Control strategy for flushing and draining a fuel cell system in a motor vehicle

Abstract

A fuel cell system (2) comprises at least one fuel cell (4) having an air supply line (6a) and an exhaust air line (6b); a water separator (24) arranged in the exhaust air line (6b); a purge valve (27) which allows the fuel cell system (2) to be purged by opening the purge valve (27); a drain valve (26) which allows water to be drained from the water separator (24) by opening the drain valve; an evaluation device (30) which is designed to determine a dynamic-related characteristic value (K) from a dynamic detected by a dynamic sensor (9) and to determine whether the dynamic-related characteristic value (K) reaches or exceeds an upper threshold value (S+) and / or whether the dynamic-related characteristic value (K) reaches or falls below a lower threshold value (S-);and a control device (32) which is designed to adapt a control strategy for flushing and / or draining the fuel cell system (2) when the upper threshold value (S+) of the dynamic-related characteristic value (K) is reached or exceeded or when the lower threshold value (S-) of the dynamic-related characteristic value (K) is reached or undershot.;

Description

[0001] The invention relates to a method for adapting a control strategy for purging and draining a fuel cell system in a motor vehicle, taking into account the dynamics of the motor vehicle. The invention also relates to a fuel cell system operable using such a method and to a motor vehicle comprising such a fuel cell system. State of the art

[0002] Fuel cell systems can be used to supply electric motors in motor vehicles with electrical energy.

[0003] Polymer electrolyte membrane (PEM) fuel cell systems convert hydrogen, which is supplied to the fuel cell system as a gas, into water using oxygen. This reaction generates electrical energy, waste heat, and waste products.

[0004] A PEM fuel cell has an anode supplied with hydrogen, a cathode supplied with oxygen-containing air, and a polymer electrolyte membrane located between the anode and cathode. To increase the electrical voltage that can be provided by the fuel cell system, several such fuel cells can be stacked and electrically connected in series.

[0005] The hydrogen supplied to the fuel cell as fuel does not completely react to form water. Therefore, the anode exhaust gas flowing out of the fuel cell still contains a significant amount of hydrogen. For this reason, the liquid water phase of the anode exhaust gas leaving the fuel cell is separated from the gaseous anode exhaust gas using a water separator via one or more valves. The gaseous portion is returned to the fuel cell. There are systems with a purge valve and a drain valve, and so-called single-valve systems, in which the drain valve also flushes. The advantages of these systems are their simplicity of design and the minimization of manufacturing costs. However, they place high demands on the quality of the drain or flushing process, since both media (product water and gas) must be regulated with sufficient precision in one process.

[0006] The water must be reliably removed from the system, while simultaneously preventing overflow of the water separator, i.e., water ingress on the inlet side of the fuel cell system. Furthermore, excessive nitrogen concentration in the anode must be prevented by adequately purging the fuel cell system. On the other hand, excessive purging leads to higher hydrogen losses.

[0007] During operation of a fuel cell system in a motor vehicle, the fuel cell system is subjected to vibrations, acceleration, and deceleration. This causes, among other things, movement of the water in the water separator. During strong acceleration, depending on the shape of the water separator and the position of the valve located in the water separator's fluid outlet, it may happen that too much or too little water is drained, or that the fuel cell system is purged with too much or too little gas.

[0008] The basic problem is that when the vehicle accelerates, vibrates and decelerates, the control strategies for the drain / flushing processes are inaccurate.

[0009] An object of the present invention is therefore to provide a method for adapting a control strategy for flushing and / or draining a fuel cell system to the dynamics of a motor vehicle and a fuel cell system that enables this in order to achieve the highest possible utilization efficiency of the fuel cell system. Disclosure of the invention

[0010] The method according to the invention for adapting a control strategy for flushing and / or draining a fuel cell system in a motor vehicle comprises the following steps: a) detecting a dynamic, in particular an acceleration state, of the motor vehicle with the aid of a dynamic sensor; b) determining a dynamic-related characteristic value from the dynamics of the motor vehicle detected by the dynamic sensor; c) comparing the dynamic characteristic value with an upper threshold value and / or with a lower threshold value; d) adapting the control strategy for purging and / or draining the fuel cell system when the dynamic-related characteristic value reaches or exceeds the upper threshold value and / or when the dynamic-related characteristic value reaches or falls below the lower threshold value.

[0011] Flushing the fuel cell system involves flushing the fuel cell system with a gas. Draining the fuel cell system involves draining water from the fuel cell system, in particular from a water separator of the fuel cell system.

[0012] In a method according to the invention, in addition to an operating-point and, if applicable, model-based control strategy, a dynamic sensor is also used to detect the dynamics of the motor vehicle. During periods of increased dynamics of the motor vehicle, the control strategy can be adjusted based on the dynamic-related characteristic value from the dynamics of the motor vehicle detected by the dynamic sensor. When the dynamics of the motor vehicle decrease again, it is possible to return to an operating-point and, if applicable, model-based control strategy.

[0013] With a method according to the invention, the vehicle's dynamic operation can be easily taken into account and the necessary flushing and / or draining of the fuel cell system when the motor vehicle is in operation can be adjusted. This means that the fuel cell system is only flushed and / or drained when necessary for dynamic reasons. The overall efficiency of the fuel cell system can thus be increased and hydrogen can be saved.

[0014] The detected dynamics of the motor vehicle can include, for example, an acceleration state, a deceleration or braking state and / or a vibration state of the motor vehicle.

[0015] In one embodiment, the flushing and / or draining of the fuel cell system is carried out at intervals, and in step d), the duration and / or the number of intervals of flushing and / or draining is increased if the dynamic-related characteristic value reaches or exceeds the upper threshold value.

[0016] In a further embodiment, in step d), the duration or intervals of flushing and / or dewatering are reduced if the dynamic-related characteristic value reaches or falls below the lower threshold. This may also include reversing a previously made extension of the duration or increase in the number of intervals of flushing and / or dewatering if the dynamic-related characteristic value reaches or falls below the lower threshold.

[0017] Switching from increasing flushing and / or draining to decreasing flushing and / or draining conversely may have hysteresis to avoid unwanted oscillations between these two states.

[0018] Purging with gas may include opening and closing a purge valve of the fuel cell system. Draining the fuel cell system may include opening and closing a drain valve.

[0019] The drain valve is also known as the “drain valve” and the flush valve is known as the “purge valve”.

[0020] In a further embodiment, the opening of the drain valve is coordinated, i.e. simultaneously with or opposite to the opening of the flush valve and vice versa.

[0021] In a further embodiment, determining the dynamic-related characteristic value comprises low-pass filtering and / or forming a moving average and / or a quantile-related evaluation of the values ​​provided by the dynamic sensor.

[0022] By using low-pass filtering, slow changes in the output values ​​of the dynamic sensor can be generated to facilitate trend detection and increase the overall signal-to-noise ratio with minimal signal degradation. Forming a moving average or quantile-based evaluation also makes it easier to detect trends in the values ​​provided by the dynamic sensor. This can reduce the hysteresis when switching from increasing flushing and / or draining to decreasing flushing and / or draining, and vice versa.

[0023] The dynamic sensor can be an acceleration sensor of the motor vehicle or an acceleration sensor of the fuel cell system.

[0024] The dynamic sensor can comprise a fill level sensor in a water separator of the fuel cell system, and the dynamics of the motor vehicle can be determined from a signal provided by the fill level sensor. With a fill level sensor in the water separator, the effect of the motor vehicle's dynamics on the water movements in the water separator can be better detected, which in turn enables improved adaptation of the control strategy to the current dynamics of the motor vehicle.

[0025] In a further embodiment, the dynamics of the motor vehicle are determined from GPS information, in particular from information about the speed profile and derived accelerations and / or decelerations. The dynamics of the motor vehicle can also be determined from route information, such as an uphill gradient, a downhill gradient, and / or a route condition. Alternatively or additionally, the dynamics of the motor vehicle can also be determined from the driver's behavior, in particular from information about the actuation of the accelerator pedal and / or the actuation of the brakes.

[0026] A driver recognition system installed in the vehicle can also be used to detect the driver’s usual driving style / dynamics and take this into account as a safety correction value.

[0027] The invention also encompasses a fuel cell system comprising at least one fuel cell, an air supply line and an exhaust line, a water separator arranged in the exhaust line, a purge valve that allows the fuel cell system to be purged by opening the purge valve, a drain valve that allows water to be drained from the water separator by opening the drain valve, and an evaluation device and a control device. The evaluation device is designed to determine a dynamic-related characteristic value from a dynamic detected by a dynamic sensor and to determine whether the dynamic-related characteristic value reaches or exceeds an upper threshold value and / or whether the dynamic-related characteristic value reaches or falls below a lower threshold value.The control device is designed to adapt a control strategy for flushing and / or draining the fuel cell system when the upper threshold value is reached or exceeded or when the lower threshold value is reached or undershot.

[0028] In one embodiment, the purge valve and the drain valve are designed as a combined purge and drain valve. This simplifies the design of the fuel cell system and can help minimize manufacturing costs.

[0029] The fuel cell system can be purged with gas by opening the purge valve. Water can be drained from the water separator by opening the drain valve.

[0030] In a further embodiment, the fuel cell system comprises a dynamic sensor which is designed to detect the dynamics of the motor vehicle, wherein the dynamic sensor is arranged in particular in or on the at least one fuel cell.

[0031] The invention further comprises a motor vehicle having at least one electric motor and a fuel cell system according to the invention, as described above, wherein the fuel cell system is designed to supply the electric motor with electrical energy.

[0032] In one embodiment, the motor vehicle comprises a dynamic sensor which is designed to detect the dynamics of the motor vehicle.

[0033] The dynamic sensor can comprise an acceleration sensor or a level sensor. If the dynamic sensor includes a level sensor, the effect of the vehicle's dynamics on the water movements in the water separator can be better detected, which in turn leads to improved adjustment of the control strategy.

[0034] The embodiments and advantages described for the fuel cell system also apply to the motor vehicle with such a fuel cell system.

[0035] An embodiment of the invention is described below with reference to the accompanying figures. Short description of the characters Fig. Figure 1 shows a schematic view of a motor vehicle driven by an electric motor powered by a fuel cell system. Fig. 2 shows a schematic view of a fuel cell system. Fig. 3 shows a flowchart of an embodiment of a method according to the invention for adapting a control strategy for flushing and / or draining a fuel cell system in a motor vehicle. Character description

[0036] Fig. 1 shows a schematic view of a motor vehicle 1 driven by an electric motor 5 fed by a fuel cell system 2.

[0037] The motor vehicle 1 has four wheels 3 and at least one electric motor 5, which is provided for driving at least two wheels 3 of the motor vehicle 1. The electric motor 5 can also be provided for driving all four wheels 3 of the motor vehicle 1. In an alternative embodiment, which is not explicitly shown in the figures, an electric motor 5 can be provided on at least one of the wheels 3, in particular on each of the wheels 3, of the motor vehicle 1.

[0038] The invention can also be used in motor vehicles 1 having more or fewer than four wheels 3.

[0039] The electric motor 5 is supplied with electrical energy via a motor control 7, which is provided by the fuel cell system 2.

[0040] The motor vehicle 1 also has a dynamic sensor 9 designed to detect the dynamics of the motor vehicle 1. The dynamic sensor can comprise, for example, an acceleration sensor and / or a fill level sensor. The dynamics of the motor vehicle can also be determined using GPS information and / or route information and / or the driving behavior of the motor vehicle 1.

[0041] Fig. 2 shows a schematic view of a fuel cell system 2 according to the invention.

[0042] The fuel cell system 2 comprises at least one fuel cell 4 with an anode 6 and a cathode 8. The fuel cell system 2 can have a plurality of fuel cells 4, which can be arranged in a fuel cell stack (“fuel cell stack”).

[0043] For the sake of simplicity, an exemplary embodiment of the invention is described below with reference to a fuel cell system 2 having only a single fuel cell 4. The invention can also be used in conjunction with fuel cell systems 2 having multiple fuel cells 4, in particular a fuel cell stack.

[0044] The anode 6 and the cathode 8 of the fuel cell 4 are separated from each other by a membrane 10, in particular a polymer electrolyte membrane 10.

[0045] The cathode 8 of the fuel cell 4 is supplied with oxygen, in particular in the form of oxygen-containing ambient air, by an oxygen supply system 12.

[0046] The fuel cell system 2 further comprises a hydrogen supply system 14, which is provided and designed to supply hydrogen from a hydrogen reservoir 16 to the anode 6 of the fuel cell 4.

[0047] The hydrogen and oxygen supplied to the fuel cell 4 react within the fuel cell 4 to form water (H2O). This reaction releases electrical energy, which is provided by the fuel cell 4 as electrical current i.

[0048] The hydrogen from the hydrogen reservoir 16 is supplied to the fuel cell 4 through a shut-off valve 18, a dosing valve 20 and a conveying device 22, for example an ejector.

[0049] The gas flow emerging from the anode 6 of the fuel cell 4 is passed through a water separator 24 in which liquid components of the gas flow are separated from gaseous components of the gas flow.

[0050] The gaseous components are returned to the conveying device 22 and from there to the anode 6 of the fuel cell 4.

[0051] The fuel cell system 2 further comprises a purge valve 27 and a drain valve 26. The purge valve 27 allows the fuel cell 4 to be purged by opening the purge valve 27 in order to reduce the nitrogen content in the anode 6 of the fuel cell 4 to a predetermined level. The drain valve 26 allows water to be drained from the water separator 24 by opening the drain valve 26.

[0052] The outlets of the flush valve 27 and the drain valve 26 can be connected to a common exhaust air and waste water line, which is located in the Fig. 2 is not explicitly shown.

[0053] The fuel cell system 2 also comprises an evaluation device 30 which is designed to determine a dynamic-related characteristic value K from a dynamic detected by the dynamic sensor 9 and to determine whether the dynamic-related characteristic value K reaches or exceeds an upper threshold value S+ and / or whether the dynamic-related characteristic value K reaches or falls below a lower threshold value S-.

[0054] A control device 32 of the fuel cell system 2 is designed to adapt the control strategy of purging the fuel cell system 2 with gas and / or dewatering the fuel cell system 2 by draining water from the water separator 24 when the upper threshold value S+ is reached or exceeded and / or when the lower threshold value S- is reached or undershot.

[0055] The evaluation device 30 and the control device 32 can be designed separately from one another or as a combined evaluation and control device 34.

[0056] Fig. 3 shows a flowchart of an embodiment of a method 100 according to the invention for adapting a control strategy for flushing and / or draining a fuel cell system 2 in a motor vehicle 1.

[0057] The method 100 comprises, in a first step 110, detecting a dynamic, in particular an acceleration state, of the motor vehicle 1 with the aid of the dynamic sensor 9.

[0058] In a subsequent step 120, a dynamic-related characteristic value K is determined from the dynamics of the motor vehicle 1 detected by the dynamic sensor 9. In the following steps 130 and 140, the dynamic-related characteristic value K is compared with an upper threshold value S+ (step 130) and / or with a lower threshold value S- (step 140).

[0059] The control strategy for flushing and / or draining the fuel cell system 2 is adjusted depending on the result of this comparison: If the dynamic-related characteristic value K reaches or exceeds the upper threshold value S+ (K ≥ S+), the duration and / or the number of intervals of flushing and / or draining is increased in step 150.

[0060] If the dynamic-related characteristic value K reaches or falls below the lower threshold value S- (K ≤ S+), the duration and / or the number of intervals of flushing and / or draining is reduced in step 160.

[0061] With a method according to the invention, as described above, the flushing and / or draining of the fuel cell system 2 can be adapted to the dynamic driving operation of the motor vehicle 1. When implementing a method according to the invention, the flushing and / or draining of the fuel cell system only takes place when necessary for dynamic driving reasons. The overall efficiency of the fuel cell system can thereby be increased and hydrogen can be saved.

Claims

[1] Method for adapting a control strategy for flushing and / or draining a fuel cell system (2) in a motor vehicle (1), comprising the following steps: a) detecting (100) a dynamic, in particular an acceleration state, of the motor vehicle (1) with the aid of a dynamic sensor (9); b) determining (120) a dynamic-related characteristic value (K) from the dynamics of the motor vehicle (1) detected by the dynamic sensor; c) comparing (130, 140) the dynamic-related characteristic value (K) with an upper threshold value (S+) and / or with a lower threshold value (S-); d) adapting (150, 160) the control strategy for purging and / or draining the fuel cell system (2) when the dynamic-related characteristic value (K) reaches or exceeds the upper threshold value (S+) and / or when the dynamic-related characteristic value (K) reaches or falls below the lower threshold value (S-); wherein the purging and / or draining of the fuel cell system (2) comprises purging the fuel cell system (2) with a gas and / or draining water from the fuel cell system (2). [2] Method according to claim 1, wherein the flushing and / or draining of the fuel cell system (2) is carried out at intervals, and wherein step d) comprises increasing the duration and / or the number of intervals of flushing and / or draining when the dynamic-related characteristic value (K) reaches or exceeds the upper threshold value (S+). [3] Method according to claim 1 or 2, wherein step d) comprises reducing the duration or intervals of rinsing and / or dewatering when the dynamic-related characteristic value (K) reaches or falls below the lower threshold value (S-). [4] Method according to one of the preceding claims, wherein the flushing of the fuel cell system (2) comprises the opening and closing of a flushing valve (27) and / or wherein the draining of the fuel cell system (2) comprises the opening and closing of a drain valve (26). [5] Method according to claim 4, wherein the opening of the drain valve (26) is coordinated with or opposite to the opening of the flush valve (27) and vice versa. [6] Method according to one of the preceding claims, wherein the determination of the dynamic-related characteristic value (K) comprises a low-pass filtering and / or the formation of a moving average and / or a quantile-related evaluation of the values ​​provided by the dynamic sensor (9). [7] Method according to one of the preceding claims, wherein the dynamic sensor (9) comprises an acceleration sensor of the motor vehicle (1) or an acceleration sensor of the fuel cell system. [8] Method according to one of the preceding claims, wherein the dynamic sensor (9) comprises a fill level sensor and wherein the dynamics of the motor vehicle (1) are determined from a signal supplied by the fill level sensor. [9] Method according to one of the preceding claims, wherein the dynamics of the motor vehicle (1) are determined from GPS information; and / or wherein the dynamics of the motor vehicle (1) are determined from route information, such as gradient, gradient or route condition; and / or wherein the dynamics of the motor vehicle (1) are determined from the driver behavior of the motor vehicle (1); wherein the method comprises, in particular, recognizing a driver of the vehicle by means of a driver recognition system present in the vehicle (1) and taking into account a usual driving style / dynamics of the driver when determining the dynamics of the motor vehicle (1). [10] Fuel cell system (2) comprising: at least one fuel cell (4) having an air supply line (6a) and an exhaust line (6b), a water separator (24) arranged in the exhaust air duct (6b), a purge valve (27) which enables the fuel cell system (2) to be purged by opening the purge valve (27); a drain valve (26) which enables water to be drained from the water separator (24) by opening the drain valve; an evaluation device (30) which is designed to determine a dynamic-related characteristic value (K) from a dynamic detected by a dynamic sensor (9) and to determine whether the dynamic-related characteristic value (K) reaches or exceeds an upper threshold value (S+) and / or whether the dynamic-related characteristic value (K) reaches or falls below a lower threshold value (S-); and a control device (32) which is designed to adapt a control strategy for flushing and / or draining the fuel cell system (2) when the upper threshold value (S+) is reached or exceeded by the dynamic-related characteristic value (K) or when the lower threshold value (S-) of the dynamic-related characteristic value (K) is reached or undershot. [11] Fuel cell system (2) according to claim 10, wherein the fuel cell system (2) comprises a dynamic sensor (9) designed to detect the dynamics of the motor vehicle (1); wherein the dynamic sensor (9) is arranged in particular in or on the at least one fuel cell (4). [12] Motor vehicle (1) with at least one electric motor (5) and a fuel cell system (2) according to claim 10 or 11, wherein the fuel cell system (2) is designed to supply the electric motor (5) with electrical energy. [13] Motor vehicle (1) according to claim 12, wherein the motor vehicle (1) comprises a dynamic sensor (9) which is designed to detect a dynamic of the motor vehicle (1). [14] Motor vehicle (1) according to claim 13, wherein the dynamic sensor (9) comprises an acceleration sensor or a fill level sensor. [15] Motor vehicle (1) according to one of claims 12 or 13, wherein the dynamic sensor (9) and / or the evaluation device (30) are designed to determine the dynamics of the motor vehicle (1) with the aid of GPS information; and / or wherein the dynamic sensor (9) and / or the evaluation device (30) are designed to determine the dynamics of the motor vehicle (1) from route information, such as gradient, gradient or the condition of the route; and / or wherein the dynamic sensor (9) and / or the evaluation device (30) are designed to detect the driver behavior of the motor vehicle (1) and to determine the dynamics of the motor vehicle (1) from the driver behavior of the motor vehicle (1).

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