Swiveling wheel assembly for a cart

A swivelling wheel assembly containing a wheel whose swivelling action around a vertical axle may be locked or unlocked by rotating the wheel in one direction or the other. A curved double control lever is housed in a space between the thrust bearing and the tread of the wheel in the area of the lateral extensions of the fork joint. A lower lever arm holds a friction device engaging the tread of the wheel. An upper lever arm contains a locking means which can be received in a locking slot constructed in a housing component which is fixed relative to the pivot axle. A circular cover of the fork joint contains a tracking groove to guide the upper lever arm.

BACKGROUND OF THE INVENTION 
This invention relates to the wheel assembly for a cart or other mobile 
mechanism, of the type which contains a wheel which swivels around a 
vertical axle, and may be locked or unlocked by the rotation of the latter 
in one direction or the other. Such wheel assemblies include a thrust 
bearing with at least one circular housing fixed by axle, a fork joint 
with at least two lateral extensions whose lower ends support the wheel's 
horizontal axle, and one upper circular cover connected to the upper ends 
of the lateral extensions. The cover cooperates with bearings placed 
around the lower end of the vertical axle so that the fork joint can 
rotate around the latter. Prior art wheel assemblies are known to contain 
devices for locking the fork joint in relation to the vertical swivel 
axle. Such devices are disclosed, for example, in British Patent 
GB-A-2106-378. 
In the device disclosed in the '378 patent, part of the fork joint's 
locking device is accessible from the outside and may be damaged. Because 
of this, the proper operation of the device cannot be assured on an 
ongoing basis. Moreover, the known wheel assembly of this patent requires 
a major modification to the fork joint, particularly in the area of the 
wheel axle, which must be capable of moving in the oblong openings made in 
the fork joint. Another problem with this known swivelling wheel is the 
fact that controlling the unlocking of the fork joint entails abruptly 
stopping the wheel for an instant. In addition, the locking devices for 
the known swivelling wheel assembly have a large number of unprotected 
individual parts, and are therefore, subject to rapid wear and 
deterioration. 
SUMMARY OF THE INVENTION 
The purpose of the present invention is to eliminate such problems and to 
provide a swivelling wheel which is simple in design, protected against 
external damage, and has a reduced number of individual parts. 
Within the framework of a swivelling wheel assembly of the type referred to 
above, the assembly of the present invention includes a double control 
lever which is pivotally mounted in the space between the external housing 
of the fork joint and the wheel's tread in the area of the fork joint's 
lateral extensions. The lever is in the form of a curved lever whose two 
arms encompass an angle of between 90.degree. and 160.degree.. The lower 
arm moves between two outermost positions located in proximity to a radial 
plane running through the pivot axis of the lever and the wheel's axis of 
rotation. The lower lever arm has at its lower end a friction device which 
is resiliently urged into engagement with the wheel's tread. The upper 
lever arm is housed in the space enclosed by the fork joint above the 
wheel's tread, and includes, as a locking means a tip which extends 
perpendicularly to the lever's pivot axle, and in the direction toward the 
periphery of the fork joint. A second locking means consists of a locking 
slot for receiving the locking tip without any significant lateral play. 
The slot is constructed in the lower end of the vertical swivel axle or a 
component which is an integral part of the latter. One of the two stops 
for limiting the pivoting movement of the control lever is placed in the 
space located about the wheel and between the lateral extensions of the 
fork joint. This stop works in conjunction with a first lower portion of 
the control lever. The second stop consists of either the bottom of the 
locking slot, or the lower bottom edge of the component containing the 
locking slot, and works in conjunction with the upper lever arm's locking 
tip. 
A circular cover of the fork joint contains a tracking groove extending 
along the center plane of the fork joint and perpendicular to both the 
wheel axle and the control lever's pivot axle. The tracking groove 
operates to guide, without significant lateral play, a portion of the 
upper lever arm or the locking tip along its entire path between the two 
outermost positions of the lever. 
With the construction of the present invention, the locking device is 
completely protected, contains a reduced number of individual parts, and 
is continually operational, despite possible wear on the part of the 
wheel's tread.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown on the attached drawings, a cart or other mobile platform, which 
is not shown, contains a wheel 2 which is capable of swivelling around the 
vertical swivel axle 3 and of being locked or unlocked by the rotation of 
the wheel 2 in one direction or the other. The wheel 2 contains a 
horizontal rotating axle 4 whose ends are supported by at least two 
lateral extensions or forks 5 of a fork joint 6. The upper end of the fork 
joint, which is in the form of a circular cover 7, is fastened by means of 
a thrust bearing 8 to the lower end of the vertical swivel axle 3. It may 
be noted that the vertical swivel axle is laterally offset in relation to 
the vertical plane passing through the horizontal axle 4 of the wheel 2. 
As can be seen on FIGS. 1 and 4, the thrust bearing 8 includes a first 
circular housing 9 and a second circular housing 10 fixedly mounted, like 
the first, on the lower end of the vertical axle 3. The two housings 9 and 
10 are open at the bottom. The first housing 9 is an external housing and 
is located above the second lower housing 10 and has an external rounded 
extension 9a and a circular downwardly turned base portion 9b which, in 
the area of the internal opening, rests on the circular base 10a of the 
lower housing 10. The two housings 9, 10 are mounted on the vertical axle 
3 and their inner edges are enclosed by two ring-shaped collars 3a, 3b of 
the vertical axle 3. 
At its lower end, the lower housing 10 has an outer circular edge 10b whose 
upper surface serves as the rolling path for a first series of roller 
bearings or similar devices 11 which support the circular cover 7 of the 
fork joint 6. In the area of the circular junction between the rounded 
extension 9a and the circular base portion 9b, the upper housing 9 defines 
a rolling path in the form of a groove 12 which houses a second series of 
roller bearings 13 resting on the upper side of the circular cover 7. 
As shown in FIGS. 1 and 4, the external housing 9 covers and surrounds, 
particularly on its lower side, the circular cover 7 and the lower housing 
10. The lower housing 10 is, in turn, enclosed by the cover 7. 
It is possible to use an upper housing 9 whose extension 9a is curved 
upwards from the outer edge of the groove 12. In such a construction, 
which is shown in FIG. 6, the housing 9 is open toward the bottom in order 
to have a circular external groove 14 adjacent to the groove 12. The 
groove 14 is open toward the top and is slightly deeper than the groove 
12. The groove 14 is bounded by a horizontal flange 15 which is slightly 
raised and can be used, for example, to fasten the bearing 8 to the 
connecting receptacle of a cart which is not shown. 
In the embodiment shown in FIG. 5, the thrust bearing 8 carries two roller 
flanges 8a, 8b. The second roller flange 8b encloses the first flange 8a 
and is fixed to the circular cover 7 for the fork joint 6. The first 
flange 8a is, in turn, fixedly mounted on the vertical axle 3 and the 
external housing 9. 
The swivelling wheel 1 also contains a locking device 16 for the fork joint 
6. The locking device includes two parts. One part is mounted on the fork 
joint while the other part is fixed relative to the vertical axle 3. The 
part of the locking device on the fork joint includes a pivot mechanism 17 
in the form of a double curved control lever which has an upper lever arm 
17a and a lower lever arm 17b, which encompass an angle of between 
90.degree. and 160.degree.. This double curved control lever 17 is housed 
in the space between the thrust bearing 8, the lateral extensions 5 of the 
fork joint 6 and the wheel 2. In the examples shown in FIGS. 1, 4 and 5, 
the lever is located vertically between the upper or external housing 9 of 
the bearing 8 and the tread 2a of the wheel 2, and laterally between the 
lateral extensions 5 of the fork joint 6. The joining piece between the 
two lever arms 17a, 17b is connected to the lateral extensions 5 of the 
fork joint 6 using a single horizontal axle 18 or two coaxial pivot axles 
18 riveted onto the extensions 5. The pivot axle 18 of the lever 17 is 
located on the side of the fork joint 6 on which the vertical distance 
between the locking device 16 and the tread 2a of the wheel 2 is the 
greatest. 
The locking device 16 also includes a friction device 19 installed on the 
lower end of the lower lever arm 17b and permanently and resiliently 
applied to the tread 2a of the wheel 2. This friction device is capable of 
causing the double control lever 17 to pivot toward one of two outermost 
positions about the pivot axle 18. In one such position, the supporting 
fork joint is immobilized in relation to the vertical axle 3; and in the 
other, the fork joint 6 is free to rotate in relation to the vertical axle 
3. 
The friction device 19 consists of a tubular piston 19a which is guided so 
that it can slide axially in a housing 20 with an appropriate section, for 
example, a circular section, constructed coaxially in the lower lever arm 
17b in such a manner as to be open at the bottom. The lower end 19b of the 
tubular piston projects from the housing 20 in the lower lever arm 17b, 
and is shaped as a spherical cap. A spring 21 is contained in the lower 
lever arm 17b and pushes the friction device 19 against the tread 2a of 
the wheel 2. This spring 21 is placed partially inside the tubular piston 
19a and partially outside the piston in the housing 20 of the lower lever 
arm 17a. The upper end of the spring engages against the pivot axle 18. 
Alternatively, the upper end of the spring can engage against an internal 
flange in the housing 20 or other internal structure of the double control 
lever 17. At its other lower end the spring engages against the friction 
device 19, and, more precisely against the internal surface of the 
spherical cap 19b. 
The locking device 16 also includes a locking means 22 consisting of a tip 
which extends from and is an integral part of the free end of the upper 
lever arm 17a. The locking means 22 extends perpendicularly to the pivot 
axle 18 of the lever 17 in the direction toward the periphery of the 
thrust bearing. 
The remaining part of the locking device 16 includes a second locking means 
23 which is located on a component of the wheel assembly which remains 
stationary during rotation of the fork joint 6 about the axle 3. The 
locking means 23 operates in conjunction with the locking means 22 to 
immobilize the supporting fork joint 6 against rotation on its vertical 
swivel axle 3. As shown in FIGS. 1 and 6, the locking means 23 is located 
in the inner, lower housing 10 of the thrust bearing 8. Alternatively, in 
the embodiments of FIGS. 4 and 5, the locking means 23 is an integral part 
of the external stationary housing 9 of the bearing 8. 
The locking means 23 consists of a locking slot open in the direction of 
the first locking means 22 and capable of receiving, without any 
significant lateral play, the first locking means, that is to say, the 
locking tip 22 which is an integral part of the upper lever arm 17a. This 
slot 23 is located along a vertical center plane of the fork joint 6. This 
plane passes through the axis of the vertical axle 3 and is perpendicular 
to the horizontal axis 4 of the wheel 2 and to the horizontal pivot axle 
18 of the double lever 17 when the cart on which the swivelling wheel 
assembly 1 is mounted moves straight ahead. As can be seen in the drawing, 
the pivot axle 18 of the double lever 17 is located near the periphery of 
the circular cover 7 of the fork joint 6 and also near the locking slot 
23. 
Finally, the locking devices 16 include two stops 24, 25 which serve to 
limit the pivot angle of the double control lever 17 between its two 
outermost positions. These two stops form with the pivot axle 18 a 
relatively small angle on the order of 3.degree. to 15.degree., and are 
located in proximity to a radial plane of the wheel 2. The latter plane 
passes through the lever's pivot axle 18 and the wheel's axle 4 of 
rotation. In this manner, the lower lever arm 17b shall not deviate overly 
from a position in which its axis extends vertically in relation to the 
tread 2a, i.e., perpendicular to the surface of the tread where engagement 
with the friction device 19 occurs. 
The first stop 24 for the control lever 17 is placed in the space located 
above the wheel 2 and between the lateral extensions 5 of the fork joint 6 
and works in conjunction with a first portion, for example, the lower 
lever arm 17b of the control lever 17, while the second stop consists of 
the downwardly facing bottom surface of the locking slot 23 and the 
downwardly facing bottom edge surface of the housing 9 or 10 which 
contains the slot 23. The stop 25 works in conjunction with the locking 
tip 22 to limit the pivoting of the lever 17 in the counter-clockwise 
direction as viewed in the drawings. 
The circular cover 7 of the fork joint 6 contains a tracking groove 26 
along the center vertical plane of the fork joint 6. This groove lies in a 
plane perpendicular to the axle 4 of the wheel 2 and the pivot axle 18 of 
the double lever 17; and, as with the locking device 16, is located on the 
side of the fork joint 6 on which the distance between the cover 7 and the 
tread 2a is the greatest. The tracking groove 26 is open at the bottom and 
25 aligned with the upper lever arm 17a and locking tip 22 so as to guide, 
with no significant lateral play, these members in their pivoting path 
between the control lever's 17 outermost positions. Due to this 
construction, the locking of the fork joint 6 is transmitted to the swivel 
axle 3 along the shortest distance between the swivelling fork joint 6 and 
housing 9 and 10 which is fixedly mounted on the vertical swivel axle 3. 
The locking slot 23 may be placed radially outwardly of the tracking groove 
26 formed in the cover 7 as in the construction of FIGS. 4 and 5 where the 
slot 23 is located on the external housing 9. The locking slot 23 may also 
be placed radially inwardly of the groove 26 as in the construction shown 
in FIGS. 1 and 6 where the slot is placed on the internal housing 10.