Disc brake apparatus suitable for bicycles

The rotor of a disc brake apparatus for bicycles comprises a spider that flatwise overlies the outer face of one spoke flange on a wheel hub and is secured by spokes that have their hook portions extending through it and that spoke flange. A flat annular disc has radially inwardly projecting tabs that are secured to the spider and hold the disc in axially spaced relation to the spokes. A U-shaped caliper body straddles an edge portion of the disc. On a shorter leg the body has a fixed brake pad; on its longer leg it carries a movable brake pad that has a compound motion for self-energization. The body is movable in directions parallel to the wheel axis and is carried, in part, by a cup-shaped adapter coaxial to the wheel shaft and confined between a bearing cone for the wheel and an adjacent frame portion. Portions of the body straddle an elongated frame member to confine the body against rotation around the adapter.

This invention relates to disc brake devices and is more particularly 
concerned with a disc-type brake assembly that is suitable for bicycles 
and similar vehicles. 
Heretofore the customary braking system for a touring type bicycle equipped 
with a change-speed gear shift has consisted of a pair of hand operated 
caliper assemblies, one for each wheel, each comprising a pair of friction 
pads that clampingly engaged the rim of its wheel. Each caliper assembly 
was individually controllable from a hand lever on the handlebars, 
connected with the caliper assembly by means of a cable. 
The rate at which a bicycle would be decelerated by means of a caliper 
brake assembly was dependent upon the clamping force applied to the 
friction pads, and this, in turn, depended upon the force that the rider 
applied to the actuating lever. Because that lever was hand actuated, the 
reasonably expectable maximum force that could be applied to it was on the 
order of 35 pounds. Some persons, of course, have hands strong enough to 
exert substantially more than a 35 pound clamping force, but many cannot 
comfortably achieve anywhere near that value. 
Other things being equal, the clamping force that has to be exerted upon 
the friction pads of a caliper brake system in order to bring a bicycle to 
a stop within a given distance from a given speed depends upon the weight 
of the rider, who may be a child weighing 70 to 80 pounds, or an adult 
weighing well over 200 pounds. Obviously there is no necessary 
relationship between the weight of a bicyclist and the maximum clamping 
force that he can exert upon a brake lever. 
The clamping force necessary to achieve a given deceleration with such 
prior brake systems also varied with the condition of the wheel rim and 
could be very much higher when the rim was wet than when dry. 
The maximum clamping force that could be exerted by the rider was an 
important consideration with prior caliper brake systems because of the 
need for having a rather low mechanical advantage in the actuating 
mechanism of the system. The rim of a bicycle wheel is seldom absolutely 
true. When the wheel is rotating with its axis fixed, the rim will usually 
be seen to have at least a slight amount of wobble or run-out, especially 
if it has had a certain amount of use. In the released condition of a 
caliper brake, both friction pads had to be spaced from the wheel rim to 
ensure that they did not drag against it. To accommodate a reasonable 
amount of run-out, the friction pads had to swing through a relatively 
large distance between their released and braking positions. This meant 
that there had to be a relatively large travel of the brake pads for a 
given amount of movement of the actuating lever, so that there was an 
unfavorable relationship between the force that the rider applied to the 
brake actuating lever and the resultant clamping force of the friction 
pads against the wheel rim. 
By reason of these factors, many bicyclists did not have sufficiently 
strong hands to achieve optimum braking action with a caliper brake 
system, especially in wet weather. 
By contrast, in a disc brake system having brake pads that engage a 
disc-like rotor, the rotor can ordinarily have sufficient rigidity to 
maintain flatness to within very small tolerance limits, and consequently 
the brake pads need to have only very small travel between their braking 
and released positions. This means that the actuating mechanism can be 
arranged for substantially greater mechanical advantage than would be 
feasible in a caliper brake system. 
A further advantage of a disc brake system is that it can be made 
self-energizing to some extent. When one of the brake pads engages the 
rotor, friction between the rotor and the brake pad urges the brake pad in 
the direction of rotor rotation. Such drag of the rotor upon the brake pad 
can be used to increase the friction-producing force with which the brake 
pad engages the rotor if the brake pad is arranged for an oblique motion 
between its released and rotor-engaging positions, so that it has both 
axial and circumferential components of such motion. 
Thus, as compared with heretofore conventional caliper brake systems, a 
disc brake system offers the very important advantage of being able to 
afford optimum braking action in response to relatively small actuating 
forces. 
Another advantage of a disc brake system is that its rotor disc and brake 
pads can be designed to cooperate with one another for optimum braking 
under all conditions. In the case of prior caliper brakes that cooperated 
with the rim of a bicycle wheel, the material of which the rim was made 
had to be selected for its suitability to the functions of a wheel rim 
rather than for its ability to serve as a brake rotor; and, 
correspondingly, the material of the brake shoes had to be selected for 
compatibility with the rim material and could afford only such braking 
action as would not cause damage to the rim. It was primarily because of 
the need for making such compromises that prior bicycle caliper brake 
systems were notoriously ineffective in rainy weather, precisely at times 
when reduced visibilities might make good braking especially important 
from a safety standpoint. 
By contrast, the rotor disc and brake pads of a disc brake system can be 
made of materials selected solely with a view to their effectiveness, 
compatibility and durability for braking purposes, and those skilled in 
the design of brake apparatus can readily achieve a disc brake system that 
is as effective in a cloudburst as in a drought. 
Hence, a satisfactory disc brake system offers the possibility of not only 
greater comfort and convenience to the bicyclist but of materially greater 
safety as well. But, important as these advantages are, they must not be 
attained at the sacrifice of other desirable factors. 
As with an airplane, the performance of a bicycle is very much affected by 
weight. Every ounce that must be added to a bicycle is cause for concern. 
Having in mind that a complete caliper brake system can weigh less than 
one pound, it is apparent that a bicyclist is likely to reject a disc 
brake system that would be substantially heavier -- notwithstanding its 
greater safety and convenience -- in view of the fact that such a disc 
brake system would tax his energy almost constantly when he was riding but 
would offer its advantages only during short and relatively infrequent 
braking intervals. 
It is also important that a disc brake system for bicycles be capable of 
being installed on a bicycle without requiring any material modification 
of the conventional bicycle structure, without detracting from the 
appearance of the bicycle, and without interfering with normal operation 
of the bicycle or with the installation of commonly used accessories such 
as luggage carriers and fenders. A particular problem in this respect is 
presented by the disc-like rotor that comprises an essential part of a 
disc brake system. The rotor must be so mounted on the wheel as to be 
constrained to rotate therewith and to be spaced axially to one side of 
all of its spokes so that both faces of the disc are accessible to brake 
pads on a caliper assembly which straddles an edge portion of the rotor. 
Nevertheless, the rotor assembly must be compact enough to fit into the 
small space between the wheel and the frame, and neither it nor the 
caliper assembly can interfere with installation or removal of the wheel 
or with the fore-and-aft adjustment of the rear wheel by which chain 
tension is maintained. 
It is hardly necessary to add that a satisfactory disc brake system for a 
bicycle will be low in cost, sturdy, dependable and trouble free. 
Having in mind these requirements, it is the general object of this 
invention to provide a disc brake system which is in all respects suitable 
for bicycles, which can be readily designed to have equally good braking 
action in wet and dry weather, and which is self-energizing so that 
optimum braking action can be obtained with very small actuating force. 
Another general object of the present invention is to provide a 
self-energizing brake system for bicycles that is substantially safer and 
more convenient than the caliper brake systems heretofore conventional on 
gear-shift bicycles, and which can be readily installed on a bicycle as a 
replacement for a caliper brake assembly, utilizing the same hand lever 
previously employed for actuation of the caliper brake assembly but 
requiring the exertion of substantially less force upon that lever to 
obtain a superior braking action. 
A further object of the invention is to provide a self-energizing disc 
brake assembly that can be quickly and easily installed on a bicycle 
without the need for modifying any of the heretofore conventional bicycle 
structure and which can be mass produced in a single model that is 
adaptable to almost all bicycles, regardless of make or size. 
Another specific object of this invention is to provide a caliper assembly 
for a disc-type brake that is especially well suited for bicycles, which 
caliper assembly is held in place by nuts conventionally present on a 
bicycle to secure its rear wheel to one side of its frame and by bumpers 
or pads on the caliper assembly that have clamping but non-marring 
engagement with one of the longitudinal frame members of the bicycle, said 
caliper assembly thus being capable of being installed or removed as 
easily as the rear wheel itself and more or less incidentally to 
installation or removal of that wheel. 
It is also a specific object of this invention to provide a simple 
disc-type brake for a wheel that normally rotates in only one direction, 
said disc-type brake being to some extent self-energizing and comprising a 
disc-like rotor constrained to rotate with the wheel, a U-shaped body that 
straddles a portion of the rotor, a first brake pad fixed to one leg of 
the body, an opposing brake pad carried on the other leg of the body for 
movement relative to the body out of a normal released position in a 
direction generally towards the first brake pad but with a component of 
motion in the direction of rotor rotation, and means so mounting the body 
on structure which carries the wheel that the first brake pad can be 
engaged against the rotor by reaction of the body to force which said 
opposing brake pad exerts against the rotor in moving away from its said 
released position. 
Still another specific object of this invention is to provide a disc-type 
brake assembly which is particularly suitable for bicycles and similar 
light vehicles and which has an actuating mechanism that is well adapted 
for connection with a lever intended to be actuated by the hand, said 
actuating mechanism comprising a cable and means by which lengthwise 
movement of the cable is translated into movement of a friction pad in a 
smooth, direct and very efficient manner. 
With these observations and objectives in mind, the manner in which the 
invention achieves its purpose will be appreciated from the following 
description and the accompanying drawings, which exemplify the invention, 
it being understood that changes may be made in the specific apparatus 
disclosed herein without departing from the essentials of the invention 
set forth in the appended claims.

Referring now to the accompanying drawings, the numeral 4 designates 
generally a bicycle on which there is installed disc brake apparatus 
embodying the principles of this invention, designated generally by 5. The 
brake apparatus is illustrated as arranged for cooperation with the rear 
wheel 6 of the bicycle and as intended for actuation by means of a more or 
less conventional hand lever 7 on the handlebars 8, which hand lever is 
connected with the brake apparatus by a cable 9. 
For purposes of example the brake apparatus 5 is shown and described only 
as applied to the rear wheel of a bicycle, but it will be understood that 
the principles of the invention are readily adaptable to front bicycle 
wheel installations, and also to motorcycles and certain other types of 
vehicles, as well as generally to the braking of wheels and other rotary 
elements that revolve in one direction. On a bicycle, the advantages of 
the invention are of particular importance with respect to the rear wheel, 
inasmuch as the rear wheel should normally receive more braking force than 
the front one. 
In general the brake apparatus 5 comprises a flat, annular rotor or disc 10 
that is concentric to the rear wheel 6 and is constratined to rotate with 
it, and a caliper assembly 11 that is secured to the bicycle frame 12 
adjacent to the rear wheel, at the side of the frame that is opposite the 
chain 13. The rotor 10 is spaced axially to one side of all of the spokes 
14 of the wheel and is between the spokes and the frame. Thus the rotor 
has an axially inner flat surface 15 which faces the wheel spokes and an 
opposite outer flat surface 16. 
The caliper assembly 11 comprises a body 11' that is generally U-shaped as 
viewed edgewise of the rotor, but with one of its legs 17 substantially 
longer than its other leg 18. The body 11' straddles an edge portion of 
the rotor, with its longer leg 17 overlying the outer surface 16 of the 
rotor and its shorter leg 18 overlying the inner rotor surface 15. A 
relatively fixed brake pad 19 is secured to the shorter leg 18, in 
flatwise opposing relationship to the inner rotor surface 15; and a 
relatively movable brake pad 20 is carried on the longer leg 17 in 
opposing relationship to the outer rotor surface 16. 
Contrary to generally conventional practice, the caliper body 11' is so 
mounted on the bicycle frame 12 (as explained hereinafter) that it can 
have limited motion in directions parallel to the wheel axis. The reason 
for such mounting of the body is to enable both of the brake pads 19 and 
20 to frictionally engage the rotor 10 during brake application, even 
though only the brake pad 20 is movable relative to the caliper body. When 
the movable brake pad 20 engages the outer surface 16 of the rotor and 
exerts an axially inward force against it, there is of course an opposite 
reaction upon the caliper body by which that body is moved in the axially 
outward direction to carry the fixed brake pad 19 into engagement with the 
inner surface 15 of the rotor. Hence the freedom of the body for movement 
allows the brake pads to exert opposed and balanced clamping forces upon 
the rotor. 
Turning now to a more specific description of the apparatus, and 
considering first the rotor 10, it comprises a flat annular member 23, 
which constitutes the rotor disc itself, and a substantially flat mounting 
portion or spider member 24 by which the disc portion 23 is secured to the 
wheel 6. The two members are connected by means of suitable fasteners such 
as bolts 25 secured by nuts 26. 
For an understanding of the spider member 24 and its connection to the 
wheel 6, it is necessary to observe that a wire-spoked wheel such as that 
for a bicycle has a rim 27 that is connected by means of the elongated 
wire spokes 14 to a hub 28 in which bearings (not shown) are housed and to 
which a chain sprocket 29 may be concentrically anchored. On the hub 28 
there are a pair of radially outwardly projecting circumferential spoke 
flanges 30, 30', one near each end of the hub, to which the spokes 14 are 
secured at their inner ends. Each spoke flange has a series of holes in 
it, at equal circumferential intervals around it. Each spoke has at its 
inner end a short laterally projecting hook portion 31 that terminates at 
an enlarged head 32. This hook portion is received in one of the holes in 
a spoke flange, with the head 32 overlying one face of the flange and a 
portion of the main length of the spoke overlying the opposite face of the 
flange. 
The spokes of the wheel are of course equally divided between the two spoke 
flanges. Furthermore, half of the spokes connected to each spoke flange 
have their heads overlying the axially inner face of that flange; the 
other half have their heads overlying its axially outer face. The spokes 
that have their heads at the axially inner face of a spoke flange, and 
which in part overlie its axially outerface, can be regarded as "outer" 
spokes 14' and are so referred to hereinafter. The remaining spokes 
connected with the spoke flanges are inner spokes 14". Inner and outer 
spokes alternate with one another around the spoke flange. 
The spider member 24 flatwise overlies the axially outer face of the spoke 
flange 30 that is remote from the chain sprocket 29. It is secured 
primarily by the outer spokes 14' that are connected to that spoke flange, 
and it can be further secured by the heads of the inner spokes connected 
thereto. 
As shown, the spider member is a substantially flat plate in the shape of 
an equilateral triangle. Near each of its apexes it has a hole in which 
can be received one of the bolts 25 by which the disc 23 is secured to the 
spider. The spider also has a substantially larger hole 35 in its center, 
in which is received a bearing housing portion 36 of the wheel hub that 
extends axially outwardly beyond the spoke flange 30. Surrounding the 
large hole is a circle of small holes 37, one for each spoke connected to 
the spoke flange 30, so located as to be registerable with the holes in 
the spoke flange. Each small hole is large enough in diameter to receive 
the hook portion of a spoke. In an outer face of the spider member there 
are spoke receiving grooves 38, there being one such groove extending 
outwardly from every alternate hole 37, and each such groove extends to 
the outer edge of the spider member. It will be observed that the grooves 
38 are lengthwise oriented in correspondence with the lengthwise 
orientation of the outer spokes 14' connected with the spoke flange 30. 
Before the spider is assembled to the wheel, all of the spokes 14 that 
connect with the spoke flange 30' can be installed. As shown in FIG. 4, 
each hole 37 in the spider can be made large enough to receive a spoke 
head 32, and in that case the spider can be placed on the spoke flange 30 
after the inner spokes 14" connected therewith have been installed. The 
heads of those inner spokes are received in those of the holes 37 from 
which grooves do not extend, to enable the spider to flatwise adjoin the 
spoke flange 30. The outer spokes 14' that connect to the spoke flange 30 
are then installed in a generally conventional manner, but through the 
spider as well as through the spoke flange. 
Alternatively, as shown in FIG. 9, the holes 37 in the spider can be made 
small enough so that the spoke heads 32 will not pass through them. In 
that case the spider is set in place on the spoke flange 30 before any 
spokes are connected to it, and the hook portions of all of the spokes 
extend through the spider as well as through that spoke flange. The spider 
will then be held in place by the heads on the inner spokes, as well as by 
the outer spokes. 
In any case, the spider is flatwise contiguous to the outer face of the 
spoke flange 30 and has its grooves 38 opening axially outwardly. 
It will be evident that the spider is snugly flatwise confined between the 
outer spokes and the spoke flange and is firmly held against rotational or 
other edgewise displacement by the hook portions of the spokes. The spider 
presents no substantial interference to conventional installation of 
spokes to the spoke flange 30, inasmuch as the annular disc member 23 need 
not be attached to the spider until after all of the spokes are installed. 
The annular disc member 23 that cooperates with the illustrated spider has 
three circumferentially equispaced tab-like connecting arms 39 projecting 
radially inwardly from its inner circumference, preferably formed 
integrally with its annular portion. Each of these arms is bent obliquely 
out of the plane of the disc, all extending in the same axial direction, 
but the inner end portions of the several arms, which flatwise overlie the 
apex portions of the spider, lie in a common plane. Each inner end portion 
of an arm has a bolt hole which can register with a bolt hole in the 
spider to receive one of the bolts 25 that connect the disc member to the 
spider member. 
Because of the axial inclination of the radially outer portions of the 
arms, the annular portion of the disc member that constitutes the rotor 
proper is in axially outwardly spaced relation to the spider and is 
therefore spaced a substantial distance from all of the spokes of the 
wheel. Hence the shorter leg 18 of the caliper body, which carries the 
fixed brake pad 19, is readily accommodated in the space between the rotor 
and the spokes. 
As illustrated the caliper body 11' comprises a larger main body member 43 
on which the movable brake pad 20 is mounted and which provides for 
attachment of the caliper assembly to a bicycle frame, and a smaller body 
member 44 that comprises the shorter leg 18 of the U and carries the fixed 
brake pad 19. Both body members can be made as aluminum castings. The body 
members 43 and 44 have flat surfaces 45, 45', respectively, at which they 
join one another, and those opposingly engaged surfaces lie in a plane 
that substantially coincides with the plane of the rotor disc. The two 
body members are connected by bolts 46. 
As viewed along the wheel axis, the main body member 43 is substantially 
elongated and is bifurcated at its end that is connected with the smaler 
body member 44. It has a large hole 47 through its other end. In the hole 
47 there is received a cup-shaped hub adapter 48 which is fixed 
concentrically to the wheel and on which the caliper body has a sliding 
fit. As the description proceeds, it will be seen that the body is free 
for axial sliding motion on the hub adapter but is confined against 
rotation around it by abutments that comprise outwardly projecting bosses 
49 on the bifurcations 50 of the main body member, which abutments engage 
opposite sides of one of the elongated frame members of the bicycle. 
Before considering the mounting of the caliper assembly 11 in more detail, 
it should be pointed out that a conventional bicycle wheel assembly 
comprises a relatively stationary axle shaft 51 which extends coaxially 
through the wheel hub 28 and which has threaded end portions that project 
substantial distances beyond the wheel hub. On the end portion of this 
shaft that is remote from the sprocket, a bearing cone 52 is threaded. The 
bearing cone projects a distance into the hub to cooperate with a bearing 
(not shown) therein, and it may project axially outwardly beyond the hub. 
There is usually a locking nut 53 threaded onto the axle shaft against the 
bearing cone. The bearing cone of course does not rotate with the wheel 
and is thus in fixed relation to the axle shaft and the frame 12. Axially 
outwardly of the cone the axle shaft projects through a flat wheel 
supporting portion 54 of the frame. A clamping nut 55 that is threaded 
onto the outer end portion of the shaft, when tightened, cooperates with 
the bearing cone or its locking nut 53 to clamp the frame portion 54 and 
releasably fix the axle to the frame. 
Conventionally, a bicycle frame has a V-shaped portion at each side of the 
rear wheel. Each such V-shaped portion comprises a lower elongated member 
57 that is nearly horizontal and an upper elongated member 58 that extends 
down to the rear end of the lower member at a substantial inclination. The 
flat wheel supporting portion 54 of the frame projects generally 
rearwardly from the junction of these two elongated members. To enable the 
axle shaft to be adjusted fore-and-aft, for maintenance of chain tension, 
the wheel supporting portion has a slot 59 in which the axle shaft is 
received. 
The caliper body extends forwardly from the cup-shaped hub adapter 48 to 
have the bosses on its bifurcated front end project across the lower 
elongated frame member 57, above and below the same, but the rest of the 
caliper body is located at the inner side of that frame member and of the 
wheel supporting portion 54. 
The cup-shaped hub adapter 48, which supports the rear end of the caliper 
body, has a cylindrical side wall 60 and a substantially flat end wall 61. 
A concentric hole 62 in its end wall receives the axle shaft 51 with a 
close sliding fit, and upon securement of the wheel assembly to the frame, 
the end wall of the hub adapter is clamped between the frame portion 54 
and the bearing cone or its locking nut 53, being thus held against all 
movement by the tightening of the clamping nut 55. 
The cylindrical side wall 60 of the hub adapter projects axially inwardly 
to surround the bearing cone 52 and has an inside diameter and depth such 
as to be spaced both radially and axially from rotating parts of the wheel 
assembly. The outer cylindrical surface of the hub adapter side wall, as 
already explained, provides a bearing support for the caliper body 11' 
that provides for translatory sliding motion of the body in directions 
parallel to the wheel axis. 
The caliper body is of course confined against rotation about the hub 
adapter 48 by its straddling cooperation with the lower elongated frame 
member 57. To prevent scratching or marring of that frame member, and to 
provide for smooth, easy motion of the caliper body in directions parallel 
to the wheel axis, the caliper body carries, at the opposing faces of its 
bifurcations, pads or bumpers 63 of nylon or similar smooth, hard but 
slightly resilient material, each in the form of a cylinder which has its 
axis parallel to that of the wheel. Each bumper 63 is held captive in a 
slot 64 in its bifurcation, which slot opens laterally towards the other 
bifurcation. In cross-section each slot 64 is arcuate and of a radius 
equal of that of the cylinder received therein, and its side walls define 
slightly more than a semi-circle so that it is somewhat narrower at its 
mouth than inwardly thereof. The cylinder is thus confined in the slot 
against radial motion relative to the body 11' but projects from the mouth 
of the slot all along its length. At its outer end each slot is closed, 
which is to say that it terminates short of the outer face of the body 
member; but it opens at its inner end to the surface 45 of the main body 
member that is overlain by the smaller body member 44. Hence the cylinders 
63 can be axially inserted into their slots from the inner face of the 
main body member, and they are confined against axial movement by 
securement of the smaller body member to the main body member. 
It will be observed that with the hub adapter in place on the shaft 51, and 
with the caliper body in place on the hub adapter, the wheel can be 
installed on a bicycle in a conventional manner, and its axle shaft can be 
adjusted along the slot 59 as necessary for chain tension, all without 
interference from the brake apparatus. 
The fixed brake pad 19 can comprise a facing member of suitable friction 
material secured to the leg portion 18 of the smaller body member 44 in 
flatwise opposing relation to the inner surface 15 of the rotor. The brake 
pad is somewhat rectangular in outline, being elongated in the 
circumferential direction of the rotor, but its longer edges are curved in 
arcs that center on the wheel axis so that all portions of its surface can 
engage the rotor. 
The movable brake pad 20 comprises a block-like shoe member 65 that is of 
the same general shape as the fixed brake pad. A friction facing 66 
overlies the surface of the shoe member that opposes the rotor. The 
movable brake pad is of course carried on the inner face of the main body 
member 43, spanning its bifurcations. 
For holding the movable brake pad in place on the body, the shoe member has 
a pair of tabs or lugs 67, one projecting lengthwise from each end 
thereof, and the main body member has opposing lugs 68, one adjacent to 
each lug 67 on the shoe member. A coiled garter spring 69 encircles each 
lug 67 on the shoe member and its contiguous lug 68 on the body. The 
garter springs of course permit the shoe member to have limited movement 
relative to the caliper body, but they tend to maintain the shoe member in 
a normal brake-disengaged position, spaced from the adjacent outer surface 
of the rotor and engaged with the inner face of the main body member. 
A bent lever or bell crank 70 that overlies the inner face of the main body 
member provides for actuation of the movable brake pad. A longer arm 71 of 
the lever projects upwardly beyond the caliper body for connection to the 
cable 9, while the shorter arm 72 of the lever is confined between the 
shoe member 65 and the inner face of the body and is so oriented that its 
free end swings generally in directions circumferentially of the rotor and 
transverse to the length of the caliper body. An inwardly projecting pin 
73 or the like, fixed on the free end of the shorter lever arm 72, rides 
in a closely fitting slot 73' in the shoe member to transmit motion of 
that lever arm to the movable brake pad. It will be seen that forward 
motion of the longer lever arm 71, in response to tension on the cable 9, 
cause the movable brake pad to move along a path and in a direction which 
correspond to normal movement of the portion of the rotor engaged by the 
movable brake pad. It will also be noted that the relationship of the 
shorter and longer arms of the bent lever 70 is such that the brake pad 
has a relatively small movement in response to a relatively large movement 
of the cable, so that a small force on the handlebar actuator lever 7 is 
translated into a large force on the brake pad. 
The brake applying motion of the movable brake pad is a compound one in 
which the brake pad has one component of motion along an arcuate path 
defined by the curvature of its longitudinal edges and has another 
component of motion axially toward the rotor; but in such motion the brake 
pad is always maintained in an orientation such that its friction surface 
is parallel to the surfaces of the rotor. To cause the brake pad to have 
such an axial component of motion while it is maintained in the 
orientation just mentioned, the caliper body member 43 and the shoe member 
65 have pockets 74 and 75, respectively, that open towards one another and 
define cooperating ramp surfaces. There are two such pockets 74 in the 
caliper body, one in the inner face of each of its bifurcations, and two 
pockets 75 in the shoe member, spaced and located to open into the pockets 
74. As best seen in FIG. 7, each pocket is of substantially V-shaped 
cross-section, to provide a pair of oppositely inclined ramp surfaces 76. 
The two inclined surfaces of each pocket converge towards a plane that 
contains the axis of the wheel, so that as viewed in plan the two pockets 
are in somewhat splayed relation to one another. Furthermore, each pocket 
diminishes in depth toward the wheel axis (that is, rearwardly), and since 
the ramp surfaces 76 of the pocket are flat, each pocket is slightly 
fan-shaped and forwardly divergent as viewed in plan. 
A tapered roller 77 is confined in each pair of opposing pockets, to 
cooperate with the opposite ramp surfaces 76. The largest diameter end of 
the roller is in the deepest portion of the pocket, and the taper of the 
roller is such as to correspond to the depthwise taper of the pockets so 
that the desired orientation of the brake pad friction surface is 
maintained. 
It will be apparent that as the movable brake member is moved lengthwise by 
swinging of the lever 70, the rollers 77, confined between the opposing 
ramp surfaces of the respective pockets 74 and 75, will cooperate with 
those ramp surfaces to impart to the shoe member a component of motion 
away from the caliper body member 43 and towards the rotor. 
It will be understood that the angle of taper of the rollers and pockets is 
so selected as to cause the brake pad to move in an arc corresponding to 
the path of motion of the portion of the rotor that it engages. For 
purposes of clarity the taper of the rollers and pockets is exaggerated in 
FIG. 6. 
Attention is directed to the fact that the two rollers 77 cooperate with 
the respective ramp surfaces in the pockets 74 and 75 to provide a support 
for the movable brake pad that is totally stable and by which it is 
maintained properly oriented at all times, and that they guide the movable 
brake pad for motion in the proper directions but permit it to have nearly 
frictionless motion relative to the caliper body. 
When the movable brake pad contacts the rotor, frictional drag of the rotor 
upon the brake pad tends to drive the latter farther in the brake applying 
direction and thus more forcefully into engagement with the rotor, to 
afford a degree of self-energization of the brake. It will be appreciated 
that the angle of inclination of the ramp surfaces 76 of the pockets will 
control the relationship between the components of arcuate and of axially 
inward motion of the brake pad, and hence will control the degree to which 
self-energization is afforded. While some amount of self-energizing action 
is highly desirable, it should not be excessive lest the braking action be 
lacking in "feel" and have a tendency to cause wheel locking. 
The manner in which the fixed brake pad 19 is caused to engage the rotor, 
due to movement of the caliper body in reaction to force that the movable 
brake pad exerts against the rotor, has been described above. 
A tension spring 78, reacting between the bent lever 70 and the main body 
member, biases that lever in the direction opposite to that of brake 
application. That tension spring therefore cooperates with the garter 
springs 69 to urge the movable brake pad towards its normal position in 
which its friction surface is slightly spaced from the rotor. 
No special provision is made for disengaging the fixed brake pad 19 from 
the rotor when the brake is released, and none is necessary. The body has 
been found to move back promptly to a position in which the fixed brake 
pad is clear of the rotor. Evidently, the very slight amount of runout 
that is inevitably present in the inner surface 15 of the rotor is 
sufficient to kick the body to its brake-disengaged position during the 
first revolution of the wheel following brake release. 
For smooth brake application it is essential that the cable 9 as well as 
other parts of the brake actuating mechanism shall have a free and 
efficient action. To this end, the rear end portion of the cable extends 
through a self-aligning cable guide 79 by which it is maintained oriented 
as nearly as possible at right angles to the lever arm 71 to which it is 
connected. The cable guide comprises a cylinder 80 of nylon or the like 
having a metal tube 81 extending transversely therethrough that receives 
the cable with an easy sliding fit. As is conventional, a sheath in which 
the cable is enclosed has a detachable connection 82 to the front end of 
the guide tube 81. The cylinder 80 is supported by a lug 83 that projects 
upwardly from the top of the main body member 43 near its front end. An 
arcuate groove in the front face of the lug receives the cylinder with a 
fit that allows the cylinder to rotate easily. The portion of the cable 
that extends to the rear of the guide tube 81 passes through a bore 84 in 
the lug 83 that is sufficiently larger in diameter than the cable to 
accommodate substantial lateral motion thereof. Note that the lug 83 so 
locates the cable guide that the rear end portion of the cable is 
substantially at right angles to the arm 71 of the bent lever when that 
lever is in the brake-disengaged position to which it is biased. 
From the foregoing description taken with the accompanying drawings it will 
be apparent that this invention provides disc brake apparatus which is 
nicely adapted for bicycle applications by reason of its light weight, 
compactness and efficiency, and which brings an unprecedented convenience 
and safety to hand-operated bicycle braking. It will also be apparent that 
the apparatus of this invention is very versatile in that it can be 
installed on practically any make, model or style of bicycle without 
requiring any modification of the bicycle structure, without detracting 
from the appearance of the bicycle and without interfering in any way with 
its normal operation or with the installation on it of commonly used 
accessories. 
Those skilled in the art will appreciate that the invention can be embodied 
in forms other than as herein disclosed for purposes of illustration.