JP2015132236A - Internal combustion engine fuel injection control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately change the output characteristics of an exhaust sensor at a time of using a gas fuel and eventually suppress occurrence of a problem resulting from deviation of the sensor output characteristics.SOLUTION: A gas fuel is injected to an engine from a first injection valve and a liquid fuel is also injected to the engine from a second injection valve. An O2 sensor 18 detects an air-fuel ratio of exhaust gas, and a fuel injection amount is controlled based on the air-fuel ratio. A constant-current circuit 72 carrying a current to a solid electrolyte layer 62 of a sensor element 61 to change sensor output characteristics is connected to the O2 sensor 18. A control unit 80 determines the composition of each fuel supplied into cylinders, and controls current-carrying by the constant-current circuit 72 on the basis of the fuel composition.

Description

  The present invention relates to a fuel injection control system for an internal combustion engine.

  For example, an engine that enables the use of liquid fuel (gasoline) and gaseous fuel (CNG) is embodied as a vehicle engine, and a technique for appropriately adjusting the usage ratio of both of the liquid fuel and gaseous fuel. Various proposals have also been made. For example, in the technique described in Patent Document 1, it is determined whether or not the purification performance of the exhaust purification catalyst is reduced, and if it is determined that the purification performance is reduced, the fuel that is advantageous for exhaust emission is determined. While increasing the use ratio, the fuel use ratio is controlled so that the fuel that is more advantageous for exhaust emission remains until the end.

  Also, in an engine for a vehicle or the like, an electromotive force output type O2 sensor that detects an oxygen concentration in exhaust gas is generally used as an exhaust sensor. This O2 sensor has a solid electrolyte body and a pair of electrodes, and has an electromotive force cell that outputs different electromotive force signals depending on whether the exhaust is rich or lean.

Japanese Patent No. 5115653

  By the way, when the fuel composition may be changed, such as when a plurality of fuels are used properly, the exhaust components may differ depending on the fuel used. For example, when gaseous fuel such as CNG is used Increases the amount of hydrogen in the exhaust. As a result, it is considered that the output characteristics of the exhaust sensor change and the inflection point of the sensor output shifts to the lean side. In this case, there is a concern that inconvenience such as deterioration of exhaust emission may occur due to unintentionally changing sensor output characteristics. That is, when the air-fuel ratio control of the engine is performed using the detection value of the exhaust sensor, the actual air-fuel ratio cannot be controlled to a desired air-fuel ratio due to a deviation in sensor output characteristics, and as a result This causes the inconvenience of worsening the exhaust mission.

  The present invention provides a fuel injection control system for an internal combustion engine that can appropriately change the output characteristics of an exhaust sensor when using gaseous fuel, and thereby suppress the occurrence of inconvenience due to the deviation of the sensor output characteristics. Is the main purpose.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The fuel injection control system for an internal combustion engine according to the present invention includes at least fuel injection means (21, 22) for injecting gaseous fuel and an exhaust sensor (18) for outputting a detection signal corresponding to the oxygen concentration in the exhaust gas. The present invention is applied to an internal combustion engine (10), and controls the fuel injection amount by the fuel injection means based on the detection result of the exhaust sensor. The exhaust sensor has an electromotive force cell (61) using a solid electrolyte body (62) and a pair of electrodes (63, 64), and generates an electromotive force according to the oxygen concentration in the exhaust. It is something to be made. And in particular, a current-carrying means (72) for changing the output characteristics of the exhaust sensor by passing a current through the solid electrolyte body in the electromotive force cell, and a composition judging means for judging the composition of fuel injected by the fuel-injecting means (80) and energization control means (80) for controlling energization by the energization means based on the fuel composition determined by the composition determination means.

  At least an internal combustion engine using gaseous fuel has a different composition from that of using only liquid fuel, and the output characteristics of the exhaust sensor are considered to change according to the fuel composition. There is a concern that an air-fuel ratio shift in fuel injection control may occur due to a change in sensor output characteristics. In this regard, in the above-described configuration, a change in the output characteristics of the exhaust sensor due to the use of gaseous fuel can be suppressed by causing a current to flow through the solid electrolyte body of the electromotive force cell by the energization means. In particular, the output characteristics of the exhaust sensor are changed in consideration of the mixing ratio of gaseous fuel and liquid fuel by determining the fuel composition and controlling the energization by the energizing means based on the fuel composition. It becomes possible to do. As a result, it is possible to appropriately change the output characteristics of the exhaust sensor when using gaseous fuel, and to suppress the occurrence of inconvenience due to the deviation of the sensor output characteristics.

The schematic block diagram which shows the whole engine control system. The figure which shows the cross-sectional structure of a sensor element, and the schematic structure of a sensor control system. The electromotive force characteristic figure which shows the relationship between an excess air ratio and the electromotive force of a sensor element. The figure which shows the relationship between the output characteristic of an O2 sensor, and an exhaust gas purification rate. The time chart which shows the relationship between an O2 sensor output, the injection correction amount, and the excess air ratio. The time chart which shows the relationship between an O2 sensor output, the injection correction amount, and the excess air ratio. The time chart which shows the relationship between an O2 sensor output, the injection correction amount, and the excess air ratio. Schematic for demonstrating reaction of the gas component in a sensor element. The flowchart which shows the process sequence of constant current control. FIG. 5 is a relationship diagram for setting an instruction current of a constant current circuit. The flowchart which shows the process sequence of abnormality determination of a constant current circuit. The flowchart which shows the process sequence of constant current control.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. This embodiment is embodied as a fuel injection system for a so-called bi-fuel type on-vehicle multi-cylinder engine that uses compressed natural gas (CNG) that is gaseous fuel and gasoline that is liquid fuel as fuel for engine combustion. . An overall schematic diagram of this system is shown in FIG.

  An engine 10 shown in FIG. 1 is an inline three-cylinder spark ignition engine, and an intake system 11 and an exhaust system 12 are connected to an intake port and an exhaust port, respectively. The intake system 11 has an intake manifold 13 and an intake pipe 14. The intake manifold 13 has a plurality of (for the number of cylinders of the engine 10) branch pipe portions 13a connected to the intake port of the engine 10, and a collective portion 13b connected to the intake pipe 14 on the upstream side. ing. The intake pipe 14 is provided with a throttle valve 15 as air amount adjusting means. The throttle valve 15 is configured as an electronically controlled throttle valve whose opening degree is adjusted by a throttle actuator 15a such as a DC motor. The opening degree of the throttle valve 15 (throttle opening degree) is detected by a throttle opening degree sensor 15b built in the throttle actuator 15a. An intake valve is provided in the intake port of the engine 10, and an air-fuel mixture is introduced into the cylinder 24 (inside the cylinder) by opening the intake valve.

  The exhaust system 12 has an exhaust manifold 16 and an exhaust pipe 17. The exhaust manifold 16 has a plurality of (for the number of cylinders of the engine 10) branch pipe portions 16a connected to the exhaust port of the engine 10 and a collecting portion 16b connected to the exhaust pipe 17 on the downstream side. ing. The exhaust port of the engine 10 is provided with an exhaust valve. Exhaust gas after combustion of the engine 10 is discharged from the cylinders 24 of the engine 10 to the exhaust pipe 17 by opening the exhaust valve.

  The exhaust pipe 17 is provided with a catalyst 19 for purifying exhaust and an O2 sensor 18 as an exhaust sensor for detecting exhaust components. The catalyst 19 is made of, for example, a three-way catalyst. As is well known, the three-way catalyst purifies CO (carbon monoxide), HC (hydrocarbon), NOx (nitrogen oxides such as NO), which are harmful three components of exhaust gas. Is formed by supporting a metal such as platinum, palladium, or rhodium on a ceramic carrier. In this case, in the three-way catalyst, CO and HC that are rich components are purified by an oxidizing action, and NOx that is a lean component is purified by a reducing action. The O2 sensor 18 is provided on the upstream side of the catalyst 19 and outputs an electromotive force signal that varies depending on whether the air-fuel ratio is rich or lean according to the oxygen concentration of the exhaust gas.

  A spark plug 20 is provided in each cylinder 24 of the engine 10. A high voltage is applied to the ignition plug 20 at a desired ignition timing through an ignition device 20a including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 20, and the fuel introduced into the cylinder 24 (combustion chamber) is ignited and used for combustion.

  Further, the present system is a fuel injection means for injecting and supplying fuel to the engine 10, a first injection valve 21 for injecting gaseous fuel (CNG fuel), and a second injection valve 22 for injecting liquid fuel (gasoline). And have. Among these injection valves 21 and 22, the first injection valve 21 is a port injection type that injects fuel into the branch pipe portion 13 a of the intake manifold 13, and the second injection valve 22 is a fuel in the cylinder 24 of the engine 10. It is a direct injection type that injects directly. Each of the injection valves 21 and 22 is an open / close type control valve in which the valve body is lifted from the closed position to the open position by electrically driving the electromagnetic drive unit. Each valve is driven to open by a valve opening drive signal. Each of these injection valves 21 and 22 is opened by energization, closed by energization interruption, and injects an amount of fuel (gaseous fuel, liquid fuel) according to the energization time.

  Here, the gaseous fuel supply part 40 which supplies gaseous fuel with respect to the 1st injection valve 21, and the liquid fuel supply part 50 which supplies liquid fuel with respect to the 2nd injection valve 22 are demonstrated. In the gaseous fuel supply unit 40, a gas tank 42 is connected to the first injection valve 21 via a gas pipe 41. In the middle of the gas pipe 41, a regulator 43 is provided as pressure adjusting means for adjusting the pressure of the gaseous fuel supplied to the first injection valve 21 to reduce the pressure. The regulator 43 is configured so that gaseous fuel in a high pressure state (for example, a maximum of 20 MPa) stored in the gas tank 42 is a predetermined set pressure (for example, in a range of 0.2 to 1.0 MPa) that is an injection pressure of the first injection valve 21. The pressure is adjusted to be constant. The gaseous fuel after the decompression adjustment is supplied to the first injection valve 21 through the gas pipe 41.

  The gas pipe 41 further includes a tank main stop valve 44 disposed near the fuel outlet of the gas tank 42, and a shut-off valve disposed downstream of the tank main stop valve 44 and near the fuel inlet of the regulator 43. 45 is provided. These valves 44 and 45 allow and block the flow of gaseous fuel in the gas pipe 41. Both the tank main stop valve 44 and the shut-off valve 45 are electromagnetic on-off valves, and are normally closed types in which the flow of gaseous fuel is blocked when not energized and the flow of gaseous fuel is allowed when energized. In the gas pipe 41, pressure sensors 46a and 46b for detecting the fuel pressure and temperature sensors 47a and 47b for detecting the fuel temperature are provided on the upstream side and the downstream side of the regulator 43, respectively.

  In the liquid fuel supply unit 50, a fuel tank 52 is connected to the second injection valve 22 via a fuel pipe 51. The fuel pipe 51 is provided with a fuel pump 53 that feeds the liquid fuel in the fuel tank 52 to the second injection valve 22.

  In addition, this system is provided with a starter 25 as a starting device that applies initial rotation to the engine 10 when the engine is started.

  The control unit 80 includes a CPU 81, a ROM 82, a RAM 83, a backup RAM 84, an interface 85, and a bidirectional bus 86. The CPU 81, ROM 82, RAM 83, backup RAM 84, and interface 85 are connected to each other by a bidirectional bus 86.

  The CPU 81 executes a routine (program) for controlling the operation of each unit in this system. The ROM 82 stores in advance various data such as a routine executed by the CPU 81, maps (including tables, relational expressions, etc. in addition to maps) and parameters referred to when the routine is executed. The RAM 83 temporarily stores data as necessary when the CPU 81 executes a routine. The backup RAM 84 appropriately stores data under the control of the CPU 81 in a state where the power is turned on, and retains the stored data even after the power is shut off.

  The interface 85 includes the throttle opening sensor 15b, the O2 sensor 18, the pressure sensors 46a and 46b, the temperature sensors 47a and 47b, and other sensors (crank angle sensor, cam angle sensor, air flow meter) provided in the system. , A cooling water temperature sensor, a vehicle speed sensor, an accelerator sensor, and the like), and outputs (detection signals) from these sensors to the CPU 81. Further, the interface 85 is electrically connected to driving units such as the throttle actuator 15a, the ignition device 20a, the injection valves 21 and 22, the tank main stop valve 44, the shutoff valve 45 and the like, and a drive signal sent from the CPU 81. Are output to the drive unit to drive these drive units. That is, the control unit 80 acquires the operating state of the engine 10 based on the output signals of the above-described sensors, and implements the above-described driving unit control based on the acquired operating state.

  Specifically, for example, a target air amount of the engine 10 is calculated based on an accelerator operation amount detected by an accelerator sensor, an engine rotation speed detected by a crank angle sensor, and the like, and based on the calculated value, the throttle actuator 15a Control the drive. Further, the fuel injection amount is calculated based on the engine rotation speed, the intake air amount (engine load) detected by the air flow meter, and the like, and the driving of the injection valves 21 and 22 is controlled based on the calculated value. Further, the optimal ignition timing is calculated based on the engine rotation speed, the intake air amount, and the like, and the drive of the ignition device 20a is controlled so that ignition is performed at the optimal ignition timing.

  In particular, regarding the fuel injection amount control, the control unit 80 performs air-fuel ratio stoichiometric feedback control based on the detection signal of the O2 sensor 18. That is, the control unit 80 calculates a feedback correction amount according to whether the actual air-fuel ratio detected by the O2 sensor 18 is lean or rich, and increases or decreases the fuel injection amount by the feedback correction amount. Thus, the actual air-fuel ratio is feedback-controlled to stoichiometric (theoretical air-fuel ratio) that is the target air-fuel ratio. It is also possible to provide an O2 sensor on the downstream side of the catalyst 19 and perform the sub-feedback control of the air-fuel ratio using the detection value of the downstream O2 sensor. In this sub-feedback control, the fuel injection amount is increased or decreased based on the lean / rich state on the downstream side of the catalyst.

  In the present embodiment, so-called dual injection, in which gaseous fuel (CNG) and liquid fuel (gasoline) are used at the same time, can be performed. Depending on the state of the vehicle and the engine 10 or the like, the dual injection can be performed. The fuel mixing ratio (the injection ratio is also agreed) is controlled. Specifically, the control unit 80 adjusts the fuel mixing ratio according to the rotational speed and load of the engine 10, and when the engine rotational speed or load is large and the engine rotational speed or load is small. Compared with gas fuel, the mixing ratio is reduced. This is because the volume of the gaseous fuel is larger than that of the liquid fuel when compared with the same amount of fuel, and the liquid fuel is used in addition to the gaseous fuel when the engine 10 is at high rotation and high load. Thus, proper fuel injection is possible in a limited period in the combustion cycle. Further, in the configuration in which the remaining amount of fuel in the tank can be monitored, for example, when the remaining amount of gaseous fuel in the gas tank 42 falls below a predetermined value, the mixing ratio of the liquid fuel is increased or the inside of the fuel tank 52 is increased. When the remaining amount of the liquid fuel falls below a predetermined value, the mixing ratio of the gaseous fuel may be increased.

  Next, the configuration of the O2 sensor 18 will be described. The O2 sensor 18 has a sensor element 61 having a cup-type structure, and FIG. Actually, the sensor element 61 is configured so that the entire element is accommodated in a housing or an element cover, and is disposed in the exhaust pipe 17. The sensor element 61 corresponds to an electromotive force cell.

  In the sensor element 61, the solid electrolyte layer 62 is formed in a cup shape in cross section, an exhaust side electrode 63 is provided on the outer surface, and an atmosphere side electrode 64 is provided on the inner surface. These electrodes 63 and 64 are provided in a layered manner on the surface of the solid electrolyte layer 62. The solid electrolyte layer 62 is made of an oxygen ion conductive oxide sintered body in which CaO, MgO, Y2O3, Yb2O3 or the like is dissolved as a stabilizer in ZrO2, HfO2, ThO2, Bi2O3 or the like. Each of the electrodes 63 and 64 is made of a noble metal having high catalytic activity such as platinum, and the surface thereof is subjected to porous chemical plating or the like. Each electrode 63, 64 is a pair of counter electrodes (sensor electrodes). An internal space surrounded by the solid electrolyte layer 62 is an atmospheric chamber 65 (reference chamber), and a heater 66 is accommodated in the atmospheric chamber 65. The heater 66 has a heat generation capacity sufficient to activate the sensor element 61, and the entire sensor element is heated by the heat generation energy. The activation temperature of the O2 sensor 18 is, for example, about 500 to 650 ° C. The atmosphere chamber 65 is maintained at a predetermined oxygen concentration by introducing the atmosphere.

  In the sensor element 61, the outer side (electrode 63 side) of the solid electrolyte layer 62 is an exhaust atmosphere, and the inner side (electrode 64 side) is an air atmosphere, and the difference in oxygen concentration between them (difference in oxygen partial pressure). Accordingly, an electromotive force is generated between the electrodes 63 and 64. That is, different electromotive forces are generated depending on whether the air-fuel ratio is rich or lean. In this case, from the atmosphere side electrode 64 which is the reference side electrode, the exhaust side electrode 63 side has a low concentration of oxygen. In the sensor element 61, the atmosphere side electrode 64 is the positive side and the exhaust side electrode 63 is the negative side. An electromotive force is generated. Thereby, the O2 sensor 18 outputs an electromotive force signal corresponding to the oxygen concentration (that is, the air-fuel ratio) of the exhaust gas.

  FIG. 3 is an electromotive force characteristic diagram showing the relationship between the air-fuel ratio of the exhaust gas and the electromotive force of the sensor element 61. In FIG. 3, the horizontal axis is the excess air ratio λ, and λ = 1 is the stoichiometric (theoretical air-fuel ratio). The sensor element 61 generates different electromotive force depending on whether the air-fuel ratio is rich or lean, and has a characteristic that the electromotive force changes suddenly near the stoichiometric range. Specifically, the sensor electromotive force at the time of rich is about 0.9V, and the sensor electromotive force at the time of lean is about 0V.

  In FIG. 2, a control unit 80 is connected to the atmosphere side electrode 64 of the sensor element 61. When an electromotive force is generated in the sensor element 61 in accordance with the air-fuel ratio (oxygen concentration) of the exhaust, it corresponds to the electromotive force. A sensor detection signal (electromotive force signal) to be output is output to the control unit 80. The control unit 80 (CPU 81) performs rich / lean determination of the air-fuel ratio based on the electromotive force signal of the sensor element 61, and controls the fuel injection amount based on the determination result.

  Further, the control unit 80 determines the active state of the sensor element 61 and controls the driving of the heater 66 through the driving unit 71 based on the determination result. Since the activation determination and the heater control are well known, they will be briefly described here. The controller 80 changes the voltage or current applied to the sensor element 61 in an alternating manner, and detects a current change or a voltage change that occurs accordingly. Then, the element resistance (element impedance) of the sensor element 61 is calculated based on the current change or voltage change, and energization control of the heater 66 is performed based on the element resistance. At this time, there is a correlation between the active state (that is, the element temperature) of the sensor element 61 and the element resistance, and the element resistance is controlled to a predetermined target value, whereby the sensor element 61 is in a desired active state (active temperature 500). To a state of ˜650 ° C.). As heater control, for example, element temperature feedback control may be performed.

  By the way, H2 (hydrogen) is present in the exhaust gas, and particularly when CNG mainly composed of methane is used, a large amount of H2 is present in the exhaust gas. In this case, since H2 has a higher moving speed than O2, if H2 and O2 exist in the exhaust gas, H2 reaches the exhaust-side electrode 63 of the O2 sensor 18 before O2 and O2 Electrode arrival (detection of O2) is inhibited. As a result, the O2 detection sensitivity of the O2 sensor 18 is lowered, and there is a risk that erroneous detection is made if the air-fuel ratio (exhaust atmosphere) is rich despite being lean. This will be supplementarily described with reference to FIG. 4A shows the O2 sensor output characteristic and the exhaust purification rate when gasoline is burned, and FIG. 4B shows the O2 sensor output characteristic and the exhaust purification rate when CNG is burned. . In addition, the output characteristic in the case of gasoline is shown with the dashed-dotted line for the comparison in the O2 sensor output characteristic of FIG.4 (b).

  When gasoline is burned, the output of the O2 sensor 18 changes suddenly due to stoichiometry (excess air ratio λ = 1). That is, λ = 1 is a rich / lean inflection point. Further, the window (shaded portion in the figure) defined by the exhaust gas purification rate of the catalyst 19 is approximately equal to λ = 1.

  On the other hand, when CNG is burned, the output of the O2 sensor 18 changes abruptly on the lean side of the stoichiometric (excess air ratio λ = 1). That is, the lean side is the inflection point of rich / lean from λ = 1. Therefore, the relationship between the window (purification characteristic) of the catalyst 19 and the output characteristic (O2 sensor inflection point) of the O2 sensor 18 is different from that of gasoline, and as a result, the air-fuel ratio using the detection value of the O2 sensor 18 is different. The feedback control is affected. It is also known that when CNG is burned, the relationship between the best purification point of the catalyst 19 and the output inflection point of the O2 sensor 18 is shifted by several percent with respect to λ.

  Also, assuming that CNG and gasoline are used simultaneously (when dual injection is performed), the O2 sensor output characteristics change according to the mixing ratio of CNG and gasoline, and the larger the mixing ratio of CNG, The characteristic shift toward the lean side is large. In short, the sensor output characteristics change according to the composition (mixing ratio) of the fuel to be used, and the change in the output characteristics affects the air-fuel ratio feedback control.

  FIG. 5 is a time chart for explaining a difference when air-fuel ratio feedback control is performed on a fuel having a high gasoline ratio and a fuel having a high CNG ratio.

  As shown in FIG. 5 (a), when the gasoline ratio is high, the output changes as the air-fuel ratio crosses the O2 sensor inflection point, and thereby the rich / lean determination is performed. An injection correction amount (feedback correction amount) is calculated based on the rich / lean determination result. In this case, if the rich determination is made, the injection correction amount is integrated to the decrease side by a predetermined amount, and the injection correction amount is skipped to the increase side when the air-fuel ratio is reversed to the lean side. If the lean determination is made, the injection correction amount is integrated to the increase side by a predetermined amount, and the injection correction amount is skipped to the decrease side when the air-fuel ratio is reversed to the rich side. As a result, the excess air ratio λ is evenly amplified on the rich side and the lean side around λ = 1.

  On the other hand, as shown in FIG. 5B, when the CNG ratio is high, the inflection point of the O2 sensor 18 is shifted to the lean side, so that even lean is actually determined to be rich ( The hatched area in the figure is an area that is actually lean but is richly determined). In this case, the rich correction is made even though the actual air-fuel ratio is lean, so that the injection correction amount shifts to the decrease side, resulting in a lean shift of the excess air ratio λ.

  Here, as a countermeasure against the lean deviation of the air-fuel ratio due to the deviation of the inflection point of the O2 sensor 18, it is conceivable to make the injection correction amount (feedback gain) asymmetric between the increase side and the decrease side. Specifically, as shown in FIG. 6, the control center is shifted to the rich side with respect to the control center before the countermeasure by setting the skip amount ΔS1 to the increase side to be larger than the skip amount ΔS2 to the decrease side. As a result, the deviation of the O2 sensor inflection point is offset by the rich shift of the injection correction amount, and the fluctuation center of the excess air ratio λ becomes λ = 1.

  However, in the configuration in which the injection correction amount is asymmetrical between the increase side and the decrease side as described above, the feedback period changes or the amplitude of the air-fuel ratio fluctuation due to feedback increases, which may lead to deterioration of drivability. .

  Therefore, in the present embodiment, as a countermeasure against the lean deviation of the air-fuel ratio due to the deviation of the inflection point of the O2 sensor 18, the adjustment of the injection correction amount (that is, the adjustment of the feedback gain) is not performed, and the sensor element 61 of the O2 sensor 18 is used. The deviation of the O2 sensor inflection point is corrected by passing a predetermined current between the pair of electrodes 63 and 64. That is, by passing a current in a predetermined direction between the pair of electrodes of the sensor element 61, as shown in FIG. 7, the excess air ratio λ is centered around λ = 1 without shifting the injection correction amount to the rich side. Thus, the amplitude is evenly distributed between the rich side and the lean side.

  The principle that the inflection point deviation is corrected (that is, the sensor output characteristics are changed) by flowing a current between the pair of electrodes 63 and 64 is as follows. As shown in FIG. 8, CO, HC, NOx, O2, and H2 exist in the vicinity of the exhaust side electrode 63 of the O2 sensor 18, and particularly, H2 generated by burning CNG is exhaust side electrode 63. Adhering to Under such circumstances, a current is passed through the sensor element 61 so that oxygen ions move from the atmosphere side electrode 64 to the exhaust side electrode 63 through the solid electrolyte layer 62. That is, oxygen pumping is performed in the sensor element 61. In this case, in the exhaust side electrode 63, oxygen moved to the exhaust side electrode 63 side through the solid electrolyte layer 62 reacts with H2, and H2O is generated. Thereby, H2 adhering to the exhaust side electrode 63 is removed, and the O2 sensitivity in the sensor element 61 is increased. That is, the deviation of the O2 sensor inflection point is corrected, and the inconvenience that the rich determination is made despite the actual air-fuel ratio being lean is solved.

  Next, a configuration for supplying a predetermined current to the sensor element 61 of the O2 sensor 18 will be described. As shown in FIG. 2, a constant current circuit 72 as an energization means is connected in the middle of an electrical path that electrically connects the atmosphere side electrode 64 of the sensor element 61 and the control unit 80, and the constant current circuit. Reference numeral 72 denotes a sensor element 61 that allows a constant current Ics to flow from the exhaust side electrode 63 toward the atmosphere side electrode 64 through the solid electrolyte layer 62. The constant current circuit 72 has a PWM drive unit, and the current amount can be adjusted by PWM control (duty control). The control unit 80 sets the constant current Ics (energization amount) of the constant current circuit 72 based on each energization request, and controls the constant current circuit 72 so that a current corresponding to the Ics flows.

  In the present embodiment, when dual injection is performed, the mixing ratio (injection ratio) of gaseous fuel (CNG) and liquid fuel (gasoline) is determined as the fuel composition, and a constant current is determined based on the mixing ratio. The constant current Ics of the circuit 72 is determined. The constant current Ics is calculated as an energization amount corresponding to the amount of deviation between the window of the catalyst 19 and the output inflection point of the O2 sensor 18.

  Further, in the configuration in which the output characteristics of the O2 sensor 18 are changed by energizing the constant current circuit 72 as described above, if an abnormality occurs in the constant current circuit 72, the exhaust emission performance is affected. Therefore, in the present embodiment, an abnormality determination function for performing abnormality determination on the constant current circuit 72 is added to the control unit 80.

  As a configuration used for abnormality detection, a current detecting shunt resistor 73 is connected to the exhaust side electrode 63 as shown in FIG. 2, and a current flowing through the shunt resistor 73 is detected by a current detecting unit 74. The current detection unit 74 may be configured by a differential amplifier circuit using, for example, an operational amplifier. In this case, according to the shunt resistor 73 and the current detection unit 74, the actual current amount flowing by the constant current circuit 72 is detected, and the control unit 80 performs abnormality determination of the constant current circuit 72 based on the actual current amount.

  In this embodiment, the feedback gain of the air-fuel ratio control is changed depending on whether the constant current circuit 72 is abnormal. When the constant current circuit 72 is normal, the increase side and the decrease side The feedback gain is controlled to be the same (see FIG. 7), and when the constant current circuit 72 is abnormal, the feedback gain is controlled to be different between the increasing side and the decreasing side (see FIG. 7). 6). In other words, when the constant current circuit 72 is normal, a constant current is passed through the sensor element 61 to deal with the inflection point deviation (characteristic error) of the O2 sensor 18, and when the constant current circuit 72 is abnormal, the feedback gain is set. By adjusting, the inflection point shift (characteristic error) of the O2 sensor 18 is dealt with.

  Next, constant current control and abnormality determination processing of the constant current circuit 72 will be described. FIG. 9 is a flowchart showing a processing procedure of constant current control, and this processing is repeatedly performed by the control unit 80 at a predetermined cycle.

  In FIG. 9, in step S <b> 11, it is determined whether or not a constant current control execution condition is satisfied. The implementation conditions include, for example, that both the O2 sensor 18 and the constant current circuit 72 are normal. If step S11 is YES, the process proceeds to step S12. When step S11 is NO, this process is ended as it is. That is, when the constant current circuit 72 is abnormal, the sensor element 61 is not energized by the constant current circuit 72.

  In step S12, the mixing ratio of gaseous fuel (CNG) and liquid fuel (gasoline) is read. This mixing ratio is calculated based on the engine operating state or the like in a fuel injection control process (not shown), and corresponds to the actual injection ratio of each of the injection valves 21 and 22. Thereafter, in step S13, an instruction current (Ics) to the constant current circuit 72 is set based on the fuel mixture ratio. At this time, for example, the command current is set based on the relationship of FIG. In FIG. 10, a larger current value is set as the command current as the fuel CNG ratio is larger. The command current is calculated as an energization amount corresponding to a deviation amount between the window of the catalyst 19 and the output inflection point of the O2 sensor 18.

  Thereafter, in step S14, the constant current circuit 72 is controlled (energization control) so that the command current set in step S13 flows through the sensor element 61.

  FIG. 11 is a flowchart showing a processing procedure of abnormality determination of the constant current circuit 72, and this processing is repeatedly performed by the control unit 80 at a predetermined cycle.

  In FIG. 11, in step S <b> 21, it is determined whether an abnormality determination execution condition is satisfied. The implementation conditions include, for example, that the sensor element 61 is in an active state, that is, the temperature (element temperature) of the sensor element 61 is equal to or higher than a predetermined activation temperature. If step S21 is YES, the process proceeds to step S22.

  In step S <b> 22, an instruction current for the constant current circuit 72 at the present time and an actual current detected by the shunt resistor 73 and the current detection unit 74 are read. At this time, if the instruction current is switched, the actual current is detected and read after the actual current converges. Specifically, the actual current is detected after a predetermined time has elapsed from the switching of the instruction current, and the detected value is read into the control unit 80.

  In the subsequent step S23, the command current and the actual current are compared, and it is determined whether or not the difference (absolute value) between the two is smaller than a predetermined determination value K. The determination value K may be determined in consideration of circuit tolerance (for example, tolerance of the sensor IC). If | indicated current−actual current | <K, it is determined in step S24 that the constant current circuit 72 is normal. In the subsequent step S25, a command is issued to make the feedback gain of the air-fuel ratio control the same on the increase side and the decrease side (see FIG. 7).

  If | indicated current−actual current | ≧ K, it is determined in step S26 that the constant current circuit 72 is abnormal. In the subsequent step S27, a command is given to make the feedback gain of the air-fuel ratio control different between the increase side and the decrease side. Specifically, as shown in FIG. 6, the feedback gain is made asymmetric between the increase side and the decrease side by making the skip amount ΔS1 to the increase side larger than the skip amount ΔS2 to the decrease side. Thereafter, in step S28, as other fail-safe processing, energization stop by the constant current circuit 72, lighting of an abnormality warning lamp provided in an instrument panel, storage of diagnostic data, and the like are performed.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  In the above configuration, the constant current circuit 72 allows a constant current to flow through the solid electrolyte layer 62 of the sensor element 61, thereby suppressing a change in output characteristics of the O 2 sensor 18 due to the use of gaseous fuel. In particular, since the mixing ratio (fuel composition) of the gaseous fuel and the liquid fuel is determined and the energization by the constant current circuit 72 is controlled based on the mixing ratio, even if the mixing ratio of the fuel is different each time, Accordingly, the output characteristics of the O2 sensor 18 can be changed. As a result, it is possible to appropriately change the output characteristics of the O2 sensor 18 when using gaseous fuel, and to suppress the occurrence of inconvenience due to the deviation of the sensor output characteristics.

  Further, the energization amount (constant current Ics) of the constant current circuit 72 calculated based on the fuel mixture ratio was set as the energization amount corresponding to the deviation amount between the window of the catalyst 19 and the output inflection point of the O2 sensor 18. Thereby, the deviation between the window of the catalyst 19 and the sensor output inflection point, which is caused by mixing the gaseous fuel with the liquid fuel, can be preferably eliminated, and as a result, highly accurate air-fuel ratio control can be performed. That is, even if the fuel composition is different, good purification performance with the catalyst 19 can be maintained.

  When dual injection is performed, the amount of change in the output characteristic of the O2 sensor 18 (the amount of deviation of the inflection point) differs depending on the mixing ratio (injection ratio) between the gaseous fuel and the liquid fuel. In this respect, since the energization amount by the constant current circuit 72 is determined based on the mixing ratio (injection ratio) of the gas fuel and the liquid fuel, even if the mixing ratio is different, appropriate air-fuel ratio control is performed each time. Can be implemented.

  The larger the gas fuel mixing ratio (injection ratio), the greater the amount of H2 in the exhaust. Focusing on this point, the energization amount to the sensor element 61 is increased as the mixing ratio (injection ratio) of the gaseous fuel is increased. As a result, even if the mixing ratio of the gaseous fuel is increased and the amount of H2 in the exhaust gas is increased and the deviation of the output inflection point of the O2 sensor 18 is increased, the deviation of the output inflection point is appropriately anticipated. Can be eliminated.

  As a countermeasure against the deviation of the air-fuel ratio in the fuel injection control due to the difference in fuel composition, when it is determined that the constant current circuit 72 is normal, the constant current circuit 72 is energized, and the constant current circuit 72 is abnormal. When it is determined that there is, the fuel increase / decrease amount is adjusted by the feedback gain (feedback correction amount). As a result, the air-fuel ratio can be appropriately controlled regardless of whether the constant current circuit 72 is abnormal.

  Note that if the feedback gain is made asymmetric between the increase side and the decrease side, drivability may be deteriorated. However, since adjustment of the feedback gain is performed only when the constant current circuit 72 is abnormal, the constant current circuit 72 In normal times when no abnormality occurs, drivability deterioration due to feedback gain adjustment does not occur.

(Other embodiments)
You may change the said embodiment as follows, for example.

  In the above embodiment, the case of performing dual injection in which gaseous fuel (CNG) and liquid fuel (gasoline) are used at the same time is illustrated, but the gaseous fuel mode using only gaseous fuel and the liquid fuel only are used. Switching to the liquid fuel mode may be performed. Switching between these modes may be performed according to the remaining amount of fuel in the tank, an input signal from a fuel selection switch (not shown), or the like.

  In such a case, the constant current control process shown in FIG. 12 is performed. Note that FIG. 12 is obtained by changing a part of FIG. 9 described above, and the difference is only step S21. In step S21 of FIG. 12, it is determined whether or not the present is the gaseous fuel mode. And if it is gaseous fuel mode, it will progress to subsequent step S13 and will energize by the constant current circuit 72. FIG. On the other hand, in the liquid fuel mode, the process is terminated without performing the energization by the constant current circuit 72. It should be noted that, in the case of the gas fuel mode, the dual injection is allowed to be performed. When the dual injection is performed, the constant current circuit 72 is configured based on the fuel mixing ratio (injection ratio) as described above. The energization amount may be controlled.

  In short, when either gaseous fuel or liquid fuel is used, there is no change in the output characteristics of the O2 sensor 18 (shift of the inflection point) if liquid fuel is used, and if gaseous fuel is used, It is considered that a change in the output characteristics of the O2 sensor 18 (inflection point shift) occurs. In this respect, since it is configured to determine whether or not to energize the constant current circuit 72 based on whether gaseous fuel or liquid fuel is used, even if the fuel used is different, an appropriate empty space is used each time. Fuel ratio control can be implemented.

  -When switching from the gaseous fuel mode to the liquid fuel mode, it is conceivable that exhaust from combustion of gaseous fuel remains in the exhaust pipe immediately after the switching. Therefore, when the gas fuel mode is switched to the liquid fuel mode, the constant current circuit 72 may be energized for a predetermined time immediately after the mode switching. Alternatively, the configuration may be such that after the mode is switched, the energization amount of the constant current circuit 72 is gradually reduced to zero.

  ・ It is also possible that the components of the exhaust gas differ due to the different components of the gaseous fuel itself. For example, if the ratio of methane, propane, butane, etc., which are the main components of gaseous fuel, is different, the fuel composition will be different. In this case, the amount of hydrogen in the exhaust gas is considered to change due to the difference in the fuel composition, so the amount of change in the output characteristics of the O2 sensor 18 (the amount of deviation of the inflection point) also changes. Therefore, it is preferable to determine the component of the gaseous fuel as the determination of the fuel composition, and to control the energization of the constant current circuit 72 based on the determination result. Thereby, even if the components of the gaseous fuel are different, appropriate air-fuel ratio control can be performed each time.

  Note that it is conceivable that the determination of the component of the gaseous fuel is performed based on information received from the replenishment facility side at the time of refueling, for example. That is, when replenishing gaseous fuel at the gas station, component information of the gaseous fuel being replenished is acquired from the equipment on the gas station side, and the information is stored in the memory. Based on the component information, energization of the constant current circuit 72 is controlled.

  In the above embodiment, the constant current circuit 72 is connected to the atmosphere side electrode 64 of the pair of electrodes 63 and 64 of the sensor element 61, but this may be changed. The constant current circuit 72 may be provided connected to the exhaust side electrode 63. Alternatively, the constant current circuit 72 may be provided on both the pair of electrodes 63 and 64.

  The gas sensor may be a so-called two-cell gas sensor including an electromotive force cell and a pump cell in addition to the O2 sensor 18 having the above-described configuration. In this case, the output characteristics can be suitably changed for the electromotive force cell of the two-cell type gas sensor.

  DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 18 ... O2 sensor (exhaust sensor), 21 ... 1st injection valve (fuel injection means), 22 ... 2nd injection valve (fuel injection means), 61 ... Sensor element (electromotive force cell) , 62 ... solid electrolyte layer, 63 ... exhaust side electrode, 64 ... atmosphere side electrode, 72 ... constant current circuit (energization means), 80 ... control unit (composition determination means, conduction control means).

Claims (7)

The exhaust gas is applied to an internal combustion engine (10) comprising at least fuel injection means (21, 22) for injecting gaseous fuel and an exhaust sensor (18) for outputting a detection signal corresponding to the oxygen concentration in the exhaust. A fuel injection control system for an internal combustion engine for controlling a fuel injection amount by the fuel injection means based on a detection result of a sensor,
The exhaust sensor has an electromotive force cell (61) using a solid electrolyte body (62) and a pair of electrodes (63, 64), and generates an electromotive force according to the oxygen concentration in the exhaust. And
Energization means (72) for changing the output characteristics of the exhaust sensor by passing a current through the solid electrolyte body in the electromotive force cell;
Composition determining means (80) for determining the composition of fuel injected by the fuel injection means;
An energization control means (80) for controlling energization by the energization means based on the fuel composition determined by the composition determination means;
A fuel injection control system for an internal combustion engine. The exhaust part of the internal combustion engine is provided with a catalyst (19) for purifying rich components and lean components in the exhaust,
The energization control means includes
Means for calculating an energization amount corresponding to a deviation amount between an air-fuel ratio window at which a high purification rate is obtained in the catalyst and an output inflection point of the exhaust sensor based on the fuel composition determined by the composition determination means;
The fuel injection control system for an internal combustion engine according to claim 1, further comprising means for controlling energization by the energization means based on the calculated energization amount. The fuel injection means has a gaseous fuel injection valve (21) for injecting gaseous fuel and a liquid fuel injection valve (22) for injecting liquid fuel, and the simultaneous use of fuel injected from each of these injection valves Applied to possible internal combustion engines,
The composition determination means determines an injection ratio between the gaseous fuel injected from the gaseous fuel injection valve and the liquid fuel injected from the liquid fuel injection valve for the fuel supplied into the combustion chamber as the determination of the fuel composition. Is what
The fuel injection control system for an internal combustion engine according to claim 1, wherein the energization control unit controls energization by the energization unit based on the injection ratio. One of the pair of electrodes in the electromotive force cell is a reference side electrode (64) that becomes a positive side when an electromotive force is output, and the other is an exhaust side electrode (63) that becomes a negative side when an electromotive force is output,
The energization means is configured to flow a current from the exhaust side electrode toward the reference side electrode through the solid electrolyte body in the electromotive force cell,
4. The fuel injection control system for an internal combustion engine according to claim 3, wherein the energization control means increases the current from the exhaust side electrode to the reference side electrode as the injection ratio of the gaseous fuel to the liquid fuel increases. The fuel injection means includes a gaseous fuel injection valve (21) for injecting gaseous fuel and a liquid fuel injection valve (22) for injecting liquid fuel, and enables fuel injection using these injection valves. Applied to internal combustion engines,
The composition determination means determines whether the fuel supplied into the combustion chamber includes gaseous fuel or does not include gaseous fuel as the determination of the fuel composition.
The energization control means performs energization by the energization means if the fuel supplied into the combustion chamber contains gaseous fuel, and energizes by the energization means if it does not contain gaseous fuel. The fuel injection control system for an internal combustion engine according to claim 1 or 2, wherein: An internal combustion engine that calculates a feedback correction amount based on a deviation between a detection result of the air-fuel ratio detected by the exhaust sensor and a target air-fuel ratio, and controls the fuel injection amount by the fuel injection means using the feedback correction amount. A fuel injection control system,
An abnormality determining means (80) for determining presence or absence of abnormality in the energizing means;
As a countermeasure against the deviation of the air-fuel ratio in the fuel injection control due to the difference in fuel composition, when the energization means is determined to be normal by the abnormality determination means, the energization means is energized by the energization control means. And when it is determined that the energizing means is abnormal, a control switching means (80) for adjusting the fuel increase / decrease amount by the feedback correction amount;
A fuel injection control system for an internal combustion engine according to any one of claims 1 to 5.   When it is determined that the energization unit is normal, the control switching unit calculates the feedback correction amount with the same feedback gain on the fuel increase side and the fuel decrease side, and determines that the energization unit is abnormal. The fuel injection control system for an internal combustion engine according to claim 6, wherein, when performed, the feedback correction amount is calculated by feedback gains that are different between the fuel increase side and the fuel decrease side.

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