Abstract:
A breather valve and arrangement for an internal combustion engine, having a scavenge hole that is open for a relatively long period of time relative to piston travel. Scavenge hole preferably subtends an angle of between 20° and 150°, and preferably is open from between 30° and 135° of piston travel. A method of replacing an existing breather valve with this novel breather valve is also described. Other arrangements for achieving the advantages of the novel breather valve are also described.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to breather valves used in internal combustion engines, and more particularly to an improved breather valve and breather valve arrangement intended for motorcycle engines, and to a method of replacing the breather valve in such engines with the improved breather valve. 
     BACKGROUND OF THE INVENTION 
     Rotary breather valves for motorcycle engines have been used for many years. The purpose of a breather valve is generally twofold. First, it expels air and oil from the crank case, on the down stroke of the pistons, to the gear case where the oil lubricates various gears and other parts. Second, it draws oil from the bottom of the oil separating pocket (also sometimes referred to as the “settling pocket”) in the bottom of the gear case. 
     Regarding the second purpose, problems arise when the engine is modified to have a larger displacement. The higher horsepower engine results in, among other things, more oil being expelled from the crank case into the gear case (and ultimately the gear case oil separating pocket). If not removed (“scavenged”) by the breather valve, this excess oil will leave the engine through the air cleaner system, which is referred to as oil carryover (sometimes also referred to as “blowby” or “puking”). Oil carryover contaminates the air filter and thereby reduces its effectiveness, undesirably enriches the fuel coming into the engine, and pollutes the environment. Excess oil in the gear case can also reduce horsepower. 
     It can be seen that a new breather valve is needed that improves the scavenging of oil from the oil separating pocket of the gear case. 
     SUMMARY OF THE INVENTION 
     The present invention can be practiced in a number of ways, including by replacing an existing breather valve with one for example like that described herein, by modifying the breather valve cavity (into which the breather valve is inserted) in an existing engine, or by constructing either or both the breather valve and the engine cavity, in an existing or new engine, so that the advantages of the present invention are obtained. 
     In one aspect of the apparatus of the present invention, a breather valve comprises a gear proximate a first end for engagement with a corresponding gear in the engine, and a generally cylindrical body fixed to and extending from the gear. The cylindrical body has an open end opposite the gear for drawing oil and air from the engine crank case into a breather valve interior. A first arcuate port in the cylindrical body is for registration with a corresponding opening in the engine to draw oil and air from the breather valve interior into the engine gear case. The first arcuate port extends substantially across the middle portion of the cylindrical body and subtends an angle between 70° and 270°. A second arcuate port in a cylindrical body is for registration with a second corresponding opening in the engine to draw oil from the gear case oil separating pocket into the breather valve interior. The second arcuate port is positioned between the first arcuate port and a second end of the breather valve, has a center offset circumferentially from the center of the first arcuate port, and subtends an angle between 20° and 150°. 
     In another aspect of the apparatus of the present invention, a breather valve arrangement comprises a breather valve including a gear engaging a corresponding gear in the engine, a cylindrical body having an open end opposite the gear, and a port formed in the body for drawing oil from the gear case oil separating pocket into a breather valve interior. Structure in the engine around the breather valve defines an opening for registration with the breather valve port. The breather valve and engine structure are constructed and arranged, and the breather valve port and corresponding opening are configured and sized, such that the port and corresponding opening are in at least partial registration for a total of between 30° and 135° of piston travel. 
     In one aspect of the method of the present invention, a method of improving the removal of oil from the gear case oil separating pocket comprises removing a first breather valve from the engine having a scavenge opening that subtends an angle of less than 20°, providing a second breather valve having a scavenge opening that subtends an angle of between 20° and 150°, and installing the second breather valve into the engine so that the second scavenge opening draws oil from the separating pocket for a longer period of time. 
     These and other advantages and features of novelty which characterize the invention are pointed out with particularly in the claims annexed hereto. However, for a better understanding of the invention and its advantages, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, wherein like reference numerals and letters refer to corresponding parts throughout the various figures: 
     FIG. 1 is a diagrammatic view of a motorcycle engine depicting the breather valve operation; 
     FIG. 2 is a plan view of a breather valve according to the present invention; 
     FIG. 3 is a cross-sectional view of the breather valve of FIG. 2, shown in the breather cavity and in engagement with the driving gear; 
     FIG. 4 is a cross-sectional view of the breather valve of FIG.  2  and the breather cavity, showing registration between the breather valve window and the corresponding opening in the engine; 
     FIG. 5 is a cross-sectional view of the breather valve of FIG. 2, taken through the scavenge hole; and 
     FIG. 6 is a graph of breather cavity scavenge hole vacuum, comparing an improved breather valve according to the present invention with a prior art breather valve. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 3, rotary breather valve  10  is shown installed in a motorcycle engine  30  within crank case  33  and gear case  34 . FIG. 1 diagramatically depicts the operation of breather valve  10  and the relevant flow of oil and air through the engine. Oil pump  32  pumps oil from oil tank  31  into different areas of the engine, including to pistons  35 . Most of that oil drains through gravity into the crank case cavity  33 . Some of the oil O drains into the gear case cavity  34 , as shown. Oil pump  32  draws the oil O from there and returns it to oil tank  31 . 
     Gear case  34  normally contains a mixture of air and oil. Much of that mixture A/O travels through a passage  53  in the gear case cover and into oil separating chamber  50 . From there, the oil O is removed from chamber  50  by breather valve  10  as will be discussed below, and the air is removed through passage  54  to air cleaner  38 . As discussed above, if breather valve  10  does not sufficiently remove oil from separating chamber  50 , this results in many adverse consequences. 
     Breather valve  10  rotates in timed relation to piston travel. Crank shaft pinion gear  39  engages and rotates cam gear  26  (and shaft  28 ) which in turn engages and rotates gear  12  of breather valve  10 . 
     Breather valve  10  includes gear  12 , cylindrical body or drum  14  and screen  17 . While gear  12  and cylindrical body  14  are formed as a single part in the preferred embodiment, as shown in FIG. 3, they could be two or more separate parts connected together within the principles of the invention. Two openings are formed in cylindrical body  14 , window  16  and scavenge hole  18 , that perform different functions (second hole  19  shown in the drawings will not be discussed herein because it is not relevant to the invention and typically serves no function). 
     Window  16  moves oil and air from crank case cavity  33  to gear case cavity  34 . As air pressure builds up in crank case cavity  33  upon downstroke of pistons  35  (moving from top dead center (“TDC”)  36  to bottom dead center (“BDC”)  37 ), air and oil A/O travels into breather valve interior  11  through open end  15  and then out window  16 , as depicted in FIGS. 1 and 4. Metal screen  17 , commonly used in breather valves, stops debris like metal particles from entering gear case  34 , and turns the oil droplets into a fine mist to better coat the parts in gear case  34 . Window  16  is at this time registering with corresponding window  22  in breather cavity  20 , as shown in FIG. 4, in timed relation to piston travel. In the preferred embodiment, window  16  begins to open at 17° after TDC and is fully closed at 82° after BDC (relative to front piston travel). Window  16  preferably subtends an angle β of approximately 170°, although a sweep anywhere between 70° and 270° could be acceptable. Window  16  is shaped as an arcuate port formed in cylindrical body  14  and extends substantially across the middle portion of cylindrical body  14 . 
     Scavenge hole  18  is for the purpose of removing oil from separating pocket  51  of oil separating chamber  50  in gear case  34 . Prior art breather valves, such as that shown and described in U.S. Pat. No. 4,869,213, have a small circular scavenge hole that does not draw enough oil out of the gear case for larger displacement engines. The stock Harley-Davidson® breather valve that has been in use for many years has only a diameter of about 0.17 inches, subtends an angle of about 16°, and is only open for 29° of piston travel, typically open at 64° before TDC and closed at 35° before TDC. The much larger elongated scavenge hole  18  of the preferred breather valve  10  results in a much stronger vacuum draw than the prior art stock breather valve, as shown in FIG. 6, showing an improvement in testing of over 50% on average and as high as about 100% on the high end of the RPM range. 
     Scavenge hole  18  functions as follows. As pistons  35  travel from BDC to TDC, and with window  16  closed at that time, vacuum builds up in crank case cavity  33  and therefore in breather valve interior  11  via open end  15 . Preferably near maximum vacuum, scavenge hole  18  begins to open by engagement with corresponding circular hole  24  in breather cavity  20 , as shown in FIGS. 1 and 3. Referring to FIG. 1, the vacuum in valve interior  11  then draws oil O from separating pocket  51 , through passage  52 , corresponding hole  24  and scavenge hole  18 , and into interior  11 . Upon the next opening of window  16 , that oil is then expelled, along with air and oil from crank case  33 , into gear case cavity  34 , as discussed above. 
     In the preferred breather valve  10 , scavenge hole  18  is an arcuate port that is shaped obround, with straight sides and semicircular ends. It is 0.48 inches long, 0.17 inches wide, subtends an angle α of 49°  51 ′ (as shown in FIG.  5 ), and the radii of curvature of its ends is 0.085 inches. Scavenge hole  18  preferably begins to open at 45° before TDC and is fully closed at 20° after TDC, for a total piston travel of 65°. The center of scavenge hole  18  is offset from the center of window  16  by 126° on cylindrical body  14 . 
     It will be understood that many of these parameters can be varied fairly significantly within the principles of the invention. For example, scavenge hole  18  could subtend an angle anywhere from 20° to 150° and obtain advantages relative to the prior art. Similarly, advantages would be obtained if the amount of time scavenge hole  18  is open is anywhere between 30° and 135° of total piston travel. 
     It will also be understood that a variety of breather valve/breather cavity configurations could achieve the advantages herein within the principles of the invention. For example, corresponding hole  24  could be made larger instead of scavenge hole  18 , or both could be made larger, in order to achieve a longer duration of scavenge hole open time and therefore higher vacuum and better oil scavenging from the separating pocket. 
     It is to be under that, even though numerous specific characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts, within the principles of the invention to the full extent indicated by the broad general meanings of the terms in which the appended claims are expressed.