JP2021127059A - Steering wheel unit - Google Patents

Abstract

To provide a steering wheel unit capable of improving the detection accuracy of an open failure state and a short circuit failure state of a steering wheel.SOLUTION: A steering angle variation detection part 62 detects a steering angle variation corresponding to a rotary speed in accordance with the operation of a steering wheel 26 by a driver. A sweep time Ts of a sweep frequency range Fr3 to measure the frequency characteristic of an impedance of a capacitive sensor 28 is changed in accordance with the detected steering angle variation, and the frequency characteristic of the impedance of the capacitive sensor 28 is measured, and an open failure state and a short circuit failure state are determined from a resonance frequency fr.SELECTED DRAWING: Figure 5

Description

The present invention relates to a steering wheel unit that detects the grip of the steering wheel of a vehicle by a capacitance sensor, and more particularly to a steering wheel unit that diagnoses a failure of the capacitance sensor.

There are vehicles that can switch between manual steering mainly performed by the driver and automatic steering performed mainly by the system. Such a vehicle detects whether or not the driver is gripping the steering wheel at a predetermined timing, for example, when returning from automatic steering to manual steering. A capacitance sensor or the like is used to detect the grip of the steering wheel.

Patent Document 1 discloses a failure determination technique for a capacitance sensor provided on the rim of a steering wheel.

JP-A-2019-23011

By the way, the rim of the steering wheel is covered with leather or the like, and a sheet-shaped capacitance sensor in which a dielectric (spacer) is sandwiched between metal electrodes is provided. The capacitance sensor has a layered structure in which an annular rim body made of hard resin is provided inside.

In this case, it was found that due to the fact that a metal cloth or the like is used as the metal electrode that comes into contact with the leather, an open failure or a short failure may gradually occur instead of simply an open failure or a short failure. rice field.

It was also found that the capacitance often changes abruptly at the transition from the gripped state to the non-grasped state of the steering wheel, or vice versa.

The present invention has been made in consideration of such a problem, and an object of the present invention is to provide a steering wheel unit capable of improving the detection accuracy of an open failure and a short failure of the steering wheel.

The steering wheel unit according to one aspect of the present invention is a steering wheel unit that detects the presence or absence of gripping on the steering wheel by a capacitance sensor provided on the steering wheel of the vehicle, and changes the steering angle of the steering wheel. A steering angle change amount detection unit that detects the amount, a frequency characteristic measurement unit that measures the frequency characteristic of the impedance of the capacitance sensor when the steering wheel is gripped, and the steering angle change amount and the frequency characteristic. The failure diagnosis unit is provided with a failure diagnosis unit for determining the presence or absence of a failure of the capacitance sensor based on the above, and the failure diagnosis unit is described according to the steering angle change amount detected by the steering angle change amount detection unit. The failure diagnosis is performed by changing the sweep time in the sweep frequency range when measuring the frequency characteristics.

According to the present invention, the sweep time in the sweep frequency range is changed according to the amount of change in the steering angle corresponding to the rotation speed due to the operation of the steering wheel by the driver, and the frequency characteristic of the impedance of the capacitance sensor is measured to diagnose the failure. Therefore, it is possible to improve the detection accuracy of the steering wheel open failure and short failure.

FIG. 1 is a block diagram showing an example of the configuration of the steering wheel unit according to the embodiment. FIG. 2 is a sectional view taken along line II-II of the steering wheel in the steering wheel unit shown in FIG. FIG. 3A is a schematic circuit explanatory diagram of the frequency characteristic measuring unit while holding the steering wheel. FIG. 3B is an equivalent circuit diagram of FIG. 3A. FIG. 4 is a frequency characteristic diagram of the impedance of the capacitance sensor. FIG. 5 is a diagnostic map. FIG. 6 is a flowchart provided for explaining the operation of the steering wheel unit.

Hereinafter, the steering wheel unit according to the present invention will be described in detail with reference to the accompanying drawings with reference to suitable embodiments.

[composition]
As shown in FIG. 1, the steering wheel unit 12 according to this embodiment is provided in the vehicle 10. The vehicle 10 can appropriately switch between manual steering in which the driver takes the lead in steering and automatic steering in which the system (automatic driving device 14) takes the lead in steering. The vehicle 10 in this embodiment is an autonomous driving vehicle in which the system can mainly perform driving and braking operations in addition to steering.

The vehicle 10 includes an automatic driving device 14, a traveling device 16, and a notification device 18 in addition to the steering wheel unit 12.

The automatic operation device 14 is composed of an ECU, and includes an arithmetic unit such as a processor and a storage device such as a ROM or RAM. The automatic operation device 14 realizes various functions by executing a program stored in the storage device by the arithmetic unit. The automatic driving device 14 acquires information necessary for automatic driving, for example, external world information (detection results of a camera, radar, etc.), running state information (running speed, acceleration / deceleration) of the vehicle 10, navigation information, and the like from various sensors and devices. Then, a control instruction for automatically performing the driving, steering, and braking operations is output to the traveling device 16.

The traveling device 16 includes a driving force device 20, a steering device 22, and a braking device 24. The driving force device 20 has a driving force ECU and a driving source including an engine / driving motor. The driving force device 20 generates a driving force in response to an operation of the accelerator pedal performed by the driver or a drive control instruction output from the automatic driving device 14. The steering device 22 includes an electric power steering system (EPS) ECU and an EPS actuator. The steering device 22 generates a steering force in response to an operation of the steering wheel 26 performed by the driver or a steering control instruction output from the automatic driving device 14. The braking device 24 includes a brake ECU and a brake actuator. The braking device 24 generates a braking force in response to the operation of the brake pedal performed by the driver or the control instruction of braking output from the automatic driving device 14.

The notification device 18 includes a notification ECU, a display device, and an audio device. The notification device 18 notifies the driver according to a notification instruction output from the automatic operation device 14 or the grip determination device 50 described later.

The steering wheel unit 12 includes a steering wheel 26, a grip determination device 50, a steering angle sensor 30, and a power switch 34. The steering wheel unit 12 further includes a capacitance sensor 28.

The grip determination device 50 includes a frequency characteristic measurement unit 52, an arithmetic unit 54, a storage device 56, and a timer (timekeeping unit) 58.

The arithmetic unit 54 includes a grip detection unit 60, a steering angle change amount detection unit 62, a failure diagnosis unit 64, and a notification instruction unit 66.

As shown in FIG. 2, the rim 40 of the steering wheel 26 has a laminated structure having a plurality of layers in cross section (cross section parallel to the central axis of the steering wheel 26). In the rim 40, the entire core metal 41 corresponding to the skeleton is covered with the hard resin 42, a part or the whole of the resin 42 is covered with the capacitance sensor 28, and the rest of the resin 42 is covered with the elastic member 43. The leather 44 covers the capacitance sensor 28 and the elastic member 43.

As shown in FIG. 1, the capacitance sensor 28 is provided along the circumferential direction of the rim 40. In the present embodiment, one capacitance sensor 28 is provided so as to orbit the rim 40 with the lower portion of the rim 40 as a boundary. Both ends of the capacitance sensor 28 are insulated at the bottom of the rim 40.

The grip detection unit 60 determines the magnitude of the combined capacitance C that changes according to the contact and non-contact of the human body with respect to the steering wheel 26 {grasping and non-grasping of the hand 49 (FIG. 3A)}. It is detected by detecting the resonance frequency fr that changes according to the magnitude.

FIG. 3A schematically shows a state in which the human hand 49 is holding the leather 44 of the steering wheel 26 showing a partially detailed cross-sectional shape, and the frequency characteristic measuring unit 52 is the capacitance sensor 28. It is a circuit explanatory drawing which shows typically the state which is electrically connected to the terminal 28d, 28e. The terminal 28d can also be used as a short-circuit detection terminal.

In this case, in the steering wheel 26, the capacitance sensor 28 having a structure in which the dielectric 28b is sandwiched between the electrodes 28a and 28c is laminated on the resin 42 inside, and the leather 44 is laminated on the capacitance sensor 28. It is configured.

The electrodes 28a and 28c of the capacitance sensor 28 and the terminals 28d and 28e are connected by an insulating coated electric wire.

FIG. 3B is an equivalent circuit diagram of FIG. 3A. In FIGS. 3A and 3B, the ground is the chassis ground through the seat or floor.

The capacitance sensor 28 forms a capacitor, and the capacitance Cs of the capacitance sensor 28 is Cs = 1000 [pF]. When the hand (human body) 49 is gripped through the leather 44 of the steering wheel 26, the hand (human body) 49 forms a capacitor between the electrode 28c and the ground. The maximum capacitance Cm of the capacitor formed by the hand (human body) 49 is about Cm = 100 [pF]. When the hand (human body) 49 is not gripping (contacting) the leather 44, there is a non-grasping capacitance Cng (Cng = 10 [pF]) of about 10 [pF] as the stray capacitance.

That is, in the steering wheel 26, Cs >> Cm >> Cng {The capacitance Cs of the capacitance sensor 28 is much larger than the capacitance Cm of the hand (human body) 49, and the static electricity of the hand (human body) 49. The capacitance Cm is much larger than the non-grasping capacitance Cng. } The relationship is established.

Here, the capacitance including the capacitance of the capacitance sensor 28 between the terminal 28e and the ground from the terminal 28e side of the frequency characteristic measuring unit 52 becomes the combined capacitance C.

In the connected state of the capacitor of FIG. 3B, as shown in the equation (1), the combined capacitance C is a parallel capacitor of the non-grasping capacitance Cng and the capacitance Cm of the hand (human body) 49, and static. It becomes the series capacitance with the capacitor of the capacitance Cs of the capacitance sensor 28.
C = {Cs (Cng + Cm)} / (Cs + Cng + Cm) ... (1)

When the capacitance sensor 28 is in a short-circuit failure state (when the electrode 28c end of the terminal 28d of the capacitance Cs shown in FIG. 3B is in the grounded state), the combined static electricity seen from the frequency characteristic measurement unit 52 side. The capacitance C = Cshort becomes Cshort = Cs.

When the capacitance sensor 28 is in an open failure state (when any of the electrodes 28a, 28c, or terminal 28e of the capacitance Cs shown in FIG. 3B is open), the combined capacitance C = Copen is , Copen = 1 [pF].

Therefore, considering the capacitance Copen in the open failure state, Cs >> Cm >> Cng >> Copen (the capacitance Cs of the capacitance sensor 28 is much larger than the capacitance Cm of the human body, and the human body The capacitance Cm is much larger than the non-grasping capacitance Cng, and the non-grasping capacitance Cng is much larger than the open failure capacitance Copen).

Let L be the stray inductance (lead inductance) including the wiring of the path from the terminal 28e of the frequency characteristic measuring unit 52 to the ground.

As is known, since the resonance frequency fr is fr = 1 / (2π√LC), the failure diagnosis unit 64 drives the frequency characteristic measurement unit 52 to drive the constant voltage Vin AC voltage generator 48 to a low frequency. By measuring the sensor current Sense when swept from to high frequency with the current meter 46, the impedance Z at each frequency can be measured as Z [Ω] = Vin / Sense.

In this case, on the low frequency side of the resonance frequency fr, the impedance Z is capacitive and decreases with increasing frequency, and on the high frequency side of the resonance frequency fr, the impedance Z is inductive. It rises with increasing frequency. At the resonance frequency fr, the impedance Z drops to the equivalent series resistance value.

Each of the above states will be described as follows with reference to the above equation (1).
At the time of short-circuit failure: Capacitance at the time of short-circuit failure of the capacitance sensor 28 Cshort = Cs≈1000 [pF].
At the time of gripping: The capacitance sensor 28 is normal, and the capacitance Cm ≈ 100 [pF] at the time of gripping the steering wheel 26 (capacitance sensor 28).
Non-grasping: The capacitance sensor 28 is normal, and the steering wheel 26 (capacitance sensor 28) has a non-grasping capacitance Cng≈10 [pF].
At the time of open failure: Capacitance Copen ≈ 1 [pF] at the time of open failure of the capacitance sensor 28.

FIG. 4 shows the frequency characteristic 100 of the impedance Z of the capacitance sensor 28 in each state measured in advance using the frequency characteristic measuring unit 52.

The frequency characteristic 100 of the impedance Z is derived from the frequency characteristic 100 short at the time of short failure, the frequency characteristic 100 g at the time of gripping in the normal state, the frequency characteristic 100 ng at the time of non-grasping in the normal state, and the frequency characteristic 100 open at the time of open failure. Become.

Each resonance frequency fr becomes the resonance frequency fshort at the time of short failure, the resonance frequency fg at the time of gripping, the resonance frequency fng at the time of non-grasping, and the resonance frequency fopen at the time of open failure.

In addition, these frequency characteristics 100short, 100g, 100ng, 100open sweep the frequency of the constant voltage AC voltage generator 48 from about 1 [kHz] to about 10 [MHz] (10000 [kHz]) in the sweep frequency range. It is obtained by measuring and plotting the impedance Z = Sense / Vin at each frequency when (logous sweep) is performed.

In FIG. 1, the steering angle sensor 30 is arranged on a steering shaft (not shown), detects the steering angle θ of the steering wheel 26, and transmits a signal (referred to as steering angle θ) indicating the steering angle θ to the grip determination device 50. Output.

The power switch 34 is a switch that is manually operated by the driver when the driver turns on or off the power supply of the vehicle 10 (hereinafter, also referred to as a vehicle power supply), and is provided in the vehicle interior. The power switch 34 outputs an operation signal to the grip determination device 50 in response to the on / off operation.

The grip determination device 50 is composed of an ECU, and includes the frequency characteristic measurement unit 52 described above, an arithmetic unit 54 such as a processor, a storage device 56 such as a ROM or RAM, and a timer 58.

The arithmetic unit 54 realizes various functions by executing a program stored in the storage device 56. In the present embodiment, the arithmetic unit 54 functions as a grip detection unit 60, a steering angle change amount detection unit 62, a failure diagnosis unit 64, and a notification instruction unit 66.

FIG. 5 shows the determination frequencies fa and fb for determining whether the failure is normal or the failure stored in the storage device 56 in advance, and the gripping / non-grasping boundary frequency (boundary frequency) fc in the normal range. A diagnostic map (diagnosis table, judgment map, judgment table) 110 overwritten on the frequency characteristic 100 of the impedance Z shown is shown.

The failure diagnosis unit 64 performs a failure diagnosis of the capacitance sensor 28 with reference to the diagnosis map 110. If the resonance frequency fr is lower than the low frequency determination frequency fa, it is determined to be a short failure, and if the resonance frequency fr is higher than the high frequency determination frequency fb, it is determined to be an open failure, and the processing performed by the arithmetic unit 54 is controlled. To control.

In the diagnostic map 110, the frequency range (sweep frequency range) Fr1 {frequency (judgment frequency) fa to frequency (boundary frequency) fc} for initial gripping / non-grasping confirmation, gripping when the capacitance sensor 28 is normal Frequency range for non-grasping confirmation (sweep frequency range) Fr2 {frequency (judgment frequency) fa to frequency (judgment frequency) fb}, frequency range for short failure and open failure judgment (sweep frequency range) Fr3 (frequency 100 [kHz) ] To 10 [MHz]) is preset.

Further, the failure diagnosis unit 64 detects an on / off operation of the power switch 34 and switches between energization and de-energization of a DC power supply (not shown) for the steering wheel unit 12.

The grip detection unit 60 performs gripping / non-grasping detection processing when the capacitance sensor 28 is normal. In this case, the grip detection unit 60 determines that grip is performed if the resonance frequency fr is between the determination frequency fa and the boundary frequency fc, and does not grip if the resonance frequency fr is between the boundary frequency fc and the determination frequency fb. Is determined.

The notification instruction unit 66 outputs a notification instruction to the notification device 18 when the driver needs to be notified.

The storage device 56 stores various programs in addition to the diagnostic map 110 shown in FIG. The timer 58 measures the sweep time Ts and the like in the sweep frequency range.

[Operation of steering wheel unit 12]
Next, the operation of the steering wheel unit 12 will be described with reference to the flowchart of FIG. The flowchart of FIG. 6 is executed, for example, when the power switch 34 is turned on or when an automatic operation switch (not shown) is turned on. It may be executed at other times.

In step S1, the failure diagnosis unit 64 determines through the grip detection unit 60 whether or not the steering wheel 26 is gripped when the power switch 34 is operated in the ON state.

In this case, the grip detection unit 60 sweeps the sweep time Ts at a predetermined sweep time Tp, and the frequency range Fr1 from the determination frequency fa to the boundary frequency fc is swept by the frequency characteristic measurement unit 52, and has a grip resonance frequency fg. Gripping or non-grasping is determined depending on whether or not it is gripped.

When it is determined that the resonance frequency fg at the time of gripping does not exist and the gripping is not performed (step S1: NO), a failure (short failure or open failure) can be detected even if the determination is slow. Covering the resonance frequency fopen at the time of open failure from the resonance frequency fshort at the time of short failure For example, the sweep time Ts of the frequency range Fr3 of 100 [Hz] to 10 [MHz] is grasped to reduce the power consumption of the determination device 50. The resonance frequency fr is detected by sweeping with a relatively long normal sweep time Tn (Ts = Tn).

On the other hand, if it is determined in step S1 that the resonance frequency fg at the time of gripping exists and the steering wheel is gripped (step S1: YES), in step S3, the steering angle change amount detection unit is passed through the steering angle sensor 30. The steering angular velocity Ss = θ [deg] / Δt [sec] of the current steering wheel 26 acquired via 62 is a threshold steering angular velocity Ssth, for example, Ssth = 40 [deg / s] or more (Ss ≧ Ssth). ) Whether or not.

When the steering angular velocity Ss is less than the threshold steering angular velocity Ssth (Ss <Ssth, step S3: NO), 1/2 of the normal sweeping time Tn applied when the sweeping time Ts is not grasped in step S4. The frequency range Fr3 is swept with a short sweep time Tx (Ts = Tx = Tn / 2) to detect the resonance frequency fr.

On the other hand, in the determination in step S3, when the steering angular velocity Ss is equal to or higher than the threshold steering angular velocity Ssth (Ss ≧ Ssth, step S3: YES), it is necessary to determine in a shorter time, so in step S5. , The sweep time Ts is swept in the frequency range Fr3 with a sweep time Ty (Ts = Ty = Tn / 4) which is 1/4 of the normal sweep time Tn, and the resonance frequency fr is detected.

The reason for shortening the sweep time Ts is that when the steering wheel 26 is being steered, the frequency characteristics change abruptly because the steering wheel 26 is repeatedly gripped and not gripped by the hand 49, so that the frequency range is surely shortened. This is to detect the resonance frequency fr in Fr3. However, shortening the sweep time Ts increases the load on the CPU, so shortening the sweep time Ts to the sweep times Tx and Ty is limited to the time of failure determination.

In step S6, it is determined whether or not the resonance frequency fr is between the low frequency determination frequency fa and the high frequency determination frequency fb (fa ≦ fr <fb).

When the resonance frequency fr is between the low frequency determination frequency fa and the high frequency determination frequency fb (step S6: YES), it is determined in step S7 that the capacitance sensor 28 is in a normal state. In step S8, the grip detection unit 60 performs normal grip detection control.

In the normal grip detection control by the grip detection unit 60, the grip detection unit 60 ensures the grip state of the frequency characteristic measurement unit 52 in the frequency range Fr2 from the determination frequency fa on the low frequency side to the determination frequency fb on the high frequency side. Sweep with a sweep time Tab at the same rate as the shortest sweep time Ty.

The sweep time Tab at the same rate as the shortest sweep time Ty is a high-speed sweep time (predetermined) calculated by the equation (2) in which the sweep time Ty for sweeping the wide frequency range Fr3 is proportionally distributed to the frequency range Fr2. Sweep time) Tp.
Tab = Ty × (Fr2 / Fr3)… (2)

The frequency range Fr2 is swept by this predetermined sweep time Tp, and the resonance frequency fg when gripping or the resonance frequency fng when not gripping is detected.

On the other hand, when the determination in step S6 is not established, in step S9, it is determined whether or not the resonance frequency fr is higher than the determination frequency fb in the high region, and it is determined that the frequency is high (step S9). : YES) In step S10, it is determined that the capacitance sensor 28 is in an open failure state.

Further, when it is determined in step S9 that the resonance frequency fr is not equal to or higher than the high frequency determination frequency fb (step S9: NO), further in step S11, the resonance frequency fr is the low frequency determination frequency fa. It is determined whether or not the frequency is lower than the lower frequency, and if it is determined that the frequency is lower (step S11: YES), it is determined in step S12 that the capacitance sensor 28 is in a short failure state.

When it is determined that the failure is an open failure or a short failure, in step S13, the failure diagnosis unit 64 stops the grip detection control and statically detects the grip / non-grip of the steering wheel 26 on the notification device 18 through the notification instruction unit 66. The failure state of the capacitance sensor 28 is notified to the driver. At the same time, the dealer or the like may be notified through a server (not shown).

[Invention that can be grasped from the embodiment]
Here, the inventions that can be grasped from the above-described embodiment will be described below. For convenience of understanding, the components are designated by the reference numerals used in the above embodiments, but the components are not limited to those with the reference numerals.

The steering wheel unit 12 according to the present invention is a steering wheel unit 12 that detects the presence or absence of gripping on the steering wheel 26 by a capacitance sensor 28 provided on the steering wheel 26 of the vehicle 10, and the steering wheel 26. The steering angle change amount detecting unit 62 that detects the steering angle change amount of the steering wheel 26, the frequency characteristic measuring unit 52 that measures the frequency characteristic of the impedance of the capacitance sensor 28 when the steering wheel 26 is gripped, and the above. A failure diagnosis unit 64 for determining the presence or absence of a failure of the capacitance sensor 28 based on the steering angle change amount and the frequency characteristic is provided, and the failure diagnosis unit 64 is detected by the steering angle change amount detection unit 62. The failure diagnosis is performed by changing the sweep time Ts of the sweep frequency range Fr3 when measuring the frequency characteristics according to the amount of change in the steering angle.

According to this configuration, the sweep time Ts of the sweep frequency range Fr3 is changed according to the amount of change in the steering angle corresponding to the rotation speed by the operation of the steering wheel 26 by the driver, and the frequency characteristic of the impedance of the capacitance sensor 28 is changed. Since the measurement is performed and the failure diagnosis is performed, the detection accuracy of the open failure and the short failure of the steering wheel 26 can be improved.

In this case, it is preferable that the failure diagnosis unit 64 compares the amount of change in the steering angle with the threshold value and shortens the sweep time Ts when the steering angle change amount is equal to or more than the threshold value.

As a result, when the amount of change in the steering angle due to the operation of the steering wheel 26 is larger than the threshold value, the sweep time for measuring the frequency characteristic of the impedance is shortened, so that the failure can be detected accurately.

Further, it is preferable that the failure diagnosis unit 64 determines whether the capacitance sensor 28 is in an open failure state, a short failure state, or a normal state based on the measured resonance frequency fr on the frequency characteristics.

As a result, the capacitance of the capacitor connected in series with the capacitance sensor 28 differs between a short-circuit failure, an open failure, and a normal state. Therefore, whether the capacitance sensor 28 is in the open failure state depending on the resonance frequency fr. It is possible to accurately (highly accurately determine) whether it is a short-circuit failure state or a normal state.

Further, when the steering wheel 26 is in a normal state, the presence or absence of gripping on the steering wheel 26 may be detected based on the resonance frequency fr of the measurement result of the frequency characteristic measuring unit 52.

According to this, the gripping state (grasping / non-grasping) of the driver can be accurately determined.

The present invention is not limited to the above-described embodiment, and based on the contents described in this specification, for example, the resonance frequency fr for each vehicle 10 is measured in advance, and the resonance frequencies fshort, fg, fng, and impedance are measured. It goes without saying that various configurations can be adopted, such as measuring the impedance of the above by sweeping each resonance frequency fr to a pinpoint by the frequency characteristic measuring unit 52.

10 ... Vehicle 12 ... Steering wheel unit 14 ... Automatic driving device 16 ... Traveling device 18 ... Notification device 20 ... Driving force device 22 ... Steering device 24 ... Braking device 26 ... Steering wheel 28 ... Capacitive sensors 28a, 28c ... Electrodes 28b ... Dielectric 28d, 28e ... Terminal 30 ... Steering angle sensor 34 ... Power switch 40 ... Rim 41 ... Core metal 42 ... Resin 44 ... Leather 46 ... Current meter 48 ... AC voltage generator 49 ... Hand (human body)
50 ... Grip determination device 52 ... Frequency characteristic measurement unit 54 ... Arithmetic device 56 ... Storage device 58 ... Timer 60 ... Grip detection unit 62 ... Steering angle change amount detection unit 64 ... Failure diagnosis unit 66 ... Notification instruction unit 110 ... Diagnostic map

Claims (4)

A steering wheel unit that detects the presence or absence of gripping on the steering wheel by a capacitance sensor provided on the steering wheel of the vehicle.
A steering angle change amount detecting unit that detects the steering angle change amount of the steering wheel, and a steering angle change amount detecting unit.
A frequency characteristic measuring unit that measures the frequency characteristic of the impedance of the capacitance sensor when the steering wheel is gripped, and a frequency characteristic measuring unit.
A failure diagnosis unit for determining the presence or absence of a failure of the capacitance sensor based on the steering angle change amount and the frequency characteristic is provided.
The failure diagnosis unit
The failure diagnosis is performed by changing the sweep time in the sweep frequency range when measuring the frequency characteristics according to the rudder angle change amount detected by the rudder angle change amount detection unit.
Steering wheel unit. The steering wheel unit according to claim 1.
The failure diagnosis unit
The amount of change in the rudder angle is compared with the threshold value, and if it is equal to or greater than the threshold value, the sweep time is shortened.
Steering wheel unit. The steering wheel unit according to claim 1 or 2.
The failure diagnosis unit
Based on the measured resonance frequency on the frequency characteristic, it is determined whether the capacitance sensor is in an open failure state, a short failure state, or a normal state.
Steering wheel unit. The steering wheel unit according to any one of claims 1 to 3.
When the steering wheel is in a normal state, the presence or absence of gripping on the steering wheel is detected based on the resonance frequency of the measurement result of the frequency characteristic measuring unit.
Steering wheel unit.

Images