U.S. patent application number 12/763697 was filed with the patent office on 2011-07-07 for vane pump.
This patent application is currently assigned to HITACHI AUTOMOTIVE SYSTEMS, LTD.. Invention is credited to Masaaki IIJIMA.
Application Number | 20110165010 12/763697 |
Document ID | / |
Family ID | 44215185 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110165010 |
Kind Code |
A1 |
IIJIMA; Masaaki |
July 7, 2011 |
VANE PUMP
Abstract
A vane pump includes: a rotor with slots; vanes mounted in the
slots, and adapted to project from the slots; a cam ring
surrounding the rotor; and a plate defining pump chambers in
cooperation with the rotor, vanes and cam ring. The plate includes:
a suction port; a discharge port; a first back pressure port that
receives a suction-side fluid pressure, and hydraulically
communicates with a first back pressure chamber corresponding to a
first vane positioned in a suction region; and a second back
pressure port that hydraulically communicates with a second back
pressure chamber corresponding to a second vane whose distal end
portion is positioned at a terminal end portion of the suction
port. The second back pressure port includes: a first portion
arranged to receive a discharge-side fluid pressure; and a
throttling portion for restricting a fluid flow between the first
portion and second back pressure chamber.
Inventors: |
IIJIMA; Masaaki;
(Maebashi-shi, JP) |
Assignee: |
HITACHI AUTOMOTIVE SYSTEMS,
LTD.
|
Family ID: |
44215185 |
Appl. No.: |
12/763697 |
Filed: |
April 20, 2010 |
Current U.S.
Class: |
418/269 |
Current CPC
Class: |
F04C 2240/80 20130101;
F01C 21/089 20130101; F01C 21/108 20130101; F04C 2/3441 20130101;
F04C 14/22 20130101; F01C 21/0863 20130101 |
Class at
Publication: |
418/269 |
International
Class: |
F04C 2/348 20060101
F04C002/348 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2010 |
JP |
2010-000528 |
Mar 18, 2010 |
JP |
2010-062861 |
Claims
1. A vane pump comprising: a rotor adapted to be rotated by a drive
shaft, the rotor including a plurality of slots at an outside
periphery of the rotor; a plurality of vanes mounted in
corresponding ones of the slots, and adapted to project from, and
travel inwards and outwards of the corresponding slots; a cam ring
adapted to be eccentric with respect to the rotor, the cam ring
surrounding the rotor; and a plate arranged to face an axial end of
the rotor, and define a plurality of pump chambers in cooperation
with the rotor, the vanes, and the cam ring, wherein the plate
includes at a side facing the rotor: a suction port opened in a
suction region in which each pump chamber gradually expands while
moving along with rotation of the rotor; a discharge port opened in
a discharge region in which each pump chamber gradually contracts
while moving along with rotation of the rotor; a first back
pressure port arranged to receive a suction-side fluid pressure,
and hydraulically communicate with a proximal end portion of at
least a first one of the slots corresponding to a first one of the
vanes positioned in the suction region; and a second back pressure
port arranged to hydraulically communicate with a proximal end
portion of at least a second one of the slots corresponding to a
second one of the vanes whose distal end portion is positioned at a
terminal end portion of the suction port, wherein the second back
pressure port includes: a first portion arranged to receive a
discharge-side fluid pressure; and a throttling portion arranged to
restrict a flow of fluid between the first portion and the proximal
end portion of the second slot.
2. The vane pump as claimed in claim 1, wherein the throttling
portion has a cross-sectional flow area that is substantially
constant as followed in a direction of rotation of the rotor.
3. The vane pump as claimed in claim 1, wherein the throttling
portion has a cross-sectional flow area that increases as followed
in a direction of rotation of the rotor.
4. The vane pump as claimed in claim 1, wherein the throttling
portion has a cross-sectional flow area that decreases as followed
in a direction of rotation of the rotor.
5. The vane pump as claimed in claim 1, wherein: the second vane is
behind in a direction of rotation of the rotor and adjacent to a
third one of the vanes whose distal end portion is positioned
between a terminal end of the suction port and a beginning end of
the discharge port; and the second back pressure port is arranged
to supply the proximal end portion of the second slot at least with
an amount of working fluid, during a period before the second vane
passes through the terminal end of the suction port after the
proximal end portion of the second slot starts to hydraulically
communicate with the second back pressure port, wherein the amount
of working fluid is sufficient to bring the distal end portion of
the second vane into contact with an inside peripheral surface of
the cam ring.
6. The vane pump as claimed in claim 1, wherein: each of the vanes
extends in a radial direction of the rotor; and the second back
pressure port overlaps with the suction port in a circumferential
direction of the plate.
7. The vane pump as claimed in claim 1, wherein the throttling
portion has a cross-sectional flow area that changes as followed in
a direction of rotation of the rotor.
8. The vane pump as claimed in claim 7, wherein the cross-sectional
flow area of the throttling portion changes with a change in depth
of the throttling portion.
9. The vane pump as claimed in claim 1, wherein the throttling
portion has a smaller depth than the first portion.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to vane pumps.
[0002] Japanese Patent Application Publication No. 7-259754
discloses a variable displacement vane pump which includes: a rotor
including a plurality of slots at its outside periphery; a
plurality of vanes mounted in corresponding ones of the slots, and
adapted to project from, and travel inwards and outwards of the
corresponding slots; a cam ring adapted to be eccentric with
respect to the rotor, the cam ring surrounding the rotor; and a
plurality of pump chambers defined by the vanes, an inside
peripheral surface of the cam ring, and an outside peripheral
surface of the rotor, wherein the displacement of the pump changes
with a change in the eccentricity of the cam ring with respect to
the rotor. The vane pump is arranged so that when the distal end
portion of a vane is positioned in a suction region or a discharge
region, the proximal end portion of the vane is applied with a back
pressure that is substantially identical to a pressure applied to
the distal end portion, in order to reduce the resistance to the
distal end portion of the vane when the vane slides on the inside
peripheral surface of the cam ring, and thereby reduce a loss in
power for driving the vane pump. The proximal end portion of the
vane starts to be applied with a discharge-side fluid pressure
(high pressure), when the vane is positioned in the suction region
before entering the discharge region. This is intended for ensuring
that even when the vane pump is operating at low temperature where
the viscosity of working fluid is relatively high, the vane
projects from the slot, so as to seal the pump chambers well, and
thereby make the pump operate normally.
SUMMARY OF THE INVENTION
[0003] Such vane pumps as disclosed in Japanese Patent Application
Publication No. 7-259754 can encounter a problem that noise is
generated due to factors such as contact between components.
Accordingly, it is desirable to provide a vane pump in which noise
is suppressed.
[0004] According to one aspect of the present invention, a vane
pump comprises: a rotor adapted to be rotated by a drive shaft, the
rotor including a plurality of slots at an outside periphery of the
rotor; a plurality of vanes mounted in corresponding ones of the
slots, and adapted to project from, and travel inwards and outwards
of the corresponding slots; a cam ring adapted to be eccentric with
respect to the rotor, the cam ring surrounding the rotor; and a
plate arranged to face an axial end of the rotor, and define a
plurality of pump chambers in cooperation with the rotor, the
vanes, and the cam ring, wherein the plate includes at a side
facing the rotor: a suction port opened in a suction region in
which each pump chamber gradually expands while moving along with
rotation of the rotor; a discharge port opened in a discharge
region in which each pump chamber gradually contracts while moving
along with rotation of the rotor; a first back pressure port
arranged to receive a suction-side fluid pressure, and
hydraulically communicate with a proximal end portion of at least a
first one of the slots corresponding to a first one of the vanes
positioned in the suction region; and a second back pressure port
arranged to hydraulically communicate with a proximal end portion
of at least a second one of the slots corresponding to a second one
of the vanes whose distal end portion is positioned at a terminal
end portion of the suction port, wherein the second back pressure
port includes: a first portion arranged to receive a discharge-side
fluid pressure; and a throttling portion arranged to restrict a
flow of fluid between the first portion and the proximal end
portion of the second slot.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a block diagram showing a continuously variable
transmission (CVT) system to which a vane pump according to each
embodiment of the present invention is adapted.
[0006] FIG. 2 is a partial sectional view of a vane pump according
to a first embodiment of the present invention in an axial
direction of a rotor under a condition that a side plate is
removed.
[0007] FIG. 3 is a plan view of a first plate of the vane pump.
[0008] FIG. 4 is a sectional view of the first plate taken along
the line IV-IV in FIG. 3.
[0009] FIG. 5 is a sectional view of the first plate taken along
the line V-V in FIG. 3.
[0010] FIG. 6 is a sectional view of a portion of the vane pump,
including a sectional view of the first plate taken along the line
VI-VI in FIG. 3.
[0011] FIG. 7 is an enlarged view of a portion indicated by VII in
FIG. 6, showing a sectional shape of a beginning end portion of a
discharge-side back pressure port.
[0012] FIG. 8 is a sectional view of the vane pump taken along the
line VIII-VIII in FIG. 6.
[0013] FIG. 9 is a graphic diagram showing a relationship among the
cross-sectional flow area and circumferential length of the
beginning end portion of the discharge-side back pressure port, and
noise level.
[0014] FIG. 10 is a sectional view of a vane pump according to a
first comparative example, which corresponds to the sectional view
of FIG. 8.
[0015] FIG. 11 is a sectional view of a vane pump according to a
second comparative example, which corresponds to the sectional view
of FIG. 8.
[0016] FIGS. 12A to 12D are plan views of beginning end portions of
discharge-side back pressure ports according to variations of a
second embodiment of the present invention.
[0017] FIGS. 13A and 13B are side sectional views of beginning end
portions of discharge-side back pressure ports according to
variations of the second embodiment.
[0018] FIGS. 14A to 14D are plan views of beginning end portions of
discharge-side back pressure ports according to variations of a
third embodiment of the present invention.
[0019] FIG. 15 is a side sectional view of a beginning end portion
of a discharge-side back pressure port according to a variation of
the third embodiment.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment/Construction
[0020] The following describes construction of a vane pump
(henceforth referred to as pump 1) according to a first embodiment
of the present invention. Pump 1 is adapted to be used to supply
hydraulic pressure to a hydraulic actuator in a motor vehicle. In
this example, pump 1 is adapted to be used to supply hydraulic
pressure to a belt-type continuously variable transmission (CVT
100). Pump 1 is not so limited, but may be used to supply hydraulic
pressure to another hydraulic actuator such as a hydraulic actuator
in a power steering system. Pump 1 is driven by a crankshaft of an
internal combustion engine, to suck and discharge working fluid. In
this example, working fluid is working oil such as ATF (automatic
transmission fluid). A typical ATF has such a relatively small
elastic modulus that a small change in volume of the ATF can cause
a large change in pressure. FIG. 1 shows a system of CVT 100 to
which pump 1 is adapted. CVT 100 includes a control valve unit 200
that is provided with various valves such as a shift control valve
201, a secondary valve 202, a secondary pressure solenoid valve
203, a line pressure solenoid valve 204, a pressure regulator valve
205, a manual valve 206, a lockup/select switch solenoid valve 207,
a clutch regulator valve 208, a select control valve 209, a lockup
solenoid valve 210, a torque converter regulator valve 211, a
lockup control valve 212, and a select switch valve 213. These
valves are controlled by a CVT control unit 300. Pump 1 discharges
and supplies working fluid through control valve unit 200 to
various parts of CVT 100 such as a primary pulley 101, a secondary
pulley 102, a forward clutch 103, a reverse brake 104, a torque
converter 105, and a lubricating and cooling system 106.
[0021] FIG. 2 is a partial sectional view of pump 1 in an axial
direction of a rotor 6 under a condition that a side plate is
removed. In the following description, a three dimensional normal
coordinate system is assumed in which an x axis is defined to
extend in a radial direction of pump 1, a y axis is defined to
extend in another radial direction of pump 1, and a z axis is
defined to extend in the axial direction of rotor 6. Specifically,
the x axis is defined to extend in a direction where a central axis
"P" of a cam ring 8 moves or swings with respect to an axis of
rotation "O" of rotor 6. The y axis is defined to extend in a
direction perpendicular to both of the x axis and z axis. FIG. 2
shows a view in the negative z-axis direction from the positive z
side. In FIG. 2, the positive x-axis direction is a direction where
the central axis P of cam ring 8 deviates from the axis of rotation
O (or in a direction from a second closing region RE4 to a first
closing region RE3 as detailed below and shown in FIG. 3). In FIG.
2, the positive y-axis direction is a direction from a suction
region toward a discharge region.
[0022] Pump 1 is a variable displacement type capable of varying
its displacement or discharge capacity or pump capacity, i.e.
amount of fluid discharged per one rotation. Pump 1 includes a
pumping section 2 for sucking and discharging working fluid, and a
control section 3 for controlling the discharge capacity, which are
integrated as a unit. Pumping section 2 is accommodated in a
housing 4, including a drive shaft 5, a rotor 6, vanes 7, and a cam
ring 8. Housing 4 includes a housing body 40, a first plate 41, and
a second plate 42, which are fixed together, for example, by
bolting.
[0023] Housing body 40 is formed with a substantially cylindrical
through hole 400 which extends in the z-axis direction, and in
which an annular adapter ring 9 is mounted. Adapter ring 9 includes
a substantially cylindrical accommodation hole 90 that extends in
the z-axis direction. Accommodation hole 90 is formed with a first
flat portion 91 which is located on the positive x side, and
substantially parallel to the y-z plane. Accommodation hole 90 is
formed also with a second flat portion 92 which is located on the
negative x side, and substantially parallel to the y-z plane.
Second flat portion 92 is formed with a recess 920 which is located
substantially at a central position of second flat portion 92 in
the z-axis direction, and extends in the negative x-axis direction.
Accommodation hole 90 is formed also with a third flat portion 93
which is located at the positive y side and slightly on the
positive x side with respect to the axis of rotation O, and
substantially parallel to the z-x plane. Third flat portion 93 is
formed with a groove or recess 930 having a semicircular section as
viewed in the z-axis direction. Third flat portion 93 is formed
also with first and second communication passages 931 and 932 on
both sides of recess 930. Specifically, first communication passage
931 opens in a portion of third flat portion 93 on the positive x
side of recess 930, whereas second communication passage 932 opens
in a portion of third flat portion 93 on the negative x side of
recess 930. Accommodation hole 90 is formed also with a fourth flat
portion 94 which is located at the negative y side, and
substantially parallel to the z-x plane. Fourth flat portion 94 is
formed with a groove or recess 940 having a rectangular section as
viewed in the z-axis direction.
[0024] Cam ring 8 is mounted in accommodation hole 90 of adapter
ring 9, and adapted to move or swing freely, wherein cam ring 8 has
an annular shape. Adapter ring 9 is thus arranged to surround cam
ring 8. As viewed in the z-axis direction, cam ring 8 has a
substantially circular inside peripheral surface 80, and a
substantially circular outside peripheral surface 81, where cam
ring 8 has a substantially uniform radial thickness. The outside
peripheral surface 81 of cam ring 8 is formed with a groove or
recess 810 having a semicircular section as viewed in the z-axis
direction, where recess 810 is located at the positive y side of
outside peripheral surface 81. The outside peripheral surface 81 of
cam ring 8 is formed also with a substantially cylindrical recess
811 having a central longitudinal axis extending in the x-axis
direction, where recess 811 is located at the negative x side of
outside peripheral surface 81. Between the recess 930 in the inside
periphery of adapter ring 9 and the recess 810 in the outside
periphery of cam ring 8 is mounted a pin 10 which extends in the
z-axis direction, and is fitted in the space defined between
recesses 930 and 810. In the recess 940 in the periphery of adapter
ring 9 is mounted a seal 11. Seal 11 is in contact with the
negative y side of outside peripheral surface 81 of cam ring 8. An
elastic member such as a spring 12 is provided, which has a
longitudinal end mounted in recess 920 in the inside periphery of
adapter ring 9. Spring 12 is a coil spring. The other longitudinal
end of spring 12 is mounted in recess 811 of cam ring 8. Spring 12
is mounted in a compressed state so as to constantly urge the cam
ring 8 in the positive x-axis direction with respect to adapter
ring 9 or housing 4. The size of accommodation hole 90 in the
x-axis direction, i.e. the distance between the first flat portion
91 and second flat portion 92, is set larger than the diameter of
outside peripheral surface 81 of cam ring 8. Cam ring 8 is
supported by adapter ring 9 or housing 4 on third flat portion 93,
for moving or swinging in the x-y plane about third flat portion 93
as a fulcrum. Pin 10 serves to restrict deviation or relative
rotation of cam ring 8 with respect to adapter ring 9.
[0025] The swinging motion of cam ring 8 is restricted on the
positive x side by contact between the outside peripheral surface
81 and the first flat portion 91 of adapter ring 9, and restricted
on the negative x side by contact between the outside peripheral
surface 81 and the second flat portion 92 of adapter ring 9. The
eccentricity or distance of the central axis P of cam ring 8 with
respect to the axis of rotation O is represented by O. When the
outside peripheral surface 81 of cam ring 8 is in contact with the
second flat portion 92 of adapter ring 9, the central axis P of cam
ring 8 is located substantially at the axis of rotation O so that
the eccentricity .delta. is equal to about zero. This position is
called minimum eccentric position. On the other hand, when the
outside peripheral surface 81 of cam ring 8 is in contact with the
first flat portion 91 of adapter ring 9, the eccentricity .delta.
is maximized. This position is called maximum eccentric position.
While cam ring 8 is swinging, the third flat portion 93 of adapter
ring 9 is in sliding contact with the outside peripheral surface 81
of cam ring 8, and the seal 11 in recess 940 is in sliding contact
with outside peripheral surface 81. The positive z side and
negative z side of the space between the inside periphery of
adapter ring 9 and the outside periphery of cam ring 8 are sealed
by first plate 41 and second plate 42, respectively, and divided
fluid-tightly or liquid-tightly by third flat portion 93 and seal
11 into first and second control chambers R1 and R2. First control
chamber R1 is located on the positive x side, whereas second
control chamber R2 is located on the negative x side. First control
chamber R1 hydraulically communicates with first communication
passage 931, whereas second control chamber R2 hydraulically
communicates with second communication passage 932. Under the
conditions that the movement of cam ring 8 is restricted, a
clearance is provided between the outside periphery of cam ring 8
and the inside periphery of adapter ring 9, so that the volumetric
capacity of each of first and second control chambers R1 and R2 is
constantly above zero.
[0026] Drive shaft 5 is rotatably supported by first and second
plates 41 and 42 of housing 4. Drive shaft 5 is linked with the
crankshaft of the internal combustion engine through a timing chain
so that drive shaft 5 rotates in synchronization with the
crankshaft. Rotor 6 is coaxially arranged with drive shaft 5, and
coupled by spline coupling to the outside periphery of drive shaft
5. Rotor 6 has a substantially cylindrical shape, and is mounted
inside the cam ring 8. Cam ring 8 is thus arranged to surround the
rotor 6. In this way, an annular chamber R3 is defined between the
inside peripheral surface 80 of cam ring 8 and an outside
peripheral surface 60 of rotor 6, and between first and second
plates 41 and 42. Rotor 6 rotates about the axis of rotation O in a
clockwise direction as viewed in FIG. 2, along with drive shaft
5.
[0027] Rotor 6 is formed with a plurality of slots 61 which extend
radially of rotor 6. Each slot 61 extends straight in a radial
direction of rotor 6 from the outside peripheral surface 60 toward
the axis of rotation O by a predetermined depth as viewed in the
z-axis direction, and extends over the entire length of rotor 6 in
the z-axis direction. Eleven slots 61 are arranged in the
circumferential direction, and evenly spaced. Eleven vanes 7 are
provided, each of which is a substantially rectangular plate, and
is mounted in a corresponding one of slots 61, and adapted to
project from, and travel inwards and outwards of slot 61. A distal
end portion 70 of vane 7, which is outward in the radial direction
of rotor 6, or one of end portions farther from the axis of
rotation O, is curved to be fitted with the inside peripheral
surface 80 of cam ring 8, as viewed in the z-axis direction. The
number of slots 61 or vanes 7 is not limited to eleven. A proximal
end portion 610 of slot 61, which is inward in the radial direction
of rotor 6, or one of longitudinal end portions closer to the axis
of rotation O, is formed in a substantially cylindrical shape as
viewed in the z-axis direction, where the cylindrical shape has a
diameter larger than the size of a main portion 611 of slot 61 in
the circumferential direction of rotor 6. The shape of proximal end
portion 610 is not limited to a cylindrical shape, but may be
formed in a rectangular shape like the main portion 611. Between
the proximal end portion 610 of slot 61 and a proximal end portion
71 of vane 7 which is inward in the radial direction of rotor 6, or
one of the longitudinal end portions closer to the axis of rotation
O, is defined a pressure-receiving portion or back pressure chamber
"br". The outside peripheral surface 60 of rotor 6 is formed with a
plurality of projections 62 each of which is located at a
corresponding one of vanes 7, and has a substantially trapezoidal
section as viewed in the z-axis direction. Projection 62 extends
over the entire length of rotor 6 in the z-axis direction, and
extends from the outside peripheral surface 60 by a predetermined
height in the radial direction of rotor 6. Slot 61 opens
substantially at the center of projection 62 as viewed in the
z-axis direction. The length of slot 61 in the radial direction of
rotor 6, i.e. the total length including the proximal end portion
610 and projection 62, is set substantially equal to the length of
vane 7 in the radial direction of rotor 6. The provision of
projection 62 serves to constantly hold vane 7 in slot 61 even when
vane 7 maximally projects from slot 61, for example, in the first
closing region RE3. In other words, this structure serves to remove
unnecessary portions from the outside peripheral surface 60 of
rotor 6 except the projections 62, while ensuring that slot 61
constantly holds vane 7. This results in increase in the volumetric
capacity of pump chambers "r", increase in the pump efficiency,
reduction in the weight of rotor 6, and reduction in the power
loss.
[0028] The annular chamber R3 between rotor 6 and cam ring 8 is
divided by eleven vanes 7 into eleven pump chambers r. In the
following, the distance between two adjacent vanes 7 in the
rotational direction of rotor 6 (the clockwise direction in FIG. 2,
represented by RD1) is defined as a unit pitch. The length of pump
chamber r in the rotor rotation direction RD1 is equal to one pitch
and unchanged. When the central axis P of cam ring 8 is displaced
or eccentric from the axis of rotation O in the positive x-axis
direction, the distance between the outside peripheral surface 60
of rotor 6 and the inside peripheral surface 80 of cam ring 8 in
the rotor radial direction (or the size of pump chamber r in the
rotor radial direction) gradually increases as followed from the
negative x side to the positive x side. Accordingly, the volumetric
capacity of pump chamber r on the positive x side is larger than
that of pump chamber r on the negative x side, where vane 7 travels
inwards and outwards of slot 61 in accordance with a change in the
size of pump chamber r in the rotor radial direction. As a result,
in a region on the negative y side of the x axis, the volumetric
capacity of pump chamber r gradually increases while moving along
with rotation of rotor 6 in the rotor rotation direction RD1 (in
the clockwise direction in FIG. 2) from the negative x side to the
positive x side. On the other hand, in a region on the positive y
side of the x axis, the volumetric capacity of pump chamber r
gradually decreases while moving along with rotation of rotor 6 in
the rotor rotation direction RD1 (in the clockwise direction in
FIG. 2) from the positive x side to the negative x side.
[0029] First and second plates 41 and 42 are a pair of disc-shaped
plates (pressure plates or side plates). First and second plates 41
and 42 are arranged to face both axial ends of rotor 6 (and vanes
7) and cam ring 8 in the z-axis direction, where rotor 6 (and vanes
7) and cam ring 8 are sandwiched therebetween. First plate 41 is
arranged to face the negative z side of rotor 6 and others. FIG. 3
shows a plan view of first plate 41 from the positive z side. The
outline of first plate 41 is schematically expressed with a
circular shape, and bolt holes and the like are omitted. FIG. 4 is
a sectional view of first plate 41 taken along the line IV-IV in
FIG. 3. FIG. 5 is a sectional view of first plate 41 taken along
the line V-V in FIG. 3. On the negative z side of first plate 41 is
arranged a pump cover 49. FIG. 5 shows a sectional view of pump
cover 49. Pump cover 49 is formed with a through hole 490, a first
communication passage 491, and a second communication passage 492.
Drive shaft 5 is inserted and rotatably supported in through hole
490. First communication passage 491 is in the form of a groove for
suction-side communication which is formed in a positive z side
surface of pump cover 49, and positioned to overlap with negative z
side openings of a communication hole 451 and a communication hole
432 of first plate 41 which are described in detail below. The
positive z side surface of pump cover 49 is formed also with a seal
groove 494 which surrounds the second communication passage 492. An
O-ring 496 is mounted in seal groove 494 for sealing. Under a
condition that the negative z side surface of first plate 41 is
placed to face the positive z side surface of pump cover 49, the
O-ring 496 is compressed in the z-axis direction into tight contact
with the negative z side surface of first plate 41, to improve the
liquid tightness of second communication passage 492 that is
subject to high pressure.
[0030] First plate 41 is formed with a suction port 43, a discharge
port 44, a suction-side back pressure port 45, a discharge-side
back pressure port 46, a pin hole 47, and a through hole 48. Pin 10
is inserted and fixed in pin hole 47. Drive shaft 5 is inserted and
rotatably supported in through hole 48. Second plate 42 is formed
with similar ports and holes in similar positions. However, the
ports of second plate 42 may be omitted. In the first embodiment,
the construction that both of first and second plates 41 and 42 are
formed with such similar ports, is effective for bringing into
balance hydraulic forces which are applied from discharge port 44
and the like to rotor 6 and vanes 7 in the z-axis direction, and
thereby suppressing the tear and resistance resulting from
unbalanced contact. Alternatively, suction port 43 and the like may
be distributed to first and second plates 41 and 42 as
appropriate.
[0031] Suction port 43 is arranged in a suction region or section
RE1 on the negative y side of first plate 41 where pump chamber r
gradually expands while moving along with rotation of rotor 6.
Working fluid is supplied through suction port 43 from the outside
to pump chambers r located in the suction region RE1. Suction port
43 includes a suction-side arc groove 430, a suction hole 431, and
a communication hole 432. Suction-side arc groove 430 is formed in
a positive z side surface 410 of first plate 41, and arranged to
receive a suction-side fluid pressure. As viewed in the z-axis
direction, the suction-side arc groove 430 has the form of an arc
about the axis of rotation O, extending in a circumferential
direction of first plate 41 through a portion in which pump
chambers r are arranged in suction region RE1. The suction region
RE1 of pump 1 is defined by an angular range of suction-side arc
groove 430, i.e. by an angle .alpha. defined by a straight line
connecting the axis of rotation O to a beginning end point "A" of
suction-side arc groove 430 on the negative x side of first plate
41 and a straight line connecting the axis of rotation O to a
terminal end point "B" of suction-side arc groove 430 on the
positive x side of first plate 41. The angle .alpha. is equivalent
to about 4.5 pitches in this example. Each of the beginning end
point A and terminal end point B of suction-side arc groove 430 is
positioned away from the x axis by an angle f3 in the negative
y-axis direction, where the angle .beta. is equivalent to about 0.5
pitch in this example.
[0032] Suction-side arc groove 430 is provided with a semicircular
terminal end portion 436 that projects in the rotor rotation
direction RD1. Suction-side arc groove 430 is provided with a
beginning end portion 435 that includes a main section beginning
end portion 433 having a semicircular shape projecting in a
direction opposite to the rotor rotation direction RD1 (referred to
as rotor reverse rotation direction), and a notch 434 formed
continuous with main section beginning end portion 433. Notch 434
extends in the rotor reverse rotation direction from main section
beginning end portion 433 by about 0.5 pitch to the beginning end
point A. The width of suction-side arc groove 430 in the rotor
radial direction is substantially uniform over the entire length in
the circumferential direction, and substantially equal to the width
of annular chamber R3 in the rotor radial direction when cam ring 8
is in the minimum eccentric position, as shown in FIG. 2.
Suction-side arc groove 430 has an inside radial edge 437 which is
positioned somewhat outside of the outside peripheral surface 60
(except projections 62) of rotor 6 in the rotor radial direction.
Suction-side arc groove 430 has an outside radial edge 438 which is
positioned somewhat outside of the inside peripheral surface 80 of
cam ring 8 in the rotor radial direction when cam ring 8 is in the
minimum eccentric position, and positioned slightly outside of the
inside peripheral surface 80 of cam ring 8 in the rotor radial
direction when cam ring 8 is in the maximum eccentric position.
Wherever cam ring 8 is positioned, pump chambers r in the suction
region overlap with suction-side arc groove 430 as viewed in the
z-axis direction and hydraulically communicate with suction-side
arc groove 430. Suction hole 431 is opened substantially at the
center of suction-side arc groove 430 in the circumferential
direction. Suction hole 431 has a substantially elliptic shape as
viewed in the z-axis direction, and has a width in the rotor radial
direction which is substantially equal to the width of suction-side
arc groove 430, and a length in the circumferential direction which
is equal to about one pitch. Suction hole 431 is located to overlap
with the y axis as viewed in the z-axis direction, extending
through first plate 41 in the z-axis direction. Communication hole
432 is opened in suction-side arc groove 430, and arranged adjacent
to suction hole 431 and in the rotor reverse rotation direction
from suction hole 431 (closer to the beginning end point A than
suction hole 431). Communication hole 432 has a similar shape as
suction hole 431, extending through first plate 41 in the z-axis
direction. In suction-side arc groove 430, the depth of the main
section beginning end portion 433, the portion between
communication hole 432 and suction hole 431, and the terminal end
portion 436 in the z-axis direction is smaller than or equal to 20%
of the thickness of first plate 41 in the z-axis direction. The
portion between main section beginning end portion 433 and
communication hole 432 is inclined so that the depth gradually
increases as followed in the rotor rotation direction RD1, and
becomes equal to the thickness of first plate 41 at communication
hole 432. The portion between suction hole 431 and terminal end
portion 436 is inclined so that the depth gradually decreases as
followed in the rotor rotation direction RD1, becomes equal to the
depth of main section beginning end portion 433 at terminal end
portion 436. The notch 434 is in the form of an acute angle
triangle whose width in the rotor radial direction gradually
increases as followed in the rotor rotation direction RD1, as
viewed in the z-axis direction. The maximum width of notch 434 in
the rotor radial direction is set smaller than that of suction-side
arc groove 430. The depth of notch 434 in the z-axis direction is
set to increase from zero to several % of the thickness of first
plate 41 as followed in the rotor rotation direction RD1.
Accordingly, the cross-sectional flow area of notch 434 is set
smaller than the main section of suction-side arc groove 430, and
set to gradually increase as followed in the rotor rotation
direction RD1, thus forming a throttling portion. Discharge port 44
is arranged in a discharge region or section RE2 on the positive y
side of first plate 41 where pump chamber r gradually contracts
while moving along with rotation of rotor 6. Working fluid is
discharged through discharge port 44 to the outside from pump
chambers r located in the discharge region RE2. Discharge port 44
includes a discharge-side arc groove 440, a communication hole 441,
and a discharge hole 442. Discharge-side arc groove 440 is formed
in the positive z side surface 410 of first plate 41, and arranged
to receive a discharge-side fluid pressure. As viewed in the z-axis
direction, the discharge-side arc groove 440 has the form of an arc
about the axis of rotation O, extending in the circumferential
direction of first plate 41 through a portion in which pump
chambers r are arranged in the discharge region RE2. The discharge
region RE2 of pump 1 is defined by an angular range of
discharge-side arc groove 440, i.e. by an angle .alpha. defined by
a straight line connecting the axis of rotation O to a beginning
end point "C" of discharge-side arc groove 440 on the positive x
side of first plate 41 and a straight line connecting the axis of
rotation O to a terminal end point "D" of discharge-side arc groove
440 on the negative x side of first plate 41. The angle .alpha. is
equivalent to about 4.5 pitches in this example. Each of the
beginning end point C and terminal end point D of discharge-side
arc groove 440 is positioned away from the x axis by an angle
.beta. in the positive y-axis direction, where the angle .beta. is
equivalent to about 0.5 pitch in this example. Discharge-side arc
groove 440 is provided with a rectangular beginning end portion
443. The width of discharge-side arc groove 440 in the rotor radial
direction is substantially uniform over the entire length in the
circumferential direction, and slightly smaller than that of
suction-side arc groove 430. Discharge-side arc groove 440 has an
inside radial edge 446 which is positioned somewhat outside of the
outside peripheral surface 60 (except projections 62) of rotor 6 in
the rotor radial direction. Discharge-side arc groove 440 has an
outside radial edge 447 which is positioned substantially identical
to the inside peripheral surface 80 of cam ring 8 in the rotor
radial direction when cam ring 8 is in the minimum eccentric
position. Wherever cam ring 8 is positioned, pump chambers r in the
discharge region RE2 overlap with discharge-side arc groove 440 as
viewed in the z-axis direction and hydraulically communicate with
discharge-side arc groove 440. Discharge hole 442 is opened in a
terminal end portion 444 of discharge-side arc groove 440 which is
located on the side of rotor rotation direction RD1 of
discharge-side arc groove 440. Discharge hole 442 has a
substantially elliptic shape as viewed in the z-axis direction, and
has a width in the rotor radial direction which is substantially
equal to the width of discharge-side arc groove 440, and a length
in the circumferential direction which is somewhat larger than one
pitch. Discharge hole 442 is formed to extend through first plate
41 in the z-axis direction. Discharge hole 442 has a semicircular
edge that projects in the rotor rotation direction RD1, and
substantially identical to the semicircular edge of terminal end
portion 444 as viewed in the z-axis direction. Communication hole
441 is opened on the side of rotor reverse rotation direction of
discharge-side arc groove 440, which is located in a position
opposite to the position of communication hole 432 with respect to
the axis of rotation O as viewed in the z-axis direction.
Communication hole 441 has a similar shape as discharge hole 442
and a length of about one pitch in the circumferential direction,
extending through first plate 41 in the z-axis direction. The
beginning end portion 443 of discharge-side arc groove 440 extends
from the beginning end point C to a rotor reverse rotation
direction side edge 445 of communication hole 441. The rotor
reverse rotation direction side edge 445 is in the form of a
semicircle projecting in the rotor reverse rotation direction as
viewed in the z-axis direction, and has a leading end point "E"
which is located about one pitch from the beginning end point C in
the rotor rotation direction RD1. The leading edge of beginning end
portion 443 facing the terminal end point B of suction-side arc
groove 430 in the rotor reverse rotation direction is formed
straight, extending in the rotor radial direction, as viewed in the
z-axis direction. In discharge-side arc groove 440, the depth (in
the z-axis direction) of a main section 448 between communication
hole 441 and discharge hole 442 is equal to about 25% of the
thickness of first plate 41 in the z-axis direction. The depth of
beginning end portion 443 in the z-axis direction is smaller than
that of main section 448, and changes as followed from the
beginning end point C to the rotor reverse rotation direction side
edge 445 of communication hole 441. Specifically, the depth of
beginning end portion 443 at the beginning end point C is equal to
zero, and set to gradually increase as followed toward the rotor
reverse rotation direction side edge 445, and become smaller than
or equal to about 10% of the thickness of first plate 41 at the
rotor reverse rotation direction side edge 445. The cross-sectional
flow area of beginning end portion 443 is set smaller than that of
main section 448, and set to gradually increase as followed in the
rotor rotation direction RD1, thus forming a throttling
portion.
[0033] In the positive z side surface 410 of first plate 41, no
groove is formed between the terminal end point B of suction-side
arc groove 430 and the beginning end point C of discharge-side arc
groove 440. This region is called first closing region RE3 which is
defined by an angle of 2.beta. made by a straight line connecting
the axis of rotation O to the terminal end point B of suction-side
arc groove 430 and a straight line connecting the axis of rotation
O to the beginning end point C of discharge-side arc groove 440.
The angle 2.beta. is equivalent to about one pitch. Similarly, in
the positive z side surface 410 of first plate 41, no groove is
formed between the terminal end point D of discharge-side arc
groove 440 and the beginning end point A of suction-side arc groove
430. This region is called second closing region RE4 which is
defined by an angle of 2.beta. made by a straight line connecting
the axis of rotation O to the terminal end point D of
discharge-side arc groove 440 and a straight line connecting the
axis of rotation O to the beginning end point A of suction-side arc
groove 430. The angle 2.beta. is equivalent to about one pitch.
When pump chamber r is positioned in the first closing region RE3
or second closing region RE4, the working fluid in pump chamber r
is closed so as to prevent fluid communication between suction-side
arc groove 430 and discharge-side arc groove 440. Each of the first
closing region RE3 and second closing region RE4 extends across the
x axis.
[0034] First plate 41 is formed with a suction-side back pressure
port 45 and a discharge-side back pressure port 46 which are
provided independently of each other, and arranged to hydraulically
communicate with the root of each vane 7 (back pressure chamber br
formed in the proximal end portion 610 of slot 61). Suction-side
back pressure port 45 is arranged to hydraulically connect the
suction port 43 to back pressure chambers br corresponding to most
of vanes 7 located in the suction region RE1, specifically, back
pressure chambers br corresponding to vanes 7 whose distal end
portions 70 overlap with suction port 43 (suction-side arc groove
430). Suction-side back pressure port 45 includes a suction-side
back pressure arc groove 450, and a communication hole 451.
Suction-side back pressure arc groove 450 is formed in the positive
z side surface 410 of first plate 41, and arranged to receive a
suction-side fluid pressure. As viewed in the z-axis direction,
suction-side back pressure arc groove 450 has the form of an arc
about the axis of rotation O, extending in the circumferential
direction of first plate 41 through a portion in which back
pressure chambers br (proximal end portion 610 of rotor 6) for
vanes 7 are arranged. Suction-side back pressure arc groove 450
extends over an angular range of about three pitches, which is
smaller than that of suction-side arc groove 430. Suction-side back
pressure arc groove 450 has a beginning end point "a" that is
located slightly ahead of the beginning end point A of notch 434 or
suction-side arc groove 430, and adjacent to main section beginning
end portion 433, in the rotor rotation direction RD1. Suction-side
back pressure arc groove 450 has a terminal end point "b" that is
located about 1.5 pitches behind the terminal end point B of
suction-side arc groove 430 in the rotor rotation direction RD1.
The size of suction-side back pressure arc groove 450 in the rotor
radial direction is substantially uniform over the entire length in
the circumferential direction, and substantially equal to that of
suction-side arc groove 430, and substantially equal to that of
proximal end portion 610 of slot 61. Suction-side back pressure arc
groove 450 has an inside radial edge 454 that is located somewhat
inside the inside radial edge of proximal end portion 610 of slot
61 in the rotor radial direction. Suction-side back pressure arc
groove 450 has an outside radial edge 455 that is located slightly
inside the outside radial edge of proximal end portion 610 of slot
61 in the rotor radial direction. Wherever cam ring 8 is
positioned, suction-side back pressure arc groove 450 overlaps with
most of back pressure chambers br (proximal end portions 610 of
slots 61) as viewed in the z-axis direction so as to hydraulically
communicate with the same. Communication hole 451 is located on the
rotor reverse rotation direction side of suction-side back pressure
port 45, closer to the beginning end point a than to the terminal
end point b, and overlaps with communication hole 432 of
suction-side arc groove 430 in the circumferential direction.
Communication hole 451 has a substantially elliptic shape as viewed
in the z-axis direction, and has a width in the rotor radial
direction which is substantially equal to the width of suction-side
back pressure arc groove 450, and a length in the circumferential
direction which is equal to about one pitch. Communication hole 451
extends through first plate 41 in the z-axis direction, and
hydraulically communicates with communication hole 432 of
suction-side arc groove 430 through first communication passage
491. In suction-side back pressure arc groove 450, a beginning end
portion 452 is formed between the beginning end point a and suction
hole 431. As viewed in the z-axis direction, beginning end portion
452 has a semicircular end which projects in the rotor reverse
rotation direction. Suction-side back pressure arc groove 450 has a
semicircular terminal end portion 453 which projects in the rotor
rotation direction RD1. The depth of beginning end portion 452 in
the z-axis direction is equal to about 40% or smaller of the
thickness of first plate 41, whereas the depth of terminal end
portion 453 in the z-axis direction is equal to about 20% or
smaller of the thickness of first plate 41. The portion between
terminal end portion 453 and communication hole 451 is inclined so
that the depth gradually increases as followed toward communication
hole 451, and becomes equal to the thickness of first plate 41 at
communication hole 451.
[0035] Discharge-side back pressure port 46 is arranged to
hydraulically connect the discharge port 44 to back pressure
chambers br corresponding to vanes 7 which are located in the
discharge region RE2, the first closing region RE3, a major part of
the second closing region RE4, and a part of the suction region
RE1, specifically, back pressure chambers br corresponding to vanes
7 whose distal end portion 70 overlaps with discharge port 44, the
part of suction-side back pressure port 45, the first closing
region RE3, or the major part of the second closing region RE4.
Discharge-side back pressure port 46 includes a discharge-side back
pressure arc groove 460, and a communication hole 461.
Discharge-side back pressure arc groove 460 is formed in the
positive z side surface 410 of first plate 41, and arranged to
receive a discharge-side fluid pressure. As viewed in the z-axis
direction, discharge-side back pressure arc groove 460 has the form
of an arc about the axis of rotation O, extending in the
circumferential direction of first plate 41 through a portion in
which back pressure chambers br (proximal end portion 610 of rotor
6) for vanes 7 are arranged. Discharge-side back pressure arc
groove 460 extends over an angular range of about seven pitches,
which is larger than that of discharge-side arc groove 440.
Discharge-side back pressure arc groove 460 extends through the
first closing region RE3, and extends in the suction region RE1,
having a beginning end point "c" that is located behind the
beginning end point C of discharge-side arc groove 440, and further
behind the terminal end point B of suction-side arc groove 430, in
the rotor rotation direction RD1. The beginning end point c of
discharge-side back pressure arc groove 460 is located about one
pitch (equivalent to the angle of 2.beta. behind the terminal end
point B of suction-side arc groove 430 in the rotor rotation
direction RD1. A terminal end point "d" of discharge-side back
pressure arc groove 460 is located about one pitch or smaller ahead
of the terminal end point D of discharge-side arc groove 440, and
thus located closer to the terminal end point of the second closing
region RE4, in the rotor rotation direction RD1. The size of
discharge-side back pressure arc groove 460 in the rotor radial
direction is substantially uniform over the entire length in the
circumferential direction, and slightly smaller than that of
discharge-side arc groove 440, and somewhat smaller than that of
proximal end portion 610 of slot 61. Discharge-side back pressure
arc groove 460 has an inside radial edge 464 that is located
somewhat outside of the inside edge of proximal end portion 610 in
the rotor radial direction. Discharge-side back pressure arc groove
460 has an outside radial edge 465 that is located slightly inside
the outside edge of proximal end portion 610 in the rotor radial
direction. Wherever cam ring 8 is positioned, discharge-side back
pressure arc groove 460 overlaps with most of back pressure
chambers br (proximal end portions 610 of slots 61) as viewed in
the z-axis direction so as to hydraulically communicate with the
same. Communication hole 461 is located closer to the beginning end
point c than to the terminal end point d, and in an angular
position between the terminal end point B of suction-side arc
groove 430 and the x axis (midpoint in the first closing region
RE3) on the beginning end side of the first closing region RE3. The
diameter of communication hole 461 is substantially equal to the
width of discharge-side back pressure arc groove 460 in the rotor
radial direction. Communication hole 461 is formed to extend
through first plate 41 with such an inclination relative to the z
axis that the cross-section of communication hole 461 as viewed in
the z-axis direction moves outwards in the rotor radial direction
as followed in the negative z-axis direction. Communication hole
461 is opened in the negative z side surface of first plate 41, and
arranged to hydraulically communicate with communication hole 441
of discharge port 44 (discharge-side arc groove 440) through second
communication passage 492.
[0036] Discharge-side back pressure arc groove 460 includes a
beginning end portion 462, and a back pressure port main section
468. FIG. 6 is a sectional view of pumping section 2 of pump 1,
including a sectional view of first plate 41 taken along the line
VI-VI in FIG. 3. Back pressure port main section 468 is a main
section of discharge-side back pressure arc groove 460, extending
from a beginning end point "e" to the terminal end point d. The
beginning end point e is located about 0.4 pitch or smaller behind
the terminal end point B of suction port 43 in the rotor rotation
direction RD1. The depth of back pressure port main section 468 in
the z-axis direction is substantially uniform. As viewed in the
z-axis direction, the beginning end edge 467 of back pressure port
main section 468 is substantially in the form of a semicircle
projecting in the rotor reverse rotation direction. The terminal
end edge 463 of back pressure port main section 468 or
discharge-side back pressure arc groove 460 is substantially in the
form of a semicircle projecting in the rotor rotation direction
RD1. Beginning end portion 462, which is located on the rotor
reverse rotation direction side of discharge-side back pressure arc
groove 460 or behind back pressure port main section 468 in the
rotor rotation direction RD1, extending in the suction region RE1
from the beginning end point c toward the edge 467 (beginning end
point e) by 0.5 pitch or more in the rotor rotation direction RD1.
The leading end of beginning end portion 462 facing the terminal
end point b of suction-side back pressure arc groove 450 is
substantially rectangular with a straight edge extending in the
rotor radial direction. FIG. 7 is an enlarged view of a portion of
pumping section 2 indicated by VII in FIG. 6, showing a sectional
shape of beginning end portion 462. The bottom (negative z side
surface) of beginning end portion 462 is substantially flat. As
viewed in the rotor rotation direction RD1, beginning end portion
462 has a rectangular section that is substantially constant as
followed in the rotor rotation direction RD1. The depth (length in
the z-axis direction) of beginning end portion 462 is substantially
uniform. Beginning end portion 462 serves as a throttling portion
which has a smaller cross-sectional flow area than back pressure
port main section 468. In the first embodiment, the cross section
of beginning end portion 462 as viewed in the rotor rotation
direction RD1 is not limited to rectangular shapes, but may have
any shape if the cross-sectional flow area is substantially uniform
as followed in the rotor rotation direction RD1. For example,
beginning end portion 462 may have a cross-section with a
moderately projected portion at the center of the bottom. The ratio
of the depth of beginning end portion 462 with respect to that of
back pressure port main section 468 may be selected arbitrarily.
Second plate 42 includes a discharge-side back pressure arc groove
460, similar to first plate 41. The discharge-side back pressure
arc groove 460 of second plate 42 includes a back pressure port
main section 468 that extends from the beginning end point e,
similar to the back pressure port main section 468 of first plate
41, but includes no beginning end portion 462 in contrast to first
plate 41. Namely, a portion of the negative z side surface of
second plate 42 that faces the beginning end portion 462 of first
plate 41 is formed with no recess. This feature serves to enhance a
throttling function of the beginning end portion 462 of first plate
41 which is described in detail below. However, second plate 42 may
be provided with beginning end portion 462 in discharge-side back
pressure arc groove 460, similar to first plate 41.
[0037] As shown in FIG. 6, the clearance between rotor 6 and first
or second plate 41 or 42 in the z-axis direction is set small
enough to prevent flow of working fluid in places (first closing
region RE3, etc.) where discharge-side back pressure arc groove 460
does not extend. On the other hand, in the place where
discharge-side back pressure arc groove 460 is provided, working
fluid flows through discharge-side back pressure arc groove 460
between rotor 6 and first or second plate 41 or 42. Communication
hole 461 is provided with an orifice 466 in a passage leading to
discharge-side back pressure port 46 (discharge-side back pressure
arc groove 460). Orifice 466 serves to restrict the flow passage of
working fluid from discharge-side back pressure port 46 to
discharge port 44, and thereby maintain the internal pressure of
discharge-side back pressure port 46 to be high, promote the
projection of vane 7, and enhance the startability of pump 1.
[0038] Referring back to FIG. 2, control section 3 is mounted in
housing 4, including a control valve 30, first and second fluid
passages 31 and 32, and first and second control chambers R1 and
R2. Control valve 30 is a hydraulically-controlled valve, such as a
spool valve, which includes a spool 302 mounted in an accommodation
hole 401 formed in housing body 40, and a solenoid 301 mounted in
housing 4 for actuating the spool 302, so as to switch the supply
of working fluid between first fluid passage 31 and second fluid
passage 32 formed in housing body 40. First fluid passage 31 and
first communication passage 931 constitute a first control fluid
passage. Second fluid passage 32 and second communication passage
932 constitute a second control fluid passage. Operation of control
valve 30 is controlled by CVT control unit 300, on the basis of
parameters, such as engine speed and throttle valve opening.
[0039] <Pumping Function> When rotor 6 is rotated under a
condition that cam ring 8 is positioned eccentric in the positive
x-axis direction with respect to the axis of rotation O, each pump
chamber r expands and contracts periodically while revolving about
the axis of rotation O. Working fluid is sucked through suction
port 43 to each pump chamber r in the suction region RE1 on the
negative y side where pump chamber r expands while moving along
with rotation of rotor 6, and working fluid is discharged through
discharge port 44 from each pump chamber r in the discharge region
RE2 on the negative y side where pump chamber r contracts while
moving along with rotation of rotor 6. Specifically, in the suction
region RE1, each pump chamber r continues to expand until the rotor
reverse rotation direction side vane 7 (rear-side vane 7) of pump
chamber r passes through the terminal end point B of suction-side
arc groove 430, namely, until the rotor rotation direction side
vane 7 (front-side vane 7) of pump chamber r passes through the
beginning end point C of discharge-side arc groove 440. During this
period, pump chamber r is maintained hydraulically connected to
suction-side arc groove 430, sucking working fluid through suction
port 43. When each pump chamber r is positioned in the first
closing region RE3, i.e. when the rotor rotation direction side
surface of the rear-side vane 7 of pump chamber r is positioned at
the terminal end point B of suction-side arc groove 430, and the
rotor reverse rotation direction side surface of the front-side
vane 7 of pump chamber r is positioned at the beginning end point C
of discharge-side arc groove 440, pump chamber r is hydraulically
separated from both of suction-side arc groove 430 and
discharge-side arc groove 440, and thereby liquid-tightly closed.
After the rotor rotation direction side surface of the rear-side
vane 7 of pump chamber r passes through the terminal end point B of
suction-side arc groove 430, and the rotor reverse rotation
direction side surface of the front-side vane 7 of pump chamber r
passes through the beginning end point C of discharge-side arc
groove 440, pump chamber r contracts while moving along with
rotation of rotor 6, and gets hydraulically connected to
discharge-side arc groove 440, so as to discharge working fluid
through discharge port 44. Similarly, when each pump chamber r is
positioned in the second closing region RE4, i.e. when the rotor
rotation direction side surface of the rear-side vane 7 of pump
chamber r is positioned at the terminal end point D of
discharge-side arc groove 440, and the rotor reverse rotation
direction side surface of the front-side vane 7 of pump chamber r
is positioned at the beginning end point A of suction-side arc
groove 430, pump chamber r is hydraulically separated from both of
suction-side arc groove 430 and discharge-side arc groove 440, and
thereby liquid-tightly closed. In the first embodiment, each of the
first closing region RE3 and second closing region RE4 has a range
of one pitch (i.e. the width of pump chamber r in the
circumferential direction). This serves to prevent fluid
communication between the suction region RE1 and discharge region
RE2, while enhancing the pump efficiency. However, each of the
first closing region RE3 and second closing region RE4 (the spacing
between suction port 43 and discharge port 44) is not limited to
one pitch, but may have an angular range of more than one pitch.
Namely, the range of each of the first closing region RE3 and
second closing region RE4 may be arbitrarily set if fluid
communication can be prevented between the suction region RE1 and
the discharge region RE2. When the rotor reverse rotation direction
side surface of the front-side vane 7 of pump chamber r moves from
the first closing region RE3 to the discharge region RE2, the
throttling function of the beginning end portion 443 of
discharge-side arc groove 440 serves to prevent rapid fluid
communication between pump chamber r and discharge-side arc groove
440, and thereby suppress fluctuations in the internal pressures of
discharge port 44 and pump chamber r. This prevents working fluid
from rapidly flowing through discharge port 44 having a higher
pressure to pump chamber r having a lower pressure, and thereby
prevents rapid decrease in the flow rate of working fluid supplied
to the outside pipe that is connected to discharge port 44 through
discharge hole 442. This suppresses fluid striking in the pipe,
namely, fluctuations in fluid pressure in the pipe. Since the flow
rate of working fluid supplied to pump chamber r is thus prevented
from rapidly increasing, the internal pressure of pump chamber r is
prevented from fluctuating. However, beginning end portion 443 of
discharge-side arc groove 440 may be omitted or modified
arbitrarily. On the other hand, when the rotor reverse rotation
direction side surface of the front-side vane 7 of pump chamber r
moves from the second closing region RE4 to the suction region RE1,
the throttling function of the notch 434 of suction port 43 serves
to prevent rapid fluid communication between pump chamber r and
suction-side arc groove 430, and thereby suppress fluctuations in
the internal pressures of suction port 43 and pump chamber r. This
prevents working fluid from rapidly flowing from pump chamber r
having a higher pressure to suction port 43 having a lower
pressure, and thereby prevents occurrence of bubbles (cavitation).
However, the notch 434 may be omitted or modified arbitrarily.
[0040] <Variable Displacement> When cam ring 8 is positioned
eccentric in the positive x-axis direction with respect to the axis
of rotation O so that the eccentricity .delta. is above zero, pump
chamber r expands while moving along with rotation of rotor 6 on
the negative y side. The volumetric capacity of pump chamber r is
maximized when pump chamber r is positioned on the positive x side
of the x axis in the first closing region RE3. On the other hand,
pump chamber r contracts while moving along with rotation of rotor
6 on the positive y side. The volumetric capacity of pump chamber r
is minimized when pump chamber r is positioned on the negative x
side of the x axis in the second closing region RE4. When cam ring
8 is positioned in the maximum eccentric position as shown in FIG.
2, the difference in volumetric capacity between the minimally
contracted pump chamber r and the maximally expanded pump chamber r
is maximized, so that the pump capacity is maximized. On the other
hand, when cam ring 8 is moved in the negative x-axis direction
into the minimum eccentric position so that the eccentricity
.delta. becomes zero, pump chamber r does not expand nor contract
while moving along with rotation of rotor 6 anywhere on the
positive y side and the negative y side. The difference in
volumetric capacity between the minimally contracted pump chamber r
and the maximally expanded pump chamber r is thus minimized to
zero, so that the pump capacity is minimized to zero. In this way,
as the eccentricity of cam ring 8 changes, the difference in
volumetric capacity changes, so that the pump capacity changes.
[0041] When no working fluid is supplied to first control chamber
R1 and second control chamber R2, cam ring 8 is positioned
eccentric in the positive x-axis direction under the biasing force
of spring 12, so that the eccentricity b is maximized. First
control chamber R1 is supplied with working fluid from control
valve 30 through the first control fluid passage. The supplied
fluid pressure serves to produce a first hydraulic force for
pressing the cam ring 8 in the negative x-axis direction against
the biasing force of spring 12. On the other hand, second control
chamber R2 is supplied with working fluid from control valve 30
through the second control fluid passage. The supplied fluid
pressure serves to produce a second hydraulic force for pressing
the cam ring 8 in the positive x-axis direction in addition to the
biasing force of spring 12. CVT control unit 300 controls operation
of control valve 30, and thereby changes the first and second
hydraulic forces by suitable supply and drain of working fluid to
and from first and second control chambers R1 and R2. This
operation causes movement of cam ring 8, so that the eccentricity b
changes. In this way, CVT control unit 300 controls the pump
capacity. More specifically, when the hydraulic pressure in first
control chamber R1 is increased, the first hydraulic force is
increased. On the other hand, when the hydraulic pressure in second
control chamber R2 is increased, the second hydraulic force is
increased. When the resultant force of the first and second
hydraulic forces is in the negative x-axis direction and the
resultant force is larger than the biasing force of spring 12 for
pressing the cam ring 8 in the positive x-axis direction, then cam
ring 8 moves in the negative x-axis direction. This results in
reduction in the eccentricity .delta., and reduction in the
difference in volumetric capacity between the contacted state and
the expanded state, and thereby results in increase in the pump
capacity. Second control chamber R2 may be omitted so that only
first control chamber R1 serves to move cam ring 8. The device for
constantly biasing the cam ring 8 is not limited to coil springs,
but may be implemented differently. When the internal combustion
engine is operating in a predetermined high speed region, the
capacity of pump 1 is controlled to be small but sufficient, in
order to reduce the torque required to drive the pump 1. This
feature is advantageous, as compared to fixed displacement
pumps.
[0042] <Reduction in Power Loss by Provision of Different Kinds
of Back Pressure Ports> When rotor 6 is rotating, vane 7 is
subject to a centrifugal force acting outwards in the rotator
radial direction. Accordingly, when a predetermined condition is
satisfied which includes a requirement that the rotational speed of
rotor 6 is sufficiently high, the distal end portion 70 of vane 7
projects form slot 61 so as to contact the inside peripheral
surface 80 of cam ring 8. The contact restricts outward movement of
vane 7 in the rotor radial direction. When vane 7 moves outwards of
slot 61, the back pressure chamber br behind the vane 7 expands. On
the other hand, when vane 7 moves inwards of slot 61, the back
pressure chamber br behind the vane 7 contracts. When rotor 6 is
rotating under a condition that cam ring 8 is positioned eccentric
in the positive x-axis direction from the axis of rotation O, the
back pressure chamber br for each vane 7 in contact with the inside
peripheral surface 80 of cam ring 8 expands and contracts
periodically along with rotation of rotor 6. On the negative y side
where back pressure chamber br is expanding, it is possible that
the distal end portion 70 of vane 7 fails to be in contact with the
inside peripheral surface 80 of cam ring 8, and thereby establish
the liquid-tightness of pump chamber r, if a sufficient amount of
working fluid is not supplied so as to allow projection of vane 7.
On the other hand, on the positive y side where back pressure
chamber br is contracting, it is possible that the distal end
portion 70 of vane 7 undergoes a high frictional resistance in
contact with the inside peripheral surface 80 of cam ring 8, if
working fluid is not smoothly discharged from back pressure chamber
br so as to allow inward movement or retraction of vane 7 into slot
61. In pump 1, on the negative y side, back pressure chamber br is
supplied with working fluid from suction-side back pressure port
45. This serves to improve the outward movement of vane 7.
[0043] On the positive y side, working fluid is discharged from
back pressure chamber br to discharge-side back pressure port 46.
This serves to reduce the resistance against the sliding movement
of vane 7. On the negative y side, the distal end portion 70 of
vane 7 is subject to pressure from suction port 43, whereas the
proximal end portion 71 of vane 7 is subject to pressure from
suction-side back pressure port 45. Since suction-side back
pressure port 45 is hydraulically connected to suction port 43
through first communication passage 491, the internal pressure of
suction port 43 is substantially equal to that of suction-side back
pressure port 45. Accordingly, the distal end portion 70 of vane 7
is prevented from being unnecessarily strongly pressed on the
inside peripheral surface 80 of cam ring 8, as compared to cases
where back pressure chamber br is adapted to receive a high
hydraulic pressure from a discharge port. This results in reduction
in the loss torque due to friction between the distal end portion
70 of vane 7 and the inside peripheral surface 80 of cam ring 8. In
other words, this feature serves to reduce the frictional
resistance to the sliding movement of the distal end portion 70 of
vane 7 on the inside peripheral surface 80 of cam ring 8, and
thereby reduce the power loss, as compared to cases where all of
the proximal end portions 71 of vane 7 positioned in the suction
region RE1 are applied with a discharge-side pressure.
[0044] On the other hand, on the positive y side, the distal end
portion 70 of vane 7 is subject to pressure from discharge port 44,
whereas the proximal end portion 71 of vane 7 is subject to
pressure from discharge-side back pressure port 46. Since
discharge-side back pressure port 46 is hydraulically connected to
discharge port 44 through second communication passage 492, the
distal end portion 70 and proximal end portion 71 of vane 7 are
subject to substantially the same pressure. Accordingly, the distal
end portion 70 of vane 7 is prevented from being unnecessarily
strongly pressed on the inside peripheral surface 80 of cam ring 8.
This serves to reduce the loss torque due to friction between the
distal end portion 70 of vane 7 and the inside peripheral surface
80 of cam ring 8.
[0045] In summary, in pump 1, suction-side back pressure port 45
and discharge-side back pressure port 46 are separately provided
for back pressure chambers br, so that both in the suction region
RE1 and in the discharge region RE2, the distal end portion 70 and
proximal end portion 71 of vane 7 are subject to substantially the
same pressure. This feature serves to suitably press the vane 7 on
cam ring 8 by the centrifugal force, while suppressing the
frictional resistance between vane 7 and cam ring 8. This serves to
reduce wear between vane 7 and the inside peripheral surface 80 of
cam ring 8, and reduce the power loss, because the required driving
torque for rotating the rotor 6 is reduced. In this way, pump 1 is
formed as an efficient low-torque type pump where: the required
driving torque is smaller with respect to rotational speed; the
fuel efficiency is enhanced by reduction in the power loss; and the
discharge rate is larger even if the exterior size is identical
(i.e. pump 1 can be formed compact), as compared to typical
variable displacement pumps.
[0046] <Prevention of Flow Through Vane by Vane Pressing> As
described above, in the suction region RE1, the projection of vane
7 from slot 61 to the inside peripheral surface 80 of cam ring 8 is
implemented mainly by the centrifugal force. Accordingly, when the
internal combustion engine is operating in a low speed region, for
example, when the engine is at start or at idle, rotor 6 is
rotating slowly so that the centrifugal force is small, and the
distal end portion 70 of vane 7 may be out of contact with the
inside peripheral surface 80 of cam ring 8 because the pressing
force for distal end portion 70 is insufficient. This is based on
the fact that the amount of projection of vane 7 depends on the
force acting on vane 7 outwards in the rotor radial direction. The
force depends mainly on the centrifugal force, the viscosity of
working fluid, and the friction between vane 7 and slot 61. Among
those, the contribution of the centrifugal force is highest. When
each pump chamber r is positioned in the first closing region RE3
or second closing region RE4, pump chamber r shifts between the
suction region RE1 and the discharge region RE2 along with rotation
of rotor 6. If vane 7 moves into the first closing region RE3 or
second closing region RE4 under a condition that vane 7 is out of
contact with the inside peripheral surface 80 of cam ring 8 due to
insufficient projection of vane 7, pump 1 may encounter the
following problem.
[0047] When the rear-side vane 7 of a first pump chamber r is
positioned in the first closing region RE3, the front-side vane 7
of the first pump chamber r is positioned in the discharge region
RE2 so that the first pump chamber r is hydraulically connected to
discharge port 44, and thereby the internal pressure of the first
pump chamber r is high, because the length of the first closing
region RE3 in the circumferential direction is equal to one pitch.
At the moment, the rear-side vane 7 of a second pump chamber r
which is adjacent to the first pump chamber r, and behind the first
pump chamber r in the rotor rotation direction RD1 is positioned in
the suction region RE1, so that the second pump chamber r is
hydraulically connected to suction port 43, and thereby the
internal pressure of the second pump chamber r is relatively low.
When the internal pressure of the first pump chamber r is thus
different significantly from that of the second pump chamber r that
is adjacent to the first pump chamber r, and the projection of the
vane 7 that divides the first and second pump chambers r from one
another is insufficient, then it is possible that working fluid
leaks or flows from the higher pressure side pump chamber r to the
lower pressure side pump chamber r through a clearance between the
distal end portion 70 of vane 7 and the inside peripheral surface
80 of cam ring 8. This phenomenon is referred to as vane through
flow. The possibility is relatively high when pump 1 is operating
at low temperature. The leaking or vane through flow of working
fluid can result in a rapid flow of working fluid, and fluctuations
in the pressures in discharge port 44 and suction port 43, and
thereby cause noises. If so, the pressure in discharge port 44
falls periodically while moving along with rotation of rotor 6, and
thereby causes pulsation of the discharge pressure. This causes a
decrease in the amount of discharged working fluid, and a fall in
the discharge-side pressure, and thereby causes a fall in the pump
efficiency, and a fall in the startability of the system (CVT 100)
that uses the pump discharge pressure.
[0048] In consideration of the problem described above, pump 1 is
configured so that the back pressure chamber br for each vane 7 is
applied with high pressure, before the vane 7 enters the first
closing region RE3. This ensures that vane 7 is pressed outwards in
the rotor radial direction, and brought into contact with the
inside peripheral surface 80 of cam ring 8, so that the vane 7
liquid-tightly divides and seals the two adjacent pump chambers r
from one another. FIG. 8 is a sectional view of pump 1 taken along
the line VIII-VIII in FIG. 6. In FIG. 8, the outside periphery of
rotor 6, the inside periphery of cam ring 8, the shape of
suction-side arc groove 430, etc. are schematically expressed by
straight lines, and the projections 62 of rotor 6 are omitted. As
shown in FIG. 8, discharge-side back pressure port 46
(discharge-side back pressure arc groove 460) extends also in the
suction region RE1, and the beginning end point c of discharge-side
back pressure port 46 is located a distance L0 (one pitch) behind
the terminal end point B of suction port 43 (suction-side arc
groove 430) in the rotor rotation direction RD1. The distance L0
may be larger than or smaller than one pitch. According to this
construction, before vane 7 enters the first closing region RE3,
i.e. when vane 7 is positioned behind the terminal end point B of
suction port 43 in the rotor rotation direction RD1, the back
pressure chamber br for the vane 7 is hydraulically connected to
discharge-side back pressure port 46. When the back pressure
chamber br for vane 7 that is out of contact with the inside
peripheral surface 80 of cam ring 8 enters the discharge-side back
pressure port 46 in the terminal end portion 436 of suction port
43, the discharge-side pressure is supplied and applied from
discharge-side back pressure port 46 to the proximal end portion 71
of vane 7, so that the vane 7 moves outwards in the rotor radial
direction, into pressing contact with cam ring 8. When the vane 7
enters the first closing region RE3 beyond the terminal end point B
of suction port 43 along with rotation of rotor 6, vane 7 is
already pressed into contact with cam ring 8, thus preventing the
fluid communication between suction port 43 and discharge port 44.
In this way, the liquid tightness of each pump chamber r is
maintained when the pump chamber r is moving from the suction
region RE1 toward the discharge region RE2. After the vane 7 enters
the first closing region RE3, the back pressure chamber br for the
vane 7 is hydraulically connected to discharge-side back pressure
port 46, and thereby subject to high pressure, so that the vane 7
is maintained in pressing contact with cam ring 8. In this way, the
back pressure chamber br for the vane 7 that defines the pump
chamber r positioned in the first closing region RE3 between the
suction region RE1 and the discharge region RE2 is applied with
high pressure, so that the distal end portion 70 of vane 7 is
pressed on the inside peripheral surface 80 of cam ring 8 by the
differential pressure between the distal end portion 70 and
proximal end portion 71 of vane 7. This serves to maintain the
liquid tightness of the pump chamber r that is positioned
immediately behind the discharge region RE2 in the rotor rotation
direction RD1, and provide sealing between the low pressure suction
side and the high pressure discharge side. This feature serves to
allow vane 7 to move out of slot 61, and thereby allow pump 1 to
perform the suction and discharge function normally, even when the
viscosity of working fluid is high, for example, during cold start,
so that the pressing force for vane 7 based on the centrifugal
force is insufficient. The startability of pump 1 at low
temperature is thus enhanced.
[0049] <Reduction in Loss torque by Range Setting of
Discharge-Side Back Pressure Port> If the angular range where
the back pressure chamber br for vane 7 is supplied with high
pressure before entering the first closing region RE3 is too wide,
the loss torque due to friction is increased, and the effect of
reduction in the power loss is reduced, because the angular range
where vane 7 slides in pressing contact with the inside peripheral
surface 80 of cam ring 8 is also wide. The size of a typical
variable displacement pump is generally larger than that of a
typical fixed displacement pump having the same capacity, due to
additional equipment. Accordingly, in a low speed region (or fixed
capacity region) where the pump capacity is unchanged, the
efficiency of a typical variable displacement pump is lower than a
typical fixed displacement pump, namely, the required driving
torque of the variable displacement pump is larger than that of the
fixed displacement pump if the rotational speed is the same.
Although the efficiency of pump 1 is improved as described above,
there is a region where the efficiency is lower than that of the
fixed displacement type, and the effect of reduction in the power
loss is insufficient. Accordingly, it is desirable to further
reduce the power loss in a variable displacement pump. In
consideration of this point, pump 1 is configured so that the shape
of discharge-side back pressure port 46 (the cross-sectional flow
area and the position of the beginning end point c) is adjusted so
as to optimize the angular range where the back pressure chamber br
for vane 7 is supplied with high pressure before entering the first
closing region RE3. This serves to prevent the flow through vane 7
between pump chambers r, and reduce the power loss even in a low
speed region where the efficiency is relatively low.
[0050] When the rotor rotation direction side surface of a first
vane 7 whose projection from slot 61 is relatively small passes
through the terminal end point B of suction port 43, the rotor
reverse rotation direction side surface of a second vane 7 that is
adjacent and ahead of the first vane 7 in the rotor rotation
direction RD1 passes through the beginning end point C of discharge
port 44. Accordingly, if the distal end portion 70 of the first
vane 7 is out of contact with the inside peripheral surface 80 of
cam ring 8, it is sufficient to supply an amount of working fluid
corresponding to the distance between vane 7 and cam ring 8 to the
back pressure chamber br for the first vane 7 through
discharge-side back pressure port 46, before the rotor rotation
direction side surface of the first vane 7 reaches the terminal end
point B of suction port 43. If working fluid is so supplied, it is
completed that the vane 7 is pressed into contact with the inside
peripheral surface 80 of cam ring 8, before the rotor rotation
direction side surface of the first vane 7 reaches the terminal end
point B of suction port 43. This serves to ensure the liquid
tightness of the pump chamber r that is defined by the first and
second vanes 7, before the pump chamber r starts to hydraulically
communicate with discharge port 44.
[0051] It is desirable to complete the supply of the amount of
working fluid corresponding to the clearance between the first vane
7 and cam ring 8, when the rotor rotation direction side surface of
the first vane 7 has reached a position as close to the terminal
end point B of suction port 43 as possible. This is because it is
desirable to reduce the range where the distal end portion 70 of
vane 7 is in pressing contact with the inside peripheral surface 80
of cam ring 8 behind the terminal end point B of suction port 43 in
the rotor rotation direction RD1, and thereby reduce the loss
torque, in consideration of the fact that until the moment the
supply of the amount of working fluid required to bring the first
vane 7 into contact with cam ring 8 is completed, the first vane 7
is out of contact with cam ring 8. Therefore, in pump 1, the shape
of discharge-side back pressure port 46 is set so that supply of
the amount of working fluid corresponding to the clearance is
completed when the rotor rotation direction side surface of the
first vane 7 has reached a position as close to the terminal end
point B of suction port 43 as possible.
[0052] Specifically, the following equation holds, where "A"
represents the cross-sectional flow area of a fluid passage from
discharge-side back pressure port 46 to the back pressure chamber
br for vane 7, i.e. the cross-sectional flow area of discharge-side
back pressure port 46 as viewed in the rotor rotation direction
RD1, Q represents an amount per unit time (volumetric flow rate) of
working fluid flowing from discharge-side back pressure port 46
into the back pressure chamber br, "C" represents a flow rate
coefficient, .rho. represent the density of working fluid, and
.DELTA.P represents the differential pressure through the fluid
passage (the difference in pressure between discharge-side back
pressure port 46 and back pressure chamber br.apprxeq.discharge
pressure):
Q=CA (2.DELTA.P/.rho.)
[0053] A quantity .intg.Q (time integral of Q), which is a total
amount of working fluid supplied to back pressure chamber br for
vane 7, is proportional to a product of a time period T when back
pressure chamber br for vane 7 is hydraulically connected to
discharge-side back pressure port 46, and the cross-sectional flow
area A. The time period T depends on the rotational speed of rotor
6 (or the travel speed of vane 7), and a travel distance L* of vane
7 in the rotor rotation direction RD1 in discharge-side back
pressure port 46 (i.e. the angular range of travel of back pressure
chamber br from the beginning end point c of discharge-side back
pressure port 46). If the rotational speed of rotor 6 is assumed to
be constant, the time period T is determined by the travel distance
L*. In summary, the quantity .intg.Q is determined by the
cross-sectional flow area A of discharge-side back pressure port 46
and the travel distance L* (or the position of the beginning end
point c).
[0054] In pump 1, the distance (angular range) from the beginning
end point c of beginning end portion 462 to the beginning end point
e of back pressure port main section 468, L, and the
cross-sectional flow area of the beginning end portion 462 of
discharge-side back pressure port 46, A, are set so that the fluid
quantity .intg.Q conforms to the amount of working fluid
corresponding to the clearance between vane 7 and cam ring 8. In
other words, the distance L and cross-sectional flow area A are set
so that while vane 7 moves from the beginning end point c of
beginning end portion 462 to the beginning end point e of back
pressure port main section 468, the fluid quantity .intg.Q which is
identical to the total quantity supplied to back pressure chamber
br so as to bring the distal end portion 70 of vane 7 into contact
with the inside peripheral surface 80 of cam ring 8. In this way,
discharge-side back pressure port 46 is arranged so that vane 7 is
brought into contact with the inside peripheral surface 80 of cam
ring 8 at the beginning end point e close to the terminal end point
B, so as to prevent the flow through vane 7 between pump chambers
r, and suppress the loss torque due to useless pressing
contact.
[0055] FIG. 9 shows, in the lower part, combinations of the
cross-sectional flow area A of the beginning end portion 462 of
discharge-side back pressure port 46 and the distance L with which
it is possible to reduce the loss torque while preventing the vane
through flow, thus bringing the power loss into an allowable
region. This relationship may be determined experimentally or
estimated on the basis of design values. Pump 1 is configured so
that the point defined by the cross-sectional flow area A and the
distance L is positioned in a region indicated by hatching pattern
in FIG. 9. The allowable region may be defined so that the total
loss torque is comparable to or smaller than the loss torque of a
typical fixed displacement pump, when in a predetermined low speed
region including a fixed displacement region or when in a mode
where such a low speed region is frequently used. The power loss of
pump 1 can be thus reduced to a level comparable to or lower than
that of a typical fixed displacement pump, even when the CVT to
which pump 1 is adapted is operating in a mode where a low speed
region where the efficiency is relatively low is frequently used.
Also, the power loss of pump 1 can be reduced to a level comparable
to or lower than that of a typical fixed displacement pump, even
when pump 1 is used as a fluid pressure supply source for a power
steering system which constantly uses a low speed region in which
the efficiency is relatively low.
[0056] The cross-sectional flow area A and the distance L are set
in such a desirable region (indicated by hatching pattern in FIG.
9) that even if vane 7 starts to contact the cam ring 8 at a point
behind the beginning end point e of back pressure port main section
468 in the rotor rotation direction RD1 under the influence of
rotational speed, fluid temperature, and others, the loss torque
due to pressing contact of vane 7 (vane loss torque) is below an
upper limit of an allowable range. If vane 7 is maintained in
contact with cam ring 8 in the suction region RE1, vane 7 continues
to be in pressing contact with cam ring 8 after passing through the
beginning end point c of the beginning end portion 462, so that the
loss torque becomes equal to the upper limit of the desirable
region. The maximum allowable value of the distance L is set to a
value Lmax that is on the boundary of the allowable range of the
vane loss torque, as shown in FIG. 9.
[0057] On the other hand, if the vane 7 starts to contact the cam
ring 8 at a point ahead of the beginning end point e of back
pressure port main section 468 in the rotor rotation direction RD1
under the influence of rotational speed, fluid temperature, and
others, the back pressure chamber br is supplied with working fluid
at a larger flow rate after vane 7 passes through the beginning end
point e than before, because the cross-sectional flow area of back
pressure port main section 468 is set larger than that of beginning
end portion 462 in discharge-side back pressure port 46. This
feature serves to ensure the prevention of vane through flow,
because supply of the amount of working fluid corresponding to the
clearance between vane 7 and cam ring 8 is completed before the
rotor rotation direction side surface of vane 7 passes through the
beginning end point e of back pressure port main section 468 and
then reaches the terminal end point B of suction port 43. Pump 1
may be modified so that when the rotor rotation direction side
surface of vane 7 reaches the terminal end point B of suction port
43, supply of the required amount of working fluid is completed.
For example, the beginning end point e of back pressure port main
section 468 may be moved to be identical to the terminal end point
B of suction port 43 so that the beginning end portion 462 extends
from the beginning end point c to the terminal end point B. In such
cases, the range where vane 7 is in sliding contact is further
reduced to reduce the loss torque more effectively. The desirable
position of the beginning end point c (or the desirable range of
the distance L) for such cases may be defined with reference to the
position of the terminal end point B of suction port 43.
[0058] <Noise Reduction by Throttling Portion> Even in the
construction that discharge-side back pressure port 46 is formed so
as to reduce the loss torque while preventing the vane through flow
as described above, noise can be generated if the cross-sectional
flow area A is large. When high pressure working fluid starts to
flow through the large cross-sectional flow area A of
discharge-side back pressure port 46 to back pressure chamber br
under condition that vane 7 is out of contact with cam ring 8, it
is possible that working fluid rapidly flows into back pressure
chamber br so that vane 7 moves toward and collapses hard with cam
ring 8, thereby generating noise.
[0059] The foregoing problem is solved by pump 1 in which
discharge-side back pressure port 46 is provided with beginning end
portion 462 that has a reduced cross-sectional flow area A, and
thus forms a throttling portion. When the back pressure chamber br
(proximal end portion 610 of slot 61) for vane 7 is positioned at
beginning end portion 462 (from the beginning end point c to the
beginning end point e of back pressure port main section 468),
working fluid flows from back pressure port main section 468
through beginning end portion 462 to back pressure chamber br.
Since the cross-sectional flow area of beginning end portion 462 is
set smaller than that of back pressure port main section 468, the
flow rate of working fluid supplied to back pressure chamber br
(flow rate Q) is restricted.
[0060] Specifically, the cross-sectional flow area A of beginning
end portion 462 is adjusted so that the travel speed of vane 7
outwards in the rotor radial direction, V, when distal end portion
70 is contacting the inside peripheral surface 80 of cam ring 8, is
optimized, and thereby noise due to contact of vane 7 is within an
allowable region. For example, speed V is set so as to permit a
some level of noise during cold start, and suppress the occurrence
of noise while pump 1 is at idle. The speed V is related to the
cross-sectional area S of vane 7 ((pressure receiving area)=(size
in the rotor rotation direction RD1).times.(size in the z-axis
direction)), and the cross-sectional flow area A of beginning end
portion 462, as follows:
V=Q/S=CA/S (2.DELTA.P/.rho.), or
H=C/V (2.DELTA.P/.rho.), where H represents an area ratio S/A.
[0061] Using the above equation, the speed V is optimized by
adjusting the area ratio H. In other words, the cross-sectional
flow area A of beginning end portion 462 is adjusted with reference
to the cross-sectional area S, to achieve the optimized speed V.
Specifically, the cross-sectional flow area A of beginning end
portion 462 is set within a range from a predetermined minimum
value Amin to a predetermined maximum value Amax. The maximum value
Amax is determined depending on an allowable noise level. The
minimum value Amin is determined depending on the distance L.
[0062] FIG. 9 shows, in the upper part, a relationship between the
cross-sectional flow area A of discharge-side back pressure port
46, and the noise level. The relationship may be experimentally
found or estimated on the basis of design values. Pump 1 is
configured so that the cross-sectional flow area A of the beginning
end portion 462 of discharge-side back pressure port 46 is set
within the desirable range from Amin to Amax, and thereby the noise
level is below an upper limit of the allowable range. As a result,
allowable combinations of the cross-sectional flow area A and
distance L are positioned within the region indicated by hatching
pattern in FIG. 9. Accordingly, when the back pressure chamber br
of vane 7 that is out of contact with cam ring 8 in the suction
region RE1 moves to overlap with the discharge-side back pressure
port 46, the throttling function of beginning end portion 462
serves to is restrict the flow rate Q of working fluid flowing into
back pressure chamber br. As a result, the speed V when vane 7
moves into contact with cam ring 8 at the beginning end point e is
reduced, so that the speed of vane 7 when vane 7 collapses with cam
ring 8 is suppressed, and thereby the noise due to contact of vane
7 is suppressed.
[0063] According to the throttling effect by beginning end portion
462, the flow rate Q of working fluid discharged from the back
pressure port main section 468 is restricted, so that the pressure
in back pressure port main section 468 is prevented from
fluctuating or pulsating, and thereby the hydraulic force applied
to vane 7 from back pressure chamber br that is hydraulically
connected to back pressure port main section 468 becomes
substantially constant. In this way, in the discharge region RE2,
each vane 7 is maintained in stable contact with cam ring 8.
[0064] The beginning end portion 462 has a substantially
rectangular section as viewed in the z-axis direction, where the
depth in the z-axis direction is constant as followed in the rotor
rotation direction. Namely, the size of beginning end portion 462
in the rotor radial direction is substantially constant as followed
in the rotor rotation direction RD1, and the depth of beginning end
portion 462 is also substantially constant. Accordingly, the
cross-sectional flow area A of beginning end portion 462 is
substantially constant as followed in the rotor rotation direction
RD1, so that the flow rate Q of working fluid supplied to back
pressure chamber br for vane 7 that is positioned at beginning end
portion 462 is substantially constant. This makes it possible to
easily set the speed V of vane 7 that moves into contact with cam
ring 8.
Comparison in Operation and Effect with Comparative Examples
[0065] FIG. 10 is a sectional view of a vane pump according to a
first comparative example, which corresponds to the sectional view
of FIG. 8. FIG. 11 is a sectional view of a vane pump according to
a second comparative example, which corresponds to the sectional
view of FIG. 8. As shown in FIG. 10, in the first comparative
example, discharge-side back pressure port 46 (discharge-side back
pressure arc groove 460) is formed to extend also in the suction
region RE1, but discharge-side back pressure port 46 has a
beginning end point c1 closer to the terminal end point B of
suction port 43, where the distance L1 between the beginning end
point c1 and the terminal end point B is equal to a value that is
much smaller than the lower limit value Lmin of the desirable range
(L1<<Lmin). Moreover, the cross-sectional flow area A of
discharge-side back pressure port 46 is the same as that of back
pressure port main section 468 according to the first embodiment,
and equal to a value A0 that is much larger than the upper limit
Amax of the desirable range (A0>>Amax).
[0066] In the first comparative example, the amount of working
fluid supplied to back pressure chamber br for vane 7 that is
entering the first closing region RE3 is to insufficient so that
the projection of vane 7 is delayed to allow the vane through flow.
Specifically, the combination of the cross-sectional flow area A0
and the distance L1 is positioned out of the desirable region in
FIG. 9, so that the occurrence of vane through flow vane is
possible. Accordingly, in the first comparative example, the fluid
quantity .intg.Q of working fluid supplied to back pressure chamber
br during the period when the rotor rotation direction side surface
of vane 7 moves from the beginning end point c1 to the terminal end
point B is below the amount corresponding to the clearance between
vane 7 and cam ring 8 (the amount for eliminating the clearance).
As a result, the vane through flow occurs, because the distal end
portion 70 of vane 7 is out of contact with the inside peripheral
surface 80 of cam ring 8 when the rotor rotation direction side
surface of vane 7 has reached the terminal end point B.
[0067] Moreover, in the first comparative example, the travel speed
of vane 7 when vane 7 collapses with cam ring 8 is high, because
the cross-sectional flow area A is excessive. Specifically, the
cross-sectional flow area A0 of the first comparative example is
larger than the upper limit Amax of the region where noise level is
in the allowable range. Since the discharge-side back pressure port
46 of the first comparative example is provided with no such
throttling portion (beginning end portion 462 according to the
first embodiment), working fluid flows rapidly into back pressure
chamber br. Accordingly, when vane 7 contacts the inside peripheral
surface 80 of cam ring 8 after passing through the terminal end
point B, the speed V of vane 7 is high. As a result, the noise due
to contact or collapse of vane 7 is out of the allowable range.
[0068] As shown in FIG. 11, discharge-side back pressure port 46
according to the second comparative example has a beginning end
point c2 that is substantially identical to the beginning end point
c according to the first embodiment, where the distance L2 between
the beginning end point c2 of discharge-side back pressure port 46
and the terminal end point B of suction port 43 is substantially
equal to the distance L0 according to the first embodiment, and
smaller than upper limit value Lmax of the desirable range
(L2.apprxeq.L0<Lmax). Moreover, the cross-sectional flow area A
of discharge-side back pressure port 46 in the suction region RE1
is the same as that of back pressure port main section 468
according to the first embodiment, and equal to a value A0 that is
much larger than the upper limit Amax of the desirable range
(A0>>Amax).
[0069] In the second comparative example, the amount of working
fluid supplied to back pressure chamber br for vane 7 that is
entering the first closing region RE3 is sufficient to prevent the
vane through flow. However, vane 7 moves into sliding contact with
cam ring 8 in earlier timing than in the first embodiment. This is
because the cross-sectional flow area A of discharge-side back
pressure port 46 of the second comparative example is larger than
that of the first embodiment, so that the fluid quantity .intg.Q of
working fluid supplied to back pressure chamber br exceeds the
amount corresponding to the clearance between vane 7 and cam ring 8
(the amount for eliminating the clearance), when the rotor rotation
direction side surface of vane 7 has traveled from the beginning
end point c2 to a point F which is behind the point for the first
embodiment that is a distance L** ahead of the beginning end point
c2. As a result, the region where the distal end portion 70 of vane
7 is unnecessarily pressed on the inside peripheral surface 80 of
cam ring 8 before passing through the terminal end point B, is
larger than in the first embodiment, so that the loss torque is
larger, but within the desirable range indicated by hatching
pattern in FIG. 9.
[0070] On the other hand, in the second comparative example, the
speed of vane 7 when vane 7 collapses with cam ring 8 is high,
because the discharge-side back pressure port 46 of the first
comparative example is provided with no such throttling portion
(beginning end portion 462 according to the first embodiment) so
that the cross-sectional flow area A is excessive. Specifically,
the cross-sectional flow area A0 of the first comparative example
is larger than the upper limit Amax of the region where noise level
is in the allowable range. Accordingly, as in the first comparative
example, when vane 7 contacts the inside peripheral surface 80 of
cam ring 8 after passing through the terminal end point B, the
speed V of vane 7 is high. As a result, the noise due to collapse
of vane 7 is out of the allowable range.
[0071] In contrast, in the first embodiment, the cross-sectional
flow area A of the beginning end portion 462 of discharge-side back
pressure port 46 in the suction region RE1 and the distance L are
set in the region indicated by hatching pattern in FIG. 9, so as to
simultaneously optimize the sealing effect, the loss torque, and
the noise level, in consideration of the relationship shown in FIG.
9 between those parameters. Accordingly, it is possible to prevent
the vane through flow, suppress the pulsation and noise, and
suppress adverse effects on the pump efficiency and startability.
Moreover, it is possible to reduce the region where vane 7 is
unnecessarily pressed on cam ring 8, and thereby reduce the power
loss. Still moreover, it is possible to prevent working fluid from
rapidly flowing into back pressure chamber br for vane 7, and
thereby further suppress the occurrence of noise. These
advantageous effects are more significant, especially when in a low
temperature condition where the viscosity of working fluid is
relatively high, or when in a drive mode where the low speed region
of the internal combustion engine is frequently used.
Advantageous Effects by First Embodiment
[0072] The following summarizes the advantageous effects produced
by the pump 1 according to the first embodiment.
[0073] <1> A vane pump (1) comprises: a rotor (6) adapted to
be rotated by a drive shaft (5), the rotor (6) including a
plurality of slots (61) at an outside periphery (60) of the rotor
(6); a plurality of vanes (7) mounted in corresponding ones of the
slots (61), and adapted to project from, and travel inwards and
outwards of the corresponding slots (61); a cam ring (8) adapted to
be eccentric with respect to the rotor (6), the cam ring (8)
surrounding the rotor (6); and a plate (first or second plate 41 or
42) arranged to face an axial end of the rotor (6), and define a
plurality of pump chambers (r) in cooperation with the rotor (6),
the vanes (7), and the cam ring (8), wherein the plate (first plate
41) includes at a side facing the rotor (6): a suction port (43)
opened in a suction region in which each pump chamber (r) gradually
expands while moving along with rotation of the rotor (6); a
discharge port (44) opened in a discharge region in which each pump
chamber (r) gradually contracts while moving along with rotation of
the rotor (6); a first back pressure port (suction-side back
pressure port 45) arranged to receive a suction-side fluid
pressure, and hydraulically communicate with a proximal end portion
(610, or back pressure chamber br) of at least a first one of the
slots (61) corresponding to a first one of the vanes (7) positioned
in the suction region; and a second back pressure port (46)
arranged to hydraulically communicate with a proximal end portion
(610, or back pressure chamber br) of at least a second one of the
slots (61) corresponding to a second one of the vanes (7) whose
distal end portion (70) is positioned at a terminal end portion
(close to terminal end point B) of the suction port (43), wherein
the second back pressure port (46) includes: a first portion (back
pressure port main section 468) arranged to receive a
discharge-side fluid pressure; and a throttling portion (beginning
end portion 462) arranged to restrict a flow of fluid between the
first portion (back pressure port main section 468) and the
proximal end portion (610, or back pressure chamber br) of the
second slot (61). This construction is effective for reducing the
power loss, enhancing the operation of the pump at low temperature,
and reducing the noise level.
[0074] <2> In the vane pump according to item <1>, the
throttling portion (beginning end portion 462) has a
cross-sectional flow area (A) that is substantially constant as
followed in a direction of rotation of the rotor (6). This feature
makes it possible to easily set the speed V of vane 7 when vane 7
moves into contact with cam ring 8, by adjusting the depth of the
throttling portion (beginning end portion 462).
<3> In the vane pump according to item <1> or
<2>: the second vane (7) is behind in a direction of rotation
of the rotor (6) and adjacent to a third one of the vanes (7) whose
distal end portion (70) is positioned between a terminal end
(terminal end point B) of the suction port (43) and a beginning end
(beginning end point C) of the discharge port (44); and the second
back pressure port (discharge-side back pressure port 46) is
arranged to supply the proximal end portion (610, or back pressure
chamber br) of the second slot (61) at least with an amount of
working fluid, during a period before the second vane (7) passes
through the terminal end (B) of the suction port (43) after the
proximal end portion (610, br) of the second slot (61) starts to
hydraulically communicate with the second back pressure port (46),
wherein the amount of working fluid is sufficient to bring the
distal end portion (70) of the second vane (7) into contact with an
inside peripheral surface (80) of the cam ring (8). This feature is
effective for enhancing the operation of the pump at low
temperature by effectively preventing the vane through flow.
Second Embodiment
[0075] In the first embodiment, the throttling portion (beginning
end portion 462) has a rectangular cross-section with a
substantially constant depth and a substantially constant width as
viewed and followed in the rotor rotation direction RD1, so that
the cross-sectional flow area A is substantially constant as
followed in the rotor rotation direction RD1. Alternatively, the
shape of the throttling portion (beginning end portion 462) may be
modified so that the cross-sectional flow area A changes as
followed in the rotor rotation direction RD1, in consideration of
the viscosity of working fluid, the density of working fluid, and
other factors, as shown in FIGS. 12A to 15. In the examples shown
in FIGS. 12A to 15, the edge 467 of back pressure port main section
468 is rectangular, not semicircular as in the first embodiment.
The other parts are the same as in the first embodiment, and
accordingly, description of the other parts is omitted.
[0076] In the examples shown in FIGS. 12A to 15, the fluid quantity
.intg.Q is set by combination of the cross-sectional flow area A
and distance L of the throttling portion (beginning end portion
462), so as to prevent the vane through flow, and the unnecessary
pressing of vane 7, as in the first embodiment. Since the
cross-sectional flow area of beginning end portion 462 is not
constant as followed in the rotor rotation direction RD1 as in the
first embodiment, the average of the cross-sectional flow area of
beginning end portion 462, which is averaged in the rotor rotation
direction RD1, may be used as the cross-sectional flow area A to
set the fluid quantity .intg.Q.
[0077] In the second embodiment, beginning end portion 462 is
formed so that the cross-sectional flow area of beginning end
portion 462 increases as followed in the rotor rotation direction
RD1. This feature makes it possible to set the ejecting speed of
vane 7 that is passing through the beginning end portion 462 as
follows. FIGS. 12A to 12D are plan views of beginning end portions
462 according to variations of the second embodiment in the z-axis
direction. In the examples shown in FIGS. 12A to 12B, the width of
beginning end portion 462 in the rotor radial direction is set to
increase as followed in the rotor rotation direction RD1, whereas
the bottom (negative z side surface) of beginning end portion 462
is substantially flat, and the depth of beginning end portion 462
is substantially constant, as in the first embodiment. However, in
consideration of the fact that the width (average width) of
beginning end portion 462 is smaller than that in the first
embodiment, the depth of beginning end portion 462 is set larger
than that in the first embodiment, so that the cross-sectional flow
area is not reduced. The shape of the bottom may be modified
arbitrarily.
[0078] In the example of FIG. 12A, the shape of beginning end
portion 462 as viewed in the z-axis direction is substantially in
the form of an acute angle triangle whose width gradually increases
as followed in the rotor rotation direction RD1 at a predetermined
substantially constant rate to a predetermined value that is
smaller than the width of back pressure port main section 468.
Accordingly, while vane 7 passes through beginning end portion 462,
the cross-sectional flow area of a passage to back pressure chamber
br gradually increases from zero to a predetermined value at a
substantially constant rate. As a result, the flow rate Q of
working fluid supplied to back pressure chamber br gradually
increases from zero, so that the ejecting speed of vane 7 is low at
first, and gradually increases at a substantially constant rate.
The shape of FIG. 12A is desirable, when such characteristics are
desired.
[0079] In the example of FIG. 12B, the shape of beginning end
portion 462 as viewed in the z-axis direction is substantially in
the form of a trapezoid whose width gradually increases as followed
in the rotor rotation direction RD1 at a predetermined
substantially constant rate from a predetermined smaller value to a
predetermined larger value that is smaller than the width of back
pressure port main section 468. Accordingly, while vane 7 passes
through beginning end portion 462, the cross-sectional flow area of
a passage to back pressure chamber br gradually increases from a
predetermined smaller value to a predetermined larger value at a
substantially constant rate. As a result, the flow rate Q of
working fluid supplied to back pressure chamber br is above zero,
at first, and then gradually increases, so that the ejecting speed
of vane 7 is moderate at first, and then gradually increases at a
substantially constant rate. This feature serves to shorten the
period in which vane 7 moves into contact with the inside
peripheral surface 80 of cam ring 8, as compared to the shape of
FIG. 12A. The shape of FIG. 12B is desirable, when such
characteristics are desired.
[0080] In the example of FIG. 12C, the shape of beginning end
portion 462 as viewed in the z-axis direction is substantially in
the form of a semi-ellipse whose width gradually increases as
followed in the rotor rotation direction RD1 from zero to a
predetermined value that is smaller than the width of back pressure
port main section 468. The rate of increase is large at first, and
then decreases. Accordingly, while vane 7 passes through beginning
end portion 462, the cross-sectional flow area of a passage to back
pressure chamber br gradually increases from zero to a
predetermined value at the rate that is large at first, and then
decreases. As a result, the flow rate Q of working fluid supplied
to back pressure chamber br rapidly increases from zero, and then
slowly increases, so that the ejecting speed of vane 7 rapidly
increases at first, and then slowly increases. This feature serves
to shorten the period in which vane 7 moves into contact with the
inside peripheral surface 80 of cam ring 8, similar to the shape of
FIG. 12B. The shape of FIG. 12C is desirable, when such
characteristics are desired.
[0081] In the example of FIG. 12D, the shape of beginning end
portion 462 as viewed in the z-axis direction is a combination of
the rectangular shape according to the first embodiment and the
trapezoidal shape of FIG. 12B, whose width is constant at first,
and then gradually increases as followed in the rotor rotation
direction RD1 at a predetermined substantially constant rate to a
predetermined value that is smaller than the width of back pressure
port main section 468. Accordingly, while vane 7 passes through
beginning end portion 462, the cross-sectional flow area of a
passage to back pressure chamber br is constant at first, and then
gradually increases at a substantially constant rate. As a result,
the flow rate Q of working fluid supplied to back pressure chamber
br is constant, at first, and then gradually increases, so that the
ejecting speed of vane 7 is constant at first, and then gradually
increases at a substantially constant rate. The ejecting speed of
vane 7 does not change significantly as in the examples shown in
FIGS. 12A to 12C. As compared to the example where the beginning
end portion 462 is rectangular, the pressing of vane 7 to cam ring
8 is ensured. The shape of FIG. 12D is desirable, when such
characteristics are desired.
[0082] FIGS. 13A and 13B are side sectional views of the beginning
end portions 462 according to other variations of the second
embodiment. In these variations, the bottom of beginning end
portion 462 is inclined as followed in the rotor rotation direction
RD1 so that the depth of beginning end portion 462 in the z-axis
direction gradually increases as followed in the rotor rotation
direction RD1. The width of beginning end portion 462 in the rotor
radial direction is substantially constant as followed in the rotor
rotation direction RD1.
[0083] In the example of FIG. 13A, the bottom of beginning end
portion 462 is composed of inclined surfaces and a level surface,
specifically, composed of a first inclined surface where the depth
of beginning end portion 462 gradually increases at a substantially
constant rate from zero to a predetermined value as followed in the
rotor rotation direction RD1, an intermediate level surface where
the depth of beginning end portion 462 is constant as viewed in the
rotor rotation direction RD1, and a second inclined surface where
the depth of beginning end portion 462 gradually increases at a
substantially constant rate from the first value to a second
predetermined value, wherein the second inclined surface is
connected to the back pressure port main section 468. The
inclination of the first inclined surface is larger than that of
the second inclined surface. Accordingly, while vane 7 passes
through beginning end portion 462, the cross-sectional flow area of
a passage to back pressure chamber br gradually increases from zero
to a predetermined value at a constant rate, and then becomes
constant, and then gradually increases at a substantially constant
and slower rate. As a result, the flow rate Q of working fluid
supplied to back pressure chamber br changes similarly, so that the
ejecting speed of vane 7 relatively rapidly increases, and then
becomes constant, and then relatively slowly increases. This is
effective for reducing the acceleration of vane 7 temporarily,
while ensuring that vane 7 is pressed on the inside peripheral
surface 80 of cam ring 8. The shape of FIG. 13A is desirable, when
such characteristics are desired. The shape of beginning end
portion 462 may be modified so that the inclination of the first
inclined surface is smaller than that of the second inclined
surface.
[0084] In the example of FIG. 13B, the bottom of beginning end
portion 462 is composed of an inclined surface, so that the depth
of beginning end portion 462 gradually increases at a substantially
constant rate from zero to a predetermined value that is smaller
than the depth of back pressure port main section 468. Accordingly,
while vane 7 passes through beginning end portion 462, the
cross-sectional flow area of a passage to back pressure chamber br
gradually increases from zero to a predetermined value at a
constant rate. As a result, the flow rate Q of working fluid
supplied to back pressure chamber br changes similarly, so that the
ejecting speed of vane 7 is low at first, and gradually accelerated
to increase at a substantially constant rate. The shape of FIG. 13B
is desirable, when such characteristics are desired. The shapes of
FIGS. 12A to 12E and the shapes of FIGS. 13A and 13B may be
combined so as to achieve a desirable set of characteristics.
[0085] In the second embodiment, the feature that beginning end
portion 462 is formed so that the cross-sectional flow area of
beginning end portion 462 gradually increases as followed in the
rotor rotation direction RD1, is effective for reliably pressing
the vane 7 on the inside peripheral surface 80 of cam ring 8. In
other words, the beginning end portion 462 according to the second
embodiment serves as a part (from the beginning end point e to the
terminal end point B) of back pressure port main section 468
according to the first embodiment, i.e. serves to supply a large
amount of working fluid to reliably prevent the vane through flow,
because beginning end portion 462 according to the second
embodiment has a larger cross-sectional flow area than the
beginning end portion 462 according to the first embodiment.
Accordingly, in the second embodiment, the angular position of the
beginning end point e of back pressure port main section 468 may be
modified to be identical to the angular position of the terminal
end point B of suction port 43, and the distance from the beginning
end point c of beginning end portion 462 to the beginning end point
e of back pressure port main section 468 may be set equal to about
one pitch (L0).
Advantageous Effect by Second Embodiment
[0086] In the second embodiment, the throttling portion (beginning
end portion 462) has a cross-sectional flow area (A) that increases
as followed in a direction of rotation of the rotor (6). This
produces an advantageous effect of further preventing the vane
through flow, in addition to the effects according to the first
embodiment.
Third Embodiment
[0087] In the third embodiment, beginning end portion 462 is formed
so that the cross-sectional flow area of beginning end portion 462
gradually decreases as followed in the rotor rotation direction
RD1. This feature makes it possible to set the ejecting speed of
vane 7 when vane 7 is passing through the beginning end portion
462. FIGS. 14A to 14D are plan views of beginning end portions 462
according to variations of the third embodiment. In these examples,
the width of beginning end portion 462 in the rotor radial
direction is set to decrease in the rotor rotation direction RD1.
The bottom shape and depth of beginning end portion 462 are the
same as in the second embodiment shown in FIGS. 12A to 12E.
[0088] In the example of FIG. 14A, the shape of beginning end
portion 462 as viewed in the z-axis direction is a combination of a
substantially circular end portion and a substantially rectangular
portion, where the width of beginning end portion 462 in the rotor
radial direction (cross-sectional flow area of passage to back
pressure chamber br) rapidly increases and decreases in the
circular end portion, and then becomes constant in the rectangular
portion, as followed in the rotor rotation direction RD1.
Accordingly, while vane 7 passes through beginning end portion 462,
the flow rate Q of working fluid supplied to back pressure chamber
br changes similarly as the width of beginning end portion 462, so
that the ejecting speed of vane 7 increases and decreases rapidly
at first, and then becomes substantially constant. The shape of
FIG. 14A is desirable, when such characteristics are desired.
[0089] In the example of FIG. 14B, the shape of beginning end
portion 462 as viewed in the z-axis direction is substantially in
the form of a triangle that is directed opposite to the triangle of
FIG. 12A, where the width of beginning end portion 462 in the rotor
radial direction (cross-sectional flow area of passage to back
pressure chamber br) gradually decreases from a predetermined
value, which is smaller than that of back pressure port main
section 468, to zero at a substantially constant rate as followed
in the rotor rotation direction RD1. Accordingly, while vane 7
passes through beginning end portion 462, the flow rate Q of
working fluid supplied to back pressure chamber br changes
similarly as the width of beginning end portion 462, so that the
ejecting speed of vane 7 is relatively fast at first, and then
decreases at a substantially constant rate to a value close to
zero. The shape of FIG. 14B is desirable, when such characteristics
are desired.
[0090] In the example of FIG. 14C, the shape of beginning end
portion 462 as viewed in the z-axis direction is substantially in
the form of a semi-ellipse that is directed opposite to the shape
of FIG. 12C, where the width of beginning end portion 462 in the
rotor radial direction (cross-sectional flow area of passage to
back pressure chamber br) gradually decreases from a predetermined
value, which is smaller than that of back pressure port main
section 468, to zero as followed in the rotor rotation is direction
RD1. The rate of decrease is relatively small at first, and is
relatively large at last. Accordingly, while vane 7 passes through
beginning end portion 462, the flow rate Q of working fluid
supplied to back pressure chamber br changes similarly as the width
of beginning end portion 462, so that the ejecting speed of vane 7
is relatively fast at first, and decreases slowly at first, and
then decreases rapidly. The shape of FIG. 14C is desirable, when
such characteristics are desired.
[0091] In the example of FIG. 14D, the shape of beginning end
portion 462 as viewed in the z-axis direction is substantially in
the form of a combination of a trapezoid and a rectangular that is
directed opposite to the shape of FIG. 12D, where the width of
beginning end portion 462 in the rotor radial direction
(cross-sectional flow area of passage to back pressure chamber br)
gradually decreases from a predetermined value, which is smaller
than that of back pressure port main section 468, to zero at a
substantially constant rate, and then becomes substantially
constant, as followed in the rotor rotation direction RD1.
Accordingly, while vane 7 passes through beginning end portion 462,
the flow rate Q of working fluid supplied to back pressure chamber
br changes similarly as the width of beginning end portion 462, so
that the ejecting speed of vane 7 is relatively fast at first, and
then decreases at a substantially constant rate, and then becomes
constant. The shape of FIG. 14D is desirable, when such
characteristics are desired.
[0092] FIG. 15 shows another variation of the third embodiment,
where the bottom of beginning end portion 462 is inclined so that
the depth of beginning end portion 462 in the z-axis direction
gradually decreases as followed in the rotor rotation direction
RD1. The width of beginning end portion 462 in the rotor radial
direction is substantially constant as followed in the rotor
rotation direction RD1. Specifically, the depth of beginning end
portion 462 gradually decreases at a substantially constant rate
from a predetermined value (somewhat smaller than the depth of back
pressure port main section 468) to a value close to zero, as
followed in the rotor rotation direction RD1. Accordingly, while
vane 7 passes through beginning end portion 462, the
cross-sectional flow area of passage to back pressure chamber br
gradually decreases from a predetermined value to a value close to
zero, so that the flow rate Q of working fluid supplied to back
pressure chamber br changes similarly, and so that the ejecting
speed of vane 7 is relatively fast at first, and then decreases at
a substantially constant rate to a value close to zero. The shape
of FIG. 15 is desirable, when such characteristics are desired. The
shape of beginning end portion 462 may be modified similarly as in
the second embodiment shown in FIG. 13A, so that the inclined
surface is formed with an intermediate level surface, so as to
reduce the deceleration of vane 7 temporarily. The shapes of FIGS.
14A to 14E and the shape of FIG. 15 may be combined to achieve a
desirable set of characteristics.
[0093] In the third embodiment, at the early stage of the ejecting
movement of vane 7, most of the amount of working fluid required
for vane 7 to contact the cam ring 8 (for vane 7 to travel the
initial clearance between vane 7 and cam ring 8) is supplied to
back pressure chamber br. This makes it possible to shorten the
length of beginning end portion 462 in the rotor rotation direction
RD1 (distance L). On the other hand, the feature that the ejecting
speed of vane 7 is reduced at the final stage of the ejecting
movement of vane 7 where vane 7 moves into contact with cam ring 8,
serves to effectively reduce the noise due to contact of vane 7.
Beginning end portion 462 according to the third embodiment is
formed so that the cross-sectional flow area of beginning end
portion 462 gradually decreases as followed in the rotor rotation
direction RD1, and thereby fluid communication between the
beginning end portion 462 and back pressure port main section 468
is restricted, as compared to the first and second embodiments.
Accordingly, even if supply of working fluid from beginning end
portion 462 to back pressure chamber br for vane 7 is started so
that the pressure in beginning end portion 462 rapidly falls, the
pressure in back pressure port main section 468 is prevented form
rapidly changing (decreasing), because the flow rate of working
fluid leaking from back pressure port main section 468 to beginning
end portion 462 for replenishing the amount supplied to back
pressure chamber br is restricted. As a result, as in the first
embodiment, beginning end portion 462 according to the third
embodiment also serves to prevent the pressure in back pressure
port main section 468 from fluctuating or pulsating, and thereby
stabilize the pressure applied to vane 7 from back pressure chamber
br that is hydraulically connected to back pressure port main
section 468.
Advantageous Effect by Third Embodiment
[0094] In the third embodiment, the throttling portion (beginning
end portion 462) has a cross-sectional flow area (A) that decreases
as followed in a direction of rotation of the rotor (6). This
feature produces an advantageous effect of enhancing the noise
reduction effect, in addition to the effects according to the first
embodiment.
[0095] The first to third embodiments may be modified as follows.
Pump 1 may use fluid other than oils (ATF) as working fluid.
Although the vane 7 (or slot 61) is formed to extend in the rotor
radial direction, the vane 7 (or slot 61) may be formed to extend
with inclination with respect to the rotor radial direction.
[0096] The portion of discharge-side back pressure port 46 in
suction region RE1 (the portion including the beginning end portion
462) is provided separately from the portion of discharge-side back
pressure port 46 in the discharge region RE2. In other words,
discharge-side back pressure port 46 may be implemented by: a first
port arranged to receive a discharge-side fluid pressure, and
hydraulically communicate with a proximal end portion (610, back
pressure chamber br) of at least a first one of slots (61)
corresponding to a first one of vanes (7) positioned in a discharge
region (RE2); and a second port arranged to receive a
discharge-side fluid pressure, and hydraulically communicate with a
proximal end portion (610, back pressure chamber br) of at least a
second one of slots (61) corresponding to a second one of vanes (7)
whose distal end portion (70) is positioned at a terminal end
portion (B) of a suction port (43).
[0097] The entire contents of Japanese Patent Application
2010-000528 filed Jan. 5, 2010 and Japanese Patent Application
2010-062861 filed Mar. 18, 2010 are incorporated herein by
reference.
[0098] Although the invention has been described above by reference
to certain embodiments of the invention, the invention is not
limited to the embodiments described above. Modifications and
variations of the embodiments described above will occur to those
skilled in the art in light of the above teachings. The scope of
the invention is defined with reference to the following
claims.
* * * * *