Nova Patents
AU8936282A

Control mechanism

Abstract

This record has no abstract on file.

AU8936282A, drawing sheet 1
Sheet 1 of 5

Term

Term ended

Projected expiry passed 14 October 2002, 23.9 years ago.

  1. Priority
  2. Filed
  3. Projected expiry
  4. Today

6 claims: 6 independent, 0 dependent

  1. 1
    THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:1. Apparatus for controlling operation of an internal ί ί. t. ΖΧ/ΎΤ4 © <3 © © & © , * ) <3 © © « e i. 3I) control valve, thereby opening the liquid fuel control valve;is also operable^ when the selector switch is in fuel position ancl i;/response to the presence of vacuum above the predetermined level to energize the liquid an amount of .,. the gaseous fuel control valve;is also operable, when the selector switch is in the liquid fuel position and in response to the an amount of vacuum below the predetermined level, to presence of the gaseous fuel control valve, and thereby close the fuel control valve, and thereafter to retain the gaseous deenergize gaseous fuel control valve deenergized regardless of vacuum variation;is also operable, when the selector switch is in the gaseous fuel position, tG deenergize the liquid fuel control valve, thereby closing the liquid fuel control valve;is also operable, when the selector switch is in the gaseous fuel position and in response to an amount of vacuum above the predetermined level, to deenergize the gaseous fuel control valve, thereby closing the gaseous fuel when the (selector switch in response to an amount control valve;arid is also operable, is in the gaseous fuel position and of vacuum below the predetermined level, to energize the gaseous fuel control valve and thereby open the gaseous fuel control valve, and thereafter to retain energization of the gaseous fuel control valve regardless of vacuum variation. In one embodiment of the invention, the apparatus further includes electrically operated spark advance means electrically connected to the control means and operable in response to energization thereof to jkdvanc# tlie sparking time, - 1/ 0 and electrically operated intake air heating means electrically i7 \ connected, to the control means, and operable in response to energization thereof to discontinue heating the incoming air, and the control « / ή mean.? is inoperable, when the selector switch is in the liquid energize the spark advance means and the and is operable, when the selector switch fuel position and in response to an amount predetermined level, to deenergize the fuel position, to air intake means;is in the gaseous of vacuum above the spark advance means and the inl&t air heating means, and is the selector switch is ins the gaseous^fuel position and in response to an amount of vacuum below the predetermined level, to energizi the spark advance means., and the inlet air heating means, and thereafter to retain energization of the spark advance means and the also operable, when intake air heating means o © ft & © © a © o » © 0 « ft e. A & e ft ft ft ft 15 ‘ \\ regardless of vacuum variation. In one embodiment of the invention, the selector switch comprises a gaseous fuel terminal, a liquid fuel terminal, and' a primary switch member connected to a source of direct current and movable between a first position energizing the gaseous a second position energizing the liquid fuel fuel terminal and terminal , and the means including ,?a control valve, to control means further includes first switchfirst terminal connected to the gaseous fuel the gaseous fuel terminal, movable relative to a position energizing the first terminal, and thereby energizing the gaseous fuel control valve, the spark advance means, and the intake air heating means, and biased away from the first terminal, and means for holding the first switch member in the position energizing \\_ the first terminal in response to energizing of the first terminal, a second switch means including a terminal connected to the gaseous fuel control valve, a holding terminal, a second switch member electrically connected to the liquid fuel terminal, of the selector switch, -4V // < --•L· —___ Ί •i movable between a first position Engaging said first terminal and a second position engaging the holding terminal and biased to said first position, and means connected to the in deta limitec holding terminal for holding the second switch member in the and the second position when the holding terminal is energized by the descrif second switch member, vacuum switch means connected to a source capable of direct current and to the first and second switch means carriec and operable between an open position in response to the presence that tT of an amount of vacuum above the predetermined level and a purpose second position which is normally closed in the absence of the presence of an amount of vacuum above the predetermined level ge/erai and which is operable to connect the first switch member to the select: first terminal and the second switch member to the holding terminal,· and a diode for preventing advance means and the intake axr heating means when the primary energization of the spark first c include switch member is in the liquid fuel position. \\ In one embodiment of the invention, the engine includes v./ - x a, fuel inlet manifold and the vacuum switch communicates with'the'/ fhel inlet manifold and .is. subject to the pressure variation connect such a, used. which in the fuel inlet manifold. through Other features and of the invention will become advantages of the embodiments known by reference to the following shown) general description, claims and appended drawings. ί' b ft- 4 & a© v « ft & cally IN THE DRAWINGS: retard means Figure 1 is a schematic view of one embodiment of in the an internal on liq combustion engine on differing fuels. TT * ' ' . ' * ;' . ' ' ' X) , . . .:. '' . ' ' (ClaTm 3 continued) control means also being operable, when said selector switch is in said/gaseous fuel position, to deenergize said liquid it r saic Ό Ο Ί to 3 © O 3 0 9 0 6 to 5 ® © to \ to > a ,& S Λ G to ft 9 to a ® to to a ft β to β S © a ¢. © & G > £ to ft 15 to u to to to Before explaining one embodiment of the t) invention in detail, it is to be understood that the invention is not ' 0 · G . limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried put in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded 7s limiting. GENERAL DESCRIPTION: Shown in Figure 1 is control apparatus 11 for selectively operating an internal combustion engine 13 on a first or gaseous fuel and on a second or liquid fuel. The engine includes a carburetor 15 incorporating a float bowl 17 which is connected through a' supply line 19 with a source 21 of liquid fuel, such as, for instance, gasoline. Other liquid fuels could be used. The engine 13 also includes a gaseous fuel air mixer 23 which communicates with the carburetor 15, and which is connected through a supply line 25 with a source 27 of gaseous fuel, such ., as, fob instance, natural gas. Other (gaseous fuels could be used. The engine 13 also includes an ignition system (not shown) which incorporates spark advancing means 31 (schematically,. illustrated) for varying the time of sparking between retarded sparking and advanced sparking. Such spark advancing means 31 is biased toward retarded sparking, permits variation in the time of sparking operation when the engine 13 is operating on liquid fuel, and maintains advances sparking/when the engine 13 0. • / / ',· 4. Apparatus in accordance with Claim 3 wherein - 5 . H said apparatus further includes ..electrically operated spark \\ Advance means electrically connected, to said control means .s /'/] . ;c sa> the is operating on gaseous./juel. The spark advance means 31 is operative in response to electrical energization to maintain the spark advanced when operating on gaseous fuel. Other, than as^expl ained-.above?-’the. detailgi of the spark advancing means 31 do-not -form's part of this invention. _.·.One suitable sparkadvancing means.-is disclosed in Application'Serial No. · _____ filed;_____- - ..and entitled ’’Spark Advance· Mechanism for ;Dual Fuel Engine (Attorney’s docket 72013/6360-2) which is incorporated herein by reference. '9 / ig· engine , w It ι is C Cr 0« c © o & & O G © , « <5 0 o © The engine 13 also includes pearls .33 for heating the Intake air when the engine 13 is operating on liquid fuel. The intake air heating means 33 is operative to prevent heating of the incoming air in response ;to electrical energization and, in the v i V \\ id, fuel, be nected such. e used not (. fe * fe % V 6 iing ion rating absence of electrical energization, serves to heat the incoming air·.· Any s.uitable intake jair. heating means can be employed. The engine 13 also includes control means 41 for selective change-over between use of liquid fuel and gaseous fuel. In this regard, the control means 41 includes a liquid fuel control Valve 43 which is incorporated in the .liquid fuel supply line 19, which is movable between open and closed positions, which it? biased to the closed position, arid which, in response to electrical energization, moves to the ope^i position to .afford liquid fuel flow to the engine 13. ,] ’ /’ '/ ’ .. ’ .. '(v .. . ” The control ipeans 41 «also» includes a gaseous fuel ’ control valve 45 which is incorporated in the gaseouis ftlel supply line 25-, which is movable between open and closed positions, in respg?/se open position’,, to Lifford 5‘ , ,'jss2 .5 a v 7} ' ' ' , the and a valve the ti of fuel d opera posit of an energi the gs gaseoi which is biased to the closed position, and which, to electrical energization, moves to the gaseous fuel flow to the engine. I? c ’ JO of vac fuel J select the si ir V) 9) 4 wherein 5. Apparatus in accordance with, Claim said selector switch comprises a gaseous fuel terminal, a/ 1 ' ' / liquid fuel terminal, and a primary switch member connected ’ ' ’ .....· “ ........ 'Ζ Ji * (Cla: pr&f respo IS i Still further in addition, tne control means 41 ii a vacuum control switch 47 which is subject to variation in the amount „of' vacuum, which is normally closed, and which opens in response to the presence at the vacuum switch 47 of/an amount of vacuum above a predetermined amount. /7 Still further in addition, fuel selector switch 51 a primary or ·£ and which is movable between a first and a second the control means 41 includes which is operator-controlled or gaseous fuel position, or liquid fuel position The control means 41 is operable, when the selector switch 51 is in the liquid fuel position, ti:7energize the liquid 1 fuel control valve 43, thereby opening the liquid fuel control valve 43. In addition, the control means 41 is operable, when the selector switch 51 is in the liquid fuel position and in response to the presence at the vacuum switch 47 of an amount of vacuum above the predetermined level, to energize the gaseous fuel control valve 45, and thereby open the gaseous fuel control valve 45. Still further in addition, the control means 41 is operable, when the selector switch 51 is in the liquid fuel position and in response to the presence at the vacuum switch 47 of an amount of vacuum below the predetermined level to degaseous fuel control valve 45, and therefore close .5 the gaseous fuel control valve, and thereafter to retain the 0 . ;gaseous fuel control valve 45 deenergized regardless of variation of vacuum until tihe fuel selector switch 51 is moved to the gaseous fuel position. Z' The control means 41 is also inoperative, when the selector switch 51 is in the gasoline position, td- energize the spark advance means 31 and the intake air heatingmeans 33. ft· Ά 'J The control means 41 is also operable, when the selector switch 51 is in the gaseous fuel position, to deenergize the liquid fuel control means 43, and thereby clbsing the liquid fuel control valve 43.· In addition,'the. control means 41.is also operable when the selector switch 51 is? in the gaseous fuel position and in response to the presence at the vacuum switch. 47—of „an- amount of vacuum above the predetermined level, to deenergize the gaseous fuel control valve 45, and thereby .0 close the. yaseous fuel control i : spark advance means 31, and to valve 45, to deenergize the deenergize the intake air © s o heating means 33. Still further in means 41 is also operable, when ijhe in the gaseous fuel position and in at the vacuum addition, the control selector switch 51 is response to the presence switch 47 of an amount of vacuum below the level, to energize the gaseous fuel control thereby open the gaseous fuel control valve 45, to energize the spark advance means 31, and the intake air heating means 33, and to thereafter retain energization of the gaseous fuel control valve 45, the spark advance i e a # ’.O' Ή ft means 31 and the intake air heating means 33, regardless of variation in vacuum until movement of the fuel selector a ft ft a © ft » ft * switch 51 to the liquid fuel position by an operator. More particularly, the selector switch 51 comprises ft S 9 O tt a gaseous fuel terminal 53, a liquid fuel terminal 55, and a primary current and movable between a first position energizing the liquid fuel terminal 55. The control means 41 further includes a first switch means 61 including ah energizing and holding germinal 63 connected to the gaseous fuel control valve 45, to the spark advance means 31, and to the intake air heating means 33. In addition, the first switch means 61 includes a first switch member^65 s P \ / connected to the gaseous fuel terminal 5| of the selector switch 51 and movable to and from a position’ energizing the energizing and holding terminal 63, means (not shown) biasing 5 the first switch member 65 away from the energizing and holding terminal 63, and means connected tc the energizing and holding terminal 63 for holding the first switch member 65 in the position energizing the energizing and holding terminal 63 when the energizing and holding Λ . rviinal is energized. 10 The control means 41 also includes a second switch means 71 including a terminal 73 connected to the gaseous fuel control valvp 45, a holding terminal 77, and a second switch member 79 electrically connect ~^to<-the liquid fuel / c to 'x, “ z,! jv'-' 9 4 < “ terminal 55 of the selector switch 51 and movable between » to ! ' c to j_ca a first position energizing the terminal 73 connected to the gaseous fuel control valve 45 for energization thereof, and 'l\ a second position energizing the holding terminal 77, means 4 6 '7 . (not shown) biasing the second switch member 79 to the first position, and means connected to the holding terminal ‘2® · 77 for holding the second switch member 79 in the second ' <· position against the action of the biasing means when the , holding terminal 77 is energized. ' Still more specifically, the first and second switches 61 and 71 respectively include solenoid coils 81 and 83 which, '25 when energized, cause movement of the respective first and v £ · · second switch members 65 and 79 from their biased positions to their respective positions in engagement with the energizing and holding terminal 63 and the holding terminal 77. The vacuum^ switch 47 includes a switch member 93 which iV connected tp the source 59 of direct current and which is movable between open and closed positions relative to a second terminal 95 which, in turn, is connected through 5 diodes 97 and 99 to the respective solenoid coils 81 'and 83. The switch member 93 is biased by a spring 101 to the closed position, and opens in response to the presence at t:he vacuum switch 47 of an amount of vacuum above a predetermined level. In this last regard, the vacuum switch 0 is connected by a suitable conduit 103 to the engine intake manifold 105 and therefore senses the vacuum condition at the intake manifold 105. In this regard, as already indicated, a small amount of vacuum below the predetermine d level is ineffective to open the vacuum switch 47. Such small amounts .5 of vacuum occur during high speed and acceleration conditions in which the engine throttle 107 is opened and, thus, there is no impediment to fuel fixture flowing to the engine cylinders (not shown). However, during idling and lesser speed operations, the engine throttle 107 is either closed or partially opened, ?C causing a greater amount of vacuum to be present in the engine intake manifold 105. When such a greater amount of vacuum above the pr- determined level is present, the vacuum switch 47 opens against the bias of the spring 101. The control means 41 also includes a diode 111 15 which prevents energization of the intake air heating ,. means 33 and the spark advance means 31 when the fuel selector switch 51 is in the liquid fuel position and the second switch member 79 is in the first position energizing the terminal 73 Still further, a diode 113 is interposed in the electrical connection between the second switch member 79 f and the liquid ^St&l terminal 55 of the primary switch 51 to prevent current flow from the second switch member 79 to the liquid fuel terminal 55 of the primary switch 51. Still further in addition, a diode 115 is provided between the energizing terminal 63 of the first switch and the solenoid coil 81 so as to prevent flow from the solenoid coil 81 to the gaseous fuel control valve 45 and/or the spark advance means 31 and/or· current flow of the first switch member 65 in engagement with the energizing ft ft terminal 63. In operation, when switching from liquid fuel to gaseous fuel, the op erat or .'moves the fuel selector switch 51 to the gaseous fuel position. As a result, the liquid fuel control valve 43 is consequently deenergized and turns off the liquid fuel supply to the carburetor 15. However, the engine continues to run on the liquid fuel in,the carburetor < a< ‘20‘:' €1 :. .< ς. t.4 <, bowl 17. The inlet manifold vacuum remains above the pre- 'x determined level of the vacuum switch 47 at idle or normal road speeds until the engine begins to run out of the liquid fuel « « ί . i·· 25 . « L in the fuel bowl 17,-, The vacuum then than or below the predetermined level the vacuum switch 47 which energizes the solenoid coils 81 and , The first solenoid coil 8Ϊ acts to displace the first switch member65 to the terminal 63, thereby energizing the gaseous fuel control valve 45 to the open position, and thereby also drops to an amount less thereby closing energizing the spark advance means 31 and the inlet air heating means 33. Energization of the terminal 63 also serves to hbld the solenoid coil 81 in the energized state, thereby retaining :i...... (I the gaseous fuel control valve 45 in opened condition, * regardless of variation of the vacuum condition at the vacuum switch 47. <-. . o'·— . . To change to liquid fuel from gaseous fuel, the, 5 operator moves the fuel selector switch 51 to the liquid fuel position. Such movement energizes the liquid fuel control ;valve 43 to the open position and the carburetor bowl 17 begins to fill. However, the engine 13 will not run on liquid fuel until the carburetor bowl 17 is nearly full. During the time 10 interval when the carburetor bowl is filling, the gaseous fuel control valve 45 is retained open by engagement of the second switch member 79 with the terminal 73. Thus, the engine 13 continues to run on gaseous fuel with the vacuum condition at the vacuum switch above the predetermined level until the engine 15·? 13 begins to run on both fuels. The vacuum condition at the © c ft ft vacuum switch 47 then drops below the predetermined level, » ifi c ® thereby closing the vacuum switch 47, which closure energizes ft £. ’ j the second solenoid coil 83. Energizing of the second «ft I ft ft solenoid coil 83 shifts the second switch member 79 to the 20 holding terminal 77, thereby deenergizing the gaseous fuel . < control valve 45 so as r;o effect clostjre thereof. At the same < \ time, energization of the holding terminal 77 serves to latch the second solenoid coil 83 in an energized state so that the gaseous fuel control valve 45 remains in the off position, notwithstanding 25 variation in vacuum condition at the vacuum switch 47. In addition, the spark advance means 31 and the inlet air heating means 33 are opened immediately upon the shifting of the fuel selector switch 51 to the liquid fuel position· If such deenergization of the spark advance means 31 and the inlet air heating means 33 30 is not accomplished, the vacuum condition at the vacuum switch 47 may remaixi greater than the predetermined leverl when idling on both fuels, thereby preventing closure of the vacuum switch Ϊ7 and . completion of the change-over to liquid fuel. and th switch fuel c 5 ;gaseou system about load, a few 10 engine mixtur .e employ t i <' : to go 151, systen ' <’ · : turns L carbui change valve, 20 off tl procec to mal shift: unique forth ο advance means from being energized during the and the spark switch-ove- to liquid fuel. The diode 113 prevents the fuel control valve 43 from being energized during normal , . gaseous fuel operation. The disclosed automatic change-over about system will work as described at idle and steady speeds below 50 mph. If the change-over is attempted at a heavy load, low-vacuum condition, the engine will lose power for a few seconds. However, inertia of the vehicle powered by the engine 13 will drive the engine 13 until the correct fuel mixture is supplied. Prior currently available dual fuel systems for employing liquid fuel and gaseous fuel require the operator to go through a specified procedure to change fuel. In these systems, to change fuel from gasoline to natural gas, the operator turns off the gasoline valve, waits until the fuel in the carburetor is used, and then turns on the natural gas. To change back to gasoline, the operator turns on the gasoline valve, waits until the engine begins to flood, and then turns to off the natural gas valve. The operator must know the specific procedure required for the particular conversion system in order to make a fuel change. Thus the disclosed apparatus 11 for shifting from gaseous fuel to liquid fuel, and vice-versa, is unique and simplifies the previous change-over procedure. Various of the features of the invention are set forth in the'following claims. 1. until L. switch is in the liquid fuel position, to energize the liquid fuel ! ' -2A ' . \! ... Z V ‘^2. and the THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. Apparatus for controlling operation of an internal combustion engine which is selectively operable using gasdous fuel or liquid fuel, said apparatus comprising a gaseous fuel supply line extending between the engine and a source of gaseous fuel, a liquid fuel supply line extending between the engine and a source of liquid1!.fuel, and means for controlling supply to the engine of the gaseous fuel and the liquid fuel, said control means including an Operator controlled fuel selector switch movable between a gaseous fuel position and a liquid fuel position, said control means being operable following prior engine operation with gaseous fuel and in response to movement of said fuel selector switch from said gaseous fuel position to said liquid fuel position for permitting liquid fuel flow through said liquid fuel supply line, for permitting continued gaseous fuel flow through said gaseous fuel supply line until^initiation of liquid fuel combustion, and thereafter preventing further gaseous fuel flow through said gaseous fuel supply line until repositioning of said fuel selector switch to said gaseous fuel position, said control means also being operable following prior engine operation with liquid fuel and in response to movement of said fuel selector switch from said liquid fuel position to said gaseous fuel position for preventing further liquid fuel flow through said liquid fuel supply line, for preventing gaseous fuel flow through said gaseous fuel supply line until termination of liquid fuel combustion, and for thereafter permitting gaseous fuel flow cont to e thro '5 through said gaseous fuel supply line until repositioning of said fuel selector switch to said liquid fuel position. i -15-....... i. n and the control of the ftft ί \\ .
  2. 2
    Apparatus in accordance with Claim 1 wherein said control means also includes vacuum operated means responsive to engine vacuum conditions for controlling gaseous fuel flow coinbus fuel c through said gaseous fuel supply line. supply liquic source which means gaseot cally which is ope openec an ele valve is ope opene< contre said ;contrt said < ’ switcl presei to en also liqui' amoun said contr ( fuel ί
  3. 3
    Apparatus for controlling operation of\an internal r _ jj combustion engine which is selectively operable using gaseous ''G ~ \ fuel or liquid fuel, said apparatus comprising means for supplying a gaseous fuel to the engine, me^ns for supplying a liquid fuel to the engine, and control means connected to a source of vacuum which is responsive to engine operation and which varies relative to a predetermined level, said control means including^ fuel selector switch movable between a gaseous fuel position and a liquid fuel position, an electrically operated, normally closed gaseous fuel control valve which is located in said gaseous fuel supply means, which •Ϊ is operable between open and closed positions, and which is opened in response to electrical energization thereof, and an electrically operated, normally closed liquid fuel control valve which is located in said liquid fuel supply means, which is operable between open and closed positions, and which is opened in response to electrical energization thereof, said control means being operable, when said selector switch is in said liquid fuel position, to energize said liquid fuel control valve, thereby opening said liquid fuel control valve, said control means also being operable, when said selector ’switch is in said liquid fuel position and in response to the presence of an amount of vacuum above said predetermined level to energize said gaseous fuel control valve, said control means also being operable, when said selector switch is in said liquid fuel position and in response to the presence of an amount of vacuum below said predetermined level, to deenergize said gaseous fuel control valve, and thereby close said gaseous fuel control valve, and thereafter to retain said gaseous fuel control valve deenergized regardless of vacuum variation, said ( ί \t i. (Claim 3 continued) control means also being operable, when said selector switch is in said gaseous fuel position, to deenergize said liquid fuel control valve, thereby closing said liquid fuel control valve, said control means also being operable, when said selector switch is in said gaseous fuel position and in response to an amount of vacuum above said predetermined level to deenergize said gaseous fuel control valve, thereby closing said gaseous fuel control valve, and said control means also being operable, when said selector switch is in said gaseous fiiel position and in response to an amount of vacuum below said predetermined level, to energize said gaseous fuel control valve and thereby open said gaseous fuel control valve, and thereafter to retain energization of said gaseous fuel control s 5“ valve regardless of vacuum variation. <! « £ Γ~;L/ & 'Λ
  4. 4
    Apparatus in accordance with Claim 3 wherein said apparatus further includes .electrically operated spark advance means electrically connected, to said control means . and operable in response to energization thereof to advance
  5. 5
    5 the sparking time, and electrically operated intake air heating means electrically connected to said control means, and operable in response to energization to prevent heating of the incoming air, and wherein said control means is inoperable' when said selector switch is in said liquid fuel position, 10 to energize said spark advance means and said air intake means, and wherein said control means also being operable, when said selector switch is in said gaseous fuel position and in response to an amount of vacuum above said predetermined level, ’ J* to deenergize said spark advance means find said inlet air . 4 - i U . 15. heating means, and said control means also being operable, =;' when said selector switch is in said gaseous fuel position and , \ in response to an amount of vacuum below said predetermined ‘ ί < level, to energize said spark advance means and said inlet air heating means, and thereafter to retain energization of 20 said spark advance means and said intake air heating means regardless of vacuum variation. 9. . (I :: Ώ 5. Apparatus in accordance with Claim 4 wherein said selector switch comprises a gaseous fuel terminal, a/> •· ..... , · ' ΐι ., liquid fuel terminal, and a primary switch member connected . · - . *♦ *’* ... // ‘ to a source of direct current, and_moyableL between a first position energizing said gaseous fuel- terminal and a s'econd position energizing said liquid fuel terminal, wilerein said control means further includes first switch means including a first terminal connected to said gaseous fuel control valve, to said spark advance means, and to said intake air heating ) means,· a first switch member electrically connected to said /7 '/ gaseous fuel terminal andmovable relative to a position energizing said first tej/minal’, and thereby energizing said gaseous fuel control valve, said spark advance means, and o? said intake air heating means, said first switch member / being biased away from said first terminal , to ‘ a and means for.holding said first switch member in said position / energizing said first terminal in response to energizing of said first.terminal·, whdrein said control means further includes second switch means including a terminal connected to said 0 , gaseous fuel control valve, a holding terminal, a second switch • member electrically connected to said liquid fuel terminal and movable between a first position engaging said terminal conk nected to said gaseous fuel control valve for energizing ‘ thereof, and a second position engaging said holding terminal, 5 said second switch member being biased to said first position, ‘‘ and means connected to said holding terminal for holding said second switch member in said second position when said holding terminal is energized by said second switch member, wherein said control means further includes vacuum switch means 0 connected to a source qf direct current and to -8 aid first and // second switch^mBlns and ^parable, between an open position in ,, (Claim 5 continued) „ 0 response to the presence of an amount of vacuum above said pre?p^rmjaed level and a second position which is normally closed in the absence of the presence of an amount of vacuum above said predetermined level and which is operable to connect said first switch member to said first terminal and said second switch member to Said holding terminal, and wherein said control means further includes a diode for preventing energization of said spark advance means and said.intake air heating means when said primary switch member is in said liquid fuel position.
  6. 6
    Apparatus in accordance with Claim 5 wherein said engine includes a fuel inlet manifold and said vacuum switch communicates with said fuel^nlet manifold and is subject to the pressure variation in said fuel inlet manifold.
Independent claims6