Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUNI:~ OF THE INVENTION
1. Field of the Invention
This invention relates generally to the design of a hydraulic motor
and more specifically to a Gerotor hydraulic motor in which provision is made
for controlling the pressure exerted on the shaft and shaft seals as well as
upon the rotor element of the gerotor assembly.
Il. Description of the Prior Art
Gerotor hydraulic motors, per se, are well known in the art. In
this arrangement an inner gear is keyed to, and rotates with, the shaft to be
10 driven. An outer gear of the internal type is driven by the hydraulic fluid
introduced through timing crescents formed in the adiacent end and front plates
and is free to rotate with a snug fit in a stator which forms a part of the housing.
The inner gear has a lesser number of teeth than is provided in the outer gear
and the teeth of the two gears are specially shaped so that the top of all teeth
of the inner gear are always in sliding contact with the teeth of the outer gear.
ln accordance with the present invention, the Gerotor elements are
sandwiched between an end plate and a front plate and one end of the shaft is
journaled for rotation in the end plate while the other end of the shaft is
journaled in suitable bearings in the front plate. A shaft seal is disposed in the
20 front plate in proximity to the front plate bearings to prevent the leakage of
hydraulic fluid along the shaft and past the front shaft bearings.
Hydraulic fluid, under high pressure, for example, 2,000 PSI may
be made to selectively flow through a first or a second port formed in the end
plate which communicates with the crescents abutting the Gerotor elements. The
remaining port communicates with the low pressure side of the Gerotor element.
In known prior art arrangements, motors of the Gerotor type are only designed
to produce unidirectional shaft rotation, either clockwise or counterclockwise,
but not both. The motor design of the present invention, however, allows a
reversal in the direction of rotation by simply controlling the flow of the high
3~ pressure hydraulic fluid to the inlet/outlet ports, while still providing pressure
relief to the shaft seal. Also, to accommodate bidirectional rotation of the shaft,
first and second motoring grooves are provided between the stator element of
the Gerotor and the internal toothed outer gear. These motoring grooves cooper-
ate with motoring groove feed channels formed in the motor front plate and with
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corresponding shadow feed channels formed in the end plate. As such, axial
thrust forces which would otherwise exist on the faces of the inner and outer
gear elements of the Gerotor assembly are balanced, irrespective of the direc-
tion of rotation of the outer gear with respect to the stator.
Also in the preferred embodiment of the present invention, means
are provided to relieve the high pressure which would exist on the end of the
motor shaft tending to displace it outwardly if this relief structure were not
prov i ded.
The Banker United States patent No. 3,433,168 discloses the use
10 of a pressure relief valve in combination with a gear-type pump such that if the
output pressure of the pump is too great, the pressure relief valve will open
to permit fluid into the input port. This patent does not disclose the feature of
the present invention wherein first and second ball-check type pressure relief
valves are disposed in relationship to the bearing end seal to provide pressure
relief thereto irrespective of the direction of rotation of the motor shaft.
Similarly, the Compton United States patent No. 3,289,601 discloses in
Figure 7 thereof a Gerotor-type motor/pump having a channel 165 communicating
with an annular recess 166 formed in the front plate. This arrangement is
designed to provide pressure relief to the bearing seal 118, but it is to be
20 noted that in the Compton patent, such pressure relief only occurs when the
high pressure side of the hydraulic system is connected to the input port 49
and the low pressure connection is made to the output port 40. If an attempt
were made to reverse the direction of rotation of the motor by interchanging
the input/output port connections, no such relief would be available. Similarly,
the Compton patent does not include a pressure relief valve in communication
w i th the annu l a r recess 166.
SUMMARY OF THE INVENTION
It is accordingly the principal object of the present invention to
provide a Gerotor-type hydraulic motor which is simple in construction and
30 which permits bidirectional rotation of the output shaf~ through the mere
reversal of the normal high pressure and low pressure ports.
The above object of the invention is accomplished by providing first
and second pressure relief valves, one of which will always communicate with
Icw pressure side of the hydraulic system, irrespective of the direction of
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~-otation of the output shaft adopted. These pressure relief valves will ensure
that only modest hydraulic force is exerted on the shaft seals, thereby greatly
extending their life. Furthermore, first and second motoring grooves are
provided in the stator element of the Gerotor and are axially disposed on either
side of the gear position defining the conventional separated fluid-tight pockets
or chambers of the Gerotor assembly. These motoring grooves, then, provide
for equalization of forces on the faces of the Gerotor elements, irrespective of
the direction of rotation that the inner gear and outer gear assume.
Also in accordance with the teachings of the present invention, the end
10 plate has a channel or groove provided on the internal face thereof which
communicates between the shaft bore therein and the normal, low pressure output
port and ensures that the hydraulic force acting in the axial direction on the end
of the motor shaft will not be excessive, at least when the motor is caused to
rotate in a first direction.
A further object of the invention is to provide a hydraulic motor
comprising: an end plate having a cylindrical axial bore, a fluid inlet port and
a fluid outlet port formed therein, each of said ports individually communicating
with first and second crescent-shaped grooves formed in one face of said end
plate and with each other by way of a by-pass bore; a needle valve threadedly
20 mounted in said end plate and cooperating with said by-pass bore for permitting
selective blocking and unlocking of said by-pass bore; a shaft having one end
thereof journaled for rotation in said cylindrical axial bore in said end plate;
a Gerotor assembly abutting said one face of said end plate and including a stator
ring having a cylindrical bore with two axial grooves extending inwardly from
said bore and arcuately spaced from one another, said stator ring being secured
to said end plate, an outer gear of the internal tooth type having a cylindrical
outer peripheral surface which is rotatable within said cylindrical bore of said
stator ring, and an inner gear secured to said shaft, said inner gear being
eccentrically disposed within said outer gear and having a lesser number of
30 teeth than said outer gear, the tops of all teeth of said inner gear being shaped
to always be in sliding contact with the teeth of said outer gear; a front plate
having one face thereof abutting said Gerotor assembly and secured to said
stator r-ing and having an axial bore extending therethrough for receiving said
shaft in rotational engagement therein, said one face of said front plate having
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"rst and second crescent-shaped grooves therein in substantial alignment with
said crescent-shaped grooves formed in said one face of said end plate and
with predetermined segments of the interface between said inner and said outer
gears of said Gerotor assembly; a seal member surrounding said shaft and
disposed within said axial bore in said front plate; first and second radial bores
in said front plate extending from said axial bore in said front plate to the outer
surface of said front plate; first and second channels individually formed
between said first and second radial bores and said first and second
crescent-shaped grooves formed in said one face of said front plate; and first
10 and second pressure relief valves disposed in said first and second radial
bores in a normal fluid blocking relationship between said axial bore in said
front plate and said first and second channels, the arrangement being such that
upon closure of said by-pass bore by said needle valve if the fluid pressure
acting on said seal member exceeds a predetermined value one of said first
and second pressure relief valves will assume a fluid passing relationship
between said axial bore in said front plate and one of said first and second
channe I s.
These and other features and advantages of the invention will become
apparent to those skilled in the art upon a reading of the following detailed
20 description of the preferred embodiment, especially when considered in light
of the accompanying drawings in which:
DESCRIPTION OF THE DRAWINGS
Figure 1 is a longitudinal, cross-sectional view of a motor driven
pump assembl y;
Figure 2 is an end view of the motor assembly of Figure 1, partially
broken away to reveal certain internal features thereof;
Figure 3 is a cross-sectional view taken along the line 3-3 in Figure
2;
Figure 4 is a plan view of the face of the end plate as observed along
30 line 4-4 inFigure 1;
Figure 5 is a plan view of the Gerotor assemb!y as observed along
the line 5-5 inFigure 1; and
Figure 6 is a plan view of the front plate portion of the motor of
Figure 1 taken along the line 6-6.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to Figure 1 there is indicated generaliy by numeral
10 a hydraulic motor driven centrifugal pump which includes a motor section
indicated generally by numeral 12 and a centrifugal pump section indicated
generally by numeral 14 which are connected together and mounted on a
common shaft 16. While the present invention is principally concerned with
the construction of the hydraulic motor 12, it is deemed beneficial to show
the physical relationship between the motor and pump 14 driven thereby.
~ith respect to the hydraulic motor 12, as can be seen from
Figure 1, it is basically comprised of three sections, namely an end plate 18,
a front plate 20 and a Gerotor assembly 22 sandwiched therebetween. The end
plate 18, the Gerotor assembly 22 and the front plate 20 are connected together
by means of bolts 24 which pass through the aligned holes 26, 28 and 30 formed
in the end plate 18, the Gerotor assembly 22 and the front plate 20, respectively.
V\tith respect to Figures 1 and 5, it can be seen that the Gerotor
assembly 22 comprises a stator member 32 having a cylindrical bore 34 formed
therethrough. Holes of differing diameter and having dowel pins 33 and 35
press fitted therein are provided, the dowel pins extending outwardly from
each face of the stator member 32 to provide registration between the mating
surfaces of the end plate 18 and the front plate 20. Formed on opposing faces
of the stator 32 are annular grooves 36 in which are disposed O-rings made
from a suitable resilient material to form a tight, fluid retaining seal betweenthe mating surfaces of the end plate 18 and the front plate 20. Contained
within the cylindrical bore 34 of the stator.element 32 is an outer gear 40
having a plurality of internal teeth 42. The diameter of the outer gear 40 is
slightly less than the diameter of the bore 34 so that the gear element 40 may
rotate freely therein. First and second motoring grooves 44 and 46 are formed
axially on the inner surface of the cyiindrical bore 34 and are disposed at
equal angles on either side of the center line 48 of the cylindrical bore 34.
Contained within the opening defined by the teeth formed in the outer
gear 40 Is an inner gear 50 which is adapted to be secured to the shaft 16 by
means of a key (not shown~ which fits into the notch 52 which is contiguous withthe bore 54 through which the shaft 16 pasSes.
lt is to be noted that the internal gear 50 has one less tooth than does
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the outer gear 40. It may also be seen from Figure 5 that the teeth of the gears
40 and 50 are rounded and they operate on the well-known Gerotor~ principle,
with the teeth on the respective gears sealingly engaging one another to define
fluid-type pockets between the gears.
The configuration of the end plate 19 will next be described by
reference to Figures 1-4. First and second hose fittings 56 and 58 are
threadedly inserted in tapped bores 60 and 62 formed in the end plate 18.
In the explanation which will follow the detailed description of the construction
of the preferred embodiment, it will be assumed that fitting 58 is adapted to be
10 connected to the high pressure side of a source of hydraulic fluid and that
fitting 56 is adapted to be connected to the low pressure side of the hydraulic
fluid source. However, in accordance with the principles of the present
invention, the direction of rotation of the shaft 16 may be reversed by a simple
reversal of the inlet and outlet connections 58 and 56. With particular
reference to Figures 2 and 3, it can be seen that there is also drilled or other-
wise formed in the end plate 18 a bore 64 which passes between the threaded
ports 60 and 62. A needle valve assembly, indicated generally by numeral 65
is disposed in another bore 68 formed in the end plate 18 and the valve stem
portion 70 can be screwed inward and outward in a blocking and unblocking
20 relationship with the bore 64 in a conventional fashion. An O-ring seal 73 is
disposed in a tapered notch and cooperates with a smooth cylindrical portion
75 of the needle valve stem to prevent leakage during adjustment of the valve
opening. A locking nut 72 may be employed to maintain a desired setting of
the needle valve stem 70 with respect to the bore 64.
Milled, cast, or otherwise formed on the inner face 74 of the end
plate 18 are first and second crescent-shaped grooves 76 and 78. The crescent
groove 76 communicates with the inlet/outlet port 62 while the crescent groove
78 communicates with the input/output port 60. Also formed in the face 74 of
the end plate 18 are first and second motoring groove feed channels 80 and 82.
30 The channel 8S~ abuts and communicates with the crescent groove 76 while the
channel 82 buts and communicates with the crescent groove 78. By observing
the disposition of the feed channels 80 and 82 in Figure 4 with respect to the
motoring grooves 44 and 46 in Figure 5, it can be seen that when the end plate
18 and the Gerotor assembly 22 are positioned in their abutting relationship
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as indicated in Figure 1, that the motoring grooves 44 and 46 will be aligned
with the motoring groove feed channels 80 and 82 respeceively. The dowel
pins 33 and 35 set into the Gerotor stator 32 fit into the holes 83 and 85 to
maintain proper registration and since the dowel pins and mating holes in the
end plate are of differing diameter, one-way orientation only is allowed such
that during assembly the feed groove channels 80 and 82 will always be aligned
with the motoring grooves 44 and 46.
Again referring to the cross-sectional view of Figure 1, there can
be seen in the end plate 18 a central bore 84 in which is disposed a needle
bearing assembly 86 w/hich rotatably supports the end of the shaft 16. A snap
ring 88 may conveniently be used to hold the bearing assembly 86 in place in
the end plate 18. A narrow relief groove 90 is formed in the face 74 of the end
plate 18 and communicates between the shaft bore 84 and the crescent groove
78. As will become more apparent when the operation of the device is described,
the relief groove 90 provides a means whereby the axial thrust acting on the
shaft 16 i s reduced.
Consideration will now be given to the construction of the front plate
assembly 20. In this regard, Figures 1 and 6 will be referred to. The front
plate 20 comprises a generally rectangular housing having an axial bore 92
formed in the face 94 thereof. The bore 92 extends for a predetermined dis-
tance where it engaged a concentric bore 96 of larger diameter and disposed
within the bore 96 is a needle bearing assembly 98 which rotatably supports the
shaft 16 within the front plate 20.
The bore 96 through the housing forming the front plate 20 also
engages an adjacent bore of somewhat larger diameter in which is disposed
a seal 99. Formed in the front surface 100 of the front plate 20 is a concentricbore 102 having a diameter which is greater than the diameter of the bore in
which the seal member 99 is fitted. Disposed in this bore 102 is a spacer ring
104 and a ball bearing assembly 106 which is held in place by means of a
snap-type retainer ring 108. The ball bearing assembly 106 supports the front
end of the shaft 16 and is designed to withstand relatively high axial thrust forces
Imp~c~D
to it by the tapered shoulder 110 of the shaft 16.
Referring to Figure 6, there is illustrated the configuration of the
crescent groove 112 and 114 formed in the face 94 of the front plate 20. Also
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tormed within the face 94 of the front plate 20 and communicating with their
respective crescent grooves 112 and 114 are motoring groove feed channel
shadow recesses 116 and 118. By referring to Figures 4 and 6, it can be seen
that when the face 74 of the end plate 18 and the face 94 of the front plate 20 are
juxtaposed against opposed surfaces of the Gerotor assembly Z2 that the crescent76 will be substantially aligned with the crescent 112 and the crescent 78 will
be aligned with the crescent 114. Similarly, the motoring groove feed channels
80 and 82 formed in the end plate will be in alignment with the corresponding
motoring groove feed channel shadow recesses 116 and ~ formed in the
face of the front plate 20. Proper registration of the parts is insured by the
dowel pins 33 and 35 cooperating with the holes 83-85 in the end plate and holes119 and 121 in the front plate.
Referring again toFigure 1, it can be seen that radially extending
bores 120 and 122 are formed in the housing and extend from the outer surface
thereof inwardly on opposite sides of the shaft 16. The bores 120 and 122 each
terminate in a concentric bore of lesser diameter indicated by numerals 124
and 126 respectively. Screwed into the bore 120 is a ball-check relief valve
12B and the bore 122 contains a similar ball-check relief valve assembly 130.
These two ball-check valve~s assembly are identical in construction and include
a spherical element which is normally held in a seating engagement with the bores
124 and 126 by means of conical springs. Communicating between the bore i20
and the crescent groove 114 is a bore 132. Similarly, a bore 134 connects
the crescent groove 112 to the bore 122.
While specifically not forming a part of the instant invention, there
is shown in Figure 1 a centrifugal pump head 14 which comprises a mounting
plate 136 which is bolted to the end surface 100 of the motor front plate 20.
The shaft 16 passes through a hole formed in the plate 136 and a seal 138
surrounds the shaft to preclude the fluid being handled by the pump 14 from
flowing back into the ball bearing assembly 106 of the motor and possible con-
taminating same. A cover plate 140 is fastened to the mounting plate 136 to
define a chamber 142 in which is iocated an impeller element i44. The impeller
144 is attached to the shaft 16 and is therefore driven thereby. The fluid
material to be pumped enters through the threaded opening 146 in the cover plate140, and is engaged by the impelier and forced out of the pump outlet (not shown).
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A slinger ring 148 is attached to the shaft 16 and is disposed in a recess formed
in the mounting plate 136 in an area between the seal 138 and the bearing
assembly 106 of the motor unit 12. Thus, any fluid which may find its way past
the seal 138 will be engaged by the sligner ring 148 and thrown radially out of
the slot 150, thus aiding further in protecting the motor bearings 106 from
contamination.
Now that the details of the construction of the preferred embodiment
have been set forth, consideration will be given to the mode of operation of the
devi ce.
OP ERAT ION
In order to drive the shaft 16 in a first direction, hydraulic fluid
under high pressure is introduced into the hose connection 58 on the end plate
18 and from there it passes through the port 62 which communicates with the
crescent groove 76 (Figure 4) and with the fluid pockets defined by the spacing
between the internal gear 50 with the external gear 40 of the Gerotor assembly
22. This fluid force tends to rotate the outer gear 40 in a clockwise direction
and in doing so also rotates the inner gear 50 in accordance with the well-known
principles of Gerotor action. The crescent 78 cooperates with the low pres-
sure port 60 which is connected at hose connection 56 back to the low pressure
side of the source of hydraulic fluid. The needle valve stem 70 being disposed
in a sealing relationship with respect to the bore 64 between the high pressure
inlet port and the low pressure outlet port can be used to control the fluid force
applied to the Gerotor elements. Specifically, when the valve stem 70 is in its
seated position with respect to the bore 64, all of the high pressure hydraulic
fluid is directed through the Gerotor gear elements to cause rotation thereof
whereas if the needle valve 70 is backed off by a desired amount, a portion of
the input fluid will bypass the Gerotor elements and pass directly to the output
port 60. The needle valve assembly 70 can then be used to control the rate of
rotation of the shaft 16 as well as the output torque delivered to the load.
Because both the inner gear S0 and the outer gear 40 of the Gerotor
assembly 22 must be free to rotate within the stator element 32 thereof, a slight
clearance must be maintained between the mating side surfaces of these gear
elements and the opposing faces 74 and 94 of the end plate and front plate
respectively. Because of this slight clearance to allow free rotation of the
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gear elements, the hydraulic fluid under high pressure is able to leak between
these mating surfaces. Hence, high pressure fluid in the crescent 76 may seep
between the interface of the inner gear 50 with the end plate '8 and through the
needle bearings 86 where it may act upon the cross-sectional area of the end
of the shaft 16 to apply an undesired axial thrust to the shaft. To alleviate
this problem, a relief groove 90 is provided which communicates with the bore
84 housing the needle bearings 86 and the crescent groove 78 associates with
the low pressure side of the hydraulic system. As such, the end of the shaft
is only exposed to the low pressure rather than to the relatively high pressure
10 appearing at the inlet port. This substantially reduces the axial thrust imparted
to the shaft 16 and prevents undue wear on the shaft and the associated thrust
bearings 1 06.
The high pressure hydraulic fluid present in the crescent gap 112
in the front plate 20 may also seep between the side surface of the inner gear
50 of the Gerotor assembly and its mating face 94 of the front plate 20. This
fluid, at a relatively high pressure, may then pass along the shaft 16 through
the needle bearing assembly 98 and will act upon the seal 99. In order to
9q
protect the seal 94 from inordinately high hydraulic fluid pressures, irrespec-
tive of the direction of rotation of the shaft 16, the ball-check valves 128 and20 130 are provided. Assuming for the moment that the high pressure line is
connected to the inlet fitting 58, as the pressure of the fluid along the shaft
16 increases above the nominal output line pressure the ball of the relief valve
128 will move out of engagement with the bore 124 against the force of the
conical spring to expose the volume defined between the cylindrical bore 96
and the shaft 16 to the low pressure connection via the bore 132, the crescent
groove 114, the exposed pockets between the Gerotor inner and outer gears,
the crescent 78 and the output port 60.
If ~ on the other hand, the motor is connected to rotate in the counter
clockwise direction and the high pressure line is connected to the coupling 56
30 while the low pressure is connected to the coupling 58, then the ball-check
valve 130 will come into play to provide pressure relief to the seal 99.
Specifically, the high pressure fluid in the volume defined by the bore 95
and the shaft 16 will operate upon the ball element of the check valve '30 and
urge it out of its seated engagement with the bore 122 to expose the above
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volume to the low pressure port by way of bore 134, crescent 112, the
pockets formed between the inner and outer gear elements of the Gerotor
assembly 22, the crescent groove 76 and the low pressure output port 58.
Thus, irrespective of the direction of rotation of the shaft, either the check
valve 128 or the check valve 130 will provide the desired relief to the seal
member 99, thereby greatly extending its useful life and decreasing the
frequency of repair of the unit.
Attention is next directed to Figures 4, 5 and 6, especially to the
provision of the motoring grooves 44 and 46 in the stator 32 of the Gerotor
assembly 22 and to the mating motoring groove feed channels 80 and 82 in the
end plate 18 and the motoring groove feed channel shadow recesses 116 and
118 in the face 94 of the front plate 20. Again, assuming that the high pres-
sure hydraulic fluid is applied to the inlet 58, the fluid will pass through the
bore 62 into the crescent 76 and into the motoring groove feed channel 80.
The fluid will, accordingly, pass through the motoring groove 44 and into the
motoring groove feed shadow 116 associated with the crescent 112 formed in the
face 94 of the front plate 20. Thus, it can be seen that the hydraulic forces
acting on opposite sides of the gear 40 will be equalized, thereby eliminating
thrust forces which would otherwise exist if such a motoring groove were not
20 provided. The fluid passing through the motoring groove 44 also serves to
lubricate the interface between the stator 32 and the rotating outer gear 40.
Similarly, if the motor of the present invention is connected to
operate in the reverse direction by connecting the high pressure side of the
source of hydraulic fluid to the port 56 rather than to the port 58, then the
high pressure fluid passes through the inlet port 50 into the crescent 78 and
through the motoring groove feed channel 82 and the motoring groove 46 into
the motoring groove feed channel shadow 118 associated with the crescent 114
in the front plate 20. Again, by providing the axial motor ing groove 46
the hydraulic pressures existing on each side of the Gerotor ring 40 will be
30 equliazed and no net axial force tending to move the shaft 16 to the right will
be imparted. Again, the hydraulic fluid, which is generally a lubricating oil,
passing through the motoring groove 46 provides lubrication to the mating
surfaces of the Gerotor outer gear 40 and the stator 32.
The structural materials for the motor described herein may include
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~noSe conventionally utilized, such as cast iron or cast aluminum. The
Gerotor assembly including the stator, the outer gear and the inner gear may
be formed from cold rolled steei, aluminum or other metal commonly used for
this purpose. The needle bearing assemblies 86, 98 and the ball bearing
assembly 106 are all commercially available and are selected based upon the
diameter of the shaft 16 and the expected axial thrust forces which are
expected to be encountered.
While there has been shown and described the preferred embodiment
of the invention and the best mode thereof which I have contemplated, it will be
10 obvious to those skilled in the art that the invention may be modified by
various substitutions and equivalents and that this disclosure is intended to
be illustrative only. The true scope of the invention is to be determined from
the aCcompanyirlg claims.
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