IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIUS007603970B2

lI2~United StateS Patent
Scuderi(54)(Io) PatentNo.:(45) Date of Patent:

et al.

SPLIT-CYCLE

AIR HYBRID ENGINE(US); Stephen P. Scuderi, Westfield,
MA (US)
Assignee: Scuderi Group, LLC, West Springfield,
MA (US)( * ) Notice:

Subject to any disclaimer, the term of thispatent is extended or adjusted under 35
U.S.C. 154(b) by 0 days.
This patent is subject to a terminal disclaimer.

Appl. No.: 12/006,9SS(22)

Filed:

Jan. 8, 2008
Prior Publication Data

(65)

US 2008/0105225 Al

May 8, 2008

Related U.S. Application Data
(63)

Continuation of application No. 11/326,909, filed on
Jan. 7, 2006, now Pat. No. 7,353,786.

(51)

Int. Cl.
FO2B 33IOO(2006.01)
U.S. Cl............................
123/68; 123/53.5; 60/712
Field of ClassiTicationSearch ................ 123/53.1,
123/53.5, 68, 70 R; 60/597, 653, 668, 698,
60/706, 712, 727, 729
See application file for complete search history.

(52)
(58)

References Cited(56)

U.S. Appl. No. 05/947,998,filed Oct. 2, 1978,FrankE. Lowther.
* cited by examiner
Pri mary Examiner Noah Kamen(74) Attorney, Agent, or Firm Fildes & Outland, P.C.
ABSTRACTA split-cycle air hybrid engine operatively connects an air
reservoir to a split cycle engine. A power piston is received
within a power cylinder and operatively connected to a crankshaft such that the power piston reciprocates through an
expansion stroke and an exhaust stroke during a single revolution of the crankshaft. A compression piston is received
within a compression cylinder and operatively connected tothe crankshaft such that the compression piston reciprocatesthrough an intake stroke and a compression stroke in a single
rotation of the crankshaft. The compression cylinder is selectively controllable to place the compression piston in a compression mode or an idle mode. An air reservoir is operatively
connected between the compression cylinder and the powercylinder and selectively operable to receive compressed air
from the compression cylinder and to deliver compressed air
to the power cylinder for use in transmitting power to the
crankshaft during engine operation.

U.S. PATENT DOCUMENTS
4,215,659 A *8/1980 Lowther

123/68

123/68... 60/39.62
123/68OTHER PUBLICATIONS

(57)
(21)

*Oct. 20, 2009

4,418,657 A * 12/1983 Wishart .........
4,696,158 A *9/1987 DeFrancisco
7,007,639 Bl * 3/2006 Luttgeharm ....

(75) Inventors: SalvatoreC. Scuderi,Westfield,MA(73)

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US 7,603,970 B2SPLIT-CYCLE

1
AIR HYBRID ENGINE

providing the hybrid system benefits. These functions include
storing pressurized air during braking and using the pressurCROSS-REFERENCE TO RELATED
ized air for driving the engine during subsequent starting andacceleration.
APPLICATION
However, the prior art appears to involve only adapting a
conventional four stroke cycle engine to perform the comThis application is a continuation of U.S. application Ser.
pression, combustion and motoring functions in a single cylNo. 11/326,909 filed Jan. 7, 2006, now U.S. Pat. No. 7,353,
786.
inder. This, then, requires a complex valve and drivetrainsystem and control which is capable of switching from a
TECHNICAL FIELD
10 compression-braking (CB) mode to an air motoring (AM)mode and back to a conventional internal combustion engine
This invention relates to split-cycle engines and, more par(ICE) mode during operation.
ticularly, to such an engine incorporating an air hybrid sysIn a typical example, when not storing or utilizing comtem.
pressed air to drive the vehicle, a prior art air hybrid engine
15 operates as a conventional internal combustion engine, where
BACKGROUND OF THE INVENTION
the four strokes of the Otto cycle (intake, compression, powerand exhaust) are performed in each piston every two revoluThe term split-cycle engine as used in the present applications of the crankshaft. However, during the compressiontion may not have yet received a fixed meaning commonly
braking mode, each cylinder of the conventional engine is
known to those skilled in the engine art. Accordingly, for 20 configured to operate as a reciprocating piston two-stroke air
purposes of clarity, the following definition is offered for thecompressor, driven from the vehicle wheels by vehicle
term split-cycle engine asmay be applied to engines disclosed
motion. Air is received from outside atmosphere into thein the prior art and as referred to in the present application.
engine cylinders, compressed there, and displaced into an
A split-cycle engine as referred to herein comprises:
air-reservoir. Work performed by the engine pistons absorbs
a crankshaft rotatable about a crankshaft axis;
25 the kinetic energy of the vehicle and slows it down or restricts
a power piston slidably received within a power cylinder
its motion. In this way the kinetic energy of the vehicle
and operatively connected to the crankshaft such that the
motion is transformed into energy o fcompressed air stored in
power piston reciprocates through a power (or expansion)
the air reservoir.
stroke and an exhaust stroke during a single rotation of theDuring the air motoring mode, each cylinder of the engine
crankshaft;
30 is configured to utilize the stored compressed air to produce
a compression piston slidably received within a comprespower strokes for propulsion without combustion. This may
sion cylinder and operatively connected to the crankshaft
be accomplished by first expanding the stored, compressedsuch that the compression piston reciprocates through an
air into the cylinders to drive the pistons down from top deadintake stroke and a compression stroke during a single rotacenter (TDC) to bottom dead center (BDC) for a first powertion of the crankshaft; and35 stroke. Then the pistons compress the expanded gas as theya gas passage interconnecting the power and compression
travel from BDC to TDC. Fuel is then injected into the cylcylinders, the gas passage including an inlet valve and aninders and ignited just before TDC. The expanding products
outlet (or crossover) valve defining a pressure chamber therof combustion then drive the pistons down again for a second
ebetween.
power stroke on the second revolution of the crankshaft.
For purposes of clarity, the following is a list of acronyms 40
Alternatively, air-motoring may be accomplished byfor the various engine operating modes described herein:
expanding the stored compressed air to drive the power piston
AC Air compressor;
down from TDC to BDC for a power stroke without combusAM Air motoring;tion for each revolution of the crankshaft. This alternative
CB Compression braking;method of air motoring may continue until the pressure in the
ICE Internal combustion engine;
45 air reservoir falls below a threshold level, whereupon the
PAP Pre-compressed air power;engine may switch to either the previously described air
PCA Pre-compressed combustion air.
motoring mode or a conventional ICE engine mode of operaU.S. Pat. Nos. 6,543,225 B2, 6,609,371 B2 and 6,952,923,
tion.
all assigned to the assignee of the present invention, disclose
Problematically, in order to switch among the CB, AM andexamples of split-cycle internal combustion engines as herein 50 ICE modes, the valve/drive train system becomes complex,
defined. These patents contain an extensive list of United
costly and hard to control or maintain. Additionally, sinceStates and foreign patents and publications cited as backeach cylinder must perform all o fthe functions for eachmode,ground in the allowance of these patents. The term "splitthey cannot be optimized easily. For example, the pistons andcycle" has been used for these engines because they literally
cylinders must be designed to withstand an explosive comsplit the four strokes of a conventional pressure/volume Otto 55 bustion event, even when just acting as an air compressor.
cycle (Le., intake, compression, power and exhaust) over two
Accordingly, due to the tolerances and materials required to
dedicated cylinders: one cylinder dedicated to the high preswithstand the heat of combustion, some sacrifice must be
sure compression stroke, and the other cylinder dedicated tomade to the efficiency of the compressor mode.
the high pressure power stroke.
Another problem with performing all functions for each
Considerable research has been recently devoted to air 60 mode (ICE, CB and AM) in every cylinder is that no twomodes can be performed in parallel (Le. simultaneously).
hybrid engines as compared, for example, to electric hybrid
Because prior art air hybrid systems utilize conventional
systems. The electric hybrid system requires the addition to
the conventional four stroke cycle engine of batteries and anengines, they are restricted to operating in each mode serially,
which imposes inherent limitations on their capabilities. For
electric generator and motor. The air hybrid needs only theaddition of an air pressure reservoir added to an engine incor- 65 example, because the CB mode cannot be utilized when the
porating the functions of a compressor and an air motor,
engine is operating as an internal combustion engine (in ICE
together with the functions of a conventional engine, formode), the air reservoir can only be charged during the brak-US 7,603,970 B2
ing function of a moving vehicle. This limitation leads toproblems in maintaining the stored charge in the air reservoir.
Additionally, this limitation also means that prior art air
hybrid systems are only applicable to moving vehicles, andare not practical for stationary applications such as stationary
generators.

The compression piston draws in and compressesinlet air for
use in the power cylinder. Compressed air is admitted to thepower cylinder with fuel shortly after the power pistonreaches its top dead center (TDC) position at the beginning ofan expansion stroke. The fuel/air mixture is then ignited,burned and expanded on the same expansion stroke of thepower piston, transmitting power to the crankshaft. The comSUMMARY OF THE INVENTION
bustion products are discharged on the exhaust stroke.
In the AC mode, the compression piston is in compression
The present invention combines the features of the split 10 mode and draws in and compresses air which is stored in thecycle engine with the air reservoir of the air hybrid concept
reservoir for later use in the power cylinder.
and various simplified control features to provide novel
In the PAP mode, the power cylinder is in power mode andarrangements for operation and control of the resulting hybrid
receives compressed air from the reservoir which is expanded
engine embodiments. A distinct advantage of the invention is
on the expansion stroke of the power piston, transmittingthat two or more engine modes as described herein can be 15 power to the crankshaft. The expanded air is discharged on theoperated simultaneously (ke., in parallel), because the splitexhaust stroke.
cycle engine includes dedicated compression and power pisIn certain preferred embodiments o fthe invention, power istons.
developed in the PAP mode in similar fashion to that of the
Taken as a broad concept, a split-cycle air hybrid engine
ICE mode. That is, during operation in the PAP mode, fuel isaccording to the invention preferably includes:
20 mixed with the compressed air shortly after the power piston
a crankshaft rotatable about a crankshaft axis;
has reached its TDC position at the beginning of an expansion
a power piston slidably received within a power cylinder
stroke. The mixture is ignited, burned and expanded on theand operatively connected to the crankshaft such that thesame expansion stroke of the power piston, transmitting
power piston reciprocates through an expansion (or power)
power to the crankshaft. The combustion products are disstroke and an exhaust stroke during a single rotation of the 25 charged on the exhaust stroke.
crankshaft;
In other alternative embodiments o fthe engine, power may
a compression piston slidably received within a compresbe developed in the PAP mode in similar fashion to that of thesion cylinder and operatively connected to the crankshaft
previously described air motoring modes. That is, during
such that the compression piston reciprocates through an
operation in the PAP mode, the compressedair admitted to theintake stroke and a compression stroke during a single rota- 30 power cylinder is expanded without adding fuel or initiatingtion of the crankshaft, the compression cylinder being seleccombustion.
tively controllable to place the compression piston in a comIn a first exemplary embodiment of the engine, the airpression mode or an idle mode;
reservoir comprises a gas passage sized to receive and store
an air reservoir operatively connected between the comcompressed air from a plurality of compression strokes, thepression cylinder and the power cylinder and selectively oper- 35 gas passageinterconnecting the compression and power cylable to receive compressed air from the compression cylinder
inders. The gas passageincludes an inlet valve and an outlet
and to deliver compressed air to the power cylinder for use invalve defining a pressure chamber therebetween.
transmitting power to the crankshaft during engine operation;
In a second exemplary embodiment of the engine, a gas
andpassagealso interconnects the compression and power cylinvalves selectively controlling gas flow into and out of the 40 ders, and the gas passageincludes an inlet valve and an outlet
compression and power cylinders and the air reservoir.
valve defining a pressure chamber therebetween. However,
Alternatively, the power cylinder may also be selectively
the air reservoir is connected by a reservoir passage to thecontrollable to place the power piston in a power mode or anpressure chamber at a location between the inlet valve and theidle mode.
outlet valve.
For purposes herein, when the compression piston is 45
A third exemplary embodiment of the engine adds a reserplaced in idle mode, it means that for a single rotation of thevoir control valve in the reservoir passageto allow separation
crankshaft, the total amount of net negative work (opposingof the reservoir from the pressure chamber during ICE operathe direction of rotation of the crankshaft) performed on thetion.
crankshaft by the compression piston is negligible. Typically,
In a fourth exemplary embodiment of the engine, the air
negligible work in the compression piston' s idle mode would 50 reservoir is an accumulator adapted to maintain a relatively
be less than 20% of the negative work performed on theconstant pressure therein within a predetermined pressure
crankshaft had the compression piston been in its compresrange.
sion mode.
A fifth embodiment o fthe engine includes multiple pairs o fAdditionally for purposes herein, when the power piston iscompression and power cylinders interconnected by gas pasplaced in idle mode, it means that for a single rotation of the 55 sageshaving pressure chambers, wherein the pressure chamcrankshaft, the total amount of net positive work (advancing
bers are all connected with a single air reservoir.
the direction of rotation of the crankshaft) performed on the
In a sixth alternative embodiment of the invention, thecrankshaft by the power piston is negligible. Typically, negengine includes a gas passage interconnecting the compresligible work in the power piston's idle mode would be lesssion and power cylinders, the gas passage including an inlet
than 20% of the positive work performed on the crankshaft 60 valve and an outlet valve defining a pressure chamber therhad the power piston been in its power mode.
ebetween. The air reservoir is connected in parallel with the
In general, an engine according to the invention is capablegas passage, with inlet and outlet connections from the airof operation in at least three modes, including an internal
reservoir to the compression and power cylinders.
combustion engine (ICE) mode, an air compressor (AC)These and other features and advantages of the invention
mode and a pre-compressed air power (PAP) mode.
65 will be more fully understood from the following detailed
description of the invention taken together with the accomIn the ICE mode, the compression piston and power piston
are typically in their respective compressor and power modes.
panying drawings.

US 7,603,970 B2
5
BRIEF DESCRIPTION OF THE DRAWINGS

port 3S opening into the closed end of the second cylinder 16
and a reservoir outlet port 40 opening into the closed end of
In the drawings:
the first cylinder 14. As opposed to a smaller gas passageof aFIG. 1 is a schematic diagram showing a first embodimenttype exemplified in the Scuderi patents, the air reservoir 36 isof a split-cycle air hybrid engine having an air reservoir and 5 sized to receive and store compressed air energy from a plucontrol valves according to the invention;
rality of compression strokes of the compression piston 26.
The second cylinder 16 also connects with a conventional
FIG. 2 is a view similar to FIG. 1 but showing a second
intake port 42 and the first cylinder 14 also connects with aembodiment with a separatecrossover (or gas) passage connected with the air reservoir and an added control valve;
conventional exhaust port 44.
FIG. 3 is a view similar to FIG. 2 but showing a third 10 Valves in the cylinder head 22, which are similar to valvesembodiment with an added reservoir control valve;of the engine in the Scuderi patents, include a reservoir inlet
FIG. 4 is a view similar to FIG. 3 but showing a fourth
check valve 46 and three cam actuated poppet valves, a resembodiment including a constantpressure accumulator in theervoir outlet valve (or crossover valve) 50, a second cylinder
intake valve 52, and a first cylinder exhaust valve 54. The
air reservoir;
FIG. 5 is a view similar to FIG. 3 showing a fifth embodi- 15 check valve 46 allows only one way compressed air flow into
the reservoir inlet port 3S from the second (compression)
ment having a common reservoir for multiple cylinder pairs;
andcylinder 16. The reservoir outlet valve 50 is opened to allow
FIG. 6 is a view similar to FIG. 3 showing a sixth embodihigh pressure air flow from the reservoir 36 into the firstment having the reservoir in parallel with the crossover pas(power) cylinder 14.
20
The present engine 10 includes two additional valves thatsage and separately valved between the cylinders.
may be solenoid actuated. These include an intake control
DETAILED DESCRIPTION OF THE INVENTION
valve 56 in the cylinder intake port 42 and a reservoir outlet
control valve 5S in the reservoir outlet port 40. These valves
Referring first to FIG. 1 of the drawings in detail, numeral
may be two position on-off valves but could include variable
10 generally indicates a first exemplary embodiment of a split 25 position controls so that they could be operated as throttle
cycle air hybrid engine according to the invention. Engine 10,
valves if desired.
shown schematically, is generally of the split-cycle type disThe poppet valves 50, 52, 54 may be actuated by any
closed in the prior U.S. Pat. Nos. 6,543,225 B2, 6,069,371 B2
suitable devices, such as camshafts 60, 62, 64 having cam
and 6,952,923 B2 (Scuderi patents), herein incorporated bylobes 66, 6S, 70 respectively engaging the valves 50, 52, 54
reference in their entirety.
30 for actuating the valves as will be subsequently discussed.
As shown, the engine includes an engine block 12 having a
Alternatively, the valves 50, 52 and 54, as well as the otherfirst cylinder 14 and an adjacent second cylinder 16 extending
valves 46, 56 and 5S, may be electronically, pneumatically or
therethrough. A crankshaft 1S is journaled in the block 12 forhydraulically actuated.
rotation about a crankshaft axis 20, extending perpendicular
A spark plug 72 is also mounted in the cylinder head withto the plane of the drawing. Upper ends of the cylinders 14, 16 35 electrodes extending into the combustion chamber 25 forare closed by a cylinder head 22
igniting air-fuel charges at precise times by an ignition conThe first and second cylinders 14, 16 define internal beartrol, not shown. It should be understood that the engine may
ing surfaces in which are received for reciprocation a firstbe made as a diesel engine and be operated without a spark
power piston 24 and a secondcompression piston 26, respecplug if desired. Moreover, the engine 10 may be designed totively. The cylinder head 22, the power piston 24 and the first 40 operate on any fuel suitable for reciprocating piston engines
cylinder 14 define a variable volume combustion chamber 25
in general, such as hydrogen or natural gas.
in the power cylinder 14. The cylinder head 22, the compresFIGS. 2 through 6 of the drawings disclose various altersion piston 26 and the second cylinder 16 define a variable
native embodiments which are variations of the engine 10 ofvolume compression chamber 27 in the compression cylinder
FIG. 1 and are described below. Operation of all six of the16.
45 exemplary embodiments will be described thereafter.
The crankshaft 1S includes axially displaced and angularly
Referring to FIG. 2, s second embodiment of engine 74 isoffset first and second crank throws 2S, 30, having a phase
disclosed wherein like reference numerals indicate like parts.
angle 31 therebetween. The first crank throw 2S is pivotally
Engine 74 is generally similar to engine 10, but differs in thatjoined by a first connecting rod 32 to the first power piston 24
a small volume crossover (or gas) passage 76 is connected
and the second crank throw 30 is pivotally joined by a second 50 between the inlet port 3S and inlet check valve 46 at one end
connecting rod 34 to the second compression piston 26 toand the outlet port 40 and outlet valve 50 at an opposite end.
reciprocate the pistons in their cylinders in timed relation
This crossover passage76 extends between the compression
determined by the angular offset of their crank throws and thechamber 27 in the second cylinder 16 and the combustion
geometric relationships of the cylinders, crank and pistons.
chamber 25 in the first cylinder 14 and is similar to theAlternative mechanisms for relating the motion and timing 55 crossover passagein the prior Scuderi patents. As opposed toof the pistons may be utilized if desired. The timing may bean air reservoir, this crossover passage76 is not sized to store
similar to, or varied as desired from, the disclosures of thea substantial amount of compressed air energy for later use.
Scuderi patents. The rotational direction of the crankshaft andRather the passage 76 is typically designed to be as small as
the relative motions of the pistons near their bottom deadpractically possible for the most efficient transfer of comcenter (BDC) positions are indicated by the arrows associated 60 pressed gas during the ICE mode of the engine 74.
in the drawings with their corresponding components.
In an additional modification, separate air reservoir 36 isconnected through a reservoir runner or reservoir passage7S
The cylinder head 22 includes any of various passages,
to the crossover passage76 and connects to the inlet and outlet
ports and valves suitable for accomplishing the desired purposes of the split-cycle air hybrid engine 10. In the illustrated
ports 3S, 40 through the crossover passage76. The reservoir
first embodiment, the gas passage/pressure chamber of the 65 outlet solenoid control valve 5S is located in the passage 76
between the outlet port 40 and the reservoir runner 7S. Valvepreviously mentioned patents is replaced by a much larger air
reservoir 36 connected to the head 22 through a reservoir inlet
5S is open during ICE mode to allow compressed air to follow

US 7,603,970 B2
the split-cycle air hybrid of the present invention has separate
the path of least resistance and flow primarily through passage76 into combustion chamber 25. Valve 5S may be closed
dedicated compression and power cylinders, the three modes,
ICE, AC and PAP, can be run either serially or in parallel as
during AC mode to pump compressedair into reservoir 36 anddesired.
may be open during PAP mode to retrieve compressed air
5from the reservoir 36.
The ICE mode is basically the normal operating mode ofReferring now to FIG. 3 of the drawings, a third embodithe engines disclosed in the previously mentioned Scuderi
ment of engine SOis disclosed, which differs from engine 74
patents. The intake, compression, power and exhaust strokes
in FIG. 3, only in the addition of a third solenoid valve S2.
of a conventional piston engine cycle are split between the
Valve S2 is located in the runner 7S at its junction with thecompression and power cylinders of the split-cycle engine.
crossover passage 76 to cut off the connection of the air 10 Referring to the embodiment of FIG. 1, split cycle engines
reservoir 36 with the crossover passagewhen desired.
as described in the Scuderi U.S. Pat. Nos. 6,543,225, 6,609,
By isolating the air reservoir 36 via valve S2, the overall
371 and 6,952,923 include structural parameters that areengine SO performance can be more effectively optimized
advantageous over prior art split-cycle engines. Many ofduring the ICE mode of operation. For example, during thethese advantageswill be described in relation to the following
ICE mode all compressed air can be made to flow through the 15 discussion of the ICE mode of the engine 10. It is important tocrossover passage76. Accordingly, the crossover passage76
note that the air reservoir 36 o fFIG. 1 performs the combined
can be designed for the most efficient transfer of gas without
functions of both the separatedcrossover (or gas) passage76
interacting with the air reservoir. Additionally valve S2 canand air reservoir 36 of subsequent FIGS. 2-6.
also be utilized as a throttling valve for part load conditions
In the ICE mode, the intake solenoid valves 56, 5S remain20
during the PAP mode.
open. On the intake stroke, intake valve 52 opens as the
FIG. 4 shows a fourth embodiment of engine S4 similar tocompression piston moves down, drawing in air to the comthe engine SOof FIG. 3. It differs in the conversion of the airpression chamber 27. On the compression stroke, the intake
reservoir into a pressure accumulator S6 by the addition of avalve 52 closes and the piston 26 moves up, compressing thediaphragm or bladder S7 and spring mechanism SS.These act
air and forcing it through the check valve 46 and the inlet port
to pressurize air that is present in the accumulator S6 and to 25
3S into the air reservoir 36.
maintain the contents at a relatively constant pressure
The power piston 24 leads the compression piston 26 by a
between conditions where the reservoir is either empty or isphaseangle 31 that is substantially greater than 0 degrees offilled up to the maximum control pressure.
rotation of the crankshaft. The phase angle 31 as defined
FIG. 5 illustrates a fifth embodiment of a multicylinder
engine S9 having at least two cylinder pairs 90, each equiva- 30 herein is the degrees of crank angle (CA) rotation the crankshaft 1S must rotate after the power piston 24 has reached its
lent to the engine SO of FIG. 3. Engine S9 is modified totop dead center (TDC) position in order for the compression
include a common supply reservoir 92 that is joined to crosspiston 26 to reach its respective TDC position. In the particuover passages 76 of all the cylinder pairs with a reservoir
lar embodiment illustrated in FIG. 1, the magnitude of thecontrol solenoid valve S2 controlling communication of eachreservoir runner 7S with its respective crossover passage 76. 35 angle between the first and second crank throws 2S and 30 isequal to the phase angle 31. Preferably this phase angle isFIG. 6 discloses a sixth embodiment of engine 94 that is
between 10 and 40 degrees CA and more preferably between
most similar to engine SOof FIG. 3. Engine 94 differs in that
20 and 30 degrees CA. The phase angle 31 is sized such thatthe air reservoir 36 is separated from direct connection withasthe compression piston 26 ascendstoward its TDC position
the crossover passage76, which remains controlled by checkvalve 46, solenoid valve 5S and outlet valve 50. The air 40 and the power piston descends from its TDC position, asubstantially equal mass of compressed air is transferred into
reservoir 36 is connected in parallel with the crossover pasand out of the air reservoir 36 (in subsequent FIGS. 2-6 asage76 by first and secondreservoir runners (or passages)96,
substantially equal mass of compressed air is transferred into
9S, respectively connecting the reservoir directly to the comand
out of the gas passage 76).
bustion chamber 25 of the first cylinder 14 and the compresOn the power stroke, outlet (or crossover) valve 50 ission chamber 27 of the second cylinder 16. Fourth and fifth 45
typically open at TDC of the power piston 24. Preferably thesolenoid control valves 100, 102 respectively control flow
outlet valve 50 is opened within a rangeof 10 to 0 degreesCA
between the runners 96, 9S and the cylinders 14, 16.
before TDC of the power piston 24, and more preferably
Operation of the described exemplary embodiments ofwithin a range of 7 to 3 degreesCA before TDC of the power
split-cycle air hybrid engines according to the invention will
now be discussed for purposes of explanation and not of 50 piston. The outlet valve 50 is preferably closed within a rangeof 10 to 40 degreesCA after TDC of the power piston 24, andlimitation, it being understood that additional methods andmore preferably closes within a rangeof 20 to 30 degreesCA
variations will be apparent that should properly fall within theafter TDC of the power piston.
intended scope of the invention.
The power piston 24 descends from its TDC position
Basically, split-cycle air hybrid engines of the present
invention are typically operable in at least three modes, an 55 toward a combustion ignition position, which is typicallywithin a range of 5 to 40 degrees CA after TDC and moreinternal combustion engine (ICE) mode, an air compressor
preferably within a range of 10 to 30 degrees CA after TDC.
(AC) mode and a pre-compressedair power (PAP) mode. The
PAP mode preferably includes a pre-compressed combusFuel may be injected and mixed with the compressed air by attion-air power (PCA) mode wherein pre-compressed air andleast two methods, i.e., either in the air reservoir 36 just up
fuel are mixed shortly after the power piston reaches its top 60 stream of the outlet valve 50 (port fuel injection), or directly
dead center position during an expansion stroke and then theinto the power cylinder 14 (direct injection). Once the power
fuel/air mixture is combusted to drive the power piston down
piston 24 reachesits combustion ignition position, the fuel/air
during the same expansion stroke. Alternatively, the PAP
mixture is ignited by spark plug 72 (or compression ignitionmode could also include various forms of air motoring (AM)if a diesel engine), forcing the piston 24 down to BDC andmodes (as previously exemplified herein) wherein pre-com- 65 delivering power to the crankshaft 1S. The pressure at whichpressed air is utilized to provide an expansion stroke without
combustion ignition occurs is the ignition (or firing) condicombustion. As will be discussed in greater detail, because
tion pressure.

US 7,603,970 B2
10
On the exhaust stroke, the exhaust valve 54 opens andAlternatively (to keep the air reservoir clean), the piston 24
crossover valve 50 is closed. As the power piston 24 moves
could be used as a conventional compression brake, drawing
in air on the downstroke, compressing it on the upstroke andupward from BDC to TDC, the spent exhaust gasesare forcedout of the combustion chamber 25 through the exhaust port
opening the exhaust valve 54 near top dead center (TDC) to44.
5 discharge the compressed air and dissipate its energy. This
could increase braking and reduce brake wear but would limit
The intake and compression strokes for a pressure/volume
cycle within the engine take place during the samecrankshaft
the recovery of energy from the compressed air in the PCA or
AM modes.
revolution as the power and exhaust strokes of the cycle,
except that the power and exhaust strokes are advanced by the
Referring still to FIG. 1, the preferred third mode of operafixed phase angle 31. Thus a new pressure/volume cycle is 10 tion is pre-compressed combustion air (PCA) which, fromcompleted each revolution of the engine crankshaft instead ofprior AC operation, has stored compressed air in the reservoir
in two revolutions as in a conventional four-stroke engine.
36 at a higher pressure than generally occurs in ICE operaHowever, the inlet valve 46 and outlet valve 50 maintain thetion. The engine has at least slowed down and is ready to begas pressure within the air reservoir 36 at or above ignition (oraccelerated. To run the PCA mode, the outlet solenoid valve
firing) condition pressure during the entire four-stroke cycle. 15 5S is opened and spark ignition and fuel injection functions
One of the basic differences between the Scuderi Splitare reactivated. Also, the compression piston is idled by holdCycle and the prior art is the parameter that pressure in the gas
ing open both the intake valve 52 and the intake solenoid
passageis maintained at or above the firing condition pressure
valve 56 so that the compression piston 26 moves freely
during all four strokes of the Otto cycle combined with thewithout resistance and no air is compressed or added to theparameter that ignition in the power cylinder occurs substan- 20 reservoir 36.
tially after top dead center (ke., more than 5 degrees andIf valve 52 is not independently adjustable, the comprespreferably more than 10 degreesATDC). This sets up a consion piston 26 may also be placed in idle mode by closing
dition where the combustion event (or flame speed) is very
solenoid valve 56. In this way the compression piston alterfast (occurring within 24 degrees CA or less), and the NOx
nately compresses and expands the gas trapped in the cylinemissions output is very low (50 to 80 percent less than a 25 der. The compression and expansion of the trapped gas alterconventional engine). Another unique aspect of the Scuderinates the negative and positive work done on the crankshaft
Split-Cycle, not found in the prior art, is that the centerline ofby the piston. Since the negative and positive work is approxithe power and compression cylinders are offset from themately equal, the net work done on the crankshaft by the
crankshaft axis. This enables the piston skirt to cylinder wall
piston operating in this mode is negligible. Still anotherfriction to be substantially reduced. All three of these advan- 30 method of placing the compression piston in idle mode is totageous features (maintaining firing condition pressures inprevent the compression piston 26 from reciprocating by
the gas passage, firing after top dead center, and the offsets)
operatively disconnecting it from the crankshaft 1S. In any ofare disclosed and claimed in the Scuderi patents.
the above examples of the compression piston's idle mode,
In addition to the above parameters, several other paramthe total amount of net negative work done on the crankshaft
eters have also been identified in the Scuderi patents, which 35 is negligible.
have a significant effect on engine efliciency. These paramShortly after or just prior to TDC of the power piston 24, as
eters include:in ICE operation, the reservoir outlet valve 50 opens, forcing
1. Maintaining the compression and expansion ratios equala charge of compressed air (preferably controlled and withto or greater than 26 to I, preferably equal to or greater
added fuel) from the reservoir 36 into the combustion cham40
than 40 to I, and more preferably equal to or greater thanber. Within a range of 5 to 40 degrees CA after TDC, and
80 to I;
preferably within a range of 10 to 20 degrees CA after TDC,
2. The crossover valve duration (amount of crank angle
the fuel is quickly ignited and burns on the power stroke,(CA) rotation needed to open and close valve 50) should
providing power to the crankshaft. Exhaust products are disbe equal to or less than 69 degrees, preferably less thancharged on the exhaust upstroke and the cycle is repeated.
50 degrees, and more preferable less than 35 degrees; 45
As the vehicle is accelerated and returns to normal operaandtion,
the stored high pressure air continues to be used for3. The crossover valve 50 should be open for a small
combustion in the power cylinder 14 until the pressure drops
percentage of time after combustion is initiated in theto a normal operating pressure and the engine is returned to
power cylinder.
full ICE operation. However, operation in PCA mode as long50
During braking of a vehicle driven by an engine 10, theas possible increases operating efficiency because compresengine is switched to operation in the air compressor (AC)sion energy from braking is returned to the PCA power cycle
mode. Fuel injection is stopped and the solenoid valve 5S iswhile the compressor piston 26 is idling using very little
closed, preventing air flow through the outlet port 40 andenergy. Thus the vehicle braking compression energy is usedsuspending power delivery from the power piston 24, thus
to provide compression energy in the PCA power mode.
placing the power piston 24 in an idle mode. However, the 55
If the engine is stopped, stored compression energy can becompression piston continues to operate, driven by the inertia
used to start the engine, and the vehicle if desired, until aof the moving vehicle, and to pump the compressed air intominimum speed is reached, whereupon the engine may be
the air reservoir 36. The pumping action effectively slows, or
returned to ICE operation. However, a backup electric starter
brakes, the vehicle and the braking action becomes increasingly effective as the reservoir air pressure increases. The 60 may be desirable.
increased pressure in the reservoir is retained for later use inReferring again to FIG. 2, operation of the engine 72 is
the PAP mode.
similar to that o fengine 10 (FIG. 1). However, use o fthe small
volume crossover passage76 for flow between cylinders subWhile in AC mode, the exhaust valve 54 may be held open
stantially avoids flow through the air reservoir 36 during ICE
to reduce idling losses on the power piston 24. Moreover, thepower piston could be used to increase the braking effect in 65 operation and potentially reduces undesirable pressure variavarious ways, such as by altering the valve timing and operations in the gas passage76 that could adversely affect engine
tion to draw in and compress further air into the air reservoir.
performance.

US 7,603,970 B2
12What is claimed is:
In the embodiment of FIG. 3, the addition of the solenoid
valve S2 at the reservoir connection with the crossover pas1. A split-cycle air hybrid engine comprising:sage76 allows cutting off the reservoir to maintain a higher ora crankshaft rotatable about a crankshaft axis;
lower pressure therein while the smaller crossover passage76
a power piston slidably received within a power cylinder
can operate with rapidly changing pressures in normal ICE 5
and operatively connected to the crankshaft such that theengine operation for a split cycle engine.
power piston reciprocates through an expansion stroke
In FIG. 4, the replacement of the air reservoir with an
and an exhaust stroke during a single rotation of theaccumulator S6 allows the storage of a rangeof air volumes at
crankshaft;a relatively constant pressure for use, primarily, in controllinga compression piston slidably received within a compresair charge volumes delivered to the combustion chamber by 10
sion cylinder and operatively connected to the crankcontrolling only the outlet valve 50 opening time.
shaft such that the compression piston reciprocates
The use of a common air reservoir, or accumulator, as inthrough an intake stroke and a compression stroke durFIG. 5, may reduce manufacturing costs. Although the coming a single rotation of the crankshaft;mon air reservoir is illustrated in FIG. 5 asconnected directly
a gas passageinterconnecting the compression and power
to the gas passages,one skilled in the art would recognize that 15
cylinders, the gas passageincluding an inlet valve and an
the air reservoir may be configured to connect to the splitoutlet valve defining a pressure chamber therebetween;
cycle engine in other ways. For example, the common air
an air reservoir connected by a reservoir passage to thereservoir may be an integral part of the gas passageas in FIG.
pressure chamber at a location between the inlet valve
1, or may be connected in parallel with the gas passageas inand the outlet valve, and selectively operable to receive
FIG. 6.
20compressed air from the compression cylinder and to
The embodiment of FIG. 6 further separatesthe effects ofdeliver compressed air to the power cylinder for use in
the air reservoir 36 on pressures in the crossover passage 76
transmitting power to the crankshaft during engine
and allows more complete separation of operation in the ICE
operation; andmode from either the AC mode or the PCA mode.
valves selectively controlling gas flow into and out of theReferring to FIGS. 1-6 in general, a distinct advantage of 25
compression and power cylinders and the air reservoir
the present invention is that air hybrid systems utilizing asuch that the engine is operable in a pre-compressed air
split-cycle engine 10, 74, SO,S4, S9 and 94 can function in thepower(PAP) mode, wherein in the PAP mode:various operating modes (ICE, AC and PAP) simultaneously
the power cylinder receives compressed air from the res(or in parallel) over the paired compression cylinders 16 andervoir at the beginning of an expansion stroke of thepower cylinders 14, rather than being restricted to operating 30
power piston which is mixed with fuel during the sameeach mode serially out of a single cylinder. This parallel mode
expansion stroke and the fuel is ignited, burned andability inherently provides added capabilities and expanded
expanded on the same expansion stroke, transmitting
applications for split-cycle air hybrid systems.
power to the crankshaft.
Referring now to FIG. 3 as an example, under part load
2. An engine as in claim 1 wherein, in the PAP mode,conditions the engine SO can simultaneously operate in the 35
compressed air from the compression cylinder is not received
ICE mode while continuously charging the air reservoir in thein the air reservoir.
AC mode. That is, a full charge of air maybemade to enter thecompression cylinder 16 on an intake stroke where it is com3. An engine as in claim 1 wherein, in the PAP mode, fuelpressed and forced into gas passage 76. However, only ais ignited within a range of 5 to 40 degrees crank angle after
fraction of the air charge is required to operate the ICE mode 40 the power piston has reached its top dead center position.
under part load conditions. Accordingly, only a portion of the
4. An engine as in claim 3 wherein, in the PAP mode, fuelcharge may be routed to the power cylinder 14 while theis ignited within a range of 10 to 30 degreescrank angle after
remainder of the charge can be diverted to the air reservoir 36
the power piston has reached its top dead center position.
to keep it fully charged. In this way, split-cycle air hybrid
5. An engine as in claim 1 wherein the air reservoir comsystems have the ability to continuously charge their air res- 45
prises a gaspassagesized to receive and store compressed air
ervoirs under part load conditions.
from a plurality of compression strokes, the gaspassageinterAdditionally, in much the samefashion, waste energy fromconnecting the compression and power cylinders, the gas
exhaust gas can be re-circulated, either directly or through a
passageincluding an inlet valve and an outlet valve defining
turbocharger, back into the intake of a split-cycle air hybrida pressure chamber therebetween.
engine SOto be stored as compressed air energy in the air 50
6. An engine as in claim 1 including a reservoir control
reservoir 36. Advantageously, this technique of recovering
valve in the reservoir passage.
exhaust gas energy while operating under part load conditions
7. An engine as in claim 6 wherein the air reservoir is an
can also be utilized in stationary applications, e.g., in stationaccumulator adapted to maintain a relatively constant presary generators.
Although the invention has been described by reference to 55 sure therein within a predetermined pressure range.
S. An engine as in claim 1 including multiple pairs ofcertain specific embodiments, it should be understood thatcompression and power cylinders interconnected by gas pasnumerous changesmay be made within the spirit and scope ofsageshaving pressure chambers, wherein the pressure chamthe inventive concepts disclosed. Accordingly, it is intended
bers are all connected with a common air reservoir.
that the invention not be limited to the described embodiments, but that it have the full scope defined by the language 60of the following claims.