Abstract:
In a suspension device including a radar sensor installed in the suspension for detecting the behavior of the suspension, high pressure is applied to the radar sensor and measurement errors tend to be caused by changes in the flow, temperature and pressure of oil around the sensor. In order to realize precise measurement even in the oil environment, a radio wave radar sensor (especially, a millimeter wave radar sensor) is employed as the radar sensor, and the radio wave radar sensor is mounted in a ceramic package, by which the precise detection of the suspension behavior in the oil environment withstanding high pressure is realized.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a suspension device, and in particular, to a suspension device which measures or controls relative behavior between a body-side structure and a wheel-side structure of a vehicle.  
         [0002]     As a known technique for a suspension device capable of measuring relative behavior between a super-spring structure and a sub-spring structure of a vehicle, there has been disclosed a vehicle behavior measurement device for measuring the relative behavior between the super-spring structure and the sub-spring structure in JP-A-11-72132.  
         [0003]     The vehicle behavior measurement device of the above document comprises: an ultrasonic wave transceiver which is fixed with respect to a first end (moving in a certain relationship with the super-spring structure) or a second end (moving in a certain relationship with the sub-spring structure) for transmitting ultrasonic waves to the other end or to a part moving in a certain relationship with the other end, receiving the ultrasonic waves, and converting the received ultrasonic waves into a reception signal; a transmission circuit in charge of transmission control of the ultrasonic waves; a detector circuit which detects reflected waves (the ultrasonic waves reflected by the other end or the part moving in the certain relationship with the other end) from the reception signal; and a behavior calculation module which calculates the relative behavior between the super-spring structure and the sub-spring structure based on the transmitted ultrasonic waves and the reflected waves.  
         [0004]     As another known technique, a shock absorber equipped with a Doppler fluid velocity sensor has been disclosed in JP-B2-7-10642.  
         [0005]     The shock absorber of the above document comprises: a first cylinder serving as a hydraulic actuator connecting a super-spring part and a sub-spring part of a car while forming a power chamber which can store a vibration damping fluid, capable of selectively changing a suspension parameter in response to a change in the velocity of the vibration damping fluid flowing in the hydraulic actuator; a piston which is placed in the first cylinder to partition the inside of the power chamber into a first part and a second part; a valve module which supplies a fixed amount of flow of the vibration damping fluid to the inside of the hydraulic actuator; a transducer module which emits and receives a sound wave propagating through the vibration damping fluid flowing through a fluid channel of the valve module; an excitation module which excites the transducer module and lets the transducer module emit the sound wave; a measurement module which measures frequency change between the sound wave emitted by the transducer module and the sound wave received by the transducer module and generates an output signal in response to the frequency change; and a velocity calculation module which calculates the velocity of the vibration damping fluid flowing through the valve module in response to the output of the measurement module.  
         [0006]     However, since the vehicle behavior measurement device for measuring the relative behavior between the super-spring structure and the sub-spring structure (JP-A-11-72132) and the shock absorber equipped with the Doppler fluid velocity sensor (JP-B2-7-10642) both use ultrasonic waves for the measurement, a transmission unit and a reception unit have to be provided separately and it is difficult to miniaturize the transmission and reception units to install them inside the suspension.  
         [0007]     Second, a signal processing unit has to be placed outside the suspension, separately from the transmission and reception units, by which the composition becomes complicated and cost reduction becomes difficult.  
         [0008]     Third, a weak signal from an ultrasonic sensor before signal processing has to be transmitted from inside the suspension to the outside by a signal wire, in which noise reduction becomes a technical challenge.  
         [0009]     Fourth, while the relative velocity V between the super-spring part and the sub-spring part can be calculated from the frequency f 0  of a driving signal, the frequency fr of the detected reception signal and the velocity C of sound in the medium based on the following expression (1): 
 
 V =( fr−f   0 )· C /( fr+f   0 )   (1) 
 
 the sound velocity C changes depending on the flow, temperature and pressure of the medium since the transmission/reception of the ultrasonic waves is carried out with the fluid inside the suspension as the medium. As a result, the calculated relative velocity V might have a considerable error. 
 
         [0010]     Fifth, while correction by use of a temperature sensor and a pressure sensor is being considered to resolve the above problem, there remain problems from the viewpoints of structure and costs.  
         [0011]     Sixth, while the fluid in the suspension can become high pressure, a high-pressure-resistant structure can not be implemented by the above prior art.  
       SUMMARY OF THE INVENTION  
       [0012]     It is an object of the present invention to provide a suspension device capable of detecting the behavior of the suspension precisely at a low cost and having high reliability against pressure.  
         [0013]     In accordance with an aspect of the present invention, a suspension device comprising a rod supporting a super-spring structure connected to a body of a vehicle, a cylinder supporting a sub-spring structure connected to a wheel (the rod and the cylinder behaves according to prescribed spring constant and damper constant) is provided with a transmitter which is provided to the rod or the cylinder to transmit a transmission wave to the cylinder or rod facing the transmitter, a receiver which receives a reflected wave from the cylinder or rod facing the transmitter as a reception wave, and a signal processing circuit which calculates relative behavior of the rod and the cylinder based on the transmission wave and the reception wave.  
         [0014]     Preferably, the transmission wave is a radio wave in a millimeter wave band.  
         [0015]     The suspension device may further comprise a mixer which outputs a frequency difference between a frequency of the transmission wave and a frequency of the reception wave. The signal processing circuit calculates the relative behavior of the rod and the cylinder by executing a Fourier transform to the output of the mixer.  
         [0016]     The transmitter may transmit the transmission wave as pulse signals, and the signal processing circuit may calculate the relative behavior of the rod and the cylinder by measuring each time from the transmission of the transmission wave to the reception of the reflected wave as the reception wave.  
         [0017]     A surface facing the transmitter may be formed in a pyramidal or circular concave shape.  
         [0018]     At least the transmitter, the receiver and the mixer may be implemented by an MMIC. The MMIC and the signal processing circuit may be mounted in a package  
         [0019]     The package may be fixed to the rod or the cylinder via a housing supporting the package.  
         [0020]     The package may be fixed to the rod or the cylinder via the housing by welding, by screws, or by bolts and nuts.  
         [0021]     The package may include a case and a cover made of ceramic or resin. The cover may be provided with a dielectric lens.  
         [0022]     The dielectric lens may be placed in a central part or at the center of the rod or the cylinder.  
         [0023]     The suspension device may further comprise a position sensor which detects relative position between the super-spring structure and the sub-spring structure in a rod axis direction. In this case, measurement values of the relative behavior of the rod and the cylinder obtained by the signal processing circuit are corrected based on positional information obtained by the position sensor. The relative position may be detected regarding two or more points.  
         [0024]     In accordance with another aspect of the present invention, a suspension device comprising a rod supporting a super-spring structure connected to a body of a vehicle and a cylinder supporting a sub-spring structure connected to a wheel (the rod and the cylinder exhibits behavior specified by prescribed spring constant and damper constant) is provided with a sensor which detects relative behavior of the rod and the cylinder and a wheel status estimating device which estimates status of the wheel based on information on the relative behavior detected by the sensor.  
         [0025]     The sensor may be one selected from an acceleration sensor, a linear sensor and a radar sensor.  
         [0026]     The estimated status of the wheel may include at least one of air pressure and attachment status of the wheel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The objects and features of the present invention will become more apparent from the consideration of the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0028]      FIG. 1  is a schematic diagram showing a suspension device installed in a vehicle;  
         [0029]      FIG. 2  is a schematic cross-sectional view showing the composition of a suspension device in accordance with an embodiment of the present invention;  
         [0030]      FIG. 3  is a flow chart showing a process executed by the suspension device;  
         [0031]      FIGS. 4A and 4B  are schematic diagrams showing examples of an RF module of the suspension device;  
         [0032]      FIGS. 5A and 5B  are graphs showing IF signal strength when the vehicle is stopped and the result of a Fourier transform executed to the IF signal strength;  
         [0033]      FIGS. 6A and 6B  are graphs showing IF signal strength when the vehicle is running and the result of a Fourier transform executed to the IF signal strength;  
         [0034]      FIG. 7  is a graph showing a method for detecting noise and a peak;  
         [0035]      FIG. 8  is a graph showing a method for detecting the peak; and  
         [0036]      FIG. 9A and 9B  are schematic diagrams showing a vertical cross section and an X-X cross section of a radio wave radar sensor of the suspension device. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0037]     In the following, an embodiment regarding a suspension device in accordance with the present invention will be described with reference to  FIGS. 1 through 9 . Referring to  FIG. 1 , a suspension device  2  is provided between a super-spring structure which is connected to a body  1  and each sub-spring structure which is connected to each wheel  3 .  
         [0038]     The suspension device  2  will be explained below referring to  FIG. 2 . An inner cylinder  10  filled with oil  14  is partitioned into an upper chamber  9  and a lower chamber  15  by a piston  12 . The piston  12  is joined to a rod  7  which is connected to the body through a rod guide  5 .  
         [0039]     When the rod  7  moves downward in the vertical direction, the oil in the lower chamber  15  moves to a reservoir chamber  8  (between the inner cylinder  10  and an outer cylinder  11 ) and the upper chamber  9  via channels  16  and a contraction-side valve  21 , respectively. On the other hand, when the rod  7  moves upward in the vertical direction, the oil in the upper chamber  9  moves to the reservoir chamber  8  and the lower chamber  15  via channels of an upper cap  6  and an expansion-side valve  20 , respectively. In this case, the channels of the upper cap  6  let through the oil only (not nitrogen  22  in the reservoir chamber).  
         [0040]     The outer cylinder  11 , sealing up the oil with the upper cap  6  and a lower cap  17 , is connected to the wheel via a connection part  18  which is attached to the lower cap  17 .  
         [0041]     On a part of the rod  7  opposite to the end connected to the body, a radio wave radar sensor  13  is attached.  
         [0042]      FIG. 3  shows a flow until the radio wave radar sensor  13  detects the behavior of the suspension. The radio wave radar sensor  13  includes an RF module  27  for detecting the behavior of the suspension and a processor  24  for carrying out information processing. Each step shown in  FIG. 3  will be explained below referring to  FIGS. 4 through 8 .  
         [0043]      FIGS. 4A and 4B  show the composition of the RF module  27  as a suspension behavior detection module. Referring to  FIG. 4A , a signal from an oscillator  50  is amplified by an amplifier  52  and transmitted by a TX/RX (transmission/reception) antenna  55 , and reflected waves from the inner cylinder  10  are received by the TX/RX antenna  55 . A reception signal obtained by the TX/RX antenna  55  is amplified by a low noise amplifier  54  and mixed with the signal from the oscillator  50  by a mixer  51 , by which an IF (Intermediate Frequency) signal  53  is obtained. While a composition employing the amplifier  52  and the low noise amplifier  54  for the radio wave radar sensor is shown in  FIG. 4A , the amplifier  52  and the low noise amplifier  54  become unnecessary when the signal strength of the IF signal  53  is high enough.  FIG. 4B  shows such an example, in which the amplifier  52  and the low noise amplifier  54  are left out and an oscillator/mixer  56  serving as both an oscillator and a mixer is connected to the TX/RX antenna  55 . The function of the suspension behavior detection module does not differ between  FIG. 4A  and  FIG. 4B .  
         [0044]     Next, a frequency detection module will be explained below referring to  FIGS. 5A through 6B . When the vehicle is stopped, the suspension does not vibrate and the distance between the radio wave radar sensor  13  and the inner cylinder  10  is almost constant, by which the strength of the IF signal  53  outputted by the RF module  27  of the radio wave radar sensor  13  behaves as shown in  FIG. 5A . On the other hand, when the vehicle is running, the suspension vibrates and the distance between the radio wave radar sensor  13  and the inner cylinder  10  changes, by which the strength of the IF signal  53  outputted by the RF module  27  of the radio wave radar sensor  13  behaves as shown in  FIG. 6A . The IF signal  53  is A/D converted (by passing the signal through a high-pass filter) and transformed by the fast Fourier transform, by which the relationship between the frequency and the signal strength is derived as shown in  FIGS. 5B and 6B  (corresponding to  FIGS. 5A and 6A , respectively). The high signal strength at low frequencies is caused by the so-called 1/F noise which is dependent on the frequency band. The peak  25  seen in  FIG. 6B  indicates the relative behavior between the radio wave radar sensor  13  and the inner cylinder  10 , that is, the behavior of the suspension.  
         [0045]     Next, a peak detection module for detecting the peak  25  shown in  FIG. 6B  will be explained below referring to  FIGS. 7 and 8 . For the detection of the peak  25 , separation of the signal from noise is essential. Since the peak  25  is higher than the noise, a method for detecting the noise will be explained first referring to  FIG. 7 . While the frequency spectrum including the peak  25  is updated at prescribed time intervals, the spectrum except the peak  25  has little time dependence, showing a continuous change with a large time constant even when it changes. Therefore, the noise  26  can be detected by taking a moving average with respect to time. Accordingly, the part A shown in  FIG. 7  sufficiently higher than the noise  26  is detected as the peak  25 . Specifically, a point P(i) satisfying P(i−1)&lt;P(i) and P(i)&gt;P(i+1) (i=1, 2, 3, . . . ) is defined as the peak  25 .  
         [0046]     Next, a velocity/position calculation module will be explained below. The frequency of the peak  25  detected in  FIG. 8  is the Doppler frequency which changes according to the relative velocity between the radio wave radar sensor  13  and the inner cylinder  10 . Therefore, the relative velocity between the radio wave radar sensor  13  and the inner cylinder  10  (i.e. relative velocity V 1  between the super-spring structure and the sub-spring structure) can be obtained from the frequency f 1  of the transmission signal, the frequency fr 1  of the detected reception signal and the velocity C 1  of the radio wave in the oil, based on the following expression (2): 
 
 V   1 =( fr   1 − f   1 )· C   1 /( fr   1 + f   1 )   (2) 
 
         [0047]     Further, the position of the radio wave radar sensor  13  (the position of the piston  12 ) can also be obtained by integrating the velocity V 1 .  
         [0048]     In this case, the velocity C 1  of the radio wave is determined by the dielectric constant of the medium and barely varies depending on the flow, temperature and pressure of the medium. Thus the variation in the radio wave velocity C 1  is small and the error included in the relative velocity V 1  between the super-spring structure and the sub-spring structure obtained from the expression (2) is also small. Therefore, the radio wave radar is more advantageous compared to ultrasonic radars.  
         [0049]     While the behavior of the suspension is calculated above based on the frequencies of the transmission wave and the reception wave, it is also possible to calculate the position of the radio wave radar sensor  13  (position of the piston  12 ) by transmitting the transmission wave as a pulse, measuring the time between the transmission of the transmission wave and the reception of a reflected wave as the reception wave, and obtaining the position from the measured time and the radio wave velocity. The velocity of the radio wave radar sensor  13  can also be obtained by differentiating the position. Also in this case, the error included in the relative velocity between the super-spring structure and the sub-spring structure is small thanks to the small variation in the radio wave velocity, which is an advantage over ultrasonic radars.  
         [0050]     As shown in  FIG. 2 , by forming the surface of the inner cylinder  10  facing the radio wave radar sensor  13  and reflecting the radio waves substantially in the shape of a trigonal pyramid  19 , the reflection coefficient for the radio waves transmitted by the radio wave radar sensor  13  is stabilized and thereby the detection of the suspension behavior can be carried out more stably compared to an ordinary inner cylinder with a plane surface, irrespective of the suspension behavior and installation conditions of the radio wave radar. While the trigonal pyramid-like shape is used here, similar effect can also be achieved by other types of pyramid, cones, spherical surfaces, etc.  
         [0051]     Further, while the radio wave radar sensor  13  is attached to the rod  7  in the above embodiment, similar effects can also be attained by attaching the radio wave radar sensor  13  to the inner cylinder  10  to detect the behavior of the rod  7 .  
         [0052]     In the following, the installation of the radio wave radar sensor  13  will be described referring to  FIGS. 9A and 9B .  
         [0053]     An MMIC (Microwave Monolithic Integrated Circuit)  105  (forming the RF module  27  of the radio wave radar sensor  13  shown in  FIG. 4A  or  4 B) and the processor  24  are mounted in a ceramic package  102 , with an antenna of the MMIC  105  placed substantially at the center of the package  102 . A ceramic cover  107  provided with a dielectric lens  106  is joined to the package  102  by a brazing material, etc. so that the axis of the dielectric lens  106  will be coaxial with the radio wave transmission axis of the antenna. The MMIC  105  and the processor  24  are connected together by wire bonding by Au wires  104 . A power line to the MMIC  105  and a signal line from the processor  24  are kept continuous and conductive via pins penetrating the package  102  and cables  100  placed in a hollow part  101  of the rod  7 . The cables  100  are connected to a connector  4  shown in  FIG. 2 . The MMIC, forming a distribution constant circuit, gets smaller as the frequency gets higher in an inversely proportional relationship. Therefore, the cost of the MMIC can be reduced excellently by employing an extremely high frequency in a millimeter wave band.  
         [0054]     The package  102  is attached to a housing  109  by swaging a part of the housing toward the package via an O ring  108 . The housing  109  has a threaded part  111 , by which the housing  109  is screwed and fastened to the rod  7  via packing  110 .  
         [0055]     By the above composition, the MMIC  105  and the processor  24  can be hermetically sealed in a highly pressure-resistant structure even in the suspension oil. The rod  7  is generally provided with a screw thread which is used for fixing the piston  12  thereon, and the radio wave radar sensor  13  is attached to the rod  7  by use of the screw thread, by which very easy attachment of the radio wave radar sensor  13  is realized. Further, since the antenna is placed substantially at the center, the radio wave transmission/reception conditions are not affected by the screwing status of the radio wave radar sensor  13 , which allows high productivity of the suspension device.  
         [0056]     The connection of the housing  109  to the rod  7  is-not restricted to the screwing described above; welding the housing  109  to the rod  7  is also an excellent method since the welding can also secure the hermeticity, highly pressure resistance, satisfactory attachment to the rod  7 , and insusceptibility of the radio wave transmission/reception conditions to welding status.  
         [0057]     As shown in  FIG. 2 , the suspension device may also be provided with a position sensor  23  for detecting positional relationship between the super-spring structure and the sub-spring structure in the rod axis direction regarding at least one point. In this case, the position of the piston  12  calculated by the processor  24  of the radio wave radar sensor  13  is corrected based on the positional information obtained by the position sensor  23 , by which precise measurement of the position and self-diagnosis of the radio wave radar sensor  13  can be realized excellently.  
         [0058]     It is also possible to provide a wheel status estimating module  29  which estimates air pressure status and attachment status of the wheel based on the relative behavior information on the rod  7  and the inner cylinder  10 . By such composition, a burst, faulty attachment, poor balance, etc. of the wheel can be detected by the suspension device and that is highly advantageous.  
         [0059]     Incidentally, the relative behavior information on the rod  7  and the inner cylinder  10  can also be obtained by use of an acceleration sensor attached to the sub-spring structure for detecting acceleration, a linear sensor for obtaining positional information on the rod  7  and the inner cylinder  10 , an ultrasonic radar sensor, an optical radar sensor, etc., instead of using the radio wave radar sensor.  
         [0060]     As set forth hereinabove, by the suspension device in accordance with the above embodiment of the present invention, the behavior of the suspension device can be detected correctly and the result of the detection can be applied to suspension control, by which contributions of the suspension devices to the improvement of riding comfort and safety control of vehicles such as cars can be increased considerably.  
         [0061]     While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by those embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.  
         [0062]     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.