JPH0348352B2 - - Google Patents

Description

Claim 1: An internal combustion engine ignition device comprising a preheating plug 11 and means 10, 12 for supplying a heating current to the preheating plug, the preheating plug being connected to one side of a Wheatstone bridge 13, comprising: the supply means comprises an electronic switch 12; said ignition device further has sensing means including a comparator 18 connected to said Wheatstone bridge and detects a predetermined value of the preheating plug in response to the cold state of said preheating plug; a comparator 18 having a first output level corresponding to the resistor set; a test pulse source 25 connected to the Wheatstone bridge; a switch providing current to the first output and to the preheating plug; means 22 responsive to the simultaneous occurrence of one of the test pulses for controlling;
24. An ignition device for an internal combustion engine, comprising:

2. The means for controlling the simultaneous occurrence of said first output and one of said test pulses is a flip-flop circuit 22, whereby the output of said flip-flop is such that upon simultaneous occurrence of said first output and said test pulse; 2. The ignition device according to claim 1, wherein the ignition device is set to a level at which only the ignition occurs.

3. further comprising a source of trigger pulses, said means for responding when said first output and said test pulse occur simultaneously, said switch means for supplying power to said flip-flop at a predetermined output level and said preheating plug; 3. Ignition device according to claim 2, characterized in that it comprises gating means (24) responsive to one of the trigger pulses for controlling the ignition device.

4. The switch means is an electronic switch 27, 28.
4. An ignition device according to claim 3, characterized in that the ignition device comprises:

5. The ignition device according to claim 4, wherein the electronic switch comprises a thyristor.

6. The ignition device according to claim 5, wherein the means for supplying heating current to the preheating plug further comprises a generator driven by an internal combustion engine.

7. The generator generates an alternating current, and the test pulse source and the trigger pulse source consist of a monostable flip-flop 25 connected to be triggered by the alternating current, so that the trigger pulse 7. The ignition system of claim 6, wherein current is supplied to said preheat plug to maintain each cycle while said predetermined level occurs simultaneously.

Description This invention relates to an ignition device with a preheating plug used in an internal combustion engine.

Preheating plugs in internal combustion engines rely on a current source to maintain the plug's glow filament in a glowing state. Although the power supplied to the filament is quite low, say 4 watts, the temperature control of the plug must be carefully done to keep the engine running smoothly. In conventional preheating plugs, a battery is used as the current source without the need for a charging device. In small engines, such as those started by rope starters, batteries are a heavy and inconvenient accessory that should be avoided. It has therefore been found appropriate to create an alternative current source for the preheating plug and to incorporate a current control device to maintain the plug at the appropriate temperature.

The invention provides an ignition system with a preheating plug supplied from a generator via an electronic control circuit. Such an ignition device is simpler and cheaper than a conventional spark ignition device or a preheating plug with a battery. Another advantage is that more effective and smoother idle operation is achieved than with spark ignition systems. Preheating plugs are smaller than regular spark plugs and do not require high voltage insulation. The advantages obtained with such a preheating plug device are achieved by implementing it according to the parts characterized in claim 1.

Embodiments of the ignition device according to the present invention will be described below with reference to the accompanying drawings, which consist of FIG. 1 showing a simplified wiring diagram of the ignition device and FIG. 2 showing graphs of voltage characteristics of each part.

The current source consists of a generator 10 driven by an engine with an ignition device. The preheating plug 11 is supplied with alternating current from the generator via an electronic switch 12, which controls the current so that the preheating plug obtains a set heating current. The temperature measurement of the plug is carried out by a Wheatstone bridge 13 on one side of which is the resistance of the preheating plug. The other side of the bridge circuit is composed of two fixed resistors 14 and 15 and a variable resistor 16. This variable resistor allows bridge balancing and plug temperature adjustment, and will be discussed in detail below. A plurality of test pulses are applied from the transistor amplifier 17 to one of the diagonal terminal pairs of the bridge circuit, and voltage pulses are output from the other diagonal terminal pair to which the comparator 18 is connected. This comparator has the equivalent of a differential relay circuit that closes one contact at a higher voltage at the first input 19, but closes the other contact at a higher voltage at the second input 20. , the comparator in this embodiment is the well-known standard module LM339. A signal in the form of a logical "1" or "0" is output depending on which of the two inputs is at its highest state.

This signal is stored in a bistable flip-flop 22, such as the well-known standard module No. 4013, for the duration of at least one cycle of the generator voltage. The stored signal is maintained during this time at the output terminal 23 of the flip-flop 22, for example at the AND gate 24 of the module LM339.
be guided by.

Generation of the test pulses takes place in a monostable flip-flop 25, such as a standard module No. 4098, which delivers a pulse through wire 26 to the transistor amplifier 17 at the beginning of each positive half cycle of the generator voltage. Measurements are therefore taken when no generator current is being supplied to the preheating plug, which is a necessary condition for only test pulses to pass through the bridge circuit during the test period. The generator current is controlled by a switch 12, which in this embodiment is connected to a monostable flip-flop 29 (module) via an AND gate 24.
It is composed of two thyristors 27 and 28 connected in anti-parallel, which receive trigger pulses from the thyristors 27 and 28. These trigger pulses are somewhat delayed compared to the pulses on wire 26, since the thyristor only begins to energize once the test pulse has passed through the bridge circuit. However, upon equilibrium of the bridge circuit, ie, when the temperature of the preheating plug rises above a certain minimum temperature and the pulses from flip-flop 22 disappear, the test pulses are stopped at the AND gate. If flip-flop 22 detects that the preheat plug is too cool during the test period, a trigger pulse is sent through the AND gate. Thereafter, one thyristor conducts during the positive half-cycle and the other thyristor conducts during the negative half-cycle, and the preheating plug is powered by the generator during the entire period. Whether the preheat plug is energized in the next cycle is determined by the test of the bridge circuit during that cycle. The control circuit controls the temperature of the preheating plug so as to maintain it constant regardless of the rotational speed of the generator and the ambient temperature. The temperature level of the preheating plug is varied by adjusting the variable resistor 16 of the bridge circuit.

FIG. 2 shows the voltage at each point in the circuit of this embodiment. The only current source used to power each component is a generator, and the voltage shown is a sine curve. A voltage converter 30, such as the previously described module LM339 with a Zener diode connected thereto, converts the sine curve into a rectangular voltage waveform 31 with a phase lag (hysteresis). The rectangular voltage waveform is applied to flip-flops 29 and 25, which provide a control pulse 32 and a trigger pulse 33, respectively, for testing the bridge circuit.
Output. The flip-flop 29 is triggered from the converter in addition to the flip-flop 25, so that the number of pulse signals 33 is equal to 2 of the pulse signals 32.
It will be doubled. In order to generate potentials and operating voltages for each component in the circuit, a rectifier circuit 34 is provided in which the generated voltage is rectified into complete direct current.

The above-mentioned engine is designed for use in small-sized electric machines such as electric saws and lawn mowers, and is started manually.

The generator is driven by the engine during the start-up procedure and powers the preheating plug so that the glow filament reaches the glow discharge temperature. And that is possible due to the fact that the glow filament has a short heating period (the result is about 4W), and the generator is already running at low speeds (about
1000 r/p/m).
When the engine is running at high speed, the generator is also running at high speed, providing a high voltage that is too high for the preheat plug. Therefore, the voltage to this preheating plug is determined by, for example, a Zener diode or a nonlinear resistor (thermistor) connected in parallel with the generator.
(not shown).

This embodiment is an example in which the present invention is implemented.
In fact, a DC generator can also be used as a current source for the preheating plug and other components.