VEHICLE STEERING SYSTEM

Abstract

Vehicle steering system comprising: an input configured to receive a signal (42) representing a target steering angle (δDES); an output configured to provide a torque output command to a steering motor based on the target steering angle (δDES); and a torque limiter module (54) configured to receive the torque output command and apply a torque limit (TDE, TMAX, TLIMIT) to it before providing it to the steering motor (24b), wherein the torque limit (TDE, TMAX, TLIMIT) is dynamically configurable based on at least one vehicle parameter, the at least one vehicle parameter being a steering input parameter applied by a driver; wherein the torque limiter module (54) is configured to maintain the motor torque value as long as a steering input parameter applied by the driver is below a first threshold, the threshold being non-zero.wherein a maximum permissible system torque (TMAX) corresponds to an upper torque threshold (TMAX_AB) as long as the steering input parameter (TFAHRER) is less than a first threshold; wherein the torque limiter module (54) is configured to limit the engine torque value to reduce the influence of the signal proportional to an increase in the steering input parameter applied by the driver when the steering input parameter applied by the driver is above the first threshold and below a second threshold that is higher than the first threshold; and wherein the torque limiter module (54) is configured to reduce the engine torque value to essentially zero when the steering input parameter applied by the driver reaches or exceeds the second threshold; wherein the target steering angle (δDES) is specified by an automated driving control device (6).

Description

TECHNICAL AREA

[0001] The present disclosure relates to a vehicle steering system. Inventive aspects further relate to a method, a control device configured to implement the method, and a vehicle equipped with the system. STATE OF THE ART

[0002] New vehicles are often equipped with one or more Advanced Driver Assistance Systems (ADAS) designed to support driving tasks and thereby enhance the vehicle's functionality. This can be achieved through guidance, warnings, and even intervention to manage driving events, thus improving driving performance, safety, and vehicle usability. Although ADAS features are typically integrated into the vehicle during manufacturing, they are sometimes available as retrofit options for existing vehicles. ADAS features are a focus of extensive research and development and are becoming increasingly sophisticated as the vehicle's ability to perceive and analyze its surroundings improves, enabling greater levels of autonomy.

[0003] Recent developments in driver assistance systems include those that support semi-automated driving, where driver assistance is provided for extended periods. For example, adaptive cruise control (ACC) provides longitudinal vehicle control, maintaining the vehicle's speed at a driver-selected value while appropriate sensor systems monitor the road ahead to ensure the vehicle does not get too close to a vehicle in front. The driver's workload is reduced because they no longer need to regulate braking and acceleration inputs in response to factors such as inclines and approaching vehicles. This would be classified as a "Level 1" system according to the SAE definition of automation levels.An ACC function can operate in combination with, or independently of, another function that provides lateral vehicle control, such as a Lane Centering Assist (LCA) function, more commonly known as a lateral assist function. In known lateral assist functions, onboard sensor systems, which may be camera-based, monitor the road ahead and provide a steering control system that ensures the vehicle remains centered in its lane. However, the driver remains fully responsible for monitoring the surroundings and would need to collaboratively steer the vehicle in situations where lane markings would not necessarily identify the correct lane, such as during lane changes or if an obstacle, such as roadworks, were present in the roadway. When combined with a longitudinal assist function, such as ACC, this becomes a Level 1 system. 2according to the automation levels defined by SAE.

[0004] Furthermore, functionality and stability can be added to create a system of this level. 3 to provide a system in which the driver no longer needs to actively monitor the driving environment. However, such driver assistance systems must allow the driver to resume control at any time in response to an intention of the driver or when the vehicle leaves the conditions under which it can operate autonomously.

[0005] The transition and interaction between human and system control must be as smooth and consistent as possible to enable functions that are both satisfactory and safe to use. The embodiments of the invention have been developed on this basis. BRIEF SUMMARY OF THE INVENTION

[0006] According to one aspect of the invention, a vehicle steering system is provided comprising: an input configured to receive a signal representing a target steering angle; an output configured to provide a torque output command to a steering motor based on the target steering angle; and a torque limiter module configured to receive the torque output command and apply a torque limit to it before providing it to the steering motor, wherein the torque limit is dynamically configurable based on at least one vehicle parameter.

[0007] Embodiments of the invention further relate to a method for controlling the torque output of a vehicle steering system, wherein the method comprises: receiving a signal indicating a desired steering angle; providing a torque output command to a steering motor based on the desired steering angle; and applying a torque limit to the torque output command before the torque output command is provided to the steering motor, wherein the torque limit is dynamically configurable based on at least one vehicle parameter. In other aspects, the invention relates to a control device for a steering system for performing the step of the method as defined above, and further to a vehicle comprising a vehicle steering system as defined above or comprising a control device as defined above.

[0008] The embodiments according to the invention are advantageous in that they improve the interaction and cooperation between human control of a vehicle and automated control of the vehicle by implementing a configurable torque limit that can be requested by the steering motor to achieve a target steering angle, as determined by an automated drive system, for example, a lateral assistance function, in which the configurable limit is dynamically determined based on at least one vehicle parameter. This vehicle parameter can relate to driver control, for example, a steering input parameter applied by a driver.

[0009] The torque limit can decrease in proportion to the magnitude of the steering input parameter applied by the driver. In the illustrated embodiments, the proportional decrease is a linear function, although it can also be configured to be non-linear.

[0010] To provide a further level of control over the configurable torque limit, the torque limit can also depend on a steering angle error, which is the difference between the target steering angle and the actual steering angle provided to the steering system's steering wheel. This allows the torque limit to be configured to account for increasing human control input into the steering system, causing the actual steering angle to deviate from the target steering angle. Here, the steering angle error can form the basis for a weighting function used to vary the proportion with which the torque limit is applied compared to an upper torque threshold.

[0011] The steering input applied by a driver can be based on an output from a torsion bar sensor of the steering system, the torsion bar sensor being operational in response to a driver input at the steering wheel.

[0012] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples, and alternatives presented in the preceding paragraphs, in the claims, and / or in the following description and drawings, and in particular their individual features, may be considered independently of one another or in any combination. This means that all embodiments and / or features of any embodiment may be combined in any way and / or in any combination, provided that these features are not incompatible.The applicant reserves the right to amend any originally filed patent claim or to file any new patent claim accordingly, including the right to amend any originally filed patent claim to depend on and / or incorporate any feature of any other claim, even if it was not previously claimed in this manner. List of characters

[0013] One or more embodiments of the invention are now described by way of example only with reference to the accompanying drawings, which show: Fig. 1 a schematic representation of a vehicle with a steering system according to embodiments according to the invention; Fig. 2. A functional block diagram of the functionality implemented by the steering system; and Fig. 3 Another functional block diagram of a functionality embodied by the steering system. DETAILED DESCRIPTION

[0014] In the following description of specific embodiments of the invention, numerous specific functions are described in detail to enable a comprehensive understanding of the concept according to the claims. However, those skilled in the art will understand that the invention can be implemented without these specific details and that, in some cases, known methods, techniques, and structures have not been described in detail to avoid unnecessarily obscuring the invention.

[0015] In this description, references to a functional block or module should be understood as referring to software code for performing the specified function or action, in which a control output is provided in response to one or more inputs. The code may be in the form of a software routine or function called by a main computer program, or it may be code that forms part of a stream of code that is not a separate routine or function. Reference is made to a functional block for the sake of clarity in explaining how the control device operates.

[0016] This description refers to the term "torque", which in its normal meaning is to be understood as a rotational force with SI units of Nm.

[0017] In relation to Fig. 1 contains a vehicle 2an electronic power assisted steering (EPAS) system 4 and an automated steering control device 6 , which are connected to the EPAS system 4 is coupled. At this point, it should be noted that when control devices and functional modules are described, this serves to explain the functionality performed by these components and does not imply any physical separation of hardware. For example, all of the functions performed by the modules and control devices mentioned herein are implemented in a single execution environment, possibly functionally separated.

[0018] The EPAS system 4 includes a steering wheel 8 , which is via a steering shaft 12 (also called torsion bar) and a gear 14 with a rack 10 is coupled. In order to allow the steering shaft 12an indirect route to the rack 10 takes the steering shaft 12 several wave sections 16 include those that are equipped with suitable swivel joints 18 are coupled together. The gear 14 It could be a pinion gear that controls the rotation of the steering shaft 12 in lateral movement of the rack 10 converts what is a known configuration of the steering system.

[0019] A pair of road bikes 20 is with each end of the rack 10 coupled. It goes without saying that the steering angle of the road wheels 20 by a movement of the rack 10 , which are achieved by turning the steering wheel 8 The way it is controlled varies. Traditionally, the steering angle of the road wheels is... 20 and also the steering wheel 8 through the symbol δ depicted, which is zero when the orientation is straight.

[0020] A torque sensor 22is connected to the steering shaft 12 linked and operational, the torque applied by the driver (torque applied by the driver, T FAHRER ) on the steering wheel 8 to measure and furthermore to provide a measurement of steering wheel position and / or steering angle. Such sensors are a known technology. Other detection techniques can also be used to appropriately measure the torque applied by a driver to the steering shaft. 12 to provide.

[0021] Power steering assist is provided by an EPAS motor and a control module 24 , which will henceforth simply be known as the EPAS module 24 The EPAS module is provided. 24 includes an EPAS control device 24a and an EPAS motor 24b in an integrated package, although this is not mandatory and the two components can be separate. The EPAS module 24is through the linked gear 26 with the rack 10 coupled so that, in addition to the torque applied by the driver, an additional torque is applied to the rack. 10 can be applied. Other configurations are possible, for example, servo control based on hydraulics. As will be described, the EPAS module can 24 furthermore, in a normal driving mode or autonomously without input from the steering shaft 12 They are operated. The interaction between these operating modes is the focus of this description.

[0022] The EPAS module 24 receives an input from the torque sensor 22 and also receives further data from additional sensors, which are referred to here as 32 are characterized, such as vehicle speed and actual steering angle, that is, the steering angle as determined by the rack and pinion. 10specified, and thus the road wheels 20 .

[0023] As experts know, the actual steering wheel angle can be measured from various points. The EPAS module 24 a measure of torque applied by a driver, T FAHRER , from the torque sensor 22 The EPAS module is provided and, based on this information and onboard algorithms and reference tables, determines the parameters. 24 an assist torque T MOTOR , with which the rack 10 via the integrated electric motor 24b to be driven during a normal operating mode in which the automatic driving function is not activated, so that the EPAS module 24 is operated in the usual way by providing steering assistance to the driver's steering input.

[0024] Under circumstances where an automatic driving function of the vehicle is activated, the EPAS module reacts24 also on one controlled by the automated driving control device 6 generated alternative steering command, as will be described.

[0025] The automated driving control device 6 is coupled to a forward-facing sensor system, which in this embodiment is a camera system 34 of the vehicle 2 This concerns [the camera system]. It is known that such camera systems are used in state-of-the-art driver assistance functions, such as lane-keeping assist (LCA), and other autonomous driving routines, and are therefore not described in detail. The camera system 34 The camera system maps the road ahead of the vehicle and determines the vehicle's current position on the road, as well as data related to the vehicle's trajectory. This camera system provides information to the automated driving control system. 6 a road path and vehicle position information via the data signal36 ready.

[0026] The automated driving control device 6 It comprises two main functional modules responsible for the road track and the vehicle position data signal. 36 to interpret and determine the desired or "target" steering angle required to maintain the vehicle's position on the road, as well as to control the way in which the automated driving control device is applied. 6 It interacts with the steering input from the driver. Firstly, the automated driving control device includes 6 a lateral control module 38 , which implements suitable algorithms that process the data signal 36 interpret, and a desired or "target" steering angle d DES outputs. Such functionality is generally known according to the state of the art and will not be described further here.

[0027] The automated driving control device 6 It also includes a dynamic limit calculation module. 40 , whose function is to ensure that the amount of motor torque, which is sent to the electric motor in the form of a torque output command, is correct 24b The steering angle used to achieve a desired steering angle is limited in all circumstances. Typically, such limits are fixed, static values; however, this approach can lead to unrestricted interaction between the vehicle's lateral control, such as that provided by the automated driving control system. 6 regulated, and guide the driver of the vehicle.

[0028] The automated driving control device 6 sends two signals to the EPAS module 24 from: a desired steering angle d DES and a configurable torque limit appropriate to a driver T DE .

[0029] It will now be on Fig. 2. Referenced, the control methodology illustrated, which is a response to the automated driving control device 6 signals provided by the EPAS module 24 will be implemented.

[0030] The desired steering angle d DES is used as an input signal by the EPAS module 42 received and passed through an absolute limit unit 44 or a speed limit unit 46 guided before being routed to a position control algorithm block 50 is entered. The two border units 44 , 46 serve to verify the validity of the input signal 42 to check to ensure that it is within specified permissible limits.

[0031] The position control algorithm block 50 It has the function of calculating a motor torque value. T MOTOR , which serves as the output signal 52on the electric motor 24b is applied. The control algorithm block 50 knows the actual steering angle d ACT as an internal state, since it is connected to the electronic motor 24b is integrated, and thus the engine torque value is determined. T MOTOR calculated to ensure that the actual steering angle d ACT to the desired steering angle d DES is driven towards. Such an algorithm can be suitable feedback control logic designed to provide the desired response and can be based on a PID (proportional-integral-derivative) or similar control routine.

[0032] The output of the motor torque signal T MOTOR from the position control algorithm block 50 is provided by a dynamic limit function 54 supplied, also known as a "torque limiter module", which provides a variable engine torque limit T LIMIT applies. The resulting torque value output is displayed as T MOTOR_L specified. The result of this is that the engine torque T MOTOR_L , which is based on the electronic motor 24b of the EPAS module 24 as a contribution of the automated driving control device 6 is applied, under certain circumstances regulated, in which the driver can also make steering inputs to the steering wheel 8 as will be described in more detail below. This ensures smooth interaction when steering authorization is transferred between the automated driving control device. 6 and is transmitted to the driver. In this way, the driver does not receive excessive and potentially misleading feedback from the steering wheel. 8 .

[0033] The configurable motor torque limit T LIMIT can be calculated in the following way.

[0034] As described above, the dynamic limit calculation module provides 40 the automated steering control device 6 a limit value for a torque appropriate to a driver T DE out and this is converted into a torque limit conversion module 56 entered. The torque limit conversion module 56 converts the torque limit from a value of a “torque corresponding to a driver”, T DE , into a comparable value of the torque at the engine T LIMIT Um. Here, the term "driver-appropriate torque" should be understood as the torque value provided by the automated driving control device. 6 is provided, which is directed by the driver onto the steering shaft 12 applied torque corresponds to achieving the desired steering angle, as determined by the lateral control module 38requested. The ratio between a value of a torque corresponding to a driver, in this case limit value. T DE , and the corresponding value of the torque at the motor, in this case T LIMIT , is a multivariate non-linear function that takes into account vehicle speed, steering wheel angle speed, and servo control curve calibrations used by the EPAS control device. 24b are known.

[0035] The output of the engine torque limit T LIMIT from the torque limit conversion module 56 is split into two signals, one of which is inverted to provide an equivalent and opposite torque limit. T LIMIT_LO to provide. The two torque limits simply represent the torque limit applied to the motor torque when operating in reverse directions, namely to limit the magnitude of the torque regardless of the direction of rotation. Determining the torque limit

[0036] As mentioned above, the dynamic limit calculation module 40 the automated driving control device 6 for setting the engine torque limit T LIMIT by providing a dynamically varying value corresponding to a driver's torque limit T DE responsible, which is then converted into a limit to be applied to the engine torque. The functional block diagram from Fig. Figure 3 illustrates the dynamic limit calculation module 40 The implemented methodology was explained in more detail.

[0037] The dynamic limit calculation module 40 receives three input signals: a desired steering angle d DES , as through the cross-control module 38 determined; an actual steering angle d ACT , as through the EPAS module 24 determined and by the operation of the electric motor 24b derived from the rack 10acts; and also a steering input parameter applied by a driver, which is a torque signal, T FAHRER , from the torque sensor 22 , linked to the steering shaft 12 .

[0038] The general function of the dynamic limit calculation module 40 consists of maximizing the amount of torque that can be generated by the electric motor. 24b during the automatic control of the vehicle 2 onto the rack 10 can be applied based on whether and to what extent the driver of the vehicle 2 a steering input on the steering wheel 8 provides, to regulate. This therefore means that the influence of the automatic driving control device 6The torque is reduced due to the configurable torque limit as the driver begins to increase steering input. This can be advantageous when the driver begins to take control of the vehicle to change direction relative to the track, based on the camera system. 34 through the automatic driving control device 6 The system follows the driver's steering input, thereby increasing the torque applied by the driver. At the same time, the configurable torque limit decreases, reducing the maximum torque that can be applied by the automatic driving control device. 6 The limit that can be applied is reduced. At a predetermined point, the limit is essentially reduced to zero, thus granting the driver full authorization.

[0039] In this embodiment, the dynamic limit calculation module includes 40 a first submodule 60and a second submodule 62 The first submodule 60 receives the torque applied by the driver T FAHRER as an input signal from the torque sensor 22 and, in response, provides a value for a maximum permissible system torque. T MAX from which it is determined that the system should be able to do this via the electric motor 24b onto the rack 10 to apply. The ratio between the two values ​​is determined by the first submodule. 60 in Fig. 3 graphs are inserted to illustrate this.

[0040] In the graph, the x-axis represents the torque applied by the driver. T FAHRER and the Y-axis represents the maximum permissible system torque T MAX . Regarding values ​​of the torque applied by the driver T FAHRER between o and 1 Nm is the maximum permissible system torque value T MAX a constant at 2Nm. This means that the torque limit for small applications of torque to the steering wheel 8 would not be reduced by the system. It should be noted that this constant value can, in principle, be any value and as such would be a configurable parameter. However, 2 Nm is provided here as an example of a realistic torque value corresponding to a driver, which an automated driving function, such as lane centering assist (LCA), should be able to deliver through the electric motor. 24b onto the rack 10 to apply. However, the difference between values ​​of the torque applied by the driver decreases. T FAHRER from 2 Nm and approximately 3.5 Nm is the maximum permissible system torque value T MAX proportional. From the above explanation, it follows that the maximum permissible system torque is proportional. T MAX , which is defined by the first submodule 60 is determined in relation to the magnitude of the increase in torque applied by the driver. T FAHRER reduced, but contains a margin to accommodate minor steering wheel disturbances. 8 to be taken into account. In practice, this therefore means that the automated driving control device 6 The steering control input provided is reduced when the driver begins to steer the car.

[0041] The purpose of the second submodule 62 It consists of regulating the extent to which the maximum permissible system torque can be used. T MAX as the torque limit corresponding to a driver T DE based on the error between the desired steering angle d DES and the actual steering angle d ACT is applied. The angular error is in Fig. 3 as d ERR represented and by the difference unit 66calculated. This means that the second submodule 62 This ensures that the reduction of the torque limit, as described later, only occurs in suitable scenarios. Again, a threshold exists below which small disturbances in the angular error do not affect the output.

[0042] In the graph, the x-axis represents the steering angle error. d ERR , as discussed above, and the Y-axis represents a weighting of T MAX against the maximum absolute torque limit or an upper torque threshold, here referred to as T MAX_AB identified, as can be seen. The weighting is ( w ) for steering angle error values ​​between 0 and 1 (Units of measure) 1 , which corresponds to a 100% weighting towards T MAX_AB corresponds. Consequently, the second submodule gives 62 simply the value T MAX_AB as the torque limit corresponding to a driver T DE to the EPAS module 24 for subsequent conversion into the configurable engine torque limit T LIMIT , as discussed above. However, the weighting between T MAX and T MAX_AB For steering angle error values ​​greater than 1 degree, the torque limit is determined by a predefined gradient that decreases in proportion to the steering angle error. Here, the ratio is shown reduced to zero for an example only, at a steering angle error value of approximately 2.3 degrees. Although the function performing the weighting could be implemented in various ways to control the torque limit depending on the steering angle error, in this embodiment the weighting is represented as T. DE = (w *T MAX_AB ) + ((1-w)*T MAX ) implemented.

[0043] This therefore means that the second submodule 62implements a weighted average function that determines the degree of authorization to use the maximum permissible system torque value T MAX , as through the first submodule 60 intended to provide. For angular error values ​​between 0 and 1 The torque limit is at the upper torque threshold value T MAX_AB set up, which in this embodiment is considered 2 Nm is set (i.e., the weighting is 100% in the direction) T MAX_AB This corresponds to driving situations in which it would not be desirable to override the automated driving control device. 6 to reduce the provided torque input, so that the torque limit is basically set at its maximum value.

[0044] For angular error values ​​above 1 degree, the weighting is gradually increased from T MAX_AB towards T MAX transferred, as by the first submodule 60calculated. It should therefore be noted that in this embodiment, the output for angular error values ​​exceeding 2.3 degrees is 100% of the maximum permissible torque value. T MAX This is weighted. This corresponds to driving situations in which significant deviations of the actual steering angle occur. d ACT , as determined by the driver who is operating the steering wheel 8 moving, which leads to the steering angle error d ERR significantly increased, which leads to a greater influence of the automatic driving control. 6 The provision of steering assistance is reduced to zero.

[0045] For example, two operating situations of the vehicle must be considered, during which the vehicle is controlled by the automated driving control device. 6 is guided by a lane centering assistance function based on information from the camera system. 34 to be received, implemented:

[0046] situation1 - the vehicle travels in a lane of a road or traffic route under the control of the automated driving control device 6 , so that the EPAS module 24 on the automated driving control device 6 provided desired steering angle d DES The driver reacts. The driver then makes a decision to deviate from the current path, for example, either to change lanes or possibly to leave the road. In such a situation, the driver makes a significant steering input through the steering wheel. 8 ready and the support of the automated driving control device 6 is no longer desirable. Such a situation is demonstrable, since the actual steering angle d ACT , as determined by the driver, from the desired steering angle d DES , as through the automated driving control device 6The steering angle, which attempts to follow the road ahead of the vehicle, is determined to be different. This increases the error between the desired steering angle and the actual steering angle. d DES and the actual steering angle d ACT In such a situation, the increase in steering angle would cause the weighting function ( w ), which outputs the maximum permissible torque value T MAX distorted, which leads to the influence of the automatic driving control device 6 , to provide steering assistance, is reduced to zero.

[0047] situation 2 - the vehicle travels in a lane of a road or traffic route under the control of the automated driving module. 6 , so that the EPAS module 24 on the automated driving control device 6 provided desired steering angle d DES It reacts. However, the radius of the road's curvature becomes tighter than the automated driver control device. 6 is entitled to follow this successfully. This requires the driver to make an additional steering input to the steering wheel. 8 to perform adjustments to keep the vehicle in its position on the road. This means that although the driver provides steering input to the steering wheel, the actual steering angle d ACT essentially the desired steering angle d DES within a certain tolerance, for example, 1 degree of the steering angle. In such a situation, where the driver, in addition to the steering control provided by the automated driving control device, 6 Since a steering input is required, it would not be desirable to minimize the influence of the automated driving control device. 6 to reduce, as this would mean that the driver would have to make another course correction.

[0048] Thus, the second submodule works 62 , in order to take into account the two situations described above, and thus provides a means of influencing the weighting based on the monitoring of further system conditions that affect the maximum permissible torque limit T MAX is assigned, which is considered T DE is output, in this case the steering angle error. d ERR This relationship is represented by the one in the second submodule. 62 in Fig. 3 graphs are inserted to illustrate this.

[0049] Numerous modifications can be made to the above examples without deviating from the scope of the present invention as defined in the attached claims.

[0050] In the embodiments described above, reference was made to steering angle values ​​used as input signals. It should be noted that, although these could be direct measurements of the steering angle, they could equally be any value that indicates the steering angle. For example, such values ​​could represent the position of the rack. 10 , the angular direction of the road wheels 20 or another equivalent value. Accordingly, references to the term "steering angle" should be interpreted as referring to any measurement indicating the steering angle of the wheels.

Claims

[1] Vehicle steering system, comprising: an input configured to receive a signal representing a target steering angle; an output configured to provide a torque output command to a steering motor based on the desired steering angle; and a torque limiter module configured to receive the torque output command and apply a torque limit to it before providing it to the steering motor, wherein the torque limit is dynamically configurable based on at least one vehicle parameter. [2] Vehicle steering system according to claim 1, wherein the at least one vehicle parameter includes a steering input parameter applied by a driver. [3] Vehicle steering system according to claim 2, wherein the torque limit decreases in relation to the order of magnitude of the steering input parameter applied by a driver. [4] Vehicle steering system according to claim 2 or 3, wherein the torque limit further depends on a steering angle error which is the difference between the nominal steering angle and an actual steering angle provided to a steering wheel of the steering system. [5] Vehicle steering system according to claim 4, wherein the steering angle error is used to calculate a weighting function which is used to vary the proportion with which the torque limit is applied compared with an upper torque threshold. [6] Vehicle steering system according to any one of claims 2 to 5, wherein the steering input applied by a driver is based on an output from a torsion bar sensor of the steering system, wherein the torsion bar sensor is operational in response to a driver input at the steering wheel. [7] Vehicle steering system according to any one of claims 1 to 6, wherein the target steering angle is provided by automated drive means. [8] Method for controlling the torque output of a vehicle steering system, the method comprising: Receiving a signal indicating a target steering angle; Providing a torque output command to a steering motor based on the desired steering angle; and Applying a torque limit to the torque output command before the torque output command is provided to the steering motor, wherein the torque limit is dynamically configurable based on at least one vehicle parameter. [9] Control device for a steering system for performing the steps of the method according to claim 8. [10] Vehicle comprising a vehicle steering system according to claims 1 to 8 or a control device according to claim 9.