Abstract:
A tire state detection device capable of detecting a tire state with high accuracy. This tire state detection device ( 100 ) is a device for detecting the tire state of a pneumatic tire ( 200 ) affixed to a wheel and comprises a vibration input unit ( 110 ) for inputting predetermined vibration to the tire ( 200 ), a frequency information acquisition unit ( 120 ) for acquiring frequency information relating to the tire ( 200 ) when the predetermined vibration is inputted, and a tire state estimation unit ( 130 ) for extracting the resonance frequency and anti-resonance frequency of the tire ( 200 ) from the acquired frequency information and calculating, from the extracted resonance frequency and anti-resonance frequency of the tire ( 200 ), an outer moment of inertia and a spring constant when the tire ( 200 ) is modeled using the outer moment of inertia, an inner moment of inertia, and the spring constant of elastic force acting therebetween.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a tire condition detection apparatus and tire condition detection method for detecting a tire condition. 
       BACKGROUND ART 
       [0002]    In recent years, demands for improvements in running stability and improvements in fuel consumption are being made with respect to vehicles such as automobiles and motorcycles, and research and development have been actively pursued in the field of elemental technologies that achieve such improvements. 
         [0003]    Tire condition may be mentioned as one factor that significantly affects running stability and fuel consumption. In the case of a pneumatic tire, wear or a fall in the tire air pressure (hereinafter referred to as “tire internal pressure”) occurs as the result of running over a long time period or the like. Such kinds of changes in the tire condition cause a deterioration in fuel consumption and running stability. Accordingly, it is important to continuously detect and monitor the condition of tires. 
         [0004]    However, when it is attempted to directly detect the tire condition by mounting a sensor that detects the tire internal pressure inside the tire or the like, although the tire condition can be detected with a high degree of precision, costs are incurred. In addition, communication processing occurs in order to notify the driver of the detection result obtained by the sensor. Therefore, in order to allow the sensor to operate while maintaining the sensor battery over a long time period, the intervals at which the sensor sends detection results to the driver must be made large. Therefore, it is difficult to ascertain the tire condition when needed. 
         [0005]    Technology that indirectly detects a change in the tire internal pressure based on a resonance frequency of the tire is described, for example, in Non-Patent Literature (hereinafter, abbreviated as NPL) 1. The technology described in NPL 1 is based, firstly, on a relationship whereby the resonance frequency of a tire depends on the tire internal pressure, and the technology assumes a dynamic model of a tire and designs a disturbance observer based on the dynamic model. The dynamic model of the tire includes a moment of inertia of an outer portion of the tire (hereinafter referred to as “outer moment of inertia”), a moment of inertia of an inner portion of the tire (hereinafter referred to as “inner moment of inertia”), and a torsional spring connecting these. The technology described in NPL 1 calculates a torsional spring constant based on a resonance phenomenon generated in the tire accompanying running, and detects a change in the tire internal pressure based on a change in the torsional spring constant on the basis of the proportional relationship between the torsional spring constant of the tire and the tire internal pressure. 
         [0006]    Further, technology that indirectly detects a tire condition based on a correlation between a tire driving force and a rotation angle of a tire is described, for example, in Patent Literature (hereinafter, abbreviated as PTL) 1. The technology described in PTL 1 detects, with respect to an electrically driven vehicle that is driven by an in-wheel motor, a correlation between a tire driving force and a rotation angle of the tire in a stopped state as a tire stiffness characteristic value. An in-wheel motor is a motor that applies a direct driving force to a tire, and has been the subject of research and development in recent years. The technology described in PTL 1 determines that the tire internal pressure has fallen if the tire stiffness characteristic value does not satisfy a criterion. 
         [0007]    According to these conventional technologies, a tire condition can be indirectly detected. 
       CITATION LIST 
     Patent Literature 
     PTL 1 
       [0000]    
       
         Japanese Patent Application Laid-Open No. 2006-151282 
       
     
       Non-Patent Literature 
     NPL 1 
       [0000]    
       
         Takaji Umeno, “Tire Pressure Estimation Using Wheel Speed Sensors”, Toyota Central R&amp;D Labs., Inc. R&amp;D Review, December 1997, Vol. 32 No. 4 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    However, with the technology described in NPL 1, the accuracy of the disturbance observer decreases as an outer moment of inertia changes due to wear of the tire or the like, and thus the accuracy of a torsional spring constant that is calculated also decreases. Further, with the technology described in PTL 1, because the tire stiffness characteristic value is a value that is affected by changes in the thickness or elasticity of the tire, when wear of the tire proceeds, it is not possible to determine with a high degree of precision whether or not the tire internal pressure satisfies the criterion. That is, with the conventional technologies, there is the problem that a tire condition can not be detected with a high degree of precision. 
         [0011]    It is an object of the present invention to provide a tire condition detection apparatus and tire condition detection method that enable a tire condition to be detected with a high degree of precision. 
       Solution to Problem 
       [0012]    A tire condition detection apparatus of the present invention detects a tire condition of a pneumatic tire fixed to a wheel, and has: a vibration input section that inputs predetermined vibration to the tire; a frequency information acquisition section that acquires frequency information of the tire when the predetermined vibration is input; and a tire condition estimation section that extracts a resonance frequency and an anti-resonance frequency of the tire from the acquired frequency information, and calculates an outer moment of inertia and a spring constant when the tire is modeled using the outer moment of inertia, an inner moment of inertia, and the spring constant of elastic force acting therebetween, from the extracted tire resonance frequency and anti-resonance frequency. 
         [0013]    A tire condition detection method of the present invention detects a tire condition of a pneumatic tire fixed to a wheel, and has: a step of inputting predetermined vibration to the tire; a step of acquiring frequency information of the tire when the predetermined vibration is input; a step of extracting a resonance frequency and an anti-resonance frequency of the tire from the acquired frequency information; and a step of calculating an outer moment of inertia and a spring constant when the tire is modeled using the outer moment of inertia, an inner moment of inertia, and the spring constant of elastic force acting therebetween, from the extracted tire resonance frequency and anti-resonance frequency. 
       Advantageous Effects of Invention 
       [0014]    According to the present invention, since a resonance frequency and an anti-resonance frequency of a tire are extracted, a torsional spring constant of a dynamic model and an outer moment of inertia of a tire can be calculated on a case-by-case basis, and the tire condition can be detected with a high degree of precision. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 1 of the present invention; 
           [0016]      FIG. 2  is a drawing showing a dynamic model of a tire in Embodiment 1; 
           [0017]      FIG. 3  is a flowchart showing an example of the operation of the tire condition detection apparatus according to Embodiment 1; 
           [0018]      FIG. 4  is a drawing showing an example of the frequency characteristic of a tire in Embodiment 1; 
           [0019]      FIG. 5  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 2 of the present invention; 
           [0020]      FIG. 6  is a flowchart showing an example of the operation of the tire condition detection apparatus according to Embodiment 2; 
           [0021]      FIG. 7  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 3 of the present invention; 
           [0022]      FIG. 8  is a flowchart showing an example of the operation of the tire condition detection apparatus according to Embodiment 3; 
           [0023]      FIG. 9  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 4 of the present invention; 
           [0024]      FIG. 10  is a flowchart showing an example of the operation of the tire condition detection apparatus according to 
           [0025]    Embodiment 4; 
           [0026]      FIG. 11  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 5 of the present invention; 
           [0027]      FIG. 12  is a control block diagram showing an example of the configuration of a motor drive system in Embodiment 5; 
           [0028]      FIG. 13  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 6 of the present invention; 
           [0029]      FIG. 14  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 7 of the present invention; 
           [0030]      FIG. 15  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 8 of the present invention; and 
           [0031]      FIG. 16  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 9 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]    Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
       [0033]    First, the configuration of a tire condition detection apparatus according to Embodiment 1 will be described. 
         [0034]      FIG. 1  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 1. 
         [0035]    As shown in  FIG. 1 , tire condition detection apparatus  100  is an apparatus connected to tire  200  fixed to a wheel (hereinafter referred to simply as “tire”). Tire condition detection apparatus  100  has vibration input section  110 , frequency information acquisition section  120 , and tire condition estimation section  130 . Tire  200  is connected to this vehicle in a stable and fixed manner, and includes a gas such as air, nitrogen, or the like, between itself and the wheel. 
         [0036]    Vibration input section  110  inputs predetermined vibration to tire  200 . In order for the anti-resonance frequency of tire  200  to be easily extracted by frequency information acquisition section  120  described later herein, the predetermined vibration is minute back-and-forth vibration applied in the direction of rotation of tire  200 , and is defined by torque magnitude and vibrational frequency. Hereinafter, this predetermined vibration is called “anti-resonance vibration”, and torque that is applied to a rim of tire  200  by anti-resonance vibration is called “anti-resonance torque”. 
         [0037]    Vibration input section  110  may apply vibration by controlling the drive system of tire  200  electrically or mechanically, or may apply vibration mechanically directly to tire  200  separately from the drive system. If vibration is directly applied mechanically, vibration input section  110  can be, for example, an electromagnetic vibrator, or an unbalanced-mass vibrator in which an eccentric mass is attached to a small motor, that is attached to the wheel of tire  200  or the like. Vibration input section  110  can also be, for example, a damper oil-pressure control apparatus, such as active suspension. 
         [0038]    Frequency information acquisition section  120  acquires tire  200  frequency information when anti-resonance vibration is input by vibration input section  110 . Frequency information is information for extracting the tire  200  resonance frequency and anti-resonance frequency described later herein. Frequency information includes the rotational angular velocity of tire  200 , for example. Also, when rim  220  of tire  200  is driven by a motor, frequency information is an inverter control voltage for the motor drive current flowing in a motor-drive vehicle. In the case of rotational angular velocity, for example, an encoder (not shown) can be installed and can acquire a rotation angle of the rim, and rotational angular velocity can be acquired by performing temporal differentiation on rim rotation angles. The encoder is constituted, for example, by a rotor that rotates in synchrony with tire  200 , and a sensor that detects a rotation angle of the rotor and converts the rotation angle into an electrical signal. The encoder may be, for example, an optical encoder such as an incremental encoder or absolute encoder, or an electromagnetic encoder comprising a Hall element or the like. 
         [0039]    Tire condition estimation section  130  extracts the resonance frequency and the anti-resonance frequency of tire  200  from frequency information acquired by frequency information acquisition section  120 , and estimates the condition of tire  200 . Then tire condition detection apparatus  100  estimates the condition of tire  200  using a dynamic model of tire  200 . Specifically, tire condition estimation section  130  calculates a torsional spring constant and an outer moment of inertia of a dynamic model of tire  200  each time detection of the condition of tire  200  is performed. Then tire condition estimation section  130  estimates the condition of tire  200  based on the calculated torsional spring constant and outer moment of inertia. 
         [0040]      FIG. 2  is a drawing showing a dynamic model of tire  200  used by tire condition estimation section  130 . 
         [0041]    As shown in  FIG. 2 , tire  200  dynamic model  210  includes a moment of inertia of tire  200  rim  220 , a moment of inertia of tire  200  tread  230 , spring (torsional spring)  240  connecting these, and damper  250 . That is to say, tire  200  dynamic model  210  models mechanical vibration generated in tire  200  as a torsional vibration phenomenon. 
         [0042]    Dynamic model  210  is represented using the following variables.
   J 1 : Moment of inertia of rim  220  (inner moment of inertia)   J 2 : Moment of inertia of tread  230  (outer moment of inertia)   K: Torsional spring constant of tire  200     D: Equivalent viscosity coefficient of tire  200     T e : Output torque applied to rim  220  from vehicle side   T d : Disturbance torque applied to tread  230  from road surface due to rolling of tire  200     ω 1 : Rotational angular velocity of rim  220     ω 2 : Rotational angular velocity of tread  230     
 
         [0051]    Here, θ s  denotes the rotation angle difference between rim  220  and tread  230 . Moment of inertia J 1  and equivalent viscosity coefficient D, are parameters that can be regarded as fixed values. Outer moment of inertia J 2  is a parameter that can change due to wear of tire  200  and the like. Torsional spring constant K is a parameter representing the elasticity of the side-surface rubber part of tire  200  that connects rim  220  and tread  230 , and is dependent upon air pressure (tire internal pressure). Output torque T e  is a control object. Disturbance torque T d  is an unknown parameter. Rotational angular velocity ω 1  is a parameter that can be measured with a high degree of precision. 
         [0052]    Although not shown in the drawings, tire condition detection apparatus  100  has, for example, a CPU (Central Processing Unit), a storage medium such as RAM (Random Access Memory), and so forth. In this case some or all of the above-described functional sections are implemented by having the CPU execute a control program. Tire condition detection apparatus  100 , for example, takes the form of an ECU (Electric Control Unit) that is installed in a vehicle and is connected to the drive system of tire  200 . 
         [0053]    Since such tire condition detection apparatus  100  extracts the resonance frequency and the anti-resonance frequency of tire  200 , it can detect the condition of tire  200  by acquiring the torsional spring constant and the outer moment of inertia of tire  200  with a high degree of precision. That is to say, even if the outer moment of inertia changes due to wear or replacement of tire  200  or the like, tire condition detection apparatus  100  can perform detection of the condition of tire  200  based on a value of the outer moment of inertia after the change. Therefore, tire condition detection apparatus  100  can detect the tire condition with a high degree of precision. 
         [0054]    The operation of tire condition detection apparatus  100  will now be described. 
         [0055]      FIG. 3  is a flowchart showing an example of the operation of tire condition detection apparatus  100  according to Embodiment 1. 
         [0056]    First, each time timing for estimating the tire condition (hereinafter referred to as “estimation execution timing”) arrives, vibration input section  110  inputs predetermined vibration to tire  200  (S 1090 ). Estimation execution timing may be while a vehicle that is a detection object is running or is stopped, and may be while the vehicle is running at a constant speed or running at an inconstant speed. Also, estimation execution timing may arrive with predetermined periodicity, or may be when a predetermined operation such as depression of a switch is performed by the driver. 
         [0057]    Then frequency information acquisition section  120  acquires tire  200  frequency information, and outputs the acquired frequency information to tire condition estimation section  130  (S 1100 ). Tire condition estimation section  130  extracts the resonance frequency and anti-resonance frequency of tire  200  from the input frequency information (S 1120 ). Then tire condition estimation section  130  calculates outer moment of inertia J 2  and torsional spring constant K of tire  200  based on the extracted resonance frequency and anti-resonance frequency. 
         [0058]    Here, a method is described whereby tire condition estimation section  130  detects a resonance frequency and an anti-resonance frequency, and calculates outer moment of inertia J 2  and torsional spring constant K based on the resonance frequency and the anti-resonance frequency. Here, a case is described in which rim  220  rotational angular velocity ω 1  is input to tire condition estimation section  130  as frequency information. 
         [0059]    Frequency information is, for example, a rotational angular velocity or a frequency of a control voltage for driving a motor. 
         [0060]      FIG. 4  is a drawing showing an example of the frequency characteristic of tire  200 . The horizontal axis indicates frequency f, and the vertical axis indicates the power spectral density of rim  220  rotational angular velocity ω 1  and the phase difference between output torque T e  and rotational angular velocity ω 1 . 
         [0061]    Tire condition estimation section  130  can obtain spectral waveform  311  shown in  FIG. 4  by performing frequency analysis such as an FFT (Fast Fourier Transform) on rim  220  rotational angular velocity ω 1 . Spectral waveform  311  indicates a frequency characteristic of tire  200 . 
         [0062]    As shown in  FIG. 4 , in spectral waveform  311 , a resonance frequency that is affected by tire internal pressure appears at frequency  312  as coupled resonance of suspension back-and-forth vibration and tire  200  torsional spring resonance. Details of this phenomenon are given in NPL, for example, and therefore a description thereof is omitted here. 
         [0063]    In spectral waveform  311 , on the one hand a peak of a sharp crest appears at above-mentioned frequency  312 , which is the resonance frequency of tire  200 , and on the other hand a peak of a sharp trough appears at anti-resonance frequency  314 . 
         [0064]    Therefore, tire condition estimation section  130  acquires resonance frequency  312  and anti-resonance frequency  314  by detecting the peak positions in spectral waveform  311 . At these peak positions, there is a property that phase difference  315  is inverted by 180 degrees. Therefore, tire condition estimation section  130  can acquire resonance frequency  312  and anti-resonance frequency  314  by identifying a frequency at which phase difference  315  is inverted from 90 degrees to −90 degrees and a frequency at which phase difference  315  is inverted from −90 degrees to 90 degrees. 
         [0065]    In  FIG. 4 , although, in addition to frequency  312 , frequency  313  is another frequency at which there is a peak, it is empirically known that a frequency of a peak that appears from around 10 Hz to 15 Hz is a frequency that depends on the specifications of the tire. Consequently, resonance frequency  312  can also be detected by suppressing the level of frequency  313  by means of a filter. 
         [0066]    Incidentally, an equation of state shown in equation 1 below is derived from the dynamic model shown in  FIG. 2 . 
         [0000]    
       
         
           
             
               
                 
                   
                       
                   
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         [0067]    Further, an input-output transfer function matrix shown in equation 2 below is obtained from equation 1. 
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         [0068]    Equivalent viscosity coefficient D of tire  200  can be set to 0 since equivalent viscosity coefficient D does not affect the resonance frequency and anti-resonance frequency of the torsional spring. Therefore, transfer function G 11 (s) from output torque T e  applied to rim  220  to rotational angular velocity ω 1  of rim  220  can be expressed with equation 3 below. Here, s denotes a Laplace operator, ω c0  denotes a resonance angular frequency, and ω a  denotes an anti-resonance angular frequency. 
         [0000]    
       
         
           
             
               
                 
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         [0069]    From equation 3, resonance frequency f c0  and anti-resonance frequency f a  of tire  200  are derived as shown in equation 4 and equation 5 below. 
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         [0070]    Therefore, tire condition estimation section  130  can calculate torsional spring constant K and outer moment of inertia J 2  by detecting resonance frequency f c0  and anti-resonance frequency f a  and performing processing that solves the simultaneous equations of equation 4 and equation 5. 
         [0071]    Here, frequency information includes a large amount of vibration noise due to vibration components other than a torsional resonance frequency, caused by a coefficient of friction between a tire and the road surface, and irregularities. Anti-resonance frequency f a  is difficult to detect with conventional technology since it tends to be buried in this noise. 
         [0072]    Thus, as explained above, tire condition detection apparatus  100  inputs to tire  200  predetermined vibration that facilitates the extraction of anti-resonance frequency f a  by vibration input section  110 . By this means, tire condition detection apparatus  100  can extract anti-resonance frequency f a  more dependably and with a high degree of precision. 
         [0073]    Tire condition estimation section  130  may also calculate resonance frequency f c0  and anti-resonance frequency f a , and calculate torsional spring constant K and outer moment of inertia J 2 , by means of the method described below, for example. 
         [0074]    Tire condition estimation section  130  may also calculate torsional spring constant K and outer moment of inertia J 2  by another method that utilizes a recursive least-squares estimation method. According to this method, tire condition estimation section  130  estimates unknown parameter vector θ=[θ 1  θ 2 ] T =[ω c0   2  ω a   2 ] T =[4π 2 f c0   2  4π 2 f a   2 ] T . 
         [0075]    In this case, as shown below, equation 8 is derived through equation 7 from the relational expression of equation 6 using equation 3 of transfer function G 11 (s) from output torque T e  to rotational angular velocity ω 1  of the rim that is described above. Then, observable vector ξ 1  and observable output y can be defined as shown in equation 9 and equation 10. 
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                         e 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
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                      
                     6 
                   
                   ) 
                 
               
             
             
               
                 
                   [ 
                   7 
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         J 
                         1 
                       
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                           . 
                         
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                   = 
                   
                     
                       
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                         a 
                         2 
                       
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                   ( 
                   
                     Equation 
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                      
                     7 
                   
                   ) 
                 
               
             
             
               
                 
                   [ 
                   8 
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       [ 
                       
                         
                           
                             
                               θ 
                               1 
                             
                           
                           
                             
                               θ 
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                       ] 
                     
                      
                     
                       [ 
                       
                         
                           
                             
                               
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                       ] 
                     
                   
                   = 
                   
                     
                       
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                         J 
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                           ... 
                         
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                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     8 
                   
                   ) 
                 
               
             
             
               
                 
                   [ 
                   9 
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   ξ 
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               
                                 J 
                                 1 
                               
                                
                               
                                 
                                   ω 
                                   . 
                                 
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                       ] 
                     
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                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     9 
                   
                   ) 
                 
               
             
             
               
                 
                   [ 
                   10 
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   y 
                   = 
                   
                     
                       
                         T 
                         ¨ 
                       
                       e 
                     
                     - 
                     
                       
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                           ... 
                         
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     10 
                   
                   ) 
                 
               
             
           
         
       
     
         [0076]    Tire condition estimation section  130  decides unknown parameter θ using observable parameter ξ and output y so that an evaluation function of equation 11 becomes a minimum. 
         [0000]    
       
         
           
             
               
                 
                   [ 
                   11 
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     J 
                      
                     
                       ( 
                       
                         θ 
                         ^ 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         i 
                         = 
                         0 
                       
                       k 
                     
                      
                     
                       
                         
                           
                             ρ 
                             
                               k 
                               - 
                               i 
                             
                           
                            
                           
                             [ 
                             
                               
                                 
                                   
                                     θ 
                                     ^ 
                                   
                                   T 
                                 
                                 · 
                                 
                                   ξ 
                                    
                                   
                                     ( 
                                     i 
                                     ) 
                                   
                                 
                               
                               - 
                               
                                 y 
                                  
                                 
                                   ( 
                                   i 
                                   ) 
                                 
                               
                             
                             ] 
                           
                         
                         2 
                       
                        
                       
                         ( 
                         
                           0 
                           &lt; 
                           ρ 
                           &lt; 
                           1 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     11 
                   
                   ) 
                 
               
             
           
         
       
     
         [0077]    Then tire condition estimation section  130  can determine unknown parameter θ by means of equation 12 and equation 13 below that are obtained by expanding equation 11. By this means, resonance frequency f c0  and anti-resonance frequency f a  can be calculated. 
         [0000]    
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     [ 
                     12 
                     ] 
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     
                       Γ 
                        
                       
                         ( 
                         k 
                         ) 
                       
                     
                     = 
                     
                       
                         1 
                         ρ 
                       
                        
                       
                         { 
                         
                           
                             Γ 
                              
                             
                               ( 
                               
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                               ) 
                             
                           
                           - 
                           
                             
                               
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                                  
                                 
                                   ( 
                                   
                                     k 
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                                   ) 
                                 
                               
                                
                               
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                                   ( 
                                   k 
                                   ) 
                                 
                               
                                
                               
                                 
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                                   ( 
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                                   ( 
                                   
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                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             
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                               + 
                               
                                 
                                   
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                                     ( 
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                                     ) 
                                   
                                 
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                                       1 
                                     
                                     ) 
                                   
                                 
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                                    
                                   
                                     ( 
                                     k 
                                     ) 
                                   
                                 
                               
                             
                           
                         
                         } 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     12 
                   
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     [ 
                     13 
                     ] 
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       θ 
                       ^ 
                     
                      
                     
                       ( 
                       k 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         θ 
                         ^ 
                       
                        
                       
                         ( 
                         
                           k 
                           - 
                           1 
                         
                         ) 
                       
                     
                     - 
                     
                       
                         
                           
                             Γ 
                              
                             
                               ( 
                               
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                                 1 
                               
                               ) 
                             
                           
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                             ξ 
                              
                             
                               ( 
                               k 
                               ) 
                             
                           
                         
                         
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                           + 
                           
                             
                               
                                 ξ 
                                 T 
                               
                                
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                              
                             
                               Γ 
                                
                               
                                 ( 
                                 
                                   k 
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                              
                             
                               ξ 
                                
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                           
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               
                                 ξ 
                                 T 
                               
                                
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                              
                             
                               
                                 θ 
                                 ^ 
                               
                                
                               
                                 ( 
                                 
                                   k 
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                           
                           - 
                           
                             y 
                              
                             
                               ( 
                               k 
                               ) 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     13 
                   
                   ) 
                 
               
             
           
         
       
     
         [0078]    Then tire condition estimation section  130  calculates torsional spring constant K and outer moment of inertia J 2  of tire  200  using equation 4 and equation 5 based on the calculated resonance frequency f c0  and anti-resonance frequency f a  (S 1130 ). 
         [0079]    Thus, if tire condition detection apparatus  100  can extract only resonance frequency f c0  and anti-resonance frequency f a , it can calculate torsional spring constant K and outer moment of inertia J 2  representing the current condition of tire  200  with a high degree of precision. 
         [0080]    As described above, tire condition detection apparatus  100  according to Embodiment 1 applies predetermined vibration to tire  200 , acquires tire  200  frequency information, and extracts the resonance frequency and the anti-resonance frequency of tire  200  from that frequency information. Then tire condition detection apparatus  100  estimates the condition of tire  200  from the extracted resonance frequency and anti-resonance frequency. By this means, tire condition detection apparatus  100  can calculate a torsional spring constant and an outer moment of inertia of a tire  200  dynamic model on a case-by-case basis, and can detect the condition of tire  200  with a high degree of precision. 
         [0081]    With the technology described in above NPL 1, since the anti-resonance frequency is not used for detection of the condition of tire  200 , input of vibration for facilitating the extraction of the anti-resonance frequency of tire  200  described later herein is not performed. Therefore, with the technology described in NPL 1, an anti-resonance frequency cannot be extracted dependably and with a high degree of precision. 
         [0082]    Further, with respect to the disturbance observer, the technology described in the aforementioned NPL 1 treats inner moment of inertia J 1  and outer moment of inertia J 2  as constants that are determined by the materials and shapes of the wheel and the tire rubber. Therefore, in a case where a value of outer moment of inertia J 2  has changed significantly due to wear or replacement of tire  200 , irrespective of the fact that the tire internal pressure has not changed, the technology described in NPL 1 estimates that torsional spring constant K has changed. 
         [0083]    Therefore, as compared with this kind of technology described in NPL 1, tire condition detection apparatus  100  according to the present invention can perform detection of the condition of tire  200  with a higher degree of precision. 
         [0084]    Although in the above description the predetermined vibration is described as anti-resonance vibration in order to facilitate extraction of the anti-resonance frequency, the predetermined vibration is not limited thereto. The predetermined vibration may be a vibration that includes not only an anti-resonance vibration but also minute back-and-forth vibration (resonance vibration) applied in the direction of rotation of tire  200  so that frequency information acquisition section  120  can easily extract the resonance frequency of tire  200 . In such case, torque applied to the rim of tire  200  may be taken as “resonance and anti-resonance torque.” 
         [0085]    By this means, frequency information acquisition section  120  can easily extract the resonance frequency also, and can detect the tire condition with a higher degree of precision. 
       Embodiment 2 
       [0086]      FIG. 5  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 2 of the present invention, corresponding to  FIG. 1  of Embodiment 1. Components that are identical to components in  FIG. 1  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0087]    Tire condition detection apparatus  100  according to Embodiment 2 mainly differs from Embodiment 1 in being provided with vibration input section  110   a  and tire condition estimation section  130   a.  Vibration input section  110   a  is a functional section that decides anti-resonance vibration based on information related to the tire condition acquired in the past. Tire condition estimation section  130   a  is a functional section that feeds back the tire condition related information. 
         [0088]    Tire condition estimation section  130   a  determines whether or not tire  200  air pressure has dropped markedly based on a change in torsional spring constant K. Then tire condition estimation section  130   a  holds resonance frequency f c0 , anti-resonance frequency f a  and a determination result as to whether or not there is a marked drop in tire air pressure (hereinafter referred to as “air pressure drop”) due to a puncture or the like. 
         [0089]    Vibration input section  110   a  acquires resonance frequency f c0 , anti-resonance frequency f a  and information on the presence or absence of an air pressure drop held by tire condition estimation section  130   a.  Then, based on these items of information, vibration input section  110   a  controls at least one or the other of torque magnitude and vibrational frequency, or both of these, so that anti-resonance frequency f a  becomes easily extracted vibration. If one or the other of torque magnitude and vibrational frequency is a fixed value, vibration input section  110   a  needs only control the one that is not a fixed value. 
         [0090]      FIG. 6  is a flowchart showing an example of the operation of tire condition detection apparatus  100  according to Embodiment 2, corresponding to  FIG. 3  of Embodiment 1. Steps that are identical to steps in  FIG. 3  are assigned the same step numbers, and descriptions thereof are omitted in the following text. 
         [0091]    Each time estimation execution timing arrives, vibration input section  110   a  reads the previous resonance frequency f c0 , anti-resonance frequency f a  and information on the presence or absence of an air pressure drop held in tire condition estimation section  130   a  (S 1050 ). Here, the term “(the) previous” refers to the frequencies and information or the like acquired at the previous estimation execution timing. 
         [0092]    In this information read, for example, provision may be made for vibration input section  110   a  to send an information request command to tire condition estimation section  130   a.  That is to say, the information read may be performed by tire condition estimation section  130   a,  on acquiring this information request command, sending the information to vibration input section  110   a.  Then, if there is no air pressure drop (S 1051 : NO), vibration input section  110   a  decides anti-resonance vibration for causing vibration including this resonance frequency f c0  and anti-resonance frequency f a  (S 1060 ). Then vibration input section  110   a  inputs the decided anti-resonance vibration to tire  200  (S 1091 ). Details of the anti-resonance vibration decision will be given later herein. If there is an air pressure drop (S 1051 : YES), vibration input section  110   a  proceeds to, for example, step S 1200  described later herein (referred to  FIG. 8 ) the processing without performing anti-resonance vibration output. 
         [0093]    On the other hand, when tire condition estimation section  130   a  calculates torsional spring constant K(t) (S 1130 ), tire condition estimation section  130   a  determines whether or not the difference between present torsional spring constant K(t) and previous torsional spring constant K(t−1) is greater than or equal to a predetermined threshold value (S 1140 ). Here, the term “(the) present” refers to the value or the like acquired at the present estimation execution timing. In addition, t indicates that the parameter is based on the latest frequency information, and t-n indicates that the parameter is based on frequency information input at estimation execution timing n times before. 
         [0094]    If the difference between present torsional spring constant K(t) and previous torsional spring constant K(t−1) is greater than or equal to the threshold value (S 1140 : YES), tire condition estimation section  130   a  determines that a tire  200  air pressure drop has occurred (S 1150 ). That is, tire condition estimation section  130   a  determines whether or not the tire internal pressure can be said to have changed sharply. Then tire condition estimation section  130   a  stores air pressure drop information indicating that an air pressure drop has occurred (S 1160 ). 
         [0095]    This air pressure drop information is read by vibration input section  110   a  in step S 1050  of the next estimation execution timing (hereinafter referred to simply as “(the) next . . . ”). Then vibration input section  110   a  stops anti-resonance vibration output until reset processing is performed after a tire change or repair—that is, until air pressure drop information indicating no air pressure drop is input. This reset processing is directed by depression of a reset button or the like (not shown) by the driver or the like after a tire change has been performed. When reset processing is directed, tire condition estimation section  130   a  discards stored tire air pressure drop information. 
         [0096]    If the difference is less than the threshold value (S 1140 : NO), tire condition estimation section  130   a  stores resonance frequency f c0 , anti-resonance frequency f a  and spring constant K(t) (S 1180 ). Of these, resonance frequency f c0  and anti-resonance frequency f a  are read by vibration input section  110   a  in next step S 1050 , while spring constant K(t) is used as previous spring constant K(t−1) in next step S 1140 . 
         [0097]    Tire condition estimation section  130   a  may also store spring constants K(t−1), K(t−2), . . . K(t−m) (where m is a positive integer) of a plurality of times. Then tire condition estimation section  130   a  may use the difference between any one, or the largest, or the average, of the stored plurality of spring constants and present spring constant K(t) in a determination. 
         [0098]    Details of the above anti-resonance frequency decision will now be given. 
         [0099]    At a stage at which anti-resonance frequency f a  is unknown, vibration that facilitates the extraction of anti-resonance frequency f a  is also unknown. Therefore, vibration input section  110   a  decides anti-resonance torque to be sinusoidal torque sweeping from a low frequency to a high frequency, or from a high frequency to a low frequency, in a wide frequency band. That is to say, in an initial state in which anti-resonance frequency is unknown, vibration input section  110   a  decides upon vibratory torque involving searching a comparatively wide range as anti-resonance torque in order to enable resonance frequency f c0  and anti-resonance frequency f a  to be extracted dependably. 
         [0100]    However, such a wide frequency band search is comparatively time-consuming. 
         [0101]    Thus, if resonance frequency f c0  and anti-resonance frequency f a  have been detected immediately before, tire condition detection apparatus  100  narrows down the search range to reduce the search time. Specifically, vibration input section  110   a  decides upon vibratory torque limited to a narrow frequency band that includes previous resonance frequency f c0  and anti-resonance frequency f a  acquired from tire condition estimation section  130   a  as anti-resonance torque. 
         [0102]    For example, vibration input section  110   a  sets frequency upper-limit and lower-limit values in a range that includes previous resonance frequency f c0  and anti-resonance frequency f a . Vibration input section  110   a  then decides upon sinusoidal torque sweeping from the lower-limit frequency to the upper-limit frequency, or from the upper-limit frequency to the lower-limit frequency, as anti-resonance torque. Alternatively, vibration input section  110   a  creates a band-pass filter that limits a pass band to a range that includes previous resonance frequency f c0  and anti-resonance frequency f a . Vibration input section  110   a  then intentionally causes white noise to be generated, and decides upon white noise torque obtained by passing this white noise through the generated band-pass filter as anti-resonance torque. 
         [0103]    Vibration input section  110   a  may also perform narrowing down of the search range only if there is little variation in resonance frequency f c0  and anti-resonance frequency f a . Also, vibration input section  110   a  may perform narrowing down of the search range using averages of resonance frequency f c0  values and anti-resonance frequency f a  values of a plurality of times. Furthermore, when performing calculation of these averages, vibration input section  110   a  may exclude a greatly deviating value from the average calculation. By this means, tire condition detection apparatus  100  can improve the precision of resonance frequency f c0  and anti-resonance frequency f a  extraction. 
         [0104]    When an air pressure drop has occurred in tire  200  or tire  200  has been changed, the condition of tire  200  changes greatly, and therefore it is highly probable that resonance frequency f c0  and anti-resonance frequency f a  have changed significantly. Therefore, in such cases, vibration input section  110   a  cancels the narrowing down of the search range, and decides upon vibratory torque involving searching a comparatively wide range as anti-resonance torque. 
         [0105]    Thus, tire condition detection apparatus  100  according to Embodiment 2 enables the resonance frequency f c0  and anti-resonance frequency f a  search time to be shortened. By this means, tire condition detection apparatus  100  according to Embodiment 2 can detect the condition of tire  200  in a short time. 
       Embodiment 3 
       [0106]      FIG. 7  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 3 of the present invention, corresponding to  FIG. 5  of Embodiment 2. Components that are identical to components in  FIG. 5  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0107]    Tire condition detection apparatus  100  according to Embodiment 3 mainly differs from Embodiment 2 in having tire internal pressure calculation section  140  and information presentation section  150 . 
         [0108]    Tire internal pressure calculation section  140  acquires torsional spring constant K(t) and outer moment of inertia J 2 (t) from tire condition estimation section  130   a,  and calculates tire  200  internal pressure based on torsional spring constant K(t). Specifically, tire internal pressure calculation section  140 , for example, stores a correlation between tire spring constant K and tire  200  internal pressure beforehand, and calculates tire  200  internal pressure from spring constant K(t) using this correlation. This correlation may be defined by means of a table, or may be defined by means of a function. Then tire internal pressure calculation section  140  outputs the calculated tire  200  internal pressure to information presentation section  150  as internal pressure information. 
         [0109]    The correlation between torsional spring constant K and tire  200  internal pressure is a proportional relationship. Details of the proportional relationship between torsional spring constant K and tire  200  internal pressure, and a tire  200  internal pressure detection method based thereon, are given in NPL 1, for example, and therefore a description thereof is omitted here. However, the tire  200  internal pressure detection method used by tire internal pressure calculation section  140  is not limited to the method described in NPL 1. 
         [0110]    If air pressure drop information is held in tire condition estimation section  130   a,  tire internal pressure calculation section  140  acquires this information and outputs it to information presentation section  150 . 
         [0111]    When internal pressure information or air pressure drop information is input from tire internal pressure calculation section  140 , information presentation section  150  presents the contents of the internal pressure information or air pressure drop information to the driver. This presentation is performed, for example, by means of display on an instrument panel or car navigation apparatus display, or by means of speech output from a loudspeaker. 
         [0112]      FIG. 8  is a flowchart showing an example of the operation of tire condition detection apparatus  100  according to Embodiment 3, corresponding to  FIG. 6  of Embodiment 2. Steps that are identical to steps in  FIG. 6  are assigned the same step numbers, and descriptions thereof are omitted in the following text. 
         [0113]    When tire condition estimation section  130   a  determines that a tire  200  air pressure drop has occurred (S 1150 ), tire condition estimation section  130   a  stores air pressure drop information, also outputs air pressure drop information to tire internal pressure calculation section  140  (S 1161 ) and proceeds to step S 1190  described later herein. Tire condition estimation section  130   a  determines whether or not the difference between present torsional spring constant K(t) and previous torsional spring constant K(t−1) is less than a predetermined threshold value (S 1140 ). If the difference in question is less than the predetermined threshold value (S 1140 : NO), tire condition estimation section  130   a  outputs torsional spring constant K(t) and outer moment of inertia J 2 (t) to tire internal pressure calculation section  140  (S 1170 ). Then tire condition estimation section  130   a  stores torsional spring constant K(t) (S 1180 ). 
         [0114]    When torsional spring constant K(t) is input, tire internal pressure calculation section  140  calculates tire  200  internal pressure from torsional spring constant K (S 1190 ). Then tire internal pressure calculation section  140  outputs the calculated internal pressure to information presentation section  150  as internal pressure information. Also, when air pressure drop information is input, tire internal pressure calculation section  140  outputs the fact that an air pressure drop has occurred in tire  200  to information presentation section  150 . As a result, internal pressure information indicating tire  200  internal pressure, and air pressure drop information indicating that an air pressure drop has occurred in tire  200 , are presented to the driver as appropriate according to the condition of tire  200  (S 1200 ). 
         [0115]    Thus, tire condition detection apparatus  100  according to Embodiment 3 presents the condition of tire  200  to the driver, enabling the driver to be prompted to take appropriate action such as inserting air or repairing a puncture. By this means, tire condition detection apparatus  100  according to Embodiment 3 enables vehicle safety and fuel consumption to be improved. 
         [0116]    The object of information presentation is not limited to a driver, but may also be a passenger, a vehicle mechanic, or a remote observer of a vehicle. When presentation is performed for a mechanic, it is necessary for tire condition detection apparatus  100  to be provided with a recording medium that records internal pressure information and air pressure drop information, or information forming the basis of these. Also, when presentation is performed for a remote observer, it is necessary for tire condition detection apparatus  100  to be provided with a communication apparatus that transmits internal pressure information and air pressure drop information to an external apparatus such as an administrative server. 
       Embodiment 4 
       [0117]      FIG. 9  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 4 of the present invention, corresponding to  FIG. 7  of Embodiment 3. Components that are identical to components in  FIG. 7  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0118]    In tire condition detection apparatus  100  according to Embodiment 4, battery section  310 , inverter section  320 , and motor section  330  are applied to tire  200  as a drive system. Tire condition detection apparatus  100  according to Embodiment 4 mainly differs from Embodiment 3 in that vibration input section  110   a  is replaced by inverter control section  111 , and frequency information acquisition section  120  is replaced by rotational angular velocity detection section  121 . 
         [0119]    Battery section  310  is a storage battery that supplies inverter section  320  with power necessary for inverter section  320  to output a current. 
         [0120]    Inverter section  320  outputs power to motor section  330  in accordance with a motor drive current output command value input from inverter control section  111  described later herein. 
         [0121]    Motor section  330  generates torque by means of power supplied from inverter section  320 , and drives tire  200 . 
         [0122]    Inverter control section  111  inputs operation information indicating a degree of depression of an accelerator pedal (not shown) depressed by the driver in order to cause the vehicle to accelerate (hereinafter referred to simply as “operation information”). Then inverter control section  111  decides a value of torque applied to tire  200  for vehicle running (hereinafter referred to as “running torque”) based on the operation information. Also, inverter control section  111  decides anti-resonance torque in the same way as vibration input section  110   a  of Embodiment 3. Then inverter control section  111  outputs to inverter section  320  a motor drive current output command value such that combined torque comprising resonance torque and running torque (hereinafter referred to simply as “combined torque”) is output from motor section  330 . 
         [0123]    Furthermore, inverter control section  111  detects an actual output value of a motor section  330  motor drive current by means of a current detection section (not shown). Then inverter control section  111  controls the inverter section  320  power supply to motor section  330  so that this actual output value matches an output command value calculated by inverter control section  111 . 
         [0124]    Inverter control section  111  may perform generation of such an output command value by calculating a combined torque value, or by combining (adding together) an anti-resonance current and running current. Here, “anti-resonance current” is a motor drive current for generating anti-resonance torque. Also, “running current” is a motor drive current for generating running torque. Further, hereinafter, where appropriate, a motor drive current for generating combined torque is referred to as “combined drive current”. 
         [0125]    Rotational angular velocity detection section  121  detects rim rotational angular velocity ω 1  of tire  200  from tire  200 , and outputs this to tire condition estimation section  130   a  as above-described frequency information. For example, rotational angular velocity detection section  121  acquires a rim rotation angle from an encoder (not shown) that is constituted by a rotor that rotates in synchrony with tire  200 , and a sensor that detects a rotation angle of the rotor and converts the rotation angle into an electrical signal. Then rotational angular velocity detection section  121  calculates rotational angular velocity ω 1  by performing temporal differentiation on rim rotation angles. 
         [0126]    Rotational angular velocity detection section  121  may acquire a rotation angle using, for example, an optical encoder such as an incremental encoder or absolute encoder, or an electromagnetic encoder comprising a Hall element or the like. 
         [0127]    Tire condition estimation section  130   a  calculates tire  200  resonance frequency f c0  and anti-resonance frequency f a  based on rotational angular velocity ω 1  input from rotational angular velocity detection section  121 . 
         [0128]      FIG. 10  is a flowchart showing an example of the operation of tire condition detection apparatus  100  according to Embodiment 4, corresponding to  FIG. 8  of Embodiment 3. Steps that are identical to steps in  FIG. 8  are assigned the same step numbers, and descriptions thereof are omitted in the following text. 
         [0129]    First, when the accelerator pedal is depressed, inverter control section  111  derives a running torque value based on the degree of depression of the accelerator pedal (S 1010 ), and derives a running current corresponding to the running torque value (S 1020 ). Then, if this is not estimation execution timing (S 1030 : NO), inverter control section  111  outputs the running current to inverter section  320  as an output specifying value. As a result, only the running current is output from motor section  330  as a motor drive current (S 1040 ), and only running torque is applied to tire  200 . 
         [0130]    On the other hand, if this is estimation execution timing (S 1030 : YES), inverter control section  111  reads previous resonance frequency f c0  and anti-resonance frequency f a  (S 1050 ). If there is no air pressure drop (S 1051 : NO), inverter control section  111  derives anti-resonance torque for causing vibration including previous resonance frequency f c0  and anti-resonance frequency f a  to be generated (S 1061 ). Then inverter control section  111  derives an anti-resonance current corresponding to the anti-resonance torque value (S 1070 ), generates an output command value of a combined drive current in which a running current and anti-resonance current are superposed, and outputs this combined drive current output command value to inverter section  320  (S 1081 ). As a result, a combined drive current is output from motor section  330  as a motor drive current (S 1091 ), and combined drive torque is applied to tire  200 . 
         [0131]    Then rotational angular velocity detection section  121  detects tire  200  rotational angular velocity ω 1 , and outputs this to tire condition estimation section  130   a  as a time series rotational angular velocity signal (S 1101 ). Tire condition estimation section  130   a  passes the input rotational angular velocity signal through an above-described band-pass filter that takes a band including previous resonance frequency f c0  and anti-resonance frequency f a  as a pass band (S 1110 ). Then tire  200  resonance frequency f c0  and anti-resonance frequency f a  are extracted from the rotational angular velocity signal that has passed through the band-pass filter (S 1120 ). 
         [0132]    Thus, tire condition detection apparatus  100  according to Embodiment 4 has operation information as input, and performs input of running torque and anti-resonance torque by controlling the motor drive current value. By this means, tire condition detection apparatus  100  according to Embodiment 4 can easily input anti-resonance vibration to tire  200  of a drive system capable of acquiring operation information and capable of specifying a motor drive current value. 
         [0133]    Also, tire condition detection apparatus  100  according to Embodiment 4 inputs anti-resonance vibration from motor section  330  connected to tire  200  in a stable and fixed manner. By this means, tire condition detection apparatus  100  according to Embodiment 4 can reduce the effects of a vibration component other than a resonance frequency and an anti-resonance frequency in frequency information. 
         [0134]    Furthermore, tire condition detection apparatus  100  according to Embodiment 4 acquires rotational angular velocity acquired from a rotational angular velocity sensor installed in order to drive motor section  330  as frequency information. Consequently, in tire condition detection apparatus  100  according to Embodiment 4, the provision of a separate sensor for detecting vibration is unnecessary. 
         [0135]    When a vehicle is stopped, the driver is not depressing the accelerator pedal, and running torque is zero. Therefore, if tire condition detection apparatus  100  performs detection of the condition of tire  200  while the vehicle is stopped, only anti-resonance torque is input to tire  200 . 
       Embodiment 5 
       [0136]      FIG. 11  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 5, corresponding to  FIG. 9  of Embodiment 4. Components that are identical to components in  FIG. 9  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0137]    Tire condition detection apparatus  100  according to Embodiment 5 mainly differs from Embodiment 4 in that rotational angular velocity detection section  121  is replaced by rotational angular velocity detection section  123  that detects a rotational angular velocity of tire  200  using an actual output value of a motor drive current. 
         [0138]    Rotational angular velocity detection section  123  calculates tire  200  rim rotational angular velocity ω 1  from motor drive current actual output value I q , and outputs this rotational angular velocity ω 1  to tire condition estimation section  130   a.  Here, motor drive current actual output value I q  is a current value acquired from a current acquisition section (not shown) installed between inverter section  320  and motor section  330 . 
         [0139]    The method of calculating rotational angular velocity ω 1  from motor drive current actual output value I q  in rotational angular velocity detection section  123  will now be described. 
         [0140]      FIG. 12  is a control block diagram showing an example of the configuration of a motor drive system. 
         [0141]    PI controller  321  of inverter control section  111  is a controller that controls actual output value I q  of a current flowing through motor section  330  so that a combined drive current actual output value flowing through motor section  330  matches a combined drive current (command value) calculated by inverter control section  111 . That is to say, PI controller  321  applies control voltage V q     —     ref  such that motor section  330  actual output value I q  matches output command value I q     —     ref  calculated by inverter control section  111  to motor section  330 . 
         [0142]    Motor circuit  331  is an electronic circuit that can be modeled by means of wound coil inductance L and wound coil resistance R. By means of actual output value I q , output torque T e  proportional to torque constant K t  is applied to tire  200 . Then the rotor of motor section  330  rotates at rotational angular velocity ω 1  together with the rotation of tire  200 . At this time, counter electromotive force—K e ω 1  (K e  is a proportional constant) proportional to rotor rotational angular velocity ω 1  is generated in motor section  330 , and voltage V=V q     —     ref −K e ω 1  is input to both ends of the wound coil of motor section  330  as an actual input voltage value. Equation 14 below is derived from this relationship. 
         [0000]    
       
         
           
             
               
                 
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         [0143]    Rotational angular velocity detection section  123  calculates motor section  330  rotational angular velocity (that is, tire  200  rim rotational angular velocity) ω 1  from actual output value I q  and control voltage V q     —     ref  using equation 14, and outputs this rotational angular velocity ω 1  to tire condition estimation section  130   a.    
         [0144]    Thus, tire condition detection apparatus  100  according to Embodiment 5 can detect rotational angular velocity ω 1  from an actual output value of a drive current output to motor section  330  and a control voltage calculated by inverter control section  111 . By this means, tire condition detection apparatus  100  according to Embodiment 5 enables an encoder or suchlike sensor to be made unnecessary. 
         [0145]    In Embodiment 5, motor section  330  is a synchronous motor with a surface magnet structure in which a permanent magnet is attached to the surface of the rotor, and current control in which the d-axis current is zero is assumed, but the configuration of motor section  330  is not limited to this. For example, it is possible to detect rotational angular velocity ω 1  in a similar way in a case in which motor section  330  is a synchronous motor with an embedded magnet structure in which a permanent magnet is embedded within the rotor, and a current control system in which the d-axis current is non-zero is assumed. 
       Embodiment 6 
       [0146]      FIG. 13  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 6, corresponding to  FIG. 9  of Embodiment 4. Components that are identical to components in  FIG. 9  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0147]    In tire condition detection apparatus  100  according to Embodiment 6, battery section  310 , inverter section  320 , motor section  330 , and inverter control section  340  are applied to tire  200  as a drive system. Tire condition detection apparatus  100  according to Embodiment 6 mainly differs from Embodiment 4 in that inverter control section  111  is replaced by control section  112 . 
         [0148]    Based on a tire  200  output torque value input from control section  112  described later herein, inverter control section  340  calculates a motor drive current output command value such that that output torque is output by motor section  330 . Alternatively, based on a motor drive current such that tire  200  output torque is output by motor section  330 , input from control section  112  described later herein, inverter control section  340  calculates an output command value to output that motor drive current. Then inverter control section  340  outputs the calculated output command value to inverter section  320 . 
         [0149]    In the same way as vibration input section  110   a  described in Embodiment 3, control section  112  decides a running torque value and an anti-resonance torque value based on operation information. Then control section  112  outputs a value of combined torque combining anti-resonance torque and running torque to inverter control section  340  as a tire  200  output torque value. Output of an output torque value may be performed by means of motor drive current output to motor section  330  for outputting output torque to tire  200 , rather than an output torque value itself. 
         [0150]    Thus, tire condition detection apparatus  100  according to Embodiment 6 inputs operation information, and performs input of running torque and anti-resonance torque by controlling the output torque value. By this means, tire condition detection apparatus  100  according to Embodiment 6 can easily input anti-resonance vibration to tire  200  of a drive system capable of acquiring operation information and capable of specifying an output torque value. 
       Embodiment 7 
       [0151]      FIG. 14  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 7 of the present invention, corresponding to  FIG. 9  of Embodiment 4. Components that are identical to components in  FIG. 9  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0152]    Tire condition detection apparatus  100  according to Embodiment 7 mainly differs from Embodiment 4 in having current command section  113 . 
         [0153]    Current command section  113  decides anti-resonance torque in the same way as inverter control section  111  of Embodiment 4. Then current command section  113  outputs a motor drive current value such that the decided anti-resonance torque is output by motor section  330 , to inverter control section  111  as an anti-resonance current value. 
         [0154]    Inverter control section  111  decides a running torque value corresponding to a degree of depression of the accelerator pedal, and calculates a running current value such that this running torque is output by motor section  330 . Then inverter control section  111  calculates a combined drive current value by adding the anti-resonance current value input from current command section  113  to the running current value, and outputs the result of this calculation to inverter section  320  as an output command value. 
         [0155]    Thus, tire condition detection apparatus  100  according to Embodiment 7 has current command section  113  that generates an anti-resonance current that causes natural vibration to be generated in tire  200 . Tire condition detection apparatus  100  according to Embodiment 7 outputs a combined drive current superposed on a running current to motor section  330 , and performs input of running torque and anti-resonance torque. By this means, tire condition detection apparatus  100  according to Embodiment 7 can easily input anti-resonance vibration to tire  200 . 
       Embodiment 8 
       [0156]      FIG. 15  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 8, corresponding to  FIG. 13  of Embodiment 6. Components that are identical to components in  FIG. 13  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0157]    Tire condition detection apparatus  100  according to Embodiment 8 mainly differs from Embodiment 6 in having anti-resonance vibration command section  114 . 
         [0158]    Anti-resonance vibration command section  114  decides anti-resonance torque in the same way as current command section  113  of Embodiment 7. Then anti-resonance vibration command section  114  outputs the decided anti-resonance torque value to control section  112 . 
         [0159]    Control section  112  decides running torque corresponding to a degree of depression of an accelerator pedal (not shown) depressed by the driver in order to cause the vehicle to accelerate. Then control section  112  calculates combined torque comprising anti-resonance torque input from anti-resonance vibration command section  114  and running torque, and outputs this combined torque to inverter control section  340 . 
         [0160]    Alternatively, control section  112  derives a motor drive current (that is, running current) value such that this running torque is output from motor section  330 . Furthermore, control section  112  derives a motor drive current (that is, anti-resonance current) such that anti-resonance torque input from anti-resonance vibration command section  114  is output by motor section  330 . Then control section  112  generates a combined drive current in which the anti-resonance current is superposed on the running current, and outputs this combined drive current to inverter control section  340 . 
         [0161]    Thus, tire condition detection apparatus  100  according to Embodiment 8 has anti-resonance vibration command section  114  that generates anti-resonance torque that causes natural vibration to be generated in tire  200 . Tire condition detection apparatus  100  according to Embodiment 8 outputs a combined drive current based on combined torque superposed with running torque to motor section  330 , and performs input of running torque and anti-resonance torque. By this means, tire condition detection apparatus  100  according to Embodiment 8 can easily input anti-resonance vibration to tire  200  of a drive system capable of specifying a motor drive current value for tire  200 . 
       Embodiment 9 
       [0162]      FIG. 16  is a block diagram showing an example of the configuration of a tire condition detection apparatus according to Embodiment 9, corresponding to  FIG. 9  of Embodiment 4. Components that are identical to components in  FIG. 9  are assigned the same reference symbols, and descriptions thereof are omitted in the following text. 
         [0163]    Tire condition detection apparatus  100  according to Embodiment 9 mainly differs from Embodiment 4 in that rotational angular velocity detection section  121  is not provided. 
         [0164]    Tire condition estimation section  130   a  inputs control voltage V q     —     ref  for motor section  330  in  FIG. 12  calculated by inverter control section  111 . Then tire condition estimation section  130   a  calculates resonance frequency f c0  and anti-resonance frequency f a , by means of the method below, for example, and estimates the condition of tire  200 . 
         [0165]    Equation 15 below is derived from the relationship illustrated in  FIG. 12 . 
         [0000]        V   q     —     ref   =K   e {circumflex over (ω)} 1   +V=K   e {circumflex over (ω)} 1 +( Lİ   q   +RI   q )   (Equation 15)
 
         [0166]    In this equation 15, the right-hand second term+third term (I q  terms) are controlled so that motor section  330  outputs motor drive current output command value I q     —     ref  input from inverter control section  111 . Consequently, the same frequency characteristic as for output command value I q     —     ref  that is the input appears in the right-hand second term+third term (I q  terms). On the other hand, the right-hand first term (K e ω 1  term) is a counter-electromotive force generated according to vibration that includes resonance frequency f c0  and anti-resonance frequency f a  as illustrated in equations 1 to 4. Therefore, by using control voltage V q     —     ref  of equation 15, it is possible to detect torsional spring resonance frequency f c0  and anti-resonance frequency f a  that are affected by tire internal pressure. 
         [0167]    Resonance frequency f c0  and anti-resonance frequency f a  can be detected from control voltage V q     —     ref  by performing above-mentioned frequency analysis on control voltage V q     —     ref  and detecting a sharp peak position indicating resonance frequency f c0  and anti-resonance frequency f a . Also, resonance frequency f c0  and anti-resonance frequency f a  can be detected from control voltage V q     —     ref  utilizing the above-mentioned recursive least-squares estimation method. 
         [0168]    When utilizing the recursive least-squares estimation method, equation 16 below is derived by introducing equation 15 into the aforementioned equation 6. Here, observable vector ξ and observable output y are defined as shown below in equation 17 and equation 18, respectively. 
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         [0169]    Tire condition estimation section  130   a  determines resonance frequency f c0  and anti-resonance frequency f a  from unknown parameter θ by the recursive least-squares estimation method described in Embodiment 1. Unknown parameter vector θ=[θ 1  θ 2 ] T =[ω c0   2  ω a   2 ] T =[4π 2 f c0   2  4π 2 f a   2 ] T  is as explained above. 
         [0170]    Thus, tire condition detection apparatus  100  according to Embodiment 9 estimates the condition of tire  200  from a control voltage for motor section  330 , enabling a rotational angular velocity detection section to be made unnecessary. That is to say, without using a sensor that detects the angle or rotational angular velocity of tire  200 , tire condition detection apparatus  100  according to Embodiment 9 can detect the condition of tire  200  with a precision equivalent to that of a configuration that uses such a sensor. 
         [0171]    Tire condition detection apparatuses according to Embodiment 4 through Embodiment 9 have been assumed to control an input signal to an inverter section as a method of inputting predetermined vibration to a tire, but an input signal (that is, a control voltage) to a motor section may also be controlled directly. That is to say, a tire condition detection apparatus may have a configuration that includes an inverter section. 
         [0172]    Tire condition detection apparatuses according to Embodiment 4 through Embodiment 9 need not necessarily be provided with a tire internal pressure calculation section and an information presentation section. 
         [0173]    Tire condition detection apparatuses according to Embodiment 6 through Embodiment 8 may be provided with rotational angular velocity detection section of Embodiment 5 that calculates from motor drive current instead of a rotational angular velocity detection section. 
         [0174]    Tire condition detection apparatuses according to Embodiment 6 through Embodiment 8 need not necessarily be provided with a rotational angular velocity detection section, and may extract a resonance frequency and an anti-resonance frequency from a control voltage as described in Embodiment 9. 
         [0175]    The disclosure of Japanese Patent Application No. 2010-229917, filed on Oct. 12, 2010, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0176]    A tire condition detection apparatus and a tire condition detection method according to the present invention are suitable for use as a tire condition detection apparatus and tire condition detection method enabling tire condition to be detected with a high degree of precision. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  Tire condition detection apparatus 
           110 ,  110   a  Vibration input section 
           111 ,  340  Inverter control section 
           112  Control section 
           113  Current command section 
           114  Anti-resonance vibration command section 
           120  Frequency information acquisition section 
           121  Rotational angular velocity detection section 
           123  Rotational angular velocity detection section 
           130 ,  130   a  Tire condition estimation section 
           140  Tire internal pressure calculation section 
           150  Information presentation section 
           200  Tire 
           310  Battery section 
           320  Inverter section 
           321  PI controller 
           330  Motor section 
           331  Motor circuit