JP4883321B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and is particularly useful when applied to a failure of an air-fuel ratio sensor in a vehicle that can use both gasoline fuel and alcohol fuel (hereinafter referred to as FFV).

  Recently, alcohol such as ethanol has attracted attention as a low-pollution fuel, and the development of FFV using this alcohol as fuel by mixing it with gasoline is advancing. Also in this type of FFV, an oxygen sensor or LAFS (linear air-fuel ratio sensor) is provided to detect the air-fuel ratio from the oxygen concentration in the exhaust, and during operation, the fuel supply amount is fed back so that the air-fuel ratio approaches the target air-fuel ratio. Control to correct. At this time, in the FFV, it is necessary to appropriately control the fuel injection amount in consideration of the difference in characteristics of both fuels, such as the difference in the theoretical air-fuel ratio between gasoline and alcohol. That is, it is necessary to accurately grasp the alcohol concentration of the alcohol-mixed fuel and perform accurate fuel supply amount control according to the alcohol concentration. Here, it is known that the alcohol concentration can be estimated based on data representing the state of the exhaust gas. Therefore, instead of the method of directly detecting the alcohol concentration with the alcohol sensor (see, for example, Patent Document 1), the alcohol concentration of the FFV is based on the output signal of the oxygen sensor or LAFS that is the air-fuel ratio sensor for detecting the exhaust air-fuel ratio. A method for performing estimation has been proposed. In this case, the fuel injection amount is controlled so that a predetermined air-fuel ratio is obtained based on the estimated alcohol value.

Japanese Patent Publication No. 7-6430

  As described above, when estimating the alcohol concentration in the alcohol-mixed fuel, it is necessary to take measures when a sensor such as an oxygen sensor or LAFS fails. In this case, it is conceivable that the alcohol concentration is changed stepwise to a predetermined set value simultaneously with the sensor failure.

  However, in this case, there is a possibility that exhaust gas and drivability deteriorate due to a sudden change in the air-fuel ratio.

  Incidentally, the change in the alcohol concentration is determined by parameters such as the amount of alcohol fuel transferred and mixed in a predetermined volume formed from the delivery pipe and the fuel pipe, and the amount of fuel injected from the injector. Therefore, the change in the alcohol concentration varies depending on the fuel injection amount that varies depending on, for example, the engine speed and load under a wide range of operating conditions that are normally assumed. For this reason, the trajectory in which the alcohol concentration changes cannot be correctly traced by instantaneous alcohol concentration switching or tailing with a fixed gain.

  In Patent Document 1, when an alcohol sensor fails, the output of the alcohol sensor is fixed to a set value, or is dealt with by tailing based on the fixed set value.

  In view of the above-described prior art, the present invention is an internal combustion engine that can eliminate the above-described disadvantages associated with a sudden change in air-fuel ratio and suppress deterioration of exhaust gas and drivability even when a sensor that estimates alcohol concentration fails. An object of the present invention is to provide a control device.

  The configuration of the present invention that achieves the above object is based on the following knowledge. FIG. 1 is a diagram showing an example of characteristics when the alcohol concentration is changed from a to b. (A) is an exhaust air-fuel ratio, (b) is a feedback coefficient (air-fuel ratio) of an oxygen sensor for estimating the alcohol concentration. (C) is a correction coefficient for controlling the fuel consumption amount to a predetermined value, and FIG. That is, the horizontal axis is the time axis.

  Referring to FIG. 1, while the fuel consumption integrated value (FIG. 1 (c)) increases linearly with time, the feedback coefficient (FIG. 1 (b)) hardly changes until time t1. From time t1 to time t2, it rises following the equivalence ratio change, and after time t2, it is found that it is saturated to a constant value. During this time, the exhaust air-fuel ratio (FIG. 1 (a)) is stable even if the equivalence ratio changes.

  Here, when focusing on the feedback coefficient between the time t1 and the time t2 and examining in more detail, it is found that the trajectory during this time can be satisfactorily approximated by the trajectory when the first-order lag processing is performed twice. It was. This is because when the sensor used in the alcohol concentration estimation control fails, the estimation of the alcohol concentration is stopped and the predetermined concentration is set. If the process is approximated by a trajectory performed twice, it means that the trajectory in which the alcohol concentration actually changes (trajectory according to the fuel consumption) can be satisfactorily followed.

  Further, at this time, the estimated alcohol concentration does not change from the start of feedback until time t1, that is, until the fuel consumption integrated value reaches the threshold A, and similarly after time t2, that is, the fuel consumption integrated value is equal to the threshold. It can be seen that the estimated alcohol concentration does not change even after exceeding B. The former is considered to be because the replacement of the fuel in the injector section is started at the time of the threshold A, and the replacement is almost completed at the time of the threshold B in the latter.

  Therefore, the optimum estimation result when the alcohol concentration estimated value is obtained by dividing into three regions of threshold A ≧ fuel consumption integrated value, A <fuel consumption integrated value ≦ threshold B, threshold B <fuel consumption integrated value. You will get.

  A first aspect of the present invention based on such knowledge is a control device for an internal combustion engine operable with an alcohol-containing fuel, the air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust system of the internal combustion engine, and the air-fuel ratio An alcohol concentration estimating means for estimating an alcohol concentration based on the air / fuel ratio detected by the detecting means; a fail determining means for determining whether or not the air / fuel ratio detecting means has failed; and the air / fuel ratio detecting means by the fail determining means. The alcohol concentration setting means for setting a predetermined alcohol concentration value instead of the estimated value of the alcohol concentration by the alcohol concentration estimating means when the alcohol concentration is determined to have failed. First-order lag processing is performed twice on the estimated alcohol concentration at the time when the determination means determines that the air-fuel ratio detection means has failed. The control device for an internal combustion engine, characterized by being configured so as to shift to the predetermined concentration.

  According to this aspect, the estimated alcohol concentration at the time of failure and the predetermined concentration are shifted to the predetermined concentration by performing the first-order lag process twice. The estimated value of alcohol concentration at the time of failure can be transferred to the concentration of. As a result, it is possible to perform accurate drive control of the internal combustion engine while suppressing deterioration of exhaust gas and drivability due to a sudden change in the air-fuel ratio at the time of switching the alcohol concentration estimated value.

  According to a second aspect of the present invention, in the control apparatus for an internal combustion engine described in the first aspect, the fuel supply determination means for determining whether or not fuel has been supplied is further provided, and the alcohol concentration setting means includes the oil supply determination means. The control apparatus for an internal combustion engine is configured to start transition to the predetermined alcohol concentration value after a predetermined period has elapsed from the time when it is determined that the fuel has been supplied.

  According to this aspect, the result of the fuel supply can be reflected in the estimation of the alcohol concentration at the time of the sensor failure, so that the control of the internal combustion engine can be performed more accurately.

  According to the present invention, when the air-fuel ratio sensor that is the basis of the alcohol concentration estimation fails, the air-fuel ratio can be shifted to a predetermined concentration along a trajectory in which the alcohol concentration actually changes according to the fuel consumption. Suppresses deterioration of exhaust gas and drivability due to sudden changes in air-fuel ratio that occur when the estimated alcohol concentration is set to a predetermined fixed value step by step at the time of sensor failure or when tailing processing is performed based on the predetermined fixed value Thus, accurate alcohol concentration estimation control can be continued.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a block diagram showing an FFV engine and its control apparatus according to an embodiment of the present invention. As shown in the figure, an ignition plug 3 is attached to each cylinder in a cylinder head 2 of an engine 1 that is an internal combustion engine mounted on an FFV, and an ignition coil 4 that outputs a high voltage is connected to the ignition plug 3. ing. An intake port 5 is formed in the cylinder head 2 for each cylinder, and an intake valve 7 is provided on the intake port 5 on the combustion chamber 6 side. The intake valve 7 is opened and closed following the cam of the camshaft 8 that rotates in accordance with the engine rotation, and communicates and shuts off the intake port 5 and the combustion chamber 6.

  One end of an intake manifold 9 is connected to and communicated with the intake port 5. An electromagnetic fuel injection valve 10 is attached to the intake manifold 9 corresponding to each cylinder, and the fuel injection valve 10 is connected to a fuel pipe 11. The fuel pipe 11 is connected to a fuel supply device (not shown), and a mixed fuel containing alcohol (ethanol) and gasoline is supplied from the fuel tank 14. The amount of fuel in the fuel tank 14 is detected by a fuel sensor 21.

  An intake pipe upstream of the intake manifold 9 is provided with a throttle valve 12 that opens and closes an intake passage, and a throttle position sensor 13 that detects a valve opening (throttle opening) of the throttle valve 12.

  On the other hand, an exhaust port 15 is formed in each cylinder head 2 for each cylinder, and an exhaust valve 17 is provided on the combustion chamber 6 side of the exhaust port 15. The exhaust valve 17 is opened and closed following the cam of the camshaft 18 that rotates in accordance with the engine rotation, and communicates and shuts off the exhaust port 15 and the combustion chamber 6. One end of an exhaust manifold 16 is connected to the exhaust port 15, and the exhaust manifold 16 communicates with the exhaust port 15.

  An exhaust pipe (exhaust passage) 20 is connected to the other end of the exhaust manifold 16, and an exhaust purification catalyst 23 is provided in the exhaust pipe 20. An oxygen sensor 22 is provided in the exhaust pipe 20 upstream of the exhaust purification catalyst 23.

  An electronic control unit I (hereinafter referred to as ECUI), which is a control device, performs comprehensive control including the engine 1, and on its input side, a throttle position sensor 13, a fuel sensor 21, an oxygen sensor 22, Various sensors such as a crank angle sensor 25 for detecting the crank angle of the engine 1 are connected, and detection information from these sensors is input. On the other hand, various output devices such as the fuel injection valve 10, the ignition coil 4, and the throttle valve 12 are connected to the output side of the ECUI. These various output devices output operation parameters such as fuel injection time, ignition timing, and throttle opening calculated by the ECU I based on detection information from various sensors. That is, based on detection information from various sensors, the air-fuel ratio corresponding to the alcohol concentration of the mixed fuel is set to an appropriate target air-fuel ratio (target A / F), and feedback control is performed based on information from the oxygen sensor 22. The

  FIG. 3 is a block diagram showing the detailed configuration of the ECU I according to this embodiment (note that the sensors show only the oxygen sensor 22 and the fuel sensor 21). As shown in the figure, the ECU I in this embodiment includes an air-fuel ratio detection unit 51, a feedback correction amount setting unit 52, a target air-fuel ratio setting unit 53, an alcohol concentration estimation unit 54, an operation parameter control unit 55, and a fuel consumption integration unit. 56, a failure determination unit 57 and an alcohol concentration setting unit 58.

  Among these, the air-fuel ratio detection unit 51 processes the output signal of the oxygen sensor 22 to detect the air-fuel ratio, and outputs this air-fuel ratio to the feedback correction amount setting unit 52. The feedback correction amount setting unit 52 compares the actually measured air-fuel ratio with the target air-fuel ratio preset in the target air-fuel ratio setting unit 53, and determines the air-fuel ratio feedback correction amount so as to reach the target air-fuel ratio. Output to the operation parameter control unit 55. The alcohol concentration estimation unit 54 normally constitutes a feedback loop system, estimates the alcohol concentration based on the air-fuel ratio feedback correction amount, generates an alcohol concentration estimated value, and outputs this to the operation parameter control unit 55. .

  Based on the outputs from the alcohol concentration estimation unit 54 and the failure determination unit 57, the alcohol concentration setting unit 58 follows a trajectory in which the concentration actually changes from the alcohol concentration estimation value at the time of the failure and shifts to a predetermined concentration. The estimated alcohol concentration value is output to the operation parameter control unit. As the “predetermined concentration” in this case, for example, a concentration mapped in advance based on an alcohol concentration estimated value at the time of failure may be used. Here, the trajectory according to the fuel consumption, which actually changes in concentration, is the first-order lag in the transient region (A <fuel consumption integrated value ≦ B) as described in the knowledge based on FIG. Good approximation can be achieved by performing the process twice.

  Furthermore, the alcohol concentration setting unit 58 according to the present embodiment changes the setting method based on the integrated value of the fuel consumption output from the fuel consumption integration unit 56. That is, as shown in FIG. 1 (c), an initial region (A ≧ fuel consumption integrated value) in which the feedback coefficient divided by the thresholds A and B hardly changes according to the fuel consumption integrated value (A ≧ fuel consumption integrated value), and a predetermined change. The setting process is performed in consideration of the presence of three regions, a transition region (A <fuel consumption integrated value ≦ B) and a saturation region (B <fuel consumption integrated value). The fuel consumption integrating unit 56 obtains an integrated value by performing a predetermined calculation based on the output of the fuel sensor 21 that measures the fuel amount.

  The operation parameter control unit 55 controls parameters related to the operation of the engine such as the fuel injection time for the fuel injection valve 10 based on the estimated alcohol concentration value or the air-fuel ratio feedback correction amount.

  According to the present embodiment, the alcohol concentration estimation unit 54 estimates the alcohol concentration based on the air-fuel ratio feedback correction amount detected by the air-fuel ratio detection unit 51 and the feedback correction amount setting unit 52 based on the output of the oxygen sensor 22 at the normal time. Based on the estimated alcohol concentration value and the air-fuel ratio feedback correction amount, the engine 1 is controlled with predetermined operation parameters set by the operation parameter control unit 55.

  On the other hand, the alcohol concentration setting unit 58 outputs a predetermined estimated alcohol concentration value instead of the alcohol concentration estimated by the alcohol concentration estimating unit 54 at the time of failure of the air-fuel ratio sensor. As a result, the operation parameter control unit 55 controls the engine 1 with predetermined operation parameters based on the estimated alcohol concentration value and the air-fuel ratio feedback correction amount supplied via the alcohol concentration setting unit 58.

  Here, the calculation method of the alcohol concentration estimated value at the time of the above-mentioned failure is explained in detail. That is, it is divided into an initial region (A ≧ fuel consumption integrated value), a transient region (A <fuel consumption integrated value ≦ B) and a saturation region (B <fuel consumption integrated value) shown in FIG. The estimated alcohol concentration is calculated using the following formula. In addition, the code | symbol in following Formula has each shown ALTest (n); alcohol concentration estimated value, ALTest_fail; alcohol concentration estimated value at the time of a sensor failure, and K: filter gain.

1) Initial region (A ≧ Fuel consumption integrated value)
ALTest (n) = ALCest (n−1) (1)
Since there is no change in the estimated value in this area, the previous value is used as it is.

2) Transition area (A <Fuel consumption integrated value ≦ B)
ALTest_ds (n) = K_ds × ALCest_ds (n−1) +
(1-K_ds) × ALCest_fail (2)
ALTest (n) = K × ALTest (n−1) + (1-K)
× ALCest_ds (n) (3)

  In this area, the estimated alcohol concentration value is obtained by performing first-order lag processing based on the estimated alcohol concentration value (current value) at the time of sensor failure in the above equation (2). Further, in the above equation (3), the primary concentration is again performed based on the result of the equation (2) to obtain an estimated alcohol concentration value as an output. Such two primary delay processes are repeated until a predetermined concentration is reached.

  FIG. 4 schematically shows two primary processes represented by the above formulas (2) and (3). In the figure, the left half block is a portion corresponding to the first primary processing, and the right half block is a portion corresponding to the second primary processing. Further, “1 / Z” means processing for returning to the previous value.

3) Saturation region (B <Fuel consumption integrated value)
ALTest (n) = ALCest_fail (4)
Since there is no change in the estimated value in this area, this value is used as it is, fixed at the time of sensor failure (current value).

  FIG. 5 is a flowchart showing a processing procedure in the ECU I according to this embodiment. As shown in FIG. 5A, the current estimated concentration ALTest (n) is stored at the time of key-off (see step S1).

On the other hand, the alcohol concentration is estimated by the following processing procedure as shown in FIG.
1) It is determined whether or not refueling has been performed (step S2).
2) If the determination result in step S2 is Yes, the fuel consumption after refueling is integrated (see step S3).
3) It is determined whether or not the fuel integrated value is a predetermined amount 2 (saturation region value) (see step S4).
4) If the determination result in step S4 is No, the value is based on the above equation (4) because it is in the saturation region (see step S5).
5) When the determination result in step S4 is Yes, the fuel integrated value is a predetermined amount 1 because it is in the transient region (A <fuel consumption integrated value ≦ B) or in the initial region (A ≧ fuel consumption integrated value). It is determined whether or not (the value of the initial region) (see step S6).
6) If the determination result in step S6 is No, the value is based on the above equation (1) because it is in the initial region (see step S7).
7) If the determination result in step S6 is Yes, since it is in the transient region (A <fuel consumption integrated value ≦ B), the alcohol concentration estimate ALEST_BU (n) at the time of failure is calculated. This is executed by performing calculations based on the above equations (2) and (3) (see step S8). That is, a predetermined alcohol concentration estimated value is obtained by performing the primary process twice. The same process (the process of step S8) is also performed when the determination result of step S2 is No.
8) It is determined whether or not the air-fuel ratio sensor has failed (see step S9).
9) If the determination result in step S9 is No, the state is normal, and the alcohol concentration estimated value ALTest (n) is updated by normal calculation (see step S10).
10) If the determination result in step S9 is Yes, it is an abnormal state, and therefore the failure concentration estimate value is updated with the failure alcohol concentration estimate value ALTest_BU (n) (see step S10). At this time, if it is in the saturation region (B <fuel consumption integrated value) to the initial region (A ≧ fuel consumption integrated value), the set value in step 4 to step S6 is used. That is, it is fixed to the value immediately before (in the case of the initial region) or the value at the time of failure (saturation region).

  In addition, when the fuel supply determination means which determines whether it has further refueled is added to the structure of the said embodiment shown in FIG. 3, and the failure determination part 57 determines with it being in a failure state, alcohol concentration The setting unit 58 may use a predetermined backup density in consideration of the result of refueling instead of the predetermined density. In this case, estimation or control reflecting the refueling result can be performed.

  The present invention can be effectively used in the automotive industry, particularly in the industrial field related to FFV.

It is a figure which shows an example of the characteristic when changing alcohol concentration from a to b, (a) is an exhaust air fuel ratio, (b) is a feedback coefficient of the oxygen sensor for estimating alcohol concentration, (c) is fuel The change with time of the consumption amount integrated value is shown. It is a block diagram which shows the engine of FFV which concerns on embodiment of this invention, and its control apparatus. It is a block diagram which shows the detailed structure of ECU which concerns on embodiment of this invention. It is explanatory drawing which shows typically the 2nd time primary delay process in embodiment of this invention. It is a flowchart which shows the process sequence in ECU which concerns on embodiment of this invention.

Explanation of symbols

I ECU
DESCRIPTION OF SYMBOLS 1 Engine 10 Fuel injection valve 21 Fuel sensor 22 Oxygen sensor 51 Air-fuel ratio detection part 52 Feedback correction amount setting part 54 Alcohol concentration estimation part 55 Operation parameter control part 56 Fuel consumption integration part 57 Fail judgment part 58 Alcohol concentration setting part

Claims (2)

A control device for an internal combustion engine operable with an alcohol-containing fuel,
Air-fuel ratio detection means for detecting an air-fuel ratio of the exhaust system of the internal combustion engine;
Alcohol concentration estimation means for estimating the alcohol concentration based on the air-fuel ratio detected by the air-fuel ratio detection means;
Fail determination means for determining whether or not the air-fuel ratio detection means has failed;
An alcohol concentration setting means for setting a predetermined alcohol concentration value instead of the estimated value of the alcohol concentration by the alcohol concentration estimating means when the fail determining means determines that the air-fuel ratio detecting means has failed. ,
The alcohol concentration setting means is configured to perform a first-order lag process twice on the estimated alcohol concentration at the time when the fail determination means determines that the air-fuel ratio detection means has failed, and to shift to the predetermined concentration. A control device for an internal combustion engine. The control apparatus for an internal combustion engine according to claim 1,
It further comprises an oil supply determining means for determining whether or not fuel has been supplied,
The internal combustion engine characterized in that the alcohol concentration setting means is configured to start shifting to the predetermined alcohol concentration value after a predetermined period has elapsed from the time when it is determined that the oil supply determining means has been refueled. Control device.

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