Grip detection device and program

Abstract

The present invention provides a grip sensing device and so forth that can sense gripping of a steering wheel with good precision.　A grip sensing device according to the present invention performs grip sensing with respect to a steering wheel. The grip sensing device includes an acquisition unit that acquires a capacitance value detected by an electrostatic capacitance sensor provided in the steering wheel, and a generating unit that generates a threshold value for performing grip sensing with respect to the steering wheel, on the basis of the capacitance value acquired by the acquisition unit and a parameter corresponding to a state relating to change in the capacitance value.

Description

[Technical Field]

[0001] The present invention relates to a grip detection device and a program. [Background technology]

[0002] A technology that uses a sensor attached to a steering wheel to monitor whether a driver is gripping the steering wheel has been widely used. The detection value of the capacitance sensor can be compared with a predetermined threshold value to determine whether the driver is gripping the steering wheel.

[0003] Patent Document 1 discloses a steering wheel unit that includes a correction unit that calculates an average value of a fixed number of detection values ​​in the immediate vicinity, including the current detection value of a capacitance sensor, and corrects an error that occurs in comparing the detection value with a contact determination threshold when the steering wheel is not in contact with the human body and the average value is greater than a correction determination threshold.The steering wheel unit disclosed in Patent Document 1 makes it possible to suppress a decrease in the accuracy of detecting contact or non-contact of the human body with the steering wheel, even if a disturbance occurs. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-23012 Summary of the Invention [Problem to be solved by the invention]

[0005] The detection value (capacitance value) detected by a capacitance sensor changes due to various disturbances, such as the vehicle's interior environment, driving conditions, and external noise. The state of change in the capacitance value varies depending on the type of disturbance. Therefore, if the process for correcting the capacitance value has a unique characteristic, it may not be able to track changes in the capacitance value or may track changes in situations where tracking is not necessary, which could result in inaccurate detection of gripping. However, conventional technologies such as those described in Patent Document 1 do not take this into consideration, and therefore the accuracy of grip detection is insufficient.

[0006] An object of the present disclosure is to provide a grip detection device and the like that can accurately detect gripping of a steering wheel. [Means for solving the problem]

[0007] A grip detection device according to one aspect of the present disclosure is a grip detection device that detects gripping of a steering wheel, and includes an acquisition unit that acquires a capacitance value detected by a capacitance sensor provided on the steering wheel, and a generation unit that generates a threshold value for gripping the steering wheel based on the capacitance value acquired by the acquisition unit and a parameter corresponding to a state related to a change in the capacitance value.

[0008] A program according to one aspect of the present disclosure causes a computer that performs grip detection on a steering wheel to acquire a capacitance value detected by a capacitance sensor provided on the steering wheel, and to execute a process of generating a threshold value for detecting grip on the steering wheel based on the acquired capacitance value and a parameter corresponding to a state related to changes in the capacitance value. [Effects of the Invention]

[0009] According to the present disclosure, gripping of the steering wheel can be detected with high accuracy. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing an example of the configuration of a steering wheel device according to an embodiment of the present invention; [Figure 2] 1 is a front view of a steering wheel of a steering wheel device according to an embodiment of the present invention. FIG. [Figure 3] 3 is an explanatory diagram for explaining detection of a capacitance value by a capacitance measuring circuit of the steering wheel device. FIG. [Figure 4] FIG. 2 is a functional block diagram showing an example of the configuration of a control unit of a grip detection ECU. [Figure 5] FIG. 10 is a diagram illustrating an example of a change in capacitance value. [Figure 6A] FIG. 4 is a diagram illustrating a method for setting a time constant T1 in the first parameter. [Figure 6B] FIG. 4 is a diagram illustrating a method for setting a time constant T1 in the first parameter. [Figure 7A] FIG. 10 is a diagram illustrating a method for setting a time constant T3 in the third parameter. [Figure 7B] FIG. 10 is a diagram illustrating a method for setting a time constant T3 in the third parameter. [Figure 8] FIG. 10 is a diagram illustrating grip detection using a third parameter. [Figure 9] 10 is a flowchart illustrating an example of a processing procedure executed by a grip detection ECU. [Figure 10] 10 is a flowchart showing an example of a detailed procedure for selecting parameters. [Figure 11] 10A and 10B are diagrams illustrating examples of grip determination when the time constant T1 is changed. [Figure 12] 10A and 10B are diagrams illustrating examples of grip determination when the time constant T1 is changed. [Figure 13] 10A and 10B are diagrams illustrating examples of grip determination when the time constant T1 is changed. [Figure 14] 10A and 10B are diagrams illustrating examples of grip determination when the time constant T1 is changed. [Figure 15] 10A and 10B are diagrams illustrating examples of grip determination when the time constant T2 is changed. [Figure 16]10A and 10B are diagrams illustrating examples of grip determination when the time constant T2 is changed. [Figure 17] 10A and 10B are diagrams illustrating examples of grip determination when the time constant T2 is changed. [Figure 18] 10A and 10B are diagrams illustrating examples of grip determination when the time constant T2 is changed. [Figure 19] 10A and 10B are diagrams illustrating an example of grip determination using a time constant T3. [Figure 20] 10A and 10B are diagrams illustrating another example of grip determination using the time constant T3. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure will be specifically described with reference to the drawings showing embodiments thereof.

[0012] Fig. 1 is a block diagram showing an example of the configuration of a steering wheel device 100 according to this embodiment. The steering wheel device 100 includes a grip detection ECU (Electronic Control Unit) 1 and a steering wheel 2. The grip detection ECU 1 corresponds to the grip detection device. The grip detection ECU 1 is communicatively connected to in-vehicle devices such as a driving assistance ECU 3 via an in-vehicle network provided in the vehicle.

[0013] 2 is a front view of the steering wheel 2 of the steering wheel device 100 according to this embodiment. The steering wheel 2 is equipped with a capacitance sensor (sensor electrode) 21. The sensor electrode 21 forms a capacitor with the steering wheel 2 and / or a human body in contact with the steering wheel 2, and detects the magnitude of the capacitance (capacitance value) which changes depending on whether the human body is in contact with or not in contact with the steering wheel 2.

[0014] The grip detection ECU 1 performs grip detection based on the capacitance value detected by the sensor electrode 21. Specifically, the grip detection ECU 1 compares the capacitance value with a predetermined threshold value to determine whether the steering wheel 2 is in a gripped state or an un-grip state (hereinafter referred to as grip determination). Here, the gripped state means a state in which the driver is gripping the steering wheel 2, and the un-grip state means a state in which the driver is not gripping the steering wheel 2 and has his hands off it.

[0015] As shown in Figure 2, the steering wheel 2 includes a circular rim portion 3 and a hub portion 4 located in the center of the rim portion 3. For example, an airbag (not shown) is installed inside the hub portion 4. The hub portion 4 is connected to the rim portion 3 by three spokes 5.

[0016] The rim portion 3 is covered with a covering layer 22 such as leather, and the hub portion 4 and spokes 5 are covered with, for example, a resin material. Sensor electrodes 21 are provided inside the rim portion 3 along the circumferential direction of the rim portion 3. The rim portion 3 is divided into three equal parts in the circumferential direction, and a sensor electrode 21 is provided inside each of these parts. The number of sensor electrodes 21 is not limited to three, and may be two or less, or four or more. The rim portion 3 is also not limited to a circular shape, and may be non-circular (for example, D-shaped or C-shaped).

[0017] As shown in FIG. 1, the grip detection ECU 1 includes a control unit 11, a storage unit 12, a communication unit 13, and a capacitance measurement circuit .

[0018] The control unit 11 includes a processor using one or more CPUs (Central Processing Units), GPUs (Graphics Processing Units), etc. The control unit 11 uses a built-in clock, counter, etc. to read and execute programs and data stored in the storage unit 12 or ROM (Read Only Memory), etc., thereby performing various control processes and arithmetic processes.

[0019] The storage unit 12 includes a nonvolatile memory element such as a flash memory or an EEPROM (Electrically Erasable Programmable Read Only Memory). The storage unit 12 stores various programs and data referenced by the control unit 11. In this embodiment, the storage unit 12 stores a program 121 for causing a computer to execute processing related to grip detection (grip determination), and determination data 122 as data necessary for executing the program 121.

[0020] The determination data 122 includes, for example, a formula for generating a threshold value Cthr used for grip determination described later, an offset value Coff, a plurality of parameters P, and information such as a correspondence relationship between the parameters P and states related to changes in capacitance value. In the present embodiment, as an example, the parameters P include a first parameter P1, a second parameter P2, and a third parameter P3.

[0021] The program (program product) stored in the storage unit 12 may be recorded on a computer-readable recording medium. The storage unit 12 stores a program read from the recording medium 1A by a reading device (not shown). The recording medium 1A is, for example, a magnetic disk, an optical disk, or a semiconductor memory. The program may also be downloaded from an external server connected to a communication network (not shown) and stored in the storage unit 12. The program 121 may be a single computer program or may be composed of multiple computer programs, and may be executed on a single computer or multiple computers interconnected by a network.

[0022] The communication unit 13 is a communication interface for transmitting and receiving information to and from other in-vehicle devices via an in-vehicle network. The communication unit 13 is connected to a communication line (LAN) provided in the vehicle, and transmits and receives information to and from the driving assistance ECU 3, etc. The communication unit 13 transmits the result of the grip determination by the control unit 11 to the driving assistance ECU 3.

[0023] The driving assistance ECU 3 is an ECU that executes processing related to the advanced driving assistance system. The driving assistance ECU 3 receives a signal indicating the result of the grip determination by the control unit 11 via the communication unit 13, and executes predetermined processing related to the advanced driving assistance system according to the result of the grip determination. For example, during autonomous driving, if the driving assistance ECU 3 receives a grip determination result from the control unit 11 indicating that the steering wheel 2 is in an ungripped state, the driving assistance ECU 3 terminates the autonomous driving. Note that the processing of the driving assistance ECU 3 is not limited to autonomous driving, and may be, for example, lane keep assist, parking assist, etc.

[0024] The capacitance measuring circuit 14 is connected to the sensor electrode 21 and is an electric circuit for detecting the electrostatic capacitance coupled to the sensor electrode 21. The control unit 11 acquires the capacitance value detected by the sensor electrode 21 through the capacitance measuring circuit 14.

[0025] 3 is an explanatory diagram for explaining detection of a capacitance value by the capacitance measuring circuit 14 of the steering wheel device 100. The sensor electrode 21 is provided so as to be covered by the covering layer 22 of the steering wheel 2, and is interposed between the covering layer 22 and a urethane layer covering the core metal (neither of which is shown).

[0026] The capacitance measuring circuit 14 is connected to the sensor electrode 21 of the steering wheel 2. After the sensor electrode 21 is activated, the capacitance measuring circuit 14 detects the electrostatic capacitance between the sensor electrode 21 and GND (ground) at predetermined intervals.

[0027] 3, the capacitance value Cm (electrostatic capacitance) detected by the capacitance measuring circuit 14 includes the capacitance Ch of the driver's hand 200 when the driver grips the steering wheel 2, and the parasitic capacitance Cp generated by the internal structure of the steering wheel 2. Normally, when the steering wheel 2 is not being gripped, the detected capacitance value Cm is equivalent to the parasitic capacitance Cp. The parasitic capacitance Cp changes due to, for example, fluctuations in the vehicle's interior environment, aging of the product, driving conditions, external noise, etc.

[0028] 4 is a functional block diagram showing an example configuration of the control unit 11 of the grip detection ECU 1. The control unit 11 reads and executes a program 121 stored in the storage unit 12, thereby functioning as an acquisition unit 111, an identification unit 112, a filter unit 113, a generation unit 114, and a determination unit 115.

[0029] The acquisition unit 111 acquires the capacitance value Cm output from the capacitance measurement circuit 14. The capacitance value Cm acquired by the acquisition unit 111 is output to the filter unit 113, the generation unit 114, and the determination unit 115, respectively.

[0030] The identification unit 112 identifies a state related to a change in the capacitance value Cm based on the time-series data of the capacitance value Cm received from the acquisition unit 111 and the determination result of the gripped state or the non-grip state received from the determination unit 115. Furthermore, based on the identified state related to the change in the capacitance value Cm, the identification unit 112 identifies a parameter P to be used for a filter process, which will be described later, from among a plurality of parameters P stored in the storage unit 12. Specifically, the identification unit 112 selects any one parameter P from a first parameter P1, a second parameter P2, and a third parameter P3.

[0031] The state regarding the change in the capacitance value Cm is information for identifying a parameter P used in the filter processing described later, and is determined based on the change trend of the capacitance value Cm. Specifically, the state regarding the change in the capacitance value Cm can be determined based on whether or not the first grip detection has occurred after the sensor electrode 21 is activated, and the increase / decrease trend of the capacitance value Cm. In the present embodiment, as an example, the state regarding the change in the capacitance value Cm is classified into a plurality of states, including four states, a first state to a fourth state. Details of each state will be described later. The identification unit 112 classifies the current state into one of the first state to the fourth state.

[0032] The parameter P has a time constant T that represents the response speed to changes in the capacitance value Cm. The time constant T differs for each parameter P. The first parameter P1 has a time constant T1 that most responsively follows changes in the capacitance value Cm. The second parameter P2 has a time constant T2 that is larger than the first time constant T1 and follows changes in the capacitance value Cm with a longer delay than the time constant T1. The third parameter P3 has a time constant T3 that is larger than the time constant T2 and follows changes in the capacitance value Cm with a longer delay than the time constant T2.

[0033] The determination unit 112 determines the parameter P associated with the determined current state by referring to the correspondence between the state related to the change in the capacitance value Cm and each parameter P, which is stored in advance in the determination data 122. The determination unit 112 outputs the determined parameter P to the filter unit 113.

[0034] The filter unit 113 performs a filter process on the capacitance value Cm received from the acquisition unit 111 using the parameter P received from the identification unit 112. The filter unit 113 functions as a low-pass filter that attenuates and blocks the capacitance value Cm corresponding to unnecessary disturbances. The value obtained by the filter process is set as a correction capacitance value Cm′. The correction capacitance value Cm′ obtained by the filter unit 113 is output to the generation unit 114.

[0035] The generation unit 114 generates a threshold value Cthr used for grasping determination based on the corrected capacitance value Cm′ received from the filter unit 113. The threshold value Cthr can be a value obtained by adding an offset value Coff to the corrected capacitance value Cm′. The offset value Coff is a capacitance value that is set in advance as an offset and is a fixed value. In other words, the threshold value Cthr dynamically increases or decreases according to changes in the capacitance value Cm. By using the capacitance value Cm to generate the threshold value Cthr, the threshold value Cthr can be set taking into account increases or decreases in the capacitance value Cm in a non-grasping state due to environmental fluctuations, etc.

[0036] The offset value Coff can be set appropriately based on, for example, the touch conditions required for grip detection (e.g., three-finger touch, four-finger touch, etc.) and a capacitance value corresponding to the noise in the steering wheel device 100 and the EMC resistance to the noise.

[0037] The generation unit 114 may generate the above-mentioned threshold Cthr only in the non-grasping state based on the determination result of the grasping state or the non-grasping state received from the determination unit 115, and may not generate the threshold Cthr in the grasping state. That is, the generation unit 114 updates the threshold Cthr as needed in the non-grasping state, and holds and uses the previous threshold Cthr without updating it from the time when the non-grasping state is switched to the grasping state until the state is switched back to the non-grasping state. The threshold Cthr generated by the generation unit 114 is output to the determination unit 115.

[0038] The determination unit 115 performs grip determination based on the capacitance value Cm received from the acquisition unit 111 and the threshold value Cthr received from the generation unit 114.

[0039] Fig. 5 is a diagram showing an example of a change in capacitance value Cm. The vertical axis of the graph shown in Fig. 5 represents electrostatic capacitance, and the horizontal axis represents elapsed time. The solid line in the graph represents capacitance value Cm, and the dashed line represents threshold value Cthr. As shown in Fig. 5, the capacitance value Cm when the steering wheel 2 is gripped is larger than the capacitance value Cm when the steering wheel 2 is not gripped.

[0040] The determination unit 115 determines that the hand is in a gripped state when the capacitance value Cm is equal to or greater than the threshold value Cthr, and determines that the hand is in a non-grip state when the capacitance value Cm is less than the threshold value Cthr. The determination result by the determination unit 115 is output to the identification unit 112 and the generation unit 114, and is also transmitted to the driving assistance ECU 3 via the communication unit 13.

[0041] The correspondence between the state regarding the change in capacitance value Cm and the parameter P, and the method for setting the time constant T for each parameter P will be described in detail below.

[0042] As described above, the states related to the change in capacitance value Cm are classified into states 1 to 4. States 1 and 2 correspond to the start-up states, which are the period from when the sensor electrode 21 is activated until the driver's initial grip on the steering wheel 2 is detected. States 3 and 4 correspond to the normal states, which are the period after the initial grip is detected.

[0043] The first state is a state in which the capacitance value Cm is constant or decreasing during the period from when the sensor electrode 21 is activated until when the initial gripping of the steering wheel 2 is detected. The second state is a state in which the capacitance value Cm is increasing during the period from when the sensor electrode 21 is activated until when the initial gripping of the steering wheel 2 is detected. The third state is a state in which the capacitance value Cm is constant or increasing during the period after the initial gripping is detected. The fourth state is a state in which the capacitance value Cm is decreasing during the period after the initial gripping is detected.

[0044] When the state of the capacitance value Cm is the first state, a first parameter P1 having the smallest time constant T1 is used as the parameter P. Similarly, when the state is the second and third states, a second parameter P2 having a time constant T2 larger than the time constant T1 is used. When the state is the fourth state, a third parameter P3 having a time constant T3 even larger than the time constant T2 is used.

[0045] After the sensor electrode 21 is activated, the first parameter P1 is selected as an initial parameter. The first parameter P1 is continuously used until the first gripping operation is detected. When the capacitance value Cm is on an increasing trend while the first parameter P1 is selected, the parameter is switched to the second parameter P2. When the capacitance value Cm is on a decreasing trend while the second parameter P2 is selected, the parameter is switched back to the first parameter P1.

[0046] When the second parameter P2 is selected and it is determined that the device is in a gripping state (when the first grip is detected), the device transitions from the start state to the normal state. In the normal state, the second parameter P2 and the third parameter P3 are switched as needed depending on the increase or decrease in the capacitance value Cm. When the capacitance value Cm is on an increasing trend, the second parameter P2 is selected, and when the capacitance value Cm is on a decreasing trend, the third parameter P3 is selected.

[0047] 6A and 6B are diagrams illustrating a method for setting the time constant T1 in the first parameter P1. FIG. 6A is a graph illustrating an example of a change in the threshold Cthr when the time constant T1 is small, and FIG. 6B is a graph illustrating an example of a change in the threshold Cthr when the time constant T1 is large. In the graphs shown in FIGS. 6A and 6B, the vertical axis represents capacitance, and the horizontal axis represents elapsed time. In the graphs, the solid line represents the capacitance value Cm, the dashed-dotted line represents the correction capacitance value Cm′, and the dashed line represents the threshold Cthr.

[0048] To perform grip determination in a normal state, it is necessary to determine the threshold value Cthr in a hands-off state in advance. If the driver is gripping the steering wheel 2 when the sensor electrode 21 is activated, it is necessary to determine the threshold value Cthr in a hands-off state and detect the initial grip in order to start grip determination in a normal state. It is preferable that the time required for such calibration is short. The first parameter P1 is a parameter to be used in such an initial state (at start-up).

[0049] The graphs in Figures 6A and 6B show the changes in capacitance value Cm, etc. when the steering wheel device 100 is started while the driver is already gripping the steering wheel 2, then the driver releases the steering wheel 2 and grips it again.

[0050] The capacitance value Cm decreases rapidly when the hand is released and then increases rapidly when the hand is gripped again. By applying a filter process to the capacitance value Cm using a first parameter P1 including a time constant T1, the corrected capacitance value Cm′ attenuates during the release period.

[0051] As shown in FIG. 6A, when the time constant T1 is set to a relatively small value, the attenuation of the correction capacitance value Cm' becomes large. As the correction capacitance value Cm' attenuates, the threshold value Cthr decreases significantly during the let-go period. When the object is gripped again, the capacitance value Cm becomes larger than the threshold value Cthr, and the grip determination result becomes "gripped."

[0052] On the other hand, as shown in FIG. 6B, when the time constant T1 is set to a relatively large value, the attenuation of the correction capacitance value Cm' becomes small (gradual). As the correction capacitance value Cm' attenuates, the threshold value Cthr gradually decreases during the hands-off period. When the hand is gripped again, the capacitance value Cm becomes smaller than the threshold value Cthr, and the grip determination result becomes "non-grip."

[0053] The time constant T1 may be set to an appropriate value so that the "grasped state" can be correctly determined when the object is re-grasped, i.e., so that the capacitance value Cm at the time of re-grasping exceeds the threshold value Cthr. For example, the time constant T1 can be calculated based on the minimum hand-off period required for grip detection, the capacitance value Cm for the gripping style assumed at startup, and the capacitance value Cm under the touch conditions required for grip detection.

[0054] By setting the time constant T1 to a relatively large value, the capacitance value Cm can be decreased with good responsiveness, thereby shortening the time required for the threshold value Cthr to be determined and for grip determination to be possible.

[0055] The second parameter P2 is a parameter for eliminating momentary increases in the capacitance value Cm that occur in a normal state, while following up on gradual increases in the capacitance value Cm due to environmental changes such as temperature and humidity changes inside the vehicle.

[0056] The time constant T2 in the second parameter P2 is set to an appropriate value that is larger than the time constant T1 and can reflect changes in the capacitance value Cm due to temperature and humidity changes inside the vehicle. The time constant T2 can be set to a value that includes a predetermined margin based on the rate of change in capacitance due to changes in temperature and humidity around the steering wheel 2, for example.

[0057] By making the time constant T2 larger than the time constant T1, it is possible to follow changes in temperature and humidity inside the vehicle while filtering out momentary increases in the capacitance value Cm caused by noise. In other words, it is possible to appropriately reflect changes in the capacitance value Cm that should be detected while cutting out unnecessary changes in the capacitance value Cm, preventing erroneous detection of a gripped state and improving the reliability of the determination. Because the increase in the capacitance value Cm due to gripping the steering wheel 2 is steeper than the increase in the capacitance value Cm due to environmental changes, grip detection can be reliably performed even when the time constant T2 is larger than the time constant T1.

[0058] 7A and 7B are diagrams illustrating a method for setting the time constant T3 in the third parameter P3. FIG. 7A is a graph illustrating an example of a change in the threshold Cthr when the time constant T3 is large, and FIG. 7B is a graph illustrating an example of a change in the threshold Cthr when the time constant T3 is small. In the graphs shown in FIGS. 7A and 7B, the vertical axis represents capacitance, and the horizontal axis represents elapsed time. In the graphs, the solid line represents the capacitance value Cm, the dashed-dotted line represents the correction capacitance value Cm′, and the dashed line represents the threshold Cthr.

[0059] The third parameter P3 is a parameter for eliminating a steep decrease in the capacitance value Cm that occurs in the normal state due to, for example, disconnection such as disconnection or chattering of the sensor electrode 21, or fluctuations in the power supply voltage.

[0060] As shown in Figures 7A and 7B, when a break or the like occurs, the capacitance value Cm decreases suddenly at the time when the break or the like occurs, and then increases suddenly when the break or the like is resolved, and returns to the original capacitance value Cm.

[0061] As shown in FIG. 7A, when the time constant T3 is set to a relatively large value, the attenuation of the correction capacitance value Cm′ due to filtering is small (gradual) during the period from when the capacitance value Cm temporarily decreases due to a disconnection or the like until it recovers (the disconnection period). As the correction capacitance value Cm′ attenuates, the threshold value Cthr gradually decreases during the disconnection period. When the capacitance value Cm recovers, the capacitance value Cm becomes smaller than the threshold value Cthr, and the grip determination result is “non-grip.” Therefore, even if the capacitance value Cm increases due to the elimination of the disconnection, erroneous detection can be prevented.

[0062] On the other hand, as shown in FIG. 7B, when the time constant T3 is set to a relatively small value, the attenuation of the correction capacitance value Cm' due to the filter processing becomes large. As the correction capacitance value Cm' attenuates, the threshold value Cthr decreases significantly during the disconnection period. When the capacitance value Cm recovers, the capacitance value Cm becomes larger than the threshold value Cthr, and the grip determination result becomes "grip." Therefore, if the capacitance value Cm increases due to the elimination of the disconnection, there is a risk of false detection.

[0063] The time constant T3 is set to a value larger than the time constant T2 so as to prevent erroneous detection when the capacitance value Cm recovers, i.e., so that the capacitance value Cm does not exceed the threshold value Cthr when the capacitance value Cm recovers. As an example, the time constant T3 can be calculated based on the capacitance value Cm expected under normal conditions, the capacitance value Cm at which a disconnection is determined (disconnection threshold), and the expected length of the disconnection period.

[0064] Note that when a large time constant T3 as described above is set, if the capacitance value Cm decreases due to environmental changes, it may not be possible to detect the grip state. FIG. 8 is a diagram illustrating grip detection using the third parameter P3. The vertical axis of the graph shown in FIG. 8 represents capacitance, and the horizontal axis represents elapsed time. In the graph, the solid line represents the capacitance value Cm, the dashed-dotted line represents the corrected capacitance value Cm', and the dashed line represents the threshold value Cthr.

[0065] When the capacitance value Cm decreases due to an environmental change, the corrected capacitance value Cm' and the threshold value Cthr experience a tracking delay and decrease gradually. When the capacitance value Cm decreases due to an environmental change, the decrease in the capacitance value Cm continues for a longer period of time than in the case of a disconnection, and then the decrease in the capacitance value Cm stops.

[0066] Here, as shown by the thick solid line in the graph, it is assumed that the capacitance value Cm increases by ΔCm when the steering wheel 2 is gripped. While the capacitance value Cm is decreasing due to an environmental change, the threshold value Cthr is smaller than the capacitance value Cm + ΔCm, so it is determined that the state is not being gripped. After the decrease in the capacitance value Cm stops, the threshold value Cthr becomes larger than the capacitance value Cm + ΔCm, so it is determined that the state is being gripped.

[0067] In this way, while the capacitance value Cm is decreasing due to environmental changes, there may be cases where grip detection is not performed, but determining that such a grip state is a non-grip state can be interpreted as a decrease in the sensitivity of grip detection.

[0068] By using the third parameter P3 having the largest time constant T3 when the capacitance value Cm decreases, it is possible to eliminate the steep decrease in the capacitance value Cm while preventing erroneous detection of a grasping state, thereby improving the reliability of the judgment.

[0069] 9 is a flowchart showing an example of a processing procedure executed by the grip detection ECU 1. The processing in each of the following flowcharts may be executed by the control unit 11 in accordance with the program 121 stored in the storage unit 12 of the grip detection ECU 1, or may be realized by a dedicated hardware circuit (for example, an FPGA or an ASIC) provided in the control unit 11, or may be realized by a combination thereof. After detecting activation of the sensor electrode 21, for example, the control unit 11 of the grip detection ECU 1 repeatedly executes the following processing at predetermined or appropriate time intervals.

[0070] The control unit 11 of the grip detection ECU 1 acquires the capacitance value Cm detected by the sensor electrode 21 (step S10), and stores the acquired capacitance value Cm in the storage unit 12 in association with the time point at which the capacitance value Cm was acquired (elapsed time).

[0071] The control unit 11 determines whether to update the threshold value Cthr (step S11). The control unit 11 may determine whether to update the threshold value Cthr based on the grip determination result for the previous capacitance value Cm.

[0072] When it is determined that the threshold value Cthr should not be updated because the grip determination result is the "grip state" (step S11: NO), the control unit 11 skips the update process of the threshold value Cthr and proceeds to step S15. In this case, the control unit 11 may read out the threshold value Cthr stored in the storage unit 12.

[0073] When it is determined that the threshold value Cthr should be updated because the grip determination result is the "non-grip state" (step S11: YES), the control unit 11 selects a parameter P to be used for generating the threshold value Cthr (step S12).

[0074] 10 is a flowchart showing an example of a detailed procedure for selecting the parameter P. The processing procedure shown in the flowchart of FIG. 10 corresponds to details of step S12 in the flowchart of FIG.

[0075] The control unit 11 determines whether the state at the time of acquiring the capacitance value Cm (current state) is the starting state (step S20). Here, not being in the starting state means that the state has already transitioned to the normal state. In step S20, the control unit 11 may determine whether the state is the starting state by determining whether the initial gripping state has been detected based on, for example, a history of determination results after activation of the sensor electrode 21 stored in the memory unit 12. The control unit 11 may also determine whether the state is the starting state by determining whether there is a history of transition to the normal state.

[0076] When it is determined that the initial gripping state has not been detected and therefore that the state is the starting state (step S20: YES), the control unit 11 determines whether or not the parameter P has already been selected (step S21).

[0077] If it is determined that the parameter P has been selected because the selected parameter P is stored (step S21: YES), the control unit 11 determines whether the capacitance value Cm has increased by comparing the previous capacitance value Cm with the current capacitance value Cm (step S22).

[0078] When it is determined that the capacitance value Cm is increasing (step S22: YES), the control unit 11 determines that the current state is the second state, and selects the second parameter P2 as the parameter P (step S23). In detail, the control unit 11 determines the second parameter P2 as the parameter P associated with the second state based on the information stored in the determination data 122 of the storage unit 12, and stores the determined second parameter P2 in the storage unit 12 as the selected parameter.

[0079] The control unit 11 determines whether or not the gripping state is being held by referring to the gripping determination result (step S24). If it is determined that the gripping state is being held (step S24: YES), the control unit 11 transitions from the start state to the normal state (step S25). The control unit 11 stores the transition history in the storage unit 12, and returns the process to step S13 in the flowchart of FIG. 9. Note that the processes of steps S24 to S25 may be performed after obtaining the gripping determination result obtained by the processes from step S13 onward in FIG. 9.

[0080] When it is determined that the state is not the gripped state, that is, the state is the non-gripped state (step S24: NO), the control unit 11 skips the transition process and returns the process to step S13 in the flowchart of FIG.

[0081] If the control unit 11 determines that the parameter P has not been selected because the currently selected parameter P has not been stored (step S21: NO), the control unit 11 selects the first parameter P1 as the initial parameter P (step S26). Alternatively, if the control unit 11 determines that the capacitance value Cm has not increased (the capacitance value Cm is constant or decreasing) (step S22: NO), the control unit 11 determines that the current state is the first state and selects the first parameter P1 (step S26). In detail, the control unit 11 determines the first parameter P1 associated with the first state based on the information stored in the determination data 122 of the storage unit 12, and stores the determined first parameter P1 in the storage unit 12. Thereafter, the control unit 11 returns the process to step S13 in the flowchart of FIG. 9.

[0082] When it is determined that the initial gripping state has already been detected and therefore the state is not the starting state (step S20: NO), the control unit 11 determines whether or not the capacitance value Cm is decreasing (step S27).

[0083] When it is determined that the capacitance value Cm is decreasing (step S27: YES), the control unit 11 determines that the current state is the fourth state and selects a third parameter P3 (step S28). In detail, the control unit 11 determines the third parameter P3 associated with the fourth state based on the information stored in the determination data 122 of the storage unit 12, and stores the determined third parameter P3 in the storage unit 12. Thereafter, the control unit 11 returns the process to step S13 in the flowchart of FIG. 9.

[0084] On the other hand, if it is determined that the capacitance value Cm has not decreased (the capacitance value Cm is constant or increasing) (step S27: NO), the control unit 11 determines that the current state is the third state and selects the second parameter P2 (step S29). In detail, the control unit 11 determines the second parameter P2 associated with the third state based on the information stored in the determination data 122 of the storage unit 12, and stores the determined second parameter P2 in the storage unit 12. Thereafter, the control unit 11 returns the process to step S13 in the flowchart of FIG. 9.

[0085] Continuing the explanation, returning to Fig. 9, the control unit 11 performs filtering on the acquired capacitance value Cm using the selected parameter P (step S13), and outputs a corrected capacitance value Cm' obtained by attenuating the capacitance value Cm.

[0086] The control unit 11 generates a threshold value Cthr based on the obtained correction capacitance value Cm′ and the offset value Coff stored in the judgment data 122 (step S14). Specifically, the threshold value Cthr is calculated by adding the offset value Coff to the correction capacitance value Cm′.

[0087] The control unit 11 determines whether the acquired current capacitance value Cm is smaller than the generated threshold value Cthr, and determines whether the current capacitance value Cm is smaller than the threshold value Cthr (step S15).

[0088] If the current capacitance value Cm is determined to be less than the threshold value Cthr (step S15: YES), the control unit 11 determines that the state is a non-gripped state (step S16).If the current capacitance value Cm is determined to be equal to or greater than the threshold value Cthr (step S15: NO), the control unit 11 determines that the state is a gripped state (step S17).

[0089] The control unit 11 outputs the obtained determination result to, for example, the driving assistance ECU 3 (step S18), and ends the series of processes.

[0090] According to this embodiment, the parameters used in the filter process can be appropriately switched depending on the state of the change in the capacitance value Cm, thereby enabling the threshold Cthr to be set and grasp determination to take into account the change trend of the capacitance value Cm, thereby improving the accuracy of grasp detection. By performing filter process using parameters with different time constants depending on the change trend of the capacitance value Cm, it is possible to appropriately remove changes in the capacitance value Cm that should be removed and appropriately track changes in the capacitance value Cm that should be picked up. Furthermore, by using the parameters with the most responsive time constant immediately after starting up the sensor electrode 21, the calibration time immediately after starting up can be shortened, improving convenience.

[0091] A method for determining the time constants T1 to T3 will be explained below using specific numerical examples.

[0092] The method for determining the time constant T1 will be explained. The parasitic capacitance of the steering wheel 2 is Cp, the offset value is Coff, and the corrected capacitance value obtained by filtering using the first parameter P1 including the time constant T1 is Cm'. Also, the capacitance generated when the driver is gripping the steering wheel 2 at startup is Ch1. After startup, the driver releases the grip and enters a hands-off state, and the capacitance generated when the steering wheel 2 is gripped again is Ch2. The minimum time required to detect gripping after a hands-off state, that is, the minimum required hands-off period, is Toff. Toff corresponds to the grip-release time required to detect gripping again after gripping is released.

[0093] The condition for correctly determining that the steering wheel 2 is gripped when it is gripped again can be expressed by the following formula (1) using Coff, Cp, Ch2, and Cm'. (Ch2+Cp)>Cthr=Cm′+Coff…(1)

[0094] Here, Cm′ can be expressed by the following formula (2). Cm′=Cp+Ch1×exp(-Toff / T1)…(2)

[0095] By solving these two equations for T1, the conditional equation for the time constant T1 can be expressed by the following equation (3) using Coff, Ch1, Ch2, and Toff. T1<(-Toff) / ln{(Ch2-Coff) / Ch1}…(3)

[0096] For example, if Cp=50pF, Coff=10pF, Ch1=45pF, Ch2=20pF, and Toff=500ms, then T1<approximately 332ms can be calculated from the above equations (1) to (3). T1 is set to a value (e.g., 80% of the upper limit value) calculated from equation (3) with a predetermined margin taken into account.

[0097] 11 to 14 are diagrams illustrating examples of grip determination when the time constant T1 is changed. The vertical axis of the graphs shown in the following Figs. 11 to 20 represents capacitance (unit: pF), and the horizontal axis represents elapsed time (unit: ms or s). In Figs. 11 to 14, the solid line represents the capacitance value Cm, the dashed-dotted line represents the corrected capacitance value Cm', and the dashed line represents the threshold value Cthr. Cm = Cp + Ch.

[0098] The graphs in Figures 11 to 13 show the changes in capacitance value Cm, etc. when the steering wheel device 100 is started while the driver is already gripping the steering wheel 2, then the driver releases the steering wheel 2 and grips it again.

[0099] Figure 11 shows the time changes of Cm, Cm', and Cthr when T1 = 332 × 0.8 = 265 ms, Ch1 = 45 pF, and Ch2 = 20 pF. As shown in Figure 11, when the capacitance value Cm increases due to re-grasping, the capacitance value Cm becomes larger than the threshold value Cthr, and therefore the "grasping" state is correctly determined at the time of re-grasping.

[0100] For comparison, Fig. 12 shows the time changes of Cm, Cm', and Cthr when T1 = 265 × 3 = 795 ms, Ch1 = 45 pF, and Ch2 = 20 pF. As shown in Fig. 12, if T1 is set to a large value that does not satisfy equation (3), the capacitance value Cm at the time of re-grasping will be smaller than the threshold value Cthr, and the state will be erroneously determined to be "non-grasping" at the time of re-grasping.

[0101] Figure 13 shows the changes in Cm, Cm', and Cthr over time when T1 = 265 ms, Ch1 = 20 pF, and Ch2 = 20 pF. As shown in Figure 13, even if the electrostatic capacitance at startup is relatively small, the capacitance value Cm after re-grasping is larger than the threshold value Cthr, and the "grasping" state is correctly determined at the time of gripping.

[0102] Fig. 14 shows the changes in capacitance value Cm and the like when the steering wheel device 100 is activated while the driver is not gripping the steering wheel 2, and then the steering wheel 2 is gripped. Fig. 14 shows the changes over time in Cm, Cm', and Cthr when T1 = 265 ms, Ch1 = 0 pF, and Ch2 = 20 pF. As shown in Fig. 14, even if the capacitance value Cm changes from the non-gripped state at activation to the gripped state without any temporary decrease, the capacitance value Cm after gripping becomes larger than the threshold value Cthr, and therefore the "gripped" state is correctly determined at the time of gripping.

[0103] A method for determining the time constant T2 will be described. The initial value of the parasitic capacitance of the steering wheel 2 (the parasitic capacitance before it increases) is Cp, the time required for Cp to increase by 1 pF is Tpp, and the offset value is Coff. Tpp corresponds to the rate of change of the parasitic capacitance Cp.

[0104] When the capacitance value Cm is on an upward trend, if the increase in Cm' is too slow relative to the increase in Cp, the increase in Cthr will also be slow, and in this case, the state will be determined as a grip state even when the actual state is not a grip state.

[0105] When the capacitance value Cm is on the rise, the conditional expression for Cp to prevent the non-gripping state from being erroneously determined to be the gripping state can be expressed by the following expression (4) using Cm′ and Coff. Cp <Cthr=Cm′+Coff…(4)

[0106] An appropriate value for T2 can be determined based on a simulation of time-series data of Cp and Cm' obtained by filtering the time-series data using T2. Specifically, the optimal value of T2 that satisfies the above formula (4) is determined by calculating the time-series change of Cp and Cm' and Cthr obtained by a first-order LPF using various T2s. Tpp for obtaining time-series data of Cp is determined, for example, by experiment.

[0107] 15 to 18 are diagrams illustrating examples of grip determination when the time constant T2 is changed. The graphs in FIGS. 15 to 18 show changes in the parasitic capacitance Cp (capacitance value Cm) when the parasitic capacitance Cp is on an upward trend. In FIGS. 15 to 18, the solid line represents the parasitic capacitance Cp, the dashed-dotted line represents the corrected capacitance value Cm', and the dashed line represents the threshold value Cthr. In FIGS. 15 to 18, the rate of change in Cp, i.e., Tpp, was set to 7.2 s, and Cm' was calculated using a first-order LPF using T2. The Tpp value was calculated from the amount of change in Cp (=25 pF) obtained by actual measurement when the temperature was changed from 25°C and humidity 30% to 50°C and humidity 80% over 3 minutes.

[0108] Figure 15 shows the time changes of Cp, Cm', and Cthr when T2 = 10 s. When T2 = 10 s, Cthr after Cp rises is much larger than Cp, and the "non-grasping" state is correctly determined at the time when the parasitic capacitance Cp rises.

[0109] Figure 16 shows the time changes of Cp, Cm', and Cthr when T2 = 60 s. When T2 = 60 s, Cthr is larger than Cp after Cp increases, and the "non-grasping" state is correctly determined at the time when the parasitic capacitance Cp increases.

[0110] Figure 17 shows the time changes of Cp, Cm', and Cthr when T2 = 120 s. When T2 = 120 s, Cthr after Cp rises is slightly larger than Cp, and the "non-grasping" state is correctly determined at the time when the parasitic capacitance Cp rises.

[0111] Figure 18 shows the time changes of Cp, Cm', and Cthr when T2 = 300 s. When T2 = 300 s, Cthr after Cp rises is smaller than Cp, and the state is erroneously determined to be "grasping" after 80 s has elapsed. Setting T2 too large increases the likelihood of false detection.

[0112] The method for determining the time constant T3 will now be described. The parasitic capacitance of the steering wheel 2 under normal conditions, i.e., when no abnormalities such as a disconnection have occurred, is defined as Cp1, and the parasitic capacitance that has temporarily decreased due to an abnormality such as a disconnection is defined as Cp2. Furthermore, the period required for the parasitic capacitance to recover after the temporary decrease (disconnection period), i.e., the expected duration of the decrease in parasitic capacitance, is defined as Tdrop. The corrected capacitance value obtained by filtering using a third parameter P3 including the time constant T3 is defined as Cm'.

[0113] When Cp2 returns to the original parasitic capacitance Cp1, the condition for Cp1 to be correctly determined to be in a non-gripping state can be expressed by the following equation (5) using Cm′ and Coff. Cp1 <Cthr=Cm′+Coff…(5)

[0114] Here, Cm′ at the time point of Tdrop can be expressed by the following equation (6). Cm′=Cp2+(Cp1-Cp2)×exp(-Tdrop / T3)…(6)

[0115] By solving these two equations for T3, the conditional equation for the time constant T3 can be expressed by the following equation (7) using Coff, Cp1, Cp2, and Tdrop. T3>(-Tdrop) / ln{(Cp1-Cp2-Coff) / (Cp1-Cp2)}…(7)

[0116] For example, if Cp1=50 pF, Cp2=30 pF, Coff=10 pF, and Tdrop=60 s, then T3 is calculated to be greater than approximately 87 s from the above equations (5) to (7). T3 is set to a value that takes into account a predetermined margin (for example, 1.7 times the lower limit value) of the lower limit value calculated from equation (7).

[0117] FIG. 19 is a diagram illustrating an example of grip determination using time constant T3. The graph in FIG. 19 shows changes in parasitic capacitance Cp and other parameters when the parasitic capacitance decreases due to an abnormality such as a wire breakage, and then returns to its original state after the decrease continues for a certain period of time. FIG. 19 shows changes in Cp, Cm', and Cthr over time when T3 = 87 × 1.7 = 147 s, Cp1 = 50 pF, and Cp2 = 30 pF. In FIGS. 19 and 20, the thin solid line indicates the parasitic capacitance Cp, the dashed-dotted line indicates the corrected capacitance value Cm', the dashed line indicates the threshold value Cthr, and the thick solid line indicates Cp + Ch. The thick solid line indicates the capacitance value Cm when the steering wheel 2 is gripped.

[0118] As shown in Figure 19, when the time constant T3 is large, Cp becomes smaller than the threshold value Cthr when the parasitic capacitance returns to its original value due to the resolution of the abnormality, and therefore the "non-grasping" state is correctly determined when the parasitic capacitance returns.

[0119] Fig. 20 is a diagram illustrating another example of grip determination using time constant T3. Fig. 20 shows the changes in Cp, Cm', and Cthr over time when T3 = 147 s and the parasitic capacitance Cp decreases due to an environmental change. The time required for Cp to decrease by 1 pF due to the environmental change is set to 7.2 s, and the rate of change of Cp is set to 7.2 s / pF.

[0120] As shown in FIG. 20, while the parasitic capacitance Cp is decreasing, the threshold Cthr decreases gradually as the parasitic capacitance Cp decreases. Even after the decrease in the parasitic capacitance Cp stops, the threshold Cthr continues to decrease for a while. When T3=147 s, the threshold Cthr becomes larger than Cp+Ch at approximately 100 s to 110 s in the latter half of the decrease period of the parasitic capacitance Cp, so a non-grasping state is determined. When the decrease in the parasitic capacitance Cp stops, the threshold Cthr becomes larger than Cp+Ch, so a grasping state is determined. As the interval between Cthr and Cp+Ch becomes narrower, the detection sensitivity of the grasping state decreases.

[0121] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The technical features described in each embodiment can be combined with each other, and the scope of the present invention is intended to include all modifications within the scope of the claims and the scope equivalent to the claims. The sequences shown in each embodiment are not limited, and the order of each process may be changed within a range consistent with the present invention, and multiple processes may be executed in parallel. The entity that performs each process is not limited, and the process of each device may be executed by another device within a range consistent with the present invention.

[0122] The matters described in each embodiment can be combined with each other. Furthermore, the independent claims and dependent claims described in the claims can be combined with each other in any combination, regardless of the reference format. Furthermore, the claims use a format in which a claim references two or more other claims (multiple claim format), but this is not limited to this. A multiple claim (multi-multi claim) that references at least one other multiple claim may also be used. [Explanation of symbols]

[0123] 100 Steering wheel device 1. Grasp detection ECU (grasp detection device) 11 Control section 12 Storage section 13 Communications Department 14 Capacitance measurement circuit 111 Acquisition Department 112 Specific section 113 Filter section 114 Generation part 115 Judgment section 121 Programs 1A Recording Media 2 steering wheels 21 Sensor electrode (capacitance sensor)

Claims

1. A grip detection device (1) for detecting gripping of a steering wheel (2), an acquisition unit (111) that acquires a capacitance value detected by a capacitance sensor (21) provided on the steering wheel (2); a generation unit (114) that generates a threshold value for detecting gripping of the steering wheel (2) by performing a filter process on the capacitance value using the parameters based on the capacitance value acquired by the acquisition unit (111) and a parameter according to a state related to a change in the capacitance value; A grip detection device (1) comprising:

2. and a determination unit (112) that determines the parameter according to a state regarding a change in the capacitance value determined based on whether or not the steering wheel (2) is initially gripped after activation of the capacitance sensor (21) and an increase or decrease in the capacitance value. The grip detection device (1) according to claim 1.

3. The parameter is set in plurality depending on the state related to the change in the capacitance value. A grip detection device (1) according to claim 1 or claim 2.

4. The parameter has a time constant that represents the responsiveness to a change in the capacitance value. A grip detection device (1) according to claim 1 or claim 2.

5. The states related to the change in the capacitance value include a first state in which the capacitance value is constant or decreasing during a period after activation of the capacitance sensor (21) and before an initial grip on the steering wheel (2) is detected; a second state in which the capacitance value is increasing during a period after activation of the capacitance sensor (21) and before an initial grip on the steering wheel (2) is detected; a third state in which the capacitance value is constant or increasing during a period after activation of the capacitance sensor (21) and after an initial grip on the steering wheel (2) is detected; and a fourth state in which the capacitance value is decreasing during a period after activation of the capacitance sensor (21) and after an initial grip on the steering wheel (2) is detected. A grip detection device (1) according to claim 1 or claim 2.

6. the parameters include a first parameter corresponding to the first state, a second parameter corresponding to the second state and the third state, and a third parameter corresponding to the fourth state; the first parameter has a time constant that represents responsiveness to a change in the capacitance value; the second parameter has a time constant that follows the change in the capacitance value with a longer delay time than the time constant of the first parameter; The third parameter has a time constant that follows the change in the capacitance value with a longer delay time than the time constant of the second parameter. The grip detection device (1) according to claim 5.

7. The time constant of the first parameter is determined based on the capacitance value when the steering wheel (2) is gripped, the capacitance value when the steering wheel (2) is gripped again after being released from gripping, and a grip release time required to detect re-gripping after the grip release. The grip detection device (1) according to claim 6.

8. The time constant of the second parameter is determined so that, when the capacitance value increases, the capacitance value according to a preset rate of change becomes less than a threshold value generated by performing a filter process on the capacitance value using the second parameter. The grip detection device (1) according to claim 6.

9. The time constant of the third parameter is determined based on the capacitance value when a predetermined abnormality occurs, the capacitance value before the predetermined abnormality occurs, and the time required for the abnormality to be resolved after it occurs. The grip detection device (1) according to claim 6.

10. The generating unit (114) generates the threshold value and updates the threshold value when gripping of the steering wheel (2) is not detected. A grip detection device (1) according to claim 1 or claim 2.

11. A computer (11) that detects whether a steering wheel (2) is being grasped, A capacitance value detected by a capacitance sensor (21) provided on the steering wheel (2) is acquired; Based on the acquired capacitance value and a parameter according to a state related to a change in the capacitance value, a filter process is performed on the capacitance value using the parameter, thereby generating a threshold value for detecting gripping of the steering wheel (2). A program (121) for executing the process.

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