JP2006291860A - Engine fuel supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust a return fuel to a minimum while reliably avoiding vaporization of a supplied fuel in an engine fuel supply device for switching a liquefied gas fuel supply method between a return type and a linkless type, and a fuel tank. Avoid excessive rise of internal temperature.
SOLUTION: A first fuel return line 9a branched in the middle of a fuel supply line and a second fuel return line 9b for returning fuel not injected by an injector 8 have shutoff valves 14 and 15, respectively. In the fuel supply device of the engine connected to the fuel tank 2, the fuel pressure sensor 52 and the fuel temperature sensor 51 are disposed at positions close to the injector 8 and the fuel rail 6 of the fuel supply line, and these output signals When the electronic control unit 50 that detects this is in a state where there is a possibility that the injected fuel is vaporized, and when the engine is started, the return type is performed and the control is performed to be the returnless type during normal operation. .
[Selection] Figure 1

Description

  The present invention relates to a fuel supply device that injects liquid fuel, such as LPG and DME, which is more easily vaporized than gasoline into an intake pipe from an injection valve and supplies the fuel to an engine, and in particular, vaporizes LPG in a fuel supply line. The present invention relates to a fuel supply device for an engine that injects the fuel in a stable liquid state without any excessive temperature rise in the fuel tank.

  A system in which liquid fuel is metered and injected as it is with an injection valve arranged in the intake pipe and supplied to the engine is well known. For gasoline, as shown in FIG. 6, liquid fuel stored in the fuel tank 2 is used. Pressurized by the pump 3 and sent to the fuel rail 6 from the fuel supply line 4B and distributed to the injection valve 8 disposed in the intake pipe 22 of the engine 21, and the surplus fuel that has not been injected is returned to the fuel with the pressure regulator 10 installed. It is common to return to the fuel tank 2 via the pipe line 9B. On the other hand, as described in Japanese Utility Model Laid-Open No. 61-138860, Japanese Utility Model Laid-Open No. 62-87162, and Japanese Patent Laid-Open No. 63-18172, LPG, which is a liquid fuel that is easily vaporized, is shown in FIG. Use the same system as shown in.

  By applying the well-known return type fuel supply system to liquid fuel injection, such as LPG, which is easy to vaporize, the liquid fuel in the fuel rail or injector generates bubbles due to temperature rise due to engine heat, and the fuel injection amount Can be avoided. However, when the engine is operated for a long time, a large amount of surplus fuel with a high temperature returns to the fuel tank, and the fuel tank pressure also rises as the fuel tank temperature rises. There arises a problem that there is a risk of damage to the fuel tank and refilling of the fuel becomes difficult.

  In order to solve this problem, the applicants of the present application previously disclosed in Japanese Patent Application Laid-Open No. 1-127700 on the first return line having a pressure regulator connected to the vicinity of the fuel tank of the fuel supply line and the fuel rail end side. A second return line with a connected pressure regulator is provided with an open / close valve, and this is controlled to open and close. Then, he presented a technology that would avoid the rise in the tank temperature.

  However, even in this technology, in consideration of the actual use state of the vehicle, particularly in taxi vehicles using LPG as fuel, the ratio of idle operation states such as traffic jams and standby is high, and cooling air to the engine room due to traveling is large. In combination with the fact that there is almost no inflow of the fuel, the chance (time) that the fuel rail and the injector are exposed to high temperature tends to increase. Therefore, if a returnless fuel supply system is employed at this time, the fuel consumption is small and the fuel flow rate is small, so that the fuel temperature in the fuel rail and the fuel supply pipe adjacent to the fuel rail gradually rises and bubbles are generated. This causes a problem that the engine operation becomes unstable.

  On the other hand, Japanese Patent Laid-Open No. 7-27030 detects the temperature state of the fuel system parts of the engine, and corrects the control amount of the fuel pump to the increase side when the high temperature state is detected. A technique is proposed that switches to the return type only when it is corrected. With such a control, a sufficient fuel flow rate can be ensured, so that it is possible to avoid an excessive increase in the fuel temperature in the fuel supply line close to the engine.

However, this technology merely controls the switching of the fuel discharge amount and the fuel supply system based on the temperature of the fuel system parts of the engine, and minimizes the return fuel to the fuel tank while avoiding the vaporization of the supplied fuel. Because it is not adjusted, high temperature return fuel accumulates in the tank for a long time when the taxi vehicle is assumed to receive heat from the engine for a long time. As a result, there is a problem that the pressure rises as well as the pressure rises excessively.
Japanese Utility Model Publication No. 61-138860 Japanese Utility Model Publication No. 62-87162 JP-A-63-18172 JP-A-1-127700 JP-A-7-27030

  The present invention is intended to solve the above-described problems, and relates to an engine fuel supply device that can switch a supply system of liquefied gas fuel between a return type and a lintless type. An object of the present invention is to adjust the return fuel to the minimum while correcting the operation state of the pump to surely avoid the vaporization of the fuel so as to avoid an excessive increase in the temperature in the fuel tank.

In order to solve the above-described problems, the present invention is configured to pressurize liquefied gas fuel in a fuel tank by a fuel pump whose output is controlled in accordance with an engine required flow rate and send the pressurized fuel gas to an injector through a fuel supply line. A first fuel return line that branches in the middle of the pipeline and a second fuel return line that returns the fuel that was not injected by the injector are each connected to the fuel tank with a shut-off valve, and are electronically controlled. In the fuel supply device for the engine that controls the switching of the fuel supply system between the return type and the returnless type by controlling the opening and closing of the two shutoff valves by the unit,
A fuel pressure sensor and a fuel temperature sensor are arranged near the injector in the fuel supply line, and the electronic control unit that detects these output signals is in a state where the injected fuel may be vaporized. When it is judged and when the engine is started, control is performed so as to be a return type and a normal operation is a returnless type.

  In such a configuration, the amount of fuel heated after passing through the engine (room) does not return to the fuel tank again (returnless), and is arranged at a position close to the injector and the fuel rail. By monitoring the state of the supplied fuel with the installed fuel temperature sensor and fuel pressure sensor, and entering a warning state where the fuel may vaporize, the fuel supply method is switched from the returnless type to the return type for a long time. It is possible to avoid an excessive increase in the temperature in the fuel tank while avoiding the trouble that the fuel is vaporized even under use conditions in operation.

  In the above-described engine fuel supply device, fuel temperature detection means for detecting the fuel temperature of the fuel tank is arranged, and the fuel temperature stored in the fuel tank by the electronic control unit is stored in the fuel tank by the fuel temperature detection means. Based on the detected fuel temperature, the switching standard value for changing the fuel supply method from the return type to the returnless type will be changed. It will be easier to avoid evaporation more reliably.

  Further, in this fuel supply apparatus for an engine, the electronic control unit stores in the storage means vapor pressure curve data indicating the relationship between the temperature and the pressure that are the boundary values between the gas phase and the liquid phase in the liquefied gas fuel to be used. If the detected fuel temperature approaches this boundary value and enters the specified warning temperature range, the fuel pump is controlled as an output for normal operation until it returns to the outside of this warning temperature range. The vaporization of the liquid fuel in the fuel supply pipe can be avoided more reliably. Then, the fuel temperature detecting means detects the fuel pressure in the fuel tank from the fuel pressure value detected by the fuel pressure sensor as the electronic control unit switches the operation of the pump between the feedback control and the open loop control at regular time intervals. If the fuel temperature is detected by estimating the fuel temperature in the fuel tank based on the above-mentioned vapor pressure curve data, the fuel temperature sensor for the fuel tank is unnecessary and the cost can be kept low. .

  Furthermore, in the fuel supply device of this engine, the temperature inside the fuel tank gradually changes and the pressure inside the tank also changes gradually during long-time operation. Therefore, the electronic control unit uses the fuel pressure in the fuel tank calculated backward. If the fuel pressure target value in the next feedback control is appropriately changed and executed, more accurate feedback control can be performed while keeping the cost low.

  In addition, in the engine fuel supply apparatus described above, the electronic control unit constantly monitors the fuel temperature and the fuel pressure with the fuel temperature sensor and the fuel pressure sensor, so that the fuel does not vaporize in the fuel supply line. The output of the fuel pump is feedback controlled. As a result, it is possible to flexibly cope with changes in fuel temperature and pressure that cannot be handled only by switching the fuel supply line. However, particularly when switching to the return type, the fuel is suddenly released by opening the second fuel return line. Therefore, vaporization can be effectively avoided by preventing a significant pressure drop. And it becomes easy to adjust the quantity of the return fuel to a fuel tank to the minimum by such feedback control.

  If the output control of the fuel pump by the electronic control unit is set to a predetermined output by changing the power supplied to the fuel pump, the output control of the fuel pump becomes easy and reliable.

  According to the present invention, with respect to a fuel supply device in which the fuel supply method is switched between the return type and the linkless type, the operation status of the pump is surely avoided in all cases to prevent vaporization of the supplied fuel. It is possible to adjust the return fuel to the minimum while correcting and to effectively avoid the excessive increase in the temperature in the fuel tank.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a layout diagram of an engine fuel supply system in which a fuel supply device according to the present embodiment is provided. A fuel pump 3 is provided on the outlet side of a fuel tank 2, and a fuel supply pipe is shown. The passage 4A is connected to a fuel rail 6 provided with a plurality of injectors 8 provided downstream of the throttle valve 7 in an intake pipe 22 of an engine (not shown).

  In addition, a first fuel return line 9a branched and connected to the fuel tank 2 is connected to the fuel tank 2 in the vicinity of the fuel tank 2 of the fuel supply line 4A (for example, in the rear trunk of the vehicle). And a shut-off valve 12 is provided. Further, a second fuel return line 9b extending from the end of the fuel rail 6 and joining downstream of the cutoff valve 12 of the first fuel return line 9a has a check valve 15 and a cutoff valve 13. These are provided to form the fuel return line 9A.

  A temperature sensor 51 for detecting the fuel temperature and a pressure sensor 52 for detecting the fuel pressure are disposed near the injector 8 (near the fuel rail 6 inlet) of the fuel supply line 4A. A data signal is output. The electronic control unit 50 adjusts the discharge amount by changing the output of the fuel pump 3 by PWM (Pulse Width Modulation) control or the like according to the load state of the engine.

  Further, the electronic control unit 50 controls the electromagnetic shut-off valves 12 and 13 disposed in the first fuel return line 9a and the second fuel return line 9b so that the fuel supply system is a return type and a returnless type. Switching control is performed between the two types, and the return type is used when the engine is started, and the returnless type is controlled during normal operation. This function is the same as the known fuel supply device described above. It is.

  The feature of the present invention is that the state of the injected fuel is detected by the temperature sensor 51 and the pressure sensor 52 disposed in the vicinity of the injector 5 and the fuel rail 6 and the return type is switched when the injected fuel is vaporized. In addition to control, the state of the fuel in the fuel tank 2 is estimated from the data stored in the storage means of the electronic control unit 50, and the switching values (temperatures) of the shutoff valves 12 and 13 are variable depending on the estimated fuel temperature in the tank. In addition, by switching the operation of the fuel pump 3 between the feedback control and the open loop control in a certain time, it is possible to change the setting of the target pressure value in the next closed loop control. is there.

  First, the basic operation of the present embodiment will be described using the layout diagram of the fuel supply system in FIG. 1. Liquid fuel (for example, liquid LPG) stored in the fuel tank 2 is supplied to the fuel tank 2 by the fuel pump 3. From the injection valve 8 that opens into the intake pipe 22 of the engine and is injected as a liquid.

  At the time of open loop control in normal operation, the injection pressure is adjusted to a predetermined constant pressure by the check valve 14 which is installed in the fuel return line 9a and also functions as pressure adjusting means, and surplus fuel passes through the fuel return line 9b. After that, when the feedback control (transition) is performed, the electronic control unit 50 causes the fuel pump 3 to have a feedback target pressure that is set slightly lower than the pressure detected by the pressure sensor 52. The output is controlled at, and the fuel return amount to the fuel tank 2 becomes zero.

  In the following, waveforms of the output signals of the sensors, the shut-off valves 12 and 13 and the drive signals of the fuel pump 3 in the special operation state different from the normal operation and the action of the characteristic portions in the present embodiment corresponding thereto. This will be described with reference to FIG.

  First, when the engine is started (time A), the fuel pump 3 is operated by open loop control for a predetermined time, the shutoff valve 12 is closed, the shutoff valve 13 is open (return type), and fuel is supplied. The surplus fuel is returned to the fuel tank 2 by following the path from the line 4A to the fuel rail 6 to the second fuel return line 9b. Then, after a predetermined time has elapsed, the fuel pump 3 is operated by feedback (closed loop) control, the shutoff valve 12 is opened, the shutoff valve 13 is shifted to a closed state (returnless type), and the surplus fuel becomes zero.

  On the other hand, in a special operation state, for example, in a sudden transient operation, the fuel pump 3 is changed from feedback control to open loop control, and the surplus fuel is maintained while the shutoff valve 12 is open and the shutoff valve 13 is closed (returnless type). Returns to the fuel tank 2 from the first fuel return line 9a. Further, depending on the temperature detected by the fuel temperature sensor 51, a calculation table is also provided in the open loop control as shown in FIG. 3, and the output value of the fuel pump 3 is controlled to be different corresponding to this temperature.

  When the fuel temperature in the fuel rail 6 and the injector 8 becomes high (time B), the fuel pump 3 changes from feedback control to open loop control. The shutoff valve 12 is closed and the shutoff valve 13 is opened (return type), and this state is maintained until the temperature sensor 51 in the vicinity is lowered to a predetermined set temperature, and surplus fuel is supplied to the second fuel return line 9b. To return to the fuel tank 2. Thereafter, the fuel pump 3 shifts to feedback control, the shutoff valve 12 is opened, the shutoff valve 13 is closed (return type), and the surplus fuel becomes zero.

  In the present embodiment, only the operation output of the fuel pump 3 is changed from the normal operation to the open loop control state at regular intervals (periodically), and the detected value of the fuel pressure sensor 52 is monitored. The electronic control unit 50 estimates the fuel pressure in the fuel tank 2 and calculates the target pressure of the next feedback control. Based on this, the output of the fuel pump 3 is gradually reduced, and a new update feedback is performed. The operation is performed with the control pressure target value, and it is easy to realize more accurate control.

  By the way, as shown in the characteristic curve showing the relationship between the pressure of the fuel pump and the fuel flow rate in FIG. 4, the fuel flow rate is determined at a point where it intersects with the set pressure by the pressure regulator (pressure regulator) in a certain operation state. By gradually lowering the pump output, the flow rate also decreases. When the pump output is further decreased, there is no intersection with the set pressure, and the fuel flow rate passing through the pressure regulator becomes zero. Therefore, at that moment, the fuel pressure in the fuel rail and the injector is significantly reduced.

  Therefore, the pressure sensor 52 disposed in the vicinity of the fuel rail 6 senses the moment when the fuel pressure drops significantly after the output reduction of the fuel pump 3 starts, and the electronic control unit 50 outputs the operation output value D1 and the output at that time. The pump output is increased to an average value D2 with the operation output value D0 at the start of the decrease. Then, the output is gradually decreased again from D2, and when the pressure is remarkably lowered as described above, the output is increased to the average value of the operation output values D3 and D2, and this operation is repeated.

  By executing such control, the amount of fuel passing through the pressure regulator can be adjusted to approach zero while maintaining the set pressure value even in a special operation state, and the fuel pressure suddenly increases. The amount of return fuel to the fuel tank 2 can be minimized while reliably avoiding the occurrence of bubbles in the fuel supply pipe line.

  On the other hand, FIG. 5 shows a vapor pressure line graph representing the relationship between the pressure and temperature, which is the boundary value between the gas phase and the liquid phase, with respect to the LPG fuel used in the fuel supply apparatus of the present embodiment. The control unit 50 stores this data in the storage means in advance, and when the fuel temperature in the vicinity of the fuel rail 6 rises during closed-loop control as shown in the figure, it is within the warning area (Tm) corresponding to this boundary value. When the temperature reaches the temperature T1, the closed loop control is canceled and the output value D4 of the normal operation is raised as the open loop control, and this output value is maintained until the temperature falls to the temperature T2 outside the warning area (Tm).

  By adopting such a control, the fuel discharge amount can be increased before the temperature at which the fuel changes to the gas phase by continuing a special operation state, and the fuel temperature can be lowered reliably and promptly. It is.

The layout which shows embodiment of this invention. The wave form diagram for demonstrating operation | movement of the fuel supply apparatus of FIG. The waveform diagram when the fuel temperature is low. The graph which shows the relationship between the fluctuation | variation of the fuel pressure by the fluctuation | variation of the output of a fuel pump, and the fluctuation | variation of a fuel flow rate for demonstrating the control method of the fuel pump of FIG. FIG. 2 is a graph of a vapor pressure line showing a relationship between pressure and temperature serving as a boundary between a gas phase and a liquid phase in the LPG used in the fuel supply apparatus of FIG. 1. The layout of a gasoline injection system.

Explanation of symbols

2 Fuel tank, 3 Fuel pump, 4A Fuel supply line, 6 Fuel rail, 8 Injector, 9 Fuel return line, 9a First fuel return line, 9b Second fuel return line, 11, 12, 13 Shut-off valve, 14, 15 Check valve, 22 Intake pipe, 50 Electronic control unit, 51 Temperature sensor, 52 Pressure sensor

Claims (7)

A fuel pump whose output is controlled in accordance with the required flow rate of the engine pressurizes the liquefied gas fuel in the fuel tank and sends it to the injector through the fuel supply line, and the first fuel return that branches in the middle of the fuel supply line A pipe line and a second fuel return line for returning fuel not injected by the injector are each connected to the fuel tank with a shut-off valve, and the electronic control unit opens and closes the two shut-off valves. In a fuel supply device for an engine that controls the fuel supply system between a return type and a returnless type by controlling,
A fuel pressure sensor and a fuel temperature sensor are disposed in the fuel supply line close to the injector, and the electronic control unit that detects the output signals of both sensors may cause the injected fuel to vaporize. When it is determined that a certain state has been reached and when the engine is started, a return type is executed and a returnless type control is executed during normal operation.
A fuel supply device for an engine. Fuel temperature detecting means for detecting the fuel temperature in the fuel tank is arranged, and the electronic control unit monitors the fuel temperature in the fuel tank by the fuel temperature detecting means, and based on the detected fuel temperature. It is supposed to change the switching standard value to shift the fuel supply method from return type to returnless type,
The fuel supply apparatus for an engine according to claim 1.   3. The fuel supply apparatus for an engine according to claim 2, wherein the electronic control unit stores, in the storage means, vapor pressure curve data indicating a relationship between a temperature and a pressure as a boundary value between a gas phase and a liquid phase in the liquefied gas fuel to be used. When the detected fuel temperature approaches the boundary value and enters a predetermined warning temperature range, the fuel pump is controlled as an output for normal operation until returning to the outside of the warning temperature range. A fuel supply device for an engine.   In the fuel supply apparatus for an engine according to claim 3, the fuel temperature detection means is configured such that the electronic control unit switches the operation of the fuel pump between feedback control and open loop control at regular time intervals. The fuel pressure in the fuel tank is calculated backward from the fuel pressure value detected by the fuel pressure sensor, and the fuel temperature is detected by estimating the fuel temperature in the fuel tank from the vapor pressure curve data. A fuel supply device for an engine.   5. The fuel supply apparatus for an engine according to claim 4, wherein the electronic control unit performs control by appropriately changing a fuel pressure target value in the next feedback control using the fuel pressure in the fuel tank calculated backward. An engine fuel supply device characterized by the above.   The electronic control unit constantly monitors the fuel temperature and the fuel pressure with the fuel temperature sensor and the fuel pressure sensor, and feedback-controls the output of the fuel pump to a predetermined pressure within a range in which the fuel is not vaporized in the fuel supply line. The fuel supply device for an engine according to claim 1, 2, 3, 4 or 5, wherein The output control of the fuel pump by the electronic control unit is set to a predetermined output by changing the power supplied to the fuel pump. 5. A fuel supply device for an engine according to 5 or 6.

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