IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIUS007513224B2

lI2~United States Patent(Io) PatentNo.:(45)Date of Patent:

Heaton(54)

SPLIT-CYCLEAIRCRAFT

ENGINE(75) Inventor: Clifford D. Heaton,Ware,MA (US)(73)

Assignee: The Scuderi Group, LLC, West
Springfield, MA (US)( * ) Notice:

US 7,513,224 B2

Subject to any disclaimer, the term of thispatent is extended or adjusted under 35
U.S.C. 154(b) by 173 days.

Apr. 7, 2009

9/1987 DeFrancisco
4,696,158 A *5/2000 Lee ................
6,058,901 A *6,340,004 Bl * 1/2002 Patton
Suhet al.........
6,789,514 B2 * 9/2004
Scuderiet al.
7,353,786 B2 * 4/2008
2004/0255882Al* 12/2004 Branyonet al.
1/2008 Mochida et al..
2008/0006739Al*.... 60/39.62
123/197.1
123/25C
123/70R....... 123/68
123/70R....... 244/60* cited by examiner(21)

Appl. No.: 11/51S,S2S

Primary Examiner Michael Cuff
Assistant Examiner Hung Q Nguyen(74) Attorney, Agent, or Firm Fildes & Outland, P.C.

(22)

Filed:(57)

Sep. 11, 2006
Prior Publication Data

(65)

US 2009/0050103 Al(51)

Feb. 26, 2009

Int. Cl.
F01B 7/12(2006.01)
U.S. Cl....................................
123/51 R; 60/39.62
Field of ClassiTicationSearch ............ 123/52.1â€” 3,
123/53.1, 533, 53.5, 55.4, 55.5, 55.2, 431,
123/68, 70 R, 51 R, 51 AC, 51 BC, 51 BD;
60/597, 653, 668, 698, 706, 712, 727, 729,
60/39.62
See application file for complete search history.

(52)
(58)

References Cited(56)

U.S. PATENT DOCUMENTS
4,185,596 A *1/1980 Noguchi et al.

123/51B

ABSTRACTA split-cycle aircraft engine includes a crankshaft rotatable
about a crankshaft axis. A power piston is slidably received
within a power cylinder and is operatively connected to the
crankshaft such that the power piston reciprocates through an
expansion stroke and an exhaust stroke during a single rotation of the crankshaft. A compression piston is slidably
received within a compression cylinder and is operatively
connected to the crankshaft such that the compression piston
reciprocates through an intake stroke and a compression
stroke during a single rotation of the crankshaft. A gas crossover passage operatively interconnects the compression cylinder and the power cylinder. An air reservoir is operatively
connected to the gas crossover passageby a reservoir passage.
The air reservoir is selectively operable to receive and delivercompressed air. The engine is mounted to an aircraft and the
air reservoir is disposed within the aircraft.
13 Claims, S Drawing Sheets

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US 7,513,224 B2SPLIT-CYCLE

1
AIRCRAFT

ENGINE

removed from the cylinders by turning the engine over byhand prior to starting the engine, which is an inconvenience to
TECHNICAL FIELD
the pilot or the ground crew.
It is also known in the art of aircraft engines to use horiThis invention relates to split-cycle engines, and more parzontally opposed engines, also known as "boxer" engines, toticularly to split-cycle aircraft engines.
drive the aircraft's propellers. Boxer-type engines differ fromother internal combustion engines in that the engine cylindersBACKGROUND OF THE INVENTION
are arranged in a horizontally opposed relationship.
Horizontally opposed engines have the advantages of
The term split-cycle engine as used in the present applica- 10 being more compact and having a lower center of gravity thantion may not have yet received a fixed meaning commonlyother engine configurations. Horizontally opposed engines,
known to those skilled in the engine art. Accordingly, forlike radial engines, potentially may be air-cooled, eliminating
purposes of clarity, the following definition is offered for thethe need for a separate engine cooling system and thereby
term split-cycle engine asmay be applied to engines disclosed
decreasing the overall weight of the engine. Therefore, horiin the prior art and as referred to in the present application. 15 zontally opposed engines are suitable for aircraft applicaA split-cycle engine as referred to herein comprises:
tions. Horizontally opposed engines are also well balanced
a crankshaft rotatable about a crankshaft axis;
because each piston's momentum is counterbalanced by thea power piston slidably received within a power cylinder
corresponding movement of the piston opposing it. This
reduces or may even eliminate the need for a balance shaft or
and operatively connected to the crankshaft such that thepower piston reciprocates through a power (or expansion) 20 counterweights on the crankshaft, further reducing the overall
stroke and an exhaust stroke during a single rotation of theweight of the engine.
crankshaft;
Horizontally opposed engines, however, are often noisiera compression piston slidably received within a compresthan other engine configurations such as V-type engines andsion cylinder and operatively connected to the crankshaft
inline engines. Also, horizontally opposed engines can besuch that the compression piston reciprocates through an 25 more difficult to fit into an engine compartment because
intake stroke and a compression stroke during a single rotahorizontally opposed engines tend to be wider than othertion of the crankshaft; andengine configurations.
a gas passage interconnecting the power and compression
It is further known in aeronautics that there are many uses
cylinders, the gas passage including an inlet valve and aninan aircraft for compressed air. However, conventional air30
outlet (or crossover) valve defining a pressure chamber thercraft lack a convenient and efficient source of compressed air,ebetween.
thereby rendering these potential uses of compressed air
infeasible.
U.S. Pat. Nos. 6,543,225, 6,609,371, and 6,952,923, allassigned to the assignee of the present invention, disclose
examples of split-cycle internal combustion engines as herein 35
SUMMARY OF THE INVENTION
defined. These patents contain an extensive list of UnitedStates and foreign patents and publications cited as backThe present invention provides various split-cycle engine
ground in the allowance of these patents. The term "splitarrangements for propeller-driven aircraft that are capable ofcycle" has been used for these engines because they literally
storing compressed air and delivering the compressed air
split the four strokes of a conventional pressure/volume Otto 40 back to the engine or to other components of the aircraft.
cycle (Le., intake, compression, power and exhaust) over two
In one embodiment of the present invention, a split-cycle
dedicated cylinders: one cylinder dedicated to the high presair hybrid aircraft engine includes a crankshaft rotatable
sure compression stroke, and the other cylinder dedicated toabout a crankshaft axis. A power piston is slidably received
the high pressure power stroke.
within a power cylinder and operatively connected to the
It is known in the art relating to aircraft engines to use radial 45 crankshaft such that the power piston reciprocates through anengines for aeronautical applications. For example, radial
expansion stroke and an exhaust stroke during a single rotaengines were commonly used in World War II aircraft and intion of the crankshaft. A compression piston is slidably
early model commercial airplanes. Radial engines are still
received within a compression cylinder and operatively conpresently used in some propeller-driven aircraft.
nected to the crankshaft such that the compression piston
Radial engines differ from other common internal combus- 50 reciprocates through an intake stroke and a compression
tion engines such as inline and V-type engines in the arrangestroke during a single rotation of the crankshaft. A gas crossment of the engine cylinders. In a radial engine, the cylinders
over passage operatively interconnects the compression cyland corresponding pistons are arranged radially around theinder and the power cylinder. The gas crossover passage
engine crankshaft in a circular pattern.
includes an inlet valve and an outlet valve defining a pressure
Radial engines are advantageous for airplane applications 55 chamber therebetween. An air reservoir is operatively conbecausethey can produce a large amount of power, they havenected to the pressure chamber by a reservoir passage at aa relatively low maximum engine speed (rpm), avoiding thelocation between the inlet valve and the outlet valve of theneed for reduction gearing to drive propellers, and they arepressure chamber. The air reservoir is selectively operable tosuitable for air cooling, eliminating the need for a water
receive compressedair from the compression cylinders and tocooling system.
60 deliver compressed air to the power cylinders for use in transAlthough radial engines have been reliable aircraft engines
mitting power to the crankshaft during engine operation. The
air reservoir may also deliver compressed air to other comand less expensive than other types of aircraft engines, use ofradial engines in airplanes has substantially decreased. Conponents of the aircraft. Valves selectively control gas flow into
ventional radial engines tend to be noisy and to consume more
and out of the compression and power cylinders and the air
oil than other engine designs. Also, conventional radial 65 reservoir. The engine is mounted to the aircraft and the air
engines have mechanical issues such as oil draining into thereservoir is disposed within the aircraft. Optionally, the air
lower cylinders during non-use of the engine. This oil must be
reservoir may be located in a wing of the aircraft, in an aft

US 7,513,224 B2
stroke during a single rotation of the crankshaft. Each comfuselage of the aircraft, or both. Alternative locations for the
air reservoir are also within the scope of the invention.
pression cylinder is paired with an associatedpower cylinder.
In another embodiment of the present invention, a splitEach compression and power cylinder pair includes a gas
cycle horizontally opposed (ke., "boxer") engine that may becrossover passage interconnecting the compression cylinderused for aircraft applications is provided. A split-cycle hori- 5 and the power cylinder of the pair. The gas crossover passage
includes an inlet valve and an outlet valve defining a pressure
zontally opposed engine allows for the power cylinders to firechamber therebetween. Valves are also provided to control
once per revolution of the crankshaft rather then every otherrevolution and allows the compression cylinders to compress
gas flow into the compression cylinders and out of the power
charge air during every revolution of the crankshaft. The
cylinders. An air reservoir may be operatively connected to
split-cycle horizontally opposed engine also allows for the 10 the pressure chambers by a reservoir passage at locations
between the inlet valve and the outlet valve of each pressurecompression cylinders to operate with a larger diameter inchamber. The air reservoir is selectively operable to receive
comparison to the power cylinders to increase the volume ofand deliver compressed air.
air inhaled into the engine, allowing for supercharging of the
These and other features and advantages of the inventionengine without the use of an external supercharger.
More particularly, a split-cycle horizontally opposed 15 will be more fully understood from the following detailed(" boxer" ) engine in accordance with the invention includes a
description of the invention taken together with the accomcrankshaft rotatable about a crankshaft axis. The split-cycle
panying drawings.
boxer engine further includes a pair of horizontally opposed
BRIEF DESCRIPTION OF THE DRAWINGS
power cylinders on either side of the crankshaft. A power
piston is slidably received within each power cylinder and is 20
In the drawings:
operatively connected to the crankshaft such that each power
FIG. I is a side schematic view of an aircraft including apiston reciprocates through an expansion stroke and an
split-cycle air hybrid engine and compressed air tanks inexhaust stroke during a single rotation of the crankshaft. The
accordance with the invention;
split-cycle boxer engine also includes a pair of horizontally
FIG. 2 is a plan schematic view of the aircraft of FIG. I;
opposed compression cylinders on either side of the crank- 25
FIG. 3 is a cross-sectional view of the aircraft taken along
shaft. A compression piston is slidably received within eachthe line 3-3 in FIG. 2;
compression cylinder and is operatively connected to the
FIG. 4 is a schematic view of a split-cycle horizontally
crankshaft such that each compression piston reciprocates
opposed (" boxer" ) engine in accordance with the invention
through an intake stroke and a compression stroke during asingle rotation of the crankshaft. A gas crossover passage 30 having an air storage tank illustrating pistons of the engine
around top dead center;interconnects each compression cylinder with an associated,
FIG. 5 is a cross-sectional view of the split-cycle horizonaxially adjacent power cylinder. The gas crossover passage
tally opposed engine taken along the line 5-5 in FIG. 4;
includes an inlet valve and an outlet valve defining a pressure
FIG. 6 is a cross-sectional view of the split-cycle horizonchamber therebetween. Valves control gas flow into the compression cylinders and out of the power cylinders. An air 35 tally opposed engine taken along the line 6-6 in FIG. 4;
FIG. 7 is another schematic view of the split-cycle horireservoir may be operatively connected to the pressure chamzontally opposed engine of FIG. 4 illustrating the pistonsbers by a reservoir passage at locations between the inlet
around bottom dead center;valve and the outlet valve of each pressure chamber. The air
FIG. S is a cross-sectional view of the split-cycle horizonreservoir is selectively operable to receive and deliver com40 tally opposed engine taken along the line S-S in FIG. 7;
pressed air.
FIG. 9 is a cross-sectional view of the split-cycle horizonIn yet another embodiment of the present invention, atally opposed engine taken along the line 9-9 in FIG. 7;
split-cycle radial engine that may be used for aircraft appliFIG. 10 is a schematic view of a split-cycle radial engine incations is provided. A split-cycle radial engine allows foraccordance with the invention having an air storage tank;sequential firing of the cylinders, which increases the torque
FIG. 11 is a schematic view of a compression bank of theof the engine. A split-cycle radial engine also allows for 45
split-cycle radial engine of FIG. 10; andoffsetting of the engine cylinders relative to the crankshaft,
FIG. 12 is a schematic view of a power bank of the splitfurther increasing the torque of the engine and reducing piscycle radial engine of FIG. 10.
ton-skirt friction. Moreover, a split-cycle radial engine iscapable of inhaling larger volumes of charge intake air, which
DETAILED DESCRIPTION OF THE INVENTION
improves the performance of the engine at high altitudes 50
where the air is thinner.
Referring now to the drawings in detail, numeral 10 genMore particularly, a split-cycle radial engine in accordance
erally indicates a propeller-driven aircraft. As illustrated inwith the invention includes a crankshaft rotatable about a
FIGS. I through 3, the aircraft 10 has a pair of wings 12, a
crankshaft axis. The split-cycle radial engine further includes
a power bank including a plurality of power cylinders radially 55 wing spar 14 in the wings 12, a cockpit 16, a tai11S,and an aftfuselage 20. The aircraft 10 may have one wing spar 14
disposed around the crankshaft. A power piston is slidably
spanning both wings 12, or a separate wing spar may bereceived within each power cylinder and operatively conlocated in each wing 12. A split-cycle engine 22 in accornected to the crankshaft such that each power piston reciprodance with the invention is mounted in the aircraft 10 forward
cates through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft. A compression bank is 60 of the cockpit 16 to drive the propeller 24. Air storagetanks 26
may be located in the wing spar 14, the aft fuselage 20, or
axially adjacent the power bank. The compression bankboth. The air storage tank(s) may also be located in any otherincludes a plurality of compression cylinders radially dissuitable location within the aircraft 10, for example, in a
posed around the crankshaft and equal in quantity to thesuitable location within the wings 12 other than the wing spar
number of power cylinders. A compression piston is slidably
received within each compression cylinder and operatively 65 14.
connected to the crankshaft such that each compression pisTurning first to FIGS. 4 through 9, in one embodiment of
ton reciprocates through an intake stroke and a compression
the invention, the split-cycle engine 22 may be a horizontallyUS 7,513,224 B2
opposed (" boxer" ) type split-cycle engine. The split-cycle
The compression pistons 42 lag slightly behind the powerboxer engine 22 includes a crankshaft 2S rotatable about apistons 36 (in degrees of crank angle rotation). This is incrankshaft axis 30. The split-cycle boxer engine 22 further
contrast to conventional horizontally opposed engines inwhich neighboring pairs of pistons travel 180 crank angle
includes a pair of horizontally opposed power cylinders 34 oneither side of the crankshaft 2S.A power piston 36 is slidably 5 degreesapart. During operation of the engine 22, as the comreceived within each power cylinder 34 and is operatively
pression pistons 42 reach top dead center (TDC), the power
connected to the crankshaft 2S such that each power piston 36
pistons 36 have already reached TDC and have begun thereciprocates through an expansion stroke and an exhaust
power stroke. Fuel is ignited in each power cylinder 34 withinstroke during a single rotation of the crankshaft 2S. Thea range of 5 to 40 degrees crank angle after the power piston
split-cycle boxer engine 22 also includes a pair of horizon- 10 36 associated with the power cylinder 34 has reached its top
tally opposed compression cylinders 40 on either side of thedead center position (degrees ATDC). Preferably, fuel iscrankshaft 2S. A compression piston 42 is slidably received
ignited in each power cylinder 34 within a range of 10 to 30
within each compression cylinder 40 and is operatively condegreesATDC.
nected to the crankshaft 2S such that each compression piston
FIGS. 4 through 6 illustrate the compression pistons 42 at
42 reciprocates through an intake stroke and a compression 15 approximately the TDC position and the power pistons 36
stroke during a single rotation of the crankshaft 2S. A gas
moving away from TDC towards bottom dead center (BDC).
The rotational direction of the crankshaft 2S (FIG. 5) and thecrossover passage 44 interconnects each compression cylinrelative motions of the power pistons 36 (FIG. 6) are indicatedder 40 with an associated, axially adjacent power cylinder 34.
by the arrows associated in the drawings with their correThe gas crossover passage44 includes an inlet valve 46 andan outlet valve 4S defining a pressure chamber 50 therebe- 20 sponding components. FIGS. 7 through 9 illustrate the comtween. The air pressure in the pressure chamber 50 is mainpression pistons 42 at approximately the BDC position andtained at an elevated minimum pressure through the engine
the power pistons 36 moving away from BDC towards TDC.
The rotational direction of the crankshaft 2S (FIGS. S and 9)
cycles. Valves 52 control gas flow into the compression cyland the relative motions of the power pistons 36 and cominders 40 and out of the power cylinders 34. The valves 44, 46,
52 may be check valves, poppet valves, or any other suitable 25 pression pistons 42 (FIGS. 7 and 9) are indicated by thevalve. The valves 44, 46, 52 may be cam actuated, electroniarrows associated in the drawings with their corresponding
components.
cally actuated, pneumatically actuated, or hydraulically actuated. The air reservoir 26 may be operatively connected to the
The power pistons 36 may be operatively connected to the
crankshaft 2S by separatecrank pins/journals 43 that are 180
pressure chambers 50 by a reservoir passage 54 at locations
between the inlet valve 46 and the outlet valve 4S of each 30 degrees apart relative to the crankshaft axis 30. The pairedpressure chamber 50. The air reservoir 26 is selectively operpower pistons 36 therefore reach top dead center simultaable to receive and deliver compressed air.
neously. Likewise, the compression pistons 42 may be operaThe split-cycle boxer engine 22 shown in FIGS. 4 throughtively connected to the crankshaft 2S by separatecrank pins/
journals 42 that are also 180 degrees apart relative to the
9 includes one pair of power cylinders 34 and one pair ofcompression cylinders 40 for a total of four cylinders. If 35 crankshaft axis 30. The paired compression pistons 42 therefore also reach top dead center simultaneously.
additional horsepower is desired, another pair of power cylinders and compression cylinders may be added for a total of
A spark plug (not shown) may extend into the each of theeight cylinders. It should be understood, however, that thepower cylinders 34 for igniting air-fuel charges at precise
times by an ignition control, also not shown. It should beengine 22 may have any number of cylinders, so long as there
are an even number of power cylinders, an even number of 40 understood that the engine 22 may be made as a diesel engine
and be operated without a sparkplug if desired. Moreover, thecompression cylinders, and an equal number of power andengine 22 may be designed to operate on any fuel suitable forcompression cylinders (since each power cylinder must be
paired with a compression cylinder).
reciprocating piston engines in general, such as hydrogen,natural gas or bio-diesel.
The power cylinders 34 may be disposed in front of theWith the use of the air reservoirs 26, the split-cycle engine
compression cylinders 40 to allow for improved air-cooling 45
22 can function as an air hybrid. The compression cylindersof the hotter power cylinders 34 during engine operation. A
40 may then be selectively controllable to place the compreslongitudinal axis 56 of each compression cylinder 40 andsion pistons 42 in a compression mode or an idle mode. The
each power cylinder 34 may be offset from the rotational axis
30 of the crankshaft 2S. The offset of the cylinder axes 56
power cylinders 34 similarly may be selectively controllable
from the crankshaft axis 30 allows for greater mechanical 50 to place the power pistons 36 in a power mode or an idle
advantage and increased torque. On each side of the engine 22
mode. Further, the engine 22 may be operable in at least threemodes, including an internal combustion engine (ICE) mode,
one of a pair of horizontally opposed cylinders is raised above
the rotational axis 30 of the crankshaft 2S and the other isan air compressor (AC) mode and a pre-compressedair power
lowered below the rotational axis 30 of the crankshaft 2S.
(PAP) mode. In the ICE mode, the compression pistons 42
Further, because the compression cylinders 40 are separate 55 and power pistons 36 are in their respective compression andpower modes, in that the compression pistons 42 draw in andfrom the power cylinders 34, the compression cylinders 40
compress inlet air for use in the power cylinders 34, andmay be designed to have a larger diameter than the powercylinders 34. This results in the compression cylinders 40
compressed air is admitted to the power cylinders 34 withhaving a larger volume than the power cylinders 34, allowing
fuel, at the beginning of an expansion stroke, which is ignited,the engine to be supercharged without the use of an external 60 burned and expanded on the same expansion stroke of thesupercharger. This also can improve engine efficiency at
power pistons 36, transmitting power to the crankshaft 2S,
and the combustion products are discharged on the exhaust
higher altitudes by allowing the engine to intake larger volumes of thin air compared to conventional engines. The
stroke. In the AC mode, the compression pistons 42 are in thecompression mode and they draw in and compress air that is
power pistons 36 may also be designed with a longer throw on
the crankshaft 2S compared to the compression pistons 42 for 65 stored in the air reservoir 26 for later use in the power cylinderor other aircraft components as described in more detaila longer stroke to over-expand the gas in the power cylinders
below. In the PAP mode, the power cylinders 34 are in the
34 and to provide increased efficiency, i.e., the Miller Effect.

US 7,513,224 B2
power mode and receive compressed air from the air reservoir
compressed air at the beginning of an expansion stroke andthe mixture is ignited, burned and expanded on the same
26 which is expanded on the expansion stroke of the power
expansion stroke of the power cylinder 34. Meanwhile, in thepistons 36, transmitting power to the crankshaft 2S, and the
expanded air is discharged on the exhaust stroke.
compression cylinder 40, compressed air admitted to the
Optionally, in the PAP mode, fuel may be mixed with the 5 compression cylinder 40 is expanded on the expansion strokeof the compression cylinder 40 without adding fuel or initicompressed air at the beginning of an expansion stroke andating combustion.
the mixture may be ignited, burned and expanded on the same
Operating the engine 22 in HP mode literally doubles the
expansion stroke of the power pistons 36, transmitting power
number ofpower strokes available to the aircraft for as long as
to the crankshaft 2S, and the combustion products may bedischarged on the exhaust stroke. Alternatively, in the PAP 10 the air reservoir 26 remains charged with enough air pressure
to maintain the HP mode. This mode is useful for increasing
mode, the compressed air admitted to the power cylinders 34
power to the aircraft during critical short-term operations,
may be expanded without adding fuel or initiating combustion.
such as gaining altitude to fly over a mountain or quickly
Excess compressed air, i.e., air that is not used for combusaccelerating to high speedsfor short take-offs. Moreover, thetion in the power cylinders 34, is transferred from the pressure 15 air reservoir can be over pressurized by an external compreschambers 50 to the air storage tank(s) 26 via the reservoir
sor on the ground to enable the engine 22 to operate in HP
mode for longer periods of time during take-offs.
passage 54. The stored compressed air may be used for a
Turning now to FIGS. 10 through 12, in an alternative
variety of applications. Such applications may include but are
not limited to: a) starting the engine in lieu of an electric
embodiment of the invention, the split-cycle engine 122 maystarter; b) cabin pressurization; c) inflation of inflatable door 20 be a radial-type split-cycle engine. The split-cycle radialengine 122 includes a crankshaft 12S rotatable about a crankseals in pressurized aircraft; d) wheel braking, by either actushaft axis 130. The engine 122 has a power bank 132 includating the brake shoes and/or through the active resistance ofpressurized air against spinning wheels; e) rotating the proing a plurality of power cylinders 134 radially disposed
around the crankshaft 12S. A power piston 136 is slidably
pellers for taxiing short distances without fuel being injected
into the engine (see PAP mode above); fj driving the wheels 25 received within each power cylinder 134 and is operativelyof the aircraft to taxi the aircraft without starting the engine
connected to the crankshaft 12S such that each power piston
136 reciprocates through an expansion stroke and an exhaust
and without having the propeller turning (allowing for safer
stroke during a single rotation of the crankshaft 12S. A comtaxiing); g) spinning up the aircraft's wheels before landing
so the tires are not subjected to as much frictional wear whenpression bank 13S is axially adjacent the power bank 132. The
they touch the ground during a landing; h) providing a break- 30 compression bank 13S includes a plurality of compression
ing force on the aircraft's wheels for quick stopping in addicylinders 140 radially disposed around the crankshaft 12S
tion to the aircraft's conventional brakes; I) operating theand equal in quantity to the number of power cylinders 134. A
compression piston 142 is slidably received within each comengine with compressed air when the compression cylinders
pression cylinder 140 and operatively connected to the crankare in an idle mode (see PAP mode above); j) operating flight
instruments that utilize gyros; k) providing fuel pressure in 35 shaft 12S such that each compression piston 142 reciprocatesthrough an intake stroke and a compression stroke during a
the event of a fuel pump failure; I) actuating flight controls
single rotation of the crankshaft 12S. Each compression cyland landing gear, for example an air pressure regulating valve
inder 140 is paired with an associated power cylinder 134.
could be used to provide finely tuned trim pressure on the
Each compression 140 and power cylinder 134 pair includes
control surfaces and could also operate leading edge slats; m)
expelling ice from the aircraft's wings; n) inflating airbags for 40 a gascrossover passage144 interconnecting the compression
cylinder 140 and the power cylinder 134 of the pair. The gas
crash protection; o) opening a whole aircraft recovery paracrossover passage 144 includes an inlet valve 146 and anchute of a whole aircraft parachute recovery system in lieu ofoutlet valve 14S defining a pressure chamber 150 therebea rocket motor; p) operating emergency evacuation chutes; q)tween. Valves 152 are also provided to control gas flow into
deploying pesticides, fire retardants, flares, munitions, andother items from special use aircraft; r) ejecting water from 45 the compression cylinders 140 and out of the power cylinders
the aircraft floats and hulls of amphibious aircraft; and s)
134. The valves 144, 146, 152 may be check valves, poppet
venting air from small holes in the top of the wings to mimic
valves, or any other suitable valve. The valves 144, 146, 152
the effects of vortex generators at slow speeds.
may be cam actuated, electronically actuated, pneumaticallyactuated, or hydraulically actuated. An air reservoir 126 may
Optionally, the engine 22 may also be operable in at least a
fourth mode, herein designated a high power (HP) mode. In 50 be operatively connected to the pressure chambers 150 by areservoir passage154 at locations between the inlet valve 146
the HP mode, the compression cylinders 40 are selectively
and the outlet valve 14S of eachpressure chamber 150. The aircontrollable to operate, in effect, as additional power cylinreservoir 126 is selectively operable to receive and deliverders having expansion strokes and exhaust strokes instead of
intake strokes and compression strokes.
compressed air.
During the HP mode, no ambient air is inhaled into the 55
The power bank 132 may be disposed in front of the compression bank 13S to allow for improved air-cooling of thecompression cylinders 40 through intake valves 52. Rather,hotter power bank 132 during engine operation. The comboth the compression cylinders 40 and power cylinders 34
receive compressed air from the air reservoir 26, which ispression cylinders 140 of the compression bank 13S may be
expanded on the compression and power cylinder's respecrotated relative to the power cylinders 134 of the power banktive expansion strokes and discharged on their respective 60 132. In other words, the compression cylinders 140 may not
exhaust strokes.
be directly in line with the power cylinders 134 but instead
may be rotated a few degrees generally relative to the crankIn a preferred embodiment of the HP mode, the power
shaft 12S to enhance the flow of air over the compression
piston 36 transmits power to the crankshaft 2S through thecylinders 140. Further, a longitudinal axis 156 of each comprocess of combustion, while the compression piston 42transmits power to the crankshaft 2S through the process of 65 pression cylinder 140 may be offset from the rotational axis
expanding air from the air reservoir 26 without combustion.
130 of the crankshaft 12S. Similarly, a longitudinal axis 156
of each power cylinder 134 also may be offset from theThat is, in the power cylinder 34, fuel is mixed with theUS 7,513,224 B2
10rotational axis 130 of the crankshaft 12S. The compression
top dead center (TDC), the power pistons 136 have alreadyreached TDC and have begun the power stroke. Fuel is ignitedcylinders 140 may have a larger diameter than the powercylinders 134 to allow for a larger volume of intake air. The
in each power cylinder 134 within a range of 5 to 40 degrees
compression pistons 142 may also have a shorter stroke thancrank angle after the power piston 136 associated with the
5 power cylinder 134 has reached its top dead center position
the power pistons 136.
One of the power pistons 136 may be operatively con(degrees ATDC). Preferably, fuel is ignited in each power
nected to the crankshaft 12Sby a first fixed master rod 15S andcylinder 134 within a range of 10 to 30 degreesATDC. The
the remainder of the power pistons 136 may be operatively
power cylinders 134 may be arranged to fire in sequential
connected to the first master rod 15S by articulating rods 160.
order as the crankshaft rotates. Further, each power cylinder
The first master rod 15S has a hub 161 at one end (and hence 10 134 fires once per revolution of the crankshaft 12S. This is incontrast to conventional four-stroke radial engines, wherein
is fixed to the hub 161). The articulating rods 160 are pivotallyconnected to the hub by knuckle pins or other suitable means.
as the crankshaft rotates, every other cylinder fires such thatfor every two rotations of the crankshaft, every cylinder fires
Similarly, one of the compression pistons 142 may be operaone time. The rotational direction of the crankshaft 12S istively connected to the crankshaft 12S by a second fixedmaster rod 162 and the remainder of the compression pistons 15 indicated by an arrow in FIGS. 10-12 that is associated withthe crankshaft.
142 may be operatively connected to the second master rod
162 by articulating rods 164. The secondmaster rod has a hub
Spark plugs 16S may be provided having electrodes
166 at one end (and hence is fixed to the hub 166). The
extending into the each of the power cylinders 134 for igniting
articulating rods 164 are pivotally connected to the hub 166
air-fuel charges at precise times by an ignition control, notby knuckle pins or other suitable pivotal connection means. It 20 shown. It should be understood that the engine 122 may beshould be understood, however, that the power and compresmade as a diesel engine and be operated without a spark plug
if desired.
sion pistons may be operatively connected to the crankshaft
Although the invention has been described by reference toby other mechanical arrangements.
specific embodiments, it should be understood that numerous
The split-cycle radial engine 122 may include between
three and nine power cylinders and an equivalent number of 25 changes may be made within the spirit and scope of thecompression cylinders. In the embodiment shown in theinventive concepts described. Accordingly, it is intended thatthe invention not be limited to the described embodiments,
drawings, the engine 122 has five power cylinders 134 andfive compression cylinders 140. It should be understood,
but that it have the full scope defined by the language of the
however, that the split-cycle radial engine 122 is not limited tofollowing claims.
What is claimed is:any particular number of power and compression cylinders, 30
so long as there are an equal number of power and compres1. A split-cycle air hybrid aircraft engine comprising:a crankshaft rotatable about a crankshaft axis;
sion cylinders and there are at least three power cylinders andthree compression cylinders.
a power piston slidably received within a power cylinderand operatively connected to the crankshaft such that theIf additional power is desired, the split-cycle radial engine
122 may also optionally include a secondpower bank having 35
power piston reciprocates through an expansion stroke
and an exhaust stroke during a single rotation of thea plurality of power cylinders radially disposed around the
crankshaft and a second compression bank axially adjacentcrankshaft;a compression piston slidably received within a compresthe second power bank including a plurality of compression
sion cylinder and operatively connected to the crankcylinders radially disposed around the crankshaft and equal in
shaft such that the compression piston reciprocatesquantity to the number of power cylinders. The second power 40
through an intake stroke and a compression stroke durbank may be axially adjacent the first compression bank insuch a way that the four banks are aligned in a row. A power
ing a single rotation of the crankshaft;piston is slidably received within each power cylinder of thea gas crossover passage operatively interconnecting thesecond power bank and is operatively connected to the crankcompression cylinder and the power cylinder, the gas
crossover passageincluding an inlet valve and an outlet
shaft such that each power piston reciprocates through an 45
expansion stroke and an exhaust stroke during a single rotavalve defining a pressure chamber therebetween;tion of the crankshaft. Likewise, a compression piston isan air reservoir operatively connected to the pressure
slidably received within each compression cylinder andchamber by a reservoir passageat a location between theoperatively connected to the crankshaft such that each cominlet valve and the outlet valve of the pressure chamber,the air reservoir being selectively operable to receive
pression piston reciprocates through an intake stroke and a 50
compression stroke during a single rotation of the crankshaft.
compressed air from the compression cylinder and to
Each compression cylinder of the second compression bankdeliver compressed air to the power cylinder for use inis paired with an associated power cylinder of the second
transmitting power to the crankshaft during engine
power bank. Each compression and power cylinder pair of theoperation;
second compression bank and second power bank includes a 55
valves selectively controlling gas flow into and out of thegas crossover passage interconnecting the compression cylcompression cylinder, the power cylinder, and the air
reservoir;inder and the power cylinder of the pair. The gas crossover
wherein the engine is mounted to an aircraft and the air
passageincludes an inlet valve and an outlet valve defining apressure chamber therebetween. Valves also control gas flow
reservoir is disposed within the aircraft;
into the compression cylinders of the second compression 60 wherein the engine is operable in a high pressure (HP)
mode, in the HP mode:bank and out of the power cylinders o fthe secondpower bank.
It should be understood that the split-cycle radial engine 122
the compression cylinder is selectively controllable tomay have any number of banks, so long as there is an equal
operate as a power cylinder having an expansion
stroke and an exhaust stroke; andnumber of power and compression banks.
both the power cylinder and the compression cylinder
The compression pistons 142 lag slightly behind the power 65
receive compressed air from the air reservoir which ispistons 136 (in degrees of crank angle rotation). During
expanded on the compression and power cylinder'soperation of the engine, as the compression pistons 142 reachUS 7,513,224 B2
12in the AC mode, the compression piston is in the compression mode and draws in and compresses air which isstored in the air reservoir for later use in the power
2. The split-cycle air hybrid aircraft engine of claim 1,
cylinder; andwherein the aircraft has wings, the air reservoir being dis5in the PAP mode, the power cylinder is in the power mode
posed in the wings.
and receives compressed air from the air reservoir which
3. The split-cycle air hybrid aircraft engine of claim 2,
is expanded on the expansion stroke of the power piston,wherein the aircraft has a wing spar in each wing, the airtransmitting power to the crankshaft, and the expanded
reservoir being disposed in at least one of the wing spars.
air is discharged on the exhaust stroke.
9. The split-cycle air hybrid aircraft engine of claim S
4. The split-cycle air hybrid aircraft engine of claim 1,
wherein, in the PAP mode, fuel is mixed with the compressed
wherein the aircraft has a cockpit, a tail, and an aft fuselage
air at the beginning of an expansion stroke and the mixture is
proximate the tail, the air reservoir being disposed in the aft
ignited, burned and expanded on the sameexpansion stroke offuselage.
the power piston, transmitting power to the crankshaft, and
5. The split-cycle air hybrid aircraft engine of claim 4,
the combustion products are discharged on the exhaust stroke.
wherein the air reservoir is disposed proximate the tail.
10. The split-cycle air hybrid aircraft engine of claim S
6. The split-cycle air hybrid aircraft engine of claim 1,
wherein, in the PAP mode, the compressed air admitted to thewherein the compression cylinder is selectively controllable
power cylinder is expanded without adding fuel or initiating
combustion.
to place the compression piston in a compression mode or an
11. The split-cycle air-hybrid aircraft engine of claim 1
idle mode.
20
wherein:7. The split-cycle air hybrid aircraft engine of claim 1,
in the power cylinder, fuel is mixed with the compressed air
wherein the power cylinder is selectively controllable to placeat the beginning of an expansion stroke and the mixture
the power piston in a power mode or an idle mode.
is ignited, burned and expanded on the same expansion
S. The split-cycle air hybrid aircraft engine of claim 7,
stroke of the power cylinder; andwherein the engine is operable in at least an internal combusin the compression cylinder, compressedair admitted to thetion engine (ICE) mode, an air compressor (AC) mode and acompression cylinder is expanded on the expansion
pre-compressed air power (PAP) mode, and wherein:stroke of the compression cylinder without adding fuelor initiating combustion.
in the ICE mode, the compression piston and power piston
12. The split-cycle air hybrid aircraft engine of claim 1,
are in their respective compression and power modes, in ~0
wherein fuel is ignited within a rangeof 5 to 40 degreescrankthat the compression piston draws in and compresses
angle (CA) after the power piston has reached its top deadinlet air for use in the power cylinder, and compressedair
center (TDC) position.
is admitted to the power cylinder with fuel, at the begin13. The split-cycle air hybrid aircraft engine of claim 12,
ning of an expansion stroke, which is ignited, burned andwherein fuel is ignited within a range of 10 to 30 degrees
expanded on the same expansion stroke of the power
crank angle (CA) after the power piston has reached its top
piston, transmitting power to the crankshaft, and thedead center (TDC) position.
combustion products are discharged on the exhauststroke;respective expansion strokes and discharged on theirrespective exhaust strokes.