Touch detection device

Abstract

This touch detection device comprises: a first sensor electrode and a second sensor electrode; a detection unit that directly charges each of the first sensor electrode and the second sensor electrode to detect a first capacitance, and directly charges one of the first sensor electrode and the second sensor electrode and indirectly charges the other to detect a second capacitance; a calculation unit that calculates a first difference value that is a difference between the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode, and that, for each of the first sensor electrode and the second sensor electrode, calculates a second difference value that is a difference between the first capacitance and the second capacitance; and a determination unit that uses the first difference value and the second difference value to determine contact of an occupant with the first sensor electrode and the second sensor electrode.

Description

Touch detection device

[0001] The present disclosure relates to a touch detection device.

[0002] In the steering unit described in Japanese Patent Application Laid-Open No. 2018-069935, a contact sensor is arranged on the steering wheel, and based on a preset threshold value and a contact signal output from the contact sensor, whether the occupant is in contact (gripping) or non-contact (non-gripping) with the steering wheel is determined. Further, in the steering unit, a first thermometer for measuring the first temperature of the outer surface of the steering wheel and a second thermometer for measuring the second temperature as the internal temperature of the steering wheel are mounted. Thereby, in the steering unit, the threshold value is changed according to the first temperature and the second temperature, and contact determination is performed.

[0003] By the way, in a capacitive touch sensor for detecting the contact of an occupant with the steering wheel, the sensor electrode and the shield electrode are used in an overlapped manner. However, by omitting the shield electrode, cost reduction can be achieved.

[0004] However, the parasitic capacitance changes according to environmental conditions such as temperature. For example, as the environmental temperature rises, the parasitic capacitance also increases. For this reason, accurate touch determination may become difficult.

[0005] The present disclosure provides a touch detection device that can suppress a decrease in determination accuracy caused by changes in parasitic capacitance while achieving cost reduction.

[0006] A touch detection device according to the first embodiment includes: a first sensor electrode and a second sensor electrode, each positioned on the steering body and accessible to the occupant, and for which capacitance is detected; a detection unit that, when detecting a first capacitance for each of the first and second sensor electrodes, directly charges each of the first and second sensor electrodes for detection, and when detecting a second capacitance for each of the first and second sensor electrodes, directly charges one of the first and second sensor electrodes and indirectly charges the other using the power from the direct charge; a calculation unit that calculates a first difference value which is the difference between the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode, and calculates a second difference value which is the difference between the first capacitance and the second capacitance for each of the first and second sensor electrodes; and a determination unit that determines occupant contact with the first and second sensor electrodes using the first difference value and the second difference value for each of the first and second sensor electrodes.

[0007] The touch detection device according to the second embodiment includes, in the first embodiment, that the first sensor electrode and the second sensor electrode are two sensor electrodes among a plurality of sensor electrodes arranged on the steering body.

[0008] A touch detection device according to a third embodiment, in the first or second embodiment, includes a first detection unit that supplies power to the first sensor electrode to detect the first capacitance and supplies power to the first sensor electrode and the second sensor electrode to detect the second capacitance, and a second detection unit that supplies power to the second sensor electrode to detect the second capacitance and supplies power to the second sensor electrode and the first sensor electrode to detect the second capacitance.

[0009] In the fourth embodiment, the touch detection device includes, in the third embodiment, a switching unit that switches between supplying power to the first sensor electrode and supplying power to the second sensor electrode together with the first sensor electrode, and switches between supplying power to the second sensor electrode and supplying power to the first sensor electrode together with the second sensor electrode.

[0010] A touch detection device according to a fifth embodiment includes, in the third or fourth embodiment, a first amplification unit that amplifies the charging power supplied to the second sensor electrode when charging the first sensor electrode, and a second amplification unit that amplifies the charging power supplied to the first sensor electrode when charging the second sensor electrode.

[0011] The touch detection device according to the sixth embodiment includes a setting unit that sets a reference value to be used as a basis for a first threshold value for the first difference value and a second threshold value for each of the second difference values, and sets the first threshold value and the second threshold value based on the set reference value, in any one of the first to fifth embodiments.

[0012] In the seventh embodiment, the touch detection device includes, in the sixth embodiment, setting the reference value from the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode when the occupant is not in contact with the first sensor electrode and the second sensor electrode.

[0013] In the eighth embodiment, the touch detection device includes, in the sixth or seventh embodiment, setting the setting unit to set the smaller of the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode as the reference value when the occupant is not in contact with either the first sensor electrode or the second sensor electrode.

[0014] The touch detection device according to the ninth embodiment includes, in any one of the first to eighth embodiments, the determination unit determining contact of an occupant with the first sensor electrode and the second sensor electrode using the first difference value and one of the second difference values ​​of the first sensor electrode and the second sensor electrode, respectively.

[0015] The touch detection device according to the tenth embodiment includes, in any one of the first to ninth embodiments, that each of the second difference values ​​is applied after being accumulated by a predetermined number of the second difference values.

[0016] In the touch detection device according to the eleventh embodiment, in any one of the first to tenth embodiments, the determination unit includes a complementation unit that complements the determination result using the second difference value of the first sensor electrode or the second sensor electrode and the first difference value using the first capacitance of the first sensor electrode and the second sensor electrode, respectively.

[0017] In the twelfth embodiment of the touch detection device, in the eleventh embodiment, the complement unit includes determining whether the occupant is in contact with both the first and second sensor electrodes based on the first capacitance of each of the first and second sensor electrodes, when it is determined that the occupant is not in contact with at least one of the first and second sensor electrodes.

[0018] In the touch detection device according to the first embodiment, a first sensor electrode and a second sensor electrode are each positioned on the steering body so that the occupant can make contact with them, and the capacitance generated at each is detected. When the detection unit detects the first capacitance for each of the first and second sensor electrodes, it directly charges each of the first and second sensor electrodes for detection. Furthermore, when the detection unit detects the second capacitance for each of the first and second sensor electrodes, it directly charges one of the first and second sensor electrodes and indirectly charges the other using the power from the direct charge.

[0019] The calculation unit calculates a first difference value, which is the difference between the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode, and also calculates a second difference value for each of the first and second sensor electrodes, which is the difference between the first capacitance and the second capacitance.

[0020] Here, the determination unit uses the first difference value, the second difference value of the first sensor electrode, and the second difference value of the second sensor electrode to determine whether the occupant is in contact with the first and second sensor electrodes. As a result, the first and second difference values, which are free from the influence of parasitic capacitance in the first and second sensor electrodes, are used, so even when cost reduction is achieved, a decrease in determination accuracy due to changes in parasitic capacitance can be suppressed.

[0021] In the touch detection device according to the second embodiment, the first sensor electrode and the second sensor electrode are two of a plurality of sensor electrodes arranged on the steering body. This makes it possible to determine, for example, whether the occupant is gripping the steering body with at least one hand by arranging them on the left and right sides of the steering body.

[0022] In the touch detection device according to the third embodiment, the detection unit includes a first detection unit and a second detection unit. The first detection unit charges the first sensor electrode to detect a first capacitance and charges the first sensor electrode and the second sensor electrode to detect a second capacitance of the first sensor electrode. The second detection unit charges the second sensor electrode to detect a second capacitance and charges the second sensor electrode and the first sensor electrode to detect a second capacitance of the second sensor electrode. This simplifies the detection of the first and second capacitances of the first and second sensor electrodes, respectively.

[0023] In the touch detection device according to the fourth embodiment, the detection unit includes a switching unit. The switching unit switches between charging the first sensor electrode and charging the second sensor electrode together with the first sensor electrode, and switches between charging the second sensor electrode and charging the first sensor electrode together with the second sensor electrode. This makes it possible to detect the second capacitance with a simplified configuration.

[0024] The touch detection device according to the fifth embodiment includes a first amplification unit and a second amplification unit. The first amplification unit amplifies the charging power when supplying charging power to the second sensor electrode to the second sensor electrode. The second amplification unit amplifies the charging power (for example, the amplitude of the charging current) when supplying charging power to the first sensor electrode to charge the second sensor electrode. This makes it possible to suppress the second difference value from becoming small.

[0025] In the touch detection device according to the sixth embodiment, the setting unit sets a reference value that serves as the basis for the first threshold value for the first difference value and the second threshold value for each of the second difference values. The setting unit also sets the first threshold value and the second threshold value based on the set reference value. This makes it possible to suppress a decrease in the accuracy of touch detection using the first difference value and the second difference value due to parasitic capacitance.

[0026] In the touch detection device according to the seventh embodiment, the setting unit sets reference values ​​from the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode when the occupant is not in contact with the first and second sensor electrodes. This allows for the setting of first and second threshold values ​​that suppress the influence of parasitic capacitance, thereby improving the accuracy of the determination.

[0027] In the touch detection device according to the eighth embodiment, when the occupant is not in contact with either the first sensor electrode or the second sensor electrode, the setting unit sets the smaller of the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode as the reference value. This allows for effective setting of the first and second thresholds, thereby improving the accuracy of the determination.

[0028] In the touch detection device according to the ninth embodiment, the determination unit uses a first difference value and either a second difference value of the first sensor electrode or the second sensor electrode to determine whether the occupant is in contact with the first sensor electrode or the second sensor electrode. This eliminates the need to detect the second capacitance for the second difference value in the first sensor electrode or the second sensor electrode, thereby simplifying the determination process.

[0029] In the touch detection device according to the tenth embodiment, the second difference value for each of the first sensor electrode and the second sensor electrode is applied by accumulating a preset number of second difference values. This effectively suppresses the influence of noise and other factors included in the second capacitance on the second difference value.

[0030] In the touch detection device according to the eleventh embodiment, the determination unit includes a complementation unit that complements the determination result using the second difference value of the first sensor electrode or the second sensor electrode, and the first difference value, using the first capacitance of the first sensor electrode and the second sensor electrode, respectively. This improves the determination accuracy of the determination unit.

[0031] In the touch detection device according to the twelfth embodiment, when the complementary unit determines that the occupant is not in contact with at least one of the first sensor electrode and the second sensor electrode, it determines from the first capacitance of each of the first and second sensor electrodes whether the occupant is in contact with both the first and second sensor electrodes. This improves the accuracy of the determination when the occupant is in contact with both the first and second sensor electrodes, and when the occupant is not in contact with both.

[0032] This is a front view showing the schematic configuration of a steering wheel on which a touch detection device according to the first embodiment is installed. This is a schematic diagram showing the schematic configuration of the main part of the steering wheel. This is a block diagram showing the schematic configuration of the control unit according to the first embodiment. This is a schematic diagram showing the schematic connection of the switching unit 40 and the sensor electrodes. This is a flowchart showing the schematic of the capacitance detection process. This is a flowchart showing the schematic of the touch determination process. This is a diagram showing the schematic of the changes in capacitance L and R. This is a schematic diagram showing the schematic of charging in the detection of capacitance L, showing a two-handed steering state. This is a schematic diagram showing the schematic of charging in the detection of capacitance L, showing a one-handed steering state. This is a schematic diagram showing the schematic of charging in the detection of capacitance Lb, showing a two-handed steering state. This is a schematic diagram showing the schematic of charging in the detection of capacitance Lb, showing a one-handed steering state. This is a diagram showing the schematic of capacitance L, R and differential values ​​DLR and DL according to the steering state. This is a diagram showing the schematic of capacitance L, R, Lb and differential value DL according to the steering state. This is a diagram showing touch determination using differential value DLR and differential value DL. This is a block diagram showing the schematic configuration of the control unit according to the second embodiment. This is a flowchart showing the schematic of the touch detection process. This is a flowchart showing the schematic of the judgment completion process. This is a diagram showing the schematic of capacitance L, R and difference values ​​DLR, DL according to the steering state. This is a diagram showing touch judgment using difference values ​​DLR and DL. This is a block diagram showing the schematic configuration of the control unit according to the third embodiment. This is a flowchart showing the schematic of the reference value setting process. This is a diagram showing the schematic of capacitance L, R and difference values ​​DLR, DL according to the steering state. This is a schematic configuration diagram showing the hardware configuration of the steering ECU.

[0033] Embodiments of the present disclosure will be described below with reference to the drawings. [First Embodiment] The touch detection device 10 according to the first embodiment is provided in the steering device (not shown) of a vehicle, and the steering device includes a steering wheel 12 which is an operating body and a steering body operated by an occupant in the vehicle. The steering wheel 12 is located on the front side of the vehicle of the seat (driver's seat) where the occupant who operates the vehicle is seated.

[0034] Figure 1 shows a schematic front view of the steering wheel 12, where the touch detection device 10 is installed, as seen from the occupant's perspective. In the drawing, the right side in the vehicle width direction is indicated by arrow HR, and the top is indicated by arrow UP.

[0035] As shown in Figure 1, the steering wheel 12 is composed of a substantially annular rim portion 14 as a gripping portion, a boss portion 16 provided at the center of the rim portion 14, and a stay portion 18 connecting the rim portion 14 and the boss portion 16, and the steering wheel 12 is formed in a substantially annular shape. In the drawing, the radial direction of the steering wheel 12 is indicated by arrow R, and the circumferential direction of the steering wheel 12 is indicated by arrow L.

[0036] The steering wheel 12 is equipped with a metal core that forms the frame, and the core is composed of a roughly annular rim core portion 20 of the rim portion 14, a boss core portion (not shown) of the boss portion 16, and a stay core portion (not shown) of the stay portion 18. The steering wheel 12 is formed by connecting the rim core portion 20 and the boss core portion with the stay core portion, so that the rim portion 14, the boss portion 16, and the stay portion 18 are integrated together.

[0037] The vehicle is equipped with a steering shaft (not shown), which is rotatably supported by the vehicle body at the front of the driver's seat with its axis oriented approximately in the longitudinal direction of the vehicle. The steering wheel 12 has a boss core metal portion of the boss portion 16 fixed to the rear end of the steering shaft, and the steering wheel 12 is supported by the vehicle body so as to be able to rotate integrally with the steering shaft. Therefore, the core metal of the steering wheel 12 is in contact with the vehicle body via the steering shaft.

[0038] In a vehicle, the steering wheel 12 is rotated, which in turn rotates the steering shaft, causing the steering wheels (front wheels) to turn and the vehicle to steer. Figure 1 shows the steering wheel 12 in a straight-ahead driving state.

[0039] Figure 2 shows a schematic diagram corresponding to a state in which the main part of the rim portion 14 of the steering wheel 12 is cut along the circumferential direction of the steering wheel 12.

[0040] As shown in Figure 2, a base body 22 made of a resin material such as urethane as an insulating material is placed on the rim portion 14 of the steering wheel 12. The base body 22 covers the rim core portion 20 of the rim portion 14, and the rim core portion 20 is housed inside the base body 22 by insert molding.

[0041] The steering wheel 12 has a decorative portion 24 positioned on the outer circumference of the base body 22 as a contact portion (surface). The decorative portion 24 is made of leather (synthetic leather) or resin (partially wood may be used) and has insulating properties. The rim portion 14 of the steering wheel 12 is covered by the decorative portion 24 all around the base body 22 in the radial cross-section of the steering wheel 12 and all around the steering wheel 12 in the circumferential direction.

[0042] As a result, the rim portion 14 of the steering wheel 12 has a rim core portion 20 that forms the ground (GND) portion, the outside of the rim core portion 20 is the base body 22, and the decorative portion 24 is arranged on the outside of the base body 22.

[0043] In such a steering wheel 12, a steering heater 26 or the like can be installed inside the base body 22. The steering heater 26 includes heater wiring (heating wire) 28, and the heater wiring 28 is embedded in the base body 22 of the steering wheel 12 and connected to a heater drive circuit (not shown). The steering heater 26 is energized from the heater drive circuit to the heater wiring 28 when a heater switch (both not shown) provided on the instrument panel of the vehicle or the like is turned on. As a result, in the steering heater 26, the heater wiring 28 generates heat to warm (temperature control) the rim portion 14 of the steering wheel 12.

[0044] On the other hand, the touch detection device 10 is of a capacitance type (self-capacitance type). The touch detection device 10 detects the contact of an occupant's (hand) with the rim portion 14 in the steering wheel 12, and determines whether the occupant is gripping (holding the steering) the rim portion 14 of the steering wheel 12.

[0045] As shown in FIG. 1, the touch detection device 10 includes a sensor unit 30 for detecting the proximity of an occupant (contact with the rim portion 14), and a steering ECU 32 as a control unit. In the touch detection device 10, the steering ECU 32 functions as a determination unit, a detection unit, a charging unit, and a switching unit.

[0046] The sensor unit 30 includes a plurality of sensor electrodes 34, and the sensor electrodes 34 are disposed on the rim portion 14 of the steering wheel 12. As shown in FIG. 2, the sensor electrodes 34 are in a sheet shape, wound around the circumferential surface of the base body 22 in the circumferential direction of the rim portion 14, extending in the circumferential direction of the steering wheel 12, and covered by the decorative portion 24.

[0047] Two sensor electrodes 34 are provided on the steering wheel 12. One of the sensor electrodes 34 is arranged in the range of approximately the left half circumference of the steering wheel 12 (hereinafter referred to as the sensor electrode 34L), and the other of the sensor electrodes 34 is arranged in the range of approximately the right half circumference of the steering wheel 12 (hereinafter referred to as the sensor electrode 34R). Thus, when the occupant steers the steering wheel 12 (rim portion 14 thereof) with the left hand, the occupant's (left hand) approaches (touches) the sensor electrode 34L as the first sensor electrode, and when the occupant steers the steering wheel 12 with the right hand, the occupant approaches (touches) the sensor electrode 34R as the second sensor electrode.

[0048] The steering ECU 32 is arranged in the boss portion 16 of the steering wheel 12 (not shown in the figure), and each of the sensor electrodes 34 (34L, 34R) is connected thereto. The steering ECU 32 detects the capacitance of the sensor electrodes 34 (34L, 34R), determines whether an occupant is in contact with each of the sensor electrodes 34L and 34R, and determines whether the occupant is steering the steering wheel 12 in a manner that enables the vehicle to be steered. FIG. 3 shows a schematic configuration of the steering ECU 32 as a control unit in a block diagram. FIG. 19 schematically shows the hardware configuration of the steering ECU 32.

[0049] As shown in FIG. 19, the steering ECU 32 includes a CPU (Central Processing Unit) 90, a ROM (Read Only Memory) 91, a RAM (Random Access Memory) 92, a storage 93, a communication I / F (Interface) 94, and an input / output I / F 95, and these are connected to each other via a bus 96 so as to be communicable. The storage 93 is realized by a non-volatile storage medium such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). Further, the steering ECU 32 may include a functional circuit 97 for realizing required functions, and the functional circuit 97 may be connected to the input / output I / F 95. The functional circuit 97 may be an electric circuit combining circuit elements such as semiconductor elements.

[0050] Furthermore, the steering ECU 32 stores a capacitance detection program and a touch detection program in ROM or storage. The steering ECU 32's CPU 90, acting as a processor, reads and executes the capacitance detection program and the touch detection program from ROM 91 or storage 93, acting as memory. As a result, as shown in Figure 3, the steering ECU 32 realizes the functions of the switching unit 40, detection control unit 42, calculation unit 44, determination unit 46, and output unit 48.

[0051] The detection control unit 42 includes a first detection unit and a second detection unit, a detection unit 50L for detecting the capacitance generated at the sensor electrode 34L and a detection unit 50R for detecting the capacitance generated at the sensor electrode 34R. When detecting the capacitance of the sensor electrodes 34L and 34R, the detection control unit 42 controls the detection units 50L and 50R, as well as the operation of the switching unit 40. The detection units 50L and 50R and the switching unit 40 may be realized by a detection circuit (first detection circuit, second detection circuit) and a functional circuit 97 as a switching circuit, respectively. Figure 4 shows a schematic configuration diagram of an example of the switching unit 40, and the connection of the sensor electrodes 34L and 34R is schematically shown.

[0052] As shown in Figure 4, the switching unit 40 is connected to the sensor electrodes 34L and 34R, respectively. Furthermore, the sensor electrode 34L is connected to the detection control unit 42 (detection unit 50L) via the switching unit 40, and the sensor electrode 34R is connected to the detection control unit 42 (detection unit 50R) via the switching unit 40 (see Figure 3).

[0053] The detection unit 50L and the detection unit 50R are capable of outputting charging power (charging current) CHG for charging the sensor electrodes 34L and 34R, grounding (GND) the sensor electrodes 34L and 34R, and detecting (IN) the capacitance of the sensor electrodes 34L and 34R, respectively.

[0054] Sensor electrode 34L is charged by the charging power CHG input from detection unit 50L, and sensor electrode 34R is charged by the charging power CHG input from detection unit 50R. Detection units 50L and 50R detect the capacitance of sensor electrodes 34L and 34R by receiving a voltage (IN) corresponding to the capacitance of sensor electrodes 34L and 34R. For the sake of simplicity, in the following explanation, it will be assumed that detection units 50L and 50R detect capacitance.

[0055] Furthermore, the switching unit 40 is equipped with amplifiers 52L and 52R, which serve as a first and second amplification unit used for indirect charging. The operation of amplifiers 52L and 52R is controlled by operation signals Ls and Rs, respectively, output from the detection control unit 42. Amplifier 52L is activated (turned on) when the operation signal Ls is input from the detection control unit 42, and amplifies the charging power of the sensor electrode 34L at a predetermined amplification factor (for example, by amplifying the charging current) and outputs it to the sensor electrode 34R. Amplifier 52R is also activated (turned on) when the operation signal Rs is input from the detection control unit 42, and amplifies the charging power of the sensor electrode 34R at a predetermined amplification factor and outputs it to the sensor electrode 34L. As a result, the sensor electrodes 34L and 34R are indirectly charged.

[0056] Here, the detection control unit 42 charges the sensor electrodes 34L and 34R individually (direct charging) by supplying charging power to the sensor electrodes 34L and 34R while the operation of amplifiers 52L and 52R is stopped. The detection units 50L and 50R individually detect the capacitance (voltage corresponding to capacitance, hereinafter referred to as capacitance L and R, respectively) at the charged sensor electrodes 34L and 34R. At this time, in the detection control unit 42, the detection unit 50R grounds the sensor electrode 34R during the direct charging of sensor electrode 34L, and the detection unit 50L grounds the sensor electrode 34L during the direct charging of sensor electrode 34R.

[0057] In the detection control unit 42, the amplifier 52L is activated (amplifier 52R is deactivated) to directly charge the sensor electrode 34L and indirectly charge the sensor electrode 34R, thereby detecting the capacitance Lb of the sensor electrode 34L. Also, in the detection control unit 42, the amplifier 52R is activated (amplifier 52L is deactivated) to directly charge the sensor electrode 34R and indirectly charge the sensor electrode 34L, thereby detecting the capacitance Rb of the sensor electrode 34R.

[0058] As a result, the detection control unit 42 detects the capacitances L and R, as well as the capacitances Lb and Rb, for each of the sensor electrodes 34L and 34R.

[0059] The calculation unit 44 includes an L / R calculation unit 60, a first difference value calculation unit 62, a second difference value calculation unit 64, and a reference calculation unit 66 as a setting unit. The L / R calculation unit 60 calculates the capacitances L and R of the sensor electrodes 34L and 34R, respectively. The first difference value calculation unit 62 calculates the difference value DLR between the capacitance L of sensor electrode 34L and the capacitance R of sensor electrode 34R as the first difference value. In this case, the difference value DLR uses the absolute value of the difference between capacitance L and capacitance R (DLR = |L - R| = |R - L|).

[0060] The second difference value calculation unit 64 calculates the difference between capacitance L and capacitance Lb as the second difference value DL (DL = L - Lb). The second difference value calculation unit 64 also calculates the difference between capacitance R and capacitance Rb as the second difference value DR (DR = R - Rb).

[0061] The reference calculation unit 66 calculates a reference value S for touch detection using the capacitances L and R detected by the sensor electrodes 34L and 34R when the touch detection device 10 is started. The reference calculation unit 66 also sets a threshold value Tha as a first threshold and a threshold value Thb as a second threshold based on the reference value S.

[0062] The determination unit 46 uses threshold values ​​Tha and Thb set based on the reference value S to determine whether an occupant is in contact with each of the sensor electrodes 34L and 34R (whether an occupant is steering the steering wheel 12) based on the difference values ​​DLR, DL, and DR. The output unit 48 outputs the determination result of the determination unit 46.

[0063] Next, the operation of the first embodiment will be described. In the touch detection device 10, the sensor electrodes 34 (34L, 34R) of the sensor unit 30 are arranged on the steering wheel 12 (rim portion 14). Therefore, when the occupant steers the steering wheel 12 (contacts, grips, or holds it in a steerable position), the capacitance of the sensor electrodes 34L and 34R increases.

[0064] The steering ECU 32 of the touch detection device 10 detects the capacitances L, R, Lb, and Rb of the sensor electrodes 34L and 34R, and uses the detected capacitances L, R, Lb, and Rb to determine the steering state of the steering wheel 12 by the occupant.

[0065] As shown in Figure 2, the touch detection device 10 has a structure in which the shield electrode on the rim core metal portion 20 side of the sensor electrode 34 is removed. As a result, the number of parts in the sensor portion 30 arranged on the steering wheel 12 is reduced in the touch detection device 10, and assembly is simplified, thereby reducing costs.

[0066] However, in the case of the sensor electrode 34, the shield electrode on the side opposite to the side where the occupant is in close proximity (the side with the rim core metal portion 20) is removed, resulting in a capacitance C_GND between the sensor electrode and the rim core metal portion 20. Also, if a steering heater 26 is located on the rim portion 14 of the steering wheel 12, a capacitance C_HEATER is generated between the sensor electrode 34 and the heater wiring 28.

[0067] The capacitances C_GND and C_HEATER become parasitic capacitances Cs at the sensor electrode 34. These parasitic capacitances Cs change according to the temperature of the steering wheel 12 (ambient temperature), and increase as the temperature rises. Therefore, in touch detection, if the ambient temperature rises and the capacitance generated at the sensor electrodes 34L and 34R increases (changes) significantly, false detection may occur. The touch detection device 10 suppresses false detection when performing touch detection (steering detection) of the steering wheel 12 using the sensor electrodes 34L and 34R.

[0068] Here, the touch detection process in the touch detection device 10 will be explained. Figure 5A shows a flowchart of the capacitance detection process performed in the steering ECU 32, and Figure 5B shows a flowchart of the touch detection process performed in the steering ECU 32.

[0069] The touch detection device 10 is activated when, for example, the ignition switch (not shown) of the vehicle is turned on, which activates the steering ECU 32. When the device is activated, the steering ECU 32 performs capacitance detection processing and touch determination processing at predetermined time intervals, detecting the capacitance detected in the capacitance detection processing and using the detected capacitance to determine whether or not the occupant is steering the steering wheel 12.

[0070] In the steering ECU 32, when the device is started, the capacitance detection process is initiated and repeated at predetermined time intervals. In the first step 100 of the flowchart in Figure 5A, the steering ECU 32 detects the capacitance L of the sensor electrode 34L, and in step 102, it detects the capacitance R of the sensor electrode 34R.

[0071] In the steering ECU 32, when detecting capacitances L and R, the operation of amplifiers 52L and 52R is stopped. The steering ECU 32 also grounds sensor electrode 34R and supplies charging power to sensor electrode 34L (direct charging) to detect capacitance L at sensor electrode 34L. The steering ECU 32 also grounds sensor electrode 34L and supplies charging power to sensor electrode 34R (direct charging) to detect capacitance R at sensor electrode 34R.

[0072] Next, in step 104, the steering ECU 32 detects the capacitance Lb at the sensor electrode 34L, and in step 106, it detects the capacitance Rb at the sensor electrode 34R.

[0073] When detecting capacitance Lb, the steering ECU 32 activates amplifier 52L with amplifier 52R deactivated. In this state, the steering ECU 32 charges sensor electrode 34R (indirectly) via amplifier 52L by charging sensor electrode 34L (directly), and detects the capacitance of sensor electrode 34L as capacitance Lb.

[0074] Furthermore, when detecting capacitance Rb, the steering ECU 32 activates amplifier 52R with amplifier 52L stopped. In this state, the steering ECU 32 charges the sensor electrode 34R (directly) and then charges the sensor electrode 34R (indirectly) via amplifier 52R, detecting the capacitance of the sensor electrode 34R as capacitance Rb.

[0075] In Figure 5A, capacitance L, capacitance R, capacitance Lb, and capacitance Rb were detected in this order, but the detection order is not limited to this. Various configurations can be applied, for example, in the order of capacitance L, capacitance Lb, capacitance R, and capacitance Rb.

[0076] The steering ECU 32 uses the capacitance L, capacitance R, capacitance Lb, and capacitance Rb detected in the capacitance detection process to perform a touch detection process.

[0077] The touch detection device 10 assumes that the occupant is not holding the steering wheel 12 immediately after the vehicle's ignition switch is turned on.

[0078] From here, the steering ECU 32 sets a reference value in the first step 120 of the flowchart in Figure 5B. In setting the reference value S, the steering ECU 32 uses the capacitance L and capacitance R of parasitic capacitance Cs only, when the occupant is not touching the sensor electrodes 34L and 34R, and sets the reference value S to, for example, the average value of capacitance L and capacitance R. The steering ECU 32 updates the reference value S using the capacitance L and R when the state in which the occupant is not in contact with the sensor electrodes 34L and 34R continues for a predetermined period of time.

[0079] In step 122, the steering ECU 32 sets threshold values. In setting the threshold values, the steering ECU 32 sets a threshold value Tha for the difference value DLR, and threshold values ​​Thb for the difference values ​​DL and DR. After this, the steering ECU 32 performs touch detection processing. The threshold values ​​Tha and Thb are set to be a predetermined difference (capacitance difference) with respect to the reference value S.

[0080] In the steering ECU 32, in the next step 124, the difference value DLR (DLR = |L - R|) is calculated using capacitance L and capacitance R. Also, in step 126, the steering ECU 32 calculates the difference value DL (DL = L - Lb) using capacitance L and capacitance Lb, and accumulates the results of N calculations (the DL from the previous N calculations). Furthermore, in step 128, the steering ECU 32 calculates the difference value DR (DR = R - Rb) using capacitance R and capacitance Rb, and accumulates the results of N calculations (the DR from the previous N calculations).

[0081] Subsequently, in step 130, the steering ECU 32 uses threshold values ​​Tha and Thb to perform a touch determination (steering determination) from the difference values ​​DLR and DL, DR. In step 132, the steering ECU 32 outputs the determination result to an external module (not shown) that is configured to use the determination result.

[0082] Here, we will explain the detection of capacitances L, R, Lb, and Rb, and the touch detection using the detection results. Note that the basic configuration for detecting capacitances L and Lb is the same as for detecting capacitances R and Rb. Therefore, in the following, we will mainly explain the detection of capacitances L and Lb on the sensor electrode 34L side, and omit the explanation of the detection of capacitances R and Rb on the sensor electrode 34R side.

[0083] Figure 6 shows a schematic diagram illustrating the changes in capacitance L and R, with the vertical axis representing capacitance (capacitance value). Furthermore, each of the threshold values ​​Tha and Thb, which are set based on the reference value S, is provided with hysteresis, so that the threshold for ON determination (above the threshold) is set higher than the threshold for OFF determination (below the threshold).

[0084] As shown in Figure 6, the reference value S is set based on the capacitances L and R detected when the occupant is not touching the sensor electrode 34 (hands off). The reference value S is also set using the capacitances L and R when the ambient temperature is relatively low and the parasitic capacitance Cs is small. Based on this reference value S, the threshold Tha for the differential value DLR and the threshold Thb for the differential values ​​DL and DR are set.

[0085] When the parasitic capacitance Cs is small, the capacitances L and R when the sensor electrodes 34L and 34R are in contact (both hands holding the steering wheel) exceed the threshold Tha. Conversely, when the sensor electrodes 34L and 34R are not in contact (both hands released), the capacitances L and R are below the threshold Tha. This enables accurate touch detection.

[0086] However, if the parasitic capacitance Cs increases due to rising temperature or other factors, the capacitances L and R may exceed the threshold Tha even when the occupant is not touching the sensor electrodes 34L and 34R (both hands off). As a result, a situation may arise where proper touch detection cannot be performed based on the capacitances L and R.

[0087] Furthermore, as shown in Figure 4, the sensor electrode 34L has parasitic capacitances Cs, namely capacitances C_GND and C_HEATER, and when an occupant touches the sensor electrode 34L, capacitance Cf(CfL) is added. Similarly, the sensor electrode 34R has parasitic capacitances Cs, namely capacitances C_GND and C_HEATER, and when an occupant touches the sensor electrode 34R, capacitance Cf(CfR) is added. Note that in Figure 4, capacitance Chb represents the capacitance of the human body.

[0088] In the touch detection device 10, when detecting the capacitance L of the sensor electrode 34L, the amplifier 52L is stopped, the sensor electrode 34R is grounded, and the sensor electrode 34L is directly charged to detect the capacitance L. Therefore, if the occupant is not touching the sensor electrode 34L, parasitic capacitance Cs is detected as the capacitance L.

[0089] Figures 7A and 7B show schematic diagrams illustrating the charging (power supply) process in the detection of capacitance L. Figure 7A shows the condition with both hands steering, and Figure 7B shows the condition with one hand steering.

[0090] As shown in Figure 7A, in the touch detection device 10, when an occupant touches the sensor electrodes 34L and 34R, charging power flows from the sensor electrode 34L through the human body (occupant's body) to the sensor electrode 34R.

[0091] Furthermore, as shown in Figure 7B, in the touch detection device 10, if the occupant is touching only the sensor electrode 34L, the charging power is grounded (GND) through the human body (occupant's body) from the sensor electrode 34L and does not flow to the sensor electrode 34R.

[0092] Furthermore, when the touch detection device 10 detects the capacitance Lb of the sensor electrode 34L, it directly charges the sensor electrode 34L and also operates the amplifier 52L to indirectly charge the sensor electrode 34R, thereby detecting the capacitance of the sensor electrode 34L as capacitance Lb. Therefore, if the occupant does not touch the sensor electrode 34L, parasitic capacitance Cs is detected as capacitance Lb.

[0093] Figures 8A and 8B show schematic diagrams illustrating the charging process in the detection of capacitance Lb. Figure 8A shows the condition where both hands are steering, and Figure 8B shows the condition where one hand is steering.

[0094] As shown in Figure 8A, in the touch detection device 10, when an occupant touches the sensor electrodes 34L and 34R, the charging power for direct charging is grounded from the sensor electrode 34L through the human body (occupant's body), and the charging power for indirect charging is grounded from the sensor electrode 34R through the human body (occupant's body).

[0095] Furthermore, as shown in Figure 8B, in the touch detection device 10, if the occupant is touching only the sensor electrode 34L, the charging power is transmitted from the sensor electrode 34L through the human body (occupant's body) to ground (GND) and does not flow to the sensor electrode 34R.

[0096] Figure 9 shows a schematic diagram illustrating the capacitance L, R, and differential values ​​DLR and DL according to the crew's steering state.

[0097] Capacitances L and R each contain a certain amount of parasitic capacitance Cs. The difference value DLR is the difference between capacitance L and capacitance R. Therefore, the parasitic capacitance Cs cancels out in the difference value DLR. As a result, as shown in Figure 9, when both sensor electrodes 34L and 34R are touching (hands-on steering) or when neither is touching (hands-off), the difference value DLR becomes small, and the difference value DLR does not exceed the threshold value Tha.

[0098] In contrast, when only one of the sensor electrodes 34L or 34R is in contact (one-handed steering), the difference value DLR will include the capacitance L or R of the sensor electrode 34 that is in contact. Therefore, the difference value DLR exceeds the threshold value Tha.

[0099] This allows for accurate determination of whether the occupant is steering the steering wheel 12 using either their right or left hand by using the difference value DLR (= |L - R|). Furthermore, while the difference value DLR (= |L - R|) alone does not clearly indicate whether the occupant is steering with their right or left hand, comparing the capacitance L, including the parasitic capacitance Cs, with the capacitance R can complement the determination of which hand is steering the steering wheel 12.

[0100] On the other hand, the capacitance L detected in Figure 7B and the capacitance Lb detected in Figure 8B have only a slight difference and can be considered almost the same (L ≈ Lb). That is, when the occupant is touching only one of the sensor electrodes 34L and 34R, the difference value DL (and the difference value DR) can be considered zero (DL ≈ 0, DR ≈ 0). Furthermore, capacitance L and capacitance Lb can be considered almost the same even when the occupant is not touching either of the sensor electrodes 34L or 34R (L ≈ Lb).

[0101] In contrast, a difference arises between the capacitance L detected in Figure 7A and the capacitance Lb detected in Figure 8A. For example, as shown in Figure 9, when an occupant touches the sensor electrodes 34L and 34R respectively, the capacitance Lb becomes smaller than the capacitance L (L > Lb).

[0102] From here, by setting a threshold value Thb relative to the reference value S according to the amplification factor in amplifiers 52L and 52R, it is possible to determine from the difference value DL (or difference value DR) whether or not the occupant is steering the steering wheel 12 with both hands.

[0103] The difference between capacitance L and capacitance Lb increases by setting a high amplification factor when amplifying with amplifier 52L. Figure 10 shows a schematic diagram of capacitances L, R, Lb, and the difference value DL.

[0104] As shown in Figure 10, when the crew member is using one-handed steering or both hands off the steering wheel (not shown), the capacitance Lb is approximately the same as the capacitance L (L ≈ Lb). Therefore, the difference value DL is also relatively small. However, even when using both hands to steer, the difference value DL is not particularly large. From this, it can be shown that by providing the amplifier 52L, the difference value DL can be increased.

[0105] However, if the amplification factor of amplifier 52L is increased, the noise component is also amplified, increasing the likelihood of misjudgment. Therefore, the touch detection device 10 uses the cumulative value of multiple (N) steps for the difference value DL, thereby preventing misjudgment caused by noise components while allowing the threshold Thb to be set higher. As a result, the touch detection device 10 can accurately determine whether the steering is being done with both hands when the difference value DL is equal to or greater than the threshold Thb.

[0106] Figure 11 shows the results of touch detection using the difference values ​​DLR (= |L - R|) and DL (= L - Lb) in the determination unit 46 of the steering ECU 32.

[0107] As shown in Figure 11, the determination unit 46 determines that the occupant is not steering the steering wheel 12 (hands off) if the difference value DLR is smaller than the threshold value Tha (OFF) and the difference value DL is smaller than the threshold value Thb (OFF).

[0108] In response to this, the determination unit 46 determines that if the difference value DL is less than the threshold Thb (OFF), but the difference value DLR is greater than or equal to the threshold Tha (ON), the occupant is steering the steering wheel 12 with one hand (one-handed steering).

[0109] Furthermore, the determination unit 46 determines that the occupant is steering the steering wheel 12 with both hands (two-handed steering) if the difference value DL is greater than or equal to the threshold Thb (ON) and the difference value DLR is greater than or equal to the threshold Tha (ON).

[0110] Thus, the touch detection device 10 can accurately determine whether the steering is being done with one hand or not by using DLR, which is the difference between the capacitance L of sensor electrode 34L and the capacitance R of sensor electrode 34R. Furthermore, the touch detection device 10 can accurately determine whether the steering is being done with both hands or not by using DL, which is the difference between the capacitance L and the capacitance Lb. As a result, even when using sensor electrodes 34L and 34R, which reduce costs by omitting shield electrodes, the touch detection device 10 can accurately determine touches without being affected by parasitic capacitance Cs.

[0111] Furthermore, the touch detection device 10 has a sensor electrode 34L positioned on the left side of the steering wheel 12 and a sensor electrode 34R positioned on the right side, so it can accurately determine the steering state of the steering wheel 12 held by the occupant.

[0112] Furthermore, in the touch detection device 10, amplifiers 52L and 52R are provided in the switching unit 40, and the operation / stopping of amplifiers 52L and 52R is controlled to switch between direct charging and indirect charging, thus simplifying the configuration for capacitance detection processing.

[0113] Furthermore, the touch detection device 10 is equipped with amplifiers 52L and 52R to perform power amplification for indirect charging. In addition, the touch detection device 10 uses the cumulative value of N steps for the differential values ​​DL and DR applied to the judgment. Therefore, the touch detection device 10 can suppress a decrease in the accuracy of touch judgment even if the differential values ​​DL and DR are small.

[0114] Furthermore, the touch detection device 10 sets a reference value S using capacitances L and R detected when it is determined that the occupant is not touching the surface. As a result, the touch detection device 10 can appropriately set the threshold values ​​Tha and Thb even if the parasitic capacitance changes, thereby suppressing a decrease in judgment accuracy caused by parasitic capacitance.

[0115] In the first embodiment described above, the difference value DL on the sensor electrode 34L side and the difference value DR on the sensor electrode 34R side are used. However, since the difference value DL and the difference value DR are approximate values, either DL or DR may be used. This eliminates the need for detection processing of one of the capacitances Lb or Rb, thus simplifying the capacitance detection process.

[0116] Furthermore, in the first embodiment, amplifiers 52L and 52R are provided in the switching unit 40 to amplify the charging power of indirect charging, thereby increasing the changes in the detected capacitances Lb and Rb. However, the amplifiers may be omitted. In this case, the capacitances Lb and Rb for multiple cycles may be integrated, and the integrated value may be used.

[0117] [Second Embodiment] Next, a second embodiment will be described. In the second embodiment, the basic configuration is the same as in the first embodiment, and functional components that are the same as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and their descriptions are omitted.

[0118] In the touch detection device 10 according to the first embodiment, the cumulative values ​​of N trials are used as the difference values ​​DL (= L - Lb) and DR (= R - Rb) used for touch determination. This suppresses the occurrence of determination errors caused by the small size of each of the difference values ​​DL and DR (calculated from the result of one detection) for a single trial.

[0119] However, when the driver holds the steering wheel 12 with both hands, there may be a delay before it is determined that the steering is being held with both hands, and when at least one hand is released from the steering wheel 12 that was being held with both hands, there may be a delay before it is determined that the steering is being held with one hand or the hands are released (determination delay). In the second embodiment, such determination delays are suppressed.

[0120] The touch detection device 70 according to the second embodiment includes a steering ECU 72 as a control unit. The steering ECU 72 is applied in the second embodiment in place of the steering ECU 32 of the first embodiment. Figure 12 shows a schematic block diagram of the control unit formed by the steering ECU 72 in the touch detection device 70. The hardware configuration of the steering ECU 72 is the same as that of the steering ECU 32 of the first embodiment shown in Figure 19.

[0121] As shown in Figure 12, the steering ECU 72 has a determination unit 74, which is formed in the steering ECU 72 in place of the determination unit 46 of the steering ECU 32 according to the first embodiment. The determination unit 74 has a determination complementation unit 76 formed as a complementary unit.

[0122] The functions of the determination unit 74 in the steering ECU 72 include the same functions as the determination unit 46 in the steering ECU 32. Furthermore, the determination complementation unit 76 uses the capacitance L detected at the sensor electrode 34L and the capacitance R detected at the sensor electrode 34R to complement the determination result of the determination unit 74 (determination unit 46), thereby suppressing the occurrence of determination delay. In other words, the steering ECU 72 suppresses the occurrence of determination delay by performing touch detection using capacitances L and R in addition to the difference values ​​DLR, DL, and DR.

[0123] Next, the operation of the second embodiment will be described, specifically the touch detection process in the touch detection device 70. Figure 13A shows a flowchart of the touch detection process according to the second embodiment, and Figure 13B shows a flowchart of the judgment completion process. Figure 14 shows a schematic of the capacitance L, R, and difference values ​​DLR, DL according to the gripping (steering) state of the steering wheel 12, and Figure 15 shows a table of the touch detection results in the judgment unit 74 of the steering ECU 72, using the difference value DLR (= |L - R|) and difference value DL (= L - Lb) in addition to capacitance L and R.

[0124] The touch detection device 70, similar to the touch detection device 10, detects capacitances L, Lb, R, and Rb (or capacitances L, Lb, and R), and sets a reference value S from capacitances L and R when the occupant is not gripping the steering wheel 12. In this case, the touch detection device 70 mainly uses capacitances L and R due to parasitic capacitance Cs to set the reference value S, and threshold values ​​Tha and Thb are set according to the set reference value S, and the reference value S and threshold values ​​Tha and Thb are updated as appropriate.

[0125] Furthermore, when the touch detection device 70 detects capacitances L, Lb, R, and Rb, it calculates the difference values ​​DLR (= |L - R|), DL (= L - Lb), and DR (= R - Rb) (the difference values ​​DLR and DL may also be used), and performs a touch determination based on the calculation results. As a result, the touch detection device 70 can achieve the same effect as the touch detection device 10. Note that in the touch determination process shown in Figure 13A, the setting process of the reference value S and threshold values ​​Tha and Thb (steps 120, 124) is omitted.

[0126] As shown in Figure 13A, in step 124, the steering ECU 72 calculates the difference value DLR (DLR = |L - R|) using capacitance L and capacitance R. In step 126, the steering ECU 72 calculates the difference value DL (DL = L - Lb) using capacitance L and capacitance Lb, and accumulates the results of N calculations (N DLs). Furthermore, in step 128, the steering ECU 32 calculates the difference value DR (DR = R - Rb) using capacitance R and capacitance Rb, and accumulates the results of N calculations (N DRs).

[0127] Subsequently, in step 130, the steering ECU 72 uses threshold values ​​Tha and Thb to perform a touch determination (steering determination) from the difference values ​​DLR and DL, DR. As a result, the touch detection device 70, similar to the touch detection device 10, determines from the difference values ​​DLR, DL, DR whether the steering wheel 12 is being held with both hands off, with one hand on either the left or right, or with both hands on. Once the steering ECU 72 determines the gripping state of the steering wheel 12, it performs the determination completion process shown in Figure 13B.

[0128] In the first step 140 of the flowchart in Figure 13B, the steering ECU 72 checks whether the determination result is anything other than one-handed steering. If the determination result is one-handed steering (steering with the right or left hand) as determined by the difference value DLR, the steering ECU 72 makes a negative determination in step 140 and proceeds to step 132, outputting the determination result (determination result in Figure 13A) to an external module (not shown).

[0129] On the other hand, if the judgment result is anything other than one-handed steering, i.e., both hands off the steering wheel or both hands on the steering wheel, the steering ECU 72 makes an affirmative judgment in step 140. When the steering ECU 72 makes an affirmative judgment in step 140, it checks whether the capacitance L is greater than or equal to the threshold Tha (step 142), and whether the capacitance R is greater than or equal to the threshold Tha (steps 144, 146).

[0130] In the steering ECU 72, if the capacitance L is greater than or equal to the threshold Tha (L ≥ Tha), it makes a positive determination in step 140, and in the next step 144, it checks whether the capacitance R is greater than or equal to the threshold Tha (R ≥ Tha). If the capacitance R is less than the threshold Tha (R < Tha), the steering ECU 72 makes a negative determination in step 144 and proceeds to step 148, where it determines that steering is being performed with one hand using the left hand, and in step 132, it outputs the determination result to the external module.

[0131] Furthermore, in the steering ECU 72, if the capacitance L is less than the threshold Tha (L < Tha), a negative determination is made in step 140, and in the next step 146, it is checked whether the capacitance R is greater than or equal to the threshold Tha (R ≥ Tha). If the capacitance R is greater than or equal to the threshold Tha (R ≥ Tha), the steering ECU 72 makes a positive determination in step 146 and proceeds to step 150, where it determines that steering is being performed with one hand using the right hand, and in step 132, the determination result is output to the external module.

[0132] In response to this, the steering ECU 72 makes a positive determination in step 144 if the capacitance L is greater than or equal to the threshold Tha (L ≥ Tha) and the capacitance R is greater than or equal to the threshold Tha (R ≥ Tha), and proceeds to step 152. In step 152, the steering ECU 72 determines that the steering wheel 12 is being steered with both hands, and proceeds to step 132, outputting the determination result to an external module.

[0133] Furthermore, in the steering ECU 72, if the capacitance L is less than the threshold Tha (L < Tha) and the capacitance R is also less than the threshold Tha (R < Tha), the ECU 72 makes a negative determination in step 146 and proceeds to step 154. In step 154, the steering ECU 72 determines that both hands are off the steering wheel 12 and proceeds to step 132, outputting the determination result to an external module.

[0134] In other words, the steering ECU 72 determines that the steering wheel 12 is being steered with both hands by making a positive judgment in each of steps 142 and 144 if both capacitances L and R are greater than or equal to the threshold Tha (L ≥ Tha, R ≥ Tha). Also, the steering ECU 72 determines that the steering wheel 12 is being released with both hands by making a negative judgment in each of steps 142 and 144 if both capacitances L and R are less than the threshold Tha (L < Tha, R < Tha).

[0135] As shown in Figure 14, the difference values ​​DL (DL = L - Lb) and DR (DR = R - Rb) gradually increase when transitioning from a hands-free state to hands-on steering. Note that the difference value DR is not shown in Figure 14.

[0136] Therefore, when transitioning from a hands-free state (or a one-handed steering state not shown) to hands-on steering, even though both capacitances L and R exceed the threshold Tha, there is a period during which hands-on steering is not detected because the difference value DL does not reach the threshold Thb. In this case, as shown in Figure 15, the steering ECU 72 determines that hands-on steering is detected if each of the capacitances L and R is equal to or greater than the threshold Tha.

[0137] Furthermore, as shown in Figure 14, when transitioning from a two-handed steering state to a two-handed release state (or a one-handed steering state not shown), the difference values ​​DL (DL = L - Lb) and DR (DR = R - Rb) gradually decrease. Therefore, when transitioning from a two-handed steering state to a two-handed release state (or a one-handed steering state not shown), even though both capacitances L and R are below the threshold Tha, the difference value DL is greater than or equal to the threshold Thb, resulting in a period during which the system is not judged as two-handed release.

[0138] In this case, as shown in Figure 15, the steering ECU 72 can determine that the steering wheel is released both hands if the capacitances L and R each fall below the threshold value Tha.

[0139] Furthermore, when transitioning from two-handed steering to one-handed steering, the difference values ​​DL (DL = L - Lb) and DR (DR = R - Rb) gradually decrease. As a result, when transitioning from two-handed to one-handed steering, there is a period during which the system is judged as two-handed steering because the difference value DLR is greater than or equal to the threshold Tha (one-handed steering judgment) and the difference value DL is greater than or equal to the threshold Thb. In this case, as shown in Figure 15, the steering ECU 72 can determine that it is one-handed steering because one of the capacitances L and R exceeds the threshold Tha.

[0140] [Third Embodiment] Next, a third embodiment will be described. In the third embodiment, the basic configuration is the same as in the second embodiment. Also, in the third embodiment, functional components similar to those in the first and second embodiments are denoted by the same reference numerals as in the first and second embodiments, and their descriptions are omitted.

[0141] In the first and second embodiments, a reference value S was set using capacitances L and R detected when both hands were released from the steering wheel 12, and threshold values ​​Tha and Thb were set based on the reference value S. However, because the parasitic capacitance Cs changes according to the ambient temperature, the updating of the reference value S and threshold values ​​Tha and Thb is delayed, increasing the likelihood of misjudgment. In the third embodiment, a touch detection device in which misjudgment is suppressed is described.

[0142] The touch detection device 80 according to the third embodiment includes a steering ECU 82 as a control unit. The steering ECU 82 is applied to the third embodiment in place of the steering ECU 32 of the first embodiment or the steering ECU 72 of the second embodiment. Figure 16 shows a schematic block diagram of the control unit formed by the steering ECU 82. The hardware configuration of the steering ECU 82 is the same as that of the steering ECU 32 of the first embodiment shown in Figure 19.

[0143] As shown in Figure 16, the steering ECU 82 has a reference calculation unit 84 as a setting unit. The reference calculation unit 84 is formed in the steering ECU 82 in place of the reference calculation unit 66 in the first and second embodiments.

[0144] The reference calculation unit 84 sets the reference value S and threshold values ​​Tha and Thb when the device is started, similar to the reference calculation unit 66. Also, similar to the reference calculation unit 66, the reference calculation unit 84 updates the reference value S and threshold values ​​Tha and Thb when the steering wheel 12 has been left with both hands off the wheel for a predetermined period of time or longer.

[0145] Furthermore, the reference calculation unit 84 updates the reference value S based on the capacitances L and R when the steering wheel 12 is being steered with one hand, and updates the threshold values ​​Tha and Thb according to the updated reference value S.

[0146] Next, the reference value update process in the touch detection device 80 will be described as the operation of the third embodiment. Figure 17 shows a schematic of the reference value update process according to the third embodiment in flowchart form, and Figure 18 shows a schematic of the capacitance L, R and difference values ​​DLR, DL according to the gripping (steering) state of the steering wheel 12 in line diagram form.

[0147] The touch detection device 80, like the touch detection devices 10 and 70, detects capacitances L, Lb, R, and Rb (or capacitances L, Lb, and R), and sets a reference value S from capacitances L and R when the occupant is not gripping the steering wheel 12. Furthermore, the touch detection device 80 performs touch detection while detecting capacitances L, Lb, R, and Rb. As a result, the touch detection device 80 can achieve the same effect as the touch detection devices 10 and 80.

[0148] Here, the touch detection device 80 performs a reference value update process not only when both hands are released, but also by executing the flowchart shown in Figure 17 at a preset timing. The reference value update process is performed by the steering ECU 82, for example, after a preset time has elapsed, when the change in ambient temperature detected by the temperature sensor as a temperature detection means exceeds a predetermined value, or when it is determined that the parasitic capacitance Cs has exceeded the threshold Tha.

[0149] As shown in Figure 17, in the first step 160, the steering ECU 82 checks whether the difference value DLR is greater than or equal to the threshold Tha. If the difference value DLR is less than the threshold Tha, the steering ECU 82 makes a negative determination in step 160 and terminates the process. However, if a negative determination is made in step 160, and it is the timing for updating the reference value S using only the parasitic capacitances Cs and L and R, the process of updating the reference value S and the thresholds Tha and Thb may be executed.

[0150] In the steering ECU 82, if the difference value DLR is greater than or equal to the threshold Tha, it makes a positive determination in step 160 and proceeds to step 162. In step 162, the steering ECU 62 compares capacitance L and capacitance R.

[0151] When the difference value DLR is greater than or equal to the threshold value Tha, one of the sensor electrodes 34L and 34R is in a non-contact state, while the occupant's hand is in contact with the other. Therefore, when the occupant is in contact with sensor electrode 34L, capacitance L is L = Cf + Cs, while capacitance R is R = Cs. Also, when the occupant is in contact with sensor electrode 34R, capacitance L is L = Cs, while capacitance R is R = Cf + Cs.

[0152] From here, in step 162, the steering ECU 82 checks whether capacitance L is greater than capacitance R (L > R?) (R > L? is also acceptable). If capacitance R is less than capacitance L (L > R), the steering ECU 82 makes a positive determination in step 162 and proceeds to step 164, updating the reference value S by setting capacitance R to the reference value S. If capacitance L is less than capacitance R (L < R), the steering ECU 82 makes a negative determination in step 162 and proceeds to step 166, updating the reference value S by setting capacitance L to the reference value S.

[0153] When the steering ECU 82 updates the reference value S, in step 168 it updates the threshold values ​​Tha and Thb respectively by setting them based on the updated reference value S. As a result, the threshold values ​​Tha and Thb are shifted along with the reference value S according to the parasitic capacitance Cs (see Figure 18). After this, the steering ECU 82 performs touch detection processing using the updated threshold values ​​Tha and Thb (threshold values ​​Tha and Thb shifted according to the parasitic capacitance Cs).

[0154] As shown in Figure 18, when the temperature rises while both hands are rudder-controlled, the parasitic capacitances Cs contained in capacitances L and R increase. At this time, parasitic capacitances Cs are generated in capacitance L and capacitance R, increasing the difference value DLR. As a result, the difference between the parasitic capacitances Cs in capacitance L and capacitance R exceeds the threshold value Tha, causing the difference value DLR to exceed the threshold value Tha even when both hands are rudder-controlled, leading to a misjudgment.

[0155] Furthermore, if the difference between the parasitic capacitance Cs contained in capacitance L and the parasitic capacitance Cs contained in capacitance R exceeds the threshold Tha, even with one-handed steering, the difference value DLR will fall below the threshold tha, and the system will no longer be recognized as having one-handed steering.

[0156] In contrast, when the reference value S is updated and the threshold values ​​Tha and Thb are updated, even if the difference between the parasitic capacitance Cs included in capacitance L and the parasitic capacitance Cs included in capacitance R becomes large, the difference value DLR will not exceed the threshold value Tha without any adjustments.

[0157] Therefore, in the touch detection device 80, even if the difference in parasitic capacitance Cs between sensor electrodes 34L and 34R becomes large due to continuous one-handed steering, misjudgment in the touch judgment process is suppressed.

[0158] In the first, second, and third embodiments described above, touch detection was performed using the sensor electrode 34L on the left side and the sensor electrode 34R on the right side of the steering wheel 12. However, sensor electrodes may also be placed on the occupant side (front side) and the opposite side (back side) of the steering body on both the left and right sides. This makes it possible to determine whether the occupant is touching the steering body on both the left and right sides, and whether they are gripping each side.

[0159] Furthermore, in the above embodiment, each process executed by the CPU 90 shown in Figure 19 after reading the software (program) may be executed by various processors other than the CPU. Examples of such processors include dedicated electrical circuits, which are processors with circuit configurations specifically designed to execute particular processes, such as FPGAs (Field-Programmable Gate Arrays), PLDs (Programmable Logic Devices) whose circuit configuration can be changed after manufacturing, and ASICs (Application Specific Integrated Circuits). Each process may be executed by one of these various processors, or by a combination of two or more processors of the same or different types (for example, multiple FPGAs, and a combination of a CPU and an FPGA). More specifically, the hardware structure of these various processors is an electrical circuit that combines circuit elements such as semiconductor elements.

[0160] Furthermore, the program described in the above embodiment may be provided in a form stored on a non-temporary storage medium such as a CD-ROM (Compact Disc Read Only Memory), DVD-ROM (Digital Versatile Disc Read Only Memory), or USB (Universal Serial Bus) memory. Alternatively, the program may be provided in a form downloaded from an external device via a network.

[0161] The disclosure of Japanese Patent Application No. 2024-196971, filed on November 11, 2024, is incorporated herein by reference in its entirety.

[0162] All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A touch detection device comprising: a first sensor electrode and a second sensor electrode, each positioned on the steering body and accessible to an occupant, and for which capacitance is detected; a detection unit that, when detecting a first capacitance for each of the first and second sensor electrodes, directly charges each of the first and second sensor electrodes for detection, and when detecting a second capacitance for each of the first and second sensor electrodes, directly charges one of the first and second sensor electrodes and indirectly charges the other using the power from the direct charge; a calculation unit that calculates a first difference value which is the difference between the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode, and calculates a second difference value which is the difference between the first capacitance and the second capacitance for each of the first and second sensor electrodes; and a determination unit that determines occupant contact with the first and second sensor electrodes using the first difference value and the second difference value for each of the first and second sensor electrodes.

2. The touch detection device according to claim 1, wherein the first sensor electrode and the second sensor electrode are two sensor electrodes among a plurality of sensor electrodes arranged on the steering body.

3. The touch detection device according to claim 1, wherein the detection unit comprises: a first detection unit that supplies power to the first sensor electrode to detect the first capacitance and supplies power to the first sensor electrode and the second sensor electrode to detect the second capacitance; and a second detection unit that supplies power to the second sensor electrode to detect the second capacitance and supplies power to the second sensor electrode and the first sensor electrode to detect the second capacitance.

4. The touch detection device according to claim 3, wherein the detection unit includes a switching unit that switches between supplying power to the first sensor electrode and supplying power to the second sensor electrode together with the first sensor electrode, and switches between supplying power to the second sensor electrode and supplying power to the first sensor electrode together with the second sensor electrode.

5. The touch detection device according to claim 3, comprising a first amplification unit that amplifies the charging power supplied to the second sensor electrode when charging the first sensor electrode, and a second amplification unit that amplifies the charging power supplied to the first sensor electrode when charging the second sensor electrode.

6. The touch detection device according to claim 1, further comprising a setting unit that sets a reference value to be used as a basis for a first threshold value for the first difference value and a second threshold value for each of the second difference values, and sets the first threshold value and the second threshold value based on the set reference value.

7. The touch detection device according to claim 6, wherein the setting unit sets the reference value from the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode when the occupant is not in contact with the first sensor electrode and the second sensor electrode.

8. The touch detection device according to claim 6, wherein the setting unit sets the smaller of the first capacitance of the first sensor electrode and the first capacitance of the second sensor electrode as the reference value when the occupant is not in contact with either the first sensor electrode or the second sensor electrode.

9. The touch detection device according to claim 1, wherein the determination unit determines contact of an occupant with the first sensor electrode and the second sensor electrode using the first difference value and one of the second difference values ​​of the first sensor electrode and the second sensor electrode.

10. The touch detection device according to claim 1, wherein each of the second difference values ​​is applied by accumulating a predetermined number of the second difference values.

11. The touch detection device according to claim 1, wherein the determination unit includes a complementation unit that complements the determination result using the second difference value of the first sensor electrode or the second sensor electrode, and the first difference value, using the first capacitance of the first sensor electrode and the second sensor electrode, respectively.

12. The touch detection device according to claim 11, further comprising the complementation unit determining whether the occupant is in contact with both the first and second sensor electrodes based on the first capacitance of each of the first and second sensor electrodes when it is determined that the occupant is not in contact with at least one of the first and second sensor electrodes.

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