JP2005220802A - Bi-fuel engine and purging method for evaporated component of liquid fuel in bi-fuel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively and ideally avoid deterioration of an emission performance and occurrence of knocking in a bi-fuel engine. <P>SOLUTION: The bi-fuel engine is equipped with a purge judging means for judging whether or not an evaporated component of liquid fuel is to be purged to the engine, an operation mode switching means for switching from the operation mode by gaseous fuel to the operation mode by liquid fuel, when the purge judging means judges that evaporated component of liquid fuel needs to be purged to the engine, and the operation mode at the judgement is the operation mode by gaseous liquid; and a purging means for purging the evaporated component of the liquid fuel to the engine after switching from the operation mode by gaseous fuel to the operation mode by liquid fuel. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bi-fuel engine that operates with at least one of gaseous fuel and liquid fuel, and in particular, can avoid deterioration of emission performance and occurrence of knocking when purging the evaporated component of liquid fuel. The present invention relates to a method for purging an evaporated component of liquid fuel in a fuel engine and a bi-fuel engine.

_2. Description of the Related Art Conventionally, there are natural gas vehicles that use natural gas such as compressed natural gas (CNG) that is low in the amount of harmful substances such as CO ₂ and NOx due to combustion and that are environmentally friendly as engine fuel. In addition, there is a hydrogen vehicle that uses hydrogen as an engine fuel that generates water by combustion and does not emit harmful substances such as CO ₂ and NOx.

  These natural gas vehicles and hydrogen vehicles maintain superiority in terms of environmental performance over gasoline vehicles and diesel vehicles, but compressed natural gas and hydrogen, which are gaseous fuels, cannot be installed in large quantities. It will be inferior in terms of long-distance cruise performance. In addition to the short cruising distance, the lack of facilities for supplying compressed natural gas and hydrogen is one of the factors that delay the introduction and expansion of natural gas vehicles.

  Here, natural gas engines and hydrogen engines have the same basic structure as gasoline engines. Therefore, a bi-fuel engine that can use both environmentally friendly fuel such as compressed natural gas and hydrogen and gasoline fuel has been developed by utilizing the same basic structure of the engine.

  A bi-fuel vehicle equipped with this bi-fuel engine is equipped with a fuel tank for environmentally friendly fuels such as compressed natural gas and hydrogen and a fuel tank for gasoline fuel. It solves the problem of fuel supply facilities and enables both environmental performance and practicality.

  In this way, practicality in the market has been improved to the level of gasoline vehicles etc. by the bi-fuel engine, but since the bi-fuel engine uses two types of fuels with different properties in combination, Such inconveniences occur.

  Gasoline fuel, which is a liquid fuel, has volatility and evaporates in the gasoline fuel tank. For this reason, a gasoline vehicle is usually provided with a purge device for sending the gasoline evaporation component into the combustion chamber. Such an evaporation phenomenon is not an exception even in a bi-fuel vehicle, and a purge device is also provided in the bi-fuel vehicle.

  Here, since the octane number is different between gasoline and, for example, compressed natural gas (compressed natural gas is about 130 while gasoline is about 90 to 100), in the bi-fuel engine, in order to avoid knocking and the like, respectively. Combustion is performed at the ignition timing according to the fuel. However, for example, when the gasoline evaporation component is purged into the combustion chamber during the compressed natural gas operation, the emission performance is deteriorated or knocked due to the difference in ignition timing.

  Therefore, conventionally, when gasoline purge control is performed during operation with compressed natural gas alone (hereinafter referred to as “compressed natural gas operation”), ignition is performed as in the technique described in Non-Patent Document 1 below. The timing is delayed to avoid emission performance deterioration and knocking.

Japan Society of Invention and Innovation Technical Bulletin No. 2002-2120 Japanese Utility Model Publication No. 63-160344 JP 2000-73819 A JP 11-36921 A

  However, deterioration in emission performance and knocking due to gasoline purge control during compressed natural gas operation can be avoided to some extent by retarding ignition timing as in the technique described in Non-Patent Document 1, but there are two types. Since it is a mixed fuel, such technology cannot avoid the deterioration of emission performance, etc., to the same extent as when operating with gasoline alone (hereinafter referred to as “gasoline operation”).

That is, the control at the time of combustion Whether to use any fuel O ₂ is performed based on the (A / F) various information of the sensor output such as, O ₂ due to the difference of the components of each of the fuel (A / F) The sensor output is slightly off. For this reason, the A / F control is performed in consideration of the deviation at the time of each individual operation. However, in the case of the two-type mixed fuel, it is difficult to consider the deviation, and the A / F control is shifted. Therefore, even if the above conventional technique is used, it is impossible to effectively avoid the deterioration of the emission performance and the knocking.

  In addition, in order to perform stratified combustion, it is necessary to control the injection timing and ignition timing of compressed natural gas fuel within a narrow region. If the gasoline purge control is performed during the stratified combustion operation, the robustness is deteriorated, and there is a possibility that misfire may occur that combustion itself is not established.

  In addition, gasoline purge control is indispensable for vehicles equipped with gasoline fuel to prevent the release of gasoline evaporating components to the outside of the vehicle. In bi-fuel vehicles, it is necessary regardless of which fuel is operated independently. Gasoline purge control is performed.

  Accordingly, the present invention provides a bi-fuel engine that can improve the disadvantages of the conventional example and can effectively and suitably avoid the deterioration of emission performance and the occurrence of knocking, and a method for purging an evaporated component of liquid fuel in the bi-fuel engine. For the purpose.

  In order to achieve the above object, according to the first aspect of the present invention, purge determining means for determining whether or not the evaporated component of the liquid fuel is purged with respect to the engine, and the purge determining means converts the evaporated component of the liquid fuel into the engine. When the operation mode at the time of such determination is an operation mode with gaseous fuel, the operation mode switching is switched from the operation mode with gas fuel to the operation mode with liquid fuel. And a purge unit that purges the evaporated component of the liquid fuel from the engine after the operation mode switching unit switches to the operation mode with the liquid fuel.

  As a result, purge control with the two types of mixed fuel can be prevented and purge can be performed in the operation mode with the liquid fuel, so that deterioration of emission performance and occurrence of knocking can be effectively avoided.

  In order to achieve the above object, according to the second aspect of the present invention, the purge determining means for determining whether or not the evaporated component of the liquid fuel is purged from the engine, and the purge determining means includes the evaporated component of the liquid fuel. When the operation mode at the time of the determination is the operation mode with the gaseous fuel, the operation mode with the gaseous fuel is switched to the operation mode with the liquid fuel. An operation mode determination means for determining whether or not it is possible, and this operation mode determination means determines that switching to the operation mode with liquid fuel is impossible, and the combustion mode at the time of such determination is the stratified combustion mode The combustion mode switching means for switching from the stratified combustion mode to the homogeneous combustion mode, and the ignition timing is retarded after the combustion mode switching means switches to the homogeneous combustion mode. And ignition timing control means for, this ignition timing control means and a purge means for purging the vaporized components to the engine of the liquid fuel from the control retarding the ignition timing.

  As a result, even when the purge control with the two types of mixed fuels must be performed, the purge is performed in the homogeneous combustion mode, so that it is possible to effectively avoid the deterioration of the emission performance and the occurrence of knocking as much as possible. it can.

  In order to achieve the above object, according to the third aspect of the present invention, the step of determining whether or not the evaporated component of the liquid fuel is purged from the engine and the evaporated component of the liquid fuel are purged from the engine. When it is determined that it is necessary and the operation mode at the time of the determination is the operation mode with the gaseous fuel, the step of switching from the operation mode with the gas fuel to the operation mode with the liquid fuel, and the operation with the liquid fuel And a step of purging the evaporated component of the liquid fuel to the engine after switching to the mode.

  As a result, purge control with the two types of mixed fuel can be prevented and purge can be performed in the operation mode with the liquid fuel, so that deterioration of emission performance and occurrence of knocking can be effectively avoided.

  In order to achieve the above object, according to the present invention, the step of determining whether or not the evaporated component of the liquid fuel is purged from the engine and the evaporated component of the liquid fuel are purged from the engine. When it is determined that it is necessary and the operation mode at the time of the determination is the operation mode with the gas fuel, it is determined whether or not the operation mode with the gas fuel can be switched to the operation mode with the liquid fuel. And switching to the homogeneous combustion mode from the stratified combustion mode when it is determined that switching to the operation mode with liquid fuel is impossible and the combustion mode at the time of the determination is the stratified combustion mode, A step of retarding the ignition timing after switching to the homogeneous combustion mode, and a step of purging the evaporated component of the liquid fuel to the engine after the retarding control of the ignition timing. .

  As a result, even when the purge control with the two types of mixed fuels must be performed, the purge is performed in the homogeneous combustion mode, so that it is possible to effectively avoid the deterioration of the emission performance and the occurrence of knocking as much as possible. it can.

  According to the bi-fuel engine and the method for purging the vapor component of the liquid fuel in the bi-fuel engine according to the present invention, the purge control can be performed in the operation mode with the liquid fuel, and the purge control with the two-type mixed fuel must be performed If it is not obtained, purge control can be performed in the homogeneous combustion mode, so that deterioration of emission performance and occurrence of knocking can be effectively and suitably avoided.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a bifuel engine according to the present invention and a liquid fuel evaporation component purging method in the bifuel engine will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments.

  A bi-fuel engine according to a first embodiment of the present invention will be described with reference to FIGS.

  The bi-fuel engine of the first embodiment is an engine that can be operated with at least one of gaseous fuel such as compressed natural gas fuel and hydrogen fuel and volatile liquid fuel such as gasoline fuel, and FIG. A longitudinal sectional view is shown. Although only one cylinder is shown in FIG. 1, the present invention is applicable to a multi-cylinder bi-fuel engine regardless of the type such as in-line or V-type.

  As shown in FIG. 1, this bi-fuel engine is surrounded by a wall surface of a cylinder bore 1 a formed in the cylinder block 1, a wall surface of a recess 2 a formed on the lower surface of the cylinder head 2, and a top surface of the piston 3. Combustion chamber is configured in space.

  Here, the cylinder head 2 is formed with at least two intake ports 2b and at least one exhaust port 2c that open to the combustion chamber (in FIG. 1, only one is shown for convenience). . The intake port 2b and the exhaust port 2c are provided with an intake valve 4 and an exhaust valve 5 that can open and close their openings, respectively.

  Further, the cylinder head 2 is provided with a spark plug 6 substantially at the center of the recess 2a. Further, the gas fuel (here, compressed natural gas fuel) is provided at the peripheral portion (the intake port 2b side) of the recess 2a. A fuel injection valve 7 for injection (hereinafter referred to as “gas fuel injection valve”) 7 is provided.

  Here, a dish-shaped cavity 3a shown in FIG. 1 is formed on the top surface of the piston 3 of the first embodiment, and the gas fuel injection valve 7 is located near the top dead center in the compression stroke. Stratified combustion is realized by spraying compressed natural gas fuel toward the cavity 3a when it is positioned. Further, when the piston 3 is positioned in the vicinity of the bottom dead center in the intake stroke, the gaseous fuel injection valve 7 sprays the compressed natural gas fuel to perform homogeneous combustion.

  Further, the cylinder head 2 is provided with a fuel injection valve for liquid fuel injection (hereinafter referred to as “liquid fuel injection valve”) 8 for spraying liquid fuel (here, gasoline fuel) in the intake port 2b. It has been.

  That is, the bi-fuel engine of the first embodiment is a compressed natural gas direct injection bi-fuel engine in which only the compressed natural gas fuel is directly sprayed into the combustion chamber. In addition, as long as this bi-fuel engine is of a type that directly sprays compressed natural gas fuel, the arrangement of the spark plug 6 and the like, the shape of the piston 3 and the like may be any. For example, a single point ignition method may be used as in the first embodiment, but a multipoint ignition method may be used. Further, the spark plug 6 may be provided at the peripheral portion of the concave portion 2a in the cylinder head 2, and the gaseous fuel injection valve 7 may be provided at substantially the center of the concave portion 2a.

  Further, the bi-fuel engine is provided with a purge device (purge means) 10 for purging the gasoline evaporation component evaporated in the gasoline tank 9 shown in FIG. 1 into the combustion chamber via the intake passage 2d.

  The purge device 10 includes a first pipe 10a that communicates with an upper space in the gasoline tank 9, a canister 10b that collects gasoline evaporation components in the gasoline tank 9 through the first pipe 10a, and an interior of the canister 10b. And a second pipe 10c that communicates with the inside of the intake passage 2d, and a purge control valve 10d that opens and closes a gasoline evaporation component flow path of the second pipe 10c.

The canister 10b is provided with a adsorbent 10b ₁ such as charcoal filter therein, when the purge control valve 10d is closed, the gasoline vaporization component generated in the adsorbent 10b ₁ in the gas tank 9 Adsorbed. Further, the canister 10b is formed with a fresh air inlet 10b ₂ for introducing air into the canister 10b.

  Here, the operations of the spark plug 6 and the gaseous fuel injection valve 7 in this bi-fuel engine are controlled by an electronic control unit (hereinafter referred to as “ECU”) 11 shown in FIG.

  The ECU 11 according to the first embodiment includes an ignition timing control unit 11a that controls the ignition timing of the spark plug 6, a gaseous fuel injection control unit 11b that controls the injection timing and the injection amount of the gaseous fuel injection valve 7, and liquid fuel. And a liquid fuel injection control means 11c for controlling the injection timing, the injection amount, and the like of the injection valve 8.

  Further, the ECU 11 operates a purge determining means 11d for determining whether or not the gasoline evaporation component collected in the canister 10b is purged into the combustion chamber, and the purge device 10 (specifically, the purge control valve 10d). Purge control means 11e for performing gasoline purge control.

  Further, the ECU 11 includes an operation mode determination unit 11f that determines which operation mode is compressed natural gas fuel or gasoline fuel, and an operation mode switching unit 11g that switches from one operation mode to the other operation mode. And are provided. The operation mode switching means 11g of the first embodiment switches the operation mode by automatic control as necessary as described later, but the occupant operates an operation switch (not shown) provided in the passenger compartment. Can also work.

  Further, the ECU 11 is provided with combustion mode switching means 11h for switching between the stratified combustion mode and the homogeneous combustion mode in the compressed natural gas operation mode.

  Various processing functions of the ECU 11 are realized by a CPU, an input / output interface unit, a memory device, a control program, and the like (not shown).

  Next, the operation at the time of gasoline purge control of the bi-fuel engine in the first embodiment will be described based on the flowchart of FIG.

  First, it is assumed that this bi-fuel engine is operated by either compressed natural gas (CNG) fuel or gasoline fuel. At that time, the purge determining means 11d of the ECU 11 determines whether or not it is necessary to perform gasoline purge control based on a predetermined condition (step ST1). Here, the predetermined condition may be any condition as long as it is set in order to determine whether or not the gasoline purge control is necessary. For example, the predetermined condition is set in a conventional bi-fuel engine or a gasoline engine. It may be the same as a known condition (the amount collected in the canister 10b exceeds a predetermined amount).

  If the purge control means 11d determines that there is no need to perform the gasoline purge control in step ST1, the determination process in step ST1 is repeated until the engine is stopped. In addition, when it is determined that it is necessary to perform gasoline purge control, the purge control unit 11e refers to, for example, used fuel information held in the memory device of the ECU 11 to determine which fuel is being operated. A determination is made (step ST2).

  If it is determined that the vehicle is operating with gasoline fuel, the purge control means 11e performs gasoline purge control (step ST3).

In this case, the purge control means 11e first opens the purge control valve 10d that is closed. As a result, the negative suction pressure of the engine is applied to the inside of the canister 10b, and the gasoline evaporation component adsorbed by the adsorbent 10b ₁ is desorbed by the air introduced from the fresh air inlet 10b ₂ . The desorbed gasoline evaporation component becomes purge gas together with air and is supplied into the intake passage 11 via the second pipe 10c. Thereafter, the purge gas is sent into the combustion chamber. When purging the adsorbed gasoline evaporation component, the purge control means 11e closes the purge control valve 10d and ends the gasoline purge control.

  When the gasoline purge control is completed as described above, the ECU 11 determines whether to continue the current gasoline operation mode or switch to the compressed natural gas operation mode by the operation mode determination unit 11f, and switches the operation mode if necessary. The means 11g switches to the compressed natural gas operation mode (step ST4) and returns to step ST1.

  When switching to the compressed natural gas operation mode in step ST4, the operation mode switching means 11g sends an operation mode switching command (here, compressed natural gas) to the ignition timing control means 11a, the gaseous fuel injection control means 11b, and the liquid fuel injection control means 11c. Command to switch to operation mode). As a result, the liquid fuel injection control means 11c stops the liquid fuel injection valve 8, and the gaseous fuel injection control means 11b is used for the gaseous fuel at the injection timing and ignition timing corresponding to the current engine speed, engine load, etc. The injection valve 7 is operated, and the ignition timing control means 11a operates the spark plug 6.

  If it is determined in step ST2 that the vehicle is operating with compressed natural gas fuel (CNG), the operation mode determination means 11f of the ECU 11 determines whether or not gasoline operation is possible (in other words, the fuel used is gasoline fuel). Whether or not it is possible to switch to (step ST5).

  The determination condition in step ST5 may use, for example, information on the remaining amount of gasoline fuel in the gasoline tank 9 transmitted to the ECU 11 and the presence / absence of a failure in the liquid fuel injection control means 11c. For example, if the remaining amount of gasoline fuel is less than a predetermined amount, it is determined that gasoline operation is not possible. Also, it is determined that gasoline operation is not possible when switching to gasoline fuel is inappropriate (for example, during high loads such as during rapid acceleration).

  Here, if the gasoline operation is possible, the operation mode switching means 11g, the fuel switching means 11e, the ignition timing control means 11a, the gas fuel injection control means 11b, and the liquid fuel injection control means 11c are changed to an operation mode switching command (here. Then, a command to switch to gasoline operation mode is sent. As a result, the gaseous fuel injection control means 11b stops the gaseous fuel injection valve 7 and the liquid fuel injection control means 11c performs the liquid fuel injection at the injection timing and ignition timing according to the current engine speed and engine load. The valve 8 is operated, and the ignition timing control means 11 a operates the spark plug 6.

  After the operation mode switching means 11g switches from the compressed natural gas operation to the gasoline operation in this way (step ST6), the ECU 11 proceeds to step ST3 to execute the gasoline purge control, and after completing this, the step ST4 Return to compressed natural gas operation at

  As described above, when the gas purge control is required during the compressed natural gas operation, the bi-fuel engine according to the first embodiment temporarily switches to the gasoline operation and executes the gasoline purge control. By avoiding, accurate A / F control can be performed. For this reason, even in such a case, it is possible to effectively prevent the occurrence of problems such as deterioration in emission performance and knocking.

  Further, when gasoline operation is impossible in step ST5, the combustion mode switching means 11h of the ECU 11 refers to the combustion mode information held in the memory device of the ECU 11, for example, and uses the current compressed natural gas fuel. It is specified whether the combustion is stratified combustion or homogeneous combustion (step ST7).

In the case of stratified combustion, the combustion mode switching means 11h sends a combustion mode switching command (in this case, a switching command to the homogeneous combustion mode) to the ignition timing control means 11a and the gaseous fuel injection control means 11b. As a result, ignition timing control by the ignition timing control means 11a, injection timing control by the gaseous fuel injection control means 11b, and the like are performed, and the homogeneous combustion mode (the O ₂ sensor or A / F sensor provided on the exhaust passage (not shown)) is performed. The mode is switched to the stoichiometric combustion mode by feedback control based on the output (step ST8).

  Thereafter, the ECU 11 retards the ignition timing by the ignition timing control means 11a (step ST9). For example, the amount of retardation is obtained in the same manner as in Non-Patent Document 1 described above. Then, the purge control means 11e executes gasoline purge control (step ST10), and after the purge is completed, the process returns to step ST1. Note that the stratified combustion may be returned to the step ST1 after the purge is completed.

  As described above, the bi-fuel engine according to the first embodiment has a combustion mode when the gasoline purge control is required during the compressed natural gas operation, the gasoline operation is not possible, and the current combustion mode is the stratified combustion mode. Since the ignition timing is retarded after switching to the homogeneous combustion mode, and then the gasoline purge control is executed, the misfire due to the deterioration of the robustness is less than when the gasoline purge control is performed during stratified combustion. Can be avoided.

  As described above, according to the bifuel engine of the first embodiment, when it is necessary to execute the gasoline purge control during the compressed natural gas operation, the gasoline purge control is performed after switching to the gasoline operation mode. Deterioration and knocking can be effectively prevented.

  In addition, when it is not possible to switch to the gasoline operation mode and it is unavoidable to be a mixed fuel of compressed natural gas fuel and gasoline fuel, even if the combustion mode at that time is the stratified combustion mode, it is homogeneous Since the gasoline purge control is executed after switching to the combustion mode and retarding the ignition timing, it is possible to avoid the occurrence of misfire due to deterioration in robustness compared to the case where the gasoline purge control is performed during stratified combustion.

  As described above, the bi-fuel engine according to the first embodiment can perform the gasoline purge control during the gasoline operation as much as possible by repeating the above-described control process, so that the emission performance is deteriorated and knocking occurs. It can be effectively and suitably prevented.

  Next, a bi-fuel engine according to a second embodiment of the present invention will be described with reference to FIG.

  Similar to the bi-fuel engine of the first embodiment, the bi-fuel engine of the second embodiment operates at least one of gaseous fuel such as compressed natural gas fuel and hydrogen fuel and volatile liquid fuel such as gasoline fuel. This is a possible engine and differs from the first embodiment in the following points. In the second embodiment, compressed natural gas fuel is exemplified as the gaseous fuel, and gasoline fuel is exemplified as the liquid fuel.

  The bi-fuel engine of the first embodiment described above is a compressed natural gas direct-injection bi-fuel engine in which compressed natural gas fuel is sprayed directly into the combustion chamber and gasoline fuel is sprayed into the intake port 2b. The bi-fuel engine of No. 2 is different in that both the compressed natural gas fuel and the gasoline fuel are a compressed natural gas and a gasoline direct injection bi-fuel engine that spray directly into the combustion chamber.

  For this reason, in the bi-fuel engine of the second embodiment, as shown in FIG. 3, the liquid fuel injection valve 8 is also provided at the peripheral portion (on the intake port 2 b side) of the recess 2 a in the cylinder head 2. Here, in this bi-fuel engine, the gaseous fuel injection valve 7 is arranged on the lower side and the liquid fuel injection valve 8 is arranged on the upper side, but the positional relationship is not necessarily limited to the mode of the second embodiment. Not what you want.

  Thus, the bi-fuel engine of the second embodiment is substantially the same as that of the first embodiment except for the arrangement of the liquid fuel injection valve 8 which is significantly different from that of the first embodiment. It should be noted that substantially the same is the type, arrangement, and quantity of the component configuration. For example, the shape itself of the intake port 2b and the like is different from that of the first embodiment.

  Further, even in the bi-fuel engine of the second embodiment, the control process during the gasoline purge control according to the present invention is performed by the ECU 11 shown in FIG. 3 provided with the same control processing means 11a to 11h as the first embodiment. . For this reason, the processing operation of the ECU 11 during the gasoline purge control is the same as that of the first embodiment shown in FIG. 2, and the spark plug 6, the gas fuel injection valve 7 and the like operate in the same manner as in the first embodiment. Furthermore, since the effect is the same as that of Example 1, description here is abbreviate | omitted.

  In the second embodiment, since the two combustion modes of the stratified combustion mode and the homogeneous combustion mode are selectively used even in the gasoline operation mode, when the gasoline purge control of step ST3 is executed in the stratified combustion mode, It is preferable to switch to the homogeneous combustion mode before in order to avoid deterioration of emission performance and occurrence of knocking.

  A bi-fuel engine according to a third embodiment of the present invention will be described with reference to FIGS.

  The bi-fuel engine of the third embodiment is similar to the bi-fuel engines of the first and second embodiments, at least one of gaseous fuel such as compressed natural gas fuel and hydrogen fuel and volatile liquid fuel such as gasoline fuel. However, unlike these, both gaseous fuel and liquid fuel are sprayed into the intake port 2b. In the third embodiment, compressed natural gas fuel is exemplified as the gaseous fuel, and gasoline fuel is exemplified as the liquid fuel.

  Therefore, in the bi-fuel engine of the third embodiment, as shown in FIG. 4, the gaseous fuel injection valve 7 and the liquid fuel injection valve 8 are provided so that the respective injection ports are located in the intake port 2b. . Here, the positional relationship between the gaseous fuel injection valve 7 and the liquid fuel injection valve 8 is not necessarily limited to the embodiment 3 shown in FIG.

  Thus, the bi-fuel engine of the third embodiment is substantially the same as that of the first embodiment except for the arrangement of the gaseous fuel injection valve 7 with respect to the first embodiment except for the configuration of the other components such as the purge device 10. is there. Here, what is substantially equivalent is the type, arrangement, and quantity of the component configuration. For example, the shape itself of the intake port 2b, the piston 3, etc. is different from that of the first embodiment.

  Further, even in the bi-fuel engine of the third embodiment, the control process during the gasoline purge control according to the present invention is performed by the ECU 21 shown in FIG. The ECU 21 of the third embodiment includes an ignition timing control means 21a, a gas fuel injection control means 21b, a liquid fuel injection control means 21c, and a purge determination means 21d having the same processing functions as the control processing means 11a to 11g of the first embodiment. , Purge control means 21e, operation mode determination means 21f, and operation mode switching means 21g are provided.

  Next, the operation at the time of gasoline purge control of the bi-fuel engine in the third embodiment will be described based on the flowchart of FIG. Note that the operation from step ST11 to ST16 shown in FIG. 5 when the gasoline purge control can be performed in the gasoline operation mode is the same as the operation from step ST1 to ST6 in the first embodiment, and thus the description thereof is omitted here. To do.

  When the operation mode determination means 21f of the ECU 21 determines that the gasoline operation is impossible in step ST15, the ignition timing control means 21a of the ECU 21 controls the ignition timing to be retarded (step ST17). Even in the third embodiment, the amount of retardation is obtained in the same manner as in Non-Patent Document 1, for example. Thereafter, the purge control means 11e executes gasoline purge control (step ST18), and after purging is completed, the process returns to step ST11.

  As described above, the bi-fuel engine according to the third embodiment performs the gasoline purge control after switching to the gasoline operation mode when it is necessary to execute the gasoline purge control during the compressed natural gas operation, as in the first and second embodiments. As a result, it is possible to effectively prevent the deterioration of emission performance and the occurrence of knocking.

  In addition, when it is not possible to switch to the gasoline operation mode and it is unavoidable to use a mixed fuel of compressed natural gas fuel and gasoline fuel, the gasoline purge control is executed after retarding the ignition timing. Deterioration of performance and occurrence of knocking can be avoided although not as much as in the gasoline operation mode.

  As described above, the bi-fuel engine of the third embodiment can execute the gasoline purge control during the gasoline operation as much as possible by repeating any one of the control processes from step ST11 to ST18, and can achieve the emission performance. It is possible to effectively and suitably prevent the occurrence of deterioration and knocking.

  In the third embodiment, the gaseous fuel injection valve 7 and the liquid fuel injection valve 8 are exemplified as the fuel supply means for each fuel, but a carburetor may be used instead. In such a case, both gaseous fuel and liquid fuel may be supplied to the intake passage 2d by a carburetor, one of which may be supplied to the intake passage 2d by a carburetor and the other by a fuel injection valve.

  As described above, the bifuel engine according to the present invention and the liquid fuel evaporative component purging method in the bifuel engine are useful for avoiding the deterioration of the emission performance and the occurrence of knocking. It is suitable for avoiding deterioration of emission performance and occurrence of knocking when the operation mode at the time of determination is based on gaseous fuel.

It is explanatory drawing which shows the structure of Example 1 of the bi-fuel engine which concerns on this invention. 3 is a flowchart illustrating the operation of the bi-fuel engine according to the first embodiment. It is explanatory drawing which shows the structure of Example 2 of the bi-fuel engine which concerns on this invention. It is explanatory drawing which shows the structure of Example 3 of the bi-fuel engine which concerns on this invention. 6 is a flowchart illustrating the operation of the bi-fuel engine according to the third embodiment.

Explanation of symbols

6 Spark plug 7 Gas fuel injection valve 8 Liquid fuel injection valve 9 Gasoline tank 10 Purge device (purge means)
11 ECU
11a Ignition timing control means 11b Gaseous fuel injection control means 11c Liquid fuel injection control means 11d Purge judgment means 11e Purge control means 11f Operation mode judgment means 11g Operation mode switching means 11h Combustion mode switching means

Claims (4)

In a bi-fuel engine that operates at least one of gaseous fuel and liquid fuel,
Purge determining means for determining whether or not to purge the evaporated component of the liquid fuel with respect to the engine;
When the purge determination means determines that the evaporated component of the liquid fuel needs to be purged from the engine, and the operation mode at the time of the determination is the operation mode with the gaseous fuel, the operation with the gaseous fuel is performed. Operation mode switching means for switching from the mode to the operation mode with the liquid fuel;
A purge means for purging the evaporated component of the liquid fuel to the engine after the operation mode switching means is switched to the operation mode with the liquid fuel;
A bi-fuel engine characterized by In a bi-fuel engine that operates at least one of gaseous fuel and liquid fuel and sprays the gaseous fuel directly into the combustion chamber,
Purge determining means for determining whether or not to purge the evaporated component of the liquid fuel with respect to the engine;
When the purge determination means determines that the evaporated component of the liquid fuel needs to be purged from the engine, and the operation mode at the time of the determination is the operation mode with the gaseous fuel, the operation with the gaseous fuel is performed. An operation mode determination means for determining whether or not switching from the mode to the operation mode with the liquid fuel is possible;
When the operation mode determination means determines that switching to the operation mode with the liquid fuel is impossible, and the combustion mode at the time of the determination is the stratified combustion mode, the stratified combustion mode is switched to the homogeneous combustion mode. Combustion mode switching means for switching;
Ignition timing control means for retarding the ignition timing after the combustion mode switching means switches to the homogeneous combustion mode;
Purge means for purging the evaporated component of the liquid fuel from the engine after the ignition timing control means delays the ignition timing;
A bi-fuel engine characterized by In a method for purging an evaporation component of liquid fuel in a bi-fuel engine that operates at least one of gaseous fuel and liquid fuel,
Determining whether to purge the evaporated component of the liquid fuel to the engine;
When it is determined that the evaporated component of the liquid fuel needs to be purged with respect to the engine, and the operation mode at the time of the determination is the operation mode with the gaseous fuel, the liquid fuel is changed from the operation mode with the gaseous fuel. Switching to the operation mode at
Purging the engine with the evaporated component of the liquid fuel after switching to the operation mode with the liquid fuel;
An evaporative component purging method for liquid fuel in a bi-fuel engine, comprising: In a vapor fuel component purge method in a bi-fuel engine that operates at least one of gaseous fuel and liquid fuel and sprays the gaseous fuel directly into the combustion chamber,
Determining whether to purge the evaporated component of the liquid fuel to the engine;
When it is determined that the evaporated component of the liquid fuel needs to be purged with respect to the engine, and the operation mode at the time of the determination is the operation mode with the gaseous fuel, the liquid fuel is changed from the operation mode with the gaseous fuel. Determining whether or not it is possible to switch to the operation mode at
When it is determined that switching to the operation mode with the liquid fuel is impossible, and the combustion mode at the time of the determination is the stratified combustion mode, the step of switching from the stratified combustion mode to the homogeneous combustion mode;
A step of retarding the ignition timing after switching to the homogeneous combustion mode;
Purging the evaporation component of the liquid fuel to the engine after retarding the ignition timing;
An evaporative component purging method for liquid fuel in a bi-fuel engine, comprising:

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