Electrostatic occupant detection system

The present application is based on and claims priority to Japanese Patent Applications No. 2010-109576 filed on May 11, 2010, and No. 2011-058204 filed on Mar. 16, 2011, the contents of which are incorporated in their entirety herein by reference.

1. Field of the Invention

The present invention relates generally to automobiles and other vehicles, and, more particularly, to an electrostatic occupant detection system.

2. Description of the Related Art

JP-A-11-271463 discloses an electrostatic occupant detection system that includes a mat-shaped electrostatic sensor and an occupant detection electronic control unit (ECU). The electrostatic sensor is supplied with a sine wave from the occupant detection ECU and generates an electric field between a main electrode disposed in a vehicle seat and a vehicle body. The electrostatic sensor outputs an electrical current or a voltage to the occupant detection ECU in accordance with a change in the electric field, and the occupant detection ECU determines the presence of an occupant based on the electrical current or the voltage. When the electrostatic occupant detection system performs a self diagnosis, in general, the occupant detection ECU stops supplying the sine wave to the electrostatic sensor and switches to a predetermined direct current (DC) voltage or the ground level only at an initial check during vehicle start-up.

The above-described occupant detection ECU supplies only the sine wave to the electrostatic sensor during the normal operation. It is preferred to correct variation in a detected capacitance of the electrostatic sensor based on the diagnosis of the electrostatic occupant detection system and a change in an environmental temperature even during the normal operation. In such a case, the sine wave supplied to the electrostatic sensor is stopped once and is switched to the predetermined DC voltage or the ground level. If the sine wave is rapidly switched to the DC voltage or the ground level, noise may be generated, the noise may adversely affect other electronic devices including a radio, and radio noise may be output.

In view of the foregoing problems, it is an object of the present invention to provide an electrostatic occupant detection system that can reduce noise having frequencies other than a sine wave frequency when a sine wave supplied from an electronic control unit to an electrostatic sensor is changed to a predetermined DC voltage or a ground level.

An electrostatic occupant detection system includes an electrostatic sensor and an electronic control unit. The electrostatic sensor includes an electrode disposed in a vehicle seat. The electrostatic sensor outputs an electrical current or a voltage as an output value in accordance with an intensity of an electric field or a change in an electric filed generated by the electrode. The electronic control unit outputs a sine wave for generating the electric field and determines the presence of an occupant based on the output value. The electronic control unit is switchable between an occupant determination state where the electronic control unit outputs a sine wave having a constant amplitude and a diagnosis state where the electronic control unit maintains a voltage of the electrostatic sensor at a constant level. The electronic control unit gradually changes at least one of an amplitude and a frequency of the sine wave in at least one of a case where the electronic control unit switches from the occupant determination state to the diagnosis state and a case where the electronic control unit switches from the diagnosis state to the occupant determination state.

In the electrostatic occupant detection system, the electronic control unit gradually changes at least one of the amplitude or the frequency of the sine wave in at least one of the case where the electronic control unit switches from the occupant determination state to the diagnosis state and the case where the electronic control unit switches from the diagnosis state to the occupant determination state. Thus, the electrostatic occupant detection system can reduce noise having frequencies other the frequency of the sine wave and can restrict an adverse effect of noise on other electronic devices including a radio.

Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. In the drawings:

FIG. 1 is a block diagram showing an electrostatic occupant detection system according to a first embodiment of the present invention;

FIG. 2 is an equivalent circuit diagram of a detected object;

FIG. 3 is a diagram showing a signal phase of electrodes in an electrostatic sensor;

FIG. 4A is a waveform diagram showing a sine wave applied from an occupant detection ECU to a detected object;

FIG. 4B is a waveform diagram showing a signal for sampling a real term R;

FIG. 4C is a waveform diagram showing a signal for sampling an imaginary term C;

FIG. 4D is a waveform diagram showing an output signal at a time when a potential difference generated at a current detection resistor is sampled based on the signal shown in FIG. 4B ;

FIG. 4E is a diagram showing an output signal at a time when a potential difference generated at the current detection resistor is sampled based on the signal shown in FIG. 4C ;

FIG. 5 is a waveform diagram showing a signal output from an occupant detection ECU in the electrostatic occupant detection system according to the first embodiment;

FIG. 6 is a flowchart showing a process performed by the occupant detection ECU in the electrostatic occupant detection system according to the first embodiment;

FIG. 7 is a block diagram showing an electrostatic occupant detection system according to a second embodiment of the present invention;

FIG. 8 is a waveform diagram showing a signal output from an occupant detection ECU in the electrostatic occupant detection system according to the second embodiment;

FIG. 9 is a flowchart showing a process performed by the occupant detection ECU in the electrostatic occupant detection system according to the second embodiment;

FIG. 10 is a block diagram showing an electrostatic occupant detection system according to a third embodiment of the present invention;

FIG. 11 is a waveform diagram showing a signal output from an occupant detection ECU in the electrostatic occupant detection system according to the third embodiment;

FIG. 12 is a flowchart showing a part of a process performed by the occupant detection ECU in the electrostatic occupant detection system according to the third embodiment;

FIG. 13 is a flowchart showing another part of the process performed by the occupant detection ECU in the electrostatic occupant detection system according to the third embodiment;

FIG. 14 is a block diagram showing an electrostatic occupant detection system according to a fourth embodiment of the present invention;

FIG. 15 is a waveform diagram showing a signal output from an occupant detection ECU in the electrostatic occupant detection system according to the fourth embodiment;

FIG. 16 is a flowchart showing a process performed by the occupant detection ECU in the electrostatic occupant detection system according to the fourth embodiment;

FIG. 17 is a block diagram showing an electrostatic occupant detection system according to a fifth embodiment of the present invention;

FIG. 18A is a diagram showing a change of a sine wave at a time when the electrostatic occupant detection system according to the fifth embodiment switches from an occupant determination state to a diagnosis state and FIG. 18B is a diagram showing a change of the sine wave at a time when the electrostatic occupant detection system according to the fifth embodiment switches from the diagnosis state to the occupant determination state;

FIG. 19A is a diagram showing a change of a sine wave when an electrostatic occupant detection system according to a first modification of the fifth embodiment switches from an occupant determination state to a diagnosis state and FIG. 19B is a diagram showing a change of the sine wave when the electrostatic occupant detection system according to the first modification of the fifth embodiment switches from the diagnosis state to the occupant determination state; and

FIG. 20A is a diagram showing a change of a sine wave when an electrostatic occupant detection system according to a second modification of the fifth embodiment switches from an occupant determination state to a diagnosis state and FIG. 20B is a diagram showing a change of the sine wave when the electrostatic occupant detection system according to the second modification of the fifth embodiment switches from the diagnosis state to the occupant determination state.

First Embodiment

An electrostatic occupant detection system 10 according to a first embodiment of the present invention will be described with reference to FIG. 1 . The electrostatic occupant detection system 10 includes an occupant detection ECU 11 and an electrostatic sensor apparatus 12 .

The electrostatic sensor apparatus 12 is disposed in a vehicle seat 33 . The vehicle seat 33 includes a seat cushion 34 on which an occupant sits and a seat back 35 against which an occupant leans. In a bottom portion of the seat cushion 34 , a seat-cushion frame 34 a is disposed. In the seat back 35 , a seat-back frame 35 a is disposed. The seat-cushion frame 34 a and the seat-back frame 35 a are electrically coupled with a vehicle body (vehicle ground) 32 . In the seat cushion 34 , an electrostatic sensor 31 is also disposed. The electrostatic sensor 31 is located opposite the seat-cushion frame 34 a at a distance from the seat-cushion frame 34 a . The electrostatic sensor 31 is coupled with the occupant detection ECU 11 through a connector wiring 36 such as a wire harness. The electrostatic sensor 31 includes a main electrode, a sub electrode, and a guard electrode.

The occupant detection ECU 11 includes a sine wave control portion 51 . The sine wave control portion 51 can function as a sine wave attenuating portion and a sine wave amplifying portion. The sine wave control portion 51 includes a sine wave generator 53 and an amplitude voltage control portion 54 . The amplitude voltage control portion 54 includes a DC voltage output portion 56 , a linear waveform output portion 57 , a switch element 58 , and a switching control portion 59 . The switch element 58 is a two-input one-output switch. An equivalent circuit of a detected object such as a human body and liquid detected by the electrostatic sensor apparatus 12 can be expressed by a parallel circuit of a resistance RMX (real term: conductance) and a capacitance CMX (imaginary term: susceptance) as shown in FIG. 2 . Thus, rather than detecting a capacitance, the electrostatic sensor apparatus 12 detects an impedance Z having a real term R and an imaginary term C as shown in FIG. 3 . The occupant detection ECU 11 applies a sine wave VSG 1 shown in FIG. 4A to the detected object. When the sine wave VSG 1 is applied, the switching control portion 59 outputs a control signal to the switch element 58 so that the switch element 58 connects the DC voltage output portion 56 and the sine wave generator 53 . The above-described state is an occupant determination state. The sine wave generator 53 generates the sine wave VSG 1 and outputs the sine wave VSG 1 to the electrostatic sensor 31 . The sine wave VSG 1 has an amplitude corresponding to a constant DC voltage and has a predetermined constant frequency.

When the sine wave VSG 1 is applied to the electrostatic sensor 31 , a potential difference is generated in a current detection resistor 9 in the occupant detection ECU 11 in accordance with an impedance of a detected object. If the impedance of the detected object includes only a real term R, the potential difference generated at the current detection resistor 9 does not include a phase-lead element with respect to the sine wave VSG 1 . Thus, when the potential difference generated at the current detection resistor 9 is sampled based on a real-term sampling signal shown in FIG. 4B , which is in the same phase as the sine wave VSG 1 , an output signal depending on the magnitude of only the real term R can be obtained as shown in FIG. 4D .

If the impedance of the detected object includes only an imaginary term C, the potential difference generated at the current detection resistor 9 includes a phase-lead element with respect to the sine wave VSG 1 . Thus, when the potential difference generated at the current detection resistor 9 is sampled based on an imaginary-term sampling signal shown in FIG. 4C , whose phase leads by 90 degrees from the sine wave VSG 1 , an output signal depending on the magnitude of only the imaginary term C can be obtained as shown in FIG. 4E . An impedance of an actual detected object includes a real term R and an imaginary term C. Thus, an impedance Z having various phases is measured, and the occupant detection ECU 11 determines the detected object based on the impedance Z.

The occupant detection ECU 11 receives the impedance Z of the detected object from the electrostatic sensor apparatus 12 when the electrostatic occupant detection system 10 is in a normal operation after vehicle start-up. The occupant detection ECU 11 determines that the vehicle seat 33 is vacant, the vehicle seat 33 is equipped with a child restraint system (CRS), or the vehicle seat 33 is occupied by an adult based on the impedance Z.

The linear waveform output portion 57 selectively outputs a first linear waveform LW 1 and a second linear waveform LW 2 . The first linear waveform LW 1 inclines in a decreasing direction from a level of the DC voltage output from the DC voltage output portion 56 to a zero level at a constant inclination angle. The second linear waveform LW 2 inclines in an increasing direction from the zero level to the level of the DC voltage at a constant inclination angle.

The switching control portion 59 outputs a control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs one of the first linear waveform LW 1 and the second linear waveform LW 2 . The switching control portion 59 also outputs a control signal to the switch element 58 so that the switch element 58 is switched between a DC side and a linear side. When the switch element 58 is switched to the DC side, the switch element 58 connects the sine wave generator 53 with the DC voltage output portion 56 . When the switch element 58 is switched to the linear side, the switch element 58 connects the sine wave generator 53 with the linear waveform output portion 57 .

When the occupant detection ECU 11 switches from the occupant determination state to a diagnosis state, the switching control portion 59 outputs a control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs the first linear waveform LW 1 and outputs a control signal to the switch element 58 so that the switch element 58 is switched from the DC side to the linear side. While the electrostatic occupant detection system 10 is in the occupant determination state, the sine wave generator 53 outputs the sine wave VSG 1 having a constant amplitude. When the occupant detection ECU 11 switches from the occupant determination state to the diagnosis state, the sine wave generator 53 outputs a sine wave VSG 2 whose amplitude is attenuated from the constant amplitude of the sine wave VSG 1 to zero at a constant inclination angle, that is, at an attenuation rate depending on the first linear waveform LW 1 while a DC bias voltage level of the amplitude is maintained. The DC bias voltage level may be referred to as a center level. Eventually, the sine wave generator 53 outputs a DC voltage DC 1 at the center level of the amplitude of the sine wave VSG 1 .

When the occupant detection ECU 11 switches from the diagnosis state to the occupant determination state, the switching control portion 59 outputs a control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs the second linear waveform LW 2 . Then, the sine wave generator 53 outputs a sine wave VSG 3 whose amplitude is amplified from zero to the constant amplitude of the sine wave VSG 1 at the same inclination angle as the sine wave VSG 2 , that is, at an amplification rate in accordance with the second linear waveform LW 2 while the center level of the amplitude is maintained. After that, the switching control portion 59 outputs a control signal to the switch element 58 so that the switch element 58 is switched from the linear side to the DC side, and the sine wave generator 53 outputs the sine wave VSG 1 .

The attenuation rate of the sine wave VSG 2 and the amplification rate of the sine wave VSG 3 are small so that when the amplitude of the sine wave changes at the attenuation rate or the amplification rate, noise having frequencies other than the sine wave frequency are not output.

Next, a process performed by the occupant detection ECU 11 when the electrostatic occupant detection system 10 makes a diagnosis will be described with reference to FIG. 6 .

At S 1 , the sine wave generator 53 outputs the sine wave VSG 1 having the constant amplitude to the electrostatic sensor 31 when the electrostatic occupant detection system 10 is in the normal operation state after vehicle start-up. The switching control portion 59 outputs the control signal to the switch element 58 so that the switch element 58 is switched to the DC side, and the sine wave generator 53 outputs the sine wave VSG 1 that has the constant amplitude corresponding to the DC voltage output from the DC voltage output portion 56 . The present state is the occupant determination state.

At S 2 , when the occupant detection ECU 11 determines to make a diagnosis, the process proceeds to S 3 . At S 3 , the switching control portion 59 outputs a control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs the first linear waveform LW 1 . At S 4 , the switching control portion 59 outputs the control signal to the switch element 58 so that the switch element 58 is switched to the linear side. Then, at S 5 , the sine wave generator 53 outputs the sine wave VSG 2 whose amplitude is attenuated from the constant amplitude of the sine wave VSG 1 to zero at the constant inclination angle, that is, at the attenuation rate depending on the first linear waveform LW 1 while the center level of the amplitude is maintained.

Eventually, the sine wave VSG 2 becomes the DC voltage DC 1 at the center level of the amplitude of the sine wave VSG 1 . Thus, at S 6 , the sine wave generator 53 outputs the DC voltage DC 1 . The present state is the diagnosis state. At S 7 , the occupant detection ECU 11 executes a diagnosis process. At S 8 , the switching control portion 59 outputs the control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs the second linear waveform LW 2 . Then, at S 9 , the sine wave generator 53 outputs the sine wave VSG 3 whose amplitude is amplified from zero to the constant amplitude of the sine wave VSG 1 at the constant inclination angle, that is, at the amplification rate depending on the second linear waveform LW 2 while the center level of the amplitude is maintained. At S 10 , the occupant detection ECU 11 determines whether the amplitude of the sine wave VSG 3 is the same level as the constant amplitude of the sine wave VSG 1 . If so, at S 11 , the switching control portion 59 outputs the control signal to the switch element 58 so that the switch element 58 is switched to the DC side. Then, the process returns to S 1 and the sine wave generator 53 outputs the sine wave VSG 1 having the constant amplitude. In other words, the electrostatic occupant detection system 10 returns to the occupant determination state.

As described above, the electrostatic occupant detection system 10 includes the electrostatic sensor 31 and the occupant detection ECU 11 . The electrostatic sensor 31 includes the electrodes disposed in the vehicle seat 33 and the electrodes generate a weak electric field. The electrostatic sensor 31 outputs an electrical current or a voltage in accordance with an intensity of the weak electric field or a change in the weak electric field. The occupant detection ECU 11 outputs the sine wave for generating the weak electric field to the electrostatic sensor 31 and determines an occupant based on the voltage or the current output from the electrostatic sensor 31 . When the occupant detection ECU 11 switches from the occupant determination state to the diagnosis state, the sine wave control portion 51 in the occupant detection ECU 11 gradually attenuates the amplitude of the sine wave to zero while maintaining the center level of the amplitude. In contrast, when the occupant detection ECU 11 switches from the diagnosis state to the occupant determination state, the sine wave control portion 51 gradually amplifies the amplitude of the sine wave to the constant amplitude of the sine wave in the occupant determination state while maintaining the center level of the amplitude. Because the amplitude of the sine wave is gradually attenuated or amplified, noise having frequencies other than the sine wave frequency can be reduced. Thus, an adverse effect of noise on other electronic devices including a radio can be restricted.

The sine wave control portion 51 includes the DC voltage output portion 56 , the linear waveform output portion 57 , the switch element 58 , the switching control portion 59 , and the sine wave generator 53 . The DC voltage output portion 56 outputs the constant DC voltage. The linear waveform output portion 57 selectively outputs the first linear waveform LW 1 and the second linear waveform LW 2 . The first linear waveform LW 1 inclines from the level of the DC voltage output from the DC voltage output portion 56 to zero at a constant decreasing rate. The second linear waveform LW 2 inclines from zero to the level of the DC voltage at a constant increasing rate that is reverse of the decreasing rate. The switch element 58 selects one of the output voltage of the DC voltage output portion 56 and the output waveform of the linear waveform output portion 57 . The switching control portion 59 outputs the control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs the first linear waveform LW 1 or the second linear wave form LW 2 . The switching control portion 59 also outputs the control signal to the switch element 58 so that the switch element 58 is switched to the DC side or the linear side. The sine wave generator 53 outputs one of the sine wave VSG 1 having the constant amplitude depending on the DC voltage output from the DC voltage output portion 56 , the sine wave VSG 2 whose amplitude is attenuated from the constant amplitude of the sine wave VSG 1 to zero at the attenuation rate depending on the first linear waveform LW 1 while the center level of the amplitude is maintained, the DC voltage DC 1 at the center level of the amplitude of the sine wave VSG 1 , and the sine wave VSG 3 whose amplitude is amplified from zero to the constant amplitude at the amplification rate depending on the second linear waveform LW 2 while the center level of the amplitude is maintained. In other words, the switching control portion 59 outputs the control signals to the linear waveform output portion 57 and the switch element 58 so that the sine wave generator 53 outputs the sine wave VSG 1 , the sine wave VSG 2 , the DC voltage DC 1 at the center level, the sine wave VSG 3 , and the sine wave VSG 1 in this order.

Therefore, in a case where the electrostatic occupant detection system 10 makes a diagnosis, firstly, the sine wave generator 53 outputs the sine wave VSG 1 having the constant amplitude. Next, the sine wave generator 53 outputs the sine wave VSG 2 whose amplitude is gradually attenuated from the constant amplitude to the center level of the constant amplitude. Then, the sine wave generator 53 outputs the DC voltage DC 1 at the center level of the constant amplitude. The occupant detection ECU 11 executes the diagnosis process with the DC voltage DC 1 . Because the sine wave is gradually attenuated into the DC voltage, noise having frequencies other than the sine wave frequency can be reduced. When the sine wave VSG 3 is amplified from the center level to the constant amplitude of the sine wave VSG 1 , the sine wave VSG 3 is gradually amplified based on the second linear waveform LW 2 . Thus, noise having frequencies other than the sine wave frequency can be reduced. Thus, the electrostatic occupant detection system 10 can restrict generation of noise when the sine wave supplied from the occupant detection ECU 11 to the electrostatic sensor 31 is changed to the DC voltage. Therefore, an adverse effect of noise on other electronic devices including a radio can be restricted.

Second Embodiment

An electrostatic occupant detection system 10 a according to a second embodiment of the present invention will be described with reference to FIG. 7 . The electrostatic occupant detection system 10 a includes an occupant detection ECU 11 a and the electrostatic sensor apparatus 12 .

The occupant detection ECU 11 a includes a sine wave control portion 51 a . The sine wave control portion 51 a includes a sine wave generator 53 a , an amplitude voltage control portion 54 a , and a clock generator 60 .

The clock generator 60 generates a predetermined-period clock signal and outputs the clock signal to the amplitude voltage control portion 54 a and the sine wave generator 53 a.

The sine wave generator 53 a outputs one of a sine wave VSG 4 , a sine wave VSG 5 , a DC voltage DC 2 , and a sine wave VSG 6 as shown in FIG. 8 . First, the sine wave generator 53 a outputs the sine wave VSG 4 having a constant amplitude at a frequency depending on the clock signal. Next, the sine wave generator 53 a outputs the sine wave VSG 5 whose amplitude is attenuated for an N-period of the sine wave VSG 4 from the constant amplitude to zero by 1/N of the constant amplitude per one period while the center level of the amplitude is maintained (“N” is a natural number). Then, the sine wave generator 53 a outputs the DC voltage DC 2 at the center level. After that, the sine wave generator 53 a outputs the VSG 6 whose amplitude is amplified for the N-period of the sine wave VSG 4 from zero to the constant amplitude by 1/N of the constant amplitude per one period while the center level of the amplitude is maintained.

The amplitude voltage control portion 54 a controls the amplitude of the sine waves VSG 4 -VSG 6 output from the sine wave generator 53 a . When the sine wave generator 53 a outputs the sine wave VSG 4 having the constant amplitude, the amplitude voltage control portion 54 a controls the sine wave generator 53 so that the sine wave generator 53 outputs the sine wave VSG 5 whose amplitude is attenuated for the N-period from the constant amplitude of the sine wave VSG 4 to zero by 1/N per one period. When the sine wave generator 53 a outputs the DC voltage DC 2 , the amplitude voltage control portion 54 a controls the sine wave generator 53 a so that the sine wave generator 53 outputs the sine wave VSG 6 whose amplitude is amplified for the N-period from zero to the constant amplitude of the sine wave VSG 4 amplitude by 1/N per one period.

Next, a process performed by the occupant detection ECU 11 a when the electrostatic occupant detection system 10 a makes a diagnosis will be described with reference to FIG. 9 .

At S 11 , the sine wave generator 53 a outputs the sine wave VSG 4 having the constant amplitude to the electrostatic sensor 31 at a clock frequency when the electrostatic occupant detection system 10 a is in a normal operation state after vehicle start-up.

At S 12 , when the occupant detection ECU 11 a determines to make a diagnosis, the process proceeds to S 13 . At S 13 , the amplitude voltage control portion 54 a controls the sine wave generator 53 a so that the amplitude of the signal output from the sine wave generator 53 a is attenuated for the N-period from the constant amplitude of the sine wave VSG 4 to the center level of the sine wave VSG 4 by 1/N per one period. Thus, the sine wave generator 53 a outputs the sine wave VSG 5 whose amplitude is attenuated from the constant amplitude to zero by 1/N per one period while the center level of the amplitude is maintained. At S 14 , the sine wave generator 53 a outputs the DC voltage DC 2 at the center level.

In the present state, the occupant detection ECU 11 a executes a diagnosis process at S 15 . After that, the amplitude voltage control portion 54 a controls the sine wave generator 53 a so that the amplitude of the signal output from the sine wave generator 53 a is attenuated for the N-period from the center level, that is, the DC voltage DC 2 to the constant amplitude of the sine wave VSG 4 by 1/N per one period. Thus, the sine wave generator 53 a outputs the sine wave VSG 5 whose amplitude is attenuated by 1/N per one period at the frequency depending on the clock signal.

At S 17 , when the amplitude of the sine wave VSG 6 becomes the same level as the constant amplitude of the sine wave VSG 4 , the process returns to S 11 , and the sine wave generator 53 a outputs the sine wave VSG 4 having the constant amplitude.

As described above, the electrostatic occupant detection system 10 a includes the occupant detection ECU 11 a including the sine wave control portion 51 a . First, the sine wave control portion 51 a outputs the sine wave VSG 4 at the constant amplitude. Next, the amplitude of the sine wave is attenuated for the N-period from the constant amplitude to the center level of the sine wave VSG 4 by 1/N per one period. Then, the sine wave control portion 51 a outputs the DC voltage at the center level. After that, the amplitude of the DC voltage is amplified for the N-period from the center level to the constant amplitude of the sine wave VSG 4 by 1/N per one period.

Thus, when the electrostatic occupant detection system 10 a makes the diagnosis after vehicle start-up, the amplitude of the sine wave is attenuated for the N-period from the constant amplitude to the center level by 1/N per one period. The diagnosis is performed with the DC voltage at the center level. Because the amplitude of the sine wave is gradually attenuated from the constant amplitude to the center level, noise having frequencies other than the sine wave frequency can be reduced. Also when the amplitude is amplified from the center level to the constant amplitude, the amplitude is increased by 1/N per period. Thus, noise having frequency other than the sine wave frequency can be reduced. Thus, the electrostatic occupant detection system 10 a can restrict generation of noise when the sine wave supplied from the occupant detection ECU 11 a to the electrostatic sensor 31 is changed to the DC voltage. Therefore, an adverse effect of noise on other electronic devices including a radio can be restricted.

Third Embodiment

An electrostatic occupant detection system 10 b according to a third embodiment of the present invention will be described with reference to FIG. 10 . The electrostatic occupant detection system 10 b includes an occupant detection ECU 11 b and the electrostatic sensor apparatus 12 .

The occupant detection ECU 11 b includes the sine wave control portion 51 described in the first embodiment, a linear waveform output portion 62 , a DC voltage output portion 63 , a switch element 65 , and an output switching control portion 66 . The switch element 65 is a three-input one-output switch.

The switch element 65 has three input terminals, and the input terminals are coupled with output terminals of the sine wave generator 53 , the linear waveform output portion 62 , and the DC voltage output portion 63 , respectively. The switch element 65 selects an output signal from one of the output terminals based on a control signal from the output switching control portion 66 and outputs the selected signal to the electrostatic sensor 31 through the connector wiring 36 .

The linear waveform output portion 62 selectively outputs a third linear waveform LW 3 and a fourth linear waveform LW 4 by a slew rate control. The third linear waveform inclines in a decreasing direction from the center level of the sine wave VSG 1 , to which the amplitude of the sine wave VSG 2 is attenuated, to a predetermined level L 3 at a constant inclination angle. The fourth linear waveform LW 4 inclines in an increasing direction from the predetermined level L 3 to the center level at a constant inclination angle. The third linear waveform LW 3 and the fourth linear waveform LW 4 are line symmetry

The DC voltage output portion 63 outputs a DC voltage DC 3 at the predetermined level L 3 .

The output switching control portion 66 outputs a control signal to the linear waveform output portion 62 so that linear waveform output portion 62 outputs the third linear waveform LW 3 or the fourth linear waveform LW 4 . Furthermore, the output switching control portion 66 outputs a control signal to the switch element 65 so that the switch element 65 selects the output signal of the sine wave generator 53 . As shown in FIG. 11 , the sine wave VSG 1 and the sine wave VSG 2 are output in order. When the amplitude of the sine wave VSG 2 is attenuated to the center level, the linear waveform output portion 62 outputs the third linear waveform LW 3 , and the switch element 65 selects the third linear waveform LW 3 . When the third linear waveform LW 3 decreases to the predetermined level L 3 , the switch element 65 selects the DC voltage DC 3 output from the DC voltage output portion 63 . After a predetermined time, the linear waveform output portion 62 outputs the fourth linear waveform LW 4 , and the switch element 65 selects the fourth linear waveform LW 4 . When the fourth linear waveform LW 4 increases to the center level, the switch element 65 selects the output signal from the sine wave generator 53 . Accordingly, the sine wave VSG 3 and the sine wave VSG 1 are output in order.

Next, a process performed by the occupant detection ECU 11 b when the electrostatic occupant detection system 10 b makes a diagnosis will be described with reference to FIG. 12 and FIG. 13 .

At S 21 , the sine wave generator 53 outputs the sine wave VSG 1 having the constant amplitude to the electrostatic sensor 31 when the electrostatic occupant detection system 10 b is in a normal operation state after vehicle start-up.

At S 22 , when the occupant detection ECU 11 b determines to make a diagnosis, the process proceeds to S 23 . At S 23 , the switching control portion 59 outputs a control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs the first linear waveform LW 1 . In addition, the switching control portion 59 controls the switch element 58 so that the switch element 58 selects the first linear waveform LW 1 . Accordingly, the sine wave generator 53 outputs the sine wave VSG 2 attenuated at the constant inclination angle.

At S 24 , when the occupant detection ECU 11 b determines that the sine wave VSG 2 becomes the center level of the amplitude of the sine wave VSG 1 , the process proceeds to S 25 . At S 25 , the occupant detection ECU 11 b performs a slew rate control where the voltage decreases from the center level to the predetermined level L 3 based on the third linear waveform LW 3 . The output switching control portion 66 outputs a control signal to the linear waveform output portion 62 and the switch element 65 so that the linear waveform output portion 62 outputs the third linear waveform LW 3 and the switch element 65 selects the third linear waveform LW 3 .

At S 26 , the output switching control portion 66 outputs a control signal to the switch element 65 so that the switch element 65 selects the DC voltage DC 3 output from the DC voltage output portion 63 . Accordingly, the DC voltage DC 3 at the predetermined level L 3 is output to the electrostatic sensor 31 . In the present state, the occupant detection ECU 11 b executes a diagnosis process at S 27 .

At S 28 shown in FIG. 13 , the occupant detection ECU 11 b performs the slew rate control for increasing the voltage from the predetermined level L 3 to the center level. In this process, the output switching control portion 66 outputs control signals to the linear waveform output portion 62 and the switch element 65 so that the linear waveform output portion 62 outputs the fourth linear waveform LW 4 and the switch element 65 selects the fourth linear waveform LW 4 . At S 29 , the occupant detection ECU 11 b determines whether the voltage becomes the center level. If so, at S 30 , the switching control portion 59 outputs a control signal to the linear waveform output portion 57 so that the linear waveform output portion 57 outputs the second linear waveform LW 2 . Then, the sine wave generator 53 outputs the sine wave VSG 3 whose amplitude is amplified from the center level at the amplification rate depending on the second linear waveform LW 2 . The output switching control portion 66 outputs a control signal to the switch element 65 so that the switch element 65 selects the sine wave VSG 3 . Accordingly, the occupant detection ECU 11 b outputs the sine wave VSG 3 whose amplitude is amplified at the constant inclination angle.

At S 17 , when the amplitude of the sine wave VSG 3 becomes the same level as the constant amplitude of the sine wave VSG 1 , the process returns to S 21 , and the switch element 65 selects the sine wave VSG 4 having the constant amplitude and output from the sine wave generator 53 through the DC voltage output portion 56 and the switch element 58 .

Thus, the electrostatic occupant detection system 10 b according to the present embodiment includes the occupant detection ECU 11 b including a DC shift control portion. The DC shift control portion decreases the output voltage from the center level of the amplitude of the sine wave attenuated by the sine wave control portion 51 to the predetermined level by the slew rate control, outputs the DC voltage at the predetermined level, and increases the voltage to the center level by the slew rate control. The DC shift control portion includes the linear waveform output portion 62 , the DC voltage output portion 63 , the switch element 65 , and the output switching control portion 66 . The DC shift control portion and the sine wave control portion 51 provide a diagnosis state transition portion and an occupant determination state transition portion.

In the electrostatic occupant detection system 10 b according to the present embodiment, after the sine wave is attenuated to the center level in such a manner that noise are not generated, the voltage is decreased to the predetermined level by the slew rate control and the voltage is increased from the predetermined level to the center level by the slew rate control. Thus, the voltage is changed between the center level and the predetermined level while generation of noise is restricted. Thus, the electrostatic occupant detection system 10 b can restrict generation of noise when the sine wave supplied from the occupant detection ECU 11 b to the electrostatic sensor 31 is changed to the DC voltage at the predetermined level.

In the above-described example, the voltage is decreased to the predetermined level L 3 , as an example. The voltage may also be decreased from the center level to the ground level. In the present case, after the voltage is decreased to the earth level by a linear wave from the linear waveform output portion 62 , the ground level is maintained for a predetermined time, and then, the voltage is increased to the center level. Thus, the DC voltage output portion 63 may be ground. Instead of the sine wave control portion 51 shown in FIG. 10 , the sine wave control portion 51 a shown in FIG. 7 may also be used.

Fourth Embodiment

An electrostatic occupant detection system 10 c according to a fourth embodiment of the present invention will be described with reference to FIG. 14 . The electrostatic occupant detection system 10 b includes an occupant detection ECU 11 c and the electrostatic sensor apparatus 12 . The occupant detection ECU 11 c includes a sine wave control portion 51 c.

The sine wave control portion 51 c includes the DC voltage output portion 56 and the sine wave generator 53 described in the first embodiment, the linear waveform output portion 62 described in the third embodiment, a switching control portion 67 , and a multiplication portion 68 .

The switching control portion 67 controls the linear waveform output portion 62 so that the linear waveform output portion 62 outputs the third linear waveform LW 3 or the fourth linear waveform LW 4 to the multiplication portion 68 or stops outputting the waveform.

The multiplication portion 68 multiplies the sine wave VSG 1 having the constant amplitude and output from the sine wave generator 53 and the third linear waveform LW 3 or the fourth linear waveform LW 4 output from the linear waveform output portion 62 and outputs an attenuated sine wave VSG 8 or an amplified sine wave VSG 9 obtained by the multiplication to the electrostatic sensor 31 through the connector wiring 36 . While the linear waveform output portion 62 stops outputting the waveform, the multiplication portion 68 does not performs a multiplication process and outputs the sine wave VSG 1 from the sine wave generator 53 .

The attenuated sine wave VSG 8 is obtained by multiplying the sine wave VSG 1 and the third linear waveform LW 3 . The attenuated sine wave VSG 8 is attenuated from the constant amplitude of the sine wave VSG 1 while decreasing to the predetermined level L 3 in a constant inclination angle depending on the third linear waveform LW 3 .

The amplified sine wave VSG 9 is obtained by multiplying the sine wave VSG 1 and the fourth linear waveform LW 4 . The amplified sine wave VSG 9 is amplified to the constant amplitude of the sine wave VSG 1 while increasing from the predetermined level L 3 in a constant inclination angle depending on the fourth linear waveform LW 4 .

Next, a process performed by the occupant detection ECU 11 c when the electrostatic occupant detection system 10 c makes a diagnosis will be described with reference to FIG. 16 .

At S 41 , the sine wave generator 53 outputs the sine wave VSG 1 having the constant amplitude to the electrostatic sensor 31 when the electrostatic occupant detection system 10 c is in a normal operation state after engine start-up and the linear waveform output portion 62 does not output the waveform.

At S 42 , when the occupant detection ECU 11 c determines to make a diagnosis, the process proceeds to S 43 . At S 43 , the switching control portion 67 outputs the control signal to the linear waveform output portion 62 so that the linear waveform output portion 62 outputs the third linear waveform LW 3 . At S 44 , the multiplication portion 68 multiplies the sine wave VSG 1 and the third waveform LW 3 and outputs the attenuated sine wave VSG 8 .

At S 45 , when the attenuated sine wave VSG 8 decreases to the predetermined level L 3 , the DC voltage DC 3 at the predetermined level L 3 is output to the electrostatic sensor 31 . In the present state, the occupant detection ECU 11 c executes a diagnosis process at S 46 .

At S 47 , the switching control portion 67 outputs the control signal to the linear waveform output portion 62 so that the linear waveform output portion 62 outputs the fourth linear waveform LW 4 . At S 48 , the multiplication portion 68 multiplies the sine wave VSG 1 and the third waveform LW 4 and outputs the amplified sine wave VSG 9 .

At S 49 , when the occupant detection ECU 11 c determines that the amplitude of the amplified sine wave VSG 9 becomes the constant amplitude of the sine wave VSG 1 , the process returns to S 41 , and the sine wave VSG 1 having the constant amplitude is output.

As described above, the electrostatic occupant detection system 10 c includes the occupant detection ECU 11 c including the sine wave control portion 51 c . The sine wave control portion 51 c multiplies the sine wave VSG 1 having the constant amplitude by the third linear waveform LW 3 or the fourth linear waveform LW 4 . The third linear waveform LW 3 decreases from the amplitude level of the sine wave VSG 1 to the predetermined level L 3 at the constant inclination angle. The fourth linear waveform LW 4 increases from the predetermined level L 3 to the amplitude level of the sine wave VSG 1 at the constant inclination angle.

Thus, when the sine wave VSG 1 having the constant amplitude is multiplied by the third linear waveform LW 3 to provide the attenuated sine wave VSG 8 , the center level of the sine wave VSG 8 decreases to the predetermined level L 3 while being attenuated constantly. At the predetermined level L 3 , the attenuation of the sine wave VSG 8 ends and the DC voltage DC 3 at the predetermined level L 3 is output. Because the sine wave VSG 8 is gradually attenuated when the output signal is changed from the sine wave VSG 1 to the DC voltage DC 3 at the predetermined level, noise having frequencies other than the sine wave frequency can be reduced. When the sine wave VSG 1 is multiplied by the fourth linear waveform LW 4 to provide the attenuated sine wave VSG 9 , the center level of the sine wave VSG 9 increases from the predetermined level L 3 to the center level of the sine wave VSG 1 while being amplified constantly. Also in the present case, because the sine wave VSG 9 is gradually amplified, noise having frequencies other than the sine wave frequency can be reduced. Thus, the electrostatic occupant detection system 10 c can restrict generation of noise when the sine wave supplied from the occupant detection ECU 11 c to the electrostatic sensor 31 is changed to the DC voltage. Therefore, adverse effects of noise on other electronic devices including a radio can be restricted.

Fifth Embodiment

In each of the above-described embodiments, the amplitude of the sine wave is changed when the occupant detection ECU 11 switches between the occupant determination state and the diagnosis state. In an electrostatic occupant detection system 10 d according to a fifth embodiment of the present invention, a frequency of a sine wave is changed. The electrostatic occupant detection system 10 d will be described with reference to FIG. 17 . The electrostatic occupant detection system 10 d includes an occupant detection ECU 11 d including a sine wave control portion 51 d . The sine wave control portion 51 d includes a clock generator 70 in addition to the configuration of the sine wave control portion 51 described in the first embodiment.

The clock generator 70 generates a clock signal and can change a clock frequency of the clock signal. The clock signal generated by the clock generator 70 is input to the sine wave generator 53 . The sine wave generator 53 generates a sine wave having a frequency depending on the clock signal. Thus, by controlling the frequency of the clock signal generated by the clock generator 70 , the frequency of the sine wave generated by the sine wave generator 53 can be controlled.

The clock generator 70 receives a diagnosis state transition signal that orders a transition from the occupant determination state to the diagnosis state and an occupant determination state transition signal that orders a transition from the diagnosis state to the occupant determination state. The signals may be generated when a predetermined diagnosis time arrives and the signals may be generated based on an operation by a user.

When the clock generator 70 receives the diagnosis state transition signal, the clock generator 70 gradually decreases the frequency of the clock signal from the frequency in the occupant determination state to a predetermined frequency with a predetermined time. When the clock generator 70 receives the occupant determination state transition signal, the clock generator 70 gradually increases the frequency of the clock signal from the frequency in the diagnosis state to the frequency in the occupant determination state with a predetermined period.

FIG. 18A is a diagram showing a change of the sine wave when the electrostatic occupant detection system 10 d switches from the occupant determination state to the diagnosis state and FIG. 18B is a diagram showing a change of the sine wave when the electrostatic occupant detection system 10 d switches from the diagnosis state to the occupant determination state. As shown in FIG. 18A , the frequency is constant before time t 0 when the diagnosis state transition signal is input. After the time t 0 , the frequency is gradually decreased while a center level of the amplitude is maintained. As shown in FIG. 18B , after the time t 1 when the occupant determination state transition state is input, the frequency is gradually increased while the center level of the amplitude is maintained. Time t 2 in FIG. 18B indicates a time when the frequency becomes the frequency in the occupant determination state.

(First Modification of Fifth Embodiment)

The electrostatic occupant detection system 10 d according to the fifth embodiment changes the frequency while maintaining the center level of the amplitude of the sine wave, as an example. As shown in FIG. 19A and FIG. 19B , the electrostatic occupant detection system 10 d may also change the center level of the amplitude while changing the frequency. FIG. 19A is a diagram showing a change of the sine wave when the electrostatic occupant detection system 10 d switches from the occupant determination state to the diagnosis state in the first modification of the fifth embodiment and FIG. 18B is a diagram showing a change of the sine wave when the electrostatic occupant detection system 10 d switches from the diagnosis state to the occupant determination state in the first modification of the fifth embodiment.

(Second Modification of Fifth Embodiment)

Alternatively, both the frequency and the amplitude may also be changed. FIG. 20A is a diagram showing a change of the sine wave when the electrostatic occupant detection system 10 d switches from the occupant determination state to the diagnosis state in the second modification of the fifth embodiment and FIG. 20B is a diagram showing a change of the sine wave when the electrostatic occupant detection system 10 d switches from the diagnosis state to the occupant determination state in the second modification of the fifth embodiment.

Other Embodiments

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

In each of the above-described embodiments, the amplitude or the frequency is gradually changed in both a case where the occupant detection ECU switches from the occupant determination state to the diagnosis state and a case where the occupant detection ECU switches from the diagnosis state to the occupant determination state. However, not limited to the above-described embodiments, the amplitude or the frequency may also be gradually changed only at one of the transitions and the amplitude or the frequency may also be changed rapidly at the other one of the transitions.