GB2161214A

GB2161214A - Controlling glow plugs in an internal combustion engine

Info

Publication number: GB2161214A
Application number: GB08516354A
Authority: GB
Inventors: Albin Licer; Miran Savli; Alojz Zorjan
Original assignee: ISKRA SOZD ELEKTRO INDUS
Current assignee: ISKRA SOZD ELEKTRO INDUS
Priority date: 1984-07-02
Filing date: 1985-06-28
Publication date: 1986-01-08
Also published as: DE3523607A1; YU115584A; ES8609593A1; GB2161214B; ES544819A0; IT1182484B; IT8567609A0; GB8516354D0; IT8553561V0

Abstract

When a switch S is closed, a comparator 2 causes an astable multivibrator 4 to close a switch 8 thereby supplying power to glow plugs A and lighting a lamp 2. Eventually the voltage across a capacitor C2 equals a reference voltage UREF2 whereupon the comparator 2 causes the multivibrator 4 to switch off the power supply to the glow plugs and also turns off the lamp 2. The engine is ready to be started. When there is no current supply to the glow plugs, they act as thermocouples whose voltage is compared in a comparator 1 with a reference voltage UREF1 to keep the glow plug temperature at that necessary for igniting fuel. An engine temperature probe R5 connected to a comparator 3 turns off the power supply to the glow plugs when the voltage across a capacitor C3 equals a reference voltage UREF3. <IMAGE>

Description

SPECIFICATION Self controlling glow device for an internal combustion engine The invention relates to a self controlling glow device for internal combustion engines, especially diesel engines.

Glow devices are applied to internal combustion engines to attain the thermal conditions forth ignition of fuel. The glow device warms up the combustion chamber before starting the engine, during starting and thereafter until defined operation conditions of the engine have been attained, whereat in a definite operational and time interval the glow plug temperature is automatically controlled by the circuitry according to the invention.

A self controlling glow device circuitry is known from U.S. Patent 4,307,688 (General Motors Corporation), where a circuitry similar to the invention is presented. Afterthe device has been turned on, the glow plugs begin to glow at a preset temperature, and this temperature is maintained by pulse power supply until the alternator voltage has attained a preset value. A pulse power supply is used since the glow plugs belong to the voltage class lower than is the voltage class of the accumulator battery or the alternator. The desired glow plug temperature is previously set through an analogue voltage level applied to one comparator unit. To the other comparator input there is applied an analogue voltage level proportional to the actual glow plug temperature, which is detected by a probe screwed into the engine casing.The comparator input signals result in the comparator output controlling the pulse power supply to the glow plugs.

The probe itself is built of elements, as e.g.

resistors and the positive temperature coefficient (PTC) resistors. They indicate the glow plug temperature. Power is supplied simultaneously to the glow plugs and to some of the resistors and of the PCT-resistors, which results in a voltage rise of the probe output. The power supply is interrupted when the probe output voltage exceeds the voltage level preset in the comparator. The glow plug temperature begins to decrease. At the same time the probe output voltage drops until the preset voltage level has been reached. Then the power supply is turned on. This procedure is repeated periodically. The device is turned off when the alternator voltage attains the preset value, i.e. when the engine begins to operate independently.

The German Patent according to DE 3.033.540 (The Champion Spark Plug Co., U.S.A.) covers a circuitry which is drawn up in a different manner.

Here the glow plug temperature is obtained experimentally. When the device is turned on power is supplied to the glow plugs and to the oscillator circuit oscillating with the frequency dependent upon the accumulator battery voltage. After 7 sec, approximately, corresponding to a definite number of pulses registered by the counter, the desired plug temperature is reached and the power supply is turned off. To maintain this temperature, afterwards power is supplied to the glow plugs pulsewise in such mannerthat longer or shorter voltage pulses are generated by the oscillator circuit, they being through the amplifier and the relay conducted to the glow plugs. The pulse length is chosen in a manner that the desired glow plug temperature is maintained.The electronic circuit according to this patent is very complicated regarding the determination of the glow plug temperature.

There is thus a need for a generally improved circuitry enabling the glow plugs and the combustion chamber to reach the fuel ignition temperature faster than by known glow devices.

Additionally, the glow plugs should be protected against fusing without any additional temperature probes. Further, the glow plug temperature should warm up the combustion chamber also after starting the engine until the limit of the operation conditions has been reached.

According to the invention there is provided a self controlling glow device for an internal combustion engine, composed of a control circuit and one or more glow plugs, wherein the glow plugs, constructed as thermocouples, are through an electronic power switch and an overcurrent protection circuit connected to the non-earthed terminal of an accumulator battery, which terminal is additionally through a switch and a voltage stabilizing circuit and through resistors connected in series and a negative temperature coefficient resistor, connected to earth, and through a resistor and capacitor connected to earth; wherein the connecting point of the latter resistor and of the latter capacitor is connected to a first input of a first comparator and a second terminal is connected to a second input of the first comparator, whereby its output is connected to the input of a power amplifier and to a first input of an astable multivibrator and the output of the power amplifier is connected through a control lamp to earth, wherein the connecting point of a further resistor and of a further capacitor is connected to a first input of a second comparator, a third terminal is connected to a second input of the second comparator, whereby the output of the second comparator is connected to a second input of the astable multivibrator, wherein the glow plugs are through a second amplifier connected to a first input of a third comparator and a first terminal is connected to a second input of the third comparator, whereby the output of the third comparator is connected to a third input of the astable multivibrator; and wherein the output of the astable multivibrator is through a second power amplifier connected to the electronic power switch and the output of the overcurrent protection circuit is connected to the first input of the second comparator.

According to another aspect of the present invention, there is provided a self controlling glow device for an internal combustion engine, including at least one glow plug connectible in communication with a combustion chamber of the engine and constructed to function as a thermocouple in the absence of an electric current supply thereto to sense the temperature in the combustion chamber and as a glow plug when electric current is supplied thereto to heat the combustion chamber, the device including a control circuit connectible to a source of electric current, which control circuit includes an astable multivibrator, and comparators operative to receive inputs from the glow plug functioning as a thermocouple, compare them with reference values, and pass a control signal to the astable multivibrator to supply pulses of electric current to the glow plug to heat the combustion chamber.

The self controlling glow device of the invention is composed of a control circuit and glow plugs. The glow plugs are constructed so that at no power supplied to them they function as a thermocouple, whose voltage for the control circuit represents the main input variable for the regulation of the glow plug temperature. The intervals of the power supply to the glow plugs are defined on the basis of the thermocouple voltage at the input of the control circuit. In this way it is reached that the glow plugs flow in a definite temperature interval below the glow plug fusing temperature until the lower engine operation limit has been reached. The glow plug as a component of the self controlling glow device circuitry according to the invention is classified into a lower voltage class than the complete circuitry.

When no energy is supplied to the glow plug its heating element functions as a thermocouple having a plus pole either on the casing or on the central electrode. The glow plug is manufactured conventionally and may be of one-pole or two-pole type. Regarding the described properties a glow plug can be used to sense the temperature of the combustion chamber during the continuous operation of the engine or indirectly to control the quality of fuel burning in the combustion chamber of the engine.

The invention will now be described by way of an example with reference to the accompanying drawings, in which: Figure 1 shows a self controlling glow device according to the invention; and Figure 2 shows a time diagram of the operation of the device of Figure 1.

The self controlling glow device of the invention shown in Figure 1 is composed of a control circuit B and glow plugs A. The control circuit B is composed of voltage comparators 1, 2, 3, astable multivibrator 4, amplifier 5, power amplifiers 6, 7, electronic power switch 8, overcurrent protection circuit 9, voltage stabilizing circuit 10 and pertinent resistors and capacitors to form the reference voltages as will be described hereinafter.

Figure 2 represents the operation of the self controlling glow device circuitry. The variation ts of the glow plug temperature and the function curve F(8) of the power switch are shown. The level 1 represents the power switch turned on, the level 0 representing the power switch 8 turned off. Further, by Ta the time interval in which the glow plug temperature attains the desired value, by Tb the power supply time interval (experimentally preset), and by Tc the time interval with zero power supply (the glow plug temperature drops to the preset value) are represented.

By closing the contacts of the switch S, which can be a known automobile starting switch or any other one-pole, one-position switch, the voltage of the accumulator battery AK is brought to the voltage stabilizing circuit 10. In this way power is supplied to the complete control circuit B, and the reference voltages Urefl, Uref2, Uref3 attain the prescribed values. The output voltage of the comparator 2 is brought to the input a of the astabl miltivibrator 4 and locks its operation so that on the output of the astable multivibrator 4 there appears the voltage activating the power amplifier 6 which turns on the power switch 8 connecting the glow plugs A through the overcurrent protection circuit 9 with the accumulator battery AK.At the same time the output voltage of the comparator 2 brings about such operation of the power amplifier 7 that the control lamp Z on its output glows up.

Power is supplied to glow plugs A until the voltage on the capacitor C2 which is through the resistor R2 and the switch S connected to the accumulator battery AK has attained the value Uref2. The voltage Uref2 is brought to the input b and the voltage of the capacitor C2 is brought to the input a of the comparator 2. At that time the comparator 2 changes the voltage level on the input so that it no longer influences the operation of the astable multivibrator 4 which through the power amplifier 6 turns off the power switch 8 which turns off the glow plugs A, and the control lamp Z on the output of the power amplifier 7 stops glowing. This represents a signal that the engine is ready to be started.

When power is supplied to the glow plugs A the output of the amplifier 5 influences the input a of the comparator 1 so that the output of the comparator 1 brought to the input c of the astable multivibrator 4 does not influence the operation of the unstable multivibrator 4. When the power supply to the glow plugs A is turned off (Uc2 = Uref2) the input of the amplifier 5 is subjected to the thermovoltage generated by the glow plugs A now operating as a thermocouple. The thermocouple (about 30mV) is amplified in the amplifier 5 and brought to the input a of the comparator 1, where it is compared to the preset reference voltage Uref1 brought to the input b of the comparator 1. The preset reference voltage Urefl is proportional to the glow plug temperature needed for the ignition of fuel. The amplified thermovoltage slightly exceeds the voltage Urefl.

For this reason the output of the comparator 1 attains the voltage which through the input c locks the astable multivibrator 4. Afterthe amplified thermovoltage on the input a of the comparator 1 has decreased to the voltage Urefl (the glow plugs A are turned on) the output of the comparator 1 attains such voltage that this voltage brought to the input c opens the astable multivibrator 4. By positive pulses the astable multivibrator 4 influences the power amplifier 6 controlling the electronic power switch 8.The duration of the positive pulses of the astable multivibrator 4 is so chosen that in general only one pulse is needed to raise the glow plug temperature, which is lower than the plug destruction temperature, and thereby also the amplifies thermovoltage rises above the voltage Urefl. During the negative pulse on the output of the astable multivibrator 6 (power supply to the glow plugs A) the above-described process of the comparation of the amplified thermovoltage to the voltage Urefl is repeated with the consequence that the output of the comparator 1 attains the voltage level resulting from the comparation of the inputs.

In the case that the glow plugs A do not reach the desired temperature after one positive pulse the amplified thermovoltage remains lower than Urefl and the output of the comparator 1 does not influence the operation of the astable multivibrator 4 so that power is supplied to the glow plugs A during one or several following pulses, which results in rising the glow plug temperature and the amplified thermovoltage to the level Urefl.

It follows from the above that the glow plugs A attain the needed fuel ignition temperature after the switch A has been turned on. By the pulse power supply the glow plugs maintain this temperature.

This process is turned off when the engine reaches the lower operation limit.

When the contact switch S is closed the output of the comparator3 attains such voltage level that it, brought to the input b, does not influence the operation of the astable multivibrator 4.

Simultaneously the capacitor C3 begins to be loaded through the resistor R3 until its voltage has attained the value Uref3 related to the environment temperature of the combustion engine or of the engine itself, in dependence upon the place where the temperature probe R5 (e.g. negative temperature coefficient resistor) is mounted.

The voltage Uref3 is brought to the input b and the voltage of the capacitor C3 is brought to the input a of the comparator 3.

When the condition U03 = Uref3 is fulfilled the output of the comparator attains such voltage level that it, applied to the input b, locks the operation of the astable multivibrator 4, in this way turning off the power supply to the glow plugs A.

In the case of an error in the circuit for the power supply to the glow plugs resulting in a current increase over the normally allowed value, the overcurrent protection circuit 9 is activated, which from the output a immediately loads the condenser C3 to such voltage that U03 = Uref3 and that the power supply to the glow plugs in described manner is turned off.

The astable multivibrator 4 is constructed so that its inputs behave like an OR-function (the presence of the voltage of any input a, b, c causes a change of the state on the output).

The glow plugs A in Figure 1 are represented in a connection in parallel. More or fewer glow plugs may be used. In dependence upon the number of cylinders of the engine, the glow plugs may also be a series connected when they are of a two-pole type.

The self controlling glow device circuitry according to the invention makes possible a much shorter time interval to reach the fuel ignition temperature (about 2 sec in comparison with known circuitries where it amounts to 7 sec). The glow plug temperature is practically independent of the power supply voltage that reflects itself positively in the turning-on time of the starter. The glow plugs remain turned on after the engine has been started until the latter reaches the minimum operation conditions whereby no outside temperature probes are needed to control the power supply to the glow plugs. The electronic circuitry is of moderate price.

Claims

1. A self controlling glow device for an internal combustion engine, composed of a control circuit and one or more glow plugs, wherein the glow plugs, constructed as thermocouples, are through an electronic power switch and an overcurrent protection circuit connected to the non-earthed terminal of an accumulator battery, which terminal is additionally through a switch and a voltage stabilizing circuit and through resistors connected in series and a negative temperature coefficient resistor, connected to earth, and through a resistor and capacitor connected to earth; wherein the connecting point of the latter resistor and of the latter capacitor is connected to a first input of a first comparator and a second terminal is connected to a second input of the first comparator, whereby its output is connected to the input of a power amplifier and to a first input of an astable multivibrator and the output of the power amplifier is connected through a control lamp to earth, wherein the connecting point of a further resistor and of a further capacitor is connected to a first input of a second comparator, a third terminal is connected to a second input of the second comparator, whereby the output of the second comparator is connected to a second input of the astable multivibrator, wherein the glow plugs are through a second amplifier connected to a first input of a third comparator and a first terminal is connected to a second input of the third comparator, whereby the output of the third comparator is connected to a third input of the astable multivibrator; and wherein the output of the astable multivibrator is through a second power amplifier connected to the electronic power switch and the output of the overcurrent protection circuit is connected to the first input of the second comparator.

2. A self controlling glow device for an internal combustion engine, including at least one glow plug connectible in communication with a combustion chamber of the engine and constructed to function as a thermocouple in the absence of an electric current supply thereto to sense the temperature in the combustion chamber and as a glow plug when electric current is supplied thereto to heat the combustion chamber, the device including a control circuit connectible to a source of electric current, which control circuit includes an astable multivibrator, and comparators operative to receive inputs from the glow plug functioning as a thermocouple, compare them with reference values, and pass a control signal to the astable multivibrator to supply pulses of electric current to the glow plug to heat the combustion chamber.

3. A self controlling glow device for an internal combustion engine, substantially as hereinbefore described with reference to the accompanying drawings.