Vehicle steering assist device and control method thereof

Abstract

To provide an apparatus of assisting steering of a vehicle and a control method thereof which enable tire turning in a steering torque equal to or greater than a limit steering torque that may be generated in a steering motor.SOLUTION: An apparatus of assisting steering of a vehicle, may include: a turning direction recognizer that recognizes a turning direction of a tire in which a vehicle is about to turn, by use of a steering angle controlled through manipulation of a handle; and a tire driving controller that determines a tire, to which a first driving force for generating a steering assisting torque that assists turning of the tire to the recognized turning direction is applied, and a tire, to which a second driving force for offsetting the first driving force to maintain a forward / rearward force of the vehicle at 0 is applied, and controls driving motors provided in the tires, respectively, to generate the first driving force and the second driving force, whereby the tire may be turned with a steering torque of a limit steering torque or more which may be generated by the steering motor, and there is also provided a control method thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle steering assist device that enables torque required for steering a vehicle while stopped to be additionally supplied from a drive motor, and a control method thereof. [Background technology]

[0002] Generally, when steering using an electric power steering (MDPS: Motor Driven Power Steering), the magnitude of the steering torque acting on each tire to steer to a desired angle changes depending on whether the vehicle is moving or stopped.

[0003] In other words, a larger steering torque is required when the vehicle is stopped than when the vehicle is moving because the coefficient of friction between the tires and the road surface is small, and the larger the steering angle, the larger the required steering torque. Accordingly, the largest steering torque is required under a full turn condition, where the steering angle is turned to the maximum while the vehicle is stopped.

[0004] In addition, in the case of a four-wheel independent steering vehicle in which all four tires can be driven independently, not only a steering motor for generating steering torque for each tire but also a drive motor for generating driving force must be installed, which poses a problem of spatial constraints when increasing the capacity and magnitude of the steering torque.

[0005] Therefore, there is still a need for a device that can minimize an increase in the capacity of the steering motor and can satisfy the steering torque required during a full turn while the vehicle is stopped, which is when the largest steering torque is required during a steering operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-054395 Summary of the Invention [Problem to be solved by the invention]

[0007] An embodiment of the present invention has a technical objective of providing a steering assist device for a vehicle and a control method thereof, which includes a turning direction recognition unit that recognizes the rotation direction of the tires in which the vehicle is about to turn, using the steering angle controlled by steering wheel operation, and a tire drive control unit that determines which tires to apply a first driving force to in order to generate a steering assist torque that assists the rotation of the tires in the recognized turning direction, and which tires to apply a second driving force that cancels out the first driving force in order to maintain the longitudinal force of the vehicle at zero, and controls the first driving force and the second driving force to be generated by the drive motors provided on the tires, and which rotates the tires with a steering torque that is equal to or greater than the limit steering torque that can be generated by the steering motors. The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0008] A vehicle steering assist device according to an embodiment of the present invention includes a turning direction recognition unit that recognizes the rotation direction of tires in which a vehicle is about to turn, using a steering angle controlled by steering wheel operation, and a tire drive control unit that determines a tire to which a first driving force is applied to generate a steering assist torque that assists the rotation of the tires in the recognized turning direction and a tire to which a second driving force that cancels out the first driving force is applied to maintain the longitudinal force of the vehicle at zero, and controls the first driving force and the second driving force to be generated by a driving motor provided in each tire.

[0009] The vehicle steering assist device according to an embodiment of the present invention is characterized by further including a vehicle stop determination unit that determines in advance whether the vehicle is stopped or not using the wheel speed of the vehicle.

[0010] The tire drive control unit is also characterized in that, as the tire to which the first drive force is applied, the outer front wheel is determined as the tire to which a positive (+) drive force is applied and the inner front wheel is determined as the tire to which a negative (-) drive force is applied, based on the turning direction in which the tire rotates.

[0011] The tire drive control unit is further characterized in that, as the tire to which the second drive force is applied, the inner rear wheel is determined as the tire to which a positive (+) drive force is applied and the outer rear wheel is determined as the tire to which a negative (-) drive force is applied, based on the turning direction in which the tire rotates.

[0012] In addition, when the vehicle in a stopped state is steered to make a left turn, the tire drive control unit controls the vehicle so that, as the first drive force, a positive (+) drive force is applied to the right front wheel of the vehicle and a negative (-) drive force is applied to the left front wheel, and, as the second drive force, a positive (+) drive force is applied to the left rear wheel of the vehicle and a negative (-) drive force is applied to the right rear wheel.

[0013] Furthermore, when the vehicle in a stopped state is steered to make a right turn, the tire drive control unit controls the vehicle so that, as the first drive force, a positive (+) drive force is applied to the left front wheel of the vehicle and a negative (-) drive force is applied to the right front wheel, and, as the second drive force, a positive (+) drive force is applied to the right rear wheel of the vehicle and a negative (-) drive force is applied to the left rear wheel.

[0014] In addition, the vehicle steering assist device according to an embodiment of the present invention is characterized in that it further includes a moment arm calculation unit that calculates data indicating the relationship between the steering angle and the increase / decrease in the moment arm in advance using characteristic values ​​of the vehicle including installation positions of the kingpin shaft and the steering motor and a motor shaft offset, and then stores the calculated data in a memory, and obtains from the memory the length of the moment arm that changes when the tire rotates using the magnitude of the steering angle.

[0015] In addition, the vehicle steering assist device according to an embodiment of the present invention is characterized by further including a steering assist determination unit that determines the magnitude of a required steering torque required to rotate tires in a left or right turning direction when the vehicle is stopped, depending on the magnitude of the steering angle, and determines to supplement a portion of the required steering torque with a driving force generated by the driving motor when the required steering torque exceeds a limit steering torque that can be generated by the steering motor.

[0016] The steering assist determination unit determines a ratio of the steering torque generated by the steering motor to the steering assist torque generated by the drive motor, out of the required steering torque.

[0017] In addition, a vehicle steering assist control method according to another embodiment of the present invention includes a turning direction recognition step of recognizing a rotation direction of tires in which the vehicle is about to turn, using a steering angle controlled by steering wheel operation; and a tire drive control step of determining a tire to which a first driving force is applied to generate a steering assist torque that assists the rotation of the tires in the recognized turning direction and a tire to which a second driving force that cancels the first driving force is applied to maintain the longitudinal force of the vehicle at zero, and controlling the first driving force and the second driving force to be generated by a driving motor provided in each tire.

[0018] In addition, a steering assist control method for a vehicle according to another embodiment of the present invention is characterized in that it further includes a vehicle stop determination step of determining whether the vehicle is stopped using a wheel speed of the vehicle before recognizing a change in the steering angle in the turning direction recognition step.

[0019] The tire drive control step is characterized in that, as the tire to which the first drive force is applied, the outer front wheel is determined as the tire to which a positive (+) drive force is applied and the inner front wheel is determined as the tire to which a negative (-) drive force is applied, based on the turning direction in which the tires rotate.

[0020] The tire drive control step is characterized in that, as the tire to which the second drive force is applied, the inner rear wheel is determined as the tire to which a positive (+) drive force is applied and the outer rear wheel is determined as the tire to which a negative (-) drive force is applied, based on the turning direction in which the tires rotate.

[0021] In addition, a vehicle steering assist control method according to another embodiment of the present invention further includes, before the tire drive control step, a steering assist determination step of determining a magnitude of a required steering torque required to rotate the tires in a left-turning or right-turning direction according to the magnitude of the steering angle, and determining that a portion of the required steering torque should be assisted by a driving force generated by the driving motor if the required steering torque exceeds a limit steering torque that can be generated by the steering motor.

[0022] The steering assist determining step determines a ratio of the steering torque generated by the steering motor to the steering assist torque generated by the drive motor, out of the required steering torque. [Effects of the Invention]

[0023] The present invention controls the steering torque required for tire rotation so that it can be supplemented by the driving force of the drive motor, thereby preventing an increase in the steering torque that needs to be generated by the steering motor and reducing the weight and cost of the steering motor.

[0024] In addition, the present invention enables the tire to be rotated with a steering torque greater than the limit steering torque that can be generated by the steering motor through cooperation with the drive motor, thereby minimizing the increase in weight and volume of the steering motor and providing flexibility in packaging design for the inner tire area.

[0025] In addition, this document can provide various other effects that can be understood directly or indirectly. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a block diagram of a vehicle steering assist device according to the present invention; [Figure 2] FIG. 10 is an illustrative diagram showing how the length of a moment arm is changed during a steering operation of a vehicle. [Figure 3] 1 is a plan view showing how additional driving force is applied to the tires of a four-wheel independently steering vehicle during steering according to the present invention; [Figure 4] 1 is a rear view showing how additional driving force is applied to the tires of a four-wheel independently steering vehicle during steering according to the present invention; [Figure 5] 1 is an exemplary diagram showing that a driving force for generating a steering assist moment is additionally applied to each tire of a four-wheel independent steering vehicle according to the present invention; [Figure 6] 1 is a block diagram of a vehicle steering assist control method according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0027] Some embodiments of the present invention will be described in detail below with reference to the accompanying drawings. When assigning reference numerals to components in each drawing, it should be noted that the same reference numerals are used for the same components even if they are shown in different drawings. Furthermore, when describing the embodiments of the present invention, if it is determined that a detailed description of related known structures or functions would hinder understanding of the embodiments of the present invention, such a detailed description will be omitted.

[0028] When describing components of an embodiment of the present invention, terms such as "first," "second," "A," "B," "(a)," and "(b)" may be used. These terms are used to distinguish the component from other components and do not limit the nature, order, or sequence of the components. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as meanings consistent with the meanings they have in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense unless expressly defined in this application.

[0029] Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.

[0030] FIG. 1 is a block diagram of a vehicle steering assist device according to the present invention.

[0031] Referring to FIG. 1, the steering assist device for a vehicle according to the present invention may include a turning direction recognition unit 200 that recognizes the rotation direction of tires in which a vehicle is about to turn, using a steering angle controlled by steering wheel operation, and a tire drive control unit 500 that determines which tires are to receive a first driving force for generating a steering assist torque to assist the rotation of the tires in the recognized turning direction and which tires are to receive a second driving force that offsets the first driving force in order to maintain the longitudinal force of the vehicle at zero, and controls the first driving force and the second driving force to be generated by driving motors provided in the respective tires.

[0032] The turning direction recognition unit 200 can recognize whether the rotation direction of the tires is turning right or left based on a change in the steering angle caused by steering wheel operation.

[0033] That is, depending on the turning direction, the tire driving control unit 500 applies a first driving force to a tire different from the tire to which the second driving force is applied, so the turning direction recognition unit 200 can first determine whether the vehicle is intending to turn right or left.

[0034] In this case, the present invention aims to generate a steering assist moment by the driving force of the tires when steering in a stopped state, which requires a large steering torque during steering operation, and can further include a stopping determination unit 100 that uses the wheel speed of the vehicle to determine in advance whether the vehicle is stopped or not.

[0035] The vehicle stop determination unit 100 can determine whether the vehicle is in a stopped state based on whether the wheel speed of the tires obtained from a wheel speed sensor provided in the vehicle is 0, and whether the gear information of the automatic transmission obtained from the vehicle's electronic control unit (ECU) is in a parked state.

[0036] When steering using an electric power steering (MDPS), the steering motor must generate a steering torque that rotates the tires by the steering angle, and a steering moment that rotates the tires in the steering direction must be applied to them.

[0037] Therefore, in order to generate a steering torque that rotates the tire, a steering motor is provided on one side of the tire, as shown in Figures 3 and 4, to generate a steering moment that rotates the tire in response to movement of the steering wheel.

[0038] 3 and 4 show an example of tires mounted on a four-wheel independent steering vehicle in which all four tires can be steered and driven independently. Each tire may be equipped with a steering motor 10 that generates a steering torque to rotate the tire in the steering direction, and a drive motor 20 that generates a front-rear driving force for the tire.

[0039] 3 and 4 show that the steering motor 10 is installed on one side of the tire, and the drive motor 20 is installed inside the tire. Also, a kingpin shaft is diagonally coupled to one side of each tire as a steering shaft for transmitting the steering operation provided by the steering wheel to each tire. As a result, since both the kingpin shaft and the steering motor need to be installed on one side of each tire, there are spatial limitations on increasing the size of the steering motor itself in order to increase the steering motor capacity.

[0040] As described above, because the kingpin shaft and steering motor are installed diagonally on one side of each tire, the steering moment applied to the tire that rotates due to the steering operation changes depending on the steering angle at which the turn is attempted. That is, as the steering angle increases, the steering moment that needs to be applied to rotate the tire increases.

[0041] That is, as shown in FIG. 2(a), in a zero turn situation where the steering angle is 0°, the tire is deformed by the vertical moment W applied while pressing against the ground by the gross vehicle weight (GVW) and the reaction force R of the ground, and a certain amount of pressing force δ0 is generated.

[0042] Furthermore, as shown in Figure 2(b), even in a full turn situation where the steering angle is at its maximum, the tire deforms due to the vertical moment W applied by the gross vehicle weight (GVW) while pressing against the ground, and the reaction force R of the ground, generating a certain amount of pressure δ1.

[0043] In this case, the greater the steering angle of the vehicle, i.e., in the case of a full turn compared to a zero turn, the greater the vertical moment W applied from the tire to the ground, and the greater the amount of pressure caused by the deformation of the tire.

[0044] Also, as shown in Figures 2(a) and 2(b), in the case of zero turn, the length of moment arm r0 from the kingpin axis to the center of the tire is longer than in the case of a full turn, and the length of moment arm r1 from the kingpin axis to the center of the tire becomes longer, so the vertical moment also increases, and the steering moment (also called kingpin moment) required to steer the tire also increases.

[0045] Generally, when a vehicle turns, a larger steering moment is required for steering when the vehicle is stopped, which is affected by the static friction coefficient, than when the vehicle is moving, which is affected by the dynamic friction coefficient, and a large steering torque is required to satisfy this steering moment.

[0046] As a result, the steering torque required to rotate the tires needs to be generated by the steering motor, and therefore, when the vehicle is stopped, when the greatest steering torque is required, a steering motor with a capacity sufficient to generate the steering torque required for a full turn must be provided, which means that the size of the steering motor also needs to increase.

[0047] In the present invention, taking into consideration that the generation of the maximum steering torque required by the steering motor is not always required, the steering moment required for steering the vehicle is normally supplied by the steering torque generated by the steering motor 10 alone, but when a steering moment exceeding the limit steering torque that can be generated by the steering motor is required (for example, when turning left or right at the maximum steering angle, i.e., a full turn, while the vehicle is stopped), the insufficient steering torque is made up by the driving force generated by the drive motor 20 provided on each tire, as shown in the following [Equation 1].

[0048] [Number 1] Required steering torque = steering torque + (motor shaft offset x driving force)

[0049] In this case, the driving force generated by the driving motor 20 is applied at a position spaced apart from the motor rotation shaft of the steering motor 10 by a distance corresponding to the motor shaft offset, as shown in FIG. 4. Therefore, in [Equation 1], the steering assist torque that contributes to steering the tires is expressed as the product of the "motor shaft offset and driving force."

[0050] In this way, by controlling the steering torque required for tire rotation to be supplemented by the driving force of the drive motor 20, the steering torque that needs to be generated by the steering motor 10 can be prevented from increasing, the weight and cost of the steering motor can be reduced, and the reduction in the volume of the steering motor can minimize the installation space in the inner tire area.

[0051] In addition, the tire drive control unit 500 determines the tire to which a first drive force is applied to generate a steering assist torque that induces rotation in the turning direction identified by the turning direction recognition unit 200, and controls the drive motor 20 provided on the determined tire to generate the first drive force that assists the rotation of the tire.

[0052] As shown in Figures 5(a) and 5(b), the tire drive control unit 500 can determine the outer front wheel as the tire to which a positive (+) drive force is applied and the inner front wheel as the tire to which a negative (-) drive force is applied, based on the turning direction in which the tires rotate.

[0053] In this case, the positive (+) driving force generated by the driving motor 20 means a force that rotates the tire in the forward direction, and the negative (-) driving force means a force that rotates the tire in the backward direction.

[0054] Typically, the center of rotation of the moment arm is on the inside of the vehicle, so a positive (+) driving force applied to the tire creates a toe-in, and a negative (-) driving force applied to the tire creates a toe-out.

[0055] Therefore, in order to generate a steering assist moment for rotating the tires in the turning direction, the outer front wheel needs to be toe-in and the inner front wheel needs to be toe-out based on the turning direction, so the tire drive control unit 500 can control the application of a positive (+) driving force to the outer front wheel and a negative (-) driving force to the inner front wheel.

[0056] In this case, the tire drive control unit 500 uses the driving force of the drive motor only to assist part of the steering torque when the steering angle is large, such as when the vehicle is making a full turn while stopped, so the vehicle must remain stopped.

[0057] As a result, the tire drive control unit 500 can cancel out the first drive force applied to the tire to generate steering assist torque, determine the tire to which the second drive force for maintaining the vehicle in a stopped state is applied, and control the drive motor 20 provided on the determined tire to generate the second drive force that maintains the longitudinal force of the vehicle at 0.

[0058] The tire drive control unit 500 can determine the inner rear wheel as the tire to which a positive (+) drive force is applied and the outer rear wheel as the tire to which a negative (-) drive force is applied, based on the turning direction in which the tires rotate.

[0059] Therefore, as shown in FIG. 5(a), when a vehicle in a stopped state is steered to make a left turn, a positive (+) driving force is applied to the right front wheel of the vehicle and a negative (-) driving force is applied to the left front wheel as a first driving force for generating a steering assist moment, and a positive (+) driving force is applied to the left rear wheel of the vehicle and a negative (-) driving force is applied to the right rear wheel as a second driving force that offsets the first driving force to maintain the longitudinal force at 0.

[0060] Also, as shown in FIG. 5(b), when a vehicle in a stopped state is steered to make a right turn, a positive (+) driving force is applied to the left front wheel of the vehicle and a negative (-) driving force is applied to the right front wheel as a first driving force for generating a steering assist moment, and a positive (+) driving force is applied to the right rear wheel of the vehicle and a negative (-) driving force is applied to the left rear wheel as a second driving force that offsets the first driving force to maintain the longitudinal force at 0.

[0061] In addition, the length of the moment arm changes depending on the magnitude of the steering angle that attempts to rotate the tire, and the moment that acts on the rotation of the tire due to the steering torque generated by the steering motor changes depending on the change in the length of the moment arm.

[0062] Therefore, the present invention may further include a moment arm calculation unit 300 that calculates the length of the moment arm that changes when the tire rotates, using the magnitude of the steering angle due to steering operation.

[0063] The moment arm calculation unit 300 can calculate data indicating the increase / decrease relationship between the steering angle and the moment arm in advance using characteristic values ​​related to vehicle specifications such as the installation positions of the kingpin shaft and the steering motor and the motor shaft offset, and then store the calculated data in a storage means such as a memory.

[0064] As a result, when the magnitude of the steering angle increases due to a steering operation, the moment arm calculation unit 300 can determine the length of the moment arm that matches the magnitude of each steering angle from data stored in a memory or the like.

[0065] In addition, the present invention may further include a steering assist determination unit 400 that determines the magnitude of the steering torque required to rotate the tires in a left or right turning direction when the vehicle is stopped, depending on the magnitude of the steering angle, and determines to supplement a part of the required steering torque with the driving force generated by the drive motor 20 when the required steering torque exceeds the limit steering torque that can be generated by the steering motor 10.

[0066] When the steering wheel of a vehicle is turned to turn left or right while the vehicle is stationary, not only does the length of the moment arm and the vertical moment increase, but the required steering torque required to rotate the vehicle's tires also increases, so that the required steering torque may exceed the limit steering torque that can be generated by the steering motor.

[0067] As a result, when the steering assist determination unit 400 determines that the required steering torque exceeds the limit steering torque, it can determine that part of the required steering torque should be borne by the tire drive control unit 500. In this way, when the steering assist determination unit 400 determines that part of the required steering torque should be borne by the drive motor, the tire drive control unit 500 can generate the steering assist torque.

[0068] The steering assist determination unit 400 can also determine the ratio of the steering torque generated by the steering motor 10 to the steering assist torque generated by the drive motor 20 out of the required steering torque.

[0069] In this case, the proportion of the auxiliary steering torque generated by the drive motor 20 can be increased, but since the auxiliary steering torque generated by the driving force of the drive motor 20 is an effect generated incidentally, it is possible to prevent an excessive proportion of the required steering torque from being shared.

[0070] This allows the steering assist determination unit 400 to set the proportion of the assist steering torque generated by the drive motor 20 so that it is borne within a range of 10% of the total steering torque required for tire rotation.

[0071] Furthermore, as the magnitude of the steering angle increases, the steering assist determination unit 400 matches the magnitude of the steering torque required to turn the tires in the right or left direction while the vehicle is stopped to the magnitude of the steering angle and stores it in memory, and can determine the required steering torque from the memory using the magnitude of the steering angle.

[0072] In addition, the steering assist determination unit 400 stores in memory the proportion and magnitude of the assist steering torque that needs to be generated by the drive motor by the tire drive control unit 500, along with the required steering torque, so that simply by recognizing the magnitude of the steering angle, it is possible to control both the generation of the steering torque by the steering motor and the generation of the steering assist torque by the drive motor.

[0073] Next, with reference to FIG. 6, a vehicle steering assist control method according to another embodiment of the present invention will be described.

[0074] FIG. 6 is a block diagram of a vehicle steering assist control method according to the present invention.

[0075] Referring to FIG. 6, the steering assist control method for a vehicle according to the present invention may include a turning direction recognition step (S200) of recognizing the rotation direction of the tires in which the vehicle is about to turn using a steering angle controlled by steering wheel operation, and a tire drive control step (S500) of determining a tire to which a first driving force is applied to generate a steering assist torque to assist the rotation of the tires in the recognized turning direction and a tire to which a second driving force is applied to offset the first driving force in order to maintain the longitudinal force of the vehicle at zero, and controlling the first driving force and the second driving force to be generated by a driving motor provided in each tire.

[0076] In the turning direction recognition step (S200), it is possible to recognize whether the rotation direction of the tires is turning right or left based on a change in the steering angle caused by steering wheel operation.

[0077] In this way, depending on the rotation direction of the tires determined in the turning direction recognition step (S200), the tire drive control step (S500) can determine which tire to apply the first driving force and which tire to apply the second driving force.

[0078] In this case, the method may further include a vehicle stop determination step (S100) for determining whether the vehicle is stopped using the vehicle wheel speed before recognizing a change in the steering angle in the turning direction recognition step (S200). That is, since the present invention is intended to supplement the steering torque when steering in a stopped state where a large steering torque is required, it is preferable to first determine whether the vehicle is stopped.

[0079] In addition, in the tire drive control step (S500), the tire to which the first drive force is applied to generate a steering assist torque that induces the rotation of the tire in the turning direction identified in the turning direction recognition step (S200) is determined, and the drive motors provided on the determined tires are controlled to generate the first drive force that assists the rotation of the tire.

[0080] In this tire drive control step (S500), the outer front wheel can be determined as the tire to which the first drive force is applied, based on the turning direction in which the tires rotate, and the inner front wheel can be determined as the tire to which the negative (-) drive force is applied.

[0081] As a result, a positive (+) driving force is applied to the outside front wheel, causing toe-in, and a negative (-) driving force is applied to the inside front wheel, causing toe-out, generating a steering assist torque that causes the tire to rotate in the direction that tries to rotate the tire.

[0082] In addition, in the tire drive control step (S500), in order to maintain the vehicle in a stopped state while steering the tires, the first drive force applied to the tires to generate steering assist torque is offset, and the tires to which the second drive force for maintaining the vehicle in a stopped state is applied are determined, and the drive motors provided on the determined tires are controlled to generate the second drive force that maintains the total longitudinal force of the vehicle at 0.

[0083] For this reason, in the tire drive control step (S500), the inner rear wheel can be determined as the tire to which the second drive force is applied, based on the turning direction in which the tires rotate, as the tire to which a positive (+) drive force is applied, and the outer rear wheel can be determined as the tire to which a negative (-) drive force is applied.

[0084] As a result, when the vehicle is stopped, the driving force applied to the tires to generate steering assist torque is applied in opposite directions to the front and rear wheels on the same side, as shown in Figures 5(a) and 5(b), so that the front and rear forces acting on the entire vehicle can be kept at zero by the driving force, and the vehicle can be kept stopped during steering operations.

[0085] In addition, after the turning direction recognition step (S200), the present invention may further include a moment arm calculation step (S300) of calculating the length of a moment arm that changes when the tire rotates using the magnitude of the steering angle.

[0086] In the moment arm calculation step (S300), data showing the relationship between the steering angle and the increase / decrease in the moment arm is calculated in advance using characteristic values ​​related to vehicle specifications such as the installation positions of the kingpin shaft and the steering motor, and the motor shaft offset, and then stored in a storage means such as a memory, and the length of the moment arm that matches the magnitude of each steering angle can be calculated and grasped from the data stored in the memory or the like.

[0087] In addition, the present invention may further include a steering assist determination step (S400) before the tire drive control step (S500), in which the magnitude of the steering torque required to rotate the tires in a left or right turning direction is determined according to the magnitude of the steering angle, and if the required steering torque exceeds the limit steering torque that can be generated by the steering motor 10, a part of the required steering torque is determined to be assisted by the driving force generated by the drive motor 20.

[0088] In the steering assist determination step (S400), if it is determined that the required steering torque exceeds the limit steering torque, it can be determined that part of the required steering torque is shared by the tire drive control step (S500).

[0089] In this way, if it is determined in the steering assist determination step (S400) that a part of the required steering torque is to be shared by the drive motor, the steering assist torque can be generated in the tire drive control step (S500).

[0090] In addition, in the steering assist determination step (S400), the ratio of the steering torque generated by the steering motor 10 to the steering assist torque generated by the drive motor 20 out of the required steering torque can also be determined.

[0091] In the steering assist determination step (S400), as the magnitude of the steering angle increases, the magnitude of the steering torque required to rotate the tires in the right or left turning direction while the vehicle is stopped is matched to the magnitude of the steering angle and stored in memory, and the magnitude of the steering angle can be used to determine the required steering torque from the memory.

[0092] Furthermore, in the steering assist determination step (S400), the proportion and magnitude of the steering assist torque that needs to be generated by the drive motor 20 in the tire drive control step (S500) are stored in memory together with the required steering torque, so that simply by recognizing the magnitude of the steering angle, it is possible to control both the generation of the steering torque by the steering motor 10 and the generation of the steering assist torque by the drive motor.

[0093] The above description is merely an illustrative example of the technical concept of the present invention, and various modifications and variations can be made by a person having ordinary knowledge in the technical field to which the present invention pertains without departing from the essential characteristics of the present invention.

[0094] Therefore, the embodiments disclosed in the present invention are for illustrative purposes only and are not intended to limit the technical idea of ​​the present invention. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be interpreted as being included in the scope of the present invention. [Explanation of symbols]

[0095] 100 Stop Judgment Department 200 Turning direction recognition unit 300 Moment arm calculation section 400 Steering assistance decision unit 500 Tire drive control unit 10 Steering motor 20 Drive motor

Claims

1. a turning direction recognition unit that recognizes the rotation direction of the tires in which the vehicle is about to turn, using a steering angle controlled by a steering wheel operation; a tire drive control unit that determines a tire to which a first driving force for generating a steering assist torque that assists the rotation of the tire in the recognized turning direction is applied and a tire to which a second driving force that cancels the first driving force is applied in order to maintain the longitudinal force of the vehicle at zero, and controls the first driving force and the second driving force to be generated by a driving motor provided in each tire, The tire drive control unit includes: As the tires to which the first driving force is applied, the outer front wheel is determined as the tire to which a positive (+) driving force is applied and the inner front wheel is determined as the tire to which a negative (-) driving force is applied, based on the turning direction in which the tires rotate; The tire drive control unit includes: The steering assist device for a vehicle is characterized in that, as the tires to which the second driving force is applied, the inner rear wheel is determined as the tire to which a positive (+) driving force is applied and the outer rear wheel is determined as the tire to which a negative (-) driving force is applied, based on the turning direction in which the tires rotate.

2. 2. The vehicle steering assist device according to claim 1, further comprising a vehicle stop determination unit that determines in advance whether the vehicle is stopped or not, using a wheel speed of the vehicle.

3. The tire drive control unit includes:

2. The vehicle steering assist device according to claim 1, wherein, when the vehicle in a stopped state is steered to make a left turn, the first driving force is controlled so that a positive (+) driving force is applied to a right front wheel of the vehicle and a negative (-) driving force is applied to a left front wheel of the vehicle, and the second driving force is controlled so that a positive (+) driving force is applied to a left rear wheel of the vehicle and a negative (-) driving force is applied to a right rear wheel of the vehicle.

4. The tire drive control unit includes:

2. The vehicle steering assist device according to claim 1, wherein, when the vehicle in a stopped state is steered to make a right turn, the first driving force is controlled so that a positive (+) driving force is applied to a left front wheel of the vehicle and a negative (-) driving force is applied to a right front wheel of the vehicle, and the second driving force is controlled so that a positive (+) driving force is applied to a right rear wheel of the vehicle and a negative (-) driving force is applied to a left rear wheel of the vehicle.

5. 2. The vehicle steering assist device according to claim 1, further comprising a moment arm calculation unit that calculates in advance data indicating the relationship between the steering angle and the increase / decrease in the moment arm using characteristic values ​​of the vehicle including installation positions of a kingpin shaft and a steering motor, and a motor shaft offset, and then stores the calculated data in a memory, and that obtains from the memory a length of the moment arm that changes when a tire rotates using the magnitude of the steering angle.

6. 2. The vehicle steering assist device according to claim 1, further comprising a steering assist determination unit that determines a magnitude of a required steering torque required to rotate tires in a left turn or a right turn direction while the vehicle is stationary, according to the magnitude of the steering angle, and determines to supplement a part of the required steering torque with a driving force generated by the driving motor when the required steering torque exceeds a limit steering torque that can be generated by the steering motor.

7. The steering assist determination unit 7. The vehicle steering assist device according to claim 6, wherein a ratio of the steering torque generated by the steering motor to the steering assist torque generated by the drive motor is determined.

8. a turning direction recognition step of recognizing a rotation direction of a tire in which the vehicle is about to turn, using a steering angle controlled by a steering wheel operation; a tire drive control step of determining a tire to which a first drive force for generating a steering assist torque to assist the rotation of the tire in the recognized turning direction is applied and a tire to which a second drive force for canceling the first drive force is applied in order to maintain the longitudinal force of the vehicle at zero, and controlling the first drive force and the second drive force to be generated by a drive motor provided in each tire, The tire drive control step includes: As the tires to which the first driving force is applied, the outer front wheel is determined as the tire to which a positive (+) driving force is applied and the inner front wheel is determined as the tire to which a negative (-) driving force is applied, based on the turning direction in which the tires rotate; The tire drive control step includes: a steering assist control method for a vehicle, characterized in that, as the tires to which the second driving force is applied, the inner rear wheel is determined as the tire to which a positive (+) driving force is applied and the outer rear wheel is determined as the tire to which a negative (-) driving force is applied, based on the turning direction in which the tires rotate.

9. 9. The steering assist control method for a vehicle according to claim 8, further comprising a vehicle stop determination step of determining whether the vehicle is stopped using a wheel speed of the vehicle before recognizing the change in the steering angle in the turning direction recognition step.

10. 9. The vehicle steering assist control method according to claim 8, further comprising a steering assist determination step of, before the tire drive control step, determining a magnitude of a required steering torque required to rotate the tires in a left-turning or right-turning direction in accordance with the magnitude of the steering angle, and, if the required steering torque exceeds a limit steering torque that can be generated by a steering motor, determining to assisted a part of the required steering torque by a driving force generated by the driving motor.

11. The steering assist determination step includes:

11. The vehicle steering assist control method according to claim 10, further comprising determining a ratio of the steering torque generated by the steering motor to the steering assist torque generated by the drive motor, out of the required steering torque.

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