ELECTRIC SERVO STEERING DEVICE AND METHOD FOR CONTROLLING IT

Abstract

Electric power steering device (100), which device includes: a rack force estimating device (151) configured to estimate a rack force by using a driver torque and an engine torque; a target torque calculation device (152) configured to calculate a lateral acceleration using the rack force and a lateral acceleration parameter determined according to a vehicle speed, and to calculate a target torque using the lateral acceleration and one or more target torque parameters, which are determined according to the vehicle speed; and a motor control device (154) configured to output a motor current for controlling a motor according to a compensation torque corresponding to a difference between the target torque and the driver torque.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present disclosure relates to an electric power steering device and a method for controlling it. 2. Description of the state of the art

[0002] An electric power steering device provides a force to assist a driver in steering a vehicle by generating an electric current to power a motor.

[0003] As an example, when the driver turns the steering wheel, the electric power steering system detects a steering torque corresponding to the steering wheel movement and generates a current to drive the motor, also corresponding to the steering torque. When the driver's steering is assisted by such a motor driven by the steering torque, the driver's steering control is made easier, and proper steering is enabled depending on the vehicle's driving conditions.

[0004] Such an electric power steering device generates a current to assist a steering force according to a detected steering torque, a current to reduce steering-induced wobble and the like, and drives the motor according to the generated currents.

[0005] Here, if excessive current is supplied to reduce steering-induced wobble in order to maintain the vehicle's yaw stability, this is not problematic for general steering. On the other hand, in the case of a rapid steering correction at the center position, the steering feel is unstable due to a high torque.

[0006] Examples of power steering systems can be found in the following publications.

[0007] US 2005 / 0049769 A1, for example, discloses a control device for a vehicle power steering system to ensure preferred steering convergence even when vehicle stability control (VSC) is active, while maintaining steering smoothness under normal driving conditions. The control device calculates the target value of a total change torque to be added as steering torque by a power steering device, based on an auxiliary steering torque calculated from at least the steering torque, a steering convergence torque based on a steering speed, and a behavior deterioration suppression torque to suppress unwanted steering movements that would cause further deterioration of vehicle behavior under oversteer or understeer conditions.In this calculation, if a predetermined condition is met, the degree of contribution of the target value of the behavior deterioration suppression torque to the target value of the total change torque is made higher than the degree of contribution of the target value of the steering convergence torque to the target value of the total change torque.

[0008] DE 10 2008 042 666 B4 discloses a method for compensating disturbances acting on a vehicle with power steering, comprising estimating an actual rack force using an observer model of the steering system, estimating an artificial target rack force using an observer model of the vehicle, subtracting the estimated actual rack force from the estimated artificial target rack force, so that a total steering force error is generated, wherein in a decision block at least a first fraction factor is determined from signals known at least from the vehicle system, which is superimposed on the total steering force error.

[0009] DE 60 2004 003 090 T2 discloses a steering device for a vehicle with a steering wheel, comprising: a steering mechanism mechanically separate from the steering wheel, comprising a steering rod and a steering actuator driving the steering rod; a steering wheel position detector for detecting the steering position of the steering wheel;a control system that determines a target steering position of the steering rod based on the detected steering position of the steering wheel, wherein the control system performs feedback control of the steering actuator based on the target steering position and an actual steering position of the steering rod, and a reaction force actuator that applies a reaction force to the steering wheel based on a force received by the control mechanism from a road, and an elastic element that connects the reaction force actuator to the steering wheel, wherein the elastic element is arranged between the steering wheel and the reaction force actuator, and wherein, with respect to the elastic element, a side located closer to the steering wheel is designated as the primary side and a side located closer to the reaction force actuator is designated as the secondary side.

[0010] DE 10 2008 019 270 A1 discloses a road surface friction coefficient estimation device suitable for comparing a rack and pinion drive force deviation value with a pre-set maximum value determination threshold. If the rack and pinion drive force deviation value is greater than the maximum value determination threshold, the device determines that tires are slipping and, in this condition, sets a front wheel friction circle utilization factor as the road surface friction coefficient. If the rack and pinion drive force deviation value is less than the maximum value determination threshold, the device refers to a pre-generated characteristic map to determine, based on the vehicle speed and a front wheel slip angle, a reset speed at which the road surface friction coefficient is reset to 1.0.While the road surface friction coefficient is being reset at the reversing speed, the device calculates and outputs the road surface friction coefficient.

[0011] DE 10 2010 029 928 A1 discloses a method for determining a target steering torque by determining an actual rack force, determining at least one first component for the target steering torque depending on the actual rack force, and determining at least one additional component for the target steering torque from a calculated rack force, wherein the calculated rack force is determined from a wheel steering angle and a vehicle speed.

[0012] DE 10 2016 012 242 A1 discloses a steering control device comprising: a sensing unit configured to detect the angle of a pinion gear positioned in the front wheel, a column torque, and a motor current; a frequency estimation unit configured to estimate a road surface frequency generated by the road on which the vehicle is traveling, based on at least one of the angle of the pinion gear, the column torque, or the motor current; a rack force estimation unit configured to estimate a rack force based on at least one of the angle of the pinion gear, the column torque, or the motor current;and a control unit configured to extract road surface information contained in the rack force based on the road surface frequency, and configured to control a steering device based on the road surface information and the rack force.

[0013] DE 10 2017 125 847 A1 discloses a control system for a power steering system that estimates the rack force and its derivative, e.g., based on lateral acceleration, yaw rate, vehicle speed, or other parameters. A control torque is calculated based on the rack force, its derivative, and the vehicle speed, and summed with an input torque from the driver to determine the amount of assist torque to be provided. The control torque can be a shape function with a sign determined by the sign of the derivative and an order of magnitude that decreases from a maximum value with an increase in the order of magnitude of the rack force. The maximum value can be determined according to the vehicle speed.

[0014] Therefore, a procedure is needed to maintain a consistent steering feel in both general and specific situations. SUMMARY OF THE INVENTION

[0015] The problem is solved by an electric power steering device with the features of claim 1 and by a method with the features of claim 11. Advantageous further developments are set out in the dependent claims.

[0016] The present disclosure serves to specify an electric power steering device for maintaining a uniform steering feel of a driver when a motor is driven according to a steering torque produced by the driver's steering, and a method for controlling the same.

[0017] The present disclosure also serves to specify an electric power steering device for separately controlling the steering in a special situation and a general situation, as well as a method for controlling the same.

[0018] One embodiment provides an electric power steering device comprising: a rack force estimator configured to estimate a rack force using driver torque and engine torque; a target torque calculator configured to calculate lateral acceleration using the rack force and a lateral acceleration parameter determined according to vehicle speed, and to calculate a target torque using the lateral acceleration and one or more target torque parameters determined according to vehicle speed; and a motor control device configured to output a motor current to control a motor according to a compensation torque corresponding to a difference between the target torque and the driver torque.

[0019] The target torque calculation device of the electric power steering system can calculate the lateral acceleration by dividing the rack force by the parameter for lateral acceleration.

[0020] The target torque calculation device can calculate the target torque by using the target torque parameters, which include a first parameter to determine the setup of the target torque, a second parameter to determine a level of the target torque, and a third parameter to determine the target torque in an off-center position.

[0021] Here, the target torque calculation device can generate a target torque map by using the first parameter, the second parameter, and the third parameter, which were determined according to the lateral acceleration and the vehicle speed, and calculate a target torque according to the lateral acceleration using the target torque map.

[0022] The electric power steering device may further include a steering control device configured to calculate a motor current to control the motor according to the driver torque, and the motor control device may add the motor current calculated by the steering control device and the motor current dependent on the compensation torque to output the added motor current.

[0023] Here, at least one of the rack force estimating device and the target torque calculation device can be switched on or off independently of the steering control device.

[0024] As an example, the target torque calculation device can maintain an ON state when the steering wheel is in the center and can maintain an OFF state when the steering wheel is off-center, such that the engine can be controlled by the steering control device.

[0025] Another embodiment provides a method for controlling such an electric power steering device, which includes: estimating a rack force by using a driver torque and a motor torque; calculating a lateral acceleration by using the rack force and a lateral acceleration parameter determined according to a vehicle speed; calculating a target torque by using the lateral acceleration and one or more target torque parameters determined according to the vehicle speed; and outputting a motor current to control a motor according to a compensation torque corresponding to a difference between the target torque and the driver torque. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The aforementioned and other aspects of the present disclosure, as well as its advantages, will become more apparent from the following detailed description, which is given in conjunction with the accompanying drawings, in which: Fig. 1 shows a schematic configuration of an electric power steering device according to embodiments of the present disclosure; Fig. 2 is a diagram showing an example of a configuration of a control device in an electric power steering device according to embodiments of the present disclosure; Fig. 3 is a diagram illustrating a method in which an electric power steering device calculates a lateral acceleration according to embodiments of the present disclosure; Fig. 4 is a diagram illustrating a method in which an electric power steering device calculates a target torque according to embodiments of the present disclosure; Fig. 5 is a diagram showing an example of an operating method of an electric power steering device according to embodiments of the present disclosure; Fig. 6 is a flowchart illustrating a method for controlling an electric power steering device according to embodiments of the present disclosure; and Fig. 7 is a diagram showing another example of an operating method of an electric power steering device according to embodiments of the present disclosure. DETAILED DESCRIPTION OF THE EXECUTIVE EXAMPLES

[0027] Exemplary embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. By adding reference numerals to elements in each drawing, the same elements are designated by the same reference numerals where possible, even though they may be shown in different drawings. Furthermore, in the following description of the present disclosure, a detailed description of its known functions and configurations is omitted where it is determined that such a description could impair the clarity of the subject matter of the present disclosure.

[0028] In describing elements of embodiments of the present disclosure, terms such as "first," "second," "A," "B," "(a)," and "(b)" may be used. Such terms are used only to distinguish one element from another, but they do not restrict the nature, sequence, order, or the like of elements. It should be noted that if one component is described as "connected," "coupled," or "united" with another component, yet another component may be "connected," "coupled," or "united" between the two components, although the component may be directly "connected," "coupled," or "united" with the other component.

[0029] Fig. Figure 1 shows a schematic configuration of an electric power steering device 100 according to embodiments of the present disclosure.

[0030] According to Fig. 1 The electric power steering device 100 according to embodiments of the present disclosure includes a steering wheel 110, a steering shaft 120, a rack 130, a torque sensor 140, a control device 150 and a steering motor 160.

[0031] The steering wheel 110 is connected to one end of the steering shaft 120 and is rotated according to an operation by a driver.

[0032] The end of the steering shaft 120 is connected to the steering wheel 110, and the other end is connected to the rack 130. When the steering wheel 110 is turned according to the driver's instructions, the steering shaft 120 is rotated by the rotation of the steering wheel 110 and moves the rack 130.

[0033] Here, a torque produced by turning the steering wheel 110 is referred to as a "driver torque".

[0034] To assist the driver with such steering, the driver's torque is detected, and an auxiliary force is provided according to the detected driver's torque, thus making steering control easier for the driver.

[0035] When the steering wheel 110 is turned by the driver, the torque sensor 140 detects the driver torque and transmits the detected driver torque to the control device 150.

[0036] The control device 150 performs a control to assist the driver's steering based on the detected driver torque.

[0037] The control device 150 calculates a current to drive the steering motor 160 based on the driver's torque and drives the steering motor 160 by outputting the calculated current, thereby performing a control to assist the driver's steering.

[0038] Here, a torque produced by the operation of the steering motor 160 is referred to as a "motor torque".

[0039] For example, to assist the driver's steering, the control device 150 can output a current to add torque in one of the driver's steering directions. Also, to prevent wobbling caused by the driver's steering, the control device 150 can output a current to control the steering motor 160. Furthermore, the control device 150 can output a current to assist the steering wheel 110 in returning to its initial position after the driver has steered.

[0040] The steering motor 160 is driven according to a current output by the control device 150 and causes the rack 130 to move, thus making it easier for the driver to steer.

[0041] In this case, if a control logic to assist the driver's steering is overridden by the control device 150, the driver's steering feel may not be consistent.

[0042] For example, if a control logic designed to prevent wobbling caused by the driver's steering is overridden in order to maintain the vehicle's yaw stability, a rapid corrective steering input in the center position may cause the steering feel to become unstable due to a strong torque.

[0043] The electric power steering device 100 according to embodiments of the present disclosure provides a method of uniformly maintaining a steering feel of the driver when logic to assist the steering of the driver is carried out.

[0044] Fig. Figure 2 is a diagram showing an example of a detailed configuration of the control device 150 in the electric power steering device 100 according to embodiments of the present disclosure.

[0045] According to Fig. 2 The control device 150 of the electric power steering device 100 according to embodiments of the present disclosure includes a rack force estimating device 151, a target torque calculation device 152, a compensation torque calculation device 153, a motor control device 154 and a steering control device 155.

[0046] The rack force estimating device 151 estimates a rack force by using a driver torque generated by the driver's steering and an engine torque generated by the steering motor 160.

[0047] For example, the rack force estimator 151 can estimate a rack force by using the sum of the driver torque and the engine torque.

[0048] The target torque calculation device 152 calculates a target torque by using the rack force estimated by the rack force estimator 151 and parameters set according to a vehicle speed.

[0049] More precisely, the target torque calculation device 152 can calculate a lateral acceleration by using the rack force and parameters for lateral acceleration set according to a vehicle speed, and can calculate the lateral acceleration as shown in Equation 1 below. Ay=RFCa

[0050] Here, Ay denotes a lateral acceleration, RF denotes a rack force, and Ca denotes a parameter for lateral acceleration that is set according to a vehicle speed.

[0051] In other words, if the rack force RF is estimated by the rack force estimator 151, the target torque calculator 152 can calculate the lateral acceleration Ay by using the estimated rack force RF and the lateral acceleration parameter Ca, which is set according to the vehicle speed.

[0052] When calculating lateral acceleration, the target torque calculation device 152 calculates a target torque by using the lateral acceleration and one or more target torque parameters that are set according to the vehicle speed.

[0053] Here, one or more target torque parameters can include a first parameter to determine the structure of the target torque, a second parameter to determine an overall level of the target torque, and a third parameter to determine the target torque at an off-center position.

[0054] The target torque calculation device 152 can calculate a target torque by using the aforementioned first, second and third parameters, and the target torque can be calculated as shown below in Equation 2. Td=1DaAy+Ka+Gr⋅Ay

[0055] Here, TD denotes a target torque, and Ay denotes a lateral acceleration. Da denotes the first parameter, Ka the second parameter, and Gr the third parameter.

[0056] When the lateral acceleration Ay is calculated, the target torque calculation device 152 can generate a target torque map by using the lateral acceleration Ay, the first parameter Da, the second parameter Ka and the third parameter Cr, which are set according to the vehicle speed, and can calculate a target torque according to the calculated lateral acceleration Ay using the target torque map.

[0057] In other words, it is possible to calculate a target torque Td by an equation between the target torque Td and the lateral acceleration Ay, in which one or more target torque parameters, set according to the vehicle speed, are used.

[0058] When the target torque is calculated, the target torque calculation device 152 transmits the calculated target torque to the compensation torque calculation device 153.

[0059] The compensation torque calculation device 153 receives the target torque calculated by the target torque calculation device 152 and is fed back with a driver torque generated by the driver's steering control.

[0060] The compensation torque calculation device 153 compares the target torque and the driver torque and calculates a compensation torque corresponding to the difference between the target torque and the driver torque. The compensation torque calculation device 153 then calculates a motor current corresponding to the compensation torque in order to output the motor current to the motor control device 154.

[0061] In other words, the compensation torque calculation device 153 performs logic to control the steering motor 160 in one direction to reduce the difference between the target torque and the driver torque.

[0062] The motor control device 154 receives the motor current value calculated by the compensation torque calculation device 153 and outputs a motor current according to the received motor current value. Accordingly, a compensation torque corresponding to the difference between the target torque and the driver torque is applied, so that steering control can be carried out.

[0063] Here, the motor control device 154 can add the motor current value according to the compensation torque calculated by the compensation torque calculation device 153 and a motor current value output by the steering control device 155 and output a motor current.

[0064] The motor control device 154 can also compare the difference between the target torque and the driver torque with a threshold value and output a motor current to control the motor according to the compensation torque corresponding to the difference between the target torque and the driver torque if the difference is greater than the threshold value. In other words, the motor control device 154 maintains the driver torque at a certain level or above based on the target torque. If the driver torque is generated by the driver operating the steering wheel 110, the steering control device 155 calculates the motor current value to assist the driver's steering based on the driver torque.

[0065] The motor current value calculated by the steering control device 155 may be intended to assist the driver's steering, prevent steering-induced wobble, or assist the return from a steering state.

[0066] Therefore, the steering motor 160 is controlled by the control device 150 on the basis of the driver torque, but a logic to compensate for the difference between the driver torque and the target torque, which was calculated on the basis of the lateral acceleration, is carried out separately, so that the steering feel can be prevented from being inconsistent as a result of the steering control based on the driver torque.

[0067] Furthermore, a steering control logic based on driver torque and a steering control logic based on compensation torque are implemented separately to compensate for the driver torque, in order to facilitate steering control and control of driver torque compensation.

[0068] Fig. Figure 3 is a diagram illustrating a method in which the electric power steering device 100 calculates a lateral acceleration according to embodiments of the present disclosure.

[0069] According to Fig. 3 denotes Tf a torque exerted on the steering shaft 120, and Fy denotes a rack force exerted on the front wheels. n also denotes the sum of a steering head caster and a pneumatic caster.

[0070] A relational equation between a rack force and a lateral acceleration can be derived from the definition of a theoretical tire reaction force, as can be represented by the following equations. Tf=Fy×n Td×As×Is=Tf Fy=Mf×Ay

[0071] Here, As denotes a steering assistance ratio, and Is denotes a steering ratio. Mf denotes a vehicle weight exerted on the front wheels, Ay denotes a lateral acceleration exerted on the front wheels, Rf denotes a rack force, and Ca denotes a parameter for lateral acceleration.

[0072] The parameter Ca for lateral acceleration is measured as Td / Ay according to a vehicle speed when As = 1 and no energy is supplied.

[0073] The following equation 6 can be derived from the aforementioned equations 3 to 5. Td×As=Ca×Ay(Ca=Mf×n / Is)

[0074] If Td × As = Rf is defined, the following equation 7 can be derived. Ay=RFCa

[0075] In other words, it is possible to calculate lateral acceleration by dividing an estimated rack force by the lateral acceleration parameter, which is set according to the vehicle speed.

[0076] Fig. Figure 4 is a diagram illustrating a method in which the electric power steering device 100 calculates a target torque according to embodiments of the present disclosure.

[0077] Fig. Figure 4 shows a relationship between a lateral acceleration set on the basis of a target torque parameter and a target torque.

[0078] The relationship between lateral acceleration and target torque can be represented as shown in Equation 8 below. Td=1DaAy+Ka+Gr⋅Ay

[0079] Here, Td denotes a target torque, Ay denotes a lateral acceleration, Da denotes a first parameter, Ka denotes a second parameter, and Gr denotes a third parameter.

[0080] Da is a parameter for determining a build-up level of the target torque, Ka is a parameter for determining an overall level of the target torque, and Gr is a parameter for determining the target torque at an off-center position.

[0081] A target torque map, representing the relationship between lateral acceleration and target torque, can be generated by using the parameters Da, Ka and Gr, which are set according to a vehicle speed, and a target torque can be calculated based on a calculated lateral acceleration using the generated target torque map.

[0082] Therefore, according to embodiments of the present disclosure, a target torque is calculated using a lateral acceleration calculated from an estimated rack force and target torque parameters set according to a vehicle speed, and logic is implemented to compensate for driver torque based on the target torque. In this way, it is possible to prevent the steering feel from being inconsistent and to maintain a smooth steering feel when steering is controlled by driver torque.

[0083] The electric power steering device 100 according to embodiments of the present disclosure can separately perform logic for calculating a target torque and applying a compensation torque and steering control logic based on a driver torque.

[0084] Accordingly, a compensating torque only needs to be applied when it is necessary to apply a compensating torque.

[0085] Fig. Figure 5 shows an example of an operation of the control device 150 in the electric power steering device 100 according to embodiments of the present disclosure.

[0086] According to Fig. 5 In the control device 150 of the electric power steering device 100 according to embodiments of the present disclosure, the rack force estimating device 151, the target torque calculation device 152 and the compensation torque calculation device 153 need to maintain an ON state only in a specific steering situation and can be in an OFF state in other situations.

[0087] As an example, components for calculating a compensation torque only need to maintain the ON state when the steering wheel is 110 in the center, and can otherwise be in the OFF state.

[0088] Alternatively, the components only need to maintain the ON state when a quick corrective steering maneuver is performed in the center position, and can otherwise be in the OFF state.

[0089] Therefore, while the rack force estimating device 151, the target torque calculation device 152 and the compensation torque calculation device 153 are in the ON state, the steering motor 160 is controlled at the same time on the basis of a driver torque and a compensation torque depending on a target torque, such that the driver's steering feel can be maintained uniformly.

[0090] On the other hand, while the rack force estimating device 151, the target torque calculation device 152, and the compensation torque calculation device 153 are in the OFF state, the steering control device 155 controls the steering motor 160 based solely on driver torque. In this way, energy consumption is reduced and a compensation torque can be applied as needed.

[0091] In other words, according to embodiments of the present disclosure, compensation control is carried out according to a target torque based on a lateral acceleration, but a control logic based on a driver torque and a control logic based on the target torque are carried out independently, such that a steering control logic appropriate for a steering condition can be carried out.

[0092] Fig. Figure 6 is a flowchart illustrating a method for controlling an electric power steering device 100 according to embodiments of the present disclosure.

[0093] According to Fig. 6 the electric power steering device 100 according to embodiments of the present disclosure estimates a rack force by using a driver torque and an engine torque (S600).

[0094] The electric power steering device 100 calculates lateral acceleration using the estimated rack force and a lateral acceleration parameter set according to a vehicle speed (S610). Here, the lateral acceleration can be calculated by dividing the rack force by the lateral acceleration parameter.

[0095] The electric power steering device 100 calculates a target torque by using the calculated lateral acceleration and one or more target torque parameters set according to the vehicle speed (S620). The one or more target torque parameters may include a first parameter to determine the build-up of the target torque, a second parameter to determine an overall level of the target torque, and a third parameter to determine the target torque in an off-center position.

[0096] The electric power steering device 100 can generate a target torque map by using the target torque parameters and calculate a target torque according to the calculated lateral acceleration based on the target torque map.

[0097] The electric power steering device 100 is fed back with a driver torque and compares the fed-back driver torque with the calculated target torque (S630).

[0098] Then the electric power steering device 100 calculates a compensation torque according to a difference between the target torque and the driver torque (S640) and controls the steering motor 160 by outputting a motor current according to the compensation torque (S650).

[0099] Fig. Figure 7 is a diagram showing another example of an operating method of an electric power steering device according to embodiments of the present disclosure.

[0100] According to Fig. 7 is a determining device 156 for an uneven road additionally in the electric power steering device, which with reference to Fig. 2 was described, contained.

[0101] The uneven road determination device 156 can compare the rate of change of a rack force estimated by the rack force estimator 151 with a determination reference value for an uneven road and generate an uneven road determination flag if the rate of change of the rack force is equal to or greater than the determination reference value for an uneven road. The generation of an uneven road determination flag can denote a change of an uneven road determination flag from 0 to 1.

[0102] Here, the reference value for an uneven road can be determined based on at least one vehicle speed and one steering angle.

[0103] As an example, the reference value for determining an uneven road surface can be set to a value inversely proportional to the speed of a moving vehicle. An increase in the vehicle's speed reduces friction against the road, and thus the rate of change of a rack force can be reduced even if the vehicle is traveling on an uneven road. Therefore, as the vehicle speed increases, the reference value for determining an uneven road surface is reduced, allowing for an accurate determination of whether the vehicle is traveling on an uneven road surface, even when the rate of change of the rack force is affected by a change in vehicle speed.

[0104] As another example, the reference value for determining an uneven road surface can be set to a value proportional to the steering angle of a moving vehicle. If the vehicle is traveling at a large steering angle, the rate of change of the rack force can be high, even with a slightly uneven road surface. Therefore, as the steering angle increases, the reference value for determining an uneven road surface is also increased, allowing for an accurate determination of whether the vehicle is traveling on an uneven road, regardless of the vehicle's steering input.

[0105] As an example of generating a flag for determining an uneven road by using a determination reference value for an uneven road, if the rate of change of the rack force is equal to or greater than the determination reference value for an uneven road during a preset or longer time, the flag for determining an uneven road can be generated.

[0106] In other words, even if the rate of change of the rack force is temporarily equal to or greater than the reference value for an uneven road, the vehicle does not necessarily have to be traveling on an uneven road. Therefore, if the rate of change of the rack force is maintained at or greater than the reference value for an uneven road for a predetermined or longer period, it is possible to determine that the vehicle is traveling on an uneven road.

[0107] As another example of generating a flag for determining a rough road by using a determining reference value for a rough road, if a time during which the rate of change of the rack force is equal to or greater than the determining reference value for a rough road assumes a certain or greater ratio in a preset time, a flag for determining a rough road can be generated.

[0108] Since the reference value for a rough road is dynamically changed according to the driving conditions of a vehicle, the rate of change of the rack force can temporarily be a smaller value than the reference value for a rough road, even if the vehicle is driving on a rough road. Therefore, if a period during which the rate of change of the rack force is equal to or greater than the reference value for a rough road occurs at a specific or greater ratio within the preset time, it is determined that the vehicle is driving on a rough road. This allows for an accurate determination of whether the vehicle is driving on a rough road, even when using the dynamically changed reference value for a rough road.

[0109] When the rough road detection flag is generated, the rough road detection device 156 can transmit information about the generated rough road detection flag to the engine control device 154. When the rough road detection flag is generated, the engine control device 154 can output an engine current to control the engine according to a compensation torque corresponding to the difference between a target torque and a driver torque.

[0110] Therefore, according to embodiments of the present disclosure, a target torque map is generated by using a lateral acceleration calculated on the basis of an estimated rack force and a target torque parameter set according to a vehicle speed, and a target torque is calculated using the generated target torque map, so that a compensating torque can be applied according to the target torque. Accordingly, when a driver controls the steering, the steering feel can be maintained uniformly.

[0111] In other words, a target torque is generated based on a rack force and used to compensate for a change in a current value of a steering control logic according to a steering state, so that the steering feel can be maintained consistently despite a change in the steering rate.

[0112] As described above, according to embodiments of the present disclosure, a lateral acceleration is calculated on the basis of an estimated rack force, a target torque is calculated by using the lateral acceleration and a parameter set according to a vehicle speed, and logic is performed to compensate for a difference between the target torque and a driver torque, so that the steering feel can be maintained uniformly during rapid corrective steering at the center position.

[0113] According to embodiments of the present disclosure, logic for controlling a target torque calculated on the basis of a lateral acceleration is carried out separately from logic for controlling a motor according to a driver torque, so that steering control logic can be carried out independently according to the steering circumstances.

[0114] The foregoing embodiments of the present disclosure have been described for illustrative purposes only, and it is obvious to the person skilled in the art that various modifications and changes can be made to them without departing from the scope and spirit of the disclosure. Therefore, the embodiments of the present disclosure are not intended to limit the technical idea of ​​the present disclosure, but rather to illustrate it, and the scope of the technical idea of ​​the present disclosure is not limited by the embodiments. The scope of the present disclosure is to be interpreted on the basis of the accompanying claims in such a way that all technical ideas contained in the scope equivalent to the claims belong to the present disclosure.

Claims

[1] Electric power steering device (100) comprising: a rack force estimating device (151) configured to estimate a rack force by using a driver torque and an engine torque; a target torque calculation device (152) configured to calculate a lateral acceleration using the rack force and a lateral acceleration parameter determined according to a vehicle speed, and to calculate a target torque using the lateral acceleration and one or more target torque parameters, which are determined according to the vehicle speed; and a motor control device (154) configured to output a motor current for controlling a motor according to a compensation torque corresponding to a difference between the target torque and the driver torque. [2] Electric power steering device (100), according to claim 1, characterized by , that the target torque calculation device (152) calculates the lateral acceleration by dividing the rack force by the parameter for lateral acceleration. [3] Electric power steering device (100) according to any one of the preceding claims, characterized by , that the target torque calculation device (152) calculates the target torque by using the target torque parameters comprising a first parameter to determine the setup of the target torque, a second parameter to determine a level of the target torque and a third parameter to determine the target torque at an off-center position. [4] Electric power steering device (100) according to claim 3, characterized by, that the target torque calculation device generates a target torque map by using the first parameter, the second parameter and the third parameter, which are determined according to the lateral acceleration and the vehicle speed, and calculates a target torque according to the lateral acceleration using the target torque map. [5] Electric power steering device (100) according to any one of the preceding claims, characterized by , that the electric power steering device (100) further comprises a steering control device (155) configured to calculate a motor current for controlling the motor according to the driver torque, wherein the motor control device (154) adds the motor current calculated by the steering control device (155) and the motor current dependent on the compensation torque to output the added motor current. [6] Electric power steering device (100) according to claim 5, characterized by, that at least one of the rack force estimating device (151) and the target torque calculation device (152) is switched on or off independently of the steering control device (155). [7] Electric power steering device (100) according to claim 5 or 6, characterized by , that the target torque calculation device (152) maintains an ON state when a steering wheel (110) is in the center, and maintains an OFF state when the steering wheel (110) is off-center. [8] Electric power steering device (100) according to any one of the preceding claims, characterized by , that the rack force estimating device (151) calculates the rack force by adding a force generated by the driver torque in accordance with a rotation of a steering wheel (110) and a force generated by the engine torque in order to assist the steering in accordance with the rotation of the steering wheel (110). [9] Electric power steering device (100) according to any one of the preceding claims, characterized by , that the motor control device (154) compares the difference between the target torque and the driver torque with a threshold value and outputs a motor current to control the motor according to the compensation torque corresponding to the difference between the target torque and the driver torque when the difference is greater than the threshold value. [10] Electric power steering device (100) according to any one of the preceding claims, characterized by, that the electric power steering device (100) has a rough road determination device (156) configured to compare a rate of change of the rack force with a rough road determination reference value, and generates a rough road determination flag when the rate of change of the rack force is greater than or equal to the rough road determination reference value, where the reference value for an uneven road is determined on the basis of at least one of the vehicle speed and a steering angle, and The motor control device (154) outputs the motor current to control the motor according to the compensation torque corresponding to the difference between the target torque and the driver torque when the flag for determining the uneven road is generated. [11] Method for controlling an electric power steering device (100), comprising: Estimating a rack force by using driver torque and engine torque; Calculating a lateral acceleration by using the rack force and a parameter for lateral acceleration determined according to a vehicle speed; Calculating a target torque by using the lateral acceleration and one or more target torque parameters, which were determined according to the vehicle speed; and Output of motor current to control a motor according to a compensation torque corresponding to a difference between the target torque and the driver torque. [12] Method according to claim 11, characterized by, that calculating the lateral acceleration involves calculating the lateral acceleration by dividing the rack force by the parameter for lateral acceleration. [13] Method according to claim 11 or 12, characterized by , that calculating the target torque involves calculating the target torque by using the target torque parameters, including a first parameter to determine the setup of the target torque, a second parameter to determine a level of the target torque, and a third parameter to determine the target torque at an off-center position. [14] Method according to claim 13, characterized by , that calculating the target torque exhibits: Generating a target torque map by using the first, second, and third parameters, which were determined according to the lateral acceleration and vehicle speed; and Calculate the target torque according to the lateral acceleration using the target torque map. [15] Method according to any one of claims 11 to 14 characterized by , that the output of the motor current exhibits: Calculating a motor current to control the motor according to the driver's torque; and Add the calculated motor current and the motor current dependent on the compensation torque to output the added motor current.

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