GB1576757A

GB1576757A - Systems for controlling the supply of fuel or fuel/air mixture to internal combustion engines

Info

Publication number: GB1576757A
Application number: GB19321/77A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1976-05-07
Filing date: 1977-05-09
Publication date: 1980-10-15
Also published as: JPS5352836A; SE7705251L; SE433103B; BR7702972A; AU2503277A; FR2350467B1; FR2350467A1; CH620275A5; AU507446B2; ES458532A1; SU952113A3; IT1114785B

Abstract

The device serves for more reliable switching of solenoid valves used in carburettors for overrun cut-off with idling fuel shutoff or idling mixture shutoff on motor vehicles. The idling fuel feed or the idling mixture feed in an internal combustion engine is prevented when the internal combustion engine is operating in overrun conditions. The device comprises an initial stage (1), sensitive to the engine speed, which triggers a solenoid valve (MV) for overrun cut-off basically when a lower speed level is reached, thereby ensuring that the solenoid valve releases the fuel feed and a vacuum switch, (S1, S2) responding to the intake pipe pressure and thereby sensing in particular the closed position of the throttle valve arranged in the intake pipe, which vacuum switch likewise causes triggering of the solenoid valve irrespective of the speed. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO SYSTEMS FOR CONTROLLING THE SUPPLY OF FUEL OR FUEL/AIR MIXTURE TO INTERNAL COMBUSTION ENGINES (71) We, ROBERT BOSCH GUSH, a German Company, of Postfach 50, 7 Stuttgart 1, Fedferal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to systems for controlling the supply of fuel or fuel/air mixture to internal combustion engines.

Such a system may be used for the switching of solenoid valves used with carburettors for the purpose of overrun cutoff with the shutting-off of the idling fuel or the shutting-off of the idling mixture in motor vehicles, which system serves to prevent the feeding of idling fuel or the feeding of idling mixture in an internal combustion engine when the engine is being driven by the vehicle.

It is already known to provide carburettors of motor vehicle engines with idling cut-off valves and to equip them such that the supply of fuel through the idling nozzle of the carburettor is shut off when the ignition is switched off, so that it is possible to prevent continued running of the internal combustion engine, this state being termed " running on ".

It is also known, in fuel injection systems for internal combustion engines, to connect the excitation winding of fuel injection valves in series with the switching path of a semiconductor switching element, the semiconductor switching element usually being triggered by a driver stage.

On the other hand, there are also types of carburettors in which, upon switching off the ignition, the idling mixture is shut off instead of the supply of idling fuel.

A mixture shut-off valve of this type has a relatively large shut-off cross section, so that, during operation, an increased pull-in force is required to allow the valve to open against the vacuum suction force during transition to normal idling when the engine is being driven by the vehicle.

According to the present invention there is provided a system for controlling the supply of fuel or fuel/air mixture to an internal combustion engine under predetermined conditions of operation, comprising a driver circuit connected to an electromagnetic shut off valve for interrupting the flow of fuel or fuel/air mixture to the engine, vacuum operated switch means connected to the driver circuit and responsive to pressure in the engine intake pipe and providing a signal indicative of the state of the engine throttle valve as either open or closed, and a primary electrical circuit responsive to engine speed related input signals and providing an engine speed indicative output signal to the driver circuit, whereby actuation of the electromagnetic shut off valve is controlled by the driver circuit such that the supply of fuel or fuel/air mixture to the engine is shut off by the valve when simultaneously the the signal from the vacuum operated switch means indicates that the throttle valve is closed and the signal from the primary circuit indicates that the engine speed is above a predetermined speed greater than the idling speed of the engin.

Advantageously, the invention can utilize existing shut-off valves for interrupting the supply of fuel through the idling nozzle or for shutting off the idling mixture in order to shut off the supply of fuel or mixture for the idling range when the engine speed is in excess of the idling speed when the vehicle is driving the engine.

In general, a simple overrun cut-off device is to be provided which is universally usable and, advantageously, is constructed such that carburettors of virtually any type can be subsequently fitted with the device.

In this connection, it is particularly advantageous to be able to detect, in a reliable manner, the two operating parameters for overrun cut-off, that is closed throttle valve (accelerator pedal is not depressed) and the engine speed in excess of the idling speed.

The use of a vacuum switch for detecting the position of the butterfly valve is particularly advantageous, since this renders it possible to use a common component for virtually all types of carburettors. On the other hand, if, for example, a screw contact having an insulated contact point is used in place of the idling setscrew conventionally used in carburettors, a very large number of types are required owing to the differing butterfly valve stop screws, lengths and thicknesses of the stop screws and their thread pitches. Furthermore, the use of a vacuum switch avoids the risk that a connecting cable required for the screw might be fractured owing to material fatigue caused by continuous movement during acceleration.For control of exhaust gas composition, it is desirable that the idling setscrew should not be adjusted in modern carburettors although, in the case of a subsequent installation of an overrun cut-off system utilising a screw contact, the original screw would necessarily have to be replaced by a contact screw, so that adjustment of the carburettor would be upset. The use of a vacuum switch for detecting the position of the throttle or butterfly valve otherwise can ensure satisfactory operation even when the conditions at the carburettor can no longer be correctly detected by means of a screw contact as a result of an automatic starter.

In general, when the vehicle is driving the engine i.e. during overrunning, it is necessary that the supply of fuel or the supply of mixture should only be shut off when two criteria are fulfilled, namely: - (a) the accelerator pedal of the internal combustion engine is released and the butterfly valve is consequently closed, and (b) the speed of the internal combustion engine is in excess of a predetermined limiting speed which is chosen for reasons of adjustment and which lies above the idling speed of the internal combustion engine.

Requirement (a) is fulfilled by the use of the vacuum switch, and the speed of the internal combustion engine is detected by way of the speed-responsive input stage which ensures that the supply of fuel or the supply of mixture is not cut off during genuine idling operation.

In accordance with an advantageous development of the invention, the increase in the emitter potential of a transistor forming the driver stage increases the switching reliability and can ensure that faulty switching does not occur even in the case of a large temperature range of the base to emitter voltage of the said transistor.

Since the invention is also particularly suitable for overrun cut-off in the case of types of carburettor in which the idling mixture is shut off, almost all current types of carburettors can be equipped with an overrun cut-off system embodying the invention. For this purpose the voltage required for the actuating i.e. switching-on the electromagnetic valve can be increased to a value in excess of the available battery voltage especially in cases in which the idling fuel/air mixture is shut off.

In accordance with an advantageous development, the input stage is particularly insensitive to interference voltages and can be combined with virtually all types of modern coil ignition systems. Only one further active semiconductor switching element is used, the switching-on threshold for triggering the electromagnetic valve being detected with great precision.In this case, the input stage includes three energystoring elements which are in the form of charging and discharging capacitors together with an active semiconductor switching element and which are so arranged that it is possible to obtain from a relatively short ignition pulse, supplied by virtually any ignition coil in a motor vehicle, information which triggers a further processing circuit such that this circuit distinguishes between overrun operation and idling of the internal combustion engine, the butterfly valve being closed in both these operating states.

Furthermore, it is advantageous that the rotational speed at which the mixture is switched on again can be kept largely independent of the supply voltage and the ambient temperature.

Finally, it is particularly advantageous that a higher voltage, obtained entirely by purely electronic means, can be available when the electromagnetic valve is actuated, i.e. switched on, so that increased reliabitity with a smaller space requirement can be combined with lower costs.

The present invention will be further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of a system according to a first embodiment of the invention for shutting off fuel or fuel/air mixture during overrunning, Fig. 2 is a detail circuit diagram of an alternative rotational-speed-responsive in put stage for the system of Fig. 1, Fig. 3 is a circuit diagram of a modification of a portion of the circuit of Fig. 1, Fig. 4 is a diagrammatic axial section detail view of an electromagnetic shut-off valve for shutting off an idling mixture supply, Fig. 5 is a circuit diagram of a system according to a second embodiment of the invention, and Fig. 6 is a detail circuit diagram of an alternative input stage for the system of Fig. 5.

The construction of the circuit arrangement of Fig. 1 will be described in detail in the first instance, wherein it will be appreciated that a large number of the circuit elements shown are not essential for basic operation (this will be further discussed below) and wherein, for the purpose of improved comprehension, specific data has been chosen for the polarities, semiconductor elements, and the like which are used, although, as will be appreciated by one skilled in the art, this data also includes the opposite embodiment (thus, for example, pnp transistor for npn transistor).

The circuit of Fig. 1 comprises an input stage 1 connected to an output stage which includes a solenoid valve MV which is to be triggered and which is connected in series with the collector to emitter path of a transistor T4 between the supply voltage lines, that is the negative line 10 on the one hand and the positive line 11 on the other hand. For the purpose of improved comprehension, it may be immediately pointed out that a solenoid valve MV is constructed such that, in the absence of a triggering operation, i.e. when its excitation winding is not energized, the solenoid valve shuts off the supply of fuel or mixture for the idling system of a carburettor in the present embodiment, while the supply of fuel or mixture is released in the case of a triggering operation when the solenoid valve MV is switched on and actuated.

As already mentioned initially, in the preferred embodiment of the invention, the adjusting member, i.e. the solenoid valve MV in the present instance or, in accordance with Fig. 3, the solenoid valve MV,; for the feeding of the mixture, is to be triggered such that the supply of fuel or mixture is interrupted during the occurrence of predetermined condition of operation. These predetermined condition of operation are chosen such that they include overrunning of the motor vehicle, that is an operating condition in which the motor vehicle is travelling with a relatively high engine speed when the throttle or butterfly valve is closed or the accelerator pedal is released, for example when travelling downhill.By preventing the supply of fuel during such an operating condition, a considerable saving of fuel of from 5% to, for example, 7% can be obtained.

Without first entering into greater details of the construction of the input stage 1 of Fig. 1 or the input stage illustrated in Fig. 2, it is pointed out that this input stage supplies the driver transistor T3 with a greater or less positive potential according to the engine speed. The input stage is designed such that, at a sufficiently low engine speed (in the range of the idling speed), the potential fed to the driver transistor T3 is sufficiently positive to trigger the latter and also to render conducting the transistor T4, so that the solenoid valve MV has been pulled up and releases the supply of fuel.

Furthermore, the vacuum switch S1 or S2 is associated with the region of the driver transistor T3, whrein the vacuum switch S1 is a switch having a normallyclosed contacts KS1, and the vacuum switch S2, which may be alternatively used, is a switch having a normally-open contacts KS2.

Details of the construction of the circuit of the output stage 2 are as follows: The driver transistor T3 has its emitter connected to the negative line 10 by way of a resistor R20 and has two collector resistors R18 and R19 connected to the positive line 11, the junction between these two resistors being connected to the base of the transistor T4 whose emitter is connected directly to the positive line 11 and whose collector is connected to the solenoid valve MV to be switched, the other lead of the solenoid valve being connected directly to earth or the negative line 10.

The solenoid valve MV is triggered without an additional series-connected protective resistor, since a special circuit design, essentialy comprising the resistor R21 between the positive line 11 and the collector of the transistor T4, and the diode D5 connected in series therewith to the base of the driver transistor T3, ensures that the output stage transistor T4 is protected against destruction if the withdrawn solenoid valve plug 12 should inadvertently come into contact with earth. In this case, the diode D5 connects the base of the drive transistor T3 directly to the negative lead, so that this transistor and the transistor T4 are blocked.The resistor R21 ensures that the cathode potential of the diode D5 is sufficiently high during normal operation, to ensure that this diode D5 is rendered non-conductive and does not block the threshold value switch formed by the transistors T3 and T4.

A first circuit variant uses the vacuum switch S2 in place of S1: the normally open contacts KS2 of the vacuum switch S2 connect the collector of the transistor T3 to the negative line 10 by way of the lead 14 when the vacuum switch S2 is closed. This vacuum switch S2 is always closed when the butterfly valve is open, even when only slightly open during slight acceleration. However, when the butterfly valve is closed, the contacts KS2 are open and the vacuum switch S2 does not affect the switching behaviour of the output stage 2 then exclusively controlled by the input stage 1.

If, however, as already mentioned, the contacts KS2 are closed even when the butterfly valve is only slightly open, since there is now present in the intake pipe a vacuum which exceeds a selected response value of, for example, 50mbar, the output stage transistor T4 is then rendered conductive independently of the engine speed, the winding of the solenoid valve MV is energized, and the idling quantity of fuel is released, so that the engine immediately receives the idling quantity of fuel when, for example, accelerating from overrun operation. When the accelerator pedal is released and an adequately high engine speed exists, the feeding of idling fuel is immediatley interrupted.

The output stage 2 of Fig. 1 also includes some additional circuit elements, namely a resistor R17 which is connected in series with the emitter resistor R20 and which raises the emitter potential of the transistor T3 to an extent where the transistor T3 can now only be switched at a multiple of the base to emitter voltage lying approximately in the range of 0.7V. Thus, even a great range of temperature of this base to emitter voltage of the driver transistor T3 becomes largely ineffective. A further advantage arises with respect to the circuit illustrated in Fig. 2 when the input terminal KI1 of the input stage shown in Fig. 2 is directly connected to the collector of the ignition transistor forming part of a fully electronic transistor ignition system and having a switching-on voltage of at least 1.5V.

A Zener diode D8 is also connected in parallel with the collector to emitter path of the output stage transistor T4 and protects this transistor against excessive interference voltage peaks. A reversed diode D9 is then connected in parallel with the excitaiton winding of the solenoid valve MV in a conventional manner in order to avoid voltage peaks occurring when the solenoid valve is witched off. The diode D10 in the positive line 11 protects the circuit against destriuction if the battery is connected with incorrect polarity.

The function of the vacuum switch S1 having normally-closed contacts KS1 will be discussed in conjunction with the explanation of the input stage circuit.

In the simplest case, the input stage circuit can be constructed in the manner described with reference to Fig. 2. In this case, it comprises a series combination connected between the positive line 11 and the negative line 10 and comprising a variable resistor R25, a further resistor R26 and a capacitor C2'. The junction between the resistor R26 and the capacitor C2' is connected, by way of a diode D3' forwardbiassed for positive voltages, to the junction between a capacitor C3' connected to the negative line 10, and a resistor R27 whose other terminal is connected to the base of the driver transistor T3.The terminal KI1 on the input side of the input stage 1' of Fig. 2 is connected either to the contact breaker of a normal coil ignition system, so that the cathode of the diode D1', connecting the terminal KI1 to the junction between the resistors R25 and R26 by way of a further resistor R28, is periodically connected to the earth line, or the terminal KI1 is connected to a switching member of a fully electronic transistor ignition system, for example to the collector of the ignition transistor. The cathode of a diode D12 connected to the negative line 10 is connected to the junction between the resistors R25 and R26.The mode of operaion of this input stage 1' is such that the capacitor C2' is charged to a positive voltage by way of the variable resistor R25 and the resistor R26, wherein peak (point-contact) rectification and charging of the capacitor C3' occurs by way of the diode D3' from a specific positive voltage value. On the other hand, the speed of the internal combustion engine affects the positive charging of the capacitor C2', since the capacitor C2', is periodically discharged when the contact breaker connected to the terminal KI1 is closed. Thus, the capacitor C2' can only be charged during the periods when the contact breaker is open; the slower the internal combustion engine is running, and thus the longer the periods when the contact breaker is open, the higher is the voltage attained by this charging operation.

Below a predetermined lower limiting speed, which can be in excess of, or equal to, the idling speed of the internal combustion engine, the capacitor C3' is positively charged to an extent where the driver transistor T3 is rendered conducting and, as already explained above, finally triggers the solenoid valve MV and thus releases the supply of idling fuel.

Importance is attached to the special circuit, comprising the resistor R28 and the resistor R26 with the parallel-connected diode D12, which prevents the charging of the capacitor C2' from being impaired by high-frequency voltage peaks developing at the time of ignition. These circuit features on the input side ensure that, with a constant engine speed, the voltage remains unchanged across the capacitor C3' charged by peak (point-contact) rectification by means of the diode D3', thereby avoiding the threshold value switch being falsely triggered in the event of stray voltage peaks. The capacitor C4, connected between the collector and the base of the driver transistor T3, also acts in a similar manner and suppresses faulty switching as a result of voltage peaks caused by the ignition.

However, in some cases, it may be desirable to use a circuit which is exclusively dependent upon the frequency of the ignition pulses instead of the simple construction of the rotational- speed-responsive input stage for triggering the threshold value switch comprising the transistors T3 and T4, since pitting of the contacts and wear on the sliding member of the ignition contact breaker can affect the switching behaviour to a certain extent in the input stage circuit 1' of Fig. 2.

The input stage 1 of Fig. 1 essentially comprising a monostable multivibrator formed by the transistor T1 and T2. The emitter of the transistor T1 is connected directly to the negative line 10 and its collector is connected to the positive line 11 by way of a series combination comprising the resistors R5 and R6. The collector of the transistor T1 acts, by way of a series combination comprising a diode D2 and a resistor R8, upon the circuit point PI which, to a certain extent, corresponds to the junction between the diode D3' and the capacitor C2' of the input stage shown in Fig. 2.The base of the transistor T2 is connected by way of a capacitor C1 to the junction between the resistors R5 and R6 and thus to the collector potential of the transistor T1, and to the positive line 11 by way of a further resistor R7. Feedback is effected by way of a resistor R3 from the collector of the transistor T2 to the base of the transistor T1, the base of the transistor T1 being connected to the negative line 10 by way of a resistor R4 and to the input terminal KI1 by way of a series combination comprising a resistor R1 and a diode D1 forward-biassed for positive voltages. Finally, there are provided a resistor R2 which connects the junction between the resistor R1 and the diode D1 to earth, and a collector resistor R9 for the transistor T2.

The capacitor C2 connected between the circuit point P1 and earth can then be charged by, for example, a parallel combination comprising a resistor R10 and a variable resistor Rill. Furthermore, the cir cuit point P1 is connected by way of the diode D3 to the junction between a further capacitor C3, connected to the negative line 10, and a resistor R14 whose other terminal is connected to the base of the driver transistor T3. The basic function of this circuit will be briefly described before discussing further circuit elements.

The transistor T1 is always switched into its conducting state, corresponding to the unstable state of the monostable multivibrator formed by transistors T1 and T2, when a positive pulse is applied to the input terminal Kiwi. A negative voltage is thereby applied to the base of transistor T2 by way of the coupling capacitor C1, so that the transistor T2 is rendered nonconducting and the transistor T1 can be maintained in its conducting state by way of the resistor R3. The unstable state of the monostable multivibrator T1, T2 ends only after the charge on the capacitor C1 has been reversed by way of the resistors R6 and R7, and the transistor T1 again becomes non-conducting.When in its con ducting state, the transistor T1 has reduced the positive potential on the circuit point P1 by way of the diode D2 and the resistor R8, or, in other words, it has discharged the capacitor C2. It will be seen that the discharge operations become increasingly less frequent at low rotational speeds (for example in the range of the idling speed), and an adequate high potential (with corresponding ripple) can be built up across the capacitor C2 that the capacitor C3 is charged by way of the diode D3, acting as a peak rectifier, to positive voltages which render the transistor T3 conducting when the engine speed is sufficiently low.The unstable period of the monostable multivibrator comprising the transistor T1 and T2 is sufficiently long to compensate for the effect of tolerances of the circuit elements used. Thus, only a single adjustment, effected by means of the resistor Rill, is required to set the rotational speed threshold for restoring the feeding of the idling fuel (transistors T3 and T4 conducting). The resistor R16, connected in parallel with the diode D5, which has already been mentioned above, otherwise serves to set the desired rotational speed hysteresis, so that permanent switching operations are not effected in the case of slight fluctuations in the rotational speed and a possible ripple on the peak rectification capacitor C3.

The vacuum switch can alternatively be in the form of vacuum switch S1 having normally-closed contacts KSl. In this case, the vacuum switch S1 opens its contacts KS1 when the butterfly valve is open, even when only slightly open during only slight acceleration, so that the selected response value of the vacuum in the intake pipe is attained. This design is shown as an alternative in Fig. 1 and includes the lead 16 which is shown by a solid line and which connects a circuit point P2 to the negative line 10 by way of the vacuum switch contacts KS1 and a resistor R12.

The circuit point P2 corresponds to the junction between a resistor R13, connected to the positive line, and a diode D4 whose cathode is connected to the capacitor C3.

As will be seen, the effect of an open vacuum switch S1 (accleerator pedal depressed or butterfly valve open) is to allow the potential at the circuit point P2 to float and thereby to immediately apply positive voltage to the base of the driver transistor T3 by way of the series combination comprising the resistor R13 and the diode D4, so that the solenoid valve MV can respond and the supply of fuel can be released. On the other hand, if the butterfly valve is closed, the contacts KS1 of the vacuum switch S1 are also closed and the diode D4 is rendered non-conducting, so that the circuit R13,D4 can no longer influence the potential across the capacitor C3, this potential then being determined exclusively by the operation of the rotaional-speed-responsive input stage 1, and thus by the rotational speed.

The diodes D6 and D7 connected in series with the base leakage resistor R15 serve to compensate for temperature and voltage variation. Furthermore, the switchinging threshold upon a reduction in temperature is shifted upwardly slightly by means of these diodes, so that, at a low temperature and the associated increased frictional resistance of the engine and the condensation of a portion of the fuel on the walls of the intake pipe, the feeding of idling fuel is effected again at a higher rotational speed.

When the circuit in accordance with the invention is used for the shutting-off of the idling mixture during overrun operation, there is then used in many types of carburettors a solenoid valve which opens and closes an opening having a large cross section. A greater magnetic force is required to actuate an electromagnetic shutoff valve MV, of this type, so that, in addition to a mechanical modification of a solenoid valve of this type, which will be discussed further below, the output stage circuit portion of Fig. 3 is preferably used in which the solenoid shut-off valve is triggered not directly by the output stage transistor T4, but through an interposed relay S3 which has two change-over contacts S31 and S32.The remaining triggers ing circuit for the driver transistor T3 is retained, and may correspond either to the circuit variant of Fig. 1 or to that of Fig.

2. The collector to emitter path of T4 is connected in series with the excitation winding of the relay S3. When the changeover contacts S31 and S32 of the relay R3 are in the position shown in Fig. 3, in which the relay S3 is non-energized and the transistor T4 is blocked, the solenoid of the shut-off valve, and which is connected in parallel with a quenching diode D12 in a conventional manner, is connected to a capacitor C5 of sufficient capacitance which is connected to the positive line 11 in series with a diode Dull.In this position, in which the solenoid of the shut-off valve MVo is not energized, and thus the feeding of the idling mixture is interrupted, the capacitor C5 is charged to the supply or battery voltage by way of the winding of the solenoid valve MVG. When the relay S3 is switched, double the battery voltage for actuating the solenoid valve MVe is available for a short period of time.As will be seen, the solenoid valve MVG is then connected to the positive line 11 by way of the changed-over relay contact S32, the lead 20, the capacitor C5 charged to the battery voltage, the changed-over relay contact S31 and the lead 21, and thus receives a voltage higher than the battery voltage until the capacitor C5 has discharged. After the capacitor has discharged, the static holding current flows by way of the diode Dli to the solenoid of the solenoid valve MV provided that the relay S3 has been pulled in when the transistor T4 is conducting.

A further measure which also increases the pull-up force of the solenoid of the shut-off valve is shown in Fig. 4. The mixture shut-off valve MVG, shown detached in Fig. 4, includes a solenoid W with a magnetic core K and an armature A which is urged away from the magnetic core by means of a spring F, so that, as indicated at 20 in Fig. 4, a valve body VK remains on its associated seat S and prevents the feeding of fuel or mixture. As is shown at 21, the magnetic core and the magnetic armature are of conical construction in order to increase the pull-up force of the solenoid magnetic cores, is that there is a considerable increase in the pull-up force compared with the pull-up force of flat magnetic cores. By virtue of this, and by means of the above-described voltage increase for switching by means of the capacitor C5, one obtains a magnetic force which is sufficiently high to open the valve against the vacuum suction force during overrun operation (static pressure beyond the butterfly valve).

The supply voltage of the overall circuit otherwise need not be stabilized, since the voltage threshold value on the base of the driver transistor T3 varies to the same extent as the speed-dependent voltage across the peak rectification capacitor C3.

It will be appreciated that a circuit of this type (reacting to external operating parameters) can also be used to influence other adjusting members, particularly on the basis of electromagnetic switching.

When operating with the vacuum switch S1 having normally-closed contacts KS1 and acting upon the triggering side of the driver transistor T3, the supply of fuel will not be immediately shut off upon releasing the accelerator pedal (closing the butterfly valve), but only after a certain time lag which can be adjusted to, for example, between 1 and 2 seconds. This might be desirable, since, in this manner, the supply of idling fuel is not interrupted at higher engine speeds when only a gear shift is effected.

In the embodiment of Fig. 5, the output stage transistor T32 is triggered by a sensor circuit dependent upon the position of the butterfly valve, substantially in the manner as already described above, that is by means of a vacuum switch US30 whose contacts KS30 may be directly arranged in the base circuit of the output stage transistor. However, an input stage circuit only comprising a transistor T30 and associated circuit elements is provided for detecting the speed-dependence and is triggered at the input terminal K30 by, for example, ignition pulses, i.e., more strictly speaking, by the voltage on the terminal 1 of the ignition coil.

In detail, the input stage circuit comprises the transistor T30 whose emitter is connected directly to the negative line or earth and whose base circuit has a base leakage resistor R32 connected in parallel with a charging capacitor C30 by way of a resistor R31. Triggering by the terminal 1 of the ignition coil is effected at the junction between the capacitor C30 and the resistor R31 by way of a series combination comprising a resistor R30, a diode D30 and a Zener diode DZ31. A further charging capacitor C3l is located in the collector circuit at the transistor T30 and is connected to the collector by way of a resistor R33. A diode D32 is connected in parallel with the capacitor C31.The capacitor C3l is charged with positive voltage by way of parallel-connected resistors R34/ R35 which are connected to positive supply voltage, that is to the vehicle supply voltage +Ug when used in a motor vehicle.

It is pointed out at this juncture that the designations which are used for the polarities and the individual semi-conductor circuit elements relate only to the illustrated embodiment and, as will be appreciated by one skilled in the art, can also embrace the complementary conducting types of transistors and correspondingly different voltage polarities.

The junction between the capacitor C31 and its charging resistors R34/R35 is connected by way of a diode D33, operating as a peak rectifier in the present instance, to a further storage capacitor C32 which is connected by way of a resistor R36 directly to the base of a further transistor T31 which can be designated " driver transistor" for the output stage transistor T32.

A base leakage resistor R37 for the transistor T3 1 is provided and also an emitter resistor R38 connected to the negative line or earth.

The collector of the transistor T31 affects the switching behaviour of the output stage transistor T32 by triggering the base voltage divider, comprising the resistors R43, R44, at the circuit point P30 which is connected to the negative line by way of the contacts KS30 of the vacuum switch US30.

It will be appreciated that the vacuum switch US30 can be replaced by any other suitable sensor which can feed to the output stage transistor T32 a triggering signal dependent upon the position of the butterfly valve of the internal combustion engine. In-the embodiment illustrated in Fig. 4, the vacuum switch US30 is comparable with the vacuum switch S2 which is illustrated in Fig. 1 and whose contacts KS2 are also connected in series with the base voltage divider of the output circuit transistor T4.

The emitter of the output stage transistor T32 is connected directly to the positive line 30; the collector is connected by way of a diode D39, forward-biassed for positive voltages, to the winding of the solenoid valve MV30 to be controlled. A diode D40 biassed in the reverse direction is connected in parallel with the solenoid valve.

The other circuit elements provided, and which have not yet been mentioned, will be discussed hereinafter in conjunction with an explanation of the mode of operation of the circuit illustrated in Fig. 5.

When an ignition operation is triggered, the voltage on the terminal 1 of the ignition coil of an optional motor vehicle is, in general, in the first instance approximately in the form of a sinusoidal pulse having a voltage level of 200 to 300V (according to the ignition coil) and a width of approximately 100 ,us. This (positive) ignition voltage pulse charges the capacitor C30 in the base of the transistor T30 by way of the series combination comprising the elements R30, diode D30, and Zener diode DZ31. The capacitor C30 can then subsequently discharge by way of the resistors R31 and R32 and the base to emitter path of the transistor T30.In this manner, one obtains from the only very short ignition pulse a discharge pulse of a longer duration required to discharge the relatively large charging capacitor C31 arranged in the collector circuit of the transistor T30. In other words, the capacitor C31 is charged by way of the resistor path R34/R35 with a relatively long charging duration and is discharged by way of the collector to emitter path of the transistor T30 when the latter is controlled into its conducting state, the resistor R33 limiting the discharge current of the capacitor C31 in a suitable manner for the purpose of protecting the discharge transistor T30.

In an assumed embodiment, that is a four-cylinder engine, the capacitor C3i is discharged for a period of approximately 0.5 to 1 ms at a rotional speed of 1500 rpm, that is within a period which is very short compared with the 20 ms charging period of the capacitor C31 in this embodiment. The discharge pulse time constant for the capacitor C30, amounting to approximately C30 x R31, is somewhat larger than the discharge pulse time constant for the capacitor C31 which amounts to approximately C31 x R33, so that reliable discharge of the capacitor C31 is always ensured at each ignition pulse. The value of the resistor R30 is sufficiently large to ensure that the present circuit constitutes virtually no load for the voltage formed on the terminal 1 of the ignition coil.The diode D30 prevents the capacitor C30 from discharging by way of the terminal K30 when the voltage on the terminal K30 declines. Any further second or third positive pulses on the terminal 1 of the ignition coil charge the capacitor C30 to a further extent, although the durations of these charges are, in all cases negligible compared with all other pulse durations occurring. Finally, the Zener diode DZ31 also provided ensures that the capacitor C30 is not charged again, and consequently the capacitor C31 is not incorrectly discharged again, at the positive voltage pulse which reaches a voltage level of approximately 50V on the ignition coil and which occurs upon the breaking of the ignition spark after approximately 1 ms.

After the discharge pulse has decayed by way of the collector to emitter path of the transistor T30, the capacitor C3i is charged in the direction of the battery voltage by way of the parallel-connected resistors R34/R35. The resistor R35 otherwise effects the single circuit adjustment required, whereby the tolerances of the other circuit components can be compensated for. If the voltage across the catpacitor C3l exceeds the voltage across the capacitor C32, the capacitor C32 together with the capacitor C31 are further charged by way of the peak rectifier diode D33 already mentioned.The voltage across the capacitor C32 then remains substantially constant even during discharge of the capacitor C31, since the charge of C32 can flow off only relatively slowly by way of the high-resistance resistors R36 and R37 and, when there is a correspondingly high voltage across the capacitor C32, by way of the conductive base to emitter path of the transistor T31 and the resistor R38.

The transistor T31 and the transistor T32 together form a rotational-speedresponsive threshold value switch. When the speed of the internal combustion engine is relatively low, i.e. it is approximately at idling speed, the supply of fuel or the supply of idling mixture must not be shut off by way of the solenoid valve.

The solenoid valve MV30 is designed and wired such that, when its winding is energized, the quantity of fuel to be fed in order to maintain the idling state of the internal combustion engine is released, or the required idling mixture can be fed to the internal combustion engine. Thus, if the succesisve discharge operations of the capacitor C3l ensue at a lower frequency determined by, for example, the idling of the internal combustion engine, the positive voltage developing across the capacitor C32 can render the transistor T31 conducting with the result that the potential of the circuit point P30 is drawn in the direction of a negative voltage and the transistor T32 is also rendered conducting. The solenoid valve MV30 is then pulled up and releases the required idling quantity of fuel or idling quantity of mixture.It will be seen that the same switching behaviour ensues with respect to the output stage transistor T32 when the sensor US30, dependent upon the position of the butterfly valve, ascertains that the butterfly valve is not fully closed, i.e. that the internal combustion engine is not being driven by the vehicle. In this case, the contacts KS30 close, and the transistor T32 is also controlled into its conducting state.

The rest of the wiring serves predominantly to render the reclosing speed threshold independent of variations in the supply voltage and the ambient temperature. Three series-connected diodes D34, D35 and D36 are provided which are connected between the positive supply voltage and the emitter of the transistor T31 by way of a resistor R39. The junction betwen the last diode D36 and the resistor A39 is connected to the base of the transistor T3 1 by way of series-connected re sistors R40,R41 and R42, wherein the capa citor C33 connecting the base and the collector serves to suppress interference pulses.

A diode D37 is connected in parallel with the resistors R41 and R42 and, as may be seen, is normally reverse biassed. The diode, together with the resistors R40 and R41, ensure that the transistor T32 forming the output stage is not destroyed if the connection M for the solenoid valve M30 inadvertently comes into contact with earth, for example when fitting the system in the vehicle or when testing the system.

Namely, if the connection M should be short-circuited to earth, the diode D37 is rendered conducting by way of the connection lead L3 and blocks the transistor T31 and thereby also the transistor T32.

The diode D39 also protects the transistor T32 if the battery voltage terminals should be inadvertently connected with incorrect polarity. The diode D32 also serves as a protection against incorrect polarity and, in this case, protects the transistor T30 and the capacitors C3i and C32. Finally, in addition to compensating for variation of voltage and temperature, the diode D34 also serves as a protective diode for the Zener diode DZ38 in the event of connection with the incorrect polarity and charging of a further capacitor R34 by way of a transistor T33 which may also be provided as an advantageous development. This will be discussed hereinafter.

It has already been pointed out that it might be necessary to trigger the solenoid valve MV30 with an increased voltage.

The electronic circuit portion shown by broken lines in Fig. 5 is constructed such that the switching-on voltage for the solenoid valve can be increased above the battery voltage without requiring an additional relay. A further transistor T33 is provided whose collector is connected to the terminal M of the solenoid valve and whose emitter is connected by way of a resistor R46 to the line L30 carrying the positive supply voltage. The emitter is also connected to the collector of the output stage transistor T32 by way of a capacitor C34. The transistor T33 is triggered by the circuit point P30, i.e. by the collector of the transistor T31, by way of a diode D41, biassed in the forward direction for negaitve voltages, and a resistor R45.

Provided that the solenoid valve MV30 is switched off, the capacitor C34 can be charged to battery voltage by'way of the resistor R46, the diode D39 and the winding of the solenoid valve MV30. When the engine speed drops below the threshold speed, i.e. when the actual rotational speed approaches the idling speed or corresponds thereto, the transistors T31 and T32 become conducting in the manner already described above, and thus the additional transistor T33 also becomes conductive, since it can be triggered with substantially earth potential by the collector of the transistor T31.The terminal of the capacitor C34 which is connected to the collector of the transistor T32, and which was previously at earth potential, is now drawn to approximately the battery voltage by the collector of the transistor T32, so that the other terminal of the capacitor C34 jumps to twice the battery voltage.

Since the transistor T33 is conducting, its collcetor, and thus also the terminal M of the solenoid valve, carry almost twice the battery voltage for a short period of time.

During the discharge of the capacitor C34, the diode D39 assumes its non-conducting state by way of the transistor T33 and the winding of the solenoid valve. Positive feedback results across the resistors R42 (positive voltage is applied to the base of the transistor T31, whereby the dynamic operation is further intensified). It will be appreciated that this positive feedback is also important for the basic circuit without votlage excess.

The diode D41 ensures that, upon the switching-off of the solenoid valve MV30, the transistor T33 is immediately blocked and is not possibly overstressed by voltage break-down as a result of momentary polarity reversal of the emitter to base path.

A further advantageous development of the voltage increase circuit ensues when the cathode of the diode D41 is connected directly to the positive line L30 as is shown by the dash-dot connection lead L32. In the normal case, i.e. when the transistor T32 is non-conducting, transistor T33 is also non-conducting and the capacitor C34 has the opportunity, as already described, of charging to virtually battery voltage +UB with the polarity shown in the drawing. When transistor T32 is then rendered conducting, the potential on the emitter of transistor T33 jumps to twice the battery voltage, the transistor T33 becomes conducting, and the desired voltage increase is realised. In this connection, it is advantageous that the transistor T31 is not loaded by the base current of transistor T33 during the voltage increase phase.

Thus, the other components (particularly R44) can be arranged in the same manner as in the circuit without the voltage increase. The function of transistor T33 is virtually unaffected, since this transistor is, in any case, conducting only until capacitor C34 has discharged and thus the voltage on the emitter of transistor T33 has reached approximately the potential of the supply voltage.

Fig. 6 shows a further advantageous development of the present invention. In Fig. 5, the voltage threshold value, from which the transistor T31 could be rendered conducting by the voltage across the capacitor C32, was adjusted by way of the diode path D34, D35 and D36 by means of the voltage divider which comprises the resistors R39 and R38. This voltage threshold value for the transistor T31 can also be set by means of a transistor T34 which is connected to the transistor T31 in the manner of a differential amplifier. The emitter of the transistor T34 is connected to the emitter of the transistor T31, its collector is connected to positive supply voltage, and the reference voltage divider.

comprising the resistors R50 and R51 and connected to the base of the transistor T34, is connected to the junction between the further diode D34 and the Zener diode DZ38. The diodes D35 and D36 can then be omitted. The terminal of the resistor R40 which has then become free is also connected to the cathode of the diode D34.

The temperature and voltage variation can be adjusted with precision by means of the transistor T34, so that this circuit variant operates virtually independently of changes in the supply voltage and in the ambient temperature.

It is advantageous that in the circuit illustrated in Fig. 5 the input stage evaluating the speed of the internal combustion engine requires only a single transistor and can be used for all current types of coil ignition. The input stage is protected against interference voltages and avoids the coupling capacitor required particularly in the case of a monostable multivibrator circuit.

The speed of release of the solenoid valve is largely independent of the supply voltage and the ambient temperature, and the voltage increase upon the switching-on of the solenoid valve is obtained by purely electronic means.

WHAT WE CLAIM IS: - 1. A system for controlling the supply of fuel or fuel/air mixture to an internal combustion engine under predetermined conditions of operation, comprising a driver circuit connected to an electromagnetic shut off valve for interrupting the flow of fuel or fuel/air mixture to the engine vacuum operated switch means connected to the driver circuit and responsive to pressure in the engine intake pipe and providing a signal indicative of the state of the engine throttle valve as either open or closed, and a primary electrical circuit responsive to engine speed related input signals and providing an engine speed indicative output signal to the driver circuit, whereby actuation of the electromagnetic shut off valve is controlled by the driver circuit such that the supply of fuel or fuel/air mixture to the engine is shut off by the valve when simultaneously the signal from the vacuum operated switch means indicates that the throttle valve is closed and the signal from the primary circuit indicates that the engine speed is above a predetermined speed greater than the idling speed of the engine.

2. A system as claimed in claim 1, in which the primary electrical circuit or speed-responsive input stage includes a charging capacitor which is chargeable by way of resistors and which is operatively connected by way of a peak rectifying diode to a further capacitor which triggers the base of a driver transistor which, together with an output stage transistor forms a threshold value switch and the charging capacitor is operatively connected to a speed-dependent discharge circuit such that the driver transistor is feedable with a triggering potential which becomes more positive as the rotational speed drops.

3. A system as claimed in claim 2, in which an input terminal of the speedresponsive input stage which is connected to a circuit breaker contact of the engine ignition system is connected by way of a diode and a resistor to the junction between the two charging resistors, a diode biassed in the forward direction for negative voltages being connected between the said junction and earth.

4. A system as claimed in claim 2 or 3, in which the driver transistor has an emitter resistor whose junction with the emitter is connected to positive potential by way of a resistor for the purpose of increasing the base switching theshold.

5. A system as claimed in claim 2, 3 or 4, in which the discharge circuit for the charging capacitor comprises a monostable multivibrator circuit which is switched by positive input pulses into its unstable state determining the discharge of the charging capacitors 6. A system as claimed in claim 5, in which the monostable multivibrator circuit comprises two transistors which are backcoupled between collector and base by way of a capacitor and a resistor respectivelv, and the collector of the transistor which is conducting during the unstable state is connected to the charging capacitor preferably by way of a series combination comprising a resistor and a diode.

7. A system as claimed in any of claims 2 to 6, in which the base of the output stage transistor, whose collector is connected directly to a negative line by way of an excitation winding of the electromagnetic shut off valve, is connected to the collector of the driver transistor by way of a series combination comprising two resistors such that, at a sufficiently positive

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Fig. 5, the voltage threshold value, from which the transistor T31 could be rendered conducting by the voltage across the capacitor C32, was adjusted by way of the diode path D34, D35 and D36 by means of the voltage divider which comprises the resistors R39 and R38. This voltage threshold value for the transistor T31 can also be set by means of a transistor T34 which is connected to the transistor T31 in the manner of a differential amplifier. The emitter of the transistor T34 is connected to the emitter of the transistor T31, its collector is connected to positive supply voltage, and the reference voltage divider. comprising the resistors R50 and R51 and connected to the base of the transistor T34, is connected to the junction between the further diode D34 and the Zener diode DZ38. The diodes D35 and D36 can then be omitted. The terminal of the resistor R40 which has then become free is also connected to the cathode of the diode D34. The temperature and voltage variation can be adjusted with precision by means of the transistor T34, so that this circuit variant operates virtually independently of changes in the supply voltage and in the ambient temperature. It is advantageous that in the circuit illustrated in Fig. 5 the input stage evaluating the speed of the internal combustion engine requires only a single transistor and can be used for all current types of coil ignition. The input stage is protected against interference voltages and avoids the coupling capacitor required particularly in the case of a monostable multivibrator circuit. The speed of release of the solenoid valve is largely independent of the supply voltage and the ambient temperature, and the voltage increase upon the switching-on of the solenoid valve is obtained by purely electronic means. WHAT WE CLAIM IS: -

1. A system for controlling the supply of fuel or fuel/air mixture to an internal combustion engine under predetermined conditions of operation, comprising a driver circuit connected to an electromagnetic shut off valve for interrupting the flow of fuel or fuel/air mixture to the engine vacuum operated switch means connected to the driver circuit and responsive to pressure in the engine intake pipe and providing a signal indicative of the state of the engine throttle valve as either open or closed, and a primary electrical circuit responsive to engine speed related input signals and providing an engine speed indicative output signal to the driver circuit, whereby actuation of the electromagnetic shut off valve is controlled by the driver circuit such that the supply of fuel or fuel/air mixture to the engine is shut off by the valve when simultaneously the signal from the vacuum operated switch means indicates that the throttle valve is closed and the signal from the primary circuit indicates that the engine speed is above a predetermined speed greater than the idling speed of the engine.

5. A system as claimed in claim 2, 3 or 4, in which the discharge circuit for the charging capacitor comprises a monostable multivibrator circuit which is switched by positive input pulses into its unstable state determining the discharge of the charging capacitors

6. A system as claimed in claim 5, in which the monostable multivibrator circuit comprises two transistors which are backcoupled between collector and base by way of a capacitor and a resistor respectivelv, and the collector of the transistor which is conducting during the unstable state is connected to the charging capacitor preferably by way of a series combination comprising a resistor and a diode.

input potential for the driver transistor corresponding to a relatively low rotational speed, the two transistors are rendered conducting and the solenoid valve releases, at least indirectly, the idling quantity of fuel or fuel/air mixture required for maintaining the idling of the engine.

8. A system as claimed in any of claims 2 to 7, in which the vacuum switch has normally-open contacts which are closed when the throttle valve is open and connect the collector of the driver transistor directly to a potential suitable for switching the output stage transistor into its conducting state.

9. A system as claimed in any of claims 2 to 7, in which the vacuum switch has normally-closed contacts which are closed when the butterfly valve is closed and which immediately prevent the feeding of positive potential to a peak rectification capacitor such that the switching behaviour of the driver transistor is exclusively determined by the speed-responsive input stage.

10. A system as claimed in claim 9, in which the peak rectification capacitor connected to the base of the driver transistor is connected to positive potential by way of a series combination comprising a forward-biassed diode and a resistor, and the junction between the diode and the resistor is connectible to earth potential by way of a connection lead and, if required, by way of a resistor and the switching contacts of the vacuum switch.

11. A system as claimed in any of claims 2 to 10, in which to prevent destruction in the event of the solenoid valve connection coming into contact with earth, the collector of the output stage transistor is connected to the base of the driver transistor by way of a diode biassed in the forward direction for negative voltages, and to positive potential by way of a resistor.

12. A system as claimed in any of claims 2 to 11, in which the output stage transistor acts upon a relay having two change-over contacts for the purpose of increasing the magnetic force when actuating the electromagnetic shut-off valve which in a solenoid valve having a large shut-off cross section, and which, when in the relay is not operated, the excitation winding of the electromagnetic shut-off valve is so connected by way of a relay contact in series with a capacitor and a diode that it is possible for the capacitor to be charged to battery voltage by way of the excitation winding of the shut-off valve, and when the relay is operated the charged capacitor connects the excitation winding of the shut-off valve to positive potential by way of the relay contacts such that twice the battery voltage is available for a short period of time for actuating the electromagnetic shut off valve.

13. A system as claimed in any of claims 2 to 12, in which at least one diode is connected in series with a base leakage resistor of the driver transistor for the purpose of compensating for temperature and voltage variations.

14. A system as claimed in claim 12 or 13, in which for the purpose of increasing the magnetic actuating force, the magnetic core and the magnetic armature of the solenoid shut-off valve are of conical construction.

15. A system as claimed in any of claims 2 to 14, in which the input stage includes a semi-conductor switching element in the base circuit of which is arranged a first capacitor which is charged by each ignition pulse, a second capacitor which is cyclically discharged by the semiconductor switching element with each ignition pulse fed and which, by way of a diode, is connected in parallel with a third capacitor which is dischargeable only gradually, and that the latter capacitor is connected to the base circuit of the driver transistor connected to the input of the output stage transistor.

16. A system as claimtd in claim 15, in which the first capacitor, charged by a relatively very short ignition pulse by way of at least one diode is discharged by way of the transistor connected on the output side, when the latter transistor is rendered conducting, whereby to form a discharge pulse of longer duration for the second capacitor, and in which the second capacitor is chargeable by a variable resistor with a charging time constant which is substantially greater than the discharging time constant determined by the first capa citor, such that, only after reaching a lower speed threshold, the voltage across the capacitor, charged by the second capacitor by way of peak rectification, is so positive that the driver transistor connected on the output side is controllable into its conducting state.

17. A system as claimed in claim 15 or 16, in which the driver transistor is in the form of a threshold value switch having a voltage divider which adjusts its emitter to a predetermined potential.

18. A system as claimed in claim 15, 16 or 17, in which the collector of the driver transistor is connected to the base voltage divider of the output stage transistor connected on the output side, and that, for the purpose of detecting the position of the engine throttle valve, this base voltage divider is additionally controlled by the contacts of a vacuum switch in the intake pipe of the internal combustion engine.

19. A system as claimed in any of claims 15 to 18, in which a further switching transistor triggered by the collector of the driver transistor is provided for increasing the voltage available initially when switching on the electromagnetic shut off valve and connects a capacitor, charged substanto battery voltage, in series with the excitation winding of the electromagnetic valve.

20. A system as claimed in claim 19, in which the capacitor for the voltage increase is connected on the one hand to positive supply voltage by way of a resistor and, on the other hand, by way of a diode and the excitation winding of the electromagnetic valve, to the other pole of the supply voltage and at the same time to the collector of the output stage transistor such that, when the output stage transistor and the additional transistor are conducting, the winding of the electromagnetic valve is connected in series with the collector to emitter paths of the two transistors and to the capacitor charged to the battery voltage.

21. A system as claimed in any of claims 15 to 20, in which, for the purpose of positive feedback, that terminal of the winding of the electromagnetic valve which is connected to positive voltage when the winding is energised is back-coupled to the base of the driver transistor by way of a resistor.

22. A system as claimed in any of claims 15 to 21, in which a Zener diode is connected on the input side of the first capacitor for the purpose of suppressing any possible interference pulses which might occur when the ignition spark breaks.

23. A system as claimed in any of claims 15 to 22, in which, for the purpose of adjusting the threshold value, the emitter of the driver transistor is connected to the emitter of a further transistor whose base circuit is fed with the reference voltage by way of a voltage divider.

24. A system as claimed in claim 19 or 20, in which the base of the additional transistor is connected to the positive pole of the supply voltage by way of a diode.

25. A system for controlling the supply of fuel or fuel/air mixture to an internal combustion engine under predetermined conditions of operation, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig.

1 or Fig. 2 or Fig. 3 of the accompanying drawings.

26. A system as claimed in claim 25 including an electromagnetic shut off valve constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 4 of the accompanying drawings.

27. A system for controlling the supply of fuel or fuel/air mixture to an internal combustion engine under predetermined conditions of operation, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 5 or Fig. 6 of the accompanying drawings.