COMPRESSED GAS SUPPLY SYSTEM, MOTOR VEHICLE EQUIPPED THEREWITH AND OPERATING METHOD FOR IT
D e s c r i p t i o n
This invention claims the priority of the Chinese patent application 102023209926.8 filed on October 11 , 2023, of which the content (Text, Drawings and Claims) is incorporated by reference.
The present invention relates to a compressed gas supply system which is able to be used in particular for supplying with a gaseous energy carrier such as for instance hydrogen in a motor vehicle, and a method for leak monitoring in such a compressed gas supply system.
Leaks in such compressed gas supply systems are economically problematic not only owing to the loss of energy carriers connected with them; when the motor vehicle is parked in a closed space, escaping gas can lead, moreover, to a risk of explosion. Therefore, e.g. from DE 102020207253 A1, a gas supply system is known with a tank for highly compressed gas and with a shutoff member between the tank and a line network, in which on the tank side from the shutoff member a temperature sensor and a pressure sensor are provided, by means of the measurement values of which an outflow of gas from the tank is able to be determined.
More frequent than external leaks, via which gas flows off out from the tank directly into the environment, is an internal leak, i.e. a leaking of the shutoff member so that, even in its closed position, gas flows off from the tank to the line network. Such a leak is not dangerous or economically problematic as such, if a further shutoff member which closes properly is additionally present on the path of the gas to the consumer. Nevertheless, the internal leak of the tank-side shutoff member must be eliminated, so that in the case of an addition of a further leakage between the line network and the environment or in the consumer-side shutoff member, gas can not escape into the environment. It is equally necessary to be able to detect a leak between the line network and the environment or the consumer when the tank-side shutoff member closes properly. For this, a pressure sensor can be provided on the line network, by which the development of the pressure is monitored after switching off of the consumer and closing of the shutoff members over a predetermined period of time of typically a few minutes.
However, it is found that such a monitoring occasionally detects a leak without one actually being found later. If such a monitoring result in the usual way leads to an automatic cutout blocking the operation of the vehicle until a supposed fault has been rectified in a workshop, then this is extremely troublesome and also expensive for a user of the vehicle.
An object of the invention is therefore to improve the reliability of leak detection in a compressed gas supply system.
The problem is solved according to an aspect of the invention in that in a compressed gas supply system with at least one tank for highly compressed gas, with a tank-side shutoff member and with a first sensor group which comprises a first pressure sensor and a first temperature sensor, the pressure sensor and the temperature sensor are arranged on a line which extends from a side of the tankside shutoff member facing away from the tank to a consumer-side shutoff member.
As has become apparent, false leak detections occur principally after refuelling and after high performance driving. If during high performance driving a strong gas stream is constantly expanded, the adiabatic expansion leads to a cooling of the gas stream and to a temperature gradient between line and environment which balances out during the leak detection, so that a pressure increase is observed in the line which, however, is not due to leakage of the tank-side shutoff member. On refuelling, a temperature difference between line and environment can be due to the fact that mostly cooled gas is filled, so that on refuelling the line is cooled down. If shortly thereafter the vehicle is switched off and the line heats up in the course of the leakage check which is then carried out, this can also lead to a pressure increase being observed. A measurement of the temperature allows such cases to be detected and false alarms to be prevented.
For this, a measurement value of the temperature in the line can be compared with a measurement value of the ambient temperature, in order to prevent or postpone a leakage check as long as the temperature of the line deviates from the ambient temperature by more than a critical extent. Preferably, the temperature measurement is combined with a simultaneous measurement of the pressure, in order to estimate the amount of gas in the line; a leakage check can then also be carried out in the case of a non-negligible temperature difference between the line and the environment.
An evaluation unit which is connected to the sensors of the first sensor group in a communicative manner, in order to detect by means of measurement data of the sensors a) a leak between the tank and the line and/or b) a leak between the line and a consumer or the environment, should be a component part of the compressed gas supply system according to the invention.
In particular, the evaluation unit can be configured in order to detect, in the case of closed shutoff members a) a leak between the tank and the line, when measurement data of the first sensor group indicate an increase of the gas quantity in the line; b) a leak between the line and a consumer or the environment, when measured data of the first sensor group indicate a decrease of the gas quantity in the line.
The consumer-side shutoff member is preferably configured to close in a delayed manner after a closing of the tank-side shutoff member. By gas thus still being able to flow off from the line to the consumer, but none more follows on from the tank, a pressure difference can be generated at the tank-side shutoff member, with the aid of the chronological development thereof after the closing of both shutoff members a possible leakage of the tank-side shutoff member is able to be detected.
The closing of the consumer-side shutoff member can - like that of the tank-side shutoff member - be controlled by the evaluation unit. According to a preferred configuration, the consumer-side shutoff member is a pressure reducer which does not require any control by the evaluation unit for closing, but rather closes automatically when the pressure on its side facing the consumer has risen to an upper threshold value.
An intermediate shutoff member can be arranged on the line between the tank-side shutoff member and the consumer-side shutoff member, which intermediate shutoff member divides the line into a tank-side and a consumer-side portion. The first and a second sensor group can be distributed to the two line portions, in order to enable a leakage check on both sides of the intermediate shutoff member.
The problem is solved according to a further aspect of the invention by a motor vehicle with a compressed gas supply system as described above. The compressed gas system can serve in particular for supplying a fuel cell with hydrogen from the tank.
The problem is further solved by a method for the leakage monitoring of a compressed gas supply system as described above, with the steps: c) measuring of temperature and pressure on the line, in order to calculate a first gas quantity in the line, then d) allowing a waiting time to elapse, then e) measuring of temperature and pressure on the line, in order to calculate a second gas quantity in the line; f) detecting a leak between the tank and the line, when the second gas quantity is greater than the first, and/or detecting a leak between the line and a consumer or the environment when the second gas quantity is smaller than the first.
The above-mentioned steps can be preceded by the steps a) closing the tank-side shutoff member; b) allowing the pressure in the line to reduce, and closing the consumer-side shutoff member.
Provision can be made that in step f) a leak is detected only when the rate of change of the gas quantity exceeds a threshold value. A subject of the invention is, furthermore, a computer program which, when it is carried out by a computer, causes it to operate as an evaluation unit in a compressed gas supply system or in a motor vehicle as described above, or to carry out the method defined above.
Further features and advantages of the invention will emerge from the following description of example embodiments with reference to the enclosed figure. There are shown:
Fig. 1 a block diagram of a compressed gas supply system according to the invention; and
Fig. 2 a flow diagram of the method.
Figure 1 shows in diagrammatic form a compressed gas supply system of a motor vehicle. A fuel cell 1 is connected to the compressed gas supply system as consumer of the gas, which delivers electrical energy for a drive motor and, if applicable, further electrical consumers and for a chargeable battery.
The compressed gas supply system comprises several high pressure tanks 2 for hydrogen, and a line 3 which connects each of the high pressure tanks 2 with the fuel cell 1 as consumer. A tank-side shutoff valve 4 is arranged between each of the high pressure tanks 2 and the line 3. A further shutoff valve 7 divides the line 3 into an upstream portion 8 or distributor portion, at which the tank-side shutoff valves 4 and tank connection 6 lie, via which the tanks 2 are able to be filled, and a downstream portion. The latter is, in turn, divided by a pressure reducer 5 into a high pressure portion 9 and a low pressure portion 15, at the end of which the shutoff valve 16 is situated.
A pressure sensor and a temperature sensor are designated at the upstream portion 8 by 10, 11, at the downstream high pressure portion 9 by 12, 13, and at the low pressure portion 15 by 17, 18.
An evaluation unit 14 is connected to the pressure- and temperature sensors 10-13, 17, 18. The evaluation unit 14 can be implemented as an independent component or as part of the software of an on-board computer of the vehicle. In step S1 of the method illustrated in Fig. 2, the evaluation unit 14 detects that the vehicle has been switched off by the user after use. It then closes each tank-side shutoff valve 4 in step S2. As the distributor line 3 still contains hydrogen at this point in time with a sufficiently high pressure for the operation of the fuel cell 1 and the fuel cell 1 is also still at operating temperature, hydrogen is also still converted in the fuel cell 1 after the closing of the shutoff valve 4, so that hydrogen flows off out from the distributor line 3 to the fuel cell 1 , and the pressure decreases in the high pressure carrying line portions 8, 9.
While the reaction is still running in the fuel cell 1 , the evaluation unit 14 closes the shutoff valve 7 (S3). The closing can take place in a time-controlled manner, therefore respectively with a predetermined delay after the switching off of the vehicle, wherein the delay is selected so that a pressure difference between the tanks 2 and the high pressure carrying line portions 8,9 is several 10 bar, e.g. 50 bar. An establishing of the point in time of closing directly by means of the pressure detected by the pressure sensor 10 or 12 is of course also possible.
Somewhat later, when the pressure in the line portion 9 has decreased by a further several 10 bar, the evaluation unit also closes the shutoff valve 16 (step S3).
First measurement values of the pressures pi,8, Pi,9, Pus and temperatures T-i.s, TI ,9, T-1,15 in the line portions 8, 9 and in the low pressure line 15 are measured in step S4.
After a predetermined waiting time Dt of several minutes has elapsed (S5), new measurement values p2,8, p2,9, P2,i5, T2,8, T2,9, T2,is are determined (S6).
By means of known volumes of the line portions 8, 9 and 15, the measurement values are converted in hydrogen quantities r , 8, rm, 9, rm, 15 and m2,8, m2,9, m2,is in the line portions 8, 9 and 15 respectively before and after the waiting time (S7).
When m2,8>rm,8, then gas must be streamed into the line portion 8, and this gas can only come out from one of the tanks 2. In step S8, a check is carried out as to whether m2,8-rm,8>m+8 Dt, wherein m+s designates a maximally cumulative permitted leak rate of the shutoff valves 4. If yes, then a significant leak of one of the shutoff valves 4 is present, and the evaluation unit 14 causes an error message to be emitted in this respect (S9). Subsequently, the method can pass on to step S12 (see below).
If m2,8<mi,8, gas must have escaped from the line portion 8, either via a leak to the environment or via the shutoff valve 7.
In step S10 a check is therefore carried out as to whether mii8-m218>m'8 Dt, wherein m's designates a maximally permitted outflow rate from the line portion 8. In a simple configuration of the method, deviating from Fig. 2, in this case an error message can be emitted which indicates a leak downstream of the shutoff valve 4.
Whether the outflow is due to leakage of the line 8 or of the shutoff valve 7 can not yet be decided by means of the measurements at the line portion 8; therefore, it is initially only stored that an outflow is present (S11).
It is not expected of the pressure reducer 5 that the latter closes in a completely tight manner. For this reason, the tightness check downstream of the shutoff vale 7 must be based on the total gas quantity in the line portions 9 and 15.
In S12 a check is carried out as to whether on the other side of the shutoff valve 7 the total gas quantity has increased or decreased, i.e. whether 012,9-011 ,9+012,15- m i ,i5>m+9,i5 Dt or 012,9-011 , 9+012, i5-m i ,i5<m'9, 15 Dt, wherein ri 9,15 designates a maximally permitted inflow rate to the line portion 9 and the low pressure line 15 or respectively 01'9,15 designates an outflow rate herefrom. When a significant outflow is present, m2, 9-011 , 9+012, i5-m i ,i5<m'9, 15 Dt, an error message is emitted in S13, which indicates a leakage of the line portions 9, 15. If step S11 was run through previously, the error message can be supplemented by an indication of a likely leak also of the line portion 8.
If it is established in S12 that an inflow is present, m219-mii9+m21i5-miii5>m+91i5 Dt, an error message S14 is generated, which indicates leakage of the shutoff valve 7. This should normally be accompanied by a measurable outflow from the line portion 8; however, a check can therefore be carried out as to whether S11 has been run through. If not, there is reason to assume that a measurement is faulty, as the simultaneous leakage of both shutoff valves 4 and 7 is unlikely.
If neither an inflow nor outflow are present, but step S11 has been previously run through, a leakage of the line portion 8 to the environment must be present, and a corresponding error message is generated in S15.
Otherwise, the method terminates without an error message and is repeated the next time the vehicle is switched off.
When the distance between the shutoff valve 7 and the pressure reducer 5 is small, in a simplified configuration the volume of the portion 9 according to the invention compared to that of the portion 8 and the low pressure line 15 can be disregarded, and m2,9-mi,9 is assumed as being zero in step S12. In this case, the sensors 12, 13 can be omitted.
List of reference numbers
1 fuel cell
2 tank
3 distributor line
4 shutoff valve
5 pressure reducer
6 tank connection
7 shutoff valve
8 line portion
9 line portion
10 pressure sensor
11 temperature sensor
12 pressure sensor
13 temperature sensor
14 evaluation unit
15 low pressure line
16 shutoff valve
17 temperature sensor
18 pressure sensor