Low reexpansion valve system

A scotch yoke compressor including a valve system wherein an annular discharge port is defined by an opening in the valve plate and a washer attached to the cylinder head. A valved piston includes a valve retainer having an annular protuberance that extends above the piston head and is received within the annular discharge port when the piston is at top dead center, thereby reducing reexpansion volume.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a reciprocating piston 
compressor assembly and, more particularly, to an improved valve system 
for such a compressor assembly, wherein a suction valve assembly 
associated with the piston interfits with a discharge port associated with 
the valve plate and cylinder head to reduce reexpansion volume in the 
cylinder. 
In a typical reciprocating piston compressor, a cylinder is defined by a 
compressor crankcase and a piston reciprocates within the cylinder to 
compress gaseous refrigerant therein. In a compressor to which the present 
invention pertains, the piston comprises a piston valve assembly wherein 
the suction valve is operably mounted on the piston head to receive gas 
through the piston from one end of the cylinder and compress the gas in 
the cylinder for discharge out of the other end. A valve plate is mounted 
to the crankcase so as to close the top of the cylinder. The valve plate 
includes a discharge valve assembly operable to discharge gas into a 
discharge space defined by a cylinder head cover mounted to the crankcase 
with the valve plate disposed therebetween. 
The present invention is particularly applicable to a scotch yoke 
compressor, wherein a plurality of radially arranged pistons are drivingly 
connected to a crankshaft by means of a scotch yoke mechanism within a 
suction cavity. An example of a scotch yoke compressor is found in U.S. 
Pat. No. 4,834,632 assigned to the assignee of the present invention and 
incorporated herein by reference. 
The aforementioned patent discloses a scotch yoke compressor having piston 
suction valve assemblies wherein a valve retainer is attached to the 
piston by means of a centrally located fastener, the head of which is 
received within a recess in the valve plate to reduce the reexpansion 
volume. Such an assembly does not ordinarily reduce the reexpansion volume 
attributable to the discharge ports. In U.S. Pat. No. 1,764,655, a suction 
valve retainer is centrally mounted to the flat top surface of the piston, 
and extends therefrom and is received within a central round discharge 
port in the valve plate. 
In prior art compressors having both discharge and suction valving 
associated with a compressor valve plate, it is known to use a piston 
having an annular upstanding portion on the piston head that fills a 
corresponding annular discharge port when the piston is at top dead 
center. 
It is desired to provide an improved valve system for a compressor 
requiring a valved piston and having discharge valving associated with a 
valve plate, whereby reexpansion volume associated with a discharge port 
in the valve plate is minimized. 
SUMMARY OF THE INVENTION 
The present invention overcomes the disadvantages of the above-described 
prior art by providing an improved valve assembly wherein a valved piston 
includes a valve retainer having an annular protuberance that occupies an 
annular discharge port when at its top dead center position to reduce 
reexpansion volume. More specifically, a recess in the piston head and a 
counterbore in the valve retainer facilitate attachment of the retainer to 
the piston and accommodate the annular discharge valve to decrease 
reexpansion volume. 
Generally, the invention provides a counterbore in the suction valve 
retainer that accommodates a central portion of the discharge valve 
assembly. Specifically, a valve washer and bolt are attached to the 
cylinder head and are received within the counterbore in the suction valve 
retainer. 
The invention also provides for an annular protuberance on the suction 
valve retainer that interfits within the discharge port adjacent the 
discharge valve to reduce reexpansion volume. 
An advantage of the present invention is that it substantially reduces the 
reexpansion volume of the cylinder during operation thereby making the 
compressor more efficient. 
The invention, in one form thereof, provides a compressor valve system for 
a scotch yoke compressor. The valve system includes a discharge valve 
assembly connected to a cylinder crankcase, and a suction valve assembly 
on a top face of a reciprocating piston. The discharge valve assembly 
comprises an annular discharge valve overlying a discharge valve seat 
defined by a valve plate and a member suspended from a cylinder head 
cover. The suspended member fills a central opening in the valve plate, 
thereby creating an annular discharge port. The suction valve assembly 
includes a valve retainer having an annular protuberance that 
substantially fills the annular discharge port when the piston is at top 
dead center. The suction valve assembly also includes a suction valve, 
sealing over suction ports in the piston. 
In one aspect of the previously described form of the invention, the 
suspended member comprises a washer attached by a bolt to the cylinder 
head. The washer creates the radially inner portion of the annular 
discharge port into which the protuberance of the suction valve retainer 
is received. 
In accord with another aspect of the invention, the suction valve is 
indexed to prevent its rotation relative the suction valve retainer. 
Specifically, notches are provided in the suction valve retainer, and 
radially inwardly extending projections or tabs are provided on the inner 
periphery of the suction valve. The interfitting of the tabs into the 
notches prevents the suction valve from rotating relative the suction 
valve retainer.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1 and 2 there is shown one cylinder of a 
multi-cylinder scotch yoke compressor. This cylinder 10 has a sidewall 
formed by crankcase 12. Crankcase 12 has a top surface 13 onto which 
cylinder 10 opens. Inside the cylinder is a piston assembly 14. On the top 
surface 13 of crankcase 12 is a valve plate 16, discharge assembly 18, and 
cylinder head 20 which will be more thoroughly described herein. 
Referring to piston assembly 14, piston assembly 14 comprises a piston 22 
having an annular piston ring 24 to allow piston 22 to operably 
reciprocate within cylinder 10 to compress gaseous refrigerant therein. 
Referring more specifically to FIG. 2, piston 22 also includes a recess 25 
with a mounting centerbore 26 extending through piston 22. A plurality of 
suction ports 28 are circularly arranged about centerbore 26 and extend 
through piston 22 to allow suction gas within suction cavity 30 to enter 
cylinder 10 on the compression side of piston 22. 
In accord with the present invention, a suction valve assembly 32 is 
associated with piston assembly 14, and will now be described with respect 
to piston assembly 14 shown in FIGS. 1 and 2. Suction valve assembly 32 
comprises a generally flat, disk-shaped suction valve 34. In its closed 
position, valve 34 covers suction ports 28 on outer top surface 36 of 
piston 22. Suction valve 34 opens and closes by virtue of fluid pressure 
forces and/or its own inertia as piston assembly 14 reciprocates in 
cylinder 10. 
A suction valve retainer 38 is attached on outer top surface 36 of piston 
22 by bolt 40. Specifically, a downward extending boss 39 is received 
within recess 25, and is retained therein by bolt 40, which also attaches 
piston 22 to the slide block of the scotch yoke mechanism. Suction valve 
retainer 38 has a counterbore 42 and an annular upwardly extending 
protuberance 43. Counterbore 42 not only receives the head of bolt 40 but, 
more importantly, enables valve retainer 38, which extends radially over 
suction valve 32, to receive discharge valve assembly 18 when piston 
assembly 14 is at top dead center. The annular protuberance 43 on top of 
suction valve retainer 38 is projected into an annular discharge port 71 
when piston assembly is at top dead center. The interfitting arrangement 
of suction valve retainer 38 with annular discharge port 71 reduces the 
amount of reexpansion of refrigerant during compressor operation. 
The suction valve 32 is indexed to prevent rotation by means of 
circumferentially arranged notches 44 in suction valve retainer 38 and 
corresponding radially inwardly extending projections 46 on the inner 
periphery of the annular suction valve 32. 
Discharge valve assembly 18 is situated on top surface 66 of valve plate 
16. Generally, compressed gaseous refrigerant within the cylinder 10 is 
discharged through annular discharge port 71 past an open discharge valve 
68 that is limited in its travel by a discharge valve retainer 70. With 
reference to cylinder 10 in FIGS. 1 and 2, a cylinder head cover 20 is 
mounted to crankcase 12 with valve plate 16 interposed therebetween. Valve 
plate 16 has a central discharge opening 60 allowing communication between 
the cylinder 10 and the top surface 66 of valve plate 16. A valve plate 
gasket 62 is provided between valve plate 16 and crankcase 12. 
Cylinder head cover 20 that fits over valve plate 16 has a suspended 
portion for defining, with opening 60 in valve plate 16, the 
aforementioned annular discharge port 71. More specifically, the suspended 
portion is a center boss 72 that is centered in discharge opening 60 of 
valve plate 16. Disk member, such as steel washer 74 and bolt 76 are 
attached to center boss 72 so that a top face 78 of washer 74 is 
substantially coplanar with the top surface 66 of valve plate 16. 
Discharge valve 68 is a flat, annular valve, having a central aperture 80. 
Valve 68 is made of thin valve steel and fits over portions of the top 
surface 66 of valve plate 16 and the top surface 78 of washer 74, which 
together comprise a discharge valve seat circumjacent annular discharge 
port 71. Valve retainer 70 is an annular, arcuate spring steel member 
corresponding substantially to the shape of discharge valve 68. Valve 
retainer 70 includes a central aperture 82. 
A pair of guide pins 84, 86 extend from valve plate 16 to underside 88 
cylinder head cover 20. For ease of assembly, guide pins 84, 86 are first 
press fit into a pair of holes 90 in valve plate 16 and are then captured 
within corresponding holes in cylinder head cover 20 as by a slip fit. The 
guide pins 84 and 96 may also fit in 20 holes in crankcase 12 as shown in 
FIGS. 1 and 2. Guide pins 84, 86 guidingly engage oval slots 92 in 
discharge valve retainer 70 at diametrically opposed locations therein. 
FIG. 5 shows a bottom view of valve plate 16 including the placement of the 
washer 74 creating an annular discharge port 71. Mounting holes 94 permit 
easy assembly with crankcase 12 and cylinder head 20 with bolts (not 
shown). Discharge holes 96 allow refrigerant at discharge pressure to flow 
from inside the cylinder head 20 to a discharge muffler system of the 
scotch yoke compressor (not shown). 
Operation of a piston in a multi-cylinder scotch yoke compressor is well 
known. Significant reductions in reexpansion of refrigerant can be 
achieved by having a counterbore 42 on the suction valve retainer 38 that 
creates an annular protuberance that substantially fills the annular 
discharge port 71 when the piston assembly 14 is at top dead center. 
It will be appreciated that the foregoing description of various 
embodiments of the invention is presented by way of illustration only and 
not by way of any limitation, and that various alternatives and 
modifications may be made to the illustrated embodiments without departing 
from the spirit and scope of the invention.