JP2008175122A - Fuel supply device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid waste of energy by reducing driving amount of a fuel pump to the minimum necessary amount, and to maintain good fuel supply capacity over a long period of time in a fuel supply system supplying liquefied gas fuel to an engine by injecting the gas fuel by an injector. <P>SOLUTION: In a return-less type fuel supply device for an engine provided with: a fuel supply line 9A including an injector 8 on a tip side extending from a fuel tank 2A; an electric fuel pump 3A; and an electric control unit 10A driving and controlling the fuel pump 3A and the injector 8, a pressure sensor 11 detecting fuel pressure and outputting the same to the electronic control unit 10A is arranged near the injector 8 of the fuel supply line 9A where fuel pressure roughly coincides with fuel injection pressure, and the drive of the fuel pump 3A is feedback-controlled to keep fuel injection pressure at a predetermined target pressure, based on the detected fuel pressure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel supply device such as LPG and DME, which is a liquid fuel that is more easily evaporated than gasoline and that is supplied as a liquid from a fuel tank to an injector.

  A system in which liquid fuel, such as LPG and DME, which evaporates more easily than gasoline is metered and injected by an injector and supplied to the engine as a liquid is well known. As shown in FIG. 3, liquefied gas stored in the fuel tank 2A A fuel pump 3B driven by a DC motor or the like constantly feeds a constant amount of fuel, and the pressure regulator 40 adjusts the fuel to a constant pressure, and supplies fuel at a required flow rate from the injector 8 via the fuel delivery line 9A. Thus, it is common to employ a return type fuel supply system in which surplus fuel is returned to the fuel tank 2A via the pressure regulator 41 through the fuel return line 9B.

  In such a fuel supply system, the discharge flow rate of the fuel pump 3B is set to be equal to or greater than the maximum fuel amount injected from the injector 8 in order to be able to cope with all engine operating conditions. However, in a situation where the fuel injection amount of the injector 8 is very small, for example, during idling or when the fuel is cut, most of the delivered fuel returns from the pressure regulator 41 to the fuel tank 2A, and thus energy (electric power) given to the fuel pump 3B. Will be wasted. In addition, if a large amount of surplus fuel that has reached a high temperature through the vicinity of the engine 1A is returned to the fuel tank 2A, the fuel temperature in the tank rises, generating fuel vapor and destabilizing the pump discharge amount. Cause inconvenience.

  Therefore, as described in Japanese Patent Application Laid-Open No. 7-54725, there is a method of reducing power consumption and excess fuel returning to the fuel tank by switching the pump discharge amount to two stages for normal operation and high zone. It is done. However, with such a rough pump control, it is not possible to accurately respond to the required fuel flow rate that changes finely or greatly depending on the operating state of the engine, so it is not possible to sufficiently reduce surplus fuel and reduce waste of power consumption. Is not enough.

  On the other hand, as shown in FIG. 4, when the gasoline stored in the fuel tank 2B is pressurized by the low-pressure fuel pump 3C and sent to the engine 1B through the fuel supply line 9A as shown in FIG. A method is known in which the flow rate of fuel to be supplied is determined by the opening / closing timing of a spill valve 31 attached to the high-pressure fuel pump 3D in accordance with the operation timing of the plunger. In this way, a returnless type fuel supply system that requires the minimum amount of fuel to be delivered is realized. Therefore, it is conceivable to adopt this method in a fuel supply system that uses liquefied gas fuel that is more easily evaporated than gasoline.

  However, since the drive source of the high pressure fuel pump 3D uses the rotational force of the engine and the pump body is attached to the engine 1B, the fuel is exposed to the heat transmitted from the engine 1B or the high temperature atmosphere of the engine room. Will end up. For this reason, when using liquefied gas fuel that evaporates more easily than gasoline, such as LPG and DME, the fuel may be vaporized at a low pressure portion upstream of the high-pressure fuel pump 3D, and fuel delivery is delayed and A / F control is performed. Becomes difficult and causes problems such as deterioration of the exhaust state.

In this case, since the plunger of the high-pressure fuel pump 3D continuously moves as the engine rotates, the use of liquid fuel having a low viscosity such as LPG or DME causes the plunger or cylinder to slide more than when gasoline is used. There is a problem that the wear of the part is easily promoted and the life of the fuel pump is shortened.
JP-A-7-54725

  The present invention is intended to solve the above-described problems, and in a fuel supply system for supplying liquefied gas fuel, which is easier to evaporate than gasoline, such as LPG and DME, to the engine by metering with a injector, It is an object of the present invention to avoid waste of energy and maintain a good fuel supply capability over a long period of time as a minimum necessary amount of driving of the fuel pump.

  In order to solve the above-described problems, the present invention provides a fuel supply line that extends from a fuel tank and has an injector on the tip side, an electric fuel pump disposed in the fuel supply line, and the fuel pump, A fuel supply for a returnless engine, which is equipped with an electronic control unit for driving and controlling the injector, pressurizes the liquefied gas fuel stored in the fuel tank with a fuel pump, sends it to the injector through a fuel supply line, and supplies it to the engine In the apparatus, a pressure sensor that detects the fuel pressure and outputs it to the electronic control unit is disposed at a position near the injector of the fuel supply line where the fuel pressure substantially matches the fuel injection pressure, and the fuel pressure detected by the electronic control unit is determined. The fuel pump drive is feedback controlled so that the fuel injection pressure maintains a predetermined target pressure.

  In this way, a returnless fuel supply system in which the fuel heated in the vicinity of the engine or through the engine room does not return to the fuel tank again is configured, and the fuel pressure is measured by the pressure sensor disposed in the vicinity of the injector by the electronic control unit. The fuel supply device is designed to precisely control the drive of the fuel pump so as to maintain the predetermined fuel injection pressure while monitoring the fuel, so that the high temperature fuel is kept in the fuel tank while maintaining the fuel injection pressure stably. In addition to not returning to, the drive of the fuel pump can be minimized.

  Further, in the fuel supply device for the engine described above, if the fuel pump is arranged at a position outside the engine room, it is possible to avoid the disadvantage that the liquid fuel upstream of the fuel pump is vaporized by the heat derived from the engine.

  Furthermore, in the fuel supply device for the engine described above, if the pressurized pipe portion downstream of the fuel pump in the combustion supply pipe has a shape whose overall length is equal to or greater than the pipe inner diameter x 250, the fuel volume of the pressurized pipe and By increasing the pressurization distance, the elastic modulus of the fuel sufficiently attenuates the pulsation width, and a good fuel supply state can be maintained.

  According to the present invention in which feedback control is performed to maintain the fuel injection pressure within a predetermined range based on the fuel pressure detected in the vicinity of the injector, the drive amount of the fuel pump is minimized while realizing stable fuel supply. As a limit, waste of energy can be avoided. In addition, the consumption of the fuel pump can be reduced thereby, and a good fuel supply capability can be maintained over a long period of time.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows a layout diagram of a fuel supply system in which a fuel supply device for an engine according to the present embodiment is arranged. The fuel supply line 9A extended from the fuel tank 2B is located near the outlet of the fuel tank 2B. An electric motor-driven fuel pump 3A is disposed, and the tip end side of the fuel supply line 9A is connected to a fuel rail 6 in which a plurality of injectors 8 attached to an engine 1A (not shown) are disposed, and fuel is returned downstream of the fuel rail 6 A returnless fuel supply system without a pipe line is constructed.

  On the downstream side of the fuel pump 3A, a pipe 22 provided with a pressure regulator 40 is branched and connected to the fuel tank 2A so as to adjust the pressure of fuel delivered from the fuel pump 3A. The fuel pump 3A and each injector 8 are connected to the electronic control unit 10A, and are driven and controlled in accordance with the engine operating state, which is well known.

  Further, a pressure sensor 11 for detecting the fuel pressure is disposed near the injector 8 (near the fuel rail 6 inlet) of the fuel supply line 9A, and a detection signal is output to the electronic control unit 10A. . The electronic control unit 10A continuously monitors the detection signal of the pressure sensor 11, and performs feedback control so that the fuel pressure immediately before the injector, which substantially matches the fuel injection pressure, becomes a predetermined target pressure. The discharge amount is adjusted by changing the drive output of the fuel pump 3A to maintain a substantially constant fuel injection pressure, which is a feature of the present invention. This feedback control is performed by storing a control program for executing a predetermined procedure / calculation method using a known control theory such as PID control or modern control theory in a storage means of a general-purpose electronic control unit. Can be performed relatively easily.

  Further, the high-pressure fuel pump 3D of the gasoline fuel supply apparatus in FIG. 4 is disposed in the engine room 50 (attached to the engine 1B) indicated by a broken line in relation to using the driving force of the engine 1B. Since the fuel pump 3A does not use the driving force of the engine 1A, the fuel supply device for the engine of this form is disposed at a position outside the engine room 50, for example, in the trunk room near the fuel tank 2A in the mounted vehicle. Yes. Therefore, it becomes difficult to receive the heat derived from the engine, and it is easy to avoid the trouble that the fuel is vaporized in the low pressure portion in front of the fuel pump 3A and the fuel delivery becomes difficult.

  And, in combination with the fuel pump 3A being arranged at a position away from the engine 1A in this way, the portion corresponding to the pressurized pipe of the fuel supply pipe 9A from the fuel pump 3A to the injector 8 is pipe length (L) = pipe The shape has an inner diameter (d) × 250 or more. In this way, the shape of the pressurized pipe is relatively large and the pressurized distance is increased, so that the elastic modulus of the internal fuel can be increased and the pulsation (pressure fluctuation) width is attenuated. This makes it easy to ensure a stable fuel injection pressure. The relationship between the pipe length (L) and the pipe inner diameter (d) is the result of experiments conducted by the inventors of the present application at various ratios. As a result, when the pipe length (L) exceeds the above ratio, the elastic modulus is This is because it suddenly improved and showed sufficient attenuation of pulsation.

  Next, the features of the operation will be described in more detail with reference to FIG. 2 showing a graph of each data in the fuel supply device for the engine of the present embodiment.

  With reference to the graph of the fuel pressure in the pipe detected by the pressure sensor 11, the fuel pump 3A controls the output by the electronic control unit 10A so that the feedback target pressure is set slightly lower than the pressure detected by the pressure sensor 11. Therefore, although there is a slight vertical movement in the pressure value, the target pressure is almost maintained.

  Looking at the relationship between the engine rotational speed at this time and the driving state of the fuel pump 3A, the rotational speed of the pump 3A, which has become high, is gradually increased as the engine rotational speed gradually decreases after reaching the peak. It is decreasing almost vertically, and the pump discharge flow rate and pump power consumption are also decreasing. On the other hand, the conventional return-type liquefied gas fuel supply device indicated by a one-dot chain line described as a reference example always maintains a constant rotational speed, pump discharge flow rate, and power consumption at a relatively high level.

  In other words, the conventional return-type liquefied gas fuel supply device is set to a pump drive amount that always ensures a fuel flow rate higher than that in order to be able to cope with the maximum required flow rate of the engine. While the pump rotation speed is maintained, the present embodiment has a fuel discharge amount that is sufficient to maintain at least the fuel pressure immediately before injection that fluctuates with fluctuations in the engine rotation speed. The pump rotation speed (amount) and power consumption are realized.

  As a result, stable fuel supply can be realized without adopting a return-type fuel supply system, and the drive amount of the fuel pump 3A can be suppressed to the minimum necessary, and wasteful power consumption can be effectively avoided. can do. In addition, since the pump drive amount is minimized, the wear of the sliding parts is reduced even when using liquefied gas fuel having a viscosity lower than that of gasoline such as LPG and DME, thereby shortening the life of the device. This can be avoided, and it is easy to maintain a good fuel supply capacity over a long period of time.

  For reference, the data of the returnless type gasoline supply system is indicated by a two-dot chain line. However, the fuel pump 3D (high pressure fuel pump) uses the driving force of the engine, and the power consumption is only for driving the spill valve 31. Although the power consumption is low, the pump rotation speed is generally higher than that of the present embodiment because the pump rotation is synchronized with the engine rotation, and the high rotation time is increased with the engine high rotation. However, shortening the life of the fuel pump due to wear of the pump sliding portion is likely to be a problem, but it can be seen that this problem is greatly improved by the present embodiment.

  As described above, an increase in the fuel temperature in the tank can be avoided by this embodiment in which the drive control of the fuel pump is feedback controlled based on the fuel pressure detected in the vicinity of the injector as a returnless fuel supply system. In addition, useless driving of the fuel pump can be avoided. This also minimizes power consumption for driving the pump and extends the life of the fuel pump.

  Further, the fuel pump is disposed outside the engine room, and the pressurized pipe downstream of the fuel pump is configured to have a pipe length (L) = pipe inner diameter (d) × 250 or more, so that fuel is vaporized upstream of the fuel pump. Can be avoided, and the pulsation of the fuel pressure can be attenuated to realize a stable fuel supply amount.

The layout which shows embodiment of this invention. Each waveform diagram for demonstrating operation | movement of the fuel supply apparatus of FIG. The layout which shows the liquefied gas fuel supply apparatus of a prior art example. The layout which shows the gasoline supply apparatus of a prior art example.

Explanation of symbols

1A engine, 2A fuel tank, 3A fuel pump, 6 fuel rail, 8 injector, 9A fuel supply line, 9B fuel return line, 10A electronic control unit, 11 pressure sensor, 21, 22 piping, 40, 41 pressure regulator, 50 engine room

Claims (3)

  A fuel supply line extending from the fuel tank and having an injector on the tip side; an electric fuel pump disposed in the fuel supply line; and an electronic control unit for driving and controlling the fuel pump and the injector A fuel supply device for a returnless engine, which pressurizes the liquefied gas fuel stored in the fuel tank by the fuel pump and sends the pressurized fuel gas to the injector through the fuel supply line. A pressure sensor that detects the fuel pressure and outputs it to the electronic control unit is disposed at a position near the injector of the fuel supply line that substantially matches the pressure, and fuel injection is performed based on the fuel pressure detected by the electronic control unit The fuel pump drive is feedback-controlled so that the pressure maintains a predetermined target pressure. Apparatus.   The engine fuel supply device according to claim 1, wherein the fuel pump is disposed outside an engine room. The fuel supply device for an engine according to claim 1 or 2, wherein a pressure pipe portion downstream of the fuel pump of the fuel supply pipe has a shape in which a total length is a pipe inner diameter x 250 or more.

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