T 0032/82 (Control Circuit) 14-03-1984

Reasons for the Decision

1. The appeal complies with Article 106 to 108 and Rule 64 EPC and is, therefore, admissible.

3. The present application aims to avoid the undesired ignition of fuse heads by spurious sources of electrical energy such as induced stray high frequency radiation and capacitor discharge, so that the fusehead will only be ignited by electrical energy of predetermined magnitude and frequency.

4. It is generally known that in order to obtain a high coefficient of mutual coupling k (i.e. an almost complete coupling) between two inductors the two inductors must be as close a possible to one another (preferably even interleaved) and that an iron core having a high permeability must be used, preferably a core closed in itself. Under such circumstances values of k as high as 0.998 may be arrived at.

5. Considering the different embodiments shown in the US-Patent, it is clear to the person skilled in the art that in many of them a complete coupling cannot be obtained, even ignoring the presence of the closed shield wich will cause a decreasing coupling between the two inductors with increasing frequency. In particular in the embodiments according to Fig. 2 and Fig. 9 a non-linked portion is clearly present (cf. column 5, lines 65- 71 and column 7, lines 8 - 13; the text erroneously refers to Figs. 3, 4 and 11 instead of 2, 3, and 9). Even if these embodiments may not be regarded by the author of the US-Patent as preferred ones, they are nevertheless disclosed.

Therefore, it is not possible to accept the applicant's contentions that in the transformers according to the US-Patent there is virtually complete flux linkage between the inductors, or that at least a coefficient of coupling as high as possible should be achieved. In column 4, lines 37 - 42 of this document no more is said than that "arrangements which provide sufficient changing magnetic flux" may be utilised.

6. Although the invention claimed in the US-Patent rests on the use of a conductive closed shield between the two inductors, this document also discloses transformers without such a shield, see Fig. 11 graph I(b)*2, 1 with corresponding text (column 7, lines 44 - 75; column 8, lines 1 - 8) and Fig. 12, graph IV with corresponding text (column 8, lines 30 - 36, 57 - 62).

These transformers are used for comparison purposes to show the improvements which can be obtained by using a conductive shield. The graphs referred to show at the same time, hower, that such transformers possess a bandpass characteristic with an appreciable attenuation of high frequency currents. Apparently the author of the US-Patent does not consider this a sufficient for his purposes but he points out that also an unshielded device provides a cut-off frequency range (col. 5, lines 12 - 15).

7. It is common knowledge of the man skilled in the art that transformers having leakage inductance possess the character of a bandpassfilter (cf. e.g. Stefanescu, Les filtres électriques, Masson et cie. Paris, 1972, page 127 - 133).

8. The person skilled in the art will therefore realise that it is also possible to obtain protection agains stray high frequency currents in an ignition assembly in the absence of a shield by using a transformer having an amount of leakage, (although to a lesser degree than by using a shield). Furthermore, he will be aware that the amount of attenuation is determined by the coefficient of coupling (cf. the cited passage in the book of Stefanescu, in particular Fig. 3.54 on page 131 and corresponding text).

9. With regard to the possible effects of iron losses in explaining the shape of the graphs I(b) *2,1 and IV shown in figures 11 and 12 respectively of US-A-3 185 093 it is observed that, as is well known, the iron losses in a transformer are independent of the secondary load current. Moreover, they are usually small (of the order of a few percent of the power transmitted under full load). The effect of skin effect losses at frequency of 100 kHz and for a wire diameter of 0,5 mm (No.24 wire) will be barely perceptible.

These losses could thus not possibly account for the voltage drops shown in these graphs, which would inevitably be attributed by the person skilled in the art to the generally known bandpass character of a transformer having a certain amount of leakage flux.

10. The condition k less than 0.9, represents in effect merely the range of values which are unusable in practice and no surprisingly favourable effect being present within this range, no inventive step appears to be involved in the use of transformers having a value for k less than 0.9.

11. Claim 1 and claim 2 are therefore not allowable for lack of inventive step.

12. In accordance with applicants request referred to under IV, the Board of Appeal will now consider the allowability of Claim 3, which is directed to the combination of leakage inductance and engergy dissipation means. As was confirmed by the applicant in his letter of 11.11.83, Claim 3 embraces the use of a saturable ferromagnetic material and the use of a resistor (80).

13. The use of a saturable ferromagnetic material to provide increased protection gainst improper fusehead ignition is known from US-A-3 762 331 and it is considered obvious to the man skilled in the art that the same measure could also be applied to ignition devices according to the present application. The combination does produce no more than the sum of the effects which could be expected. For these reasons alone, Claim 3 is already unallowable as no inventive step is involved.

14. With respect to the use of a resistor the following is observed. In his letter of 06.06.83 the applicant has stated that "this resistor must have a low impedance compared with that of the transformer primary inductance and the reflected impedance of the ignition element circuit". In his letter of 11.11.83, however, it is stated that "the resistor value would need to be comparable with the impedance of the transformer and detonator circuit ... at the lowest frequency at which the additional protection ... is required to begin to take effect". These two conditions, neither of which can be found in the application as filed, do not coincide but even so it is clear that to obtain the desired effect it is essential that the resistance meets certain requirements as to its value.

15. Article 84 EPC requires amongst other things that the claims, which define the matter for which protection is sought (i.e. the object of the invention as implied by Article 52(1) EPC) be clear. The Board of Appeal considers that this has to be interpreted as meaning not only that a claim from a technical point of view must be comprehensible, but also that it must define clearly the object of the invention, that is to say indicate all the essential features thereof. As essential features have to be regarded all features which are necessary to obtain the desired effect or, differently expressed which are necessary to solve the technical problem with which the application is concerned. In the present case, Claim 3 which does not state an essential feature concerning the resistor (80) does in this respect not satisfy Article 84 EPC and is thus not allowable.

16. The applicant asserts that it would be obvious to the person skilled in the art how to choose the value of the resistor in question, wich statement seems to imply that it would not be necessary to state any requirement as to the value of the resistor in the claim.

17. In the application as filed it is merely said that the resistor increases energy dissipation at high frequencies (page 23, lines 11 - 14). Moreover in two letters the applicant himself states two requirements for its value which lead to different results. Under these circumstances, the Board of Appeal cannot accepthe applicant's contention that the man skilled in the art would know what value to choose.

18. Rule 66(1) EPC in effect instructs a Board of Appeal to conduct its examination in accordance with the provisions of inter alia Article 96(2) EPC and Rule 51(2) EPC. These provisions leave open the possibility in appropriate cases for the Board to indicate to an applicant that the grant of a European patent based on the subject-matter of certain dependent claims would be favourably considered. Nevertheless, it remains the prime responsibility of the applicant to define in the claims submitted to the Board the subject matter for which he wishes to obtain protection (with alternatives if he so desires).

19. In accordance with Article 113(2) EPC, the Board can only decide upon the European patent application in the text submitted to it or agreed by the applicant. It follows that when deciding the appeal the Board has no authority under the EPC to order the grant of a European patent containing claims which are different from those submitted by the applicant in their content or interdependency. Even if the Board has indicated to an applicant that a dependent claim might be allowable if rewritten as an independent claim but the applicant has not expressly requested the Board to consider it as such claim, the Board is not obliged to do so.

20. In the present case, the Board informed the applicant that Claim 11 (with some modifications) was the only claim which would appear to be allowable, but the applicant in his reply stated that he did not wish to proceed with the application on that basis. The applicant did not effectively rebut the Board's objections to the other dependent claims and only made the auxiliary request to consider claim 3 as a possible independent claim. Under these circumstances, the Board is of the opinion that the dependent claims 4 to 12, need not be considered separately once it has been established that the independent claim from which they depend is unallowable.