Gear pump, gear and method

A relatively simple gear-forming process is disclosed, which enables the production of a set of gears that is especially useful for a particular type of gear pump, and which also produces a set of gears which operates with a high degree of rolling contact. The gears are produced by first forming an initial cutter gear having teeth with cylindrical tips supported by narrow supports, and using this initial cutter on a gear shaper to cut a first gear having bullet-shaped teeth. The first gear can then be used as the cutter on a gear shaper to cut other gears with bullet-shaped teeth or to cut gears with pole-shaped teeth. In a gear pump wherein fluid is forced through an axial passage opening into the space between teeth of the sun gear, the sun gear is formed with pole-shaped teeth while the planetary gear is formed with bullet-shaped teeth.

BACKGROUND OF THE INVENTION 
This invention relates to a novel gear-production method, novel gears 
resulting therefrom, and a gear pump utilizing a set of such gears. 
My earlier U.S. Pat. No. 3,259,073 discloses a gear pump wherein a sun gear 
is provided with radial passages leading from an axial hole to the space 
between adjacent teeth, and planetary gears are provided which force fluid 
into the passages. The teeth of the sun and planetary gears must be 
designed so that as a planetary gear tooth enters the space between a pair 
of sun gear teeth there is substantially contact of the planetary gear 
tooth with a sun gear teeth to prevent the escape of fluid. The design of 
a pair of gears for achieving such interfitting, especially where contact 
must begin early during the engagement of a tooth in order to trap a large 
volume, is extremely difficult. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment of the present invention, a gear set is 
provided which can easily be produced, and which operates effectively in a 
gear pump of the type wherein the planetary gear forces fluid into a 
radial passage of the sun gear. A set of gears can be constructed by first 
forming an initial cutter gear whose teeth have tips forming at least 
180.degree. of a cylinder. This initial cutter is utilized on a gear 
shaper to form a second gear, with only the cylindrical tips of the 
initial cutter cutting away material of the gear blank. The second gear is 
then used as a cutter to cut the sun gear and planetary gears of the gear 
pump, using the second gear as the cutter on a gear shaper. When operating 
the gear shaper to form planetary gears, the axes of the cutter and gear 
blank are held far enough apart to form bullet shaped gears, while when 
cutting the sun gear, the axes of the cutter and gear blank are held close 
enough together to form narrow pole-shaped teeth. 
Planetary gear teeth can be utilized in a gear train, because the meshing 
planetary gears substantially roll on one another along wide areas of 
their teeth, to minimize friction and reduce wear. 
The novel features of the invention are set forth with particularity in the 
appended claims. The invention will be best understood from the following 
description when read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an initial cutter 10 being utilized as the cutter on a gear 
shaper to form a gear 12 with bullet-shaped teeth 14. The manner of 
operation of a gear shaper is shown in FIG. 4, wherein it can be seen that 
the cutter 10 is rotatably mounted on a ram R that moves up and down, 
while a gear blank 12b is mounted on an axle A that rotates. The cutter 10 
and blank 12b slowly rotate in the indicated directions, while the ram R 
moves up and down, so that the cutter generates teeth on the blank. This 
process is also utilized as illustrated in FIG. 2, to cut another gear 16 
with narrow post-like teeth 18, utilizing the bullet gear 12 as the 
cutter. The bullet gear 12 also can be utilized, as indicated in FIG. 3, 
to generate another gear 12A with bullet-shaped teeth of the same shape as 
those of the gear 12. 
The two gears 12, 16 of FIG. 2 can be utilized in a special gear pump of 
the type illustrated in FIGS. 6 and 7 wherein the gear 16 serves as a 
central or sun gear while the gear 12 serves as a planetary gear engaged 
with the sun gear. As shown in FIG. 6, the pump 22 includes a housing 50 
with an inlet 20 for receiving a fluid and an outlet 28 for discharging 
fluid under pressure. A sun gear 16 is rotatably mounted on a central 
shaft 52 which is driven by a motor (not shown) and a group of six 
planetary gears 12 are mounted on six axles 54 spaced about the sun gear. 
A pair of side plates 56, 58 lie on either side of the sun gear 16, and 
each planetary gear 12 fits closely between the side plates 56, 58. Fluid 
to be pumped enters an inlet 20 of the pump and flows into the region 
surrounding the gears 12 and 16. The sun gear has radial passages 24 (FIG. 
6) that lead from the space 26 between its teeth to an outlet 28 at the 
center of the sun gear. As the gears 12, 16 rotate, a tooth 14a of the 
planetary gear begins entering the space or recess 26 between two teeth 
18a and 18b of the sun gear. During the next approximately 25 degrees of 
rotation of the planetary gear, its tooth 14a enters continually deeper 
into the recess 26 between the teeth 18a, 18b to force fluid therein down 
through a corresponding radial passage 24 into the outlet 28 of the pump. 
In this way, fluid can be efficiently moved by the gear pump. This type of 
pump is shown in my U.S. Pat. No. 3,259,073. 
As shown in FIG. 8, efficient pumping of fluid requires that the leading 
portion of the tooth make contact with, or come extremely close to, a side 
of the sun gear tooth 18a such as at the point 30. Such substantial 
contact is required to assure that the fluid in the space 26a will be 
pumped down into the radial passage 24a instead of leaking past the 
planetary tooth 14a. It may be noted that the other side of the cavity 26a 
is sealed by virtue of contact of the next planetary tooth at point 32 
with a side of the sun gear tooth 18b. In addition to the necessity for 
substantial sealing contact of the gear teeth, it is also necessary for 
substantial contact, such as at 30, to occur near the beginning of entry 
of the tooth 14a into the recess 26a in order for a large amount of fluid 
to be trapped in the recess of 26a. This assures that considerable fluid 
will be pumped and therefore a pump of small size will have a large 
pumping capacity. 
The design of a sun gear and planetary gear combination which will achieve 
the two requirements, that there be relatively good sealing of the sun 
gear recesses and that a relatively high volume of fluid be pumped in the 
course of engagement of each planetary tooth with the sun gear, can be 
extremely difficult. Even after such a gear set is designed, it is 
difficult to accurately grind a set of gears so that they will run 
accurately on one another. The gear set developed by the processes 
illustrated in FIGS. 1 and 2, results in the development of two gears 12, 
16 which can be utilized respectively as the planetary and sun gears in 
the pump of FIGS. 6 and 7, with additional planetary gears being easily 
produceable by the method shown in FIG. 3. 
The initial cutter of FIG. 1 consists of a body 36, a plurality of 
cylinders 38, and a plurality of supports 40 for supporting the cylinders 
38 away from the body. In forming the cylinder-developed or bullet gear 12 
on a gear shaper, only the cylindrical tips 38 perform cutting, and in 
fact, only a region extending along an angle 42 of approximately 
210.degree. about the cylinder actually performs all of the cutting. The 
supports 40 can therefore be formed to any shape that is sufficiently cut 
away to prevent interference with cutting. A support shape indicated at 
40a can be utilized to firmly support the cylindrical tip without 
interfering with cutting. The diameter 44 of each cylindrical tip is 
preferably about one-third the spacing 46 between the axes of adjacent 
cylindrical tips. 
It has been found that pairs of planetary gears constructed in accordance 
with the present invention operate exceedingly well when engaged with one 
another in a gear train. The plan view of FIG. 3 is the same as the view 
of two gears, 12, 12a of a gear train employing bullet gears of the 
present invention. It has been found that pairs of bullet gears rotate on 
one another with the surfaces of the gear teeth primarily rolling on one 
another and with the rolling action occurring along a large proportion of 
the tooth surfaces. FIG. 9 illustrates a portion of a pair of gears 12, 
12a engaged with one another. Contact of the gears with one another 
extends along a wide region of each tooth, which includes the area between 
60 of each tooth, along the side of the tooth which is driving or which is 
being driven. As a result, the two bullet gears provide smooth action and 
high efficiency, and with distributed wear, so that smaller gears can be 
utilized to transmit given loads, while providing a longer lifetime of use 
than prior art gears. 
The shape of each tooth 14 of a bullet gear can be defined in several 
different ways. As shown in FIG. 5, a pitch circle 62 is defined which 
extends near the bottom of the tooth. The pitch circle 62 is spaced from 
the bottom of the tooth, as measured from the dedendum circle 68, by a 
distance 64 which is approximately 26% of the entire height 66 of the 
tooth. The dedendum of the gear (the portion below the pitch circle) lies 
substantially on a circle 70 centered on the pitch circle 62. The addendum 
of the gear, which is the portion lying above the pitch circle 62, may be 
defined by the locations of the points 80-101 indicated in FIG. 5, as 
defined in the following table, for a 13 tooth gear. In the table the 
distance X is the distance from the center line 72 of the gear and the 
distance Y is the distance from an imaginary line 74 which passes through 
the axis 76 of the gear and which is perpendicular to the center line 72, 
the gear has 13 teeth and a radius of 0.80097 inch. 
______________________________________ 
X Y 
______________________________________ 
80 .00000 .80097 
81 .00272 .79849 
82 .00804 .79349 
83 .01300 .78849 
84 .02228 .77849 
85 .03060 .76849 
86 .03811 .75849 
87 .04497 .74849 
88 .05144 .73849 
89 .05763 .72849 
90 .06352 .71849 
91 .06928 .70849 
92 .07466 .69849 
93 .07952 .68849 
94 .08386 .67849 
95 .08732 .66849 
96 .09030 .65849 
97 .09280 .64849 
98 .09486 .63849 
99 .09640 .62849 
100 .09728 .61849 
101 .09745 .60849 
______________________________________ 
In constructing the above gear, the tip thereof was rounded along the line 
79, which reduced the actual diameter of the gear by 14 mil (thousandth of 
an inch). One disadvantage of the present gears, as compared with standard 
involute gears is that the spacing of the axes of a pair of meshed gears 
must be precisely controlled. The rounding of the tips prevents 
interference of the gears if they are mounted at axes that are slightly 
too close together. 
As illustrated in FIG. 8, the shape of each tooth 18 of the sun gear can be 
approximated by a pair of ellipses 82, 84. The tip portion 18t of the 
tooth has a cross-section which is substantially 200.degree. of a 
45.degree. ellipse whose length extends in a circumferential direction. 
The recess 26 between teeth can be defined substantially by 200.degree. of 
an isometric (approximately 35.degree.) ellipse 84 whose length 86 is 
approximately 3 times the length 88 of the 45.degree. ellipse 82 and whose 
length dimension extends radially. Of course, the foregoing is merely an 
approximation of the pole-shaped tooth of a sun gear. The tip portion 18t 
of the tooth 18 does not serve any function during operation of the sun 
gear in the above gear pump, but is only the result of development by the 
planetary gear in the manner shown in FIG. 2. Accordingly, the tips of the 
sun gear above a pre-determined pitch circle 90 may be removed, if 
desired, to leave stub teeth. The pitch circle 90 of the sun gear with 
pole-like teeth, lies near the extreme periphery, or addendum circle of 
the gear at a height preferably more than two-thirds the total height of 
the teeth, as measured between the dedendum and the addendum circles of 
the gear. 
In the gear pump, the gears are positioned, as indicated in FIG. 8, with 
the pitch circle 62 of the planetary gear 12 tangent to the pitch circle 
90 of the sun gear. A separation of the axes of the planetary and sun 
gears is the same as is used in the generation of one gear by the other 
(or by a cutter identical to the other), as in a manner shown in FIG. 2. 
If a planetary gear 12 and a sun gear 18 generated from the planetary 
gear, are held with their peripheral portions pressed against one another, 
the separation of their axes is the same as is used in the gear pump. 
When two bullet gears, such as those shown at 12 and 12a (FIG. 3) are to be 
run on one another, their axes are mounted at a separation distance equal 
to the distance utilized during generation of one gear from the other (or 
from an identical cutter gear), as in the process of FIG. 3. It can be 
seen that the pitch circles 62 of the two gears 12, 12a do not intersect 
one another. 
In the generation of the gears of the present invention, the separation 
distance of the axis of the cutter from the axis of the gear blank 
determines the shape of the generated gear. In one example, the initial 
cutter 10 of FIG. 1 is constructed with cylinders 38 of a diameter 44 of 
0.100 inch, spaced apart by a distance 46 of 0.296 inches. The gear 12 to 
be cut has 13 teeth and therefore must have a pitch diameter 110 equal to 
0.296 times 13 divided by pi, which equals 1.226 inches. Thus, the 
distance from the axis 112 of the gear blank for the bullet gear 12 and 
the pitch circle of the initial cutter 10 is one-half of 1.226 inch. The 
distance 114 between the axis of rotation 116 of the initial cutter and 
its pitch circle equals the distance 46 between teeth times the number of 
teeth on the cutter, divided by pi. 
When making the setup of FIG. 2, the distance between the axes 102, 108 of 
the planetary and sun gears can be calculated in the same manner as in 
FIG. 1. The pitch diameter of the planetary gear 12 is 1.226 inches, as 
derived above. The pitch diameter of the sun gear equals the tooth spacing 
(0.296 inch) times the number of teeth (24 teeth) divided by pi. The two 
gears are positioned so their pitch circles are tangent, and therefore 
their axes are separated by a distance equal to the sum of their pitch 
diameters divided by 2. 
In making the setup of FIG. 3, where both gears 12, 12a are to be 
identical, the separation of the axes 102, 110 of the two gears is equal 
to the pitch diameter of the gear 12, plus the distance between the tip of 
a tooth 14 and the pitch circle 62, this distance being determined by 
measurement and equal to 0.188 inch for the earlier described gear. If the 
axis 110 of the gear blank is moved a distance s closer to the axis 102 of 
the cutter, so that the pitch circle 62 of gear 12a is tangent to the 
pitch circle of the other cutter gear 12, then the gear blank will be cut 
to form post-like teeth (shown in phantom lines at 117) similar to those 
of the sun gear, instead of forming bullet-like teeth. 
As mentioned above, the planetary gear 12 with bullet-like teeth can be 
utilized to cut either a sun gear with post-like teeth or another 
planetary gear. The sun gear, 16 can be utilized to cut a planetary gear, 
but is not efficient for this operation because all cutting by the sun 
gear would be performed by the rounded tips thereof, which would soon 
wear. A sun gear with elliptical tooth tips could be used instead the 
initial cutter 10 with cylindrical tooth tips, except that it is difficult 
to design the teeth of the sun gear. The bullet-like teeth 14 of the 
planetary gear, are of the general type commonly referred to as an 
enlarged tooth form, since the width of each tooth along the pitch circle 
is greater than the space between teeth as measured along the pitch 
circle. Each tooth 18 of the sun gear may be referred to as having a 
reduced tooth form, since the width of the recess between teeth is greater 
than the width of each tooth, as measured along the pitch circle of the 
gear. For use in the gear pump of the present invention, a large recess 
between teeth is desirable because this allows more fluid to be trapped in 
the recess between teeth. 
In the commercial manufacture of the present gears for a gear pump, it is 
desirable to use one planetary gear to cut both the sun gear and other 
planetary gears, in order to help assure proper meshing of gears without 
requiring exceedingly small tolerances. One method for high production of 
gears of the present invention involves the cuttng of only one gear 16 and 
12A using the operations of FIGS. 1-3. Then the gears 16 and 12A are 
utilized to form cavities for mass production. Each gear is formed by 
filling the cavity with powder, compressing the powder, and sintering the 
resulting gear. 
Thus, the invention provides novel types of gears and methods for producing 
them, and provides an improved gear pump. The gears can be formed by using 
an initial cutter having tips which perform all of the cutting and that 
are portions of cylinders. The initial cutter can be used to form a gear 
with bullet-shaped teeth, and this gear can be utilized as a cutter to 
form additional gears with bullet-shaped teeth or with post-shaped teeth. 
By varying the distance between the axis of a cutter gear and the axis of 
the gear to be cut, gear teeth of different shapes can be obtained. A gear 
pump of the type wherein fluid is pumped through radial passages in the 
sun gear, can be made more efficient by utilizing planetary and sun gears 
with teeth of the shape which results from the gear-forming method of the 
invention. Additionally, a pair of gears with bullet-shaped teeth of the 
invention can be utilized in a gear train to transmit motion with largely 
rolling engagement of one gear with the other. 
Although particular embodiments of the invention have been described and 
illustrated herein, it is recognized that modifications and variations may 
readily occur to those skilled in the art and consequently it is intended 
that the claims be interpreted to cover such modifications and 
equivalents.