JP4305826B2 - Bi-fuel engine and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bi-fuel engine and a control method thereof.
[0002]
[Prior art]
2. Description of the Related Art Recently, in automobiles and the like, gaseous fuel such as compressed natural gas (CNG) is attracting attention in place of liquid fuel such as gasoline and light oil from the viewpoint of air pollution control and resource saving. However, in the case of CNG, its energy density is lower than gasoline etc. (about 20-30% of gasoline), so vehicles equipped with engines that use CNG are compared to vehicles equipped with engines that use gasoline. The cruising range is short. In addition, due to delays in infrastructure development, the number of filling stations is not sufficient, and there are concerns about long-distance movement. Therefore, a dual fuel that can supply at least one of the gaseous fuel and the liquid fuel to the engine, that is, a bi-fuel engine has been proposed.
[0003]
As such a bi-fuel engine, for example, the one described in Patent Document 1 is known. In this bi-fuel engine, the fuel is switched in conjunction with the operation of a fuel switch for switching the fuel to either gasoline or LPG. When the LPG fuel is selected, the ignition timing is advanced by a predetermined amount compared to the gasoline fuel.
[0004]
In the bifuel engine supply fuel control device described in Patent Document 2, when the remaining amount of the gaseous fuel is equal to or less than the first set value, the supply fuel is switched to the liquid fuel, and at the same time the liquid fuel is switched to the liquid fuel. The engine output is limited. In this way, the driver is urged to replenish gaseous fuel.
[0005]
Furthermore, the bi-fuel engine described in Patent Document 3 includes a gaseous fuel injection valve that supplies CNG fuel to the intake port in a high load range, and a carburetor that supplies gasoline fuel in a low load range, and the magnitude of the load. In response to this, the fuel is switched and supplied.
[0006]
[Patent Document 1]
JP 2000-120519 A [Patent Document 2]
JP 2002-38986 A [Patent Document 3]
No. 5-58584 microfilm (Japanese Utility Model Publication No. 7-30344)
[0007]
[Problems to be solved by the invention]
By the way, when a gas such as CNG is used as fuel in a bi-fuel engine, in order to increase the cruising distance by effectively using the characteristics, a high compression ratio is achieved and CNG is directly injected into the cylinder. It is preferable to supply and stratify combustion. For this reason, normally, the CNG filling pressure (for example, 20 MPa) of CNG is reduced to a pressure (for example, 5 MPa) that can be controlled and injected by a regulator so that it can be directly injected into the cylinder. When the residual pressure in the container is in the range of 20 to 5 MPa, direct in-cylinder injection is possible without any problem, and reduction of CO _{2 in} super lean combustion by stratified combustion can be expected. Note that stratified combustion is a process in which a rich mixture and a lean mixture are formed in layers in a combustion chamber, and first a portion of the rich mixture is ignited and the portion of the lean mixture is burned by the flame. A lean mixture as a whole is burned while avoiding complete combustion and misfire, thereby improving the fuel consumption rate (hereinafter referred to as fuel efficiency).
[0008]
However, just like the bi-fuel engine described in the prior art, as described in Patent Document 1, the fuel is switched in conjunction with the operation of the fuel changeover switch, or as described in Patent Document 2, the gaseous fuel is changed. There is a problem that it is not always possible to perform efficient combustion only by switching the fuel according to the pressure, or by switching the fuel according to the magnitude of the load as described in Patent Document 3. is there. This is because the simple switching as described above cannot perform the stratified charge combustion operation that can fully utilize the characteristics of the gaseous fuel.
[0009]
Moreover, even if it is a bi-fuel engine, if the switching of the operation mode is possible according to the user's preference according to the driving situation, the convenience is improved.
[0010]
Accordingly, an object of the present invention is to enable not only stratified combustion with gas fuel but also stratified combustion with liquid fuel, to improve the output of the bi-fuel engine and reduce fuel consumption, and to extend the cruising distance of the vehicle on which it is mounted. In addition, it is an object of the present invention to provide a bi-fuel engine and a control method thereof that can improve convenience.
[0011]
[Means for Solving the Problems]
A bi-fuel engine according to an embodiment of the present invention that solves the above problem is a bi-fuel engine that can be operated with either gaseous fuel or liquid fuel, a liquid fuel injection valve that injects liquid fuel into an intake port or a cylinder, and A gas fuel injection valve for injecting gaseous fuel into the cylinder, and the user can designate an optimum fuel based on the operating state of the engine, and the optimum fuel is selected from the liquid fuel injection valve or the An automatic operation mode in which operation is performed by supplying from a gaseous fuel injection valve, a liquid fuel operation mode in which operation is performed by injecting liquid fuel from the liquid fuel injection valve, and a gas in operation by injecting gaseous fuel from the gaseous fuel injection valve It is configured to have three operation modes including a fuel operation mode.
[0012]
According to this structure, since it is comprised so that it may have three operation modes, a user's convenience improves. When the automatic operation mode is designated, the optimum fuel is selected on the basis of the engine operating state, so that the optimum combustion according to the engine operating state can be realized.
[0013]
Here, in the automatic operation mode, it is preferable that the optimum fuel is selected corresponding to a region determined by the engine load and the engine speed.
[0014]
In this way, since the optimum fuel is selected corresponding to the region determined by the engine load and the engine speed, the most efficient combustion is performed, and the output can be improved and the fuel consumption can be reduced.
[0015]
Of the above-mentioned regions, stratified combustion with gaseous fuel in the low load / low rotation region, stratified combustion with liquid fuel in the medium load and low / medium rotation region and low load / medium rotation region, high load and low / medium rotation region And in the high rotation area | region, you may be comprised so that the homogeneous combustion by a liquid fuel may be performed.
[0016]
In this way, fuel consumption can be reduced by stratified combustion in the low load / low rotation range and the medium load / low / medium rotation range and the low load / medium rotation range. The output in the area can be improved.
[0017]
A bi-fuel engine control method according to another aspect of the present invention that solves the above-described problem is a bi-fuel engine control method that supplies gas fuel or liquid fuel by switching and supplying liquid fuel based on the operating state of the engine. And a step of adding gaseous fuel to the liquid fuel and supplying it in the knock generation region of the operation region in which homogeneous combustion is performed or at the time of occurrence of the knock.
[0018]
According to this configuration, since the high-octane gas fuel is added to the liquid fuel and supplied, the output resulting from the ignition timing retarding control generally performed conventionally to avoid knocking during the homogeneous combustion of the liquid fuel. It is possible to effectively suppress the occurrence of knock without deteriorating performance.
[0019]
Here, the knock generation region to which the gaseous fuel is added and supplied is a high load and low / medium rotation region, and the high rotation region may include a step of performing ignition timing control based on detection of a knock sensor. .
[0020]
By doing so, the ignition timing control based on the detection of the knock sensor is performed because there is little decrease in the output performance due to the ignition timing retardation control in the high rotation region. And since the operation area | region which adds and supplies gaseous fuel is limited, more efficient combustion can be performed.
[0021]
A bi-fuel engine control method according to still another embodiment of the present invention for solving the above-described problem is a bi-fuel engine control method for switching and supplying gaseous fuel or liquid fuel based on the operating state of the engine. A fuel injection valve is disposed on the exhaust port side in the cylinder, and a gaseous fuel injection valve is disposed in the intake port or the cylinder, and gaseous fuel is supplied from the gaseous fuel injection valve when the engine is restarted at a high temperature. And starting and then switching to operation with liquid fuel.
[0022]
According to this configuration, since the fuel temperature becomes high at the time of high temperature restart, there is a possibility that bubbles are generated in the liquid fuel injection valve disposed on the exhaust port side in the cylinder, but gaseous fuel is supplied. Since the engine is started, deterioration of startability is prevented.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0024]
First, an outline of a bi-fuel engine 100 to which the present invention is applied will be described with reference to FIG. 101 is an engine body, 102 is a cylinder block, 103 is a cylinder head, 104 is a piston, 105 is a combustion chamber, 106 is an intake port, 107 is an exhaust port, 108I is an intake valve, 108E is an exhaust valve, 109 is an ignition plug Show. The intake port 106 is connected to a surge tank 111 via an intake manifold 110, and the surge tank 111 is connected to an air cleaner 113 via an intake duct 112. A throttle valve 115 driven by a step motor 114 is disposed in the intake duct 112. On the other hand, the exhaust port 107 is connected to the NOx occlusion catalytic converter 118 via an exhaust manifold 116 and an exhaust pipe 117.
[0025]
The engine 100 in FIG. 1 includes a gaseous fuel supply system and a liquid fuel supply system, and uses CNG as the gaseous fuel and gasoline as the liquid fuel. The gaseous fuel supply system includes a CNG injection valve 120, and this CNG injection valve 120 is connected to a CNG cylinder 124 as a gaseous fuel container mounted on a vehicle via a CNG supply pipe 122. Note that a fuel cutoff valve and regulator 126 (not shown) are arranged in the CNG supply pipe 122. The CNG filled in the CNG cylinder 124 with a filling pressure (for example, 20 MPa) is decompressed to a constant set pressure (for example, 5 MPa) by the regulator 126, and in a normal engine control state, the CNG is maintained with the set pressure PR. The fuel is injected from the injection valve 120 into the cylinder.
[0026]
Similarly, the liquid fuel supply system includes a gasoline injection valve 130. In the present embodiment, the gasoline injection valve 130 is disposed so as to be able to inject into the cylinder in the same manner as the CNG injection valve 120, and is mounted on the vehicle via a gasoline supply pipe 132. Connected to a gasoline tank 134 as a liquid fuel container. A fuel pump (not shown) is disposed in the gasoline supply pipe 132. These CNG injection valve 120 and gasoline injection valve 130 are controlled based on output signals from electronic control unit 300, respectively.
[0027]
Further, the combustion chamber structure will be described. In this embodiment, as shown in an enlarged view in FIG. 4, the above-described spark plug 109 is arranged at the upper center of the combustion chamber 105 between the intake port 106 and the exhaust port 107. It is installed. A CNG injection valve 120 as a gaseous fuel injection valve and a gasoline injection valve 130 as a liquid fuel injection valve are both arranged in parallel so as to sandwich the intake port 106 on the intake port 106 side. Furthermore, a common piston cavity 104 </ b> C corresponding to the CNG injection valve 120 and the gasoline injection valve 130 is formed in the upper part of the piston 104 so as to be offset toward the intake port 106. The piston cavity 104C is formed in the shape of a boat bottom that is offset toward the intake port 106 so that the spray flow from the CNG injection valve 120 and the gasoline injection valve 130 wraps around and reaches the gap of the spark plug 109. . Further, the spray angle and the spray shape of the CNG injection valve 120 and the gasoline injection valve 130 with respect to the piston cavity 104C are set to be the same so that stratified combustion can be performed with any fuel of CNG and gasoline in the common piston cavity 104C. .
[0028]
The electronic control unit 300 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 320, a RAM (Random Access Memory) 330, a CPU (Microprocessor) 340, and a constant power source connected to each other via a bidirectional bus 310. B-RAM (backup RAM) 350, an input port 360, and an output port 370 are provided.
[0029]
A pressure sensor 140 that generates an output voltage proportional to the absolute pressure in the surge tank 111 is attached to the surge tank 111. A CNG residual pressure sensor 141 that generates an output voltage proportional to the amount of residual CNG in the CNG cylinder 124, that is, the residual pressure, is disposed in the CNG supply pipe 122 at the outlet of the CNG cylinder 124. A gasoline remaining amount sensor 142 that generates an output voltage proportional to the remaining gasoline amount is disposed. The output voltages of these sensors 140, 141, and 142 are input to the input port 360 via corresponding AD converters 380, respectively. The input port 360 is connected to a rotational speed sensor 143 that generates an output pulse representing the engine rotational speed N and an operation mode changeover switch 144. On the other hand, the output port 370 is connected to the spark plug 109, the step motor 114, the CNG injection valve 120, and the gasoline injection valve 130 via corresponding drive circuits 390.
[0030]
For example, fuel is supplied in the form described below to the bi-fuel engine 100 according to the embodiment of the present invention having the above-described configuration. That is, as shown in FIG. 2A, in normal operation, the combustion type corresponds to the operating state of the engine 100, for example, the absolute pressure in the surge tank 111 representing the engine load and the engine speed. Thus, it is divided into a region (I) where stratified combustion is performed in a low / medium rotation and low / medium load region and a region (II) where homogeneous combustion is performed in a low / medium rotation and high load region and a high rotation region. ing. Further, as shown in FIG. 2 (B), even in the same stratified combustion region (I) in consideration of the optimum characteristics of the fuel, the stratified combustion region (I-1) by CNG in the low load and low rotation region, It is divided into a stratified combustion region (I-2) with gasoline in a medium load and low / medium rotation region and a low load and medium rotation region. The homogeneous combustion region (II) is also divided into a homogeneous combustion region (II-1) in which CNG is added to gasoline in a high load and low / medium rotation region, and a homogeneous combustion region (II-2) in which only high rotation region gasoline is added. It has been.
[0031]
For any fuel, data relating to the injection timing and injection time of fuel injected from the CNG injection valve 120 and the gasoline injection valve 130 and parameters for establishing combustion (ignition timing, VVT opening, throttle opening, EGR The opening degree and the like) are stored in advance in the ROM 320 in the form of a map as a function of the engine operating state indicated by the load and the rotational speed of the engine 100 described above. This CNG injection time is a time required to inject CNG into the cylinder by the required amount under the set pressure PR set to be reduced by the regulator 126. The gasoline injection time is the time required to inject gasoline into the cylinder by the required amount under a constant pressure boosted by the fuel pump.
[0032]
In this embodiment of the present invention, for example, fuel is supplied to the engine 100 according to the fuel injection control routine shown in FIG. This control routine is executed by interruption every predetermined crank angle. First, in step S301, it is determined which operation mode is selected based on an input from the operation mode changeover switch 144 by a user operation.
[0033]
"CNG operation mode"
Therefore, when the CNG operation mode as the gaseous fuel operation mode is selected, the process proceeds to step S302, and the remaining amount of CNG is checked. That is, it is determined whether or not the residual pressure in the CNG cylinder 124 detected by the CNG residual pressure sensor 141 is higher than the normal injection pressure that is the pressure at which in-cylinder injection is possible in the compression stroke (the remaining amount is sufficient). In the case of YES, it progresses to step S303 and the driving | operation by CNG is performed in all the driving | running regions. In the CNG operation mode, a necessary amount of CNG is injected from the CNG injection valve 120 toward the piston cavity 104C in the compression stroke or the intake stroke at the injection timing and the injection time corresponding to the operation state at that time. If the remaining amount of the CNG is not sufficient in step S302, the process proceeds to step S304, a warning that the remaining capacity is not sufficient is given, and the process proceeds to step S305 described later.
[0034]
"Gasoline operation mode"
If it is determined in step S301 that the gasoline operation mode as the liquid fuel operation mode is selected, the process proceeds to step S305, and the remaining amount of gasoline is checked. That is, it is determined whether or not the remaining gasoline amount in the gasoline tank 134 detected by the gasoline remaining amount sensor 142 is larger than a predetermined amount. In the case of YES, the process proceeds to step S306, and operation with gasoline is performed in the entire operation region. In the gasoline operation mode, a required amount of gasoline is injected from the gasoline injection valve 130 toward the piston cavity 104C in the compression stroke or the intake stroke at the injection timing and the injection time corresponding to the operation state at that time. If NO in step S305, the process proceeds to step S307, a warning is issued to prompt replenishment, and then the process proceeds to step S302 described above.
[0035]
In the above-described CNG operation mode and gasoline operation mode, if the remaining amount of fuel to be used in the selected operation mode is not sufficient, a warning is issued to prompt replenishment, and then the operation is performed with the remaining fuel. Is called.
[0036]
"AUTO mode"
If the AUTO mode as the automatic operation mode is selected in the determination in step S301, the process proceeds to step S308, where it is determined whether or not the region is an area where the operation with CNG fuel is efficiently performed. If YES, the process proceeds to step S309, and the remaining amount of CNG is checked. That is, whether the residual pressure in the CNG cylinder 124 detected by the CNG residual pressure sensor 141 is higher than the normal injection pressure that is the pressure that enables in-cylinder injection in the compression stroke (the remaining amount is sufficient) as in step S302 described above. It is determined whether or not. And in the case of YES, it progresses to step S310 and the driving | operation by CNG is performed. In this CNG operation mode, a required amount of CNG is injected from the CNG injection valve 120 toward the piston cavity 104C in the compression stroke at the injection timing and injection time corresponding to the operation state of the CNG stratified combustion region (I-1). Is injected. The injected CNG has a high injection speed in the cylinder and does not need to be vaporized like gasoline. Therefore, stratified combustion is achieved by easily taking in air and forming a stratified mixture easily and being ignited by the spark plug 109. Is done. If the remaining amount of CNG is not sufficient in step S309, the process proceeds to step S311 to give a warning that the remaining amount is not sufficient, and the process proceeds to step S312 described later.
[0037]
Further, if it is determined in step S308 described above that the region is not efficiently operated with CNG fuel, the process proceeds to step S312 to check the remaining amount of gasoline. That is, it is determined whether or not the remaining gasoline amount in the gasoline tank 134 detected by the gasoline remaining amount sensor 142 is larger than a predetermined amount as described above. If NO, the process proceeds to step S313 to give a warning that the remaining amount is not sufficient, and then proceeds to the above-described step S309.
[0038]
If it is determined in step S312 that the remaining amount of gasoline is sufficient, the process proceeds to step S314, and it is determined whether or not the operating state is in the “knock occurrence region” of the high load and low / medium rotation region. Here, in the case of NO, the process proceeds to step S315 and operation with gasoline is performed. In this gasoline operation mode, a required amount of gasoline is injected from the gasoline injection valve 130 toward the piston cavity 104C at the injection timing and injection time corresponding to the operation state at that time. This injection is performed in the compression stroke in the case of the gasoline stratified combustion region (I-2), and in the intake stroke in the case of the gasoline homogeneous combustion region (II-2).
[0039]
On the other hand, when it is determined in step S314 that it is in the “knock occurrence area”, the process proceeds to step S316, and it is determined again whether or not the remaining amount of CNG is sufficient. When it remains sufficiently, the process proceeds to step S317, and an operation in which CNG is added to gasoline is performed. That is, in this case, in addition to gasoline injection from the gasoline injection valve 130, CNG is injected from the CNG injection valve 120 toward the piston cavity 104C. Since CNG has a high octane number and has a knock suppressing action, it is possible to prevent knock without retarding the ignition timing of the spark plug 109 and prevent performance degradation.
[0040]
In addition, when the remaining CNG amount is not sufficient in the determination in step S316, the above-described CNG addition cannot be performed, and therefore, based on the detection of the normal knock control sensor (KCS) in step S319 after the warning in step S318. The advance mode (retard angle) control, that is, the KCS control is performed, and the operation mode with gasoline in step S315 is performed.
[0041]
In addition, even when the operation with gasoline in step S315 is performed in the determination in step S314 described above and the operation with gasoline in step S315 is performed, in the high rotation range, the detection is based on the normal knock control sensor (KCS). KCS control is performed. In this region, there is little decrease in output performance due to ignition timing retardation control, so ignition timing control based on the detection of the knock sensor is sufficient, and CNG can be saved correspondingly.
[0042]
In the above description, CNG is added as long as the operating state is in the “knock occurrence region” and the CNG remaining amount is sufficient, but the present invention is not limited to this. That is, CNG may be injected from the CNG injection valve 120 only when a knock occurs in response to the detection of the knock by the knock control sensor (KCS). In this way, as described above, CNG can be saved accordingly.
[0043]
Next, another embodiment of the present invention is shown in FIG. In this embodiment, the spark plug 109 is disposed at the upper center of the combustion chamber 105 between the intake port 106 and the exhaust port 107, the CNG injection valve 120 is disposed on the intake port 106 side, and the gasoline injection valve 130 is provided. Is disposed on the exhaust port 107 side. The piston cavity 104Cc corresponding to the CNG injection valve 120 is on the intake port 106 side, and the piston cavity 140Cg corresponding to the gasoline injection valve 130 is on the exhaust port 107 side so that stratified combustion can be performed with either CNG or gasoline fuel. Each is formed offset.
[0044]
According to the combustion chamber structure according to this embodiment, the piston cavity 104Cc having a shape suitable for combustion of CNG injected from the CNG injection valve 120 and the piston cavity having a shape appropriate for combustion of gasoline injected from the gasoline injection valve 130 Since 104 Cg can be set, the spray angle and the spray shape can be set independently for each of the CNG injection valve 120 and the gasoline injection valve 130, and the injection fuel pressure and the like can be optimized.
[0045]
Also in this other embodiment of the present invention, fuel can be supplied to the engine 100 according to the fuel injection control routine shown in FIG. 3 in the normal operation state as in the previous embodiment. By the way, since the CNG injection valve 120 is disposed on the intake port 106 side and the gasoline injection valve 130 is disposed on the exhaust port 107 side, the temperature on the exhaust port 107 side is increased and the vaporization of gasoline is promoted. As a result, the homogeneity combustibility is improved, the necessary increase rate is reduced at a low engine temperature, and the dilution action of the lubricating oil is reduced. However, as a contradiction, there is a possibility that bubbles may be generated in the gasoline at the time of high temperature restart or the like. In order to deal with such a case, in another embodiment of the present invention, at the time of high temperature restart or the like First, the engine is started using CNG and is switched to gasoline after a predetermined time has elapsed.
[0046]
In the above-described embodiment, both the CNG injection valve 120 and the gasoline injection valve 130 are arranged so that fuel can be directly injected into the combustion chamber 105 in the cylinder, but stratified combustion is not required. Depending on these conditions, the CNG injection valve 120 and / or the gasoline injection valve 130 may be arranged in the intake port 106.
[0047]
Furthermore, in the embodiments described so far, an example in which CNG is used as the gaseous fuel and gasoline is used as the liquid fuel has been described. However, as the gaseous fuel, for example, natural gas and petroleum gas which are primary fuels, or coal conversion gas and petroleum conversion gas which are secondary fuels can be used. Needless to say, hydrocarbons such as isooctane, hexane, heptane, light oil, and kerosene, hydrocarbons such as butane and propane that can be stored in a liquid state, and methanol can be used as the liquid fuel.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of an embodiment of a bi-fuel engine according to the present invention.
FIG. 2 is a graph showing an example of (A) combustion separation and (B) combustion / fuel separation in a bi-fuel engine.
FIG. 3 is a flowchart showing an example of a control routine of the embodiment of the bi-fuel engine according to the present invention.
FIG. 4 is a cross-sectional view showing an example of an injection valve arrangement of a bi-fuel engine according to the present invention.
FIG. 5 is a cross-sectional view showing another example of the injection valve arrangement of the bi-fuel engine according to the present invention.
[Explanation of symbols]
100 Bi-fuel engine 103 Cylinder head 103C Cylinder head cavity 104C Piston cavity 104Cc Piston cavity (for CNG)
104Cg piston cavity (for gasoline)
105 Combustion chamber 106 Intake port 107 Exhaust port 109 Spark plug 120 CNG injection valve 124 CNG cylinder 130 Gasoline injection valve 134 Gasoline tank 141 CNG residual pressure sensor 142 Gasoline remaining amount sensor 300 Electronic control unit

Claims (1)

In a bi-fuel engine that can be operated with either gaseous or liquid fuel,
Comprising a liquid fuel injection valve for injecting liquid fuel into a cylinder, and a gas fuel injection valve for injecting gaseous fuel into a cylinder,
An automatic operation mode in which the user can specify an optimum fuel based on an operating state of the engine, and the optimum fuel is supplied from the liquid fuel injection valve or the gas fuel injection valve to operate. It is configured to have three operation modes: a liquid fuel operation mode that operates by injecting liquid fuel from a liquid fuel injection valve, and a gas fuel operation mode that operates by injecting gaseous fuel from the gaseous fuel injection valve ,
In the automatic operation mode, the optimum fuel is selected in accordance with the region determined by the engine load and the engine speed, and the stratified combustion by the gaseous fuel is performed in the low load / low rotation region among the regions. In the medium load and low / medium rotation region and in the low load and medium rotation region, stratified combustion with liquid fuel is performed, and in the high load and low / medium rotation region and high rotation region, homogeneous combustion with liquid fuel is performed. This is a bi-fuel engine.

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