Electrically operated disc brake with back-off protector

The electrically operated disc brake (10, 110, 310, 410) may be operated by either hydraulic pressure and an electric motor or operated solely by means of an electric motor. The electric motor (40, 340, 440) drives a sun gear (52, 352, 452) of a planetary gear assembly (50, 150, 350, 450). The planetary gear assembly (50, 150, 350, 450) includes a fixed ring gear (70, 370, 470) and a rotatable ring gear (80, 180, 380, 480), the rotatable ring gear (80, 180, 380, 480) having fewer teeth than the fixed ring gear (70, 370, 470) so that rotation of the planetary gears (54, 56, 58) effects a slower rate of rotation of the rotatable ring gear (80, 180, 380, 480). The rotatable ring gear (80, 180, 380, 480) engages a screw (88, 188, 388, 488) which is connected with the piston (30, 130, 330, 430). The piston (30, 330, 430) may be displaced by hydraulic fluid for a service application and the electric motor (40, 340, 440) utilized for a parking application. Alternatively, the piston (130) may be displaced by the electric motor (40) for both service and parking brake applications.

This invention relates generally to a disc brake that may be operated both 
hydraulically and electrically, or solely by motor means. 
Disc brakes have been utilized for many years in passenger cars, heavy duty 
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 either solely by means of an 
electrically or hydraulically operated motor or be operated hydraulically 
for a service brake application and operated by the motor for a parking 
brake application. The result is a highly reliable, low cost, electrically 
operated disc brake which will fit readily within the packaging 
constraints of several vehicles. 
The present invention comprises a disc brake that may be operated by motor 
means, comprising a caliper having a bore with a piston slidably received 
therein, the caliper and piston actuable to displace a pair of friction 
elements into engagement with a rotor, a planetary gear assembly disposed 
within said bore and comprising a sun gear, planetary gears, and a pair of 
ring gears, and the motor means coupled with said sun gear which drives 
the planetary gears, one ring gear fixed to said caliper and the other 
ring gear rotatable by said planetary gears, the other ring gear engaging 
screw means which is connected with said piston, operation of said motor 
means causing rotation of said other ring gear and operative displacement 
of said piston into engagement with one of said friction elements so that 
the caliper, by reaction, displaces the other friction element into 
engagement with said rotor.

The 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 either 
hydraulic pressure or an electric motor. 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 stepped bore 
having a piston 30 slidably disposed therein, the piston having a seal 32 
located thereabout in order to prevent hydraulic fluid from exiting bore 
16. Caliper housing 14 is connected with an electric motor housing 24 
which has a bore 26 housing an electric motor 40. Motor 40 may comprise 
other types of motors, such as an hydraulic motor. Housing 24 is coupled 
to caliper housing 14 by means of a clamp band 43, the clamp band 43 held 
together by a nut and bolt connection 44 (see FIG. 2). A planetary gear 
assembly 50 is disposed within bore 16, the planetary gear assembly 50 
comprising a sun gear 52, three planetary gears 54, 56, and 58 (see FIG. 
3), a two-part carrier 60 comprising carrier parts 61 and 62, pins 63 
which carry the planetary gears, and two ring gears 70 and 80. Each ring 
gear has internal teeth, and ring gear 80 is rotatable but has fewer teeth 
than ring gear 70 which is fixed to caliper housing 14. Rotatable ring 
gear 80 includes thereabout a pair of seals 84, the seals preventing 
hydraulic fluid from entering into the planetary gear assembly. Rotatable 
ring gear 80 is coupled nonrotatably through a tapered spline connection 
86 with screw means 88. Screw means 88 has external threads engaging the 
threads of nut 90, and is supported in opening 31 of piston 30 (see FIGS. 
1 and 5). Nut 90 is coupled nonrotatably through a key connection 92 (see 
FIG. 4) with piston 30. Piston 30 is coupled nonrotatably by means of 
connection 93 with friction element 18. Disposed about screw means 88 is a 
screw-retaining plate 89 which is held in axial position between housing 
shoulder 15 and rotatable ring gear 80, the retaining plate 89 having a 
central opening 91 for screw means 88. Fixedly positioned retaining plate 
89 prevents screw means 88 from moving axially within bore 16. Located at 
the other end of bore 16 is a motor plate 100 that encloses the end of 
bore 16 and also engages the steel ring 102 of motor 40. Plate 100 has an 
opening 103 which effects alignment of the drive shaft of motor 40, and 
the plate also extends within steel ring 102 in order to position the 
motor. Steel plate 100 keeps gearbox oil from entering into bore 26 and 
motor 40. 
The planetary gear assembly has a high reduction ratio which is achieved by 
having fewer internal teeth on rotatable ring gear 80 than on fixed ring 
gear 70. Sun gear 52 causes planet carrier 60 to rotate in the same 
direction as the sun gear, but at a reduced speed due to the fixed ring 
gear 70. The two ring gears 70 and 80 have different numbers of teeth, the 
difference being equal to the number of planetary gears, (normally two or 
three). Thus, as planet carrier 60 rotates, the planetary gear teeth 
engage with the adjacent teeth of the two ring gears 70 and 80, and for 
each rotation of the planet carrier 60, rotatable ring gear 80 advances by 
three teeth (for a design with three planetary gears) or two teeth (for a 
design with two planetary gears). Hence, the overall ratio of the gear 
train is the ratio of speed of the sun gear to the planet carrier 
multiplied by the number of teeth of the output rotatable ring gear 
divided by the number of planetary gears. A typical system might have 18 
teeth on the sun; 72 teeth on the fixed ring; 69 teeth on the output 
rotatable ring, and three planetary gears. The overall ratio would be: 
EQU (72/18+1).times.69/3=115/1 
The difference in tooth numbers is achieved by modifying the operating 
pressure angles of the internal teeth so that the gear with fewer teeth 
(preferably the rotatable ring gear 80) engages at a higher pressure angle 
than that with more teeth. The high pressure angle teeth can be generated 
with a standard 20.degree. involute cutter working on an enlarged internal 
gear blank at the appropriate ratio. 
The screw means 88 can have a friction reducing surface treatment in order 
to improve drive efficiency. However, for parking brake use it is 
essential to choose a drive screw which is irreversible so that the brake 
remains applied after the motor current is turned off. A reverse motor 
torque is used to release the brake. 
A motor control circuit which controls motor torque (or current) is used. 
In a parking brake application, a hand lever with force feedback can be 
used to control a variable sensor such as a rheostat or force transducer 
which signals the controller to provide the appropriate motor current. 
Alternatively, a parking switch can activate the brake and an inclination 
sensor can provide a motor current level more than adequate for the grade, 
with a fully laden vehicle. With either system (and unlike a spring 
brake), the motor is controlled to provide enough torque to park the 
vehicle, without using unnecessarily high torques which load the mechanism 
excessively. Also, because current is proportional to torque, when the 
brake is applied for a parking brake application a datum point may be set 
when a predetermined force level is reached, and this datum point would be 
utilized by the controller during the release of the brake. Brake release 
would be accomplished by reversing the motor, but in order to maintain 
proper brake adjustment, the motor should be stopped when a small brake 
pad clearance is reached. To do this, the motor controller senses a 
predetermined low level current at the datum, during backoff, then 
continues turning the motor for a desired number of motor turns, which 
creates the necessary pad clearance. 
Drive shaft flat 42 (see FIGS. 1 and 6) permits the attachment of a hand 
crank so that the brake can be applied or released manually. 
Turning now to FIG. 6, there is illustrated an electrically operated disc 
brake 110 which utilizes an electric motor for both service and parking 
brake applications. Similar structure will be indicated by the same 
numerals utilized above. The caliper housing 114 includes a stepped bore 
116, the stepped bore having a radially extending wall 118 which extends 
to an opening 119 that provides journalling for the output shaft of the 
electric motor 40. The planetary gear system 150 includes a fixed ring 
gear 70 and a rotatable ring gear 180. The rotatable ring gear 180 has 
fewer teeth than the fixed ring gear 70. Rotatable ring gear 180 includes 
a seal 84 disposed thereabout and gear 180 engages a ring 85 extending 
radially inwardly of stepped bore 116. Piston 130 is disposed at the 
entrance of stepped bore 116 and is positioned on rotatable ring gear 180. 
Another seal 184 is disposed about rotatable ring gear 180 and engages the 
interior surface of opening 131 of piston 130. Rotatable ring gear 180 
engages screw means 188 by means of internal ring gear threads 185 and 
screw means threads 189. Screw means 188 is fixed nonrotatably through a 
key connection 190 with piston 130. Piston 130 is fixed nonrotatably by a 
key connection 192 with the inner friction element 118. In this embodiment 
of the invention, the rotatable ring gear 180 engages directly screw means 
188 which is fixed nonrotatably with the piston that is fixed to the 
nonrotatable friction element 118. Thus, as rotatable ring gear 180 
rotates, screw means 188 is displaced axially to engage friction element 
118 with rotor 22, and by reaction, friction element 120 with the other 
side of rotor 22. The caliper housing 114 has an extension 124 which 
houses the electric motor 40. Because rotatable ring 180 engages directly 
screw means 188 which is fixed nonrotatably to piston 130, that portion of 
the structure is substantially shortened axially in relation to the 
previous embodiment. This enables electric motor 40 to be housed directly 
within extension 124 of caliper housing 114, the overall length of 
electric brake 110 being shortened. Electrically operated disc brake 110 
has a planetary gear system which operates identically to that described 
above, but does not utilize any hydraulic pressure to actuate piston 130. 
Piston 130 is actuated both for service brake and parking brake 
applications by electric motor 40. In all other respects, electric disc 
brake 110 operates as described above for the first embodiment. FIG. 7 
illustrates an alternative piston-screw means-rotatable ring gear 
structure. Screw means 288 is connected nonrotatably by spline connection 
286 with rotatable ring gear 280, and screw means threads 289 engage 
piston threads 285 of piston 230. 
The disc brake of FIG. 6 may be utilized for a parking brake application 
and a separate hydraulic disc brake utilized for service brake 
applications. FIG. 8 illustrates a duplex support plate 300 which supports 
both the electric disc brake 110 and a separate hydraulically operated 
disc brake 400 (both shown in dotted line outlines). 
FIG. 9 illustrates a twin bore disc brake 310 having a pair of disc brake 
mechanisms disposed within twin bores and actuated by an electric motor 
disposed adjacent or parallel to the bores of the actuators. Twin bore 
disc brake 310 includes a caliper 312 which engages outer friction element 
320, caliper housing 314 having bores 316 receiving therein pistons 330. 
Each piston 330 is displaced either by pressurized hydraulic brake fluid 
or by the electric motor 340 via the planetary gear assembly 350. Each 
piston 330 engages the inner brake pad 318 disposed adjacent rotor 322, 
piston 330 receiving nonrotatably by means of a key connection the nut 390 
engaging the screw means 388. Piston 330 engages non-rotatably by means of 
key connection 393 the friction element 318. Each planetary gear assembly 
350 is identical to those described above, in that it includes a 
non-rotatable ring gear 370 disposed coaxially with the rotatable ring 
gear 380, the gear assembly 350 including a sun gear 352 which drives 
three planatary gears. Sun gear 352 is connected with gear 351 that is 
engaged by idler 353 (see FIG. 10). The electric motor 340 is disposed 
parallel to the axis of bore 316, and includes a drive shaft 341 with 
drive gear 345 that powers idler 353. Idler 353 drives the two gears 351 
each of which is connected via a shaft with an associated sun gear. FIG. 
10 illustrates an end section view of the disc brake 310, and each bore of 
the twin bore disc brake includes a planetary gear assembly 350 and other 
structure identical to that shown in FIG. 9. Disc brake 310 includes an 
outer end plastic housing cover 317 which is held in place by clamp 
bracket 321 (see FIG. 11). Clamp bracket 321 includes legs 323 which hold 
housing cover 317 in place. As shown by FIG. 9, caliper housing 314 
includes end portion 315 which is integral with the remaining portions of 
caliper housing 314 so that the Planetary gear assemblies 350 and pistons 
330 are both enclosed within the bores 316. The outer diameter of the 
planetary gear assemblies 350 located within the twin bores of disc brake 
310 are essentially the same as the outer piston diameters. Thus, the gear 
assemblies 350 are small enough to be housed within bores 316 and provide 
the required actuation loads while permitting the utilization of an 
integral caliper housing which is disposed about the ends of gear 
assemblies 350 in order to receive the reaction loading or forces effected 
by assemblies 350 when they operate and displace pistons 330 outwardly 
against rotor 322. 
FIGS. 12 and 13 represent an embodiment which comprises a twin bore disc 
brake 410 having one piston actuated solely by means of hydraulic fluid 
pressure and the other piston actuated by either hydraulic fluid pressure 
or by means of a planetary gear assembly 450 actuated by an electric motor 
440 disposed parallel to the twin bores. Structure similar to that 
described above is identified by the same numeral increased by 100. Disc 
brake 410 comprises a right side bore 416 housing the piston 430, screw 
means 488, nut 490, and planetary gear assembly 450. The left side bore 
428 (see FIG. 13) includes a typical disc brake piston (not shown) which 
is actuated or displaced solely by pressurized brake fluid. The electric 
motor 440 is disposed upon an axis located parallel to the longitudinal 
axis of disc brake 410, and includes a motor shaft 441 connected to a 
drive gear 445 which drives the idler 453 that engages gear 451 connected 
with sun gear 452. As a result, the left side bore 428 (see FIG. 13) 
containing the hydraulically actuated piston may be utilized for service 
brake applications, while the right side bore 416 containing the planetary 
gear assembly 450 may be actuated by electric motor 440 via idler 453 for 
parking brake applications and actuated hydraulically for service brake 
applications. 
Referring now to FIG. 14, there is illustrated an electrically operated 
disc brake 510 which utilizes an electric motor for both service and 
parking brake applications. Similar structure will be indicated by the 
same reference numerals utilized above. The caliper housing 114 includes a 
stepped bore 116, the stepped bore providing support for an electric motor 
40. The planetary gear system 150 includes a fixed ring gear 570 and a 
rotatable ring gear 580. The rotatable ring gear 580 has fewer teeth than 
the fixed ring gear 570. Rotatable ring gear 580 includes a seal 584 
disposed thereabout and gear 580 engages a ring 583 extending radially and 
axially inwardly of stepped bore 116. A piston or nut 530 is disposed at 
the entrance of stepped bore 116 and is positioned on screw means 588 
connected non-rotatably with rotatable ring gear 50. Rotatable ring gear 
580 includes an axial recess 581 which includes peripheral radial slots 
582. Screw means 588 comprises a radial flange 586 which is received 
non-rotatably within the radial slots 582 of recess 581. Screw means 
threads 589 engage nut threads 585 of nut 530. Nut 530 engages a backing 
plate 192 of friction element 118. Disposed about screw flange 586 is a 
rubber or resilient disc 587, the disc 587 providing a resilient surface 
for engagement by the nut 530 when the nut translates to the right in FIG. 
14, during release of the brake. 
Non-rotatable ring gear 570 includes a radial recess 571 which receives a 
rubber or resilient ring member 572. The resilient member 572 may, 
alternatively, comprise a spring clutch 573. Both the rubber ring 572 and 
spring clutch 573 provide low rotational friction for the fixed ring gear 
when the disc brake operates to reverse or release the nut 530. However, 
during operation of brake 510 to effect braking by application of the nut 
530 against friction element 118, the reaction forces through the brake 
effect a very high frictional force between fixed ring gear 570, resilient 
member 572 or clutch 573, and the surface of stepped bore 116. 
When brake 510 is operated to apply friction element 118 against rotor 22, 
the axial thrust effected by nut 530 against friction element 118 and 
rotor 22, coupled with the application of friction element 120 against 
rotor 22, effects a substantial axial thrust through the planetary gear 
assembly so that the ring gear 570 effects substantial frictional 
engagement with the stepped bore 116 and will not rotate relative thereto. 
In other words, ring gear 570 becomes fixed relative to housing 114 during 
the application operation of brake 510. However, when the brake 510 is 
operating to release friction elements 118, 120 from engagement with rotor 
22, nut 530 moves along screw means 588 toward the right in FIG. 14, and 
toward planetary gear assembly 150. If motor 40 is not stopped before nut 
530 reaches the end of screw means thread 589, the engagement of nut 530 
with rotatable ring gear 580 may cause damage to the assembly 150 or nut 
530 may become jammed against rotatable ring gear 580. In order to prevent 
mechanical damage, ring gear 570 is permitted to rotate relative to 
housing 114 during the release phase of braking. During the release phase 
of braking, there is essentially no axial load reaction through planetary 
gear assembly 150. During the release of braking, the presence of 
resilient rubber ring 572 or spring clutch 573 provides a small frictional 
resistance which may be overcome easily by the torque imposed upon ring 
gear 570. This small residual friction effected by resilient member 572 or 
clutch 573 permits friction elements 118, 120 to be backed off, by means 
of motor 40, so that they are clear of rotor 22, and if the release phase 
of braking results in nut 530 being backed off to the extent that it 
engages the rubber disc 587 and flange 586 of screw means 588 which is 
fixed non-rotatably to rotatable ring member 580, then back-off torque 
effected through planetary gear assembly 150 will cause ring gear 570 to 
rotate relative to housing 114. This prevents any damage being caused by 
the back-off of nut 530. The rubber disc 587 is mounted on screw means 588 
in order to prevent hard contact of nut 530 against the flange 586, and 
other mechanical stops may be utilized therefor. Rubber disc 587 insures 
that nut 530 will then be able to drive forward (in the leftward 
direction) when the rotation of screw means 588 is reversed for the 
application phase of braking. 
The back-off protector of disc brake 510 provides substantial advantages 
during the operation of the brake. Any possible damage to brake 510, and 
in particular the planetary assembly 150, is avoided because excessive 
back-off is eliminated. A less sophisticated motor controller is required 
because the mechanical structure of brake 510 compensates for any 
excessive back-off of nut 530. Also, the need to use closely controlled 
dimensions on the outside of ring gear 570 and for bore 116 of housing 114 
is eliminated, because resilient member 572 or clutch 573 positions 
centrally the ring gear 570. This effects substantial cost savings between 
the two components which more than offsets the costs of adding two rubber 
parts or a coil spring to the brake. Of course, the back-off protector 
prevents the nut 530 from jamming against its stop comprising flange 586, 
so that the brake 510 can be reapplied and effect braking of rotor 22. 
The various embodiments of the disc brake having the planetary gear 
assembly may be utilized for drive line braking of a vehicle. The "rotor" 
to be braked may be attached to the vehicle's propulsion shaft or driven 
by it, and the caliper mounted on the transmission or rear axle assembly. 
All of the above-described motors may be electric motors, hydraulic 
motors, and any other appropriate driving source. 
Other provisions of the invention or variations will become apparent to 
those skilled in the art and will suggest themselves from the specific 
applications of the invention. It is intended that such variations and 
revisions of the invention as reasonably to be expected on the part of 
those skilled in the art, to suit individual design preference and which 
incorporate the herein disclosed principles, will be included within the 
scope of the following claims as equivalents thereof.