Patent Publication Number: US-2023141330-A1

Title: Active suspension device and vehicle with active suspension device

Description:
CROSS-REFERENCE STATEMENT 
     The present application is based on, and claims priority from, Japanese Patent Application Number 2021-182452, filed Nov. 9, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to an active suspension device and a vehicle with the active suspension device. 
     Related Art 
     Vehicles equipped with electric suspensions have in recent years been implemented mainly with skyhook control, providing ride comfort that cannot be achieved with conventional suspensions. In addition, preview control has been proposed for the purpose of realizing a vehicle body (a body) that does not vibrate (body vibration of 0) through the use of electric suspensions. The preview control detects an unevenness, a level difference, or the like of a road surface in advance with a sensor and uses the detected result to control an electric suspension. 
     Through the use of preview control, an electric suspension is capable of being controlled to make the body vibration zero. 
     Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 5-96922) discloses “an active suspension control device that detects a displacement X of a road surface and a vertical acceleration G at the front end of a body of a vehicle and stores them in time series. When the detection of the displacement is normal, a displacement of a road surface that the vehicle will pass over is estimated from the displacement X, and actuators at a front wheel and a rear wheel are controlled according to the estimated displacement of the road surface. When the detection of the displacement is abnormal, a vertical acceleration of a part corresponding to a rear wheel of the vehicle body is estimated from the vertical acceleration G in accordance with a wheelbase and vehicle speed, and an actuator of a rear wheel is controlled according to the estimated vertical acceleration” (see Abstract of Patent Literature 1). 
     A control means of the active suspension control device disclosed in Patent Literature 1 determines whether the detection of displacement by a road surface detection means is normal or abnormal. When it is determined that the detection of displacement is normal, the control means performs preview control. When it is determined that the detection of displacement is abnormal, the control means does not perform the preview control but controls the actuator of the rear wheel using the vertical acceleration stored in a storage means. 
     Here, when the detection of displacement is determined to be abnormal, because the control means controls the actuator of the rear wheel using the vertical acceleration stored in the storage means, vibration above a spring does not become zero. Because of this, it is possible for the ride comfort of a person on the vehicle to deteriorate. 
     Furthermore, when preview control cannot correctly be applied to a front wheel due to an effect of disturbance, noise, or the like, it is not preferable to apply preview control to the rear wheel. When, in a situation where preview control is not applicable, preview control is operated regardless, the ride comfort of the person on the vehicle might become worse. 
     SUMMARY 
     An active suspension device includes: a road surface state detector configured to detect a height of a road surface in front of a wheel; and a controller. The controller is configured to control a stroke of a suspension according to a variation of the height of the road surface detected by the road surface state detector to perform a preview control. The controller is configured to: change, as a front wheel preview control, a stroke of a suspension of a front wheel according to the variation of the height of the road surface detected by the road surface state detector to perform a preview control of the front wheel; determine, as a determination part, whether the preview control that has been performed by the front wheel preview control by changing the stroke of the suspension of the front wheel is successful; and control, as a rear wheel control, a stroke of a suspension of a corresponding rear wheel based on the determination of the determination part. In response to determining that the preview control of the front wheel is successful, the controller is configured, as the rear wheel control, to perform a preview control and a skyhook control of the corresponding rear wheel to control the stroke of the suspension of the corresponding rear wheel. In response to determining that the preview control of the front wheel is unsuccessful, the controller is configured, as the rear wheel control, to cancel the preview control of the corresponding rear wheel and perform the skyhook control of the corresponding rear wheel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic block diagram of a vehicle equipped with a suspension device in accordance with at least one embodiment of the disclosure. 
         FIG.  2    is a schematic diagram of a suspension of at least one embodiment. 
         FIG.  3    is a schematic diagram of a vehicle equipped with an active suspension device in accordance with at least one embodiment. 
         FIG.  4    is a functional block diagram showing a function of an ECU of an active suspension device in accordance with at least one embodiment. 
         FIG.  5    is an explanatory diagram for explaining load control of an ECU included in an active suspension device that is in accordance with at least one embodiment. 
         FIG.  6    is a flowchart showing an operation of the active suspension device in accordance with at least one embodiment. 
         FIG.  7 A  is an explanatory diagram showing a concept of a rear wheel control part of an ECU controlling a rear wheel with a success processing part when a preview control of a front wheel has been successful. 
         FIG.  7 B  is an explanatory diagram showing a concept of a rear wheel control part of an ECU controlling a rear wheel with a failure processing part when a preview control of a front wheel has been unsuccessful. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     An embodiment of the disclosure will be described in detail with reference to the drawings.  FIG.  1    is a schematic block diagram of a vehicle equipped with a suspension device in accordance with at least one embodiment of the disclosure.  FIG.  2    is a schematic diagram of a suspension in the present embodiment. 
     As shown in  FIGS.  1  and  2   , a vehicle body  12  of a vehicle  10  is configured to include a wheel  16  on the left and right and a wheel  56  on the left and right. The left and right wheels  16  are each fitted with a front wheel tire  14 . The left and right wheels  56  are each fitted with a rear wheel tire  54 . A front wheel is configured to include a front wheel tire  14  and a wheel  16 . A rear wheel is configured to include a rear wheel tire  54  and a wheel  56 . A front wheel may sometimes be indicated by a front wheel tire  14  or wheel  16 . A rear wheel may sometimes be indicated by a rear wheel tire  54  or wheel  56 . 
     Each of the wheels  16 ,  56  is suspended from the vehicle body  12  via a suspension. The suspension is configured to include a suspension arm  18 , a spring  20 , a variable-damping-force damper  22  (hereinafter referred to simply as a “damper  22 ”), or the like. The vehicle  10  is equipped with an electronic control unit (ECU)  24  that is configured to perform various types of control. The vehicle  10  is also equipped with a wheel speed sensor  26  for each of the wheels  16 ,  56  (wheels  16  and  56 ). Each wheel speed sensor  26  is configured to detect a wheel speed V of a corresponding wheel  16 ,  56  (a wheel  16  or  56 ). The wheel speed sensor  26  detects a rotational speed of a corresponding wheel  16 ,  56  as a detected signal (also referred to as a wheel speed signal). In the present embodiment, the ECU  24  changes (controls) a stroke of the suspension by controlling a length of the damper  22 . 
     The ECU  24  (a controller) is configured to include a microcomputer, ROM (read-only memory), RAM (random-access memory), a peripheral circuit, an input/output interface, various drivers, or the like. The microcomputer is configured to include a microprocessor. The ECU  24  is electrically connected to a damper  22  and vehicle speed sensor  26  of individual wheels  16 ,  56  (wheels  16  and  56 ) via a communication line (in the case of the present embodiment, via a Controller Area Network [CAN]  28 ). A suspension system is configured to include the ECU  24  and the wheel speed sensors  26 . The ECU  24  realizes a front wheel preview control part  241 , a preview control success determination part  242 , and a rear wheel control part  243  by executing a predetermined control program stored in the ROM. 
     By way of an example, the present embodiment is described for a case where an electromagnetic damper is used, but the disclosure is not limited thereto. The disclosure is applicable to active suspension that uses an air suspension and an active stabilizer. The vehicle  10  may be a front wheel drive vehicle, a rear wheel drive vehicle, or a four wheel drive vehicle. 
     In the present embodiment, the damper  22  is configured, for example, from a mono-tube type (de Carbon type) damper. This damper  22  includes a cylinder (in the shape of a cylinder and having an axis) filled with a magneto-rheological fluid (MRF). The damper  22  slidably accommodates a piston rod so that the piston rod is capable of axial movement relative to the cylinder. A piston mounted at the tip of the piston rod divides the inner side of the cylinder into an upper oil chamber and a lower oil chamber. A communicating passage for communicating the upper oil chamber and the lower oil chamber is provided between the upper oil chamber and the lower oil chamber. An MLV coil is disposed inside the communicating passage. 
     For example, the damper  22  is configured so that: a lower end of the cylinder is connected to a suspension arm  18  serving as a wheel-side member; and an upper end of the piston rod is connected to a damper base serving as a vehicle-body-side member. As shown in  FIG.  2   , each damper  22  is configured to connect, together with a spring  20 , a below-spring element having a mass M 1  and an above-spring element having a mass M 2  of a vehicle body  12 . The below-spring element is a movable element on a lower side of the suspension and includes a wheel  16 ,  56  (a wheel  16  or  56 ), a knuckle, a suspension arm  18 , or the like. 
     When an electric current is supplied from the ECU  24  to the MLV coil (not shown) of the damper  22 , a magnetic field is applied to the MRF flowing through the communicating passage causing ferromagnetic particles to form chain-like clusters. As a result, an apparent viscosity (hereinafter simply referred to as “viscosity”) of the MRF passing through the communicating passage increases, and the damping force of the damper  22  increases. Although a mono-tube type damper is employed as the damper  22  in the present embodiment, other types of dampers may be employed as deemed appropriate. 
     Further, the above-spring element is provided with an acceleration sensor  29  for detecting an acceleration of the vehicle body  12  (above spring) along a stroke axis of the damper  22 . The stroke axis refers to an axis along which a suspension stroke movement occurs. When the acceleration sensor  29  detects an acceleration of the vehicle body  12  (above spring), the ECU  24  obtains said acceleration as an above-spring acceleration. The ECU  24  obtains an above-spring speed by time integrating the above-spring acceleration with time series information. The acceleration sensor  29  may obtain a below-spring acceleration of the below-spring element, and the ECU  24  may obtain a below-spring speed of the below-spring element. The calculation of the above-spring speed or below-spring speed is not limited to time integration by the ECU  24 . The above-spring speed or below-spring speed may be obtained by using, for example, a gyroscope. 
     The vehicle  10  is equipped with a preview sensor (road surface state detector)  3  in front of a front wheel tire  14 . The preview sensor  3  is configured to detect a condition of a road surface  100  (see  FIG.  3   ) at the front of the vehicle  10 . A preview sensor  3  for the front wheel tire  14  on the left is provided on the left side of the vehicle  10 . A preview sensor  3  for the front wheel tire  14  on the right is provided on the right side of the vehicle  10 . Each preview sensor  3  detects a height of the road surface in front of each wheel  16 . The ECU  24  performs a preview control by controlling the stroke of a suspension according to a variation of the height of the road surface that is detected by a preview sensor  3 . An active suspension device  1  of the present embodiment is configured to include the preview sensor  3  and the ECU  24 . 
       FIG.  3    is a schematic diagram of a vehicle equipped with an active suspension device  1  in accordance with the present embodiment. As shown in  FIG.  3   , the preview sensor  3  detects a state (road surface state) of the road surface  100  at the front side of the vehicle  10 . 
     The preview sensor  3  is provided on a frame member F that make up a front portion of the vehicle body of the vehicle  10  (that is, the preview sensor  3  is provided on the vehicle body  12 ). The preview sensor  3  is located further to the front of the frame member F relative to a wheel  16  of a front wheel. As indicated by the outlined arrow, the preview sensor  3  detects the state of the road surface  100  immediately in front of the wheel  16  of the front wheel. The preview sensor  3  may be selected from a radar-type sensor, a camera-type sensor, a laser-type sensor, an ultrasonic-type sensor, or the like as deemed appropriate. The preview sensor  3  is not limited to being configured from a single sensor. The preview sensor  3  may be configured from a combination of sensors including different types of sensors, for example a camera-type sensor and a laser-type sensor. A preview sensor  3  is provided in front of a wheel  16  of each of the left and right front wheels. 
       FIG.  4    is a functional block diagram showing a function of the ECU  24  of the active suspension device  1  in accordance with the present embodiment. 
     The ECU  24  is configured to include a front wheel preview control part  241 , a preview control success determination part  242  (determination part), and a rear wheel control part  243 . The rear wheel control part  243  is configured to include a success processing part  244  and a failure processing part  245 . The ECU  24  controls the stroke of a suspension (the length of a damper  22 ) according to a variation of the height of the road surface  100  that has been detected by a preview sensor  3  (see  FIG.  3   ). 
     The front wheel preview control part  241  obtains the height of the road surface  100  in front of a wheel  16  of a front wheel from the preview sensor  3 . The front wheel preview control part  241  changes the stroke of the suspension of the front wheel according to a variation of the height of the road surface  100  detected by the preview sensor  3  to perform a preview control. For example, in accordance with an obtained height of the road surface  100 , the front wheel preview control part  241  adjusts the length of the damper  22  of a corresponding front wheel. 
     In other words, the front wheel on the right side of the vehicle  10  adjusts the length of the damper  22  of the front wheel on the right side according to a height of the road surface  100  on the right side. The front wheel on the left side of the vehicle  10  adjusts the length of the damper  22  of the front wheel on the left side according to a height of the road surface  100  on the left side. 
     The preview control success determination part  242  (determination part) determines whether a preview control by the front wheel preview control part  241 , which involves changing the length of the damper  22  (the stroke of the suspension) of a front wheel to control said stroke, is successful. 
     To determine whether the preview control has been successful (or unsuccessful), the preview control success determination part  242 , for example, compares an actual body operation with a theoretical vehicle model that assumes an operation when the preview control of the front wheel is turned off. The preview control success determination part  242  determines that the preview control of the front wheel has been unsuccessful (has failed) when the actual body operation is worse than the theoretical vehicle model. For example, the preview control success determination part  242  determines that the preview control of the front wheel has been unsuccessful (has failed) when a value of the actual body operation is worse than a value for the theoretical vehicle model. More specifically, the preview control success determination part  242  may determine that the preview control has been unsuccessful (has failed) when a value of a corresponding acceleration sensor  29  at a time when the front wheel is passing over a level difference of the road surface  100  is equal to or greater than a predetermined value. 
     Note that the determination of the preview control success determination part  242  is not limited to the comparison between the theoretical vehicle model and the actual body operation. For example, when the acceleration sensor  29  has an absolute value, the preview control success determination part  242  may determine that the preview control has been unsuccessful when the absolute value is equal to or greater than a predetermined threshold value of the acceleration sensor  29 , and cancel (in other words, turn off) a preview control of the rear wheel. 
     The rear wheel control part  243  controls the stroke of the suspension of a corresponding rear wheel based on the determination result of the preview control success determination part  242 . For example, the rear wheel control part  243  controls the stroke of the suspension by adjusting the length of a damper  22 . 
     For example, when the preview control success determination part  242  determines that a preview control of a front wheel has been successful, the rear wheel control part  243  performs, through the success processing part  244 , a preview control and a skyhook control of a corresponding rear wheel. 
     When, on the other hand, the preview control success determination part  242  determines that a preview control of a front wheel has failed, the rear wheel control part  243 , through the failure processing part  245 , cancels a preview control of a corresponding rear wheel and performs a skyhook control of the corresponding rear wheel. The skyhook control is a control for damping the vibration of the above-spring element (vehicle body  12 ) by actively adjusting the length of a damper  22  based on a skyhook theory. With skyhook control, information from the preview sensor  3  is not used. 
     As described above, when a preview control of a front wheel has been unsuccessful, the ECU  24  of the active suspension device  1  according to the present embodiment cancels a preview control for the suspension of a corresponding rear wheel and performs a skyhook control for the suspension of the corresponding rear wheel. 
     When the preview control of the front wheel fails, it is highly possible that a preview control of the rear wheel will also fail. The present embodiment is able to avoid performing a preview control for a rear wheel when the possibility of failure of the preview control is high. 
     In the above situation, the active suspension device  1  performs only the skyhook control on the rear wheel. This way, the present embodiment is able to prevent a possibility of the ride comfort of a person on the vehicle from becoming worse. In other words, because preview control that is highly likely to deteriorate ride comfort is not performed on the rear wheel, deterioration of the ride comfort can be avoided. 
     Furthermore, the rear wheel control part  243  may increase (change) a gain of the skyhook control of the rear wheel when the preview control of the front wheel has been successful compared to when the preview control of the front wheel has been unsuccessful. That is, the rear wheel control part  243  may increase the weight of the skyhook control of the rear wheel when the preview control of the front wheel has been successful. 
     To explain further, when the preview control of a front wheel has been successful, because skyhook control is performed for a portion that cannot be covered by preview control, a ratio of the skyhook control is smaller compared to when the preview control of the front wheel has been unsuccessful (when the preview control of the front wheel has been unsuccessful, the suspension of the rear wheel is controlled entirely by skyhook control). Therefore, when the preview control of the front wheel is successful, by increasing (changing) the gain of the skyhook control of the rear wheel, an amount of control for the rear wheel that may be deemed necessary may be outputted. Here, the rear wheel control part  243  according to the present embodiment is not limited to increasing the gain of the skyhook control of the rear wheel when the preview control of the front wheel has been successful compared to when the preview control of the front wheel has been unsuccessful. For example, the rear wheel control part  243  according to the present embodiment may change the gain so that a smaller gain is used when the preview control of the front wheel is successful compared to when the preview control of the front wheel is unsuccessful. 
     The rear wheel control part  243  controls, for each rear wheel, the stroke of the suspension of the rear wheel based on the determination result of the preview control of a corresponding front wheel. When the preview control of the left front wheel and the preview control of the right front wheel have been unsuccessful, the preview control is cancelled for each of the left and right rear wheels and the skyhook control is performed for each of the left and right rear wheels. When, on the other hand, the preview control of, for example, the right front wheel fails, the preview control of the right rear wheel is cancelled and the skyhook control of the right rear wheel is performed. 
     As described above, the active suspension device  1  according to the present embodiment performs preview control of a front wheel and, when the preview control fails, performs skyhook control on a corresponding rear wheel. In this way, the active suspension device  1  according to the present embodiment is able to prevent the possibility of a deterioration of the ride comfort of a person on the vehicle. 
     Next, load control related to preview control and skyhook control will be described. 
     Load Control of ECU 
       FIG.  5    is an explanatory diagram for explaining a load control of the ECU  24  of the active suspension device  1  according to an embodiment of the disclosure. It should be noted that the load control of the ECU  24  is an example of a function of the ECU  24  of the active suspension device  1  shown in  FIG.  4    and is not limited to this. 
     The ECU  24  shown in  FIG.  5    is configured to include an information obtaining part  251 , a target load calculation part  256 , and a load control part  255 . The target load calculation part  256  is configured to include a first target load calculator  252 , a second target load calculator  253 , and an integrating part  254 . 
     The information obtaining part  251  obtains information on a height (relative road-surface height) of the road surface  100  as time-series information of a road surface state of a road on which the vehicle  10  travels. The road surface condition is related to a road surface along a direction of travel of the vehicle  10 . The information on relative road-surface height is, for example, obtained by detecting a relative road-surface height of the vehicle  10  with by the preview sensor  3 . The relative road-surface height refers to a height of the above-spring element (vehicle body  12 ) relative to the road surface  100 . 
     For example, the information obtaining part  251  obtains time series information on each of the above-spring acceleration and the below-spring acceleration. Information on the above-spring acceleration is obtained based on a detected value of the acceleration sensor  29  that the above-spring element (vehicle body  12 ) of the vehicle  10  is equipped with. Information on the below-spring acceleration is obtained based on a detected value of an acceleration sensor (not shown) that the below-spring element of the vehicle  10  is equipped with. Note that the below-spring acceleration is an arbitrary component, and an embodiment is not particularly limited to the information obtaining part  251  obtaining the below-spring acceleration. In one or more embodiments, the information obtaining part  251  does not obtain the below-spring acceleration. 
     The information obtaining part  251  estimates an “above-spring speed” and an “absolute road-surface height” based on the height (relative road-surface height) of the road surface  100 , above-spring acceleration, and below-spring acceleration that have been obtained. For example, the information obtaining part  251  estimates the “above-spring speed” as a current vehicle state. The “absolute road-surface height” means an absolute height of the above-spring element (vehicle body  12 ) with respect to the road surface  100 . 
     In this case, based on the time series information of each of the above-spring acceleration, below-spring acceleration, and height of the road surface  100  (relative road-surface height), the information obtaining part  251  estimates the “absolute road-surface height”, which is obtained by subtracting an error associated with vehicle body vibration from a relative road-surface height that includes said error. In one or more embodiments, the information obtaining part  251  may obtain the “above-spring speed” and “below-spring speed” directly by using, for example, a gyroscope (and obtaining the “above-spring speed” and “below-spring speed” directly from the gyroscope). 
     Information on the “above-spring speed” (vehicle state quantity) estimated by the information obtaining part  251  is sent to the first target load calculator  252 . Information on the “absolute road-surface height” estimated by the information obtaining part  251  is sent to the second target load calculator  253 . 
     Next, based on the various information that has been obtained by the information obtaining part  251 , the target load calculation part  256  calculates, for example using arithmetic operation, an integrated target load. The integrated target load is a target value of a damping operation and an expansion/contraction operation of the damper  22 . 
     The first target load calculator  252  of the target load calculation part  256  calculates a first target load related to skyhook control based on the “above-spring speed” (vehicle state quantity) estimated by the information obtaining part  251 . More specifically, for example, the first target load calculator  252  calculates the first target load by using a control law based on the skyhook theory and multiplying the estimated “above-spring speed” (vehicle state quantity) by a skyhook damping coefficient. The first target load calculated by the first target load calculator  252  is sent to the integrating part  254 . 
     For the skyhook control of a rear wheel, when it is determined that a preview control of a front wheel is successful, the target load calculation part  256  may further multiply the first target load with a gain to change the gain of the skyhook control. 
     The second target load calculator  253  of the target load calculation part  256  calculates a second target load related to preview control based on the “absolute road-surface height” (an actual road-surface height) estimated by the information obtaining part  251 . More specifically, for example, the second target load calculator  253  calculates the second target load by using a control law based on the skyhook theory and multiplying the “absolute road-surface height” (actual road-surface height) with a preview-control gain. The second target load calculated by the second target load calculator  253  is sent to the integrating part  254 . 
     The integrating part  254  of the target load calculation part  256  adds the first target load calculated by the first target load calculator  252  and the second target load calculated by the second target load calculator  253  to obtain a combined target load. Information on the combined target load that has been obtained by the integrating part  254  is sent to the load control part  255 . 
     The load control part  255  calculates a target value of an electric current (target electric-current value) capable of achieving the combined target load calculated by the target load calculation part  256 . For example, the load control part  255  performs a drive control of an electric motor, that each of the dampers  22  is equipped with, so that a motor current of the electric motor (not shown) follows the calculated target electric-current value. 
     By performing the drive control of the electric motor in this manner, the length of the corresponding damper  22  may be adjusted to control the stroke of the corresponding suspension. 
     Operation of Active Suspension Device 
     Next, an operation of the active suspension device  1  according to the present embodiment will be described.  FIG.  6    is a flowchart showing the operation of the active suspension device  1  according to the present embodiment. The operation of the active suspension device  1  will be described with reference to  FIGS.  1 - 4    as appropriate. 
     First, a preview sensor  3  detects a height of the road surface  100  in front of a front wheel (wheel  16 ) of a travelling vehicle  10  (step S 11 ). 
     The front wheel preview control part  241  of the ECU  24  obtains the height of the road surface  100  in front of the front wheel from the preview sensor  3 . The front wheel preview control part  241  performs a preview control by changing the stroke of a suspension of the front wheel according to a variation of the height of the road surface  100  detected by the preview sensor  3  (step S 12 ). 
     For example, according to the obtained height of the road surface  100 , the front wheel preview control part  241  adjusts the length of the damper  22  of a corresponding wheel  16 . In the case of this example, a wheel  16  on the right side of the vehicle  10  adjusts the length of the damper  22  of the wheel  16  on the right side according to a height of the road surface  100  on the right side. Furthermore, in the case of this example, a wheel  16  on the left side of the vehicle  10  adjusts the length of the damper  22  of the wheel  16  on the left side according to a height of the road surface  100  on the left side. 
     The preview control success determination part  242  determines whether the preview control by the front wheel preview control part  241  involving changing the length (the stroke of the suspension) of the damper  22  of the front wheel and controlling said stroke is successful (or unsuccessful) (step S 13 ). 
     For example, the preview control success determination part  242  compares an actual body operation with a theoretical vehicle model that assumes an operation when a preview control of a wheel  16  is turned off. When the actual body operation is worse than the theoretical vehicle model, the preview control success determination part  242  determines that the preview control of the wheel  16  has been unsuccessful. For example, when a value of the actual body operation is worse than a value of the theoretical vehicle model, the preview control success determination part  242  determines that the preview control of the wheel  16  has been unsuccessful. More specifically, the preview control success determination part  242  may determine that the preview control has been unsuccessful when a value of a corresponding acceleration sensor  29  at a time when the wheel  16  is positioned over a level difference (for example, a bump) of the road surface  100  is equal to or greater than a predetermined value. 
     Note that the preview control success determination part  242  is not limited to comparing the theoretical vehicle model and the actual body operation. For example, when the acceleration sensor  29  has an absolute value, the preview control success determination part  242  may determine that the preview control has failed (not succeeded) when the absolute value is equal to or greater than a predetermined threshold value and cancel (i.e., turn off) the preview control of the rear wheel. 
     When the preview control success determination part  242  determines that the preview control of a wheel  16  has been successful (Yes in step S 13 ), the rear wheel control part  243  performs a preview control and a skyhook control to adjust the length of the damper  22  of a corresponding rear wheel through the success processing part  244  (step S 14 ). 
     When the preview control success determination part  242  determines that the preview control of a wheel  16  has been unsuccessful (No in step S 13 ), the rear wheel control part  243  cancels a preview control of a corresponding rear wheel and performs a skyhook control of the corresponding rear wheel through the failure processing part  245  (step S 15 ). 
     As described above, when the preview control of a front wheel fails (is unsuccessful), the ECU  24  of the active suspension device  1  according to the present embodiment cancels a preview control for the suspension of a corresponding rear wheel and performs a skyhook control for said suspension. In this way, the active suspension device  1  reduces the above-spring vibration to 0 through the skyhook control and therefore prevents the possibility of deterioration of a ride comfort of a person travelling in the vehicle  10 . 
     Effect of the Present Embodiment 
     An object of the disclosure is to provide an active suspension device and a vehicle equipped with the active suspension device that are capable of preventing a deterioration in a ride comfort of a person on a vehicle. 
     According to the disclosure, it is possible to provide an active suspension device and a vehicle equipped with the active suspension device that are capable of preventing a deterioration in a ride comfort of a person on a vehicle. 
       FIG.  7 A  is an explanatory diagram showing a concept of the rear wheel control part  243  of the ECU  24  controlling a rear wheel through the success processing part  244  when a preview control of a front wheel is successful.  FIG.  7 B  is an explanatory diagram showing a concept of the rear wheel control part  243  of the ECU  24  controlling the rear wheel through the failure processing part  245  when the preview control of the front wheel is unsuccessful. 
     After a preview control of a front wheel is performed, the ECU  24  determines whether the preview control of the front wheel has been successful or unsuccessful through the preview control success determination part  242 . The rear wheel control part  243  controls the stroke of the suspension of a rear wheel corresponding to the front wheel based on the determination result of the preview control success determination part  242 . 
     As shown in  FIG.  7 A , when the preview control success determination part  242  determines that a preview control of the front wheel tire  14  on the right side of the vehicle  10  has been successful, the rear wheel control part  243  performs a preview control and a skyhook control through the success processing part  244  to control the stroke of the suspension for the rear wheel (rear wheel tire  54 ) on the right side of the vehicle  10  (in other words, the rear wheel on the same side as the front wheel). 
     The left side of  FIG.  7 A  (see [A- 1 ] of  FIG.  7 A ) shows that, after the front wheel tire  14  on the right side has passed over a projection  104 , the preview control success determination part  242  determines that a preview control by the front wheel preview control part  241  has been successful. The right side of  FIG.  7 A  (see [A- 2 ] of  FIG.  7 A ) shows that, due to the success of the preview control, the rear wheel control part  243  performs a preview control and a skyhook control for the rear wheel (rear wheel tire  54 ) on the right side through the success processing unit  244 . 
       FIG.  7 B  shows a different case.  FIG.  7 B  is an illustration of when the preview control success determination part  242  determines that a preview control of the front wheel tire  14  on the right side of the vehicle  10  has been unsuccessful, and the rear wheel control part  243  cancels a preview control for the rear wheel (rear wheel tire  54 ) on the right side and performs a skyhook control for the rear wheel (rear wheel tire  54 ) on the right side through the failure processing part  245 . 
     The left side of  FIG.  7 B  (see [B- 1 ] of  FIG.  7 B ) shows that, after the front wheel tire  14  on the right side has passed over the projection  104 , the preview control success determination part  242  determines that the preview control by the front wheel preview control part  241  has been unsuccessful (failed). The right side of  FIG.  7 B  (see [B- 2 ] of  FIG.  7 B ) shows that, due to the failure of the preview control, the rear wheel control part  243  cancels a preview control for the rear wheel (rear wheel tire  54 ) on the right side (the same side as the front wheel) and performs a skyhook control for the rear wheel (rear wheel tire  54 ) on the right side (the same side as the front wheel) through the failure processing part  245 . 
     Through the failure processing part  245 , the rear wheel control part  243  may, by performing a skyhook control, perform a suspension control that uses skyhook control without preview control. In this way, the ECU  24  absorbs the vibration generated in the rear wheel tire  54  on the right side. Failure of the preview control of a front wheel occurs, for example, when the projection  104  is unable to be detected. 
     As described above, the rear wheel control part  243  may increase the gain of the skyhook control of the rear wheel tire  54  when the preview control of the front wheel tire  14  is successful compared with the gain of the skyhook control of the rear wheel tire  54  when the preview control of the front wheel tire  14  is unsuccessful. In this way, by increasing the gain of the skyhook control of the rear wheel when the preview control of the front wheel is successful, a required amount of control may be outputted, and the damper  22  of the rear wheel tire  54  is able to absorb the vibration of the vehicle  10  more compared to when the gain is not increased. 
     As described above, the active suspension device  1  according to the first embodiment is configured to include a preview sensor  3  and an ECU  24 . The ECU  24  is configured to include a front wheel preview control part  241 , a preview control success determination part  242 , and a rear wheel control part  243 . 
     When the preview control success determination part  242  determines that a preview control of a front wheel has been successful, the rear wheel control part  243  performs a preview control and a skyhook control to control the stroke of a suspension for a corresponding rear wheel through the success processing unit  244 . When, on the other hand, the preview control success determination part  242  determines that a preview control of a front wheel has been unsuccessful, the rear wheel control part  243  cancels a preview control for a corresponding rear wheel and performs a skyhook control for the corresponding rear wheel through the failure processing part  245 . 
     In this way, the active suspension device  1  according to the first embodiment prevents a risk of deterioration of the ride comfort of a person on the vehicle  10  even when the preview control success determination part  242  determines that the preview control of the front wheel has been unsuccessful. 
     In the present embodiment, the preview control success determination part  242  determines the preview control by the front wheel preview control part  241 . However, the determination of a preview control is not limited to the description of above. 
     For example, when the preview sensor  3  detects an object such as a plastic bag or a plastic bottle and detects a height of the road surface  100 , the front wheel preview control part  241  changes the length (the stroke of the suspension) of the damper  22  of a front wheel based on a height of the object such as a plastic bag or a plastic bottle. In this case, when a front wheel tire  14  steps on the object such as a plastic bag or a plastic bottle, the object becomes deformed. This means that the height of the road surface  100  that was detected by the preview sensor  3  is erroneous. 
     An embodiment according to the disclosure is able to determine the failure of the preview control even in such a case, as will be described next. When an erroneous detection of a height of the road surface  100  by the preview sensor  3  occurs due to an object such as a plastic bag or a plastic bottle, the length of the damper  22  of a front wheel becomes inappropriate as the object deforms. The inappropriate length of the damper  22  of the front wheel causes an above-spring acceleration of the above-spring element or a below-spring acceleration of the below-spring element of the vehicle body  12  to change. 
     By setting a predetermined threshold value of the acceleration sensor to a relatively low value, the preview control success determination part  242  may make a detailed determination on whether the preview control of the front wheel is successful. This way, when the height of the road surface  100  is erroneously detected by the object such as a plastic bag or a plastic bottle, the rear wheel control part  243  is able to perform a skyhook control for a rear wheel tire  54  through the failure processing part  245 .