Detection device

Abstract

To suppress influence of presence / absence of steering wheel warming.SOLUTION: A detection device 1 has: a heater wire 2 provided on a steering wheel SW; a series circuit 10 for connecting the heater wire 2 to a DC power supply PS and a ground EG; switches 51 and 52 provided between the heater wire 2 and the DC power supply PS; switches 53 and 54 provided between the heater wire 2 and the ground EG; a capacitance sensor 30 for detecting a capacitance of the heater wire 2; a sensor circuit 3 for connecting the capacitance sensor 30 between the switch 52 and the switch 53 in the series circuit 10; and a control part 7 for controlling the switches 51, 52, 53 and 54. When detecting the capacitance of the heater wire 2 in a non-driving period different from a non-driving period of the heater when detecting the capacitance, the control part 7 connects the heater wire 2 and the DC power supply PS for a predetermined time in a state where connection of the heater wire 2 and the ground EG is blocked, prior to detection of the capacitance of the heater wire 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a detection device having a function of detecting a gripping state of a steering wheel. [Background technology]

[0002] Patent Document 1 discloses an occupant information detection device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6145569 Summary of the Invention [Problem to be solved by the invention]

[0004] The occupant information sensing device of Patent Document 1 detects the gripping state of the steering wheel by the occupant by utilizing a heater electrode provided on the steering wheel. The steering wheel is provided with multiple heater electrodes that generate heat when electricity is applied. When the steering wheel is heated, electricity is supplied to the multiple heater electrodes from a heater power source. When detecting the gripping state of the steering wheel by the occupant, after stopping the supply of electricity to the heater electrodes, a first signal is input to one of the two heater electrodes, and a control device (not shown) detects the gripping state of the steering wheel by the occupant based on a second signal output from the other heater electrode. [Means for solving the problem]

[0005] Here, the second signal output from the heater electrode reflects the capacitance of the steering wheel. The capacitance value when the steering wheel is gripped by the occupant is higher than the capacitance value when the steering wheel is not gripped by the occupant. The occupant information detection device of Patent Document 1 detects the gripping state of the steering wheel by comparing the capacitance value determined according to the second signal with a threshold value.

[0006] The capacitance value of the steering wheel differs when the steering wheel is in a heated state and when it is in an unheated state. When the steering wheel is in a heated state, power is supplied to the steering wheel from the power supply source, and the transfer of charge to the steering wheel accompanying the supply of power reduces the capacitance value of the steering wheel.

[0007] Therefore, when detecting the gripping state of the steering wheel while the steering wheel is being heated, it is necessary to suppress the effect of the electric charge caused by heating. Therefore, every time the gripping state is detected, heating of the steering wheel is stopped before the capacitance value is acquired so that the electric charge transferred to the steering wheel is discharged to the outside. However, even if the heating of the steering wheel is stopped, there are cases where the charge does not completely disappear from the steering wheel before the capacitance value is acquired (the gripping state is detected). In such a case, the acquired capacitance value may deviate from the value that should be obtained due to the influence of the charge remaining on the steering wheel. Therefore, whether or not the steering wheel is heated may affect the determination of the gripping state of the steering wheel.

[0008] Therefore, it is necessary to reduce the influence of whether or not the steering wheel is heated when determining the gripping state of the steering wheel.

[0009] The present invention relates to A heater provided in a steering wheel of a vehicle; a series circuit connecting the heater to a power source and ground; a power supply side switch provided between the heater and the power supply in the series circuit; a ground-side switch provided between the heater and the ground in the series circuit; a capacitance sensor for detecting a capacitance of the heater; a sensor circuit for connecting the capacitance sensor between the power supply side switch and the ground side switch in the series circuit; a control unit for controlling the power supply side switch and the ground side switch, The control unit is During a driving period of the heater in which the heater is connected to the power supply and the ground, When detecting the capacitance of the heater, detecting the capacitance during a stop period of the heater in which the connection between the heater and the power source and the ground is cut off; In the case where the electrostatic capacitance of the heater is detected during a non-driving period in which the heater is not connected to the power supply and the ground, The detection device connects the heater to the power source for a predetermined time in a state where the connection between the heater and the ground is interrupted, prior to detecting the electrostatic capacitance of the heater. Effect of the Invention

[0010] According to the present invention, the influence of whether or not the steering wheel is heated can be suppressed in determining the gripping state of the steering wheel. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram illustrating a schematic configuration of a detection device. [Diagram 2] 5A and 5B are diagrams illustrating the influence of whether or not a heater is operated on a capacitance value detected by a capacitance sensor. [Diagram 3] 4 is a flowchart of a process for determining a gripping state of a steering wheel. [Figure 4] 6 is a timing chart for carrying out a process for determining the gripping state of the steering wheel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a detection device according to the present invention will be described by taking as an example a case where it is applied to a detection device 1 having a steering wheel SW heating function and a determination function for determining the gripping state of the steering wheel SW. FIG. 1 is a diagram illustrating a schematic configuration of a detection device 1 according to an embodiment.

[0013] The detection device 1 has a first series circuit 11 connected to a DC power supply PS and a second series circuit 12 connected to a ground EG. The first series circuit 11 and the second series circuit 12 constitute a series circuit 10 of the detection device 1. The first series circuit 11 connects one end 21 of the heater wire 2 to a DC power source PS. The second series circuit 12 connects the other end 22 of the heater wire 2 to the ground EG. In the series circuit 10, the first series circuit 11 is located on the DC power source PS side when viewed from the heater wire 2. In the series circuit 10, the second series circuit 12 is located on the ground EG side when viewed from the heater wire 2. The heater wire 2 (heater) is connected to a DC power source PS and a ground EG via a series circuit 10 (a first series circuit 11 and a second series circuit 12).

[0014] The heater wire 2 is a strip-shaped member that generates heat when electricity is applied. The heater wire 2 is provided around the entire circumference of a steering wheel SW for steering mounted on a vehicle. As an example, the heater wire 2 is disposed inside a covering member that covers the surface of the steering wheel SW. The DC power source PS (power source) is, for example, a battery mounted on a vehicle. The DC power source PS is a power supply source for supplying power to the heater wire 2.

[0015] The first series circuit 11 is provided with switches 51 and 52 and a thermostat TS. In the first series circuit 11, the switch 51, the switch 52, and the thermostat TS are arranged in series in this order from the DC power supply PS side. The switches 51 and 52 are power supply side switches provided between the heater wire 2 and the DC power supply PS.

[0016] The second series circuit 12 is provided with switches 53 and 54. In the second series circuit 12, the switches 53 and 54 are arranged in series in this order from the heater wire 2 side. The switches 53 and 54 are ground-side switches provided between the heater wire 2 and ground EG.

[0017] The thermostat TS is located in the first series circuit 11 between the heater wire 2 and the switch 52. When a set temperature is reached, the thermostat TS cuts off the connection between the heater wire 2 and the switch 52 to cut off the power supply to the heater wire 2. The thermostat TS is provided to prevent the heater wire 2 from overheating.

[0018] The switches 51, 52, 53, and 54 are used to switch between supplying and not supplying power to the heater wire 2. The switches 51, 52, 53, and 54 are, for example, configured with FETs (Field effect transistors). As shown in FIG. 1, in this embodiment, an N-channel metal-oxide-semiconductor field-effect transistor (MOSFET) is used as the FET.

[0019] An N-channel MOSFET is a transistor that turns on when a voltage is applied to the gate electrode (G) and a current flows between the source electrode (S) and drain electrode (D). An N-channel MOSFET turns on when the voltage (gate voltage) applied to the gate electrode (G) is at a high level, and turns off when it is at a low level. When using an N-channel MOSFET, the drain electrode (D) is placed on the DC power supply PS side, and the source electrode (S) is placed on the ground EG side.

[0020] It should be noted that, instead of the N-channel MOSFET, a P-channel MOSFET may be adopted as the FET. A P-channel MOSFET is a transistor that turns on when the voltage (gate voltage) applied to the gate electrode (G) is at a low level and turns off when the voltage is at a high level. When a P-channel MOSFET is used, the source electrode (S) is arranged on the DC power supply PS side and the drain electrode (D) is arranged on the ground EG side, in contrast to an N-channel MOSFET.

[0021] The gate electrodes (G) of the switches 51, 52, 53, and 54 are connected to the control unit 7 via signal lines 91, 92, 93, and 94, respectively. The control unit 7 is configured, for example, from an integrated circuit equipped with a microprocessor, a memory, and the like, such as an MCU (Micro Control Unit). The control unit 7 has a switch control unit 71 that controls the on / off switching of the switches 51, 52, 53, and .

[0022] The switch control unit 71 outputs control signals (High signal, Low signal) whose voltage levels have been changed to the gate electrodes (G) of the switches 51, 52, 53, and 54 via signal lines 91, 92, 93, and 94.

[0023] The switches 51, 52, 53, and 54 are turned "on" when the control signal input to the gate electrode (G) is a High signal (High level), and are turned "off" when the control signal is a Low signal (Low level). In the detection device 1, the control unit 7 switches the power supply state from the DC power source PS to the heater wire 2 by switching the switches 51, 52, 53, and 54 on / off. For example, when all of the switches 51, 52, 53, and 54 are turned "on," the DC power supply PS is connected to the ground EG via the series circuit 10 and the heater wire 2. This causes power to be supplied from the DC power supply PS to the heater wire 2, causing the heater wire 2 to generate heat.

[0024] As described above, in the detection device 1, the switches 51 and 52, the thermostat TS, the heater wire 2, and the switches 53 and 54 are arranged in series on the series circuit 10. The switch control unit 71 outputs a control signal to switch the switches 51, 52, 53, and 54 on / off to control the state of power supply to the heater wire 2. When power is supplied to the heater wire 2, the heater wire 2 generates heat and the steering wheel SW is heated. When power supply to the heater wire 2 is stopped, the heater wire 2 stops generating heat and the heating of the steering wheel SW ends.

[0025] The detection device 1 further includes a sensor circuit 3 (3A, 3B). The sensor circuit 3 is provided to realize a determination function for determining the gripping state of the steering wheel SW. The sensor circuit 3 has a capacitance sensor 30. The capacitance sensor 30 has two paths: a path (sensor circuit 3A: first sensor circuit) connected to the first series circuit 11 via signal lines 311 and 312, and a path (sensor circuit 3B: second sensor circuit) connected to the second series circuit 12 via signal lines 321 and 322.

[0026] The signal line 311 connects the capacitance sensor 30 and the first series circuit 11. In the first series circuit 11, a connection point P11 between the signal line 311 and the first series circuit 11 is located between the thermostat TS and the source electrode (S) of the switch 52. It can also be said that the connection point P11 is located between the heater wire 2 and the switch 52. The capacitance sensor 30 is connected to the heater wire 2 via the signal line 311 and the first series circuit 11.

[0027] A parallel circuit including an inductance element L1, a resistance element R1, and a capacitance element C1 is provided on the signal line 311. In the signal line 311, the inductance element L1 is located between the parallel circuit and a connection point P11. The inductance element L1, resistance element R1, and capacitance element C1 are provided to remove electromagnetic noise from an AC signal Sa, which will be described later. The AC signal Sa is supplied to the heater wire 2 from a capacitance sensor 30, which will be described later, via a signal line 311.

[0028] The signal line 312 connects the capacitance sensor 30 and the first series circuit 11. In the first series circuit 11, a connection point P12 between the signal line 312 and the first series circuit 11 is located between the source electrode (S) of the switch 51 and the drain electrode (D) of the switch 52.

[0029] The signal line 321 connects the capacitance sensor 30 and the second series circuit 12. In the second series circuit 12, a connection point P21 between the signal line 321 and the second series circuit 12 is located between the heater wire 2 and the drain electrode (D) of the switch 53. It can also be said that the connection point P21 is located between the heater wire 2 and the switch 53. The capacitance sensor 30 is connected to the heater wire 2 via a signal line 321 and a second series circuit 12 .

[0030] A parallel circuit including an inductance element L2, a resistance element R2, and a capacitance element C2 is provided on the signal line 321. In the signal line 321, the inductance element L2 is located between the parallel circuit and a connection point P21. The inductance element L2, the resistance element R2, and the capacitance element C2 are provided to remove electromagnetic noise from an AC signal Sa, which will be described later. The AC signal Sa is supplied to the heater wire 2 from a capacitance sensor 30, which will be described later, via a signal line 321.

[0031] The signal line 322 connects the capacitance sensor 30 and the second series circuit 12. In the second series circuit 12, a connection point P22 between the signal line 322 and the second series circuit 12 is located between the source electrode (S) of the switch 53 and the drain electrode (D) of the switch 54.

[0032] The control unit 7 of the detection device 1 further includes a sensor control unit 72 and a determination unit 73 in addition to the switch control unit 71 described above.

[0033] The switch control unit 71 outputs a High signal to the gate electrodes (G) of the switches 51, 52, 53, and 54 via the signal lines 91, 92, 93, and 94 when the steering wheel SW is heated. As a result, all of the switches 51, 52, 53, and 54 are turned "on," and the DC power supply PS is connected to the ground EG via the series circuit 10 and the heater wire 2. Then, power is supplied from the DC power supply PS to the heater wire 2, causing the heater wire 2 to generate heat. In other words, the heater is in an operating state.

[0034] The switch control unit 71 outputs a Low signal to the gate electrodes (G) of the switches 51, 52, 53, and 54 through the signal lines 91, 92, 93, and 94 while the steering wheel SW is not being heated. As a result, all of the switches 51, 52, 53, and 54 are turned "off," and the connection between the heater wire 2 and the DC power supply PS and the connection between the heater wire 2 and the ground EG are cut off. In this state, no power is supplied from the DC power supply PS to the heater wire 2, so the heater wire 2 does not generate heat. In other words, the heater is in a non-driven state.

[0035] In the detection device 1, the process of determining the gripping state of the steering wheel SW is repeatedly performed at predetermined execution intervals Ta (see FIG. 4). When the steering wheel SW is being heated (while the heater is being driven), when it is time to determine the gripping state of the steering wheel SW, the switch control unit 71 outputs a Low signal to the gate electrode (G) of each switch 51, 52, 53, and 54 to turn each switch 51, 52, 53, and 54 "off." This cuts off the connection between the heater wire 2 and the DC power supply PS and the connection between the heater wire 2 and the ground EG, cutting off the power supply from the DC power supply PS to the heater wire 2. The gripping state of the steering wheel SW, which will be described later, is determined when no power is being supplied from the DC power supply PS to the heater wire 2. The cutoff of the power supply to the heater wire 2 continues for a predetermined period during which the gripping state of the steering wheel SW is determined. The power supply to the heater wire 2 is resumed after the determination of the gripping state of the steering wheel SW is completed.

[0036] When the switch control unit 71 determines the gripping state of the steering wheel SW while the steering wheel SW is not being heated (when the heater is not being driven), the switch control unit 71 performs on / off operation of the switches 51 and 52 prior to determining the gripping state. As a result, the gripping state of the steering wheel SW, which will be described later, is determined in a state in which no power is being supplied from the DC power source PS to the heater wire 2 following the on / off operation of the switches 51 and 52. Note that the non-driving period of the heater referred to here is a temporary non-driving period (stop period) of the heater at the timing of determining the gripping state of the steering wheel SW, i.e., a non-driving period different from the non-driving period of the heater when detecting the heater capacitance.

[0037] The sensor control unit 72 controls the operation of the capacitance sensor 30 . Specifically, the sensor control unit 72 controls the output of the AC signals Sa and Sb from the capacitance sensor 30 , and also controls the acquisition of the capacitance value of the heater wire 2 by the capacitance sensor 30 .

[0038] The capacitance sensor 30 outputs an AC signal Sa (first AC signal) to signal lines 311 and 321 at a preset implementation period Ta (see FIG. 4) based on an instruction from the sensor control unit 72. When outputting the AC signal Sa, the capacitance sensor 30 outputs an AC signal Sb (second AC signal) of the same potential and voltage as the AC signal Sa to signal lines 312 and 322.

[0039] As described above, the detection device 1 has two paths for outputting the AC signal Sa to the heater wire 2. One path is a first path through which the AC signal Sa is input to one end 21 of the heater wire 2 via a signal line 311 and a first series circuit 11. The other path is a second path through which the AC signal Sa is input to the other end 22 of the heater wire 2 via a signal line 321 and a second series circuit 12.

[0040] Therefore, when detecting the gripping state of the steering wheel SW, the sensor control unit 72 sequentially outputs an AC signal Sa to the heater wire 2 via signal line 311 and then outputs an AC signal Sa to the heater wire 2 via signal line 321. Furthermore, while the sensor control unit 72 is outputting the AC signal Sa to the heater wire 2 via the signal line 311, the sensor control unit 72 outputs to the signal line 312 an AC signal Sb having the same potential and voltage as the AC signal Sa. While outputting the AC signal Sa to the heater wire 2 via the signal line 321, the sensor control unit 72 outputs to a signal line 322 an AC signal Sb having the same potential and voltage as the AC signal Sa.

[0041] The capacitance sensor 30 outputs an AC signal Sa (AC voltage) to the heater wire 2 via signal lines 311 and 321. The capacitance sensor 30 acquires a capacitance value indicating the magnitude of capacitance from a current value when the AC signal Sa is output to the heater wire 2. The capacitance sensor 30 outputs the acquired capacitance value to the control unit 7.

[0042] Here, the relationship between the current value and the capacitance value will be described by taking as an example a case where an AC signal Sa is input to the sensor circuit 3A. For example, when an AC signal Sa is input from the capacitance sensor 30 to the heater wire 2 via the sensor circuit 3A, an electric charge is sent to the heater wire 2 and a current flows through the sensor circuit 3A. Current is the amount of change in charge per unit time. When an AC signal Sa is input to the heater wire 2 while the power supply from the DC power source PS to the heater wire 2 is cut off, charge is sent to the heater wire 2, causing a current to flow through the sensor circuit 3A. The current flowing through the sensor circuit 3A is greatest immediately after the input of the AC signal Sa begins. Then, as charge accumulates in the heater wire 2, the current gradually becomes more difficult to flow, and finally the current stops. The capacitance sensor 30 obtains a capacitance value from the maximum value of the current that flows when the AC signal Sa is input to the heater wire 2.

[0043] The magnitude of the capacitance of the heater wire 2 is proportional to the amount of charge that can be sent to the heater wire 2. The greater the amount of charge that can be sent to the heater wire 2, the greater the current value detected by the capacitance sensor 30, and as a result, the greater the capacitance value. The capacitance sensor 30 outputs a capacitance value determined according to the detected current value to the control unit 7.

[0044] The determination unit 73 determines the gripping state of the steering wheel SW. As an example, the gripping state of the steering wheel SW includes a "gripped state" in which the steering wheel SW is gripped by the occupant, and an "ungripped state" in which the steering wheel SW is not gripped by the occupant.

[0045] In this embodiment, the gripping state of the steering wheel SW is determined using the electrostatic capacitance of a heater wire 2 (heater) wound around the steering wheel SW. When the AC signal Sa is input to the heater wire 2, a current flows through the heater wire 2, generating an electric field. When an occupant's hand approaches the generated electric field, the electric field changes, and the capacitance of the heater wire 2 changes. The capacitance value is different when the steering wheel SW is gripped and when it is not gripped.

[0046] Specifically, more charge can be sent into the steering wheel SW being gripped by the occupant than into the non-gripped steering wheel SW. Therefore, the current value (capacitance value) detected by the capacitance sensor 30 is greater when the steering wheel SW is being gripped than when it is not being gripped.

[0047] The determination unit 73 compares the capacitance value A acquired by the capacitance sensor 30 with a threshold value ThA (see FIG. 2). Here, a case will be described as an example where the threshold value ThA is set on the side where the capacitance value is larger than the capacitance value A1 when the steering wheel SW is not being gripped. When the capacitance value A is located on the side where the capacitance value is larger than the threshold value ThA including the threshold value ThA (A ≥ ThA), the determination unit 73 determines that the state of the steering wheel SW is the "gripped state". Here, "determining that the steering wheel SW is in the gripped state" in this specification means "the capacitance value of the steering wheel SW indicates a value when the steering wheel SW is in the gripped state". Also, when the capacitance value A is located on the side where the capacitance value is smaller than the threshold value ThA (A < ThA), the determination unit 73 determines that the state of the steering wheel SW is the "non-gripped state".

[0048] The determination unit 73 outputs the determination result of the gripped state of the steering wheel SW to an external device connected to the detection device 1. Note that the current value or capacitance value A of the heater wire 2 acquired by the capacitance sensor 30 may be output to an external device so that the state of the steering wheel SW is determined on the external device side.

[0049] Here, in the detection device 1, the capacitance sensor 30 is connected to the heater wire 2 via two paths (sensor circuit 3A, sensor circuit 3B). The capacitance sensor 30 acquires the capacitance value of the heater wire 2 and outputs it to the control unit 7. The determination unit 73 uses at least one of the capacitance value acquired via the sensor circuit 3A and the capacitance value acquired via the sensor circuit 3B to determine the gripping state of the steering wheel SW. In addition, when the determination result based on the capacitance value acquired through the sensor circuit 3A and the determination result based on the capacitance value acquired through the sensor circuit 3B match, the matched determination result may be adopted. In such a case, the accuracy of determining the grip state of the steering wheel SW is improved.

[0050] 2 is a time chart illustrating the effect of whether or not the heater is operating on the capacitance value detected by the capacitance sensor 30. Here, whether or not the heater is operating corresponds to whether or not power is supplied to the heater wire 2 and whether or not the steering wheel SW is heated. In Fig. 2, the capacitance values ​​A acquired at a predetermined execution cycle Ta are arranged on the time axis (horizontal axis) (see the enlarged view of Fig. 2). Furthermore, whether or not the heater was operating during the period in which the capacitance values ​​A were acquired and whether or not the steering wheel SW was actually gripped are shown along with the time axis of the capacitance values ​​A.

[0051] 2, the capacitance value A is smaller than the threshold value ThA during the period from time Tv to Tw and during the period from time Tx to Ty, so the determination unit 73 determines that the state of the steering wheel SW is the "non-gripped state." Furthermore, during the period from time Tw to time Tx, the capacitance value A is located on the side where the capacitance value is greater than the threshold value ThA. Therefore, the determination unit 73 determines that the state of the steering wheel SW is in the "gripped state." These determinations are the results of determination when the heater is off.

[0052] Here, whether the steering wheel SW is heated (whether power is supplied to the heater wire 2) affects the detected capacitance value. Specifically, the charge supplied to the heater wire 2 when the steering wheel SW is heated affects the capacitance value. Therefore, when detecting the gripping state of the steering wheel while the steering wheel is being heated (while power is being supplied to the heater wire 2), in order to suppress the effects of heating, the power supply to the heater wire 2 is interrupted each time the gripping state is detected prior to obtaining the capacitance value. However, even if the power supply to the heater wire 2 is interrupted, there are cases where the charge does not completely disappear from the heater wire 2 before the capacitance value is acquired (the gripping state is detected). In such cases, the acquired capacitance value may deviate from the value that should be obtained due to the influence of the charge remaining in the heater wire 2.

[0053] If charge remains on the heater wire 2, a smaller amount of charge can be sent from the capacitance sensor 30 to the heater wire 2. This reduces the current value detected by the capacitance sensor 30, causing the detected capacitance value to shift toward the smaller side. In the case of Fig. 2, heating of the steering wheel SW starts at time Tz. Therefore, the capacitance value between time Ty and time Tz is acquired when the steering wheel SW is not heated. The capacitance value A after time Tz is acquired when the charge caused by heating remains in the heater wire 2. Therefore, after time Tz, the amount of current flowing is reduced by the amount of the remaining charge, and the current value is reduced, so that the acquired capacitance value A also decreases (becomes smaller). As a result, even if the steering wheel SW is being gripped, the acquired capacitance value A may be a value that is smaller than the threshold value ThA. In such a case, even if the steering wheel SW is being gripped, it will be determined that the steering wheel SW is in an "unheld state" (see FIG. 2, effect of residual charge).

[0054] Therefore, in this embodiment, in order to suppress the influence of whether or not the steering wheel SW is heated in determining the gripping state of the steering wheel SW, the following configuration is adopted. (a) When the heater is not in operation (when the steering wheel SW is not heated), prior to detecting the capacitance of the heater wire 2, the heater wire 2 is connected to the DC power supply PS for a predetermined time Tx with the connection between the heater wire 2 and ground EG cut off (see FIG. 4).

[0055] When the heater wire 2 is connected to the DC power supply PS with the heater wire 2 disconnected from the ground EG, charge moves from the DC power supply PS to the heater wire 2, increasing the capacitance of the heater wire 2. In other words, when the steering wheel is not heated, charge is supplied to the heater wire 2 without operating the heater, prior to obtaining the capacitance value.

[0056] As a result, even when the steering wheel SW is not heated, the capacitance value is acquired in a state in which the charge has not been completely discharged from the heater wire 2, in the same manner as when the steering wheel SW is heated. In other words, when the steering wheel is not heated (when the heater is not driven), before detecting the capacitance of the heater wire 2, the capacitance of the heater wire 2 is made to approach the capacitance when the steering wheel SW is heated (when the heater is driven).

[0057] This makes it possible to suppress the influence of the charge remaining in the heater wire 2 when acquiring the capacitance value, whether the heater is in operation or not. This makes it possible to reduce the possibility of erroneously determining that the steering wheel SW is in a "not gripped state" even when it is actually being gripped, even if the steering wheel grip state is determined using one threshold value, for example, ThA.

[0058] The operation of the detection device 1 will now be described. FIG. 3 is a flowchart showing a process of determining the gripping state of the steering wheel SW in the detection device 1. FIG. 4 is a timing chart for carrying out the process of determining the gripping state of the steering wheel SW.

[0059] In the detection device 1, a process (determination process) for determining the gripping state of the steering wheel SW is performed at each predetermined execution cycle Ta. Furthermore, in the detection device 1, prior to carrying out the determination process, the presence or absence of operation of the heater is checked at a predetermined confirmation period Tb. 4, the execution period Ta and the confirmation period Tb are the same period. In the detection device 1, the presence or absence of operation of the heater is confirmed a predetermined time ΔT before the determination process is started.

[0060] In the detection device 1, when the confirmation period Tb for checking whether the heater is operating or not comes (step S101, Yes), the presence or absence of the heater being operated is confirmed (step S102). Specifically, it is confirmed whether all of the switches 51 to are on or not. In the case of FIG. 4, whether the heater is operating or not is confirmed at times t1, t3, t5, t12, t16, and t20. As an example, the switch control unit 71 checks whether the heater is operating based on whether a high signal is being output to the signal lines 91, 92, 93, and 94. This is because when a high signal is being output to the signal lines 91, 92, 93, and 94, all of the switches 51, 52, 53, and 54 are turned on.

[0061] When all of the switches 51, 52, 53, 54 are on, power is supplied from the DC power source PS to the heater wire 2, causing the heater wire 2 to generate heat. This state in which power is supplied to the heater wire 2 is the state in which the heater is operating (heater operating: heater drive period).

[0062] If the heater is not operating (step S102, No), the sensor control unit 72 outputs a High signal to the signal lines 91 and 92 for a predetermined time Tx (step S103). This causes the switches 51 and 52 to be turned on for the predetermined time Tx. 4, the heater is not in operation at times t1, t3, and t5 (heater non-driving period). Therefore, the switches 51 and 52 are turned on for a predetermined time Tx from times t1, t3, and t5.

[0063] When the switches 51 and 52 are turned on, the DC power supply PS and the heater wire 2 are connected via the first series circuit 11. In this state, the switches 53 and 54 are off, so that no power is supplied from the DC power supply PS to the heater wire 2. That is, although the heater wire 2 does not generate heat, because it is connected to the DC power supply PS, an electric charge is supplied to the heater wire 2, and the potential of the heater wire 2 rises toward the DC power supply PS.

[0064] Then, when it is time to determine the gripping state of the steering wheel SW (the execution period Ta of the determination process) (step S104, Yes), the sensor control unit 72 causes the capacitance sensor 30 to output an AC signal Sa to the signal line 311 of the sensor circuit 3A, and also causes an AC signal Sb of the same voltage and potential as the AC signal Sa to be output to the signal line 312 (step S105). As a result, the AC signal Sa is supplied to the heater wire 2 via the signal line 311 and the first series circuit 11. The capacitance sensor 30 acquires the capacitance value of the heater wire 2 when the AC signal Sa is supplied to the heater wire 2 (step S106).

[0065] At this time, in the first series circuit 11, an AC signal Sb having the same voltage and potential as the AC signal Sa is supplied to a connection point P12 with the signal line 312 between the switch 51 and the switch 52. This makes it possible to suppress (substantially eliminate) the potential difference between the DC power supply PS side of the switch 52 and the heater wire 2 side of the switch 52 in the series circuit 10. This makes it possible to suppress the inflow of electromagnetic noise from the DC power supply PS side of the switch 52 to the heater wire 2 side of the switch 52, thereby reducing the possibility that electromagnetic noise will inflow into the AC signal Sa and affect the detection of the capacitance value of the heater wire 2 by the capacitance sensor 30.

[0066] The sensor control unit 72 checks whether the acquisition of the capacitance value has been completed (step S107). As described above, in this embodiment, the capacitance sensor 30 acquires the capacitance value of the heater wire 2 using two paths. Therefore, if only the acquisition of the capacitance value on the sensor circuit 3A side has been completed (step S107, No), the process returns to the process of step S105. As a result, in step S105 newly implemented, the sensor control unit 72 causes the capacitance sensor 30 to output an AC signal Sa to the signal line 321 of the sensor circuit 3B, and outputs an AC signal Sb having the same voltage and the same potential as the AC signal Sa to the signal line 322. As a result, the AC signal Sa is supplied to the heater wire 2 via the signal line 321 and the second series circuit 12. The capacitance sensor 30 acquires the capacitance value of the heater wire 2 from the current value when the AC signal Sa is supplied to the heater wire 2 (step S106).

[0067] In the case of FIG. 4, the capacitance value A of the heater wire 2 is acquired at times t2, t4, and t6 at the timing of determining the gripping state of the steering wheel SW.

[0068] When the acquisition of the capacitance value on the sensor circuit 3A side and the acquisition of the capacitance value on the sensor circuit 3B side are completed, step S107 is affirmed and the process proceeds to the process of step S108. In step S108, the determination unit 73 compares the acquired capacitance value A with the threshold value ThA.

[0069] As an example, when the capacitance value A is a value on the larger side than the threshold value ThA including the threshold value ThA (A≧ThA), the determination unit 73 determines that the state of the steering wheel SW is the "gripping state". When the capacitance value A is a value on the smaller side than the threshold value ThA (A<ThA), the determination unit 73 determines that the state of the steering wheel SW is the "non-gripping state". Then, when the process of step S108 ends, the process returns to the process of step S101.

[0070] In the above-mentioned step S102, if the heater is operating (step S102, Yes), the switch control unit 71 turns off each of the switches 51, 52, 53, and 54 at a stage a predetermined time before the timing at which the gripping state of the steering wheel SW is determined (step S109). Specifically, the switch control section 71 switches the control signals input to the switches 51, 52, 53, and 54 via the signal lines 91, 92, 93, and 94 from a High signal to a Low signal.

[0071] In the case of FIG. 4, at times t13, t17, and t21, the switches 51, 52, 53, and 54 are on and the heaters are operating. Therefore, at times t13, t17, and t21, the switch control unit 71 switches the control signals input to the switches 51, 52, 53, and 54 from a High signal to a Low signal, thereby cutting off the supply of power to the heater wire 2 until the timing at which the gripping state of the steering wheel SW is determined. In the case of FIG. 4, the supply of power to the heater wire 2 is cut off between times t14, t18, and t22, and the heater is turned off.

[0072] Then, when it is time to determine the gripping state of the steering wheel SW (the execution period Ta of the determination process) (step S110, Yes), the sensor control unit 72 causes the capacitance sensor 30 to output an AC signal Sa to the signal line 311 of the sensor circuit 3A, and also causes an AC signal Sb of the same voltage and potential as the AC signal Sa to be output to the signal line 312 (step S111). As a result, the AC signal Sa is supplied to the heater wire 2 via the signal line 311 and the first series circuit 11. The capacitance sensor 30 acquires the capacitance value of the heater wire 2 from the current value when the AC signal Sa is supplied to the heater wire 2 (step S112).

[0073] The sensor control unit 72 checks whether acquisition of the capacitance value has been completed (step S113). For example, if only the acquisition of the capacitance value on the sensor circuit 3A side has been completed (step S113, No), the process returns to step S111. As a result, in the newly executed step S111, the sensor control unit 72 causes the capacitance sensor 30 to output an AC signal Sa to the signal line 321 of the sensor circuit 3B, and also causes the capacitance sensor 30 to output an AC signal Sb of the same voltage and potential as the AC signal Sa to the signal line 322. As a result, the AC signal Sa is supplied to the heater wire 2 via the signal line 321 and the second series circuit 12. The capacitance sensor 30 acquires a capacitance value from the current value of the heater wire 2 when the AC signal Sa is supplied to the heater wire 2 (step S112).

[0074] In the case of FIG. 4, the capacitance value of the heater wire 2 is acquired at times t14, t18, and t22, which are the timings for determining the gripping state of the steering wheel SW.

[0075] When the acquisition of the capacitance value on the sensor circuit 3A side and the acquisition of the capacitance value on the sensor circuit 3B side are completed, the result of step S113 becomes YES and the process proceeds to step S114. In step S114, the switch control section 71 switches the control signals input to the switches 51, 52, 53, and 54 via the signal lines 91, 92, 93, and 94 from a low signal to a high signal, thereby turning on the switches 51, 52, 53, and 54 (step S114). As a result, after times t15, t19, and t23 when the switches 51, 52, 53, and 54 are turned on, the supply of power to the heater wire 2 is resumed, and heating of the steering wheel SW is resumed.

[0076] When the power supply to the heater wire 2 is resumed, the determination unit 73 compares the capacitance value A acquired in step S112 with the threshold value ThA to determine the state of the steering wheel SW (step S108). Then, when the process of step S108 ends, the process returns to the process of step S101.

[0077] Here, the capacitance value of the heater wire 2 detected by the capacitance sensor 30 will be different between the case where the power supply to the heater wire 2 is stopped and the capacitance of the heater wire 2 is detected during the heater drive period when the heater is driven, and the case where the capacitance of the heater wire 2 is detected during the heater non-drive period (a non-drive period different from the heater non-drive period when the heater capacitance is detected during the heater drive period). As described above, the capacitance value of the heater wire 2 is affected by the amount of charge remaining in the heater wire 2. When power is being supplied to the heater wire 2, a large amount of charge is supplied to the heater wire 2, and therefore, if the capacitance value is detected while power is being supplied to the heater wire 2, the detected capacitance value will be low.

[0078] Therefore, when detecting the gripping state of the steering wheel while the steering wheel is being heated (while power is being supplied to the heater wire 2), in order to suppress the effects of heating, the power supply to the heater wire 2 is interrupted each time the gripping state is detected prior to obtaining the capacitance value. However, even if the power supply to the heater wire 2 is interrupted, there are cases where the charge does not completely disappear from the heater wire 2 before the gripping state is detected. The capacitance value acquired in such a case is smaller than the capacitance value acquired when the steering wheel is not heated (when no power is supplied to the heater wire 2).

[0079] In this case, a discrepancy may occur between the capacitance value obtained when the steering wheel is not heated (when power is not being supplied to the heater wire 2) and the capacitance value obtained when the steering wheel is heated (when power is being supplied to the heater wire 2) due to the influence of charge remaining in the heater wire 2.

[0080] In such a case, if the gripping state of the steering wheel SW is determined by comparing the acquired capacitance value A with the threshold value ThA, there is a possibility that the gripping state will be erroneously determined due to a discrepancy in the acquired capacitance value.

[0081] Therefore, when detecting the capacitance of the heater wire 2 while the heater is not driven, the heater wire 2 is disconnected from the ground EG and connected to the DC power supply PS for a predetermined time Tx prior to detecting the capacitance value of the heater wire 2. This causes a transfer of charge between the heater wire 2 and the DC power supply PS, and the capacitance value of the heater wire 2 changes in a direction approaching the capacitance value when power is being supplied from the DC power supply PS. This makes it possible to reduce the difference between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven. If there is a large difference between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven, there is a possibility that the steering wheel SW may be erroneously determined to be in a "non-gripped state" even when it is actually being gripped. Since the amount of deviation can be reduced, the occurrence of such a situation can be suitably prevented.

[0082] In the embodiment described above, the determination unit 73 compares the acquired capacitance value A with the threshold value ThA to determine the state of the steering wheel SW. The state of the steering wheel SW may be determined by comparing the amount of change ΔA (=A-As) from the capacitance value (reference value As) when the steering wheel SW is not gripped by the occupant with a threshold value ThB. For example, the judgment unit 73 can judge that the steering wheel SW is in a "gripped state" when the difference between the capacitance value A detected by the capacitance sensor 30 and the reference value As, i.e., the change ΔA from the reference value As, is greater than or equal to a threshold value ThB (ΔA≧ThB). The reference value As and the threshold values ​​ThA and ThB may be preset through experiments or simulations and stored in memory. The threshold values ​​ThA and ThB may be changed as appropriate in response to changes in the environment, such as humidity and temperature.

[0083] In the above embodiment, there are two switches (power supply side switches) between the heater wire 2 and the DC power supply PS, and two switches (ground side switches) between the heater wire 2 and the ground EG. The total number of power supply side switches and ground side switches may each be three or more. Also, in the example shown, when detecting the capacitance of the heater wire 2 while the heater is not driven and power is not being supplied to the heater wire 2, all the ground side switches are turned off to cut off the connection between the heater wire 2 and the ground EG. When there are multiple ground side switches, at least one of the ground side switches may be turned off. By turning off at least one of the ground side switches, the connection between the heater wire 2 and the ground EG can be cut off.

[0084] As described above, the detection device 1 according to the embodiment has the following configuration. (1) The detection device 1 is A heater wire 2 (heater) provided on a steering wheel SW of a vehicle; A series circuit 10 that connects the heater wire 2 to a DC power source PS (power source) and a ground EG; In the series circuit 10, switches 51 and 52 (power supply side switches) are provided between the heater wire 2 and the DC power supply PS; In the series circuit 10, switches 53 and 54 (ground side switches) are provided between the heater wire 2 and the ground EG; a capacitance sensor 30 for detecting the capacitance of the heater wire 2; a sensor circuit 3 that connects a capacitance sensor 30 between a switch 52 (a power supply side switch) and a switch 53 (a ground side switch) in a series circuit 10; and a control unit 7 that controls switches 51 and 52 (power supply side switches) and switches 53 and 54 (ground side switches). When the control unit 7 detects the capacitance of the heater wire 2 during a non-driving period other than the heater non-driving period in which power supply to the heater wire 2 is temporarily stopped to detect the heater capacitance while power is being supplied to the heater wire 2, the control unit 7 connects the heater wire 2 to the DC power supply PS for a predetermined time with the connection between the heater wire 2 and the ground EG cut off prior to detecting the capacitance of the heater wire 2.

[0085] The capacitance of the heater wire 2 detected by the capacitance sensor 30 may be different between when the power supply to the heater wire 2 is stopped and the capacitance of the heater wire 2 is detected when the heater is driven and when the capacitance of the heater wire 2 is detected when the heater is not driven. This is because even if the power supply to the heater wire 2 is interrupted, the charge may not be completely removed from the heater wire 2 before the capacitance value is acquired. In such a case, the acquired capacitance value may deviate from the value that should have been obtained due to the influence of the charge remaining on the heater wire 2. If there is a large discrepancy between the capacitance value obtained when the heater is not turned on and the capacitance value obtained when the heater is turned on, there is a possibility that the steering wheel SW will be erroneously determined to be in an "unheld state" even though it is actually being gripped.

[0086] As described above, when the heater wire 2 is connected to the DC power supply PS with the connection between the heater wire 2 and the ground EG cut off, charge transfer occurs between the heater wire 2 and the DC power supply PS, and the capacitance value of the heater wire 2 changes in a direction approaching the capacitance value when power is being supplied from the DC power supply PS. This makes it possible to suppress the difference between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven. If there is a large difference between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven, there is a possibility that the steering wheel SW is erroneously determined to be in a "non-gripped state" even though it is being gripped, but as described above, since the amount of difference can be suppressed, the occurrence of such a situation can be suitably suppressed. This makes it possible to suppress the influence of whether the steering wheel is heated or not on the determination of the grip state of the steering wheel.

[0087] (i) When driving the heater, the control unit 7 supplies power to the heater wire 2 by connecting the DC power supply PS, the heater wire 2, and the ground EG. When detecting the capacitance of the heater wire 2, the control unit 7 turns off the switches 51, 52, 53, and 54 to cut off the connection between the heater wire 2 and the DC power supply PS and the connection between the heater wire 2 and the ground EG, and inputs an AC signal Sa (first AC signal) from the sensor circuit 3 to the heater wire 2. The control unit 7 acquires, via the capacitance sensor 30, the capacitance value of the heater wire 2 to which the AC signal Sa is being input.

[0088] With this configuration, the heater wire 2 wound around the steering wheel SW can be used for both heating the steering wheel SW and detecting whether the steering wheel SW is being gripped.

[0089] (2) The ground-side switch is composed of a plurality of switches 53 and 54 arranged in series on the second series circuit 12 of the series circuit 10. The control unit 7 At least one of the multiple switches 53, 54 arranged in series on the second series circuit 12 is turned off to cut off the connection between the heater wire 2 and the ground EG.

[0090] By turning off at least one of the ground side switches, the connection between the heater wire 2 and the ground EG can be cut off, so that the connection between the heater wire 2 and the ground EG can be quickly cut off before the capacitance of the heater wire 2 is detected. This allows the heater wire 2 to be connected to the DC power supply PS for a predetermined time with the heater wire 2 disconnected from the ground EG, without affecting the execution cycle Ta of the determination of the gripping state of the steering wheel SW.

[0091] (3) The ground side switch includes a switch 53 (second ground side switch) and a switch 54 (first ground side switch). The control unit 7 turns off at least one of the switch 53 and the switch 54 to cut off the connection between the heater wire 2 and the ground EG.

[0092] With this configuration, the connection between the heater wire 2 and the ground EG can be quickly cut off before the capacitance of the heater wire 2 is detected. This allows the heater wire 2 to be connected to the DC power supply PS for a predetermined time with the heater wire 2 disconnected from the ground EG, without affecting the execution cycle Ta of the determination of the gripping state of the steering wheel SW.

[0093] (4) In the series circuit 10, the switch 54 and the switch 53 are provided in this order from the ground EG side. The sensor circuit 3 is a sensor circuit 3B (second sensor circuit) connected between the switch 53 and the heater wire 2 in the series circuit 10; and a signal line 322 (second signal line) connected between the switch 53 and the switch 54 in the series circuit 10. The control unit 7 When detecting the capacitance of the heater wire 2, an AC signal Sa (first AC signal) is input from the capacitance sensor 30 to a sensor circuit 3B (second sensor circuit), and an AC signal Sb (second AC signal) having the same voltage and potential as the AC signal Sa is input from the capacitance sensor 30 to a signal line 322.

[0094] With this configuration, an AC signal Sb having the same voltage and potential as the AC signal Sa is input to the series circuit 10 via the signal line 322 connected between the switch 53 and the switch 54. This makes it possible to suppress (substantially eliminate) the potential difference between the ground EG side of the switch 53 and the heater wire 2 side of the switch 53 in the series circuit 10. This makes it possible to suppress the inflow of electromagnetic noise from the ground EG side of the switch 53 to the heater wire 2 side of the switch 53, thereby reducing the possibility that electromagnetic noise will inflow into the AC signal Sa and affect the detection of the capacitance value of the heater wire 2 by the capacitance sensor 30.

[0095] (5) The power supply side switch includes a switch 51 (first power supply side switch) and a switch 52 (second power supply side switch). In the series circuit 10, the switch 51 and the switch 52 are provided in this order from the DC power supply PS side. The sensor circuit 3 is a sensor circuit 3A (first sensor circuit) connected between the switch 52 and the heater wire 2 in the series circuit 10; and a signal line 312 (first signal line) connected between the switch 51 and the switch 52 in the series circuit 10. The control unit 7 When detecting the capacitance of the heater wire 2, an AC signal Sa (first AC signal) is input from the capacitance sensor 30 to a sensor circuit 3A (first sensor circuit), and an AC signal Sb (second AC signal) having the same voltage and potential as the AC signal Sa is input from the capacitance sensor 30 to a signal line 312.

[0096] When the AC signal Sa is output to the series circuit 10 via the sensor circuit 3A, the switches 51 to 54 are turned off so that no current flows between the upstream and downstream sides of each of the switches 51 to 54 in the series circuit 10. Here, the switches 51 to 54 each made up of a FET include a diode, and a slight leakage current occurs in the switches 51 to 54 each made up of a FET. Therefore, electromagnetic noise caused by the diode or leakage current may flow into the AC signal Sa. If electromagnetic noise flows into the AC signal Sa, it may affect the detection of the capacitance value of the heater wire 2 by the capacitance sensor 30.

[0097] With the above configuration, an AC signal Sb having the same voltage and potential as the AC signal Sa is input to the series circuit 10 via the signal line 312 connected between the switches 51 and 52. This makes it possible to suppress (substantially eliminate) the potential difference between the DC power supply PS side of the switch 52 and the heater wire 2 side of the switch 52 in the series circuit 10. This makes it possible to suppress the inflow of electromagnetic noise from the DC power supply PS side of the switch 52 to the heater wire 2 side of the switch 52, thereby reducing the possibility that electromagnetic noise will inflow into the AC signal Sa and affect the detection of the capacitance value of the heater wire 2 by the capacitance sensor 30.

[0098] (6) The control unit 7 An AC signal Sa (first AC signal) is input to the sensor circuit 3A (first sensor circuit) and then an AC signal Sa (first AC signal) is input to the sensor circuit 3B (second sensor circuit). The control unit 7 The gripping state of the steering wheel SW is determined using at least one of the capacitance value of the heater wire 2 (heater) when an AC signal Sa is input to the sensor circuit 3A and the capacitance value of the heater wire 2 (heater) when an AC signal Sa is input to the sensor circuit 3B.

[0099] For example, if the gripping state of the steering wheel SW is determined using both the capacitance value of the heater wire 2 (heater) when an AC signal Sa is input to the sensor circuit 3A and the capacitance value of the heater wire 2 (heater) when an AC signal Sa is input to the sensor circuit 3B, the accuracy of determining the gripping state of the steering wheel SW is improved compared to when the gripping state of the steering wheel SW is determined using only one of the capacitance values. Furthermore, since there are two circuits for detecting the gripping state of the steering wheel SW, redundancy in determining the gripping state of the steering wheel SW can be ensured.

[0100] (7) The capacitance sensor 30 acquires the capacitance value of the heater wire 2 when the AC signal Sa is input to the series circuit 10. The control unit 7 determines the gripping state of the steering wheel SW by comparing the amount of change ΔA in the capacitance value acquired by the capacitance sensor 30 with a threshold value ThB.

[0101] As described above, when the heater wire 2 is connected to the DC power supply PS with the connection between the heater wire 2 and the ground EG cut off, charge transfer occurs between the heater wire 2 and the DC power supply PS, and the capacitance of the heater wire 2 changes in a direction approaching the capacitance value when power is being supplied from the DC power supply PS. This makes it possible to suppress the deviation between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven. If there is a large deviation between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven, there is a possibility that the steering wheel SW may be erroneously determined to be in a "non-gripped state" even when it is being gripped, but since the amount of deviation can be suppressed as described above, the occurrence of such a situation can be suitably suppressed.

[0102] (8) The capacitance sensor 30 acquires the capacitance value of the heater wire 2 when the AC signal Sa is input to the series circuit 10. The control unit 7 determines the gripping state of the steering wheel SW by comparing the capacitance value A acquired by the capacitance sensor 30 with a threshold value ThA.

[0103] With this configuration, it is possible to suppress the deviation between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven. If there is a large deviation between the capacitance value acquired when the heater is not driven and the capacitance value acquired when the heater is driven, there is a possibility that the steering wheel SW may be erroneously determined to be in a "non-gripped state" even though it is being gripped. However, since the amount of deviation can be suppressed as described above, it is possible to suitably suppress the occurrence of such a situation.

[0104] (ii) The series circuit 10 has a first series circuit 11 on the DC power source PS side as viewed from the heater wire 2, and a second series circuit 12 on the ground EG side as viewed from the heater wire 2. In the first series circuit 11, a switch 51 and a switch 52 (power supply side switches) are provided in this order from the DC power supply PS side. In the second series circuit 12, the switch 54 and the switch 53 (ground side switch) are provided in this order from the ground EG side. The sensor circuit 3 is a sensor circuit 3A (first sensor circuit) that connects the capacitance sensor 30 and the first series circuit 11; The sensor circuit 3B (second sensor circuit) connects the capacitance sensor 30 and the second series circuit 12. The capacitance sensor 30 is connected between the switch 52 and the heater wire 2 in the first series circuit 11 via a sensor circuit 3A. The capacitance sensor 30 is connected between the switch 51 and the switch 52 in the first series circuit 11 via a signal line 312 (first signal line). The capacitance sensor 30 is connected between the switch 53 and the heater wire 2 in the second series circuit 12 via a sensor circuit 3B. The capacitance sensor 30 is connected between the switch 54 and the switch 53 in the second series circuit 12 via a signal line 322 (second signal line). The control unit 7 When detecting the capacitance of the heater wire 2, an AC signal Sa is input from the sensor circuit 3A to the first series circuit 11, and an AC signal Sb having the same voltage and potential as the AC signal Sa is input from a signal line 312 to the first series circuit 11. The control unit 7 When detecting the capacitance of the heater wire 2, an AC signal Sa is input from the sensor circuit 3B to the second series circuit 12, and an AC signal Sb having the same voltage and potential as the AC signal Sa is input from a signal line 322 to the second series circuit 12.

[0105] With this configuration, it is possible to detect capacitance using the sensor circuit 3A and the first series circuit 11, and to detect capacitance using the sensor circuit 3B and the second series circuit 12. This allows capacitance detection to be performed in two systems, which is expected to improve the accuracy of capacitance detection.

[0106] (iii) The switches 51, 52, 53, and 54 are each configured using a FET that operates in response to the voltage of a control signal input to the gate G. The control unit 7 When detecting the capacitance of the heater wire 2, an AC signal Sa is input from the sensor circuit 3 (3A, 3B) to the series circuit 10 (first series circuit 11, second series circuit 12), and an AC signal Sb having the same voltage and potential as the AC signal Sa is input from signal lines (signal line 312: first signal line, signal line 322: second signal line) to the series circuit 10 (first series circuit 11, second series circuit 12).

[0107] With this configuration, in the series circuit 10, it is possible to reduce the potential difference between the DC power supply PS side of the switch 52 and the heater wire 2 side of the switch 52. Furthermore, it is possible to reduce the potential difference between the ground EG side of the switch 53 and the heater wire 2 side of the switch 53. This makes it possible to suppress the inflow of electromagnetic noise from the DC power supply PS side of the switch 52 or the ground EG side of the switch 53 to the heater wire 2 side, thereby reducing the possibility that electromagnetic noise will flow into the AC signal Sa and affect the detection of the capacitance value of the heater wire 2 by the capacitance sensor 30.

[0108] Although the embodiment and modifications of the present invention have been described above, the present invention is not limited to these and can be modified as appropriate within the scope of the technical concept of the invention. [Explanation of symbols]

[0109] 1. Detection device 2 Heater wire (heater) 3 Sensor Circuit 3A 1st sensor circuit 3B Second sensor circuit 7 Control section 10 Series Circuits 11 1st series circuit 12 Second series circuit 51 Switch (power supply side switch: 1st power supply side switch) 52 Switch (power supply side switch: second power supply side switch) 53 Switch (Ground side switch: 2nd ground side switch) 54 Switch (Ground side switch: 1st ground side switch) 312 Signal line (first signal line) 322 signal line (second signal line) Sa AC signal (first AC signal) Sb AC signal (second AC signal) PS DC power supply (power supply) EG Grand

Claims

1. A heater provided in a steering wheel of a vehicle; a series circuit connecting the heater to a power source and ground; a power supply side switch provided between the heater and the power supply in the series circuit; a ground-side switch provided between the heater and the ground in the series circuit; a capacitance sensor for detecting a capacitance of the heater; a sensor circuit for connecting the capacitance sensor between the power supply side switch and the ground side switch in the series circuit; a control unit for controlling the power supply side switch and the ground side switch, The control unit is When detecting the capacitance of the heater during a driving period of the heater in which the heater is connected to the power supply and the ground, the detection of the capacitance is performed during a stop period of the heater in which the connection of the heater to the power supply and the ground is cut off; When detecting the capacitance of the heater during a non-driving period of the heater when the heater is not connected to the power supply and the ground, the detection device connects the heater to the power supply for a predetermined time with the connection between the heater and the ground cut off prior to detecting the capacitance of the heater.

2. 2. The detection device according to claim 1, the ground-side switch is composed of a plurality of switches arranged in series in the series circuit, The control unit is A detection device that turns off at least one of a plurality of switches arranged in series in the series circuit to interrupt the connection between the heater and the ground.

3. 2. The detection device according to claim 1, The ground side switch is a first ground side switch and a second ground side switch, The control unit is The detection device turns off at least one of the first ground side switch and the second ground side switch to cut off the connection between the heater and the ground.

4. 4. The detection device according to claim 3, the first ground side switch and the second ground side switch in the series circuit are provided in this order from the ground side: the first ground side switch, the second ground side switch; The sensor circuit includes: a second sensor circuit connected between the second ground side switch and the heater; a second signal line connected between the first ground side switch and the second ground side switch, The control unit is A detection device, when detecting the capacitance of the heater, inputting a first AC signal from the capacitance sensor to the second sensor circuit, and inputting a second AC signal having the same voltage and potential as the first AC signal from the capacitance sensor to the second signal line.

5. 5. The detection device according to claim 4, The power supply switch includes a first power supply switch and a second power supply switch, the first power supply side switch and the second power supply side switch in the series circuit are provided in this order from the power supply side: the first power supply side switch, the second power supply side switch; The sensor circuit includes: a first sensor circuit connected between the second power supply side switch and the heater; a first signal line connected between the first power supply side switch and the second power supply side switch, The control unit is When detecting the capacitance of the heater, a first AC signal is input from the capacitance sensor to the first sensor circuit, A detection device that inputs a second AC signal having the same voltage and potential as the first AC signal from the capacitance sensor to the first signal line.

6. 6. The detection device according to claim 5, The control unit is inputting the first AC signal to the first sensor circuit and inputting the first AC signal to the second sensor circuit in sequence; The control unit is A detection device that determines the gripping state of the steering wheel using at least one of the capacitance value of the heater when the first AC signal is input to the first sensor circuit and the capacitance value of the heater when the first AC signal is input to the second sensor circuit.

7. The detection device according to any one of claims 1 to 6, The control unit determines the gripping state of the steering wheel by comparing the amount of change in capacitance value acquired by the capacitance sensor with a threshold value.

8. The detection device according to any one of claims 1 to 6, The control unit determines the gripping state of the steering wheel by comparing the capacitance value acquired by the capacitance sensor with a threshold value.

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