Piston assembly having multiple piece compression ring

A piston assembly for an internal combustion engine includes a piston having at least one annular compression ring groove within which is disposed a plurality of split piston rings. Each of the rings includes a ring gap and the rings are arranged in the groove with the respective gaps angularly misaligned and with adjacent flat surfaces of the rings contacting one another so as to close the gaps to prevent fluids from passing through the gaps when the piston operates in its cylinder bore.

TECHNICAL FIELD 
This invention relates to the construction of pistons and piston rings for 
internal combustion engines, compressors and other equipment and, more 
particularly, to the construction and arrangement of compression rings on 
a piston. 
BACKGROUND OF THE INVENTION 
In piston-type internal combustion engines, piston rings are used to 
prevent both losses of air and/or a mixture of air and fuel during the 
compression stroke of the pistons as well as preventing the products of 
combustion from entering the engine crankcase during the expansion stroke. 
During the compression and exhaust strokes of the pistons, lubricating oil 
is supplied to the cylinder walls of the engine. Such lubricating oil 
bathes the cylinders when the pistons are in any position within their 
stroke except at bottom dead-center. The rings of the piston scrape this 
oil into the crankcase during the downward intake and expansion strokes of 
the piston. 
The rings of the piston are split so that there is a ring gap formed 
between adjacent opposite ends of each ring. The gap can be measured to 
determine if the appropriate ring size is being used and the split 
construction facilitates installation of the rings within associated ring 
grooves extending circumferentially about the piston. The gaps further 
enable radial expansion and contraction of the rings caused by temperature 
variation and also to permit the rings to radially expand against the 
cylinder walls to compensate for wear. As the piston rings and cylinder 
walls continue to wear, the rings expand further outwardly increasing the 
size of their respective gaps. Thus, the gaps serve an important role in 
proper functioning of the piston rings. 
However, as well recognized by those skilled in this industry, the ring 
gaps are also detrimental to the performance of the engine. During the 
downward intake stroke of the piston, the gaps allow small quantities of 
the lubricating oil to enter the combustion chamber and likewise allow 
small quantities of the air or air/fuel mixture to enter the crankcase 
during the compression and expansion strokes of the pistons as well as 
some portions of the exhaust stroke. Oil in the combustion chamber is 
undesirable as it reduces performance, increases emissions, and increases 
oil consumption. The combustion gases entering the crankcase mixes with 
the crankcase oil causing it to degrade and produce noxious gases which 
eventually leave the crankcase as pollutants. 
Heretofore, there have been several approaches taken to solve the problem 
of gas and oil blow-by past the piston rings in an effort to increase 
engine efficiency and decrease emissions and oil consumption. These 
efforts include increasing the ring pressure on the cylinder walls and 
adding additional grooves and rings to the piston. The first approach 
increases friction between the piston rings and cylinder walls and thus 
negatively affects fuel consumption and increases the rate of wear. The 
latter approach adds to the size, weight and complexity of the piston and 
still permits a certain amount of blow-by since each additional ring is 
disposed in its own groove and hence spaced from the other rings allowing 
gas and oil to continue passing through the ring gaps. 
Multi-piece compression-type piston rings, have been proposed prior to this 
invention but are usually limited to the oil control ring of the piston. 
Such oil control rings include a pair of steel rails disposed in a single 
oil control ring groove of the piston and separated by a discreet 
spacer/expander element which maintains the rails spaced from one another 
and serves to force the rails with great radial tension against the 
cylinder walls when the piston is disposed within the cylinder. The rails 
are constructed much like the remaining compression rings of the piston 
but are generally much thinner and are made of steel with their rounded 
contact edge chrome plated. Because the rails are spaced from one another 
the oil and gases can pass through the gaps of the rails. 
Many of the same problems mentioned above also effect piston-type air 
compressors, as well as other mechanisms which utilize pistons to raise 
the pressure of working fluids or to extract power from them (piston-based 
expanders). 
Thus there is a need to provide a piston assembly having piston rings 
constructed and arranged so as to eliminate or substantially reduce the 
amount of oil and gas blow-by past the rings during operation of the 
engine, compressor or other machinery. 
SUMMARY OF THE INVENTION 
This invention overcomes the problems discussed above by providing a piston 
assembly having an annular compression ring groove and at least two split 
compression rings disposed in the groove with the gaps of the rings 
angularly misaligned and with adjacent side surfaces of the rings directly 
contacting one another advantageously sealing the gaps to effectively 
prevent the passage of fluids, such as oil and gases within a piston 
cylinder of an internal combustion engine through the gaps in the rings. 
Another advantage of this invention resides in the substantial reduction of 
radial tension applied by such a multiple-piece compression ring as 
compared to that of the single-piece compression rings. Less tension is 
needed on the multi-piece rings of this invention since each ring piece 
can expand outwardly against the cylinder walls independently of the other 
ring pieces to give improved ring conformity with the cylinder walls with 
less tension. The lower tension results in a corresponding increase in 
fuel efficiency and decrease in wear. 
The multi-piece compression ring of this invention may also result in a 
size and weight reduction of the piston assembly by requiring a fewer 
number of compression ring grooves and compression rings further adding to 
an increased fuel economy and reduction in the weight and complexity of 
the piston assembly. 
This invention is useful for automotive and other internal combustion 
engine applications as well as other mechanisms which utilize pistons to 
raise the pressure of working fluids or to extract power from working 
fluids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now in more detail to the drawings, a fragmentary exploded 
perspective view of a piston assembly constructed according to a presently 
preferred embodiment of this invention is indicated generally at 10 in 
FIG. 1 and comprises a cylindrical piston 12 mounted pivotally to a 
connecting rod 14 by a piston pin 16 in known manner. The piston 12 is 
adapted for traveling with reciprocating sliding movement inside a piston 
cylinder 18 of an internal combustion engine, compressor or expander 20, a 
fragmentary cross-sectional view of which is shown in FIG. 2. The piston 
could also be used in a compressor or expander device. The connecting rod 
14 is coupled to a crank shaft (not shown) mounted within a crankcase 
cavity 22 of the engine wherein rotation of the crank shaft imparts a 
reciprocating up and down movement of the piston 12 as viewed in FIG. 2. 
In the case of a four stroke internal combustion engine, the crank shaft 
moves the piston 16 through the various intake, compression, expansion and 
exhaust strokes. 
The piston 12 includes at least one annular compression ring groove 24 
extending circumferentially about an outer periphery of the piston 12. The 
groove 24 has a uniform width and depth. 
A multiple-piece compression ring assembly 26 is disposed in the groove 24 
and importantly comprises two or more discrete compression rings, there 
being three shown in the Figures wherein the first of the three is 
indicated at 28, the second at 30, and the third at 32. Each of these 
rings 28, 30, 32 is substantially circular and of a split construction 
such that each ring includes an associated pair of adjacent split ends 
spaced from one another so as to form associated ring gaps 34, 36, 38 
respectively there. The ends are perfectly squared off so as to be 
perpendicular to the thickness of the rings. 
Importantly, the rings 28, 30, 32 are arranged in the groove 24 having 
their respective gaps 34, 36, 38 angularly misaligned and with adjacent 
flat side surfaces (i.e., adjacent top and bottom surfaces) of the rings 
substantially contacting one another (i.e., either directly contacting or 
having a thin layer of lubricating oil at the interface) in order to 
axially close off or seal the gaps 34, 36, 38 thereby effectively 
producing a zero gap or gapless compression ring so as to prevent fluids 
within the piston cylinder from passing through the gaps 34, 36, 38 in the 
rings (i.e., eliminate or substantially reduce blow-by as compared to 
conventional single-piece compression ring arrangements having open ring 
gaps). When installing the rings 28, 30, 32 it is preferable to orient the 
gaps 34, 36, 38 with the maximum amount of angular spacing. Thus, when 
employing two rings, for example, the gaps should be spaced 180.degree. 
apart, with three rings 120.degree. apart (as shown in FIGS. 1 and 2), 
with four rings 90.degree. apart, and so on. 
Although the individual rings are free to rotate within the groove 24 
during operation of the piston assembly 10, statistically there is little 
probability of the gaps ever aligning so as to permit the passage of 
fluids therethrough. The probability of alignment decreases with 
increasing numbers of compression rings. With internal combustion engine 
20, the fluids within the piston cylinder 18 include oil which splashes up 
into the cylinder 18 from the crankcase 22 and gaseous fluids such as air 
and/or a mixture of air and fuel injected or otherwise drawn into a 
combustion chamber 40 of the engine 20 on the working side (i.e., top 
portion above the compression ring assembly 26) of the piston 12. 
Importantly, the multiple-piece compression ring assembly 26 substantially 
prevents any oil from entering the combustion chamber 40 and likewise 
prevents any gaseous fluids from the combustion chamber from entering the 
crankcase 22. 
One or more of the rings of the assembly 26 preferably comprises a very 
thin steel rail of the type typically used for multiple-piece oil control 
rings, but with a deeper crosssection. In the embodiment shown, the first 
28 and third 32 rings comprise such steel rails. The second ring 30 is a 
conventional split compression ring. It is preferred that the uppermost 
ring (i.e., the fire ring) be a steel rail whereas the remaining rings can 
be compression rings or rails or combinations thereof. As can be seen best 
in FIG. 3, the steel rails are substantially thinner than the compression 
ring and have rounded outer contact edges whereas the conventional 
compression ring 30 has a flat or "barrel-shaped" contact edge with the 
cylinder wall 18. The rails preferably are made of steel which may be 
plated with chrome. 
Often times, the piston cylinder 18 will distort under mechanical or 
thermal loads losing its preferable round bore shape and tending toward an 
oval shape. Conventional single-piece compression rings have difficulty 
conforming to such changes in cylinder wall shape producing a small amount 
of clearance between the ring and cylinder wall which in turn allows 
crankcase oil to enter the combustion chamber 40 of the cylinder 18. 
Increasing the ring tension against the cylinder wall helps to some degree 
but is generally undesirable as it increases the friction between the ring 
and cylinder wall thereby increasing wear and reducing fuel efficiency. 
Importantly, the multiple-piece compression ring assembly 26 of this 
invention overcomes such ring conformability problems experienced with 
conventional single-piece compression rings in that each of the ring 
pieces 28, 30, 32 can conform in different arcs of the piston cylinder 
providing a greater opportunity for the compression ring assembly 26 as a 
whole to conform to the outer roundness of the piston cylinder 18. That 
is, in regions where one of the rings may be deficient in conforming to 
the cylinder wall, there is opportunity for one or more of the other rings 
in the assembly 26 to achieve conformance. Also important is that the 
multiple-piece compression ring assembly 26 can be utilized with 
substantially less (i.e., 50% or more) radial tension than the 
conventional single-piece compression rings and yet provide equal or 
greater ring conformability. This feature is advantageous in that it 
decreases piston ring and cylinder wear and increases engine performance 
and fuel economy. Consequently, each of the rings in the multiple-piece 
compression ring assembly 26, including the steel rails, can be utilized 
without a circumferential expander element, as is normally associated with 
multiple-piece oil control rings which act to expand the steel rails with 
great force against the cylinder wall. Hence, the compression ring groove 
24 is devoid of any such expanding elements as shown in FIG. 3. 
The piston 12 may also include one or more additional annular compression 
ring grooves 42 extending circumferentially about the piston 12 within 
which may be disposed another multiple-piece compression ring assembly as 
described above or a conventional single-piece split compression ring 44 
as shown in the drawings. It is believed, however, that additional 
compression rings and grooves may not be required for most automotive 
internal combustion engine applications. Reducing the number of ring 
grooves reduces the weight and height of the piston, significantly 
reducing the height and weight of the engine block. 
The piston 12 may also include an oil control ring groove 46 below the 
compression ring grooves 24, 42 within which may be disposed any of a 
number of conventional oil control rings such as the multiple-piece 
control ring indicated at 48 in the Figures. Such an oil control ring 48 
includes a circumferential expander spacer element 50 sandwiched between 
and separating a pair of thin steel rails 52, 54 which are substantially 
similar (except for the radial depth) in construction to the rails 28, 32. 
In operation, as the piston 12 is moved downwardly through the intake 
stroke, air and/or a mixture of air and fuel is injected or otherwise 
drawn into the combustion chamber 40. The downward movement of the piston 
12 creates low pressure within the chamber 40 thus creating the 
opportunity for crankcase oil to be drawn on into the chamber. The 
multiple-piece compression ring assembly 26, however, closes the gaps in 
the rings 28, 30, 32 and conforms closely to the contours of the cylinder 
wall 18 so as to prevent such oil from entering the combustion chamber 40. 
Similarly, as the piston 12 move upwardly through the compression stroke, 
the compression generated in the process above the piston forces air or 
air-fuel mixture into the crankcase 22, as "blowby". The multiple-piece 
compression ring assembly 26 also prevents such combustion chamber gases 
from entering the crankcase 22. 
While the above description was directed toward a piston assembly for use 
with an internal combustion engine, it will be appreciated to one of 
ordinary skill in the art that the same multi-piece compression ring 
arrangement may be employed on other types of machinery using pistons for 
the purpose of pumping or compressing fluids and hence such applications 
are within the scope of this invention. 
While a preferred embodiment of this invention has been shown and 
described, other modifications will be apparent to those skilled in the 
art. Accordingly, the scope of this invention is set forth in the 
following claims.