Vehicle steering system

Abstract

Vehicle steering system with an electric motor (2) which provides a steering torque and / or a steering angle and whose stator and / or rotor is supplied with electric current as required by an electronic control unit (3a, 3b) via at least two functionally parallel connected electrical lines (9a, 9b), which control unit (3a, 3b) takes into account the steering input of the driver of the vehicle and / or a system guiding the vehicle, wherein, for the purpose of providing safety redundancy, at least two parallel operating control units (3a, 3b) are provided, each of which supplies one of the functionally parallel connected electrical lines (9a, 9b) of the electric motor (2) with electric current as required, characterized in that at least two rotor position sensors (8a, 8b) provided for the control units (3a, 3b) are arranged such thatthat they receive the signals from a single rotor position sensor (7) provided on the shaft of the rotor of the electric motor (2).

Description

[0001] The invention relates to a vehicle steering system according to the preamble of claim 1, comprising an electric motor that provides a steering torque and / or a steering angle (at the steerable vehicle wheels) and whose stator and / or rotor are supplied with electronic current as needed via at least two functionally parallel-connected electrical lines by an electronic control unit. This control unit takes into account the steering input of the vehicle driver and / or a vehicle-guiding system. Regarding the prior art, reference is made to DE 10 2010 062 499 A1 and DE 10 2008 049 065 A1.

[0002] Vehicle steering systems with, for example, electric motor-driven steering torque assistance (so-called "power steering systems") are usually designed in the state of the art in such a way that a failure of the steering assistance is defined as a safe condition. This is because, in the event of a failure of the system generating the steering torque assistance (e.g. in the form of a suitably controlled electric motor), the driver can still steer mechanically. The driver's steering wheel is mechanically connected via the steering line to a steering gear, which acts on the steerable wheels via tie rods. Although the steering is then heavier due to the lack of torque assistance, the vehicle remains steerable in accordance with the regulations. However, a failure of the torque assistance is extremely uncomfortable for the driver.

[0003] Vehicle steering systems are currently being developed that are intended to enable highly automated or even autonomous driving. These systems eliminate the driver from the control loop, meaning that the driver temporarily ceases to intervene at all while driving. In these steering systems, an electric motor preferably provides not only assisted steering torque, but also the entire required steering torque and the required steering angle. In such a steering system, failure scenarios that cannot be completely eliminated must be controlled in such a way that the steering system can steer the vehicle without driver intervention at least for a certain period of time, either until the vehicle comes to a standstill or until the driver resumes steering intervention (e.g., after a few seconds).This requires redundancy in the steering system so that it continues to operate (at least with limited performance) even in the event of a fault, which is also referred to as a fail operational system.

[0004] The basic structure of a modern "electromechanical" steering system with electric motor steering assistance is characterized by three essential components, namely firstly a mechanical part which ensures the power transmission from the driver's steering wheel and from the electric motor providing the assistance torque to the steerable wheels of the vehicle, secondly the said electric motor and thirdly an electronic control unit which controls the electrical currents in the electric motor according to the desired functionality (= "demand-based") and switches it off in the event of a fault so that no (undesired) counter-torque is generated in the steering system.The electronic control unit determines the demand-based supply or application of power to the electric motor to generate a desired torque support from the steering input of the driver (with his steering wheel) and / or based on the steering input of some kind of system, preferably an electronic control system, which takes over control of the vehicle instead of the driver, at least for a short time.

[0005] In the attached Fig. Figure 2 shows the electrical circuit diagram of such a conventional electric steering assistance motor, abstracted to its essentials. The three phases of the stator windings of a permanent-magnet synchronous machine are designated by reference numerals 101, 102, and 103, and a direct current voltage source (designated by its two poles "+", "-") is available as the electrical voltage source, which is stabilized by a capacitor 104. A converter, designated as a whole by reference numeral 105, switches this direct current for each phase in such a way that the stator windings 101, 102, and 103 are supplied with three-phase current. For this purpose, a total of six electronic "switches," designed in particular as MOSFETs, are suitably interconnected in the converter 105.

[0006] Between this converter 105 and the stator windings 101, 102, 103, a separate isolating switch, for example also in the form of a MOSFET, is provided for each phase, which are combined here to form an isolating relay 106 and with which the current-free switching mentioned in the previous paragraph is carried out in the event of a fault.

[0007] Even in today's steering systems, the mechanics—that is, the aforementioned "mechanical component" and, essentially, the servomotor (= electric motor)—are designed in such a way that sudden failure over their service life can be virtually eliminated. These two components take up the majority of the installation space required by a steering system and also largely determine the system's weight.

[0008] The remaining electronic control unit is significantly more complex than the previously mentioned "mechanical" components, so failure or shutdown due to misdiagnosis or defective components cannot be completely ruled out over its lifetime. However, the latter is fundamentally undesirable and impermissible in the case of highly automated or autonomous driving, and of course also in steer-by-wire systems.

[0009] DE 10 2010 050 818 A1 shows a motor vehicle with electric power steering. An electric motor is supplied with power by two independently operating units. If one unit fails, the other unit can still provide power.

[0010] DE 10 2010 050 799 A1 discloses a motor vehicle with electric power steering. This motor vehicle includes a steering handle for steering at least one wheel and an electric motor for providing an assisting torque for steering the at least one wheel. The electric motor has at least two winding groups, which are supplied with electric current by at least partially separate units. If one unit fails, the other unit can still supply the associated winding group with current and thus ensure the rotation of the rotor of the electric motor.

[0011] DE 198 34 870 A1 discloses a fault-tolerant electromechanical steer-by-wire steering actuator. This electromechanical steering actuator comprises an electronic control unit that generates steering signals for an electric servomotor that acts on a steering actuator element of a rack-and-pinion steering system via a gear mechanism. The control unit comprises a process computer that supplies control signals to the servomotor via a control unit. The control unit is characterized in that the steering actuator is divided into two diversely redundant systems. The control unit comprises two diversely redundant process computers, each of which supplies the control signals to two diversely redundant servomotors acting on the same steering shaft via an associated diversely redundant control unit.

[0012] DE 603 ​​11 391 T2 relates to a vehicle steering control system and refers in particular to the steer-by-wire design.

[0013] The object of the present invention is therefore to show a measure by means of which the reliability of a vehicle steering system according to the preamble of claim 1 can be significantly increased (= object of the present invention). The solution to this problem provides for at least two parallel-operating control units to provide safety-related redundancy, each of which supplies electrical current to one of the functionally parallel-connected electrical lines of the electric motor as needed. In the vehicle steering system according to the invention, a rotor position sensor of each control unit is arranged such that it receives the signals of a single rotor position sensor provided on the rotor shaft.

[0014] The rotation angle signal of the single rotor of the single electric motor according to the invention, with the exception of the aforementioned functionally parallel and electrically separated lines, is thus received separately by the two (or more) control units according to the invention via their respective individual rotor position sensors, which further increases reliability. Of course, even if more than two electronic control units are provided for any reason, two rotor position sensors, whose signals are fed to these multiple control units, are sufficient to provide safety-related redundancy.

[0015] Further advantageous training and further education are part of the remaining claims.

[0016] The present invention is also based on the consideration that maximum steering power is only necessary for comfortable parking or turning in a few turns, while only a relatively low level of assistance is required during primary vehicle operation. According to the invention, the maximum assistance torque to be provided by the electric motor is therefore divided between two or more "generators," so to speak, so that if one "generator" fails, the other (or more) "generators" can continue to steer the vehicle safely with their remaining torque potential. The term "generator" of assistance torque used here refers to an electric motor including an electronic control unit that controls it appropriately.By definition, a control unit is any electrical-electronic system that, beyond simply conducting electrical current, carries out any switching operations or the like (in the broadest sense) influenced by a variable input variable. The control unit can therefore be formed solely by the or a power output stage and / or contain its necessary peripherals, such as a control circuit for operating the power transistors and / or the control logic for enabling control and motor control. In its most advanced form, a control unit is the complete control and regulation electronics (Electronic Control Unit, "ECU") of the steering system. It should be expressly emphasized again that by no means all of these elements mentioned by way of example need to be contained in a single electronic control unit according to the present invention.Rather, only some of these elements may be part of an electronic control unit according to the invention, while other of these elements may be provided in another additional control unit or the like.

[0017] According to the invention, the aforementioned or such an electronic control unit is physically present at least twice, so that there is simple redundancy of the component of the vehicle steering system with the highest probability of failure. It is advantageous that the installation space required for such an electronic control unit - unlike the installation space required for the additional component "electric motor" - is relatively small. In order to minimize the need for a single electric motor while still being able to provide a certain degree of reliability, according to the invention each electronic control unit supplies so-called "functionally parallel-connected electrical lines" of the electric motor with electrical current as required. These functionally parallel-connected electrical lines can be implemented in different ways.

[0018] The windings of the electric motor can thus be designed with two or more wires running parallel to one another. In some current electric motors, the windings are already designed with several wires connected in parallel for production reasons. According to the invention, these winding wires connected in parallel are assigned or allocated to the various electronic control units in an essentially electrically separate manner. In the case of two control units, each control unit on a single electric motor can thus independently request the provision of, for example, half of the total torque that can be generated by the electric motor if two wires running parallel to one another, in particular of the same diameter, are provided, so that the two control units can coordinate their request for the maximum generateable motor torque without interference.If, in this example, one of the two electronic control units fails, the other still-functional control unit can still supply the steering system according to the invention with 50% of the maximum torque that can be generated as steering torque (namely, as assisted steering torque in the case of "power steering" or as a torque that also adjusts the steering angle in the case of autonomous driving), which is entirely sufficient for many driving conditions of the vehicle. For the sake of completeness, it should be mentioned that, of course, three (or more) wires or electrical lines running parallel to each other can also be distributed asymmetrically between, for example, two control units.In principle, in such a vehicle steering system, the said electrical lines, which are functionally connected in parallel and are thereby continuously connected to one another in a substantially non-current-conducting manner, are continued in the same windings or coils of the single stator and / or (generally) the single rotor of the single electric motor.

[0019] According to a second possibility—as is already common with conventional power steering motors in the form of permanent magnet synchronous machines—the stator of the electric motor can be designed with several coils distributed around the circumference, on which the rotor magnets act. In principle, each phase of the electric motor (briefly explained above) is assigned a group of coils. If two or more coil groups are used per phase, these groups can be electrically separated from one another and distributed evenly among the several, preferably two, electronic control units. This also allows for independent torque generation as described in the previous paragraph.In such a vehicle steering system, the said electrical lines, which are functionally connected in parallel and are not continuously connected to one another in a current-conducting manner, lead to different windings or coils in the single stator and / or (generally) in the single rotor of the single electric motor.

[0020] For the two embodiments just described, compared to the current state of the art, only extended internal wiring is required in the still single electric motor with additional connections for a relatively easily implemented additional electronic control unit. Thus, the vehicle steering system according to the invention can be operated in such a way that if one electronic control unit or one of the said electrical lines fails, the other electronic control unit(s) go into emergency operation, in which the required steering torque is provided as far as possible by the still functional parts of the vehicle steering system. In particular, if such emergency operation is only permitted for a limited period of time, in the sense of an advantageous further development, a (temporary) limited operation with overload, i.e.With a higher torque output than during normal operation, at least until a specified (and suitably monitored) maximum temperature is reached. Autonomously executed driving maneuvers with high energy requirements, such as parking or turning, can alternatively or additionally be performed at a reduced, very slow driving speed. Should a component of the vehicle's steering system fail during such a maneuver, the vehicle can be brought to a halt, at least briefly, by automatic active braking intervention to prevent a dangerous situation from occurring.

[0021] Furthermore, in a vehicle steering system according to the invention, it can be provided that each electronic control unit receives the relevant input data or its relevant input data via its own data bus and / or has its own power supply or electrical voltage supply, thereby significantly further reducing the probability of a total failure by largely avoiding potential sources of error in data transmission and energy supply through redundancy. However, a synchronization connection and / or data exchange connection should be provided between the electronic control units, in particular to synchronize the control of the electric motor in the absence of a fault, but also to transfer important information, for example.to be able to exchange information between the control units in a suitable manner about the implemented steering angle or the torque specified by the driver with his steering wheel or the target steering torque which is essentially derived from these variables and is to be made available by the vehicle steering system.

[0022] For a compact, space-saving arrangement, the two or more electronic control units can be housed in a common housing that is conveniently connected to the electric motor housing. This offers further advantages, for example, with regard to contacting the motor phases, interference current return for electromagnetic compatibility, efficiency due to short electrical cables, and much more.

[0023] Similar to the rotor position sensors described above, at least two sensors provided for the said control units for measuring the steering torque or manual torque specified by the driver (= "steering torque sensors") can be arranged in such a way that they receive the signals of at least one steering torque sensor provided on the shaft of the steering line connected to the driver's steering wheel.

[0024] According to a further development of the operating procedure, if a control unit fails and a steering command is issued by a system controlling the vehicle, the driver can be prompted to take over control of the vehicle. The control unit, which is still functional, can register the driver's takeover using a standard steering torque sensor signal on the steering system connected to the steering wheel, which is familiar to those skilled in the art.

[0025] If necessary, an isolating relay (for example in the form of a so-called phase separator or a star point isolator) can also be provided which becomes effective in the event of a component failure, as described above with reference to Fig. 2 as the current state of the art. Alternatively, in the event of a fault in one phase or in a three-phase system, a suitable counter-torque can be generated by the second or further rotating field system(s) of the electric motor in a vehicle steering system, which counteracts or at least overcomes the braking effect of the failed system. Without compromising safety and / or comfort, a previously required shutdown circuit can thus be eliminated. Fig. 2 With reference to this, the nine current-carrying MOSFET switches provided there can then be replaced by twelve weaker MOSFET switches, six of which each have to carry half the electrical current and are therefore more cost-effective.

[0026] In the attached Fig.1 shows a schematic representation of a steering system according to the invention. Reference numeral 1 denotes a rack-and-pinion steering gear conventional for passenger cars, from which tie rods 1a, 1b extend laterally (top and bottom in the figure), the movement of which into and out of the steering gear 1 is transmitted in a suitable manner to the steerable wheels of the vehicle. The aforementioned displacement of the tie rods 1a, 1b is based on the driver's steering inputs, which the driver transmits to the steering gear 1 using the steering wheel 10 and a connected steering line 10a. To assist the manual torque applied by the driver, an electric motor 2 is provided, which, suitably controlled by two electronic control units 3a, 3b, delivers an assist torque which, via a torque superposition gear 4 provided in the steering gear 1, together with the aforementioned manual torque, causes the desired displacement of the tie rods 1a, 1b.

[0027] For the appropriate control of the electric motor 2, the electronic control units 3a, 3b each receive signals from an associated steering torque sensor 6a, 6b, to which a single steering torque sensor 5 (conventional and known to those skilled in the art) provided on the steering line 10a is assigned. Furthermore, the control units 3a, 3b each receive signals from an associated rotor position sensor 8a, 8b, to which a single rotor position sensor 7 (conventional and known to those skilled in the art) provided on the rotor of the electric motor 2 is assigned. With these essential input variables, "rotor position" and "driver's steering torque" (= so-called manual torque), the two control units 3a, 3b can calculate the torque amount that the electric motor 2 should deliver, possibly taking into account additional information supplied to them via a respective individual data bus 12a, 12b.Accordingly, the control units 3a, 3b supply the electric motor 2 with electrical current, which is supplied to them via their respective individual voltage supplies 11a, 11b.

[0028] As described above, the two control units 3a, 3b with their rotor position sensors 8a, 8b provided therein (i.e. in or on their housing) are suitably arranged for receiving the signals of the single rotor position sensor 7 and, in particular, a common housing for the control units 3a, 3b is connected to the housing of the electric motor 2 for this purpose, which is shown in the figure by the dashed lines between these two "blocks". In particular, however, three electrical lines 9a and 9b are shown in the figure, with lines 9a leading from the control unit 3a and lines 9b leading from the control unit 3b and each leading into the electric motor 2.Not shown in the figure is that the lines 9a, 9b, which each consist of three individual lines because the three phases of the electric motor 2 designed as a permanent magnet synchronous machine are transmitted via the three individual lines, are "electrically separated from one another" (i.e. not electrically connected to one another) within the electric motor and are either continued in the same windings or coils of the (in this case) stator of the electric motor 2 or lead to different windings or coils in the stator. According to the preceding description, this vehicle steering system forms an optimal fail operational system, whereby it should be expressly pointed out that the principle according to the invention can of course also be implemented on other types of electric motors (other than permanent magnet synchronous machines).

Claims

[1] Vehicle steering system with an electric motor (2) which provides a steering torque and / or a steering angle and whose stator and / or rotor is supplied with electrical current as required by an electronic control unit (3a, 3b) via at least two functionally parallel-connected electrical lines (9a, 9b), which control unit (3a, 3b) takes into account the steering input of the driver of the vehicle and / or of a system controlling the vehicle, wherein at least two control units (3a, 3b) operating in parallel are provided to represent safety-related redundancy, each of which supplies one of the functionally parallel-connected electrical lines (9a, 9b) of the electric motor (2) with electrical current as required, characterized bythat at least two rotor position sensors (8a, 8b) provided for the control units (3a, 3b) are arranged such that they receive the signals of a single rotor position sensor (7) provided on the shaft of the rotor of the electric motor (2). [2] Vehicle steering system according to claim 1, characterized by that said functionally parallel-connected and thereby continuously substantially non-current-conducting electrical lines (9a, 9b) are continued in the same windings or coils of the stator and / or rotor. [3] Vehicle steering system according to claim 1 or 2, characterized by that the said functionally parallel-connected and continuously non-conductively connected electrical lines (9a, 9b) lead to different windings or coils in the stator and / or rotor. [4] Vehicle steering system according to one of the preceding claims, characterized bythat each electronic control unit (3a, 3b) receives the relevant input data via its own data bus (12a, 12b) and / or has its own electrical power supply (11a, 11b). [5] Vehicle steering system according to one of the preceding claims, characterized by a synchronization connection and / or data exchange connection between the control units (3a, 3b). [6] Vehicle steering system according to one of the preceding claims, characterized by that the control units (3a, 3b) are provided in a common housing adjoining the housing of the electric motor (2). [7] Vehicle steering system according to one of the preceding claims, characterized by that at least two steering torque sensors (6a, 6b) provided for the control units (3a, 3b) are arranged such that they receive the signals of at least one steering torque sensor (5) provided on the shaft of the steering line (10a) connected to the steering wheel (10).

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