Note: Descriptions are shown in the official language in which they were submitted.
BACK~ROUND OF ~HE INYENTION
This Inventlon rol~t~s to ~ tooth~d pow~r tran~mlsslon b~le
and pulley drTve.
U.S. Patent No. 2,507,~52, to R. Y. Case, describes a power
transmission belt comprising an inextensible tenslle ~mber haviilg
teeth bonded to one side and a protective Jack~t fabric covering
the teeth. Ths t~eth are preferably made of an elastomeric material,
such as rubber, and the belt may also include a backing layer of
iden~lsal or similar material to that which the teeth are construct~d.
lQ Many different elastomeric materials have been utilized for
the constructîon of belts made in accordance with tho Case patent,
some of the more common materials being neoprene and polyur~thane.
These belts are designed to mesh with toothed pulleys that are con- -
structed of a material havlng a higher Young s modulus than the
elastomeric material used for the construction of the belt. The
conventional toothed belt, as described in tho Case patent, util;zes
a ~ooth cross-sectional configuratTon that is essentially trapezoidal
and which is very si~Tlar to a conven~ional rack tooth. Many ~ -
attempts have be~n made to alter the belt and pulley teeth configura- ~ `
2Q tions to relieve the problem of belt failure. In such trapezoidal
tooth belts, the common failure is that of tooth shear due to stress
concentration. In seeking to reduce tooth shear, UOS. Patent No.
3,756,091 to H. Miller, discloses belt teeth having a cross-sectional `~configura~ion which approxima~es the contour of the one-half order ;~
isochromatic fringe in a bele tooth under a defined rated load. The
pulley grooves in accordan e with the Mill~r patent are tn matlng
engagement with and ar~ s~bstantially conJugate to the belt teeth.
Th0 belt having substantlally curvilinear teeth in accordanco with
the Miller patent reduced bclt tooth shear and ~ncreased horsepoweF
capacity. One mode of failure tn the belt configuration accord;ng
to Mi~ler may occur becaus~ of land wear In the belt, especially with
smal I diamet~r pulleys. Land we~r between th~ belt teeth is due
to abrasion of the protective layer and exposure of the tensile
member by action of the pulley tooth against the belt. this
land wear leads to premature failure due to a detachment of the
teeth from the tensile member and/or a break in the tensile
member. :
U.S. Patent ~o. 4,037,485, to Hobackg propos~s a solution ~:
to the land wear problem. As disclosed ln the Hoback pat~nt,
the dimensio~al relatlonship of tho belt teeth and grooves and the
pulley taeth and grooves is such that in th~ longitudinal extent
of the be)t between the pulleys, the height of the belt teeth is ~ :
greater than the ~epth Gf the pulley grooves while as the belt
travels around the pulleys, the extreme outwardly facing portions
of the belt teeth wh kh con~ront the pulleys comes into contact
with the portions of the toothed pulley which define the bottom of
the pulley grooves. At the sam~ tims, Hoback discloses that the
belt teeth are compressed to reduce thoir height so that the extreme
radially outwardly facing portlons of the ~ulley teeth co~e into
contact with the portions of the belt disposed between the belt
teeth which define the bottoms of th~ belt grooves.
Relatively early in ths operat;ng life of th~ toothe~ power
transmission bele and pulley as disclosed in Hoback, the compressive
engage~ent of the elasto~eric teeth against the bottom of the pulley
groove results in a substantially perm2nent deformation of the belt
tooth. This d~fofmation is acceleraeed at elevated operating ~em-
peratures such as occur in automotive applications. The deformation
results in a significant permanent decrease in the tooth beight.
The deformed teeth no longer support the tensil~ member as desired
by Hoback. Subsec;uently the same wear pattern develops ;n the toothed
belt and pulley drive according to Hoback as in the too~hed power
'
transmission configuration according eo the Hiller patent.
5~
It has been found in accordance with the present inv~ntion that
the land wear problem of the Miller and Hoback patents can be sub-
stantially reduced. The reduction results in an increase in the
operating life of the toothed belt. Furthermore, in accordance ~lith
the present invention the toothed power transmission drive has improved
belt 1ife, even under severe operating conditions such as elevated
temperature and torsiona) vibration environments. The improve~ent is
most beneficial with small pulleys.
The present invention is a pulley for use in conjunction with
a flexible drive belt, such as disclosed in Miller.
As used herein, the terms describing the features of the present
invention are defined in the patent to Miller.
The present inventlon reduces the problem of land area wear
between belt teeth by changing the pulley configuratio~ to increase
the contact area between the pulley tooth tips and the land area of the --
belt teeth. It further relieves the pressure in the belt tooth lænd
area by providing support ~or the belt tooth in the pulley groove.
, .
The pulley of the present invention is a non-conjugate form of the
b~lt. Each of the pulley grooves is form~d by a substan~ially cir-
cular arc ~onnecting the tips of adjacent pulley teeth. The belt teeth,
as the belt travels around the pulley, is Tn compressiveengagement
with the pulley groove. Each of the pulley tooth tips has a longitu-
dinal cross-sectional contour generally as disclosed tn Miller and
is partially composed of two substantially circular arcs having centers
of curvature displaced from each other. The centers of curvature ar~
each 10cated on the same side of ~he tooth tip as its respective arc.
The tooth tip arcs ~re connected by a line segment which is substantially
straight or sllghtly curved. The line seqment defines the pulley
-- 3 -
tooth tlp wldth. In accord~nco wi~h th~ pro~ont Inv~nttQn, tho
s~rf3ce contact r~tlo of tho ~olt tooth wldth to th~ lln~ ~ogm~ne
Is b~twcon 20:1 ~nd 1:1. Tho l~ngeh of thls lln~ s~gm~nt 15 from
5~ to 100% of the width of the belt tooth on the belt wlth which the
pulley Is to be used, and preferably botween 6% and 33% oF the width
of the belt tooth.
Both the cQmpresslve engage~cnt of th~ belt tooth with the
pulley groove and the surface con~act ratio as definecl, d~ act ~ndivi- ~:
dually to reduce land wear ;n the b~lt. However, in combination,
as ~oro fully descr;bed herein, they reduce l~nd wear In the be!t to
an extent greater than the s~m of their Individual effects.
In accordance with its broadest aspect, the present
invention relates to a power transmission system con-
sisting of at least one small diameter toothed pulley in
combination with a flexible toothed belt having belt
teeth of cross-sectional contour substantially composed of
two su~stantially circular arcs, the pulley teeth being com-
posed of tip portions connected by cavity portions, each
tip portion having a longitudinal cross-sectional
contour partially composed of two substantial circular
arcs, said arcs having centers of curvature displaced
from each other, the center of curvature of each arc
being located on the same side of the center line of said
tip portion as its respective arc, the outermost portion
of each toot,h tip joining the two arcs forming a line - . :
segment, the length of the line segment being from 6~ `~
to 33~ of the width of the belt teeth, and the distance
between the outermost portion of the pulley teeth cavitles
and the innermost portion of the pulley teeth cavities
being less than the depth of the belt teeth which are not
in contact with the pulley.
,
., ", .. .
,~, .
. .
BRIEF n~s~cR~ T~oh~ ~ Y~
__
The invention wlll be more clearly understoot from the following
description read together with the drawlng in wh;ch:
Fig. 1. is a long;tudinal cross-sectional view 700king trans-
versely of the preferred embodlment of the cooperatlng pulleys in
accordance wlth the present tnvention Tn ~ngagement with a belt to
form a positive drive system;
Fig. 2. ts an enlarged fragmen~ary longitudlnal cross~seGtional
vtew of the pulley in accordance wlth the preferred embodtmKnt;
Fig. 3. 1~ an enlarged fragmentary longitudinal cross-secttonal
view of the pulley of Fig. 2 superimposed on a view of a corresponding
conjugate pulley accordlng to the Miller patent; and
Ftg~ 4. is an enlarged fragmentary longttudTnal cross-sectional
vtew of the pulley of Ftg. 2 tn m3tTng engagement with a belt constructed
in accordance with the Miller patent under a no~load condition.
D~ETAILED DESCRIPTION OF THE l~iVENT!ON
As seen in Fig. 1., the eldless belt 10 engages the driving and
driven pu11eys 11 and 12. ~eit 10 Is provided with a tensile me~ber 13
ccmpr;sing a plurality of turns of a contlnuous stra~d of ftlamentary
_ 4 (a) ~ :`
',. ' :.' .
,.. j ~ ~
~.
.~ matcri 1. The tcnsTle member 1~ car.ies substantially ~he cntirc
workin9 load ;mposed on the belt 10, and up to the max;mum load for
whtch the belt is designed, the sensile member 13 is substantially
Inextensible. The above ci~ed Case and Miller paten~s may be con~
sulted for a mor~ detailed description of the princ~ples of this ~ -
general class of ~o~thed belt and pulley system. The entire contents
of the Case and Miller patents are each incorporated herein by
reference. The belt further includes a backing layer 14 and a
protective jacke~ (not shown) extending over the entire ~oothed sur-
face of the belt. A thin 1ay~r of elastomeric or other material
(not shown) between the jacket and the t~nsile member 13 may be added
to improve adhesion Tn the land areas of the beltD The belt may be : :
made in any one of a number of ways, but i~ is pre~erable to use the
~ethod described in Canadi~n Patent ~o. 637,926 to W. S~m ra
An alternative method for m~nufacture is described in the above
cited Case patent.
The pulleys 11 and 12 of Fig. I ac seen in Fig. 2 eaoh compr7se a
hody portion 20 having ourvilinear teeth 21 separated by curvilinear
cavlties 22. The tooth tip 23 viewed in 10ngitudinal cross-section
has an outer configuration which is composed of two circular ares
24 ant 2~ having displaced centers of curvature 26 and 27 displaced
from a tooth tip center line 28. Arcs 24 and ~5 have two equal radii
29 and 30 with centers of curvature 26 and 27 displaced equal amounts
on opposite stde of the center line 28 of the tooth 21 but on the
same stde a5 their cnrresponding arcs. Both centers of curvature are
within the pulley tooth. The non-intersecting arcs 24 and 25 are
connected by a line 5e~ment 31. The arc 24 extends from potnt A to
polnt B. The arc 25 extends from point C to point D. The centers 26
and 27 lie at equal distances fram a tangent to the outside d;ameter
:,. .
.~ . ~ 5
... ..
of the pulley at the c~nt~r ltn~ 28 o~ the tooth, llo at ~q~al dls-
eances to opposlt~ sld~s of th~ e~nter llna 28 and lle at oqual
radial dista~ces from the center of the pulley. The line segment 31
is part of an arc of a circle having a radius drawn from a center
Iying on the extension of the center line 28. The center of curvature
of line 31 may lie on center line 28, i.e. within the body of the
pulley. Alternatively the center of curvature of line segment 31
may lie on a~ extensTon of center line 28 which is outside ~he body
of the pulley. The line segment 31 is shown as being a straight line,
.
but n~y be concave or convex wlth respect to the body of the pulley.
Fig. 3 showc an enlarged fragmentary longitudinal cross-section
vlew of the pulley of Flg. 2 superTmposed on a view of a corresponding
conj~gate pulley according to the Miller pa~ent. ThTs figure emphasizes
the difference in the longitudinal cross-sectional profiles of the
respective pulley grooves and teeth. FTg. 3 shows the cavity 22 of
this invention which is formed by the arc of radius 32 at a center
of curvature 33. The arcs 24 and 25 which partially form the pulley
tooth tTp of this 7nvention ~re generated by respective radii 29 and 30
havTng center~ of curvature at 26 and 27. The line segment formTng
the outermo~t ~ortion of the tooth tip and connectTng the arcs ~4 ~nd
25, accordTng to the ~nvention, has a length equal to the distance
between points ~ and C. The arc forming the cavity 22 may intersect
with ~he arc~ 24 and 25 of this invantton at points A and D.
in contrast~ the conjugate pulley according to the Miller patent,
ha~ a cavity 41 formed by arc having a radius 40 and a center of
curvature 39. The arcs 46 and 47 which partia~ly form the ~ulley
tooth tip according to the HTller p3tent are generated by respective
radii 44 and 45 having centers of curvature at 42 and 43. The line
segment forming th~ outermost portion of the tooth tip and connecting
the arcs 46 and L7 has a length e~ual to the distance between poin~s
.
'.
- 6 -
a~
E and F. Th~ arc forming the cavlty 41 ;ntersects the arcs 46 and
47 at points G and H~
The length of the line segm~nt BC of the present Tnventlon is
greater than the length of the line segment EF of the pulley tooth
~ip according to the ~iller patent. The centers of curvature 26
and 27 of the present 5nvention are displaced on opposite sides of
the can~er line 28 a distanca greater than the displacement of the
centers of curvaturè 42 and 43 of the pulley tooth tip according eo
the Mi11er patent. The cross-hatch~d area 48 represents the addi-
tlonal material present in the pulley groove and ~ooth tlp profile
according to this Tnventlon as compared to the same profile according
to the Miller patent.
Fig. 4. is an enlarged fragmentary longitudinal cross-sectional
view of the pulley o~ Fig. ~ in ~ating engagement wlth a belt con-
s~ructed In accordance wlth the Miller patent under a no-load con-
di~ion. in longltudinal cross-sec~lon each tooth 49 of the belt 50
is composed of two circular arcs 51 and 52 of equal radius 53 and 54
Ineersecting at a polnt 55 on the center line 34. The centers of
curvature 56 and 57 from which the arcs 51 and 52 are drawn are iocated
on a ITne 58 as shown in the Miller p~tent. The extent of th~ arcs
51 and 52 ts such that they extend to the line 58. The centers of
curvature 56 and 57 for the arcs 51 and 52 are displaced on opposite
sides of the center line 34 from their corresponding arcs by an a~ount
that Ts generally equal to or less than 10% of the radlus of curvature
of the aros 51 and 52u
The depth of the groove between adJacent pul1ey teeth in the
pulley of the inventlon is less than the depth of the groove in the
conjugate pulley and is thus less than the depth of a t~oth of the belt.
This Ts shown clearl~ In Fig. 4t where the tlp of the belt tooth Is
shown as overlapping the base of the p~iley groove. Obviously this
will not happen in practice and the belt tooth wlll be distorted
due to contact with the pulley groove. It is preferred that the :.
pulley groove depth be between 1% and 15% less than the belt too~h depth.
In designing a drive according to the invention, Tn addition to
the criteria already de~cribed, it is desirable that the surface
contact ratio of belt tooth width (th~ width represented by the
length of broken line 59 between the points J and K in Fig. 4) to
the length of the line segment 31 (the wtdth represented by the length
of the llne BC in F~g. 2.~ be between 20:1 and 1;1 and desirably
between 15:1 and 3~
The cross-sectional confTguration of cavity ~2 has a radius 32
much larger than radil ~9 and 30 and has a eenter 33 wh7~h is outside
the pulley body and is on a center ltne 34. The centers of radii ~;
26, 27 and 33 are located on the same or slightly spaced clrcles 35
and 36 which are concentric with and within a circle connecting the
outermost line segments 31 of the tooth tTps. The circles 35 and 36
are spaced radially inwardly from this circle a distance equal to or
less than 30 per cent of the total tooth depth. The total tooth depth . ~ ~ :
is the radial distance between the intersectlon of line segment 31
and center line 28,~;.e. a po;nt on the addendum 37 and a circle con-
necting the innermost points of cavtty 22, The Tnnermost point of :
cavity 22 is at the intersection of the arc generated by the radius
32 and the center Itne 34, i.e, a point on the dedendum 38.
The cavity 22 Ts formed by an arc of a circle having a radlus 32
2~ drawn from a center 33 on center line 34. The arc for~ing cavity 22
may Intersect the arc 24 on one side of the overall pulley groove
profile and intersect arc 25 on the other side of the profile. The
profile cf the pulley groove ~rom the intersec~ton of line segment 31 ~
and eenter line 28 So a corresp~nding intersection of the next adJacent . .
3 tooth Is repeated around th~ circumference of the pulley go deflne
.
- ~ 8 - ;
. .. . ~
the other teeeh and grooves4
The ~otal depth of tho pullsy gr~ove 13 ~qu~l to th~ dlstanc~
measured along center line 34 between the Tntersections of llne 34
and the addendum 37 and the dedendum 38. As shown in ~ig. 2., the
to~al depth of th~ pulley groove Ts tho sum of the length of the
radius 32 and the distance d. Preferably the total depth of the
pulley groove is not more than IS% less than the depth ~ ~he belt
tooth which en~ages wTth the pulley groove. Consequently ~he belt
tooth may be in compress7ve engagement with the cav;ty 22. Alter-
natively the dimensional relationship between the p~lley yroove depeh
and the depth of the bèlt tooth may be as describad Tn the patent
to Mlller.
In designing the pulley groovo and tooth form, It is desTrable
that the arc formTng ths cavity 22 smoothiy intersect with the arcs 24
and 25. However, ia order to provide a smooth transition from the
arc forming the cavity 22 to the arcs 24 or 25 forming a portion of
the p~lley tooth tip, it may be desirable to provlde a connecting
line. This connecting line may be sTmilar to lino segment~31,
EXAMPLE
~ In order to compere the performance of power transmisslon systems
having pulleys with the novel dlmansional relattonship of this
tnventton wtth those having convsntional dlmenslonal relationships,
the following procedure was followed. Several positive or synchronous
drlve belt samples were manufactured by conventlonal methods ustng
conventional matertals well known in tho art. All the belts were
formed of a neoprens rubber compositton having a nylon fabrtc facing
on the belt teeth, and tnc~uding a tensile member of fiber glass
cords disposed substaneially on ~he dedendum line of the belt teeth.
The belt samples after manufacture were dynamically tested on toothed
3 pulleys of appropriate dimsnsion and con~Tguratton as will be
here;nafter described.
Three power transmission syst~ms werè tested. These combina-
tions are identified as A, B and C: -
Combination A comprises belts and pulleys manufactured strictly
in accordance wtth the Miller patent. These belts and pulle~s are
sold commercially by UNIR~YAL, Inc. as its 8 mm, pitch Powergrip HT~
Belt and Pulley system,
The elghteen belt samples produced had the fo11Owing dimensTons
as measured in the longitudinal extent of the belt between the pulleys:
a pltch between belt teeth of 0.315 inches; a belt tooth width of 0.260
inches; a distance between the belt teeth of 0.055 inches; and a
belt tooth depth of 0.135 inches. The belts were 15 mm. wide and
936 ~m. in pitch length.
The pulleys had a tooth depth of 0.142 tnches and were substan-
. .
tially conJugate to the belt teeth~ As taught in the Miller patent,
the tooth tips had a longitudinal cross-sectional contour composed
of two circular arcs conneceed by a line segment. The line segment -
length was O.all inches. In ~he resul~ing power transmission system
the line segment is 4.2% of the width of the be1t too~h.
Combination ~ comprises a poh~r transmissTon system exactly as
found in Comb;nation A except that the belt tooth depth had been
increased by 0,012 inches (8.9%) to 0.147 inches, This corresponds
to the teachings in U,S, Patent No. 4,037~485 to Hoback. Seven belt
samples were made. ~ ~ -
Combina~ion C comprTses a power trans~ission system in accordance
wTth the present invention. The belt has the same dimens;ons as the
belt in Combination Ao The pulley tooth had a depth of 0.130 inches;
the pulley cavity had a radius of curvature of 0~106 inches. Th~
line segment length was G.020 inches.
Table 1 is a comparison of the ~y dim~nsions of Ccmbinations A,
1 0
B and C and the resultTng compression of the belt teeth.
TABLE I Comblnations
A B C
eelt Tooth Width .Z60 .260 .260
~elt Tooth Depth .135 D147 .13
Pulley Tooth Depth .142 .142 ~130
Line Segment Length .011 .Oi 1 .020
Line Segment Length 4.2% 4.2~o 7.7Yo
(as percentage of belt
tooth width)
Percent Belt Tooth Compression 0% 3.4% 3.7%
(Belt Tooth Depth-Pulle~ Tooth Dep~th)
Pulley Tooth Depth
Each belt sa~plo was mounted on a dead w~ight~flex tester havlng .,
a two pulley arrangement consisting of a drlver and a driven pulley
each having an outslda diameter of 2.160 7nches. The drtver pulley
as operated at 350 rpm wTth a f~rce between pulley shaft centers of
250 Ibs. The test was conducted at ambient te~peraturc. The belts
,
were tested ts failure unless o.therwlse tndicat~d. The laps~d tTme
.
to ehe nearest hour of each group o~ belt sa~ples to failure ;s
shown in Ta~le~TI.
TABLE I I
Llfe on Test, Hours
. ~ .
_A B _ _ __~
83.459.0 298.~ (test suspended) :
46.9117.2 690.7
65.599.1 18706
75.7120.8 23304
Average 65.1 99.0 34501
'
The test was repeated 7n an environmental chamber held at 190F~
Th~ results are shawn in Table 111
TABLE ~
Life on Test" H_urs
A a c
_
93.0 118.2 lg~.2
~7.~ 98.5 105.7
82.~ 117.5 1~9.3 ::
.4 _ ~LZ! ~
,
Average9i.6 111.4 162.0
The results in Tables 11 and 111 clearly show that the pulley~
belt Comb1nation C having the pulley to belt relationship of this ~;
invention provides a significantly improved belt life over Comblna-
tions A and B. This 1mprovement was shcwn on the tests made at ;~
amblent temperature and on the tests ma~de on accelerated tests at
190 deg. f.
The only signlficant varlable in ~he comparative teats was the
relatlonship o~ the pulley dimensTons to the belt dimens10ns. Comr :
btnatlon B had belt teeth~that were greater In depth than th~ depth
of the corresponding pulley grooves~ Combin~tion C also had belt teeth
.
that were grsater In~depth than the d~pth of the correspondlng pulley
grooves. However ~the line segment length.of the Combinatlon C
pulleys was substantially greater than that of the line segment lengths .
of the Combinatlon A or the Combinatlon B pulleys. The pulley of the
prlor arc Comblnatlons A and B had tnadequate line segment lengths
causing the belt to be:subjec~ed to excess stress on the tensile
.
members. This excess stress caused abraston of the belt:betw~#n the
belt teeth and the failure resulted prim3rlly from excessive wear tn
th7s area.
in the pulleys o~ Combination S ehe llne segment length was of
,
,
':
, ~
- 12 -
:
su~ficient l~ngth to distrtbute the load over a larger area and thus
reduce the stress in the araa betwoen the belt teeth. Consequently,
wear in the area of the balt between the teeth was reduced, and ~he
belt life was signlficantly increased at both ambient and e)evated
tempe rat ures .
The pulley described herein may be uied in combination with
toothed belts other than that dtsclosed In th~ pa~ents to Case~
M~11er and Hoback. Tho longitudln21 cross^seceTonal con~our of the
Jndlvidual belt teeth may be trapezoldal~ curviiinear or wedge-
shaped or a comblnation or a modlflcation of these contours9 The
belt may also have ~eeth on both sldes of ehe tens~le member.
While there has been descrlbed what 5s at present considered to
be preferred embodimants of thls Tnvention, it will be obvious to
thoseskllled in the art that various changes and modiftcations may be
~ade thereln w7thout departing fro~ the spirlt of the inventlon, and
it lsr therefore, ai~od to cover all such changes and mociificatTons
as fall withln the scop~ and spirtt of this Invention.
~ 13 ~
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