US3464396A

US3464396A - Impulse generator

Info

Publication number: US3464396A
Application number: US661339A
Authority: US
Inventors: Hermann Scholl
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1966-08-31
Filing date: 1967-08-17
Publication date: 1969-09-02
Anticipated expiration: 1986-09-02
Also published as: AT280694B; BE703274A; NL6711920A; CH461579A; GB1127068A; SE316204B; ES344644A1

Description

p 2, 1959 H. SCHOLL 3,464,396

IMPULSE GENERATOR Filed Aug. 17, 1967 2 Sheets-Sheet l INTER/VAL COMBUS 77011 5N6 [NE INVENTOR Hermann SCHOLL ll fc lh rx'i! v his ATTORNEY Sept. 2, 1969 H. SCHOLL IMPULSE GENERATOR 2 Sheets-Sheet 2 Filed Aug. 17, 1967 llllluvlllll INVENTOR Hermann SCHOLL his ATTORN :6

3,464,396 IMPULSE GENERATOR Hermann Scholl, Stuttgart, Germany, assignor to Robert Bosch GmbH. Stuttgart, Germany, a limited-liability company of Germany Filed Aug. 17, 1967, Ser. No. 661,339 Claims priority, application ligrmany, Aug. 31, 1966,

B 8 Int. Cl. F02m 51 H03k 3/295 U.S. Cl. 123-32 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an impulse generator, in which the time duration of the pulses is widely variable, and including a multivibrator circuit.

It is often desirable to change the time duration of pulses generated in a multivibrator over a wide range. Known arrangements utilize inter-stage coupling, including a R-C network, thus changing the time constant by change of the resistance or the capacity; it has also been proposed to change the inductance in multivibrator circuits in which the coupling is an inductive-resistance coupling, or the resistance of such a L-R network.

Multivibrator circuits which are to operate under difiicult conditions, such as in the machine area of a factory, in rolling mills, motor vehicle or the like, must have a sturdy adjustment element to change the impulse frequency, an element which is not subject to wear and tear, even under constant change. Inductive elements are much better suited to change, then resistance potentiometers, since movement of an iron core, or of a coil, can be caused with substantially no wear, or maintenance requirements. Even quality potentiometers are subject to a certain amount of wear and further, potentiometers are ordinarily quite sensitive to vibration.

Inductive adjustment members, in which the inductive value changes with motion of an adjustable element, are comparatively expensive. This is particularly true if, in mass production, a large number of such inductive elements are to be built having identical characteristics, for example, for use with a fuel injection arrangement for motor vehicles, in which the adjustable element of an inductive coupling unit is movable in dependence on the vacuum in the intake manifold of the internal combustion engine. Final adjustment and alignment of such inductive elements is required, such adjustment being costly and time-consuming.

Inductive coupling elements, when used for low frequencies, as is the case in gasoline injection systems for gasoline engines, cause further problems. The iron core must be of substantial mass, so that the lower limiting frequency is sufiiciently low. This further increases the price of such coupling elements, and increases their size so that inductive elements are often much larger than the remainder of circuit components with which they are used, particularly when printed circuits or integrated circuit elements are used therewith.

It is an object of the present invention to provide an impulse generator, utilizing an inductive coupling eleatent C 3,464,396 Patented Sept. 2, 1969 ment in which the aforementioned disadvantages are avoided. More particularly, the impulse generator of the present invention, utilizing an inductive coupling element, to adjust the time duration of impulses should be so designed that the inductivity of this coupling element has no essenial influence on the time duration of the impulses themselves, and which does not place high requirements on the lower limiting frequency thereof.

Subject matter of the present invention Briefly, in accordance with the present invention, a multivibrator circuit has a differential transformer coupled to the output thereof, the differential transformer having an adjustable core element so that the coupling to the secondary can be varied. An electronic, voltage-sensitive switch, having a predetermined threshold is connected to the output of the differential transformer over a charging condenser. The switching state of the voltage-sensitive switch is then determined by the potental on the condenser.

The dilferential transformer thus has a couple only a sort, square wave pulse, generated by the multivibrator, which charges the condenser to a certain value. The wave shape of this pulse, transmitted by the differential trans former, has very little influence on the pulse duration, so that the steepness of the flanks, both on the rising as well as on the falling side, is not critical.

The threshold voltage-sensitive switch then causes a stretching out of the impulse duration by a predetermined factor, so that when the multivibrator supplies an impulse of duration t,, the impulse duration at the output of the voltage-sensitive switch will be a xt The lower limiting frequency of the differential transformer is thus determined by t and not by the much longer time period of the pulses at the output of the voltage-sensitive switch, and the differential transformer can thus be constructed in simpler, and hence cheaper, form.

The output signal of the differential transformer may be applied to the condenser over a rectifier and thus the charging time constant of the condenser will become independent of its discharge time.

The structure, organization, and operation of the invention will now be described more specifically with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit in accordance with the present invention, applied to an internal combustion engine;

FIG. 2 is a longitudinal section through a differential transformer along line IIII of FIG. 3;

FIG. 3 is a front view of the differential transformer in accordance with FIG. 2; and

FIG. 4 is a series of graphs of voltage (ordinate) versus time (abscissa) illustrating the operation of the circuit of FIG. 1.

Referring now to the drawings, and more particularly to FIG. 1:

A monostable multivibrator 10, including a pair of

pnp transistors

11 and 12 has its output connected to a differential transformer 13. The output of the differential transformer 13 is applied over a diode 14 to a condenser 15; and then through a coupling resistance 48 to a voltagesensitive switch 16, having a lower threshold value. Switch 16 is in the form of a Schmitt trigger, the switching state of which depends on the potential on condenser 15; switch 16 contains two pnp transistors 17 and 18.

The monostable multivibrator 10 is conventional. The base of transistor 11 has, over a condenser 21, positive pulses schematically indicated at 22 applied thereto; pulses 22 are obtained from an impulse generator IG, associated with the shaft S of an internal combustion engine E. The pulses thus are synchronized with the speed of the engine. The connections are schematically indicated by dashed lines and the impulse generator may be of any well known 3 type, such as a cam cyclically closing a switch, a magnetic element passing a coil, photoelectric means or the like. The base of transistor 11 is further connected over a resistance 23 to a negative bus 24 of a source of power; the emitter is connected to positive bus 25. The potential between

lines

24, 25 may be, for example, 12 v.

A condenser 26 connects the base of transistor 11 to the collector of transistor 12. The collector of

transistors

11 and 12, each, is connected over a

collector resistance

27, 28, respectively with negative line 24; further, the collector of transistor 11 is connected directly to the base of transistor 12, the emitter of which connects directly to positive bus 25.

In operation of the multivibrator 10, transistor 11 is usually conductive and transistor 12 is blocked, if no positive pulse 22 is supplied. As soon as a positive pulse 22 is applied to the base of transistor 11, this transistor will block, its collector will become strongly negative, and the base of transistor 12 will thus likewise become negative. Transistor 12 will become conductive. The collector potential will then shift in a positive direction. Condenser 26 retransmits this potential jump to the base of transistor 11 and retains it positive. Only when condenser 26 has sufliciently discharged over resistance 23, then transistor 11 after an impulse period indicated in FIG. 4 with t, will again become conductive, causing transistor 12 to block.

Differential transformer 13 is connected to the output of multivibrator 10. It has two

primary windings

35, 36; the

windings

35, 36 are in parallel with the collector resistance 28 of transistor 12. A secondary 37 of transformer 13 has one terminal connected to positive bus 25, the other to the cathode of a diode 14; the anode of diode 14 connects to one electrode of condenser 15, the other side of which is again connected to positive bus 25.

Differential transformer 13 has a movable element indicated as movable core element 38. It is connected by means of a linkage 39 with a pressure sensing element 40 connected to the intake manifold of engine E, in wellknown manner. Pressure sensing element 40, may, for example, be a vacuum chamber with a diaphragm. The intake manifold has a vacuum therein which depends on the position of the throttle of the engine; if the throttle is closed, the vacuum is high, and link 39 is shifted upwardly in the direction of arrow 41. If the throttle is open, there is little, or hardly any vacuum in the intake manifold, and linkage 39 moves against the direction of arrow 41, that is downwardly in FIG. 1. With motion of linkage 39, the iron core 38 shifts accordingly.

FIGS. 2 and 3 illustrate one form of a differential transformer 13, generally containing a rectangular frame 43 having a pair of bores in which a brass tube 44 is secured. A pair of

coil formers

46, 47, separated by a center part of ferro-magnetic material 45, are arranged upon the brass tube 44. l

Coil 46 has an inner winding forming the primary 35, and an outer winding forming one half of secondary 37; coil 47 contains an inner winding forming the primary 36 and an outer winding forming the second half of secondary 37. The direction of winding of the separate coils is indicated in conventional form by a point or a cross, respectively. As clearly appears from FIG. 2, the two

primaries

35, 36 are wound in opposite sense whereas the two halves of the secondary 37 have the same sense of winding. This is further indicated by the dots in FIG. 1.

When movable core 38, within the brass tube 44, is in its center position, indicated with dashed lines, then the coupling between the two

primary windings

35 and 36 with the secondary 37 is symmetrical. An alternating current potential applied to the primaries will thus induce in the secondary equal and opposite potentials which cancel each other. If core 38 is shifted from its center position to the full line position of FIG. 2, then the windings on coil 47 are coupled more tightly than those of coil 46 and a potential will appear at secondary 37. The input inductivity of the dilferential transformer 13 has only a negligible influence on the amplitude of this secondary potential.

FIG. 4 illustrates, in the upper row, the output impulses of multivibrator 10; the second row from above indicates the potential 11 at the output of differential transformer 13 for various positions of iron core 38. With a high vacuum, the potential will be that shown under the column (a), that is when the core 38 is practically in its center position; the column (b) indicates the potentials with some cut-of-center position of core 38; and under (c) a potential with substantial out-of-center position is indicated. As seen, the potential a increases as the out-ofcenter position of core 38 increases.

The potential u is supplied over diode 14 to condenser 15 to charge the condenser to a predetermined potential. After the termination of the impulse, the condenser discharges over a pair of serially connected

resistances

48, 49, in parallel therewith. Condenser 15 thus will have a potential thereacross as seen in the third row of FIG. 4, that is u (t) indicated for the three cases (a), (b), (c).

The base of transistor 17 of the threshold switch 16 is connected to the junction or tap points of

resistances

48, 49. Its collector is connected over a collector resistance 52 with a negative line 24, and over a coupling resistance 53 with a base of transistor 18, which, in turn, is connected over a resistance 54 to the positive bus 25.

The emitters of transistors 17, 18, respectively, is connected together, and over a common emitter resistance, 55 to positive line 25. The collector of transistor 18 connects over a collector resistance 56 with negative bus 24. Further, between the collector and resistance 56, a load, generally indicated at 57, is connected which may, for example, be an electromagnetic fuel injection unit of a gasoline injection system for engine E.

When the potential 1 on the condenser 15 is zero, transistor 17 is blocked and transistor 18 conductive, since it has a negative potential on its base, applied by the resistances 53, 54, forming a voltage divider. If condenser 15 charges, its anode, connected to the diode 14, will become negative with respect to the positive line 25. When a certain, predetermined negative potential is reached, which is indicated in FIG. 4 with w and which is the threshold potential, transistor 17 becomes conductive and transistor 18 blocks. This condition persists until the condenser 15 is discharged so that the potential of the base of transistor 17 drops below the threshold potential of voltage-sensitive switch 16. Switch 16 returns to its quiescent state, that is, transistor 17 becomes blocked and transistor 18 conductive.

The time between the switchover of the threshold switch 16 depends on the charge applied to the condenser 15. Thus, the time duration of pulses 11., applied to the load 57 will depend on the position of iron core 38 of the differential transformer 13, as indicated in FIG. 4 in the lowest horizontal row. When iron core 38 is almost in its center position, that is, column (a), pulse 11 will be short. As the iron core 38 moves out of the center position, pulses in; become longer, as illustrated in the columns under (b) and (c). It has been found that the impulse duration t, of the multivibrator 10 can be changed in a range of from 1:10.

The circuit here described enables adaptation to a number of engines with difierent characteristics, and provides ready change of the duration of the pulses 11 For example, resistances 48 and/or 49 can be changed to change the threshold potential u either by raising or lowering it; the impulse duration 1, of the multivibrator 10 can be changed in a known manner; rather than having a single condenser 15, a condenser network with switches can be used. Thus, the application of the invention can be adapted to widely varying requirements which are not limited to the application for a gasoline injection system for a motor vehicle, but also can be applied for ignition systems for motor vehicles, to control electromagnetic clutches and many other devices.

What is claimed is:

1. An impulse generator providing impulses of widely varying time duration comprising a multivibrator circuit a differential transformer (13) of adjustable inductivity, said difierential transformer being coupled to the output of said multivibrator circuit; an electronic threshold voltage sensitive switch (16); and a charging condenser said charging condenser interconnecting the output of said differential transformer and said threshold voltage-sensitive switch, the switching state of said switch being determined by the potential (u across the condenser.

2. Impulse generator as claimed in claim 1 including a rectifier (14) interconnecting the output of the differential transformer (13) and said condenser (15).

3. Impulse generator as claimed in claim 1 wherein said multivibrator (10) is a monostable multivibrator, adapted to be connected to a source of trigger pulses (22).

4. Impulse generator as claimed in claim 3 in combination with an internal combustion engine (B), said trigger impulses being synchronized in time with the rotation of the output shaft (S) of said engine; the adjustable differential transformer being provided with an adjustable element (38) adjustably coupling the primary and secondary coils of said transformer; and means adjustably interconnecting the adjustable elements of said transformer with said engine so that the position of said adjustable element within the transformer is dependent upon an operating parameter of the engine, whereby the switching points, in time, of said threshold voltage-sensitive switch (16) will be a function of speed of the engine and of the respective operating parameter.

5. Impulse generator as claimed in claim 4 wherein said engine has a manifold vacuum transmitter and said interconnection means are coupled to the core elements of said transformer, and said vacuum transmitter, so that, with increasing vacuum, said interconnection means cause adjustment of said core element in a direction which decreases the switching times of said threshold voltagesensitive switch (16) upon charging and discharging of said condenser.

References Cited UNITED STATES PATENTS 3,005,447 10/ 1961 Baumann et a1. 3,338,221 8/ 1967 Scholl.

LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R. 123-119, 139