Method and system for idle speed control

Abstract: In a system for controlling the idle speed of an internal combustion engine the rotations of the internal combustion engine is detected by a crank angle sensor (l0), the flow rate of air supplied to the engine is detected by an air flow sensor (9), the amount of fuel supplied to the engine is controlled by a fuel supply unit (4), an idle condi­ tion of the engine is detected by another sensor (3), and an abnormal condition with the engine speed exceed­ ing a predetermined level in idle state is detected by an electronic control unit (l3) by use of electrical signals from the sensors. The number of times fuel is supplied to the engine is counted and the fuel supply is suspended each time the count of the counter reaches a predetermined value.

Description: The present invention relates to a method and a system for controlling the idle speed of an internal combustion engine having a plurality of cylinders. In the case of a trouble with an idle speed control system in which a solenoid valve is left open or a power transistor is left on, it is known from JP-A-57-186038 to prevent an increased idle speed through controlling an exhaust gas reflux (hereinafter referred to as the EGR) valve in such a manner as to open that valve. That method, however, has the disadvantage that a change in the amount of EGR deteriorates the combustion and renders the engine speed unstable. Further, US-A-3 463 130 discloses a fuel injection control system with which the application of fuel injection pulses to fuel injection valves is inhibited by a blocking circuit under control of the engine speed, and a switch coupled to the fuel control prevents fuel feeding when, with the throttle valve being in a closed or almost closed state, the engine speed exceeds a predetermined minimum value. With another control apparatus known from EP-A-0 073 518 the fuel supply is stopped for only predetermined ones of a plurality of engine cylinders in response to the operating conditions of the engine. Under idling conditions of the engine with rather low speed, however, stopping the fuel supply to only particular ones of the engine cylinders will result in unstable engine operation, since every cylinder the fuel supply to which is stopped will not generate torque which has the consequence of lengthening the time interval between the combustion change from one cylinder to another and remarkably varying the engine speed. Accordingly, it is an object of the present invention to provide a method and a system for controlling the idle speed in which upon detection of a trouble of the idle speed control system (i.e. an abnormally high engine speed) the idle speed is prevented from increasing to thereby stabilize the engine speed. According to the present invention, the said object is achieved by means of an idle speed control method as defined in claim 1 and by an idle speed control system as defined in claim 4 further developments and improvements being defined in sub-claims. With an arrangement according to the present invention the choice of the cylinders to be stopped with regard to their fuel supply at the time of an abnormal idling operation of the engine can be uniformed so that an undue increase of the engine speed can be suppressed while maintaining a stable rotational condition of the engine during the abnormal idling operation. Summing up the present invention provides a method and a system for the idle speed control for a multi-cylinder internal combustion engine in which if the engine speed is higher than a predetermined value in idle mode, the fuel supply is interrupted for each cylinder and the number of cylinders in which fuel is burnt is reduced. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 and 5 are flowcharts showing embodiments of the present invention. Fig. 2 is a diagram showing an engine control system. Fig. 3 is a block diagram showing an injector drive unit. Fig. 4 is a time chart showing the operating conditions of the flip-flop, register and counter for each cylinder. Fig. 6 is a time chart for a fuel injection pulse output according to the embodiments of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be explained below. In Fig. 2, the air taken into the engine is applied through an air cleaner 8 and measured in an air flow sensor 9, and through a throttle 2 and an intake manifold 1, is introduced into cylinder 7. An electronic control unit 13 is supplied with signals from the air flow sensor 9, a crank angle sensor 10, a cooling water temperature sensor 12 and an idle switch 3 for detecting a full throttle closure, and converts these signals into digital signals. On the basis of these digital signals, the amount of fuel required by the engine is computed by a digital computer in the electronic control unit 13 thereby to produce a signal representing the valve opening time of the injector 4. The fuel is pressured by a fuel pump 5 from the fuel tank 6 and supplied into the injector 4. Also, a BP solenoid valve 11 is disposed in a passage bypassing the throttle valve 2, and by controlling this BP solenoid valve 11, the area of the bypass is controlled thereby to regulate the engine speed at a predetermined level in idle mode. A block diagram of the injector drive unit is shown in Fig. 3. The digital computer (hereinafter referred to as the CPU) 301 in the electronic control unit 13 computes the amount of fuel required by the engine, converts the amount of fuel thus calculated into an injector valve opening time, writes the resultant time into one of the registers 306 to 309 associated with the cylinder into which fuel is to be injected, and further writes data specifying the cylinder to be supplied with fuel in the cylinder register 310. The signal applied from the cylinder register 310 to the decoder 311 opens an AND gate for passing a signal REF representing a predetermined angle. The REF signal sets a predetermined flip-flop (hereinafter referred to as the FF). One of the counters 302 to 305 corresponding to the registers 306 to 309 which is associated with the FF thus set is impressed with a clock signal which is counted. When a comparator shows that the resultant count of the counter is larger than the value of the register mentioned above, the FF is set. During the time period from when the FF is set and to the time point when it is reset, a drive signal is applied to a corresponding one of the injectors 316 to 319. This signal opens the injector valve for a predetermined length of time thereby to supply fuel into the cylinder of the particular injector. A time chart indicating the operations of the register, the FF, and the counter of each cylinder in Fig. 3 is shown in Fig. 4. Each cylinder is adapted to be supplied with fuel as required at predetermined timings. Now, explanation will be made of the manner in which the idle engine speed is controlled with reference to Fig. 5. In this control method, which is well known, an idle trouble is detected regardless of the cylinders. First, step 501 checks to see whether an idle switch 3 is turned on or off. If the idle switch 3 is turned on, that is, if the throttle is closed up step 502 reads the engine speed and sets it to N. (Stored in RAM) Next, step 503 sets the target engine speed in idle mode to NREF, followed by step 504 for comparing N and NREF with each other. If N is equal to NREF, step 513 clears an idle control fault flag ISCNG. If N is larger than NREF, on the other hand, the duty factor ISCON of the duty signal applied to the solenoid valve is reduced by ΔD (Step 505). In the case where N is smaller than NREF, step 506 increases ISCON by ΔD thereby to increase the engine speed. Step 507 checks to see whether the flag ISCON has exceeded 100%, and if it is exceeded, step 509 renders ISCON equal to 100%, followed by step 513. If ISCON is smaller than 100%, by contrast, step 508 checks whether ISCON is lower than 0%. If ISCON is larger than 0%, the process proceeds to step 513, while if ISCON is smaller than 0%, step 510 renders ISCON equal to 0%. Further, step 511 makes a comparison to see whether the engine speed N is higher than 100 rpm, and if N is smaller than 1000 rpm, the process proceeds to step 513, while if N is equal to or higher than 1000 rpm, it indicates that the engine speed is excessively high in spite of the supply signal to the solenoid valve being stopped, so that the idle control system is regarded as faulty and the flag ISCNG is set to 1. In other cases, ISCNG is set to 0 at step 513. Step 514 produces a pulse to be supplied to the solenoid valve. A flowchart for a fuel injection system for supplying each cylinder is shown in Fig. 1 as an embodiment most closely related to the features of the present invention. The parts shown in this flowchart are adapted to run in synchronism with the signal from the crank angle sensor generated at every 180° of crank angle of the engine. First, step 601 checks a first cylinder decision signal by use of a sensor mounted on, say, the distributor, and if the first cylinder is involved, step 604 clears the flag COUNT1. If the first cylinder is not involved, on the other hand, step 602 increments COUNT1 by one, folowed by step 603 for checking whether COUNT1 has become 4 or not. If it has become 4, step 604 clears the flag COUNT1. Step 605 then checks whether the idle control system is in trouble, and if it is found normal, steps 606, 608 and 610 check the content of flag COUNT1 thereby to determine a cylinder for injection. If COUNT1 is zero, by contrast, step 607 injects into the first cylinder, while if COUNT1 is 1, step 609 injects fuel into the third cylinder. When COUNT1 is 2, step 611 injects into the fourth cylinder, and if COUNT1 is 2, step 612 makes injection into the second cylinder. As a result, fuel is injected into the first, third, fourth and second cylinders in that order at regular intervals of 180° in crank angle. If step 616 decides that the idle switch is turned on while the idle control system is found faulty at step 605, on the other hand, step 613 increments the flat COUNT2 by one, followed by step 614 for checking whether or not COUNT2 has become 3. If COUNT2 is smaller than 3, steps 606 to 612 inject fuel into predetermined cylinders. If COUNT2 is equal to or larger than 3, step 615 clears the flag COUNT2, thereby preventing fuel from being injected into any of the cylinders. A time chart of a fuel injection pulse output according to the present embodiment is shown in Fig. 6. The pulse indicated by dashed line shows that no injection is made. According to this embodiment, a cylinder is not injected at regular intervals of three injections thereby to prevent the engine speed from increasing, while the cylinders injected with fuel are supplied with the required amount of fuel and therefore perform a combustion with the right mixing ratio to attain a smooth engine operation. In the embodiment shown in Fig. 1, an injection is omitted the cylinders sequentially. Specifically, following each two injections, a third injection is omitted for each cylinder. In Fig. 6, injections 3-3, 6-3 and 9-3 are omitted. It will thus be understood from the foregoing description that according to the present invention, even in the case where the idle speed control system is in trouble, the idle engine speed is prevented from increasing abnormally on the one hand, and a smooth engine rotation is obtained on the other hand.

Claims: A method for controlling the idle speed of an internal combustion engine having a plurality of cylinders, said method comprising the steps of: (a) detecting the rotations of the engine using a signal from a crank angle sensor (10), (b) measuring the flow rate of air supplied to the engine using a signal from an air flow sensor (9), (c) controlling the amount of fuel supplied to the engine using fuel supply means (4), (d) detecting that the engine is in idle state using a signal from an idle switch (3), and (e) detecting an abnormal condition in which the engine speed exceeds a predetermined value in idle state using electrical signals supplied from said sensors to an electronic control unit (13), characterised in that it further comprises the steps of in the case of detecting that the engine is in idle state in step (d) setting a target idle speed and adjusting the area of a bypass for flowing air to said cylinders so as to keep the actual idle speed of the engine in consistency with said target idle speed and in the case of detecting an abnormal engine condition in step (e) generating a cylinder signal for determining the cylinder to be supplied with fuel at every predetermined rotational speed on the basis of an output signal from said crank angle sensor (10), counting said cylinder signal and stopping the fuel supply when said count value reaches a predetermined number greater than one and having no common divisor with the number of cylinders other than one. A method according to claim 1, characterised in that fuel is supplied to different ones of said plurality of cylinders at regular intervals of time. A method according to claim 1, characterised in that fuel is not supplied to a predetermined specific one of said plurality of cylinders. A system for controlling the idle speed of an internal combustion engine having a plurality of cylinders, comprising a crank angle sensor (10) for detecting the rotations of said engine, an air flow sensor (9) for detecting the flow rate of air supplied to said engine, fuel supply means (4) for controlling the amount of fuel supplied to said engine, an idle switch (3) for detecting that said engine is in idle state, and an electronic control unit (13) capable to detect an abnormal condition in which said engine speed exceeds a predetermined value in idle state using electrical signals supplied from said sensors, characterised by means (301) which in the case that said idle switch (3) detects that said engine is in idle state set a target idle speed and adjust the area of a bypass for flowing air to said cylinders so as to keep the actual idle speed of the engine in consistency with said target idle speed and means (302 to 305) which in the case that said electronic control unit (13) detects said abnormal engine condition generate a cylinder signal to determine the cylinder (7) to be supplied with fuel at every predetermined rotational speed on the basis of an output signal from said crank angle sensor (10), counting said cylinder signal and stopping the fuel supply when said count value reaches a predetermined number greater than one and having no common divisor with the number of said cylinders (7) other than one. A system according to claim 4, characterised in that fuel supply is suspended to different ones of said plurality of cylinders at regular intervals of time. A system according to claim 4, characterised in that fuel supply is suspended to a predetermined specific one of said plurality of cylinders.

Inventors: SAKAMOTO MASAHIDE, SHIDA MASAMI, SAKAMOTO, MASAHIDE, SHIDA, MASAMI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1986
Main classification: F02D41
IPC codes: F02D41, F02D31