JP2003301746A - Lpg supply method for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practicable system that injects vaporized gas of LPG at a low positive pressure precluding liquefaction and supplies an engine-required flow rate. <P>SOLUTION: One injection valve 17 is disposed, for every cylinder 22, in an intake manifold 23 to inject vaporized gas regulated in a pressure regulator 6 to a positive pressure lower than the critical pressure, at injection timing set in a range of an exhaust stroke and a subsequent suction stroke of the corresponding cylinder 22. Fuel for an operating range with a small engine- required flow rate is injected in a range with a small pressure difference between the vaporized gas pressure and an intake manifold negative pressure, and fuel for an operating range with a large engine-required flow rate is injected in a range with a large pressure difference, so that an appropriate quantity of fuel is supplied through a limited dynamic range of the injection valve 17. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of supplying LPG (liquefied petroleum gas) into a cylinder by adjusting it to a vaporized gas having a predetermined positive pressure and injecting the vaporized gas into each cylinder. The present invention relates to a method capable of appropriately supplying

[0002]

2. Description of the Related Art The use of LPG as fuel for a spark ignition engine is widely known, and it has been practiced for a long time to use a regulator (vaporizer) and a mixer to suck vaporized gas into an intake pipe line. Instead of the known method, as disclosed in Japanese Utility Model Laid-Open No. 59-43659, a method of injecting a liquid as it is into an intake pipe line, and as described in Japanese Patent Application Laid-Open No. 6-17709, etc. A method of adjusting the vaporized gas to a predetermined positive pressure and injecting it into the intake pipe is being studied.

The method of injecting the LPG as a liquid by utilizing the saturated vapor pressure in the cylinder or by pressurizing it with a pump has an unstable property that the LPG of the liquid is easily affected by the temperature and easily vaporizes. Therefore, at present, a method of adjusting and injecting a vaporized gas of a predetermined positive pressure and injecting the vaporized gas is the mainstream of the study.

[0004]

Generally, when the flow rate of gaseous fuel is controlled by an injection valve and is injected into an intake pipe and supplied to an engine, the pressure of the gaseous fuel fed into the injection valve is equal to or higher than a critical pressure. The flow velocity at the injection nozzle, which is the outlet of the injection valve, is sonic, and the flow rate is determined only by the state of the gaseous fuel at the injection nozzle inlet side, that is, the pressure and temperature.

Therefore, CNG (compressed natural gas), which maintains the gas state stably at high pressure, is adjusted to a pressure above the critical pressure to control the injection valve without being affected by the negative pressure in the intake pipe line. It is possible to inject fuel at a compliant flow rate and to supply the required engine flow rate accurately, and for that reason, use of CNG as fuel for the engine has been partially put into practical use.

However, LPG becomes liquid at a high pressure, and a stable gas state is maintained in a considerably low pressure range, which is lower than the critical pressure. As described above, when the gaseous fuel having a positive pressure but lower than the critical pressure is injected by the injection valve, the flow rate changes due to the influence of the negative pressure in the intake pipe line on the injection nozzle outlet side. That is, the flow rate increases in an operating range where the intake negative pressure is high, such as when idling, and the flow rate decreases in an operating range where the intake negative pressure is low, such as at full load. It is inconvenient to be supplied.
In particular, excess fuel during idling causes engine stop due to rich air-fuel mixture.

As a countermeasure against this, it is conceivable to expand the dynamic range of the injection valve to cope with a large change in the flow rate, but for that purpose, a plurality of injection valves per cylinder are required, and the device is extremely complicated and expensive. It is not suitable for practical use because of the problem of making it difficult. As another countermeasure, it is possible to pressurize the vaporized gas obtained by depressurizing and vaporizing it to a pressure higher than the critical pressure with a pump and send it to the injection valve. Therefore, it is also inappropriate for practical use.

The present invention has the above-mentioned problem that there is no system which can be easily put into practical use and which can appropriately supply the vaporized gas of LPG by the injection method within the pressure range where the gas state is stably maintained in accordance with the required flow rate of the engine. Therefore, it is possible to properly supply the vaporized gas at the required flow rate of the engine, especially even in the low load region, by using one injection valve per cylinder, and thus it is possible to easily put it into practical use. The purpose is to provide a system that can.

[0009]

According to the present invention, when the vaporized gas of LPG adjusted to a predetermined positive pressure is injected by the injection valve and supplied to the engine, the vaporized gas is sent to the injection valve at a pressure lower than the critical pressure. Inject each injector into the intake manifold for each cylinder and inject the vaporized gas at each timing according to the negative pressure change on each outlet side; the vaporization gas injection timing is the exhaust stroke of the corresponding cylinder and It is set within the range of the subsequent intake stroke, and in the low load region, the injection is performed by setting at the end of the exhaust stroke where the negative pressure on the outlet side of the injection valve becomes the lowest, thereby solving the above problems. And

As described above, one injection valve is installed at the inlet of each cylinder to inject fuel at a set timing within the range of the exhaust stroke and the subsequent intake stroke, and the pressure is adjusted to be lower than the critical pressure. According to the present invention, in which vaporized gas that maintains the gas state in a stable manner is sent to the injection valve, the pressure difference between the vaporized gas pressure and the negative pressure on the outlet side of the injection valve is relatively small. It is possible to accurately supply the vaporized gas having the required flow rate of the engine by selecting and injecting the timing at which the flow rate is optimum according to the engine operating state within the limited dynamic range. In particular, since the injection is performed at the time when the pressure difference becomes the minimum in the low load region, excess fuel is not supplied at the time of idling, and stable low speed operation can be performed.

In addition to the above, by injecting fuel at a time when the pressure difference becomes maximum in the high load range, it is possible to supply the fuel required for full load operation without deficiency.

Here, when the vaporized gas injection timing is set within the latter part of the exhaust stroke of the corresponding cylinder in the partial load range and the initial range of the subsequent intake stroke, the pressure difference is small and the negative pressure on the outlet side of the injection valve changes. Since the fuel is injected in a relatively small region, it is possible to supply the required flow rate of fuel by a simple control means that controls the injection time according to the engine operating state. In addition, since the vaporized gas injection timing in the low load range is also within this range, there is an advantage that the transition between the partial load range and the low load range can be smoothly performed without impairing drivability.

When the vaporized gas injection timing is set within the latter part of the exhaust stroke of the corresponding cylinder in the partial load range and the initial range of the subsequent intake stroke, the injection at the time of shifting from the partial load range to the high load range is performed. Moving the timing toward the end of the intake stroke with increasing load has the advantage that the transition between these is smooth without impairing drivability.

Further, by correcting the basic pulse width of the injection valve control signal in accordance with the amount of change in the average value of the injection valve outlet side negative pressure at the vaporized gas injection timing, it is possible to accurately supply the required amount of fuel. Is obtained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a layout view of the LPG supply system, in which a delivery pipe line 2 extending from a liquid phase portion of a fuel tank 1 made of a pressure-resistant container filled with LPG is connected to a pressure regulator 6 and extends from the pressure regulator 6. Vaporized gas line 1
5 is connected to the fuel gallery 16. The delivery line 2 includes a manual opening / closing valve 3, a filter 4, and an electromagnetically driven shutoff valve 5.
have. Further, from the fuel gallery 16, injection valves 17 installed in branch pipes of the intake manifold 23 corresponding to the cylinders 22 of the engine 21 are branched.

The pressure regulator 6 includes a cooling water chamber 7 for passing engine cooling water, a preheating chamber 8 to which the delivery pipe line 2 is connected,
The cooling water chamber 7 and the preheating chamber 8 are adjacent to each other to form a heat exchange portion between the engine cooling water and the LPG. The volume of the pressure adjusting chamber 9 is variable by a diaphragm 11 on which an adjusting spring 10 is actuated, and a passage 12 communicating with the preheating chamber 8 is an inlet valve 14 attached to a lever 13 that rotates according to the displacement of the diaphragm 11. It is opened and closed by.

The liquid-phase LPG that has entered the preheating chamber 8 from the fuel tank 1 through the delivery conduit 2 is heated by the engine cooling water in the cooling water chamber 7 and becomes vaporized gas. This vaporized gas flows into the pressure adjusting chamber 9 by opening the communication passage 12 by the inlet valve 14 when the pressure in the pressure adjusting chamber 9 becomes lower than the set pressure, and when the pressure becomes higher than the set pressure, the inlet valve 14 opens the communicating passage. By closing 12 the inflow to the pressure adjusting chamber 9 is stopped. As a result, the vaporized gas adjusted to a predetermined positive pressure is sent to the injection valve 17 through the vaporized gas pipe line 15 and the fuel gallery 16.

In the present embodiment, the pressure regulator 6 regulates the vaporized gas to a pressure required to inject the vaporized gas in a stable state, for example, about 30 KPa, and this pressure is standard. About 20 which is the critical pressure of LPG
It is considerably lower than 0 KPa.

As is well known, a four-cycle multi-cylinder engine has intake, compression, expansion, and exhaust strokes as one cycle, and the stroke of one cylinder and the branch pipe of the intake manifold 23 that is the inlet thereof are generated. The negative pressure fluctuation situation has a relationship shown in FIG.

Here, when the injection valves 17 are all-cylinder synchronous injection or group injection is performed for each of a plurality of cylinders, the negative pressure value is different for each branch pipe of the intake manifold 23 on the injection valve outlet side, and therefore each injection valve 17 From the injection valve 1 to each of the branch pipes so that the flow rate of the vaporized gas injected at a pressure lower than the critical pressure varies greatly, and the required flow rate is the same.
It is virtually impossible to control each of the seven.
Therefore, the present invention adopts an all-cylinder independent injection system,
Further, basically, as shown in FIG. 2 (A), the vaporized gas is injected at a set timing within the range S of the exhaust stroke and the subsequent intake stroke.

The range S includes the exhaust stroke at which the negative pressure in the branch pipe of the intake manifold 23 is relatively low to the end of the intake stroke at which the negative pressure becomes highest, and the dynamic range of the injection valve 17 is limited within the range S. By selecting and injecting the timing at which the flow rate is optimum within the range according to the engine operating state, it is possible to accurately supply the vaporized gas of the engine required flow rate over the entire operating range of the engine.

Next, in the low load region of the engine 21, the negative pressure generated in the branch pipe of the intake manifold 23 is higher than that in the partial load region and the high load region.
As shown in, the injection is performed at the end of the exhaust stroke, that is, at the time when the negative pressure becomes the lowest immediately before reaching the top dead center and immediately before shifting to the intake stroke. Since the pressure difference between the vaporized gas pressure and the negative pressure on the outlet side of the injection valve 17 becomes the smallest at the timing B,
By controlling the injection time within the limited dynamic range of the injection valve 17, it is possible to eliminate the fear of injecting an appropriate amount of vaporized gas and supplying excessive fuel especially during idling.

Further, in the high load region of the engine 21, the negative pressure generated in the branch pipe of the intake manifold 23 is lower than that in the low load region, so that the intake stroke is indicated by the symbol C in FIG. 2 (C). It is assumed that the injection is performed at the end of, that is, at the time when the negative pressure becomes highest immediately before reaching the bottom dead center and shifting to the compression stroke. Since the pressure difference between the vaporized gas pressure and the negative pressure on the outlet side of the injection valve 17 becomes the largest at the above-mentioned timing C, an appropriate amount of vaporized gas can be obtained by controlling the injection time within the limited dynamic range of the injection valve 17. It is possible to inject and in particular supply the required fuel at full load.

Further, the vaporized gas injection timing is basically as shown in FIG.
Although it is set within the range S shown in (A), in the present embodiment, in the partial load range, as shown by the symbol A in FIG. 2 (A), the latter half of the exhaust stroke and the subsequent intake stroke It was decided to inject within the initial range. This range A
Is a region where the pressure difference between the vaporized gas pressure and the negative pressure on the outlet side of the injection valve 17 and the change in the negative pressure are relatively small, and the required flow rate is controlled by a simple control means that controls the injection time according to the operating state of the engine 21. It is possible to supply the fuel.
In addition, since the vaporized gas injection timing B in the low load range is included in this range A, the transition between the partial load range and the low load range is smoothly performed, and the drivability of the engine 21 is not impaired. There is an advantage.

When the vaporized gas injection is performed in the partial load range in the range A, the vaporized gas injection timing is gradually changed toward the end of the intake stroke as the load increases when shifting to the high load range. If it is moved to reach the range C, the engine 21 due to a sudden change in fuel supply timing
It is possible to shift to full-load operation without causing a malfunction.

Furthermore, in the present embodiment, a negative pressure sensor 26 is installed in each branch pipe of the intake manifold 23, and the negative pressure sensor 26 is provided when the injection valve 17 is injecting vaporized gas.
The absolute value of the negative pressure on the outlet side of the injection valve 17 detected by is stored in the electronic control unit 25 and the average value is calculated repeatedly. When this average value changes from the previously calculated average value, The basic pulse width of the control signal sent from the electronic control unit 25 to the injection valve 17 is corrected according to the amount of change. For example, when the negative pressure changes to the lower side, the average value of the negative pressure absolute values increases, so correction is performed in the direction of increasing the basic pulse width to increase the fuel flow rate, and Correct the decrease in fuel flow rate due to the decrease in pressure difference on the outlet side.

Further, in the present embodiment, a temperature sensor 27 is provided in a pipe line for feeding the engine cooling water from the engine 21 to the cooling water chamber 7 of the pressure regulator 6, and based on the temperature detected by the temperature sensor 27. The electronic control unit 25 controls the injection valve 17
It is supposed that the temperature of the vaporized gas sent to is judged. Since the flow rate of the vaporized gas passing through the injection nozzle at the outlet of the injection valve 17 depends on the pressure and temperature at the inlet side of the injection nozzle and the pressure at the outlet side as described above, the temperature sensor 2
By correcting the injection timing or the injection time based on the value detected by 7, it is possible to inject the vaporized gas at a predetermined flow rate. After the engine 21 has been warmed up, the temperature of the engine cooling water is almost constant, so the vaporized gas flow rate is determined by the pressure difference, but in the last warming state, the temperature changes as the warming progresses. The correction is useful.

[0028]

As described above, according to the present invention, LPG adjusted to a low positive pressure so as to stably maintain the gas state.
It is possible to inject a predetermined amount of vaporized gas in a limited dynamic range of the injection valve by utilizing the change in suction negative pressure. In addition, it is possible to properly supply even in a low load range.

[Brief description of drawings]

FIG. 1 is a layout view showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a suction negative pressure and a vaporized gas injection timing.

[Explanation of symbols]

1 fuel tank, 6 pressure regulator, 17 injection valve, 21
Engine, 22 cylinders, 23 intake manifold, 25
Electronic control unit, 26 pressure sensor,

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3G092 AA08 AB07 BB06 DE01S                       DE09S DG09 EA03 EA04                       FA05 FA06 GA04 GA05 HA05Z                       HE08Z                 3G301 HA01 HA22 JA04 JA06 JA28                       KA07 KA08 LB02 LB06 LC01                       LC07 MA11 MA19 NB14 NE11                       NE12 PA07Z PE08Z

Claims (5)

[Claims] 1. A method of injecting a vaporized gas of LPG adjusted to a predetermined positive pressure from an injection valve and supplying the same to an engine, the vaporized gas being fed into the injection valve at a pressure lower than a critical pressure,
One injection valve for each cylinder is installed in the intake manifold to inject vaporized gas at individual timings according to the negative pressure change on the outlet side.The vaporized gas injection timing is the exhaust stroke of the corresponding cylinder and The LPG supply method for the engine is characterized in that the injection is performed within the range of the subsequent intake stroke, and at the end of the exhaust stroke where the negative pressure on the outlet side of the injection valve becomes the lowest in the low load region. 2. The LPG supply method for an engine according to claim 1, wherein the vaporized gas injection timing is set within the range of the exhaust stroke of the corresponding cylinder and the subsequent intake stroke, and the injection valve outlet is in the low load range. Injection at the end of the exhaust stroke where the negative pressure on the side of the injection valve is the lowest, and in addition to the end of the intake stroke where the negative pressure on the outlet side of the injection valve is the highest in the high negative pressure region An LPG supply method for an engine, comprising: 3. The LPG supply method for an engine according to claim 1, wherein the vaporized gas injection timing is set within an end range of an exhaust stroke of a corresponding cylinder and an initial range of a subsequent intake stroke in a partial load range. 4. The vaporized gas injection timing is set within the end range of the exhaust stroke of the corresponding cylinder in the partial load range and the initial range of the subsequent intake stroke, and the injection timing is set when shifting to a higher load range. The engine L according to claim 2, wherein the engine is moved toward the end of the stroke as the load increases.
PG supply method. 5. The basic of the injection valve control signal is detected by repeatedly detecting the negative pressure on the outlet side of the injection valve at the vaporized gas injection timing and obtaining the average value thereof, and changing the average value in accordance with the change amount. The LPG supply method for an engine according to claim 1, wherein the pulse width is corrected.