Saturday, 19 November 2011

T 715/09 – Classy

The inventive step assessment carried out in this decision contains an interesting statement on patent classification.

The Opposition Division maintained the opposed patent in amended form. Claim 1 of the request found allowable read as follows :

A glow plug for diesel engines, comprising:

  • a metal tubular body (12) provided with means (14) for fixing it to the cylinder head of an engine;
  • a metal sheath (24) carried by a the tubular body (12) and driven with interference into a cavity (16) of the tubular body;
  • a first electrical terminal (30) connected to a heating resistor (33) set inside the aforesaid sheath (24);
  • a second electrical terminal (32) electrically connected to the sheath (24); and
  • means for electrical insulation of the metal sheath (24) from the metal tubular body (12), wherein said sheath (24) comprises a layer (36) of insulating material applied on a portion (34) of the outer surface of said sheath (24),
characterized in that said layer (36) of insulating material is applied by means of plasma deposition.

The Board examined whether this claim involved an inventive step :

[4.2.4] The claimed glow plug differs from the embodiment shown in Figure 4 of E3 only that the coating of insulating material has been applied by plasma deposition.

Objective Problem

[4.3] E3 simply states that the insulation is formed by a ceramic coating and no indication is given as to how the coating is to be applied […]. The objective problem to be solved is therefore, as formulated by the [opponent], to select a suitable method for coating the metal sheath, bearing in mind that the coating lies between two parts that are held together by means of an interference fit.


[4.4.1] Plasma deposition is a generally well known technique for coating objects with a ceramic layer that is hard and wear resistant, but the question is whether it is obvious to use plasma deposition for applying the insulating coating as described in E3.

Documents E7, E8 and E9 all describe the manufacture of glow plugs in which a ceramic coating step carried out by plasma deposition.

[4.4.2] E7 discloses a glow plug having a metal sheath (17) and a tubular body (11) that corresponds to tubular body (12) of the disputed patent. The metal sheath (17) extends beyond tubular body (11), and in this region it is coated with two insulation layers (23 and 27); a heating element (24) is sandwiched between these layers. These insulation layers are applied by plasma deposition. Hence plasma deposition is known for coating the metal sheath, albeit not in the region between the metal sheath and the tubular body which, as pointed out by the [patent proprietor], is coated with glass.

[4.4.3] E8 also concerns a glow plug and describes coating the plug by plasma deposition with a protective layer to protect the plug from the corrosive environment. Use of such a coating to form an insulating layer between a metal tubular body and a sheath is not described.

[4.4.4] E9 describes the application of a coating (20) by plasma deposition to the surface of a glow plug (see last paragraph on page 5). The coating (20) is porous and is intended to reduce the effects of thermal gradients (see sentence bridging pages 4 and 5); it is applied on top of a dense, abrasive resistant, insulating coating (13); it is not said how the latter coating (13) is applied.

[4.4.5] The skilled person reading E3 is looking for a means for applying the insulating coating. None of the documents E7, E8 or E9 explicitly discloses plasma deposition of an insulating coating in the region between the tubular body and sheath of a glow plug, hence the opposition division concluded that the claimed subject-matter had an inventive step.

[4.4.6] In addition, the [patent proprietor] submits that the skilled person versed in the art of glow plugs would not, as part of his common knowledge, be aware of plasma deposition technology. Support for this submission is that glow plugs and surface treatment techniques are in two completely different classes according to the international patent classification scheme, namely F23Q7/00 and C23C respectively. The Board disagrees for the following reasons.

IPC classification alone is no reason for determining whether or not two pieces of prior art can be combined. The mere fact that two documents have the same classification is no reason for saying the combination of the teachings is obvious (see T 745/92 [1.4]). Likewise the mere fact that the technologies have been given different IPC classes does not necessarily mean that they cannot be combined.

[4.4.7] In the present case E7 to E9 indicate that it is well known to use plasma deposition in the manufacture of glow plugs. Faced with the problem of finding a suitable method for applying the insulation coating shown in Figure 4 of E3, the skilled person would first turn to known methods in the field of glow plug manufacture.

Aware that plasma deposition generally provides hard, wear resistant ceramic coatings, it does not require any inventive activity for the skilled person to select this technique for making the glow plug of Figure 4 of E3.

[4.5] Consequently, the glow plug of claim 1 lacks an inventive step.

Should you wish to download the whole decision, just click here.

The file wrapper can be found here.

Another decision dealing with classification can be found here.