JP7558075B2 - Method for detecting compression stroke in internal combustion engine for work machine - Google Patents

Description

The present invention relates to a method for detecting the compression stroke of an internal combustion engine for a work machine.

Internal combustion engines mounted on work machines use a generator connected to the crankshaft as a power source for the spark plugs (Patent Document 1). This generator is composed of a rotor with a permanent magnet and a stator with a generating coil, and generates electricity using electromotive force excited by the rotation of the rotor. The electricity generated by the generator is charged into a capacitor, and the charge stored in the capacitor is released at each ignition timing to ignite the spark plugs.

A work machine is a tool that is essentially required to be lightweight and compact. The above-mentioned Patent Document 1 proposes using an ignition generator to supply power to drive a solenoid valve built into a carburetor. In other words, Patent Document 1 proposes using an ignition generator as a power source to operate the solenoid valve with minimal power. Specifically, the invention disclosed in Patent Document 1 proposes employing a solenoid valve that maintains an open state with spring force when the solenoid valve is not energized in order to minimize the power consumption of the solenoid valve.

As is well known, each cycle of an internal combustion engine consists of four strokes: intake stroke, compression stroke, combustion stroke, and exhaust stroke. In a four-stroke engine, each cycle is completed by two revolutions (720° rotation) of the crankshaft. In a two-stroke engine, each cycle is completed by one revolution (360° rotation) of the crankshaft.

The internal combustion engines installed in modern automobiles and motorcycles (two-wheeled vehicles) are becoming increasingly electronic. For example, Patent Document 2 discloses a generator that is used to ignite the internal combustion engine installed in a motorcycle and drive the fuel injection valve.

The development of electronics is also progressing in work machines. This development of electronics is becoming more and more likely to include multiple electric devices. And as the number of electric devices increases, the power of the generator of the work machine must inevitably be increased. The aforementioned Patent Document 2 discloses a generator with increased power generation capacity not only for ignition of the spark plug but also for driving the fuel injection device. More specifically, Patent Document 2 discloses a generator in which six magnets and six generating coils are both arranged at equal intervals in the circumferential direction. A generator equipped with multiple electromagnets and generating coils in this way has the problem that multiple peaks occur in the generating waveform during each cycle of the internal combustion engine, making it unclear which peak to use as a reference for determining the ignition timing and fuel injection timing.

Regarding this problem, the invention disclosed in Patent Document 2 proposes detecting the rotation angle of the crankshaft using a combination of the following two elements in order to control the injection timing of a fuel injection device installed in an internal combustion engine. The first element detects the rotation angle of the rotor by shaping the power generation waveform. The second element mechanically detects the rotation angle of the rotor. The invention disclosed in Patent Document 2 proposes detecting the rotation angle of the crankshaft by combining these first and second elements, and controlling the fuel injection timing based on this detected rotation angle.

US 7,140,352B2 JP 2009-191689 A

As mentioned above, working machines are essentially required to be lightweight and compact. The inventors noticed that the compression stroke of an internal combustion engine has a characteristic that is not present in other strokes in the power generation waveform of a generator equipped with multiple magnets and power generation coils. That is, the speed of the piston during the compression stroke, especially at the end of the compression stroke, slows down as it approaches top dead center. As a result, the period of the portion of the power generation waveform related to the compression stroke becomes longer. Based on the characteristics of this power generation waveform, the compression stroke can be distinguished from other strokes.

An object of the present invention is to provide a compression stroke detection method for an internal combustion engine for a work machine, which detects the compression stroke from an electric power generation waveform and determines, for example, ignition timing based on the detected compression stroke.

The above technical problem is solved by the present invention .
a spark plug disposed in a combustion chamber defined by a piston inserted in a cylinder;
A crankshaft that converts the reciprocating motion of the piston between the top dead center and the bottom dead center into rotational motion and outputs the rotational motion;
a generator mechanically connected to the crankshaft to generate electricity by rotation of the crankshaft;
A method for determining a compression stroke of an internal combustion engine for a work machine in which electric power generated by a generator is supplied to the ignition plug to ignite an air-fuel mixture in a combustion chamber, comprising:
a cycle time measuring step of measuring a cycle time of each waveform included in a period corresponding to one cycle of the internal combustion engine in a power generation waveform of the generator;
a longest period waveform identifying step of comparing the period times of the waveforms included in a period corresponding to one cycle of the internal combustion engine to determine the waveform with the longest period time;
a compression stroke determination step of determining that a stroke of the internal combustion engine to which the waveform with the longest cycle time belongs is a compression stroke,
Furthermore,
a waveform numbering step of numbering the periods of each waveform included in a period corresponding to one cycle of the internal combustion engine;
This can be achieved by providing a compression stroke determination method for an internal combustion engine for a work machine , which includes a waveform number storage step of storing the number of the waveform having the longest cycle time in a memory, following the waveform numbering step .

The effects and other objects of the present invention will become apparent from the detailed description of the preferred embodiments of the present invention below.

1 is a perspective view of an internal combustion engine according to an embodiment; 1 is a side view of an internal combustion engine according to an embodiment; 1 is an example internal combustion engine shown with the cover removed from the generator to expose the generator rotor. FIG. 1 illustrates an example internal combustion engine with the rotor removed. FIG. 1 is a side view of an example internal combustion engine with the rotor removed. FIG. 2 is a diagram for explaining a rotor and magnets extracted from a generator of an internal combustion engine according to an embodiment. FIG. 4 is a diagram showing a waveform of power generated by a generator of the internal combustion engine according to the embodiment. FIG. 8 is a diagram showing a shaped waveform obtained by shaping the power generation waveform shown in FIG. 7 . FIG. 2 is a block diagram related to the control of the internal combustion engine of the embodiment. 4 is a flowchart for explaining an example of a process for determining a compression stroke and controlling ignition in the control of the internal combustion engine of the embodiment. FIG. 10 is a diagram for explaining numbering of a periodic waveform corresponding to one engine cycle, in relation to the interruption interval of a power generation waveform, i.e., a periodic waveform, in the embodiment. FIG. 2 is a diagram for explaining the relationship between the numbering of each waveform period of the power generation waveform and each stroke of the engine, including intake, compression, combustion, and exhaust, in the embodiment.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. Figures 1 and 2 show an internal combustion engine according to the embodiment. Figure 1 is a perspective view, and Figure 2 is a side view. The internal combustion engine 2 shown in the figure is a four-stroke engine with a single cylinder. The internal combustion engine 2 is mounted on a portable work machine such as a brush cutter, trimmer, blower, or chain saw. In the drawings, reference numeral 4 denotes an air cleaner, and 6 denotes a fuel tank.

In Figure 1, the air cleaner 4 is shown disassembled. The housing 8 of the air cleaner 4 is composed of a case body 10 and a case lid 12, and the case body 10 is fixed to the engine body 2a by mounting bolts 14. The case lid 12 is detachably fixed to the case body 10 by lid mounting bolts 16.

The air cleaner 4 contains an air cleaner element 18 and a pre-element 20 arranged above it, and the air cleaner element 18 and pre-element 20 can be maintained by removing the case lid 12.

The internal combustion engine 2 can be started by operating the recoil starter operating handle 22. In FIG. 1, reference numeral 30 denotes a control unit, and 32 denotes a generator. The generator 32 is mechanically connected to the crankshaft 48, and generates electricity using the internal combustion engine 2 as a drive source.

The intake system 36 of the internal combustion engine 2 has an electronic throttle valve unit 38, which controls the output of the internal combustion engine 2. Note that in FIG. 1, the intake pipe 36a is shown in a state before being connected to related parts. The electricity generated by the generator 32 is used as a driving power source not only for the spark plug 34, but also for the electronic throttle valve unit 38 and various sensors.

Figure 3 shows the internal combustion engine 2 with the cover 32a (Figure 1) removed from the generator 32 to expose the rotor 40 of the generator 32. The basic structure of the generator 32 is the same as in the conventional case, and is composed of a rotor 40 and a stator 42. Figure 4 shows the internal combustion engine 2 with the rotor 40 removed, exposing the stator 42. In Figure 4, the permanent magnets 44 are shown separated from the rotor 40, but this is to clarify the presence of the permanent magnets 44, and in reality, the permanent magnets 44 are assembled to the rotor 40. In Figure 5, the rotor 40 is not shown. In Figure 5, the permanent magnets 44 are shown arranged around the stator 42, but this is to explain the arrangement of the permanent magnets 44.

Figure 6 is a diagram of the rotor 40 and stator 42. The stator 42 has six cores 42a, which are arranged at equal intervals in the circumferential direction. A generator coil 46 is wound around each core 42a of the stator 42. The rotor 40 has six permanent magnets 44, the same number as the cores 42a of the stator 42, which are arranged at equal intervals in the circumferential direction.

As is well known, the internal combustion engine 2 has a spark plug 34 (Figs. 4 and 5). Referring to Fig. 6, in the generator 32, the power generated by the generating coil 46 wound around some of the six cores 42a of the stator 42, i.e., the generating coil 46 wound around one or more cores 42a, is output from first terminals A1 and A2 and supplied to the spark plug 34 via the ignition circuit 60. The electromotive force of the generating coil 46 wound around the remaining cores 42a is output from second terminals B1 and B2 and used as a power source for the electronic throttle valve unit 38 (Fig. 1) and the like.

Four mounting holes 42c are formed in the center 42b of the stator 42. The stator 42 is fixed in position to the engine body 2a with four bolts inserted into the four mounting holes 42c. The rotor 40 is attached to the crankshaft 48 in a state aligned with a key 48a (Figure 4) installed on the crankshaft 48, and rotates together with the rotation of the crankshaft 48.

The generator 32 outputs a roughly sinusoidal AC voltage as the rotor 40 rotates (Figure 7). As in the past, the generated waveform of the generator 32 is half-wave rectified by, for example, a diode incorporated in the ignition circuit 60 (Figure 6). That is, the positive or negative components contained in the generated waveform of the generator 32 are shaped to only positive components (Figure 8). In addition to this half-wave rectification, the ignition circuit 60 may adjust and step down the voltage as necessary. The voltage is then stored in a capacitor. Figure 8 shows the output waveform of the generator 32, i.e., the generated waveform, after it has been shaped by half-wave rectification.

Referring to FIG. 7, the generator 32 has three peaks in the power generation waveform every time the crankshaft 48 rotates once (360°). Since the internal combustion engine 2 of the embodiment is a four-stroke engine, two rotations (720°) of the crankshaft 48 complete one cycle, i.e., the intake stroke, compression stroke, combustion stroke, and exhaust stroke. As shown in the figure, the generator 32 is preferably installed in a state where it is positioned on the crankshaft 48 so that 0 volts in the power generation waveform appears when the piston of the internal combustion engine 2 is located at top dead center and bottom dead center. In this way, by installing the generator so that 0 volts appears at top dead center and bottom dead center, the length of the interruption interval in the compression stroke becomes more noticeable, which has the advantage of making it easier to determine.

For the sake of convenience, the first through fourth strokes of the power generation waveform shown in Figure 7 constitute one cycle of the internal combustion engine 2. In Figure 7, the period of the first stroke is marked with "T1", the period of the second stroke is marked with "T2", the period of the third stroke is marked with "T3", and the period of the fourth stroke is marked with "T4" in chronological order.

As mentioned above, the movement of the piston of the internal combustion engine 2 slows down as the piston approaches top dead center during the compression stroke. When the first to fourth periods T1 to T4 are measured and compared, if the second period T2 is the longest, it can be determined that the second period T2, i.e., the second stroke, corresponds to the compression stroke. The order of the intake stroke, compression stroke, combustion stroke, and exhaust stroke of each cycle of the internal combustion engine 2 remains unchanged. If the second period T2, i.e., the second stroke, is the compression stroke, then the immediately preceding first period T1, i.e., the first stroke, is the intake stroke. In addition, the third period T3 following the second period T2, i.e., the third stroke, is the combustion stroke, and the following fourth period T4, i.e., the fourth stroke, is the exhaust stroke.

Figure 9 is an overall configuration diagram relating to the control of the internal combustion engine 2. Referring to Figure 9, the internal combustion engine 2 is controlled by a control unit 30. The control unit 30 has an engine control section 52 and a memory 54, and executes engine control according to a predetermined program stored in the memory 54. The control unit 30 receives the power generation waveform of the generator 32 as well as signals from a group of sensors 56, such as an engine temperature sensor, required for engine control. The power source for the control unit 30 and the group of sensors 56 is the generator 32.

Figure 10 is a flowchart for explaining an example of the compression stroke determination and ignition control process. To give an overview of the process in Figure 10, when the internal combustion engine 2 starts, the generator 32 starts generating electricity. Next, when the engine speed during idle operation stabilizes, the compression stroke determination mode is executed. The purpose of the compression stroke determination mode is to determine the compression stroke from the power generation waveform of the generator 32.

Referring to FIG. 7, the power generation waveform in which six peaks appear in each cycle of the internal combustion engine 2 continues from start to stop of the internal combustion engine 2. Based on this continuous power generation waveform, it is unclear which period T is the compression stroke. For this reason, ignition is performed in all strokes of the internal combustion engine 2 immediately after the engine is started. Then, when the engine speed during idle operation stabilizes, the compression stroke determination mode is executed under ignition in all strokes, and the longest period among the periods T1 to T4 of the power generation waveform described above is found with reference to FIG. 7. In a specific example described later with reference to FIG. 10, instead of comparing the periods T1 to T4 of the power generation waveform, the interruption intervals of each of the six peaks that appear in the power generation waveform in each cycle, that is, the periods iT1 to iT6 of each waveform, are compared. However, it is optional whether to adopt a comparison of the periods T1 to T4 of the power generation waveform corresponding to each stroke of the engine or to adopt a comparison of each period of the waveform, that is, the interruption intervals iT1 to iT6.

If, as described above, the second period T2 (FIG. 7) is the longest, it is determined that the second period T2 is the compression stroke. Once the compression stroke has been determined in the compression stroke determination mode, the engine control mode is changed to the normal engine control mode, that is, engine control in which ignition is performed once per cycle at a predetermined ignition timing. In the normal operation mode, the internal combustion engine 2 operates in the order of intake stroke, compression stroke, combustion stroke, and exhaust stroke, and based on this stroke order, when the compression stroke comes, the ignition timing is determined with the compression stroke as the reference. When determining the ignition timing, it is best to determine the ignition timing with the previous compression stroke as the reference. This normal engine control mode is executed continuously until the engine is stopped.

In the compression stroke determination mode, the compression stroke may be determined based on the power generation waveform shown in FIG. 7, or based on the shaped waveform shown in FIG. 8. Note that the waveform in FIG. 8 is a waveform in which only the positive side of the approximately sine wave obtained from the generator has been shaped, but it is preferable to also shape the negative side of the approximately sine wave and perform the compression stroke determination process based on the shaped waveforms on the positive and negative sides. Therefore, the term "power generation waveform" should be understood to include both the power generation waveform that is the output of the generator 32 and the shaped waveform obtained by shaping this.

To explain this in more detail, with reference to FIG. 10, when the internal combustion engine 2 starts, ignition is performed synchronously in all strokes (S1, S2). Then, once it is confirmed in step S3 that the idle operation has stabilized, the compression stroke determination process is immediately performed (S4 to S8).

In step S4, the six peaks that appear in the power generation waveform in each cycle of the internal combustion engine 2, that is, each period of the waveform, are numbered in order from 1st to 6th. The circled numbers 1 to 6 in the time series shown in FIG. 11 represent the first to sixth numbering. This numbering is reset when one cycle of the engine 2 ends. FIG. 11 corresponds to FIG. 7 described above. Referring to FIG. 11, the period of the power generation waveform, that is, each time of the interruption intervals iT1 to iT6, that is, the period of each waveform, is measured (S5), and this is stored in memory 54 (FIG. 9) together with the interruption order number (S6). In the next step S7, the interruption intervals iT1 to iT6 stored in memory 54, that is, the period of the power generation waveform for each period, are compared to determine the longest interruption interval (S7). If the third interruption interval iT3, i.e., the third waveform period, is the longest, then this third interruption interval iT3 belongs to the second stroke described in FIG. 7, and so this second stroke is determined to be the compression stroke (S8). As a result, when the third interruption signal appears in each cycle of the internal combustion engine 2, this corresponds to the compression stroke and can be distinguished from other strokes. The interruption number, i.e., the period number, determined to be the compression stroke is stored in memory 54. FIG. 12 is a diagram for explaining the relationship between the numbering, which assigns numbers 1 to 6 in the order of the six periods, i.e., interrupts, of the power generation waveform, and each stroke.

After the compression stroke is determined in the compression stroke determination process (S4 to S8) and the associated interrupt number, i.e., cycle number, is stored in memory 54, ignition is stopped for each cycle and the mode is changed to normal engine control mode (S9). This normal engine control mode continues until the internal combustion engine 2 is stopped. In the normal engine control mode, based on the cycle number "No. 3" stored in memory 54, if an interrupt with the corresponding cycle number occurs in the subsequent power generation waveform, it is determined that this corresponds to the compression stroke and ignition is performed. The ignition timing is determined, for example, by taking into consideration the engine speed at the time of the previous third interrupt. The trigger that serves as the basis for determining the ignition timing may be a characteristic point of the waveform, such as the rising edge, falling edge, or positive or negative side peak of the power generation waveform.

Without any physical detection element such as mechanically detecting the rotation angle of the rotor, it is possible to recognize that the internal combustion engine 2 is currently in the compression stroke, and control the ignition timing and the like based on this compression stroke. In addition, although ignition occurs in each stroke of the engine 2 from engine start until the compression stroke determination process is completed, after the compression stroke is determined, the mode is switched from the compression stroke determination mode to the normal engine control mode and ignition occurs only when the ignition timing of the engine 2 arrives. This prevents the adverse effect of continuing ignition in all strokes of the internal combustion engine 2, i.e., shortening the life of the ignition plug, and also prevents reverse rotation of the engine 2. Furthermore, by eliminating the waste of using electricity generated by the generator 32 to ignite in all strokes, the electromotive force of the generator 32 can also be used as a power source for electric devices other than the ignition plug.

The present invention has been described above using a four-stroke internal combustion engine 2 as an example, but it will be obvious to those skilled in the art that the present invention can also be applied to two-stroke internal combustion engines. In addition, the embodiment has been described based on a generator with six coils and six magnets, but the present invention is not limited to six and can be applied to internal combustion engines with generators with multiple coils and magnets. The number of coils and magnets may be odd or even, but is preferably an even number to suppress noise generation. The present invention can be suitably applied to single-cylinder engines that are typically mounted on portable work machines.

2. Engine of the embodiment (four-stroke engine)
30 Control unit 32 Generator 34 Spark plug 38 Electronic throttle valve unit 40 Generator rotor 42 Generator stator 44 Permanent magnet 46 Coil 48 Crankshaft 52 Engine control unit 54 Memory 56 Sensor group
iT1 to iT6: Interval between each waveform (waveform period) corresponding to one cycle of the engine

Claims (1)

a spark plug disposed in a combustion chamber defined by a piston inserted in a cylinder;
A crankshaft that converts the reciprocating motion of the piston between the top dead center and the bottom dead center into rotational motion and outputs the rotational motion;
a generator mechanically connected to the crankshaft to generate electricity by rotation of the crankshaft;
A method for determining a compression stroke of an internal combustion engine for a work machine in which electric power generated by a generator is supplied to the ignition plug to ignite an air-fuel mixture in a combustion chamber, comprising:
a cycle time measuring step of measuring a cycle time of each waveform included in a period corresponding to one cycle of the internal combustion engine in a power generation waveform of the generator;
a longest period waveform identifying step of comparing the period times of the waveforms included in a period corresponding to one cycle of the internal combustion engine to determine the waveform with the longest period time;
a compression stroke determination step of determining that a stroke of the internal combustion engine to which the waveform with the longest cycle time belongs is a compression stroke,
Furthermore,
a waveform numbering step of numbering the periods of each waveform included in a period corresponding to one cycle of the internal combustion engine;
The compression stroke determination method for an internal combustion engine for a work machine includes a waveform number storage step of storing the number of the waveform having the longest cycle time in a memory, following the waveform numbering step .

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