Patent Publication Number: US-2021179224-A1

Title: Posture control actuator unit and leaning vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part application of International Application PCT/JP2019/034102 filed on Aug. 30, 2019, which claims priority from a Japanese Patent Application No. 2018-161335, filed on Aug. 30, 2018. The contents of the applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present teaching relates to a posture control actuator unit and a leaning vehicle including a posture control actuator configured to output a posture control torque to control the posture of a vehicle body frame. 
     BACKGROUND ART 
     For example, a motorcycle disclosed in Patent Literature 1 is known as a conventional leaning vehicle. This motorcycle includes a vehicle body frame and an IMU (inertial measurement unit). The vehicle body frame leans leftward when the motorcycle is turning left and leans rightward when the motorcycle is turning right. The IMU includes three kinds of angular rate sensors and three kinds of acceleration sensors. The IMU obtains the pitch rate, the yaw rate and the roll rate of the vehicle body frame from the three kinds of angular rate sensors. The IMU obtains the acceleration in an x-axis direction, the acceleration in a y-axis direction and the acceleration in a z-axis direction of the vehicle body frame from the three kinds of acceleration sensors. The x-axis direction is a left-right direction of the motorcycle in an upright posture. The y-axis direction is an up-down direction of the motorcycle in an upright posture. The z-axis direction is a front-back direction of the motorcycle in an upright posture. The pitch rate is an angular rate when the vehicle body frame is rotating around the x-axis. The yaw rate is an angular rate when the vehicle body frame is rotating around the y-axis. The roll rate is an angular rate when the vehicle body frame is rotating around the z-axis. 
     The IMU can calculate the speed of the motorcycle and the angle of the vehicle body frame, based on the pitch rate, the yaw rate, the roll rate, the acceleration in the x-axis direction, the acceleration in the y-axis direction and the acceleration in the z-axis direction. The IMU, for example, calculates a bank angle of the vehicle body frame based on the roll rate. The bank angle is an angle formed by the y-axis and a center line of the vehicle body frame in a backward view thereof. The center line of the vehicle body frame is a line extending along the y-axis from a center of the vehicle body frame in an upright posture with respect to a vehicle-body-frame-left-right direction in a backward view thereof. The vehicle body-frame-left-right direction is the left-right direction of the vehicle body frame. Thus, in the motorcycle disclosed in Patent Literature 1, the IMU detects the posture (angle) of the vehicle body frame, such as a bank angle or the like. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2016-531046 
     SUMMARY OF INVENTION 
     Technical Problem 
     In leaning vehicles such as motorcycles, detection of a posture change (angular rate) such as a roll rate is required in some cases, depending on what kind of posture control is employed for posture control of the vehicle body frame. Then, in some leaning vehicles, the posture control of the vehicle body frame is possibly performed based on the roll rate detected by an angular rate sensor included in an IMU. For accurate posture control of the vehicle body frame, it is preferred to detect the roll rate accurately. 
     Therefore, the present invention provides a posture control actuator unit including an angular rate sensor that can detect a posture change of a vehicle body frame with high accuracy and a leaning vehicle. 
     Solution to Problem 
     The present inventors conducted studies about detection of a posture change (angular rate) of a vehicle body frame by use of an IMU. The IMU includes an acceleration sensor and an angular rate sensor. The acceleration sensor is to detect the acceleration of the vehicle body frame caused by a run of the leaning vehicle. The acceleration of the vehicle body frame includes an acceleration of the vehicle body frame caused by a run of the leaning vehicle and an acceleration of the vehicle body frame caused by engine vibration. The absolute value of the acceleration of the vehicle body frame caused by engine vibration is greater than the absolute value of the acceleration of the vehicle body frame caused by a run of the leaning vehicle. For example, the absolute value of the acceleration of the vehicle body frame caused by engine vibration is tens of G. On the other hand, the absolute value of the acceleration of the vehicle body frame caused by a run of the leaning vehicle is several G. The acceleration of the vehicle body frame caused by engine vibration is noise for detection of the acceleration of the vehicle body frame caused by a run of the leaning vehicle. Therefore, the acceleration sensor preferably detects the acceleration of the vehicle body frame caused by a run of the leaning vehicle while not detecting the acceleration of the vehicle body frame caused by engine vibration. 
     In the circumstances, such an IMU is typically attached to a vehicle body frame via an elastic member such as a rubber mount or the like. This makes it harder for engine vibration to propagate to the vehicle body frame, and the acceleration sensor can accurately detect the acceleration of the vehicle body frame caused by a run of the leaning vehicle. 
     However, the present inventors found that there are some cases in which the elastic member prevents the IMU from accurately detecting a posture change (angular rate) of the vehicle body frame. More specifically, when the vehicle body frame makes a posture change, an inertial force acts on the IMU, and the rubber mount is deformed. Accordingly, a posture change of the angular rate sensor of the IMU delays from the posture change of the vehicle body frame. 
     The present inventors conducted studies about what kind of sensor is necessary to detect a posture change of a vehicle body frame. Then, the present inventors found out that an angular rate sensor is necessary to detect a posture change of a vehicle body frame and that an acceleration sensor is not necessary. The present inventors conceived of not using the angular rate sensor of the IMU but using an angular rate sensor disposed outside the IMU for detection of a posture change of the vehicle body frame. Then, it would become possible to attach the angular rate sensor to the vehicle body frame not via an elastic member. This would inhibit a delay of a posture change of the angular rate sensor from a posture change of the vehicle body frame, and detection of a posture change of a leaning vehicle by use of an angular rate sensor would become more accurate. 
     However, an angular rate sensor is to detect a posture change (angular rate) of a vehicle body frame, and therefore, the angular rate sensor is required to be attached to the vehicle body frame in a proper position and in a proper direction (which will hereinafter be referred to as with high positional accuracy). The present inventors conducted studies about where in a vehicle body frame an angular rate sensor can be attached with high positional accuracy. The present inventors took notice of a posture control actuator used for posture control of the vehicle body frame. The posture control actuator is configured to output posture control power to control the posture of the vehicle body frame. Therefore, the posture control actuator is designed to be positioned at a predetermined angle to a roll axis or the like that is associated with a posture change of the vehicle body frame. For example, when the posture control actuator is an EPS (electric power steering) actuator, in some cases, the posture control actuator is positioned such that the rotation axis thereof is parallel to a steering shaft. For example, when the posture control actuator is an EPL actuator, in some cases, the posture control actuator is positioned such that the rotation axis thereof is parallel to a rotation axis of the vehicle body frame. Thus, a posture control actuator is attached to a vehicle body frame with high positional accuracy. Accordingly, the present inventors conceived of using an existing posture control actuator for attachment of an angular rate sensor to a vehicle body frame. In other words, the present inventors conceived of integrating an angular rate sensor and a posture control actuator into a posture control actuator unit (i.e., a posture control actuator device) and attaching the posture control actuator unit to a vehicle body frame. 
     (1) A posture control actuator unit for a leaning vehicle, the leaning vehicle including a vehicle body frame that is configured to lean in a leaning-vehicle-leftward direction when the leaning vehicle is turning left and to lean in a leaning-vehicle-rightward direction when the leaning vehicle is turning right, 
     the posture control actuator unit comprising:
         a posture control actuator configured to output posture control power to control posture of the vehicle body frame; and   an angular rate sensor configured to detect an angular rate that is an amount of change per unit time of a rotation angle of the vehicle body frame around a rotation axis, the rotation angle changing as the vehicle body frame is rotating around the rotation axis;       

     wherein the posture control actuator unit is supported by the vehicle body frame in such a manner as to be attachable to and detachable from the vehicle body frame, the posture control actuator and the angular rate sensor being incorporated in such a manner as not to be displaceable relative to each other. 
     The angular rate sensor of the posture control actuator unit of (1) can detect a posture change of the vehicle body frame with high accuracy. More specifically, the posture control actuator outputs posture control power to control the posture of the vehicle body frame. For this purpose, the posture control actuator unit is supported by the vehicle body frame in such a manner as to be attachable to and detachable from the vehicle body frame. Accordingly, a posture change of the posture control actuator is unlikely to delay from a posture change of the vehicle body frame. The posture control actuator and the angular rate sensor are incorporated in such a manner as not to be displaceable relative to each other. Accordingly, a posture change of the angular rate sensor is unlikely to delay a posture change of the vehicle body frame. Therefore, the angular rate sensor of the posture control actuator unit of (1) can detect a posture change of the vehicle body frame with high accuracy. 
     The angular rate sensor of the posture control actuator unit of (1) can detect a posture change of the vehicle body frame with high accuracy. More specifically, the posture control actuator outputs posture control power to control the posture of the vehicle body frame. For this purpose, the posture control actuator is designed to be positioned at a predetermined angle to a roll axis or the like that is associated with a posture change of the vehicle body frame. For example, when the posture control actuator is an EPS actuator, the posture control actuator may be positioned such that the rotation axis thereof is parallel to a steering shaft. For example, when the posture control actuator is an EPL actuator, the posture control actuator may be positioned such that the rotation axis thereof is parallel to a rotation axis of the vehicle body frame. Thus, the posture control actuator is attached to the vehicle body frame with high positional accuracy. The posture control actuator and the angular rate sensor are incorporated in such a manner as not to be displaceable relative to each other. Accordingly, the angular rate sensor is attached to a sensor mounting position of the vehicle body frame with high accuracy. Therefore, the angular rate sensor of the posture control actuator unit of (1) can detect a posture change of the vehicle body frame with high accuracy. 
     Also, the posture control actuator of the posture control actuator unit of (1) is attached to the vehicle body frame with high positional accuracy. Accordingly, it is easy to make the axis for the angular rate detection carried out by the angular rate sensor almost parallel to the rotation axis of the vehicle body frame. Then, the angular rate sensor can detect the angular rate of the vehicle body frame with high accuracy. Even when the axis for the angular rate detection carried out by the angular rate sensor is not parallel to the rotation axis of the vehicle body frame, it is easy to identify the angle formed between the axis for the angular rate detection carried out by the roll rate sensor and the rotation axis of the vehicle body frame. Accordingly, it is easy to make a correction to the roll rate detected by the angular rate sensor. 
     The posture control actuator unit of (1) can be downsized. More specifically, in the posture control actuator unit of (1), the posture control actuator and the angular rate sensor are incorporated in such a manner as not to be displaceable relative to each other. Accordingly, it is not necessary to provide a mount for attachment of the roll rate sensor to the vehicle body frame. Therefore, the number of components of the posture control actuator unit of (1) can be reduced, and the posture control actuator unit of (1) can be downsized. 
     (2) The posture control actuator unit according to (1), further comprising a posture control actuator controller configured to control the posture control actuator based on the angular rate detected by the angular rate sensor, wherein 
     the posture control actuator unit is supported by the vehicle body frame in such a manner as to be attachable to and detachable from the vehicle body frame, the posture control actuator controller, the posture control actuator and the angular rate sensor being incorporated in such a manner as not to be displaceable relative to one another. 
     (3) A leaning vehicle comprising: 
     a vehicle body frame that is configured to lean in a leaning-vehicle-leftward direction when the leaning vehicle is turning left and to lean in a leaning-vehicle-rightward direction when the leaning vehicle is turning right; 
     at least one steerable wheel supported by the vehicle frame body; 
     a steering mechanism configured to steer the at least one steerable wheel in accordance with a rider&#39;s manipulation; and 
     the posture control actuator unit according to (1) or (2). 
     The leaning vehicle of (3) comprises the posture control actuator unit of (1) or (2), and therefore, the angular rate sensor can detect a posture change of the vehicle body frame with high accuracy. 
     (4) The leaning vehicle according to (3), wherein, in a vehicle-body-frame-backward view, the posture control actuator unit overlaps a center line passing a center of the vehicle body frame with respect to a vehicle-body-frame-left-right direction and extending along a vehicle-body-frame-up-down direction. 
     (5) The leaning vehicle according to (3) or (4), wherein the angular rate sensor is a roll rate sensor configured to detect a roll rate that is an amount of change per unit time of a rotation angle of the vehicle body frame around a roll axis, the rotation angle changing as the vehicle body frame is rotating around the roll axis. 
     The roll rate sensor of the leaning vehicle of (5) can detect a change of the roll angle accurately. 
     (6) The leaning vehicle according to (5), wherein: 
     the steering mechanism includes a handlebar to be manipulated by the rider, and a steering shaft supported by the vehicle body frame in such a manner as to be rotatable on its axis in accordance with the rider&#39;s manipulation of the handlebar; and 
     the posture control actuator is configured to output posture control power to cause the steering shaft to rotate on its axis. 
     (7) The leaning vehicle according to (5), wherein: 
     the at least one steerable wheel includes a left steerable wheel that is positioned farther in a vehicle-body-frame-leftward direction than a center of the vehicle body frame with respect to a vehicle-body-frame-left-right direction and is rotatable around a left front axle, and a right steerable wheel that is positioned farther in a vehicle-body-frame-rightward direction than the center of the vehicle frame with respect to the vehicle-body-frame-left-right direction and is rotatable around a right front axle; 
     the leaning vehicle further comprises a link mechanism including a plurality of link members that are displaceable relative to the vehicle body frame and supporting the left steerable wheel and the right steerable wheel, the link mechanism being configured to cause the leaning vehicle to lean in the vehicle-body-frame-leftward direction when the leaning vehicle is turning left by displacing the vehicle body frame and the plurality of link members relative to one another such that the left steerable axle is positioned farther in a vehicle-body-frame-upward direction than the right steerable axle, and to cause the leaning vehicle to lean in the vehicle-body-frame-rightward direction when the leaning vehicle is turning right by displacing the vehicle body frame and the plurality of link members relative to one another such that the right steerable axle is positioned farther in the vehicle-body-frame-upward direction than the left steerable axle; and 
     the posture control actuator is configured to output posture control power to displace the vehicle body frame and the plurality of link members relative to one another. 
     In the leaning vehicle of (7), the posture control actuator controller controls the operation of the link mechanism, based on the roll rate of the vehicle body frame accurately detected by the roll rate sensor. When the link mechanism operates, the vehicle body frame rotates around the roll axis. Therefore, the posture control actuator controller of the leaning vehicle of (7) can control the posture of the vehicle body frame with high accuracy. 
     Some embodiments of the present teaching will hereinafter be described in detail with reference to the drawings, and the detailed description of the embodiments will provide a clearer picture of the above-mentioned object and other objects, the features, the aspects and the advantages of the present teaching. 
     The term “and/or” used herein includes one of the associated items in a list and all possible combinations of the associated items. 
     The terms “including”, “comprising”, or “having”, and variations thereof used herein specify the presence of stated features, steps, operations, elements, components, and/or equivalents thereof, and can include one or more of steps, operations, elements, components, and/or their groups. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present teaching pertains. 
     It should be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the present disclosure and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     It should be understood that the description of the present teaching discloses a number of techniques and steps. Each of these has individual benefit, and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques. Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, Description and Claims should be read with the understanding that such combinations are entirely within the scope of the present teaching and the claims. 
     In the description given below, for the purpose of explanation, numerous specific details are set forth in order to provide a complete understanding of the present teaching. It will be apparent, however, that those skilled in the art may practice the present teaching without these specific details. The present disclosure is to be considered as an exemplification of the present teaching, and is not intended to limit the present teaching to the specific embodiments illustrated by drawings or descriptions below. 
     Advantageous Effects of Invention 
     The present teaching permits highly accurate detection of a posture change of a vehicle body frame by use of an angular rate sensor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a looking-to-the-right (R) view of a leaning vehicle  1 . 
         FIG. 1B  is a looking-to-the-right (R) view of a leaning vehicle  1   a.    
         FIG. 2  is a looking-to-the-back (B) view of the leaning vehicle  1   a.    
         FIG. 3  is a looking-to-the-down (D) view of the leaning vehicle  1   a.    
         FIG. 4  is a looking-to-the-back (B) view of the leaning vehicle  1   a.    
         FIG. 5  is a block diagram of a posture control actuator controller  606 . 
         FIG. 6  is a flowchart showing operations carried out by the posture control actuator controller  606 . 
         FIG. 7  is a looking-to-the-right (r) view of the leaning vehicle  1   b  when its vehicle body frame  21  is in an upright posture. 
         FIG. 8  is a looking-to-the-back (b) view of a front part of the leaning vehicle  1   b  when its vehicle body frame  21  is in an upright posture. 
         FIG. 9  is a looking-to-the-down (d) view of the front part of the leaning vehicle  1   b  when its vehicle body frame  1021  is upright. 
         FIG. 10  is a looking-to-the-down (d) view of the front part of the leaning vehicle  1   b  when the leaning vehicle  1   b  is steered leftward. 
         FIG. 11  is a looking-to-the-back (b) view of the front part of the leaning vehicle  1   b  when its vehicle body frame  1021  is leaning in a leftward direction L. 
         FIG. 12  is a block diagram of a posture control actuator controller  1606 . 
         FIG. 13  is a flowchart showing operations carried out by the posture control actuator controller  1606 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (Outline) 
     The overall structure of a leaning vehicle  1  according to the gist of the present teaching will hereinafter be described with reference to the drawings. A two-wheeled leaning vehicle (which will hereinafter be referred to simply as a leaning vehicle) including a vehicle body frame  21  capable of leaning, a front wheel, and a rear wheel will hereinafter be described as an example of the leaning vehicle  1 .  FIG. 1  is a looking-to-the-right (R) view of the leaning vehicle  1 . 
     A posture control actuator unit (posture control actuator device)  599  is used for the leaning vehicle  1  wherein the vehicle body frame  21  leans leftward when the leaning vehicle  1  is turning left and leans rightward when the leaning vehicle  1  is turning right. 
     The posture control actuator unit  599  includes a posture control actuator  600   o  and an angular rate sensor  602   o . The posture control actuator  600   o  is configured to output posture control power to control the posture of the vehicle body frame  21 . The posture control actuator  600   o  is, for example, an EPS actuator, an EPL actuator, or the like. 
     As the vehicle body frame  21  is rotating around a rotation axis Axo, the rotation angle of the vehicle body frame  21  around the rotation axis Axo changes, and the angular rate sensor  602   o  is configured to detect the angular rate that is the amount of change per unit time of the rotation angle. The rotation axis Axo is, for example, a roll axis, a pitch axis, a yaw axis, or the like. In the example shown in  FIG. 1 , the angular rate is, for example, a roll rate, a pitch rate, a yaw rate, or the like. 
     The posture control actuator unit  599  is supported by the vehicle body frame  21  in such a manner as to be attachable to and detachable from the vehicle body frame  21 , and the posture control actuator  600   o  and the angular rate sensor  602   o  are incorporated in such a manner as not to be displaceable relative to each other. The statement that “the posture control actuator unit  599  is supported by the vehicle body frame  21  in such a manner as to be attachable to and detachable from the vehicle body frame  21 ” means, for example, that the posture control actuator unit  599  is fastened to the vehicle body frame  21  via a fastener member such as a screw, a combination of a bolt and a nut, or the like. The statement that “the posture control actuator unit  599  is supported by the vehicle body frame  21  in such a manner as to be attachable to and detachable from the vehicle body frame  21 ” does not include, for example, that the posture control actuator unit  599  is bonded to the vehicle body frame  21  only via an adhesive. However, the statement that “the posture control actuator unit  599  is supported by the vehicle body frame  21  in such a manner as to be attachable to and detachable from the vehicle body frame  21 ”, includes, for example, that the posture control actuator unit  599  is fastened to the vehicle body frame  21  mainly via a fastener member such as a screw, a combination of a bolt and a nut, or the like, and subsidiarily via an adhesive. The statement that the posture control actuator  600   o  and the angular rate sensor  602   o  are not displaceable relative to each other means that the relative positional relationship between the posture control actuator  600   o  and the angular rate sensor  602   o  is not variable. In this specification, when it is stated that a first member and a second member are not displaceable relative to each other, it also means that there is no elastic member for impact absorption, such as a rubber mount or the like, in the power transmission route between the first member and the second member. 
     The angular rate sensor  602   o  of the posture control actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. More specifically, the posture control actuator  600   o  outputs posture control power to control the posture of the vehicle body frame  21 . For the purpose, the posture control actuator unit  599  is supported by the vehicle body frame  21  in such a manner as to be attachable to and detachable from the vehicle body frame  21 . This inhibits a delay of a posture change of the posture control actuator  600   o  from a posture change of the vehicle body frame  21 . The posture control actuator  600   o  and the angular rate sensor  602   o  are incorporated in such a manner as not to be displaceable relative to each other. This inhibits a delay of a posture change of the angular rate sensor  602   o  from a posture change of the vehicle body frame  21 . Accordingly, the angular rate sensor  602   o  of the posture control actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. 
     The angular rate sensor  602   o  of the posture control actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. More specifically, the posture control actuator  600   o  outputs posture control power to control the posture of the vehicle body frame  21 . For the purpose, the posture control actuator  600   o  is designed to be positioned at a predetermined angle to the roll axis or the like that is associated with the posture change of the vehicle body frame  21 . For example, when the posture control actuator  600   o  is an EPS actuator, the posture control actuator  600   o  may be positioned such that the rotation axis of the posture control actuator  600   o  is parallel to a steering shaft. For example, when the posture control actuator  600   o  is an EPL actuator, the posture control actuator  600   o  may be positioned such that the rotation axis of the posture control actuator  600   o  is parallel to a rotation axis of the vehicle body frame  21 . Thus, the posture control actuator  600   o  is attached to the vehicle body frame  21  with high positional accuracy. Then, the posture control actuator  600   o  and the angular rate sensor  602   o  are incorporated in such a manner as not to be displaceable relative to each other. Accordingly, the angular rate sensor  602   o  is also mounted at a sensor mounting position of the vehicle body frame  21  with high positional accuracy. Therefore, the angular rate sensor  600   o  of the posture control actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. 
     The posture control actuator  600   o  of the posture control actuator unit  599  is attached to the vehicle body frame  21  with high positional accuracy. Therefore, it is easy to make the axis for the angular rate detection carried out by the angular rate sensor  602   o  almost parallel to the rotation axis Axo of the vehicle body frame  21 . Accordingly, the angular rate sensor  602   o  can detect the angular rate of the vehicle body frame  21  with high accuracy. Also, even when the axis for the angular rate detection carried out by the angular rate sensor  602   o  is not parallel to the rotation axis Axo of the vehicle body frame  21 , the angle formed between the axis for the angular rate detection carried out by the angular rate sensor  602   o  and the rotation axis Axo of the vehicle body frame  21  is easily identified. Then, it is easy to make a correction to the angular rate detected by the angular rate sensor  602   o.    
     Also, the posture control actuator unit  599  can be downsized. More specifically, in the posture control actuator unit  599 , the posture control actuator  600   o  and the angular rate sensor  602   o  are incorporated in such a manner as not to be displaceable relative to each other. Therefore, it is not necessary to provide a mount for attachment of the angular rate sensor  602   o  to the vehicle body frame  21 . Accordingly, the number of components of the posture control actuator unit  599  is reduced, and the posture control actuator unit  599  is downsized. 
     First Embodiment 
     [Overall Structure] 
     The overall structure of a leaning vehicle  1   a  according to a first embodiment will hereinafter be described with reference to the drawings. In the present embodiment, as an example of a leaning vehicle, a two-wheeled leaning vehicle (which will hereinafter be referred to simply as a leaning vehicle) including a vehicle body frame capable of leaning, a front wheel, and a rear wheel is described.  FIG. 1B  is a looking-to-the-right (R) view of the leaning vehicle  1   a .  FIG. 2  is a schematic looking-to-the-back (B) view of the leaning vehicle  1   a . In  FIG. 2 , the leaning vehicle  1   a  is in an upright posture. Since  FIG. 2  is a schematic view, there are some inconsistencies in size, etc. between  FIG. 1B  and  FIG. 2 .  FIG. 2  shows only principal parts, and a vehicle body cover  22  is omitted in  FIG. 2 . 
     In the following paragraphs, a forward direction in a front-back direction of the leaning vehicle  1   a  is referred to as a forward direction F (leaning-vehicle-forward direction). A backward direction in the front-back direction of the leaning vehicle  1   a  is referred to as a backward direction B (leaning-vehicle-backward direction). A leftward direction in a left-right direction of the leaning vehicle  1   a  is referred to as a leftward direction L (leaning-vehicle-leftward direction). A rightward direction in the left-right direction of the leaning vehicle  1   a  is referred to as a rightward direction R (leaning-vehicle-rightward direction). An upward direction in an up-down direction of the leaning vehicle  1   a  is referred to as an upward direction U (leaning-vehicle-upward direction). A downward direction in an up-down direction of the leaning vehicle  1   a  is referred to as a downward direction D (leaning-vehicle-downward direction). The front-back direction of the leaning vehicle  1   a  is referred to as a front-back direction FB (leaning-vehicle-front-back direction). The left-right direction of the leaning vehicle  1   a  is referred to as a left-right direction LR (leaning-vehicle-left-right direction). The up-down direction of the leaning vehicle  1   a  is referred to as an up-down direction UD (leaning-vehicle-up-down direction). The forward direction in the front-back direction of the leaning vehicle  1   a  is a forward direction relative to a rider straddling the leaning vehicle  1   a . The backward direction in the front-back direction of the leaning vehicle  1   a  is a backward direction relative to a rider straddling the leaning vehicle  1   a . The leftward direction in the left-right direction of the leaning vehicle  1   a  is a leftward direction relative to a rider straddling the leaning vehicle  1   a . The rightward direction in the left-right direction of the leaning vehicle  1   a  is a rightward direction relative to a rider straddling the leaning vehicle  1   a . The upward direction in the up-down direction of the leaning vehicle  1   a  is an upward direction relative to a rider straddling the leaning vehicle  1   a . The downward direction in the up-down direction of the leaning vehicle  1   a  is a downward direction relative to a rider straddling the leaning vehicle  1   a.    
     The vehicle body frame  21  of the leaning vehicle  1   a  is capable of leaning in the leftward direction L and the rightward direction R. When the vehicle body frame  21  leans in the leftward direction L or the rightward direction R, the up-down direction and the left-right direction of the vehicle body frame  21  do not respectively coincide with the up-down direction UD and the left-right direction LR of the leaning vehicle  1   a . On the other hand, when the vehicle body frame  21  is in an upright posture, the up-down direction and the left-right direction of the vehicle body frame  21  coincide with the up-down direction UD and the left-right direction LR, respectively, of the leaning vehicle  1   a . In the following paragraphs, a forward direction along the front-back direction of the vehicle body frame  21  is referred to as a forward direction f (vehicle-body-frame-forward direction). A backward direction along the front-back direction of the vehicle body frame  21  is referred to as a backward direction b (vehicle-body-frame-backward direction). A leftward direction along the left-right direction of the vehicle body frame  21  is referred to as a leftward direction  1  (vehicle-body-frame-leftward direction). A rightward direction along the left-right direction of the vehicle body frame  21  is referred to as a rightward direction r (vehicle-body-frame-rightward direction). An upward direction along the up-down direction of the vehicle body frame  21  is referred to as an upward direction u (vehicle-body-frame-upward direction). A downward direction along the up-down direction of the vehicle body frame  21  is referred to as a downward direction d (vehicle-body-frame-downward direction). The front-back direction of the vehicle body frame  21  is referred to as a front-back direction fb (vehicle-body-frame-front-back direction). 
     The left-right direction of the vehicle body frame  21  is referred to as a left-right direction lr (vehicle-body-frame-left-right direction). The up-down direction of the vehicle body frame  21  is referred to as an up-down direction ud (vehicle-body-frame-up-down direction). 
     In the present specification, a shaft or a member that extends along the front-back direction does not necessarily mean a shaft or a member that extends in parallel to the front-back direction. A shaft or a member that extends along the front-back direction includes a shaft or a member that is inclined from the front-back direction at an angle within ±45 degrees. In a similar way, a shaft or a member that extends along the up-down direction includes a shaft or a member that is inclined from the up-down direction at an angle within ±45 degrees. A shaft or a member that extends along the left-right direction includes a shaft or a member that is inclined from the left-right direction at an angle within ±45 degrees. The upright posture of the vehicle body frame  21  means a state wherein nobody is riding the leaning vehicle  1   a , the leaning vehicle  1   a  is out of fuel, and the front wheel is neither steered nor caused to lean. 
     In the present specification, a statement that a first member is supported by a second member includes a case in which the first member is attached to the second member such that the first member is immovable (that is, fixed in a place) relative to the second member and a case in which the first member is attached to the second member such that the first member is movable relative to the second member. The statement that the first member is supported by the second member also includes a case in which the first member is directly attached to the second member and a case in which the first member is attached to the second member via a third member. 
     In the present specification, a statement that the first member and the second member are arranged in the front-back direction means the following situation. When the first member and the second member are viewed from a direction perpendicular to the front-back direction, both the first member and the second member are on an arbitrary line representing the front-back direction. In the present specification, a statement that the first member and the second member are arranged in the front-back direction when viewed along the up-down direction means the following situation. When the first member and the second member are viewed along the up-down direction, both the first member and the second member are on an arbitrary line representing the front-back direction. In this case, when the first member and the second member are viewed along the left-right direction, which is different from the up-down direction, not both the first member and the second member are necessarily on the arbitrary line representing the front-back direction. Further, the first member and the second member may be in contact with each other. The first member and the second member may be out of contact with each other. A third member may be positioned between the first member and the second member. Such definitions apply to other directions as well as the front-back direction. 
     In the present specification, a statement that the first member is positioned farther in the forward direction than the second member means the following situation. The first member is positioned farther in the forward direction than a plane that passes a front edge of the second member and is perpendicular to the front-back direction. The first member and the second member may or may not be arranged in the front-back direction. This definition applies to other directions as well as the front-back direction. 
     In the present specification, the statement that the first member is positioned in front of the second member means the following situation. At least a part of the first member is positioned in a range that the second member passes during a translation thereof in the forward direction. Accordingly, the first member may be positioned within the range that the second member passes during a translation thereof in the forward direction, or may protrude from the range that the second member passes during a translation thereof in the forward direction. In this case, the first member and the second member are arranged in the front-back direction. This definition applies to other directions as well as the front-back direction. 
     In the present specification, a statement that the first member is positioned in front of the second member in a view along the left-right direction means the following situation. The first member and the second member are arranged in the front-back direction in a view along the left-right direction, and the part of the first member facing the second member is positioned farther in the forward direction than the second member in a view along the left-right direction. According to this definition, three-dimensionally, the first member and the second member are not necessarily arranged in the front-back direction. This definition applies to other directions as well as the front-back direction. 
     In the present specification, unless otherwise noted, parts of the first member are defined as follows. A front part of the first member means the front half of the first member. A rear part of the first member means the rear half of the first member. A left part of the first member means the left half of the first member. A right part of the first member means the right half of the first member. An upper part of the first member means the upper half of the first member. A lower part of the first member means the lower half of the first member. An upper edge of the first member means the edge of the first member in the upward direction. A lower edge of the first member means the edge of the first member in the downward direction. A front edge of the first member means the edge of the first member in the forward direction. A rear edge of the first member means the edge of the first member in the backward direction. A right edge of the first member means the edge of the first member in the rightward direction. A left edge of the first member means the edge of the first member in the leftward direction. An upper end part of the first member means the upper edge and its vicinity of the first member. A lower end part of the first member means the lower edge and its vicinity of the first member. A front end part of the first member means the front edge and its vicinity of the first member. A rear end part of the first member means the rear edge and its vicinity of the first member. A right end part of the first member means the right edge and its vicinity of the first member. A left end part of the first member means the left edge and its vicinity of the first member. The first member is a component of the leaning vehicle  1   a.    
     As shown in  FIG. 1B , the leaning vehicle  1   a  includes a vehicle body  2 , a front wheel  3 , a rear wheel  4 , and a steering mechanism  7 . The vehicle body  2  includes a vehicle body frame  21 , a vehicle body cover  22 , a seat  24 , a power unit  25 , and a swing arm  26 . 
     The vehicle body frame  21  leans in the leftward direction L when the leaning vehicle  1   a  is turning left. The vehicle body frame  21  leans in the rightward direction R when the leaning vehicle  1   a  is turning right. In FIG.  1 B, the vehicle body frame  21  is indicated by bold lines. However, the vehicle body frame  21  is covered by the vehicle body cover  22 , and therefore, under ordinary conditions, the vehicle body frame  21  cannot be seen in  FIG. 1B . 
     The vehicle body frame  21  includes a head pipe  211 , a main frame  212 , and a seat rail  213 . The head pipe  211  is positioned in the front part of the leaning vehicle  1   a . The front part of the leaning vehicle  1   a  is a part thereof that is farther in the forward direction f than the front edge of the seat  24 . The rear part of the leaning vehicle  1   a  is a part thereof that is farther in the backward direction b than the front edge of the seat  24 . In a view in the leftward direction  1  or the rightward direction r, the head pipe  211  is inclined from the up-down direction ud such that the upper end part of the head pipe  211  is positioned farther in the backward direction b than the lower end part of the head pipe  211 . 
     In a view in the rightward direction r, the main frame  212  is positioned farther in the backward direction b than the head pipe  211 . The seat rail  213  linearly extends from the main frame  212  to a backward and upward direction b, u. 
     In a view in the rightward direction r, the swing arm  26  extends from the lower and rear part of the main frame  212  to the backward direction b. The swing arm  26  is supported by the main frame  212  in such a manner as to be capable of turning on the front end part of the swing arm  26 . Thereby, the rear end part of the swing arm  26  is movable up and down. 
     The vehicle body cover  22  covers the vehicle body frame  21 . The vehicle body cover  22  also covers some part of the power unit  25 . 
     The seat  24  is to be sat on by a rider. The seat  24  is supported by the seat rail  213 . The power unit  25  includes a power source, such as an engine, an electric motor or the like, and a power transmission system, such as a transmission device or the like. The power unit  25  is supported by the main frame  212 . 
     The steering mechanism  7  is arranged around the head pipe  211 . The steering mechanism  7  is configured to steer the front wheel  3  in accordance with the rider&#39;s manipulation. As shown in  FIG. 2 , the steering mechanism  7  includes a handlebar  60 , a steering shaft  62 , a front fork  64 , an upper bracket  66 , and an under bracket  68 . The handlebar  60  is to be manipulated by the rider. The steering shaft  62  is supported by the vehicle body frame  21  in such a manner as to be rotatable on its central axis in accordance with the rider&#39;s manipulation of the handlebar  60 . More specifically, the upper bracket  66  and the under bracket  68  are, as shown in  FIG. 2 , plate-like members extending along the left-right direction lr. The upper bracket  66  is positioned farther in the upward direction u than the head pipe  211 . The under bracket  68  is positioned farther in the downward direction d than the head pipe  211 . The steering shaft  62  is inserted in the head pipe  211  and thereby is supported by the head pipe  211  in such a manner as to be rotatable. Further, the steering shaft  62  is fixed to the upper bracket  66  and the under bracket  68 . The handlebar  60  is fixed to the upper bracket  66 . 
     The front fork  64  is fixed to the upper bracket  66  and the under bracket  68 . Specifically, as shown in  FIG. 2 , the front fork  64  includes a left shock absorber  64 L and a right shock absorber  64 R. The left shock absorber  64 L extends from the upper bracket  66  and the under bracket  68  to the downward direction d. The left shock absorber  64 L is positioned farther in the leftward direction  1  than the center of the vehicle body frame  21  in an upright posture with respect to the left-right direction lr. The right shock absorber  64 R extends from the upper bracket  66  and the under bracket  68  in the downward direction d. The right shock absorber  64 R is positioned farther in the rightward direction r than the center of the vehicle body frame  21  in an upright posture with respect to the left-right direction lr. Accordingly, when the rider turns the handlebar  60 , the steering shaft  62 , the front fork  64 , the upper bracket  66  and the under bracket  68  rotate around the central axis of the steering shaft  62  in a body. 
     The left shock absorber  64 L and the right shock absorber  64 R are what are called telescopic shock absorbers. The left shock absorber  64 L and the right shock absorber  64 R each, for example, include a combination of a damper and a spring. The left shock absorber  64 L and the right shock absorber  64 R expand and contract along the up-down direction ud and thereby absorb displacements of the front wheel  3  along the up-down direction ud. 
     The front wheel  3  is a steerable wheel of the leaning vehicle  1   a . The front wheel  3  is positioned in the front part of the leaning vehicle  1   a . The front wheel  3  is supported by the lower end part of the front fork  64  in such a manner as to be rotatable around an axle. Thus, the front wheel  3  is supported by the vehicle body frame  21  via the steering mechanism  7 . Accordingly, the rider can steer the front wheel  3  by manipulating the handlebar  60 . 
     The rear wheel  4  is a driving wheel of the leaning vehicle  1   a . The rear wheel  4  is rotated by a driving force generated by the power unit  25 . The rear wheel  4  is positioned in the rear part of the leaning vehicle  1   a . The rear wheel  4  is supported by the lower end part of the swing arm  26  in such a manner as to be rotatable around an axle. 
     [Steering Motion] 
     Next, steering motions of the leaning vehicle  1   a  are described with reference to the drawings.  FIG. 3  is a schematic looking-to-the-down (D) view of the leaning vehicle  1   a .  FIG. 3  shows a state wherein the front wheel  3  is steered in the leftward direction L, a state wherein the front wheel  3  is not steered, and a state wherein the front wheel  3  is steered in the rightward direction R. As indicated in  FIG. 3 , the direction in which the handlebar  60  is turned counterclockwise in a view in the downward direction d is defined as a positive direction. The direction in which the handlebar  60  is turned clockwise in a view in the downward direction d is defined as a negative direction. 
     As shown in  FIG. 3 , in a view in the downward direction D, the front wheel  3  is turned counterclockwise when the rider turns the handlebar  60  counterclockwise (in the positive direction). Then, the front wheel  3  is steered in the leftward direction L (steered leftward). 
     As shown in  FIG. 3 , in a view in the downward direction D, the front wheel  3  is turned clockwise when the rider turns the handlebar  60  clockwise (in the negative direction). Then, the front wheel  3  is steered in the rightward direction R (steered rightward). 
     [Leaning Motion] 
     Next, leaning motions of the leaning vehicle  1   a  are described with reference to the drawings.  FIG. 4  is a schematic looking-to-the-back (B) view of the leaning vehicle  1   a .  FIG. 4  shows a state wherein the vehicle body frame  21  leans in the leftward direction L and a state wherein the vehicle body frame  21  leans in the rightward direction R.  FIG. 4  shows that the front wheel  3  is steered leftward by self-steering when the vehicle body frame  21  leans in the leftward direction L.  FIG. 4  shows that the front wheel  3  is steered rightward by self-steering when the vehicle body frame  21  leans in the rightward direction R. 
     The vehicle body frame  21  leans in the leftward direction L or the rightward direction R by rotating around a roll axis Ax. The roll axis Ax is an axis extending along the front-back direction FB. More specifically, as shown in  FIG. 1B , the roll axis Ax is a straight line that passes the contact point between the rear wheel  4  and the ground and is perpendicular to the steering shaft  62  when the vehicle body frame  21  is in an upright posture. In a view in the backward direction d, the roll axis Ax is in the center of the vehicle body frame  21  in an upright posture with respect to the left-right direction lr. 
     As the vehicle body frame  21  is rotating around the roll axis Ax, the rotation angle of the vehicle body frame  21  around the roll axis Ax changes, and the rotation angle of the vehicle body frame  21  around the roll axis Ax is referred to as a roll angle θ. In the following paragraphs, as shown in  FIG. 2 , the straight line that passes the center of the vehicle body frame  21  in an upright posture with respect to the left-right direction lr and extends along the up-down direction ud is defined as a center line C. As shown in  FIG. 4 , when the vehicle body frame  21  leans in the leftward direction L or the rightward direction R, the center line C leans in the leftward direction L or the rightward direction R together with the vehicle body frame  21 . The roll angle θ is an angle formed between the vertical axis and the center line C. The vertical axis is an axis parallel to the up-down direction UD. 
     Further, as shown in  FIG. 4 , when the vehicle body frame  21  leans in the leftward direction L, the direction of the lean is referred to as a positive direction of the roll angle θ. In other words, the clockwise direction around the roll axis Ax in a view in the backward direction B is defined as a positive direction of the roll angle θ. When the vehicle body frame  21  leans in the rightward direction R, the direction of the lean is referred to as a negative direction of the roll angle θ. In other words, the counterclockwise direction around the roll axis Ax in a view in the backward direction B is defined as a negative direction of the roll angle θ. The roll angle θ changes within a range of −90° to 90°. 
     As shown in  FIG. 4 , in a view in the backward direction B, the vehicle body frame  21  rotates clockwise around the roll axis Ax and leans in the leftward direction L. In this case, the roll angle θ is a positive value. Also, the front wheel  3  is steered leftward by self-steering. Then, the leaning vehicle  1   a  turns in the leftward direction L. 
     As shown in  FIG. 4 , in a view in the backward direction B, the vehicle body frame  21  rotates counterclockwise around the roll axis Ax and leans in the rightward direction R. Also, the front wheel  3  is steered rightward by self-steering. In this case, the roll angle θ is a negative value. The leaning vehicle  1   a  turns in the rightward direction R. 
     [Posture Control Actuator Controller] 
     Next, the posture control actuator controller  606  of the leaning vehicle  1   a  is described with reference to the drawings.  FIG. 5  is a block diagram of the posture control actuator controller  606 . 
     First, a steering torque T is described. The steering torque T is a torque that is generated by the rider&#39;s manipulation of the handlebar  60  and acts on the steering shaft  62 . More specifically, the steering torque T is a torque that is generated and inputted to the steering shaft  62  by the rider&#39;s manipulation of the handlebar  60  when the roll angle θ of the vehicle body frame  21  of the leaning vehicle  1   a  running at a speed V is changing at a roll rate ω. The steering torque T acts around the rotation axis of the handlebar  60  (central axis of the steering shaft  62 ). When the steering torque T causes a counterclockwise rotation of the steering shaft  62  in a view in the downward direction d, the direction of the torque is defined as a positive direction of the steering torque T. When the steering torque T causes a clockwise rotation of the steering shaft  62  in a view in the downward direction d, the direction of the torque is defined as a negative direction of the steering torque T. 
     As shown in  FIG. 1B , the leaning vehicle  1   a  further includes a posture control actuator unit  599  and a speed sensor  604 . 
     The posture control actuator unit  599  includes an EPS (electric power steering) actuator  600  and a roll rate sensor  602  as well as the posture control actuator controller  606 . The EPS actuator  600  (an example of a posture control actuator) is supplied with electric power and outputs a posture control torque Tc (an example of posture control power) to cause the steering shaft  62  to rotate on its central axis. The posture control torque Tc is a torque to control the posture of the vehicle body frame  21 . More specifically, as shown in  FIG. 2 , the EPS actuator  600  is fixed in the upper end part of the head pipe  211 . The EPS actuator  600  is a combination of an electric motor and a gear. The electric motor generates a torque. The torque generated by the electric motor is outputted to the steering shaft  62  as a posture control torque Tc via the gear. 
     The roll rate sensor  602  detects the roll rate ω that is the amount of change per unit time of the roll angle θ. When the vehicle body frame  21  leans in the leftward direction L, the direction of the lean is referred to as a positive direction of the roll rate ω. In other words, the clockwise direction around the roll axis Ax in a view in the backward direction B is defined as a positive direction of the roll rate ω. When the vehicle body frame  21  leans in the rightward direction R, the direction of the lean is referred to as a negative direction of the roll rate ω. In other words, the counterclockwise direction around the roll axis Ax in a view in the backward direction B is defined as a negative direction of the roll rate ω. 
     The speed sensor  604  detects the speed V of the leaning vehicle  1   a . The speed V is a positive value when the leaning vehicle  1   a  is running forward. 
     The posture control actuator controller  606  controls the EPS actuator  600  based on the roll rate ω detected by the roll rate sensor  602 . The posture control actuator controller  606  is, for example, an IC (integrated circuit) for control of the EPS actuator  600 . However, the posture control actuator controller  606  does not need to be achieved by a single IC, and the posture control actuator controller  606  may be a combination of one or more ICs, one or more electronic components and/or one or more circuit boards. 
     In the posture control actuator unit  599 , the EPS actuator  600 , the roll rate sensor  602  and the posture control actuator controller  606  are incorporated in such a manner as not to be displaceable relative to one another, and the posture control actuator unit  599  is supported by the vehicle body frame  21  in such a manner as to be attachable to and detachable from the vehicle body frame  21 . More specifically, for example, the roll rate sensor  602  and the posture control actuator controller  606  are fixed in a case of the EPS actuator  600  as shown in  FIG. 2 . The means for fixing the roll rate sensor  602  and the posture control actuator controller  606  to the EPS actuator  600  may be a combination of a bolt and a nut, a screw, a snap-fit, an adhesive, an adhesive tape, welding, brazing, etc. The EPS actuator  600  is to output a posture control torque Tc to the steering shaft  62 . Therefore, the EPS actuator  600  is supported by the vehicle body frame  21  in such a manner as not to be displaceable relative to the vehicle body frame  21 . In this structure, the roll rate sensor  602  and the posture control actuator controller  606  are not displaceable relative to the EPS actuator  600 , and the EPS actuator  600  is not displaceable relative to the vehicle body frame  21 . In the present specification, when it is stated that a first member is supported by a second member in such a manner as not to be displaceable relative to the second member, it also means that there is no elastic member for impact absorption, such as a rubber mount or the like, between the first member and the second member. 
     As shown in  FIG. 2 , the EPS actuator  600  is fixed in the upper end part of the head pipe  211 . Therefore, in a view in the backward direction d, the EPS actuator  600  overlaps the center line C. Accordingly, in a view in the backward direction d, the posture control actuator unit  599  overlaps the center line C. In the leaning vehicle  1   a , in a view in the backward direction d, the roll rate sensor  602  overlaps the center line C. 
     The description is now returned to the posture control actuator controller  606 . The posture control actuator controller  606  obtains the roll rate ω from the roll rate sensor  602 . Specifically, an electric signal representing the roll rate ω (which will hereinafter be referred to simply as roll rate ω) detected by the roll rate sensor  602  is inputted to the posture control actuator controller  606 . 
     The posture control actuator controller  606  obtains the speed V from the speed sensor  604 . Specifically, an electric signal representing the speed V (which will hereinafter be referred to simply as speed V) detected by the speed sensor  606  is inputted to the posture control actuator controller  606 . 
     The posture control actuator controller  606  does not use a torque sensor that detects the steering torque T that is generated by the rider&#39;s manipulation of the handlebar  60  and acts around the rotation axis (central axis of the steering shaft  62 ), and uses the roll rate sensor  602 . Then, the posture control actuator controller  606  controls the EPS actuator  600  not based on the steering torque T that is generated by the rider&#39;s manipulation of the handlebar  60  and acts around the rotation axis (central axis of the steering shaft  62 ) but based on the roll rate ω sent from the roll rate sensor  602 . In the present embodiment, the posture control actuator controller  606  uses neither a torque sensor that detects the steering torque T nor a roll sensor that detects the roll angle θ. The posture control actuator controller  606  uses the roll rate sensor  602  and the speed sensor  604 . Then, the posture control actuator controller  606  controls the EPS actuator  600  based on neither the steering torque T detected by a torque sensor nor the roll angle θ detected by a roll sensor. The posture control actuator controller  606  controls the EPS actuator  600  based on the roll rate ω sent from the roll rate sensor  602  and the speed V sent from the speed sensor  604 . The statement that the posture control actuator controller  606  uses neither a torque sensor nor a roll sensor means, for example, that the posture control actuator controller  606  does not use signals sent from a torque sensor and a roll sensor for control. The statement that the posture control actuator controller  606  uses the roll rate sensor  602  and the speed sensor  604  means, for example, that the posture control actuator controller  606  uses signals sent from the roll rate sensor  602  and the speed sensor  604  for control. 
     The posture control actuator controller  606  includes a torque estimation section  614  and a current determination section  616 . The torque estimation section  614  determines an estimated steering torque value T(m, n), which is an estimated value of the steering torque T, based on the speed V and the roll rate ω. The values m and n are integers. The estimated steering torque value T(m, n) is a value of the steering torque T that is estimated to be inputted to the steering shaft  62  by the rider&#39;s manipulation of the handlebar  60  when the roll angle θ of the vehicle body frame  21  is changing at a roll rate ω while the leaning vehicle  1   a  is running at a speed V. The torque estimation section  614  stores an estimated torque determination table as shown by TABLE 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 ω(n)(deg/s) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 . . . 
                 ω(−5) 
                 ω(−4) 
                 ω(−3) 
                 ω(−2) 
                 ω(−1) 
                 ω(0) = 0 
                 ω(1) 
                 ω(2) 
                 ω(3) 
                 ω(4) 
                 ω(5) 
                 . . . 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 V(m) 
                 V(1) 
                 . . . 
                 T(1, −5) 
                 T(1, −4) 
                 T(1, −3) 
                 T(1, −2) 
                 T(1, −1) 
                 T(1, 0) = 0 
                 T(1, 1) 
                 T(1, 2) 
                 T(1, 3) 
                 T(1, 4) 
                 T(1, 5) 
                 . . . 
               
               
                 (km/h) 
                 V(2) 
                 . . . 
                 T(2, −5) 
                 T(2, −4) 
                 T(2, −3) 
                 T(2, −2) 
                 T(2, −1) 
                 T(2, 0) = 0 
                 T(2, 1) 
                 T(2, 2) 
                 T(2, 3) 
                 T(2, 4) 
                 T(2, 5) 
                 . . . 
               
               
                   
                 V(3) 
                 . . . 
                 T(3, −5) 
                 T(3, −4) 
                 T(3, −3) 
                 T(3, −2) 
                 T(3, −1) 
                 T(3, 0) = 0 
                 T(3, 1) 
                 T(3, 2) 
                 T(3, 3) 
                 T(3, 4) 
                 T(3, 5) 
                 . . . 
               
               
                   
                 V(4) 
                 . . . 
                 T(4, −5) 
                 T(4, −4) 
                 T(4, −3) 
                 T(4, −2) 
                 T(4, −1) 
                 T(4, 0) = 0 
                 T(4, 1) 
                 T(4, 2) 
                 T(4, 3) 
                 T(4, 4) 
                 T(4, 5) 
                 . . . 
               
               
                   
                 V(5) 
                 . . . 
                 T(5, −5) 
                 T(5, −4) 
                 T(5, −3) 
                 T(5, −2) 
                 T(5, −1) 
                 T(5, 0) = 0 
                 T(5, 1) 
                 T(5, 2) 
                 T(5, 3) 
                 T(5, 4) 
                 T(5, 5) 
                 . . . 
               
               
                   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                   
               
            
           
         
       
     
     In the estimated torque determination table, values of the estimated steering torque T(m, n) are stored in association with values of the speed V(m) and values of the roll rate ω(n). The values of the speed V(m) are greater than 0 km/h. The greater the value m is, the greater the speed V(m) is. Accordingly, V(m)&lt;V(m+1) holds. 
     When the value n is positive, the roll rate ω(n) is a positive value. In this case, the greater the value n is, the greater the roll rate ω(n) is. On the other hand, when the value n is negative, the roll rate ω(n) is a negative value. In this case, the greater the value n is, the smaller the roll rate ω(n) is (the greater the absolute value of the roll rate ω(n) is). Accordingly, ω(n)&lt;ω(n+1) holds. 
     While the leaning vehicle  1   a  is running forward, when the rider turns the handlebar  60  clockwise (in the negative direction), the front wheel  3  is rotated at a roll rate ω(n) of a positive value. For example, while the vehicle body  21  is in an upright posture, when the rider turns the handlebar  60  clockwise (in the negative direction), the front wheel  3  is steered rightward. Then, the vehicle frame body  21  leans in the leftward direction L. On the other hand, while the leaning vehicle  1   a  is running forward, when the rider turns the handlebar  60  counterclockwise (in the positive direction), the front wheel  3  is rotated at a roll rate ω(n) of a negative value. For example, while the vehicle body  21  is in an upright posture, when the rider turns the handlebar  60  counterclockwise (in the positive direction), the front wheel  3  is steered leftward. Then, the vehicle body frame  21  leans in the rightward direction R. Thus, the rider performs counter-steering to generate a roll rate ω(n). Therefore, the estimated steering torque T(m, n) has the following relationship with the values m and n. 
     When the value n is positive (when the roll rate ω(n) is a positive value), the estimated steering torque T(m, n) is a negative value. In this case, the estimated steering torque T(m, n) indicates a steering torque to cause the steering shaft  62  to rotate clockwise (in the negative direction) in a view in the downward direction d. In this case, the greater the value n is (the greater the roll rate value ω(n) is), the smaller the estimated steering torque T(m, n) is (the greater the absolute value of the estimated steering torque T(m, n) is). Also, the greater the value m is (the greater the speed V(m) is), the smaller the estimated steering torque T(m, n) is (the greater the absolute value of the estimated steering torque T(m, n) is). 
     On the other hand, when the value n is negative (when the roll rate ω(n) is a negative value), the estimated steering torque T(m, n) is a positive value. In this case, the estimated steering torque T(m, n) indicates a steering torque to cause the steering shaft  62  to rotate counterclockwise (in the positive direction) in a view in the downward direction d. In this case, the smaller the value n is (the smaller the roll rate ω(n) is), the greater the estimated steering torque T(m, n) is. Also, the greater the value m is (the greater the speed V(m) is), the greater the estimated steering torque T(m, n) is. 
     The torque estimation section  614  identifies a speed V(m) that is closest to the speed V that the posture control actuator controller  606  has obtained. Also, the torque estimation section  614  identifies a roll rate ω(n) that is closest to the roll rate ω that the posture control actuator controller  606  has obtained. Then, the torque estimation section  614  determines an estimated steering torque T(m, n) in association with the speed value V(m) and the roll rate ω(n) with reference to TABLE 1. 
     The current determination section  616  controls the EPS actuator  600  based on the estimated steering torque T(m, n) determined by the torque estimation section  614 . Specifically, the current determination section  616  determines a control current I(m, n) to be outputted to the EPS actuator  600 , based on the estimated steering torque T(m, n). For this purpose, the current determination section  616  stores a control current determination table as shown by TABLE 2. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                 . . . 
                 T(1, −5) 
                 T(1, −4) 
                 T(1, −3) 
                 T(1, −2) 
                 T(1, −1) 
                 T(1, 0) = 0 
                 T(1, 1) 
                 T(1, 2) 
                 T(1, 3) 
                 T(1, 4) 
                 T(1, 5) 
                 . . . 
               
               
                 . . . 
                 I(1, −5) 
                 I(1, −4) 
                 I(1, −3) 
                 I(1, −2) 
                 I(1, −1) 
                 I(1, 0) = 0 
                 I(1, 1) 
                 I(1, 2) 
                 I(1, 3) 
                 I(1, 4) 
                 I(1, 5) 
                 . . . 
               
               
                 . . . 
                 T(2, −5) 
                 T(2, −4) 
                 T(2, −3) 
                 T(2, −2) 
                 T(2, −1) 
                 T(2, 0) = 0 
                 T(2, 1) 
                 T(2, 2) 
                 T(2, 3) 
                 T(2, 4) 
                 T(2, 5) 
                 . . . 
               
               
                 . . . 
                 I(2, −5) 
                 I(2, −4) 
                 I(2, −3) 
                 I(2, −2) 
                 I(2, −1) 
                 I(2, 0) = 0 
                 I(2, 1) 
                 I(2, 2) 
                 I(2, 3) 
                 I(2, 4) 
                 I(2, 5) 
                 . . . 
               
               
                 . . . 
                 T(3, −5) 
                 T(3, −4) 
                 T(3, −3) 
                 T(3, −2) 
                 T(3, −1) 
                 T(3, 0) = 0 
                 T(3, 1) 
                 T(3, 2) 
                 T(3, 3) 
                 T(3, 4) 
                 T(3, 5) 
                 . . . 
               
               
                 . . . 
                 I(3, −5) 
                 I(3, −4) 
                 I(3, −3) 
                 I(3, −2) 
                 I(3, −1) 
                 I(3, 0) = 0 
                 I(3, 1) 
                 I(3, 2) 
                 I(3, 3) 
                 I(3, 4) 
                 I(3, 5) 
                 . . . 
               
               
                 . . . 
                 T(4, −5) 
                 T(4, −4) 
                 T(4, −3) 
                 T(4, −2) 
                 T(4, −1) 
                 T(4, 0) = 0 
                 T(4, 1) 
                 T(4, 2) 
                 T(4, 3) 
                 T(4, 4) 
                 T(4, 5) 
                 . . . 
               
               
                 . . . 
                 I(4, −5) 
                 I(4, −4) 
                 I(4, −3) 
                 I(4, −2) 
                 I(4, −1) 
                 I(4, 0) = 0 
                 I(4, 1) 
                 I(4, 2) 
                 I(4, 3) 
                 I(4, 4) 
                 I(4, 5) 
                 . . . 
               
               
                 . . . 
                 T(5, −5) 
                 T(5, −4) 
                 T(5, −3) 
                 T(5, −2) 
                 T(5, −1) 
                 T(5, 0) = 0 
                 T(5, 1) 
                 T(5, 2) 
                 T(5, 3) 
                 T(5, 4) 
                 T(5, 5) 
                 . . . 
               
               
                 . . . 
                 I(5, −5) 
                 I(5, −4) 
                 I(5, −3) 
                 I(5, −2) 
                 I(5, −1) 
                 I(5, 0) = 0 
                 I(5, 1) 
                 I(5, 2) 
                 I(5, 3) 
                 I(5, 4) 
                 I(5, 5) 
                 . . . 
               
               
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                   
               
            
           
         
       
     
     In the control current determination table, values of the estimated steering torque T(m, n) and values of the control current I(m, n) are stored in association with each other. The control current I(m, n) is a current that the EPS actuator  600  requires to output a posture control torque Tc corresponding to the assist rate (for example, 20%) of the estimated steering torque T(m, n) to the steering shaft  62 . The EPS actuator  600  outputs a posture control torque Tc corresponding to 20% of the estimated steering torque T(m, n) to the steering shaft  62 . Accordingly, the rider only needs to manipulate the handlebar  60  to apply 80% of the estimated steering torque T(m, n) to the steering shaft  62 . In this way, the ESP actuator  600  assists the rider&#39;s manipulation of the handlebar  60 . The assist rate is an arbitrary value and may be a value other than 20%. In order to allow the rider to manipulate the handlebar  60  with less power, the assist rate should be more than 20%. In order to allow the rider to manipulate the handlebar  60  with more power, the assist rate should be less than 20%. The assist rate may be a negative value. In this case, the EPS actuator  600  outputs a posture control steering torque Tc to inhibit the rider&#39;s manipulation of the handlebar  60 . Then, the EPS actuator  600  functions as a steering damper. 
     When the value n is positive, the control current I(m, n) is a negative value. The greater the value n is, the smaller the control current I(m, n) is (the greater the absolute value of the control current I(m, n) is). Also, the greater the value m is, the smaller the control current I(m, n) is (the greater the absolute value of the control current I(m, n) is). 
     On the other hand, when the value n is negative, the control current I(m, n) is a positive value. The smaller the value n is, the greater the control current I(m, n) is. Also, the greater the value m is, the greater the control current I(m, n) is. 
     The EPS actuator  600  outputs a posture control torque Tc to the steering shaft  62  by the control current I(m, n) outputted from the current determination section  616 . However, the current determination section  616  does not need to output the control current I(m, n) to the EPS actuator  600  directly. The control current I(m, n) may be supplied to the EPS actuator  600  from a power source that is provided separately from the posture control actuator controller  606 . 
     When receiving a negative control current I(m, n), the EPS actuator  600  outputs a posture control torque Tc to rotate the steering shaft  62  clockwise (in the negative direction). In this case, the greater the absolute value of the control current I(m, n) is, the greater the absolute value of the posture control torque Tc is. Then, in a view in the backward direction B, the vehicle body frame  21  rotates clockwise (in the positive direction) around the roll axis Ax at a roll rate ω. 
     On the other hand, when receiving a positive control current I(m, n), the EPS actuator  600  outputs a posture control torque Tc to rotate the steering shaft  62  counterclockwise (in the positive direction). In this case, the greater the absolute value of the control current I(m, n) is, the greater the absolute value of the posture control torque Tc is. Then, in a view in the backward direction B, the vehicle body frame  21  rotates counterclockwise (in the negative direction) around the roll axis Ax at a roll rate ω. 
     As described above, the posture control actuator controller  606  controls the EPS actuator  606  to output a posture control torque Tc, based on the speed V and the roll rate ω. Then, the steering shaft  62  rotates, and the vehicle body frame  21  rotates clockwise or counterclockwise around the roll axis Ax in a view in the backward direction B. Accordingly, the posture of the vehicle body frame  21  changes. In this way, the posture control actuator controller  606  controls the posture of the vehicle body frame  21  based on the speed V and the roll rate ω. 
     Next, operations of the posture control actuator controller  606  will be described with reference to the drawings.  FIG. 6  is a flowchart showing operations performed by the posture control actuator controller  606 . The posture control actuator controller  606  performs a process that will be described below along a software program stored in a storage device (not shown). 
     The process is started when an ignition source of the leaning vehicle  1   a  is turned on. As long as the ignition source is on, the roll rate sensor  602  keeps outputting the roll rate ω to the posture control actuator controller  606 . Also, the speed sensor  604  keeps outputting the speed V to the posture control actuator controller  606 . 
     The torque estimation section  614  obtains the roll rate ω from the roll rate sensor  602  (step S 1 ). Further, the torque estimation section  614  obtains the speed V from the speed sensor  604  (step S 2 ). 
     Next, the torque estimation section  614  identifies one of the roll rate values listed in the estimation steering torque table as shown in TABLE 1 as a roll rate ω(n) closest to the roll rate ω. Further, the torque estimation section  614  identifies one of the speed values listed in the estimation steering torque table as shown by TABLE 1 as a speed V(m) closest to the speed V. Then, the torque estimation section  614  determines an estimated steering torque T(m, n) in association with the roll rate ω(n) and the speed V(m) with reference to the estimation steering torque table as shown by 
     TABLE 1 (step S 3 ). 
     Next, the current determination section  616  determines a control current I(m, n) corresponding to the estimated steering torque T(m, n) determined by the torque estimation section  614  by using the control current determination table as shown by TABLE 2 (step S 4 ). The current determination section  616  outputs the control current I(m, n) to the EPS actuator  600 . The EPS actuator  600  outputs a posture control torque Tc corresponding to the control current I(m, n) to the steering shaft  62 . Thereafter, the process returns to step S 1 . The process from step S 1  to S 4  is repeated until the ignition source is switched from on to off. 
     [Effects] 
     The roll rate sensor  602  of the posture control actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. More specifically, the EPS actuator  600  outputs posture control power to control the posture of the vehicle body frame  21 . For this purpose, the posture control actuator unit  599  is supported by the vehicle body frame  21  in such a manner as to be attachable to and detachable from the vehicle body frame  21 . Accordingly, a posture change of the EPS actuator  600  is unlikely to delay relative to a posture change of the vehicle body frame  21 . The EPS actuator  600  and the roll rate sensor  602  are incorporated in such a manner as not to be displaceable relative to each other. Accordingly, a posture change of the roll rate sensor  602  is unlikely to delay relative to a posture change of the vehicle body frame  21 . Therefore, the roll rate sensor  602  of the posture change actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. 
     The roll rate sensor  602  of the posture control actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. More specifically, the EPS actuator  600  outputs posture control power to control the posture of the vehicle body frame  21 . For this purpose, the EPS actuator  600  is designed to be positioned at a predetermined angle to the roll axis Ax or the like that is associated with a posture change of the vehicle body frame  21 . For example, the EPS actuator  600  may be positioned such that its rotation axis is parallel to the steering shaft. Thus, the EPS actuator  600  is attached to the vehicle body frame  21  with high positional accuracy. The EPS actuator  600  and the roll rate sensor  602  are incorporated in such a manner as not to be displaceable relative to each other. Accordingly, the roll rate sensor  602  is attached to a sensor mounting position of the vehicle body frame  21  with high accuracy. Therefore, the roll rate sensor  602  of the posture control actuator unit  599  can detect a posture change of the vehicle body frame  21  with high accuracy. 
     The roll rate sensor  602  of the posture control actuator unit  599  can detect the roll rate of the vehicle body frame  21  with high accuracy also for the following reason. More specifically, the posture control actuator unit  599  is positioned to overlap the center line C in a view in the backward direction b. The roll rate sensor  602  is included in the posture control actuator unit  599 . Accordingly, the roll rate sensor  602  is positioned near the center line C in a view in the backward direction b. Accordingly, the roll rate sensor  602  of the posture control actuator unit  599  can detect the roll rate ω with high accuracy. Since the roll rate sensor  602  can detect the roll rate ω with high accuracy, the posture control actuator controller  606  can accurately control the posture of the vehicle frame body  21  through the EPS actuator  600 . 
     Also, the EPS actuator  600  of the posture control actuator unit  599  is attached to the vehicle body frame  21  with high positional accuracy. Accordingly, it is easy to make the axis for the roll rate detection carried out by the roll rate sensor  602  almost parallel to the roll axis Ax of the vehicle body frame  21 . Then, the roll rate sensor  602  can detect the roll rate of the vehicle body frame  21  with high accuracy. Even when the axis for the roll rate detection carried out by the roll rate sensor  602  is not parallel to the roll axis Ax of the vehicle body frame  21 , it is easy to identify the angle formed between the axis for the roll rate detection carried out by the roll rate sensor  602  and the roll axis Ax of the vehicle body frame  21 . Accordingly, it is easy to make a correction to the roll rate detected by the roll rate sensor  602 . 
     The posture control actuator unit  599  can be downsized. More specifically, in the posture control actuator unit  599 , the EPS actuator  600  and the roll rate sensor  602  are incorporated in such a manner as not to be displaceable relative to each other. Accordingly, it is not necessary to provide a mount for attachment of the roll rate sensor  602  to the vehicle body frame  21 . Therefore, the number of components of the posture control actuator unit  599  can be reduced, and the posture control actuator unit  599  can be downsized. 
     The posture control actuator controller  606  of the posture control actuator unit  599  controls the rotation of the steering shaft  62  based on the roll rate ω of the vehicle body frame  21  accurately detected by the roll rate sensor  602 . When the steering shaft  62  rotates, the vehicle body frame  21  rotates around the roll axis Ax. Accordingly, the posture control actuator controller  606  of the posture control actuator unit  599  can control the posture of the vehicle body frame  21  accurately. 
     Second Embodiment 
     [Overall Structure] 
     The overall structure of a leaning vehicle  1   b  according to a second embodiment will hereinafter be described with reference to the drawings. In the present embodiment, a three-wheeled leaning vehicle including a vehicle body frame capable of leaning, two front wheels, and a rear wheel is described as an example of the leaning vehicle  1   b .  FIG. 7  is a looking-to-the-right (r) view of the leaning vehicle  1   b  when the vehicle body frame is in an upright posture.  FIG. 8  is a looking-to-the-back (b) view of the front part of the leaning vehicle  1   b  when the vehicle body frame is in an upright posture. In  FIG. 8 , the vehicle body cover is shown as being transparent. 
     As shown in  FIG. 7 , the leaning vehicle  1   b  includes a vehicle body  1002 , a left front wheel  1031 , a right front wheel  1032  (see  FIG. 8 ), a rear wheel  1004 , a link mechanism  1005 , and a steering mechanism  1007 . The vehicle body  1002  includes a vehicle body frame  1021 , a vehicle body cover  1022 , a seat  1024 , and a power unit  1025 . 
     The vehicle body frame  1021  leans in the leftward direction L when the leaning vehicle  1   b  is turning left. The vehicle body frame  1021  leans in the rightward direction R when the leaning vehicle  1   b  is turning right. The vehicle body frame  1021  includes a head pipe  1211 , a down frame  1212 , an underframe  1214 , and a rear frame  1215 . In  FIG. 7 , the part of the vehicle body frame  1021  behind the vehicle body cover  1022  is indicated by a chain line. The vehicle body frame  1021  supports the seat  1024 , the power unit  1025 , etc. 
     The head pipe  1211  is positioned in the front part of the leaning vehicle  1   b . The front part of the leaning vehicle  1   b  is a part thereof that is farther in the forward direction f than the front edge of the seat  1024 . The rear part of the leaning vehicle  1   b  is a part thereof that is farther in the backward direction b than the front edge of the seat  1024 . The head pipe  1211  is inclined from the up-down direction ud such that the upper end part of the head pipe  1211  is positioned farther in the backward direction b than the lower end part of the head pipe  1211  in a view in the leftward direction  1  or the rightward direction r. 
     The down frame  1212  is positioned farther in the backward direction b than the head pipe  1211 . The down frame  1212  is a cylindrical member extending along the up-down direction ud. The upper end part of the down frame  1212  is positioned farther in the backward direction b than the head pipe  1211  in a view in the rightward direction r. The down frame  1212  extends from the upper end part of the down frame  1212  to the downward direction d. The upper end part of the down frame  1212  is fixed to the lower end part of the head pipe  1211  via a connecting part (not shown). 
     The underframe  1214  extends from the lower end part of the down frame  1212  to the backward direction b. The rear frame  1215  linearly extends from the rear edge of the underframe  1214  to a backward and upward direction b, u. 
     The vehicle body frame  1021  is covered by the vehicle body cover  1022 . The vehicle body cover  1022  includes a front cover  1221 , a pair of right and left front fenders  1223 , and a leg shield  1225 . The front cover  1221  is positioned farther in the forward direction f than the seat  1024 . The front cover  1221  covers at least some part of the steering mechanism  1007  and the link mechanism  1005 . 
     The power unit  1025  includes a power source, such as an engine, an electric motor or the like, and a power transmission system, such as a transmission device or the like. 
     The seat  1024  is to be sat on by a rider. The seat  1024  is supported by the rear frame  1215 . 
     The left front wheel  1031  is a left steerable wheel of the leaning vehicle  1   b . The left front wheel  1031  is positioned in the front part of the leaning vehicle  1   b . As shown in  FIG. 8 , the left front wheel  1031  is positioned farther in the leftward direction  1  than the center of the vehicle body frame  1021  with respect to the left-right direction lr. The left front wheel  1031  is rotatable around a left front axle  1314  (an example of an axle of a left steerable wheel). 
     The right front wheel  1032  is a right steerable wheel of the leaning vehicle  1   b . The right front wheel  1032  is positioned in the front part of the leaning vehicle  1   b . As shown in  FIG. 8 , the right front wheel  1032  is positioned farther in the rightward direction r than the center of the vehicle body frame  1021  with respect to the left-right direction lr. The right front wheel  1032  is rotatable around a right front axle  1324  (an example of an axle of a right steerable wheel). The left front wheel  1031  and the right front wheel  1032  are arranged lateral-symmetrically with respect to the center. 
     As shown in  FIG. 8 , the pair of front fenders  1223  includes a left front fender  1227  and a right front fender  1228 . The left front fender  1227  is positioned farther in the upward direction u than the left front wheel  1031 . The right front fender  1228  is positioned farther in the upward direction u than the right front wheel  1032 . 
     The rear wheel  1004  is a driving wheel of the leaning vehicle  1   b . The rear wheel  1004  is rotated by a driving force generated by the power unit  1025 . The rear wheel  1004  is positioned in the rear part of the leaning vehicle  1   b . The rear wheel  1004  is rotatable around an axle. 
     [Steering Mechanism] 
     The steering mechanism  1007  will hereinafter be described with reference to the drawings.  FIG. 9  is a looking-to-the-down (d) view of the front part of the leaning vehicle  1   b  when the vehicle frame body  1021  is in an upright posture. In  FIG. 9 , the vehicle body cover  1022  is shown as being transparent. 
     The steering mechanism  1007  is configured to steer the left front wheel  1031  and the right front wheel  1032  in accordance with the rider&#39;s manipulation. As shown in  FIGS. 8 and 9 , the steering mechanism  1007  includes a left shock absorber  1033 , a right shock absorber  1034 , a handlebar  1060 , a steering shaft  1062 , a tie rod  1067 , a left bracket  1317 , a right bracket  1327 , and a center bracket  1337 . 
     The left shock absorber  1033  supports the left front wheel  1031  such that the left front wheel  1031  is movable along the up-down direction ud relative to the vehicle body frame  1021 . The left shock absorber  1033  includes a left lower portion  1033   a , a left upper portion  1033   b , and a left support portion  1033   c . The left lower portion  1033   a  extends along the up-down direction ud. The left support portion  1033   c  is positioned in the lower end part of the left lower portion  1033   a . The left support portion  1033   c  supports the left front wheel  1031  such that the left front wheel  1031  is rotatable. The left front wheel  1031  is rotatable around the left front axle  1314 . The left front axle  1314  extends from the left support portion  1033   c  to the leftward direction  1 . The left upper portion  1033   b  extends along the up-down direction ud. The left upper portion  1033   b  is positioned farther in the upward direction u than the left lower portion  1033   a  with the lower end part thereof inserted in the left lower portion  1033   a . The upper end part of the left upper portion  1033   b  is fixed to the left bracket  1317 , which will be described later. Accordingly, the left upper portion  1033   b  is supported by a left-side member  1053 , which will be described later. 
     The left shock absorber  1033  is what is called a telescopic shock absorber. The left shock absorber  1033 , for example, includes a combination of a damper and a spring. The left upper portion  1033   b  moves relative to the left lower portion  1033   a  in the extending direction of the left lower portion  1033   a , and accordingly, the left shock absorber  1033  is expandable in the direction. In this way, the left shock absorber  1033  absorbs displacements of the left front wheel  1031  in the up-down direction ud relative to the left upper portion  1033   b.    
     The right shock absorber  1034  supports the right front wheel  1032  such that the right front wheel  1032  is movable along the up-down direction ud relative to the vehicle body frame  1021 . The right shock absorber  1034  includes a right lower portion  1034   a , a right upper portion  1034   b , and a right support portion  1034   c . The right lower portion  1034   a  extends along the up-down direction ud. The right support portion  1034   c  is positioned in the lower end part of the right lower portion  1034   a . The right support portion  1034   c  supports the right front wheel  1032  such that the right front wheel  1032  is rotatable. The right front wheel  1032  is rotatable around the right front axle  1324 . The right front axle  1324  extends from the right support portion  1034   c  to the rightward direction r. The right upper portion  1034   b  extends along the up-down direction ud. The right upper portion  1034   b  is positioned farther in the upward direction u than the right lower portion  1034   a  with the lower end part thereof inserted in the right lower portion  1034   a . The upper end part of the right upper portion  1034   b  is fixed to the right bracket  1327 , which will be described later. Accordingly, the right upper portion  1034   b  is supported by a right side member  1054 , which will be described later. 
     The right shock absorber  1034  is what is called a telescopic shock absorber. The right shock absorber  1034 , for example, includes a combination of a damper and a spring. The right upper portion  1034   b  moves relative to the right lower portion  1034   a  in the extending direction of the right lower portion  1034   a , and accordingly, the right shock absorber  1034  is expandable in the direction. In this way, the right shock absorber  1034  absorbs displacements of the right front wheel  1032  in the up-down direction ud relative to the right upper portion  1034   b.    
     The handlebar  1060  is to be manipulated by the rider. The steering shaft  1062  is supported by the vehicle body frame  1021  in such a manner as to be rotatable on its central axis in accordance with the rider&#39;s manipulation of the handlebar  1060 . More specifically, the steering shaft  1062  is inserted in the head pipe  1211  and thereby is supported by the head pipe  1211  in such a manner as to be rotatable. The handlebar  1060  is fixed to the upper end part of the steering shaft  1062 . Then, when the rider manipulates the handlebar  1060 , the steering shaft  1062  rotates on its central axis. 
     The center bracket  1337  is fixed to the lower end part of the steering shaft  1062 . Accordingly, the center bracket  1337  is rotatable around the central axis of the steering shaft  1062  together with the steering shaft  1062 . 
     The tie rod  1067  transmits the rotation of the steering shaft  1062  caused by the rider&#39;s manipulation of the handlebar  1060  to the left shock absorber  1033  and the right shock absorber  1034 . The tie rod  1067  extends along the left-right direction LR. The center of the tie rod  1067  with respect to the left-right direction LR is supported by the center bracket  1337 . The left end part of the tie rod  1067  is supported by the left bracket  1317 . The right end part of the tie rod  1067  is supported by the right bracket  1327 . 
     [Link Mechanism] 
     The link mechanism  1005  will hereinafter be described with reference to  FIGS. 8 and 9 . The link mechanism  1005  is a parallelogram link mechanism. The link mechanism  1005  is positioned farther in the downward direction d than the handlebar  1060 . The link mechanism  1005  is supported by the head pipe  1211  of the vehicle body frame  1021 . 
     The link mechanism  1005  includes an upper cross member  1051 , a lower cross member  1052 , a left side member  1053  and a right side member  1054 . The upper cross member  1051 , the lower cross member  1052 , the left side member  1053  and the right side member  1054  are link members that are displaceable relative to the vehicle body frame  1021 . In the present specification, a displacement includes a displacement by translation, a displacement by rotation, and a displacement by combination of translation and rotation. 
     The upper cross member  1051  extends along the left-right direction LR. The upper cross member  1051  is positioned farther in the forward direction f than the head pipe  1211  and farther in the upward direction u than the left front wheel  1031  and the right front wheel  1032 . The upper cross member  1051  is supported by the head pipe  1211  via a support C. The support C is positioned in a middle part of the upper cross member  1051  and in the upper part of the head pipe  1211 . When the upper cross member  1051  is divided into three equal parts along the left-right direction LR, the part positioned farthest in the leftward direction L of the three parts is a left part of the upper cross member  1051 . The part positioned farthest in the rightward direction R of the three parts is a right part of the upper cross member  1051 . The middle part of the upper cross member  1051  is the part positioned in the middle of the three parts. The support C is a shaft extending along the front-back direction fb. The support C extends from the head pipe  1211  to the forward direction f, slightly inclined to the upward direction u. The upper cross member  1051  is rotatable around the support C and accordingly rotatable relative to the head pipe  1211 . 
     The lower cross member  1052  includes a front lower cross member  1052 A and a rear lower cross member  1052 B. The front lower cross member  1052 A extends along the left-right direction LR. The front lower cross member  1052 A is positioned farther in the forward direction f than the head pipe  1211 , farther in the downward direction d than the upper cross member  1051 , and farther in the upward direction u than the left front wheel  1031  and the right front wheel  1032 . The front lower cross member  1052 A is supported by the head pipe  1211  via a support F. The support F is positioned in a middle part of the front lower cross member  1052 A and in the lower part of the head pipe  1211 . When the front lower cross member  1052 A is divided into three equal parts along the left-right direction LR, the part positioned farthest in the leftward direction L of the three parts is a left part of the front lower cross member  1052 A. The part positioned farthest in the rightward direction R of the three parts is a right part of the front lower cross member  1052 A. The middle part of the front lower cross member  1052 A is the part positioned in the middle of the three parts. The support F is a shaft extending along the front-back direction fb. The support F extends from the head pipe  1211  to the forward direction f, slightly inclined to the upward direction u. The front lower cross member  1052 A is rotatable around the support F and accordingly rotatable relative to the head pipe  1211 . 
     The rear lower cross member  1052 B extends along the left-right direction LR. The rear lower cross member  1052 B is positioned farther in the backward direction b than the head pipe  1211 , farther in the downward direction d than the upper cross member  1051 , and farther in the upward direction u than the left front wheel  1031  and the right front wheel  1032 . The rear lower cross member  1052 B is supported by the head pipe  1211  via the support F. The support F is positioned in a middle part of the rear lower cross member  1052 B and in the lower part of the head pipe  1211 . When the rear lower cross member  1052 B is divided into three equal parts along the left-right direction LR, the part positioned farthest in the leftward direction L of the three parts is a left part of the rear lower cross member  1052 B. The part positioned farthest in the rightward direction R of the three parts is a right part of the rear lower cross member  1052 B. The middle part of the rear lower cross member  1052 B is the part positioned in the middle of the three parts. As mentioned above, the support F is a shaft extending along the front-back direction fb. The support F extends from the head pipe  1211  also to the backward direction b, slightly inclined to the downward direction d. The rear lower cross member  1052 B is rotatable around the support F and accordingly rotatable relative to the head pipe  1211 . 
     The left side member  1053  extends along the up-down direction ud. Accordingly, the extending direction of the left side member  1053  is parallel to the extending direction of the head pipe  1211 . The left side member  1053  is positioned farther in the leftward direction  1  than the head pipe  1211 . The left side member  1053  is positioned farther in the upward direction u than the left front wheel  1031  and farther in a left-upward direction lu than the left shock absorber  1033 . The left side member  1053  is supported by the upper cross member  1051  via a support D. The support D is positioned in the upper part of the left side member  1053  and in the left part of the upper cross member  1051 . The support D is a shaft extending along the front-back direction fb. The left side member  1053  is rotatable around the support D and accordingly rotatable relative to the upper cross member  1051 . 
     Also, the left side member  1053  is supported by the front lower cross member  1052 A and the rear lower cross member  1052 B via a support G. The support G is positioned in the lower part of the left side member  1053 , in the left part of the front lower cross member  1052 A and in the left part of the rear lower cross member  1052 B. The support G is a shaft extending along the front-back direction fb. The left side member  1053  is rotatable around the support G and accordingly rotatable relative to the front lower cross member  1052 A and the rear lower cross member  1052 B. 
     The left bracket  1317  is supported by the lower end part of the left side member  1053 . The left bracket  1317  is rotatable around a left central axis Y1 and rotatable relative to the left side member  1053 . The left central axis Y1 is a central axis of the left side member  1053 . The left central axis Y1 extends along the up-down direction ud. 
     The right side member  1054  extends along the up-down direction ud. 
     Accordingly, the extending direction of the right side member  1054  is parallel to the extending direction of the head pipe  1211 . The right side member  1054  is positioned farther in the rightward direction r than the head pipe  1211 . The right side member  1054  is positioned farther in the upward direction u than the right front wheel  1032  and farther in a right-upward direction ru than the right shock absorber  1034 . The right side member  1054  is supported by the upper cross member  1051  via a support E. The support E is positioned in the upper part of the right side member  1054  and in the right part of the upper cross member  1051 . The support E is a shaft extending along the front-back direction fb. The right side member  1054  is rotatable around the support E and accordingly rotatable relative to the upper cross member  1051 . 
     Also, the right side member  1054  is supported by the front lower cross member  1052 A and the rear lower cross member  1052 B via a support H. The support H is positioned in the lower part of the right side member  1054  and in the right part of the front lower cross member  1052 A and in the right part of the rear lower cross member  1052 B. The support H is a shaft extending along the front-back direction fb. The right side member  1054  is rotatable around the support H and accordingly rotatable relative to the front lower cross member  1052 A and the rear lower cross member  1052 B. 
     The right bracket  1327  is supported by the lower end part of the right side member  1054 . The right bracket  1327  is rotatable around a right central axis Y2 and rotatable relative to the right side member  1054 . The right central axis Y2 is a central axis of the right side member  1054 . The right central axis Y2 extends along the up-down direction ud. 
     As described above, the upper cross member  1051 , the lower cross member  1052 , the left side member  1053  and the right side member  1054  are connected to one another such that the upper cross member  1051  and the lower cross member  1052  are kept parallel to each other and such that the left side member  1053  and the right side member are kept parallel to each other. 
     The left shock absorber  1033  is positioned farther in a right-downward direction rd than the left side member  1053 . The left shock absorber  1033  is supported by the left bracket  1317 . Specifically, the upper end part of the left shock absorber  1033  is fixed to the left bracket  1317 . Further, the left shock absorber  1033  supports the left front wheel  1031 . Accordingly, the left side member  1053  supports the left front wheel  1031  via the left bracket  1317  and the left shock absorber  1033 . In this way, the link mechanism  1005  supports the left front wheel  1031 . The left shock absorber  1033  leans in the left-right direction LR together with the left side member  1053 . 
     The right shock absorber  1034  is positioned farther in a left-downward direction ld than the right side member  1054 . The right shock absorber  1034  is supported by the right bracket  1327 . Specifically, the upper end part of the right shock absorber  1034  is fixed to the right bracket  1327 . Further, the right shock absorber  1034  supports the right front wheel  1032 . Accordingly, the right side member  1054  supports the right front wheel  1032  via the right bracket  1327  and the right shock absorber  1034 . In this way, the link mechanism  1005  supports the right front wheel  1032 . The right shock absorber  1034  leans in the left-right direction LR together with the right side member  1054 . 
     [Steering Motion] 
     Next, steering motions of the leaning vehicle  1   b  are described with reference to  FIG. 10 .  FIG. 10  is a looking-to-the-down (d) view of the front part of the leaning vehicle  1   b  when the leaning vehicle  1   b  is steered leftward. 
     As shown in  FIG. 10 , when the rider steers the handlebar  60  leftward, the steering shaft  1062  rotates counterclockwise in a view in the downward direction d. Since the center bracket  1337  is fixed to the lower end part of the steering shaft  1062 , the center bracket  1337  rotates counterclockwise in a view in the downward direction d together with the steering shaft  1062 . 
     The tie rod  1067  makes a parallel translation in a backward and leftward direction  1 , b with the rotation of the center bracket  1337 . The left end part of the tie rod  1067  is supported by the front end part of the left bracket  1317 . The left bracket  1317  is rotatable around the left central axis Y1 (see  FIG. 8 ). Accordingly, with the parallel translation of the tie rod  1067 , the left bracket  1317  rotates counterclockwise in a view in the downward direction d. Also, the right end part of the tie rod  1067  is fixed to the front end part of the right bracket  1327 . The right bracket  1327  is rotatable around the right central axis Y2 (see  FIG. 8 ). Accordingly, with the parallel translation of the tie rod  1067 , the right bracket  1327  rotates counterclockwise in a view in the downward direction d. 
     The left front wheel  1031  is connected to the left bracket  1317  via the left shock absorber  1033 . Therefore, with the rotation of the left bracket  1317 , the left front wheel  1031  rotates counterclockwise around the left central axis Y1 (see  FIG. 8 ) in a view in the downward direction d. Also, the right front wheel  1032  is connected to the right bracket  1327  via the right shock absorber  1034 . Therefore, with the rotation of the right bracket  1327 , the right front wheel  1327  rotates counterclockwise around the right central axis Y2 (see  FIG. 8 ) in a view in the downward direction d. 
     When the rider steers the handlebar  1060  rightward, each of the elements described above rotates in a direction opposite to the direction of rotation when the rider steers the handlebar  1060  leftward (that is, rotates clockwise). Thus, the motion of each of the elements is laterally reversed, and no more description will be provided. 
     [Leaning Motion] 
     Next, leaning motions of the leaning vehicle  1   b  are described with reference to the drawings.  FIG. 11  is a looking-to-the-back (b) view of the front part of the leaning vehicle  1   b  when the vehicle body frame  1021  leans in the leftward direction L. 
     The vehicle body frame  1021  rotates around the roll axis Ax and thereby leans in the leftward direction L or the rightward direction R. The roll axis Ax is an axis extending along the front-back direction FB. More specifically, as shown in  FIG. 7 , the roll axis Ax is a straight line that passes the contact point between the rear wheel  1004  and the ground and is perpendicular to the steering shaft  1062  when the vehicle body frame  1021  is in an upright posture. 
     As the vehicle body frame  1021  is rotating around the roll axis Ax, the rotation angle of the vehicle body frame  1021  around the roll axis Ax changes, and the rotation angle of the vehicle body frame  1021  around the roll axis Ax is referred to as a roll angle θ. The roll angle θ of the leaning vehicle  1   b  is the same as the roll angle θ of the leaning vehicle  1   a , and the description is omitted. 
     As shown in  FIG. 11 , when the leaning vehicle  1   b  is turning left, the upper cross member  1051 , the lower cross member  1052 , the left side member  1053  and the right side member  1054  of the link mechanism  1005  displace relative to the vehicle body frame  1021  such that the left front axle  1314  is positioned farther in the upward direction u than the right front axle  1324 , and thereby, the vehicle body frame  1021  is caused to lean in the leftward direction L. In this case, the roll angle θ is a positive value. Also, when the leaning vehicle  1   b  is turning right, the upper cross member  1051 , the lower cross member  1052 , the left side member  1053  and the right side member  1054  of the link mechanism  1005  displace relative to the vehicle frame body  1021  such that the right front axle  1324  is positioned farther in the upward direction u than the left front axle  1314 , and thereby, the vehicle body frame  1021  is caused to lean in the rightward direction R. In this case, the roll angle θ is a negative value. A case in which the vehicle body frame  1021  leans in the leftward direction L will be described below as an example. 
     As shown in  FIG. 11 , the vehicle body frame  1021  is changed from an upright posture to a leaning posture in the leftward direction L by a shape change of the link mechanism  1005 . Specifically, as shown in  FIG. 8 , when the vehicle body frame  1021  is in an upright posture, the upper cross member  1051 , the lower cross member  1052 , the left side member  1053  and the right side member  1054  form a rectangle in the leaning vehicle  1   b . On the other hand, as shown in  FIG. 11 , when the vehicle body frame  1021  leans in the leftward direction L, the upper cross member  1051 , the lower cross member  1052 , the left side member  1053  and the right side member  1054  form a parallelogram in the leaning vehicle  1   b.    
     When the rider causes the vehicle body frame  1021  to lean in the leftward direction L, the head pipe  1211  leans in the leftward direction L. When the head pipe  1211  leans in the leftward direction L, the upper cross member  1051  rotates around the support C in such a manner as to rotate counterclockwise relative to the head pipe  1211  in a view in the backward direction b. In the same way, the lower cross member  1052  rotates around the support F in such a manner as to rotate counterclockwise relative to the head pipe  1211  in a view in the backward direction b. Then, in a view in the backward direction b, the upper cross member  1051  moves in the leftward direction L relative to the lower cross member  1052 . 
     With the movement of the upper cross member  1051 , the left side member  1053  rotates around the support D in such a manner as to rotate clockwise relative to the upper cross member  1051  in a view in the backward direction b. The right side member  1054  rotates around the support E in such a manner as to rotate clockwise relative to the upper cross member  1051  in a view in the backward direction b. With the movement of the upper cross member  1051 , also, the left side member  1053  rotates around the support G in such a manner as to rotate clockwise relative to the lower cross member  1052  in a view in the backward direction b. The right side member  1054  rotates around the support H in such a manner as to rotate clockwise relative to the lower cross member  1052  in a view in the backward direction b. In this way, the left side member  1053  and the right side member  1054  lean in the leftward direction L while being kept parallel to the head pipe  1211 . 
     The left bracket  1317  is supported by the lower end part of the left side member  1053 . Therefore, when the left side member  1053  leans in the leftward direction L, the left bracket  1317  leans in the leftward direction L. The left shock absorber  1033  is supported by the left bracket  1317 , and therefore, when the left bracket  1317  leans in the leftward direction L, the left shock absorber  1033  leans in the leftward direction L. The left front wheel  1031  is supported by the lower end part of the left shock absorber  1033 , and therefore, when the left shock absorber  1033  leans in the leftward direction L, the left front wheel  1031  leans in the leftward direction L. 
     The right bracket  1327  is supported by the lower end part of the right side member  1054 . Therefore, when the right side member  1054  leans in the leftward direction L, the right bracket  1327  leans in the leftward direction L. The right shock absorber  1034  is supported by the right bracket  1327 , and therefore, when the right bracket  1327  leans in the leftward direction L, the right shock absorber  1034  leans in the leftward direction L. The right front wheel  1032  is supported by the lower end part of the right shock absorber  1034 , and therefore, when the right shock absorber  1034  leans in the leftward direction L, the right front wheel  1032  leans in the leftward direction L. 
     The rear wheel  1004  (not shown in  FIG. 11 ) is supported by the vehicle body frame  1021 . Therefore, the rear wheel  1004  leans in the leftward direction L together with the vehicle body frame  1021 . 
     When the vehicle body frame  1021  leans in the rightward direction R, each of the elements described above moves in a direction opposite to the direction of motion when the vehicle body frame  1021  is leaning in the leftward direction L. Thus, the motion of each of the elements is laterally reversed, and no more description will be provided. 
     [Posture Control Actuator Controller] 
     Next, the posture control actuator controller  1606  of the leaning vehicle  1   b  will be described with reference to the drawings.  FIG. 12  is a block diagram of the posture control actuator controller  1606 . 
     As shown in  FIG. 7 , the leaning vehicle  1   b  further includes a posture control actuator unit (posture control actuator device)  1599 , and a speed sensor  1604 . 
     The posture control actuator unit  1599  includes a lean actuator  1600 , a roll rate sensor  1602 , and a posture control actuator controller  1606 . The lean actuator (an example of a posture control actuator) outputs a posture control torque Tc to displace the upper cross member  1051 , the lower cross member  1052 , the left side member  1053  and the right side member  1054  relative to the vehicle body frame  1021 . The posture control torque Tc is a torque to control the posture of the vehicle body frame  1021 . In order to cause the vehicle body  1021  to lean, it is necessary to apply a torque to the lower cross member  1052 . A lean torque Tl is applied to the lower cross member  1052 , and the lean torque Tl has a strength required to cause the vehicle body frame  1021  running at a speed V to roll at a roll rate ω. The lean torque Tl acts around the support F. The direction of the lean torque Tl that causes a counterclockwise rotation of the lower cross member  1052  in a view in the backward direction b is defined as a positive direction of the lean torque Tl. The direction of the lean torque Tl that causes a clockwise rotation of the lower cross member  1052  in a view in the backward direction b is defined as a negative direction of the lean torque Tl. The lean actuator  1600  outputs a posture control torque Tc to assist the lean torque Tl that the rider applies to the lower cross member  1052 . 
     The lean actuator  1600  is fixed to the support F of the vehicle body frame  1021 . The lean actuator  1600  is a combination of an electric motor and a gear. The electric motor generates a torque. The torque generated by the electric motor is outputted to the lower cross member  1052  as a posture control torque Tc via the gear. In this way, the lean actuator  1600  causes the lower cross member  1052  to rotate around the support F relative to the head pipe  1211 . 
     The roll rate sensor  1602  detects the roll rate ω that is the amount of change per unit time of the roll angle θ. The roll rate ω of the leaning vehicle  1   b  is the same as the roll rate ω of the leaning vehicle  1   a , and the description is omitted. 
     The speed sensor  1604  detects the speed V of the leaning vehicle  1   b . The speed V is a positive value when the leaning vehicle  1   b  is running forward. 
     The posture control actuator controller  1606  controls the lean actuator  1600  based on the roll rate ω detected by the roll rate sensor  1602 . The posture control actuator controller  1606  is, for example, an IC (integrated circuit) for control of the lean actuator  1600 . However, the posture control actuator controller  1606  does not need to be achieved by a single IC, and the posture control actuator controller  1606  may be a combination of one or more ICs, one or more electronic components and/or one or more circuit boards. 
     As shown in  FIG. 7 , the lean actuator  1600 , the roll rate sensor  1602  and the posture control actuator controller  1606  are incorporated in such a manner as not to be displaceable relative to one another, and the lean actuator  1600  is supported by the vehicle body frame  1021  in such a manner as to be attachable to and detachable from the vehicle body frame  1021 . More specifically, for example, the roll rate sensor  1602  and the posture control actuator controller  1606  are fixed in a case of the lean actuator  1600 . The means for fixing the roll rate sensor  1602  and the posture control actuator controller  1606  to the lean actuator  1600  may be a combination of a bolt and a nut, a screw, a snap-fit, an adhesive, an adhesive tape, welding, brazing, etc. The lean actuator  1600  is to output a posture control torque Tc to the lower cross member  1052 . Therefore, the lean actuator  1600  is supported by the vehicle body frame  1021  in such a manner as not to be displaceable relative to the vehicle body frame  1021 . In this structure, the roll rate sensor  1602  and the posture control actuator controller  1606  are not displaceable relative to the lean actuator  1600 , and the lean actuator  1600  is not displaceable relative to the vehicle body frame  1021 . 
     The lean actuator  1600  is fixed to the support F as shown in  FIG. 8 . Therefore, in a view in the backward direction b, the lean actuator  1600  overlaps the center line C. Accordingly, in a view in the backward direction b, the posture control actuator unit  1599  overlaps the center line C. 
     The description is now returned to the posture control actuator controller  1606 . The posture control actuator controller  1606  obtains the roll rate ω from the roll rate sensor  1602 . Specifically, an electric signal representing the roll rate ω (which will hereinafter be referred to simply as roll rate ca) detected by the roll rate sensor  1602  is inputted to the posture control actuator controller  1606 . 
     The posture control actuator controller  1606  obtains the speed V from the speed sensor  1604 . Specifically, an electric signal representing the speed V (which will hereinafter be referred to simply as speed V) detected by the speed sensor  1604  is inputted to the posture control actuator controller  1606 . 
     The posture control actuator controller  1606  does not use a torque sensor that detects the steering torque T that is generated by the rider&#39;s manipulation of the handlebar  1060  and acts around the rotation axis (central axis of the steering shaft  1062 ), and uses the roll rate sensor  1602 . Then, the posture control actuator controller  1606  controls the lean actuator  1600  not based on the steering torque T that is generated by the rider&#39;s manipulation of the handlebar  1060  and acts around the steering shaft  1062  but based on the roll rate ω sent from the roll rate sensor  1602 . In the present embodiment, the posture control actuator controller  1606  uses neither a torque sensor that detects the steering torque T nor a roll sensor that detects the roll angle θ. The posture control actuator controller  1606  uses the roll rate sensor  1602  and the speed sensor  1604 . Then, the posture control actuator controller  1606  controls the lean actuator  1600  based on neither the steering torque T detected by a torque sensor nor the roll angle θ detected by a roll sensor. The posture control actuator controller  1606  controls the lean actuator  1600  based on the roll rate ω sent from the roll rate sensor  1602  and the speed V sent from the speed sensor  1604 . 
     As shown in  FIG. 12 , the posture control actuator controller  1606  includes a torque estimation section  1614  and a current determination section  1616 . The torque estimation section  1614  determines an estimated lean torque value Tl (m, n), which is an estimated value of the lean torque Tl, based on the speed V and the roll rate ω. The values m and n are integers. The torque estimation section  1614  stores an estimated lean torque determination table as shown by TABLE 3. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 ω(n)(deg/s) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 . . . 
                 ω(−5) 
                 ω(−4) 
                 ω(−3) 
                 ω(−2) 
                 ω(−1) 
                 ω(0) = 0 
                 ω(1) 
                 ω(2) 
                 ω(3) 
                 ω(4) 
                 ω(5) 
                 . . . 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 V(m) 
                 V(1) 
                 . . . 
                 TI(1, −5) 
                 TI(1, −4) 
                 TI(1, −3) 
                 TI(1, −2) 
                 TI(1, −1) 
                 TI(1, 0) = 0 
                 TI(1, 1) 
                 TI(1, 2) 
                 TI(1, 3) 
                 TI(1, 4) 
                 TI(1, 5) 
                 . . . 
               
               
                 (km/h) 
                 V(2) 
                 . . . 
                 TI(2, −5) 
                 TI(2, −4) 
                 TI(2, −3) 
                 TI(2, −2) 
                 TI(2, −1) 
                 TI(2, 0) = 0 
                 TI(2, 1) 
                 TI(2, 2) 
                 TI(2, 3) 
                 TI(2, 4) 
                 TI(2, 5) 
                 . . . 
               
               
                   
                 V(3) 
                 . . . 
                 TI(3, −5) 
                 TI(3, −4) 
                 TI(3, −3) 
                 TI(3, −2) 
                 TI(3, −1) 
                 TI(3, 0) = 0 
                 TI(3, 1) 
                 TI(3, 2) 
                 TI(3, 3) 
                 TI(3, 4) 
                 TI(3, 5) 
                 . . . 
               
               
                   
                 V(4) 
                 . . . 
                 TI(4, −5) 
                 TI(4, −4) 
                 TI(4, −3) 
                 TI(4, −2) 
                 TI(4, −1) 
                 TI(4, 0) = 0 
                 TI(4, 1) 
                 TI(4, 2) 
                 TI(4, 3) 
                 TI(4, 4) 
                 TI(4, 5) 
                 . . . 
               
               
                   
                 V(5) 
                 . . . 
                 TI(5, −5) 
                 TI(5, −4) 
                 TI(5, −3) 
                 TI(5, −2) 
                 TI(5, −1) 
                 TI(5, 0) = 0 
                 TI(5, 1) 
                 TI(5, 2) 
                 TI(5, 3) 
                 TI(5, 4) 
                 TI(5, 5) 
                 . . . 
               
               
                   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                   
               
            
           
         
       
     
     In the estimated lean torque determination table, estimated lean torque values Tl (m, n) are stored in association with values of the speed V(m) and values of the roll rate ω (n). The speed V(m) and the roll rate ω(n) of the leaning vehicle  1   b  are the same as the speed V(m) and the roll rate ω(n) of the leaning vehicle  1   a , and the description thereof is omitted. 
     When the value n is positive (when the roll rate ω(n) is a positive value), the estimated lean torque Tl (m, n) is a positive value. In this case, the estimated lean torque Tl (m, n) indicates a lean torque to cause the lower cross member  1052  to rotate counterclockwise (in the positive direction) in a view in the backward direction b. In this case, the greater the value n is (the greater the roll rate ω(n) is), the greater the estimated lean torque Tl (m, n) is. Also, the greater the value m is (the greater the speed V(m) is), the greater the estimated lean torque Tl (m, n) is. 
     On the other hand, when the value n is negative (when the roll rate ω(n) is a negative value), the estimated lean torque Tl (m, n) is a negative value. In this case, the estimated lean torque Tl (m, n) indicates a lean torque to cause the lower cross member  1052  to rotate clockwise (in the negative direction) in a view in the backward direction b. In this case, the smaller the value n is (the smaller the roll rate ω(n) is), the smaller the estimated lean torque Tl (m, n) is (the greater the absolute value of the estimated lean torque Tl (m, n) is). Also, the greater the value m is (the greater the speed V(m) is), the smaller the estimated lean torque Tl (m, n) is (the greater the absolute value of the estimated lean torque Tl (m, n) is). 
     The torque estimation section  1614  identifies a speed V(m) that is closest to the speed V that the posture control actuator controller  1606  has obtained. Also, the torque estimation section  1614  identifies a roll rate ω(n) that is closest to the roll rate ω that the posture control actuator controller  606  has obtained. Then, the torque estimation section  1614  determines an estimated lean torque value Tl(m, n) in association with the speed V(m) and the roll rate ω(n) with reference to TABLE 3. 
     The current determination section  1616  controls the lean actuator  1600  based on the estimated lean torque value Tl(m, n) determined by the torque estimation section  1614 . Specifically, the current determination section  1616  determines a control current I(m, n) to be outputted to the lean actuator  1600 , based on the estimated lean torque value Tl(m, n). Therefore, the current determination section  1616  stores a control current determination table as shown by TABLE 4. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                 . . . 
                 TI(1, −5) 
                 TI(1, −4) 
                 TI(1, −3) 
                 TI(1, −2) 
                 TI(1, −1) 
                 TI(1, 0) = 0 
                 TI(1, 1) 
                 TI(1, 2) 
                 TI(1, 3) 
                 TI(1, 4) 
                 TI(1, 5) 
                 . . . 
               
               
                 . . . 
                 I(1, −5) 
                 I(1, −4) 
                 I(1, −3) 
                 I(1, −2) 
                 I(1, −1) 
                 I(1, 0) = 0 
                 I(1, 1) 
                 I(1, 2) 
                 I(1, 3) 
                 I(1, 4) 
                 I(1, 5) 
                 . . . 
               
               
                 . . . 
                 TI(2, −5) 
                 TI(2, −4) 
                 TI(2, −3) 
                 TI(2, −2) 
                 TI(2, −1) 
                 TI(2, 0) = 0 
                 TI(2, 1) 
                 TI(2, 2) 
                 TI(2, 3) 
                 TI(2, 4) 
                 TI(2, 5) 
                 . . . 
               
               
                 . . . 
                 I(2, −5) 
                 I(2, −4) 
                 I(2, −3) 
                 I(2, −2) 
                 I(2, −1) 
                 I(2, 0) = 0 
                 I(2, 1) 
                 I(2, 2) 
                 I(2, 3) 
                 I(2, 4) 
                 I(2, 5) 
                 . . . 
               
               
                 . . . 
                 TI(3, −5) 
                 TI(3, −4) 
                 TI(3, −3) 
                 TI(3, −2) 
                 TI(3, −1) 
                 TI(3, 0) = 0 
                 TI(3, 1) 
                 TI(3, 2) 
                 TI(3, 3) 
                 TI(3, 4) 
                 TI(3, 5) 
                 . . . 
               
               
                 . . . 
                 I(3, −5) 
                 I(3, −4) 
                 I(3, −3) 
                 I(3, −2) 
                 I(3, −1) 
                 I(3, 0) = 0 
                 I(3, 1) 
                 I(3, 2) 
                 I(3, 3) 
                 I(3, 4) 
                 I(3, 5) 
                 . . . 
               
               
                 . . . 
                 TI(4, −5) 
                 TI(4, −4) 
                 TI(4, −3) 
                 TI(4, −2) 
                 TI(4, −1) 
                 TI(4, 0) = 0 
                 TI(4, 1) 
                 TI(4, 2) 
                 TI(4, 3) 
                 TI(4, 4) 
                 TI(4, 5) 
                 . . . 
               
               
                 . . . 
                 I(4, −5) 
                 I(4, −4) 
                 I(4, −3) 
                 I(4, −2) 
                 I(4, −1) 
                 I(4, 0) = 0 
                 I(4, 1) 
                 I(4, 2) 
                 I(4, 3) 
                 I(4, 4) 
                 I(4, 5) 
                 . . . 
               
               
                 . . . 
                 TI(5, −5) 
                 TI(5, −4) 
                 TI(5, −3) 
                 TI(5, −2) 
                 TI(5, −1) 
                 TI(5, 0) = 0 
                 TI(5, 1) 
                 TI(5, 2) 
                 TI(5, 3) 
                 TI(5, 4) 
                 TI(5, 5) 
                 . . . 
               
               
                 . . . 
                 I(5, −5) 
                 I(5, −4) 
                 I(5, −3) 
                 I(5, −2) 
                 I(5, −1) 
                 I(5, 0) = 0 
                 I(5, 1) 
                 I(5, 2) 
                 I(5, 3) 
                 I(5, 4) 
                 I(5, 5) 
                 . . . 
               
               
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                   
               
            
           
         
       
     
     In the control current determination table, estimated lean torque values Tl (m, n) and control current values I (m, n) are stored in association with each other. The control current I (m, n) is a current that the lean actuator  1600  requires to output a posture control torque Tc corresponding to the assist rate (for example, 20%) of the estimated lean torque value Tl (m, n) to the lower cross member  1052 . The lean actuator  1600  outputs a posture control torque Tc corresponding to 20% of the estimated lean torque value Tl (m, n) to the lower cross member  1052 . Accordingly, the rider only needs to tilt the vehicle body frame  1021  to apply 80% of the estimated lean torque value Tl (m, n) to the lower cross member  1052 . In this way, the lean actuator  1600  assists the rider&#39;s manipulation to tilt the vehicle body frame  1021 . The assist rate is an arbitrary value and may be a value other than 20%. In order to allow the rider to cause the vehicle body frame  1021  to lean with less power, the assist rate should be more than 20%. In order to allow the rider to cause the vehicle body frame  1021  to lean with more power, the assist rate should be less than 20%. The assist rate may be a negative value. In this case, the lean actuator  1600  outputs a posture control torque Tc to inhibit the rider&#39;s manipulation to cause the vehicle body frame  1021  to lean. 
     When the value n is positive, the control current I (m, n) is a positive value. In this case, the greater the value n is, the greater the control current I (m, n) is. Also, the greater the value m is, the greater the control current I (m, n) is. On the other hand, when the value n is negative, the control current I (m, n) is a negative value. In this case, the smaller the value n is, the smaller the control current I (m, n) is (the greater the absolute value of the control current I (m, n) is). Also, the greater the value m is, the smaller the control current I (m, n) is (the greater the absolute value of the control current I(m, n) is). 
     The lean actuator  1600  outputs a posture control torque Tc to the lower cross member  1052  based on the control current I(m, n) outputted from the posture control actuator controller  1606 . When receiving a positive control current I (m, n), the lean actuator  1600  outputs a posture control torque Tc to cause a counterclockwise rotation of the lower cross member  1052 . In this case, the greater the absolute value of the control current I(m, n) is, the greater the absolute value of the posture control torque Tc is. Then, in a view in the backward direction B, the vehicle body frame  1021  rotates clockwise (in the positive direction) around the roll axis Ax at a roll rate ω. When receiving a negative control current I(m, n), the lean actuator  1600  outputs a posture control torque Tc to cause a clockwise rotation of the lower cross member  105 . In this case, the greater the absolute value of the control current I(m, n) is, the greater the absolute value of the posture control torque Tc is. Then, in a view in the backward direction B, the vehicle body frame  1021  rotates counterclockwise (in the negative direction) around the roll axis Ax at a roll rate ω. 
     Next, operations of the posture control actuator controller  1606  will be described with reference to the drawings.  FIG. 13  is a flowchart showing operations performed by the posture control actuator controller  1606 . The posture control actuator controller  1606  performs a process that will be described below along a software program stored in a storage device (not shown). 
     The process is started when an ignition source of the leaning vehicle  1   b  is turned on. As long as the ignition source is on, the roll rate sensor  1602  keeps outputting the roll rate ω to the posture control actuator controller  1606 . Also, the speed sensor  1604  keeps outputting the speed V to the posture control actuator controller  1606 . 
     The torque estimation section  1614  obtains the roll rate ω from the roll rate sensor  1602  (step S 11 ). Further, the torque estimation section  1614  obtains the speed V from the speed sensor  1604  (step S 12 ). 
     Next, the torque estimation section  1614  identifies a roll rate ω(n) closest to the roll rate ω. Further, the torque estimation section  1614  identifies a speed V(m) closest to the speed V. Then, the torque estimation section  1614  determines an estimated lean torque value Tl (m, n) corresponding to the roll rate ω(n) and the speed V(m) with reference to the the estimation lean torque table as shown by TABLE 3 (step S 13 ). 
     Next, the current determination section  1616  determines a control current I(m, n) corresponding to the estimated lean torque value Tl (m, n) determined at step S 13  (step S 14 ). The current determination section  1616  outputs the control current I(m, n) to the lean actuator  1600 . The lean actuator  1600  outputs a posture control torque Tc corresponding to the control current I(m, n) to the lower cross member  1052 . Thereafter, the process returns to step S 11 . The process from step S 11  to S 14  is repeated until the ignition source is switched from on to off. 
     [Effects] 
     The roll rate sensor  1602  of the posture control actuator unit  1599  can detect the roll rate ω of the vehicle body frame  21  with high accuracy for the same reasons as described above in connection with the posture control actuator unit  599 . In the posture control actuator unit  1599 , it is easy to make the axis for the detection of the roll rate ω carried out by the roll rate sensor  1602  almost parallel to the roll axis Ax of the vehicle body frame  1021  for the same reason as described above in connection with the posture control actuator unit  599 . Also, the posture control actuator unit  1599  can be downsized for the same reason as described above in connection with the posture control actuator unit  599 . Accordingly, the posture control actuator controller  1606  of the posture control actuator unit  1599  can control the posture of the vehicle body frame  1021  accurately for the same reasons as described above in connection with the posture control actuator unit  599 . 
     Other Embodiments 
     The embodiments and modifications described or illustrated herein are to make the present teaching easier to understand and not to limit the concept of the present teaching. It is possible to adapt or alter the embodiments and modifications described above without departing from the gist thereof. 
     The gist includes all equivalent elements, modifications, omissions, combinations (for example, combination of features of the embodiments and modifications), adaptations and alterations as would be appreciated by those in the art based on the embodiments and modifications disclosed herein. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to the embodiments described in the present specification or during the prosecution of the present application. Such embodiments and modifications are to be understood as non-exclusive. For example, the terms “preferable” and “good” in the present specification are to be understood as non-exclusive, and these terms mean “preferable but not limited to this” and “good but not limited to this”, respectively. 
     In the leaning vehicle  1   a , instead of the roll rate sensor  602 , a yaw rate sensor or a pitch rate sensor may be supported by the ESP actuator  600 . The yaw rate sensor detects a yaw rate. As the vehicle body frame  21  is rotating around a yaw axis, the rotation angle of the vehicle body frame  21  around a yaw axis changes, and the yaw rate sensor is configured to detect the yaw rate that is the amount of change per unit time of the rotation angle of the vehicle body frame  21  around the yaw axis. The yaw axis is an axis extending along the up-down direction UD. The pitch rate sensor detects a pitch rate. As the vehicle body frame  21  is rotating around a pitch axis, the rotation angle of the vehicle body frame  21  around the pitch axis changes, and the pitch rate sensor is configured to detect the pitch rate that is the amount of change per unit time of the rotation angle of the vehicle body frame  21  around the pitch axis. The pitch axis is an axis extending along the left-right direction LR. As descried above, the sensor supported by the EPS actuator  600  may be any angular rate sensor that detects the amount of change per unit time of a rotation angle of the vehicle body frame  21  around a rotation axis, the rotation angle changing as the vehicle body frame  21  is rotating around the rotation axis. 
     In the leaning vehicle  1   b , instead of the roll rate sensor  1602   a , a yaw rate sensor or a pitch rate sensor may be supported by the lean actuator  1600 . The yaw rate sensor detects a yaw rate. As the vehicle body frame  1021  is rotating around a yaw axis, the rotation angle of the vehicle body frame  21  around the yaw axis changes, and the yaw rate sensor is configured to detect the yaw rate that is the amount of change per unit time of the rotation angle of the vehicle body frame  1021  around the yaw axis. The yaw axis is an axis extending along the up-down direction UD. The pitch rate sensor detects a pitch rate. As the vehicle body frame  1021  is rotating around a pitch axis, the rotation angle of the vehicle body frame  1021  around the pitch axis changes, and the pitch rate sensor is configured to detect the pitch rate that is the amount of change per unit time of the rotation angle of the vehicle body frame  1021  around the pitch axis. The pitch axis is an axis extending along the left-right direction LR. As described above, the sensor supported by the lean actuator  1600  may be any angular rate sensor that detects the amount of change per unit time of a rotation angle of the vehicle body frame  1021  around a rotation axis, the rotation angle changing as the vehicle body frame  1021  is rotating around the rotation axis. 
     In the leaning vehicle  1   a , the posture control actuator controller  606  may control the vehicle body frame  21  by using an angular rate detected by an angular rate sensor other than the angular rate sensor supported by the ESP actuator  600 . Also, in the leaning vehicle  1   b , the posture control actuator controller  1606  may control the vehicle body frame  1021  by using an angular rate detected by an angular rate sensor other than the angular rate sensor supported by the lean actuator  1600 . 
     The posture control torque Tc may be used for any other purpose than the purpose of posture control of the vehicle body frame  21  or  1021  around the roll axis Ax. The posture control torque Tc may be used for posture control of the vehicle body frame  21  or  1021  around the yaw axis or for posture control of the vehicle body frame  21  or  1021  around the pitch axis. 
     The leaning vehicles  1 ,  1   a  and  1   b  each may include a steering torque sensor configured to detect the steering torque T. The posture control actuator controller  606  may control the EPS actuator  600  based on the steering torque T or not based on the steering torque T. The posture control actuator controller  1606  may control the lean actuator  1600  based on the steering torque T or not based on the steering torque T. 
     The leaning vehicles  1 ,  1   a  and  1   b  each may include a roll sensor configured to detect the roll angle θ. In this case, the posture control actuator controller  606  may control the ESP actuator  600  based on the roll angle θ or not based on the roll angle θ. The posture control actuator controller  1606  may control the lean actuator  1600  based on the roll angle θ or not based on the roll angle θ. 
     Each of the leaning vehicle  1  and  1   a  may be a vehicle including two front wheels and at least one rear wheel, like the leaning vehicle  1   b . The leaning vehicle  1   b  needs to include at least one rear wheel. 
     The link mechanism  1005  of the leaning vehicle  1   b  is a parallelogram link mechanism. However, the link mechanism  1005  does not need to be a parallelogram link mechanism, and may be a double wishbone link mechanism. 
     In the leaning vehicle  1   a , the posture control actuator controller  606  determines an estimated steering torque T(m, n) based on the speed V and the roll rate ω, and thereafter determines a control current value I (m, n) based on the estimated steering torque T(m, n). However, the posture control actuator controller  606  may determine a control current I(m, n) based on the speed V and the roll rate ω. In this case, the posture control actuator controller  606  stores a table in which control current values I (m, n) are stored in association with various values of the speed V(m) and various values of the roll rate ω(n). Instead of such a table, a mathematical expression or a map may be used for the determination of an estimated steering torque T(m, n) and/or the determination of a control current I(m, n). 
     In the leaning vehicle  1   b , the posture control actuator controller  1606  determines an estimated lean torque value Tl(m, n) based on the speed V and the roll rate ω, and thereafter determines a control current value I (m, n) based on the estimated lean torque value Tl(m, n). However, the posture control actuator controller  1606  may determine a control current I(m, n) based on the speed V and the roll rate ω. In this case, the posture control actuator controller  1606  may store a table in which control current values I (m, n) are stored in association with various values of the speed V and various values of the roll rate ω. Instead of such a table, a mathematical expression or a map may be used for the determination of an estimated lean torque value Tl (m, n) and/or the determination of a control current I(m, n). 
     The above-described control method of the EPS actuator  600  based on the speed V and the roll rate ω in the leaning vehicle  1   a  is only an example, and the control method of the EPS actuator  600  is not limited to this. In the control method of the EPS actuator  600  based on the speed V and the roll rate ω, the estimated steering torque determination table and the control current determination table are not necessarily used. The posture control actuator controller  606 , for example, stores a reference control current value that is to be used for determination of a control current value to be outputted to the EPS actuator  600 . The reference control current value may be a constant value or may be a variable value that varies in association with any other parameter (for example, temperature) than the speed V and the roll rate ω. Then, the posture control actuator controller  606  may determine a control current value by multiplying the reference control current value with a coefficient determined based on the speed V and the roll rate ω. 
     The above-described control method of the lean actuator  1600  based on the speed V and the roll rate ω carried out in the leaning vehicle  1   b  is only an example, and the control method of the lean actuator  1600  is not limited to this. In the control method of the lean actuator  1600  based on the speed V and the roll rate ω, the estimated lean torque determination table and the control current determination table are not necessarily used. The posture control actuator controller  1606 , for example, stores a reference control current value that is to be used for determination of a control current value to be outputted to the lean actuator  1600 . The reference control current value may be a constant value or may be a variable value that varies in association with any other parameter (for example, temperature) than the speed V and the roll rate ω. Then, the posture control actuator controller  1606  may determine a control current value by multiplying the reference control current value with a coefficient determined based on the speed V and the roll rate ω. 
     Each of the leaning vehicle  1  and  1   a  may be a two-wheeled off-road motorcycle, a two-wheeled scooter-type motorcycle, or a moped bicycle. 
     The roll axis Ax may pass through the roll rate sensor  602  or  1602 . In this case, the roll rate sensor  602  or  1602  detects the roll rate ω still more accurately. 
     When the leaning vehicle  1   a  is running at a low speed, the posture control torque Tc may be outputted to the steering shaft  62  so as to inhibit the vehicle body frame  21  from leaning in the leftward direction L or the rightward direction R. More specifically, the posture control actuator controller  606  carries out such leaning inhibition control, for example, under the condition of 0 km/h&lt;V≤10 km/h. When the front wheel  3  is steered leftward while the vehicle body frame  21  is leaning in the leftward direction L, a negative roll rate ω occurs, and when the front wheel  3  is steered rightward while the vehicle body frame  21  is leaning in the rightward direction R, a positive roll rate ω occurs. 
     Therefore, the current determination section  616  outputs a positive control current I(m, n) when the vehicle body frame  21  is leaning in the leftward direction L (when the roll rate ω is a positive value). The EPS actuator  600  outputs a positive posture control torque value Tc to the steering shaft  62 . Accordingly, the front wheel  3  is steered leftward, and the vehicle body frame  21  is returning to the upright posture. The current determination section  616  outputs a negative control current I(m, n) when the vehicle body frame  21  is leaning in the rightward direction R (when the roll rate ω is a negative value). The EPS actuator  600  outputs a negative posture control torque value Tc to the steering shaft  62 . Accordingly, the front wheel  3  is steered rightward, and the vehicle body frame  21  is returning to the upright posture. In this way, the vehicle body frame  21  of the leaning vehicle  1   a  is inhibited from leaning in the leftward direction L or the rightward direction R. Further, the posture control actuator controller  606  may control the EPS actuator  600  based on the yaw rate in addition to the roll rate ω. The yaw rate is an angular rate of a rotation of the vehicle body frame  21  around an axis extending along the up-side direction UD. Also, depending on the characteristics of the leaning vehicle  1   a , the posture control actuator controller  606  may control the ESP actuator  600  to assist the leaning motion of the leaning vehicle  1   a.    
     The posture control actuator controller  606  may carry out a control process as described below. When the speed V is, for example, greater than 10 km/h, the posture control actuator controller  606  controls the EPS actuator  600  with reference to the estimated steering torque determination table as shown by TABLE 1 and the control current determination table as shown by  FIG. 2 . However, when the speed V is, for example, equal to or less than 10 km/h, the posture control actuator controller  606  controls the EPS actuator  606  to perform the above-described leaning inhibition control. 
     When the leaning vehicle  1   b  is running at a low speed, the posture control torque Tc may be outputted to the lower cross member  1052  so as to inhibit the vehicle body frame  1021  from leaning in the leftward direction L or the rightward direction R. More specifically, the posture control actuator controller  1606  carries out the leaning inhibition control, for example, under the condition of 0 km/h&lt;V 10 km/h. The current determination section  1616  outputs a negative control current I(m, n) when the vehicle body frame  1021  is leaning in the leftward direction L (when the roll rate ω is a positive value). The lean actuator  1600  outputs a negative posture control torque value Tc to the lower cross member  1052 . Accordingly, the lower cross member  1052  rotates clockwise relative to the vehicle body frame  1021  in a view in the backward direction b, and the vehicle body frame  1021  is returning to the upright posture. The current determination section  1616  outputs a positive control current I(m, n) when the vehicle body frame  1021  is leaning in the rightward direction R (when the roll rate ω is a negative value). The lean actuator  1600  outputs a positive posture control torque value Tc to the lower cross member  1052 . Accordingly, the lower cross member  1052  rotates counterclockwise relative to the vehicle body frame  1021  in a view in the backward direction b, and the vehicle body frame  1021  is returning to the upright posture. In this way, the vehicle body frame  1021  of the leaning vehicle  1   b  is inhibited from leaning in the leftward direction L or the rightward direction R. Further, the posture control actuator controller  1606  may control the lean actuator  1600  based on the yaw rate in addition to the roll rate ω. Also, depending on the characteristics of the leaning vehicle  1   b , the posture control actuator controller  1606  may control the lean actuator  1600  to assist the leaning motion of the leaning vehicle  1   b.    
     The posture control actuator controller  606  does not necessarily use the speed V and may use only the roll rate ω for control of the EPS actuator  600 . Alternatively, the posture control actuator controller  606  may control the EPS actuator  600  based on not only the roll rate ω but also any other parameter. The posture control actuator controller  1606  does not necessarily use the speed V and may use only the roll rate ω for control of the lean actuator  1600 . Alternatively, the posture control actuator controller  1606  may control the lean actuator  1600  based on not only the roll rate ω but also any other parameter. 
     The lean actuator  1600  may output the posture control torque Tc to the upper cross member  1051  instead of the lower cross member  1052 . Alternatively, the lean actuator  1600  may output the posture control torque Tc to the left side member  1053  or to the right side member  1054 . 
     The roll rate sensor  602  and the posture control actuator controller  606  may be connected to each other by an electrical signal line or an optical fiber. The speed sensor  604  and the posture control actuator controller  606  may be connected to each other by an electrical signal line or an optical fiber. The roll rate sensor  602 , the speed sensor  604  and the posture control actuator controller  606  may be connected to one another by a CAN (controller area network) or any other connection means. When a CAN is used, various kinds of information are multiplexed through the line interconnecting the roll rate sensor  602 , the speed sensor  604  and the posture control actuator controller  606 . A connection means other than a CAN is, for example, connecting the roll rate sensor  602  and the posture control actuator controller  606  by a line and connecting the speed sensor  604  and the posture control actuator controller  606  by a line. Through the line connecting the roll rate sensor  602  and the posture control actuator controller  606 , only the roll rate ω is transmitted. Through the line connecting the speed sensor  604  and the posture control actuator controller  606 , only the speed V is transmitted. 
     The roll rate sensor  1602  and the posture control actuator controller  1606  may be connected to each other by an electrical signal line or an optical fiber. The speed sensor  1604  and the posture control actuator controller  1606  may be connected to each other by an electrical signal line or an optical fiber. The roll rate sensor  1602 , the speed sensor  1604  and the posture control actuator controller  1606  may be interconnected by a CAN (controller area network) or any other connection means. When a CAN is used, various kinds of information are multiplexed through the line interconnecting the roll rate sensor  1602 , the speed sensor  1604  and the posture control actuator controller  1606 . A connection means other than a CAN is, for example, connecting the roll rate sensor  1602  and the posture control actuator controller  1606  by a line and connecting the speed sensor  1604  and the posture control actuator controller  1606  by a line. Through the line connecting the roll rate sensor  1602  and the posture control actuator controller  1606 , only the roll rate ω is transmitted. Through the line connecting the speed sensor  1604  and the posture control actuator controller  1606 , only the speed V is transmitted. 
     The leaning vehicle  1   b  may further include a posture control actuator controller  606  and an EPS actuator  600 . In this case, in the leaning vehicle  1   b , the posture control actuator controller  606  controls the EPS actuator  600 , and the posture control actuator controller  1606  controls the lean actuator  1600 . The operations of the posture control actuator controller  606  of the leaning vehicle  1   b  are the same as the operations of the posture control actuator controller  606  of the leaning vehicle  1   a . Also, the posture control actuator controllers  606  and  1606  may change the assist rate depending on the speed V(m) and/or the roll rate ω(n). For example, when the leaning vehicle  1   b  is running at a low speed, the posture control actuator controller  606  increases the assist rate of the EPS actuator  600 , and the posture control actuator controller  1606  decreases the assist rate of the lean actuator  1600 . On the other hand, when the leaning vehicle  1   b  is running at a high speed, the posture control actuator controller  606  decreases the assist rate of the EPS actuator  600 , and the posture control actuator controller  1606  increases the assist rate of the lean actuator  1600 . However, how the assist rate is changed is not limited to this. 
     In each of the leaning vehicles  1   a  and  1   b , the posture control actuator unit  599  or  1599  does not need to overlap the center line C in a view in the backward direction b. 
     Each of the EPS actuator  600  and the lean actuator  1600  outputs a posture control torque Tc. The posture control torque Tc is a force to cause an object to make a rotary movement. However, the EPS actuator  600  or the lean actuator  1600  may be a posture control actuator that causes an object to make any other movement than a rotary movement (for example, a translatory movement). 
     The roll rate sensor  602  may be fixed on the outer surface of the case of the EPS actuator  600 . The roll rate sensor  1602  may be fixed on the outer surface of the case of the lean actuator  1600 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  1   a ,  1   b  leaning vehicle 
               2 ,  1002  vehicle body 
               3  front wheel 
               4 ,  1004  rear wheel 
               7 ,  1007  steering mechanism 
               21 ,  1021  vehicle body frame 
               24 ,  1024  seat 
               25 ,  1025  power unit 
               60 ,  1060  handlebar 
               62 ,  1062  steering shaft 
               64  front fork 
               64 L,  1033  left shock absorber 
               64 R,  1034  right shock absorber 
               66  upper bracket 
               68  under bracket 
               211 ,  1211  head pipe 
               599 ,  1599  posture control actuator unit 
               600  EPS actuator 
               600   o  posture control actuator 
               602 ,  1602  roll rate sensor 
               602   o  angular rate sensor 
               604 ,  1604  speed sensor 
               606 ,  1606  posture control actuator controller 
               612 ,  1612  posture control actuator control section 
               614 ,  1614  torque estimation section 
               616 ,  1616  current determination section 
               1005  link mechanism 
               1031  left front wheel 
               1032  right front wheel 
               1051  upper cross member 
               1052  lower cross member 
               1053  left side member 
               1054  right side member 
               1067  tie rod 
               1314  left front axle 
               1317  left bracket 
               1324  right front axle 
               1327  right bracket 
               1337  center bracket 
               1052 A front lower cross member 
               1052 B rear lower cross member 
               1600  lean actuator 
             Ax roll axis