Shoe brake

A shoe or friction brake having the brake levers thereof connected both at the pivotably mounted end and also at the end driven by a brake spring mutually independently of one another at the brake housing. The pivotably mounted end is connected with the brake housing by elements which have a resilient or spring action perpendicular to the direction of action of the brake spring. These resilient elements are in the form of plate springs and/or a leaf or blade spring. The bearing means for each brake lever is arranged between the plate springs. Each brake lever has operatively associated therewith a choke or reactance coil, and the choke yoke or the like is arranged at the bearing means and the choke core at the brake housing. With the brake levers located in their braking position the latter, when subjected to load, are movable perpendicular to the direction of action of the brake springs, so that the air gaps of the choke coils can be reduced or increased in size, as the case may be. The resultant voltage difference is used to control a drive motor of an elevator such that it produces a torque which relieves the shoe or friction brake.

BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved construction of a shoe 
or friction brake which is of the type comprising two separate brake 
systems. Each brake system consists of a brake lever, a brake jaw or shoe, 
a brake spring and a brake venting device. The brake levers are connected 
independently of one another with a stationary brake housing both at their 
pivotably mounted end and also at the end driven by the brake spring. 
Swiss Patent No. 374,413 discloses a shoe or friction brake which can be 
particularly used for elevators. With that prior art brake system the shoe 
brake is vented by load measurement and producing a counter torque or 
moment of rotation of the drive motor, so that the elevator, after brake 
venting, can start up without any jerky movements. During the load 
measurement the shoe or friction brake performs a pivotal movement about 
the center of the brake disk. For this purpose the brake levers are 
mounted at a beam carrying at both ends rollers guided in arcuate cams. At 
the centre of the beam there is arranged an actuation arm acting upon the 
load measuring device. The free ends of the brake levers are 
interconnected with one another by means of brake springs and a traction 
rod. The drawback of this shoe brake resides particularly in the fact 
that, upon rupture of a brake spring both of the brake shoes or jaws 
become ineffectual. Other drawbacks of this state-of-the-art system reside 
in the relatively complicated guiding of the brake lever in the arcuate 
cams and the therewith associated disadvantage that the load measuring 
device must be capable of absorbing the entire load which is to be 
measured, and hence, must be correspondingly constructed. 
On the other hand, Swiss Patent No. 530,338 discloses a safety shoe brake 
for elevators, wherein the two brake levers are connected independently of 
one another with a stationary brake housing both at the pivotably mounted 
end and also at the end which is driven by the brake spring. At the driven 
end this connection is obtained by providing for each brake lever a rod 
secured at one end at the stationary brake housing, and possessing at the 
other end a support for the brake spring which acts upon the brake lever. 
Since with this system design there are provided two independently 
operating brake levers, with this brake system, upon failure of one of the 
brake shoes or jaws, for instance due to rupture of a brake spring, the 
second brake shoe or jaw nonetheless remains operative. This safety shoe 
brake is not suitable for performing the load measurements needed for the 
jerk-free start-up at elevators. This is so because due to the stationary 
arrangement of the brake lever-pivot axis and the rod carrying the brake 
springs, the brake cannot perform any pivotal movement about the center of 
the brake disk. 
SUMMARY OF THE INVENTION 
Therefore, with the foregoing in mind it is a primary object of the present 
invention to provide a new and improved construction of shoe or friction 
brake which is not afflicted with the aforementioned limitations and 
drawbacks of the prior art proposals. 
Another and more specific object of the present invention aims at providing 
a new and improved construction of shoe brake having two mutually 
independently operating brake levers and which is suitable for carrying 
out a load measurement. 
Yet a further significant object of the present invention aims at a novel 
construction of friction brake which is relatively simple in design, 
economical to manufacture, extremely reliable in operation and can be used 
in conjunction with a load measurement as is needed for the start-up of 
elevators without any jerky motion. 
Now in order to implement these and still further objects of the invention, 
which will become more readily apparent as the description proceeds the 
shoe or friction brake of the present development is manifested by the 
features that the brake levers are connected at least at one end by means 
of elements, with the stationary brake housing, these elements being 
resilient or springy in a direction perpendicular to the line or direction 
of action of the brake springs. A load measuring device is provided for 
converting the stroke or displacement movements of the resilient elements 
into electrical signals. 
According to a preferred embodiment of the invention the load measuring 
device consists of two choke or reactance coils. Each brake lever has 
operatively associated therewith one of the choke coils and the choke yoke 
is attached to the bearing means of the brake lever and the choke core is 
adjustably arranged at the brake housing. 
The advantages which can be realized when practising the present invention 
particularly reside in the fact that upon rupture of a brake spring the 
second brake shoe or jaw still remains operative, so that with appropriate 
contact force the load is retained. A further benefit of the ivention is 
in the resilient mounting arrangement of the brake lever which takes up 
the load, so that there is relieved the actual load measuring device, 
which, in turn, can be designed to be small and favorable in terms of cost 
factors. Moreover, it is advantageous if a load measuring choke is 
operatively associated with each brake lever. In this way there is 
realized the possibility, by evaluating the electrical signals produced 
during the load measurement, to determine whether or not one of the brake 
shoes has become ineffectual.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Describing now the drawings, it is to be understood that since the 
invention is concerned with the construction of a novel shoe or friction 
brake there has been omitted from the illustration details of the elevator 
system and drive with which the shoe brake can be advantageously employed, 
in order to simplify the illustration. In FIG. 1, reference character 1 
designates a brake disk which is rigidly connected with the conventional 
drive of an elevator. The brake apparatus contains two brake levers 2 at 
which there are movably arranged the brake shoes or jaws 3. A suitable 
rubber buffer or cushion 4 supports the related brake shoe or jaw 3 when 
the shoe brake is vented, so that a uniform or equal size air gap is 
present between each brake shoe 3 and the brake disk 1. The brake levers 2 
are each pivotably mounted at a related bearing or support means 5. Each 
bearing means 5 is connected by means of resilient elements, here shown in 
the form of plate springs 6 and a bolt 7 with a brake housing 8, as best 
recognized by referring to FIGS. 1 and 3. 
The bearing means 5 possesses a forked or bifurcated end 5.1, by means of 
which it is connected, as shown in FIGS. 1 and 3, with a leaf or blade 
spring 10 attached at the brake housing 8 through the intermediary of a 
pivot bolt 9. Prior to tightening the pivot bolt 9 the brake lever 2, in 
order to adjust the related brake shoe or jaw 3 at the brake disk 1, can 
be pivoted through a path determined by the play between the bolt 7 and 
bearing means 5. 
The end 2.2 of the brake lever 2, which is situated opposite the pivotably 
mounted end 2.1, is connected by a brake spring 11, producing the 
requisite braking force or pressure, and a tension or traction rod 12 with 
the brake housing 8. The brake spring 11 bears at one end at the brake 
lever 2 and at the other end at a pressure nut 13 or equivalent structure 
which is threadably connected with the traction rod 12. By means of a nut 
member 14 it is possible to secure the traction rod 12 which has been 
threaded into the brake housing 8. The pressure or compression nut 13 is 
provided at the side thereof facing away from the traction rod 12 with a 
semi-spherical end surface 13.1. Bearing against this semi-spherical end 
surface 13.1 is a piston 15 of a fluid-actuated, here a hydraulic cylinder 
16 which is fixedly connected with the brake lever 2 and serves as a brake 
venting device. Upon infeed of a pressurized fluid medium through any 
suitable and therefore not particularly illustrated pressure hose the vent 
stroke of the shoe brake is limited by the shoulder 17.1 of a threaded 
sleeve 17 which is threadably connected with the traction rod 12, as best 
seen by referring to FIGS. 1 and 4. 
Reverting to FIGS. 1, 2 and 4 there will be recognized a cover member 18 
which covers an opening 19 in the brake lever 2, this opening 19 rendering 
possible adjustment of the pressure nut member 13 when the brake lining 
has worn. At the bearing means 5 there is attached by means of a support 
20 the yoke 22 or equivalent structure of a choke coil 21 serving as a 
load measuring device. The core 23 of the choke coil 21 is adjustably 
arranged in the brake housing 8 by means of the screws or threaded bolts 
24 or equivalent structure (FIGS. 1 and 3). A microswitch 25 secured to 
the brake housing 8, upon venting of the shoe brake, is activated, as best 
seen by referring to FIG. 2, by an actuation arm 26 arranged at the brake 
lever 2. Reference character 27 designates pins provided at the brake 
levers 2, serving for receiving a manual brake or venting lever 28 or the 
like (FIGS. 1 and 4). 
Having now had the benefit of the discussion of the shoe brake employing 
two separate brake systems as described above, its mode of operation will 
now be considered and is as follows: if no torque or rotational moment is 
applied to the brake disk 1, then both of the air gaps between the yoke 22 
and core 23 of the related choke coil 21 are of the same size. As soon as 
a torque is present with the brake levers 2 located in their braking 
position, then the brake levers 2 move opposite to one another 
approximately in their lengthwise direction. Hence, one of the air gaps is 
increased in size and the other air gap is reduced in size. By means of 
the thus generated potential or voltage difference of both choke coils 21 
there is controlled in a manner known to the art, for instance as 
disclosed in the aforementioned Swiss Patent No. 374,413, the elevator 
drive motor in such a way that it produces a counter torque which relieves 
the beam brake and electrically retains at standstill the elevator, so 
that upon arrival of a travel command the elevator can start-up free of 
any jerky movement. 
Upon venting the jaw brake a conventional hydraulic unit produces a 
constant oil pressure, under the action of which the piston 15 is pressed 
against the pressure nut member 13. Now the hydraulic cylinder 16 together 
with the related brake lever 2 of the brake jaw 3 are lifted, against the 
force of the brake spring 11, from the brake disk 1. At the moment of 
lift-off of the brake shoe 3 the microswitch 25 is actuated, so that the 
load measuring operation is completed and the elevator system is freed for 
travel of the elevator. 
As the resilient element there also can be used the traction rods 12 formed 
as circular rod springs, wherein the brake lever 2 is guided at its driven 
end free of play to be displaceable upon the traction rod 12 and at its 
pivotably mounted end is arranged to be displaceable perpendicular to the 
line of action of the brake spring 11 at the brake housing 8. It is also 
possible to connect the brake lever 2 at both ends by means of resilient 
elements, for instance circular rod springs, with the brake housing 8. 
While there are shown and described present preferred embodiments of the 
invention, it is to be distinctly understood that the invention is not 
limited thereto, but may be otherwise variously embodied and practised 
within the scope of the following claims. ACCORDINGLY,