Internal combustion engine

A two-cycle, two-cylinder opposed piston internal combustion engine having means for continuously adjusting the stroke of the engine and the blocking and unblocking of intake, transfer and exhaust ports with respect to each other as the engine is operating. Corresponding pistons of each cylinder are connected to respective ends of pivotally mounted rocker arms so that pistons in one cylinder move oppositely with respect to pistons in the other cylinder, the piston side surfaces alternately blocking and unblocking transfer and exhaust ports. Two connecting rods are provided, one of which is attached at one end to each of the rocker arms at a pivot point distal from the rocker arm pivotal mount and at the other end to a rotatably mounted eccentric, one end of which is formed into a shaft containing a power drive gear operatively connected to a drive shaft, the eccentric being rotated due to an up and down motion of the connecting rod. Means are provided for continuously varying the attachment points of the connecting rods to the rocker arms, thereby altering the allowable pivotable movement of the rocker arm and consequently the stroke or maximum spaced-apart distance of the pistons in each cylinder. Also, the shaft portion of one of the eccentrics forms twisted splines on its outer surface, its associated power drive gear being adapted to mesh with the twisted splines so that the gear is rotated as it is longitudinally displaced along the shaft. Means are provided for continuously displacing this gear thereby changing the angular relationship between the two rocker arms, and thus the relative positioning of the pistons contained in each cylinder. This changed position alters the blocking of the exhaust ports with respect to the unblocking of the transfer ports. Also disclosed is a remote combustion chamber and a means for ensuring that the volume in which combustion takes place remains substantially constant during the combustion process.

FIELD OF THE INVENTION 
The field of art to which the invention pertains includes internal 
combustion engines and, more specifically, two-cycle, opposed piston 
internal combustion engines. 
BACKGROUND AND SUMMARY OF THE INVENTION 
Two-cycle internal combustion engines are well known in the art and have 
been used for many and varied purposes. One specific variation of the 
two-cycle engine utilizes two cylinders, each having first and second 
opposed pistons whose surfaces are moved together and apart to define a 
combustion chamber. The first pistons of each cylinder are operatively 
connected at opposite ends of a pivotally mounted rocker arm, the second 
pistons of each cylinder also being operatively connected to a second 
rocker arm. The sides of the pistons in such an engine alternately open 
and close input and transfer ports whereby air or an air/fuel mixture may 
be entered into the piston-defined combustion chamber and the combustion 
products removed therefrom. (Hereinbelow, reference to "air" will comprise 
an "air-fuel" mixture whenever appropriate). However, the efficiency of 
conventional internal combustion engines varies as a function of engine 
r.p.m., manifold pressure, altitude, octane rating, and many other 
parameters. Consequently, engines are designed so that their peak 
efficiency occurs under certain predetermined conditions which are 
representative of anticipated or probable operating parameters. If the 
engine is operated under conditions different from this predetermined set 
of conditions, engine efficiency drops and the net effect is more fuel 
consumption. 
Three basic factors contribute to reduced efficiency as the engine is 
operated under conditions apart from the predetermined conditions. The 
first factor is the closing of the exhaust port either too early or too 
late with respect to the opening of the transfer port. In a two-cycle 
engine, the exhaust port is opened prior to opening of the transfer port 
for pressure equalization, the opening of the transfer port then forcing 
combustion products out the exhaust port. As one can appreciate, an 
optimum time for closing the exhaust port would be at the moment when the 
incoming air just reaches the exhaust port and has forced the last of the 
combustion products out through the exhaust port. If the exhaust port is 
closed prematurely, all of the prior combustion products will not be 
expelled, whereas if it is closed too late, some of the fuel within the 
air will be wasted. In conventional engines, this optimum closing of the 
exhaust port only occurs under one set of operating conditions. Another 
factor contributing to reduced efficiency in conventional engines is that 
the stroke, that is the maximum distance apart the pistons attain, is 
fixed. As is well known, the stroke determines the compression ratio of 
the engine, that is, the ratio of the pressure internal to the combustion 
chamber at the time of combustion with respect to the outside or manifold 
pressure. Therefore as the outside pressure decreases below an assumed 
design pressure due to a reduced throttle setting, increased engine speed, 
or increased altitude, the pressure in the combustion chamber at the time 
of combustion decreases. This lower pressure results in a less than 
optimum fuel burning efficiency. A third factor contributing to reduced 
efficiency in combustion engines is a change in volume of the combustion 
chamber during combustion, the change occurring because of piston travel 
during the combustion process. This volume change affects the efficiency 
of combustion and results in a less efficient use of the fuel. All of the 
above disadvantages of conventional engines combine to define an engine 
having less overall fuel efficiency than that potentially achievable. 
The present invention provides a two-cycle, opposed cylinder internal 
combustion engine which is more efficient than any conventional engine. 
The engine consists of a pair of cylinders each of which has first and 
second pistons that act oppositely in a predetermined phase relationship 
so that their facing surfaces are moved together and apart to define a 
stroke length and to at least partially define a combustion chamber. Also 
the piston side surfaces alternately block and unblock transfer ports and 
exhaust ports as they move together and apart. Means are provided for 
providing fuel to the combustion chamber through the transfer ports or for 
injection directly into a remote combustion chamber. A pivotally mounted 
first rocker arm is provided, the arm having opposite ends connected to a 
first piston in each cylinder for reciprocal movement thereof. A means 
connected to the second pistons for reciprocal movement thereof is also 
provided, in a specific embodiment the means being a second rocker arm. 
Two connecting rods are provided, one of which is rotatably attached at 
one end to each of the rocker arms at a pivot point distal from the rocker 
arm pivotal mount, and at the other end to a crankshaft which in a 
specific embodiment is an eccentric containing a power drive gear 
operatively connected to a drive shaft. The eccentric and power drive gear 
rotate as the connecting rod pivot point moves up and down due to 
oscillation of the rocker arm about its pivot point. The second rocker arm 
is similarly configured. The previously described disadvantages of 
conventional engines are minimized in an engine of the present invention 
which provides means for continuously varying the stroke or maximum spaced 
apart distance of the first and second pistons in each cylinder in 
accordance with changes in a predetermined performance parameter of the 
engine, a means for continuously varying the positional relationship of 
the first piston with respect to the second piston so that blocking an 
exhaust port by the second piston with respect to the unblocking of a 
transfer port by the first piston can be altered in accordance with a 
predetermined engine performance parameter, and a means for defining a 
combustion chamber which maintains a substantially constant volume during 
combustion. 
The stroke of the engine is adjusted by providing a means for continuously 
varying during engine operation the pivot point at which each connecting 
rod is attached to its respective rocker arm, the point of attachment 
determining the allowable pivotal movement of the rocker arm and thereby 
the maximum spaced-apart distance of the first and second pistons in each 
cylinder. By varying the rocker arm pivot point in accordance with engine 
manifold pressure, a means for compensating for changes in external 
pressure in order to achieve a predetermined pressure within the 
combustion chamber at the time of combustion is possible. In addition, the 
invention discloses a means for manually adjusting the stroke also as the 
engine is operating, thereby allowing an operator to adjust for differing 
gasoline octane ratings. 
Means for continuously varying the positional relationship of the first 
piston with respect to the second piston comprises one of the eccentrics 
forming a shaft having twisted splines on its outer surface, its 
associated power drive gear being adapted to mesh with the twisted splines 
so that as the gear is longitudinally displaced along the shaft, it will 
rotate in accordance with the twisted splines. In operation, as the power 
drive gear is displaced on the splined shaft, the shaft itself is forced 
to rotate thereby causing its associated rocker arm to pivot, the other 
rocker arm remaining stationary. Means are provided to control the 
longitudinal positioning of the power drive gear on the splined shaft as a 
function of engine r.p.m., thereby ensuring that the exhaust ports will be 
closed at the proper time with respect to the arrival of the input air. In 
addition, the phasing of the first rocker arm with respect to the second 
rocker arms is chosen so that during the time of combustion both first and 
second piston surfaces are traveling in substantially the same direction 
at the same velocity. This ensures that during the time of combustion, the 
combustion chamber volume is substantially constant. 
A remote combustion chamber is also disclosed, the chamber incorporating 
means whereby direct fuel injection, spark plug ignition or compression 
ignition can be utilized.

DETAILED DESCRIPTION 
As previously explained, the invention discloses a two cylinder, opposed 
piston, two-stroke internal combustion engine in which both the stroke of 
and phase relationship between two pistons contained within each cylinder 
piston pair can be varied during engine operation in accordance with 
various engine performance parameters. In addition, the invention provides 
the means by which a combustion chamber volume is maintained substantially 
constant during the combustion process. These three features allow the 
engine to operate with an efficiency heretofore unobtainable by 
conventional internal combustion engines. 
The basic elements of the engine can be seen in FIGS. 1 and 2. The engine 
consists of a left cylinder 10 and a right cylinder 12, the left cylinder 
containing a first piston 14 and a second piston 16 and the right cylinder 
12 containing a first piston 18 and a second piston 20. A first or upper 
rocker arm 24 pivots about an upper pivot point as shown at 26, the ends 
of the upper rocker arm 24 being connected to the first pistons 14 and 18 
through corresponding piston rods 28 and 30. In a similar manner, a second 
or lower rocker arm 34 pivots about a lower pivot point as shown at 36 and 
is connected to the second pistons 16 and 20 through corresponding piston 
rods 38 and 40. Thus one can appreciate that as the first and second 
pistons 14 and 16 of the left cylinder 10 move apart, the first and second 
pistons 18 and 20 of the right cylinder 12 necessarily move together due 
to the pivoting action of the upper and lower rocker arms 24 and 34. Thus 
a power stroke driving apart the first and second pistons 14 and 16 of the 
left cylinder 10 will provide some of the force necessary to effect a 
compression stroke by the first and second pistons 18 and 20 of the right 
cylinder 12. The length of a stroke, that is the maximum distance apart 
that the internal face 44 of the first piston 14 achieves in relation to 
the internal face 46 of the second piston 16, is determined by the angular 
travel of the upper rocker arm 24 and the lower rocker arm 34. Therefore, 
if this angular travel is restricted, a shorter stroke will be effected 
and if the angular travel is relaxed, a longer stroke will be effected. 
Also, if the angular relationship between the first rocker arm 24 and the 
second rocker arm 34 is changed, then the relative motion of the first 
piston 14 with respect to the second piston 16 will be altered. This 
relative motion will then alter the positioning of the internal faces 44 
and 46 of the left cylinder pistons 14 and 16 with respect to transfer and 
exhaust ports as will be explained below, thereby providing a means for 
altering the opening and closing of these ports. 
As previously stated, the stroke in both the left cylinder 10 and right 
cylinder 12, can be varied by controlling the pivotal angle through which 
the upper rocker arm 24 and lower rocker arm 34 can rotate. With respect 
to the pivotal rotation of the upper rocker arm 24, elongated slots 47 are 
provided in the left half of the rocker arm 24, the slots 47 being 
oriented so that their longitudinal axes are parallel to the longitudinal 
axis of the rocker arm. Referring to FIG. 3 in conjunction with FIGS. 1 
and 2, an upper or first connecting rod 48 is rotatably attached to a 
cross member 50, both ends of which extend through and are supported by 
the elongated slots 47. The lower end of the connecting rod 48 is 
rotatably connected to an eccentric 52 one end of which forms a twisted 
splined shaft 54, the eccentric 52 being rotatably secured by parallel 
mounting plates 55 so that it maintains a fixed relationship with respect 
to the upper rocker arm pivot point 26. Slidably received on the twisted 
splined shaft 54 is a power transfer gear 56 which is in meshing contact 
with a clutch boss gear 58, the rotation of which turns a drive shaft 60 
extending through the center of the engine. As the upper rocker arm 24 
rotates about its pivot point 26, the up and down motion of the upper 
connecting rod 48 in conjunction with the eccentric 52 will cause the 
twisted splined shaft 54 to rotate. The use of the eccentric 52 provides 
an action similar to that of the axially offset connecting rod attachment 
surfaces in a crankshaft of a conventional engine. In a similar manner, as 
further shown in FIGS. 5 and 6, power is transferred from the lower rocker 
arm 34 through a lower connecting rod 59 to also drive the clutch boss 
gear 58. It should be noted that the shaft 61 on which a lower power 
transfer gear 62 is mounted does not have twisted splines as does the 
upper shaft 54, for reasons that will be explained below. 
Referring again to the upper rocker arm 24, it can be seen that its angular 
travel will be determined by the length of the connecting rod 48 and the 
position of the cross member 50 in the elongated slots 47. As the 
cross-member 50 is repositioned within the elongated slots 47, the 
allowable angular travel of the upper rocker arm 24 will also vary, 
thereby changing the stroke of both the left cylinder 10 and the right 
cylinder 12. The limit over which this variance can occur is determined by 
the length of the elongated slots 47. Thus as one can appreciate, 
adjusting the position of the cross member 50 within its associated 
elongated slots 47, while at the same time adjusting the position of a 
lower cross member 63 in its corresponding elongated slots 64, both 
adjustments being effected while the engine is operating, will allow the 
stroke of each piston pair 14 and 16, and 18 and 20 to be continuously 
adjusted without changing the relative phase relationship between each 
piston pair. To effect this positioning, an upper stroke adjustment 
assembly 66 and an identical lower stroke adjustment assembly 67 are 
provided. Referring to the upper stroke adjustment assembly 66 for 
purposes of explanation, the adjustment can be effected in two ways, 
either by manually turning a control knob 68 or by rotating an adjustment 
bolt 70 which is in threaded contact with a holding bracket 72 attached to 
the upper rocker arm 24. Rotation of the adjustment bolt 70 or the control 
knob 68, will move the upper stroke adjustment assembly, thereby moving 
the cross member 50 within the elongated slots 47. In an operative engine, 
the control knob 68 could be mechanically coupled to a control knob in an 
automobile dashboard, and the threaded bolt 70 could be controlled 
automatically by any one of several engine performance parameters, 
examples of which include intake manifold pressure, engine speed, 
temperature, etc. Many devices for controlling the adjustment bolt 70 are 
well known in the art, one example of which could be a mechanical 
governor. In a similar manner, although not explained in detail, the lower 
stroke adjustment assembly 67 is simultaneously adjusted in accordance 
with adjustments to the upper stroke adjustment assembly 66, the 
assemblies 66 and 67 working together to change the stroke of the engine 
without changing the phasing of the pistons within each cylinder. 
Referring to the right cylinder 12 for illustrative purposes, intake air is 
drawn into the engine through a reed valve 80 in which the two inwardly 
slanting reeds 82 and 84 open outwardly to allow air to flow therethrough, 
the opening occurring when the pressure in the volume 86 internal to the 
reed valve 80 is less than the pressure external to the reed valve 80. 
However, as the pressure internal to the reed valve 80 exceeds the 
external pressure, then the reeds 82 and 84 seal against each other 
thereby preventing air from escaping back out through the valve 80. This 
type of valve is widely utilized in the fluid transfer art. Internal to 
the cylinder 12, an upper ring of air intake ports 88, a ring of transfer 
ports 90 and a lower ring of air intake ports 92 are provided. All air 
entering between the first piston 18 and second piston 20 internal faces 
93 and 94 respectively must pass through the transfer ports 90. The upper 
air intake ports 88 and lower air intake ports 92 allow air to be drawn 
into the cavities created between the pistons 18 and 20 external surfaces 
95 and 96 and the cylinder ends 97 and 98, the cavities being created as 
the pistons 18 and 20 move together. As the pistons 18 and 20 move apart, 
this air is compressed, the air in both volumes being connected via a 
transfer duct 99. As the pistons 18 and 20 continue to move apart, the air 
pressure continues to increase, the reed valve 80 being closed as 
previously explained until the internal face 93 of the first piston 18 
rises above the transfer ports 90. 
A ring of exhaust ports 102 is provided between the lower ring of air 
intake ports 92 and transfer ports 90. It is essential that the second 
piston 20 be of sufficient length that the exhaust ports 102 are always 
sealed from the cavity 103 directly below the second piston 20, thereby 
ensuring that combustion products will not contaminate input air. As the 
first and second pistons 18 and 20 move apart, the exhaust ports 102 open 
as a result of the second piston 20 moving downwardly. After the exhaust 
ports 102 open, an influx of pressurized air present at the transfer ports 
90, as previously explained, forces the combustion products out through 
the exhaust ports 102. It is desirable that all of the combustion 
products, but none of the input air, escape through the exhaust ports 102. 
Having thus explained operation of the pistons 18 and 20 in conjunction 
with the air input, transfer and exhaust ports 88, 92, 90 and 102, a 
further aspect of the invention can be appreciated. Referring again to 
FIGS. 1 and 2, one can appreciate that if the angle of one of the rocker 
arms 24 or 34 can be changed without changing the angle of the other 
rocker arm, then the closing of the exhaust ports 102 with respect to the 
opening of the transfer ports 90 can be varied. A means to vary closing of 
the exhaust ports 102 with respect to the time the transfer ports 90 are 
open would allow a more efficient engine operation as operating parameters 
change, the closing being regulated by any one of several engine 
performance parameters such as manifold pressure or engine r.p.m. As 
previously explained, a twisted spline shaft 54 is formed at one end of 
the eccentric 52. Slidably mounted on the twisted splined shaft 54 is a 
power transfer gear 56 which mates with the clutch boss gear 58. Referring 
now specifically to FIGS. 2 and 3, an adjustment collar 104 is formed as 
part of the power transfer gear 56. A positioning fork, not shown, mates 
with an annular ring 106 in the adjustment collar 104. As the positioning 
fork which is in sliding contact with the angular ring 106 moves outwardly 
as indicated by the arrow 110, the twisted splining of shaft 54 causes the 
upper connecting rod 48 to be repositioned due to rotation of the 
eccentrically formed twisted splined shaft 54 induced by movement of the 
power transfer gear 56. Thus, as the shaft 54 is rotated due to a change 
in the lateral positioning of the power transfer gear 56, the upper rocker 
arm 24 angle with respect to the lower rocker arm 34 angle is changed. As 
this angular change is effected, one can appreciate, by referring to the 
position of the first piston 14 in the left cylinder 10, that the position 
of its internal face 44 will change with respect to the transfer ports 109 
without any change in the position of the second piston 16 internal face 
46 with respect to the exhaust ports 111. Thus as the lateral positioning 
of the power transfer gear 56 is changed the opening and closing of the 
transfer ports 90 with respect to the opening and closing of the exhaust 
ports 102 is changed. As the power transfer gear 56 is moved inwardly and 
outwardly during engine operation, the phase relationship of the upper 
rocker arm 24 with respect to the lower rocker arm 34 is continuously 
varied. Means for positioning the gear 56 in accordance with any of a 
various number of engine parameters are well known in the art. As can be 
seen by reference to FIG. 4, a lower power transfer gear 62 which is 
operatively connected to the lower rocker arm 34 by the lower connecting 
rod 60 also drives the clutch boss gear 58. However, the shaft 61 on which 
the lower power transfer gear 62 is mounted is not splined as was the 
shaft 54 for the upper power transfer gear 56 because all of the necessary 
phase relationship changes can be effected by positioning only the upper 
power transfer gear 56. 
A needle bearing 120 is provided at the top of each piston rod 28, 30, 38 
and 40, each needle bearing being positioned in a notch 122 at each end of 
the upper and lower rocker arms 24 and 34. The notch 122 is important 
because each piston rod is fixedly attached to its respective piston, 
thereby resulting in a slight lateral movement with respect to the end of 
the rocker arm as the rocker arm pivots. Each piston rod in turn is 
positioned by an insert bearing 124 provided at each end of the cylinders 
10 and 12. 
Referring to FIGS. 1, 6 and 7 each of the cylinders has a remote combustion 
chamber 128 and 129. For purposes of explanation, the right cylinder 
remote combustion chamber 128 will be discussed, the left cylinder 
combustion chamber being identical in operation. The remote combustion 
chamber can accommodate an engine utilizing fuel injection in conjunction 
with spark plug ignition, spark plug ignition in conjunction with an 
air/fuel mixture entering through the transfer ports, and diesel operation 
in which fuel is ignited through compression heat. To achieve these 
various modes of operation, the remote combustion chamber has a first 
threaded orifice 130 for receiving a fuel injecting insert (not shown) and 
a second threaded orifice 132 for receipt of an igniting device such as a 
spark plug (not shown). Combustion occurs in a spherical cavity 136 
contained within the remote combustion chamber 128, a connecting channel 
138 leading from the spherical chamber 136 to the inside of cylinder 12, 
and the volume 140 defined by the internal faces 93 and 94 of the first 
and second pistons 18 and 20. The phasing of the upper rocker arm 24 with 
respect to the lower rocker arm 34 is chosen so that at the moment of 
ignition, and throughout the fuel burning process, the first piston 18 and 
second piston 20 are both moving in the same direction. Thus the volume 
140 between the pistons remains substantially constant throughout the 
burning process. With this volume relatively constant, and the volume of 
the spherical cavity 136 and the connecting channel 138 being fixed, then 
one can readily see that the total combustion volume does in fact remain 
substantially constant throughout the burning process, whereas in a 
conventional internal combustion engine movement of a single piston as a 
result of the burning process results in the combustion volume changing 
prior to the fuel being completely burned. The connecting channel 138 is 
angled downwardly and off-center from the spherical cavity 136 to the 
piston-enclosed volume 140. This downward angling establishes a swirling 
motion in the volume 140 thereby increasing fuel-burning efficiency 
therein. 
In operation, an engine according to the present invention has a stroke and 
transfer and exhaust port phasing which can be automatically varied in 
accordance with various engine operating parameters, thereby allowing it 
to be operated at near maximum efficiency under all conditions rather than 
at an assumed set of design conditions as with conventional engines. 
Referring to FIG. 1, as the first piston 18 and second piston 20 of the 
right cylinder 12 move towards each other, air, which could comprise an 
air/fuel mixture, is drawn through the reed intake valve 80 and into the 
upper intake ports 88, and lower intake ports 92, while at the same time 
compressing air supplied through the transfer ports 90. After combustion, 
the air entering through the upper and lower intake ports 88 and 92 is 
compressed as previously explained as the pistons 18 and 20 move apart. As 
the first piston 18 reaches the position shown in the left cylinder 10, 
the compressed air is forced through the transfer ports 90 into the volume 
partially defined by the first piston internal face 93 and the second 
piston internal face 94. At this time the second piston 20 is in the 
position shown for the second piston 16 in the left cylinder 10, thereby 
opening the exhaust ports 102. The compressed air entering through the 
transfer ports 90 forces the combustion products inside the cylinder out 
through the exhaust ports 102. Positioning of the second piston 16 is 
controlled by the lower rocker arm 34 so that the exhaust ports 102 will 
be blocked just as a wave of air entering through the transfer ports 90 
reaches them. The transfer ports 90 remain open after the exhaust ports 
102 are closed for maximum cylinder charging. Thus one can appreciate that 
this opening and closing of the exhaust ports 102 with respect to the 
transfer ports 90 will vary as a result of engine operating conditions. 
For example, the ratio of time it takes incoming air to travel from the 
transfer ports 90 to the exhaust ports 102 with respect to the time of a 
compression/combustion cycle will vary as a function of engine r.p.m. Thus 
the angle of the upper rocker arm 24 with respect to the angle of the 
lower rocker arm 34 must be continuously adjusted if maximum engine 
efficiency is to be achieved. The invention provides a means for 
continuously effecting this adjustment by changing the lateral position of 
the power transfer gear 56 on the twisted splined shaft 54 in accordance 
with engine r.p.m. 
In addition, it can be appreciated that pressure exerted on the incoming 
air as a result of the piston movement is determined by the stroke of the 
engine, a longer stroke providing more highly pressurized air at the 
transfer ports 90. As already explained, the invention provides a means 
for continuously varying the stroke as the engine is operating by 
positioning of the cross-members 50 and 63 in each of the rocker arm 
elongated slots 47 and 64, respectively. Thus, the stroke is increased to 
compensate for the loss of air mass due to reduced throttle settings. 
Also, as previously explained, the invention provides for a manual 
adjustment of the stroke through the control knob 68 which can be 
manipulated from the dashboard of a car. Thus, an operator can vary the 
compression ratio of the engine to accommodate any octane or cetane rated 
fuel. Also as previously explained, the remote combustion chamber 128 is 
fitted to receive both a fuel injector fixture or a spark plug. This 
allows the engine to function either as a spark ignition or a compression 
ignition engine. 
Advantages of the above described engine include a means for automatically 
varying the phasing of each piston in order to compensate for sluggishness 
of fuel flow occasioned by increasing engine speeds. Also both the air 
incoming through the transfer ports 90 and the combustion products 
outgoing through the exhaust ports 102 are transferred at the point in the 
piston travel where piston movement per degree of crankshaft rotation is 
at a minimum. Thus, the transfer ports and the exhaust ports are open a 
maximum possible time for the minimum possible piston movement. Also since 
the exhaust piston leads the intake piston, the intake piston is moving in 
the same direction and at substantially the same velocity as the exhaust 
piston at the time of combustion, thereby resulting in a substantially 
constant volume throughout the burning period. As one can also appreciate, 
any number of these basic two-cylinder units can be attached by utilizing 
the drive shaft 60 as a common drive shaft for all units.