U.S. patent application number 10/699809 was filed with the patent office on 2004-05-27 for volume control apparatus of radial piston pump or motor and positioning apparatus.
This patent application is currently assigned to KOMATSU LTD.. Invention is credited to Arai, Mitsuru, Ishizaki, Naoki.
Application Number | 20040101417 10/699809 |
Document ID | / |
Family ID | 32321990 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040101417 |
Kind Code |
A1 |
Arai, Mitsuru ; et
al. |
May 27, 2004 |
Volume control apparatus of radial piston pump or motor and
positioning apparatus
Abstract
The invention provides a volume control apparatus of a radial
pump or motor which downsizes a hydraulic pump or motor, reduces a
weight thereof and improves a freedom in arrangement, and a
positioning apparatus. Accordingly, a servo piston (8) is operated
following to a control valve (9), presses a cam ring (2) so as to
position the cam ring at a position in correspondence to a volume
control pressure, and regulates a volume.
Inventors: |
Arai, Mitsuru; (Oyama-shi,
JP) ; Ishizaki, Naoki; (Minamikawachi-machi,
JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
KOMATSU LTD.
Tokyo
JP
|
Family ID: |
32321990 |
Appl. No.: |
10/699809 |
Filed: |
November 3, 2003 |
Current U.S.
Class: |
417/218 ;
417/219; 417/222.1; 91/491 |
Current CPC
Class: |
F04B 49/125 20130101;
F04B 1/07 20130101 |
Class at
Publication: |
417/218 ;
417/219; 417/222.1; 091/491 |
International
Class: |
F04B 049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 2002 |
JP |
2002-342560 |
Claims
What is claimed is:
1. A volume control apparatus of a radial piston pump or a motor
for regulating a volume by positioning a cam ring of the radial
piston pump or the motor, comprising: a control valve positioned at
a position in correspondence to a volume control pressure; and a
servo piston having said control valve built-in, being operated
following to the control valve and pressing said cam ring so as to
position the cam ring.
2. A volume control apparatus of a radial piston pump or a motor as
claimed in claim 1, wherein one set of said control valve and said
servo piston and another set of said control valve and said servo
piston are provided at opposing positions with respect to said cam
ring.
3. A positioning apparatus comprising: a control valve positioned
at a position in correspondence to a control pressure; and a servo
piston having said control valve built-in, being operated following
to the control valve and pressing a positioning member so as to
position the positioning member.
4. A positioning apparatus comprising: a control valve carrying out
a stroke in correspondence to a control pressure applied to a
pressure receiving surface; and a servo piston having said control
valve built-in and pressing a positioning member in correspondence
to a driving pressure, wherein a throttle is formed between said
control valve and said servo piston, in such a manner that the
driving pressure introduced to said servo piston is increased in
accordance that said control valve carries out the stroke
relatively close to said positioning member with respect to said
servo piston, and the driving pressure introduced to said servo
piston is reduced in accordance that said servo piston carries out
the stroke relatively close to said positioning member with respect
to said control valve, wherein a spring for generating a spring
force opposing to said control pressure is applied to said control
valve, wherein said control pressure is applied to said pressure
receiving surface so as to carry out a stroke of said control
valve, said servo piston carries out a stroke following to said
control valve on the basis of the driving pressure introduced via
said throttle, and wherein said control valve is positioned at a
position where the spring force of said spring and said control
pressure are balanced, and said servo piston is positioned in
accordance the positioning of the control valve.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a volume control apparatus
of a radial piston pump or a motor in which each of pistons is
arranged so as to slide in a radial direction with respect to a
rotation axis, and a positioning apparatus for a cam ring of the
radial piston pump or a swash plate of an axial piston pump.
BACKGROUND OF THE INVENTION
[0002] In a hydraulic working machine such as a construction
machine or the like, there is mounted a hydraulic pump and a
hydraulic motor, in order to drive an upper revolving body, a lower
traveling body and the like.
[0003] As one kind of the hydraulic pump, there is a radial piston
pump in which each of pistons is arranged so as to slide in a
radial direction with respect to a rotation axis. In the radial
piston pump, a cam ring is pressed by an actuator for regulating a
volume, and a center of the cam ring is positioned at a position
which is eccentric with respect to a center of the rotation axis
(or a main axis). A volume (cc/rev) is determined in correspondence
to an eccentric amount of the cam ring.
[0004] Further, as one kind of the hydraulic pump, there is an
axial piston pump in which each of the pistons is arranged so as to
slide in parallel to the rotation axis. In the axial piston pump, a
swash plate is oscillated by an actuator for regulating a volume,
and the swash plate is positioned at a tilted position with respect
to the rotation axis (or a main axis). A volume is determined in
correspondence to a tilting amount of the swash plate.
[0005] In this case, in recent years, in the case that the
hydraulic pump or the like is mounted on the construction machine
or the like, there is a request of making a weight of the hydraulic
pump light by making a place product of the hydraulic pump itself
small on the basis of a constraint of a mounting space, a demand
from a market and the like, and improving a freedom for arranging
the hydraulic pump. Accordingly, a downsizing and a weight
reduction are required in the volume regulating actuator mounted to
the hydraulic pump. The same matter is applied to the hydraulic
motor.
[0006] The present invention is made by taking the actual condition
mentioned above into consideration, and a first achieving object of
the present invention is to downsize a radial piston pump or a
motor, reduce a weight and improve a freedom in arrangement.
[0007] Further, a second achieving object of the present invention
is to reduce a weight by downsizing a positioning apparatus for
positioning a cam ring of a radial piston pump or a motor, and a
swash plate of an axial piston pump or a motor.
[0008] A general technical level in connection with the achieving
object of the present invention is as follows.
[0009] In a document listed up as one example of a prior art:
Japanese Unexamined Patent Publication No. 11-50968, there is
disclosed a positioning apparatus in which a position of a cam ring
in a radial piston pump is detected by a distance sensor, a
detection signal of the distance sensor is amplified by an
amplifier, the amplified signal is incorporated as a feedback
amount into a servo valve, and the cam ring is positioned at a
target position by controlling so as to drive the piston by the
servo valve.
[0010] Since the positioning apparatus described in the publication
is constituted by the distance sensor, the amplifier, the servo
valve and the piston, there is a problem that a place product is
increased in the case of being used as the actuator for regulating
the volume of the radial piston pump.
SUMMARY OF THE INVENTION
[0011] In order to achieve the first achieving object, in
accordance with a first aspect of the present invention, there is
provided a volume control apparatus of a radial piston pump or a
motor for regulating a volume by positioning a cam ring of the
radial piston pump or the motor, comprises a control valve
positioned at a position in correspondence to a volume control
pressure, and a servo piston having said control valve built-in,
being operated following to the control valve and pressing the cam
ring so as to position the cam ring.
[0012] In the volume control apparatus in accordance with the first
aspect, as shown in FIG. 1, a servo piston 8 is operated following
to a control valve (a spool) 9, presses a cam ring 2 so as to
position the cam ring 2 at a position in correspondence to a volume
control pressure, and regulates a volume. Accordingly, the same
servo mechanism as that of the prior art can be achieved. Further,
since the volume control apparatus has the control valve 9 built in
the servo piston 8, the place product becomes small, and the weight
becomes light. Therefore, the radial piston pump or the motor is
downsized, the weight is reduced, and a freedom in arrangement is
improved.
[0013] In accordance with a second aspect of the present invention,
there is provided a volume control apparatus of a radial piston
pump or a motor as recited in the first aspect, wherein one set of
the control valve and the servo piston and another set of the
control valve and the servo piston are provided at opposing
positions with respect to the cam ring.
[0014] In accordance with the second aspect, as shown in FIG. 5A,
the control valve (a spool) 9 and the servo piston 8, and a control
valve (a spool) 19 and a servo piston 18 are provided at opposing
positions with respect to the cam ring 2, and the cam ring 2 can be
made eccentric in both sides with respect to a center of a piston
valve 5. Accordingly, as shown in FIG. 5B, in the case that the
volume control apparatus is applied to an alternating type
hydraulic pump 61 which can change a discharging direction to two
directions, it is possible to regulate the volume in both
discharging directions on the basis of a small place product.
[0015] In order to achieve the second achieving object, in
accordance with a third invention, there is provided a positioning
apparatus comprises a control valve positioned at a position in
correspondence to a volume control pressure, and a servo piston
being said control valve built-in, being operated following to the
control valve and pressing a positioning member so as to position
the positioning member.
[0016] In order to achieve the second achieving object, in
accordance with a fourth invention, there is provided a positioning
apparatus comprises a control valve carrying out a stroke in
correspondence to a control pressure applied to a pressure
receiving surface, and a servo piston having the control valve
built-in and pressing a positioning member in correspondence to a
driving pressure,
[0017] wherein a throttle is formed between the control valve and
the servo piston, in such a manner that the driving pressure
introduced to the servo piston is increased in accordance that the
control valve carries out the stroke relatively close to the
positioning member with respect to the servo piston, and the
driving pressure introduced to the servo piston is reduced in
accordance that the servo piston carries out the stroke relatively
close to the positioning member with respect to the control valve,
and
[0018] wherein a spring for generating a spring force opposing to
the control pressure is applied to the control valve, the control
pressure is applied to the pressure receiving surface so as to
carry out a stroke of the control valve, the servo piston carries
out a stroke following to the control valve on the basis of the
driving pressure introduced via the throttle, the control valve is
positioned at a position where the spring force of the spring and
the control pressure are balanced, and the servo piston is
positioned in accordance the positioning of the control valve.
[0019] In the positioning apparatuses in accordance with the third
aspect and the fourth aspect, as exemplified in FIGS. 1 and 6, the
servo piston is operated following to the control valve (the spool)
9, presses a positioning member (a cam ring or a swash plate) 2 or
50, and positions the positioning member 2 or 50 at a position in
correspondence to the control pressure. Since the positioning
apparatus has the control valve 9 built in the servo piston 8, the
place product becomes small and the weight becomes light.
Accordingly, the radial pump or the motor, and the axial piston
pump or the motor are downsized, the weight thereof is reduced, and
a freedom in arrangement is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a view showing an entire structure of a radial
piston pump in accordance with an embodiment of the present
invention;
[0021] FIG. 2 is a view showing a detailed structure of a volume
control apparatus of the radial piston pump shown in FIG. 1;
[0022] FIG. 3 is a view showing details of a volume control
apparatus having a different structure from that shown in FIG.
2;
[0023] FIG. 4 is a view showing details of a volume control
apparatus having a different structure from those shown in FIGS. 2
and 3;
[0024] FIGS. 5A and 5B are views showing a structure embodiment in
which volumes in both discharging directions of a radial piston
pump are changed; and
[0025] FIG. 6 is a view showing a structure embodiment in the case
that a volume control apparatus in accordance with the present
embodiment is applied to an axial piston pump.
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] A description will be given below of an embodiment of a
volume control apparatus and a positioning apparatus in accordance
with the present invention with reference to the accompanying
drawings.
[0027] FIG. 1 shows an entire structure of a radial piston pump in
accordance with the present embodiment. The radial piston pump in
FIG. 1 is used as a driving pressure source for a hydraulic motor
mounted on a construction machine and driving an upper revolving
body, or a hydraulic motor driving a lower traveling body.
[0028] FIG. 1 is a view of a radial piston pump 1 as seen along a
vertical cross section to a rotation axis, and shows an eccentric
type radial piston pump. The radial piston pump 1 is structured
such as to receive a cylinder block 3 and the like in an inner
portion of a case 14.
[0029] The cylinder block 3 is integrally formed with a rotation
axis (not shown). A cylindrical piston valve 5 is fitted and fixed
to the case 14 in accordance with an arrangement aspect that a
rotation axis and a center axis are set identical.
[0030] A pump port P is formed in the piston valve 5 over a
predetermined circumferential length along a circumferential
direction of the piston valve. The pump port P is open to an outer
peripheral surface of the piston valve 5. Further, a suction port S
is formed in the piston valve 5 over a predetermined
circumferential length along a circumferential direction of the
piston valve. The suction port S is open to the outer peripheral
surface of the piston valve 5.
[0031] A plurality of bores are formed in the cylinder block 3 at
an even pitch in a radial direction of a rotation axis. A piston 4
is slidably provided within each of the bores. A shoe 49 is
slidably connected to each of the pistons 4. A cam ring 2 is
arranged in an outer side of the shoe 49. The cam ring 2 is
arranged such that an inner peripheral surface can slide against a
sliding surface of each of the shoe 49.
[0032] The case 14 is provided with a servo piston 8 and an
opposing piston 7 constituting a volume control apparatus, in such
a manner as to hold a rotation axis therebetween. The servo piston
8 and the opposing piston 7 press the cam ring 2 so as to support
in such a manner as to freely eccentrically move a center of the
cam ring 2 with respect to a center of the rotation axis. A bearing
6 for slidably moving the cam ring 2 is arranged between the cam
ring 2 and the case 14.
[0033] Further, a cylinder side port 4a communicating with each of
the bores is formed in the cylinder block 3. The cylinder side port
4a is open to positions opposing to a pump port P and a suction
port S in the side of the piston valve 5.
[0034] When the rotation axis is driven so as to rotate by a
driving source, for example, an engine, the cylinder block 3 is
relatively rotated with respect to the piston valve 5. Accordingly,
the shoe 49 slides along an inner periphery of the cam ring 2.
[0035] The servo piston 8 and the opposing piston 7 is operated,
whereby the center of the cam ring 2 is made eccentric with respect
to the center of the rotation axis at a predetermined eccentricity
amount. Accordingly, when the piston 4 is positioned at a position
where the piston valve 5 and the cam ring 2 are closest, the piston
4 is in a top dead center state. When the piston 4 is rotated
further half along the circumferential direction of the piston
valve 5 from the position, the piston 4 is in a bottom dead center
state at a position where the piston valve 5 and the cam ring 2 are
most apart from each other. When the piston is rotated further
half, the piston 4 becomes in the top dead center state from the
bottom dead center state. As mentioned above, the piston 4 carries
out one stroke (the top dead center-the bottom dead center-the top
dead center) every one rotation along the circumferential direction
of the piston valve 5, and an amount of one stroke corresponds to
twice an amount of eccentricity. In the course of one stroke of the
piston 4, a pressure oil at a volume (cc/rev) corresponding to the
stroke amount is sucked and then discharged.
[0036] In other words, when the piston 4 is positioned at the
position where the cylinder side port 4a is communicated with the
suction port S, the pressure oil is sucked from a tank into the
bore via the suction port S and the cylinder side port 4a. Next,
when the piston 4 is positioned at the position where the cylinder
side port 4a is communicated with the pump port P, the pressure oil
compressed by the piston 4 is discharged from the bore via the
cylinder side port 4a and the pump port P, and is supplied to a
hydraulic actuator in an outer portion. As mentioned above, the
pressure oil at the volume corresponding to the amount of
eccentricity of the cam ring 2 is supplied to the hydraulic
actuator in the outer portion via the pump port P.
[0037] The opposing piston 7 is slidably provided in the case 14,
an oil chamber 28 is formed in an inner side of the opposing piston
7, and a spring 27 is attached. In the opposing piston 7, a thrust
is generated in correspondence to a hydraulic pressure within the
oil chamber 28 and a spring force of the spring 27, and the cam
ring 2 is pressed against the side of the servo piston 8.
[0038] The servo piston 8 is slidably provided in the case 14, and
an oil chamber 20 is formed in an inner side of the servo piston 8.
In the servo piston 8, a thrust is generated in correspondence to a
hydraulic pressure within the oil chamber 20, and the cam ring 2 is
pressed against the side of the opposing piston 7. In this case, a
fixed driving pressure is supplied to an inner side of the oil
chamber 28 in the side of the opposing piston 7, and a fixed thrust
is generated in the opposing piston 7.
[0039] On the contrary, the driving pressure within the oil chamber
20 in the side of the servo piston 8 is changed in accordance with
a volume control pressure supplied to the pilot port 12, and the
thrust of the servo piston 8 is changed in accordance with the
volume control pressure. Accordingly, the cam ring 2 is made
eccentric at the position in correspondence to the volume control
pressure supplied to the pilot port 12 of the servo piston 8. In
accordance that the cam ring 2 is moved to the opposing piston 7 by
the servo piston 8, the volume is reduced from the maximum
volume.
[0040] FIG. 2 is an enlarged view of the servo piston 8 in FIG. 1,
and shows a volume control apparatus in accordance with the present
embodiment.
[0041] A spool 9 corresponding to the control valve is built in the
servo piston 8 in such a manner as to be slidable with respect to
the servo piston 8. The pilot port 12 to which the pilot pressure
serving as the volume control pressure is supplied is formed on an
outer peripheral surface of the servo piston 8. In the servo piston
8, there is formed a pilot pressure introducing oil passage 21 for
introducing the pilot pressure supplied to the pilot port 12 to an
inner side of the servo piston 8.
[0042] Further, an original pressure port 13 to which the driving
pressure for driving the servo piston 8 is supplied is formed on an
outer peripheral surface of the servo piston 8. In the servo piston
8, there is formed a driving pressure introducing oil passage 22
for introducing the driving pressure supplied to the original
pressure port 13 to an inner side of the servo piston 8. Further,
in the servo piston 8, there is formed a tank discharging oil
passage 24 communicating a tank 26 with the inner side of the servo
piston 8.
[0043] The spool 9 is provided with a small diameter portion having
a diameter D1 and a large diameter portion having a diameter D2,
and is provided with a pressure receiving surface 9a formed as a
step between the small diameter portion and the large diameter
portion. The pressure receiving surface 9a has a pressure receiving
area corresponding to a difference of pressure receiving areas
((D2)-(D1)).pi./4 between the small diameter portion and the large
diameter portion.
[0044] The pressure receiving surface 9a of the spool 9 is formed
at a position in correspondence to the pilot pressure introducing
oil passage 21. Accordingly, the pilot pressure is applied to the
pressure receiving surface 9a of the spool 9 from the pilot port 12
via the pilot pressure introducing oil passage 21. The spool 9
carries out a stroke toward the cam ring 2 in accordance with the
pilot pressure applied to the pressure receiving surface 9a
thereof.
[0045] A spring 11 and a spring 10 which are expanded and
contracted in the same direction as the stroke direction of the
spool 9 are received in an inner side of the spool 9.
[0046] One end of the spring 11 is brought into contact with the
servo piston 8, and another end of the spring 11 is brought into
contact with the spool 9. Further, one end of the spring 10 is
brought into contact with the spool 9, and another end of the
spring 10 is brought into contact with an adjusting screw 15. The
adjusting screw 15 is fixed to the case 14 via a lock nut 16.
[0047] A spring chamber in which the spring 11 is received is
defined by the servo piston 8 and the spool 9, and forms the oil
chamber 20. An oil passage 9d for communicating the oil chamber 20
(the spring chamber of the spring 11) with a spring chamber in
which the spring 10 is received is formed in an inner side of the
spool 9.
[0048] An oil passage 9c for communicating the inner oil chamber 20
with an outer side of the spool 9 is formed in the spool 9. The oil
passage 9c is formed at a position corresponding to the tank
discharging oil passage 24. A throttle 25 is formed between the oil
passage 9c and the tank discharging oil passage 24. When the
pressure of the pilot port 12 is reduced, the spool 9 carries out a
stroke toward an upper side in the drawing, that is, an opposite
side to the cam ring 2. An opening area of the throttle 25 is
increased in accordance with a stroke of the spool 9 toward an
opposite side to the cam ring 2, and the pressure oil is discharged
from the oil chamber 20 to the tank 26 via the oil passage 9c, the
throttle 25 and the tank discharging oil passage 24. Accordingly,
since the driving pressure within the oil chamber 20 is reduced and
the thrust of the servo piston 8 is reduced, the cam ring 2 carries
out a stroke toward an upper side on the basis of the thrust of the
opposing piston 7. Therefore, the servo piston 8 carries out a
stroke toward an upper side. The opening area of the throttle 25 is
reduced in accordance with a stroke of the servo piston 8 toward an
upper side, and the reduction in the driving pressure within the
oil chamber 20 is inhibited. Accordingly, the servo piston 8
carries out a stroke toward an upper side in the drawing at a
moving amount of the spool 9.
[0049] An oil passage 9b for communicating the spring chamber of
the inner spring 10 with the outer side of the spring 9 is formed
in the spool 9. The oil passage 9b is formed at a position
corresponding to the driving pressure introducing oil passage 22. A
throttle 23 is formed between the oil passage 9b and the driving
pressure introducing oil passage 22.
[0050] When the pressure of the pilot port 12 is increased, the
spool 9 carries out a stroke toward a lower side in the drawing,
that is, toward the cam ring 2. An opening area of the throttle 23
is increased in accordance with the stroke of the spool 9 toward
the cam ring 2, and the pressure oil supplied from the original
pressure port 13 to the oil chamber 20 via the driving pressure
introducing oil passage 22, the throttle 23, the oil passage 9b,
the spring chamber of the spring 10 and the oil passage 9d is
increased.
[0051] A thrust in correspondence to the driving pressure within
the oil chamber 20 is generated in the servo piston 8, and presses
the cam ring 2. Since the pressure receiving area of the opposing
piston 7 is smaller than the pressure receiving area of the servo
piston 8, the cam ring 2 carries out a stroke toward a lower side
in the drawing on the basis of the thrust generated in the servo
piston 8, and the servo piston 8 also carries out a stroke toward a
lower side. When the servo piston 8 carries out the stroke toward
the lower side, the opening area of the throttle 23 is reduced, and
the increase in the driving pressure within the oil chamber 20 is
inhibited. Accordingly, the servo piston 8 carries out a stroke
toward a lower side at a moving amount of the spool 9.
[0052] In this case, a seal member 27 is fixed to the servo piston
8 by a snap ring 28, and seals in the inner side of the servo
piston in such a manner that the pressure oil in the outer side of
the spool 9 does not leak to the external portion.
[0053] A description will be given of an operation of the volume
control apparatus in accordance with the present embodiment.
[0054] In a steady state, as shown in FIG. 2, the spool 9 is at a
standstill under a state in which a force downward in the drawing
in correspondence to the pilot pressure applied to the pressure
receiving surface 9a and a spring force K (obtained by subtracting
the spring force of the spring 10 from the spring force of the
spring 11) upward in the drawing applied by the spring 11 and the
spring 10 are balanced. Further, the opening areas of the throttle
23 and the throttle 25 are regulated, and the thrust generated in
the servo piston 8 and the thrust obtained by adding the thrust of
the opposing piston 7 to the thrust of the piston 4 applied via the
cam ring 2 are balanced and at a standstill.
[0055] In this case, when the pilot pressure supplied to the pilot
port 12 is increased, the force in correspondence to the pilot
pressure applied to the pressure receiving surface 9a becomes
larger than the spring force K applied by the spring 11 and the
spring 10, and the spool 9 carries out a stroke toward a lower
side, that is, toward the cam ring 2.
[0056] When the spool 9 relatively carries out a stroke toward the
cam ring 2 with respect to the servo piston 8, the opening area of
the throttle 23 is increased, the pressure oil supplied from the
original pressure port 13 to the oil chamber 20 via the driving
pressure introducing oil passage 22, the throttle 23, the oil
passage 9b, the spring chamber of the spring 10 and the oil passage
9d is increased, and the driving pressure is increased.
Accordingly, the thrust generated in the servo piston 8 becomes
larger than the thrust obtained by adding the thrust of the
opposing piston 7 to the thrust of the piston 4 applied via the cam
ring 2, and the servo piston 8 presses the cam ring 2 against the
opposing piston 7, and moves toward the opposing piston 7.
[0057] Since the spool 9 moves toward the cam ring 2 and the servo
piston 8 moves toward the cam ring 2, the spring 10 is expanded
while the length of the spring 11 is not changed, so that the
spring force K (obtained by subtracting the spring force of the
spring 10 from the spring force of the spring 11) upward in the
drawing is increased. Accordingly, the movement of the spool 9 is
inhibited. Therefore, the opening area of the throttle 23 is
reduced, and the increase of the driving pressure supplied to the
oil chamber 20 from the original pressure port 13 via the driving
pressure introducing oil passage 22, the throttle 23, the oil
passage 9b, the spring chamber of the spring 10 and the oil passage
9d is inhibited.
[0058] As mentioned above, the spool 9 stands still at a position
where the downward force corresponding to the pilot pressure and
the spring force K upward in the drawing applied by the spring 10
are balanced. In other words, the spring 10 is positioned at the
lower position expanding from the state shown in FIG. 2.
[0059] The servo piston 8 stands still at the position
corresponding to the position at which the spool 9 is positioned in
a standstill state, in a state in which the thrust generated in the
servo piston 8 is balanced with the thrust obtained by adding the
thrust of the opposing piston 7 to the thrust of the piston 4
applied via the cam ring 2.
[0060] As a result, the cam ring 2 moves further closer to the
opposing piston 7 rather than the state in FIG. 2 by the servo
piston 8, and the volume of the radial piston pump 1 is
reduced.
[0061] On the other hand, when the pilot pressure supplied to the
pilot port 12 is reduced from the state in FIG. 2, the force in
correspondence to the pilot pressure applied to the pressure
receiving surface 9a becomes smaller than the spring force K
applied by the spring 11 and the spring 10, and the spool 9 carried
out a stroke toward an upper side, that is, in a direction of
moving apart from the cam ring 2.
[0062] When the spool 9 carries out the stroke in the direction of
relatively moving apart from the cam ring 2 with respect to the
servo piston 8, the opening area of the throttle 25 is increased,
the pressure oil discharged from the oil chamber 20 to the tank 26
via the oil passage 9c, the throttle 25 and the tank discharging
oil passage 24 is increased, and the driving pressure is reduced.
Accordingly, the thrust generated in the servo piston 8 becomes
smaller than the thrust obtained by adding the thrust of the
opposing piston 7 to the thrust of the piston 4 applied via the cam
ring 2, and the servo piston 8 moves in the direction of moving
apart from the opposing piston 7 while being pressed by the cam
ring 2.
[0063] Since the spool 9 moved in the direction of moving apart
from the cam ring 2, and the servo piston 8 moves in the direction
of moving apart from the opposing piston 7, the spring 10 is
contracted while the length of the spring 11 is not changed, so
that the upward spring force K applied by the spring 11 and the
spring 10 is reduced. Accordingly, the movement of the spool 9 is
inhibited. Accordingly, the opening area of the throttle 25 is
reduced, the pressure oil discharged from the oil chamber 20 to the
tank 26 via the oil passage 9c, the throttle 25 and the tank
discharging oil passage 24 is reduced, and the reduction in the
driving pressure is inhibited.
[0064] As mentioned above, the spool 9 stands still at a position
where the downward force in correspondence to the reduced pilot
pressure and the upward spring force K applied by the spring 11 and
the spring 10 are balanced. In other words, the spool 9 is
positioned at a further upper position where the spring 10 is
contracted from the state in FIG. 2.
[0065] Further, the servo piston 8 stands still at a position
corresponding to the position where the spool 9 is positioned at a
standstill, in a state in which the thrust generated in the servo
piston 8 is balanced with the thrust obtained by adding the thrust
of the opposing piston 7 to the thrust of the piston 4 applied via
the cam ring 2.
[0066] As a result, the cam ring 2 moves toward the side of moving
further apart from the opposing piston 7 in comparison with the
state in FIG. 2 by the servo piston 8, and the volume of the radial
piston pump 1 is increased.
[0067] As mentioned above, in accordance with the present
embodiment, the servo piston 8 presses the cam ring 2 following to
the spool 9, and positions the cam ring 2 at the position
corresponding to the pilot pressure so as to regulate the volume.
Accordingly, the same servo mechanism as that in accordance with
the prior art can be achieved. Further, since the volume control
apparatus has the spool 9 built in the servo piston 8, the place
product becomes small, and the weight becomes light. Therefore, the
radial piston pump 1 is downsized, the weight is reduced, and the
freedom in arrangement is improved.
[0068] In this case, when rotating a head portion of the adjusting
screw 15 so as to regulate the screwing position with respect to
the case 14, it is possible to change the length of the spring
regulated by the adjusting screw 15. Accordingly, a corresponding
relation between the pilot pressure (the volume control pressure)
and the actual volume of the radial piston pump 1 can be set. When
the corresponding relation between the pilot pressure and the
volume is set to a desired relation in accordance with the
adjustment of the adjusting screw 15, the adjusting screw 15 is
fixed to the case 14 by the lock nut 16.
[0069] Various modifications (applications) can be employed in the
present embodiment mentioned above. A description will be given
below of the various modifications by attaching the same reference
numerals to the same constituting elements as those in FIGS. 1 and
2 and omitting overlapping portions.
[0070] FIG. 3 shows a volume control apparatus having a structure
corresponding to FIG. 2, and a description will be given of
different parts from those in FIG. 2. In FIG. 2, the original
pressure port 13 is formed in the lower side of the servo piston 8
close to the cam ring 2, and the pilot port 12 is formed in the
upper side apart from the cam ring 2. On the contrary, in FIG. 3,
the pilot port 12 is formed in the lower side of the servo piston 8
close to the cam ring 2, and the original pressure port 13 is
formed in the upper side apart from the cam ring 2. In
correspondence to this structure, the pressure receiving surface 9a
of the spool 9 is formed in the lower side closer to the cam ring 2
in FIG. 3 than in FIG. 2. Further, the seal member 27 is provided
in the upper side of the servo piston 8 and the spool 9 in FIG. 2,
however, is provided in the lower side of the servo piston 8 and
the spool 9 in FIG. 3.
[0071] In this case, in FIGS. 2 and 3, two springs 10 and 11 are
attached to the spool 9, and the force corresponding to the pilot
pressure is balanced with the spring force, however, one spring may
be provided.
[0072] FIG. 4 shows a structure of the volume control apparatus in
correspondence to FIGS. 2 and 3, and shows an embodiment in which
only one spring 10 is attached to the spool 9. In other words, the
spring 10 expanding and contracting in the same direction as the
direction of stroke of the spool 9 is received in the inner side of
the spool 9. One end of the spring 10 is brought into contact with
the spool 9, and another end of the spring 10 is brought into
contact with the adjusting screw 15.
[0073] In a steady state, as shown in FIG. 4, the spool 9 is at a
standstill under a state in which a downward force in
correspondence to the pilot pressure applied to the pressure
receiving surface 9a and an upward spring force K applied by the
spring 10 are balanced. Further, the opening areas of the throttle
23 and the throttle 25 are regulated, and the thrust generated in
the servo piston 8 and the thrust obtained by adding the thrust of
the opposing piston 7 to the thrust of the piston applied via the
cam ring 2 are balanced and at a standstill.
[0074] In this case, when the pilot pressure supplied to the pilot
port 12 is increased, the force in correspondence to the pilot
pressure applied to the pressure receiving surface 9a becomes
larger than the spring force K applied by the spring 10, and the
spool 9 carries out a stroke toward a lower side, that is, toward
the cam ring 2.
[0075] When the spool 9 relatively carries out a stroke toward the
lower side, that is, toward the cam ring 2 with respect to the
servo piston 8, the opening area of the throttle 23 is increased,
the pressure oil supplied from the original pressure port 13 to the
oil chamber 20 via the driving pressure introducing oil passage 22,
the throttle 23, the oil passage 9b and the oil passage 9d is
increased, and the driving pressure is increased. Accordingly, the
thrust generated in the servo piston 8 becomes larger than the
thrust obtained by adding the thrust of the opposing piston 7 to
the thrust of the piston 4 applied via the cam ring 2, and the
servo piston 8 presses the cam ring 2 against the opposing piston
7, and moves toward the opposing piston 7.
[0076] Since the servo piston 8 moves relatively downward, that is,
toward the cam ring 2, with respect to the spool 9, whereby the
opening area of the throttle 23 is reduced, and the increase of the
driving pressure supplied to the oil chamber 20 from the original
pressure port 13 via the driving pressure introducing oil passage
22, the throttle 23, the oil passage 9b and the oil passage 9d is
inhibited.
[0077] As mentioned above, the spool 9 stands still at a position
where the downward force corresponding to the pilot pressure and
the upward spring force K applied by the spring 10 are balanced. In
other words, the spring 10 is positioned at the lower position
contracting from the state shown in FIG. 4.
[0078] The servo piston 8 stands still at the position
corresponding to the position at which the spool 9 is positioned in
a standstill state, in a state in which the thrust generated in the
servo piston 8 is balanced with the thrust obtained by adding the
thrust of the opposing piston 7 to the thrust of the piston 4
applied via the cam ring 2.
[0079] As a result, the cam ring 2 moves further closer to the
opposing piston 7 rather than the state in FIG. 4 by the servo
piston 8, and the volume of the radial piston pump 1 is
reduced.
[0080] On the other hand, when the pilot pressure supplied to the
pilot port 12 is reduced from the state in FIG. 4, the force in
correspondence to the pilot pressure applied to the pressure
receiving surface 9a becomes smaller than the spring force K
applied by the spring 10, and the spool 9 carried out a stroke
toward an upper side, that is, in a direction of moving apart from
the cam ring 2.
[0081] When the spool 9 carries out the stroke relatively toward
the upper side, that is, in the direction of relatively moving
apart from the cam ring 2 with respect to the servo piston 8, the
opening area of the throttle 25 is increased, the pressure oil
discharged from the oil chamber 20 to the tank 26 via the oil
passage 9c, the throttle 25 and the tank discharging oil passage 24
is increased, and the driving pressure is reduced. Accordingly, the
thrust generated in the servo piston 8 becomes smaller than the
thrust obtained by adding the thrust of the opposing piston 7 to
the thrust of the piston 4 applied via the cam ring 2, and the
servo piston 8 moves in the direction of moving apart from the
opposing piston 7 while being pressed by the cam ring 2.
[0082] Since the servo piston 8 moves relatively upward, that is,
in the direction of moving apart from the cam ring 2, with respect
to the spool 9, the opening area of the throttle 25 is reduced, the
pressure oil discharged from the oil chamber 20 to the tank 26 via
the oil passage 9c, the throttle 25 and the tank discharging oil
passage 24 is reduced, and the reduction in the driving pressure is
inhibited.
[0083] As mentioned above, the spool 9 stands still at a position
where the downward force in correspondence to the reduced pilot
pressure and the upward spring force K applied by the spring 10 are
balanced. In other words, the spool 9 is positioned at a further
upper position where the spring 10 is expanded from the state in
FIG. 4.
[0084] The servo piston 8 stands still at a position corresponding
to the position where the spool 9 is positioned at a standstill, in
a state in which the thrust generated in the servo piston 8 is
balanced with the thrust obtained by adding the thrust of the
opposing piston 7 to the thrust of the piston 4 applied via the cam
ring 2.
[0085] As a result, the cam ring 2 moves toward the side of moving
further apart from the opposing piston 7 in comparison with the
state in FIG. 4 by the servo piston 8, and the volume of the radial
piston pump 1 is increased.
[0086] Either the embodiments mentioned above are based on the
one-flow-way type radial piston pump in which the discharging
direction is fixed. However, the present invention can be applied
to an alternating type radial piston pump in which the discharging
direction can be changed to two directions.
[0087] FIG. 5A is a view corresponding to FIG. 1. The case 14 is
provided with the servo piston 8 having the spool 9 built-in in the
same manner as the structure shown in FIG. 2, and the opposing
piston 7, in such a manner as to oppose to each other so as to hold
the rotation axis therebetween. In the same manner, the servo
piston 18 having the spool 19 built-in and the opposing piston 17
are provided in such a manner as to oppose to each other so as to
hold the rotation axis therebetween. Further, the servo piston 8
having the spool 9 built-in, and the servo piston 18 having the
spool 19 built-in are provided at opposing positions with holding
the cam ring 2 therebetween. Accordingly, it is possible to make
the cam ring 2 to be eccentric in both sides with respect to the
center of the rotation axis, and the center of the piston valve
5.
[0088] The radial piston pump 1 capable of flowing in two direction
shown in FIG. 5A is used as a constituting element of a hydraulic
circuit shown in FIG. 5B. The hydraulic circuit in FIG. 5B is used
in a hydro static transmission (HST) vehicle such as a bulldozer or
the like. In the HST vehicle, right and left traveling bodies
(wheels or crawler belts) of a vehicle body are independently
driven by the HST provided respectively in right and left sides. In
a hydraulic circuit of the HST, in the case that the pressure oil
is discharged from one discharge port of a hydraulic pump 61 and
the pressure oil is flowed into one port of a hydraulic motor 60,
the hydraulic motor 60 rotates forward and the vehicle moves
forward. Further, in the case that the pressure oil is discharged
from another discharge port of the hydraulic pump 61 and the
pressure oil is flowed into another port of the hydraulic motor 60,
the hydraulic motor 60 rotates backward and the vehicle moves
backward. A gear change is performed by changing the volume of the
hydraulic pump 61 and the hydraulic motor 60.
[0089] As shown in FIG. 5A, in order to change the moving direction
of the vehicle to the forward moving direction and the backward
moving direction, and change the volume of the radial piston pump 1
in each of the directions, there are provided a switching valve 40
for changing between the forward movement and the backward
movement, an electromagnetic proportional control valve 31 for
controlling the volume at a time of forward moving, and an
electromagnetic proportional control valve 32 for controlling the
volume at a time of moving backward. As hydraulic pressure sources
of the pilot pressure and the driving pressure supplied to the
servo pistons 8 and 18, there are provided respectively pilot
hydraulic pressure sources 27 and 27 and a driving pressure source
29. In this case, the driving pressure source 29 can employ the
radial piston pump 1 itself.
[0090] When a forward movement command signal Si is applied to an
electromagnetic solenoid of the electromagnetic proportional
control valve 31 by an operation lever (not shown) or the like, the
electromagnetic proportional control valve 31 is driven to an open
side, and the pilot pressure is applied to a pilot port 40d of the
switching valve 40 via the electromagnetic proportional control
valve 31 from the pilot hydraulic pressure source 27. Accordingly,
the switching valve 40 is changed to a forward moving position 40a
from a neutral position 40c. Therefore, the electromagnetic
proportional control valve 31 is opened at an opening degree in
proportional to the forward movement command signal S1, and the
pilot pressure of the pilot hydraulic pressure source 27 is reduced
to the pilot pressure in correspondence to the opening degree of
the electromagnetic proportional control valve 31, and is supplied
to the pilot port 12 of the servo piston 8 via the switching valve
40 and the oil passage 41.
[0091] The driving pressure of the driving pressure source 29 is
supplied to the original pressure port 13 of the servo piston 8 via
the switching valve 40 and the oil passage 42. Further, the driving
pressure of the driving pressure source 29 is supplied to the oil
chamber 28 of the opposing piston 7 opposing to the servo piston 8
via the switching valve 40 and the oil passage 46. In this case,
the opposing piston 17, the pilot port 12 of another servo piston
18 and the original pressure port 13 are respectively communicated
with the tank 26 via an oil passage 43, an oil passage 44, an oil
passage 45 and the switching valve 40.
[0092] Accordingly, the servo piston 8 and the spool 9 are operated
as described in FIG. 2, and the cam ring 2 is made eccentric to the
position corresponding to the pilot pressure supplied to the pilot
port 12 of the servo piston 8. The cam ring 2 is made eccentric to
a left side in the drawing with respect to the rotation axis.
Accordingly, the pressure oil at a volume corresponding to the
forward movement command signal S1 is discharged from one
discharging direction of the radial piston pump 1, and the vehicle
travels forward at a speed corresponding to the forward movement
command signal S1.
[0093] On the contrary, in the case that a backward movement
command signal S2 is applied to an electromagnetic solenoid of the
electromagnetic proportional control valve 32 by the operation
lever or the like, the electromagnetic proportional control valve
32 is driven to an open side, and the pilot pressure is applied to
a pilot port 40e of the switching valve 40 from the pilot hydraulic
pressure source 27 via the electromagnetic proportional control
valve 32. Accordingly, the switching valve 40 is changed to a
backward moving position 40b from the neutral position 40c.
Therefore, the electromagnetic proportional control valve 32 is
open at an opening degree in proportion to the backward movement
command signal S2, and the pilot pressure of the pilot hydraulic
pressure source 27 is reduced to a pilot pressure corresponding to
the opening degree of the electromagnetic proportional control
valve 32 and is supplied to the pilot port 12 of the servo piston
18 via the switching valve 40 and the oil passage 44.
[0094] The driving pressure of the driving pressure source 29 is
supplied to the original pressure port 13 of the servo piston 18
via the switching valve 40 and the oil passage 45. Further, the
driving pressure of the driving pressure source 29 is supplied to
an oil chamber 38 of the opposing piston 17 opposing to the servo
piston 18 via the switching valve 40 and the oil passage 43. In
this case, the opposing piston 7, the pilot port 12 of another
servo piston 8 and the original pressure port 13 are communicated
respectively with the tank 26 via the oil passage 46, the oil
passage 41, the oil passage 42 and the switching valve 40.
[0095] Accordingly, the servo piston 18 and the spool 19 are
operated as described in FIG. 2, and the cam ring 2 is made
eccentric to a position corresponding to the pilot pressure
supplied to the pilot port 12 of the servo piston 18. The cam ring
2 is made eccentric to a right side in the drawing with respect to
the rotation axis. Therefore, the pressure oil at the volume
corresponding to the backward movement command signal S2 is
discharged from another discharging direction of the radial piston
pump 1, and the vehicle travels backward at a speed corresponding
to the backward movement command signal S2.
[0096] In this case, the structure in FIG. 5A is based on the
volume control apparatus having the structure shown in FIG. 2,
however, can employ the volume control apparatus having the
structure shown in FIGS. 3 or 4.
[0097] The embodiment mentioned above is described on the basis of
the radial piston pump, however, can be applied also to the radial
piston motor as it is.
[0098] Further, the embodiments mentioned above are not limited to
the volume control apparatus for the radial piston pump or motor,
but can be applied to a volume control apparatus for a swash plate
type axial piston pump or motor.
[0099] FIG. 6 shows an embodiment employing the volume control
apparatus shown in FIG. 2 as a volume control apparatus for
regulating the volume by pressing a swash plate 50 of an axial
piston pump 55 and oscillating the swash plate 50.
[0100] The servo piston 8 having the spool 9 built-in in the same
manner as the structure shown in FIG. 2 is brought into contact
with the swash plate 50, and the servo piston 8 presses the swash
plate 50 on the basis of a thrust corresponding to the pilot
pressure so as to oscillate the swash plate 50, and positions the
swash plate 50 at a position tilted from a rotation axis 51. A
stroke amount of a piston 54 is determined in correspondence to a
tilting amount of the swash plate 50 with respect to the rotation
axis 51, and a volume of the axial piston pump 55 is determined. In
FIG. 6, the structure is made such that a position of a supporting
point of a ball for supporting the tilting motion of the swash
plate 50 is displaced to a left side in the drawing from a position
of a working point of a resultant force applied to the swash plate
50 by the shoe of the piston 54, thereby generating a force
opposing to the thrust of the servo piston 8 existing in a right
side in the drawing with respect to the ball, and achieving the
same function as that of the opposing piston 7 in FIG. 1.
[0101] In this case, the structure in FIG. 6 can be applied also to
the axial piston motor as it is.
[0102] Further, the structure in FIG. 6 is based on the volume
control apparatus having the structure shown in FIG. 2, however,
may employ the volume control apparatus having the structure shown
in FIGS. 3 or 4.
[0103] Further, the apparatus having the structure shown in FIGS.
2, 3 and 4 is not limited to the apparatus for positioning the cam
ring or the swash plate of the hydraulic pump or motor, and may be
used as a positioning apparatus for positioning the other members
to be positioned than the cam ring and the swash plate to a desired
position.
* * * * *