JPH0241349Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an ignition system for a two-stroke engine, and in particular, when the engine rotates in the opposite direction, the ignition system is controlled so that the spark plug is discharged in a stroke other than the compression stroke. The present invention relates to an ignition device configured to prevent reverse rotation.

As an example of such an ignition device, for example, a so-called CDI type ignition device 26 (FIG. 4), which will be described later, is known. The ignition device 26 is shown in FIGS.
It has an ignition timing control device 10 shown in the figure. The device 10 has a rotor 12 that rotates synchronously with the crankshaft of a two-stroke engine. An elongated magnetic member 14 extending in the rotational direction is fixed to the outer peripheral surface of the rotor 12, and a coil 16 is disposed near the rotor 12. A magnet (not shown) is provided near the coil 16 to generate magnetic flux that interlinks with the coil 16. The magnetic member 14 has both ends 18,
20 pass near the coil 16, induced voltages of mutually opposite polarities are generated in the coil 16. That is, when the rotating member 12 rotates in the forward rotation direction A of the engine, the third a
As shown in the figure, when the front end 18 of the magnetic member passes in front of the coil 16, a positive voltage pulse 22 is output from the coil 16, and when the rear end 20 passes, a negative voltage pulse is output. pulse 2
4 is output. When the rotor 12 rotates in the reverse rotation direction B, the change in the magnetic flux surrounding the coil 12 is the opposite to that of the forward rotation. Therefore, as shown in FIG. It will be output from.

In the so-called CDI type ignition device 26 shown in FIG. 4, the spark plug 28 is discharged when the ignition timing control device 10 outputs an ignition signal, that is, a positive polarity pulse 22 or 24b. That is, in this ignition system, the capacitor 34 is charged by the output of the coil 30 of the magnet generator G connected to the crankshaft. A thyristor 36 is connected between the cathode of the diode 32 and ground. The ignition signal from the coil 16 of the ignition timing control device 10 is passed through a diode 36 and a resistor 38 to a time constant circuit 40 consisting of a resistor and a capacitor.
is input. The ignition signal passed through the time constant circuit causes the thyristor 36 to conduct, thereby discharging the charge accumulated in the capacitor 34. When the capacitor 34 discharges, a high voltage is induced in the secondary coil 44 of the transformer 42, and this high voltage is applied to the ignition plug 28, causing the ignition plug to discharge into the cylinder, causing sparks to fly.

As is well known, in a two-stroke engine, if ignition is performed while the piston and crankshaft are within a certain range of positions, the engine continues to rotate in reverse. This specific range, that is, the reversible range θ expressed as an angular range with respect to the crankshaft rotation axis, corresponds to the cylinder center axis direction, that is, the top dead center of the piston, as shown in FIG. 5 for the angular position of the crankshaft or rotor 12. (assuming that the piston reaches the top dead center immediately after the end 18 of the magnetic member 20 reaches the position TOP), and this position in the reverse rotation direction.
The range θ _f before reaching the TOP is wider than the range θ _r after. In order to prevent the engine from rotating in reverse, the ignition position of the magnetic member 14 during reverse rotation, that is, the position where the end portion 20 faces the coil 16 (FIG. 7), must be outside this reversible range. That is, if the coil 16 is located at a position separated by an angle θ _i from the position TOP as shown in FIG. 6, and the length of the magnetic member converted into an angle is θ _l , then FIG. 7 shows the ignition position at the time of reverse rotation. As can be seen, the condition θ _l −θ _i >θ _f must be satisfied. This range θ _f is usually about 80°, so if θ _i = 10°, θ
_l
must be approximately 90° or more.
Note that the longitudinal direction of the crank arm is indicated by a dashed line Z.

Therefore, in the conventional device described above, regarding the length of the magnetic member 14, the end portion 20 reaches the coil 16 before the longitudinal direction Z of the crank arm enters the range of θ _f .
It is necessary to make the magnetic member 14 quite long so that it faces the magnetic member 14, and it is necessary to improve the surface finishing precision to prevent noise induction in the coil output waveform. This is disadvantageous in that it requires high cost.

Therefore, an object of the present invention is to improve the ignition timing control device of the conventional device described above, and set the length of the magnetic member that cooperates with the coil 16 to generate an ignition signal to be smaller than that of the conventional device. Our goal is to provide you with an ignition system that will get you started.

For this purpose, the ignition device of the present invention ignites a voltage pulse induced in the coil when the rear end of a magnetic member fixed to a rotating member rotating in synchronization with the crankshaft passes near the coil. This ignition signal causes the spark plug to discharge.

FIG. 8 is a diagram schematically showing the ignition timing control device in the ignition system of the present invention. Similar to the above conventional example, a magnetic member 50 is fixed to the outer peripheral surface of a rotating member, that is, a rotor 12 that rotates in synchronization with the crankshaft, and a coil 1 is attached near the rotor 12.
6 is provided, and a magnet (not shown) that generates a magnetic flux that interlinks with the coil 16 is provided near the coil 16. When the engine rotates in the forward rotation direction and the rotor 12 rotates in the direction of arrow A in FIG. 8, as shown in FIG. 9a,
When the tip 52 of the magnetic member 50 passes near the coil 16, a negative pulse 52a is output from the coil 16, and when the rear end 54 passes near the coil 16, a positive pulse 54a is output just before TDC. Ru. That is, the rear end portion 54 is located forward of the crank arm longitudinal direction Z in the forward rotation direction.
This positive pulse triggers the ignition device as shown in FIG. 4, as in the prior art device described above. On the other hand, if the engine rotates in the opposite direction and the rotor 12 rotates in the direction of arrow B, then
As shown in the figure, when the ends 54 and 52 of the magnetic member 50 pass near the coil 16, a negative pulse 54b and a positive pulse 52b are sequentially output from the coil 16. That is, even when the engine rotates in either direction, when the rear end of the magnetic member 50 in the rotating direction (54 in the forward rotation, 52 in the reverse rotation) passes near the coil 16, the magnetic member 50 is induced in the coil 16. The positive polarity pulse generated is output as an ignition pulse.

In the device of the present invention, the length of the magnetic member 50 in the rotational direction converted into an angle is θ _L , and the engine piston reaches the top dead center when one end 54 of the magnetic member 50 reaches the position TOP. In order to prevent this, the conditions imposed on θ _L are found in the same manner as in the conventional example above, and from FIG. 8 the conditions are θ _L + θ _i > θ _r , that is, θ _L > θ _{r −θ} I understand that. Since θ _r is approximately 20° as is well known,
It can be seen that according to the present invention, the length of the magnetic member 50 can be set extremely short.

As is clear from the above, according to the present invention, the length dimension of the magnetic member in the rotational direction can be set to a small value that is a fraction of that of the conventional device, and the machining accuracy of the magnetic member can be improved. This is preferable because it is easy to raise the device, thereby reducing the weight of the device and the manufacturing cost.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of an ignition timing control device in a conventional ignition system, FIG. 2 is a plan view of the conventional device, and FIG. 3a and FIG. FIG. 4 is a circuit diagram showing an example of an ignition device that operates in response to a positive polarity pulse, and FIGS. 5 to 7 are diagrams showing the induced voltage waveform output from the device, respectively. FIG. 8 is a plan view showing the relationship between the position of the magnetic member and the ignition timing. FIG. 8 is a schematic plan view showing an ignition timing control device of an ignition device according to an embodiment of the present invention. FIGS. 9a and 9b are respectively FIG. FIG. 3 is a diagram showing induced voltage waveforms generated according to the rotational direction of the engine in the device of FIG. Explanation of symbols of main parts, 12...Rotor, 16
... Coil, 50 ... Magnetic member.

Claims (1)

[Scope of utility model registration request] A spark plug provided in a cylinder of a two-stroke engine; a means for applying a high voltage to the spark plug in response to an ignition signal to cause the spark plug to discharge; A rotating member that rotates, a coil provided near the rotating member, and a magnet that generates a magnetic flux that interlinks with the coil, such that both ends thereof are located at positions separated from each other in the rotation direction of the rotating member. and a single magnetic protrusion member fixed to the rotating member so as to generate induced voltages of opposite polarities in the coil when each of the ends thereof passes a position facing the coil. In the ignition device for a two-stroke engine, the magnetic protrusion member is disposed forward in the forward rotation direction of the crank arm longitudinal direction Z, and an end portion of the magnetic protrusion member rearward in the forward rotation direction of the rotary member is arranged in front of the coil. An induced voltage generated in the coil when passing near the coil is supplied as the ignition signal to the means, and the angular position of the coil with respect to the crankshaft rotation axis and the length of the magnetic member are determined by the ignition signal when the crankshaft rotates in the forward direction. An ignition device characterized in that an ignition signal is generated before top dead center, and when the crankshaft is reversed, an ignition signal is generated outside the range in which reverse rotation is possible after top dead center.