Abstract:
A combustion engine having at least one pair of longitudinal opposed cylinder with electricity generating stator means fixed relative thereto and having pistons arranged in the cylinders for cycles of reciprocating compression and power strokes, the pistons being linked together with a linear actuator for movement therewith.

Description:
FIELD OF THE INVENTION 
     This invention relates to internal combustion engines. More particularly although not exclusively it discloses an improved form of free-piston engine. 
     BACKGROUND OF THE INVENTION 
     With known prior art free-piston engines such as those described by M. Goertz and L. Peng in March 2000 SAE Paper 2000-01-0996, entitled FREE-PISTON ENGINE ITS APPLICATION AND OPTIMIZATION, and Galileo Research, Inc. at www.galileoresearch.com, 1999 entitled FREE-PISTON ENGINE-GENERATOR TECHNOLOGY the gas enters the combustion chamber via intake slots through the wall of the cylinder sleeve. This is typical of the method used on most conventional two stroke internal combustion engines. The disadvantage of such intake arrangement is that as the piston rings slide over the intake slots (twice during each stroke) the radial support area is reduced and a slight ring deformation occurs. The deformation results from the elasticity of the unsupported ring material when subjected to radial forces imposed by gas pressure and the pre-tension in the rings. This deformation accelerates the wear rate of the rings and cylinder sleeve and is partly responsible for abandonment of the two stroke engine in modern passenger cars. 
     It is also known to provide a valve-in-piston arrangement in a reciprocating piston crankcase engine as described in Australian patent application 63021/99 by E. Wechner. Such engines however are are relatively inefficient when used in modern hybrid vehicles as additional mechanical linkage is required to generate the electrical power required for the drive wheels and energy storage cells. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to ameliorate the aforementioned disadvantages and accordingly an internal combustion engine is disclosed having at least one pair of longitudinally opposed cylinders with electricity generating stator means fixed relative thereto, respective pistons arranged in said cylinders for cycles of reciprocating compression and power strokes, inlet valve means for introducing air or a fuel mixture into said cylinders prior to said compression strokes, outlet valve means for the expulsion of exhaust gases following said power strokes and said pistons being linked together with a linear actuator for movement therewith whereby during operation of said engine the reciprocating strokes of said pistons and linear actuator with respect to said stator means generates usable electrical energy and said inlet valve means being located in said pistons and comprising a portion of the heads thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The currently preferred embodiment of the invention will now be described with reference to the attached drawings in which: 
     FIG. 1 shows a cross-sectional schematic view of a free-piston engine along the centre axis of the cylinders, 
     FIG. 2 shows a cross-sectional view of the engine along the lines A—A of FIG. 1, and 
     FIG. 3 is a cross-sectional view of the engine along the lines B—B of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1 the main components of the engine are the longitudinally opposed cylinder blocks  1  and  2 , the cylinder heads  3  and  4 , the pistons  5  and  6 , linear actuator  7  and electricity generating stator  8 . 
     As with prior art free-piston engines the cylinders fire alternately in the two stroke cycle and the resulting reciprocating linear motion is converted into electrical energy by means of relative movement between the linear actuator and stator assemblies. 
     In accordance with this invention however the inlet valves comprise poppet valves  9  which are located in the heads  5 A and  6 A of the pistons. 
     In FIG. 1 the piston  5  is shown at the end of the expansion or power stroke in cylinder  1 . Both the inlet valve  9  and exhaust valve  10  are thus open to enable the two stroke gas exchange or scavenging process to take place. The intake gas  10 A for this scavenging process was compressed in the linear actuator compression chamber  11  during the preceding expansion stroke of piston  5 . The pressure obtained for the intake gas  10 A is sufficient to open the inlet valve  9  in the piston  5  against both the force of coil spring  20  and the opposing kinetic force from deceleration of the valve mass  9  at the end of the power stroke. During this gas exchange process the cool intake gas  10 A passes through the linear actuator heat exchanger  23 , the charge pipe  13 , the piston heat exchanger  14  and the inlet valve  9  before entering the combustion chamber  15 . The incoming pressure of this gas  10 A assists the evacuation of the exhaust gas through the exhaust or outlet valve  10  and port  32 . There is a control solenoid  21  in the cylinder head  3 . This opens the exhaust valve  10  for selected variable time periods to optimise the efficiency of the gas exchange at a given power consumption. For example, at low power consumption only a small amount of exhaust gas is evacuated through the valve  10 . This in turn limits the entry of intake gas  10 A to the mass required to maintain the desired idle speed of the engine. Such arrangement releases a minimum amount of pressure in the combustion chamber during the gas exchange process to reduce pumping losses. At maximum power the valve  10  is held open long enough to evacuate substantially all of the exhaust gas. This allows the maximum mass of fresh intake gas  10 A to enter the combustion chamber. As with the prior art valve-in-piston engine the inlet valve  9  is held closed during the subsequent compression stroke against the opposing kinetic forces of deceleration by gas pressure in the chamber  15 . 
     The opposite engine piston  6  is shown by FIG. 1 in the ignition position after having completed a compression stroke. There is a linear heat exchanger  24 , charge pipe  13 A and outlet port  32 A associated with piston  6  and cylinder  2  similar to that described earlier but orientated at 90 degrees as shown in FIG.  3 . During this compression stroke of piston  6  fresh intake gas  10 B was drawn by the linear actuator  7  in through the inlet  17 , the ring chamber  18 , the ring valve  19  and into the compression chamber  12 . During the next expansion or power stroke of piston  6  after ignition this gas  10 B will be compressed in chamber  12  to comprise the subsequent intake charge for the combustion chamber  16  of cylinder  2 . 
     The linear actuator  7  is equipped with gas seals  22  on both ends to facilitate its function as a compressor piston for the gas exchange process. This eliminates the need for a external intake gas charging device. Between the electricity generating stator  8  and the linear actuator there is also a cylindrical sleeve  25  which provides a dynamic mating surface for the gas seals  22 . This sleeve  25  should be electrically non-conductive, non-magnetic and sufficiently thin to avoid adverse effects on the generating process. Suitable material may include ceramics or high temperature composite plastics which may be either deposited on the surface or pressed into the stator  8 . 
     Although in the illustrated example of the engine only a single inlet and outlet valve are shown for each cylinder the invention extends to the use of more than one inlet valve in each piston and more than one outlet valve in each cylinder head. 
     Other components of the preferred embodiment as shown in the drawings are as follows: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 27 
                 Cooling water jacket 
               
               
                 28 
                 Electricity generating coils 
               
               
                 29 
                 Electric power outlet junction box 
               
               
                 30 
                 Permanent magnets 
               
               
                 31 
                 Permanent magnet back iron 
               
               
                   
               
             
          
         
       
     
     It will be thus be appreciated that this invention at least in the form of the embodiment disclosed provides a novel and useful improvement to free-piston internal combustion engines. Clearly however the example disclosed is only the currently preferred form of the invention and a wide variety of modifications may be made which would be apparent to a person skilled in the art. For example the shape and configuration of the valves and linear actuator gas compressor may be changed according to engine design requirements. Also, while the engine described has only two opposed cylinders the invention could be extended to any number of pairs.