Grip detection device

Abstract

To reduce the generation of electromagnetic noise in a heater.SOLUTION: A grip detection device 1 comprises: a series circuit 10 which has a heater wire 200 and a DC power source 11 that supplies power to the heater wire 200; an electrostatic capacitance sensor circuit 30 which outputs an AC signal S1 for detecting change in the electrostatic capacitance to the heater wire 200; a grip detection unit 73 which detects grip of a steering wheel SW by an occupant DP of a vehicle from the change in the electrostatic capacitance; switches 51-54 which switch the connection state between the DC power source 11 and the heater wire 200; and a switch control unit 72 which outputs a control signal for controlling the operations of the switches 51-54 and blocks connection between the DC power source 11 and the heater wire 200 when the electrostatic capacitance sensor circuit 30 outputs the AC signal S1. The switch control unit 72 includes a delay circuit that delays the operation of the switch 51.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Patent Document 1 discloses a grip detection device that detects whether an occupant is gripping the steering wheel by sending an AC signal to a heater provided on the steering wheel of a vehicle. [Prior art documents] [Patent documents]

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

[0004] FIG. 10 is a diagram showing the configuration of a conventional grip detection device 100. As shown in FIG. As shown in FIG. 10, the heater 200A is connected by a series circuit 110 to a DC power supply 120 that supplies power to the heater 200A. The grip detection device 100 includes a capacitance sensor circuit 300 connected to one end of the heater 200A. The capacitance sensor circuit 300 includes a capacitance sensor 310. The capacitance sensor 310 outputs an AC signal to the heater 200A to detect a change in the capacitance of the heater 200A. When an occupant grips the steering wheel, the capacitance of the heater 200A changes. The grip detection device 100 detects the grip of the steering wheel from the change in the capacitance of the heater 200A.

[0005] The grip detection device 100 includes switches 510, 520 configured with FETs or the like provided in a series circuit 110, and a switch control unit 700 that controls the on and off of the switches 510, 520. When an AC signal is output from the capacitance sensor 310 to the heater 200A, the switch control unit 700 turns off the switches 510, 520 to cut off the power supply from the DC power supply 120 to the heater 200A. Since grip detection is performed periodically, switches 510 and 520 are switched on and off in accordance with the grip detection period, and heater 200A operates intermittently. When heater 200A operates intermittently, the current flowing through heater 200A changes suddenly, which makes it more likely that electromagnetic noise will occur.

[0006] From the viewpoint of EMC (Electromagnetic Compatibility) in vehicles, there is a demand for reducing the electromagnetic noise generated by heaters. [Means for solving the problem]

[0007] The present invention relates to a series circuit including a heater provided in a steering wheel of a vehicle and a power source for supplying power to the heater; a capacitance sensor circuit connected to the heater and configured to output a first AC signal to the heater for detecting a change in capacitance; a detection unit that detects gripping of the steering wheel by an occupant of the vehicle based on the change in capacitance; a switch provided in the series circuit for switching a connection state between the power source and the heater; A gripping detection device including a switch control unit that outputs a control signal for controlling an operation of the switch and cuts off a connection between the power source and the heater when the capacitance sensor circuit outputs the first AC signal, The switch control unit includes a delay circuit that delays the operation of switching the connection state of the switch. 、 The capacitance sensor circuit includes: a first connection portion connected to one end of the heater and configured to output the first AC signal to the heater; a second connection portion connected between the first connection portion of the series circuit and the power source, for outputting a second AC signal having the same voltage and potential as the first AC signal to the series circuit; The switch includes a first switch and a second switch provided on both sides of the second connection part in the series circuit. do. Effect of the Invention

[0008] According to the present invention, it is possible to reduce the generation of electromagnetic noise in a heater. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a vehicle interior including a grip detection device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a configuration of a grip detection device. [Diagram 3] FIG. 2 is a diagram illustrating a configuration of a control unit. [Figure 4] FIG. 1A is a diagram showing the voltage of a control signal output by a PWM signal generator, FIG. 1B is a diagram showing the voltage of a control signal output by a smoothing circuit, and FIG. 1C is a diagram showing the current flowing through a heater wire. [Diagram 5] 5A to 5C are diagrams illustrating an operation of the grip detection device according to the embodiment. [Figure 6] 1A is a diagram showing the gate voltages of switches 52, 53, and 54, and FIG. 1B is a diagram showing the gate voltage of switch 51. FIG. [Figure 7] FIG. 6 is a diagram showing a change in current flowing through a heater wire in the embodiment. [Figure 8] FIG. 11 is a diagram showing a change in current flowing through a heater wire in a comparative example. [Figure 9] 13 is a diagram showing a configuration of a control unit of a grip detection device according to a modified example. FIG. [Figure 10] FIG. 1 is a diagram showing a configuration of a conventional grip detection device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described. Fig. 1 is a schematic diagram of the inside of a vehicle compartment VR including a grip detection device 1 according to an embodiment of the present invention. In Fig. 1, a heater wire 200 is simplified and shown by cross-hatching. As shown in Fig. 1, a steering wheel SW for an occupant DP to control the traveling direction of the vehicle is provided in the passenger compartment VR of the vehicle. A heater wire 200 (heater) that generates heat when a current flows is provided around the entire circumference of the steering wheel SW. Although a detailed description is omitted, the heater wire 200 is wound around the steering wheel SW from the outer periphery side inside a covering member that covers the steering wheel SW.

[0011] As shown in Fig. 1, an occupant DP grips the steering wheel SW when controlling the traveling direction of the vehicle. When the occupant DP grips the steering wheel SW, the hands of the occupant DP approach a heater wire 200 provided on the steering wheel SW. By outputting an AC signal S1 (described later) to the heater wire 200, a current flows through the heater wire 200 and an electric field is generated, and when the hands of the occupant DP approach this electric field, the electrostatic capacitance flowing through the heater wire 200 changes. The grip detection device 1 of the embodiment periodically detects a change in capacitance of the heater wire 200, and determines whether the detected change in capacitance indicates that the occupant DP is gripping the steering wheel SW. In other words, in this specification, "the grip detection device 1 detects the grip of the steering wheel SW by the occupant DP" is synonymous with "the grip detection device 1 detects a capacitance change value indicating that the occupant DP is gripping the steering wheel SW."

[0012] FIG. 2 is a diagram showing the configuration of the grip detection device 1. As shown in FIG. As shown in FIG. 2, the grip detection device 1 includes a series circuit 10, a capacitance sensor circuit 30, switches 51 to 54, and a control unit . The series circuit 10 is a circuit including a heater wire 200 and a DC power supply 11 that supplies power to the heater wire 200. The series circuit 10 has a connection line 210 that connects one end 200a of the heater wire 200 to the DC power supply 11, and a connection line 220 that connects the other end 200b of the heater wire 200 to ground 13. The connection line 210 connects the heater wire 200 to the DC power supply 11 via switches 51 and 52. The connection line 220 connects the heater wire 200 to the ground 13 via switches 53 and 54. A thermostat 250 for preventing overheating of the heater wire 200 is connected to the connection line 210. When the temperature of the heater wire 200 reaches or exceeds a certain temperature, the thermostat 250 is activated and the supply of power from the DC power supply 11 to the heater wire 200 is cut off.

[0013] The capacitance sensor circuit 30 is connected to the heater wire 200 via connection lines 210 and 220. The capacitance sensor circuit 30 outputs an AC signal S1 (first AC signal) for detecting gripping of the steering wheel SW to the heater wire 200 via the connection lines 210 and 220. The capacitance sensor circuit 30 includes a capacitance sensor 31, signal lines 32, 33, and signal lines 34, 35. The signal line 32 (first connection part) connects the capacitance sensor 31 to the connection line 210 at a connection point P1 via an inductance element I1 and a parallel circuit made up of a resistance element R1 and a capacitance element C1. The signal line 33 (third connection part) connects the capacitance sensor 31 to the connection line 220 at a connection point P2 via the inductance element I1 and a parallel circuit made up of a resistance element R1 and a capacitance element C1. A signal line 34 (second connection portion) connects the capacitance sensor 31 between the source electrode (S) of the switch 51 and the drain electrode (D) of the switch 52 in the series circuit 10. A signal line 35 (fourth connection portion) connects the capacitance sensor 31 between the source electrode (S) of the switch 53 and the drain electrode (D) of the switch 54 in the series circuit 10. The capacitance sensor 31 is a sensor that outputs an AC signal S1 to the heater wire 200 via signal lines 32 and 33, and detects a capacitance value of the heater wire 200 based on a current value flowing through the heater wire 200 due to the output of the AC signal S1. A resistance element R1, a capacitance element C1, and an inductance element I1 connected to the signal lines 32 and 33 are provided to remove electromagnetic noise from the AC signal S1. The capacitance sensor 31 detects the capacitance value of the heater wire 200 via each of the pair of signal lines 32 and 33, thereby improving detection accuracy. When outputting the AC signal S1 to the heater wire 200, the capacitance sensor 31 outputs an AC signal S2 (second AC signal) having the same voltage and potential as the AC signal S1 to the series circuit 10 via signal lines 34 and 35. The action of the AC signal S2 will be described later.

[0014] 2, the grip detection device 1 includes four switches 51, 52, 53, and 54 connected to the series circuit 10. The switches 51, 52, 53, and 54 switch the electrical connection state between the DC power supply 11 and the heater wire 200, i.e., switch between electrical connection and disconnection between the DC power supply 11 and the heater wire 200. A switch 51 (a first switch) and a switch 52 (a second switch) are connected to either side of a connection point P3 of a signal line 34 in the series circuit 10. The switch 51 is connected between the DC power supply 11 and the signal line 34 in the series circuit 10. The switch 52 is connected between the signal line 34 and the signal line 32 in the series circuit 10. A switch 53 (a third switch) and a switch 54 (a fourth switch) are connected to either side of a connection point P4 of the signal line 35 in the series circuit 10. The switch 53 is connected between the signal line 33 and the signal line 35 in the series circuit 10. The switch 54 is connected between the signal line 35 and the ground 13 in the series circuit 10.

[0015] The switches 51 to 54 can be composed of, for example, FETs (Field effect transistors). In the example of FIG. 2, an N-channel MOSFET (metal-oxide-semiconductor field-effect transistor) is used as the FET. The 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 the drain electrode (D). The N-channel MOSFET turns on when the voltage (gate voltage) applied to the gate electrode (G) becomes a high level, and turns off when the voltage becomes a low level. When an N-channel MOSFET is used, the drain electrode (D) is arranged on the DC power supply 11 side, and the source electrode (S) is arranged on the ground 13 side. Instead of the N-channel MOSFETs, P-channel MOSFETs may be used as the switches 51 to 54. The P-channel MOSFET is a transistor that turns on when the voltage (gate voltage) applied to the gate electrode (G) becomes low level and turns off when it becomes high level. When using a P-channel MOSFET, the source electrode (S) is arranged on the DC power supply 11 side and the drain electrode (D) is arranged on the ground 13 side, in contrast to the N-channel MOSFET.

[0016] When the switches 51 to 54 are turned on, the DC power source 11 and the heater wire 200 are connected, and power is supplied from the DC power source 11 to the heater wire 200. When the switches 51 to 54 are turned off, the connection between the DC power source 11 and the heater wire 200 is interrupted, and the supply of power to the heater wire 200 is interrupted.

[0017] The grip detection device 1 further includes a capacitive element C2 connected in parallel to the heater wire 200. Specifically, capacitive element C2 is connected to connection line 210 connected to one end 200a of heater wire 200, and connection line 220 connected to the other end 200b of heater wire 200. More specifically, capacitive element C2 is connected across connection point P1 between connection line 210 and signal line 32, and connection point P2 between connection line 220 and signal line 33. Although details will be described later, capacitive element C2 is provided to reduce electromagnetic noise generated from heater wire 200.

[0018] 2 controls the operations of the capacitance sensor 31 and the switches 51, 52, 53, and 54, and processes the detection results of the capacitance sensor 31. In order to make the drawing easier to understand, signal lines connecting the gate electrodes (G) of the switches 52 to 54 and the control unit 70 are not shown in FIG.

[0019] FIG. 3 is a diagram showing the configuration of the control unit 70. As shown in FIG. As shown in FIG. 3, the control unit 70 includes a sensor control unit 71, a switch control unit 72, and a grip detection unit 73 (detection unit). The control unit 70 can be configured, for example, from an integrated circuit equipped with a microprocessor, a memory, etc., such as an MCU (Micro Control Unit). Note that the sensor control unit 71, the switch control unit 72, and the grip detection unit 73 may each be configured from an individual MCU (Micro Control Unit).

[0020] The sensor control unit 71 controls the operation of the capacitance sensor 31 . The capacitance sensor 31 outputs an AC signal S1 to signal lines 32 and 33 at a preset detection period in response to an instruction from the sensor control unit 71. The capacitance sensor 31 detects the capacitance value of the heater wire 200 when the AC signal S1 is output. In other words, the capacitance sensor 31 outputs an AC signal S1 at each detection period to detect a change in capacitance that can confirm whether the steering wheel SW is being gripped or not, and detects the capacitance value of the heater wire 200.

[0021] When outputting the AC signal S1, the capacitance sensor 31 outputs to the signal lines 34 and 35 an AC signal S2 having the same potential and voltage as the AC signal S1.

[0022] The switch control unit 72 controls the operations of the switches 51, 52, 53, and . The switch control unit 72 outputs a control signal for controlling the on and off of the switches 51 to 54. The control signal is output from the switch control unit 72 in accordance with the detection cycle of the capacitance sensor 31. The switch control unit 72 switches the switches 51 to 54 from on to off when the capacitance sensor 31 outputs the AC signal S1. When the output of the AC signal S1 from the capacitance sensor 31 ends, the switch control unit 72 switches the switches 51 to 54 from off to on. In other words, while detecting gripping of the steering wheel SW, the switch control unit 72 cuts off the connection between the DC power supply 11 and the heater wire 200 to temporarily stop the operation of the heater wire 200.

[0023] As described above, the switches 51 to 54 each made up of an FET are turned on when a voltage is applied to their gate electrodes (G). The switch control section 72 outputs a control signal with a changed voltage level to the gate electrodes (G) of the switches 51, 52, 53, and 54, thereby switching the switches 51 to 54 on and off.

[0024] The switch control unit 72 includes a PWM (Pulse Width Modulation) signal generator 74 connected to the switch 51, and a GPIO (General-purpose input / output) 75 connected to the switches 52 to . The PWM signal generator 74 is connected to the gate electrode (G) of the switch 51 via a signal line 91. A resistive element R3 and a capacitive element C3 are connected to the signal line 91. The resistive element R3 and the capacitive element C3 form a smoothing circuit. The PWM signal generator 74 outputs a control signal to a signal line 91. The control signal input to the signal line 91 is smoothed by a smoothing circuit (resistance element R3 and capacitance element C3) and input to the gate electrode (G) of the switch 51. The GPIO 75 serving as an output terminal is connected to the gate electrodes (G) of the switches 52, 53, and 54 via signal lines 92, 93, and 94. The GPIO 75 outputs control signals to the switches 52 to 54 via the signal lines 92, 93, and 94, respectively.

[0025] PWM signal generator 74 connected to switch 51 and a smoothing circuit consisting of resistive element R3 and capacitive element C3 form a delay circuit that delays the on and off operations of switch 51. Note that "on operation" refers to the operation of the switch switching from off to on, and "off operation" refers to the operation of the switch switching from on to off. Fig. 4(A) is a diagram showing the voltage of the control signal output by the PWM signal generator 74. Fig. 4(B) is a diagram showing the voltage of the control signal output by the smoothing circuit, and also shows the voltage (gate voltage) input to the gate electrode (G) of the switch 51. Fig. 4(C) is a diagram showing the current flowing through the heater wire 200. The PWM signal generator 74 outputs a PWM signal as a control signal. The PWM signal is a signal obtained by modulating the pulse width of a pulse signal. The pulse signal is a signal that periodically repeats a period during which the voltage is at a high level (high pulse width Tp) and a period during which the voltage is at a low level (low pulse width Tq). The PWM signal generator 74 generates a PWM signal by changing the setting of the duty ratio D in one pulse period T. The duty ratio D means the proportion of the high pulse width Tp in one pulse period T (D=Tp / T).

[0026] 4A, the PWM signal generator 74 sets the duty ratio D to 100% when operating the heater wire 200. As a result, the PWM signal generator 74 outputs a control signal (ON signal) whose voltage is at a high level while the duty ratio D is 100%. As shown in FIG 4B, the input of the ON signal causes the gate voltage of the switch 51 to go to a high level, and the switch 51 is turned on. 4A, when stopping the operation of the heater wire 200, the PWM signal generator 74 sets the duty ratio D to 0%. As a result, the PWM signal generator 74 outputs a control signal (off signal) whose voltage is at a low level while the duty ratio D is 0%. As shown in FIG 4B, by inputting the off signal, the gate voltage of the switch 51 becomes low level, and the switch 51 is turned off.

[0027] As shown in FIG. 4A, the PWM signal generator 74 gradually changes the duty ratio D of the PWM signal when switching the switch 51 from on to off (period D1) and when switching it from on to on (period D2). In period D1, the PWM signal generator 74 gradually reduces the duty ratio D from 100% to 0%. As a result, in period D1, the PWM signal transitions from a high-level control signal (on signal) to a PWM signal in which high pulse width Tp and low pulse width Tq are alternately repeated. In period D1, the high pulse width Tp of the PWM signal gradually shortens while the low pulse width Tq gradually lengthens, eventually transitioning to a low-level control signal (off signal). In period D1, the duty ratio D gradually decreases, and the average voltage of the PWM signal gradually decreases. Here, the average voltage means the average voltage in one pulse period T of the PWM signal.

[0028] In period D2, the PWM signal generator 74 gradually increases the duty ratio D from 0% to finally 100%. As a result, in period D2, the PWM signal transitions from a low-level control signal (off signal) to a PWM signal in which high pulse widths Tp and low pulse widths Tq are alternately repeated. In period D2, the high pulse width Tp of the PWM signal gradually becomes longer while the low pulse width Tq gradually becomes shorter, and finally transitions to a high-level control signal (on signal). In period D2, as the duty ratio D gradually increases, the average voltage of the PWM signal gradually increases. It should be noted that FIG. 4 is merely a schematic diagram, and the period during which the heater wire 200 is operated, the period during which the heater wire 200 is stopped operating, and the lengths of the periods D1 and D2 can be changed as appropriate.

[0029] In this way, the average voltage of the PWM signal gradually changes during periods D1 and D2 when the switch 51 is turned on and off. However, the actual voltage waveform of the PWM signal simply switches between High and Low levels, as shown in (A) of FIG. The PWM signal output from the PWM signal generator 74 is smoothed by a smoothing circuit (resistance element R3 and capacitance element C3) and then input to the gate electrode (G) of the switch 51. The smoothing circuit smoothes the voltage waveform by reducing the steep rise and fall of the voltage through charging and discharging the capacitive element C3. As shown in (B) of Figure 4, the smoothing circuit smoothes the PWM signal, whose voltage switches steeply between high and low levels, and outputs it as a control signal whose voltage changes gradually. The PWM signal during period D1 in which the average voltage gradually decreases is smoothed to become a control signal whose voltage gradually decreases from a high level to a low level. The gate voltage of switch 51 to which this control signal is input also gradually decreases from a high level to a low level. The PWM signal during period D2 in which the average voltage gradually increases is smoothed to become a control signal whose voltage gradually increases from a low level to a high level. The gate voltage of switch 51 to which this control signal is input also gradually increases from a low level to a high level. In this way, a control signal obtained by smoothing the PWM signal is input to the gate electrode (G) of the switch 51. This causes the gate voltage of the switch 51 to vary gently, so that the switch 51 switches on and off slowly.

[0030] On the other hand, the output terminal GPIO75 simply switches the voltage of the control signal between a high level and a low level and outputs it. When the heater wire 200 is operated, the GPIO 75 outputs a high-level control signal (on signal) to turn on the switches 52 to . When the heater wire 200 is to be stopped, the GPIO 75 outputs a low-level control signal (off signal) to turn off the switches 52 to . The GPIO 75 switches the control signal from an on signal to an off signal when switching the switches 52 to 54 from on to off, and switches the control signal from an off signal to an on signal when switching the switches 52 to 54 from off to on. Therefore, the gate voltages of the switches 52 to 54 change sharply between high and low levels when they are switched on and off, so that the switches 52 to 54 operate more quickly than the switch 51.

[0031] 3, the grip detection unit 73 detects a change in capacitance (capacitance change value) from the capacitance value of the heater wire 200 detected by the capacitance sensor 31. Whether or not the steering wheel SW is being gripped can be identified from the detected capacitance change value. The capacitance value detected by the capacitance sensor 31 when the AC signal S1 is output to the heater wire 200 differs depending on whether the occupant DP is gripping the steering wheel SW or not gripping the steering wheel SW. The detected capacitance value is higher when the steering wheel SW is gripped than when the steering wheel SW is not gripped.

[0032] As an example, the capacitance value when the steering wheel SW is not gripped is set as a reference value As. The grip detection unit 73 detects the difference Δ(A-As) between this reference value As and the actually detected capacitance value A as a change in capacitance (capacitance change value). The grip detection unit 73 compares the detected capacitance change value Δ(A-As) with a threshold value Th to determine whether the occupant DP is gripping the steering wheel SW. Here, the threshold value Th indicates that the amount of change in the capacitance value A from the reference value As is a value at which it can be determined that the steering wheel SW is being gripped. The grip detection unit 73 compares the capacitance change value Δ(A-As) with the threshold value Th, and can determine that the occupant DP is gripping the steering wheel SW when the capacitance change value Δ(A-As) is greater than the threshold value Th (Δ(A-As)>Th). As another example, the grip detection unit 73 may use the capacitance value A detected by the capacitance sensor 31 itself as a capacitance change value and compare it with the threshold value Th'. In this case, the threshold value Th' indicates a capacitance value at which it can be determined that the steering wheel SW is being gripped. When the capacitance value A is larger than the threshold value Th' (A>Th'), the grip detection unit 73 can determine that the occupant DP is gripping the steering wheel SW. The reference value As and threshold values ​​Th and Th' mentioned here may be preset through experiments or simulations and stored in memory, or may be set from the capacitance value A detected by the capacitance sensor 31 and updated as necessary in response to changes in the environment, etc. Further, the method of detecting gripping of the steering wheel SW described here is merely one example, and gripping of the steering wheel SW may be determined by other methods.

[0033] As described above, in this embodiment, the capacitance sensor 31 is configured to output the AC signal S1 to the heater wire 200 from each of the signal line 32 and the signal line 33. In other words, the capacitance sensor 31 can output the AC signal S1 to one end 200a and the other end 200b of the heater wire 200. The grip detection unit 73 can determine whether the capacitance change value of the heater wire 200 when an AC signal S1 is output from the signal line 32 and the capacitance change value of the heater wire 200 when an AC signal S1 is output from the signal line 33 exceed a threshold value. The grip detection unit 73 may set a flag for identifying gripping of the steering wheel SW when at least one of the capacitance change values ​​exceeds a threshold value. Setting the flag means that the occupant DP is gripping the steering wheel SW.

[0034] The grip detection unit 73 is connected to a notification unit 270 provided outside the grip detection device 1. The notification unit 270 can be, for example, a display, an indicator, a speaker, or the like provided in the vehicle interior VR. For example, when the grip detection unit 73 does not detect gripping of the steering wheel SW, the notification unit 270 can output a message to the occupant DP to encourage gripping. The message may be a character or an image, or may be a sound.

[0035] Next, the operation and function of the grip detection device 1 according to the embodiment will be described. Fig. 5 is a diagram showing the operation of the grip detection device 1 according to the embodiment. Fig. 5 shows the operation of the grip detection device 1 when detecting gripping of the steering wheel SW. Fig. 6A is a diagram showing the voltage (gate voltage) of the gate electrodes (G) of the switches 52, 53, and 54, and Fig. 6B is a diagram showing the gate voltage of the gate electrode (G) of the switch 51. Fig. 6 shows the change in the gate voltage when the switches 51 to 54 are switched from on to off.

[0036] As shown in FIG. 5, when the capacitance sensor 31 outputs an AC signal S1, the switches 51 to 54 are turned off. By turning off all of the switches 51 to 54 in the series circuit 10, the power supply from the DC power supply 11 to the heater wire 200 is cut off.

[0037] Specifically, as shown in FIG. 6(A), the switches 52 to 54 are turned off by a control signal output from the GPIO75 of the switch control unit 72, and the gate voltage rapidly decreases from the High level to the Low level. That is, in the switches 52 to 54, the time T1 until the gate voltage drops from the High level to the Low level is short, and the OFF operation of the switches 52 to 54 is performed rapidly.

[0038] On the other hand, as described above, the PWM signal output from the PWM signal generator 74 is smoothed by a smoothing circuit (resistive element R3 and capacitive element C3) and input to the switch 51 as a control signal with a gradually decreasing voltage (see the period D1 in FIGS. 4(A) and 4(B)). Therefore, as shown in FIG. 6(B), in the switch 51, the time T2 until the level of the gate voltage drops from the High level to the Low level is longer than the time T1 (T1 < T2). That is, the speed of the OFF operation of the switch 51 is delayed, and the OFF operation of the switch 51 is performed more slowly than the switches 52 to 54. As shown in FIG. 4(C), the current flowing through the heater wire 200 gradually decreases in accordance with the delayed OFF operation of the switch 51. That is, by delaying the OFF operation of the switch 51, a rapid change in the current in the heater wire 200 is suppressed. Although not shown in the figure, the same thing happens when the switch 51 switches from off to on. The PWM signal output from the PWM signal generator 74 is smoothed by a smoothing circuit (resistance element R3 and capacitance element C3) and input to the switch 51 as a control signal whose voltage increases gradually (see period D2 in FIG. 4A and FIG. 4B). Therefore, the time it takes for the gate voltage of the switch 51 to rise from a low level to a high level is longer than the time it takes for the gate voltages of the switches 52 to 54 to rise from a low level to a high level. This causes a delay in the speed of the ON operation of the switch 51, and the ON operation of the switch 51 is performed more slowly than the ON operations of the switches 52 to 54. As shown in FIG. 4C, the current flowing through the heater wire 200 increases slowly in accordance with the delayed ON operation of the switch 51.

[0039] In this way, the delay circuit constituted by the PWM signal generator 74 and the smoothing circuit made up of the resistive element R3 and the capacitive element C3 slowly changes the voltage of the control signal input to the switch 51. This delays the on / off switching of the switch 51, and as a result, the switching of the connection state between the DC power supply 11 and the heater wire 200 is performed slowly.

[0040] FIG. 7 is a diagram showing a change in the current flowing through the heater wire 200 in the embodiment. FIG. 8 is a diagram showing a change in the current flowing through the heater wire 200 in the comparative example. The comparative example in FIG. 8 is an example showing a case where the grip detection device 1 is not provided with a delay circuit. In the comparative example, the switch control unit 72 is not provided with a PWM signal generator 74. Furthermore, the signal line 91 (see FIG. 3) connecting the switch control unit 72 and the switch 51 is not provided with a resistive element R3 and a capacitive element C3. In the comparative example, the GPIO 75 outputs control signals to all of the switches 51 to . That is, the switches 51 to operate quickly because control signals that simply switch the voltage between a high level and a low level are input to the switches 51 to .

[0041] As shown in FIG. 7, as switches 51 to 54 start to be turned off, the current flowing through heater wire 200 also decreases, and when all of switches 51 to 54 have been turned off, the flow of current from DC power supply 11 to heater wire 200 is cut off. As described above, in this embodiment, the speed of the turn-off operation of switch 51 is delayed by the delay circuit (a smoothing circuit consisting of PWM signal generator 74, and resistive element R3 and capacitive element C3). The current flowing through heater wire 200 decreases slowly in proportion to the delay in the operating speed of switch 51. Although not shown in the figure, when switch 51 is turned on, the current flowing through heater wire 200 also increases slowly in proportion to the delay in the operating speed of switch 51.

[0042] On the other hand, in the comparative example shown in Fig. 8, a delay circuit is not provided in switch 51, so there is no delay in the speed of the switching operation of switch 51 between the connection state of DC power supply 11 and heater wire 200. All of switches 51-54 are quickly switched from on to off, so that the current flowing through heater wire 200 decreases rapidly, as shown in Fig. 8. Although not shown, in the comparative example, when switches 51-54 are switched from off to on, the current flowing through heater wire 200 also increases rapidly.

[0043] Since the grip of the steering wheel SW is detected periodically, in the comparative example, the current in the heater wire 200 repeatedly undergoes rapid decreases and increases. Such drastic changes in the current in the heater wire 200 make it easier for electromagnetic noise to be generated from the heater wire 200. Specifically, a sudden change in current generates power supply noise in the DC power supply 11, and this power supply noise flows into the heater wire 200, making it easier for electromagnetic noise to be generated from the heater wire 200. From the viewpoint of EMC (Electromagnetic Compatibility) in a vehicle, it is required to reduce the generation of electromagnetic noise from the heater wire 200.

[0044] In the embodiment, the delay circuit (a smoothing circuit consisting of the PWM signal generator 74, and the resistive element R3 and the capacitive element C3) delays the operating speed of the switch 51, so that the connection state (connected and disconnected) of the DC power supply 11 and the heater wire 200 is switched slowly, and the change in the current flowing through the heater wire 200 is also gradual. This reduces the generation of electromagnetic noise in the heater wire 200.

[0045] As shown in FIG. 5, when the switches 51 to 54 are turned off, the capacitance sensor 31 outputs an AC signal S1 from the signal line 32. The AC signal S1 is input to one end 200a of the heater wire 200 via the signal line 32 and the connection line 210. The capacitance sensor 31 detects the capacitance value of the heater wire 200 from a change in the value of the current flowing through the heater wire 200. The capacitance sensor 31 then outputs an AC signal S1 from the signal line 33. The AC signal S1 is input to the other end 200b of the heater wire 200 via the signal line 33 and the connection line 220. The capacitance sensor 31 detects the capacitance value of the heater wire 200 from a change in the value of the current flowing through the heater wire 200. The order in which the AC signal S1 is output to the signal lines 32 and 33 may be reversed.

[0046] The capacitance sensor 31 outputs an AC signal S1 from the signal lines 32 and 33, and outputs an AC signal S2 having the same voltage and potential as the AC signal S1 from the signal lines 34 and 35. Here, when the switches 51 to 54 are omitted, the connection point P3 of the signal line 34 with the series circuit 10 is located between the connection point P1 of the signal line 32 with the series circuit 10 and the DC power supply 11. The connection point P4 of the signal line 35 with the series circuit 10 is located between the connection point P2 of the signal line 33 with the series circuit 10 and the ground 13. When the AC signal S1 is output, the switches 51 to 54 are off, but the switches 51 to 54 made of FETs include diodes, and a small leakage current is generated from the FETs. Therefore, there is a possibility that electromagnetic noise from the DC power supply 11 or the ground 13 side flows into the AC signal S1 through the diodes or leakage current of the FETs.

[0047] Therefore, in the embodiment, the capacitance sensor 31 outputs an AC signal S2 having the same voltage and potential as the AC signal S1 between the connection point P1 of the series circuit 10, to which the AC signal S1 is input, and the DC power supply 11, and between the connection point P2 of the series circuit 10, to which the AC signal S1 is input, and the ground 13. The voltage of the series circuit 10 to which the AC signal S2 is input approaches the voltage of the capacitance sensor circuit 30 or the heater wire 200 to which the AC signal S1 is input. By reducing the potential difference between the series circuit 10 and the capacitance sensor circuit 30 or the heater wire 200, it is possible to suppress electromagnetic noise from the DC power supply 11 or the ground 13 side from flowing into the AC signal S1 via the diode or leakage current of the FET. In the embodiment, switches 51 and 52 are provided on both sides of the signal line 34 in the series circuit 10, and switches 53 and 54 are provided on both sides of the signal line 35. This makes it possible to suppress electromagnetic noise from both the DC power supply 11 and the ground 13 side from flowing into the AC signal S1 via the diode or leakage current of the FET.

[0048] 5, a capacitance element C2 is connected in parallel to the heater wire 200. As a result, as shown by the black arrow in the figure, power supply noise generated in the DC power supply 11 bypasses the capacitance element C2 and flows to ground 13, thereby reducing the occurrence of electromagnetic noise from the heater wire 200 due to the power supply noise flowing into the heater wire 200.

[0049] After the capacitance sensor 31 outputs the AC signal S1 and detects the capacitance value of the heater wire 200, the switches 51 to 54 are switched from off to on. When all of the switches 51 to 54 are turned on, power supply from the DC power supply 11 to the heater wire 200 begins. At this time, in the embodiment, the speed of the on operation of the switch 51 is delayed by the delay circuit (a smoothing circuit composed of the PWM signal generator 74, and the resistive element R3 and the capacitive element C3), so that the current flowing through the heater wire 200 increases slowly (see FIG. 4C), and the generation of electromagnetic noise in the heater wire 200 is reduced.

[0050] As described above, the grip detection device 1 according to the embodiment has the following configuration. (1) The grip detection device 1 determines whether or not a capacitance change value (change in capacitance) detected from the capacitance value of a heater wire 200 (heater) provided on the steering wheel SW of a vehicle is a capacitance change value indicating that a vehicle occupant DP is gripping the steering wheel SW. That is, the grip detection device 1 detects the grip of the steering wheel SW by the vehicle occupant DP from the capacitance change value of the heater wire 200. The grip detection device 1 includes a series circuit 10, a capacitance sensor circuit 30, a grip detection unit 73 (detection unit), switches 51 to 54, and a switch control unit 72. The series circuit 10 includes a heater wire 200 and a DC power supply 11 (power supply) that supplies power to the heater wire 200. The capacitance sensor circuit 30 is connected to the heater wire 200 via connection lines 210 and 220. The capacitance sensor circuit 30 outputs an AC signal S1 (first AC signal) to the heater wire 200 for detecting a capacitance change value (change in capacitance). The grip detection unit 73 detects a capacitance change value from the capacitance value detected by the capacitance sensor circuit 30. The grip detection unit 73 determines whether or not the capacitance change value of the heater wire 200 is a capacitance change value indicating that the vehicle occupant DP is gripping the steering wheel SW. That is, the grip detection unit 73 detects the grip of the steering wheel SW by the vehicle occupant DP from the capacitance change value. The switches 51 to are provided in the series circuit 10. The switches 51 to change the connection state (connection and disconnection) between the DC power source 11 and the heater wire 200. The switch control unit 72 outputs a control signal that controls the operation of the switches 51 to 54. A PWM signal generator 74 outputs a control signal to the switch 51, and a GPIO 75 outputs a control signal to the switches 52 to 54. The switch control unit 72 cuts off the connection between the DC power supply 11 and the heater wire 200 when the capacitance sensor circuit 30 outputs the AC signal S1. The switch control section 72 includes a delay circuit (a PWM signal generator 74, and a smoothing circuit made up of a resistive element R3 and a capacitive element C3) that delays the operation of switching the connection state (connection and disconnection) of the switch 51.

[0051] With this configuration, the electromagnetic noise generated from the heater wire 200 can be reduced. Specifically, when the capacitance sensor 31 outputs the AC signal S1 to detect gripping of the steering wheel SW, the switches 51-54 are switched from on to off, and then switched from off to on again after the AC signal S1 is output. If all the switches 51-54 operate quickly, the current flowing through the heater wire 200 changes abruptly. If the AC signal S1 is output periodically, the heater wire 200 is likely to generate electromagnetic noise because the sudden changes in the current will be repeated. In the embodiment, the delay circuit slows down the operating speed of the switch 51, thereby making it possible to make the change in the current of the heater wire 200 gentler and reduce the generation of electromagnetic noise from the heater wire 200. This makes it possible to provide a grip detection device 1 that meets the EMC requirements in a vehicle.

[0052] (2) The switches 51 to are configured using FETs that operate in response to the voltage of a control signal applied to a gate electrode (G). The delay circuit has a PWM signal generator 74 and a smoothing circuit made up of a resistive element R3 and a capacitive element C3. The PWM signal generator 74 outputs a PWM signal when switching the connection state (connected and disconnected) of the switch 51. The smoothing circuit made up of the resistive element R3 and the capacitive element C3 smoothes the PWM signal output by the PWM signal generator 74 and outputs the smoothed signal to the switch 51 as a control signal.

[0053] For example, the switches 51 to 54, which are configured with N-channel MOSFETs, are turned on when the voltage (gate voltage) applied to the gate electrode (G) becomes high level, and are turned off when the voltage becomes low level. In the embodiment, when switching the connection state (connection and disconnection) of the switch 51, the PWM signal generator 74 gradually changes the duty ratio D of the PWM signal, so that the average voltage of the PWM signal can be gradually changed. The smoothing circuit (resistance element R3 and capacitance element C3) can smooth the PWM signal and output it to the gate electrode (G) of the switch 51 as a control signal whose voltage changes gradually. As a result, the gate voltage of the switch 51 to which the control signal is input changes gradually, so that the speed of the on and off operations of the switch 51 can be slowed down. By the slow on / off operation of the switch 51, the change in the current of the heater wire 200 also becomes gentle, and the generation of electromagnetic noise from the heater wire 200 can be reduced.

[0054] (3) The grip detection device 1 includes a capacitance element C2 connected in parallel to the heater wire 200. The capacitance element C2 bypasses power supply noise (noise) from the DC power supply 11 and causes it to flow to the ground 13, thereby suppressing the inflow of power supply noise to the heater wire 200. This makes it possible to reduce the generation of electromagnetic noise from the heater wire 200.

[0055] (4) The capacitance sensor circuit 30 has a signal line 32 (first connection portion) and a signal line 34 (second connection portion). The signal line 32 is connected to one end 200a of the heater wire 200 via a connection line 210. The signal line 32 outputs an AC signal S1 to the heater wire 200. The signal line 34 is connected between the signal line 32 of the series circuit 10 and the DC power supply 11. The signal line 34 outputs to the series circuit 10 an AC signal S2 (second AC signal) having the same voltage and potential as the AC signal S1. The switches include a switch 51 (first switch) and a switch 52 (second switch). The switches 51 and 52 are provided on both sides of a connection point P3 between the series circuit 10 and the signal line .

[0056] With this configuration, the voltage of the series circuit 10 to which the AC signal S2 is input becomes close to the voltage of the capacitance sensor circuit 30 and the heater wire 200 to which the AC signal S1 is input. This makes it possible to suppress electromagnetic noise from the DC power supply 11 or the ground 13 from flowing into the AC signal S1 through the diodes or leakage current of the switches 51 and 52 composed of FETs. Furthermore, by providing the switches 51 and 52 on both sides of the signal line 34, it is possible to suppress electromagnetic noise from both the DC power supply 11 and the ground 13 from flowing into the AC signal S1 through the diodes or leakage current of the FETs.

[0057] (5) A delay circuit (a smoothing circuit including a PWM signal generator 74, a resistive element R3, and a capacitive element C3) is connected to either the switch 51 (first switch) or the switch 52 (second switch). Even when multiple switches are provided in the series circuit 10, delaying the operation of any one of the switches can reduce abrupt changes in the current of the heater wire 200. By providing a delay circuit only for any one of the switches, installation costs can be reduced. In the embodiment, an example in which the delay circuit is connected to the switch 51 has been described, but the delay circuit may be connected to the switch 52.

[0058] (6) The capacitance sensor circuit 30 includes a signal line 33 (third connection portion) and a signal line 35 (fourth connection portion). The signal line 33 is connected to the other end 200b of the heater wire 200. The signal line 33 outputs an AC signal S1 to the heater wire 200. The signal line 35 is connected between the signal line 33 of the series circuit 10 and the ground 13. The signal line 35 outputs to the series circuit 10 an AC signal S2 having the same voltage and potential as the AC signal S1. The switches include a switch 53 (a third switch) and a switch 54 (a fourth switch). The switches 53 and 54 are provided on both sides of a connection point P4 between the series circuit 10 and the signal line 35.

[0059] When configured in this manner, the capacitance sensor 31 can output an AC signal S1 to the heater wire 200 from each of the signal line 32 connected to one end 200a of the heater wire 200 and the signal line 33 connected to the other end 200b of the heater wire 200, and can detect the capacitance value from each. The grip detection unit 73 determines whether each of the capacitance change values ​​detected from both ends of the heater wire 200 indicates gripping of the steering wheel SW, thereby improving the accuracy of grip detection. Moreover, by providing the signal line 35 and outputting the AC signal S2 to the series circuit 10, the voltage of the series circuit 10 to which the AC signal S2 is input becomes close to the voltage of the capacitance sensor circuit 30 and the heater wire 200 to which the AC signal S1 is input. This makes it possible to suppress electromagnetic noise from the DC power supply 11 or the ground 13 from flowing into the AC signal S1 through the diodes or leakage current of the switches 53 and 54 composed of FETs. Furthermore, by providing the switches 53 and 54 on both sides of the signal line 35, it is possible to suppress electromagnetic noise from both the DC power supply 11 and the ground 13 from flowing into the AC signal S1 through the diodes or leakage current of the FETs.

[0060] (7) To any one of the switches 51, 52, 53, and 54, a delay circuit (a smoothing circuit including a PWM signal generator 74, a resistive element R3, and a capacitive element C3) is connected. Even when multiple switches are provided in the series circuit 10, by delaying the operation of any one of the switches, it is possible to reduce abrupt changes in the current of the heater wire 200. By providing a delay circuit only for any one of the switches, it is possible to reduce installation costs. In the embodiment, an example in which the delay circuit is connected to the switch 51 has been described, but the delay circuit may be connected to the switch 53 or the switch 54.

[0061] In the embodiment, in order to improve the detection accuracy of the grip detection device 1, an example has been described in which the capacitance sensor 31 outputs the AC signal S1 to both ends (one end 200a and the other end 200b) of the heater wire 200 via a pair of signal lines 32 and 33, but the present invention is not limited to this. The capacitance sensor 31 may output the AC signal S1 to only one of the end 200a or the other end 200b of the heater wire 200.

[0062] <Modification> FIG. 9 is a diagram showing the configuration of a control unit 70A of a gripping detection device 1A according to a modified example. The overall configuration of the grip detection device 1A of the modified example is the same as that of Fig. 2, and therefore is not illustrated in the figure. Moreover, the same components as those of the grip detection device 1 of the embodiment are given the same reference numerals, and detailed description thereof is omitted. 9, a switch control unit 72A of a control unit 70A in the modified example includes a DA (Digital Analog) converter 76 capable of outputting any voltage, instead of a PWM signal generator 74 (see FIG. 3). The DA converter 76 is connected to a gate electrode (G) of a switch 51 via a signal line 91, and outputs a control signal to the switch 51. In the modified example, the DA converter 76 forms a delay circuit that delays the operation of the switch 51. The switches 52 to 54 are connected to the GPIO 75 in the same manner as in the embodiment, and operate in the same manner as in the embodiment.

[0063] In this modification, the voltage of the control signal output by the DA converter 76 is set in advance as a program and stored in the memory of the control unit 70A so as to change in accordance with the output period (detection period) of the AC signal S1. The DA converter 76 outputs a control signal (on signal) whose voltage is at a high level when operating the heater wire 200, and outputs a control signal (off signal) whose voltage is at a low level when stopping the operation of the heater wire 200. The DA converter 76 gradually decreases the voltage of the control signal from a high level to a low level when switching the switch 51 from on to off. The DA converter 76 gradually increases the voltage of the control signal from a low level to a high level when switching the switch 51 from off to on (similar to (B) of FIG. 4). As a result, the gate voltage of the switch 51 to which the control signal is input changes gradually, and the speed of the on and off operations of the switch 51 is delayed as in the embodiment.

[0064] By delaying the speed of the on and off operations of switch 51, the change in the current flowing through heater wire 200 becomes gentler, as in the embodiment, so that the electromagnetic noise generated from heater wire 200 can be reduced.

[0065] As described above, the grip detection device 1A according to the modified example has the following configuration. (8) In the grip detection device 1A in the modified example, the delay circuit has a DA converter 76 that outputs a control signal of an arbitrary voltage. Since the DA converter 76 can output a signal of any voltage, the voltage of the control signal can be gradually changed when switching the connection state of the switch 51, thereby delaying the operation speed of the switch 51. This makes it possible to reduce the generation of electromagnetic noise in the heater wire 200, as in the embodiment. Furthermore, since there is no need for a smoothing circuit (resistance element R3 and capacitance element C3) (see FIG. 3) that smoothes the PWM signal as in the embodiment, the delay circuit can be configured simply. In the example of FIG. 9, the DA converter 76, which is a delay circuit, is connected to the switch 51. However, the present invention is not limited to this, and the DA converter 76 may be connected to any one of the switches 52 to .

[0066] In the above-described embodiment and modified example, no particular time difference is provided for the timing at which the switches 51 to 54 start turning on or off when outputting the AC signal S1, but the switches 51 to 54 may start operating with a time difference. In this case, by connecting a delay circuit to the switch that is turned off last and turned on first among the switches 51 to 54, a sudden change in current through the heater wire 200 can be suppressed.

[0067] 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]

[0068] 1, 1A: Grip detection device 10: Series circuit 11:DC power supply (power supply) 13: Grand 30: Capacitive sensor circuit 31: Capacitive sensor 32: Signal line (first connection part) 33: Signal line (third connection part) 34: Signal line (second connection part) 35: Signal line (fourth connection part) 51: Switch (first switch) 52: Switch (second switch) 53: Switch (third switch) 54: Switch (4th switch) 70, 70A: Control section 71: Sensor control unit 72, 72A: Switch control section 73: Grasp detection unit 74: PWM signal generator 75: GPIO 76: DA converter R1, R3: Resistance elements C1, C2, C3: Capacitive elements I1: Inductance element 91, 92, 93, 94: Signal lines 200: Heater wire (heater) 210, 220: Connection lines 250: Thermostat 270: Information Department VR: Vehicle interior DP: :Crew SW: Steering wheel

Claims

1. a series circuit including a heater provided in a steering wheel of a vehicle and a power source for supplying power to the heater; a capacitance sensor circuit connected to the heater and configured to output a first AC signal to the heater for detecting a change in capacitance; a detection unit that detects gripping of the steering wheel by an occupant of the vehicle based on the change in capacitance; a switch provided in the series circuit for switching a connection state between the power source and the heater; a switch control unit that outputs a control signal to control an operation of the switch and cuts off a connection between the power source and the heater when the capacitance sensor circuit outputs the first AC signal, the switch control unit includes a delay circuit that delays an operation of switching the connection state of the switch, The capacitance sensor circuit includes: a first connection portion connected to one end of the heater and configured to output the first AC signal to the heater; a second connection portion connected between the first connection portion of the series circuit and the power source, for outputting a second AC signal having the same voltage and potential as the first AC signal to the series circuit; A grip detection device, characterized in that the switch includes a first switch and a second switch provided on both sides of the second connection portion in the series circuit.

2. the switch is configured using a FET that operates in response to a voltage of the control signal input to a gate, The grip detection device according to claim 1, characterized in that the delay circuit has a PWM signal generator that outputs a PWM signal when switching the connection state of the switch, and a smoothing circuit that smoothes the PWM signal and outputs it to the switch as the control signal.

3. the switch is configured using a FET that operates in response to a voltage of the control signal input to a gate, The grip detection device according to claim 1 , wherein the delay circuit has a DA converter that outputs the control signal of an arbitrary voltage.

4. The grip detection device according to any one of claims 1 to 3, further comprising a capacitive element connected in parallel to the heater and bypassing noise from the power supply to suppress inflow of noise to the heater.

5. The grip detection device according to any one of claims 1 to 4, wherein the delay circuit is connected to either the first switch or the second switch.

6. The capacitance sensor circuit includes: a third connection portion connected to the other end of the heater and configured to output the first AC signal to the heater; a fourth connection portion connected between the third connection portion of the series circuit and a ground, for outputting a second AC signal having the same voltage and potential as the first AC signal; The grip detection device according to any one of claims 1 to 4, characterized in that the switch includes a third switch and a fourth switch provided on both sides of the fourth connection portion in the series circuit.

7. The grip detection device according to claim 6, wherein the delay circuit is connected to any one of the first switch, the second switch, the third switch, and the fourth switch.

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