at optimal speeds and in its normal operating modes, and also so that the engine power can be effectively used in any driving situations by simply changing the gear ratio.
In order to start moving a car and gain an initial low speed, as well as to move in off-road conditions, a torque close to maximum is required. It can be achieved in the middle engine speed range. There is no need for high speed in this case. For this purpose, the gearbox has lower gears - first, second, sometimes third. At the same time, even at high speeds in first gear the car will drive quite slowly.
To move evenly at higher speeds, the wheels must rotate at a high frequency. In this case, the engine speed should be optimal. For this, there are higher gears - fourth, fifth (and if the gearbox is 6-speed, then sixth). Here the gear ratios are lower. The car will move quickly at the same optimal speed until the internal combustion engine reaches the maximum or maximum permissible speed. In higher gears, acceleration will no longer be as effective. Also, in higher gears it will not be possible to drive at low speeds. The car will not be able to move. The engine simply will not be able to provide the required torque.
There are now a lot of different manual transmission designs in the world. Most front-wheel drive cars have two-shaft mechanisms. Three-shaft ones are installed on rear-wheel drive vehicles. It must be said that even in our time, when technology is developing very quickly, mechanics are very popular. The fact is that repairs of this type are simple and inexpensive, unlike automatic transmissions and CVTs.
It is based on the primary and secondary shaft of the gearbox. Also in the vehicle gearbox there is a gear block along with synchronizers. The metal transmission housing houses the main gear mechanism and the differential.
Using the input shaft, the vehicle's transmission can be connected to the clutch assembly. A block with gears is rigidly fixed to the shaft. The gearbox also has a secondary shaft. It is located parallel to the primary. It is also equipped with a gear block. The latter are constantly in rigid engagement with elements from the block on the input shaft. Also, the transmission secondary shaft is connected through a gear to the main gear. The gear block is equipped with synchronizers. In different designs there may be several secondary shafts.
Additionally, the box is equipped with a gear shift mechanism. Most often it is remote. Since the car's transmission housing is small, the elements are located under the hood.
The input shaft serves to connect the gearbox mechanism to the clutch assembly. There are splines on the shaft onto which the driven disk is placed. The torque from the engine is transmitted through the gearbox gear, which is in mesh with these elements. There is an intermediate element located in parallel. It is equipped with a block of gears that are in rigid engagement with the shaft.
The secondary shaft is on the same axis as the primary. The gears are not rigidly meshed and rotate freely. The intermediate and secondary shaft gears, as well as the part on the input shaft, are constantly engaged.
Synchronizers are installed between the gears. The shift mechanism is installed directly in the vehicle's transmission housing. It consists of a shift lever, as well as sliders and forks.
So, we found out what a gearbox is. As you can see, this is a very important component in the design of any car. It is this that allows the vehicle to move with different forces and speeds. The movement of the car is largely determined by the gearbox.
4. Transfer and additional gearboxes.
1. Purpose and types of gearboxes.
The purpose of the gearbox is to change the traction force, speed and direction of the vehicle. In automobile engines, as the crankshaft rotation speed decreases, the torque increases slightly, reaches a maximum value, and with a further decrease in rotation speed also decreases. However, when driving a car on hills, on bad roads, when starting from a stop and rapid acceleration, it is necessary to increase the torque transmitted from the engine to the drive wheels. The gearbox serves this purpose, which also includes a gear that allows the car to move in reverse. In addition, the gearbox ensures that the engine is decoupled from the transmission.
A manual transmission consists of a set of gears that mesh in various combinations to form several gears or stages with different ratios. The greater the number of gears, the better the car “adapts” to different driving conditions. The gearbox should operate silently, with minimal wear; This is achieved by using gears with helical teeth.
Based on the number of forward gears, step transmissions are divided into four- and five-speed. Typically, the transmissions of passenger cars, small buses and light-duty trucks have four stages, while the transmissions of large buses and heavy-duty trucks have five stages. All domestically produced passenger cars, buses of the RAF, KAVZ, PAZ families and trucks of the U AZ and G AZ families have four-speed gearboxes, and buses of the ZIL, LAZ families and trucks of the ZIL, Ural, MAZ and KamAZ families have five-speed gearboxes.
Step transmissions can be simple or planetary. Most cars use simple stepped gearboxes, in which gear shifting occurs in two ways: by moving gears or moving clutches.
Sometimes cars are equipped with continuously variable transmissions with continuously variable gear ratios and combined gearboxes, which use both methods of changing the gear ratio. The latter include gearboxes of buses of the LiAZ family, consisting of a torque converter operating in conjunction with a two-stage gearbox, and gearboxes of passenger cars of the Chaika and ZIL families, as well as gearboxes of dump trucks of the BelAZ family, consisting of a torque converter operating in conjunction with an automatic transmission. planetary three-speed gearbox. Stepless change of the gear ratio in these boxes is carried out using a torque converter.
2.Scheme and principle of operation of a manual transmission.
In a simple stepped gearbox (Fig. 126) there are three shafts: drive (primary) A, connected through the clutch to the engine crankshaft; driven (secondary) B, connected through a cardan transmission and other mechanisms to the driving wheels of the car; intermediate B. The drive gear 1 is manufactured as a single unit with the drive shaft and is in constant engagement with the driven gear 8, rigidly connected to the intermediate shaft. When the clutch is engaged, the drive and intermediate shafts rotate.
Rice. 126 - Three-speed gearbox diagram:
A - drive shaft; B - driven shaft; B - intermediate shaft; G - axis of the reverse gear gear; 1-8 - gears.
Movable gears 2 and 3 are installed on the driven shaft, and gears 7, 6 and 4, as well as wheel 8, are rigidly connected to the intermediate shaft. The ratio of the number of teeth of the driven gear to the number of teeth of the drive wheel, the inverse of the ratio of their rotational speeds, is called the gear ratio. For example, the gear ratio of a gear consisting of gears 8 and 1,
Iv = Z8/Z1, where Z8 is the number of teeth of the driven gear 8; Z 1 - number of teeth of drive gear 1.
When any gear on the driven shaft meshes with one of the gears on the intermediate shaft, torque from the engine is transmitted through the drive, intermediate and driven shafts of the transmission to the driveline and then to the drive wheels of the vehicle. To engage first gear, wheel 3 is moved forward, engaging it with gear 6 of the first gear of the intermediate shaft. The total gear ratio of the first gear is determined as the product of the gear ratios of individual pairs of gears, i.e. where ZЗ. and Z6 are the numbers of teeth of wheel 3 and gear 6, respectively.
When first gear is engaged, the torque of the MK on the driven shaft of the gearbox increases compared to the torque of the engine Dm by N times, i.e. Z8 ZЗ.
MK = DmU1 = Dm
And it has the maximum value, since gear 6 is the smallest of the gears of the intermediate shaft, and wheel 3 is the largest of the gears of the driven shaft.
First gear is used when driving the car in the most difficult road conditions, on steep climbs, as well as when starting off on a bad road and with a load. For passenger cars, the first gear ratio is Ш = 3 -;- 4, for buses I! = 3 -;- 7, for trucks UJ = 4 -;- 7.
The second gear is provided by the inclusion of gears 2 and 7. Then where Z2 and z7 are the numbers of teeth of the gears, respectively 2 and 7. The second gear is intermediate. In the above diagram of a three-speed gearbox, it is the only one. Four- and five-speed transmissions may have two or even three intermediate gears.
When direct (in this case third) gear is engaged, the drive and driven shafts are connected directly through gears 1 and 2 (Iz = 1). Direct transmission is the main transmission used when driving a car on a good road.
Gear shifting is performed with the clutch disengaged, bringing the movable gear wheels (carriages) of the driven shaft into engagement with the stationary gear wheels of the intermediate shaft. This engagement is accompanied by impacts of the ends of the teeth and their increased wear. Therefore, cars often use gearboxes with constant mesh gears, which are characterized by high durability.
With the gear 4 of the intermediate shaft in constant engagement is the intermediate gear 5 of the reverse gear, which in Fig. 126 is conventionally depicted in the plane of the drawing. To engage reverse gear, gear 3 moves backward, engaging it with the intermediate gear 5 of reverse gear, which rotates freely on its axis.
3. Gearbox control mechanism.
The control mechanism that changes gears is usually located in the gearbox cover and is operated by a rocker lever. For example, in the gearbox control mechanism of a ZIL-130 car, lever 51 (see Fig. 129), mounted directly on the gearbox, swings freely in the spherical socket of the gearbox cover, resting on it with a ball thickening. The lever is held by a spring and a latch 50. The lower end of the lever 51 fits into the groove of one of the forks mounted on the sliders 54 and 55. The movement of the lever forward or backward causes the slider to move in the opposite direction, as a result of which its fork moves a gear wheel or clutch, including one of transmission To reduce the travel of the gear shift lever when engaging first gear or reverse gear, an intermediate lever 52 mounted on the axis 49 is used. Thus, the travel of the lever is the same for engaging all gears: both when moving the sliders connected by forks with synchronizers, and when moving the slider, moving the gear wheel 16 of first gear and reverse gear using a fork.
Precise installation of the gears in the on and off positions is ensured by clamps consisting of 9 balls and 10 springs placed vertically in the bosses of the gearbox housing cover. The balls fit into the recesses of the sliders. There are three recesses on each slider: one (middle) for the neutral position and two for the corresponding gears. The distance between the recesses ensures that the gears engage along the entire length of the teeth.
Accidental engagement of two gears at the same time is prevented by a lock consisting of a pin 11 and two pairs of balls 12. If one of the sliders moves, the other two are locked by the balls. There are corresponding recesses on the sliders for the lock balls. When the middle slider moves, the balls come out of its recesses, enter the recesses of the outer sliders and lock them. If one of the outer sliders moves, the balls come out of its recesses and enter the recess of the middle slider, and the other outer slider is locked due to the fact that the pin 11 moves towards it and presses on the balls on the other side of the middle slider. To move one of the sliders, the other two must be placed in a neutral position.
To engage first gear or reverse gear, it is necessary to apply additional force to use lever 51 to compress the spring of fuse 48 until it stops. Only after this can the gear shift lever be moved to the position corresponding to engaging first gear or reverse gear.
The transfer case is used to distribute torque from the gearbox between the drive axles of the vehicle. A device for turning the front drive axle on and off is also placed in the transfer case.
On vehicles designed to operate in difficult road conditions, an additional gearbox is installed with two reduction gears or one direct and one reduction gear, which can further increase the traction force on the drive wheels in any gear in the main gearbox. The additional gearbox, as a rule, is structurally combined with the transfer case.
Typically, a transfer case downshift is engaged when the vehicle is used as a tractor, towing heavy flails, when driving on steep inclines and in difficult road conditions. For example, the transfer case of a GAZ-66 off-road truck with two drive axles is one unit with an additional two-speed gearbox (Fig. 134a).
The drive shaft 4 of the transfer case is connected by a cardan transmission to the driven shaft of the gearbox. The front ball bearing of shaft 4 is located in the wall of the transfer case housing, and the rear roller bearing is located in the groove of gear 6, manufactured as one piece with the driven shaft of the rear axle. Shaft 11 of the front axle, the shaft of the rear axle and the intermediate shaft 9 rotate on ball bearings.
Moving along the splines, gear 10 of the intermediate shaft can engage with gears 6 and 12, and gear 5 of the drive shaft with wheel 13. Gear 6, in addition to the outer ring gear, has an internal ring for engagement with gear 5. Gears 13 and 12 are fixedly fixed on the shaft splines.
The ends of the drive shafts of the front and rear axles coming out of the transfer case housing are splined.
Rice. 134 - Transfer case:
a - design; b - locking device; 1, 2 and 14 - plugs; 3 ~ breather; 4 - drive shaft; 5 - drive shaft gear; 6 - driven shaft gear; 7 - worm wheel of the speedometer drive; 8 - drive worm, cardan joint flanges are installed, secured with nuts and washers. 9 - intermediate shaft; 10 and 13 - intermediate shaft gears; 11 - front axle drive shaft; 12 - front axle drive gear; 15 - cap; 16 - cracker; 17 - spring; 18 and 25 - forks; 19 and 20 - sliders; 21 - nut; 22 - ring; 23 - washer; 24 – oil seal.
The torque from the drive shaft 4 of the transfer case is transmitted to the front axle by gears 5, b, 10 and 12. When introducing the gear speedometer; Wheel 5 engages with the internal gear ring of wheel 6 of the driven shaft, and the highest (direct) gear of the rear axle is engaged. If you also engage gear 10 with gears b and 12, then the direct transmission of the front axle will be engaged. When gear 5 moves to the left until it engages with wheel 13 (gear 10 remains engaged), a downshift is engaged. In this case, torque is transmitted to the rear axle through gears 5, 13, 10 and 6, and to the front axle through gears 5, 13, 10 and 12. The reduction gear ratio is 1.96. To make it easier to engage the front axle, gears 10 and 6 are constantly meshed to an incomplete tooth length.
Oil is poured into the crankcase through a hole closed with plug 2, which is also used to control the oil level. The oil is drained through the hole closed by plug 1. Breather 3 is used to ventilate the transfer case housing. The transfer case control mechanism of the GAZ-66 car consists of a forward and downshift shift lever and a front axle lever. Both levers are connected by rods to the transfer case sliders. When the left lever is in the forward position, the front axle of the car is on, and when this lever is in the rear position, it is off. If the right lever is moved from the neutral position forward, a direct gear is engaged, and from the neutral position backwards, a downshift is engaged.
When driving the car in difficult road conditions (mud, sand, snow), the front axle is turned on. However, this should not be done unless necessary, as it increases fuel consumption and accelerates the wear of tires and transmission parts. While the vehicle is moving with the direct transmission engaged in the transfer case, the front axle is engaged without disengaging the clutch.
The downshift in the transfer case is switched on when the car is moving on an incline or in difficult road conditions. This gear can only be engaged after stopping the car and engaging the front axle. The front axle can be turned off only after switching the downshift in the transfer case to direct. All this protects the parts of the cardan transmission and rear axle from overload. The locking device (Fig. 134.6), available in the transfer case control system, does not allow you to engage a downshift when the front axle is turned off and disengage the front axle when the downshift is engaged.
In the transfer case housing, sliders 19 and 20 can move, on which forks 18 and 25 are secured with screws pinned with wire. Between the sliders in the crankcase wall, two crackers 16 are placed with a spring 17 between them. The outlet hole for the crackers is closed with a plug 14 screwed into the thread. The holes at the outer ends of the sliders are closed with caps 15. On the opposite side, seals are installed in the crankcase wall, consisting of seals 24, washers 23, rings 22 and nuts 21.
On the slider 19, used to turn the front axle on and off, there are two recesses of different depths for the locking device's crackers. On the slider 20, which turns off direct or downshift, three recesses are made for crackers: the left one corresponds to the inclusion of direct gear, the middle one to the neutral position and the right one to the engagement of downshift. There is a weasel between the left and middle notches. The position of the crackers in Fig. 134, b corresponds to the disabled front axle. In this case, the slider 20 can move from the neutral position to the position corresponding to the engaged direct transmission. Due to the presence of weasels on the slider between the grooves, the crackers do not interfere with this movement. Further movement of the slider 20 is impossible, since the crackers, compressing the spring, will rest against one another and will impede movement.
When the front axle is turned on, a deep recess in the slider 19 will be installed opposite the runners. When the runner 20 moves, the runners will not rest against each other, and engaging a downshift will become possible. In this case, it will be impossible to turn off the front axle without first turning off the downshift.
LECTURE No. 8
TOPIC: CARDAN GEARS.
PLAN:
1.Types of cardan gears.
1.Types of cardan gears.
The rear drive axle is suspended from the car frame on springs and changes its position relative to the frame while driving; The gearbox is fixed to the frame. Therefore, to transmit torque from the driven shaft of the gearbox to the drive shaft of the main gear, the axes of which intersect and are located at an angle that changes with increasing or decreasing load, as well as due to shocks when the vehicle moves on an uneven road, cardan transmissions are used.
The cardan transmission consists of shafts, their supports and cardan joints. Cardan drives are installed between the clutch and the gearbox, located separately from the engine; between the gearbox and the transfer or additional box; between the main gears of two driving rear axles of a three-axle vehicle; between the main gear and the axle shafts of the drive wheels with independent suspension; between the axle shafts and the front steered wheels; in drive to the winch and other auxiliary mechanisms.
Cardan transmissions are divided into single and double according to the number of cardan joints. If a transmission has only one universal joint located at the gearbox, then such a transmission is called a single transmission. Such gears are used only when the shafts are located at a slight angle and are rarely installed on cars nowadays. In a double driveline, the universal joints are located at both ends of the driveshaft.
Regardless of the speed of the vehicle, the driveshaft should not experience any significant torsional vibrations or beats. To reduce runout, dynamic balancing of the driveshaft assembly with cardan joints is performed. The imbalance is eliminated by welding balancing plates at the ends of the cardan tubes, and, if necessary, by installing balancing plates under the cardan joint covers. The correct relative position of the spline joint parts after balancing is fixed with special marks.
If there is a gearbox extension (Fig. 136, a), the cardan transmission of passenger cars (G AZ-24 Volga, Moskvich-2140) is made in the form of a cardan shaft 2 with two cardan joints. The cardan drive directly connects the gearbox to the rear axle 3. A splined connection of the front cardan joint to the driven shaft of the gearbox is placed inside the extension. The same type of cardan transmission is used on the MAZ-5335 short-wheelbase truck and its modifications.
Cars G AZ-53A, G AZ-53-12, ZIL-130, VAZ “Zhiguli” family and others have a cardan drive (Fig. 136), consisting of an intermediate 4, a main 2 shaft and three hinges. This eliminates the possibility of strong shaft vibration. In the GAZ-66 car, the torque from the gearbox (Fig. 136, c) is transmitted through shaft 4 to the transfer case 6, and from it through shafts 2 and 7, respectively, to the rear 3 and front 8 drive axles. Cardan joints are placed at the ends of the shafts, one of which is rigidly fixed, and the other has a sliding connection with the shaft.
The cardan transmission of three-axle vehicles (ZIL-131, KrAZ-260), having a 6 x 6 wheel arrangement, with sequential through drive of the rear axles is shown in Fig. 136, g. The first rear drive axle has a through shaft of the main gear, which transmits torque through the cardan shaft 9 to the second rear drive axle 10. In Fig. 136, d shows the cardan transmission of three-axle vehicles (<<Урал-4320») с колесной формулой 6 х 6 с параллельным приводом задних мостов. В этом случае на картере первого заднего моста устанавливают промежуточную опору и привод второго заднего моста осуществляют от раздаточной коробки через валы 11 и 9.
Three-axle vehicles with a 6 x 4 wheel arrangement do not have a cardan drive to the front axle. The angular movement of the cardan shafts is ensured by the design of the cardan joints, and the change in the distances between the joints is ensured by the presence of splined connections of the cardan joint forks with the cardan shaft. Typically, for a stationary vehicle, the angles between the shafts connected by cardan joints do not exceed 5-90, but when moving they can be 20 - 300. In the drive between the main drive of the front drive axle and the driving steered wheels when turning, these angles can reach 30 - 400, depending on the size of the angles between the axes of the shafts being connected, soft and hard cardan joints can be used. In the first, the angular displacement of the shafts occurs due to the deformation of elastic (usually rubber) elements, and in the second, due to the hinge joints of metal parts. In cars, mainly rigid universal joints are used.
2. Design and operation of universal joints and shafts.
Rice. 136 - Location of cardan gears on cars: a - passenger cars; b - cargo; c - d - off-road cargo; 1 - gearbox; 2, 4, 7, 9 and 11 - cardan shafts; 3 and 10 - rear drive axles: 5 - intermediate support; 6 - transfer case; 8 - front drive axle.
Rice. 137 - Cardan joints:
a - c - unequal angular velocities; d and d - equal angular velocities; 1 - cover; 2 - locking plate: 3 - bearing cup; 4 - needles; 5 - felt seals; 6, 10. 24 and 28 - forks; 7 - safety valve; 8 - cross; 9 - oiler; 11 - cardan shaft; 12 - reflector; 13 - self-clamping oil seal; 14 - retaining ring; 15 and 16 - radial and mechanical seal seals; 17 - inner fist; 18 - central ball; 19 - outer fist; 20 - driving balls; 21 - pin; 22 - hairpin; 23 - axle shaft; 25 and 27 - semi-cylindrical fists; 26 - central disk.
According to kinematics, cardan joints are divided into joints of unequal and equal angular velocities. Typically, in all automobile drives, except for the drive to the driven steered wheels, unequal velocity joints are used.
Consider, for example, the cardan transmission of a G AZ-53A car with rigid cardan joints of unequal angular velocities (Fig. 137, a). Cardan transmissions of this type are most widespread. Such cardan joints consist of two steel forks 6 and 10 mounted on the shafts and a crosspiece 8 pivotally connecting them, installed in the ears of the forks on needle bearings. The bearings, consisting of cups 3 and needles 4, are put on the ground spikes of the cross 8, made of chromium steel, and secured in the eyes of the forks 6 and 10 by locking plates 2 with covers 1 placed under them. Oil seals 5 prevent the leakage of lubricant from the bearings, which enters through oiler 9 and channels in the cross. Safety valve 7 is used to remove excess lubricant.
Another universal joint with a needle bearing, in which rubber self-clamping seals 13 are used, and the bearing cups are secured in the forks with retaining rings 14, is shown in Fig. 137, b. Such universal joints are used on the GAZ-3102 Volga car. To more reliably protect needle bearings from oil leakage, two oil seals are sometimes installed - radial and mechanical, as, for example, on KamAZ family vehicles (Fig. 137.6). The design of one of the joints included in the cardan transmission must allow axial movement of the cardan shaft. Typically, a splined connection of one of the universal joint forks with the shaft is used for this purpose.
A simple rigid cardan joint, at large angles between the axes of the shafts it connects, cannot ensure uniform rotation of the driven shaft. When the driving fork rotates uniformly, the driven fork rotates unevenly. During one revolution of the propeller shaft, the driven fork, when rotating, twice overtakes the driving fork and twice lags behind it. As a result, additional loads arise on the parts of the main gear, differential, axle shafts and wheels, and their wear increases. To eliminate uneven rotation of the driven shaft, use a double cardan drive with rigid cardan joints or a single cardan drive with a cardan joint of equal angular velocities.
If in a double cardan drive the angle between the axes of the driven shaft of the gearbox and the cardan shaft is equal to the angle between the axes of the cardan shaft and the drive shaft of the main gear, then with uniform rotation of the driven shaft of the gearbox, the drive shaft of the main gear will also rotate evenly. In this case, both forks mounted on the cardan shaft must be located in the same plane.
Constant-velocity universal joints that ensure uniform rotation of the driven shaft are most often ball and cam joints. In the front drive axles of cars of the ZIL, GAZ and UAZ families, ball joints of equal angular velocities with long grooves are used (Fig. 137, d). The outer knuckle 19, on the splines of which the wheel hub is mounted, is made as one piece with the driven fork, and the inner knuckle 17 with the splines entering the hole of the differential axle gear is forged as one piece with the drive fork. The forks are connected to each other using four leading balls 20 located in the grooves of the forks. To center the forks, there are spherical recesses at their ends, into which the central ball 18 is placed. The driving balls 20 transmit torque from the driving fork to the driven one. The central ball 18 prevents the drive balls from rolling out of the grooves. The central ball has a weasel, which, when assembling the universal joint, is rotated towards the inserted drive ball. The pin 22, located in the axial channel of the driven fork, with one end enters the hole of the central ball 18, locking the assembled cardan joint.
The dividing grooves have a shape in which the driving balls, regardless of the angular movements of the forks, are always located in a plane bisecting the angle between the axes of the driving and driven forks. Thanks to this, both forks have the same rotation speed.
The cam universal joint (Fig. 137, e) consists of forks 24 and 28, semi-cylindrical knuckles 25 and 27 and a central disk 26 inserted into the internal grooves of these fists, the cylindrical surfaces of which cover the forks 24 and 28. Such a joint works like two articulated joints unequal angular velocities. In one plane, the forks rotate relative to the fists, and in the other plane, together with them relative to the central disk. Such hinges are installed on the Ural-4320 vehicle.
To achieve sufficient strength with low weight, cardan shafts are usually made in the form of steel pipes. The universal joint forks are welded to the shafts or put on the splines of the tip welded to the pipe. This sliding joint is covered with a rubber boot.
In passenger cars with an extension in the gearbox, a cardan transmission with one driveshaft is used (Fig. 138, a).
Rice. 138 - Cardan transmissions:
a - with one shaft; b - with two shafts (ZIL-l30 car); c - with two shafts and an elastic joint (VAZ-2101 Zhigulya car; 1 and 3 - forks; 2 and 19 - oil nipples; 4 - splined bushing; 5 - tip with splines; 6. 14 and 18 - oil seals; 7 - sewn cover; 8 - driveshaft; 9 - cardan joint; 10 - intermediate driveshaft; 11 - support cushion; 12 - cushion mounting bracket; 13 - intermediate support bearing mounting nut; 15 - crosspiece needle bearing; 16 - crosspiece; 17 - sliding fork; 20 - clamp; 21 - support bracket; 22 - ball bearing; 23 - plug; 24 - elastic rubber coupling from cardan joints, consisting of forks 1 and 3, can move along the splines of the tip 5, welded to the shaft 8. To the other The end of the shaft is welded to the tip of the universal joint 9. The rubber corrugated cover 7 protects the spline joint from dirt.
The lubricant enters through the oiler 2 and is retained by the oil seal 6.
In two-axle trucks with rear axle drive, the most widely used driveline transmission, consisting of an intermediate shaft and a rear axle shaft (Fig. 138.6). In this case, one universal joint connects the driven shaft of the gearbox to the front end of the intermediate shaft 10. The other, the middle universal joint, connects the intermediate shaft 10 and the propeller shaft 8 of the rear axle.
A transmission with an elastic joint, consisting of a hinge with an elastic rubber coupling 24, of the VAZ-2101 Zhiguli car is shown in Fig. 138, v. On the support of the intermediate driveshaft of the ZIL-130 car (Fig. 138.6), inside the cushion 11 with a bracket 12 secured with a clamp 20, a ball bearing 22 with seals 18 is placed
LECTURE No. 9
TOPIC: CAR BRIDGES.
PLAN:
1.Types of bridges.
2. Drive axle beam.
3. Steered bridge.
1.Types of bridges.
The front and rear axles of a vehicle perceive vertical, longitudinal and transverse forces acting between the supporting surface and the frame or body of the vehicle. The rear axle is usually driven, and the front axle is steered. Vertical forces are transmitted by elastic suspension elements, and longitudinal and transverse forces are transmitted both by the suspension and by special rods. When transmitting torque on the drive axle, a reactive torque arises, tending to turn the axle in the direction opposite to the direction of rotation of the drive wheels. When braking, the vehicle's axles are subject to braking torques in the opposite direction. Typically, these moments are transmitted from the axles to the frame through springs, but with balanced, pneumatic and independent suspensions, levers or rods are used to transmit them.
The rear drive axle is usually made in the form of a hollow beam, inside of which the main gear, differential and axle shafts are placed, and wheel hubs are attached outside.
Rice. 139 - Bridges:
a - rear drive continuous; b - split drive with independent wheel suspension; c - front continuous with dependent wheel suspension; d - front split with independent wheel suspension, carved bridges - rigid beams connecting the right and left wheels (Fig. 139, a). In cars with independent suspension, the drive axle is made split (Fig. 139.6).
The front axle can also be made continuous (Fig. 139, c) with dependent wheel suspension, or split if the suspension is independent (Fig. 139, d) for off-road vehicles, the front axle is combined, i.e., simultaneously driven and steered. In multi-axle vehicles, support axles are sometimes used, which serve only to transmit vertical loads from the frame to the wheels.
2. Drive axle beam.
The drive axle beam can be detachable and consist of two parts connected by bolts (passenger cars and light- and medium-duty trucks) or one-piece, made in the form of a solid beam with a ring-shaped central part (passenger cars and medium- and heavy-duty trucks).
In Fig. 140 shows the rear axle beam of the GAZ-53A. Trunnions 5 are welded to the crankcase 7, having machined journals 1 and 2 for wheel hub bearings. A cover 13 is welded to the rear of the crankcase. Recesses 11 provide mounting clearances when installing the gearbox. Steel flanges 4 are pressed and welded onto the axles 5, to which the brake shields are attached. The pressed-in bushing 3 of the oil seal serves as a stop for the inner ring of the wheel hub bearing. The hub bearings are installed on the ground journals 1 and 2 of the axles and secured with nuts and locknuts screwed onto the ends of the axles. Bracket 8 and bracket 9, welded to the rear wall of the housing, serve to secure the brake pipes. The oil filler hole is located on the final drive housing.
Types of main gears. The purpose of the main gear is to increase torque and transmit it to axle shafts located at an angle of 900 to the longitudinal axis of the vehicle. Its design should be compact, and its operation should be smooth and silent. The main gear parts are subject to heavy loads, so high precision is required when adjusting its bearings and gear engagement. The main gears can be gear or worm. The main gear, in which one pair of gears is called single, two pairs - double.
Rice. 141 – single main gear.
A single main gear (Fig. 141, a and 6), consisting of a pair of bevel gears in constant mesh, is used primarily on cars and light- and medium-duty trucks. The drive gear in it is connected to the cardan transmission, and the driven wheel is connected to the differential box and, through the differential, to the axle shafts. A single main gear can be equipped with conventional bevel (Fig. 141, a) and hypoid (Fig. 141,6) gears. Hypoid gearing operates more reliably, smoothly and silently than conventional spiral bevel gears.
Rice. 140 - Rear drive axle beam:
1 and 2 - journals for hub bearings; 3 - oil seal bushing; 4 - flange; 5 - axle; 6 - spring cushion"; 7 - crankcase; 8 - bracket; 9 - tee bracket; 10 - hole for breather; 11 - recesses; 12 - hole for oil drain; 13 - crankcase cover.
Single gears with bevel gears with spiral teeth are used on cars of the ZAZ and UAZ families, and hypoid single gears are used on cars GAZ-53A, GAZ-53-12, GAZ-3102 Volga, and the VAZ Zhiguli family. A hypoid gear allows the floor of a passenger car body to be lowered lower, since the axis of its drive gear can be positioned below the axis of the driven gear (rear axle axis). As a result, the center of gravity of the car is lowered and its stability is improved.
Double gears are installed on heavy-duty vehicles and on some medium-duty vehicles when the overall transmission ratio must be significant, as large torques are consumed. In a double main gear (Fig. 141.6), the torque is increased sequentially by two pairs of gears, one of which is bevel and the other is cylindrical. The total gear ratio of a double gear is equal to the product of the gear ratios of the component pairs.
3. Steered bridge.
The front axle of the GAZ-53A car (Fig. 154, a) is a beam in which steering knuckles 10 are installed on 15 pins 11 fixedly fixed in it with stoppers. The beam is a stamped I-section, with two platforms for attaching springs connecting it to frame. The middle part of the beam is curved to ensure a lower center of gravity of the vehicle.
Brake discs 9 are attached to the flanges of the steering knuckles 10. The wheel hubs are mounted on two tapered roller bearings 4 and 5. To attach the wheel hubs to the steering knuckles, there is a washer and a castle nut, which is cottered and covered with a cap.
The steering knuckles can rotate freely on the pivots thanks to bearings in the form of two bronze bushings pressed into the eyes of the steering knuckles, and a thrust bearing 16 installed between the steering knuckle and the eye of the front axle beam. Axial clearance between the steering knuckle and the beam eye.
Rice. 153 - Drive elements for the front drive wheels of the GAZ-66 car:
1 - leading flange; 2 ~ air supply channel; 3 - flange cover; 4 and 5 ~ bearing nuts; 6 - lock washer; 7 - footrest; 8 - hub; 9 ~ outer fist; 10 - air shut-off valve; 11 - wheel; 12 - seal block; 13 - kingpin; 14 ~ lever; 15 - bushing; 16 - oil seal; 17 - ball joint; 18 - inner fist; 19 - axle; 20 - the brake disc is adjusted by installing washers 12.
The wheel hub bearings contain a grease lubricant, the leakage of which is prevented by the oil seal.
In the conical holes of the eye in the left steering knuckle, the steering gear levers 13 and 21 are secured with nuts. Bolts 20 on levers 21 limit the maximum angles of rotation of the wheels, resting against the front axle beam. Oilers 22 serve to lubricate the thrust bearing 16 and the bronze bushings of the steering axle.
7 ..> Gearbox (gearbox)
The gearbox is used to vary the torque transmitted from the engine to the drive wheels of the car over a wide range 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.
The gearbox consists of:
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 the gearbox gears experience heavy loads during operation, 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).
Box shafts gears rotate in bearings mounted 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.
Switching mechanism gear is used 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.
How does the amount of torque (rpm) change in different gears? Let's understand this with an example.
Gear ratio of one pair of gears
Let's take two gears, don't be lazy and count the number of their 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).
Gear ratio of two gears
In the picture, the first gear (“A”) has 20 teeth, the second (“B”) has 40, the third (“C”) has 20 again, the fourth (“D”) has 40 again. And then there’s very simple arithmetic. The gearbox input shaft and gear “A” rotate at a speed of say 2cc rpm. Gear “B” rotates 2 times slower, that is, it has 1cc rpm, and since gears “B” and “C” are mounted on the same shaft, the third gear also makes 1cc rpm. Then gear “G” will rotate 2 times slower - 500 rpm. From the engine, 2cc rpm comes to the gearbox input shaft, and 500 rpm comes out. At this time, the intermediate shaft of the gearbox is 1ccc 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 of the gearbox decreases by 4 times compared to the primary one. Please note that if we disengage gears “B” and “D”, the secondary shaft of the box will not rotate. At the same time, the transmission of torque to the drive wheels of the car stops, which corresponds to neutral gear in the box. Reverse gear, that is, rotation of the secondary shaft of the gearbox in the other direction, is provided 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
Since the gearbox of a real car has a large set of gears, by engaging different pairs of them, we have the opportunity to change the overall gear ratio of the box.
For example, in the gearbox of a VAZ-2105 car the following gear ratios are:
R. 3.53 - reverse
Such inconvenient numbers are obtained by dividing the number of teeth of one gear by the inconveniently 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 and, as a rule, this is fourth gear.
Let's look at the meaning of gear shifting using the example of a sports bike, since modern bicycles also have gears. Owners of such vehicles have noticed that when a sprocket with a large number of teeth is engaged at the rear, it is easy to pedal, but the speed of the bicycle is low. If you switch to a smaller sprocket (with fewer teeth), the speed increases, but the effort on the pedals increases. By changing the sprockets (switching gears) on your bicycle, you find the optimal driving mode, taking into account your strength and road conditions.
The same principle is used in a car. Depending on the road conditions and taking into account the capabilities of the engine, it is necessary to change gears in the gearbox. First gear and reverse gear are the “strongest” and it is not difficult for the engine to turn the wheels, but in this case the car moves slowly. And, for example, when driving uphill in “nimble” fifth and fourth gears, the engine does not have enough strength (as does the cyclist), and you have to switch to lower, but “strong” gears. First gear is necessary to start the car moving, so that the engine can move the heavy iron “monster”. Further, having increased the speed of movement and made a certain reserve of inertia, you can switch to second gear, which is weaker but faster, then to third, fourth and fifth gears. All stages of gear shifting up - from the first to the fifth - should be passed sequentially. Shifting gears in a descending order can be done by “jumping through a step” and even after several - two, three, and so on. The normal driving mode of the car is in fourth or fifth gears, because they are the fastest and most economical.
