Fuel Control System For Internal Combustion Engines

Abstract

A fuel control system for internal combustion engines comprising a control voltage generation circuit for generating a control voltage representative of the operating conditions of an engine, a capacitor-resistor coupled type monostable timer circuit composed of two transistors and having the time constant fixed at a certain value, said control voltage being applied through the resistor to the collector of that one of said transistors which is in the cut-off state when said timer circuit is in its stable state, a current amplifier circuit adapted to amplify for current amplification the output timing pulse from said monostable timer circuit to operate an electromagnetic metering valve, and a trigger signal generating circuit for producing a trigger signal at the fuel metering time of the engine to trigger said monostable timer circuit.

Description

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates mainly to a system for controlling the amount of fuel supplied to an internal combustion engine through an electrical control circuit.

2. Description of the Prior Art

The fuel control system of this kind is designed to perform the so-called metering function in that a timing pulse generated by a monostable timer circuit is amplified for current amplification by a current amplifier circuit to actuate an electromagnetic metering valve such that the duration of the timing pulse, i.e., the timing pulse width is controlled to vary the valve open duration of the electromagnetic metering valve to ensure a fuel supply of varying quantities suitable for different operating conditions of the engine, such as, the engine rpm, the accelerator position and the amount of air taken in.

With the conventional systems of the type which controls the pulse width of timing pulses, a variable type resistor or capacitor is employed to provide a time constant element which directly determines the timing pulse width of a monostable timer circuit in accordance with the operating conditions of an engine, and the time constant itself is caused to vary.

With these conventional devices, however, if the so-called separate fuel metering system for each engine cylinder is employed wherein each of a plurality of cylinders of a multiple-cylinder engine is provided with an electromagnetic metering valve so as to meter the quantity of fuel supply to the respective cylinders on an individual basis and both monostable timer circuits and electromagnetic amplifier circuits are respectively provided one for each electromagnetic metering valve, it is necessary to vary the time constants of all the monostable timer circuits provided for the respective cylinders in accordance with different operating conditions of the engine so that the time constant elements, such as, variable resistors and variable capacitors which are equal in number to the engine cylinders must be caused to vary in an interlocked relation. However, these requirements give rise to various practical disadvantages in that such a multiple variable resistors or capacitors tend to cause metering errors because the multiple resistors or capacitors result in a complicated and bulky construction and moreover there are inevitable variations in the resistance values or electrostatic capacities of these resistors or capacitors, and that there is a need to convert the required fuel metering pattern of the engine into a physical quantity such as the resistance or electrostatic capacity of time constant elements and this makes it technically very difficult to improve the accuracy of fuel metering characteristics.

SUMMARY OF THE INVENTION

In order to solve the above-described deficiencies, the present invention has for its object the provision of a fuel control system for internal combustion engines comprising a control voltage generation circuit for producing a control voltage representative of the operating conditions of an engine, a capacitor-resistor coupled type monostable timer circuit composed of two transistors and having the time constant fixed at a certain value, said control voltage being applied through the resistor to the collector of that one of said transistors which is in the cut-off state when said timer circuit is in its stable state, a current amplifier circuit adapted to amplify for current amplification the timing pulse generated by the monostable timer circuit to actuate an electromagnetic metering valve, and a trigger signal generating circuit for producing a trigger signal at the fuel metering time of the engine to trigger the monostable timer circuit, whereby by controlling the monostable timer circuit through the control voltage generated by the control voltage generation circuit in order to produce a timing pulse which suits the amount of fuel supplied to the engine through the electromagnetic metering valve to the operating conditions of the engine, the timing pulse duration is rendered to be controllable with the time constant element of the monostable timer circuit being fixed at a certain value, and moreover by thus rendering the timing pulse duration of the monostable timer circuit controllable by the said control voltage, it is made possible to simultaneously control a plurality of such monostable timer circuits by a single control voltage generation circuit to easily realize a separate fuel metering for the respective cylinders of a multiple-cylinder engine, and at the same time a more accurate fuel metering characteristic may be achieved by merely converting the fuel metering pattern into the form of a control voltage.

By virtue of the construction described above, the fuel control system for internal combustion engines according to the present invention has remarkable effects in that since a plurality of monostable timer circuits are simultaneously controllable by a single control voltage generation circuit, the construction of a separate fuel metering means for the respective cylinders of a multiple-cylinder internal combustion engine is simplified with a resultant improvement in the reliability and decrease in the production cost.

The above and other objects, features and advantages will be made apparent by the description of the embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a fuel supply system of the type known to the prior art.

FIG. 2 is a longitudinal sectional view showing the principal part of an exemplified electromagnetic metering valve.

FIG. 3 is a characteristic diagram of the electromagnetic metering valve.

FIG. 4 is a block diagram showing the electric circuit of an embodiment of the system according to the present invention.

FIG. 5 is a wiring diagram showing an embodiment of the various circuits of the system according to the present invention.

FIG. 6 is a characteristic diagram showing the relationship of an equation (1) for explaining the operation of the system of the present invention.

FIG. 7 is a characteristic diagram of a monostable timer circuit incorporated in the system of the present invention.

FIG. 8 is a diagram showing a basic fuel metering pattern of a Diesel engine.

FIG. 9 is a characteristic diagram of the control voltage generation circuit incorporated in the system of the present invention.

FIG. 10 is a schematic diagram showing the construction of the principal part of another embodiment of the control voltage generation circuit in the system of the present invention.

FIG. 11 is a diagram showing the fuel metering characteristics of the system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be explained with reference to the illustrated embodiments. FIG. 1 is a block diagram showing a conventional fuel supply system incorporated in the prior art system of the type wherein the fuel is metered separately with respect to the individual cylinders of a four-cylinder engine. In this figure, numeral 1 designates a fuel tank; 2 a fuel feed pump; 3 a fuel pressure head regulator; 4, 5, 6 and 7, electromagnetic metering valves; 8, 9, 10 and 11, injectors. The fuel tank 1 stores fuel and the fuel pressure head at the discharge side of the fuel feed pump 2 is maintained at a certain level by means of the fuel pressure regulator 3 with the surplus fuel being returned to the fuel tank 1. Thus, the fuel pressure head at the fuel inlet of the respective electromagnetic metering valves 4, 5, 6 and 7 is maintained at a predetermined level. The electromagnetic metering valves 4, 5, 6 and 7 are valve mechanisms actuated by means of electromagnetic force and a longitudinal sectional view of the principal part of an example of such a valve mechanism is as shown in FIG. 2, in which a housing 12 contains therein a solenoid coil 13, a fixed core 14 and a movable core 15, and a valve 17 disposed at the top of the movable coil is usually seated on a valve seat 28 by a spring 16 so that the fuel at an inlet port 19 is not permitted to flow into an outlet port 20. However, when a current pulse of a fixed current level is applied to the solenoid coil 13, the electromagnetic attractive force produced between the fixed core 14 and the movable core 15 overcomes the restoring force of the spring 16 attracting the movable core 15 towards the fixed core 14. This causes the valve 17 to move away from the valve seat 18 to provide a fuel passage as shown by the arrows and the fuel at the inlet port 19 is now admitted into the outlet port 20. When the current pulse terminates, the valve 17 is reseated on the valve seat 18 thus completing a cycle of the operations. Therefore, so far as a delay in action can be disregarded, the valve open duration of the electromagnetic metering valves 4, 5, 6 and 7 will be the same as the duration of the current pulse applied to the solenoid coil 13. Consequently, if the pressure difference between the inlet port and the outlet port of the respective electromagnetic metering valves 4, 5, 6 and 7 is maintained constant, as shown in FIG. 3, the fuel quantity Q admitted to pass for each cycle of operation of the electromagnetic metering valve varies in proportion to the duration T of a current pulse applied to the solenoid coil 13. The fuel admitted through the electromagnetic metering valves 4, 5, 6 and 7 is injected through the respective injectors 8, 9, 10 and 11 to the engine cylinders as the supply of fuel which is burnt within the cylinders. If the injectors 8, 9, 10 and 11 are of the type which comprises only an injection nozzle, the fuel injection pressure will be restricted by the pressure as determined by the fuel pressure head regulator 3 and the valve opening times of the electromagnetic metering valves 4, 5, 6 and 7 directly coincide with the fuel injection timing. On the other hand, if the injectors are of the type which comprises a suitable fuel pressurizing mechanism and an injection nozzle, not only any fuel injection pressure may be selected as desired, but also the fuel injection timing may be determined independently of the valve opening times of the electromagnetic metering valves. Thus, the control of the fuel quantity supplied to the engine can be achieved by controlling the duration of the current pulse which determines the valve open duration of the electromagnetic metering valves 4, 5, 6 and 7. Accordingly, in order to perform the so-called fuel metering function which adjusts the amount of fuel supplied to the engine to suit various operating conditions of the engine, that is, different fuel metering patterns of the engine, it is necessary to control the duration of the current pulse which determines the valve open duration of the electromagnetic metering valves 4, 5, 6 and 7, in accordance with the fuel metering patterns of the engine, and this is the most important function of the fuel control systems of the type described. The method for controlling the duration of the current pulse which determines the valve open duration of the electromagnetic metering valves 4, 5, 6 and 7 in the system of the present invention will now be explained hereunder. FIG. 4 is a block diagram showing an electric circuit of a fuel control system according to the present invention which, by way of example, is adapted for separately metering fuel into the respective cylinders of a four-cylinder internal combustion engine, and the construction of the fuel supply system employed is the same with the one shown in FIG. 1. In this figure, numerals 21, 22, 23 and 24 respectively designate capacitor-resistor coupled type (hereinafter simply referred to as a C-R coupled type) monostable timer circuits disposed correspondingly for the respective cylinders of the engine; 25, 26, 27 and 28, corresponding current amplifier circuits; 4, 5, 6 and 7 corresponding electromagnetic metering valves; 29 a control voltage generating circuit; 30 a trigger signal generating circuit.

The C-R coupled type monostable timer circuits 21, 22, 23 and 24 are designed to perform the ordinary time delaying function wherein the timer circuit remains in its stable state when it is not triggered, but when triggered by a trigger pulse the circuit is caused to pass from the stable state to an unstable state and it then returns to its original stable state after the lapse of a certain unstable period to generate during this unstable period a timing pulse having a duration equivalent with that of the unstable period, and at the same time these monostable timer circuits differ from the conventional timer circuits in that the duration of a timing pulse, i.e., the timing pulse duration can be controlled by means of a control voltage produced by the control voltage generating circuit 29 with the time constant element being fixed at a certain valve. The current amplifier circuits 25, 26, 27 and 28 amplify for current amplification the timing pulses produced by the respective monostable timer circuits 21, 22, 23 and 24 so that the timing pulses are amplified to a current level sufficient to open the respective electromagnetic metering valves 4, 5, 6 and 7 when they are applied to the solenoid coils of the electromagnetic metering valves. On the other hand, as previously explained with reference to FIGS. 2 and 3 by way of example, the valve open duration of the electromagnetic metering valves 4, 5, 6 and 7 is equivalent to the timing pulse duration so far as the delay in action can be disregarded for all practical purposes. Accordingly, the fuel quantity Q admitted through the electromagnetic metering valves 4, 5, 6 and 7 will be given as Q = .sub.M when the timing pulse duration T = T.sub.M and Q = Q.sub.m when T =T.sub.m. The trigger signal generation circuit 30 produces a trigger signal whenever the time comes to meter the fuel to the respective engine cylinders. The control voltage generating circuit 29 produces a control voltage representing different engine operating conditions which controls the monostable timer circuits 21, 22, 23 and 24 to produce timing pulses such that the fuel quantity admitted through the electromagnetic metering valves 4, 5, 6 and 7 suits the engine operating conditions. In this case, the input signal factors which determine the control voltage from the control voltage generating circuit 29 are the number of revolutions of the engine, the accelerator position, the pressure in the intake pipe or the like, and the necessary input signal factors differ according to the types of engines. Moreover, since the fuel metering pattern differs for different types of engines, the control voltages for the different engine operating conditions should assume different values according to the kinds of engines. Consequently, the pattern of control voltages produced by the control voltage generating circuit 29 also assumes the different forms correspondingly.

Next, an embodiment of the respective electrical circuits for the essential units of the system will be explained hereinafter with reference to FIG. 5. By way of example, the monostable timer circuit whose timing pulse duration is controllable by a control voltage with the time constant being fixed at a certain value is designated at a reference numeral 21 in FIG. 5. Numerals 35 and 36 designate two transistors which constitute a C-R coupled type monostable timer circuit 21, and the product CR of the resistance value R of a resistor 37 and the electrostatic capacity C of a capacitor 38 determines the time constant. Numerals 39 and 40 designate the collector load resistors of the transistors 35 and 36, respectively. Numerals 41 and 42 designate resistors. Numeral 43 designates a trigger circuit, 44 a capacitor, 45 a diode, 46 and 47 resistors. A first control voltage V.sub.C is applied at a first control voltage application point D to the collector of the transistor 35 through the collector load resistor 39, and the collector of the transistor 36 is connected to a constant DC power source V.sub.B through the collector load resistor 40, while one end F of the resistor 37 which is opposite to the junction point between the capacitor 38 and the resistor 37 constituting the time constant element provides a second control voltage application point to which a second control voltage V.sub.C ' is applied. When a trigger signal is applied to a triggering point G.sub.1, the monostable timer circuit 21 is triggered passing from its stable state to an unstable state where it remains for a given time, and the duration T of a timing pulse signal developed at this time at the collector H.sub.1 point of the transistor 36 is given by a relation

where RC is the time constant as previously explained. V.sub.C is a first control voltage and V.sub.c ' is a second control voltage both of which are positive voltages with respect to a point E as a reference. Then, if the relationship of the above expression (1) is graphically represented by drawing the values of T/RC as the ordinate and the values of V.sub.c /V.sub.c ' as the abscissa, a characteristic curve is obtained as shown by the solid line in FIG. 6. When confined to a certain practical limit defined by a relation V.sub.c << V.sub.c ', there results an approximate expression

and hence the aforesaid expression (1) is approximated as T .apprxeq. RC (V.sub.c /V.sub.c ') so that the timing pulse duration T can be controlled by means of the first and second control voltages V.sub.c and V.sub.c ' even if the RC time constant is fixed at a certain value. In other words, if the value of the second control voltage V.sub.c ' is fixed, the timing pulse duration T is proportionally related to the first control voltage V.sub.c. Alternatively, if the value of the first control voltage V.sub.c is fixed, the timing pulse duration T is related to the second control voltage V.sub.c ' in inverse proportion, while on the other hand a control in which the first control voltage V.sub.c is divided by the second control voltage V.sub.c ' is possible, if the values of the two control voltages are made variable. Furthermore, for purposes of simplification in the present embodiments if the second control voltage V.sub.c ' is fixed and coupled in common with the fixed DC power source V.sub.B so that there results V.sub.c ' = V.sub.B, it is possible to control the timing pulse duration T in proportion to the first control voltage V.sub.c even though the value of the time constant RC is fixed and the monostable timer circuit 21 exhibits the characteristics as shown in FIG. 7.

In the discussion to follow the first control voltageV.sub.c will be simply referred to as the control voltage V.sub.c, where T = T.sub.M when V.sub.c = V.sub.M and T = T.sub.m if V.sub.c = V.sub.m. In FIG. 5, the circuits 22, 23, and 24 enclosed by the two-dot chain lines are C-R coupled type monostable timer circuits of the same circuit construction as the previously described C-R coupled type monostable timer circuit 21 and, although their detailed electrical circuits are not shown, points D represent control voltage application points, G.sub.2, G.sub.4 and G.sub.3 trigger signal application points and H.sub.2, H.sub.3 and H.sub.4 output terminals for the timing pulse signals. In this connection, if the output resistance of the control voltage generating circuit 29 is properly chosen, the collector load resistor 39 of the monostable timer circuit 21 may apparently be omitted, however this merely means that the collector load resistor 39 is included in the output resistance of the control voltage generating circuit 29. On the other hand, an example of the current amplifier circuit is shown at numeral 25 in FIG. 5, and a transistor 48 is a current amplification transistor whose base is connected to a base input point H.sub.1 through a resistor 49 and a positive source voltage V.sub.B is applied to the collector through a solenoid coil 31 of the electromagnetic metering valve 4 inserted between load connecting points J.sub.1 and K.sub.1. Thus, a timing pulse signal produced at the point H.sub.1 is amplified for current amplification by the transistor 48 and it is then applied to the solenoid coil 31 of the electromagnetic metering valve 4 so that the electromagnetic metering valve 4 is caused to operate and stay open for a time equal to the timing pulse duration. In FIG. 5 those circuits 26, 27 and 28 which are enclosed by two-dot chain lines are current amplifier circuits of the same circuit construction as the current amplifier circuit 25. While the detailed electrical circuits of these circuits are omitted, points H.sub.2, H.sub.3 and H.sub.4 designate base input points respectively and solenoid coils 32, 33 and 34 of the respective electromagnetic metering valves 5, 6 and 7 are connected between points J.sub.2 and K.sub.2, points J.sub.3 and K.sub.3 and points J.sub.4 and K.sub.4 respectively. Also designated at numeral 30 in FIG. 5 is an example of the trigger signal generating circuit 30 comprising four contact breakers 50, 51, 52 and 53 and a cam 54 linked to the engine crankshaft to drive the contact breakers so that four trigger signals having certain phase difference corresponding to the respective engine cylinders are produced. Since V.sub.B is a positive power source voltage, each time the contact breakers 50, 51, 52 and 53 are closed by the cam 54, trigger signals of a negative polarity are produced and are applied to the triggering points G.sub.1, G.sub.2, G.sub.3 and G.sub.4 of the respective monostable timer circuits 21, 22, 23 and 24. An example of the control voltage generating circuit 29 is shown in FIG. 5 and this circuit 29 generates a control voltage which suits the basic fuel metering pattern of a Diesel engine. In other words, with a Diesel engine the combustion can take place at any air-fuel mixing ratios so far as the excess air ratio is higher than a certain level. Therefore, the amount of fuel supply which suits different operating conditions of the engine is basically determined only by the rotational speed N of the engine and the accelerator position .theta. so that the basic fuel metering pattern will be as shown in FIG. 8. In this figure only the basic pattern is shown omitting those supplementary correcting functions, such as increasing the amount of fuel for starting and metering the fuel in accordance with variations in the absorption efficiency against the engine rotational speed N. Here, .theta. = 0 indicates a zero accelerator position, .theta. = .theta..sub.M a full accelerator position and there is a relation 0 < .theta..sub.2 < .theta..sub.M. Further, Q = Q.sub.M indicates the maximum amount of fuel supplied to the engine, Q = Q.sub.m the minimum amount of fuel supply and N.sub.M is the maximum engine rpm thus determining N.sub.1, N.sub.1 ', N.sub.2, N.sub.2 ', N.sub.3 and N.sub.M as shown in the figure. Then, since the duration of timing pulses generated by the monostable timer circuits 21, 22, 23 and 24 can be controlled in proportion to the control voltage and the fuel admitted to pass through the electromagnetic metering valves varies in proportion to the timing pulse duration as previously explained, the pattern of control voltage which controls the monostable timer circuits 21, 22, 23 and 24 to achieve a fuel metering pattern as shown in FIG. 9, will be the same with the pattern in FIG. 8. In this case, however, the vertical axis represents values of the control voltage V.sub.c replacing Q.sub.M and Q.sub.m with V.sub.M and V.sub.m, respectively. The control voltage generating circuit 29 shown in FIG. 5 is designed to provide such a control voltage pattern and its operation will now be explained hereunder.

In the control voltage generating circuit 29 of FIG. 5, numerals 55 and 56 designate transistors and numeral 57 designates a speed voltage generating circuit for producing a speed voltage proportional to the rotational speed of the engine, the circuit being composed of a tachometer generator 59 linked to the engine crankshaft, a rectifying diode 60, smoothing capacitors 61 and 62 and resistors 63 and 64. Numeral 58 designates a preset voltage generating circuit for producing the preset voltage proportional to the accelerator position and a voltage dividing resistor 65 whose resistance value varies in association with the governing rod of the engine. Numerals 66, 67, 68 and 69 designate resistors and 70 a capacitor. It is so arranged that the speed voltage is applied to the base of the transistor 55 and the preset voltage is applied to the transistor emitter. Thus, if the speed voltage is lower than the preset voltage, the transistor 55 is cut off since there is no forward bias voltage applied to the transistor 55 with the result that the transistor 56 is also cut off since it has zero bias. Consequently, with a ground point E in FIG. 5 as a reference, the control voltage developed at the emitter point C of the transistor 56 is equivalent to the voltage V.sub.M (positive voltage) of a power source to which the resistor 68 is connected. On the other hand, if the speed voltage becomes higher than the preset voltage, a bias voltage is supplied to the transistor 55 in the forward direction in accordance with the difference voltage between the two voltages so that the transistor 55 conducts to permit the collector current to flow through the resistor 66. When this happens, a forward bias voltage is applied to the transistor 56 in accordance with the terminal voltage of the resistor 66 so that the transistor 56 conducts to thereby permit the flow of the collector current through the resistor 68 with the result that the voltage at the point C is reduced by the value of the terminal voltage of the resistor 68. Then, as the difference voltage between the speed voltage and the preset voltage becomes higher than a certain value, the transistor 56 is rendered fully conductive so that the voltage developed at the point C is a given minimum value V.sub.m as determined by the voltage dividing ratios of the resistors 68 and 69.

Referring to FIG. 8 and if it is assumed that the accelerator position .theta. = .theta..sub.2, when the speed voltage becomes lower than the preset voltage with the rotational speed N of the engine being lower than N.sub.2, then the control voltage V.sub.c = V.sub.M. Where N.sub.2 < N < N.sub.2 ', as the speed voltage exceeds the preset voltage, a control voltage is generated which suits the limit V.sub.m < V.sub.c < V.sub.M in accordance with the difference voltage. When N .gtoreq. N.sub.2 ', if the subtraction of the preset voltage from the speed voltage results in the difference voltage which is greater than a certain value, then the control voltage V.sub.c = V.sub.m. With other accelerator positions .theta. = 0 and .theta. = .theta..sub.M, the rotational speed N merely makes parallel movements and functionally there is no difference from the previously discussed cases, hence no further explanation will be made. Consequently, the control voltage produced by the control voltage generating circuit of FIG. 5 is as shown in FIG. 9 and a control voltage pattern is provided which is substantially the same as the basic fuel metering pattern for Diesel engines shown in FIG. 8. Since there is a linear relationship between this control voltage V.sub.c and the duration T of the timing pulses produced by the monostable timer circuits 21, 22, 23 and 24 and the fuel quantity Q which passes through the electromagnetic metering valves 4, 5, 6 and 7 as shown in FIGS. 7 and 3, and since T = T.sub.M, Q = Q.sub.M where V.sub.c = V.sub.M and T = T.sub.m, Q = Q.sub.m where V.sub.c = V.sub.m, it follows that the electric circuitry of FIG. 5 provides the fuel control characteristic as shown in FIG. 11 which is substantially the same as the basic fuel metering pattern for Diesel engines such as shown in FIG. 8. While the control voltage generating circuit 29 illustrated in FIG. 5 is designed to first convert both of the two input signal factors, i.e., the rotational speed of the engine and the accelerator position into a voltage form and then to produce a control voltage in a purely electrical manner, a mechanical control voltage generating circuit may also be employed in which a corresponding mechanical displacement is produced from these two input signal factors so that the voltage dividing ratios of voltage dividing resistors are changed by means of said mechanical displacement to thereby provide the required control voltage. FIG. 10 shows, by way of example, the construction of the principal part of such a mechanical control voltage generating circuit wherein arms 75 and 75' of fly-weights 72 and 72' are connected to a rotary shaft 71 by means of pivots 73 and 73', and numerals 74, 74' and 80, 80' designate stoppers. In operation, as the shaft 71 rotates, the fly-weights 72 and 72' produce centrifugal force and move in the directions shown by arrows. The arms 75 and 75' are designed to transmit force to a spring 77 through the intermediary of a connecting plate 76 and the preset load of the spring 77 is made variable by a governing rod 78 which determines the accelerator position .theta.. A slider 79a of a voltage dividing resistor 79 is connected to the connecting plate 76. When the accelerator position .theta. is determined by the governing rod 78, the preset load is established with respect to the resultant distortion of the spring 77. In addition, the fly-weights 72 and 73 produce centrifugal force in accordance with the rotational speed of the engine so that a speed load corresponding to the rotational speed is applied to the connecting plate 76. Accordingly, if the speed load is smaller than the preset load, the arms 75 and 75' engage the stoppers 74 and 74' to rest thereat so that the position of the connecting plate 76 is correspondingly established to thereby cause a control voltage V.sub.c = V.sub.M at the slider 79a of the voltage dividing resistor 79, that is, a point I. As the number of revolutions of the engine increases and the speed load becomes larger than the preset load, the connecting plate 76 is moved in the direction shown by the arrows in accordance with the difference between the two loads with the result that the voltage dividing ratio of the voltage dividing resistor 79 is correspondingly changed to cause the control voltage V.sub.c at the point I to become lower than the value of V.sub.M. As the rotational speed of the engine further increases and exceeds a certain level, the arms 75 and 75' engage the stoppers 80 and 80' so that the control voltage V.sub.c at the point I becomes V.sub.m and the control voltage pattern is achieved which is the same as in FIG. 9. Therefore, the control voltage generation circuit shown in FIG. 10 is capable of satisfying the same functions as met by the control voltage generating circuit 29 illustrated in FIG. 5.

The system according to the present invention is not limited to the single embodiment which has been described hereinbefore. On the contrary, other embodiments of the system of the present invention are possible, as follows:

1. Instead of providing electromagnetic metering valves and injectors separately, the electromagnetic metering valve may be provided with an injection nozzle for fuel injection on the fuel discharging port side thereof thereby combining the functions of both the electromagnetic metering valve and the injector in one unit. In this case, the fuel metering time coincides with the fuel injection timing.

2. Instead of the control voltage generation circuit 29 shown in FIG. 8 which is adapted to generate the control voltage corresponding to the basic fuel metering pattern for Diesel engines, a control voltage generating circuit may be employed which is adapted to produce a control voltage corresponding to a fuel metering pattern which more precisely suits the operating conditions of the engine, such as increasing the initial amount of fuel for starting the engine and the non-linear control of the volume of injection to meet the varying engine rpm.

3. In order to adapt the system of the present invention for use with a gasoline engine, the system may comprise a first control voltage generation circuit for producing a first control voltage V.sub.c by detecting, for example, the intakemanifold pressure of the engine as an input signal factor representing a first engine operating condition, and a second control voltage generating circuit for producing a second control voltage V.sub.c ' by detecting, for example, the temperature of the engine through the cooling water as an input signal factor representing a second engine operating condition, whereby the first control voltage V.sub.c is applied to the first control voltage application point D of the monostable timer circuit 21 in the preferred embodiment and the second control voltage V.sub.c ' is applied to the second control voltage application point F so as to control the timing pulse duration T.

4. With any internal combustion engines other than Diesel and gasoline engines, a control voltage generating circuit may be used which is designed to produce a control voltage corresponding to the fuel metering pattern from an input signal factor that depends on different engines, whereby the control voltage thus provided is applied to either the first control voltage application point D or the second control voltage application point F of the monostable timer circuit 21 in the preferred embodiment so as to control the timing pulse duration.

Claims

We claim:

1. A fuel control system for controlling a fuel supply to an internal combustion engine through an electromagnetic valve comprising

a control voltage generating circuit for producing a first control voltage representing operating conditions of the engine,

a trigger signal generating circuit for producing a trigger signal at the fuel metering time of the engine,

a monostable multivibrator type timer circuit having a normally stable state and an unstable state and having first and second input terminals respectively connected to said generating circuits for respectively receiving said first control voltage and said trigger signal,

said timer circuit being triggered from said stable state to said unstable state by said trigger signal and further having a third input terminal for receiving a second control voltage and having only first and second transistors which are connected to said three terminals,

each of said transistors having respective collector, emitter and base electrodes with the emitter electrodes being connected together, said collector electrodes of each transistor being cross coupled to the base electrode of the other transistor,

means including a first resistor in the said cross coupling of the collector electrode of said second transistor with the base of the first transistor for causing the second transistor to be normally conductive while said timer circuit is in said stable state,

a capacitor in the said cross coupling from said first transistor collector electrode to the second transistor base electrode and forming first and second junction points therewith respectively,

a first path including said second transistor base and emitter electrodes and a second resistor connected only between said first input terminal and said first junction point for charging said capacitor by said first control voltage when said second transistor is conductive as aforesaid,

there being between said second junction point and said third input terminal only a resistance having a resistance value which is independent of the value of said second control voltage and which forms with said capacitor and first transistor collector and emitter electrodes a second path for discharging said capacitor when said timer circuit is triggered to said unstable state to cause from said second transistor an output timing pulse having a time duration proportional to said first control voltage and inversely proportional to said second control voltage, and

an amplifier connected to said timer circuit and adapted for connection to said electromagnetic valve for supplying thereto an amplification of said timing pulse.

2. A fuel control system for controlling a fuel supply to an internal combustion engine through an electromagnetic valve comprising

a control voltage generating circuit for producing a control voltage representing operating conditions of the engine,

a trigger signal generating circuit for producing a trigger signal at the fuel metering time of the engine,

a capacitor-resistor coupled type monostable timer circuit composed of two transistors and having a time constant fixed at a given value, said monostable timer circuit being connected to receive the control voltage generated by said control voltage generating circuit through the resistor at the collector of that one transistor of said two transistors which is in the cutoff state when said timer circuit is in the stable state, said monostable timer circuit being provided with a further control voltage application terminal at one end of the resistor opposite the junction point between the capacitor and the resistor constituting the time constant element, and said monostable timer circuit also being connected to said trigger signal generating circuit to receive said trigger signal to thereby be triggered to an unstable state and produce a timing pulse signal having a time duration dependent substantially upon the ratio of said control voltage to said further control voltage,

a current amplifier circuit connected to said monostable timer circuit for current amplification of the timing pulse produced by said monostable timer circuit so as to actuate the electromagnetic valve,

said system being for internal combustion engines having a crankshaft and accelerator, and wherein said control voltage generating circuit comprises

a speed voltage generating circuit which includes an AC generator linked with the engine crankshaft, a diode for rectifying the output of said generator and a smoothing capacitor;

a preset voltage generating circuit including a variable resistor linked with the accelerator for producing a voltage proportional to the accelerator position;

and a transistor connected so that the output thereof is controlled by the difference between the output of said speed voltage generating circuit and the output of said preset voltage generating circuit,

whereby a control voltage related to the accelerator position and the engine speed is produced.

3. A fuel control system for controlling a fuel supply to an internal combustion engine through an electromagnetic valve comprising

a control voltage generating circuit for producing a control voltage representing operating conditions of the engine,

a trigger signal generating circuit for producing a trigger signal at the fuel metering time of the engine,

a capacitor-resistor coupled type monostable timer circuit composed of two transistors and having a time constant fixed at a given value, said monostable timer circuit being connected to receive the control voltage generated by said control voltage generating circuit through the resistor at the collector of that one transistor of said two transistors which is in the cutoff state when said timer circuit is in the stable state, said monostable timer circuit being provided with a further control voltage application terminal at one end of the resistor opposite the junction point between the capacitor and the resistor constituting the time constant element, and said monostable timer circuit also being connected to said trigger signal generating circuit to receive said trigger signal to thereby be triggered to an unstable state and produce a timing pulse signal having a time duration dependent substantially upon the ratio of said control voltage to said further control voltage,

a current amplifier circuit connected to said monostable timer circuit for current amplification of the timing pulse produced by said monostable timer circuit so as to actuate the electromagnetic valve,

said system being for internal combustion crankshaft and accelerator engines and wherein said control voltage generating circuit comprises a centrifugal governor means linked with the engine crankshaft, a variable resistor having a slidable contact coupled with said governor so as to vary the resistance value thereof in relation to the engine speed, and a mechanism interlinking said governor means with the accelerator mechanism of the engine, whereby a control voltage related to the accelerator position and the engine speed is obtained.

4. A fuel control system as defined in claim 1 wherein said third input terminal of said monostable timer circuit is connected to a constant DC voltage source to thereby produce a timing pulse having a duration dependent substantially upon said control voltage supplied by said control voltage generating circuit.

5. A fuel control system as defined in claim 1 wherein said monostable timer circuit and said current amplifier circuit are provided respectively in the same number as that of engine cylinders, and a single control voltage generating circuit and a single trigger signal generating circuit are provided.

6. A fuel control system for controlling a fuel supply to an internal combustion engine through an electromagnetic valve mounted to the engine comprising

means for producing a first control voltage representing the operating condition of the engine,

means for producing a trigger signal at the fuel metering time of the engine,

means for supplying a second control voltage,

a monostable timer circuit for producing a timing pulse and having an input transistor connected to receive said trigger signal and an interconnected output transistor and a time constant element including a capacitor and a resistor connected directly to said second control voltage, the capacitor of said element being charged by said first control voltage through a second resistor to said output transistor and discharged through said input transistor and the resistor of said element to said second control voltage supply means when said trigger signal renders said input transistor conductive, and

means for applying said timing pulse so as to actuate said electromagnetic valve.

7. A system as in claim 6, wherein said second control voltage is constant.

8. A system as in claim 6, wherein said means for producing said first control voltage comprises:

means for generating a voltage corresponding to engine speed,

means for producing a voltage proportional to the accelerator position of the engine,

and means in said timer circuit for producing said timing pulse in response to the difference between said engine speed and accelerator position voltages.