DE2211335A1 - ELECTRICALLY CONTROLLED FUEL INJECTION SYSTEM FOR A COMBUSTION ENGINE - Google Patents

Description

0782

February 14, 1972 Lr / Dr

Attachment to
Patent application

ROBERT BOSCH GMBH, 7 Stuttgart 1

Electrically controlled fuel injection system for an internal combustion engine

The invention relates to an electrically controlled, preferably intermittently operating fuel injection system for an internal combustion engine, with an electrical control unit for at least one electromagnetic, the Injection valve determining the injection quantity and with a Air flow meter, which contains a temperature-dependent resistor arranged in the intake air flow of the internal combustion engine, which is traversed by a heating current.

In known injection systems this. Art becomes the im Intake channel of the internal combustion engine arranged, temperature-dependent resistance thereby externally heated that in its

- 2 309837/0231

Aj

" ^ά ' 078;

Robert Bosch GmbH _: R «,;. = De

Stuttgart

■ ··. ■: ■ ':.' ■: ■■ ^ * " ·:.; .-: - · Λα ^^!" a heating coil is provided in the immediate vicinity, which remains constant due to radiation or conduction

'' - ■ · il'l transfers the amount of heat to the resistor, whereby the resistor heated in this way is cooled down all the more and its electrical conductivity changes the more the greater the amount of intake air. In order to be able to use these changes ⁵ to control the opening duration * of the injection valve or valves, the temperature-dependent resistor is arranged in a measuring bridge circuit in the known system and generates a voltage that increases with the amount of intake air in a diagonal branch of the bridge. In the known system, the diagonal voltage is used to control the tilting duration of a multivibrator equipped with mutually blocking transistors, which supplies pulses used to open the valve or valves.

If the heat effective at the temperature-dependent resistor is generated by a separate heating resistor, all changes in the operating voltage provided for the heating resistor are included in the accuracy of the air volume measurement. A much greater accuracy can be achieved when a heating current-forming controller is provided according to the invention, which keeps the resistance to at least approximately constant temperature, and further when a controlled from the heating current squaring circuit is provided whose From output voltage linearly with the amount of intake air increases, and as a control variable for the injection quantity is used.

The heating current Jh required to maintain a constant temperature at the temperature-dependent resistor, or a probe voltage Us proportional to this, depends on the fourth root of the low intake air Q

BAD ORtQJNAt

309837/0231 " ³ "

0782

Robert Bosch GmbH R. Lr / Dr

Stuttgart 2211 335

together as follows:

Jh ^ US = I k ₁ + k ₂ IQ (1)

Since the during an intake stroke in one of the cylinders of the internal combustion engine the amount of intake air reaching that amount of fuel determines which can be burned residue-free in a subsequent work cycle and to achieve the full power of the internal combustion engine is required, a control voltage is to be set with the aid of the above-mentioned squaring circuit for the control unit of the injection system, which are linearly related to the respective intake air quantity Q stands.

The desired goal can be achieved in a simple manner that with the aid of a probe resistor through which the heating current flows, a probe voltage proportional to the heating current generated and that a differential voltage is formed with respect to that initial voltage that is applied to the probe resistor with the internal combustion engine at a standstill, but constant held temperature value of the temperature-dependent resistor is set by the controller, and that this differential voltage is used as the control voltage for the squaring circuit. The squaring circuit can advantageously be used as an oscillator Contain generation of rectangular auxiliary pulses, where of the characteristic quantities of the auxiliary pulses, namely their frequency, pulse duration and amplitude, two quantities in Dependence on. Heating current or a voltage proportional to the heating current can be changed, whereas the third variable is kept constant, and that the auxiliary pulses to form the output voltage via a rectifier be fed to an integrator. Another possibility,

-I ₁ -

309837/0231

0782

Robert Bosch GmbH R. Lr / Dr

Stuttgart 221 1335

is to perform the squaring with the help of a sawtooth voltage, in which both the period and the slope of the sawtooth voltage is changed as a function of the differential voltage to be squared. In particular, the squaring circuit may include a storage capacitor that is used during one of the. Differential voltage dependent charging time with a likewise dependent on the differential voltage current charged, in the charged State held for a specified short holding time and recharged after a subsequent, specified discharge time will. A further storage capacitor can expediently be provided, the voltage of which is periodic during the hold time is compared with the respective voltage of the first storage capacitor and brought to the same level with this.

A further improvement can be achieved by providing a threshold value for the probe voltage below which the control voltage effective in the squaring circuit has a different, preferably linear dependence on the differential voltage has to be above this value. Further details and expedient refinements result from the exemplary embodiments described below.

Show it:

1 shows a gasoline injection system operating with an air flow meter in an overview image and in a partially schematic representation,

2 shows a characteristic curve to explain the relationship between the heating current of the air flow meter and the amount of intake air,

FIG. 3 is a circuit diagram of one used in the system of FIG Squaring circuit,

- 5 -309837/0231

Robert Bosch GmbH R.O?

Stuttgart 2 2 1 Ί 3 3 5

Pig. M a time chart for several, themselves in the squaring circuit according to Fig. 3 playing electrical. Operations,

Fig. 5 shows a modified squaring circuit, which in contrast for the circuit according to FIG. 3 instead of rectangular Auxiliary impulses generated with a sawtooth shape,

FIG. 6 shows a time diagram for the auxiliary pulses generated by the squaring circuit according to FIG. 5,

7 shows a diagram for an improved approximation curve,

8a shows a diagram of the partial function provided for the improved approximation curve and

8b shows a modification of such a partial function,

9 shows a squaring circuit which is constructed similarly to that of FIG. 5, but by means of a Characteristic curve according to Fig. 8a resulting threshold level is added,

Fig.10 shows another squaring circuit like that of constructed according to Fig. 3 and indicated by a threshold level indicated by strong lines is supplemented.

The gasoline injection system shown is intended and includes for the operation of a four-cylinder four-stroke internal combustion engine IO as essential components four electromagnetically actuated injection valves 11, which from a distributor 12 The fuel to be injected is supplied via a pipe 13, an electric motor-driven fuel feed pump 15, a pressure regulator 16 ,. the fuel pressure regulates to a constant value, as well as an electronic control device, described in more detail below, which by a signal transmitter 18 coupled to the camshaft 17 of the internal combustion engine two-

309837/0231 - ⁶ "

0782

Robert Bosch GmbH R. Lr / Dr

Stuttgart 22.11335

■ is triggered times and then a rectangular, electrical opening pulse S for the injectors 11,., supplies. The duration indicated in the drawing ti of the opening pulses determines d 3e opening duration of the injection valves and consequently the amount of fuel which during an injection process from the interior of the under a practically constant fuel pressure from 2 atü standing injectors 11 exits. The magnet windings 19 of the injection valves each have a decoupling resistor 20 connected in series and connected to a common gain and power stage, which contains at least one power transistor indicated at 22, which with its emitter-collector path arranged in series with the decoupling resistors 20 and the magnet windings 19 connected to ground on one side is.

In the case of mixture-compressing internal combustion engines of the type shown, working with Pr ignition, the amount of air entering a cylinder during a single intake stroke defines the amount of fuel that can be completely burned during the subsequent work cycle. For good utilization of the internal combustion engine, it is also necessary that there is no substantial excess of air after the work cycle. In order to achieve the desired stoichiometric ratio between intake air and fuel, a temperature-dependent resistor 30 through which a heating current Jh flows is provided in the intake pipe 25 of the internal combustion engine in the direction of flow behind its filter 26 and in front of its throttle valve 28, which can be adjusted with an accelerator pedal 27. The resistor 30 is wound from a thin wire, which consists of platinum and has a resistance temperature coefficient * 6 of 3 _f 9 'IQ ^ / grd. It heats up under the influence of the heating current flowing through it

309837/0231 ~ ⁷ ~

0782

Robert Bosch GmbH R. ¹ LTfDv

Stuttgart 22113

and is cooled all the more by the intake air flow, which flows in the intake pipe 25 and is indicated by an arrow 32, the greater the flow velocity of the intake air flow and consequently the greater the amount of air Q sucked in in the unit of time.

To be as stable as possible and from external conditions, for example

To get conditions independent of the respective charge of the battery cooperating with the internal combustion engine 10, not shown in the drawing, the temperature-dependent resistor 30 is arranged as one of four bridge members in a resistor bridge, the remaining three resistors 33 »34 and 35 largely independent of temperature and outside of the intake air duct are arranged. The input of a control amplifier R is connected to the diagonal of this bridge, which supplies the heating current Jh and for this purpose provides an operating voltage on the other bridge diagonal which The greater the bridge imbalance caused by the cooling of the temperature-dependent resistor 30, the greater is. In the event that the internal combustion engine is at a standstill and consequently the amount of intake air has the value zero, the controller R is set so that it gives the initial value of the heating current indicated by Jo in FIG. 2 and thus a certain operating temperature of the wire. As the amount of intake air Q increases, the heating current Jh must be increased in the manner shown in FIG. 2 according to the approximation formula Jh = "| kl + k2" ^ Q ¹ , where kl and k2 are system constants. Since the left branch of the bridge, formed from the two resistors 33 and 3 ^ , divides the supply voltage supplied by the regulator R in a constant and constant manner, the tendency of the regulator R is that it increases the heating current Jh until the operating temperature is reached of resistor 30 is as close as possible to the setpoint temperature set at the initial value Q = O,

309837/0231 - & - ■

" ⁸ " 0782

Robert Bosch GmbH R. Lr / Dr

Stuttgart '2211335

this approximation is the more perfect the higher the gain of the controller.

From the above-described dependence of the heating current Jh on the intake air quantity Q, a more difficult one results Relationship between the opening duration ti and to be provided by the electronic control unit of the injection system the amount of intake air allotted to each cylinder of the internal combustion engine. The one omitted per cylinder The amount of air is proportional to the product of the time average value Q and the cycle time tp required to pass through a specified crankshaft rotation angle, for example, is required for half a crankshaft revolution.

In order to be able to obtain a voltage Uk proportional to the duration ti of the opening pulses S from the heating current Jh and this voltage in an integrating stage 37 connected upstream of the power stage 22 into an electrical quantity to be able to convert the amount of intake air reaching one of the cylinders per stroke of the internal combustion engine q = Q / η is proportional (n = crankshaft speed) and through a subsequent differentiation stage 38 can be converted directly into an opening pulse S with the pulse duration ti proportional to the cylinder air quantity q can, a squaring stage 40 is provided according to the invention.

FIG. 2 shows the relationship between the heating current Jh and the intake air quantity Q. Jo is the value of the heating current denotes at which the temperature-dependent resistor 30 reaches the intended operating temperature when the Internal combustion engine 10 is at a standstill and the amount of intake air is consequently Q = O. On the other hand, Jr denotes the amount by which the heating current Jh must be increased beyond the initial heating current value Jo if the intake air quantity is running. Internal combustion engine is increased and then at the temperature

309837/0231 - 9 -

0782

Robert Bosch GmbH R, Lr / Dr

Stuttgart 2211 335

hang resistor 30 dissipates heat. This heat loss will covered by the heating current increased by Jr. In order to be able to obtain a voltage proportional to the heating current Jh, with the temperature-dependent resistor 30 in Resistor 35 lying in series and through which the heating current flows is used as a probe. The one proportional to the heating current Probe voltage Us is increased by the value of the initial heating current Jo associated initial voltage value Uo is reduced. The difference both voltages can be used approximately to determine the amount of air according to the formula:

Us - Uo = k3.

By squaring in the following described squaring

p circuit 40 results in a voltage Um = (Us - Uo) = k4. Q.

In the squaring circuit of FIG. 3, one is as active Elements a first transistor 58 and a second transistor 68 containing oscillator 50 is provided, which approximately rectangular, in Fig. 4 by the curve 4a supplies indicated pulses which are picked up at the collector of the second transistor 68. The frequency of these pulses is kept constant, the pulse duration in the exemplary embodiment according to Fig. 5, however, depends on the differential voltage (TJs Uo) changes. The sharp back flank 51 of the oscillator pulses is iter a differentiator, which consists of a Capacitor 69, a diode 72 and the two resistors 71 and 71 are used to trigger a monostable Multivibrators used, which comprises the transistors 76, 80 and 86 as active components.

The service life ti of this multivibrator is dependent on changed by the voltage difference (Us - Uo); this happens

- 10 309837/0231

ft 7 ß °

Robert Bosch GmbH R. 'Tbf / Dr

Stuttgart 2211 335

in the following way:

The voltage Us is applied to the inverting input 101 of a differential amplifier 100 and a voltage is set at the non-inverting input using the voltage divider consisting of the two voltage divider resistors 111, 112, which corresponds to the initial voltage Uo proportional to the initial heating current value Jo. An amplified voltage k corresponding to the resistance ratio of the two resistors 116 and 113 results at the output of the differential amplifier 100. (Us - Uo) = Ua. This is applied via an emitter follower transistor 88 and a resistor 87 to the electrode of the feedback capacitor 81 connected to the transistor 86. The capacitor 81 is discharged with a constant current which is defined by the transistor 76 and the resistor 75. The pulse duration ti of the monostable multivibrator is therefore proportional to the height of the voltage jump at the capacitor 81 and thus depending on the amplified output voltage Vout of the differential amplifier 100. This is shown in Fig. L \ indicated by the curve 4c, which the pressure prevailing at the collector of transistor 86 voltage reproduces.

In order to achieve a square-wave voltage influenced in its amplitude by the output voltage Ua or (Us - Uo), is on the output of the differential amplifier 100 is an emitter follower transistor 91 connected to its base through a resistor 93 and also to its emitter through a resistor 90 applied to the operating voltage Ub. At the emitter of the transistor 91 there is a corresponding to the divider ratio of the resistors 93/92 reduced voltage UJ as long as the diode 89 blocks, i.e. during the pulse duration ti, da during the pulse pause the transistor 80 is conductive and

- 11 -

309837/0231

0782

Robert Bosch GmbH R » _oo JjVL DiL

Stuttgart «. 335

Via the diode 89, the potential at the emitter of the transistor 91 practically corresponds to that of the common ground line 52. The square-wave signal produced at the emitter of transistor 91 is fed to an integrator 54, which consists of a resistor 9 ¹ ^ and capacitor 95 and rectifies the square-wave signal. A downstream transistor 96 acts as an impedance converter, which supplies a direct voltage Um at its emitter connected to an output terminal 55, which is proportional to the square of the voltage Ua.

So that a purely quadratic function of Ua appears at the output 55, the punctures ti = f (Ua) and Ul = f (Ua) go through the zero point, or in other words: at the punctures

ti = A + B. A.o.
Ul = C + D. A.o.

A and G must be zero. This requirement can only be met with greater circuit complexity; because of this the following option is used in the circuit shown in Fig. 3:

Multiplying ti and Ul results in ti. Ul = AC + (AD + BC). Ua + BD. Including ² .

If one of the two quantities A and G is negative, one can be Find setting by which the expression (AD + BC) equals Becomes zero. This results in a purely square puncture with a parallel shift through AC, which is not taken into account needs to become.

-. - - - \ O mm

309837/0231

0782

Robert Bosch GmbH R. Lr / Dr

Stuttgart 2211 335

In the circuit of Fig. 3, the term A is negative. The quantity C can be determined by the voltage divider resistors 92 so set so that the size (AD + BC) is zero and the circuit works properly.

The above-described method of squaring with the aid of square-wave pulses requires that one of the three sizes of these pulses, namely frequency, amplitude and pulse duration, be kept constant, since any change results in a measurement error. In the embodiment of FIG. 3, the frequency is kept constant. Another difficulty is that the integration of the voltage swing at the output 55 becomes smaller, so that the further processing of the voltage Um arising at the output 55 becomes less precise.

In the second embodiment shown in FIG these difficulties are largely avoided for a squaring circuit. The circuit shown there works in a large frequency range with the help of a sawtooth voltage, in which both the period duration and the slope of the sawtooth voltage can be changed as a function of the differential voltage to be squared (Us-Uo).

The operation of the squaring circuit according to FIG. 5 is based insists that a capacitor 156 during one of the To be squared voltage (Us - Uo) dependent duration T by a current also dependent on this voltage being charged. The voltage across the capacitor 156 at the end of the duration T is short holding time t3 kept constant and in a so-called "Sample-and-hold circuit" transferred. The holding time t3 is provided by a first timing element Zl. During an immediately following one, through a second

309837/0231 - 13 -

0782

Robert Bosch GmbH R. Lr / Dr

Stuttgart 2211 335

Discharge time t4 defined by timer Z2, capacitor 156 is discharged. After the discharge time t4 has elapsed, the charging process, which extends over the voltage-dependent duration T, begins again. The charging time T is determined by a second capacitor 147 'is charged with a constant, of an emitter follower transistor 146 geliefertem stream. The voltage generated at the capacitor 147 is fed to a differential amplifier 121, which is designed as a threshold switch and whose non-inverting input is connected to the voltage Ua to be squared via a resistor 122. When the voltage generated at the capacitor 147 reaches the value of this voltage Ua, the differential amplifier switches through and thereby triggers the first timing element Z1, which triggers the second timing element Z2 after the hold time t3 has elapsed.

In Fig. 6 the temporal assignment of these processes is shown with the two curves 6b and 6c.

In detail, the squaring circuit shown in Fig. 5 operates as follows:

A differential amplifier, not shown, provides how in the circuit of FIG. 3 at the input 56 the to squaring voltage Ua, which is inversely proportional to the differential voltage (Us - Uo). This tension is connected to the non-inverting input of the differential amplifier 121 and is fed to the inverting input Voltage of capacitor 147 compared. If the on Capacitor 147 during the charging time T linearly increasing voltage reaches the value of the voltage Ua, arises on Output of the differential amplifier 121 a negative voltage jump, with which the first timing element Zl will be triggered, which consists of the transistor 130, a capacitor 125 and a resistor 126. With the curve 6b

309837/0231 - i4 -

- ¹⁴ - 078C

Robert Bosch GmbH R / Lr / Kb

Stuttgart 2211 335

the collector potential of transistor 130 is shown. After the hold time t3 has elapsed, the second timer Z2 is triggered. This consists of a transistor 1 * 12, a capacitor 137 and a resistor 138. In FIG. 6c, the time profile of the potential at the collector of the transistor 142 is shown. As long as this transistor blocks, a discharge transistor 148 connected in parallel with the second storage capacitor 147 with its emitter-collector path is kept conductive so that the capacitor 147 can discharge quickly. The transistor 148 is operated inversely in this case, since in this case the saturation voltage in the conductive state is lower and consequently the residual voltage on the capacitor 147 has only very low values. In FIG. 6, the curve 6a shows the course of the voltage across the capacitor% AJ. It can be seen there without further ado that the charging time T becomes longer, the more absolute J $ | i £ re the voltage Ua and consequently the 'Q' has.

To achieve the squaring effect, de? 156 not only during this of the voltage Ua Duration T charged, but its charging current increases | Likewise linear with the voltage Ua to be squared. The respective size of this charging current is determined by the transistor 155 'which is operated as an emitter follower and is determined by its emitter resistance 154. The base this transistor is connected to the collector of an amplification transistor 151, which has its base over a resistor 150 across the voltage to be squared Ua lies. This ensures that the charging current of the capacitor 156 is linear with the voltage Ua

enter.

During the holding time t3, after the expiry of the

30S837A0231 - 15 -

Robert Bosch GmbH R. Lr / Kb

Charging time T at capacitor 156 voltage reached held. This is achieved in that the emitter of transistor 155 is connected to negative line 52 through transistor 157, which is conductive during hold time t3, and transistor 155 is blocked in the process. Since the transistor 159 is also still blocked, the voltage at the capacitor 156 is retained and can be processed further via the very high-resistance emitter follower transistor! During the immediately following discharge time 1 ¹ T, the transistor 159, which is also operated inversely, is kept conductive so that. the capacitor 156 can discharge through this transistor.

The further processing of those maintained during the holding time t3 Voltage across capacitor 156 is made with the aid of emitter follower transistor 16I and diode 166, which make sure there is a third storage capacitor on the held. Voltage of the first storage capacitor 156 discharged or connected via one to the transistor I61 Emitter follower transistor I65 and a diode that interacts with it. 167 on the respective during the hold time t3 existing. , Charge the voltage value at the capacitor I56 can. This ensures that the third storage capacitor 171 is at the voltage value in each case that the first storage capacitor I56 after its expiration had reached the voltage-dependent charging time. The charge equalization on the capacitor 17I can only occur during the Hold time t3 take place. During the rest of the time, the voltage on capacitor I7I remains and changes only during the next holding time if the intake air quantity Q has changed. To the third storage capacitor 171, a high-resistance emitter follower transistor 173 is connected. This delivers at its connected to the output terminal 55 Emitter the voltage Um, which is proportional to the square of the

- 16 3 09837 ^ 0231 e

- 16 - 07

Robert Bosch GmbH R. Lr / Kb

Stuttgart

Voltage Ua and consequently also proportional to the square of the voltage difference (Us - Uo) and the changes in this Sizes follows very quickly, i.e. after each period, it assumes the correct value again.

The voltage Um is converted into a pulse duration ti of the opening pulses S in the integrating stage 37, which is proportional to it converted that each during half a crankshaft revolution a bistable multivibrator * J1 controlled by the signal generator 18 a charging current source in the integrating stage 37 keeps switched on, which is connected to an integrating capacitor (not shown) which is proportional to the voltage Um Charging current supplies. This capacitor is at the beginning of the next half crankshaft revolution with a constant Discharge discharge current and then delivers the opening pulses S with the pulse duration ti.

The above-described squaring is based on the fact that the target curve Us = Vkl + k2 V ^ through the puncture Us - Uo = k3. Vo "is approximated. This is shown in Fig. 7 by the first approximation curve N1. This can easily be selected so that in the range of small air quantities Q5 to Q6 only very small deviations from the target curve occur To achieve an approximation of equally good quality air volume values, a further development of the invention provides that a non-linearity is introduced into one of the two punctures proportional to the differential voltage (Us - Uo), which are multiplied with one another in the squaring circuit, namely in the manner that The slope of this straight line changes from a certain probe voltage, for example belonging to the air volume Q6. There are two possibilities for this: either the straight line χ = f (Us Uo) can pass through the zero point as shown in FIG The second possibility is that the upper part of the straight line as shown in Fig. 8b in the

309837/0231

- 1 1 -

Robert Bosch GmbH R. Lr / Kb

Stuttgart

Extension would go through zero, but at smaller values of the differential voltage (Us - Uo) is flatter. The variable χ can, for example, be the amplitude or the pulse duration of a square-wave voltage as used in the first squaring circuit or the slope or the period of a sawtooth voltage when a squaring circuit of FIG. 5 is used.

An implementation option for a puncture course after Pig. 8a is drawn with thick lines in the otherwise unchanged circuit according to FIG. 5 and reproduced in FIG. 9. As far as in Fig. 9 the same components are used as in Fig. 5, they have the same reference numerals. In addition to those used in FIG . Components are two transistors 184 and 190 and two Diodes 180 and 182 are provided. The cathode of the first diode 180 is connected to the emitter of the transistor 146 and is at its anode with a leading to the positive line. Resistor l8l and the anode of the second diode 182 connected, which is connected to the collector of the transistor 190 and its working resistor 191 leading to the negative line 52 is. The transistor 190 is of the PNP type and its emitter is connected to the battery voltage Ub connected. Its base is connected to the collector of the NPN type via a coupling resistor 188 Transistor 184 in connection, the base of which is connected to the second storage capacitor via a coupling resistor 179 147 and is connected to the negative line 52 via a base bleeder resistor 183.

The two transistors 184 and 190 work together with the two diodes 180 and 182 as a threshold stage and act as follows;

309837/0231

-is- 0782

Robert Bosch GmbH R. Lr / Kb

Stuttgart

At the beginning of the charging of the capacitor 147 are the transistors 184 and 19O blocked. This will the diode 182 is kept conductive and, as a result, the diode I80 is blocked. The charging of the capacitor 147 with the intended constant current therefore initially only takes place via the resistor 145 in the emitter lead of the ^ Emitter follower transistor 146. From a certain value of the voltage given by the voltage divider I86 / 187 At the capacitor 147, the transistor 184 becomes current-conducting via the very high-resistance resistor 179. This will the transistor 190 is also conductive and the diode 182 is blocked. The capacitor 147 is charged now with a larger current through the two resistors 145 and I8I, which are connected in parallel to one another. It thus arises a curve as sketched in FIG. 8a, in which case the ordinate χ corresponds to the voltage across the capacitor 147.

The same method can also be implemented with the squaring circuit according to FIG. In this case the above would be described, in Fig. 9 thick drawn circuit parts preferably in the constant current charging of the capacitor 8l intervene, since this is the duration ti of the rectangular Auxiliary impulses determined.

A realization of the function sequence according to FIG. 8b is required in terms of circuitry, a significantly low expenditure. The threshold value stage provided for achieving the kinked function curve is shown in solid lines in FIG. 10 shown. The other components of FIG. 10 correspond to those of the circuit according to FIG. 3 and carry the same reference numerals. The threshold level comprises two Voltage divider resistors 98 and 99, from whose connection point a resistor II8 and a diode 119 to the base of the Emitter follower transistor 91 lead. For small values of the output voltage supplied by the differential amplifier 100 Ua * k. (Us - Uo) becomes the au3 of the resistors 92 and 93

309837/0231 - 19 -

-I ₉ - 078C

Robert Bosch GmbH R. Lr / Kb

Stuttgart

existing voltage divider via the then conductive diode 119 is loaded by the network consisting of resistors 98, 99 and 118. Only when the voltage Ua over the If the specified minimum value increases, the diode 119 blocks and the straight line according to FIG. 8b then becomes steeper. In this Case corresponds to the ordinate χ of the .Amplitude of the rectangular Auxiliary impulses.

The same method can also be used with the squaring circuit according to FIG. 5, which operates using a sawtooth voltage use. In this case, the network consisting of the resistors 98,99,118 and the diode 119 would have to be connected to the non-inverting one Input of the differential amplifier 121 operated as a threshold switch intervene.

- 20 -

309837/0231

Claims (12)

Robert Bosch GmbH R. Lr / Kb Stuttgart Expectations l.j Electrically controlled, preferably intermittent Fuel injection system for an internal combustion engine, with an electrical control unit for at least one electromagnetic, The injection valve determining the injection quantity and with an air flow meter, the one in the intake air flow of the Internal combustion engine arranged, temperature-dependent Contains resistance through which a heating current flows, characterized in that a heating current (Jh) supplying controller (R) is provided, which keeps the resistor (30) at least approximately constant temperature, and that a squaring circuit (JJO) controlled by the heating current is provided, the output voltage (Um) of which is linear increases with the intake air quantity (Q) and serves as a control variable for the injection quantity. 2. Injection system according to claim 1, characterized in that with the aid of a heating current (Jh) flowed through Probe resistor (35) generates a probe voltage (Us) proportional to the heating current and that a differential voltage (Ua # v Us - Uo) compared to that initial voltage (Uo) is that on the probe resistor (35) at a standstill. Internal combustion engine, but kept constant temperature value of the temperature-dependent resistor (30) from the controller. (R) is set, and that this differential voltage is used as a control voltage for the squaring circuit (40). 309837/0231 - 21 - - 21 - 0782 Robert Bosch GmbH R. Lr / Kb Stuttgart 3. Injection system according to claim 2, characterized in that · the squaring circuit (40) has an oscillator (50) for Generation of rectangular auxiliary pulses, of which characteristic variables frequency, pulse duration and amplitude two variables depending on the heating current (Jh) or by a voltage (Ua) proportional to the heating current, while the third variable is kept constant and that the auxiliary impulses for the formation of the output voltage (Um) are fed to an integrator (94.95). 4. Injection system according to claim 3> characterized in that an astable operating at a constant frequency Multivibrator (50) is provided for triggering a monostable trigger stage (53), the tilt duration (ti) in Depending on the heating current (Jh) or on a voltage proportional to the heating current (Ua <v Us - Uo) can be changed is. 5. Injection system according to claim 2, characterized in that the squaring circuit (40) a storage capacitor (156) contains, which is dependent on the differential voltage (Us-Uo) charging time (T) with a also of the Differential voltage-dependent current charged, held in the charged state for a defined short holding time (t3) ■ and recharged after a specified discharge time (t4) will. 309837/0231 " ²² " - ^{from 22 to} 078 £ Robert Bosch GmbH R * Lr / Kb Stuttgart 2211 335 6. Injection system according to claim 5, characterized in that / aie holding time (t3) has a first monostable time stage (Zl) and a second monostable time stage (Z2) is provided for the discharge time (t4) and is connected to the first time stage is. 7. Injection system according to claim 6, characterized in that to achieve one of the differential voltage (Us-Uo) Depending on the charging time (T), a second storage capacitor (1 ^ 7) is provided, which is via a Constant current source acting emitter follower transistor (146) is loaded and at one of the two inputs of an operational amplifier designed as a threshold switch (121), at the second input of which the differential voltage (Us-Uo) is effective. 8. Injection system according to claim 7 »characterized in that that for the second storage capacitor (147) the emitter-collector path of a - preferably inversely operated discharge transistor (148) is connected in parallel, the base of which is connected to the second time stage (Z2) is. 9. Injection system according to claim 8, characterized in that a second, to the first storage capacitor (156) with his Eraitter collector path parallel-connected discharge transistor 309837/0231 - 23 - Robert Bosch GmbH R. Lr / Kb Stuttgart. 2211335 (159) is provided, which is connected at its base to the second time stage (Z2). 10. Injection system according to claim 8 or 9> characterized in that that a charging transistor (155) working as an emitter follower for the first storage capacitor (156) is provided and a charging current for the " Storage capacitor supplies. 11. Injection system according to claim 10, characterized in that that a third storage capacitor (171) is provided, which during the hold time (t3) on the same Voltage value is charged or discharged, which the first storage capacitor (156) at the end of the charging period (T) has reached. 12. Injection system according to claim 11, characterized in that the third storage capacitor (171) with the anode a first (166) and with the cathode a second (167) of two diodes which allow charge equalization is connected, of which the first diode (166) leads to the emitter of a first emitter-follower transistor (I6I), while the second diode (I67) to the emitter of a second Emitter follower transistor (I65) is connected to the 30 9837/0 231 " ^2k " - "- C 7 BZ Robert Bosch GmbH R. Lr / Kb Stuttgart 2211 335 to the first emitter follower transistor (16l) is complementary and its base is on its emitter. 13 · Injection system according to claim 12, characterized in that to the emitter-collector path of the second emitter-follower transistor (165) a switching transistor (168) with its emitter-collector track connected in parallel is, «a« · with its base to the collector of one of the first time stage (Zl) controlled intermediate transistor (135) is connected, the collector of which with the emitter of the first emitter follower transistor (I6l) - preferably via a diode (I63) - is connected. 1 * 1. Injection system according to one of Claims 2 to 13> characterized in that a threshold value stage (98,99,118,119 in Fig. 10 or 179 to 191 in Fig. 9) for the probe voltage is provided, below which the effective voltage in the squaring circuit is another linear Dependence on the differential voltage (Ua or Us-Uo) has as above this value. vv 309837/0231 Blank page