Method for Optimizing the Cryogenic Pressure Tank Fill Level Which Can Be Achieved During a Refill in a Motor Vehicle

Abstract

A method optimizes the cryogenic pressure tank fill level which can be achieved during a refill in a motor vehicle. A heating device for heating a gas in the pressure tank has at least two modes, namely a regular operating mode, in which the heating device heats the gas in the pressure tank such that a specified pressure of the gas in the pressure tank is reached, and a continuous operation mode in which the heating device constantly heats the gas in the pressure tank such that the pressure of the gas in the pressure tank rises above the specified pressure. The method has the following steps: detecting the density of the gas in the pressure tank; comparing the detected density of the gas in the pressure tank with a specified density value; and if during the comparison it is determined that the detected density falls below the specified density value, either operating the heating device in the regular operating mode or switching the heating device from the regular operating mode to the continuous operation mode, in particular on the basis of a specified path to the destination of the motor vehicle and the service stations provided on the specified path to the destination for refilling the pressure tank with gas.

Claims

1. A method for optimizing a filling level, which is able to be reached during a refilling procedure, of a cryogenic pressure tank for a motor vehicle, wherein a heating device for heating a gas in the pressure tank has at least two modes: a regular operation mode, in which the heating device heats the gas in the pressure tank such that a predefined pressure of the gas in the pressure tank is reached, and a continuous operation mode, in which the heating device heats the gas in the pressure tank continuously such that the pressure of the gas in the pressure tank rises beyond the predefined pressure, wherein the method comprises the steps of: detecting a density of the gas in the pressure tank; comparing the detected density of the gas in the pressure tank with a predefined density value; and, if during the comparison it is determined that the detected density drops below the predefined density value, then, depending on at least one item of route information of the motor vehicle and/or on a target range of the motor vehicle, either (a) operating the heating device in the regular operation mode, or (b) switching the heating device from the regular operation mode into the continuous operation mode.

2. The method as claimed in claim 1, wherein the at least one item of route information of the motor vehicle is a determined route to a destination of the motor vehicle and refueling stations provided on the determined route to the destination for refilling the pressure tank with gas.

3. The method as claimed in claim 1, wherein the decision as to whether the heating device is operated in the regular operation mode, or whether the heating device is switched from the regular operation mode into the continuous operation mode, is additionally dependent on a selected refueling management mode which is selectable from multiple different refueling management modes, wherein the different refueling management modes weight differently multiple goals.

4. The method as claimed in claim 3, wherein the multiple goals weighted differently comprise: a short travel time of the motor vehicle to the destination, a low number of required refueling procedures for refilling the pressure tank until reaching the destination, and a maximum range of the motor vehicle with the gas in the pressure tank after a refilling procedure of the pressure tank is carried out.

5. The method as claimed in claim 3, wherein a refueling station for refilling the pressure tank is furthermore selected, depending on a current gas consumption, a detected density of the gas in the pressure tank, the at least one item of route information and/or the target range of the motor vehicle and/or the selected refueling management mode, from the refueling stations which are able to be reached with the available gas in the pressure tank, and a driver is informed about the selected refueling station.

6. The method as claimed in claim 3, further comprising the step of: displaying the route to the selected refueling station via a navigation system.

7. The method as claimed in claim 1, wherein a maximum possible refilling quantity of the pressure tank with gas and/or a maximum possible driving distance of the motor vehicle after the pressure tank has been completely refilled with gas is calculated in dependence on the temperature of the gas in the pressure tank and depending on the density of the gas in the pressure tank, and the decision as to whether the heating device is operated in the regular operation mode, or whether the heating device is switched from the regular operation mode into the continuous operation mode, is additionally dependent on the result of said calculation.

8. The method as claimed in claim 2, wherein if during the comparison it is determined that the detected density is below the predefined density value, the heating device is operated in the regular operation mode in case of a positive determination that, on the determined route to the destination, a refueling station is able to be reached with the available gas in the pressure tank without switching the heating device into the continuous operation mode.

9. The method as claimed in claim 5, wherein if it is detected that the selected refueling station is not being approached by the motor vehicle, a new decision is made as to whether the heating device is operated in the regular operation mode, or whether the heating device is switched from the regular operation mode into the continuous operation mode.

10. The method as claimed in claim 5, wherein if it is detected that the selected refueling station is not being approached by the motor vehicle, a refueling station for refilling the pressure tank is again selected, depending on the current gas consumption, the detected density of the gas in the pressure tank, the at least one item of route information and/or the target range of the motor vehicle and/or the refueling management mode, from the refueling stations which are able to be reached with the available gas in the pressure tank, and the driver is informed about the newly selected refueling station.

11. A filling level optimization device for optimizing a filling level, which is able to be reached during a refilling procedure, of a cryogenic pressure tank in a motor vehicle, comprising: a heating device for heating a gas in the pressure tank, the heating device having at least two modes: (1) a regular operation mode, in which the heating device heats the gas in the pressure tank such that a predefined pressure is reached, and (2) a continuous operation mode, in which the heating device heats the gas in the pressure tank continuously such that the pressure of the gas in the pressure tank rises beyond the predefined pressure, wherein the filling level optimization device is configured such that, if a detected density of the gas in the pressure tank is below a predefined density value, the filling level optimization device switches the heating device from the regular operation mode into the continuous operation mode depending on the at least one item of route information and/or on a target range of the motor vehicle.

12. A pressure tank with a filling level optimization device as claimed in claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 shows a pressure-time diagram.

[0028] FIG. 2 shows a temperature-time diagram.

[0029] FIG. 3 is a schematic view of a filling level optimization device with a pressure tank.

DETAILED DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 shows a pressure-time diagram in which the pressure (measured in bar) is represented on the y-axis and the time (measured in seconds) is represented on the x-axis. In the region on the right in FIG. 1, the pressure profile is shown in the continuous operation mode 20, in which the pressure rises above the predefined pressure value. From point in time t0 onward, two alternatives are illustrated in FIG. 1. The upper line in the region on the right in FIG. 1 shows the pressure profile 20 if at the point in time t0 the heating device 3 is switched (due to the predefined density being undershot and in dependence on route information) from the regular operation mode into the continuous operation mode and is subsequently operated in the continuous operation mode. The lower line shows the pressure profile 10 if at the point in time t0 the heating device 3 is left in the regular operation mode or is operated in the regular operation mode. The point in time t0 is determined by the filling level optimization device 1 depending on the route information (and on the density of gas in the pressure tank). The regular operation mode is the normal, conventional operating mode if sufficient gas is available in the pressure tank 2 while gas is extracted from the pressure tank 2. In the region on the left in FIG. 1, the pressure drops continuously. In this region, no heating of the gas or the pressure tank 2 by the heating device 3 takes place. The regular operation mode of the heating device 3 is activated (region with sawtooth-like profile) only if the pressure of the gas in the pressure tank 2 drops below a predefined minimum pressure. Immediately before the point in time t0, the heating device 3 is operated in the regular operation mode.

[0031] If the heating device 3 is in the regular operation mode, the gas in the pressure tank 2 is heated by the heating device 3 at intervals in order to reach or re-establish a predefined pressure of the gas in the pressure tank 2. In the regular operation mode, the heating device 3 heats at intervals, that is to say switches on and off again. Between the heating cycles (and also during the heating cycles), gas is extracted from the pressure tank 2 and is fed to a fuel cell of the motor vehicle in order to drive the vehicle. The extraction of the gas from the pressure tank 2 results in the pressure and the temperature of the gas in the pressure tank 2 dropping. The heating device 3 must therefore repeatedly heat (slightly, that is to say by a few kelvin, for example approximately 1 K to approximately 10 K) the gas in the pressure tank 2 in order for the predefined pressure in the pressure tank 2 to again be reached or to be kept constant. The predefined pressure of the gas in the pressure tank 2 allows the gas to be extracted from the pressure tank 2 in a technically simple manner.

[0032] The cyclical heating of the gas in the pressure tank 2, when the heating device 3 is in the regular operation mode, results in the sawtooth-like form of the pressure profile 10 in the regular operation mode. The heating device 3 is or includes, in particular, a heat exchanger. It is also contemplated, however, that the heating device 3 has an electrical heater, a laser heat device and/or a wire heater. It is also possible that the heat is supplied to the pressure tank 2 or to the gas in the pressure tank 2 not at intervals but continuously. Furthermore, the heating device is also still able to (post-)heat the pressure tank 2 or the gas in the pressure tank 2 if the heating device 3 has been switched off.

[0033] In the region on the left in FIG. 2, the temperature drops continuously since gas is extracted from the pressure tank 2. In this region, no heating of the gas or the pressure tank 2 by the heating device 3 takes place. The regular operation mode of the heating device 3 is activated (region with sawtooth-like profile) only if the pressure of the gas in the pressure tank 2 drops below a predefined minimum pressure.

[0034] If the density of the gas in the pressure tank 2 drops below a predefined value, the heating device 3 is, depending on the route information, switched from the regular operation mode into the continuous operation mode (and subsequently operated in the continuous operation mode until the next refilling procedure of the pressure tank 2 with gas is carried out or the motor vehicle is powered off).

[0035] FIG. 2 shows a temperature-time diagram in which the temperature (measured in kelvin) is represented on the y-axis and the time (measured in seconds) is represented on the x-axis. The temperature profile in the regular operation mode 30 of the heating device 3 (region with sawtooth-like profile of the temperature) rises on average since a heat exchange of the gas in the pressure tank 2, or of the pressure tank 2, with the surroundings, which is not entirely avoidable, takes place. It is also possible for the sawtooth form of the temperature to have a more even profile. Moreover, in the case of continuous heat supply, no sawtooth-like profile can occur.

[0036] From point in time t0 onward, two alternatives are illustrated in FIG. 2. The upper line shows the temperature profile 40 if at the point in time t0 the heating device 3 is switched (due to the predefined density being undershot and in dependence on route information) from the regular operation mode into the continuous operation mode, and the lower line shows the temperature profile 30 if at the point in time t0 the heating device 3 is left in the regular operation mode or is further operated in the regular operation mode. In the region on the right in FIG. 2, the temperature profile is shown in the continuous operation mode 40, in which the temperature rises continuously and considerably, by the upper line.

[0037] FIG. 1 and FIG. 2 show the same timing, that is to say they show in each case pressure and temperature at the same point in time. The point in time t0 in FIG. 1 thus corresponds to the point in time t0 in FIG. 2.

[0038] FIG. 3 shows a filling level optimization device 1 with a pressure tank 2. A heating device 3 is arranged for heating the gas in the pressure tank 2 or for heating the pressure tank 2. The heating device 3 is arranged on an outer side or on the pressure tank 2. Alternatively, it is possible for the heating device to be arranged (partially or completely) inside the pressure tank 2. The filling level optimization device 1 detects the pressure of the gas in the pressure tank 2 via a pressure sensor 6. The density of the gas in the pressure tank 2 is detected via a density sensor 7. The filling level optimization device 1 detects the temperature of the gas in the pressure tank 2 via a temperature sensor 5. Gas is extracted from the pressure tank 2 via an extraction line 8 and fed to the fuel cell. A throughflow measurement device 9 measures the quantity of gas which flows through the extraction line 8. This measurement variable too is detected by the filling level optimization device 1. It is also contemplated that the quantity of gas which flows through the extraction line 8 is calculated via the temperature profile and the pressure profile of the gas in the pressure tank 2. The filling level optimization device 1 is connected to a navigation system 4. The route information is received from the navigation system 4. The navigation system 4 can be a conventional navigation system. The navigation system 4 determines or calculates (after specification of a destination) the route to the destination. The filling level optimization device 1 can in particular be a control unit. The control unit can also perform further tasks. It is also contemplated that the navigation system 4 is integrated in the filling level optimization device 1.

[0039] The filling level optimization device 1 with the pressure tank 2 is arranged in a motor vehicle, for example a passenger motor vehicle, a truck or a motorcycle.

[0040] The temperature profile 40 in the continuous operation mode (upper line in the region on the right in FIG. 2) rises continuously since the heating device 3 heats the gas in the pressure tank 2 continuously. The heating lies in the region of several dozen kelvin. Consequently, the pressure rises above the predefined pressure value. After a certain time, the quantity of gas in the pressure 2 tank becomes low, with the result that the pressure in the pressure tank 2 drops again despite further heating by the heating device 3 in the continuous operation mode.

[0041] Without consideration of the route information, the heating device 3 would already be switched from the regular operation mode into the continuous operation mode before the point in time t0, since the detected density was below the predefined density value. Through the consideration of the route information, switching into the continuous operation mode occurs later, so that the gas in the pressure tank 2, or the pressure tank 2 itself, is colder when the next refilling procedure is carried out, with the result that quantity of gas or the gas density in the pressure tank is increased after the (maximum) refilling procedure is carried out.

[0042] If the predefined or predetermined density value is undershot, the current consumption of gas and the remaining quantity of gas in the pressure tank 2 is detected. Subsequently (if appropriate in consideration of the current consumption), the residual range of the motor vehicle, which residual range is possible with the available quantity of gas in the pressure tank 2, is determined without switching the heating device 3 from the regular operation mode into the continuous operation mode. Also, (open) refueling stations, in particular gas refueling stations, which are available on the route to the destination or along the route to the destination, are determined. In this case, the selected refueling management mode, that is to say whether a lowest possible number of refueling stops on the route to the destination, a shortest possible travel time to the destination, or a largest possible range after refilling is carried out has the higher priority, is taken into consideration. As long as the quantity of gas in the tank is sufficient to reach (on the route to the destination of the motor vehicle) a refueling station, in particular a gas refueling station without switching the heating device 3 from the regular operation mode into the continuous operation mode, the heating device 3 is (firstly) not switched into the continuous operation mode or operated in the continuous operation mode, but rather the heating device 3 is (further) operated in the regular operation mode. Then one of the reachable refueling stations, in particular gas refueling stations, is selected on this basis, and the driver is informed about the decision or recommendation. In addition, the route to the selected gas refueling station can be displayed to the driver on the navigation system 4.

[0043] If the driver does not approach the selected gas refueling station or communicates via an input unit that the approach to the selected gas refueling station is not desired, a new (other) gas refueling station is selected according to the available data concerning the gas in the pressure tank 2, and the route information, and according to the selected refueling management mode, and the driver is informed about the newly selected or recommended gas refueling station. Moreover, it is determined whether the heating device 3 has to be switched from the regular operation mode into the continuous operation mode in order to reach a (another) gas refueling station.

[0044] If it is determined that no gas refueling station is able to be reached (any more) on the route to the destination with the available gas in the pressure tank 2 without the heating device 3 being switched into the continuous operation mode, the heating device 3 is switched into the continuous operation mode and operated in the continuous operation mode in order to avoid a breakdown of the motor vehicle due to lack of fuel.

[0045] The density value of the gas in the pressure tank 2 can be detected in various ways: By measuring the weight of the gas in the pressure tank 2 in consideration of the volume of the pressure tank 2, it is possible for the density of the gas in the pressure tank 2 to be determined. Alternatively, the density of the gas in the pressure tank 2 can be determined via a throughflow measurement device 9, which measures the quantity of gas which flows out of the pressure tank 2 or is extracted from the pressure tank 2 and is passed to the fuel cell, at a known initial density of the gas in the pressure tank 2 and at a known volume of the pressure tank 2. Other methods for detecting the density of the gas inside the pressure tank 2, for example by way of a gas density measurement device or a density sensor 7, are possible.

LIST OF REFERENCE SIGNS

[0046] 1 Filling level optimization device [0047] 2 Pressure tank [0048] 3 Heating device [0049] 4 Navigation system [0050] 5 Temperature sensor [0051] 6 Pressure sensor [0052] 7 Density sensor [0053] 8 Extraction line [0054] 9 Throughflow measurement device [0055] 10 Pressure profile in the regular operation mode [0056] 20 Pressure profile in the continuous operation mode [0057] 30 Temperature profile in the regular operation mode [0058] 40 Temperature profile in the continuous operation mode

[0059] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.