FUEL SUPPLY SYSTEM FOR INJECTION CARBURETORS

Abstract: A fuel supply system for injection carburetors includes an orifice (26), a constant flow rate control device (3), alnd a fuel supply source (4) and is provided with a first fuel channel circulating fuel of a predetermined flow rate, a second fuel channel branching off from the first fuel channel between the orifice and the constant flow rate control device for injecting the fuel into a suction tube (2) of the carburetor, an air flow rate detecting device (1) capable of detecting a flow rate of air flowing through the suction tube, and a fuel ejection control device (6) capable of metering the flow rate of fuel to be ejected so that a pressure difference with atmospheric pressure which is detected by the air flow rate detecting device (1) is balanced with a fuel pressure difference between the upstream side (23) and the downstream side (24) of the orifice. The fuel supply system is simple in structure and can hold an air-fuel ratio of a gas mixture with a high degree of accuracy to a desired constant value, over the entire operation region, through a single fuel control unit.

Description: The invention relates to a fuel supply system for injection carburetors as per the preamble of claim 1. A fuel system of such type is described in US-A-4 632 788. The said known fuel supply system comprises amongst other items a suction tube which can meter a flow rate of fuel to render an air-fuel ratio of a gas mixture constant by balancing a difference between the negative pressure produced in the suction tube and the atmospheric pressure with a difference in fuel pressure between the upstream side and the downstream side of an orifice provided in a fuel passage. Such fuel supply systems suffer from a severe drawback: It is not always possible to conduct the measuring of the fuel flow rate with a high degree of accuracy over a wide range even in a single fuel control unit. In the past, a system metering a flow rate of fuel in accordance with relationship between the flow rate of fuel passing through an orifice and a difference in fuel pressure between the upstream side and the downstream side of the orifice, as in fuel injection systems of stationary venturi type carburetors and EPC Patent Application No. 89107517.8, has been designed so that only the fuel supplied to an engine passes through the orifice. When the passed fuel is metered by the orifice, as diagrammed in Fig. 1, the fuel pressure difference is proportional to the square of the fuel flow rate, with the result that, for example, if the fuel of the amount six times the minimum supply fuel flow rate of the system flows through the orifice, the fuel pressure difference will be increased as much as 36 times the difference at that time and reach a limit value in practical use. However, general engines for automobiles, which need to be capable of metering the fuel supply flow rate from the minimum to about 40 times that, cannot make use of such a conventional fuel injection system as in the foregoing. Accordingly, in order to solve this problem, as in EPC Patent Application EP-A-399 065, a system has been proposed in the past which is constructed to arrange at least two fuel control units for a slow zone and a main zone. This system, however, has defects that its structure is complicated and the transition from the slow zone to the main zone is not performed smoothly. Further, although another system is available which is capable of covering such a wide metering range as is mentioned above in the fuel supply system with a single fuel control unit, like SU carburetors, this system brings about defects that since the arrangement is such that the fuel flow rate is metered by change of the sectional area of the fuel passage (i.e., change of channel resistance) according to the flow rate of air, metering accuracy is reduced. It is the main object of the invention to provide a fuel supply system according to the preamble of claim 1 whereby the measuring of the fuel flow rate with a high degree of accuracy can be materialized over a wide range even in a single fuel control unit. This object is achieved by the characterizing portion of claim 1. Fig. 1 is a characteristic diagram showing the relationship between a fuel flow rate and a fuel pressure difference in a conventional fuel supply system; Fig. 2 is a schematic view showing a general arrangement of a fuel supply system according to the present invention; Fig. 3A is a sectional view showing concrete structure of an air flow rate detecting means; Fig. 3B is a schematic view of an end face of the air flow rate detecting means viewed in the direction of an arrow of Fig. 3A; Fig. 4 is a sectional view showing concrete structure of a constant flow rate control means; Fig. 5 is a sectional view showing concrete structure of a fuel ejection control means used in a first embodiment of the present invention; Fig. 6 is a characteristic diagram showing the relationship between a fuel ejection flow rate and a fuel pressure difference in the first embodiment; Fig. 7A is a characteristic diagram showing the relationship between a pressure difference between the upstream side and the downstream side of an orifice and a fuel ejection flow rate in the first embodiment; Fig. 7B is a characteristic diagram showing the relationship required between an air flow rate and a pressure difference in the first embodiment; Figs. 8 and 9 are sectional views showing concrete structure of the fuel ejection control means used in second and third embodiments, respectively; First of all, referring to Figs. 2 to 5, a first embodiment of the present invention will be described below. Fig. 2 shows an example of conceptional structure of a fuel supply system according to the present invention. In this figure, reference numeral 1 represents an air flow rate detecting means detecting a flow rate of air sucked into a suction tube 2, 3 a constant flow rate control means adapted to return only fuel of a constant flow rate, from the fuel fed from a fuel supply source 4 through a fuel pump 5 to a fuel ejection control means which will be mentioned later, to the fuel supply source 4, and 6 a fuel ejection control means injecting the fuel of the amount corresponding to the air flow rate detected by the air flow rate detecting means and discharging the remainder of the fuel fed from the fuel supply source 4 into the constant flow rate control means 3. Fig. 3A depicts an example of concrete structure of the air flow rate detecting means 1. In the figure, reference numeral 7 designates a piston valve having a through-hold 7a in its top face for sliding in a direction normal to the suction tube 2 to form a variable venturi section 2a in the suction tube 2, 8 a spring biasing the piston valve 7 in a direction to narrow the variable venturi section 2a, 9 an adjusting screw capable of adjusting the resilient force of the spring 8 through a receiver 9a, 10 an atmospheric chamber provided under a large diameter section of the piston valve 7 so that atmosphere of an air horn is conducted thereinto, 11 a negative pressure passage opened in the variable venturi section 2a for taking out negative pressure created in the venturi section 2a, and 12 an air passage opened in the air horn for taking out relatively high reference pressure (for instance, atmospheric pressure). Fig. 4 shows concrete structure of the constant flow rate control means 3, in which reference numeral 13 represents an inlet chamber having a fuel inlet port 13a, 14 an outlet chamber separated form the inlet chamber 13 by a diaphragm 15, having a fuel outlet port 14a, 16 an orifice communicating the inlet chamber 13 with the outlet chamber 14, 17 a valve having an end portion connected to the diaphragm 15 to be capable of controlling an opening degree of the fuel inlet port 13a of the inlet chamber 13, 18 a spring urging the diaphragm 15 toward the inlet chamber 13, and 19 an adjusting screw capable of adjusting the resilient force of the spring 18 through a receiver 19a. Fig. 5 shows concrete structure of the fuel ejection control means used in the first embodiment of the present invention, in which reference numeral 20 represents an atmosphere chamber adapted to conduct the atmospheric pressure thereinto through the air passage 12 of the air flow rate detecting means, 21 a depression chamber adapted to conduct the negative pressure of the venturi section 2a thereinto through the negative pressure passage 11 of the air flow rate detecting means 1, 22 a diaphragm constituting a partition between the atmosphere chamber 20 and the depression chamber 21, 23 a fuel pressure chamber adapted to feed the fuel from the fuel supply source thereinto, 24 a fuel ejection chamber divided from the fuel pressure chamber 23 by a fuel diaphragm 25, having a fuel ejection port 24a open to the suction tube 2, and 26 an orifice communicating the fuel pressure chamber 23 with the fuel ejection chamber 24. Reference numeral 27 designates a connecting member connected between the diaphragms 22 and 25, having a fuel ejection valve 27a capable of opening and closing the fuel ejection port 24a, 28 a spring pressing the negative pressure diaphragm 22 to open the fuel ejection valve 27a, and 29 an adjusting screw adjusting the resilient force of the spring 28 through a receiver 29a. In the air flow rate detecting means 1 described above, the venturi section 2a is configured as depicted in Fig. 3B so that the difference of the pressure (the magnitude of the negative pressure) produced between the negative pressure passage 11 and the air passage 12 in accordance with the air flow rate can accommodate the relationship of the fuel flow rate and the fuel pressure difference between the upstream side and the downstream side of the orifice through which the fuel passes. Also, the constant flow rate control means 3 is constructed so that the opening degree of the valve 17 is adjusted by operating the adjusting screw 19 and thereby the flow rate of the fuel flowing through the fuel inlet chamber 13 and the fuel outlet chamber 14 is controlled. Further, in the fuel ejection control means 6, the flow rate of the fuel passing through the orifice 26 in the injection of the fuel is such that a variable ejection flow rate Qa of the fuel delivered form the ejection port 24a which is metered in response to the air flow rate is added to a predetermined flow rate Q A of the fuel returned to the fuel supply source through the constant flow rate control means 3. Now, when the fuel pressure difference between the upstream side and the downstream side of the orifice 26 is taken as P and that in the case where the ejection flow rate Qa = 0 in particular is P₀, the relationship between the ejection flow rate Qa and the fuel pressure difference (P - P₀), although dependent on the setting value of the predetermined flow rate Q A , will exhibit a characteristic curve, near a straight line, deflected slightly downward as shown in Fig. 6. Further, when the effective area of each of the diaphragms 22, 25 is taken as S, the resilient force of the spring 28 as Fs, and the differential pressure detected by the air flow rate detecting means 1 as Fa, a mutual relationship is given by P x S + Fa x S + Fs = 0 (1) and the function of the fuel ejection control means 6 is that the pressure differences are counterbalanced with each other as shown in this equation, resulting in the delivery of the fuel of the flow rate (ejection flow rate) according to the air flow rate. Also, Fig. 7A is a characteristic diagram showing the relationship of the fuel pressure difference P between the outstream side and the downstream side of the orifice 26 and the ejection flow rate Qa, and Fig. 7B the relationship of the air flow rate required accordingly for the air flow rate detecting means 1 and the pressure difference. Next, the functions of the fuel supply system which has been mentioned will be explained below. In this system, prior to an engine start, the fuel pump 5 is first started by an initial operation of a start key and the fuel is fed from the fuel supply source 4 to the fuel ejection control means 6 (refer to arrows of solid lines in Fig. 2). At this step that the engine is not started, since the pressure difference is not detected by the air flow rate detecting means 1, the fuel ejection valve 27a is in a closed state, and the fuel introduced into the fuel pressure chamber 23 flows into the fuel ejection chamber 24 at the predetermined flow rate Q A under the differential pressure P₀ and is returned to the fuel supply source 4 through the constant flow rate control means 3. That is, in the state that the engine is not yet started, the fuel of a constant flow rate is circulated by the fuel pump 5 within a closed channel constructed from the fuel supply source 4, the fuel ejection control means 6, and the constant flow rate control means. Next, when the engine is started by a further operation of the engine key, negative pressure corresponding to the flow rate of air sucked into the venturi section 2a of the suction tube 2 is produced. The negative pressure is introduced into the depression chamber 21 of the fuel ejection control means 6 through the negative pressure passage 11 and consequently the negative pressure diaphragm 22 will be displaced toward the depression chamber 21 in virtue of the pressure difference generated between the atmosphere chamber 20 and the depression chamber 21. Accordingly, the fuel ejection valve 27a is opened so that the fuel is injected into the suction tube 2 from the fuel ejection chamber 24. At the same time, the fuel pressure difference P between the upstream side and the downstream side of the orifice becomes greater than the differential pressure P₀ and the fuel of the flow rate Qa higher than the predetermined flow rate Q A is metered by the orifice 26 to be included in the fuel ejection chamber 24. Thus, the state that the differential pressure between the negative pressure according to the flow rate of air sucked into the suction passage 2 and the atmospheric pressure is balanced with the fuel pressure difference (P - P₀) between the upstream side and the downstream side of the orifice 26 renders an air-fuel ratio of a gas mixture constant, and the fuel pressure difference (P - P₀) and the flow rate Qa of the fuel to be ejected maintain the relationship such as is shown by a characteristic curve of Fig. 6, with the result that fuel flow rate control with a considerable degree of accuracy can be secured over a wide operation range. Fig. 8 shows concrete structure of the fuel ejection control means used in a second embodiment of the present invention. In this figure, reference numeral 30 represents a first diaphragm constituting a partition between the fuel pressure chamber 23 and the atmosphere chamber 20, 31 a second diaphragm constituting a partition between the fuel ejection chamber 24 and the depression chamber 21, and 32 a partition wall dividing the atmosphere chamber 20 from the depression chamber 21 and having a small hole 32a into which the connecting member 27 is inserted. In such structure, a flow control valve 27b is configured at the upper end of the connecting rod 27, associated with a fuel inlet port 23a of the fuel pressure chamber 23, and actuated by the second diaphragm 31 displaced in response to the negative pressure of the venturi section 2a which is introduced into the depression chamber 21 to control the flow rate of the fuel introduced into the fuel pressure chamber 23. Even in the case where the negative pressure is not conducted into the depression chamber 21, however, the valve 27b is held to a predetermined opening degree by the spring 28 and the like to secure the predetermined flow rate Q A . Reference numeral 33 denotes an injection nozzle ejecting the fuel, through an ejection port 33a, supplied from a discharge port 24b of the fuel ejection chamber 24 and incorporating a diaphragm 34 connected with a needle valve 34a and a spring 35. Accordingly, when the negative pressure detected by the air flow rate detecting means 1 is conducted into the depression chamber 21, the valve 27a is moved in its opening direction and resultant increase of the amount of a fuel flow from the fuel supply source 4 causes the fuel pressure in each of the chambers 23, 24 to be raised, so that force acting upward on the diaphragm 34 of the injection nozzle 33 is increased to open the valve 34a against the resilient force of the spring 35, thereby injecting the fuel into the suction tube 2. Thus, the fuel pressure difference between the upstream side and the downstream side of the orifice 26 is increased so that the negative pressure accommodating the flow rate of air flowing through the suction tube 2 is balanced with the fuel pressure difference. Fig. 9 shows concrete structure of the fuel ejection control means used in a third embodiment of the present invention. This embodiment is such that the fuel ejection valve 27a is configured at the lower end of the connecting member 27 to open and close the ejection port 24a of the fuel ejection chamber 24. Specifically, the fuel ejection valve 27a is actuated by the displacement of the second diaphragm 31 according to the negative pressure conducted into the depression chamber 21 for control of the amount of fuel injection. Reference numeral 36 denotes a spring arranged opposite to the spring 28 across the first diaphragm 30 to urge the valve 27a in its opening direction and the difference of the resilient force between the springs 28 and 36 corresponds to Fs of the equation (1) mentioned above. In each embodiment described above, a bearing may be used to smooth the movement of the piston valve 7 in the air flow rate detecting means 1.

Claims: A fuel system of an injection carburetor comprising a first channel including a first orifice (26), a second channel branching off from said first channel downstream said orifice (26) and injecting the fuel passing through said orifice into a suction tube of an engine, air flow rate detecting means (1) associated with and arranged in said suction tube (2) detecting a flow rate of air sucked into said suction tube (2) as a pressure difference between the atmospheric pressure and the pressure of the air in said suction tube (2), fuel ejection control means comprising a fuel pressure chamber (23) upstream said orifice (26), a fuel ejection chamber downstream said orifice, said fuel chambers being separated by a first diaphragm (25) connected by means of a rod (27) to a second diaphragm (24) which separates a negative pressure chamber (21) receiving the negative pressure of the suction tube (2) of an engine and an atmospheric chamber receiving the atmospheric pressure, said negative pressure chamber and said atmospheric chamber being disposed in a manner that an increase of the depression in the suction tube moves the first diaphragm (25) toward a diminution of the volume of the fuel pressure chamber (23), characterized in that the fuel supply system comprises constant flow rate control means returning only fuel of a predetermined flow rate from the fuel fed from a fuel supply source, to said fuel supply source through said first orifice (26) and said constant flow rate control means, said constant flow rate control means being integrated in said first channel downstream said orifice means, said second channel, which comprises said fuel ejection chamber, branching off between said orifice and said constant flow rate control means. A fuel supply system according to claim 1, wherein said constant flow rate control means (3) comprises a diaphragm (15) dividing a fuel inlet chamber (13) from a fuel outlet chamber (14), a valve (17) connected with said diaphragm (15) to be capable of opening and closing an inlet port of said fuel inlet chamber (13), a second orifice (16) communicating said fuel inlet chamber (13) with said fuel outlet chamber (14), and a spring (18) pressing said diaphragm (15) in a direction in which said valve (17) is opened. A fuel supply system according to claim 1 or 2, wherein said air flow rate detecting means (1) comprises a piston valve (7) advancing into or retracting from said suction tube (2) in accordance with the flow rate of air sucked into said suction tube (2), a spring (8) pressing said piston valve (7) in a direction in which said piston valve (7) advances into said suction tube (2), a negative pressure passage (11) opened in an internal wall of said suction tube which is directed to an end face of said piston valve (7), and an air passage opened in an air horn. A fuel supply system according to claim 1, 2 or 3 wherein said fuel ejection control means comprises a fuel diaphragm dividing a fuel pressure chamber having a fuel inlet port (13a) from a fuel ejection chamber having a fuel ejection port, a negative pressure diaphragm dividing a depression chamber from an atmosphere chamber, a connecting member connected between said fuel diaphragm and said negative pressure diaphragm, having a fuel ejection valve capable of opening and closing said fuel ejection port, and a spring pressing said fuel ejection valve in a direction in which said fuel ejection valve is opened, and said fuel ejection valve is associated with said fuel ejection port so that fuel of the flow rate according to the pressure difference with atmospheric pressure which is detected by said air flow rate detecting means is ejected from said fuel ejection port. A fuel supply system according to claim 1, 2 or 3, wherein said fuel ejection control means comprises a first diaphragm dividing a fuel pressure chamber having a fuel inlet port from an atmosphere chamber, a second diaphragm dividing a fuel ejection chamber having a fuel ejection port from a depression chamber, a connecting member connected between said first diaphragm and said second diaphragm, having a valve associated with said fuel inlet port, a spring pressing said valve in a direction in which said valve is opened, and a fuel ejection nozzle connected to said fuel ejection port, ejecting the fuel into said suction tube, and said valve controls the flow rate of the fuel to be supplied to said fuel pressure chamber in accordance with the pressure difference with atmospheric pressure which is detected by said air flow rate detecting means. A fuel supply system according to claim 1, 2 or 3, wherein said fuel ejection control means comprises a first diaphragm dividing a fuel pressure chamber having a fuel inlet port from an atmosphere chamber, a second diaphragm dividing a fuel ejection chamber having a fuel ejection port from a depression chamber, a connecting member connected between said first diaphragm and said second diaphragm, having a fuel ejection valve capable of opening and closing said fuel ejection port, and a spring pressing said fuel ejection valve in a direction in which said fuel ejection valve is closed, and said fuel ejection valve is associated with said fuel ejection port so that fuel of the flow rate according to the pressure difference with atmospheric pressure which is detected by said air flow rate detecting means is ejected from said fuel ejection port. A fuel supply system according to any one of claims 2 to 6, wherein means for adjusting resilient force of said spring is provided.

Inventors: MURAJI, TETSUO C/O MIKUNI KOGYO K.K.
Applicants: MIKUNI KOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: F02M17
IPC codes: F02M69