A method for operating a drive unit powered by gaseous fuel.

Abstract

A method for operating a drive unit (11) operated with gaseous fuel, comprising providing gaseous fuel under high pressure to a plurality of pressure tanks (3; 3a; 3b; 3c), which are connectable via a supply line (7) to a metering valve (12) through which the gaseous fuel can be released to the drive unit (11). One of the pressure tanks is configured as a high-load pressure tank (3), which is connected to the supply line (7) only when the drive unit (11) is under high load, while simultaneously disconnecting from the supply line (7) the pressure tanks (3a; 3b; 3c) which have a lower gas pressure than the high-load pressure tank (3).

Description

Technical Field

[0003]

[0001] The present invention relates to a method for operating a drive unit operated by a gaseous fuel, for example an internal combustion engine or a fuel cell operated by a gaseous fuel, which is used for the purpose of being used in a vehicle, for example.

[0002] Background Art Drive units operated by gaseous fuels are known based on the prior art. As an example, it may be known in the form of an internal combustion engine operated by a gaseous fuel, particularly hydrogen or natural gas, instead of a liquid fuel. Further, another drive unit operated by a gaseous fuel, for example, a fuel cell that generates an electric current from a gaseous fuel and can drive an electric motor with this electric current, is known. An internal combustion engine operated by a gaseous fuel and a fuel cell equipped with an electric motor unit may be used to drive a passenger car or a truck, or may be used for a stationary drive unit, for example, a generator. Since gaseous fuels have only a small energy density per volume at normal pressure, gaseous fuels are strongly cooled and thus liquefied or compressed to a pressure of several hundred bar and stored in a corresponding pressure vessel. Usually, a plurality of pressure tanks are used in vehicles. This has various advantages. On the one hand, in the case of a large gas tank, a significantly large wall thickness and further stabilizing elements are required, but relatively small pressure tanks, for example, cylindrical gas cylinders, can be manufactured with a relatively small wall thickness. On the other hand, small pressure tanks can be more easily arranged in a vehicle, whereby a given construction space can be utilized better. Such an arrangement form is known based on, for example, German Patent Application Publication No. 102017212485.

[0003] A certain amount of gas pressure is required to supply fuel to drive units that operate on gaseous fuel. When the load on the drive unit is particularly high, a very large amount of gaseous fuel must be supplied in a short time. This is only possible at a certain minimum pressure. If the gas tank is already partially empty as a result of longer operation, the gas pressure that continues to be supplied will no longer be sufficient to supply enough fuel to the internal combustion engine or other drive units that operate on gaseous fuel, even under extremely high loads, and as a result, it will no longer be possible to demand the maximum load.

[0004] Disclosure of the invention Advantages of the invention The method according to the present invention for operating a drive unit powered by a gaseous fuel has the advantage that even after a longer period of operation of the drive unit, it is possible to request a full load that requires a large amount of gaseous fuel in a short time. In the method according to the present invention, the gaseous fuel is supplied to a plurality of pressure tanks under high pressure, and these pressure tanks are connectable to a metering valve via a supply line, through which the gaseous fuel can be released to the drive unit. In this case, one of the pressure tanks is formed as a high-load pressure tank, and this high-load pressure tank is connected to the supply line only when the drive unit is under high load, at which point a pressure tank with a lower gas pressure inside is disconnected from the supply line.

[0005] The pressure tanks are initially filled with hydrogen at a pressure of, for example, 700 bar (70 MPa). As the drive unit operates, the gaseous fuel is gradually consumed, and the pressure in the pressure tanks decreases accordingly. When all the pressure tanks are emptied uniformly, the pressure in all the pressure tanks decreases and then falls below a critical value. When the drive unit is operated at full load, which increases the rotational speed of the internal combustion engine, a very large amount of gaseous fuel is required in a short time, and this fuel must be supplied to the corresponding combustion chamber of the internal combustion engine. When the pressure tanks can no longer provide the pressure required for this, it becomes impossible to demand the maximum output from the drive unit.

[0006] Therefore, according to the present invention, it is proposed that one or more pressure tanks be configured to function as high-load pressure tanks and connected to the supply line only when it is desired to operate the drive unit under full load or high load. The remaining pressure tanks, which are producing lower pressure, are disconnected from the supply line when under full load. Then, when a lower output from the drive unit is again required, the multiple high-load pressure tanks (or one high-load pressure tank) are disconnected from the supply line again, and the remaining pressure tanks are connected to the supply line. This is because a lower gas pressure is sufficient at this operating point. In this way, even pressure tanks that have already been partially emptied are always provided with a sufficiently high gas pressure to enable the maximum output of the drive unit to be requested, without the need for any other structural means, such as an interposed compressor.

[0007] In one improved version of the method according to the present invention, a high-load pressure tank is connected to the supply pipeline only when the gas pressure in the remaining pressure tank is no longer sufficient to supply fuel to the drive unit under high load conditions. This ensures that the high-load pressure tank maintains its sufficient gas pressure for as long as possible and is used to achieve the highest load conditions of the drive unit.

[0008] In one improved version of the method according to the present invention, each pressure tank can be connected to a supply line via a connecting pipe, and a shut-off valve is provided in each connecting pipe. Preferably, each pressure tank can be individually connected to or disconnected from the supply line by an electrically controllable shut-off valve. This is desirable from a safety standpoint, as it allows for the disconnection of the corresponding connection in the event of failure of any one pressure tank. The freely controllable nature of the shut-off valves allows one or more pressure tanks to function as high-load pressure tanks. That is, these pressure tanks are used only when the drive unit is at maximum or full load, while the remaining pressure tanks are provided for normal operation.

[0009] In one improved embodiment of the method according to the present invention, there are multiple high-load pressure tanks, and at least one of these high-load pressure tanks is connected to the supply pipeline under high load conditions of the drive unit. For example, if two pressure tanks are provided as high-load pressure tanks, then under full load conditions of the drive unit, only one high-load pressure tank can initially be connected to the supply pipeline. After the gas storage capacity in this high-load pressure tank is depleted, the second high-load pressure tank takes over this role. This allows the high pressure level supplied to the drive unit to be maintained within the high-load pressure tanks for a longer period of time. Alternatively, it may be specified that all high-load pressure tanks are always connected together to the supply pipeline.

[0010] If multiple high-load pressure tanks are provided, and only one high-load pressure tank is connected to the supply pipeline at any given time, then when the drive unit is fully loaded, that single high-load pressure tank is emptied until its gas pressure equals that of the remaining pressure tanks used during the normal operating load of the drive unit.

[0011] In an advantageous improved form of the method, the drive unit operated by gaseous fuel is either an internal combustion engine or a fuel cell that supplies current to an electric motor. In both cases, gaseous fuel under a specified pressure is required to maintain function, thereby ensuring continuous operation and optimal use of existing gaseous fuel in a pressure tank by the method according to the present invention.

[0012] In an improved version of the method according to the present invention, a pressure reducer is placed in the supply pipeline between the pressure tank and the metering valve. This pressure reducer generates the optimal gas pressure for operating the metering valve, depending on the operating point of the drive unit. If the pressure in the pressure tank decreases excessively, the pressure reducer may be stopped, thereby ensuring that sufficient pressure from the pressure tank is used in the metering valve.

[0013] In an improved version of the method according to the present invention, for example, multiple metering valves are provided and connected to a supply pipeline to supply gaseous fuel to multiple cylinders of an internal combustion engine or to multiple fuel cells. [Brief explanation of the drawing]

[0014] The drawings show various embodiments of a device that can be operated by the method according to the present invention. [Figure 1] This diagram schematically shows a drive unit operated by gaseous fuel, along with a pressure tank assembly for supplying fuel to the drive unit. [Figure 2] This figure shows another embodiment of a pressure tank assembly with alternative circuits for individual pressure tanks. [Figure 3] This is a flowchart illustrating the method according to the present invention.

[0015] Description of the Examples To illustrate the method according to the present invention, Figure 1 schematically shows a drive unit operated by gaseous fuel. In this embodiment, the drive unit 11 is formed as an internal combustion engine and comprises four combustion chambers 14. Each of these combustion chambers 14 has an opening for a metering valve 12. Through these metering valves 12, gaseous fuel can be metered and supplied to each combustion chamber 14, where it burns and, as is known, moves each piston. A pressure tank assembly 1 is provided to supply gaseous fuel to the drive unit 11. This pressure tank assembly 1 comprises a plurality of pressure tanks 3, 3a, 3b, and 3c. Of these pressure tanks 3, 3a, 3b, and 3c, pressure tank 3 is used as a high-load pressure tank 3. This high-load pressure tank 3 is otherwise structurally no different from the remaining pressure tanks 3a, 3b, and 3c. These pressure tanks 3, 3a, 3b, and 3c are formed in the form of substantially cylindrical high-pressure gas containers. The gas pressure inside pressure tanks 3, 3a, 3b, and 3c is measured by one pressure sensor 15, 15a, 15b, and 15c, respectively. These pressure sensors 15, 15a, 15b, and 15c transmit their measured values ​​to a control device 9, which is schematically shown in Figure 1.

[0016] To supply gaseous fuel to the drive unit 11, all pressure tanks 3, 3a, 3b, and 3c are connected to a supply line 7 via connecting lines 4, 4a, 4b, and 4c. This supply line 7 branches out toward individual metering valves 12. Within each of the connecting lines 4, 4a, 4b, and 4c, there is one shut-off valve 5, 5a, 5b, and 5c. These shut-off valves 5, 5a, 5b, and 5c are electrically controllable and connected to a control device 9 via an electrical connection line 8. This allows each shut-off valve 5, 5a, 5b, and 5c to be opened and closed independently of each other. A pressure reducer 10 is located within the supply line 7. This pressure reducer 10 can adjust the required gas pressure of the gaseous fuel supplied from the pressure tanks to the metering valve when the gaseous fuel has an excessively high gas pressure.

[0017] A method according to the present invention for operating a drive unit and supplying gaseous fuel to the drive unit will be described in detail with reference to the flowchart in Figure 3. In the first step 100, the drive unit is operated, that is, an internal combustion engine is started, for example. In the second step 200, the shut-off valves of at least one of the pressure tanks 3a, 3b, 3c, generally one of the shut-off valves 5a, 5b, 5c under normal load conditions of the internal combustion engine, are opened, while the shut-off valve 5 of the high-load pressure tank 3 remains closed.

[0018] In the next step 300, it is checked whether the pressure thresholds in the pressure tanks 3a, 3b, and 3c are below a preset threshold that no longer guarantees fuel supply to the drive unit 11 under the highest load. This is done based on the pressure measured by the individual pressure sensors 15a, 15b, and 15c and transmitted to the control device 9. If the pressure in the pressure tanks 3a, 3b, and 3c is sufficient (branch "N"), the shut-off valve 5 remains closed (step 600) and the shut-off valves 5a, 5b, and 5c remain open, thereby continuing to supply gaseous fuel from the pressure tanks 3a, 3b, and 3c to the drive unit, in this embodiment, the internal combustion engine. However, if the pressure in the pressure tanks 3a, 3b, and 3c falls below the threshold (branch "J"), in the subsequent step 400, it is checked whether the drive unit 11 is under high load. If the answer is no (branch "N"), shut-off valves 5a, 5b, and 5c remain open, while shut-off valve 5 remains closed. If the answer is yes (branch "J"), in step 500, shut-off valves 5a, 5b, and 5c are closed, and shut-off valve 5 is opened, allowing gaseous fuel to flow from the high-load pressure tank 3 into the supply pipeline 7 under high pressure, and from there to the metering valve 12. The pressure reducer 10 is only used when the gas pressure is excessively high. The next step is a check of the pressure thresholds in the pressure tanks 3a, 3b, and 3c in step 300, and the subsequent steps are repeated until the control device recognizes that the drive unit 11 is no longer under full load or the highest load. Once this is confirmed, in step 600, shut-off valve 5 of the high-load pressure tank is closed, and shut-off valves 5a, 5b, and 5c of the pressure tanks 3a, 3b, and 3c are opened again.

[0019] Figure 2 shows alternative circuits for pressure tanks 3a, 3b, and 3c. Instead of directly connecting each connecting conduit 4a, 4b, and 4c, each equipped with shut-off valves 5a, 5b, and 5c, to the supply conduit, in this embodiment, the connecting conduits 4a, 4b, and 4c open to a single subsequent connecting conduit 4'. A normal shut-off valve 6 is located within this connecting conduit 4'. In this case, the connection of pressure tanks 3a, 3b, and 3c to the supply conduit 7 may be interrupted by the normal shut-off valve 6, whereas the shut-off valves 5a, 5b, and 5c remain open even under full load.

[0020] The pressure tank assembly 1 described herein includes four pressure tanks 3, 3a, 3b, and 3c. Of these pressure tanks, one is configured as a high-load pressure tank 3. This high-load pressure tank 3 does not need to be structurally different from the remaining pressure tanks 3a, 3b, and 3c, but is distinguished only by its use, thereby forming a high-load pressure tank that takes on the responsibility of supplying fuel to the drive unit at full load. Alternatively, a larger number of pressure tanks may be used, and more pressure tanks than one of these tanks may be designated as high-load pressure tanks. For example, if two pressure tanks are provided as high-load pressure tanks, one of the high-load pressure tanks can first take on the role of providing the required gaseous fuel pressure until the pressure level in that high-load pressure tank is no longer sufficient when the drive unit is at full load. Subsequently, a second high-load pressure tank is used, which ensures fuel supply to the drive unit 11 even under full load conditions, and even when the drive unit is an internal combustion engine and its rotational speed is extremely high.

Claims

1. A method for operating a drive unit (11) which is operated by a gaseous fuel, The gaseous fuel is supplied to a plurality of pressure tanks (3; 3a; 3b; 3c) under high pressure, and the pressure tanks (3; 3a; 3b; 3c) can be connected to a metering valve (12) via a supply pipeline (7), and the gaseous fuel can be released to the drive unit (11) via the metering valve (12). Each of the pressure tanks (3; 3a; 3b; 3c) can be connected to the supply pipeline (7) via connecting pipelines (4; 4a; 4b; 4c), and shut-off valves (5; 5a; 5b; 5c) are located within each of the connecting pipelines (4; 4a; 4b; 4c). The shut-off valves (5; 5a; 5b; 5c) are electrically controllable by the control device (9). In the method, The pressure tank (3; 3a; 3b; 3c) includes a plurality of high-load pressure tanks (3), When the drive unit (11) is under high load, the control device (9) controls the shut-off valves (5; 5a; 5b; 5c) to connect only one of the multiple high-load pressure tanks (3) to the supply line (7) until that tank (3) has a gas pressure equal to that of the remaining pressure tanks (3a; 3b; 3c) which have a lower gas pressure inside than the high-load pressure tank (3), and simultaneously disconnect the remaining pressure tanks (3a; 3b; 3c) from the supply line (7), and then connect the next high-load pressure tank (3) to the supply line (7) when the drive unit (11) is under high load. A method characterized by the following features.

2. The method according to claim 1, characterized in that the control device (9) controls the shut-off valves (5; 5a; 5b; 5c) to connect the high-load pressure tank (3) to the supply pipeline (7) only when the gas pressure in the remaining pressure tanks (3a; 3b; 3c) is no longer sufficient to supply fuel to the drive unit (11) under high load conditions.

3. The method according to claim 1 or 2, characterized in that the drive unit (11), which is operated by a gaseous fuel, is an internal combustion engine or a fuel cell that supplies power to an electric motor.

4. The method according to any one of claims 1 to 3, characterized in that a pressure reducer (10) is located in the supply pipeline (7) between the pressure tank (3; 3a; 3b; 3c) and the metering valve (12).

5. The method according to any one of claims 1 to 4, characterized in that a plurality of metering valves (12) are connected to the supply pipeline (7).

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