DE2338875A1 - FUEL METERING SYSTEM FOR COMBUSTION MACHINES - Google Patents

Description

R. 16 2 4 ·;
July 31, 1973 Su / Kb

Attachment to. Patent and
Utility model registration

ROBERT BOSCH GMBH, Stuttgart

Fuel metering system for internal combustion engines

The invention relates to a fuel metering system for Internal combustion engines with a fuel tank and a fuel line leading from this to the intake manifold, with the amount of fuel metered in for the amount of air flowing through the intake manifold by the pressures in the fuel tank as well as i * ird in the intake manifold and at which the pressure in the fuel tank can be changed by means which is dependent on engine parameters, in particular on the output signal of the composition of the exhaust gas detecting measuring probe controlled v / ground.

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Robert Bosch GmbH Stuttgart

Given today's technical requirements, the purpose of such fuel metering systems is for an internal combustion engine to automatically create a favorable fuel-air mixture ratio under all operating conditions in order to so to burn the fuel as completely as possible, and thereby with the highest possible performance of the internal combustion engine or the lowest possible fuel consumption to avoid or greatly reduce the formation of toxic exhaust gases. For this purpose, the amount of fuel must meet the requirements of each operating condition the internal combustion engine are accordingly measured very precisely. So it must be the average best proportionality between the amount of air and the amount of fuel can be changed as a function of engine parameters, in particular exhaust gas values, which is the case with the initially described Fuel metering system takes place by changing the pressure in the fuel tank.

The invention is based on the object of developing a fuel metering system mentioned at the outset, in which a Such a change in the pressure in the fuel tank can be achieved with advantageous and inexpensive means

This object is achieved in that the Air space of the fuel tank through air lines with controllable cross-section with the intake pipe sections before and after is connected to a throttle point provided in the intake manifold and the cross-section control as a function of the output signal the measuring probe can be determined, a chamber with a constant fuel fill level serving as the fuel tank can, which is preferably controllable by a float. The pressure in this air space then arises depending on the steer

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Robert Bosch GMbH Stuttgart

cross section in the air lines to a pressure that is lower than the pressure before the throttle point of the intake manifold and usually higher than the pressure after the throttle point. In the rest position there should be a pressure in the air space,. which is 20 % lower than the pressure in the intake manifold upstream of the throttle point. This enables the air sucked in by the engine to be enriched with fuel by up to 10 % , a range that is sufficient for sensor control.

According to an advantageous embodiment of the invention a change in the cross section in one air line an opposite change in the cross section in the other air line result, the air lines being advantageously controlled by a three-way solenoid valve can, which is preferably designed as a membrane valve, in which the membrane as a movable valve part between the mouths of the air lines in the valve housing and depending on the excitation current, the opening time cross-section per Muzzle corresponds to the excitation current. In this case, the membrane can either have different divisions (Proportional character) or alternately close one mouth each (integral character).

According to another advantageous embodiment of the invention, a solenoid valve is plugged into each of the two air lines * tet, which iöt closed in the rest position. An oxygen sensor, which consists of a oxygen-ion-conducting plague electrolyte - preferably zirconium dioxide - consists of microporous platinum layers on both sides is vaporized, one side of which is in contact with the outside air, the other with the exhaust gases, whereby, a potential difference occurs between the platinum layers,

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Robert Bosch GmbH Stuttgart

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as soon as the oxygen partial pressure of the outside air deviates from that of the exhaust gas. This potential difference • changes abruptly in the area of the air ratio X = 1.

According to the invention, the lower and upper threshold values of this potential difference can be used for the clocked control of one solenoid valve each, which brings about an integral control character. The use of two solenoid valves that work in a clocked manner prevents the air ducts from creating a bypass that could interfere with the control behavior of the system. Basically, however, the cross-section of the air lines is chosen so small that the amount of air flowing through as if through a bypass is less than 5 - 10 % of the amount of idle air of the motor vehicle engine and can therefore be controlled by the probe control.

Two embodiments of the subject matter of the invention are shown in greatly simplified form in the drawing and are described in more detail below. Show it:

Fig. 1 shows the first embodiment with a diaphragm control valve for controlling the air lines,

Fig. 2 shows the second embodiment with solenoid valves works in the air ducts,

Fig. 3-6 show diagrams for various control options the solenoid valves.

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Robert Bosch GMBH
Stuttgart

In a suction pipe 1, an air measuring element 2 and an arbitrarily actuatable throttle valve 3 are arranged one behind the other. The air measuring element 2 controls the opening cross section 5 of a fuel metering point at which a line 6 ends with a needle 4. The line 6 protrudes into a fuel tank 7 and its end facing away from the metering point 5 is immersed in fuel. The air space 8 above the fuel can be connected to lines 11 and 12 via a line 9 and a valve 10. The line 11 leads from the valve 10 to a point in the suction pipe in front of the air measuring element, the line 12 to a point after the air measuring element, but before the throttle valve 3. The valve 10 is designed as a diaphragm solenoid valve in which an armature lh via a solenoid 13 which is at least a part of the diaphragm 15 is actuated. The membrane 15 is arranged between two seats 16 and 17 which are located at the ends of the lines 11 and 12. In the membrane 15 openings 18 are provided through which the air can flow from the line 11 to the line 9 unhindered. Like in Pig. I not shown in more detail, the magnetic coil 13 is controlled by the amplified current of a measuring probe arranged in the exhaust pipe of the motor vehicle. Depending on the strength of the excitation, the armature IM, which closes the seat 17 in idle mode, is pulled against the seat 16, the line 11 being opened and the line 12 being more or less closed.

The actuation of the armature 1 * 1 is also conceivable in a clocked manner, d. H. that the movable valve part closes one of the seats 16 or 17 alternately. In any case, the Air space 8 of the fuel tank 7 more or less the pressure prevailing in the intake manifold 1 before or after Metering point 2 exposed.

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Robert Bosch GMBH
Stuttgart

In the embodiment shown in Fig. 2 are of the fuel metering opposite Pig. I only the line 9, which is in contact with the liquid container, and the control lines 11 and 12 ending in the suction pipe are shown. In this embodiment, the lines 11 and 12 are controlled by solenoid valves 20 and 21, which can alternatively and simultaneously open and close. In an exhaust pipe 22, the measuring probe 23 is arranged, which consists of a tube 2k which is closed on one side and which is made of a solid electrolyte, for example zirconium dioxide, by sintering. The tube 24 is vapor-coated on both sides with microporous platinum layers 25, which are provided with contacts, not shown, which can have an electrical potential. The tube is in contact with the outside air on the one hand and the exhaust gases from the vehicle on the other. The solid electrolyte conducts oxygen ions at higher temperatures, such as those prevailing in the exhaust gas flow.

When the oxygen partial pressure of the exhaust gas from the oxygen fpartial pressure of the outside air deviates, then occurs between the two platinum layers or between the terminals, not shown, a potential difference with a characteristic curve that depends on the air ratio X. This potential difference depends logarithmically on the quotient of the oxygen partial pressures on both sides of the solid electrolyte. Therefore, the output voltage of the oxygen sensor changes in the closer range of the air ratio λ = 1.0 suddenly. At X> 1.0 This is because unused oxygen suddenly appears in the exhaust gas. As a result of the strong Dependency of the output voltage of the sensor on the

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Air ratio, the oxygen sensor can be used extremely well to control the above-mentioned solenoid valves. The 0 “probe voltage is large in the range% - <1, and small in the range Λ> 1.

According to the invention for controlling the solenoid valves only the large and small voltages are used, each from a certain threshold value. In this way the pressure in the air space 8 of the fuel tank 7 is changed until an air ratio A «1 is reached, which has proven to be particularly favorable and a stoichiometric mixture of air volume and fuel volume is equivalent to. In order to obtain the desired regulation, the solenoid valve 20 is below the low voltage the lower threshold limit and the solenoid valve by the high one above the upper threshold limit Voltage controlled. When the valve 20 is opened, the pressure in the fuel tank 7 and the proportion of fuel rise increases, but when the solenoid valve 21 is turned on, the proportion of fuel decreases.

Figures 3 ~ 6 show diagrams showing the Better visualize the puncture of the regulation and show the probe voltages or control voltages over time are. In Fig. 3, the probe output voltage is in the upper diagram shown with their jump-like course. The horizontal lines Sl and S2 represent the upper and lower Threshold value. For the control of the solenoid valves only those above or below this threshold value limits exploited existing tensions. As soon as the voltage rises above the line S1, or below the line S2 decreases, one of the solenoid valves is actuated as it is on

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Robert Bosch GMBH
Stuttgart

the two lower diagrams of the Pig. 3 is shown. While the pulses in the middle diagram apply to solenoid valve 20, those in the lower diagram apply to solenoid valve 21. The switch-on times of solenoid valves 20 and 21 can always be either ti or t2, as shown, i.e. the switch-on time is controlled by the probe , the switch-off time occurs after the time ti or t2. This ', -. can be an advantage if fast but even switching times are required.

As shown in Fig. 2, are in the circuit between Probe 23 and solenoid valves 20, 21 threshold amplifier 26 and 27 arranged, each only reacting to the high or low voltages and these accordingly amplify for the control of the solenoid valves. However, it can also be advantageous to use the threshold amplifiers upstream a pulse shaper stage 28 by a clear rectangular shape is generated from the erratic curve shape of the probe voltages, which <fenn over an integral regulator stagej is divided into uniformly rising and falling curve sections, from which then through the threshold amplifiers, the high or low voltages are separated.

In Pig. M is the voltage curve in the second diagram shown after a pulse shaper stage, in the third diagram after the integral controller stage.

So that the threshold voltages from the integral controller are neither exceeded too far upwards nor too far downwards, it is advisable to limit the voltage by means of a component of the integral controller, as a result of which a better re-

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Robert Bosch GMBH
Stuttgart

gel behavior is achieved and the solenoid valves 20, 21 are switched off again quickly after the probe voltage has been reversed will. In Pig. 5 corresponds to the first diagram of the voltage after the pulse shaper stage, the second diagram the voltage according to an integral regulator with voltage limitation.

The integral regulator can also be designed in such a way that, when the voltage direction is reversed, it delivers a steep voltage jump with the an existing hysteresis of the threshold amplifier can be skipped. In Fig. 6 is the first diagram the integral regulator output voltage shown for a such a trained controller.

If the voltage profiles of the probe 23 shown in Figures 3 to 6 over the time considered _s so that resulting from the exhaust frequency of the motor a Periodisität, which has a large frequency with correspondingly small wavelengths at high speed and appropriate for low speed large wavelengths. In an embedded catalytic converter connected downstream of the engine, these alternately more rich and lean exhaust gas surges, which occur at a high frequency, are processed well, while slow exhaust gas changes, i.e. large wavelengths, cannot be processed as well.

To these low frequencies or long wavelengths, evoked to reduce dead times of the carburetor in connection with the intake manifold, engine and exhaust system is according to the invention, As shown in Fig. 7, the suction pipe section before

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Air measuring element 2 and after the throttle valve 3 are connected to one another by a bypass 35, which is controlled by a solenoid valve 36 is controlled. The solenoid valve 36 in turn can preferably controlled by the probe 23 using the same electronic device as used for Control of the pressure in the fuel tank 7 is present. This control reduces the dead time of the entire Regulation. It acts correspondingly quickly and results in the desired rapid change in exhaust gas from rich to lean. As a first approximation, this air bypass control only has an additive effect on the air ratio λ, i.e. at low throughputs long wavelength, is their influence great, at high throughputs, that is, high frequency, its influence is small. For this reason, it compensates for the disadvantages mentioned. The solenoid valve 36 can operate analog or digital and will in practice be adapted to the operation of the valves 20 and 21. It can also be controlled instead of the oxygen measuring probe to be operated depending on the engine speed or the ignition frequency. This would result in the additive air bypass control get a share proportional to the speed.

She could get a load-dependent share if im Bypass an intake manifold pressure-controlled throttle would be arranged.

In the control of the solenoid valves 20 and 21 described above, this exhaust frequency of the engine has a disadvantageous effect in that the opening times of the solenoid valves are unequal due to the different wavelengths, so that a direct influence of the speed and thus also the load on the Control time is available. The mixture flow rate of an engine varies for example in the ratio 1: 30 to 1: 40, so that it takes different lengths of time until the effect of the described control interventions by the probe displayed correctly JP ^ emäß one embodiment of the invention is, therefore, the speed-dependent part _(which from the

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Running times and dead times resulting in mixture throughput are eliminated, so that only one variation in the Ratio of about 1: 5 to 1: 6 can be taken into account when determining the time response of the control system got to. According to the invention, the opening time of the solenoid valves 20 and 21 is therefore dependent on the ignition time controlled and the opening time of the respective valve ■ by the probe voltage curve. An electrical circuit, which can be used for such a control is shown in DOS 2 202 61 14. There is through the distributor under certain circumstances the switch-on pulse for one of the valves 20 or 21 is given with a delay element, the opening time of which is then controlled as a function of the probe voltage. Here the second opens Valve when the first one has closed. The total opening time will advantageously be kept constant in order to to prevent any fluctuations in the pressure build-up in the air space 8 of the fuel tank 7. Because the valves naturally In each case a different amplitude of the wave belonging to the engine suction stroke frequency can be ordered according to the invention the control sequence of the valves could also be changed, i.e. instead of the control sequence of the valves 20, 21 per wavelength they also be 21.20. Such a change of the Corrections would be possible for the tax consequences. In any case, the switching on by the timer 37 (ignition distributor)

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be placed in one section of the engine suction strokes in order to obtain the highest possible effective pressure for the pressure control of the fuel tank 7, which is free from the effects of engine valve overlaps. The electronic control unit designated in FIG. 7 with then contains control elements as they were described for FIG. 2, but as they are primarily described in DOS 2 202 61 14.

According to a further embodiment of the invention, the change in pressure in the fuel tank 7 and thus

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the change in the fuel-air mixture supplied to the internal combustion engine use to obtain an enrichment of this mixture when the internal combustion engine is cold. For this purpose, a temperature sensor 39 measured the engine temperature in order to then determine the change in the control times of the valve 20 or 21 obtain the fuel-air mixture change. Circuits that could serve this purpose are in the German U.S. Patent 1,528,5O6. The corresponding circuit could be arranged in the electronic control unit 38.

The whole system according to the invention, namely the air pressure control in the fuel tank 7, depending on the output voltage of a measuring probe in the exhaust, is used to regulate the fuel-air mixture ratio, which is fed to the engine. Less is used for gross changes in the air-fuel ratio intended because the available pressures and opening times are too low for this. To that extent will it is also used as a warm-up firing primarily for fine control to serve. The coarse warm-up control is as usual via a bimetal or other thermocouple take place, for example up to a temperature of 20 C. The exhaust probe-dependent If necessary, the control does not set until the warm-up period has ended taxation.

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Claims (27)

16 2 4 Robert Bosch GmbH Stuttgart - 2338875 claims 1.! Fuel metering system for internal combustion engines, with a fuel tank and a fuel line leading from this to the intake manifold, in which the the amount of air flowing through the intake manifold, the amount of fuel metered by the pressures in the fuel tank and is determined in the intake manifold and in which the pressure in the fuel tank can be changed by means which is dependent on engine parameters, in particular on the output signal of the composition the measuring probe determining the exhaust gas, characterized in that the air space (8) of the fuel tank (7) through air lines (11, 12) with controllable cross-section with the intake pipe sections is connected before and after a throttle point (2) provided in the suction pipe (1), and the Cross-sectional control can be determined as a function of the output signal of the measuring probe (23). 2, fuel metering system according to claim 1, characterized in that the fuel tank (7) contains fuel of constant filling height, which is preferably - " controllable by a float. • -14- ,; ' _ 50 9 810/0386 originally inspected 16 2 4 Robert Bosch GMBH Stuttgart 2338875 3. Fuel metering system according to claim 1 or 2, characterized characterized in that the throttle point (2) in the intake manifold (1) a largely constant one regardless of the air flow rate Causes pressure drop. 4. Fuel metering system according to one of the preceding an. Proverbs, characterized in that as a throttle point (2) an air meter is used. 5. Fuel metering system according to one of claims 1 to 4, characterized in that a change in the cross section in one air line (11, 12) results in an opposite change in the cross section in the other air line (11, 12) (Fig. 1) _s generating a variable pressure in the float chamber. 6. Fuel metering system according to one of the preceding claims, characterized in that the air lines (11, 12) are controlled by, in particular, a 3/2-way solenoid valve (10), which is preferably designed as a diaphragm valve in which the diaphragm (15) is arranged as a movable valve part between the mouths (16, 17) of the air lines (11, 12) in the valve housing , "-15- 50111 U / OiIS ORIGINAL INSPECTED · -15- 16 2 4 Robert Bosch GMBH Stuttgart and depending on the excitation current, digital or analog clocked, the opening time cross-section per opening (16, 17) dem Excitation current corresponds. 7. Fuel metering system according to claim 6, characterized in that that in the rest position of the valve (10) connected to the intake pipe section in front of the throttle point (3) Air line (11) is blocked. 8. Fuel metering system according to one of the preceding claims, characterized in that in the rest position of the solenoid valve (10) the air pressure in the fuel tank (7) is lower than the air pressure in the Suction pipe (1) in front of the throttle point (2), 9. Fuel metering system according to one of claims 1 to 4, characterized in that a solenoid valve (20, 21) is connected in each of the two air lines (11, 12), which is closed in rest position. 10. Fuel metering system according to claim 9, characterized in that that the mean float pressure is achieved by applying the float chamber to the pressures (p1 or p3) in a timed manner (p2) corresponds to the cycle ratio of the respective connection time with (pl) or with (p3). 509810/0386 -16- -16- I δ 1 * ■ Robert Bosch GMBH Stuttgart 2338875 11. Fuel measuring system according to one of the preceding Claims, characterized in that an oxygen measuring sensor is used as the measuring probe (23), which consists of a Oxygen-ion-conducting solid electrolyte (24) - preferably zirconium dioxide - consists of both sides with microporous platinum layers (25) are vapor-deposited, one side of which is exposed to the outside air, the other side is in contact with the exhaust gases, whereby a potential difference occurs between the platinum layers, as soon as the oxygen partial pressure of the outside air deviates from that of the exhaust gas and. that this potential difference changes by leaps and bounds in the area of the air ratio X = I. . 12. Fuel metering system according to claim 9 and 11, characterized characterized in that the lower and upper threshold values of the potential difference are clocked to the control each of a solenoid valve (20, 21) serve, causing an integral control character. 13. Fuel metering system according to claim 12, characterized in that that the upper threshold values the Λ "< 1, control the solenoid valve (21) in the line opening into the suction pipe (1) after the throttle point (2) (12) is arranged. -17- 509810/0386 16 2 4 Robert Bosch GmbH -17- Stuttgart ■ -2338875 14. Fuel metering system according to claim 12 or 13, characterized characterized in that the output voltage of the measuring probe (23) in the respective threshold range through corresponding electrical devices responding depending on the difference (26, 27) is reinforced. 15 * fuel locking system according to claim 14, characterized in that that the threshold amplifiers (26, 27) have a pulse shaper (28) for the voltage with the following Integral controller (29) is connected upstream. 16. Fuel metering system according to claim 15, characterized in that that the integral regulator (29) has a component for limiting the voltage upwards and downwards. 17. Fuel metering system according to claim 15 or 16, characterized characterized in that the integral regulator (29) causes a certain voltage jump when the voltage change changes. 18. Fuel metering system according to one of the preceding claims, characterized in that in the air lines (11, 12) additionally arbitrarily changeable throttle points (3.0, 31) are arranged. -18- 509810/0386 -ie-: ^{i62 <} 19. Fuel metering system according to one of the preceding claims, characterized in that the cross-section control of the air lines (11 and 12) by engine parameters, such as ignition timing (Speed) and engine temperature influenced which as output signals from devices (37,39) operating with electrical means into which the output signals the measuring probe (23) processing control device (38) can be entered. 20. Fuel metering system according to claim 9 and 19, characterized in that the opening time of the solenoid valves (20,21) is controlled as a function of the ignition point (37) (exhaust frequency). And the opening time is controlled by the Probe voltage curve is determined. 21. Fuel metering system according to claim 20, characterized in that ,. that the solenoid valves (20, 21) in the middle section of the engine suction strokes are shifted open relative to the ignition point in order to obtain the highest possible differential pressure, free of valve overlap influences. 22. Fuel metering system according to claim 20 or 21, characterized in that the opening sequence of the solenoid valves (20, 21) can be changed per cycle between two consecutive ignition times. -19- 509810/0386 -19- ' ^{6 2} ' 23. Fuel Zuraeßanlage according to any one of claims 20 to 22, characterized in that the sum of the opening times the solenoid valves (20,21) is constant per cycle. 2Ά. Fuel metering system according to one of Claims 20 to 22, characterized in that the opening time per solenoid valve (20 or 21) is constant at least over a specific speed range. 25. Fuel metering system according to claim 19, characterized in that that the output signals of temperature measuring elements (39) are input and that in the warm-up control of the motor, these inputs are quartered out for pinpoint control. 26. Fuel metering system according to claim 25 _S, characterized in that in addition to the warm-up control by means of the electronic control unit, a mechanical warm-up generator, for example with a bimetal, is provided and that preferably the mechanical warm-up generator controls the engine temperature up to 20 ° C and the electronically amplified warm-up generator for the higher temperatures (39) works. 27. Fuel metering system according to claim 25 or 26, characterized characterized in that the exhaust gas probe-dependent control (26 to 28 and 37,38), if necessary, only after the end of the warm-up control begins. 509810/0386