This brake is a self-energizing mechanical friction brake and is intended for use in a rotary drive system. It incorporates a torque sensor which cuts power to the power unit on any overload condition. The brake is capable of driving against an opposing load or driving, paying-out, an aiding load in either direction of rotation. The brake also acts as a no-back device when torque is applied to the output shaft. The advantages of using this type of device are: (1) low frictional drag when driving; (2) smooth paying-out of an aiding load with no runaway danger; (3) energy absorption proportional to load; (4) no-back activates within a few degrees of output shaft rotation and resets automatically; and (5) built-in overload protection

Cacciola, M. J.

English

NASA Technical Reports Server

LOAD PROPORTIONAL SAFETY BRAKE 
Michael J .  C a c c i o l a  
B o e i n g  C o m m e r c i a l  A i r p l a n e  Company 
INTRODUCTION 
This  brake  i s  a se l f - ene rg iz ing  mechanical f r i c t i o n  brake  and is in-  
tended f o r  u s e  i n  a r o t a r y  d r i v e  system. It inco rpora t e s  a torque  sensor  
which c u t s  power t o  t h e  power u n i t  on any overload condi t ion .  The brake  i s  
capable  of d r i v i n g  a g a i n s t  an  opposing load  o r  d r i v i n g ,  paying-out, an a id-  
i n g  load i n  e i t h e r  d i r e c t i o n  of r o t a t i o n .  The brake  a l s o  acts as a no-back 
device  when torque  i s  appl ied  t o  t h e  output  s h a f t .  
The advantages of us ing  t h i s  type  of device  are: 
1. Low f r i c t i o n a l  d rag  when d r i v i n g .  
2. Smooth paying-out of an a i d i n g  load wi th  no runaway danger. 
3 .  Energy absorp t ion  p ropor t iona l  t o  load.  
4 .  No-back a c t i v a t e s  w i t h i n  a few degrees  of ou tput  s h a f t  r o t a t i o n  
and resets au tomat ica l ly .  
5. Bu i l t - i n  overload p ro tec t ion .  
DESCRIPTION 
Figure  1 shows a s e c t i o n  view of t h e  brake  which is  made up of two 
major components, t h e  braking component and t h e  torque  sens ing  component. 
The braking component i s  comprised of t h r e e  s e p a r a t e  elements;  t h e  energi-  
z ing  brake,  t h e  load sens ing  cams, and t h e  holding brake.  The torque  sensor  
i s  comprised of load  sens ing  d e t e n t s ,  load r e a c t i n g  sp r ings  and a swi tch  
assembly. The brake  absorbs energy i n  propor t ion  t o  t h e  load and d i s s i p a t e s  
t h e  energy as hea t  through an o i l  f i l l e d ,  f inned  aluminum housing. 
F igure  2 shows t h e  brake assembly without  t h e  torque  sens ing  element 
a t t ached .  
r e q u i r e  overload p ro tec t ion .  
This  type  of brake can be used i n  a p p l i c a t i o n s  which do not  
The inpu t  s h a f t  (1) has  one ou te r  and one inne r  set of d r i v i n g  s l o t s ,  
see Figures  1 and 3. 
s h a f t  (2) and provide a s t r a i g h t  through d r i v e .  They a l s o  provide  a second- 
a r y  load pa th  i n  case of brake f a i l u r e .  The o u t e r  d r i v i n g  s l o t s  con tac t  
l ugs  on t h e  sp r ing  cage (6)  which i s  index sp l ined  t o  t h e  input  c a m  p l a t e  
(10). Th i s  arrangement of d r i v i n g  s l o t s  and l u g s  main ta ins  alignment of t h e  
b a l l  d e t e n t  p o s i t i o n  on t h e  cam p l a t e s  (10) (12) and keeps t h e  hold ing  brake 
de-energized. 
The inner  set  of s l o t s  con tac t  l ugs  on t h e  main brake  
Because of t h e  symmetry of t h e s e  p a r t s ,  t h e  brake w i l l  
95 
https://ntrs.nasa.gov/search.jsp?R=19790014377 2020-03-21T23:47:35+00:00Z
func t ion  when d r iven  i n  e i t h e r  d i r e c t i o n .  Return s p r i n g s  (33) provide  an  
axial  f o r c e  t o  t h e  output  cam p l a t e  (12) which keeps t h e  t h r e e  b a l l s  (11) 
sea t ed  i n  t h e i r  d e t e n t  p o s i t i o n  and main ta ins  a gap a t  t h e  brake  p l a t e s  t o  
e l imina te  hold ing  brake  drag.  
t a i n e d  i n  t h e  s p r i n g  cage (6) provide  a n  axial  f o r c e  t o  t h e  energ iz ing  brake  
which gene ra t e s  a r e a c t i o n  torque  f o r  energ iz ing  t h e  hold ing  brake. The re- 
a c t i o n  torque  i s  t r ansmi t t ed  by t h e  s t a t o r  p l a t e s  (9) which are grounded t o  
t h e  e x t e r n a l  housing (3) through s p l i n e  t e e t h  on t h e  s t a t o r  (37).  Anti- 
f r i c t i o n  t h r u s t  bea r ings  (5) (35) are used t o  c a r r y  t h e  f o r c e  of the energiz-  
i n g  sp r ings  (7)  t o  minimize f r i c t i o n a l  drag  developed by t h e  relative 
r o t a t i o n  of t h e  inpu t  c a m  p l a t e  (10) and main brake  s h a f t  (2) dur ing  brake  
a p p l i c a t i o n .  Nut (4) i s  used t o  react t h e  energ iz ing  sp r ing  f o r c e  and t o  
a d j u s t  t h e  gap a t  t h e  energ iz ing  brake  p l a t e s .  The load  sens ing  element of 
t h e  brake is  made up of c i r c u l a r  b a l l  cams on both t h e  inpu t  and output  cam 
p l a t e s  (10) (12) ,  three b a l l s  ( l l) ,  and a b a l l  cage (36),  see Figure  4 and 5. 
The b a l l  cams are designed t o  o p e r a t e  i n  e i t h e r  d i r e c t i o n .  
forms a vee  which h a s  a r a d i u s  smaller than  t h e  b a l l  r ad ius .  Th i s  provides  
a d e t e n t  e f f e c t  which prevents  movement u n t i l  t h e  t r ansmi t t ed  torque  a c t u a t e s  
t h e  c a m  p l a t e s .  
l a r g e r  than  t h e  b a l l  r ad ius .  This  a l lows  t h e  b a l l s  t o  seek  a p o s i t i o n  where 
a l l  t h e  b a l l s  share t h e  load ,  and compensates f o r  t o l e r a n c e s  on t h e  ind iv id-  
u a l  p a r t s .  The b a l l  cage (36) i s  used t o  cap tu re  t h e  t h r e e  b a l l s  and f o r c e s  
t h e  b a l l s  t o  move i n  unison up t h e  cam su r faces .  The brake  p l a t e s  (8) (13) 
are  a s p e c i a l  des ign  which have a con t ro l l ed  uniform c o e f f i c i e n t  of f r i c t i o n .  
The f r i c t i o n  l i n i n g  i s  non-metall ic and is bonded t o  a steel  co re  which i s  
sp l ined  t o  t h e  cam p l a t e s .  The s t a t o r  p l a t e s  (9) (14) have an  e x t e r n a l  
s p l i n e  wi th  every o t h e r  t o o t h  removed, see Figure  3, and provide t h e  mating 
s u r f a c e  f o r  t h e  brake p l a t e s  (8) (13) .  The s t a t o r  (37) a l s o  has  every o t h e r  
t o o t h  removed on t h e  i n t e r n a l  s p l i n e  i n  t h e  area of t h e  holding brake  only.  
Spacers  (15) are provided i n  both t h e  energ iz ing  and hold ing  brake t o  change 
t h e  braking c a p a c i t y  depending on t h e  load.  The load s p r i n g s  (34) are re- 
t a ined  i n  s p r i n g  cage (16). 
brake  i n  d i r e c t  p ropor t ion  t o  t h e  load .  The sp r ings  are s e l e c t e d  so t h a t  
t h e  f o r c e  generated by t h e  load sens ing  cams i s  w i t h i n  t h e i r  working range. 
Th i s  enhances t h e  smoothness of t h e  brake when d r i v i n g  an  a id ing  load .  Shim 
(32) i s  a laminated shim used t o  a d j u s t  the gap on t h e  holding brake.  
(18) is  used t o  l o c k  t h e  p re s su re  p l a t e  (17) t o  t h e  main brake  s h a f t  (2) f o r  
r e a c t i n g  t h e  load  s p r i n g  fo rce .  
d e t e n t  s h a f t  which r e t a i n  t h r e e  b a l l s  (20) i n  countersunk d e t e n t s .  The inpu t  
d e t e n t  s h a f t  (19) i s  s p l i n e d  t o  t h e  main brake  s h a f t  (2) and t r a n s f e r s  l oad  
t o  t h e  output  d e t e n t  s h a f t  (31) through t h e  t h r e e  b a l l s  (20).  I n  case of 
b a l l  d i s i n t e g r a t i o n ,  a secondary load  pa th  i s  provided through a p a i r  of 
d r i v i n g  l u g s  w i t h  enlarged c l ea rances  t o  a l low normal opera t ion .  
d e t e n t  s h a f t  (31)  is  sp l ined  t o  t h e  output  s h a f t  (26) and has  a f l a n g e  which, 
when d isp laced ,  c o n t a c t s  a n  a n t i - f r i c t i o n  bear ing  (22) on t h e  swi tch  assembly. 
F ive  b e l l e v i l l e  s p r i n g s  (30) provide  the f o r c e  t o  t h e  output  d e t e n t  s h a f t  f o r  
r e t a i n i n g  t h r e e  b a l l s  (20) i n  t h e  d e t e n t s .  The sp r ing  f o r c e  is reac t ed  t o  
t h e  inpu t  d e t e n t  s h a f t  through washers (28) ,  a n  a n t i - f r i c t i o n  t h r u s t  bear ing  
(29) , and nu t  (27).  A lever (24) and s h a f t  (23) are used t o  t r a n s f e r  t h e  
d e t e n t  s h a f t  motion t o  a c t u a t e  t h e  swi tch  (21).  An a d j u s t a b l e  s t o p  (25) is 
provided f o r  t h e  lever (24) t o  main ta in  a c l ea rance  gap a t  a n t i - f r i c t i o n  
bea r ing  (22) dur ing  normal opera t ion .  
The energ iz ing  sp r ings  (7) which are re- 
The cam s l o p e  
Transverse t o  t h e  d i r e c t i o n  of r o t a t i o n  t h e  cam r a d i u s  is  
They supply an  a x i a l  f o r c e  t o  t h e  hold ing  
Nut 
The torque  sensor  has  an  inpu t  and output  
The output  
96 
PRINCIPLES OF OPERATION 
Driving Against  A Load (Figure 6) 
When d r i v i n g  from a stopped p o s i t i o n  wi th  t h e  brake  f u l l y  energized,  
(no-back a c t i v a t e d )  t h e  i n i t i a l  r o t a t i o n  of t h e  inpu t  s h a f t  (1) releases t h e  
holding brake.  The inpu t  s h a f t  (1) s u p p l i e s  to rque  d i r e c t l y  t o  t h e  main 
brake  s h a f t  (2) through a p a i r  of d r i v i n g  lugs ,  see Figure  3. The output  
cam p l a t e  (12) i s  d r iven  by t h e  main brake  s h a f t  (2)  t o  a l i g n  t h e  b a l l  
d e t e n t s .  The holding brake  a l lows  t h e  cam p l a t e  (12) t o  r o t a t e  because of 
t h e  enlarged c l ea rance  between t h e  s t a t o r  p l a t e  (14) and t h e  s t a t o r  (37) 
s p l i n e  t e e t h .  The input  s h a f t  (1) s imultaneously d r i v e s  t h e  s p r i n g  cage (6) 
through another  p a i r  of d r i v i n g  l u g s  which provide torque  t o  t h e  inpu t  cam 
p l a t e  (10) t o  overcome t h e  energ iz ing  brake  torque.  The cam p l a t e s  are keyed 
so t h a t  t h e  b a l l  d e t e n t s  are a l igned  when t h e  d r i v i n g  f a c e s  of both sets of 
l ugs  are i n  con tac t .  With t h e  b a l l  d e t e n t s  a l igned  t h e  r e t u r n  s p r i n g s  (33) 
provide  a n  a x i a l  f o r c e  t o  t h e  output  c a m  p l a t e  (12) which keeps t h e  t h r e e  
b a l l s ( l 1 )  s ea t ed  i n  t h e  d e t e n t s .  Since t h e  t h r e e  b a l l s  (11) cannot r ise up 
t h e  cam s u r f a c e s  t h e  brake  remains de-energized. Torque is  then  app l i ed  
through a s p l i n e  t o  t h e  input  d e t e n t  s h a f t  (19) of t h e  torque  sensor  and 
t r a n s f e r r e d  through t h r e e  b a l l s  (20) t o  t h e  d e t e n t  s h a f t  (31).  The output  
d e t e n t  s h a f t  (31) i s  coupled t o  t h e  output  s h a f t  (26) through a s p l l n e  and 
t r a n s m i t s  t h e  torque  t o  t h e  d r i v e  system. When an overload cond i t ion  i s  
developed t h e  load r e a c t i n g  s p r i n g s  (30) are not  supplying enough f o r c e  t o  
keep t h e  t h r e e  b a l l s  (20) s ea t ed  i n  t h e  d e t e n t s .  The output  d e t e n t  s h a f t  
(31) i s  then  d isp laced  a x i a l l y  t o  ope ra t e  a l e v e r  (24) which t r i p s  t h e  swi tch  
(21) i n  t h e  e l e c t r i c a l  c o n t r o l  c i r c u i t  and c u t s  power t o  t h e  d r i v e  motor. 
Stopped-No-Back (Figure 7 )  
When t h e  d r i v e  motor i s  s topped,  t h e  load back d r i v e s  t h e  main brake  
s h a f t  (2) and t h e  output  cam p l a t e  (12).  The energ iz ing  sp r ings  ( 7 )  main ta in  
a f o r c e  on t h e  energ iz ing  brake  p l a t e s  which provide a r e a c t i o n  torque  t o  t h e  
load  through t h e  t h r e e  b a l l s  (11) .  A s  to rque  i s  app l i ed ,  relative r o t a t i o n  
occurs  between t h e  inpu t  cam p l a t e  (10) and t h e  output  cam p l a t e  (12) .  This  
causes  t h e  output  cam p l a t e  (12) t o  d i s p l a c e  a x i a l l y  as t h e  t h r e e  b a l l s  (11) 
r i se  up t h e  cam s u r f a c e s  and remove t h e  holding brake  p l a t e  c learance .  
Fur ther  i nc rease  i n  back d r i v i n g  torque  d i s p l a c e s  t h e  output  cam p l a t e  (12) 
t o  compress t h e  load s p r i n g s  (34) t o  some f o r c e  l e v e l .  When t h e  s p r i n g  f o r c e  
appl ied  t o  t h e  holding brake p l a t e s  (13) (14) gene ra t e s  s u f f i c i e n t  to rque  a l l  
movement s t o p s  and t h e  load i s  f u l l y  r eac t ed .  
Driving An Aiding Load - Paying Out (Figure 8) 
When d r i v i n g  a n  a i d i n g  load ,  t h e  inpu t  s h a f t  (1) r o t a t e s  i n  t h e  d i r ec -  
t i o n  of t h e  load and t h e  o u t e r  set of d r i v i n g  l u g s  con tac t  t h e  sp r ing  cage 
(6) which a p p l i e s  to rque  t o  t h e  input  c a m  p l a t e  ( l o ) ,  see Figure  3. When 
t h i s  to rque  exceeds t h e  d i f f e r e n c e  between t h e  energ iz ing  brake  torque  and 
t h e  r e a c t i o n  torque  of t h e  t h r e e  b a l l s  (111, t h e  main brake s h a f t  (2) r o t a t e s  
under t h e  in f luence  of t h e  load .  The load sp r ings  (34) modulate t h e  f o r c e  of 
t h e  load sens ing  cams on t h e  holding brake  p l a t e s  (13) (14) which gene ra t e  a 
holding torque  pe rmi t t i ng  t h e  load t o  pay out  smoothly a t  d r i v e  motor speed. 
97 
SYMBOLS 
- 
Input  Torque To - 
Drag Torque TM = 
Torque Across B a l l  FE = 
Modulating Spring Force FR = 
Axial Force A t  B a l l  Ft = 
Coeff ic ien t  Of F r i c t i o n  r D  = 
Main Brake P l a t e  Radius r g  = 
Number Of Drag Brake Surfaces  nM = 
Cam Slope Angle 
Output Torque 
Main Brake Torque 
Energizing Spring Force 
Return Spring Force 
Tangent ia l  Force A t  B a l l  
Drag Brake P l a t e  Radius 
Radius To B a l l  
Number Of Main Brake Surfaces 
MAXIMUM CAM SLOPE ANGLE 
For a given load t h e  axial  f o r c e  on the  b a l l  is: (See Figure 7) 
Minimum Holding Brake is: 
Solut ion of t h e  above equat ion reso lves  i n t o  a quadra t ic  of t he  form: 
A tan02 + B tan0 - c = o 
Subs t i t u t ing  values  f o r  a l l  t h e  known terms and so lv ing  f o r  0 w i l l  
g i v e  the  maximum cam s lope  angle  which w i l l  hold t h e  load without s l i pp ing .  
BRAKE STABILITY 
The brake as descr ibed i n  Figures  1 and 2 is e a s i l y  proportioned t o  be  
self-energizing and capable of holding a load i n  the  s t a t i c  o r  stopped 
98 
condi t ion .  
smoothly without  brake c h a t t e r .  
t h e  brake  i s  r a p i d l y  cyc l ing  between locked-up and r e l eased .  
The c r i t i c a l  cond i t ion  i s  d r i v i n g  o r  paying ou t  an  a i d i n g  load 
Chat te r  i s  an uns t ab le  cond i t ion  i n  which 
The fo l lowing  i t e m s  are  requi red  t o  i n su re  s t a b l e  ope ra t ion  of t h e  
brake: 
1. F r i c t i o n  material wi th  a s t a b l e  c o e f f i c i e n t  of f r i c t i o n  throughout 
t h e  ope ra t ing  range of temperature  and brake  p l a t e  pressure .  
2. Combination of f r i c t i o n  material and o i l  which minimizes t h e  
f l u c t u a t i o n  between s t a t i c  and dynamic c o e f f i c i e n t  of f r i c t i o n .  
3 .  Correc t  load  ba lance  between t h e  ene rg iz ing  brake  and t h e  main 
holding brake. 
4 .  Modulating sp r ing  ra te  t o  balance maximum a x i a l  load developed by 
t h e  b a l l  cams. 
Another method of producing a s t a b l e  brake  is  t o  reduce t h e  torque  
capac i ty  of t h e  energ iz ing  brake  t o  a va lue  below t h e  b a l l  to rque  and then 
add a cons t an t  drag  brake  t o  t h e  input  s h a f t .  The a f f e c t  of reducing t h e  
energ iz ing  brake i s  t o  make t h e  brake r e v e r s i b l e ,  bu t  t h e  a d d i t i o n  of t h e  
cons tan t  d rag  brake  i n  conjunct ion  w i t h  t h e  o the r  braking elements makes 
t h e  brake  i r r e v e r s i b l e  and capable  of r e a c t i n g  t h e  f u l l  load.  
a n  a i d i n g  load ,  t h e  inpu t  to rque  need only overcome t h e  margin of t h e  
cons tan t  drag  brake which a l lows  t h e  load t o  pay-out. F igure  9 shows a 
cons tan t  drag  brake  app l i ed  t o  t h e  inpu t  s h a f t  w i th  a r a t c h e t i n g  device  
which bypasses  t h e  brake  when d r i v i n g  a g a i n s t  a load.  
When d r i v i n g  
F igu re  10 shows t h e  d r i v e  system of t h e  Boeing Model 747 On-Board 
Loader which used two brakes i n  a dua l  load pa th  arrangement. 
des ign  of t h e  brake  as de l ive red  w a s  as shown i n  F igure  1. 
The f i n a l  
ANALYSIS OF ON-BOARD LOADER BRAKE 
Weight of p la t form and payload - 34,000 l b .  
Torque a t  c a b l e  drum - 102,000 in-lb.  
Torque a t  brake  - 1,090 in-lb.  
Brake Design Parameters:  
rD = 2.47 i n .  
r M  = 2.47 i n .  
r g  = 2.50 i n .  
nD = 4 
nM = 6 
FE = 60 l b .  
FR = 30 l b .  
FM = 552 l b .  
lu = .12-.10 oper.  
IJ = .06 Min. 
99 
CHECK CAN SLOPE ANGLE 
S u b s t i t u t i n g  va lues  f o r  a l l  known t e r m s  and t h e  minimum c o e f f i c i e n t  of 
f r i c t i o n ,  t h e  above equat ion  r e s o l v e s  i n t o  t h e  fol lowing quadra t i c :  
172.975 t a n  f12 + 20.5079 0 - 14.5885 = 0 
So lu t ion  of t h e  q u a d r a t i c  g ives  t h e  maximum c a m  s l o p e  ang le  which w i l l  
a l low t h e  brake  t o  support  t h e  load without  s l i pp ing .  
Solu t ion :  13 = 13.34O 
To allow f o r  . t o l e r a n c e s  w e  w i l l  use  0 =: 12.50' 
DRIVING AN OPPOSING LOAD (See F igure  6) 
Input  Torque: 
T 1 = FEprDnD + To 
= 60 (.11) 2.47 (4) + 1090 
T1 = 1155 in-lb 
STOPPED WITH LOAD APPLIED (See Figure 7)  
Axial Force: 
To + F P r M %  
p =  
A prMnM + tanOrg 
- 1090 + 30 (.11) 2.47 (6) - 
. l l  (2.47) 6 + tan 12.50° (2.5) 
FA = 521.4 l b  
For brake t o  b e  i r r e v e r s i b l e :  
TD' TB 
TD = F p r  n A D D  
= 521.4 (.11) 2.47 (4) 
TD = 566.7 in- lb  
100 
TB = FtrB 
= FA tanOrB 
= 521.4 t a n  12.50° (2.5) 
TB = 288.9 in-lb 
TD' TB 
566.7> 288.9 .*,Brake i s  i r r e v e r s i b l e  
BRAKE HOLDING MARGIN 
TM = FMpr'M% 
= (521.4 - 30) -11 (2.47) 6 
TM = 801.1 in-lb 
Margin: 
566.7 + 801.1 
1090 
-t 'M = 
To 
Margin = 1.25 
DRIVING AN A I D I N G  LOAD (See Figure 8) 
Input Torque: 
= 521.4 c.11 (2.47) 4 - t a n  12.50' (2.511 
= 566.7 - 288.9 
T1 = 277.8 in-lb 
101 
102 
I I 
103 
c-c 
STOPPED 
Figure 3 
ctions Through Driving Members 
104 
RELIEF GROOVE 
CAM GROOVE 
t- + 
PLAN VIEW 
SECTION A-A 
(UNWRAPPED) Figure 4 
07%- 105% Rb 
SECTION B-B 
CAM GROOVE 
LIEF GROOVE 
Figure 5 
Ball Cam Groove 
MODULATING 
SPRtNG 
Figure 6 
Driving an Opposing Load 
106 
r STATOR 
MODULA 
SPRING 
BRAKE 
TlNG 
Figure 7 
With L plie 
107 
SPRING 
L MODULATING 
SPRING 
Figure 8 
Driving An Aiding Load 
108 
109 
‘H 
I
 
-- --- 
I I I 
I 
I I 
I I 
m
 
s 


Load proportional safety brake

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server