Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF INVENTION
This invention relates to a crescent gear set having dual cycloidal tooth
profiles; and in particular relates to a crescent pump gear having inner and outer gears
with dual cycloidal tooth profiles.
BACKGROUND TO THE INVENTION
Crescent pump gear systems consists of an inner gear and an outer gear
located at an offset. The gear set operates in a sealed housing with the inner gear
driving the outer gear in mesh at the top dead band. The bottom dead band is sealed
using a crescent shaped section of housing between the major diameter of the inner gear
and the minor diameter of the outer gear.
Crescent pump gear systems are typically used in pumps with high pressure
applications since the sealing capability of the gears against the crescent is enhanced due
to the number of teeth on both the inner and outer gears that seal across the crescent
of the pump at any particular point in time.
Conventional crescent pumps usually have heretofore utilized involute gear
forms. However due to the mathematical generated of involute curves the gear teeth on
a crescent system utilizing involute gear forms will be small and require a large offset in
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order to function properly. This greatly reduces the displacement of the pump for a
given pump size.
In the construction of gear pumps having a high output, significant value
is placed on ~ltili7ing fewer number of teeth since fewer number of teeth will result in
low tooth mesh or engagement frequency and consequently a low frequency noise is
observed during operation.
Furthermore a small number of teeth is further desirable since it will result
10 in larger tooth gaps and hence bring about a larger discharge or delivery volume and
therefore increase the pumping characteristics of a given pump.
Various tooth profiles have heretofore been proposed.
For example United States Patent Number 1,516,591 teaches that the
addendum sections of an inner gear are formed on epi cycloidal curves while the
dedendum sections are formed on hypo cycloidal curves. However this patent teaches
that the generation of the epi cycloidal and hypo cycloidal curves of the gear teeth are
the same in diameter.
Moreover United States Patent Number 3,907,470 illustrates that the
outermost flanks of two adjacent teeth on an annual gear wheel are defined by a circular
arc or an arc of a curve equidistant from a hypo cycloid.
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Moreover United States Patent Number 4,504,202 illustrates a centred
outer rotor for a rotary pump utili7.ing the trocoidal curve and m~mlf~ctllring method for
the-rotor, whereby the rotor is formed to make a combinational gap between an inner
rotor and the outer rotor as small and constant as possible in order that both the inner
and outer rotors are rotatable.
Another device is disclosed in United States Patent Number 4,518,332
which teaches an oil pump using internal gearing wherein the difference in the number
of teeth between the internal and external gears is one and wherein the inner rotor is
10 directly connected to the crank shaft of the internal combustion engine or to the
tr~n~mi~ion shaft.
Finally United States Patent Number 4,657,492 teaches a rotor for a rotary
pump.
These and other gear sets and rotary gear pumps present relatively
complicated structures which have relative utility.
It is an object of this invention to provide an improved crescent gear set
20 and in particular to provide an illlproved crescent gear pump displacing more oil from
an equivalent size gear set.
It is an aspect of this invention to provide a crescent gear set comprising;
externally toothed ~nmll~r gear journaled for rotation about a first axis; an internally
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toothed :~nn~ r gear rotatably engageable within said externally toothed ~nmll~r gear
about a second axis; a crescent contacting a portion of said internally and externally
toothed ~nmll~r gears; said externally toothed gear ha~ing dual cycloidal iooth profiles
generating about a first generating circle and said internally toothed gear having dual
cycloidal tooth profiles generated about a second generating circle.
It is a further aspect of this invention to provide a crescent pump gear
inclllding; a housing having a chamber collllllunicating with an intake port and a
discharge port; a shaft journaled for rotation within said chamber; an externally toothed
10 inner gear mounted centrally on said shaft about a first axis; an internally toothed
~nmll~r gear eccentrically mounted for rotational engagement within said inner gear
about a second axis; a crescent contacting a portion of said inner and outer gears; said
inner gear having dual cycloidal tooth profiles generated about a first generating circle,
and said outer gear having dual cycloidal tooth profiles generated about a second
generating circle.
It is a further aspect of this invention to provide; a method of producing
tooth profiles of externally toothed inner gears eccentrically offset and engageable with
internally toothed ~nnnl~r outer gears, said inner and outer gears contacting a crescent
20 having an inner crescent radius and an outer crescent radius, said method including the
steps of: generating the pitch circle of said outer gear; producing an epi cycloid of a first
cycloid set by rolling said epi cycloid in a clockwise direction about the pitch circle of
said outer gear starting at the vertical axis for a full 180 of roll; producing a hypo cycloid
of a first cycloid set by rolling in a counterclock~,vise direction around the pitch circle of
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said outer gear starting at the vertical axis until the generated curve intersects at outer
crescent radius; producing an epi cycloid of a second cycloid set by rolling in a
counterclockwise direction about said pitch circle of said outer gear starting at an angle
from the vertical axis equal to 360 divided by the number of teeth of said outer gear
minus two times the angle resulting from the length of roll of said first epi cycloid roll
for a complete 180; producing a hypo cycloid of a second cycloid set by rolling in a
clockwise direction about said pitch circle of said outer gear starting at an angle from the
vertical axis equal to 360 divided by the number of teeth on said outer gear minus two
times the angle resulting from the roll of said first epi cycloid roll until the generated
10 curve intersects said outer crescent radius; connecting the resulting gear profiles with an
arc slightly offset from said outer crescent radius in order to provide running clearance;
copying the resulting gear form about the centre of said pitch circle of said outer gear
at increments equal to 360 divided by the number of teeth of said outer gear; generating
the pitch circle of said inner gear; producing an epi cycloid of a first cycloid set by rolling
said epi cycloid in a clockwise direction about said pitch circle of said inner gear by
starting at the vertical axis of said pitch circle of said inner gear until the generated curve
intersects said inner crescent radius; producing a hypo cycloid of a first cycloid set by
rolling in a counterclockwise direction about said pitch circle of said inner gear by
starting at the vertical axis until the generated curve is slightly smaller in length than said
20 hypo cycloid curve generated on said outer gear; producing an epi cycloid of a second
cycloid set by rolling in a clockwise direction about said pitch circle of said inner gear
starting at an angle from the vertical axis equal to 360 divided by the number of teeth
on said inner gear minus two times the angle resulting from a full 180 theoretical roll
of said first epi cycloid until the generated curve intersects at inner crescent radius;
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providing a hypo cycloid of a second cycloid set by rolling in a clockwise direction around
the pitch circle of said inner gear starting at an angle from the vertical axis equal to 360
divided by the number of teeth on the inner gear minus two times the angle resulting
from the full 180 theoretical roll of said first epi cycloid until the generated curve is
slightly smaller in length than the hypo cycloid curve generated on the outer gear and
is equal in length to the hypo cycloid curve generated by said first cycloid set; connecting
the resulting gear profiles with an arc offset slightly from the connecting arc on the outer
gear set to provide a running clearance; copying the resulting gear form about the centre
of said pitch circle of said inner gear at increments equal to 360 divided by the number
10 of teeth of said inner gear; connecting the gaps left between said epi cycloids with an arc
slightly smaller than the inner crescent arc in order to provide running clearance.
DESCRIPTION OF DRAVVINGS
These and other objects and features of the invention shall now be
described in relation to the following drawings.
Figure 1 illustrates a prior art crescent involute gear pump arrangement.
Figure 2 is a top plan view of the dual cycloidal crescent gear set.
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Figure 3 is a partial top plan view of the tooth engagement of the invention.
Figure 4 is a partial top plan view of the crescent area of the gear pump.
Figure S is a cross-sectional view of said dual cycloidal crescent gear set.
Figure 6 illustrates the generation of an inner cycloid profile.
10 Figure 7 illustrates the generation of an outer cycloid profile.
Figure 8 illustrates a top plan view of the gear set or rotary assembly.
Figure 9 is another top plan view of the dual cycloidal crescent gear set.
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DESCRIPIION OF THE INVENTION
Like parts have been given like numbers throughout the figures.
Figure 1 illustrates the top plan view of a prior art involute crescent gear
set. In particular Figure 1 illustrates the outer gear or rotor 2 having internal teeth 4.
An inner gear or rotor 6 is concentrically journaled for rotation about a shaft 8. The
inner gear 6 includes exterior teeth 10. The teeth 4 and 10 have involute gear profiles.
A crescent shaped piece of metal 12 is inserted between the gears 4 and 8 at the lower
10 dead band location. The gears 4 and 6 are located within a housing chamber (not
shown) which housing has an intake port (not shown) and a discharge port (not shown).
The resulting pump seals across the drive surface on the involute at the top dead band
12 as well as between the ends of the internal and external gear teeth 4 and 6 and the
crescent 12.
Involute crescents generally have a large number of teeth relative to other
types of pumps. Furthermore involute crescent gear pumps require a large offset in
order to function properly which greatly reduces the displacement of the pump for a
given pump size.
Figure 2 illustrates the crescent gear set 20 of the invention to be described
herein which comprises of an internally toothed ~nmll~r gear 22 journaled for rotation
about a second axis 24 and an externally toothed ~nmll~r gear 26 rotatably engageable
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with the internally toothed ~nn~ r gear 22 about a first axis 28. The interior gear 26
is also journaled for rotation about a shaft 30 as best illustrated in Figures 2 and 5.
In the arrangement illustrated in Figure 2, the inner and outer gears 26 and
22 are adapted to be placed within a housing (not shown) which housing includes a
chamber to receive said crescent gear set 20. Furthermore, the housing includes an
intake port (not shown) and a discharge port (not shown?. As the shaft 30 rotates, it
drives the inner gear 26 so as to rotate the outer gear 22.
The inner gear 26 includes teeth 34 presenting dual cycloidal profiles.
Furthermore, the outer gear 22 includes teeth 36 having a dual cycloidal profile. The
crescent 32 seals across the teeth 34 and 36 along the bottom dead band.
As the outer gear 22 rotates, the fluid, such as oil or the like, is drawn
from the intake port (not shown) and fills the space between the teeth 34 and 36 until
such teeth contact the crescent 32. Upon further rotation of the inner and outer gears
26 and 22, the fluid between the teeth after the crescent 32 becomes compressed and
then discharged out of the discharge port (not shown).
The outer gear 22 includes a pitch circle or outer or second generating
circle 38 and the inner gear 26 includes an inner pitch circle or first generating circle 40.
The outer pitch circle 38 is concentric about second axis 24 and the inner pitch circle 38
is centred about first axis 28.
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The inner and outer pitch circles 40 and 38 are tangent at the top dead
band 42 as shown in Figure 2.
Figure 3 shows the exterior tooth 34 of inner gear 26 meshing with interior
tooth 36 of outer gear 22 at point 44. The b~c~ ch 46 is illustrated in Figure 3 and
comprises of the space between the teeth 34 and 36. Furthermore, the inner crescent
radius with clearance is illustrated at 48 and the outer crescent radius with clearance is
illustrated at 50 as best shown in Figure 3.
The inner crescent radius with clearance 48 and outer crescent radius with
clearance 50 is also shown in Figure 4.
The generation of the dual cycloidal outer gear 22 shall now be described
in relation to Figure 7. The dual cycloidal outer gear 22 is generated using a pair of a
epi and hypo cycloid sets rolling around a single generating circle (ie. second generating
circle) or pitch circle of the outer gear 38. The sum of the radii R1 and R2 equals the
offset of the inner and outer gears 26 and 22. In particular the offset is defined by the
distance between the second axis 24 and the first axis 28 as shown in Figure 2. The
radius of the pitch circle 38 of outer gear 22 equals half the number of teeth 36 on the
20 outer gear 22 multiplied by the offset. The radius R1 of the epi cycloid will be between
20% to 25%
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of the offset and the radius R2 f the hypo cycloid will be between 75% to 80% of the
offset.
The tooth 36 of the outer gear 22 is generated as follows:
(a) The epi cycloid 52 of a first cycloid set is rolled in a clockwise direction
54 about the generating circle 38 starting at the vertical axis for a full
180 of roll.
(b) The hypo cycloid 56 of the first cycloidal set is rolled in a counter-
clockwise direction 58 around the generating or pitch circle 38 starting at
the vertical axis until the generated curve intersects the radius of the
outer crescent 50.
(c) The epi cycloid of a second cycloidal set is rolled in a counter-clockwise
direction about the generating circle 38 starting at an angle from the
vertical axis equal to 360 divided by the number of teeth of the outer
gear 22 minus two times the angle resulting from the length of roll of the
first epi cycloid 52 roll for a complete 180 of roll.
(d) The hypo cycloid of the second cycloidal set is rolled in a clockwise
direction around the generating circle 38 starting at an angle from the
vertical axis equal to 360 divided by the number of teeth on the inner
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gear minus two times the angle resulting from the roll of the first epi
cycloid roll, until the generated curve intersects the radius of the outer
crescent arch 50.
(e) The resulting gear profiles are connected with an arch slightly offset from
the outer crescent arch 50 in order to provide running clearance.
(f) The resulting tooth form 36 can be ~ lored and rotated about the centre
of the generating circle 38 to create a complete outer gear.
The generation of the dual cycloidal inner gear shall now be described
in relation to Figure 6. The dual cycloidal inner gear 26 is generated using a pair of
epi and hypo cycloid sets rolling around a single generating circle 40. The sum of the
radii of the cycloid set R3 and R4 equals the offset of the inner and outer gear 26 and
22. The radius of the generating circle 40 equals half the number of teeth 34 on the
inner gear 26 multiplied by this offset. The radius of the epi cycloid R3 will be
between 20% to 25% of the offset, and the radius of the hypo cycloid will be between
75% to 80% of the offset.
A tooth 34 of the inner gear 26 is generated as follows:
(a) The epi cycloid 60 of the first cycloid set is rolled in a clockwise direction
62 until the generated cu~ve intersects the inner crescent radius 48.
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(b) The hypo cycloid 64 of the first cycloid set is rolled in a counter-clockwise
direction 66 around the generating circle 40 starting at the vertical axis
until the generated curve is slightly smaller in length than the hypo cycloid
curve generated on the outer gear 22.
(c) The epi cycloid of the second cycloid set is rolled in a counter-clockwise
direction about the pitch circle 40 starting at an angle from the vertical
axis equal to 360 divided by the number of teeth on the inner gear minus
two times the angle resulting from a full 180 theoretical roll of the first
epi cycloid 60 until the generated curve intersects the inner crescent
radius 48.
(d) The hypo cycloid of the second cycloid set is rolled in a clockwise
direction around the generating circle 40 starting at an angle from the
vertical axis equal to 360 divided by the number of teeth on the inner
gear 26 minus two times the angle resulting from the full 180 theoretical
roll of the first epi cycloid 60 until the generated curve is slightly smaller
in length than the hypo cycloid curve generated on the outer gear 22 and
is equal in length to the hypo cycloid curve generated by the first cycloid
set.
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(e) The resulting gear profiles are connected with an arch offset slightly from
the connecting arch on the outer gear set to provide a running clearance.
(f) The resulting gear form is rotated an copied about the centre of the
generating circle at angle increments equal to 360 divided by the number
of teeth on the inner gear 26.
(g) The gaps left between the truncated epi cycloids are connected with an
arch slightly smaller than the inner crescent arch in order to provide
running clearance.
The resulting gear set 22 and 26 will have two more teeth on the outer
gear 22 than the inner gear 26 and will operate as a crescent gear pump.
Figure 9 illustrates the top dead band seal point 80 at the rotor drive.
Furthermore, Figure 9 also illustrates the intake and exhaust dwell 82 which in the
configuration shown in Figure 9 dwell of 141.78. Furthermore, an intake separation
84 is shown as well as the bottom seal across the tooth and crescent 86. The bottom
dead band 88 as shown in Figure 9 co~ ises of 60.
Figure 8 illustrates the pitch radius 90 of inner rotor 26 and the pitch
radius 92 of the outer rotor 22. Furthermore, line 94 shows the continuation of the
lower tooth profile generated in the manner as described above.
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Furthermore, the pocket area 96 of the inner rotor 26 as well as the
pocket area 98 of the outer rotor 22 is shown in Figure 8.
The displacement generated per revolution of the dual cycloidal gear set
is equal to the number of inner gear teeth 34 times the sum of the pocket area 96 of
the inner gear 26 and the pocket area 98 of the outer gear 22 to the crescent 32.
The teeth of the inner and outer gears 26 and 22 area shaped to conform
to the shape of the crescent 32 where they are in contact with the crescent 32 to
obtain a more restrictive leakage path. The actual clearance between the inner and
out teeth tip to the crescent 32 and the number of teeth in contact with the crescent
will determine the amount of leakage of the pump.
The pump which utilizes the dual cycloidal gear sets as described herein
allows the pump to displace more oil from an equivalent size gear set or the same
amount of oil from a smaller more efficient gear set.
Furthermore, optimized sealing capabilities are observed with the
invention as described herein as the bottom dead band through the large crescent 32
to gear sealing area resulting from the square tooth shape which is generated by
Iltili7.illg the invention as described herein.
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Although the preferred embodiment as well as the operation and use
have been specifically described in relation to the drawings, it should be understood
that variations in the plefelled embodiment could easily be achieved by a man skilled
in the art without departing from the spirit of the invention. Accordingly the invention
should not be understood to be limited to the exact form revealed by the drawings.
