On MAZ-64227, MAZ-54322 vehicles, an eight-speed dual-range gearbox YaMZ-238A with synchronizers in all gears, except for reverse gear, is installed
The gearbox consists of a main two-stage gearbox and a two-stage additional gearbox (downshift).
The gearbox arrangement is shown in fig. 1.
The installation of all parts of the gearbox is carried out in the crankcases of the main and additional boxes, which are interconnected, and then assembled to the clutch housing: a single power unit is formed as part of the engine, clutch and gearbox.
The input shaft 1 of the main box is mounted on two ball bearings; driven clutch discs are installed on the front splined end, and the rear end is made in the form of a ring gear of the main gear of the main box.
The output shaft 5 of the main box is supported in front by a cylindrical roller bearing mounted in the bore of the gear rim of the drive shaft, and at the back by a ball bearing mounted in the front wall of the crankcase of the additional box.
The rear end of the secondary shaft is made in the form of a ring gear, which is a gear of constant engagement of the additional box.
The gears of the second and fourth gears of the secondary shaft of the main box are mounted on plain bearings made in the form of steel bushings with a special coating and impregnation, and the gears of the first gear and reverse are on roller bearings.
The intermediate shaft 26 of the main box rests in front on a roller bearing mounted in the front wall of the main box crankcase, and in the back - on a double-row spherical bearing placed in a glass installed in the rear wall of the main box crankcase.
An additional axle for the reverse intermediate gear is installed in the lugs of the crankcase of the main box.
The reverse gear is switched on by moving the reverse carriage 24 forward until it is connected to the ring gear of the reverse gear 25, which is in constant engagement with the reverse intermediate gear.
The secondary shaft 15 of the additional box in front rests on a cylindrical roller bearing located in the bore of the gear rim of the secondary shaft of the main box, at the back on two bearings: a cylindrical roller bearing and a ball bearing, installed respectively in the rear wall of the crankcase of the additional box and the bearing cover of the output shaft.
On the splines of the middle part of the output shaft of the additional box, gearshift synchronizers are installed, and on the rear splined end there is a driveshaft mounting flange.
The gear 11 of the additional box is mounted on cylindrical roller bearings on the middle cylindrical part of the shaft.
The intermediate shaft 19 of the additional box rests at the front on a cylindrical roller bearing installed in the front wall of the additional box crankcase, and at the back on a double-row spherical bearing placed in a glass mounted in the rear wall of the additional box crankcase.
A downshift gear 22 is installed on the front splined end of the intermediate shaft of the additional box.
At the rear of the intermediate shaft, a ring gear is made, mated with the downshift gear of the secondary shaft of the additional box.
To shift gears in the main gearbox, inertial synchronizers with conical friction rings are used, and in the additional one - with friction discs.
Shifting gears in the main box is performed using a mechanical remote drive, and the additional box is controlled using a pneumatic drive.
Remote drive of the main box (Fig. 2). Telescopic type, consists of a mechanism located directly on the gearbox 13, and a system of rods and levers associated with a 3 gear lever mounted in the cab.
In the tides of the top cover 1 (Fig. 3) of the main box, three rods are mounted: on the far right (along the direction of the car) the fork 3 of the reverse gear is fixed, on the middle - the fork 4 of the first and second gears of the main box and on the third - fork 8 for shifting the third and fourth gears of the main gearbox.
Rods 5, 20 and 21 move in the guide supports of the top cover using lever 22. On the reverse rod and the switching rod of the first and second There are heads (respectively 11 and 17) in the main box.
The lever 22 enters the head 17 directly, and the lever 22 enters the head 11 through the reverse gear 15.
To engage the third and fourth gears of the main gearbox, the lever 22 can enter directly into the groove of the fork 8 for shifting these gears.
The position of the reverse rod is fixed in the cover using the fuse 16, which is included in the leash 15 under the action of the spring 12, placed in a special glass 1З.
Only by overcoming the spring force of this fuse, you can turn on the reverse.
When the gear is engaged and in the neutral position, the rods are held by ball clamps, to prevent the possibility of simultaneously engaging two gears, a special ball-type lock is installed in the rods.
On the top cover of the main box, a crankcase 11 (see Fig. 2) of the remote control mechanism of the main box is mounted, in which the gear shift shaft 12 is located with a lever 14 fixed on it and an intermediate lever 18 connected to the longitudinal rod 7 of the remote drive .
In the crankcase of the remote mechanism there is a ball lock 9 for gear selection.
Longitudinal rod 7 can perform both longitudinal and angular movements.
The angular movement of the stem causes axial movement of the shaft 12, which leads to the connection of the lever 14 sitting on it with a certain slider in the top cover of the main box 13.
Longitudinal movement of the longitudinal rod causes rotation of the shift shaft 12 and the lever 14 sitting on it. In this case, the shift fork rod moves together with the fork until the corresponding gear is engaged.
The additional box is controlled by means of a pneumatic valve by the switch 1 (see Fig. 2) of the ranges located on the handle of the gear lever 3.
The switching mechanism of the additional box (Fig. 4) - Consists of a pressure reducing valve 12, an air distributor 6, a pneumatic cock 5, an inlet valve 8, a working cylinder 1 and air ducts.
Reducing valve 3 (Fig. 5) is used to reduce the pressure of compressed air supplied from the vehicle's pneumatic system to 4.75 kgf / cm2 - the operating pressure of the gearbox pneumatic system.
The air distributor 23 directs compressed air from the inlet valve 17 into one or another cavity of the working cylinder 25 and bleeds air from its cavities.
Pneumocrane 5 controls the air distributor.
With the 6 range switch down, the air distributor spool is set to the position corresponding to the direct transmission in the additional box. With the shifter up to the downshift position.
The inlet valve 17 provides compressed air through the air distributor 23 to the working cylinder 25 only when the gear in the main box is off.
When the gear is on in the main box, the valve inlet is closed by the pusher 16 and air does not enter the air distributor and the working cylinder, the unloading hole in the valve body is open, both cavities of the working cylinder are connected to the atmosphere.
When the range switch 1 is raised (see Fig. 2), the cable 6 moves the spool 3 (Fig. 6) to a position in which compressed air supplied from the pressure reducing valve to channel "A" through the channel of the pneumatic valve enters the channel " B "and then to the air distributor for downshifting.
Channel "B", at this time, through filter 8 is connected to the atmosphere.
When the range switch is lowered, the cable moves spool 3 to a position where compressed air enters channel B through port A and from there to the air distributor for direct transmission. At this time, channel "B" through cover 5 is connected to the atmosphere.
The gearshift mechanism of the additional box is located in the top cover of its crankcase.
Here is the rod 13 (see Fig. 1), connected with the piston of the pneumatic cylinder 14.
The direction of movement of the rod with the fork 10 of the gear shift of the additional box fixed on it depends on the pressure supplied to the pneumatic cylinder to the left or right of the piston, which causes the inclusion of a large 20 or small 21 synchronizer, i.e. a reduction or direct gear of the additional box.
On the top cover of the additional box, there is a switch indicator sensori downshift.
When the rod 13 and the shift fork 10 of the additional gearbox are moved from one position to another, the control lamp connected to the switch terminal 35 lights up in the driver's cab.
The light goes out as soon as the selected gear (direct or downshift) is fully engaged.
In addition, there is a locking device on the top cover of the additional box to turn off the additional box when the vehicle is towed.
To do this, having set the fork 10 in the neutral position, the locking bolt 9 is screwed all the way into the hole made on the stem, and lock it in this position with a nut.
The lubrication system of the gearbox is combined: the gear bearings of the secondary shafts of the main and additional boxes are lubricated under pressure, the gear teeth and shaft bearings are spray lubricated.
Oil is sucked from the oil bath of the crankcase through the intake 29 and the channel system by the gear oil pump 34.
The pump is driven from the end of the intermediate shaft of the main box.
The pump has a pressure reducing valve, which is adjusted to a pressure of 0.78 kgf / cm2 and, in case of an excessive increase in oil pressure, connects the pump discharge channel to the suction channel.
The oil baths of both crankcases are interconnected by a channel to ensure the same oil level in them.
The internal cavity of the gearbox housings communicates with the atmosphere with the help of a breather.
The gearbox has an oil filler hole on the cover of the main box, an oil level control hole on the side wall of the crankcase of the main gearbox, and two drain holes each from the bottom of the crankcases of the main and additional boxes.