JP2009221868A - Fuel composition determination method for lpg engine and lpg injection control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine a fuel component by using a pressure sensor for feedback control to implement a fuel injection control responding to change in fuel composition at low cost, in an LPG injection system. <P>SOLUTION: An LPG injection control device maintains target injection pressure by a feedback control while detecting fuel pressure of downstream of a fuel pump. In a fuel composition determination method for an LPG engine determining the fuel composition of LPG from fuel pressure and a fuel temperature of upstream of the fuel pump 3, an electronic control unit 10A as an LPG injection control device estimates the fuel pressure of the upstream of the fuel pump 3 by subtracting boost-up margin from target injection pressure, and determines the fuel composition without direct detection of the fuel pressure of the upstream of the fuel pump 3. The target injection pressure is acquired by a predetermined deriving method from an electric current value of the detected drive current of the fuel pump 3, and the boost-up margin is differential pressure between the target injection pressure and the fuel pressure of the upstream of the fuel pump 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an LPG engine fuel composition determination method and an LPG injection control device, and more particularly to a fuel for an LPG engine for determining an LPG fuel composition from detected fuel pressure and fuel temperature and using it for various engine controls. The present invention relates to a composition determination method and an LPG injection control apparatus that implements the determination method.

  Liquefied petroleum gas (hereinafter referred to as “LPG”) generally has different fuel components (such as the composition ratio of propane and butane) depending on the manufacturer, the season of manufacture, the production lot, and the like. Therefore, when the fuel components of LPG are different, the calorific value and octane number of propane and butane are different, leading to a decrease in power performance and a deterioration in fuel consumption with the same air-fuel ratio control and ignition timing control. is there.

  On the other hand, as described in JP-A-61-275555 and JP-A-2004-324509, the LPG injection control device detects the fuel temperature and the gas phase fuel pressure in the fuel tank storing the LPG. Based on this, the composition ratio of propane and butane of LPG used is determined by using a predetermined data table, etc., to determine the fuel composition, and to correct the reference fuel injection amount, the reference ignition timing, etc. It has become common to do.

  FIG. 4 shows a layout of a conventional LPG injection system that performs such control. An electronic control unit 10B as an LPG injection control device pressurizes LPG fuel stored in the fuel tank 2 by driving a motor. The fuel injection pressure is maintained at the set target pressure by driving the fuel pump 3 to be discharged by feedback control.

  The fuel tank 2 is provided with two sensors, a pressure sensor 12a and a temperature sensor 11a, so that the pressure data and temperature data of the LPG stored from these sensors are input to the electronic control unit 10B. The fuel component is determined (estimated) from a fuel temperature / pressure relationship table or the like set in advance in the electronic control unit 10B, and a reference value or the like in the fuel injection control according to the content (ratio) of the fuel component Is corrected.

However, in this LPG injection system, the pressure sensor 12a on the fuel tank 2 (upstream of the fuel pump 3) side and the pressure sensor 12b provided on the injector 4 (downstream of the fuel pump 3) side for feedback control of the injection pressure, Where it is necessary to provide two pressure sensors, there is a problem that the pressure sensor is disadvantageous in terms of cost because it is a relatively expensive part.
JP-A 61-275555 JP 2004-324509 A

  The present invention relates to an LPG injection control apparatus that maintains a target injection pressure by feedback control while detecting a fuel pressure downstream of a fuel pump, and for determining a fuel composition of LPG from the fuel pressure and fuel temperature upstream of the fuel pump. The LPG engine fuel composition determination method according to claim 1, wherein the LPG injection control device detects the target injection pressure obtained by a predetermined derivation method from the detected current value of the drive current of the fuel pump and the fuel upstream of the fuel pump. A fuel pressure upstream of the fuel pump is estimated by subtracting a pressure increase, which is a pressure difference, from the target injection pressure, and the fuel composition is determined without directly detecting the fuel pressure upstream of the fuel pump. An LPG injection control device that maintains the target injection pressure by feedback control while detecting the fuel pressure downstream of the fuel pump The fuel composition determination method of the LPG engine for determining the fuel composition of the LPG from the fuel pressure and the fuel temperature upstream of the fuel pump, wherein the LPG injection control device detects the detected drive current of the fuel pump. The fuel pressure on the upstream side of the fuel pump is estimated by subtracting, from the target injection pressure, the pressure increase that is the differential pressure between the target injection pressure and the fuel pressure on the upstream side of the fuel pump obtained from the current value by a predetermined derivation method An object of the present invention is to solve the above-mentioned problem characterized in that the fuel composition is determined without directly detecting the fuel pressure upstream of the fuel pump. The fuel component can be determined using a pressure sensor, and fuel injection control that can respond to changes in fuel composition can be realized at low cost. As it is an object of the present invention to.

  Accordingly, the present invention is an LPG injection control device that maintains a target injection pressure by feedback control while detecting a fuel pressure downstream of the fuel pump, and determines a fuel composition of the LPG from the fuel pressure and fuel temperature upstream of the fuel pump. A fuel composition determination method of an LPG engine for performing the target injection pressure obtained by a predetermined derivation method from the detected current value of the drive current of the fuel pump and the upstream side of the fuel pump The fuel pressure upstream of the fuel pump is estimated by subtracting the pressure increase, which is the differential pressure of the fuel pressure, from the target injection pressure, and the fuel composition is determined without directly detecting the fuel pressure upstream of the fuel pump It is characterized by doing.

  Conventionally, the LPG injection control device detects the fuel pressure / temperature on the upstream side of the fuel pump and determines the fuel composition while maintaining the fuel injection pressure at the target injection pressure by feedback control. However, in the present invention, the difference between the target injection pressure and the fuel pressure upstream of the fuel pump (≈the LPG vapor pressure in the fuel tank) is increased in the present invention. The pressure sensor on the upstream side of the fuel pump can be omitted by calculating the fuel pressure upstream side of the fuel pump by obtaining the pressure increase margin that is the pressure.

  Further, in this case, the derivation of the boosting margin is calculated using a predetermined relational expression representing the relationship between the current value and the boosting margin, or using a predetermined data table representing the relationship between the current value and the boosting margin. Thus, it is possible to easily derive the boosting margin without increasing the processing load of the LPG injection control device.

  Further, in the fuel composition determination method of the LPG engine described above, the fuel temperature upstream of the fuel pump is detected from the fuel stored in the fuel tank, and the fuel pressure and fuel temperature downstream of the fuel pump are detected from the fuel near the injector. If it is to be done, a more reliable determination can be made.

  Furthermore, an output signal from a temperature sensor disposed in the fuel injection system of the LPG engine and disposed on the upstream side of the fuel pump is input, and from the temperature sensor and pressure sensor disposed on the downstream side of the fuel pump. LPG injection control characterized in that each of the output signals is input and includes a fuel pump current value detection means, a fuel pressure estimation means, and a fuel composition determination means, and implements the above-described LPG engine fuel composition determination method. If it is an apparatus, the above-described functions can be surely exhibited only by disposing it in the fuel injection system of the LPG engine.

  According to the present invention, the fuel composition of the LPG used is determined by estimating the fuel pressure upstream from the fuel pump drive current and estimating the fuel pressure upstream of the fuel pump. Thus, fuel injection control that can cope with changes in the fuel composition can be realized at low cost.

  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 an LPG injection system in which an electronic control unit 10A is provided as an LPG injection control device for carrying out a fuel composition determination method for an LPG engine which is a preferred embodiment of the present invention. The major difference between this system and the conventional LPG injection system shown in FIG. 4 is that no pressure sensor is provided in the fuel tank 2 on the upstream side of the fuel pump 3, so that the cost can be kept low. There is in point.

  The electronic control unit 10A is similar to the electronic control unit 10B, which is a conventional LPG injection control device, in hardware, and also detects the fuel pressure (fuel injection pressure) downstream of the fuel pump 3 in software. In this respect, the fuel injection system is provided with a fuel composition determination means (not shown) that maintains the target injection pressure by feedback control and determines the fuel composition of the LPG from the fuel pressure and fuel temperature upstream of the fuel pump 3.

  On the other hand, in the electronic control unit 10A of the present embodiment, a driving current for the fuel pump 3 is input, and a program for executing a fuel composition determination method for an LPG engine unique to the present invention is installed. A fuel pump current value detecting means 100 for detecting the drive current of the fuel pump 3 and a fuel pressure estimating means 101 for estimating the fuel pressure upstream of the fuel pump are functionally provided. The LPG described in detail below. The point that the fuel composition determination method of the engine is implemented is a point that is greatly different from the conventional electronic control unit 10B.

  Next, the principle of the fuel composition determination method for the LPG engine of the present embodiment and the function of the electronic control unit 10A which is an LPG injection control device will be described.

  When fuel injection is performed from the injector 4, the fuel pressure on the downstream side of the fuel pump 3 instantaneously drops, but the fuel pump 3 is driven to perform feedback control so as to reach the set target injection pressure. At this time, the work of the fuel pump 3 is to increase the fuel by an amount corresponding to the differential pressure across the pump (= set target pressure−LPG vapor pressure in the fuel tank 2).

  On the other hand, the fuel pump 3 has the relationship of the boosting proxy current as shown in the graph of FIG. 2, so that the boost value can be known by knowing the current value (current consumption value) for driving the fuel pump 3. it can. That is, the current value flowing through the fuel pump 3 is detected by the fuel pump current value detecting means 100, the pressure increase margin is obtained by the fuel pressure estimating means 101 using a predetermined relational expression or a data table, and this is set as a set target value. By subtracting from LPG, the LPG vapor pressure in the fuel tank 2 can be estimated.

  The procedure for determining the fuel composition may be the same as that in the prior art. The estimated fuel pressure upstream of the fuel pump 3 (vapor pressure in the fuel tank 2) and the temperature sensor 11a disposed in the fuel tank 2 are used. By comparing the detected fuel temperature using a fuel pressure and fuel temperature data table or a predetermined relational expression (approximate expression) for each fuel composition, the fuel composition can be determined relatively accurately.

  FIG. 3 is a relationship diagram of the fuel pressure and the fuel temperature LPG in each fuel composition. An approximate expression of such a vapor pressure diagram is set in advance in the electronic control unit 10A in increments of 10% of the fuel component, for example. In this case, the LPG fuel component may be determined by performing interpolation calculation.

  Then, based on the fuel composition of the LPG determined in this manner, more accurate engine control can be performed by correcting reference values in various controls such as fuel injection control using a predetermined data table or the like. It becomes like this. Each procedure of the fuel composition determination method for the LPG engine described above is not at a level that imposes an excessive processing burden on the CPU of the electronic control unit 10A, and therefore needs to be more sophisticated as a control device than the conventional one. Since there is no need to use an expensive electronic control unit, there is no worry of increasing the cost in terms of hardware.

  As described above, for the LPG injection system, according to the present invention, fuel components can be determined using a pressure sensor for feedback control, and fuel injection control compatible with different fuel compositions can be realized at low cost. I can do it now.

The layout of the LPG injection system which shows embodiment of this invention. The graph which shows the pressure | voltage rise of a fuel pump, and the relationship of an electric current. The graph which shows the relationship between fuel pressure and fuel temperature LPG. The layout which shows a prior art example.

Explanation of symbols

2 fuel tank, 3 fuel pump, 4 injector, 10A electronic control unit, 11a, 11b temperature sensor, 12b pressure sensor, 100 fuel pump current value detection means, 101 fuel pressure estimation means

Claims (5)

  In an LPG injection control device that maintains a target injection pressure by feedback control while detecting a fuel pressure downstream of a fuel pump, an LPG engine for determining a fuel composition of LPG from the fuel pressure and fuel temperature upstream of the fuel pump. In the fuel composition determination method, the LPG injection control device is configured to detect a differential pressure between the target injection pressure obtained by a predetermined derivation method from the detected current value of the drive current of the fuel pump and the fuel pressure upstream of the fuel pump. The fuel pressure upstream of the fuel pump is estimated by subtracting the pressure increase allowance from the target injection pressure, and the fuel composition is determined without directly detecting the fuel pressure upstream of the fuel pump. A method for determining the fuel composition of an LPG engine.   2. The method for determining a fuel composition of an LPG engine according to claim 1, wherein the derivation of the boosting margin is calculated using a predetermined relational expression representing a relationship between the current value and the boosting margin.   2. The method for determining a fuel composition of an LPG engine according to claim 1, wherein the pressure margin is derived using a predetermined data table representing a relationship between the current value and the pressure margin.   The fuel temperature upstream of the fuel pump is detected from the fuel stored in the fuel tank, and the fuel pressure and fuel temperature downstream of the fuel pump are detected from fuel near the injector. 2. A fuel composition determination method for an LPG engine according to 2 or 3. An output signal from a temperature sensor disposed in the fuel injection system of the LPG engine and disposed upstream of the fuel pump is input, and outputs from a temperature sensor and a pressure sensor disposed downstream of the fuel pump. 5. The fuel composition determination method for an LPG engine according to claim 1, 2, 3 or 4, wherein each of the signals is input and provided with fuel pump current value detection means, fuel pressure estimation means, and fuel composition determination means. An LPG injection control device.

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