U.S. patent application number 12/186625 was filed with the patent office on 2009-02-12 for variable displacement type gear pump.
This patent application is currently assigned to KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Toshiro Fujii, Kazuo Murakami, Masaki Ota, Shigeru Suzuki, Katsumi Yamashita, Hironao Yokoi.
Application Number | 20090041593 12/186625 |
Document ID | / |
Family ID | 39967920 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090041593 |
Kind Code |
A1 |
Yokoi; Hironao ; et
al. |
February 12, 2009 |
VARIABLE DISPLACEMENT TYPE GEAR PUMP
Abstract
A variable displacement type gear pump has gear chambers, one of
which is a specific gear chamber. A suction passage is formed in
the housing so as to communicate with suction-side spaces. An
outlet passage communicates with discharge-side spaces. A return
passage returns the fluid discharged to the discharge-side space of
the specific gear chamber to the suction passage. The return
passage communicates with the suction passage at a confluence
portion located upstream side of the suction-side space. An opening
and closing valve opens the return passage in a small displacement
operational state. A check valve is located between the
discharge-side space of the specific gear chamber and the outlet
passage for preventing the fluid discharged from the gear chamber
other than the specific gear chamber from flowing into the
discharge-side space of the specific gear chamber in the small
displacement operational state.
Inventors: |
Yokoi; Hironao; (Kariya-shi,
JP) ; Suzuki; Shigeru; (Kariya-shi, JP) ;
Yamashita; Katsumi; (Kariya-shi, JP) ; Fujii;
Toshiro; (Kariya-shi, JP) ; Ota; Masaki;
(Kariya-shi, JP) ; Murakami; Kazuo; (Kariya-shi,
JP) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
CIRA CENTRE, 12TH FLOOR, 2929 ARCH STREET
PHILADELPHIA
PA
19104-2891
US
|
Assignee: |
KABUSHIKI KAISHA TOYOTA
JIDOSHOKKI
Aichi-ken
JP
|
Family ID: |
39967920 |
Appl. No.: |
12/186625 |
Filed: |
August 6, 2008 |
Current U.S.
Class: |
417/307 ;
418/205 |
Current CPC
Class: |
F04C 11/001 20130101;
F04C 14/065 20130101; F04C 2/18 20130101; F04C 2240/30 20130101;
F04C 2/086 20130101; F04C 14/26 20130101 |
Class at
Publication: |
417/307 ;
418/205 |
International
Class: |
F04C 14/26 20060101
F04C014/26; F04C 2/14 20060101 F04C002/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2007 |
JP |
2007-207331 |
Feb 12, 2008 |
JP |
2008-030926 |
Claims
1 . A variable displacement type gear pump for introducing and
discharging fluid, comprising: a housing; plural gear chambers
formed in the housing, one of which is a specific gear chamber; a
gear mechanism accommodated in the respective gear chamber; a
suction-side space formed in the respective gear chamber; a suction
passage formed in the housing so as to communicate with the
suction-side spaces; a discharge-side space formed in the
respective gear chamber; an outlet passage communicating with the
discharge-side spaces; a return passage returning the fluid
discharged to the discharge-side space of the specific gear chamber
to the suction passage, the return passage communicating with the
suction passage at a confluence portion located upstream side of
the suction side space; an opening and closing valve provided in
the return passage and opening the return passage in a small
displacement operational state; and a check valve located between
the discharge-side space of the specific gear chamber and the
outlet passage for preventing the fluid discharged from the gear
chamber other than the specific gear chamber from flowing into the
discharge-side space of the specific gear chamber in the small
displacement operational state.
2. The variable displacement type gear pump according to claim 1,
wherein the gear mechanism includes a drive shaft, wherein the
suction passage is formed along a rotational axis of the drive
shaft, wherein the suction passage has an inlet, wherein the inlet
is open at an end face of the housing so as to face in the
direction of the rotational axis.
3. The variable displacement type gear pump according to claim 1,
wherein the return passage, the outlet passage, and the check valve
are formed in the housing.
4. The variable displacement type gear pump according to claim 1,
wherein the suction passage has a circular cross-sectional surface,
wherein the return passage communicates with the suction passage in
a tangent direction with respect to the circular cross-sectional
surface at the confluence portion.
5. The variable displacement type gear pump according to claim 1,
wherein the return passage communicates with the suction passage at
the confluence portion in an inclined manner with respect to a flow
direction of the suction passage, wherein the inclination is in a
direction to increase the speed of the fluid in the suction
passage.
6. The variable displacement type gear pump according to claim 1,
wherein the confluence portion has a guide portion at an end of the
return passage adjacent to the suction passage, wherein a flow
direction of the outflow from the return passage is coincident with
a flow direction of the suction passage.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application Nos. 2007-207331 filed Aug. 9, 2007 and 2008-030926
filed Feb. 12, 2008.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a variable displacement
type gear pump. Specifically, the variable displacement type gear
pump has plural gear mechanisms including a drive gear and a driven
gear, and the plural gear mechanisms are accommodated in plural
gear chambers which are independently formed.
[0003] Generally, a gear pump includes a gear mechanism having a
drive gear and a driven gear therein. The gear pump introduces
fluid from the outside, pressurizes the fluid through a gear
mechanism, and discharges the fluid to the outside. In case that
hydraulic oil is utilized as the fluid for the gear pump, the gear
pump is capable of operating a hydraulic equipment located in a
hydraulic circuit. The gear pump has a simple structure, compared
to other type pumps. Therefore, the operation and the maintenance
are easily performed, and further, the manufacturing cost is low.
In addition, the gear pump is not easily affected by foreign
matters in the fluid. The gear pump is appropriate for downsizing
and reducing weight. Thus, the gear pump is utilized, for example,
as a hydraulic pump in an industrial vehicle such as a forklift
truck, and is operated by a combustion engine for running the
industrial vehicle.
[0004] The discharge flow rate of the gear pump is determined in
accordance with the rotational speed of the gear pump, and it is
difficult to change the flow rate irrespective to the rotational
speed. When the gear pump is operated more than demands, the gear
pump generates excessive flow rate, and performs excessive work as
a gear pump. A variable displacement type gear pump with plural
gear mechanisms has been proposed for achieving discharge
displacement. The variable displacement type gear pump is shifted
between two states. That is, in one state, a specific gear
mechanism in the plural gear mechanisms discharges pressurized
fluid to the outside, and in other state, the fluid is returned
from the specific gear mechanism to the suction side, thereby
achieving the discharge displacement.
[0005] Japanese Unexamined Patent Publication No. 2002-70757
discloses a double gear pump as a variable displacement type gear
pump. In the double gear pump, a drive gear and two driven gears
engaging with the drive gear are accommodated in a casing, and
function as first and second pumps. An inlet and an outlet of the
second gear pump are connected through an unload passage. An
electromagnetic valve is provided in the unload passage. When the
electromagnetic valve is closed, the first pump and the second pump
are operated in parallel, thereby increasing the discharge
displacement. In this state, the gear pump is in large displacement
operational state. When the electromagnetic valve is opened, the
second pump is unloaded, thereby decreasing the discharge
displacement. In this state, the gear pump is in small displacement
operational state.
[0006] In this type of variable displacement gear pump, the first
pump and the second pump are located parallely. The inlet and the
outlet of the first pump are located reversely to the inlet and the
outlet of the second pump, due to the rotational direction of the
drive shaft. That is, the inlet of the first pump and the outlet of
the second pump are located at one side of the drive shaft, and the
outlet of the first pump and the inlet of the second pump are
located at the other side. In the variable displacement type gear
pump, a suction passage and a discharge passage are formed by
connecting fluid passages at the inlet side and the outlet side of
the first and the second pumps.
[0007] However, in the variable displacement type gear pump as
disclosed in the above reference, the inlet and the outlet of the
first pump are located reversely to the inlet and the outlet of the
second pump. The structure is complicated if the pump body includes
therein the suction and discharge passages formed by connecting the
fluid passages at the inlet side and the outlet side. It is also
difficult to form such a pump body with the complicated passages.
Further, this kind of variable displacement gear pump increases the
size of the whole equipment, since the unload passage is located
outside the gear pump for returning the fluid from the second pump
to the inlet. Further, the fluid in the unload passage is divided
into the first the second pumps, and joins the flow delivered from
the inlet of the gear pump at the outlet of each pump so as to be
discharged from each outlet, when small displacement operation is
continued. Thereby the fluid flowing through the unload passage
continuously circulates through a specific part in the body of the
gear pump, due to the continuation of the small displacement
operation. That may cause a problem that the temperature
distribution is uneven in the housing of the gear pump. The
unevenness of the temperature distribution in the housing may
result in deforming the housing and decreasing the operational
efficiency of the gear pump.
[0008] The present invention is directed to provide a variable
displacement type gear pump that has a suction passage by
connecting passages at the suction side in a housing, and that
prevents specific fluid from continuously circulating in a specific
passage in a gear pump body, even if continuing small displacement
operation.
SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, a variable
displacement type gear pump introduces and discharges fluid. The
gear pump includes a housing, plural gear chambers having a gear
mechanism, a suction-side space, and a discharge-side space. The
plural gear chambers are formed in the housing, one of which is a
specific gear chamber. The gear mechanism is accommodated in the
respective gear chamber. The suction-side space is formed in the
respective gear chamber. The discharge-side space is formed in the
respective gear chamber. The gear pump further includes a suction
passage, an outlet passage, a return passage, an opening and
closing valve, and a check valve. The suction passage is formed in
the housing so as to communicate with the suction-side spaces. The
outlet passage communicates with the discharge-side spaces. The
return passage returns the fluid discharged to the discharge-side
space of the specific gear chamber to the suction passage. The
return passage communicates with the suction passage at a
confluence portion located upstream side of the suction-side space.
The opening and closing valve is provided in the return passage,
and opens the return passage in a small displacement operational
state. The check valve is located between the discharge-side space
of the specific gear chamber and the outlet passage for preventing
the fluid discharged from the gear chamber other than the specific
gear chamber from flowing into the discharge-side space of the
specific gear chamber in the small displacement operational
state.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
The invention together with objects and advantages thereof, may
best be understood by reference to the following description of the
presently preferred embodiments together with the accompanying
drawings in which:
[0011] FIG. 1 is a longitudinal cross-sectional view of a variable
displacement type gear pump according to a first preferred
embodiment;
[0012] FIG. 2 is a cross-sectional view of the gear pump taken
along the line I-I in FIG. 1;
[0013] FIG. 3 is a cross-sectional view of the gear pump taken
along the line II-II in FIG. 2;
[0014] FIG. 4 is a cross-sectional view of the gear pump in small
displacement operational state;
[0015] FIG. 5 is a partial cross-sectional view of a variable
displacement type gear pump according to a second preferred
embodiment;
[0016] FIG. 6 is a partial cross-sectional view of a variable
displacement type gear pump according to a third preferred
embodiment; and
[0017] FIG. 7 is a longitudinal cross-sectional view of a variable
displacement type gear pump according to a fourth preferred
embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] A first preferred embodiment according to the present
invention will be described with reference to FIGS. 1 through 4.
FIG. 1 shows a variable displacement type gear pump 10 in large
displacement operational state. As shown in FIG. 1, the variable
displacement type gear pump 10 includes a body 11 which
accommodates drive gears 22, 25 and driven gears 23, 26 therein.
The body 11 has two spaces which are formed so as to extend from
both axial end faces of the body 11. One space is a first gear
chamber 12 and the other space is a second gear chamber 13. In this
embodiment, the second gear chamber 13 serves as a specific gear
chamber. A partition 14 is formed between the first gear chamber 12
and the second gear chamber 13.
[0019] A front housing 15 is joined to one end of the body 11. A
rear housing 16 is joined to the other end of the body 11. In this
embodiment, the body 11, the front housing 15, the rear housing 16
constitute a housing assembly. The body 11 and the front and the
rear housings 15, 16 are joined by through bolts 30 with each other
as shown in FIG. 2. It is noted that the front side where the front
housing 15 is located corresponds to the left side in the drawings
(referring to FIGS. 1, 3, and 4). Similarly, the rear side where
the rear housing 16 is located corresponds to the right side in the
drawings. The front housing 15 closes the first gear chamber 12,
and the rear housing 16 closes the second gear chamber 13. A side
plate 17 is interposed between the first gear chamber 12 and the
end face of the front housing 15, and a side plate 18 is interposed
between the second gear chamber 13 and the end face of the rear
housing 16. Similarly, a side plate 19 is interposed between the
first gear chamber 12 and the partition 14, and a side plate 20 is
interposed between the second gear chamber 13 and the partition
14.
[0020] The drive gear 22 and the driven gear 23 at the front side
are externally engaged with each other so as to form a first gear
mechanism 21. The first gear mechanism 21 is accommodated in the
first gear chamber 12 as shown in FIGS. 2 and 3. The drive gear 25
and the driven gear 26 at the rear side are externally engaged with
each other so as to form a second gear mechanism 24. The second
gear mechanism 24 is accommodated in the second gear chamber 13 as
shown in FIG. 3. The front drive gear 22 accommodated in the first
gear chamber 12 is formed integrally with a drive shaft 27. The
drive gear 22 is coaxial with the drive shaft 27. The rear drive
gear 25 is fitted to the drive shaft 27 by way of spline coupling
or serration coupling. The drive gear 25 is coaxial with the drive
shaft 27. That is, the drive gears 22, 25 are formed so as to have
a common rotational axis.
[0021] The drive shaft 27 extends through the side plates 17, 18,
19, 20 and the partition 14 into the front housing 15 and the rear
housing 16. The drive shaft 27 is rotatably supported by the body
11, the front housing 15, and the rear housing 16 through a bearing
29. One end of the drive shaft 27 extends out of the front housing
15 so as to be connected to an external drive source which is not
shown, and receives driving force from the external drive
source.
[0022] The front driven gear 23 is formed integrally with a driven
shaft 28, and is coaxial with the driven shaft 28. The rear driven
gear 26 is fitted to the driven shaft 28 by way of spline coupling
or serration coupling. The driven gear 26 is coaxial with the
driven shaft 28. Similar to the drive shaft 27, the driven shaft 28
extends into the front housing 15 and the rear housing 16. The
driven shaft 28 is supported by the body 11, the front housing 15
and the rear housing 16 through an another bearing 29. The driven
gears 23, 26 are formed so as to have a common rotational axis.
Unlike the drive shaft 27, the end of the driven shaft 28 does not
extend out of the front housing 15.
[0023] As shown in FIG. 2, the first gear chamber 12 includes a
suction-side space 31 and a discharge-side space 32 defined by the
inner surface of the first gear chamber 12, the drive gear 22, and
the driven gear 23. The suction-side space 31 is formed at the
suction side for introducing oil as a fluid. The discharge-side
space 32 is formed at the discharge side for discharging the oil.
Similar to the first gear chamber 12, a suction-side space 33 and a
discharge-side space 34 are defined in the second gear chamber 13
as shown in FIG. 1.
[0024] A front suction passage 36 is formed in the body 11 along
the rotational axes of the drive shaft 27 and the driven shaft 28.
The oil is introduced into the first and the second gear chambers
12, 13 through the front suction passage 36. A rear suction passage
37 is formed in the rear housing 16 and communicates with the front
suction passage 36. The rear suction passage 37 has an inlet 38
which is open at the axial end face of the rear housing 16. The
inlet 38 is in communication with the outside. The front suction
passage 36 and the rear suction passage 37 have circular
cross-sectional surfaces, respectively. The front and rear suction
passages 36, 37 are linearly connected with each other. The front
suction passage 36 and the rear suction passage 37 constitute a
suction passage 35. The suction passage 35 is communicated with the
suction-side spaces 31, 33. The oil from the outside of the
variable displacement type gear pump 10 flows into the first and
the second gear chambers 12, 13 through the suction passage 35.
[0025] A front discharge passage 42 and a rear discharge passage 43
are formed in the body 11 for discharging the oil pressurized in
the gear chambers 12, 13 to the outside. The front discharge
passage 42 extends from the discharge-side space 32 of the first
gear chamber 12. The rear discharge passage 43 extends from the
discharge-side space 34 of the second gear chamber 13. The front
and rear discharge passages 42, 43 are connected with each other so
as to flow into a single outlet passage 41 downstream thereof
inside the body 11. Thereby the outlet passage 41 communicates with
the discharge-side spaces 32, 34 through the front and rear
discharge passages 42, 43. Further, the outlet passage 41 has an
outlet 44 which is in communication with the outside. The oil is
discharged to the outside of the gear pump 10 through the outlet
passage 41 and the outlet 44, and is supplied to a hydraulic
circuit which is connected to a hydraulic device, which is not
shown. A check valve 45 is provided in the rear discharge passage
43 in the body 11 and is located between the discharge-side space
34 of the specific gear chamber 13 and the outlet passage 41. The
check valve 45 serves to prevent the oil discharged from the gear
chamber 12, which is other than the specific gear chamber 13
(second gear chamber 13), from flowing into the discharge-side
space 34 of the specific gear chamber 13 in a small displacement
state.
[0026] The check valve 45 includes a ball-shaped valve body 46, a
coil spring 47, and a support member 48. The valve body 46 opens
and closes the rear discharge passage 43. The coil spring 47 is an
urging device for urging the valve body 46. The support member 48
supports the coil spring 47. The coil spring 47 applies urging
force to the valve body 46 in the direction to close the rear
discharge passage 43. The valve body 46 is moved in the direction
to open the rear discharge passage 43 against the urging force of
the coil spring 47 when the pressure in the rear discharge passage
43 is equal to or greater than a predetermined value. The valve
body 46 closes the rear discharge passage 43 by the urging force of
the coil spring 47 when the pressure in the rear discharge passage
43 is below the predetermined value. The urging force of the coil
spring 47 may be set small, since the valve body 46 is urged to a
seat surface in the support member 48 by the pressure difference.
The form of the valve body 46 is not limited to the ball-shape, and
may be a conical shape.
[0027] The rear housing 16 includes a return passage 50. The return
passage 50 communicates with the rear discharge passage 43, and
also communicates with the rear suction passage 37. That is, the
return passage 50 communicates with the suction passage 35 and the
discharge-side space 34 of the second gear chamber 13 so as to
return the oil discharged to the discharge-side space 34 to the
suction passage 35. An opening and closing valve 51 is provided in
the return passage 50 to open and close the return passage 50. The
valve 51 has a piston mechanism in which a cylindrical piston 53 is
slidably accommodated in a hollow cylinder 52 with a bottom.
[0028] The valve 51 opens and closes the return passage 50 by the
sliding movement of the piston 53 in the cylinder 52. The sliding
movement of the piston 53 is performed by the pressure difference
applied to the both end faces of the piston 53. That is, the
sliding movement of the piston 53 is performed by the pressure
difference between the pressure in the space at the side of the
return passage 50 and the pressure in the space in the cylinder 52
at the opposite side of the piston 53.
[0029] In this embodiment, the pressure difference applied on the
both end faces of the piston 53 is controlled by the actuation of
an electromagnetic valve 55 in the rear housing 16. The
electromagnetic valve 55 includes a spool 57, a coil 58, and a coil
spring 59. The spool 57 slides in a spool hole 56 formed in the
rear housing 16. The coil 58 moves the spool 57 frontward. The coil
spring 59 is an urging device for urging the spool 57. It is noted
that "upstream side of the return passage 50" corresponds to the
part of the return passage 50 between the valve 51 and the rear
discharge passage 43. Similarly, "downstream side of the return
passage 50" corresponds to the part of the return passage 50
between the valve 51 and the rear suction passage 37. The spool
hole 56 is in communication with the downstream side of the return
passage 50. The spool 57 includes a suction-pressure communication
passage 60 for communicating the return passage 50 to the cylinder
52. When the coil 58 is excited, the spool 57 is moved frontward.
When the coil 58 is de-excited, the spool 57 is moved rearward by
the coil spring 59.
[0030] A discharge-pressure communication passage 61 is formed in
the body 11 and the rear housing 16 for supplying the oil under
discharge pressure from the rear discharge passage 43 to the spool
hole 56. The discharge-pressure communication passage 61 includes
passages 62, 63 and a groove 64. The groove 64 is formed at the
outer periphery of the spool 57. When the coil 58 is de-excited and
the spool 57 is at the rear position, the discharge pressure in the
rear discharge passage 43 is applied to the cylinder 52 through the
discharge-pressure communication passage 61. When the coil 58 is
excited and the spool 57 is in the front position, the
suction-pressure communication passage 60 releases oil under
discharge pressure in the cylinder 52 to the return passage 50.
When the pressure in the cylinder 52 becomes to suction pressure
due to the excitation of the coil 58, the piston 53 opens the
return passage 50. When the pressure in the cylinder 52 becomes to
discharge pressure due to the de-excitation of the coil 58, the
piston 53 closes the return passage 50.
[0031] The following will describe the operation of the variable
displacement type gear pump 10 of the first preferred embodiment
according to the present invention. As shown in FIG. 1, the first
gear mechanism 21 and the first gear chamber 12 at the front side
constitute a front gear pump portion P1. The second gear mechanism
24 and the second gear chamber 13 at the rear side constitute a
rear gear pump portion P2. The front gear pump portion P1 and the
rear gear pump portion P2 respectively have 50 percent of the
entire discharge displacement of the variable displacement type
gear pump 10.
[0032] The following will describe the operation of the drive gear
22 and the driven gear 23 in the front gear pump portion P1. When
the driving force is applied to the drive shaft 27 from the
outside, the drive gear 22 is rotated in one direction as shown in
FIG. 2. According to the rotation of the drive gear 22, the driven
gear 23 engaging with the drive gear 22 is rotated with the driven
shaft 28 in the direction opposite to the rotational direction of
the drive gear 22. When the drive gear 22 and the driven gear 23
are rotated while being engaged with each other, oil is introduced
into the suction-side space 31 from the suction passage 35.
[0033] The oil introduced in the suction-side space 31 is confined
in a space defined by teeth of the drive gear 22 and the inner
surface of the first gear chamber 12, and also in a space defined
by teeth of the driven gear 23 and the inner surface of the first
gear chamber 12. The oil confined in the spaces is transferred
along the inner surface of the first gear chamber 12 in the
rotational direction of the drive gear 22 and the rotational
direction of the driven gear 23, respectively. The oil confined in
the spaces is discharged to the discharge-side space 32. The oil in
the discharge-side space 32 is discharged to the outside of the
gear pump 10 through the front discharge passage 42, the outlet
passage 41, and the outlet 44, and delivered to a hydraulic device
not shown to operate the hydraulic device. The discharge pressure
is increased in accordance with the load of the hydraulic
device.
[0034] In the front gear pump portion P1, when the driving force is
applied to the drive shaft 27 from the outside, the drive gear 22
and the driven gear 23 in the first gear chamber 12 are driven, and
the oil is discharged to the discharge-side space 32. The
discharged oil is supplied to the front discharge passage 42. In
the rear gear pump portion P2, when the driving force is applied to
the drive shaft 27 from the outside, the drive gear 25 and the
driven gear 26 in the second gear chamber 13 are driven, and the
oil is discharged to the discharge-side space 34.
[0035] When the coil 58 of the electromagnetic valve 55 is not
excited, the spool 57 is located in the rear position, by receiving
the urging force of the coil spring 59. When the spool 57 is
located in the rear position, the discharge-pressure communication
passage 61 is communicated with the cylinder 52 of the valve 51.
The communication between the suction-pressure communication
passage 60 and the cylinder 52 is shut off. Therefore, the oil is
introduced from the rear discharge passage 43 through the
discharge-pressure communication passage 61, and the cylinder 52 is
filled with the oil under the discharge pressure. In the state
where the piston 53 does not close the return passage 50 yet, the
pressure in the return passage 50 communicating with the suction
passage 35 is lower than the pressure in the cylinder 52, and the
piston 53 is moved in the direction to close the return passage
50.
[0036] When the piston 53 closes the return passage 50, the
pressure in the discharge-side space 34 receiving the oil
discharged from the rear gear pump portion P2 is increased, and the
valve body 46 of the check valve 45 opens the rear discharge
passage 43. Thereby the oil discharged from the rear gear pump
portion P2 is supplied to the rear discharge passage 43 and the
return passage 50. As shown in FIG. 1, the oil flows from the rear
discharge passage 43 to the outlet passage 41, and does not flow to
the suction passage 35 through the return passage 50. In this
state, the oil discharged from the front gear pump portion P1 and
the rear gear pump portion P2 joins together, and is delivered to
the outside of the variable displacement type gear pump 10 through
the outlet passage 41. Therefore, in this state, the discharge
displacement of the variable displacement type gear pump 10 is 100
percent, and the gear pump 10 is in the large displacement
operational state. When the gear pump 10 is utilized in a material
handling device of a forklift truck, the large displacement
operational state of 100 percent may be set to correspond to the
load lifting-up state. The piston 53 has a larger diameter at the
side adjacent to the cylinder 52 (rear side), and is reliably urged
frontward to close the return passage 50, even when the pressures
at the front and rear sides of the piston 53 are equal with each
other.
[0037] Then, when the coil 58 of the electromagnetic valve 55 is
excited, the spool 57 receives the frontward force overcoming the
urging force of the coil spring 59, and is moved frontward. When
the spool 57 is located in the front position, the communication
between the discharge-pressure communication passage 61 and the
cylinder 52 is shut off. In this state, the spool hole 56, the
suction-pressure communication passage 60, and the cylinder 52 are
communicated with each other. Thereby the pressure in the cylinder
52 of the valve 51 is decreased from the discharge pressure to the
suction pressure. Since the upstream side of the return passage 50
equals the discharge pressure, the piston 53 is moved into the
cylinder 52 by receiving the pressure difference when the pressure
in the cylinder 52 becomes the suction pressure. By the retreat of
the piston 53 into the cylinder 52, the return passage 50 becomes
to the opened state.
[0038] Since the pressure at the upstream side of the return
passage 50 is decreased, the valve body 46 closes the rear
discharge passage 43 by the urging force of the coil spring 47 of
the check valve 45. As shown in FIG. 4, when the check valve 45
closes the rear discharge passage 43 and the valve 51 opens the
return passage 50, only the oil discharged from the front gear pump
portion P1 is delivered to the outside through the outlet passage
41. The oil discharged from the rear gear pump portion P2 is
supplied to the return passage 50. Then the oil joins the upstream
side of the suction passage 35 at a confluence portion, that is,
between the inlet 38 of the suction passage 35 and the suction-side
space 33. In other words, the confluence portion is located
upstream side of the suction-side spaces 31, 33 which communicate
with the suction passage 35 in the gear pump 10. Therefore, in this
state, the discharge displacement of the variable displacement type
gear pump 10 gets to 50 percent, and is in the small displacement
operational state. In this embodiment, the state where the
electromagnetic valve 55 is activated is set as the 50-percent
discharge displacement. However, the location of the groove 64 and
the suction-pressure communication passage 60 in the spool 57 may
be modified so that a state activating the electromagnetic valve 55
is set as 100-percent discharge displacement, while a state
deactivating the electromagnetic valve 55 is set as 50-percent
discharge displacement.
[0039] When the variable displacement type gear pump 10 is operated
in the small displacement state, the oil from the return passage 50
joins the upstream side of the suction passage 35 at the confluence
portion. The oil in the suction passage 35 is supplied to the front
gear pump portion P1 and the rear gear pump portion P2. The oil in
the suction passage 35 is in the state where newly introduced oil
from the inlet 38 is mixed with the returned oil from the return
passage 50. That is, even if the small displacement operation is
continued, the oil flowing through the return passage 50 does not
continuously circulate in the rear gear pump portion P2 and the
return passage 50. The suction passage 35 is formed in the body 11
along the rotational axes of the drive shaft 27 and the driven
shaft 28, and it is not required to form a suction passage 35
outside of the body 11.
[0040] The first preferred embodiment has the following
advantageous effects.
[0041] (1) Even if the variable displacement type gear pump 10
continues small displacement operation, the returned oil from the
return passage 50 is mixed with newly introduced oil at the
upstream side of the suction passage 35. Therefore, the specific
oil in the return passage 50 does not continue to circulate through
a specific passage in the front gear pump portion P1 and the rear
gear pump portion P2. Therefore, unevenness of temperature
distribution in the body 11 and the housings 15,16 is prevented or
suppressed.
[0042] (2) The suction passage 35 is formed in the housing assembly
along the rotational axes of the drive shaft 27 and the driven
shaft 28, and it is not required to form a suction passage outside
of the housing assembly. Therefore, the variable displacement type
gear pump 10 does not need to prepare an additional piping member
for providing a suction passage outside of the gear pump 10. The
gear pump 10 does not need an oil piping outside of the housing
assembly, and the pressure loss hardly occurs in the suction
passage 35, since the suction passage 35 is linear shape along the
rotational axes of the drive shaft 27 and the driven shaft 28.
[0043] (3) Since the return passage 50 is formed in the body 11 and
the rear housing 16, the variable displacement type gear pump 10
does not need a return passage outside of the gear pump 10.
Therefore, the gear pump 10 does not need an additional piping
member for providing a return passage outside of the gear pump 10.
Further, since the outlet passage 41 is formed in the body 11 so as
to communicate with the front and rear discharge passages 42, 43,
the gear pump 10 does not need an outlet passage downstream of the
confluence portion of the discharge passages 42, 43 outside of the
gear pump 10.
[0044] (4) With the operation of the electromagnetic valve 55, the
return passage 50 is opened and closed by the valve 51. In
accordance with the opening and closing of the return passage 50 by
the valve 51, the rear discharge passage 43 is opened and closed by
the check valve 45, and the discharge displacement of the gear pump
10 is controlled.
[0045] The second preferred embodiment will be described according
to FIG. 5. The gear pump of the second preferred embodiment differs
from that of the first embodiment in that the structure of the
return passage is modified, and the rest of the structure of the
gear pump of the second embodiment is substantially the same as the
first embodiment. Therefore, like or same parts or elements will be
referred to by the same reference numerals as those in the first
embodiment, and the description thereof will be omitted.
[0046] As shown in FIG. 5, a variable displacement type gear pump
71 has a return passage 72. The return passage 72 connects the rear
discharge passage 43 and the rear suction passage 37. The
downstream side of the return passage 72 is formed substantially
linearly in the radial direction in the rear housing 16. The return
passage 72 communicates with the upstream side of the suction
passage 35 at a confluence portion. A guide portion 73 is formed at
the confluence portion, or at the vicinity of the end of the return
passage 72 in the rear housing 16 so as to incline the return
passage 72 frontward. The inclination at the vicinity of the end of
the return passage 72 by the guide portion 73 is in the direction
to increase the flow speed of the newly introduced oil in the
suction passage 35 by introducing the oil from the return passage
72 into the suction passage 35.
[0047] According to the variable displacement type gear pump 71 of
this embodiment, the oil discharged from the rear gear pump portion
P2 at the small displacement operation flows through the return
passage 72. The oil flowing through the return passage 72 joins the
newly introduced oil flowing through the suction passage 35. At
this time, the oil in the return passage 72 flows in the direction
perpendicular to the oil flow in the suction passage 35, and then
is guided by the guide portion 73 so as to flow frontward. The oil
guided by the guide portion 73 joins the oil in the suction passage
35 so as to flow in the direction to increase the speed of the oil
flow. In this embodiment, the guide portion 73 guides the oil of
the return passage 72 into the suction passage 35 so as to increase
the speed of the oil flow in the suction passage 35 at the small
displacement operation. Thereby the oil flowing in the return
passage 72 can be effectively mixed with the newly introduced oil
into the suction passage 35.
[0048] The following will describe a third preferred embodiment
with reference to FIG. 6. FIG. 6 is a partially enlarged
cross-sectional view of a variable displacement type gear pump 81
according to the third preferred embodiment, and taken along a
return passage 82 in the rear housing 16. The gear pump of the
third preferred embodiment differs from that of the first
embodiment in that the structure of the return passage is modified,
and the rest of the structure of the gear pump of the third
embodiment is substantially the same as the first embodiment.
Therefore, like or same parts or elements will be referred to by
the same reference numerals as those in the first embodiment, and
the description thereof will be omitted.
[0049] As shown in FIG. 6, the suction passage 35 in the variable
displacement type gear pump 81 has a circular cross-sectional
surface. Specifically, the rear suction passage 37 in the rear
housing 16 has a circular cross-sectional surface. The rear
discharge passage 43 and the suction passage 35 are connected by
the return passage 82. The return passage 82 communicates with the
suction passage 35 at a confluence portion located the upstream
side of the suction passage 35. The confluence portion of the
return passage 82 is formed by connecting the return passage 82 in
the tangent direction with respect to the circular cross-sectional
surface of the rear suction passage 37, as shown in FIG. 6. With
the construction where the return passage 82 is connected to the
rear suction passage 37 in the tangent direction, the oil flowing
through the return passage 82 enhances the swirling flow of the oil
flowing through the suction passage 35.
[0050] According to the variable displacement type gear pump 81 of
this embodiment, the return passage 82 is connected to the suction
passage 35 in the tangent direction with respect to the circular
cross-sectional surface of the suction passage 35. The oil flowing
through the return passage 82 at the small displacement operation
is introduced into the suction passage 35 along the inner
circumferential surface of the suction passage 35. The oil joining
together while being guided along the inner circumferential surface
of the suction passage 35 enhances the swirling flow in the suction
passage 35. With the swirling flow in the suction passage 35, the
newly introduced oil in the suction passage 35 is effectively mixed
with the oil from the return passage 82.
[0051] The following will describe a variable displacement type
gear pump of a fourth preferred embodiment according to the present
invention with reference to FIGS. 7. The gear pump of the fourth
preferred embodiment differs from that of the first embodiment in
that the structure of the return passage is modified, and the rest
of the structure of the gear pump of the fourth embodiment is
substantially the same as the first embodiment. Therefore, like or
same parts or elements will be referred to by the same reference
numerals as those in the first embodiment, and the description
thereof will be omitted.
[0052] FIG. 7 shows a variable displacement type gear pump 91 in
small displacement operational state. The gear pump 91 has a return
passage 92 which connects the rear discharge passage 43 and the
rear suction passage 37. The return passage 92 is connected to the
upstream side of the suction passage 35 so as to form a confluence
portion. The confluence portion of the return passage 92 with the
suction passage 35 has a parallel guide portion 94 at the end of
the return passage 92 adjacent the suction passage 35. The parallel
guide portion 94 is formed so as to guide the oil flow from the
return passage 92 frontward and parallel to the suction passage 35.
The oil from the return passage 92 joins parallely the oil flowing
through the suction passage 35.
[0053] When the coil 58 of the electromagnetic valve 55 is not
excited, the piston 53 is moved in the direction to close the
return passage 92. When the piston 53 closes the return passage 92,
the pressure in the discharge-side space 34 increases, and the
valve body 46 of the check valve 45 opens the rear discharge
passage 43. Therefore, the oil discharged from the rear gear pump
portion P2 is supplied to the rear discharge passage 43 and the
return passage 92. The oil flows from the rear discharge passage 43
to the outlet passage 41. The oil from the front gear pump portion
P1 joins the oil flow from the rear gear pump portion P2. In this
state, the discharge displacement of the variable displacement type
gear pump 91 is 100 percent, and is in the large displacement
operational state.
[0054] When the coil 58 of the electromagnetic valve 55 is excited,
the piston 53 is retreated into the cylinder 52, and the return
passage 92 is in the fully opened state. Further, the pressure at
the upstream side of the return passage 92 decreases, and the valve
body 46 closes the rear discharge passage 43 due to the urging
force of the coil spring 47 of the check valve 45. In the state
where the check valve 45 closes the rear discharge passage 43 and
the valve 51 opens the return passage 92, only the oil discharged
from the front gear pump portion P1 is discharged to the outside
through the outlet passage 41. The oil discharged from the rear
gear pump portion P2 is supplied to the return passage 92, and
joins the upstream side of the suction passage 35. Therefore, in
this case, the discharge displacement of the variable displacement
type gear pump 91 is 50 percent, and is in the small displacement
operational state.
[0055] When the variable displacement type gear pump 91 is in the
small displacement operational state, the oil from the return
passage 92 joins the upstream side of the suction passage 35. The
oil flow from the return passage 92 is parallel to the oil flow in
the suction passage 35. Since the oil flow from the return passage
92 does not have a velocity component in the traverse direction
with respect to the suction passage 35, the dynamic pressure of the
oil from the return passage 92 is effectively introduced into the
suction-side space 31 for increasing the pressure therein.
[0056] By increasing the pressure in the suction-side space 31 at
maximum, the pressure difference between the discharge-side space
32 and the suction-side space 31 at the front side is going to be
decreased, compared to a case without the guide portion 94. The
decreased pressure difference between the spaces 31, 32 affects the
load applied on the front gear pump portion P1 being reduced.
[0057] Generally, oil is trapped in a trap region at the engaging
portion of the drive gear 22 and the driven gear 23 by the
engagement of the gears 22, 23 at the front side. At the small
displacement operation, the pressure difference between the
discharge-side space 32 and the suction-side space 31 at the front
side is going to be reduced, compared to a case where energy loss
is occurred due to the confluence. Thereby the oil leakage from the
trap region to the suction passage 35 is reduced, compared to a
case where the pressure difference between the spaces 31, 32 is
large. Similarly, oil leakage from the clearance between the gears
22, 23 and the first gear chamber 12 at the front side into the
suction passage 35 is small, compared to a case where the pressure
difference between the spaces 31, 32 is large. The reduction of oil
leakage is effective in increasing the volume efficiency. Further,
due to the pressure difference between the spaces 31, 32, the load
applied from the drive shaft 27 and the driven shaft 28 to the
bearings 29 is reduced. Thereby the sliding friction between the
shafts 27, 28 and the bearings 29 is reduced and the mechanical
efficiency is improved.
[0058] Generally, when a gear pump is driven, oil in an oil storage
tank in atmospheric state is introduced into a suction passage of
the gear pump. The oil at the time of being introduced into the
suction passage is affected by the pressure loss due to the piping,
and becomes low-pressure state lower than the atmospheric pressure.
Specifically, when the gear pump is far from the storage tank and
requires a long piping, the piping has severe pressure loss. When
oil is in low-pressure state lower than the atmospheric pressure,
cavitation may occur in the oil. The generated cavitation bubbles
may be collapsed to cause shock when the pressure in the gear pump
is increased, and thereby cause problems such as noise, vibration,
and erosion of the pump parts. At the small displacement operation,
the outflow of the oil from the return passage 92 joins the oil in
the suction passage 35 flowing in the same direction, and the
pressure of the oil in the suction passage 35 downstream side of
the confluence portion is increased. Due to the pressure increase
of the oil in the suction passage 35, the cavitation in the oil is
in advance prevented.
[0059] The fourth preferred embodiment has the following
advantageous effects.
[0060] (5) In the gear pump 91, the flow direction of the outflow
from the return passage 92 is coincident with that of the suction
passage 35 at the vicinity of the confluence portion. Therefore,
the oil in the front suction-side space 31 is pressurized maximally
due to the confluence of the oil flowing through the return passage
92. Thereby, the pressure difference between the discharge-side
space 32 and the suction-side space 31 at the front side decreases,
compared to a case where the flow directions are not coincident at
the vicinity of the confluence portion. The pressure difference
between the spaces 31, 32 is reduced, and the work load of the
front gear pump portion P1 is reduced.
[0061] (6) In the gear pump 91, the pressure difference between the
discharge-side space 32 and the suction-side space 31 at the front
side is reduced, compared to a case where the flow directions at
the vicinity of the confluence portion is not coincident. The gear
pump 91 reduces oil leakage from the trap region formed by the
engagement of the gears 22, 23 at the front side, and from the
first gear chamber 12, compared to a case having large pressure
difference between the spaces 31, 32. Thereby the volume efficiency
as a gear pump is improved. Further, the load applied from the
drive shaft 27 and the driven shaft 28 to the bearings 29 is
reduced, and the sliding friction between the shafts 27, 28 and the
bearings 29 is reduced thereby improving the mechanical
efficiency.
[0062] (7) At the small displacement operation, the outflow of the
oil from the return passage 92 joins parallely the oil flow in the
suction passage 35. Thereby the dynamic pressure of the oil in the
suction passage 35 downstream side of the confluence portion is
effectively increased, and the cavitation in the oil of the suction
passage 35 is in advance prevented. Thereby, noise, vibration, and
erosion of the pump parts are prevented.
[0063] The present invention is not limited to the above-described
embodiments and may be modified into following alternative
embodiments within the scope of the invention.
[0064] In the first through fourth preferred embodiments, when the
maximum displacement of the variable displacement type gear pump is
set as 100 percent, and the displacement of each of the front and
rear gear pump portions is set as 50 percent. However, the
performance of the gear pump portions is not limited to 50 percent.
The performance of the each gear pump portion is set appropriately,
for example, as 70 percent and 30 percent, depending on the
condition.
[0065] In the first through fourth preferred embodiments, two gear
pump portions, that is, the front gear portion and the rear gear
portion are provided. however, the number of gear pump portion may
be more than two. In this case, the oil discharged from at least
one gear pump portion may be returned through the return passage at
the small displacement operation.
[0066] In the first through fourth preferred embodiments, the
suction passage has the circular cross-sectional surface over the
entire longitudinal direction. However, the suction passage may not
have a circular cross-sectional surface in the first, second, and
fourth embodiments. The cross-sectional surface of the suction
passage may be, for example, polygonal, elliptical, or oblong
shape. In the third embodiment, the cross-sectional surface of the
suction passage may be formed only at the vicinity of the
confluence portion with the return passage. Specifically, if the
downstream side of the confluence portion has a circular cross-
sectional surface, it is appropriate for enhancing the swirling
flow of oil in the suction passage.
[0067] In the first through fourth preferred embodiments, the
discharge passages are provided so as to connect the discharge-side
spaces of the gear chambers and the outlet passage. The
discharge-side space of each gear chamber may be connected directly
to the outlet passage without a discharge passage. In this case, a
check valve is required to shut off the outlet passage connecting
the gear chambers.
[0068] In the first through fourth embodiments, the return passage
is formed so as to pass through the rear side of the rear ends of
the drive shaft and the driven shaft. However, the location of the
return passage is not limited to the above position. For example,
the return passage may pass around at least one of the outer
peripheries of the drive shaft and the driven shaft. In this case,
the return passage may be preferably formed between the rear gear
chamber and the rear ends of the drive shaft and the driven shaft,
in order to form the confluence portion of the return passage with
the suction passage at the upstream side of the suction
passage.
[0069] Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein but may be
modified within the scope of the appended claims.
* * * * *