Contact determination method and contact determination device

Abstract

Provided is a contact determination method in which a sheet-like electrode part 20, which is constituted by layering a first electrode 21 and a second electrode 22 with an insulator therebetween, is provided so as to cover an outer peripheral part of a steering wheel 10, and in which determination of contact of a driver with the steering wheel 10 is performed on the basis of an electrical signal detected from the electrode part 20. The contact determination method comprises: a detection step for detecting an electrostatic capacitance generated in the electrode part 20; a determination step for comparing a determination value calculated from the electrostatic capacitance detected in the detection step with a determination threshold to determine whether the steering wheel is in a hands-on state in which a hand of the driver is in contact with the steering wheel 10 or in a hands-off state in which the hand of the driver is not in contact with the steering wheel 10; and a setting step for setting the determination threshold on the basis of a determination initial value of the determination value in the hands-off state. In the setting step, when the determination value exceeds the determination threshold and then the determination value decreases and becomes a fixed value different from the determination initial value, the determination initial value is updated to the fixed value and the determination threshold is set on the basis of the updated determination initial value.

Description

Contact detection method and contact detection device

[0001] The present invention relates to a contact determination method and a contact determination device for determining whether a driver has contacted a steering wheel.

[0002] WO2021 / 095478 discloses a technology in which two electrodes are provided on the outer periphery of a steering wheel, stacked with an insulator between them, to determine whether the driver is touching the steering wheel.

[0003] Japanese Patent Application Laid-Open No. 2017-177857

[0004] Generally, steering wheels are often not flat but have complex surfaces. Therefore, when attaching the sheet-shaped electrodes and insulators to the steering wheel, it is necessary to use a jig or other tool to attach them according to the complex surface of the steering wheel. However, if the electrodes are defective or damaged, there is a risk that part of the electrode will be cut off. In such a state, the capacitance of the sheet-shaped electrode will change from its initial value, making it impossible to determine whether the driver is touching the steering wheel.

[0005] The present invention provides a contact determination method and a contact determination device that can determine whether or not a driver is in contact with a steering wheel even when the capacitance of an electrode portion has changed from its initial value.

[0006] The present invention solves the above problem by detecting the capacitance generated in the electrode portion, comparing a judgment value calculated from the detected capacitance with a judgment threshold to determine whether the state is hands-on or hands-off, and if the judgment value exceeds the judgment threshold and then decreases to a constant value different from the initial judgment value, updating the initial judgment value to the constant value and setting the judgment threshold based on the updated initial judgment value.

[0007] According to the present invention, when the capacitance of the electrode portion changes from the initial value, it is possible to determine whether or not the driver is touching the steering wheel.

[0008] FIG. 1 is a simplified diagram showing an example of the configuration of a contact determination device. FIG. 2 is a diagram showing an example in which a part of the second electrode is cut off. FIG. 3A is a diagram showing an example of contact determination as a comparative example. FIG. 3B is a diagram showing an example of contact determination as a comparative example. FIG. 4 is a graph for explaining a hands-on state and a determination value for the hands-on state. FIG. 5 is a diagram showing an example of a determination process for determining contact determination based on capacitance and impedance generated in the electrode portion. FIG. 6 is a diagram showing an example of a determination process for determining contact determination based on capacitance and impedance generated in the electrode portion. FIG. 7 is a flowchart showing an example of a contact determination process in the contact determination device.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0010] 1 is a simplified diagram showing an example of the configuration of a contact determination device 1. The contact determination device 1 is a device installed in a vehicle, and determines whether or not the hands H1, H2 of a driver of the vehicle are in contact with a steering wheel 10. The steering wheel 10 is installed in front of a seat (driver's seat) in which the driver sits.

[0011] The contact determination device 1 includes a sheet-like electrode unit 20 installed on the steering wheel 10, and an ECU (Electronic Control Unit) 30. The electrode unit 20 functions as a so-called touch sensor, and is a sheet-like electrode unit configured by stacking a first electrode 21 and a second electrode 22 with an insulator 23 sandwiched therebetween. The first electrode 21 can also be referred to as an active shield electrode, and the second electrode 22 can also be referred to as a sensor electrode. The touch sensor realized by the electrode unit 20 is, for example, a capacitance-type touch sensor.

[0012] Here, the steering wheel 10 is an operating member including a metal core 11 that forms the framework of the steering wheel 10, and is used by a driver of a vehicle when steering the vehicle. The substantially annular grip portion of the steering wheel 10 is the portion that is gripped by the driver's hand when driving the vehicle, and the periphery of the core 11 is covered with a base. An insulating material is used as the base. For example, a resin material such as urethane is used as the base.

[0013] The first electrode 21 is a sheet-like electrode electrically connected to the ECU 30 via a signal line S1. The second electrode 22 is a sheet-like electrode electrically connected to the ECU 30 via a signal line S2. The insulator 23 is an elastic sheet-like insulator, for example, an insulating sheet.

[0014] An electrode unit 20 is attached to the outer periphery of a base constituting the grip portion of the steering wheel 10 so as to cover the base in the circumferential direction of the steering wheel 10. A first electrode 21 is arranged on the inner periphery of the steering wheel 10, and a second electrode 22 is arranged on the outer periphery of the steering wheel 10. While FIG. 1 shows an example in which the electrode unit 20 is provided on the entire circumferential portion of the steering wheel 10, the electrode unit 20 may be provided on only a portion of the circumferential direction of the steering wheel 10. An exterior portion is attached to the outer periphery of the electrode unit 20 as a contact portion that is gripped by the driver's hand. This exterior portion is preferably made of insulating leather, resin, or the like. In this way, the electrode unit 20 is arranged between the base and the exterior portion in the grip portion of the steering wheel 10. That is, the electrode unit 20 is covered by the exterior portion.

[0015] The ECU 30 controls each component based on various programs stored in a storage unit (not shown), and includes a detection unit 31, a determination unit 32, and a setting unit 33. The ECU 30 is implemented by, for example, a processing device such as a CPU (Central Processing Unit). The storage unit stores various pieces of information (e.g., control programs, various detected values) required for the ECU 30 to perform various processes. The storage unit may be, for example, a read-only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof.

[0016] The ECU 30 determines whether the vehicle is in a hands-off state or a hands-on state while the vehicle is traveling using autonomous driving such as lane keeping. For example, when the vehicle is traveling autonomously in a hands-off state, the ECU 30 controls the steering wheel 10 to continue the autonomous driving while determining whether the state is hands-on or hands-off, in order to notify the driver to switch from autonomous driving to manual driving according to the traveling state of the vehicle. In the following description, the determination of the hands-on or hands-off state and the operation of the steering wheel 10 are collectively referred to as "steering control."

[0017] The detection unit 31 is connected to the first electrode 21 via signal line S1 and to the second electrode 22 via signal line S2. It detects the capacitance and impedance occurring across the first electrode 21 and the second electrode 22 and outputs the detection results to the determination unit 32. For example, the detection unit 31 supplies an AC signal to the electrode unit 20 and detects the capacitance and impedance occurring across the first electrode 21 and the second electrode 22 based on a response signal acquired in response to the AC current. Known measurement methods can be used to measure the capacitance and impedance. For example, an AC signal can be applied to the electrode unit 20, and impedance can be detected based on the signal ratio (current / voltage) obtained from the measurement results obtained by simultaneously measuring the voltage and current. For example, an absolute self-capacitance electrostatic IC, which can simultaneously measure sensor inputs from multiple zones and has a sinusoidal sensor drive waveform, can be used as the detection unit 31. This electrostatic IC drives the shield electrode (first electrode 21) and compares the drive waveform with the input waveform from the sensor electrode (second electrode 22). The electrostatic IC then digitally converts the compared differential waveform, demodulates it with the sine and cosine components of the drive frequency, and integrates it to calculate a detection value. Of these detection values, the impedance is calculated based on the calculation result of the sine component, and the capacitance is calculated based on the calculation result of the cosine component. In this way, the detection unit 31 outputs a sine wave to the electrode unit 20, and can detect the capacitance and impedance based on the difference in phase and amplitude between the sine wave and the response wave.

[0018] Furthermore, for example, when the driver's hand touches or approaches the steering wheel 10, the driver's hand approaches the second electrode 22, causing a change in the capacitance Chg of the second electrode 22. The capacitance Chg of the second electrode 22 can be detected by a capacitance method such as a self-capacitance method or a mutual capacitance method. That is, the detection unit 31 can detect the capacitance generated in the second electrode 22 in response to the driver's contact with the steering wheel 10 by a capacitance method such as a self-capacitance method or a mutual capacitance method.

[0019] The determination unit 32 calculates a determination value from the capacitance detected by the detection unit 31. The determination value is a parameter for determining whether the state is a hands-on state or a hands-off state, and varies depending on the capacitance Chg. The hands-on state is a state in which the driver's hands are in contact with the steering wheel 10, and the hands-off state is a state in which the driver's hands are not in contact with the steering wheel 10. The determination unit 32 compares the determination value with a determination threshold value to determine whether the state is a hands-on state or a hands-off state.

[0020] The setting unit 33 sets the determination threshold based on the initial determination value of the determination value in the hands-off state. The method of determining the hands-on state by the determination unit 32 and the method of setting the determination threshold by the setting unit 33 will be described later.

[0021] 2A and 2B are diagrams showing an example in which a portion of the second electrode 22 is cut. Fig. 2A shows a simplified view of a position 25 in the steering wheel 10 where a portion of the second electrode 22 is cut. Note that Fig. 2A omits some of the components of the contact determination device 1 shown in Fig. 1. Fig. 2B also shows a schematic view of the relationship between the first electrode 21, the second electrode 22, and the ECU 30 for ease of explanation.

[0022] Here, the process of attaching the electrode unit 20 to the steering wheel 10 will be described. Here, an example is shown in which conductive cloth, which is a cloth woven into a mesh structure and metal-plated, is used as the sheet-like first electrode 21 and second electrode 22. This conductive cloth is flexible and extensible, but it is also possible that the metal plating may peel off or the mesh of the conductive cloth may easily widen.

[0023] For example, when attaching the sheet-shaped electrode unit 20 to the steering wheel 10, it is necessary to wrap the sheet-shaped electrode unit 20 around the steering wheel 10 using a jig such as a punching rod. However, because the steering wheel 10 does not have a flat surface, the sheet-shaped electrode unit 20 must be wrapped around a complex surface. During this installation, it is possible that the conductive cloth may stretch, or that excessive pressure with the punching rod may further damage the conductive cloth when the conductive cloth is already stretched. It is also possible that the conductive cloth may have defects such as defects. If the electrode is defective or damaged during installation, a portion of the electrode may be severed. In this state, after the leather wrapping process of wrapping the exterior part around the sheet-shaped electrode unit 20, gripping the exterior part with a screwdriver may cause the conductive cloth to stretch and expand, further widening the cut portion of the electrode. If the cut portion of the electrode further widens, the resistance value of the cut portion will increase.

[0024] For example, as shown in Fig. 2A, a case is assumed in which a portion of the second electrode 22 is cut at position 25 on the steering wheel 10. For ease of explanation, Fig. 2B schematically shows a case in which the sheet-like first electrode 21 and second electrode 22 are parallel to each other. Such a cut portion is sometimes referred to as a plating crack.

[0025] For example, even if a portion of the second electrode 22 is cut at the position 25 shown in Figure 2(A), the electrodes are electrically connected as long as they are in contact with each other at the cut portion. This connected state can also be called pseudo-contact.

[0026] However, when the driver grips the cut portions of the steering wheel 10 via the exterior, the load causes slight deformation and the cut portions separate slightly. In this case, the electrical resistance between the cut portions increases, making it difficult for current to flow, and the resistance of the cut portions of the second electrode 22 increases abnormally.

[0027] Furthermore, if the separation distance of the cut portion becomes too large, the cut portion will also be completely disconnected electrically, resulting in a loss of area of ​​the second electrode 22 following the cut portion indicated by position 25, and the capacitance will decrease in accordance with this reduction in area. Note that in FIG. 2B , the range of the area of ​​the second electrode 22 following the cut portion indicated by position 25 is indicated by R1. In this way, if the cut portion of the second electrode 22 also becomes disconnected electrically, the resistance value at the cut portion will increase, but the capacitance will decrease.

[0028] 3A and 3B are diagrams illustrating examples of contact determination, specifically, examples of the relationship between the capacitance generated in the electrode unit 20 and the determination value (ΔAD) used to determine whether the driver has contacted the steering wheel 10.

[0029] Fig. 3A shows an example in which the electrode unit 20 is in a normal state, i.e., there is no abnormality in the electrode unit 20, and Fig. 3B shows an example in which the electrode unit 20 is in a disconnected state. Note that the disconnected state shown in Fig. 3B is a state in which a part of the second electrode 22 is disconnected at position 25, but the electrodes at the disconnected portion can make pseudo-contact with each other. Fig. 3B shows an example in which position 25 is the disconnected portion, similar to the example shown in Fig. 2B.

[0030] First, the judgment value (ΔAD) will be explained. The judgment value (ΔAD) can be calculated by the following formula 1. That is, the judgment value (ΔAD) is expressed as a function including capacitances (Chg, Crs). Chg is the capacitance that occurs between the driver's hand and the second electrode 22 when the driver's hand approaches the second electrode 22. Crs is the capacitance between the first electrode 21 and the second electrode 22. That is, Crs means the capacitance that the electrode unit 20 originally holds. ΔAD=f[Chg / (Crs+Chg)]...Formula 1

[0031] The capacitance Crs between the first electrode 21 and the second electrode 22 can be calculated by the following formula 2. εrs is the dielectric constant between the first electrode 21 and the second electrode 22. drs is the distance between the first electrode 21 and the second electrode 22. Srs is the area of ​​the second electrode 22. Crs=εrs(Srs / drs) (Formula 2)

[0032] In the electrode portion 20, a capacitance Chgl between the metal core 11 and the second electrode 22 and a capacitance Csg between the metal core 11 and the first electrode 21 also occur, but a description thereof will be omitted here.

[0033] The capacitance Crs between the first electrode 21 and the second electrode 22 is normally fixed. In contrast, the capacitance Chg changes in value depending on the driver's contact state with the steering wheel 10. Specifically, when the driver's hands are not touching the steering wheel 10, the capacitance Chg is 0 or close to 0. On the other hand, when the driver's hands are touching the steering wheel 10, the capacitance Chg increases in value depending on the degree of contact. That is, when the driver grips the steering wheel 10, the capacitance Chg is increased, and the judgment value (ΔAD) increases. Furthermore, when the driver continues to grip the steering wheel 10, the judgment value (ΔAD) remains high. On the other hand, when the driver releases the steering wheel 10, the judgment value (ΔAD) decreases rapidly.

[0034] In this embodiment, when the judgment value (ΔAD) exceeds the judgment threshold value TH1, it is judged that contact has occurred. For example, as shown by the curve L1 in the lower graph of FIG. 3A, when the judgment value (ΔAD) exceeds the judgment threshold value TH1, it is judged that contact has occurred.

[0035] Here, the capacitance and resistance between the first electrode 21 and the second electrode 22 when the electrode unit 20 is in a normal state (see FIG. 3A) and when the electrode unit 20 is in a disconnected state (see FIG. 3B) will be described.

[0036] Comparing the case where the electrode unit 20 is in a normal state (see FIG. 3A ) with the case where the electrode unit 20 is in a disconnected state (see FIG. 3B ), when the electrode unit 20 is in a disconnected state, the area of ​​the second electrode 22 following the disconnected portion indicated by position 25 is lost. This makes it difficult for electricity to flow between the first electrode 21 and the second electrode 22, and the resistance value Rs2 between the first electrode 21 and the second electrode 22 when the electrode unit 20 is in a disconnected state is greater than the resistance value Rs1 between the first electrode 21 and the second electrode 22 when the electrode unit 20 is in a normal state.

[0037] Furthermore, since the area of ​​the second electrode 22 is lost, the capacitance Crs2 between the first electrode 21 and the second electrode 22 when the electrode portion 20 is in a disconnected state is lower than the capacitance Crs1 between the first electrode 21 and the second electrode 22 when the electrode portion 20 is in a normal state.

[0038] As described above, when the area of ​​the second electrode 22 decreases, the capacitance Crs2 between the first electrode 21 and the second electrode 22 decreases, and therefore the denominator of Equation 1 also increases, resulting in a larger value of the judgment value (ΔAD). Furthermore, if the electrode unit 20 remains disconnected after the driver releases his / her hands from the steering wheel 10, the judgment value (ΔAD) may remain large and exceed the judgment threshold value TH1. For example, as shown by the curve L2 in the lower graph of FIG. 3B , the judgment value (ΔAD) may remain in excess of the judgment threshold value TH1 even though the driver has released his / her hands from the steering wheel 10. In this case, unless the judgment threshold value is changed, the contact determination device 1 may erroneously determine that the vehicle is in a hands-on state. Therefore, in this embodiment, as shown by curve L2, if the determination value (ΔAD) decreases after exceeding the determination threshold TH1 and becomes a constant value different from the initial value of the determination value (ΔAD), the determination threshold TH1 is changed to another determination threshold. This makes it possible to implement logic for determining whether or not the driver is touching the steering wheel even if the capacitance of the electrode unit 20 has changed from the initial value due to, for example, a part of the electrode unit 20 being cut.

[0039] Next, referring to FIG. 4 , a method for setting the judgment threshold by the setting unit 33 will be described. FIGS. 4A and 4B are graphs showing the relationship between the judgment value (AD) and the judgment threshold when the state of hand contact with the steering wheel 10 changes in the following order: hang-off state, hang-on state, and hang-off state. The threshold (TH1a) in FIG. 4A indicates the judgment threshold before the initial judgment value is updated, and the threshold (TH1b) in FIG. 4B indicates the judgment threshold after the initial judgment value is updated. The judgment threshold is a value obtained by adding a predetermined value (P) to the initial judgment value. Note that in FIGS. 4A and 4B , as in FIG. 3B , a break occurs in the electrode unit 20, and the electrodes at the break can make pseudo-contact with each other. The initial judgment value corresponds to the judgment value (ΔAD) calculated from the capacitance of the electrode unit 20 when the electrode unit 20 is in a normal state and in a hands-off state. The judgment value (ΔAD) can be calculated using the above formula (1). That is, the initial value for determination is the value calculated when Chg=0 in equation (1), and ΔAD=C0.

[0040] As shown in the leftmost graph in FIG. 4A, the determination value (ΔAD) in the hang-off state is C0. When the hang-on state is entered, the capacitance of the electrode unit 20 decreases, and the determination value (ΔAD) becomes C1 (>C0) (see the center graph in FIG. 4A). The determination unit 32 determines that the hands-on state is entered because the determination value (ΔAD) is equal to or greater than the determination threshold value (TH1a). If there is no disconnection in the electrode unit 20, the determination value (ΔAD) returns to C0 when the hands-off state is entered. If there is a disconnection in the electrode unit 20, gripping the steering wheel 10 widens the disconnected portion, reducing the capacitance Crs between the first electrode 21 and the second electrode 22. Therefore, even when the hands-on state is changed to the hands-off state, the determination value (ΔAD) does not return to C0 but remains at a constant value (C0') greater than C0. The judgment value (C0′) for the hands-off state is greater than the judgment threshold (TH1a). Therefore, unlike the present embodiment, if the hands-on / hands-off state judgment is performed without changing the judgment threshold, the state will be erroneously judged to be the hands-on state.

[0041] When steering control is terminated (after steering operation), the setting unit 33 calculates a determination value (ΔAD) from the capacitance of the electrode unit 20 detected by the detection unit 31. The setting unit 33 calculates the determination value (ΔAD) until the determination value (ΔAD) becomes constant. The setting unit 33 compares the determination value (ΔAD) at the start of steering control with the determination value (ΔAD) after the start of steering control to determine whether the determination value (ΔAD) has changed from the determination value (ΔAD) at the start of steering control. If the determination value (ΔAD) has changed from the determination value (ΔAD) at the start of steering control, the setting unit 33 changes the determination initial value to the determination value (ΔAD) after the start of steering control. In the example of FIG. 4A , the determination value (C0′) after the end of steering control is different from the determination value (C0) at the start of steering control, so the setting unit 33 updates the determination initial value to the determination value (C0′). The setting unit 33 also sets (offsets) the new determination threshold value by adding a predetermined value (P) to the updated determination initial value (C0').

[0042] As shown in FIG. 4B , the determination threshold is changed from TH1a to TH1b, so that the determination value (C0′) in the hands-off state is less than the determination threshold (TH1b), and the determination unit 32 determines that the vehicle is in a hands-off state (see the leftmost graph in FIG. 4B ). Next, when the vehicle enters a hang-on state, the determination value (ΔAD) becomes C1, which is equal to or greater than the determination threshold (TH1b), and the determination unit 32 determines that the vehicle is in a hands-on state (see the center graph in FIG. 4B ). Then, when the steering control ends, the determination value (ΔAD) becomes C0′. In this way, if the determination value (ΔAD) exceeds the determination threshold (TH1a) and then decreases to a constant value (C0′) different from the initial determination value (C0), the setting unit 33 updates the initial determination value (C0) to the constant value (C0′). Then, the setting unit 33 sets the determination threshold value (TH1b) based on the updated determination initial value (C0').

[0043] Next, a method for determining whether the vehicle is in a hands-on state or a hands-off state based on capacitance and impedance, and a method for determining an abnormality in the electrode unit 20, performed by the ECU 30, will be described. Fig. 5 is a diagram showing an example of a determination process for determining contact based on a determination value (ΔAD) calculated from the capacitance generated in the electrode unit 20 and an amount of change in impedance (ΔZ). The horizontal axis in Fig. 5 represents the determination value (ΔAD), and the vertical axis in Fig. 5 represents the amount of change in impedance (ΔZ). Impedance refers to resistance when an alternating current flows, and is also referred to as AC resistance.

[0044] 5 is calculated from the capacitance generated at the second electrode 22 in response to the driver's contact with the steering wheel 10. The change in impedance (ΔZ) is the amount of change in impedance generated at the electrode unit 20 (the impedance between the first electrode 21 and the second electrode 22) relative to the initial impedance value. The initial impedance value is the impedance between the first electrode 21 and the second electrode 22 in a hands-off state.

[0045] Here, when the electrode unit 20 is in a normal state, when the driver grips the steering wheel 10, the capacitance Chg increases according to the driver's contact with the steering wheel 10. However, the resistance between the first electrode 21 and the second electrode 22 does not change due to the driver's contact, so the amount of change in impedance (ΔZ) is small or almost zero.

[0046] On the other hand, when the second electrode 22 is in the disconnected state, when the driver grips the steering wheel 10, the capacitance Chg increases depending on the driver's contact with the steering wheel 10. Furthermore, when the second electrode 22 is disconnected due to the driver's contact, the resistance between the first electrode 21 and the second electrode 22 changes due to the driver's contact, as shown in FIGS. 2 and 3 . That is, when the second electrode 22 is disconnected due to the driver's contact, the resistance value changes to a smaller value depending on the driver's contact state. Therefore, the impedance between the first electrode 21 and the second electrode 22 changes relative to the initial impedance value, and the amount of change in impedance (ΔZ) increases. That is, since the impedance decreases significantly depending on the driver's contact state, the amount of change in impedance (ΔZ) also increases.

[0047] When the second electrode 22 is in a disconnected state, when the driver grips the steering wheel 10, the change amount ΔAD becomes larger than the change amount threshold (TH11), and the change amount (ΔZ) of impedance also becomes larger. Furthermore, the change amount (ΔZ) of impedance also differs depending on the degree of disconnection of the electrode unit 20. For example, when the electrode unit 20 is in a disconnected state in which Crs is slightly reduced, such as when the electrode unit 20 is partially disconnected, the change amount (ΔZ) of impedance is small. On the other hand, when the electrode unit 20 is in a disconnected state in which Crs is significantly reduced, such as when the electrode unit 20 is completely disconnected, the change amount (ΔZ) of impedance is large.

[0048] Therefore, in this embodiment, the determination unit 32 performs contact determination using the determination value (ΔAD), and further performs abnormality determination of the electrode unit 20 using the relationship between the determination value (ΔAD) and the change in impedance (ΔZ). Specifically, if the determination value (ΔAD) is equal to or less than the determination threshold value TH11 indicated by the line SL2, it determines that there is no contact. If the intersection of the determination value (ΔAD) and the change in impedance (ΔZ) is in the non-contact area NCA1, the determination unit 32 determines that there is no contact.

[0049] On the other hand, if the judgment value (ΔAD) exceeds the judgment threshold TH11 indicated by the straight line SL2, it is determined that contact has occurred. However, even if the judgment value (ΔAD) exceeds the judgment threshold TH11 (straight line SL2), if the impedance (ΔZ) is equal to or greater than the stepped broken line SL1, it is assumed that the electrode unit 20 is in an abnormal state, for example, that the second electrode 22 is in a disconnected state, and therefore it is determined that an abnormality has occurred. In other words, if the intersection of the judgment value (ΔAD) and the change in impedance (ΔZ) is located in the contact area CA1, it is determined that contact has occurred, but if the intersection of the judgment value (ΔAD) and the change in impedance (ΔZ) is located in the abnormal area AA1, it is determined that an abnormality has occurred.

[0050] Here, the determination threshold TH11 is a contact determination threshold used when determining whether the driver has contacted the steering wheel 10. The determination threshold TH11 can be set appropriately based on experimental data, etc. The determination threshold TH11 may be a fixed value, or may be variable depending on the driver, the internal environment of the vehicle, and the environment around the vehicle, such as temperature and humidity.

[0051] The stepped broken line SL1 represents the abnormality determination threshold used when determining whether or not there is an abnormality in the electrode unit 20. For example, when the determination value (ΔAD) is greater than the determination threshold TH11 and falls within a range equal to or less than TH12, the abnormality determination threshold is set to TH21. When the determination value (ΔAD) is greater than TH12 and falls within a range equal to or less than TH13, the abnormality determination threshold is set to TH22. Similarly, the abnormality determination thresholds TH23 to TH25 are set in accordance with the range (TH13 to TH15) of the determination value (ΔAD). In this way, values ​​TH21 to TH25 that increase as the determination value (ΔAD) increases can be set as the abnormality determination thresholds.

[0052] 5 shows an example in which the abnormality determination thresholds TH21 to TH25 are set to increase stepwise, but other thresholds that increase in accordance with the increase in the determination value (ΔAD) may be set as the abnormality determination thresholds. For example, the value TH shown in the following formula 3 can be set as the abnormality determination threshold. Note that DC1 and α1 are diagnostic coefficients and can be set appropriately based on experimental data, etc. TH = ΔAD × DC1 + α1 ... formula 3

[0053] That is, if the judgment value (ΔAD) is greater than the judgment threshold TH11 and the change in impedance (ΔZ) satisfies the following formula 4, it is judged that contact has occurred. On the other hand, if the judgment value (ΔAD) is greater than the judgment threshold TH11 but the impedance ΔZ does not satisfy the following formula 4, it is judged that an abnormality has occurred. ΔZ<ΔAD×DC1+α1 ... formula 4

[0054] In the above manner, the determination unit 32 determines that the vehicle is in a hands-on state when the determination value (ΔAD) is equal to or greater than the determination threshold (TH11), and determines that the vehicle is in a hands-off state when the determination value (ΔAD) is less than the determination threshold (TH11). For example, when the driver's hand touches the steering wheel 10 in a hands-off state where the intersection of the determination value (ΔAD) and the change in impedance (ΔZ) is at the origin (point 0), the intersection of the determination value (ΔAD) and the change in impedance (ΔZ) moves from the origin to point Q1. The determination value (ΔAD) exceeds the determination threshold TH11, and the determination unit 32 determines that the vehicle is in contact. When the electrode unit 20 is normal, the intersection of the determination value (ΔAD) and the change in impedance (ΔZ) returns from point Q1 to point Q1 when the vehicle is in a hands-off state.

[0055] Furthermore, the determination unit 32 determines that the electrode unit 20 is abnormal if the determination value (ΔAD) is equal to or greater than the determination threshold (TH11) and the amount of change in impedance is equal to or greater than the abnormality determination thresholds TH21 to TH25. For example, when the intersection of the determination value (ΔAD) and the amount of change in impedance (ΔZ) is at the origin (point 0) in a hands-off state, if the driver's hand touches the steering wheel 10, the intersection of the determination value (ΔAD) and the amount of change in impedance (ΔZ) moves from the origin to point R1. Because the intersection (R1) is in the abnormality area AA1, the determination unit 32 determines that the electrode unit 20 is abnormal.

[0056] Furthermore, if the determination value (ΔAD) is equal to or greater than the determination threshold (TH11) and the change in impedance is less than the abnormality determination thresholds TH21 to TH25, the determination unit 32 determines that no abnormality has occurred in the electrode unit 20 and that the vehicle is in a hands-on state. For example, in a hands-off state, when the intersection of the determination value (ΔAD) and the change in impedance (ΔZ) is at the origin (point 0), if the driver's hand touches the steering wheel 10, the intersection of the determination value (ΔAD) and the change in impedance (ΔZ) moves from the origin to point R2. Because the intersection (R2) is in contact area CA1, the determination unit 32 determines that the electrode unit 20 is not abnormal but that the vehicle is in a hands-on state.

[0057] 5, for ease of explanation, an example of determining contact using the relationship between the most recent determination value (ΔAD) and the impedance ΔZ is shown. However, since it is expected that abnormal values ​​may be detected due to variations, radio wave noise, etc., multiple detection results may be used to eliminate such abnormal values ​​and improve reliability.

[0058] If the judgment value (ΔAD) does not return to the initial judgment value after determining that the vehicle is in a hands-on state, the setting unit 33 sets new judgment thresholds and contact judgment thresholds. For example, in FIG. 5 , after the intersection of the judgment value (ΔAD) and the change in impedance (ΔZ) moves from the origin to point R2, if the electrode unit 20 is partially disconnected and steering control ends and the driver's hands leave the steering wheel 10, the judgment value ΔAD decreases but does not return to the initial judgment value corresponding to the origin (point 0). That is, the intersection of the judgment value (ΔAD) and the change in impedance (ΔZ) moves from point R2 to point R3. Because the judgment value (ΔAD) has changed from the initial judgment value, the setting unit 33 updates the initial judgment value to the judgment value (ΔAD) at point R3. The setting unit 33 also sets a new judgment threshold (TH11′) by adding a predetermined value (P) to the updated initial judgment value. That is, the setting unit 33 offsets (shifts) the determination threshold value (TH11) to the positive side of the determination value (ΔAD) in the coordinate system of the determination value (ΔAD) and the amount of change in impedance (ΔZ) as shown in Fig. 5. Furthermore, the setting unit 33 updates (offsets) the abnormality determination threshold values ​​(TH21 to TH25).

[0059] Fig. 6 is a diagram showing an example of an update process for updating the threshold value based on a determination value (ΔAD) calculated from the capacitance generated at the electrode unit 20 and an amount of change in impedance (ΔZ). The horizontal axis in Fig. 6 represents the determination value (ΔAD), and the vertical axis in Fig. 6 represents the amount of change in impedance (ΔZ). Note that the dotted polygonal line SL1 and the dotted straight line SL2 represent the abnormality determination threshold and the determination threshold before updating, and the dotted vertical and horizontal axes represent the coordinate axes of the threshold value before updating.

[0060] In this embodiment, when the determination threshold is changed by updating the initial determination value, the abnormality determination threshold is also updated. For example, the setting unit 33 sets ΔAD included in Equation 3 as the updated initial determination value (C0'), changes the diagnostic coefficient to another coefficient, and then sets the value TH shown in Equation 3 as the abnormality determination threshold. The new abnormality determination threshold increases in a stepwise manner, just like the abnormality determination threshold before the update, but the first step threshold (TH21') is smaller than the first step threshold (TH21) before the update. In other words, the determination threshold moves from the threshold (line SL2) to the threshold (line SL2'). The distance from the origin before the offset to the threshold (line SL2') is the same as the distance from the origin after the offset to the threshold (line SL2), and the magnitude of the determination threshold remains unchanged. The abnormality determination threshold also moves from the threshold (broken line SL1) to the threshold (broken line SL1'). Furthermore, the distance from the origin before the offset to the abnormality determination threshold (the magnitude of the first step of the broken line SL1') is smaller than the distance from the origin after the offset to the abnormality determination threshold (the magnitude of the first step of the broken line SL1), and the magnitude of the abnormality determination threshold becomes smaller.

[0061] As shown in FIG. 5 , when steering control is terminated while the electrode unit 20 is partially disconnected, the intersection point of the determination value (ΔAD) and the change in impedance (ΔZ) moves from point (R2) to point (R3). That is, the determination value (ΔAD) and the initial impedance value do not return to their original values. The setting unit 33 changes the initial impedance value, which serves as a reference for the change in impedance (ΔZ), to the value of the change in impedance (ΔZ) at point (R3). That is, in the coordinate system of the determination value (ΔAD) and the change in impedance (Z), the setting unit 33 offsets the origin from point 0 to point R3 and sets the determination threshold (TH11′) and the abnormality determination thresholds (TH21′-TH25′). In this way, when the determination value (ΔAD) exceeds the determination threshold (TH1a) and then becomes a constant value (C0′) different from the initial determination value (C0), the setting unit 33 updates the initial impedance value and the abnormality determination threshold.

[0062] In this embodiment, in the coordinate system of the determination value (ΔAD) and the change amount of impedance (Z), the determination initial value and the impedance initial value corresponding to the origin are offset, and the determination threshold and the abnormality determination threshold are also offset, as shown in Fig. 6. This makes it possible to implement logic for determining whether or not the driver is touching the steering wheel and logic for determining whether or not an abnormality exists in the electrode unit 20, even if the capacitance and impedance of the electrode unit 20 have changed from their initial values ​​due to, for example, the cutting of a part of the electrode unit 20.

[0063] Next, an example of the operation of the contact determination device 1 will be described. Fig. 7 is a flowchart showing an example of contact determination processing in the contact determination device 1. This contact determination processing is executed by the ECU 30 based on a program stored in a storage unit (not shown). When steering control is started, the ECU 30 executes the following control flow.

[0064] In step S1, the detection unit 31 detects the capacitance and impedance of the electrode unit 20. In step S2, the determination unit 32 calculates a determination value (ΔAD) from the detected capacitance. In step S3, the determination unit 32 compares the determination value (ΔAD) with a determination threshold (TH11) and determines whether the determination value (ΔAD) is equal to or greater than the determination threshold (TH11). If the determination value (ΔAD) is equal to or greater than the determination threshold (TH11), the determination unit 32 determines in step S4 that the hand is in a hands-on state.

[0065] In step S5, the determination unit 32 calculates the amount of change in impedance (ΔZ). In step S6, the determination unit 32 compares the amount of change in impedance (ΔZ) with the abnormality determination threshold (TH21 to TH25) and determines whether the amount of change in impedance (ΔZ) is less than the abnormality determination threshold (TH21 to TH25). If the amount of change in impedance (ΔZ) is less than the abnormality determination threshold (TH21 to TH25), the ECU 30 determines whether the steering control has ended. If the steering control has not ended, the control flow returns to step S1, and the ECU 30 executes the control flow from step S1 onwards.

[0066] When the steering control is ended, in step S8, the detection unit 31 detects the capacitance and impedance of the electrode unit 20. If the capacitance has changed after the steering control, the detection unit 31 repeats the control flow of step S8 and detects the capacitance when it has become a constant value. In step S9, the determination unit 32 calculates a determination value (ΔAD) from the detected capacitance. In step S10, the setting unit 33 calculates the determination value (ΔAD) at the start of the steering control. ０ ) is compared with the judgment value (ΔAD) at the end of the steering control, and the judgment value (ΔAD) is ０ ) and determine whether it is a value different from the judgment value (ΔAD ０ ) corresponds to the value calculated in the control flow of step S2, and the determination value (ΔAD) at the time of the steering control termination corresponds to the value calculated in the control flow of step S9.

[0067] The judgment value (ΔAD) is the judgment value (ΔAD ０), in step S11, the setting unit 33 updates the initial determination value and the initial impedance value. The control flow in step S11 corresponds to the offset of the origin shown in FIGS. 5 and 6. In step S12, the setting unit 33 updates the determination threshold value (TH11) and the abnormality determination threshold values ​​(TH21 to TH25) based on the updated initial determination value and initial impedance value. Then, the control flow ends.

[0068] In the determination flow of step S3, if it is determined that the determination value (ΔAD) is less than the determination threshold (TH11), the determination unit 32 determines in step S13 that the hand is off. The control flow proceeds to step S7. Also, in the determination flow of step S6, if it is determined that the amount of impedance change (ΔZ) is equal to or greater than the abnormality determination threshold (TH21 to TH25), the determination unit 32 determines in step S14 that the electrode unit 20 is abnormal. Then, the control flow ends. Also, in the determination flow of step S10, if the determination value (ΔAD) is less than the determination threshold (TH21 to TH25), the determination unit 32 determines in step S14 that the electrode unit 20 is abnormal. ０ ), the control flow ends.

[0069] As described above, in the contact determination method or contact determination device according to this embodiment, the ECU 30 detects the capacitance generated in the electrode unit 20, compares the determination value calculated from the detected capacitance with the determination threshold, determines whether the vehicle is in a hands-on state or a hands-off state, and sets the determination threshold based on the initial determination value for the hands-off state. Furthermore, if the determination value exceeds the determination threshold and then decreases to a constant value different from the initial determination value, the ECU 30 updates the initial determination value to the constant value and sets the determination threshold based on the updated initial determination value. This makes it possible to determine whether the driver is in contact with the steering wheel when the capacitance of the electrode unit 20 has changed from its initial value.

[0070] In this embodiment, the ECU 30 detects the impedance generated in the electrode unit 20, calculates the amount of change in the impedance generated in the electrode unit 20, and determines that the electrode unit 20 is abnormal if the amount of change in impedance is equal to or greater than the abnormality determination threshold. Furthermore, if the determination value exceeds the determination threshold and then becomes a constant value different from the initial determination value, and the amount of change in impedance is less than the abnormality determination threshold, the ECU 30 updates the abnormality determination threshold. This makes it possible to determine whether or not the electrode unit 20 is abnormal, even if the capacitance and / or impedance of the electrode unit 20 has changed from their initial values.

[0071] In a first modification of this embodiment, the setting unit 33 may count the number of offsets used to update the initial determination value, and may perform the offset when the offset count is less than a predetermined threshold value. However, if the offset count reaches the predetermined threshold value, the setting unit 33 may not perform the offset. That is, in this modification, the origin shown in FIGS. 5 and 6 may be offset to set an upper limit on the number of offsets used to update the determination threshold (TH11) and the abnormality determination thresholds (TH21-TH25). For example, in the exemplary operation of the contact determination device 1 shown in the control flow of FIG. 7 , when the control flow of steps S11 and S12 is executed once each, the number of offsets is counted once. The upper limit of the number of offsets is preset, such as three. Note that when repeatedly performing the offsets, the ECU 30 may maintain the magnitude of the determination threshold and decrease the magnitude of the abnormality determination threshold according to the number of offsets. When the offset count reaches the upper limit, the determination unit 32 may determine that the electrode unit 20 is abnormal.

[0072] Furthermore, in Modification 1, if the offset count is less than the upper limit, the determination unit 32 may not perform an abnormality determination of the electrode unit 20 based on the impedance change amount ΔAD. For example, if it has been experimentally confirmed that a decrease in capacitance due to partial cutting of the first electrode 21 or the second electrode 22 occurs in stages, the determination threshold can be changed to determine whether the driver has touched the steering wheel if the capacitance has decreased for the first or second time. Therefore, in Modification 1, if the offset count is less than the upper limit, even if the electrode unit 20 is partially cut, such as moving from the origin (point 0) to the intersection (R1) in Figure 6, the ECU 30 does not determine whether the electrode unit 20 is abnormal, and instead offsets the origin, the determination threshold (TH11), and the abnormality determination thresholds (TH21 to TH25). 7 , if the number of offsets is less than the upper limit, the control flow of steps S5, S6, and S14 is omitted, and a control flow of counting the number of offsets and a control flow of determining whether the number of offsets has reached the upper limit are added after the control flow of steps S11 and S12. If the number of offsets has reached the upper limit, the determination unit 32 may execute the control flow of steps S5, S6, and S14 without performing offsetting, or may determine that the electrode unit 20 is abnormal without executing the control flow of steps S5, S6, and S14.

[0073] In the example of operation of the contact determination device 1 shown in the control flow of Figure 7, the offset (updating of the determination threshold and / or abnormality determination threshold) corresponding to the control flow of step S11 and / or step S12 is executed after steering control (after "Yes" in the control flow of step S7), but it may also be executed after the vehicle power is switched from off to on.

[0074] REFERENCE SIGNS LIST 1 Contact determination device 10 Steering wheel 11 Core metal 20 Electrode portion 21 First electrode 22 Second electrode 23 Insulator 30 ECU 31 Detection portion 32 Determination portion 33 Setting portion

Claims

1. A contact determination method in which a sheet-like electrode section, consisting of a first electrode and a second electrode stacked with an insulator sandwiched between them, is provided to cover the outer periphery of a steering wheel, and which determines whether a driver has come into contact with the steering wheel based on an electrical signal detected from the electrode section, the method comprising: a detection step of detecting capacitance generated in the electrode section; a judgment step of comparing a judgment value calculated from the capacitance detected in the detection step with a judgment threshold to determine whether the steering wheel is in a hands-on state in which the driver's hands are in contact with the steering wheel, or a hands-off state in which the driver's hands are not in contact with the steering wheel; and a setting step of setting the judgment threshold based on an initial judgment value of the judgment value in the hands-off state, in which, after the judgment value exceeds the judgment threshold, if the judgment value decreases to a constant value different from the initial judgment value, the initial judgment value is updated to the constant value, and the judgment threshold is set based on the updated initial judgment value.

2. A contact determination method as described in claim 1, wherein in the detection step, the impedance generated in the electrode portion is detected; in the determination step, the amount of change in impedance generated in the electrode portion is calculated; if the amount of change in impedance is equal to or greater than an abnormality determination threshold, the electrode portion is determined to be abnormal; and in the setting step, if the determination value exceeds the determination threshold and then becomes a constant value different from the initial determination value, the abnormality determination threshold is updated.

3. A contact determination method according to claim 1 or 2, wherein in the setting step, the number of offsets for updating the determination initial value is counted, and if the number of offsets is less than a predetermined number threshold, the offset is performed, and if the number of offsets has reached the predetermined number threshold, the offset is not performed.

4. A contact determination method according to claim 3, wherein in the setting step, the offset is performed after the vehicle power is switched from off to on or after the steering wheel is operated.

5. A contact determination device in which a sheet-like electrode section, consisting of a first electrode and a second electrode stacked with an insulator sandwiched between them, is arranged to cover the outer periphery of a steering wheel, and which determines whether a driver has made contact with the steering wheel based on an electrical signal detected from the electrode section, comprising: a detection section that detects the capacitance and impedance generated in the electrode section; a determination section that compares a determination value calculated from the capacitance detected by the detection section with a determination threshold to determine whether the driver is in a hands-on state where his / her hands are in contact with the steering wheel, or a hands-off state where the driver's hands are not in contact with the steering wheel; and a setting section that sets the determination threshold based on an initial determination value of the determination value in the hands-off state, wherein the setting section, when the determination value decreases to a constant value different from the initial determination value after exceeding the determination threshold, updates the initial determination value to the constant value, and sets the determination threshold based on the updated initial determination value.

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