Torque compensation device and method for sudden steering action in a motor-driven power steering system

Abstract

Torque compensation device for an MDPS (Motor Driven Power Steering) system, including: a steering column torque sensor (100) configured to detect a steering column torque applied to a steering shaft; a steering angle sensor (200) configured to detect a steering angle (θ) of a steering wheel; and a control device (400) configured to calculate a compensation ratio for a sudden steering operation based on one or more of the steering column torques detected by the steering column torque sensor (100) and a steering angle velocity calculated from the steering angle (θ) detected by the steering angle sensor (200), and to differentially compensate the basic auxiliary torque output by the MDPS system according to the compensation ratio, further comprising a vehicle speed sensor (300) configured to detect a vehicle speed, characterized by that the control device (400) further calculates the compensation ratio taking into account the vehicle speed detected by the vehicle speed sensor (300). and that the control device (400) calculates the compensation ratio based on a steering column torque compensation gain factor, which is calculated as a larger value when the steering column torque increases in a preset torque compensation section, a steering angle velocity compensation gain factor, which is calculated as a larger value when the steering angle velocity increases in a preset angular velocity compensation section, and a vehicle speed compensation gain factor, which is calculated as a larger value when the vehicle speed increases in a preset vehicle speed compensation section, wherein, when the compensation ratio has a value between 0 and 1, the control device (400) compensates the base auxiliary torque by adding a sudden steering action compensation torque to the base auxiliary torque,where the sudden steering compensation torque is calculated as the product of the basic auxiliary torque and the compensation ratio.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a torque compensation device and a torque compensation method for an MDPS (Motor Driven Power Steering) system and in particular to a torque compensation device and a torque compensation method for an MDPS system which are capable of compensating the auxiliary torque of the MDPS system during a sudden steering operation.

[0002] The MDPS system is a system that allows the driver to perform a steering operation effortlessly by generating part of the steering force that the driver must apply to a steering wheel when steering a vehicle using an auxiliary power source.

[0003] The MDPS system determines the vehicle's driving conditions via a steering column torque sensor to measure driver steering column torque applied to the steering wheel, a steering angle sensor to measure steering angle or steering angle velocity of the steering wheel, and a vehicle speed sensor to measure vehicle speed, and generates an auxiliary torque based on the steering column torque by means of an electric motor, which is applied to a steering shaft when the driver operates the steering wheel.

[0004] Unlike existing hydraulic steering systems, the MDPS system generates torque by controlling the motor's electrical output. This control is managed by a control unit such as an ECU (Electronic Control Unit). The system therefore incorporates various control logic devices for motor operation. These include logic for implementing a driver-desired steering feel, logic aimed at improving vehicle stability, and logic for enhancing overall system stability. The output signals of each logic device are generated according to preset tuning parameter values.

[0005] The MDPS motor has an output torque that decreases with increasing operating speed, and the auxiliary torque output by the MDPS system depends on the tuning parameters of the respective logic devices. Therefore, if the tuning parameters of the respective logic devices are incorrectly set, the driver may experience a heavy steering feel during a sudden steering maneuver. Furthermore, because damping logic and feedback logic, which are included in the MDPS system for performing damping and feedback functions, amplify the vehicle's self-aligning torque, the response to the sudden steering maneuver may be impaired. A torque compensation device for an MDPS system with the features of the preamble of claim 1 is known from US 2009 / 0266641 A1.KR 10 2003 0 033 845 A discloses a torque compensation device for an MDPS system with a sudden steering assistance control. Another torque compensation device for an MDPS system is known from DE 10 2012 107 597 A1.

[0006] The prior art relevant to the present invention is disclosed in Korean patent publication KR 2013 0066835 A, filed on June 21, 2013. OVERVIEW OF THE INVENTION

[0007] Embodiments of the present invention relate to a torque compensation device and a torque compensation method for an MDPS system, by means of which the degree of freedom during tuning can be reliably ensured and the problem of a driver experiencing a stiff steering feel during a sudden steering maneuver can be solved. This stiffness occurs when output signals from logic devices included in the conventional MDPS system are based on tuning parameters. It is therefore an object of the present invention to provide an improved torque compensation device for an MDPS system and a corresponding torque compensation method with respect to sudden steering maneuvers. This object is achieved by the features of claims 1 and 3, respectively.

[0008] According to one embodiment, a torque compensation device for an MDPS system comprises: a steering column torque sensor configured to detect a steering column torque applied to a steering shaft; a steering angle sensor configured to detect a steering angle of a steering wheel; and a control device configured to calculate a compensation ratio during a sudden steering operation based on one or more of the steering column torques detected by the steering column torque sensor and a steering angle velocity calculated from the steering angle detected by the steering angle sensor, and to differentially compensate the basic auxiliary torque output by the MDPS system according to the compensation ratio.

[0009] The torque compensation device further includes a vehicle speed sensor configured to detect a vehicle speed, the control device further calculating the compensation ratio taking into account the vehicle speed detected by the vehicle speed sensor.

[0010] The control device calculates the compensation ratio based on a steering column torque compensation gain factor, which is calculated as a larger value when the steering column torque increases in a preset torque compensation section, a steering angle velocity compensation gain factor, which is calculated as a larger value when the steering angle velocity increases in a preset angular velocity compensation section, and a vehicle speed compensation gain factor, which is calculated as a larger value when the vehicle speed increases in a preset vehicle speed compensation section.

[0011] If the compensation ratio has a value between 0 and 1, the control device compensates the basic auxiliary torque by adding a sudden steering compensation torque to the basic auxiliary torque, the sudden steering compensation torque being calculated as the product of the basic auxiliary torque and the compensation ratio.

[0012] The control device cannot compensate for the basic auxiliary torque when the compensation ratio is 0, but can compensate for the basic auxiliary torque using a preset maximum auxiliary torque when the compensation ratio is 1.

[0013] According to a further embodiment, a torque compensation method for an MDPS system comprises: determining, by means of a control device, whether a steering state of a vehicle is a sudden steering state, based on one or more steering column torques and steering angular velocity; calculating, by means of the control device, a compensation ratio for a sudden steering operation based on one or more steering column torques and steering angular velocity, if the steering state of a vehicle is a sudden steering state; and differentially compensating, by means of the control device, the basic auxiliary torque output by the MDPS system according to the compensation ratio.

[0014] When calculating the compensation ratio, the control device also calculates the compensation ratio taking into account the vehicle speed.

[0015] When calculating the compensation ratio, the control device calculates the compensation ratio based on a steering column torque compensation gain factor, which is calculated as a larger value when the steering column torque increases in a preset torque compensation section, a steering angle velocity compensation gain factor, which is calculated as a larger value when the steering angle velocity increases in a preset angular velocity compensation section, and a vehicle speed compensation gain factor, which is calculated as a larger value when the vehicle speed increases in a preset vehicle speed compensation section.

[0016] When compensating the basic auxiliary torque, if the compensation ratio has a value between 0 and 1, the control device compensates the basic auxiliary torque by adding a sudden steering compensation torque to the basic auxiliary torque, the sudden steering compensation torque being calculated as the product of the basic auxiliary torque and the compensation ratio.

[0017] When compensating the base auxiliary torque, the control device can compensate the base auxiliary torque using the preset maximum auxiliary torque if the compensation ratio has a value of 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a block diagram of a torque compensation device intended for an MDPS system according to an embodiment of the present invention. Fig. Figure 2 shows an operation of the torque compensation device provided for an MDPS system according to the embodiment of the present invention. Fig. Figure 3 shows a flowchart to illustrate a torque compensation method provided for an MDPS system according to an embodiment of the present invention. DESCRIPTION OF SPECIAL EXECUTION FORMS

[0018] The following describes in detail a torque compensation device and a torque compensation method for an MDPS system according to an embodiment of the present invention, with reference to the accompanying drawings. It should be noted that the drawings are not precisely to scale and may be exaggerated with regard to line thickness or the size of components, solely for the sake of clarity and comprehensibility. Furthermore, the terms used here are chosen with consideration for the functions of the invention and may be modified according to the custom or intention of the users or operators. Therefore, the definitions of the terms are to be understood in accordance with the entirety of the disclosures presented herein.

[0019] Fig. Figure 1 shows a block diagram of a torque compensation device intended for an MDPS system according to an embodiment of the present invention, and Fig. Figure 2 shows an operation of the torque compensation device provided for an MDPS system according to the embodiment of the present invention.

[0020] According to Fig. 1 The torque compensation device provided for an MDPS system according to the embodiment of the present invention can comprise a steering column torque sensor 100, a steering angle sensor 200, a vehicle speed sensor 300 and a control device 400.

[0021] The steering column torque sensor 100 detects the steering column torque Tcol applied to a steering shaft when the driver operates a steering wheel and outputs the detected steering column torque Tcol to the control device 400. The detected steering column torque Tcol is used when the control device 400 calculates the basic auxiliary torque and a compensation ratio that depends on a sudden steering operation, as described below.

[0022] The steering angle sensor 200 detects a steering angle θ of the steering wheel and transmits the detected steering angle θ to the control device 400. The steering angle sensor 200 can include an optical sensor for detecting a steering angle velocity ω. Furthermore, the steering angle sensor 200 can measure the steering angle θ and differentiate the measured steering angle with respect to time in order to detect the steering angle velocity ω. According to another embodiment, the control device 400 can receive the steering angle θ from the steering angle sensor 200 and calculate the steering angle velocity ω by differentiating the steering angle θ with respect to time. In the present embodiment, however, the steering angle sensor 200 can detect the steering angle θ and the steering angle velocity ω and transmit the detected steering angle and the detected steering angle velocity to the control device 400.The steering angle θ and the steering angle velocity ω can be used when the control device 400 calculates the basic auxiliary torque and the compensation ratio, which depends on a sudden steering operation, as will be described later.

[0023] The vehicle speed sensor 300 detects the vehicle speed V of the vehicle in operation and transmits the detected vehicle speed V to the control device 400. The vehicle speed sensor 300 can have various sensors, for example, a sensor for detecting the vehicle speed V using the angular velocity of a wheel, a sensor for detecting the vehicle speed V by measuring rpm (revolutions per minute), and a sensor for detecting the vehicle speed V using GPS (Global Positioning System). The detected vehicle speed V can be used when the control device 400 calculates the basic auxiliary torque and the compensation ratio, which depends on a sudden steering maneuver, as described below.

[0024] The control device 400 is able to calculate the compensation ratio in the event of a sudden steering operation on the basis of one or more of the steering column torque Tcol detected by the steering column torque sensor 100 and the steering angle velocity ω, which is calculated from the steering angle θ detected by the steering angle sensor 200, and to differentiate compensation of the basic auxiliary torque output by the MDPS system 410 according to the compensation ratio.

[0025] The following describes the operation of the control device 400 when compensating the basic auxiliary torque, based on... Fig. 2 described in detail. According to Fig. 2 The control device 400 includes an MDPS system 410, a compensation ratio calculation device 430 and a selector 450. Fig. Figure 2 shows that the MDPS system 410 is included in the control device 400. However, according to another embodiment, the MDPS system 410 can be implemented independently in parallel to the control device 400. In this case, the control device 400 can receive the basic auxiliary torque from the MDPS system 410 and compensate for the basic auxiliary torque according to the sudden steering operation.

[0026] The MDPS system 410 is capable of calculating the basic auxiliary torque based on a main auxiliary torque calculated by a boost calculation unit 411 and a self-aligning torque calculated by a damping calculation unit 413 and a return calculation unit 415. Since the process of calculating the basic auxiliary torque using the MDPS system 410 is publicly known to experts in the field, it is not described in detail here.

[0027] As described above, the basic auxiliary torque, which is calculated based on the main auxiliary torque and the self-aligning torque, is based on the preset tuning parameters without taking into account compensation for a sudden steering maneuver. Therefore, according to the present embodiment, the control device 400 is provided that, by means of the compensation ratio calculation device 430 and the selector 450, it can calculate a predetermined compensation ratio and can compensate the basic auxiliary torque differentially according to the calculated compensation ratio.

[0028] The compensation ratio calculator 430 calculates the compensation ratio during a sudden steering maneuver based on one or more of the steering column torque Tcol and the steering angular velocity ω. This means that, since the steering column torque Tcol or the steering angular velocity ω increases rapidly due to the sudden steering maneuver initiated by the driver, the compensation ratio calculator 430 determines the sudden steering maneuver and calculates the compensation ratio based on one or more of the steering column torque Tcol and the steering angular velocity ω. The compensation ratio calculator 430 also calculates the compensation ratio using only one of the steering column torque Tcol and the steering angular velocity ω.Preferably, however, the compensation ratio calculation device 430 can calculate the compensation ratio using both the steering column torque Tcol and the steering angular velocity ω to improve the precision of determining the sudden steering operation and calculating the compensation ratio.

[0029] The compensation ratio calculation device 430 further calculates the compensation ratio taking into account the vehicle speed V calculated by the vehicle speed sensor 300. This is advantageous because, when the vehicle is traveling at high speed, a higher compensation torque must be calculated to assist the driver's sudden steering maneuver in order to effectively prevent a collision with an external obstacle. Conversely, when the vehicle is traveling at low speed, the compensation torque required to avoid a collision may be lower than when the vehicle is traveling at high speed.Therefore, it is provided that the compensation ratio calculation device 430 further calculates the compensation ratio taking into account the vehicle speed V, thereby further improving the driver's steering feel against a sudden steering feel, while effectively avoiding a collision with an obstacle.

[0030] The following section describes in detail the procedure for calculating the compensation ratio.

[0031] The compensation ratio calculation device 430 calculates the compensation ratio on the basis of a steering column torque compensation gain factor, a steering angle velocity compensation gain factor and a vehicle speed compensation gain factor, which are calculated from the steering column torque Tcol or the steering angle velocity ω or the vehicle speed V.

[0032] In particular, the compensation ratio calculation device 430 is capable of calculating the compensation ratio based on the steering column torque compensation gain factor, which according to Fig. 2 is calculated as a larger value when the steering column torque increases in a preset torque compensation section [A, B], the steering angle velocity compensation gain factor is calculated as a larger value when the steering angle velocity increases in a preset angular velocity compensation section [C, D], and the vehicle speed compensation gain factor is calculated as a larger value when the vehicle speed increases in a preset vehicle speed compensation section [E, F].

[0033] The torque compensation section and the angular velocity compensation section can specify a steering column torque section and a steering angular velocity section, respectively, in which the basic auxiliary torque must be compensated for due to a sudden steering input by the driver. These sections are preset to establish reference values ​​used to determine whether the driver is making a sudden steering input. The vehicle speed compensation section can specify a preset reference vehicle speed section to prevent a collision with an external obstacle. Depending on the MDPS system specification and the results of tests performed by the designer, the torque compensation section, the angular velocity compensation section, and the vehicle speed compensation section can be configured in various ways and preset in the control device 400.

[0034] If the steering column torque Tcol is detected as a value that corresponds to the minimum steering column torque (value A in Fig. 2) If the torque compensation section is equal to or less than this, the compensation ratio calculation device 430 can determine that no sudden steering action by the driver has been detected and set the steering column torque compensation gain factor to 0. Furthermore, if the steering column torque Tcol is detected as a value that is equal to the maximum steering column torque (value B in Fig. 2) If the torque compensation factor of the torque compensation section is equal to or greater than this value, the compensation ratio calculation device 430 sets the steering column torque compensation gain factor to 1 to prevent excessive torque compensation. In the torque compensation section, the steering column torque compensation gain factor can be calculated as a larger value if the steering column torque Tcol increases. The compensation ratio calculation device 430 can use various methods for this, such as a method to set the steering column torque compensation gain factor proportionally to the steering column torque and a method to set the steering column torque compensation gain factor so that it increases incrementally in accordance with the steering column torque.The compensation ratio calculation device 430 can calculate the steering column torque compensation gain factor by referring to a predefined map or lookup table between the steering column torque and the steering column torque compensation gain factor, or by various methods, such as as a function of the steering column torque compensation gain factor relative to the steering column torque.

[0035] The steering angle velocity compensation gain factor and the vehicle speed compensation gain factor can be calculated in the same way as in the procedure described above for calculating the steering column torque compensation gain factor.

[0036] Consequently, the compensation ratio can be calculated as 0 if any of the three compensation amplification factors is calculated as a value of 0, and it can be broken as 1 if all of the compensation amplification factors are calculated as a value of 1, and in the other cases it is calculated as a value between 0 and 1.

[0037] Fig. Figure 2 illustrates the procedure for calculating the compensation ratio as the product of the steering column torque compensation gain factor, the steering angle velocity compensation gain factor, and the vehicle speed compensation gain factor. However, the calculation method is not applicable to the one described in Fig. The two methods shown are limited, and various other methods can be used, such as a method using a 3D map of the compensation ratio for the three types of compensation gain factors.

[0038] When the compensation ratio is calculated, the control device 400 compensates the basic auxiliary torque in a differentiated manner depending on the compensation ratio.

[0039] In particular, the control device 400 calculates a sudden steering assist torque by multiplying the base assist torque by the compensation ratio, and it can compensate the base assist torque by adding the calculated sudden steering compensation torque to the base assist torque. Thus, the final compensation torque can be calculated in the manner expressed below by Equation 1. Final Auxiliary Torque = Sudden Steering Compensation Torque + Base Auxiliary Torque = Base Auxiliary Torque × Compensation Ratio + Base Auxiliary Torque = Base Auxiliary Torque × (1 + Compensation Ratio)

[0040] Depending on the compensation ratio, the final auxiliary torque calculated by Equation 1 is calculated as follows. If the compensation ratio is 0, the final auxiliary torque is equal to the basic auxiliary torque. Thus, if the compensation ratio is 0, the control device 400 does not compensate for the basic auxiliary torque.

[0041] If the compensation ratio has a value between 0 and 1, e.g. the value 0.5, the final auxiliary torque is calculated as (1.5 * base auxiliary torque), and the control device 400 increases the base auxiliary torque to reduce the heavy steering feel experienced by the driver during a sudden steering maneuver.

[0042] If the compensation ratio is 1, the final auxiliary torque is derived at twice the level of the base auxiliary torque. In this case, because the base auxiliary torque is excessively compensated, there is a potential risk of excessive steering input. Therefore, according to the present embodiment, the control device 400 is provided to compensate the base auxiliary torque using the preset maximum auxiliary torque.

[0043] This means that the control device 400 is capable of compensating the base auxiliary torque by a method in which the maximum auxiliary torque is preset and the final auxiliary torque is set to the maximum auxiliary torque when the compensation ratio is 1, or by a method in which the preset maximum auxiliary torque is added to the base auxiliary torque. The preset maximum auxiliary torque can be set within a range such that it is equal to or greater than the base auxiliary torque, but not twice the base auxiliary torque.

[0044] Fig. Figure 2 shows that the selector 450 receives the base auxiliary torque, the maximum auxiliary torque, and the torque obtained by adding the sudden steering compensation torque to the base auxiliary torque, and selects and outputs a torque according to the compensation ratio. However, various methods can also be used, provided that the base auxiliary torque can be compensated in a differentiated manner according to the compensation ratio, and the present invention is not limited to the method shown in Figure 2. Fig. The two illustrated procedures are limited.

[0045] Although this in Fig. If 2 is not shown, the output signal of the final auxiliary torque can be limited according to the specification of the MDPS system, and the final auxiliary torque can be output between the lower limit and the upper limit of the output limitation.

[0046] Up to now, the MDPS system 410, the compensation ratio calculation device 430, and the selector 450 have been described as separate components within the control device 400. However, according to a further embodiment, the control device 400 can be configured as a combined unit that performs all the operations of the respective units 410, 430, and 450.

[0047] Fig. Figure 3 shows a flowchart to illustrate a torque compensation method provided for an MDPS system according to an embodiment of the present invention.

[0048] The following will be based on Fig.3 describes the torque compensation method provided for an MDPS system according to the embodiment of the present invention. First, the control device 400 determines, based on one or more of the steering column torque Tcol and the steering angular velocity ω, whether the steering state of the vehicle is a sudden steering state. If the steering column torque Tcol is detected as a value equal to or greater than the minimum steering column torque of the torque compensation section, or if the steering angular velocity ω is detected as a value equal to or greater than the minimum steering angular velocity of the angular velocity compensation section, the control device 400 can determine that the steering state of the vehicle is a sudden steering state.

[0049] If the vehicle's steering state is a sudden one, the control device 400 calculates the compensation ratio for the sudden steering maneuver in step S200 based on one or more of the steering column torque Tcol and the steering angular velocity ω. When calculating the compensation ratio, the vehicle speed V is still taken into account as described above, with the specific procedure for calculating the compensation ratio already described above. Therefore, these procedures are not described again here.

[0050] In step S300, the control device 400 then compensates the basic auxiliary torque output by the MDPS system 410 according to the compensation ratio.

[0051] In particular, if the compensation ratio has a value between 0 and 1, the control device 400 compensates the basic auxiliary torque by adding the sudden steering compensation torque to the basic auxiliary torque, wherein the sudden steering compensation torque is calculated as the product of the basic auxiliary torque and the compensation ratio.

[0052] Furthermore, if the compensation ratio has the value 1, the control device 400 can compensate the basic auxiliary torque using the preset maximum auxiliary torque.

[0053] If, however, the compensation ratio has a value of 0, the control device 400 can determine that the vehicle's steering state does not correspond to the sudden steering operation state, meaning that the steps following S200 cannot be performed and the process can be terminated. Consequently, the basic auxiliary torque cannot be compensated.

[0054] As such, the torque compensation device and method can enable the driver to effortlessly operate the steering wheel in the event of a sudden steering maneuver, effectively avoiding a collision with an external obstacle while improving the driver's steering feel. Furthermore, the torque compensation device and method can calculate the sudden steering compensation torque using parameters such as the steering column torque, which the existing MDPS system used, allowing the auxiliary torque to be detected without an additional device and thus simplifying the system.

[0055] Although preferred embodiments of the invention have been described for illustrative purposes, it will be apparent to those skilled in the art that various modifications, additions and substitutions can be made without deviating from the scope and content of the invention as defined in the accompanying claims.

Claims

[1] Torque compensation device for an MDPS (Motor Driven Power Steering) system, comprising: a steering column torque sensor (100) configured to detect a steering column torque applied to a steering shaft; a steering angle sensor (200) configured to detect a steering angle (θ) of a steering wheel; and a control device (400) configured to calculate a compensation ratio for a sudden steering operation based on one or more of the steering column torques detected by the steering column torque sensor (100) and a steering angle velocity calculated from the steering angle (θ) detected by the steering angle sensor (200), and to differentially compensate the basic auxiliary torque output by the MDPS system according to the compensation ratio, further comprising a vehicle speed sensor (300) configured to detect a vehicle speed, characterized by , that the control device (400) further calculates the compensation ratio taking into account the vehicle speed detected by the vehicle speed sensor (300). and that the control device (400) calculates the compensation ratio based on a steering column torque compensation gain factor, which is calculated as a larger value when the steering column torque increases in a preset torque compensation section, a steering angle velocity compensation gain factor, which is calculated as a larger value when the steering angle velocity increases in a preset angular velocity compensation section, and a vehicle speed compensation gain factor, which is calculated as a larger value when the vehicle speed increases in a preset vehicle speed compensation section, wherein, when the compensation ratio has a value between 0 and 1, the control device (400) compensates the base auxiliary torque by adding a sudden steering action compensation torque to the base auxiliary torque,where the sudden steering compensation torque is calculated as the product of the basic auxiliary torque and the compensation ratio. [2] Torque compensation device according to claim 1, wherein the control device (400) does not compensate the basic auxiliary torque when the compensation ratio has the value 0, but compensates the basic auxiliary torque using a preset maximum auxiliary torque when the compensation ratio has the value 1. [3] Torque compensation method for an MDPS system, comprising: Determining, by means of a control device (400), whether a steering state of a vehicle is a sudden steering process state, on the basis of one or more steering column torques and steering angle velocity; Calculation of a compensation ratio for a sudden steering maneuver by means of the control device (400) on the basis of one or more of the steering column torque and the steering angle velocity, when the steering state of the vehicle is a sudden steering maneuver state; and Differentiated compensation of the basic auxiliary torque output by the MDPS system by means of the control device (400) according to the compensation ratio, characterized by , that when calculating the compensation ratio, the control device further calculates the compensation ratio taking into account a vehicle speed and that when calculating the compensation ratio, the control device calculates the compensation ratio based on a steering column torque compensation gain factor, which is calculated as a larger value when the steering column torque increases in a preset torque compensation section, a steering angle velocity compensation gain factor, which is calculated as a larger value when the steering angle velocity increases in a preset angle velocity compensation section, and a vehicle speed compensation gain factor, which is calculated as a larger value when the vehicle speed increases in a preset vehicle speed compensation section, wherein when compensating the basic auxiliary torque, the control device (400) compensates the basic auxiliary torque if the compensation ratio has a value between 0 and 1.by adding a sudden steering compensation torque to the basic auxiliary torque, where the sudden steering compensation torque is calculated as the product of the basic auxiliary torque and the compensation ratio. [4] Torque compensation method according to claim 3, wherein when compensating the basic auxiliary torque the control device (400) compensates the basic auxiliary torque using the preset maximum auxiliary torque when the compensation ratio has the value 1.

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