Patent Publication Number: US-2022212747-A1

Title: Straddle type vehicle and control device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of International Patent Application No. PCT/JP2020/032519 filed on Aug. 28, 2020, which claims priority to and the benefit of Japanese Patent Application No. 2019-177706 filed on Sep. 27, 2019, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a straddle type vehicle and a control device. 
     Description of the Related Art 
     A straddle type vehicle provided with a steering damper is known. International Publication No. 2013/168422 discloses a technique for suppressing a vibration of a steering mechanism by controlling a damping force of a steering damper, based on a state of a vehicle, such as a load applied to a front wheel and a steering angle of the steering mechanism. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the present invention, there is provided a straddle type vehicle comprising: 
     a steering mechanism configured to steer a front wheel; 
     a steering damper device capable of variably generating a damping force working on a rotating action of the steering mechanism; and 
     a control unit configured to control the damping force of the steering damper device to increase, when the front wheel of the straddle type vehicle in a wheelie state lands on a ground, wherein 
     the control unit controls the damping force to increase, after the front wheel lands on the ground and an oscillation occurs in the steering mechanism. 
     According to another embodiment of the present invention, there is provided a control device to be applied to a straddle type vehicle, the straddle type vehicle including a steering mechanism that steers a front wheel and a steering damper device capable of variably generating a damping force working on a rotating action of the steering mechanism, the control device being configured to control the damping force of the steering damper device to increase, when the front wheel of the straddle type vehicle in a wheelie state lands on a ground, wherein 
     the control device controls the damping force to increase, after the front wheel lands on the ground and an oscillation occurs in the steering mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a vehicle according to one embodiment. 
         FIG. 2  is a front view of the vehicle of  FIG. 1 . 
         FIG. 3  is a schematic view illustrating a configuration of a steering damper device according to one embodiment. 
         FIG. 4  is a block diagram illustrating an example of a control configuration of the straddle type vehicle according to one embodiment. 
         FIG. 5  is a flowchart illustrating a process example of a control unit according to one embodiment. 
         FIG. 6A  is a flowchart illustrating a process example of the control unit according to one embodiment. 
         FIG. 6B  is a flowchart illustrating a process example of the control unit according to one embodiment. 
         FIG. 7  is a timing chart illustrating a state of the vehicle in a case where the processes of  FIGS. 5 to 6B  are performed. 
         FIG. 8  is a block diagram illustrating an example of a control configuration of the straddle type vehicle according to one embodiment. 
         FIG. 9  is a flowchart illustrating a process example of the control unit according to one embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A straddle type vehicle, by the way, may become in a wheelie state in which the front wheel is separated from the ground during traveling. When the front wheel lands on the ground from the wheelie state, the steering mechanism may oscillate in some cases, and there is a demand for suppressing such an oscillation. 
     An embodiment of the present invention provides a technique for suppressing an oscillation of a steering mechanism after wheelie landing. 
     Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention, and limitation is not made to an invention that requires a combination of all features described in the embodiments. Two or more of the multiple features described in the embodiments may be combined as appropriate. Furthermore, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. 
     In addition, in each drawing, arrows X and Y indicate horizontal directions orthogonal to each other, and an arrow Z indicates a vertical direction. In the following description, the traveling direction of the vehicle is defined as X direction, which is set to a front-and-rear direction, and the front and the rear are defined. In addition, a vehicle width direction of the vehicle is defined as Y direction, which is set to a left-and-right direction with a forward direction of the vehicle as a reference, and the left and the right are defined. 
     First Embodiment 
     Outline of Straddle Type Vehicle 
       FIG. 1  is a side view (a right side view) of a straddle type vehicle  100  according to one embodiment, and  FIG. 2  is a front view of the vehicle  100 , illustrating an outline of the vehicle  100 .  FIGS. 1 and 2  respectively illustrate a side view and a front view in a state in which the vehicle  100  stands in a vertical posture. For the vehicle  100  in the present embodiment, a motorcycle including a front wheel  101  and a rear wheel  102  is given as an example, but the present invention is also applicable to any other type of the straddle type vehicle. 
     The vehicle  100  includes a vehicle body frame  103  forming its backbone. A power unit  104  that drives the rear wheel  102  is supported at the vehicle body frame  103 . The power unit  104  includes an engine  104   a  (for example, a multi-cylinder four-cycle engine) and a transmission  104   b  that changes an output from the engine  104   a,  and the output from the transmission  104   b  is transmitted by a chain transmission mechanism to the rear wheel  102 . 
     A seat frame  103   a  that supports a seat  108  on which the rider is seated is coupled with a rear portion of the vehicle body frame  103 . A swing arm  109  is swingably supported by the rear portion of the vehicle body frame  103 , and the rear wheel  102  is rotatably supported by the swing arm  109 . 
     A head pipe is provided in a front portion of the vehicle body frame  103 . The head pipe rotatably supports a steering mechanism  10 . 
     The steering mechanism  10  steers the front wheel  101 , and includes a pair of front forks  11 , a top bridge  12 , a bottom bridge  13 , and left and right handlebars  14 . The pair of front forks  11  are rotatably supported by the head pipe. The pair of front forks  11  are coupled at upper end portions by the top bridge  12 , and are coupled by the bottom bridge  13  below the top bridge  12 . A steering stem (not illustrated) is attached to extend between the top bridge  12  and the bottom bridge  13 , and the steering stem is rotatably attached in the head pipe. 
     In upper portions of the pair of front forks  11 , separate-type left and right handlebars  14  for steering the front wheel  101  are provided, and the handlebars  14  are each provided with a grip  14   a  to be gripped by the rider. The left and right handlebars  14  are disposed to be inclined downward toward the outside in the vehicle width direction in a vehicle front view, and are disposed for the rider to easily get on the vehicle in a forward inclined posture. 
     The vehicle  100  includes braking devices  112  and  113 . The braking device  112  is a braking device for the front wheel  101 , and includes a brake disc  112   a  provided on the front wheel  101  and a brake caliper  112   b  supported by the front fork  11 . The right handlebar  14  is provided with a brake lever  114   a  for operating the brake caliper  112   b.  The left handlebar  14  is provided with a clutch lever  114   b  for operating the clutch of the transmission  104   b.    
     The braking device  113  is a braking device for the rear wheel  102 , and includes a brake disc  113   a  provided on the rear wheel  102  and a brake caliper  113   b  supported by the swing arm  109 . A brake pedal  115  for operating the brake caliper  113   b  is provided on a right side portion of the vehicle  100 . Steps  116  on which the rider places its legs are respectively provided on the left and the right side portions of the vehicle  100 . A brake pedal  115  is disposed near the step  116  on the right side, and a shift pedal, not illustrated, is disposed near the step  116  on the left side. 
     Configuration of Steering Damper 
       FIG. 3  is a schematic view illustrating a configuration of a steering damper device  20 . The steering damper device  20  is a device capable of variably generating the damping force working on a rotating action of the steering mechanism  10 . For example, in order to reduce a so-called kickback (reaction) that is a sudden oscillation of the handlebars  14 , when an external force from the road surface during traveling works on the front wheel  101 , the steering damper device  20  generates the damping force against the oscillation. 
     In the present embodiment, the steering damper device  20  is an electronically controlled steering damper, and is capable of variably controlling the damping force by controlling the drive current of a solenoid valve  21 . 
     The steering damper device  20  is a hydraulic rotary type in which a swingable vane  23  is disposed in an oil chamber  22  having a fan shape in a plan view, and uses, as the damping force, a flow resistance of hydraulic oil in the oil chamber  22  generated when the vane  23  swings. The top bridge  12  is coupled through a link mechanism  24  with a base portion of the vane  23 . 
     The steering damper device  20  includes a hydraulic control circuit  25 . The hydraulic control circuit  25  includes the solenoid valve  21 . The solenoid valve  21  is driven by a control unit  50  to be described later. The control unit  50  drives the solenoid valve  21  to change the opening area of the valve and change the flow resistance of the hydraulic oil. That is, the control unit  50  controls the drive current of the solenoid valve  21  to control the damping force generated by the steering damper device  20 . The hydraulic control circuit  25  also includes a check valve  26 , a relief valve  27 , and an accumulator  28 . Solid arrows in the drawing each indicate a flow of the hydraulic oil when the steering mechanism  10  makes a turn to the left. Furthermore, dotted arrows in the drawing each indicate a flow of the hydraulic oil when the steering mechanism  10  makes a turn to the right. 
     Note that, in the present embodiment, the configuration of the steering damper device  20  is given as an example, and any other known configuration is adoptable. For example, the steering damper device  20  may be a cylinder type. 
     Control Configuration 
       FIG. 4  is a block diagram illustrating an example of a control configuration of the vehicle  100 .  FIG. 4  mainly illustrates a configuration necessary in relation to the present embodiment to be described later. 
     The vehicle  100  includes the control unit  50  configured with an electric control unit (ECU) or the like. The control unit  50  includes a processing unit  51 , a storage unit  52  such as a RAM and a ROM, and an interface unit  53  (I/F unit) that relays transmission and reception of signals between an external device and the processing unit  51 . The processing unit  51  is a processor represented by a CPU, and executes a program stored in the storage unit  52 . In the storage unit  52 , data and the like used by the processing unit  51  for processing, in addition to the program executed by the processing unit  51 , are stored. 
     In the present embodiment, the control unit  50  controls the damping force of the steering damper device  20 . More specifically speaking, the control unit  50  controls the damping force of the steering damper device  20  to increase, when the vehicle  100  returns to a state in which the front wheel  101  lands on the ground from the wheelie state. 
     Note that the control unit  50  may include a plurality of electric control units (ECUs), and each of them may include a processor, a storage device, and an external I/F. For example, the control unit  50  may include a drive controlling ECU that controls driving of the power unit  104  and a damping force controlling ECU that controls the damping force of the steering damper device  20 . Note that the number of ECUs and the functions assigned to the respective ECUs can be designed as appropriate, and can be subdivided or integrated as compared with the above example. 
     The vehicle  100  includes a front wheel rotation speed sensor  101   a  that detects the rotation speed of the front wheel  101 , and a rear wheel rotation speed sensor  102   b  that detects the rotation speed of the rear wheel  102 . As will be described later, the control unit  50  determines a control current value of the solenoid valve  21 , based on detection results of these sensors. 
     Process Example of Control Unit 
     A process example of the control unit  50  will be described.  FIGS. 5 to 6B  are flowcharts each illustrating an example of a process performed by the control unit  50 . These process examples are process examples for damping force control of the steering damper device  20  to be conducted by the control unit  50 . More specifically,  FIGS. 5 to 6B  are each an example of the damping force control, of the steering damper device  20  at the time of wheelie landing, to be conducted by the control unit  50 . For example, the control unit  50  determines whether the vehicle  100  is in the wheelie state in a process different from the present process, and repeatedly performs the present process while determining that the vehicle  100  is in the wheelie state. Note that the control unit  50  may determine whether the vehicle is in the wheelie state, based on, for example, a difference or the like in the rotation speed between the front and rear wheels. In addition, the magnitude of the damping force in the wheelie state is set to an initial value, and such an initial value can be appropriately set, based on the configuration or the like of the vehicle  100  or the steering damper device  20 . 
     In S 1 , the control unit  50  determines whether the front wheel  101  of the vehicle  100  in the wheelie state has landed on the ground. In a case of determining that the front wheel  101  has landed on the ground, the control unit  50  advances the process to S 2 , whereas in a case of determining that the front wheel has not landed on the ground, the control unit  50  ends the flowchart. 
     The control unit  50  determines whether the front wheel  101  has landed on the ground, based on, for example, a detection result of the front wheel rotation speed sensor  101   a.  For example, in the wheelie state in which the front wheel  101  is separated from the ground, the front wheel  101  gradually decreases. However, when the front wheel  101  lands on the ground, its rotation speed starts to increase. Therefore, the control unit  50  may determine that the front wheel  101  has landed on the ground, when the rotation speed of the front wheel  101  starts to increase in the case where it is determined that the vehicle  100  is in the wheelie state. Further, for example, in a case where the vehicle  100  has a configuration capable of detecting a load generated on the front wheel  101 , the control unit  50  may determine whether the front wheel  101  has landed on the ground, based on a change in the load. 
     In S 2 , the control unit  50  makes an oscillation start determination of the steering mechanism  10 . In S 3 , in a case of determining that the steering mechanism  10  has started oscillating in S 2 , the control unit  50  advances the process to S 4 , whereas in a case of determining that the steering mechanism has not started oscillating, the control unit  50  ends the flowchart. 
     In S 4 , the control unit  50  conducts the damping force control of the steering damper device  20 . Then, the control unit  50  ends the flowchart. 
     Here, as an aspect of the damping force control of the steering damper device  20 , it is conceivable that when the front wheel  101  lands on the ground from the wheelie state, the damping force is increased beforehand before the steering mechanism  10  starts oscillating, or the damping force is increased simultaneously with the start of the oscillation. However, the oscillation for the first time (a first oscillation) when the steering mechanism  10  starts oscillating cannot be suppressed effectively by an increase in the damping force, in some cases. In addition, when the damping force is caused to generate against the first oscillation, an impact is input into the vehicle body. This may lead to a swing of the vehicle body, and may affect the riding feeling, in some cases. In the present embodiment, in the process of  FIG. 5 , after the front wheel  101  lands on the ground from the wheelie state and then the steering mechanism  10  starts oscillating, the control unit  50  controls the damping force of the steering damper device  20  to increase. Accordingly, after the steering mechanism  10  starts oscillating, the damping force starts to increase. Therefore, it is possible to suppress the oscillation of the steering mechanism  10 , while suppressing the swing of the vehicle body and an unnatural vehicle body behavior and improving the riding feeling. 
       FIG. 6A  illustrates a process example of determining whether the oscillation has occurred in the steering mechanism  10  in S 2  in the flowchart of  FIG. 5 . As described above, in the wheelie state, a difference in the rotation speed may be occurring between the front wheel  101  and the rear wheel  102 , in some cases. In addition, the oscillation of the steering mechanism  10  may occur in some cases, after the front wheel  101  lands on the ground from the wheelie state, in a case where the difference in the rotation speed between the front wheel  101  and the rear wheel  102  disappears, or in a case where the difference in the rotation speed decreases. Therefore, in the present embodiment, the occurrence of the oscillation of the steering mechanism  10  is determined, based on the difference in the rotation speed between the front wheel  101  and the rear wheel  102 . 
     In S 21 , the control unit  50  acquires the respective rotation speeds of the front wheel  101  and the rear wheel  102 , based on detection results of the front wheel rotation speed sensor  101   a  and the rear wheel rotation speed sensor  102   b.    
     In S 22 , in a case where the difference in the rotation speed between the front wheel  101  and the rear wheel  102  is equal to or smaller than a threshold, the control unit  50  advances the process to S 23 , and determines that the steering mechanism  10  starts oscillating. On the other hand, in a case where the difference in the rotation speed between the front wheel  101  and the rear wheel  102  is larger than the threshold, the control unit  50  advances the process to S 24 , and determines that the steering mechanism  10  has not started oscillating. 
     Through the above process, the control unit  50  is capable of determining whether the steering mechanism  10  has started oscillating. 
       FIG. 6B  illustrates a process example of the damping force control (S 4  in the flowchart of  FIG. 5 ) of the steering damper device  20  to be conducted by the control unit  50 . 
     As described above, even when the damping force is generated against the oscillation for the first time (the first oscillation) after the wheelie landing, the vibration of the steering mechanism  10  cannot be effectively suppressed, in some cases. Therefore, in the present embodiment, the control unit  50  increases the damping force after a predetermined period of time has lapsed since the determination that the steering mechanism  10  starts oscillating. Accordingly, the damping force of the steering damper device  20  is generated, when the steering mechanism  10  oscillates on an opposite side (a second oscillation) to the first oscillation. Hereinafter, a specific process example will be described. 
     In S 41 , the control unit  50  waits for a predetermined period of time. In S 42 , the control unit  50  increases the damping force of the steering damper device  20 . 
     The magnitude of the damping force after the increase can be appropriately set. As an example, the magnitude of the damping force after the increase may be determined before the increase, that is, within a range of 1.5 to 10 times the initial value. Note that in the present embodiment, the damping force of the steering damper device  20  is changed by the drive of the solenoid valve  21 . Therefore, the control unit  50  controls the drive current of the solenoid valve  21  to control the damping force. For example, the control unit  50  increases the drive current of the solenoid valve  21  to increase the damping force. 
     Here, the vibration cycle when the steering mechanism  10  is oscillated depends on the inertia of the steering mechanism  10  and the front wheel  101 . Therefore, the predetermined period of time in S 41  can be appropriately set, based on the configuration of the vehicle body such as the weights of the steering mechanism  10  and the front wheel  101 . As an example, the predetermined period of time in S 41  may be determined within a range of 30 msec to 70 msec. In addition, as an example, the predetermined period of time in S 41  may be determined within a range of 40 msec to 60 msec. More specifically speaking, the predetermined period of time in S 41  may be, for example, 50 msec. 
     Further, in the process of S 42 , the control unit  50  may gradually increase the damping force of the steering damper device  20 . That is, the control unit  50  may increase the drive current of the solenoid valve  21  at a constant rate. This enables suppression of the oscillation of the vehicle  100 , while suppressing the unnatural vehicle behavior due to a sudden increase of the damping force. The control unit  50  may hold the drive current for a predetermined period of time after the drive current of the solenoid valve  21  rises to a target value, and then may lower the drive current at a constant rate. The period of time for increasing, holding, or decreasing the damping force can be appropriately set in accordance with the configuration of the vehicle  100  or the like. As an example, the rising period of time may be 10 to 40 msec, the holding period of time may be 50 to 200 msec, and the decreasing period of time may be 30 to 70 msec. 
       FIG. 7  is a timing chart illustrating a state and the like of the vehicle  100 , when the processes of  FIGS. 5 to 6B  are performed. Regarding the steering angle in the drawing, an upper side from the center broken line indicates a steering angle in a case of making a turn to the left, and a lower side from the center broken line indicates a steering angle in a case of making a turn to the right. In addition, regarding the steering speed (angular velocity) in the drawing, the angular velocity on the left turn side is positive, and the angular velocity on the right turn side is negative. 
     In normal traveling that the vehicle  100  is not in the wheelie state, the rotation speeds of the front wheel  101  and the rear wheel  102  are substantially the same. On the other hand, when the vehicle  100  becomes in the wheelie state, the front wheel  101  rotates by inertia, and the rotation speed of the front wheel  101  gradually decreases. As a result, a difference occurs in the rotation speed between the front wheel  101  and the rear wheel  102 . 
     When the front wheel  101  lands on the ground with the difference in the rotation speed between the front wheel  101  and the rear wheel  102 , the rotation speed of the front wheel  101  returns to almost the same level as the rotation speed of the rear wheel  102 . Here, in a case where the steering mechanism  10  oscillates either to the left or right when the front wheel  101  lands on the ground, the steering mechanism  10  starts oscillating, when the rotation speed of the front wheel  101  returns to almost the same level as the rotation speed of the rear wheel  102 . In  FIG. 7 , the steering mechanism  10  makes a turn to the right side, when the front wheel  101  lands on the ground. Therefore, after the rotation speed of the front wheel  101  returns to almost the same level as the rotation speed of the rear wheel  102 , the oscillation of the steering mechanism  10  occurs. 
     The above-described first oscillation is occurring for a predetermined period of time since the steering mechanism  10  starts oscillating, and the control unit  50  maintains the damping force of the steering damper device  20  during such a period of time (S 41  in  FIG. 6B , section A in  FIG. 7 ). After a predetermined period of time lapses, the control unit  50  gradually increases the damping force of the steering damper device  20  (section B 1 ). Then, the control unit  50  holds the damping force of the steering damper device  20  for a predetermined period of time (section B 2 ). The control unit  50  gradually increases and then holds the damping force of the steering damper device  20  so as to be capable of generating a high damping force in a region where the amplitude of the above-described second oscillation is large. Furthermore, after that, the control unit  50  gradually reduces the damping force of the steering damper device  20  (section B 3 ). This enables the control unit  50  to reduce the damping force, while suppressing an occurrence of the unnatural vehicle body behavior of the vehicle  100  due to a sudden decrease of the damping force, and improving the riding feeling. 
     As described heretofore, according to the present embodiment, the control unit  50  controls the damping force of the steering damper device  20  to increase the damping force, after the vehicle  100  becomes in the state in which the front wheel  101  lands on the ground from the wheelie state, and the oscillation occurs in the steering mechanism  10 . This enables suppression of the vibration of the steering mechanism  10 , while suppressing the vehicle body vibration and an occurrence of the unnatural vehicle body behavior and improving the riding feeling. Therefore, the vibration of the steering mechanism  10  after the wheelie landing can be suppressed in a more effective manner. 
     Second Embodiment 
       FIG. 8  is a block diagram illustrating an example of a control configuration of the vehicle  100  according to a second embodiment. The present embodiment is different from the first embodiment in that the vehicle  100  includes a steering angular velocity sensor  20   a.  In the following description, the same components as those of the first embodiment are denoted by the same reference numerals, and the descriptions will be omitted. 
     The steering angular velocity sensor  20   a  detects a steering angular velocity around a steering stem that is a rotation shaft of the steering mechanism  10 , as information relate to a steering angle of the steering mechanism  10 . As the steering angular velocity sensor  20   a,  a potentiometer, an encoder, or any other known configuration is adoptable. In addition, the steering angular velocity sensor  20   a  may be capable of directly detecting the steering angular velocity, or may be capable of detecting the steering angle. In a case where the steering angular velocity sensor  20   a  detects the steering angle, the control unit  50  may differentiate the steering angle based on a detection result to acquire the steering angular velocity. 
       FIG. 9  is a flowchart illustrating an example of damping force control of the steering damper device  20  according to the second embodiment, and illustrates a process example (corresponding to the process of S 4  in  FIG. 5 ) in a case where the damping force is controlled, based on the detection result of the steering angular velocity sensor  20   a.  In the first embodiment, the damping force is increased after a predetermined period of time has lapsed since the steering mechanism  10  starts oscillating (S 41 ). However, in the second embodiment, the damping force is increased in a case where the steering angular velocity satisfies a predetermined condition after the steering mechanism  10  starts oscillating. 
     In S 411 , the control unit  50  acquires the steering angular velocity, based on the detection result of the steering angular velocity sensor  20   a.  In S 412 , the control unit  50  determines whether the steering angular velocity acquired in S 411  satisfies a predetermined condition. In a case where the steering angular velocity satisfies the predetermined condition, the control unit  50  advances the process to S 413 , whereas in a case where the steering angular velocity does not satisfy the predetermined condition, the control unit  50  ends the flowchart. The process of S 413  is similar to the process of S 42 . 
     As an example, the predetermined condition in S 412  may be whether the steering angle of the first oscillation of the steering mechanism  10  becomes equal to or larger than a predetermined value and the velocity direction of the steering angular velocity in the first oscillation has been reversed. A description will be given with reference to  FIG. 8 . The steering angular velocity changes from positive (turn to a left direction) to negative (turn to a right direction) at a timing proceeding from the section A to the section B 1 , and the velocity direction of the steering angular velocity has been reversed. That is, it can be said that the process proceeds from the first oscillation to the second oscillation. By starting to increase the damping force at this timing, the damping force can be increased at the timing when the second oscillation becomes large. Therefore, the vibration of the steering mechanism  10  can be suppressed in a more effective manner. 
     As described above, according to the present embodiment, the information related to the steering angle of the steering mechanism  10  is directly acquirable by the steering angular velocity sensor  20   a.  Therefore, the control unit  50  is capable of increasing the damping force at a more effective timing. 
     Other Embodiments 
     In the above embodiments, the power unit  104  is an engine. However, a configuration including an electric motor as the power unit  104  or a configuration including both an internal combustion engine and an electric motor is also adoptable. That is, the vehicle  100  may be an electric vehicle or a hybrid vehicle. 
     In the above embodiments, the description has been given by focusing on the damping force control of the steering damper device  20  to be conducted by the control unit  50 , at the time of wheelie landing. However, the control unit  50  may conduct the damping force control of another steering damper device  20  in parallel, in addition to the damping force control at the time of the wheelie landing. For example, the control unit  50  may conduct the damping force control (referred to as another type of damping force control) of the steering damper device  20 , based on a traveling state such as the speed, the acceleration, or the like of the vehicle  100 . Then, the control unit  50  may control the damping amount of the steering damper device  20  such that the maximum value of the target value of the damping force based on the damping force control at the time of the wheelie landing and the target value of the damping force based on another type of damping force control becomes the actual damping force of the steering damper device  20 . 
     Summary of Embodiments 
     The above-described embodiments disclose at least a work machine to be described as follows. 
     1. A straddle type vehicle ( 1 ) of the above embodiments comprises: 
     a steering mechanism ( 10 ) configured to steer a front wheel; 
     a steering damper device ( 20 ) capable of variably generating a damping force working on a rotating action of the steering mechanism; and 
     a control unit ( 50 ) configured to control the damping force of the steering damper device to increase, when the front wheel of the straddle type vehicle in a wheelie state lands on a ground, wherein 
     the control unit controls the damping force to increase, after the front wheel lands on the ground and an oscillation occurs in the steering mechanism (S 1 -S 4 ). 
     According to this embodiment, the damping force increases after the steering mechanism starts oscillating. Therefore, it is possible to suppress the vibration of the steering mechanism after the wheelie landing, while suppressing the occurrence of the swing of the vehicle body and the unnatural vehicle body behavior and improving the riding feeling. 
     2. In the above embodiments, the control unit determines whether the steering mechanism has started oscillating after the front wheel lands on the ground (S 2 ), and controls the damping force such that the damping force increases, after a predetermined period of time has lapsed since a determination that the steering mechanism has started oscillating (S 41 , S 42 ). 
     According to this embodiment, the damping force starts to increase after a predetermined period of time has lapsed since the occurrence of the first oscillation of the steering mechanism. Therefore, it is possible to further suppress the vibration of the steering mechanism after the wheelie landing, while further suppressing the occurrence of the swing of the vehicle body and the unnatural vehicle body behavior. 
     3. In the above embodiments, the straddle type vehicle further comprises a first detection unit ( 101   a ) configured to detect a rotation speed of the front wheel, and a second detection unit ( 102   a ) configured to detect a rotation speed of a rear wheel, wherein 
     the control unit determines that the steering mechanism has started oscillating, in a case where a difference in the rotation speed between the front wheel and the rear wheel becomes equal to or smaller than a threshold, based on detection results of the first detection unit and the second detection unit (S 22 ). 
     According to this embodiment, it is possible to determine the start of the oscillation of the steering mechanism from a difference in the rotation speed between the front wheel and the rear wheel. 
     4. In the above embodiments, the control unit controls the damping force such that the damping force gradually increases. 
     According to this embodiment, the damping force gradually increases. Therefore, it is possible to increase the damping force, while a natural vehicle body behavior is being kept. 
     5. In the above embodiments, the straddle type vehicle further comprises a third detection unit ( 20   a ) capable of detecting a steering angle of the steering mechanism, wherein 
     the control unit controls the damping force such that the damping force increases, after the front wheel lands on the ground and the oscillation occurs in the steering mechanism, based on a detection result of the third detection unit (S 413 ). 
     According to this embodiment, the damping force is controlled by the third detection unit, based on the information related to the steering angle. Therefore, it is possible to increase the damping force of the steering mechanism at a more effective timing. 
     6. In the above embodiments, the control unit controls the damping force such that the damping force increases, in a case where a steering angular velocity of the steering mechanism based on the detection result of the third detection unit satisfies a predetermined condition (S 412 , S 413 ). 
     According to this embodiment, it is possible to increase the damping force of the steering mechanism at a more effective timing. 
     7. A control device ( 50 ) of the above embodiments is a control device to be applied to a straddle type vehicle ( 1 ), the straddle type vehicle including a steering mechanism ( 10 ) that steers a front wheel and a steering damper device ( 20 ) capable of variably generating a damping force working on a rotating action of the steering mechanism, the control device being configured to control the damping force of the steering damper device to increase, when the front wheel of the straddle type vehicle in a wheelie state lands on a ground, wherein 
     the control device controls the damping force to increase, after the front wheel lands on the ground and an oscillation occurs in the steering mechanism (S 1 -S 4 ). 
     According to this embodiment, the damping force increases after the steering mechanism starts oscillating. Therefore, it is possible to suppress the vibration of the steering mechanism after the wheelie landing, while suppressing the occurrence of the swing of the vehicle body and the unnatural vehicle body behavior. 
     The invention is not limited to the foregoing embodiments, and various variations/changes are possible within the spirit of the invention.