EP1788228A2

EP1788228A2 - Fuel injection control apparatus having fail-safe function for protection against occurence of short-circuit to ground at connecting lead of fuel injector coil

Info

Publication number: EP1788228A2
Application number: EP06024219A
Authority: EP
Inventors: Takamichi Kamiya
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2005-11-22
Filing date: 2006-11-22
Publication date: 2007-05-23
Anticipated expiration: 2026-11-22
Also published as: JP4650387B2; EP1788228B1; EP1788228A3; JP2007170373A

Abstract

A fuel injection control apparatus monitors the amplitude of a discharge current pulse supplied from a capacitor to a currently selected one of a group of fuel injectors, and judges that a short-circuit to ground is occurring in a connection lead of the group if the amplitude exceeds a regular threshold value. If that occurs, the judgement threshold value is changed to a lower value during a succeeding fixed number of judgement operations. If the regular threshold value is exceeded for a predetermined number of times in succession, operations for driving the injectors of that group are terminated.

Description

BACKGROUND OF THE INVENTION

Field of Application

The present invention relates to an apparatus which drives the fuel injectors (referred to in the following simply as injectors) that inject fuel into the cylinders of an internal combustion engine. In particular the invention relates to a fuel injection control apparatus for controlling the opening of each injector by discharging energy through a coil of the injector from a capacitor that has been charged to a high voltage.

Description of Related Art

Types of fuel injection control apparatus are known whereby the duration of the conduction intervals and conduction timings of current flow through the coil of an injector are controlled such as to control the amounts of fuel that are injected into an internal combustion engine and the durations of the injection intervals. Such a fuel injection control apparatus has a voltage step-up circuit which performs step-up of a supply voltage and which charges a capacitor (referred to herein as the charge capacitor) to the stepped-up voltage, with the stored high-voltage energy of the charge capacitor being then discharged through an injector coil. A predetermined high peak level of current thereby flows in the injector coil, and the corresponding injector is thereby quickly opened (where "opening" signifies a valve-opening operation whereby fuel is injected by an injector into a cylinder of an internal combustion engine), and thereafter, during the conduction interval of that injector, a fixed level of current is passed through the injector coil, so that a constant injection condition is maintained for that injector. Such a system is described for example in Japanese patent publication No. 2002-180878 , referred to in the following as reference document 1.
In general, with such a type of fuel injection control apparatus, a plurality of injectors are provided respectively corresponding to the cylinders of the engine, with that plurality being divided into two groups. This is referred to as the common 2-system method (as described for example in reference document 1). With such a configuration, even if an abnormality occurs in a connecting lead that connects to the injector coils of one of the groups, so that the injectors of that group cannot be driven (i.e., cannot be opened), the injectors of the other group can continue to be driven, so that at least a minimum level of operation of the engine can be maintained, so that the vehicle (in which the internal combustion engine is installed) can continue to be driven and is not completely disabled.
Alternatively, a method referred to as the overlap injection method (or multiplexed injection) can be used whereby injectors belonging to different groups are driven within the same interval.
With the common 2-system configuration, in which respective charge capacitors are provided for each of the groups of injectors, the unit that controls the injectors may become large in scale and expensive to manufacture. For that reason, it would be desirable to use only a single charge capacitor for each group, i.e., a common 2-system with single capacitor configuration.
A specific example of such a fuel injection control apparatus will be described referring to Figs. 5 to 7. The apparatus shown in Fig. 5 is based on a electronic control unit (hereinafter abbreviated to ECU) 100, which controls the conduction intervals and conduction timings of coils 101a, 102a, 103a, 104a that respectively correspond to injectors 101, 102, 103,104 of the four cylinders (respectively designated as the #1∼#4 cylinders) of a 4-cylinder internal combustion engine, to thereby control the fuel injection quantities and injection timings for each of the cylinders.
Each of the injectors 101∼104 is a normally-closed type of electromagnetic valve, and each injector becomes opened when a current is passed through the corresponding one of the coils 101a~104a. When current flow through the corresponding coil is interrupted, the injector is closed and fuel injection is thereby halted.
With this example, the injectors 101∼104 of the four cylinders are divided into two groups, with each group corresponding to two cylinders. The injectors 101, 103 constitute the No. 1 group, each having one end (the upstream end) of the corresponding injector coil connected to the common terminal COM1 of the ECU 100, while the injectors 102, 104 constitute the No. 2 group, each having the upstream end of the corresponding injector coil connected to the common terminal COM2 of the ECU 100. With this example, it is ensured that injectors within the same group will not be driven simultaneously.
The downstream ends of the coils 101a~104a are connected via the terminals INJ1, INJ2, INJ3, INJ4 of the ECU 100 to respective output terminals of transistors T10, T20, T30, T40. The other terminals of the transistors T10, T20, T30, T40 are connected through resistors R10, R20 (corresponding to respective injector groups) to ground potential. For that reason, a current that flows through transistor T10 or T30 and the coil 101a or 103a of the injectors 101, 103 will be detected as a voltage that appears across the resistor R10. Similarly, a current that flows through transistor T20 or transistor T40 and the coil 102a or 104a of the injectors 102, 104 will be detected as a voltage that appears across the resistor R20. With this example, each of the switching elements within the ECU 100 is a MOS FET (metal oxide semiconductor field effect transistor).
The ECU 100 also includes, in addition to the resistors R10, R20 and the transistors 10~40, transistors T11,T21, T22, diodes D11, D12, D21,D22, resistors R11, R12, R21, R22, charge capacitor C10, charging circuit (voltage step-up circuit) 30, a drive control circuit 120, a charging circuit 50, and a microcomputer 130 which is made up of a CPU, ROM, RAM, etc. The charging circuit 50 steps up the voltage VB of the vehicle battery, which constitutes the power supply voltage of this example and is a positive voltage with respect to the system ground potential, and the resultant stepped-up voltage is applied to charge the capacitor C10, i.e., to a voltage that is higher than VB. The drive control circuit 120 controls respective transistors in the ECU 100, and also controls the charging circuit 50. Circuit leads that are at ground potential and so are connected to the low potential of the DC power source of the apparatus (e.g., battery) are referred to herein collectively as "the ground line".
The microcomputer 130 generates injection command signals TQ1~TQ4 corresponding to the respective #1~#4 cylinders, based on the engine speed Ne, the accelerator degree of opening ACC, the engine coolant temperature THW, etc., and engine operation information that is detected by respective sensors, and outputs the injection command signals TQ1∼TQ4 that are supplied to the drive control circuit 120. When one of the injection command signals TQ1∼TQ4 is at the high level (and only during that time), a current is passed through the corresponding one of the coils 101a~104a of the injectors 101~104, whereby that injector becomes opened. The drive control circuit 120 outputs each of the injection command signals TQ1~TQ4 to the gate of the corresponding one of the transistors 10~40, i.e., the gate of the transistor corresponding to the cylinder which is predetermined as corresponding to that injection command signal. For example the injection command signal TQ1 is applied to the gate of the transistor T10, while the injection command signal TQ2 is applied to the gate of the transistor T20.
The charging circuit 50 includes an inductor L00, a transistor T00, and a charging control circuit 110 which drives the transistor T00. The inductor L00 has one end connected to the power supply lead Lp which supplies the battery voltage VB and the other end connected to one output terminal of the transistor T00. A current detection resistor R00 is connected between the other output terminal of the transistor T00 and the ground line. The gate of the transistor T00 is connected to the charging control circuit 110, with the transistor T00 being switched on and off in accordance with the output signal from the charging control circuit 110.
One terminal (positive polarity terminal) of the charge capacitor C10 is connected through a reverse current blocking diode D13 to the connection point between the inductor L00 and the transistor T00, while the other terminal (negative polarity terminal) of the capacitor C10 is connected to the connection point between the transistor T00 and the resistor R00.
When on/off switching of the transistor T00 is performed, the charging circuit 50 generates a flyback voltage (induced reverse voltage) which is higher than the battery voltage VB, at the connection point between the inductor L00 and the transistor T00, and the capacitor C10 is charged by this flyback voltage, passed through the diode D13. As a result, the capacitor C10 becomes charged to a voltage that is higher than the battery voltage VB. When a charge enabling signal, produced from the drive control circuit 120, goes to the active level (for example, high level), the charging control circuit 110 performs on/off switching of the transistor T00. The voltage at the positive polarity terminal of the charge capacitor C10 (referred to in the following as the capacitor voltage VC) is used as a monitor value. When the capacitor voltage VC attains a predetermined target value (> VB) or the charging enabling signal goes to the inactive level, the transistor T00 is left in the off condition and charging of the capacitor C10 is halted.
Furthermore in the ECU 100, the transistor T12 is provided for discharging the charge capacitor C10 through the coils 101a, 103a that are connected to the common terminal COM1. When the transistor T12 is set on, the positive terminal (high voltage terminal) of the capacitor C10 becomes connected to the common terminal COM1.
In this description and in the appended claims, the term "switch on" or "set in the on state" as applied to a switching element such as a FET is to be understood as setting the switching element in a conducting condition, e.g., by applying a suitable potential to the gate electrode of a FET to enable conduction between the drain and source electrodes.
Similarly, the transistor T22 is provided in the ECU 100, for discharging the capacitor C10 through the coils 102a, 104a that are connected to the common terminal COM2. When the transistor T22 is set on, the positive terminal of the capacitor C10 becomes connected to the common terminal COM2.
The transistor T11 is provided in the ECU 100 for passing a fixed level of current through the coils 101a, 103a that are connected to the common terminal COM1. When either of the transistors T10, T30 is in the on state, then if the transistor T11 is set on, the coil (101a or 103a) that is connected to the one of the transistors T10 or T30 that is in the on state will receive a flow of current from the power line Lp, through the diode D12, which is a return current diode for control of the current through the coils 101a, 103a. When either of the transistors T10, T30 is in the on state, if the transistor T11 is switched from the on to the off state, a return current flows in the corresponding one of the coils 101a, 103a.
Similarly, the transistor T21 passes a fixed level of current through the coils 102a, 104a that are connected to the common terminal COM2. When either of the transistors T20, T40 is in the on state, then if the transistor T21 is set on, the coil (102a or 104a) that is connected to the one of the transistors T20 or T40 that is in the on state will receive a flow of current from the power line Lp, through the done-shot circuit 21. The diode D22 is a return current diode for control of the current through the coils 102a, 104a. When either of the transistors T20, T40 is in the on state, if the transistor T21 is switched from on to the off state, a return current flows in the corresponding one of the coils 102a, 104a.
In the ECU 100, the pair of series-connected resistors R11, R12 and the pair of series-connected resistors R21, R22 are respectively connected between the power supply line Lp and the ground line. The connection point between the resistors R11, R12 is connected to the common terminal COM1, while the connection point between the resistors R21, R22 is connected to the common terminal COM2.
The resistors R11, R12, R21, R22 are provided for setting the voltage levels of the common terminals COM1, COM2, when these terminals are in the open-circuit (i.e., floating) state. In this example, each of the resistors R11, R12, R21, R22 are of identical value, so that when the common terminals COM1, COM2 are in the open-circuit state, each of these terminals will be fixed at a potential of VB/2.
The basic operations performed by the drive control circuit 120 will be described in the following.

Basic Operation No. 1

This is an operation whereby, as described above, the injection command signals TQ1~TQ4 are outputted from the microcomputer 130 of the drive control circuit 120, to the gates of the transistors T10 to T40 respectively.

Basic Operation No. 2

With this operation, the drive control circuit 120 sets the charging enabling signal (supplied to the charging control circuit 110) at the active level during each interval in which discharge current is not being supplied from the capacitor C10 to the coils 101a~104a (i.e., while the transistors T12, T22 are both in the off state). The charging circuit 50 is thereby activated, so that the charge voltage of the capacitor C10 increases from the voltage VC to reach the target voltage (as shown by the stage labeled "VC" in the timing diagrams of Fig. 6).

Basic Operation No. 3

With this operation, the drive control circuit 120 sets the transistor T12 on, concurrent with either of the injection command signals TQ1, TQ3 (corresponding to the No. 1 group) going from the low to the high level. In the following, the designation "TQx" will be used to indicate an injection command signal which goes to the high level.
As a result, as shown in Fig. 6, the one of the transistors T10, T30 that corresponds to the injection command signal TQx is set to the on state, while in addition the capacitor voltage VC is applied to the common terminal COM1, and the energy stored in the capacitor C10 is then discharged through the injector coil that corresponds to the injection command signal TQx. A high level of current thereby begins to flow through that coil, and as result of that current flow, the injector corresponding to the injection command signal TQx becomes opened. In Fig. 6, the designation "ICOM1" indicates the current that flows through the common terminal COM1, i.e., that flows in the coil of the injector that corresponds to the injection command signal TQx.
After the transistor T12 has been turned on, the drive control circuit 120 detects the level of current flowing in the aforementioned coil, based on the voltage appearing across the resistor R10. As shown in Fig. 6, the drive control circuit 120 turns the transistor T12 off, when the level of current in that coil (injector current) attains a predetermined target value, designated herein as ip.

Basic Operation No. 4

With this operation, when the transistor T12 has become switched off by the basic operation No. 3, the drive control circuit 120 continues to detect the current flowing in the aforementioned coil, based on the voltage across the resistor R10. During the interval which elapses until the injection command signal TQx goes from the high to the low level, the drive control circuit 120 performs on/off switching of the transistor T11 such as to maintain the detected level of current at a constant value which is close to, but lower than, the target value ip.
This will be explained more specifically in the following. As shown in Fig. 6, while the injection command signal TQx is at the high level, the drive control circuit 120 performs control for regulating the current flowing in the aforementioned coil to a constant value, by switching the transistor T11 on when the coil current falls below a lower threshold value designated as icL, and switching off the transistor T11 when the coil current exceeds a threshold value designated as icH. As a result, when the current flowing in the coil departs from the target value ip to fall below the lower limit threshold value icL, then thereafter on/off switching of the transistor T11 is repetitively performed, so that the average value of the coil current is held approximately midway between the upper and lower threshold values icH and icL.
Fig. 6 assumes the case in which the upper limit threshold value icH and lower limit threshold value icL are each constant, so that the current flowing the coil is held at a single fixed value. However as shown in Fig. 7 (described hereinafter), concerning the current ICOM2 that flows in the common terminal COM2 (shown in the fourth stage in Fig. 7) it is also possible to perform control whereby the coil current is controlled to a first fixed value until a fixed interval has elapsed since the flow of current through the coil was started, and whereby thereafter, until the injection command signal TQx goes to the low level (i.e., until current flow through the coil is terminated) the coil current is controlled to be held at a second fixed value. That is to say, in that case, after a fixed time interval has elapsed following the start of current flow through the coil, the upper and lower threshold values icH and injector coil are respectively changed to values whereby the coil current will be held at the second fixed value.
With this form of constant current regulation, after the transistor T12 has been turned off, current will flow through the coil (of the first group) that corresponds to the injection command signal TQx, with that current passing from the power supply line Lp through the transistor T11 and the diode D11. The corresponding injector is thereby held in the open condition. Furthermore as shown in Fig. 6, when the injection command signal TQx thereafter goes from the high to the low level, then when the one of the transistors T10, T30 that corresponds to the injection command signal TQx becomes turned off, the drive control circuit 120 holds the transistor T11 in the off state. When the flow of current through the coil is halted, the corresponding injector becomes closed, and fuel injection by that injector is terminated.

Basic Operation No. 5

With this operation, the drive control circuit 120 performs a similar type of control to that of basic operation No. 3, operating on the transistor T22.
That is to say, when either of the injection command signals TQ2, TQ4 corresponding to the No. 2 group goes from the low to the high level, then at the same time, the drive control circuit 120 sets the transistor T22 in the on state.
The one of the transistors T10∼T40 corresponding to the injection command signal TQx that has gone to the high level is then set in the on state, while at the same time the capacitor voltage VC is applied to the common terminal COM2. Thus the energy stored in the capacitor C10 is discharged through the injector coil that corresponds to the injection command signal TQx, and the corresponding injector is thereby opened.
After the transistor T22 has been turned on, the drive control circuit 120 detects the current flowing in the coil based on the voltage appearing across the resistor R20, and turns off the transistor T22 when the detected current attains the target value ip.

Basic Operation No. 6

With this operation, the drive control circuit 120 also performs similar control to that of the basic operation No. 4 described above, with respect to the transistor T21.
That is to say, after the transistor T22 has been turned off by the basic operation No. 5, the drive control circuit 120 detects the coil current based on the voltage across the resistor R20. In the interval until the injection command signal TQx goes from the high to the low level, the drive control circuit 120 performs on/off switching of the transistor 21 such that the detected value of current attains a fixed value that is less than the target value ip. As a result of this current regulation, after the transistor T22 has been turned off, a fixed level of current is fixed through the coil of the injector (of group No. 2) that corresponds to the injection command signal TQx, with the current being passed from the supply line Lp through the transistor T21 and diode D21. That injector is thereby held in the open state.
The fail safe functions that are executed by the ECU 100 will be described referring to the timing diagrams of Fig. 7. The fail-safe functions described in the following are implemented respectively separately for each of the groups of injectors, however for brevity of description only the fail-safe functions applied to the No. 1 group (made up of injectors 101, 103) will be described. In Fig. 7, "ICOM1" denotes the current flowing through the common terminal COM1, "ICOM2" denotes the current flowing through the common terminal COM2, "VOCM1" denotes the voltage appearing at the common terminal COM1, and "VCOM2" the voltage at the common terminal COM2, "VINJ1" denotes the voltage at the INJ1 terminal, "VINJ2" denotes the voltage at the INJ2 terminal. Timing diagrams relating to driving of the injectors 102, 104 are omitted from Fig. 7. The above points concerning Fig. 7 are also true for the timing diagrams of Figs. 6 and 8.

First Fail Safe Function

With this function, when either of the injection command signals TQ1, TQ3 goes from the low to the high level, for opening one of the injectors 101, 103 of the No. 1 group, so that the discharge transistor T12 corresponding to the No. 1 group is set in the on state, the drive control circuit 120 judges whether the level of the discharge current flowing from the capacitor C10 exceeds an overcurrent judgement threshold value Ith. If the current is found to exceed Ith, then the drive control circuit 120 forcibly sets the discharge transistor T12 in the off state. The drive control circuit 120 detects the level of discharge current as the value of return current that flows to the capacitor C10 through the resistor R00 from the ground line during discharge, i.e., with the discharge current detected as the voltage appearing across the resistor R00. A suitable circuit configuration for implementing the first fail-safe function is described for example in Fig. 2 of reference document 1.
With the first fail-safe function, if a short-circuit to ground occurs at the common terminal COM1 (i.e., that terminal becomes connected to the apparatus ground potential) then as shown in the third timing diagram of Fig. 7 (labeled as "ICOM1"), the current that flows through the transistor T12 from the capacitor C10 will exceed the overcurrent judgement threshold value Ith. However at that time point, the transistor T12 will be forcibly switched to the off state, and so protected against destruction due to excessive current flow.
The drive control circuit 120 performs the first fail-safe function in a similar manner for the discharge control transistor T11. That is to say, when either of the injection command signals TQ1, TQ3 goes from the low to the high level, the drive control circuit 120 detects the level of current flowing in the transistor T11. If the current exceeds an overcurrent judgement threshold value Ith', then the transistor T11 is forcibly set in the off state. Hence if a short-circuit to ground occurs at the common terminal COM1, so that the current flow through the transistor T11 exceeds the overcurrent judgement threshold value Ith', the transistor will be forcibly turned off.
With the No. 3 basic operation, the current that flows in a coil from the capacitor C10 is detected by using the resistor R10, so that an excessive level of current that results from a short-circuit to ground at the common terminal COM1 cannot be detected. Hence the transistor T11 will not be protected.

Second Fail-safe Function

With the No. 1 basic operation applied to the No. 1 group, the microcomputer 130 counts the number of times that the discharge current of the capacitor C10 exceeds the overcurrent judgement threshold value Ith (as judged by the first fail-safe function). When it is judged that the number of times exceeds a prescribed value k, the microcomputer 130 then inhibits the outputting of injection command signals TQ1 and TQ3 (TQ1, TQ3 are each held at the low level) so that operations for opening the injectors 101, 103 of the No. 1 group are halted.
Specifically, with the ECU 100 shown in Fig. 5, the respective voltages appearing at the common terminals COM1 and COM2 are supplied to the drive control circuit 120. The drive control circuit 120 compares the magnitude of each of these voltages with a threshold value Vth, which is used for judging whether or not there is a short-circuit to ground at either of the common terminals COM1 or COM2, and outputs monitor signals M1, M2 which express the respective comparison results obtained for the common terminals COM1 and COM2, with the monitor signals M1, M2 being supplied to the microcomputer 130. For example, the threshold value Vth may be set as ¼ of the battery voltage VB. If the voltage at the common terminal COM1 falls below the threshold value Vth, the monitor signal M1 becomes set at the high level, while if the voltage at the common terminal COM2 falls below the threshold value Vth, the monitor signal M2 becomes set at the high level. Otherwise, each of the monitor signals M1, M2 remains at the low level.
After changing an injection command signal TQ1 or TQ3 (i.e., corresponding to the No. 1 group) from the high to the low level, the microcomputer 130 acquires the level of the monitor signal M1 during the interval that elapses until the next point at which one of the injection command signals TQ1 or TQ3 goes to the high level. If the monitor signal M1 is at the high level (i.e., VCOM1 ≤ Vth), a counter is incremented. That is to say, if the monitor signal M1 is at the high level in spite of the fact that each of the injection command signals TQ1 and TQ3 are at low level and the transistors T10, T30 are in the off state, then this may signify that there is a short-circuit to ground at the common terminal COM1. Specifically, it indicates that immediately previously, when one of the signals TQ1, TQ3 was at the high level, the first fail-safe function (for the No. 1 group) judged that the discharge current of the capacitor C10 exceeded the threshold value Ith.
With the second fail-safe function, each time this condition occurs, the microcomputer 130 increments the aforementioned counter by one. If the microcomputer 130 judges that the count value of this counter has reached the prescribed value k, then it inhibits further processing for outputting the injection command signals TQ1, TQ3, i.e., each of these signals is held at the low level.
With the second fail-safe function, assuming the prescribed value k is for example 3, then when there is a short-circuit to ground at the common terminal COM1, the injection command signals TQ1, TQ3 for the No. 1 group will be outputted three times following the time point at which the short circuit condition arises, and thereafter, outputting of the injection command signals TQ1, TQ3 will cease. In that way, it can be ensured that damage to the circuit elements such as for example T11 and T12, as a result of the short-circuit to ground of the common terminal COM1, can be prevented.
When such a short-circuit to ground at the common terminal COM1 occurs, driving of the injectors of the No. 2 group will proceed normally, so that the engine can continue to be operated with fuel injection being performed by the injectors 102, 104. Hence, the vehicle can continue to be driven, in a "limp home" mode.
Similarly, with the first fail-safe function of the No. 2 group, each time either of the injection command signals TQ2, TQ4 goes from the low to high level, a decision is made as to whether the discharge current from the capacitor C10 exceeds the threshold value Ith. If the threshold value is exceeded then the transistor T22 is forcibly set in the off condition. The number of times that the discharge current from the capacitor C10 is judged to have exceeded the threshold value Ith is counted, and when that number of times is found to have attained the prescribed value k, then thereafter, outputting of the injection command signals TQ2, TQ4 is inhibited by the microcomputer 130.
In Fig. 7, the time points indicated by the upwardly-directed arrows, designated as ("monitor timings for short-circuit detection" shown in the fifth and sixth stages (the VCOM1 and VCOM2 stages) are points at which the microcomputer 130 acquires the respective states of the monitor signals M1, M2.
With a configuration as described above in which a single charge capacitor is used with the common 2-system configuration, it is possible to achieve more compact size and lower cost, by comparison with an arrangement in which respective charge capacitors are provided for each of the groups of injectors. In addition, the size of the charge capacitor can be made smaller, further assisting in enabling the overall size of the apparatus to be made more compact and the manufacturing cost made lower. The reasons for this will be described in the following.
Firstly, with the ECU 100 of Fig. 5 it will be assumed that a short-circuit to ground occurs at one of the common terminals COM1 or COM2. In that case, as shown in Fig. 7, from a time point at which the injection control signals TQ1, TQ3 (with signal TQ3 being omitted from the diagram) start to be outputted (i.e., go to the high level) until the point at which the transistor T12 becomes turned off as a result of the first fail-safe function, a higher level of current will be discharged from the capacitor C10 than would flow during normal operation. As a result, as shown in the lowermost timing diagram in Fig. 7 the capacitor voltage VC will reliably return to the target value, as a result of the basic operation No. 2 of the drive control circuit 120 described hereinabove, during an interval in which neither of the injection command signal TQ1, TQ3 is being outputted.
However if there is a short-circuit to ground at the common terminal COM1, then it will be difficult for the capacitor voltage VC to return to the target value. That is to say, if a short-circuit results in an excessive amount of energy being discharged from the charge capacitor C10 when it becomes connected to the common terminal COM1, then the charging time may be too short for the capacitor voltage to recover to the target value.
As a result, as indicated by the dotted-line portion in the lowermost stage of Fig. 7, if the capacitance of the charge capacitor C10 is made smaller, then the capacitor voltage VC may become lower than a level which enables fuel injection operation to be performed normally for the injectors of the No. 2 group, during the interval that elapses from the time point at which outputting of the injection control signals TQ1, TQ3 becomes inhibited by the second fail-safe function. Hence during that interval, the injectors 102, 104 whose coils are connected to the common terminal COM2 (which does not have a short-circuit to ground) would not be driven normally. Thus it would not be possible to continue to operate the engine.
As a result, if such an internal combustion engine were to be used to power a vehicle (i.e., with the capacitance value of the charge capacitor made substantially smaller than is usual in the prior art), the vehicle would become completely immobilized in the event of a short-circuit occurring at only one of a plurality of common terms which are each connected to the charge capacitor and which supply respective groups of fuel injectors.
For that reason, it has not been possible in the prior art to set a small value of capacitance for the charge capacitor.
It should be noted that if for example as shown in Fig. 8, the prescribed value k for the second fail-safe function were to be set as 1, and a short-circuit to ground were to occur momentarily at the common terminal COM1 (assuming in this example that the short-circuit occurs only during a time approximately corresponding to a single fuel injection operation) then as a result of the operation of the second fail-safe function, control of driving the injectors 101, 103 belonging to the No. 1 group (i.e., whose coils are connected to the common terminal COM1) would be inhibited. As a result, fuel injection would be performed only by the injectors 102, 104 of the No. 2 group, so that deterioration of the driveability of the vehicle could occur. This is clearly illustrated by the lowermost timing diagram in Fig. 8, showing the variations in capacitor voltage VC.
It should be noted that the term "short-circuit to ground" at a common terminal, as used herein, refers to a short-circuit to ground that occurs at the terminal itself, or in a connecting lead which is connected to that common terminal.

SUMMARY OF THE INVENTION

It is an objective of the present invention to overcome the above problem, by providing an improved fuel injection control apparatus whereby the capacitance value of a charge capacitor that is used for controlling the opening of one or more fuel injectors of an internal combustion engine can be made smaller than has been practicable in the prior art, while ensuring that when a short-circuit to ground occurs at a common terminal that is coupled to the charge capacitor, normal operation can be continued for fuel injectors that are connected to another common terminal which is also connected to that same charge capacitor, so that operation of the internal combustion engine can be continued, in a restricted mode.
More specifically, it is an objective to provide an improved fuel injection control apparatus that is applicable to an internal combustion engine in which a charge capacitor is used for controlling the opening of injectors in each of a plurality of groups of injectors, with charge current being supplied from the capacitor to the respective groups via respective corresponding switching elements of the groups, and whereby it can be ensured that when a short-circuit to ground occurs in a connecting lead or connection terminal of one group of injectors, operation of the remaining group(s) of injectors will remain possible, and to achieve this while enabling the capacitance value of the charge capacitor to be made smaller than has been possible in the prior art.
Essentially, this is achieved by reducing successive amounts of capacitor charge that are dissipated through such a short-circuit to ground, in respective injector drive operations, so long as such a short-circuit condition continues. When a short-circuit to ground occurs in a connecting lead or connection terminal of a group of injectors, and is detected when the drive current of an injector of the group is judged to exceed a regular (i.e., normal) threshold value, then for each of a fixed number of subsequent judgement operations, the threshold value is lowered. As a result, at each judgement operation performed using the lower threshold value, the supplying of capacitor discharge current is more rapidly interrupted (while the short-circuit condition continues) than when the regular threshold value is utilized, so that smaller amounts of charge are lost due to the short-circuit.
More specifically, a fuel injection control apparatus according to the present invention basically differs from the prior art, such as that of the example described in detail hereinabove, with respect to the following:

(1) With the present invention, an overcurrent judgement threshold value utilized by the first fail safe means can be selectively set at a regular value, which is appropriate for detecting occurrence of a short-circuit to ground for the corresponding group of injectors, and at a second value that is lower than the regular value.
(2) When it is detected that the discharge current from the charge capacitor exceeds the regular value of the overcurrent judgement threshold, then for each of a fixed number (one or more) of successive judgement operations performed thereafter by the first fail safe means, the overcurrent judgement threshold is set at the (lower) second value.

The invention thereby enables a capacitor to be utilized as the charge capacitor that has a lower capacitance value than has been possible in the prior art, while ensuring that a vehicle powered by such an internal combustion engine can be driven at least in a "limp home" mode in the event that a short-circuit to ground occurs at only one of a plurality of common terminals that supply respective groups of fuel injectors.
Furthermore as a result of the capability for utilizing a smaller value of capacitance, it becomes possible to use an aluminum electrolytic capacitor for the purpose, which has the advantages of enabling the charge capacitor to be made more compact and inexpensive by comparison with other types such as film capacitors, etc. In the past, this has not been possible, due to the fact that the ESR (equivalent series resistance) of an aluminum electrolytic capacitor at low temperature is high, so that deterioration of the discharge characteristics occurs under such a condition.
The above features and advantages of the invention will be readily understood from the following description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the configuration of an embodiment of a fuel injection control apparatus.
Fig. 2 is a flow diagram of processing executed by a microcomputer of an ECU of the embodiment, for performing a second fail-safe function.
Fig. 3 is a timing diagram for describing the operation of the embodiment in the event of a long-duration short-circuit to ground at a common terminal of a group of injectors.
Fig. 4 is a timing diagram for describing the operation of the embodiment in the event of a momentary short-circuit to ground at a common terminal of a group of injectors.
Fig. 5 shows the configuration of an example of a prior art type of fuel injection control apparatus.
Fig. 6 is a timing diagram for describing the basic operation of the prior art fuel injection control apparatus.
Fig. 7 is a timing diagram for describing problems that occur with a prior art fail-safe function and prior art technology.
Fig. 8 is a timing diagram for describing other problems of the prior art.

DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 shows the configuration of an embodiment of a fuel injection control apparatus according to the present invention. As shown, in the same way as for the example of a prior art type of fuel injection control apparatus shown in Fig. 5 and described hereinabove, the embodiment includes four injectors 101∼104 that are respectively provided for the #1∼#4 cylinders of an engine, and an ECU 1 for controlling the conduction intervals and conduction timings of the coils 101a~104a of the injectors 101∼104 respectively. In Fig. 1, components corresponding to components in the example of Fig. 5 are designated by identical reference numerals to those of Fig. 5, and further description of these will be omitted. The capacitor C10 is an aluminum electrolytic capacitor.
By comparison with the ECU 100 of Fig. 5, the ECU 1 of this embodiment differs with respect to the first and second fail-safe functions. Hence, a drive control circuit 3 is utilized in place of the drive control circuit 120 of Fig. 5. The drive control circuit 3 performs the same basic operations (No. 1 to No. 6) described hereinabove.
Firstly, the apparatus sections relating to the first fail-safe function will be described. The drive control circuit 3 of the ECU 1 of this embodiment includes discharge control sections 5 and 7, respectively corresponding to the two groups of injectors 101~104.
The discharge control section 5 is a circuit block for driving the transistor T12, to control discharging of the capacitor C10 through the coils 101a, 103a of the No. 1 group of injectors (injectors 101, 103). In addition to performing the basic operation No. 3 described above, circuits in the discharge control section 5 implement the first fail-safe function with respect to the No. 1 group, to protect the transistor T12 against excessive current flow. Similarly, the discharge control circuit 7 is a circuit block for driving the transistor T22, to control discharging of the capacitor C10 through the coils 102a, 104a of the No. 2 group of injectors (injectors 102, 104), and also for performing the basic operation No. 5 described above. Circuits in the discharge control section 5 implement the first fail-safe function with respect to the No. 2 group, to protect the transistor T22 against excessive current flow, and the discharge control section 5 also performs the basic operation No. 5 Since each of the discharge control sections 5 and 7 have an identical configuration, only the discharge control section 5 will be described in detail in the following.
The discharge control section 5 is made up of a discharge control signal generating circuit 9, NOR gate 11, latch circuits 13 and 15, a comparator 17, a counter 19, one- shot circuits 21 and 23, an inverter 25, a PNP transistor 27, a zener diode 29, and resistors 31 to 36.
The discharge control signal generating circuit 9 performs the basic operation No. 3 described above, outputting a low-active signal as a discharge control signal for setting the transistor T12 in the on state. That is to say, of the signals injection command signals TQ1~TQ4 produced from the microcomputer 130, when either of the injection command signals TQ1, TQ3 goes from the low to the high level, the discharge control signal generating circuit 9 changes the discharge control signal from the high level to the low level, to thereby set the transistor T12 in the on state. When the discharge control signal generating circuit 9 detects a flow of current through either of the coils 101a, 103a (based on the voltage appearing across the resistor R10), it changes the discharge control signal from the low to the high level when the level of detected current (injector current) reaches the target value ip.
In addition in the discharge control section 5, the output signal from the discharge control signal generating circuit 9 and the output signal (Q terminal output) from the latch circuit 13 are inputted to the NOR gate 11, and the output signal from the NOR gate 11 is applied to the gate of the transistor 12, as a high-active drive signal. Hence, if the output signal from the latch circuit 13 is at the low level, then when the output signal from the discharge control signal generating circuit 9 goes to the low level, the transistor T12 becomes set in the on state, and the discharge control signal generating circuit 9 executes the basic operation No. 3 described above.
Sections of the discharge control section 5 other than the discharge control signal generating circuit 9 serve to implement the first fail-safe function, for protecting the transistor T12 against excessive current flow.
The junction of the negative polarity terminal of the capacitor C10 and the resistor R00 is connected via the series-connected resistor pair 31, 32 to the inverting input terminal (- input terminal) of the comparator 17, and in addition, the inverting input terminal of the comparator 17 is pulled up by the resistor 33 to the fixed voltage VD (for example, 5 V). A zener diode 29 is connected between the junction of the series-connected resistors 31, R32 and the ground line, for protecting the comparator 17. The anode of the zener diode 29 is connected to the ground side.
The non-inverting input terminal (+ terminal) of the comparator 17 is connected to the reference voltage Vref, which is formed by voltage dividing the fixed voltage VD, by the resistors 34 and 35. The output terminal of the comparator 17 is connected to the respective set terminals (S) of the latch circuits 13 and 15.
When the signal applied to the set terminal of either of the latch circuits 13 or 15 goes to the high level, then that latch circuit becomes set, whereby the Q output terminal of the circuit goes to the high level.
The output signal from the one-shot circuit 21 is applied to the reset R terminal of the latch circuit 13. Each time either of the injection command signals TQ1, TQ3 (corresponding to the No. 1 group) goes from the low to high level, the one-shot circuit 21 produces a pulse signal at the high level, during a brief time interval. Thus, the latch circuit 13 becomes reset each time that either of the injection command signals TQ1, TQ3 changes to the high level.
The output signal from the counter 19 is inputted to the reset (R) terminal of the latch circuit 15. The counter 19 receives the pulse signal from the one-shot circuit 21 as a clock input signal, and performs counting of these pulses. When the count reaches the value N, where N is a plural integer, the output from the counter 19 goes to the high level for a brief interval, and that signal is applied to reset the latch circuit 15. When the Q output signal from the latch circuit 15 goes from the low to high level, the one-shot circuit 23 outputs a pulse signal to the reset terminal of the counter 19, to reset the counter 19.
The output signal from the latch circuit 15 is supplied via the inverter 25 to the base of the PNP transistor 27. When the output of the latch circuit 15 goes to the high level, the PNP transistor 27 becomes set on, so that the opposite terminal of the resistor 36 from the terminal that is connected to the junction of the resistors 34, 35 becomes connected to the fixed voltage VD, applied through the PNP transistor 27.
As a result, when the output signal from the latch circuit 15 goes to the high level, the reference voltage Vref that is inputted to the non-inverting input terminal of the comparator 17 becomes changed from the aforementioned voltage-divided value Vr1 (obtained by the resistors 34, 35 operating on the fixed voltage VD) to a voltage Vr2 (> Vr1) that is obtained by voltage division of the fixed voltage VD, performed by a resistive voltage divider formed by the parallel combination of the resistors 34 and 36 connected in series with the resistor 35.
The operation of sections of the discharge control section 5 other than the discharge control signal generating circuit 9 will be described in the following.
Firstly, when either of the injection command signals TQ1, TQ3 goes to the high level, resetting of the latch circuit 13 is performed by the one-shot circuit 21, so that the output signal from the latch circuit 13 goes to the low level. Hence, when either of the injection command signals TQ1, TQ3 is at the high level and the output signal from the discharge control signal generating circuit 9 goes to the low level, the output signal from the NOR gate 11 goes to the high level. The transistor T12 is thus set to the on state, and discharging of the capacitor C10 begins.
When discharging of the capacitor C10 begins, the discharge current from the capacitor flows from the ground line through the resistor R00, to return to the capacitor C10. Hence the potential at the junction between the resistor R00 and the capacitor C10 becomes lower (more negative) than 0 V. Due to this negative voltage, the potential at the inverting input terminal of the comparator 17 becomes lowered (with that potential being referred to in the following as the input voltage of the comparator 17).
During normal operation, i.e., when there is no short-circuit to ground at the common terminal COM1, the input voltage of the comparator 17 will never fall to the level of voltage Vr1. The count value of the counter 19 is initialized to a count that is greater than N, when operation of the ECU 1 is started. Hence, during normal operation, the output from the counter 19 will remain at the low level, so that the latch circuit 15 will remain in the reset state, and the PNP transistor 27 will be held in the off state, so that the reference voltage Vref of the comparator 17 will be set at Vr1.
Thus during normal operation, when either of injection command signals TQ1, TQ3 goes to the high level, so that the transistor T12 is turned on and discharge of the capacitor C10 occurs, the output from the comparator 17 will remain at the low level, so that the latch circuits 13 and 15 will each remain in the reset condition.
On the other hand, as shown in Fig. 3, if a short-circuit to ground occurs at the common terminal COM1, then when either of the injection command signals TQ1, TQ3 goes to the high level, and the transistor T12 is thereby set to the on state, the discharge current from the capacitor C10 will be higher than during normal operation.

(1) If the discharge of the capacitor C10 exceeds the overcurrent judgement threshold value IH (corresponding to Ith in Fig. 7) the input voltage to the inverting input terminal of comparator 17 will become higher than Vr1. The output from the comparator 17 thereby goes to the high level, so that the latch circuits 13 and 15 each become set, and the respective output signals from these latch circuits each go to the high level.
When the output signal from the latch circuit 13 goes to the high level, then (irrespective of the state of the output signal from the discharge control signal generating circuit 9) the output signal of the NOR gate 11 goes to the low level. As a result, the transistor T12 is forcibly set in the off state, and the flow of discharge current from the capacitor C10 is halted.
When the output signal of the latch circuit 15 goes to the high level, then since the PNP transistor 27 is thereby set in the on state, the reference voltage of the comparator 17 is changed from Vr1 to the higher voltage Vr2. In addition, due to the change of the output signal of the latch circuit 15 to the high level, the one-shot circuit 23 is triggered, so that the counter 19 becomes reset.
(2) Thereafter, each time that either of the injection command signals TQ1, TQ3 goes to the high level, the count value of the counter 19 is incremented by one, and the output signal of the latch circuit 15 remains at the high level until the count value reaches N. Hence, during that time, the reference voltage Vref of the comparator 17 is set at Vr2.
When there is a short-circuit to ground at the common terminal COM1, then as shown in Fig. 3, until the count value of the counter 19 reaches N, each time the transistor T12 is set in the on state, the discharge current from the capacitor C10 becomes higher than the lower value IL of the overcurrent judgement threshold (i.e., which is lower than the regular value IH), whereby the input voltage to the inverting input terminal of comparator 17 becomes lower than Vr2. Hence, the output voltage of the comparator 17 goes to the high level, so that the transistor T12 is forcibly set in the off state, and the flow of discharge current from the capacitor C10 is thereby halted.
With this embodiment, the values of the resistors 34 to 36 are set such that when the discharge current of the capacitor C10 is identical to the target value ip (i.e., the target maximum value of current that flows through a coil from the capacitor during normal operation) the input voltage of the comparator 17 becomes identical to Vr2.
That is to say, the threshold value IL is made identical to the target value ip.
(3) When the count value of the counter 19 reaches N, the latch circuit 15 becomes reset, and the PNP transistor 27 becomes set in the off state so that (when a short-circuit to ground is occurring) the reference voltage of the comparator 17 is returned from Vr2 to the higher value Vr1.

Thereafter, the above operations (1) to (3) are cyclically repeated. Fig. 3 illustrates an example in which N is 2.
Basically, the discharge control section 5 performs the following. During normal operation, the reference voltage of the comparator 17 remains at the higher value Vr1, so that the overcurrent judgement threshold value Ith is at the regular (high) level IH. Each time the transistor T12 is set in the on state in order to open one of the injectors 101, 103 of the No. 1 group, the comparator 17 judges whether or not the discharge current from the capacitor C10 exceeds the overcurrent judgement threshold value Ith. If Ith is judged to be exceeded, the transistor T12 is forcibly set in the off state, and then during each of the succeeding (N - 1) judgement operations, the overcurrent judgement threshold value Ith is set at the value IL, that is lower than the regular value IH.
This is illustrated in the example of Fig. 3, in which a short-circuit to ground occurs at the common terminal COM1 (corresponding to the No. 1 group of injectors). As a result, the overcurrent judgement threshold value Ith is set at the lower value IL during each of (N - 1) of a total of N operations for judging successive levels of charge current supplied to the injectors of the No. 1 group.
In this example, N is equal to 2.
As can be understood from Fig. 3, while the short-circuit condition is occurring, only a small amount of charge is supplied from the charge capacitor in each drive operation (applied to the injectors of the No. 1 group) in which the overcurrent judgement threshold value is set at the lower value IL. Thus, these amounts of charge that are lost to the short-circuit can be quickly restored, before the next drive operation is performed (i.e., to open an injector of the No. 2 group). This is the basic reason why the invention enables a smaller value of capacitance to be utilized for the charge capacitor, as a consequence of periodically setting the overcurrent judgement threshold at a lower value than the regular value, while a short-circuit to ground is occurring for the connecting leads of an injector group.
The discharge control circuit 7, corresponding to the No. 2 group, has the same configuration as the discharge control section 5 described above. However in the discharge control circuit 7, a discharge control signal generating circuit 9 and a one-shot circuit 21 each receive as inputs the injection command signals TQ2, TQ4, and the output signal from the NOR gate 11 of the discharge control circuit 7 is applied as a drive signal to the gate of the transistor T22.
In Fig. 1, the constant- current control sections 37 and 39 in the drive control circuit 3 are circuit blocks that control the transistors T11 and T21, which correspond to those shown in the drive control circuit 120 of Fig. 5 ?? The configuration and operation of the constant- current control sections 37 and 39 will be described in the following.
The constant-current control section 37 performs the aforementioned basic operation No. 4, for regulating the current flowing in the coils 101a, 103a of the No. 1 group (i.e., corresponding to the injectors 101, 103) to a constant value. In addition, the constant-current control section 37 performs a fail-safe function for overcurrent protection of the transistor T11. Similarly, the current regulator circuit 39 is a circuit block for regulating the current flowing in the coils 102a, 104a of the No. 2 group (i.e., corresponding to the injectors 102, 104) to a constant value, and also performs a fail-safe function for overcurrent protection of the transistor T21.
Since the constant- current control sections 37 and 39 each have an identical configuration, only the constant-current control section 37 will be described in the following.
The constant-current control section 37 is made up of a current regulation control signal generating circuit 41, a OR gate 43, a latch circuit 45, a comparator 47, a one-shot circuit 49, and resistors 51, 52. The current regulation control signal generating circuit 41 performs the basic operation No. 4, and outputs a low-active signal as a current regulation control signal for on/off switching of the transistor T11. That is to say, while either of the injection command signals TQ1, TQ3 is at the high level, the current regulation control signal generating circuit 41 detects the current flowing in the corresponding coil, based on the voltage developed across the resistor R10, and produces an output signal that is switched between the low and high level. That output signal is used as a current control signal, to control the discharge current to a constant value. Specifically, if the detected value of current falls slightly below the target value of current, the output signal of the current regulation control signal generating circuit 41 goes to the low level, to thereby switch on the transistor T11, while if the detected value of current exceeds the target value of current, the output signal of the current regulation control signal generating circuit 41 goes to the high level, to thereby switch off the transistor T11. While both of the injection command signals TQ1, TQ3 are at the low level, the output signal of the current regulation control signal generating circuit 41 remains at the high level.
In addition, in the constant-current control section 37, the output signal from the current regulation control signal generating circuit 41 and the output signal (Q output) from the latch circuit 45 are each inputted to the OR gate 43, and the output signal from the OR gate 43 is applied as a low-active drive signal to the gate of the transistor T11, which is a P-channel MOS FET in this embodiment. If the output signal from the latch circuit 45 is at the low level, then when the output signal from the current regulation control signal generating circuit 41 goes to the low level, the transistor T11 is set in the on state. In that way, the current regulation control signal generating circuit 41 performs the aforementioned basic operation No. 4.
In the constant-current control section 37, sections other than the current regulation control signal generating circuit 41 serve to perform overcurrent protection of the transistor T11.
A resistor R13 is connected, external to the drive control circuit 3, between the power supply line Lp and the transistor T11, for use in detecting the level of current that flows in the transistor T11. Similarly, a resistor R23 is connected between the power supply line Lp and the transistor T21, for use in detecting the level of current that flows in the transistor T21. The resistors R13, R23 are omitted from Fig. 5.
In the constant-current control section 37, the voltage appearing at the junction between the resistor R13 and the transistor T11 is applied to the inverting input terminal (- terminal) of the comparator 47. The voltage Vr3, obtained by voltage dividing the supply voltage VD by means of the resistors 51, 52, is inputted as a reference voltage to the non-inverting input terminal (+ terminal) of the comparator 47. The output terminal of the comparator 47 is connected to the set (S) terminal of the latch circuit 45.
When the output signal from the comparator 47, applied to the set terminal of the latch circuit 45, goes to the high level, then the latch circuit 45 enters a condition in which its output signal (Q output) is set at the high level. The reset terminal of the latch circuit 45 is coupled to receive the output signal from the one-shot circuit 49, and each time that either of the injection command signals TQ1, TQ3 (corresponding to the No. 1 group) goes from the low to high level, the one-shot circuit 49 outputs a short-duration high level pulse. Hence, the latch circuit 45 becomes reset when either of the signals TQ1, TQ3 becomes high, and is set when the output signal of the comparator 47 becomes high.
Sections of the constant-current control section 37 other than the current regulation control signal generating circuit 41 will be described in the following. Firstly, when either of the injection command signals TQ1, TQ3 goes to the high level then since the latch circuit 45 becomes reset by the one-shot circuit 49, the output from the latch circuit 45 goes to the low level. Hence, after either of the injection command signals TQ1, TQ3 goes to the high level, then when the output signal from the current regulation control signal generating circuit 41 goes to the low level, the output signal from the OR gate 43 goes to the low level so that the transistor T11 is set in the on state.
When the transistor T11 is set on, and current flows in the resistor R13, the voltage at the inverting input terminal of the comparator 47 (referred to in the following as the input voltage of the comparator 47) goes to the low level. During normal operation, (i.e., when there is no short-circuit to ground at the common terminal COM1), the input voltage of the comparator 47 will never fall to the aforementioned voltage Vr3. Hence the output from the comparator 47 will remain at the low level, so that the latch circuit 45 will be held in the reset state.
However if a short-circuit to ground occurs at the common terminal COM1, then when the transistor T11 is set in the on state, the current that flows through the resistor R13 to the transistor T11 will become higher than the level that flows during normal operation. When that current reaches the overcurrent judgement threshold value Ith', the input voltage of the comparator 47 will fall below Vr3.
As a result, the output signal from the comparator 47 goes to the high level, so that the latch circuit 45 enters the set state and the output signal of the latch circuit 45 goes to the high level. Due to this, the output signal from the OR gate 43 will go to the low level, irrespective of the state of the output signal from the current regulation control signal generating circuit 41. As a result, the transistor T11 will be forcibly set in the off state, and is thereby protected against damage due to excessive current. This condition will continue until the next occasion when either of the injection command signals TQ1, TQ3 changes from the low to high level.
The current regulator circuit 39 (corresponding to the No. 2 group) has the same configuration as the constant-current control section 37. In the case of the current regulator circuit 39, the injection command signals TQ2, TQ4 are respectively inputted to the current regulation control signal generating circuit 41 and to the one-shot circuit 49, and the output signal from the OR gate 43 is applied as a drive signal to the gate of the one-shot circuit 21.
Furthermore, in Fig. 1, the circuit formed by the comparators 55, 57 and the resistors 59, 60 serves to produce the monitor signals M1, M2 described hereinabove, that are supplied to the microcomputer 130. Such a circuit is also provided within the drive control circuit 120 shown in Fig. 5.
In that circuit, the voltage VCOM1 of the common terminal COM1 and the voltage VCOM2 of the common terminal COM2 are respectively applied to the inverting input terminals of the comparators 55, 57, while a voltage obtained by voltage-dividing the battery voltage VB by the resistors 59, 60 is inputted as the threshold voltage Vth to the non-inverting input terminals of the comparators 55, 57. The values of the resistors 59, 60 can for example be set to have a 3:1 ratio, so that the threshold voltage Vth will be ¼ of the battery voltage VB.
As a result, when the voltage VCOM1 of the common terminal COM1 falls below the threshold voltage Vth, the monitor signal M1 goes to the high level, while similarly, when the voltage VCOM2 of the common terminal COM2 falls below the threshold voltage Vth, the monitor signal M2 goes to the high level. In any other case, each of the monitor signals M1, M2 remains at the low level.
The sections relating to the second fail-safe function will be described in the following. Fig. 2 is a flow diagram of the processing that is executed by the microcomputer 130, to implement the second fail-safe function. This processing is executed respectively for the No. 1 group and No. 2 group of injectors, however only the processing executed for the No. 1 group will be described. In the case of the processing of Fig. 1 being executed for the No. 1 group, the * symbol indicates the value 1, while the symbol ** indicates the value 1 or 3. In the case of the processing of Fig. 1 being executed for the No. 2 group, the * symbol indicates the value 2, while the symbol formed of two diagonal crossed lines and four dots indicates the value 2 or 4.
When the processing of Fig. 2 begins to be executed for the No. 1 group by the microcomputer 130, then firstly, in S110, the count of the counter CT1 is initialized to zero, by software, and the judgement value m is set for the counter CT1.
The counter CT1 counts the number of times that the injection command signals TQ1, TQ3 are outputted after a short-circuit to ground has occurred at the common terminal COM1. Alternatively stated, the counter CT1 serves to count the number of times that the transistor T12 is forcibly set in the off state, by the first fail-safe function that is implemented by the discharge control section 5 as described above.
When the count of the counter CT1 exceeds the judgement value m, then subsequent outputting of the injection command signals TQ1, TQ3 is halted. Specifically, the value of m is set in accordance with equation (1) below: $m = 1 + (k - 1) \times (N - 1)$
In the above, k is the aforementioned prescribed value used with the second fail-safe function, which is the threshold value used in judging the number of times in succession that the discharge current from the capacitor C10 exceeds the overcurrent judgement threshold value Ith. N is the maximum count value of the counter 19 described above referring to Fig. 1, and (N - 1) is the number of successive judgement operations that are performed by the first fail-safe function (i.e., judgement of the capacitor discharge current) with the overcurrent judgement threshold value set at the low value IL, as described above referring to Fig. 3.
Next in S120, waiting is performed until the next change from the high to low level occurs for either of the injection command signals TQ1, TQ3. When this occurs, (YES in S120), a wait is performed during a predetermined interval, in S130. This predetermined interval is an interval in which the voltage VCOM1 of the common terminal COM1 becomes stable, after either of the injection command signals TQ1, TQ3 has gone to the low level.
Next, in S140 the level of the monitor signal M1 is acquired, and based on the level of M1 a decision is made as to whether the voltage VCOM1 of the common terminal COM1 is below the threshold voltage Vth (= VB/4). That is to say, if the monitor signal M1 is at the high level then it is judged that VCOM1 ≤ Vth, while if M1 is at the low level then it is judged that VCOM1 > Vth.
If it is judged in S140 that VCOM1 > Vth, i.e., a NO decision in S140, then operation proceeds to step S150 in which a decision is made as to whether a time point has been reached at which a rising edge (low to high level transition) of either of the injection command signals TQ1, TQ3 occurs. If not, operation then returns to step S140, while if it is judged that a time point of such a rising edge has been reached, operation then returns to step S120.
If it is judged in S140 that VCOM1 ≤ Vth (YES decision in S140) then this indicates that there is a short-circuit to ground at the common terminal COM1, and so the first fail-safe function is executed by the discharge control section 5, to forcibly set the transistor T12 in the on state. Operation then goes to step S160, in which the counter CT1 is incremented by one.
Next, in S170 a decision is made as to whether the count of the counter CT1 exceeds the judgement value N. If not, then operation then returns to step S120, while if the count exceeds N, then operation proceeds to S180 in which processing is performed to inhibit outputting of the injection command signals TQ1, TQ3 (i.e., these signals are held at the low level).
The processing shown in Fig. 2 has been described for the case of the second fail-safe function being applied to the No. 1 group. As shown in Fig. 3, each time one of the injection command signals TQ1, TQ3 go to the low level, a judgement is made as to whether VCOM1 ≤ Vth, and in addition the number of times that the condition VCOM1 ≤ Vth has consecutively occurred is counted, as the count value of the counter CT1 (S120~S160), with that count indicating the number of times in succession that the transistor T12 has been forcibly set in the off state. If it is judged that this count value exceeds the judgement value m (i.e., YES decision in S170) then outputting of the injection command signals TQ1, TQ3 is inhibited, so that driving of the injectors 101, 103 is halted (S180).
It should be noted that since the judgement value m is established by using the aforementioned equation (1), the decision step S170 serves to judge the number of successive times for which the first fail-safe function has found that the discharge current of the capacitor C10 exceeds the regular threshold value IH, i.e., to judge whether that number of times has reached the prescribed value k. Thus, the processing of S180 for inhibiting outputting of the injection command signals TQ1, TQ3 is executed if the number of times is found to have reached the prescribed value k.
With the example shown in Fig. 3, the prescribed value k is 3 and (N - 1) is 1, (i.e., N = 2) so that from equation (1), m is made equal to 5. In that case, as shown in Fig. 3, after a short-circuit to ground occurs at the common terminal COM1 and the injection command signals TQ1, TQ3 are then outputted five times in succession, subsequent outputting of these signals is inhibited. This is due to the fact that after the short-circuit to ground at the common terminal COM1 occurs, the first fail-safe function judges three times in succession that the discharge current of the capacitor C10 has exceeded the regular value IH.
As can be understood from the above, with the ECU 1 of this embodiment, if a short-circuit to ground occurs at either of the terminals COM1 or COM2, the discharge current that flows from the capacitor C10 at each drive operation for an injector belonging to the group concerned (i.e., the group that corresponds to the common terminal where the short-circuit occurs) will be lower than for the case of the prior art.
The reasons for this are as follows. When a drive operation is performed to open an injector belonging to the group that corresponds to the common terminal at which a short-circuit to ground occurs, the discharge current that flows from the capacitor C10 through the discharge transistor (T12 or T22) is higher than the level of current that would normally flow. With the first fail-safe function of the discharge control sections 5 and 7, when it is judged that the level of discharge current from the capacitor C10 has exceeded the regular threshold value IH, then for the next successive (N - 1) judgement operations, the threshold value used in the judgement is set at a value IL which is lower than the regular threshold value IH. Hence, during each of the corresponding (N-1) drive operations performed for the injector group corresponding to the common terminal at which the short-circuit to ground is occurring, the discharge current from the capacitor C10 becomes limited, due to use of the low threshold value IL.
As stated above, "occurrence of a short-circuit to ground" at a common terminal COM1 or COM2, is used herein to refer to a short-circuit to ground that occurs at the terminal itself or that occurs in a connecting lead which is coupled to that terminal.
Thus with this embodiment, even if the capacitance value of the capacitor C10 is made small, when a short-circuit to ground occurs at either of the common terminals COM1, COM2 as illustrated in Fig. 3, it is ensured that the capacitor voltage VC will not fall below the level that enables satisfactory fuel injection operation. Hence, the fuel injector belonging to the group for which no short-circuit occurs, i.e., which are functioning normally, will continue to driven for opening in the normal manner, so that the vehicle will not be immobilized and can be driven temporarily.
In addition with this embodiment, the problem of abnormal detection sensitivity (described above referring to Fig. 8) can be avoided. That is to say, with the prior art technology, if it is attempted to enable the capacitance value of the charge capacitor to be made smaller by reducing the prescribed value k to 1, then even if only a momentary short-circuit to ground occurs at either of the common terminals COM1 or COM2, drive operations for opening the injectors that belong to the group corresponding to the common terminal where the short-circuit occurs will be inhibited, and engine operation can only be continued by using only the injectors of the other group. However with the present invention that problem will not arise, since even if the value of k is made higher than 1, it can be ensured that occurrence of a momentary short-circuit at a common terminal will not result in the operation of the corresponding ground potential of injectors being halted, and driving of these injectors will be immediately resumed when recovery from the short-circuit condition occurs.
This is due to the fact that the overcurrent judgement threshold value used by the discharge control sections 5 and 7 can be switched between different values, with the low threshold value IL being made substantially identical to the target value ip of current that should flow through an injector coil when the injector is opened. Hence, even if a momentary short-circuit to ground occurs at a common terminal COM1 or COM2, there will be no adverse effect upon control of driving the injectors.
This will be described more specifically in the following, taking the example of Fig. 4 in which it is assumed that a momentary short-circuit to ground occurs at the common terminal COM1 (corresponding to the No. 1 group). When such a short-circuit occurs, the discharge control section 5 (corresponding to the No. 1 group) will judge that the discharge current from the capacitor C10 is greater than or equal to IH, and thereafter during (N-1) judgement operations, the overcurrent judgement threshold value Ith is set at the low value IL. Thus, so long as the short-circuit condition continues (more specifically, until the count value m is reached in step S170 of the processing of Fig. 2), only a limited amount of charge will flows from the capacitor C10 at each drive operation for the injectors of the group corresponding to the connection terminal COM1, as described referring to Fig. 3. In addition, if the short-circuit to ground occurs only momentarily (specifically, recovery from the short-circuit condition occurs before the count value m is reached in step S170 of the processing of Fig. 2), then when recovery from the short-circuit condition occurs, at the time point indicated as t2 in Fig. 4, the next drive operation for the injectors of the group concerned (i.e., those corresponding to the common terminal COM1) will take place normally.
Thereafter, at the time point t3, the threshold value Ith is restored to the regular value.
Thus, by making low threshold value IL equal to the regular value ip, it is ensured that a momentary short-circuit to ground will have only a minimum effect upon the operation of the engine.
It should be noted that it is not essential that the low threshold value IL be made exactly identical to the target value ip, however preferably, it should be made close to ip.
Specifically, if IL is made higher than ip, then while a short-circuit to ground is occurring, the amount of capacitor charge that is dissipated in the short-circuit will be increased, by comparison with a lower value for IL.
If on the other hand, IL were to be made lower than ip, then the following would be true, as can be understood from the discharge current waveforms ICOM1 for the common terminal COM1 shown in Fig. 4. Immediately following recovery from a momentary short-circuit to ground condition (i.e., before Ith has been restored from IH to the IL level), the amount of charge current supplied to the injectors of the group concerned would be lowered, by comparison with the use of a higher value for IL. However this would result in smaller amounts of capacitor charge being transferred to the short-circuit during each drive operation performed (for the injector group concerned) while the short-circuit condition continues.
Hence, it can be understood that the respective values of the low threshold value IL and of N can each be predetermined in accordance with design requirements, such as a required speed of recovery of the charge voltage VC of the charge capacitor after that voltage has been lowered due to the effects of a momentary short-circuit to ground at a common terminal. As described above, the lower the value of IL, the smaller will be the amount of charge that flows (during the short-circuit condition) at each drive operation for the injector group concerned. Similarly, as can be readily understood from the variation of the charge capacitor voltage VC shown in the example of Fig. 3, the larger the value of N (i.e., the higher the value of the judgement threshold m used in step S170 of the processing of Fig. 2), the greater will be the extent to which the charge capacitor voltage VC will fall, during a momentary short-circuit to ground at a common terminal.
In the above embodiment, the transistors T10, T20, T30, T40 correspond to respective drive switching elements and the transistors T20, T22 correspond to discharge switching elements. The microcomputer 130, the discharge control signal generating circuit 9 of each of the discharge control section 5 and the discharge control circuit 7, in combination, constitute an overall control circuit for the apparatus. The sections of the discharge control section 5 and discharge control circuit 7 other than the discharge control signal generating circuit 9 implement the first fail-safe function, while the processing executed by the microcomputer 130 that is shown in Fig. 2 serves to implement the second fail-safe function.
The above embodiment is of the common 2-system type with a single charge capacitor. However the invention could equally be applied to a configuration having a single common terminal and a single charge capacitor, with respective connecting leads of one or more injectors (i.e., a single group of injectors) connected only to that common terminal, or a configuration (as described in the reference document 1) in which there are two systems having respective charge capacitors provided for each of the systems.
The processing performed by the discharge control sections 5 and 7 of the above embodiment can be applied to such an alternative configuration, so that when a short-circuit to ground occurs at a common terminal, the level of discharge current that flows from the charge capacitor during driving of an injector to the open state can be held to a low level. Hence if the short-circuit to ground is a momentary occurrence, and is resolved before driving of injectors to the open state is inhibited by the processing shown in Fig. 2 (i.e., before the count value reaches m, in an execution of step S170) it can be ensured that the voltage of the discharge capacitor will not become excessively low by the time that recovery from the short-circuit occurs. Hence, normal fuel injection operation can be rapidly resumed. In the case of an apparatus having a plurality of drive capacitors, this enables the value of each charge capacitor to be made small, so that the apparatus can be made more compact in size and lower in cost.
It should thus be noted that the present invention is not limited to the above embodiment, and that various other configurations could be envisaged that fall within the scope claimed for the invention.
For example in Fig. 1, it would be possible to input the injection command signals TQ1~TQ4 from the exterior of the ECU 1, rather than from the microcomputer 130 within the ECU 1. Furthermore, the drive control circuit 3 could be integrated with the microcomputer 130.
To avoid undue complexity of claim language, the term "opening-object fuel injector" is used in the appended claims to refer to a fuel injector that is currently to be driven to the opened state.

Claims

A fuel injection control apparatus operating from a source of a DC supply voltage, comprising:
a plurality of fuel injectors corresponding to respective ones of a plurality of cylinders of an internal combustion engine, each fuel injector adapted to be opened when a current is passed through a coil thereof for injecting fuel into said corresponding cylinder, said fuel injectors being divided into a plurality of groups,

a plurality of drive-use switching elements respectively corresponding to said fuel injectors, each switching element connected in series in a circuit path between a first end of said coil of the corresponding fuel injector and a low potential supply lead of said supply voltage source,

charging means for generating a voltage that is higher than said supply voltage, and for charging a capacitor to said generated voltage,

a plurality of sets of connecting leads corresponding to respective ones of said groups of fuel injectors, with each connecting lead of each said set having one end thereof connected to a second end of a coil of a fuel injector of said corresponding group,

a plurality of discharge-use switching elements each corresponding to a specific one of said groups of fuel injectors, with each said discharge-use switching element connected between a high voltage-end terminal of said capacitor and a second end of each of said connecting leads of a connecting lead set corresponding to said specific group of fuel injectors, and

control means for repetitively selecting one of said fuel injectors as an opening-object injector, and for switching on a drive-use switching element corresponding to said opening-object fuel injector and concurrently switching on a discharge switching element corresponding to a group containing said opening-object fuel injector, for thereby passing a discharge current from said capacitor through said coil of said opening-object fuel injector,

and comprising, respectively corresponding to each of said groups of fuel injectors,

fail safe means for performing a judgement operation to determine whether or not said discharge current exceeds a predetermined overcurrent judgement threshold value when said corresponding discharge switching element is switched on to thereby open a fuel injector of said group, and when said overcurrent judgement threshold value is found to be exceeded, for forcibly switching off said corresponding discharge switching element;
wherein:
said fail safe means is adapted to selectively set said overcurrent judgement threshold value at a regular value and at a second value that is lower than said regular value, and, when it is judged that said discharge current exceeds said regular threshold value, to thereafter set said overcurrent judgement threshold value at said second value.
A fuel injection control apparatus according to claim 1 wherein when opening of an fuel injector of one of said groups is to be executed, said control means switches the discharge switching element corresponding to said group to the on state, and maintains said on state until a current that flows in the coil of said opening-object fuel injector attains a target value;
wherein said second value that can be selected as said overcurrent judgement threshold value of said fail safe function is made identical to or close to said target value.
A fuel injection control apparatus according to claim 1, wherein said capacitor is an aluminum electrolytic capacitor.
A fuel injection control apparatus operating from a source of a DC supply voltage, comprising:
a plurality of fuel injectors corresponding to respective ones of a plurality of cylinders of an internal combustion engine, each fuel injector adapted to be opened when a current is passed through a coil thereof for injecting fuel into said corresponding cylinder, said fuel injectors being divided into a plurality of groups,

a plurality of drive-use switching elements respectively corresponding to said fuel injectors, each switching element connected in series in a circuit path between a first end of said coil of the corresponding fuel injector and a low potential supply lead of said supply voltage source,

charging means for generating a voltage that is higher than said supply voltage, and for charging a capacitor to said generated voltage,

a plurality of sets of connecting leads corresponding to respective ones of said groups of fuel injectors, with each connecting lead of each said set having one end thereof connected to a second end of a coil of a fuel injector of said corresponding group,

a plurality of discharge-use switching elements each corresponding to a specific one of said groups of fuel injectors, with each said discharge-use switching element connected between a high voltage-end terminal of said capacitor and a second end of each of said connecting leads of a connecting lead set corresponding to said specific group of fuel injectors, and

control means for repetitively selecting one of said fuel injectors as an opening-object injector, and for switching on a drive-use switching element corresponding to said opening-object fuel injector and concurrently switching on a discharge switching element corresponding to a group containing said opening-object fuel injector, for thereby passing a discharge current from said capacitor through said coil of said opening-object fuel injector, and comprising, respectively corresponding to each of said groups of fuel injectors,

first fail safe means for performing a judgement operation to determine whether or not said discharge current exceeds a predetermined overcurrent judgement threshold value when said corresponding discharge switching element is switched on to thereby open a fuel injector of said group, and, when said overcurrent judgement threshold value is found to be exceeded, for forcibly switching off said corresponding discharge switching element, and

second fail safe means for deriving a count value of a successive number of times that said discharge current is found to exceed said overcurrent judgement threshold value by the first fail safe function;
wherein:
said first fail safe means is adapted to selectively set said overcurrent judgement threshold value at a regular value and at a second value that is lower than said regular value, and, when it is judged that said discharge current exceeds said regular threshold value, to thereafter set said overcurrent judgement threshold value at said second value, and

said second fail-safe means is adapted to inhibit operations by said control means for opening fuel injectors of the group corresponding to said second fail safe means, when said count value is found to attain a prescribed value.
A fuel injection control apparatus according to claim 4 wherein when opening of an fuel injector of one of said groups is to be executed, said control means switches the discharge switching element corresponding to said group to the on state, and maintains said on state until a current that flows in the coil of said opening-object fuel injector attains a target value;
wherein said second value that can be selected as said overcurrent judgement threshold value of said first fail safe function is made identical to or close to said target value.
A fuel injection control apparatus according to claim 4, wherein said capacitor is an aluminum electrolytic capacitor.
A fuel injection control apparatus operating from a source of a DC supply voltage, comprising:
a fuel injector that is opened when a current is passed through a coil thereof, for thereby injecting fuel into an internal combustion engine;

a drive-use switching element that is connected in series in a circuit path between a first end of said coil of said fuel injector and a low-potential supply lead of said supply voltage source;

charging means for generating a voltage that is higher than said power supply voltage, and for charging a capacitor to said generated voltage,

a connecting lead having a first end thereof connected to a second end of said coil, opposite said first end,

a discharge-use switching element controllable for connecting a second end of said connecting lead to a high-voltage terminal of said capacitor,

control means functioning when said fuel injector is to be opened, to switch on said drive-use switching element to the on state and to concurrently switch on said discharge-use switching element, to thereby pass a discharge current from said capacitor through said coil,

first fail safe means for performing a judgement operation to determine whether or not said discharge current exceeds a predetermined overcurrent judgement threshold value when said discharge switching element is switched on to thereby open said fuel injector, and when said overcurrent judgement threshold value is found to be exceeded, for forcibly switching off said discharge switching element, and

second fail safe means for deriving a count value of a successive number of times that said discharge current is found to exceed said overcurrent judgement threshold value by said first fail safe function;
wherein:
said first fail safe function is adapted to selectively set said overcurrent judgement threshold value at a regular value and at a second value that is lower than said regular value, and, when it is judged that said discharge current exceeds said regular threshold value, to thereafter set said overcurrent judgement threshold value at said second value during each of a predetermined number of successive ones of said judgement operations performed by said first fail safe function, and

said second fail-safe function is adapted to inhibit operations by said control means for opening said fuel injector, when said count value is found to attain a prescribed value.
A fuel injection control apparatus according to claim 7 wherein when opening of said fuel injector is to be executed, said control means switches said discharge switching element to the on state, and maintains said on state until a current that flows in the coil of said fuel injector attains a target value;
wherein said second value that can be selected as said overcurrent judgement threshold value of said first fail safe function is made identical to or close to said target value.
A fuel injection control apparatus according to claim 7, wherein said capacitor is an aluminum electrolytic capacitor.