Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
1998-12-10
2001-02-27
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S617000, C123S1490FA
Reexamination Certificate
active
06192861
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ignition device for igniting a fuel-air mixture supplied to an engine. More particularly, it relates to an engine ignition device which is adapted so that an ignition timing may be advanced or delayed in response to a change in an engine speed.
2. Description of the Related Art
A small-sized simple general-purpose engine has been heretofore used as a drive source in a small-sized working machine or the like including a mower, for example. In this type of general-purpose engine, a self-trigger type ignition device having a relatively simple constitution is used in order to ignite a fuel-air mixture supplied to a combustion chamber.
This type of ignition device comprises a spark plug disposed in the combustion chamber of the engine; a flywheel disposed in a crankshaft of the engine; a magnet disposed in the flywheel; and a cored ignition coil adjacent to a revolution locus of the magnet and connected to the spark plug through a high-tension cord.
The magnet is revolved in synchronization with a rotation of the crankshaft. The magnet passes besides the core, whereby a high voltage is generated in the ignition coil. This high voltage is supplied to the spark plug, whereby sparks are generated in the spark plug, so that the fuel-air mixture supplied to the combustion chamber is ignited. In such an ignition device, the timing of the generation of the sparks in the spark plug, i.e., the timing of the ignition of the fuel-air mixture is a constant timing to a rotation cycle of the crankshaft, regardless of a difference in a rotational speed of the crankshaft. Due to this, when the rotational speed of the crankshaft, namely, an engine speed is high, the ignition timing may be too late to obtain a sufficient engine output. When the engine speed is low, the ignition timing may be so early that an idle operation is unstable. Thus, this type of ignition device also requires a function of advancing or delaying the ignition timing in response to the difference in the engine speed.
Japanese Patent Publication No. 61-10672 discloses an example of a trigger type ignition device capable of advancing the ignition timing (hereinafter referred to as “the first prior art”). This ignition device has a control circuit for controlling the ignition timing. The control circuit includes an advance capacitor. The engine speed is increased, whereby a charging potential is increased in the advance capacitor. The timing when a main transistor for actuating the ignition coil is turned on is thus advanced. The timing of the ignition of the spark plug by the ignition coil is consequently advanced.
On the other hand, Japanese Patent Application Laid-open No. 1-262367 discloses another example of the trigger type ignition device capable of advancing the ignition timing (hereinafter referred to as “the second prior art”). In the engine incorporating a flywheel/magnet type generator, this ignition device allows a stator of the generator to be rotatably supported by an electromagnetic force generated between the stator and the magnet on the side of the flywheel rotated in synchronization with the engine. The ignition device has a spring member for suppressing the rotation of the stator in a direction of rotation of the flywheel. The ignition device has a drive mechanism for moving a self-trigger type ignition unit (including a pickup core, etc.) sharing the flywheel. This drive mechanism moves the ignition unit in the opposite direction to the direction of rotation along an outer periphery of the flywheel in response to the rotation of the stator. The ignition unit is moved in response to the difference in the engine speed, whereby the ignition timing of the engine is advanced or delayed.
However, the ignition device according to the first prior art tends to have a relatively narrow advance range of the ignition timing which can be changed by the advance capacitor. Moreover, for a mass-production of the advance capacitor, the set values of time constant associated with the charge of the advance capacitor may be varied and thus the advance values of the ignition timing may be varied.
On the other hand, the ignition device according to the second prior art tends to have a relatively large ignition unit and thus to have a complicated large-sized drive mechanism and support mechanism for moving the ignition unit. Thus, the ignition device is structurally unstable and also has a problem in operation reliability.
SUMMARY OF THE INVENTION
The present invention is made in view of the above-described facts. An object of the present invention is to provide an engine ignition device capable of automatically controlling an ignition timing in a stable manner in response to a difference in an engine speed within a relatively wide variable range by a relatively simple constitution.
To achieve the purpose of the invention, there is provided an engine ignition device for igniting a fuel-air mixture supplied to an engine by emitting sparks to the fuel-air mixture by igniting means, which includes a rotation detector for detecting a rotation of an output shaft of the engine at each predetermined rotational angle and for outputting a detection signal changed in response to a rotational speed of the output shaft; and a timing controller for changing an operating timing of the igniting means in accordance with the detection signal and for operating the igniting means in accordance with the changed operating timing.
According to the above-mentioned constitution, a waveform of the detection signal outputted from the rotation detector is changed in response to the difference in the rotational speed of the output shaft. Thereby, the operating timing of the igniting means is changed in response to the change by the timing controller, so that the timing of the ignition of the fuel-air mixture in the engine is advanced or delayed. Therefore, the timing of the combustion of the fuel-air mixture can be changed in response to the difference in conditions such as a low-speed operation or a high-speed operation of the engine.
For example, in the above-described constitution of the present invention, desirably, the rotation detector includes a protrusion or notch disposed in a flywheel on the output shaft and a magnet pickup, adjacent to a revolution locus of the protrusion or notch, for detecting a passage of the protrusion or notch near the magnet pickup and for outputting, in a pulse manner, a detection signal having a maximum value proportional to its passing speed. The timing controller includes a comparator circuit for comparing the detection signal to a threshold value in order to operate the igniting means when the detection signal outputted from the magnet pickup with the passage of the protrusion or notch is larger than a predetermined threshold value.
According to the above-described constitution, the flywheel is rotated with the rotation of the output shaft, whereby the protrusion or notch passes near the magnet pickup. The pickup outputs, in the pulse manner, the detection signal having the maximum value proportional to the passing speed, i.e., the rotational speed of the output shaft. At this time, the detection signal is compared to the threshold value by the comparator circuit. When the detection signal is larger than the threshold value, the igniting means is operated. When the maximum value of the detection signal is relatively large in proportional to the rotational speed of the output shaft, the detection signal exceeds the threshold value at a relatively early timing to the rotation cycle of the output shaft. On the other hand, when the maximum value of the detection signal is relatively small, the detection signal exceeds the threshold value at a relatively late timing to the rotation cycle of the output shaft.
Accordingly, during the high-speed operation of the engine, the operating timing of the igniting means is relatively advanced. The ignition timing of the fuel-air mixture is advanced. The combustion timing of the fuel-air mixture is adapted
Hamada Mikio
Wada Satomi
Aisan Kogyo Kabushiki Kaisha
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Wolfe Willis R.
LandOfFree
Engine ignition device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Engine ignition device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Engine ignition device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590456