US2803233A

US2803233A - Carburetors

Info

Publication number: US2803233A
Application number: US436902A
Authority: US
Inventors: Demtchenko Basile
Original assignee: Societe du Carburateur Zenith SA
Current assignee: Societe du Carburateur Zenith SA
Priority date: 1954-06-15
Filing date: 1954-06-15
Publication date: 1957-08-20
Anticipated expiration: 1974-08-20

Description

Aug. '20, 1957 B. DEMTcHENKo 2,803,233

" cARBuRr-:Toas

Filed June 15,y 1954 3 Sheets-Sheet 2 55 s2 54 s? s@ 8O 53 5a j `i l r4 'f8 I v 59 .M-

ze 33 a2 86 so a3 84 so x BASILE DEMTCHENKO Aug. 20, 1957 Filed June 15, 1954 B. DEMTcHENKo 2,803,233

cARBuREToRs 3 Sheets-Sheet 3 1N VENTOR BASILE DEMTCHENKO United States Patent() M CARBURETORS Basile Demtchenko, Issy-les-Moulineaux, France, assignor to Societe du Carburateur Zenith, Lyon, France Application June 15, 1954, Serial No. 436,902

11 Claims. (Cl. 12S-119) This application relates to an improved carburetor for internal combustion engines.

It concerns a carburetor adapted to supply fuel to internal combustion engines and comprising a volumetric fuel pump driven responsive to engine speed and also comprising a metering device dividing into two parts the fuel flow supplied bythe pump to a fuel inlet chamber, one of said parts being dispatched into an injection duct through a calibrated passage, the said injection duct being connected to an injector opening into the engine inlet manifold, while the other of said parts is dispatched into a return duct through a calibrated return passage, the pressure in the said return duct being regulated by a valve disposed therein downstream of said calibrated return passage and controlled by a pressure regulator actuated in dependence upon the pressure diiference between the said injection duct and the said return duct, the ratio between the cross-sections of said calibrated injection passage and of said calibrated return passage being regulated responsive to the engine inlet pressure.

One of the objects of the invention is to eifect an accurate metering of the fuel.

v Another object of the invention is to reduce to theminimum the fuel pressure needed to make the device operate.

Another object of the invention is to correct the fuel flow responsive to temperature.

Other objects of the invention will become apparent from the following description taken in connection with the appended drawings given by way of example, in which:

Fig. l diagrammatically illustrates a cross-section through the volumetric pump of a carburetor according to the invention.

Fig. 2 diagrammatically illustrates a longitudinal section through the fuel metering device of said carburetor.

Fig. 3 is a section along the line III- III through a vpart of the metering device illustrated in Fig. 2.

Fig. 4 diagrammatically illustrates in partial elevation, a part of the inlet manifold of the engine supplied by said carburetor, and also illustrates the injection arrangement and various accessories of the said carburetor.

Fig. 5 illustrates to an enlarged scale the needle of the metering device illustrated in Figs. 2 and 3.

Fig. 6 illustrates an alternative form of the needle illustrated in Fig. 5.

Fig. 7 illustrates the assembly of the complete system on an internal combustion engine.

According to one feature of the invention, a manometric device operated responsive to the engine inlet pressure simultaneously so regulates the calibrated injection passage and the calibrated return passage as to increase the cross-section of the calibrated injection passage and to reduce the cross-section of the calibrated return passage when the inlet pressure increases, and vice versa. The action of the manometric device can be compensated for in dependence upon the atmospheric pressure.

Preferably, the sum of the cross-sections of the cali- 2,8%,233 Patented Aug. 20, 1957 ICC brated injection passage and of the calibrated return passage is maintained substantially constant when the respective cross-sections of said two passages vary.

In a preferred embodiment of the invention, the calibrated injection passage and the calibrated return passage are formed by calibrated orifices, the flow crossections of which are regulated by a single profiled needle.

Preferably, the free annular spaces between said needle and each of said calibrated orifices are of small Width relatively to the needle diameter.

According to a further feature of the invention, a bypass is provided between the fuel inlet chamber and the return duct. The flow cross-section of the by-pass is controlled by a ,valve controlled by a thermostatic device. Preferably, the latter is subjected to the temperature prevailing in the engine inlet manifold. When the total of the cross-sections of the calibrated injection passage and of the calibrated return passage is maintained substantially constant, the cross-section of the said bypass is preferably so regulated that the total of the crosssections of the calibrated injection passage, of the calibrated return passage, and of said by-pass is substantially proportional to the absolute inlet temperature.

In a preferred embodiment of the invention, the manometric device regulating the ratio between the cross-sections of the calibrated injection passage and of the calibrated return passage is subjected to the pressure prevailing in a chamber connected on the one hand, through a calibrated suction passage, to the engine inlet manifold downstream of a throttle disposed in said engine inlet manifold, and on the other hand, through a calibrated air passage, to the air supply pressure to said manifold, the ratio between the cross-sections of the said suction passage and of the said air passage being variable. The last-mentioned ratio can be regulated responsive to the opening of said throttle in order to regulate the richness of the mixture supplied to the engine at small openings of said throttle. The said ratio can also be modified in order to obtain a momentarily richer mixture when the engine is running cold.

In a preferred embodiment, the volumetric pump supplying fuel to the metering device comprises a gear pump element and a metering element having the same structure as a gear pump arranged in tandem. The pump element supplies the metering element and has a greater delivery than said metering element. The delivery chamber of the pump element, which chamber also forms the inlet chamber of the metering element, is connected to the inlet chamber of the pump element through a return passage controlled responsive to the pressure differential between the input and delivery of the metering element in such manner as to maintain said pressure differentialI substantially constant and positive.

For the sake of clarity in the drawings and description, certain constructional details known to the engineer in the art such as fixing devices, fluid-tight packings, devices for locking threaded members, etc., have been simplilied or are not shown or are shown but not described.

The carburetor illustrated in the drawings comprises a volumetric fuel pump 1 (Fig. l), a fuel measuring device 2 (Figs. 2 and 3), an injector-3, and an ancillary slow-running and cold-running device 4 (Fig. 4). The assembly of the various parts of said carburetor on an engine 200 is shown on Fig. 7.

The volumetric pump 1 illustrated in Fig. l comprises a gear pump element and a metering element having the same structure as a gear pump.

The pump element comprises two

interengaging pinions

5 and 6, one of which is driven responsive to 'engine speed. For example, said pump element can run at half the engine speed as does the camshaft, but could also run at engine speed or at any other suitable speed iu relation with the engine speed. Pinions and 6 rotate in the direction indicated by the arrows. k

The pump element comprises an inlet chamber 7 connected to a fuel supply pipe 8 and to a delivery chamber 9. The latter communicates with inlet chamber 7 through a return duct 10-11 controlled by a slide valve 12 which is loaded by a spring 13 and which slides in a cylinder 14.

The metering element comprises two interengaging pinions 1'5 and 16. As the pump element, one of the

pinions

15 or 16 is driven responsive to engine speed, for example at half engine speed or at any other suitable speed in relation with the engine speed. Pinions 1S and 16 rotate in the direction of the arrows.

The delivery chamber 9 of the pump element forms the inlet chamber of the metering element, and the delivery chamber 17 of the metering element is connected to the metering device 2 (Fig. 2) through a pipe 18. Y Delivery chamber 17 communicates with cylinder 14 through a passage 19. Thus, slide valve 12 is subjected, ononeY of its faces, to the pressure prevailing in chamber 9 and transmitted through pipe 10 and, on its other face, to the pressure prevailing in chamber 17 and transmitted through passage 19. The respective sizes of the

pinions

5 and 6 of the pump element and of the

pinions

15 and 16 of the metering element are so chosen that the delivery per engine revolution of the pump element is greater than the delivery per engine revolution of the metering element. In such circumstances, the metering element only draws off part of the delivery of the pump element, and a part of the last-mentioned delivery returns from charnber 9 to inlet chamber 7 through the return pipe 10-11. The liow through return pipe 10-11 causes slide valve 12 to open and to assume such an equilibrium position that the pressure differential between chamber 9 and chamber 17 substantially balances the force of spring 13. The metering device 2 (Figs. 2 and 3) comprises a body 20 having a cylindrical housing 21 in which is fixed a sleeve 22. A guide Z3, a return jet 24 and an injection jet 25 are fixed in sleeve 22. Jet 24 comprises a calibrated return orifice 26, and jet 25 comprises a calibrated injection orifice 27.

The fuel piperlS from pump 1 communicates with a fuel inlet chamber 28 through an annular throat 29 and radial passages 30. The delivery end of the calibrated injection orifice 27 is connected through an injection passage 31 and pipe 32 to injector 3 (Fig. 4).

The delivery end of the calibrated return orifice 26 opens into a chamber 33 connected through radial passagesv 34 and an annular throat 35 to a return pipe 36. A slide valve 37 regulates the communication between return pipe 36 and a chamber 38 connected through a discharge pipe 39 to the inlet of pump 1 or to the fuel tank.

Slide valve 37 is guided in a sleeve 40 fixed in body 2, and is connected to a piston 41 sliding in a cylindrical housing in sleeve 40. Chamber 42 above the piston 41 and chamber 38 are closed by a cover 43.

Chamber 42 communicates with injection passage 31 through a pipe 44, while chamber 45 below the piston 41 communicates with return pipe 36 through a pipe 46. Since piston 41 is subjected on the one hand to the pressure` in injection passage 31 and on the other hand to the pressure in return pipe 36, said piston 41 so regulates the opening of slide valve 37 that the last-mentioned two pressures are substantially equal. l

A valve 47 enables a pipe 48 connected to injection passage 31 to communicate with chamber 38 and discharge pipe 39. Valve 47 is normally maintained closed by a spring 49. Valve 47 can be opened by means of a lever 50 acting on the push-rod 51 associated with said valve and guided in cover 43.

A valve 52 (Fig. 3) enables chamber 33 to be connected to atmosphere through a pipe 53 and an orifice 54. Valve 52 is normally maintained closed by a spring 55. Valve 52 can be opened by means of a push-rod 56 guided in a plug 57 and return by a spring 58. The object of valve 52 is to enable the air contained in the fuel piping of the device to be removed when the engine is started.

The fiow cross-section of the calibrated

orifices

26 and 27 is regulated by means of a needle 59 comprising a profiled part 60 illustrated to an enlarged scale in Fig. 5. Needle S9 is guided in sleeve 22 and guide 23.

Starting from the left, needle 59 illustrated in Fig. 5 comprises a cylindrical end 136, a conical part 137 which in normal running co-operates with calibrated orifice 27, a cylindrical part 138, a short cylindrical part 139 of greater diameter, a conical part co-operating during normal operation with calibrated orifice 26, a cylindrical part 141, and, finally, a cylindrical part 142 of greater diameter guided in guide 23. Guide 23 and calibrated

orifices

26 and 27 are of the same internal diameter. The guide and the two orifices are bored simultaneously in order to obtain centering of the profiled part of the needle 59 in the calibrated

orifices

26 and 27.

In Vthe alternative illustrated in Fig. 6, needle 59 is substantially the same as that illustrated in Fig. 5, differing merely in the following features: conical part 137 (Fig. 5) is replaced by two

conical parts

143 and 144 of different angles, and conical part 140 (Fig. 5) is replaced by two conical parts and 146 of different angles.

Needle 59 is attached to a manometric capsule 61 disposed in chamber 62. Capsule 61 is preferably evacuated and comprises a shank 63 screwed into cover 64 of chamber 62, this shank enabling the position of said capsule to be adjusted. j

Chamber 62 communicates with the engine inlet manifold 65 (Fig. 4) through a calibrated orifice 66 and pipe 67, and also communicates through a pipe 68 with a chamber 69 of the auxiliary slow-running and cold-running device 4 (Fig. 4) which will be well described hereinafter.

The pressure in chamber 62 is transmitted through a passage 70 to a cylinder 71 disposed in a lid 81 fixed to body 2. A piston 72 loaded by a spring 73 slides in cylinder 71. A guided rod 74 is intercalated between piston 72 and needle 59. Rod 74 is of the same diameter as the cylindrical part of needle 59, so that the position of the latter is unaffected by the fuel pressures. A chamber 75 separated from cylinder 71 by piston 72 communicates with atmosphere through a filter 76 adapted to prevent dust from entering chamber 75.

Fuel leaks which may occur between needle 59 and guide 23 are drained ofi through channels 77, a groove 78, a passage 79 (Fig. 3), and a draining tube 80. Any fuel leaks between rod 74 and the guiding means thereof are similarly drained off through a groove 82 connected to draining tube 80. The mounting of needle 59 and of rod 74 in their guiding means is sufficiently exact to maintain the said leaksat a very low level and to prevent them from having any appreciable effect upon the metering of the fuel.

The thermostatic correcting device illustrated in Fig. 3 comprises a by-pass between fuel inlet chamber 28 and chamber 33 formed by two

passages

83 and 84 communicating through a calibrated orifice 85 fitted in a sleeve 86. The Alatter is screwedin'to body 20, so that its' position is adjustable. The locking device adapted to fix sleeve v86 in the set position is not shown.

A needle 87 guided in sleeve 86 and comprising a profiled part 88 regulates the flow cross-section of calibrated orifice 85. The left-hand end of needle 87 is held against a cam 89 by a spring 90. Adjustment of the position of sleeve 86 enables to adjust the flow cross-section of calibrated orifice 85 corresponding to a predetermined position of cam 89 of needle 87.

The rotation of cam 89 is controlled by a thermostatic device 91 disposed in the engine inlet manifold. Said device 91 comprises a bimetallic spiral spring 92 arranged in a casing 93. One of the ends of bimetallic spring 92 is fixed at 94 to casing 93, while the other end of spring 92 is fixed to a spindle 95. Sheathing 96 connects casing 95 to body 20. A piano string 97 disposed in sheathing 96 is fixed by its ends on the one hand to spindle 95 of the thermostatic device and on the other hand to spindle 98 of cam 89. Sheathing 96 is mounted in duid-tight fashion upon body 20 and casing 93 in order to prevent any fuel leakage.

Depending upon the variations in the inlet manifold temperature to which the thermostatic device isexposed, bimetallic spring 92 rolls up or unrolls, and the rotation of spindle 95 is transmitted to cam 39 by piano string 97. Thermostatic spring 92, cam 89 and profile S8 of needle 87 are so contrived that an increase in the inlet temperature causes an increase in the flow cross-section of calibrated orifice 85. In the drawings, an increase in thel inlet temperature corresponds to a movement of needle 87 to the left.

Inlet manifold 65 partly illustrated in Fig. 4 comprises .a throttle member 99 to which air is supplied through an air intake i) which can be connected to an air scoop or air filter. The quantity of air admitted to the engine is regulated by means of a throttle 101 controlled by a lever 102.

Fuel injector 3 is fitted to inlet manifold 65.

The fuel passage 103 of injector 3 is supplied with metered fuel through pipe 32 connected to metering device 2. A valve 104 loaded by a spring 105 is disposed in fuel passage 103. Valve 104 is subjected on the one hand to the pressure of the fuel in passage 103 and on the other hand to the engine air supply pressure transmitted from air intake 100 through orifice 106, passage 107, pipe 108 and passage 109. Loaded valve 104 has the task of constantly maintaining in the fuel supply circuit a pressure greater than atmospheric pressure. During normal operation, the pressure in fuel passage 103 is sufficient to keep valve 104 applied to a packing washer 110, this preventing fuel leakage towards the air intake through pipe 108.

A socket 111 fitted in the injector body is maintained imposition by the nosepiece 112 of the injector screwed into said body. A member 113 having helical grooves is fitted in a chamber 114 disposed inside socket 111 which comprises a fuel outlet orifice 115. An annular space 116 between the injector body and socket 111 is connected to air intake 100 through a passage 117 communicating with pipe 108. Annular space 116 communicates with an aerated fuel outlet 118, disposed in nosepiece 112, through tangential slots 119 in the upper part of socket 111.

When valve 104 is opened by the fuel pressure in passage 103, the metered fuel supplied through pipe 32 flows away towards fuel outlet orifice 115 through chamber 114 and the helical grooves in member 113. When throttle 101 is wide open, and the Vengine speed relatively high, the fuel pressure is sufficient to ensure satisfactory fuel atomisation at the outlet of orifice 115. The helical grooves in member 113 impart whirl to the fuel and improve atomisation.

v When throttle 101 is near its closed position and the engine speed is relatively low, the 4fuel flow is too small to create through orifice 115 a pressure drop adequate for ensuring satisfactory atomisation, but the suction is high in inlet manifold 65 downstream of throttle 101 so that air is sucked from air intake 100 towards the aerated fuel outlet 113 through orifice 106, passage 107, pipe 108, passage 117, annular space 116 and tangential slots 119, Due to the high suction, this air flows at greatA specdand Q lever 102. 1

The ancillary slow-running and cold-running device 4 comprises a chamber 69 which is connected to passage 107 through two

ducts

124 and 125. Passage 107 cornmunicates with air intake through orifice 106.

A calibrated orifice 126 is disposed between chamber 69 and duct 124. Said orifice 126 is controlled by a profiled valve 127 which tends to be returned into the closed positions by a spring 128. At small openings o f throttle 101, a setting screw 129 on a lug 130 of throttle lever 102 so urges rod 131 of valve 127 as to cause the opening of the same. The ow cross-section of orifice 126 is the greater as throttle 101 is more closed. The setting screw 129 makes it possible to setl that opening of throttle 101 above which orifice 126 is completely closed by valve 127. p

The communication between chamber 69 and passage 107 is also regulated by a needle valve 132 which adjusts the inlet cross-section of channel 124. Needle valve 132 permits of setting the maximum flow cross-section of the communication between chamber 69 and air intake 100 when throttle 101 is completely closed and when valve 127 is at maximum opening.

Channel is controlled by a valve 133, the stem 134 of which is guided in the body of auxiliary device 4. Valve 133 is controlled by means of a lever 135. Valve 133 is normally kept closed and is only opened when the engine is running cold.

The operation of the device is as follows:

In theory, the quantity of fuel q which must be supplied to the engine in order to obtain a combustible mixture of constant richness under all operating conditions is given by the formula:

Q le 1) T (p. C)

where N=engine speed, ptr-:inlet pressure, pe=exhaust back pressure, T=absolute temperature in the inlet maniis only a correcting term which is small with respect to the terms pa. Exhaust back pressure pe varies chiely according to atmospheric pressure, but it varies also as engine load and speed change. However, for the application of Formula l, the influence of engine load and speed on the exhaust back pressure may be neglected and atmospheric pressure may be taken with sufficient accuracy as an equivalent of exhaust back pressure pe.

Pump V1, when driven, for example, at half the engine speed, supplies to the metering device 2 a quantity of fuel proportional to the engine speed.

It is known that a gear pump is only approximately volumetric, its output per revolution varying slightly with the speed of the pump and with the pressure differential between the delivery and input chambers. This variation cannot be controlled, because it depends upon play within the pump and upon the state of wear thereof.

In the pump illustrated in Fig. l, there is a substantially constant pressure differential between input chamber 9 and delivery chamber 17 of the metering element 15-16 supplied by the higher-delivery pump element 5-6, said pressure differential being due to the operation of slide valve 12 controlling return pipe 10-11.

The constancy of the pressure differential between chambers 9 and 17 need not be achieved `.very accurately, and ,it issufficient that said pressure differential below enoughforleakages in the metering element- 15-16 to be negligible relatively tothe delivery thereof.

l Experiments have shown that the best results were btained when the pressure in input chamber 9 was slightly above the pressure in delivery chamber 17. The metering element 15-16 therefore has the structure of a pump but does not operate as one, the delivery pressure being less than Vthe input pressure. The metering element 15-16 has in effect the function of a flow metering device.

t This can be explained as follows: the engagement of the teeth of the

pinions

15 and 16 on the delivery side thereof forces fuel out of the spaces between said teeth,

which creates a local rise in pressure on said delivery side.

On the contrary, the disengagement of the teeth of the

pinions

15 and 16 on the input side thereof creates a suctionA and a local fall in pressure on said input side. If the pressures in input chamber 9 4and delivery chamber 17 were maintained equal, this local rise in pressure on the deliveryside and this local fall in pressure on the input side would create a local pressure differential resulting in a slight leakage from the delivery side towards the input side. The provision of a pressure slightly higher in the input chamber 9 than in the delivery chamber 17 compensates for said local pressure differential and for the slight leakage resulting therefrom.

Apart from the constancy of delivery per revolution of metering element 15-16, the maintenance of a higher pressure in input chamber 9 than in delivery chamber 17 assists in the priming of the pump at starting when the pump contains air.

The fuel supplied by pump 1 to metering device 2 through pipe 18 is divided into two parts, one of which passes to injector 3 through calibrated orifice 27 and injection passage 31, while the other part passes to return pipe 36 and discharge pipe 39 through calibrated return orifice 26 on the one hand and, on the other hand, through calibrated orifice 85 disposed in the thermostatic correction by-pass 83-84.

As has been shown, the operation of slide valve 37 controlling return pipe 36 and controlled by piston 41 is such that the pressure in return pipe 36 on the delivery side of calibrated orifices 26 and 85 is substantially equal to the pressure in injection passage 31 on the delivery side of calibrated orifice 27. The quantities of fuel delivered through the calibrated orifices 27, 24 and 85 are therefore proportional to the flow cross-sections s1, s2, 'sa thereof. and that fraction of the total delivery of pump 1 supplied to the injector is equal to:

Sri-Srl- Since the total pump delivery is proportional to the engine speed N, the quantity q supplied to the injector is given by the formula:

where k1=constant.

During normal operation, since throttle 101 is open sufficiently for valve 127 to be closed, and since valve 133 itself is closed, chamber 62 containing capsule 61 has no communication through pipe 68 with air intake 100. Chamber 62 is only in communication, through pipe 67, with the inlet manifold downstream of throttle 101, and the pressure transmitted to chamber 62 and thence to cylinder 71 through passage 70 is equal to the inlet pressure pa. Since piston 72 is subjected to atmospheric pressure which may be taken as an vequivalent of exhaust back pressure, it will be immediately apparent that the movements of needle 59 under the combined influence of manometriccapsule 61 and-piston 72 are proportional to:

Pac

Needle 59 is so designed that, under all conditions of normal operation, the cross-section of calibrated orifice 27 `may bel regulated'by part 137 (Fig. 5) of needle 59 without part 138 ever penetrating into said calibrated orifice. Similarly, the cross-section of calibrated orifice 26 is regulated by part 140 of needle 59. l

If the (width of the annular space between needle 59 and calibrated orifice 27 is small relatively to the diameter thereof, part 137 of needle 59 being conical, the variations in the crossfsection of calibrated orifice 27 are substantially proportional to the movements of needle 59, so that the ow cross-sections of calibrated orifice 27 is therefore proportional to:

Conical part 140 of needle 59 is so designed that the sum of the flow-cross-section s1 of calibrated orifice 27 and of flow cross-section s2 of calibrated orifice 26 remains substantially constant and equal to s.

lThermostatic device 91 being subjected to the inlet temperature T, the profile of cam 89 and of profiled partr77 o-f needle 87 regulating Vthe flow cross-section sa of calibrated orifice 8S can be so contrived that the sum of the cross-sections s+ss=s1js2+s3 varies proportionally to T.

Since the cross-section si varies proportionally to pac and the sum of the cross-sections sl-j-s2}s3 varies proportionally to T, Formula 2 can be rewritten:

This latter formula is identical with Formula l; therefore the quantity of fuel supplied to the injector by the metering device corresponds to the theoretical quantity required to effect a mixture of constant richness.

In practice, it-is not desirable for the richness of the mixture to remain exactly constant under all operating conditions.A It is particularly desirable to enrich the mixture upon reaching the region of full-load operation corresponding to maximum opening of throttle 101. This result is obtained by modifying the profile of needle 59 as illustrated in Fig. 6.

At medium load, the flow cross-section of calibrated orifice 27 is regulated by part 144 of the needle, which part has the same profile as the corresponding part 137 on the needle illustrated in Fig. 5. In the full load region, the flow cross-section of calibrated orifice 27 is regulated by the conical part 143 of the needle, said part 143 being adapted to increase said flow cross-section more rapidly,

when the vneedle moves towards the right. That part 140 (Fig. 5) of the needle regulating the flow cross-section of calibrated orifice 26 is likewise replaced by two conical parts y146 and 145 having different angles.

In some cases, it is not necessary to regulate the quantity of fuel with great accuracy, and the thermostatic correction of the quantity of fuel can then be omitted. To this end, it is sufficient to omit by-pass 83-84 and the elements controlling the same.

Fuel delivery correction in dependence upon the cxhaust back pressure is usually necessary when the engine is to operate at considerable altitudes. Contrary thereto, this correction can usually be omitted if the engine is merely adapted to operate at ground level. The removal of this correcting means is effected by omitting cover 81 -(Fig. 2) containing piston 72 and rod 74 and to replace said cover by a solid cover.

It has beenshown that the fact of giving to needle 59 such a profile, that the sum of the flow cross-sections s1 and s2 of calibrated injection orifice 27 and of calibrated return `orifice 24 lremains constant, makes it possible to carry into effect with great accuracy the law of correct 9 variation of the quantity of fuel supplied to the engine. This arrangement has two important further advantages, firstly enabling the volumetric capacity of the pump to be reduced to a minimum and also enabling the pressure absorbed by the metering device to be reduced at a minimum.

For example, if the calibrated return orifice 24 of variable cross-section were replaced by an orifice of fixed cross-section and if the maximum cross-section of the calibrated injection orifice 27 corresponding to maximum inlet pressure were equal to the fixed cross-section of the return orifice, the fuel flow would be divided into two equal parts between the two orifices and the pump delivery would therefore have to be twice as great as would be necessary for supplying the engine. Contrary thereto, if in the arrangement hereinbefore described returnorifice 24 is substantially completely closed when the inlet pressure is at` a maximum, the entire pump delivery passes through injection orifice 27, with the result that the volumetric capacity of the pump can be half that of theI case just described.

In order that the fuel may be metered exactly, the pressure drop across the calibrated orifices must not decrease below a predetermined value even with small rates of flow corresponding to slow running. On the other hand, it is also desirable that the maximum pressure absorbed by the metering device at maximum engine speed, which pressure adds to the pressure absorbed by the injector, is not very high in order not to increase unduly the pressure which the pump must set up.

' The arrangement by which the sum of the flow crosssections of the calibrated injection orifice and of the calibrated return orifice is maintained substantially constant makes it possible to reduce to a minimum the variation in the pressure absorbed by the metering device. For a given speed, the pressure drop through the calibrated orifices is constant since the sum of the ow cross-sections of the said orifices is constant. Thus, the variations in the pressure absorbed by the metering device are merely the result of variations in engine speed.

If, on the contrary, the sum of the fiow cross-sections of the calibrated injection orifice and of the calibrated return orifice is variable, the pressure drop through the said calibrated orifices at a given engine speed varies in dependence upon the said sum, and this variation in pressure drop is added to the variations associated with engine speed.

For example, if the engine speed varies between 400 to 4000 R. P. M. and if the pressure drop necessary to obtain correct metering is 0.05 p. s. i., this pressure drop will change from 0.05 p. s. i. at 400 R. P. Ml. to p. s. i. at 4000 R. P. M. in the device described. If the device should have a return orifice of fixed cross-section and an injection orifice, the cross-section of which varies between the cross-section of the return orifice and half of the last-mentioned cross-section, the pressure drop in the calibrated orifices would still change from 0.05 p. s. i. to 5 p. s. i. when the cross-section of the injection orifice is at a maximum, but would increase up to 9 p. s. i. if, at the speed of 4000 R. P. M., the cross-section of the said injection orifice were brought to its minimum value.

In the preceding explanations, the thermostatic correction by-pass 83-84 comprising calibrated orifice 85 has been neglected, and the sum of the cross-sections s,+s,}s, of the calibrated orifices through which the fuel passes is not exactly constant. In fact, a temperature `variation of 25 C. either side of a mean inlet temperature, that is to say a total temperature variation of 50 C., merely represents an 8% variation of the absolute temperature on either side of the mean temperature and merely causes an 8% variation in the sum of the flow cross-sections of the three calibrated orifices sharing the fuel delivered by the pump. It can therefore be considered that, even taking into account the thermostatic correction device, the sum of the fiow cross-sections of the said lcalibrated orifices remain substantially constant,

and the described device fully benefits fromthe advantages hereinbefore mentioned. A

Generally speaking, it is sufficient, for a partial benefit from the said advantages, to embody according to the invention an arrangement wherein both the calibrated injection orifice and the calibrated return orifice are variable, an increase in the flow cross-section of one of the said orifices corresponding to a decrease in the flow crosssection of the other orifice and vice versa.

Preferably, the width of the annular spaces between needle 59 and calibrated

orifices

26 and 27 is small relatively to the diameter of said calibrated orifices. As has already been explained, the variations in the fiow crosssections of the said calibrated orifices are then proportional to the needle displacements, this fact making it possible to use conical profiles for the needle and to determine the said proles very readily when the value of the rates of fiow to be effected are known.

This arrangement has a further advantage. The ows through the annular spaces in the calibrated

orifices

26 and 27 are physically similar and the ratio Ibetween the rates of fiow therefore depends solely upon the ratio between the flow cross-sections of the said orifices and is not affected by physical characteristics such as density and viscosity of the fuel used. Preferably the active edges of the calibrated orifices 26 and 27m-operating with needle 59 are thin.

When the carburetor is intended to supply an aircraft engine, a safety device must be provided to re-establish the rate of fuel flow corresponding to full throttle ,at ground level if the capsule 61 bursts. In such circumsatnces, the capsule 61 which is normally evacuated fills with air and expands up to its maximum length, urging needle 59 towards the left beyond the positions of normal operation. Cylindrical part 138 of the needle engages in calibrated orifice 27, while cylindrical part 141 engages in calibrated orifice 26. The diameter of parts 138 and 141 is so determined that the ratio between the fiow cross-sect-ions of calibrated

orifices

27 and 26 correspond in these circumstances to the rate of fuel flow necessary to ensure full throttle operation at ground level.

At small throttle openings, the combustible mixture must be richer than during normal operation. Enrichment of the mixture at small throttle openings is effected by opening valve 127 (Fig. 4). Air from the air intake 100 is admitted into chamber 62 containing capsule 61 through orifice 106, channel 124, orifice 126 regulated by valve 127, chamber 69 and pipe 68. This intake of air has the effect of reducing the suction transmitted to chamber 62'through calibrated orifice 66 and pipe 67 connected to the inlet manifold. This reduction of suction causes a contraction of capsule 61 and a corresponding movement of needle 59 in `the sense of an increase in the rate of fuel flow.

The reduction in the suction transmitted to chamber 62 is regulated by means of screw 132 (Fig. 4) and that opening of throttle 101 below which this reduction in suctionbegins to become effective is regulated by means of screw 129.,

It is also necessary to enrich the mixture during starting and cold running. This enrichment is obtained by opening valve 133 by means of lever 135 (Fig. 4).' The opening of valve 133 has the effect of placing the capsule chamber 62 in communication with air intake 100, this enriching the mixture in the manner hereinbefore explained.

At the instant that throttle 101 is opened by means of lever 102, the movement of the same is transmittedto lever 122 by link 123, and the accelerating pump diaphragm 121 is thrust upwards. This movement of diaphragm 121 causes an injection of fuel through fuel outlet 115, and also produces in chamber a pressure increase which is transmitted through pipe 32 to injection passage 31 and to the upper face of piston 41 situated in chamber 42. As a result of this pressure increase, piston 41 closes return pipe 36, and a greater quantity of the delivery of pump 1 is directed through calibrated injection orifice 27 to injector 3.

If it is desired to stop the engine by interrupting the fuelsupply thereto, valve 47 is opened by means of lever 50. This places injection passage 31 in communication with discharge pipe 39 through passage 48 and chamber 38, and pressure drops in injection passage 31. At the same time, slide valve 37 opens and all the fuel flows to discharge pipe 39, on the one hand through injection passage 31, passage 48 and open valve 47, and on the other hand through return pipe 36 and open slide valve 37. The supply of the injector through pipe 32 is therefore interrupted.

The described device can be modified as to its details without for that reason departing from the scope of the invention.

In particular, the pistons illustrated can be replaced by flexible diaphragms and vice versa.

It has already been proposed to control a regulating member in dependence upon the difference Pre The control of needle 59 by a combined action of capsule 61 and of piston 72 can be replaced by any other known control of this type. For example, piston 72 can be omitted and replaced by a small secondary capsule disposed in chamber 62 and interposed between capsule 61 and shank 63 fixed to cover 64, the interior of the said secondary capsule being connected to atmosphere.

When the carburetor is merely intended for operation at ground level, not only it is possible to omit, as hereinbefore described, piston 72 which effects a correction in dependence upon the atmospheric pressure, but it is also possible for the manometric capsule 61 to be replaced by a flexible diaphragm which closes chamber 62 and which has its outer face subjected to atmospheric pressure. Said diaphragm would be attached to needle 59 and would be spring-loaded.

The law of the rate of fuel flow which must be ernbodied in practice often differs considerably from the theoretical law of the rate expressed hereinbefore in Formula 1, this difference depending upon the constructional features of the engine. The regulating members of the device described may therefore be modified. In particular the profile of needle 59 can be modified, and can, ifdesired, be so determined that the sum of the fiow cross-sections of the calibrated orifices 27 y and 26 is not constant in the manner hereinbefore described.

I claim:

1. A carburetor for an internal combustion engine having a source of fuel an inlet manifold and injecting means opening into said inlet manifold, which comprises, in combination, a volumetric fuel pump supplied from said source of fuel and driven responsive to engine speed, an inlet chamber supplied with fuel from said pump, an injection duct connecting said inlet chamber with said injecting means, a calibrated injection passage in said injectionduct, a return duct from said inlet chamber connected to said source of fuel, a calibrated return passage in said return duct, valve means in said return duct responsive to the pressure differential between said injection duct downstream of said calibrated injection passage and said return duct downstream of said calibrated return passage, and manometric means responsive to the presssure in saidl inlet manifold for controlling both said calibrated injection passage and said calibrated return passage so as to increase the cross-section of said calibrated injection passage as the cross-section of said calibrated return passage is decreased and conversely.

2. The invention defined in claim 1, wherein'said manometric means are further responsive to atmospheric pressure.

12 Y 3'. The invention defined in claim 1, wherein the sum of the cross-section of said calibrated injection passage and of said calibrated return passage is maintained substantially constant when the respective cross-sections of said two passages is varied.

4. A carburetor for an internal combustion engine having a source of fuel an inlet manifold and injecting means opening into said inlet manifold, which comprises, in combination, a volumetric fuel pump supplied from said source of fuel and driven responsive to engine speed, an inlet chamber supplied with fuel from said pump, an injection duct connecting said inlet chamber with said injecting means, a calibrated injection orifice in said injection duct, a return duct from said inlet chamber connected to said source of fuel, a calibrated return orifice in said return duct, valve means in said return duct responsive to the pressure differential between said injection duct downstream of said calibrated injection orifice and said return duct downstream of said calibrated return orifice, a profiled needle for controlling both said calibrated injection orifice and said calibrated return orifice so as to increase the cross-section of said calibrated injection orice as the cross-section of said calibrated return orifice is decreased and conversely, and manometric means responsive to the pressure in said inlet manifold for controlling said needle.

5. The invention defined in claim 4, wherein the free annular spaces between said needle and each of said calibrated orifices are of small width relatively to the needle diameter.

6. A carburetor for an internal combustion engine having a source of fuel an inlet manifold and injecting means opening into said inlet manifold, which comprises, in combination, a volumetric fuel pump supplied from said source of fuel and driven responsive to engine speed, an inlet chamber supplied with fuel from said pump, an injection duct connecting said inlet chamber with said injecting means, a calibrated injection passage in said injection duct, a return duct from said inlet charnber connected to said source of fuel, a calibrated return passage in said return duct, valve means in said return duct responsive to the pressure differential between said injection duct downstream of said calibrated injection passage and lsaid return duct downstream of said calibrated return passage, manometric means responsive to the pressure in said inlet manifold for controlling both said calibrated injection passage and said calibrated return passage so as to increase the cross-section of said calibrated injection passage as the cross-section of said calibrated return passage is decreased and conversely, a by-pass between said inlet chamber and said return duct downstream of said calibrated return passage, and thermostatic means responsive to the temperature prevailing in said inlet manifold for controlling said by-pass.

7. A carburetor for an internal combustion engine having a source of fuel an inlet manifold and injecting means opening into said inlet manifold, which comprises, in combination, a volumetric fuel pump supplied from said source of fuel and driven responsive to engine speed, an inlet chamber supplied with fuel from said pump, an injection duct connecting said inlet chamber with said injecting means, a calibrated injection passage in said injection duct, a return duct from said inlet chamber connected to said source of fuel, a calibrated return passage in said return duct, valvel means in said return duct responsive to the pressure differential between said injection duct downstream of said calibrated injection passage and said return duct downstream of said calibrated return passage, manometric means responsive to the pressure in said inlet manifold for controlling both said calibrated injection passage and said calibrated return passage so as to increase the cross-section of said calibrated injection passage as the cross-section of said calibrated return passage is decreased and conversely, a by-pass between said inlet chamber and said return duct said two passages is varied, and said bypass is so controlled by said thermostatic means that the sum of the cross-sections of said'calibrated injection passage, of said calibrated return passage, and of said by-pass is substantially proportional to the absolute temperature in said inlet manifold.

9. A carburetor for an internal combustion engine having a source of fuel an inlet manifold supplied with air, a throttle in said inlet manifold, an injecting means opening into said inlet manifold, which comprises, in combination, a volumetric fuel pump supplied from said source oi fuel and driven responsive to engine speed, an inlet chamber supplied with fuel from said pump, an injection duct connecting said inlet chamber with said injecting means, a calibrated injection passage in said injection duct, a return duct from said inlet chamber connected to said source of fuel, a calibrated return passage in said return duct, valve means in said return duct responsive to the pressure differential between said injection duct downstream of said calibrated injection passage and said return duct downstream of said calibrated return passage, an air chamber, a suction passage connecting said air chamber with said inlet manifold downstream of said throttle, an air passage connectingv said air chamber with the air supply pressure to said inlet manifold, means for varying the ratio between the cross-sections of said suction passage and said air passage, and manometric means responsive to the pressure in said air chamber for controlling both said calibrated injection passage and said calibrated return passage so as to increase the cross-section of said calibrated injection passage as the cross-section of said calibrated return passage is decreased and conversely.

10. The invention defined in claim 9, wherein said ratio is varied responsive to the opening of said throttle.

1l. A carburetor for an internal combustion engine having a source of fuel, an inlet manifold and injecting means opening into said inlet manifold, which comprises, in combination, a gear pump element supplied from said source of fuel, a metering element having the structure of a gear pump of lower flow capacity than said gear pump element, supplied with fuel from said gear pump element, means for driving both said gear pump element and said metering element responsive to engine speed, an intermediate chamber between the outlet of said gear pump element and the inlet to said metering element, a conduit for returning fuel from said intermediate chamber to the inlet of said gear pump element, valve means in said conduit responsive to the pressure differential between said intermediate chamber and the outlet of said metering element for maintaining said pressure differential substantially constant and positive, an inlet chamber supplied with fuel from said metering element, an injection duct connecting said inlet chamber with said injecting means, a calibrated injection passage in said injection duct, a return duct from said inlet chamber connected to said source of fuel, a calibrated return passage in said return duct, valve means in said return duet responsive to the pressure differential between said injection duct downstream of said calibrated injection passage and said return duct downstream of said calibrated return passage, and manometric means responsive to the pressure in said inlet manifold for controlling both said calibrated injection passage and said calibrated return passage so as to increase the cross-section of said calibrated injection passage as the cross-section of said calibrated return passage is decreased and conversely.

No references cited.