Abstract:
An engine and associated methods are disclosed. An engine in accordance with the present invention comprises a housing defining a cavity and a slidable member disposed in the cavity. The slidable member is preferably configured to form one or more combustion chambers, and the slidable member adapted to slide back and fourth relative to the housing in a cycle. One or more intake ports are provided for selectively providing fuel to the one or more combustion chambers during selected timed during the cycle. One or more exhaust ports are provided for selectively venting exhaust from the one or more combustion chambers during selected times during the cycle. The intake and exhaust ports are preferably disposed so that intake and exhaust flows are in the same direction (e.g. uniflow).

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to internal combustion engines. More particularly, the present invention relates to uniflow scavenging internal combustion engines.  
         BACKGROUND OF THE INVENTION  
         [0002]    An engine may be defined generally as a cyclical device used for power production. Most readers will be familiar with the internal combustion engines that have been widely used in automotive applications. A typical automotive engine includes a plurality of pistons, each residing in a separate cylinder. Each piston is coupled to a crankshaft by a piston rod. The typical automotive engine includes a large number of parts. The large number of parts has an impact on the expense of building or fabricating automotive engines, and on the reliability of the engines (e.g., since there are a large number of parts, the likelihood that one of them will fail is increased.) The large number of parts and complexity of the typical automotive engine also has the effect that this type of engine is typically not applicable to very small (i.e., miniature or micro) applications and not economically feasible.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention relates generally to internal combustion engines. More particularly, the present invention relates to uniflow scavenging internal combustion engines. An engine in accordance with one embodiment of the present invention comprises a housing defining an elongated cavity. The elongated cavity has a first end, a second end, and internal walls extending therebetween. A fixed piston is located in the cavity and fixedly attached to the housing. The fixed piston has a first end toward the first end of the cavity and a second end toward the second end of the cavity.  
           [0004]    A slider is slidably disposed within the cavity. The slider has a first end toward the first end of the cavity and a second end toward the second end of the cavity. The slider further has a central channel for slidably receiving the fixed piston. The central channel has a first end adjacent the first end of the fixed piston and a second end adjacent the second end of the fixed piston. A first combustion chamber is defined by a space between the first end of the channel and the first end of the fixed piston. A second combustion chamber is defined by a space between the second end of the channel and the second end of the fixed piston.  
           [0005]    The housing also defines a first intake port and a second intake port. The first intake port is preferably in fluid communication with a first intake space defined by the space between the first end of the slider and the first end of the cavity when the slider is slidably disposed toward the second end of the cavity. The second intake port is preferably in fluid communication with a second intake space defined by the space between the second end of the slider and the second end of the cavity when the slider is slidably disposed toward the first end of the cavity.  
           [0006]    The housing also defines a first exhaust port and a second exhaust port. The first exhaust port is preferably in fluid communication with the first combustion chamber when the slider is slidably disposed toward the first end of the cavity. The second exhaust port is preferably in fluid communication with the second combustion chamber when the slider is slidably disposed toward the second end of the cavity.  
           [0007]    The housing also defines one or more first intake channels and one or more second intake channels. The first intake channels provide a fluid flow path between the first intake space and the first combustion chamber when the slider is moved toward the first end of the cavity. The second intake channels provide a fluid flow path between the second intake space and the second combustion chamber when the slider is moved toward the second end of the cavity.  
           [0008]    In a preferred embodiment, the engine is configured such that the first intake space may be selectively placed in fluid communication with the first combustion chamber. In this preferred embodiment, the motion of the slider may be used to pump a combustible charge from the first intake space into the first combustion chamber. The first intake space and the first combustion chamber may be configured such that compression of the combustible charge within the first combustion chamber causes the combustible charge to ignite by spontaneous combustion.  
           [0009]    An engine in accordance with another embodiment of the present invention comprises a housing having an elongated cavity. The elongated cavity has a first chamber, a second chamber and a third chamber. The first chamber is separated from the second chamber by a first wall and the second chamber is separated from the third chamber by a second wall. A first channel then extends through the first wall between the first chamber and the second chamber and a second channel extends through the second wall between the second chamber and the third chamber.  
           [0010]    The engine also includes a piston assembly having a first piston portion, a second piston portion and a third piston portion. The first piston portion is attached to the second piston portion via a first connecting member and the second piston portion is connected to the third piston portion via a second connecting member. The first piston portion is slidably positioned within the first chamber, the second piston portion is slidably positioned within the second chamber, and the third piston portion is slidably positioned within the third chamber. The first connecting member extends through the first channel and the second connecting member extending through the second channel of the housing. A first combustion chamber is defined by a space between the first piston portion and the first wall, and a second combustion chamber defined by a space between the third piston portion and the second wall.  
           [0011]    The housing further includes a first exhaust port, a second exhaust port, and an intake port. The intake port is preferably in fluid communication with the second cavity when the second piston portion is slidably positioned either toward the first wall or second wall. The first exhaust port is preferably in fluid communication with the first combustion chamber when the second piston portion is slidably positioned toward the first wall. The second exhaust port is preferably in fluid communication with the second combustion chamber when the second piston portion is slidably positioned toward the second wall.  
           [0012]    A first intake space is defined between the second piston portion and the first wall, and a second intake space is defined between the second piston portion and the second wall. One or more of first intake channels preferably extend between the first intake space and the first combustion chamber when the second piston portion is slidably positioned toward the first wall. One or more of second intake channels also preferably extend between the second intake space and the second combustion chamber when the second piston portion is slidably positioned toward the second wall.  
           [0013]    It is contemplated that the engine of the present invention may be formed on a larger scale using conventional casting techniques or on a smaller micro scale using integrated circuit processing techniques.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a cross sectional view of an engine in accordance with an exemplary embodiment of the present invention;  
         [0015]    [0015]FIG. 2 is a plan view of a slider of the engine of FIG. 1;  
         [0016]    [0016]FIG. 3 is a cross sectional view of a housing of the engine of FIG. 1;  
         [0017]    [0017]FIG. 4 is an additional cross sectional view of the engine of FIG. 1 in which the slider of the engine in disposed in a first position;  
         [0018]    [0018]FIG. 5 is an additional cross sectional view of the engine of FIG. 4 in which the slider of the engine has been advanced in a leftward direction away from the first position shown in FIG. 4;  
         [0019]    [0019]FIG. 6 is an additional cross sectional view of the engine of FIG. 1 in which the slider of the engine in disposed in a second position;  
         [0020]    [0020]FIG. 7 is an additional cross sectional view of the engine of FIG. 6 in which the slider of the engine has been advanced in a rightward direction away from the second position shown in FIG. 6;  
         [0021]    [0021]FIG. 8 is a partial cross sectional view of the engine of FIG. 1, in which it may be appreciated that the housing of the engine includes a cover;  
         [0022]    [0022]FIG. 9 is a cross sectional view of the engine taken along a section line  9 - 9  shown in FIG. 8;  
         [0023]    [0023]FIG. 10 is a cross sectional view of a substrate of the engine of FIG. 8 taken along section line A-A shown in FIG. 8;  
         [0024]    [0024]FIG. 11 is a cross sectional view of an assembly including the substrate of FIG. 10;  
         [0025]    [0025]FIG. 12 is a cross sectional view of an assembly including the assembly of FIG. 11;  
         [0026]    [0026]FIG. 13 is a cross sectional view of an assembly including the assembly of FIG. 12;  
         [0027]    [0027]FIG. 14 is a cross sectional view of an assembly including the assembly of FIG. 13;  
         [0028]    [0028]FIG. 15 is a cross sectional view of an assembly including the assembly of FIG. 14; and  
         [0029]    [0029]FIG. 16 is a cross sectional view of an engine in accordance with an additional exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. In some cases, the drawings may be highly diagrammatic in nature. Examples of constructions, materials, dimensions, and manufacturing processes are provided for various elements. Those skilled in the art will recognize that many of the examples provided have suitable alternatives which may be utilized.  
         [0031]    [0031]FIG. 1 is a cross sectional view of an engine  100  in accordance with an exemplary embodiment of the present invention. The engine  100  comprises a housing  102  including a plurality of housing walls  104  defining an elongated cavity  106  having a first end  120  and a second end  122 . A fixed piston  108  is located in the cavity  106  and fixedly attached to the housing  102 . The fixed piston  108  has a first end  124  toward the first end  120  of the cavity  106  and a second end  126  toward the second end  122  of the cavity  106 .  
         [0032]    A slider  128  is slidably disposed within the cavity  106 . The slider  128  has a first end  130  toward the first end  120  of the cavity  106  and a second end  132  toward the second end  122  of the cavity  106 . The slider  128  further has a central channel  134  for slidably receiving the fixed piston  108 . The central channel  134  has a first end  136  adjacent the first end  124  of the fixed piston  108  and a second end  138  adjacent the second end  126  of the fixed piston  108 . The position of slider  128  in the embodiment of FIG. 1 may be referred to as a central position.  
         [0033]    A first combustion chamber  140  is defined by a space between the first end  136  of the central channel  134  and the first end  124  of the fixed piston  108 . A first intake space  142  is defined by the space between the first end  130  of the slider  128  and the first end  120  of the cavity  106 .  
         [0034]    In a preferred embodiment, the engine  100  is configured such that the first intake space  142  may be selectively placed in fluid communication with the first combustion chamber  140 . In this preferred embodiment, the motion of the slider  128  may be used to pump a combustible charge from the first intake space  142  into the first combustion chamber  140 . The first intake space  142  and the first combustion chamber  140  may be configured such that compression of the combustible charge within the first combustion chamber  140  causes the combustible charge to ignite by spontaneous combustion.  
         [0035]    In the embodiment of FIG. 1, a plurality of first intake channels  144  are defined by the housing  102 . The first intake channels  144  may be utilized to selectively provide a fluid (liquid or gas) flow path between the first intake space  142  and the first combustion chamber  140  when the slider  128  is moved toward the first end  120  of the cavity  106 .  
         [0036]    A second combustion chamber  146  is defined by a space between the second end  138  of the central channel  134  and the second end  126  of the fixed piston  108 . A second intake space  148  is defined by the space between the second end  132  of the slider  128  and the second end  122  of the cavity  106 .  
         [0037]    In a preferred embodiment, the engine  100  is configured such that the second intake space  148  may be selectively placed in fluid communication with the second combustion chamber  146 . In this preferred embodiment, the motion of the slider  128  may be used to pump a combustible charge from the second intake space into the second combustion chamber  146 . The second intake space  148  and the second combustion chamber  146  may be configured such that compression of the combustible charge within the second combustion chamber  146  causes the combustible charge to ignite by spontaneous combustion.  
         [0038]    In the embodiment of FIG. 1, a plurality of second intake channels  150  are defined by the housing. The second intake channels  150  selectively provide a fluid flow path between the second intake space  148  and the second combustion chamber  146  when the slider  128  is moved toward the second end  122  of the cavity  106 .  
         [0039]    In one embodiment of the present invention, the combustible charge comprises fuel and air. Examples of fuels that may be suitable in some applications include liquid fuels, gaseous fuels, vaporous fuels, or combinations thereof so that an essentially gaseous combustible charge can be moved to the combustion chambers. The intake channels preferably are used to provide a fluid path for moving the fuel/air mixture into the combustion chambers.  
         [0040]    [0040]FIG. 2 is a plan view of the slider  128  of the engine  100  of FIG. 1. In FIG. 2 it may be appreciated that the slider  128  defines a plurality of first intake cavities  152  and a plurality of second intake cavities  154 . In a preferred embodiment, the first intake cavities  152  and the second intake cavities  154  are configured such that they are selectively covered and uncovered by the fixed piston  108 . Also in a preferred embodiment, the first intake cavities  152  are configured such that they are selectively placed in fluid communication with the first intake channels  144  defined by the housing  102 . Also in a preferred embodiment, the second intake cavities  154  are configured such that they are selectively placed in fluid communication with the second intake channels  150  defined by the housing  102 .  
         [0041]    [0041]FIG. 3 is a cross sectional view of the housing  102  of the engine  100  of FIG. 1. The housing  102  includes a plurality of housing walls  104  defining an elongated cavity  106  having a first end  120  and a second end  122 . A fixed piston  108  is located in the cavity  106  and fixedly attached to the housing  102 . The fixed piston  108  has a first end  124  toward the first end  120  of the cavity  106  and a second end  126  toward the second end  122  of the cavity  106 .  
         [0042]    Housing  102  also defines a first intake port  156 . During operation of engine  100 , the first intake port  156  is selectively covered and uncovered by slider  128 . First intake port  156  is preferably in fluid communication with the first intake space  142  defined by the space between the first end  130  of the slider  128  and the first end  120  of the cavity  106  when the slider  128  is slidably disposed toward the second end  122  of the cavity  106 .  
         [0043]    Housing  102  also defines a second intake port  158 . During operation of engine  100 , the second intake port  158  may be selectively covered and uncovered by slider  128 . The second intake port  158  is preferably in fluid communication with the second intake space  148  defined by the space between the second end  132  of the slider and the second end  122  of the cavity  106  when the slider  128  is slidably disposed toward the first end  120  of the cavity  106 .  
         [0044]    A first exhaust port  160  and a second exhaust port  162  are also defined by the housing  102 . During operation of engine  100 , first exhaust port  160  and a second exhaust port  162  are preferably selectively covered and uncovered by slider  128 . The first exhaust port  160  is preferably in fluid communication with the first combustion chamber  140  when the slider  128  is slidably disposed toward the first end  120  of the cavity  106 . The second exhaust port  162  is preferably in fluid communication with the second combustion chamber  146  when the slider  128  is slidably disposed toward the second end  122  of the cavity  106 .  
         [0045]    [0045]FIG. 4 is an additional cross sectional view of the engine  100  of FIG. 1. The engine  100  comprises a housing  102  including a plurality of housing walls  104  defining an elongated cavity  106  having a first end  120  and a second end  122 . A fixed piston  108  is located in the cavity  106  and fixedly attached to the housing  102 . The fixed piston  108  has a first end  124  toward the first end  120  of the cavity  106  and a second end  126  toward the second end  122  of the cavity  106 .  
         [0046]    A slider  128  is slidably disposed within the cavity  106 . The position of slider  128  in the embodiment of FIG. 4 may be referred to as a first position. In FIG. 4, it may be appreciated that the slider  128  and the fixed piston  108  are configured such that the first exhaust port  160  is at least partially uncovered and the first intake cavities  152  are completely covered by the fixed piston  108  when the slider  128  is in the first position. When the first exhaust port  160  is at least partially uncovered, burned gasses within the first combustion chamber  140  may exit the first combustion chamber  140  through the first exhaust port  160 .  
         [0047]    [0047]FIG. 5 is an additional cross sectional view of the engine  100  of FIG. 1 and FIG. 4. In the embodiment of FIG. 5, slider  128  has been advanced in a leftward direction away from the first position shown in FIG. 4. Travel by the slider  128  in the leftward direction causes the first intake cavities  152  defined by slider  128  to be at least partially uncovered while the first exhaust port  160  remains uncovered.  
         [0048]    Uncovering first intake cavities  152  preferably allows a combustible charge to pass from the first intake space  142  to the first combustion chamber  140  via the first intake cavities  152  and the first intake channels  144 . Uncovering the first exhaust port  160  allows burned gasses within the first combustion chamber  140  to exit the first combustion chamber  140 . In a preferred embodiment, the burned gasses exiting the first combustion chamber  140  and the combustible charge entering the first combustion chamber  140  travel in a similar general direction, with the pressure of the combustible charge helping to expel the burned gasses from the first combustion chamber  140 .  
         [0049]    [0049]FIG. 6 is an additional cross sectional view of the engine  100  of FIG. 1. The engine  100  comprises a housing  102  including a plurality of housing walls  104  defining an elongated cavity  106  having a first end  120  and a second end  122 . A fixed piston  108  is located in the cavity  106  and fixedly attached to the housing  102 . The fixed piston  108  has a first end  124  toward the first end  120  of the cavity  106  and a second end  126  toward the second end  122  of the cavity  106 .  
         [0050]    A slider  128  is slidably disposed within the cavity  106 . The position of slider  128  in the embodiment of FIG. 6 may be referred to as a second position. In FIG. 6, the slider  128  and the fixed piston  108  are configured such that the second exhaust port  162  is at least partially uncovered and the second intake cavities  154  are completely covered by the fixed piston  108  when the slider  128  is in the second position. When the second exhaust port  162  is at least partially uncovered, burned gasses within the second combustion chamber  146  may exit the second combustion chamber  146  through the second exhaust port  162 .  
         [0051]    [0051]FIG. 7 is an additional cross sectional view of the engine  100  of FIG. 1 and FIG. 6. In the embodiment of FIG. 7, slider  128  has been advanced in a rightward direction away from the second position shown in FIG. 6. Travel by the slider  128  in the rightward direction causes the second intake cavities  154  defined by slider  128  to be at least partially uncovered while the second exhaust port  162  remains uncovered.  
         [0052]    Uncovering second intake cavities  154  preferably allows a combustible charge to pass from the second intake space  148  to the second combustion chamber  146  via the second intake cavities  154  and the second intake channels  150 . Uncovering the second exhaust port  162  allows burned gasses within the second combustion chamber  146  to exit the second combustion chamber  146 . In a preferred embodiment, the burned gasses exiting the second combustion chamber  146  and the combustible charge entering the second combustion chamber  146  travel in a similar general direction, with the pressure of the combustible charge helping to expel the burned gasses from the second combustion chamber  146 .  
         [0053]    [0053]FIG. 8 is a partial cross sectional view of the engine  100 . In FIG. 8 it may be appreciated that the housing  102  of the engine  100  includes a cover  164 . Cover  164  is preferably fixed to housing walls  104  and fixed piston  108 . Cover  164  preferably partially encloses first intake space  142 , first combustion chamber  140 , second intake space  148 , and second combustion chamber  146 . It is contemplated that the intake channels  144  and  150  may be provided in cover  164 , rather than or in addition to, the housing  102 .  
         [0054]    [0054]FIG. 9 is a cross sectional view of the engine  100  taken along section line  9 - 9  shown in FIG. 8. In FIG. 9 it may be appreciated that the housing  102  includes a substrate  166 , the housing walls  104 , and the cover  164 . In the embodiment of FIG. 9, a first gap  168  is defined by the substrate  166  and the slider  128 , and a second gap  170  is defined by the cover  164  and the slider  128 . For purposes of illustration, the first gap  168  and the second gap  170  are shown to be relatively large. In a preferred embodiment of the present invention, the first gap  168  and the second gap  170  are relatively small.  
         [0055]    [0055]FIG. 10 is a cross sectional view of the substrate  166  taken along section line  9 - 9  shown in FIG. 8. A method of fabricating engine  100  may begin with the step of providing the substrate  166 . The method may also include the step of etching the substrate  166  to form a plurality of first intake channels  144  and a plurality of second intake channels  150 .  
         [0056]    [0056]FIG. 11 is a cross sectional view of an assembly including the substrate  166  of FIG. 10. The assembly shown in FIG. 11 includes a fixed piston  108  and a plurality of housing walls  104  disposed on substrate  166 . The fixed piston  108  and the housing walls  104  are preferably fixed or integral with substrate  166 .  
         [0057]    [0057]FIG. 12 is a cross sectional view of the assembly of FIG. 11 with a first sacrificial layer  172  disposed upon substrate  166 . FIG. 13 is a cross sectional view of the assembly of FIG. 12 with a slider  128  disposed upon the first sacrificial layer  172 . In FIG. 13 it may be appreciated that slider  128  defines a plurality of first intake cavities  152  and a plurality of second intake cavities  154 . FIG. 14 is a cross sectional view of the assembly of FIG. 13 with a second sacrificial layer  174  disposed upon the slider  128  and the first sacrificial layer  172 , as shown. FIG. 15 is a cross sectional view of the assembly of FIG. 14 with a cover  164  disposed upon the second sacrificial layer  174  and the housing walls. To free the slider from the housing, the sacrificial layers  172  and  174  may be selectively removed, using well known etching techniques.  
         [0058]    Having thus described FIGS.  1 - 15 , methods for forming the engine are now described. It should be understood that these steps are only illustrative. It should also be understood that steps may be omitted from each process and/or the order of the steps may be changed without deviating from the spirit or scope of the invention. It is anticipated that in some applications, two or more steps may be performed more or less simultaneously to promote efficiency.  
         [0059]    A method of fabricating engine  100  may include the steps of:  
         [0060]    1) Providing a substrate;  
         [0061]    2) Etching the substrate to form a plurality of first intake channels and a plurality of second intake channels;  
         [0062]    3) Growing or otherwise providing a plurality of housing walls and a fixed piston on the substrate;  
         [0063]    4) Growing or otherwise providing a first sacrificial layer on top of the substrate proximate the housing walls and the fixed piston;  
         [0064]    5) Growing or otherwise providing a slider on top of the first sacrificial layer;  
         [0065]    6) Growing or otherwise providing a second sacrificial layer on top of the slider;  
         [0066]    7) Growing a cover on top of the housing walls, the fixed piston, and the second sacrificial layer;  
         [0067]    8) Etching a back side of the substrate forming a first exhaust port, a second exhaust port, a first intake port, and a second intake port; and  
         [0068]    9) Removing the first sacrificial layer and the second sacrificial layer through one or more of the first exhaust port, second exhaust port, first intake port and/or second intake port to release the slider.  
         [0069]    An additional method of fabricating engine  100  may include the steps of:  
         [0070]    1) Providing a substrate;  
         [0071]    2) Etching the top surface of the substrate to form a plurality of walls and a fixed piston;  
         [0072]    3) Etching substrate to form a plurality of first intake channels and a plurality of second intake channels;  
         [0073]    4) Growing or otherwise providing a first sacrificial layer on top of the substrate proximate the housing walls and the fixed piston;  
         [0074]    5) Growing or otherwise providing a slider on top of the first sacrificial layer;  
         [0075]    6) Growing or otherwise providing a second sacrificial layer on top of the slider;  
         [0076]    7) Growing or otherwise providing a cover on top of the housing walls, the fixed piston and the second sacrificial layer;  
         [0077]    8) Etching a backside of the substrate forming a first exhaust port, a second exhaust port, a first intake port, a second intake port; and  
         [0078]    9) Removing the first sacrificial layer and the second sacrificial layer through one or more of the first intake port, second intake port, first exhaust port and/or the second exhaust port to release the slider.  
         [0079]    [0079]FIG. 16 is a cross sectional view of an engine  200  in accordance with another exemplary embodiment of the present invention. The engine  200  comprises a housing  202  defining an elongated cavity  206  having a first end  220 , a second end  222 , a first chamber  276 , a second chamber  278 , and a third chamber  280 . The first chamber  276  is preferably separated from the second chamber  278  by a first wall  282  and the second chamber  278  is preferably separated from the third chamber  280  by a second wall  284 . A first channel  286  extends through the first wall  282  between the first chamber  276  and the second chamber  278  and a second channel  288  extends through the second wall  284  between the second chamber  278  and the third chamber  280 .  
         [0080]    The engine  200  also includes a piston assembly having a first piston portion  290 , a second piston portion  292 , and a third piston portion  294 . The first piston portion  290  is preferably attached to the second piston portion  292  via a first connecting member  293 , and the second piston portion  292  is preferably connected to the third piston portion  294  via a second connecting member  295 , the first piston portion  290  is slidably positioned within the first chamber  276 , the second piston portion  292  is slidably positioned within the second chamber  278  and the third piston portion  294  is slidably positioned within the third chamber  280 . The first connecting member  293  extends through the first channel  286  and the second connecting member  295  extends through the second channel  288  of the housing  202 .  
         [0081]    A first combustion chamber  240  is defined by a space between the first piston portion  290  and the first wall  282 , and a second combustion chamber  246  is defined by a space between the third piston portion  294  and the second wall  284 . An intake port  296  is in fluid communication with the second chamber  278  when the second piston portion  292  is slidably positioned either toward the first wall  282  or the second wall  284 .  
         [0082]    A first exhaust port  260  is in fluid communication with the first combustion chamber  240  when the second piston portion  292  is slidably positioned toward the first wall  282 . A second exhaust port  262  is in fluid communication with the second combustion chamber  246  when the second piston portion  292  is slidably positioned toward the second wall  284 .  
         [0083]    A first intake space  242  is defined between the second piston portion  292  and the first wall  282 . A second intake space  248  is defined between the second piston portion  292  and the second wall  284 . One or more of first intake channels  244  extend between the first intake space  242  and the first combustion chamber  240  when the second piston portion  292  is slidably positioned toward the first wall  282 . A network of second intake channels  250  extend between the second intake space  248  and the second combustion chamber  246  when the second piston portion  292  is slidably positioned toward the second wall  284 .  
         [0084]    During the operation of engine  200 , the intake port  296  may be selectively covered and uncovered by second piston portion  292 . Intake port  296  is preferably in fluid communication with the first intake space  242  when the second piston portion  292  is slidably disposed toward the second end  222  of the cavity  206 . Intake port  296  is preferably in fluid communication with the second intake space  248  when the second piston portion  292  is slidably disposed toward the first end  220  of the cavity  206 .  
         [0085]    Also during operation of engine  200 , the first exhaust port  260  is preferably selectively covered and uncovered by the first piston portion  290  and the second exhaust port  262  is preferably selectively covered and uncovered by the third piston portion  294 . The first exhaust port  260  is preferably in fluid communication with the first combustion chamber  240  when the first piston portion  290  is slidably disposed toward the first end  220  of cavity  206 . A second exhaust port  262  is preferably in fluid communication with the second combustion chamber  246  when the second piston portion  292  is slidably disposed toward the second end  222  of the cavity  206 .  
         [0086]    In a preferred embodiment, the engine  200  is configured such that the first intake space  242  may be selectively placed in fluid communication with the first combustion chamber  240 . In this preferred embodiment, the motion of the second piston portion  292  may be used to pump a combustible charge from the first intake space  242  into the first combustion chamber  240 . The first intake space  242  and the first combustion chamber  240  may be configured such that combustion of the combustible charge within the first combustion chamber  240  causes the combustible charge to ignite by spontaneous combustion. In the embodiment of FIG. 16, one or more first intake channels  244  are defined by the first connecting member  293 . The first intake channels  244  may be utilized to selectively provide a fluid path between a first intake space  242  and the first combustion chamber  240  when the first connecting member  293  is moved towards the first end  220  of the cavity  206 .  
         [0087]    Also in a preferred embodiment, the engine is configured such that the second intake space  248  may be selectively placed in fluid communication with the second combustion chamber  246 . In this preferred embodiment, the motion of the second piston portion  292  may be used to pump by combustible charge from the intake space  248  through to the second combustion chamber  246 . The second intake space  248  and the second combustion chamber  246  may be configured such that compression of the combustible charge within the second combustion chamber  246  causes the combustible charge to ignite by spontaneous combustion. In the embodiment of FIG. 16, one or more second intake channels  250  are defined by the second connecting member  295 . The intake channels  250  selectively provide a fluid flow path between the second intake space  248  and the second combustion chamber  246  when the second connecting member  295  is moved toward the second end  222  of the cavity  206 .  
         [0088]    Having thus described the preferred embodiments of the present invention, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The inventions&#39;s scope is, of course, defined in the language in which the appended claims are expressed.