Method and device for detecting a hands-on / off state on a steering wheel of a vehicle

Abstract

The invention relates to a method for detecting a hands-on / off state (6, 7) on a steering wheel (51) of a vehicle (50), wherein at least one steering variable (4) on the steering wheel (51) is detected in a time-resolved manner, wherein the detected at least one steering variable (4) is subjected to an autocorrelation, and wherein at least the hands-off state (6) is determined based on a resulting autocorrelation signal (R xx) is detected. Furthermore, the invention relates to a device (1) for detecting a hands-on / off state (6, 7) on a steering wheel (51) of a vehicle (50), comprising at least one steering variable sensor (2), configured for the time-resolved detection of at least one steering variable (4) on the steering wheel (51), and a control device (3), wherein the control device (3) is configured to receive the detected at least one steering variable (4), to subject the detected steering variable (4) to an autocorrelation, and to determine at least the hands-off state (6) based on a resulting autocorrelation signal (R xx ) can be recognized.

Description

[0001] The invention relates to a method and a device for detecting a hands-on / off state on a steering wheel of a vehicle.

[0002] Sensors such as a capacitive steering wheel are used in vehicles to monitor driver activity. Such a steering wheel detects when the driver has touched (“hands-on”) or not touched (“hands-off”) the steering wheel using a capacitive sensor. The result is transmitted to the functions being used, such as a longitudinal and / or lateral guidance assistance system. Driver activity and attention can be determined from the contact of the hands on the steering wheel. For example, the driver can be advised to put their hands on the steering wheel if it is detected that their hands have not been on the steering wheel for a specified time during lateral guidance.

[0003] In order to save additional costs for a capacitive sensor in the steering wheel, it is known to monitor driver activity using artificial neural networks based on a torque (hand torque) detected on the steering wheel.

[0004] From DE 10 2017 219 467 A1, a method for operating a vehicle function based on a natural frequency and / or a moment of inertia of a steering wheel arrangement in a steering system is known, comprising the following steps: specifying an electromotive steering intervention in order to move the steering system by providing a steering intervention force or a steering intervention torque; determining a natural frequency and / or a moment of inertia of the steering wheel arrangement depending on the reaction of the steering wheel arrangement due to the electromotive steering intervention; operating the vehicle function based on the determined natural frequency and / or the determined moment of inertia of the steering wheel arrangement.

[0005] The invention is based on the object of improving a method and a device for detecting a hands-on / off state on a steering wheel of a vehicle.

[0006] The object is achieved according to the invention by a method having the features of patent claim 1 and a device having the features of patent claim 10. Advantageous embodiments of the invention emerge from the subclaims.

[0007] In particular, a method for detecting a hands-on / off state on a steering wheel of a vehicle is provided, wherein at least one steering variable on the steering wheel is detected in a time-resolved manner, wherein the detected at least one steering variable is subjected to an autocorrelation, and wherein at least the hands-off state is detected based on a resulting autocorrelation signal.

[0008] Furthermore, in particular, a device for detecting a hands-on / off state on a steering wheel of a vehicle is provided, comprising at least one steering variable sensor which is configured for the time-resolved detection of at least one steering variable on the steering wheel, and a control device, wherein the control device is configured to receive the detected at least one steering variable, to subject the detected at least one steering variable to an autocorrelation, and to detect at least the hands-off state based on a resulting autocorrelation signal.

[0009] The method and device make it possible to detect a hands-on / off state with low computing and storage resources and without additional sensors, such as a capacitive steering wheel. Particularly compared to detection using machine learning methods, such as trained neural networks, the computing and storage resources required to perform autocorrelation are extremely low. The method involves recording at least one steering variable on the steering wheel in a time-resolved manner. The recorded at least one steering variable is subjected to autocorrelation. At least the hands-off state is then detected based on a resulting autocorrelation signal.It is one of the basic ideas of the invention that autocorrelation can be used to detect when the steering wheel is in a state of natural vibration, i.e. when the steering wheel can swing freely without this natural vibration being damped, changed in terms of frequency or completely prevented by a driver's hand.

[0010] Parts of the device, in particular the control device, can be implemented individually or collectively as a combination of hardware and software, for example, as program code executed on a microcontroller or microprocessor. However, it can also be provided that parts are implemented individually or collectively as an application-specific integrated circuit (ASIC) and / or a field-programmable gate array (FPGA). The control device comprises, in particular, at least one computing device and at least one memory.

[0011] The general definition of autocorrelation for the stationary discrete case is: R^xx(τ)=1N˜∑j=1N˜XtjXtj+τ where Ñ is the size of the window or the number of measured values considered, X tj is a measured value at time t j and τ is an autocorrelation parameter that specifies the extent to which the measurement sequence is shifted during the correlation. The parameter τ is chosen in particular such that the autocorrelation is sensitive to a natural vibration of the steering wheel in the hands-off state. In other words, the parameter τ is chosen in particular such that it corresponds to a frequency of the natural vibration of the steering wheel (i.e., in particular, corresponds to the inverse of the natural frequency). The parameter Ñ can be determined based on test drives and / or simulations.

[0012] A steering variable is, in particular, a variable that represents and / or describes a current state of the steering wheel. In particular, exactly one steering variable is detected and evaluated according to the method. A steering variable is, in particular, a torque, which is detected in particular by means of a torque sensor on the steering wheel. In principle, however, a steering variable can also be another variable detected directly or indirectly on the steering wheel. For example, it can be provided to detect a current at an electrical machine on the steering wheel and use it as a steering variable. The hands-on / off state can be detected exclusively on the basis of the at least one steering variable detected on the steering wheel, in particular a detected torque. However, it is also possible, in particular, for further (steering) variables detected on the steering wheel (e.g., a steering wheel angle and / or a steering wheel angular velocity, etc.) to be used.) are subjected to autocorrelation and at least the hands-off state is detected from the resulting autocorrelation signal(s).

[0013] A hands-off state is, in particular, a state in which the driver is not touching the steering wheel. In particular, none of the driver's fingers are in contact with the steering wheel. Detecting the hands-off state may, in particular, include providing a hands-off state signal. This includes, for example, a coded signal for the "hands-off detected" state.

[0014] A hands-on state is, in particular, a state in which the driver touches the steering wheel. Detecting the hands-on state can, in particular, include providing a hands-on state signal. This includes, for example, a coded signal for the "hands-off detected" state.

[0015] In one embodiment, the hands-off state is detected when the autocorrelation signal assumes a negative value. This allows the hands-off state to be reliably detected. The idea behind this is that the autocorrelation signal becomes negative when the natural vibration of the steering wheel is correlated with itself after being shifted by half a period, since one of the measured values multiplied during the autocorrelation is then negative. For this purpose, in particular the parameter τ is selected appropriately, i.e. such that it corresponds to the natural frequency of the steering wheel. In particular, τ is selected according to half the period of the natural frequency (e.g. τ = 0.02 s if the natural frequency is 25 Hz).

[0016] In one embodiment, the hands-off state is only detected when the autocorrelation signal assumes a negative value for a predetermined minimum number of time steps. This prevents the hands-off state from being detected at the first occurrence of a negative value of the autocorrelation signal. In particular, this prevents a rapid, repetitive state change upon detection of the hands-off signal (chatter inhibit).

[0017] In one embodiment, the hands-off state is only detected when the negative value of the autocorrelation signal exceeds a predetermined threshold. This ensures that the autocorrelation signal must have a minimum magnitude in the negative value range before the hands-off state is detected. This allows small signals to be ignored. In particular, noise in the autocorrelation signal can be ignored or suppressed.

[0018] In one embodiment, a hands-on state is determined if the autocorrelation signal has a positive value and / or is above a predetermined threshold. This allows for reliable detection of a hands-on state.

[0019] In one embodiment, the hands-on state is only detected when the autocorrelation signal has exclusively positive values for a predetermined minimum number of time steps and / or is exclusively above the predetermined threshold. This can prevent the hands-on state from being detected upon the first occurrence of a positive value of the autocorrelation signal and / or a value above the predetermined threshold. In particular, this can prevent a rapid, repetitive state change upon detection of the hands-on signal (chatter blocking).

[0020] In one embodiment, the autocorrelation signal is averaged, with the hands-off state and / or the hands-on state being detected based on the averaged autocorrelation signal. This allows the hands-off state and / or the hands-on state to be detected based on an averaged autocorrelation signal. Individual outliers can thus be neglected or have less influence on the detection. In particular, the autocorrelation signal is averaged over time, for example, over a period of 0.5 seconds or 1 second.

[0021] In one embodiment, the autocorrelation signal is filtered, with the hands-off state and / or the hands-on state being detected based on the filtered autocorrelation signal. This allows the hands-off state and / or the hands-on state to be detected based on a filtered autocorrelation signal. Individual outliers can thus be neglected or have less influence on the detection. In particular, it can be provided to use a smoothing filter over multiple time steps.

[0022] In one embodiment, a torque is applied to the steering wheel by means of an actuator at least during a selected time to detect the hands-on / off state. This ensures that the hands-on / off state can be reliably detected on smooth and straight roads where there is insufficient external stimulation of the steering wheel.

[0023] Further features of the device design will become apparent from the description of embodiments of the method. The advantages of the device are the same as those of the embodiments of the method.

[0024] Furthermore, in particular, a steering system is provided, comprising a device according to one of the described embodiments.

[0025] Furthermore, in particular, a vehicle is also created, comprising a steering system according to one of the described embodiments and / or a device according to one of the described embodiments.

[0026] The invention will be explained in more detail below using preferred embodiments with reference to the figures. Fig. 1 is a schematic representation of an embodiment of the device for detecting a hands-on / off state on a steering wheel of a vehicle; Fig. 2a, Fig. 2b show schematic representations of an exemplary autocorrelation signal; Fig. 3a, Fig. 3b show schematic diagrams to illustrate the evaluation of the autocorrelation signal according to embodiments of the device and the method; Fig. 4 shows a schematic flow diagram to illustrate embodiments of the method for detecting a hands-on / off state on a steering wheel of a vehicle; Fig. 5 shows a schematic representation to illustrate embodiments of the method and the device.

[0027] The Fig. 1 shows a schematic representation to illustrate embodiments of the device 1 for detecting a hands-on / off state 6, 7 on a steering wheel 51 of a vehicle 50. The device 1 is arranged in particular in a vehicle 50. The method described in this disclosure is illustrated and explained in more detail below using the device 1.

[0028] The device 1 comprises a steering variable sensor 2 and a control device 3. The steering variable sensor 2 is configured to detect a steering variable 4 at the steering wheel 51 of the vehicle 50. The steering variable sensor 2 is, for example, a torque sensor, and the steering variable 4 is a torque.

[0029] The control device 3 comprises a computing device 3-1 and a memory 3-2. The computing device 3-1 is configured to perform the computing operations necessary for implementing measures of the method and can access data stored in the memory 3-2 for this purpose.

[0030] The control device 3 is configured to receive the detected steering variable 4, to subject the detected steering variable 4 to an autocorrelation, and to detect at least the hands-off state 6 based on a resulting autocorrelation signal.

[0031] The hands-off state 6 is fed, for example, as a status signal to a control unit 52 of the vehicle 50 for further processing. The control unit 52 can, for example, be a lateral guidance assistant or another assistance system. The status signal can, for example, be a binary status value with the two states "hands-off detected" and "hands-off not detected." It can be provided that an assistance system is operated based on the status signal.

[0032] The device 1 is in particular part of a steering system 60.

[0033] It may be provided that the hands-off state 6 is detected when the autocorrelation signal assumes a negative value.

[0034] It can be provided that the hands-off state 6 is only detected when the autocorrelation signal assumes a negative value for a predetermined minimum number 8 of time steps.

[0035] It can be provided that the hands-off state 6 is only detected when the negative value of the autocorrelation signal exceeds a predetermined threshold value R off A suitable value of the specified threshold R off can be determined, for example, by means of empirical test drives and / or simulations.

[0036] It can be provided that a hands-on state 7 is detected if the autocorrelation signal has a positive value and / or is above a predetermined threshold value R on A suitable value of the specified threshold R on can be determined, for example, by means of empirical test drives and / or simulations.

[0037] It can be provided that the hands-on state 7 is only determined when the autocorrelation signal has exclusively positive values for a predetermined minimum number 8 of time steps and / or exclusively above the predetermined threshold value R on A value for the specified minimum number of 8 can be determined, for example, by means of empirical test drives and / or simulations. For example, the value can be selected such that the minimum number of 8 corresponds to a duration of 0.5 seconds or 1 second.

[0038] It can be provided that the autocorrelation signal is averaged, with the hands-off state 6 and / or the hands-on state 7 being detected based on the averaged autocorrelation signal. Averaging is performed, in particular, over a predetermined number of time steps. A suitable number can be determined, for example, by means of empirical test drives and / or simulations.

[0039] It can be provided that the autocorrelation signal is filtered, wherein the hands-off state 6 and / or the hands-on state 7 is detected based on the filtered autocorrelation signal.

[0040] It can be provided that, at least during a selected time for detecting the hands-on / off state 6, 7, a torque is applied to the steering wheel 51 by means of an actuator 9. For this purpose, the control device 3 can generate a control signal 10 and supply it to the actuator 9.

[0041] The Fig. 2a and Fig. 2b show schematic representations of an exemplary autocorrelation signal R xx , which was determined from a torque measured at the steering wheel as a steering variable. Time steps between 0 and 70 seconds are shown for different values of the parameter τ. Fig. 2a shows an autocorrelation signal R xx when the steering wheel is held with one hand (“Hands-On”). Fig. 2b shows at least temporarily the autocorrelation signal R xx , which occurs when no hand is touching the steering wheel (“hands-off”). The autocorrelation signal R xx then always takes a negative value.

[0042] The Fig. 3a and Fig. 3b show schematic diagrams to illustrate the evaluation of the autocorrelation signal R xx according to embodiments of the device and the method. The Fig. 3a shows the time course (in seconds) of the recorded steering value, in this example the recorded torque M in Nm. Fig. 3b shows the time course (in seconds) of the autocorrelation signal R corresponding to the time course of the recorded steering variable xx The times at which no hand was on the steering wheel are marked with an arrow. As can be seen, these times always correspond to a negative value of the autocorrelation signal R xx .

[0043] It is therefore specifically intended that the hands-off state is detected when the autocorrelation signal R xx takes on a negative value. With reference to the Fig. 3b, the hands-off state would be detected particularly at the times marked with the arrows.

[0044] It can be provided that the hands-off state is only detected when the autocorrelation signal R xx assumes a negative value for a specified minimum number of time steps. For example, the minimum number can be 10, 20, or 50 time steps. The number of time steps can also be specified with reference to a minimum time, so that the negative value must be present for at least 0.5 seconds, 1 second, or 2 seconds, for a hands-off state to be detected.

[0045] It can be provided that the hands-off state is only detected when the negative value of the autocorrelation signal R xx in terms of amount a predetermined threshold value R off exceeds (in the Fig. 3b is the threshold R off shown as an example at -0.5; however, in principle, another value can also be chosen).

[0046] It can be provided that a hands-on state is detected when the autocorrelation signal R xx has a positive value and / or is above a predetermined threshold R on lies (in the Fig. 3b is the threshold R on shown as an example at 0.5; however, in principle, another value can also be chosen).

[0047] It can be provided that the hands-on state is only determined when the autocorrelation signal R xx for a given minimum number of time steps has only positive values and / or only above the given threshold R onFor example, the minimum number can be 10, 20, or 50 time steps. The number of time steps can also be specified with reference to a minimum time, so that the negative value must be at least 0.5 seconds, 1 second, or 2 seconds, for a hands-off state to be detected.

[0048] The Fig. Figure 4 shows a schematic flow diagram illustrating embodiments of the method for detecting a hands-on / off state on a steering wheel of a vehicle. The method is carried out, for example, by means of a device as described with reference to Fig. 1 was described.

[0049] In a measure 100, at least one steering variable is detected in a time-resolved manner using a steering variable sensor on the steering wheel. In particular, a torque can be detected as a steering variable using a torque sensor.

[0050] In a measure 101, the detected at least one steering variable is subjected to autocorrelation. This is done using a predefined parameter τ. A resulting autocorrelation signal is provided. The autocorrelation signal is calculated continuously based on currently detected values of the at least one steering variable.

[0051] In an action 102, it is checked whether a hands-off state exists. In particular, it is checked whether the autocorrelation signal has a negative value. If this is the case, a hands-off signal, for example with the content "Hands-off detected," is generated and provided in an action 103. Based on this, an assistance function can be operated.

[0052] Measure 102a may provide that the hands-off state is only detected when the autocorrelation signal assumes a negative value for a specified minimum number (e.g., 10, 20, 50,...) of time steps. If the minimum number is not reached, the system returns to measure 100. If, however, the minimum number is reached, the hands-off state is detected and the system jumps to measure 103.

[0053] If no hands-off state is detected in step 102, in particular because there is no negative value of the autocorrelation signal, the system can proceed with step 104. Alternatively, if hands-on detection is not planned, the system returns to step 100.

[0054] Measure 104 specifically provides for a hands-on state to be detected if the autocorrelation signal has a positive value and / or is above a predefined threshold. If a hands-on state has been detected, a hands-on signal, for example, with the content "Hands-on detected," is generated and provided in measure 105. Based on this, an assistance function can be operated.

[0055] It may be provided in a measure 104a that the hands-on state is only determined when the autocorrelation signal has exclusively positive values for a predetermined minimum number of time steps and / or is exclusively above the predetermined threshold value.

[0056] It can be provided that the autocorrelation signal is averaged, wherein in measures 102 and / or 104 the hands-off state and / or the hands-on state is detected based on the averaged autocorrelation signal.

[0057] It may be provided that the autocorrelation signal is filtered, wherein in measures 102 and / or 104, the hands-off state and / or the hands-on state are detected based on the filtered autocorrelation signal. Averaging and filtering may also be provided. The filtering may, for example, comprise low-pass filtering and / or smoothing.

[0058] Measure 100 may provide for a torque to be applied to the steering wheel by means of an actuator at least during a selected time to detect the hands-on / off state. This can occur, for example, whenever there is insufficient external stimulation from road irregularities.

[0059] The Fig. Figure 5 shows a schematic representation to illustrate embodiments of the method and the device. In particular, the autocorrelation signal R xx for different values of the parameter τ (unit s) for the hands-off state (cf. the equation for the autocorrelation in the general description section), i.e., the steering wheel can oscillate freely with a natural frequency and harmonics. It can be seen that the autocorrelation signal R xxin the negative value range, it has several maxima (or several minima in absolute terms) with respect to a given value. These maxima coincide with the natural vibration or harmonics of this natural vibration of the steering wheel. In the specific example shown, maxima can be seen at 0.03 s and 0.04 s, and then again at 0.08 s and 0.09 s, and then again between 0.16 s and 0.19 s. Accordingly, the parameter τ can be selected in the range of 0.03 s and 0.04 s. Other steering systems or other vehicles may have different values because the natural frequency of the steering wheel or steering system differs. The value of the parameter τ is then selected accordingly for these steering systems or vehicles.

[0060] Empirical test drives and / or simulations can be used to determine a suitable parameter τ. Based on the values contained in the autocorrelation signal R xxThe magnitude maxima occurring in the negative range can be used to identify suitable values for the parameter τ, as can be seen from the Fig. 5 was illustrated by way of example. List of reference symbols 1 device 2 steering size sensor 3 Control device 3-1 Calculation device 3-2 Memory 4 Steering size 6 Hands-off state 7 Hands-On State 8 minimum number 9 Actuator 10 Control signal 50 vehicles 51 Steering wheel 52 Control unit 60 Steering system 100-105 Measures of the procedure M torque τ parameter (for autocorrelation) R off predefined threshold (hands-off) R on predefined threshold (hands-on) R xx Autocorrelation signal QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 219 467 A1

[0004]

Claims

[1] Method for detecting a hands-on / off state (6,7) on a steering wheel (51) of a vehicle (50), wherein at least one steering variable (4) on the steering wheel (51) is detected in a time-resolved manner, wherein the detected at least one steering variable (4) is subjected to an autocorrelation, and wherein at least the hands-off state (6) is determined based on a resulting autocorrelation signal (R xx ) is recognized. [2] Method according to claim 1, characterized by that the hands-off state (6) is detected when the autocorrelation signal (R xx ) takes a negative value. [3] Method according to claim 2, characterized by that the hands-off state (6) is only detected when the autocorrelation signal (R xx ) takes a negative value for a given minimum number (8) of time steps. [4] Method according to claim 2 or 3, characterized bythat the hands-off state (6) is only detected when the negative value of the autocorrelation signal (R xx ) exceeds a predetermined threshold value (R off ) exceeds. [5] Method according to one of the preceding claims, characterized by that a hands-on state (7) is detected when the autocorrelation signal (R xx ) has a positive value and / or is above a predetermined threshold (R on ) lies. [6] Method according to claim 5, characterized by that the hands-on state is only detected when the autocorrelation signal (R xx ) has exclusively positive values for a given minimum number (8) of time steps and / or exclusively above the given threshold value (R on ) lies. [7] Method according to one of the preceding claims, characterized by that the autocorrelation signal (R xx), wherein the hands-off state (6) and / or the hands-on state (7) are determined from the averaged autocorrelation signal (R xx ) is recognized. [8] Method according to one of the preceding claims, characterized by that the autocorrelation signal (R xx ), wherein the hands-off state (6) and / or the hands-on state (7) are determined from the filtered autocorrelation signal (R xx ) is recognized. [9] Method according to one of the preceding claims, characterized by that at least during a selected time for detecting the hands-on / off state (6,7) a torque is applied to the steering wheel (51) by means of an actuator (9). [10] Device (1) for detecting a hands-on / off state (6, 7) on a steering wheel (51) of a vehicle (50), comprising: at least one steering variable sensor (2) configured for the time-resolved detection of at least one steering variable (4) on the steering wheel (51), and a control device (3), wherein the control device (3) is configured to receive the detected at least one steering variable (4), to subject the detected steering variable (4) to an autocorrelation, and to determine at least the hands-off state (6) based on a resulting autocorrelation signal (R xx ) can be recognized.

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