Abstract:
A four-stroke combustion engine is lubricated by a mixture of lubricant, fuel and air received from a rotary valve type carburetor. A cylinder of the engine houses a reciprocating piston and together they generally define a combustion chamber segregated from a generally sealed cavity which contains a mechanism for operating intake and exhaust valves communicating with the combustion chamber. Generally non-burning lubricant along with fuel-and-air enters the combustion chamber from the rotary-type carburetor and blows-by the piston into the sealed cavity through a clearance defined generally between the cylinder and piston for cooling the engine and lubricating the mechanical linkage assembly. Preferably, the sealed cavity is vented directly into a rotary throttle valve of the carburetor for controlled flow back into the engine without use of a check valve, enhanced idling characteristics of the engine and substantially reduced spit-back through the carburetor air inlet.

Description:
FIELD OF THE INVENTION 
     This invention relates to a four-stroke combustion engine, and more particularly to a four-stroke combustion engine having a crankcase venting rotary valve type carburetor. 
     BACKGROUND OF THE INVENTION 
     Government agencies of an increasing number of countries are applying exhaust emission control regulations to protect the environment. These regulations are being applied to all combustion engines including portable engines used in common equipment such as chain saws, lawn mowers and hedge trimmers. One means of reducing exhaust emissions even in small portable engines is to utilize four-stroke engines instead of the more conventional two-stroke engines. In the larger prior art conventional four cycle engines, an atmospheric vented crankcase includes an oil reservoir and oil pump or oil splash system for lubrication of the crankshaft, piston rings, and overhead combustion chamber intake and exhaust valves. Because small versions of the well-known larger conventional four-stroke engines are typically expensive to manufacture, they are generally not practical for smaller capacity applications. Hence, various alterations of the prior art conventional four-cycle engines have been developed for smaller and less demanding applications. One such alteration is known as a fuel mixture-lubricated four-stroke engine described in U.S. Pat. No. 6,199,532, to Haberlein et al, issued Mar. 13, 2001 and incorporated herein by reference. 
     In this fuel mixture-lubricated four-stroke engine, the lubricant or oil is pre-mixed with the combustion liquid fuel prior to flowing through a carburetor in much the same way as a two-stroke engine. The intake manifold is in direct communication with the valve cover and crankcase which is part of a sealed system. During the typically downward intake or induction stroke of this scavenging four-stroke engine, the fuel-air-lubricant mixture flows into the combustion chamber from the crankcase, valve chamber and the carburetor. During the upward compression and exhaust strokes, the fuel-air-lubricant mixture flows into the valve chamber and crankcase from the carburetor. 
     The primary source of lubrication for the crankshaft, intake and exhaust valves and related components is supplied to the valve cover chamber and crankcase during the compression and exhaust strokes. During these strokes, fuel-air-lubricant mixture generally flows directly into the valve cover chamber and crankcase while bypassing the combustion chamber altogether. The piston rings and cylinder walls are also lubricated primarily from below by this source of lubricant. Although not the primary source of lubricant, some lubrication of the piston rings from above or within the combustion chamber occurs when the fuel-air-lubricant mixture enters the combustion chamber during the intake stroke. 
     Also, in such engines during the downward power stroke, when the intake and exhaust valves are closed, the crankcase is overpressurized and requires venting. Such venting in prior art four-stroke engines is typically achieved by routing a vent passage to either the inlet or outlet side of the carburetor through a check valve which is normally closed and opens when the crankcase is pressurized at a predetermined superatmospheric pressure. Unfortunately, such venting is expensive to manufacture and thus not practical for smaller engine applications. Moreover, should the check valve fail in its open position or generally lack the necessary responsive reaction, spit back through the carburetor and oil drippage through the air filter can result. Other alternatives include routing the vent passage to the intake manifold without a check valve. Unfortunately, this leads to engine stalls during cold idle operation and rough engine idling during normal temperatures. 
     SUMMARY OF THE INVENTION 
     A four-stroke combustion engine receives a mixture of lubricant, fuel and air from a rotary-valve type carburetor. Because the lubricant is pre-mixed with the incoming fuel, the engine preferably does not have a conventional oil pan or oil pump. A cylinder of the engine houses a reciprocating piston and together they generally define a combustion chamber. A generally sealed cavity located opposite the piston contains intake and exhaust valves of the combustion chamber and mechanical mechanism operably connected with the valves and the piston. During an induction stroke of the piston, the lubricant along with fuel-and-air enters the combustion chamber from the rotary-type carburetor. Collected lubricant in the combustion chamber generally does not burn with the fuel, and instead leaches or blows by into the cavity through a small clearance defined generally between the cylinder and piston. In this way, the lubricant reduces friction between the reciprocating piston and cylinder and is the primary source of lubricant for the mechanical mechanism. 
     Preferably, the cavity is vented directly into a rotary throttle valve assembly of the carburetor so that during the induction and power strokes of the piston, air and residual lubricant flow through a vent passage and controllably into the mixing passage of the carburetor via the rotary throttle valve assembly and preferably without a check valve. Because the rotary throttle valve also controls the flow of vented air and residual oil from the cavity, idling characteristics of the engine are enhanced. The valve assembly preferably has a rotary member seated rotatably in a valve chamber which traverses the mixing passage. The rotary member has a through-bore which adjustably aligns to the mixing passage for controlling the quantity of lubricant, fuel and air flowing into the engine. When the rotary member is in an idle position, it forms an adjustable downstream idle opening with the carburetor body at a downstream end of the through-bore for flow into the mixing passage. Similarly, the rotary member when in the idle position forms an upstream idle opening at an upstream end of the through-bore, and which is diametrically opposite the downstream idle opening. The vent passage communicates directly with the through-bore between the downstream and upstream idle openings. 
     Objects, features and advantages of this invention include an economical four-stroke combustion engine which does not require an oil reservoir, oil pump or crankcase vent passage check valve. Moreover, the present invention provides a smoother running engine which is less likely to stall during cold idle conditions, reduces emissions for small engine applications, is relatively simple in design, is robust, and has a long, useful and maintenance-free life. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiment and best mode, appended claims and accompanying drawings in which: 
         FIG. 1  is a schematic sectional view of a four-stroke combustion engine with a carburetor of the present invention; 
         FIG. 2  is another schematic sectional view of the four-stroke combustion engine; 
         FIG. 3  is a schematic sectional view of a rotary valve type carburetor of the four-stroke combustion engine show in a wide open throttle position; 
         FIG. 4  is a schematic sectional view of the rotary valve type carburetor similar to  FIG. 3  except shown in a low speed position; 
         FIG. 5  is a perspective end view of the rotary valve type carburetor; 
         FIG. 6  is a sectioned perspective view of a carburetor body of the rotary valve type carburetor taken along line  6 — 6  of  FIG. 5 ; 
         FIG. 7  is a side view of a rotary valve assembly at the carburetor; 
         FIG. 8  is a perspective bottom view of a rotary member of the rotary valve assembly; 
         FIG. 9  is a cross section of the rotary member taken along line  9 — 9  of  FIG. 7 ; 
         FIG. 10  is a cross section of the rotary valve assembly taken along line  10 — 10  of  FIG. 7 ; and 
         FIG. 11  is partial cross section of the rotary valve type carburetor taken along line  11 — 11  of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings,  FIGS. 1–2  illustrate a four-stroke combustion engine  20  with a carburetor  78  of the present invention. The engine  20  has a reciprocating piston  22  slidably received in a cylinder  24  and delimiting a combustion chamber  26 . Generally isolated from the combustion chamber  26  by the piston  22  is a substantially sealed cavity  28  generally defined by a cylinder head  36  and crankcase  42 . The cavity  28  contains a mechanical linkage assembly  30  that transfers power of the engine  20  and operably connects the reciprocating piston  22  with overhead intake and exhaust valves  32 ,  34  which cooperate with the combustion chamber and mount operably to the valve housing or cylinder head  36 . 
     Preferably, the linkage assembly  30  has a piston rod  38  pivotally connected with the piston  22  and a rotary crankshaft  40  which is journaled for rotation in the crankcase  42  which generally defines a lower portion  44  of the sealed cavity  28 . The crankcase is engaged and communicates with the cylinder  24 . Preferably, a cogged timing belt  46  is looped about a cogged crankshaft pulley  48  fixed to the crankshaft  40  and a cogged cam pulley  50  fixed to an overhead, lobed, camshaft  52  of the mechanical linkage assembly  30  journaled for rotation in the valve head  36  and which sequentially operates the intake and exhaust valves  32 ,  34 . Generally, the valves  32 ,  34  and lobed camshaft  52  are in an upper portion or valve chamber  53  of the sealed cavity  28  defined at least in part by the valve housing  36 . As is generally known by one skilled in the art of four-stroke engines, the mechanical linkage assembly  30  and operation of the intake and exhaust valves  32 ,  34  is not limited to that described above. For instance, but not limited to, the cogged belt  46 , pulleys  48 ,  50  and overhead cam shaft  52  can be replaced with any combination of pivoting valve levers and push rods which ride upon non-concentric lobes of a camshaft journaled for rotation in the crankcase  42  and engaged operably to the crankshaft via a chain or gears (not shown). 
     As is generally known in the art for four-stroke engines, communicating with the combustion chamber  26  and carried generally by the valve head  36  is an intake port  56  and an exhaust port  58  associated with respective intake and exhaust valves  32 ,  34 . Each valve  32 ,  34  is generally biased in a closed direction sealing off the respective ports  56 ,  58  by compression springs  54  which also prevent valve chatter or noise during engine operation. When the intake valve  32  is open, the combustion chamber communicates with an intake channel  60  of the valve head  36  via the intake port  56 , and when the exhaust valve  34  is open the combustion chamber communicates with an exhaust channel  62  of the valve head  36  via the exhaust port  58 . 
     Opening and closing of the valves  32 ,  34  is generally dictated by which of four distinctive strokes the piston  22  is moving through. The strokes of the piston  22  are generally known as intake, compression, power, and exhaust. During the intake stroke (see  FIGS. 1 and 2 ), the intake valve  32  is generally open and the exhaust valve  34  is closed as the piston  22  moves downward. The increasing volume of the combustion chamber  26  induces a mixture of lubricant-fuel-and-air to flow through the intake channel  60  and into the combustion chamber  26 . The intake stroke is followed by a compression stroke where the intake and exhaust valves  32 ,  34  are generally closed and the piston  22  moves upward compressing the lubricant-fuel-and-air mixture in the combustion chamber  26 . Near a top-dead-center of the piston  22  (i.e. full compression) the mixture is ignited preferably by a spark plug (not shown) sending the piston  22  downward, known as the power stroke, and driving the crankshaft  40 . Following the power stroke is the exhaust stroke where the intake valve  32  is closed and the exhaust valve  34  is open as the piston  22  moves upward and pushes the burnt gasses, but generally not the lubricant, out of the combustion chamber  26  and through the exhaust channel  62  via the exhaust port  58 . 
     Unlike conventional four-stroke combustion engines, the crankcase  42  of the combustion engine  20  does not generally have a lubricant reservoir or a conventional oil pan and preferably does not have an oil pump or an oil splash system for lubrication and cooling of moving components such as the mechanical linkage assembly  30 . Instead, the lubricant is pre-mixed with the fuel-and-air mixture and generally enters the engine  20  through the intake channel  60 , the combustion chamber  26  and into the cavity  28  preferably solely by blow-by of the piston rings  65 . The lack of a lubricant reservoir and oil pump is particularly advantageous for smaller capacity more economical four-stroke engines having less expensive manufacturing techniques which do not lend themselves to high tolerances. That is, for more expensive, high tolerance, manufactured engines having a lubricant reservoir and oil pump, it is ideal to have a tight tolerance between the piston and cylinder thus achieving maximum compression of the fuel-and-air mixture, maximum power production during the power stroke, and typically higher fuel efficiency. Because of the closer or smaller tolerances between the typical cylinder and piston of larger four-stroke engines, little to no lubricant transfers between the combustion chamber and the crankcase except that necessary to lubricate the cylinder wall and a series of piston rings. 
     Generally, the less expensive four-stroke engine  20  of the present invention has a small annular clearance or piston ring end gap  64  defined between an outer cylindrical face  66  of the piston  22  and an inner cylindrical wall  68  of the cylinder  24 . Empirical data has demonstrated that the annular clearance or piston ring end gap  64  can be large enough to transfer, leach or blow-by un-burnt lubricant out of the combustion chamber  26  and into the lower portion  44  of the sealed cavity  28 , and yet small enough to maintain a substantial degree of compression during the compression stroke. This relatively small amount of lubricant which is not prone to combustion is sufficient to lubricate and cool the mechanical linkage assembly  30  and the reciprocating piston  22  and piston rings  65 . Collection of lubricant in and about the annular clearance  64  also promotes some friction-free sealing between the cylinder wall  68  and the face  66  of the piston  22 . Preferably, the intake channel or manifold  60  does not communicate directly with the cavity  28  other than through the combustion chamber  26  and annular clearance  64 . Alternatively, the annular clearance  64  can be replaced with, or assisted by, an oil scraping type of piston ring  65  as described in United States Patent Application Publication US 2004/0182355 A1, filed Mar. 18, 2003 and incorporated herein in its entirety. 
     The reciprocating motion of the piston  22  is generally used to move or pump the blow-byed lubricant as a mist about the sealed cavity  28 . A conduit  70  of the sealed cavity  28  generally communicates the lower portion  44  with the upper portion  53  of the sealed cavity  28  and provides a flow path as indicated by the arrows identified as  72  for movement of the lubricating mist from the lower portion  44  of the cavity  28  and into the upper portion  53  of the cavity  28  for lubrication of the intake and exhaust valves  32 ,  34 . During the induction stroke with the intake valve  32  open, the volume of the lower portion  44  becomes smaller and the lubricating mist is induced to flow into the upper portion  53  via the conduit  70  and at least partially through a vent passage  74  communicating controllably with a fuel-and-air mixing passage  76  of a rotary-type carburetor  78  of the engine  20 . 
     During the compression stroke, lubricant which entered the combustion chamber  26  during the induction stroke substantially blow-bys into the lower portion  44  of the sealed cavity  28 . During the power stroke, both the intake and exhaust valves  32 ,  34  are closed and the sealed cavity  28  is slightly over-pressurized with some lubricating mist flowing into the carburetor  78  through the vent passage  74 . Spit-back of air and lubricant through the carburetor  78  is generally prevented based on location of the vent passage  74  relative to a rotary-type throttle valve assembly  80  of the carburetor  78  and an inherent back pressure characteristic of the rotary-type throttle valve assembly. During the exhaust stroke, the intake valve  32  is closed and the sealed cavity  28  becomes slightly under-pressurized with the upward movement of the piston  22  causing some lubricant-fuel-and-air to reverse flow from the carburetor  78 , through the vent passage  74  and into the sealed cavity  28  for later scavenging of the fuel (similar to two-stroke engine applications). 
     Referring to  FIGS. 3–11 , more specific to the rotary-type carburetor  78  of the four-stroke combustion engine  20 , the vent passage  74  is defined at least in part by a carburetor body  82  which also defines the mixing passage  76  extending there-through and communicating with the intake channel  60 . A valve chamber or generally blind bore  84  in the body  82  traverses the mixing passage  76  for rotatable receipt of a substantially cylindrical rotary valve member  86  of the rotary throttle valve assembly  80 . The rotary member  86  has a through-bore  88  which selectively and progressively aligns with the lubricant-fuel-and-air mixing passage  76  as the rotary member  86  controllably rotates and is cam-raised by the assembly  80  to move it between idle and wide open positions to thereby control the flow of air, fuel and lubricant through the carburetor  78 . One embodiment of a cam structure which can controllably raise and rotate the rotary member  86  is described in U.S. Pat. No. 6,585,235, to Pattullo, issued Jul. 1, 2003, and incorporated herein by reference in its entirety. 
     The axial movement of the rotary member  86 , as the member is rotated, axially moves a fuel mixture needle  90  carried by the member  86  within and relative to a tubular fuel jet  92  carried by the carburetor body  82  to thereby vary the flow cross-section of a side orifice  94  of the fuel jet  92  to control, at least in part, the amount of liquid fuel and lubricant discharged from the orifice  94 . A throttle valve plate  96  traps a coiled spring  98  generally against the top of the rotary member  86  to provide a force biasing the rotary member  86  axially downward in its valve chamber  84  and into the idle position (as best shown in  FIGS. 4 and 11 ). An annular flexible seal  100  is disposed around an upper segment  102  of the rotary member  86  to provide a liquid tight seal between the rotary member and throttle valve plate  96 . From a lubricant and fuel metering chamber (not shown), the lubricant and fuel flows to the fuel jet  92  through a fuel passage  103  of the body  82  and into the mixing passage  76  in response to a differential pressure across the fuel jet, in a known manner. Although not limited to, one preferred example of a fuel metering assembly is disclosed in U.S. Pat. No. 5,711,901 which is incorporated herein by reference in its entirety. 
     At the bottom of the valve chamber  84  is an annular or continuous groove  104  which opens upward and is defined radially between a substantially cylindrical surface  106  of the chamber  84  disposed generally below the mixing passage  76  and an upward projecting annular prominence or shoulder  108  of the body  82  disposed generally in the valve chamber  84  and concentrically about the fuel passage  103  and needle  90 . A vent aperture  110  of the vent passage  74  is carried or defined by the cylindrical surface  106  of the body  82  and opens into the annular groove  104 . A downward projecting annular collar  112  of the rotary member  86  rotatably fits into the annular groove  104  and is spaced from an annular bottom  114 , which defines in-part the groove  104 , by a varying annular gap portion  116  having a minimum distance when the rotary member  86  is in the idle position (see  FIG. 11 ) and by a maximum distance when the rotary member  86  is in the wide open position. Communicating with the annular gap portion  116  of the annular groove  104  is a continuous radial gap portion  118  of the annular groove  104  disposed radially between the prominence  108  of the body  82  and the collar  112 . 
     The radial gap portion  118  communicates with the through-bore  88  of the rotary member  86  through a hole  120  generally defined circumferentially by the collar  112 . Because the rotary member  86  moves axially when rotated, a tapered notch  122  is defined by an outer wall  124  of the collar  112  generally at the vent aperture  110  location providing a continuous free flowing vent path to the through-bore  88  which generally does not alter in flow cross section when the rotary member  86  is rotated and lifts partially out of the annular groove  104 . When the rotary member  86  is in the idle position and thus closest to the bottom  114  of the annular groove, a large end  126  of the tapered notch  122  is circumferentially and axially aligned to the vent aperture  110 , and when the rotary member  86  is in the wide open position and thus furthest from the bottom  114 , a small end  128  of the tapered notch  122  is aligned to the vent aperture  110 . In this way, a continuous flow path for venting of the sealed cavity  28  is provided first through the vent passage  74 , then the vent aperture  110 , the tapered notch  122 , the varying annular gap portion  116 , the radial gap portion  118 , the hole  120 , the through-bore  88 , and then into the mixing passage  76  through an adjustable downstream opening  130  generally formed between the body  82  at the mixing passage  76  and the rotary member  86  at a downstream end  132  of the through-bore  88 . 
     As previously discussed, a back pressure exists generally within the mixing passage  76  which prevents spit back of lubricant and air through the carburetor  78  when the piston  22  is traveling in its power stroke and generally when the engine  22  is running at lower speeds. This back pressure is created at least in part by the tapered notch  122  and a second adjustable upstream opening  134  opposed diametrically to the downstream opening  130  with respect to the rotary member  86  and generally formed between the body  82  at the mixing passage  76  and the rotary member  86  at an upstream end  136  of the through-bore  88 . The vent passage  74  utilizes this back pressure by communicating with the mixing passage  76  between the two diametrically opposed openings  130 ,  134  and not upstream or downstream of both openings. 
     With the vent passage  74  integrated in this way through the rotary throttle valve assembly  80 , the vent passage  74  does not require a conventional check valve, or positive crankcase valve, when venting the sealed cavity  28 . Because the vent passage  74  does not communicate directly upstream of the throttle valve assembly  80  and instead communicates in the more controlled environment of the mixing passage, drooling or dripping of oil through an air filter, air leaks, and other undesirable effects caused possibly due to an otherwise required, malfunctioning, check valve are minimized or eliminated. Moreover, because the vent passage  74  does not communicate with the mixing passage  76  directly downstream of the throttle valve assembly  80 , or directly into the intake channel  60 , and without a check valve, the idle performance characteristics of the engine  20  are not significantly degraded. Specifically, because the vent passage  74  is integrated into the rotary throttle valve assembly  80  (i.e. between diametrically opposed idle control openings  130 ,  134 ) and not the intake channel  60 , the opening(s) through the mixing passage  76  of the rotary member  86  is significantly larger at engine idle producing greater idle stability and an economical four-stroke engine which is less likely to stall at initial warm-up conditions and is more stable at normal temperature operation. 
     Preferably, a mounting face  138  of the carburetor body  82  is sealed and engaged to the valve head or housing  36 . The vent passage  74  preferably of the body  82  and the mixing passage  76  both extend through the mounting face  138  to respectively communicate with the upper portion  53  of the sealed cavity  28  through the valve housing  76 , and to communicate with the intake channel  60 . 
     While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. For instance, the vent passage  74  can be formed by hose(s) and fittings communicating directly between the lower portion  44 , or upper portion  53 , of the sealed cavity  28  and the carburetor  78 . Yet further, the four-stroke engine  20  can conceivably have multiple cylinders and pistons  22  sharing a common sealed cavity. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing form the spirit or scope of the invention.