Wheel hub assembly with integrated reduction gear and brake mechanism

A wheel hub assembly for heavy-duty vehicles comprises a hollow body containing a liquid lubricant having a first compartment housing wheel drive reduction gear and a second compartment adjacent the first compartment housing a wheel brake mechanism. A portion of the sidewall of the hollow body annularly surrounds one of the compartments (preferably the second) and comprises at least one pair of longitudinally extending, oppositely sloping generally oblique grooves for circulating the lubricant between the compartments. The grooves of each pair are preferably symmetrical. Grooves sloping in a first direction are arranged along a first semi-circumferential zone and the grooves sloping in the opposite direction are arranged in a second semi-circumferential zone. In the illustrated embodiment and annular interior wall separates the compartments and comprises a planetary pinion carrier and has channels in alignment with the oblique grooves for carrying liquid between the oblique grooves and the first compartment. The depth of the grooves may vary in accordance with the circumferential position thereof.

The present invention relates generally to wheel hub assemblies 
particularly for heavy-duty vehicles such as trucks, industrial vehicles, 
agricultural vehicles and earth-moving equipment, and more particularly to 
wheel hub assemblies comprising a hollow body. 
Known hollow body wheel hub assemblies contain a liquid lubricant and 
comprise a first compartment housing wheel drive reduction gear and a 
second compartment adjacent to and communicating with the first 
compartment housing a brake mechanism. In such a wheel hub assembly 
advantage is taken of the presence of a liquid lubricant, normally 
provided for lubricating the wheel drive reduction gear for cooling, in 
operation, the associated brake mechanism. 
Yet, in practice, it has frequently been observed that there is little or 
no circulation of the liquid lubricant between the first compartment 
housing the reduction gear and the second compartment housing the 
associated brake mechanism. This is all the more so since most often the 
first compartment is separated from the second compartment by an annular 
internal wall for supporting the planet pinions or gears of the reduction 
gear and the liquid lubricant can only partially fill the compartments to 
prevent an excessive loss of power by the circulation of the lubricant in 
use and also to prevent leaks which owing to thermal expansion would 
otherwise be inevitable if the hollow body were completely filled. Owing 
to centrifugation two separate liquid "rings" result which are isolated 
from each other on opposite sides of the annular internal wall. 
Now, although the temperature in the first compartment in which the 
reduction gear is housed is always rather moderate, of the order of 
40.degree. C., particularly because that compartment has a greater amount 
of liquid lubricant, such is not the case with the second compartment 
which houses the brake mechanism where the temperature may, on the 
contrary, reach relative high levels, of the order of 110.degree. C., 
particularly because of the thermal energy given off during braking. This 
produces the dual risk of a possible destruction of the friction linings 
of the brake mechanism which are not properly cooled and overheating some 
of the liquid lubricant which may cause deterioration thereof. 
The object of the present invention is to provide an arrangement capable of 
overcoming this drawback. 
According to the invention there is provided a wheel hub assembly for 
heavy-duty vehicles, the wheel hub assembly comprising a hollow body 
containing, in use, a liquid lubricant and having a first compartment for 
housing wheel drive reduction gear and a second compartment adjacent to 
the first compartment and housing a wheel brake mechanism, at least a 
portion of the sidewall of the hollow body which annularly surrounds one 
of the compartments has at least a pair of longitudinally extending, 
oppositely sloping generally oblique grooves for longitudinally 
circulating the liquid lubricant between the compartments when the wheel 
hub assembly is in operation. 
Preferably, there are a plurality of pairs of oblique grooves, one groove 
of each of the pairs sloping in a first direction and the other groove of 
each of the pairs sloping in a second or opposite direction, the said one 
grooves being spaced circumferentially along a first semi-circumferential 
zone and the said other grooves being spaced circumferentially along a 
second semi-circumferential zone opposite the first semi-circumferential 
zone. 
In any event the grooves act as endless worms in opposite directions, the 
liquid lubricant is necessarily taken up by the grooves when the liquid is 
centrifuged into "rings" since the grooves are formed along the inner 
surface of the sidewall of the hollow body where the liquid rings are 
formed. The grooves sloping in the first direction ensure the forward flow 
of the lubricant and the grooves sloping in the second or opposite 
direction the return flow of the lubricant between the respective 
compartments. 
Such an arrangement provides between the compartments of the hollow body of 
the wheel assembly a systematic flow of liquid lubricant which tends to 
average the temperatures in the compartments for the benefit of the 
cooling of the second compartment which houses the brake mechanism. The 
improved circulation of lubricant between the compartments works for 
forward or reverse movement of the vehicle with which it is equipped. In 
the case of reverse movement of the vehicle the above-described functions 
of the grooves are reversed.

As shown in the drawings the wheel hub assembly 10 is adapted to be 
installed at the end of a stub axle 11 and comprises a hollow generally 
bell-shaped body which contains, in use, a liquid lubricant (not shown). 
In practice, the sidewall of the hollow body comprises three parts. 
To begin with, a first part 13 which defines the actual wheel hub which is 
mounted on the free end of the stub axle 11 by means of anti-friction 
bearings, not shown in the drawings. The first part 13 comprises at its 
axial end remote from the stub axle 11 a transverse flange 14. A second 
part 14 comprises, in contact with the flange 14, a transverse flange 17 
to which it is secured by threaded fasteners (not shown), the combined 
radial flange 18 defining the web of the rim by which the wheel may be 
secured (by threaded fasteners, not shown) to the wheel hub assembly 10. 
Finally, the hollow body comprises a third part 20 forming a mere annular 
spacer which is closed by a cover 21 at its axial end remote from the 
second part 15, the cover and spacer being secured by threaded fasteners 
22 to the second part 15. 
Inside the second part 15 of the peripheral sidewall 12 of the hollow body 
of the wheel hub assembly 10 is formed a first compartment 23 which houses 
wheel drive reduction gear 24. Inside the third part 20 of the peripheral 
sidewall is formed a second compartment which is adjacent to the first 
compartment 23 and houses a brake mechanism 27. 
In practice, and as shown, the first compartment 23 is separated from the 
second compartment 26 by an annular interior wall 28 which comprises a 
planetary pinion carrier for supporting the planet gears or pinions 29 of 
the wheel drive reduction gear 24 which comprises a planetary gearset and 
having a central opening 30 for the sun gear shaft 31 of the wheel drive 
reduction gear 24 to protrude into the second compartment 26, shaft 31 
carrying a cylindrical ring 34 defining the braking member for the brake 
mechanism 27 housed in the second compartment 26. 
An annular passageway 35 is left between the central opening 30 through the 
annular wall 28 and a sleeve or bush surrounding part of the sun gear 
shaft 31 of the drive reduction gear 24 through which the first and second 
compartments 23 and 26 normally communicate with each other. 
The above arrangements are well known per se and their features are not 
part of the invention and therefore need not be described in greater 
detail. In particular the structure and operation of the reduction gear 24 
and the brake mechanism 27 will not be described herein. 
For improved axial or longitudinal circulation of the liquid lubricant 
between compartments 23 and 26, at least the portion of the inner surface 
of the peripheral wall of the hollow body that surrounds one of the 
compartments 23, 26 comprises at least a pair of longitudinally extending, 
oppositely sloping grooves 36A, 36B generally oblique with respect to the 
axis of the wheel hub assembly. 
Preferably, the oppositely sloping grooves 36A, 36B are provided in the 
portion of the sidewall surrounding the second compartment 26 which houses 
the brake mechanism 27. The grooves 36A, 36B are therefore formed along 
the inner surface of the annular spacer defining the second part 20 of the 
sidewall 12 of the hollow body of the wheel hub assembly 10. 
According to the illustrated embodiment a plurality of pairs of oppositely 
sloping grooves 36A, 36B are provided on the inner surface of the annular 
spacer 20 and are arranged symmetrically to one another about an axis of 
symmetry (not marked). A first group of the grooves 36A slope in a first 
direction which is counterclockwise of the axis and are preferably 
circumferentially spaced along a semi-circumferential zone A of the inner 
surface of the annular spacer 20 and a second group of the grooves 36B 
slope in a second or opposite direction which is clockwise of the axis and 
are preferably circumferentially spaced along a semi-circumferential zone 
B, opposite zone A, of the inner surface of annular spacer 20 as shown in 
FIGS. 2 to 4. 
In the illustrated embodiment there are five oblique grooves 36A sloping in 
the first direction and five oblique grooves 36B sloping in the opposite 
direction which are arranged in symmetrical pairs. In practice the slope 
of all the oblique grooves 36A is the same and the slope of all the 
oblique grooves 36B is also the same. Also in practice, the absolute value 
of the slopes of the oblique grooves 36A, 36B are the same though the 
senses are different. The slope may, for example, be between 20.degree. 
and 25.degree. relative to the axis of the wheel hub assembly and, in 
particular, about 23.degree.. 
In the illustrated embodiment the inner surface of the annular spacer 20 on 
which the oblique grooves 36A, 36B are formed is eccentric with respect to 
the outer surface of the annular spacer. It follows, however, in this case 
that the pairs of oblique grooves 36A, 36B are arranged symmetrically with 
respect to the axial plane of symmetry of the wheel hub assembly. 
It goes without saying that, alternatively, when the inner surface of the 
annular spacer 20 is not eccentric the pairs of oblique grooves 36A, 36B 
are all of the same depth. Further, the grooves 36A, 36B are then arranged 
in symmetrical pairs with respect to the axis of the wheel hub assembly. 
In any event, in operation, assuming the direction of rotation of the wheel 
hub assembly 10 is as indicated by arrow F1 in FIG. 2, the axial grooves 
36A produce an axial flow of the liquid lubricant in the second 
compartments 26 in the direction F3 in FIG. 3, and the oppositely sloping 
grooves 36B produce an axial flow of the liquid lubricant in the opposite 
direction. Circulation of the liquid lubricant between the compartments 23 
and 26 of the wheel hub assembly 10 is improved accordingly. 
As will be readily understood the variation of the depth of the pairs of 
oblique grooves 36A, 36B as a function of their position facilitates the 
adaptation to the configuration of the liquid ring which forms, in 
operation, by centrifugation of the liquid in second compartment 26, which 
liquid ring is represented by the phantom line 49 in FIG. 2, centered on 
the axis of the wheel hub assembly. 
To further contribute to the circulation of the liquid lubricant between 
compartments 23 and 26, channels 41A, 41B are preferably formed in the 
annular wall 28 provided between the two compartments, as schematically 
illustrated by chain-dotted lines in FIG. 1. 
Finally, the present invention is not intended to be limited to the 
illustrated and disclosed embodiment but on the contrary is intended to 
cover all modifications and alternatives falling within the scope of the 
appended claims.