Method for monitoring the hydrogen concentration in the exhaust gas of a hydrogen-powered unit, control unit

Abstract

The invention relates to a method for monitoring the hydrogen concentration in the exhaust gas of a hydrogen-powered unit (1), for example an internal combustion engine or a fuel cell stack, comprising the steps: - Measuring the hydrogen concentration in the exhaust gas using a hydrogen sensor (2) and - Plausibility check of the hydrogen sensor reading (2) by using a software-based model to calculate the hydrogen concentration from an increase in the oxygen content in the exhaust gas and comparing the calculated hydrogen concentration with the measured hydrogen concentration. The invention further relates to a control unit (10) for carrying out steps of the method according to the invention.

Description

[0001] The invention relates to a method for monitoring the hydrogen concentration in the exhaust gas of a hydrogen-powered unit, for example, an internal combustion engine or a fuel cell stack. Furthermore, the invention relates to a control unit for executing steps of the method.

[0002] The preferred field of application of the invention is mobile applications, in particular vehicles with an internal combustion engine that can be operated with hydrogen, or fuel cell vehicles. State of the art

[0003] In hydrogen-powered combustion engines, hydrogen is burned as a fuel with air in a combustion chamber. It can happen that the hydrogen in the engine's combustion chambers is not burned completely or not at all, so that the exhaust gases emitted from the combustion chambers contain hydrogen. This unburned hydrogen, combined with oxygen, can form a highly flammable gas mixture and lead to an explosion. The danger is particularly high if a safety limit of 4% is exceeded, i.e., the volume fraction of hydrogen relative to the total volume of the gas mixture exceeds 4%.

[0004] The severity of the impacts that can result from exceeding the safety limit leads to increased safety requirements. In particular, attention must be paid to safety integrity in accordance with ISO 26262:2018.

[0005] To detect critical hydrogen concentrations in the exhaust gas of a hydrogen-powered engine, hydrogen sensors located in the exhaust system are typically used. However, the hydrogen sensors currently available on the market are generally single-channel and therefore not immune to single-channel faults (e.g., stuck, drift, or shortcut to X). As a result, they also lack sufficient safety integrity.

[0006] The present invention addresses the task of ensuring the safety integrity required by ISO 26262:2018 when using a hydrogen sensor to monitor the hydrogen concentration in the exhaust gas of a hydrogen-powered unit. The use of an additional hydrogen sensor should be avoided.

[0007] To achieve this objective, the method with the features of claim 1 is proposed. Advantageous further developments of the invention are set forth in the subclaims. Furthermore, a control device for executing steps of the method according to the invention is specified. Disclosure of the invention

[0008] The proposed method for monitoring the hydrogen concentration in the exhaust gas of a hydrogen-powered unit, such as an internal combustion engine or a fuel cell stack, comprises the following steps: - Measuring the hydrogen concentration in the exhaust gas using a hydrogen sensor and - Plausibility check of the measured value of the hydrogen sensor, whereby the hydrogen concentration is calculated from an increase in the oxygen content in the exhaust gas using a software-based model and the calculated hydrogen concentration is compared with the measured hydrogen concentration.

[0009] In the proposed method, the hydrogen concentration is both measured and calculated. A software-based model is used for the calculation. This model, for example, has a secure memory area and is sufficiently independent of the actual measurement task to ensure the required safety integrity according to ISO 26262:2018 or a comparable functional safety standard. The method thus eliminates the need for a redundant hydrogen sensor. This means that the software-based approach eliminates the need for a second hydrogen sensor and thus saves costs.

[0010] The proposed method assumes the oxygen content in the exhaust gas is known. This is because, especially in an internal combustion engine, an exhaust gas sensor is usually present, which detects the oxygen content due to other requirements, such as torque control and / or exhaust aftertreatment. If no exhaust gas sensor is present and the oxygen content in the exhaust gas cannot be assumed to be known, the oxygen content is preferably detected using a lambda sensor based on the actual lambda value. A lambda sensor, for example, a broadband lambda sensor, is significantly less expensive than a second hydrogen sensor.

[0011] Lambda (λ) refers to the ratio of air to fuel, in this case, air to hydrogen, compared to the stoichiometric ratio. At the stoichiometric ratio (λ = 1), the exact amount of air required to completely burn or consume the fuel or hydrogen is present. In this case, the actual lambda value corresponds to a specified target lambda value, which is required to regulate the mixture ratio.

[0012] If the supplied hydrogen is not completely burned or consumed, the oxygen concentration in the exhaust gas increases, and the actual lambda value exceeds the specified target lambda value. The greater the deviation between the actual lambda value and the target lambda value, the more unburned or unconsumed hydrogen has entered the exhaust system. This relationship, which can be mathematically represented by the following formula, allows the hydrogen concentration to be calculated: H2unburned=f(mair;mfuel;Lambdaexhaust;Pexhaust;Texhaust;...)

[0013] In a further development of the invention, it is therefore proposed that the increase in the oxygen content in the exhaust gas, from which the hydrogen concentration is calculated, be determined by comparing an actual lambda value with a target lambda value. Preferably, the actual lambda value is measured using a lambda sensor, for example, a broadband lambda sensor. The measured actual lambda value is provided to the software-based model for comparison with the target lambda value.

[0014] When calculating the hydrogen concentration from the increase in the oxygen content in the exhaust gas using the software-based model, at least one state variable of the exhaust gas, in particular the pressure and / or the temperature, is preferably taken into account. This can further improve the accuracy of the calculation.

[0015] In the software-based model, the value measured using the hydrogen sensor is then checked against the calculated value. This check identifies errors that can be traced back to a problem with the safety-critical hydrogen sensor. In this case, the problem can be alerted to in a timely manner to protect the engine and the surrounding area from serious consequences, such as a hydrogen explosion in the exhaust system.

[0016] As a further development measure, it is proposed that in the event of an error or in the event of a deviation between the calculated hydrogen concentration and the measured hydrogen concentration detected by the software-based model, an error reaction is triggered, preferably - shut down the hydrogen supply to the unit and / or - the hydrogen contained in the exhaust gas is more diluted by an increased air supply.

[0017] The error response can prevent further damage, such as a hydrogen explosion. Depending on the magnitude of the detected deviation, the error response can also be implemented in stages. For example, in a first stage, a control function can be requested to stop the injection / injection of hydrogen. In a second stage, if there is no immediate response from the control function, the injection / injection can be stopped by directly shutting down the output stages. This path is advantageously tested cyclically for its functionality.

[0018] Furthermore, it is proposed that a safety limit be set for a maximum hydrogen concentration in the exhaust gas, and that an error reaction be triggered if the safety limit is exceeded. The safety limit is preferably 4 vol.% hydrogen based on the total volume of the exhaust gas, since a hydrogen concentration in the exhaust gas above this value results in a highly flammable mixture, thus increasing the risk of explosion.

[0019] The fault response triggered when the safety limit is exceeded can, as previously described, involve reducing the hydrogen supply and / or increasing the air supply. Both measures—individually or in combination—contribute to reducing the hydrogen concentration in the exhaust gas, thus safely preventing a hydrogen explosion.

[0020] The error response in the event of a fault and / or when a specified safety limit is exceeded can be triggered, in particular, by a control unit, such as an engine control unit, which is usually present. If the control unit is designed for this purpose, it can also assume control functions within the framework of the proposed method.

[0021] In a further development of the invention, a control unit is therefore proposed that is configured to execute steps of a method according to the invention. The control unit preferably has a data memory in which the software-based model for verifying the hydrogen concentration in the exhaust gas measured by the hydrogen sensor is stored.

[0022] Furthermore, the data storage is preferably divided into storage areas, with a first storage area containing QM (quality management) software and a second storage area containing ASIL (automotive safety integrity level) software that includes the software-based model. This means that the software-based model is located in a protected area and is thus sufficiently independent of the actual measurement task.

[0023] According to a preferred embodiment, general security integrity, i.e., sufficient independence from security-relevant measures or control functions, is ensured by a three-level security concept. This can be structured as follows: - Level 1: QM software (functional level) - Level 2: ASIL software (monitoring of level 1 or safety level) - Level 3: Hardware safety (ensuring the integrity of level 2).

[0024] The invention and its advantages are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a hydrogen-powered unit in the form of an internal combustion engine, Fig. 2 a schematic representation of the processes of a method according to the invention for monitoring the hydrogen concentration in the exhaust gas of a hydrogen-powered unit and Fig. 3 a schematic representation of the processes of a further method according to the invention for monitoring the hydrogen concentration in the exhaust gas of a hydrogen-powered unit. Detailed description of the drawings

[0025] The Fig. Figure 1 shows, by way of example, a hydrogen-powered unit 1 in the form of an internal combustion engine. The hydrogen is injected or blown into a combustion chamber 5 of the internal combustion engine using an injector 4. The injector 4 is controlled by a control unit 10. Since the combustion of hydrogen requires the presence of air, air is introduced into the combustion chamber 5 via an intake manifold 6. The air flow is monitored by an air mass sensor 7 and a pressure and / or temperature sensor 8.

[0026] Combustion in the combustion chamber 5 produces exhaust gas, which is discharged via an exhaust system 9. Since the exhaust gas may contain unburned hydrogen, the hydrogen concentration in the exhaust gas is monitored using a hydrogen sensor 2. Furthermore, a lambda sensor 3 is provided, which detects the oxygen content in the exhaust gas.

[0027] Since an increased hydrogen concentration in the exhaust gas can lead to a hydrogen explosion in the exhaust system 9, increased safety requirements must be met when monitoring the hydrogen concentration in the exhaust gas. These typically require a redundant design of the hydrogen sensor 2. Using the method according to the invention, which pursues a software-based approach, a second hydrogen sensor 2 can be dispensed with.

[0028] The software-based approach of the method according to the invention requires an electronic control unit to execute control functions. As exemplified in the Fig. As shown in Figure 2, the control unit 10 can be used as an electronic control unit. For this purpose, the control unit 10 is connected to the hydrogen sensor 2 and the lambda probe 3. Furthermore, the control unit 10 has a data memory 11, which is divided into various memory areas 11.1, 11.2, and 11.3.

[0029] In a first step S1, the measured values ​​of the hydrogen sensor 2 are read in via operating software stored in a first memory area 11.1 of the data memory 11. In parallel, in a further step S2, the measured values ​​of the lambda sensor 3 are read in. The measured values ​​of the hydrogen sensor 2 are evaluated using QM software stored in a second memory area 11.2 of the data memory 11 and, in a further step S4, are checked for plausibility using a software-based model. The software-based model is stored in a third memory area 11.3 of the data memory 11 and is thus protected from the actual measurement task. In addition, the measured values ​​of the lambda sensor 3 are used for plausibility checks; from these values, the software-based model determines an increase in the oxygen content in the exhaust gas and uses this to calculate the hydrogen concentration in the exhaust gas.If a discrepancy between the measured hydrogen concentration and the calculated hydrogen concentration is detected during the plausibility check, this is attributed to a fault in the hydrogen sensor 2, and an error response is triggered in step S5. This may include a step S6, which influences the control of the hydrogen injection / injection in such a way that the supply of hydrogen is stopped. In a step S7, a corresponding control command can be transmitted to an actuator connected to the injector 4.

[0030] In addition to the measured values ​​of the hydrogen sensor 2 and the lambda sensor 3, further measured values ​​can be taken into account when monitoring the hydrogen concentration according to the method according to the invention. This is shown, for example, in the Fig. 3 shown.

[0031] In the Fig. 3, the control unit 10 receives further information about at least one state variable of the exhaust gas via a pressure and / or temperature sensor 12 located on the exhaust system 9. Taking this information into account when calculating the hydrogen concentration in the exhaust gas increases the accuracy of the calculation.

[0032] Furthermore, the Fig.3, the control unit 10 shown in FIG. 3 receives the measured values ​​of the air mass sensor 7 and the pressure and / or temperature sensor 8 arranged on the intake manifold 6. From these measured values, the air mass in the intake manifold 6 is recorded in a step S10. From this, in combination with a hydrogen injection quantity calculated in step S11, a target lambda value is determined in a step S12. This is required to calculate the hydrogen concentration in the exhaust gas in a further step S14. Step S14 is preceded by the determination of the actual lambda value in a step S13, which is determined from the measured values ​​of the lambda probe 3. By comparing the actual lambda value with the target lambda value, an increase in the oxygen content in the exhaust gas can be determined. From the increase in the oxygen content, the hydrogen concentration can then be calculated in step S14, whereby in this case the measured values ​​of the pressure and / or temperature sensor 12 are also taken into account.In step S15, the calculated hydrogen concentration is then compared with the measured hydrogen concentration to verify its plausibility. After the plausibility check, a check can be made in step S16 to determine whether the verified hydrogen concentration exceeds a predefined safety limit. If this is the case, an error response can be triggered in step S17, which may include stopping the injection of hydrogen and / or shutting down the output stages. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] ISO 26262:2018

[0009]

Claims

[1] Method for monitoring the hydrogen concentration in the exhaust gas of a hydrogen-powered unit (1), for example an internal combustion engine or a fuel cell stack, comprising the steps: - Measuring the hydrogen concentration in the exhaust gas using a hydrogen sensor (2) and - Plausibility check of the measured value of the hydrogen sensor (2), whereby the hydrogen concentration is calculated from an increase in the oxygen content in the exhaust gas using a software-based model and the calculated hydrogen concentration is compared with the measured hydrogen concentration. [2] Method according to claim 1, characterized by that the increase in the oxygen content in the exhaust gas is determined by comparing an actual lambda value with a target lambda value, wherein the actual lambda value is preferably measured with the aid of a lambda probe (3), for example a broadband lambda probe. [3] Method according to claim 1 or 2, characterized by that when calculating the hydrogen concentration from the increase in the oxygen content in the exhaust gas using the software-based model, at least one state variable of the exhaust gas, in particular the pressure and / or the temperature, is taken into account. [4] Method according to one of the preceding claims, characterized by that in the event of a deviation between the calculated hydrogen concentration and the measured hydrogen concentration detected by the software-based model, an error reaction is triggered, preferably - shut down the hydrogen supply to the unit and / or - the hydrogen contained in the exhaust gas is more diluted by an increased air supply. [5] Method according to one of the preceding claims, characterized bythat a safety limit value is set for a maximum hydrogen concentration in the exhaust gas, which is preferably 4 vol.% hydrogen based on the total volume of the exhaust gas, and that an error reaction is triggered if the safety limit value is exceeded. [6] Control unit (10) which is configured to carry out steps of a method according to one of the preceding claims, wherein preferably the control unit (10) has a data memory (11) in which the software-based model is stored. [7] Control device (10) according to claim 6, characterized by that the data memory (11) is divided into memory areas (11., 11.2, 11.3), wherein a QM software is stored in one memory area (11.1) and an ASIL software including the software-based model is stored in a further memory area (11.2).

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