Internal-combustion engines – Engine speed regulator – Engine speed reduction by partial or complete omission of...
Reexamination Certificate
2001-07-16
2002-11-12
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Engine speed regulator
Engine speed reduction by partial or complete omission of...
C123S406530, C123S406660
Reexamination Certificate
active
06478010
ABSTRACT:
(E) BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention refers to an arrangement for starting a motor, especially in hand-held machines using a magnetic generator which induces alternating current dependent on the revolutions and thus charges an ignition charger element for ignition spark energy which serves the accumulation and provision of energy to generate an ignition spark. Moreover, the arrangements cover a trigger which scans the alternating current which is designed to activate an ignition circuit which is discharged with the primary coil of an ignition transfer interacting with an ignition charger element. The trigger has a circuit or other module to limit the revolution speed of the motor and this revolution limiter module works with a trigger charger element which is charged from a source of alternating current from the magnetic generator which can be discharged by at least one path for activating the ignition circuit. Further more, the invention refers to a revolution threshold regulator or toggle switch for same.
2. Description of the Related Art
As is known, an ignition spark is generated using an ignition module with which one revolution of the crankshaft of a machine is initiated. Hand-held tools with motors or combustion engines are already used, whose ignition is connected with a revolution governor in order to prevent too many revolutions as a result of failure or incorrect use. Too many revolutions can endanger the motor and the user. In order to limit the revolution speed of the motor, no ignition sparks are produced by the ignition device or ignition module above a preset revolution. The preset revolution upper limit is only slightly above the working revolution speed. This requires a precise revolution working limit with a narrow tolerance so that the ignition does not stop during normal operation.
However, current ignition modules with revolution limiters are relatively expensive. The accuracy of the revolution limits depends, on the one hand, on the accuracy of the parts used and their tolerances and, on the other hand, on the control and electricity supply of the energy for the revolution limiter circuit. This energy comes from the ignition spark generation. This problem has already been approached in patent publication WO 96/23 971 and U.S. Pat. No. 4,538,586. A substantial role in triggering the ignition process and thus also for the revolution limiter is the so-called ignition thyristor which ensures that the charged ignition capacitor connected to the ignition transformer or transfer is suddenly discharged. The ignition thyristor is not only used to trigger the ignition process but also to prevent the ignition trigger processes in order to limit the number of revolutions. This is managed by the energy for the ignition capacitor, which is induced by a charge coil, and is short circuited by the ignition thyristor so that the ignition capacitor is not charged.
We further refer to the current state of the technology in DE 196 45 466 A1, DE-AS 19 54 874, EP 0 584 618 A2 and U.S. Pat. No. 4,449,497.
DE-AS 19 54 874 has an ignition device for a motor where a switch with anode-cathode paths can be controlled in the conductive state when a maximum revolution speed is exceeded. In order to guarantee a defined switch through of the anode-cathode paths when the maximum admissible revolution is exceeded, the named publication suggests connecting a Zener diode to the control electrode of the ignition thyristor, whose anode is connected to the control cathode and whose cathode is connected to a monitoring capacitor. The effect of the Zener diode with the trigger capacitor, which provides energy for controlling the ignition thyristor, however, is not mentioned.
DE 196 45 466 A1 includes an ignition circuit for a motor with trigger coil and trigger capacitor which is charged therefrom. The control connection of an ignition thyristor to discharge the ignition capacitor charged from one of the ignition coils is controlled via a potentiometer-type resistor together with the charging of the trigger capacitor. In order to guarantee a precise and constant number of revolutions despite the longer duration of the ignition spark, connecting a Zener diode in blocking direction to earth in parallel to the trigger capacitor is planned whose Zener voltage drops out at the potentiometer-type resistor. As a result, the capacitor voltage is limited to the voltage of the Zener diode to approximately 120 Volts. The trigger capacitor, the Zener diode and the potentiometer-type resistor are connected in parallel in the known ignition circuit. The decisive factor in the situation of the maximum admissible revolution is the ON period activated by the trigger capacitor at the control input of the ignition thyristor. Its end is determined by the size of the trigger capacitor and the resistances of the potentiometer-type resistors, as well as by the sensitivity of the control input of the ignition thyristor and the amplitude of the alternating current which charges the trigger capacitor. The use of a sole parallel Zener diode in accordance with the known suggestion does not produce a sufficient avoidance of time fluctuations in the revolution limit. For example, with the ignition thyristor, the input lines which set the sensitivity differ from version to version. In the revolutions limiter circuit according to the design, the gate control current typically fluctuates between, for example, 200 nA and 1 &mgr;A. A control threshold voltage of, for example, 700 mV can fluctuate by ±150 mV, which in turn affects the current sensitivity in the circuit of the control input of the ignition thyristor. The sensitivity of the ignition thyristor is defined by the gate control current at which the thyristor switches through. The control threshold voltage does not change the sensitivity of the thyristor (based on its control current) but it does influence the gate control current in the circuit. In order to keep these effects as small as possible, the resistances of the potentiometer-type resistors are optimised according to the known suggestions and operate the revolution limitation with a relatively high control energy. Generally, typical values for the trigger capacitor are 220 nF, with the charge voltage being between 100 and 150V. In the discussed publication DE 196 45 466 A1, the charge voltage of the trigger capacitor is given as 120V.
The invention is based on the task of reducing the tolerances and inaccuracies in limiting the revolutions which are caused by the parts used in the revolutions limiting module and also the control energy required for the ignition circuit. In particular, the dynamics of the revolution-limiting module should be increased considerably if the working point is within the deviating control area of the ignition circuit.
As a solution, it is proposed, for the arrangement with the features discussed at the start, that a series Zener diode, which is operated in the blocking direction, be connected to the ignition circuit or its control input from the trigger charger element when it discharges a control current. The proposal differs from the statement in the patent publication mentioned above, DE 196 45 466 A1, because the control input of the ignition thyristor, according to the latter, is activated by a trigger capacitor via a potentiometer-type resistor—without the serial circuit for a Zener diode.
To increase the accuracy of the revolutions limiter further and, in particular, to compensate for unavoidable fluctuations in the available series Zener diodes, especially within their Zener breakdown voltages, after developing the invention, it is planned that a similar parallel Zener diode in the blocking direction be connected against the trigger charger element such that the charge voltage from the trigger charger element, especially for the trigger capacitor, is limited to the sum of the Zener breakdown voltages of the two Zener diodes. Preferably, the two Zener diodes will come from the same manufacturer so that they have the same electrical chara
Foster Frank H.
Kremblas, Foster Phillips & Pollick
Mohanty Bibhu
Prüfrex-Elektro-Apparatebau Inh Helga Müller, geb. Dutschke
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