JP4116315B2 - Engine LPG supply method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a method of supplying LPG (liquefied petroleum gas) to an engine by adjusting the vaporized gas to a predetermined positive pressure and injecting it into each cylinder, and in particular, appropriately supplying the required vaporized gas at a low load range. It relates to a method that can be performed.
[0002]
[Prior art]
The use of LPG as a fuel for a spark ignition engine is widely known, and it replaces the conventionally known method of sucking vaporized gas into an intake pipe using a regulator (vaporizer) and a mixer. As described in Japanese Utility Model Laid-Open No. 59-43659, the liquid is injected into the intake pipe as it is, and as described in Japanese Patent Laid-Open No. 6-17709, vaporization at a predetermined positive pressure is performed. A method of adjusting to gas and injecting it into the intake pipe is being studied.
[0003]
The method of injecting the LPG using the saturated vapor pressure in the cylinder or pressurizing with the pump as the liquid has an unstable property that the liquid LPG is easily affected by the temperature and easily vaporizes. Then, a method of adjusting and injecting the vaporized gas to a predetermined positive pressure is the mainstream of investigation.
[0004]
[Problems to be solved by the invention]
In general, when gaseous fuel is flow-controlled by an injection valve and injected into an intake pipe and supplied to an engine, if the pressure of the gaseous fuel fed into the injection valve is equal to or higher than a critical pressure, the injection at the outlet of the injection valve The flow velocity at the nozzle is the speed of sound, and the flow rate is determined only by the state of gaseous fuel on the injection nozzle inlet side, that is, pressure and temperature.
[0005]
Therefore, CNG (compressed natural gas) that maintains the gas state stably at a high pressure is adjusted to a pressure higher than the critical pressure, and the flow rate according to the control of the injection valve without being affected by the negative pressure of the intake pipe. In order to supply the required engine flow rate accurately, the use of CNG as engine fuel has been partly put into practical use.
[0006]
However, LPG becomes liquid at high pressure, and it is in a fairly low pressure range that maintains a stable gaseous state, which is below the critical pressure. As described above, when gaseous fuel having a pressure lower than the critical pressure is injected by the injection valve even if the pressure is positive, the flow rate changes due to the negative pressure of the intake pipe on the injection nozzle outlet side. In other words, the flow rate increases in the operating range where the suction negative pressure is high, such as when idling, and the flow rate decreases in the operating range where the suction negative pressure is low, such as at full load. The disadvantage of being supplied arises. In particular, excessive fuel during idling will cause the engine to stop due to the rich mixture.
[0007]
As a countermeasure, it is conceivable to expand the dynamic range of the injection valve to cope with a large change in flow rate. To that end, multiple injection valves per cylinder are required, making the device extremely complicated and expensive. Is unsuitable for practical use. As another countermeasure, it is conceivable that the vaporized gas obtained by once vaporizing under reduced pressure is pressurized to a critical pressure or higher by a pump and sent to the injection valve. It is also inappropriate for practical use.
[0008]
The present invention will solve the above-mentioned problem that there is no system that can easily supply LPG vaporized gas in a pressure range in which the state of gas is stably maintained by an injection method in accordance with the engine required flow rate. A system that can properly supply the vaporized gas at the required flow rate of the engine using one injection valve per cylinder, particularly in a low load range, and can be easily put to practical use. The purpose is to provide.
[0009]
[Means for Solving the Problems]
In the present invention, when the LPG vaporized gas 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. Each one is installed in the intake manifold and vaporized gas is injected at individual timing according to the negative pressure change at each outlet side; the vaporized gas injection timing is set within the range of the exhaust stroke of the corresponding cylinder and the subsequent intake stroke In the low load range, the above problem is solved by setting the injection at the end of the exhaust stroke in which the negative pressure on the injection valve outlet side is the lowest.
[0010]
In this way, one injection valve is installed at the inlet of each cylinder, and injection is performed at the timing set within the range of the exhaust stroke and the subsequent intake stroke, and the gas is adjusted to a pressure lower than the critical pressure. According to the present invention in which vaporized gas that stably maintains the state is sent to the injection valve, the pressure difference between the vaporized gas pressure and the negative pressure on the injection valve outlet side is relatively small. By selecting and injecting the optimum flow rate according to the engine operating state within the dynamic range, it is possible to accurately supply the vaporized gas at the required flow rate of the engine. In particular, the injection is performed at a time when the pressure difference becomes minimum in the low load region, so that it is possible to perform stable low speed operation without supplying excess fuel during idling.
[0011]
Further, in addition to the above, the fuel is injected at the time when the pressure difference becomes maximum in the high load region, so that it is possible to supply the fuel required at the time of full load operation without any shortage.
[0012]
Here, when the vaporized gas injection timing is set within the latter stage of the exhaust stroke of the corresponding cylinder in the partial load region and the initial range of the subsequent intake stroke, the pressure difference is small and the change in the negative pressure on the injection valve outlet side is relatively small. Since the injection is performed in a small region, it is possible to supply the fuel at the required flow rate with 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 region is also within this range, there is an advantage that the transition between the partial load region and the low load region can be performed smoothly without impairing the drivability.
[0013]
In addition, when the vaporized gas injection timing is set within the late stage of the exhaust stroke of the corresponding cylinder in the partial load range and the initial range of the subsequent intake stroke, the injection timing when shifting from the partial load range to the high load range is set as the intake timing. When moving with increasing load toward the end of the stroke, there is an advantage that the transition between them is smoothly performed without impairing drivability.
[0014]
Furthermore, if the basic pulse width of the injection valve control signal is corrected in accordance with the amount of change in the average value of the injection valve outlet negative pressure at the vaporized gas injection timing, it becomes possible to accurately supply fuel at the required flow rate. Benefits are gained.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a layout diagram of an LPG supply system, and a delivery line 2 extending from a liquid phase portion of a fuel tank 1 composed of a pressure vessel filled with LPG is connected to a pressure regulator 6 and extends from the pressure regulator 6. A vaporized gas line 15 is connected to the fuel gallery 16. The delivery line 2 has a manual on-off valve 3, a filter 4, and an electromagnetically driven shut-off valve 5. Further, from the fuel gallery 16, the injection valves 17 installed in the branch pipes of the intake manifold 23 are branched corresponding to the cylinders 22 of the engine 21.
[0016]
The pressure regulator 6 includes a cooling water chamber 7 through which engine cooling water passes, a preheating chamber 8 to which the delivery pipe 2 is connected, and a pressure regulation chamber 9 to which the vaporized gas pipe 15 is connected. The 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 pressure adjusting chamber 9 is variable in volume by a diaphragm 11 on which an adjusting spring 10 is applied, and a conduction path 12 communicated 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. Is opened and closed by.
[0017]
The liquid phase LPG that has entered the preheating chamber 8 from the fuel tank 1 through the delivery line 2 is heated by the engine cooling water in the cooling water chamber 7 to become vaporized gas. The vaporized gas flows into the pressure regulating chamber 9 by opening the conduction path 12 when the pressure regulation chamber 9 is lower than the set pressure, and when the pressure becomes higher than the set pressure, the inlet valve 14 is connected to the conduction path. By closing 12, the flow into the pressure regulation chamber 9 is stopped. Thus, the vaporized gas adjusted to a predetermined positive pressure is sent to the injection valve 17 through the vaporized gas line 15 and the fuel gallery 16.
[0018]
In the present embodiment, the pressure regulator 6 adjusts the vaporized gas to a pressure that is stably maintained and is required for injection, for example, about 30 KPa, and this pressure is the criticality of standard LPG. This is considerably lower than the pressure of about 200 KPa.
[0019]
Next, as is well known, a four-cycle multi-cylinder engine has each stroke of intake, compression, expansion, and exhaust as one cycle, and the negative pressure generated in the branch pipe of the intake manifold 23 that is the stroke of one cylinder and its inlet. The fluctuation state is in the relationship shown in FIG.
[0020]
Here, when each injection valve 17 is all-cylinder synchronous injection or group injection of a plurality of cylinders, the negative pressure value differs for each branch pipe of the intake manifold 23 on the injection valve outlet side. Therefore, it is practically impossible to control each of the injection valves 17 for each branch pipe so that the flow rate of the vaporized gas injected at a lower pressure is greatly varied and the required flow rate is the same. It is. For this purpose, the present invention adopts an all-cylinder independent injection method, and basically injects the vaporized gas at a timing set within the range S of the exhaust stroke and the subsequent intake stroke as shown in FIG. I was allowed to do it.
[0021]
The range S includes from the exhaust stroke where the negative pressure of the branch pipe of the intake manifold 23 is relatively low to the end of the intake stroke where the negative pressure is the highest, and within the limited dynamic range of the injection valve 17 within this range S. By selecting and injecting the optimum flow rate according to the engine operating state, it is possible to accurately supply the vaporized gas at the required engine flow rate over the entire engine operating range.
[0022]
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, so that as indicated by the symbol B in FIG. The fuel is injected at the end of the exhaust stroke, that is, when the negative pressure immediately before reaching the top dead center and shifting to the intake stroke is lowest. 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 above-mentioned time B, an appropriate amount of vaporized gas is controlled by controlling the injection time within the limited dynamic range of the injection valve 17. The worry of injecting and supplying excess fuel, especially during idling, can be eliminated.
[0023]
Further, since the negative pressure generated in the branch pipe of the intake manifold 23 is lower in the high load region of the engine 21 than in the low load region, the end of the intake stroke as shown by reference C in FIG. In other words, the fuel is injected at the time when the negative pressure becomes the 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 time C, an appropriate amount of vaporized gas is controlled by controlling the injection time within the limited dynamic range of the injection valve 17. It is possible to inject fuel, and in particular to supply the fuel required at full load.
[0024]
Further, the vaporized gas injection timing is basically set within the range S shown in FIG. 2A. In this embodiment, the exhaust gas is exhausted as indicated by symbol A in FIG. It was decided to inject within the latter half of the stroke and the initial range of the subsequent intake stroke. This range A is a region in which 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 simple control means for controlling the injection time according to the operating state of the engine 21. It is possible to supply fuel at the required flow rate. 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 performed smoothly, and the operability of the engine 21 is not impaired. There is an advantage.
[0025]
When the vaporized gas injection in the partial load region is performed in the range A, the vaporized gas injection timing is sequentially moved as the load increases toward the end of the intake stroke when shifting to the high load region. Assuming that the range C is reached, it is possible to shift to full load operation without causing malfunction of the engine 21 due to a sudden change in fuel supply timing.
[0026]
Furthermore, in this embodiment, a negative pressure sensor 26 is installed in each branch pipe of the intake manifold 23, and the outlet side of the injection valve 17 detected by the negative pressure sensor 26 when the injection valve 17 is injecting vaporized gas. The absolute value of the negative pressure is stored in the electronic control device 25 and the average value is repeatedly calculated. When the average value changes from the previously obtained average value, the electronic control is performed according to the change amount. The basic pulse width of the control signal sent from the device 25 to the injection valve 17 is corrected. For example, when the negative pressure is changed to a lower value, the average value of the negative pressure absolute value is increased. Therefore, the basic pulse width is increased to correct the direction of increasing the fuel flow rate, and the inlet side of the injection valve 17 is corrected. Correct the decrease in fuel flow rate due to the decrease in the pressure difference on the outlet side.
[0027]
In the present embodiment, a temperature sensor 27 is provided in a pipe line for sending engine cooling water from the engine 21 to the cooling water chamber 7 of the pressure regulator 6, and the electronic type is based on the temperature detected by the temperature sensor 27. The temperature of the vaporized gas sent to the injection valve 17 is determined by the control device 25. 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 on the injection nozzle inlet side and the pressure on the outlet side as described above, it is based on the value detected by the temperature sensor 27. By correcting the injection timing or the injection time, the vaporized gas at a predetermined flow rate can be injected. Since the engine coolant temperature is almost constant after the engine 21 is warmed up, the vaporized gas flow rate is determined by the pressure difference. However, in the end warm-up state, the temperature changes as the warm-up progresses, and therefore, based on the temperature. Correction is useful.
[0028]
【The invention's effect】
As described above, according to the present invention, the predetermined amount of the LPG vaporized gas adjusted to a low positive pressure so as to stably maintain the gas state is limited to the injection valve by utilizing the change in the suction negative pressure. The fuel can be injected in a dynamic range, and it is possible to appropriately supply the vaporized gas at the required flow rate of the engine even in a low load region by using one injection valve per cylinder.
[Brief description of the drawings]
FIG. 1 is a layout view showing an embodiment of the present invention.
FIG. 2 is a diagram for explaining the relationship between suction negative pressure and 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,

Claims (2)

A method of injecting LPG vaporized gas adjusted to a predetermined positive pressure from an injection valve and supplying the vaporized gas to the engine at a pressure lower than the critical pressure. Each one is installed in the intake manifold, and the vaporized gas is injected at an individual timing according to the negative pressure change on each outlet side. The vaporized gas injection timing is within the range of the exhaust stroke of the corresponding cylinder and the subsequent intake stroke. set, and that in the low load region for injecting set at the end of the exhaust stroke the negative pressure of the injection valve outlet becomes the lowest, the addition, the negative pressure of the injection valve outlet side in the high load region An LPG supply method for an engine, characterized in that the injection is set at the end of the intake stroke at which the intake becomes the highest.   The vaporized gas injection timing is set to the end of the exhaust stroke of the corresponding cylinder in the partial load region and the initial range of the subsequent intake stroke, and when shifting to a higher load region, the injection timing is set toward the end of the intake stroke. The LPG supply method for an engine according to claim 1, wherein the engine is moved as the load increases.

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