Motor vehicle with hybrid power supply system and method for its operation

Abstract

A motor vehicle has an electric drive motor (6), an input instrument (9) for inputting a performance requirement of the drive motor (6) by a driver, and a hybrid power supply system. The hybrid power supply system comprises a fuel cell arrangement (2), a battery (4), a power converter unit (3) for supplying a consumer (5), formed at least partially by the motor (6), with electrical energy from the fuel cell arrangement (2) or the battery (4) and for charging the battery (4) with electrical energy from the fuel cell arrangement (2) or regenerated electrical energy from the consumer (5), and a control unit (8), which is configured to control the performance of the fuel cell arrangement (2) and the distribution of electrical energy of the fuel cell arrangement (2) to the battery (4) and the consumer (5) by means of a deviation between actual and target state of charge of the battery (4). The control unit (8) is connected to the input instrument (9) and is configured to vary the target state of charge as a function of the performance requirement.

Description

[0001] MOTOR VEHICLE WITH HYBRID POWER SUPPLY SYSTEM AND METHOD FOR ITS OPERATION

[0002] D e s c r i p t i o n

[0003] The present invention relates to a motor vehicle with a hybrid power supply system and an operating system for that.

[0004] Such a hybrid power supply system conventionally comprises an arrangement of one or more fuel cells, a tank for the supply of the fuel cell arrangement with an energy carrier, typically hydrogen gas, a battery, a power converter unit for supplying an external consumer with electrical energy from the fuel cell arrangement or the battery and for charging the battery with electrical energy from the fuel cell arrangement or regenerated electrical energy from the consumer, and a control unit which is configured to control the performance of the fuel cell arrangement and the distribution of electrical energy of the fuel cell arrangement to the battery and to the consumer inter alia by means of a deviation between the actual and target state of charge of the battery.

[0005] As the electrical energy generated by the fuel cell arrangement is more expensive than network-based electrical energy, generally it is not economical, in a current supply system for a motor vehicle, to design the fuel cell arrangement to be so high- performance that it can cover on its own the energy requirement of the vehicle permanently. For a user, it is more economical to charge a battery of such a vehicle whenever possible on the network and to only use the fuel cell arrangement when a driving distance which is to be covered exceeds the range which is able to be achieved with battery operation. By the fuel cell arrangement being thus dimensioned closely, saving can be made in the vehicle with regard to costs, installation space and weight. A disadvantage of this approach is that the fuel cell arrangement is not able, on its own, to cover the high traction requirement which can result from a combination of high payload, uphill driving and / or high vehicle speed.

[0006] Therefore, the battery must compensate these performance gaps. Critical situations occur when the battery can not discharge owing to thermal restrictions or a low state of charge (SOC) of the battery. In such situations, conventionally the electrical power of the motor must be throttled. This leads to a lower acceleration or lower speed of the vehicle and is unsatisfactory for the user of the vehicle.

[0007] An object of the invention is therefore to create a motor vehicle with hybrid power supply system, in which the likelihood of such restrictions is minimized.

[0008] The problem is solved according to an aspect of the invention by a motor vehicle having an electric drive motor, an input instrument for the inputting of a performance requirement of the drive motor by a driver, and having a hybrid power supply system, wherein the hybrid power supply system comprises a fuel cell arrangement, a battery, a power converter unit for the optional supplying of an external consumer with electrical energy from the fuel cell arrangement or the battery and for charging the battery with electrical energy from the fuel cell arrangement or regenerated electrical energy from the consumer, and a control unit which is configured to control the performance of the fuel cell arrangement and the distribution of electrical energy of the fuel cell arrangement to the battery and to the consumer by means of a deviation between the actual and target state of charge of the battery, and is connected to the input instrument, typically an accelerator pedal, in order to vary the target state of charge as a function of the performance requirement.

[0009] In his actuation of the accelerator pedal, the driver takes into consideration intuitively requirements for the traction which are variable depending on the road gradient and surface conditions, vehicle load etc., and the expected acceleration behaviour; thereby it reflects, although briefly variably, a drive load which is to be expected and can be used in order to increase the target state of charge with a high load which is to be expected and to thus make provision that the power supply system maintains a high load state for a long time before the battery is discharged so far that the performance must be reduced. As a result of the variability of the actuation of the input instrument, the varying of the target state of charge should be based on a sliding mean value of the performance requirement or on a value derived from the performance requirement.

[0010] The duration of a time span over which the sliding mean value is formed, can amount to some 10 s to some minutes, in particular ca. 60 s.

[0011] According to the differentiation between an operation of the vehicle with normal and with increased performance requirement, the control unit can be configured as a function of the performance requirement to change between two stationary target states of charge, a high and a low one.

[0012] In order to bring about a gradual transition between the two and to avoid inefficient, abrupt changes to the operating conditions of the fuel cell arrangement, provision can be made that during a change between the stationary target states of charge the control unit controls the operation of the battery by means of non-stationary target states of charge, the values of which lie between those of the high and of the low target state of charge. This means that whereas the control unit can maintain the stationary target states of charge over times of any desired length, in so far as the performance requirement of the driver permits this, the transient target states of charge are only possible temporarily, in the course of the change from one stationary target state of charge to the other.

[0013] The decision as to which of the stationary target states of charge is to be used can be based on a comparison of the sliding mean value with a threshold value. In particular, the control unit can be configured to change to the high target state of charge, when the sliding mean value increases over a first threshold value, and to change to the low target state of charge when the sliding mean value falls above a second threshold value. When the first threshold value is greater by a hysteresis value than the second threshold value, the number of switching processes and hence the proportion of less efficient transient operating phases can be kept small.

[0014] The problem is further solved by a method for operating a motor vehicle with an electric drive motor, an input instrument for the inputting of a performance requirement of the drive motor by a driver, and a hybrid power supply system, wherein the hybrid power supply system comprises a fuel cell arrangement, a battery, a power converter unit for the optional supplying of a consumer, formed at least partially by the motor, with electrical energy from the fuel cell arrangement or from the battery and for charging the battery with electrical energy from the fuel cell arrangement or regenerated electrical energy from the consumer, with the steps: detecting a performance requirement inputted by the driver via the input instrument; varying a target state of charge of the battery as a function of the performance requirement; regulating the performance of the fuel cell arrangement by means of the target state of charge.

[0015] A further subject of the invention is a computer program, for instance in a form stored on a data carrier, comprising instructions able to be executed by a computer, the execution of which by a computer arranged as described above as a control unit in a hybrid power supply system, causes it to execute the method defined above.

[0016] Further features and advantages of the invention will emerge from the following description of example embodiments with reference to the enclosed figures. There are shown

[0017] Fig. 1 a block diagram of a motor vehicle with a hybrid power supply system;

[0018] Fig. 2 a flow diagram of a working method of a control unit of the hybrid power supply system; and

[0019] Fig. 3 an exemplary characteristic of the fuel cell target performance P as a function of the state of charge Q of the battery.

[0020] Figure 1 shows in schematized form a motor vehicle with a hybrid power supply system. A hydrogen tank 1 is connected in a manner known per se to a fuel cell arrangement 2, in order to supply the latter with hydrogen gas which is converted in the fuel cells of the arrangement with atmospheric oxygen, in order to generate electrical energy.

[0021] A power converter unit 3 connects the fuel cell arrangement 2 with a battery 4 and with a consumer 5 in the form of an electric motor 6, which acts on a drive train 7 of the vehicle, and possibly other electrically operated equipment such as infotainment system, windscreen wiper, fan or control electronics.

[0022] Part of the control electronics inter alia is a control unit 8, the task of which is to control the performance of the fuel cell arrangement 2 so that the fuel cell arrangement 2 and the battery 4 cover the requirement of the consumer 5 and the state of charge Q of the battery 4 is maintained close to a predetermined target value.

[0023] During a majority of the operating time, the power input of the consumer 5 is positive, so that when it exceeds the output performance of the fuel cell arrangement 2, lack of performance must be contributed by the battery 4. When the power input of the consumer lies below the output performance of the fuel cell arrangement 2, the battery 4 is charged with the excess energy. This also applies to the case of regenerative operation; when the motor, on braking or on uphill driving, works as a generator, the power input of the consumer 5 is negative, then the battery 4 is to be capable of receiving this energy. Therefore, the target value for the state of charge of the battery 4 is at least so much smaller than 100% that the battery 4 always has sufficiently residual capacity for regenerated energy which is to be realistically expected.

[0024] During travel, the control unit 8 determines the target value of the state of charge Q continually by means of the position of an accelerator pedal 9, actuated by the driver, through cyclically repeating the method of Fig. 2.

[0025] In step S1 , the control unit 8 interrogates the current deflection of the accelerator pedal, stores the obtained deflection value and calculates (S2) a mean value therefrom and deflection values which are stored from preceding iterations of the last 60 s. In S3 the mean value is compared with an upper threshold value . If the latter is exceeded, then a high value Qi is set (S4) as a target desired value QT of the state of charge of the battery 4; otherwise, the method branches to step S5.

[0026] In S5 the mean value is compared with a lower threshold value ^2. If the latter is fallen below, then a low value Q2 is set (S6) as target desired value of the state of charge of the battery 4; otherwise the target value remains unchanged with respect to the previous iteration.

[0027] The setting of the target desired value in steps S4 and S6 is not to be understood to the effect that this would have to be changed; the target desired value set in the previous iteration can also be confirmed unchanged.

[0028] In S7 an instantaneous target value QM still stored from the previous iteration can be compared with the target desired value QT. If both are identical, then the instantaneous target value QM remains unchanged. If they are different, then the instantaneous target value QM is approximated to the target desired value QT by a predetermined increment D Q (S8). Thus, in the case of a change of the target desired value, the instantaneous target value QM adapts itself thereto gradually and in a slowed-down manner.

[0029] In step S9, the control unit 8 determines the present state of charge Q of the battery 4 via any suitable measuring instrument 10. A control of the performance of the fuel cell arrangement 2 based on the present state of charge Q and the instantaneous target value QM of the state of charge can be based on various methods, only one of which is explained here below by way of example.

[0030] Fig. 3 shows as characteristic C2 a conventional correlation between the state of charge of the battery 4 and the target performance of the fuel cell arrangement 2, predetermined by a conventional control unit, not taking into account the performance requirement of the driver, as a function of this state of charge. With a low state of charge, between 0 and ca. 40% of the charging capacity, the fuel cell arrangement 2 is operated with maximum performance, in order to prevent, with continuously high performance requirement of the consumer 5, that a critically low state of charge is reached, in which the performance available for the consumer 5 must be throttled below the requirement of the consumer 5 to protect the battery 4, or to delay such a situation at least for as long as possible. In a middle range of the state of charge, here between ca. 40% and ca. 55%, the target performance is a linearly decreasing function of the state of charge; with a still higher state of charge, the dependence of the target performance on the state of charge decreases continually, and finally, at ca. 90%, reaches the value zero. A target value of the state of charge can not be clearly read from this curve; the state of charge which occurs for a long time on driving under standardized conditions, e.g. on a flat road at a predetermined speed, can be regarded here as target value of the state of charge. For the purposes of this description, it can be assumed that the target value for the shown characteristic Ch = 50%.

[0031] The control unit 8 according to the invention selects (S11) the characteristic C2 for establishing the performance of the fuel cell arrangement as a function of the state of charge Q, when the performance requirement of the driver is low and the instantaneous target value QM is equal to Q2 (S10).

[0032] A second characteristic Ci in Fig. 3 is obtained from the characteristic C2 by moving to the right, here e.g. by 20 percentage points of the state of charge scale Q. It is immediately understandable that if, instead of the characteristic C2, the characteristic Ci were the basis of the control of the fuel cell arrangement 2, this would correspond to a target value Qi = 70%. Therefore, the control unit 8 uses the characteristic Ci (S13) when the performance requirement of the driver is high and the instantaneous target value QM is equal to Qi (S12).

[0033] As described above in connection with step S8, the instantaneous target value QM besides the stationary values Qi and Q2 can temporarily also assume non-stationary values between these two extremes.

[0034] When the instantaneous target value QM lies between Qi and Q2, the control unit 8 generates a temporary characteristic C, by moving the characteristic Ci or C2 along the Q axis in the diagram of Fig. 3, so that the performance value at which the curve C2 assumes the target value Q2 (or the curve Ci assumes the target value Qi), corresponds to the instantaneous target value QM at the temporary characteristic C (S14). From the characteristic which is thus obtained, in S15 the value of the performance P is determined, which corresponds to the state of charge Q detected in S9, and the fuel cell arrangement 2 is controlled in order to deliver this performance P.

[0035] Reference numbers

[0036] 1 tank

[0037] 2 fuel cell arrangement

[0038] 3 power converter unit

[0039] 4 battery

[0040] 5 consumer

[0041] 6 electric motor

[0042] 7 drive train

[0043] 8 control unit

[0044] 9 accelerator pedal

[0045] 10 measuring instrument

Claims

C l a i m s1. A motor vehicle with an electric drive motor (6), an input instrument (9) for inputting a performance requirement of the drive motor (6) by a driver, and a hybrid power supply system, wherein the hybrid power supply system comprises a fuel cell arrangement (2), a battery (4), a power converter unit (3) for supplying a consumer (5), formed at least partially by the motor (6), with electrical energy from the fuel cell arrangement (2) and / or from the battery (4) and for charging the battery (4) with electrical energy from the fuel cell arrangement (2) and / or regenerated energy from the consumer (5), and a control unit (8), which is configured to control the performance of the fuel cell arrangement (2) and the distribution of electrical energy of the fuel cell arrangement (2) to the battery (4) and to the consumer (5) by means of a deviation between the actual and target state of charge of the battery (4), characterized in that the control unit (8) is connected to the input instrument (9) and is configured to vary the target state of charge (Qi, Ch, Q’) as a function of the performance requirement (^).

2. The motor vehicle according to Claim 1 , in which the function of the performance requirement ( ) comprises the forming of a sliding mean value (^) of the performance requirement or of a value derived from the performance requirement ( ).

3. The motor vehicle according to Claim 2, in which a time span over which the sliding mean value (^) is formed has a duration of some 10 s to some minutes, in particular ca. 60 s.

4. The motor vehicle according to one of the preceding claims, in which the control unit (8) is configured, as a function of the performance requirement (^), to change between two stationary target states of charge, a high one (Qi) and a low one (Ch).

5. The motor vehicle according to Claim 4, in which the control unit (8) is configured, during a change between the stationary target states of charge(Qi , Q2), to control the operation of the battery (4) by means of non- stationary target states of charge (QM) (S14, S15), the values of which lie between those of the high state of charge (Qi) and the low state of charge (Q2).

6. The motor vehicle according to Claim 2 or 3 and Claim 4 or 5, in which the control unit (8) is configured to change to the high target state of charge (Qi) when the sliding mean value (^) rises above a first threshold value, and to change to the low target state of charge (Q2) when the sliding mean value falls over a second threshold value, wherein optionally the first threshold value is greater than the second threshold value by a hysteresis value.

7. A method for operating a motor vehicle with an electric drive motor (6), an input instrument for inputting a performance requirement of the drive motor (6) by a driver, and with a hybrid power supply system, wherein the hybrid power supply system comprises a fuel cell arrangement (2), a battery (4), a power converter unit (3) for supplying a consumer (5), formed at least partially by the motor (6), with electrical energy from the fuel cell arrangement or the battery (4) and for charging the battery (4) with electrical energy from the fuel cell arrangement (2) or regenerated electrical energy from the consumer 95), with the steps: detecting (S1) a performance requirement inputted by the driver via the input instrument; varying (S10-S14) a target state of charge (QM) of the battery (4) as a function of the performance requirement; regulating (S15) the performance of the fuel cell arrangement (2) by means of the target state of charge.

8. A computer program, comprising instructions which are able to be executed by a computer, the execution of which through a computer arranged as control unit (8) in a hybrid power supply system according to one of Claims 1 to 6 causes it to execute the method according to Claim 7.

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