Fuel injection system for internal combustion engine

A booster circuit installed in a fuel injection device of an internal combustion engine, wherein malfunctions and characteristic changes of the booster circuit are detected, among which the detection distinguishes between decreases in capacity caused by deterioration or broken wires in a booster capacitor, and failures of a current monitor circuit, coil, externally connected fuel injection valve, and other components. The range of decrease in boost voltage when the fuel injection valve is opened is monitored, as is the range of increase per switch performed in order to restore the boost voltage. This makes it possible to detect malfunctions and characteristic changes of the booster circuit.

TECHNICAL FIELD

The present invention relates to a booster circuit of a fuel injection system of an inter al combustion engine.

BACKGROUND ART

Examples of background art of the present field include JP 2011-247192 A. In this publication, in a booster circuit of a fuel injection system, the number of times of boost switching until restoration to a set voltage after a booster capacitor discharges is measured; and, when the criteria of a set number of times of switching is exceeded, drive of a fuel injection valve is permitted. It is not an object of this publication to carry out deterioration judgment, but is to wait for recovery of the capacitor having lowered capability in initial usage and restart operation of the booster circuit.

Moreover, examples of background art of the present field also include JP 2011-247192 A. In this publication, in a booster circuit of a fuel injection system, a steady-state value of a charge voltage for a booster capacitor is monitored. If it is normal, a fuel injection valve is driven by a control signal indicating a normal injection pulse width and injection timing; and, if it is not normal, the injection pulse width and injection timing are corrected. In this publication, the stead-state value is monitored for the charge voltage for the booster capacitor. However, since no change is generated in the steady-state value, it is difficult to detect the deterioration of the booster capacitor.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

It is an object of the present invention to distinguish and detect capacity decrease due to deterioration or a broken wire of a booster capacitor and failure of a current monitor circuit, a coil, an externally connected fuel injection valve, etc. among malfunctions and characteristic changes of a booster circuit in the booster circuit used in fuel injection.

Solution to Problem

The object of the present invention can be achieved, for example, by monitoring charge/discharge of a booster capacitor.

Advantageous Effects of Invention

According to the present invention, capacity decrease due to deterioration or a broken wire of a booster capacitor and failure of a current monitor circuit, a coil, an externally connected fuel injection valve, etc. can be distinguished and detected among malfunctions and characteristic changes of a booster circuit in the booster circuit used in fuel injection.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment according to the present invention will be described in detail based on drawings.

First, a configuration of an internal combustion engine system in which a fuel-injection controlling device according to the present embodiment is installed will be described by usingFIG. 1. An engine1is provided with a piston2, an air intake valve3, and an air exhaust valve4. Intake air passes through an air flow meter (AFM)20, enters a throttle valve19, and is supplied from a collector15serving as a branching part to a combustion chamber21of the engine1via an air intake pipe10and an air intake valve3. Fuel is supplied from a fuel tank23to an internal combustion engine by a low-pressure fuel pump24, and the pressure thereof is further increased by a high-pressure fuel pump25to a pressure required for fuel injection. The fuel subjected to pressure increase by the high-pressure fuel pump25is injected and supplied from a fuel injection valve5to the combustion chamber21of the engine1and is ignited by an ignition coil7and an ignition plug6. The pressure of the fuel is measured by a fuel pressure sensor26.

An exhaust gas after combustion is discharged to an air exhaust pipe11via an air exhaust valve4. The air exhaust pipe11is provided with a three-way catalyst12for exhaust gas purification. A fuel-injection controlling device27is built in an ECU (engine control unit)9; and signals of a crank angle sensor16of the engine1, air-volume signals of the AFM20, signals of an oxygen sensor13which detect the oxygen concentration in the exhaust gas, an accelerator opening degree of an accelerator opening degree sensor22, signals of a fuel pressure sensor26, etc. are input thereto. The ECU9, for example, calculates the torque required for the engine from the signals of the accelerator opening-degree sensor22and judges an idle state. The ECU9is provided with a rotating-speed detecting means, which computes an engine rotating speed from the signals of the crank angle sensor16.

Moreover, the ECU9calculates an intake air volume required for the engine1and outputs an opening-degree signal corresponding to that to the throttle valve19. Moreover, the fuel-injection controlling device27of the ECU9calculates a fuel quantity corresponding to the intake air volume, outputs a current for the fuel injection valve5to carry out fuel injection, and outputs an ignition signal to the ignition plug6.

The air exhaust pipe11and the collector15are connected to each other by an EGR passage18. An EGR valve14is provided at an intermediate part of the EGR passage18. The opening degree of the EGR valve14is controlled by the ECU9, and, in accordance with needs, the exhaust gas in the air exhaust pipe11is flowed back to the air intake pipe10.

FIG. 2shows a circuit block diagram of fuel-injection-system drive circuit. A fuel injection system is generally built in the ECU9shown inFIG. 1. The voltage of a battery41is supplied to the ECU9, and this voltage is supplied to a power source IC43, a driver IC47, a fuel-injection-system driving booster circuit51, a high-side driver52, etc. Moreover, voltages are supplied by the power source IC43to a microcomputer44, the driver IC47, etc. The driver IC47has a communication unit49for the microcomputer44, a booster-circuit driving unit50, and a driver driving unit48. A switching signal is transmitted from the booster-circuit driving unit50to the booster circuit51, and the voltage increased by the booster circuit is supplied to a high-side driver52. Meanwhile, the voltage increased by the booster circuit51is fed back to the booster-circuit driving unit50, and whether a switching signal is to be transmitted again or not is determined by the driver IC47. Meanwhile, the voltage increased by the booster circuit51can be fed back to an A/D converter45of the microcomputer44, and, based on an A/D value, a signal can be transmitted from a communication unit46in the microcomputer44to the driver IC47. Meanwhile, other than boost voltages, signals from a fuel pressure sensor, a temperature sensor, etc. can be input to and monitored by the A/D converter owned by the microcomputer44. Other than that, the microcomputer44has an input/output port42, which drives an external load and/or monitors signals from outside. The high-side driver52can obtain power supplies from the booster circuit51and the battery41and has a driver52adriven by the boost voltage and a driver52bdriven by the battery voltage. It has a role to cause a current to flow to a load54, which has a coil, by drive signals (A, B) of the driver driving unit48. A low-side driver53has a role to cause the current from the load54, which has the coil, to flow to a ground electric potential by a drive signal (C) from the driver driving unit48. Meanwhile, either one of or both of the high-side driver52and the low-side driver53has a current detecting function and a terminal voltage detecting function using a shunt resistance, etc., wherein driver driving is carried out by detecting the values of the currents which flow to the driver and the load54and feeding back the current values. Meanwhile, by these functions, overcurrent to the driver, power-source short circuit and ground short circuit of terminals can be also detected. Herein, the booster circuit51, the high-side driver52, and the low-side driver53may be provided inside or outside the driver IC47, and the driver IC47may be used as either role as a driver or a pre-driver.

FIG. 3is a diagram describing details of the booster circuit51. When a gate voltage Vg of a booster driver63is turned on, a current I flows from the battery41to GND via a shunt resistance61, a booster coil62, and the booster driver63. The current at this point is detected as a both-end voltage of the shunt resistance61by the booster-circuit driving unit50. When a set maximum current value is detected, the booster driver63is turned off. At that point, the current I flows to a booster diode64because of back electromotive force of the booster coil62. A booster capacitor65functions to temporarily store the current, which has flowed to the diode. Then, when the current flowing through the shunt resistance61becomes small, the booster driver63is turned on again, and the current value is increased. By repeating this, the current is kept flowing to the booster diode64and storing the current in the booster capacitor65, thereby generating a boost voltage. Moreover, a circuit66which monitors the boost voltage is provided in the booster circuit; wherein, voltage boosting is carried out when the voltage is low, and the boost voltage is monitored in order to stop voltage boosting when the voltage reaches a predetermined value. The waveforms of a voltage boosting operation are shown by a diagram inFIG. 4. The gate signal for turning on the booster driver63is Vg. When this is turned on, a drain voltage Vd of the booster driver63is reduced to the vicinity of 0 V, and the current I is increased. When the current I reaches the set Max current, the gate signal Vg of the booster driver63is turned off. At that point, Vd reaches a voltage equivalent to the boost voltage, the current I flows to the booster diode64side and is stored in the booster capacitor65; however, the current value per se is reduced along with time. Since the booster driver63is turned on again when the current reaches a set Min current, the operation ofFIG. 4is carried out by repeating this operation. This operation is carried out until the boost voltage reaches a set value. Note that hatched parts in the diagram represent the currents which actually flow through the booster diode64and represent the currents which are used in boosting. When this operation is carried out, the booster circuit has a waveform like that of the boost voltage ofFIG. 4. When injection to a fuel drive valve is started, the boost voltage is reduced until a fuel injection current reaches a peak current. After the fuel injection current reaches the peak current, the boost voltage is not used. Therefore, the boost voltage is gradually recovered by switching drive of the booster circuit. When Vg is off, the current flows to the booster capacitor, and the boost voltage is therefore increased. When Vg is on, the current does not enter the booster capacitor, and the boost voltage is therefore not increased (is slightly reduced since natural discharge is carried out). Voltage boosting is carried out by Vg switching until the boost voltage becomes a predetermined value as a result of the repetition thereof.

It is an object of the present invention to check the deterioration state of the booster circuit by monitoring the movement in the boost voltage.

FIG. 5andFIG. 6are diagrams described as embodiments of claims1to3of the present invention.FIG. 5is a diagram in which a determination unit67for read boost signals and boost voltages is provided with respect toFIG. 3. The determination unit67is provided inside or outside the driver IC47and is a part which monitors and diagnoses differences in the boost voltage and on/off drive of the booster circuit two times at measurement points. InFIG. 6, a boost voltage waveform of a case in which the capacity of the booster capacitor65has been reduced is added toFIG. 4(broken line in the diagram). If the capacity is reduced due to deterioration or a broken wire of the booster capacitor65, the range of reduction of the boost voltage in valve opening of the fuel injection valve is increased (normal case (1)→capacity reduced case (1)′). When it is reduced largely from that of the normal case, diagnosis is carried out by reading the difference between a voltage Va of a point when injection of the fuel injection valve is started and a boost voltage Vb of a point when the current to the fuel injection valve reaches the peak.

Then, after the current to the fuel injection valve reaches the peak, a boost-voltage restoring operation is started; wherein, the voltage Vb of a point immediately before the booster driver63is turned off in order to check the voltage value increased by one time of switching and a voltage Vc at a point it is turned on are monitored. The difference is increased if the capacity is reduced due to deterioration or a broken wire of the booster capacitor65(normal case (2)→capacity reduced case (2)′). As a result of reading the booster voltage difference therebetween, if the difference has been largely increased from the normal case, diagnosis is carried out.

FIG. 7andFIG. 8are flow charts of the contents of the description inFIG. 6. InFIG. 7, the boost voltage Va before fuel injection is monitored (101), and the boost voltage Vb at the point when the fuel injection current reaches the peak is monitored (102). Then, the difference (1) is obtained (103). If the difference is equal to or less than a predetermined value V1, normal drive is carried out (104). If the difference is equal to or more than V1, diagnosis is carried out (105). InFIG. 8, the voltage Vb at the point immediately before the booster driver63is turned off (when Max current is detected) is monitored (201), and the voltage Vc at the point immediately before the booster driver63is turned on (when Min current is detected) is also monitored (202). Then, the difference (2) therebetween is obtained (203). If the difference is equal to or less than a predetermined value V2, normal drive is carried out (204). If the difference is equal to or more than V2, diagnosis ms carried out (205).

When the measurement method as described above is carried out, diagnosis can be carried out when there is a difference from a normal case. In a case of a diagnosis method byFIG. 7orFIG. 8, distinguishment from deterioration and characteristic variations of other elements cannot be made in some cases. Therefore, when both ofFIG. 7andFIG. 8are used, characteristic changes due to deterioration, broken wire, etc. of the booster capacitor65can be specified. A diagram thereof is shown inFIG. 9, and this is the diagram described as embodiments of claims1and4. Examples of characteristic changes include, other than the capacity value of the booster capacitor65, the resistance value of the shunt resistance61for current monitoring, inductance of the booster coil62, and the resistance value of an externally-connected fuel injection valve. The changes of the voltage (1) and voltage (2) in the cases in which the numerical values thereof become large or small are shown in the diagram. For example, if the change of the voltage (1) is larger than that in the normal operation and is larger than the threshold value V1 and if the change of the voltage (2) is larger than that in the normal operation and is larger than the threshold value V2 it can be distinguished as abnormality (deterioration, broken wire, etc.) of the booster capacitor65. Moreover, if the change of the voltage (1) is not different from that in the normal operation, but the change of the voltage (2) is larger than that in the normal operation and is larger than the threshold value V2, the resistance value of the shunt resistance61has been reduced, or the inductance of the booster coil62has been increased. In this manner, if either one of (1) and (2) is monitored, there is a part that cannot be distinguished from other characteristic changes. However, if both of (1) and (2) are monitored, it can be distinguished from the other characteristic changes. (Effects of the Invention) As described above, according to the present invention, in a fuel injection system of an internal combustion engine driven to be opened/closed by a boost voltage higher than a battery voltage and by the boost voltage, the system having a drive circuit configured to control electric power distribution to a coil driven to open/close a fuel injection valve, the range of decrease in the boost voltage when the fuel injection valve is opened and the range of increase per 1 switching carried out for restoring the boost voltage are monitored. As a result, malfunctions and characteristic changes of the booster circuit can be detected, and, among them, capacity decrease due to deterioration or a broken wire of the booster capacitor and malfunctions and characteristic changes of the current monitor circuit, the coil, and the externally connected fuel injection valve, etc. can be distinguished and detected.

REFERENCE SIGNS LIST