GB2028431A

GB2028431A - Improvements in and relating to Carburettors

Info

Publication number: GB2028431A
Application number: GB7926600A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1978-08-01
Filing date: 1979-07-31
Publication date: 1980-03-05
Also published as: JPS5519963A; DE2931078A1

Abstract

A carburettor 10 comprises a sensor 36 for providing a signal indicative of the intake air flow, A control means 37 responsive to the signal fed thereto from the sensor to provide a drive pulse signal of airflow indicative pulse width and an electromagnetic valve 24 operating for a period of time determined by the pulse width of the drive pulse signal so as to allow a controlled amount of fuel to pass through a fuel jet 19. Other engine parameters may modify the pulse signal whose frequency is related to engine stroke frequency. <IMAGE>

Description

SPECIFICATION Improvements in and Relating to Carburettors This invention relates to a variable venturi type carburettor for use in an internal combustion engine and, more especially, to an electrically controlled variable venturi type carburettor including an electromagnetic valve operable for opening and closing a fuel jet to pass a controlled amount of fuel through the fuel jet in accordance with the opening degree of the variable venturi so as to provide a controlled air/fuel ratio.

Systems including an electromagnetic valve operable to pass a controlled amount of fuel in accordance with intake air flow have been employed in electrically controlled fuel injection apparatus, but they have required a highly precise and thus expensive electromagnetic valve and fuel pump since the electromagnetic valve operates under high fuel pressures, for example, pressures above 2.5 kg/cm2.

Conventional variable venturi type carburettors have employed a needle drivingly associated with a piston or a butterfly air valve to adjust the diameter of a fuel jet so that a controlled amount of fuel can pass through the fuel jet to provide a desirable air/fuel ratio. However, sophisticated manufacturing techniques have been required for machining the needle with accuracies of 1 to 2 microns or better on diameter in order to control the air/fuel ratio with the high accuracy required to accommodate today's exhaust emission regulations. Further, it is very difficult, if not impossible, to obtain a satisfactory control accuracy when considering changes in flow coefficient caused by changes in fuel temperature.

Furthermore, such conventional variable venturi type carburettors have been sophisticated in structure in order to meet today's requirements for providing air/fuel ratio control in various modes, for example, during cold starting and warming-up of the engine, for exhaust gas regulation, or in accordance with various engine parameters. However, it is impossible to control the air/fuel ratio such as to render it richer only when the exhaust gas recirculation is large due to their structure where the needle is drivingly associated with the piston or the butterfly air valve.

It is therefore one object of the present invention to provide an improved variable-venturi type carburettor which will be free from the above mentioned disadvantages.

Another object of the present invention is to provide a variable-venturi type carburettor which is easy and inexpensive to produce.

Still another object of the present invention is to provide a variable-venturi type carburettor which can provide an optimum air/fuel ratio with ease and greater accuracy.

According to the present invention, these and other objects are accomplished by providing a variable-venturi type carburettor comprising an electromagnetic valve for opening and closing a fuel jet, a sensor responsive to an intake air flow for developing at its output a signal corresponding to the intake air flow, and control means responsive to the signal fed from the sensor for providing to the electromagnetic valve a drive pulse signal having a pulse width determined by the first-mentioned signal thereby operating the electromagnetic valve.

One form of carburettor constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of the carburettor; and Fig. 2 is an enlarged sectional view of the carburettor.

Referring now to Figs. 1 and 2, in which like parts are denoted by like reference numerals, there is illustrated generally at 10 a variableventuri type carburettor as incorporated in an internal combustion engine. The engine includes an enginebody 11 containing therein a plurality of cylinders which communicate at their inlets with an intake passage 12 and at their outlets with an exhaust passage 1 3. A throttle valve 14 is provided within the intake passage 12.

The carburettor 10 includes an air valve 1 5 provided within the intake passage 12 at a location upstream of the throttle valve 14. The valves 14 and 15 define a mixing chamber 1 6 therebetween when closed. Extending into the mixing chamber 1 6 is a fuel nozzle 1 7 which communicates, through a fuel passage 18 and a fuel jet 19, with a float chamber 20 and also, through an emulsion tube 21 disposed within the fuel passage 18 and an air bleed 22, with the atmosphere.

The carburettor 10 also includes an electromagnetic valve mechanism 23 which comprises a valve 24, a diaphragm 25 supporting the valve 24 in the fuel jet 19, and a solenoid 26 for driving the valve 24 so as to open and close the fuel jet 19.

A diaphragm mechanism 27 is provided which includes a diaphragm 28 so arranged within a housing 29 as to divide its interior into two chambers 30 and 31. The chamber 30 opens to the atmosphere and the chamber 31 communicates through a negative pressure passage 32 with the mixing chamber 16. A spring 33 is provided in the chamber 31 for urging the diaphragm 28 toward the chamber 30. The diaphragm 28 is mechanically connected through a link 34 and a lever 35 to the air valve 1 5. When the negative pressure in the mixing chamber 16 increases (or decreases) with a change in engine rotational frequency and throttle valve opening degree, the diaphragm mechanism 27 increases (or decreases) the degree of opening of the air valve 1 5 in proportion to the change in intake air flow so that the negative pressure in the mixing chamber 16 is held substantially constant.

The air valve 1 5 is directly coupled to an air valve opening sensor 36 which develops at its output a voltage signal having a magnitude corresponding to the degree of opening of the air valve 1 5. The air valve opening sensor 36 may be taken in the form of a potentiometer. The output of the air valve opening sensor 36 is applied to a control circuit 37. The control circuit 37 provides a drive pulse signal to the solenoid 26 of the electromagnetic valve mechanism 23 to energise it thereby operating the valve 24.

The period of the drive pulse signal fed from the control circuit 37 is constant or is a function of engine rotational frequency. Preferably, the period of the drive pulse signal is a function of engine intake stroke frequency (once per an engine rotation in 2-cylinder 4-stroke engines, twice per an engine rotation in 4-cylinder 4-stroke engines, and three times in 6-cylinder 4-stroke engines), in which case, a rotation frequency sensor is required for detecting the frequency of rotation of the engine and providing a signal representing this to the control circuit 37.

The drive signal has a pulse width controlled in accordance with the signal fed from the air valve opening sensor 36 to the control circuit 37. In more detail, the pulse width of the drive signal increases (or decreases) with an increase (or decrease) in air valve opening degree and thus in intake air flow to increase (or decrease) the period of time while the valve 24 is held open, thereby increasing (or decreasing) the amount of fuel passing through the fuel jet 1 9 so as to hold the air/fuel ratio of the mixture produced by the carburettor substantially constant.

In the illustrated embodiment, the fuel passing through the fuel jet 19 is mixed with the air introduced through the air bleed 22 and the emulsion tube 21 and is discharged through the fuel nozzle 17 into the mixing chamber 1 6. The air bleed 22 and the emulsion tube 21 aid in providing finely divided fuel particles. It is to be noted, however, that the air bleed 22 and the emulsion tube 21 may be removed to permit the fuel jet 1 9 to be positioned near the fuel nozzle 1 7 so that fuel discharge is related more directly to the difference between the atmospheric pressure in the float chamber and the negative pressure in the mixing chamber.

An oxygen sensor 38 may be provided in the exhaust passage 13 as shown in Fig. 1 to detect the oxygen concentration of the exhaust gases passing through the exhaust passage 13 and which feeds back information about the air/fuel ratio to the control circuit 37 thereby providing more accurate air/fuel ratio control. Further, a temperature sensor may be provided in a suitable place and connected to the control circuit 37 to detect engine temperature, such as for example, cooling water temperature, and which provides information about the engine temperature to the control circuit 37 so that the pulse width of the drive signal can be corrected in accordance with the detected engine temperature.Similarly, other various sensors may be provided in suitable places and connected to the control circuit 37 to detect changes in various engine operation parameters and provide information about them to the control circuit 37 thereby correcting the pulse width of the drive signal in accordance with the changes in the engine operation parameters.

Although the present invention has been illustrated and described in connection with an air valve type carburettor, it is to be noted that the present invention is applicable to any other type of variable-venturi type carburettors such as SU carburettors having a suction piston, in which case, the intake air flow may be detected in accordance with the displacement of the suction piston.

The above described variable-venturi carburettor of the present invention provides the following distinct advantages: First, there is no need for any fuel jet diameter adjusting needle which has to be machined with very high accuracy to provide accurate air/fuel ratio control.

Thus, the carburettor of the present invention is easy and inexpensive to produce. Second, although the accuracy of the air/fuel ratio control is dependent mainly on the response or sensitivity of the electromagnetic valve, it is greatly improved as compared to that obtained with conventional variable-venturi type carburettors.

Third, since the air/fuel ratio is controlled by controlling the period of time while fuel passes through the fuel jet having a fixed diameter, changes in flow coefficient have the same tendency regardless of the amount of the fuel passing through the fuel jet. Further, since the diameter of the fuel jet is fixed and larger as compared to that of conventional ones, changes in Reynolds number are relatively small and have less effect on the control accuracy. Fourth, since the amount of fuel to be injected through the fuel jet is electrically controlled, it is easy to set the air/fuel ratio at an optimum value by the application of various signals representing engine operation parameters. Fifth, since the valve operates under pressures (0.2 to 0.3 kg/cm2) lower than those created in electrically-controlled fuel injection systems, there is no need for any highly precise and expensive pump.

Claims

1. In a carburettor for use in an internal combustion engine including an intake passage provided therein with a throttle valve, said carburettor including a variable venturi provided upstream of said throttle valve within said intake passage, a fuel nozzle opening into said intake passage upstream of said throttle valve and communicating through a fuel passage with a float chamber, the improvement comprising: a) a sensor responsive to the flow of the air passing through said variable venturi for providing a signal indicative of the intake airflow; b) a control means responsive to the signal fed thereto from said sensor for providing a drive pulse signal having a pulse width determined by the airflow indicative signal; and c) an electromagnetic valve responsive to the drive pulse signal for operating for a period of time determined by the pulse width of the drive pulse signal so as to allow a controlled amount of fuel to pass through said fuel jet.

2. A carburettor according to Claim 1 , wherein said variable venturi comprises a butterfly air valve and said sensor is arranged to detect the degree of opening of said air valve.

3. A carburettor according to Claim 2, wherein said sensor is in the form of a potentiometer drivingly connected to said air valve.

4. A carburettor according to Claim 1, wherein said variable venturi comprises a suction piston and said sensor is arranged to detect the displacement of said suction piston.

5. A carburettor according to any one of Claims 1 to 4, which further comprises an air bleed and an emulsion tube disposed within said fuel supply passage between said fuel jet and said fuel nozzle.

6. A carburettor according to any one of Claims 1 to 5, which further comprises means for correcting the pulse width of the drive signal in accordance with at least one engine parameter other than the air flow.

7. A carburettor according to any one of Claims 1 to 6, which further comprises means for correcting the pulse width of the driving signal in accordance with air/fuel ratio.

8. A carburettor according to any one of Claims 1 to 7, which further comprises means for correcting the pulse width of the driving signal in accordance with engine temperature.

9. A carburettor according to any one of Claims 1 to 8, which further comprises means for controlling the pulse interval of the drive signal as a function of engine intake stroke frequency.

10. A carburettor substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.