US3917760A - Carburetters fitted to internal combustion engines - Google Patents

Abstract

A constant depression or velocity carburetter incorporates an enriching device which acts to increase fuel enrichment with decreasing engine temperature. The carburetter can also include a manifold depression sensor which additionally acts to increase fuel enrichment with decreasing manifold depression.

Description

United States Patent 11 1 Swatman 5] Nov. 4, 1975 CARBURETTERS FITTED TO INTERNAL 3,460,814 8/1969 0116111 261/44 R COMBUSTION ENGINES 3,576,315 4/1971 Sutton 123/180 R X 3,677,241 7/1972 Gele et a1. 1 1 261/50 A X Inventor Peter Phlllimflre n, Sclihull. 3,746,321 7/1973 DePontac 261/50 A England 3,835,831 9/1974 Ross 123/180 R X [73] Assignee: British Leyland (Austin-Morris) FOREIGN PATENTS OR APPLICATIONS Limited, Birmingham England 335,680 2/1936 Italy 123/180 R [22] Filed: Jan. 25, 1974 Primary Examiner-Tim R. Miles 1 1 pp N062 36,650 Assistant Examiner-William Cuchlinski, Jr.

Attorney, Agent, or Firm-Brisebois & Kruger [52] US. Cl. 261/39 B; 123/1875 R; 261/39 E;

261/44 R; 261/D1G. s 1 1 ABSTRACT [51 1 Int. C1. FOZM 1/12 A constant depression or velocity carburetter incorpo- [58] Field of Search. 261/44 R, 39 D, 39 B, DIG. 1, rates an enriching device which acts to increase fuel 26l/D1G. 8, 39 E, 50 A; 123/180 A, 187.5 R enrichment with decreasing engine temperature. The carburetter can also include a manifold depression [56] References Cited sensor which additionally acts to increase fuel enrich- UNITED STATES PATENTS ment with decreasing manifold depression. 3,285.585 l 1/1966 Mennesson .1 261/50 A X 4 Claims, 2 Drawing Figures l i l US. Patent Nov. 4, 1975 Sheet 1 of 2 U.S. Patent Nov. 4, 1975 Sheet 2 of2 3,917,760

CARBURETTERS FITTED TO INTERNAL COMBUSTION ENGINES This invention relates to carburetters fitted to inter nal combustion engines either of the constant depression or constant velocity type. Both types are characterised by having a region of depression of several inches of water within the carburetter (referred to subsequently as the constant depression region). The depression in the constant depression region is used to maintain fuel flow into an air stream passing a jet fed with fuel from a flow chamber or other constant fuel level device open to atmospheric pressure. Downstream of the jet a throttle disc is used to govern the total air/fuel mixture flow.

According to the present invention a carburetter of the constant depression or constant velocity type having a region of constant depression within the carburet ter includes:

a. a temperature-sensitive device adapted to provide an output signal which varies from a first to a second value in inverse proportion to engine operating temperature, the first value corresponding to normal engine operating temperature, the second value corresponding to a low engine operating temperature; and

b. an enrichment means adapted, in response to the output signal, to control the degree of enrichment of fuel mixture leaving the carburetter the variation of output signal from the first to the second value causing the degree of enrichment to increase; and the variation of the output signal from the second to the first value causing the degree of enrichment to decrease.

The purpose of the invention is to provide a means of enrichment of the normal mixture metered by the carburetter for engine cold start and during warm up.

In a preferred form of the invention engine manifold depression sensing means are provided adapted to cause the output signal to be varied in inverse proportion to the engine manifold depression. Preferably the temperature sensitive device includes a depression control valve which provides as output signal a depression varying from a small or zero amount as first value to a larger amount of several inches water gauge as second value.

The invention also encompasses a vehicle fuel system including a carburetter according to the present invention and also a motor vehicle incoporating such a fuel system.

The carburetter of the invention essentially consists of a temperature sensitive device which is a depression control valve which transmits a depression which is nil at normal engine operating temperatures and which in creases as the engine temperature gets colder and which may also be subject to the influence ofinlet manifold depression so that the depression signalled by the device increases as manifold depression decreases. the source of the depression to the depression control valve being manifold depression. The device is so arranged that the maximum depression signalled is somewhat less than the minimum manifold depression when the engine is on full load. For example when the sensor temperature is 50C the depression could be min. water gauge and when 30C 8 min. water gauge.

The depression thus controlled is transmitted via a flexible small bore pipe to operate an enrichment device which can take various forms. It may be part of the carburetter or a separate device feeding into the induc- 2 tion tract downstream of the throttle disc of the carbu retter.

In each arrangement the depression from the sensor unit is applied to a diaphragm or other pressure sensi tive member of known area loaded by a rated spring the diaphragm being mounted in a sealed chamber on one side and open to atmospheric pressure on the other, the depression transmitted causing the diaphragm to assume a given position for a given depression.

Movement of the diaphragm thus engendered controls the degree of enrichment and the engine fast idle speed.

In one considered arrangement movement of the diaphragm imparts movements to a pressure balanced valve which controls the degree of communication be tween the constant depression region of the carburetter and the induction system downstream of the throttle disc. lnitial movement of the valve opens a limited connection area to provide a faster idling speed than normal at normal mixture ratios. Further movement of the valve uncovers a cross drilling or orifice which admits additional fuel or rich fuel air mixture into the communication passage on the constant depression side of the zone which enriches the overall mixture passing to the engine. Further movement uncovers successive cross drillings which may be graduated in size to provide an appropriate overall degree of enrichment for the temperature prevailing.

The area of the communicating port to the manifold may be tailored by means ofa profiled orifice arranged so that movement of the valve gives a non-linear opening relationship with its excursion.

An adjustable screw may be provided at the centre of the housing on the atmospheric side of the diaphragm to limit its movement towards atmosphere and so control communicating port area at zero depression condi tions thus providing an idle speed adjustment which re places the normal idling adjusting screw which limits throttle disc closure.

In another arrangement the sensor unit is used in conjunction with an auxiliary miniature constant depression carburetter tuned so that the mixture it provides is akin to the mixture ratios of the main carburetter at idling air flows but increases in richness with increasing air flows. The depression from the sensor is then arranged to control the degree of air/mixture communication between the auxiliary carburetter and the inlet manifold by means of a balanced valve.

The sensor unit can in fact be used to signal any enrichment system which requires virtually zero effort to operate it.

An embodiment of the invention will now be described with reference to the accompanying drawing of which:

FIG. 1 is a diagrammatic layout of an internal combustion engine and intake system; and

FIG. 2 is a part sectioned view of two components represented diagrammatically in H6. 1.

FIG. I shows a four cylinder spark ignition engine block ll having an intake manifold 12. The intake manifold 12 is fed fuel mixture from a constant depression carburetter 13 adapted to draw in air along intake 14 from a conventional air filter 15. A temperature sensitive device 16 is mounted on block 11 and communi cates with manifold 12 by duct 17 and with carburetter 13 by duct 18.

FIG. 2 shows in more detail carburetter l3 and device l6. The carburetter 13 contains a piston 20 slidable within housing 21. The piston carries at its lower end a tapered needle 22 which is movable in a jet 23 the size of whose orifice is regulated by means of needle 22. The jet is disposed on a bridge 24 providing a choke in flow passage 25. Float chamber 26 supplies fuel 27 to jet 23 by an unshown duct in the conventional way. Constant depression region 28 in passage lies between bridge 24 and butterfly valve 29. Induction region 30 lies downstream of valve 29. Passage 31 opens into constant depression region 28 and passage 32 into induction region 30. Valve shuttle 33 is slidably disposed in valve chamber 34. Clearance 32a is defined between the end of shuttle 33 and passage 32. The shuttle 33 is resiliently biassed by compression spring 35 into contact with one end of push rod 36 whose other end seats on air-tight resiliently loaded diaphragm 37 defining volumes 38, 39 within chamber 40 in the lower part of the carburetter body.

Valve chamber 34 is in communication with passage 32 by way of pressure balance duct 33a in shuttle 33. Auxiliary passage 44 links annulus 45 to passage 31. The shuttle 33 has around it annular recesses 45, 46.

Volume 39 in chamber 40 is open to ambient atmospheric pressure by way of vent 47. Volume 38 is coupled to temperature sensitive device 16 by the duct 18. An air bleed 38a provides restricted communication between chamber 38 and, effectively, atmospheric pressure. The temperature sensitive device 16 comprises a housing 48 secured to the engine block 11 and in good heat exchange contact with the engine block water cooling system. Diaphragm 49 divides the interior of the housing into a major volume 50 open to atmospheric pressure and minor volume 51. Duct 18 opens into minor volume 51 from which duct 17, by way of valve seat 52, leads to the intake manifold. A disc valve 53 secured to the diaphragm provides for isolation of duct 17 from the minor volume 51 when the diaphragm is moved downwardly. Motion of the diaphragm 49 is imparted by a bimetallic spring strip 54 linked to the diaphragm 49 by a link 55. The bimetallic strip 54 has a heating element 56 surrounding it energisable by a battery 57 on operation of switch 58.

The bimetallic strip 54 senses the temperature in major volume 50 and is arranged to vary the upward load on diaphragm 49 so that the load is greater when the temperature is lower and less when the temperature is higher diminishing to zero at a predetermined temperature. Any upward load on diaphragm 49 causes valve 53 to lift from seat 52 admitting the depression acting in duct 17 into minor volume 51 where it acts on the effective area of diaphragm 53 tending to close valve 53. When the depression acting on the diaphragm 53 creates a downward force equal to the upward load of bimetallic strip 54 the valve 53 closes. Due to air bleed 38a the depression in volume 51 then gradually falls causing valve 53 to open thus again admitting to volume 51 the depression acting in duct 17 in this manner maintaining on diaphragm 49 a force which just balances the load of bimetallic strip 54. Thus the greater the upward load applied by the bimetallic strip (as the temperature in volume 50 falls) the greater will be the depression in volume 51. When the temperature in volume 50 is such that bimetallic strip 54 exercises no load on diaphragm 49 valve 53 seals against seat 52 isolating volume 51 from duct 17. In addition to the spring force exercised by bimetallic strip 54 on diaphragm 49 a pneumatic load is applied by virtue of the depression in duct 17 acting on the exposed area of 4 valve 53 in opposition to the load applied by the bimetallic strip thus creating: a lower depression in volume 51 with increase in depression in duct 17; and a higher depression in volume 51 with reduction in depression in duct 17. The depression in duct 17 is inlet manifold depression so that as the engine load increases the depression in volume 51 will increase and vice versa. By selecting a suitable area of valve seat 53 it is possible to vary the depression created in volume 51 as a function of engine load as well as temperature.

The device is arranged so that the maximum depression fed into duct 18 is somewhat less than the minimum manifold depression when the engine is on full load. Typically when the sensed temperature in major volume 50 is 50C the depression is 0 min. water gauge and when the temperature is -30C the depression is 8 min. water gauge.

The modified depression supplied to duct 18 from device 16 is fed to volume 38 on one side of diaphragm 37. Volume 39 on the opposite side of diaphragm 37 is maintained at ambient atmospheric pressure.

Diaphragm 37 takes up a resultant position in response to the temperature moderated manifold depression from duct 18 and the ambient air pressure. This position is transmitted by way of push rod 36 to shuttle 33. The shuttle 33 serves to control the degree of communication between the constant depression region 28 and the induction region 30 and by passing the butterfly valve 29.

The flow of fuel from port 41 to auxiliary passage 44 is regulated by the degree of overlap of annular recess 45 and port 41 and the depression acting across the port which is constant depression region depression. Likewise communication between passage 31 and passage 32, by way of clearance 32a, is governed by the overlap of annular recess 46 and clearance 32a.

With the position of the shuttle 33 as shown in FIG. 2 a limited flow of fuel from float chamber 26 to auxiliary passage 44 occurs by way of annular recess 45 partially overlapping port 41. This limited flow passes into air/fuel mixture flowing down passage 31 which has already entrained the fuel supplied in a known manner through jet 23. The subsequently enriched flow then passes by way of annular recess 46 to passage 32 by way of clearance 32a. In the shuttle position shown the clearance 32a serves to limit the flow of enriched fuel, by-passing the butterfly valve 29, into induction region 30.

Movement of shuttle 33 to the left under the action of push rod 36 increases the overlap of the annular recesses 45, 46 with their corresponding passages with a consequent increase in mass flow along passage 32. Displacement of shuttle 33 to the left occurs with displacement of diaphragm 37 to the left as will occur, for example, with increasing depression in volume 38 (cold engine).

Heating element 56 is used to heat the bimetallic strip 54 to improve response of the strip with a cold engine. As the engine water cooling system heats up the effect of the heating element on the strip will be reduced until the engine coolant temperature control of the strip predominates over that provided by the element 56.

In order to ensure full travel of valve 33 during engine cranking under very cold start conditions, the slow run adjustable screw on cover 40 may be replaced by a solenoid rotation of which effects the initial slow run stop adjustment. The solenoid is electrically connected via a thermal sensitive switch to the starter motor circuit so that the solenoid is energised coincidental with engagement of the starter. Immediately the solenoid is energised its armature moves so as to move diaphragm 37 push pin 36 and spool valve 33 into a position where maximum enrichment is provided.

When the engine fires and the starter circuit is disengaged spool valve 33 will return to its normal position of enrichment dictated by temperature in volume 50 and depression in volume 51.

The thermal sensitive switch is arranged to pass current at a temperature when additional enrichment is required such as 5C and below.

We claim:

I. A vehicle engine fuel system comprising:

1. a temperature-sensitive device adapted to provide an output signal which varies from a first to a second value in inverse proportion to engine operating temperature, the first value corresponding to normal engine operating temperature, the second value corresponding to low engine operating temperature;

2. a carburetter of the constant depression or constant velocity type having a housing defining a duct and a throttle disc dividing said duct into a region of constant depression upstream of said disc and an induction region downstream of said disc, said carburetter further comprising:

a. a passage by-passing said disc and providing communication between said constant depression region and the duct downstream of the throttle disc;

b. enrichment means connected to said temperature-sensitive device and comprising a plurality of orifices communicating with said passage, which orifices are connected, when open, to admit fuel or a mixture of fuel and air into said passage, and a pressure balanced valve in said passage which is adapted to control the degree of communication between said constant depression region and said duct downstream of the throttle disc in dependence on the value of said output signal by at least partially opening and closing at least one of said orifices.

2. A vehicle engine fuel system as claimed in claim 1 comprising an engine manifold depression sensing means connected to said signal providing means to vary the output signal in inverse proportion to engine mani fold depression.

3. A vehicle engine fuel system as claimed in claim I in which the temperature sensitive device includes a depression control valve providing as the output signal a depression varying from a small or zero amount as said first value to several inches watergauge as said second value.

4. A vehicle engine fuel system as claimed in claim 1 comprising engine idle speed control means, said control means being connected to provide a faster idling speed than normal with the output signal at the first value.

Claims (7)

1. A TEMPERATURE-SENSITIVE DEVICE ADAPTED TO PROVIDE AN OUTPUT SIGNAL WHICH VARIES FROM A FIRST TO A SECOND VALUE IN INVERSE PROPORTION TO ENGINE OPERATING TEMPERATURE, THE FIRST VALUE CORRESPONDING TO NORMAL ENGINE OPERATING TEMPERATURE, THE SECOND VALUE CORRESPONDING TO LOW ENGINE OPERATING TEMPERATURE,

1. A VEHICLE ENGINE FUEL SYSTEM COMPRISING::

2. A CARBURETTER OF THE CONSTANT DEPRESSION OR CONSTANT VELOCITY TYPE HAVING A HOUSING DEFINING A DUCT AND A THROTTLE DISC DIVIDING SAID DUCT INTO A REGION OF CONSTANT DEPRESSION UPSTREAM OF SAID DISC AND AN INDUCTION REGION DOWNSTREAM OF SAID DISC, SAID CARBURETTER FURTHUR COMPRISING: A. A PASSAGE BY-PASSING SAID DISC PROVIDING COMMUNICATION BETWEEN SAID CONSTANT DEPRESSION REGION AND THE DUCT DOWNSTREAM OF THE THROTTLE DISC, B. ENRICHMENT MEANS CONNECTED TO SAID TEMPERATURE-SENSITIVE DEVICE AND COMPRISING A PLURALITY OF ORIFICES COMMUNICATING WITH SAID PASSAGE, WHICH ORIFICES ARE CONNECTED,WHEN OPEN, TO ADMIT FUEL OR A MIXTURE OF FUEL AND AIR INTO SAID PASSAGE, AND A PRESSURE BALANCED VALVE IN SAID PASSAGE WHICH IS ADAPTED TO CONTROL THE DEGREE OF COMMUNICATION BETWEEN SAID CONSTANT DEPRESSION REGION AND SAID DUCT DOWNSTREAM OF THE THROATTLE DISC IN DEPENDENCE ON THE VALUE OF SAID UOTPUT SIGNAL BY AT LEAST PARTIALLY OPENING AND CLOSING AT LEAST ONE OF SAID ORIFICES.

2. A vehicle engine fuel system as claimed in claim 1 comprising an engine manifold depression sensing means connected to said signal providing means to vary the output signal in inverse proportion to engine manifold depression.

2. a carburetter of the constant depression or constant velocity type having a housing defining a duct and a throttle disc dividing said duct into a region of coNstant depression upstream of said disc and an induction region downstream of said disc, said carburetter further comprising: a. a passage by-passing said disc and providing communication between said constant depression region and the duct downstream of the throttle disc; b. enrichment means connected to said temperature-sensitive device and comprising a plurality of orifices communicating with said passage, which orifices are connected, when open, to admit fuel or a mixture of fuel and air into said passage, and a pressure balanced valve in said passage which is adapted to control the degree of communication between said constant depression region and said duct downstream of the throttle disc in dependence on the value of said output signal by at least partially opening and closing at least one of said orifices.

3. A vehicle engine fuel system as claimed in claim 1 in which the temperature sensitive device includes a depression control valve providing as the output signal a depression varying from a small or zero amount as said first value to several inches watergauge as said second value.

4. A vehicle engine fuel system as claimed in claim 1 comprising engine idle speed control means, said control means being connected to provide a faster idling speed than normal with the output signal at the first value.

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