Electrically operated disc brakes

The electrically operated disc brakes (10, 210) may include a high efficiency screw and nut mechanism (60) and/or a one-way clutch mechanism (230). The high efficiency screw and nut mechanism (60) includes a screw (86) with a screw thread (89) that has a predetermined pitch, and at least one nut (77, 97) disposed about the screw (86) and having an interior opening (78, 98) with a nut thread (79, 99) therein. The pitch of the nut thread (79, 99) is equal to the pitch of the screw thread (89), and the pitch diameter of the nut thread (79, 99) is greater than the pitch diameter of the screw thread (89). The screw (86) is driven by the electric motor (40) of the disc brake (10, 210). The one-way clutch mechanism (230) includes a sun gear drive member (252) which has oppositely disposed radial drive slots (257) through which extends a drive pin (243) that extends transversely through the drive shaft (241) of the electric motor (240). The sun gear drive member (252) is journalled within a cage member (281) which has oppositely disposed radial cage slots (282) into which extends the drive pin (243). The radial cage slots (282) are in circumferential non-alignment with the radial drive slots (257) of the sun gear drive member (252). The sun gear drive member (252) includes cam surfaces (253) receiving roller bearings (290) thereat, the roller bearings (290) extending through oppositely disposed openings (284) within the cage member (281) to engage at interior surface (297) of an annular housing (295). The clutch mechanism (230) permits the sun gear drive member (252) to be rotated in both directions by the drive shaft (241), but when reaction forces attempt to reverse rotation of the drive member (252) and electric motor (240), the clutch mechanism (230) locks and prevents such reverse rotation.

This invention relates generally to disc brakes that may be operated 
electrically, and in particular to an electrically operated disc brake 
containing a high efficiency screw and nut mechanism and/or a one-way 
clutch mechanism having a unique release feature. 
Disc brakes have been utilized for many years in passenger cars, heavy 
trucks, and aircraft. Because of the increasing emphasis on reducing the 
weight of vehicles and simplifying the components thereof, it is desirable 
to develop a braking system that is operated electrically. Such a braking 
system must be highly reliable, cost effective, and practical within the 
packaging constraints of the particular vehicle. The present invention 
provides a disc brake that may be operated by an electric motor and which 
may contain a highly efficient nut and screw mechanism and/or a one-way 
clutch mechanism having a unique release feature. The high efficiency 
screw and nut mechanism provides a simplified structure that is highly 
reliable, low cost, and which will fit readily within the packaging 
constraints of several vehicles that may utilize an electrically operated 
disc brake. Likewise, the one-way clutch mechanism with unique release 
feature provides a highly reliable, low cost clutch mechanism which 
enables the disc brake to meet Federal requirements for vehicle parking 
brakes, while at the same time being small enough so that the overall size 
of the electrically operated disc brake will continue to fit readily 
within the packaging constraints of several vehicles. 
The present invention comprises a screw having a screw thread about the 
circumference thereof, the screw thread having a predetermined pitch, a 
nut disposed about said screw and having an interior opening, the interior 
opening having a nut thread which engages at a circumferential portion 
thereof the screw thread, the nut thread having a pitch equal to the pitch 
of the screw thread, the screw thread having a predetermined pitch 
diameter and the nut thread having a predetermined pitch diameter, the 
pitch diameter of the nut thread being greater than the pitch diameter of 
the screw thread, whereby rotation of the screw causes said nut to rotate 
at a different rotational speed relative to the rotational speed of the 
screw. The present invention may be utilized in a disc brake comprising a 
caliper having a bore and a piston housing actuatable to displace a pair 
of friction elements into engagement with a rotor, motor means for 
actuating operatively a high efficiency screw and nut mechanism, the screw 
and nut mechanism effective to displace axially said piston housing and 
cause the displacement of the pair of the friction elements, the screw 
comprising a screw thread having a predetermined pitch and a predetermined 
pitch diameter, a first nut disposed about said screw and having an 
interior opening with a nut thread disposed therein, the nut thread 
engaging at a circumferential portion thereof the screw thread, the nut 
thread having a pitch equal to the predetermined pitch of the screw 
thread, and the nut thread having a predetermined pitch diameter greater 
than the predetermined pitch diameter of the screw thread, whereby 
rotation of said screw by the motor means effects rotation and axial 
displacement of said first nut to effect said axial displacement of the 
piston housing. The present invention also comprises a clutch mechanism 
which includes a drive shaft having a drive pin extending transversely 
therefrom, the drive shaft and drive pin disposed within a drive member, 
the drive member having therein a pair of oppositely disposed radially 
extending drive slots, the drive pin extending radially through said drive 
slots, the drive member having cam surfaces about the periphery thereof 
receiving bearing means thereat, a cage member disposed about said drive 
member and having oppositely disposed radial cage slots, the drive pin 
extending radially into said radial cage slots, the radial cage slots 
being in circumferential nonalignment with said drive slots, and a housing 
disposed about said cage member and having an interior surface engaged by 
said bearing means.

A disc brake of the present invention is referenced generally by numeral 10 
in FIG. 1. Disc brake 10 comprises a brake that is operated by motor means 
40. Motor means 40 may comprise an electric motor or other motor 
mechanisms that provide a rotary output via shaft 41. Disc brake 10 
includes a caliper 12 having a caliper housing 14 with a bore 16. Caliper 
12 extends over a pair of friction elements 18 and 20 which may be 
displaced toward one another in order to brake a rotor 22. The bore 16 
comprises a groove 17 adjacent opening 19 and bore end 21. Seal 32 is 
disposed within groove 17. Located within bore 16 is an actuating 
mechanism referenced generally by numeral 90. Actuating mechanism 90 
comprises a planetary gear assembly 50 which includes a sun gear 52, three 
planetary gears 54 (the other two not shown in the section view), a 
carrier 55, pins 53 which carry the planetary gears, two ring gears 70, 
80, and thrust bearings 75. Each ring gear has internal teeth, the ring 
gear 80 being rotatable but having fewer teeth than ring gear 70 which is 
operatively coupled with caliper housing 14. The planetary gear assembly 
50 comprises the planetary gear assembly disclosed in copending patent 
application Ser. No. 946,400 entitled "Electrically Operated Disc Brake" 
which is incorporated by reference herein. Because the two ring gears 70 
and 80 have different numbers of teeth, the planeary gear assembly has a 
high reduction ratio, as disclosed in copending Ser. No. 946,400. 
Rotatable ring gear 80 has a recess 82 with splines 84 therein. A screw 86 
includes a first end 87 having splines 88 which engage the splines 84 of 
rotatable ring member 80 and thereby couple together nonrotatably the 
screw 86 and ring member 80 while permitting axial misalignment 
therebetween. First end 87 and recess 82 are curved so that the screw may 
self-center itself relative to ring gear 80. Located within bore 16 is a 
piston housing 68 which has an interior opening 69. Piston housing 68 
includes a key 71 received within slot 31 of friction element 18 so that 
the two are coupled nonrotatably together. The high efficiency screw and 
nut mechanism is referenced generally by numeral 60. Disposed about screw 
86 is at least one nut 77. Nut 77 has an interior opening 78 containing a 
nut thread 79. Nut thread 79 engages, at a circumferential portion 
thereof, a screw thread 89. The nut 77 includes a bearing race 73 which 
receives ball bearings 100. Located at the closed end of piston housing 68 
is a bearing race member 91 which includes a bearing race 92 that receives 
the bearings 100. Second nut 97 includes an interior opening 98 having a 
second nut thread 99 which engages at a circumferential portion thereof 
the screw thread 89. Second nut 97 includes a race 96 which receives 
bearing members 101 that are seated within the correspondingly shaped race 
106 of thrust race member 95. Thrust race member 95 abuts a sleeve 105 
that also abuts at the other end the bearing race member 91. Disposed 
between nut 77 and sleeve 105 is a needle type clutch 107. Clutch 107 
permits nut 77 to rotate freely in only one direction of rotation but 
eliminating, absent rotation of the screw, rotation of the nut in the 
other direction. 
It is desirable to use a highly efficient screw and nut mechanism which, in 
at least one direction of rotation, minimizes as much as possible the 
frictional contact between threads 89 of screw 86 and nut threads 79, 99. 
In order to accomplish this, screw threads 89 and nut threads 79, 99 have 
the same pitch (see Distance A). However, the pitch diameter of nuts 77, 
97 (as indicated by Distance B on nut 97) is slightly greater than the 
pitch diameter C of screw 86. Thus, the pitch diameters of nuts 77 and 97 
may be equal to each other or slightly different, but the pitch diameters 
of both nuts are at least slightly greater than the pitch diameter of 
screw 86, which results in the rotation of nuts 77, 97 at a speed 
different than the rotation of screw 86. Nut 97 engages bearings 101 that 
engage the thrust race member 95, and thrust race member 95 engages sleeve 
105 in order to transmit thrust to the bearing race member 91 and piston 
housing 68. As nuts 77, 97 advance axially and slowly along screw 86, the 
nuts engage the respective bearings 100, 101. A balancing of the mechanism 
is accomplished by bearings 100 and 101 being offset and the threads 79 
and 99 engaging opposite radial sides of screw thread 89. 
The electric motor 40, in response to signals from a controller (not 
shown), drives sun gear 52 of planetary gear mechanism 50. As planetary 
gear mechanism 50 effects the rotation of rotatable ring gear 80, 
rotatable ring gear 80 rotates screw 86 which, through the difference in 
pitch diameters B and C, causes nuts 77,97 to rotate and advance slowly 
along screw thread 89. The substantial advantage of the present invention 
is that circumferential sliding friction between the screw and nuts is 
virtually eliminated, and only low velocity radial sliding will occur as 
the screw and nuts rotate together. A very high mechanical efficiency is 
achieved so that a fully reversible action is possible, and is thus 
suitable for a service brake actuator. It is desirable to provide a 
mechanism that may be utilized as a parking brake mechanism wherein the 
same high efficiency can be achieved to apply the brake, but a low 
efficiency in the reverse drive direction be provided in order to allow 
the actuator to hold in its applied position until reverse motor torque is 
effected. To accomplish this, the needle type clutch 107 allows nut 77 to 
rotate freely in one direction, but prevents and eliminates any free 
rotation of the nut in the reverse direction of rotation. Thus, in order 
to release disc brake 10, screw 86 must be rotated in the reverse 
direction in order to cause sliding between screw 86 and nut 77, 97. By 
suitable selection of the pitch of the threads of the screw and nuts, the 
brake mechanism can be made irreversible, all without affecting the 
application efficiency of the brake. Because the differential screw and 
nut mechanism is utilized in order to advance the nut or nuts slowly along 
the screw thread, a lower ratio reduction gear box may be utilized for the 
driving of the screw. The screw 86 functions like a fine pitch screw but 
without the high frictional losses associated with fine pitch screw 
threads. 
FIGS. 2 and 3 illustrate an embodiment in which the disc brake is 
referenced generally by numeral 210. Similar structure will be indicated 
by the same reference numeral increased by 200. The electric motor 240 
drives a planetary gear assembly 250 which is housed within the caliper 
housing 214 of caliper 212. The planetary gear assembly 250 includes a sun 
gear drive member 252 which drives a carrier 255, pins 263, and planetary 
gears 254. The fixed ring gear 270 nonrotatably engages the caliper 
housing 214 by means of the housing shoulder 213 received within the gear 
recess 271. Rotatable ring gear 280 includes a helical groove 289 with 
bearing balls 285 disposed therein and engaging helical grooves 269 of the 
actuator sleeve 268. The structure of the planetary gear assembly 250, 
ring gears 270 and 280, and actuator sleeve 268 is similar to that 
disclosed in copending patent application Ser. No. 105,756 entitled 
"Electrically Actuated Disc Brake" which is incorporated by reference 
herein. The ring gears have a tooth differential, with rotatable ring gear 
280 having fewer teeth than ring gear 270, so that planetary gear assembly 
250 provides a high reduction ratio. 
The one-way clutch mechanism with unique release feature is designated 
generally by reference numeral 230. Electric motor 240 includes a motor 
drive shaft 241 that includes transverse opening 242 (see FIG. 2). 
Transverse opening 242 receives therein a drive pin 243. Drive pin 243 is 
also received within the sun gear drive member 252 (see FIG. 3). Sun gear 
drive member 252 has a bore 251 which receives the motor drive shaft 241. 
Sun gear drive member 252 includes oppositely disposed radial drive slots 
257 which have abutment edges 257a and 257b. Drive member 252 is 
journalled within a cage member 281. Cage member 281 includes oppositely 
disposed radial cage slots 282 which have abutment surfaces 283. Cage 
member 281 also includes oppositely disposed radial openings 284. About 
the periphery of sun gear drive member 252 are cam surfaces 253 which 
receive roller bearings 290. Roller bearings 290 extend through radial 
openings 284 of cage member 281. Drive pin 243 extends through the radial 
drive slots 257 and into the radial cage slots 282. Drive slots 257 are in 
circumferential nonalignment with the radial cage slots 282. Disposed 
about cage member 281 is an annular housing 295 which extends into 
radially extending flange portions 296 that are fixed to caliper housing 
214. The interior surface 297 of housing 295 is engaged by roller bearings 
290. Planetary gear assembly 250 is driven by electric motor 240 via the 
one-way clutch mechanism 230 which prevents a back drive of the motor by 
mechanism 250. A reversal of the electric motor direction of rotation 
automatically unlocks clutch mechanism 230 and allows reverse rotation of 
drive shaft 241 as long as electric motor 240 is turning drive shaft 241. 
Clutch mechanism 230 may be used in place of the one-way roller clutch 107 
illustrated in the electric disc brake of FIG. 1. The utilization of 
clutch mechanism 230 to prevent back-off of the brake mechanism allows 
high efficiency screw mechanisms such as those described above to be used 
with a consequent savings in motor power and the sizes of component parts. 
When motor 240 operates and rotates motor shaft 241 in the counterclockwise 
direction (see Arrow A in FIG. 3), drive pin 243 engages abutment surfaces 
257a of sun gear drive member 252 (as illustrated) and causes roller 
bearings 290, as member 252 rotates relative to cage member 281, to move 
to the deep ends of cam surfaces 253 where there is sufficient radial 
clearance to prevent jamming of roller bearings 290 between the interior 
surface 297 of housing 295 and cam surfaces 253. Thus, motor 240 can drive 
sun gear drive member 252 in a counterclockwise direction and effect 
operation of planetary gear assembly 250 and axial displacement of 
friction element 218 into engagement with rotor 222 and, by reaction, the 
axial displacement of friction element 220 into engagement with the other 
face of rotor 222. When electric current to motor 240 is terminated, 
reaction forces cause the actuator sleeve 268 and rotatable ring member 
280 to turn sun gear drive member 252 in a clockwise direction. Drive 
mmber 252 can rotate slightly in the clockwise direction (see Arrow B) 
until roller bearings 290 ride up cam surfaces 253 and move radially 
outwardly so that they become wedged between cam surfaces 253 and interior 
surface 297 of housing 295. Thus, sun gear drive member 252 cannot back 
drive motor 240 and brake 210 remains mechanically locked in the applied 
position. If electric motor 240 receives a signal which requires rotation 
of drive member 252 in the clockwise direction (Arrow B), motor 240 
initially rotates pin 243 relative to drive member 252, drive shaft 241 
being journalled within bore 251 of drive member 252. Drive pin 243 
rotates in the clockwise direction within radial cage slots 282 and radial 
slots 257 such that the drive pin engages abutment surfaces 283 of cage 
member 281 before the pin ever engages abutment surfaces 257b of drive 
member 252. This causes cage member 281 to rotate relative to member 252, 
the rotation of cage member 281 causing roller bearings 290 to rotate in 
the clockwise direction and move into the radially recessed portions of 
cam surfaces 253. This effects an unlocking of drive member 252 relative 
to housing 295, and drive member 252 can be driven in the clockwise 
direction as pin 243 then engages surface 257b, and continously driven as 
long as electric motor 240 is rotating drive shaft 241. When motor 240 
terminates its rotation of drive shaft 241, roller bearings 290 can 
immediately reengage the radially outer portions of cam surfaces 253 and 
become wedged between the radially outer portions of the cam surfaces and 
interior surface 297 of fixed housing 295. This locks sun gear drive 
member 252 relative to fixed housing 295. Thus, electric motor 240 is 
utilized to apply and release brake 210, and with only minimal electric 
power utilized for release of the brake. The one-way clutch mechanism 230 
with unique release feature can be utilized equally well for a service or 
parking brake application and has the advantage of utilizing high motor 
power only when the braking force is being increased. When steady braking 
is occurring, the clutch mechanism 230 will remain applied and no further 
motor power is needed. Motor power need only be applied in order to either 
apply the brake further or to effect a release of the brakes via a release 
of the clutch mechanism. 
The one-way clutch mechanism with unique release feature enables the brake 
to be highly efficient for either parking or service brake applications, 
and with a consequent savings in energy requirements for actuation. The 
drive motor is able to control both the application and release of the 
brake. The one-way clutch mechanism operated by the motor is very compact, 
and has a low cost. 
While the invention has been described with respect to the detailed 
embodiments, it will be understood that the invention is capable of 
numerous rearrangements, modifications, and alterations, and such are 
intended to be within the scope of the appended claims. It is reasonably 
to be expected that those skilled in the art can make numerous revisions 
and additions to the invention and it is intended that such revisions and 
additions will be included in the scope of the following claims as 
equivalents of the invention.