U.S. patent application number 10/990394 was filed with the patent office on 2005-08-04 for expander.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Ishikawa, Seiichiro, Saito, Bunichi.
Application Number | 20050169770 10/990394 |
Document ID | / |
Family ID | 34719353 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050169770 |
Kind Code |
A1 |
Ishikawa, Seiichiro ; et
al. |
August 4, 2005 |
Expander
Abstract
An expander includes a piston formed from a top portion, a skirt
portion, and a land portion. A hollow heat-insulating space is
formed within the piston making heat transfer difficult. It is
possible to maintain the land portion, which is in contact with the
high temperature, high pressure steam in an expansion chamber, at a
high temperature, thereby minimizing any decrease in the
temperature of the high temperature, high pressure steam to prevent
any decrease in the efficiency of the expander. Any increase in the
temperature of the skirt portion, which is in sliding contact with
a cylinder sleeve, is suppressed to ensure the performance of the
lubrication. Piston rings are provided on the land portion to
separate the high temperature, high pressure steam in the expansion
chamber from the oil in the skirt portion for preventing the oil
and the high temperature, high pressure steam from being mixed
together.
Inventors: |
Ishikawa, Seiichiro;
(Wako-shi, JP) ; Saito, Bunichi; (Wako-shi,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
34719353 |
Appl. No.: |
10/990394 |
Filed: |
November 18, 2004 |
Current U.S.
Class: |
417/269 ;
417/373; 417/375; 417/521 |
Current CPC
Class: |
F04B 27/0834
20130101 |
Class at
Publication: |
417/269 ;
417/373; 417/521; 417/375 |
International
Class: |
F04B 041/04; F04B
001/12; F04B 027/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2003 |
JP |
2003-392757 |
Claims
What is claimed is:
1. A piston for use in a rotor comprising: an axial piston cylinder
group arranged in the rotor for surrounding an axis of the rotor,
said rotor being adapted to be rotated by supplying
high-temperature, high-pressure steam to an expansion chamber
defined between a piston and a cylinder sleeve of the axial piston
cylinder group with sliding sections of the piston and the cylinder
sleeve being lubricated with oil; a land portion formed on said
piston of the axial piston cylinder group, said land portion being
exposed to the high temperature, high pressure steam in the
expansion chamber; a top portion formed on said piston adapted to
abut against a swash plate; a skirt portion formed on said piston
that is disposed between the land portion and the top portion for
sliding against the cylinder sleeve; a hollow heat-insulating space
formed within the piston; and a piston ring provided on the land
portion, the piston ring separating high temperature, high pressure
steam in the expansion chamber from oil in the skirt portion.
2. The piston for use in a rotor according to claim 1, wherein a
plurality of piston rings are provided along the longitudinal
direction of the piston.
3. The piston for use in a rotor according to claim 2, wherein a
depression is provided between the plurality of piston rings.
4. The piston for use in a rotor according to claim 1, wherein an
oil channel is provided in at least one of an outer peripheral face
of the skirt portion of the piston and an inner peripheral face of
the cylinder sleeve.
5. The piston for use in a rotor according to claim 1, wherein the
top portion includes a spherical portion adapted to abut against
the swash plate.
6. The piston for use in a rotor according to claim 1, wherein the
heat-insulating space is evacuated.
7. The piston for use in a rotor according to claim 1, wherein the
heat-insulating space includes air sealed therein.
8. The piston for use in a rotor according to claim 1, wherein a
ceramic selected from the group consisting of TiN and CrN is formed
on an outer surface of said piston ring.
9. The piston for use in a rotor according to claim 1, and further
including an oil channel formed in a mid-section of the skirt
portion of said piston.
10. The piston for use in a rotor according to claim 9, wherein a
plurality of spiral oil channels are formed in the mid-section of
the skirt portion of said piston.
11. An expander comprising: a casing; a rotor rotatably supported
in the casing; and an axial piston cylinder group arranged in the
rotor so as to surround an axis of the rotor; the rotor being
rotated by supplying high-temperature, high-pressure steam to an
expansion chamber defined between a piston and a cylinder sleeve of
the axial piston cylinder group with sliding sections of the piston
and the cylinder sleeve being lubricated with oil; said piston of
the axial piston cylinder group including a land portion that is
exposed to the high temperature, high pressure steam in the
expansion chamber, a top portion that abuts against a swash plate,
and a skirt portion that is disposed between the land portion and
the top portion and slides against the cylinder sleeve; a hollow
heat-insulating space formed within the piston; and a piston ring
provided on the land portion, the piston ring separating high
temperature, high pressure steam in the expansion chamber from oil
in the skirt portion.
12. The expander according to claim 11, wherein a plurality of
piston rings are provided along the longitudinal direction of the
piston.
13. The expander according to claim 12, wherein a depression is
provided between the plurality of piston rings.
14. The expander according to claim 11, wherein an oil channel is
provided in at least one of an outer peripheral face of the skirt
portion of the piston and an inner peripheral face of the cylinder
sleeve.
15. The expander according to claim 11, wherein the top portion
includes a spherical portion for abutting against the swash
plate.
16. The expander according to claim 11, wherein the heat-insulating
space is evacuated.
17. The expander according to claim 11, wherein the heat-insulating
space includes a air sealed therein.
18. The expander according to claim 11, wherein a ceramic selected
from the group consisting of TiN and CrN is formed on an outer
surface of said piston ring.
19. The expander according to claim 11, and further including an
oil channel formed in a mid-section of the skirt portion of said
piston.
20. The expander according to claim 19, wherein a plurality of
spiral oil channels are formed in the mid-section of the skirt
portion of said piston.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 USC 119 to
Japanese Patent Application No. 2003-392757 filed on Nov. 21, 2003
the entire contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an expander that includes a
casing, a rotor rotatably supported in the casing, and an axial
piston cylinder group arranged in the rotor so as to surround an
axis of the rotor. The rotor is rotated by supplying
high-temperature, high-pressure steam to an expansion chamber
defined between a piston and a cylinder sleeve of the axial piston
cylinder group. Sliding sections of the piston and the cylinder
sleeve are lubricated with oil.
[0004] 2. Description of Related Art
[0005] An expander is known as disclosed in Japanese Patent
Application Laid-open No. 2002-256805. This expander includes a
first axial piston cylinder group arranged on the radially inner
side and a second axial piston cylinder group arranged on the
radially outer side. A piston of the first axial piston cylinder
group has a solid structure with one end facing an expansion
chamber, to which high temperature, high pressure steam is
supplied. The other end abuts against a swash plate, while sliding
sections of the piston and a cylinder sleeve are lubricated with
oil.
[0006] In a piston of an axial piston cylinder group of an
expander, it is desirable that an end thereof facing an expansion
chamber is maintained at a high temperature so that the high
temperature, high pressure steam supplied to the expansion chamber
does not decrease. However, it is desirable for sliding sections of
the piston and a cylinder sleeve to be maintained at a low
temperature so as to ensure proper lubrication. However, if the
piston has a solid structure, heat is quickly transmitted from the
high temperature side to the low temperature side, so that the
temperature of the end on the expansion chamber side, which should
be maintained at a high temperature, easily decreases. In addition,
the temperature of the sliding sections of the piston and the
cylinder sleeve, which should be maintained at a low temperature,
easily increases.
SUMMARY OF THE INVENTION
[0007] The present invention has been developed to eliminate the
above-mentioned circumstances. It is an object of the present
invention to suppress the escape, via a piston, of the heat from
the high temperature, high pressure steam supplied to an expansion
chamber of an axial piston cylinder group of an expander, for
ensuring that the lubrication performance is in sliding sections of
the piston and a cylinder sleeve.
[0008] In order to achieve the above-mentioned object, in
accordance with a first aspect of the present invention, there is
proposed an expander that includes a casing, a rotor rotatably
supported in the casing, and an axial piston cylinder group
arranged in the rotor so as to surround an axis of the rotor. The
rotor is rotated by supplying high-temperature, high-pressure steam
to an expansion chamber defined between a piston and a cylinder
sleeve of the axial piston cylinder group, with sliding sections of
the piston and the cylinder sleeve being lubricated with oil. The
piston of the axial piston cylinder group has a land portion that
is exposed to the high temperature, high pressure steam in the
expansion chamber with a top portion that abuts against a swash
plate, and a skirt portion that is disposed between the land
portion and the top portion and slides against the cylinder sleeve.
The piston has a hollow heat-insulating space formed therewithin.
The land portion has a piston ring provided thereon with the piston
ring separating the high temperature, high pressure steam in the
expansion chamber from oil in the skirt portion.
[0009] Furthermore, in accordance with a second aspect of the
present invention, a plurality of piston rings are provided along
the longitudinal direction of the piston.
[0010] Moreover, in accordance with a third aspect of the present
invention, a depression is provided between the plurality of piston
rings.
[0011] Furthermore, in accordance with a fourth aspect of the
present invention, an oil channel is provided in at least one of an
outer peripheral face of the skirt portion of the piston and an
inner peripheral face of the cylinder sleeve.
[0012] A second land channel 63e of an embodiment corresponds to
the depression of the present invention, and a top ring 65 and a
second ring 66 of the embodiment correspond to the piston rings of
the present invention.
[0013] In accordance with the arrangement of the first aspect, the
piston of the axial piston cylinder group is formed from the land
portion exposed to the high temperature, high pressure steam in the
expansion chamber with the top portion abutting against the swash
plate, and the skirt portion disposed between the land portion and
the top portion and sliding against the cylinder sleeve. A hollow
heat-insulating space is formed therewithin to make heat transfer
difficult. Therefore, it is possible to maintain the land portion,
which is in contact with the high temperature, high pressure steam
supplied to the expansion chamber, at a high temperature, thereby
minimizing any decrease in the temperature of the high temperature,
high pressure steam to prevent any decrease in efficiency of the
expander. Also, it is possible to suppress any increase in the
temperature of the skirt portion, which is in sliding contact with
the cylinder sleeve, to ensure lubrication performance. Moreover,
since the piston ring provided on the land portion separates the
high temperature, high pressure steam in the expansion chamber from
the oil in the skirt portion, it is possible to prevent the oil
from entering the expansion chamber side and cooling the land
portion, and to prevent the high temperature, high pressure steam
from entering the skirt portion side and degrading the lubricating
effect of the oil.
[0014] In accordance with the arrangement of the second aspect,
since the plurality of piston rings are provided along the
longitudinal direction of the piston, not only is it possible and
more reliably to prevent the high temperature, high pressure steam
from blowing past the land portion to the skirt portion, it is also
possible to effectively prevent the oil and the high temperature,
high pressure steam from mixing together by imparting the function
of an oil ring to the piston ring which is on the side far from the
expansion chamber.
[0015] In accordance with the arrangement of the third aspect, the
depression is provided between the plurality of piston rings.
Therefore, even if some of the high temperature, high pressure
steam blows past the piston ring on the expansion chamber side, it
is possible to prevent, by the effect of the volume of the
depression, a pressure difference between the expansion chamber
side and the depression side of the piston ring from abruptly
decreasing, to thus urge radially outwardly the piston ring by the
pressure difference to prevent the piston ring from floating above
an inner peripheral face of the cylinder sleeve or a piston ring
channel face, thereby ensuring sealing performance.
[0016] In accordance with the arrangement of the fourth aspect,
since the oil channel is provided in at least one of the outer
peripheral face of the skirt portion of the piston and the inner
peripheral face of the cylinder sleeve, it is possible to retain
oil in this oil channel to enhance the lubrication performance
between the sliding surfaces of the piston and the cylinder
sleeve.
[0017] A mode for carrying out the present invention is explained
below with reference to an embodiment of the present invention
shown in the attached drawings.
[0018] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings, which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0020] FIG. 1 is a vertical sectional view of an expander;
[0021] FIG. 2 is a sectional view along line 2-2 in FIG. 1;
[0022] FIG. 3 is a view taken along line 3-3 in FIG. 1;
[0023] FIG. 4 is an enlarged view of part 4 in FIG. 1;
[0024] FIG. 5 is an exploded perspective view of a rotor;
[0025] FIG. 6 is a sectional view along line 6-6 in FIG. 4;
[0026] FIG. 7 is a sectional view along line 7-7 in FIG. 4; and
[0027] FIG. 8 is an enlarged view of part 8 in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] An expander E of this embodiment is used in, for example, a
Rankine cycle system. The expander E converts the thermal energy
and the pressure energy of the high-temperature, high-pressure
steam as a working medium into mechanical energy, and outputs the
energy. A casing 11 of the expander E is formed from a casing main
body 12, a front cover 15 joined via a seal 13 to a front opening
of the casing main body 12 by a plurality of bolts 14, a rear cover
18 joined via a seal 16 to a rear opening of the casing main body
12 by a plurality of bolts 17, and an oil pan 21 joined via a seal
19 to a lower opening of the casing main body 12 by a plurality of
bolts 20.
[0029] A rotor 22 is arranged rotatably around an axis L extending
in the fore-and-aft direction through the center of the casing 11.
The rotor 22 includes a front part supported by combined angular
bearings 23 provided in the front cover 15, and a rear part thereof
supported by a radial bearing 24 provided in the casing main body
12. A swash plate holder 28 is formed integrally with a rear face
of the front cover 15. A swash plate 31 is rotatably supported by
the swash plate holder 28 via an angular bearing 30. The axis of
the swash plate 31 is inclined relative to the axis L of the rotor
22, and the angle of inclination is fixed.
[0030] The rotor 22 includes an output shaft 32 supported in the
front cover 15 by the combined angular bearings 23 with three
sleeve support flanges 33, 34, and 35 being formed integrally with
a rear part of the output shaft 32 via cutouts 57 and 58 having
predetermined widths (see FIG. 4 and FIG. 8). A rotor head 38 is
joined by a plurality of bolts 37 to the rear sleeve support flange
35 via a metal gasket 36 and is supported in the casing main body
12 by the radial bearing 24. A heat-insulating cover 40 is fitted
over the three sleeve support flanges 33, 34, and 35 from the front
and joined to the front sleeve support flange 33 by a plurality of
bolts 39.
[0031] Sets of five sleeve support holes 33a, 34a, and 35a are
formed in the three sleeve support flanges 33, 34, and 35
respectively at intervals of 72.degree. around the axis L. Five
cylinder sleeves 41 are fitted into the sleeve support holes 33a,
34a, and 35a from the rear. A flange 41a is formed on the rear end
of each of the cylinder sleeves 41. An axial positioning is carried
out by abutting the flange 41a against the metal gasket 36 while
fitting the flange 41a into a step 35b formed in the sleeve support
holes 35a of the rear sleeve support flange 35 (see FIG. 8). A
piston 42 is slidably fitted within each of the cylinder sleeves 41
with the front end of the piston 42 abutting against a dimple 31 a
formed on the swash plate 31. A steam expansion chamber 43 is
defined between the rear end of the piston 42 and the rotor head
38.
[0032] A plate-shaped bearing holder 92 is superimposed on a front
face of the front cover 15 via a seal 91 and is fixed thereto by
means of bolts 93. A pump body 95 is superimposed on a front face
of the bearing holder 92 via a seal 94 and is fixed thereto by
means of bolts 96. The combined angular bearings 23 are held
between a step of the front cover 15 and the bearing holder 92,
thereby fixing them in the axis L direction.
[0033] A shim 97 having a predetermined thickness is held between
the inner race of the combined angular bearings 23 and a flange 32d
formed on the output shaft 32 supporting the combined angular
bearings 23. The inner race of the combined angular bearings 23 is
tightened by a nut 98 screwed around the outer periphery of the
output shaft 32. As a result, the output shaft 32 is positioned in
the axis L direction relative to the combined angular bearings 23,
that is, relative to the casing 11.
[0034] An oil passage 32a is formed so as to extend along the axis
L within the output shaft 32 which is integral with the rotor 22.
The front end of the oil passage 32a branches in a radial direction
and communicates with an annular channel 32b on the outer periphery
of the output shaft 32. An oil passage blocking member 45 is
screwed into the inner periphery of the oil passage 32a via a seal
44 at a position that is radially inside the middle sleeve support
flange 34 of the rotor 22. A plurality of oil holes 32c extend
radially outwardly from the oil passage 32a in the vicinity of the
oil passage blocking member 45 and open on the outer periphery of
the output shaft 32.
[0035] A trochoidal oil pump 49 is disposed between a recess 95a
provided in a front face of the pump body 95 and a pump cover 48
fixed via a seal 46 to the front face of the pump body 95 by a
plurality of bolts 47. The trochoidal oil pump 49 includes an outer
rotor 50 that is rotatably fitted in the recess 95a, and an inner
rotor 51 that is fixed to the outer periphery of the output shaft
32 and meshes with the outer rotor 50. An internal space of the oil
pan 21 communicates with an intake port 53 of the oil pump 49 via
an oil pipe 52 and an oil passage 95b of the pump body 95. A
discharge port 54 of the oil pump 49 communicates with the annular
channel 32b of the output shaft 32 via an oil passage 95c of the
pump body 95.
[0036] The structure of the piston 42 is now explained in detail
with reference to FIG. 5 to FIG. 8.
[0037] The piston 42 is formed from a top portion 61, a skirt
portion 62, and a land portion 63. The top portion 61 is a member
having a spherical portion 61a that abuts against a dimple 31a of
the swash plate 31, and is joined to the front end of the skirt
portion 62 by welding. The land portion 63 and the skirt portion 62
are formed integrally and have a large volume with an evacuated,
heat-insulating space 64 defined therewithin. An annular oil
channel 62a is formed by slightly decreasing the diameter in a
middle section of the skirt portion 62 which is slidably fitted
into an inner peripheral face of the cylinder sleeve 41. A
plurality of spiral channels 62b are formed in an outer peripheral
section of the skirt portion 62 on the front side relative to the
oil channel 62a.
[0038] The land portion 63 has a top land 63a on the expansion
chamber 43 side and a second land 63b on the skirt portion 62 side.
A top ring channel 63c is formed between the top land 63a and the
second land 63b with a top ring 65 being fitted around the top ring
channel 63c. A second ring channel 63d is formed between the second
land 63b and the skirt portion 62 with a second ring 66 being
fitted around the second ring channel 63d. A second land channel
63e is formed in a middle section of the second land 63b. The top
land 63a and the second land 63b have an outer diameter that is
slightly smaller than the outer diameter of the skirt portion 62. A
gap a is formed between outer peripheral faces of the top land 63a
and the second land 63b and the inner peripheral face of the
cylinder sleeve 41. Therefore, a thrust load in the peripheral
direction for rotating the rotor 22 is transmitted from the skirt
portion 62 to the cylinder sleeve 41 without passing through the
land portion 63.
[0039] A top ring 65, which is disposed at a position comparatively
close to the end of the piston 42 (on the order of 10% of the
diameter of the piston 42), has a rectangular cross-section with a
face that is in sliding contact with the cylinder sleeve 41 which
is a curved barrel face. A hard coating of a ceramic such as TiN or
CrN is formed on the surface thereof. The second ring 66 has a
rectangular cross-section (or an internal bevel cut cross-section);
a face that is in sliding contact with the cylinder sleeve 41 which
is a curved barrel face. A hard coating of a ceramic such as TiN or
CrN is formed on the surface thereof. For both the top ring 65 and
the second ring 66, the gap across the ends is set to be the
minimum gap at which the ends do not make contact when hot with the
thickness being set as small as possible (on the order of 3% of the
diameter of the piston 42), and the initial tension being set
fairly small.
[0040] Applying such a hard coating to the top ring 65 and the
second ring 66 decreases the amount of wear and the amount of
leakage of steam to be reduced. Since the initial tension of the
top ring 65 and the second ring 66 is set to be small and the
thickness is set to be small so that the load pushing the inner
peripheral face of the cylinder sleeve 41 due to the pressure of
the steam is reduced, it is possible to reduce the frictional force
between the cylinder sleeve 41 and the top ring 65 and the second
ring 66, while enhancing the sealing effect by improving the
ability of the top ring 65 and the second ring 66 to follow the
cylinder sleeve 41.
[0041] An annular channel 41b is formed on the outer periphery of a
middle part of the cylinder sleeve 41 (see FIG. 5 and FIG. 8), and
a plurality of oil holes 41c are formed in the annular channel 41b.
The oil channel 62a formed in the middle section of the skirt
portion 62 communicates with the oil holes 41c of the cylinder
sleeve 41.
[0042] An annular cover member 69 is welded to the front side or
the expansion chamber 43 side of the rotor head 38 which is joined
to the rear face of the rear sleeve support flange 35 of the rotor
22 by the bolts 37. Thus, an annular heat-insulating space 70 is
defined at the back face or rear face of the cover member 69 (see
FIG. 8). The rotor head 38 is positioned rotationally relative to
the rear sleeve support flange 35 by a knock pin 55.
[0043] As shown in FIG. 1, a rotary valve 71 is provided between
the rear cover 18 of the casing 11 and the rotor head 38 of the
rotor 22. The rotary valve 71 supplies the high temperature, high
pressure steam from a steam supply pipe 67 sequentially to five
expansion chambers 43, accompanying rotation of the rotor 22, and
discharges a low temperature, low pressure steam from the expansion
chambers 43 to a steam discharge chamber 68 formed between the main
body casing 12 and the rear cover 18.
[0044] The five cylinder sleeves 41 and the five pistons 42 form an
axial piston cylinder group A of the present invention.
[0045] The operation of the expander E of this embodiment having
the above-mentioned arrangement is now explained.
[0046] When the high temperature, high pressure steam generated by
heating water in an evaporator that is supplied from the steam
supply pipe 85 via the rotary valve 71 to the expansion chamber 43
within the cylinder sleeve 41, the piston 42 fitted in the cylinder
sleeve 41 is pushed forward from a top dead center toward a bottom
dead center, so that the top portion 61 at the front end of the
piston 42 pushes against the dimple 31 a of the swash plate 31. As
a result, the reaction force that the pistons 42 receive from the
swash plate 31 gives a rotational torque to the rotor 22. For each
one fifth of a revolution of the rotor 22, the high-temperature,
high-pressure steam is supplied into a fresh adjoining expansion
chamber 43, thus continuously rotating the rotor 22. While the
piston 42, having reached the bottom dead center accompanying the
rotation of the rotor 22, retreats toward the top dead center by
being pushed by the swash plate 31, the low-temperature,
low-pressure steam pushed out of the expansion chamber 43 is
discharged into the steam discharge chamber 68 via the rotary valve
71.
[0047] The oil pump 49 provided on the output shaft 32 operates
together with the rotation of the rotor 22. Oil is taken in from
the oil pan 21 via the oil pipe 52, the oil passage 95b of the pump
body 95, and the intake port 53 and is discharged from the
discharge port 54, and supplied to the oil channel 62a formed in
the skirt portion 62 of the piston 42 via the oil passage 95c of
the pump body 95, the oil passage 32a of the output shaft 32, the
annular channel 32b of the output shaft 32, the oil holes 32c of
the output shaft 32, the annular channel 41b of the cylinder sleeve
41, and the oil holes 41c of the cylinder sleeve 41. A portion of
the oil retained by the oil channel 62b flows into the spiral oil
channels 62b formed in the skirt portion 62 of the piston 42,
lubricates the surface that slides against the cylinder sleeve 41,
and is then returned to the oil pan 21. Another portion of the oil
lubricates the surfaces of the top ring 65 and the second ring 66
that slide against the cylinder sleeve 41, the top ring 65 and the
second ring 66 are provided in the land portion 63 of the piston
42. Since the oil channel 62a formed in the skirt portion 62 has
the function of temporarily retaining oil, it is possible to
continuously supply oil to the sliding sections of the piston 42
and the cylinder sleeve 41, thus improving the lubrication
conditions.
[0048] Since the evacuated, heat-insulating space 64 is formed in
the interior of the piston 42, it is possible to suppress the
escape, via the piston 42, of the heat of high temperature, high
pressure steam supplied to the expansion chamber 43 which faces the
end of the piston 42, thus minimizing any decrease in the
temperature of the high temperature, high pressure steam in the
expansion chamber 43 to increase the output of the expander E.
Furthermore, since the top of the piston 42 is maintained at a high
temperature, it becomes difficult for the steam to condense and
liquify between the land portion 63 of the piston 42 and the
cylinder sleeve 41, thus improving the lubrication conditions of
the land portion 63 to improve the sealing performance and the wear
resistance of the top ring 65 and the second ring 66.
[0049] Since the rear side of the top ring channel 63c of the land
portion 63 of the piston 42 communicates with the expansion chamber
43 which is at a high pressure, and the front side thereof
communicates with the second land channel 63e which is at a low
pressure, the difference in pressure pushes the top ring 65 from
the bottom part of the top ring channel 63c to make the top ring 65
come into intimate contact with the inner peripheral face of the
cylinder sleeve 41 and the side face of the top ring channel 63c,
thereby improving the sealing performance. Even if a part of the
high temperature, high pressure steam in the expansion chamber 43
blows past the top ring 65 toward the second land channel 63e, it
is possible to suppress an abrupt decrease in the difference in
pressure by virtue of the volume of the second land channel 63e,
thus maintaining the tension of the top ring 65 to prevent the
sealing performance from deteriorating. Moreover, the second land
channel 63e also has the function of retaining oil, thus
contributing to an improvement in the lubrication performance.
[0050] The second ring 66 maintains the compression when the high
temperature, high pressure steam blows past the top ring 65, and
has the function of an oil ring to scrape off oil attached to the
inner peripheral face of the cylinder sleeve 41. In this way, the
high temperature, high pressure steam in the expansion chamber 43
is separated from the oil in the skirt portion 62 by means of the
top ring 65 and the second ring 66 provided on the land portion 63,
to thereby prevent the oil from entering the expansion chamber 43
side and cooling the land portion 63. Thus, the high temperature,
high pressure steam is prevented from entering the skirt portion 62
side and degrading the lubricating effect of the oil.
[0051] Although an embodiment of the present invention is explained
above, the present invention can be modified in a variety of ways
without departing from the subject matter thereof.
[0052] For example, the axial piston cylinder group A of the
embodiment includes the five pistons 42 and the five cylinder
sleeves 41, but the numbers thereof are not limited to those of the
embodiment.
[0053] Furthermore, the heat-insulating space 64 of the embodiment
is evacuated. However, the heat-insulting space 64 may have a gas
such as air sealed inside.
[0054] Moreover, in the embodiment, the oil channel 62a is provided
in the outer peripheral face of the piston 42, but an oil channel
may be provided in the inner peripheral face of the cylinder sleeve
41.
[0055] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *