AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention title: INJECTOR CONTROL METHOD AND INJECTOR CONTROL DEVICE The following statement is a full description of this invention, including the best method of performing it known to us: chbm AO113567899v1 306253688 INJECTOR CONTROL METHOD AND INJECTOR CONTROL DEVICE Field of the invention The present invention relates to an injector control method and an injector 5 control device. More particularly, it relates to a control method of an injector for injecting a gas fuel such as an LPG and a control device which performs the control method. Background of the invention In this specification, where a document, act or item of knowledge is 10 referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date: (i) part of common general knowledge; or (ii) known to be relevant to an attempt to solve any problem with which this 15 specification is concerned. In a leaf spring type injector (a fuel injection valve) used for a gas fuel, the injection diameter of the injector has to be larger than that of an injector for a liquid fuel to inject the fuel as much as the same weight as in the case of the injector for the liquid fuel. Consequently, when the valve is closed, a holding 20 force of the valve increases, and hence it is necessary to increase a valve suction force. Thus, when a coil resistance is decreased and a coil winding number is increased, the valve suction force can be increased. However, when the coil resistance is decreased, heat generation increases. Therefore, as shown by a graph 25 of FIG. 2, a battery voltage is generally applied until the valve opens (Tip control), and after the valve has opened, a current is controlled to inhibit power consumption (PWM control). However, in a case where a viscous substance such as oil sticks to the surface of a valve seat of the injector, a resistance against a valve opening/closing 30 operation increases. In consequence, at a startup at a low temperature or during 2 idling, a requested suction force is larger than the valve suction force generated by the Tip control, and hence a valve opening time is liable to delay. Moreover, when the PWM control is begun after the end of the Tip control, the valve suction force decreases. At this time, an actual injection time becomes 5 shorter than a calculated injection time, and hence the operation state of an engine easily deteriorates owing to the attenuation of an air-fuel ratio. To cope with this problem, it has been suggested in Japanese Unexamined Patent Publication No.11-264334 that a control device detects a pressure in a cylinder at the startup of the engine to verify the stuck state of the injector, and then a control 10 is performed so as to prolong the fuel injection time in accordance with the stuck state, thereby optimizing the air-fuel ratio. However, even after the sticking of the injector at the engine startup is removed, the increase of the valve resistance by the viscous substance cannot be solved on occasion. In this case, the valve suction force does not sufficiently 15 increase only by prolonging the calculated injection time, and hence a desired fuel injection time and fuel injection amount cannot be obtained frequently. Moreover, if the calculated injection time is further prolonged until the desired fuel injection time is obtained, the heat generation of the coil becomes excessive, and therefore the injector is easily damaged. 20 Summary of the invention According to the present invention, there is provided an injector control method which is performed by an injector control device connected to an injector for a gas fuel, and the method comprises the steps of: in a usual case, executing injector control constituted of a combination of Tip control by a valve opening 25 current to open a closed valve and subsequent PWM control by an opened valve holding current to hold the opened valve; and in a case where the injector control device judges that the increase of a valve suction force is necessary based on predetermined data detected by the injector control device, switching the injector control of the combination to injector control in which the portion of the PWM 30 control is also replaced with the Tip control, to execute the switched injector control for a predetermined period of time.
3 The present invention has been developed to address, at least in part, the above problems. An advantage of the present invention is to secure a desired fuel injection amount while minimizing the damage occurrence of an injector, thereby avoiding the attenuation of an air-fuel ratio, even when the valve opening/closing 5 operation of the injector is influenced by a viscous substance or the like during the injection of a gas fuel. In this way, in a case where the injector control device judges that the increase of the valve suction force is necessary based on the detected predetermined data, the control of the combination is switched to the injector 10 control in which the portion of the opened valve holding current with a weak valve suction force is also replaced with the valve opening current with a strong valve suction force, whereby even in a situation where the opening/closing operation of the valve is influenced by a viscous substance or the like, a difference between an actual injection time and a scheduled fuel injection time can be 15 minimized. In this case, if the data which is used when the injector control device judges that the increase of the valve suction force is necessary includes at least one of an engine rotation speed, an engine water temperature and a recovery rotation speed after fuel cut, it is easy to exactly judge the situation where the valve 20 opening/closing operation is influenced. Furthermore, in the above injector control method, if the injector control of the only Tip control without the PWM control is executed only for such a necessary and minimum time when the increase of the valve suction force is required, the excessive heat generation of the injector can easily be avoided. 25 Additionally, if there is provided an injector control device which is disposed in a fuel supply system of a gas engine, connected to an injector by a wiring line, and includes a control program to execute injector control, and if the injector control device is characterized by performing the above injector control method in accordance with the control program, the above function can securely 30 be exerted only by disposing the injector control device in the fuel supply system of the gas engine.
4 According to the present invention, in a case where the injector control device judges that the increase of the valve suction force is necessary, the injector control of the combination is switched only for the predetermined period of time to the injector control constituted of the only Tip control in which the portion of 5 the opened valve holding current is also replaced with the valve opening current. Therefore, even when the valve opening/closing operation is influenced by the viscous substance or the like, a desired fuel injection amount is secured while minimizing the damage occurrence of the injector, whereby the attenuation of the air-fuel ratio can be avoided. 10 Brief description of the drawings FIG. 1 is a graph showing a control state according to an embodiment of the present invention; and FIG. 2 is a graph showing a control state according to a conventional example. 15 Description of the preferred embodiment Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. The hard constitution and arrangement of an injector control device which performs an injector control method of the present embodiment are similar to 20 those of a well known conventional example, and hence the drawing and detailed description thereof are omitted. It is to be noted that the injector control device (an electronic control unit) of the present embodiment is connected to an injector disposed in a suction air pipeline, via a wiring line, and is configured to output an injector driving current to execute the opening/closing control of the injector, and 25 the present invention is characterized by the injector control method as the contents of the control. FIG. 1 is a graph for comparison between a calculated injection time based on the injector control method of the present embodiment and the actual operating situation of a valve. In injector control by a conventional example 30 described above with reference to FIG. 2, owing to the influence of a viscous substance or the like stuck to the valve, the valve operation area of the injector 5 decreases as much as a+b+(c), so that an air-fuel ratio attenuates, and the rotation speed of an engine fluctuates on occasion. On the other hand, the injector control method of the present embodiment is characterized in that the injector control device detects an engine cooling water 5 temperature and the engine rotation speed, recognizes a recovery rotation speed after judging that a fuel has been cut, and executes predetermined control in accordance with a predetermined engine operating situation as shown in the following table 1. Table 1 Startup / Steady / Acceleration During deceleration At startup After startup [Entire water [Entire water temperature region] [water temperature of 80*C or temperature region] 9 TIP=TILPG (Max. TIP= oms) less TP=TILPG within X[s] after startup at 2000 P=TILPG (Max. TIP= l0is) rpm or less for 3[s] at recovery RPM+200rpm (or less in accordance with water . TI=TIPG Max.T[P l~ns) temperature with respect to after X[s] after startup at injection after judgment of fuel fdoeRPM+200 rpm or less in cut accordance with water temperature Usual control in a case other than Usual control in a case other than the above case the above case 10 That is, in the injector control device of the present embodiment, when the opening/closing operation of the valve is influenced by the viscous substance or the like as shown in the graph of FIG. 2, it is judged whether or not to increase a valve suction force generally from elements such as the engine cooling water 15 temperature, the engine rotation speed and the recovery rotation speed after the fuel cut, and the control of the driving of the injector is switched to control which does not comprise PWM control and which comprises only Tip control, while limiting the injection duty of the injector to a region as small as possible, whereby a requested valve suction force can be realized. 20 In this way, to secure engine operation properties, the control region is limited to that shown in Table 1, thereby executing the injector control of the present embodiment. In consequence, while minimizing the heat value of a coil 6 of the injector, the valve opening/closing operation is not easily influenced by the viscous substance or the like (b and c in FIG. 2), and an excessively attenuated air fuel ratio can effectively be avoided to prevent the excessive fluctuation of the rotation number of the engine. 5 As described above, even when the valve opening/closing operation of the injector is influenced by the viscous substance or the like during the injection of a gas fuel, according to the present invention, the attenuation of the air-fuel ratio can effectively be avoided while securing a desired fuel injection amount. The word 'comprising' and forms of the word 'comprising' as used in this 10 description and in the claims do not limit the invention claimed to exclude any variants or additions. Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.