System and method for detecting a hands-free state of a steering wheel

Abstract

A method for detecting a hands-free state of a steering wheel, the method comprising: Obtaining (S20), by a control device (CLR), a steering torque, a steering angle and a steering angular velocity while a vehicle is being driven, Determining (S30), by the control device (CLR), a variance value of the steering angular velocity by accumulation for a first predetermined period of time, Determining (S40), by the control device (CLR), a difference value by cumulating over a second predetermined period of time the differences between a steering angular velocity estimated by a steering system model determined on the assumption that the steering wheel is in the hands-free state and a steering angular velocity measured by a steering sensor when the variance value of the steering angular velocity is less than a first threshold value, and Determining (S70, S90), by the control device (CLR), whether the steering wheel is in the hands-free state or in the hands-on state, according to the difference value between the measured and the estimated steering angular velocity.

Description

Background of the inventionField of the invention

[0001] The present invention relates to a system and method for detecting a hands-free state of a steering wheel, wherein an indirect hands-on / hands-free detection logic is improved and therefore a hands-on / hands-free detection performance can be improved. Description of the technology used

[0002] In some autonomous driving modes in which a driving state of the vehicle is controlled to control or prevent road and lane departure, an autonomous driving mode is executed only in a hands-on state in which a driver grips the steering wheel, a warning of a release situation is provided, and then the corresponding autonomous driving mode is turned off in a hands-free state in which the driver removes his or her hands from the steering wheel, and therefore it is necessary to detect the hands-free state of the steering wheel.

[0003] A steering sensor provided in a motor driven power steering system (MDPS) is configured to measure and detect a steering torque of a steering wheel, and using such a steering sensor can indirectly detect whether a driver is gripping the steering wheel or not.

[0004] That is, when the driver grips the steering wheel and when the driver takes his or her hands off the steering wheel, different torque fluctuations are detected, and therefore, the hands-on state of the steering wheel (in a state in which the driver holds or grips the steering wheel with his or her hands) and the hands-off state of the steering wheel (in a state in which the driver takes his or her hands off the steering wheel) can be determined based on such a torque fluctuation difference.

[0005] For example, if a measure of torque fluctuation detected by the steering sensor is within a predetermined torque fluctuation range, such a state can be determined as the hands-free state.

[0006] However, in the case of the above-described technique which indirectly detects the hands-on / hands-off state, when the vehicle is driven on a rough road generating noise or vibration due to a reaction force with the road surface, such noise or vibration may generate a torque change and an increase in a degree of torque fluctuation, and therefore the hands-off state may be erroneously detected as the hands-on state.

[0007] In addition, if the driver grips an equal left and right position of the steering wheel using both hands or the driver grips the steering wheel weakly or negligibly, a magnitude of the torque may be small and a measure of the torque fluctuation may be small, and therefore the hand-on state may be erroneously determined as the hands-free state.

[0008] As a method for directly detecting the hands-on or hands-free state of a steering wheel, a sensor may be mounted in the steering wheel to detect whether the driver is gripping the steering wheel or not.

[0009] However, if the driver grips an area of ​​the steering wheel where the sensor is not installed, it is difficult to detect the hand-on state, and if the driver has only one finger on the steering wheel or the driver is wearing gloves and therefore conductivity is low, it is difficult to detect the hand-on state.

[0010] In addition, the above sensor can only detect whether the driver is gripping the steering wheel or not, and in order to detect a grip strength or holding strength of the driver's hands on the steering wheel, a plurality of sensors must be additionally attached, and therefore the manufacturing cost of the steering wheel is increased.

[0011] The information disclosed in this "Background of the Invention" section is provided for the sole purpose of facilitating an understanding of the general background of the invention and is not intended as an acknowledgement or any form of suggestion that this information constitutes prior art already known to those skilled in the art.

[0012] For example, from DE 10 2016 209 833 A1 a method and a system for detecting a hands-free state of a steering wheel is known, the method comprising: obtaining, by a control device, a steering torque, and comparing the steering torque with a threshold value to determine whether a hands-free state of the steering wheel exists.

[0013] Further methods and systems for detecting a hands-free state of a steering wheel based on a steering torque are known, for example, from DE 10 2014 208 862 A1 and DE 10 2009 058 001 A1. Brief explanation of the invention

[0014] It is an object of the present invention to provide a system and a method for detecting a hands-free state of a steering wheel, in which indirect hands-on / hands-free detection logic is improved and, therefore, hands-on / hands-free detection performance is improved. The above object is achieved by a method for detecting a hands-free state of a steering wheel with the features according to claim 1 and, respectively, by a system for detecting a hands-free state of a steering wheel with the features according to claims 12 and 14. Further embodiments of the systems and the method are described in the respective dependent claims.

[0015] That is, a method for detecting a hands-free state of a steering wheel is provided, which method comprises: obtaining, by a control device, a steering torque (e.g., a steering torque value), a steering angle (e.g., a steering angle value), and a steering angular velocity (e.g., a steering speed value, i.e., a steering angle derived from time), while a vehicle is being driven (e.g., straight ahead), determining (e.g., calculating), by the control device, a variance value of the steering angular velocity (e.g., variation of the steering angular velocity, e.g., variation of the steering speed value around the value 0; e.g., size of an interval around the value 0 in which the steering angular velocity varies) by cumulating for a predetermined first period of time, determining (e.g.,Calculating), by the control device, a difference value between a steering angular velocity, which is estimated by a steering system model on the assumption that the steering wheel is in the hands-free state, and a steering angular velocity, which is measured by a steering or steering wheel sensor (hereinafter referred to as: steering sensor), by accumulating the differences for a predetermined second time period if the variance value of the steering angular velocity is less than a first threshold value, and determining (e.g. determining for a predetermined time period, ie, in distinguishable time period sub-ranges), by the control device, according to the difference value between the measured and the estimated steering angular velocity, whether the steering wheel is in the hands-free state (e.g. a state in which the driver is not gripping or touching the steering wheel with any hand) or in the hands-on state (e.g.a condition in which the driver grips or touches the steering wheel with at least one hand) or not.

[0016] For example, when determining whether the steering wheel is in the hands-free state or the hands-on state according to the difference value between the measured and the estimated steering angular velocity, the control device may be configured to determine that the steering wheel is in the hands-free state when the difference value between the measured and the estimated steering angular velocity is less than a second threshold value, and to determine that the steering wheel is in the hands-on state when the difference value between the measured and the estimated steering angular velocity is not less than the second threshold value.

[0017] For example, the method may further comprise determining, by the control device, whether or not the difference value between the measured and the estimated steering angular velocity is maintained for a predetermined third period of time or longer.

[0018] For example, the variance value of the steering angle velocity can be determined by the following equation 1. vθ=∑i=nn−N(θ˙i−θ˙¯)2N, where v θ is the variance value of the steering angle velocity, θ ̇ the steering angle speed is, θ˙¯ is the mean value of the steering angle speed and N is a test or determination time period (e.g. first time period).

[0019] For example, the difference value between the measured and the estimated steering angular velocity can be determined by the following equation 2. ∑i=nn−N(θ˙h,i(model)−θ˙h,i(measure))2, where θ̇ h,i (model) is the steering angular velocity estimated by the steering system model, which is determined on the assumption that the steering wheel is in the hands-free state, and θ ̇ h,i(measure) is the steering angle speed measured by the steering sensor.

[0020] For example, the steering angular velocity estimated by the steering system model can be determined by: establishing an equation of motion of the steering system model which has the steering wheel provided at an upper end portion of a torsion bar and which is determined on the assumption that the steering wheel is in the hands-free state, establishing state equations using the steering angle and the steering angular velocity as state quantities from the equation of motion, and determining the steering angular velocity of the hands-free state from the state equations.

[0021] For example, the method performed by the control device may further comprise determining a variance value of the steering torque by accumulation for a predetermined fourth time period when the variance value of the steering angular velocity is not less than the first threshold value, and determining, by the control device, whether or not the steering wheel is in the hands-free state or the hands-on state according to the variance value of the steering torque.

[0022] For example, in determining whether or not the steering wheel is in the hands-free state or the hands-on state according to the variance value of the steering torque, the control device may be configured to determine that the steering wheel is in the hands-free state when the variance value of the steering torque is less than a third threshold value, and to determine that the steering wheel is in the hands-on state when the variance value of the steering torque is not less than the third threshold value.

[0023] For example, the method may further comprise determining, by the controller, whether the steering torque variance value is maintained for a predetermined fifth period of time or longer.

[0024] For example, the variance value of the steering torque can be determined by the following equation 3: vr=∑i=nn−N(τi−τ¯)2N, where v τis the variance value of the steering torque, τ is the steering torque, τ is the torque average and N is a test or determination time period (e.g. fifth time period).

[0025] For example, the method may further comprise determining, by the controller, whether a current driving mode of the vehicle is an autonomous driving mode, and issuing a warning about the hands-free state upon determining that the current driving mode of the vehicle is the autonomous driving mode and the steering wheel is in the hands-free state.

[0026] Furthermore, a system for detecting a hands-free state of a steering wheel comprises: a steering angular velocity variance calculation unit configured to determine a variance value of a steering angular velocity detected by a steering sensor while a vehicle is being driven by accumulation for a predetermined first period of time; a steering angular velocity estimation unit configured to estimate a steering angular velocity by a steering system model determined on the assumption that the steering wheel is in the hands-free state; a steering angular velocity difference calculation unit configured to determine a difference value between the steering angular velocity estimated by the steering system model and the steering angular velocity measured by the steering sensor by accumulation of the differences for a predetermined second period of time;if the variance value of the steering angular velocity is not less than the first threshold value, and a hands-on / hands-free determination unit configured to determine the hands-free state or a hands-on state of the steering wheel according to the difference value between the measured and the estimated steering angular velocity.

[0027] For example, the system may further comprise a steering torque variance calculation unit configured to determine a variance value of the steering torque by accumulation for a predetermined third period of time when the variance value of the steering angular velocity is less than the first threshold value, and the hands-on / hands-off determination unit may determine the hands-off state or the hands-on state of the steering wheel according to the variance value of the steering torque.

[0028] The methods and apparatus of the present invention have other features and advantages which will be apparent from, or set forth in greater detail in, the accompanying drawings incorporated herein and the following detailed description, which together serve to explain certain principles of the present invention. Short description of the drawings Fig. 1 is a block diagram illustrating a system for detecting a hands-free condition of a steering wheel in accordance with various aspects of the present invention, Fig. 2 is a view exemplifying a steering system model used in the present invention, Fig. 3A and Fig. 3B are flowcharts illustrating a complete control flow of a method for detecting a hands-free state of a steering wheel in accordance with various aspects of the present invention, Fig. 4 is a graph showing a detection result of a hands-on / hands-free state of the steering wheel before and after applying the system and method in accordance with various aspects of the present invention when a vehicle is driven on a rough road in a hands-free state of the steering wheel, Fig. 5 is a graph showing a detection result of the hands-on / hands-free state of the steering wheel before and after applying the system and method in accordance with various aspects of the present invention when the vehicle is driven in a state in which a driver places a single hand at a position of the steering wheel, and Fig. 6 is a graph showing a detection result of the hands-on / hands-free state of the steering wheel before and after applying the system and method in accordance with various aspects of the present invention when the vehicle is driven in a state in which the driver places both hands at respective equal left and right positions of the steering wheel.

[0029] It should be understood that the attached drawings are not necessarily to scale and provide a somewhat simplified representation of various features embodying the basic principles of the present invention. Specific design features of the present invention, as included herein, such as specific dimensions, orientations, locations, and shapes, will be determined in part by the intended application and environment of use.

[0030] Throughout the numerous figures of the drawing, reference numerals in the figures designate the same or essentially equivalent parts of the present invention. Detailed description

[0031] Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. Although the invention has been described in connection with the exemplary embodiments, it is to be understood that the present description is not intended to limit the invention to these exemplary embodiments.

[0032] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, like reference numerals designate like or similar elements throughout the drawings.

[0033] The Fig. 1 is a block diagram illustrating a system for detecting a hands-free state of a steering wheel applied to the present invention, wherein the hands-on / hands-free state of the steering wheel is detected using steering information measured by a steering sensor 10.

[0034] For the present purpose, in accordance with various aspects of the present invention, the steering sensor 10 is used as a steering sensor capable of measuring a steering angle and a steering torque, for example, a torque angle sensor (TAS) used in a motor driven power steering system (MDPS).

[0035] Also, in an exemplary embodiment of the present invention, an autonomous driving mode switch 20 may be provided through which a driver can operate and select an autonomous driving mode.

[0036] Therefore, when the vehicle is driven at a desired speed or more, if the driver turns on the autonomous driving mode switch 20, the vehicle can be driven in the autonomous driving mode, and at the same time, the hands-free detection logic of the present invention can be executed, thereby detecting a hands-free state of the steering wheel.

[0037] To implement such a hands-free state detection function, the system is provided with a steering angular velocity variance calculation unit 100, a steering angular velocity estimation unit 200, a steering angular velocity difference calculation unit 300, and a hands-on / hands-free determination unit 500, and these modules may be included in a control device CLR.

[0038] With reference to the Fig. 1, the steering angular velocity variance calculation unit 100 determines a variance value of the steering angular velocity detected by the steering sensor 10 while the vehicle is running by accumulation for a predetermined period of time.

[0039] Further, the steering angular velocity estimation unit 200 determines a steering angular velocity by a steering system model, which is determined on the assumption that the steering wheel is in the hands-free state.

[0040] Here, the steering system model may be a model, and an upper end part (e.g., of the steering system) having the steering wheel attached thereto provided at an upper end portion of a torsion bar may be mathematically expressed as the model.

[0041] Furthermore, the steering angular velocity difference calculation unit 300 determines a difference value between the steering angular velocity estimated by the steering system model and the steering angular velocity measured by the steering sensor 10 by accumulation for a predetermined period of time when the variance value of the steering angular velocity is not less than a first threshold value.

[0042] The hands-on / hands-free determining unit 500 determines the hands-free state or the hands-on state of the steering wheel according to the difference value between the measured and the estimated steering angular velocity.

[0043] As a result of the determination, if the hands-on / hands-off determination unit 500 determines that the steering wheel is in the hands-off state and whether the vehicle is currently being driven in the autonomous driving mode, it is determined according to a signal transmitted from the autonomous driving mode switch 20, and upon determining that the vehicle is currently being driven in the autonomous driving mode, a warning that the steering wheel is in the hands-off state is output or displayed through a cluster or a speaker.

[0044] Furthermore, in accordance with various aspects of the present invention, the system may further include a torque variance calculation unit 400 that determines a variance value of the steering torque by accumulating for a predetermined period of time when the variance value of the steering angular velocity is smaller than the first threshold value.

[0045] Therefore, the hands-on / hands-off determining unit 500 determines the hands-off state or the hands-on state of the steering wheel according to the variance value of the steering torque.

[0046] The control device CLR in accordance with various exemplary embodiments of the present invention may be implemented by a processor configured to perform an operation described below using an algorithm configured to control operations of various components of the vehicle, and a non-volatile memory configured to store data concerning software instructions for reproducing the algorithm and the stored data in the corresponding memory. Here, the memory and the processor may be implemented as separate chips. Alternatively, the memory and the processor may be implemented as an integral chip. One or more processors may be provided.

[0047] The system in accordance with various aspects of the present invention determines whether the steering wheel is in the hands-on state or the hands-free state using steering information measured or provided by the steering sensor 10 and steering information determined using the steering system according to the driving state of the vehicle by the control device CLR described above.

[0048] With reference to the Fig. 1 and Fig. 3 describes a method for detecting a hands-free state of a steering wheel in accordance with various aspects of the present invention. First, the control device CLR detects a steering torque, a steering angle, and a steering angular velocity while the vehicle is being driven.

[0049] For example, the steering torque and the steering angle can be measured by the steering sensor 10 and the steering angular velocity can be determined by deriving the steering angle.

[0050] Subsequently, the control device CLR determines a variance value of the steering angular velocity by accumulation for a predetermined period of time.

[0051] Here, the variance value of the steering angular velocity can be calculated by the following equation 1. vθ=∑i=nn−N(θ˙i−θ˙¯)2N, where ve is a variance value of the steering angular velocity, θ ̇ : a steering angle velocity, θ˙¯ is an average of the steering angle velocity and N is a test time period.

[0052] That is, if a driver changes the direction of the steering wheel or the vehicle drives on an uneven road / lane and thus generates vibrations of the steering wheel, a cumulative variance value of the steering angular velocity is increased.

[0053] However, since a variance value of the steering angular velocity determined when the driver changes a driving direction in the hands-on state of the steering wheel is larger than a variance value of the steering angular velocity determined when the vehicle is driven on a rough road in the hands-free state of the steering wheel, it is possible to determine whether the steering wheel is in the hands-on state or the hands-free state as needed according to the variance value of the steering angular velocity.

[0054] Subsequently, when the variance value of the steering angular velocity is smaller than a first threshold value, the control device CLR determines a difference value between a steering angular velocity estimated by the steering system model obtained on the assumption that the steering wheel is in the hands-free state and a steering angular velocity measured by the steering sensor 10 by accumulating the differences for a predetermined period of time.

[0055] Here, the difference between the measured and the estimated steering angle speed can be determined using the following equation 2. ∑i=nn−N(θ˙h,i(model)−θ˙h,i(measure))2, where θ ̇ h.i(model) is a steering angular velocity estimated by the steering system model, which is determined on the assumption that the steering wheel is in the hands-free state, and θ ̇ h,i(measure)a steering angle speed measured by the steering sensor.

[0056] The following describes a method for estimating a steering angle velocity using the steering system model. As described, for example, in the Fig. 2, assuming that the steering wheel of the steering system model is in the hands-free state, an equation of motion of the steering system model is established, wherein a steering wheel is provided at an upper end portion of a torsion bar projecting upward. For this purpose, the upper end portion of the steering system model may relate to the steering wheel, as shown in Fig. 2 and is described as a mathematical model by the following equation 2.1. Jhθ¨h+Chθ˙h+ktor(θh−θc)+τh,fsgn(θ˙h)=τh, where J h an inertia of the steering wheel, C h a damping of the steering wheel, θ h is a measured steering angle value, θ c: steering column angle (e.g. a rotation angle of the steering column), τ h is the driver's steering torque, τ sensor is a measured steering torque value, τ h,f a friction force of the steering wheel, k tor is a stiffness of the torsion bar, T s is a probationary period and τ h,f sgn(θ ̇ h ) a formula related to the friction force of the steering wheel is modeled.

[0057] Here, since the torque value τ measured by the steering sensor 10 sensor with a magnitude k tor (θ h - θ c ) of a torque applied to the torsion bar, and the friction force of the steering wheel is very small and can thus be ignored, the following equations 2.2 can be expressed. τsensor=ktor(θh−θc) and Jhθ¨h+Chθ˙h+τsensor=τh

[0058] Furthermore, assuming that the torque applied by the driver in the hands-free state of the steering wheel is 0 (τ h =0), an equation of motion of the steering system model in the hands-free state of the steering wheel can be given by the following equation 2.3. Jhθ¨h+Chθ˙h+τsensor=0

[0059] Subsequently, state equations in which the steering angle and the measured and estimated steering angular velocity are used as state variables can be set as the following equations 2.4. θ¨h=−ChJhθ˙h+τsensorX˙=AX+BuA=[−ChJh010],B=[−1Jh 0],X=[θ˙hθh],u=τ [θ˙h,i+1θh,i+1]=[1−TsChJh0Ts0][θ˙h,iθh,i]+[−TsJh 0]τsensor

[0060] Accordingly, the steering angular velocity of the steering wheel in the hands-free state is determined from the state equations expressed in equations 2.4.

[0061] That is, a difference between an estimated steering angular velocity determined by the steering system model from the assumption that the steering wheel is in the hands-free state and the steering angular velocity actually measured in the hands-free state of the steering wheel is insignificant, but a difference between the estimated steering angular velocity and a steering angular velocity measured in the hands-on state of the steering wheel is large because the steering system model is determined on the assumption that the steering wheel is in the hands-free state.

[0062] Therefore, the control device CLR can determine the hands-free state or the hands-on state of the steering wheel according to the difference value between the measured and the estimated steering angular velocity, which is expressed by the above equation 2 ∑i=nn−N(θ˙h,i(model)−θ˙h,i(measure))2 is determined.

[0063] For example, if the difference value between the measured and the estimated steering angular velocity is less than a second threshold value, the difference between the estimated steering angular velocity value determined by the steering system model, which is determined on the assumption that the steering wheel is in the hands-free state, and the actually measured steering angular velocity value is small, and therefore it is determined that the steering wheel is in the hands-free state.

[0064] On the other hand, if the difference value between the measured and the estimated steering angular velocity is not less than the second threshold value, the difference value between the estimated angular velocity value determined by the steering system model, which is determined on the assumption that the steering wheel is in the hands-free state, and the actual steering angular velocity value is large, and therefore it is determined that the steering wheel is in the hands-on state.

[0065] [Here, since a predetermined time period is required to determine the estimated steering angular velocity value, the difference value accumulated for a sample time period may be compared with the second threshold value.

[0066] Further, when determining whether the steering wheel is in the hands-free state or the hands-on state, it may be further determined whether the difference value between the measured and estimated steering angular velocity is maintained for a predetermined period of time or longer.

[0067] For example, if the difference value between the measured and estimated steering angular speeds is less than the second threshold value, it may be further determined whether or not a state in which the difference value between the measured and estimated steering angular speeds is less than the second threshold value is maintained for the predetermined period of time or longer, and upon determining that the state is maintained for the predetermined period of time or longer, it may be finally determined that the steering wheel is in the hands-free state.

[0068] Of course, even if the difference value between the measured and estimated steering angular velocity is not less than the second threshold value, it may be further determined whether or not a state in which the difference value between the measured and estimated steering angular velocity is not less than the second threshold value is maintained for a predetermined period of time or longer, and upon determining that the state is maintained for the predetermined period of time or longer, it may be finally determined that the steering wheel is in the hand-on state.

[0069] That is, by ultimately determining that the steering wheel is in the hands-on state or the hands-free state if the same detection result is maintained for a predetermined period of time, a frequently occurring change in the detection of the hands-free state when a disturbance occurs is suppressed, and therefore the robustness of the hands-free detection logic is improved.

[0070] The Fig. 4 is a graph showing detection results of the hands-free state of the steering wheel when the vehicle is driven on a rough road in the hands-free state of the steering wheel.

[0071] Before applying the present invention, when noise or vibration of a certain value or more is generated from the steering sensor 10 due to the uneven road surface or the uneven road, the hands-free state may be erroneously detected as the hands-on state.

[0072] However, after applying the present invention, even if the steering torque is generated by a reaction force of the road (1), the steering angular velocity, which is changed according to the physical conditions, compensates for the steering torque (2), as in Equation 2.5 given below, which is derived from Equation 2.4. Therefore, it can be confirmed that even if the steering torque is generated by the uneven road surface, the hands-free state can be normally detected. where C1J1 the damping of the steering angle / inertia of the steering wheel.

[0073] In the exemplary embodiment of the present invention, when the variance value of the steering angular velocity is not less than the first threshold value, a variance value of the steering torque may be averaged by accumulation for a predetermined period of time.

[0074] Here, the variance value of the steering torque can be determined by the following equation 3. vr=∑i=nn−N(τi−τ¯)2N, where v τ is a variance value of the steering torque, τ is a steering torque, τ is an average (steering) torque and N is the test time period.

[0075] That is, when the vehicle is driven straight, if the driver places one hand at a 6 o'clock position of the steering wheel or places both hands at a same left and right position of the steering wheel, the size of a value of the steering information and the change of the steering information detected by the steering sensor 10 are insignificant, and therefore, it may be difficult to detect the hands-free state.

[0076] Therefore, when the variance value of the steering torque is determined by the above equation 3, a large difference may occur between the hand-on state and the hand-free state.

[0077] Accordingly, the hands-free state or the hands-on state of the steering wheel can be determined according to the variance value of the steering torque determined by the above equation 3.

[0078] For example, if the steering torque variance value is smaller than a third threshold, it is determined that the steering wheel is in the hands-free state. That is, since the driver is not gripping the steering wheel in the hands-free state, the determined steering torque variance value is not large.

[0079] On the other hand, if the variance value of the steering torque is not less than the third threshold value, the driver grasps the steering wheel, and the determined variance value of the steering torque is relatively large, and therefore, it can be determined that the steering wheel is in the hand-on state.

[0080] Here, the hand-on state or the hand-free state of the steering wheel can be detected by comparing a variance value of a cumulative torque value determined for a sample period with the third threshold value.

[0081] In addition, when it is determined whether or not the steering wheel is in the hands-free state or the hands-on state, it can be further determined whether or not the variance value of the steering torque is maintained for a predetermined period of time or longer.

[0082] For example, if the variance value of the steering torque is less than the third threshold value, it may be further determined whether or not a state in which the variance value of the steering torque is less than the third threshold value is maintained for a predetermined period of time or longer, and upon determining that the state is maintained for the predetermined period of time or longer, it may be finally determined that the steering wheel is in the hands-free state.

[0083] Of course, even if the variance value of the steering torque is not less than the third threshold value, it may be further determined whether the state in which the variance value of the steering torque is not less than the third threshold value is maintained for a predetermined period of time or longer, and upon determining that the state is maintained for the predetermined period of time or longer, it may be finally determined that the steering wheel is in the hand-on state.

[0084] The Fig. 5 and Fig. 6 are graphs showing detection results of the hands-free state of the steering wheel when a driver places one hand at a 6 o'clock position of the steering wheel or places both hands at a same left and right position of the steering wheel when the vehicle is driven straight.

[0085] Before applying the present invention, even if the driver grips the steering wheel, a steering torque is too small and therefore the hand-on state may be misdetected as the hand-free state.

[0086] However, after applying the present invention, it can be confirmed that even if the steering torque is small, there is a variance of the steering torque, a variance value of the steering torque is large and therefore the hand-on state can be normally detected.

[0087] Further, in an exemplary embodiment of the present invention, the control device CLR may determine whether or not the driving mode is the autonomous driving mode by detecting a signal output from the autonomous driving mode switch 20.

[0088] Subsequently, upon determining that the current driving mode is the autonomous driving mode, upon determining that the steering wheel is in the hands-free state, a warning that the steering wheel is in the hands-free state may be provided by a display unit 30, such as the instrument cluster of the vehicle.

[0089] With reference to the Fig. 3A and Fig. 3B describes a process of detecting the hands-free state of the steering wheel in accordance with various aspects of the present invention. First, while the vehicle is traveling, the control device CLR monitors whether the autonomous driving mode switch 20 is turned on or not (process S10).

[0090] When monitoring whether the autonomous driving mode switch 20 is turned on, the control device CLR receives a steering signal through the steering sensor 10 and detects a steering torque, a steering angle, and a steering angular speed (process S20).

[0091] Thereafter, the control device CLR determines a variance value of the steering angular velocity using the above equation 1 (process S30) and compares the determined variance value of the steering angular velocity with the first threshold value (process S40).

[0092] As a result of the comparison in operation S40, if the variance value of the steering angular velocity is not less than the first threshold value, the control device CLR determines a difference value between a steering angular velocity based on the steering system model and the steering sensor 10 as indicated in the above equation 2 (operation S50).

[0093] Subsequently, the control device CLR compares the determined difference value between the measured and the estimated steering angular velocity with the second threshold value (process S51), and as a result of the comparison in process S51, if the difference value between the measured and the estimated steering angular velocity is less than the second threshold value, the control device CLR determines whether or not the state in which the difference value between the measured and the estimated steering angular velocity is less than the second threshold value is maintained for a predetermined period of time (process S52).

[0094] Subsequently, upon determining that the state in which the difference value between the measured and the estimated steering angular velocity is less than the second threshold value and is maintained for the predetermined period of time, the control device CLR determines that the steering wheel is in the hands-free state (process S70).

[0095] Subsequently, the control device CLR may control the display unit 30, such as the instrument cluster, to issue a warning to the driver that the steering wheel is in the hands-free state for a predetermined period of time (process S80) and may release the autonomous driving mode.

[0096] On the other hand, as the result of the comparison in operation S51, if the difference value between the measured and the estimated steering angular velocity is not less than the second threshold value, the control device CLR determines whether or not a state in which the difference value between the measured and the estimated steering angular velocity is not less than the second threshold value is maintained for a predetermined period of time (operation S53).

[0097] Subsequently, if the state in which the difference value between the measured and the estimated steering angular velocity is not less than the second threshold value is maintained for the predetermined period of time, the control device CLR determines that the steering wheel is in the hand-on state (process S90).

[0098] On the other hand, as the result of the comparison in operation S40, if the variance value of the steering angular velocity is not less than the first threshold value, the control device CLR determines a variance value of the steering torque using the above equation 3 (operation S60).

[0099] Subsequently, the control device CLR compares the determined variance value of the steering torque with the third threshold value (process S61), and as a result of the comparison in process S61, if a variance value of the steering torque is less than the third threshold value, the control device CLR determines whether or not a state in which the variance value of the steering torque is less than the third threshold value is maintained for a predetermined period of time (process S62).

[0100] Thereafter, upon determining that the state in which the variance value of the steering torque is less than the third threshold is maintained for the predetermined period of time, the control device CLR determines that the steering wheel is in the hands-free state (process S70).

[0101] Subsequently, the control device CLR may control the display unit 30, such as the instrument cluster, to issue a warning to the driver that the steering wheel is in the hands-free state for a predetermined period of time (process S80), and then release (e.g., terminate) the autonomous driving mode.

[0102] On the other hand, as the result of the comparison in operation S61, if the variance value of the steering torque is not less than the third threshold value, the control device CLR determines whether or not a state in which the variance value of the steering torque is not less than the third threshold value is maintained for a predetermined period of time (operation S63).

[0103] Thereafter, if the state in which the variance value of the steering torque is not less than the third threshold is maintained for the predetermined period of time, the control device CLR determines that the steering wheel is in the hand-on state (process S90).

[0104] As described above, in the system and method in accordance with various aspects of the present invention, the hands-on / hands-off state of the steering wheel is detected using steering information detected by the steering sensor 10 without an additional sensor to detect the hands-on / hands-off state of the steering wheel, and therefore, manufacturing costs can be reduced and hands-on / hands-off detection logic using the steering information can be improved, and therefore, hands-on / hands-off detection performance can be greatly improved.

[0105] Furthermore, the system and method in accordance with various aspects of the present invention solve misdetection of the hands-on state as the hands-off state due to detecting an excessively small steering torque in the hands-on state, solve misdetection of the hands-off state as the hands-on state due to a reaction force of a road surface in the hands-off state, and can therefore improve the robustness of the detection logic and reduce user dissatisfaction caused by misdetection.

[0106] As is clear from the above description, in a system and method for detecting a hands-free state of a steering wheel in accordance with various aspects of the present invention, the hands-on / hands-free state of the steering wheel is detected using steering information detected by a steering sensor, without an additional sensor to detect the hands-on / hands-free state of the steering wheel, and therefore, the manufacturing cost can be reduced and hands-on / hands-free detection logic can be improved using the steering information, and therefore, the hands-on / hands-free detection performance can be greatly improved.

[0107] Furthermore, the system and method in accordance with various aspects of the present invention solve misdetection of the hands-on state as the hands-off state due to detecting an excessively small steering torque in the hands-on state, solve misdetection of the hands-off state as the hands-on state due to a reaction force of a road surface in the hands-off state, and can thus improve the robustness of the detection logic and minimize user dissatisfaction caused by such misdetection.

[0108] For ease of explanation and to accurately define the appended claims, the terms "upper...", "lower...", "inner...", "outer...", "top", "bottom", "upward", "downward", "front...", "backward...", "front", "backward", "inside", "outside", "inside", "outside", "inward / inward", "outside / outward", "forward / forward" and "backward / rearward" are used to describe features of the exemplary embodiments with reference to positions of those features shown in the drawings.

[0109] The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed.

Claims

[1] A method for detecting a hands-free state of a steering wheel, the method comprising: Erlangen (S20), by a control device (CLR), a steering torque, a steering angle and a steering angular velocity while a vehicle is being driven, Determining (S30), by the control device (CLR), a variance value of the steering angular velocity by accumulation for a first predetermined period of time, Determining (S40), by the control device (CLR), a difference value by cumulating over a second predetermined period of time the differences between a steering angular velocity estimated by a steering system model determined on the assumption that the steering wheel is in the hands-free state and a steering angular velocity measured by a steering sensor when the variance value of the steering angular velocity is less than a first threshold value, and Determining (S70, S90), by the control device (CLR), whether the steering wheel is in the hands-free state or in the hands-on state, according to the difference value between the measured and the estimated steering angular velocity. [2] The method according to claim 1, characterized by that when determining (S70, S90) whether the steering wheel is in the hands-free state or in the hands-on state according to the difference value between the measured and the estimated steering angular velocity, the control device (CLR) is arranged to: to determine (S70) that the steering wheel is in the hands-free state if the difference between the measured and the estimated steering angular velocity is less than a second threshold value, and to determine (S90) that the steering wheel is in the hand-on state when the difference value between the measured and the estimated steering angular velocity is not less than the second threshold value. [3] The method according to claim 2, characterized by that it further comprises determining (S52, S53), by the control device (CLR), whether the difference value between the measured and the estimated steering angular velocity is maintained for a third predetermined period of time or longer than the third predetermined period of time. [4] The method according to any one of the preceding claims, characterized by that the variance value of the steering angle velocity is determined by equation 1: vθ=∑i=nn−N(θ˙i−θ˙¯)2N, where v θ indicates the variance value of the steering angle velocity, θ ̇ indicates the steering angle speed, θ˙¯ indicates the mean value of the steering angle speed and N indicates a test time period. [5] The method according to any one of the preceding claims, characterized by that the difference between the measured and the estimated steering angle speed is determined by equation 2: ∑i=nn−N(θ˙h,i(model)−θ˙h,i(measure))2, where θ ̇ h,i(model) is the steering angular velocity estimated by the steering system model, which is determined on the assumption that the steering wheel is in the hands-free state, and θ ̇ h,i(measure) indicates the steering angle speed measured by the steering sensor. [6] The method according to any one of the preceding claims, characterized by that the steering angle velocity, which is estimated by the steering system model, is determined by: Establishing an equation of motion of the steering system model which has the steering wheel provided at an upper end portion of a torsion bar and is determined on the assumption that the steering wheel is in the hands-free state, Establishment of state equations using the steering angle and the steering angular velocity as state variables from the equation of motion and Determine the steering angular velocity, which is estimated by the steering system model, from the state equations. [7] The method according to any one of the preceding claims, characterized by that it further features: Determining (S60), by the control device (CLR), a variance value of the steering torque by accumulation for a fourth predetermined period of time when the variance value of the steering angular velocity is not less than the first threshold value, and Determining (S70, S90), by the control device (CLR), whether the steering wheel is in the hands-free state or the hands-on state according to the variance value of the steering torque. [8] The method according to claim 7, characterized by that when determining (S70, S90) according to the variance value of the steering torque whether the steering wheel is in the hands-free state or in the hands-on state, the control device (CLR) is arranged to: to determine (S61) that the steering wheel is in the hands-free state when the variance value of the steering torque is less than a third threshold value, and to determine (S61) that the steering wheel is in the hand-on state when the variance value of the steering torque is not less than the third threshold value. [9] The method according to claim 8, characterized bythat it further comprises determining (S63), by the control device (CLR), whether the variance value of the steering torque is maintained for a fifth predetermined period of time or longer than the fifth predetermined period of time. [10] The method according to any one of claims 7 to 9, characterized by that the variance value of the steering torque is determined by equation 3: vr=∑i=nn−N(τi−τ¯)2N, where v τ where τ is the variance value of the steering torque, τ is the steering torque, τ is the average torque, and N is a test time period. [11] The method according to any one of the preceding claims, characterized by that it further features: Determining (S10), by the control device (CLR), whether the current driving mode of the vehicle is an autonomous driving mode, and Outputting (S80) a warning about the hands-free state upon determining that the current driving mode of the vehicle is the autonomous driving mode and the steering wheel is in the hands-free state. [12] A system for detecting a hands-free state of a steering wheel, the system comprising: a steering angular velocity variance calculation unit (100) configured to determine a variance value of a steering angular velocity detected by a steering sensor (10) while a vehicle is being driven by accumulation for a first predetermined period of time, a steering angular velocity estimation unit (200) configured to estimate a steering angular velocity by a steering system model determined on the assumption that the steering wheel is in the hands-free state, a steering angular velocity difference calculation unit (300) configured to determine a difference value by cumulating, over a second predetermined period, the differences between the steering angular velocity estimated by the steering system model and the steering angular velocity measured by the steering sensor when the variance value of the steering angular velocity is not less than a first threshold value, and a hands-on / hands-free determining unit (500) configured to determine the hands-free state or a hands-on state of the steering wheel according to the difference value between the measured and the estimated steering angular velocity. [13] The system according to claim 12, characterized by that it further features: a steering torque variance calculation unit (400) configured to determine a variance value of a steering torque by accumulation for a third predetermined period of time when the variance value of the steering angular velocity is less than the first threshold value, wherein the hands-on / hands-free determining unit (500) determines the hands-free state or the hands-on state of the steering wheel according to the variance value of the steering torque. [14] A system for detecting a hands-free state of a steering wheel, the system comprising a control device (CLR) arranged to: to obtain a steering torque, a steering angle and a steering angular velocity while driving a vehicle, to determine a variance value of the steering angle speed by cumulation for a first predetermined period of time, to determine a difference value by cumulating over a second predetermined period of time the differences between a steering angular velocity estimated by a steering system model, which is determined on the assumption that the steering wheel is in the hands-free state, and the steering angular velocity measured by a steering sensor when the variance value of the steering angular velocity is less than a first threshold value, and, to determine whether the steering wheel is in the hands-free state or the hands-on state according to the difference value between the measured and the estimated steering angular velocity. [15] The system according to claim 14, characterized by that when determining whether the steering wheel is in the hands-free state or in the hands-on state according to the difference value between the measured and the estimated steering angular velocity, the control device (CLR) is arranged to: to determine that the steering wheel is in the hands-free state if the difference between the measured and the estimated steering angular velocity is less than a second threshold value, and to determine that the steering wheel is in the hand-on state if the difference between the measured and the estimated steering angular velocity is not less than the second threshold value. [16] The system according to claim 14 or 15, characterized by that the variance value of the steering angle velocity is determined by equation 1: vθ=∑i=nn−N(θ˙i−θ˙¯)2N, where v θ indicates the variance value of the steering angle velocity, θ ̇ indicates the steering angle speed, θ˙¯ indicates the mean value of the steering angle speed and N indicates the test time. [17] The system according to any one of claims 14 to 16, characterized bythat the difference between the measured and the estimated steering angle speed is determined by equation 2: ∑i=nn−N(θ˙h,i(model)−θ˙h,i(measure))2, where θ̇ h,i(model) is the steering angular velocity estimated by the steering system model, which is determined on the assumption that the steering wheel is in the hands-free state, and θ ̇ h,i(measure) indicates the steering angle speed measured by the steering sensor. [18] The system according to any one of claims 14 to 17, characterized by that the steering angular velocity, which is determined or estimated by the steering system model, is determined by: Establishing an equation of motion of the steering system model which has the steering wheel provided at an upper end portion of a torsion bar and is determined on the assumption that the steering wheel is in the hands-free state, Establishment of state equations using the steering angle and the steering angular velocity as state variables based on the equation of motion and Determine the steering angular velocity, which is estimated by the steering system model, from the state equations. [19] The system according to any one of claims 14 to 18, characterized by that it further features: Determining, by the control device (CLR), a variance value of the steering torque by accumulation for a fourth predetermined period of time when the variance value of the steering angular velocity is not less than the first threshold value, and Determining, according to the variance value of the steering torque, by the control device (CLR), whether the steering wheel is in the hands-free state or in the hands-on state, wherein, upon determining whether the steering wheel is in the hands-free state or the hands-on state according to the variance value of the steering torque, the control device (CLR) is configured to: to determine that the steering wheel is in the hands-free state when the variance value of the steering torque is less than a third threshold value, and to determine that the steering wheel is in the hand-on state if the variance value of the steering torque is not less than the third threshold value. [20] The system according to claim 19, characterized by that the variance value of the steering torque is determined by equation 3: vr=∑i=nn−N(τi−τ¯)2N, where v τ where τ is the variance value of the steering torque, τ is the steering torque, τ is the average torque, and N is a test time period.

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