WO2023195907A1

WO2023195907A1 - Electrical steering system and related method

Info

Publication number: WO2023195907A1
Application number: PCT/SE2023/050316
Authority: WO
Inventors: Peter Johansson; Thomas Li; Tayfun HEKIMOGLU
Original assignee: Chassis Autonomy Sba Ab
Priority date: 2022-04-06
Filing date: 2023-04-05
Publication date: 2023-10-12
Also published as: SE546175C2; SE545691C2; SE545628C2; SE545693C2; SE2230180A1; SE2230175A1; SE2250437A1; SE2230176A1; SE546174C2; SE2230177A1; SE2230179A1; SE2230178A1; SE545784C2; SE2230181A1

Abstract

A method and an electrical steering system for steering a vehicle. The method comprises: receiving an electrical steering command, detecting a linear displacement of a shaft with first and second position sensors, comparing the first linear displacement value with the second linear displacement value, and detecting a linear displacement of the shaft with a third position sensor, if the first linear displacement value deviates more than the predetermined value from the second linear displacement value. The method comprises determining a validated linear displacement value. The validated linear displacement value is respectively the second linear displacement value or the first linear displacement value if the third linear displacement value is respectively equal to the second linear displacement value or the first linear displacement value within a respective predetermined value. The method comprises receiving a further electrical steering command based on the validated linear displacement value.

Description

ELECTRICAL STEERING SYSTEM AND RELATED METHOD

Technical field

The present invention relates to electrical steering systems for vehicles, and methods for controlling such electrical steering systems.

Background

When designing vehicular electrical steering systems, also called steer-by- wire, steer-by-actuation or drive-by-wire systems, arguably some important parameters are energy efficiency, low weight and compactness. However, the most critical parameters for realizing a commercial solution, especially when it comes to electrical steering systems in autonomous vehicles, is safety and reliability.

There are some existing solutions aimed at solving this by providing steering systems with improved redundancy in terms of having multiple electrical control units and electrical motors. This way, the system may continue to operate in absence of power input from any specific motor, or if any one of the electrical control units fail.

However, there exists some problems in the prior art. Even though a redundancy in terms of multiplicity of controllers and motors ensure a certain level of reliability, there are still room for improvements, especially when it comes to autonomous vehicles.

Summary

An object of the present invention is therefore to alleviate at least some of the above-mentioned problems with the current state of the art.

According to a first aspect of the present invention, a method for steering a vehicle comprising an electrical steering system is provided, the method comprising: receiving an electrical steering command by at least one controller connected to at least one electrical motor, wherein the at least one electrical motor is configured to rotatably engage with a rotor carrier connected to a linear motion device connected to a shaft so as to actuate the linear motion device in order to displace the shaft along a longitudinal axis of the shaft; detecting a linear displacement of the shaft along the longitudinal axis with a first position sensor, and providing a first linear displacement value to the at least one controller, detecting a linear displacement of the shaft along the longitudinal axis with a second position sensor, and providing a second linear displacement value to the at least one controller; comparing the first linear displacement value with the second linear displacement value; determining a validated linear displacement value, if the first linear displacement value is equal to the second linear displacement value within a predetermined value, such that the validated linear displacement value is the first linear displacement value, and receiving a further electrical steering command by the at least one controller, wherein the further electrical steering command is based on the validated linear displacement value; detecting a linear displacement of the shaft along the longitudinal axis with a third position sensor, if the first linear displacement value deviates more than the predetermined value from the second linear displacement value, and providing a third linear displacement value to the at least one controller; comparing the third linear displacement value with the first and second linear displacement value; and determining a validated linear displacement value, if the third linear displacement value is equal to any one of the first and second linear displacement value within a predetermined value, such that the validated linear displacement value is the second linear displacement value if the third linear displacement value is equal to the second linear displacement value within a predetermined value and is the first linear displacement value if the third linear displacement value is equal to the first linear displacement value within a predetermined value, and receiving a further electrical steering command by the at least one controller, wherein the further electrical steering command is based on the validated linear displacement value.

By providing multiple sources of data regarding the linear displacement of the shaft, a method of steering with improved reliability and safety is provided.

The electrical steering system may comprise a plurality of electrical motors and a plurality of controllers. A controller may be any unit configured for controlling any electrical motor of the electrical steering system. A controller may e.g. be a vehicle control unit (VCU). Preferably, the controller is at least one electrical control unit (ECU). An ECU may be connected to any number of electrical motors. Alternatively, every ECU in a plurality of ECUs may be connected to a single respective electrical motor. As such, sending an electrical steering command may comprise sending an electrical steering command to every ECU. Sending an electrical steering command may comprise sending different steering commands to different ECUs. An electrical steering command may e.g. be sent from a vehicle control unit (VCU). The VCU may e.g. be configured for sending a first electrical steering command to a first ECU connected to a first electrical motor, and a second electrical steering command to a second ECU connected to a second electrical motor.

That a linear displacement value deviates from another linear displacement value is to be understood that the values are not equal to each other, and that they are different over a certain predetermined value. A predetermined value may e.g. be 0.05 mm, or 0.04 mm, or 0.03 mm, or 0.02 mm, or 0.01 mm. Moreover, that a linear displacement value is equal to another linear displacement value is consequently to be understood as the values being within the predetermined value of each other.

Preferably, the first position sensor is different from the second position sensor. In some embodiments, the first position sensor is a linear sensor. A linear sensor is to be understood by the term conventional in the art. A linear sensor is therefore a position sensor capable of detecting an absolute position amongst a continuum of positions. In some embodiments, the second position sensor is a hall effect switch. A hall effect switch may be configured to detect a specific feature of the shaft. A hall effect switch is preferably contactless. A variety of specific features are possible. For example, the hall effect switch may be configured to detect an irregular shape of the shaft. An irregular shape of the shaft may e.g. be a notch in the shaft. In some embodiments, the shaft may be provided with a plurality of notches, such that a hall effect switch is configured to detect the plurality of notches. Alternatively, the hall effect switch may be configured to detect a material irregularity of the shaft. A material irregularity may e.g. be a strip or a dot being made of a material different than the material of the shaft, such that it has different inductive properties. For example, it may be a strip or dot of coating of a magnetic material. By providing two different sensors, i.e. two sensors that sense the same parameter, but in different ways, a more robust, reliable and safe system is provided. Hereby, if the system is affected in a way that only affects one type of sensor, the system will still be provided with reliable shaft position data from at least one source. In other words, common cause failures are avoided. The system may comprise a plurality of hall effect switches. Accordingly, the system may comprise a plurality of specific features configured for interaction with a respective hall effect switch. Alternatively, at least two hall effect switches may be configured to detect the same specific feature of the shaft. Hereby, a system with improved redundancy is provided.

According to at least one embodiment, detecting a linear displacement of the shaft along the longitudinal axis by a second position sensor comprises: detecting a shaft center position with the hall effect switch; and measuring rotation of the rotor carrier by at least one rotation sensor, such that a linear displacement of the shaft along the longitudinal axis may be determined.

Data of rotation of the rotor carrier may therefore be used together with data of a center position as provided by the hall switch sensor so as to determine a position of the shaft. Hereby, a further alternative way of measuring the same parameter, i.e. the position of the shaft, is provided, such that a method with improved redundancy is provided, and common cause failures are avoided.

According to at least one embodiment, detecting a linear displacement of the shaft along the longitudinal axis by a third position sensor comprises measuring rotation of the rotor carrier by a reluctor ring in cooperation with at least one hall effect sensor.

Hereby, a further alternative way of measuring the same parameter, i.e. the position of the shaft, is provided, such that a method with improved redundancy is provided, and common cause failures are avoided.

According to at least one embodiment, detecting a linear displacement of the shaft along the longitudinal axis with a third position sensor comprises measuring an angular position of the rotor with at least one resolver.

According to at least one embodiment, detecting a linear displacement of the shaft along the longitudinal axis by a third position sensor comprises detecting at least one end position of the shaft by an end position sensor, such as an end position hall switch.

Hereby, a further alternative way of measuring the same parameter, i.e. the position of the shaft, is provided, such that a method with improved redundancy is provided. An end position sensor is to be understood as a sensor that detects that the shaft has reached an end position, i.e. that the shaft has been displaced as far as possible in either direction along the longitudinal extension of the shaft. An end position sensor may e.g. be an end position hall switch, an optical sensor, a laser sensor, or an electrical circuit sensor, etc. An end position sensor may further be configured to stop the shaft. Hereby, the shaft may be stopped before reaching a mechanical hard stop, thereby avoiding physical damage to the steering system. The system may comprise a plurality of end position sensors.

According to at least one embodiment, the method further comprises a step of issuing a warning signal if the first linear displacement value deviates from the second linear displacement value and the third linear displacement value deviates from both the first linear displacement value and the second linear displacement value.

Hereby, the steering system may react to a major fault in the steering system.

A warning signal may e.g. be an emergency steering command. The warning signal may e.g. be issued by the at least one controller. An emergency steering command may e.g. be issued by the at least one controller for reducing the speed of the vehicle. Alternatively, the vehicle may be completely stopped. Additionally or alternatively, an emergency steering command may be provided by the at least one controller for steering the vehicle to a side of the road. In some embodiments where the system comprises more than one controller, any one controller may issue a warning signal to another controller. For example, if the system comprises two ECUs, any ECU may issue a warning signal to the other ECU.

According to a second aspect of the present invention, an electrical steering system is provided, the electrical steering system comprising: at least one controller connected to at least one electrical motor and configured for receiving an electrical steering command; a rotor carrier; a linear motion device connected to the rotor carrier; a shaft connected to the linear motion device, wherein the at least one electrical motor is configured to rotatably engage with the rotor carrier so as to actuate the linear motion device in order to displace the shaft along a longitudinal axis of the shaft; a first position sensor configured for detecting a linear displacement of the shaft along the longitudinal axis and providing a first linear displacement value to the at least one controller, a second position sensor configured for detecting a linear displacement of the shaft along the longitudinal axis and providing a second linear displacement value to the at least one controller, and a third position sensor configured for detecting a linear displacement of the shaft along the longitudinal axis and providing a third linear displacement value to the at least one controller; and wherein the at least one controller is configured for comparing the first linear displacement value with the second linear displacement value and, if the first linear displacement value deviates from the second linear displacement value more than a predetermined value, comparing the third linear displacement value with the first and second linear displacement value, and, if the third linear displacement value is equal to any one of the first and second linear displacement value within the predetermined value, determining a validated linear displacement value such that the validated linear displacement value is the second linear displacement value if the third linear displacement value is equal to the second linear displacement value within a predetermined value and is the first linear displacement value if the third linear displacement value is equal to the first linear displacement value within a predetermined value, and receiving a further electrical steering command by the at least one controller, wherein the further electrical steering command is based on the validated linear displacement value.

Any technical effect and benefit relating to the first aspect of the present invention is applicable to the second aspect of the present invention. Specifically, the modifications and embodiments which relates to structural features of the first aspect of the present invention are to be understood as equally applicable for the second aspect of the present invention. The controller may e.g. be a controller having a processor and memory with software such as a vehicle control unit (VCU). Preferably, the at least one controller is an electrical control unit (ECU).

According to at least one embodiment, the linear motion device is a roller screw comprising a rotation sleeve encasing a plurality of planetary rollers, wherein the electrical steering system comprises a further rotation sensor configured for measuring rotation of the rotation sleeve or any one of the plurality of planetary rollers of the roller screw.

By providing an electrical steering system where the linear motion device is a roller screw, a further robust and reliable system is provided, since a linear displacement of the shaft actuated by a roller screw is more precise than that of e.g. a ball screw. Furthermore, owing to the improved precision of the roller screw, by measuring the rotation of the rotation sleeve of the roller screw or any one of the plurality of rolling screws, a more precise determination of the linear displacement of the shaft can be made. Moreover, a roller screw may withstand significantly higher shock loads than e.g. a ball screw. As such, a more durable system is provided.

According to at least one embodiment, the electrical steering system further comprises a linear guiding device arranged on the shaft, the linear guiding device comprising a longitudinal slit such that the shaft is accessible through the bearing, wherein one of the first position sensor and second position sensor is arranged so as to access the shaft through the slit of the linear guiding device.

Hereby, the shaft may be stabilized along the longitudinal axis thereof while at the same time permitting access for the sensor to the shaft. As such, a more compact and space-efficient solution is provided. In some embodiments, the electrical steering system may comprise a quarter-linear bearing such that the shaft is accessible through the bearing for a plurality of position sensors.

According to at least one embodiment, the linear guiding device further comprises a protrusion on an inner surface of the linear guiding device, wherein the shaft further comprises a groove configured for receiving the protrusion so as to rotatably fix the shaft to the linear guiding device.

Hereby, the rotation of the shaft around the longitudinal axis thereof is hindered. Thus, a more mechanically stable solution is provided. Furthermore, by integrating such a mechanism for stopping axial rotation of the shaft into the linear guiding device, a more compact solution is provided.

According to at least one embodiment, the electrical steering system further comprises a warning module configured for issuing a warning signal if the first linear displacement value differs from the second linear displacement value and the third linear displacement value differs from both the first linear displacement value and the second linear displacement value.

Hereby, the steering system may react to a major fault in the steering system.

A warning module may e.g. be at least one ECU or a sub-component thereof. Alternatively, the warning module may be a VCU or a sub-component thereof. Alternatively, a warning module may be a subsystem of the at least one ECU or any other control system.

Brief description of the drawings

These and other variants of the present inventive concept will now be described in more detail, with reference to the appended drawings showing exemplary variants of the present inventive concept, wherein:

Fig. 1 is a schematic view of an electrical steering system according to the second aspect of the present invention.

Fig. 2 is a schematic view of the shaft of Fig. 1 connected to a rod through a ball joint. Fig. 3A is a schematic perspective view of a linear guiding device arranged on a shaft.

Fig. 3B is a cross sectional view of the linear guiding device arranged and the shaft of Fig. 3A.

Fig. 4 is a schematic view of the method according to the first aspect of the present invention.

Detailed description of the drawings

In the following detailed description, some variants of the present inventive concept will be described. However, it is to be understood that features of the different variants are exchangeable between the variants and may be combined in different ways, unless anything is specifically indicated. Even though in the following description, numerous details are set forth to provide a more thorough understanding of the present inventive concept, it will be apparent to one skilled in the art that the present inventive concept may be practiced without these details. In other instances, well known constructions or functions are not described in detail, so as not to obscure the present inventive concept.

Fig. 1 shows an electrical steering system 1 according to the second aspect of the present invention. The electrical steering system 1 comprises at least one controller 2. Here, the controller 2 is at least one electrical control unit (ECU) 2. However, the controller may be any unit configured for controlling the electrical motors of the steering system. For example, a controller may be a vehicle control unit (VCU). Furthermore, the system may comprise any number of controllers. The at least one ECU 2 is configured for receiving an electrical steering command. The at least one ECU 2 may be communicatively connected to a vehicle control system (VCU) (not shown). The system 1 may e.g. comprise two ECUs or three ECUs 2 or four ECUs 2. Alternatively, an ECU 2 may comprise a first subsystem and a second subsystem, wherein each subsystem functions like an ECU. Preferably, the system 1 comprises a first and a second ECU 2. For example, the first ECU 2 is a slave ECU, and the second ECU 2 is a master ECU.

The at least one ECU 2 is connected to at least one electrical motor 3. In Fig. 1 , the ECU 2 is connected to a first and a second electrical motor 3. Each electrical motor 3 comprises a rotor 4 and a stator 5. Here, the two electrical motors 3 are separated by a rotor spacer 7 and a stator spacer 9. The electrical steering system 1 comprises a housing and the components of the electrical steering system 1 are mounted therein. The housing of the electrical steering system 1 is mountable to a vehicle structure (not shown) e.g. a chassis via one or more mounting connections (not shown). The mounting connections may comprise fastener holes configured to receive screw fasteners such as bolts. In some examples, there are preferably three or more mounting connections such that electrical steering system 1 is fixed in a plane with respect to the vehicle structure.

Each rotor 4 is connected to a rotor carrier 11 . The rotor carrier 11 is configured to receive rotational motion of a rotor 4. The rotational motion is transmitted by the rotor carrier 11 to a linear motion device 13. Here, the linear motion device 13 is a screw actuator such as a roller screw or a ball screw. Fig. 1 shows a roller screw 13, however this can alternatively be a ball screw or any other suitable screw actuator. The roller screw 13 comprises a plurality of planetary rollers 15. The plurality of planetary rollers 15 are configured to engage with a threaded portion 17 of the shaft 19. As such, the roller screw 13 is configured to transmit rotational motion of the rotor carrier 11 to the shaft 19. Thus, the at least one electrical motor 3 is configured to rotatably engage with the rotor carrier 11 so as to actuate the roller screw 13 in order to displace the shaft 19 along a longitudinal axis of the shaft 19. In some alternative examples, the roller screw of the linear motion device 13 is replaced with a ball screw (not shown). Likewise, the ball screw is configured to engage with the threaded portion 17 of the shaft 19. Thus, an electrical steering command instructs the at least one ECU 2 on a desired position of the shaft 19, such that the at least one ECU 2 provides, through the rotors 4 of the electrical motors 3, rotational motion so as to displace the shaft 19 to a desired position. In other words, when the rotors 4 rotate with respect to the housing of the electrical steering system 1 , the roller screw 13 rotates and engages with the threaded portion 17. Accordingly, the engagement of the roller screw 13 with the threaded portion 17 causes the shaft 19 to move in a direction along the longitudinal axis of the shaft 19.

The system 1 further comprises a plurality of position sensors for detecting a position, or displacement, of the shaft 19. A first position sensor 21 is in Fig. 1 a linear sensor configured to detect an absolute position amongst a continuum of positions of the shaft 19. As such, the linear sensor 21 is configured for detecting a linear displacement of the shaft 10 along the longitudinal axis thereof and providing a first linear displacement value to the at least one ECU 2. The linear sensor 21 comprises a sensor target 23 and a sensor strip 25, wherein the sensor target 23 is configured to in a contactless manner through magnetic induction detect positions of the sensor strip 25. The sensor strip 25 is arranged on the shaft 19. Thus, movement in the shaft 19 equates to movement of the sensor strip 25, and an absolute position and displacement of the shaft may be detected by the sensor target 23 of the linear sensor 21 .

The system 1 further comprises a second position sensor 27. Here, the second position sensor 27 is a hall effect switch. The hall effect switch 27 is configured to detect a specific feature of the shaft 19. In Fig. 1 , the hall effect switch 27 is configured to detect an irregular shape of the shaft 19. Here, the irregular shape of the shaft 19 is a notch 29. However, the irregular shape may be any machined pattern of the shaft 19 In some embodiments, the shaft 19 may be provided with a plurality of notches 29, such that the hall effect switch 27 is configured to detect the plurality of notches 29. The hall effect switch 27 is therefore configured for detecting a specific position of the shaft 19. Therefore, the hall effect switch 27 may detect displacement of the shaft 19 every time the notch 29 moves past the switch 27. The system 1 further comprises a rotation sensor 31 . Here, the rotation sensors 31 is a resolver. The resolver 31 comprises a resolver rotor 33 and a resolver stator 35 The resolver 31 is configured for measuring rotation of the rotor carrier 11 . Furthermore, the hall effect switch 27 is configured for detecting a center position of the shaft 19. As such, data of rotation of the rotor carrier 11 as provided by the resolver 31 may be used together with data of a center position as provided by the hall effect switch 27 so as to infer position and displacement of the shaft 19. In Fig. 1, the system 1 comprises two resolvers 31 . The resolvers 31 are separated by a resolver rotor spacer 37 and a resolver stator spacer 39.

The system 1 further comprises at least one third position sensor. In Fig. 1 , the system 1 comprises multiple sensors that may function as a third position sensor. In particular, the system 1 comprises multiple sensors that may function as a third position sensor in the method according to the first aspect of the present invention (described in detail in relation to Fig. 3).

The third position sensor may be a reluctor ring 41 in cooperation with a hall effect sensor 43. The reluctor ring 41 is configured for rotating with the rotor carrier 11 . The hall effect sensor 43 is configured for measuring the rotation of the reluctor ring 41 . As such, the hall effect sensor 43 is configured for measuring rotation of the rotor carrier 11 .

The third position sensor may alternatively be an end position sensor 45. Here, the end position sensor 45 is an end position hall switch. Referring now to Fig. 2, where the end position hall switch 45 is shown in more detail. In Fig. 2, the end of the shaft 19 is also shown in more detail. Here, the shaft 19 is connected to a rod 20 by a ball joint 22. It is to be understood that the rod 20 and ball joint 22 is present in any embodiment discussed in relation to Fig. 1. The end position hall switch 45 is configured to detect that the shaft 19 has reached an end position, i.e. that the shaft has been displaced as far as possible in either direction along the longitudinal extension of the shaft 19. The end position hall switch 45 may e.g. detect that an end position of the shaft 19 has been reached by detecting a ball joint housing 24, i.e. the end position hall switch 45 indicates that an end position is reached when the ball joint housing 24 is within a predetermined distance from the end position hall switch 45. The end position hall switch 45 may further be configured to stop the shaft 19, such that the shaft 19 is prevented from moving further than the end position.

The first position sensor 21 , the second position sensor 27 and the third position sensor 43, 45 are configured for detecting a linear displacement of the shaft 19 along the longitudinal axis thereof and for providing a first, second and third linear displacement value to the ECU 2. The ECU 2 is configured for comparing the first linear displacement value with the second linear displacement value. If the first linear displacement value deviates from the second linear displacement value more than a predetermined value. A predetermined value level may e.g. be 0.05 mm, or 0.04 mm, or 0.03 mm, or 0.02 mm, or 0.01 mm. The ECU 2 is configured for comparing the third linear displacement value with the first and second linear displacement value. If the third linear displacement value is equal to any one of the first and second linear displacement value within the predetermined value, the ECU 2 is configured for determining a validated linear displacement value such that the validated linear displacement value is the second linear displacement value if the third linear displacement value is equal to the second linear displacement value within a predetermined value and is the first linear displacement value if the third linear displacement value is equal to the first linear displacement value within a predetermined value. The ECU 2 is furthermore configured for receiving a further electrical steering command, wherein the further electrical steering command is based on the validated linear displacement value.

The system 1 further comprises a linear guiding device 47.

In Fig. 3A and 3B, the linear guiding device 47 is shown in more detail. The linear guiding device 47 is arranged on the shaft 19, such that it prevents the shaft 19 from pivoting in any direction transverse to the longitudinal extension of the shaft 19. As such, the linear guiding device 47 may be a half-linear bearing, a quarter-linear bearing, a ball spline, a ball spline bearing or a sliding bushing, etc. The linear guiding device 47 further comprises a longitudinal slit 49 such that the shaft 19 is accessible through the bearing 47. As such, one of the first position sensor and second position sensor may be arranged so as to access the shaft 19 through the slit 49 of the linear guiding device 47. In Fig. 1 , the sensor strip 25 of the linear sensor 21 is arranged such that it may slide through the slit 49 when the shaft 19 is moving. Furthermore, the sensor strip 25 is accessible for the sensor head 23 through the slit 49. The linear guiding device 47 further comprises a protrusion 51 on an inner surface 53 of the linear guiding device 47. The shaft 19 further comprises a groove 55 configured for receiving the protrusion 51 so as to rotatably fix the shaft 19 to the linear guiding device 47. Hereby, rotation of the shaft 19 around the longitudinal axis thereof is hindered. In Fig. 3A and Fig. 3B, the linear guiding device 47 comprises two protrusions 51 and the shaft 19 comprises two grooves 55.

Fig. 4 is a flow chart of the method for steering a vehicle comprising an electrical steering system according to the first aspect of the present invention. During receiving S1 , an electrical steering command by at least one controller connected to at least one electrical motor 3 is received. The at least one electrical motor 3 is configured to rotatably engage with a rotor carrier 11 connected to a linear motion device 13 connected to a shaft 19 so as to actuate the linear motion device 13 in order to displace the shaft 19 along a longitudinal axis of the shaft 19. The electrical steering command may e.g. be received from a vehicle control unit (VCU), an electrical control unit (ECU). The electrical steering command instructs the controller 2 which position the shaft 19 is to, such that the controller 2 may, by the at least one electrical motor 3, apply an adequate amount of torque to the linear motion device 13, such that the shaft 19 is adequately displaced.

Detecting S2 a linear displacement of the shaft 19 along the longitudinal axis is performed with a first position sensor 21, thereby providing a first linear displacement value to the at least one controller 2. Detecting S3 a linear displacement of the shaft 19 along the longitudinal axis is performed with a second position sensor 27, thereby providing a second linear displacement value to the at least one controller 2.

Thereafter, comparing S4 the first linear displacement value with the second linear displacement value is performed. If the first linear displacement value is equal to the second linear displacement value within a predetermined value, determining S5 a validated linear displacement value, such that the validated linear displacement value is the first linear displacement value, is performed. The steps of comparing S4 and determining S5 a validated displacement value is performed by the controller 2. After the controller 2 has determined S5 a validated displacement value, receiving S6 a further electrical steering command by the controller 2 is performed. The further electrical steering command is based on the validated linear displacement value.

If the first linear displacement value deviates more than the predetermined value from the second linear displacement value, detecting S7 a linear displacement of the shaft 19 along the longitudinal axis is performed by a third position sensor 45, thereby providing a third linear displacement value to the at least one controller 2. Afterwards, comparing S8 the third linear displacement value with the first and second linear displacement value is performed. If the third linear displacement value is equal to any one of the first and second linear displacement value within a predetermined value, determining S9 a validated linear displacement value, such that the validated linear displacement value is the second linear displacement value if the third linear displacement value is equal to the second linear displacement value within a predetermined value and is the first linear displacement value if the third linear displacement value is equal to the first linear displacement value within a predetermined value, is performed. After the controller 2 has determined S9 a validated displacement value, receiving S10 a further electrical steering command by the controller 2 is performed. The further electrical steering command is based on the validated linear displacement value.

Optionally the method further comprises a step of issuing S11 a warning signal. Issuing S11 a warning signal is performed if the first linear displacement value deviates from the second linear displacement value. Furthermore, issuing S11 a warning signal is performed if the third linear displacement value deviates from both the first linear displacement value and the second linear displacement value. A warning signal may e.g. be an emergency steering command. The warning signal may e.g. be issued by the at least one controller 2. The warning signal may e.g. be sent to another controller 2, such as a VCU. An emergency steering command may e.g. be issued by the at least one controller 2 for reducing the speed of the vehicle. Alternatively, the vehicle may be completely stopped.

It should be noted that Fig. 1 shows a side view of an electrical steering system 1 e.g. steer-by-wire steering assembly. The electrical steering system 1 is generally elongate in construction and extends along a longitudinal axis of the shaft 19. As discussed below, one or more components of the electrical steering system 1 are aligned along the longitudinal axis thereof.

The electrical steering system 1 as shown in Fig. 1 is coupled to a rod 20 e.g. a first tie rod 20 at a first end 106 of the electrical steering system 1 . The electrical steering system 1 is also coupled to a second tie rod (not shown) at a second end of the electrical steering system 1 .

The electrical steering system 1 is coupled to the first tie rod 20 with a first tie rod coupling e.g. ball joint 22 (best shown in Fig 2).

The electrical steering system 1 comprises a first bellow sleeve and a second bellow sleeve which extends over and covers the shaft 19 respectively at the first end and the second end of the electrical steering system 1 . The first bellow sleeve and the second bellow sleeve protect the steering shaft 19 and the first and second tie rod couplings from dirt and debris. The first and second bellow sleeves are mounted to the main housing and permit relative movement of the first and second tie rods 20 with respect to the main housing whilst maintaining a seal against the main housing and the first and second tie rods 20.

The first and second tie rods 20 are respectively connected to a first tie rod end and a second tie rod end. The first and second tie rod ends 20 are configured to be respectively pivotally connected to a first and second steering knuckle, for example this may be a ball-joint (not shown). The wheel bearing assemblies of a vehicle are operatively mounted to the first and second steering knuckles. The wheels of the vehicle are mounted to the respective wheel bearing assemblies. The tie rods, steering knuckles, and wheel bearing assemblies are known and will not be discussed in any further detail.

The person skilled in the art realizes that the present invention by no means is limited to the variants described above. The features of the described variants may be combined in different ways, and many modifications and variations are possible within the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of other elements or steps than those listed in the claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

Claims

1 . Method for steering a vehicle comprising an electrical steering system, the method comprising: receiving an electrical steering command by at least one controller connected to at least one electrical motor, wherein the at least one electrical motor is configured to rotatably engage with a rotor carrier connected to a linear motion device connected to a shaft so as to actuate the linear motion device in order to displace the shaft along a longitudinal axis of the shaft; detecting a linear displacement of the shaft along the longitudinal axis with a first position sensor, and providing a first linear displacement value to the at least one controller; detecting a linear displacement of the shaft along the longitudinal axis with a second position sensor, and providing a second linear displacement value to the at least one controller; comparing the first linear displacement value with the second linear displacement value; determining a validated linear displacement value, if the first linear displacement value is equal to the second linear displacement value within a predetermined value, such that the validated linear displacement value is the first linear displacement value, and receiving a further electrical steering command by the at least one controller, wherein the further electrical steering command is based on the validated linear displacement value; detecting a linear displacement of the shaft along the longitudinal axis with a third position sensor, if the first linear displacement value deviates more than the predetermined value from the second linear displacement value, and providing a third linear displacement value to the at least one controller; comparing the third linear displacement value with the first and second linear displacement value; and determining a validated linear displacement value, if the third linear displacement value is equal to any one of the first and second linear displacement value within a predetermined value, such that the validated linear displacement value is the second linear displacement value if the third linear displacement value is equal to the second linear displacement value within a predetermined value and is the first linear displacement value if the third linear displacement value is equal to the first linear displacement value within a predetermined value, and receiving a further electrical steering command by the at least one controller, wherein the further electrical steering command is based on the validated linear displacement value.

2. Method according to claim 1 , wherein the first position sensor is a linear sensor.

3. Method according to claim 1 or 2, wherein the second position sensor is a hall effect switch.

4. Method according to claim 3, wherein detecting a linear displacement of the shaft along the longitudinal axis with a second position sensor comprises: detecting a shaft center position with the hall effect switch; measuring rotation of the rotor carrier by at least one rotation sensor, such as a resolver, and calculating a linear displacement of the shaft along the longitudinal axis based on the detected shaft center position and the measured rotation of the rotor.

5. Method according to any preceding claim, wherein detecting a linear displacement of the shaft along the longitudinal axis by a third position sensor comprises measuring rotation of the rotor carrier with a reluctor ring in cooperation with at least one hall effect sensor.

6. Method according to any one of claims 1 to 5, wherein detecting a linear displacement of the shaft along the longitudinal axis with a third position sensor comprises detecting at least one end position of the shaft with an end position sensor, such as a end position hall switch.

7. The method according to any one of the preceding claims, further comprising a step of issuing a warning signal if the first linear displacement value deviates from the second linear displacement value and the third linear displacement value deviates from both the first linear displacement value and the second linear displacement value.

8. Method according to any one of the preceding claims, wherein the at least one controller is an electrical control unit (ECU).

9. Method according to any one of claims 1-7, wherein the at least one controller is a vehicle control unit (VCU)

10. Electrical steering system for a vehicle, comprising: at least one controller connected to at least one electrical motor and configured for receiving an electrical steering command; a rotor carrier; a linear motion device connected to the rotor carrier; a shaft connected to the linear motion device, wherein the at least one electrical motor is configured to rotatably engage with the rotor carrier so as to actuate the linear motion device in order to displace the shaft along a longitudinal axis of the shaft; a first position sensor configured for detecting a linear displacement of the shaft along the longitudinal axis and providing a first linear displacement value to the at least one controller, a second position sensor configured for detecting a linear displacement of the shaft along the longitudinal axis and providing a second linear displacement value to the at least one controller, and a third position sensor configured for detecting a linear displacement of the shaft along the longitudinal axis and providing a third linear displacement value to the at least one controller; and wherein the at least one controller is configured for comparing the first linear displacement value with the second linear displacement value and, if the first linear displacement value deviates from the second linear displacement value more than a predetermined value, comparing the third linear displacement value with the first and second linear displacement value, and, if the third linear displacement value is equal to any one of the first and second linear displacement value within the predetermined value, determining a validated linear displacement value such that the validated linear displacement value is the second linear displacement value if the third linear displacement value is equal to the second linear displacement value within a predetermined value and is the first linear displacement value if the third linear displacement value is equal to the first linear displacement value within a predetermined value, and receiving a further electrical steering command by the at least one controller, wherein the further electrical steering command is based on the validated linear displacement value.

11 . Electrical steering system according to claim 10, wherein the first position sensor is a linear sensor.

12. Electrical steering system according to claim 10 or 11, wherein the second linear position sensor is a hall effect switch.

13. Electrical steering system according to any one of claims 10 to 12, further comprising at least one rotation sensor configured for measuring rotation of the rotor carrier.

14. Electrical steering system according to claim 13, wherein the linear motion device is a roller screw comprising a rotation sleeve encasing a plurality of planetary rollers, wherein the electrical steering system comprises a further rotation sensor configured for measuring rotation of the rotation sleeve or any one of the plurality of planetary rollers of the roller screw.

15. Electrical steering system according to any one of claims 10 to 14, further comprising a linear guiding device arranged on the shaft, the linear guiding device comprising a longitudinal slit such that the shaft is accessible through the bearing, wherein one of the first position sensor and second position sensor is arranged so as to access the shaft through the slit of the linear guiding device.

16. Electrical steering system according to claim 15, wherein the linear guiding device further comprises a protrusion on an inner surface of the linear guiding device, wherein the shaft further comprises a groove configured for receiving the protrusion so as to rotatably fix the shaft to the linear guiding device.

17. Electrical steering system according to any one of claims 10 to 16, wherein the third position sensor is a reluctor ring in cooperation with at least one hall effect sensor configured for measuring rotation of the rotor carrier.

18. Electrical steering system according to any one of claims 10 to 16, wherein the third position sensor is an end position sensor, such as an end position hall switch, configured for detecting an end position of the shaft.

19. Electrical steering system according to any one of claims IQ- 18, further comprising a warning module configured for issuing a warning signal if the first linear displacement value differs from the second linear displacement value and the third linear displacement value differs from both the first linear displacement value and the second linear displacement value.

20. Electrical steering system according to any one of claims 10 to 19, wherein the at least one controller is an electrical control unit (ECU).

21 . Electrical steering system according to any one of claims 10 to 19, wherein the at least one controller is a vehicle control unit (VCU).