Publish Time: 2022-02-22 Origin: Site
2. Tandem Final Drive
Tandem final drive is used normally for the middle axle of tandem drive axle. It may divide
engine power from universal driving device into two sections. One is to drive middle axle,
and the other is to lead towards rear axle.
For tandem final drive of STR series drive axle, see Figure 1-6. Engine torque will pass
through transmission shaft and Flange 4 to Differential Case (front) 1 of inter-axle
differential through spline input. Inter-axle differential will distribute the above torque to two Half Axles 13 and 16. Tandem Axle 32 will transfer the torque of front half axle gear to
Output Flange 29 of middle axle and lead it to rear axle with one transmission shaft.
Hollow Shaft 20 uses spline to drive Driving Cylinder Gear 19 to rotate and transfer the
power of Rear Half Axle Gear 16 to Driving Bevel Gear 35 through the mesh of Driving
and Driven Cylinder Gear 19 and 38. It can transfer the power to Inter-axle Differential 34
of middle axle after realizing speed reduction, torque increasing and commutation through
the meshing of Driving and Driven Bevel Gears 35 and 33. The rest contents are same as
that of rear axle (central) final drive.
Figure 1-6 STR Series Tandem Final Drive (Middle Axle Final Drive)
1 – Differential Case (front) 2,31 – Flange Nut 3, 30 – Cotter Pin 4, 29 – Flange 5, 27, 41 – Bearing Block
6, 18, 21, 28 – Deep Groove Ball Bearing 7 – Locking Ring 8 – Lock Pin 9 – Shifting Fork 10 – Pin 11 – Pressure Switch 12 – Half Axle Gear (Front) Washer 13 – Front Half Axle Gear 14 – Planet Gear Gasket 15 –
Inter-axle Planet Gear 16 – Rear Half Axle Gear 17 – Differential Case (rear) 19 – Driving Cylinder Gear 20 – Hollow Axle 22 – Axial Spring Collar 23 – Round Nut 24 – Axle Housing 25 – Half Axle 26 – Sliding Mesh
Sleeve 32 – Tandem Axle 33 – Driven Bevel Gear 34 – Inter-axle Differential 35 – Driving Bevel Gear 36 –
Final Drive Housing 37 – Cylindrical Roller Bearing 38 – Driven Cylinder Gear 39 – Axle Box 40 – Spacer
Bush 42 – Tapered Roller Bearing 43 – Bearing Outer Ring Pressure Plate 44 – Axle Box Cover 45 – Half
Axle Gear (Rear) Washer 46 – Cross Shaft
3. Wheel Reducer
Wheel reducer is another type of final drive. The total reduction ratio of STR series drive
axle equals to the product of reduction ratios of central final drive and wheel reducer. The
reduction ratios of STR series drive axle shall have series such as 3.93, 4.42, 4.8, 5.73,
6.72, 9.49 and 10.89.
For end view of STR series wheel-side planetary reducer mechanism, see Figure 1-7. In
Figure 1-7, Internal Gear Ring 1 is stationary, and Sun Gear 3 in the middle is a driving
part to fit with half axle through spline in its inner bore. Half axle drives Sun Gear 3 to
rotate after receiving engine torque transferred through clutch, transmission, universal
shaft, final drive and differential. There are five Planet Gears 2 meshing together with sun
gear and internal gear ring among them. When Sun Gear 3 is rotating, any Planet Gear
meshing with it can only rotate around its own axis but also revolute around sun gear
because internal gear ring is stationary. The above revolution speed is the output one of
planetary reducer mechanism. Now, the transmission ratio of wheel reducer is as following:
i = number of internal gear ring/sun gear +1. Obviously, i＞1. This shows that the wheel
reducer mechanism is decelerated, and this means the output speed (revolution speed of
planet gear) is less than the input speed (sun gear speed).
Figure 1-7 Planetary Wheel Reducer
1 – Internal Gear Ring 2 – Planet Gear 3 - Sun Gear
For the structure of STR series drive axle wheel reducer, see Figure 1-8. Half Axle 17
passes through Axle Housing 16 to transfer engine power with deceleration, torque
increasing and commutation through central final drive to wheel reducer. Sun Gear 29 will
fit with Half Axle 17 through spline and limit its axial position through Sun Gear Gasket 28.
Half axle is floating in axle housing. To avoid any factor such as centrifugal force because
of steering to pull half axle away externally and effect on the operation of gear in wheel
reducer, there shall be a lifting pin that its head is a sphere at the middle of End Cover 30
to press its half axle end face so as to limit it shifting. There are 5 Planet Gears 3 to mesh
with sun gear around it. Two ends of every Planet Gear are installed with a Planet Gear
Gasket 32 to reduce any friction between planetary and relevant parts and improve the
lubricating condition of the part. The central hole of Planet Gear is installed with Planet
Axle 31. There are two Needle Roller Bearings 4 between Planet Gear and planet axle to
guarantee both with relative rotation smoothly. That between needle roller bearings can be
separated with Gasket 33. Both ends of every planet axle shall pass through
corresponding position holes of Planet Carrier 5 and Wheel Reducer Housing 1
respectively. Both planet carrier and wheel reducer housing are fastened together with
bolts. At the outside of five planet gears, Internal Gear Ring 2 meshing with planet gears
will fit with Gear Bracket 8 through spline and can be stuck in the slot of internal gear ring
with spring collar to fasten them together firmly. Gear Bracket 8 shall be fit with Axle
Housing 16 through spline. Axle housing may be connected with frame through
suspension system, and they are stationary relatively. Therefore, Gear Bracket 8 and
Internal Gear Ring 2 are stationary in the above parts. The shaft of gear bracket is
installed with Tapered Roller Bearing 22. It may support Rear Hub 21 together with
Tapered Roller Bearing 18 installed at axle housing so as to make rear hub rotate around
its axis. Three parts including Rear Hub 21, Wheel Reducer Housing 1 and Brake Drum 11 can be fastened together with Wheel Bolt 9 and Wheel Nut 10.
Figure 1-8 STR Series Wheel Reducer Mechanism
1 – Wheel Reducer Housing; 2 – Internal Gear Ring; 3 – Planet Gear; 4 – Needle Roller Bearing; 5 – Planet Carrier;6 – Oil Baffle Disc; 7 – Hole Spring Collar; 8 – Gear Bracket; 9 – Wheel Bolt; 10 – Wheel Nut; 11 – Brake Drum; 12– Splash Cover; 13, 14, 23 – Axel Seal; 15 – Bearing Spacer; 16 – Axle Housing;17 – Half Axle; 18, 22 – Tapered Roller Bearing;19 – Brake Shoe; 20 – O-Seal Ring; 21 – Rear Hub;24 – Round Nut; 25 – Adjustable Gasket;26 – Pilot Pin; 27, 34 – Screw Plug; 28 – Sun Gear Gasket;29 - Sun Gear; 30 – End Cover; 31 – Planet Axle;32 – Planet Gear Gasket; 33 – Gasket;
When Sun Gear 29 is driven by Half Axle 17 to rotate, Planet Gear 3 will mesh with Sun
Gear and Internal Gear Ring 2 to make Planet Gear rotating about Planet Axle 31 but also
revolute around sun gear so as to drive planet axle to revolute together with it. Planet axle
is connected with Planet Carrier 5 and Wheel Reducer Housing 1 to make 1 rotating with
Rear Hub 21 fastened on it. Wheel Bolt 9 at rear hub is connected with hub so as to make
wheels having the power from engine.
That adjusting gasket thickness through Round Nut 24 can make axial position
fine-adjustment of gear bracket at axle housing so as to adjust the preload of two Bearings
18 and 22.
Wheel reducer is a relatively closed place and the oil level of lubricating oil is about at the
position of half axle centerline. In a space enclosed by End Cover 30, Wheel Reducer
Hosing 1, Rear Hub 21, Spacing Ring 15, Axle Housing 16, Axle Seal Ring 13, 14, 23 and
Half Axle, that between end cover and wheel reducer housing as well as between spacing
ring and axle housing may be smeared with sealant. That between wheel reducer housing
and rear hub may be sealed with O-Ring 20, that between spacing ring and rear hub may
be sealed with shaft seal and that between half axle and axle housing may be sealed with
shaft seal. Then, there is not any connection with outside except air vent under inner bore
of Gear Bracket 8. The air vent is higher than the level of lubricating oil not to make any
lubricating oil in wheel reducer into axle housing so as to meet the requirements that the
necessary oil level of wheel reducer shall be more than that in the middle of axle housing.
When the temperature of oil in wheel reducer is risen caused by the operation of gear and
bearing, both air and lubricating oil in wheel reducer shall be expanded at the same time.
High pressure air will be exhausted to the middle of axle housing from the above vent and
connected with the atmosphere through air vent at the upper of axle housing. There shall
be one screw plug 27 and 34 respectively at end cover and wheel reducer housing.
Through corresponding holes of these screw plugs, lubricating oil may be filled into and
discharged out of wheel reducer. At the same time, the hole of Screw Plug 27 can also be
an oil level observation hole. In oil injection, it shall be rotated to the position that is at the
same level with centerline. That filling with lubricating oil to the hole and beginning to
overflow means there has been enough oil already.
Following with continuously deepening understanding with STR series drive axle and
market competition intensification, SINOTRUK is always committed to improving the
quality of products. To improve the reliability of seal between wheel reducer housing and
rear hub, SINOTRUK changes one O-ring 20 in original STR structure into 2. To improve
lubrication conditions of central final drive and reduce oil temperature of wheel reducer,
SINOTRUK cancelled Axle Seal 23 in some axle types, and increase the oil level at the
middle section of axle housing same as that in wheel reducer. To improve the carrying
capacity of axle and reduce the failure rate of hub bearings (Tapered Roller Bearings 18
and 22), SINOTRUK unified these two bearings as 32222 Width series. To improve the
lock reliability of axle nut (Round Nut 24), SINOTRUK changed it as dual-nut locking
structure.
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