Low profile disk brake caliper

A low profile disk brake caliper in which a disk brake pad is mounted on a flexible diaphragm contained within a piston cavity. Pressurization of the piston cavity by a master cylinder expands the diaphragm and urges the brake pad sidewardly from the housing to engage an adjacent rotor. In the preferred embodiment, the diaphragm is received within a cap seal slidably mounted within the cavity, and the brake pad is mounted removably within a pad carrier attached to the cap. A backing seal is positioned adjacent to the underside of the top wall of the diaphragm and is clamped against the cap by assembly bolts, so that the top wall of the diaphragm is compressed between the cap and backing seal, thereby preventing the top wall from bulging outwardly when the cavity is pressurized. The housing is mounted on the hub of a bicycle front wheel and includes a set screw positioned for camming engagement against the front fork to prevent rotation of the brake caliper relative to the fork. Alternately, the housing includes a torque arm attached to the front fork.

BACKGROUND OF THE INVENTION 
The present invention relates to disk brakes and, more particularly, to 
disk brake calipers for lightweight vehicles such as bicycles. 
Due to the superior characteristics of disk brakes with respect to 
simplicity of design, ease of repair, resistance to fading and long life, 
it is desirable to mount disk brakes on smaller vehicles such as bicycles. 
However, a disadvantage with conventional disk brake designs is that the 
disk brake pads are mounted on solid pistons which are slidably retained 
within cylindrical cavities formed in the calipers which include return 
springs that urge the pistons sidewardly to disengage the attached pads 
with the associated rotor when the cylinders are depressurized. Such 
structure adds to the overall weight and expense of the bicycle and 
presents a relatively high profile for a device which is mounted at or on 
the hub of a bicycle wheel. 
Attempts have been made to design a low profile disk brake, such as that 
disclosed in Campagnolo U.S. Pat. No. 3,971,457. That patent discloses a 
wheel hub disk brake in which the wheel hub of a bicycle or motorcycle 
includes an inner, rotating segment attached to the wheel and positioned 
between two outer, non-rotating segments. The non-rotating segments are 
urged inwardly by ring pistons to bring ring disks into engagement with 
corresponding metal disks mounted on the rotating, inner hub to prevent 
relative rotation of the inner hub with respect to the outer hub segments 
in order to brake the wheel. 
A disadvantage with such structure is that the hub design and ring pistons 
are relatively complex, requiring high tolerances and expensive castings. 
Further, while the structure may provide a strong braking force, the 
amount of metal required is relatively substantial, making such a hub 
unsuitable for lightweight bicycles. Accordingly, there is a need for a 
low profile disk brake caliper which is suitable for mounting on a bicycle 
wheel. 
SUMMARY OF THE INVENTION 
The present invention is a low profile disk brake caliper suitable for 
mounting on the wheel of a bicycle. The caliper includes a housing having 
a piston cavity, a flexible diaphragm mounted within the cavity, a brake 
pad mounted on the diaphragm and a master cylinder for selectively 
pressurizing the cavity. When the cavity is pressurized, the diaphragm 
expands within the cavity and urges the brake pad against an adjacent 
rotor to provide the braking force. Accordingly, the disk brake caliper of 
the present invention eliminates the need for solid pistons and return 
springs. The flexible diaphragm moves within the cavity to displace the 
brake pad, and the inherent resilience of the diaphragm, which preferably 
is made of rubber, provides the force necessary to return the diaphragm to 
its original shape and disengage the brake pad when the cavity is 
depressurized. 
A seal cap is provided which receives the diaphragm and provides an 
interface between the diaphragm and both the sidewalls of the cavity and 
the brake pad. Consequently, when the cavity is pressurized and the 
diaphragm expands, the seal cap is displaced within the cavity outwardly 
with the brake pad, and it returns within the cavity when the brake 
caliper is depressurized. A backing plate is provided which is attached to 
the underside of the top wall of the diaphragm, so that the diaphragm top 
wall is clamped between the backing plate and the seal cap. This clamping 
engagement prevents the top wall from becoming convex when the diaphragm 
is pressurized. The seal cap, backing plate and brake pad carrier are all 
retained by assembly bolts, which pass through these components, as well 
as the diaphragm top wall. 
The housing of the brake caliper of the present invention includes a base 
having a recess shaped to receive a peripheral flange formed on the 
diaphragm, and a cavity block, bolted to the base and having the cavity 
which receives the diaphragm. When the cavity block is bolted to the base, 
the diaphragm flange is clamped between these components and held within 
the base recess. In a preferred embodiment, the peripheral flange includes 
a rib which is received within corresponding slots formed in the cavity 
block. 
The compactness of the unit is enhanced by providing a master cylinder 
which is integral with the housing. The housing includes internal channels 
which interconnect the master cylinder and diaphragm cavity, thereby 
eliminating the need for hydraulic hoses. The master cylinder is actuated 
by a push pull cable which is hand operated. 
Also in the preferred embodiment, the caliper housing includes a pair of 
opposing brake pads, each mounted on a diaphragm connected to the master 
cylinder. Thus, the rotor is clamped between two pads to provide braking 
action. 
The housing includes a mounting bracket having a set screw and a boss, 
which engage the drop out and drop out slot, respectively, to prevent 
rotation of the caliper during braking. Alternately, the bracket includes 
a torque arm attached to the fork. 
Accordingly, it is an object of the present invention to provide a disk 
brake caliper which has a relatively low profile and is suitable for 
mounting on a bicycle wheel hub; a disk brake caliper in which a flexible 
diaphragm replaces the solid piston and return spring of conventional disk 
brake calipers; a disk brake caliper in which the master cylinder is 
integral with the caliper housing and employs internal passages to convey 
hydraulic fluid from the master cylinder to the diaphragms; and a disk 
brake caliper which is relatively inexpensive to fabricate, is relatively 
easy to attach to a bicycle wheel or remove from a bicycle wheel for 
maintenance or repair and has a relatively simple construction. 
Other objects and advantages will be apparent from the following 
description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION 
As shown in FIGS. 1 and 2, the low profile disk brake caliper, generally 
designated 10, is mounted on the hub 12 of a bicycle front wheel 14 and 
engages a drop out 16, having slot 17, of the front fork 18. The caliper 
10 includes a housing, generally designated 20 which includes left and 
right base plates 22, 24, each attached to a cavity plate 26, 28 by screws 
29. The cavity plates 26, 28 are spaced apart to define a gap 30 shaped to 
receive a rotor 32 which is mounted on and rotates with the axle 34 of the 
wheel 14. 
The housing 20 is attached by bolts 36 to a mounting bracket 38 that 
receives the hub 12 therethrough and includes a boss 40 having a bolt 42 
therethrough which engages a flat 44 formed on the drop out 16. A boss 45 
on bracket 38 fits within slot 17. The engagement of the boss 45 and slot 
17, as well as bolt 42 and flat 44, prevents the rotation of the caliper 
10 relative to the front fork 18 when the caliper engages the rotor 32. 
As shown in FIGS. 2 and 3, cavity plate 28 includes a piston cavity 44 
which communicates with a master cylinder 46 by a passage 48 which is 
internal to the base plate 24. Master cylinder 46 includes a piston 50 
which is actuated by a threaded rod 52 pivotally attached to a lever 54 
that, in turn, is mounted on a pivot 56 attached to the cavity plate 28. A 
push-pull cable 58 includes a control wire 60 which is attached to the 
lever 54. The sheath 62 is attached to a bracket 64 which projects 
upwardly from the master cylinder 46. 
Accordingly, actuation of the push-pull cable 58 causes the piston 50 to be 
displaced within the master cylinder 46, thereby forcing hydraulic fluid 
through the passageway 48 to the piston cavity 44. The master cylinder 46 
is charged through nipple 65, and cylinder 44 is bled through nipple 66. 
It is to be understood that the construction of the corresponding piston 
cavity in left cavity plate 26 and left base plate 22 is identical, but is 
of reverse hand. 
As shown in FIGS. 4 and 5, the caliper 10 includes a disk brake pad 67 and 
a diaphragm assembly, generally designated 68. The diaphragm assembly 
includes a flexible diaphragm 70, preferably made of rubber, which is 
mounted within the piston cavity 44. The diaphragm 70 preferably is 
kidney-shaped, as is the cavity 44 within which it is mounted (see also 
FIG. 3). The diaphragm includes a top wall 72, a sidewall 74 and a 
peripheral bottom flange 76 extending about the entire periphery of the 
diaphragm and which includes a rib 78 about its outer periphery. 
The cavity plate 28 includes a recess 80 having a peripheral slot 82. The 
peripheral slot 82 receives the rib 78 of the diaphragm 70 and the recess 
80 receives the peripheral flange 76. When the cavity plate 28 is bolted 
to the corresponding base plate 24, the flange 76 is clamped between the 
base plate and cavity plate, and is prevented from creeping out of that 
engagement by the engagement of the rib 78 with slot 82. Consequently, the 
diaphragm 70 creates a chamber 84 within the piston cavity which receives 
hydraulic fluid through passage 48 from the master cylinder 26 (see FIG. 
2). 
The diaphragm 70 is received within a cap seal 84 having a top wall 86 and 
a sidewall 88 which corresponds in shape to the kidney shape of the cavity 
44. The top wall contains two bevelled holes 90, 92 which are in registry 
with holes 94, 96 formed in the diaphragm 70. A backing plate 98 is fitted 
underneath the top wall 72 of the diaphragm 70 and includes holes 100, 102 
which are in registry with holes 94, 96, respectively, of the diaphragm. 
The backing plate 98 also includes a rib 104 which projects upwardly into 
the diaphragm top wall 72. 
The diaphragm 70 is retained within the seal cap 84 by the clamping 
engagement provided by the seal plate 98. This clamping engagement is 
secured by assembly screws 106, 108 which are retained by nuts 110, 112. 
Thread seals 114 are provided to prevent leakage of hydraulic fluid from 
the chamber 83 through the diaphragm holes 94, 96. 
The brake pad 67 is retained on a pad carrier plate 116 which has chamfered 
holes 118, 120 shaped to receive screws 106, 108. As best shown in FIG. 4, 
the pad carrier 106 has side slots 122, 124 which receive the bevelled 
lateral edges 126, 128 of the brake pad 66 in a locking engagement. The 
side slots 122, 124 are tapered in spacing, corresponding to the tapered 
width of the brake pad 67, so that the pad is held in locking engagement 
with the slots. The pad 67 is oriented on the caliper 10 so that it is 
driven into the narrow end of the carrier plate 116 when the pad is urged 
into braking engagement with a rotating rotor. 
The operation of the caliper 10 is as follows. When the wheel 14 is 
rotating in a forward direction, the rotor 32 rotates in the direction of 
arrows A in FIGS. 2 and 3. When it is desired to brake the wheel, the 
push-pull cable 58 is actuated to displace the lever 54 inwardly toward 
the master cylinder 46, thereby displacing piston 50 to drive hydraulic 
fluid through passageway 48 into the piston cavity 44 of the cavity plates 
26, 28. This pressurizes the chambers 82 formed by the flexible diaphragms 
70, elastically elongating the sidewalls 74 of the diaphragms, thereby 
urging the brake pads 66 sidewardly away from the housings 20 and into the 
caliper 32. When it is desired to release the caliper 32 from the clamping 
engagement from pads 66, the cable 58 is actuated to displace the lever 54 
outwardly, thereby drawing hydraulic fluid back into the master cylinder 
46. This, plus the resiliency of the diaphragm 74 causes the brake pad 66 
to be withdrawn sidewardly toward the housing 20. 
It should be noted that the seal cap 88 reduces the frictional resistance 
of movement of the diaphragm 70 with respect to the cavity wall 44. The 
cap seal 84 preferably is made of stainless steel or other metal which 
will slide against the metal of the cavity wall more easily of the rubber 
of the diaphragm 70. The rib 104 urges the top wall 72 of the diaphragm 70 
against the top wall 86 of the cap seal 84 and thereby provides a seal 
which prevents leakage of hydraulic fluid through the holes 94, 96. 
FIG. 6 shows an alternate embodiment of the caliper 10' in which the 
bracket 38' torque arm 130 which is attached to a boss 132 by nut and bolt 
combination 134. Boss 132 is permanently attached to front fork 18'. 
Consequently, the engagement of torque arm 130 and boss 132 prevents 
rotation of caliper 10' about hub 12 during braking, and provides greater 
leverage than the attachment mechanism shown in FIG. 1. 
While the form of apparatus herein described constitutes a preferred 
embodiment of the invention, it is to be understood that the invention is 
not limited to this precise form of apparatus, and that changes may be 
made therein without departing from the scope of the invention.