U.S. patent application number 15/125837 was filed with the patent office on 2016-12-29 for pump device.
This patent application is currently assigned to KYB Corporation. The applicant listed for this patent is KYB Corporation. Invention is credited to Koichiro AKATSUKA, Tomoyuki FUJITA, Hiroki GOMI, Fumiyasu KATOU, Tomoyuki NAKAGAWA.
Application Number | 20160377078 15/125837 |
Document ID | / |
Family ID | 55533095 |
Filed Date | 2016-12-29 |
United States Patent
Application |
20160377078 |
Kind Code |
A1 |
AKATSUKA; Koichiro ; et
al. |
December 29, 2016 |
PUMP DEVICE
Abstract
A pump device includes a pump, a flow control valve having a
spool that returns a part of working fluid discharged from the pump
to a suction side, and a differential pressure adjusting device
that adjusts a differential pressure acting on both end portions of
the spool to a target differential pressure, and the differential
pressure adjusting device includes a pressure regulating chamber
that communicates with a second fluid pressure chamber and a pilot
chamber into which pressure in the discharge channel is guided: and
a pressure in the pressure regulating chamber is adjusted such that
a differential pressure between the pressure in the pressure
regulating chamber and a pressure in the pilot chamber becomes the
target differential pressure.
Inventors: |
AKATSUKA; Koichiro; (Gifu,
JP) ; FUJITA; Tomoyuki; (Gifu, JP) ; NAKAGAWA;
Tomoyuki; (Gifu, JP) ; KATOU; Fumiyasu;
(Aichi, JP) ; GOMI; Hiroki; (Gifu, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYB Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
KYB Corporation
Tokyo
JP
|
Family ID: |
55533095 |
Appl. No.: |
15/125837 |
Filed: |
September 2, 2015 |
PCT Filed: |
September 2, 2015 |
PCT NO: |
PCT/JP2015/074984 |
371 Date: |
September 13, 2016 |
Current U.S.
Class: |
417/310 |
Current CPC
Class: |
F04C 14/26 20130101;
F04C 2/3446 20130101; F04C 2270/215 20130101; F04C 15/06 20130101;
F04C 2240/10 20130101; F04C 2270/86 20130101; F04C 2270/585
20130101; F04C 2210/206 20130101; F04C 2240/20 20130101 |
International
Class: |
F04C 14/26 20060101
F04C014/26; F04C 15/06 20060101 F04C015/06; F04C 2/344 20060101
F04C002/344 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2014 |
JP |
2014-187279 |
Claims
1. A pump device for supplying working fluid to a fluid pressure
apparatus comprising: a pump configured to discharge the working
fluid into a discharge channel by sucking and pressurizing the
working fluid; a flow control valve having a first valve body
configured to operate in accordance with a differential pressure
acting on both end portions thereof to return a part of the working
fluid discharged from the pump to a suction side; and a
differential pressure adjusting device configured to adjust the
differential pressure acting on both end portions of the first
valve body to a target differential pressure; wherein the flow
control valve comprises: a first fluid pressure chamber provided so
as to face against a first-side end portion of the first valve
body, the first fluid pressure chamber communicating with the
discharge channel; a second fluid pressure chamber provided so as
to face against a second-side end portion of the first valve body,
the second fluid pressure chamber communicating with the discharge
channel; and a biasing member accommodated in the second fluid
pressure chamber in a compressed state, the biasing member being
configured to bias the first valve body in a valve-closing
direction; and the differential pressure adjusting device has: a
second valve body; a pressure regulating chamber provided so as to
face against a first-side end portion of the second valve body, the
pressure regulating chamber communicating with the second fluid
pressure chamber; and a pilot chamber provided so as to face
against a second-side end portion of the second valve body, a
pressure in the discharge channel being guided into the pilot
chamber; and wherein a pressure in the pressure regulating chamber
is adjusted such that a differential pressure between the pressure
in the pressure regulating chamber and a pressure in the pilot
chamber becomes the target differential pressure.
2. The pump device according to claim 1, wherein the pump device
further comprises an orifice provided in a communicating passage
that allows the discharge channel to communicate with the second
fluid pressure chamber.
3. The pump device according to claim 1, wherein the differential
pressure adjusting device further comprises: a biasing member
accommodated in the pressure regulating chamber in a compressed
state, the biasing member being configured to bias the second valve
body in a valve-opening direction; and a proportional solenoid
configured to bias the second valve body in the valve-closing
direction, the proportional solenoid being capable of changing the
biasing force biasing the second valve body in the valve-closing
direction.
4. The pump device according to claim 1, wherein the target
differential pressure is adjusted in accordance with a rotation
speed of the pump.
5. The pump device according to claim 1, wherein the target
differential pressure is adjusted in accordance with pressure
required by the fluid pressure apparatus.
Description
TECHNICAL FIELD
[0001] The present invention relates to a pump device.
BACKGROUND ART
[0002] In the related art, there are known pump devices, in which a
flow control valve is provided in order to keep a discharge flow
amount of the pump constant.
[0003] JP05-61482U describes a pump device in which a flow control
valve is provided at an intermediate position in a drain passage
that is connected between a suction passage and a discharge passage
of a vane pump. With the pump device described in JP05-61482U,
working oil discharged from pump chambers to the discharge passage
in a manner proportional to the rotation speed of the pump is
supplied to a hydraulic driving device through an orifice. In
addition, with the pump device described in JP05-61482U, the flow
control valve is controlled so as to be opened/closed such that the
amount of the working oil supplied from the vane pump to the
hydraulic driving device is controlled so as to be substantially
constant.
SUMMARY OF INVENTION
[0004] However, with the pump device in JP05-61482U, a restrictor
is provided in the discharge passage of the pump. Therefore, a
pressure loss is caused at the restrictor, and torque required for
driving the pump becomes correspondingly greater.
[0005] The present invention has been conceived in light of the
problems mentioned above, and an object thereof is to provide a
pump device capable of controlling a flow amount while reducing a
driving torque for a pump.
[0006] According to one aspect of the present invention, a pump
device for supplying working fluid to a fluid pressure apparatus
includes: a pump configured to discharge the working fluid into a
discharge channel by sucking and pressurizing the working fluid; a
flow control valve having a first valve body configured to operate
in accordance with a differential pressure acting on both end
portions thereof to return a part of the working fluid discharged
from the pump to a suction side; and a differential pressure
adjusting device configured to adjust the differential pressure
acting on both end portions of the first valve body to a target
differential pressure; wherein the flow control valve comprises: a
first fluid pressure chamber provided so as to face against a
first-side end portion of the first valve body, the first fluid
pressure chamber communicating with the discharge channel; a second
fluid pressure chamber provided so as to face against a second-side
end portion of the first valve body, the second fluid pressure
chamber communicating with the discharge channel; and a biasing
member accommodated in the second fluid pressure chamber in a
compressed state, the biasing member being configured to bias the
first valve body in a valve-closing direction; and the differential
pressure adjusting device has: a second valve body; a pressure
regulating chamber provided so as to face against a first-side end
portion of the second valve body, the pressure regulating chamber
communicating with the second fluid pressure chamber; and a pilot
chamber provided so as to face against a second-side end portion of
the second valve body, a pressure in the discharge channel being
guided into the pilot chamber; and wherein a pressure in the
pressure regulating chamber is adjusted such that a differential
pressure between the pressure in the pressure regulating chamber
and a pressure in the pilot chamber becomes the target differential
pressure.
BRIEF DESCRIPTION OF DRAWINGS
[0007] FIG. 1 is a hydraulic circuit diagram of a pump device
according to a first embodiment of the present invention.
[0008] FIG. 2 is a map showing the relationship between the pump
rotation speed at a certain target flow amount and the target
differential pressure.
[0009] FIG. 3 is a map showing the relationship between the target
differential pressure and the current applied to a proportional
solenoid.
[0010] FIG. 4 is a map showing the relationship between the pump
rotation speed at a certain target flow amount and the target
differential pressure for a pump device according to a second
embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0011] A pump device 100 according to a first embodiment of the
present invention will be described below with reference to the
drawings.
[0012] FIG. 1 is a hydraulic circuit diagram of the pump device
100. The pump device 100 includes a pump 1 in which working oil
serving as working fluid is sucked from a suction channel 81
connected to a tank 4 and in which the working oil is pressurized
and discharged to a discharge channel 82 and a flow control valve 2
having a spool 21 serving as a first valve body that operates in
accordance with the differential pressure acting on both end
portions thereof in such a mariner that a part of the working fluid
discharged from the pump 1 is returned to the suction channel 81 on
the suction side.
[0013] The pump 1 is a fixed displacement vane pump. The pump 1
includes a rotor 11 that is rotationally driven by a driving
device, such as an engine (not shown), a plurality of vanes 12 that
are provided so as to be movable in a reciprocating manner in the
radial direction with respect to the rotor 11, and a cam ring 13 in
which the rotor 11 is accommodated and tip ends of the vanes 12 are
brought into sliding contact with a cam face 13a on the inner
circumference thereof by rotation of the rotor 11.
[0014] In the rotor 11, slits 14 having openings in an outer
circumferential surface are formed in a radiating pattern with
predetermined gaps therebetween, and the vanes 12 are respectively
inserted into the slits 14 in a freely slidable manner.
[0015] At base-end sides of the slits 14, back pressure chambers 15
into which discharge pressure of the pump 1 is guided are defined.
The adjacent back pressure chambers 15 communicate with each other
through an arc-shaped groove 16 formed in the rotor 11, and the
pump discharge pressure is constantly guided to the groove 16. The
vanes 12 are pushed in the directions in which the vanes 12 project
out from the slits 14 by the pressure in the back pressure chambers
15 and the centrifugal force caused by the rotation of the rotor
11, and thereby, the tip ends of the vanes 12 are brought into
contact with the cam face 13a on the inner circumference of the cam
ring 13. With such a configuration, a plurality of pump chambers 17
are defined within the cam ring 13 by the outer circumferential
surface of the rotor 11, the cam face 13a of the cam ring 13, and
pairs of adjacent vanes 12.
[0016] The cam ring 13 is an annular member whose circumferential
cam face 13a on the inner circumference has a substantially oval
shape, and the cam ring 13 has suction regions 13b and 13d in which
the volume of the pump chambers 17 are expanded as the rotor 11 is
rotated and discharge regions 13c and 13e in which the volume of
the pump chambers 17 are contracted as the rotor 11 is rotated.
[0017] While the rotor 11 is fully rotated, the respective pump
chambers 17 suck the working oil from the suction channel 81
through a suction port (not shown) in the suction region 13b of the
cam ring 13, discharge the sucked working oil to the discharge
channel 82 through a discharge port 18 of the discharge region 13c
of the cam ring 13, subsequently suck the working oil from the
suction channel 81 through the suction port (not shown) in the
suction region 13d of the cam ring 13, and discharge the sucked
working oil to the discharge channel 82 through the discharge port
18 in the discharge region 13e of the cam ring 13. As described
above, the respective pump chambers 17 are expanded/contracted by
the rotation of the rotor 11, and the working oil is
sucked/discharged twice while the rotor 11 is fully rotated. The
pump rotation speed N of the pump 1 changes in accordance with the
rotation speed of the driving device. As the pump rotation speed N
is increased, the discharge flow amount of the pump 1 is increased
in a manner proportional to the rotation speed.
[0018] As long as the pump 1 is of a rotationally-operated fixed
displacement type, the pump 1 may be of any type, such as a gear
pump.
[0019] The flow control valve 2 includes the spool 21 that is
inserted into a valve accommodating bore 25 in a freely slidable
manner, a first fluid pressure chamber 23 that is provided so as to
face against a first-side end portion of the spool 21, a second
fluid pressure chamber 24 that is provided so as to face against a
second-side end portion of the spool 21, and a return spring 22
serving as a biasing member accommodated in the second fluid
pressure chamber 24 in a compressed state for biasing the spool 21
in the valve-closing direction.
[0020] The spool 21 includes a first land part 21a and a second
land part 21b that slide along the inner circumferential surface of
the valve accommodating bore 25.
[0021] In the first fluid pressure chamber 23, a first stopper
portion 21c is arranged by being connected to the first land part
21a so as to be brought into contact with a bottom portion of the
valve accommodating bore 25 when the spool 21 is moved in the
direction in which the volume of the first fluid pressure chamber
23 is contracted and so as to restrict the movement of the spool 21
exceeding a predetermined amount.
[0022] A first communicating passage 83, which is branched off from
the discharge channel 82, is connected to the first fluid pressure
chamber 23 and a second communicating passage 84, which is branched
off from the discharge channel 82, is connected to the second fluid
pressure chamber 24. In addition, a drain passage 85, which is
communicated with or shut off from the first fluid pressure chamber
23 by the first land part 21a, is connected to the flow control
valve 2.
[0023] The spool 21 is stopped at a position where the load exerted
by the pressure of the working oil guided to the first fluid
pressure chamber 23 and the second fluid pressure chamber 24, which
are defined at both end portions thereof, and the biasing force by
the return spring 22 are balanced.
[0024] When the total load, acting on the spool 21, of the load
exerted by the pressure P2 in the second fluid pressure chamber 24
and the biasing force by the return spring 22 is greater than the
load exerted by the pressure P1 in the first fluid pressure chamber
23 acting on the spool 21, the return spring 22 is extended and the
spool 21 is in a state in which the first stopper portion 21c is in
contact with the bottom portion of the valve accommodating bore
25.
[0025] In this state, the first land part 21a of the spool 21 shuts
off the communication between the first fluid pressure chamber 23
and the drain passage 85. Thus, all of the working oil discharged
from the pump 1 is supplied to a fluid pressure apparatus 50.
[0026] In contrast, when the load exerted by the pressure P1 in the
first fluid pressure chamber 23 acting on the spool 21 is greater
than the total load, acting on the spool 21, of the load exerted by
the pressure P2 in the second fluid pressure chamber 24 and the
biasing force by the return spring 22, the spool 21 is moved
against the biasing force by the return spring 22.
[0027] In this state, the first land part 21a of the spool 21
allows communication between the first fluid pressure chamber 23
and the drain passage 85. Thus, a part of the working oil
discharged from the pump 1 is returned to the suction channel 81
through the first fluid pressure chamber 23 and the drain passage
85.
[0028] As described above, the flow control valve 2 operates in
accordance with the differential pressure acting on both end
portions of the spool 21. Therefore, by controlling the
differential pressure acting on both end portions of the spool 21,
it is possible to control the flow amount of the working oil
returning to the suction channel 81 through the flow control valve
2, and it is possible to control the flow amount of the working oil
supplied to the fluid pressure apparatus 50 from the pump 1 so as
to become the desirable flow amount.
[0029] The pump device 100 further includes a differential pressure
adjusting device 3 that adjusts the differential pressure Pd,
acting on both end portions of the spool 21 of the flow control
valve 2, between the pressure P1 in the first fluid pressure
chamber 23 and the pressure P2 in the second fluid pressure chamber
24 to a target differential pressure Pt and an orifice 40 that is
provided in the second communicating passage 84 communicating the
discharge channel 82 and the second fluid pressure chamber 24.
[0030] The differential pressure adjusting device 3 includes a
spool 31 serving as a second valve body, a pressure regulating
chamber 34 that is provided so as to face against a first-side end
portion of the spool 31 and that communicates with the second fluid
pressure chamber 24, a pilot chamber 35 that is provided so as to
face against a second-side end portion of the spool 31 and into
which the pressure in the discharge channel 82 is guided, a spring
33 serving as a biasing member accommodated in the pressure
regulating chamber 34 in a compressed state for biasing the spool
31 in the valve-opening direction, and a proportional solenoid 32
that biases the spool 31 in the valve-closing direction and that is
capable of changing the biasing force biasing the spool 31 in the
valve-closing direction. The biasing force exerted by the
proportional solenoid 32 can be changed in accordance with the
level of the applied current I applied thereto.
[0031] The pressure regulating chamber 34 communicates with the
second communicating passage 84 at the downstream side of the
orifice 40 through a second pilot passage 86. With such a
configuration, the pressure regulating chamber 34 communicates with
the second fluid pressure chamber 24 through the second pilot
passage 86 and the second communicating passage 84. Therefore, the
pressure P4 in the pressure regulating chamber 34 becomes equal to
the pressure P2 in the second fluid pressure chamber 24. In
addition, the pilot chamber 35 communicates with the discharge
channel 82 through a first pilot passage 88, which is branched off
from the discharge channel 82. Because the pilot chamber 35 and the
first fluid pressure chamber 23 respectively communicate with the
discharge channel 82, the pressure P3 in the pilot chamber 35
becomes equal to the pressure P1 in the first fluid pressure
chamber 23.
[0032] A relief passage 87 that is branched off from the second
communicating passage 84 at the downstream side of the orifice 40
and that communicates with the tank 4 is connected to the
differential pressure adjusting device 3.
[0033] The spool 31 includes a third land part 31a and a fourth
land part 31b that slide along the inner circumferential surface of
a valve accommodating bore 36. The communication between the relief
passage 87 and the tank 4 is allowed or shut off by the third land
part 31a of the spool 31.
[0034] The spool 31 is stopped at a position where the load exerted
by the pressure of the working oil guided to the pressure
regulating chamber 34 and the pilot chamber 35 and the biasing
force by the proportional solenoid 32 and the spring 33 are
balanced. When the total load of the load exerted by the pressure
P3 in the pilot chamber 35 and the biasing force by the
proportional solenoid 32 is greater than the total load of the load
exerted by the pressure P4 in the pressure regulating chamber 34
and the biasing force by the spring 33, the communication between
the relief passage 87 and the tank 4 is shut off by the third land
part 31a. In contrast, when the total load of the load exerted by
the pressure in the pilot chamber 35 and the biasing force by the
proportional solenoid 32 is smaller than the total load of the load
exerted by the pressure in the pressure regulating chamber 34 and
the biasing force by the spring 33, the communication between the
relief passage 87 and the tank 4 is allowed by the third land part
31a.
[0035] A controller 60 controls the applied current I applied to
the proportional solenoid 32. In addition, the pump rotation speed
N of the pump 1 detected by a pump-rotation-speed detector 70 is
input to the controller 60.
[0036] A map (see FIG. 2) showing the relationship between the pump
rotation speed N and the target differential pressure Pt at a
certain target flow amount of the pump device 100 and a map (see
FIG. 3) showing the relationship between the target differential
pressure Pt and the proportional-solenoid applied current I are
stored in advance in the controller 60. Here, the target flow
amount is a predetermined value of the flow amount required by the
fluid pressure apparatus 50, and in FIG. 2, the target flow amount
corresponds to the flow amount discharged from the pump 1 at the
pump rotation speed Nm. In addition, the target differential
pressure Pt is a target value of the differential pressure Pd,
acting on both end portions of the spool 21 of the flow control
valve 2, between the pressure P1 in the first fluid pressure
chamber 23 and the pressure P2 in the second fluid pressure chamber
24. The controller 60 controls the proportional solenoid 32 such
that the differential pressure Pd becomes the target differential
pressure Pt.
[0037] In the pump device 100, the flow amount returning from the
discharge channel 82 to the suction channel 81 is controlled by the
flow control valve 2, and thereby, a control is performed such that
the flow amount of the working oil supplied to the fluid pressure
apparatus 50 from the pump 1 through the discharge channel 82
becomes the target flow amount. Specifically, the controller 60
refers to the maps shown in FIGS. 2 and 3 and adjusts the degree of
opening of the spool 21 of the flow control valve 2 by performing
an adjustment in which operation of the differential pressure
adjusting device 3 is controlled such that the differential
pressure Pd between the pressure P1 in the first fluid pressure
chamber 23 and the pressure P2 in the second fluid pressure chamber
24 becomes the target differential pressure Pt. The controller 60
thereby performs a control such that the flow amount of the working
oil supplied to the fluid pressure apparatus 50 from the pump 1
becomes the target flow amount.
[0038] The map shown in FIG. 2 will be described. In the pump 1, as
the pump rotation speed N increases, the discharge flow amount also
increases in a manner proportional to the rotation speed. The
controller 60 refers to the map shown in FIG. 2, and when the
rotation speed is less than or equal to the rotation speed Nm,
because the discharge flow amount of the pump 1 has not reached the
target flow amount, the controller 60 performs a control such that
the target differential pressure Pt becomes zero so as not to allow
the working oil to return from the discharge channel 82 to the
suction channel 81. In addition, when the rotation speed of the
pump 1 is greater than the rotation speed Nm that corresponds to
the target flow amount, because the discharge flow amount of the
pump 1 is greater than the target flow amount, the excessive flow
amount is caused. Furthermore, in a case in which the rotation
speed of the pump 1 is greater than the rotation speed Nm, the
increase/decrease in the pump rotation speed N results in the
increase/decrease in the excessive flow amount. Therefore, in order
to keep the supplying-flow amount from the pump 1 to the fluid
pressure apparatus 50 constant, the returning-flow amount from the
flow control valve 2 needs to be adjusted by adjusting the degree
of opening of the spool 21 of the flow control valve 2 in
accordance with the increase/decrease in the pump rotation speed N.
Thus, the controller 60 adjusts the target differential pressure Pt
in accordance with the pump rotation speed N. Because the spool 21
of the flow control valve 2 is biased by the return spring 22 in
the valve-closing direction, the spool 21 does not open unless the
differential pressure Pd acting on both end portions of the spool
21 becomes greater than or equal to the differential pressure Pm
corresponding to the load by the biasing force exerted by the
return spring 22.
[0039] Next, the map shown in FIG. 3 will be described. The target
differential pressure Pt and the applied current I of the
proportional solenoid 32 of the differential pressure adjusting
device 3 are in the negatively proportional relationship.
Specifically, in order to increase the target differential pressure
Pt, the applied current I of the proportional solenoid 32 is
lowered. When the applied current I of the proportional solenoid 32
is lowered, the biasing force by the differential pressure
adjusting device 3 in the valve-closing direction of the spool 31
is decreased. Thus, because the differential pressure Pe between
the pressure P3 in the pilot chamber 35 and the pressure P4 in the
pressure regulating chamber 34 is increased, the differential
pressure Pd between the pressure P1 in the first fluid pressure
chamber 23 and the pressure P2 in the second fluid pressure chamber
24 is also increased. In contrast, in order to reduce the target
differential pressure Pt, the applied current I of the proportional
solenoid 32 is increased. As the applied current I of the
proportional solenoid 32 is increased, the biasing force by the
differential pressure adjusting device 3 in the valve-closing
direction of the spool 31 is increased. Thus, because the
differential pressure Pe between the pressure P3 in the pressure
regulating chamber 34 and the pressure P4 in the pilot chamber 35
is decreased, the differential pressure Pd between the pressure P1
in the first fluid pressure chamber 23 and the pressure P2 in the
second fluid pressure chamber 24 is also decreased.
[0040] Next, operation of the pump device 100 will be
described.
[0041] The pump 1 is rotationally driven by a motive force from a
driving device, such as an engine (not shown), and thereby, the
working oil is sucked from the tank 4 through the suction channel
81 and the working oil is pressurized and discharged to the
discharge channel 82. The working oil discharged into the discharge
channel 82 is supplied to the fluid pressure apparatus 50.
[0042] The pump rotation speed N of the pump 1 is changed in
accordance with the rotation speed of the driving device. As the
pump rotation speed N is increased, the discharge flow amount of
the pump 1 is also increased in a manner proportional to the
rotation speed.
[0043] When the pump 1 is driven, the working oil is supplied to
the first fluid pressure chamber 23 from the discharge channel 82
through the first communicating passage 83, and the working oil is
supplied to the pilot chamber 35 from the discharge channel 82
through the first pilot passage 88. With such a configuration, the
equal amount of pressure acts on the first fluid pressure chamber
23 and the pilot chamber 35. In addition, the working oil is
supplied to the second fluid pressure chamber 24 from the discharge
channel 82 through the second communicating passage 84, and the
working oil is supplied to the pressure regulating chamber 34 from
the discharge channel 82 through the second communicating passage
84 and the second pilot passage 86. With such a configuration, the
equal amount of pressure acts on the second fluid pressure chamber
24 and the pressure regulating chamber 34.
[0044] Therefore, the differential pressure Pd, acting on both end
portions of the spool 21 of the flow control valve 2, between the
pressure P1 in the first fluid pressure chamber 23 and the pressure
P2 in the second fluid pressure chamber 24 becomes equal to the
differential pressure Pe, acting on both end portions of the spool
31 of the differential pressure adjusting device 3, between the
pressure P3 in the pilot chamber 35 and the pressure P4 in the
pressure regulating chamber 34.
[0045] In addition, when the pump 1 is driven, the pump rotation
speed N is input to the controller 60 from the pump-rotation-speed
detector 70. The controller 60 refers to the map shown in FIG. 2
and selects the target differential pressure Pt corresponding to
the input pump rotation speed N.
[0046] For example, when the pump rotation speed N is less than or
equal to the rotation speed Nm, the discharge flow amount of the
pump 1 has not reached the target flow amount required by the fluid
pressure apparatus 50.
[0047] Therefore, as shown in the map in FIG. 2, the controller 60
sets the target differential pressure Pt to zero such that the flow
amount discharged from the pump 1 does not return through the flow
control valve 2. Next, by referring to the map shown in FIG. 3, the
controller 60 selects the applied current Ia for the proportional
solenoid 32 such that the target differential pressure Pt becomes
zero. In this way, the controller 60 sets the target differential
pressure Pt to zero by applying the applied current Ia to the
proportional solenoid 32 of the differential pressure adjusting
device 3.
[0048] When the target differential pressure Pt is set to zero, the
applied current Ia is applied to the proportional solenoid 32 of
the differential pressure adjusting device 3, and thereby, the
biasing force acting on the spool 31 in the valve-closing direction
of the proportional solenoid 32 is maximized. Therefore, the total
load of the load exerted by the pressure P3 in the pilot chamber 35
and the biasing force by the proportional solenoid 32, in the
valve-closing direction, becomes greater than the total load of the
load exerted by the pressure P4 in the pressure regulating chamber
34 and the biasing force by the spring 33, in the valve-opening
direction. Thus, the spool 31 of the differential pressure
adjusting device 3 is closed, and the communication between the
relief passage 87 and the tank 4 is shut off. Thereby, the working
oil is supplied to the pressure regulating chamber 34 from the
discharge channel 82 through the second communicating passage 84
and the second pilot passage 86, and the pressure P4 in the
pressure regulating chamber 34 becomes equal to the pressure P3 in
the pilot chamber 35. At the same time, the working oil is supplied
to the second fluid pressure chamber 24 from the discharge channel
82 through the second communicating passage 84, and the pressure P2
in the second fluid pressure chamber 24 becomes equal to the
pressure P1 in the first fluid pressure chamber 23. Therefore, the
differential pressure Pd acting on both end portions of the flow
control valve 2 becomes zero. In other words, the biasing force in
the valve-opening direction by the pressure P1 in the first fluid
pressure chamber 23 and the biasing force in the valve-closing
direction by the pressure P2 in the second fluid pressure chamber
24, both acting on the spool 21 of the flow control valve 2, are
cancelled out. At this time, because the spool 21 of the flow
control valve 2 is biased in the valve-closing direction by the
biasing force by the return spring 22, the flow control valve 2 is
closed. In this way, the working oil discharged from the pump 1
does not return through the flow control valve 2, and all of the
working oil discharged form the pump 1 is supplied to the fluid
pressure apparatus 50.
[0049] When the pump rotation speed N is increased and becomes, for
example, the rotation speed Nb, which is greater than the rotation
speed Nm, because the discharge flow amount of the pump 1 is
greater than the target flow amount required by the fluid pressure
apparatus 50, the excessive flow amount is caused. Thus, the
controller 60 refers to the map shown in FIG. 2 and selects, as the
target differential pressure Pt, the differential pressure Pb
corresponding to the rotation speed Nb.
[0050] In order to increase the differential pressure Pd from zero
to the differential pressure Pb, the controller 60 refers to the
map shown in FIG. 3 and lowers the applied current I from the
applied current Ia for the proportional solenoid 32 corresponding
to zero differential pressure to the applied current Ib
corresponding to the differential pressure Pb. By doing so, because
the biasing force by the proportional solenoid 32 acting on the
spool 31 is decreased, the total load of the load exerted by the
pressure in the pressure regulating chamber 34 and the biasing
force by the spring 33, in the valve-opening direction, becomes
greater than the total load of the load exerted by the pressure in
the pilot chamber 35 and the biasing force by the proportional
solenoid 32, in the valve-closing direction. Therefore, the spool
31 of the differential pressure adjusting device 3 is opened, and
the relief passage 87 communicates with the tank 4. As the spool 31
is opened, the working oil in the pressure regulating chamber 34 is
returned to the tank 4 through the second pilot passage 86, the
second communicating passage 84, and the relief passage 87. By
doing so, because the pressure P4 in the pressure regulating
chamber 34 is decreased, the differential pressure Pe between the
pressure P3 in the pilot chamber 35 and the pressure P4 in the
pressure regulating chamber 34 is increased, and the set target
differential pressure Pb is achieved. When the differential
pressure Pe becomes the set target differential pressure Pb,
because the total load of the load exerted by the pressure in the
pressure regulating chamber 34 and the biasing force by the spring
33 becomes equal to the total load of the load exerted by the
pressure in the pilot chamber 35 and the biasing force by the
proportional solenoid 32, the degree of opening of the spool 31 of
the differential pressure adjusting device 3 is maintained in that
state.
[0051] Because the differential pressure Pd and the differential
pressure Pe are equal to each other as described above, when the
differential pressure Pe is increased from zero to the differential
pressure Pb, the differential pressure Pd is also increased from
zero to the differential pressure Pb. Therefore, the spool 21 of
the flow control valve 2 is opened against the biasing force by the
return spring 22, and thereby, the working oil (the excessive flow
amount) in the discharge channel 82 returns to the suction channel
81 through the first fluid pressure chamber 23 and the drain
passage 85. By doing so, even when the discharge flow amount is
increased due to the increase in the rotation speed of the pump 1
to the rotation speed Nb, because the flow control valve 2 is
opened and the working oil (the excessive flow amount) in the
discharge channel 82 is returned to the suction channel 81 through
the first fluid pressure chamber 23 and the drain passage 85, the
flow amount of the working oil supplied to the fluid pressure
apparatus 50 from the pump 1 is kept constant (at the target flow
amount).
[0052] When the pump rotation speed N is changed from the rotation
speed Nb to the even greater rotation speed Nc, the discharge flow
amount discharged from the pump 1 to the discharge channel 82 is
increased even further. At this time, as shown in FIGS. 2 and 3, in
order to increase the target differential pressure Pt from the
differential pressure Pb to the differential pressure Pc
corresponding to the rotation speed Nc, the controller 60 lowers
the applied current I from the applied current Ib to the applied
current Ic. By doing so, the differential pressure Pe is increased
from the differential pressure Pb to the differential pressure Pc,
and the degree of opening of the spool 31 of the differential
pressure adjusting device 3 is increased. At the same time, because
the differential pressure Pd is also increased from the
differential pressure Pb to the differential pressure Pc, the
degree of opening of the spool 21 of the flow control valve 2 is
increased, thereby increasing the returning-flow amount. Therefore,
even when the discharge flow amount is increased due to the
increase in the rotation speed of the pump 1 to the rotation speed
Nc, because the returning-flow amount returning from the discharge
channel 82 to the suction channel 81 is also increased, the flow
amount of the working oil supplied to the fluid pressure apparatus
50 from the pump 1 is kept constant (at the target flow
amount).
[0053] In contrast, when, for example, the pump rotation speed N is
decreased from the rotation speed Nc to the rotation speed Nb
within a range in which the pump rotation speed is greater than the
predetermined rotation speed Nm, the discharge flow amount
discharged from the pump 1 to the discharge channel 82 is
decreased, and the excessive flow amount is also decreased. At this
time, in order to reduce the target differential pressure Pt from
the differential pressure Pc corresponding to the rotation speed Nc
to the differential pressure Pb corresponding to the rotation speed
Nb, the controller 60 refers to the maps shown in FIGS. 2 and 3 and
increases the applied current I of the proportional solenoid 32 of
the differential pressure adjusting device 3 from the applied
current Ic to the applied current Ib. By doing so, because the
biasing force by the proportional solenoid 32 acting on the spool
31 of the differential pressure adjusting device 3 is increased,
the total load of the load exerted by the pressure in the pilot
chamber 35 and the biasing force by the proportional solenoid 32,
in the valve-closing direction, becomes greater than the total load
of the load exerted by the pressure P4 in the pressure regulating
chamber 34 and the biasing force by the spring 33, in the
valve-opening direction. Therefore, the spool 31 of the
differential pressure adjusting device 3 moves in the valve-closing
direction, and the degree of opening of the spool 31 is decreased.
By doing so, because the flow amount returning from the relief
passage 87 to the tank 4 is decreased, the pressure P4 in the
pressure regulating chamber 34 is increased by the working oil
supplied from the discharge channel 82 through the orifice 40. When
the pressure P4 in the pressure regulating chamber 34 is increased,
the differential pressure Pe between the pressure P3 in the pilot
chamber 35 and the pressure P4 in the pressure regulating chamber
34 is decreased, and the set target differential pressure Pb is
achieved. When the differential pressure Pe is the set target
differential pressure Pb, because the total load of the load
exerted by the pressure in the pressure regulating chamber 34 and
the biasing force by the spring 33 becomes equal to the total load
of the load exerted by the pressure in the pilot chamber 35 and the
biasing force by the proportional solenoid 32, the degree of
opening of the spool 31 is maintained in that state.
[0054] Because the differential pressure Pd and the differential
pressure Pe are equal to each other as described above, when the
differential pressure Pe is decreased from the differential
pressure Pc to the differential pressure Pb, the differential
pressure Pd is also decreased from the differential pressure Pc to
the differential pressure Pb. Therefore, because the biasing force
in the valve-closing direction is increased, the degree of opening
of the spool 21 of the flow control valve 2 is decreased, and
thereby, the returning-flow amount is decreased. In this way, even
when the discharge flow amount is decreased due to the decrease in
the rotation speed of the pump 1 to the rotation speed Nb, because
the returning-flow amount returning from the discharge channel 82
to the suction channel 81 is also decreased, the flow amount of the
working oil supplied to the fluid pressure apparatus 50 from the
pump 1 is kept constant (at the target flow amount).
[0055] As described above, with the pump device 100, by adjusting
the pressure P4 in the pressure regulating chamber 34 such that the
differential pressure Pe between the pressure P4 in the pressure
regulating chamber 34 and the pressure P3 in the pilot chamber 35
becomes the target differential pressure Pt, the differential
pressure Pe between the pressure P1 in the first fluid pressure
chamber 23 and the pressure P2 in the second fluid pressure chamber
24 is adjusted to the target differential pressure Pt, and thereby,
the returning-flow amount returning through the flow control valve
2 is controlled. By doing so, even when the discharge flow amount
is changed due to the change in the pump rotation speed N of the
pump 1, it is possible to keep the flow amount of the working oil
supplied to the fluid pressure apparatus 50 constant.
[0056] When, for example, the pressure of the discharge channel 82
is increased by the operation of the fluid pressure apparatus 50
while the flow amount is controlled so as to be constant (at the
target flow amount), the pressure P1 in the first fluid pressure
chamber 23 is also increased through the first communicating
passage 83. By doing so, the biasing force biasing the spool 21 of
the flow control valve 2 in the valve-opening direction is
increased, and the spool 21 tends to move in the valve-opening
direction.
[0057] With the pump device 100, because an increase in the
pressure in the discharge channel 82 results in an increase in the
pressure in the pilot chamber 35, the biasing force biasing the
spool 31 of the differential pressure adjusting device 3 in the
valve-closing direction is increased. Therefore, the spool 31 is
moved in the valve-closing direction and the degree of opening of
the spool 31 is decreased, and thereby, the flow amount returning
from the relief passage 87 to the tank 4 is decreased. By doing so,
the pressure P4 in the pressure regulating chamber 34 and the
pressure P2 in the second fluid pressure chamber 24 are increased
by the working oil supplied from the discharge channel 82 through
the orifice 40.
[0058] As described above, with the pump device 100, even when the
pressure P1 in the first fluid pressure chamber 23 is increased due
to the increase in the pressure in the discharge channel 82,
because the pressure P4 in the pressure regulating chamber 34 and
the pressure P2 in the second fluid pressure chamber 24 are
accordingly adjusted so that the target differential pressure Pt
set by the differential pressure adjusting device 3 is achieved,
and because the differential pressure Pd is kept at the target
differential pressure Pt, the degree of opening of the spool 21
does not change. Therefore, the returning-flow amount returning
through the flow control valve 2 does not change substantially, and
so, even if the pressure is changed, it is possible to keep the
flow amount of the working oil supplied to the fluid pressure
apparatus 50 constant (at the target flow amount).
[0059] In contrast, when the pressure in the discharge channel 82
is decreased by the operation of the fluid pressure apparatus 50,
the pressure P1 in the first fluid pressure chamber 23 is also
decreased through the first communicating passage 83. By doing so,
the biasing force biasing the spool 21 of the flow control valve 2
in the valve-opening direction is decreased, and the spool 21 tends
to move in the valve-closing direction.
[0060] With the pump device 100, because the decrease in the
pressure in the discharge channel 82 results in the decrease in the
pressure in the pilot chamber 35, the biasing force biasing the
spool 31 in the valve-closing direction is decreased. Therefore,
the degree of opening of the spool 31 is increased, and the flow
amount returning from the relief passage 87 to the tank 4 is
increased. By doing so, the pressure in the second fluid pressure
chamber 24 and the pressure regulating chamber 34 are
decreased.
[0061] As described above, with the pump device 100, even when the
pressure P1 in the first fluid pressure chamber 23 is decreased due
to the decrease in the pressure in the discharge channel 82,
because the pressure P4 in the pressure regulating chamber 34 and
the pressure P2 in the second fluid pressure chamber 24 are
accordingly adjusted so that the target differential pressure Pt
set by the differential pressure adjusting device 3 is achieved,
and the differential pressure Pd is kept at the target differential
pressure Pt, the degree of opening of the spool 21 does not change.
Therefore, the returning-flow amount returning through the flow
control valve 2 does not change substantially, and so, even if the
pressure is changed, it is possible to keep the flow amount of the
working oil supplied to the fluid pressure apparatus 50 constant
(at the target flow amount).
[0062] With the above-mentioned first embodiment, the following
effects can be afforded.
[0063] While a restrictor is conventionally provided in a discharge
channel connecting a pump and a fluid pressure apparatus and a flow
control valve is controlled on the basis of the pressure difference
between the upstream side and the downstream side thereof, in this
embodiment, by adjusting the pressure P4 in the pressure regulating
chamber 34 such that the differential pressure Pe between the
pressure P4 in the pressure regulating chamber 34 and the pressure
P3 in the pilot chamber 35 becomes the target differential pressure
Pt by the differential pressure adjusting device 3, the
differential pressure Pd between the pressure P1 in the first fluid
pressure chamber 23 and the pressure P2 in the second fluid
pressure chamber 24 of the flow control valve 2 is adjusted to the
target differential pressure Pt. By doing so, it is possible to
control the flow amount of the working oil supplied from the pump 1
to the fluid pressure apparatus 50 so as to be constant without
providing the restrictor in the discharge channel 82. In addition,
because the restrictor is not provided in the discharge channel 82,
no pressure loss is caused, and it is possible to reduce the torque
for driving the pump 1. Furthermore, because the flow control valve
2 is controlled with the differential pressure Pd between the
pressure P1 in the first fluid pressure chamber 23 and the pressure
P2 in the second fluid pressure chamber 24, even when the pressure
in the discharge channel 82 is changed due to operation of the
fluid pressure apparatus 50, it is possible to keep the flow amount
of the working oil supplied to the fluid pressure apparatus 50
constant.
[0064] In addition, in this embodiment, because the differential
pressure Pe between the pressure P4 in the pressure regulating
chamber 34 and the pressure P3 in the pilot chamber 35 with a
narrow variable range is controlled by the differential pressure
adjusting device 3 without controlling the pressure itself in the
first fluid pressure chamber 23 or the second fluid pressure
chamber 24, there is no need to set the control range for the
biasing force by the proportional solenoid 32 to a wide range.
Therefore, because the control range for the biasing force is
narrow with respect to the range for the current applied to the
proportional solenoid 32, it is possible to improve the
controllability. In addition, the size of the proportional solenoid
32 can be reduced.
Second Embodiment
[0065] A pump device 200 according to a second embodiment of the
present invention will be described. In the following, the
differences from the above-mentioned first embodiment will be
described mainly, and the configurations that are the same as those
of the pump device according to the first embodiment are given the
same reference signs and the descriptions thereof will be
omitted.
[0066] The second embodiment will be specifically described below
with reference to FIG. 4.
[0067] When the variation in the pressure required by the fluid
pressure apparatus 50 is large, the variation in the pressure in
the discharge channel 82 also becomes large, and in turn, the
variation in the differential pressure between the first fluid
pressure chamber 23 and the pressure in the tank 4 becomes large.
When the variation in the differential pressure between the first
fluid pressure chamber 23 and the pressure in the tank 4 is large,
there is the possibility of variation in the returning-flow amount
even with the same degree of opening of the spool 21 of the flow
control valve 2. In addition, the greater the differential pressure
between the first fluid pressure chamber 23 and the pressure in the
tank 4 is, the faster the speed of the fluid becomes. Depending on
the shape of the spool 21, it is possible that, as the fluid speed
is increased, the fluid force acts in the valve-closing direction
due to the difference between the static pressure and the dynamic
pressure acting on the spool 21, and the returning-flow amount is
reduced.
[0068] As shown in FIG. 4, with the pump device 200, in order to
improve the precision of the control to keep the flow amount of the
working oil supplied to the fluid pressure apparatus 50 constant
(at the target flow amount), the characteristics of the pump
rotation speed N and the target differential pressure Pt are
changed on the basis of the pressure of the fluid pressure
apparatus 50.
[0069] With the pump device 200, a signal for the pressure required
by the fluid pressure apparatus 50 is input to the controller 60.
As the signal for the pressure required by the fluid pressure
apparatus 50 is input, the controller 60 selects, from the map
shown in FIG. 4 stored in advance, the characteristics of the
relationship between the pump rotation speed N and the target
differential pressure Pt in accordance with the pressure required
by the fluid pressure apparatus 50.
[0070] For example, while the control is performed at the pump
rotation speed Nc with a medium-pressure characteristic B, when the
pressure required by the fluid pressure apparatus 50 is increased,
the controller 60 selects a high-pressure characteristic A shown in
FIG. 4. In other words, the set pressure of the target differential
pressure Pt is changed from the differential pressure Pc with the
medium-pressure characteristic B to the differential pressure Pf
with the high-pressure characteristic A. By doing so, the
differential pressure Pd acting on the spool 21 of the flow control
valve 2 is decreased. The pressure in the discharge channel 82 is
increased when the pressure required by the fluid pressure
apparatus 50 is increased, and the differential pressure between
the pressure P1 in the first fluid pressure chamber 23 and the
pressure in the tank 4 is increased. Correspondingly, the
differential pressure Pd is decreased to reduce the degree of
opening of the spool 21, thereby adjusting the returning-flow
amount so as not to be changed. Thus, it is possible to keep the
flow amount of the working oil supplied to the fluid pressure
apparatus 50 constant (at the target flow amount).
[0071] In addition, while the control is performed at the pump
rotation speed Nc with the medium-pressure characteristic B, when
the pressure required by the fluid pressure apparatus 50 is
decreased, the controller 60 selects a low-pressure characteristic
C shown in FIG. 4. In other words, the target differential pressure
Pt is changed from the differential pressure Pc with the
medium-pressure characteristic B to a differential pressure Pg with
the low-pressure characteristic C. By doing so, the differential
pressure Pd acting on the spool 21 of the flow control valve 2 is
increased. When the pressure required by the fluid pressure
apparatus 50 is decreased, the pressure in the discharge channel 82
is decreased, and the differential pressure between the pressure P1
in the first fluid pressure chamber 23 and the pressure in the tank
4 is decreased. Correspondingly, the differential pressure Pd is
increased to increase the degree of opening of the spool 21,
thereby adjusting the returning-flow amount so as not to be
changed. Thus, it is possible to keep the flow amount of the
working oil supplied to the fluid pressure apparatus 50 constant
(at the target flow amount).
[0072] In this way, even when the pressure required by the fluid
pressure apparatus 50 is changed, in accordance with the pressure,
the controller 60 selects the characteristic of the relationship
between the pump rotation speed N and the target differential
pressure Pt and performs the control on the basis of the selected
characteristic such that the differential pressure Pd and the
differential pressure Pe become the target differential pressure
Pt, and thereby, it is possible to keep the flow amount of the
working oil supplied to the fluid pressure apparatus 50 constant
(at the target flow amount).
[0073] Although FIG. 4 shows stepwise characteristics like the
high-pressure characteristic A, the medium-pressure characteristic
B, and the low-pressure characteristic C, in practice, the
characteristics are changed continuously between the high-pressure
characteristic A and the low-pressure characteristic C. Of course,
the characteristics may be changed in a stepwise manner. The
medium-pressure characteristic B shown in FIG. 4 is only a
conceptual illustration of a characteristic between the
high-pressure characteristic A and the low-pressure characteristic
C.
[0074] With the above-mentioned second embodiment, the following
effects can be afforded.
[0075] With the pump device 200, the pressure required by the fluid
pressure apparatus 50 is input to the controller 60, and the target
differential pressure Pt is adjusted in accordance with the signal
for this pressure. In other words, because the target differential
pressure Pt is adjusted in accordance with the pressure required by
the fluid pressure apparatus 50, it is possible to keep the flow
amount of the working oil supplied to the fluid pressure apparatus
50 constant at a higher precision.
[0076] The above-mentioned second embodiment is configured such
that the signal for the pressure required by the fluid pressure
apparatus 50 is input to the controller 60. Instead of this
configuration, a pressure detector may be provided in the discharge
channel 82, and the signal from this pressure detector may be input
to the controller 60. As the signal is input from the pressure
detector, the controller 60 refers to the map shown in FIG. 4 and
selects an appropriate characteristic for the relationship between
the pump rotation speed N and the target differential pressure Pt
in accordance with the pressure in the discharge channel 82
detected by the pressure detector. By doing so, it is possible to
control the pump device 200, as in the case in which the signal for
the pressure required by the fluid pressure apparatus 50 is input
to the controller 60.
[0077] Configurations, operations, and effects of the embodiments
according to the present invention will be collectively described
below.
[0078] According to this embodiment, the pump device 100 includes
the flow control valve 2 having the spool 21 that operates in
accordance with the differential pressure Pd acting on both end
portions thereof in such a manner that a part of the working fluid
discharged from the pump 1 is returned to the suction channel 81
and the differential pressure adjusting device 3 that adjusts the
differential pressure Pd acting on both end portions of the spool
21 to the target differential pressure Pt, wherein the differential
pressure adjusting device 3 has the pressure regulating chamber 34
that is provided so as to face against the first-side end portion
of the spool 31 and that communicates with the second fluid
pressure chamber 24 and the pilot chamber 35 that is provided so as
to face against the second-side end portion of the spool 31 and
into which the pressure in the discharge channel 82 is guided. The
pump device 100 is characterized in that the pressure P4 in the
pressure regulating chamber 34 is adjusted such that the
differential pressure Pe between the pressure P4 in the pressure
regulating chamber 34 and the pressure P3 in the pilot chamber 35
becomes the target differential pressure Pt.
[0079] With this configuration, by adjusting the pressure P4 in the
pressure regulating chamber 34 such that the differential pressure
Pe between the pressure P4 in the pressure regulating chamber 34
and the pressure P3 in the pilot chamber 35 becomes the target
differential pressure Pt, the differential pressure Pd acting on
both end portions of the spool 21 of the flow control valve 2 is
adjusted to the target differential pressure Pt. By doing so,
because the working fluid discharged from the pump 1 is returned to
the suction channel 81 through the flow control valve 2 in
accordance with the target differential pressure Pt, it is possible
to control the flow amount without providing a restrictor in the
discharge channel 82. As described above, because a restrictor is
not provided in the discharge channel 82, it is possible to reduce
the torque for driving the pump 1.
[0080] In addition, in this embodiment, the pump device 100 is
characterized in that the orifice 40 is further provided in the
second communicating passage 84 communicating the discharge channel
82 and the second fluid pressure chamber 24.
[0081] With this configuration, by providing the orifice 40 in the
second communicating passage 84, it is possible to adjust the
pressure P2 in the second fluid pressure chamber 24 even when the
flow amount of the working oil discharged through the differential
pressure adjusting device 3 is small. Therefore, the size of the
differential pressure adjusting device 3 can be reduced.
[0082] In addition, in this embodiment, the differential pressure
adjusting device 3 is characterized in that the spring 33 that is
accommodated in the pressure regulating chamber 34 in a compressed
state and that biases the spool 31 in the valve-opening direction
and the proportional solenoid 32 that is capable of changing the
biasing force biasing the spool 31 in the valve-closing direction
are further provided.
[0083] With this configuration, because the proportional solenoid
32 is used, it is possible to adjust the differential pressure Pd
acting on both end portions of the spool 21 of the flow control
valve 2 with high precision.
[0084] In addition, in this embodiment, it is characterized in that
the target differential pressure Pt is adjusted in accordance with
the pump rotation speed N of the pump 1.
[0085] With this configuration, even when the discharge flow amount
is changed due to the change in the rotation speed N of the pump 1,
because the target differential pressure Pt is adjusted in
accordance with the rotation speed N of the pump 1, it is possible
to control the flow amount of the working fluid supplied to the
fluid pressure apparatus 50 to the target flow amount with high
precision.
[0086] In addition, in this embodiment, it is characterized in that
the target differential pressure Pt is adjusted in accordance with
the pressure required by the fluid pressure apparatus 50.
[0087] With this configuration, even when the pressure required by
the fluid pressure apparatus 50 is changed, because the target
differential pressure Pt is adjusted in accordance with the changed
pressure, it is possible to control the flow amount of the working
fluid supplied to the fluid pressure apparatus 50 to the target
flow amount with high precision.
[0088] Embodiments of this invention were described above, but the
above embodiments are merely examples of applications of this
invention, and the technical scope of this invention is not limited
to the specific constitutions of the above embodiments.
[0089] In the above-mentioned embodiment, the target differential
pressure Pt is changed by the pump rotation speed N of the pump 1.
Instead of this configuration, a flow meter that detects a flow
amount discharged by the pump 1 may be provided, and the target
differential pressure Pt may be changed in accordance with the
detected flow amount.
[0090] In addition, the pump device 100 may be configured such that
a plurality of maps of the target flow amount shown in FIG. 2 or 4
may be stored in the controller 60 for each of different target
flow amounts, and the controller 60 may appropriately select a map
corresponding to the target flow amount in accordance with an
instruction from the fluid pressure apparatus 50. In order to
create a map with a different target flow amount, the position of
the rotation speed Nm forming a break point of a graph should be
shifted to the position of pump rotation speed corresponding to the
target flow amount.
[0091] This application claims priority based on Japanese Patent
Application No. 2014-187279 filed with the Japan Patent Office on
Sep. 16, 2014, the entire contents of which are incorporated into
this specification.
* * * * *