Abstract:
A method and apparatus for controlling an air input in a rotary engine, including selectively controlling a plurality of inlet ports communicating with an internal combustion cavity of the engine, the ports located serially downstream of the exhaust port relative direction of a revolution of a rotor of the engine. The inlet ports are controlled to alter air intake at various engine operational stages, such as start up, idle, etc., to allow for varying operational requirements to be met. For example: when a power demand on the engine lower than a predetermined threshold, control may be effected by opening a primary inlet port and closing a secondary inlet port; and, when the power demand exceeds the predetermined threshold, control may be effected by opening the primary inlet port and opening the secondary inlet port, the secondary inlet port being located such as to be in communication with the exhaust port throughout portions of the revolution of the engine to purge exhaust gases of the engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/273,488 filed Oct. 14, 2011, which claims priority on provisional U.S. application No. 61/512,563 filed Jul. 28, 2011, the entire contents of which are incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The application relates generally to an internal combustion engine using a rotary design to convert pressure into a rotating motion, more particularly, to controlling such an engine. 
       BACKGROUND OF THE ART 
       [0003]    Rotary engines, such as for example Wankel engines, use the eccentric rotation of a piston to convert pressure into a rotating motion, instead of using reciprocating pistons. In these engines, the rotor includes a number of apex or seal portions which remain in contact with a peripheral wall of the rotor cavity of the engine throughout the rotational motion of the rotor to create a plurality of rotating cavities when the rotor rotates. 
         [0004]    In Wankel engines, the inlet and exhaust ports are usually designed mechanically to allow a minimum overlap between them during the intake and exhaust portions of the cycle, such as to purge the exhaust cavity of combustion gases prior to re-filling the intake cavity with a fresh supply of air. Failure to purge the exhaust cavity of the combustion gases may result in a reduction in cycle volumetric efficiency. However, overlap of the ports may limit the range of volumetric compression ratio that can be obtained. Therefore, the need remains for improvement in optimizing how rotary engines may be operated. 
       SUMMARY 
       [0005]    In one aspect, there is provided a method of controlling an air input in a rotary engine, the engine having at least primary and secondary inlet ports in communication with an air source and an exhaust port, the method comprising during start-up of the engine, closing the primary inlet port and opening the secondary inlet port, the secondary inlet port being located rearwardly of the primary inlet port and forwardly of the exhaust port along a direction of a revolution of a rotor of the engine, after start up and with a power demand on the engine lower than a predetermined threshold, opening the primary inlet port and at least partially closing the secondary inlet port, and when the power demand exceeds the predetermined threshold, leaving the primary inlet port open and opening the secondary inlet port, the secondary inlet port being located such as to be in communication with the exhaust port throughout portions of the revolution of the engine to purge exhaust gases of the engine. 
         [0006]    In another aspect, there is provided a method of controlling the volumetric ratios of a rotary engine having rotating chambers with variable volume, the method comprising providing at least a secondary inlet port of the engine rearwardly of a primary inlet port thereof and forwardly of an exhaust port thereof along a direction of a revolution of a rotor of the engine, and controlling a communication between an air source and the inlet ports of the engine, including selecting between a first configuration where the primary inlet port communicates with the air source and communication between the air source and the secondary inlet port is blocked to obtain a first volumetric compression ratio, and a second configuration where the secondary inlet port communicates with the air source and communication between the air source and the primary inlet port is blocked to obtain a second volumetric compression ratio being higher than the first volumetric compression ratio. 
         [0007]    In a further aspect, there is provided a rotary engine comprising a stator body having walls defining an internal cavity, a rotor body mounted for eccentric revolutions within the cavity, the rotor and stator bodies cooperating to provide rotating chambers of variable volume when the rotor rotates relative to the stator, the stator body having at least a primary inlet port, a secondary inlet port and an exhaust port defined therein and communicating with the cavity, with the inlet ports being in communication with an air source, the secondary inlet port being located rearwardly of the primary inlet port and forwardly of the exhaust port along a direction of rotor revolutions, the inlet ports being distinct from one another and spaced apart along the direction of the revolutions, a primary valve regulating a flow of air provided to the primary inlet port, and a secondary valve regulating a flow of air provided to the secondary inlet port, the primary and secondary valves being operable independently of one another. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0008]    Reference is now made to the accompanying figures in which: 
           [0009]      FIG. 1  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with a particular embodiment; 
           [0010]      FIG. 2  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with an alternate embodiment; 
           [0011]      FIG. 3  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with another alternate embodiment; 
           [0012]      FIG. 4  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with yet another alternate embodiment; and 
           [0013]      FIG. 5  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with a further alternate embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , a rotary internal combustion engine  10  known as a Wankel engine is schematically shown. In a particular embodiment, the rotary engine  10  is used in a compound cycle engine system such as described in Lents et al.&#39;s U.S. Pat. No. 7,753,036 issued Jul. 13, 2010 or as described in Julien et al.&#39;s U.S. Pat. No. 7,775,044 issued Aug. 17, 2010, the entire contents of both of which are incorporated by reference herein. The compound cycle engine system may be used as a prime mover engine, such as on an aircraft or other vehicle, or in any other suitable application. In any event, in such a system, air is compressed by a compressor before entering the Wankel engine, and the engine drives one or more turbine(s) of the compound engine. In another embodiment, the rotary engine  10  is used without a turbocharger. 
         [0015]    The engine  10  comprises an outer body  12  having axially-spaced end walls  14  with a peripheral wall  18  extending therebetween to form a rotor cavity  20 . The inner surface of the peripheral wall  18  of the cavity  20  has a profile defining two lobes, which is preferably an epitrochoid. 
         [0016]    An inner body or rotor  24  is received within the cavity  20 . The rotor  24  has axially spaced end faces  26  adjacent to the outer body end walls  14 , and a peripheral face  28  extending therebetween. The peripheral face  28  defines three circumferentially-spaced apex portions  30 , and a generally triangular profile with outwardly arched sides. The apex portions  30  are in sealing engagement with the inner surface of peripheral wall  18  to form three rotating working chambers  32  between the inner rotor  24  and outer body  12 . The geometrical axis of the rotor  24  is offset from and parallel to the axis of the outer body  12 . 
         [0017]    The working chambers  32  are sealed, which may typically improve efficiency. Each rotor apex portion  30  has an apex seal  52  extending from one end face  26  to the other and protruding radially from the peripheral face  28 . Each apex seal  52  is biased radially outwardly against the peripheral wall  18  through a respective spring. An end seal  54  engages each end of each apex seal  52 , and is biased against the respective end wall  14  through a suitable spring. Each end face  26  of the rotor  24  has at least one arc-shaped face seal  60  running from each apex portion  30  to each adjacent apex portion  30 , adjacent to but inwardly of the rotor periphery throughout its length. A spring urges each face seal  60  axially outwardly so that the face seal  60  projects axially away from the adjacent rotor end face  26  into sealing engagement with the adjacent end wall  14  of the cavity. Each face seal  60  is in sealing engagement with the end seal  54  adjacent each end thereof. 
         [0018]    Although not shown in the Figures, but as well understood, the rotor is journaled on an eccentric portion of a shaft and includes a phasing gear co-axial with the rotor axis, which is meshed with a fixed stator phasing gear secured to the outer body co-axially with the shaft. The shaft rotates the rotor and the meshed gears guide the rotor to perform orbital revolutions within the stator cavity. The shaft performs three rotations for each orbital revolution of the rotor. Oil seals are provided around the phasing gear to prevent leakage flow of lubricating oil radially outwardly thereof between the respective rotor end face  26  and outer body end wall  14 . 
         [0019]    During one orbital revolution, each chamber varies in volumes and moves around the stator cavity to undergo the four phases of intake, compression, expansion and exhaust, these phases being similar to the strokes in a reciprocating-type internal combustion engine having a four-stroke cycle. 
         [0020]    The engine includes a primary inlet port  40  defined through one of the walls of the stator body  12 . In the embodiment shown, the primary inlet port  40  is a side port defined in one of the end walls  14 . Another opposed primary inlet port may be similarly defined in the other end wall. The primary inlet port  40  is in communication with an air source through an intake duct  34  which is defined as a channel in the end wall  14 . The air has a pressure slightly greater than the exhaust pressure of the engine. In a particular embodiment the air source is the air output of the compressor of a compound engine, though any suitable source may be used. The primary inlet port  40  delivers air to each of the chambers  32 , and a fuel injection port (not shown) is also provided for delivering fuel into each chamber  32  after the air therein has been compressed. Fuel, such as kerosene (jet fuel) or other suitable fuel, is delivered into the chamber  32  such that the chamber  32  is stratified with a rich fuel-air mixture near the ignition source and a leaner mixture elsewhere, thus providing a so-called stratified charge arrangement, and the fuel-air mixture may be ignited within the housing using any suitable ignition system known in the art. In another embodiment, fuel and air can be mixed outside the engine and delivered as a pre-mixed charge through the primary inlet port  40 . 
         [0021]    The engine also includes an exhaust port  44  defined through one of the walls of the stator body  12 . In the embodiment shown, the exhaust port  44  is a peripheral port defined as an opening through the peripheral wall  18 . The rotary engine  10  operates under the principle of the Atkinson or Miller cycle, with its compression ratio lower than its expansion ratio. For example, the ratio obtained by dividing the volumetric compression ratio by the volumetric expansion ratio may be between 0.3 and 0.8. Accordingly, the primary inlet port  40  is located further away (i.e. measured as a function of piston rotation) from the exhaust port  44  when compared to an engine having compression and expansion ratios that are equal or approximately equal to one another. The angle of the primary inlet port  40 , relative to the angle of the exhaust port  44 , can then be determined to achieve a desired peak cycle pressure given the inlet air pressure. The position of the primary inlet port  40  may vary between the 7 o&#39;clock position up to the 10 o&#39;clock position. In the embodiment shown, the primary inlet port  40  extends between the 8 o&#39;clock and the 9 o&#39;clock positions. 
         [0022]    Because of the Miller cycle implementation, the primary inlet port  40  is positioned relative to the exhaust port such that the compression ratio is significantly lower than the expansion ratio. In the embodiment shown, the primary inlet port  40  is spaced from the exhaust port  44  so that the rotor  24  at least substantially prevents communication therebetween in all rotor positions. In other words, each revolution of the rotor  24  can be said to include, for each of the chambers  32 , an exhaust portion where the chamber  32  directly communicates with or contains the exhaust port  44 , and an intake portion where the chamber  32  directly communicates with or contains the inlet port  40 , and the exhaust and intake portions of the revolution for a same chamber do not overlap. 
         [0023]    The engine  10  also includes a secondary inlet port or purge port  42  defined through one of the walls of the stator body  12 , and communicating with an air source, which may be the same source communicating with the primary inlet port  40 . In the embodiment shown, the purge port  42  is a side port defined in one of the end walls  14  and communicates with the air source through the same intake duct  34  as the primary inlet port  40 . The purge port  42  is located rearwardly of the primary inlet port  40  and forwardly of the exhaust port  44  relative to the direction R of the rotor revolution and rotation. The purge port  42  is located such as to be in communication with the exhaust port  44  through each of the chambers  32  along a respective portion of each revolution. In other words, each revolution of the rotor  24  can be said to include, for each chamber  32 , a purge portion, which is a final stage of the exhaust portion, where the chamber  32  directly communicates with or contains both the purge port  42  and the exhaust port  44 . In the embodiment shown, the purge port  42  is also located such as to be in communication with the primary inlet port  40  through each of the chambers  32  along a respective portion of each revolution. Alternately, the purge port  42  may be spaced from the primary inlet port  40  so that the rotor  24  at least substantially prevents communication therebetween in all rotor positions. 
         [0024]    The purge port  42  may thus allow for smaller volumetric compression ratios to be achieved while still achieving adequate purging of the exhaust cavity. 
         [0025]    Although not shown, the inlet ports  40 ,  42  may be connected to Helmholtz resonators for which may enhance volumetric efficiency and/or minimize the pumping loss during the intake phase. 
         [0026]    In an alternate embodiment, the primary inlet port  40  is also located such as to be in communication with the exhaust port  44  through each of the chambers  32  along a respective portion of each revolution. 
         [0027]    In use, through each orbital revolution of the rotor, each chamber  32  is filled with air (pressurized air from a compressor for example) through the primary inlet port  40  during the respective intake portion of the revolution, i.e. the portion of the revolution where the chamber  32  directly communicates with the primary inlet port  40 . The air is then further compressed by the reducing volume of the rotating chamber  32 . Once the air is further compressed, near minimum volume of the chamber  32 , the air is mixed with fuel and the resulting air-fuel mixture is ignited. The combustion gases expand and force the volume of the chamber  32  to increase. As mentioned above, the primary inlet port  40  is positioned relative to the exhaust port  44  such that the volumetric expansion ratio is higher than the volumetric compression ratio. The combustion or exhaust gases exit the chamber  32  through the exhaust port  44  during the exhaust portion of the revolution, i.e. the portion of the revolution where the chamber  32  communicates with the exhaust port  44 . The last part of the exhaust portion defines the purge portion of the revolution, where the chamber  32  is in communication with both the purge port  42  and the exhaust port  44 , and the air entering the chamber  32  through the purge port  42  is used to purge remaining exhaust gases from the chamber  32 . 
         [0028]    In a particular embodiment, the communication of the chamber  32  with the exhaust port  44  is closed prior to re-filling the chamber  32  with air through the inlet port  40 , i.e. the inlet port  40  does not participate in the purge of the exhaust gases. In an alternate embodiment, the exhaust port  44  is still open when the inlet port  40  starts to open. 
         [0029]    Referring to  FIG. 2 , an engine  110  according to another embodiment is shown, with similar elements being indicated by the same reference numerals employed in the description above. In this embodiment, the primary inlet port  140  is defined through the end wall  114  between the  9  o′clock and the  10  o′clock positions, and communicates with the air source by an intake duct  134  which is independent from the purge port  142 . The secondary inlet port or purge port  142  is defined by an exit port of a purge line  136  extending through the peripheral wall  118  and having an entry port  137  opening into the cavity  20  adjacent the primary inlet port  140 . As such, the air enters the adjacent chamber in communication with the primary inlet port  140 , and circulates to the chamber being purged through the purge line  136  and the purge port  142 . The purge port  142  is located such as to be in communication with the exhaust port  44  through each of the chambers  32  along a respective portion of each revolution, to purge the exhaust gases from the chamber  32 . 
         [0030]    The engine  110  also operates under the principle of the Atkinson or Miller cycle, with its compression ratio lower than its expansion ratio. In the embodiment shown, the rotor  24  at least substantially prevents direct communication between the primary inlet port  140  and the exhaust port  44  in any rotor position, with communication being provided through the purge line  136 . Alternately, the rotor  24  may allow the primary inlet port  140  and exhaust port  44  to be in momentary direct communication with each other through each chamber  32  sufficiently to purge burnt exhaust gases prior to ingestion of a fresh charge of air for the next combustion cycle. 
         [0031]    Referring to  FIG. 3 , an engine  210  according to another embodiment is shown, again with similar elements being indicated by the same reference numerals. Like in the previous embodiment, the primary inlet port  140  is defined through the end wall  214  and communicates with the air source through an intake duct  134 . The exhaust port  244  is a side port, defined in one or both of the end walls  214 , and is in communication with the environment of the engine  210  through an exhaust duct  246  which is defined as a channel in the end wall  214 . 
         [0032]    The purge port  242  is a peripheral port, defined as an opening through the peripheral wall  218 . The purge port  242  and exhaust port  244  communicate through each of the chambers  32  along a respective portion of each revolution to purge the exhaust gases. The purge port  242  is connected to the air source, which may be air bled from the adjacent cavity in communication with the primary inlet port  140  or the air source to which the primary inlet port  140  is connected, through a valve  248  (only schematically shown), such as to modulate the purge flow as a function of engine operation conditions, allowing selective recirculation of some of the exhaust gases, for example to optimize the power output, minimize the emission levels, or for another purpose, as will be further detailed below. Although not shown, a similar valve may connect the primary inlet port  140  to the air source. 
         [0033]    The engine  210  also operates under the principle of the Atkinson or Miller cycle, with its compression ratio lower than its expansion ratio. In the embodiment shown, the rotor  24  prevents direct communication between the primary inlet port  140  and the exhaust port  244  in any rotor position. Alternately, the rotor  24  may allow the primary inlet port  140  and exhaust port  244  to be in momentary direct communication with each other through each chamber  32 . 
         [0034]    Referring to  FIG. 4 , an engine  310  according to yet another embodiment is shown. The engine  310  is similar to the engine  210 , with a similar purge port  242  and corresponding valve  248  (and optional valve, not shown, on the inlet port  140 ), but the position of the exhaust port  344  differs. In this embodiment, the rotor  24  prevents direct communication between the secondary inlet port or purge port  242  and the exhaust port  344  in all rotor positions. A secondary exhaust port  347  is provided in the form of a peripheral port defined as an opening through the peripheral wall  318 . The secondary exhaust port  347  is located forwardly of the primary exhaust port  344  and rearwardly of the purge port  242  along the direction of revolution R, in proximity to the primary exhaust port  344 . The purge port  242  and secondary exhaust port  347  communicate through each of the chambers  32  along a respective portion of each revolution to purge the exhaust gases, after communication of the chamber  32  with the primary exhaust port  344  has been blocked, to purge the chamber  32 . 
         [0035]    The engine  310  also operates under the principle of the Atkinson or Miller cycle, with its compression ratio lower than its expansion ratio. In the embodiment shown, the rotor  24  prevents direct communication between the primary inlet port  140  and the exhaust ports  347 ,  344  in all rotor positions. 
         [0036]    Referring to  FIG. 5 , an engine  410  according to a further embodiment is shown. The engine  410  has a primary inlet port  440  located between the  8  o′clock and  9  o′clock positions, and a secondary inlet port or purge port  442 , with both inlet ports  440 ,  442  being defined in the form of peripheral ports as openings through the peripheral wall  418 . The primary inlet port  440  and secondary inlet port  442  are each connected to a same connecting duct  456 , which can be for example a plenum, a Y-piece, etc., through a respective conduit  434 ,  436 . Each conduit includes a valve  448 ,  450  therein that can selectively open or close it. The connecting duct  456  communicates with the air source, for example the exhaust of a compressor in the case of a compound cycle engine system, through an intake duct  458 . The exhaust port  44  is a peripheral port similar to that of the embodiments of  FIGS. 1-2 . 
         [0037]    In the embodiment shown, the rotor  24  prevents direct communication between the primary inlet port  440  and the exhaust port  44  in any rotor position. Alternately, the rotor  24  may allow the primary inlet port  440  and exhaust port  44  to be in momentary direct communication with each other through each chamber  32 . 
         [0038]    The valves  448 ,  450  which can be for example pneumatic, electric or hydraulic valves, are controlled, either passively or electronically, to modulate the flow between the primary and secondary inlet ports  440 ,  442 , to vary the pressure ratios of the engine to optimize the engine operation at off-design conditions. Such modulation may allow for a suitable trade-off between mission fuel burn, engine power and exhaust gas atmospheric emissions or other factors. 
         [0039]    In a particular embodiment, the valves  448 ,  450  are controlled as follows during three different stages of operation of the engine. 
         [0040]    In use, in one example such as during a first operational stage, which corresponds to engine start-up, the primary valve  450  is closed or substantially closed, and the secondary valve  448  is open, so that only (or primarily) the secondary inlet port  442  delivers air to the chambers  32 . Doing so may allow for a relatively higher volumetric compression ratio than would otherwise be available, which increases the air temperature and facilitates combustion, which it turn may facilitate start-up, and perhaps especially during cold starts. The secondary inlet port  442  may be positioned such that the engine in this configuration has a volumetric compression ratio which is near, e.g. equal or substantially equal, to the volumetric expansion ratio of the engine. 
         [0041]    In another example, during a second operational stage of the engine, which corresponds to engine idle or low power operation, the secondary valve  448  is closed or substantially closed, either abruptly or progressively, and the primary valve  450  is open. With the secondary valve  448  closed, purging of the exhaust gases is significantly reduced/impeded (if the primary inlet port  440  and exhaust port  44  communicate) or prevented (if the rotor  24  prevents communication between the primary inlet port  440  and exhaust port  44 ), which reduces exhaust and thus may help minimize the emission levels of the engine when in this condition. The primary inlet port  440  is positioned such that the engine in this configuration operates under the principle of the Atkinson or Miller cycle, with its compression ratio lower than its expansion ratio. 
         [0042]    In another example, during a third operational stage of the engine, which corresponds to high power operation of the engine, both valves  448 ,  450  are open, so that the secondary inlet port  442  acts as a purge port as discussed above. The secondary valve  448  may be opened, partially or completely, as the power demand increases. The relatively lower volumetric compression ratio of the Atkinson or Miller cycle (as compared to standard cycles) combined with the purging of the exhaust gases from the cavities help maximize power output. In a particular embodiment, the third operational stage may start at approximately 50-80% of maximum power of the engine. However this point can be varied by an electronic control (not shown) sending a signal to the valve actuator to vary the opening of the valve such that the desired outputs (power, emissions, fuel consumption and exhaust gas temperature) are optimized for different operating conditions such as ambient temperature, altitude, throttle levels and rotor speeds. 
         [0043]    Similar valves and controls may be provided with other embodiments, for example the embodiments shown in  FIGS. 3-4 . Air to the inlet ports may be controlled in other engine operational stages, or scenarios, to provide specific benefits or operational effects, as desired. 
         [0044]    The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention(s) disclosed. For example, elements of different embodiments such as locations, configurations and shapes of the various ports may be combined differently than shown. The examples apply to both peripheral and side inlet/exhaust ports, or any suitable combination thereof. Any suitable fuel &amp; ignition systems may be employed. The term “valve” is intended to encompass any suitable airflow regulation apparatus which may be used to achieve the airflow control effects described; any suitable valving arrangement may be employed. Any suitable number of inlet ports may be employed. The present teachings may be applied to any suitable rotary engine, such as a rotary vane pumping machine or other suitable engine, and is thus not limited in application to Wankel engines. Other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.