Abstract:
An internal combustion engine comprising at least one rotating, oscillating or reciprocating piston ( 20, 21 ) in a cylinder ( 11, 12 ), each piston ( 20, 21 ) defining with the cylinder ( 11, 12 ) a combustion chamber ( 35 ), each combustion chamber ( 35 ) having at least one inlet valve ( 36 ) and one exhaust valve ( 37 ), and means ( 40 ) to periodically open the inlet and exhaust valves, characterised in that the valves are closed by a gas spring ( 80, 82 ) having a closing force proportional to the speed of the engine.

Description:
INTRODUCTION  
         [0001]    This invention relates to internal combustion engines and particularly the valve control of internal combustion engines that run on a four stroke cycle.  
         DISCUSSION OF THE PRIOR ART  
         [0002]    The majority of internal combustion engines used in motor cars, trucks and motorcycles operate on a four stroke cycle. The four stroke cycle internal combustion engine has been in use for the bulk of the 20 th  century. Over the years engine designers have constantly strived to improve the efficiency of such engines. In modern times these improvements in efficiency have dictated a need to also consider the environmental effects of the engine namely the production of pollutants including noxious gases that escape through the exhaust. Compromises have been reached in which the overall efficiency of the engine has been reduced by the need to introduce power absorbing equipment to purify the exhaust gases such as catalytic converters. Environmental issues have also dictated controls on fuels, consequently the addition of lead as an anti-knocking agent in high compression internal combustion engines has been phased out with the introduction of lead-free petrol resulting in further compromises in engine design.  
           [0003]    Four stroke engines usually include at least one inlet and one exhaust valve per cylinder. In some small sophisticated engines pluralities of exhaust and inlet valves may be provided per cylinder. The valves are usually driven to an open position by the lobes of a camshaft. This drive can either be direct or indirect. The valves usually return to the closed position by the use of metal coil springs that simply urge the valve once open, back to the closed position. The size of spring force of the coil spring is designed to accommodate the engine when the largest demand is placed on the springs which is usually when the engine is running at the highest revolutions per minute (RPM). Thus, the valve springs have to be of sufficient size, weight and spring ratio to operate efficiently at the highest RPM. This means that at lower RPM the valve springs are too strong and thus unnecessary work is done against the springs causing a dramatic reduction in the engine efficiency in its normal operation range. Valve springs also have to be compressed during the starting procedure thus increasing the power required to tun over an engine to start it requiring large lead acid batteries and charging systems.  
           [0004]    It is these considerations and the many problems discussed above that have brought about the present invention.  
         SUMMARY OF THE INVENTION  
         [0005]    According to the present invention there is provided an internal combustion engine comprising at least one rotating, oscillating or reciprocating piston in a cylinder, each piston defining with the cylinder a combustion chamber, each combustion chamber having at least one inlet valve and one exhaust valve, and means to periodically open the inlet and exhaust valves, characterised in that the valves are closed by a gas spring pressurised by a source of gas pressure taken from each combustion chamber and monitored so that the closing force is proportional to the RMP of the engine. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0006]    Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:  
         [0007]    [0007]FIG. 1 is a schematic end on view of an engine in accordance with one embodiment of the invention;  
         [0008]    [0008]FIG. 2 is a schematic underside view of the engine shown in FIG. 1;  
         [0009]    [0009]FIG. 3 is a schematic illustration of the gas valve control mechanism,  
         [0010]    [0010]FIG. 4 is a perspective view of the engine from the top,  
         [0011]    [0011]FIG. 5 is a perspective view of the engine from the bottom,  
         [0012]    [0012]FIG. 6 is a perspective view of the engine with the crankcase and cylinder walls removed,  
         [0013]    [0013]FIG. 7 is a perspective view of the camshaft and valve assemblies, and  
         [0014]    [0014]FIG. 8 is a cross sectional view of a conventional in line engine utilising a gas valve assembly in accordance with a second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    The engine shown in FIGS.  1  to  7  is the subject of a co-pending patent application of even date. The engine utilises a gas controlled valve spring details of which are described hereunder. FIG. 8 shows a more conventional engine using gas controlled valve springs.  
         [0016]    The drawings illustrate the engine schematically to illustrate the method of operation. It is understood that the actual engine could be considerably different in structural detail and it is envisaged that those skilled in this art would appreciate and understand the additional detail that would be required to put the schematic illustration of the engine into practical effect.  
         [0017]    The drawings of the preferred embodiment (FIGS.  1  to  7 ) illustrate an engine in the form of a horizontally opposed flat twin configuration. The engine  10  comprises cylinders  11  and  12  that extend radially outwardly from a central crankcase  13 . The crankcase  13  houses a crankshaft  25  that supports reciprocating pistons  20  and  21  in cylinders  11  and  12 . Each piston  20  and  21  is connected to the crankshaft  25  via a con-rod  23  and big end bearings  24 . The pistons/cylinders are spaced horizontally as shown in FIG. 2. The face of each cylinder  11  and  12  is closed off by a cylinder head  30  that supports spark plug  31 . The space between the interior of the cylinder head  30  and the piston crown  22  defines the combustion chamber  35 . Inlet and exhaust valve port  36  and  37  communicate with the combustion chamber  35  along the wall of the cylinders  11  or  12  to constitute a side valve arrangement. Each valve port supports a valve  50  having a head  51  and stem  53 . The valve head  51  seals against a valve seat  52  defined by the mouth of the port. The valves are driven by cam followers  42  that directly contact with the lobes  41  of a camshaft  40  that is driven from the crankshaft  25  by a chain, gears or toothed belt.  
         [0018]    The opposed cylinders&#39; housings define the central crankcase  13  that is sealed at either end. The crankshaft  25  is mounted for axial rotation about main bearings (not shown) in the crankcase. The crankshaft  25  includes a circular sealing lobe  60  with arcuate cut-outs  61 ,  62  that open and close an inlet air/fuel passageway  63  via a crankcase inlet port  69  at the top of the crankcase  13  and an exit passageway  65  via a crankcase outlet port  70  at the base of the crankcase  13 . The air fuel mixture is derived from suitably positioned fuel injectors  66 ,  67  at the inlet passage  63  controlled by a conventional throttle  68 . The exit passageway  65  feeds the inlet port  36  via a camshaft chamber  39 . In the engine described above, the inlet and exhaust valves are controlled through direct contact with the camshaft via cam followers but are closed by a gas drive that is controlled by gas pressure coming from the combustion chamber  35  during the combustion stroke and crankcase during the starting cycle.  
         [0019]    The engine operates on a four stroke cycle but utilises crankcase pressure to supercharge each cylinder. The air fuel mixture is pressurised within the crankcase for subsequent transfer to the combustion chamber of each cylinder via the inlet port  36  from the camshaft chamber  39 . Side positioned inlet and exhaust valves  50  control the inlet of the air/fuel mixture and exhaust of the exploded gases. These valves, instead of using conventional springs to return to the closed position use a gas drive having pressure that is proportional to the RPM of the engine.  
         [0020]    The opening of the exhaust and inlet valves is carefully controlled through the lobes on the camshaft that act against cam followers. The closing is effected by the gas spring which is pressurised by gas pressure taken from the combustion chamber during combustion stroke as well as the crankcase in a starting sequence.  
         [0021]    The gas valve spring for each cylinder comprises a valve pressure chamber  80  that slidingly supports valve return pistons  81  and  82  that are attached respectively to the ends of the valve stems  53  of the inlet and exhaust valves  50 . As shown in FIG. 2 the valve stems  53  enter the housing  80  in a spaced parallel array and the return pistons  81 ,  82  form part of the cam followers  42  that are in turn driven open by the lobes  41  of the camshaft  40 . Each valve stem  53  extends out of the valve pressure chamber  80  to join the head  51  of the valve which communicates with the combustion chamber  35  through the side mounted inlet and exhaust ports  36  and  37  described above. In one embodiment the valve pressure chamber  80  is pressurised at start up by a source of pressure that comes from the crankcase  13  via a first gallery  88 . In start up, one way control ball valve  90  is controlled by a coil spring  92 , or reed valve (not shown). Once the engine has started this valve stays closed.  
         [0022]    The primary source of gas pressure for the valve pressure chamber  80  comes from a second gallery  89  communicating from the combustion chamber  35  through a valve pressure control assembly  114  to the valve pressure chamber  80 . A two-way control ball valve  91  is floating between two sealing seats with combustion pressure on one side and valve pressure on the opposite side. The volume of gas allowed to enter the valve pressure chamber  80  is controlled by a jet  111 . Reservoir  113  increases valve pressure volume. This extra volume dampens pressure input pulses and allows for missed firing strokes. The reservoir  113  receives gas from the valve pressure chambers  80 . The entries are controlled one way by reed valves  115 . The valve pressure chambers  80  are balanced by returning gas from the reservoir  113  through the two-way valves  91 . The reservoir  113  can also have a pressure release valve  101  that is controlled by the electronic control unit (ECU) that orchestrates the timing and fuel injection of the engine. In this situation also connected to the reservoir  113  is a pressure sensor  105  that sends a signal to the ECU proportional to the gas pressure. Thus the pressure in the valve pressure chambers  80  and reservoir  113  can be controlled by the ECU.  
         [0023]    The gas valve pressure control assemblies  114  also include a third lubricating gallery  110  that communicates between the inlet valve port and the valve stems of both valves to provide a source of cooling and lubrication for the valves by introducing unburnt air fuel mixture to the valve stems. The cross sectional area of the return pistons  81  and  82  are sufficiently great that the force caused by the gas pressure within the pressure housing forces the return pistons to slide towards the camshaft  40  and thus close the valves. In this manner, the valves are closed by gas pressure and not a metal coil spring. The return pistons  81  and  82  require a sealing of cast iron or Teflon™. The ECU can ensure that the pressure and closing force is proportional to the RPM of the engine as can a mechanical control system. Although the valve pressure chambers are pressurised by the comparatively hot exhaust gases the volume of transfer and size of the second gallery is such that the assembly does not overheat. Furthermore, in one embodiment the valve pressure chambers are surrounded by a liquid cooled jacket (not shown).  
         [0024]    It is understood that the engine could be manufactured in suitable lightweight aluminium and although the preferred embodiment illustrates a two cylinder arrangement, it is understood that these cylinders can be arranged in banks of opposed pairs so that a 2, 4, 6, 8, 10 or 12 cylinder configurations are envisaged depending on the desired power output. It is also understood that the engine could incorporate traditional liquid cooling passageways with the conventional cooling radiator and fans.  
         [0025]    The use of a gas spring to control the closure of the inlet and exhaust valves provides an important advantage because the pressure of the gas spring is proportional to the RPM of the engine. Thus, at all times the pressure corresponds to the demands of the engine. This is in contrast with conventional coil springs that are used to close valves. These springs are designed to provide the necessary force for high RPM, thus, at lower engine speeds the springs are far too strong, thus absorbing a considerable amount of power. Springs also have other problems caused with their mass, resulting in valve bounce and other cyclic vibrations that are detrimental to engine performance. The elegance of the gas spring is that the pressure of the system is actually supplied by the combustion pressure produced during the combustion cycle. Furthermore, the gas spring assembly enables the exhaust valve to be opened later due to pressure bleed being required by pressure chambers as engine RPM increases, relieving combustion pressure towards bottom dead centre on the combustion stroke during acceleration. This gives a longer push available on the piston crown. When the engine decelerates, with a closed throttle valve, the engine naturally reduces combustion pressure. Pressure is not available to increase valve spring but is not required and the bleed of pressure from the valve pressure chambers can be reduced via an electronic control valve, controlled by an ECU in conjunction with the fuel injection and ignition systems or its own internal natural bleeding.  
         [0026]    However, one problem exists with using gas pressure to close the valves of the engine. At start-up there is no gas to close off the valves, which would mean it would not be possible to pressurise the cylinders. The start cycle is thus illustrated in the sheets of FIGS.  1  to  3  marked “starting cycle”.  
         [0027]    The fact that the valves are unsprung means that little power is required to spin the crankshaft and turn over the engine, thus reducing the demands on the starter motor.  
         [0028]    After a few initial revolutions driven by the starter motor to prime the engine, the inducted air fuel mixture is compressed in the crankcase and transferred to the camshaft intake cavity through the unsprung intake valves and to the combustion chambers. The crankcase pressure is also transferred via a gallery to the valve pressure chambers through the one way valve  90  in the valve pressure control assembly  114 . At this point the pressure in all engine cavities except the exhaust port has been equalised. Intake and exhaust valves now have effective valve timing. Pressure in valve pressure chamber  80  will return the exhaust valve because only ambient pressure exists under the valve head and the intake valve will return because the area of the intake valve head facing the port is less than the return piston surface area.  
         [0029]    After valve control is obtained, combustible mixture compressed and ignition has occurred piston is driven down the cylinder and the combustion pressure is fed to the valve chambers via the gallery through the two way valve  91  (reed or ball) for the first time. This raises the pressure in the valve pressure chamber to a level capable of valve control for normal operation and closed one way valves  90  stop escape of pressure to crankcase. At this stage engine assumes the normal operation cycle.  
         [0030]    Another option to close the valves for start-up is to couple a small air priming pump to the starter motor that supplies air pressure to the valve chambers to close the valves and allow the engine to start.  
         [0031]    [0031]FIG. 8 illustrates a typical in line four or six cylinder engine  200  with twin overhead camshafts  240  driving an inlet  241  and exhaust  242  valve per cylinder. Each cylinder  280  includes a piston  221  driven by a crankshaft  222  via a conned  223 . The valve heads  251 ,  252  are of conventional design seating on valve seats  253 ,  254  in the cylinder head  255 . The valves  241 ,  242  have valve stems  265 ,  266  that slide axially in valve guides  267 ,  268 . The end of each stem opposite the head is attached to a valve piston  242  that is arranged to be a sliding fit within a cylindrical bore  243  found in a valve pressure chamber  236 . The valve piston  242  has a head  217  that is engaged by the lobe  248  of the camshaft  240  to drive the valve piston down  242  and open the valve  241 ,  242 . The valve pressure chamber  236  is pressurised with exhaust gases that are taken from the combustion chamber  235  via a bleed passageway  275  located in the cylinder wall  280 .  
         [0032]    As can be seen from FIG. 8, the valve pressure chamber  236  has an infeed  281  that is fed from the bleed passageway  275  in the cylinder wall. The infeed  281  is on one side of the cylinder head whilst on the opposite side there is an outlet feed passageway  282  from the pressure chamber  236  that is inturn fed to a reservoir  213  that includes a one way valve  215 , a pressure sensor  201  and a pressure bleed valve  205 . The pressure reservoir  213  has an outlet  216  that inturn communicates with the infeed  281 . In this way there is a closed circuit constantly pressurising the valve pressure chamber  236 . The pressure and thus force that closes the valves is directly dependent to the RPM of the engine and the pressure is controlled during running and start up in the same manner as described with reference to the first embodiment.