Slant plate type compressor with variable displacement mechanism

A reciprocating piston type refrigerant compressor includes a compressor housing having a cylinder block provided with a plurality of cylinders and a crank chamber adjacent the cylinder block. A piston slides within each cylinder and is reciprocated by a wobble plate driven by a cam rotor mounted on a drive shaft. The cam rotor includes an adjustable slant angle in close proximity to the wobble plate. Accordingly, the stroke of the pistons within the cylinders can be changed by adjusting the slant angle of the sloping surface. The slant angle of the sloping surface is adjusted in response to the change of pressure in the crank chamber. The crank chamber communicates with the suction chamber through a passageway and a valve control mechanism controls the opening and closing of the passageway. Thus, the capacity of the compressor of can be adjusted by changing the slant angle of the sloping surface of the slant plate in response to the operation of the valve control mechanism.

BACKGROUND OF THE INVENTION 
The present invention relates to a refrigerant compressor, and more 
particularly, to a wobble plate type piston compressor for an air 
conditioning system in which the compressor includes a mechanism for 
adjusting the capacity of the compressor. 
Generally, in air conditioning apparatus, thermal control is accomplished 
by intermittent operation of the compressor in response to a signal from a 
thermostat located in the room being cooled. Once the temperature in the 
room has been lowered to a desired temperature, the refrigerant capacity 
of the air conditioning system generally need not be very large in order 
to handle supplementary cooling due to further temperature changes in the 
room or for keeping the room at the desired temperature. Accordingly, 
after the room has cooled down to the desired temperature, the most common 
technique for controlling the output of the compressor is by intermittent 
operation of the compressor. However, intermittent operation of the 
compressor results in intermittent application of a relatively large load 
to the driving mechanism of the compressor in order to drive the 
compressor. 
In automobile air conditioning compressors, the compressor is driven by the 
engine of the automobile through an electromagnetic clutch. These 
automobile air conditioning compressors face the same intermittent load 
problems described above once the passenger compartment reaches a desired 
temperature. Control of the compressor normally is accomplished by 
intermittent operation of the compressor through the electromagnetic 
clutch which couples the automobile engine to the compressor. Thus, the 
relatively large load which is required to drive the compressor is 
intermittently applied to the automobile engine. 
Furthermore, since the compressor of an automobile air conditioner is 
driven by the engine of the automobile, the rotation frequency of the 
drive mechanism changes from moment to moment, which causes the 
refrigerant capacity to change in proportion to the rotation frequency of 
the engine. Since the capacity of the evaporator and condenser of the air 
conditioner does not change when the compressor is driven at high rotation 
speed, the compressor performs useless work. To avoid performing useless 
work, prior art automobile air conditioning compressors often are 
controlled by intermittent operation of the magnetic clutch. Again, this 
results in a large load being intermittently applied to the automobile 
engine. 
Recently, it was recognized that it is desirable to provide a wobble plate 
type piston compressor with a displacement or capacity adjusting mechanism 
to control the compression ratio in response to demand. In a wobble plate 
type piston compressor, control of the compression ratio can be 
accomplished by changing the slant angle of the sloping surface of the 
slant plate in response to operation of the valve control mechanism as 
disclosed in U.S. Pat. No. 4,586,874 issued May 6, 1986 to Masaharu Hiraga 
et al. Referring to FIG. 8, this application discloses a mechanism for 
controlling the compression ratio of the compressor which includes a 
passageway 391 formed between suction chamber 35 and crank chamber 13. 
This passageway 391 is formed by drilling a hole through cylinder block 
101 and valve plate 24. The machining operation required to form the 
passageway 391 adds to the manufacturing cost of the compressor. 
Furthermore, the formation of passageway 391 through cylinder block 101 
tends to decrease the mechanical strength and structural integrity of 
cylinder block 101. The mechanical strength and structural integrity of 
the cylinder block in a wobble plate type compressor is of considerable 
importance due to the high pressures which are present inside the cylinder 
block during operation of the compressor. Thus, in order to maintain the 
requisite strength and integrity, the diameter of the cylinder block 101 
must be enlarged, further adding to manufacturing cost, weight and overall 
size of the compressor. 
SUMMARY OF THE INVENTION 
In order to overcome the above noted deficiencies of wobble plate type 
compressors known in the prior art, it is a primary object of this 
invention to provide an improved refrigerant compressor wherein a 
communicating path is provided between the crank chamber and the suction 
chamber through the central bore formed in the cylinder block. 
It is another object of the present invention to provide an improved wobble 
type refrigerant compressor which achieves the above objective without the 
presence of an axially penetrating hole in the cylinder block. 
It is another object of this invention to provide a refrigerant compressor 
wherein the central bore connects a part of the communicating path with a 
female thread portion for an adjusting screw which adjusts the axial 
location of the compressor drive shaft. 
These and other objects of the present invention are achieved by a 
refrigerant compressor which includes a housing having a cylinder block 
with a plurality of cylinders and a crank chamber adjacent the cylinder 
block. A piston is slidably disposed within each cylinder and is 
reciprocated by a wobble plate driven by an input cam rotor. The cam rotor 
is provided with an adjustable slant plate which includes a slopping 
surface at an adjustable slant angle in close proximity to the wobble 
plate. A drive shaft is connected to the cam rotor and is rotatably 
supported by the compressor housing. A front end plate, which rotatably 
supports the drive shaft through a bearing, is disposed on an opening of 
the crank chamber. A rear end plate, which is disposed on the opposite end 
of the housing, includes a suction chamber and a discharge chamber for 
refrigerant. The rear end plate is fixed on the housing together with a 
valve plate. A central bore is formed at the center of the cylinder block, 
wherein the drive shaft is also rotatably supported. An adjusting screw is 
screwed into the central bore to adjust the axial location of the drive 
shaft. A portion of a communicating path between the crank chamber and the 
suction chamber is formed at the central bore. Opening and closing of the 
communicating path is controlled by a valve control mechanism. The angle 
of the sloping surface of the slant plate can be changed in response to a 
change in pressure in the crank chamber. Thus, the stroke of the piston 
may be controlled to adjust the capacity of the compressor. 
Further objects, features and other aspects of this invention will be 
understood from the following detailed description of the preferred 
embodiment of this invention with reference to the annexed drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the FIG. 1, a refrigerant compressor 1 in accordance with one 
embodiment of the present invention is shown. The compressor 1 includes 
closed cylindrical housing assembly 10 formed by cylinder block 101, a 
crank chamber 13 within cylinder block 101, front end plate 11 and read 
end plate 25. 
Front end plate 11 is mounted on the left end portion of crank chamber 13, 
as shown in FIG. 1, by a plurality of bolts (not shown). Rear end plate 25 
and valve plate 24 are mounted on cylinder block 101 by a plurality of 
bolts (not shown). Opening 111 is formed in front end plate 11 for 
receiving drive shaft 12. 
Drive shaft 12 is rotatably supported by front end plate 11 through bearing 
20 which is disposed within opening 111. The inner end portion of drive 
shaft 12 is also rotatably supported by cylinder block 101 through bearing 
23 which is disposed within central bore 102. Central bore 102 is a cavity 
formed in the center portion of cylinder block 101. Thrust needle bearing 
22a is disposed between the inner end surface of front end plate 11 and 
the adjacent axial end surface of cam rotor 14. 
Cam motor 14 is fixed on drive shaft 12 by pin member 15 which penetrates 
cam rotor 14 and drive shaft 12. Cam rotor 14 is provided with arm 141 
having slot 142. Slant plate 16 has opening 161 through which passes drive 
shaft 12. Axial annular projection 162 extends from the circumference of 
opening 161 in the front end surface of slant plate 16. Slant plate 16 
includes arm 163 having pin 21 which is inserted in slot 142. Cam rotor 14 
and slant plate 16 are joined by the hinged joint of pin 21 and slot 142. 
The pin 21 is able to slide within slot 142 so that the angular position 
of slant plate 16 can be changed with respect to the longitudinal axis of 
drive shaft 12. 
Wobble plate 17 is rotatably mounted on slant plate 16. The rotation of 
wobble plate 17 is prevented by a fork-shaped slider 172 which is attached 
to the outer peripheral end of wobble plate 17 and is slidably mounted on 
sliding rail 173 held between front end plate 11 and cylinder block 101. 
In order to slide slider 172 on the sliding rail 173, wobble plate 17 
wobbles in a non-rotating manner in spite of the rotation of cam rotor 14. 
Cylinder block 101 has a plurality of annularly arranged cylinder chambers 
32 in which respective pistons 33 slide. All pistons 33 are connected to 
wobble plate 17 by a corresponding plurality of connecting rods 34. Ball 
34a at one end of rod 34 is received in socket 331 of pistons 33 and ball 
34b at the other end of rod 34 is received in socket 171 of wobble plate 
17. It should be understood that, although only one such ball socket 
connection is shown in the drawing, there are a plurality of sockets 
arranged peripherally around wobble plate 17 to receive the balls of 
various rods, and that each piston 33 is formed with a socket for 
receiving the other ball of rods 34. 
Rear end plate 25 is shaped to define suction chamber 35 and discharge 
chamber 36. Valve plate 24, which is fastened to the end of cylinder block 
101 by screws (not shown) together with rear end plate 25, is provided 
with a plurality of valved suction ports 24a is connected between suction 
chamber 35 and the respective cylinders 32, and a plurality of valved 
discharge ports 24b connected between discharge chamber 36 and the 
respective cylinders 32. Suitable reed valves for suction port 24a and 
discharge port 24b are described in U.S. Pat. No. 4,011,029 issued to 
Shimizu. Gaskets 37, 38 are placed between cylinder block 101 and the 
inner surface of valve plate 24, and the outer surface of valve plate 24 
and rear end plate 25, to seal the mating surfaces of the cylinder block, 
the valve plate and the rear end plate. 
Referring to FIG. 2 in addition to FIG. 1, the axial position of drive 
shaft 12 can be adjusted by adjusting screw 27 into the threaded portion 
41 of central bore 102. That is to say, the axial clearance between cam 
rotor 14 and front end plate 11 through bearing 22a can be adjusted by 
adjusting screw 27. Central bore 102 is partitioned into front chamber 
102a and rear chamber 102b by adjusting screw 27. Front chamber 102a 
communicates with crank chamber 13. A plurality of axial grooves 42 are 
formed at inner peripheral threaded portion 41 of central bore 102 to 
communicate between front chamber 102a and rear chamber 102b of central 
bore 102. 
Groove 43 is formed at the front end surface of cylinder block 101 facing 
gasket 37. Groove 43 extends radially from rear chamber 102b of central 
bore 102 to pressure sensitive chamber 44 which is formed in the cylinder 
block 101. Therefore the crank chamber 13 communicates with pressure 
sensitive chamber 44 through grooves 42 and groove 43. A hole 45 is formed 
through gasket 37, valve plate 24 and gasket 38 to connect pressure 
sensitive chamber 44 and suction chamber 35. Bellows valve device 46 is 
fixed to one surface of pressure sensitive chamber 44 with valve 461 
arranged to close off hole 45 in response to the pressure within pressure 
sensitive chamber 44. The operation of bellows valve device is as follows: 
The pressure within crank chamber 13 is communicated to pressure sensitive 
chamber 44 through grooves 42 and 43. Thus, the pressure within pressure 
sensitive chamber 44 is the same as the pressure within crank chamber 13. 
When the pressure within crank chamber 13 and pressure sensitive chamber 
44 are below a predetermined pressure, the bellows of the bellows valve 
device 46 expands causing valve 461 to close hole 45. Therefore when the 
compressor is not being driven, the pressure within crank chamber 13 is 
balanced pressure, valve 461 of the bellows valve device 46 closes the 
hole 45. When the pressure within crank chamber 13 and pressure sensitive 
chamber 44 is above a predetermined pressure, the bellows of bellows valve 
device 46 is compressed causing valve 461 to open hole 45. 
In operation of the compressor, drive shaft 12 is rotated by the engine of 
the vehicle through an electromagnetic clutch. Cam rotor 14 is rotated 
together with drive shaft 12 to cause a non-rotating wobbling motion of 
wobble plate 17. Rotating motion of wobble plate 17 is prevented by 
fork-shape slider 172 which is attached to the outer peripheral end of 
wobble plate 17 and is slidably mounted on sliding rail 173 held between 
front end plate 11 and cylinder block 101. As wobble plate 17 moves, 
pistons 33 reciprocates out of phase in their respective cylinders 32. 
Upon reciprocation of pistons 33, the refrigerant gas, which is introduced 
into suction chamber 35 from a fluid inlet port 35a, is taken into each 
cylinder 32 and compressed. The compressed refrigerant is discharged to 
discharge chamber 36 from each cylinder 32 through discharge port 24b, and 
therefrom into an external fluid circuit, for example, a cooling circuit, 
through a fluid outlet port 36b. 
At the beginning of compressor operation, hole 45 is closed by valve 461 of 
the bellows valve device 46 because the pressure within crank chamber 13 
is low. As the compressor operates, the pressure within crank chamber 13 
gradually rises to create a small pressure difference between crank 
chamber 13 and suction chamber 35. This pressure difference occurs because 
blow-by-gas, which leaks from the cylinder chambers to crank chamber 13 
through a gap between the pistons 33 and cylinders 32 during the 
compression stroke, is contained in crank chamber 13. The movement of 
pistons 33 is hindered by the pressure difference between crank chamber 13 
and suction chamber 35, i.e., as the pressure in the crank chamber 
approaches the mid-pressure of the compressed gas in the cylinder chambers 
during the suction stroke, movement of the pistons is hindered because the 
slant angle of slant plate 16 gradually decreases until it approaches 
zero, i.e., slant plate 16 would be perpendicular to the drive shaft 12. 
As the slant angle of slant plate 16 decreases, the stroke of pistons 33 
in the cylinders 32 is reduced and the capacity of the compressor 
gradually decreases. 
When the pressure of crank chamber 13 and pressure sensitive chamber 44 
rises over the predetermined pressure, the bellows of bellows valve device 
46 is sufficiently compressed and valve 461 of bellows valve device 46 
opens hole 45. Simultaneously, crank chamber 13 communicates with suction 
chamber 35 through central bore 20 via grooves 42 and groove 43 formed at 
the front end surface of cylinder block 101, pressure sensitive chamber 44 
and hole 45. Accordingly, the pressure of crank chamber 13 falls to the 
pressure of suction chamber 35. In this condition, wobble plate 17 usually 
is urged toward slant plate 16 during the compression stroke of the 
pistons 33 so that slant plate 16 moves toward rotor 14. Thus, the slant 
angle of slant plate 16 is maximized relative to a vertical plane through 
the hinged joint of pin 21 and slot 142. This results in the maximum 
stroke of pistons 33 within cylinders 32 which corresponds to the normal 
refrigerant capacity of the compressor. However, the falling pressure of 
crank chamber 13 causes valve 461 of bellows valve device to close hole 
45. Thus the compressor is placed in a reduced compression stage again. 
Thus, in accordance with the above mentioned states, full and reduced 
displacement of compressor is achieved. 
In this embodiment, the bellows valve device 46 is disposed in pressure 
sensitive chamber 44 formed in the cylinder block 101. Bellows valve 
device 46 also may be disposed in suction chamber 35 as shown in FIG. 3. 
In the embodiment shown in FIG. 3, the opening and closing of hole 45 are 
accordingly controlled by the change of pressure in suction chamber 35. 
Referring to FIG. 4, a refrigerant compressor 1 in accordance with another 
embodiment of the present invention is shown. In this embodiment, an 
annular shim 51 is disposed between adjusting screw 27 screwed into the 
threaded portion 41 of central bore 102 and the inner end of the drive 
shaft 12. Shim 51 prevents friction which would otherwise occur by the 
contact of rotating drive shaft 12 with adjusting screw 27. An annular 
thrust bearing 61 may also be used in place of shim 51 as shown in FIG. 5. 
Referring to FIG. 6, a refrigerant compressor 1 is shown in accordance with 
a further embodiment of the present invention. In this embodiment, 
electromagnetic valve 40 is disposed in suction chamber 35 in place of 
bellows valve device 46 which is shown in FIG. 3. 
Referring to FIG. 7, and adjusting screw 271 is shown in accordance with 
another embodiment of the present invention. In this embodiment, a 
plurality of axial grooves 421 are formed at an outer peripheral surface 
of adjusting screw 271 to communicate the front chamber 102a and rear 
chamber 102b of central bore 102. 
The present invention has been described in accordance with preferred 
embodiments. These embodiments, however, are merely for example only, and 
the invention should not be construed as limited thereto. It should be 
apparent to those skilled in the art that other variations or 
modifications can be made within the scope of this invention.