JP4247716B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a fuel injection control device for an internal combustion engine that can use alcohol and gasoline as fuels individually or in combination.

  In recent years, a system that can simultaneously use alcohol as an alternative fuel in addition to gasoline fuel is being put into practical use. In vehicles such as automobiles (FFV) equipped with this system, not only gasoline, The vehicle can be run only with a mixed fuel of alcohol and gasoline, or alcohol.

  In this FFV engine, as disclosed in, for example, Patent Document 1, the alcohol concentration in the fuel is detected by an alcohol concentration sensor, the fuel injection amount is corrected according to the alcohol concentration, and the actual air-fuel ratio is desired. The air-fuel ratio is controlled so as to be maintained.

  The theoretical air-fuel ratio when the fuel is 100% gasoline (alcohol concentration 0%) is about 14.9, while the theoretical air-fuel ratio when the fuel is 100% alcohol is 6.45 when the alcohol is methanol, Is 9.01 when is ethanol. Accordingly, the higher the alcohol concentration, the lower the stoichiometric air-fuel ratio, and it is necessary to increase the fuel injection amount in the same engine operating state. Therefore, as described above, the actual air-fuel ratio is controlled to a desired air-fuel ratio such as a theoretical air-fuel ratio corresponding to the alcohol concentration by correcting the fuel injection amount in accordance with the alcohol concentration.

JP-A-5-99023

  By the way, even when the alcohol concentration of the fuel changes due to fueling or the like, in principle, the actual air-fuel ratio can be controlled to a desired air-fuel ratio by correcting the fuel injection amount based on the alcohol concentration.

  However, it has been found that even with such correction, the actual air-fuel ratio cannot be controlled to the desired air-fuel ratio immediately after the alcohol concentration changes.

  That is, for example, when fuel injection is performed by an injector attached to an intake port, a part of the fuel injected from the injector evaporates after adhering to the inner wall of the intake port, the cylinder bore surface, etc. Part of That is, the fuel that does not adhere is consumed in the cycle in which the fuel injection is performed, but the fuel for the adhering amount is consumed in the subsequent cycle, not the cycle in which the fuel injection is performed. An amount in which this adhesion → vaporization is expected is injected from the injector.

  However, if it is assumed that the present is the first cycle immediately after the alcohol concentration has changed, the amount of fuel that is injected in the current cycle will be consumed in the next cycle, and consumed in the current cycle. Instead, the part corresponding to the amount of fuel injected in the previous cycle is consumed in this cycle. Since the alcohol concentration of the fuel in the previous cycle is different from that in this cycle, the amount corresponding to the adhesion is also different from the amount scheduled in this cycle, so the amount of fuel burned in this cycle is different from the amount scheduled. End up. As a result, it may be difficult to control the actual air-fuel ratio to a desired air-fuel ratio even if the fuel injection amount is corrected based on the alcohol concentration.

  When the fuel injection amount is corrected based on the alcohol concentration of the fuel as described above, if a certain amount of time elapses after the alcohol concentration changes, the amount corresponding to the adhesion of the fuel injection amount and the current cycle Consumption will be balanced as planned. However, immediately after the alcohol concentration is changed, such correction is not sufficient, and there is still room for solution.

  Accordingly, the present invention has been made in view of such circumstances, and its object is to set the amount of fuel burned immediately after the change to an appropriate amount when the alcohol concentration of the fuel changes, and the actual air-fuel ratio to the desired air-fuel ratio. It is an object of the present invention to provide a fuel injection control device for an internal combustion engine that can be maintained at a low level.

  In order to achieve the above object, a fuel injection control device for an internal combustion engine according to an aspect of the present invention is a fuel injection control device for an internal combustion engine capable of using alcohol and gasoline as fuels alone or in combination. And a vapor pressure detecting means for detecting the vapor pressure of the fuel, and a vapor pressure correcting means for correcting the fuel injection amount based on the detected vapor pressure.

  As a result of earnest research, the present inventor has found that there is a certain relationship between the alcohol concentration of the fuel and the vapor pressure, and that the total amount of fuel to be injected is attached to the port wall surface, etc. We found that the amount of fuel carried over was related to the vapor pressure of the fuel. Accordingly, by correcting the fuel injection amount based on the vapor pressure of the fuel as in this configuration, the amount of fuel burned immediately after the alcohol concentration of the fuel is changed is set to an appropriate amount, and the actual air-fuel ratio is set to a desired air-fuel ratio. The fuel ratio can be maintained.

  Here, it is preferable that the apparatus further includes a change amount calculation unit that calculates a change amount of the detected vapor pressure, and the vapor pressure correction unit is configured to detect when the calculated change amount of the vapor pressure exceeds a predetermined amount. The fuel injection amount is corrected.

  When the alcohol concentration of the fuel changes, the fuel vapor pressure usually changes accordingly. According to this configuration, correction of the fuel injection amount is executed when the amount of change in the vapor pressure of the fuel exceeds a predetermined amount, so that necessary and sufficient correction can be performed.

  Preferably, the steam pressure correcting means corrects the fuel injection amount for a predetermined time from when the calculated change amount of the steam pressure exceeds a predetermined amount.

  It is a short time immediately after the alcohol concentration of the fuel changes that the change in the vapor pressure of the fuel (that is, the change in the amount of attached fuel) affects the air-fuel ratio. According to this configuration, the fuel injection amount can be corrected based on the vapor pressure of the fuel for the short time, and the correction can be executed for a necessary and sufficient time.

  Preferably, the vapor pressure correction means corrects the fuel injection amount to decrease when the calculated change amount of the vapor pressure is larger than a predetermined positive first threshold value, and calculates the calculated vapor pressure. The fuel injection amount is corrected to be increased when the amount of change is smaller than a predetermined negative second threshold value.

  When the fuel vapor pressure changes to the increasing side due to the change in the alcohol concentration of the fuel, a relatively large amount of attached fuel in the cycle immediately before the change is added, and conversely, when the fuel vapor pressure changes to the decreasing side, In the cycle immediately after the change, a relatively small amount of attached fuel in the cycle before the change is added. Therefore, as in this configuration, when the change amount of the steam pressure is larger than the predetermined positive first threshold value, the fuel injection amount is corrected to decrease, and conversely, the change amount of the steam pressure is less than the predetermined negative second threshold value. By correcting the fuel injection amount to be increased when the value is small, it is possible to decrease or increase the excess or deficiency with respect to the appropriate amount in the cycle immediately after the change, and it is possible to make a suitable correction according to the actual situation Become.

  According to the present invention, when the alcohol concentration of fuel changes, the amount of fuel burned immediately after the change can be set to an appropriate amount, and the actual air-fuel ratio can be maintained at a desired air-fuel ratio. It is possible to provide an excellent effect.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a system diagram showing a fuel injection control device for an internal combustion engine according to the present embodiment. As shown in the figure, air is sucked into the combustion chamber of each cylinder of the engine 1 mounted on the vehicle via the surge tank 4 and the intake passage 5 under the control of the electric throttle valve 3 from the air cleaner 2. The The intake passage 5 includes an intake port formed in the cylinder head of the engine 1 for each cylinder, and an intake manifold that communicates with the intake port and is attached to the cylinder head. An electromagnetic injector 6 is provided for each cylinder so as to inject fuel into the intake passage 5 (particularly the intake port). The injector 6 is opened by an on signal output from an electronic control unit (hereinafter referred to as ECU) 30, injects fuel, is closed by an off signal output from the ECU 30, and stops fuel injection. In the case of intake stroke injection, the injected fuel diffuses into the combustion chamber to form a homogeneous mixture, and is ignited by the spark plug 7 and burned based on the ignition signal from the ECU 30. Exhaust gas from the engine 1 is exhausted through an exhaust passage 8. The exhaust passage 8 includes an exhaust port formed for each cylinder in the cylinder head of the engine 1 and an exhaust manifold that communicates with the exhaust port and is attached to the cylinder head. An exhaust purification catalyst 9 is disposed on the downstream side of the exhaust manifold, and an exhaust pipe is connected to the downstream side of the catalyst 9.

  The fuel stored in the fuel tank 10 is supplied to each injector 6 via the fuel supply system 12. Here, the engine 1 of the present embodiment can use alcohol and gasoline as fuels alone or as a mixture, and therefore, fuel having an arbitrary alcohol concentration is stored in the fuel tank 10. This fuel may be 100% gasoline, may be a mixed fuel in which alcohol such as methanol or ethanol is mixed with gasoline, or may be 100% alcohol. The fuel that is supplied to the fuel tank 10 often depends on the user's usage environment, such as what kind of gas station is available to the user.

  The fuel supply system 12 includes a delivery pipe 17 commonly connected to each injector 6, a fuel supply pipe 16 for supplying fuel in the fuel tank 10 to the delivery pipe 17, and a fuel supply pipe 16 to the fuel supply pipe 16 in the fuel tank 10. A feed pump 14 for feeding the fuel and a regulator valve 18 for adjusting the fuel pressure in the delivery pipe 17 by adjusting the fuel supply pressure.

  The fuel supply system 12 is provided with an alcohol concentration sensor 21 serving as an alcohol concentration detection means for detecting the alcohol concentration of the fuel. The alcohol concentration sensor 21 of the present embodiment is a capacitance type sensor that detects the alcohol concentration based on the dielectric constant of the fuel. However, an optical type that detects the alcohol concentration based on the refractive index of the fuel can also be used. In the present embodiment, the alcohol concentration sensor 21 is attached to the fuel supply pipe 16.

  The ECU 30 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like, receives input signals from various sensors, and performs predetermined arithmetic processing based on the signals. The operation of the injector 6, spark plug 7, drive motor 19 for the electric throttle valve 3, regulator valve 18, feed pump 14, etc. is controlled.

  The sensors include the alcohol concentration sensor 21 described above. In addition, the following are also included. That is, the engine 1 is provided with a crank sensor 24 for detecting the crank phase. The crank sensor 24 outputs a pulse signal at a predetermined crank phase interval. Based on this pulse signal, the ECU 30 detects the actual crank phase of the engine 1 and calculates the rotational speed.

  Further, an upstream sensor immediately before the catalyst 9 is provided with an O2 sensor or an air-fuel ratio sensor 25 that generates an output signal proportional to the oxygen concentration in the exhaust gas. The air-fuel ratio sensor 25 is a global air-fuel ratio sensor (linear air-fuel ratio sensor) that generates a signal having a voltage value proportional to the air-fuel ratio of the exhaust.

  In addition, an intake air temperature sensor 26 that detects the intake air temperature, an accelerator opening sensor 27 that detects the amount of depression of the accelerator pedal (accelerator opening), a throttle position sensor 28 that detects the opening of the throttle valve 3, and cooling of the engine 1 A water temperature sensor (not shown) for detecting the water temperature, an intake pressure sensor (not shown) for detecting the pressure in the intake passage 5 downstream of the throttle valve 3, and a float for detecting the remaining amount of fuel in the fuel tank 10 A sensor 29 is included in the sensors. A meter for displaying the remaining amount of fuel, a remaining amount warning lamp for indicating that the remaining amount of fuel is low, and the like are operated by the ECU 30.

  Next, the control performed by the ECU 30 regarding the fuel injection control apparatus having the above configuration will be described below.

  First, basic fuel injection amount control will be described. In the memory (ROM) of the ECU 30, a map of basic injection amounts associated with the rotation speed and load of the engine 1 is stored in advance. The basic injection amount is calculated with reference to a map from the actual rotational speed calculated based on the output signal and the actual load calculated based on the output signal of the intake pressure sensor. In this case, the basic injection amount input to the map is that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio (= about 14.9) when the fuel is 100% gasoline and the engine is operating at the same speed and load. It is such a value.

  After completing the calculation of the basic injection amount, the ECU 30 performs the following calculation to determine the target injection amount to be finally injected, and at the same time as the target injection time has come, the injector 6 is in the energization time corresponding to the target injection amount. Turn on. As a result, the injector 6 is opened and fuel corresponding to the target injection amount is injected.

  The target injection timing is determined in the same manner as described above with reference to the injection timing map similar to the basic injection amount map described above. The target ignition timing is also determined in the same manner, and ignition by the spark plug 7 is executed in accordance with the target ignition timing. The opening control of the electric throttle valve 3 is basically feedback control that controls the drive motor 19 so that the output value of the throttle position sensor 28 becomes a value corresponding to the output value of the accelerator opening sensor 27. .

Now, the aforementioned target fuel injection amount is determined based on the following equation.
Qt = Qb × K1 × Kalc × K2 + TAU (1)

  Here, Qt is a target injection amount, Qb is a basic injection amount, K1 is an air-fuel ratio feedback correction coefficient, Kalc is an alcohol concentration correction coefficient, TAU is a steam pressure correction amount, K2 is another correction amount based on water temperature, intake air temperature, and the like. It is.

  In the present embodiment, air-fuel ratio feedback correction means for performing air-fuel ratio feedback correction on the fuel injection amount is provided. In particular, in the present embodiment, so-called stoichiometric control is performed in which the fuel injection amount is increased or decreased so that the air fuel ratio of the exhaust gas (that is, the air fuel ratio of the in-cylinder mixture) matches the stoichiometric air fuel ratio of the fuel. Here, the theoretical air-fuel ratio when the fuel is 100% gasoline (alcohol concentration 0%) is about 14.9, and the theoretical air-fuel ratio when the fuel is 100% alcohol is 6.45 when the alcohol is methanol. It is 9.01 when the alcohol is ethanol. When the alcohol concentration changes in this way, the stoichiometric air-fuel ratio changes. However, since the oxygen concentration in the exhaust gas when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio does not change even if the alcohol concentration changes, the oxygen concentration at this time ( That is, the output value of the air-fuel ratio sensor 25 corresponding to the target oxygen concentration is stored in the ECU 30 as a rich / lean discrimination reference value.

  In the air-fuel ratio feedback correction, the oxygen concentration in the exhaust gas is first detected by the air-fuel ratio sensor 25, and the actual exhaust rich-lean is determined by comparing this value with the rich-lean determination reference value. If the sensor output value is a rich value, an air-fuel ratio feedback correction coefficient K1 having a value smaller than 1 is calculated to reduce the fuel injection amount, and conversely if the sensor output value is a lean value, In order to correct the fuel injection amount to be increased, an air-fuel ratio feedback correction coefficient K1 having a value larger than 1 is calculated. In the case of lean burn instead of stoichiometric control, combustion may change when the alcohol concentration changes (the combustion stability with respect to the excess air ratio may change). At this time, depending on the alcohol concentration in the fuel The rich / lean discrimination reference value will be changed.

  In the present embodiment, alcohol concentration correction means for executing alcohol concentration correction for the fuel injection amount is also provided. This is because, as described above, the higher the alcohol concentration of the fuel, the smaller the stoichiometric air-fuel ratio, and it is necessary to increase the fuel injection amount. The ECU 30 stores a map represented by the relationship between the alcohol concentration of the fuel and the alcohol concentration correction coefficient Kalc as shown in FIG. In this map, when the alcohol concentration of the fuel is 0% (that is, when the fuel is 100% gasoline), the alcohol concentration correction coefficient Kalc is 1, and as the alcohol concentration of the fuel increases from 0% (that is, the fuel concentration). As the proportion of gasoline decreases, the alcohol concentration correction coefficient Kalc is increased from 1. Therefore, an alcohol concentration correction coefficient Kalc corresponding to the actual alcohol concentration of the fuel detected by the alcohol concentration sensor 21 is obtained from the map, and the target fuel injection amount Qt is calculated from the equation (1) using the correction coefficient Kalc. By calculating, correction of the fuel injection amount based on the alcohol concentration of the fuel is executed.

  Next, correction of the fuel injection amount (vapor pressure correction) based on the vapor pressure of the fuel, which is the gist of the present invention, and the vapor pressure correction amount TAU used in the equation (1) will be described.

  As described above, when the alcohol concentration of the fuel changes due to refueling or the like, in principle, the actual air-fuel ratio can be controlled to the target air-fuel ratio by the above-described alcohol concentration correction. However, even with this correction, the actual air-fuel ratio may not be controlled to the target air-fuel ratio immediately after the alcohol concentration changes.

  That is, part of the fuel injected from the injector 6 adheres to the inner wall of the intake port and evaporates to become part of the air-fuel mixture. That is, the amount of fuel attached is consumed not in the cycle in which the fuel injection is performed, but in the subsequent cycle. On the other hand, the remainder is consumed in the cycle in which the fuel is injected, and directly forms an air-fuel mixture for combustion. In this way, the amount in which this adhesion → vaporization is expected is determined in advance as the basic injection amount Qb.

  However, if it is assumed that the current cycle is the first cycle immediately after the change in alcohol concentration, the amount of fuel that is injected in this cycle is not consumed in this cycle, and instead the previous cycle is consumed. An amount corresponding to adhesion of the injected fuel is added to the current cycle for combustion. Since the alcohol concentration of the fuel of the previous cycle is different from the alcohol concentration of the fuel of the current cycle, the amount corresponding to the adhesion is also different from that of the previous cycle, so the amount of fuel burned in this cycle is It is different from the planned amount. As a result, the actual air-fuel ratio may not be controlled to a desired air-fuel ratio.

  This will be described more specifically with reference to FIG. The horizontal axis of the figure shows the fuel injection execution cycle. In the case of the four-cylinder engine of this embodiment, five cycles 1, 2, 3, 4, and 5 are shown at 180 ° crank angle intervals. The vertical axis in the figure indicates the amount of fuel that is used for combustion among the total fuel injection amount. In particular, here, the amount of fuel provided for combustion in each cycle 1 to 5 is shown, where F is an appropriate amount that can make the actual air-fuel ratio the desired air-fuel ratio.

Of the total amount of fuel T to be injected, A is the amount of fuel consumed in the injection cycle, B is the amount of fuel that is once attached to the port wall surface and consumed in the next cycle, and is consumed in the next cycle. When the amount of fuel to be used is C, these relationships are: T = A + B + C (2)
It becomes.

These A, B, and C were found to be affected by the fuel vapor pressure. That is, Ah, Bh, Ch and fuel values with low vapor pressure (that is, difficult to evaporate or low vaporization rate) for fuels with a high vapor pressure (that is, easy to evaporate or high vaporization rate) in steady state. If each value of Al is B1, Cl,
Ah> Al, Bh <Bl, Ch <Cl
The relationship is established.

  Here, it is assumed that the alcohol concentration of the fuel changes suddenly due to refueling or the like. In the example of FIG. 3, such a sudden change occurs between cycle 2 and cycle 3, and the alcohol concentration is increased from a low value L to a high value H.

  FIG. 4 shows the relationship between the alcohol concentration (horizontal axis) of fuel and the vapor pressure (vertical axis). As understood from the figure, the alcohol concentration and the vapor pressure are not proportional to each other, and as the alcohol concentration increases from 0%, the vapor pressure once increases to the maximum value in the extremely low concentration region and then gradually decreases. Show the trend.

  In the example of FIG. 3, the alcohol concentration is increased from, for example, 0% indicated by L in FIG. 4 (that is, gasoline 100%) to a concentration at which the vapor pressure indicated by H in FIG. Then, from cycle 2 to cycle 3, the vapor pressure of the fuel increases rapidly.

  In the cycle 3 immediately after the alcohol concentration is increased from L to H, the fuel amount Ah for the current combustion of the fuel injected in the cycle 3 is added to the fuel amount B1 for the deposit in the cycle 2 and the adhesion in the cycle 1. The amount of fuel Cl is added. At this time, the amount of fuel for the current combustion increases from Al to Ah due to the change in the alcohol concentration, but in this cycle 3, the amount of attached fuel more than Bh and Ch is carried forward, so that the fuel is carried over. The amount becomes excessive from the appropriate amount and the air-fuel ratio becomes rich.

  In the next cycle 4, the value of B becomes Bh corresponding to the alcohol concentration H of the original fuel, but Cl still remains in the cycle 2, the fuel amount still exceeds the appropriate amount, and the air-fuel ratio rich continues. .

  As soon as the next cycle 5 is reached, consumption of the previously attached fuel amount is completed, and the values of B and C become Bh and Ch corresponding to the alcohol concentration H of the original fuel, and the fuel amount becomes an appropriate amount. A proper air-fuel ratio can be obtained.

  In this way, immediately after the alcohol concentration of the fuel changes, the air-fuel ratio temporarily does not become a desired value, and when the alcohol concentration increases, it becomes instantaneously rich, and when the alcohol concentration decreases, it becomes instantaneously lean. End up. The effects of such instantaneous rich or instantaneous lean are further increased during engine transients, leading to deterioration in emissions and drivability.

  Such instantaneous rich or instantaneous lean is difficult to correct even by the aforementioned air-fuel ratio feedback control. This is because there is a time lag until the air-fuel ratio sensor 25 detects the air-fuel ratio of the exhaust gas generated by such instantaneous rich or instantaneous lean. When such an instantaneous rich or instantaneous lean is detected by the air-fuel ratio sensor 25, it is highly likely that the fuel amount has already returned to the appropriate amount, and conversely, the appropriate state is destroyed by the air-fuel ratio feedback control. It can be. This also contributes to deterioration of emissions when the alcohol concentration of the fuel changes.

  Therefore, in the fuel injection control device for an internal combustion engine according to the present invention, in order to solve such a problem, the vapor pressure detection means for detecting the vapor pressure of the fuel, and the fuel injection amount based on the detected vapor pressure. A vapor pressure correction unit for correcting the fuel injection amount is provided, and the fuel injection amount is corrected based on the vapor pressure of the fuel. This is the reason why the vapor pressure correction amount TAU is added in the equation (1).

  First, the vapor pressure detecting means will be described. The ECU 30 stores the relationship between the alcohol concentration of the fuel and the vapor pressure as shown in FIG. 4 as a map. Then, the ECU 30 obtains the vapor pressure corresponding to the alcohol concentration of the actual fuel detected by the alcohol concentration sensor 21 from the map. As described above, the vapor pressure detecting means includes the ECU 30 and the alcohol concentration sensor 21.

  Next, the vapor pressure correcting means will be described. FIG. 5 shows a processing routine for calculating the steam pressure correction amount TAU, and the ECU 30 calculates the steam pressure correction amount TAU according to this processing routine and corrects the fuel injection amount. This processing routine is executed for each injection cycle (every 180 ° crank angle).

  First, when the process is started, the alcohol concentration alcohol detected by the alcohol concentration sensor 21 is read in step S10.

  In the next step S20, the vapor pressure calculation map of FIG. 4 is referred to, and the vapor pressure evap corresponding to the alcohol concentration alcohol is obtained. In step S30, whether or not the difference (evap−evap_old) between the obtained vapor pressure evap of the current cycle and the vapor pressure evap_old of the previous cycle is greater than a first threshold A having a predetermined positive value. Judgment is made (see FIG. 6). This is to determine whether or not the amount of change in vapor pressure exceeds a predetermined amount.

  When it is determined that the difference in vapor pressure (evap−evap_old) is greater than the first threshold A (step S30: Yes), the process proceeds to step S40, and the negative vapor pressure correction amount TAU (−) is calculated. This vapor pressure correction amount TAU (−) is a function of the vapor pressure difference (evap−evap_old), is obtained by a calculation formula or map stored in the ROM of the ECU 30, and is represented by g (evap−evap_old). Thereafter, the process proceeds to step S50 where the identifier i is set to 1. This identifier i is a parameter for specifying the change state of the vapor pressure, and is roughly 1 for an increase, 2 for a decrease, and 0 for no change (see FIG. 6). Note that the identifier i is also set to 0 in the case of the first process after initialization or in the case of completion of correction.

  On the other hand, if it is determined in step S30 that the vapor pressure difference (evap−evap_old) is equal to or less than the first threshold A (step S30: No), the process proceeds to step S80, where the vapor pressure difference (evap−evap_old) is Then, it is determined whether or not it is smaller than the second threshold value B having a predetermined negative value (see FIG. 6). This is also for determining whether or not the change amount of vapor pressure (here, on the negative side) exceeds a predetermined amount.

  When it is determined that the difference in vapor pressure (evap−evap_old) is smaller than the second threshold B (step S80: Yes), the process proceeds to step S90, and a positive vapor pressure correction amount TAU (+) is calculated. This vapor pressure correction amount TAU (+) is also a function of the vapor pressure difference (evap−evap_old), is determined by a calculation formula or map stored in the ROM of the ECU 30, and is represented by h (evap−evap_old). Thereafter, the process proceeds to step S100 where the identifier i is set to 2.

  When it is determined that the vapor pressure difference (evap−evap_old) is equal to or greater than the second threshold B (step S80: No), the process proceeds to step S110, where it is determined whether the value of the identifier i is not zero. This is to determine whether or not the vapor pressure has changed. When the value of the identifier i is not 0 (step S110: Yes), the process proceeds to step S120, and it is determined whether or not the value of the identifier i is 1. This is to determine whether or not the change in vapor pressure is on the increase side.

  When the value of the identifier i is 1 (step S120: Yes), the process proceeds to step S130, and a further negative vapor pressure correction amount TAU (−) is calculated. The vapor pressure correction amount TAU (−) here is a function of the difference (evap_old−evap_old2) between the vapor pressure evap_old of the previous cycle and the vapor pressure evap_old2 of the cycle before the previous cycle, and is a calculation formula stored in the ROM of the ECU 30 or It is obtained from the map and expressed by g ′ (evap_old−evap_old2). Thereafter, the process proceeds to step S150 where the identifier i is set to 0. This means that the correction has been completed.

  On the other hand, when the value of the identifier i is not 1 in step S120 (step S120: No), the process proceeds to step S140, and a further positive vapor pressure correction amount TAU (+) is calculated. The steam pressure correction amount TAU (+) here is a function of the difference (evap_old−evap_old2) between the steam pressure evap_old of the previous cycle and the steam pressure evap_old2 of the cycle before the last cycle, and is a calculation formula or map stored in the ROM of the ECU 30. And expressed by h ′ (evap_old−evap_old2). Thereafter, the process proceeds to step S150 where the identifier i is set to 0.

  When the value of the identifier i is 0 in step S110 (step S110: No), the process proceeds to step S160 and the steam pressure correction amount TAU is set to 0.

  After steps S50, S100, S150, and S160, the process proceeds to step S60, where the vapor pressure evap of the current cycle is replaced with the vapor pressure evap_old of the previous cycle, and in step S70, the vapor pressure evap_old of the previous cycle is changed to the vapor pressure evap_old2 of the previous cycle. Replaced. This process is completed.

  As understood from the above description and as shown in FIG. 6, in this process, the difference in vapor pressure (evap−evap_old) or (evap_old−evap_old2) is larger than the positive first threshold A. When the identifier i is set to 1 and the negative steam pressure correction amount TAU (−) is calculated and the difference is smaller than the negative second threshold B, the identifier i is set to 2 and the positive steam pressure When the correction amount TAU (+) is calculated and the difference is not more than the first threshold value A and not less than the second threshold value B, the identifier i is set to 0 and the vapor pressure correction amount TAU is set to 0.

  When this process is applied to a situation during actual engine operation, first, when there is no change in the alcohol concentration of the fuel, and therefore there is no change in its vapor pressure, the process proceeds with steps S10, S20, S30, S80, and S110. Then, the steam pressure correction amount TAU is set to 0 in step S160, and the current value and the previous value of the difference in steam pressure are replaced in steps S60 and s70. Therefore, the vapor pressure correction of the fuel injection amount is not performed from the above equation (1).

  When the fuel vapor pressure increases, for example, to the extent that the vapor pressure of the fuel satisfies the condition of step S30, the process proceeds to steps S10 and S20 in the first cycle (corresponding to cycle 3 in FIG. 3) immediately after this change. , S30, S40, S50, S60, and s70, and the negative vapor pressure correction amount TAU (−) is calculated. Therefore, the target fuel injection amount is corrected to decrease from the equation (1), and as a result, the actual fuel injection amount is also corrected to decrease to the appropriate amount shown in FIG. As a result, the exhaust air-fuel ratio is maintained at a desired target air-fuel ratio. That is, the vapor pressure correction amounts TAU (+) and TAU (−) are set to values that make the fuel injection amount an appropriate amount so that the actual air-fuel ratio becomes the desired air-fuel ratio.

  In the next cycle (corresponding to cycle 4 in FIG. 3), the process proceeds to steps S10, S20, S30, S80, and S110. Since i = 1, the process proceeds to steps S120 and S130, and the negative steam pressure correction amount is again obtained. TAU (−) is calculated, and i = 0 is set in step S150. Therefore, the target fuel injection amount is corrected to decrease again, the actual fuel injection amount is also corrected to decrease to an appropriate amount, and the exhaust air-fuel ratio is maintained at the desired target air-fuel ratio.

  The negative vapor pressure correction amount TAU (−) calculated here is smaller than the negative vapor pressure correction amount TAU (−) calculated in the previous cycle (that is, the absolute value is small). This is because, as can be seen by comparing the cycle 3 and the cycle 4 in FIG. 3, the amount of excess in the current cycle is less than the appropriate amount in the current cycle.

  Further, in the next cycle (corresponding to cycle 5 in FIG. 3), the process proceeds to steps S10, S20, S30, S80, and S110. Since i = 0 in S110, the process proceeds to step S160. Here, the vapor pressure correction amount TAU is set to 0, and the vapor pressure correction of the fuel injection amount is not performed. This is because the influence of the previously attached fuel has already been eliminated.

  The above is an example in the case where the alcohol concentration is increased, but this processing is naturally applicable to a case where the alcohol concentration is decreased. Briefly describing the main part, when the alcohol concentration of the fuel changes to such an extent that the condition of step S80 is satisfied, a positive vapor pressure correction amount TAU (+) is calculated in step S90 in the cycle immediately thereafter, and step In S100, the identifier i = 2 is set. In the next cycle, a smaller positive steam pressure correction amount TAU (+) is calculated in step S140, and the identifier i = 0 is set in step S150. This substantially completes the vapor pressure correction.

  As can be understood from the above, according to the fuel injection control device of the internal combustion engine according to the present embodiment, the fuel injection amount is corrected based on the vapor pressure of the fuel, so even if the alcohol concentration of the fuel changes, The amount of fuel burned immediately after the change can be set to an appropriate value, the actual air-fuel ratio can be kept stable at the desired air-fuel ratio, and the emission and drivability can be kept good.

  Since the instantaneous rich or instantaneous lean based on the change in alcohol concentration is fundamentally eliminated by the vapor pressure correction, even when air-fuel ratio feedback control is performed as in the present embodiment, the instantaneous rich or instantaneous lean The air-fuel ratio feedback correction does not work so as to cancel out the above, and this also makes it possible to stably maintain the actual air-fuel ratio at the desired air-fuel ratio.

  Various other embodiments of the present invention are conceivable. For example, in the above embodiment, when the alcohol concentration of the fuel is changed, the vapor pressure correction is executed only in the two cycles immediately after that. However, it is possible to change the number of times (and thus the correction execution time), for example, once, or 3 times or more. The above embodiment is an example in the case where the influence of the change in vapor pressure is eliminated in two cycles. However, the number of cycles to be resolved differs depending on the installation position of the injector, the engine water temperature, and the like, and the optimum number of times may be determined through experiments. Further, the correction execution time can be defined by a timer or counter of the ECU.

  In the above embodiment, the alcohol concentration sensor 21 is attached to the fuel supply pipe 16, but it may be attached to the delivery pipe 17, the injector 6, or the fuel tank 10.

1 is a system plan view showing an embodiment of a fuel injection control device for an internal combustion engine according to the present invention. 6 is a map for calculating an alcohol concentration correction coefficient Kalc. It is a time chart which showed transition of the amount of fuel burned in a cylinder for every fuel injection cycle, and is an example in case vapor pressure correction concerning the present invention is not performed. It is the graph which showed the relationship between the alcohol concentration of a fuel, and vapor pressure. It is the flowchart which showed the processing routine for performing vapor pressure correction | amendment which concerns on this embodiment. It is a graph which shows the correspondence of the steam pressure correction amount with respect to the difference in steam pressure.

Explanation of symbols

1 Engine 6 Injector 10 Fuel Tank 12 Fuel Supply System 16 Fuel Supply Pipe 17 Delivery Pipe 21 Alcohol Concentration Sensor 25 Air-fuel Ratio Sensor 30 Electronic Control Unit (ECU)
alcohol Fuel alcohol concentration
evap, evap_old, evap_old2 Fuel vapor pressure Qt Target injection amount Qb Basic injection amount TAU, TAU (+), TAU (-) Steam pressure correction amount Kalc Alcohol concentration correction factor K1 Air fuel ratio feedback correction factor A First threshold B Second Threshold

Claims (3)

A fuel injection control device for an internal combustion engine capable of using alcohol and gasoline as fuels alone or in combination,
Alcohol concentration detecting means for detecting the alcohol concentration of the fuel;
Alcohol concentration correction means for correcting the fuel injection amount based on the detected alcohol concentration;
Vapor pressure detection means for detecting the vapor pressure of the fuel based on the detected alcohol concentration ;
A change amount calculating means for calculating the detected change amount of the vapor pressure;
Vapor pressure correction means for correcting the fuel injection amount based on the change amount of the vapor pressure during a predetermined number of fuel injection execution cycles from when the calculated change amount of the vapor pressure exceeds the predetermined amount . A fuel injection control device for an internal combustion engine. The vapor pressure correction means calculates a correction amount that causes a subsequent fuel injection execution cycle to be smaller than an initial fuel injection execution cycle when the change amount of the vapor pressure exceeds the predetermined amount. 2. The fuel injection control apparatus for an internal combustion engine according to claim 1, wherein The steam pressure correction means corrects the fuel injection amount by decreasing when the calculated change amount of the steam pressure is larger than a predetermined positive first threshold value, and the calculated change amount of the steam pressure is a predetermined value. The fuel injection control device for an internal combustion engine according to claim 1 or 2, wherein the fuel injection amount is corrected to be increased when the value is smaller than a negative second threshold value.

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