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Патент USA US2404378

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> July 23, 1946.
_
H. s. HOFFAR
2,404,373
ANTIFRICTION WORM ‘DRIVE
Filed Aug. 1, 1.944
2 Shéets-Sheet 1
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INVENTOR.“
Henry S. Hoffar
VBYVI W,‘
ATTORNEYS
‘
July 23, 1946;
‘
H_ a HQFFAR
‘
2,404,378
ANTIFRICTION WORM DRIVE
Filed Aug. 1. 1944
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2 Sheets-Sheet 2
4.27 .
4
6
¢.ar Angle-Dayna
mm
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1.5
90
45
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8
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/ 5,
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Warm Angle-Degrees
Jig. 6‘, " INVENTORL' Y
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‘Henry 5. Hoffar v
BY I
4W
ATTORNEYS
21,404,378
Patented July 23, 1946
UNITED-STATES PATENT OFFICE
2,404,378- r
ANTIERICTION WORM DRIVE '
" Henry S.‘ Ho?far, Vancouver. British Columbia,
Canada, assignor to The Cleveland Pneumatic
Tool Company, Cleveland, Ohio, a corporation
of Ohio
Application August 1, 1944, Serial No. 547,579
16 Claims. (o1. 74-458)
1
2.
This invention pertains to antifriction worm
conditions will be present ‘each to a lesser degree.
drive mechanism, particularly that type which
It has been proposed heretofore, in an anti
friction worm drive, to utilize a cylindrical worm
The resultant effect, however, is virtually the same
amount of sliding friction between the parts.
Such friction also tends to crowd together the
balls moving toward the worm center and to
spread apart the balls moving away from‘ the
about which bearing balls circulate, and which
worm center, which also increases the friction.‘
is adapted for incorporation in automotive steer
ing gears.
7
balls engage complemental grooves of a gear sec
tor. Such antifriction worm and gear mecha
When a cylindrical worm, as shown in Fig
ure 8 of my prior application, is used, onlya
nism is shown, for example, in Figures '7 and 8 10 single' row of balls is in contact between the
of my patent application SerialNo. 517,927, ?led
Jan. 12, 1944. In that instance the balls in only
worm and Worm wheel ‘at any given instant, so
that the unequal and antagonistic movement of
a single row engage the worm gear or sector at
balls engaging different gear grooves, as described '
any given time.
above,‘ does not occur. In this instance, how
It has further been proposed, as illustrated in 15. ever, since the periphery of the Worm is notex
Figures 11 and 12 of my aforesaid patent appli
actly complemental to the periphery of the worm .
cation, for example, to utilize in such a combina
wheel, the interengaged balls are in closest con
tion a, worm having a central portion of smaller
tact with the grooves of such members when
size than its end portions, so that the concavity
disposed‘ in that axial plane of the worm gear or
of its periphery inan axial plane would corre 20 gear sector which is perpendicular to the rota
spond to the peripheral convexity of the worm
tive axis of the Worm. When the balls inter
gear or sector in a plane perpendicular to its axis.
In such an arrangement at least two, and at
times perhaps three, rows of balls would be inter
engaged between the worm and gear.
The principal advantage of using an antifric
engaged between the worm and Worm gear are I
spaced appreciably from either side of this plane
they do not ?t closely in the groove of either ele
25 ment, because the bottoms of such grooves are.
spaced farther apart than are the bottoms of
tion worm and gear combination is the increased
such grooves in such axial plane of the gear.
e?iciency of the drive resulting from the reduc
tion in friction. Minimum drag can only be ob
Consequently the play or backlash between the
worm and ‘gear becomes progressively greater as
tained if all sliding friction between the worm 80 the load carrying balls move farther away from
and gear or gear sector is eliminated, and only
such plane.
'
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rolling friction is present. In a concave type of
It is therefore the principal object of my pres
worm, therefore, such as disclosed in Figures 11
ent invention, to provide a worm and gear are
and 12 of my aforesaid application, maximum
rangement in which only a single row of load
e?iciency is not obtained because sliding friction v35 transmitting balls is interengaged between such
is not completely eliminated.
members at any given time, so that no sliding
Although the balls midway between the ends
friction will be created either between any balls
of such a concave worm, which are closest‘ to its
and the Worm grooves, or between different balls
because of their rotation at different speeds, nor
at the same speed as the balls nearer one end 40 will any resistance to movement of balls toward
of the worm, and hence farther from its axis of
the worm center occur.‘ Since there will be sev
rotation, the peripheral velocity ofthe worm por
eral balls in such single row interengaged be
tion engaging balls farther from the worm’s ro
' ‘tween the worm and worm gear members it is
tative axis is greater than that of the portion
necessary, in order to eliminate all sliding fric
closer to the rotative axis engaging ‘the balls 45 tion between‘ these balls, to provide alternate"
centrally of the worm. Consequently the worm
spacer balls separating the load carrying balls
groove portions near each end must slide on the
in the manner disclosed in my Patent No. 2,298,
axis of rotation, must move along the worm groove
balls engaged with a gear groove or rotate them
faster, while the balls centrally of the worm in
011, issued Oct. 6, 1942. It is preferred, how
ever, that the relationship between the diameter
contact with the gear will slide on the worm 50 of the balls and the thickness of the worm gear
groove or rotate more slowly than the outer balls.
be such that at least two load carrying balls will’
Sliding friction will therefore occur between the
be engaged with a single groove of the'worm at
central or the outer balls and the worm groove,
all times.
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‘ or between the central and .outer balls rotating
Another object of my invention is to maintain
at different speeds, or more than one of these 55 a close ?t of the load carrying balls with both
2,404,378
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4
the worm groove and the worm wheel groove
in the grooves of a worm and worm gear is much
more pronounced where the worm gear is rela
r
regardless of the position of such balls axially
of the worm relative to the axial plane of the
tively small, its radius being not appreciably
worm Wheel Perpendicular to the worm’s axis.
Such object is accomplished by forming the worm
being less, as in the automotive steering gear as
groove so that the distance between-its bottom
and the .rotative axisof the worm vincreases pro
the gear travelsthroughwsuch a large angle each
greater than that of the worm, and perhaps even
sembly illustrated.
The reason .ior this is that .
gressively from such Worm wheel plane centrally
time the worm makes a complete revolution. In
of the worm in each direction through a worm
the typical instance selected the gear moves 20
V10
convolution of 180 degrees, and thereafter such
distance does not increase ata rat-e s-uf?cien-t ‘to
.maintain a close ?t of the balls in the worm‘ and
worm wheel grooves, and plieferablygactually.de-L
degrees for each revolution of the worm. The
‘pitch ‘of aworm helix is slight, and consequently
the distance between allportions of any given
‘worm'gear groove and the axis of the worm is
nearly un-itorm if the worm gear periphery has
More speci?cally it is anrobject of my invention 15 the proper ‘concavity axially to embrace the
creases.‘
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.worm, as is customary. The average spacing be
tween the Worm’s ‘axis and the bottom of a worm
to incorporate such worm and gear mechanism in
an automotive steering gearffor which “applica4
tion it is important that there be no backlash‘b'e
gear groove through which that axial plane of
'the worm gear perpendicular to the worm’s ro
tween the steering column, on which the worm is
20 tative axis passes, and'the average spacing .be
mounted, and that portion of the steering appa-v
ratus'towhich the norm ‘gearsectorvqr quadrant
is connected. ' Otherwise undesired’ looseness of
the whéél'mounting 'mayoccurl ,At the‘ same time
it’ is ndefs'irabletthatlthe ef?cicncy'jof'such .mecha
nismib'e as high 'asposs'ibleto reduce the turning.
tween the worm’s axisand the .bottom of .agear
groove spaced 10 degrees .fromsuch groove, how
ever, are appreciably different. Whileall the
balls in any single groove, whicharelof the-same
25
trucks and ,bus'ses.
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>A
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To utilize my, novel worm'an'dgear mechanism
most effectively it"is a "further object to enable
the relationsmpbrme worm and ‘worm gear sec-‘
tor't'o'be adjusted re'latively'within close limits,
size, will bear substantially vequally against both
the worm and gear, therefore, whether the Worm
is of the cylindrical type or is concave axially, .the
balls in ‘gear grooves spaced apart a substantial
effort “which must‘ be exerted by the driver on the
steering wheel, especiallyin installations for large
' angle, for example 10 degrees, will not ‘bear simi
so
larly in .the worm and gear grooves if the worm
is cylindrical.
' [
Figures 1 and 2 illustrate the worm .l and the
worm gear sector 2 in a relationship in whichthe
gear groove is intersected by an axial plane of the
so that'the proper clearance between the bottoms
of the‘fworm'and gear sectorgrooves may be es
tablis‘hed, and .maintained‘ev’en' though the parts 35 gear perpendicular to the Worm’s axis. In this
may become Worn" to a greater or" lesser degree.
In ‘fact, to ‘insure that no play yvilloccur'be
tween the bearing balls and either member en
gaged‘therébyLit is'ah objector my invention to
grip’the'loalls‘between such members by resilient
pressure thereof toward each other','when desired,
The degree of such resilient pressure maybe rege
ulate‘d as required.
particular instance the gear sector groove thus '
,located happens to be its central groove, but it is
immaterial which one of its grooves is thus dis
posed as'far as the engagement-of balls I0 is con
40 cerned. "With the worm and gear .in this particu
lar relationship-they may ‘be spaced so that the
load carrying 'balls'bear'properly and without ap
'
‘Additional features of my invention, and more ,
particularly of‘my preferred structure‘intended '
precia'ble ‘backlashin fthegrooves of both elements
regardless of the contour of the worm. .Myiinvené
tion enables such engagement in the .grooves‘of
for‘usein automotive steeringgears, will'be 'menf
both thegear and worm to ‘be preserved in auro
tioned'in the following detailed description of the
embodiment ‘illustrated in the accompanying
drawings. Various“ changes may, of course, be
tative positions of the worm.
elevationthe-shaft carrying the worm gear.
gear sec'tor'2 will be rotated througha'compara- .
’
,
It 'will‘be understood, of course, that'when al
ternate large and small ‘balls are employed, as
made in ‘the construction within the scope of my '50 ‘taught in my aforementioned Patent- 'No.
2,298,011, ‘which is‘ preferred, onlyithe larger .or
invention as de?ned in the appended claims, and
load ‘carrying halls will "be thus engaged. ‘As
it may‘befincorporated ‘in worm and'gear mecha_
shown in‘Figure ‘2, however, the ball size and
nisms‘ for other uses than in steering gears.
worm gear widthshould‘berelated so 'thatat least
‘Figure ‘l is a sectional view through .an autol
motive steering gear assembly in which the worm 55 two of such ‘larger 'balls will always contact the
worm gear groove, to provide proper distribution
is in elevation. 'Figure 2 is a sectional view
7
through the same ,mechan'ism’taken perpendicu; " of the load.
As the worm'l is rotated about its axis the worm
larly to' the section of ‘Figure .1 and showing in
tively small angle. In the present instance the
pitch of the worm and the radius of the worm
worm and worm gear sector mechanism similar
gear sector have been selected so that .rotationof
to Figure 2, but showing ‘parts broken away and
the worm through an angle .of'lB degrees swings
' illustrating a modi?ed'form of mounting. Figure
the sector through an angle of .1 ‘degree. Hence
4.-'is a sectional view through'the same device
65 for each complete revolution or the worm thegear
‘taken on line 4—4 or Figure 3.
a g
' ‘
sector '2 will be ‘iswung through anang‘le .o‘f'f2.0
Figure :5 is a " fragmentary sectional" view
Figure 3 is a transverse sectional vieWthroujg'h
7 "through a worm of the'type shown in Figures 1,
2 and 13., provided with a di?erenttype of by-pass
passage through the worm.
‘Figure ,6 is a graph illustrating, 'ona greatly
enlarged scale, the developed contour'of ‘the worm
groove with relation to ‘the worm’s rotativelaxis
measured in degrees of worm and worm‘gear'ro
degrees as mentioned.
.
a
“If the root diameter of the worm were "uniform
throughout its length, following conventional
practice, the spacing ‘between the bottoms of a
given gear sector groove and of the adjacentpor- '
tion of the worm groove would increase as -.'the
gear ‘sector rotated ‘in either, direction Ifrom ,the
. centered position of ,one io'fji‘ts'ball engaging
tation.
.
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' The problem of maintaining a close ?t of "balls 75 ‘grooves shown inl'Figure 1, in which such‘ groove
2,404,378 .
6
so that for other degrees
intersects or ‘substantially coincides with the axial
plane‘ of the gear sector which is perpendicular
tortheaxis of worm I.
,
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(l—cos a)=(1-—cos 1*’)a2 '
Therefore, substituting in the above equation,
,; As the worm, continued to rotate for swinging
the sector in the direction indicated by the arrow
Y—K=R(l—cos 1°)a2
in Figure 1, for example, this distance would in
crease until the worm had rotated through ‘sub
stantially 180 degrees. At that time the load
would be transferred from the balls at the left
in Figure 1 to the balls at the right, so that the
forces between the parts previously transmitted
through the central grooveof the gear sector‘
would then-be transmitted through the groove
next ‘on- the right ofsuch central groove. The
bottom- of this groove,>as, rotation of the, parts in
I
Proof that the quantity ‘(l-cos a) varies in pro
portion to a2 may be a?orded 'bycomparing cal
culations of (1-cos<'a) and (1-cos 1°)a2' for
angles of worm gear change from‘ .1 degree to 10
degrees.‘ These comparative values are listed in
the following table.
Worm gear sector degrees
(1-005 41)
(1—cosl°)aI
the same direction continued. would approach
the, worm axis until such groove reached the posi
tion of the central wormv groove shown in Fig.1.
0. 0001 523
. 00061
The spacing between the bottoms of the worm
and gear grooves would not changegreatly. dur
ing swinging of a gear sector groovethrough 10
degrees either side of its central position, but the
variation would be sufficient to permit play in
the parts, even though there was no play when
the .worm gear groovewas centered relative to
the worm“ To eliminate this play as the worm
and gear sector rotate conjointly, the contour of
the worm groove bottom may be shaped so that
the spacing ‘between the bottom of the ball receiv
ing gear sector groove and the bottom of the 30
worm groove portion adjacent thereto will ‘re
vThis equation is the same form as the equation '
main constant during rotation of the gear through
for a parabola. related to rectangular coordinates
an angle of 20 degrees, corresponding to a com
plete revolution of the worm, provided that such
as follows:
X2=4f(Y-K)
gear angle is substantiallybisected by the axial
plane of the gear perpendicular to the wormlaxis.
'
Where X and Y are the coordinate values, .
This result is accomplished by forming the
f is the distance between the focus and the apex,
worrngroove of decreasing depth, or increasing
which is constant for any selected parabola,
the spacing between the bottom of the worm
groove and the worm’s axis, each side of the 40 and I
K is the o?set of the apex from the X axis. \,
central portion of the worm,'namely, that por
tion which is intersected by the axial plane of
It will be seen by comparing the values of
the gear sector perpendicular to the worm’s axis.
(1- cos a) with those of (1—cos 10°)a2 in the
The rate at' which the groove depth decreasesor
above table that for any angular departure from
groove bottom spacing increases is not uniform,
but on thercontrary, such spacing is found to in:
crease almost exactly in proportion to the square
about 7 degrees, the difference between the values
central position of a worm gear groove up to
Y—K using (1-005 a) and the equation for a "
of the gear segment’s angle of rotation for small
angles.
curve of true parabolic shape ofrdeveloped worm
root curve is less than .00001 R. Hence where
the worm gear pitch radius is 1 inch the Worm
_
‘For any given angle of worm gear movement
the bottom of one of its grooves in the central po
sition of closest approach :to the worm recedes
root would conform to true parabolic shape with
in one one hundred thousandth of an inch for
an angular worm gear movement of 7 degrees.
from the Worm’s axis a distance equal to the
difference between the root radius of the gear
Even for an angular gear. movement of 10 degrees
sector and such radius multiplied by the cosine 56 the difference in such calculations is only about
o'f/such given angle through which the gear sector
.00004 of‘ an inch, which is negligible. Conse
is rotated._ To ?nd the root radius of the worm
quently we may assume that if the developed
curve of the worm groove bottom is of parabolic
shape, for small angles of worm gear movement
the ‘spacing between the bottoms of the worm
at any point this relationship ‘may be written
mathematically as follows:
’
Y--K=R-R cos a=R(1--cos a.)
gear groove and the adjacent portion of the
where '
worm groove will, remain constant.
Y is the root radius of the worm,
K is the minimum root radius of the worm located
‘ in the axial plane of the worm gear perpendicu
If, on the other hand, the bottom of the worm
groove, when developed, were merely a straight
line, as in a conventional cylindrical worm, in
stead of a parabolic curve, the worm gear groove
lar to the worm’s axis,
'
the worm groove a distance of .01523 of an inch,
Since for small changes in angle a the change
in the factor (l-cos a) is found to be propor
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(1—cos a) =C'a2
where C is a constant. Forc=1 degree,
my:
5.‘
.
.‘ , (1:._.cos 1e)"='c
.
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bottom would have receded from the bottom of
R is the root radius of the worm gear, and
a is the angle of rotation of the worm gear.
tional to a2,
65
'
or approximately 1/64 of an inch, if the root di
ameter of the worm were one inch, during a. 10'
degree angular movement ,of the worm gear
groove from its central location of closest ap
proach to the worm axis. This variation would
, allow appreciable backlash in the mechanism,
which my invention eliminates.
shorter-s
F8
torzgroovesiarelprovided- at eacheside sdiiitscnen-i
In Figure 6 of the drawings the-nevelopedzcon
tour of the .parabolic-wormggroove bottom is
shown on a greatly exaggerated scale.’ In de
termining this developedl'shape ~of the worm
groove bottom-iei-therioneofgtheiollowing equa
tions maybe used at the will of the designer:
trail-groove. .‘During~one>~complete' revolutioniiof
the worm from the position r's'howniinli-Fiigmie'iil
it will :retur-n-‘Lto ithe identical-position, 'Poutiithe
balls 1 will ‘engage rit'he worm --gea‘r ig-roovesadia- .
centdto' its center-groove:either ongtherir‘i-g" t or
on the_ ‘left depend-ing uponithe direction-in which
thexwormiislrotated.
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‘If the engagement ‘of 1balls 1 I11) in" ‘the grooves
_
10
:In applying either of these formulasf'it-wil-ljbe
understood 'that'the maximum ‘value of the gear
sector angle a ‘will be that through which such
gear. sector is moved ‘by one-‘half a revolution of
the ‘worm. 'This'is necessary so that only one
gear grooveiwill be engagedby ‘balls at
of dboth theworm andfithe tgearisector is alto be
maintained constantl'throughout eachrevo'lution
offthe worm,=as describediabove, ‘i'rbes'tmdvantage
of such ‘operation-can ibe 'taken'ior-rly ‘if ~‘sudh=-en-‘
easement
extremely accurate. 1As ‘previously
pointed. out, this *is =particularlyidesirab~lelin *the
case led .an automotive steering *gear, where an
playiinlthe ‘parts shouldllbe avoided. “The Worm
any fgiven time-except perhaps ‘for a brief in-v
l “ islsheldi?xedbetweenvtapered rtwutiiric’tion"bear;
stant du'ring'which balls are being ‘disengaged
lugs-5H Jtar-rd t2 *which-uaoe‘iin-=opposite vdirec
from 'one wormgear grooveandengaged with an 20 tions. - iOne sot-these bearingssuoh as >1 2-,'~'is3seat-1
adjacent groove. Duringsuch transition,_ how
ed in a shouldered cavity ‘in-"the casingfilgwhile
‘the other hearing ll V1 "is held=1in<place<by ‘a- ‘cover
ever, the balls in the two gear grooves will en
gage worm portions of equal radii, so that no "re
#3 boltecli-to'the-‘casing. The-shaft ‘fl-“carrying
sistance to movement of the balls, tending to
the worm I extends through a bore :I'=5~‘>‘in the
..cause sliding Jfriction, ‘occurs. The maximum 25 casing, so that its-criterend ‘is “accessible *for
value of worm gear angle a will, of course, depend
rotating the worm. ‘This shaft may constitute
upon the pitch =of the‘worm grooveandfthe worm the steering column “of Jan ‘automotive’ vehicle.
gear radius.
The worme'gear sector/*2 is ‘mounted on‘a shaft
For angles of worm gear movement a greater
22, which may ibe'supported iby- spaced fantii‘ricé
than that corresponding to a 180 degree rotation
tion bearings ‘23 of‘theneedlefbea?ngiype. ' The
of the Worm the value of Y must be less than
outer end F24 of this (shaft ‘may ‘be spiined ‘and
threaded for attachment to *a-‘s‘teer'ing am.- A
cover 25 ‘bolted to thepasing r‘1H v‘removable for
that which Woul‘dfbe obtained by 'a solution of
either ‘of ‘the equations above, ‘so that ‘the balls
will be released abruptly from the gear groove
accessto thewormegearsector.
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moving away from'aw position centrally of the
wormlas the [balls .engrageiin the adjacent gear
groove moving toward said position. Although Y
might still continue to increase ‘beyond 180 de-'
The worm bearings -H lands‘l'lwvil-l lbe'located
so ‘that ‘the central plane "through the worm'?,
perpendicular to shaft ll-ll,~-cdincides>with theaxis
grees'from the worm center, the rate of increase
inthe location 10f such plane axially of lthe'worm ,
of the gear sec-tor shaft 12/2. A =~smail ‘variation
must be .more gradual than thatlgoverned by the 40 from its center lis'not serious. -‘-'I‘he"b'ea?n'g"'23
above equations; but it 'is‘pre'ferred that‘beyond
suchlworm 'a'ngleithe value of Yiactually decrease.
should-‘however, be located-so 'that‘the' axes'of
shait§22 and warm *I are spaced apart exactly
The ifurther alternative is for”Y to‘remain con
stant above the worm angle of ~180?degrees1-irom
center. ‘For iconvenience the rategof ':Y-.decrease 45
7 may ‘bet-he same as its previous rate-ofgincrea'se,
the {correct distanceito-enable'lthe balls ‘I 0 'to‘ibear
proper-1y~~againstlmth>the ‘worm and'worm gear
sector without appreciable-backlash. "Ordinarily
so thatl'either'of lthe same equationsicould‘begused
to establish this relationship, ‘even ‘ ‘initially, "it "is
necessary'to ' machine the bpar'ts’jwith'greatpare,
by substituting decreasing angles of. az'beyond .10
and'if the parts ‘wear this ‘relationship éis'not'pre
degrees. ‘The sections .of the developed "Worm
served. Consequently it is desirable tofmoun't
curve atioppo'site sides of each 180degreezsection 50 the worrnand #gear~sector’foradjustment of ‘the
thus ‘join ‘to form isubstantialiy .va ceratoid -.=cusp;.
distance between their ‘axes.
This .conformation is shown in:»the;curve . of Fig. i6,
__ ' ‘Bea-rings 323~may 'be received in "a sleeve “26
and't-he worm groove may-be .ground'in this-fash
?tting closely Yin‘a-“borein "casing'fZ'I ' an’djrotat
ion éby ‘shifting e, grinding '_wheel towardand
able relative tO'j-‘t. If ‘these-hearings- are'locate'd
away from the wormlaxis :under theiicontrol :xof 55 slight-1y?-eccentrica}lly of the axisj'ojf the cylin
a'cam- of ‘proper contour. "This worm construc
drical exterior [of 1 this ‘sleeve, "the; ails er “shaft
tion :insures that the load will fbeitransmit-ted be
242 may 1 be- moved ' slightly; toward'or away "from
twee’nuthe worm and worm .gear ' elements .‘by
balls in :only .a single wormsgear groove. atiany
' the casing.
The spacingbetween‘theaxes of’the
given time,‘with'the'negligibleexception of the 60 sleeve’s inner .and?aouteryperipheriesmay be of
instant the load is I-being transferred ;;from :the
the order of one sixty-fourth of an inch. The
balls in one worm gear groove 'tothe balls in an
adjacent groove.
_As ‘an example. ofaa
desired spacing between the axes of the ‘worm
l and gear 2 maytherefore"abetestabishedneither
installation slt;has
initially or \after 'ithe: igiZQOME-l‘s’. in the {worm {and
worm :gear sector have abecume somewhat :morn,
been-stated that thefworm gearxigma'y be rotated 65
through 2.0 degrees for eachoomplete rotation of
merely by setting such sieeveiin
correspond
the worm i. :StopzscreWs2B.threaded-into-case
ing rotative v.position. The. ssleeveunay; then the
‘held. inwsuch setting :by :a I set :screw '22:‘! rzthrieaded
ing .2l, ?newhic'h the worm gears.-s,ector is, j.ou13-.
naled, limit rotation ‘of the sector to .an angle of
in the wall of-casing .2] and having-an inner
approximately ,40 degrees in ‘each’ direction .from 70 tip adapted to ‘press againstthesleeve .or'td?t
in any one of a number of'hdles disposedcircum
theacentral position shown, :or a totalof 89 de:
grees. .riti‘would thereforehe necessary'to revolve
ferentially arounduit, Such holes 28 are shown
worm '.l through'fapproximately .four complete
in Figure 4, disclosing a structure slightly dif
revolutions to swing gear-sector 2 sir-omt-onerex-g'
treme position to the-other,sothattwosgeansec 75
ferent frOmIthat'iof-FigL-QI
" 7'
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T
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The modi?cation. ofVgFiguresB and 4 also in
2,404,378
9
'10
corporates a'sleeve v26 having a slightly eccentric
bore, and which ?ts closely ‘within casing 2|. In
this instance, however, the bearings 23 do not
‘not vary too greatly because the maximum vari
ation in the distance between the bottom of a
groove of a ?xed gear‘sector and the axis of the
worm during rotation of the worm through 180‘
degrees would be only about 1/64 of an inch in a
seat directly upon the inner periphery ‘of the
sleeve 26. On the contrary, a resilient bushing
29 of rubber, or preferably of similar synthetic
material, is interposed between the sleeve 26 and
an‘ inner tube 26' which retains the bearings.
typical instance. The variation is nevertheless
su?icientlylarge to'permit undesirable backlash
if no compensation is provided.
.
The rubber bushing should be suitably bonded to
Since it is desirable to‘ lubricate needle bear
both of these'parts so that the composite resil 10 ings 23, as well as the worm and gear, for ex
ample through lubrication ?ttings 3 of conven
lent unit can be rotated to adjust the position of
tional type shown in Fig. 1, it is preferred that
the gear sector shaft axis toward or away from
the axis of worm I.
'
'
the resilient bushing 29 be of material not de
teriorated by petroleum'products. Reference to
Since sleeve‘ 26 is of varying wall thickness
the axis of gear shaft 22 will be closest to the
such bushing as of rubber, therefore, is intended
axis of worm I when the thickest ‘part of the
to include synthetic rubbers such as Neoprene and
sleeve is located farthest from the worm and
other resilient lubricant resistant substances suit;
able for the purpose described. 7
.
.
immediately beneath locking screw 21, as shown
in Figure 4. If the balls 10 are engaged fairly
As in the'worm, and gear mechanism shown‘ in
tightly between the worm and the worm gear 20 my previous application Serial No. 517,927, the
balls circulate through a by-pass aperture IS in
sector when the‘parts are in the relative posi
the worm body extending between the ends of the
tions of Fig. 1, rotation of sleeve 26 to locate a
thicker wall portion beneath the locking screw
effective portion of the worm groove, which is
would compress the side of resilient bushing 29
preferably about oneand one-half turns. The
remote from the worm radially between sleeve
balls are guided for movement through passage
l6 by suitable de?ectors shown in Figure 1. Also
26 and tube 26'. The balls VIII‘ would then be
clamped between the worm, and worm sector
the balls may be held more closely in the groove
. under resilient pressure, which may be varied in
to prevent variation in clearance between the
balls by forming the casing of a contour comple
30 mental to the variation in groove depth. 1Thus
degree by proper rotative'adjustment of sleeve
26. '
Where a two-part sleeve for carrying bearings
'23 is used, as shown in Fig. 3,‘ sleeve 26 may be
turned su?iciently so that, when a gear sector
groove is located centrally of the worm, the bush-.
ing 29 will be compressed to a substantial degree.
the casing may have a hump or ridge located cen
trally of the worm, as shown exaggerated in size
in Fig. 1. Since the difference in spacing between
the worm’s axis and the bottoms of extreme por
All backlash between the worm and the worm gear
pedient may not be necessary.
sector will be eliminated by this expedient when
the parts are in the ‘relationship of Figure 1,} yet
Where‘ antifriction mechanism of the type de- '
scribed is incorporated in an automotive steering
gear it is usually desirable for the steering column
tions of the groove is so slight, however, thisex
.
.'
'
’
‘
the friction of the mechanism will not be in
creased appreciably because, as mentioned pre 4:0 M to be tubular so that electrical wires may pass
viously, the use of alternate large and small balls
through its hollow interior l1. In such event an
aperture 18,‘ as shown in Fig. 5, may extend axi
eliminates all sliding friction between adjacent
ally through the worm I. Such an“, aperture
balls, provided that they all rotate at the same
peripheral speed.
would con?ict with a ball by-pass passage such
' As worm ‘I is now turned the pressure ‘of the 45 as 16 in Fig. 2, which is disposed in a diametral
compressed bushing 29 will continually urge
plane of the worm. The balls may, however, pass
between the same portions of the worm groove
worm‘ gear shaft 22 toward the worm axis to
through the passage l9v of Fig. 5, composed of end
prevent backlash in all rotative positions of the
portions meeting at‘ an angle. Alternatively a
worm. Moreover, when the spacing between the
bottoms of the worm gear groove engaged by the 50 linear by-pass passage may be located, in ‘a
chordal plane at one side or the other of the axial
balls and of the worm groove is kept constant by
aperture I8, instead of in a diametral plane as
use of the structure described above, the resil
, shown in Fig. 2.
ient pressure of the worm and worm gear sec
tor against the balls will remain constant. If
I claim as my invention:
.
'
V
the worm is of conventional cylindrical type, 55
1. Antifriction worm and gear mechanism, com
prising a gear having an inclined groove therein,
however, such pressure .will vary .somewhatpas
a worm, adjacent to said gear and having only a
bushing 29 expands to move gear shaft 22 toward
‘single helical groove therein complemental to the
the worm to compensate for the tendency of the
spacing between the bottoms of the gear’s ball
engaging groove and of the cooperating portion
of the worm grooveto increase.’
'
v
inclined groove of said gear, the spacing of the
to
bottom of the worm groove vfrom the worm axis
being minimum substantially in an axial plane of .
said gear disposed ‘perpendicular to the axis of
said worm,vand such spacing between the’ worm
sum of the lengths of the- maximum worm and
groove bottom and the .worm axis increasing pro
gear‘ radii must. be less than‘ the perpendicular
distance betweentheir axes, so that the point of 65 gressively away from such plane throughout a dis
tance to each side of such planenot appreciably
the gear periphery closest to the‘ worm will not come
exceeding one-half a turn of the Worm groove,
ifito engagement with it. - Even though the worm is
and balls engaged closely by the grooves of said
of the cylindrical type, therefore, having a‘ constant
gear and worm.
‘
'
v
.
root diameter, and although the pressure on the
2. Antifriction worm and gear mechanism,
bearing" balls It! may vary, the resilient worm
comprising a gear having an inclined groove
gear mounting can ‘cause the worm and gear to
therein, a worm adjacent to said gear and have
exert su?icient pressure upon such balls in all
ing only aisingle helical groove therein comple
rotative positions of the Worm to prevent'appreci—
mental' to the inclined groove of said gear,'the
able backlash between the parts.v I The variation‘
in pressure on the balls insuch anassembly‘will 75 spacing of the bottom of the worm' groove from
'_ Tovpermit such movement of the gear sector the
11
2,404,378,
therein, a worm adjacent to said gear and having“.
an-aXialplane of said gear. disposed .perpendicue ‘
only a single. helical;v groove~ thereimcomplemental.
Iar. tothe axis ofjsaid.worm,, and such spacingbe
to. the; inclined ;. groove. of ‘said ~ gear,
bottom:
of the worm? groove as developedon a- plane _be-»
‘ tween. the wormgroove bottomand the. ‘worm.
ing, of. substantially parabolically concave ,con->
‘ axis increasing progressively, substantially inpro- .
1 portion to the ‘root radiuseo-f said gear minus.
‘ tour axially of said. worm throughout- a- distance
"the cosine of. the gear angle. multiplied by the
not. appreciably exceeding a. complete turn’, and
balls engaged closely by the. groove offsaid gear.
gear’s root radius, awayv > from such. ‘plane
1 throughout a distance toeachuside of- such..plane
and the parabolic portionot the Worm groove as
' ‘ not appreciably exceeding one-half a. turn of 10;
‘ theworm groove, and balls. engaged, closely by ,
V
12
the worm“ axis . being minimum substantially in
the. grooves. of. said gear and‘ WornL -
7.3. Antifriction worm and, gear mechanism,
developed‘,
r
-
'
>
7
~. 8.. Antifriction, worm and; gear mechanism,»
comprising a gear having , an. inclined groove.
therein, a worm adjacent to said gear and-thav
"' comprising. a gear having. an. inclined groove
‘ therein. a. worm adjacent; to said. gear and hav
ing a. helicalgroove. therein complemental toQt-he
‘ ingl. only a single helical groove. therein comple
. mental. to-the. inclinedgroove. otsaidgear, the
worm groove as. developed on. a plane ‘being-of...
substantially parabolically concave contour axial?
1 spacing of the bottom .oithe worm groove from Y
‘ the... worm. axis. being .minimum. substantially in
ly of said. worm. throughout approximately a. complete turn, a. portion oiv the. developed. worm
inclined. groove. of rsaidz-gear, the bottom of: the
groove. adjoining .an.end_ of such parabolic porm
an axial plane of‘ said gear; disposed perpendicu
. lar to the axislof said. worm-,,and.such. spacing. be- ‘
tion. departing substantially from. a. continuation.
‘
of suchrparabolically concave. contour; and balls:
axis. increasing, progressively away from, such 7‘
1 plane substantially in proportion to the. square. of
the ' parabolic portion. oil the. worm groove. as
j the .worm angle throughout a- distanceto each
developed.
‘ tween the Wormgroove bottom and. the; worm
side of 'such plane not. appreciably exceedingone
half.‘ a turn of theworm groove,‘ andballs engaged
engaged closely by the groove-oi said. gearv and.
‘
v
1' ” J
.
‘
9. Antifriction worm: and. gear mechanism;
comprising; a gear having an. inclined; groove
thereinra worm adj acent said gear andhavingra.
‘ closely by the grooves of. said. gear. andworm.
helical 'gro'oveltherein complementalto the. ‘in-.
‘ 4. 'Antif'riction worm. and. gear. mechanism,
A comprising, a gear having. an. inclined groove
clined. groove of‘sai‘d gear, the bottom of the worm’
groove as developed. on. a. plane. being.v of substan
therein,'_ a worm. adjacentzto said gear and have
‘ ing. only a._sing1e. helical. groove. therein comple
j mentalgto theihclinedigroove ofsaid gear, the.
spacing of the bottom of. the worm groove from
tially parabolically concave. contour axially. of.
said. worm. throughout‘. approximately a. complete
turn,.a‘ portion. of. the developedgworm groovead;
‘ the worm axis. being. minimum substantially in 55
joining an end. of such. parabolic. portion being
1 an axial plane of said; gear disposed perpendicu
of reverse...curvature,. and .ballsengaged closely by '
the; groove of. said. gear and. the.’ parabolic por
lar. tothe axis of. said? worm,,.and. such- spacing
‘ between the wormgroove bottom and. the worm
‘ axis'increasing progressively away from.‘ such
tion of. the Worm groove as. developed, . .
10.. Antifriction worm and gear mechanism
planethroughout adistance- to eachside of such
40 comprising- a gear having} an. inclined groove
planenot appreciably exceeding one-half-a turn
1 worm. axis. decreasing progressively immediately
therein, a worm adjacent. to sai'dgear and having.
a. helical groove, therein .complemental to the. in-?.
clined‘ groove of.’ said; gear, balls engaged‘jbetween
the groove of said‘ gear and the wormgroove,.and_
means supporting. said. wormandlgear. andlresil
‘ beyond. eachsuch. half.‘ turn of.‘ the. worm to. re:
iently urging them relatively toward eachlother to
"j 1ease..the..bal1s abruptlyfrom close engagement
clamp sai'dballs under resilient pressure. between.
such gear. and ‘worm grooves in all'grotative posi
ofithe, worm groove,: and‘ balls. engaged, closely
by. the groovesgof. said gear. and. worm, the spac
‘ ing. between the. worm groove bottomand ‘the
with said gear. and worm grooves.
5.. Antifri'ction wormand'gear. mechanism com
prising. a . gear having. 1 an. inclined . groove there.
tionsof the worm andgear.
50
in,..a worm adjacent tosaid gear and. having a
‘ helical‘.- groove therein, complemental to.v the in.
clined' groove of‘ said ‘gear, the worm. groove. as
‘ developed on a planebeing. concaveaxially. of
i said, worm. throughout approximately. one com
‘ pljete turn, andLa, portion. of the developed worm
_
.
11‘; Antifriction worm and gear. mechanism.
comprising, a gear having an inclined . groove
55
therein, a worm adjacent to said. gear and'havi‘ng,
a. helical.‘ groove therein..complemental'to‘. thein
clined. groove of said. gear, ballsen'gagedl'between
the groove of. said gear. and the worm groove, two
shafts, one. supporting said‘ worm and the other.
supportingsaidv gear, adjusting means incl‘udi‘nga.
sleeve of varying wall. thickness ‘encircling, one
of‘ said shafts: and‘ circumferentially' adjustable
; ofisaidgear and by such concave portion of the
worm groove. as developed.
.
60 to‘ vary‘the position of such shaft toward or: away
from the other shaft; to‘adjust the engagement‘
6'. >Antifri0tion worm and‘ gear mechanism com
‘ groove joiningan endjof“ said concave portion. in
r. a, crest,,and‘ balls engagedlcl'osely by the groove
‘ prising‘v a. gear having an inclined groove
ytherei‘nga worm. adjacent to said gear and
of said balls by such‘ gear‘ and’ wormxgroove‘sii‘n
all rotative positions of thezworm and gear‘n a tube
interposed between said sleeve, and the shaft‘en
j havinga helical‘fgroove therei'ncomplemental’ to
1 the inclined groove offsaid ge_ar,_ thewormgroove 65 circled thereby, and a resilient‘ bushing intera
asdevel'oped‘on a plane being concave axially of
posedbetween' said‘tube" and said sleeve‘, adapted
said, Worm throughout approximately one com
to‘ be deformed,‘ by circumferential‘ adjustmentio‘f
said sleeve tending’to effect‘ approach‘ movement
j pl'etevturn, and" a portion of.- the dev'elopedworm
of. said shafts; and. ‘thereby resiliently urging
‘ groove adjoining an'end" of 'said" concave portion
1 being similarly concave and joining. such ?rst 70 them relatively toward each other‘t'o: clamp, said
‘cncave portion‘. in a crest, and balls. ‘engaged 1 b'alls‘under‘resilient pressure; _
closely by the gyrooveof saidgearand such. ?rst
1'2; Antifriction worm and‘ gear mechanism;
‘ concave portion oi'thewormgroove asdevelopedi.
comprising a gear having. an inclined groove
therein, a'worm' adjacentto said gear ancl'having
'7’. Antif'riction Worm. and’. gear mechanism,.
1 Comprising. a. gear. havinganinclined groove .75 onlyv a single helical groovetherein c‘omplement'a'l.
2,404,378 ‘
13
14
to the inclined groove of said gear, balls engaged
between the .groove of said gear and the worm
therein, a worm adjacent to said gear and having
only a single helical groove therein complemental
to the inclined groove of said gear, balls engaged
between the groove of said gear and the worm
groove, two shafts, one supporting said worm and
the other supporting said gear, adjusting means
groove, and means supporting said worm and gear
and urging them relatively toward each other to
clamp said balls under resilient pressure between
such’ gear and worm grooves, the spacing of the
bottom of the worm groove from the worm axis
including a sleeve of varying wall thickness en
circling said gear supporting shaft and circum
ferentially adjustable to vary the position of such
the axis of said worm, and said spacing between 10 shaft toward or away from said worm supporting
being minimum substantially in an axial plane
of said gear disposed perpendicularly relative to
the worm groove bottom and the worm axis in
creasing progressively away from such plane
throughout a distance to each side of such plane
not appreciably exceeding one-half a turn of the
worm groove, and sufliciently to maintain the
spacing between the bottom of the gear groove
and the bottom of the worm groove substantially
constant throughout a complete turn of the worm,
shaft, a tube interposed between said sleeve and
said gear shaft, and a resilient bushing inter
posed between said sleeve and said tube, and com
pressible by circumferential adjustment of said
sleeve to press said gear resiliently against said
balls, the worm groove developed on a plane be
ing concave axially of said worm throughout ap
proximately one compl’ete’ turn to maintain the
spacing between the bottoms of the gear groove
thereby to maintain substantially constant the
resilient pressure of said supporting means on 20 and of such portion of the worm groove substan
tially constant, so that the resilient pressure of
said balls in all rotative positions of the worm
said gear on the balls effected by said bushing
and gear.
'
remains substantially constant in all rotative
13. Antifriction worm and gear mechanism,
positions of the worm and gear.
,
comprising a gear having an inclined groove
15. Antifriction worm and gear mechanism,
therein, a worm adjacent to said gear and hav
comprising a gear having an inclined groove
ing only a single helical groove therein comple
therein, a worm adjacent to said gear and having
mental to the inclined groove of said gear, balls
a helical groove therein complemental to the in
engaged between the groove of said gear and the
clined groove of said gear, the worm groove as
worm groove, two shafts, one supporting said
worm and the other supporting said gear, and 30 developed on a plane being concave axially of said
worm throughout its central portion, and a por
adjusting means including a sleeve of varying
tion of the worm groove, in its developed form,
wall thickness encircling said gear supporting
joining an end of said concave portion to form
shaft and circumferentially adjustable to vary
therewith substantially a ceratoid cusp, and balls
the position of such shaft toward or away from
said worm supporting shaft, to adjust the engage 35 engaged closely by the groove of said gear and by
such portion of the worm groove concave in its
ment of said balls by said gear and worm grooves,
developed form.
‘
the spacing of the bottom of the worm groove
16, Antifriction worm and gear mechanism,
from the worm axis being minimum substantially
comprising a gear having an inclined groove
in an axial plane of said gear disposed perpen
dicularly relative to the axis of said worm, and 40 therein, a worm adjacent to said gear and having
a helical groove therein complemental to them
said spacing between the worm groove bottom and
clined groove of said gear, balls engaged between
the worm axis increasing progressively away from
the groove of said gear and the worm groove, two
such plane throughout a distance to each side of
such plane not appreciably exceeding one-half a
shafts one supporting said worm and the other
supporting said gear, a sleeve encircling one of
said shafts, a tube interposed between said sleeve‘
and the shaft encircled thereby, bearing means
interposed between said tube and said shaft, and
a resilient bushinginterposed between said tube
of the worm, thereby to maintain substantially
constant the adjusted engagement of said gear 60 and said sleeve adapted to be stressed to urge said
tube therewithin in a direction to press said gear
and worm grooves on said balls in all rotative
and worm resiliently toward each other to clamp
positions of the Worm and gear.
said balls under resilient pressure.
,
14. Antifriction worm and gear mechanism,
HENRY S. HOFFAR.‘
comprising a gear having an inclined groove
turn of the worm groove, and sufficiently to main
tain the spacing between the bottom of the gear
groove and the bottom of the worm groove sub
stantially constant throughout a complete turn
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