JP2007309199A - Fuel supply device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce waste at low cost by enabling a relatively small fuel pump to cope with maximum fuel demand flow rate of an engine in a fuel supply device for an engine. <P>SOLUTION: In a fuel supply device for the engine in which an electronic control unit 10 detects fuel pressure by a pressure sensor 11 provided in a downstream of a fuel pump 3 of a fuel supply piping, and secures fuel injection quantity according to engine demand fuel flow rate while performing feed-back control of drive of the fuel pump to keep fuel pressure at predetermined normal operation fuel pressure P1, the electronic control unit 10 controls drive of the fuel pump 3 to keep fuel pressure at high output operation pressure P1' dropped from normal operation pressure by predetermined level, and keep fuel delivery flow rate within a predetermined range while the engine operates at predetermined high output or higher. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an engine fuel supply device, and more particularly to a fuel supply device that is disposed in an engine fuel injection system and that supplies liquid fuel to an engine by being pumped by an electric fuel pump.

  2. Description of the Related Art Conventionally, a fuel supply apparatus in which liquid fuel stored in a fuel tank is pressurized by a fuel pump driven by an electric motor, injected by an injector disposed at the end of a fuel supply pipe, and supplied to an engine is widely used. In the case of such an apparatus, the fuel discharge flow rate of the fuel pump increases as the rotational speed increases in proportion to the rotational speed of the pump, and decreases as the rotational speed decreases. As in the device described in the publication No. 229924, the electronic control unit that detects the operating state of the engine outputs an instruction value corresponding to the engine required fuel flow rate to the motor driver of the fuel pump and is instructed. It is known to realize an optimum fuel flow rate (injection amount) while rotating at a rotational speed.

  By the way, when trying to cope with a higher output engine using such a fuel supply device, the size of the fuel pump is increased, or a plurality of devices such as the device described in JP-A-2006-37920 are used. It is necessary to dispose a fuel pump. For this reason, the cost required for installing the fuel pump is likely to increase.

However, as can be seen in the graph showing the distribution of the required fuel flow of the engine in the general usage state of the automobile (ordinary passenger car) shown in FIG. 5, most of the required fuel flow of the engine is concentrated in the “relatively low flow” band. It can be seen that the ratio of the “maximum required flow rate” zone is extremely small. Therefore, as shown in the graph (PQ diagram) showing the relationship between the fuel pressure P and the flow rate Q in FIG. 4, the fuel pump designed in anticipation of the maximum required fuel flow rate of the engine is the majority of the operation. Is used with a low flow rate fuel supply, which is extremely inefficient, leading to waste of power consumption and deterioration of vehicle fuel consumption.
Japanese Patent Laid-Open No. 11-229924 JP 2006-37920 A

  The present invention is intended to solve the above-described problems. In an engine fuel supply apparatus, a fuel pump having a relatively small discharge capacity can be used to cope with the maximum required fuel flow rate of the engine, and is low-cost and untitled. The problem is to make it less.

  Accordingly, the present invention provides a fuel tank, a fuel supply pipe extending from the fuel tank, an electric fuel pump attached to the fuel supply pipe, and a terminal of the fuel supply pipe. And an electronic control unit for controlling the rotation speed of the fuel pump and controlling the opening and closing of the injector, and this electronic control unit uses a pressure sensor provided downstream of the fuel pump in the fuel supply pipe to control the fuel pressure. The fuel supply device for the engine is designed to ensure the fuel injection amount corresponding to the required fuel flow rate while feedback controlling the drive of the fuel pump so as to maintain the predetermined fuel pressure value for normal operation. In this case, while the engine is operating at a high output above a predetermined level, the electronic control unit reduces the fuel pressure to a predetermined level from that for normal operation. And controls the driving of the fuel pump to maintain the fuel pressure value for the high output operation was decided to reduce the discharge flow rate within a predetermined range.

  As described above, the reference fuel pressure value (injection pressure) is switched from the normal operation to the high output operation when it is close to the maximum output operation of the engine. Discharge capacity (maximum fuel discharge flow rate) that can be handled at the maximum output operation of the engine, which is short in frequency, was required for the fuel pump and was wasteful, but it became possible to cope with discharge capacity lower than this Cost is low and waste is low.

  Further, in this engine fuel supply device, a temperature sensor for detecting the fuel temperature is disposed in the vicinity of the injector of the fuel supply pipe, and the numerical value calculated by the electronic control unit by a predetermined method based on the detected fuel temperature is predetermined. If it is determined that the fuel pressure control is performed based on the pressure value for high-power operation, the fuel flow rate will increase or decrease due to the change in fuel temperature immediately before injection. In addition to being able to easily determine, the balance between the fuel temperature and the fuel pressure makes it easy to control the drive of the fuel pump to a minimum while avoiding vaporization of the fuel in the piping.

  Furthermore, if the numerical value calculated based on the detected fuel temperature in this case is calculated in consideration of the engine required fuel flow rate, further appropriate control can be easily realized.

  According to the present invention, the fuel pressure is controlled to decrease near the maximum output operation of the engine, so that even a small fuel pump having a relatively small discharge capacity can cope with the maximum required fuel flow rate of the engine at low cost. It can be less untitled.

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

  FIG. 1 is a layout diagram of a fuel supply device for an engine according to the present embodiment. A fuel tank 1 is filled with liquid fuel, and a fuel pump 3 disposed inside the fuel tank 1 is placed outside the tank. A fuel supply pipe 2 is extended, and an injector 5 is disposed at the tip thereof to supply liquid fuel to an engine (not shown).

  The fuel pump 3 is an electric motor drive type, and its drive is controlled by the electronic control unit 10. Further, a pressure sensor 11 for detecting the pressure of the fuel immediately before injection and a temperature sensor 12 for detecting the temperature are disposed in the vicinity of the injector 5 of the fuel supply pipe 2, and the electronic control unit 10 outputs an output signal from these sensors. It is designed to detect continuously. Further, the injector 5 is controlled to open and close at a predetermined duty cycle by the electronic control unit 10 so as to realize a fuel injection amount corresponding to the engine required fuel flow rate.

  In this engine fuel supply device, the fuel discharge flow rate of the fuel pump 3 is proportional to the pump rotation speed, the flow rate increases as the rotation speed increases, and the flow rate decreases as the rotation speed decreases. An instruction value for securing a fuel injection amount corresponding to the engine required fuel flow rate is output from the electronic control unit 10 to the fuel pump 3 to discharge the fuel. During the normal output operation of the engine, the fuel pressure immediately before injection is detected by the pressure sensor 11 and the fuel pressure value for normal operation is maintained to avoid vaporization of the fuel in the pipe, while maintaining a predetermined fuel pressure (injection). Feedback control is performed to ensure pressure.

  In addition, the electronic control unit 10 continuously detects the fuel temperature detected by the temperature sensor 12 disposed in the fuel supply pipe 2. Then, by using the detected fuel temperature data and the detected engine fuel flow data such as the throttle opening, a numerical value for pressure switching determination is continuously calculated by a predetermined calculation method, preset and stored. While it is determined that this value exceeds the “threshold value”, the fuel pump 3 is driven and controlled so that the fuel pressure maintains the fuel pressure value for high-power operation, which will be described in detail below. This is a characteristic part of the present invention.

  This “threshold value” is based on the relationship with the fuel temperature at which the liquid fuel is not vaporized even if the fuel pressure is lowered by a predetermined level by utilizing the fact that the fuel temperature in the vicinity of the injector 5 is lowered as the fuel flow rate is increased. An appropriate value is set in advance and stored in advance in the electronic control unit 10, and the reference value is determined based on whether or not the pressure switching determination value calculated using the detected fuel temperature data exceeds this value. This is used to determine whether or not the engine high output operation is required to reduce the fuel pressure value. It should be noted that more accurate control of the fuel discharge pressure by the fuel pump 3 is possible by taking into account the engine required fuel flow rate data such as the throttle opening. Moreover, the calculation method of the numerical value for pressure switching determination should just determine an appropriate calculation method using the least squares method etc. from several experimental data.

  The operation and effect of the present embodiment will be described below using the graphs of FIGS.

  FIG. 3 shows the relationship between the engine required fuel flow rate, the fuel temperature by the temperature sensor 12, the fuel pressure by the pressure sensor 11, and the fuel discharge flow rate by the fuel pump 3 in the engine fuel supply apparatus of the present embodiment. It is the graph shown in series.

  During normal operation of the engine, the fuel pressure value that the electronic control unit 10 maintains by driving and controlling the fuel pump 3 is stored as the pressure P1 for normal operation, and the fuel flow rate at this time is relatively small. The fuel temperature in the fuel supply pipe 2 near the engine is higher than the fuel temperature in the fuel tank 1 by a predetermined temperature due to the heat of the engine. When the engine required fuel flow rate increases to a1, a large amount of fuel flows from the fuel tank 1 having a low temperature, and the fuel temperature at that time decreases to b1.

  Based on this fuel temperature b1, the numerical value for pressure switching determination calculated by the electronic control unit 10 using the predetermined calculation method in consideration of the engine required fuel flow rate a1 exceeded the previously stored “threshold value”. As a result, the fuel pressure value is stored as a fuel pressure value for high output operation, and the pressure P1 ′ is switched to maintain the pressure P1 ′ lower than the normal operation pressure P1 by a predetermined level. The fuel discharge flow rate of the fuel pump 3 is maintained so that the pressure P1 'is maintained until the fuel flow rate is decreased to the engine required fuel flow rate a2 and the fuel temperature becomes b2 and the numerical value for pressure switching determination falls below the "threshold value". Control.

  Then, in the conventional fuel supply apparatus, in order to secure the fuel injection amount corresponding to the engine required fuel flow rate shown in the uppermost part of FIG. 3, the fuel discharge flow rate indicated by the broken line is required in the lowermost part of FIG. In this embodiment, the fuel discharge flow rate indicated by the solid line lower than this is sufficient. That is, as shown in the graph (PQ diagram) in FIG. 2, the fuel injection amount from the injector 5 can be increased by lowering the fuel pressure from P1 to P1 ′, and the maximum required flow rate of the engine. In order to secure the fuel injection amount corresponding to the above, even a small fuel pump having a smaller maximum fuel discharge capacity than the conventional fuel supply device can be used.

  As can be seen from the graph showing the relationship between the engine required fuel flow rate and its frequency in general use of a normal passenger car shown in FIG. 5, the portion near the maximum required fuel flow rate of the engine is extremely infrequent and short in time. Therefore, when the fuel pressure value serving as a control reference is set to a pressure P1 ′ which is a predetermined level lower than the pressure P1, the predetermined time is not changed even if the fuel injection amount is increased by changing the duty cycle of the injector 5. This is because it can sufficiently maintain the fuel flow rate required for the engine without increasing the discharge flow rate of the fuel pump 3.

  In addition, by changing the fuel pressure value, which is the control reference, based on the change in fuel temperature proportional to the fuel flow rate, it is easy to accurately respond to the increase in the required fuel flow rate of the engine, and the decrease in fuel temperature. Even if the fuel pressure is lowered, the fuel is less likely to be vaporized, so that accurate fuel injection control can be easily realized.

  Therefore, the fuel supply apparatus according to the present embodiment is small in size and has a lower pump discharge capacity than the fuel pump in the conventional fuel supply apparatus, so that the manufacturing cost is low. This also reduces the amount of power consumed, resulting in improved vehicle fuel efficiency.

The layout which shows embodiment of this invention. The graph which shows the relationship between the pressure P and the flow volume Q by the fuel supply apparatus of FIG. The graph for demonstrating the effect | action by the fuel supply apparatus of FIG. The graph which shows the relationship between the pressure P and flow volume Q by a prior art example. The graph which shows the engine required fuel flow zone of the motor vehicle (normal passenger car) by general use.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel tank, 2 Fuel supply piping, 3 Fuel pump, 5 Injector, 10 Electronic control unit, 11 Pressure sensor, 12 Temperature sensor

Claims (3)

A fuel tank, a fuel supply pipe extending from the fuel tank, an electric fuel pump attached to the fuel supply pipe, and an end of the fuel supply pipe. And an electronic control unit that controls the rotational speed of the fuel pump and controls the opening and closing of the injector, and the electronic control unit uses a pressure sensor provided downstream of the fuel pump in the fuel supply pipe. A fuel supply device that secures a fuel injection amount corresponding to a required fuel flow rate while feedback controlling the drive of the fuel pump so as to maintain a predetermined fuel pressure value for normal operation by detecting pressure In
While the engine is operating at a high output above a predetermined level, the electronic control unit maintains the fuel pressure value for high output operation in which the fuel pressure value is reduced by a predetermined level from that for normal operation. A fuel supply apparatus for an engine, wherein the fuel discharge amount of the fuel pump is suppressed within a predetermined range by controlling driving of the fuel pump.   A temperature sensor for detecting a fuel temperature is disposed near the injector of the fuel supply pipe, and the numerical value calculated by the electronic control unit based on the detected fuel temperature by a predetermined method exceeds a predetermined threshold value. 2. The engine fuel supply apparatus according to claim 1, wherein the fuel pressure control is performed based on the fuel pressure value for the high-power operation while the fuel pressure is determined to be. 3. The engine fuel supply device according to claim 2, wherein the numerical value is calculated in consideration of an engine required fuel flow rate.

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