JP4333577B2 - Fuel property determination device for internal combustion engine - Google Patents

Description

  The present invention relates to a technique for determining fuel properties of an internal combustion engine.

Biofuels such as ethanol, methanol, and methyl ester are known as fuels for internal combustion engines and the like. When such a mixed fuel of biofuel and fossil fuel (light oil, gasoline, etc.) is used, air-fuel ratio sensors are arranged before and after the oxidation catalyst, and the output signals of these air-fuel ratio sensors are selectively used. There has been proposed a technique for performing accurate air-fuel ratio control regardless of variation in biofuel concentration by controlling the fuel injection amount (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 5-209549 JP 2003-254037 A Japanese Patent No. 2861377

  By the way, when unburned fuel is supplied to the catalyst by injecting fuel from the fuel injection valve during the exhaust stroke or by injecting fuel from the fuel addition valve provided in the exhaust passage, the fuel is supplied to the upstream end of the catalyst. Is easy to adhere. When fuel adheres to the upstream end of the catalyst, the air-fuel ratio (oxygen concentration in the exhaust) downstream of the catalyst changes. In the conventional technique described above, when fuel adheres to the upstream end of the catalyst, it is considered that the biofuel concentration in the mixed fuel has changed, and the fuel injection amount may be controlled.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of accurately grasping the change in the concentration of different fuels in the fuel.

  In order to solve the above-described problems, the present invention provides an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor disposed upstream and downstream of the exhaust purification catalyst, and an upstream air-fuel ratio sensor from the upstream toward the exhaust purification catalyst. In an internal combustion engine having a fuel supply means for supplying fuel for the internal combustion engine, the difference between the downstream air-fuel ratio sensor output and the base air-fuel ratio when the fuel supply means supplies the fuel is integrated and the upstream air-fuel ratio The sensor output is monitored, and the fuel property is determined by using the upstream air-fuel ratio sensor output as a parameter on the condition that the integrated value is substantially equal to a predetermined reference value (downstream reference value). .

  Specifically, the internal combustion engine fuel property determination apparatus according to the present invention uses the downstream reference value as the integrated value of the deviation between the downstream air-fuel ratio sensor output and the base air-fuel ratio when the fuel supply means normally supplies fuel. First storage means for storing the value as a value, second storage means for storing the output of the upstream air-fuel ratio sensor when the fuel supply means normally supplies the reference fuel having the assumed property as the upstream reference value, The calculating means for integrating the deviation between the downstream air-fuel ratio sensor output and the base air-fuel ratio when the fuel supplying means supplies the fuel, and the difference between the calculated value of the calculating means and the downstream reference value is not more than a predetermined amount. A determination means for comparing the output of the upstream air-fuel ratio sensor and the upstream reference value on the condition, and determining that the current fuel property is different from the reference fuel if the difference between the two exceeds an allowable range; I was prepared to. The base air-fuel ratio is the exhaust air-fuel ratio when no fuel is supplied from the fuel supply means, and is equivalent to the air-fuel ratio of the internal combustion engine unless secondary air or the like is added.

A fuel in which different types of fuels such as biofuels are mixed (hereinafter referred to as different types of mixed fuels) has a different evaporability (evaporable temperature) than a fuel in which different types of fuels are not mixed (reference fuel). For this reason, the output of the upstream air-fuel ratio sensor differs between the case where the fuel supply means supplies the heterogeneous mixed fuel and the case where the reference fuel is supplied even if the fuel supply amount is the same.

  For example, when the concentration of biofuel in the fuel increases, the evaporability of the fuel decreases, so that the fuel supplied from the fuel supply means cannot evaporate until it reaches the upstream air-fuel ratio sensor. If the supplied fuel cannot evaporate before reaching the upstream air-fuel ratio sensor, the upstream air-fuel ratio sensor outputs a signal that is leaner than the actual air-fuel ratio. This tendency becomes more prominent as the biofuel concentration in the fuel increases.

  Therefore, when the output of the upstream air-fuel ratio sensor shows a value different from a predetermined upstream reference value, it can be considered that the fuel of the internal combustion engine has a fuel property different from that of the reference fuel. . In this way, by using the output of the upstream air-fuel ratio sensor as a parameter, it is possible to determine the fuel properties without being affected even if the supplied fuel adheres to the upstream end face of the exhaust purification catalyst. It becomes.

  The upstream air-fuel ratio sensor output and the upstream reference value to be compared are as follows: (1) When the upstream air-fuel ratio sensor output starts to change from the base air-fuel ratio to the rich side due to the fuel supply of the fuel supply means. An integrated value (hereinafter, upstream side) of the deviation between the base air-fuel ratio and the upstream air-fuel ratio sensor output during a period until the upstream side air-fuel ratio sensor output returns to the base air-fuel ratio (hereinafter referred to as upstream air-fuel ratio change period). (2) Minimum value of upstream air-fuel ratio sensor output during upstream air-fuel ratio change period, (3) Upstream air-fuel ratio sensor output and base air-fuel ratio during upstream air-fuel ratio change period The maximum value of the deviation can be used.

  Incidentally, the output of the upstream side air-fuel ratio sensor changes not only when the concentration of the different fuel in the fuel changes, but also when the fuel supply means cannot supply a specified amount of fuel due to deterioration or failure. For example, if the actual fuel supply amount becomes larger or smaller than the target supply amount due to deterioration or failure of the fuel supply means, the output of the upstream air-fuel ratio sensor becomes lower or higher than the reference value even if the fuel properties are the same.

  As described above, when the actual fuel supply amount is different from the target supply amount due to deterioration or failure of the fuel supply means, when the fuel property determination is performed, the fuel property is not changed even though the fuel property is not changed. May be erroneously determined to have changed. For example, if the above-described fuel property determination is performed when the actual fuel supply amount of the fuel supply means is lower than the target supply amount, it may be erroneously determined that the concentration of the heterogeneous fuel having lower evaporation than the reference fuel is high. There is sex.

  Therefore, in order to accurately determine the fuel property, the difference between the upstream air-fuel ratio sensor output and the reference value is due to the deterioration of the fuel addition valve or due to the change in the different fuel concentration. It is necessary to distinguish whether there is.

  In contrast, the fuel property determination apparatus for an internal combustion engine according to the present invention uses the downstream reference value as the integrated value of the deviation between the downstream air-fuel ratio sensor output and the base air-fuel ratio when the fuel supply means normally supplies fuel. As an integrated value of the deviation between the downstream air-fuel ratio sensor output and the base air-fuel ratio when the fuel supply means actually supplies fuel (hereinafter referred to as downstream air-fuel ratio integrated deviation amount) And calculating the output of the upstream air-fuel ratio sensor and the upstream reference value on condition that the difference between the downstream air-fuel ratio integrated deviation amount and the downstream reference value is equal to or less than a predetermined amount. did.

The amount of fuel supplied from the fuel supply means is the period from the time when the downstream air-fuel ratio sensor output begins to become lower (rich) than the base air-fuel ratio to the time when the output returns to the base air-fuel ratio (hereinafter referred to as downstream air-fuel ratio change) This is correlated with the value (downstream air-fuel ratio integrated deviation amount) obtained by integrating the deviation between the downstream air-fuel ratio sensor output and the base air-fuel ratio. This correlation holds even when the concentration of different fuels changes or when the supplied fuel adheres to the upstream end face of the exhaust purification catalyst.

  This is thought to be due to the following factors. That is, even when the evaporability of the fuel changes due to the change in the concentration of the different fuel, when the fuel supplied from the fuel supply means passes through the exhaust purification catalyst, the exhaust purification catalyst induces evaporation and reduction reactions. Therefore, the output of the downstream air-fuel ratio sensor becomes a value corresponding to the fuel supply amount. In addition, when the supplied fuel adheres to the upstream end face or the like of the exhaust purification catalyst, the downstream air-fuel ratio sensor output temporarily increases (becomes a lean value) by the amount of the adhering fuel. However, since the evaporation and reduction reactions are induced by the exhaust purification catalyst, the downstream side air-fuel ratio integrated deviation amount is a value that takes into account the amount of attached fuel.

  Therefore, since the downstream air-fuel ratio integrated deviation amount corresponds to the amount of fuel actually supplied from the fuel supply means, the difference between the downstream air-fuel ratio integrated deviation amount and the downstream reference value is not more than a predetermined amount. Thus, it can be considered that the fuel supply means has normally supplied the fuel. If the comparison between the upstream air-fuel ratio sensor output and the upstream reference value is made on condition that the difference between the downstream air-fuel ratio integrated deviation amount and the downstream reference value is equal to or less than a predetermined amount, the fuel property is accurately determined. Can be determined. That is, when the output of the upstream air-fuel ratio sensor changes due to deterioration of the fuel supply means, it is not erroneously determined that the fuel property has changed.

  According to the present invention, when different types of fuel are mixed in the fuel of the internal combustion engine or when the concentration of different types of fuel changes, it is possible to accurately determine the event.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine).

  An exhaust manifold 2 is connected to the internal combustion engine 1. The exhaust manifold 2 communicates with the exhaust pipe 4 via the turbine housing 30 of the turbocharger 3. The exhaust manifold 2 is provided with a fuel addition valve 5 for adding fuel to the exhaust gas flowing through the exhaust manifold 2.

  In the middle of the exhaust pipe 4, a particulate filter 6 carrying an NOx storage reduction catalyst is arranged. An upstream A / F sensor 7 is attached to the exhaust pipe 4 upstream of the particulate filter 6. A downstream A / F sensor 8 is attached to the exhaust pipe 4 downstream of the particulate filter 6. An exhaust temperature sensor 9 is attached to the exhaust pipe 4 downstream of the particulate filter 6.

  The internal combustion engine 1 configured as described above is provided with an ECU 10. In addition to the upstream A / F sensor 7, the downstream A / F sensor 8, and the exhaust gas temperature sensor 9, various sensors such as an accelerator position sensor 11, a crank position sensor 12, and an air flow meter 13 are electrically connected to the ECU 10. Has been. The ECU 10 executes fuel property determination control, which is the gist of the present invention, in addition to known control such as fuel injection control based on the output signals of the various sensors described above.

The ECU 10 executes fuel property determination control when fuel is added from the fuel addition valve 5 such as rich spike control or PM forced regeneration control. The ECU 10 may execute the fuel property determination control every time fuel is added from the fuel addition valve 5, but the fuel property does not change unless fuel is supplied. The fuel property determination control may be executed only when the addition is executed.

  In the fuel property determination control, the ECU 10 determines the fuel property using the output of the upstream A / F sensor 7 when the fuel addition valve 5 performs fuel addition as a parameter. The main purpose of the fuel property determination control of this embodiment is to determine the concentration of the different fuel contained in the fuel.

  Light oil is assumed as a reference fuel for the compression ignition internal combustion engine 1, but in recent years, it is expected that a mixed fuel of biofuel and light oil (heterogeneous mixed fuel) is used for the purpose of reducing exhaust emissions.

  When a heterogeneous mixed fuel is used as the fuel for the internal combustion engine 1, the fuel evaporability (evaporable temperature) varies depending on the mixing ratio (concentration) of the biofuel. For example, if the concentration of biofuel in the fuel increases, the evaporability of the fuel decreases (the evaporable temperature increases). Therefore, when such fuel is added from the fuel addition valve 5, the added fuel becomes upstream A / It will not evaporate until it reaches the F sensor 7.

  Since the A / F sensor does not easily react to liquid fuel, when the added fuel that has not evaporated completely passes through the upstream A / F sensor 7, the output of the upstream A / F sensor 7 is higher than the actual air-fuel ratio. (Lean) value.

  FIG. 2 shows a case in which the same amount of a heterogeneous mixed fuel having a high biofuel concentration, a heterogeneous mixed fuel having a low biofuel concentration, and a reference fuel (a fuel having a light oil concentration of 100%) are added from the fuel addition valve 5. It is a figure which shows the output of the upstream A / F sensor. The solid line in the figure shows the output A / F1 of the upstream side A / F sensor 7 when the heterogeneous mixed fuel having a low biofuel concentration is added, and the one-dot chain line in the figure shows the addition of the heterogeneous mixed fuel having a high biofuel concentration The output A / F2 of the upstream A / F sensor 7 at the time is shown, and the dotted line in the figure shows the output A / Fs of the upstream A / F sensor 7 when the reference fuel is added.

  As apparent from FIG. 2, the outputs A / F1 and A / F2 of the upstream side A / F sensor 7 when the different fuel mixture is added are generally leaner than the outputs A / Fs when the reference fuel is added. This tendency is more pronounced as the biofuel concentration increases.

  As a method for quantitatively detecting this phenomenon, (1) the upstream air-fuel ratio integrated deviation amount ΣΔA / F (in FIG. 2) during the upstream air-fuel ratio change period (the period from t1 to t2 in FIG. 2). (2) The upstream air-fuel ratio change period, and the upstream air-fuel ratio integrated deviation amount ΣΔA / Fs when the reference fuel is added under the same conditions A minimum value A / F1min and A / F2min of the output A / F of the upstream side A / F sensor 7 at A, and a comparison with the minimum value A / Fsmin when the reference fuel is added under the same conditions (3 ) Maximum deviation (A / Fb-A / F1min, A / Fb-A / F2min) between the output A / F of the upstream A / F sensor 7 and the base air-fuel ratio A / Fb during the upstream air-fuel ratio change period The maximum value when the reference fuel is added under the same conditions (A / F b-A / Fsmin) can be exemplified.

  In the fuel property determination control of this embodiment, the method (1) described above is used. At this time, the upstream air-fuel ratio integrated change amount ΣΔA / Fs when the reference fuel is added is experimentally obtained in advance, and the upstream air-fuel ratio integrated deviation amount ΣΔA / Fs is determined as the upstream reference value. Is stored in the ROM of the ECU 10.

When the above method (1) is used, the ECU 10 determines that the upstream air-fuel ratio integrated deviation amount ΣΔA / F is smaller than the upstream reference value ΣA / Fs and the difference between the two exceeds the allowable range. If
It is determined that biofuel is mixed in the fuel. Then, the ECU 10 determines that the biofuel concentration is higher as the difference between the upstream air-fuel ratio integrated deviation amount ΣΔA / F and the upstream reference value ΣA / Fs increases.

  Even if the fuel properties are the same, if the exhaust temperature is different, the output of the upstream A / F sensor 7 changes. Therefore, the upstream reference value ΣΔA / Fs is a two-dimensional map using the exhaust temperature as a parameter. May be stored in the ROM. As the exhaust temperature used as a parameter at that time, the output of the exhaust temperature sensor 9 can be used.

  Further, when the operating state of the internal combustion engine 1 changes during the upstream air-fuel ratio change period described above, the base air-fuel ratio A / Fb and the amount of added fuel required for the fuel addition valve 5 change accordingly. It is preferable that the fuel property determination control is performed when the engine is in the steady operation state, preferably in the idle operation state.

  According to the method as described above, even when the fuel supplied from the fuel addition valve 5 adheres to the upstream end face or the like of the particulate filter 6, the biofuel concentration is determined without being affected by the influence. Can do.

  By the way, the output of the upstream A / F sensor 7 changes not only due to the change in the biofuel concentration but also due to deterioration or failure of the fuel addition valve 5. That is, if the amount of fuel actually added from the fuel addition valve 5 becomes larger or smaller than the target addition amount due to deterioration or failure of the fuel addition valve 5, the upstream air-fuel ratio integrated deviation amount even if the fuel properties are the same. ΣΔA / F changes. For this reason, if the fuel property determination is performed when the actual amount of fuel added to the fuel addition valve 5 is different from the target addition amount, an erroneous determination may be caused.

  For example, when the fuel property determination is executed when the actual amount of fuel added to the fuel addition valve 5 is less than the target addition amount, the biofuel concentration is not changed even though the biofuel concentration in the fuel has not changed. May increase (or be higher than the actual biofuel concentration). In addition, when the fuel property determination is performed when the actual amount of fuel added to the fuel addition valve 5 exceeds the target addition amount, the biofuel concentration is increased despite the increase in the biofuel concentration in the fuel. There is a possibility of misjudging that it has not changed (or is lower than the actual biofuel concentration).

  For this reason, in order to accurately determine the fuel property, the change in the upstream air-fuel ratio integrated deviation amount ΣΔA / F is caused by the deterioration or failure of the fuel addition valve 5, or the biofuel concentration It is necessary to distinguish whether it is due to change.

  Therefore, in this embodiment, the ECU 10 determines the deterioration of the fuel addition valve 5 before determining the fuel property based on the upstream air-fuel ratio integrated deviation amount ΣΔA / F.

  Specifically, when the fuel addition valve 5 performs fuel addition, the ECU 10 calculates the downstream air-fuel ratio integrated deviation amount ΣΔA / Fd in addition to the upstream air-fuel ratio integrated deviation amount ΣΔA / F. Then, the deterioration determination of the fuel addition valve 5 is performed using the downstream side air-fuel ratio integrated deviation amount ΣΔA / Fd as a parameter.

  The downstream side air-fuel ratio integrated deviation amount ΣΔA / Fd correlates with the actual added fuel amount of the fuel addition valve 5 regardless of the nature of the added fuel. FIG. 3 is a diagram illustrating the output of the downstream A / F sensor 8 when the same amount of the different fuel mixture and the reference fuel is added from the fuel addition valve 5. The solid line in the figure shows the output A / Fd of the downstream A / F sensor 8 when the different mixed fuel is added, and the dotted line in the figure shows the output A of the downstream A / F sensor 8 when the reference fuel is added. / Fds is shown.

  In FIG. 3, the downstream air-fuel ratio change period (period from t3 to t5 in FIG. 3) when the different fuel mixture is added is the downstream air-fuel ratio change period (FIG. 3) when the reference fuel is added. The minimum value A / Fdmin of the output of the downstream side A / F sensor 8 when the mixed fuel is added is the downstream side when the reference fuel is added. It becomes higher than the minimum value A / Fdsmin of the output of the A / F sensor 8. For this reason, the downstream side air-fuel ratio integrated deviation amount ΣΔA / Fd (the area of the portion filled with the vertical line in FIG. 3) when the different fuel mixture is added and the downstream side when the reference fuel is added The air-fuel ratio integrated deviation amount ΣΔA / Fds (the area of the portion painted with a horizontal line in FIG. 3) is substantially equal. This correlation holds even if the biofuel concentration in the heterogeneous mixed fuel changes.

  Therefore, the downstream air-fuel ratio integrated deviation amount ΣΔA / Fds when the fuel addition valve 5 normally adds the reference fuel is stored in the ROM in advance as the downstream reference value, and the downstream reference value ΣΔA. / Fds is compared with the downstream air-fuel ratio integrated deviation amount ΣΔA / Fd calculated when the fuel addition valve 5 performs fuel addition to determine whether or not the fuel addition valve 5 has deteriorated. be able to.

  Hereinafter, the fuel property determination control will be described with reference to the flowchart of FIG. The flowchart of FIG. 4 is a flowchart showing a fuel property determination control routine. This fuel property determination control routine is a routine repeatedly executed by the ECU 10 at predetermined intervals.

  In the fuel property determination control routine, the ECU 10 first determines whether or not the value of the fuel addition flag is “1”. The fuel addition flag is a flag that is set to “1” when fuel addition is started from the fuel addition valve 5 and is reset to “0” when fuel addition from the fuel addition valve 5 is finished.

  If a negative determination is made in S101, the ECU 10 once ends the execution of this routine. If an affirmative determination is made in S101, the ECU 10 proceeds to S102 and determines whether or not the value of the idle flag is “1”. The idle flag is a flag that is set to “1” when the internal combustion engine 1 is in an idle operation state and is reset to “0” when the internal combustion engine 1 is not in an idle operation state.

  If a negative determination is made in S102, the ECU 10 once ends the execution of this routine. When an affirmative determination is made in S102, the ECU 10 proceeds to S103, and determines whether or not the NOx storage reduction catalyst carried by the particulate filter 6 is in an active state.

  If a negative determination is made in S103, the ECU 10 once ends the execution of this routine. This is because when the NOx storage reduction catalyst is not in an active state, the NOx storage reduction catalyst cannot induce the evaporation and reduction reaction of the fuel supplied from the fuel addition valve 5, or the particulate filter 6 There is a possibility that the evaporation and reduction reaction of the added fuel adhering to the upstream end face cannot be induced, and thus the correlation between the downstream air-fuel ratio integrated deviation amount ΣΔA / Fd and the added fuel amount may not be established. Because.

  If an affirmative determination is made in S103, the ECU 10 proceeds to S104, and calculates an upstream air-fuel ratio integrated deviation amount ΣΔA / F and a downstream air-fuel ratio integrated deviation amount ΣΔA / Fd.

  In S105, the ECU 10 reads the upstream reference value ΣA / Fs and the downstream reference value ΣΔA / Fds stored in advance in the ROM.

  In S106, the ECU 10 calculates the absolute value (| ΣΔA / Fd−ΣΔA / Fds |) of the deviation between the downstream air-fuel ratio integrated deviation amount ΣΔA / Fd and the downstream reference value ΣΔA / Fds. It is determined whether or not it is a predetermined amount A or less. The predetermined amount A is a value set in view of the detection error of the downstream A / F sensor 8 and the like.

  If an affirmative determination is made in S106 (| ΣΔA / Fd−ΣΔA / Fds | ≦ A), the ECU 10 proceeds to S107, where the upstream air-fuel ratio integrated deviation amount ΣΔA / F and the upstream reference Based on the deviation from the value ΣA / Fs, the biofuel concentration in the fuel is determined.

  For example, the ECU 10 determines that the biofuel concentration is 0% if the deviation between the upstream air-fuel ratio integrated deviation amount ΣΔA / F and the upstream reference value ΣA / Fs is within an allowable range. If the upstream air-fuel ratio integrated deviation amount ΣΔA / F is smaller than the upstream reference value ΣA / Fs and the deviation between the two exceeds the allowable range, the ECU 10 considers that biofuel is mixed in the fuel. At the same time, the biofuel concentration is determined using the above deviation as a parameter.

  When determining the biofuel concentration based on the deviation (ΣA / Fs−ΣA / F) between the upstream air-fuel ratio integrated deviation amount ΣΔA / F and the upstream reference value ΣA / Fs, the ECU 10 determines that the deviation is large. It is determined that the biofuel concentration is high. Note that the relationship between the biofuel concentration and the deviation may be mapped in advance, and the biofuel concentration may be calculated from the map and the deviation.

  When the amount of fuel added to the fuel addition valve 5 is feedback controlled so that the output of the upstream A / F sensor 7 or the downstream A / F sensor 8 becomes the target air-fuel ratio, the determination is made in S107. The output of the upstream A / F sensor 7 or the downstream A / F sensor 8 may be corrected according to the biofuel concentration. In this case, even if the output of the upstream A / F sensor 7 or the downstream A / F sensor 8 shows a value different from that at the time of adding the reference fuel due to the change in the biofuel concentration, the added fuel is controlled to an appropriate amount. .

  If the negative determination is made in S106 (| ΣΔA / Fd−ΣΔA / Fds |> A), the ECU 10 proceeds to S108 and determines that the fuel addition valve 5 has deteriorated.

  If it is determined that the fuel addition valve 5 has deteriorated, the ECU 10 may correct the target amount for the next and subsequent times so that the actual added fuel amount becomes equal to the target amount. That is, the ECU 10 converts the deviation between the downstream air-fuel ratio integrated deviation amount ΣΔA / Fd and the downstream reference value ΣΔA / Fds into the fuel amount, and corrects the target amount at the next fuel addition by the converted value. You may make it do. In this case, if the deviation between the downstream air-fuel ratio integrated deviation amount ΣΔA / Fd and the downstream reference value ΣΔA / Fds is reduced to a predetermined amount or less at the next fuel addition, the biofuel concentration is accurately determined. Can be determined.

  According to the embodiment described above, since the biofuel concentration is determined using the output of the upstream A / F sensor 7 as a parameter, accurate determination is possible even when the added fuel adheres to the upstream end face of the particulate filter. It can be performed. Furthermore, according to this embodiment, since the determination of the biofuel concentration is performed under the condition that the actual amount of added fuel is substantially the same as the target amount, the determination accuracy decreases due to the deterioration of the fuel addition valve 5. It can also be prevented.

In the present embodiment, the example in which the evaporability of the heterogeneous mixed fuel is low with respect to the reference fuel has been described. However, the present invention can also be applied to the case where the evaporability of the heterogeneous mixed fuel is high with respect to the reference fuel. Is possible. In this case, the amount of fuel that evaporates before reaching the upstream A / F sensor 7 among the fuel added from the fuel addition valve 5 increases from the time when the reference fuel is added, so the output of the upstream A / F sensor 7 Becomes a lower value (a value closer to rich) than when the reference fuel is added.

  Therefore, (1) the upstream air-fuel ratio integrated deviation amount ΣΔA / F is larger than the upstream air-fuel ratio integrated deviation amount ΣΔA / Fs when the reference fuel is added, and (2) the upstream side in the upstream air-fuel ratio change period. The minimum value A / Fmin of the A / F sensor 7 is lower than the minimum value A / Fsmin when the reference fuel is added, or (3) the output A / F and the base of the upstream A / F sensor 7 during the upstream air-fuel ratio change period When the maximum deviation (A / Fb-A / Fmin) from the air-fuel ratio A / Fb becomes larger than the maximum value (A / Fb-A / Fsmin) at the time of adding the reference fuel, different fuels are mixed in the fuel. It can be determined that the different fuel concentration is higher as the difference in each of the above (1) to (3) becomes larger.

The figure which shows schematic structure of the internal combustion engine to which this invention is applied. The figure which shows the upstream A / F sensor output when fuel addition is performed from the fuel addition valve The figure which shows the downstream A / F sensor output when fuel addition is performed from the fuel addition valve Flow chart showing fuel property determination control routine

Explanation of symbols

1 ... Internal combustion engine 2 ... Exhaust manifold (exhaust passage)
4. Exhaust pipe (exhaust passage)
5 ... Fuel addition valve 6 ... Particulate filter (exhaust gas purification catalyst)
7: Upstream A / F sensor (upstream air-fuel ratio sensor)
8: Downstream A / F sensor (downstream air-fuel ratio sensor)
13 .... ECU

Claims (4)

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
An upstream air-fuel ratio sensor provided in an exhaust passage upstream of the exhaust purification catalyst;
A downstream air-fuel ratio sensor provided in an exhaust passage downstream of the exhaust purification catalyst;
Fuel supply means for supplying the fuel of the internal combustion engine from upstream to the exhaust purification catalyst from the upstream air-fuel ratio sensor;
First storage means for storing, as a downstream reference value, an integrated value of a deviation between the downstream air-fuel ratio sensor output and the base air-fuel ratio when the fuel supply means normally supplies fuel;
Second storage means for storing, as an upstream reference value, an output of the upstream air-fuel ratio sensor when the fuel supply means normally supplies a reference fuel having properties assumed in advance;
Calculating means for integrating the deviation between the downstream air-fuel ratio sensor output and the base air-fuel ratio when the fuel supply means supplies fuel;
Comparing the output of the upstream air-fuel ratio sensor with the upstream reference value on condition that the difference between the calculated value of the calculation means and the downstream reference value is not more than a predetermined amount, if the difference between both exceeds the allowable range Determining means for determining that the fuel property of the fuel is different from the reference fuel;
A fuel property determination apparatus for an internal combustion engine, comprising:   The determination means according to claim 1, wherein if the difference between the output of the upstream air-fuel ratio sensor and the upstream reference value exceeds an allowable range, it is determined that different types of fuel are mixed in the fuel. A fuel property determination device for an internal combustion engine.   3. The fuel for an internal combustion engine according to claim 2, wherein the determination means determines that the concentration of the different fuel contained in the fuel is higher as the difference between the output of the upstream air-fuel ratio sensor and the upstream reference value is larger. Property determination device.   The determination unit according to claim 1, wherein the determination unit determines that the fuel supply unit has deteriorated or failed when the difference between the calculation value of the calculation unit and the downstream reference value exceeds a predetermined amount. A fuel property determination device for an internal combustion engine.

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