EXHAUST TIMING CONTROL APPARATUS

Abstract: An exhaust timing control apparatus in a two-cycle engine of the type having one or more exhaust ports extending outwardly from the cylinder. A valve body (19) is pivotally mounted within the exhaust passage in a recess (17) specifically provided therefor. The valve body has a control surface (22) approaching the cylinder to define an apparent upper timing edge of the exhaust port. Holes (25) are provided through the valve body for flow to operate to inhibit the build up of carbon deposits which could affect the operation of the valve. Edges may also be provided on the valve body which cooperate with the walls of the recess in the exhaust passage to knock off carbon build up, for it to be conveyed through the exhaust pipe and out of the system.

Description: This invention relates to timing control apparatus for an exhaust port of a two-cycle engine. Two-cycle engines typically employ the upper edge of a piston as the means for timing the opening and closing of an exhaust port. In such an engine, the exhaust passage may be tuned such that a reflected wave of pressure initiated by the opening of the exhaust port can force unburned air fuel mixture, trailing the exhaust gases through the exhaust passage, back into the cylinder just prior to closure of the exhaust port. This tuning is specifically effective over a limited range of engine speeds. Often power can drop off remarkably when the engine speed does not fall within the tuned range. To broaden the effective power range for two-cycle engines, exhaust timing control devices have been employed which provide an apparent upper timing edge to the exhaust port that may be moved upwardly or downwardly depending on engine speed. In this way, power can be realized across a broader range of engine speeds. As the timing for both the opening and closing of the exhaust port is changed through movement of a valve mechanism, the timing can better employ the pressure wave in the exhaust passage. A difficulty which has been encountered with such timing mechanisms located within the exhaust passages of a two-cycle engine is that carbon can build up and prevent the proper actuation of the timing device. This can eventually result in a totally inoperative condition. According to the present invention there is provided, in a two-cycle engine cylinder having an exhaust port and passage extending from the sidewall of the cylinder, an exhaust timing control apparatus comprising a valve body pivotally mounted about a pivot axis in the exhaust passage and extending to a control surface at the exhaust port to define an apparent upper timing edge of the exhaust port, said valve body having at least one hole extending through said body at a location on said body between said pivot axis and said control surface. The hole or holes which extend through the valve body enable flow in the exhaust passage to move about the valve and advantageously therethrough, to rid the valve of carbon which might otherwise accumulate and interfere with valve operation. A variety of hole arrangements are proposed in several embodiments, including holes extending directly through the main portion of the valve body which holes may be tapered through a portion of their length. Holes may also be employed extending through an upstanding ridge adjacent the control surface so as to provide flow into the area above the valve body. Furthermore, strategically placed ridges may be employed which act to dislodge carbon from locations of possible interference. Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which;- Fig. 1 is a cross-sectional elevation of a two-cycle engine employing an exhaust timing control apparatus of the present invention; Fig. 2 is a cross-sectional plan view taken along line II-II of Fig. 1; Fig. 3 is an oblique view of a valve body of the embodiment of Figs. 1 and 2; Fig. 4 is a plan view similar to the view of Fig. 2 illustrating an alternate hole pattern 1 in the valve body thereof; Fig. 5 is a cross-sectional plan view as in Fig. 4 illustrating yet another hole pattern; Fig. 6 is an oblique view illustrating yet another hole pattern; Fig. 7 is a cross-sectional elevation of a two-cycle engine illustrating another embodiment of the present invention; Fig. 8 is a plan view in cross-section of the device of Fig. 7; Fig. 9 is an oblique view of the valve body of the device of Figs. 7 and 8; Fig. 10 is a cross-sectional elevation of a two-cycle engine illustrating another embodiment of the present invention; and Fig. 11 is a cross-sectional plan view of the embodiment of Fig. 10. Figs. 1, 2 and 3 illustrate a first embodiment of the present invention. The two-cycle engine illustrated includes a cylinder block 10 having a cylinder head 12 and a piston 13 slidably operating within the cylinder. Scavenging passages 14 and an exhaust passage 15 extend from the cylinder. A reinforcing rib 16 extends parallel to the axis of the cylinder and is disposed in the vicinity of the exhaust port 15a of the exhaust passage 15 to divide it into two openings. The rib 16 has the function of preventing a piston ring from spreading out in the radial direction so as to interfere with the upper or lower edge of the exhaust port 15a. Further, the rib 16 has the function of reinforcing the portion of the cylinder block 10 in the vicinity of the openings of the exhaust passage 15. A recessed portion 17 is provided in the upper portion of the exhaust passage 15 for accommo­ dating the exhaust timing control apparatus. In the recessed portion 17, a shaft 18 is rotatably provided which lies in a plane extending perpendi­ cularly to the center line of the cylinder. The center portion of the shaft 18 is shaped in a square cross-section to avoid relative rotation with the valve body carried thereon. Two elements of a valve body 9 for controlling the exhaust timing are mounted on the shaft 18 so as to be disposed on opposite sides of the rib 16. Ring grooves 18a are formed to either side of the valve body 19 on the shaft 18 in the support portion thereof. The two elements of the valve body 19 are symmetrical with each other. Each element has a shaft bearing portion 20 through which the shaft 18 is inserted. A plate-like body portion 21 extends from the bearing portion 20. A control surface 22 is provided at the opposite end of the valve body 19 from the bearing portion 20. The control surface 22 has a curvature which is nearly equal to that of the inner surface of the cylinder such that it approximates a segment of the cylinder when in position. An upwardly extending ridge 24 is provided on the upper portion of the control surface 22. The ridge 24 is connected to the upper edge of the control surface 22 and has an inclined surface 23, inclined upwardly and rearwardly from the control surface 22. The plate-like body portion 21 of the valve body 19 is provided with a plurality of holes 25. The holes 25 extend through the body of the valve from adjacent the recessed portion 17 of the passage 5 to communicate with the main portion of the exhaust passage. The upper portion of each of the holes 25 is chamfered to about twice the diameter of the main cylindrical portion of each hole 25. Thus, an inclined surface is formed. The arrangement of the valve body 19 in the cylinder block 10 is such that a small clearance x is provided between the control surface 22 and a projection of the wall of the cylinder. The surface of the recessed portion 17 has a shape which generally corresponds to the upper surface of the respective valve bodies 19. A first recess 7a, triangular in cross-section, is arranged to accommodae the upwardly extending ridges 24. A flat portion 17b accommodates the plate-like body portions 21. A curved portion 17c receives the bearing portions 20. The valve body 19 is arranged to be operated by a drive mechanism 30 through the shaft 18 in accordance with the rotational speed of the engine. The valve body 19, the shaft 18 and the drive mechanism 30 make up an exhaust timing control apparatus for opening and closing the upper portions of the respective halves of the exhaust port 15a. The drive mechanism 30, as shown in Fig. 2, includes a wire guide 31 coupled with one end of the shaft 18 and extending out of the cylinder block 10. A motor (not shown) may be connected to the wire guide 31 through a wire 32. A controller for rever­ sibly rotating the motor in accordance with the rotational speed of the engine would be employed in such an instance. The portion of the shaft 18 extending out of the cylinder block 10 and the wire guide 31 are covered by a case 33 mounted on the cylinder block 10. A case cover 34 is screwed onto the wire case 33. A bushing 35, a positioning retainer 36 and a sealing member 37 are disposed on one end of the shaft 18. Passages R represent cooling water flow passages for cooling the engine. In operation, when the engine is operated at low speeds, the shaft 18 is rotated to swing the valve body 19 downwardly such that it projects into the exhaust passage 15. By the movement of the valve body 19, the control surface 22 is positioned in the middle of the upper portion of the port 15a to lower the effective upper timing edge of the exhaust port by an apparent distance L. Accor­ dingly, as the control surface 22 is lowered by the distance L, the exhaust port 15a is opened later and closed earlier by the working piston. This adjustment aids in timing the closing of the exhaust valve to the return of the exhaust pressure wave reflected within the exhaust passage. Thus, engine efficiency can be improved at low speeds. With the engine running at high speeds, the valve body 19 is moved upwardly from the main path of the exhaust passage. Thus, the exhaust port a is opened earlier and closed later by the working piston. This allows a reflected wave to again improve efficiency at high speeds. A variety of controls including a two position control or a continuous control might be employed with the foregoing arrangement. Since the holes 25 are provided through the valve body 19, exhaust gases can pass through the holes 25 as shown by the arrows in Fig. 1. This provides flow through the area between the upper surface of the valve body 19 and the surfaces of the accommodating recessed portion 17. Accordingly, carbon deposits are minimized between the valve body 19 and the recessed portions 17. If carbon does proceed to develop, the small surface areas around the through holes 25, such as ridges 25b as seen in Fig. 6, can impact on the deposits and prevent further accumulation of carbon. Again, the flow through the holes 25 can then draw off the carbon from these problem areas. It has been found that the holes 25 do not appear to interfere with the operation and effective­ ness of the valve body 19. At the same time, the build up of carbon is reduced. As can be seen from the embodiments, several hole shapes may be provided without affecting the operability thereof. Elongate holes in plan with major axes in a variety of orientations, such as seen in Figs. 4 and 5, may be employed. Further, as any hole is helpful, a single hole may be employed. Fig. 6 illustrates yet another embodiment with rectangular holes 25 having the major axis extending along the lengthwise direction of the valve body. With the inclined surfaces illustrated therein, the whole upper surface of the valve body 19 is covered with the inclined surfaces 25a, with the exception of the ridges 25b. Looking next to the embodiment of Figs. 7, 8 and 9, the same reference numerals are applied to each embodiment where identical or equivalent components are illustrated, and repetitive description of such components will be minimized. Directing attention to the shaft bearing portion 19a of the valve body 19, an end surface 19c is formed on the upper surface of the shaft bearing portion 19a and extends to the main body portion 19b. The end surface 19c rises steeply in a substantially perpendicular manner from the body portion 19b. Thereby, an edge F is formed between the end surface 19c and the upper portion of the shaft bearing portion 19a. The edge P functions to work on carbon deposited on the upper surface 17c of the recessed portion 17 whenever the valve body 19 is actuated. The valve body portion 19b is provided with a upwardly extending ridge 24. The end surface of the ridge 24 is formed to have a curvature nearly equal to that of the inner surface of the cylinder for the purpose of matching with that inner surface. A plurality of ridges 40 are formed on the upper surface of the valve body portion 19b, parallel to the shaft bearing portion 19a. Holes 25 extend through the body portion 19b and are arranged between adjacent ridges 40. The holes 25 and the components of the valve body surfaces operate in cooperation with the contoured recess area in a manner similar to that of the prior embodiments in removing carbon from the valve apparatus. Furthermore, the valve apparatus also works as described with regard to the prior embodiment. Turning next to the embodiment of Figs. 10 and 11, a similar engine is illustrated which, in general, need not be described further. Again, corresponding reference numerals have been employed in this embodiment. Holes 42 extend through the upwardly extending ridge from the area adjacent the control surface 22 to above the main body of the valve body 19. The relative size of these holes 42 is dependent on the effect at low engine speeds. The effect of the holes 42 on reducing carbon build up is achieved by the flow of gas associated with the exhaust passage. In this way, carbon may be ejected into the exhaust passage through gaps about the valve body 19, as a result of the pressure created through the holes 42. Naturally, holes such as employed in the first embodiment herein may also be incorporated in this embodiment. It is to be clearly understood that there are no particular features of the foregoing speci­ fication, or of any claims appended hereto, which are at present regarded as being essential to the performance of the present invention, and that any one or more of such feature or combinations thereof may therefore be included in, added to, omitted from or deleted from any of such claims if and when amended during the prosecution of this application or in the filing or prosecution of any divisional application based thereon.

Claims: 1. In a two-cycle engine cylinder having an exhaust port (15a) and passage (15) extending from the sidewall of the cylinder, an exhaust timing control apparatus comprising a valve body pivotally mounted about a pivot axis in the exhaust passage and extending to a control surface (22) at the exhaust port to define an apparent upper timing edge of the exhaust port, said valve body having at least one hole (25) extending through said body at a location on said body between said pivot axis and said control surface. 2. Apparatus as claimed in claim 1, wherein the or each said hole (25) extends through said valve body (19) in a direction generally parallel to the axis of the cylinder. 3. Apparatus as claimed in claim 1 or 2, wherein there are a plurality of said holes. 4. Apparatus as claimed in any preceding claim, wherein the or each said hole is elongate in cross-­ section. 5. Apparatus as claimed in any preceding claim, wherein the or each said hole includes a first portion toward the upper wall of the exhaust passage having a tapered cross-section tapering outwardly toward the upper wall of the exhaust passage, and a second portion of cylindrical cross-section extending from said tapered portion through the remainder of said valve body. 6. Apparatus as claimed in any preceding claim, wherein the upper surface of the valve body adjacent the pivot axis inlcudes an edge portion (19c) extending parallel to the pivot axis and extending to adjacent the upper surface of the exhaust passage. 7. Apparatus as claimed in any of claims 1 to 4, wherein said valve body includes an upwardly extending ridge (24) adjacent said control surface (22) and an upper surface adjacent said upwardly extending ridge recessed below said ridge, the or each said hole (42) extending through said upwardly extending ridge from adjacent said control surface to above said upper surface.

Inventors: IKEDA, TSUGIO, OKAZAKI, KOUJI, TOTTORI, TAKUMI, YAMAMOTO, HITOSHI
Applicants: HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1986
Main classification: F02D13
IPC codes: F02D13, F02B75