JP2006177371A - Internal combustion engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the accuracy of failure diagnosis which is performed in accordance with the output of an air-fuel ratio sensor. <P>SOLUTION: The air-fuel ratio sensor 28 of a limiting current type is installed in an exhaust pipe 26 of an engine 11. From a voltage variation ΔV and a current variation ΔI when varying voltage applied to the air-fuel ratio sensor 28 in a positive direction (or in a negative direction), an element resistance value Z (=ΔV/ΔI) is calculated as substitute information for an element temperature. Depending on whether the element resistance value Z is lower than a resistance value (60Ω, e.g.) equivalent to a lower limit temperature in a completely active temperature range or not, whether the air-fuel ratio sensor 28 is in a completely active condition or not is determined. In a period when that the air-fuel ratio sensor 28 is in the completely active condition is determined, the failure diagnosis of a fuel supply system or others is performed in accordance with the output of the air-fuel ratio sensor 28. This prevents the failure diagnosis when the air-fuel ratio sensor 28 is in a semi-active condition and improves the accuracy of the failure diagnosis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for an internal combustion engine that performs an abnormality diagnosis based on an output of an air-fuel ratio detecting means for detecting an air-fuel ratio of exhaust gas.

  For example, in a system that purifies the exhaust gas of an internal combustion engine with a three-way catalyst, the air-fuel ratio of the exhaust gas is detected by an air-fuel ratio sensor (or oxygen sensor), and the air-fuel ratio of the exhaust gas is feedback controlled near the theoretical air-fuel ratio, The exhaust gas purification efficiency of the three-way catalyst is increased. In this system, if the fuel supply system becomes abnormal or the air-fuel ratio sensor becomes abnormal, the output behavior of the air-fuel ratio sensor becomes abnormal. There is one that performs an abnormality diagnosis of a fuel ratio sensor or the like.

  Since the air-fuel ratio sensor cannot detect the air-fuel ratio when it is in the inactive state (the temperature of the sensor element is low), the air-fuel ratio sensor is in the active state in the air-fuel ratio feedback control and abnormality diagnosis based on the output of the air-fuel ratio sensor. It is necessary to do after becoming.

  Therefore, for example, in Japanese Patent Application Laid-Open No. 61-197738, it is determined whether or not the air-fuel ratio sensor is in an active state based on whether or not the output voltage of the air-fuel ratio sensor is equal to or higher than a predetermined voltage. The air-fuel ratio feedback control is started. In addition, there is also an apparatus in which the air-fuel ratio feedback control is started by determining the active state of the air-fuel ratio sensor based on the elapsed time after the start and the energization time integrated value of the heater built in the air-fuel ratio sensor. Furthermore, when performing abnormality diagnosis based on the output of the air-fuel ratio sensor, if the air-fuel ratio feedback control is being executed, it is determined that the air-fuel ratio sensor is in an active state and abnormality diagnosis is performed.

In Japanese Patent Publication No. 6-39932, air-fuel ratio sensors are installed on both the upstream and downstream sides of the catalyst, and when the output voltage of the downstream air-fuel ratio sensor becomes equal to or higher than a predetermined voltage, Determination is made, and the abnormality diagnosis of the catalyst is started from the output change width of the downstream air-fuel ratio sensor.
JP-A-61-197738 (page 4, etc.) Japanese Patent Publication No. 6-39932 (page 4, etc.)

  By the way, the active state of the air-fuel ratio sensor includes a semi-active state in which the temperature of the sensor element is slightly insufficient and a fully active state in which the sensor element temperature is sufficiently raised to the active temperature. Although the air-fuel ratio can be detected even in the semi-active state, as shown in FIG. 2, the air-fuel ratio is abnormal in the semi-active state because the detection range of the air-fuel ratio sensor (width between the lean detection limit and the rich detection limit) is narrow. Even if it becomes a value (for example, λ = 1.2), it cannot be detected. In addition, as shown in FIG. 3, in the semi-active state, the response of the air-fuel ratio sensor is slow, so the convergence of the air-fuel ratio feedback control at the time of the disturbance is deteriorated, and it is determined to be abnormal although it is normal. There is a risk of being. Therefore, in order to ensure the detection range and responsiveness of the air-fuel ratio sensor necessary for performing reliable abnormality diagnosis, it is necessary to raise the temperature of the air-fuel ratio sensor to a fully active state.

  However, in recent air-fuel ratio feedback control systems, air-fuel ratio feedback control is started when the temperature of the air-fuel ratio sensor is raised to a semi-active state in order to start air-fuel ratio feedback control early after startup. For this reason, if abnormality diagnosis is performed during air-fuel ratio feedback control as in the prior art, abnormality diagnosis is performed even when the air-fuel ratio sensor is in a semi-active state, which is necessary for performing reliable abnormality diagnosis. The detection range and responsiveness of the air-fuel ratio sensor cannot be ensured, and the abnormality diagnosis accuracy decreases.

  Further, in Patent Document 2, the output voltage of the air-fuel ratio sensor changes depending on the air-fuel ratio of the exhaust gas, so that the activity determination of the air-fuel ratio sensor is affected by the air-fuel ratio. Accordingly, in this case as well, abnormality diagnosis may be performed when the air-fuel ratio sensor is in a semi-active state, and the abnormality diagnosis accuracy is lowered.

  On the other hand, in the method of determining the active state of the air-fuel ratio sensor based on the elapsed time after the start and the energization time integrated value of the built-in heater of the air-fuel ratio sensor, the activity determination can be performed without being affected by the air-fuel ratio. When starting at a low temperature or traveling in an extremely low temperature environment, the temperature of the air-fuel ratio sensor is delayed, so that an abnormality diagnosis may be started in a semi-active state, which also reduces the accuracy of the abnormality diagnosis. .

  The present invention has been made in view of such circumstances, and therefore an object of the present invention is to provide an internal combustion engine control apparatus capable of improving the accuracy of abnormality diagnosis performed based on the output of the air-fuel ratio detection means. .

  In order to achieve the above object, according to the first aspect of the present invention, the air-fuel ratio control means performs air-fuel ratio feedback control when the air-fuel ratio detection means is in either the semi-active state or the fully active state. The abnormality diagnosis means performs abnormality diagnosis when the air-fuel ratio detection means is in a fully active state. In this way, since the abnormality diagnosis can be performed during the period when the air-fuel ratio detection means is actually in the fully active state, the air-fuel ratio detection range and responsiveness of the air-fuel ratio detection means at the time of abnormality diagnosis are ensured. It is possible to improve the accuracy of abnormality diagnosis by increasing the detection accuracy of the air-fuel ratio detection means. The abnormality diagnosis means includes, for example, a fuel supply system, an air-fuel ratio detection means, and a catalyst as in claims 4 to 6.

  According to the second aspect of the present invention, the air-fuel ratio control means performs air-fuel ratio feedback control when the cooling water temperature detected by the cooling water temperature detection means is equal to or higher than the first predetermined water temperature, and the abnormality diagnosis means detects the cooling water temperature. An abnormality diagnosis is performed when the cooling water temperature detected by the detecting means is equal to or higher than a second predetermined water temperature that is higher than the first predetermined water temperature. In this way, the air-fuel ratio detection range and responsiveness of the air-fuel ratio detection means at the time of abnormality diagnosis can be ensured, and the detection accuracy of the air-fuel ratio detection means can be improved to improve the abnormality diagnosis accuracy.

  According to a third aspect of the present invention, it is preferable not to perform abnormality diagnosis when the cooling water temperature detected by the cooling water temperature detecting means is equal to or higher than a third predetermined water temperature higher than the second predetermined water temperature. Accordingly, it is possible to prohibit abnormality diagnosis in a high temperature range where the influence of the temperature characteristics of the sensors and actuators becomes large.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine. An intake air temperature sensor 14 that detects the intake air temperature THA and an intake air amount Ga are detected downstream of the air cleaner 13. An air flow meter 10 is provided. A throttle valve 15 and a throttle opening sensor 16 that detects the throttle opening TH are provided on the downstream side of the air flow meter 10.

  Further, an intake pipe pressure sensor 17 for detecting the intake pipe pressure PM is provided on the downstream side of the throttle valve 15, and a surge tank 18 is provided on the downstream side of the intake pipe pressure sensor 17. An intake manifold 19 that introduces air into each cylinder of the engine 11 is connected to the surge tank 18, and a fuel injection valve 20 that injects fuel is attached to a branch pipe portion of each cylinder of the intake manifold 19. Yes. The fuel injection valve 20 constitutes a fuel supply system together with a fuel tank (not shown), a fuel pump (not shown), etc., and the fuel pumped up from the fuel tank by the fuel pump passes through a fuel pipe (not shown). It is distributed to the fuel injection valve 20 of each cylinder.

  The engine 11 is provided with a spark plug 21 for each cylinder, and a high-voltage current generated by the ignition circuit 22 is supplied to each spark plug 21 via a distributor 23. The distributor 23 is provided with a crank angle sensor 24 that outputs, for example, 24 pulse signals every 720 ° C. A (two rotations of the crankshaft). The engine rotational speed Ne is determined by the frequency of the output pulses of the crank angle sensor 24. It comes to detect. Further, a water temperature sensor 39 for detecting the engine cooling water temperature THW is attached to the engine 11.

  On the other hand, an exhaust pipe 26 is connected to an exhaust port (not shown) of the engine 11 via an exhaust manifold 25, and a three-way catalyst that reduces CO, HC, NOx, etc. in the exhaust gas in the middle of the exhaust pipe 26. Etc., a catalyst 27 is provided. An air-fuel ratio sensor 28 (air-fuel ratio detecting means) is provided on the upstream side of the catalyst 27. The air-fuel ratio sensor 28 includes a sensor element 38 that generates a limit current that is substantially proportional to the oxygen concentration in the exhaust gas when a reference voltage is applied, and detects the air-fuel ratio λ from the limit current. Further, an oxygen sensor 29 that reverses the output voltage R / L depending on whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio is provided on the downstream side of the catalyst 27.

  The outputs of the various sensors described above are read into the engine control circuit 30 via the input port 31. The engine control circuit 30 is mainly composed of a microcomputer, and includes a CPU 32, a ROM 33 (storage medium), a RAM 34, a backup RAM 35 backed up by a battery (not shown), and the like, which will be described later and stored in the ROM 33. The fuel injection control program and the ignition control program (not shown) shown in FIGS. 6 and 9 are executed, and the required fuel injection amount TAU and the ignition timing Ig are used using the engine operation parameters detected by various sensors. Etc., and a signal corresponding to the calculation result is output from the output port 36 to the fuel injection valve 20 and the ignition circuit 22 to control the operation of the engine 11.

  Further, the engine control circuit 30 stores in the ROM 33 each program for diagnosing the fuel supply system shown in FIGS. 10 to 12, which will be described later, and the abnormality diagnosis reference value map and initial values shown in FIG. Then, by executing the programs shown in FIGS. 10 to 12, it is determined whether or not the air-fuel ratio sensor 28 is in a fully active state, and during the period in which the air-fuel ratio sensor 28 is in a fully active state. Based on the output of the air-fuel ratio sensor 28, the presence or absence of abnormality in the fuel supply system is diagnosed. Therefore, each program shown in FIGS. 10 to 12 functions as an abnormality diagnosis means in the scope of claims.

[Air-fuel ratio control]
The air-fuel ratio control program shown in FIG. 4 is a program for setting the required fuel injection amount TAU through air-fuel ratio feedback control, and is started at every predetermined crank angle (for example, every 360 ° C. A). When this program is started, first, at step 101, detection signals from the various sensors (for example, engine speed Ne, intake pipe pressure PM, cooling water temperature THW, air-fuel ratio λ, oxygen concentration R / L in exhaust gas, etc.) Is read. Thereafter, in step 102, the basic fuel injection amount Tp is calculated from a map or the like according to the engine operating state (engine speed Ne and intake pipe pressure PM, etc.).

Then, in the next step 103, it is determined whether the air-fuel ratio feedback condition is satisfied. Here, the air-fuel ratio feedback condition is satisfied when all of the following conditions (A1) to (A4) are satisfied, and is not satisfied if any one of the conditions is not satisfied.
(A1) Various fuel increase corrections are not performed (A2) The fuel is not being cut (A3) The engine is not operating at a high load (A4) The air-fuel ratio sensor 28 is semi-active or fully active Whether the air-fuel ratio sensor 28 of the above (A4) is semi-active or fully active is determined, for example, based on whether the coolant temperature THW is equal to or higher than a predetermined temperature (for example, 30 ° C.), or the elapsed time after starting Is determined based on whether or not the output λ is actually output from the air-fuel ratio sensor 28, or is determined from the element resistance value of the air-fuel ratio sensor 28 described later. May be.

  If it is determined in step 103 that the air-fuel ratio feedback condition is not satisfied, the routine proceeds to step 104, where the air-fuel ratio correction coefficient FAF (corresponding to the feedback correction amount) is set to “1.0”, and step 109 is performed. move on. In this case, the air-fuel ratio is not corrected.

  On the other hand, if it is determined in step 103 that the air-fuel ratio feedback condition is satisfied, the routine proceeds to step 105, where it is determined whether or not the catalyst 28 is activated. The presence / absence of the activity of the catalyst 28 is determined, for example, based on whether the coolant temperature THW is equal to or higher than a predetermined temperature (for example, 40 ° C.). When it is determined in step 105 that the catalyst 28 is activated, the process proceeds to step 106, a target air-fuel ratio setting program shown in FIG. 6 described later is executed, and the output R / L of the oxygen sensor 29 downstream of the catalyst 28 is set. Based on this, the target air-fuel ratio λTG is set, and then the routine proceeds to step 108.

  On the other hand, when it is determined in step 105 that the catalyst 28 is not activated, the routine proceeds to step 107, where a target air-fuel ratio map using the cooling water temperature THW shown in FIG. The target air-fuel ratio λTG corresponding to the coolant temperature THW is set, and the routine proceeds to step 108.

As described above, after setting the target air-fuel ratio λTG in step 106 or 107, the routine proceeds to step 108, where the air-fuel ratio correction coefficient FAF is based on the target air-fuel ratio λTG and the output λ (air-fuel ratio) of the air-fuel ratio sensor 28. Is calculated by the following equation.
FAF (k) = K1 · λ (k) + K2 · FAF (k−3) + K3 · FAF (k−2) + K4 · FAF (k−1) + ZI (k)
However, ZI (k) = ZI (k−1) + Ka · {λTG−λ (k)}
Here, k is a variable indicating the number of times of control from the start of the first sampling, K1 to K4 are optimum feedback constants, and Ka is an integration constant.

In the next step 109, the basic fuel injection amount Tp, the air-fuel ratio correction coefficient FAF, and the learning correction amount KGj belonging to the current operating region among the air-fuel ratio learning correction amount KGj stored in the backup RAM 35 are used. Then, the calculation of the following equation is executed, the required fuel injection amount TAU is calculated, and this program ends.
TAU = Tp ・ FAF ・ KGj ・ FALL
Here, FALL is another correction coefficient that does not depend on the air-fuel ratio correction coefficient FAF and the learning correction amount KGj (for example, a correction coefficient due to engine temperature, a correction coefficient during acceleration / deceleration, etc.).

[Target air-fuel ratio setting]
The target air-fuel ratio setting program shown in FIG. 6 is a subroutine executed in step 106 of the air-fuel ratio control program in FIG. When this program is started, first, in steps 111 to 113, based on the output R / L of the oxygen sensor 29, the difference between the actual air-fuel ratio and the output λ (detected air-fuel ratio) of the air-fuel ratio sensor 28 is corrected. Thus, the median value λTGC of the target air-fuel ratio is set. Specifically, first, at step 111, it is determined whether the output R / L of the oxygen sensor 29 is rich (R) or lean (L). If rich (R), the routine proceeds to step 112 where the median λTGC is set. It is increased by a predetermined value λM, that is, it is set to be lean by λM (λTGC ← λTGC + λM).

  On the other hand, when the output R / L of the oxygen sensor 29 is lean (L), the routine proceeds to step 113, where the median value λTGC is set smaller by a predetermined value λM, that is, rich by λM (λTGC ← λTGC is equal to λM). FIG. 7 shows an example in which the median value λTGC of the target air-fuel ratio is set based on the output R / L of the oxygen sensor 29 as described above.

  After setting the median value λTGC of the target air-fuel ratio as described above, in steps 114 to 123, the target air-fuel ratio λTG is set as follows by so-called dither control. First, in step 114, it is determined whether or not the count value CDZA of the dither cycle counter is equal to or greater than the dither cycle TDZA. The dither cycle TDZA is a factor that determines the resolution of the dither control. A desirable value corresponding to the operating state of the engine 11 is set each time by the processing of step 118 described later.

  If the count value CDZA of the dither cycle counter is smaller than the dither cycle TDZA, the process proceeds to step 115, the count value CDZA of the dither cycle counter is incremented by 1, and the process of step 123 is executed. In this case, the value of the target air-fuel ratio λTG set at that time is maintained without updating the value of the target air-fuel ratio λTG.

  On the other hand, if the count value CDZA of the dither cycle counter is equal to or greater than the dither cycle TDZA, the process proceeds to step 116, and after resetting the count value CDZA of the dither cycle counter to “0”, the target air-fuel ratio λTG is set to the median value by dither control. The following processing is executed so as to change stepwise alternately on the rich / lean side around λTGC.

  First, in steps 117 and 118, a dither amplitude λDZA and a dither period TDZA are set. Here, the dither amplitude λDZA is a factor that determines the control amount of dither control, and a desirable value corresponding to the operating state of the engine 11 is set each time, as in the dither cycle TDZA. The dither amplitude λDZA and the dither period TDZA are obtained by searching a two-dimensional map (not shown) using the engine speed Ne and the intake pipe pressure PM as parameters, and calculating the engine speed Ne and the intake pipe pressure PM at that time. A corresponding dither amplitude λDZA and a dither period TDZA are obtained.

  Thereafter, in step 119, it is determined whether or not the dither processing flag XDZR is “0”. The dither processing flag XDZR is set to XDZR = 1 when the target air-fuel ratio λTG is set rich with respect to the target air-fuel ratio median value λTGC, and is reset to XDZR = 0 when set to lean.

  If it is determined in step 119 that XDZR = 0, that is, if the target air-fuel ratio λTG is set to lean with respect to the target air-fuel ratio median λTGC in the previous dither control, the process proceeds to step 120, and this time The dither processing flag XDZR is set to “1” so that the target air-fuel ratio λTG is set to rich by the dither control. On the other hand, if it is determined in step 119 that XDZR = 1, that is, if the target air-fuel ratio λTG is set rich with respect to the target air-fuel ratio median λTGC in the previous dither control, step 121 is performed. Then, the dither processing flag XDZR is reset to “0” so that the target air-fuel ratio λTG is set to lean in the current dither control.

In this way, the dither processing flag XDZR is inverted at step 120 or 121. Further, when XDZR = 1, the dither amplitude λDZA is inverted to a negative value at step 122 (when XDZR = 0, the step is reversed). The dither amplitude λDZA set in 112 or 113 is used as it is). Thereafter, in step 123, the target air-fuel ratio λTG is set from the target air-fuel ratio median λTGC and the dither amplitude λDZA. For example, when the target air-fuel ratio λTG is set lean relative to the target air-fuel ratio median value λTGC in the previous dither control, the target air-fuel ratio λTG is set to the dither amplitude λDZA with respect to the median value λTGC in the current dither control. The target air-fuel ratio λTG is calculated by the following equation so as to set only rich.
λTG = λTGC-λDZA
On the contrary, when the target air-fuel ratio λTG is set to be rich with respect to the target air-fuel ratio median value λTGC in the previous dither control, the dither amplitude of the target air-fuel ratio λTG with respect to the median value λTGC is set in the current dither control. The target air-fuel ratio λTG is calculated by the following equation so that only λDZA is set to be lean.
λTG = λTGC + λDZA
By such dither control, as shown in FIG. 8, the target air-fuel ratio λTG is set so as to change in a stepwise manner by the dither amplitude λDZA alternately on the rich / lean side around the median value λTGC.

[Air-fuel ratio learning]
The air-fuel ratio learning program shown in FIG. 9 is started at every predetermined crank angle. When this program is started, first, in step 201, it is determined whether or not all air-fuel ratio learning for, for example, eight operation regions 0 to 7 described later has been completed. This determination is made based on whether or not the learning flags XDOM0 to XDOM7 corresponding to the respective operation areas 0 to 7 are “1” meaning the learning end. When the air-fuel ratio learning of all the eight operation regions 0 to 7 has been completed (when XDOM0 to XDOM7 = 1), the process proceeds to step 203, and the learning end flag XAFLN is set to “1” which means the end of all region learning. Set to.

  On the other hand, if the air-fuel ratio learning has not ended in any one of the operation regions 0 to 7, the process proceeds from step 201 to step 202, and the learning end flag XAFLN is reset to “0”.

Thereafter, in step 204, it is determined whether or not the following learning conditions (B1) to (B6) are satisfied.
(B1) Air-fuel ratio feedback control is in progress (B2) Cooling water temperature THW is, for example, 80 ° C. or higher (B3) Increase after startup is “0” (B4) Increase in warm-up is “0” (B5) A predetermined crank angle has elapsed since entering the current operation region (B6) The battery voltage is, for example, 11.5 V or more. Any one of the conditions (B1) to (B6) is satisfied. If there is nothing, the learning condition is not satisfied, and the program is terminated without performing the learning process in step 205 and subsequent steps.

  On the other hand, if all of the conditions (B1) to (B6) are satisfied, the learning condition is satisfied, and the learning process after step 205 is executed as follows. First, in step 205, the average value FAFAV of the air-fuel ratio correction coefficient FAF stored in the RAM 34 is read. Then, in step 206, it is determined whether or not the engine is idling (IDLON). In response, the following learning process is executed.

  That is, when the vehicle is traveling, the process proceeds to step 207, where it is determined whether or not the engine speed Ne at that time is within the range of 1000 to 3200 rpm (stable traveling state). This program is terminated without performing the subsequent processing. On the other hand, if the engine speed Ne is in the range of 1000 to 3200 rpm, it is determined that the learning process is possible, and the process proceeds to step 208, where the operating range of the engine 11 corresponds to any of “1” to “7”. Judge whether to do. The determination of the operation region is performed based on the load of the engine 11 (for example, the intake pipe pressure PM), and any one of the operation regions “1” to “7” is learned according to the magnitude of the load. Set as processing area. Thereafter, in step 209, the learning flag XDOMi corresponding to the area i (i is any one of “1” to “7”) set in step 208 is set.

  On the other hand, if it is determined in step 206 that the engine is idling, whether or not the engine speed Ne is within a range of 600 to 1000 rpm (stable idle state) (step 210), and the intake pipe pressure PM Is determined to be higher than 173 mmHg, for example (step 211). If any one of these two conditions is not satisfied, the program is terminated without performing the subsequent processing.

  On the other hand, if both of the two conditions are satisfied, it is determined that the learning process is possible, and the process proceeds to step 212. After setting the operation region to the region “0”, in step 213, the above step 212 is performed. A learning flag XDOM0 corresponding to the set region “0” is set.

  As described above, after the learning flag XDOMi or XDOM0 is set according to the current operating state, the learning correction amount KGj (j = 0 to 7) of the air-fuel ratio is set or already set in steps 214 to 217. The learning correction amount KGj is updated. In this learning process, first, in step 214, a deviation amount (1-FAFAV) from the reference value (1.0) of the average value FAFAV of the air-fuel ratio correction coefficient read in step 205 is determined, and the deviation amount is a predetermined value. If it is (for example, 2%) or more, the learning correction amount KGj in the area is corrected by a predetermined value K% (step 215). The correction amount KGj is corrected by a predetermined value L% (step 217). If the deviation amount is within the predetermined value, the learning correction amount KGj in the area is maintained (step 216).

  Thereafter, in step 218, the upper and lower limit checks (guard processing) of the learning correction amount KGj set (updated) in steps 215 to 217 are executed. In this upper / lower limit check, the upper limit value of the learning correction amount KGj is set to “1.2”, for example, and the lower limit value is set to “0.8”, for example. These upper and lower limit values may be set for each operation region of the engine 11 described above. The learning correction amount KGj set in this way is stored in the backup RAM 35 for each operation region.

[Error diagnosis execution condition judgment]
The abnormality diagnosis execution condition determination program shown in FIG. 10 is started every predetermined time (for example, every 256 ms), and determines whether or not the abnormality diagnosis execution condition for the fuel supply system is satisfied as follows. First, in step 301, in order to determine whether or not the operating state after engine startup has been stabilized, it is determined whether or not the elapsed time after engine startup has exceeded, for example, 60 seconds, and the elapsed time has reached 60 seconds. If not, it is determined that the operating state is still unstable, and the process proceeds to step 311 to reset the abnormality diagnosis permission flag XDGFUELEX to “0” which means that abnormality diagnosis is prohibited, and the program ends.

  On the other hand, when the elapsed time after the engine start exceeds 60 seconds, it is determined that the operation state after the engine start is stable, the process proceeds from step 301 to step 302, and the element temperature of the air-fuel ratio sensor 28 is determined. Whether or not the air-fuel ratio sensor 28 is fully active is determined based on whether or not the element resistance value Z obtained as substitute information for the air is lower than a resistance value (for example, 60Ω) corresponding to the lower limit temperature of the complete activation temperature range. To do. The processing in step 302 functions as complete activity determination means in the claims.

In step 302, the element resistance value Z is calculated as follows. When the element resistance value Z is detected, the voltage applied to the sensor element 38 is temporarily changed in the positive direction and then changed in the negative direction. Then, the element resistance value Z is calculated from the voltage change amount ΔV and the current change amount ΔI when the applied voltage is changed in the positive direction (or negative direction) by the following equation.
Z = ΔV / ΔI
This detection method is an example, and the element resistance value Z is detected based on the amount of change in voltage and current on both the positive and negative sides, or the element resistance value Z (from the sensor current Ineg when the negative applied voltage Vneg is applied. = Vneg / Ineg) may be calculated. The function of calculating the element resistance value Z in this way corresponds to the resistance value detecting means in the claims.

  If it is determined in step 302 that Z ≧ 60, that is, as shown in FIGS. 2 and 3, when the air-fuel ratio sensor 28 is not fully activated, the air-fuel ratio detection range of the air-fuel ratio sensor 28 is Since it is narrow and slow in response, the detection accuracy of the air-fuel ratio sensor 28 is low, and there is a risk of erroneously detecting an abnormality in the fuel supply system. Therefore, in this case, the process proceeds to step 311 to reset the abnormality diagnosis permission flag XDGFUELEX to “0” which means that abnormality diagnosis is prohibited, and the program is terminated. On the other hand, if it is determined in step 302 that Z <60, it is determined that the air-fuel ratio sensor 28 is fully active, and the routine proceeds to step 303.

  In step 303, it is determined whether the air-fuel ratio feedback control is being performed (when the air-fuel ratio feedback condition is satisfied in step 103 in FIG. 4). If the air-fuel ratio feedback control is not being performed, the process proceeds to step 311. Then, the abnormality diagnosis permission flag XDGFUELEX is reset to “0” which means that abnormality diagnosis is prohibited, and this program ends.

  If air-fuel ratio feedback control is in progress, the routine proceeds from step 303 to step 304, where it is determined whether or not the coolant temperature THW is, for example, 70 ° C. <THW <90 ° C. If THW ≦ 70 ° C. (before engine warm-up is completed) ), Or if THW ≧ 90 ° C. (high temperature range where the influence of the temperature characteristics of the sensors and actuators is large), the process proceeds to step 311 and the abnormality diagnosis permission flag XDGFULEX is set to “0” indicating that abnormality diagnosis is prohibited. ”To end this program.

  If 70 ° C. <THW <90 ° C., the routine proceeds from step 304 to step 305, where it is determined whether the intake air temperature THA is, for example, −10 ° C. <THA <60 ° C., and THA ≦ −10 ° C. If the temperature is low) or if THA ≧ 60 ° C. (high temperature range where the influence of the temperature characteristics of the sensors and actuators becomes large), the process proceeds to step 311 and the abnormality diagnosis permission flag XDGFUELEX is prohibited from abnormality diagnosis. Reset to "0" to end this program.

  If −10 ° C. <THA <60 ° C., the process proceeds from step 305 to step 306 to determine whether the engine speed Ne is, for example, 700 rpm <Ne <3600 rpm, and if Ne ≦ 700 rpm, or Ne ≧ In the case of 3600 rpm, the operating state of the engine 11 is unstable, and there is a possibility that an abnormality in the fuel supply system may be erroneously detected. Therefore, the process proceeds to step 311 and the abnormality diagnosis permission flag XDGFUELEX is set to “0” meaning that abnormality diagnosis is prohibited. To reset the program to end.

  If 700 rpm <Ne <3600 rpm, the process proceeds from step 306 to step 307 to determine whether the intake pipe pressure PM is, for example, 200 mmHg <PM <630 mmHg. If PM ≦ 200 mmHg, or if PM ≧ 630 mmHg In this case, since the operating state of the engine 11 is unstable and there is a possibility that an abnormality in the fuel supply system may be erroneously detected, the process proceeds to step 311 and the abnormality diagnosis permission flag XDGFUELEX is reset to “0” meaning that abnormality diagnosis is prohibited. Exit this program.

  If 200 mmHg <PM <630 mmHg, the process proceeds from step 307 to step 308, and all the sensors that affect the air-fuel ratio, such as the intake pipe pressure sensor 17, the water temperature sensor 39, the intake air temperature sensor 14, and the air-fuel ratio sensor 28, are normal. If there is even one abnormal sensor, there is a possibility that an abnormality in the fuel supply system may be erroneously detected. Therefore, the process proceeds to step 311 and the abnormality diagnosis permission flag XDGFULEX is set to “0” indicating that abnormality diagnosis is prohibited. ”To end this program.

  If all the sensors that affect the air-fuel ratio are normal, the process proceeds from step 308 to step 309 to determine whether all the systems that affect the air-fuel ratio, such as the misfire detection system and the evaporation purge system, are normal. If there is any abnormal system, there is a possibility that an abnormality in the fuel supply system may be erroneously detected. Therefore, the process proceeds to step 311 to reset the abnormality diagnosis permission flag XDGFUELEX to “0” which means that abnormality diagnosis is prohibited. finish.

  When all the conditions determined in steps 301 to 309 described above are satisfied, the abnormality diagnosis execution condition is satisfied, the process proceeds to step 310, and the abnormality diagnosis permission flag XDGFUELEX is set to "1" meaning abnormality diagnosis permission. Exit this program.

[Error diagnosis parameter calculation]
The abnormality diagnosis parameter calculation program shown in FIG. 11 is started at every predetermined crank angle (for example, every 180 ° C. A). When this program is started, first, in step 401, it is determined whether or not an abnormality diagnosis execution condition is satisfied (that is, whether or not the abnormality diagnosis permission flag XDGFULEEX is set to “1”), and abnormality diagnosis is executed. When the condition is not satisfied (XDGFULEEX = 0), the process proceeds to steps 408 and 409, and both the abnormality diagnosis parameter DGDELAF and the abnormality diagnosis parameter smoothed value DGDELAFSM are set to “1.0” which means that there is no abnormality. To finish this program. In this case, no abnormality in the fuel supply system is detected.

On the other hand, if the abnormality diagnosis execution condition is satisfied (XDGFULEEX = 1), the air-fuel ratio correction coefficient FAF, the learning correction amount KGj, the air-fuel ratio λ, and the target air-fuel ratio λTG are read in steps 402 to 405. Thereafter, in step 406, the difference between the air-fuel ratio λ detected by the air-fuel ratio sensor 28 and the target air-fuel ratio λTG, the air-fuel ratio correction coefficient FAF (feedback correction amount), and the learning correction amount KGj are summed up to diagnose abnormality. The parameter DGDELAF is obtained.
DGDELAF = (λ−λTG) + FAF + KGj
Thereafter, in step 407, the abnormality diagnosis parameter DGDELAF is smoothed by the following equation to calculate the abnormality diagnosis parameter smoothed value DGDELAFSM.
DGDELAFSM (i) = {3 × DGDELAFSM (i−1) + DGDELAF} / 4
In the above equation, the smoothing coefficient is 1/4, but may be 1/3, 1/6, 1/8, or the like.

[Error diagnosis execution]
The abnormality diagnosis execution program shown in FIG. 12 is started every predetermined time (for example, every 1024 ms). When this program is started, first, in step 501, it is determined whether or not the state of the abnormality diagnosis permission flag XDGFUELEX = 1 (abnormality diagnosis permission) has continued, for example, for 20 s. Proceeding to steps 514 and 515, the rich-side diagnosis counter cDFAFR and the lean-side diagnosis counter cDFAFL are reset to “0”.

  After that, when the state of the abnormality diagnosis permission flag XDGFUELEX = 1 continues for 20 s, the process proceeds from step 501 to step 502, and after reading the abnormality diagnosis parameter simulated value DGDELAFSM calculated in step 407 of FIG. 11, in step 503, The rich-side abnormality diagnosis reference value tDFAFR and the lean-side abnormality diagnosis reference value tDFAFL are read from the abnormality diagnosis reference value map of FIG. 13 according to the current intake air amount Ga.

  Thereafter, in step 504, the abnormality diagnosis parameter smoothed value DGDELAFSM is compared with the rich-side abnormality diagnosis reference value tDFAFR. If DGDELAFSM ≦ tDFAFR (rich-side abnormality), the process proceeds to step 509 and the rich-side diagnosis counter cDFAFR is set. Increment by one. Then, in the next step 510, it is determined whether or not the count value of the rich-side diagnosis counter cDFAFR is 20 or more, that is, whether or not the rich-side abnormality has continued for 20 seconds, for example. Then, the process proceeds to step 512, where the rich side abnormality of the fuel supply system is finally diagnosed and the rich side abnormality diagnosis flag DGFUERRNG is set to “1” meaning the rich side abnormality. In the next step 513, the warning lamp 37 is lit to warn the driver and the program is terminated.

  When the count value of the rich side diagnosis counter cDFAFR is less than 20 in the above step 510, that is, when the rich side abnormality does not continue for 20 seconds, the present program is terminated without giving a final diagnosis result. .

  If it is determined in step 504 that DGDELAFSM> tDFAFR (rich side normal), the process proceeds to step 505, where the abnormality diagnosis parameter smoothed value DGDELAFSM is compared with the lean side abnormality diagnosis reference value tDFAFL, and DGDELAFSM ≧ tDFAFL If (lean side abnormality), the routine proceeds to step 506, where the lean side diagnosis counter cDFAFL is incremented by one. Then, in the next step 507, it is determined whether or not the count value of the lean side diagnosis counter cDFAFL has become 20 or more, for example, whether or not the lean side abnormality has continued for 20 seconds, for example. Then, the process proceeds to step 508, where it is finally diagnosed that the fuel supply system is abnormal on the lean side, and the lean side abnormality diagnosis flag DGFULLNG is set to “1” which means the abnormality on the lean side. The lamp 37 is lit to warn the driver and the program is terminated.

  If the count value of the lean-side diagnosis counter cDFAFL is less than 20 in step 507, that is, if the lean-side abnormality has not continued for 20 seconds, the program is terminated without giving a final diagnosis result. .

  An example when the abnormality diagnosis of the fuel supply system is performed by the program described above will be described based on FIG. In the example of FIG. 14, the air-fuel ratio correction coefficient FAF is stuck to the lower limit guard value midway, and the learning correction amount KGj is not updated. Even during the period in which the learning correction amount KGj is not updated, the rich-side diagnosis counter cDFAFR is incremented when the abnormality diagnosis parameter smoothing value DGDELAFSM becomes equal to or less than the rich-side abnormality diagnosis reference value tDFAFR. This increment operation is repeated approximately every 1 second as long as the condition of DGDELAFSM ≦ tDFAFR continues, and when the count value of the counter cDFAFR reaches 20 (seconds), the rich side abnormality diagnosis flag DGFUERRNG is set to “1”. Then, an abnormality in the fuel supply system is detected.

  According to the embodiment described above, since the fact that the air-fuel ratio sensor 28 is fully activated (element resistance value Z <60Ω) is added as one of the abnormality diagnosis execution conditions, even during the air-fuel ratio feedback control. If the air-fuel ratio sensor 28 is not fully activated, abnormality diagnosis of the fuel supply system is not performed, and abnormality diagnosis is performed after the air-fuel ratio sensor 28 is completely activated. Thereby, the detection range and responsiveness of the air-fuel ratio sensor 28 at the time of abnormality diagnosis can be ensured, the air-fuel ratio can be detected with high accuracy, and the abnormality diagnosis accuracy can be improved.

  In addition, since the activation determination of the air-fuel ratio sensor 28 is performed based on the element resistance value Z by utilizing the characteristic that the element resistance value Z changes according to the element temperature of the air-fuel ratio sensor 28, the air-fuel ratio sensor 28 Even if a temperature sensor such as a thermocouple is not attached to the sensor, the element temperature (active state) can be accurately detected based on the element resistance value Z calculated from the applied voltage change amount ΔV and the current change amount ΔI of the air-fuel ratio sensor 28. It is possible to meet the demands for reducing the number of parts and reducing the cost.

  However, in the present invention, a temperature sensor may be provided in the air-fuel ratio sensor 28, and it may be determined whether the air-fuel ratio sensor 28 is fully activated based on the element temperature detected by the temperature sensor. However, the intended purpose of the present invention can be sufficiently achieved.

  Incidentally, since the element resistance value Z decreases as the element temperature increases, the air-fuel ratio sensor 28 is fully activated depending on whether or not the element resistance value Z is lower than a predetermined value (for example, 60Ω) as in the above embodiment. When it is determined whether or not it is in a state, even if the element temperature becomes too high, it is determined that it is in a fully active state. However, since the detection error of the normal air-fuel ratio sensor 28 increases when the element temperature becomes too high, the manufacturer of the air-fuel ratio sensor 28 increases the detection accuracy according to the specifications (standards) of the air-fuel ratio sensor 28. The guaranteed temperature range (the range of the element resistance value Z) is set as the guaranteed range, and the reliability of the air-fuel ratio detection value is guaranteed only within this guaranteed range. Therefore, if the element temperature becomes too high and the element resistance value Z becomes smaller than the lower limit value of the guaranteed range, the reliability of the air-fuel ratio detection value is not guaranteed.

  Considering this point, it may be determined whether the element resistance value Z of the air-fuel ratio sensor 28 is in the guaranteed range (for example, 20Ω <Z <60Ω) or not is in a fully active state. In this way, in the region where the element temperature of the air-fuel ratio sensor 28 becomes too high and the detection accuracy is lowered, it is not determined as a fully active state, and abnormality diagnosis is not performed, so the reliability of abnormality diagnosis is further increased. It can be improved.

  In the above embodiment, the abnormality diagnosis of the fuel supply system is performed based on the output of the air-fuel ratio sensor 28. However, for example, the abnormality diagnosis of the air-fuel ratio sensor 28 and the abnormality diagnosis of the catalyst 27 may be performed. good. The abnormality diagnosis of the air-fuel ratio sensor 28 is performed, for example, by determining the air-fuel ratio follow-up during the air-fuel ratio feedback control from the output of the air-fuel ratio sensor 28 and diagnosing whether there is an abnormality in the response of the air-fuel ratio sensor 28, or In a system in which air-fuel ratio sensors are installed on both the upstream side and downstream side of the catalyst, there is no abnormality in the output of the air-fuel ratio sensor by comparing the output of one air-fuel ratio sensor with the output of the other air-fuel ratio sensor. It may be diagnosed. Further, the abnormality diagnosis of the catalyst is performed in a system in which air-fuel ratio sensors are installed on both the upstream side and downstream side of the catalyst, and the output of the upstream air-fuel ratio sensor (upstream air-fuel ratio) and the downstream air-fuel ratio sensor. The deterioration of the catalyst may be diagnosed from the relationship with the output (downstream air-fuel ratio). Also in the abnormality diagnosis of the air-fuel ratio sensor and the abnormality diagnosis of the catalyst, the abnormality diagnosis accuracy can be improved if the abnormality diagnosis is performed with the air-fuel ratio sensor fully activated.

1 is a schematic configuration diagram of an entire engine control system showing an embodiment of the present invention. The figure which shows the relationship between the element resistance value of the air fuel ratio sensor and the detection range The figure which shows the relationship between the element resistance value and response of the air fuel ratio sensor Flow chart showing the flow of processing of the air-fuel ratio control program A diagram conceptually showing the target air-fuel ratio map Flow chart showing the flow of processing of the target air-fuel ratio setting program Time chart showing the relationship between the output of the oxygen sensor and the median value λTGC of the target air-fuel ratio Time chart showing relationship between output of oxygen sensor and target air-fuel ratio λTG Flow chart showing the flow of processing of the air-fuel ratio learning program Flow chart showing the flow of processing of the abnormality diagnosis execution condition determination program Flow chart showing the flow of processing of the abnormality diagnosis parameter calculation program Flow chart showing the flow of processing of the abnormality diagnosis execution program A diagram conceptually showing an abnormality diagnosis reference value map Time chart showing an example of abnormality diagnosis of the fuel supply system

Explanation of symbols

11 Engine (Internal combustion engine)
26 Exhaust pipe 27 Catalyst 28 Air-fuel ratio sensor (air-fuel ratio detection means)
29 Oxygen sensor 30 Engine control circuit (abnormality diagnosis means, complete activity determination means, resistance value detection means)
37 Warning lamp 38 Sensor element

Claims (6)

An air-fuel ratio detecting means having a sensor element that generates a limit current substantially proportional to the oxygen concentration in the exhaust gas, and capable of detecting the air-fuel ratio even in a semi-active state;
Air-fuel ratio control means for performing air-fuel ratio feedback control based on the output of the air-fuel ratio detection means;
An abnormality diagnosis means for making an abnormality diagnosis based on the output of the air-fuel ratio detection means,
The air-fuel ratio control means performs air-fuel ratio feedback control when the air-fuel ratio detection means is in a semi-active state or a fully active state,
The control apparatus for an internal combustion engine, wherein the abnormality diagnosis means performs abnormality diagnosis when the air-fuel ratio detection means is in a fully active state. An air-fuel ratio detecting means having a sensor element that generates a limit current substantially proportional to the oxygen concentration in the exhaust gas, and capable of detecting the air-fuel ratio even in a semi-active state;
Air-fuel ratio control means for performing air-fuel ratio feedback control based on the output of the air-fuel ratio detection means;
Abnormality diagnosis means for performing abnormality diagnosis based on the output of the air-fuel ratio detection means;
Cooling water temperature detecting means for detecting the cooling water temperature of the internal combustion engine,
The air-fuel ratio control means performs air-fuel ratio feedback control when the cooling water temperature detected by the cooling water temperature detection means is equal to or higher than a first predetermined water temperature;
The control apparatus for an internal combustion engine, wherein the abnormality diagnosis means performs abnormality diagnosis when the cooling water temperature detected by the cooling water temperature detection means is equal to or higher than a second predetermined water temperature higher than the first predetermined water temperature. The abnormality diagnosis unit does not perform abnormality diagnosis when the cooling water temperature detected by the cooling water temperature detection unit is equal to or higher than a third predetermined water temperature higher than the second predetermined water temperature. Control device for internal combustion engine. 4. The control apparatus for an internal combustion engine according to claim 1, wherein the abnormality diagnosis unit diagnoses an abnormality in the fuel supply system. 4. The control apparatus for an internal combustion engine according to claim 1, wherein the abnormality diagnosis unit diagnoses an abnormality of the air-fuel ratio detection unit. A catalyst for purifying exhaust gas provided in an exhaust system of an internal combustion engine;
Provided on the downstream side of the catalyst, and comprises a catalyst downstream air-fuel ratio detecting means for detecting an air-fuel ratio downstream of the catalyst,
4. The abnormality diagnosis unit according to claim 1, wherein the abnormality diagnosis unit diagnoses the abnormality of the catalyst from a relationship between an output of the air-fuel ratio detection unit and an output of the catalyst downstream air-fuel ratio detection unit. The internal combustion engine control device described.

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