U.S. patent application number 10/798136 was filed with the patent office on 2004-09-16 for gear pump.
Invention is credited to Fujii, Toshiro, Suzuki, Shigeru.
Application Number | 20040179953 10/798136 |
Document ID | / |
Family ID | 32767976 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040179953 |
Kind Code |
A1 |
Suzuki, Shigeru ; et
al. |
September 16, 2004 |
Gear pump
Abstract
A two-stage gear pump has a pump section. The pump section has
an internal space that is located adjacent to a driven gear and
about a cylindrical surface of the driven shaft. A discharge
section of a first gear train is connected to a suction section of
a second gear train with a communication passage. The internal
space is connected to the communication passage with a pressure
introduction passage. The pressure of the communication passage is
introduced to the internal space by the pressure introduction
passage, so that the pressure atmosphere of the internal space is
an intermediate pressure atmosphere of the suction pressure and the
discharge pressure of the pump section.
Inventors: |
Suzuki, Shigeru;
(Kariya-shi, JP) ; Fujii, Toshiro; (Kariya-shi,
JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
32767976 |
Appl. No.: |
10/798136 |
Filed: |
March 10, 2004 |
Current U.S.
Class: |
417/310 ;
417/410.4 |
Current CPC
Class: |
F04C 11/001 20130101;
F04C 15/0038 20130101; F04C 2/18 20130101; F04C 2210/20 20130101;
F04C 2/086 20130101; F04C 2210/201 20130101 |
Class at
Publication: |
417/310 ;
417/410.4 |
International
Class: |
F04B 049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2003 |
JP |
2003-069529 |
Claims
1. A gear pump for sending fluid under pressure, the gear pump
comprising a pump section that draws fluid and discharges
pressurized fluid, wherein the pump section includes: a gear train
having a pair of meshed gears, wherein each gear defines a
plurality of pump chambers for conveying fluid in the pump section;
a drive shaft having a cylindrical surface, wherein one of the
gears is coupled to the drive shaft such that the gear rotates
integrally with the drive shaft; and a driven shaft having a
cylindrical surface, wherein the driven shaft supports the other
one of the gears, wherein the pump section has an internal space
that is located at a position adjacent to at least one of the gears
and about the cylindrical surface of at least one of the drive
shaft and the driven shaft, and wherein the pressure atmosphere of
the internal space is an intermediate pressure atmosphere of the
pressure of fluid drawn into the pump section and the pressure of
fluid discharged from the pump section.
2. The gear pump according to claim 1, wherein the pump section has
a fluid conveying passage that includes the pump chambers, wherein
the pump section discharges fluid drawn into the fluid conveying
passage from the fluid conveying passage through the pump chambers,
wherein the fluid conveying passage has an intermediate-pressure
zone, the pressure atmosphere of which is an intermediate pressure
atmosphere of the pressure of fluid drawn into the fluid conveying
passage and the pressure of fluid discharged from the fluid
conveying passage, and wherein the pump section has a pressure
introduction passage that connects the internal space with the
intermediate-pressure zone.
3. The gear pump according to claim 2, wherein the gear train is
one of a plurality of gear trains that include at least a first
gear train and a second gear train, wherein the fluid conveying
passage includes a communication passage for guiding fluid
discharged from the first gear train to the second gear train, and
wherein the communication passage functions as the
intermediate-pressure zone.
4. The gear pump according to claim 1, further comprising a
pressure regulating valve, wherein the pressure regulating valve is
capable of releasing the pressure of the internal space, thereby
adjusting the pressure of the internal space to an intermediate
pressure of the pressure of fluid drawn into the pump section and
the pressure of fluid discharged from the pump section.
5. The gear pump according to claim 4, wherein the pump section has
a fluid conveying passage that includes the pump chambers, wherein
the pump section discharges fluid drawn into the fluid conveying
passage from the fluid conveying passage through the pump chambers,
wherein the fluid conveying passage has a high-pressure zone, the
internal pressure of which is higher than the pressure of the
internal space, and wherein the pressure regulating valve prevents
the pressure of the internal space from being increased due to
pressure leakage from the high-pressure zone to the internal
space.
6. The gear pump according to claim 4, wherein the internal space
is connected to a tank with a pressure regulation passage, the tank
storing fluid that is supplied to the pump section, and wherein the
pressure regulating valve is located in the pressure regulation
passage.
7. The gear pump according to claim 6, further comprising: a
housing for accommodating the pump section; and a sub tank, wherein
the sub tank stores in the housing fluid supplied from the tank to
supply the fluid to the pump section, wherein the sub tank is
provided in a section of the pressure regulating passage that is
located between the pressure regulating valve and the tank.
8. The gear pump according to claim 6, further comprising: a motor
for rotating the drive shaft; and a housing for accommodating the
pump section and the motor, wherein the pump section has a gear
housing for accommodating the gears, and wherein the pump section
is located between the pressure regulating valve and the motor, and
wherein the gear housing has a passage for connecting the internal
space with the pressure regulating valve.
9. The gear pump according to claim 1, further comprising: a motor
for rotating the drive shaft; and a housing for accommodating the
pump section and the motor.
10. The gear pump according to claim 1, wherein the internal space
is one of a pair of internal spaces that are defined about the
cylindrical surface of the drive shaft and about the cylindrical
surface of the driven shaft, respectively, and wherein the pressure
atmosphere of each internal space is an intermediate pressure
atmosphere of the pressure of fluid drawn into the pump section and
the pressure of fluid discharged from the pump section.
11. The gear pump according to claim 1, wherein the fluid is
liquefied gas fuel.
12. The gear pump according to claim 1, wherein the gear pump is
mounted on a vehicle.
13. A gear pump for sending fluid under pressure, the gear pump
comprising a pump section that draws fluid and discharges
pressurized fluid, wherein the pump section includes: a plurality
of gear trains that include at least a first gear train and a
second gear train, wherein each gear train has a pair of meshed
gears, wherein each gear defines a plurality of pump chambers for
conveying fluid in the pump section; a drive shaft having a
cylindrical surface, wherein one of the gears of each gear train is
coupled to the drive shaft such that the gear rotates integrally
with the drive shaft; a driven shaft having a cylindrical surface,
wherein the driven shaft supports the other one of the gears of
each gear train; and a fluid conveying passage that includes the
pump chambers, wherein the fluid conveying passage includes a
communication passage for guiding fluid discharged from the first
gear train to the second gear train, wherein the pump section
discharges fluid drawn into the fluid conveying passage from the
fluid conveying passage through the pump chambers, wherein the pump
section has an internal space that is located at a position
adjacent to at least one of the gears and about the cylindrical
surface of at least one of the drive shaft and the driven shaft,
and wherein the pump section has a pressure introduction passage
that connects the internal space with the communication passage.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a gear pump used to send
fluid under pressure.
[0002] Conventionally, a gear pump as disclosed, for example, in
Japanese Laid-Open Patent Publication No. 2001-140770 has been
known. This gear pump has a pump section 101 as shown in FIG. 9.
The pump section 101 has two stages of gear trains 111, and each of
the gear trains 111 has two pairs of drive gears 111a and driven
gears 111b meshing with each other. In the pump section 101, a
plurality of pump chambers 111c for conveying fluid are defined by
the gears 111a and 111b. Both drive gears 111a are connected to a
drive shaft 102 so as to be rotatable integrally with the drive
shaft 102, and both driven gears 111b are supported by a driven
shaft 103.
[0003] When the drive shaft 102 is rotated, both drive gears 111a
connected to the shaft 102 rotate. When the drive gear 111a rotate,
the corresponding driven gear 111b supported by the driven shaft
103, which meshes with the drive gear 111a, rotates following the
rotation of the drive gear 111a. Therefore, the pump chambers 111c
convey the fluid, and thereby the pressure of the fluid is
increased.
[0004] In the above-described gear pump, each end portion of the
drive shaft 102 and driven shaft 103 is supported via a bearing
104. For the reason of this support construction, a gap, i.e., an
internal space 105 exists around the cylindrical surface of each of
the shafts 102 and 103 at a position adjacent to the gears 111a and
111b in the pump section 101. Therefore, there arises a problem in
that the fluid leaks from the pump chambers 111c into the internal
space 105, so that the efficiency of gear pump decreases.
[0005] There exists a fuel supply system for supplying a liquefied
gas fuel such as dimethyl ether (hereinafter abbreviated to DME) to
a vehicular internal combustion engine. This fuel supply system
sometimes uses the above-described gear pump. The gear pump has no
expansion stroke. Therefore, the gear pump is superior in handling
DME that is easy to vaporize.
[0006] DME has a low viscosity and hence is liable to leak.
Therefore, leakage of fluid, i.e., leakage of DME from the
above-described pump chambers 111c into the internal space 105
poses a serious problem. The gear pump mounted on a vehicle is
especially required to have a small size. Therefore, it is
difficult to arrange a sealing member in a leakage path between the
pump chambers 111c and the internal space 105.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a gear pump
in which fluid leakage from pump chambers to an internal space is
reduced.
[0008] To achieve the above-mentioned objective, the present
invention provides a gear pump for sending fluid under pressure.
The gear pump includes a pump section that draws fluid and
discharges pressurized fluid. The pump section includes a gear
train, a drive shaft and a driven shaft. The gear train has a pair
of meshed gears. Each gear defines a plurality of pump chambers for
conveying fluid in the pump section. The drive shaft has a
cylindrical surface. One of the gears is coupled to the drive shaft
such that the gear rotates integrally with the drive shaft. The
driven shaft has a cylindrical surface. The driven shaft supports
the other one of the gears. The pump section has an internal space
that is located at a position adjacent to at least one of the gears
and about the cylindrical surface of at least one of the drive
shaft and the driven shaft. The pressure atmosphere of the internal
space is an intermediate pressure atmosphere of the pressure of
fluid drawn into the pump section and the pressure of fluid
discharged from the pump section.
[0009] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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 cross-sectional view of a pump in accordance
with a first embodiment of the present invention;
[0012] FIG. 1A is an enlarged view of a portion surrounded by a
chain line 1A in FIG. 1;
[0013] FIG. 2 is a sectional view taken along the line II-II of
FIG. 1;
[0014] FIG. 3 is a sectional view taken along the line III-III of
FIG. 1;
[0015] FIG. 4 is a schematic view of a fuel supply system provided
with the pump shown in FIG. 1;
[0016] FIG. 5 is an enlarged cross-sectional view of an essential
portion of a pump in accordance with a second embodiment of the
present invention;
[0017] FIG. 6 is a cross-sectional view of a pump in accordance
with a third embodiment of the present invention;
[0018] FIG. 7 is a cross-sectional view of a pump in accordance
with a fourth embodiment of the present invention;
[0019] FIG. 8 is a cross-sectional view of a pump in accordance
with a fifth embodiment of the present invention; and
[0020] FIG. 9 is a cross-sectional view of a prior art pump.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] First to fifth embodiments of the present invention will now
be described. In the second to fifth embodiments, only points
different from the first embodiment are explained, that is, the
same reference numerals are applied to the same or equivalent
elements, and the explanation thereof is omitted.
[0022] As shown in FIG. 4, a fuel supply system has a two-stage
gear pump 1. The fuel supply system supplies a fuel to an internal
combustion engine (an engine), which is a driving source for
running a vehicle. The suction side of the pump 1 is connected to a
tank 2 through a suction pipe 3. The tank 2 stores DME (dimethyl
ether) used as fluid, or as a liquefied gas fuel. The discharge
side of the pump 1 is connected to an injection pump 5 through a
discharge pipe 4. An engine 6 is connected to the discharge side of
the injection pump 5. The injection pump 5 supplies the DME, which
is sent under pressure from the pump 1, to the engine 6 in a
high-pressure state.
[0023] As shown in FIG. 1, the pump 1 has a casing 7 and a lid 9.
The lid 9 is fixed to the opening end of the substantially bottomed
cylindrical casing 7, that is, at the left end as viewed in FIG. 1
via a plurality of bolts 8. The casing 7 and the lid 9 constitute a
pump housing of the pump 1. The pump 1 is mounted on the vehicle in
a state such that the left-hand side as viewed in FIG. 1 is the
upper side and the right-hand side therein is the lower side. The
casing 7 contains a motor section 10 fixed to the internal surface
of the lid 9 and a pump section 11 connected to the motor section
10. Thus, the pump 1 incorporates a motor 10. That is to say, the
pump 1 requires no external drive source, and the interior of the
pump 1 is sealed from the outside. In the casing 7, a space outside
the motor section 10 and the pump section 11 forms a sub tank 7a.
In the motor section 10 and the pump section 11, a drive shaft 12
is rotatably provided through these portions.
[0024] The motor section 10 has a substantially bottomed
cylindrical motor housing 10a. The motor section 10 includes
stators 10b and a rotor 10c. Each stator 10b has a winding arranged
along the inner circumferential surface of the motor housing 10a.
The rotor 10c consists of an iron core arranged in a state of being
surrounded by the stators 10b. In the motor section 10, that is, in
the motor housing 10a, a space containing the stators 10b and the
rotor 10c constitutes a motor chamber 60. The rotor 10c is fixed to
and rotates integrally with the drive shaft 12. The winding of each
stator 10b is connected to a terminal 15. When a current is caused
to flow in the winding of the stators 10b via the terminals 15 by
the power supplied from the outside, the drive shaft 12 is rotated
by electromagnetic induction between the winding and the iron core
of the rotor 10c.
[0025] As shown in FIGS. 1 and 1A, the pump section 11 includes a
base block 16, a connection plate 19, a side plate 20, a connection
plate 21, and a tip-end plate 22 in that order from the motor
section 10. The base block 16 and the plates 19 to 22 are fixed to
each other by a plurality of through bolts 23 (see FIGS. 2 and 3)
in a state in which the drive shaft 12 is inserted. The pump
section 11 is fixed to the motor section 10 by fixing a flange
portion 16a of the base block 16 to the motor housing 10a via a
plurality of bolts 24 (in FIG. 1, only one bolt is shown).
[0026] The drive shaft 12 extends through the base block 16 and the
plates 19 to 22. The upper end (left end in FIG. 1) of the drive
shaft 12 is supported by the motor housing 10a via a bearing 13. On
the end surface of the motor housing 10a, a recess 61 that opens
toward the lid 9 is formed. The upper end of the drive shaft 12 and
the bearing 13 are located in the recess 61. The lower end (right
end in FIG. 1) of the drive shaft 12 is supported by the tip-end
plate 22 via a bearing 14. The tip-end plate 22 is formed with a
recess 62. The lower end of the drive shaft 12 and the bearing 14
are located in the recess 62. The bearings 13 and 14 each consist
of a needle bearing serving as a roller bearing.
[0027] As shown in FIG. 1A, a groove 12a is formed in part of the
outer circumferential surface that is in the vicinity of the lower
end the drive shaft 12. The groove 12a extends in the axial
direction of the drive shaft 12. In the groove 12a, a key 25 having
a substantially rectangular shape in cross section is arranged.
[0028] As shown in FIGS. 1 to 3, on the drive shaft 12, a first
drive gear 26 and a second drive gear 27 are provided in that order
from the lower end along the axial direction of the drive shaft 12.
On the outer circumferential surfaces of the drive gears 26 and 27,
teeth 26a and 27a are formed, respectively. In the inner
circumferential surfaces of the drive gears 26 and 27, key grooves
26b and 27b are formed, respectively. The drive gears 26 and 27
each are made to be rotatable integrally with the drive shaft 12 by
engaging the key 25 with the surface defining the key groove 26b,
27b.
[0029] In the pump section 11, a driven shaft 29 is rotatably
housed in parallel with the drive shaft 12. The driven shaft 29
extends through the base block 16 constituting the pump section 11
and the plates 19 to 22 constituting the pump section 11. The upper
end (left end as viewed in FIG. 1) of the driven shaft 29 is
supported by the base block 16 via a bearing 30. The base block 16
is formed with a recess 63. The upper end of the driven shaft 29
and the bearing 30 are located in the recess 63. The lower end
(right end in FIG. 1) of the driven shaft 29 is supported by the
tip-end plate 22 via a bearing 31. The tip-end plate 22 is formed
with a recess 64. The lower end of the driven shaft 29 and the
bearing 31 are located in the recess 64. The bearings 30 and 31
each consist of a needle bearing serving as a roller bearing.
[0030] On the driven shaft 29, a first driven gear 32 and a second
driven gear 33 are provided in that order from the lower end side
along the axial direction of the driven shaft 29. On the outer
circumferential surfaces of the driven gears 32 and 33, teeth 32a
and 33a are formed, respectively. The first driven gear 32 is
provided so as to be rotatable relatively to the driven shaft 29.
The second driven gear 33 is formed integrally with the driven
shaft 29. The first driven gear 32 meshes with the corresponding
first drive gear 26 on the drive shaft 12, and the second driven
gear 33 meshes with the corresponding second drive gear 27 on the
drive shaft 12.
[0031] On the outer circumferential surface of the casing 7, a
suction connecting portion 35 is provided. The suction connecting
portion 35 has a suction port 35a communicating with the sub tank
7a, and is connected with the suction pipe 3 extending from the
tank 2 (see FIG. 4). The DME in the tank 2 is introduced through
the suction pipe 3 and the suction port 35a, and is stored in the
sub tank 7a. When the pump section 11 is operated, the pump section
11 sucks the DME in the sub tank 7a. The pump section 11 increases
the pressure of DME through a plurality of gear trains. That is,
the pump section 11 is of a tandem type.
[0032] Specifically, the pump section 11 has a first-stage gear
train 36 that is a first gear train, or a low-pressure side gear
train, consisting of the first drive gear 26 and the first driven
gear 32, and a second-stage gear train 37 that is a second gear
train consisting of the second drive gear 27 and the second driven
gear 33. The first-stage gear train 36 functions as a low-pressure
side gear train. The second-stage gear train 37 functions as a
high-pressure side gear train. The pump section 11 increases the
pressure of DME stepwise by causing the DME to flow through the
first-stage gear train 36 and the second-stage gear train 37
successively. On the external surface of the lid 9, a discharge
connecting portion 39 is provided. The discharge connecting portion
39 has a discharge port 39a, and is connected with the discharge
pipe 4 extending from the injection pump 5 (see FIG. 4). The pump
section 11 discharges the DME, the pressure of which has been
increased, from the discharge port 39a to the discharge pipe 4
through a first pump section internal passage (not shown).
[0033] As shown in FIG. 2, the connection plate 21 has a hole 21a
for accommodating the first drive gear 26 and a hole 21b for
accommodating the first driven gear 32. The connection plate 21 has
an upstream passage 40 and a downstream passage 41. Because having
the upstream passage 40 and the downstream passage 41, the
connection plate 21 has some space on both sides of the meshed
portions of the first drive gear 26 and the first driven gear 32.
The upstream passage 40 and the downstream passage 41 serve as
passages for DME. The upstream passage 40 communicates with the sub
tank 7a through a second pump section internal passage (not shown).
Although not illustrated, the connection plate 19 also has holes,
an upstream passage, and a downstream passage, which are the same
as the holes 21a and 21b, the upstream passage 40, and the
downstream passage 41 in the connection plate 21.
[0034] The drive shaft 12 rotates in the direction of a black arrow
in FIG. 2, that is, in the clockwise direction. The driven shaft 29
rotates following the rotation of the drive shaft 12 via the gear
trains 36 and 37. That is to say, the driven shaft 29 rotates in
the direction indicated by the white arrow in FIG. 2, that is, in
the counterclockwise direction. When the drive shaft 12 and the
driven shaft 29 rotate, the DME having been sent into the pump
section 11 flows into the first-stage gear train 36 through the
upstream passage 40. The first-stage gear train 36 has a plurality
of low-pressure pump chambers 36a and 36b. The DME having reached
the first-stage gear train 36 is conveyed toward the downstream
passage 41 through the pump chambers 36a or 36b. Each of the pump
chambers 36a is defined by the two adjacent teeth 26a of the first
drive gear 26 and the inner circumferential surface of the hole
21a. Each of the pump chambers 36b is defined by the two adjacent
teeth 32a of the first driven gear 32 and the inner circumferential
surface of the hole 21b.
[0035] As shown in FIG. 3, the side plate 20 has a hole 20a for
inserting the drive shaft 12 and a hole 20b for inserting the
driven shaft 29, these two holes 20a and 20b being located
adjacently. The diameter of the hole 20a is set larger than the
diameter of the drive shaft 12. Therefore, a clearance is provided
between the drive shaft 12 and the hole 20a. The diameter of the
hole 20b is set larger than the diameter of the driven shaft 29.
Therefore, a clearance is provided between the driven shaft 29 and
the hole 20b.
[0036] The side plate 20 has a communication passage 43 for
connecting the downstream passage 41 of the first-stage gear train
36 to the upstream passage 42 of the second-stage gear train 37.
The communication passage 43 includes a first passage 43a, a second
passage 43b, and a third passage 43c. The first passage 43a extends
in the radial direction of the pump 1. The second passage 43b
extends in the axial direction of the pump 1 from the downstream
passage 41 of the first-stage gear train 36 and communicates with
the first passage 43a. The third passage 43c extends in the axial
direction of the pump 1 from the upstream passage 42 of the
second-stage gear train 37 and communicates with the first passage
43a. Therefore, the DME, the pressure of which has been increased
by the first-stage gear train 36, passes through the second passage
43b, the first passage 43a, and the third passage 43c in that order
from the downstream passage 41 and is sent to the upstream passage
42 of the second-stage gear train 37.
[0037] The second-stage gear train 37 has a plurality of
high-pressure pump chambers 37a and 37b. As shown in FIG. 1A, the
DME having reached the second-stage gear train 37 is conveyed to
the discharge port 39a through the pump chambers 37a or 37b. Each
of the pump chambers 37a is defined by the two adjacent teeth 27a
of the second drive gear 27 and the inner circumferential surface
of the corresponding hole in the connection plate 19. Each of the
pump chambers 37b is defined by the two adjacent teeth 33a of the
second driven gear 33 and the inner circumferential surface of the
corresponding hole in the connection plate 19. The DME, which has
been sent to the discharge port 39a after the pressure thereof has
been increased by the second-stage gear train 37, is supplied to
the injection pump 5 through the discharge pipe 4. That is, the
pump section 11 discharges fluid that has been drawn into a fluid
conveying passage, which includes the pump chambers 36a to 37b,
from the fluid conveying passage through the pump chambers 36a to
37b. The pressure at the starting point of the fluid conveying
passage is the suction pressure of the pump section 11, and the
pressure at the endpoint of the fluid conveying passage is the
discharge pressure of the pump section 11.
[0038] The lid 9 is fitted with a pipe connecting portion 54. The
pipe connecting portion 54 is connected with a leak pipe 55
extending from the tank 2 (see FIG. 4). The pipe connecting portion
54 has a leak port 56 for connecting the internal space of the
recess 61 to the leak pipe 55. The motor housing 10a has a
communication hole 65 for connecting the internal space of the
recess 61 to the motor chamber 60. The side wall of the motor
housing 10a is provided with a vent hole 57 for connecting the
motor chamber 60 to the upper space of the sub tank 7a.
[0039] The sliding portions in the motor section 10 and the sliding
portions in the pump section 11, for example, the gears 26, 27, 32
and 33, generate heat by means of sliding operation. Being
subjected to the influence of such heat generation, the DME in the
sub tank 7a and the DME leaking from the gear trains 36 and 37 into
the motor chamber 60 may be vaporized. In this embodiment, the
interior of the pump 1 is sealed from the outside. In other words,
the pump 1 incorporating the motor 10 is of a shaft enclosed type
in which the drive shaft 12 is sealed in the casing 7 and the lid
9. In the shaft enclosed type pump 1, the vaporized DME is possibly
accumulated in the sub tank 7a or the motor chamber 60. However,
the vaporized DME in the sub tank 7a moves to the motor chamber 60
through the vent hole 57, and the vaporized DME in the motor
chamber 60 is returned to the tank 2 through the communication hole
65, the internal space of the recess 61, the leak port 56, and the
leak pipe 55 in that order. Therefore, the occurrence of troubles,
such as insufficient cooling of the motor section 10 caused by the
filling of evaporated DME, is prevented.
[0040] In the pump section 11, an internal space 51 is present
around a cylindrical surface 12b of the drive shaft 12 at a
position adjacent to the drive gears 26 and 27. The internal space
51 includes a first space 51a, a second space 51b, and a third
space 51c. The first space 51a is located between the first drive
gear 26 and the bearing 14. The first space 51a is a part of the
recess 62 provided in the tip-end plate 22. The second space 51b is
located between the drive gears 26 and 27. The third space 51c is
located on the upper side of the second drive gear 27. In the drive
shaft 12, the diameter of a portion ranging from a midway point of
the base block 16 to the lower end of the drive shaft 12 is smaller
than that of the upper portion. Between this small-diameter portion
on the lower end side of the drive shaft 12 and the base block 16,
the third space 51c is located.
[0041] The first space 51a and the second space 51b are connected
to each other by some gap around the key 25 and the groove 12a.
Similarly, the second space 51b and the third space 51c are
connected to each other by some gap around the key 25 and the
groove 12a. As necessary, a communication passage for connecting
the first space 51a to the second space 51b may be formed in the
first drive gear 26, or a communication passage for connecting the
second space 51b to the third space 51c may be formed in the second
drive gear 27.
[0042] In the recess 62 in the tip-end plate 22, a space 62a is
present on the lower end face of the drive shaft 12 beyond the
bearing 14. The space 62a is connected to the first space 51a
through a gap that the bearing 14 has. The third space 51c is
connected to the motor chamber 60 through a gap between the base
block 16 and the large-diameter portion of the drive shaft 12, that
is, a communication hole 76. As described above, the internal space
of the recess 61 of the motor housing 10a is connected to the motor
chamber 60 through the communication hole 65 in the motor housing
10a. Specifically, a space 61a, in which the upper end face of the
drive shaft 12 is exposed, is connected to the motor chamber 60
through the communication hole 65.
[0043] Therefore, the pressure atmosphere of the space 61a exposed
to the upper end face of the drive shaft 12 and the pressure
atmosphere of the space 62a exposed to the lower end face of the
drive shaft 12 are the same as the pressure atmosphere of the motor
chamber 60. The pressure in the motor chamber 60 is approximately
equal to the suction pressure of the pump section 11. Therefore,
the force based on the pressure in the recess 61, which is applied
to the upper end face of the drive shaft 12, and the force based on
the pressure in the recess 62, which is applied to the lower end
face of the drive shaft 12, are balanced. As a result, opposing
thrust loads applied to the drive shaft 12 due to the imbalance of
the pressure in the recess 61 and the pressure in the recess 62
cancel each other, so that the thrust load borne by the bearing 13
is alleviated, whereby the durability of the bearing 13 is
enhanced.
[0044] Also, the pressure atmosphere of the first space 51a is the
same as the pressure atmosphere of the second space 51b located
adjacently to the first space 51a with the first drive gear 26
being held therebetween. Therefore, the opposing thrust loads
applied to the first drive gear 26 due to the imbalance of the
pressure in the first space 51a and the pressure in the second
space 51b cancel each other. As a result, wear and other types of
impairment of the first drive gear 26 are prevented. Similarly, the
pressure atmosphere of the second space 51b is the same as the
pressure atmosphere of the third space 51c located adjacently to
the second space 51b with the second drive gear 27 being held
therebetween. Therefore, opposing thrust loads applied to the
second drive gear 27 due to the imbalance of the pressure in the
third space 51c and the pressure in the second space 51b cancel
each other. As a result, wear and other types of impairment of the
second drive gear 27 are prevented.
[0045] In the pump section 11, an internal space 52 is present
around a cylindrical surface 29a of the driven shaft 29 at a
position adjacent to the driven gears 32 and 33. The internal space
52 includes a first space 52a, a second space 52b, and a third
space 52c. The first space 52a is located between the first driven
gear 32 and the bearing 31. That is, the first space 52a is a part
of the recess 64 provided in the tip-end plate 22. The second space
52b is located between the driven gears 32 and 33. The third space
52c is located between the second driven gear 33 and the bearing
30. That is, the third space 52c is a part of the recess 63
provided in the base block 16.
[0046] The first space 52a and the second space 52b are connected
to each other by some gap between the first driven gear 32 and the
cylindrical surface 29a of the driven shaft 29. In the recess 64 in
the tip-end plate 22, a space 64a is present on the lower end face
of the driven shaft 29. The space 64a is connected to the first
space 52a through a gap that the bearing 31 has. In the recess 63
in the base block 16, a space 63a is present on the upper end face
of the driven shaft 29. The space 63a is connected to the third
space 52c through a gap that the bearing 30 has. The space 63a
exposed to the upper end face of the driven shaft 29 in the base
block 16 is connected to the space 64a exposed to the lower end
face of the driven shaft 29 in the tip-end plate 22 through an
in-shaft passage 66 formed in the driven shaft 29. The in-shaft
passage 66 extends along the axis of the driven shaft 29.
[0047] Therefore, the pressure atmosphere of the space 63a exposed
to the upper end face of the driven shaft 29 is the same as the
pressure atmosphere of the space 64a exposed to the lower end face
of the driven shaft 29. Therefore, the force based on the pressure
in the recess 63, which is applied to the upper end face of the
driven shaft 29, and the force based on the pressure in the recess
64, which is applied to the lower end face of the driven shaft 29,
are balanced. As a result, a thrust load applied to the driven
shaft 29 due to the imbalance of the two forces is canceled.
Further, the pressure atmosphere of the second space 52b is the
same as the pressure atmosphere of the third space 52c located
adjacently to the second space 52b with the second driven gear 33
being held therebetween. Therefore, opposing thrust loads applied
to the second driven gear 33, which are a thrust load due to the
imbalance of pressure in the second space 52b and pressure in the
third space 52c and a thrust load due to the imbalance of pressure
in the recess 63 and pressure in the recess 64, cancel each other.
As a result, wear and other types of impairment of the second
driven gear 33 are prevented.
[0048] Also, the pressure atmosphere of the first space 52a is the
same as the pressure atmosphere of the second space 52b located
adjacently to the first space 52a with the first driven gear 32
being held therebetween. Therefore, opposing thrust loads applied
to the first driven gear 32 due to the imbalance of the pressure in
the first space 52a and the pressure in the second space 52b cancel
each other. As a result, wear and other types of impairment of the
first driven gear 32 are prevented.
[0049] The pressure in the communication passage 43 for connecting
the first-stage gear train 36 to the second-stage gear train 37 is
equal to the discharge pressure of the first-stage gear train 36,
in other words, the suction pressure of the second-stage gear train
37. Specifically, the pressure in the communication passage 43 is
higher than the suction pressure of the first-stage gear train 36,
i.e., the suction pressure of the pump section 11, and is lower
than the discharge pressure of the second-stage gear train 37,
i.e., the discharge pressure of the pump section 11. In other
words, it can be said that the pressure atmosphere of the
communication passage 43 is the pressure atmosphere of intermediate
pressure of the pump section 11. In this embodiment, the
communication passage 43 functions as an intermediate-pressure
zone.
[0050] As shown in FIGS. 1A and 3, the side plate 20 has a pressure
introduction passage 67. The pressure introduction passage 67
connects the first passage 43a of the communication passage 43 to
the second space 52b of the internal space 52, which is close to
the driven shaft 29. The intermediate pressure in the communication
passage 43 is introduced to the second space 52b through the
pressure introduction passage 67. As described above, the second
space 52b is connected to the internal space of the recess 64 in
the tip-end plate 22, that is, to the first space 52a and the space
64a. The internal space of the recess 64 is connected to the third
space 52c. Therefore, the pressure atmosphere of the internal space
52 around the cylindrical surface 29a of the driven shaft 29, the
pressure atmosphere of the space 63a exposed to the upper end face
of the driven shaft 29, and the pressure atmosphere of the space
64a exposed to the lower end face of the driven shaft 29 are the
same as the pressure atmosphere of the communication passage 43,
i.e., the pressure atmosphere of intermediate pressure of the pump
section 11.
[0051] This embodiment having the above-described configuration has
the following advantages.
[0052] (1) The pressure atmosphere of the internal space 52, which
is close to the driven shaft 29 of the pump section 11, is the
pressure atmosphere of intermediate pressure of the pump section
11. Therefore, for example, when compared with the case where the
pressure atmosphere of the internal space 52 is the same as the
suction pressure or the discharge pressure of the pump section 11,
the maximum value of difference in pressure produced between the
pump chambers 36b, 37b close to the driven shaft 29 and the
internal space 52 is decreased.
[0053] Thereupon, for example, when compared with the case where
the pressure in the internal space 52 is equal to the suction
pressure of the pump section 11, the leakage of DME from the
high-pressure pump chambers 37b to the internal space 52 is
decreased. Also, for example, when compared with the case where the
pressure in the internal space 52 is equal to the discharge
pressure of the pump section 11, the leakage of DME from the
internal space 52 to the low-pressure pump chambers 36b is
decreased. As a result, the efficiency of the pump 1 is improved in
total.
[0054] Since the leakage of DME between the pump chambers 36b, 37b
close to the driven shaft 29 and the internal space 52 is decreased
without the use of a sealing member as described above, the size of
the pump 1 is made small. Therefore, the pump 1 of this embodiment
is suitable as a pump mounted on a vehicle.
[0055] (2) According to this embodiment, in the pump section 11,
the internal space 52 is connected to the communication passage 43,
which functions as an intermediate-pressure zone, via the pressure
introduction passage 67. Therefore, the internal space 52 is made
to have a pressure atmosphere of intermediate pressure by a simple
construction such as the pressure introduction passage 67.
[0056] (3) The communication passage 43 connecting the discharge
side of the first-stage gear train 36 to the suction side of the
second-stage gear train 37 forms an intermediate-pressure zone. For
example, when compared with the intermediate pressure in the case
where the low-pressure pump chambers 36a and 36b during the
conveyance under pressure in the first-stage gear train 36 function
as intermediate-pressure zones, a high pressure, which is the
discharge pressure of the first-stage gear train 36, is introduced
to the internal space 52. Therefore, the maximum difference in
pressure produced between the pump chambers 36b, 37b and the
internal space 52 is further decreased. As a result, the efficiency
of the pump 1 is further improved.
[0057] Also, for example, when compared with the case where an
intermediate-pressure zone is set in the pump chambers 36a, 36b,
37a, 37b during the stroke of conveyance under pressure, the layout
of the pressure introduction passage 67 is simple, which is
advantageous in decreasing the size of the pump 1.
[0058] As shown in FIG. 5, in a second embodiment, a shaft seal
device 71 is provided between the base block 16 and the drive shaft
12. The shaft seal device 71 disconnects the motor chamber 60 from
the third space 51c of the internal space 51 in the pump section
11. The shaft seal device 71 includes, for example, a lip type
seal. The side plate 20 has a pressure introduction passage 72. The
pressure introduction passage 72 connects the first passage 43a of
the communication passage 43 to the second space 51b of the
internal space 51.
[0059] Therefore, the intermediate pressure of the communication
passage 43 is introduced to the second space 51b of the internal
space 51 through the pressure introduction passage 72. That is to
say, the pressure atmosphere of the internal space 51 around the
cylindrical surface 12b of the drive shaft 12 and the pressure
atmosphere of the space 62a exposed to the lower end face of the
drive shaft 12 are the same as the pressure atmosphere of
intermediate pressure of the pump section 11.
[0060] In this embodiment, therefore, the maximum difference in
pressure produced between the pump chambers 36a, 37a close to the
drive shaft 12, and the internal space 51 is also decreased. As a
result, in the relationship between the pump chambers 36a, 37a and
the internal space 51 close to the drive shaft 12 as well, as in
the case of the above-described first embodiment, that is, as in
the relationship between the pump chambers 36b, 37b and the
internal space 52 close to the driven shaft 29, an effect of
decreasing DME leakage is achieved. Since the leakage of DME is
decreased in both of the relationship between the pump chambers
36a, 37a and the internal space 51 close to the drive shaft 12 and
the relationship between the pump chambers 36b, 37b and the
internal space 52 close to the driven shaft 29, the efficiency of
the pump 1 is further improved.
[0061] As shown in FIG. 6, in a third embodiment, the vent hole 57
in the motor housing 10a and the pressure introduction passage 67
in the side plate 20 are eliminated from the above-described first
embodiment. The space 63a (see FIG. 1A) exposed to the upper end
face of the driven shaft 29 in the recess 63 is connected to the
motor chamber 60 through a communication hole 75 penetrating the
base block 16. The third space 51c (see FIG. 1A) of the internal
space 51 close to the drive shaft 12 is connected to the motor
chamber 60 through the gap between the base block 16 and the
large-diameter portion of the drive shaft 12, that is, the
communication hole 76. Therefore, the pressure atmosphere of the
internal spaces 51 and 52 is the same as the pressure atmosphere of
the motor chamber 60.
[0062] At a midway point of the leak port 56 in the pipe connecting
portion 54, a pressure regulating valve 77 is disposed. The
pressure regulating valve 77 is a differential pressure regulating
valve including a valve element 77a and an urging spring 77b. The
pressure regulating valve 77 opens and closes the leak port 56
according to a difference between the pressure on the motor chamber
60 side applied to the valve element 77a and the pressure on the
tank 2 (see FIG. 4) side similarly applied to the valve element
77a.
[0063] The high-pressure pump chambers 37a and 37b (see FIG. 1A)
function as a high-pressure zone. The pressure in the high-pressure
zone is higher than the pressure in the internal spaces 51 and 52.
The pressure in the internal spaces 51 and 52 and the motor chamber
60 is increased due to the leakage of DME from the pump chambers
37a and 37b, that is, the pressure leakage, and the vaporization of
DME in the motor chamber 60. If the pressure in the internal spaces
51 and 52 and the motor chamber 60 becomes higher than a
predetermined value, the valve element 77a of the pressure
regulating valve 77 moves in the valve opening direction against
the urging force in the valve closing direction generated by the
urging spring 77b and a force in the valve closing direction
generated by the pressure in the section connected to the tank 2.
Thus, the valve element 77a releases the leak port 56. Therefore,
the pressure in the internal spaces 51 and 52 and the motor chamber
60 tends to be decreased by the sending-out of pressure to the tank
2 through the leak port 56, so that the pressure returns to the
aforementioned predetermined value.
[0064] In a state in which the leak port 56 is open, if the
pressure in the internal spaces 51 and 52 and the motor chamber 60
becomes lower than the predetermined value, the valve element 77a
of the pressure regulating valve 77 is moved in the valve closing
direction by the urging force in the valve closing direction of the
urging spring 77b and a force in the valve closing direction
generated by the pressure of the section connected to the tank 2,
so that the leak port 56 is closed. Therefore, the pressure in the
internal spaces 51 and 52 and the motor chamber 60 tends to be
increased by the leakage and vaporization of DME, so that the
pressure returns to the aforementioned predetermined value.
[0065] That is to say, the pressure regulating valve 77 opens and
closes the leak port 56 autonomously so as to keep the pressure in
the internal spaces 51 and 52 and the motor chamber 60 at the
predetermined value. The construction of the pressure regulating
valve 77 of an autonomous type is simpler than that of a pressure
regulating valve of, for example, an external control type. The
aforementioned predetermined value, that is, the target of
regulation of the pressure in the internal spaces 51 and 52 and the
motor chamber 60 accomplished by the pressure regulating valve 77
is set to the intermediate pressure of the pump section 11 in the
steady-state operating condition, for example, to the discharge
pressure of the first-stage gear train 36. The setting of the
pressure regulation target is concretely performed by the
adjustment of the spring force of the urging spring 77b. Therefore,
as in the case of the above-described second embodiment, the
internal spaces 51 and 52 have the pressure atmosphere of
intermediate pressure of the pump section 11. Therefore, the
leakage of DME between the pump chambers 36a, 36b, 37a, 37b and the
corresponding internal space 51, 52 is decreased.
[0066] In this embodiment, the target value of the pressure in the
internal spaces 51 and 52 is changed easily by changing the
operating characteristics of the pressure regulating valve 77, for
example, the spring force of the urging spring 77b. Therefore, the
pressure in the internal spaces 51 and 52, which varies from pump
to pump, is corrected to a desired value by simple work. For
example, in the above-described second embodiment, in order to
correct the pressure in the internal spaces 51 and 52, which varies
from pump to pump, it is necessary to change the diameters etc. of
the pressure introduction passages 67 and 72. Such work for
changing the diameter and other measurements is troublesome. In
this embodiment, the correction of pressure is made easily.
[0067] The pressure leakage from the pump section 11 is an
inevitable phenomenon. The pressure leakage tends to increase the
pressure in the internal spaces 51 and 52. In this embodiment, the
internal spaces 51 and 52 are caused to have an intermediate
pressure atmosphere by utilizing the tendency for the pressure in
the internal spaces 51 and 52 to increase due to this inevitable
pressure leakage from the pump section 11. Unlike the pump 1 of the
second embodiment, in the pump 1 of this embodiment, the internal
spaces 51 and 52 need not be isolated from the motor chamber 60. In
the pump 1 of this embodiment, in which the internal spaces 51 and
52 and the motor chamber 60 communicate with each other, the DME
leaking from, for example, from the second-stage gear train 37 is
positively supplied to the motor chamber 60 through the internal
spaces 51 and 52 and the communication holes 75 and 76. As a
result, the motor section 10 is cooled properly by the liquid DME
supplied to the motor chamber 60. Thereby, the operation of the
motor section 10 is stabilized.
[0068] In this embodiment, the communication holes 75 and 76, the
motor chamber 60, the communication hole 65, the internal space of
the recess 61, the leak port 56, and the leak pipe 55 (see FIG. 4)
function as a pressure regulation passage that connects the tank 2
functioning as a low-pressure zone to the internal spaces 51 and
52.
[0069] As shown in FIG. 7, in the pump 1 in accordance with a
fourth embodiment, the pump 1 of the above-described third
embodiment is changed. Specifically, the upstream-side of the leak
port 56 of the pipe connecting portion 54 is connected to the upper
space of the sub tank 7a. The lid 9 has an internal passage 79 for
connecting the internal space of the recess 61 to the upper space
of the sub tank 7a. The vaporized DME in the motor chamber 60 is
discharged through the communication hole 65, the internal space of
the recess 61, and the internal passage 79, and is returned to the
tank 2 through the leak port 56 and the leak pipe 55 together with
the DME vaporized in the sub tank 7a.
[0070] In the internal passage 79, the pressure regulating valve 77
is disposed to regulate the pressure in the motor chamber 60 so as
to be an intermediate pressure by the same operation as that in the
above-described third embodiment. In this embodiment, the sub tank
7a functions as a low-pressure zone. The communication holes 75 and
76, the motor chamber 60, the communication hole 65, the internal
space of the recess 61, and the internal passage 79 function as a
pressure regulation passage that connects the internal spaces 51
and 52 to the low-pressure zone, i.e., the sub tank 7a.
[0071] As shown in FIG. 8, in a fifth embodiment, the
above-described third embodiment is changed. Specifically, the
motor section 10 is arranged at the lower part (right-hand side as
viewed in FIG. 8) of the casing 7, and the pump section 11 is
arranged at the upper part (left-hand side as viewed in FIG. 8) of
the casing 7. That is to say, the pump 1 is mounted on a vehicle in
a state in which the pump section 11 is at the upper position and
the motor section 10 is at the lower position.
[0072] By this configuration, the pump section 11 and the discharge
connecting portion 39 installed to the lid 9 are arranged so as to
be close to each other. Therefore, the first pump section internal
passage (not shown) for connecting the pump section 11 to the
discharge connecting portion 39 is laid out easily, which is
advantageous in decreasing the size of the pump 1. Also, since the
motor section 10 is arranged at the lower part of the casing 7, the
liquid level of DME in the motor chamber 60 is surely located at
the upper part of the motor chamber 60. Therefore, the stators 10b
and the rotor 10c are less liable to be exposed above the liquid
level of DME, so that they are cooled properly by DME (liquid).
[0073] In this embodiment, the upstream-side of the leak port 56 is
connected to the internal space of the recess 62 in the tip-end
plate 22. The leak port 56 and the motor chamber 60 are connected
to each other through the internal space 51 close to the drive
shaft 12 and the communication hole 76. Therefore, the vaporized
DME in the motor chamber 60 is discharged into the tank 2 through
the communication hole 76, the internal space 51, the leak port 56,
and the leak pipe 55 (see FIG. 4).
[0074] The pressure in the internal space 51 tends to be increased
under the influence of DME leakage from the high-pressure pump
chambers 37a and 37b (see FIG. 1A), which function as high-pressure
zones, and under the influence of vaporization of DME in the motor
chamber 60. On the other hand, the pressure in the internal space
51 is released into the tank 2 through the leak port 56 and the
leak pipe 55. The pressure regulating valve 77 regulates the
pressure in the internal space 51 so as to be the intermediate
pressure of the pump section 11 by regulating the opening of the
leak port 56 and the degree of sending-out of pressure from the
internal space 51.
[0075] In this embodiment, the communication hole 75 is eliminated.
That is to say, the internal space 52 close to the driven shaft 29
is isolated from the motor chamber 60. However, the internal space
52 is connected to the communication passage 43 between the gear
trains 36 and 37 through the pressure introduction passage 67. That
is to say, the internal space 52 close to the driven shaft 29 is
made to have a pressure atmosphere of intermediate pressure of the
pump section 11 by the same method as that in the above-described
first embodiment.
[0076] In this embodiment, the pressure in the internal space 51
close to the drive shaft 12 is regulated directly by the pressure
regulating valve 77. Contrarily, for example, in the
above-described third embodiment, the pressure in the motor chamber
60 is regulated directly, and resultantly the pressure in the motor
chamber 60 is reflected to the pressure in the internal space 51.
In this embodiment, therefore, when compared with the
above-described third embodiment, the operation of the pressure
regulating valve 77 is immediately reflected to the pressure in the
internal space 51. Therefore, the pressure in the internal space 51
is further stabilized. As a result, the leakage of DME between the
low-pressure pump chambers 36a, the high-pressure pump chamber 37a
and the internal space 51 close to the drive shaft 12 is restrained
more effectively.
[0077] In this embodiment, the internal space of the recess 62, the
leak port 56, and the leak pipe 55 (see FIG. 4) function as a
pressure regulation passage that connects the internal space 51 to
the tank 2.
[0078] The invention may be embodied in the following forms.
[0079] By changing the above-described first or second embodiment,
in the first-stage gear train 36 or the second-stage gear train 37,
the pump chambers 36a, 36b, 37a, 37b during the conveyance under
pressure are grasped as intermediate-pressure zones. Specifically,
in the case of the modification of the first embodiment, the
internal space 51 is connected to the intermediate-pressure zone
through the pressure introduction passage. In the case of the
modification of the second embodiment, the internal spaces 51 and
52 are connected to the intermediate-pressure zone through the
pressure introduction passage.
[0080] In the above-described second embodiment, the pressure
introduction passage 67 is eliminated. That is to say, only the
internal space 51 is made to have the intermediate pressure.
[0081] In the above-described third to fifth embodiments, the
pressure regulating valve 77 is of an autonomous type (differential
pressure regulating valve). By changing this, a valve of an
external control type, such as a solenoid valve, is used as a
pressure control valve. In this case, the modification of the third
to fifth embodiments is provided with a pressure sensor and control
means (described below). The pressure sensor detects the pressure
in the corresponding internal spaces 51 and 52 or the pressure in a
space having the same pressure atmosphere as that of the said
space. The control means, which is, for example, a computer,
controls the opening and closing of the pressure control valve
based on detected information sent from the pressure sensor. Thus,
the pressure regulation passage that connects the internal spaces
51 and 52 to the low-pressure zone can be opened or closed
according to the pressure in the corresponding internal spaces 51
and 52 without being affected by the pressure state on the
low-pressure zone side. Therefore, the pressure in the
corresponding internal spaces 51 and 52 can surely be regulated so
as to have a predetermined value.
[0082] In the above-described embodiments, the invention is
embodied in the pump 1 of a type such as to be mounted outside the
tank 2. By changing this, the invention is embodied in a gear pump
of what is called an in-tank type, which is contained in the tank
2. In this case, the casing 7 is eliminated.
[0083] The fluid handled by the gear pump is not limited to DME.
The invention may be embodied in a gear pump that handles a liquid
(gas) other than DME.
[0084] In the above-described embodiments, the invention is
embodied in the two-stage gear pump. However, the invention is not
limited to the gear pump of this type. The invention may be
embodied in the gear pump of a plurality of stages other than two
stages, such as three stages or four stages. Alternatively, the
invention may be embodied in a one-stage gear pump.
[0085] In the above-described embodiments, the gear pump is of a
shaft enclosed type, i.e., a type such that the motor is
incorporated. However, the gear pump may be of a shaft open type,
i.e., a type such that the pump section is driven by an external
motor.
[0086] The gear pump in accordance with the present invention is
not limited to a vehicular gear pump that sends a liquefied gas
fuel under pressure to an internal combustion engine. The present
invention may be applied to a gear pump used to send hydraulic
fluid etc. under pressure, for example, in a machine tool.
[0087] 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 and equivalence of the appended claims.
* * * * *