GB1588349A - Ignition distributors for internal combustion engines - Google Patents

Description

(54) IMPROVEMENTS RELATING TO IGNITION DISTRIBUTORS FOR INTERNAL COMBUSTION ENGINES (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 ignition distributors for internal combustion engines and particularly to the suppression of interference radiated during discharge of a high tension ignition pulse from a rotor arm of an ignition distributor to an electrode in the distributor cap.

A distributor such as is used to distribute ignition voltage in ignition systems for internal combustion engines commonly has a distributor electrode in an arm of a rotor that is rotated successively past electrodes secured in the distributor cap. The distributor electrode is connected to the secondary winding of an ignition coil and each of the cap electrodes to one of several sparkplugs, and the ignition voltage is conveyed to the spark-plugs by way of a resistive suppressor.

It is known (according to DT-PS 1 123 866) to form the distributor electrode of a material which is a good conductor of electricity and introduce a resistor suppressor as an independent structural unit electrically connected in series with the electrode. The electric discharges which occur during the ignition process between the distributor electrode and each one of the cap electrodes can be suppressed all the more effectively the nearer the resistor suppressor is located to the discharge path. In the known embodiment limits are placed on an arrangement where the resistor is near to the spark-over path due to the intervening distributor electrode.A relatively high spark-over current is still produced which requires a resistor suppressor which is highly resistive and of robust construction, if this resistor is not to be overloaded and the interference is to be sufficiently suppressed.

Accordingly the present invention provides a device for suppressing inteference generated by discharge of a high tension ignition pulse in an ignition distributor for an internal combustion engine, the device comprising an electrode for the distributor, the electrode being made of resistive material consisting of at least one oxide-nitride of metals with a high melting point.

Since the present invention places the resistive suppressor directly adjacent to the discharge path the shortcomings of hitherto known suppression techniques are reduced.

Furthermore the resistive suppressor of the present invention can have a considerably lower resistive value than the known suppressors with the same suppressive effect and thus in the same design of ignition system more energy is supplied to the sparkplugs.

The non-conventional difficult-to-work resistive material used in accordance with the invention, due to difficulties of its processing, has previously not found application in ignition systems.

Processes which may be used to prepare the difficult-to-work non-conventional resistive material are processes according to plasma injection, VD (chemical-vapourdeposition) or PVD (physical-vapourdeposition). Extensive experiments have shown that oxide-nitrides can be easily prepared by the aforementioned processes.

As a supporting element for the electrode functioning as a resistive suppressor that is manufactured from a difficult-to-work material, a ceramic body is advisable which by way of example can comprise aluminium oxide, magnesium aluminium spinel or a stabilised zirconium oxide. The ceramic body is embedded in the arm of the distributor rotor that is manufactured from insulative material.

As regards the configuration of the distributor electrode functioning as a resistive suppressor, then it is proposed that the distributor electrode should preferably project beyond the front edge of the ceramic body by from one to several tenths of a millimetre. In order additionally to vary the resistance of the distributor electrode due to its shaping it is moreover further advan tageous to make the central section of the electrode with a reduced cross-section, the reduced cross-section having appropriately a width of 0.5 to 1.5 millimetres.

The present invention is further described hereinafter by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side elevation of a distributor rotor according to the present invention; and Fig. 2 is a plan view of part of the rotor of Fig. 1.

A rotor 10 forming part of a distributor for an internal combustion engine is of insulating material and includes a shaft 11 adapted to be driven and an arm 12 tapered in the radially outward direction.

A ceramic body 1 3b, which by way of example is manufactured from aluminium oxide, is constructed as a strip that is rectangular in cross-section and embedded in the rotor 10 with its outer end section projecting beyond the arm 12 by a few millimetres.

The distributor electrode 13 that functions as a resistive suppressor is mounted onto this ceramic body 13b in such a way that a tip of the electrode projects beyond the front edge 30 of the body 13b, preferably by several tenths of a millimetre and the tip also encloses the under side of the edge 30 to form a hook-like shape.

The tip of the distrbutor electrode 13 merges into a strap which in relation to the electrode tip is greatly reduced in crosssection and which leads to a central contact 32 of the electrode. The strap may have a width in the range from 0.5 to 1.5mm. The central contact 32 for the purpose of supplying the high tension to the electrodes secured to the distributor cap, is in contact with a stationary central electrode of the distributor in a conventional manner. The thickness of the ceramic body 1 3b is approximately 1 mm but it can vary however between 0.5 and 1.5 mm.

It is advisable that first the ceramic body 13b is joined to the electrode 13 including the tip, the strap and the central contact 32, and the pre-fabricated unit thus formed then mounted in a recess 17 in the arm 12 of the distributor rotor 10 and secured therein.

Difficult-to-work non-conventional materials constitute the electrode 13 which functions as a resistive suppressor. In accordance with the invention, the electrode 13 consists of at least one oxide-nitride of metals with a high melting point. Suitable metals are titanium and zirconium of sub-group 1VB of the Periodic Table.

The ceramic body may be made of aluminium-oxide as mentioned above, or magnesium aluminium-spinel or stabilised zirconium-oxide.

The following methods are suitable for processing the non-conventional difficult to-work materials for the electrode 13, viz.

plasma injection, (chemical-vapourdeposition) and PVD (physical-vapourdeposition).

WHAT WE CLAIM IS: 1. A device for suppressing interference generated by discharge of a high tension ignition pulse in an ignition distributor for an internal combustion engine, the device comprising an electrode for the distributor, the electrode being made of resistive material consisting of at least one oxide-nitride of metals with a high melting point.

2. A device as claimed in Claim 1, wherein said metals are titanium and zirconium.

3. A device as claimed in Claim 1 or Claim 2, wherein a ceramic body serves as a supporting element for the electrode.

4. A device according to Claim 3, wherein the electrode comprises a tip portion projecting beyond an end of the ceramic body.

5. A device according to Claim 4, wherein the tip portion projects beyond the end of the ceramic body by from one to several tenths of a millimetre.

6. A device as claimed in any one of Claims 3 to 5, wherein the ceramic body comprises aluminium-oxide, magnesium aluminium-spinel or stabilised zirconium oxide.

7. A device as claimed in any of Claims 3 to 6, wherein the thickness of the ceramic body is in the range 0.5 to 1.5 millimetres.

8. A rotor for an ignition distributor, the rotor having a device as claimed in any pre

Claims (1)

1. ceding claim.

   9. A rotor as claimed in Claim 8, wherein the ceramic body is embedded in an arm of the rotor.

   10. A rotor as claimed in Claim 8 or Claim 9, wherein the electrode comprises a strap portion of reduced cross-section and a central portion for contact with a stationary central contact of the distributor.

   11. A rotor for a distributor of an internal combustion engine, substantially' as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

   12. A method of making a device according to any one of Claims 1 to 7 or a rotor according to any one of Claims 8 to 11, wherein plasma injection is used for processing the resistive material.

   13. A method of making a device according to any one of Claims 1 to 7 or a rotor according to any one of Claims 8 to 11, wherein the CVD-process is used for processing the resistive material.

   14. A method of making a device according to any one of Claims 1 to 7 or a rotor according to any one of Claims 8 to 11, wherein the PVD-process is used for processing the resistive material.