Variable capacity single headed piston swash plate type compressor having piston abrasion preventing means

A variable capacity single headed piston, swash plate type compressor provided with a rotation-to-reciprocation conversion mechanism having a swash plate rotated by a drive shaft and formed with annularly extended engaged portions on opposite faces thereof, a pair of shoes located between the swash plate and each of the single headed pistons, each shoe having formed therein an engaging portion circumferentially slidably engaged with one of the annular engaged portions of the swash plate, and a spherical face to be in a displaceable and turnable contact with a cylindrical support wall of a radial recess of each piston and permitting a passage of the swash plate during the rotation thereof. The engagement and contact of the shoes with the swash plate and the pistons provide the respective pistons with an accurate and stable axial support, to thereby prevent a local abrasion of the single headed pistons.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a variable capacity single headed 
piston-swash plate type refrigerant compressor mainly used for an 
air-conditioner for a car. More particularly, it relates to a variable 
capacity single headed piston-swash plate type compressor provided with a 
motion converting mechanism for converting a rotation of the swash plate 
into a reciprocation of the single headed pistons and effectively 
preventing a local abrasion of the reciprocating pistons and/or cylinder 
bores of the compressor to thereby obtain a reliable and long-life 
compression operation of the variable capacity compressor. 
2. Description of the Related Art 
A typical conventional variable capacity single headed piston-swash plate 
type compressor is disclosed in Japanese Unexamined ( Kokai ) Patent 
publication No. 60-175783 published on Sep. 9, 1985, by the Japanese 
Patent Office, whose corresponding U.S. Pat. No. 4,664,604. 
FIG. 8 illustrates a compressor corresponding to the compressor of this 
publication. The compressor of FIG. 8 has a cylinder block 82 encased in a 
cylindrical shell 80, and provided with a plurality of cylinder bores 81. 
The cylindrical shell 80 defines a closed crank chamber 83 therein located 
axially in front of an inner end of the cylinder block 82. The crank 
chamber 83 is closed by a front housing 84 holding a radial bearing to 
support an outer portion Of a drive shaft 89. Rear ends of the cylinder 
block 82 and the cylindrical shell 80 are commonly closed by a rear 
housing 86 via a valve plate 85. The rear housing 86 is provided with an 
annularly extended suction chamber 87, and a cylindrical discharge chamber 
88 communicated with the plurality of cylinder bores 81 of the cylinder 
block 82. The cylinder block 82 is centrally formed with a shaft bore in 
which a radial bearing is seated to rotatably support an inner end of the 
shaft 89. The drive shaft 89 has a central portion thereof on which a 
rotary support 90 is mounted to be rotated with the shaft 89 about the 
axis of the drive shaft 89 within the crank chamber 83. The rotary support 
90 is connected with a swash plate 93 via a hinge mechanism 91, which 
includes an elongated aperture 91a formed in the rotary support 90, and a 
hinge pin 93b fixed to a swing plate 93a to be engaged in the elongated 
aperture 91a; The swing plate 93a is projected from a front face 93d of 
the swash plate 93, a rear face 93c of which faces an inner end of the 
cylinder block 82. As shown in FIG. 9, the swash plate 93 is slidably 
mounted on a spherical sleeve element 92 axially slidably mounted on the 
drive shaft 89. Namely, the swash plate 93 can be rotated together with 
the drive shaft 89 and slide on the spherical sleeve element 92 to change 
an angle of inclination with respect to a plate vertical to the drive 
shaft 89. The swash plate 93 is engaged with each of pistons 94 slidably 
fitted in the cylinder bores 81, via a pair of shoes 95 having a 
half-sphere shape. Each of the pair of shoes 95 has a flat face 95a 
engaged with the front or rear face 93d or 93c of the swash plate 93 and a 
spherical portion 95b slidably engaged with a spherical recess 94a formed 
in a frontmost portion of the piston, as shown in FIG. 9. 
The cylinder block 82 is provided with a passageway 96 for providing a 
fluid communication between the crank chamber 83 and the suction chamber 
87, and the passageway 96 can be closed and opened by a control valve 97. 
When the drive shaft 89 is rotated by a drive force such as a force given 
by a car engine, the swash plate 93 is rotated together, and the pistons 
94 are driven to perform a reciprocating movement in the cylinder bores 
81. Namely, the rotation of the swash plate 93 is converted to a 
reciprocatory sliding movement of the piston 94 in the cylinder bore 81 by 
the pair of shoes 95 performing a complicated movement between the swash 
plate 93 and the piston 94. Namely, during the rotation of the swash plate 
93, each shoe 95 slides, at the flat face 95a thereof, on the front or 
rear face 93d or 93c of the swash plate 93 along an ellipsoidal locus, and 
turns, at the spherical portion 95b thereof, in the spherical recess 94a 
of the piston 94 about the center of the spherical recess 94a of the 
piston 94. The sliding movement of the shoe 95 taking the ellipsoidal 
locus includes a first circumferential sliding movement relative to a 
plane lying in the front or rear face 93d or 93c of the swash plate 93, 
indicated by an arrow "A" in FIG. 9, and a second radial sliding movement 
relative to the same plate, indicated by an arrow "C" in FIG. 9. The 
rotating movement of the shoe 95 in the spherical recess 94a of the piston 
94 is indicated by an arrow "B". The combination of the sliding and 
rotating movements of the shoe 95 contributes to the conversion of the 
rotation of the swash plate 93 into the reciprocation of each piston 94, 
and thus the reciprocation of the respective pistons 94 compresses a 
refrigerant gas pumped from the suction chamber 87 into the cylinder bores 
81, and delivers the compressed refrigerant gas from the cylinder bores 81 
toward the discharge chamber 88, from which the compressed refrigerant gas 
is further discharged toward an air-conditioning or refrigerating circuit. 
The entire amount of the refrigerant gas discharged from the compressor, 
i.e., the whole compression capacity of the compressor, is controlled by 
adjusting a pressure level in the crank chamber 83 due to controlling 
operation of a capacity control valve 97. 
When the capacity control valve 97 is moved to a position establishing a 
fluid communication between the crank chamber 83 and the suction chamber 
87 via the passageway 96, the pressure level in the crank chamber 83 
acting as a back pressure against the pistons 94 is lowered, and thus the 
angle of inclination of the swash plate 93 is made larger. Consequently, 
the hinge pin 93b of the hinge mechanism 91 is moved in the elongated 
aperture 91a to a position radially farthest from the drive shaft 89, and 
the sleeve element 92 is axially slid on the drive shaft 89 toward the 
front side of the compressor to thereby turn the swash plate 93 to a 
position having a larger angle of inclination. Accordingly, the 
ellipsoidal locus of the sliding movement performed by the respective 
shoes 95 is made to lengthen the long diameter thereof, and the stroke of 
the respective pistons 94 is extended. Accordingly, the compression 
capacity of the compressor becomes large. 
When the capacity control valve 97 is moved to a position preventing the 
fluid communication between the crank chamber 83 and the suction chamber 
87 via the passageway 96, the pressure level in the crank chamber 83 is 
raised by a blow-by gas leaking from the cylinder bores 81 into the 
chamber 83, and thus the pressure acting as a back pressure against the 
pistons 94 is made high to reduce the angle of inclination of the swash 
plate 93 with respect to a plane perpendicular to the axis of the drive 
shaft 89. Accordingly, the hinge pin 93b of the hinge mechanism 91 is 
moved in the elongated aperture 91a to a position radially approaching the 
drive shaft 89, and the sleeve element 92 is slid on the drive shaft 89 
toward the rear side of the compressor. Therefore, the swash plate 93 is 
turned toward an erect position thereof, and thus the ellipsoidal locus of 
the sliding movement performed by the respective shoes 95 is made to 
shorten the long diameter thereof, and the stroke of the respective 
pistons 94 is shortened. As a result, the compression capacity of the 
compressor becomes small. 
With the above-mentioned reciprocation-drive mechanism of the pistons 94 of 
the variable capacity single-headed swash plate type compressor, since 
each of the shoes 95 is held in the spherical recess 94a of the piston 94, 
it is prevented from performing a random displacement. Nevertheless, as 
previously stated, the shoe 95 is permitted to slide on the front or rear 
face 93d or 93c of the swash plate 93 at the flat face 95a thereof along 
the ellipsoidal locus, and this ellipsoidal sliding movement of the shoe 
95 results in a radial displacement thereof relative to the axis of the 
drive shaft 89 of the compressor. Therefore, when the compression of the 
refrigerant gas is performed by the piston 94 in the cylinder bore 81, and 
when the piston 94 receives a pressure of the compressed gas, the piston 
94 transmits a corresponding force to the swash plate 93 via each shoe 95, 
which always includes an axial force component, and a radial force 
component transmitted in the radial direction with respect to the axis of 
the drive shaft 89 from the piston 94 to the swash plate 93 via the shoe 
95. The extent of the latter radial force component changes depending on 
the angle of inclination of the swash plate 93, and due to the radial 
force from the piston 94 acting on the swash plate 93 via each shoe 95, 
the single headed piston 94 supported by the wall of the cylinder bore 81 
at the cylindrical body portion thereof, but not supported at the 
frontmost portion thereof, comes into a tight contact with the wall of the 
cylinder bore 81 at a given portion thereof, and thus a local abrasion of 
the piston 94 and/or the wall of the cylinder bore 81 of the cylinder 
block 82 necessarily occurs, whereby a reliable long operation life of the 
compressor is prevented. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to obviate the problem of 
the local abrasion encountered by the prior art variable capacity single 
headed piston-swash plate type compressor. 
Another object of the present invention is to provide a variable capacity 
single-headed piston swash plate type refrigerant compressor provided with 
a novel motion conversion mechanism, i.e., a rotation-to-reciprocation 
conversion mechanism for pistons thereof. 
In accordance with the present invention, there is provided a variable 
capacity single headed piston-swash plate type compressor provided with an 
axially extended cylinder block having front and rear ends thereof and a 
plurality of axial cylinder bores formed therein, a front housing 
connected to the front end of the cylinder block and defining a sealed 
crank chamber therein extending in front of the front end of the cylinder 
block, a rear housing connected to the rear end of the cylinder block and 
defining therein a suction chamber for a refrigerant gas before 
compression and a discharge chamber for the refrigerant gas after 
compression, a drive shaft rotatably held by the cylinder block and the 
front housing to have an axis thereof axially extended through the crank 
chamber, a rotary support mounted on the drive shaft to be rotated with 
the drive shaft in the crank chamber, a swash plate hinged to the rotary 
support to be rotated together with the drive shaft and slidably mounted 
on the drive shaft via a sleeve element to be slid in the axial direction 
of the drive shaft to be capable of turning about an axis perpendicular to 
the axis of the drive shaft, and a plurality of reciprocatory single 
headed pistons fitted in the cylinder bores of the cylinder block and 
engaged with the swash plate via a motion conversion means including 
spherical shoes for converting a rotation of the swash plate into a 
reciprocation of the single headed pistons in the cylinder bores, and a 
valve means for adjusting a fluid communication between the crank chamber 
and the suction chamber to control a capacity of the compressor through 
changing a pressure differential between the crank and suction chambers, 
wherein the motion converting means comprises means for preventing a local 
abrasion of at least the single headed pistons during reciprocating 
thereof in the cylinder bores. The local abrasion preventing means 
comprises first means for preventing a radial displacement of each of the 
spherical shoes at face thereof engaging the swash plate, and a second 
means for permitting a radial displacement of each of the shoes at a 
spherical face thereof engaged with the single headed piston. 
Preferably, the first means comprises an annularly extended engaged portion 
formed in the swash plate, and an arcuate engaging portion formed in each 
of the spherical shoes and engaging the annularly extended engaged portion 
of the swash plate in manner such that each of the shoes is permitted to 
perform only a circumferential displacement thereof. The second means 
comprises a cylindrical support recess formed in the piston for supporting 
the spherical face of each of the shoes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a variable capacity, single headed piston, swash plate 
type refrigerant compressor has a cylinder block 1 having a plurality of 
cylinder bores 1a, and front and rear ends of the cylinder block 1 are 
sealingly closed by front and rear housings 2 and 3. The cylinder block 1 
and the front housing 2 define an airtightly sealed cylindrical crank 
chamber 2a therebetween, for housing a later-described swash 
plate-operated compressing mechanism. A valve plate 12 is located between 
the rear end of the cylinder block 1 and the rear housing 3 having formed 
therein an annularly extending suction chamber 3a and a central discharge 
chamber 3b which can be communicated with the cylinder bores 1a of the 
cylinder block 1 via suction and discharge valve mechanisms, respectively. 
An axial drive shaft 4 is centrally arranged to extend through the front 
housing 2 and the cylinder block 1, and rotatably supported by bearings 
mounted in the front housing 2 and the cylinder block 1. A front end of 
the drive shaft 4 is outwardly extended from the front housing 2 to be 
connectable to a drive source such as a car engine, and a rear end thereof 
is rotatably supported by the bearing in the cylinder block 1. 
A rotary support 5 is fixedly mounted on the drive shaft 4 in the crank 
chamber 2a to be rotatable with the drive shaft 4. The rotary support 5 is 
axially supported by a thrust bearing seated on an inner end of the front 
housing 2, and has an rearwardly extended support arm 6 for supporting a 
cylindrical rotary drive element 11 via a hinge mechanism generally 
designated by "K". Namely, the support arm 6 of the rotary support 5 has 
formed therein a through-hole 6a in which a race member 8 having a 
spherical socket for movably receiving a ball element 9 is tightly fitted. 
The race member 8 and the ball element 9 form a ball and socket joint, and 
the ball element 9 has formed therein a through-bore 9a in which is 
slidably engaged a guide pin 10 press-fitted in a through-bore 11a of the 
rotary element 11. The cylindrical rotary drive element 11 is extended 
toward an axially rear end of the crank chamber 2a to form an cylindrical 
mount on which a swash plate 15 of the swash plate-operated compression 
mechanism is mounted and tightly held by a threaded ring 16. 
As best illustrated in FIG. 2, the swash plate 15 in the shape of a 
circular plate has formed in both faces thereof annularly extended engaged 
portions 15c recessed at the peripheral portion of the plate member to 
have the same diameter with regard to the center of the swash plate 15. 
The swash plate 15 is mounted on the drive element 11 in a manner such 
that the center of the swash plate 15 is positioned on the axis of the 
drive shaft 4. A pair of shoes 17 in the shape of a semi-sphere member is 
engaged in the annular engaged portions 15c to be displaceable in only a 
circumferential direction (a direction shown by an arrow "A" in FIG. 2 ). 
Each of the pair of shoes 17 is provided with a flat face 17a to be kept 
in contact with an annular bottom of the engaged portion 15c, an inner 
arcuate side 17b to be kept in contact with an inner annular side wall of 
the engaged portion 15, and an outer arcuate side 17c to be in contact 
with an outer annular side wall of the engaged portion 15. The shoe 17 is 
also provided with a spherical face 17d on the back thereof. The pair of 
shoes 17 are arranged between the swash plate 15 and one of single-headed 
pistons 19 axially slidably fitted in the cylinder bores 1a. Each shoe 17 
is engaged with the piston 19 to be moved in a direction indicated by an 
arrow "B", and displaced in a direction indicated by an arrow "C" in FIG. 
2, relative to the piston 19. The single headed piston 19 includes a 
cylindrical body having a compressing head at an end thereof, and a neck 
portion axially extending from the opposite end of the cylindrical body 
and having formed therein a deep cutout 19a through which the swash plate 
15 is rotated together with the rotary drive element 11. The neck portion 
of the piston 19 is provided with a pair of mutually confronting 
cylindrical support walls 19b between which the above-mentioned cutout 19a 
is defined. The confronting cylindrical walls 19b have the same radius of 
curvature as the spherical face 17d of the shoe 17 and are extended in a 
direction perpendicular to the axis of the piston 19, so that the pair of 
shoes 17 engaged in the annular engaged portions 15c of the swash plate 15 
are turnably and displaceably held by the cylindrical walls within the 
cutout 19a of the piston 19. Therefore, the respective pistons 19 engaged 
with the swash plate 15 via corresponding pairs of shoes 17 are held in 
the respective cylinder bores 1a, to thereby implement a stable and smooth 
reciprocation in the cylinder bores 1a. Namely, the shoes 17 contribute to 
an accurate conversion of the rotation of the swash plate into the 
reciprocation of the single headed pistons 19. 
In FIG. 1, the rotary drive element 11 is mounted around the drive shaft 4 
via a slidable sleeve element 13. The sleeve element 13 is supported on 
the drive shaft 4 and subjected to axially opposite spring forces of a 
pair of springs 18 and 20 wound around the drive shaft 4. The sleeve 
element 13 is provided with a pair of lateral trunnion pins 14 fixed 
thereto and laterally projected to be engaged with the rotary drive 
element 11 at outer ends thereof. Therefore, the swash plate 15 mounted on 
the rotary drive element 11 is rotated with the drive shaft 4 about the 
axis of the shaft 4 via the rotary support 5 and the rotary drive element 
11, and turned about the trunnion pins 14 via the hinge mechanism K and 
the slidable sleeve element 13 to thereby change an angle of inclination 
thereof with respect to a plane perpendicular to the axis of the drive 
shaft 4. 
The compressor of FIG. 1 is further provided with two fluid control valves 
21 mounted in the rear housing 3 to control a pressure level in the crank 
chamber 2a. 
When the compressor is connected to a drive source, i.e., a car engine, the 
drive shaft 4 is rotated to thereby rotate the swash plate 15, and in 
turn, the single headed pistons 19 are reciprocated in the cylinder bores 
1a by the above-described rotation-to-reciprocation conversion mechanism 
including the shoes 17. The refrigerant gas before compression is pumped 
from the suction chamber 3a of the rear housing 3 into the cylinder bores 
1a, and the refrigerant gas after compression by the pistons 19 is 
delivered into the discharge chamber 3b. 
During the compressing operation of the compressor, each of the shoes 17 of 
the rotation-to-reciprocation conversion mechanism is engaged with the 
swash plate 15 via the engagement of the flat face 17a, and the inner and 
outer arcuate sides 17b and 17c of the shoe 17 and the annular engaged 
portion 15c of the swash plate 15, so that the shoe 17 is permitted to 
move circumferentially relative to the rotating swash plate 15, as 
illustrated in FIG. 2. Nevertheless, the shoe 17 is prevented from being 
shifted in a radial direction of the swash plate 15 due to the 
above-mentioned engagement. The shoe 17 is, however, permitted to turn 
about the center of the spherical face 17d kept in line contact with the 
cylindrical support wall 19b of the piston 19 in the direction indicated 
by the arrows C in FIG. 2. Thus, the force acting on the piston 19 against 
the compression of the refrigerant gas is transmitted from the cylindrical 
support wall 19b of the piston 19 to the shoe 17, and in turn, transmitted 
to the swash plate 15. At this stage, since the engagement of the inner 
and outer arcuate sides 17b and 17c of the shoe 17 and the recessed 
engaged portion 15c of the single headed swash plate 15 does not allow any 
random play of the shoe 17 relative to the piston 19, and accordingly, the 
piston 19 is always maintained at an accurate axial posture to smoothly 
reciprocate in the axial cylinder bore 1a, a strong contact of a part of 
the piston 19 with the wall of the cylinder bore 1a does not occur. 
Accordingly, a local abrasion of the piston 19 and/or the wall of the 
cylinder bore 1a can be prevented. 
When the swash plate 15 is turned about the trunnion pins 14 to change an 
angle of inclination thereof, each of the shoes 17 can be relatively 
displaced in the cutout 19a of the piston 19 (the direction of the arrow 
"C") while turning about the center thereof (the direction of the arrow 
"B") by the guide of the cylindrical wall 19b of the piston 19. 
The compression capacity of the compressor, i.e., the entire amount of the 
refrigerant gas discharged from the cylinder bores 1a toward the discharge 
chamber 3b during one complete revolution of the drive shaft is adjustably 
changed by controlling the pressure level in the crank chamber 2a by the 
fluid control valves 21. 
For example, when the control valves 21 are operated to establish a fluid 
communication between the crank chamber 2a and the suction chamber 3a, the 
back pressure acting on the respective pistons 19 is lowered to increase 
the angle of inclination of the swash plate 15 from the erect position 
thereof. Namely, the ball element 9 and the race member 8 of the hinge 
mechanism K are moved to turn the rotary drive element 11 about the 
trunnion pins 14 via the guide pin 10 in the clockwise direction in FIG. 
1, and the sleeve element 13 is axially slid on the drive shaft 4 toward 
the front side of the compressor. Thus, the swash plate 15 is turned 
toward a position where an angle of inclination of the swash plate is 
large. During the turning of the swash plate 15 toward the large 
inclination angle position, each shoe 19 of the rotation-to-reciprocation 
conversion mechanism is gradually turned and displaced in the cutout 19a 
of the piston 19 under the guide of the cylindrical support wall 19b of 
the piston 19 to thereby permit a stable increase of the stroke of the 
piston 19. 
To the contrary, when the capacity control valves 21 are operated to 
prevent a fluid communication between the crank chamber 2a and the suction 
chamber 3a, the pressure level in the crank chamber 2a is raised by a 
blow-by gas leaking from the respective cylinder bores la to thereby 
increase the back pressure action on the pistons 19. Thus, the swash plate 
15 is turned toward a position where the angle of inclination of the swash 
plate 15 is smaller. Namely, the hinge mechanism K causes a turning of the 
rotary drive element 11 about the trunnion pins 14 in a counter clockwise 
direction in FIG. 1 and an, axial slide of the sleeve element 13 toward 
righthand direction in FIG. 1. Therefore, the swash plate 15 is turned 
toward the erect position thereof having the smallest inclination angle. 
Each shoe 17 is displaced and turned in the cutout 19a of the piston 19 by 
the guide of the cylindrical support wall 19a of the piston toward inside 
the cutout 19a to thereby permit a stable decrease of the stroke of the 
piston 19. 
In the described embodiment of FIG. 1, the engaged portions 15c of the 
swash plate 15 are annular recesses easily formed by a machine tool, and 
each of the pair of shoes 17 can be identical mechanical elements. 
Accordingly, the motion conversion mechanism of the compressor can be 
produced at a rather low manufacturing cost. 
FIG. 3 illustrates a different motion conversion mechanism, i.e., a 
rotation-to-reciprocation conversion mechanism according to another 
embodiment of the present invention, which can be incorporated in a 
variable capacity single headed piston, swash plate type compressor. In 
FIG. 3, a swash plate 31 is substantially identical with the swash plate 
15 of the first embodiment, and has a pair of engaged portions 31c in the 
shape of annularly extended recesses formed in the peripheral portion of 
the opposite faces of the swash plate 31. The engaged portions 31c of the 
swash plate 31 have a radial width narrower than those of the first 
embodiment. 
Each of a pair of shoes 32 is provided with a projection engaged with the 
engaged portion 31c of the swash plate 31, and a spherical face 32d to be 
fitted in the cutout 19a of the piston 19 (FIG. 1 ). The projection of the 
shoe 32 has a flat face 32a to be in contact with the bottom face of the 
engaged portion 31c, and inner and outer arcuate sides 32b and 32c to be 
in contact with inner and outer annular side walls of the engaged portion 
31c of the swash plate 31, respectively. 
The operation of the motion conversion mechanism, including the 
above-mentioned swash plate 31 and the shoes 32 is identical with that of 
FIG. 2 of the first embodiment, and therefore, a detailed description 
thereof is omitted. 
FIG. 4 illustrates a further different embodiment of a motion conversion 
mechanism, i.e., a rotation-to-reciprocation conversion mechanism able to 
be accommodated in a variable capacity single headed piston, swash plate 
type compressor. The motion conversion mechanism of FIG. 4 includes a 
swash plate 41 and a plurality of pairs of shoes 42 (only one pair of 
shoes is shown in FIG. 4 ) to be held between the swash plate 41 and 
respective pistons similar to those shown in FIG. 2. The swash plate 41 is 
provided with annularly extended engaged portions 41c on both faces 
thereof, to be engaged with a recess of each shoe 42. The recess of the 
shoe 42 has a annular flat face 42a to be in contact with an uppermost 
face of the engaged portion 41c of the swash plate 41, and inner and outer 
arcuate side walls 42b and 42c to be in contact with inner and outer sides 
of the engaged portion 41c of the swash plate 41. The shoe 42 is also 
provided with a spherical face 42d to be in contact with the cutout 19 a 
of the piston 19 (FIG. 2) when assembled in the compressor. It will be 
easily understood that the operation and advantage of the motion 
conversion mechanism according to the embodiment of FIG. 4 is 
substantially the same as that of the embodiments of FIGS. 2 and 3. 
Namely, the motion conversion mechanism of FIG. 4 can effectively prevent 
a local abrasion of the single headed reciprocatory pistons 19 of the 
variable capacity swash plate type refrigerant compressor, and 
accordingly, can contribute to a long operation life of the compressor per 
se. 
FIG. 5 illustrates a variable capacity single headed piston, swash plate 
type compressor according to a further embodiment of the present 
invention. Although the external appearance of the compressor of this 
embodiment is slightly different from that of FIG. 1, the basic internal 
construction and the operation of the compressor of FIG. 5 is identical 
with those of the compressor of FIG. 1. Therefore, elements of the 
compressor of FIG. 5 identical with or the same as those of the compressor 
of FIG. 1 are designated by reference numerals corresponding to the 
reference numerals of FIG. 1, plus "100". 
In the compressor of FIG. 5, a plurality of pistons 119 slidably fitted in 
cylinder bores 101a of a cylinder block 101 are reciprocated by a 
rotation-to-reciprocation mechanism arranged in an airtightly closed crank 
chamber 102a of the cylinder block 101, and including a plurality of pairs 
of shoes 117 intervened between a swash plate 115 mounted on a rotary 
drive element 111 and the respective pistons 119 as typically shown in 
FIG. 6. The rotation of the swash plate 115 is driven by a drive shaft 104 
via a rotary support element 105 and the rotary drive element 111, and a 
turning of the swash plate 115 about trunnion pins 114 is caused by a 
change in a pressure level in the crank chamber 102a, which pressure level 
is adjustably controlled by a pair of flow control valves 121. A hinge 
mechanism K including a ball element 109, a race element 108, and a guide 
pin 110 is provided in the crank chamber 102a for permitting the turning 
of the rotary drive element 111 and the swash plate 115. A rear housing 
103 has formed therein a suction chamber 103a for a refrigerant gas before 
compression, and a discharge chamber 103b for the refrigerant gas after 
compression, and these chambers 103a and 103b are communicatable with the 
cylinder bores 101a of the cylinder block 101. 
A description of the characteristic construction and operation of the 
compressor of FIG. 5 will be further provided below with reference with 
FIGS. 6 and 7 in addition to FIG. 5. 
As best illustrated in FIG. 6, each of the single headed pistons 119 is 
provided with an axial neck portion 119e and a cylindrical head portion 
119d integral with the neck portion 119e. A back face 119f is a boundary 
portion of the neck and head portions 119e and 119d. The neck portion 119e 
of the piston 119 has a partial cylindrical surface radially remote from 
the drive shaft 104, and a cutout 119a radially opening toward the drive 
shaft 104. The partial cylindrical surface of the neck portion 119e has 
the same diameter as that of the head portion 119d of the piston 119, and 
accordingly the partial cylindrical surface is formed as an extension of 
the head portion 119d of the piston. The cutout 119a of the neck portion 
119e has a bottom face 119c and a pair of confronting cylindrical support 
walls 119b to permit passage of the swash plate 115 during the rotation of 
the swash plate 115 and to hold a pair of shoes 117 operative to convert 
the rotation of the swash plate 115 into the reciprocation of the piston 
119 in the cylinder bore 101a. Each of the pair of shoes 117 includes an 
outer shoe element 118a slidably and turnably fitted in the cylindrical 
support wall 119b, and an inner shoe element 117a received by the outer 
shoe element 118a and having an arcuate groove slidably engaged with one 
of annularly extended engaged portions 141c of the swash plate 115. 
Namely, the rotation-to-reciprocation mechanism of FIG. 6 has 
substantially the same construction as that of the afore-described 
embodiment of FIG. 4. Thus, the rotation-to-reciprocation mechanism of 
FIG. 6 can provide the respective pistons 119 with an accurate and stable 
support to perform an axial reciprocation in the cylinder bore 101a 
without permitting any radial play of the pistons 119. Accordingly, the 
respective pistons 119 can continue a smooth reciprocation to compress a 
refrigerant gas for a long operation life of the compressor without 
causing a local abrasion thereof and of the wall of the cylinder bore 
101a. 
Further, in the compressor of FIG. 5, the cylinder block 101 has a thin 
cylindrical wall portion 101b at a front side thereof, and a thick 
cylindrical wall portion 101c at a central portion thereof. The thick 
cylindrical wall portion 101c of the cylinder block 101 has formed in an 
inner cylindrical surface thereof a plurality of partly circular recesses 
101d extended axially from the respective cylinder bores 101a. FIG. 7 
illustrates a cross-section of the cylinder block 101, clearly showing the 
shape of the plurality of equiangularly arranged partly circular recesses 
101d, e.g., seven recesses 101d in the present embodiment for the 
compressor incorporating therein seven single headed pistons 119. These 
partly circular recesses 101d are provided for presenting the neck 
portions 119e of the respective single headed pistons 119 with an axial 
guide during the reciprocation of the pistons. Namely, the partly circular 
recesses 101d can prevent random play of the pistons 119 when they are 
subjected to a non-axial force such as a radial force or side force, as 
indicated in FIG. 7, during the operation of the rotation-to-reciprocation 
conversion mechanism. As a result, the respective single headed pistons 
119 will always perform an accurate axial reciprocation in the cylinder 
bores 101a, and thus a local abrasion thereof can be prevented. A local 
abrasion of the wall of the cylinder bores 101a can be also prevented. The 
axial length of the part circular recesses 101d of the cylinder block 101 
preferably should be sufficient for presenting an axial guide to at least 
a part of the neck portions 119e of the respective pistons 119 even when 
each piston is slid to the bottom dead center thereof under a condition 
where the swash plate 115 is turned toward the largest inclination angle 
position. 
From the foregoing description of the preferred embodiments of the present 
invention it will be understood that, according to the present invention, 
a local abrasion of the single headed pistons incorporated in a variable 
capacity swash plate type refrigerant compressor can be effectively 
prevented during the reciprocation thereof, and accordingly, a long 
operation life of the single headed pistons and the compressor per se can 
be obtained.