Abstract:
The purpose of the present invention is to provide an inertial force detection device that can more accurately detect faults in a temperature sensor. Provided is an inertial force detection device configured so that in a state where an oscillating body is made to oscillate in a first direction, the amount of displacement when the oscillating body is displaced in a second direction due to the generation of angular velocity is detected as angular velocity, wherein the inertial force detection device has a means for performing control so that the oscillating body enters a state of resonance in the first direction, a temperature detection means for detecting temperature, and a means for detecting faults in the temperature detection means, and outputs a plurality of signals, which indicate the fault detection results of the three means, continuously from a single signal wire.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an inertial force detecting apparatus for detection inertial force acting at the time of automobile travel. 
       BACKGROUND ART 
       [0002]    An exemplary inertial force detection apparatus is an angular velocity sensor that is used as an anti-skid control device to ensure safety at automobile travel in order to detect angular velocity attributed to skids or turnings on compacted snow roads or frozen roads. In order to enhance angular velocity detection accuracy, a temperature characteristic output by a sensor is corrected, in some cases, by using a temperature sensor. Unfortunately, however, when the temperature sensor has a failure, erroneous correction might be performed at temperature characteristic correction. This erroneous correction would lead to the output of a value from the angular velocity sensor, that is different from the original output value. In order to prevent this, detection of a failure in the temperature sensor is needed, and techniques as described in PTL 1 and 2 are disclosed as methods for detecting a failure in the temperature sensor attached to the angular velocity sensor. PTL 1 describes an exemplary case where a sensor failure is determined by comparing a change amount of resonant frequency from a reference value with a change amount of the temperature sensor output from a reference value. PTL 2 describes an exemplary case where temperature sensors are provided on an angular velocity detection element and on a control unit, and the sensor outputs are compared with each other to determine a temperature sensor failure. 
       CITATION LIST 
     Patent Literatures 
       [0003]    PTL 1: JP 2009-508130 A 
         [0004]    PTL 2: JP 2000-105125 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    Nevertheless, in order to ensure normality of operation of each of these failure detection functions, it would be necessary to provide a function of detecting a failure in the failure detection function itself, in addition to the above-described techniques. 
         [0006]    The present invention is intended to provide an inertial force detection apparatus capable of detecting a failure in a temperature sensor with higher accuracy. 
       Solution to Problem 
       [0007]    An inertial force detection apparatus configured to detect a displacement amount when an oscillating body oscillating in a first direction is displaced in a second direction due to generation of angular velocity, as an angular velocity, includes a unit configured to control the oscillating body to be in a resonant state in the first direction, a temperature detection unit configured to detect temperature, and a unit configured to detect a failure in the temperature detection unit. The inertial force detection apparatus sequentially outputs a plurality of signals indicating failure detection results of the three units, from one signal line. 
       Advantageous Effects of Invention 
       [0008]    It is possible to provide an inertial force detection apparatus capable of detecting failures in a temperature sensor with higher accuracy. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a block diagram of a sensor control circuit in an exemplary embodiment. 
           [0010]      FIG. 2  is a diagram illustrating a frequency-amplitude characteristic in an oscillation axis direction and a detection axis direction. 
           [0011]      FIG. 3  is a timing chart of an oscillation frequency adjustment unit in an exemplary embodiment. 
           [0012]      FIG. 4  is a diagram illustrating a resonant frequency-temperature characteristic of an oscillator in a drive direction. 
           [0013]      FIG. 5  is a diagram illustrating an output-temperature characteristic of a drive frequency adjustment unit. 
           [0014]      FIG. 6  is a diagram illustrating an output-temperature characteristic of a temperature determination value generator in an exemplary embodiment. 
           [0015]      FIG. 7  is a time chart illustrating output of a temperature sensor failure detection unit in an exemplary embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0016]    Hereinafter, exemplary embodiments of the present invention will be described with reference to  FIGS. 1 to 7 . 
         [0017]      FIG. 1  is a block diagram of a control circuit of an angular velocity sensor in a first exemplary embodiment. An angular velocity detection element  101  in the present exemplary embodiment includes an oscillator  102 , a fixed electrode (external force applying unit)  103 , electrodes (displacement detection units)  104  and  105 , fixed electrodes (displacement detection units)  106  and  107 . The oscillator  102  has a predetermined mass and oscillates with a predetermined oscillation frequency (resonant frequency) fd in an oscillation axis direction. The fixed electrode  103  activates electrostatic force for adjusting oscillation amplitude and oscillation frequency of the oscillator  102  in the oscillation direction. The electrodes  104  and  105  detect oscillation amplitude and oscillation frequency of the oscillator  102  by a change in the capacitance. The fixed electrodes  106  and  107  detect displacement generated in the oscillator  102  in a direction perpendicular to the oscillation axis by the Coriolis force generated by application of angular velocity, by a change in the capacitance. 
         [0018]    Also provided are a capacitance detector  110 , an AD converter  145 , a synchronous detector  131 , and an oscillation frequency adjustment unit  151 . The capacitance detector  110  detects displacement acting on the detection element  101  in the oscillation axis direction by detecting a difference between the capacitance across the detection element  101  and the fixed electrode  104 , and the capacitance across the detection element  101  and the fixed electrode  105 . The AD converter  145  converts output of the capacitance detector  110  into a digital signal. The synchronous detector  131  is formed with a multiplier  113  that performs synchronous detection with a detection signal ø 1 . The oscillation frequency adjustment unit  151  is formed with an integrator  118  that adds output of the synchronous detector  131  for every fixed cycle. 
         [0019]    Also provided are a capacitance detector  112 , an AD converter  146 , a multiplier  115 , and an angular velocity detection unit  153 . The capacitance detector  112  detects displacement acting on the oscillator  102  by the Coriolis force by detecting a difference between the capacitance across the oscillator  102  and the fixed electrode  106 , and the capacitance across the oscillator  102  and the fixed electrode  107 , and converts the displacement into a digital signal. The AD converter  146  converts output from the capacitance detector  112  into a digital signal. The multiplier  115  is provided for performing synchronous detection with the detection signal col. The angular velocity detection unit  153  is formed with an integrator  120  that adds output of the multiplier  115  for every fixed cycle. 
         [0020]    Also provided are a voltage controlled oscillator (VCO)  122  and a clock generator  123 . The VCO  122  outputs a basic clock of a frequency in accordance with the output of the integrator  118 . The clock generator  123  performs frequency-division of the output of the VCO  122  and outputs a drive signal and the detection signal col. 
         [0021]    Also provided is a characteristic correction  139  configured to correct the output of the angular velocity sensor in accordance with the output of the temperature sensor  137 . 
         [0022]    Also provided is a temperature sensor failure detection unit  161 . The temperature sensor failure detection unit  161  includes a half-cycle integration  162 , a resonance determination value register  163 , a temperature determination value generator  164 , a switch  165 , a switch  166 , and a comparison unit  167 . The half-cycle integration  162  performs integration of synchronous detection output for ½ cycle with the synchronous detector  131 . The resonance determination value register  163  is provided for detecting, from output of the synchronous detector  131 , that the angular velocity detection element  101  is oscillating at the resonant frequency. The temperature determination value generator  164  is provided to detect a failure in the temperature sensor  137 . The switch  165  performs changeover between failure detection target signals. The switch  166  performs changeover between failure determination values. The comparison unit  167  determines a failure by comparing the failure detection target signal with the determination value. 
         [0023]    The configuration also includes a communication unit  143  configured to output angular velocity detection results from the angular velocity characteristic correction unit  139  and failure detection results from the temperature sensor failure detection unit  161 , to an external device. 
         [0024]    Next, operation will be described.  FIG. 2  illustrates a frequency characteristic of the angular velocity detection element  101  in an oscillation axis direction and a detection axis direction. From  FIG. 2 , it is understandable that the oscillation amplitude in the oscillation axis direction indicates a steep attenuation characteristic having a resonant frequency at a peak, and that in a case where oscillation occurs at a frequency other than the resonant frequency, the amplitude becomes extremely small, and that, at the same time, the oscillation amplitude in the detection axis direction also attenuates. The frequency of the displacement oscillation in the detection axis direction, caused by generation of the angular velocity, substantially matches the oscillation frequency in the oscillation axis direction. Accordingly, in order to increase the oscillation amplitude in the detection axis direction, it is necessary to constantly drive the oscillation axis direction at the resonant frequency. 
         [0025]    For the above-described reasons, the oscillation frequency adjustment unit  151  automatically adjusts the frequency of the drive signal all the time such that the oscillation of the oscillator  102  in the oscillation axis direction is in the resonance state. Displacement of the angular velocity detection element  101  by the drive signal is detected by the fixed electrodes  104  and  105  and is input into the capacitance detector  110 . Oscillation displacement in the oscillation axis direction is detected by performing synchronous detection at the synchronous detector  131  onto the oscillator displacement signal obtained via the capacitance detector  110  and the AD converter  145 . Next, the signal obtained at the synchronous detector  131  is integrated on the integrator  118 . 
         [0026]      FIG. 3  illustrates a time chart of the oscillation frequency adjustment unit  151 . The drive signal and the displacement signal have a characteristic that their phases are mutually different by 90° when they are in the resonance states, namely, fv (drive signal frequency)=fd (resonant frequency in oscillation axis direction). Accordingly, at synchronous detection performed onto the displacement signal with the detection signal ø 1 , when the synchronous detection output for one cycle turns out to be zero by canceling out, this indicates the resonance state. At this time, the output from a one-cycle integration  162  is a value that is close to zero. The output of the integrator  118  inside the oscillation frequency adjustment unit  151  is converged to a fixed value. The signal obtained by the integrator  118  is output to the VCO  122 . The clock generator  123  generates a drive signal. As illustrated in the time chart in  FIG. 3 , the basic clock output by the VCO controls such that the frequency is a fixed integral multiple in synchronization with the drive signal all the time. 
         [0027]    Next, in order to determine a value set on a drive amplitude register  125  as amplitude, multiplication with the output of the clock generator  123  is performed at the multiplier  124  to generate a drive signal. 
         [0028]      FIG. 4  illustrates an exemplary resonant frequency characteristic of the oscillator  101  with respect to the temperature change. As illustrated in  FIG. 4 , the resonant frequency of the oscillator  101  has a characteristic to be lowered as the temperature increases. Therefore, the oscillation frequency adjustment unit  151  controls such that the drive signal to be supplied to the oscillator  101  is constantly at a resonant frequency, and thus, as illustrated in  FIG. 5 , the output of the oscillation frequency adjustment unit  151  has a temperature characteristic similar to the one illustrated in  FIG. 4 . 
         [0029]      FIG. 6  is a diagram illustrating operation of the temperature determination value generation  164 . Since the output of the temperature sensor  137  changes in accordance with the temperature, in a case where failure detection is performed based on the output value, it would be necessary to change a threshold for determination in accordance with the temperature. Determination thresholds A. and B are obtained by an expression illustrated in  FIG. 6  using an output value i of the oscillation frequency adjustment unit  151 , illustrated in  FIG. 5 . As one implementation method, it is possible to pre-store coefficients k, ka, and kb in a register and memory and calculate the values by calculation using a multiplier and an adder. When the temperature sensor output is in a range of the determination thresholds A and B, a signal “0” indicating normality is output. When the output is out of range, a signal “1” indicating a failure is output. 
         [0030]      FIG. 7  is diagram illustrating a time chart of the output signal, for illustrating operation of the temperature sensor failure detection unit  161  of the present invention. After a reset signal is input from an external device, input on the “0” side is selected for each of the switches  165  and  166 . After the reset input, “1” indicating non-resonance is output as a failure detection signal during the time until the oscillator  101  is changed from the non-resonance state to the resonance state, for example, for a period of 1 ms. Thereafter, when it is normal, the state is changed to the output of “0” indicating resonance. Determination whether it is non-resonance or resonance is performed by comparison determination using the output of the one-cycle integrator  162  and the determination threshold stored in the resonance determination value register  163 , at the comparison unit  167 . As illustrated in the output of the synchronous detection  113  on the timing chart of the oscillation frequency adjustment unit in  FIG. 3 , when integration is performed, at non-resonance, onto the synchronous detection  113  output by the one-cycle integrator  162  for a drive signal one-cycle period, the result would be a large positive value. In contrast, when it is at resonance, the phases for the drive signal and the displacement signal are mutually shifted by 90°, and thus, the output of the one-cycle integrator  162  is a value extremely close to zero. Accordingly, by storing values close to zero, for example, values ranging from −5 to +5, into the resonance determination value register  163  as resonance determination threshold, it is possible to determine whether the oscillator  1010  is in the resonance state. As a result, it is possible to confirm that a signal indicating resonance of the oscillator  101  is input from the oscillation frequency adjustment unit  151  into the temperature determination value generator  164 , and that wiring inside a circuit that forms the comparison unit  165  and the communication unit  143  is not fixed to one of “0” and “1”. Thereafter, switch changeover signal is switched to “1” and failure detection results for the temperature sensor are output. Changeover of the switches  165  and  166  can be performed with a method of performing changeover by the communication from an external device, or with a method of automatically performing changeover after a fixed time period after reset signal input has elapsed, that is the time taken for the operation that the oscillator  101  changes from the non-resonance state to the resonance state, or more. As described above, by initially executing detection of a failure in the temperature sensor failure detection unit  161  and confirming whether it is normal, and subsequently executing detection of a failure in the temperature sensor  137 , failure detection accuracy of the temperature sensor  137  would be enhanced. As a result, in a case where an output signal line of the temperature sensor failure detection unit  161  is constantly fixed to “0” output due to a failure regardless of the existence of failure in the temperature sensor, by the fact that “1” indicating the non-resonance state of the oscillator  101  has not been output, it is possible to detect, at that point, that failure detection by the temperature sensor is impossible. 
       REFERENCE SIGNS LIST 
       [0031]      101  angular velocity detection element 
         [0032]      102  oscillator 
         [0033]      103 ,  104 ,  105 ,  106 ,  107  fixed electrode 
         [0034]      110 ,  112  capacitance detector 
         [0035]      113 ,  115 ,  124  multiplier 
         [0036]      118 ,  120  integrator 
         [0037]      122  voltage control oscillator 
         [0038]      123  clock generator 
         [0039]      125  drive amplitude register 
         [0040]      137  temperature sensor 
         [0041]      138 ,  145 ,  146  AD converter 
         [0042]      139  angular velocity characteristic correction unit 
         [0043]      143  communication unit 
         [0044]      147  DA converter 
         [0045]      151  oscillation frequency adjustment unit 
         [0046]      153  angular velocity detection unit 
         [0047]      154  servo signal generator 
         [0048]      161  temperature sensor failure detection unit 
         [0049]      162  one-cycle integrator 
         [0050]      163  resonance determination value register 
         [0051]      164  temperature determination value generator 
         [0052]      165 ,  166  changeover switch 
         [0053]      167  comparison unit