Steering system with redundant control system, in particular steer-by-wire steering system, and motor vehicle with such a steering system

Abstract

The invention relates to a steering system with a redundant control system (20) comprising a first control device (22) and at least one second control device (24), wherein the first control device (22) and the second control device (24) are interconnected in such a way that they can control a functionally connected steering system both simultaneously and separately, wherein the first control device (22) and the second control device (24) are designed for different average lifetimes (L1, L2).

Description

[0001] The invention relates to a steering system according to the preamble of claim 1, in particular a steer-by-wire steering system. The invention further relates to a motor vehicle with such a steering system, in particular a motor vehicle with a corresponding steer-by-wire steering system.

[0002] Steer-by-wire steering systems, which will be used in mass production in the automotive sector in the future, must exhibit significantly higher reliability than conventional steering systems with a mechanical connection between the steering wheel and the steerable wheels. This is because steer-by-wire systems do not have a mechanical connection between the steering wheel and the steerable wheels of a vehicle. Consequently, the driver can no longer directly control the steerable wheels from the steering wheel. The connection between the steering wheel and the steerable wheels is purely electronic, and a system failure renders the vehicle unsteerable. Therefore, a complete failure of the steering system must be prevented in steer-by-wire systems. Faults in the steering system must be detected as early as possible. Furthermore, autonomous driving assistance systems require increased reliability of the vehicle components.In practice, redundant control units are therefore used to ensure fail-safe operation; that is, a first control unit and a second control unit are interconnected in such a way that they can control a functionally linked steering system both simultaneously and separately. For the redundant functions, a reliable failure behavior must be implemented beyond the required service life in order to achieve the safety objectives according to ISO 26262 ASIL D.

[0003] Total failures of a steering system, especially a steer-by-wire system with a redundant control system, are problematic. These failures occur when the first and second control devices of a redundant control system fail simultaneously due to age. This refers to total failures that occur towards the end of the system's service life, not failures that occur relatively early in the life cycle due to faulty manufacturing.

[0004] Safety and stability systems for steering systems with redundant control systems are known from CN 108715163 A and CN 108501944 A. It is known that the risk of failure of individual control systems is increased at the beginning of a life cycle and after a certain period of service. Particularly critical situations can arise if both control systems of a steer-by-wire steering system with redundant control systems fail simultaneously or almost simultaneously, resulting in an undesired total failure of the entire steering system.

[0005] The invention is based on the objective of improving a steering system, in particular a steer-by-wire steering system, with a redundant control system in such a way that the probability of a total failure of the entire steering system towards the end of its service life is reduced with the least possible design effort.

[0006] The problem is solved according to the invention by the features of the independent claims. Further practical embodiments and advantages of the invention are described in connection with the dependent claims.

[0007] A steering system according to the invention with a redundant control system comprises a first control device and at least one second control device, wherein the first control device and the second control device are interconnected in such a way that they can control a functionally linked steering system both simultaneously and separately. The first control device and the second control device are designed for different average service lives. This design results in a high probability that the actual service lives of the first control device and the second control device will differ. Furthermore, as the difference in the design average service lives of the first and second control devices increases, so does the probability that both control devices will not fail completely at the same time.Accordingly, the steering system according to the invention makes it possible to significantly reduce the probability of a total failure with relatively little design effort.

[0008] The invention relates in particular to steering systems in which the first and second control devices are part of a steer-by-wire steering system. These steering systems are also referred to as steer-by-wire steering systems. Reference is made here again to the technical details already explained in the introduction to the description. The invention offers particular advantages for such steer-by-wire steering systems, especially because a reduced probability of failure is of particular importance in these cases, since a total failure of the steering system renders the motor vehicle completely unsteerable.

[0009] In another practical embodiment of a steering system according to the invention, the first control device and the second control device are structurally identical, with the different average service lives being achieved through a structurally different design or configuration of at least one element of the first control device compared to the second. The aforementioned structurally different design or configuration of at least one element of the control device refers in particular to different electrical, thermal, or mechanical loads on the first and second control devices during operation. This results in the control device with the lower load having a longer service life, so that the statistical probability of failure of the other, more heavily loaded control device is predominantly probable.Preferably, the design is such that the failure of the more heavily loaded control device is highly likely to occur before the probability of failure of the other control device increases. How the structurally different design or different configuration of at least one element of the control device can be implemented in detail is explained below in conjunction with the further dependent claims.

[0010] A different design of the first control device compared to the second control device can be achieved, in particular, through an asymmetrical current distribution. This refers specifically to an increased average and / or maximum current flowing through the first control device compared to the corresponding current flowing through the second control device, especially an increase of at least 3%. Increases of at least 5%, 8%, or 10% are also acceptable. Preferably, the deviation in the current distribution is chosen to be in a range between 3% and 30%, more preferably between 5% and 25%, and more preferably between 5% and 20%.By selecting one of the aforementioned areas, the probability of failure of the first system towards the end of its service life can be largely decoupled compared to the second system, so that a total failure due to the simultaneous failure of both control devices is virtually impossible. A key advantage of the asymmetric current distribution is that practically no additional design effort is required to implement this embodiment.

[0011] In another practical embodiment of a steering system according to the invention, a structurally different design is achieved by using at least partially different thermal pastes on corresponding components of the first and second control devices. This refers in particular to the use of thermal pastes with different thermal conductivities. By selecting a thermal paste with a higher thermal conductivity, heat dissipation at the corresponding components can be improved compared to heat dissipation at the corresponding component of the other control device, and the service life can be increased accordingly. Reference is made here again to the advantages already explained above in connection with the asymmetric current distribution.When using different thermal pastes, it should be noted that this requires modifications to the manufacturing process of a steering system according to the invention, in particular modifications to the production of the circuit boards of the control devices. For the sake of completeness, it should also be noted that different thermal pastes can be used by applying different amounts of thermal paste, in particular to influence the amount of heat transferred via the thermal paste, especially from an element towards a heat sink. This embodiment has the advantage that no different thermal pastes need to be used to achieve a structurally different design.

[0012] In a further practical embodiment of a steering system according to the invention, a structurally different design is achieved by forming at least one solder joint between an element arranged on the circuit board and the circuit board of the first control device, which has a different specific resistance than the corresponding solder joint on the circuit board of the second control device. In this way, the generation of heat can be reduced, and thus the thermal stress lowered, particularly by using a solder with a lower specific resistance. This in turn results in an increased service life compared to the other control board with a solder joint with a higher specific resistance.

[0013] The invention relates in particular to steering systems in which the first control device and the second control device are each formed from at least one circuit board with elements soldered onto it.

[0014] The first control device and the second control device each preferably comprise at least one arrangement consisting of a circuit board with elements soldered onto it and a cooling plate, wherein a thermal paste is arranged between the cooling plate and at least one element as a thermal coupling element. The invention was specifically made for steering systems designed as described above.

[0015] The invention also relates to motor vehicles with a steering system as described above. Explicit reference is hereby made to such motor vehicles, in particular four-wheeled passenger vehicles and trucks.

[0016] Further practical embodiments of the invention are described below in connection with the drawings. They show: Fig. 1. A motor vehicle with a schematically represented steer-by-wire steering system in a side view, Fig. 2 a first embodiment of a steering system according to the invention with asymmetric current distribution, Fig. 3 a second embodiment of a steering system according to the invention with different thermal paste between an element of the circuit board and a heat sink, Fig. 4 another embodiment of a steering system according to the invention with differently designed solder joints, by means of which an element is fixed on the circuit board, and Fig. 5 a diagram showing the probability of failure over time for a steering system according to the invention

[0017] Fig. Figure 1 shows a motor vehicle 10 with steerable front wheels 12 and non-steerable rear wheels 14. A steering wheel 16 is connected to the steerable front wheels 12 via a purely electrical connection, which is represented by a dashed line 18.

[0018] Fig. Figure 2 shows a first embodiment of a steering system according to the invention with a redundant control system 20. The control system 20 comprises a first control device 22 and a second control device 24. Only a partial view of the first control device 22 and the second control device 24 is shown.

[0019] The first control device 22 is formed by a circuit board 26 and elements 28 soldered onto the circuit board 26, of which only one element is in Fig. Figure 2 shows the connection between the element 28 shown and the circuit board 26, which is made via solder 30. Optionally, and therefore shown with dashed lines, are a heat sink 32 located on the top side of the element 28 and thermal paste 34 arranged between the heat sink 32 and the element 28.

[0020] The second control device 24 is of identical construction, with the same reference numerals used for identical elements as in the first control device 22. In the Fig. In the embodiment shown in Figure 2, all individual components are indeed identical in construction, so that there are no design differences between the first control device 22 and the second control device 24.

[0021] At the in Fig. In the embodiment shown in Figure 2, an asymmetrical current distribution is provided insofar as the first control device 22 is supplied with a current I1, whereas the second control device 24 is supplied with a current I2. The current I1 is smaller than the current I2, resulting in a lower thermal load for the first control device 22.

[0022] As a result of the lower thermal stress on the first control device 22, there is an increased service life, which in Fig. 5 is realized by the solid line L1. The dashed line L2 corresponds to the lifetime of the second control device 24, which is on average shorter than the lifetime L1 of the first control device 22. This significantly reduces the probability of a simultaneous failure of the first control device 22 and the second control device 24, since the higher thermal load due to the current being supplied by two of the second control devices 24 at a time leads with near certainty to a premature failure of the second control device 24.

[0023] Fig. Figure 3 shows a further embodiment of a steering system according to the invention, wherein identical elements as in the Fig. In the embodiment shown in 2, the same reference numerals are used as in Fig. 2. The above also applies analogously to the in Fig. 4 third embodiment shown. In the Fig. In the second embodiment shown in Figure 3, a different thermal paste 34a was used in the second control device 24 than in the first control device, in which the same thermal paste 34 was used as in Figure 3. Fig. 2 is used. This involves a structurally different design of the first control device 22 and the second control device 24. This also allows for a similar design to that in Fig. The failure probability shown in section 5 can be achieved over the lifetime.

[0024] Fig. Figure 4 shows another embodiment. In the embodiment shown in Fig. In the embodiment shown in Figure 4, a different solder 30a was used for fastening the element 28 and, optionally, other elements not shown, than in the first control device 22. The solder 30a used in the second control device 24 has a higher specific resistance. Accordingly, the thermal stress in the first control device 22 is lower than in the second control device 24, which in turn results in a longer service life L1 for the first control device 22 than for the second control device 24 (see Figure 4). Fig. 5)

[0025] The features of the invention disclosed in the present description, the drawings, and the claims can be essential for realizing the invention in its various embodiments, both individually and in any combination. The invention can be varied within the scope of the claims and taking into account the knowledge of the person skilled in the art. Reference symbol list 10 motor vehicle 12 steerable front wheel 14 steerable rear wheel 16 Steering wheel 18 dashed line 20 Control system 22 first control device 24 second control device 26 circuit boards 28 Element 30 Lot 32 heat sinks 34 Thermal paste I1 Electricity 12 Electricity L1 Lifetime (first control device) L2 lifetime (second control device) QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 108715163 A

[0004] CN 108501944 A

[0004]

Claims

[1] Steering system with redundant control system (20) comprising a first control device (22) and at least one second control device (24), wherein the first control device (22) and the second control device (24) are interconnected in such a way that they can control a functionally connected steering system both simultaneously and separately, characterized by that the first control device (22) and the second control device (24) are designed for different average lifetimes (L1, L2). [2] Steering system according to the preceding claim, characterized by that the first control device (22) and the second control device (24) are part of a steer-by-wire steering system. [3] Steering system according to one of the preceding claims, characterized bythat the first control device (22) and the second control device (24) are structurally identical elements, wherein the design for differing average service lives (L1, L2) is realized by a structurally different design or different design of at least one element of the first control device (22) compared to the second control device (24). [4] Steering system according to claim 3, characterized by that a different design of the first control device (22) compared to the second control device (24) is realized by an asymmetric current distribution. [5] Steering system according to one of claims 3 or 4, characterized by that a structurally different design is realized by at least partially different use of thermal paste (34) on corresponding components of the first control device (22) and the second control device (24). [6] Steering system according to the preceding claim, characterized by that a thermally conductive paste (34) with a different thermal conductivity is arranged on at least one element of the first control device (22) than on the corresponding element of the second control device (24). [7] Steering system according to one of claims 3 to 6, characterized by that a structurally different design is realized by forming at least one soldering point between an element (28) arranged on the circuit board (26) and the circuit board (26) of the first control device (22), which has a different specific resistance than the corresponding soldering point on the circuit board (26) of the second control device (24). [8] Steering system according to one of the preceding claims, characterized by that the first control device (22) and the second control device (24) are each formed from at least one circuit board (26) with elements (28) soldered thereon. [9] Steering system according to the preceding claim, characterized by that the first control device (22) and the second control device (24) each have at least one arrangement consisting of the circuit board (26) with elements (28) soldered thereon and a cooling plate (32), wherein a thermally conductive paste (34) is arranged between the cooling plate (32) and at least one element (28) as a thermal coupling element. [10] Motor vehicle with a steering system according to one of the preceding claims.

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