DE3322209A1 - Starting time limitation for internal combustion engines with fuel injection - Google Patents

Abstract

Circuits are described for starting time limitation for internal combustion engines with fuel injection. During the starting process the mixture is enriched as usual, but once the freely selectable starting time limit has expired the enrichment is prematurely switched off. Unavoidable interference pulses and the voltage ramp on completion of the starting process, characteristic of certain types of starter, can no longer lead to a further mixture enrichment and hence to overrich running of the internal combustion engine. This is made possible by an additional monostable circuit, which is set on starting and is automatically reset on completion of the starting time limit duration. The starting time limiting circuit is especially suitable for motor vehicles with an injection engine. <IMAGE>

Description

R. 18761
05/13/1983 ch / dö

ROBERT BOSCH GMBH, 7000 STUTTGART 1

Start time limit for internal combustion engines with injection

State of the art

The invention is based on a method for enriching the fuel-air mixture for internal combustion engines with fuel injection according to the preamble of the main claim.

Simple start enrichment circuits of this type have recently become known. With the beginning of the During the starting process, a circuit is activated that causes the mixture to be enriched in the injection system. With At the end of the start process, the mixture enrichment should be switched off again.

However, the conventional circuit arrangement has a number of disadvantages. When restarting after a standstill of the internal combustion engine or

When starting an internal combustion engine that has already warmed up, there is a risk that the mixture will become over-rich will. But starters with a permanent magnet can also use the usual start enrichment circuit irritate, because such starters drag a relatively slow decay after being switched off Voltage ramp after. The usual start enrichment arrangement is switched on again by the voltage ramp. Finally, there are also unavoidable interference voltage peaks for retriggering the usual start enrichment circuits.

Advantages of the invention

The inventive method with the characterizing Features of the main claim has the advantage that the start enrichment for the internal combustion engine can be optimally designed regardless of the possibly disadvantageous usages of the user and regardless of the possibly disadvantageous properties the components used in the drive system.

The corresponding advantages are with a device with the characterizing features of the independent claim achievable. It is particularly advantageous that the method can be operated with a relatively simple circuit can be realized.

The measures listed in the subclaims are advantageous developments and improvements of the The method specified in the main claim and the facility specified in the secondary claim are possible. Particularly it is advantageous that one of the other conditions

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independent start enrichment time with the help of a simple circuit is determined and that of This circuit was kept away from all interference pulses by an equally simple evaluation stage ■ become. Retriggering is achieved through sufficient control voltage intervals and through a hysteresis behavior a comparison level as well as a proportionate very high input threshold for the evaluation level switched off. Although the start enrichment time is specified per se, if the start-up process is terminated prematurely start enrichment canceled.

Incidentally, with those also evident from the description of the exemplary embodiments and the drawing advantageous features of the embodiments of Invention over-greasing of the internal combustion engine is reliably avoided. This also means standing still the internal combustion engine is practically excluded when starting and especially when restarting, even if the start-up process takes a relatively long time. There are no more problems when starters with permanent magnet excitation are used. Achieved with permanent magnet starters there is a considerable weight reduction compared to conventional starters with electromagnetic excitation, So far, permanent magnet starters have solved because of them trailed voltage ramp, after the end of the starting process, a start enrichment is carried out again.

Finally, with the method according to the invention and the associated enrichment after the

18761

Post-start enrichment begins at the end of the start time limitation period put in a simple way.

Simpler variants serve to save components and costs. For example, a variant with a simpler amplitude limiting stage for the start signal is specified in which the start signal prepared in this way is used as a trigger signal for the monostable multivibrator. In a further variant, the constituent elements which cause the service life of the monostable multivibrator, placed directly into _a rtsignalleitung St. Finally, interference peaks that can occur at the comparator inputs are advantageously largely suppressed by parallel-connected Zener diodes.

drawing

Embodiments of the invention are shown in the drawing and explained in more detail in the description below. FIG. 1 shows a typical start enrichment circuit in a starting system for an internal combustion engine; FIG. 2 shows a diagram of the input voltage on such a circuit. FIG. 3 is a circuit diagram of an exemplary embodiment of the invention with details of a start enrichment circuit, in FIG. K the voltage profile at various measuring points is shown schematically. Figures 5 and 6 each show a further embodiment of the invention.

R.

Description of the exemplary embodiments

FIG. 1 gives an overview of the components which are used in a conventional starting liner arrangement. An ignition switch 11 is on the one hand via the line ϋ_ _Λ to a vehicle battery (not shown) and on the other hand via a voltage supply line U-. connected to consumers in the motor vehicle · A start relay 13 is connected via a connecting line 12, the start relay 13 is in operative connection with a starter lk . The starter 14 is electrically between the line U "" and the

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Ground line IL .. The actual start enrichment circuit 15 comprises an input resistor R 301, which is connected to the connecting line 12, a switching combination with a voltage divider resistor R 302, a smoothing capacitor C 301 and a Zener diode D 301 and a voltage comparator B k. The input combination is connected to the inverting input B 6 of the comparator B ^. The non-inverting input B 7 of the comparator B k is located on a fixed voltage divider consisting of resistors R 351 »R 352 and R 353 · From the output B 1 of the comparator B k a connecting line leads to an input of a Nachstartschaltung l6 and a connecting line to an addition amplifier 17 · Furthermore, the output B 1 is connected via a resistor R 303 to an input of an acceleration enrichment circuit 18.

In a diagram, FIG. 2 shows schematically the typical profile of the control voltage υ _ς _ at the input of the start enrichment circuit 15 in front of the input resistor R 301.

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The starter Ik is switched on at a point in time T 1 and switched off again at a point in time T 2. You first see the switch-on voltage peak at time T 1, then a voltage dip with a subsequent voltage rise up to time T 2. After that, the starter I ^ is switched off, but the negative switch-off voltage peak is followed by a voltage ramp, which is particularly pronounced in permanent magnet starters Beginning only by a value .DELTA.U less than the battery voltage U ". is.

The arrangement according to FIG. 1 and the mode of operation described below after the ignition contact of the ignition switch 11 has been closed, the individual assemblies receive their supply voltage U _n

On

Closing the start contact of the ignition switch 11 receives the lines 12 and U _s _ voltage; the start relay 13 actuates the starter Ik and the start enrichment circuit 15 is supplied with the control voltage U _qT . The voltage U__ is reduced to a certain value by the voltage divider R 301, R 302, the capacitor C 301 intercepts the voltage peaks and the diode D 301 clamps the control voltage to a predetermined value. A Η signal appears at the input B 6 of the comparator B k and the comparator B k is activated. The addition amplifier 17 is switched on with the output signal B 1. With the aid of the addition amplifier 17, the injection output stage, which supplies the current for the injection valves, is controlled. With the aid of the addition amplifier 17, the basic setting for the enrichment is made. With the output signal B 1, the acceleration enrichment stage l8 is switched on and finally the restart circuit l6 is set. With the help of the restart

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circuit l6 is connected to the internal combustion engine End of the start enrichment time an additional ■ amount of fuel for a further short time delivered.

If, after switching off the starter 1A at time T 2, the control voltage υ _ς _ rises again in an undesired manner, a signal with the potential value H appears again at the input B 6 of the comparator B ^ k. The start enrichment circuit 15 is therefore switched on again, although the starter 1Λ is not operated at all · The start enrichment then continues until the voltage ramp has become sufficiently low. The voltage peaks that arise in the course of the control voltage U _c _, especially in the area of the voltage ramp, trigger further undesired switching processes.

A first embodiment of the invention is shown in FIG. The input voltage divider R 301 and R 302 with the filter capacitor C 301 is the same as in the circuit example according to Figure 1. The start enrichment circuit 15 now includes a Evaluation circuit 21 and a monostable multivibrator 22. The evaluation circuit 21 contains a comparator BS 7031 its inverting input to a fixed Voltage divider with resistors R 310 and R 311 and a filter capacitor C 303 is connected. Of the The non-inverting input of the comparator BS 703 is connected to the input voltage divider mentioned above. The output of the comparator BS 703 is connected to a working resistor R 3O4 to a fixed supply voltage U_n, which has a value of about two thirds of the battery voltage U. The output is further through resistors R 309 and R 312 with the non-inverting input tied together. The monostable multivibrator 22 is at the partial point

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from R 309 and - "R 312 coupled via the capacitor C 302. The monostable multivibrator 22 contains a comparator BS 4, which in the usual way to the Battery voltage line U_. and to the ground line IL, is connected. The non-inverting input is connected to a fixed resistor via a series resistor R 305 Voltage divider with resistors R 3O8 and R 313 · An the anode of the Zener diode D 301 'is connected to the same voltage divider point, and its cathode at the non-inverting input of the comparator BS 703 of the evaluation esc holding 21 is located. The inverting one The input of the comparator BS 4 of the monostable multivibrator is connected to the resistor R 306 Ground line tL, and through a diode D 302 at the top mentioned connection point of the voltage divider resistors R 3O8, R 313; the cathode / diode D 303 is dem inverting input of the comparator BS 4 facing. The output of the comparator BS 4 is on the one hand above a working resistor R 307 on the supply line ULn and on the other hand at a measuring point MP 4o. The meaning of the measuring point MP 40 is explained below.

FIG. 4 shows schematically the respective voltage curve at different points in the circuit. In FIG. 4a shows the course of the control voltage U "_, in Figure 4b the voltage curve at the non-inverting input of the comparator BS 703 of the evaluation circuit 21, in Figure 4c the voltage curve at the non-inverting input of the comparator BS 4 of the monostable multivibrator 22 and in FIG. 4d the voltage profile at the output of the raonostable multivibrator 22 at the measuring point MP 40. The voltage curves are for the start time T

• / 3 · η. 1 8 7 R 1

(Figure ka) and the subsequent time shown; the service life of the monostable multivibrator 22 is _{indicated by T 11x} .. (FIG

It was already mentioned above that the numerous interference pulses, especially when using permanent magnet starters and false signals are a major disadvantage, mainly those that occur at the end of the start-up process Pulses and the voltage ramp that has been dragged along for a long time In the first exemplary embodiment according to the invention the start enrichment circuit is therefore divided into the evaluation circuit 21 and the monostable multivibrator 22nd

The comparator BS 703 contained in the ^A uswerteschaltung 21 is provided with a hysteresis. 0 ± e switching threshold U _K at its non-inverting input is fixed:

π _B π

Kl ~ ^U BA R 311 + R 310

When the ignition switch 11 is closed, that is

Start signal U available. The start signal is U__ οι ST

proportional to the battery voltage U _ß , it is at most 0.5 volts below the battery voltage. In the idle state before the start process, the comparator BS 703 is not activated; there is an L signal at its output. The switching threshold at the non-inverting input of the comparator BS 703 is

TT - TT. R 3O2 // R 3OQ _TT

^U ST1 - ^U BA R 302 // R 309 + R 301 ^Ä ° ' ^{9 U} BA

- 10 - ■

_{As soon as the control voltage U ST is} greater than 0.9 U _ßA • during the starting process after the ignition switch 11 is closed, the comparator BS 703 switches its output to H and triggers the subsequent monostable multivibrator 22.

As soon as the control voltage is applied at the end of the starting process

π _ becomes smaller than a certain value U _c _ _o , then ST switches al ^

the output of the comparator BS 703 back to L. The hysteresis of the comparator BS 703 is AU = U _ea , _o - U _c _.

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The lower switching threshold U ", _ ₂ is

R 3O2 // R 309 _TT R 301 // R

ST2 ~ BA 'R 3O2 // R 309 + R 301 D8 * R301 // R 302 + R 3O9 ~

Here, R 3θ4 + R 312 «R 3O9i R 301, R 302.

The fast interference peaks, which _{are superimposed on the control voltage U s} ", are smoothed by the low-pass filter R 301, C 301. The interference peaks on the battery voltage U ". are attenuated by the low-pass filter R 310, C 303. Further switching security against interference pulses on the U _{gT signal is ensured not only} by the smoothing with R 301 and C 301 but also by the hysteresis of the comparator BS 703 and the associated safety margin to the control voltage U _ST2 .

The earlier to be feared false triggering at the end of the start signal after the time T _gT has elapsed is prevented by the smoothing with R 301 and C 301 and by the switch-on threshold raised to the value with the help of the hysteresis of the comparator BS 703.

- 11 -

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If the output of the evaluation circuit 21 _{switches to H 1} , the subsequent monostable multivibrator 22 is set by the positive jump at the coupling capacitor C 302. During the charging time of C 103 (FIG. 4c), the output MP 40 of the monostable multivibrator 22 is at L. The charging constant is a first approximation

^τ ΜΚ = ^{C 302} · ^{R 3O6}
where R 3O4, R 312, R 309 is «R 306.

As soon as the potential at the resistor R 306 has _{fallen to a value U "2} , the output of the monostable multivibrator 22 switches back to H (FIG. 4d). It is

_{TT TT} R 303 _

^U K2 ~ ^U D8 R 303 + R 308 ~

The following applies to the service life T _{ffl of the monostable multivibrator 22}

U
MK ~ ~ ΊΜ '"

R 306 (t)

^U R 306 ^{Ä u} d8 '

The voltage at the inverting input of the comparator BS k is increased by the diode D 302

^U - = ^U K - ^U D 302 *

- 12 -

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limited, so that the output (MP 4o) overturns when A drop in voltage U_ below -0.3 volts (latch-up effect) is avoided.

The same effect, i.e. preventing the output from tipping over, is achieved with the help of the Zener diode D 301 for the non-inverting input of the comparator BS 703 ο By designing the diode D 301 as a Zener diode, the positive interference pulses that are generated on the start signal U -, which may still be present, are limited to values that are harmless to the BS 703 comparator.

If the starting process ends before the downtime Ί ^ ™. the aborted monostable flip-flop 22, the output of the comparator BS 703 toggles from H to L. Due to the dynamic coupling of the evaluation circuit 21 to the monostable multivibrator 22 with the aid of the coupling capacitor C 302 becomes the service life T., _ Of the monostable

MK.

Flip-flop 22 also abbreviated and the monostable Toggle switch 22 reset.

A second exemplary embodiment is shown in FIG. Compared to the first embodiment shown in Figure 3, it is a simpler variant. This second embodiment, however, meets the requirements when using starters with Electromagnet are placed. In Figure 5, the same components as in Figures 1 and 3 are the same Provided with reference numerals. In contrast to the first exemplary embodiment according to FIG. 3, there is a separate evaluation circuit (21) not provided. Has been added

- 13 -

a feedback resistor R 309 between the Output B 1 of the comparator BS'i and the voltage divider point between the voltage divider resistors R 3O8 and R 313 is located. The coupling capacitor C 302 is directly connected to the input circuit with the voltage divider resistors R 301, R 302, the smoothing capacitor 301 and that between the voltage divider point between the voltage divider resistors 301 and 302. and the ground line IL. lying Zener diode D 301 'connected.

The processing of the start signal U ₀ .- takes place with the help of the low-pass filter R 301, C 301 and by limiting the control voltage with the help of the Zener diode D 301 '. The Zener diode D 301 'simultaneously specifies the voltage swing with which the coupling capacitor C 302 is recharged. The service life T _1. , ^. the monostable

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Toggle switch 22 is determined. Otherwise, the function of the second embodiment is essentially the same as that of the first embodiment. [Another inexpensive and space-saving variant is shown in the third exemplary embodiment shown in FIG. In this embodiment, the coupling capacitor C 302 is in series with the voltage divider resistor R 301 in the control line Uqm · The voltage divider with the resistors R 351, R 352 and R 353 of the restart circuit 16 is also used. The voltage divider from the restart circuit 16 supplies the reference voltage U _K ″ for the non-inverting input B 7 of the comparator BS k of the monostable multivibrator 22.

The time-determining switching elements - mainly the switching elements R 302, R 301, C 302 - are here directly in the path of the input signal U " _T. The constant voltage swing

- Ik -

is determined by the Zener diode D 301 *. As long as there is no start and consequently the control line υ _{ςτ is} open, the resistor R 302 ensures a clean differential voltage at the inverting input of the comparator BS 4 = possible interference peaks are attenuated by the low-pass filters R 301, C 301.

The service life of the monostable multivibrator 22 is X ₁ = C 302. (R 301 + R 302)

The free / earth time after the end of the start signal T_ _{T is} then when the control line U _c _ is open

T = C 301 · R 302

Because of the dynamic coupling with the coupling capacitor C 302, the third embodiment according to FIG. 6 is also Applicable to starters with permanent magnet excitation.

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Claims (1)

.18761 05/13/1983 ch / dö ROBERT BOSCH GMBH, 7OOO STUTTGART 1 Start time limitation for internal combustion engines with fuel tongue Claims II »/ Process for enriching the fuel-air mixture for internal combustion engines with fuel injection during the time of starting the engine, characterized in that, that the time of the start enrichment is limited to a specifiable value (T .. ^.) regardless of the length of the start pulse MJv will . 2. The method according to claim I _1, characterized in that at the beginning of the start pulse a monostable trigger circuit (22) is set and the service life (T. ™) of the monostable trigger circuit represents the time of the start enrichment, 3 »Method according to claim 2, characterized in that in a separate evaluation stage (21) in the input circuit of the Raonostable flip-flop (22) interference pulses are suppressed. ■ λ- -IB / 61 k. Method according to Claim 3, characterized in that in the evaluation stage (21) with the aid of a comparison stage (BS 703) the supply voltage (U_.) And the voltage of the standard pulse es (U ₃ -,) are compared with one another. 5. The method according to claim 4, characterized in that the reference voltage of the comparison stage (BS 703 _{) is made proportional to the supply voltage (U "A} ) (R 309)" 6. The method according to claim k or 5i, characterized in that the comparison stage (21) emits an output signal when the _{start pulse} voltage (U crp) in a .vor immbar en (hysteresis) range of a previously determinable part of the supply voltage '(U ".) Lies. 7. The method according to any one of claims k to 6, characterized in that with the help of a raised input threshold for the comparison stage (BS 703) the voltage ramp _{following the start pulse (U g} _ / T "_) is made ineffective. 8. The method according to any one of claims 2 to 7j, characterized in that - if necessary with the help of a resettable monostable flip-flop (22) - regardless of the length of the predeterminable time value (T _MK .) For the start enrichment, the start enrichment is canceled when the start is terminated . 9. The method according to any one of the preceding claims, characterized in that after the end of the start enrichment time (TV _n ^.) A restart circuit (l6) is set. 10. Device for performing a method for enriching the fuel-air mixture for internal combustion engines with fuel injection during the time of starting the engine, characterized by the following Characteristics: - A monostable multivibrator (22) is provided, - the set input (B 6) of the monostable multivibrator (22) is connected to the start pulse line (U _ca ,), - The output of the monostable multivibrator (22) is connected to a restart circuit (16). 11. Device according to claim 10, characterized in that the set input (B 6) of the monostable multivibrator (22) to enable a reset via a capacitor (C 302) - possibly via further switching elements (evaluation circuit 21) - with the start pulse line (U _c _t) is connected. 12. Device according to claim 10 or 11, characterized in that that between the start impulse line (U "_,) and an evaluation circuit (21) is inserted into the monostable multivibrator (22). 13 · Device according to claim 11, characterized by the following features: - An input of the comparison stage (BS 703) is with the Supply voltage line (U_.) Connected, - the other input of the comparison stage (BS 703) is connected to the start impulse line (U), ο Χ - The output of the comparison circuit (BS 703) is connected to the input of the monostable multivibrator (22). R · l4. Device according to claim 13, characterized in that to enable an additional control by the verse or confining voltage (U_, ₄₎ the control input of tSA Comparison stage (BS 703) via a feedback resistor (R 309) with the output of the comparison stage (BS 703) connected is. 15. Device according to claim l4, characterized in that that the input threshold (U, ^.,) of the comparison stage (BS 703) with the help of the feedback resistor (309) a value of about ninety percent of the supply voltage (U ".) is set. l6. Device according to one of Claims 10 to 12, characterized in that the evaluation circuit (21) Contains switching elements (D 301 ") for limiting the amplitude. 17. Device according to one of Claims 10 to 12 or 16, characterized in that the _{coupling capacitor (C 302) determining the service life (IV n} ^) of the monostable multivibrator (22) is inserted into the start pulse line (U ^). l8. Device according to one of Claims 10 to 17, characterized in that for suppressing interference voltage peaks the control input of at least one of the active components (21, 22) with a voltage divider from resistors and a diode (D 301 ', D 302) is connected.