GB1600076A

GB1600076A - Switching devices

Info

Publication number: GB1600076A
Application number: GB1133578A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-03-25
Filing date: 1978-03-22
Publication date: 1981-10-14
Also published as: DE2713217A1; FR2385217A1; FR2385217B1

Description

(54) SWITCHING DEVICES (71) We, ROBERT BoscH GmbH, a German company of Postfach 50, 7 Stuttgart 1, Federal 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 controllable electric high voltage switching devices.

One known construction of such high voltage switching devices has a gas-filled hollow body made of an insulating material and into which project a cathode electrode and an anode electrode. By means of an adjacent control electrode an electrical discharge can be induced in the space between the cathode electrode and the anode electrode. The cathode electrode has a laterally widened part which extends almost as far as the side wall of the hollow body and is situated at a greater distance from the discharge end of the anode electrode than from the discharge end of the cathode electrode.

Outside the hollow body an electrically conducting and movable clip is provided in the area of the widened part of the cathode electrode. When this clip is opposite the widened part, the clip potential has acaacitative effect on the electrode potential and by means of the electric field between the clip and the cathode, a discharge is initiated to establish a conductive path between the anode and the cathode. When the cathodeanode path is required periodically to be rendered conductive, the clip is periodically pivoted into the vicinity of the widened part of the cathode. With an appropriate arrangement of several such high voltage switching devices and periodic operation such a combination of high voltage switching devices can be used as an ignition distributor in ignition systems for internal combustion engines.

A disadvantage of the known high voltage switching device, however, lies in the movable clip which, to produce the discharge and render the cathode-anode path conductive, must in each case be moved into the effective area of the widened part of the cathode. Moreover, exact adjustment of the clip and of the hollow body is required in order to make the high voltage switching device operate at a low ignition voltage. A further disadvantage is the necessarily limited repetition frequency stemming from the inertia of the movable clip.

It has also been proposed in the case of flash tubes for flash devices, to establish conductivity of cathode-anode paths at certain times in order to produce light. These flash tubes, however, due to the special purpose for which they are used, have a lower ignition voltage and a gas filling having a lower pressure than high voltage switching devices and the techniques which are used in such flash tubes cannot be readily transferred to high voltage switching devices.

According to the present invention there is provided a controllable electric high voltage switching device for supplying high voltage pulses to at least one load, comprising a gas-filled hollow body made of an insulating material, a cathode main electrode and an anode main electrode projecting into the interior of said hollow body to define a discharge gap between them, a stationary control electrode supported by said hollow body in capacitatively coupled relation with at least one of said main electrodes and in which at least one of the main electrodes, in the region of the discharge gap, comprises more than 90% by weight of a nitride of one of the metals Al, Ce, Hf, La, Nb, Ta, Ti, V and Zr or of a mixture of a nitride of one of these metals with an oxide or oxinitride of one of these metals in which mixture the oxygen content is less than 25 atomic percent, the gas pressure lying between 2 and 15 bar.

The gas filling should comprise a gas which does not react with the components within the hollow body and preferably consists of nitrogen, an inert gas, hydrogen or a mixture of these gases with a maximum of 10% hydrogen and the gas pressure should be between 2 and 15 bar.

The invention may with advantages be used as an ignition distributor in ignition systems for internal combustion engines, several switching devices then conveniently being assembled into a unit, preferably in a common hollow body.

In general, a value of between 3 an 32kv may be provided for the ignition voltage.

The switching device provided by the invention has the advantage that high voltages can be switched through the device reliably and without unacceptable losses, at times which can be set to within a few ,u sec.

The triggering takes place purely electronically without mechanically moved parts.

High service lives can be achieved in a compact design and also high repetition frequencies whose limit is determined by the heating up process. Furthermore a wide difference can be achieved between the ignition voltage of the switching device, as determined by the control voltage, and the conducting voltage which maintains the conducting path, energy losses thus remaining low.

In one preferred construction, one of the main electrodes, is directly enclosed by a tubular insulator which projects beyond the said electrode and into the discharge gap.

This enables a creepage spark to be established between the main electrode and the control electrode, running at least partially in the direction of the discharge gap, by which means the ignition voltage is lowered.

It is also advantageous to provide a gas space of at least one millimetre between the insulating hollow body and the main electrode so that a conductive path does not occur between the cathode and anode in the form of a creepage spark on the inner surface of the hollow body.

The present invention will now be further described with reference to the accompanying drawings in which: Fig. 1 shows the basic circuit diagram of a complete high voltage switching device; Fig. 2 shows a representation of a voltage cycle with respect to time; Fig. 3 shows the temporal correlation of the control voltage; Fig. 4 shows four embodiments of high voltage switching devices having a gas space between the mam electrodes and the insulated control electrode; Fig. 5 shows three embodiments of high voltage switching devices in which a striking of the spark is possible between the main and the control electrode; Fig. 6 shows an example of the use of four controllable high voltage switching devices for a four-cylinder internal combustion engine; and Fig. 7 a high voltage switching device having four individual switches in a common hollow body.

Fig. 1 shows a basic circuit diagram of a complete high voltage switching device comprising a high voltage generator 10, a control device 11, the actual high voltage switching device 12 including a main cathode electrode 13 and a main anode electrode 14, a control electrode 15 in a hollow body 16 of an insulating material and a load 17. A further high voltage switching device 18 with associated control electrode 19 is shown by the dashed lines.

The high voltage to be fed to the load 17 is produced in the generator 10. The control device 11 (which may be but is not necessarily coupled to the generator as shown) transmits a switching signal to the control electrode 15. The control device 11 may, if desired, supply control pulses for several high voltage switching devices 12 and thus correlate the high voltage pulses to several loads in a preset sequence. One example of such use of the high voltage switching device has already been mentioned in connection with the ignition distribution for internal combustion engines. Fig. 2 shows a representation of the cathode-anode voltage in such an example with respect to time. The ignition coil voltage during idling is drawn in dashed lines.The dash-dot line indicates the free striking voltage Ull of the switching device, i.e. the voltage at which the cathode-anode path becomes conductive in the absence of a control voltage. Since a high voltage switch is not intended to conduct in the absence of a signal applied to the control electrode, the free striking voltage should not be reached under normal operational conditions. The curve plotted characterises the voltage with respect to the cathode-anode path. The marked voltage values are on the one hand the ignition voltage UZ, which in the present example can lie between 3 and 30kV and the conducting voltage UB. The latter is advantageously selected not to exceed lkV in order to keep power losses low, especially through heating up of the switching device.

Fig. 3 shows on the same time scale as Fig.

2 the control voltage plotted as an output signal of the control device 11. By means of the selectable delay time tv, any desired point can be selected on the voltage curve of Fig. 2, shown by the dashed line, to achieve any desired ignition voltage within the available range. The control pulse can be triggered either after a definite set delay time or by way of a threshold value switch at a certain instantaneous value. This instantaneous value can lie between the maximum value of the ignition coil idling voltage and one third of the ignition coil idling voltage, thus between e.g. 10kV and 30kV when the switch 12 itself has a striking voltage of 35kV. In the case of switching devices in accordance with the invention and having a lower striking voltage the discharge between the main electrodes 13 and 14 can occur at even lower ignition voltages e.g. at 3 to 5kV.

The control voltage may take the form of an individual pulse having a peak value of 6 to 16kV or it may alternatively comprise a train of e.g. 10 such individual pulses.

The embodiments of Fig. 4 have in common that a gas space 21 is located between the main electrodes and an insulator 20 and that the control electrode 15 is thereby so well insulated from the main electrodes that no direct spark can strike between the latter and the control electrode.

Fig. 4a shows a high voltage switching device having a control electrode 15 which is placed externally on the insulating hollow body 16. At least one of the main electrodes in the region of the discharge gap between the two, comprises more than 90% by weight of a nitride of one of the metals Al, Ce, Hf, La, Nb, Ta, Ti, V and Zr or a mixture of a nitride of one of these metal with an oxide or oxinitride of one of these metals, in which mixture the oxygen content is less than 25 atomic percent.

In Fig. 4b the control electrode 15 is ain which passes through the hollow body leo at a position intermediate the anode and the cathode of the high voltage switching device and is enclosed in the insulator 20. A further embodiment is shown in Fig. 4c, in which a hollow cylinder of insulating material encloses the main electrodes coaxially and the control electrode 15 is provided as a ring seated externally on the hollow cylinder, remote from the main electrodes.

The embodiment shown in Fig. 4d corresponds substantially to that of Fig. 4a but employs a different fusion technique in its manufacture. The hollow body of insulating material is not constructed as an ampoule but in the shape of a tube provided with end caps. The control electrode is constructed either as in Figs. 4a and 4b or it divides the insulating body as an annular intermediate piece and is completely covered on the inside by an insulator, e.g. glass.

A common feature of all embodiments of Fig. 4 is that both an insulator as well as a gas space are provided between the main electrodes and the control electrode.

Embodiments without this gas space are shown in Fig. 5.

In Fig. 5a, the main electrode 13 is directly enclosed by a tubular insulator 25 which projects out over the surface opposite the other main electrode that is, into the discharge gap between the main electrode, and carries on its outer face a control electrode 15. A modified embodiment, using a different fusion technique, is shown in Fig.

5b. The basic principle corresponds to that of Fig. 5a but end caps which conveniently may be integral with the main electrodes are provided as sealing elements for a hollow body which itself is divided into two parts joined by a control electrode 15 somewhat as shown in Fig. 4d.

An alternative arrangement is shown in Fig. 5c, in which one main electrode 13 and the control electrode 15 are axially arranged within the hollow body 16, with their opposed front faces separated from each other by an insulator 26. The second main electrode 14 is disposed at least partially concentrically about this configuratlon. The high voltage switching operation is triggered by a corona discharge between the main electrode 14 and the control electrode 15.

It is essential in these embodiments that a creep age spark path can be established between the main electrode 13 and the control electrode 15 over the surface of the insulator 25, 26 and in the direction of the main discharge gap. The insulator additionally causes a marked fanning out of the control spark. As the control electrode 15 is separated from the main electrode 13 by an insulator 26 no direct spark-over occurs.

The steep rising flank of the control pulse, rather, generates by way of a displacement current in the insulator, a charge which is uniformly distributed on its inner surface facing the main electrode 13. These charges are neutralised in a diffuse, corona-like discharge. This discharge, like the positively guided creep age spark in the case of the switching devices of Fig. 5, causes a uniform pre-ionisation of the main discharge gap which immediately triggers a discharge across that gap. In the case of the switching devices of Fig. 4, a steep rising flank or low pulse width of the control signal is thus absolutely necessary, whilst switching devices of Fig. 5 can be controlled by means of wider pulses.

The switching devices of Fig. 5 require a lower control voltage than those of ig. 4 but in their case there is the danger that the main discharge may spark over onto the control electrode and damage the control circuitry. The switching devices of Fig. 5 also have the advantage that the main discharge does not run along the inner wall of the hollow body as a creepage spark, which reduces the static scatter of the minimum operating voltage in the non-triggered state (free striking voltage). The safety margin between the free-striking voltage of the switch and the maximum switched voltage can be reduced without there being the danger of "wild" spark-overs.

The polarity of the discharge gap is preferably so arranged that the main electrode which is surrounded by the control electrode works as a cathode, i.e. is connected to the negative pole of the voltage source.

The advantages of using the invention as an ignition distributor in a motor vehicle are: a) the ability to set the ignition timing precisely b) the compact space-saving design even when the voltages to be switched are high c) the possibility of undertaking the high voltage distribution without driven parts. It is thus no longer necessary to accommodate the ignition distributor on the engine, it can rather be mounted on a site behind the engine, whereby the triggering takes place in a fully electronic manner by way of a generator without driven parts d) the possibility of undertaking the high voltage distribution even with an odd number of cylinders in the engine.

Fig. 6 shows a case of use as an ignition distributor in the ignition system of internal combustion engines using the example of a four cylinder engine. An extension to any number of cylinders is possible without any fundamental difficulties.

The Figure shows the ignition coil 30, four high voltage switching devices 31 to 34, associated spark-plugs 35 to 38 as well as a control device 39. The cathodes of the high voltage switching devices are preferably connected to each other and to the output of the ignition coil 30, whilst the individual anodes of the high voltage switching devices 31 to 34 are coupled to the spark-plugs 35 to 38.

In the ignition system shown in Fig. 6, the four high voltage switching devices 31 to 34 take over the function of the conventional mechanically driven distributor and the trig gering of the individual switching devices to distribute the high voltage to the spark plugs takes place by way of the control device 39 which is controlled periodically and dependent on the speed.

Whilst Fig. 6 shows four separate high voltage switching devices, an embodiment is shown in Fig. 7 in which the individual con trollable cathode-anode paths 40 to 43 are shown in one hollow body. The advantage of this arrangement lies, among others, in the simplicity of the overall concept.

WHAT WE CLAIM IS: 1. A controllable high voltage switching device for supplying high voltage pulses to at least one load, comprising a gas-filled hol low body made of an insulating material, a cathode main electrode and an anode main electrode projecting into the interior of said hollow body to define a discharge gap bet ween them, a stationary control electrode supported by said hollow body in capacita tively coupled relation with at least one of said main electrodes and in which at least one of the main electrodes, in the region of the discharge gap, comprises more than 90% by weight of a nitride of one of the metals Al, Ce, Hf, La, Nb, Ta, Ti, V and Zr or of a mixture of a nitride of one of these metals with an oxide or oxinitride of one of these metals in which mixture the oxygen content is less than 25 atomic percent, the gas pressure lying between 2 and 15 bar.

2. A device as claimed in claim 1 in which an insulator and a gas space are provided between the control electrode and the main electrodes.

3. A device as claimed in claim 2 in which the control electrode and the insulator surround coaxially and at least partially at least one of the main electrodes.

4. A device as claimed in claim 3 in which the control electrode is a ring seated on the exterior of the insulator, remote from the main electrodes.

5. A device as claimed in claim 3 in which the hollow body is constructed as a hollow cylinder provided with end caps.

6. A device as claimed in claim 2, wherein the control electrode is a pin which passes into the interior of the hollow body and which is surrounded by an insulator in the area of at least one of the main electrodes.

7. A device as claimed in claim 1, in which one of the main electrodes is surrounded at its discharge gap end directly by a tubular insulator on which the control electrode is located.

8. A device as claimed in claim 7, in which the insulator projects out beyond the main electrode and into the discharge gap.

9. A device as claimed in claim 7 or claim 8, in which the main electrode which is surrounded by the control electrode is connected as the cathode.

10. A device as claimed in any one of claims 1 to 9 in which a gas space of at least one millimetre is provided between the main electrodes and the hollow body of insulating material.

11. A device as claimed in claim 1 in which one of the main electrodes and the control electrode are arranged axially within the hollow body with an insulator positioned between them, and in which the other main electrode surrounds at least partially the assembly comprising the control electrode, the insulator and the first-mentioned main electrode.

12. A device as claimed in any one of claims 1 to 11 in which the gas comprises nitrogen, an inert gas, hydrogen or a mixture of these gases.

13. A switch assembly comprising a plurality of switching devices as claimed in any one of claims 1 to 12 and arranged in a common hollow body of insulating material.

14. An ignition distributor for an inter nal combustion engine ignition system, comprising a switch assemb y as claimed in claim 13 or one or more switching devices as claimed in any one of claims 1 to 12.

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

Claims

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

b) the compact space-saving design even when the voltages to be switched are high

c) the possibility of undertaking the high voltage distribution without driven parts. It is thus no longer necessary to accommodate the ignition distributor on the engine, it can rather be mounted on a site behind the engine, whereby the triggering takes place in a fully electronic manner by way of a generator without driven parts d) the possibility of undertaking the high voltage distribution even with an odd number of cylinders in the engine.

Fig. 6 shows a case of use as an ignition distributor in the ignition system of internal combustion engines using the example of a four cylinder engine. An extension to any number of cylinders is possible without any fundamental difficulties.

The Figure shows the ignition coil 30, four high voltage switching devices 31 to 34, associated spark-plugs 35 to 38 as well as a control device 39. The cathodes of the high voltage switching devices are preferably connected to each other and to the output of the ignition coil 30, whilst the individual anodes of the high voltage switching devices 31 to 34 are coupled to the spark-plugs 35 to 38.

In the ignition system shown in Fig. 6, the four high voltage switching devices 31 to 34 take over the function of the conventional mechanically driven distributor and the trig gering of the individual switching devices to distribute the high voltage to the spark plugs takes place by way of the control device 39 which is controlled periodically and dependent on the speed.

Whilst Fig. 6 shows four separate high voltage switching devices, an embodiment is shown in Fig. 7 in which the individual con trollable cathode-anode paths 40 to 43 are shown in one hollow body. The advantage of this arrangement lies, among others, in the simplicity of the overall concept.

WHAT WE CLAIM IS: 1. A controllable high voltage switching device for supplying high voltage pulses to at least one load, comprising a gas-filled hol low body made of an insulating material, a cathode main electrode and an anode main electrode projecting into the interior of said hollow body to define a discharge gap bet ween them, a stationary control electrode supported by said hollow body in capacita tively coupled relation with at least one of said main electrodes and in which at least one of the main electrodes, in the region of the discharge gap, comprises more than 90% by weight of a nitride of one of the metals Al, Ce, Hf, La, Nb, Ta, Ti, V and Zr or of a mixture of a nitride of one of these metals with an oxide or oxinitride of one of these metals in which mixture the oxygen content is less than 25 atomic percent, the gas pressure lying between 2 and 15 bar.
2. A device as claimed in claim 1 in which an insulator and a gas space are provided between the control electrode and the main electrodes.
3. A device as claimed in claim 2 in which the control electrode and the insulator surround coaxially and at least partially at least one of the main electrodes.
4. A device as claimed in claim 3 in which the control electrode is a ring seated on the exterior of the insulator, remote from the main electrodes.
5. A device as claimed in claim 3 in which the hollow body is constructed as a hollow cylinder provided with end caps.
6. A device as claimed in claim 2, wherein the control electrode is a pin which passes into the interior of the hollow body and which is surrounded by an insulator in the area of at least one of the main electrodes.
7. A device as claimed in claim 1, in which one of the main electrodes is surrounded at its discharge gap end directly by a tubular insulator on which the control electrode is located.
8. A device as claimed in claim 7, in which the insulator projects out beyond the main electrode and into the discharge gap.
9. A device as claimed in claim 7 or claim 8, in which the main electrode which is surrounded by the control electrode is connected as the cathode.
10. A device as claimed in any one of claims 1 to 9 in which a gas space of at least one millimetre is provided between the main electrodes and the hollow body of insulating material.
11. A device as claimed in claim 1 in which one of the main electrodes and the control electrode are arranged axially within the hollow body with an insulator positioned between them, and in which the other main electrode surrounds at least partially the assembly comprising the control electrode, the insulator and the first-mentioned main electrode.
12. A device as claimed in any one of claims 1 to 11 in which the gas comprises nitrogen, an inert gas, hydrogen or a mixture of these gases.
13. A switch assembly comprising a plurality of switching devices as claimed in any one of claims 1 to 12 and arranged in a common hollow body of insulating material.
14. An ignition distributor for an inter nal combustion engine ignition system, comprising a switch assemb y as claimed in claim 13 or one or more switching devices as claimed in any one of claims 1 to 12.
15. A controllable high voltage switch

ing device substantially as hereinbefore described with reference to and as illustrated in any of Figs. 1 and 4 to 7 of the accompanying drawings.