Carburetor

Abstract

 A carburetor provided with a fuel flow rate control device (11) disposed midway in a fuel passageway between a fuel pump (8) and a metering jet (4); a level sensor (13) arranged in a passageway (12) for detection connected upright to a portion between the fuel flow rate control device and the metering jet provided in the fuel passageway; an electrical control circuit operating the fuel flow rate control device in accordance with the output delivered from the level sensor so that the level of a fuel column to be formed in the passageway for detection is maintained at a predetermined positon, in order to enable fuel supply with permanent stability to be performed without using a float chamber or without being affected by the vibration of the engine and the turn of a car body.

Description

[0001] The present invention relates to a carburetor and more particularly a carburetor provided with a liquid level sensor for controlling a flow rate of fuel.

[0002] A type of conventional carburetors is described in, for example, European Patent Publication No. 0207796 filed by the same applicant as in this application. The carburetor of this kind, as shown in Fig. 1, comprises essentially an intake passageway 1, a throttle valve 2 located in the passageway 1, a nozzle 3 disposed at a venturi section in the passageway 1, a float chamber 5 connected to the nozzle 3 through a metering jet 4, a fuel pump 8 supplying fuel into the float chamber 5 through a fuel passageway 7 from a fuel tank 6, a float 9 pivotally mounted in the float chamber 5, and a needle valve 10 disposed on an arm of the float 9 and adjusting the amount of fuel flowing into the float chamber 5 due to the vertical movement of the float 9 caused by the fluctuation of a liquid level of fuel to form a reference level S of fuel.

[0003] However, because the conventional carburetors are such that the reference level is held by the functions of the float 9 and the needle valve 10 as mentioned above, various problems have been encountered that the float 9 vibrates together with the vibration of low frequency of an engine to cause the fuel liquid level to be raised and when the fuel liquid level is inclined by the turn or incli­nation of a car body due to a broad surface of the fuel liquid lying in the float chamber 5, the height from the metering jet 4 to the fuel liquid level is liable to consid­erably fluctuate and as a result, a great fluctuation of fuel pressure makes fuel supply unstable and brings about the failure of the engine. Also, there have been further problems that since the carburetor has a portion occupying a comparatively large capacity of the float chamber 5, the compaction of the carburetor itself is prevented and the layout of the carburetor is made difficult.

[0004] A primary object of the present invention, in view of the above circumstances, is to provide a carburetor in which a float chamber device comprising a float chamber, a float and a needle valve is eliminated.

[0005] Another object of the present invention is to provide a carburetor which is not essentially affected by the vibra­tion of the engine and the turn or inclinaiton of the car body and which can always perform stable fuel supply.

[0006] Still another object of the present invention is to provide a carburetor in which the carburetor itself is compacted and the layout is facilitated.

[0007] These objects, according to the present invention, are accomplished by being provided with a fuel flow rate control device disposed midway in a fuel passageway between a fuel pump and a metering jet, a level sensor disposed in a passageway for fuel liquid level detection connected to a portion of the fuel passageway between the fuel flow rate control device and the metering jet, and an electrical control circuit driving the fuel control device in response to an output delivered from the level sensor to operate so that the fuel liquid level is always held at a reference level.

[0008] These and other objects as well as the features and the advantages of the present invention will be apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings. In the drawings:

Fig. 1 is a sectional view showing the basic struc­ture of a fuel flow rate control system for conventional carburetors;

Fig. 2 is a sectional view showing the basic struc­ture of a first embodiment of a carburetor provided with a liquid level sensor of a fuel flow rate control system according to the present invention;

Figs. 3A and 3B are an enlarged sectional view of a portion where the liquid level sensor of the first embodi­ment is provided and a graph showing the variation of its output, respectively;

Figs. 4A and 4B are an enlarged sectional view of a modified example of the liquid level sensor shown in Fig. 3A and a graph showing the variation of its output, respectively;

Fig. 5 is a view showing an example of an output circuit connected to the liquid level sensor;

Fig. 6 is a view showing an example of a control circuit connected to the output circuit of Fig. 5;

Fig. 7 is a sectional view showing the basic struc­ture of a second embodiment of the carburetor provided with the liquid level sensor of the fuel flow rate control system according to the present invention;

Figs. 8A to 8C are an enlarged plan view and an en­larged longitudinal sectional view showing another modified example of the liquid level sensor and a graph showing the variation of its output, respectively;

Figs. 9A and 9B are an enlarged plan view showing still another modified example of the liquid level sensor and a graph showing the variation of its output, respectively;
and

Figs. 10A and 10B are an enlarged plan view showing a further modified example of the liquid level sensor and a graph showing the variation of its output, respectively.

[0009] Based on the embodiments shown in the drawings in which like reference numerals are used for like members with respect to the above-mentioned prior art, the present invention will be described in detail below.

[0010] Fig. 2 is a sectional view of the first embodiment of the carburetor with the fuel flow rate control system according to the present invention, in which reference numeral 11 designates a solenoid valve serving as a fuel flow rate control device disposed midway in the fuel passage­way 7 between the fuel pump 8 and the metering jet 4, 12 a passageway for detecting the liquid level of fuel connected upright to a portion of the fuel passageway 7 between the solenoid valve 11 and the metering jet 4 at the lower end and communicating with the atmosphere at the upper end, and 13 a level sensor disposed at a predetermined position of height of the passageway 12.

[0011] The level sensor includes, for example, a light-emitting device 131 and a light-receiving device 132 shown in Fig. 3A and a circuit configuration for detection shown in Fig. 5. When the level of a fuel column 121 raised in the passage­way 12 against atmospheric pressure by the fuel pump 8 is lower than a preset position of height, light emitted from the light-emitting device 131 transmits the passageway 12 as it is (Fig. 3A), so that electromotive power generated by the light-receiving device 132 is high and as a result, a sensor output delivered from the output circuit shown in Fig. 5 which will be described later becomes low. In contrast to this, when the level of the fuel column 121 is higher than the preset position of height, the light from the light-emitting device 131 is to traverse the fuel column 121, so that the light is dispersed by the fuel liquid during the traverse and the amount of light reaching the light-­receiving device 132 becomes reduced. Therefore, the electromotive power generated by the light-receiving device 132 is low, with the result that the sensor output becomes high as shown in Fig. 3B. In this embodiment, the difference in light transmissivity between air and fuel is comparative­ly small and therefore the variation of the sensor output is little (Fig. 3B). However, if a float 133 formed of an opaque material is provided on the top surface of the fuel column 121 as in the modified example (float type) shown in Fig. 4A, the travel of the light coming from the light-­emitting device 131 is completely blocked by the float 133 interposing between the light-emitting device 131 and the light-receiving device 132 when the level of the top surface of the fuel column 121 is higher than the preset position and consequently the electromotive power produced in the light-receiving device 132 substantially becomes zero. Thus, the variation of the sensor output will advantageously be increased (see Fig. 4B).

[0012] Fig. 5 shows an output circuit 134 connected to the level sensor 13, in which symbol COP₁ represents an opera­tional amplifier and R₁ a resistor. This circuit operates so that when the electromotive power generated in the light-­receiving device 132 is high, an input voltage applied to a terminal (-) of the operational amplifier COP₁ increases and the output of the operational amplifier COP₁ becomes "L", whereas, when the electromotive power generated in the light-receiving device 132 is low, the input voltage applied to the terminal (-) of the operational amplifier COP₁ decreases and the output of the operational amplifier COP₁ becomes "H".

[0013] Fig. 6 shows a control circuit 135 controlling the operation of the solenoid valve 11 in accordance with the output coming from the output circuit 134, in which symbol COP₂ represents an operational amplifier, R₂ a resistor, and Tr a transistor. This circuit operates so that when the level of the top surface of the fuel column 121 is lower than the preset position of height, that is, when the output of the level sensor 13 is lower than a reference voltage E_O, the output of the operational amplifier COP₂ becomes "H" to conduct the transistor Tr, thereby opening the sole­noid valve 11, and the increase of the fuel flow rate causes the fuel column 121 to be raised, while on the other hand, when the level of the fuel column 121 is higher than the preset position, that is, when the output voltage from the output circuit 134 is higher than the reference voltage, the output of the operational amplifier COP₂ becomes "L" to cut off the conduction of the transistor Tr, thereby closing the solenoid valve 11, and the decrease of the fuel flow rate causes the fuel column 121 to be lowered.

[0014] Since the carburetor according to the present inven­tion is constructed as stated above, when the height of the top surface of the fuel column 121 in the passageway 12 is positioned below the preset height, that is, the output level from the output circuit 134 is low, the solenoid valve 11 is opened by the control circuit 135 to raise the fuel column 121 and thus when the height is above the preset height, the output from the output circuit 134 increases, so that the solenoid valve 11 is closed by the control circuit 135 to lower the fuel column 121. It follows from this that such operations are repeated alternately, thereby the level of the fuel column 121 is always held at the preset position, and a proper amount of fuel corresponding to the amount of air sucked into the intake passageway is jetted from the nozzle 3.

[0015] As mentioned above, the carburetor according to the present invention is such that the reference level of the fuel column 121 is maintained through electrical control, with the result that a float chamber, a float, a needle valve, etc. can be eliminated. Accordingly, members affected by the vibration of the engine and the fuel liquid surface with a wide area are not included in the carburetor, so that the raise of the fuel liquid level due to the vibration and the fluctuation of the level from the metering jet 4 to the fuel liquid surface due to the turn or inclination of the car body are not caused and as a result, the fuel pressure becomes constant to enable the fuel supply with permanent stability to be performed. Also, since the float chamber occupying a considerably large capacity becomes unnecessary, the carburetor itself is compacted and the layout of the carburetor is facilitated.

[0016] Fig. 7 is a sectional view of the second embodiment with the fuel flow rate control system according to the present invention. This embodiment further comprises a fuel pressure regulator 14 disposed between the fuel pump 8 and the solenoid valve 11 provided in the fuel passageway 7, in addition to the components of the first embodiment. The fuel pressure regulator 14 operates so that when the pressure of the fuel discharged from the fuel pump 8 is higher than a predetermined value, a diaphragm 14a is displaced upward against the resilience of a spring 14b, thereby a valve 14c opens wide to return more fuel to the fuel tank 6, and the pressure of the fuel fed to the fuel passageway 7 is lowered, while, when the pressure of the fuel discharged from the fuel pump 8 approximates to the predetermined value, the valve 14c is closed to maintain the pressure of the fuel fed to the fuel passageway 7 near the predetermined value. Therefore, there is an advantage that this function of the fuel pressure regulator 14 makes it possible to apply always constant fuel pressure to the solenoid valve 11 even if the output of the fuel pump 8 fluctuates and consequently control can be performed with a considerable degree of accuracy.

[0017] Figs. 8A to 10B show various modifications of the level sensor 13. In Figs. 8A and 8B, which illustrate the level sensor of the so-called lens system, when the level of the top surface of the fuel column 121 is lower than the preset position as indicated in a solid line in Fig. 8B, the light emitted from the light-emitting device 131 is scattered while transmitting a transparent pipe 15 formed of glass or the like and the passageway 12, so that the amount of light incident on the light-receiving device 132 is small, therefore the electromotive power produced therein is low, and as a result, the output from the output circuit 134 becomes high as shown in Fig. 8C, while on the other hand, when the level of the fuel column 121 is above the preset position as shown in a broken line in Fig. 8B, the light from the light-emitting device 131 is condensed to the light-receiving device 132 due to a lens function of the medium of fuel, so that high electromotive power is generated therein and as a result, the output from the out­put circuit 134 becomes low as shown in Fig. 8C.

[0018] Fig. 9A shows the level sensor of the so-called refraction system, in which when the level of the fuel column 121 is below the preset position, the light from the light-­emitting device 131 transmits the transparent pipe 15 and the passageway 12 as it is and reaches the light-receiving device 132, so that the electromotive power generated in the light-receiving device 132 increases and as a result, the output from the output circuit 134 becomes reduced as shown in Fig. 9B, whereas, when the level of the fuel column 121 is above the preset position, the light from the light-­emitting device 131 is not incident on the light-receiving device 132 due to a refracting function of the medium of fuel, so that the electromotive power becomes small and therefore the output from the output circuit 134 increases as shown in Fig. 9B.

[0019] In Fig. 10A, when also illustrates the level sensor of the refraction system, when the level of the fuel column 121 is positioned below the preset height, the light from the light-emitting device 131 is not incident on the light-­receiving device 132, so that the electromotive power generated in the light-receiving device 132 is low and consequently the output from the output circuit 134 becomes high as shown in Fig. 10B, while, when the level of the fuel column 121 is above the preset height, the light from the light-emitting device 131 reaches the light-receiving device 132, so that the electromotive power generated in the light-­receiving device 132 is high and the resulting output from the output circuit 134 decreases as shown in Fig. 10B. Also, in the modifications shown in Figs. 8A, 8B and 10A, it is necessary for the control circuit 135 shown in Fig. 6 to connect an output terminal 134a of the output circuit 134 for the level sensor to the terminal (+) of the opera­tional amplifier COP₂ and to connect the reference voltage E_O to the terminal (-).

[0020] Although the solenoid valve 11 in the above embodi­ments has been explained as the one of the type which is opened and closed by the electrical control circuit 135, this circuit may be made up so that the output delivered from the sensor output circuit 134 brings about a continuous pulse which is different in width at low and high levels and so that the solenoid valve 11 is opened and closed with a different duty ratio.

Claims

1. A carburetor comprising:
      a fuel flow rate control means disposed in a fuel passageway between a fuel pump and a metering jet;
      a passageway for detection connected upright to said fuel passageway between said fuel flow rate control means and said metering jet and forming a fuel column therein;
      a level sensor arranged adjacent to said passageway for detection at a predetermined position of height of said passageway for detection and capable of detecting whether or not the level of said fuel column lies at the predetermined position of height; and
      an electrical control means capable of controlling the operation of said fuel flow rate control means so that the level of the fuel column is maintained at the predeter­mined position of height, in response to an output signal issued from said level sensor.

2. A carburetor according to claim 1, wherein:
      said fuel passageway is composed of a transparent cylinder and said level sensor comprises a light-emitting device and a light-receiving device between which said cylinder is arranged so that said light-receiving device can produce electromotive power with different levels in cases where the level of said fuel column lies at the predetermined position and not.

3. A carburetor according to claim 1, wherein:
      said fuel flow rate control means is an electromagne­tic valve connected to said electrical control means.

4. A carburetor according to one of claims 1 through 3, wherein:
      said carburetor further comprises a fuel pressure regulator disposed in said fuel passageway between said fuel pump and said fuel flow rate control means.

Drawing