Fluid power engine

A fluid power engine is disclosed. A pair of axially aligned and opposed combustion pistons oscillate in a pair of opposed cylinders. The pistons are connected to each other by a common axial shaft. A fluid power piston is adapted to the shaft and oscillates in a fluid cylinder. Upon oscillating action of the combustion pistons, the fluid power piston oscillates to produce fluid power. By means of a fluid power return assembly, a portion of the fluid power produced is returned to the fluid power piston to urge the combustion pistons in their return directions after their respective firing strokes. The fluid power return assembly includes a spool valve that is actuated by means of physical contact with the combustion pistons.

BACKGROUND OF THE INVENTION 
1. Field 
The present invention is directed to an engine having a combustion piston 
linked with a fluid power assembly to pressurize a fluid, a portion of the 
pressurized fluid being returned to urge the combustion piston in the 
direction of its return stroke. 
2. State of the Art 
Internal combustion engines typically have one or more pistons linked with 
a crankshaft. After ignition of the fuel, energy released from the ignited 
fuel is delivered to the crankshaft, which rotates in response to the 
reciprocating motion of the piston. This energy is typically ultimately 
delivered to a machine that the engine is adapted to power. A common use 
of internal combustion engines is, of course, their use in automobiles. 
Crankshaft-style internal combustion engines in automobiles inherently 
allow for energy loss at various junctures. For example, energy is lost 
through friction in the transfer of the reciprocating motion of the piston 
to rotational motion of the crankshaft. Further energy is lost in 
transferring the rotational motion of the crankshaft to rotation, for 
example, of parts within a transmission, differential, and ultimately the 
wheels of the automobile. The engine is subject to vibration and wear at 
various locations due to internal forces exerted on various mechanical 
parts. 
One engine design that eliminates a crankshaft is known as the "free 
piston" engine. Free piston engines typically have two opposed pistons 
connected by an axial shaft. They are typically two-stroke engines, and 
are typically used as air compressors. 
A problem with free piston engines is that as the work load that the engine 
is operating against increases, the engine may power down more easily than 
a crankshaft-style engine. The free piston engine does not have the 
rotational momentum of a crankshaft to aid in returning the pistons in the 
direction of their return strokes. 
Fluid power systems are recognized as being highly efficient. Once fluid 
pressure is generated within a system, that pressure is transmitted 
essentially instantaneously throughout the fluid in the system and is 
immediately available for work at selected points in the system. Hydraulic 
systems are particularly useful because of the essential 
noncompressibility of liquids. When crankshaft-style engines are used to 
develop fluid power, the reciprocating motion of the combustion piston is 
transferred to rotational motion of the crankshaft, which is then 
transferred in some form to a pump to pressurize the selected fluid. 
Free pistons have been recognized for their utility in air compressors 
because the linearly reciprocating motion of the combustion piston may be 
transferred directly to a linearly reciprocating pumping piston of a 
compressor piston. However, once a substantial load is placed on the 
engine in a fluid power system (pneumatic or hydraulic), the power-down 
problems previously discussed may occur. 
There remains a need for an engine adapted to be useful in a fluid power 
setting that avoids the power-down problems of currently known free piston 
engines while avoiding the energy losses inherent in a crankshaft-style 
engine. 
SUMMARY OF THE INVENTION 
The present invention provides a fluid power engine. A combustion piston is 
reciprocatingly associated with a combustion cylinder and has a firing 
direction and a return direction. Carburetion means is associated with the 
cylinder to introduce fuel into the cylinder. Ignition means is associated 
with the cylinder to ignite the fuel in the combustion cylinders to 
thereby urge the combustion piston in its firing direction. Fluid power 
output means is associated with the combustion piston to pressurize the 
fluid upon movement of the combustion piston in its firing direction. And 
a fluid power return assembly is associated with the combustion piston and 
the fluid power output means and has a directional control valve adapted 
to direct the pressurized fluid to force the combustion piston toward its 
return direction. 
In a preferred embodiment, the engine comprises two combustion pistons. 
These combustion pistons are preferably mechanically opposed. In a highly 
preferred embodiment, the pistons are linked together by means of a common 
axial shaft. 
The directional control valve may be a spool valve, and may be adapted to 
actuate based upon physical engagement with the combustion pistons. The 
fluid power return assembly may include a fluid return piston mechanically 
linked with the combustion pistons to be actuated by the pressurized fluid 
to force the combustion pistons toward their respective return directions. 
Fluid power engines of the invention avoid the inherent energy losses of a 
crankshaft-style engine. Nevertheless, by means of a direction control 
valve, a portion of the fluid power energy produced by the internal 
combustion is returned to force the combustion piston in its return 
direction, thus helping the engine avoid the power-down problems typically 
found with free piston engines.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
Referring to FIG. 1, the illustrated fluid power engine includes a first 
piston 20, second piston 22, first cylinder 24, second cylinder 26, 
carburetor 30, carburetor 32, crossover tube 34, crossover tube 36, fluid 
input tube 38, fluid output tube 40, fluid piston 42, spool valve 44, and 
spool valve 46. 
The engine of FIG. 1 operates in a two-stroke mode, as described more 
completely below. The carburetion and ignition systems of the disclosed 
engine are typical of those found on crankshaft-style two-stroke engines, 
such as those found on motorcycles, snowmobiles, etc. The construction of 
such engines is well known in the art. Therefore, the carburetion and 
ignition systems of the engine of FIG. 1 are shown schematically. Although 
the shown engine is a two-stroke engine, an engine of the invention may 
also be adapted to be a four-stroke engine. Also, although two positions 
are shown, an engine may be constructed consistent with the invention to 
have only one piston operating in a single cylinder. 
Carburetor 30 associates with cylinder 24 at a port 50 formed in the wall 
of cylinder 24. Similarly, carburetor 32 associates with cylinder 26 at a 
port 52 formed in the wall of cylinder 26. Carburetor 30 includes a reed 
valve 54 and carburetor 32 includes a reed valve 56. These reed valves 
preclude gases from reentering the carburetors after the gases have been 
expelled into cylinders 24 and 26, as described more completely below. 
Crossover tube 34 associates with cylinder 24 at ports 58 and 60, which 
are formed in the walls of cylinder 24. Similarly, crossover tube 36 
associates with cylinder 26 at ports 62 and 64 formed in the walls of 
cylinder 26. An exhaust port 66 is formed in the walls of cylinder 24 and 
an exhaust port 68 is formed in the walls of cylinder 26. A spark plug 70 
is attached to cylinder 24 as shown and a spark plug 72 is attached to 
cylinder 26, as shown. 
Fluid input tube 38 is connected to the engine at ports 78 and 80 formed in 
the engine wall 82, as shown. Similarly, fluid output tube 40 is connected 
to the engine at ports 82 and 84 formed in wall 86 of the engine. 
Fluid piston 42 and piston shaft 28 associate within a cylindrical channel 
formed in the engine block to form an annular chamber 90 between shaft 28 
and cylindrical wall 92 of the engine. Fluid input tube 38 fluidly 
associates with annular chamber 90 by means of ports 96 and 98 formed in 
wall 92. Similarly, output tube 40 fluidly associates with annular chamber 
90 by means of ports 100 and 102 formed in wall 92, as shown. Because of 
the action of spool valve 44, only one of ports 96 or 98 is open at any 
given time. Similarly, because of the action of spool valve 46, only one 
of ports 82 or 84 is open at any given time. 
Spool valve 46 forms an integral part of a fluid power output assembly 
adapted to direct fluid power produced by the oscillation of pistons 20 
and 22 to a fluid power circuit, described below. Spool valve 46 forms an 
integral part of a fluid power return assembly adapted to return a portion 
of the fluid power produced to urge the combustion pistons 20 and 22 in 
their respective return directions. 
Both spool valves 44 and 46 are directional control valves. They are not 
check valves that merely preclude backward motion of fluid, but actuate in 
response to oscillating motion of the combustion pistons to direct fluid 
to different parts of the fluid circuit based upon the position of the 
piston. Rather than being spool valves, either valve 44 or valve 46 may 
optionally be replaced with another type of directional control valve, 
such as a rotary valve, a solenoid-actuated valve, a servo valve, or any 
other type of valve system adapted to control the direction of fluid, 
based on the position of other mechanical elements. 
Cylinders 24 and 26 are preferably formed of cast iron. Pistons 20 and 22 
are preferably formed of lightweight aluminum alloy. Other moving elements 
of the engine such as shaft 28, spool valve 44, and spool valve 46 are 
formed of hardened steel. 
The operation of the engine is now described in reference to FIGS. 1-7. In 
the position shown in FIGS. 1 and 2, piston 20 has reached the end of its 
return stroke and piston 22 has reached the end of its firing stroke. 
Piston 20 is ready to begin its firing stroke and piston 22 is ready to 
begin its return stroke. The direction of the firing stroke of piston 20 
is indicated by arrow 51 and the direction of the firing stroke of piston 
22 is indicated by arrow 53. Conversely, the direction of the return 
stroke of piston 20 is indicated by arrow 53 and the direction of the 
return stroke of piston 22 is indicated by arrow 51. In other words, the 
firing and return stroke directions of pistons 20 and 22 are directly 
opposite. 
With piston 20 in its orientation shown in FIG. 1, it covers ports 60 and 
66. Piston 22 is in contact with spool valves 44 and 46 and has urged the 
spool valves into their positions shown in FIG. 1. In this configuration, 
input tube 38 is fluidly connected to annular chamber 90 by means of ports 
78 and 96. Output tube 40 is fluidly connected to annular chamber 90 by 
means of ports 102 and 84. 
In this configuration, inductive sensor 76 senses the close proximity of 
piston 22 and a signal is given to ignite spark plug 70 to introduce a 
spark into cylinder 24. This spark ignites the fuel that has been recently 
introduced into cylinder 24 in a manner that will become clear below to 
urge piston 20 in its firing direction (arrow 51). A preselected pressure 
of fluid in tube 38 also acts against surface 114 of piston 42 to aid in 
urging piston 42 in the direction of arrow 51. A useful such pressure for 
the liquid pressure in tube 38 has been found to be approximately 1500 
pounds per square inch. 
With the engine in its configuration shown in FIG. 2, fresh fuel mixture 
has entered cylinder 24 from carburetor 32. At the same time, fresh fuel 
mixture that has entered cylinder 26 has been squeezed through crossover 
tube 36 and into cylinder 26 ahead of piston 22. Spent exhaust fumes are 
at the same time forced out of cylinder 26 out of exhaust port 68. 
Pistons 20 and 22 continue to move in the direction of arrow 51 until they 
eventually assume the configuration shown in FIG. 3. Fresh fuel mixture is 
then being compressed by piston 22 in cylinder 26 while fresh fuel mixture 
enters behind piston 22. Hydraulic liquid in annular chamber 90 is 
compressed ahead of piston 42 to exit port 84 and tube 40 (FIG. 1). The 
pressure in tube 40 also preferably maintains a preselected value. A 
useful value for this pressure is approximately 2500 pounds per square 
inch. 
Pistons 20 and 22 continue to move in the direction of arrow 51 until 
piston 20 makes initial contact with spool valves 44 and 46, as shown in 
FIG. 4. At this time, the fresh fuel mixture has mostly been urged into 
crossover tube 34 and the interior of cylinder 24. Much of the spent 
exhaust gas has been expelled from cylinder 24. Meanwhile, fresh fuel 
mixture has entered behind piston 22 to fill cylinder 26 and behind piston 
22. 
As pistons 20 and 22 continue their movement in the direction of arrow 51, 
piston 20 urges spool valves 44 and 46 to their configuration shown in 
FIG. 5. At this time, port 78 is closed while port 80 is opened and port 
82 is opened while port 84 is closed. Piston 20 has reached the end of its 
firing stroke, while piston 22 has reached the end of its return stroke. 
Inductive sensor 74 (FIG. 1) senses the close proximity of piston 20 and 
produces a signal to cause spark plug 72 to ignite. 
FIGS. 6 and 7 depict the exact reverse of the carburetion and exhaust 
action as depicted in FIGS. 3 and 4 with the movement of pistons 20 and 22 
in the direction of arrow 53, rather than in the direction of arrow 51. At 
the same time, fluid pressure present at port 80 and port 98 exerts fluid 
pressure on surface 134 (FIG. I) of piston 42 to aid in urging piston 42 
in the direction of arrow 53. Port 82 is connected through spool valve 46 
to port 100 so that piston 42 is allowed to pressurize the fluid ahead of 
its annular chamber 90 to continue to pressurize the fluid in tube 40. 
The engine continues to oscillate in this fashion back and forth in the 
direction of arrows 50 and 52 and act as a pump to pressurize the fluid in 
tube 40 at a higher pressure than the pressure received at tube 38. The 
energy used to do work on the hydraulic fluid is gained from the chemical 
energy released upon combustion of the fuel. The pressure in tube 38 acts 
somewhat like a crankshaft in helping to return the pistons in the 
direction of their return strokes. 
A description of a fluid power circuit used in conjunction with the engine 
of FIGS. 1 through 7 is described in reference to FIG. 8. The fluid power 
system of FIG. 8 includes a fluid piston 150, directional control valve 
152, pressure relief valve 154, charge pump 156, hydraulic motor 158, 
fluid reservoir 160, and flywheel 162. 
Fluid piston 150 is constituted by piston 42 operating with annular chamber 
90 and the associating ports shown in FIG. 1. Energy to operate pump 156 
is obtained from ignition of fuel in the internal combustion engine shown 
in FIG. 1. 
Pump 156 is therefore connected to output tube 40 and to input tube 38, as 
shown. When the engine of FIG. 1 is not moving, it is necessary to begin 
motion of the engine in some fashion. Typical internal combustion engines 
used in automobiles have an electric starter motor that mechanically 
engages the flywheel to begin rotational motion of the crankshaft and 
operation of the piston assembly. In the present engine, a charge pump 156 
driven by the flywheel 162 forces fluid under pressure into line 38, the 
pressure in tube 38 is directed through the directional control valve 152 
to urge piston 42 (FIG. 1) towards its firing stroke. With each 
reciprocation of the fluid piston 150, the directional control valve 152 
reverses the fluid flow to allow a return stoke. When the intake system 
finally provides a properly mixed intake charge, ignition takes place and 
the fluid piston 150 transfers the pressure of combustion to fluid 
pressure in tube 40. The fluid in tube 40 is forced under pressure through 
the hydraulic motor 158. At this point, the flywheel 162 is being driven 
by fluid under pressure in tube 40 through hydraulic motor 158. The fluid 
in the reservoir is at approximately zero pressure, or zero energy. In a 
preferred construction, the charge pump 156 raises the fluid pressure to 
approximately 1500 psi, this charge pressure allows the directional 
control valve 152 to control mechanical movement of the fluid piston 150. 
Compression of the air fuel mixture towards the firing stroke absorbs some 
of the energy in the pressurized fluid supplied by the charge pump 156. 
The added pressure of the ignited air fuel mixture is imparted to the 
pressurized fluid and preferably increases the pressure to approximately 
6000 psi. The directional control valve 152 diverts the high energy fluid 
under pressure to the hydraulic motor 158 where the energy of the high 
pressure fluid is converted to mechanical rotating energy imparted to the 
flywheel 168, and charge pump 156. The fluid from the hydraulic motor 158 
is released to the fluid reservoir at approximately zero pressure and 
approximately zero energy. 
As the directional control valve 152 controls mechanical movement of fluid 
piston 150, when the engine speed is required to slow, inertia in the 
flywheel 162 continues to power the charge pump 156, and pressurize fluid 
in tube 38. This excess fluid energy is relieved by the pressure relief 
valve 154 and returns the fluid to the reservoir 160. 
As shown in FIG. 8, the energy in the flywheel 162 may be used, as is 
common in most automobiles, to drive a transmission system to propel the 
drive wheels. 
Reference herein to details of the illustrated embodiment is not intended 
to limit the scope of the appended claims, which themselves recite those 
features regarded as important to the invention.