JPS63230933A - Fuel switching method and device for dual fuel engine - Google Patents

Abstract

PURPOSE:To prevent degradation of engine performance by supplying proper quantity of liquid fuel or gas fuel according to accelerating or decelerating condition of engine when fuel is switched, thereby eliminating possibility of over lean or over rich. CONSTITUTION:Liquid fuel is injected through an injector 19 which is controlled by a gasoline fuel control circuit 22. On the other hand, gas fuel is regulated of its supply quantity through CNG control circuit 13 and mixed in a mixer 26. A fuel exchange switch 9 feeds signals which indicate switching of fuel to both control circuits 22, 13. If a vehicle is accelerating or decelerating during switching from gas fuel to liquid fuel, liquid fuel supply is started when residual gas pressure of gas fuel detected through a gas pressure sensor 45 drops to a predetermined level. If the vehicle is decelerating during switching from liquid fuel to gas fuel, liquid fuel supply is interrupted upon increase of fuel gas pressure to a predetermined level. Consequently, air-fuel ratio is optimized and degradation of engine performance is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a dual fuel engine that alternately supplies liquid fuel and gas fuel, and provides a dual fuel engine for preventing deterioration of operating performance when switching between liquid fuel and gas fuel. The present invention relates to a switching method and device.

2. Description of the Related Art For example, a dual-fuel engine is known in which compressed natural gas (CNG) and gasoline are selectively switched and supplied to a combustion chamber.

In vehicles equipped with this type of dual fuel engine, the fuel is switched to gasoline when the CNG in the cylinder becomes insufficient, and the fuel is switched to CNG when the gasoline becomes insufficient (Japanese Patent Application Laid-Open No. 57-1989-1). No. 59048).

Furthermore, according to Japanese Patent Application No. 61-234375 disclosed by the present applicant, in order to eliminate the shock caused by poor connection when switching between CNG and gasoline, for example, when switching from CNG to Ganrin, from the time of fuel switching, Gasoline supply is started after a predetermined period of time has elapsed.

Problems to be Solved by the Invention However, in the conventional fuel switching method or device for a dual fuel engine, the fuel after switching is supplied in accordance with the operating condition until the predetermined time has elapsed from the time of fuel switching. Therefore, if the opening of the throttle valve changes as the vehicle accelerates or decelerates immediately after switching fuel, there is a problem that the fuel may run out or the air-fuel ratio may become over-rich, resulting in deterioration of engine performance. . For example, (1) When switching from gas fuel to liquid fuel,
During medium-speed operation or long low-speed idling operation in which it takes a relatively long time to complete the switching, if you accelerate immediately after the switching, the gas fuel will run out before the predetermined time, and the period when no fuel will be supplied (fuel can be cut).

(2) If the speed is decelerated immediately after switching, gas fuel continues to be supplied at a flow rate corresponding to the operating state even after the predetermined period of time has elapsed, and liquid fuel starts to be supplied, resulting in over-rich condition.

(2) When switching from liquid fuel to gas fuel,
If you decelerate immediately after switching fuel during medium-speed operation or long low-speed idling, where it takes a relatively long time to complete the switching, the gas fuel flow rate will reach the level corresponding to the operating state before the predetermined time, resulting in overrich condition. becomes.

The present invention was created in view of these problems, and by eliminating the risk of becoming over-lean or over-rich during acceleration or deceleration after switching fuels, the present invention reduces the deterioration of engine performance when switching fuels. It is an object of the present invention to provide a fuel switching method and device for a dual fuel engine that prevents this.

Means for Solving the Problems In order to achieve the above object, the fuel switching method for a dual fuel engine of the present invention provides the following steps: When the vehicle is accelerated or decelerated when switching from gas fuel to liquid fuel, the gas fuel is switched from gas to liquid fuel. When the residual gas pressure drops to a predetermined pressure, liquid fuel supply starts, and when the vehicle decelerates when switching from liquid fuel to gas fuel, when the gas pressure of gas fuel rises to the predetermined pressure, the liquid fuel supply starts. It is characterized by cutting off the supply.

As shown in FIG. 1, the apparatus for carrying out the fuel switching method includes: a liquid fuel supply means for supplying liquid fuel to the engine; a gas fuel supply means for supplying gas fuel to the engine; and the gas fuel supply means. A gas pressure sensor provided in the dark piping of the low pressure regulator and the high pressure regulator provided upstream of the means, a means for determining the acceleration or deceleration driving state of the vehicle, and a detected pressure value detected by the gas pressure sensor. and liquid fuel supply control means for comparing the pressure value with a reference pressure value and controlling the supply of liquid fuel based on the comparison result and the acceleration/deceleration state of the vehicle, and the determination means determines whether the driving state is accelerated or decelerated at the time of fuel switching. When detected, the liquid fuel supply control means starts or cuts off the supply of liquid fuel when the detected pressure of the gas pressure sensor becomes less than or more than a predetermined value.

Effect When switching from gas fuel to liquid fuel, if the vehicle is accelerating immediately after the fuel switch, when the thrower I valve opens and the gas pressure of the gas fuel falls below the set value, the set time (
For example, without having a timer set time during steady state,
At the same time as reducing the flow rate of gas fuel to zero, supply of liquid fuel is started at a flow rate commensurate with acceleration. During deceleration immediately after fuel switching, when the throttle valve opens, the gas pressure of the gas fuel will not fall below the set value even if the set time (timer set time during steady state) has elapsed. At the same time, the flow rate of gas fuel is reduced to zero, and at the same time, supply of liquid fuel is started at a flow rate commensurate with deceleration.

When switching from liquid fuel to gas fuel, if the vehicle is decelerating, the throttle valve closes and the gas pressure of the gas fuel exceeds the set value. Cut out liquid fuel without carrying it.

Friend-1-μ Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

Turning 1° to FIG. 2, an example of a dual fuel engine to which the present invention is applied is shown. In this case, the fuel in the cylinder 1 is, for example, 200 K! CNG filled at a pressure of j/aA and gasoline in the gasoline tank 2 are used. In the figure, 3 is a valve provided in the cylinder 1 and used for filling and taking out CNG, 4 is a shutoff valve connected to the valve 3 via a high pressure pipe 5, and 6 is a shutoff valve 4.
7 represents a low pressure regulator connected to the high pressure regulator 6 via piping 8. The shutoff valve 4 is composed of an electromagnetic valve configured using, for example, a solenoid, and is controlled to open and close by a signal sent from the C N G ft, II fit circuit 13 via a line 15 .

With the shutoff valve 4 open, CNG is first reduced in pressure to 4 to 6 Kg/cd by the high pressure regulator 6, and then reduced to 0.1 to 0.2 Ng/ll by the low pressure regulator 7.
1i and is provided in the intake passage 11 of the engine via the piping 12 and the variable orifice 10.
and mixed with intake air.

The desired orifice opening degree of the variable orifice 10 is set by the rotation of a stepping motor that can be driven by a pulse signal sent from the CN G III fi1 circuit 13 via the line 14, thereby adjusting the CNG supply m. do.

On the other hand, the gasoline in the gasoline tank 2 is sent to the injector 19 at a predetermined pressure by a fuel pump 16 provided in the gasoline tank 2 via a pipe 17 and a fuel filter 18 installed in the middle. The injector 19 is actually provided for each cylinder, and is controlled to open and close according to the electric drive pulse sent from the gasoline fuel control circuit 22 via the line 21, and the injector 19 is fed at a predetermined pressure (not shown). The fuel is intermittently injected into the intake passage 11 near the intake valve.

The flow rate of the intake air taken in through the air cleaner 44 is detected by the air flow sensor 23 having the movable vane 24 . The amount of intake air is controlled by a throttle valve 25 that is linked to an accelerator pedal (not shown). A signal from the throttle position switch 40, which works in conjunction with the throttle valve 25 and closes when the throttle valve 25 is in the fully open position (idle position), is transmitted through the line 41.
The fuel is sent to the CN Gill control circuit 13 and the gasoline fuel control circuit 22 via the CN Gill control circuit 13 and the gasoline fuel control circuit 22.

mixture! A mixture of air and fuel in which CNG is mixed in the engine body 26 or gasoline fuel is injected by the injector 19 is combusted in a combustion chamber (not shown) in the engine body 27, and the exhaust gas after combustion is passed through the exhaust passage. 28 and a catalytic converter 29 provided in the middle thereof, the gas is discharged into the atmosphere.

The air flow sensor 23 is provided in the intake passage 11' upstream of the throttle valve 25, and generates a voltage determined by the position of the movable vane 24, which rotates in response to changes in the amount of intake air. This output voltage is fed to the gasoline fuel control circuit 22 via line 30. 31 is a movable vane 24
The actuator 31 is connected to the gasoline fuel control circuit 22 via a line 32, and rotates the movable vane 24 when the fuel selector switch 9 is on the gasoline side. When the fuel selector switch 9 is on the CNG side, the movable vane 24 is controlled to bring the intake air passage into the full IHI state.

Reference numeral 33 is an engine distributor which outputs a pulse signal every time the crankshaft rotates by a predetermined angle, and this pulse signal is sent to the engine via a line 34.
It is sent to @circuit 13 and gasoline fuel control circuit 22.

The exhaust passage 28 has two values that generate output in response to the oxygen concentration in the exhaust gas, that is, two values that influence each other depending on whether the air-fuel ratio is on the lean side or rich side with respect to the stoichiometric air-fuel ratio. An 02 sensor υ 35 is provided for generating an output voltage, the output voltage of which is fed to the gasoline fuel control circuit 22 via line 36.

A conduit 37 is provided downstream of the throttle valve 25 in the intake passage 11.
An intake pipe pressure sensor 38 is provided via the intake pipe pressure sensor 38 , which sends a voltage signal generated in response to the negative pressure in the intake passage 11 via a line 39 to the CNG control circuit 13 and the gasoline fuel control circuit 22 .

The fuel disconnect switch 9 connects the CNG via lines 42 and 43.
For example, an open/close signal indicating that the fuel has been switched is sent to the control circuit 13 and the gasoline fuel control circuit 22.

Piping 8 connecting high pressure regulator 6 and low pressure regulator 7
A gas pressure sensor 45 that detects one mocha of gas fuel is provided in the middle of the pipe 8, and the gas pressure sensor 45 sends a voltage signal generated according to the pressure inside the pipe 8 to the gasoline fuel control circuit 22 via $146. send to.

FIG. 3 is a block diagram showing one embodiment of the gasoline fuel control circuit 22 shown in FIG.

The voltage signals from the air flow sensor 23.
The signals are sequentially converted into binary signals according to instructions from 2.

Pulse signals for each predetermined crank angle from the distributor 33 are sent to a well-known speed signal forming circuit provided in the input interface circuit (110 circuit) 54, thereby forming a binary signal representing the rotational speed of the engine. Ru. Further, this pulse signal is also used to form an interrupt request signal for fuel injection pulse width operation, a fuel injection start signal, a cylinder discrimination signal, etc., along with other pulse signals for each predetermined angle.

The signal from the throttle position switch 40 is I1
The signal is sent to a predetermined pit position of the 0 circuit 54 and temporarily stored.

The signal from the fuel disconnect switch 9 is the same <I10 circuit 5
A timer is sent to a predetermined pit position of No. 4 and measures an interrupt request signal for activation/stop of the injector 19, an activation signal for the air flow sensor actuator 31, and a gasoline fuel injection start time and end time at the time of fuel switching, which will be described later. It is used to form set/reset signals, etc.

In the output interface circuit (110 circuit) 56,
A well-known fuel injection control circuit including a register and the like is provided, and the I10 circuit 56 forms an injection pulse signal having the pulse width from binary data regarding the injection pulse width sent from the CPU 52. This injection pulse signal is transmitted to the injector 19 via a drive circuit (not shown).
It is sent sequentially or simultaneously to a to 19d and monitors them. As a result, fuel is injected in an amount corresponding to the pulse width of the injection pulse signal. Further, this I10 circuit 56 is provided with a circuit for forming a binary signal for driving the air flow sensor actuator 31, and this signal causes the air flow sensor actuator 31 to control the vane when in the CNG fuel mode. 24 fully opens the intake air passage and locks it in this state,
When in gasoline fuel mode, the vane 24 is unlocked so that it can rotate freely according to the amount of intake air.

Δ/D conversion converter 5011ro0 CPU52 which is the main component of the microcomputer
, a random access memory (RAM>58), and a read-only memory (ROM) 60 via a common bus 62, and data and instructions are transferred via this bus 62.

The ROM 60 contains a main processing routine program, an interrupt processing routine program for calculating fuel injection pulse width, an interrupt processing routine program for calculating various correction coefficients, and a program that starts liquid fuel injection from the time of switching fuel from CNG during steady operation. A program (timer function) for counting down the time t2 until the liquid fuel injection is stopped after switching to CNG and the time to until the liquid fuel injection is stopped linearly, and other programs, as well as those necessary for calculation processing. Various data are stored in advance.

The voltage signal from the gas pressure sensor 45 is sent to an A/D converter 50 having an analog multiplexer function,
Other sensors such as the air flow sensor 23, 02 sensor 35, and the intake pipe pressure sensor 8 are treated in the same way.

The signal from the throttle position switch 40 is used as a determination signal for accelerating or decelerating the vehicle.

In the ROM 60, if an acceleration or deceleration signal is input immediately after the fuel is switched from CNG to gasoline, the gas pressure detected by the gas pressure sensor 45 is set to a predetermined value, for example, 0.3 to 9.
A program is set to start gasoline injection when the fuel pressure drops below /ai. This injection m at the start of gasoline injection is determined according to the driving state.

Furthermore, in the ROM 60, if a deceleration signal is input immediately after switching from gasoline to CNG, the gas pressure detected by the gas pressure sensor 45 is set to a predetermined value, for example 3.5Kt/ci.
A program is set to immediately stop the injection of Ganlin when the temperature rises above this level.

On the other hand, FIG. 4 shows the CNG Ill shown in FIG.
FIG. 2 is a block diagram showing one embodiment of the m circuit 13. FIG. In this case, A/D converter 50', CPU 52', I10 circuits 54' and 56', RAM 58', and ROM
The basic function and configuration of the hardware such as 60' is similar to the hardware of the gasoline fuel control circuit shown in FIG. 3, so a description thereof will be omitted.

As the Ganlin fuel control circuit 22 and the CNG control circuit 13, various configurations different from those described above can be applied. For example, without providing a speed signal forming circuit in the I10 circuits 54 and 54', it is also possible to configure the CPUs 52 and 52' to receive pulse signals for each predetermined crank angle and form speed signals using software. be. Furthermore, the air flow meter actuator 31 and the cutoff valve 4 may be configured to be directly connected to the fuel selector switch 9 without going through the control circuits 22 and 13 as described above.

Then, the gasoline fuel mode, that is, the fuel selector switch 9
is on the gasoline fuel side, the gasoline fuel control circuit 22 functions, and based on the data regarding the intake air amount from the air flow sensor 23 and the engine rotational speed data from the distributor 33, first, the basic fuel injection amount is falsified. It will be done. This basic fuel injection amount is corrected each time according to signals from other sensors, and the injector 19 is driven by a fuel injection pulse formed according to the corrected fuel injection amount.

In the CNG mode, that is, when the fuel selector switch 9 is on the CNG side, the CNGfblJtl11 circuit 13 functions, and based on the intake pipe pressure data from the intake pipe pressure sensor 38 and the engine rotational speed data from the distributor 33, first , the variable orifice 10 is stored in the ROM 60' using these data as parameters.
The basic opening degree of is read out. This basic opening degree is corrected each time according to signals from other sensors, and the variable orifice 10 is driven to achieve the corrected opening degree.

Next, regarding the characteristic mode switching control of the present invention,
This will be explained in detail using flowcharts and timing charts.

FIG. 5 is a flowchart regarding control when switching from gasoline to CNG, and FIG. 6 is a timing chart showing the operation of each member at that time.

In step 70, it is determined whether or not the fuel selector switch 9 has been switched from the gasoline fuel mode to the CNG mode. If it is determined that the fuel selection switch 9 has not been switched, the process proceeds to step 80, and the control in the gasoline fuel mode described above continues. be done. In addition, in the gasoline fuel mode, the variable orifice 10
The reason why is kept fully open is to prevent fluctuations in the air-fuel ratio and deterioration of engine startability due to incomplete gas sealing between the high-pressure side regulator 6 and the variable orifice 1001.

On the other hand, if it is determined in step 70 that the mode has been switched to CNG mode, the cutoff valve 4 is opened in step 71, and the variable orifice 10 is driven to a predetermined opening degree E in step 72. This opening degree E is an opening degree that corresponds to the operating state of the engine (throttle opening degree A) in the CNG mode described above.

In step 73, air 70 - sensor actuator 3
1 starts to drive, and as a result, the air flow sensor 23
The vane 24 is displaced from a position corresponding to the operating state of the engine in the gasoline fuel mode to a fully open position and is locked in this state. The time required for this displacement is at most
Since the distance is about 200 m5, the signal between the air flow sensors is on for 200 m5.

Next, in step 74, the timer starts integrating, and if in step 76, the deceleration signal is not input and the situation is steady, in step 78, the timer starts counting for a set time t, which will be described later. The operations from step 75 onwards are continued until the time elapses. Step 7
5, the fuel injection amount of the injector 19 is set to ff1G according to the operating state of the engine in the gasoline fuel mode.
to set time t. After the elapsed time, it starts decreasing to zero.

It is desirable that the rate of decrease is constant.

This setting time t. The pressure of CNG in the pipe 8 reaches the maximum set pressure (
For example, 4Ky/ai>, that is, the time required for the high pressure regulator 6 to reach a normal pressure regulation state, is mapped in the ROM 60 in advance and is taken out as appropriate at the time of switching.

If it is determined in step 78 that the predetermined time to has elapsed in the steady-state operating state, the process proceeds to step 79 to completely stop gasoline fuel injection, terminate this routine, and shift to the CNG mode control described above.

If a deceleration signal is input in step 76, that is, if the throttle opening changes from A to 8 and the throttle position switch 40 detects deceleration, the process proceeds to step 77, where the piping between the high pressure regulator 6 and the low pressure regulator 7 is detected. It is determined based on the signal from the gas pressure sensor 45 whether or not the gas pressure in the chamber 8 is 3.5 kg/cd or more. If it is less than to, the determination is repeated until to has elapsed. Immediately stop gasoline injection without waiting for the period to elapse. The operation of each member between step 76 and step 79 is as follows: the throttle opening changes from 8 to B;
The 1F11 degree of the variable orifice changes from E to F, and the CNG flow rate decreases from target C to D.

During deceleration immediately after switching from gasoline to CNG, the gas pressure at the gas pressure sensor 45 suddenly increases, and from the time of switching to t
At the time when 1 o'clock rg+u has passed, which is earlier than the steady state time 1o, the gas pressure in the pipe 8 becomes 3.5 m/cd, creating a condition in which the gasoline fuel injection m becomes zero.

In step 79, a signal indicating that the gas pressure is 3.5 to 9/cd or higher is received from the gas pressure sensor 45, and gasoline fuel injection is completely stopped.
Shift to NG mode control.

FIG. 7 is a flowchart regarding υ control when switching from CNG to gasoline, and FIG. 8 is a timing chart showing the operation of each member at that time.

In step 90, it is determined whether or not the fuel selector switch 9 has been switched from the CNG mode to the gasoline fuel mode. If it is determined that the fuel mode has not been switched, the process proceeds to step 101, and the aforementioned CNGE-mode control is continued. Ru. On the other hand, if it is determined in step 90 that the CNG mode has been switched to gasoline fuel mode, the cutoff valve 4 is opened in step 91. Next, in step 92, the airflow sensor vane 24 is unlocked to respond to the intake airflow. In step 93, the timer starts integrating, and in step 94, a countdown is performed to start injection of gasoline fuel after the fuel changeover switch 9 is actuated. In step 95, the variable orifice 10 is maintained at the same position immediately before switching.

If no acceleration/deceleration signal is received in step 96, it is assumed that the operating state is steady, and in step 98, this timer is set for the set time t2.
The eyelid creation in steps 94 and 95 continues until the time elapses. This set time t2 is the time from the closing of the shutoff valve 4 during fuel switching during steady operation until the CNG pressure in the pipe 8 drops to the minimum set pressure (for example, 0.3 KfF/ai), and is stored in advance in the ROM 60. It is mapped to , and is taken out as appropriate when switching.

In the steady state of operation, if it is determined in step 98 that the set time rat2 has elapsed, the process proceeds to step 99, and gasoline is supplied commensurate with the intake air m measured by the vane position tlJ of the air 70-sensor 23 at that time. Shifts to the above-mentioned gasoline fuel mode ailJIl. Further, in step 100, the variable orifice 10 is fully opened,
Exit this routine.

When switching from CNG to gasoline, the fuel pump 16 is always operated and gasoline fuel is constantly circulated so that vapor is not generated in each gasoline pipe 17, 20 and there is no delay in gasoline fuel injection. It is desirable to leave it in good condition.

If an acceleration signal or deceleration signal is input in step 96, that is, the throttle opening changes from 8 to 8 (during acceleration) or from A to C (during deceleration), and the throttle position switch 40 is activated to accelerate or decelerate. If it is detected, the process proceeds to step 97, and the gas pressure in the pipe 8 between the high pressure regulator 6 and the low pressure regulator 7 is 0.3υ/cd.
Judging from the signal of the gas pressure sensor 45 whether or not the
If the value does not exceed 0.3cd/ei, the judgment is repeated, and if the value is less than 97cd at 0.3, the process proceeds to step 99.

In step 99, the amount of gasoline to be injected is determined according to the amount of intake air, and then in step 100, the variable orifice 10 is fully opened.

The operation of each member between step 96 and step 99 is as follows:
During acceleration when the throttle opening changes from A to 8, CN
The G flow rate increases from D to E, and the variable orifice is at steady state (
The gap is reached (t3) earlier than t2), and the vane position of the air flow sensor 23 changes from the target J to K and becomes balanced at the opening of K.

During deceleration when the throttle opening changes from A to C, CN
G1ff1 decreases from D to F, the variable orifice fully opens later than the steady state (t2) (t4), and the vane position of the air flow sensor 23 changes to the target J mustard and becomes balanced at the opening degree of L.

In step 99, during acceleration, the gasoline fuel injection amount is H, and injection is started after t3 hours have elapsed, and during deceleration, the gasoline fuel injection amount is (■), and injection is started after 14 hours have elapsed.

In this way, in this embodiment, when the gas pressure detected by the gas pressure sensor 45 becomes 0.3 to 9/l:d or less due to the fuel switching when switching from CNG to gasoline, the timing to start gasoline injection is determined. , when accelerating, it is faster than when it is steady, and when decelerating, it is slower than when it is steady. CN from gasoline
When switching to G, if the gas pressure detected by the gas pressure sensor 45 becomes, for example, 3.5 kg/ci or more due to fuel switching,
During deceleration, the stop timing of gasoline injection is set later than during steady state.

Effects of the Invention According to the present invention, since an appropriate amount of liquid fuel or gas fuel is supplied depending on the acceleration or deceleration driving state when switching between dual fuels, the air-fuel ratio is not over lean when switching between fuels. This eliminates the risk of over-riching and deterioration of vehicle performance, and also prevents pack fires that tend to occur when the engine is lean, thereby preventing damage to the measuring plate of the air flow sensor.

Furthermore, misfires and hourly turbulence that tend to occur when overrich are prevented, and damage to the catalyst, exhaust pipe, and muffler is therefore prevented.

In addition, during the process leading up to over-lean during acceleration immediately after fuel switching, that is, during acceleration when a particularly large amount of NOx is generated, it is possible to eliminate the lean region in which there is little hope of purification by the catalyst, thereby reducing NOx emissions. be able to. When over-rich during deceleration immediately after fuel switching, that is, during deceleration when a particularly large amount of HC is generated, the condition that made rich even more severe (Situation B where HC increases due to misfires and afterfires and there is little hope for purification by the catalyst) has been resolved. Therefore, HC emissions can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram showing the basic configuration of the device of the present invention, Fig. 2 is a system configuration diagram showing an embodiment of an engine to which the present invention is applied, and Fig. 3 is a block diagram showing the basic configuration of the device of the present invention. FIG. 4 is a block diagram showing an example of the CNG Ill 10 circuit shown in FIG. 2. FIG. 5 is a block diagram showing an example of the CNG Ill 10 circuit shown in FIG. Flowchart I for explaining the control when switching from CNG to gasoline fuel, FIG. 6 is a timing chart of this control, FIG. 7 is a flowchart for explaining the control when switching from CNG to gasoline fuel, and FIG. The figure is a timing chart of this control. 4...Shutoff valve, 6...High pressure regulator, 7...Low pressure regulator, 8...Piping, 9...
- Selector switch, 10... Variable orifice, 11.11'... Intake passage, 13... CNG control circuit, 16... Fuel pump, 19... Injector, 22... Gasoline fuel control circuit , 23... Air flow sensor, 24... Movable vane, 27... Engine body, 2
8...Exhaust passage, 29...Catalytic converter, 3
3...Distributor, 45...Gas pressure sensor.

Claims (2)

[Claims] (1) In a dual fuel engine that switches between supplying liquid fuel and gas fuel, when the vehicle accelerates or decelerates when switching from gas fuel to liquid fuel, the gas in the gas fuel supply piping When the pressure drops to a predetermined pressure, it starts supplying liquid fuel, and when the vehicle decelerates when switching from liquid fuel to gas fuel, when the gas pressure of gas fuel rises to a predetermined pressure, it cuts off the supply of liquid fuel. A fuel switching method for a dual fuel engine, characterized in that: (2) A liquid fuel supply means for supplying liquid fuel to the engine, a gas fuel supply means for supplying gas fuel to the engine, and a piping section between a low pressure regulator and a high pressure regulator provided upstream of the gas fuel supply means. a gas pressure sensor provided for the vehicle; a means for determining whether the vehicle is accelerating or decelerating; and comparing the detected pressure value detected by the gas pressure sensor with a reference pressure value; liquid fuel supply control means for controlling the supply of liquid fuel based on a deceleration state, and when the determination means detects an acceleration or deceleration driving state at the time of fuel switching, the detected pressure of the gas pressure sensor is lower than or higher than a predetermined value. 1. A fuel switching device for a dual fuel engine, wherein the liquid fuel supply control means starts or cuts off supply of liquid fuel when