Electronically Controlled Fuel Injection System

Abstract

An electronically controlled fuel injection system which is so designed as to adapt itself to operation of high engine speed by effecting a switching from two-cylinder simultaneous injection to four-cylinder simultaneous injection. When the engine is operating at speeds below a predetermined value, a fuel injection pulse signal, which occurs at the rate of two pulses for each rotation of the engine shaft, is applied alternately to the injection valve associated with the first and third cylinders and the injection valve associated with the second and fourth cylinders, so that fuel injection takes place simultaneously in the first and third cylinders and it is followed by a simultaneous fuel injection in the second and fourth cylinders. On the other hand, when engine speed increases to the predetermined value, a switching is effected from the two-cylinder simultaneous injection to four-cylinder simultaneous injection. A switching from the four-cylinder simultaneous injection to two-cylinder simultaneous injection occurs when engine speed decreases to another predetermined value lower than said predetermined value. This invention relates to a fuel injection system for a multi-cylinder internal combustion engine and more particularly to an electronically controlled fuel injection system in which a switching from two-cylinder simultaneous injection to four-cylinder simultaneous injection is effected when engine speed increases to a predetermined value. In the ordinary electronically controlled fuel injection system, a timed fuel injection method is employed. For a four-cylinder engine intake method is to effect a simultaneous fuel injection in two earlier-ignited cylinders which is followed by a simultaneous fuel injection in the remaining two later-ignited cylinders, rather than to effect a fuel injection in each one of the four cylinders on its suction stroke. The fuel injection takes place while an injection valve is kept actuated through application thereto of a fuel injection pulse which is generated at the rate of one for each rotation of the engine by a computing circuit which functions to calculate a proper pulse width responsively to engine operating conditions, such as, engine speed, intr(e manifold pressure and engine temperature. When the engine speed rises to, for example, 6000 rpm -- it takes 10 ms for one complete rotation of the crank shaft, the computing circuit is required to generate such a narrow pulse as having its width shorter than 5 ms. However, further increase in engine speed tends to incapacitate the computing circuit from generating such pulse because of its limiting capability in computing operation, thus rendering the fuel injection system incapable of functioning properly. It is therefore an object of this invention to provide a new and improved fuel injection control system for a multi-cylinder internal combustion engine with a view to overcoming the above-stated disadvantages. It is another object of this invention to provide a fuel injection control system which functions to effect a switching from two-cylinder simultaneous injection to four-cylinder simultaneous injection when engine speed increases to a predetermined value. It is a further object of this invention to provide a fuel injection control system having a computing circuit adapted to function properly even when the engine speed increases to a relatively high value.

Description

In the drawings:

FIG. 1 is a schematic diagram of a fuel injection control system according to one embodiment of this invention;

FIG. 2 is a circuit diagram of a switching unit of the fuel injection system shown in FIG. 1;

FIGS. 3(a) through (e) show pulse waveforms appearing at various points of the system of FIG. 1 when a two-cylinder simultaneous fuel injection method is being employed;

FIGS. 4(a) through (e) are views similar to FIGS. 3(a) through (e), but showing pulse waveforms appearing when a four-cylinder simultaneous injection method is being employed; and

FIG. 5 shows a relationship between fuel injection methods employed and engine speed.

Referring now to FIG. 1, numeral 10 designates an engine driven triggering device incorporated in a distributor housing (not shown). The engine driven triggering device 10 comprises a cam 11 mounted on an engine driven shaft 12 and two triggering switches 13 and 14 adapted to be alternately actuated by rotation of the cam 11 as a function of engine speed. Each triggering switch 13, 14 has respectively a movable contact connected to ground and a stationary contact connected to a power supply, such as, a battery 15 via resistors 16 and 17, respectively. The stationary contacts of the triggering switches 13 and 14 are also connected to a waveshaping circuit 18 by means of leads 19 and 20, respectively. The waveshaping circuit 18 has two output terminals 21 and 22 corresponding to the leads 19 and 20, respectively. One such a waveshaping circuit and its configuration is shown in FIG. 4 of U. S. Pat. No. 3,430,616 to Glockler et al which may be readily applicable to the present invention. One of output terminal 21 is connected by means of a lead 23 to one of the input terminals of an OR gate 24. The other output terminal 22 of the waveshaping circuit 18 is connected by means of a lead 25 to one of the fixed contacts A of a relay switch 26. The relay switch 26 has another fixed contact B and a movable contact C which is connected to the other input terminal of the OR gate 24. The output terminal of the OR gate 24 is connected to the input of an computing circuit 27 so that a pulse signal indicating engine speed is supplied to the computing circuit 27. Also applied to the computing circuit 27 are two signals representing intake manifold pressure and engine temperature, designated at 28 and 29, respectively. In dependence on these signals representing engine operating conditions, the computing circuit 27 calculates a proper pulse width and generates a train of pulses having the proper pulse width. The pulses thus generated are supplied to two terminals of the AND gates 30 and 31 at their one inputs by way of leads 32 and 33, respectively. One such a computing circuit and its configuration is shown in FIG. 5 of U. S. Pat. No. 3,430,616 which may be readily applicable to the present invention.

The lead 25 form one output terminal 22 of the waveshaping circuit 18 is connected by means of a lead 34 to one of the fixed contacts A' of another relay switch 35, the movable contact C' of which is connected by means of a lead 36 to the other input terminal of the AND gate 30. Likewise, the lead 23 from the other output terminal 21 of the waveshaping circuit 18 is connected by means of a lead 37 to one of the fixed contacts A" of still another relay switch 38 whose movable contact C" is connected by means of a lead 39 to the other input terminal of the AND gate 30. The leads 34 and 37 are also connected by means of leads 40 and 41 to the two input terminals of another OR gate 42, the output terminal of which is connected to each fixed terminal B' and B" of the two relay switches 35 and 38.

The AND gate 30 has its output terminal connected to an amplifier 43 which in turn is connected to an injection valve 44 associated with the first and third cylinders. Likewise, the AND gate 31 has its output terminal leading to another amplifier 45 which in turn is connected to an injection valve 46 associated with the second and fourth cylinders. The leads 23 and 25 from the output terminals 21 and 22 of the waveshaping circuit 18 are also connected by means of leads 47 and 48 to a switching circuit 49, the construction and operation of which will be fully described later with reference to FIG. 2. The output of the circuit 49 is connected to a relay coil 50 which, upon energization, moves the movable contacts C, C' and C" of the relay switches 26, 35 and 38 from contact with their fixed contacts A, A' and A" into engagement with B, B' and B" .

FIG. 2 shows a circuit diagram of the switching circuit 49 which functions to effect a change-over in injection method between two and four-cylinder simultaneous injection. The input terminals 51 and 52 of the switching circuit 49 are connected to the leads 47 and 48, respectively, so that rectangular pulse signals representing engine speed are supplied from the waveshaping circuit 18 to the switching circuit 49. Connected to the input terminals 51 and 52 are two series connections of capacitors 53 and 54, diodes 55 and 56 and resistors 57 and 58, respectively, the resistors 57 and 58 being connected together to a capacitor 59 having one end grounded. These two series connections and the capacitor 59 act as a means for converting the pulse signal into dc voltage proportional to engine speed. The dc voltage is applied to the base of transistor 60 which forms a major part of a voltage comparing unit or a Schmitt circuit, generally indicated at 61. The base of the transistor 60 is grounded via a resistor 62 and is also connected via a resistor 63 to a bus line 64 connected to a battery. The transistor 60 has its emitter grounded via a resistor 65 and its collector connected to the bus line 64 via a resistor 66. The collector is also connected to the base of another transistor 67 by way of a resistor 68. The emitter of the transistor 60 is also connected to the emitter of the transistor 67 by way of a resistor 681. The transistor 67 has its collector connected to a terminal 101 and the bus line 64 via a resistor 69 and its base connected to ground via a resistor 70. The resistance value of the resistors 62, 63 and 65 are adjusted so that when the engine speed increases to a predetermined value the potential at the base of the transistor 60 is high enough to turn it on. Upon the transistor 60 conducting, the potential at the collector thereof decreases so much that the transistor 67 is rendered nonconductive. When this occurs, the potential at the collector of the transistor 67 builds up.

Shown in the upper right-hand portion of FIG. 2 is a relay unit 71 adapted for use with the Schmitt circuit 61 by connecting the terminal 101 with a terminal 102 to actuate the three relay switches 26, 35 and 38 when the engine speed rises to the predetermined value. The relay unit 71 comprises a transistor 72 having its base connected via a resistor 73 to the terminal 102 and a relay coil 74 connected in series to the transistor 72. The emitter of the transistor 72 is connected directly to ground and the relay coil 74 is connected to a battery. Thus, when the engine speed rises to the predetermined value, the transistor 60 is rendered into conduction, causing the transistor 67 to be rendered nonconductive, which in turn renders the transistor 72 conductive. As a result, the relay coil 74 is energized to move the movable contacts C, C' and C" of the three relay switches 26, 35 and 38 into engagement with the respective fixed contacts B, B' and B".

A transistor circuit 75 including circuits 26', 35' and 38' may take the place of the relay unit 71 by disconnecting the terminal 101 from the terminal 102 and connecting the terminal 101 with a terminal 103. The circuits 26', 35' and 38' are the same circuit and correspond to the relay switch 26, 35 and 38, respectively. Specially expressing the circuit 26', the terminal 103 is connected via a resistor 76 to the base of a transistor 77, the emitter thereof being grounded. The transistor 77 has its collector connected to a battery via a resistor 78 and also to the base of another transistor 79 via a resistor 80. The collector of the transistor 79 is connected through a resistor 81 to a terminal A.sub.1 which corresponds to the fixed contact A of the relay switch 26. The transistor 79 has its emitter connected to a terminal C.sub.1 which corresponds to the movable contact C of the relay switch 26. Connected to the terminal C.sub.1 is the emitter of a transistor 82 whose base is connected to the collector of the transistor 67 via a resistor 83. The transistor 82 has its collector connected through a resistor 84 to a terminal B.sub.1 which corresponds to the fixed contact B of the relay switch 26.

Operation of this transistor circuit 75 is such that when the engine is operating at speeds below the predetermined value the transistor 67 is held conductive and therefore the transistor 77 is nonconducting. Thus, a high voltage at the collector of the transistor 77 is applied to the base of a transistor 79 to render it conductive, so that a current path is established between the terminals A.sub.1 and C.sub.1 by way of the transistor 79. On the other hand, when the engine speed increases to a certain predetermined value, the transistor 67 is rendered nonconductive causing the potential at the collector thereof to build up. Thus, the transistor 77 is turned on and render the transistor 79 nonconductive so as to cutoff the current path between the terminals A.sub.1 and C.sub.1, while the transistor 82 is rendered conductive to establish a current path between the terminals B.sub.1 and C.sub.1 by way of the transistor 82.

In the operation of the control system shown in FIG. 1, when the engine is operating, the cam 11 mounted on the engine driven shaft 12 opens and closes the two triggering switches 13 and 14 alternately in dependence on the rotation of the engine driven shaft to generate alternate pulse signals to the leads 19 and 20. The pulse signal is supplied to the waveshaping circuit 18 where it is shaped into rectangular wave as shown in FIGS. 3(a) and (b), in which (a) represents a rectangular wave-form appearing at the output terminal 21 and (b) at the output terminal 22. As described above, when the engine is operating at speeds below a predetermined value, each of the movable contacts C of the relay switches 26, 35 and 38 are kept in electrical contact with their associated fixed contact A, A' and A", so that the rectangular wave signals on both of the leads 23 and 25 are applied to the respective input terminals of the OR gate 24. Each time the two triggering switches 13 and 14 are made to open and close their contacts by rotation of the cam 11, one rectangular pulse is applied to the computing circuit 27. The computing circuit 27 functions to calculate a proper pulse width on the basis of engine speed, intake manifold pressure and engine temperature to generate a train of pulses having such width, the pulses being shown in FIG. 3(c). The train of pulses are applied to the AND gates 30 and 31 at their one inputs by means of the leads 32 and 33. The rectangular wave signal at the output terminal 22 of the waveshaping circuit 18 is also fed to the relay switch 35 by means of the leads 25 and 34 and thence to the other input of the AND gate 30 by means of the lead 36. Likewise, the rectangular wave signal at the other output terminal 21 of the waveshaping circuit 18 is also fed to the relay switch 38 by means of the leads 23 and 37 and thence to the other input of the AND gate 31 by means of the lead 39.

When the pulse signals applied to the two input terminals of the AND gate 30 are in phase with each other, that is, coincide with each other, the AND gate 30 produces an output pulse during the overlap of these signals, as shown in FIG. 3(d). Likewise, the output pulse of the AND gate 31 occurs during the overlap of the pulse signals applied thereto, as shown in FIG. 3(e). These output pulses are transmitted to the respective amplifiers 43 and 45 and are then applied to the respective injection valves 44 and 46. The injection valve 44, which is mounted in the first and third injection nozzles (not shown), is kept open while the output pulse is applied to the injection valve 44, and the injection valve 46 mounted in the second and fourth cylinders (not shown) is kept open while the output pulse is applied to the injection valve 46. Since, as shown in FIGS. 3(d) and (e), the output pulse is generated alternately by the AND gates 30 and 31 at the rate of two for each rotation of the engine, fuel injection occurs simultaneously in the first and third cylinders and it is followed by the simultaneous fuel injection in the second and fourth cylinders.

On the other hand, when the engine speed increases above the predetermined value, the switching circuit 49 operates to energize the relay unit 71 so that the movable contacts C, C' and C" of the relay switches 26, 35 and 38 are moved from contact with the respective fixed contacts A, A' and A" into contact with the respective fixed contacts B, B' and B". In the case of the transistor circuit 75 shown in FIG. 2, a current path is established between the terminals B.sub.1 and C.sub.1 while the current path between the terminals A.sub.1 and C.sub.1 is cutoff. Since the relay switch 26 disconnects the one input of the OR gate 24 from the lead 25 connected to one of the outputs of the waveshaping circuit 18, the computing circuit 27 is actuated only by the output pulse supplied through the lead 23. Therefore, the computing circuit 27 generates a pulse signal which occurs at the rate of one pulse per each rotation of the engine, as shown in FIG. 4(c). This pulse signal is applied to the AND gates 30 and 31 at their one inputs.

The rectangular wave signals on the leads 23 and 25 are transmitted to the input terminals of the OR gate 42 by way of the leads 41 and 40, respectively. Since, as shown in FIG. 4(a) and (b), the output pulse always exists on either the lead 23 or 25, the OR gate 42 is kept "ON" at all times, so that the output signal is always applied to the AND gates 30 and 31 at the other outputs thereof. Thus, the AND gates 30 and 31 produce output pulses simultaneously AND they receive input signals from the computing circuit 27, as shown in FIGS. 4(d) and (e). The output pulses are supplied to the amplifiers 43 and 45 for amplification and thence to the injection valves 44 and 46, so that fuel injection occurs in the four cylinders simultaneously.

It has been found that from the viewpoint of engine operation it is preferable to effect a changeover from four-cylinder simultaneous injection to two-cylinder simultaneous injection at a point of engine speed lower than that at which the switching from two to four-cylinder simultaneous injection is effected, as shown in FIG. 5. This hysteresis characteristic of the relationship between the fuel injection methods employed and engine speed can be obtained by adjusting the resistance value of the resistors 65 and 681 of the Schmitt circuit 61 shown in FIG. 2.

Although description of this invention has been made in connection with the fuel injection system in which a switching between two and four-cylinder fuel injection is effected this invention is applicable also to the following cases:

one-cylinder injection .fwdarw.two-cylinder .fwdarw.simultaneous four-cylinder invention engine two-cylinder .fwdarw.four-cylinder simultaneous .fwdarw.simultaneous injection injection one-cylinder injection .fwdarw.three-cylinder .fwdarw.simultaneous six-cylinder injection engine three-cylinder .fwdarw.six-cylinder simultaneous injection .fwdarw.simultaneous injection one-cylinder injection .fwdarw.two-cylinder .fwdarw.simultaneous injection either-cylinder two-cylinder .fwdarw.four-cylinder engine simultaneous injection .fwdarw.simultaneous injection four-cylinder .fwdarw.eight-cylinder simultaneous injection .fwdarw.simultaneous injection

Claims

What is claimed is:

1. An electronically controlled fuel injection system for a multi-cylinder internal combustion engine, comprising: first means for producing at least one pulse signal having a repetition frequency proportional to the speed of the internal combustion engine; second means for producing a control signal during a time interval from a moment when said repetition frequency of the pulse signal exceeds a first predetermined value to another moment when said repetition frequency lowers below a second predetermined value smaller than said first predetermined value; third means simultaneously producing at least two drive signals each having a pulse width proportional to said repetition frequency of the pulse signal, the intake manifold pressure and the engine temperature when said third means receives said control signal; and at least two injection valves each adapted to receive one of said drive signal and associated with a nozzle positioned within one of the cylinders, each of said valves being adapted to supply fuel to said nozzle.

2. An electronically controlled fuel injection system according to claim 1, wherein said first means includes an engine-driven triggering device having a cam mounted on an engine-driven shaft and two triggering switches adapted to be actuated by the cam in dependence upon the motion of the engine-driven shaft, and a waveshaping circuit having two input terminals connected to said triggering switches and having two output terminals.

3. An electronically controlled fuel injection system according to claim 1, wherein said third means comprises a first OR gate having two input terminals, one of said input terminals being connected directly to one of the two output terminals of said waveshaping circuit, a first switching element for connecting and disconnecting the other input terminal of said first OR gate to and from the other output terminal of said wave-shaping circuit, a computing circuit having its input terminal connected to the output terminal of said first OR gate, two AND gates each having two input terminals, one of said two input terminals of each said AND gate being connected to the output of said computing circuit, a second OR gate having two input terminals each connected to a respective output terminal of said waveshaping circuit, and second and third switching elements each for selectively connecting the other input terminals of the respectively associated AND gates to the output terminals of said waveshaping circuit and to the output terminal of said second OR gate.

4. An electronically controlled fuel injection system according to claim 1, wherein said second means includes an OR gate having two inputs connected to said two output terminals of the waveshaping circuit and an output, a Schmitt circuit having an input connnected to said output of the OR gate and an output, and an amplifier having an input connected to said output of the Schmitt circuit and an output connected to said switching elements.

5. An electronically controlled fuel injection system according to claim 3, wherein said first, second and third switching elements are relay switches.

6. An electronically controlled fuel injection system according to claim 3, wherein said first, second and third switching elements are switching circuits including transistors.