METHOD FOR CONTROLLING A THERMODYNAMICAL SYSTEM

Description

[0001] The invention relates to the field of control methods, or control methods, of thermodynamic systems with a gas turbine cycle with cooled compression, regeneration and intermediate heating during expansion, of the turbomachine type.

[0002] Gas turbine-type power converters are currently being studied for highly electrified powertrains, particularly those known as range extenders in production hybrid vehicles. Such a converter operates as an Auxiliary Power Unit (APU), where its role is to recharge the batteries of an electric vehicle. It is thus mechanically decoupled from the powertrain and therefore operates at its maximum efficiency.

[0003] In particular, a thermodynamic system with a gas turbine cycle featuring cooled compression, regeneration, and reheating during expansion (a device known in English as an "Intercooled Reheat Gas Turbine," or IRReGT) is a device with strong potential for automotive applications. This cycle allows for very high efficiency as well as very high power density (i.e., high net specific work).

[0004] In addition, the prior art is known from documents US2012324903A1, FR3095007A1 and US5497615A.

[0005] The objective of this application is to propose control strategies, i.e., control methods, for a thermodynamic system of the aforementioned "Intercooled Regenerative Reheat Gas Turbine" type, featuring two separate stages of electrified turbochargers. These methods must optimize the operation and control the machine during its operating phases.

[0006] The invention thus proposes a method for controlling a thermodynamic system for a motor vehicle, the system comprising: a first turbocharger comprising an electric machine forming a motor-generator, a first compressor and a first turbine; a second turbocharger comprising a second compressor and a second turbine; two combustion chambers; a flow cooler connected to the first compressor and the second compressor; a heat recovery unit connected to the second compressor and to a first combustion chamber, itself connected to the second turbine, itself connected to the second combustion chamber, itself connected to the first turbine; the system being configured to implement a fluid flow between the different elements; the process comprising successively: a step of activation of the electric machine, until a minimum engine speed is reached (speed at which the respective electric machine can switch from engine mode to generator mode) for each of the first and second turbochargers; a step of injection and combustion of fuel in the second combustion chamber until the temperature at the inlet of the first turbine reaches a predetermined minimum temperature α; a step of increasing the temperature at the inlet of the second turbine and the heat recovery unit until the electric machine switches to generator mode and the temperature at the outlet of the heat recovery unit towards the first combustion chamber reaches at least a predetermined minimum temperature;a fuel injection stage into the first combustion chamber.

[0007] This process optimizes the operation of the thermodynamic system during startup, which is the most polluting phase. It optimizes the airflow characteristics before initiating injection into the second combustion chamber, thus allowing the thermodynamic system to reach temperature quickly, minimizing pollutant emissions (such as gaseous emissions), and optimizing the efficiency of the thermodynamic system right from the startup phase.

[0008] In addition, crossing the required temperature threshold (the predetermined minimum temperature α) at ​​the inlet of the first turbine, and increasing the fuel flow at its inlet, allows it to generate more power than the first compressor consumes, thus switching the corresponding electric machine into generator mode.

[0009] Furthermore, reaching this temperature at the outlet of the recuperator towards the first combustion chamber, at least a predetermined minimum temperature, allows the process to move to the next stage, thus starting combustion when the first combustion chamber is already hot and further reducing pollutant emissions.

[0010] Advantageously, the fuel injection step into the first combustion chamber includes a sub-step of flow cooler activation.

[0011] Delaying the activation of the flow cooler until the fuel injection stage in the first combustion chamber, which itself follows the fuel injection stage in the second combustion chamber, allows the system to reach operating temperature before the air density entering the second compressor increases due to cooling in the flow cooler. This advantageously allows the heat recovery unit to reach operating temperature quickly, right from system startup.

[0012] Alternatively, the electrical machine activation step includes a flow cooler activation substep.

[0013] Advantageously, the fuel injection step in the first combustion chamber is followed by a parameter adjustment step during which the inlet temperatures of the first turbine and the second turbine are controlled by acting on the quantity of fuel injected into the second combustion chamber and the first combustion chamber respectively, and / or by regulating the temperature at the outlet of the flow cooler by the flow cooler.

[0014] Proceeding in this way allows for the optimization of the overall operation of the thermodynamic system at the end of the start-up phase and at the beginning of its stabilized operating phase.

[0015] Advantageously, an electric heater is respectively disposed upstream of at least one combustion chamber among the first combustion chamber and the second combustion chamber, preferably an electric heater is respectively disposed upstream of at least the second combustion chamber, and, the process includes at least one substep of heating the gas stream entering at least one combustion chamber before the step of injecting fuel into the second combustion chamber and / or before the step of injecting fuel into the first combustion chamber.

[0016] The invention also relates to a thermodynamic system comprising: a first turbocharger comprising an electric machine forming a motor-generator, a first compressor and a first turbine, a second turbocharger comprising a second compressor and a second turbine, two combustion chambers, a flow cooler connected to the first compressor and the second compressor, a heat recovery unit connected to the second compressor and a first combustion chamber, itself connected to the second turbine, itself connected to the second combustion chamber, itself connected to the first turbine, the system being configured to implement a fluid flow between the different elements, characterized in that it includes a control device configured to control the thermodynamic system according to the steps of the process of the invention.

[0017] Advantageously, the second compressor and the second turbine, as well as the first compressor and the first turbine, are mounted on the shaft of the electric machine forming a motor-generator.

[0018] Advantageously and alternatively, the electric motor-generator is a first electric motor-generator, the first compressor and the first turbine being mounted on a shaft of the first electric motor-generator, and in that the second turbocharger comprises a second electric motor-generator, which comprises a shaft on which the second compressor and the second turbine are mounted.

[0019] The invention also relates to a motor vehicle comprising a thermodynamic system as mentioned above.

[0020] The invention will be better understood upon reading the detailed description of non-limiting embodiments, and on the basis of the accompanying figures illustrating variants of the invention, in which: [ Fig.1 ] is a functional diagram of an example of a two-stage thermodynamic system, of the IRReGT (Intercooled Recuperative Reheat Gas Turbine) type; [ Fig.2 ] is a schematic representation of an electrical energy production and storage circuit in a hybrid vehicle; [ Fig.3 ] is a functional diagram of the two-stage thermodynamic system of the Figure 1 , further showing the installation of pressure and temperature sensors in the system, as well as two optional electric heaters; Fig.4 ] is a flowchart of the steps in a startup phase of the thermodynamic system of the figure 1 that is to say, without an electric heater; [ Fig.5 ] is a flowchart of the steps in a startup phase of the thermodynamic system of the figure 3 that is to say, with the implementation of electric heaters.

[0021] The invention relates to a method for controlling a gas turbine cycle thermodynamic system with cooled compression, regeneration, and reheating during expansion (IRReGT), for example, a turbomachine. The invention relates in particular to applications of the method in such a thermodynamic system intended for use in a motor vehicle.

[0022] With reference to the Fig. 2 This section describes an example of integrating such a gas turbine cycle thermodynamic system into a hybrid vehicle, specifically within the vehicle's electrical energy production and storage circuit. This thermodynamic system can notably operate as an auxiliary power unit (APU). When operating as an auxiliary power unit in a steady-state configuration, it recharges the vehicle's main battery(ies) B via its electric motors (EMGs). Fig. 2 , or more specifically EMG1 and EMG2 in Fig. 1 And 3 The battery is connected via AC-DC power converters (DC-AC blocks). Fig. 2 ) on the one hand to the thermodynamic system as an APU, and on the other hand to the vehicle's electric drive motor ELM. A drive chain of a known type then connects the main electric motor to the vehicle's wheels W.

[0023] We then detail a thermodynamic system of the aforementioned gas turbine cycle type with reference to Fig. 1 And 3 .

[0024] Such a thermodynamic system comprises a first turbocharger TC1 and a second turbocharger TC2.

[0025] The first TC1 turbocharger comprises a first compressor C1 and a first turbine T2.

[0026] The second TC2 turbocharger includes a second C2 compressor and a second T1 turbine.

[0027] More specifically, the first turbocharger forms a "low pressure" stage, and the second turbocharger forms a "high pressure" stage.

[0028] The turbochargers here are electrified, that is to say they each include an electric machine EMG1, EMG2 operating both in motor and generator mode, that is to say as a motor to drive and start the system; and as a generator to recover the energy produced by combustion.

[0029] The thermodynamic system also includes two combustion chambers CC1 and CC2, and a flow cooler IC (also called an air / air exchanger, or air / water exchanger, or in English "intercooler").

[0030] The IC flow cooler is connected to the first compressor C1 and the second compressor C2.

[0031] The thermodynamic system also includes a heat recovery unit (HRU) (or heat exchanger). The HRU is connected to the second compressor (C2) upstream and to a first combustion chamber (CC1) upstream. The first combustion chamber (CC1) is then connected to the second turbine (T1).

[0032] The second combustion chamber CC2 is connected to both turbines, namely in particular to the second turbine T1 upstream and to the first turbine T2 downstream.

[0033] The thermodynamic system further includes a recovery branch RB1 connecting the first turbine T2 to the heat recovery unit TR and passing through it. The side of the recuperator TR through which the recovery branch RB1 passes is called the hot side of the recuperator, since the gas flow comes directly from the first turbine T2 after undergoing a second combustion in the combustion chamber CC2. Conversely, the side of the recuperator TR receiving compressed air from the compressor C2, and from which the air is directed to the first combustion chamber CC1, is called the cold side of the recuperator.

[0034] The thermodynamic system is configured to be traversed by a gaseous flow F1, described later, between the different elements composing it.

[0035] The use of a second CC2 combustion chamber (for reheat) between the turbines increases power density, which reduces the required airflow at the same power output and reduces the size of the device.

[0036] In the embodiment illustrated in Fig. 3 The system is equipped with an AF air filter and an AMF air flow meter (from the English "Air Mass Flow" meter).

[0037] The system is also equipped with a fuel injection system in the first combustion chamber FUEL 1 and a fuel injection system in the second combustion chamber FUEL 2.

[0038] To control the operation of the thermodynamic system, a control device is provided, configured to control the thermodynamic system according to the steps of the control method of the invention. The control device includes the means for data acquisition, processing via software instructions stored in memory, and the control means required to implement the steps of the control method of the invention. Various pressure sensors (P) and temperature sensors (T) can be implemented in different locations. The temperature sensors are preferably thermocouples. These locations are indicated by letters or numbers and correspond to the following points: 0: Air filter inlet 1: Air filter outlet / First compressor inlet C1 2: Compressor outlet C1 / Flow cooler inlet IC 2': Cooler outlet IC / Second compressor inlet C2 2": Compressor outlet C2 / Cold side recuperator inlet x: Cold side recuperator outlet / First combustion chamber inlet CC1 3: Combustion chamber outlet CC1 / Second turbine inlet T1 3': Turbine outlet T1 / Second combustion chamber inlet CC2 3": Combustion chamber outlet CC2 / First turbine inlet T2 4: First turbine outlet T2 / Hot side recuperator inlet (i.e., located on the heat recovery branch RB1) y: Recuperator outlet to ambient air

[0039] Hereafter, as needed, measured values ​​will be designated by the letter of the unit of measurement and the symbol, as a subscript to distinguish them from the turbine designations T1 and T2, of the measurement location. For example, temperature measurements in x or 3" will be noted as T x and T 3".

[0040] In the embodiment illustrated in Fig. 3 The thermodynamic system also includes a first electric heater EH1 and a second electric heater EH2, each optional. The first electric heater EH1 is located at the outlet of the cold side of the heat exchanger TR. Therefore, the temperature measurement Tx is taken, for example, downstream of the first electric heater EH1, i.e., also at the inlet of the first combustion chamber CC1, and not directly at the outlet of the cold side of the heat exchanger TR. The second electric heater EH2 is located between the outlet of the second turbine T1 and the second combustion chamber CC2.

[0041] In an alternative not shown, the system may consist of only one electric heater, for example the first electric heater EH1 alone, or the second electric heater EH2 alone.

[0042] We now describe the gas flow F1 in the system.

[0043] In general, the gas flow F1 follows the arrows illustrated in Fig. 1 And 3which connect the various components and pass through them. Ambient air is first drawn into the air filter AF by the compressor C1. This air then passes through the flow meter AMF and enters the compressor C1. The air is compressed there before entering the flow cooler IC where it is cooled. At the cooler outlet, the air temperature T2' reaches a temperature between 45 and 60°C depending on the outside temperature (and depending on the cooling efficiency of the flow cooler). It then enters the compressor C2 where it is compressed a second time before entering the recuperator TR, specifically the cold side of the recuperator. In the recuperator TR, the air is preheated by the hot gases from the recovery branch RB1 coming from the outlet of the turbine T2. The air exiting the recuperator TR thus enters the first combustion chamber CC1.Upon exiting the first combustion chamber CC1, an initial expansion occurs in the high-pressure turbine T1, followed by a reheating phase in the second combustion chamber CC2 before entering the first turbine T2 for a second expansion. Exiting the first turbine, the hot gases enter the hot side of the recuperator TR to preheat the air coming from the second compressor C2, which is the cold side of the recuperator TR.

[0044] We are now describing, with reference to the Fig. 4 an example of a thermodynamic system control process that corresponds to a cold start phase.

[0045] During this phase, all machine components are cold. This thermodynamic system start-up process allows for a rapid temperature rise, which minimizes pollutant emissions. Step 1 (E1): Activation of electrical machines EMG1 and EMG2.

[0046] The two electric machines EMG1 (110) and EMG2 (120), corresponding respectively to the low-pressure and high-pressure stages of the thermodynamic system, are set in rotation. At this stage, the electric machines EMG1 and EMG2 are in motor mode, meaning they are powered by current from the battery to drive the turbines T1 and T2 and the compressors C1 and C2. Furthermore, no fuel is injected at this stage.

[0047] Once the respective RPM1 and RPM2 rotation regimes of the two electric machines EMG1 and EMG2 reach setpoint values ​​R1 and R2 (conditions 115 and 125), step 2 is initiated. Step 2 (E2): Fuel injection and combustion in the low-pressure combustion chamber CC2

[0048] In this phase, fuel is injected into the second combustion chamber CC2 (210). The fuel injection increases the temperature T3" at the turbine inlet T2 and the temperature in the recuperator TR.

[0049] The electric machines EMG1 and EMG2 are still in motor mode at this stage. No injection is taking place at this stage in the first combustion chamber CC1.

[0050] The temperature T3" is controlled to remain below a maximum setpoint temperature C, i.e., T3" < C (condition 215). This advantageously prevents the turbine temperature T2 from exceeding the resistance limit of its constituent materials. This temperature T3" is controlled by the amount of fuel injected into the second combustion chamber CC2. Step 3 (E3): Increase in temperature at the inlet of the second turbine T1 and the recuperator TR

[0051] During this stage, fuel injection into combustion chamber CC2 continues, and the temperature T3" at the inlet of the first turbine T2 is ensured to increase (310) until it reaches or exceeds a predetermined threshold temperature α (condition 315), while remaining below the maximum setpoint temperature C (condition 215). The increase in temperature T3" will allow turbine T2 to generate more power than the first compressor C1, thus enabling the first electric machine EMG2 to switch to generator mode. In other words, the mechanical energy produced by turbine 2 then allows the first electric machine EMG2 to generate current to recharge the main battery B. At this stage, no injection is yet performed in the first combustion chamber CC1.

[0052] With the heating of the flow at the inlet of turbine T2, the temperature T4 of the heat recovery unit TR, i.e., on its hot side, also rises via branch RB1 (312). An increasing heat transfer occurs from the hot side to the cold side of the heat recovery unit TR.

[0053] When the operating condition of the first electric machine EMG2 in generator mode is met (condition 320) and when a temperature Tx at the outlet of the recuperator TR, i.e., at the inlet of the first combustion chamber CC1, reaches or exceeds a setpoint temperature B (condition 322), the process continues with injection step 4. Reaching this temperature allows combustion in the first combustion chamber CC1 to be initiated at a high temperature, thus reducing pollutant emissions. Step 4 (E4): Fuel injection into the first combustion chamber CC1 (and cooling of the gas flow F1 by the flow cooler IC)

[0054] During this step, fuel is also injected into the first combustion chamber CC1 (410).

[0055] Preferably, but not exclusively, the IC flow cooler cooling circuit is also activated in step 4 (420). Alternatively, this cooling circuit is activated at another point in the cycle, for example, as early as step 1, i.e., from the start of the thermodynamic system. However, delayed activation of the IC flow cooler until step 4 is preferred so that the TR recuperator can reach temperature more quickly, thereby heating the gas stream F1 entering the first combustion chamber CC1 more rapidly and reducing pollutant emissions more quickly.

[0056] The operation of the thermodynamic system is controlled until the power of the high-pressure turbine, i.e., the second turbine T1, exceeds the power required by the second compressor C2, and thus the second electric machine EMG1 also switches to generator mode (430). At this point, fuel is injected into both the first and second combustion chambers CC1 and CC2. Furthermore, both electric machines EMG1 and EMG2 now operate in generator mode. Step 5 (E5): Checking, or adjusting, the parameters

[0057] During this step, the inlet temperatures of the first turbine T2 (T3", control 512) and the second turbine T1 (T3, control 510) are controlled by adjusting the amount of fuel injected. Alternatively or cumulatively, the temperature T2' of the gas stream F1 exiting the IC flow cooler is regulated by the IC flow cooler itself (control 514).

[0058] Depending on whether the process described above is implemented for a cold start, i.e., after cooling to ambient temperature, or for a hot start, i.e., an interruption of the thermodynamic system's operation after a previous operating cycle during which its components will have reached operating temperature, the time required to reach the minimum temperatures α and B will differ. The sequence of actions from step 1 onward, however, remains the same.

[0059] With reference to the Fig. 5 , an optional substep (E5a) of using electric heaters such as the EH1 and EH2 heaters illustrated in Fig. 3 is now described.

[0060] The implementation of a sub-step for activating an electric heater, for example by the electric heater EH1 upstream of the combustion chamber CC1 (145), or, by the electric heater EH2 upstream of the combustion chamber CC2, see diagram of the Fig. 3 This allows the incoming gas stream F1 to be heated before fuel is injected in sub-steps 210 and 410, respectively. This makes it possible to start the combustion chamber hot. Furthermore, since the gas stream returns to the heat recovery unit TR via the recovery branch RB1, some of the energy from the gas stream is recovered in the TR, thus enabling the heat recovery unit to reach operating temperature even more quickly.

[0061] The power supply for the EH1 and / or EH2 electric heater is drawn from the car battery. This phase, however, only lasts for the heating time, i.e., less than 3 minutes, preferably less than 2 minutes (depending on the power of the electric heating element and, above all, on the mass of the parts to be heated / their thermal inertia). The heating time depends on the power of the electric heating element and the thermal inertia of the components of the thermodynamic system as a whole.

[0062] In the illustrated example, exceeding a threshold temperature by the measured temperature T3' at the inlet of combustion chamber CC2, due to the activation of one (145) and / or the other (314) of the electric heaters EH2 and EH1, can serve as an additional, optional prerequisite for starting the injection stage in one and / or the other of combustion chambers CC2 and CC1 (see Fig. 5 ).

[0063] Finally, when one or both of the temperatures TEH1 and TEH2 at the electric heaters EH1 and EH2 exceeds a threshold temperature D1 (520) and D2 (530), respectively, it is possible to deactivate the electric heaters EH1 and EH2 (525 and 535). Fig. 5 ).

[0064] Another object of the invention relates to a motor vehicle configured to be able to implement the control method, described above, of a thermodynamic system.

[0065] This is, for example, a vehicle with a series hybrid powertrain (or range extender), in which the thermodynamic system is configured to recharge the vehicle's drive battery(ies). This electric vehicle is equipped with an energy converter in the form of a thermodynamic system of the type described above, operating in APU (Auxiliary Power Unit) mode, to recharge the drive battery.

[0066] In a structural variant not shown, the coupling of components within the thermodynamic system may differ. For example, the first turbine T2 can be mounted on the shaft common to the second compressor C2 and the second electric machine EMG1, meaning the high-pressure compressor is mechanically connected to the low-pressure turbine. Conversely, the second turbine T1 is then mounted on the shaft common to the first compressor C1 and the first electric machine EMG2, meaning the low-pressure compressor is mechanically connected to the high-pressure turbine. The control method will be the same, except that the order in which the electric machines switch to generator mode will be reversed, since the low-pressure turbine—that is, the one benefiting from the combustion process initiated first—is then, in a sense, located within the other turbocharger.

[0067] In an alternative configuration not shown, the two turbochargers share a common electric motor-generator. In other words, both turbines and both compressors are mounted on the same rotating shaft of the common electric machine. The control strategies remain the same. This structure offers the advantage of weight savings, thanks to the elimination of one of the electric machines in the embodiment shown in the figures.

Claims

1. Steering process of a thermodynamic system for motor vehicles, the system comprising: - a first turbocharger (TC1) consisting of an electric machine forming an engine-generator (EMG2), a first compressor (C1) and a first turbine (T2); - a second turbocharger (TC2) comprising a second compressor (C2) and a second turbine (T1); - two combustion chambers (CC1, CC2); - a flow cooler (IC) connected to the first compressor (C1) and the second compressor (C2); - a thermal recuperator (TR) connected to the second compressor (C2) and a first combustion chamber (CC1), which is connected to the second turbine (T1), which is connected to the second combustion chamber (CC2), which is connected to the first turbine (T2); the system being configured to implement a fluid flow (F1) between the various elements; the process consisting successively of: - an activation stage (E1) of the electric machine (EMG2), until the achievement of a respective minimum engine speed (RPM2) for each of the first and second turbocompressors (TC1, TC2); - an injection (E2) and fuel combustion stage in the second combustion chamber (CC2) until the temperature "T3" at the inlet of the first turbine (T2), at a predetermined minimum temperature (315); - an increase (E3) in the input temperature of the second turbine (T1) and the heat recovery (TR) until the electrical machine (EMG2) is switched in generator mode (320) and the temperature Tx is reached out of the recovery (TR) towards the first combustion chamber (CC1), at least a minimum free temperature predetermined (322); - one fuel injection stage (E4) in the first combustion chamber (CC1).

2. Control process according to Claim 1, characterized that the fuel injection stage (E4) in the first combustion chamber (CC1) includes an activation substage (420) of the flow cooler (IC).

3. Control process according to Claim 1, characterized that the activation stage (E1) of the electric machine (EMG2) includes a substage of activation of the flow cooler (IC).

4. Control process according to one of the claims 1 to 3, characterized by the fuel injection stage (E4) in the first combustion chamber (CC1) followed by an adjustment stage (E5) of the parameters during which the input temperatures (T3", T3) of the first turbine (T2) and the second turbine (T1) are controlled by action on the quantity of fuel injected (FUTURE) EL 2, FUEL 1) in the second combustion chamber (CC2) and in the first combustion chamber (CC1) respectively, and / or temperature control (T2') at the flow cooler (IC) outlet by the flux cooler (IC).

5. Pilotage process according to one of the claims 1 to 4, characterized that an electric heater (EH1, EH2) is located upstream of at least one combustion chamber (CC1, CC2) from the first combustion chamber (CC1) and the second combustion chamber (CC2), respectively, preferably an electric heater (EH2) is located upstream of at least one second combustion chamber (CC2)), the process involving at least one substage (145); 314) of heating of the gas flow (F1) entering at least one combustion chamber (CC2, CC1) before the fuel injection stage (E2) in the second combustion chamber (CC2) and / or before the fuel injection stage (E4) in the first combustion chamber (CC1).

6. Thermodynamic system comprising: - a first turbocharger (TC1) comprising an electric machine forming an engine-generator (EMG2), a first compressor (C1) and a first turbine (T2), - a second turbocharger (TC2) comprising a second compressor (C2) and a second turbine (T1), - two combustion chambers (CC1, CC2), - a flux cooler (IC) connected to the first compressor (C1) and the second compressor (C2), - a thermal recuperator (TR) connected to the second compressor (C2) and a first combustion chamber (CC1), which is connected to the second turbine (T1), which is connected to the second combustion chamber (CC2), which is connected to the first turbine (T2), the system being configured to implement a flow of fluid (F1) between the various elements, characterized as it includes a control device configured to control the thermodynamic system according to the process steps according to one of the claims 1 to 5.

7. Thermodynamic system according to claim 6, characterized as the second compressor (C2) and the second turbine (T1) as well as the first compressor (C1) and the first turbine (T2) are mounted on the axis of the electric machine forming engine-generator (EMG2).

8. Thermodynamic system according to claim 6, characterized as the electric machine forming engine-generator (EMG2) is a first electric machine forming engine-generator, the first compressor (C1) and the first turbine (T2) are mounted on an axis of the first electric machine forming engine-generator (EMG2), and the second turbo-compressor (TC2) includes a second electric machine forming engine-generator (EMG1)), which has an axis on which the second compressor (C2) and the second turbine (T1) are mounted.

9. Motor vehicle with a thermodynamic system according to one of the claims 6 to 8.