Note: Descriptions are shown in the official language in which they were submitted.
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PISTON ENGINE FOR CONVERTING A PRESSURIZED GAS INTO MECHANICAL
ENERGY
FIELD OF THE INVENTION
The present invention relates to external heat engines, and more particularly
to a piston engine
for converting a pressurized gas into mechanical energy.
BACKGROUND OF THE INVENTION
In present day industrialized countries there are numerous sources of waste
heat such as, for
example, factory smokestacks, internal combustion engine cooling or exhaust
heat, which
provide large amounts of thermal energy at a relatively low temperature ¨
typically in the 230 F
to 280 F temperature range ¨ and which are generally released as waste heat
into the
environment. Another source of thermal energy in this temperature range is
solar heat.
External heat engines such as, for example, the Stirling engine, are well
known in the art. In fact,
the first types of external heat engines have been developed in the early
nineteenth century.
Unfortunately, such engines are only efficient at large temperature
differences requiring
provision of the thermal energy at relatively high temperatures. Furthermore,
such engines are
typically complex and costly to manufacture, thus impeding widespread
employment in less
efficient applications such as conversion of waste heat or solar heat into
mechanical energy.
It is desirable to provide a piston engine for converting a pressurized gas
into mechanical energy
that is simple, compact, and cost-effective to manufacture.
It is also desirable to provide a piston engine for converting a pressurized
gas into mechanical
energy that is capable of converting waste heat or solar heat into mechanical
energy.
It is also desirable to provide a piston engine for converting a pressurized
gas into mechanical
energy that has substantially reduced maintenance requirements.
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It is also desirable to provide a piston engine for converting a pressurized
gas into mechanical
energy that is easily adapted for use with different working fluids.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a piston engine
for converting a
pressurized gas into mechanical energy that is simple, compact, and cost-
effective to
manufacture.
Another object of the present invention is to provide a piston engine for
converting a pressurized
gas into mechanical energy that is capable of converting waste heat or solar
heat into mechanical
energy.
Another object of the present invention is to provide a piston engine for
converting a pressurized
gas into mechanical energy that has substantially reduced maintenance
requirements.
Another object of the present invention is to provide a piston engine for
converting a pressurized
gas into mechanical energy that is easily adapted for use with different
working fluids.
According to one aspect of the present invention, there is provided a piston
engine for converting
a pressurized gas into mechanical energy. A housing of the piston engine has
disposed therein at
least a cylinder. At least a piston is housed in a respective cylinder. A
crankshaft is rotatable
mounted to the housing and connected to each of the at least a piston. At
least an inlet valve is
disposed in the housing. The inlet valve is a disc valve movable mounted to
the housing between
a closed position and an open position such that the inlet valve is moved in
an outward direction
from a respective cylinder volume for enabling provision of a working fluid in
the open position.
The working fluid has a first pressure and a first temperature. At least an
outlet valve is disposed
in the housing. The outlet valve is movable between a closed position and an
open position for
exhausting the working fluid having a second lower pressure and a second lower
temperature. A
valve control mechanism is disposed in the housing and connected to the
crankshaft, the inlet
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valve and the outlet valve.
According to another aspect of the present invention, there is provided a
piston engine for
converting a pressurized gas into mechanical energy. A housing of the piston
engine has disposed
therein a crankshaft with the crankshaft being rotatable mounted thereto. Two
cylinders are
disposed in the housing on opposite sides of the crankshaft with the two
cylinders being disposed
along a same longitudinal axis. Two pistons are connected to the crankshaft.
Each is piston
housed in one of the two cylinders and linearly movable along the longitudinal
axis. At least an
inlet valve is disposed in the housing and movable between a closed position
and an open
to position for enabling provision of a working fluid in the open position.
The working fluid has a
first pressure and a first temperature. At least an outlet valve is disposed
in the housing and
movable between a closed position and an open position for exhausting the
working fluid. The
working fluid has a second lower pressure and a second lower temperature. A
valve control
mechanism is disposed in the housing and connected to the crankshaft, the
inlet valve and the
outlet valve.
The advantage of the present invention is that it provides a piston engine for
converting a
pressurized gas into mechanical energy that is simple, compact, and cost-
effective to
manufacture.
A further advantage of the present invention is that it provides a piston
engine for converting a
pressurized gas into mechanical energy that is capable of converting waste
heat or solar heat into
mechanical energy.
A further advantage of the present invention is that it provides a piston
engine for converting a
pressurized gas into mechanical energy that has substantially reduced
maintenance requirements.
A further advantage of the present invention is that it provides a piston
engine for converting a
pressurized gas into mechanical energy that is easily adapted for use with
different working
fluids.
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BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention is described below with
reference to the
accompanying drawings, in which:
Figures la and lb are simplified block diagrams illustrating a cross sectional
side view
and a cross sectional top view, respectively, of a piston engine according to
a preferred
embodiment of the invention;
Figure 1 c is a simplified block diagram illustrating a cross sectional top
view of a
cylinder head of the piston engine according to the preferred embodiment of
the
invention;
Figures 1d and le are simplified block diagrams illustrating cross sectional
side views of
a cylinder head of the piston engine according to the preferred embodiment of
the
invention;
Figure 2 is a simplified block diagram illustrating a perspective view of a
crankshaft of
the piston engine according to the preferred embodiment of the invention;
Figures 3a to 3c are simplified block diagrams illustrating perspective views
of a cam
wheel of the piston engine according to the preferred embodiment of the
invention;
Figures 4a and 4b are simplified block diagrams illustrating a front view and
a side view,
respectively, of a piston rod of the piston engine according to the preferred
embodiment
of the invention;
Figures 5a to 5d are simplified block diagrams illustrating a two cycle
process performed
by the piston engine according to the preferred embodiment of the invention;
and,
Figure 6 is a simplified block diagram illustrating a system for converting
thermal energy
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into mechanical energy employing the piston engine according to the preferred
embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Unless defined otherwise, all technical and scientific terms used herein have
the same meaning as
commonly understood by one of ordinary skill in the art to which the invention
belongs.
Although any methods and materials similar or equivalent to those described
herein can be used
in the practice or testing of the present invention, the preferred methods and
materials are now
described.
While embodiments of the invention will be described for a piston engine for
converting a
pressurized gas into mechanical energy employing a refrigerant such as, for
example, Freon, as
working fluid, it will become evident to those skilled in the art that the
embodiments of the
invention are not limited thereto, but are also adaptable for employing
various other types of
pressurized gases such as, for example, air or steam.
Referring to Figures la to le, a piston engine 100 for converting a
pressurized gas into
mechanical energy according to a preferred embodiment of the invention is
provided. The piston
engine 100, preferably, comprises a single unit housing 102 having two
substantially symmetrical
housing portions 102A and 102B with each housing portion forming half of a
crank case and one
cylinder block housing a respective cylinder 104A, 104B therein. Preferably,
the two cylinders
104A, 104B are disposed in the housing 102 on opposite sides of the crankshaft
118 with the two
cylinders 104A, 104B being disposed along a same longitudinal axis 116
oriented substantially
perpendicular to a rotational axis 120 of the crank shaft 118. The crankshaft
118 is rotatable
mounted to the housing 102 in a conventional manner employing, for example,
ball or roller type
bearings 122 and 126 with the bearing 122 being disposed in the housing 102
and the bearing
126 being disposed in crankcase cover 110. The crankcase cover 110 is of
sufficient size for
enabling insertion of: pistons 106A, 106B; piston rods 108A, 108B; and
crankshaft 118, and for
assembly of the same therein. Further access to the crankcase is enabled via
crankcase access
cover 113. The crankcase cover 110 is designed to be of sufficient structural
strength for
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supporting mounting of the crankshaft 118 via bearing 126 thereto. Preferably,
the crankcase
cover 110 comprises an extension 111, for example, in the form of a collar
fitting snugly into a
respective opening of the housing 102 for centering the same with respect to
the housing 102 to
ensure proper alignment of the crankshaft 118. Preferably, the housing 102 is
made of aluminum
in a conventional manner with the cylinder bores being machined and,
optionally, surface treated
such as, for example, Nikasil coated for high load applications. Disposing the
two cylinders
104A, 104B along the same longitudinal axis 116 substantially facilitates the
machining process,
for example, by enabling line boring of both cylinders in a single machining
process. Optionally,
the two housing portions 102A, B are provided as separate units - splitting,
for example, the
to housing along a plane through an axis of rotation of the crankshaft 118
¨ and mounted together in
a conventional manner.
Cylinder heads 112A, B are mounted to the respective housing portions 102A, B
in a
conventional manner. The cylinder heads 112A, B each comprise inlet channel
150A, B and
outlet channel 152A, B having inlet port 140A, B and outlet port 144A, B
mounted thereto,
respectively. The cylinder heads 112A, B each house inlet valves, outlet
valves, and associated
valve mechanisms.
Two pistons 106A, 106B are connected to the crankshaft 118 with each piston
106A, 106B being
housed in one of the two cylinders 104A, 104B, respectively, and linearly
movable along the
longitudinal axis 116. Preferably, the two pistons 106A, 106B are connected to
a single
crankshaft journal 180, illustrated in Figures la and 2, via piston rods 108A,
108B, respectively,
with the piston rods 108A, 108B being pivotally movable mounted to the
crankshaft journal 180
in a conventional manner. The pistons 106A, 106B are, preferably, made of cast
aluminum in a
conventional manner. The piston rods 108A, 108B, are pivotally movable mounted
to the pistons
106A, 106B in a conventional manner via, for example, piston pins and needle
bearings. Sealing
between the pistons 106A, 106B and the respective walls of the cylinders 104A,
104B is
provided in a conventional manner using, for example, one oil control ring and
two sealing rings.
Preferably, the top sealing ring comprises a slight upward facing bevel in
order for the cylinder
pressure to provide a stronger seal for substantially preventing the
pressurized gas from leaking
into the crankcase.
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Referring to Figures 4a and 4b, the piston rods 108A, 108B, preferably,
comprise a
predetermined offset-distance D between a first end portion 108.1A, 108.1B -
mounted to the
crankshaft journal 180 - and a second end portion 108.2A, 108.2B - mounted to
the respective
piston 106A, 106B. The offset-distance D provides alignment between the first
end portion
108.1A, 108.1B ¨ mounted side-by-side to the crankshaft journal 180 - and the
second end
portion 108.2A, 108.2B mounted to the respective piston 106A, 106B in
alignment with the
center axis 116. Preferably, the piston rods 108A, 108B are made of aluminum
or steel in a
conventional manner. Alternatively, the piston rods 108A, 108B are straight
and mounted to the
respective piston 106A, 106B at an offset-distance.
As illustrated in Figure 2, the crankshaft 118 further comprises
counterweights 130 to reduce
vibrations caused by the piston movement. The crankshaft 118 is made, for
example, as a one-
piece cast-steel design or forged-steel design. Alternatively, the crankshaft
118 is made of a
plurality of pieces using, for example, conventional press-fitting technology,
to enable provision
of needle bearings on the crankshaft journal 180 for higher load applications.
Furthermore, the crankshaft 118 has mounted thereon - using, for example,
conventional form
fitting technology - cam wheel 132 for controlling the movement of inlet
valves 142A, 142B and
outlet valves 146A, 146B in dependence upon the rotational movement of the
crankshaft 118 and
wheels 124 and 128 such as, for example, sprocket wheels, for providing the
mechanical energy
generated by the piston engine 100.
As illustrated in Figures 3a to 3c, the cam wheel 132, preferably, comprises a
cam wheel center
element 132.1 having removable mounted thereto, on a first side, inlet cam
ring segment 132.2
with inlet cam 182 and, on a second opposite side, outlet cam ring segment
132.3 with outlet cam
184. The cam ring segments 132.2 and 132.3 are removable mounted to the cam
wheel center
element 132.1 in a conventional manner using, for example, screw bolts.
Removable mounting of
the inlet cam ring segment 132.2 substantially facilitates adjustment of the
time interval the inlet
valves 142A, B are kept in the open position by simply exchanging a first
inlet cam ring segment
132.2 with a second inlet cam ring segment 132.2 having a different shaped cam
182 in order to,
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for example, adapt the piston engine 100 to at least one of: the type of
working fluid; the pressure
of the working fluid; and the output power. Preferably, the crankcase access
cover 113 is placed
and of sufficient size to enable insertion and assembly of at least the inlet
cam ring segment
132.2 therethrough.
Preferably, the cam wheel center element 132.1 is designed to have sufficient
mass, thus enabling
the cam wheel 132 to act as a flywheel. Further preferably, fins are disposed
on a side surface of
the cam wheel center element 132.1 for providing splash lubrication by picking
up lubricant
disposed in the bottom of the crankcase and splashing the same.
Conventional roller style cam followers are mounted to a first end of inlet
pushrods 134A, B and
outlet pushrods 136A, B to follow the inlet portion and the outlet portion of
the cam wheel 132,
respectively. The pushrods 134A, B and 136A, B are accommodated in respective
bores disposed
in the housing 102A, 102B and in the cylinder heads 112A, 112B.
Referring to Figures 1 c to 1 e, the cylinder heads 112A, B are mounted to the
respective housing
portions 102A, B with each comprising inlet channel 150A, B and outlet channel
152A, B having
inlet port 140A, B and outlet port 144A, B mounted thereto, respectively. The
cylinder heads
112A, B each house the inlet valves 142A, 142B, the outlet valves 146A, 146B,
and associated
valve mechanisms, which are covered by cylinder head covers 114A, B. The inlet
valves 142A,
142B and the outlet valves 146A, 146B are provided as disc valves disposed in
the respective
cylinder heads 112A, 112B and kept in a closed position in a conventional
manner using, for
example, coil return springs (not shown). Preferably, the cylinder heads 112A,
112B are made of
aluminum in a conventional manner with the valve seats 156A, B and 160A, B
being directly
machined into the cylinder heads 112A, B or with steel valve seats being
mounted thereto
depending on the grade of the aluminum employed. The mechanism for opening the
outlet valve
146A, B is of conventional design with a second opposite end of outlet pushrod
136A, B pushing
a first end of pivotally movable mounted - at pivot 170A, B - rocker arm
164A,B which in turn
pushes outlet valve disc 158A, B into the cylinder volume - indicated by block
arrows. The
cylinder head 112A, 112B is designed to be of sufficient thickness for
providing proper guidance
(by way of, for example, a Teflon coated valve guide securely positioned
within a bore disposed
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in the cylinder head 112A, 112B) to a stem of the outlet valve 146A, B
disposed in a bore
through the Teflon coated valve guide.
In order to prevent misfiring of the piston engine due to high pressure of the
pressurized gas in
inlet channel 150A, B acting on inlet valve disc 154A, B the same is designed
to operate in
reverse direction, i.e. the inlet valve 142A, B is moved in an outward
direction from a respective
cylinder volume for opening, as indicated by the block arrow. High pressure of
the pressurized
gas in the inlet channel 150A, B acting on the inlet valve disc 154A, B pushes
the same into the
valve seat 156A, B, thus preventing the pressurized gas from entering the
cylinder volume when
the inlet valve 142A, B is in the closed position. The inlet valve mechanism
comprises a linear
movable bridge 162A, B guided along linear bearings 168A, B having the inlet
valve 142A, B
mounted thereto at a first end. Inlet pushrod 134A, B pushes a second opposite
end of the bridge
162A, B which in turn pulls the inlet valve 142A, B with the inlet valve disc
154A, B outward
from the cylinder volume - as indicated by the block arrows.
Preferably, the inlet valve 142A, B is inserted through opening 165A, B
disposed in the cylinder
head 112A, B and liner movable mounted thereto via inlet valve nut 166A, B
having a threaded
collar, as illustrated in Figure 1 c. The inlet valve nut 166A, B is designed
to be of sufficient
thickness for providing proper guidance (by way of, for example, a Teflon
coated valve guide
163A,B securely positioned within the inlet valve nut 166A) to a stem of the
inlet valve 142A, B
disposed in a bore through the Teflon coated valve guide 163A, B , providing a
proper seal for
preventing leakage of the working fluid disposed in the inlet channel 150A, B.
Inlet valve return
spring 167A, B is, for example, disposed in the inlet channel 150A, B between
a shoulder
disposed on the inlet valve disc 154A, B and a bottom surface of the inlet
valve nut 166A, B and
abutted thereto. The inlet valve return spring 167A, B pushes the valve disc
154A, B into the
inlet valve seat 156A, B when the inlet valve 142A, B is in the closed
position.
Alternatively, a rocker arm is pivotally movable mounted at a first end and
pushed by the inlet
pushrod 134A, B at a second opposite end, thus pulling the inlet valve 142A, B
which is
pivotally movable mounted to the rocker arm between the first end and the
second end.
Preferably, a small linkage is employed to reduce side loading acting on the
inlet valve 142A, B.
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As is evident to one skilled in the art, the inlet valve 142A, B and the
corresponding valve
mechanism is not limited for use with the two cylinder piston engine described
hereinabove, but
is also applicable for use with various other types of pressurized gas driven
piston engines.
In operation, the piston engine 100 performs a two cycle process with the down-
stroke being the
power cycle and the up-stroke being the exhaust cycle with each cycle
corresponding to a half
revolution of the crankshaft, as illustrated in Figures 5a to 5d. Pressurized
gas is received having
a first pressure and a first temperature. During the down-stroke the
pressurized gas is provided to
the cylinder volume and expanded therein, thus pushing the piston down. During
the up-stroke
the expanded gas is exhausted with the gas then having a second lower pressure
and a second
lower temperature. The thermal energy corresponding to the difference between
the first and the
second pressure and the first and the second temperature of the gas is
substantially converted into
mechanical energy acting on the crankshaft. Each of the two pistons performs
the same two cycle
process a half revolution apart, for example, while piston 106A is at Top Dead
Center (TDC)
piston 106B is at Bottom Dead Center (BDC) or, while piston 106A moves towards
Top Dead
Center (TDC) piston 106B moves towards Bottom Dead Center (BDC) and vice
versa.
Vaporized and pressurized Freon is supplied to each cylinder 104A, B entering
the inlet channels
150A, B via inlet ports 140A, B. When piston 106A reaches TDC, the inlet cam
182 on the cam
wheel 132 actuates the inlet push rod 134A which then actuates the bridge
162A, thus lifting the
inlet valve 142A off its seat ¨ Figure 5a. The Freon then passes into the
cylinder 104A pushing
the piston 106A down. As the inlet push rod 134A comes off the cam 182 ¨
typically after one
quarter to one half of the down-stroke ¨ the spring in concert with the
pressurized Freon closes
the inlet valve 142A ¨ Figure 5b. Once the piston 106A is at BDC, the outlet
cam 184 on the cam
wheel 132 actuates the outlet push rod 136A which then actuates the rocker arm
164A, thus
pushing the outlet valve 146A off its seat ¨ Figure 5c. As the piston 106A
moves back up to TDC
the expanded Freon is exhausted through the outlet channel 152A ¨ Figure 5d.
For example, vaporized and pressurized Freon is supplied to each cylinder
104A, B of the piston
engine 100 having a pressure in the range of, for example, preferably 240-250
psi ¨ and further
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preferably 250 psi - and a temperature in the range of for example, preferably
240-300 F ¨
further preferably 250 F. Based on a piston bore of 2.5 inches and a stroke of
5 inches the Freon
is passed through a 1.5 inch throttle valve and the supply is then split into
two .75 inch lines
connected to each cylinder. The Freon is then exhausted having a pressure in
the range of for
example, preferably 4-15 psi ¨ further preferably 5 psi - and a temperature in
the range of for
example, preferably 78-110 F ¨ further preferably 90 F. The piston engine 100
preferably
provides, for example, a substantially constant torque of approximately 122
ft=lbf and a
horsepower in the range of 80-160 net horse power at a rotational speed in the
range of 25-4000
rpm ¨ preferably 1800 rpm.
The aligned twin cylinder design of the piston engine 100 substantially
reduces the number of
moving parts and provides a piston engine that is simple, compact, cost
effective to manufacture
and has substantially reduced maintenance requirements. The maintenance is
further reduced
when the piston engine 100 is operated at lower temperatures, i.e. when
operated with
refrigerants such as Freon.
Referring to Figure 6, the piston engine 100 is implemented in a system 200
for converting heat
into mechanical energy according to a preferred embodiment of the invention.
Preferably, the
piston engine 100 is disposed on table 201 together with a heat exchanger 208
of conventional
design and a condenser 202 of conventional design. Heat such as, for example,
waste heat from
an engine cooling system or smokestack is received at inlet 210 of the heat
exchanger 208,
indicated by the block arrow. The heat exchanger 208 vaporizes the Freon
received at inlet 214
from the condenser 202 via pump 218 ¨ indicated by a dashed line - and
provides the vaporized
and pressurized Freon via outlet 216. The outlet 216 is connected via throttle
valve 220 to the
inlet ports 140A, B of the piston engine 100 ¨ indicated by a solid line.
Furthermore, a bypass
directly connects the outlet 216 to the inlet 204 of the condenser 202
controlled by safety valve
222 - indicated by a solid line.
The outlet ports 144A, B of the piston engine 100 are connected to the inlet
204 of the condenser
202 - indicated by a dotted line. Furthermore, the crankcase of the piston
engine 100 is connected
to the inlet 204 of the condenser 202 for venting Freon leaked therein -
indicated by a dotted line.
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Optionally the venting line is omitted in case other working fluids are
employed such as air or
steam which are vented into the environment. The condensed Freon is then
provided via outlet
206 to the pump 218 ¨ indicated by a dashed line. Operation of the system 200
is controlled, for
example, by processor 228 of control unit 226 executing executable commands
stored in memory
230 and in dependence upon operator instructions received via user interface
232. The processor
228 is connected to ¨ indicated by a dash-dot line: governor 224 sensing the
rotational speed of
the crankshaft 118; the throttle valve 220; the safety valve 222; the pump
218; control valve 224;
as well as pressure and temperature sensors (not shown) disposed, for example,
in the piston
engine 100, the condenser 202, and the heat exchanger 208. For example, the
rotational speed of
the crankshaft is adjusted via the throttle valve 220 while provision of the
Freon to the heat
exchanger is adjusted accordingly via the pump 218 and the control valve 224.
The pump 218 is
driven, for example, by the piston engine 100 using a belt drive. Furthermore,
a starter motor is
connected to the crankshaft 118 for starting the piston engine 100.
Optionally, electric heaters are
disposed in the cylinder head and the cylinder walls to vaporize liquid Freon
left during engine
shutdowns.
The present invention has been described herein with regard to preferred
embodiments. However,
it will be obvious to persons skilled in the art that a number of variations
and modifications can
be made without departing from the scope of the invention as described herein.
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