MIXER FOR GAS FUEL

Abstract: In a fuel gas mixer 1 comprising a throttle valve 4 provided in an air intake passage 2 connected to an engine for opening and closing the air intake passage 2 and a fuel gas supply passage 6 connected to the air intake passage 2 upstream of the throttle valve 4, there are provided a fuel gas control valve 5 in the air intake passage 2 upstream of the connecting part of the fuel gas supply passage 6 for opening and closing the air intake passage 2, and fuel gas control valve controlling means 11 for varying the degree of the opening of the fuel gas control valve 5 depending upon the operating state of the engine.

Description: The present invention relates to a fuel gas mixer. A fuel gas mixture is used in an engine using a fuel gas such as LPG or natural gas as its fuel. One conventional fuel gas mixer is a fixed venturi type mixer generally having a structure shown in Fig.8. A throttle valve 32 is provided in an air intake passage 31 connected to an engine for opening and closing the air intake passage 31. A main venturi (throttle part) 33 is formed upstream of the throttle valve 32. A main fuel gas passage 34 is connected to the main venturi 33 and a flow control valve 36 driven by a step motor 35 is provided in the main fuel gas passage 34. A gas injector 37 is provided closely downstream of the throttle valve 32. In a low-load operation range, the opening of the throttle valve 32 is small and a suction negative pressure is hardly created at the main venturi 33. Thus, high-pressure fuel gas is injected from the gas injector 37 and the air-fuel ratio is controlled by adjusting the injection time. In an intermediate- or high-load operation range, the opening of the throttle valve 32 is large and a suction negative pressure is created at the main venturi 33. Thus, the air-fuel ratio is controlled by adjusting the cross-sectional area of the main fuel gas passage 34 with the step motor 35. In the case of the fixed venturi type mixer, the venturi diameter (passage diameter) is limited by the flow rate characteristic of the gas injector 37 and thus has a low degree of freedom. Namely, in order to prevent a range where the air-fuel ratio is low from being generated between an operation range where the fuel is supplied from the gas injector 37 and an operation range where the fuel is supplied from the main venturi part, the fuel must start to be supplied from the main venturi part when the flow rate of the gas injector 37 gets close to the maximum. Thus, the venturi diameter is limited by the flow rate characteristic of the injector 37. As a result, in order to enlarge the main venturi diameter so as to be suitable for a large-displacement engine or a high-power engine, a plurality of injectors are needed, resulting in increase in costs. Additionally, it is necessary to control air-fuel ratios of the two systems: a main system for supplying fuel from the main venturi part and a slow system for supplying fuel from the gas injector. This makes the control system complicated and increases costs. From document SU 1 444 551 A2 a carburetor is known having throttle valves which are coupled so that one valve can be operated freely when it opens in response to the further valve. The valves are connected by an intermediate lever which has one end held by a spring to the control lever of the first valve and the other end engaging with the tie connected to the drive lever of the second valve. Within said carburetor, it is allowed to fully open the second valve initially and then after the winding-up of the spring to fully open the first valve. It is an objective of the present invention to provide a fuel gas mixer which is simple in structure and capable of reducing costs. According to the present invention, said objective is solved by a fuel gas mixer having the features of independent claim 1. Accordingly, it is a special advantage for such kind of fuel gas mixer that the same does not need a main venturi and a gas injector, and said fuel gas mixer is applicable from a small displacement engine to a large displacement engine. Preferred embodiments of the present invention are laid down in the dependent claims. Hereinafter, the present invention is illustrated and explained by means of preferred embodiments in conjunction with the accompanying drawings. In the drawings, wherein: Fig. 1 is a structural view of a system of a fuel gas mixer according to an embodiment; Fig. 2 is a schematic structural view of the mixer; Fig. 3 is a graph showing opening characteristics of a fuel gas control valve of the mixer; Fig. 4 is a flowchart for explaining an operation of the mixer; Fig. 5 is a flowchart for explaining an operation of the mixer; Fig. 6 is a flowchart for explaining an operation of the mixer; Fig. 7 is maps for explaining operations of the mixer; Fig. 8 is a schematic structural view of a conventional fuel gas mixer. Fig. 1 to Fig. 7 are views for explaining an embodiment. Fig. 1 is a view illustrating a driving system of a fuel gas mixer of this embodiment, Fig. 2 is a schematic view of a link mechanism of the mixer, Fig. 3 is a view showing opening characteristics of a fuel gas control valve, Fig. 4 to Fig.6 are flowcharts for explaining operations of the mixer and Fig. 7 shows maps of various types. In Fig. 1 and Fig. 2, designated as 1 is a fuel gas mixer connected to an engine. In an air intake passage 2 of the mixer 1, a butterfly type throttle valve 4 and a fuel gas control valve 5 for opening and closing the air intake passage 2 are provided downstream and upstream, respectively, of a main venturi part 3 narrowing the air intake passage 2. The air intake passage 2 has an upstream end to which an air cleaner is connected. At the main venturi part 3, a discharge port 6a of a fuel gas passage 6 is opened. In fuel gas passage 6, an orifice (throttle) 6b is formed in the vicinity of the discharge port 6a. The fuel gas passage 6 is connected to a fuel gas source via a fuel cutoff valve 6c. An air passage 7 is connected to the fuel gas passage 6 upstream of the orifice 6b. The air passage 7 has an upstream end to which an air cleaner is connected. An orifice 7a is formed in the air passage 7 and there is provided an air bleed control valve 8 for varying the opening area of the orifice 7a. The air bleed control valve 8 is driven to move back and forth by a step motor 9 to control the flow rate of air passing therethrough. The throttle valve 4 has a valve shaft 4a having an outer end to which a driving pulley 10 is secured. The driving pulley 10 is connected via a throttle cable to a throttle pedal in the driver's compartment, although not shown. The throttle valve 4 is rotated in accordance with the amount by which the driver depresses the pedal. The fuel gas control valve 5 has a valve shaft 5a connected to the valve shaft 4a of the throttle valve 4 by a link mechanism 11. More specifically, the valve shaft 4a of the throttle valve 4 is connected to a throttle arm 11a such that they are incapable of rotating relative to each other, and the throttle arm 11a is in turn connected to a control arm 11c of the fuel gas control valve 5 by a connecting link 11b. The fuel gas control valve 5 abuts on a stopper when fully opened. The control arm 11c is connected to the valve shaft 5a of the fuel gas control valve 5 such that they are rotatable relative to each other and rotationally urged to its minimum open position by an urging spring. Thereby, the control arm 11c can be rotated following the movement of the throttle valve 4 and the connecting link 11b connected thereto even after the fuel gas control valve 5 is fully opened. When the throttle pedal is not stepped on, the throttle valve 4 and the fuel gas control valve 5 are maintained in their minimum open positions. The opening of the throttle valve 4 is increased in general proportion to the amount by which the throttle pedal is depressed. The fuel gas control valve 5 is fully opened when the opening of the throttle valve 4 becomes about 20-30 % and maintained in its full open position thereafter (see the characteristic curve A in Fig. 3). It is possible to omit the main venturi 3 from the air intake passage 2. In this case, the fuel gas control valve 5 is adapted to open not fully but by 40-50 % at the maximum as shown in the characteristic curve B in Fig. 3. Thereby, a suction negative pressure can be created at the connecting part of the fuel gas passage 6 without a main venturi. The opening of the throttle valve 4 is detected and inputted into the ECU 13 by a throttle position sensor 12. Also inputted into the ECU 13 are various signals such as a signal representing an oxygen concentration in exhaust gas from an O 2 sensor, a crank angle signal, a top signal representing the upper dead center, a suction pressure signal, a water temperature signal, and a catalyst temperature signal. From the ECU 13 are outputted various signals such as a driving signal to the step motor 9, an ignition timing signal, an OTP warning lamp signal for indicating that the catalyst is at an overheat temperature, and a radiator fan driving signal. Description will be next made of the operations and effects of this embodiment. A controlling operation by the ECU 13 will be first described by a flowchart in Fig. 4. When the ignition key is turned on, the temperature of the engine cooling water is read and the opening of the air bleed control valve 8 is set to a value in a start table (see Fig. 7(b)) depending upon the engine cooling water temperature at the moment (Steps S1 to S3). When cranking of the engine is started, a crank angle signal is read. When the crank angle signal is inputted, a fuel cutoff valve in a fuel gas supply system is opened and the rotational speed of the engine is read (Steps S4 to S8). When the thus read engine rotational speed is not lower than the start judging rotational speed and the idle switch is off, the engine rotational speed and the suction pressure are read. Then, based on the engine rotational speed and the suction pressure, the opening of the air bleed control valve 8 is set to a value in a basic A/F map (see Fig. 7(a)) as a normal operation mode. Then, when an A/F feedback flag is on, an A/F feedback control is started (Steps S9 to S14). The idle switch is not off in Step S10, the engine cooling water temperature is read again. Then, the opening of the air bleed control valve 8 is set to a value in an idle table shown in Fig. 7(c) and the engine rotational speed is read (Steps S15 to S17). Then, when an A/F feedback flag is not on, the process goes back to Step S15. When an A/F feedback flag is on, an A/F feedback control is started (Steps S18 and S19). Then, when the engine rotational speed is lower than a fuel cutoff rotational speed, the process goes back to Step S5. When the engine rotational speed is not lower than the fuel cutoff rotational speed (such as when the engine brake is in operation), a deceleration fuel cutoff is performed until the engine rotational speed becomes lower than the fuel cutoff rotational speed (Steps S20 and S21). When the ignition key is turned off (Step S22) or when a crank angle signal is not inputted in Step S6, the air bleed control valve 8 is fully opened and an initial setting thereof (correction of the initial value) is executed, whereby the air bleed control valve 8 is moved to a position of the designated step value (Steps S23 to S25). Hereupon, the fuel cutoff valve is closed and the power source of the ECU is turned off (Steps S26 and S27). Specifically, the A/F feedback control is performed as shown in Fig. 5. When the engine cooling water temperature is read and it is not lower than a temperature for starting an A/F feedback control, an O 2 sensor signal is read (Steps S31 to S33). When the O 2 sensor signal is a rich signal, the air bleed control valve 8 is opened at a specific rate selected from a map shown in Fig. 7 (e) based on the suction pressure and the engine rotational speed at the moment and by a specific degree selected in the same manner from a map shown in Fig. 7 (f) at a time until the rich signal is changed to a lean signal. Hereupon, the air bleed control valve 8 is closed at a specific rate selected in the same manner as above from a map shown in Fig. 7 (g) and by a specific degree selected in the same manner from a map shown in Fig. 7 (h) at a time until the O 2 sensor signal is changed to a rich signal (Steps S34 to S37). Then, when a rich signal is outputted from the O 2 sensor, the process goes to Step S35. When a rich signal is not outputted from the O 2 sensor, the process goes to Step S37 (Step S38). Specifically, the deceleration fuel cutoff control is performed as shown in Fig. 6. When the opening of the throttle is read and it is an idle opening, the engine rotational speed in read. When the thus read engine rotational speed is not lower than the deceleration fuel cutoff rotational speed (such as when the engine brake is in operation), the air bleed control valve 8 is opened to a value in a deceleration fuel cutoff table shown in Fig. 7(d) (Steps S41 to S45). Thereby, the amount of bleed air introduced is increased and the amount of fuel gas is decreased. Then, the process goes back to Step S41. The supply of the fuel gas may be cut off by closing the fuel cutoff valve 6c instead of opening the air bleed control valve 8. When the opening of the throttle is not the idle opening in Step S42, the opening of the air bleed control valve 8 is set to a value in a basic A/F map as a normal operation mode in Step S46. Then, the process goes back to Step S41. When the engine rotational speed is lower than the deceleration fuel cutoff rotational speed in Step S44, the opening of the air bleed control valve 8 is set to a value in the idle table map shown in Fig. 7(c) (Step S47). As described above, in the fuel gas mixer of this embodiment, since the fuel gas control valve 5, whose opening is adapted to vary depending upon the opening of the throttle valve 4 so that, in an operation range in which the opening of the throttle valve 4 is small, the opening of the fuel gas control valve 5 may be also small, is provided in the air intake passage 2 upstream of the connecting part of the fuel gas supply passage 6, it is possible to create a suction negative pressure, by which the flow rate of the fuel can be arbitrarily controlled, at the opening 6a of the fuel gas passage 6. The fuel gas mixer does not need a high-pressure gas injector as seen in a conventional device and thus receives no limitation caused by the characteristics of the injector. It is thus unnecessary to provide more than one mixer even in an engine with a large capacity per cylinder, so that an A/F feedback control can be performed with a simple control. Also, since a slow fuel system is unnecessary, it is only necessary to provide a main fuel system (the fuel gas passage 6). Thus, an A/F feedback control can be achieved over the entire operation range only by controlling the main fuel system. Additionally, in this embodiment, the fuel gas control valve 5 is connected to the throttle valve 4 by the link mechanism 11, thereby constituting the means for controlling the opening of the fuel gas control valve 5. Thus, it is possible to create a suction negative pressure by which the fuel flow rate can be controlled at the opening 6a of the fuel gas passage 6 by reducing the opening of the fuel gas control valve 5 when the opening of the throttle valve 4 is small with a simple structure. Moreover, since the link mechanism 11 is so constituted that the fuel gas control valve 5 is fully opened prior to the throttle valve 4 being fully opened, it is possible to prevent the fuel gas control valve 5 from being a resistance to the intake air flow because the fuel gas control valve 5 has fully been opened when the engine enters an intermediate-or high-load operation range in which the opening of the throttle valve 4 is large. Furthermore, since the air passage 7 is connected partway along the fuel gas supply passage 6 and the cross-sectional area of the air passage 7 is adapted to be controlled, the amount of the fuel gas to be supplied can be controlled more accurately and easily as compared with the case of being controlled only by the fuel gas control valve 5. The main venturi 3 can be omitted when the opening characteristic of the fuel gas control valve 5 is controlled to draw a characteristic curve like the curve B shown in Fig. 3. In this case, since a throttling loss of intake air caused by the main venturi 3 is not created, the amount of intake air at the time when the throttle valve 4 is fully opened can be increased, making it possible to obtain a high power. According to the embodiments, since a fuel gas control valve, whose opening is adapted to vary depending upon the operating state of the engine, is provided in an air intake passage upstream of the connecting part of a fuel gas supply passage, a suction negative pressure, by which the flow rate of the fuel can arbitrarily be controlled, can be created at the connecting part of the fuel gas supply passage by reducing the opening of the fuel gas control valve in an operation range in which the opening of the throttle valve is small. This makes a main venturi unnecessary and thus can eliminate a throttling loss of intake air caused by the main venturi, making it possible to obtain a high power. Also, since there is no need to provide more than one mixer even in an engine having a large capacity per cylinder, an A/F feedback operation can be performed with a simple control. Additionally, since a slow fuel system is unnecessary, it is only necessary to provide a main fuel system. Thus, an A/F feedback control can be achieved over the entire operation range by controlling only the main fuel system. Moreover, since a high pressure gas injector is also unnecessary, a high pressure gas system including a regulator can be omitted, resulting in simplification of the structure and decrease in costs. According to a specific embodiment, since the fuel gas control valve is connected to the throttle valve by a link mechanism, it is possible to create a suction negative pressure by which the fuel flow rate can be controlled at the connecting part of the fuel gas passage by reducing the opening of the fuel gas control valve when the opening of the throttle valve is small with a simple structure. Also, since the link mechanism is so constituted that the fuel gas control valve is fully opened prior to the throttle valve being fully opened, it is possible to prevent the fuel gas control valve from being a resistance to intake air flow in an intermediate- or high-load operation range in which the opening of the throttle valve is large. According to an embodiment, since the air passage is connected partway along the fuel gas supply passage and the cross-sectional area of the air passage is adapted to be controlled, the amount of fuel gas to be supplied can be controlled with accuracy and ease.

Claims: A fuel gas mixer comprising an air intake passage (2) connected to an engine, a throttle valve (4) provided in said air intake passage (2) for opening and closing said air intake passage (2), and a fuel gas supply passage (6) connected to said air intake passage (2) at a position upstream of said throttle valve (4), wherein a fuel gas control valve (5) for opening and closing said air intake passage (2) is provided in said air intake passage (2) at a position upstream of the position at which said fuel gas supply passage (6) is connected to said air intake passage (2) and in that fuel gas control valve controlling means (11) is provided for varying the degree of opening of said fuel gas control valve (5) according to the operating state of said engine, and said fuel gas control valve controlling means (11) is adapted to open said fuel gas control valve (5) to a maximum opening position thereof before said throttle valve (4) is fully opened, wherein an air passage (7) is connected partway along said fuel gas supply passage (6), wherein the amount of fuel gas to be supplied is controlled by controlling the cross-sectional area of said air passage (7). A fuel gas mixer according to claim 1, wherein said fuel gas control valve controlling means comprises a link mechanism (11) connecting said fuel gas control valve (5) to said throttle valve (4). A fuel gas mixer according to claim 1 or 2, wherein said air passage (7) is connected to said fuel gas supply passage (6) upstream of an orifice (6b) of said fuel gas supply passage (6). A fuel gas mixer according to at least one of the claims 1 to 3, wherein an air bleed control valve (8) is provided for varying an opening area of an orifice (7a) in said air passage (7). A fuel gas mixer according to claim 4, wherein said air bleed control valve (8) is driven by a step motor (9) to control the flow rate of air passing therethrough. A fuel gas mixer according to at least one of the claims 1 to 5, wherein a main venturi part (3) narrowing said air intake passage (2) is provided between said fuel gas control valve (5) and said throttle valve (4). A fuel gas mixer according to at least one of the claims 1 to 6, wherein said fuel gas supply passage (6) is connected to a fuel gas source via a fuel cutoff valve (6c).

Inventors: IIDA YOSHIKATSU, IIDA, YOSHIKATSU
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 2001
Main classification: F02M21
IPC codes: F02D9, F02M13, F02M21