Overrunning drum having an amplifying device

A wheel brake, particularly an overrunning wheel brake comprising a brake drum, first and second brake shoes movable in forward and rearward directions, amplifying formations arranged to cooperate with the first brake shoe and to amplify a force with which the first brake shoe is pressed against the brake drum, a displacing element for displacing the first brake shoe in the forward direction and thereby pressing the same against the brake drum with amplified pressure force, and an urging projection provided on the first brake shoe and arranged so that when the first brake shoe is displaced in the rearward direction, the projection displaces the second brake shoe which acts upon the amplifying formations and thereby the first brake shoe is again pressed against the brake drum with the amplified pressure force.

BACKGROUND OF THE INVENTION 
The present invention relates to a wheel brake, and particularly to an 
overrunning wheel brake. 
Overrunning wheel brakes are known, which have two brake shoes, a support 
provided with at least one guiding cam, guiding roller and the like and 
supporting one of the brake shoes which is operative to be pressed against 
a brake drum during movement in forward direction, and a tightening member 
acting in the operative direction of the first brake shoe and pressing the 
support member toward the brake drum. The second brake shoe abuts against 
the support member. The first brake shoe is provided, in the region of the 
guiding cam, guiding roller and the like of the support, with lifting 
tracks which, together with the outer curved wall of the brake shoe, form 
wedging faces converging in the operative direction of the first brake 
shoe. The second brake shoe abuts during the forward movement against a 
stationary abutment member. 
The provision in the above-mentioned wheel brake of the lifting tracks on 
the first brake shoe and the abutment of these lifting tracks against the 
guiding cams, guiding rollers or the like of the support member provide 
for enormous braking force in forward direction, inasmuch as the first 
brake shoe is substantially wedged against the brake drum via the 
above-mentioned lifting tracks. However, this action does not take place 
during reverse movement. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a wheel 
brake which avoids the disadvantages of the prior art. 
More particularly, it is an object of the present invention to provide a 
wheel brake in which a brake shoe is firmly pressed against a brake drum 
not only during braking in forward direction, but also during braking in 
reverse direction. 
In keeping with these objects and with others which will become apparent 
hereinafter, one feature of the present invention resides, briefly stated, 
in a wheel brake having a brake drum, first and second brake shoes, 
amplifying means arranged to amplify a force with which the first brake 
shoe is pressed against the brake drum, means for displacing the first 
brake shoe so that when the first brake shoe displaces in a forward 
direction it cooperates with the amplifying means and is pressed against 
the brake drum with the amplified pressure force, wherein urging means is 
provided on the first brake shoe and arranged so that when the first brake 
shoe is displaced in a rearward direction, the urging means displaces the 
second brake shoe, the second brake shoe acts upon the amplifying means, 
and the amplifying means cooperates with the first brake shoe whereby the 
latter is again pressed against the brake drum with the amplified pressure 
force. 
When the wheel brake is constructed in accordance with the present 
invention, the second brake shoe during braking in reverse direction is 
displaced in circumferential direction by the first brake shoe. A support 
which carries the first brake shoe is respectively displaced in 
circumferential direction. The amplifying means is formed by guiding cams, 
guiding rolls and the like provided on the support member, on the one 
hand, and lifting tracks provided on the first brake shoe, on the other 
hand. When the support displaces in the circumferential direction, the 
guiding elements of the support act upon the lifting tracks of the first 
brake shoe whereby the latter is pressed against the braking drum. 
Thereby, during braking in reverse direction the above-mentioned 
enormously high braking force also takes place as a result of the 
provision of the lifting tracks and the abutment of the latter against the 
guiding cams, rollers and the like of the support member. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DESCRIPTION OF A PREFERRED EMBODIMENT 
An overrunning wheel brake in accordance with the invention has a first 
brake shoe 1 which is operative during forward movement or, in other 
words, is arranged to move toward a brake drum 9 during forward movement. 
The first brake shoe 1 is mounted on a support member 3. The support 
member 3 is provided with guiding elements such as guiding rollers 2 (FIG. 
1). The guiding elements may also be formed as guiding cams 2a (FIG. 1a) 
and the like. 
A second brake shoe abuts against the support member 3 via a locking piece 
4. The other end of the second brake shoe 5 abuts against a stationary 
abutment member 6 during the forward movement. A double headed arrow 
provided with the letters V and R designates the forward movement and the 
reverse movement. 
The first braking shoe 1 has regions in which it rests on the guiding 
rollers 2 of the support member 3. In these regions the first brake shoe 1 
is provided with lifting tracks 7. The lifting tracks 7 together with the 
outer curve of the first brake shoe 1 form a wedge surface which converges 
in the operative or running direction of the first brake shoe. A 
tightening member 8 is provided, which forces the support member 3 toward 
the brake drum 9. 
The wheel brake shown in the drawing is an overrunning wheel brake. A 
characteristic feature of this overrunning wheel brake resides in that the 
tightening member 8 during running of a trailer toward a tractor is 
actuated by an overrunning mechanism. 
When the tightening member 8 during forward movement from the normal 
position shown in FIG. 1 is actuated by the overrunning mechanism, the 
support member 3 is first insignificantly displaced in forward direction 
and simultaneously forced toward the braking drum 9. Thereby, the first 
brake shoe 1 is pressed against the brake drum 9, and the first brake shoe 
1 because of the thus caused friction contact, is also displaced in 
forward direction. During this circumferential displacement, the first 
brake shoe 1 runs by its lifting tracks 7 firmly against the brake drum 9 
and thereby very high braking force takes place. The second brake shoe 5 
is also firmly pressed against the brake drum 9 via the support 3, so as 
to provide for uniform braking via both braking shoes 1 and 5. 
When a trailer provided with the inventive overrunning wheel brake moves in 
reverse direction by the tractor, the tightening member 8 is again 
actuated via the overrunning mechanism and assumes a position shown in 
FIG. 2. During the reverse movement the first brake shoe 1 is displaced in 
reverse direction because of the friction contact between its friction 
coating and the brake drum 9. The first brake shoe 1 runs along its 
lifting tracks 7 "freely". In other words, during reverse movement the 
first brake 2 does not provide for braking action. 
In overrunning wheel brakes with so-called "reverse automatic means", it is 
conventional to adjust the tightening member 8 further via a hand brake 
mechanism, as in the case of the overrunning mechanism. This construction 
can also be utilized in the present overrunning wheel brake. The greater 
adjustment of the tightening element which can be attained by a hand 
braking mechanism allows to force the support member 3 against the brake 
drum 9 to considerably higher extent than in the case of the overrunning 
mechanism. 
The above-mentioned stronger forcing of the support 3 against the brake 
drum 9 results in the fact that the first braking shoe 1 is taken along 
circumferentially in direction of the reverse movement, when the vehicle 
moves in reverse direction. 
As can be seen from the drawings, the first braking shoe 1 is provided with 
a projection 10 which during displacement of the first brake shoe 1 in 
reverse direction, acts upon the second brake shoe 5. More particularly, 
it acts upon an end portion of the second brake shoe 5, the end portion 
facing toward the tightening member 8. Thereby, the second braking member 
5 is urged in circumferential direction, that is the first braking member 
1 displaces the second brake member 5 in reverse direction. Thereby, the 
support member 3 is also displaced in reverse direction, and the guiding 
rollers 2 run along the lifting tracks 7 of the first brake shoe 1 in 
lifting direction. As a result of this the first brake shoe 1 is pressed 
stronger against the brake drum 9. 
In order to prevent excessive loading of the tightening member 8 by the 
generated braking force, the tightening member 8 is actuated via an 
actuating mechanism which allows swinging of the tightening member 8 
against the action of the tightening force in the case when the generated 
braking force is greater than the tightening force, as is the case during 
braking in reverse direction. As can be seen further from FIG. 3, the 
tightening member 8 during braking in reverse direction turns back in 
direction of the abutment 6 and finally comes to abutment against the 
latter so that the generated braking force is absorbed by the abutment 6. 
An actuating mechanism which is torsionally elastic and dependent on load, 
and arranged to displace the tightening member 8 is shown in FIG. 4. As 
can be seen from this Figure, the tightening member 8 is mounted on a 
shaft 17 which is supported by a bearing 16 mounted on a wheel axle 15, on 
the one hand, and by a bearing 16a of a brake cover, on the other hand. A 
lever 19 is pivotally supported by a further bearing 18 which is also 
mounted on the wheel axle 15. The lever 19 can be actuated via an 
overrunning brake-rod linkage, via a hand brake lever or via other means. 
No firm connection is provided between the shaft 17 and a pivot pin 19a of 
the lever 19. A torsion spring is arranged between the above-mentioned 
members and is so prestressed that the tightening member 8 is always 
loaded in a tightening direction, whereby the corresponding movement is 
transmitted via the torsion spring 20 to the shaft 17 and the tightening 
member 8. When the force acting in the case of the tightened lever 19 onto 
the tightening member 8 is greater than the force of the torsion spring 
20, the tightening member 8 can turn back against the action of the 
torsion spring 20. 
Even though the guiding elements of the support member 3 are shown as 
guiding rollers, other guiding elements such as guiding cams and the like 
may be provided. Furthermore, the inventive concept can be realized also 
in a wheel brake without overrunning mechanism. 
In a wheel brake without the overrunning mechanism, the tightening member 8 
is actuated, for example, via a pressure-medium-operated 
cylinder-and-piston unit, so that during movements in both directions the 
braking process can be carried out exclusively by actuation of the 
tightening member 8. In this case it is advantageous to form the 
projection 10 of such a length that the projection 10 in unbraked 
condition is located almost directly on the facing end of the second brake 
shoe 5. Thereby, during reverse movement and actuation of the tightening 
member 8, the braking action takes place without any delay. 
The locking member 4 via which the support member 3 and the second brake 
shoe 5 abut against one another, is preferably formed as an adjusting 
device which allows spreading apart of the support member 3 and the second 
brake shoe 5 when the braking coating is worn to high extent. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
wheel brake, it is not intended to be limited to the details shown, since 
various modifications and structural changes may be made without departing 
in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.