T 0911/98 (Air conditioner/NIPPONDENSO) 09-04-2003

Reasons for the Decision

1. The appeal complies with the requirements of Articles 106 to 108 and Rules 1(1) and 64 EPC and is thus admissible.

The appeal is also allowable since the interlocutory decision under appeal, deciding that the amended patent meets the requirements of the EPC, cannot stand in respect of the requirement for an inventive step (Articles 56, 100(a) and 102(3) EPC) and must thus be set aside.

Moreover, the patent must be revoked, as requested by the appellant, since none of the requests submitted by the respondent is allowable.

Main request

2. It follows from the legal definition of Article 56 that an invention is considered to lack an inventive step if having regard to the prior art it is obvious to a person skilled in the art. This obviousness criterion is generally applied by starting from an appropriate point in the prior art (the "closest prior art") and analyzing the invention on the basis of the so-called problem-and-solution approach (see Case Law of the Boards of Appeal of the European Patent office, 4th edition, 2002, pages 101 and 102).

Prior art document D1 is in the field of automotive air conditioning systems and clearly relevant to the invention to which claim 1 relates. It discloses an air conditioner for automobiles (see Figure 1 with the accompanying parts of the text) comprising blow off air control means (elements 18 to 21), internal air temperature detecting means ("in-car sensor" 10), and air conditioning control means (elements 11 to 17) controlling said blow off air control means so that said detected internal air temperature equals a setting target temperature (see "temperature setting means" 13 and page 6, lines 1 to 6 and 24 to 27) . In the embodiment described in document D1 on page 17, lines 9 and 10, the variables of blow off air controlled by said blow off air control means include at least the amount of air flow (see also page 5, lines 12 to 17 "rate of air flow") from a blower motor ("blower motor" 3), cooling capability for cooling air sent by said blower motor (loc. cit.), and an actuator ("position adjusting actuator" 19) which causes the temperature of the blow off air to rise by reheating ("air mixing damper" 6 in cooperation with "heater core" 5). The air conditioning control means ("microcomputer" 16) determines a feedback control amount of the air conditioning control means (see page 8, line 27 to page 9, line 12).

3. The claimed air conditioner is distinguished from this prior art in that the air conditioning control means "is formed as an integral-added optimal regulator" comprising a perturbation component computing portion P3 for computing a perturbation component DeltaTR derived from the measured internal air temperature TR and from a reference parameter value TRa;

a state observer P4 for estimating state variables DeltaTB, DeltaTC, DeltaTD; and

feedback amount determining means P5 for determining the feedback control amount, providing an optimal feedback gain F which is predetermined according to dynamic models of said air conditioning system.

In other words, the invention as set forth in claim 1 of the main request differs from the disclosure of document D1 in that it provides

(a) a general state-space approach to the control system design,

the design including

(b) a "state observer" for estimating the state variables, and

(c) a regulator which is

(d) "optimal", i.e. the system provides for an optimal feedback gain, and

(e) "integral-added", i.e. the control loop includes an integrating function.

The state-space approach is substantially a control algorithm for calculating, in the present context, the feedback signals for driving the respective actuators of the automotive air conditioner from the measured internal temperature TR. Except for the definition of the measuring and controlling variables TR, VB, VC, and VD, claim 1 defines the control system only in terms of the abstract components and parameters of the state- space model, with the consequence that the invention as claimed does not manifest itself in any concrete physical properties of the control system. If for example the control features necessary for implementing the control algorithm (not present in claim 1) are chosen inappropriately as a result of an inadequate system analysis or of an inappropriate definition of the optimization problem, the time-response and the power consumption of the air conditioner will turn out to be worse than the results achieved with a simple on- off control or the control system of document D1, regardless of the measuring and controlling variables used in the state-space model and the potentially advantageous effects achievable by features (b) to (e) cited above.

Thus, the mere use of the state-space approach does not in itself provide any advantage over the D1 system. Accordingly, in the context of the problem-and-solution approach for assessing inventive step, the technical problem to be solved is seen as providing an alternative to the control algorithm used in the air conditioning system of document D1.

4. In seeking such an alternative control algorithm the skilled person could be expected to take prior art document D12 into account since this document deals with matters relating to air conditioning and temperature control systems in confined spaces. The circumstance that the confined spaces are part of life support systems is not relevant since the technical issues in respect to air conditioning and temperature control are largely the same as in an automotive system.

It is apparent from document D12, in particular page 151, last paragraph, that "the modern optimal control theory is very much suited for such systems", the skilled person thus being taught that these control methods are a very suitable alternative to known control schemes, and thus as a possible solution of the technical problem defined above.

5. Regarding the expression "modern control theory", it was not contested by the respondent that well before the priority date of the contested patent, it had a known meaning in the art, being synonymous with the use of a state-space digital control method, which is based on a linearised mathematical model of the control system. Having decided in favour of the "modern optimal control theory" suggested by document D12 as an appropriate alternative to the prior art system of document D1, the skilled person, therefore, could be expected to realise an automotive air conditioning and temperature control system of the type comprising features (a), (c) and (d) cited above.

6. Nevertheless, various technical problems remain to be solved since document D12 contains no relevant details concerning the theory or the design of such modern optimal control systems, although "many facets to the modern control theory" are said to exist (see document D12, page 151, penultimate paragraph). The skilled person, however, can be expected to apply his common technical knowledge in this field, which is, to a considerable extent, acknowledged in the present patent specification itself (see page 4, lines 17 ff. and following pages).

7. In the first place, a mathematical model of the automotive air conditioning and temperature control system has to be formulated. For such a complex system normal practice requires that this model be determined through system identification and experimental system analysis.

8. Secondly, the complex environmental conditions inside and outside of automobiles generally do not allow the measurement of all relevant model parameters of the automotive air conditioning and temperature control system. In the prior art system of document D1 for example, the temperature is measured only at a few locations. The normal practice to deal with the problem of incomplete information regarding the model parameters is the use of so-called "observers" as described in the present patent specification, page 5, lines 9 ff. and also shown as "Regelgrößen-be-obachter" in the prior art document D14, page 362, Figure 7.25. A state observer according to feature (b) above thus does not contribute to inventive step, at least if considered in isolation.

9. A third problem to be solved is the residual errors which are commonly known to exist in closed-loop controllers under steady process conditions. Adding an integrator to the control loop is a standard technique to solve this problem, which is also applied in modern control methods as acknowledged for example in the present patent specification at page 4, lines 17 ff. Therefore, at least if considered in isolation, the integral-added regulator defined in the last feature (e) does not involve an inventive step either.

10. Finally, features (a) to (e) remain obvious even if their contribution to the prior art is considered as a whole and possible combinatorial effects are taken into account.

The technical contribution to the prior art indicated by feature (a) resides in the general decision for using a modern state-space control method as an alternative to the document D1 system. This decision is the first step which has to be taken and which is, under technical aspects, independent from possible subsequent embodiments of the general state-space model, which the embodiments according to features (b) to (e) above actually are.

Taking feature (e) first, it is clear that steady-state errors and the use of an integrator to reduce them are not specific to any particular control method. They are also relevant in the classical regime of control techniques. Using feature (e) in the context of an optimal state-space model with observers does not add any technically relevant aspects so that even in combination with such other claim features the integrating function remains a technically independent aspect of the invention and thus is an obvious addendum to the state-space model defined in claim 1.

Regarding feature (b), the situation is slightly different since the model building of the state-space approach (feature (a)) may be understood as a prerequisite of implementing the state observer defined in feature (b). However, as explained in T 623/97 ((not pub. in OJ EPO), point 4.4 of the reasons, an invention even requiring two or more steps for arriving at a complete solution may be obvious to the skilled person if the technical problem to be solved leads the skilled person step-by-step to the solution, each individual step being obvious in the light of what has been accomplished and of the residual task remaining to be solved.

In the present case indeed, the information gap present in document D12 forces the skilled person, after having decided in favour of a modern optimal control system, to make further steps to arrive at a workable design. Choosing to solve first the one or the other from the many design problems evidently present and solving this in an obvious manner does not involve an inventive step.

11. In conclusion, the subject-matter of claim 1, even if considered as a whole, lacks inventive step , which prejudices maintenance of the patent amended on the basis of respondent's main request (Articles 52(1), 56 and 102(3) EPC).

First auxiliary request

12. The first auxiliary request amends claim 1 of the main request by introducing features from the second part into the first part of the claim, without adding any technical information to the claim. As follows from respondent's letter of 24 September 2002 these amendments merely serve the purpose of bringing the claim wording into compliance with the requirements of Rule 29(1)(a) EPC. The amendments are thus not occasioned by any grounds of opposition, with the consequence that they are not admissible into the appeal proceedings, and the first auxiliary request thus not being allowable (see Rule 57a EPC and chapter VII.C.10.1.1 in Case Law of the Boards of Appeal of the European Patent Office, 4th edition 2001, pages 483 f.).

Second auxiliary request

13. Claim 1 of the second auxiliary request was filed at the oral proceedings held before the Board, which was thus obliged to decide whether to exercise its discretion whether to admit it to the proceedings (see chapter VII.C.14 in Case Law of the Boards of Appeal of the European Patent Office, 4th edition 2001, pages 545 ff.).

The amended claim only adds to claim 1 of the main request an explanation of the term "dynamic model" appearing in the penultimate paragraph of claim 1 of 12. May 1998. This explanation, however, is of a very general character and indicates only what was already normal practice in applying a state-space model to complex systems. These amendments do not prima facie render the subject-matter of claim 1 patentable. In addition, the amendments were not occasioned by any new evidence or arguments which were produced at this stage of the appeal proceedings. Neither has the respondent given any other acceptable reason for the late filing. The Board, therefore, decided not to admit the amended claim to the proceedings.