JP2007100709A - Method and device for controlling fuel change-over internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent worsening of operability of an internal combustion engine during changing over of fuel, in an internal combustion engine using by changing over two or more kinds of fuels. <P>SOLUTION: When a maximum estimated torque Tgaswot at estimated torque Tcal>CNG of present gasoline is obtained ('NO' at S116), torque down due to switching to CNG cannot be avoided, therefore, switching from gasoline injection (S104) to CNG injection (S110) is prohibited, and torque-down of an engine is avoided, thereby a sense of incompatibility is not exerted on a driver. Thus, worsening of operability of the engine during change-over of fuel is prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control method and an internal combustion engine control device that use a plurality of types as fuel.

  2. Description of the Related Art An internal combustion engine that is used by switching a plurality of types as a fuel, for example, a bi-fuel engine used for a vehicle is known. This bi-fuel engine uses, for example, two types of fuel, gasoline and CNG (compressed natural gas) as fuel. This makes it possible to drive the internal combustion engine using CNG as a fuel when driving in urban areas from the viewpoint of reducing harmful exhaust components such as NOx, and to drive the internal combustion engine using gasoline with a higher output than CNG when driving in the suburbs. Can do.

  However, as described above, when the type of fuel is switched as necessary, the operating state of the internal combustion engine obtained by the fuel before switching cannot be continued or smoothly changed because the nature of the fuel is different. is there.

  For example, under the same conditions for gasoline and CNG, engine output is lower when CNG is used as fuel. For this reason, when the internal combustion engine is operated with gasoline on the high output side and is switched to CNG, the engine output before switching cannot be achieved even if the throttle opening is fully opened, and the torque is reduced. May cause the driver to feel uncomfortable.

  Further, since gasoline is a liquid fuel, a part of the injected gasoline adheres to the intake passage wall and the like. For this reason, even if it switches to CNG, until all the adhering gasoline is vaporized, not only CNG is supplied, but it is supplied to the combustion chamber in a mixed state of gasoline and CNG. Therefore, if the operation control of the internal combustion engine is switched from the operation for gasoline to the operation for CNG at the same time as the fuel switching operation, knocking may be deteriorated and the operability of the internal combustion engine may be deteriorated.

  An object of the present invention is to prevent deterioration of operability of an internal combustion engine at the time of fuel switching in an internal combustion engine that uses a plurality of types as fuel.

In the following, means for achieving the above object and its effects are described.
The fuel switching internal combustion engine control method according to claim 1 is a control method for an internal combustion engine that uses a plurality of types of fuel in response to a switching request, and when there is a request to switch the fuel type from fuel A to fuel B. When the engine output due to combustion of the fuel A at the engine speed at the time of the switching request is larger than the maximum engine output possible due to combustion of the fuel B at the engine speed, switching to the fuel B is prohibited. It is characterized by doing.

  If the engine output at the current engine speed due to the combustion of fuel A is greater than the maximum engine output possible due to the combustion of fuel B at the same engine speed, a throttle valve or the like is set so as to maximize the engine output at the time of switching. Even if operated, torque reduction due to switching to fuel B cannot be avoided. In such a situation, switching from the fuel A to the fuel B is prohibited to avoid a torque reduction of the internal combustion engine so that the driver of the internal combustion engine does not feel uncomfortable. In this way, in an internal combustion engine that uses a plurality of types as fuel, it is possible to prevent deterioration of the operability of the internal combustion engine when the fuel is switched.

  When there is a request to switch from fuel A to fuel B, the engine output due to combustion of fuel A at the engine speed at the time of the switching request is greater than the maximum engine output possible due to combustion of fuel B at that engine speed. It is temporary. Therefore, even if switching from fuel A to fuel B is prohibited, the engine output due to combustion of fuel A at the engine speed at the time of the switching request is the maximum engine output possible due to combustion of fuel B at the same engine speed even after a short time. Larger conditions are eliminated. Therefore, the prohibition of fuel switching does not hinder the characteristics of an internal combustion engine that uses a plurality of types as fuel.

  The fuel switching internal combustion engine control method according to claim 2 is a control method for an internal combustion engine that uses a plurality of types of fuel in response to a switching request, and when a fuel switching request is automatically made, the type of fuel is selected. When there is a request to switch from fuel A to fuel B, the engine output due to combustion of fuel A at the engine speed at the time of the switch request is greater than the maximum engine output possible due to combustion of fuel B at the engine speed. In this case, when switching to the fuel B is prohibited and a request for switching the fuel type from the fuel A to the fuel B is made according to an instruction from the engine operator, the combustion of the fuel A at the engine speed at the time of the switching request is made. Even when the engine output by the engine is larger than the maximum engine output possible by the combustion of the fuel B at the engine speed, the switch to the fuel B is prohibited. And characterized by the absence.

  That is, when the request for switching the fuel automatically is made, the engine driver cannot predict, so the switching prohibition is executed as in the first aspect. However, when the engine driver makes a request to switch fuel consciously, the engine driver predicts a state change that occurs in the internal combustion engine, so even if a torque down of the internal combustion engine occurs, There is no sense of incongruity. For this reason, when making a request to switch the fuel type in accordance with an instruction from the engine driver, the prohibition of switching to the fuel B is not executed. Therefore, the internal combustion engine can be quickly switched to the combustion of the fuel B.

  Thus, in any case, it is possible to prevent the driver of the internal combustion engine from feeling uncomfortable. As described above, prohibition of fuel switching is also temporary and does not hinder the characteristics of the internal combustion engine. For this reason, in an internal combustion engine that uses a plurality of types as fuel, it is possible to prevent deterioration of the drivability of the internal combustion engine when the fuel is switched.

A fuel-switching internal combustion engine control method according to a third aspect is characterized in that, in the first or second aspect, the fuel A is gasoline and the fuel B is CNG or LPG.
More specifically, the fuel A can be gasoline, and the fuel B can be CNG or LPG. As described above, the driver of the internal combustion engine can be made uncomfortable.

  In the fuel switching internal combustion engine control method according to claim 4, in any one of claims 1 to 3, the maximum engine output is a value obtained when an intake air amount is maximized at an engine speed at the time of the switching request. It is an engine output obtained by combustion of fuel B.

  Here, as the maximum engine output, the engine output obtained for the fuel B when the intake air amount is maximized at the engine speed at the time of the switching request is used. By determining the maximum engine output from a map or a calculation formula based on the operating state of the internal combustion engine at the time of switching, for example, as described above, whether or not switching is prohibited is determined so as not to give the driver of the internal combustion engine a sense of incongruity. it can.

  A fuel-switching internal combustion engine control device according to claim 5 is a control device for an internal-combustion engine that uses a plurality of types of fuel in response to a switching request, the switching request detection means for detecting a request to switch the fuel type, A fuel switching unit that switches the fuel type according to the request detected by the switching request detection unit, and a switching request from the fuel A to the fuel B detected by the switching request detection unit. When the request output calculation means for calculating the engine output due to the combustion of the fuel A at the engine speed and the switching request detection means detect the switching request from the fuel A to the fuel B, the engine at the time of the request The maximum engine output calculation means after switching for calculating the maximum engine output possible by the combustion of the fuel B at the number of revolutions, and the engine output calculated by the demand output calculation means are the maximum after switching. When the engine output is smaller than the maximum engine output calculated by the power output calculation means, the switching to the fuel B by the fuel switching means is permitted. When the engine output is larger than the maximum engine output, the fuel switching means Fuel switching control means for prohibiting switching to fuel B is provided.

  The fuel switching control means can avoid a torque reduction at the time of fuel switching when the engine output by fuel A at the engine speed at the time of switching request is smaller than the maximum engine output by fuel B at the engine speed at the time of switching request. Switching from fuel A to fuel B is permitted. However, if the engine output by fuel A at the engine speed at the time of switching request is greater than the maximum engine output by fuel B at the engine speed at the time of switching request, torque reduction at the time of fuel switching cannot be avoided, so fuel A to fuel B Switching to is prohibited. This avoids torque reduction and prevents the driver of the internal combustion engine from feeling uncomfortable. In this way, in an internal combustion engine that uses a plurality of types as fuel, it is possible to prevent deterioration of the operability of the internal combustion engine when the fuel is switched.

  When a request for switching from fuel A to fuel B is detected, the engine output by fuel A at the engine speed at the time of the switch request is greater than the maximum engine output by fuel B at the engine speed. Temporary. Therefore, even if the fuel switching control means prohibits the switching from the fuel A to the fuel B, after a short time, the engine output due to the combustion of the fuel A at the engine speed at the time of the switching request is the combustion of the fuel B at the engine speed. The condition larger than the maximum possible engine output is eliminated. For this reason, since the fuel switching control means permits the switching from the fuel A to the fuel B, the prohibition of the fuel switching by the fuel switching control means hinders the characteristics of the internal combustion engine used by switching a plurality of types as the fuel. There is no.

  A fuel-switching internal combustion engine control device according to claim 6 is a control device for an internal-combustion engine that uses a plurality of types of fuel in response to a switching request, the switching request detection means for detecting a request to switch the type of fuel, A fuel switching unit that switches the fuel type according to the request detected by the switching request detection unit, and a switching request from the fuel A to the fuel B detected by the switching request detection unit. When the request output calculation means for calculating the engine output due to the combustion of the fuel A at the engine speed and the switching request detection means detect the switching request from the fuel A to the fuel B, the engine at the time of the request The switching maximum engine output calculating means for calculating the maximum engine output possible by the combustion of the fuel B at the rotational speed and the switching request detected by the switching request detecting means are automatically made. If the engine output calculated by the demand output calculation means is smaller than the maximum engine output calculated by the maximum engine output calculation means after switching, the fuel by the fuel switching means When switching to B is permitted and the engine output is greater than the maximum engine output, switching to fuel B by the fuel switching means is prohibited, and the switching request detected by the switching request detecting means Fuel switching control means for permitting switching to the fuel B when it is made in accordance with an instruction from the engine driver is provided.

  The fuel switching control means may consider whether or not the switching request detected by the switching request detection means is made according to an instruction from the engine operator. That is, when the switching request detected by the switching request detecting means is automatically made, the fuel switching prohibition and permission are executed by comparing the engine output and the maximum engine output in the same manner as in the fifth aspect. To do. Also at this time, as described above, the prohibition of fuel switching by the fuel switching control means is temporary, and does not hinder the characteristics of the internal combustion engine.

  On the other hand, when the switching request detected by the switching request detection means is made according to the instruction of the engine driver, switching to the fuel B is permitted regardless of the comparison between the engine output and the maximum engine output. To do.

  That is, when the fuel is switched by an automatic switching request and the torque is reduced, the driver feels uncomfortable because the driver has an unexpected torque reduction. However, when the driver gives an instruction to switch the fuel consciously, the driver predicts a state change that occurs in the internal combustion engine, so even if the torque of the internal combustion engine is reduced, the driver feels uncomfortable. Never give. Therefore, the fuel switching control means does not prohibit the switching to the fuel B when making a request to switch the fuel type according to the instruction of the engine driver. Therefore, the internal combustion engine can be quickly switched to the combustion of the fuel B.

  In this way, the fuel switching control means can prevent the driver of the internal combustion engine from feeling uncomfortable in any case. For this reason, in an internal combustion engine that uses a plurality of types as fuel, it is possible to prevent deterioration of the drivability of the internal combustion engine when the fuel is switched.

The fuel-switching internal combustion engine controller according to claim 7 is characterized in that, in claim 5 or 6, the fuel A is gasoline and the fuel B is CNG or LPG.
More specifically, the fuel A can be gasoline, and the fuel B can be CNG or LPG. As described above, the driver of the internal combustion engine can be made uncomfortable.

  The fuel-switching internal combustion engine control device according to claim 8, wherein the post-switching maximum engine output calculation means maximizes the intake air amount at the engine speed at the time of the switching request. The engine output obtained by the combustion of the fuel B in this case is obtained as the maximum engine output.

  Since the maximum engine output calculation means after switching obtains the maximum engine output as described above, the driver of the internal combustion engine does not feel uncomfortable if the fuel switching control means determines permission / prohibition of fuel switching as described above. You can

[Embodiment 1]
FIG. 1 is a block diagram showing a schematic configuration of a vehicular bi-fuel engine to which the above-described invention is applied. Here, the engine 2 introduces intake air into an internal combustion chamber (not shown) via an intake passage 4 and an intake valve (not shown). A throttle valve 6 driven by a motor is provided in the middle of the intake passage 4 to adjust the intake air flowing through the intake passage 4. The intake air amount GA flowing through the intake path 4 is detected by an intake air amount sensor 8.

  An intake port (not shown) in front of the combustion chamber is provided with two fuel injection valves 10 and 12 for each cylinder. These fuel injection valves 10 and 12 are supplied with different types of fuel from dedicated delivery pipes 10a and 12a, respectively, and fuel is injected from one of the fuel injection valves 10 and 12 into the intake port at the fuel injection timing. Among them, the gasoline from the gasoline tank 14 is pumped by the pumping device 16 through the gasoline supply path 15 to the first fuel injection valve 10. A fuel level sensor 14a is provided in the gasoline tank 14 to detect the remaining amount of gasoline. Although not shown, excessively supplied gasoline that has not been injected by the delivery pipe 10a is returned to the gasoline tank 14 or the pressure feeding device 16 side by a return path.

  Further, CNG is sent from the CNG tank 18 to the second fuel injection valve 12 via the pressure regulator 20 through the CNG supply path 19. Therefore, in the engine 2, either gasoline or CNG is introduced into the combustion chamber and ignited by the spark plug 22 for combustion. A first fuel pressure sensor 15a is arranged in the gasoline supply path 15 downstream of the pressure feeding device 16 to detect the gasoline injection pressure Pf1. A CNG pressure sensor 19 a is disposed upstream of the pressure regulator 20 in the CNG supply path 19 to detect the remaining amount of CNG, and a second fuel pressure sensor 19 b is disposed downstream of the pressure regulator 20. Thus, the CNG injection pressure Pf2 is detected.

  Exhaust gas generated in the combustion chamber by combustion is discharged to the exhaust passage 24 via an exhaust valve (not shown). An air-fuel ratio sensor 26 is provided in the exhaust path 24 to detect the air-fuel ratio AF based on the exhaust component.

  The ECU (electronic control unit) 28 is an engine control circuit that is configured around a microcomputer. The ECU 28 receives signals from the intake air amount sensor 8, the fuel level sensor 14a, the fuel pressure sensors 15a and 19b, the CNG pressure sensor 19a, the air-fuel ratio sensor 26, and the throttle opening sensor 6a built in the throttle valve 6. Yes. The ECU 28 further includes an engine speed sensor 30 that detects the rotation of the crankshaft of the engine 2, a knock sensor 31 that detects knocking, an accelerator opening sensor 32a that detects an operation amount of the accelerator pedal 32, a fuel changeover switch 34, and others. Necessary signals are received from other sensors. The ECU 28 is also connected to other ECUs 36 that execute processing such as shift shifting and exchanges information with each other.

  Based on these pieces of information, the ECU 28 adjusts the opening of the throttle valve 6 (throttle opening TA) and the amount of fuel injected from the fuel injection valves 10 and 12 into the intake port. Specifically, the output torque required by the engine 2 is calculated based on the operation amount (accelerator opening ACCP) of the accelerator pedal 32 detected by the accelerator opening sensor 32a, and this output torque is realized. The throttle valve 6 is operated so that the throttle opening degree TA is reached. Further, during the idle feedback control, the throttle valve 6 is operated so that the engine speed NE becomes the target idle speed.

  When the idling is stable or steady running, any of the fuel injection valves 10 and 12 is realized so that combustion at the stoichiometric air-fuel ratio is realized based on the intake air amount GA detected from the intake air amount sensor 8. The fuel injected from the fuel is metered by the opening time of the fuel injection valves 10 and 12 in consideration of the detection values of the fuel pressure sensors 15a and 19b. Further, the valve opening time is feedback-controlled so as to be the stoichiometric air-fuel ratio with high accuracy based on the air-fuel ratio AF detected by the air-fuel ratio sensor 26.

  Further, the ignition timing by the spark plug 22 is set by a map based on the engine load and the engine speed NE appearing in the intake air amount GA and the like so that the knock detected by the knock sensor 31 falls within the reference range. Limit control is performed to adjust the advance amount of the ignition timing. The map for setting the ignition timing is different for the case where gasoline is used as the fuel and the case where CNG is used as the fuel. Therefore, a map provided for each type of fuel is used. .

  Next, among the processes executed by the ECU 28, a process related to fuel switching between gasoline and CNG will be described. FIG. 2 shows a flowchart of the fuel switching process. This process is repeatedly executed every time the crankshaft rotates a predetermined crank angle corresponding to the number of cylinders of the engine 2 (for example, 180 ° for four cylinders and 120 ° for six cylinders).

  When this process is started, it is first determined whether or not the fuel required for injection in the current control cycle is CNG (S100). Here, the injection request for the fuel type is made as follows. For example, in the case of the driver's will, it is performed by an instruction via the fuel changeover switch 34. Further, when the ECU 28 performs automatically, it is determined whether the vehicle is traveling in the city or the suburb by the shift shift state or the vehicle speed, and CNG is used in the city and gasoline is used as the fuel required for injection in the suburb. Further, if it can be determined from the detection results of the fuel level sensor 14a and the CNG pressure sensor 19a that the remaining amount of the currently injected fuel is almost exhausted, the ECU 28 uses the other fuel as the injection required fuel. Performs automatic switching. In addition to the contents described above, automatic fuel switching is a system that uses CNG with priority from the viewpoint of low pollution and automatically switches to gasoline when the remaining amount of CNG falls below a judgment value. But it ’s okay.

  If the current fuel required for injection is not CNG, that is, gasoline ("NO" in S100), the gasoline setting flag F is set to "ON" (S102), and the fuel injection control target is set to gasoline ( S104). In this way, this process is once completed.

  As described above, since the fuel injection control target is gasoline, the intake air amount GA, the engine speed NE, the air-fuel ratio AF, the gasoline fuel injection pressure Pf1, and the like are determined by the fuel injection amount control process for gasoline separately performed by the ECU 28. Based on the value, the gasoline fuel injection time is calculated so as to be the target air-fuel ratio (here, the stoichiometric air-fuel ratio). At the fuel injection timing, the first fuel injection valve 10 is opened during the gasoline fuel injection time, and gasoline is injected into the intake port of the engine 2.

  If the current required fuel for injection is CNG (“YES” in S100), it is next determined whether or not the required fuel for injection in the previous control cycle was gasoline (S106). If the fuel required for injection is CNG also in the previous time (“NO” in S106), it is next determined whether or not the gasoline setting flag F is “OFF” (S108). If F = “OFF” remains set in the initial setting (“YES” in S108), the fuel injection control target is set to CNG (S110). In this way, this process is once completed.

  Thus, since the fuel injection control target is CNG, the target air flow is determined based on the values of the intake air amount GA, the engine speed NE, the air-fuel ratio AF, the CNG fuel injection pressure Pf2, and the like by the CNG fuel injection amount control process. The CNG fuel injection time is calculated so as to achieve the fuel ratio. When the fuel injection timing comes, the second fuel injection valve 12 is opened during the CNG fuel injection time, and CNG is injected into the intake port of the engine 2.

  Here, the last time the fuel required for injection was gasoline, but now consider the case where CNG is the fuel required for injection. In this case, “YES” is determined in both step S100 and step S106. Therefore, the estimated torque Tcal is calculated when gasoline is used as fuel in the current engine operating state (S112). For example, based on the current intake air amount GA and the engine rotational speed NE, a map showing the relationship between the intake air amount GA and the output torque corresponding to the engine rotational speed NE obtained in advance during the combustion of gasoline is used. An estimated torque Tcal is obtained.

  Next, at the current engine speed NE, the estimated torque Tgasshot when the throttle valve 6 is fully opened and CNG is used as fuel is calculated (S114). For example, the engine speed detected by the engine speed sensor 30 based on a map representing the relationship of the output torque with respect to each engine speed NE obtained in advance during the combustion of CNG when the throttle valve 6 is fully open. Based on NE, an estimated torque Tgasshot when the throttle valve is fully opened is obtained.

  Next, it is determined whether or not the current estimated torque Tcal is equal to or lower than the estimated torque Tgasshot when the throttle valve is fully opened (S116). Here, if Tcal ≦ Tgasshot (“YES” in S116), it is found that torque reduction of the engine 2 at the time of fuel switching from gasoline to CNG can be eliminated by increasing the throttle opening TA. Therefore, next, the gasoline setting flag F is set to “OFF” (S118), and the fuel injection control target is changed to CNG (S110). In this way, this process is once completed.

  Thereafter, the throttle valve 6 is opened by the throttle opening control for CNG so that the output torque is in accordance with the degree of depression of the accelerator pedal 32. Then, the CNG fuel injection time is calculated so as to achieve the target air-fuel ratio based on values such as the intake air amount GA, the engine speed NE, the air-fuel ratio AF, and the CNG fuel injection pressure Pf2 at this time. At the fuel injection timing, the second fuel injection valve 12 is opened during the CNG fuel injection time, and CNG is injected into the intake port of the engine 2. In this way, the engine control is performed so that the torque level is smoothly connected with the previous gasoline combustion.

  The timing chart of FIG. 3 shows an example in which the fuel injection control target is immediately switched from gasoline to CNG when Tcal ≦ Tgasshot when the fuel required for injection is switched from gasoline to CNG as described above (t0).

  On the other hand, if Tcal> Tgasshot (“NO” in S116), the torque reduction of the engine 2 when the fuel is switched from gasoline to CNG cannot be eliminated by increasing the throttle opening TA. The setting of the injection control target is maintained at gasoline (S104). That is, switching the fuel injection control target to CNG (S110) is prohibited. In this way, this process is once completed. Therefore, even if there is a request for switching the fuel from gasoline to CNG, the fuel injection amount control process for gasoline and the throttle opening control are continued.

  In the next control cycle, the fuel required for injection is CNG both this time and the last time, so “YES” in step S100, but “NO” is determined in step S106. Therefore, it is next determined whether or not the gasoline setting flag F is “OFF” (S108). Since “NO” is determined in step S116 in the previous control cycle, F remains “ON”, and therefore “NO” is determined in step S108. Accordingly, the above-described current estimated torque Tcal calculation (S112) and throttle valve fully opened estimated torque Tgasot calculation (S114) are executed. Then, it is determined whether Tcal ≦ Tgasshot (S116). If Tcal> Tgasshot (“NO” in S116), the fuel injection control target is set to gasoline (S104). Thereafter, as long as Tcal> Tgasshot, “NO” is determined in the step S116, and the state in which the fuel injection control target is gasoline (S104) continues.

  Then, when the state of temporary Tcal> Tgasshot ends and Tcal ≦ Tgasshot is satisfied (“YES” in S116), “OFF” is then set to the gasoline setting flag F (S118), and the fuel injection control target Is changed to CNG (S110). In this way, this process is once completed. As a result, the fuel injection amount control process for CNG and the throttle opening degree control are switched, and CNG is injected into the intake port.

  After the next control cycle, as long as the fuel required for injection is CNG, “YES” is determined in step S100, “NO” in step S106, and “YES” in step S108, and the fuel injection control target is set to CNG. Since the process (S110) is continued, the fuel injection amount control process for CNG and the throttle opening degree control are performed.

  In the timing chart of FIG. 4, when the fuel required for injection is switched from gasoline to CNG as described above (t10), Tcal> Tgasot is set so that the fuel injection control target is temporarily in the gasoline state (t10 to t11). An example of maintaining is shown. If Tcal ≦ Tgasshot (t11), the fuel injection control object is immediately switched from gasoline to CNG.

  In the above-described configuration, reading of information from the fuel changeover switch 34 and fuel change determination by the ECU 28 described above correspond to processing as a change request detection unit. Steps S100, S104, and S110 are processing as fuel switching means, Steps S106, S108, and S112 are processing as demand output calculation means, and Steps S106, S108, and S114 are processing as maximum engine output calculation means after switching. Step S116 corresponds to processing as fuel switching control means.

According to the first embodiment described above, the following effects can be obtained.
(I). When Tcal> Tgasshot, even if the throttle valve 6 is operated so as to maximize the engine output when switching from gasoline to CNG, torque reduction due to switching to CNG cannot be avoided. In such a situation, switching from gasoline to CNG is prohibited (“NO” in S116), and torque reduction of the engine 2 is avoided to prevent the driver from feeling uncomfortable. In this way, in the engine 2 used by switching between gasoline and CNG as fuel, it is possible to prevent deterioration of the operability of the engine 2 at the time of fuel switching.

  In addition, when switching from gasoline to CNG, it is only temporarily that Tcal> Tgasshot. Therefore, even if the fuel switching from gasoline to CNG is prohibited, Tcal ≦ Tgasshot is satisfied after a short time. Therefore, the prohibition of switching to CNG does not hinder the characteristics of the engine 2 used by switching between gasoline and CNG.

[Embodiment 2]
The process at the time of fuel switching in the present embodiment is shown in the flowchart of FIG. This process is also a process that is repeatedly executed each time the crankshaft rotates at a predetermined angle. In this process, the fuel switching instruction from the fuel switching switch 34 by the driver does not prohibit the fuel switching from gasoline to CNG as described in the first embodiment. Other configurations are the same as those in the first embodiment.

  In the fuel switching process of the first embodiment (FIG. 2), it is determined whether or not switching of the fuel required for injection is not an instruction from the driver after it is determined “YES” in step S100. The difference is that (S105) is provided. When it is not switching of the fuel required for injection according to the instruction from the driver (“YES” in S105), that is, when it is the fuel switching determination by the ECU 28 described in the first embodiment, the process proceeds to step S106, and the driving In the case of an instruction from a person (“NO” in S105), the process proceeds to step S118.

  Therefore, when it is a fuel switching determination by the ECU 28 (“YES” in S105), as described in the first embodiment, when Tcal> Tgasshot, the fuel switching from gasoline to CNG is prohibited (in S116). "NO"). If Tcal ≦ Tgasshot, the fuel can be switched from gasoline to CNG (“YES” in S116).

  When the fuel changeover switch 34 is operated by the driver ("NO" in S105), the gasoline setting flag F is set to "OFF" (S118), and the fuel injection control target is immediately set to CNG. (S110).

  In the configuration described above, steps S105 and S116 correspond to processing as fuel switching control means. The processing as the switching request detecting means, the fuel switching means, the on-demand output calculating means, and the maximum engine output calculating means after switching is the same as in the first embodiment.

According to the second embodiment described above, the following effects can be obtained.
(I). When the fuel switching request is automatically made by the ECU 28, it is determined whether to prohibit or permit the fuel switching from gasoline to CNG by comparing Tcal and Tgasshot (S116). This prevents the driver from feeling uncomfortable and produces the effect as described in (a) of the first embodiment.

  However, when the driver gives an instruction to switch the fuel consciously (“NO” in S105), the driver himself predicts the torque reduction that occurs in the engine 2, so that the torque reduction actually occurs. Even the driver will not feel uncomfortable. For this reason, switching to CNG is not prohibited, and switching to CNG is executed immediately, so that switching to CNG combustion can be performed quickly.

[Embodiment 3]
In this embodiment, when the fuel type is switched from gasoline as liquid fuel to CNG as gas fuel, the ignition timing for CNG immediately after switching is considered in consideration of gasoline adhering to the intake port in a liquid state. Is retarded and then gradually returned to the original ignition timing of CNG. Note that the fuel type switching may be a fuel switching process as in the first or second embodiment, or may be a control for switching the fuel immediately upon request.

  FIG. 6 shows a fuel change timing ignition timing retard amount calculation process in the present embodiment. This process is a process that is repeatedly executed every time the crankshaft rotates a predetermined crank angle corresponding to the number of cylinders of the engine 2 (for example, 180 ° for four cylinders and 120 ° for six cylinders).

  When this process is started, it is first determined whether or not CNG is a fuel injection target in the current control cycle (S200). If gasoline is the fuel injection target (“NO” in S200), the process is temporarily terminated as it is. That is, in this case, the process ends without setting an ignition timing retard amount aopdec described later.

  On the other hand, when CNG is the fuel injection target in the current control cycle (“YES” in S200), it is next determined whether or not the previous fuel injection target was CNG (S202). Until the previous time, gasoline is the target of fuel injection, and if this time it is switched to CNG (“NO” in S202), the ignition timing retard amount aopdec for the next fuel change is the intake air amount GA and the engine speed. The ignition delay amount map f (GA, NE) with NE as a parameter is calculated (S204). This ignition retard amount map f (GA, NE) shows the retard amount of the ignition timing that is affected by the degree of vaporization of gasoline adhering to the intake port in a liquid state when the fuel is switched from gasoline to CNG. These are obtained by experiments and are mapped and stored in the ROM of the ECU 28. That is, since the combustion of CNG is less likely to knock than in the case of gasoline, the optimal ignition advance angle is advanced more than in the case of gasoline, so the ignition delay map f (GA, NE) It represents the degree of retardation of the optimum ignition timing affected.

  In this way, this process is temporarily terminated. The ignition timing retard amount aopdec calculated from the map f (GA, NE) is obtained by retarding the ignition timing obtained according to the operating state of the engine 2 in the CNG ignition timing control processing separately performed by the ECU 28. To do. As a result, it is possible to cope with a delay in the optimum ignition timing due to the vaporization of gasoline in a liquid state adhering to the intake port at the initial stage of fuel switching from gasoline to CNG.

  In the next control cycle, the current fuel injection target is CNG (“YES” in S200), but since the previous fuel injection target was also CNG (“YES” in S202), the ignition timing retarded next. It is determined whether the amount aopdec is “0” (S206).

  Since the ignition timing retardation amount aopdec has just been set in the immediately preceding control cycle (“NO” in S206), the ignition timing retardation amount aopdec is calculated by attenuation as shown in the following equation (S208).

[Equation 1]
aopdec ← aopdec-β ... [Formula 1]
Here, the attenuation correction value β is a value corresponding to the vaporization speed of gasoline adhering to the intake port, and may be a constant. For example, the attenuation correction value β is increased as the engine speed NE is increased, and is decreased as the cooling water temperature is decreased. Also good.

Next, it is determined whether or not the ignition timing retardation amount aopdec is “0” or more (S210). If aopdec ≧ 0 (“YES” in S210), the process is temporarily terminated as it is.
As a result, the ignition timing for CNG is retarded based on the ignition timing retardation amount aopdec attenuated as shown in Equation (1). Since the ignition timing retard amount aopdec is smaller than the previous time, the ignition timing is approaching the optimal ignition timing for CNG.

  In the next and subsequent control cycles, as long as CNG fuel injection continues, “YES” is determined in step S200, “YES” is determined in step S202, and ignition is not performed unless aopdec = 0 (“NO” in S206). The timing retardation amount aopdec is attenuated (S208).

  If aopdec = 0 due to the attenuation of the ignition timing retardation amount aopdec, “YES” is determined in step S206 in the next control cycle, and “YES” in steps S200, S202, and S206 in the subsequent control cycles. And aopdec = 0 is maintained.

  If aopdec <0 in the attenuation process (S208) (“NO” in S210), the ignition timing retardation amount aopdec is immediately set to “0” (S212), and this process is temporarily terminated. In subsequent control cycles, “YES” is determined in steps S200, S202, and S206, and aopdec = 0 is maintained.

  Thus, the ignition timing retardation amount aopdec gradually decreases, and finally aopdec = 0, whereby the ignition timing retardation processing at the time of fuel switching is completed, and the ignition timing control for CNG is completely performed.

  When switching from CNG to gasoline, “NO” is determined in step S200, and aopdec = 0 is immediately set to 0 (S212). Therefore, the retard or advance with respect to the ignition timing associated with the fuel switch to gasoline is Not done.

  In the configuration described above, the fuel switching process performed by the ECU 28 in response to a request corresponds to the process as the fuel switching unit. Further, the process for calculating the optimum ignition timing performed for each fuel is the process as the engine operation amount setting means for each fuel, and the correction of the ignition timing performed based on the ignition timing retard amount aopdec is the fuel timing ignition timing correction. This corresponds to processing as execution means. Steps S200, S202, and S204 correspond to processing as the ignition timing correction amount setting means, and steps S206, S208, and S210 correspond to processing as the engine operation amount control means at the time of fuel switching. The processing as the switching request detection unit is the same as that in the first embodiment.

According to the third embodiment described above, the following effects can be obtained.
(I). When the fuel type is switched from gasoline, which is liquid fuel, to CNG, which is gaseous fuel, the ignition timing is retarded more than the ignition timing that is appropriate for CNG, instead of immediately switching to the ignition timing that is appropriate for CNG. Delay by aopdec. After that, the ignition timing retardation amount aopdec is gradually attenuated, and finally the retardation due to the ignition timing retardation amount aopdec is stopped. For this reason, after switching to CNG, it is possible to set the ignition timing corresponding to the vaporization of gasoline adhering to the wall surface of the intake port in a liquid state. Therefore, knocking can be maintained at a more appropriate level, and deterioration of engine operability can be prevented.

Furthermore, in the present embodiment, the ignition timing is retarded according to the degree of gasoline mixing with CNG, which contributes to NOx reduction.
[Other embodiments]
(A). In the first to third embodiments, CNG is used as the gaseous fuel, but LPG which is another gaseous fuel may be used.

  (B). In the third embodiment, the attenuation correction value β is set based on the cooling water temperature, which is a value representing the engine temperature, as an example when considering the gasification rate of gasoline. Based on this, the value of β may be set smaller as the engine temperature becomes lower. Alternatively, the temperature of the engine 2 may be estimated by periodically calculating the balance between the heat generation amount and the heat release amount from the operating state of the engine 2 and used for setting the attenuation correction value β.

  (C). In the third embodiment, the ignition retard amount map f (GA, NE) for setting the ignition timing retard amount aopdec is the optimum ignition timing due to the remaining gasoline at the initial stage of fuel switching from gasoline to CNG. Although it represents the degree of retardation, the ignition timing retardation amount aopdec may not be used. For example, when the fuel injection target is switched from gasoline to CNG, the ignition timing corresponding to gasoline and the ignition timing corresponding to gasoline are also calculated for a while, and the ignition timing corresponding to gasoline or between gasoline and CNG is calculated. You may make it gradually approach the ignition timing of CNG gradually from the ignition timing.

  Also, for example, when the fuel injection target is switched from gasoline to CNG, the difference between the ignition timing corresponding to CNG and the ignition timing corresponding to gasoline at this time is calculated. The retardation may be corrected by using the difference or a value smaller than the difference as a correction amount. Then, the correction amount is gradually reduced to approach the CNG ignition timing.

1 is a block diagram illustrating a schematic configuration of a vehicular bi-fuel engine as a first embodiment. Fig. 3 is a flowchart of a fuel switching process executed by the ECU according to the first embodiment. 3 is a timing chart illustrating an example of processing in Embodiment 1. The timing chart which similarly shows an example of a process. 10 is a flowchart of processing at the time of fuel switching in the second embodiment. 10 is a flowchart of a fuel switching point fire retard amount calculation process in a third embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Engine, 4 ... Intake path, 6 ... Throttle valve, 6a ... Throttle opening sensor, 8 ... Intake air amount sensor, 10 ... First fuel injection valve, 10a, 12a ... Delivery pipe, 12 ... Second fuel injection valve , 14 ... gasoline tank, 14a ... fuel level sensor, 15 ... gasoline supply path, 15a ... first fuel pressure sensor, 16 ... pressure feeding device, 18 ... CNG tank, 19 ... CNG supply path, 19a ... CNG pressure sensor, 19b ... Second fuel pressure sensor, 20 ... pressure adjusting device, 22 ... spark plug, 24 ... exhaust path, 26 ... air-fuel ratio sensor, 28 ... ECU, 30 ... engine speed sensor, 31 ... knock sensor, 32 ... accelerator pedal, 32a ... accelerator opening sensor, 34 ... fuel changeover switch, 36 ... other ECUs.

Claims (8)

A control method for an internal combustion engine using a plurality of types of fuel in response to a switching request,
When there is a request to switch the fuel type from fuel A to fuel B, the engine output due to combustion of the fuel A at the engine speed at the time of the switching request is the maximum possible by the combustion of the fuel B at the engine speed. The fuel-switching internal combustion engine control method, wherein switching to the fuel B is prohibited when the engine output is larger than the engine output. A control method for an internal combustion engine using a plurality of types of fuel in response to a switching request,
When a fuel switching request is automatically made, when there is a request to switch the fuel type from fuel A to fuel B, the engine output due to combustion of fuel A at the engine speed at the time of the switching request is the engine output. If greater than the maximum engine output possible due to combustion of the fuel B at the rotational speed, switching to the fuel B is prohibited,
When a request is made to switch the fuel type from fuel A to fuel B in accordance with an instruction from the engine operator, the engine output due to combustion of the fuel A at the engine speed at the time of the switch request is the engine output of the fuel B at the engine speed. The fuel-switching internal combustion engine control method, wherein prohibition of switching to the fuel B is not executed even when the maximum engine output possible by combustion is larger.   3. The fuel switching internal combustion engine control method according to claim 1, wherein the fuel A is gasoline and the fuel B is CNG or LPG.   4. The maximum engine output according to claim 1, wherein the maximum engine output is an engine output obtained by combustion of fuel B when an intake air amount is maximized at an engine speed at the time of the switching request. A fuel switching internal combustion engine control method. A control device for an internal combustion engine that uses a plurality of types of fuel in response to a switching request,
A switching request detecting means for detecting a request to switch the fuel type;
Fuel switching means for switching the type of fuel according to the request detected by the switching request detection means;
When a request for switching from fuel A to fuel B is detected by the switching request detecting means, an on-demand output calculating means for calculating an engine output due to combustion of the fuel A at the engine speed at the time of the request;
When the switching request detecting means detects a switching request from fuel A to fuel B, the maximum engine output after switching is calculated to calculate the maximum engine output possible by combustion of the fuel B at the engine speed at the time of the request. A calculation means;
When the engine output calculated by the demand output calculation means is smaller than the maximum engine output calculated by the maximum engine output calculation means after switching, switching to the fuel B by the fuel switching means is permitted. Fuel switching control means for prohibiting switching to fuel B by the fuel switching means when the engine output is greater than the maximum engine output;
A fuel-switching internal combustion engine control device comprising: A control device for an internal combustion engine that uses a plurality of types of fuel in response to a switching request,
A switching request detecting means for detecting a request to switch the fuel type;
Fuel switching means for switching the type of fuel according to the request detected by the switching request detection means;
When a request for switching from fuel A to fuel B is detected by the switching request detecting means, an on-demand output calculating means for calculating an engine output due to combustion of the fuel A at the engine speed at the time of the request;
When the switching request detecting means detects a switching request from the fuel A to the fuel B, the maximum engine output after switching for calculating the maximum engine output possible by the combustion of the fuel B at the engine speed at the time of the request A calculation means;
When the switching request detected by the switching request detecting means is automatically made, the engine output calculated by the demand output calculating means is calculated by the maximum engine output calculating means after switching. When the engine output is smaller than the maximum engine output, the switching to the fuel B by the fuel switching means is permitted, and when the engine output is larger than the maximum engine output, the switching to the fuel B by the fuel switching means is prohibited. And a fuel switching control means for permitting switching to the fuel B when the switching request detected by the switching request detection means is made according to an instruction of the engine operator;
A fuel-switching internal combustion engine control device comprising:   7. The fuel switching internal combustion engine control device according to claim 5, wherein the fuel A is gasoline, and the fuel B is CNG or LPG. 8. The post-switching maximum engine output calculating means according to any one of claims 5 to 7, wherein the engine output obtained by combustion of the fuel B when the intake air amount is maximized at the engine speed at the time of the switching request, A fuel-switching internal combustion engine control device characterized by obtaining the maximum engine output.

Images