T 2368/13 11-02-2019

1. Main Request

1.1 Unity of invention, Article 82 EPC

1.1.1 The Board shares the examining division's view that the two independent apparatus claims 1 and 7 lack unity and that the same applies to the two independent method claims 12 and 13. The reasons are as follows.

1.1.2 The appellant argued on page 6/9 of the grounds of appeal that "the common inventive concept is to use the duty ratio together with input and/or output voltages to handle a failure event". The Board does not find this argument convincing because there is nothing in claims 7 and 13 that is suggestive of a failure event. Claims 7 and 13 cover a voltage conversion system (and method) which has (or which is carried out with) a converter that only ever comprised one voltage sensor (input or output), i.e. in which there has been no failure event. Hence, such a system/method does not have an inventive concept in common with claims 1 and 12 which relate to the detection of a failure event in a method/system with two voltage sensors (input and output).

1.1.3 In the letter dated 9 January 2019 the appellant argued further that whilst independent claims 7 and 13 did not expressly mention a failure, the measures defined in claims 7 and 13 could be applied for a failure case in which one of the input and output voltages was not detected (see page 2/10, last paragraph). The Board does not find this argument persuasive. Whilst claims 7 and 13 might be applicable in such a failure case, that does not change the fact that they are also applicable to cases in which the converter only ever comprised one voltage sensor (input or output), i.e. in which there has not been any failure event. It is this aspect, which is covered by claims 7 and 13, that lacks unity with claims 1 and 12.

1.1.4 For these reasons the Board considers that the claims of the main request do not meet the requirement for unity of invention, Article 82 EPC.

1.2 Clarity, Article 84 EPC

1.2.1 Further to the above, given that it is not evident what precisely is meant by "duty ratio by which the voltage is to be converted", this formulation itself is not clear. The appellant has argued that it means "the ratio between the input voltage and the output voltage" (grounds for appeal, page 3/9, second paragraph), but the word "duty" makes no sense in that context. In the letter dated 9 January 2019 the appellant argued that this formulation is to be understood as the duty ratio or duty cycle of the switching elements in the converter. The very fact that such conflicting arguments have been presented as to how the formulation is to be understood emphasises that the formulation itself is unclear.

1.2.2 According to claim 1 of the main request the control unit 26 determines the presence of an abnormality of the input voltage sensor 20 or the output voltage sensor 22 just on the basis of the duty ratio by which the voltage is to be converted controlled by the control unit 26. It is evident from the disclosure of the application as a whole, however, that the control unit 26 would not be able to determine the presence of an abnormality in one of the input and output voltage sensors without having knowledge of the voltages as detected by those sensors. Thus, it is an essential feature of the invention that the input voltage of the converter detected by the input voltage sensor and the output voltage of the converter detected by the output voltage sensor are also used as the basis for determining the presence of an abnormality. The appellant's argument that the use of the input and output voltages forms part of the inventive concept (letter of 9 January 2019, page 2/10, last paragraph) supports the finding that this is an essential feature. Claim 1 of the main request fails to include this essential feature, cf. Rule 43(1) and (3) EPC.

1.2.3 Furthermore, it is evident from the application as a whole that for the control unit to be able to determine the presence of an abnormality in the input or output voltage sensor on the basis of the duty cycle of the switching element and the detected input and output voltages, it would also have to know what the relationship between the input and output voltages should be, depending on the duty cycle. Without knowledge of what this relationship (sometimes referred to as the "transfer function") should be, the control unit would be unable to determine whether or not there is an abnormality in one of the input and output voltage sensors. Claim 1 of the main request fails to include this essential feature, cf. Rule 43(1) and (3) EPC.

1.2.4 For these reasons claim 1 of the main request does not meet the requirements for clarity, Article 84 EPC.

1.3 Amendments, Article 123(2) EPC

In view of the Board's findings on Articles 82 and 84 EPC it was not necessary to decide on the question, raised in the Board's communication, of whether the feature "duty ratio by which the voltage is to be converted" is directly and unambiguously derivable from the application as filed (see IV. above).

1.4 Conclusion on the main request

For the reasons set out above the Board was not able to accede to the appellant's main request.

2. First Auxiliary Request

2.1 In the first auxiliary request, claims 7 to 10 and 13 of the main request have been deleted, thereby removing the lack of unity, Article 82 EPC.

2.2 Furthermore, the essential feature referred to in paragraph 1.2.2 above has been introduced into the independent claims 1 and 8, thereby removing the deficiency under Article 84 EPC referred to in that paragraph.

2.3 Nevertheless, the amendments made according to the first auxiliary request do not address the deficiencies identified in paragraphs 1.2.1 and 1.2.3 above. In view of these deficiencies the Board was not able to accede to the appellant's first auxiliary request.

3. Second Auxiliary Request

3.1 The amendments made according to the second auxiliary request do not address the deficiencies identified in paragraph 1.2.1 above.

3.2 Regarding the deficiency identified in paragraph 1.2.3, the independent claims according to the second auxiliary request specify that the converter is constituted of a plurality of switching elements, and that changes in the conversion ratio between the input voltage and output voltage of the converter are only dependent on the duty ratio that [is] used for operation of the switches of the converter.

The Board recognises that in switching converters, at least under certain conditions, the manner in which the relationship between the input and output voltages depends on the duty cycle is determined by the topology of the converter, i.e. the arrangement of its key components. Hence, defining the converter topology has the potential to overcome the deficiency identified in paragraph 1.2.3. Nevertheless, merely specifying that the converter is constituted of a plurality of switching elements does not define the converter topology sufficiently to determine how the relationship between the input and output voltages would depend on the duty cycle. Hence, the amendments according to the second auxiliary request do not overcome the deficiency identified in paragraph 1.2.3 above.

3.3 In view of these deficiencies the Board was not able to accede to the appellant's second auxiliary request.

4. Third Auxiliary Request

4.1 The amendments made according to the third auxiliary request do not address the deficiency identified in paragraph 1.2.3 above.

4.2 In view of this deficiency the Board was not able to accede to the appellant's third auxiliary request.

5. Fourth Auxiliary Request

5.1 With the amendments made according to the fourth auxiliary request, the Board is satisfied that the definition of the converter topology in both of the independent claims is sufficient to clearly define the manner in which the relationship between the input and output voltages would depend on the duty cycle of the first switching element (Q1). With that the deficiency identified in paragraph 1.2.3 above is overcome.

5.2 The converter topology as specified in the independent claims is directly and unambiguously derivable from the application as filed, in particular from figure 1 and the corresponding description. Furthermore, "duty cycle" is the term usually used to refer to the fraction of the commutation period during which the switch of a switching converter is on (see https://en.wikipedia.org/wiki/Boost_converter, Circuit analysis, Operation, Continuous Mode) and the use of the duty cycle of the transistor Q1 located in the upper side of the converter 12 to determine the presence of an abnormality has a basis in paragraph [0035] of the published application. Thus, the amendments according to the fourth auxiliary request overcome the objection under Article 123(2) EPC raised in the Board's communication (see IV. above).

5.3 Inventive Step, Article 56 EPC

5.3.1 Considering inventive step in view of document D1, the Board notes that the D1 converter has four switches and can be put into boost or buck mode by switching two of the transistors permanently on/off as shown in figure 4. In the boost mode the transistor Q1 is on and the transistor Q4 is off. Transistors Q2 and Q3 are connected with respect to the inductor L in the same way as the transistors Q1 and Q2 are connected in the independent claims of the fourth auxiliary request. Furthermore they are switched by anti-phase PWM signals that would switch the two transistors alternately, variably controlling the duty cycle of each transistor. Sensing of input voltage (12) and output voltage (15) is provided by an A/D converter (16).

5.3.2 Hence, document D1 discloses a voltage conversion system that has all of the features of the preambles of claims 1 and 7.

5.3.3 The question remains whether it would be obvious to determine the presence of an abnormality of the input voltage sensor or the output voltage sensor on the basis of the duty cycle controlled by the control unit, the input voltage of the converter detected by the input voltage sensor and the output voltage of the converter detected by the output voltage sensor.

5.3.4 According to the preamble of claims 1 and 7, the duty cycle controlled by the control unit" is the "duty cycle of the first switching element (Q1)" which is connected between the inductor and the positive output line.

5.3.5 The Board can see no obvious reason for the skilled person starting from document D1 to use the duty cycle of this specific switching element of the converter as a basis for the abnormality check.

5.3.6 With the benefit of hindsight it is perhaps derivable that using the duty cycle of this specific switching element is advantageous. The converter arrangement claimed is that of a boost (step-up) converter that is able to boost the battery voltage V1 up to the higher voltage V2 that should exist across the capacitor C (see also paragraph [0004] of the published application). In continuous mode, with the duty cycle of transistor Q2 represented as DQ2, the ratio of the output and input voltages in such a boost converter would be (cf. Wikipedia reference above):

V2 / V1 = 1 / (1 - DQ2) (Equation 1)

With the transistor Q1 switched on and off alternately with transistor Q2, in the manner described for the same circuit arrangement in the prior art (see paragraph [0006]), the duty cycle DQ1 of transistor Q1 would be equal to 1 minus the duty cycle DQ2 of transistor Q2, i.e.

DQ1 = 1 - DQ2 (Equation 2)

Using this in equation 1, the ratio of the output and input voltages can be represented as:

V2 / V1 = 1 / DQ1 (Equation 3)

This can be rewritten as:

V1 = V2 x DQ1 (Equation 4)

From equation 4 it can be seen that the duty cycle of the transistor Q1 is equal to the ratio of the input and output voltages and thus might provide a convenient basis for the abnormality check of the invention. However this seems only to be evident with the benefit of hindsight.

5.3.7 For these reasons the Board considers that the claims of the fourth auxiliary request meet the requirements for inventive step, Article 56 EPC.

5.4 Correction in Figure 5

In figure 5 of the application as filed, the step S31 state "INPUT INVERTER INPUT VOLTAGE V1". This is erroneous and should state "INPUT BATTERY VOLTAGE V1".

5.5 Conclusion on the fourth auxiliary request

For the reasons set out above the Board decided to accede to the appellant's fourth auxiliary request.