(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)(19) World Intellectual Property Organization

11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111

International Bureau(10) International Publication Number(43) International Publication Date

22 December 2011 (22.12.2011)

PCT(51) International Patent Classification:
F02B 33122 (2006.01)(21) International Application Number:
PCT/US20ll/040437(22) International Filing Date:
15 June20ll (15.06.2011)(25) Filing Language:

English(26) Publication Language:

English(30) Priority Data:

61/356,157

18 June 2010 (18.06.2010)us(71) Applicant (for all designated States except US): SCUD-ERI GROUP, LLC [US/US]; 1111 Elm Street, Suite 33,
West Springfield, MA 01089 (US).
(72) Inventor; and(75) Inventor/Applicant (for US only): MELDOLESI, Riccardo [IT/GB]; 55 New Road, Shoreham-by-Sea, West
Sussex BN436RB (GB).

WO 2011/159756 A1(74) Agents: VISCONTI, Michael P. III et al.; Nutter McClennen & Fish LLP, Seaport West, 155 Seaport Boulevard, Boston, MA 02210-2604 (US).
(81) Designated States (unless otherwise indicated, for every
kind of national protection available): AE, AG, AL, AM,
AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ,
CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM, DO,
DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT,
HN, HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP,
KR, KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD,
ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI,
NO, NZ, OM, PE, PG, PH, PL, PT, RO, RS, RU, SC, SD,
SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR,
TT, TZ, VA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
(84) Designated States (unless otherwise indicated, for every
kind of regional protection available): ARIPO (BW, GH,
GM, KE, LR, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG,
ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ,
TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK,
EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU,
LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK,-=== --------------------------------------------------------------------------------------- FIG. 5[Continued on next page](54) Title: SPLIT-CYCLE ENGINE WITH CROSSOVER PASSAGE COMBUSTION;;;;;;;;;;;;;;;(57) Abstract: Methods, systems, and devices are disclosed that generally involve split-cycle engines in which a combustion event is initiated in a crossover passage that interconnects a compression cylinderand an expansion cylinder of the split-cycle engine. In one embodiment, the compression piston leads the expansion piston by a phaseshift angle so that, for example, a substantial amount of the combustion event can occur in the crossover passage at a constant volume.

--72;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

66

W 0 2011/15 9756 A 1 11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ,
GW, ML, MR, NE, SN, TD, TG).
Published:-with international search report (Art. 21 (3))

before the expiration of the time limit for amending theclaims and to be republished in the event of receipt ofamendments (Rule 48.2(h))

wo 2011/159756

PCT/US2011/040437- 1SPLIT -CYCLE ENGINE WITH CROSSOVER PASSAGE COMBUSTIONCROSS-REFERENCE TO RELATED APPLICATIONSThis application claims the benefit of priority of U.S. Provisional Patent

5

Application Number 61/356,157, filed on June 18, 2010, the entire contents ofwhich areincorporated herein by reference.

FIELD
10

The present invention relates to internal combustion engines. More particularly,
the invention relates to split-cycle engines with crossover passage combustion.

BACKGROUND
For purposes of clarity, the term "conventional engine" as used in the present
15

application refers to an internal combustion engine wherein all four strokes ofthe wellknown Otto cycle (the intake, compression, expansion and exhaust strokes) arecontained in each piston/cylinder combination of the engine. Each stroke requires one
half revolution ofthe crankshaft (180 degrees crank angle ("CA")), and two full
revolutions of the crankshaft (720 degrees CA) are required to complete the entire Otto

20

cycle in each cylinder of a conventional engine.
Also, for purposes of clarity, the following definition is offered for the term
"split-cycle engine" as may be applied to engines disclosed in the prior art and as
referred to in the present application.
A split-cycle engine generally comprises:25

a crankshaft rotatable about a crankshaft axis;
a compression piston slidably received within a compression cylinder andoperatively connected to the crankshaft such that the compression piston reciprocatesthrough an intake stroke and a compression stroke during a single rotation of the
crankshaft;30

an expansion (power) piston slidably received within an expansion cylinder andoperatively connected to the crankshaft such that the expansion piston reciprocatesthrough an expansion stroke and an exhaust stroke during a single rotation of the
crankshaft; andwo 2011/159756

PCT/US2011/040437-2-

a crossover passage interconnecting the compression and expansion cylinders,the crossover passage including at least a crossover expansion (XovrE) valve disposed
therein, but more preferably including a crossover compression (XovrC) valve and a5crossover expansion (XovrE) valve defining a pressure chamber therebetween.
A split-cycle air hybrid engine combines a split-cycle engine with an air
reservoir (also commonly referred to as an air tank) and various controls. This
combination enables the engine to store energy in the form of compressed air in the air
reservoir. The compressed air in the air reservoir is later used in the expansion cylinder10

to power the crankshaft. In general, a split-cycle air hybrid engine as referred to hereincomprises:
a crankshaft rotatable about a crankshaft axis;
a compression piston slidably received within a compression cylinder andoperatively connected to the crankshaft such that the compression piston reciprocates15

through an intake stroke and a compression stroke during a single rotation of the
crankshaft;an expansion (power) piston slidably received within an expansion cylinder andoperatively connected to the crankshaft such that the expansion piston reciprocatesthrough an expansion stroke and an exhaust stroke during a single rotation of the20

crankshaft;a crossover passage (port) interconnecting the compression and expansion
cylinders, the crossover passage including at least a crossover expansion (XovrE) valve
disposed therein, but more preferably including a crossover compression (XovrC) valve
and a crossover expansion (XovrE) valve defining a pressure chamber therebetween; and25

an air reservoir operatively connected to the crossover passage and selectively
operable to store compressed air from the compression cylinder and to delivercompressed air to the expansion cylinder.
FIG. 1 illustrates one exemplary embodiment of a prior art split-cycle air hybrid
engine. The split-cycle engine 100 replaces two adjacent cylinders of a conventional

30

engine with a combination of one compression cylinder 102 and one expansion cylinder
104. The compression cylinder 102 and the expansion cylinder 104 are formed in anengine block in which a crankshaft 106 is rotatably mounted. Upper ends ofthecylinders 102, 104 are closed by a cylinder head 130. The crankshaft 106 includes

wo 2011/159756

PCT/US2011/040437- 3axially displaced and angularly offset first and second crank throws 126, 128, having aphase angle therebetween. The first crank throw 126 is pivotally joined by a firstconnecting rod 138 to a compression piston 110 and the second crank throw 128 is5

pivotally joined by a second connecting rod 140 to an expansion piston 120 toreciprocate the pistons 110, 120 in their respective cylinders 102, 104 in a timed relation
determined by the angular offset of the crank throws and the geometric relationships ofthe cylinders, crank, and pistons. Alternative mechanisms for relating the motion andtiming of the pistons can be utilized if desired. The rotational direction of the crankshaft

10

and the relative motions of the pistons near their bottom dead center (BDC) positions areindicated by the arrows associated in the drawings with their corresponding components.
The four strokes of the Otto cycle are thus "split" over the two cylinders 102 and104 such that the compression cylinder 102 contains the intake and compression strokes
and the expansion cylinder 104 contains the expansion and exhaust strokes. The Otto

15

cycle is therefore completed in these two cylinders 102, 104 once per crankshaft 106
revolution (360 degrees CA).
During the intake stroke, intake air is drawn into the compression cylinder 102
through an inwardly-opening (opening inward into the cylinder and toward the piston)poppet intake valve 108. During the compression stroke, the compression piston 110

20

pressurizes the air charge and drives the air charge through a crossover passage 112,
which acts as the intake passage for the expansion cylinder 104. The engine 100 canhave one or more crossover passages 112.
The volumetric (or geometric) compression ratio ofthe compression cylinder
102 ofthe split-cycle engine 100 (and for split-cycle engines in general) is herein25

referred to as the "compression ratio" ofthe split-cycle engine. The volumetric (orgeometric) compression ratio of the expansion cylinder 104 of the engine 100 (and for
split-cycle engines in general) is herein referred to as the "expansion ratio" of the splitcycle engine. The volumetric compression ratio of a cylinder is well known in the art as
the ratio of the enclosed (or trapped) volume in the cylinder (including all recesses)

30

when a piston reciprocating therein is at its BDC position to the enclosed volume (i.e.,
clearance volume) in the cylinder when said piston is at its top dead center (TDC)
position. Specifically for split-cycle engines as defined herein, the compression ratio of
a compression cylinder is determined when the XovrC valve is closed. Also specificallywo 2011/159756

PCT/US2011/040437-4-

for split-cycle engines as defined herein, the expansion ratio of an expansion cylinder isdetermined when the XovrE valve is closed.
Due to very high volumetric compression ratios (e.g., 20 to 1, 30 to 1, 40 to 1, or
5greater) within the compression cylinder 102, an outwardly-opening (opening outwardly
away from the cylinder and piston) poppet crossover compression (XovrC) valve 114 at
the inlet of the crossover passage 112 is used to control flow from the compression
cylinder 102 into the crossover passage 112. Due to very high volumetric compression
ratios (e.g., 20 to 1, 30 to 1, 40 to 1, or greater) within the expansion cylinder 104, an

10

outwardly-opening poppet crossover expansion (XovrE) valve 116 at the outlet of thecrossover passage 112 controls flow from the crossover passage 112 into the expansion
cylinder 104. The actuation rates and phasing ofthe XovrC and XovrE valves 114, 116
are timed to maintain pressure in the crossover passage 112 at a high minimum pressure(typically 20 bar or higher at full load) during all four strokes of the Otto cycle.

15

At least one fuel injector 118 injects fuel into the pressurized air at the exit end
ofthe crossover passage 112 in coordination with the XovrE valve 116 opening.
Alternatively, or in addition, fuel can be injected directly into the expansion cylinder
104. The fuel-air charge fully enters the expansion cylinder 104 shortly after the
expansion piston 120 reaches its TDC position. As the piston 120 begins its descent

20

from its TDC position, and while the XovrE valve 116 is still open, one or more spark
plugs 122 are fired to initiate combustion (typically between 10 to 20 degrees CA after
TDC of the expansion piston 120). Combustion can be initiated while the expansion
piston is between 1 and 30 degrees CA past its TDC position. More preferably,
combustion can be initiated while the expansion piston is between 5 and 25 degrees CA

25

past its TDC position. Most preferably, combustion can be initiated while the expansion
piston is between 10 and 20 degrees CA past its TDC position. Additionally,
combustion can be initiated through other ignition devices and/or methods, such as withglow plugs, microwave ignition devices, or through compression ignition methods.
The XovrE valve 116 is then closed before the resulting combustion event enters30

the crossover passage 112. The combustion event drives the expansion piston 120
downward in a power stroke. Exhaust gases are pumped out of the expansion cylinder
104 through an inwardly-opening poppet exhaust valve 124 during the exhaust stroke.

wo 2011/159756

PCT/US2011/040437-5With the split-cycle engine concept, the geometric engine parameters (i.e., bore,
stroke, connecting rod length, compression ratio, etc.) of the compression and expansion
cylinders are generally independent from one another. For example, the crank throws
5126, 128 for the compression cylinder 102 and expansion cylinder 104, respectively,
have different radii and are phased apart from one another with TDC of the expansion
piston 120 occurring prior to TDC of the compression piston 110. This independence
enables the split-cycle engine to potentially achieve higher efficiency levels and greater
torques than typical four-stroke engines.

10

The geometric independence of engine parameters in the split-cycle engine 100
is also one of the main reasons why pressure can be maintained in the crossover passage
112 as discussed earlier. Specifically, the expansion piston 120 reaches its TDC position
prior to the compression piston 110 reaching its TDC position by a discrete phase angle(typically between 10 and 30 crank angle degrees). This phase angle, together with15

proper timing of the XovrC valve 114 and the XovrE valve 116, enables the split-cycle
engine 100 to maintain pressure in the crossover passage 112 at a high minimumpressure (typically 20 bar absolute or higher during full load operation) during all four
strokes of its pressure/volume cycle. That is, the split-cycle engine 100 is operable totime the XovrC valve 114 and the XovrE valve 116 such that the XovrC and XovrE

20

valves 114, 116 are both open for a substantial period oftime (or period of crankshaft
rotation) during which the expansion piston 120 descends from its TDC position towards
its BDC position and the compression piston 110 simultaneously ascends from its BDC
position towards its TDC position. During the period oftime (or crankshaft rotation)that the crossover valves 114, 116 are both open, a substantially equal mass of gas is25transferred (1) from the compression cylinder 102 into the crossover passage 112 and (2)from the crossover passage 112 to the expansion cylinder 104. Accordingly, during thisperiod, the pressure in the crossover passage is prevented from dropping below apredetermined minimum pressure (typically 20, 30, or 40 bar absolute during full load
operation). Moreover, during a substantial portion of the intake and exhaust strokes

30(typically 90% ofthe entire intake and exhaust strokes or greater), the XovrC valve 114
and XovrE valve 116 are both closed to maintain the mass oftrapped gas in the
crossover passage 112 at a substantially constant level. As a result, the pressure in thewo 2011/159756

PCT/US2011/040437-6-crossover passage 112 is maintained at a predetermined minimum pressure during all
four strokes of the engine's pressure/volume cycle.
For purposes herein, the method of opening the XovrC 114 and XovrE 116
5valves while the expansion piston 120 is descending from TDC and the compression
piston 110 is ascending toward TDC in order to simultaneously transfer a substantiallyequal mass of gas into and out of the crossover passage 112 is referred to as the "pushpull" method of gas transfer. It is the push-pull method that enables the pressure in the
crossover passage 112 of the engine 100 to be maintained at typically 20 bar or higher

10

during all four strokes of the engine's cycle when the engine is operating at full load.
The crossover valves 114, 116 are actuated by a valve train that includes one ormore cams (not shown). In general, a cam-driven mechanism includes a camshaft
mechanically linked to the crankshaft. One or more cams are mounted to the camshaft,each having a contoured surface that controls the valve lift profile of the valve event

15(i.e., the event that occurs during a valve actuation). The XovrC valve 114 and the
XovrE valve 116 each can have its own respective cam and/or its own respective
camshaft. As the XovrC and XovrE cams rotate, eccentric portions thereof impart
motion to a rocker arm, which in turn imparts motion to the valve, thereby lifting(opening) the valve off of its valve seat. As the cam continues to rotate, the eccentric

20

portion passes the rocker arm and the valve is allowed to close.
For purposes herein, a valve event (or valve opening event) is defined as thevalve lift from its initial opening off of its valve seat to its closing back onto its valve
seat versus rotation of the crankshaft during which the valve lift occurs. Also, forpurposes herein, the valve event rate (i.e., the valve actuation rate) is the duration in time25

required for the valve event to occur within a given engine cycle. It is important to notethat a valve event is generally only a fraction of the total duration of an engine operating
cycle (e.g., 720 degrees CA for a conventional engine cycle and 360 degrees CA for a
split-cycle engine).
The split-cycle air hybrid engine 100 also includes an air reservoir (tank) 142,30

which is operatively connected to the crossover passage 112 by an air reservoir tankvalve 152. Embodiments with two or more crossover passages 112 may include a tankvalve 152 for each crossover passage 112, which connect to a common air reservoir 142,

wo 2011/159756

PCT/US2011/040437-7or alternatively each crossover passage 112 may operatively connect to separate air
reservoirs 142.
The tank valve 152 is typically disposed in an air tank port 154, which extends
5from the crossover passage 112 to the air tank 142. The air tank port 154 is divided intoa first air tank port section 156 and a second air tank port section 158. The first air tankport section 156 connects the air tank valve 152 to the crossover passage 112, and thesecond air tank port section 158 connects the air tank valve 152 to the air tank 142. The
volume of the first air tank port section 156 includes the volume of all additional

10

recesses which connect the tank valve 152 to the crossover passage 112 when the tankvalve 152 is closed. Preferably, the volume of the first air tank port section 156 is small
relative to the second air tank port section 158. More preferably, the first air tank port
section 156 is substantially non-existent, that is, the tank valve 152 is most preferably
disposed such that it is flush against the outer wall of the crossover passage 112.

15

The tank valve 152 may be any suitable valve device or system. For example,
the tank valve 152 may be a pressure activated check valve, or an active valve which isactivated by various valve actuation devices (e.g., pneumatic, hydraulic, cam, electric, or
the like). Additionally, the tank valve 152 may comprise a tank valve system with two
or more valves actuated with two or more actuation devices.

20

The air tank 142 is utilized to store energy in the form of compressed air and tolater use that compressed air to power the crankshaft 106. This mechanical means forstoring potential energy provides numerous potential advantages over the current state of
the art. For instance, the split-cycle air hybrid engine 100 can potentially provide many
advantages in fuel efficiency gains and NOx emissions reduction at relatively low

25

manufacturing and waste disposal costs in relation to other technologies on the market,
such as diesel engines and electric-hybrid systems.
The engine 100 typically runs in a normal operating or firing (NF) mode (alsocommonly called the engine firing (EF) mode) and one or more of four basic air hybrid
modes. In the EF mode, the engine 100 functions normally as previously described in

30

detail herein, operating without the use of the air tank 142. In the EF mode, the air tankvalve 152 remains closed to isolate the air tank 142 from the basic split-cycle engine. In
the four air hybrid modes, the engine 100 operates with the use ofthe air tank 142.

wo 2011/159756

PCT/US2011/040437-8-

The four basic air hybrid modes include:
1) Air Expander (AE) mode, which includes using compressed air energy fromthe air tank 142 without combustion;
52) Air Compressor (AC) mode, which includes storing compressed air energy
into the air tank 142 without combustion;3) Air Expander and Firing (AEF) mode, which includes using compressed air
energy from the air tank 142 with combustion; and
4) Firing and Charging (FC) mode, which includes storing compressed air energy

10

into the air tank 142 with combustion.
Further details on split-cycle engines can be found in U.S. Patent No. 6,543,225
entitled Split Four Stroke Cycle Internal Combustion Engine and issued on AprilS,
2003; and U.S. Patent No. 6,952,923 entitled Split-Cycle Four-Stroke Engine and issued
on October 11, 2005, each ofwhich is incorporated by reference herein in its entirety.

15

Further details on air hybrid engines are disclosed in U.S. Patent No. 7,353,786
entitled Split-Cycle Air Hybrid Engine and issued on April 8, 2008; U.S. Patent
Application No. 611365,343 entitled Split-Cycle Air Hybrid Engine and filed on July 18,
201 0; and U.S. Patent Application No. 61/313,831 entitled Split-Cycle Air Hybrid
Engine and filed on March 15, 2010, each ofwhich is incorporated by reference herein20

in its entirety.
Direct fuel injection has various advantages which are well known in the art.
Direct fuel injection in gasoline engines enables increased fuel efficiency and reduced
emission levels at low loads. Diesel engines, which are typically more fuel efficientthan gasoline engines, usually require direct fuel injection.

25

The high expansion ratio in the expansion cylinder 104, however, can make it
difficult for split-cycle engines of the type shown in FIG. 1 to utilize direct fuel injection
into the expansion cylinder 104. For one thing, the very small clearance distance (e.g.,
1.0, 0.9, 0.8, 0.7 millimeter(s), or less) between the cylinder head 130 and the expansion
piston 120 when the expansion piston 120 is at TDC makes packaging injectors into the30

expansion cylinder 104 difficult to accomplish. In addition, direct fuel injection into thesmall space available in the expansion cylinder 104 can lead to wetting of the cylinderwalls, which is detrimental to engine efficiency.

wo 2011/159756

PCT/US2011/040437-9In addition, the expansion stroke in prior art split-cycle engines of the typeshown in FIG. 1 is a variable-volume combustion process. As a result, very rapid
combustion is required in order for the flame front to apply pressure to the expansion
5

piston 120, since it is descending away from the flame front towards its BDC position
when combustion occurs. Such rapid combustion is typically accomplished in theengine of FIG. 1 by utilizing very high pressures in the crossover passage, which in turncauses the air/fuel mixture entering the expansion cylinder 104 to flow in at very rapid
flow rates, in some cases reaching the speed of sound (i.e., sonic flow). This10

phenomenon creates substantial turbulence in the expansion cylinder 104 prior to andduring the combustion event initiated by the spark plug 122, which leads to rapid
combustion ofthe air/fuel mixture.
There remains a need, however, for other techniques for achieving rapid
combustion, particularly in diesel engines in which high crossover passage pressures can

15lead to undesirable pre-combustion ofthe fuel. As set out below, a combustion processthat takes place at a constant-volume or that is at least initiated under constant-volume
conditions can provide an alternative means of rapidly increasing the temperature andpressure of an air/fuel mixture.

20

SUMMARY
The methods, systems, and devices disclosed herein generally involve initiating
and/or performing combustion within the crossover passage of a split-cycle engine. Thiscan advantageously permit substantially constant-volume combustion and can facilitate
direct injection of fuel into the combustion chamber.

25

In one aspect of at least one embodiment ofthe invention, an engine is provided
that includes a crankshaft rotatable about a crankshaft axis and a compression piston
slidably received within a compression cylinder and operatively connected to the
crankshaft such that the compression piston is operable to reciprocate through an intake
stroke and a compression stroke of a four stroke cycle during a single rotation of the30

crankshaft. The engine also includes an expansion piston slidably received within an
expansion cylinder and operatively connected to the crankshaft such that the expansion
piston is operable to reciprocate through an expansion stroke and an exhaust stroke ofsaid four stroke cycle during a single rotation of the crankshaft. The engine further

wo 2011/159756

PCT/US2011/040437- 10includes a crossover passage interconnecting the compression cylinder and the
expansion cylinder, a crossover compression valve operable to control fluid
communication between the compression cylinder and the crossover passage, and a5crossover expansion valve operable to control fluid communication between the
crossover passage and the expansion cylinder. The engine is operable to initiate a
combustion event in the crossover passage. A phase shift angle, defined as the numberof degrees the crankshaft must rotate after the compression piston reaches its top deadcenter position in order for the expansion piston to reach its top dead center position, is10

greater than approximately 5 degrees and less than approximately 90 degrees.
Related aspects of the invention provide an engine, e.g., as described above, inwhich the phase shift angle is greater than approximately 5 degrees and less thanapproximately 60 degrees.
Related aspects ofthe invention provide an engine, e.g., as described above, in

15

which the phase shift angle is greater than approximately 10 degrees and less thanapproximately 35 degrees.
Related aspects of the invention provide an engine, e.g., as described above, inwhich a ratio of a volume in the expansion cylinder when the expansion piston is at its
bottom dead center position to a volume in the expansion cylinder when the expansion

20

piston is at its top dead center position is approximately 40 to 1 or greater.
Related aspects of the invention provide an engine, e.g., as described above, inwhich a ratio of a volume in the compression cylinder when the compression piston is at
its bottom dead center position to a volume in the compression cylinder when thecompression piston is at its top dead center position is approximately 40 to 1 or greater.

25

Related aspects of the invention provide an engine, e.g., as described above, inwhich the crossover compression valve is operable to open outwardly away from aninterior of the compression cylinder.
Related aspects of the invention provide an engine, e.g., as described above, inwhich the crossover expansion valve is operable to open outwardly away from an

30interior of the expansion cylinder.
Related aspects of the invention provide an engine, e.g., as described above, inwhich the engine is operable to initiate said combustion event while the expansion piston
is ascending from its bottom dead center position towards its top dead center position.

wo 2011/159756

PCT/US2011/040437- 11 Related aspects of the invention provide an engine, e.g., as described above, inwhich the engine is operable to initiate said combustion event while the expansion piston
is descending from its top dead center position towards its bottom dead center position.
5

Related aspects of the invention provide an engine, e.g., as described above, inwhich the engine is operable to initiate said combustion event while the compression
piston is descending from its top dead center position towards its bottom dead center
position.
Related aspects of the invention provide an engine, e.g., as described above, in

10which the engine is operable to open the crossover expansion valve while the expansion
piston is within ± 10 degrees of rotation of the crankshaft from its top dead center
position.
Related aspects of the invention provide an engine, e.g., as described above, that
includes a fuel injection system operable to add fuel to the crossover passage.

15

Related aspects of the invention provide an engine, e.g., as described above, inwhich the engine is operable to initiate said combustion event via compression ignition.
Related aspects of the invention provide an engine, e.g., as described above, that
includes a spark plug at least partially disposed in the crossover passage and operable toinitiate said combustion event.

20

Related aspects of the invention provide an engine, e.g., as described above, that
includes an air tank operatively coupled to the crossover passage and a tank valve
configured to selectively place the air tank in fluid communication with the crossover
passage.
Related aspects of the invention provide an engine, e.g., as described above, in25

which the engine is operable to initiate the combustion event while the crossovercompression valve and the crossover expansion valve are closed.
In another aspect of at least one embodiment of the invention, a method of
operating an engine is provided that includes supplying air compressed by acompression piston to a crossover passage and, after said supplying, transitioning the30

crossover passage to a closed, constant-volume configuration. The method also
includes, after said transitioning, adding fuel to the crossover passage and initiating
combustion of an air-fuel mixture disposed within the crossover passage. The method
further includes, after said initiating, transferring pressure generated during combustion

wo 2011/159756

PCT/US2011/040437- 12to an expansion cylinder to exert force on an expansion piston, the expansion piston
driving a crankshaft. The initiating is performed after the compression piston reaches
top dead center and before the expansion piston reaches top dead center.
5

Related aspects of the invention provide a method, e.g., as described above, inwhich said transitioning comprises closing a crossover compression valve and closing acrossover expansion valve.
Related aspects of the invention provide a method, e.g., as described above, inwhich said transitioning comprises closing an air tank valve.

10

Related aspects ofthe invention provide a method, e.g., as described above, inwhich said supplying comprises transferring the air compressed by the compression
piston from an air tank to the crossover passage.
Related aspects of the invention provide a method, e.g., as described above, inwhich the pressure generated during combustion is transferred to the expansion cylinder

15

before combustion is completed.
In another aspect of at least one embodiment of the invention, a method of
operating an engine is provided that includes supplying air compressed by acompression piston to a crossover passage and, after said supplying, transitioning thecrossover passage to a closed, constant-volume configuration. The method also

20

includes, after said transitioning, adding fuel to the crossover passage and initiating
combustion of an air-fuel mixture disposed within the crossover passage. The method
further includes, after said initiating, transferring pressure generated during combustion
to an expansion cylinder to exert force on an expansion piston, the expansion piston
driving a crankshaft. The initiating is performed after the compression piston reaches

25

top dead center and after the expansion piston reaches top dead center.
The present invention further provides devices, systems, and methods as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood from the following detailed
30

description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic diagram of a prior art split-cycle air hybrid engine;

wo 2011/159756

PCT/US2011/040437- 13 FIG. 2 is a schematic diagram of an exemplary embodiment of a split-cycle four
stroke internal combustion engine in accordance with the present invention during theintake stroke;

5
FIG. 3 is a schematic diagram of the split-cycle engine ofFIG. 2 during partial
compression ofthe compression stroke;
FIG. 4 is a schematic diagram of the split-cycle engine of FIG. 2 after the10compression stroke and during the beginning of fuel injection into the crossover passage;
FIG. 5 is a schematic diagram of the split-cycle engine ofFIG. 2 during initiation of
combustion in the crossover passage;

15

FIG. 6 is a schematic diagram ofthe split-cycle engine of FIG. 2 during combustion
and at the beginning of an expansion stroke;
FIG. 7 is a schematic diagram of the split-cycle engine of FIG. 2 during the
expansion stroke;

20
FIG. 8 is a schematic diagram of the split-cycle engine of FIG. 2 at the end of the
expansion stroke and the beginning of the exhaust stroke;
FIG. 9 is a schematic diagram of the split-cycle engine of FIG. 2 during the exhaust25

stroke; andFIG. 10 is a schematic diagram of an exemplary embodiment of an air hybrid splitcycle four stroke internal combustion engine in accordance with the present invention.

30

DETAILED DESCRIPTION
Certain exemplary embodiments will now be described to provide an overall
understanding of the principles of the structure, function, manufacture, and use of themethods, systems, and devices disclosed herein. One or more examples of theseembodiments are illustrated in the accompanying drawings. Those skilled in the art will

35

understand that the methods, systems, and devices specifically described herein andillustrated in the accompanying drawings are non-limiting exemplary embodiments andwo 2011/159756

PCT/US2011/040437- 14that the scope of the present invention is defined solely by the claims. The features
illustrated or described in connection with one exemplary embodiment may be combinedwith the features of other embodiments. Such modifications and variations are intended
5

to be included within the scope of the present invention.
The term "air" is used herein to refer both to air and mixtures of air and othersubstances such as fuel or exhaust products. The term "fluid" is used herein to refer toboth liquids and gasses. Features shown in a particular figure that are the same as, orsimilar to, features shown in another figure are designated by like reference numerals.

10

Referring to FIGS. 2-9, an exemplary embodiment of a four stroke internal
combustion engine 50 in accordance with the present invention is shown passing
through its four strokes.
The split-cycle engine 50 includes a compression cylinder 66 with a compression
piston 72 reciprocating therein. The split-cycle engine 50 further includes an expansion

15cylinder 68 with an expansion piston 74 reciprocating therein. A crossover passage 55
interconnects the compression cylinder 66 and the expansion cylinder 68. The
compression piston 72 is connected to a crankshaft 52 via a first crank throw 58. The
expansion piston 74 is similarly connected to the same crankshaft 52 via a second crankthrow 56. The crankshaft 52 is rotatable about a crankshaft axis 54. A cylinder head 70

20

is disposed over an open end of the compression cylinder 66 and the expansion cylinder
68 to cover and seal the cylinders.
Referring to FIG. 2, at substantially the beginning of an intake stroke(represented by arrow 60), an inwardly-opening intake valve 82 opens into thecompression cylinder 66. The compression piston 72 descends within the compression

25

cylinder 66, which draws outside air into the compression cylinder.
Referring to FIG. 3, the intake valve 82 closes when the compression piston 72 issubstantially at its BDC position and beginning its compression stroke (represented byarrow 61 ). At substantially the same time or shortly thereafter, an outwardly-opening
crossover compression valve 84 opens. An outwardly-opening crossover expansion

30

valve 86 remains closed at this time such that, as the compression piston 72 ascends inthe compression stroke, it compresses air into the crossover passage 55.

wo 2011/159756

PCT/US2011/040437- 15 Referring to FIG. 4, the outwardly-opening crossover compression valve 84
closes at approximately the end of the compression stroke 61 when the compression
piston 72 is substantially at its TDC position. At about the same time or shortly
5

thereafter, a fuel injector 90 begins to inject fuel (e.g., diesel, gasoline, ethanol, etc.) into
the crossover passage 55. The crossover expansion valve 86 remains closed at this time,such that the crossover passage 55 is in a closed, constant-volume configuration as fuelis added. The engine 50 utilizes very high compression ratios (e.g., 40 to 1, 80 to 1, or
greater). This means that, at TDC, the compression piston 72 comes very close to the10cylinder head 70 (e.g., 1.0, 0.9, 0.8, 0.7 millimeters, or less). The high compression ratio
enables the engine 50 to pump as much air as possible into the crossover passage 55.
Referring to FIG. 5, a spark plug 92 initiates combustion of the fuel in the
crossover passage 55 shortly after the beginning of fuel injection. At this point, thecompression piston 72 is descending toward its BDC position and the expansion piston

15

74 is ascending towards its TDC position. Preferably, combustion is initiated in the
crossover passage 55 while the expansion piston 74 is approximately 10 to 20 degrees ofrotation of the crankshaft 52 before its TDC position. As shown, combustion is initiated(and optionally completed) while the crossover compression valve 84 and the crossover
expansion valve 86 are both closed. As a result, some or all of the combustion event

20

occurs at a constant volume. The rapid pressure increase associated with such constantvolume combustion can produce significant efficiency improvements.
In alternative embodiments, the combustion event in the crossover passage 55
can be initiated by other appropriate means such as compression or microwave ignition.
If compression ignition of diesel fuel is utilized, the combustion event can be initiated at25

substantially the same time that the fuel injection begins. In such diesel applications, thebeginning of fuel injection preferably begins while the expansion piston 74 isapproximately 10 to 20 degrees of rotation ofthe crankshaft 52 before its TDC position.
In some embodiments, the fuel injection and/or ignition described above withrespect to FIGS. 4 and 5 can be performed (or can be initiated) while the crossover

30

compression valve 84 is still open. This can allow the motion of air flowing into thecrossover passage 55 from the compression cylinder 66 to assist with distribution of
injected fuel within the crossover passage 55.

wo 2011/159756

PCT/US2011/040437- 16Referring to FIG. 6, the outwardly-opening crossover expansion valve 86 opensat (or close to) the same time that the expansion piston 74 reaches its TDC position inorder to allow the com busting (or possibly fully com busted) air/fuel mixture, and the5immense pressure associated therewith, to drive the expansion piston 74 down in an
expansion (or power) stroke (represented by arrow 62). More specifically, the engine 50
is operable to open the crossover expansion valve 86 while the expansion piston 74 iswithin plus(+) or minus(-) 10 degrees of rotation ofthe crankshaft 52 from the TDC
position of the expansion piston 74. The engine 50 utilizes very high expansion ratios

10(e.g., 40 to 1, 80 to 1, or greater). This means that, at TDC, the expansion piston 74
comes very close to the cylinder head 70 (e.g., 1.0, 0.9, 0.8, 0.7 millimeters, or less).
The very high expansion ratio allows the pressure generated by the combustion event toapply as much force as possible to the expansion piston 74.
Referring to FIG. 7, the pressure generated by the combustion event drives the15

expansion piston 74 down in the expansion stroke (represented by arrow 62), whichpowers the crankshaft 52. Referring to FIG. 8, when the expansion piston 74 issubstantially at its BDC position, the outwardly-opening crossover expansion valve 86
closes and the inwardly-opening exhaust valve 88 opens as the expansion piston 74
begins its exhaust stroke (represented by arrow 63).

20

Although not shown in specific detail in FIG. 8 (for ease of illustration), some ofthe products of the combustion event can be trapped in the crossover passage 55
between cycles. These products of combustion can be substantially scavenged out of thecrossover passage 55 in subsequent cycles.
Referring lastly to FIG. 9, the expansion piston ascends upward in the exhaust25

stroke (represented by arrow 63), which forces the products of combustion out throughthe exhaust port 53. At this point, the engine cycle is completed and the process repeats
for subsequent cycles.
As shown in FIGS. 2-9, the engine 50 is configured such that the compression
piston 72 leads the expansion piston 74. In other words, during each cycle of the engine,30

the compression piston 72 reaches TDC before the expansion piston 74 reaches TDC.
This is in direct contrast to prior art split-cycle engines of the type shown in FIG. I, in
which the expansion piston 120 leads the compression piston 110 (i.e., the expansion

wo 2011/159756

PCT/US2011/040437- 17piston 120 reaches TDC before the compression piston 110 reaches TDC, usually by
about 20 degrees CA).
As used herein, the "phase shift angle" of a split-cycle engine refers to the5number of degrees the crankshaft must rotate after the compression piston of the splitcycle engine reaches its TDC position in order for the expansion piston of the split-cycle
engine to reach its TDC position.
The phase shift angle of the engine 50 is preferably greater than 0 and less than
90 degrees. The phase shift angle is more preferably between 5 and 60 degrees, even10

more preferably between 10 and 35 degrees, and most preferably between 20 and 25
degrees.
When the compression piston 72leads the expansion piston 74, (1) air can becompressed into the crossover passage 55, (2) the crossover compression and crossover
expansion valves 84, 86 can be closed, and (3) ignition can be initiated, all prior to the15

expansion piston 74 reaching its TDC position. As a result, a substantial amount of the
combustion event, and possibly the entirety of the combustion event, can occur in the
crossover passage 55 at a constant volume. The crossover expansion valve 86 can thenbe opened when the expansion piston 74 is substantially at TDC, so that the pressure of
the combustion event can apply a maximum amount of force to the expansion piston 74.

20

It will be appreciated that, in some embodiments, additional combustion can occur inexpansion cylinder 68 after the crossover expansion valve 86 is opened. In other words,
the combustion process can be initiated in the crossover passage 55 and then allowed tocontinue in the expansion cylinder 68 once the crossover expansion valve 86 is opened.
Because the engine 50 uses the crossover passage 55 as a combustion chamber, it

25

can be particularly beneficial to minimize the volume of the crossover passage 55.
Alternative embodiments of the present invention can also utilize two or more crossover
passages 55 to interconnect the compression cylinder 66 and the expansion cylinder 68.
Initiating combustion in the crossover passage can also provide benefits indiesel-powered split-cycle engines. As noted above, prior art split-cycle engines of the30

type shown in FIG. 1 generally inject gasoline into the crossover passage and thentransfer the air/fuel mixture to the expansion cylinder under pressure to promote evenfuel distribution within the combustion chamber. Diesel fuel, on the other hand, has atendency to pre-combust too quickly when injected into the high pressure environment

wo 2011/159756

PCT/US2011/040437- 18of the crossover passage. As a result, in these prior art split-cycle engines, the fuelinjector must typically be placed in the expansion cylinder in order to support diesel
operation.
5

Placing the diesel fuel injector within the expansion cylinder carries its own
difficulties, however, such as packaging concerns raised by the low clearance space
between the top of the expansion piston when it is at TDC and the bottom of the cylinder
head or fire deck. In addition, without the benefit of post-injection pressurized flowfrom the crossover passage, the diesel fuel injected directly into the expansion cylinder

10

is not well-distributed within the combustion chamber, and can end up wetting thecylinder walls and piston face, undesirably reducing efficiency and performance.
Many of these issues can be eliminated by allowing the diesel fuel to combust in
the crossover passage with the crossover valves closed, as described above with respect
to FIGS. 2-9. Such combustion allows packaging of the fuel injector in the crossover

15

passage instead of in the clearance-space-constrained expansion cylinder. In addition,
the constant-volume combustion helps ensure an evenly distributed burn, while theability to control the crossover expansion valve opening timing allows optimization of
the timing at which the combustion force is applied to the expansion piston, and thus
reduces pre-combustion concerns.

20

Crossover passage combustion and its associated benefits can also be achieved
with air hybrid split-cycle engines. For example, the engine 50 of FIGS. 2-9, which
utilizes crossover passage combustion, can be modified to include an air hybrid systemsuch as the one depicted in FIG. 1. In particular, as shown in FIG. 10, the engine 50 canbe modified to include an air tank 94 that is operatively coupled to the crossover passage

25

55 by a tank valve 96. The tank valve can be controlled to selectively place thecrossover passage 55 in fluid communication with the air tank 94. Preferably, the tankvalve 96 is inwardly-opening (e.g., opening by moving into the crossover passage 55)
such that its valve seat provides a positive mechanical stop to prevent the tank valve 96
from opening under the high pressures generated during a combustion event within the

30

crossover passage 55. In use, the air tank 94 is utilized to store energy in the form ofcompressed air and to later supply that compressed air to power the crankshaft 52.

wo 2011/159756

PCT/US2011/040437- 19-

In EF mode, the tank valve 96 remains closed to isolate the air tank 94 from theengine 50, and the engine 50 functions normally as described above with respect to
FIGS. 2-9.
5

In AE mode, fuel injection and combustion are disabled, and compressed air
stored in the air tank 94 is supplied to the expansion cylinder 68 to drive the expansion
piston 74 during the power stroke.
In one exemplary embodiment, the intake valve 82 is held open and thecrossover compression valve 84 is held closed to idle the compression cylinder 66. The

10tank valve 96 is also held open to place the air tank 94 in fluid communication with thecrossover passage 55. During each engine cycle, the crossover expansion valve 86 is
opened just prior to and/or during the expansion stroke to supply compressed air fromthe combined volume of the air tank 94 and the crossover passage 55 to the expansion
cylinder 68 and thereby exert a rotating force on the crankshaft 52. The crossover

15

expansion valve 86 is closed once the desired amount of air is supplied to the expansion
cylinder 68. The exhaust valve 88 is opened during the exhaust stroke such that the
expansion piston 74 does not have to recompress the air in the expansion cylinder 68 as
it ascends towards its TDC position for the next engine cycle. The cycle then repeats.
In AC mode, fuel injection and combustion are disabled, and air that is20

compressed in the compression cylinder 66 is supplied to the air tank 94 for storage.
In one exemplary embodiment, the intake valve 82 is opened and air is drawn
into the compression cylinder 66 during the intake stroke. As the compression piston 72
ascends during the compression stroke, the crossover compression valve 84 and the tankvalve 96 are opened while the crossover expansion valve 86 and the intake valve 82 are25

held closed such that the compression piston 72 compresses air into the air tank 94. The
crossover expansion valve 86 remains closed and the exhaust valve 88 is held open
during this time and during the expansion and exhaust strokes to idle the expansion
cylinder 68. The cycle is then repeated.
In AEF mode, compressed air that was previously stored in the air tank 94 is

30

used with combustion to drive the expansion piston 74.
In one exemplary embodiment, the intake valve 82 is held open and thecrossover compression valve 84 is held closed to idle the compression cylinder 66. With
the crossover expansion valve 86 closed, the air tank valve 96 is opened briefly towo 2011/159756

PCT/US2011/040437-20pressurize the crossover passage 55 with air stored in the air tank 94. The air tank valve
96 is then closed to isolate the air tank 94 from the forthcoming combustion event. With
the crossover compression valve 84, the crossover expansion valve 86, and the air tank5

valve 96 all closed, fuel is added to the compressed charge in the crossover passage 55
and ignited (e.g., by a spark plug or by compression ignition) to initiate constant-volume
combustion within the crossover passage 55. The crossover expansion valve 86 is thenopened to transfer the combustion pressure to the expansion cylinder 68 during the
expansion stroke, which is effective to drive the expansion piston 74 downward to10

impart rotational force to the crankshaft 52. The crossover expansion valve 86 is thenclosed and the exhaust valve 88 is opened during the exhaust stroke such that
combustion products disposed within the expansion cylinder 68 are evacuated throughthe exhaust port 53, after which the cycle repeats.
In PC mode, air compressed in the compression cylinder 66 is used both to15

charge the air tank 94 and to support combustion. In prior art split-cycle air hybrid
engines of the type illustrated in FIG. 1, in which combustion occurs only in the
expansion cylinder, the air tank is usually charged after combustion occurs when
operating in PC mode. In embodiments in which combustion occurs in the crossover
passage, on the other hand, the ordering of these steps can be reversed. In other words,

20

the air tank 94 is filled first, and then combustion occurs thereafter.
In one exemplary embodiment, the intake valve 82 is opened and the crossovercompression valve 84 is closed during an intake stroke. During the subsequent
compression stroke, the intake valve 82 and the crossover expansion valve 86 are heldclosed, while the crossover compression valve 84 and the air tank valve 96 are opened.

25

This allows the compression piston 72 to compress the intake air charge into thecrossover passage 55 and the air tank 94. With the crossover expansion valve 86 still in
the closed position, the crossover compression valve 84 and the air tank valve 96 arethen closed to seal the crossover passage 55. It will be appreciated that the timing ofthese valve closures can be controlled to meter the amount of air remaining in the

30

crossover passage 55. In other words, the valve timing can be controlled to regulate thepercentage of the compression charge that is added to the tank versus the percentage ofthe compression charge that remains in the crossover passage 55 to support combustion.
Fuel is then added to this remaining air mass and combustion is initiated in the crossoverwo 2011/159756

PCT/US2011/040437- 21 passage 55 with the crossover compression valve 84, the crossover expansion valve 86,
and the tank valve 96 closed to achieve constant-volume combustion. During suchcombustion, or after such combustion is completed, the crossover expansion valve 86 is
5

opened to supply the pressure generated by combustion to the expansion cylinder 68,
thereby forcing the expansion piston 74 downwards in a power stroke. The crossover
expansion valve 86 can then be closed and the exhaust valve 88 opened during an
exhaust stroke to evacuate the combustion products from the expansion cylinder 68, at
which time the cycle repeats.

10

It will thus be appreciated that the concepts disclosed herein have application inboth non-hybrid split-cycle engines and in air hybrid split-cycle engines.
Although the invention has been described by reference to specific embodiments,
it should be understood that numerous changes may be made within the spirit and scopeof the inventive concepts described. Accordingly, it is intended that the invention not be

15

limited to the described embodiments, but that it have the full scope defined by thelanguage of the following claims.
What is claimed is:wo 2011/159756

PCT/US2011/040437-22CLAIMS:

1.

An engine, comprising:a crankshaft rotatable about a crankshaft axis;

5

a compression piston slidably received within a compression cylinder andoperatively connected to the crankshaft such that the compression piston is operable toreciprocate through an intake stroke and a compression stroke of a four stroke cycle
during a single rotation of the crankshaft;an expansion piston slidably received within an expansion cylinder and

10

operatively connected to the crankshaft such that the expansion piston is operable toreciprocate through an expansion stroke and an exhaust stroke of said four stroke cycle
during a single rotation of the crankshaft;a crossover passage interconnecting the compression cylinder and the expansion
15cylinder;a crossover compression valve operable to control fluid communication between
the compression cylinder and the crossover passage; anda crossover expansion valve operable to control fluid communication between
the crossover passage and the expansion cylinder;
wherein the engine is operable to initiate a combustion event in the crossover

20

passage; andwherein a phase shift angle defined as the number of degrees the crankshaft mustrotate after the compression piston reaches its top dead center position in order for the
expansion piston to reach its top dead center position is greater than approximately 5
25degrees and less than approximately 90 degrees.

2.

The engine of claim 1, wherein the phase shift angle is greater thanapproximately 5 degrees and less than approximately 60 degrees.

30

3.

The engine of claim 1, wherein the phase shift angle is greater thanapproximately 10 degrees and less than approximately 35 degrees.

wo 2011/159756

PCT/US2011/040437-234.

The engine of claim 1, wherein a ratio of a volume in the expansion cylinderwhen the expansion piston is at its bottom dead center position to a volume in the
expansion cylinder when the expansion piston is at its top dead center position is5

approximately 40 to 1 or greater.

5.

The engine of claim 1, wherein a ratio of a volume in the compression cylinderwhen the compression piston is at its bottom dead center position to a volume in thecompression cylinder when the compression piston is at its top dead center position is10

approximately 40 to 1 or greater.

6.

The engine of claim 1, wherein the crossover compression valve is operable toopen outwardly away from an interior of the compression cylinder.

15

7.

The engine of claim 1, wherein the crossover expansion valve is operable to open

outwardly away from an interior of the expansion cylinder.

8.

The engine of claim 1, wherein the engine is operable to initiate said combustion

event while the expansion piston is ascending from its bottom dead center position
20

towards its top dead center position.

9.

The engine of claim 8, wherein the engine is operable to initiate said combustion

event while the compression piston is descending from its top dead center position
towards its bottom dead center position.
25
10.

The engine of claim 1, wherein the engine is operable to open the crossover

expansion valve while the expansion piston is within approximately± 10 degrees ofrotation of the crankshaft from its top dead center position.

30

11.

The engine of claim 1, further comprising a fuel injection system operable to add

fuel to the crossover passage.

wo 2011/159756

PCT/US2011/040437-2412.

The engine of claim 1, wherein the engine is operable to initiate said combustion

event via compression ignition.

5

13.

The engine of claim 1, further comprising a spark plug at least partially disposedin the crossover passage and operable to initiate said combustion event.

14.

The engine of claim 1, further comprising an air tank operatively coupled to thecrossover passage and a tank valve configured to selectively place the air tank in fluid
10communication with the crossover passage.

15.

The engine of claim 1, wherein the engine is operable to initiate the combustion

event while the crossover compression valve and the crossover expansion valve areclosed.
15
16.

A method of operating an engine, comprising:supplying air compressed by a compression piston to a crossover passage;
after said supplying, transitioning the crossover passage to a closed, constant-volume configuration;
after said transitioning, adding fuel to the crossover passage and initiating

20

combustion of an air-fuel mixture disposed within the crossover passage; andafter said initiating, transferring pressure generated during combustion to an
expansion cylinder to exert force on an expansion piston, the expansion piston driving acrankshaft;wherein said initiating is performed after the compression piston reaches top

25

dead center and before the expansion piston reaches top dead center.

17.

The method of claim 16, wherein said transitioning comprises closing acrossover compression valve and closing a crossover expansion valve.
30
18.
valve.

The method of claim 17, wherein said transitioning comprises closing an air tankwo 2011/159756

PCT/US2011/040437-2519.

The method of claim 16, wherein said supplying comprises transferring the aircompressed by the compression piston from an air tank to the crossover passage.

5

20.

The method of claim 16, wherein the pressure generated during combustion istransferred to the expansion cylinder before combustion is completed.

wo 2011/159756

PCT/US2011/040437

1/10

FIG. 1
Prior Art/

120

SUBSTITUTE SHEET (RULE 26)100

wo 2011/159756

PCT/US2011/040437

2/10

FIG. 2

70

72 --t"'"fHJ..

58
54

SUBSTITUTE SHEET (RULE 26)

wo 2011/159756

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3/10

FIG. 353.....................
.... ............ .........
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.

61

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58
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wo 2011/159756

PCT/US2011/040437

4/10

FIG. 472.J..Hff-::>1---

74

68

61

63

SUBSTITUTE SHEET (RULE 26)

wo 2011/159756

PCT/US2011/040437

5/10

FIG. 5

SUBSTITUTE SHEET (RULE 26)

wo 2011/159756

PCT/US2011/040437

6/10

FIG. 6

f

50

SUBSTITUTE SHEET (RULE 26)

wo 2011/159756

PCT/US2011/040437

7110

50

FIG. 7

I

66

SUBSTITUTE SHEET (RULE 26)

wo 2011/159756

PCT/US2011/040437

8/10

FIG. 8
92

86

70
0

Ooo

0

0

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oo 0 o 0 o ooao 0 oooo 0
ooooooo oa 0 oao 0 0 o 0
0 0

0 0 0 00

0 00 0aoo 0 a 0 ooa

00

0 0 0 0 0

ooo 0 ooo 0 0oao oa 0 ooaoo 00

66

ooo 0 oaoo ooa 0 aoo 0 oa o0 o o o o o o 0 o o 0 o o o
0 0 0 0 0 0 0 0 0 oo 0 0 0 0 0
ooo 0 oo ooo 0 oo0 0 o
0 o 0 ooooaoo oa 0 0 0oo 0o o o o o o 0 oo o 0 o 0 oooaooooaooo oooaoo
0 0 0
oo 0 00 0 0 0 0 0 0o 0 o 0 o0 0 oo 0 Ooooooo°°

oooOo 00 ooaooaOoo°

oo 0 0 0 0 0 oo 0
0 0 oo 0
oo 0 o o oa coo oao oo ao

72

74

SUBSTITUTE SHEET (RULE 26)

wo 2011/159756

PCT/US2011/040437

9/10

FIG. 9

50

/
92

0

66

oOOQQ

0

°

°

0 0
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0 0 0 oo 0 0 Q 0 0 0 0 0 0 0 0::~ o o 0 o o o o o o 0 o o o 0 o 0::~oo 0 oooo 0 ooo 00 ooo
I

00 0

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wo 2011/159756

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10/10

FIG. 1070

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INTERNATIONAL SEARCH REPORTInternational application No.
PCT/US2011/40437

A.

CLASSIFICATION OF SUBJECT MATTER

IPC(8)- F028 33/22 (2011.01)
USPC- 123/?0R
According to International Patent Classification (I PC) or to both national classification and IPC
B.

FIELDS SEARCHED

Minimum documentation searched (classification system followed by classification symbols)
IPC(8)- F02B 33/02, 33/22 (2011.01)
USPC- 60/620; 123/52.2, 52.3, 68, 70R, 70V
Documentation searched other than minimum documentation to the extent that such documents are included in the fields searchedElectronic data base consulted during the international search (name of data base and, where practicable, search terms used)
PatBaseC.

DOCUMENTS CONSIDERED TO BE RELEVANT
Citation of document, with indication, where appropriate, of the relevant passages

Category*

Relevant to claim No.

y

US 6,397,579 B1 (NEGRE) 04 June 2002 (04.06.2002) entire document

1-20

y

US 2009/0038596 A1 (PIRAULT et al) 12 February 2009 (12.02.2009) entire document

1-20

y

US 2008/0202454 A 1 (PI RAULT) 28 August 2008 (28.08.2008) entire document

14, 18,19

D

D

Further documents are listed in the continuation of Box C.

•

Special categories of cited documents:"A" document defining the general state of the an which is not considered
to be of panicular relevance"E" earlier application or patent but published on or after the international
filing date"L" document which may throw doubts on priority claim(s) or which iscited to establish the publication date of another citation or otherspecial reason (as specified)"0" document referring to an oral disclosure, use, exhibition or othermeans"P" document published prior to the international filing date but later thanthe priority date claimed
Date of the actual completion of the international search
12 October 2011
Name and mailing address of the ISA/US
Mail Stop PCT, Attn: ISA/US, Commissioner for Patents
P.O. Box 1450, Alexandria, Virginia 22313-1450
Facsimile No. 571-273-3201
Form PCT/ISA/21 0 (second sheet) (July 2009)"T"

later document published after the international filing date or/eriority
date and not in conflict with the aphlication but cited to un erstandthe principle or theory underlying t e invention"X" document of panicular relevance; the claimed invention cannot be
considered novel or cannot be considered to involve an inventive
step when the document is taken alone"Y" document of panicular relevance; the claimed invention cannot be
considered to involve an inventive step when the document iscombined with one or more other such documents, such combination
being obvious to a person skilled in the an"&" document member of the same patent family

Date of mailing of the international search report

18 OCT 2011
Authorized officer:
Blaine R. Copenheaver
PCT Helpdesk: 571-272-4300
PCT OSP: 571-272-7774