T 0271/93 19-06-1996

Reasons for the Decision

1. The appeal is admissible.

Claim 1 filed on 14 June 1996

2. Amendments

The amendments to Claim 1 in relation to the version as granted included inter alia the feature that the condenser is so arranged that the liquid coolant is not separated from the gaseous coolant. This statement which has to be interpreted in its general meaning excludes that in any passage of the condenser there is a separation of the liquid coolant from the gaseous coolant.

Column 4, lines 11 to 33 of the patent in suit, based upon the passage bridging pages 5 and 6 of the original description, specifies, however, that in the inlet section (A) the coolant is in its gaseous state and that in the outlet section (C) the coolant is in its liquid state, which means that, contrary to the feature in dispute, there are regions of the condenser in which either gaseous or liquid-state coolant is present and thus a separation of these phases occurs. Furthermore, as the coolant in a given pass flows from the individual tubes into the header there is at least a partial separation of the liquid and the gaseous portions since the liquid portion due to the adhesion effect clings to the header wall and is therefore at least locally separated from the gaseous portion. Additionally, the difference of the density between the gaseous and the liquid coolant portion leads, in accordance with basic laws of physics, to the effect that gravity causes the liquid to collect in the lowermost range of the header and the tubes, respectively.

Decision G 1/93 (OJ 1994, 541) does not apply here, the feature in dispute being of a technical, physical character: it provides the technical teaching to conduct the liquid coolant in close connection with the gaseous coolant through the condenser. Acccording to the decision however, only the addition of a non-disclosed feature which provides no technical contribution to the subject-matter of the claimed invention can be allowed.

Therefore, the Board could not admit that claim in view of Articles 123(2) and 84 EPC.

Claim 1 as presented in oral proceedings

3. Amendments

Claim 1 is supported essentially by the original Claims 1, 5, 6 and 14. The feature that each tubular element (11) has one or more internal reinforcing portions connecting the upper and the lower walls thereof is disclosed on page 5, paragraph 2 in combination with Figures 3 to 6 and 9 to 13 of the original description and drawings, respectively.

The feature that the opposite ends of the tubular elements (11) are brazed in the slits (15) provided in the headers is based on page 7, lines 2 to 4 of the original description where the soldering substance is described as being an AlSi alloy preferably containing 6. to 13% by weight of Si. "Soldering" is known to be a generic term which comprises "soft soldering" and "hard soldering". The AlSi-composition of the "soldering substance" refers to a substance used for hard soldering, that is brazing, due to its relatively high melting point, in contrast to tin used for soft soldering. The skilled person concludes therefore that the term "soldered" used throughout the original application means "brazed".

The feature that the partition (20, 21) is fluid tight derives from page 7, line 22 to page 8, line 3 of the original description.

The feature that the flow of both gaseous and condensed coolant is enabled to make at least one U-turn in the header (13, 14) is supported by the flow pattern of coolant shown in Figure 8 of the original drawings which illustrates in combination with the passage bridging pages 5 and 6 of the original description that the gaseous and the condensed fractions of the coolant have a common flow channel throughout the zone of heat exchange.

The term "A condenser adapted for use in a car air conditioning system in such a manner that the condenser cooperates with an evaporator, compressor and other apparatuses..." substituted in Claim 1 for the term "A condenser for use in a car cooling system..." according to the original and the granted Claim 1 derives from page 1, paragraphs 1 and 2, of the original description in which the car cooler is described to use a high pressure gaseous coolant. A condenser is only needed with gaseous coolants under pressure which must be condensed and this applies only to refrigeration and air conditioning systems.

Claim 1 is not objectionable under Article 123(2) and (3) and complies also with Article 84 EPC.

4. Novelty

None of the prior art condensers discussed in the opposition and appeal proceedings comprises all the features of Claim 1 so that Claim 1 is considered to be novel within the meaning of Article 54 EPC. Since novelty was, in fact, not disputed by the Respondents, no further arguments in this respect are required.

5. Inventive step

5.1. As already illustrated in the communication dated 30. October 1995, the Board agrees with the opinion of the Appellant that the skilled person in the present case is a design engineer with knowledge of thermodynamics who is aware of the differences between one sort of heat exchanger and another. That is, he is an expert in the field of heat exchangers in general including also condensers for use in car air conditioning systems.

5.2. The Board considers document (D4) to describe the nearest prior art.

This citation relates to a combined condenser and sub-cooler which, though being particularly for use in connection with oil refining, is adapted "to do all work in which it is desired to condense vapour and cool the condensate" (page 1, left-hand column, lines 1 to 5). The citation addresses, therefore, the person skilled in the art of heat exchangers, in particular condensers, in general. Document (D4) describes a condenser which when appropriately sized and dimensioned in response to the predetermined design conditions is suitable for use in a car cooling system. It is commonly known that in such a system a gaseous coolant under high pressure and temperature is used.

The condenser comprises a pair of parallel headers (11, 13, 12, 14) and a plurality of tubular elements (10) whose opposite ends are connected to the headers. The headers are internally divided by fluid-tight partitions (23, 28) into at least two groups of coolant passageways thereby enabling the flow of both gaseous and condensed coolant to make at least one U-turn in the header, the first of the at least two such groups being located towards the inlet side and one other of such groups being located towards the outlet side and the effective cross-sectional areas of the passageways being progressively reduced from the inlet side to the outlet side. The groups of tubes close to the inlet form a condensing zone in which, according to the definition given in the patent in suit (column 1, lines 31 to 41), the coolant is mainly gaseous and the groups of tubes close to the outlet form a super-cooling zone in which - per definition - the coolant becomes liquid.

Further, reference is made to page 2, left-hand column, line 75, to right-hand column, line 21, of document (D4), in particular the passage: "If no sub-cooling is desired, all drainage ports may be opened or both dam plates (15, 16) may be entirely removed and the apparatus operated as a standard condenser." By the term "sub-cooling" cooling of the condensate is meant (see document (D4), page 1, left-hand column, lines 43 to 49) which does not correspond to the term "super cooling" i.e. liquifying of the coolant according to the patent in suit. Thus, the above-cited passage teaches the skilled person that if no substantial sub-cooling of the condensate is desired the dam plates according to the condenser of Figure 1 can be entirely omitted as is the case with the condenser according to Claim 1 of the patent in suit.

5.3. According to the problem-and-solution approach consistently advocated by the Boards of Appeal, (see e.g. decisions T 24/81 (OJ EPO 1983, 133) and T 248/85 (OJ EPO 1986, 261), in order to assess the presence of an inventive step, objectivity in such assessment is, first of all, achieved by starting out from the objectively ruling state of the art, in the light of which the technical problem is determined which the invention addresses and solves. The application of this approach minimises the risk that the departments of the EPO responsible for the examination and the appeal rely on combinations of prior art documents originating from basically different technical fields. That is the assessment of inventive step is based on essentially objective criteria.

Returning to the case to be decided at present, Claim 1 differs from the disclosure of document (D4) by the following features:

(A) Fins are provided in air paths present between adjacent tubular elements.

(B) Each header comprises a pipe of circular cross-section and each tubular element comprises a flat hollow tube having its opposite ends inserted into slits provided in the headers.

(C) The headers and the tubular elements are made of aluminum and brazed together.

(D) Each tubular element has one or more internal reinforcement portion(s) which connect(s) an upper wall of the tubular element to a lower wall thereof.

Feature (A) serves the purpose of improving the heat transfer from the coolant to the cooling air and of achieving a stable condenser structure, features (B) and (C) serve the purpose of easily assembling the condenser and reducing its weight and feature (D) achieves an increased strength of the tubular elements.

The inherent problem resides, therefore, in providing a condenser suitable for use in a car cooling system which has a high efficiency of heat transfer, is easy to assemble, of compact shape and of low weight and is resistant to mechanical loads.

Such a problem arises within the normal development activities of the skilled person in the technical field of heat exchangers, since achieving a high efficiency of heat transfer and an easy-to-assemble and a low-weight structure are constant goals of the design engineer for economical reasons. Equally, ensuring a high strength of the condenser components is also a primary objective in view of a high-reliability product.

The posing of the underlying problem does not, therefore, require the presence of an inventive step.

5.4. The document (D18) relates to a heat exchanger, in particular to a highly pressure resistant heat exchanger being useful for the oil cooler or the like.

In air paths present between adjacent tubular elements (2) fins (4) are provided. Each header comprises a pipe of square cross-section and each tubular element comprises a flat hollow tube having its opposite ends inserted into slits (6) provided in the headers (1) (Figure 3). The headers and the tubular elements are made of aluminum and brazed together and each tubular element has several internal reinforcement portions, that is three such portions according to the embodiment depicted in Figure 3, which connect an upper wall of the tubular element to a lower wall thereof.

In search of a solution to the inherent problem of the patent in suit as outlined in section 5.3, the skilled person would take account of the disclosure of document (D18) since this citation tackles also the problem of an easy manufacture and of a highly resistant heat exchanger (see page 2, paragraph 2 of the English translation).

As the Appellant has also conceded, the construction of the headers and the tubular elements of aluminum leads to a small overall weight and the use of fins, besides increasing the heat transfer between the air and the tubular elements, takes account of stability considerations. Furthermore, the brazing together of the headers and the tubular elements enables an easy assembly of the condenser and the flattened configuration of the tubular elements with reinforcement portions connecting the respective upper and lower tube walls leads to a compact and high-strength condenser.

In expectation of these advantages, the skilled person is induced to substitute in the condenser described in document (D4) the above-cited features known from document (D18). He arrives thereby in an obvious manner at the subject-matter of Claim 1 except for the feature that the header is of circular cross-section. A circular cross-section is, however, the basic and most commonly used shape of a fluid-conducting pipe which the skilled person will select whenever a simple manufacturing method or a minimisation of material consumption per unit of pipe flow area is required.

Moreover, a header comprising a pipe of circular cross-section is known from document (D1) relating to a car radiator assembly so that the choice of such a shape of the header does not even require closer considerations.

5.5. The Appellant argues that document (D18) relates to an oil cooler in which the level of the operating coolant pressure is different from that of a condenser and that therefore a combination of features of (D4) and (D18) would be based on hindsight.

This argument ignores the fact that in the assessment of the issue of inventive step it has to be examined whether the prior art or the common knowledge of the skilled person provided a suggestion of the claimed solution in order to obtain the advantageous effects arising therefrom (see decision T 2/83, OJ EPO 1984, 265). There can be no doubt that the distinguishing features (A) to (D) (see section 5.3) known from the documents (D18) and (D1), respectively, have the same advantageous effects as the corresponding features according to the patent in suit. In this context, the circumstance that Claim 1 relates to a condenser for use in a car air conditioning system whereas the documents (D18) and (D1) relate to a heat exchanger in general and a car radiator assembly, respectively, is irrelevant since the effects resulting from the cited distinguishing features are not in causal relationship with the operation of a condenser for use in a car air conditioning system but are achieved whenever applied to a heat exchanger.

The further argument of the Appellant that there is no pointer in document (D4) to making the condenser smaller in adaptation to the use in a car does not take into account that the size of a condenser used in a car air conditioning system depends to a large extent on the cooling and heating performance required which manifestly differs considerably depending on the operation purpose of the car. Irrespective of this consideration, Claim 1 does not comprise any indication as to the performance data and size of the condenser so that the Appellant's argument is without any basis.

The Board has also examined the question whether in applying the above-cited distinguishing features, to a condenser for automotive purposes any new and unexpected effect occurred or whether any particular difficulty had to be overcome. No evidence in this direction was, however, shown by the Appellant and the Board could also not identify any such difficulty or synergistic effect resulting from such a use.

5.6. Summarising, the Board comes to the conclusion that Claim 1 can not form a basis for maintaining the patent in amended form since its subject-matter does not involve an inventive step (Article 56 EPC). Under these circumstances, it was not necessary to examine whether also other combinations of prior-art documents as forwarded by the Respondents would lead the skilled person in an obvious way to the subject-matter of Claim 1.