CA1134226A - Apparatus for alternate liquid or gaseous fuel operation of internal combustion engines - Google Patents

Abstract

ABSTRACT

An attachment for operating an internal combustion engine on either gaseous or liquid fuel incorporates a modified air cleaner assembly having spaced cover and adapter plates be-tween which is sandwiched a typical annular filter element, the adapter plate fitting over the engine air intake. An annular diaphragm connects an inner plate to the cover plate to form a chamber therewith on one side of the inner plate into which gaseous fuel is admitted. During gaseous fuel operation gas pressure in the chamber maintains the inner plate adjacent the adapter plate to form therewith and with the other side of the inner plate an annular venturi into which gaseous fuel from the chamber is admitted through a ring of ports through the inner plate at the venturi. During liquid fuel operation incoming air lowers the pressure in the chamber sufficiently so that the inner plate automatically moves away from the adapter plate to provide an unobstructed air only path to the engine air intake.

Description

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Dual ~uel operation of internal combustion engines, though long known and practiced, is nowadays becoming more and more to the fore in view of the growing shortage and cost of liquid fuel, particularly gasoline. Especially in the cases of larger vehicles, such as trucks, motor homes and the like, their inna~e higher fuel consumption has made the ability to operate them either on liquid or gaseous fuel increasingly attractive owing to the relatively plentiful supplies and lower cost of gaseous fuels, such as propane, compared to gasoline.
Currently, several schemes to this end are in practice.
Some replace the typical air filter assembly with one which in-corporates a fixed venturi arrangement for metering the gaseous fuel, A separate arrangement, exterior of the air cleaner assembly, is usually also fitted for slow-run operation. Some other approaches attempt to incorporate both the main and slow run systems into the air cleaner assembly. These employ, for instance, a diaphragm operated valve which controls a small variable venturi for slow run and a separate fixed large ventùri or high speed operation, or a diaphragm operated air valve in ~0 ~on~unction with a fuel valve which together meter both air and fuel throughout the engine speed and load range including slow-run. These two latter approaches, however, are both fairl~
intricate and thus expensive and elaborate to manufacture.
In any event, since all the prior art devices whatever ~5 their nature, fit upstream of those means in the engine air intake passage which meter liquid fuel and air in carbureted and fuel injected engines, their paraphernalia of venturis, air valves and the like would improperly throttle air supply and upset functioning af the liquid fuel metering means downstream af aix ~ilter assembly when operating on liquid fuel. Hence, the foregoing systems necessarily incorporate some manner by which the incoming air can bypass the gaseous fuel metering a~d mixing ~3~26 means when the engine operates on li~uid fuel. Typically the bypass constitutes a separate or alternate air intake route which is closed off during gaseous fuel operation and opened during liquid fuel operation either manually, as by a handworked cable, or electrically as by a solenoid operated valve. Such a manual approach, of course, requires extra parts and the running of the cable ~rom the engine to the driver's station. The electrical approach, while it can be arranged to ~perate automatically when the engine is shifted from one fuel to the other, also requires additional, not inexpensive parts and is not always reliable in operation.
Accordingly, the present invention seeks to provide a modified air cleaner assembly which provides gaseous or liquid ~uel operation of an internal combustion engine but which at the 1~ same time is simple in structure, inexpensive to produce, effi-cient in operation, and capable of automatically accommodating either fuel without the need of a separate air bypass route in ~onjunction with additional manual, electrical or other means for opening and closing the same.
~0 In one broad aspect, the invention contemplates a con-version means for use with an internal combustion engine having an ~ir inlet upstream of means for controlling supply of liquid fuel and/or air to the engine, the inlet including an air cleaner assembly having spaced circular and annular closure members and ~5 an annular air filter element therebetween with air passing first through the fil~er element and then between the closure members.
The conversion means connects the air cleaner assembly for opera-tion of the engine on either liquid or gaseous fuel and includes a diaphragm assembly and an annular cover plate, the diaphragm assem-bly including a circular diaphragm plate having an annular portion and a flexible annular diaphragm. The inner margin o~ the diaphragm : .

is adapted to be attached around the o,uter margin of the dia-phragm plate and the outer maxgin of the diaphragm around an outer margin of the circular closure member LO form a chamber between the diaphragm assembly and the circular closure member.
The annular cover plate has an annular portion and is adpated to fit over and on the annular closure member in spaced relation to the diaphragm plate, the diaphragm plate being thereupon movable toward and away from the annular closure member to provide an annular venturi between the annular plate portions when the diaphragm plate is moved toward the annular cover plate. Spaced apertures are through one of the annular portions for passage of gaseous fuel into the venturi.
- In another aspect the invention also pertains to an attachment for operating an internal combusion engine having an lS air inlet on liquid or alternately on gaseous fuel, the attach-ment including a housing having an opening for the air inlet of an internal combustion engine. The housing comprises first wall means having a first surface portion, second wall means disposed in spaced relation to the first wall means with a face of the second wall means including a second surface portion disposed in opposed spaced relation to the first surface portion. The first and second surface portions define a passage therebetween for communicating at an upstream end with the atmosphere and at a downstream end with the opening. At least one of the surface portions is reciprocally movable relative to the other surface portion between first and second positions respectively adjacent and more remote from the other surface portion during engine operation on respectively gaseous and liquid fuel. The passage when the one surface portion is in its first position forming venturi means for controlling supply of gaseous fuel to the engine and the one surface portion when in its second position providing substantially less impedance to flow of air through the passage. A chamber is operatively associated with the one c~
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342;~6 surface portion so that move~ent of the one surface portion bet-ween the positions is responsive to difference of fluid pressures in the passage and in the chamber. One or more gaseous fuel out-let ports open into the venturi means through one of the surface portions and in fluid communication with the chamber during opera-tion of the engine on liquid fuel. Inlet means are provided for supplying gaseous fuel to the outlet ports, the gaseous fuel inlet means being in fluid communication with the chamber during operation of the engine on gaseous fuel.
A still further aspect of the invention pertains to a system for operating an internal combustion engine on li~uid fuel or alternately on gaseous fuel in which the engine has an engine air inlet disposed upstream of means for controlling the supply of liquid fuel and/or air to the engine and intake means lS communicating with the inlet for mixing air and gaseous fuel from a supply source in proper proportions and supplying the mixture to the engine when operated on gaseous fuel and for pro-viding for a supply of air only to the air inlet when the engine is alternately operated on liquid fuel. The improvement in which the intake means includes a first closure member having an opening therethrough communicating with the engine air inlet.
first surface is associated with the first closure member and surrounds the opening. There is a second closure member having -opposite faces with a second surface associated with one of the faces of the second closure member and in opposed spaced relation to the ~irst surface. The first and second surfaces define a passage therebetween communicating at its upstream end with the atmosphere and at its downstream end with the opening. A third closure member is provided, the second and third closure members at least partially defining a chamber on the other face of the second closure member and the second closure member and surface being movable relative to and between the first and third closure '~ .

~ .34Z26 iembers between a ~irst limit position ~djacent the first closure member and surface and a second limit position more adiacent the third closure member. The first and second surfaces when the second closure member ana surface are in their first limit position forms an annular throat in the passage of venturi shape in cross-section around and adjacent the opening for flow of mixed air and gaseous fuel to the opening. The second closure member and surface when in their second limit position provides for a substantially less restricted flow of air only through the passage to the opening.
One or more gaseous fuel outlet ports are spaced around the throat and open thereinto through one of the surfaces, the gaseous fuel outlet ports being in fluid communication with the chamber during engine operation on liquid fuel. A gaseous fuel inlet is in fluid communi-cation with the chamber and the outlet ports for supply of gaseous fuel to the outlet ports at a pressure sufficient to maintain the second closure member and surface in their first limit position during operation of the engine on gaseous fuel. The second closure member and surface are effective to be automatically disposed toward their second limit position when supply of gaseous fuel to the in-let is closed off during operation of the engine on liquid fuel.
The disclosed exemplary embodiment of the invention em-ploys a modified air cleaner assembly which incorporates within it an annular venturi formed between an adapter plate, which encircles the engine air intake, and one side of a reciprocally ~5 movable diaphragm plate when disposed adjacent the adapter plate.
The diaphragm plate is surrounded and suspended by a thin flex-ible diaphragm connected at its outer margin to a cover plate to form a chamber with the other side of the diaphragm plate, a typical air filter element being also sandwiched between the adapter and cover plates. Gaseous fuel is supplied to the cham-ber from the customary zero pressure governor and is drawn from the chamber through a ring of outlet ports through the diaphragm D :

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plate at the venturi formed when the latter plate is adjacent the adapter plate. During gaseous fuel operation, gas pressure in the chamber maintains the diaphragm plate in its venturi forming position, but during liquid fuel operations when supply of gaseous fuel to the chamber is closed off, the diaphragm plate automatically retreats from the adapter plate to open up the venturi and provide a substantially unobstructed passage for air only to the engine. The latter movement of the diap~lragm plate occurs by virtue of the rush o~ incoming air past the aforesaid 10 outlet ports in the diaphragm plate which in turn decreases the pressure in the chamber on one side of the diaphragm plate below that exerted on the other side of the latter plate by the incom-ing air. Hence the need for an alternate air passage and means to open and close it is entirely eliminated, lS The parts required are few and rudimentary inso~ar as materials and manu~acture are concerned, being stamped or spun from simple sheet stock, so cost is low and reliability and efficiency high. For slow-run operation a separate system is employed, such as one admitting the gaseous fuel through a meter-20 ing valve directly into the engine's intake manifold below the throttle plate, or one in which the fuel is admitted into the aoresaid chamber through a separate inlet and valve controlled by intake manifold vacuum. The present invention is suitable for all types of gaseous fuels and, while hereafter shown and de-25 scribed for use with a downdraft carburetor, it can be readilyadapted for sidedraft and updraft carburetors or even fuel iniec-tion applications in either gasoline or diesel versions. Other features and advantages of the present invention will appear from the more detailed description which follows and the drawings, in 30 which:
Figure 1 is a diametrical cross-section of an air cleaner assembly incorporating the invention mounted on the air-horn of a downdraft liquid fuel carburetor .

~4~26 Figure 2 is a sectional plan view taken along the line

2-2 of Figure 1.
Figures 3 and 4 are enlarged sectional views taken respectively along the lines 3-3 and 4-4 of Figure 2 and illus-5 trating in more detail the mounting of the diaphragm to the coverand diaphragm plates.
Figure 5 is a sectional view taken along the line 5-5 of Figure 2.
Figure 1 depicts an internal combustion engine 10 10 equipped with a multi-barrel, downdraft carburetor 11 having liquid fuel metering venturi 12 and throttle plates 13 surmounted by a carburetor air inlet horn 14. The air horn 14 includes ân annular seat 15 Eor the lower end of an air cleaner assembly which is retained thereon by a typical hold-down post 16 extend-15 ing centrally upright from the mouth of the air horn 14, beingthreaded at 17 at its upper end and provided with a stop collar ~nd gasket 18.
The air cleaner assembly of the present invention, generally indicated at 20, includes an inner annular adapter 21 ~0 whose lower end 22 is inwardly flanged to press against a gasket 23 about the air horn seat 15 and whose upper end 24 is outwardly flanged and surmounted by a gasket 25. The neck 26 of an outer annular adapter 27 seats atop the gasket 25, its inner edge being do~nwàrdly flanged at 28 to locate the adapter 27 within the 25 upper mouth of the inner adapter 21. (The inner and outer adapters 21 and 27 are preferably separate parts so that the air horns o different carburetors or other air intakes can be more easily and economically accommodated.) The upper annular surface 29 of the outer adapter 27 slopes downwardly from its neck 26 to 30 a shelf 30, the outer edge of the latter having an upturned flange 31 to form an upwardly facing annular seat 32 for the lower end of a typical annular air filter element 33 having ~ ~ 3~ ~ 5 gasketed end caps 34. The upper end of the filter element 33 is received in a complementary opposed seat 35 formed by a down-turned flange 36 on a shelf 37 at the outer margin of a removable cover 38. The latter cover includes an annular wall 39 sloping upwardly ~rom the shelf 37 and a central concavity 40 up through which extends the hold-down post 16. The latter post is fitted with a thumbnut 41 in order to retain the adapters 21 and 27, the ~ilter element 33 and the cover 38 assembled atop the carburetor air horn 14. Despite the concavity 40, which is to improve 10 underhood clearance by in effect lowering the upper end of the post 16, the cover 38 is essentially of inverted dished configu-ration and its sloped wall 39 is apertured to provide a large main gaseous fuel inlet 42 from a hose fitting 43 in the form of an aluminum casting bolted at 44 with a gasket 45 to thè exterior lS of the wall 39.
The upper end of the filter element 33 suspends a dia-phragm assembly 50 comprising an annular diaphragm 51 of thin 1exible material whose outer margin is sandwiched between the upper filter end gasket 34 and an additional gasket 52 (see ~0 Figure 3) in the filter upper end seat 35. The radially inter-mediate portion of the diaphragm 51 is sinuously disposed as shown in Figure 1, Its inner margin is sandwiched in turn be- -~
tween the outer margin of a rigid circular diaphragm plate 53 and the outer face of a channel section, annular clamp ring 54, a pair of gaskets 55 (see Figure 4) being interposed on each side of the diaphragm 51 and the parts secured, for instance, by rivets.56. Radially inward from the clamp ring 54 the diaphragm plate 53 is shaped to form an annular depression 57 whose lower convex face lies closely adjacent the adapter neck 26 where, when the diaphragm àssembly 50 is in its position shown in full lines in Figure 1, it forms an annular vent~ri passage 58 therebetween having an intermediate section or portion constituting a throat ';
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~ 2 ~6 S9. The immediate central area of the diaphragm plate 53 is dished at 60 and provided with an upwardly coined aperture 61 which slidably receives the mid-section of the post 16 for guided reciprocal movement of ~he diaphragm assembly 50 along the post 16, as indicated in Figure 1. The cover 38 and the diaphragm assembly 50 thus define a chamber 62 into which gaseous fuel is admitted through the inlet 42. Through the diaphragm plate 53 at the throat 59 is a ring of spaced gaseous fuel outlet ports ~3 from the chamber 62 into the venturi passage 58.
The upward travel of the diaphragm assembly 50 is limited by contact of the coined aperture 61 with the stop collar 18, and in order to limit the downward travel of the diaphragm assembly 50, and thus also to adjust the width of the venturi throat 59, the diaphragm plate 53 is fitted with several adjust-lS ing screws 64 evenly spaced around the throat 59. The lower ends of the screws 64 engage the adapter neck 26 therebelow, the screws 64 being threaded through nuts 65 (see Figure 5) crimped in apertures in the diaphragm plate 53 between the outlet ports 63. Conical springs 66 encompass the screws 64 and seat against ~0 the under face of their heads 67 to secure the adjustment.
When operating on gaseous fuel, the latter is supplied to the chamber 62 through the inlet 42. The pressure of the gas in the chamber 62 above the diaphragm assembly 50, which is typi-cally in the range of -0.10 to -3.0 inches of water column, main-tains the assembly 50 in its lowermost position with the ends ofthe adjusting screws 64 sitting atop the adapter neck 26 to form the venturi passage 58 since that pressure is greater than the pressure of the incoming air below the assembly 50, which is typically in the neighborhood of -0.10 and -0.70 inches o~ water column respectively upstream and downstream of the throat 59 and -30.0 inches at the latter. Accordingly, the low air pressure at the throat 59 draws gaseous fuel from the outlet ports 63 into - : .: , .:, , . , , ;

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the incoming air stream. The annular shape of the venturi pas-sage 58 and the distribution of the outlet port 63 around it especially enhance gas distribution and mixture with the air.
For slow-run operation a typical separate slow-run system may be S incorporated into the engine manifold, as previously mentioned, or, as also mentioned, a slow-run system in which a valve 70, controlled by manifold vacuum, introduces gaseous fuel into the ehamber 62 through an inlet 71 in the cover wall 39 opposite the main inlet 42.
When operating on liquid fuel, the gaseous fuel supply to the inlet 42 (and the inlet 71) is, of course, closed off.
The chamber 62 thereby becomes closed except for the outlet ports 63. The incoming air to the carburetor 11 past the outlet ports 63 lowars the pressure in the chamber 62 against the upper face of the diaphragm assembly 50 below that against the lower face of the latter, whereupon the diaphragm assembly 50 automatically risas, as indicated in broken lines in Figure 1, toward its uppa~most limit against the stop collar 18 depending upon the air demand of the engine. The venturi passage 58 is thus "destroyed"
~0 and the incoming air passes substantially unimpeded to the car-buretor 11. In short, the assembly 20 then functions just as would a normal air cleaner assemblyj as if the diaphragm assembly 50 were wholly absent. It will be appreciated by those skilled in the art that for the diaphragm assembly 50 to rise as afore-said, its effective diaphragm area, whose diameter is indicatedby the line A-A in Figure 2, must be sufficient to enable the pressure differential between the opposite sides of the diaphragm assembly 50 to overcome the weight and friction of the latter.
This is readily achieved by constructing the diaphragm assembly S0 o light-weight materials.
As will be apparent, the parts of the air cleaner assembly 20 are all simple and straightforward. The adapters 21 ~ .

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and 27~ the cover 38 and the diaphragm plate 53 can all be stamped or spun from sheetmetal such as aluminum. The diaphragm Sl is preferably a 0.008 inch ~hick sheet of Dacron or Nylon impregnated with epochlorhydron. The overall size o the as-sembly 20 is also ~odest, an overall diameter of about 14 inches,a height o~ about four to five inches between the air horn 14 and the top of the post 16, a diameter of the diaphragm plate 53 between the outlet ports 63 of about six inches, and an outer free diameter of the diaphragm 51 of about 11 inches all being 10 adequate or engines as làrge S00 cubic inch displacement. The diameter o~ the outlet ports 63 is preferably between 5/32 and

3/16 inches and their number vary from 4 to 20 or so depending upon engine displacement. Different sized engines can thus bê
accommodated simply by different diaphragm plates 53 as well as 15 by adjustment of the width of the throat 59 by the screws 64.
For side draft and updraft applications, especially the latter, a light coil spring around the post 16 between the stop collar 18 and the coined aperture 63 may be necessary to maintain the dia-phragm assembly 50 in its position for gaseous fuel operation.
~0 Finally, rather than requiring a special air cleaner assembly, it is conceivable that the invention could be incorporated in a standard air cleaner assembly by supplying a conversion kit con-sisting essentially of a diaphragm and diaphragm plate of the foregoing nature plus an adapter plate to form the other half of the vènturi. Some alternate arrangement might also be used to supply the gaseous fuel to the chamber from through the side or rom the bottom of the assembly in order not to encroach on underhood clearance involved in bringing the fuel into the top of the assembly.

In any event, though the present invention has been described in terms of a particular embodiment, being the best mode known of carrying out the invention, it is not limited to that embodiment alone. Instead, the following claims are to be .
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read as encompassing all adaptations and modifications of the invention falling within its spirit and scope.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An attachment for operating an internal combustion engine having an air inlet on liquid or alternately on gaseous fuel, the attachment including a housing having an opening for the air inlet of an internal combustion engine, the housing comprising: first wall means having a first surface portion;
second wall means disposed in spaced relation to the first wall means, a face of the second wall means including a second surface portion disposed in opposed spaced relation to said first surface portion, said first and second surface portions defining a pas-sage therebetween for communicating at an upstream end with the atmosphere and at a downstream end with said opening, at least one of said surface portions being reciprocally movable relative to the other surface portion between first and second positions respectively adjacent and more remote from said other surface portion during engine operation on respectively gaseous and liquid fuel, said passage when said one surface portion is in its first position forming venturi means for controlling supply of gaseous fuel to the engine, said one surface portion when in its second position providing substantially less impedance to flow of air through said passage; a chamber operatively associated with said one surface portion so that movement of said one surface portion between said positions is responsive to difference of fluid pressures in said passage and in said chamber; one or more gaseous fuel outlet ports opening into said venturi means through one of said surface portions and in fluid communication with said chamber during operation of the engine on liquid fuel; and inlet means for supplying gaseous fuel to said outlet ports, said gaseous fuel inlet means being in fluid communication with said chamber during operation of the engine on gaseous fuel.

2. The attachment of claim 1 further characterized by the second wall means partially defining said chamber; and by third wall means disposed in spaced relation to and opposite the other face of said second wall means and further defining said chamber.
3. The attachment of claim 2 further characterized by a periphery of the second wall means being articulately connected to the third wall means to allow said reciprocal movement of the second wall means.
4. The attachment of claims 1, 2 or 3 further charac-terized by said gaseous fuel inlet means opening into said chamber; and by said gaseous fuel outlet ports opening into said venturi means from said chamber through said second surface portion.
5. The attachment of claim 3 further characterized by the first wall means being a portion of an annular adapter assembly having an annular face portion forming at least part of said first surface portion; by the second wall means being a circular inner member having a face portion forming said second surface portion; and by the third wall means being a circular cover member, the annular assembly, inner member and cover member being all coaxially disposed with respect to each other.
6. The attachment of claim 5 further characterized by said articulate connection being a flexible diaphragm sealingly connected to the inner member and to the cover member to provide an annular flexible diaphragm area between the inner and cover members allowing said reciprocal movement of the inner member;
and by adjusting means carried by one of the adapter assembly and the inner member and engaging the other for adjustably varying the distance between said face portions when the inner member is in its first position.
7. The attachment of claim 6 further characterized by the outer peripheral areas of the cover member and adapter assembly additionally defining opposed annular seat portions for receiving an annular air filter element therebetween upstream of said passage; and by means for confining said movement of the inner member to a linear path and for retaining the air filter element in assembled relationship with and between the adapter assembly and the cover member.
8. The attachment of claims 5, 6 or 7 further charac-terized by said gaseous fuel inlet means opening into said chamber; and by said gaseous fuel outlet ports opening into said venturi means from said chamber through said second surface portion.
10. In a system for operating an internal combustion engine on liquid fuel or alternately on gaseous fuel in which the engine has an engine air inlet disposed upstream of means for controlling the supply of liquid fuel and/or air to the engine and intake means communicating with said inlet for mixing air and gaseous fuel from a supply source in proper proportions and sup-plying the mixture to the engine when operated on gaseous fuel and for providing for a supply of air only to said air inlet when the engine is alternately operated on liquid fuel, the improve-ment in which the intake means comprises: a first closure member having an opening therethrough communicating with the engine air inlet; a first surface associated with the first closure member (claim 10 cont'd) and surrounding said opening; a second closure member having opposite faces; a second surface associated with one of said faces of the second closure member and in opposed spaced relation to the first surface, said first and second surfaces defining a passage therebetween communicating at its upstream end with the atmosphere and at its downstream end with said opening; a third closure member, the second and third closure members at least partially defining a chamber on the other face of the second closure member, the second closure member and surface being movable relative to and between the first and third closure members between a first limit position adjacent the first closure member and surface and a second limit position more adjacent the third closure member, said first and second surfaces when the second closure member and surface are in their first limit posi-tion forming an annular throat in said passage of venturi shape in cross-section around and adjacent said opening for flow of mixed air and gaseous fuel to said opening, the second closure member and surface when in their second limit position providing for a substantially less restricted flow of air only through said passage to said opening; one or more gaseous fuel outlet ports spaced around said throat and opening thereinto through one of said surfaces, said gaseous fuel outlet ports being in fluid communication with said chamber during engine operation on liquid fuel; and a gaseous fuel inlet in fluid communication with said chamber and said outlet ports for supply of gaseous fuel to said outlet ports at a pressure sufficient to maintain the second closure member and surface in their first limit position during operation of the engine on gaseous fuel, the second closure member and surface being effective to be automatically disposed toward their second limit position when supply of gaseous fuel to said inlet is closed off during operation of the engine on liquid fuel.
11. The system of claim 10 further characterized by the first closure member including a generally annular adapter plate having said opening therein and formed to a cross-sectional configuration providing at least part of said first surface; by the second closure member including a circular diaphragm plate and a flexible diaphragm sheet secured between the diaphragm plate and the third closure member effective to provide said movement of the second closure member, the diaphragm plate having an annular portion disposed coaxially with the adapter plate and forming said second surface; and by guide means for the diaphragm plate for confining said movement thereof to a linear path.
12. The system of claim 11 further characterized by adjusting means carried by said annular portion of the diaphragm plate and engageable through said passage with the annular plate in order to adjust the spacing between said surfaces and thus the first limit position of the diaphragm plate.
13. The system of claims 10, 11 or 12 further charac-terized by said gaseous fuel outlet ports opening into said chamber through the second surface; and by said gaseous inlet means being carried by the third closure member and also opening into said chamber.
14. For use with an internal combustion engine having an air inlet upstream of means far controlling supply of liquid fuel and/or air to the engine, said inlet including an air cleaner assembly having spaced circular and annular closure mem-bers and an annular air filter element therebetween, air passing first through the filter element and then between said closure members, means for converting the air cleaner assembly for opera-tion of the engine on either liquid or gaseous fuel, the convert-ing means comprising: a diaphragm assembly and an annular cover plate, the diaphragm assembly including a circular diaphragm plate having an annular portion and a flexible annular diaphragm, the inner margin of the diaphragm being adapted to be attached around the outer margin of the diaphragm plate and the outer margin of the diaphragm around an outer margin of the circular closure member to form a chamber between the diaphragm assembly and the circular closure member, the annular cover plate having an annular portion and being adapted to fit over and on the annular closure member in spaced relation to the diaphragm plate, the diaphragm plate being thereupon movable toward and away from the annular closure member to provide an annular venturi between said annular plate portions when the diaphragm plate is moved toward the annular cover plate, and spaced apertures through one of said annular portions for passage of gaseous fuel into said venturi.

15. The converting means of claim 14 further charac-terized by said apertures being disposed in the annular portion of the diaphragm plate.