Motorcycle gearboxes are a mechanism consisting of several pairs of gears with different gear ratios, selected in a certain way. The purpose of the gearbox is to change the amount of torque on the driving wheel of the motorcycle in a wider range than can be done by changing the engine speed, and to allow the engine to idle with the clutch engaged when it is started or during short stops. By changing the amount of torque on the drive wheel, inertia is overcome when starting the motorcycle from a standstill, further acceleration of the motorcycle and the required speed in various road conditions, which is achieved by changing the gear ratio when shifting gears. The motorcycles are equipped with a two-way, four-speed gearbox model 6204, used on the K-750M, MV-750 and K-650 motorcycles, or a two-shaft, four-speed gearbox with a reverse gear and an automatic clutch release mechanism. Gearbox model MT-804, used on motorcycles MT-9, MV-750M and MV-650.
Gear box device 6204
Gearbox 6204 assembly and its longitudinal section are shown in fig. 38 and 39. The box mechanism is assembled in a cast one-piece aluminum crankcase 9 with three removable front 3 covers that serve as a bearing support, and two side covers - right 32 and left 38. The torque from the engine through the clutch is reported to the input shaft 7 (Fig. 39 ) box, mounted on two bearings - roller No. 12204K, mounted in a common housing with a clutch release slider 18, and ball No. 205, pressed into the front crankcase cover. Gears of the 1st, 2nd and 3rd gears are made in one piece with the input shaft, and the 4th gear is mounted near the ball bearing on a special segment key. In the inner cavity of the input shaft, the rod 6 for disengaging the clutch with the tip moves. The output shaft 16 of the box also has an internal but non-obtrusive cavity with radial holes for lubrication and is mounted on two ball bearings No. 304 mounted in the crankcase and in the front cover. Oil deflector washers are installed in front of the bearings on the shaft. Along its entire length, the secondary shaft 16 has longitudinal splines, on which gears of 1st, 2nd, 3rd and 4th gears rotate freely. On the side, the gears have an end crown, on the outer generatrix of which splines of an involute profile are cut. Between the ends of the gears, on the splines of the secondary shaft, two splined couplings 45 are installed, which, in addition to the internal splines, also have external splines of the involute profile, which coincide in configuration with the splines on the protrusions of the gears. On the splined couplings 45, in turn, the engagement clutch 49 of the 1st and 2nd gears and the clutch 8 of the engagement of the III and IV shifts with internal splines of the involute profile corresponding to the outer splines of the couplings 45 and the splines of the end projections of the gears are installed and can move, but to facilitate engagement in the clutches 8 slots are made through one. To move the couplings on their outer surface there are annular grooves, which include the ends of the forks 29 and 34 of the gear change. To turn on the gear (for example, I), the clutch 49 is shifted to the left on the splines of the end crown of the gear of the 1st gear of the secondary shaft and blocks it, thus, with the splined clutch 45 and the output shaft 16. The clutch 8 is in the middle neutral position, and the rest of the gears the secondary shaft, not being blocked, rotate idly. At the splined end of the secondary shaft, the drive disk of the flexible coupling of the cardan shaft is installed, tightened with a castellated splinted nut 47. There are two cylindrical spikes on the back of the disk for installing a flexible cardan coupling, and a spiral gear is cut in front, which is in constant engagement with gear 48 of the speedometer drive. The output shaft ends with a ball designed to center the driveshaft.
The gearshift mechanism provides the possibility of foot and manual shifting and consists of a shift fork shaft installed in the charter of the box, a shift sector 30 with a shaft and other related parts. Switching forks 29 and 34 sit freely on roller 33 (Fig. 38), fixed with a locking screw in the crankcase. On the hubs of the shift forks there are cylindrical spikes included in the figured slots of the shift sector 30. On the outer arc of the sector 30 there are five holes, which include the lock ball 31 when the gears are engaged. At the right end of the sector shaft 30, a manual shift lever 28 is installed, and a ratchet 36 sits on the square of the left end. Sector 30 is held on the spikes of the shift forks under the action of a coil spring installed between the sector and the right cover 32 of the box crankcase. On the neck of the ratchet 36 sits a crank 35 with a stop for the return spring 37 and the axis of the double-sided pawl 26 of the switching mechanism. The pawl 26 is constantly pressed against the teeth of the ratchet 36 by a spring, and the return spring 37 rests with its bent ends against the left cover 38 of the crankcase and against the stop of the crank 35. The crank pin 35 enters the lug of the lever 27 of the crank of the pawl of the switching mechanism, and the lever itself sits on the splines of the pedal axis 25 foot switch and secured with a nut. At a certain angle of rotation of the sector, corresponding to the blocking of one or another gear of the secondary shaft, the lock ball 31 falls into the hole on the sector, fixing the engaged gear. Four possible gears correspond to four holes of sector 30, and the fifth hole, located between the holes of I and II gears, fixes the idle position, at which the weight of the output shaft gear is unlocked and rotates freely on the shaft. The sector 30 can be rotated using the foot switch pedal 25 or the manual switch lever 28 . When the lever 28 is in the rearmost position, the 1st gear is engaged, when the lever is moved forward, the central is switched on first, and then the 2nd, 3rd and 4th gears in sequence. The main purpose of the lever 28 is the installation of clutches 8 and 49 (Fig. 39) for engaging gears in the central position. The foot switch mechanism works by pressing the two-arm pedal 25 with the foot (Fig. 38), which, moving the lever 27 and the crank 35, turns the ratchet 36 with the pawl 26, and with it the sector 30 until the gear is switched on, coinciding with the alignment of the lock ball 31 with the corresponding well of the sector. To adjust the gearshift mechanism on the crankcase 9 of the box behind the left cover 38 of the crankcase there are two adjusting screws 24, upper and lower, locked with locknuts. The starting mechanism is designed to start the engine. A pawl 44, a trigger lever 41, a return spring 1 are fixed on the shaft 21 of the trigger mechanism, and a freely rotating gear 20 with a mechanical ratchet having internal teeth is installed. The trigger shaft rotates freely in two bushings - the front 2, installed in the front cover 3, and the rear 23, installed on the rear wall of the box crankcase. In the cam of the shaft 21 there are holes into which the axis of the pawl 44 of the trigger mechanism and the pin 43 with a spring 42 are inserted, pressing the pawl 44 to the teeth of the mechanical ratchet of the gear 20. The trigger gear is in constant engagement with the gear of the first transmission of the secondary shaft and through it with the gear I transmission of the input shaft. When you press the trigger lever 41 with your foot, the shaft 21 rotates and the pawl 44, resting against the teeth of the ratchet of the gear 20, turns it, and through the gears and the clutch and the crankshaft of the engine engaged with it. When the lever 41 is released, the return spring 1 of the trigger mechanism returns the shaft 21 together with the pawl 44 to its original position with its force. To avoid shock when the lever is suddenly released, a buffer 40 of the trigger is installed in the crankcase of the box, held by a spring and plug 39. In addition, the downward travel of the trigger lever is limited by a rubber buffer attached to the motorcycle frame. When the engine is running and the lever 41 is in reverse, under the action of a return spring, the pawl 44 is taken away from the ratchet teeth by a heel-shaped pawl switch installed inside the crankcase. The box is filled with oil through a hole on the left wall of the crankcase, closed with a threaded plug. The drain hole located near the plug 39 of the trigger buffer is also closed with the same plug.
Gearbox adjustment 6204
During operation, it becomes necessary to adjust the synchronism of the operation of the mechanisms of manual and foot switching. To ensure the normal operation of the foot shift mechanism, it is necessary to install the adjusting screws 24 (Fig. 38) so that, at the extreme positions of the pedal 25, the fixing holes of the II and III gears on the sector 30 reach the lock ball 31. The fixation of the sector is well felt when moving the manual shift lever . In operation, adjustment violations are possible when the fixing holes of sector 30 pass the fixer ball or do not reach it, so the correct adjustment is checked by the manual shift lever (Fig. 40). When switching from ІІ to III gear with a false pedal, if the fixing hole of the 3rd gear does not reach the detent ball, the manual shift lever should be turned forward until the hole coincides with the ball. In this case, you need to unscrew the lower adjusting screw. If the fixation well passes over the fixative ball, the manual shift lever must be turned back until the socket meets the ball. In this case, the lower adjusting screw must be screwed in. When shifting from III to II gear with a foot pedal, if the fixing hole of the II gear does not reach the detent ball, the manual shift lever should be turned back until the hole coincides with the ball. In this case, you need to unscrew the upper adjusting screw. If the fixation hole goes over the fixer ball, the manual shift lever should be turned forward until the hole is in line with the ball. In this case, the upper adjustment screw must be screwed in.
MT-804 gearbox device
The MT-804 gearbox is shown in fig. 41 and consists of a mechanism with four pairs of constantly meshed gears, designed to receive four gears for moving forward, a gear change mechanism, a reverse gear, an engine start mechanism, an automatic clutch release mechanism when shifting gears. All parts of the box are installed in a cast crankcase made of silumin. Behind the crankcase is closed with a cover made of the same material. At the front, the crankcase has a flange with which it is attached to the engine crankcase using three studs and one bolt. The main mechanism of the gearbox, designed to transmit torque from the engine to the main gear with different gear ratios, like the gearbox 6204, consists of two parallel shafts - primary 7 and secondary 24. Both shafts are mounted on ball bearings mounted in the housing and gearbox cover. The input shaft is made integral with the gear rims of I, II gears and reverse gear. The 4th gear gear and the 3rd gear are freely installed on the shaft on the segment key. Both of these gears are interconnected by means of end projections. Thus, when the shaft rotates, the gear rims of all gears sitting on it rotate as one. The splines at the end of the input shaft fit into the splined hubs of the clutch discs. On the secondary shaft, freely rotating gears of the 4th, 2nd, 2nd and 1st gears of the secondary shaft are installed, which are in constant engagement with the corresponding gears of the input shaft. These gears, in addition to the main crown, have crowns with small involute splines cut on the end ledges and designed to engage gears. Bushings made of anti-friction material are pressed into the mounting holes of the gears: metallographic bushings for the gears of I, II and III gears and bronze for the gear of the IV gear. Between the gears of IV and III gears and the gears of II and I gears on the secondary shaft, splined couplings 30 with involute splines on the outer surface sit on segment keys. On the splines of the couplings, clutches 26 of gear engagement are planted, having the ability to move freely along the splines. On the outer surface of each gear clutch there are annular grooves for the forks 22 and 23 of the gears. The fork cheeks sit freely in the grooves and do not interfere with the coupling rotating with the shaft. To enable the transmission, it is necessary to block one or another gear of constant engagement with the output shaft. This is achieved by moving along the splines of the gear engagement clutch until the moment when the internal teeth of the clutch are fully pushed onto the involute splines of the end crown of the output shaft gear. In this case, the output shaft gear will be interlocked with the shaft, which ensures the transfer of torque from the input shaft to the secondary. On fig. 41 shows the neutral position of the transmission when the shift clutches with forks are in the middle position. In this position, when the input shaft rotates, the gears of the output shaft will rotate idly. The movement of the clutches 26 of the inclusion is carried out by the forks using the gear shift mechanism, which ensures the inclusion of the desired pair of gears from the foot pedal. To facilitate the inclusion of the internal splines of the coupling and the teeth of the splined rim of the gear, as well as the box 6204, are made with a pass through one tooth. The rarefaction of the teeth increases the angle of rotation of the connected parts relative to each other, which is possible for engagement. This measure also contributes to a smoother (without sharp blows) gear shifting in the event of a significant difference in the speeds of rotation of the connected parts. In addition to the gears of I, II, III and IV gears, a reverse gear 32 is installed on the secondary shaft. This gear sits on splines and can move freely but with it. On the splines of the shank of the secondary shaft, a disc 35 of the elastic coupling of the cardan is mounted, fixed with a slotted nut. The secondary shaft ends with the same ball head as the shaft of the box 6204, designed to center the front end of the driveshaft. All pinion gears are made of 18KhGT alloy steel, case-hardened and hardened.
gear shift mechanism
The gear shift mechanism consists of a gear shift pedal 43 (Fig. 41) with a shift shaft assembly, a crank cam 40, a pawl 56, a shift disc 48 with a lock, two forks 22 and 23. The shift shaft is installed in a long sleeve 45, pressed in the hole of the crankcase tide) of the gearbox. On the splined end of the roller inside the box body, a crank cam is mounted and fixed with a castellated nut. A pin is inserted into the hole of the crank cam, one end of which enters the groove of the switching pawl, and the second is located between the ends of the spring 41. The spring is mounted on a sleeve loosely put on the end of the switching shaft, the ends of the spring are separated (with pre-twisting) and cover the stop bar 42 , which is mounted on the roller and fixed with a bolt on the body boss. Thus, the cam-crank, and with it the roller with the shift pedal, are fixed in a strictly defined neutral position. When the roller is turned in one direction or another from the neutral position, the crank cam pin presses on one of the ends of the spring, forcing it to move away from the stop bar, and since the second end of the spring rests against the bar on the other side, the spring twists, resisting turning more and more along as the angle of deviation of the crank cam from the neutral position increases. The rotation of the roller occurs at the moment of gear shifting under the action of a force applied to one of the legs of the foot shift pedal. When the force is removed, the roller with the pedal returns to its original position from the action of the spring. The limiting angle at which the switching shaft can turn is limited by special protrusions along the edges of the profile of the cam-crank 40, which can rest against the roller of the inner lever 37. The pawl 56 of the switching mechanism is a plate welded to the sleeve on one side and bent at a right angle shelf on the other side. The pawl sleeve is loosely seated on the roller 55, installed in the holes of the body and cover. When the crank cam is turned, its pin, which enters the pawl groove, moves the pawl along the roller in one direction or another. Under the action of the spring 54, put on the pin of the crank cam, the pawl is pressed all the time with its shelf against the pins of the switching disk. The switching disc 48 made of sheet steel, with two through curly grooves cut out in it, is installed on a vertical axis pressed into the hole in the bottom of the box body. Two gearshift forks are mounted on shaft 52, fixed in the holes of the housing and crankcase cover, above the plane of the gearshift disc, and with their spikes enter the grooves of the disc.
The operation of the gear shift mechanism
Gear shifting occurs when the shift disc is rotated to a certain angle. At the same time, the profile grooves of the disk, pressing on the spikes of the forks, move them along the roller 52 (Fig. 41), and with them the engagement clutch to engage a particular gear. The rotation of the disk is carried out with the help of a pawl, which, moving along its roller, acts on the pins of the disk. The position of the disk is fixed by means of a lever lock 51, the tooth of which enters the grooves on the outer side of the disk. The disk has six working slots for fixing I, II, III and IV gears, a main neutral position slot between I and II gears and a second neutral position between III and IV gears used for coasting. The seventh groove is technological. On fig. 41 the gearshift mechanism is shown in the main neutral position of the gearbox. To turn on the 1st gear, it is necessary to press the front shoulder of the pedal to failure, while the crank cam will turn counterclockwise, and the pawl, moving forward and pressing the disc pin, will turn it to the position where the lever lock tooth enters the groove of the disc for fixation I transfer. During the rotation of the disk, its groove acts on the stud of the 1st and 2nd gear shift fork like a profile cam and moves the fork to the position corresponding to the 1st gear engaged. The pin of the shift fork of III and IV gears remains motionless, since at the moment of rotation of the disk it does not go beyond the concentric part of the second groove of the disk. When the foot shift pedal is released, all parts of the shift mechanism, except for the fixed disc and associated shift forks, automatically return to their original position. Engagement of the 2nd, 3rd and 4th gears is carried out by sequentially pressing the rear shoulder of the foot pedal to the stop. In this case, the pawl makes a series of backward movements, each time turning the switch disk at an angle of 50º, equal to the step between the pins, and returning to its original position after removing the force from the pedal. The protrusion of the pawl at the moment of switching on the gear enters the gap between the pins of the disk 48. When the pawl returns to its original position, its protrusion, sliding its outer bevel along the pin, forces the pawl to overcome the force of the spring 54, turn on the axis and disengage from the pins. The order of movement of the forks when the disk is rotated is determined by the configuration of the slots in the disk 48, which is selected so that when one fork moves, the second one remains stationary. This ensures that two gears cannot be engaged at the same time. The gear shift mechanism has a device for signaling the main neutral position of the gearbox (between I and II gears). The device consists of a sensor spring and a neutral position sensor 49, which is an insulated contact screwed into a threaded hole in the wall of the gearbox housing against the shift disc. The sensor is connected by a wire to a signal lamp installed in the headlight housing. The sensor spring is riveted to disk 48 and in the main neutral position of the disk touches the sensor, closing the electrical circuit of the signal lamp, which lights up.
Reverse gear
trigger mechanism
The starting mechanism of the MT-804 box (Fig. 41) includes an intermediate shaft 6 with freely rotating gears 4 and 5 installed on it. The large gear 5 is constantly engaged with the gear of the second gear of the input shaft. The small gear 4 is pressed against the end face of the large gear by a spring. Ratchet teeth are made on the contact ends of both gears. The stationary intermediate shaft 6 is pressed with its front end into the box crankcase, and its rear end is installed in the opening of the crankcase cover. The shaft 20 of the trigger mechanism rests with its front end in a blind sleeve 1 installed in the front wall of the crankcase, and passes through a hole in a steel sleeve pressed into the crankcase cover. At the outer end of the starting shaft, a lever 19 of the starting mechanism is fixed with a wedge bolt. A toothed sector sits on the splines of the shaft 20, into the hole of which the bent end of the return spring 2 of the trigger mechanism enters. The second end of the spring through the stop is connected to the blind bushing of the front wall of the box crankcase. The return spring is pre-twisted by turning the sleeve 1 counterclockwise, due to which the toothed sector is constantly pressed against the rubber rebound buffer, and the start lever is in the upper position.
The operation of the trigger mechanism
The engine is started by pressing the foot on the start lever. In this case, the sector of the launch shaft, turning, with its teeth engages with the small gear 4 (Fig. 41) of the intermediate shaft and makes it rotate. The small gear with the help of a mechanical ratchet transmits rotation to the large gear 5, and it - to the input shaft of the gearbox and through the clutch to the crankshaft of the engine. When the force is removed from the start lever, it, together with the shaft and sector, returns to its original position under the action of a return spring. In this case, the start shaft sector turns the small gear in the opposite direction, which is not transmitted to the large gear because the ratchet teeth on the ends of the gears, overcoming the resistance of the axial spring 3, disengage from each other. With a sharp release of the start lever, the impact of the sector on the box body is absorbed by a rubber buffer with a metal lining. If the engine is started at the moment when the start lever is delayed in the upper position and the sector has not yet disengaged from the crown of the small gear, the rotation from the large gear to the small gear will also not be transmitted due to the disengagement of the ratchet, but a characteristic crackle will be heard emitted by the ratchet. During engine operation, both start gears rotate together on shaft 6, since the magnitude of the friction torque between the ends of the spring and the small gear is insufficient to disengage the ratchet. However, in the cold season, due to the thickening of the lubricant, the small gear of the starting mechanism may slow down, lag behind the large one, which will cause the ratchet to disengage and crack. As the box warms up, the ratchet noise stops. The device and operation of the mechanism for automatically disengaging the clutch when shifting gears are described above, when describing the clutch device. All friction surfaces of the gearbox are lubricated with oil poured into the gearbox housing through the hole in the crankcase tide on the left. A plug with a dipstick (to control the level of lubrication) and a breather is wrapped in the hole, with the help of which the gearbox cavity is connected to the atmosphere. There is no special supply of lubrication to rubbing surfaces. In places of possible oil leaks, the box body is sealed with oil seals (at the shaft exit points), rubber knees (start shaft bushing, reverse gear lever shaft, clutch release rod slider) and a paper gasket along the plane of the box crankcase connector with the engine crankcase.
They have fans of one kind or another. Disputes about the merits and demerits do not stop between them. That's just a semi-automatic transmission has no ardent opponents or supporters. Most likely, because there is no clear idea about it.
Operation of the semi-automatic transmission
The work of shifting gears when a semi-automatic gearbox is engaged is based on the operation of two clutch mechanisms, as opposed to a conventional mechanical one.
As a rule, each of the mechanisms is associated when interacting with a certain set of gears. For example, the first clutch includes the first, third and fifth of the six gears, and the second - only the "even" ones - the second, fourth and sixth.
This is done to reduce the time spent by the driver on switching, as well as to increase the smoothness of switching and getting the most out of the engine during acceleration.
Automatically there is no need for the clutch pedal itself, since there is no need to disconnect the engine from the transmission parts. 
Gear shifting occurs due to the operation of electronic systems that take into account various parameters of the vehicle’s movement, the operation of internal mechanisms, and give commands to hydraulic mechanisms to switch on a particular mode.
In necessary cases, such a box is also subject to driver control. This may be required, for example, if, after intensive acceleration, you need to fix a calm driving mode, or this particular gear is needed when cornering.
In this case, the box will obey when exposed to special steering column switches.
Distinctive features of the semi-automatic box
Like any mechanism, a semi-automatic box has its own distinctive features, which can be understood by considering the advantages and disadvantages. 
Advantages:
- smooth uniform acceleration due to fast gear shifting (from 8 milliseconds);
- full use of the engine's capabilities, which also affects the dynamism of the car;
- fuel efficiency is recognized at the level of 10-20%, which is associated not only with the possibilities that the box gives, but also the ability to effectively use less powerful engines;
- comfort for the driver.
Flaws:
- the complexity of the design and, as a result, repair;
- high cost;
- unwillingness to respond in a timely manner in non-standard traffic situations.
What is the result
Nevertheless, such a box has proven its performance. Despite the appearance in the arsenal of auto manufacturers of the option of using stepless variators, where gears do not need to be switched at all, the semi-automatic transmission continues to improve.
According to various estimates, up to a quarter of the car market will be equipped with a similar box. After all, she has more advantages than disadvantages.
GEARBOX ASSEMBLY MOTORCYCLES "DNEPR" AND "URAL" - PART 2
Transmission model MT-804. The nominal dimensions, tolerances and tightness in the main mating parts are shown in Table 18. When assembling the gearbox, the gearshift shaft bushings, the buffer and the driven shaft assembly, the intermediate shaft assembly with gears and the spring, the trigger shaft in assembly with a sector, the sleeve of the shaft of the starting mechanism, the shift and reverse forks, the gear shift disc, the gear lever lock, the axle of the forks, the pawl axle, the axle of the gear shift disc, the axle of the gear wheel, the shift mechanism assembly, the gear shift cam spring , neutral contact plug, oil seals assy, reverse shift lever assy, transmission gear.
Table 18 Nominal dimensions, tolerances and tightness in the main mates parts of the gearbox model MT-804
The bushings of the engine start mechanism with an interference of no more than 0.001 mm and the axles of the gear gear with an interference of at least 0.02 mm are pressed into the crankcase of the box (see Fig. 55). Preload is provided by the selection of parts. The intermediate shaft is pressed in with the small end flush with the outer wall of the crankcase, while ensuring an interference of at least 0.01 mm, and the stop of the intermediate gear is screwed in to failure. Then the ball bearing No. 303 of the drive shaft is pressed into the cover until it stops with an interference of no more than 0.025 mm and the bushing of the trigger shaft with an interference of no more than 0.02 mm. The axis of the transmission gear is pressed flush with the outer wall of the cover, providing an interference of at least 0.01 mm, and locking pins with an interference of at least 0.03 mm. Put on the axle gear gear and install the bracket assembly with the lever.
On the drive shaft of the gearbox (see Fig. 53) put on the gear wheel 6 of the third
Gears with key 8 until it stops against the shoulder without distortion. The feeler gauge 0.05 mm must not pass between the end face of the gear wheel and the shoulder of the shaft. After that, the gear wheel 5 of the fourth gear is put on the shaft with a gap of not more than 0.1 mm, and the cams of the gear 5 must be engaged with the cams of the gear 6 until it stops. Next, a ball bearing No. 205 is pressed onto the drive shaft 7 until it stops at the end of the gear wheel, the interference should be no more than 0.03 mm. Ring 3 is put on the shaft and ring 2 is pressed in until it stops, ensuring a minimum tightness of 0.018 mm.
When assembling the driven shaft, gears 24, 21, 19 and 15 are checked for engagement in pairs with gears of the drive shaft, gear 28 - with a gear gear on a special device. The engagement gap is 0.08 ... 0.065 mm, fluctuation within one pair is allowed up to 0.02 mm. The sleeve 25 is put on the front end of the driven shaft 26 until it stops, and the gear wheel 24 is pressed on it. Two keys 27 are pressed in and the coupling 23 is put on them, and the coupling 22 is put on its splines. Two bushings 20 are put on and gears 21 and 19 are put on them Two keys 27 are pressed into the shaft, the coupling 18 is pressed on them, and the second switching coupling 17 is put on its splines. The sleeve 16 is put on the shaft until it stops into the coupling, and the gear wheel 15, ring 14 are pressed onto it and ball bearing No. 304 is pressed all the way . Gear wheel 28 is put on the splines of the shaft until it stops, washers 29 and 37. Ball bearing No. 304 is pressed onto the other end of the shaft until it stops.
All bushings of the driven shaft must have an interference of no more than 0.003 mm, and gears - a gap of at least 0.02 mm. The gear wheels should rotate easily, without jamming, on the shaft, the radial clearance should be 0.02 ... 0.05 mm. The gear shift couplings must move freely along the splines of the driven shaft couplings.
With the general assembly of the gearbox model MT-804 on the intermediate shaft 26 (see Fig.
55) put on washer 11 (see Fig. 53), gear wheels 9 and 10, second washer 11 and spring
12. The drive shaft assembly is installed and pressed into the crankcase, the preload for the ball bearing is no more than 0.025 mm. The driven shaft assembly is installed and pressed in with the same bearing preload. Install and press in the shift fork shaft 10 (see Fig. 54) with an interference of no more than 0.03 mm and put on it the shift forks 7.8 and 9 with a gap of no more than 0.025 mm. The forks must first be inserted into the grooves of the shift couplings.
The reverse gear lever 31 (see Fig. 55) is installed in the crankcase, the gap should be no more than 0.02 mm, and the foot shift shaft 5 (see Fig. 54), with the pedal assembly, the gap in the sleeve 43 (see Fig. 55) - not less than 0.01 mm. They put a return spring 4 on the gear shift shaft (see Fig. 54), a crank 3, a spring 2 and a washer, tighten the nut. The axle 16 of the switching pawl is pressed into the crankcase, the pawl 17 is put on the axle with a gap of not more than 0.1 mm. The gearshift mechanism is assembled, for which the gearshift disk 15 is put on the axis of the transmission gear, and the end of the spring 14 is brought onto it. The lever lock 13 is installed on the axle, the washer 12 and cottered. The gaps in all connections of the switching mechanism must be at least 0.08 mm. Install the neutral position sensor spring and sensor contact with the plug.
The trigger shaft 44 is installed (see Fig. 53) in the sleeve 49, the return spring 46 is put on it, its end is inserted into the thrust washer 47, the gear sector 45 of the trigger shaft is put on the splines, the other end of the spring is inserted into the sector hole by 3 /4 turns and fix the sleeve 49 with screws 50.
Lubricate the plane of the crankcase connector and the gasket with bakelite varnish, place the gasket under the assembled cover on the crankcase, aligning the shaft holes. With light blows of a hammer, the cover is planted until it comes into contact with the plane of the crankcase. After tightening the bolts in a checkerboard pattern, the shafts and gears should rotate by hand without jamming. The trigger lever assembly is put on the shaft and secured with a wedge bolt. Rocking the lever is not allowed. Put on the end of the engagement handle
reverse gear lever 17 (see Fig. 55) and fix it with a nut until it stops.
The operation of the shift mechanism of these gearboxes is provided during assembly, and during operation only the automatic clutch release mechanism is regulated. The remaining requirements are similar to the requirements for assembling the Ural motorcycle gearbox.
The assembled gearbox must have a free travel of the trigger pedal of no more than 33 °, the runout of the toe of the drive shaft relative to the crankcase locks is no more than 0.15 mm, the axial movement of the starting shaft is no more than 1.5 mm, the position of the clutch release lever relative to the vertical axis of the box gears - at an angle of 26 ± 1, the beating of the cams of the flexible coupling disk - no more than 0.4 mm; wedge bolts for fastening the levers must have a preload of at least 5 mm for the trigger mechanism and at least 3 mm for the manual gear lever. Rolling of the sector roller relative to the gearshift ratchet is not allowed. The absence of pitching is checked by hand, resting the ratchet through the foot shift pedal and shaking the manual shift lever. The latter, moreover, should not move with great effort or have free play in a fixed position in second and third gears and in a neutral position between first and second gears. The lever should have free play in fourth gear back. The foot switch pedal must ensure a clear engagement of each gear, work without jamming, the trigger pedal must return freely and quickly to its original position. The distance of the pedal lever from the clutch release lever in its uppermost position must be at least 5 mm. When the driven shaft rotates in the direction opposite to the working movement, jamming or crackling of the start ratchet pawl is not allowed.
Most modern automakers provide the buyer with the option to choose a semi-automatic type of installed gearbox, although the mass introduction of such a transmission began as early as the 1930s. Despite its considerable age, the semi-automatic transmission still has no obvious opponents or fans.
According to experts, this is due to a poor understanding of its structure and principle of operation. To provide conditions for a gear change, the driver of a car with a semi-automatic gearbox just needs to take his foot off the gas pedal. It provides the most optimal conditions for the operation of the motor when driving a car, which not only prolongs its service life, but also reduces fuel consumption.
Semi-automatic box device
In any semiautomatic device, there are two clutch mechanisms at once - this is the main difference between such a system and a classic mechanical box. The most common scheme of operation of such semiautomatic devices is the interaction of mechanisms only with a certain group of available gears, which can be even or odd. This arrangement can significantly reduce the time spent on switching, and also increases the clarity and smoothness of this process.
In practice, it looks like this. When the car is moving, the system analyzes information from all sensors and other systems. Based on the information received, with the gear already engaged, the semi-automatic box prepares in advance to turn on the next one. This happens immediately after the occurrence of certain conditions. As a result, it was possible to reduce the switching time to 8 milliseconds - not every modern “automatic” can boast of such indicators.
The semi-automatic box, the principle of operation of which is quite complicated, is distinguished by the presence of a mass of electronic systems that take into account numerous parameters when driving a car in which there is no clutch pedal as unnecessary. All internal mechanisms must work synchronously and very clearly - it is in this case that high convenience is achieved when driving such a car. The driver can make his own adjustments to the operation of such a box using special switches, usually located under the steering wheel. To date, several variations of such boxes are already known - the final design will depend on the automaker. The types of boxes are described in the video:
Advantages and disadvantages of semi-automatic boxes
As practice shows, it is impossible to consist of advantages alone - any node in a car has certain disadvantages. Among the undeniable advantages of semiautomatic devices over manual transmissions are the following:
- maximum comfort for the driver;
- excellent dynamic performance of the car during acceleration;
- use of all engine capabilities, which also increases its dynamics;
- a number of modifications of such boxes are also distinguished by their compactness, which is important for small cars;
- a pronounced reduction in fuel consumption, due not only to the box itself, but also to the possibility of installing less powerful engines.
Among the main disadvantages of semi-automatic boxes are the following:
Automatic or semi-automatic - which is more reliable
Many drivers who buy a new car cannot decide until the last moment what to prefer. Many consider the machine to be more modern, reliable and convenient to use, but in fact, all this is far from the truth. The semi-automatic gearbox, in fact, is a mechanics proven for decades, equipped with modern additional systems - an automatic clutch switch and a gear shift system. While driving, the control unit of such a box is “guided” not only by the operation algorithms embedded in it, but also receives signals from the driver and other vehicle sensors.
A semi-automatic transmission is distinguished by increased reliability and, unlike an automatic transmission, allows you to save on fuel, since it reduces its consumption. Since installing a semi-automatic is cheaper for the automaker, the cost per car is reduced for the buyer. The number of serious breakdowns in semi-automatic boxes is also significantly lower, and it is much easier to repair them, compared to an automatic one. As a result, it turns out that a semi-automatic device allows you to save not only on the purchase of a car, but also reduces its operating costs.
The principle of operation of the semi-automatic box
All the work of the mechanical part of such a box is almost identical to the "actions" of the mechanical one. Significant differences are observed in the presence of an electronic component, which determines all the existing driving comfort. A special unit is responsible for managing this complex system, containing all the algorithms necessary for efficient gear shifting. At the same time, during operation, he is able to take into account the information coming from the systems available in the car and the driver himself. This provides unrivaled precision and efficiency in shift control.
Despite the presence of a sufficient number of electronic systems in the box, the main work when changing gears is performed by its steel mechanical parts, which take on the main load. Considering that all electronics are reliably protected, a semi-automatic box has a huge service life. The only condition is that it is serviced only by professional mechanics - their incorrect actions can lead to the fact that the car will try to “move off on its own”, for example, from a traffic light at a busy intersection. As a result, it turns out that a semi-automatic transmission, today, is the most optimal means of ensuring a gear change in a car.
Dnepr motorcycle gearbox
Motorcycle gearboxes are a mechanism consisting of several pairs of gears with different gear ratios, selected in a certain way. The purpose of the gearbox is to change the amount of torque on the driving wheel of the motorcycle in a wider range than can be done by changing the engine speed, and to allow the engine to idle with the clutch engaged when it is started or during short stops. By changing the amount of torque on the drive wheel, inertia is overcome when starting the motorcycle from a standstill, further acceleration of the motorcycle and the required speed in various road conditions, which is achieved by changing the gear ratio when shifting gears. The motorcycles are equipped with a two-way, four-speed gearbox model 6204, used on the K-750M, MV-750 and K-650 motorcycles, or a two-shaft, four-speed gearbox with a reverse gear and an automatic clutch release mechanism. Gearbox model MT-804, used on motorcycles MT-9, MV-750M and MV-650.
Gear box device 6204
Gearbox 6204 assembly and its longitudinal section are shown in fig. 38 and 39. The box mechanism is assembled in a cast one-piece aluminum crankcase 9 with three removable front 3 covers that serve as a bearing support, and two side covers - right 32 and left 38. The torque from the engine through the clutch is reported to the input shaft 7 (Fig. 39 ) box, mounted on two bearings - roller No. 12204K, mounted in a common housing with a clutch release slider 18, and ball No. 205, pressed into the front crankcase cover. Gears of the 1st, 2nd and 3rd gears are made in one piece with the input shaft, and the 4th gear is mounted near the ball bearing on a special segment key. In the inner cavity of the input shaft, the rod 6 for disengaging the clutch with the tip moves. The output shaft 16 of the box also has an internal but non-obtrusive cavity with radial holes for lubrication and is mounted on two ball bearings No. 304 mounted in the crankcase and in the front cover. Oil deflector washers are installed in front of the bearings on the shaft. Along its entire length, the secondary shaft 16 has longitudinal splines, on which gears of 1st, 2nd, 3rd and 4th gears rotate freely. On the side, the gears have an end crown, on the outer generatrix of which splines of an involute profile are cut. Between the ends of the gears, on the splines of the secondary shaft, two splined couplings 45 are installed, which, in addition to the internal splines, also have external splines of the involute profile, which coincide in configuration with the splines on the protrusions of the gears. On the splined couplings 45, in turn, the engagement clutch 49 of the 1st and 2nd gears and the clutch 8 of the engagement of the III and IV shifts with internal splines of the involute profile corresponding to the outer splines of the couplings 45 and the splines of the end projections of the gears are installed and can move, but to facilitate engagement in the clutches 8 slots are made through one. To move the couplings on their outer surface there are annular grooves, which include the ends of the forks 29 and 34 of the gear change. To turn on the gear (for example, I), the clutch 49 is shifted to the left on the splines of the end crown of the gear of the 1st gear of the secondary shaft and blocks it, thus, with the splined clutch 45 and the output shaft 16. The clutch 8 is in the middle neutral position, and the rest of the gears the secondary shaft, not being blocked, rotate idly. At the splined end of the secondary shaft, the drive disk of the flexible coupling of the cardan shaft is installed, tightened with a castellated splinted nut 47. There are two cylindrical spikes on the back of the disk for installing a flexible cardan coupling, and a spiral gear is cut in front, which is in constant engagement with gear 48 of the speedometer drive. The output shaft ends with a ball designed to center the driveshaft.
The gearshift mechanism provides the possibility of foot and manual shifting and consists of a shift fork shaft installed in the charter of the box, a shift sector 30 with a shaft and other related parts. Switching forks 29 and 34 sit freely on roller 33 (Fig. 38), fixed with a locking screw in the crankcase. On the hubs of the shift forks there are cylindrical spikes included in the figured slots of the shift sector 30. On the outer arc of the sector 30 there are five holes, which include the lock ball 31 when the gears are engaged. At the right end of the sector shaft 30, a manual shift lever 28 is installed, and a ratchet 36 sits on the square of the left end. Sector 30 is held on the spikes of the shift forks under the action of a coil spring installed between the sector and the right cover 32 of the box crankcase. On the neck of the ratchet 36 sits a crank 35 with a stop for the return spring 37 and the axis of the double-sided pawl 26 of the switching mechanism. The pawl 26 is constantly pressed against the teeth of the ratchet 36 by a spring, and the return spring 37 rests with its bent ends against the left cover 38 of the crankcase and against the stop of the crank 35. The crank pin 35 enters the lug of the lever 27 of the crank of the pawl of the switching mechanism, and the lever itself sits on the splines of the pedal axis 25 foot switch and secured with a nut. At a certain angle of rotation of the sector, corresponding to the blocking of one or another gear of the secondary shaft, the lock ball 31 falls into the hole on the sector, fixing the engaged gear. Four possible gears correspond to four holes of sector 30, and the fifth hole, located between the holes of I and II gears, fixes the idle position, at which the weight of the output shaft gear is unlocked and rotates freely on the shaft. The sector 30 can be rotated using the foot switch pedal 25 or the manual switch lever 28 . When the lever 28 is in the rearmost position, the 1st gear is engaged, when the lever is moved forward, the central is switched on first, and then the 2nd, 3rd and 4th gears in sequence. The main purpose of the lever 28 is the installation of clutches 8 and 49 (Fig. 39) for engaging gears in the central position. The foot switch mechanism works by pressing the two-arm pedal 25 with the foot (Fig. 38), which, moving the lever 27 and the crank 35, turns the ratchet 36 with the pawl 26, and with it the sector 30 until the gear is switched on, coinciding with the alignment of the lock ball 31 with the corresponding well of the sector. To adjust the gearshift mechanism on the crankcase 9 of the box behind the left cover 38 of the crankcase there are two adjusting screws 24, upper and lower, locked with locknuts. The starting mechanism is designed to start the engine. A pawl 44, a trigger lever 41, a return spring 1 are fixed on the shaft 21 of the trigger mechanism, and a freely rotating gear 20 with a mechanical ratchet having internal teeth is installed. The trigger shaft rotates freely in two bushings - the front 2, installed in the front cover 3, and the rear 23, installed on the rear wall of the box crankcase. In the cam of the shaft 21 there are holes into which the axis of the pawl 44 of the trigger mechanism and the pin 43 with a spring 42 are inserted, pressing the pawl 44 to the teeth of the mechanical ratchet of the gear 20. The trigger gear is in constant engagement with the gear of the first transmission of the secondary shaft and through it with the gear I transmission of the input shaft. When you press the trigger lever 41 with your foot, the shaft 21 rotates and the pawl 44, resting against the teeth of the ratchet of the gear 20, turns it, and through the gears and the clutch and the crankshaft of the engine engaged with it. When the lever 41 is released, the return spring 1 of the trigger mechanism returns the shaft 21 together with the pawl 44 to its original position with its force. To avoid shock when the lever is suddenly released, a buffer 40 of the trigger is installed in the crankcase of the box, held by a spring and plug 39. In addition, the downward travel of the trigger lever is limited by a rubber buffer attached to the motorcycle frame. When the engine is running and the lever 41 is in reverse, under the action of a return spring, the pawl 44 is taken away from the ratchet teeth by a heel-shaped pawl switch installed inside the crankcase. The box is filled with oil through a hole on the left wall of the crankcase, closed with a threaded plug. The drain hole located near the plug 39 of the trigger buffer is also closed with the same plug.
Gearbox adjustment 6204
During operation, it becomes necessary to adjust the synchronism of the operation of the mechanisms of manual and foot switching. To ensure the normal operation of the foot shift mechanism, it is necessary to install the adjusting screws 24 (Fig. 38) so that, at the extreme positions of the pedal 25, the fixing holes of the II and III gears on the sector 30 reach the lock ball 31. The fixation of the sector is well felt when moving the manual shift lever . In operation, adjustment violations are possible when the fixing holes of sector 30 pass the fixer ball or do not reach it, so the correct adjustment is checked by the manual shift lever (Fig. 40). When switching from ІІ to III gear with a false pedal, if the fixing hole of the 3rd gear does not reach the detent ball, the manual shift lever should be turned forward until the hole coincides with the ball. In this case, you need to unscrew the lower adjusting screw. If the fixation well passes over the fixative ball, the manual shift lever must be turned back until the socket meets the ball. In this case, the lower adjusting screw must be screwed in. When shifting from III to II gear with a foot pedal, if the fixing hole of the II gear does not reach the detent ball, the manual shift lever should be turned back until the hole coincides with the ball. In this case, you need to unscrew the upper adjusting screw. If the fixation hole goes over the fixer ball, the manual shift lever should be turned forward until the hole is in line with the ball. In this case, the upper adjustment screw must be screwed in.
MT-804 gearbox device
The MT-804 gearbox is shown in fig. 41 and consists of a mechanism with four pairs of constantly meshed gears, designed to receive four gears for moving forward, a gear change mechanism, a reverse gear, an engine start mechanism, an automatic clutch release mechanism when shifting gears. All parts of the box are installed in a cast crankcase made of silumin. Behind the crankcase is closed with a cover made of the same material. At the front, the crankcase has a flange with which it is attached to the engine crankcase using three studs and one bolt. The main mechanism of the gearbox, designed to transmit torque from the engine to the main gear with different gear ratios, like the gearbox 6204, consists of two parallel shafts - primary 7 and secondary 24. Both shafts are mounted on ball bearings mounted in the housing and gearbox cover. The input shaft is made integral with the gear rims of I, II gears and reverse gear. The 4th gear gear and the 3rd gear are freely installed on the shaft on the segment key. Both of these gears are interconnected by means of end projections. Thus, when the shaft rotates, the gear rims of all gears sitting on it rotate as one. The splines at the end of the input shaft fit into the splined hubs of the clutch discs. On the secondary shaft, freely rotating gears of the 4th, 2nd, 2nd and 1st gears of the secondary shaft are installed, which are in constant engagement with the corresponding gears of the input shaft. These gears, in addition to the main crown, have crowns with small involute splines cut on the end ledges and designed to engage gears. Bushings made of anti-friction material are pressed into the mounting holes of the gears: metallographic bushings for the gears of I, II and III gears and bronze for the gear of the IV gear. Between the gears of IV and III gears and the gears of II and I gears on the secondary shaft, splined couplings 30 with involute splines on the outer surface sit on segment keys. On the splines of the couplings, clutches 26 of gear engagement are planted, having the ability to move freely along the splines. On the outer surface of each gear clutch there are annular grooves for the forks 22 and 23 of the gears. The fork cheeks sit freely in the grooves and do not interfere with the coupling rotating with the shaft. To enable the transmission, it is necessary to block one or another gear of constant engagement with the secondary shaft. This is achieved by moving along the splines of the gear engagement clutch until the moment when the internal teeth of the clutch are fully pushed onto the involute splines of the end crown of the output shaft gear. In this case, the output shaft gear will be interlocked with the shaft, which ensures the transfer of torque from the input shaft to the secondary. On fig. 41 shows the neutral position of the transmission when the shift clutches with forks are in the middle position. In this position, when the input shaft rotates, the gears of the output shaft will rotate idly. The movement of the clutches 26 of the inclusion is carried out by the forks using the gear shift mechanism, which ensures the inclusion of the desired pair of gears from the foot pedal. To facilitate the inclusion of the internal splines of the coupling and the teeth of the splined rim of the gear, as well as the box 6204, are made with a pass through one tooth. The rarefaction of the teeth increases the angle of rotation of the connected parts relative to each other, which is possible for engagement. This measure also contributes to a smoother (without sharp blows) gear shifting in the event of a significant difference in the speeds of rotation of the connected parts. In addition to the gears of I, II, III and IV gears, a reverse gear 32 is installed on the secondary shaft. This gear sits on splines and can move freely but with it. On the splines of the shank of the secondary shaft, a disc 35 of the elastic coupling of the cardan is mounted, fixed with a slotted nut. The secondary shaft ends with the same ball head as the shaft of the box 6204, designed to center the front end of the driveshaft. All pinion gears are made of 18KhGT alloy steel, case-hardened and hardened.
gear shift mechanism
The gear shift mechanism consists of a gear shift pedal 43 (Fig. 41) with a shift shaft assembly, a crank cam 40, a pawl 56, a shift disc 48 with a lock, two forks 22 and 23. The shift shaft is installed in a long sleeve 45, pressed in the hole of the crankcase tide) of the gearbox. On the splined end of the roller inside the box body, a crank cam is mounted and fixed with a castellated nut. A pin is inserted into the hole of the crank cam, one end of which enters the groove of the switching pawl, and the second is located between the ends of the spring 41. The spring is mounted on a sleeve loosely put on the end of the switching shaft, the ends of the spring are separated (with pre-twisting) and cover the stop bar 42 , which is mounted on the roller and fixed with a bolt on the body boss. Thus, the cam-crank, and with it the roller with the shift pedal, are fixed in a strictly defined neutral position. When the roller is turned in one direction or another from the neutral position, the crank cam pin presses on one of the ends of the spring, forcing it to move away from the stop bar, and since the second end of the spring rests against the bar on the other side, the spring twists, resisting turning more and more along as the angle of deviation of the crank cam from the neutral position increases. The rotation of the roller occurs at the moment of gear shifting under the action of a force applied to one of the legs of the foot shift pedal. When the force is removed, the roller with the pedal returns to its original position from the action of the spring. The limiting angle at which the switching shaft can turn is limited by special protrusions along the edges of the profile of the cam-crank 40, which can rest against the roller of the inner lever 37. The pawl 56 of the switching mechanism is a plate welded to the sleeve on one side and bent at a right angle shelf on the other side. The pawl sleeve is loosely seated on the roller 55, installed in the holes of the body and cover. When the crank cam is turned, its pin, which enters the pawl groove, moves the pawl along the roller in one direction or another. Under the action of the spring 54, put on the pin of the crank cam, the pawl is pressed all the time with its shelf against the pins of the switching disk. The switching disc 48 made of sheet steel, with two through curly grooves cut out in it, is installed on a vertical axis pressed into the hole in the bottom of the box body. Two gearshift forks are mounted on shaft 52, fixed in the holes of the housing and crankcase cover, above the plane of the gearshift disc, and with their spikes enter the grooves of the disc.
The operation of the gear shift mechanism
Gear shifting occurs when the shift disc is rotated to a certain angle. At the same time, the profile grooves of the disk, pressing on the spikes of the forks, move them along the roller 52 (Fig. 41), and with them the engagement clutch to engage a particular gear. The rotation of the disk is carried out with the help of a pawl, which, moving along its roller, acts on the pins of the disk. The position of the disk is fixed by means of a lever lock 51, the tooth of which enters the grooves on the outer side of the disk. The disk has six working slots for fixing I, II, III and IV gears, a main neutral position slot between I and II gears and a second neutral position between III and IV gears used for coasting. The seventh groove is technological. On fig. 41 the gearshift mechanism is shown in the main neutral position of the gearbox. To turn on the 1st gear, it is necessary to press the front shoulder of the pedal to failure, while the crank cam will turn counterclockwise, and the pawl, moving forward and pressing the disc pin, will turn it to the position where the lever lock tooth enters the groove of the disc for fixation I transfer. During the rotation of the disk, its groove acts on the stud of the 1st and 2nd gear shift fork like a profile cam and moves the fork to the position corresponding to the 1st gear engaged. The pin of the shift fork of III and IV gears remains motionless, since at the moment of rotation of the disk it does not go beyond the concentric part of the second groove of the disk. When the foot shift pedal is released, all parts of the shift mechanism, except for the fixed disc and associated shift forks, automatically return to their original position. Engagement of the 2nd, 3rd and 4th gears is carried out by sequentially pressing the rear shoulder of the foot pedal to the stop. In this case, the pawl makes a series of backward movements, each time turning the switch disk at an angle of 50º, equal to the step between the pins, and returning to its original position after removing the force from the pedal. The protrusion of the pawl at the moment of switching on the gear enters the gap between the pins of the disk 48. When the pawl returns to its original position, its protrusion, sliding its outer bevel along the pin, forces the pawl to overcome the force of the spring 54, turn on the axis and disengage from the pins. The order of movement of the forks when the disk is rotated is determined by the configuration of the slots in the disk 48, which is selected so that when one fork moves, the second one remains stationary. This ensures that two gears cannot be engaged at the same time. The gear shift mechanism has a device for signaling the main neutral position of the gearbox (between I and II gears). The device consists of a sensor spring and a neutral position sensor 49, which is an insulated contact screwed into a threaded hole in the wall of the gearbox housing against the shift disc. The sensor is connected by a wire to a signal lamp installed in the headlight housing. The sensor spring is riveted to disk 48 and in the main neutral position of the disk touches the sensor, closing the electrical circuit of the signal lamp, which lights up.
Reverse gear
trigger mechanism
The starting mechanism of the MT-804 box (Fig. 41) includes an intermediate shaft 6 with freely rotating gears 4 and 5 installed on it. The large gear 5 is constantly engaged with the gear of the second gear of the input shaft. The small gear 4 is pressed against the end face of the large gear by a spring. Ratchet teeth are made on the contact ends of both gears. The stationary intermediate shaft 6 is pressed with its front end into the box crankcase, and its rear end is installed in the opening of the crankcase cover. The shaft 20 of the trigger mechanism rests with its front end in a blind sleeve 1 installed in the front wall of the crankcase, and passes through a hole in a steel sleeve pressed into the crankcase cover. At the outer end of the starting shaft, a lever 19 of the starting mechanism is fixed with a wedge bolt. A toothed sector sits on the splines of the shaft 20, into the hole of which the bent end of the return spring 2 of the trigger mechanism enters. The second end of the spring through the stop is connected to the blind bushing of the front wall of the box crankcase. The return spring is pre-twisted by turning the sleeve 1 counterclockwise, due to which the toothed sector is constantly pressed against the rubber rebound buffer, and the start lever is in the upper position.
The operation of the trigger mechanism
The engine is started by pressing the foot on the start lever. In this case, the sector of the launch shaft, turning, with its teeth engages with the small gear 4 (Fig. 41) of the intermediate shaft and makes it rotate. The small gear with the help of a mechanical ratchet transmits rotation to the large gear 5, and it - to the input shaft of the gearbox and through the clutch to the crankshaft of the engine. When the force is removed from the start lever, it, together with the shaft and sector, returns to its original position under the action of a return spring. In this case, the start shaft sector turns the small gear in the opposite direction, which is not transmitted to the large gear because the ratchet teeth on the ends of the gears, overcoming the resistance of the axial spring 3, disengage from each other. With a sharp release of the start lever, the impact of the sector on the box body is absorbed by a rubber buffer with a metal lining. If the engine is started at the moment when the start lever is delayed in the upper position and the sector has not yet disengaged from the crown of the small gear, the rotation from the large gear to the small gear will also not be transmitted due to the disengagement of the ratchet, but a characteristic crackle will be heard emitted by the ratchet. During engine operation, both start gears rotate together on shaft 6, since the magnitude of the friction torque between the ends of the spring and the small gear is insufficient to disengage the ratchet. However, in the cold season, due to the thickening of the lubricant, the small gear of the starting mechanism may slow down, lag behind the large one, which will cause the ratchet to disengage and crack. As the box warms up, the ratchet noise stops. The device and operation of the mechanism for automatically disengaging the clutch when shifting gears are described above, when describing the clutch device. All friction surfaces of the gearbox are lubricated with oil poured into the gearbox housing through the hole in the crankcase tide on the left. A plug with a dipstick (to control the level of lubrication) and a breather is wrapped in the hole, with the help of which the gearbox cavity is connected to the atmosphere. There is no special supply of lubrication to rubbing surfaces. In places of possible oil leaks, the box body is sealed with oil seals (at the shaft exit points), rubber knees (start shaft bushing, reverse gear lever shaft, clutch release rod slider) and a paper gasket along the plane of the box crankcase connector with the engine crankcase.
