Reciprocating piston machine

This invention relates to reciprocating piston machines which use the crankcase for pumping air or charge. The connecting rod with extension partitions the interior of the crankcase including the lower cylinder into two varying volumes during a portion of each revolution of the crankshaft. A unique feature is that the designer can choose the capacity of the crankcase pump independent of other significant design parameters such as the ratio length of connecting rod/stroke and the ratio stroke/bore.

FIELD OF THE INVENTION 
My invention relates to reciprocating piston machines in which the piston, 
the cylinder, the connecting rod with extension, the crankshaft and 
crankcase form the elements of an oscillating vane machine. 
DESCRIPTION OF RELATED ART 
In substantially all of the present day reciprocating piston machines a 
crankshaft and a connecting rod are used to transmit power to or away from 
the piston. Since a crankshaft, a connecting rod, a piston, and the 
structure surrounding these components are already present is desirable 
objective to have these components function in a manner so that they 
provide the air induction capacity desired by the designer. This invention 
accomplishes this objective in a simple, unique way. In my earlier U.S. 
Pat. No. 2,844,131, Jul. 22, 1958, I disclosed a similar reciprocating 
piston machine in which the piston, the cylinder, the crankshaft, the 
crankcase and the connecting rod formed the elements of an oscillating 
vane pump. The invention did not provide the designer with a choice of the 
magnitude of the volume of air pumped by the crankcase compared to the 
piston volumetric displacement. As a result there was a limited range of 
flexibility in design. The invention disclosed herein overcomes the 
inherent design limitation of the previous invention without increasing 
the number of moving parts or significantly increasing the weight, overall 
physical size or cost of the machine. As a result the utilization of the 
present invention is expected to be much greater than was the case of my 
previous invention, U.S. Pat. No. 2,844,13 1. Other related prior art 
includes U.S. Pat. No. 3,402,705, J. D. Stevenson, Sep. 24, 1968. In his 
invention several additional components are included in the crankcase to 
form a oscillating vane pump. These additional components cause added 
complexity, friction, wear, cost and weight not present in the current 
invention. 
My invention overcomes the above discussed difficulties inherent in 
presently known crankcase compressor reciprocating piston machines. For 
similar reciprocating piston machines (engines) the power output potential 
is proportional to the maximum air induction capacity per cycle. Thus an 
increase in air induction capacity without materially increasing the 
physical size, weight or cost of the machine is expected to provide 
increased power. 
An object of my invention is the design, construction and arrangement of 
components to increase the aspirating or air induction capacity per cycle 
to an amount substantially in excess of the volumetric displacement of the 
piston. Another object of my invention is to achieve the above mentioned 
increase in aspirating or breathing capacity without the use of auxiliary 
machinery, without increasing the number of moving parts and without 
materially increasing the size, weight, or cost of the machine. Another 
object of my invention is to provide a basic configuration in which the 
designer can choose or adjust the volume of air induced relative to the 
volumetric displacement of the piston. Thus the designer may choose 
increased pumping capacity to supercharge the cylinder. Another object of 
this invention is to make a crankcase scavenge pump with a pumping 
characteristic which corresponds to the cylinder inlet transfer port open 
area, i.e., substantial pumping occurs while the cylinder inlet transfer 
ports are open. Another object of this invention is to make a two-cycle 
engine whose power and operating characteristics are relatively 
insensitive to back pressure of the exhaust system thereby allowing an 
effective muffler system. Another object of my invention is to make a 
reciprocating piston machine having a large breathing capacity and having 
small vibration forces, i.e., the design is compatible with my co-pending 
patent application having Ser. No. 08/144,675. Another object of my 
invention is to provide a bypass control system for the reciprocating 
piston machine that minimizes the partial load pumping power required. 
BRIEF DESCRIPTION OF THE DRAWINGS 
In accomplishing these and other objects, I have provided improved details 
of structure, exemplary forms of which are illustrated in the accompanying 
drawings, wherein:

DESCRIPTION OF PREFERRED EMBODIMENT 
In FIGS. 1 and 2, I have shown an embodiment of a two-cycle internal 
combustion engine designated generally as 20. The engine 20 comprises a 
cylinder 21 having inlet port or transfer port 22 and exhaust port 23 
which are periodically opened and closed by the reciprocating motion of 
the piston 24. The crankshaft 25, rotatably mounted within the crankcase 
28, has full circular webs or discs 26 which have their inner faces or 
surfaces 27 machined so they are flush or aligned with the bore of the 
cylinder at its maximum dimensions in the planes perpendicular to the axis 
of the crankshaft. The peripheries of the webs are machined to allow no 
more than a close clearance in the crankcase 28. The crankshaft turns in a 
counterclockwise direction, FIG. 1. 
The connecting rod 29 is pivotally connected at the upper end to the piston 
24 and rotatably connected to the crankshaft 25 at the central section. 
The connecting rod 29 is substantially as wide as the bore of the cylinder 
or the distance between the inner faces of the crankshaft webs 27 and the 
inner surface of the wall of the cylinder. The cylinder wall has diametric 
reliefs 31 machined in it to prevent interference with the side edges of 
the connecting rod 30. The diametric cylinder reliefs 31, hereinafter 
referred to as flats, are flush with the inner faces of the crankshaft 
webs 27. 
The connecting rod 29 has an extension 32 opposite the piston pin end of 
the connecting rod 33. The extension 32 is as wide as the bore and has no 
more than a close clearance with respect to the inner surfaces of the 
crankcase 28 during a portion of each revolution of the crankshaft 25. In 
addition., the piston pin end of the connecting rod 33 is circular and 
forms a close clearance with respect to the inside or underside of the 
piston 24. Furthermore, the upper ends of the connecting rod side webs 34 
form a close clearance with respect to the piston 24. 
Thus, there is formed partition means including the connecting rod 29 with 
extension 32, said partition means divides the crankchamber or the 
interior of the crankcase and the interior of the cylinder below the 
piston into two mutually isolated compartments or chambers during a 
portion of each revolution of the crankshaft. One chamber 38, is on the 
left hand side of the connecting rod 29 and one chamber 39, is on the 
right hand side of the connecting rod 29 with extension 32. 
The crankcase 28 is provided with a charge suction port or crankcase port 
35. In communication with the crankcase port 35 is carburetor 36. A 
transfer passage 37 extends between the interior of the crankcase or 
crankchamber and the cylinder inlet port 22. The cylinder 21 may be fitted 
with a spark plug for ignition of the charge (not shown). The extension 32 
may be provided with a balance weight 50 per my co-pending U.S. patent 
application Ser. No. 08/144,675. The balance weight is sized to cause the 
center of gravity of the piston-connecting rod assembly to be 
substantially on the axis of rotation of the crankpin 51. Thus 
counterweights (not shown) on the crankshaft 25 can balance the vertical 
and horizontal inertial forces of the reciprocating piston machine 20. 
OPERATION 
In operation when the piston 24 is at the top of its stroke, the entire 
crankchamber, or interior of the crankcase, is in communication with the 
interior of the cylinder below the piston and the crankcase port 35. This 
condition exists during the down stroke of the piston until the extension 
of the connecting rod 32 passes the crankcase port 35. At this point the 
connecting rod 29 with extension 32 and piston 24 divide the interior of 
the crankcase and the interior of the cylinder below the piston into two 
chambers or two compartments. One chamber, designated 38, is associated 
with the crankcase port 35 and the other chamber, designated 39, is 
associated with the transfer passage 37. This condition is maintained 
until the crankshaft 25, connecting rod 29 with extension 32 and piston 24 
reach a predetermined position, which is usually after the scavenging 
process is over. 
It is apparent that during the down stroke of the piston, after the 
extension of the connecting rod 32 has passed the crankcase port 35, the 
chamber 38 associated with the crankcase port 35 is increases in volume 
and the chamber 39 associated with, or in communication with, transfer 
passage 37 is decreases in volume. The continuously changing volumes of 
the two chambers 38 and 39 produce the pumping or compressing action of 
the crankcase compressor. 
The cylinder scavenging process commences during the down stroke of the 
piston when the piston 24 uncovers the cylinder inlet port 22. Charge 
compressed in the chamber 39 flows through the transfer passage 37 and the 
cylinder inlet port 22 thereby scavenging the interior of the cylinder 
above the piston 40. The scavenging process continues until the piston 24 
covers the cylinder inlet port 22 on the up stroke of the piston 24. 
The chamber 39 associated with or in communication with the transfer 
passage 37, i.e., the crankcase compressor clearance volume, continues to 
decrease in volume for an interval after the bottom-dead-center position 
of the piston even though the piston 24 has commenced its up stroke due to 
the motion of the connecting rod 29 with extension 32 compared to the 
motion of the piston 24. This occurs because the extension 32 is moving 
rapidly to the right causing the crankcase compressor clearance volume 39 
to decrease while the piston 24 is slowly rising in the cylinder 21 
tending to cause the clearance volume 39 to increase. 
At some position, usually after the scavenging process is over, the chamber 
39 associated with the transfer passage 37 begins to increase in volume 
because of the relative motions or displacements of the connecting rod 29 
with extension 32 and the piston 24 during the latter portion of the up 
stroke of the piston 24. When this condition is reached, or shortly 
thereafter, the close clearance between the extension 32 and the inner 
surface of the crankcase 28 is terminated and the cycle is concluded when 
the piston reaches top-dead-center position. Thus, the piston and the 
connecting rod with extension function as a unit within the cylinder and 
crankcase to divide the interior of the cylinder below the piston and the 
interior of the crankcase into two mutually isolated chambers during a 
portion of each revolution of the crankshaft. 
The pumping capacity of the crankcase pump compared with the piston 
displacement per my original invention, U.S. Pat. No. 2,844,131, is 
approximately proportional to the ratio stroke/bore. Thus an engine 
designed with a ratio stroke/bore equal to 0.7 has only 70 percent of the 
crankcase pumping capacity of an engine designed with a ratio stroke/bore 
of 1.0. Since engines with a lower ratio stroke/bore (approximately 0.70) 
are relatively more compact, have lower weight and can run at higher speed 
for increased power the inherent reduced pumping capacity is a 
shortcoming. In the present invention, the designer can choose the 
crankcase pumping capacity per unit piston displacement independent of the 
choice of the parameter stroke/bore. Increased pumping capacity is 
obtained by increasing the length of the extension on the connecting rod 
and the surrounding structure. 
In recent years there has been a trend to design two-cycle engines using a 
short connecting rod compared to the stroke of the engine, i.e., the ratio 
of length of the connecting rod (from the axis of the crankpin to the 
piston pin) to the stroke of the piston is in the range 1.6-1.5, down from 
2.0-1.8. A short connecting rod results in a much more compact engine 
having relatively lower weight. Since the pumping capacity of a connecting 
rod per my original U.S. Pat. No. 2,844,131, is approximately proportional 
to the length of the connecting rod, a reduced length connecting rod is 
accompanied by a reduced pumping capacity. 
The invention disclosed herein provides a means for the designer to 
increase the pumping capacity of the crankcase pump independently of the 
selection of the major engine design parameter, ratio length of connecting 
rod/stroke. Increased length of the extension provides increased pumping 
capacity without affecting the choice of stroke/bore or length of 
connecting rod/stroke. 
Another significant feature of the extension of the connecting rod opposite 
the piston per this invention is that the extension for pumping is 
compatible with the moment arm for the balance weight means described in 
my co-pending patent application Ser. No. 08/144,675. Thus the extension 
on the connecting rod per this invention and the balance weight per my 
co-pending invention can provide a single cylinder piston machine with 
large breathing capacity (designer's choice) and near zero vertical and 
horizontal vibration forces. 
Another facet of this invention is that the positive displacement pumping 
occurs primarily during the portion of the cycle when the transfer ports 
are open. Conventional crankcase pumps have precompression and essentially 
no pumping capacity during the portion of the cycle when the transfer 
ports are open. Thus the scavenge flow process is essentially a blowdown 
flow process which is relatively independent of speed. This results in an 
excessive mixing loss at low speed causing poor scavenge efficiency and 
hard starting. Also, the large clearance volume without positive 
displacement pumping makes the engine power very sensitive to back 
pressure, i.e., more back pressure less through flow and less power 
output. As a result, most two-cycle engines are fitted with ineffective 
mufflers causing noisy operation. The current invention provides a 
majority of the scavenge flow at/near bottom dead center when the transfer 
ports are at/near maximum opening. As a result, the scavenge flow process 
is more nearly at constant pressure (as a function of crank angle) which 
means that scavenge efficiency is greatly improved at all speeds and the 
engine can tolerate a higher back pressure without loss of through flow 
and a corresponding loss of power output, i.e., the exhaust flow can be 
effectively muffled making a powerful and quiet engine. 
In FIG. 3 there is shown a bypass flow control system which reduces pumping 
power at partial load as compared with a throttle type system. The bypass 
valve 60 and return to suction duct 61 provide an alternative flow path 
for the air/charge pumped by the crankcase compressor per this invention. 
The alternative flow path (versus the transfer passage) minimizes the 
pressure rise across the connecting rod with extension thereby reducing 
the power input to the positive displacement crankcase pump. 
Although the invention is described with respect to a preferred embodiment, 
modifications thereto will be apparent to those skilled in the art. 
Therefore, the scope of the invention is to be determined by reference to 
the claims which follow.