JP2006342689A - Control device of bi-fuel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid an output shortage, by smoothly switching fuel, even when requiring predetermined high load operation when selecting CNG fuel. <P>SOLUTION: This control device of a bi-fuel engine is injectably constituted by automatically selecting any one of the CNG fuel or gasoline fuel in response to an intention of a user or an operation condition. The CNG fuel is selected (YES in Step S10), and request output of present time is a predetermined high load boundary value or more to be switched to the gasoline fuel (YES in S20), and when operation is continued for a predetermined time or more by its request output (YES in S30), combustion is controlled by switching to the gasoline fuel (S40 and 50). The request output at its time is a predetermined re-switching boundary value or less to be re-switched to the CNG fuel (YES in S60), and when the CNG fuel is selected (YES in S70), the combustion is controlled by switching to the CNG fuel (S80 and 90). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for a bi-fuel engine capable of switching between compressed natural gas (CNG) fuel and gasoline fuel according to the driver's intention, and more specifically, when a CNG fuel is selected. The present invention relates to a control device for a bi-fuel engine that can smoothly perform fuel switching even when a high-load operation is required, and can avoid an output shortage.

  In recent years, gaseous fuel such as CNG has attracted attention as an alternative fuel to liquid fuel such as gasoline from the viewpoint of energy countermeasures and environmental countermeasures, and a bi-fuel engine capable of selectively switching between liquid fuel and gaseous fuel has been developed. Has been developed.

  In order to improve fuel consumption and output, various techniques have been proposed in which the gaseous fuel is injected into the intake port while the liquid fuel is injected into the intake port or the cylinder.

  For example, as a related prior art, when switching from CNG fuel to gasoline fuel at high engine speed in a bi-fuel engine capable of operating mode with CNG fuel and gasoline fuel, the energy generation difference between CNG fuel and gasoline fuel depends on the difference in energy generation. A technique for reducing the throttle opening has been proposed (see, for example, Patent Document 1).

  In addition, in a bi-fuel engine capable of operating with CNG fuel and gasoline fuel, when switching from CNG fuel to gasoline fuel during high-load operation, gasoline fuel injection is performed after a predetermined time has elapsed after CNG fuel supply is stopped. A technique for starting is proposed (for example, see Patent Document 2).

  As another related prior art, in a bi-fuel engine capable of switching between CNG fuel and gasoline fuel according to the driver's intention, a technology for prohibiting switching to CNG fuel during high load operation has been proposed ( For example, see Patent Document 3).

JP 2004-211161 A JP 7-34915 A JP 2003-293807 A

  As is well known, since CNG is a gaseous fuel, in the case of port injection, the amount of intake air is reduced by the volume of this gaseous fuel, and compared to gasoline fuel, the amount of intake air is insufficient and the output (torque) is insufficient. . In addition, since the combustion speed of CNG fuel is slower than that of gasoline fuel, the output is often insufficient during high load operation.

  For this reason, in a vehicle equipped with a bi-fuel engine, when the user (engine driver) has selected the operation mode using CNG fuel, there is a possibility that the output becomes insufficient during high-load operation, resulting in dissatisfaction.

  In the case of a direct injection engine, a dynamic range of the injection amount can be secured (easily on the low rotation side). However, even with CNG fuel, it is possible to secure an intake air amount equivalent to gasoline fuel by injecting in the compression stroke. it can.

  In such an operating region, although the CNG fuel has a problem of combustion speed, the gasoline fuel is also restricted by knocking, so the output is not always lower for the CNG fuel. Therefore, there are cases where fuel switching is not necessary.

  However, in a normal bi-fuel engine in which both CNG fuel and gasoline fuel are port-injected, the amount of intake air is absolutely insufficient for CNG fuel, so the output of CNG fuel is always lower.

  In other words, the purpose of switching to gasoline fuel does not necessarily match between the direct injection specification and the port specification, and the switching also depends on the engine speed and system configuration in the case of the direct injection specification, but in the case of the port injection specification, the engine speed There is no need to consider the number.

  As described above, in a bi-fuel engine in which both CNG fuel and gasoline fuel are port-injected and the user can select which fuel to operate, a predetermined high-load operation is required when selecting CNG fuel. However, there has been a demand for provision of means that can smoothly perform fuel switching and avoid output shortage.

  The present invention has been made in view of the above, and even when a predetermined high-load operation is requested at the time of selecting CNG fuel, the fuel can be smoothly switched and an output shortage can be avoided. An object of the present invention is to provide a control device for a bi-fuel engine.

  In order to solve the above-described problems and achieve the object, a control device for a bi-fuel engine according to claim 1 of the present invention includes at least a gaseous fuel injection valve that injects gaseous fuel into an intake port, and liquid fuel. A liquid fuel injection valve for injecting into the intake port; and an electronic throttle configured to be capable of electronically controlling the throttle opening, and automatically supplying the gaseous fuel according to the intention of the engine driver or according to operating conditions Alternatively, in the control apparatus for a bi-fuel engine configured such that either one of the liquid fuels is selected and injection is possible, the gaseous fuel is selected according to the intention of the engine operator, and the current required output is the liquid If it is greater than or equal to a predetermined high load boundary value to be switched to fuel, it is determined whether continuous operation has been performed for a predetermined time or more at the required output, When a continuous operation has been performed for a predetermined time or more at a desired output, combustion control with the liquid fuel is performed by switching to the liquid fuel, and the required output at that time should be switched to the gaseous fuel again. When the gaseous fuel is selected by the intention of the engine operator and is not more than a switching boundary value, the gaseous fuel is switched to the gaseous fuel and combustion control with the gaseous fuel is performed. To do.

  According to a second aspect of the present invention, there is provided a control device for a bi-fuel engine according to the first aspect of the present invention, wherein the required output is continuously operated for a predetermined time or more, and when switching to the liquid fuel, The opening degree of the electronic throttle is set to approximately half of the switching target value and the current value, and the injection amount of the gaseous fuel is set to approximately half of the current value based on the calorific value, while the injection amount of the liquid fuel is set to Based on the heat generation amount, it is set to approximately half of the switching target value, and after the exhaust air / fuel ratio feedback control is performed for a predetermined time or more with only the liquid fuel, the opening of the electronic throttle is further set to the switching target value. And prohibiting the injection of the gaseous fuel, while setting the injection amount of the liquid fuel to the switching target value based on the calorific value, It is characterized in that so as to implement control.

  According to a third aspect of the present invention, there is provided a control device for a bi-fuel engine according to the first or second aspect, wherein the required output is not more than a predetermined re-switching boundary value to be switched to the gaseous fuel. When the gaseous fuel is selected according to the intention of the engine driver, the opening degree of the electronic throttle is set to approximately half of the switching target value and the current value, and the injection amount of the gaseous fuel is set to the calorific value. Is set to approximately half of the current value based on the above, while the injection amount of the liquid fuel is set to approximately half of the switching target value based on the calorific value, and the feedback control of the exhaust air-fuel ratio is performed for a predetermined time only by the liquid fuel. After performing the above, the opening degree of the electronic throttle is further set to the switching target value, and the injection of the gaseous fuel is prohibited while the injection of the liquid fuel is prohibited. It is characterized in that after setting the switching target value as the base and adapted to implement the combustion control in the gaseous fuel heating value.

  According to the control device for a bi-fuel engine according to the present invention (Claim 1), the gas fuel is selected according to the intention of the engine operator, and even when a high load operation is requested, the output becomes insufficient. In this case, the engine driver can smoothly switch to liquid fuel before feeling the output shortage, and can return to gaseous fuel if the required output falls, so the engine driver can Comfortable high-load operation can be performed without feeling.

  Further, according to the control device for a bi-fuel engine according to the present invention (Claim 2), when the fuel is switched at the time of high load operation, a rapid change in the throttle opening is suppressed, and an equal torque control by fuel injection is performed. Smooth fuel switching can be realized. Therefore, occurrence of torque shock due to response delay of intake air, occurrence of air-fuel ratio rich or air-fuel ratio lean, misfire, etc. can be suppressed.

  Further, according to the control device for a bi-fuel engine according to the present invention (Claim 3), at the time of fuel switching at the time of high load operation, a sudden change in the throttle opening is suppressed, and an equal torque control by fuel injection or the like is performed. Smooth fuel switching can be realized. Therefore, occurrence of torque shock due to response delay of intake air, occurrence of air-fuel ratio rich or air-fuel ratio lean, misfire, etc. can be suppressed.

  Embodiments of a control device for a bi-fuel engine according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 2 is a schematic diagram showing a schematic configuration of the bi-fuel engine. As shown in FIG. 2, the bi-fuel engine (hereinafter abbreviated as “engine” as appropriate) 10 injects CNG fuel (gaseous fuel) into the intake port 15 by a CNG injection injector (gaseous fuel injection valve) 23, Gasoline fuel (liquid fuel) is injected into the intake port 15 by a gasoline injection injector (liquid fuel injection valve) 24.

  Each of the injectors 23 and 24 is controlled by a later-described electronic control unit (hereinafter referred to as an ECU) 50 for fuel injection timing, injection amount, and the like. In FIG. 2, for convenience of explanation, only some of the injectors 23 and 24 are shown connected to the ECU 50. Moreover, the code | symbol 10a in FIG. 2 shows a combustion chamber, and 11 has shown the cylinder bore.

  The CNG fuel is supplied from a CNG tank 32 that stores the CNG fuel to a CNG injection injector 23 via a fuel supply path 33 and a delivery pipe 35. The fuel supply path 33 is provided with a pressure sensor 32a for detecting the pressure of the CNG fuel, a temperature sensor 32b for detecting the temperature, and a regulator 34 for reducing the pressure of the CNG fuel to a predetermined injection pressure.

  These sensors 32 a and 32 b are for measuring the remaining amount of CNG fuel in the CNG tank 32. The delivery pipe 35 is provided with a pressure sensor 35a for detecting the injection pressure and a temperature sensor 35b for detecting the temperature in order to calculate the injection amount of CNG fuel. Although these sensors 32a, 32b, 35a, 35b and the regulator 34 are also connected to the ECU 50, connection lines are not shown for convenience of explanation.

  On the other hand, the gasoline fuel is supplied from the gasoline tank 37 to the gasoline injection injector 24 by a feed pump 40 through a fuel supply path 38 and a delivery pipe 39 at a predetermined pressure.

  The intake passage 14 includes an air cleaner 16, an intake air amount sensor 14a that detects the actual intake air amount, and a throttle opening sensor 20a that detects the throttle opening. 20. The sensors 14a and 20a and the electronic throttle 20 are also connected to the ECU 50, but the connection lines are not shown for convenience of explanation. Although not shown in the figure, the intake passage 14 is also provided with an intake air temperature sensor for detecting the intake air temperature.

  The exhaust passage 19 that communicates with the exhaust manifold 18 is provided with a catalyst 42 that purifies the exhaust and an air-fuel ratio sensor 19a that detects the air-fuel ratio of the exhaust. The air-fuel ratio sensor 19a is connected to the ECU 50 so that the air-fuel ratio can be feedback controlled.

  The fuel changeover switch 52 connected to the ECU 50 is provided so that the user can manually select between CNG fuel and gasoline fuel.

  The basic control of the engine 10 configured as described above includes output values of an accelerator opening sensor, an engine speed sensor, a cooling water temperature sensor, etc. (not shown), the throttle opening sensor 20a, the intake air amount sensor 14a, and the pressure. It is executed by the ECU 50 based on the output values of the sensors 32a, 35a, temperature sensors 32b, 35b, and air-fuel ratio sensor 19a.

  Next, a control method according to the first embodiment will be described with reference to FIGS. 2 and 3 based on FIG. Since the basic control of the engine 10 as the bi-fuel engine is the same as the conventional basic control, detailed description thereof will be omitted, and the characteristic control method according to the first embodiment will be described in detail. The following control is executed by the ECU 50 every time the engine 10 rotates.

  Here, FIG. 1 is a flowchart showing a control method according to Embodiment 1 of the present invention, and FIG. 3 is an explanatory diagram showing a performance concept of the engine 10. In each of the following drawings, CNG fuel is simply referred to as CNG, and gasoline fuel is simply referred to as gasoline.

  In FIG. 3, the thick solid line indicates the full load performance during gasoline, and the thin solid line indicates the full load performance during CNG. The alternate long and short dash line indicates a boundary at which CNG is automatically switched to gasoline, and the broken line indicates a boundary at which CNG is switched to gasoline and then is switched again from gasoline to CNG.

  A hatched area with hatching indicates an area where the output of CNG fuel cannot be achieved. Note that a two-dot chain line indicates a boundary that requires throttle control when switching a high load, which will be described in the second embodiment.

  First, it is determined whether or not CNG fuel is selected by the operation of the fuel changeover switch 52 by the user (step S10). If CNG fuel has not been selected (No at Step S10), that is, if gasoline fuel has been selected, combustion control using gasoline by a known technique is performed (Step S100), and the process returns to Step S10.

  If CNG fuel has been selected (Yes in step S10), as shown in FIG. 3, the current driver request output becomes a switching high load boundary (one point in FIG. 3) that serves as a threshold for switching from CNG fuel to gasoline fuel. It is determined whether or not it is greater than or equal to the automatic switching boundary that is a chain line (step S20).

  This switching high load boundary (see the one-dot chain line in FIG. 3) is set at a slightly lower load than the CNG fuel output unachievable region (see the hatched region in FIG. 3). As a result, even if the output fluctuates, the fuel can be switched reliably. Whether the driver request output is a high load is determined from the throttle opening information by the throttle opening sensor 20a and the intake air amount actually measured by the intake air amount sensor 14a.

  If it is not less than this switching high load boundary (Yes at Step S20), it is determined whether or not the vehicle is continuously operated for a certain period of time (Step S30). Since this continuity is good as long as the user does not recognize the dissatisfaction that the output is insufficient, for example, about 1 to 2 seconds is appropriate. If this continuity is not taken into account, it is not preferable because the fuel is switched even during an instant acceleration or the like.

  If the engine has been continuously operated for a certain time or longer (Yes at Step S30), it is switched to gasoline fuel (Step S40), and combustion control with gasoline by a known technique is performed (Step S50). Since the intake air amount with respect to the throttle opening is different between CNG fuel and gasoline fuel, a throttle operation (close side) is required to switch at equal torque. For this reason, in order to switch on the high load side as described above, the throttle opening is controlled to the closed side by the electronic throttle 20.

  Next, after switching to gasoline fuel, the user closes the accelerator opening, and the current required output (torque) is below the boundary for switching from gasoline fuel to CNG fuel (see the broken line in FIG. 3). It is determined whether or not there is (step S60).

  As shown in FIG. 3, the re-switching boundary (see the broken line) is set slightly on the low load side than the switching boundary (see the alternate long and short dash line). As a result, hysteresis can be given to switching, and switching can be smoothly performed without being repeated more than necessary.

  If the current request output is below the re-switching boundary (Yes at Step S60), it is further determined whether or not the user has selected switching to CNG fuel by operating the fuel switch 52 (Step S70). ).

  If the CNG fuel is selected (Yes at Step S70), the CNG fuel is switched (Step S80), the combustion control with the CNG fuel by the known technique is performed (Step S90), and the process returns to the determination at Step S10.

  On the other hand, if no CNG fuel is selected (No at Step S70), the combustion control with gasoline is performed as it is (Step S100), and the process returns to the determination at Step S10.

  As described above, according to the control device for the bi-fuel engine 10 according to the first embodiment, even when the CNG fuel is selected according to the user's intention and a high load operation is requested, the output is insufficient. In this case, it is possible to smoothly switch to gasoline fuel before the user feels that the output is insufficient, and to return to CNG fuel when the required output decreases. Therefore, the user can comfortably perform high-load driving without feeling insufficient output.

  In the second embodiment, the system configuration shown in FIG. 2 used in the first embodiment is used. Accordingly, in the following description, members that are the same as or correspond to the members that have already been described are assigned the same reference numerals, and redundant descriptions are omitted or simplified.

  Regardless of whether the fuel changeover switch 52 is operated by the user or automatically, when the gasoline fuel and the CNG fuel are switched at the time of high load operation, the intake air amount at the same torque is different, so the throttle opening / closing control is required. Become. For this reason, an electronic throttle 20 is provided. A boundary where the throttle control by the electronic throttle 20 is necessary at the time of switching the high load is shown by a two-dot chain line in FIG.

  Even if the electronic throttle 20 is suddenly operated in the region beyond the throttle control necessary boundary (two-dot chain line) shown in FIG. 3, the amount of intake air is large at high loads. There is a possibility that a delay in response occurs, causing problems such as occurrence of torque shock, air-fuel ratio rich or air-fuel ratio lean, and misfire.

  Thus, the second embodiment is intended to suppress the occurrence of such a problem. For convenience of explanation, the description will be divided into two types of flowcharts shown in FIGS. 4 and 5 according to the type of fuel switching.

  That is, FIG. 4 is a flowchart showing a control method at the time of high load switching from CNG fuel to gasoline fuel according to Embodiment 2 of the present invention, and the control from Steps S10 to S30 in FIG. Is the same, and corresponds to a more detailed configuration of the control content of step S40.

  FIG. 5 is a flowchart showing a control method at the time of high load switching from gasoline fuel to CNG fuel. The control from step S10 to step S70 in FIG. This corresponds to a more detailed configuration of the control content of S80.

  Hereinafter, the control method according to the second embodiment will be described with reference to FIGS. 2 and 3 based on FIGS. 4 and 5. First, as shown in FIG. 4, a control method at the time of high load switching from CNG fuel to gasoline fuel will be described. In the first step, it is determined whether or not it is during high load switching to gasoline (step S110).

  If it is not at the time of high load switching to gasoline fuel (No at Step S110), combustion control with CNG fuel by a known technique is performed (Step S170), and the control is terminated. On the other hand, if it is during high load switching to gasoline fuel (Yes at step S110), the process proceeds to the next step S120.

  In step S120, first, the injection amount of CNG fuel is set to half of the current value on a heating value basis, and the injection amount of gasoline fuel is set to be half of the switching target value on a heating value basis. Thereby, it can control with substantially equal torque.

  Further, the electronic throttle 20 is set to the closed side so as to be a half position between the switching target and the current value (step S120). Thereby, a rapid change in the throttle opening can be suppressed.

  Next, in the air-fuel ratio feedback control based on the output of the air-fuel ratio sensor 19a, the fine correction is always performed on the gasoline side (step S130). Thereby, it is possible to prevent the intake air amount from being changed due to the difference in fuel.

  Next, when these controls are performed and a predetermined time or more has elapsed (Yes in step S140), the electronic throttle 20 is set to the closed side so as to become the switching target value as the initial target, and the fuel to be switched is injected. Conversion is performed (step S150). That is, the injection of CNG fuel is prohibited, and the injection amount of gasoline fuel is set to the target value based on the calorific value (step S150).

  When switching from CNG fuel to gasoline fuel is completed in step S150, combustion control using gasoline fuel according to a known technique is performed and the control is terminated (step S160).

  Next, as shown in FIG. 5, a control method at the time of high load switching from gasoline fuel to CNG fuel will be described. In the first step, it is determined whether or not it is during high load switching to CNG fuel (step S210).

  If it is not at the time of high load switching to CNG fuel (No at Step S210), combustion control with gasoline fuel by a known technique is performed (Step S270), and the control is terminated. On the other hand, if it is during high load switching to CNG fuel (Yes at step S210), the process proceeds to the next step S220.

  In step S220, first, the injection amount of CNG fuel is set to half of the current value on a heating value basis, and the injection amount of gasoline fuel is set to be half of the switching target value on a heating value basis. Thereby, it can control with substantially equal torque.

  Further, the electronic throttle 20 is set to the open side so as to be half the position between the switching target value and the current value (step S220). Thereby, a rapid change in the throttle opening can be suppressed.

  Next, in the air-fuel ratio feedback control based on the output of the air-fuel ratio sensor 19a, the fine correction is always performed on the gasoline side (step S230). Thereby, it is possible to prevent the intake air amount from being changed due to the difference in fuel.

  Next, when these controls are performed and a predetermined time or more has elapsed (Yes in step S240), the electronic throttle 20 is set to the open side so as to become the switching target value as the original target, and the fuel to be switched is injected. Conversion is performed (step S250). That is, the injection of gasoline fuel is prohibited, and the injection amount of CNG fuel is set to the target value based on the calorific value (step S250).

  When switching from gasoline fuel to CNG fuel is completed in step S250, combustion control using CNG fuel according to a known technique is performed, and the control is terminated (step S260).

  As described above, according to the control device for the bi-fuel engine 10 according to the second embodiment, when the fuel is switched during the high load operation, a rapid change in the throttle opening is suppressed, and the equal torque control by the fuel injection is performed. Thus, smooth fuel switching can be realized. Therefore, occurrence of torque shock due to response delay of intake air, occurrence of air-fuel ratio rich or air-fuel ratio lean, misfire, etc. can be suppressed.

  In the first embodiment and the second embodiment, the application example of the present invention to the bi-fuel engine using gasoline as the liquid fuel and CNG as the gas fuel has been described. It may be applied to bi-fuel engines that use gasoline mixed with alcohol and use liquefied petroleum gas (LPG), hydrogen, dimethyl ether (DME), etc. as gas fuel. Further, the present invention may be applied to a bi-fuel engine that is used in any combination with the gaseous fuel.

  As described above, the control device for a bi-fuel engine according to the present invention is useful for a bi-fuel engine capable of switching between CNG fuel and gasoline fuel according to the intention of the driver or automatically, and particularly when fuel is selected. Even when a predetermined high-load operation is required, the fuel can be switched smoothly and is suitable for a bi-fuel engine that can avoid a shortage of output.

It is a flowchart which shows the control method which concerns on Example 1 of this invention. It is a schematic diagram which shows schematic structure of a bi-fuel engine. It is explanatory drawing which shows the performance concept of a bi-fuel engine. It is a flowchart which shows the control method at the time of high load switching from the CNG fuel to gasoline fuel which concerns on Example 2 of this invention. It is a flowchart which shows the control method at the time of high load switching from gasoline fuel to CNG fuel.

Explanation of symbols

10 engine (bi-fuel engine)
14a Intake air amount sensor 15 Intake port 16 Air cleaner 18 Exhaust manifold 19 Exhaust passage 19a Air-fuel ratio sensor 20 Electronic throttle 20a Throttle opening sensor 23 CNG injection injector (gaseous fuel injection valve)
24 Gasoline injector (liquid fuel injection valve)
50 ECU
52 Fuel switch

Claims (3)

At least a gaseous fuel injection valve for injecting gaseous fuel into the intake port;
A liquid fuel injection valve for injecting liquid fuel into the intake port;
An electronic throttle configured to be able to electronically control the throttle opening;
With
In a control apparatus for a bi-fuel engine configured to be able to select and inject either one of the gaseous fuel or the liquid fuel automatically according to the intention of an engine driver or according to operating conditions,
When the gaseous fuel is selected according to the intention of the engine operator and the current required output is equal to or higher than a predetermined high load boundary value to be switched to the liquid fuel, the required output continues for a predetermined time or longer. Determine if you are driving,
When continuous operation is performed for a predetermined time or more at the required output, switching to the liquid fuel and performing combustion control with the liquid fuel,
If the required output at that time is less than or equal to a predetermined re-switching boundary value to be switched to the gaseous fuel and the gaseous fuel is selected according to the intention of the engine operator, switch to the gaseous fuel. A control apparatus for a bi-fuel engine, wherein combustion control using the gaseous fuel is performed. When the required output has been continuously operated for a predetermined time or more and when switching to the liquid fuel, the opening of the electronic throttle is set to approximately half of the switching target value and the current value, and the injection amount of the gaseous fuel Is set to approximately half of the current value based on the calorific value, while the injection amount of the liquid fuel is set to approximately half of the switching target value based on the calorific value,
After the exhaust air / fuel ratio feedback control has been performed for a predetermined time or more with only the liquid fuel, the opening degree of the electronic throttle is further set to the switching target value to prohibit the injection of the gaseous fuel, 2. The control device for a bi-fuel engine according to claim 1, wherein combustion control with the liquid fuel is performed after an injection amount is set to the switching target value based on a calorific value. 3. When the required output is not more than a predetermined re-switching boundary value to be switched to the gaseous fuel again, and the gaseous fuel is selected by the engine operator's intention, the opening degree of the electronic throttle is switched. The target value is set to approximately half of the current value, and the injection amount of the gaseous fuel is set to approximately half of the current value based on the calorific value, while the injection amount of the liquid fuel is set to the switching target value based on the calorific value. Set to almost half of
After the exhaust air / fuel ratio feedback control has been performed for a predetermined time or more with only the liquid fuel, the opening degree of the electronic throttle is further set to the switching target value to inhibit the liquid fuel injection, The control apparatus for a bi-fuel engine according to claim 1 or 2, wherein combustion control with the gaseous fuel is performed after an injection amount is set to the switching target value based on a calorific value.

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