DE2612120A1 - CONTROL SYSTEM FOR MIXTURE CONTROL OF A COMBUSTION ENGINE - Google Patents

Description

PATENT ADVOCATES A. GRÜNECKER

DlPL-ING.

H. KlNKELDEY

DR-INQ.

W. STOCKMAIR

9 R 1 9 1 9 Π DR-INO.

Z 0 I £ I £ U _K SCHUMANN

DR nsi Nat. · Om.-mYS

P. H. JAKOB

G. BEZOLD

MUNICH E. K. WEIL

LINDAU

8 MUNICH 22

MAXIMILIANSTRASSE 43

March 22, 1976 P 10 189

Mssan Motor Company, Limited

Ho. 2, Takara-machi, Kanagawa-ku, Yokohama City, Japan

Control system for regulating the mixture of an internal combustion engine

The invention relates to a control system for setting the air / fuel ratio of a multi-cylinder internal combustion engine supplied air-fuel mixture to a certain ratio. The invention relates to in particular a control system of the aforementioned type, which is equipped with an electromagnetic valve which opens intermittently at a constant frequency each time for a different period of time is to determine the amount of fuel or air delivered into the intake system as a function of a control signal to change which is generated by a sensor measuring the gas concentration in the exhaust system.

One of the basic requirements for internal combustion

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machinery consists of most of the harmful To eliminate exhaust gas components or at least reduce the air / fuel ratio of a the internal combustion engine supplied air-fuel mixture is kept as precisely as possible at a certain value. However, it is quite difficult to get the air / fuel keep the ratio exactly at a constant value when the intake system of the internal combustion engine is not with is equipped with a feedback control loop, since the air / fuel ratio is determined by the physical properties is influenced by air and fuel, such as density and viscosity, these being physical Properties depend on the atmospheric pressure, the ambient temperature and the fuel temperature.

A change in the air / fuel ratio not only leads to changes in the concentrations of HC, CO and NOx in exhaust gas, but also affects the performance of a thermal reactor built into the exhaust system or catalytic converter.

Various feedback control systems have hitherto been proposed which are intended to control the air / fuel ratio with great accuracy. In these systems, the actually existing air / fuel ratio of an air / fuel mixture sucked into the combustion chambers of the internal combustion engine is detected with the aid of a sensor measuring the gas concentration, which can generate an output signal of variable voltage that shows the concentration of a specific exhaust gas component, such as O ₂ , CO, CO ₂ , HC or NOx, since the concentration shown is dependent on the actual air / force ratio of the air-fuel mixture. A

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typical embodiment for a control system of the above Art shown in Pig. 1 to 3, which will be discussed later.

The invention is directed to a control system for adjusting an air / fuel ratio according to FIG To create the aforementioned type, which can be used for a multi-cylinder internal combustion engine and an electromagnetic one Has valve of the on-off type, which is operated at a constant frequency that is the suction frequency each cylinder of the internal combustion engine does not collapse at normal engine speeds.

The invention is also directed to a control system for setting an air / fuel ratio according to of the type described above, in which the operating frequency of the electromagnetic valve is chosen so that this operating frequency does not coincide with the suction frequency any cylinder of the internal combustion engine coincides regardless of the engine speed.

The invention consists in that an additional channel is provided through which a component of the air-fuel mixture the intake system of the internal combustion engine can be supplied to the total amount of air supplied to the intake system relative to change the total amount of fuel supplied to the intake system that in the exhaust system of the internal combustion engine an exhaust gas sensor is arranged, which measures the concentration of a specific exhaust gas component and as a function emits an electrical signal from the measured concentration, the concentration from the air / fuel ratio of the air-fuel mixture burned in the cylinders of the internal combustion engine depends on a control device

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is provided which generates electrical pulses with a constant frequency, the pulse width being individual is changed as a function of the electrical signal emitted by the exhaust gas sensor that an electromagnetic Valve of the on-off type is provided, which the inflow of one component of the air-fuel mixture in the additional channel allows or interrupts by the electromagnetic valve either only the opening state or assumes the closed state when the respective pulses are applied to the valve, and that the constant frequency is such is chosen so that it does not have any frequency with which the intake strokes of each cylinder of the internal combustion engine take place at any speed in the normal driving range.

The constant frequency with which the electromagnetic valve is controlled is preferably greater than a frequency with which the intake strokes of each cylinder take place when the internal combustion engine is at its highest Speed runs in the normal driving range, and is preferably even higher than a frequency with which the intake strokes take place when the internal combustion engine is running at its maximum speed.

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Further features, details and advantages of the invention emerge from the following description of exemplary embodiments based on the drawing. Show in it:

1 shows a schematic representation of an inventive Control system for setting the air / fuel ratio, which is used in a multi-cylinder internal combustion engine Is used, which is equipped with a carburetor;

2 shows a block diagram of the control loop of the invention Control system according to Figure 1;

3 shows a schematic representation of the intake system of internal combustion engine shown in FIG.

Fig. 4 schematic diagrams showing the changes in the Operation of the control system shown in FIG. 1 with regard to the individual cylinders of the in the internal combustion engine shown in FIG. 1 as a function of changes in speed, if an electromagnetic valve of the control system is intermittently opened at a specific frequency will, and

Fig. 5

and FIG. 6 is similar diagrams showing two cases which the same electromagnetic valve works at different frequencies.

In Fig.1 is a conventional four-cylinder internal combustion engine 10 shown, which in a known manner with a carburetor 12, an inlet pipe 14 and an outlet pipe or exhaust 16 is equipped. The carburetor 12 has

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a float chamber 18, a main fuel passage 20 and one in the area of a main venturi section 26 into an intake pipe 24 emptying main fuel nozzle 22. The air is in a manner known per se through a main air duct 28 into a main immersion pipe 20a of the main fuel channel 2O initiated. Reference numeral 30 denotes a main throttle valve.

The control system shown in Figure 1 for controlling the Air / fuel ratio is a typical embodiment of the previously proposed control systems and has an additional air duct 32 which is in the main air duct 28 opens, as well as an electromagnetic valve 34, which ensures that air from the atmosphere into the additional air duct 32 can flow in when the electromagnetic valve 34 is open, or that the additional air channel through the valve is locked. In the outlet pipe 16 there is an exhaust gas sensor 36, which is dependent on the concentration a certain exhaust gas component generates an electrical signal through which the electromagnetic valve 34 over an electronic control circuit 38 is controlled. The electromagnetic valve 34 is an on-off type valve, such as a solenoid valve, so that ^ the air can only get into the additional air duct 32 when the electromagnetic Valve 34 assumes its open state, that is, the setting. The exhaust gas sensor 36 consists of an oxygen sensor of the concentration cell type with an ion-conducting solid electrolyte. The control circuit 38 continuously generates square pulses at a constant frequency so that the electromagnetic valve is opened every time one of these impulses is applied to the valve.

When the electromagnetic valve 34 is in its opening

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position or on position, then the through the main fuel nozzle 22 into the intake pipe 24 is reduced amount of fuel flowing into the main fuel passage 20 supplied amount of air is increased. As a result, the carburetor 12 alternately promotes a relative rich air-fuel mixture or a relatively lean air-fuel mixture into the inlet pipe 14. Since the alternating conveyance of rich and lean mixtures can be achieved with one Repeated considerably high frequency, the combustion chambers of the internal combustion engine 10 is a mixture with a certain Air / fuel ratio supplied, which turns out to be the average ratio from the air / fuel ratios of the rich and lean mixtures. With this rule system becomes the air / fuel ratio of the internal combustion engine 10 controlled in that the duration or width of the individual to open the electromagnetic valve 34 is used Pulses is changed by changing the size of the voltage output by the exhaust gas sensor 36. Because the impulses are generated at a constant frequency, a change in the width of the individual pulses means a change in the ratio of the width of a single pulse to that between the corresponding pulse and the next pulse lying interval.

2 shows, for example, a block diagram for the Control circuit 38 with which such pulses of varied width are produced. This control circuit 38 includes a Amplifier 40 for amplifying the output signals of the exhaust gas sensor 36, a comparator 42 for comparing the amplified output signal with a reference voltage, an oscillator 44, which generates a continuous triangular wave of a certain frequency, a PI control amplifier 46 (proportional and integral) for controlling the output signal emitted by the comparator 42 and a pulse generator 48,

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which generates square pulses with a frequency that corresponds to the frequency of the triangle wave. If the output voltage emitted by the exhaust gas sensor 36 deviates from the reference voltage, which indicates, for example, that the air / fuel ratio actually present in the internal combustion engine 10 is below the intended ratio, then the amplitude of the output signal of the PI control amplifier 46 increasingly decreases, as indicated, for example, by the sketch (B) in FIG. 2 in comparison to a schematic representation of the waveform of the output signal of the exhaust gas sensor 36 by the sketch (A) in FIG. The oscillator 44 generates an uninterrupted constant triangular wave with a constant frequency, which is indicated by the sketch (C), but the width of the individual pulses of the pulse generator 48 decreases differently, as shown by the sketch (D) when the The amplitude of the output signal of the PI control amplifier 46 continues to decrease. These square pulses are usually supplied to the electromagnetic valve 34 via an amplifier 50. It has now been found that the frequency with which the electromagnetic valve 34 is opened intermittently, at the in the Fig.! The control system shown for regulating the air / fuel ratio should be selected in such a way that the maximum operating speed and an average speed of the internal combustion engine 10 are taken into account. In principle, the frequency should be selected as high as possible so that precise control of the air / fuel ratio is achieved. For practical reasons, however, the frequency cannot be increased indefinitely, as would be desirable, since the electromagnetic valve 34 has only a limited sensitivity and / or service life. It is very difficult to increase this frequency significantly above the maximum operating speed of the internal combustion engine 10.

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When the frequency of the movements of the electromagnetic valve 34 is in a certain proportion to a frequency stands at which the respective intake stroke takes place in each cylinder of the internal combustion engine 10, then some certain cylinders have a high probability of always having one of the intentionally manufactured grease and lean mixtures are supplied, while the remaining cylinders are supplied with the other mixture. This phenomenon leads to the fact that two differently composed exhaust gases alternately are discharged from the internal combustion engine 10 into the exhaust pipe. The output from the exhaust gas sensor 36 The output signal is therefore repeated at a very high frequency and increases and decreases considerably, and the fluctuations of the air / fuel ratio are not limited to a desired narrow range in use of the control system shown in FIG. 1 for controlling the air / fuel ratio is expected.

The essence of the invention now consists in limiting the operating frequency of the electromagnetic valve 34 a known control system for setting the air / fuel ratio, the limitation as a function on the intake frequency of each cylinder of the internal combustion engine 10 takes place. The intake frequency depends on the speed of the internal combustion engine and the number of cylinders addicted. As a result, a control system according to the invention does not differ in general construction of the previously proposed control systems for setting the air / fuel ratio, which an electromagnetic Valve for intermittently changing the air / fuel ratio of an internal combustion engine Have supplied air-fuel mixture. That in the The control system shown in FIG. 1 is only an exemplary embodiment known systems in which the invention applies

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is cash. Of course, the electromagnetic valve 34 could also be used to supply fuel to be controlled by an additional fuel duct instead of regulating the introduction of air into the main fuel duct 20. In a further advantageous embodiment, either additional air could be activated by actuating the electromagnetic valve 34 or fuel is supplied to a portion of the intake pipe 24 located downstream of the throttle valve 30 will. To implement the control system according to the invention, only the oscillator 44 of the known control systems is required to be modified.

For the following description of the relationship between the operating frequency of the electromagnetic valve 34 according to FIG. 1 and the suction frequency of each cylinder of the internal combustion engine 10 according to the diagrams shown in FIGS. 4 to 6, it is assumed that the internal combustion engine 10 is formed by a four-cylinder engine and that the inlet pipe 14 has four branches B ₁ to B ₄ , as shown in FIG. The indices 1 to 4 of the branches B ₁ to B _{4 represent} the cylinders No. 1 to No. 4 of the internal combustion engine 10 accordingly. The schematic representation according to FIG. 3 shows that the branches B ₁ to B4 are divided into two groups, one group being formed by the two branches B ^ and B2, while the other group is formed by the two branches B3 and B4 is, and it can also be seen that the two branches (z. BB. And B ₂ ) of each group start from a common channel and are arranged close to each other. The four cylinders No. 1 to No. 4 of this internal combustion engine are ignited in the sequence 2-1-3-4. The maximum operating speed and the idling speed of the internal combustion engine 10 are 6,000 rpm and 750 rpm, respectively. Each of the diagrams shown in FIGS. 4 to 6 shows a particular case,

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at which the proportion of the on-time to the off-time of a cycle * of the on-off movements of the electromagnetic valve 34 is 1: 1.

In Figure 4, the three diagrams (A), (B) and (C) show three Operating states in which the speed of the internal combustion engine is 1500 rpm, 30000 rpm or 6000 rpm, while the electromagnetic valve 34 is operated at a constant frequency of 50 Hz. Circled by each Numbers 1 to 4 indicate a cylinder intake stroke with the corresponding number of cylinders. Because every cylinder of the internal combustion engine 10, one duty cycle per two revolutions of the crankshaft of the internal combustion engine 10 executes, the intake strokes of each cylinder take place at a frequency of 12.5 Hz, if the speed of the internal combustion engine 1500 RPM. In other words, that for four successive suction strokes in the four Cylinders are required 80 milliseconds. Since the electromagnetic valve 34 is opened for 10 ms at an interval of 10 ras 1 to 4, each cylinder becomes both relatively rich and relatively rich during each intake stroke of each cylinder # 1 through # 4 also supplied relatively lean mixtures, as can be seen from diagram (A). As a result, arise no problems if the electromagnetic valve 34 is operated at 50 Hz and the internal combustion engine 10 is operated with a Speed of 1500 rpm runs.

If the speed of the internal combustion engine 10 is 30OO rpm, then the intake strokes of each cylinder take place at a frequency of 25 Hz, and the intake strokes of all four cylinders of a work cycle ¹ take place in 40 ms. As a result, cylinders # 2 and # 3 are always fed with either a rich or a lean mixture while

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the other two cylinders no. 1 and no. 4 are always fed with the other mixture, as shown in the diagram (B) can be found. At the maximum speed of the internal combustion engine 10 of 6000 rpm, the same working cycle takes place in 20 ms, so that the intake strokes of each cylinder take place at a frequency of 50 Hz, that is with the same frequency with which the on-off movements of the electromagnetic valve 34 take place. In this case, two cylinders ignited one after the other, that is cylinders No. 2 and No. 1 are always fed with either the rich mixture or the lean mixture, while the rest Both cylinders No. 3 and No. 4, which are also ignited one after the other, are always fed with the other mixture as can be seen from diagram (C).

In short, are those shown in Diagrams 3) and (C) Appearances are undesirable if the air / fuel ratio is to be precisely regulated. In the operating state in which the internal combustion engine 10 is running at 3000 rpm, each cylinder can, however, also With the help of the configuration of the inlet pipe shown in FIG 14 contrary to the phenomenon shown in the diagram (B) are fed with a mixture that is made up of composed of a rich and a lean mixture. The rich mixture and the lean mixture can be at least in mixed in a certain section of the common channel leading to the adjacent branches B-] and B2, or in a section of the common channel which leads to the adjacent branches B and B. If the arrangement the branches of the inlet pipe 14 differs from the embodiment shown in Figure 3, so that the The rich mixture fed to cylinder no. 1 and the

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the lean mixture fed to No. 2 does not interfere with each other can mix in the inlet pipe 14, then alternately differently composed exhaust gases are in the outlet pipe 16 ejected not only at 6000 rpm but also at 3000 rpm.

The undesirable properties shown in diagrams (B) and {C) are present as long as the frequency of the electromagnetic valve 34 matches the suction frequency of each cylinder at a certain engine speed. In the ideal case, the frequency of the circuits of the electromagnetic valve 34 in the control system according to the invention is selected such that it is greater than the intake frequency of each cylinder at the maximum speed of the internal combustion engine. In the embodiment described above, in which the internal combustion engine 10 is a four-stroke four-cylinder engine, the switching frequency of the electromagnetic valve 34 should be constant and higher than 50 Hz.

The critical frequency, that is 50 Hz in the embodiment described above, depends on the number of cylinders Internal combustion engine. The critical frequency increases proportionally in the ratio of the number of cylinders of a four-cylinder engine to the number of cylinders of a six-cylinder engine and an eight-cylinder engine, so that critical frequencies of 75 Hz or 100 Hz result.

In practical terms, the above-described critical frequencies can sometimes have a serious influence on the control system for setting the air / fuel ratio. From the following description, however, it can be seen that there are practically no noticeable problems even if the switching frequency of the

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electromagnetic valve 34 is slightly below the critical frequency defined above.

In the internal combustion engine in which the invention is used finds, it is preferably a motor vehicle machine. In the previous discussion, assumed that the internal combustion engine 10 is running at the maximum speed, but this is the case with a motor vehicle engine rarely occurs in boroughs. In sparsely populated rural districts, even then, there are none worth mentioning Difficulties arise when the control system shown in Figure 1 for setting the air / fuel ratio works with less accuracy when the internal combustion engine is running at maximum speed. It is very It is important that the air / fuel ratio is exactly the intended one Has value when the machine is operated in city districts so that the exhaust gases do not pollute the ambient air. That is, the rule system to set the air / fuel ratio with must work with great accuracy when the machine is operating at a speed in the normal driving range. If you like it it is assumed that the idling speed of the internal combustion engine 10 at 750 rpm or the maximum speed at 6000 rpm then the middle driving range extends from approx. 1500 rpm to approx. 3000 rpm.

According to the invention it is therefore proposed that the switching frequency of the electromagnetic valve 34 is chosen so that it does not operate with any suction frequency of each cylinder the internal combustion engine 10 coincides at any speed within the normal driving range.

In Figure 5, the diagrams (A) and (B) give the same

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Relationships like the diagrams in Fig. 4 again, with the Exception that the switching frequency of the electromagnetic valve 34 is 12.5 Hz. In this operating state That is, the electromagnetic valve 34 is intermittent during the required for all strokes of the four cylinders 80 ms 40 ms open. If the internal combustion engine 10 with runs at a speed of 1500 rpm, then the strokes of each cylinder take place with the same frequency (12.5 Hz) like the circuits of electromagnetic valve 34, so cylinders # 1 and # 2 always either are fed with the rich mixture or the lean mixture, while the remaining two cylinders No. 3 and No. 4 can always be fed with the other mixture, as shown in diagram (A). This phenomenon is special undesirable, which has already been discussed in connection with the diagram (C) of FIG. Done at 3000 rpm four successive suction strokes of the four cylinders in 40 ms. As a result, each cylinder becomes alternate fed with a rich mixture and a lean mixture as shown in diagram (B). This phenomenon is less undesirable than the phenomenon shown in the diagram (A), but results in two differently composed Exhaust gases are alternately discharged into the outlet pipe 16. When the electromagnetic valve 34 with a frequency of 25 Hz is obtained for the suction strokes of the individual cylinders at Ί500 rpm and 3000 rpm on-off switching of the electromagnetic valve 34, as shown in Figure 6. One cycle of the on-off operations of the electromagnetic valve 34 takes place in these cases in 40 ms. At 1500 rpm, cylinders No. 2 and No. 3 are z. B. always with a lean one Mixture fed, while the remaining cylinders No. 1 and No. 4 are fed with the rich mixture, as shown in the Diagram (A) is shown. This corresponds to the state according to

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Diagram (B) according to Fig. 4 and does not lead to any noteworthy Problems when the inlet pipe 14 is designed as shown in FIG is. At 3000 rpm, cylinders No. 1 and No. 2 are always fed with the lean mixture, as shown in the diagram (B) is shown. This phenomenon is similar to the phenomenon according to diagram (C) of FIG. 4 and leads independently of the Design of the inlet pipe 14 to cause serious problems.

From the above description it can be seen that the problem mentioned that either the rich or the lean mixture is constantly supplied to certain cylinders, then can occur when the frequency of the on-off switching of the electromagnetic valve 34 with a certain suction frequency of each cylinder at a certain engine speed can coincide in the normal driving range. In the case of a four-cylinder internal combustion engine, the switching frequency should of the electromagnetic valve 34 are selected so that they cannot be calculated with a by the formula S / (2 χ 60) Hz Frequency coincides, where S is the speed of the internal combustion engine in rpm in a medium driving range indicates. If the mean driving range is between 1500 rpm and 3000 rpm, then the switching frequency should of the electromagnetic valve 34 are outside the range between 12.5 Hz and 25 Hz. These critical frequencies depend on the number of cylinders, as has already been stated. In a six-cylinder internal combustion engine the frequency ranges from 18.75 to 37.5 Hz and, for an eight-cylinder internal combustion engine, Von 25 Hz to 50 Hz should be excluded if the mean driving range of these machines is between 1500 rpm and 3000 rpm lies.

In practice, the electromagnetic valve 34 is preferably switched at a frequency that is higher than the maximum

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value, which results from the form S / (2 χ 60) Hz, since either the rich mixture or the lean mixture is possibly fed to all cylinders essentially one after the other, as shown in diagram (B) according to Fig. 5, if the switching frequency of the valve is below the minimum value that results from the formula S / (2 χ 60) Hz.

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Claims (5)

P 10 189 Claims .y control system for regulating the air / fuel ratio of an air / fuel mixture supplied to a multi-cylinder internal combustion engine to a specific ratio, characterized in that an additional duct (32) is provided through which a component of the air / fuel mixture is fed to the intake system (14, 24) can be supplied to the internal combustion engine (10) in order to change the total amount of air supplied to the intake system relative to the total amount of fuel supplied to the intake system that in the exhaust system (16)
an exhaust gas sensor (36) is arranged in the internal combustion engine, which measures the concentration of a certain exhaust gas component and emits an electrical signal as a function of the measured concentration, the concentration being dependent on the air / fuel ratio of the in the cylinders (1, 2, 3, 4) the internal combustion engine burned air-fuel mixture depends _e that a
Control means (38) is provided which generates electrical pulses at a constant frequency, the pulse width being changed individually depending on the electrical signal emitted by the exhaust gas sensor, that an electromagnetic valve (34) of the on-off type is provided, which .Allows or interrupts the flow of one component of the air-fuel mixture into the additional channel, in that the electromagnetic valve either only assumes the open state or the closed state when the respective pulses are applied to the valve, and that the constant 609842/0647 Frequency is chosen so that it is not at any frequency with which the suction strokes of each Cylinder of the internal combustion engine take place at any speed in the normal driving range, matches. 2. Control system according to claim 1, characterized in that the constant frequency is higher is the frequency with which the intake strokes of each cylinder (1, 2, 3, 4) of the internal combustion engine (10) take place when the internal combustion engine is within the normal driving range with ■ the highest Speed is running. 3. Control system according to claim 1, characterized in that the constant frequency is higher is the frequency with which the intake strokes of each cylinder (1, 2, 3, 4) of the internal combustion engine (10) take place when the internal combustion engine is running at maximum speed, 4. Control system according to claim 1, characterized in that the additional channel (32) is an additional air channel which opens into the main fuel channel (20) of the intake system (24, 14) of the internal combustion engine. 5. Control system according to claim 1, characterized in that the control device (38) comprises means (42) for comparing the amplitude of the electrical signal with a predetermined reference voltage, means (46) for generating one of the difference between the amplitude and the reference span 609842/0647 -2C- voltage- dependent control signal, a device (44) for generating a continuous triangular wave with the constant frequency and a device (48) for converting the triangular wave into a series of square pulses with the constant frequency, the. Pulse width varies individually, depending on: from. the control signal changes, 609842/0647