US3815559A

US3815559A - Crankcase valve structure for a two-cycle engine

Info

Publication number: US3815559A
Application number: US00281036A
Authority: US
Inventors: R Anderson
Original assignee: Brunswick Corp
Current assignee: Brunswick Corp
Priority date: 1972-08-16
Filing date: 1972-08-16
Publication date: 1974-06-11
Anticipated expiration: 1991-06-11
Also published as: FR2196665A5; BE803662A

Abstract

An induction reed valve includes a valve block with a flat end face having ports. A bulb type reed is secured overlying each port. Each reed has an outer closure portion integrally interconnected to a common mounting strip by an hourglassshaped connecting portion defining a reduced width thickness within its length and thereby reduces the spring constant and the effects of inertia as the reed moves. A stop arm is located outwardly slightly in excess of the normal full position.

Description

United States Patent [191 Anderson CRANKCASE VALVE STRUCTURE FOR A TWO-CYCLE ENGINE [75] Inventor: Ronald R. Anderson, Winneconne,

Wis.

[73] Ass'ignee: Brunswick Corporation, Chicago,

22 Filed: Aug, 16, 1972 [2]] Appl. No.: 281,036

52 US. Cl 123/73 v 511 m. c1. r021 33/04 [581 Field of Search 123/73 v; 137/5253 [56] References Cited UNITED STATES PATENTS 2,689,552 9/1954 Kiekhaefer ,.123/73v [451 June 11, 1974 l/l957 Morgenroth l23/73 V. 11/1961 Kauffman 123/73 V Primary Examiner-Laurence M. Goodridge Attorney, Agent, or Firm-Andrus, Sceales, Starke & Sawall [5 7] ABSTRACT An induction reed valve includes a valve block with a flat end face having ports. A bulb type reed is secured overlying each port. Each reed has an outer closure portion integrally interconnected to a common mounting strip by an hourglassshaped connecting portion defining a reduced width thickness withinits length and thereby reduces the spring constant and the effects of [inertia as the reed moves. A stop arm is located outwardly slightly in excess of the normal full position.

10 Claims, 5 Drawing Figures CRANKCASE VALVE STRUCTURE FOR A 'IVVO-CYCLE ENGINE BACKGROUND OF THE INVENTION This invention relates to a two-cycle engine crankcase valve structure and particularly to an induction type reed valve.

Two-cycle internal combustion engines may, advantageously, be'constructed employing the crankcase as a pressurizing fuel and, mixture transfer source. Such systems are widely employed, for example, in internal two-cycle combustion engines for outboard motors and the like. A reed valve unit interconnects the crankcase chambers to the source of the fuel-air mixture such as the carburetor and is pressure actuated to selectively introduce the fuel-air mixtureinto the crankcase for transfer to the cyiindersrAs the piston unit moves outwardly, a vacuum is created within the corresponding crankcase which causes the reed valve to open and introduce the air-fuel mixture into the'crankcase. As-the piston moves in the opposite direction toward the crankcase, a positive pressure is created within the crankcase which closes the reed valve and transfers the fuel into the appropriate cylinder as the piston uncovers transfer and scavenging ports. Generally, thereed valve structure-includes a plurality of openings with a corresponding plurality of individual valve reeds overlying the individual openings for simultaneous opening and closing. Each of the individual reeds consist of a flexible thin spring steel member which is secured flatwiseadjacent one end and extends outwardly therefrom in overlaping overlying relationship to a corresponding valve port or hole. The reeds are formed as extremely flat members lying adjacent to and in overlapping closing relationship to the reed block. A reed back-stop member will normally be provided to limit the opening of the reed valve under the pressure of the piston movement. Generally, the reed valves have been of a stri pdike configruation with a relatively narrow securement end portion and a laterally increasing dimension in a linear or straight line manner from the secured end to the outermost unsecured or closure end portion for purposes of distributing the stresses evenly throughout the length of the reed, for example, as disclosed in US. Pat. Nos. 2,669,979, 2,706,972 and 3,541,657. The multiple openings establish a relatively large flow area and provide for the rapid and sufficient transfer of fuel into the crankcase to permit maximum filling of the cylinder. A plurality of openings are employed as it is not practical to have a single large reed valve.

For optimum operation, the reed valve should open and remain open during the complete intake period in order to establish maximum transfer of fuel into the crankcase. Applicant considered use of a relatively thin reed to increase the opening rate and to reduce the tendency to rebound and thereby increase the engine horsepower. Although an increased power output was obtained, Applicant found this resulted in a significant increase in reed failure. Thus, the conventional reed made-of suitable spring steel is 0.008 inch thick. Reducing the thickness of the reed to 0.007 inches, resulted in both a very significant increase in horsepower output and in reed failure. It appeared that some form of self-destruction was associated with the vibrating characteristic. However, analysis indicated that in fact the thicker reed vibrated at its natural frequency over the normal operating range'of 4,000 RPM to 5,800 RPM while the thinner reed did not in fact vibrate at its natural frequency. Applicant thus found that failure was not theresult of a natural frequency vibration characteristic but rather the result of the stress that was developed within the reed. The static stress within-the spring would in fact be less in the thinner reedJThe outer fibers of a relatively thin reed are stretched less when opened to a maximum position than those of the thicker reed and, consequently, the static stresses should be correspondingly less. The impact stresses of the reed resulting from the striking of the reed against the valve block upon closing, or the stop upon opening, therefore appeared to constitute a source of failure. It was this analysis which led to the present invention.

SUMMARY OF THE PRESENT INVENTION The present invention provides an induction type,

reed valve having an improved reed of a minimum thickness. The reed of the present invention is generally of a bulb type configuration including an outer closure portion integrally interconnected to 'a mounting means by a connecting portion which has a reduced thickness within its length and thereby reducesthe spring constant and the effects of inertia as the reed moves. Further, the stop member is located outwardly slightly in excess of the normal position which allows the full open position for amaximum period without creating damaging stresses within the reed member. The reduced connecting neck portion is, in a preferred and particularly novel construction, a generally hourshaped junction having curved sidewalls between the closure portion and the mounting means. Applicant has found that this invention produces a valve reed which will provide a characteristic closely approximating that of the 0.007 inch thick reed. In particular, Applicant has found that the present invention. provides a valve which may be constructed of a spring metal of the order of 0.008 inches thickness-.-

BRIEF DESCRIPTION OF THE DRAWING .The drawing furnished herewith illustrates a pre-' ferred constructionof the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the drawing and description thereof;

In the drawing: v

FIG. 1 is a cross section of a two-cycle alternate firing two cylinder engine with a crankcase induction valve constructed in accordance with the present invention;

FIG. 2 is a sectional view taken on line 22 of FIG. 1 and showing the valve block incorporating the improved valve reed units constructed inaccordance with the invention;

FIG. 3 is an enlarged plan view of a section of a reed shown in FIGS. ,1 and 2 and clearly illustrating the construction of the'present inventionj v FIG. 4 is an enlarged fragmentary vertical section showing the position of a reedvalve moving between an opened and closed position; and

FIG. 5 is a set of characteristic curves illustrating the operating characteristic of reeds in accordance with this invention and other reed forms. I

DESCRIPTION OF THE ILLUSTRATED v EMBODIMENT Referring to the drawing and particularly to FIG. 1, a two-cycle engine suitable for outboard motor units and the like is shown. The engine includes a cylinder block 1 with an interconnected crankcase 2 with a transverse plane passing through the axis of the engine crankshaft. A crankschaft 3 is supported at each end in suitable bearing assemblies 4 and 5 which also serve to close the opposite ends of the openings through which the crankcase shaft passes. The two cylinder engine shown includes a pair of cylinder bores 6 within the cylinder block 1. The cylinder bores 6 open into the crankcase member 2 and are interconnected in a wellknown manner. A pair of similar pistons 7 are slidably located within the cylinderbores 6 and similarly connected to the crankshaft 3 with the crank throws oppositely spaced by 180 with respect to the crankshaft such that the pistons 7 reciprocate in opposite direction for alternate firing with each 180 of crankshaft rotation, in accordance with well-known constructions. The central portion of the crankcase 2 is divided into a pair of individual chambers 8 and9 by an intermediate combination bearing and valve block 10 secured in position between the crankcase member 2 and the engine block 1. The individual crankcase chambers 8 and 9 are thus in alignment with the respective cylinder bores 6. The combined bearing and valve block 10 is provided with a peripheral intake port 11 aligned with a transfer port 12 in the crankcase, generally in accordance with the structure of US. Pat. No. 2,669,979. A carburetor 13 or other fuel source is secured in overlying relationship to the transfer port 12 to a fuel mixture from a suitable source into the valve block 10. The intake port 11 extends circumferentially about the valve block 10 which is provided with opposite end face openings or ports 14 for transfer of the fuel mixture into the respective crankcase chambers 8 and 9. Reed valve membersl5 and i6, particularly constructed in accordance with the teaching-of the present invention, are secured to the end faces in overlying relationship to the ports 14 to control the transfer of the fuel mixture alternately to the chambers. Once introduced into the chambers '8 and 9, the fuel mixture is automatically transfered to the cylinders through the usual sidewall passageway and port 17 in the respective portions of the cylinder block 1. Exhaust ports 18 are provided on the opposite wall of the corresponding cylinder bore, with the respective port's correspondingly controlled by the position of the piston 7. The ports 17 and 18 are closed during the compression and firing of the power stroke of the piston 7 and are appropriately opened during the exhaust and charge stroke to permit exhaust of the burnt mixture and the introducing of a new charge.

Reed members and 16 are correspondingly constructed of a suitable flexible, thin, stainless steel and reed member 15 is described in detail with corresponding primed numbers employed to identify the correponding elements of reed member 16.

Referring particularly to FIGS. 2 4, the reed member 15 includes an individual leaf spring reed 19 for each of the ports 14 interconnected to a common annular mounting strip 20. The mounting strip 20 is mounted adjacent to the crankshaft 3 by suitable interconnecting mounting screws 21 and each of the leaf spring reeds 19 extend generally radially into overlying relationship to the valve ports. g

In accordance with the present invention, each of the reeds 19 includes an outer circular closure portion 22 which is spaced from the mounting strip 20 and is integrally connected thereto by a significantly reduced neck or connecting portion 23 extending therebetween. The outer closure portion 22 is generally a cylindrical or circular member which will completely cover and similarly overlap theouter edges of each round port 14. The connecting portions 23 are generally integral hourglass shaped with correspondingly curved circular edges 23a defining a similar connection to closure portion 23 and the strip 20. This reed member is conveniently formed by a stamping process with the neck portion 23 formed by oppositely disposed circular cut out portions with a significantly smaller radius than the closure portion to define a relatively small similar interconnection to the mounting strip. The reed member 15 is formed of the usual leaf spring material which has been widely employed in reed type valves.

A multiple armed reed stop 24 issecured in overlapping relationship to the reed unit 15 and includes a plurality of arms 25 which extend outwardly with each individual arm 25 overlying and aligned with a reed '19. Each of the arms 25 is similarly bent or curved outwardly along a predetermined curvature. Applicant has found that the stop arms 25 are preferably located to be spaced slightly outwardly of the normal maximum movement of the associated reed 19, as shown in full line illustration at 26 in FIG. 4. The stop arms 25 are located within the elastic limits of the reeds and pre- 'vent extraordinary or exceptional outward deflection without creating interengagement with the normal reed movement. Further, if desired, the stop arms 25 can advantageously be provided with a resilient cover 27 such that any engagement is damped 'as'a result of the resiliency of the cover. The'valve block may be similarly coveredto dampen the stress as the reeds close.

In the drawing, FIG. 5 is a set of characteristic curves showing the horsepower on the vertical axis versus the speed of an engine in revolutions per minute on the horizontal axis for various reeds. The curves were obtained from a production type engine employed in the Merc I400 manufactured and sold by the Marine Division of Brunswick Corporation. Curve 28 is for a conventional 0.008 thickness reed. Reducing the thickness of the reed to 0.007 inches results in the movement of the curve as at 30. The curve closely follows the 0.008 thickness reed curve up to 4,500RPM. Thereafter, the

thinner reed continues upwardly to a significantly.

higher horsepower at 5,500 RPM, at which point it approximately levels off. Applicant has found that this type of a reed, however, creates severe breakage problems at the higher speed. By employinga corresponding 0.008 thickness with the necked down construction in accordance with the present invention, a characteris- I 0.007 inch thickness reed is essentially duplicated with the 0.008 inch reed of the present invention but without the horsepower loss characteristics or' the reed breakage.

The present invention thus provides a readily constructed reed valve Construction which will produce highly satisfactory and improved operating characteristics in a simple and inexpensive manner.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims, particularlypoin'ting out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

l. A crankcase induction valve for a two-cycle engine employing a valve block means adapted to be mounted within an engine crankcase and having an induction passageway means connected to a series of port means in a flat face of the block means, and wherein a' series of flexible reeds are secured against the face of the block means and extend circumferentially into a normally seated position over said port means to close the latter, said reeds having an outer'closure portion essentially corresponding to the opening of the ports and located in overlying covering relation to saidports and connected to an inner securement portion by a connecting portion, said connecting portion including a reduced width substantially less than the width of said closure portion and said securement portion and located intermediate the closure and securement portions.

2. The crankcase valve of claim 1 wherein said plurality of valve reeds are connected in common to an inner mounting strip and formed of a uniform thickness and said outer port closure portions being generally circular disc-like members disposed in circumferentially spaced relation and said connecting portion being generally hourglass shaped with curved edges extending between the closure portion and the strip.

3. The crankcase valve apparatus of claim 1 wherein said series of flexible reeds are secured to a common mounting strip, each of said connecting portion includes corresponding concave edges defining a minimum width in spaced relation to the closure and mounting portions.

4. The crankcase valve of claim 1 wherein said plurality of valve reeds are connected in common to an innter annular mounting strip and said outer port clo- 6 sure portions being generally circular disc-like members disposed in circumferentially spaced relation and said connecting portion being generally hourglass shaped with curved edges extending between the closure portion and the strip. 7 I

5. The crankcase valve of claim 1 inclusing stop means secured in overlying relationwith each valve reed and spaced outwardly from the valve reed a distance slightly in excess of the normal outward deflection of the corresponding reed.

6. The crankcase valve of claim ll including stop means secured in overlying relation witheach valve reed and a resilient damping means secured to the stop means.

7. A crankcase valve reed unit ,for a valve block adapted tobe mounted within an engine crankcase and having an induction passageway means connected to a port opening from the flat face of the block, comprising an integral flat resilient metal member having an outer closure portion essentially corresponding to a port opening and an inner fixed securement portion connected by a connecting portion to define a valve reed, said reed unit being of a generally uniform thickness, said connecting portion including a reduced width between the closure and securement portions and selected to minimize the spring force and move the reed from a deflected position to the planar sealing position without establishing excessive damaging stresses in the reed.

8. The reed unit of claim 7 wherein said outer closure portionis generally circular discflike member and said connecting portion being generally hourglass shaped with curvedvedges extending between the closure portion and the securement portion.

9. The reed unit of claim 8 including a plurality of said reeds equicircumferentially spaced and connected to an annular mounting strip defining said securement portions by corresponding hourglass shaped connecting portions, said curved edges being defined by circular openings between the connecting portion of adjacent reeds. j y

10. The reed unit of claim 9 wherein said reed unit is 0.008 inches thick.

Claims

1. A crankcase induction valve for a two-cycle engine employing a valve block means adapted to be mounted within an engine crankcase and having an induction passageway means connected to a series of port means in a flat face of the block means, and wherein a series of flexible reeds are secured against the face of the block means and extend circumferentially into a normally seated position over said port means to close the latter, said reeds having an outer closure portion essentially corresponding to the opening of the ports and located in overlying covering relation to said ports and connected to an inner securement portion by a connecting portion, said connecting portion including a reduced width substantially less than the width of said closure portion and said securement portion and located intermediate the closure and securement portions.

4. The crankcase valve of claim 1 wherein said plurality of valve reeds are connected in common to an innter annular mounting strip and said outer port closure portions being generally circular disc-like members disposed in circumferentially spaced relation and said connecting portion being generally hourglass shaped with curved edges extending between the closure portion and the strip.

5. The crankcase valve of claim 1 inclusing stop means secured in overlying relation with each valve reed and spaced outwardly from the valve reed a distance slightly in excess of the normal outward deflection of the corresponding reed.

6. The crankcase valve of claim 1 including stop means secured in overlying relation with each valve reed and a resilient damping means secured to the stop means.

7. A crankcase valve reed unit for a valve block adapted to be mounted within an engine crankcase and having an induction passageway means connected to a port opening from the flat face of the block, comprising an integral flat resilient metal member having an outer closure portion essentially corresponding to a port opening and an inner fixed securement portion connected by a connecting portion to define a valve reed, said reed unit being of a generally uniform thickness, said connecting portion including a reduced width between the closure and securement portions and selected to minimize the spring force and move the reed from a deflected position to the planar sealing position without establishing excessive damaging stresses in the reed.

8. The reed unit of claim 7 wherein said outer closure portion is generally circular disc-like member and said connecting portion being generally hourglass shaped with curved edges extending between the closure portion and the securement portion.

9. The reed unit of claim 8 including a plurality of said reeds equicircumferentially spaced and connected to an annular mounting strip defining said securement portions by corresponding hourglass shaped connecting portions, said curved edges being defined by circular openings between the connecting portion of adjacent reeds.

10. The reed unit of claim 9 wherein said reed unit is 0.008 inches thick.