JP5361803B2 - Fuel injection control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control system which can perform failure diagnosis by always monitoring a state of an oxygen sensor and continue satisfactory air-fuel ratio feedback control even during failure diagnosis. <P>SOLUTION: A control unit C sets a normal limit range L2 as upper and lower values whose usage is permitted for calculating a correction injection amount T1 to an air-fuel ratio feedback correction factor KO2 and executes failure diagnosis of an oxygen sensor 32 when it is sensed that output of the oxygen sensor 32 is made to be a prescribed state during normal operation of an internal combustion engine E and sets a limit range L3 upon failure smaller than the limit range L2 upon normal operation during execution of failure diagnosis. The control unit C starts failure diagnosis of the oxygen sensor 32 if a prescribed time has passed in a state that output value of the oxygen sensor 32 is nearly 0V or when a prescribed time has passed in a state that the output value of the oxygen sensor 32 is nearly 3V. When it is determined that the oxygen sensor 32 is normal, the limit range is returned from the limit range L3 upon failure to the normal limit range L2. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a fuel injection control apparatus, and more particularly to a fuel injection control apparatus that performs air-fuel ratio feedback control based on an air-fuel ratio sensor output.

  Conventionally, in order to burn an internal combustion engine in a region near the stoichiometric air-fuel ratio (stoichiometric), the fuel injection amount is feedback controlled based on the air-fuel ratio detected by an air-fuel ratio sensor (oxygen sensor) provided in the exhaust pipe. There is known a fuel injection device. In such a fuel injection device, in order to continue good air-fuel ratio feedback control, it is conceivable to perform a failure diagnosis of the oxygen sensor during operation of the internal combustion engine.

  In Patent Document 1, in a fuel injection control device in which an oxygen sensor is provided in each exhaust pipe of a two-cylinder engine and air-fuel ratio feedback control is performed for each cylinder, a failure diagnosis of one oxygen sensor is performed. In the meantime, a configuration is disclosed in which failure diagnosis of the other oxygen sensor is not performed. According to this technique, it is possible to avoid a situation in which the failure diagnosis of the two oxygen sensors is executed at the same time and the air-fuel ratio feedback control becomes impossible for both of the two cylinders.

JP 2007-315305 A

  However, since the technique described in Patent Document 1 performs failure diagnosis by observing a current generated when a reverse voltage is applied to the oxygen sensor, the failure diagnosis can be executed only periodically. It was not possible to constantly monitor the state of. If the configuration is such that learning of the air-fuel ratio feedback correction coefficient is prohibited during failure diagnosis, the output value of the oxygen sensor immediately before entering the failure diagnosis may be used for air-fuel ratio feedback control during failure diagnosis. In the case where the oxygen sensor has failed immediately before entering the failure diagnosis, the combustion state during the failure diagnosis may become excessively rich or lean.

  An object of the present invention is to solve the above-described problems of the prior art, and to perform fuel diagnosis by constantly monitoring the state of the oxygen sensor and enabling good air-fuel ratio feedback control to be continued even during failure diagnosis. To provide an apparatus.

  In order to achieve the above object, the present invention obtains a target air-fuel ratio based on an output of an oxygen sensor (32) provided in an exhaust device (15) of an internal combustion engine (E) as a power source of a vehicle. A control means for determining a correction injection amount (T1) by calculating an air-fuel ratio feedback correction coefficient (KO2) used for the feedback control of the engine and multiplying the basic injection amount (T0) by the air-fuel ratio feedback correction coefficient (KO2) ( In the fuel injection control apparatus having C), the control means (C), when the internal combustion engine (E) is in normal operation, supplies the corrected injection amount (T1) to the air-fuel ratio feedback correction coefficient (KO2). When a normal limit range (L2) is set as an upper and lower limit value that is permitted to be used for calculation, and it is detected that the output of the oxygen sensor (32) is in a predetermined state. Run the failure diagnosis of the oxygen sensor (32), wherein during the execution of the failure diagnosis, there is a first feature that sets the normal limit range (L2) less than the failure time of the limit range (L3).

  Further, the control means (C) passes a predetermined time when the output value of the oxygen sensor (32) is substantially 0V, or passes a predetermined time when the output value of the oxygen sensor (32) is substantially 3V. Then, the second feature is that a failure diagnosis of the oxygen sensor (32) is started.

  The control means (C) executes fuel injection for failure diagnosis when failure diagnosis is started after a predetermined time has elapsed with the output value of the oxygen sensor (32) being substantially 0V. A third feature is that a failure determination is performed by detecting a change in the output of the oxygen sensor (32) with respect to the fuel injection.

  Further, when it is determined by the failure diagnosis that the oxygen sensor (32) is normal, the control means (C) terminates the failure diagnosis and determines the normal limit from the limit range (L3) at the time of the failure. There is a fourth feature in returning to the range (L2).

  The air-fuel ratio feedback control is executed by PID control with respect to the target output value of the oxygen sensor (32), and the air-fuel ratio feedback correction coefficient (KO2) corresponds to the functional limit of the oxygen sensor (32). An upper gain switching threshold (HI) and a lower gain switching threshold (LO) are set, and the control means (C) has the air / fuel ratio feedback correction coefficient (KO2) set the upper gain switching threshold (HI). There is a fifth feature in that the gain of the PID control is reduced when it exceeds or falls below the lower gain switching threshold (LO).

  The basic injection amount (T0) is determined by the throttle opening (TH) of the throttle valve (21) provided in the intake device (14) of the internal combustion engine (E) and the rotational speed of the internal combustion engine (E) ( NE) is derived from a basic injection amount map (33) that defines the relationship between NE and the basic injection amount (T0).

  Further, the normal limit range (L2) has a predetermined vertical width from the reference value (Ba), and the limit range (L3) at the time of failure is maintained with the reference value (Ba). The seventh feature is that the upper limit value (MAXa) and the lower limit value (MINa) of the normal limit range (L2) are respectively reduced at a predetermined rate.

  Further, when the control means (C) determines that the oxygen sensor (32) is in failure by the failure diagnosis, a predetermined air-fuel ratio feedback correction coefficient (KO2) that is between the limit range (L3) at the time of failure. There is an eighth feature in that the corrected injection amount (T1) is determined by using as an alternative value.

  According to the first feature, the control means, during normal operation of the internal combustion engine, uses the second limit as an upper and lower limit value permitted to be used for calculating the corrected injection amount with respect to the air-fuel ratio feedback correction coefficient. When the range is set, and it is detected that the output of the oxygen sensor is in a predetermined state, a failure diagnosis of the oxygen sensor is executed. During the failure diagnosis, a third limit range smaller than the second limit range is set. Therefore, it is possible to quickly detect a failure of the oxygen sensor by constantly monitoring the oxygen sensor output. In addition, during the execution of failure diagnosis, the fuel injection amount is calculated using the third limit range smaller than normal, so even if the oxygen sensor has failed at the start of failure diagnosis, the reliability immediately before failure diagnosis is A low air-fuel ratio feedback correction coefficient is not applied during failure diagnosis, and an excessive rich or lean state can be prevented during failure diagnosis.

  According to the second feature, the control means causes a failure of the oxygen sensor when a predetermined time elapses when the output value of the oxygen sensor is approximately 0 V, or when a predetermined time elapses when the output value of the oxygen sensor is approximately 3 V. Since diagnosis is started, it is possible to promptly proceed to failure diagnosis based on the output value of the oxygen sensor.

  According to the third feature, the control means executes fuel injection for failure diagnosis when the failure diagnosis is started after a predetermined time has elapsed with the output value of the oxygen sensor being substantially 0 V, Since the failure determination is performed by detecting the change in the output of the oxygen sensor with respect to the injection, it is possible to easily determine the failure of the oxygen sensor.

  According to the fourth feature, when it is determined by the failure diagnosis that the oxygen sensor is normal, the control unit ends the failure diagnosis and returns the third limit range to the second limit range. When the sensor is normal, it is possible to quickly return to normal air-fuel ratio feedback control.

  According to the fifth feature, the air-fuel ratio feedback control is executed by PID control with respect to the target output value of the oxygen sensor, and the air-fuel ratio feedback correction coefficient includes an upper gain switching threshold value corresponding to the function limit of the oxygen sensor and a lower side. A gain switching threshold is set, and the control means reduces the gain of PID control when the air-fuel ratio feedback correction coefficient exceeds the upper gain switching threshold or falls below the lower gain switching threshold. When the PID control gain is increased to enable feedback control with a high response speed, and when the air-fuel ratio feedback correction coefficient fluctuates greatly, the response speed is decreased by decreasing the PID control gain. Low-reliability air-fuel ratio feedback correction factor when the sensor has failed It is possible to prevent a major impact.

  According to the sixth feature, the basic injection amount is derived from a basic injection amount map that defines the relationship among the throttle opening of the throttle valve provided in the intake device of the internal combustion engine, the rotational speed of the internal combustion engine, and the basic injection amount. Therefore, the basic injection amount is obtained without considering the values of the intake pressure and the atmospheric pressure, and effective air-fuel ratio feedback control can be performed in a vehicle that does not have the intake pressure sensor or the atmospheric pressure sensor.

  According to the seventh feature, the normal limit range has a predetermined vertical width from the reference value, and the limit range at the time of failure is the upper limit value of the normal limit range and the normal value while maintaining the reference value. Since the lower limit value is reduced by a predetermined ratio, the limit range at the time of failure corresponding to the current combustion state is set based on the latest reference value even if the reference value is updated sequentially. It becomes possible to set.

  According to the eighth feature, when the control unit determines that the oxygen sensor is in failure by the failure diagnosis, the control unit uses the predetermined air-fuel ratio feedback correction coefficient between the limit ranges at the time of failure as a substitute value, thereby correcting the oxygen sensor. Since the injection amount is determined, an air-fuel ratio feedback coefficient that is too large or too small due to a failure of the oxygen sensor is not applied, and an excessive rich or lean state can be prevented from occurring.

It is a figure which shows the whole structure of an internal combustion engine. It is a block diagram which shows the structure of a control unit. It is a map for searching a load area of an engine. It is a map which shows an air fuel ratio feedback area | region. It is a figure which overlaps and shows FIG. 4 and FIG. It is a conceptual diagram which shows the structure of the limit set with respect to an air fuel ratio feedback correction coefficient. It is a graph which shows the relationship between the output value of an oxygen sensor, and an air fuel ratio. It is a graph which shows an example of the output value of an oxygen sensor. It is a time chart which shows transition of the limit set to an air fuel ratio feedback correction coefficient. It is a graph which shows the limit setting method at the time of failure diagnosis of an oxygen sensor. 3 is a time chart showing the relationship between an output value of an oxygen sensor, a control gain of air-fuel ratio feedback control, and an air-fuel ratio feedback correction coefficient. It is a graph which shows the relationship between KO2 and KBU. It is a flowchart which shows the flow of an oxygen sensor failure diagnostic process.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a fuel injection control device for an internal combustion engine according to an embodiment of the present invention. A piston 12 is slidably fitted to a cylinder bore 11 of a water-cooled internal combustion engine E mounted on a motorcycle. Connected to the cylinder head 16 of the internal combustion engine E are an intake device 14 for supplying air-fuel mixture to the combustion chamber 13 facing the top of the piston 12 and an exhaust device 15 for exhausting exhaust gas from the combustion chamber 13. Has been. An intake passage 17 is formed in the intake device 14, and an exhaust passage 18 is formed in the exhaust device 15. A spark plug 20 is attached to the cylinder head 16 so that the tip of the cylinder head 16 faces the combustion chamber 13.

  A throttle valve 21 for controlling the amount of intake air flowing through the intake passage 17 is disposed in the intake device 14 so as to be openable and closable, and a fuel injection valve 22 for injecting fuel downstream of the throttle valve 21. Is attached. A bypass passage 27 that bypasses the throttle valve 21 is connected to the intake passage 17, and the amount of air flowing through the bypass passage 27 is adjusted by an actuator 28. The exhaust device 15 is provided with a catalytic converter 25.

The control unit C as control means controls the ignition timing by the spark plug 20, the fuel injection amount from the fuel injection valve 22, and the operation of the actuator 28. The control unit C includes a detection value of a throttle sensor 26 that detects a throttle opening that is the opening of the throttle valve 21, a detection value of a rotation speed sensor 30 that detects the rotation speed of a crankshaft 29 connected to the piston 12, An oxygen sensor (O) attached to the exhaust device 15 downstream of the catalytic converter 25 in order to detect the detected value of the water temperature sensor 31 for detecting the coolant temperature of the engine cooling water and the concentration of residual oxygen in the exhaust gas flowing through the exhaust passage 18. ₍₂ sensors) 32 detection values are input.

  FIG. 2 is a block diagram showing the configuration of the control unit C. The part of the control unit C that controls the injection amount of the fuel injection valve 22 is based on the rotational speed obtained by the rotational speed sensor 30 and the throttle opening obtained by the throttle sensor 26 while referring to the basic injection amount map 33. A basic injection amount calculating means 34 for determining a basic fuel injection amount for obtaining an air-fuel ratio, and an air-fuel ratio for calculating a feedback correction coefficient KO2 for bringing the air-fuel ratio closer to the target air-fuel ratio based on the oxygen concentration obtained by the oxygen sensor 32. Corresponding to the feedback correction coefficient calculation means 35, the correction means 36 for correcting the basic fuel injection amount based on the correction amount obtained by the feedback correction coefficient calculation means 35, and the final fuel injection amount obtained by the correction means 36 And a final fuel injection time calculating means 37 for obtaining the fuel injection time. Thereby, the control unit C can obtain the fuel injection amount without being based on the intake pressure and the atmospheric pressure.

  The feedback correction coefficient calculation means 35 is based on the rich / lean determination means 38 for determining the rich / lean degree of the exhaust gas based on the oxygen concentration detected by the oxygen sensor 32 and the determination result of the rich / lean determination means 38. Parameter calculating means 39 for correcting the feedback correction coefficient KO2 and the basic fuel injection amount T0. The parameter calculation means 39 stores the parameters in the nonvolatile storage unit 40 such as an EPROM or a flash memory at a predetermined cycle, and when the ignition key is turned on (when the system is started), the parameter calculation unit 39 stores the parameters from the nonvolatile storage unit 40. Read.

  The parameter calculation means 39 uses the air-fuel ratio feedback correction coefficient KO2 and the temporal change corresponding correction coefficient KBU periodically stored in the non-volatile storage unit 40 to integrate the correction coefficient KT for air-fuel ratio control based on the detected value of the oxygen sensor 32. Is calculated by a calculation formula of KT = KO2 × KBU. Here, the time-dependent correction coefficient KBU is determined for each engine load while learning to change according to changes over time such as deterioration of the internal combustion engine E, and is stored in the nonvolatile recording unit 40 at a predetermined cycle. The value is recorded and retained even after the vehicle power is turned off (system stopped), and is read at the next system startup.

  The air-fuel ratio feedback correction coefficient KO2 is a variable that is temporarily used at predetermined intervals when performing air-fuel ratio feedback control. Basically, feedback control is performed based on the air-fuel ratio feedback correction coefficient KO2. To bring the air-fuel ratio closer to the target air-fuel ratio. The air-fuel ratio feedback correction coefficient KO2 is determined based on the determination result by the rich / lean determination means 38.

  In a plurality of air-fuel ratio feedback regions, the parameter calculation means 39 calculates a correction coefficient KBU corresponding to time-dependent change for each air-fuel ratio feedback region based on the engine speed NE and the throttle opening TH, and this time-dependent change The integrated correction coefficient KT is calculated using the corresponding correction coefficient KBU, and in the engine load region other than the air-fuel ratio feedback region, the fuel injection amount is controlled using the learning value in the feedback region adjacent to the load region.

  FIG. 3 is a map for searching the engine load region. The control unit C searches in which region the engine load is based on the engine speed NE and the throttle opening TH. In this figure, a set lower limit throttle opening THO2L and a set upper limit throttle opening THO2H, and a plurality of set throttle openings THFB0, THFB1, THFB2, and THFB3 between the set lower limit and upper limit throttle openings THO2L, THO2H It is set in advance such that THO2L <THFB0 <THF1 <THF2 <THB3 <THO2H as it increases as the rotational speed NE increases. A solid line indicating each set throttle opening THO2L, THFB0, THFB1, THFB2, THFB3, THO2H is a boundary value applied when the throttle opening TH is increased, and a broken line adjacent to the solid line is a reduction side of the boundary. The value for giving hysteresis when straddling is shown.

  FIG. 4 is a map showing the air-fuel ratio feedback region. The air-fuel ratio feedback region indicated by the hatched portion is a region determined by the set lower limit rotational speed NLOP, the set upper limit rotational speed NHOP and the idle region upper limit rotational speed NTHO2L, and the set lower limit throttle opening THO2L and the set upper limit throttle opening THO2H. Further, in the idle region upper limit rotational speed NTHO2L, the value on the increase side of the engine speed NE is indicated by a solid line, and the value on the decrease side of the engine speed NE is indicated by a broken line. Further, the set lower limit throttle opening THO2L and the set upper limit throttle opening THO2H are indicated by a solid line with a value on the increasing side of the throttle opening TH, and a broken line with a value on the decreasing side of the throttle opening TH, It is set with hysteresis.

  FIG. 5 is a view in which the regions determined in FIGS. 3 and 4 are overlapped. In this figure, a plurality of load regions including a plurality of air-fuel ratio feedback regions are set based on the engine speed NE and the throttle opening TH, and in this embodiment, six air-fuel ratio feedback regions are “1”. ”To“ 6 ”, and regions other than the air-fuel ratio feedback region are indicated by numbers“ 0 ”and“ 7 ”to“ 11 ”.

  The boundaries between the plurality of load regions shown in FIG. 5 are determined with hysteresis, and the air-fuel ratio feedback region indicated by “1” to “6” becomes narrower as the throttle opening TH becomes smaller. Is set to When the operating state of the engine is in the air-fuel ratio feedback, it is detected which one of the air-fuel ratio feedback regions “1” to “6”, and the corresponding KBU1 to KBU6 are selected, and the air-fuel ratio is selected. In the engine load regions “0”, “7” to “11” other than the feedback region, the fuel injection amount is controlled by using the air-fuel ratio feedback regions KBU1 to KBU6 adjacent to the load region.

  The basic injection amount calculating means 34 derives the basic fuel injection amount T0 based on the basic injection amount map 33, and the correcting means 36 obtains the corrected fuel injection amount T1 as (T0 × KT). The final injection fuel time calculation means 37 obtains the fuel injection time corresponding to the corrected fuel injection amount T1, and the control unit C performs learning control for bringing the air-fuel ratio based on the detection value of the oxygen sensor 32 closer to the target air-fuel ratio. The amount of fuel injection from the performed fuel injection valve 22 is controlled.

  Here, when a predetermined time elapses when the value of KO2 is constant, the KBU selects KBU1 to 6 from the map shown in FIG. 5, and the selected KBUx is multiplied by the value of KO2 at that time to be a new KBUx ′. (KBUx ′ = KO2 × KBUx). The value of KO2 is returned to the reference (1.0) when KBUx is updated to KBUx ′. That is, KBUx is updated as KBUx ′, KBUx ″ (= KO2 × KBUx ′)... Every predetermined time while the value of KO2 is constant. KBUx ′, KBUx ″... Have the same value as the integrated correction coefficient KT at the time of each update. As described above, since KT = KO2 × KBU, the value of KT until the next KBU is updated. Fluctuates according to the fluctuation of KO2.

  With reference to the graph of FIG. 12, the relationship between KO2 and KBU described above will be specifically described. In the air-fuel ratio feedback control according to the present embodiment, as the correction amount for obtaining the stoichiometric air-fuel ratio increases, KO2 increases accordingly, but KO2 is set to a value close to 1.0 in the calculation process. I want. Therefore, the present embodiment is configured to update the value of KBU in order to return the value of KO2 to 1.0 when a predetermined time elapses while the value of KO2 is constant.

  In the example of FIG. 12, at time t1, KO2 starts increasing from 1.0 in response to a decrease in the oxygen sensor output. Next, at time t2, the increase in KO2 stops at 1.2 as the air-fuel ratio approaches V1 at which the stoichiometric state is reached. At time t3, KO2 is updated to KBUx ′ (1.2 = 1.2 × 1.0) by updating KBUx to KBUx ′ (1.2 = 1.2 × 1.0) as KO2 remains constant for a predetermined time Ta. .

  Furthermore, in the example of FIG. 12, at time t4, KO2 starts increasing again from 1.0 in accordance with the decrease in the oxygen sensor output. Next, at time t5, the increase in KO2 stops at 1.2 as the air-fuel ratio converges to the stoichiometric state. Then, at time t6, as KO2 remains constant for a predetermined time Tb, KBUx ′ is updated to KBUx ″ (1.44 = 1.2 × 1.2), so that KO2 becomes 1. Rounded down to zero. The updated value of KBUx is held, and thereby, it functions as a correction coefficient for change with time that keeps the value of KO2 within an appropriate range. The predetermined times Ta and Tb can be set arbitrarily.

  The control unit C determines the basic fuel injection amount for setting the air-fuel ratio to the target air-fuel ratio based on the throttle opening and the engine speed, the feedback correction coefficient KO2 determined according to the detection value of the oxygen sensor 32, the internal combustion engine By multiplying the basic fuel injection amount T0 by the correction coefficient KBU corresponding to change over time determined for each engine load while learning to change according to the change over time of the engine E, fuel injection can be performed without being based on the intake pressure and the atmospheric pressure. Control the amount.

  As a result, it becomes unnecessary to use an intake pressure sensor and an atmospheric pressure sensor in the fuel injection control system, and the cost of the system can be reduced and the number of parts can be reduced. In particular, in the region where the throttle opening is low, air-fuel ratio control that captures engine deterioration such as a change in friction of the internal combustion engine E and a change in intake amount due to soot adhering to the throttle valve 21 becomes possible. Further, the characteristic of the output deviation of the throttle sensor 26 tends to depend on the throttle opening, and even when the output deviation becomes large in the region of the high throttle opening, an appropriate air-fuel ratio can be set.

  In the air-fuel ratio feedback region, the control unit C performs fuel injection control using the air-fuel ratio feedback correction coefficient KO2 and the temporal change correspondence correction coefficient KBU. In addition, since the air-fuel ratio feedback region is set to become narrower as the throttle opening becomes smaller, fine learning control is performed in a low throttle opening region that is easily affected by deterioration of the bypass valve, etc. Appropriate air-fuel ratio control can be performed.

  By the way, when the air-fuel ratio feedback control is applied, if the air-fuel ratio feedback correction coefficient KO2, that is, the feedback correction amount becomes too large or too small for some reason, it may be excessively rich or leaned. In order to prevent this, it is conceivable to set a limit value for the air-fuel ratio feedback correction coefficient KO2. On the other hand, in the fuel injection control device in which the correction amount of the fuel injection amount corresponding to the intake pressure and the atmospheric pressure is provided by the air-fuel ratio feedback control in order to eliminate the intake pressure sensor and the atmospheric pressure sensor, for example, exceeds 2000 m. It is necessary to widen the limit of the air-fuel ratio feedback correction amount so that proper stoichiometric combustion can be obtained even when the vehicle is used at such high altitudes.

  Furthermore, if the limit of this correction amount is set to a value that takes into account the effects of parts accuracy of the vehicle and variations during assembly on the air-fuel ratio, feedback corresponding to this even when the vehicle is in various states. Appropriate stoichiometric combustion can be obtained by applying the correction amount.

  The present invention is characterized in that the limit setting is devised so that both of these, that is, the advantage of providing a limit to the air-fuel ratio feedback correction amount and the advantage of widening the limit are satisfied at the same time. is there. Specifically, when the internal combustion engine (engine) is started for the first time, the limit of the air-fuel ratio feedback correction amount is set wider, and after the first engine start, the subsequent air-fuel ratio feedback correction coefficient KO2 is expected. Learning the fluctuation range narrows the limit.

  FIG. 6 is a conceptual diagram showing a limit configuration set for the air-fuel ratio feedback correction coefficient KO2. The graph on the left side of the drawing shows a first limit range L1 applied when the vehicle engine is started for the first time. On the other hand, the graph on the right side of the figure shows a second limit range L2 (normal limit range) that is applied when a predetermined condition is satisfied after the engine is turned on for the first time and the engine is started.

  The first limit range L1 and the second limit range L2 allow the air-fuel ratio feedback correction coefficient KO2, which is a correction amount for bringing the air-fuel ratio at the time of engine operation close to the theoretical air-fuel ratio, to what value during engine operation. This is the upper and lower limit values of the air-fuel ratio feedback correction coefficient KO2 permitted to be used for calculating the corrected injection amount T1. The vertical width composed of the upper and lower limit values MAX2 and MIN2 of the second limit range L2 is set smaller than the vertical width composed of the upper and lower limit values MAX1 and MIN1 of the first limit range L1. The first limit range L1 is smaller than the limit at which an excellent operating state of the engine cannot be expected in the application range of the air-fuel ratio feedback correction coefficient KO2, that is, the upper and lower absolute limits MAXLIM and MINLIM, and is smaller than the second limit range L2. It is set large.

  Note that whether or not the engine has been started for the first time is determined by whether or not the starting history remains in the nonvolatile storage unit 40 in the control unit C. The start history can be set to be recorded when the engine is started for the first time after being received at a dealer, for example, excluding a finished vehicle test at a factory. In the present embodiment, the first limit range L1 is applied when the vehicle is turned on and the engine is started only after the battery is connected after being received at the store. Once switched from the first limit range L1 to the second limit range L2, the second limit range L2 is continuously applied thereafter, and the first limit range L1 is not applied again. .

  The first limit range L1 has a predetermined width up and down with the output value of the oxygen sensor 32 detected in the stoichiometric air-fuel ratio state as a reference B1, and the influence of parts accuracy, assembly variation, etc. on the air-fuel ratio is affected. The first numerical value S1 that is considered, the second numerical value S2 that considers the influence of the outside air temperature on the air-fuel ratio, the third numerical value S3 that considers the influence of the outside air pressure on the air-fuel ratio, and the vehicle are used. The fourth numerical value S4 considering the influence of the altitude on the air-fuel ratio is added to the fifth numerical value S5 considering the influence of the alcohol concentration in the fuel on the air-fuel ratio.

  On the other hand, the second limit range L2 is configured by subtracting the first numerical value S1 from the first limit range L1 and adding a sixth numerical value S6 that sets an update condition for the air-fuel ratio feedback correction coefficient KO2. Yes. As a result, the vertical range of the limit can be widened by the update condition of the air-fuel ratio feedback correction coefficient.

  In the present embodiment, after the vehicle is turned on and the engine is started, when the rate of change of the output value of the oxygen sensor 32 changes from positive to negative or negative to positive a predetermined number of times (for example, three times), the first The limit range L1 is set to be switched to the second limit range L2.

  FIG. 7 is a graph showing the relationship between the output value of the oxygen sensor 32 and the air-fuel ratio. FIG. 8 is a graph showing an example of the output value of the oxygen sensor 32. As shown in FIG. 7, the oxygen sensor 32 according to this embodiment shows a step-like output with the stoichiometric air-fuel ratio (stoichiometric) state as a boundary. As a result, the output value of the oxygen sensor 32 that outputs the predetermined voltage Vs at the stoichiometric air-fuel ratio decreases its fluctuation width as shown in FIG. 8 when the combustion state approaches the stoichiometric air-fuel ratio λs after the engine is started. While trying to converge to the predetermined voltage Vs. At this time, it is assumed that the change rate of the output value of the oxygen sensor 32 from positive to negative or negative to positive is “inverted output value”, and the number of inversions can be counted. In the present embodiment, it is determined that the output value of the oxygen sensor 32 has been inverted three times at time ts after the engine is started, so that the first limit range L1 is switched to the second limit range L2. Is set to

  FIG. 9 is a time chart showing the transition of the limit set in the air-fuel ratio feedback correction coefficient KO2. At time t1, the vehicle is turned on to start the engine, and application of the first limit range L1 is started. As a result, even if the altitude of the place where the vehicle is used, the accuracy of parts of the vehicle, or variations during assembly greatly affect the air-fuel ratio, the first limit range wider than the second limit range is set. Therefore, the internal combustion engine can be operated satisfactorily using a large air-fuel ratio feedback correction coefficient KO2.

  Next, when the engine is started and it is detected that the output value of the oxygen sensor 32 is inverted three times at time t2, the upper and lower limit values MAX2, MIN2 are set with the air-fuel ratio feedback correction coefficient KO2 at that time as the reference value B2. Application of the second limit range L2 consisting of is started. Thereafter, the reference value for determining the position of the second limit range L2 in the illustrated vertical direction is updated every time the update condition is satisfied. That is, the vertical width of the second limit range L2 remains unchanged even after the reference value is updated, and only moves in the vertical direction in the drawing every time the reference value is updated.

  When the reference value is updated after switching to the second limit range L2, the curve (not shown) showing the transition of the air-fuel ratio feedback correction coefficient KO2 is greater than or equal to a predetermined ratio (for example, 6% or more) with respect to the second limit range L2. ) And a predetermined number of times (for example, three times) continuously. The sixth numerical value S6 of the second limit range L2 is set as an allowable range for the update condition of the reference value. In this figure, at time t3, the first update of the reference value is executed, and the reference value changes from B2 to B3. For the sake of explanation, in this time chart, the reference values are connected with a broken line, but the reference value remains unchanged until the next update. For example, the reference value B2 changes until the update at time t3. Applied without.

  At time t4, the update condition is satisfied, and the second update of the reference value is executed. In this update, as the reference value is updated from B3 to B4, the upper and lower limit values of the second limit range L2 become MAX4 and MIN4. In this case, the upper limit MAX4 exceeds the upper absolute limit MAXLIM, but even if the air-fuel ratio feedback correction coefficient KO2 exceeding the upper absolute limit MAXLIM is calculated, the value is not used for calculating the corrected injection amount T1. .

  At time t5, the update condition is satisfied and the third update of the reference value is executed. In this update, with the update of the reference value from B4 to B5, the upper and lower limit values of the second limit range L2 become MAX5 and MIN5. Thereafter, at time t6, the vehicle is turned off.

  When the vehicle power is turned on again at time t7, the reference value B5 stored in the nonvolatile storage unit 40 after time t5 is read, and the upper and lower limit values MAX5 with reference to this reference value B5. , MIN5, the second limit range L2 is set.

  FIG. 10 is a graph showing a limit setting method at the time of failure diagnosis of the oxygen sensor 32. The fuel injection control device according to the present embodiment is configured to perform a failure diagnosis of the oxygen sensor 32 by shifting to a failure diagnosis mode when it is detected that the output value of the oxygen sensor 32 is not normal. When the failure diagnosis mode is entered, instead of the continuously applied second limit range L2, the third limit range L3 having a lower vertical width than the second limit range L2 (limit at the time of failure) Range) is configured to apply.

  The oxygen sensor 32 according to the present embodiment is configured to be capable of outputting approximately 0 to 3 V. However, during normal operation during normal feedback control, an output value (for example, 1 V) corresponding to the theoretical air-fuel ratio. ) Within a small range of vibration (for example, 0.6 to 1.5 V).

  In this embodiment, when the sensor output of approximately 3V continues for a predetermined time or when the sensor output of approximately 0V continues for a predetermined time, the normal mode is switched to the failure diagnosis mode. When the sensor output of approximately 3V continues for a predetermined time, the state shifts to the failure diagnosis mode, and it is determined that the oxygen sensor 32 has failed at that time, while the sensor output of approximately 0V continues for the predetermined time. In this case, after shifting to the failure diagnosis mode, the fuel injection amount is increased for a predetermined time, and the failure diagnosis is performed by detecting whether or not the output value changes according to the increase amount. For example, if the engine is in a high rotation and high load state and the output value does not change even when the fuel injection amount is increased when approximately 0 V is output, it is determined that the oxygen sensor 32 has failed. .

  The graph (a) shows the relationship between the second limit range L2 and the third limit range L3. The second limit range L2 that has been continuously applied from time t1 is replaced with the third limit range L3 by entering the failure diagnosis mode at time t2. The third limit range L3 maintains the reference value Ba, and the upper limit value MAXa and the lower limit value MINa of the second limit range L2 are reduced by a predetermined ratio to the upper limit value MAXb and the lower limit value MINb, respectively. Is.

  The graph (b) shows the relationship between the air-fuel ratio feedback correction coefficient KO2 and the limit range. In the example of this figure, since KO2 has continued to rise, it has shifted to the failure diagnosis mode at time t2. Therefore, after time t2, KO2 sticks to the upper limit value MAXb of the third limit range L3. Thereby, even if the calculated value of KO2 becomes an abnormal value due to a failure of the oxygen sensor 32, the value applied to the calculation of the corrected injection amount T1 while entering the failure diagnosis mode is the upper limit value MAXb. The lower limit value MINb is not exceeded. Therefore, it is possible to prevent excessive leaning or enrichment from occurring during failure diagnosis.

  When it is determined that the oxygen sensor 32 has failed as a result of the failure diagnosis process in the failure diagnosis mode, an appropriate air-fuel ratio feedback coefficient KO2 within the third limit range L3 is applied as an alternative value. In addition, a warning can be given by a warning means provided in a vehicle meter device or the like. On the other hand, when it is determined that the oxygen sensor 32 is normal, the failure diagnosis mode is shifted to the normal mode, and the third limit range L3 is returned to the second limit range L2.

  Here, the flow of the oxygen sensor failure diagnosis process is organized with reference to the flowchart of FIG. In step S1, the output of the oxygen sensor 32 is detected, and in step S2, it is determined whether or not a 3V output or a substantially 0V output has passed a predetermined time. If an affirmative determination is made in step S2, the process proceeds to step S3, and the transition from the normal mode to the failure diagnosis mode is performed. On the other hand, if a negative determination is made in step S2, the process returns to step S1.

  In the subsequent step S4, switching from the second limit range (normal limit range) L2 to the third limit range (limit range at the time of failure) L3 is executed with the transition to the failure diagnosis mode. In step S5, it is determined whether or not the operation has shifted to the failure diagnosis mode due to the approximately 0V output. If the determination is affirmative, the fuel injection amount is increased. In step S7, it is determined whether or not a change has occurred in the output of the oxygen sensor 32. If a negative determination is made, the process proceeds to step S8. On the other hand, if a negative determination is made in step S5, that is, it is determined that the failure diagnosis mode has been entered due to the approximately 3V output, steps S6 and 7 are skipped and the process proceeds to step S8. In step S8, it is determined that the oxygen sensor 32 is out of order, the substitute value is applied to KO2, and the series of controls ends. This alternative value can be an appropriate value in the third limit range L3 or a predetermined value corresponding to the theoretical air-fuel ratio.

  Further, when an affirmative determination is made in step S7, that is, when the output of the oxygen sensor 32 has changed with respect to the increase in the injection amount, the process proceeds to step S9, where it is determined that the oxygen sensor 32 is normal. Return from the failure diagnosis mode to the normal mode, and end the series of controls.

  FIG. 11 is a time chart showing the relationship between the output value of the oxygen sensor 32, the control gain of the air-fuel ratio feedback control, and the air-fuel ratio feedback correction coefficient. In the fuel injection control device according to the present embodiment, during the air-fuel ratio feedback control, if the calculated value of the air-fuel ratio feedback correction coefficient KO2 exceeds a predetermined value, the large PID control gain that was applied during normal operation is replaced with a smaller one. It is configured.

  In the example of this figure, the output voltage of the oxygen sensor 32 exceeds Va at time t1, and accordingly, the feedback correction coefficient KO2 starts to increase toward the upper gain switching threshold HI. At time t2, the air-fuel ratio feedback correction coefficient KO2 reaches the upper gain switching threshold value HI, and accordingly, the control gain is switched to a smaller value.

  When the control gain is reduced, the response speed of the feedback correction coefficient KO2 with respect to the output value of the oxygen sensor 32 is reduced. For example, even when the oxygen sensor 32 fails and outputs an abnormal output value, the influence on the feedback correction coefficient KO2 Can be reduced. That is, during normal control, a large control gain is applied to enable feedback control with a high response speed.When the air-fuel ratio feedback correction coefficient is too large or too small, the response speed can be reduced by reducing the control gain. In this case, it is possible to prevent the low-reliability air-fuel ratio feedback correction coefficient KO2 from affecting the combustion state in the unlikely event that the oxygen sensor has failed.

  The switching of the control gain is similarly performed when the air-fuel ratio feedback correction coefficient KO2 falls below the lower gain switching threshold LO. Each of the upper gain switching threshold value HI and the lower gain switching threshold value LO is set to a value corresponding to the functional limit of the oxygen sensor 32. When the output value of the oxygen sensor 32 satisfies the entry condition to the failure diagnosis mode, the operation shifts to the failure diagnosis mode.

  The configuration of the control unit, the structure and form of the oxygen sensor, the setting ranges of the first limit range and the second limit range, etc. are not limited to the above embodiment, and various changes can be made. The fuel injection control device according to the present invention is not limited to motorcycles, and can be applied to various vehicles such as straddle-type three / four-wheeled vehicles, general-purpose engines, and the like.

  DESCRIPTION OF SYMBOLS 14 ... Intake device, 15 ... Exhaust device, 21 ... Throttle valve, 22 ... Fuel injection valve, 26 ... Throttle sensor, 30 ... Revolution sensor, 32 ... Oxygen sensor, 33 ... Basic injection amount map, 34 ... Basic injection amount calculation Means 35 ... Feedback correction coefficient calculation means 36 ... Correction means 37 ... Final fuel injection time calculation means E ... Internal combustion engine (engine) C ... Control unit (control means) KO2 ... Air-fuel ratio feedback correction coefficient, L1 ... 1st limit range, L2 ... 2nd limit range (normal limit range), L3 ... 3rd limit range (limit range at the time of failure), S1-S6 ... 1st numerical value-6th numerical value

Claims (8)

An air-fuel ratio feedback correction coefficient (KO2) used for feedback control for obtaining a target air-fuel ratio based on the output of an oxygen sensor (32) provided in an exhaust device (15) of an internal combustion engine (E) as a power source of the vehicle. ) And a fuel injection control apparatus having control means (C) for determining the correction injection amount (T1) by multiplying the basic injection amount (T0) by the air-fuel ratio feedback correction coefficient (KO2).
The control means (C) is permitted to be used for calculating the corrected injection amount (T1) with respect to the air-fuel ratio feedback correction coefficient (KO2) during normal operation of the internal combustion engine (E). Set the normal limit range (L2) as the lower limit,
When it is detected that the output of the oxygen sensor (32) is in a predetermined state, a failure diagnosis of the oxygen sensor (32) is executed,
During the execution of the failure diagnosis, a failure limit range (L3) smaller than the normal limit range (L2) is set.   When the output value of the oxygen sensor (32) is approximately 0V and a predetermined time elapses or the output value of the oxygen sensor (32) is approximately 3V and the control means (C) is The fuel injection control device according to claim 1, wherein a failure diagnosis of the oxygen sensor (32) is started.   The control means (C) executes fuel injection for failure diagnosis when the failure diagnosis is started when a predetermined time elapses with the output value of the oxygen sensor (32) being substantially 0 V, The fuel injection control device according to claim 2, wherein the failure determination is performed by detecting a change in output of the oxygen sensor (32) with respect to injection.   When it is determined by the failure diagnosis that the oxygen sensor (32) is normal, the control means (C) terminates the failure diagnosis and determines the normal limit range (L3) from the limit range (L3) at the time of the failure. 5. The fuel injection control device according to claim 1, wherein the fuel injection control device returns to L2). The air-fuel ratio feedback control is executed by PID control for a target output value of the oxygen sensor (32),
In the air-fuel ratio feedback correction coefficient (KO2), an upper gain switching threshold value (HI) and a lower gain switching threshold value (LO) corresponding to the functional limit of the oxygen sensor (32) are set.
When the air-fuel ratio feedback correction coefficient (KO2) exceeds the upper gain switching threshold (HI) or falls below the lower gain switching threshold (LO), the control means (C) gains the PID control gain. The fuel injection control device according to claim 1, wherein the fuel injection control device is made smaller.   The basic injection amount (T0) includes the throttle opening (TH) of the throttle valve (21) provided in the intake device (14) of the internal combustion engine (E) and the rotational speed (NE) of the internal combustion engine (E). The fuel injection control device according to any one of claims 1 to 5, wherein the fuel injection control device is derived from a basic injection amount map (33) that defines a relationship between a fuel injection amount and a basic injection amount (T0). The normal limit range (L2) has a predetermined vertical width from the reference value (Ba),
The upper limit value (MAXa) and the lower limit value (MINa) of the normal limit range (L2) are respectively maintained at a predetermined ratio while the limit range (L3) at the time of the failure is maintained with the reference value (Ba). 7. The fuel injection control apparatus according to claim 1, wherein the fuel injection control apparatus is reduced.   When the control means (C) determines that the oxygen sensor (32) is in failure by the failure diagnosis, the control means (C) substitutes for a predetermined air-fuel ratio feedback correction coefficient (KO2) between the limit range (L3) at the time of failure. 8. The fuel injection control device according to claim 1, wherein the correction injection amount (T1) is determined by using the value as a value.

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