Abstract:
An exhaust valve for a two-cycle engine. The exhaust valve includes a valve body and an actuator. The valve body, in turn, includes a valve insert and a shaft extending from the valve insert. A substantially axial slot may be defined on an upper surface of the valve insert. The actuator may include an actuator housing, the piston, an actuator spring, and an actuator cover. In the embodiment shown, the actuator housing defines a plurality of orifices and feelingly accommodates the piston. The piston may be mechanically connected to the valve body shaft and is biased toward a front surface of the actuator housing by a spring. The actuator cover may accommodate one end of the spring and cooperates with the actuator housing to define a generally cylindrical cavity therein. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 U.S.C. § 119 (e) to, and hereby incorporates by reference, U.S. Provisional Application No. 60/xxx,xxx, filed 1 Apr. 2003 as Attorney Docket No. 2647.02US01. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to two-cycle engines and, in particular, this invention relates to exhaust valves for two-cycle engines.  
           [0004]    2. Background  
           [0005]    Two-cycle engines are widely used for applications such as snow blowers, water craft, all-terrain vehicles, snow mobiles, and the like. The two-cycle engine is generally economically produced because many of the components necessary for four-cycle engines are unnecessary. In contrast to four-cycle engines which use valves, the piston itself blocks and exposes intake and exhaust ports as the piston is reciprocally displaced during operation.  
           [0006]    In contrast to four-cycle engines, two-cycle engines have two strokes: 1) intake/compression; and 2) power/exhaust. During the intake/compression stroke in the two-cycle engine, the piston travels upward, thereby generating a low-pressure area in the crank case below the piston and compressing an air/fuel/oil mixture in the cylinder above the piston. Higher atmospheric pressure surrounding the crankcase forces air through the carburetor or throttle valve and, in turn, forces the reed valve open to admit more of the air/fuel/oil mixture to the crankcase When air pressures in the crank case and surrounding atmosphere are approximately equal, the read valve then closes. During the power/exhaust stroke, the piston travels downward, thereby compressing the air or air/fuel/oil mixture in the crankcase. Also during the power/exhaust stroke, the piston movement begins to open transfer ports, thereby forcing the charge from the crankcase, through the transfer ports, and into the cylinder and head chamber. During the foregoing transfer, the exhaust expansion chamber causes a low pressure area to occur at the exhaust port. This low pressure causes spent charge (combusted air/fuel/oil mixture), from the previous stroke, to be drawn out into the exhaust, thereby allowing entry of the new charge.  
           [0007]    As the piston travels during the intake/compression stroke the charge pressures are equalized between the cylinder and crankcase. As the piston continues the intake/compression stroke, the transfer ports are closed and the piston begins to compress the fresh charge. At this point, the exhaust port remains open and the piston forces spent charge out through the open exhaust port. As the spent charge is forced through the open exhaust port, a pressure wave is produced. The pressure wave usually impacts a baffle in the exhaust pipe and is deflected back through the exhaust port and toward the cylinder. The effect of the deflected pressure wave is to retain the unspent charge in the cylinder. As the piston continues to travel upwardly, it travels past the exhaust port, thereby trapping the new charge within the cylinder and head chamber for subsequent combustion. Hence, lowering the top (reducing the effective diameter) of the exhaust port causes the new charge to be trapped in the cylinder and head chamber.  
           [0008]    In view of the foregoing, one would think that a low exhaust port top (an exhaust port with a relatively small diameter) would always be advantageous. However, a low exhaust port top is actually advantageous only at low rpm when the engine is producing relatively small amounts of exhaust gases. At higher rpm, the exhaust port top must be disposed at a higher position to allow time for the increased combustion pressure to be reduced to less than the atmospheric pressure present in the crankcase. If the cylinder gas pressure is higher than the crankcase gas pressure, exhaust gases will be forced into the crankcase, thereby contaminating the fresh charge and disrupting entry of the new charge into the cylinder. When the exhaust port closes or the exhaust gate is closed by the piston during the compression/intake stroke, the charge is compressed by the piston and at near top dead center, the charge is ignited by the ignition. The piston is then forced down to begin the two stroke cycle anew. Thus, during operation at high rpm, maximum power is attained if the exhaust (combustion products) is efficiently removed from the cylinder. Efficient removal of exhaust gases may be accomplished by comparatively large-diameter exhaust ports. However, a two-stroke engine designed to accommodate expeditious removal of exhaust is often inefficient at low rpm. Inefficiency at low rpm is due in part because the enlargement of the exhaust port diameter diminishes the compression within the cylinder, thereby allowing the uncombusted fuel/oil/air mixture to exit the exhaust port before being combusted. When uncombusted fuel/oil/air mixture is allowed to exit before being combusted, the amount of trapped charge available for combustion is reduced and the efficiency of the engine (as measured by the energy produced per unit fuel) is reduced.  
           [0009]    There is then a need for a two-cycle engine which efficiently adjusts the diameter of the exhaust port to a smaller dimension for low rpm and a larger dimension for high rpm.  
         SUMMARY OF THE INVENTION  
         [0010]    This invention substantially meets the aforementioned needs of the industry by providing an exhaust valve for a two-cycle engine. The exhaust valve may include a valve body and an actuator. The valve body may display a generally planar upper surface and a substantially axial slot defined from the valve body upper surface. The actuator may include a piston, an actuator housing, and a spring. The piston may be mechanically connected to the valve body. The actuator housing may sealingly accommodate the piston and may further define at least one orifice. The spring may be biased against the piston.  
           [0011]    There is also provided a process for manufacturing an exhaust valve of the present invention, in which the effected a diameter of an exhaust port of the two-cycle engine is altered. The process may include forming a valve body with a generally planar upper surface and a substantially axial slot defined from the valve body upper surface. The process may further include connecting the valve body to a distant, the piston sealingly disposed in an actuator housing. The process may still further include biasing the piston against the actuator housing with a spring.  
           [0012]    It is a feature of the present invention to include a valve body having a generally planar upper surface and a substantially axial slot defined from the valve body upper surface.  
           [0013]    It is an advantage of the present invention that exhaust gases are transferred efficiently to the exhaust valve via the axial slot on the valve body upper surface.  
           [0014]    It is another feature of the present invention to include an actuator housing with at least one orifice with a relatively small diameter.  
           [0015]    It is an advantage of the present invention that the at least one orifice acts as a buffer to slow the return of the valve body to a fully extended position.  
           [0016]    It is yet another feature of the present invention to include a piston with a plurality of extension surfaces and a plurality of recessed surfaces, the recessed surfaces concentrically disposed between the extension surfaces.  
           [0017]    It is yet another advantage of the present invention that pressure exerted by exhaust against the surfaces on the piston initially displaces the piston slowly, then more quickly until an equilibrium is attained.  
           [0018]    These and other objects, features, and advantages of this invention will become apparent from the description which follows, when considered in view of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a perspective view of one embodiment of the present exhaust valve installed on a two-cycle engine block;  
         [0020]    [0020]FIG. 2 is a partial cross section of the exhaust valve taken along line  2 - 2  of FIG. 1;  
         [0021]    [0021]FIG. 3 is a cross section of the exhaust valve taken along line  3 - 3  of FIG. 2;  
         [0022]    [0022]FIG. 4 is a cross section of the exhaust valve of FIG. 3 in a retracted position; and  
         [0023]    [0023]FIG. 5 is an exploded view of the exhaust valve of FIG. 1. 
     
    
       [0024]    It is understood that the above-described figures are only illustrative of the present invention and are not contemplated to limit the scope thereof.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Comprehension of this invention can be gained through reference to the drawings in conjunction with a thorough review of the following explanation. Any references to such relative terms as front and rear, right and left, top and bottom, upper and lower, horizontal and vertical, or the like, are intended for convenience of description and are not intended to limit the present invention or its components to any one positional or spatial orientation. Representative examples of the teachings of the present invention, which examples utilize many of these additional features and methods in conjunction, will now be described in detail with reference to the drawings. This detailed description is merely intended to teach a person of ordinary skill in the art further details for practicing aspects of the present teachings and is not intended to limit the scope of the invention. Therefore, combinations of features and methods disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense and are instead taught merely to particularly describe representative and preferred embodiments of the invention.  
         [0026]    A two-cycle engine block  100  operatively fitted with an exhaust valve  102  of the present invention is depicted in FIGS. 1 and 2. The engine block  100  includes a block wall  104 , the block wall  104  defining a cylinder  106 , a cylinder wall  107  (FIG. 3), an exhaust port  108 , and a valve slot  110 . The cylinder  106  accommodates a piston (not shown). An exploded view of the exhaust valve  102  is depicted in FIG. 5, wherein a valve body  120  and an actuator  122  are shown.  
         [0027]    In this embodiment, the valve body  120  unitarily (or otherwise integrally) includes a valve insert  130  and a shaft  132 . The valve insert  130 , in turn, displays substantially planar respective upper and lower surfaces  136  and  138  (FIG. 2), first and second lateral edge surfaces  140  and  142  (FIG. 4), a front edge surface  144 , and a rear edge surface  146 . The upper surface  136  defines a substantially axially aligned slot  150 . The slot  150  extends between the front and rear edges  144  and  146 . The first and second lateral edges  140  and  142  may be rounded. The generally arcuate front edge  144  may be formed by respective, sloped upper and lower surfaces  154  and  156 . The surfaces  154  and  156  meet at an edge  158 . The base  160  extends from the rear edge  146  and unitarily joins the shaft  132  at a disk-like member  162 .  
         [0028]    The actuator  122  may be considered to include an actuator housing  170 , an actuator piston  172 , an actuator spring  174 , and an actuator cover  176 . The actuator housing  170 , in turn, may be unitarily (or otherwise integrally) formed from aluminum and may be considered to include an attachment portion  180  and a generally cylindrical portion  182  and defines a generally coaxial bore  184 . The bore  184  accommodates a sleeve  186 . The sleeve  186  snugly accommodates the shaft  132  of the valve body  120 . The actuator housing  170  also accommodates a pair of orifices  188  and  190  (FIG. 3). The orifices  188  and  190  straddle the bore  184  in this embodiment. The attachment portion  180  includes a pair of projections of  194  and  196 , which straddle the orifices  188  and  190 . The attachment portion  180  also defines respective lateral bores  198  and  200 , which are dimensioned to accommodate sleeves  202  and  204 . The sleeves  202  and  204  accommodate bolts (not shown) when the exhaust valve  102  is installed in the engine block  100 . The cylindrical portion  182  displays an outer surface  206  and a pair of lateral grooves  208  and  210  (not shown). The grooves  208  and  210  are dimensioned to accommodate the bolts extending through the sleeves  202  and  204 . The cylindrical portion  182  also defines a cavity  212  (FIG. 3) and an annular extension  214  therein. The extension  214  surrounds the bore  184  and extends into the cavity  212  from a front surface  215 . The cavity  212  is dimensioned to receive the actuator piston  172  therein. A rear rim  216  of the cylindrical portion  182  may accommodate three threaded bores therein (not shown).  
         [0029]    The actuator piston  172  displays a circumferential rim  220  and defines a pair of grooves  222  and  224  (FIG. 4). The grooves  222  and  224  accommodate a pair of rings  226  and  228 . The circumferential rim  220  and rings  226  and  228  are dimensioned so as to achieve a substantially air-tight seal when the actuator piston  172  is operably disposed in the cavity  212  of the actuator housing  170 . The piston  172  defines a generally axial bore  232  (FIG. 5). The front face of the piston  172  displays respective and annular inner and outer recessed surfaces  234  and  236 , an annular inner extension surface  238 , and an annular outer extension surface  240 . The inner extension surface  238  is dimensioned to receive an end of the shaft  132  snugly therewithin. The rear face of the piston  172  displays a recessed surface  244  and respective inner and outer extension surfaces  246  and  248  (FIG. 2). The inner extension surface  246  substantially surrounds the bore  232  in this embodiment. The spring  174  is dimensioned so that an end thereof fits around the inner extension surface  246  and is thereby held in place when the present exhaust valve is assembled.  
         [0030]    The actuator cover  176  (FIG. 5) is substantially unitary (or otherwise integral) in this embodiment, but may be considered to include a disk-like member  252  and an extension  254 . The member  252  displays a front surface  262  and defines holes  256 ,  258 , and  260 . The holes  256 ,  258 , and  260  substantially align with the threaded bores (discussed above) present proximate the rear rim  216  of the actuator housing  170 . The member  252  also defines a hole  264 . The hole  264  threadably accommodates a vent member  266 . In the embodiment depicted, the extension  254  extends rearwardly from the member  252 . An inner surface  268  of the extension  254  is dimensioned so as to substantially snugly accommodate in the spring  174 . When the present exhaust valve is assembled, the spring  174  abuttingly contacts the rear surface  270 .  
         [0031]    During assembly, the sleeves  186 ,  202 , and  204  may be pressed into respective bores  184 ,  198 , and  200 . A gasket  276  is then installed such that the gasket  276  contacts a front surface  278  of the attachment portion  180 . The gasket  276  has holes  280  and  282  accommodating the sleeves  202  and  204  and another hole  280  for accommodating the sleeve  186  and the projections  194  and  196 . The shaft  132  of the valve body  120  is extended through the sleeve  186  (the sleeve  186  having been pressed into the bore  184 ). The actuator piston  172  is then fixed to the shaft  132  by disposing the end of the shaft  132  within the inner extension surface  238  until an end surface  286  of the shaft  132  contacts the inner recessed surface  234  of the piston  172 . The piston  172  is then affixed to the shaft  132  by using a connector such as a machine screw  288 . The machine screw  288  is optionally extended through a washer  290 , then threaded into the bore  164  of the shaft  132 . A gasket  294  is then disposed to contact the front surface  262  of the actuator cover  176  such that holes  294 ,  296 , and  298  of the gasket  292  align with respective holes  256 ,  258 , and  260  of the actuator cover  176 . One end of the spring  174  is then disposed around the inner extension surface  246  of the piston  172 , such that the spring  174  contacts the recessed surface  244  thereof. The actuator cover  176  is then situated such that the other end of the spring  174  is disposed in the extension  254  and contacts the rear surface  270 . Assembly is completed by aligning the holes  256 ,  258 , and  260  with the holes proximate the rear rim  216  of the actuator housing  170  and threading connectors such as machine screws  300 ,  302 , and  304  into the threaded holes proximate the rear rim  216  of the actuator housing  170 . Components of the present exhaust valve have been made from aluminum. However, other satisfactory materials include titanium or steel ceramic. Satisfactory materials for the rings include Teflon®), iron, steel, aluminum, and other thermoplastics with the desired degree of tolerance to high temperatures and gas pressures.  
         [0032]    Referring now to FIGS. 1 and 2, the assembled exhaust valve  102  is installed in the engine block  100 . Installation is effected by inserting the valve insert  130  to the valve slot  110  of the engine block  100  and such that the slot  150  faces up, and such that the upper surface  136  contacts the block wall  104  of the engine block  100 . At this point, the front end upper surface  154  will conform to the contours of the cylinder wall  107 , the shaft  132  will be housed in a cylindrical enlargement  306  within the block wall  104 , and the gasket  276  will contact an outer surface  308  of the engine wall  104 . The exhaust valve  102  is then fixed to the engine block  100  by extending connectors such as machine screws  310  and  312  through the sleeves  202  and  204  (sleeves  202  and  204  having been pressed into bores  198  and  200 ) and threading the screws  310  and  312  (FIG. 3) into bores  314  and  316  (bores  314  and  316  being present in the block wall  104 ). One end of a piece of tubing (not shown) may be attached to the vent member  266  and the tubing routed away from the engine block  100 .  
         [0033]    When installed in a two-cycle engine, the present exhaust valve is operationally configured in a continuum between a fully extended position (FIG. 3) and a fully retracted position (FIG. 4). In the fully extended position, the spring  174  is minimally biased and presses the actuator piston  170  against the front surface  215  of the actuator housing cavity  212 . Also in the extended position, the front edge upper surface  154  substantially aligns with the cylinder wall  107 . In the fully retracted position, the valve insert  130  has been displaced away from the cylinder wall  107 , thereby displacing the actuator piston  172  toward the actuator cover  176  and compressing the spring  174 . In between the fully extended and retracted positions, the valve insert effects a continually changing effective exhaust port diameter in response to engine rpm by being displace in the continuum from the cylinder wall  107  to well away from the cylinder wall. The effective exhaust port diameter is at a minimum with the present valve insert is in the fully extended position and is at a maximum when the present valve insert is in the fully retracted position.  
         [0034]    When the engine on which the present exhaust valve has been installed is operating at a low rpm speed, the pressure exerted by exhaust gases is at a minimum and the valve insert  130  is in a fully extended position. As the engine is operated at higher rpm, the pressure from exhaust gases increases. The increased pressure forces the exhaust gases through a tunnel formed by the slot  150  and the upper wall of the exhaust port  108 , through the orifices  188  and  190 , and into the actuator housing cavity  212 . In the cavity  212  the exhaust gases exert pressure against the outer recessed surface  236  of the piston  172 . When the present exhaust valve is in the fully extended position, the exhaust gases initially contact only the outer recessed surface  236 . As the piston  172  becomes displaced backward, the exhaust pressure also exerts against the inner and outer extension surfaces  238  and  240  of the piston  172 . The effect of this progressive exhaust gas pressure on the surfaces of the piston  172  is that the piston  172  is initially displaced slowly, then more rapidly as greater surface area is exposed to the pressure exerted by the exhaust gas. Exhaust gas pressure forces the piston  172  toward the actuator cover  176  and compresses the spring  174 . The vent member  266  allows air in the cavity  212  between the piston  172  and the actuator cover  176  to be vented out as the spring  174  is compressed and admits air thereinto as the spring returns toward an unbiased position. At a given rpm, an equilibrium will be reached between the pressure exerted by exhaust gases on the piston  172  and the counter force exerted by the compressed spring  174 . The equilibrium will depend on the amount of exhaust gas pressure present, hence on the engine rpm at any given instant. When in the fully extended position, the front edge  144  of the valve insert  130  substantially aligns with the cylinder wall  107  and effectively reduces the diameter of the exhaust port to configure the exhaust port to an optimum diameter for low rpm. When in the fully retracted position, the valve insert  130  is displaced away from the cylinder wall, effectively maximizing the effective diameter of the exhaust port for high engine rpm. The presence of the slot  150  on the valve insert upper surface  136  more efficiently conducts cylinder pressure into the present exhaust valve actuator. Hence, the present exhaust valve is more sensitive to cylinder pressure and more quickly displaces the valve insert  130  in response to changing exhaust gas pressure from changing engine rpm. In addition to admitting exhaust gases into the actuator housing cavity  212 , the orifices  188  and  190  perform a buffering function as well. Because of the relatively small diameter of the orifices  188  and  190 , compressed gases are vented back into the exhaust port rather slowly, thereby allowing the valve insert to slowly displace toward the fully extended position. The position of the slot  150  (extending from upper surface  136 ) is advantageous over other valves of the prior art. The slot  150  receives the exhaust pressure directly from the cylinder  106  and does so at the earliest possible instant. Exhaust pressures of 20-25 pounds per square inch are delivered to the present exhaust valve bore at or near maximum rpm in most two-cycle engine bores. By contrast, slots of the prior art disposed on a lower surface of the valve insert or as a bore (totally defined within the valve insert) receive pressure only from the exhaust ports of these engines. Pressure from the exhaust port would only be expected to be 1-1½ pounds per square inch at or near maximum rpm. The present exhaust valve also requires an actuator spring  174  with a greater degree of bias to offset the greater forces produced by cylinder exhaust gas pressures. By contrast, the exhaust valves of the prior art would require springs with a lower degree of bias—due to the much lower gas pressures from exhaust ports. Because of the greater gas pressure (from the cylinder) utilized in the present exhaust valve and greater amount of offsetting forces generated by the springs, the present exhaust valve is more responsive to rapidly changing engine rpm, i.e., opening and closing more quickly.  
         [0035]    A person of ordinary skill in the art will recognize that the type and size of spring  174 , diameter of the orifices  188  and  190 , and the cross sectional dimension of the slot  150  can be altered to accommodate engines with differing rpm ranges. A person of ordinary skill in the art will also recognize that the sizes of the various components of the present exhaust valve can be altered to accommodate engines of differing sizes and configurations.  
         [0036]    A person of ordinary skill in the art will readily appreciate that individual components shown on various embodiments of the present invention are interchangeable and may be added or interchanged on other embodiments without departing from the spirit and scope of this invention and without undue experimentation.  
         [0037]    Because numerous modifications of this invention may be made without departing from the spirit thereof, the scope of the invention is not to be limited to the embodiments illustrated and described. Rather, the scope of the invention is to be determined by the appended claims and their equivalents.