Abstract:
An intake control device for an air intake system includes one or more stationary intake pipes that communicate with one or more intake ports of an engine. One or more movable intake pipes are movable relative to the stationary intake pipes and, in one position, cooperate with the stationary intake pipes to define engine air intake passages. An actuator applies a force tending to move the movable intake pipes in a first direction. A controller controls the actuator. The movable intake pipes are inhibited from moving beyond a first position in the first direction. The controller directs the actuator to apply a force to the movable intake pipes when the movable intake pipes are in the first position.

Description:
RELATED APPLICATIONS 
   This application is related to, and claims priority from, Japanese Patent Application Nos. 2006-255049, filed Sep. 20, 2006, and 2006-197883, filed Jul. 20, 2006, the entireties of which are hereby incorporated by reference herein and made a part of the present specification. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a variable length intake control device, which varies a length of an intake passage of an engine. The present invention also relates to a straddle-type vehicle incorporating such an intake control device. 
   2. Description of the Related Art 
   Conventionally, an intake control device is known, which varies a length of an engine air intake passage of an engine to change an intake efficiency to change an output characteristic of the engine. For example, when the engine speed is low, the intake control device lengthens an intake pipe length to increase the torque output of the engine at lower engine speeds. In contrast, when the engine speed is high, the intake pipe length is shortened to increase the torque output of the engine at higher engine speeds. 
   Some intake control devices include a movable intake pipe that is moved between a coupled position, in which it is coupled to a stationary intake pipe coupled to an intake port of an engine, and a separated position, in which it is separated from the stationary intake pipe, by a driving force of an actuator (see, for example, Japanese Patent Publication No. 09-184423). Such intake control devices comprise a potentiometer for detection of a position of the movable intake pipe. The control device detects positional deviation of the moving intake pipe on the basis of a detected value of the potentiometer to correct a position of the moving intake pipe. 
   SUMMARY OF THE INVENTION 
   An aspect of the present invention involves the realization by the present inventors that, because the conventional intake control device controls the actuator on the basis of a detected value of the potentiometer, the resulting processing for controlling the actuator is rather complex. In addition, the position of the movable intake pipe may be affected by outside forces, such as vibrations due to operation of the associated vehicle. 
   A preferred embodiment of the present invention involves an intake control device capable of accurately controlling a variable length intake passage with a relatively simple control process. In one arrangement, the intake control device moves a movable intake pipe for a period of time, rather than based on feedback from a position sensor. In addition, once the movable intake pipe is in a desired position, the control device may apply a force to the movable intake pipe to ensure the intake pipe remains in the desired position. A preferred embodiment of the present invention also involves a straddle-type vehicle incorporating such a control device. 
   In one embodiment, an intake air control device includes a stationary intake pipe that at least partially defines an intake passage the communicates with an intake port of an engine. A movable intake pipe is movable relative to the stationary intake pipe to vary a length of the intake passage. An actuator is capable of moving the movable intake pipe. A controller controls the actuator. The movable intake pipe is inhibited from moving beyond a first position relative to the stationary intake pipe in a first direction. The controller directs the actuator to apply a force tending to move the movable intake pipe in the first direction when the movable intake pipe is in the first position. 
   One preferred embodiment involves a straddle-type vehicle that incorporates an intake control device as described above. The straddle-type vehicle may be, for example, a motorcycle (including a scooter), four-wheeled buggy, snowmobile, all-terrain vehicle (ATV), and the like. 
   An aspect of a preferred embodiment involves an intake control device as described above in which the first position is a coupled position. In the coupled position, the movable intake pipe is coupled to the stationary intake pipe. Accordingly, it is possible to control the actuator with a simple control process to prevent positional deviation of the movable intake pipe when the movable intake pipe is desired to be in the coupled position. Also, a stop may be provided that inhibits the movable intake pipe from moving beyond the coupled position. 
   Another aspect of a preferred embodiment involves an intake control device as described above in which the set position is a separated position. In the separated position, the movable intake pipe is separated from the stationary intake pipe. With such an arrangement, it is possible to control the actuator with a relatively simple control process to prevent positional deviation of the movable intake pipe. In addition, a stop may be provided that inhibits the movable intake pipe from moving beyond the separated position. 
   Yet another aspect of a preferred embodiment involves an intake control device as described above in which the force applied to the movable intake pipe by the actuator when the movable intake pipe is moving toward the first position is of a first magnitude and the force applied to the movable intake pipe by the actuator when the movable intake pipe is in the first position is of a second magnitude. The second magnitude is smaller than the first magnitude. Accordingly, it is possible to efficiently drive the actuator when the movable intake pipe is in the first position. 
   Still another aspect of a preferred embodiment involves an intake control device as described above in which the controller drives the actuator so that a force applied to the movable intake pipe in the first position is intermittent. As a result, it is possible to efficiently drive the actuator when the movable intake pipe is in the first position. Also, a vehicle condition sensor that detects an operating condition of a vehicle associated with the control device may be provided. The controller directs the actuator to apply the force to the movable intake pipe at a time interval that is dependent on the operating condition of the vehicle. Thereby, it is possible to appropriately drive the actuator according to an operating condition of the vehicle to further stably maintain the movable intake pipe in the first position. 
   Another aspect of a preferred embodiment involves an intake control device as described above in which the movable intake pipe is movable in a coupling direction, in which it approaches the stationary intake pipe, and in a separation direction, in which it separates from the stationary intake pipe. The controller drives the actuator so that the movable intake pipe is moved in the separation direction when an operation of the intake control device is terminated. Accordingly, the movable intake pipe is separated from the stationary intake pipe when an operation of the intake control device is terminated so that the durability of the intake control device is improved. 
   Still another aspect of a preferred embodiment involves an intake control device as described above in which the movable intake pipe may be movable between a coupled position, in which it is coupled to the stationary intake pipe, and a separated position, in which it is separated from the stationary intake pipe, and the controller may drive the actuator so that the movable intake pipe is arranged between the coupled position and the separated position when an operation of the intake control device is terminated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention are described with reference to drawings of preferred embodiments, which are intended to illustrated but not to limit the present invention. The drawings contain fourteen (14) figures. 
       FIG. 1  is a side view of a motorcycle incorporating an intake control device having certain features, aspects and advantages of the present invention. 
       FIG. 2  is a partial schematic, side view of the engine and intake control device of  FIG. 1 . The intake control device includes an intake pipe length varying mechanism. 
       FIG. 3  is a plan view of the intake pipe length varying mechanism of  FIG. 2 . 
       FIG. 4  is a cross sectional view of the intake pipe length varying mechanism taken along the line IV-IV in  FIG. 3 . The intake pipe length varying mechanism includes movable intake pipes that are movable relative to stationary intake pipes. In  FIG. 4 , the movable intake pipes are separated from the stationary intake pipes. 
       FIG. 5  is a cross sectional view taken along the line IV-IV in  FIG. 3 . In  FIG. 5 , the movable intake pipes are coupled to the stationary intake pipes. 
       FIG. 6  is a front view of an actuator that moves the movable intake pipes between the separated position of  FIG. 4  and the coupled position of  FIG. 5 . 
       FIG. 7  is a cross sectional view of a moving member that transmits an actuation force from the actuator to the movable intake pipes. In  FIG. 7   a , the moving member is moving in a first direction and, in  FIG. 7   b , the moving member is moving in a second direction. 
       FIG. 8  is a block diagram of a control unit of the intake control device. 
       FIG. 9  is a flowchart of a preferred control process that may be executed by the control unit to control the movement of the movable intake pipes. 
       FIG. 10  is a block diagram illustrating another example of a preferred control process that may be executed by the control unit. 
       FIG. 11  is a table of a preferred coupling energizing stoppage time for various engine speeds. 
       FIG. 12  is a table of a preferred separation energizing stoppage time for various engine speeds. 
       FIG. 13  is a flowchart of an example of a preferred control process that may be executed by a coupled state maintaining unit of the control unit. 
       FIG. 14  is a flowchart of an example of a preferred control process that may be executed by a separated state maintaining unit of the control unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the invention are described below with reference to the drawings.  FIG. 1  is a side view of a motorcycle  1  provided with an intake control device  10  having certain features, aspects and advantages of the present invention.  FIG. 2  illustrates a preferred construction of an engine  50  and the intake control device  10 . 
   As shown in  FIG. 1 , the motorcycle  1  includes, among other components and systems, a body frame  3 , the intake control device  10 , and the engine  50 . Also, as shown in  FIG. 2 , the intake control device  10  includes a control unit  11 , a storage unit  12 , an actuator drive circuit  13 , an intake pipe length varying mechanism  14 , and a holding circuit  15 . 
   As shown in  FIG. 1 , the body frame  3  includes a main frame  3   a  and a steering head portion  3   b  is provided on a front end of the main frame  3   a  to rotatably support a steering shaft (not shown). A front suspension fork  4  is coupled to the steering shaft and, thus, is also rotatable with respect to the steering head portion  3   b . The main frame  3   a  extends obliquely downward toward the rear of a vehicle body from the steering head portion  3   b . A rear swing arm  5  is mounted to a rear end of the main frame  3   a  to be able to swing vertically about a pivot shaft  3   e.    
   The engine  50  is arranged below the main frame  3   a . As shown in  FIG. 2 , the engine  50  is formed with exhaust ports  50   a  that communicate with combustion chambers of the engine  50 . Exhaust pipes  8  are coupled to the exhaust ports  50   a . Rear ends of the exhaust pipes  8  open into a muffler  9  ( FIG. 1 ), which reduces a sound level of exhaust gases that are discharged to the atmosphere. Also, intake ports  50   b  communicate with the combustion chambers of the engine  50 . Throttle bodies  49  are coupled to the intake ports  50   b . Fuel delivery devices, such as fuel injectors  47 , are mounted to the throttle bodies  49  to deliver fuel into intake passages of the throttle bodies  49 . Also, air intake control valves control an amount of intake air deliver to the combustion chambers. In the illustrated arrangement, throttle valves  49   a  are arranged in the intake passages of the throttle bodies  49 . Throttle position sensors  48  are mounted to sides of the throttle bodies  49  to detect throttle opening positions. The throttle position sensors  48  output to the control unit  11  voltage signals that correspond to throttle opening position (in units of angular degrees, for example) as throttle opening signals. Although the illustrated arrangement is preferred, other suitable exhaust, intake and fuel delivery control systems may be employed. 
   An air cleaner  7 , including an air cleaner box or housing that defines an air cleaner chamber, is arranged above the engine  50 . Intake air is filtered by a filter  7   a  of the air cleaner  7  prior to flowing into the throttle bodies  49 . In addition, movable intake pipes  30  and stationary intake pipes  40 , which are described hereinafter, are accommodated in the air cleaner  7 . An air introduced into the air cleaner  7  passes through the stationary intake pipes  40 , or through both the stationary intake pipes  40  and the movable intake pipes  30 , and then flows into the throttle bodies  49 . Also, an air duct (not shown) is coupled to the air cleaner  7  and intake air enters the air cleaner  7  through the air duct. 
   Pistons  52  are accommodated in cylinders  51  of the engine  50 . Upper ends of coupling rods  53  are mounted to the pistons  52  and lower ends thereof are mounted to a crank shaft  54 . A fly wheel  55  is mounted to the crank shaft  54 . A plurality of projections (not shown) aligned at equal intervals in a circumferential direction are formed on an outer peripheral surface of the fly wheel  55 . A crank angle sensor  57  is mounted to a crank case  56  to face the outer peripheral surface of the fly wheel  55 . Whenever the projections of the fly wheel  55  passes the crank angle sensor  57 , the crank angle sensor  57  outputs to the control unit  11  a signal (referred below to as crank angle signal). The control unit  11  detects the rotating speed of the engine  50  on the basis of the frequency at which the crank angle signals are received. In addition, a description is given herein assuming that the engine  50  is a four-cylinder engine and four cylinders  51  are aligned in a vehicle width direction. However, other suitable engine configurations are possible, such as other numbers of cylinders, for example. In addition, the illustrated engine  50  is a four-cycle engine, but engines operating on other engine principals (e.g., two-cycle crankcase compression) may also be used. 
   As described above, the intake control device  10  includes the control unit  11 , the storage unit (or memory)  12 , the actuator drive circuit  13 , the intake pipe length varying mechanism  14 , and the holding circuit  15 . The intake pipe length varying mechanism  14  includes the movable intake pipes  30 , an actuator  21  that displaces the movable intake pipes  30 , and stationary intake pipes  40 . In addition, the control unit  11 , the storage unit  12 , the actuator drive circuit  13 , and the holding circuit  15  are mounted as an engine control unit  16  on a vehicle body. 
   The control unit  11  includes a CPU (Central Processing Unit) to control various electrical equipment mounted on the vehicle body according to a program stored in the storage unit  12 . According to the embodiment, a control process is performed, in which an intake pipe length is varied by driving the actuator  21  to displace the movable intake pipes  30  according to an operating state such as the rotating speed of the engine  50 , a throttle manipulation made by a passenger, etc. A preferred control process executed by the control unit  11  is described below. 
   The storage unit  12  comprises a nonvolatile memory to preserve a program being executed by the control unit  11 . The actuator drive circuit  13  supplies the actuator  21  with electric power, which corresponds to a signal input from the control unit  11 . The holding circuit  15  supplies the control unit  11  and the actuator drive circuit  13  with electric power of a battery (not shown) for a predetermined period of time after a main switch  18  is moved to OFF. 
   The movable intake pipes  30  move relative to the stationary intake pipes  40  between a coupled position, in which they are coupled to the stationary intake pipes  40 , and a separated position separated from the coupled position to vary an intake pipe length. Preferably, the coupled position and the separated position are preset positions that correspond to a desired intake pipe length, such that in the event that the movable intake pipes  30  are in the coupled position, the intake pipe length is relatively lengthened and in the event that the movable intake pipes  30  are in the separated position, the intake pipe length is relatively shortened. The term “pipe” is intended to construed in accordance with its ordinary meaning, and includes a variety of constructions that at least partially define a passage through which a substance, such as engine intake air, may be directed. In the illustrated arrangement, the pipes are generally funnel-like in shape. 
   The illustrated actuator  21  includes a DC motor and is driven by DC power fed from the actuator drive circuit  13  to move the movable intake pipes  30  in a coupling direction or in a direction tending to move the movable intake pipes  30  toward the coupled position from the separated position (a direction denoted by A in  FIG. 2 ), or in a separation direction toward the separated position from the coupled position (opposite of direction A). 
   A description of a preferred construction of the intake pipe length varying mechanism  14  is provided below.  FIG. 3  is a plan view of the intake pipe length varying mechanism  14 .  FIGS. 4 and 5  are cross sectional views taken along the line IV-IV in  FIG. 3 , and  FIG. 6  is a front view showing the actuator  21 . In addition,  FIG. 4  shows a state in which the movable intake pipes  30  are in a separated position X, and  FIG. 5  shows a state in which the movable intake pipes  30  are in a coupled position Y. 
   As shown in  FIG. 4 , the stationary intake pipes  40  are generally cylindrical in shape and the upper ends  40   a  thereof are generally funnel-shaped. The lower ends  40   b  of the stationary intake pipes  40  are coupled to the throttle bodies  49  (see  FIG. 2 ). Column portions  41  extend upwardly from the ends  40   a  of the stationary intake pipes  40  on a side of the movable intake pipes  30  adjacent the actuator  21 . As described later, the column portions  41  support upper levers  22  and lower levers  23 , which transmit a drive force of the actuator  21  to the movable intake pipes  30 . 
   In addition, here, as shown in  FIG. 3 , four stationary intake pipes  40  and movable intake pipes  30  are arranged to be aligned in the vehicle width direction (a direction denoted by H in  FIG. 3 ) and the respective stationary intake pipes  40  are coupled to the throttle bodies  49  provided on the respective cylinders. Also, the column portions  41  of the stationary intake pipes  40  are formed between the two adjacent stationary intake pipes  40 . 
   The movable intake pipes  30  are generally cylindrical in shape and the lower ends  30   a  thereof are slightly smaller in outside diameter than funnel-shaped ends  40   a  of the stationary intake pipes  40 . Annular sealing members (for example, rubber lips)  35 , preferably having some amount of elasticity, are mounted to outer peripheries of the ends  30   a . The sealing members  35  seal clearances between the ends  30   a  of the movable intake pipes  30  and the stationary intake pipes  40  when the movable intake pipes  30  are arranged in the coupled position Y. In addition, the upper ends  30   b  of the movable intake pipes  30  are generally funnel-shaped, similar to the upper ends  40   a  of the stationary intake pipes  40 . 
   Upper support shafts  32  and lower support shafts  33 , which are arranged parallel to each other, bridge between two adjacent movable intake pipes  30 . The upper support shafts  32  are coupled for rotation relative to the upper levers  22  and the lower support shafts  33  are coupled for rotation relative to the lower levers  23 . 
   The upper levers  22  are able to rotate vertically about an upper support shaft  42  supported by the column portions  41  and the lower levers  23  are likewise able to rotate vertically about a lower support shaft  43  supported by the column portions  41 . 
   Specifically, the upper support shaft  42  and the lower support shaft  43 , respectively, extend in the vehicle width direction and are arranged in parallel to the upper support shafts  32  and the lower support shafts  33  to bridge the two column portions  41 . Intermediate portions  22   a  of the upper levers  22  include openings and the upper support shaft  42  is inserted through the openings. Also, bases  23   a  of the lower levers  23  also include openings, through which the lower support shaft  43  is inserted. Thereby, the upper levers  22  and the lower levers  23  turn about the upper support shaft  42  and the lower support shaft  43  and ends  22   b ,  23   b , which grasp the upper support shafts  32  and the lower support shafts  33 , move vertically in parallel to one another. 
   In addition, bases  22   e  of the upper levers  22  are mounted to a moving member  24 , which is driven by the actuator  21  to move in a vertical direction. The moving member  24  is described in greater detail below. 
   Rotational driving of the actuator  21  is transmitted to the upper levers  22  through a transmission mechanism  29 , which converts rotational driving movement of the actuator  21  into vertically linear driving movement to transmit the same. As shown in  FIG. 6 , the transmission mechanism  29  includes a vertical arm  26 , a moving member  24  coupled to the arm  26  to be displaced in a vertical direction, and a coupling member  25 , which converts rotational driving movement of the actuator  21  into vertical driving movement. One end  25   a  of the coupling member  25  ( FIG. 6 ) is coupled to an output shaft  21   a  of the actuator  21  and the coupling member  25  extends radially of the output shaft  21   a . The other end  25   b  of the coupling member  25  is coupled to a lower end  26   a  of the arm  26 . In addition, the end  25   b  of the coupling member  25  and the lower end  26   a  of the arm  26  are coupled to each other through a coupling shaft  27 , which is rotatable relative to the respective ends  25   b ,  26   a.    
   With reference to  FIG. 6 , the actuator  21  accommodates therein a source of power, which preferably is a DC motor  21   d . In addition, the actuator  21  includes a worm gear  21   b , which rotates coaxially with a rotating shaft  21   e  of the motor  21   d , and a gear  21   c , which meshes with the worm gear  21   b  to transmit a driving force to the output shaft  21   a.    
   The upper end  26   b  of the arm  26  is coupled to the moving member  24 .  FIG. 7  is a cross sectional view showing the moving member  24 .  FIG. 7(   a ) shows a state in which the arm  26  pulls the moving member  24  downward (a direction denoted by B in  FIG. 7)  and  FIG. 7(   b ) shows a state in which the arm  26  pushes the moving member  24  upward (opposite the direction B). 
   The moving member  24  includes a box-shaped case  24   a  and a spring  24   b , which biases the case  24   a  upward or downward relative to the arm  26 . The arm  26  is inserted vertically into the case  24   a . The spring  24   b  is arranged in the case  24   a  in a manner to surround the arm  26 . Engaging members  24   c ,  24   d  contact respective ends of the spring  24   b  and also engage the inside of the case  24   a . Engaging portions  26   c ,  26   d  are formed on the arm  26  on opposing sides of the engaging member  24   c , the spring  24   b , and the engaging member  24   d.    
   When the arm  26  pulls the moving member  24  downward, the engaging portion  26   c  pushes the case  24   a  downward through the engaging member  24   c , the spring  24   b , and the engaging member  24   d  ( FIG. 7(   a )). On the other hand, when the arm  26  pushes the moving member  24  upward, the engaging portion  26   d  pushes the case  24   a  upward through the engaging member  24   d , the spring  24   b , and the engaging member  24   c  ( FIG. 7(   b )). 
   In addition, the case  24   a  is formed with openings  24   e ,  24   f , through which the engaging portion  26   c  and the engaging portion  26   d  move into and out of the case  24   a . Also, the case  24   a  is formed with projections  24   g ,  24   h , which project in a lateral direction, and the base  22   e  of the upper lever  22  is mounted to the projections  24   g ,  24   h  ( FIGS. 3 and 4 ). 
   With reference to  FIG. 4 , the intake pipe length varying mechanism  14  includes at least one stop, or stopper mechanism, which inhibits the movable intake pipes  30  from going beyond the coupled position Y and the separated position X. Specifically, the upper levers  22  are formed with projections  22   c , which project laterally to abut against the column portions  41  when the movable intake pipes  30  are in the coupled position Y. Also, the upper levers  22  are formed with projections  22   d , which project laterally to abut against the column portions  41  when the movable intake pipes  30  are in the separated position X. When the movable intake pipes  30  are present in the coupled position Y or the separated position X, the projections  22   c ,  22   d  abut against the column portions  24  to inhibit the upper levers  22  from further movement in that direction. In addition, the stopper mechanism is not limited to the arrangement described above. For example, a stopper for restriction of a rotating angle of the output shaft  21   a  of the actuator  21  may be formed around the output shaft  21   a . Other similar or suitable arrangements may also be employed in the alternative or in addition to the arrangements described above. 
   The operation of the intake pipe length varying mechanism  14  is described below. When the actuator  21  pulls the arm  26  downward, the arm  26  draws the case  24   a  of the moving member  24  to pull the bases  22   e  of the upper levers  22  downward. Consequently, in one operational state, the upper levers  22  and the lower levers  23  turn about the upper support shaft  42  and the lower support shaft  43  to pull the movable intake pipes  30  upward until the projections  22   c  abut against the column portions  41 . When the projections  22   c  about against the column portions  41 , the movable intake pipes  30  are in the separated position X ( FIG. 4 ). 
   On the other hand, when the actuator  21  pushes the arm  26  upward, the arm  26  pushes the bases  22   e  of the upper levers  22  upward through the case  24   a . Consequently, until the projections  22   d  abut against the column portions  41 , the upper levers  22  and the lower levers  23  turn about the upper support shaft  42  and the lower support shaft  43  to push the movable intake pipes  30  downward (see  FIG. 5 ). At this time, the movable intake pipes  30  are arranged in the coupled position Y and the sealing members  35  abut against the ends  40   a  of the stationary intake pipes  40 . 
   As described above, the control unit  11  executes a control process to drive the actuator  21  according to an operating state of a vehicle to vary an intake pipe length.  FIG. 8  is a functional block diagram for one preferred control process executed by the control unit  11 . As shown in  FIG. 8 , the control unit  11  includes start-up coupling operation unit  11   a , a normal processing unit  11   b , and a shutdown separating operation unit  11   g . In addition, in the illustrated arrangement, the control unit  11  controls electric power supplied to the actuator  21  by the actuator drive circuit  13  ( FIG. 2 ). 
   When the control unit start-up is initiated, such as when engine start-up is initiated, for example, the start-up coupling operation unit  11   a  drives the actuator  21  to displace the movable intake pipes  30  in the direction of coupling. For example, when the main switch  18  (which can be an ignition switch of the motorcycle  1 ) is moved to the ON position, the start-up coupling operation unit  11   a  drives the actuator  21  for a preset period of time (referred herein as the start-up coupling operation time). Here, the start-up coupling operation time is the time required for movement of the movable intake pipes  30  to the coupled position Y from a position before displacement begins. The start-up coupling operation time may be set, for example, during manufacture of the intake control device  10 . In addition, in the illustrated arrangement, before displacement at start-up begins, the movable intake pipes  30  are arranged between the coupled position Y and the separated position X by a processing of the shutdown separating processing unit  11   g  described below. 
   The start-up coupling operation unit  11   a  may decrease the output torque of the actuator  21  in the course of movement in the coupling direction to reduce a moving speed of the movable intake pipes  30 . For example, until a predetermined time, which preferably is shorter than a start-up movement time, from the start of displacement, the actuator  21  may be driven at a predetermined duty ratio (referred herein to as high duty ratio, for example, 100%) and after the lapse of the predetermined time, the actuator  21  may be driven at a predetermined duty ratio, which preferably is lower than the high duty ratio. 
   After the processing of the start-up coupling operation unit  11   a  is terminated, the normal processing unit  11   b  performs a processing to drive the actuator  21  according to an operating state of a vehicle to vary an intake pipe length. The normal processing unit  11   b  functionally includes a coupled state maintaining unit  11   c , a separating operation unit  11   d , a separated state maintaining unit  11   e , and a coupling operation unit  11   f.    
   When the movable intake pipes  30  are stationary in the coupled position Y, the coupled state maintaining unit  11   c  drives the actuator  21  to energize the movable intake pipes  30  in the coupling direction. Specifically, when the processing by the start-up coupling operation unit  11   a  or the coupling operation unit  11   f , described below, is terminated, the coupled state maintaining unit  11   c  intermittently drives the actuator  21  to energize the movable intake pipes  30  in the coupling direction. For example, after the actuator  21  is driven for a predetermined time (referred to herein as coupling direction energizing time), the coupled state maintaining unit  11   c  stops driving for a predetermined time (referred to herein as the stoppage time), which preferably is longer than the coupling direction energizing time, and thereafter repeats such driving and stoppage. At this time, the projections  22   c  of the upper levers  22  remain abutted against the column portions  41 . Also, the spring  24   b  of the moving member  24  contracts so as to energize the movable intake pipes  30  downward (see  FIG. 7(   b )). 
   In addition, the coupled state maintaining unit  11   c  may drive the actuator  21  in a manner to output a smaller torque than that at the time of movement of the movable intake pipes  30  by the coupling operation unit  11   f  described below. That is, the coupled state maintaining unit  11   c  may make a duty ratio at the time of standstill of the movable intake pipes  30  lower than a duty ratio at the time of movement. Also, the actuator  21  may be fed at all times by the coupled state maintaining unit  11   c  at a lower duty ratio than that at the time of movement of the movable intake pipes  30  by the coupling operation unit  11   f.    
   When an operating state meets a predetermined condition (referred below to as separating operation starting condition), the separating operation unit  11   d  drives the actuator  21  so that the movable intake pipes  30  present in the coupled position Y are moved to the separated position X. For example, in the case where an operating state meets a separation processing starting condition when the movable intake pipes  30  are in a coupled state, the separating operation unit  11   d  drives the actuator  21  for a preset time (referred to herein as the separating operation time) such that the movable intake pipes  30  are moved in the separation direction. Here, the separating operation time is the time required for movement of the movable intake pipes  30  to the separated position X from the coupled position Y. The separating operation time may be set, for example, during manufacture of the intake control device  10 . Also, the separating operation starting condition is one in which an engine rotating speed remains above a preset speed (referred to herein as condition speed) and a throttle opening degree remains above a predetermined value (referred to herein as condition opening degree) continues for a predetermined time or longer. 
   Also, like the start-up coupling operation unit  11   a , the separating operation unit  11   d  may decrease the output torque of the actuator  21  in the course of movement of the movable intake pipes  30  to decrease a moving speed of the movable intake pipes  30 . That is, the separating operation unit  11   d  may drive the actuator  21  at a predetermined duty ratio (for example, 100%) for a predetermined time, which preferably is shorter than the separating operation time, and may drive the actuator  21  at a lower duty ratio than the predetermined duty ratio after the predetermined time lapses. 
   When the movable intake pipes  30  are stationary in the separated position X, the separated state maintaining unit  11   e  drives the actuator  21  so as to energize the movable intake pipes  30  in the separation direction. Specifically, when the movable intake pipes  30  reach the separated position X as a result of the processing by the separating operation unit  11   d , the separated state maintaining unit  11   e  intermittently drives the actuator  21  to energize the movable intake pipes  30  in the separation direction. For example, after the actuator  21  is driven for a predetermined time (referred to herein as the separating direction energizing time), the separated state maintaining unit  11   e  stops driving for the stoppage time described above, and thereafter repeats such driving and stoppage. At this time, the separating direction energizing time may be shorter than the stoppage time. The actuator  21  energizes the movable intake pipes  30  whereby the projections  22   d  of the upper levers  22  abut against the column portions  41 . Also, the spring  24   b  of the moving member  24  contracts so as to energize the movable intake pipes  30  upward ( FIG. 7(   a )). 
   In addition, the separated state maintaining unit  11   e  may drive the actuator  21  in a manner to output a smaller torque than that at the time of movement of the movable intake pipes  30  in the separation direction. That is, the separated state maintaining unit  11   e  may make a duty ratio at the time of standstill of the movable intake pipes  30  in the separated position X lower than a duty ratio at the time of movement. Also, the separated state maintaining unit  11   c  may supply the actuator  21  at all times with electric power, which is at a lower duty ratio than that at the time of movement. 
   When an operating state meets a predetermined condition (referred to herein as coupling operation starting condition), the coupling operation unit  11   f  drives the actuator  21  for a preset time (referred to herein as coupling operation time) so that the movable intake pipes  30  is moved in the direction of connection. Here, the coupling operation time is time required for movement of the movable intake pipes  30  to the coupled position Y from the separated position X. The coupling operation time may be set, for example, during manufacture of the intake control device  10 . Also, the coupling operation starting condition is one in which an engine rotating speed becomes lower than the condition speed described above, or a throttle opening degree becomes smaller than the condition opening degree described above. 
   Similar to the separating operation unit  11   d , the coupling operation unit  11   f  may decrease a moving speed of the movable intake pipes  30  in the course of movement thereof. That is, the coupling operation unit  11   f  may drive the actuator  21  at a predetermined duty ratio (for example, 100%) for a predetermined time, which preferably is shorter than the coupling operation time, and may drive the actuator  21  at a lower duty ratio than the predetermined duty ratio after the predetermined time lapses. 
   When an operation of the intake control device  10  is terminated (such as when the engine  50  of the motorcycle  1  is shutdown), the shutdown separating operation unit  11   g  drives the actuator  21  to displace the movable intake pipes  30  in the separation direction. Specifically, when the main switch  18  is moved to the OFF position, the shutdown separating operation unit  11   g  drives the actuator  21  for a preset period of time (referred to herein as shutdown separating operation time) so that the movable intake pipes  30  are moved in the separation direction. Here, the shutdown separating operation time is time required for movement of the movable intake pipes  30  to an intermediate position between the coupled position Y and the separated position X from the coupled position Y. Also, the shutdown separating operation time is shorter than the time during which electric power is supplied from the holding circuit  15  after the main switch  18  is moved to the OFF position. The shutdown separating operation time is set, for example, during manufacture of the intake control device  10 . In this manner, when an operation of the intake control device  10  is terminated, the movable intake pipes  30  are arranged in the intermediate position whereby the sealing members  35  and the stationary intake pipes  40  are prevented from sticking to one another. 
   In addition, the shutdown separating operation unit  11   g  may drive the actuator  21  for the shutdown separating operation time with electric power, which is at the same duty ratio as that at the time of movement of the movable intake pipes  30  by the separating operation unit  11   d , or may drive the actuator  21  with electric power, which is at a smaller duty ratio than that at the time of movement. 
   Below, a description of the processing executed by the control unit  11  is described.  FIG. 9  is a flowchart illustrating an example of the control process executed by the control unit  11 . 
   When the main switch  18  is moved to the ON position, the start-up coupling operation unit  11   a  drives the actuator  21  for the start-up coupling operation time (S 101 ). Thereby, the movable intake pipes  30  are moved to the coupled position Y. In addition, before the movement, the movable intake pipes  30  are arranged in the intermediate position between the coupled position Y and the separated position X by the processing of the shutdown separating operation unit  11   g  during the previous operation. 
   When the start-up coupling operation time lapses, the coupled state maintaining unit  11   c  intermittently drives the actuator  21  to energize the movable intake pipes  30  in the coupling direction (S 102 ). Also, the separating operation unit  11   d  detects the rotating speed of the engine  50  and a throttle opening degree to determine whether the separating operation starting condition has been met (S 103 ). Here, when the separating operation starting condition is not met, the shutdown separating operation unit  11   g  determines whether the main switch  18  has been turned to the OFF position (S 104 ), and in case of the main switch  18  not being moved to OFF, the processing returns to S 102  and the coupled state maintaining unit  11   c  continues to energize the movable intake pipes  30 . 
   On the other hand, in S 103 , in the case where the separating operation starting condition is met, the separating operation unit  11   d  moves the actuator  21  for the separating operation time (S 105 ). Thereby, the movable intake pipes  30  are moved to the separated position X. When the separating operation time lapses, the separated state maintaining unit  11   e  intermittently drives the actuator  21  to begin energizing the movable intake pipes  30  in the separation direction (S 108 ). Also, the coupling operation unit  11   f  detects an operating state to determine whether the coupling operation starting condition has been met (S 107 ). Here, when the coupling operation starting condition is not met, the shutdown separating operation unit  11   g  determines whether the main switch  18  has been moved to OFF (S 108 ). In the case where the main switch  18  has not been moved to OFF, the processing returns to S 106  and the separated state maintaining unit  11   e  continues to energize the movable intake pipes  30  in the direction of separation. 
   On the other hand, in S 107 , when the coupling operation starting condition is met, the coupling operation unit  11   f  drives the actuator  21  for the coupling operation time (S 109 ). Consequently, the movable intake pipes  30  are moved to the coupled position Y. When the coupling operation time lapses, the coupled state maintaining unit  11   c  intermittently drives the actuator  21  to energize the movable intake pipes  30  in the coupling direction (S 110 ). Also, the separating operation unit  11   d  detects an operating state to determine whether the separating operation starting condition has been met (S 111 ). Here, in the case where the separating operation starting condition is not met, whether the main switch  18  has been moved to OFF is determined (S 112 ), and in case of not having been moved to OFF, the processing returns to S 110 , so that the coupled state maintaining unit  11   c  continues to energize the movable intake pipes  30  in the direction of connection. 
   On the other hand, in S 111 , when an operating state meets the separating operation starting condition, the processing returns to S 1105  and the separating operation unit  11   d  drives the actuator  21  for the separating operation time so that the movable intake pipes  30  are moved in the separation direction. 
   In S 104 , S 108 , and S 112 , in the case where the main switch  18  is moved to OFF, the shutdown separating operation unit  11   g  drives the actuator  21  for the shutdown separating operation time to move the movable intake pipes  30  in the separation direction (S 113 ). In addition, in S 108 , in the case where the main switch  18  is moved to OFF, the movable intake pipes  30  may be moved in the separation direction for the shutdown separating operation time in S 113  after the movable intake pipes  30  initially in the separated position X are moved in the coupling direction for the coupling operation time. With such an arrangement, the movable intake pipes  30  are surely positioned in the intermediate position when an operation of the intake control device  10  is terminated. 
   With the intake control device  10  described above, when the movable intake pipes  30  are stationary in the coupled position Y or the separated position X, the actuator  21  drives the movable intake pipes  30  in the coupling direction or in the separation direction. Consequently, positional deviation of the movable intake pipes  30  is corrected and control of the movable intake pipes  30  is made simple without the provision of any potentiometer, which detects positions of the movable intake pipes  30 . 
   In addition, the present invention is not limited to the intake control device  10  described above but is susceptible to various modifications. With the intake pipe length varying mechanism  14  described above, the movable intake pipes  30  translate in the same direction as a direction of intake in the stationary intake pipes  40 . However, the movable intake pipes  30  may be turned in a circumferential direction to move between the coupled position and the separated position. 
   Also, in the case where the movable intake pipes  30  are present in the coupled position Y or the separated position X, time intervals at which the actuator  21  is driven may be determined on the basis of a traveling state of the vehicle. The actuator  21  is driven at the time intervals whereby the movable intake pipes  30  may be repeatedly energized intermittently, that is, at the time intervals in the coupling direction or in the separation direction. Here, a value indicative of a traveling state of the vehicle is, for example, an engine rotating speed and a throttle opening degree. Thereby, the frequency at which the actuator  21  is driven varies corresponding to those vibrations of a vehicle body, which increase or decrease according to a traveling state of the vehicle, so that the movable intake pipes  30  are stably maintained in the coupled position Y or the separated position X irrespective of an increase and a decrease in vibrations of a vehicle body. Subsequently, another intake control device having certain features, aspects and advantages of the present invention is described below. In addition, since the construction of the intake control device described below is the same as the intake control device  10  described above, a detailed explanation with respect to the construction of the intake control device is omitted. Also, a description of an example in which a crank angle sensor  57  is used as a sensor, which detects the degree of those vibrations of a vehicle body, increase or decrease according to a traveling state of the vehicle. 
     FIG. 10  is a functional block diagram illustrating a control process that may be executed by a control unit  11 . As illustrated, a coupled state maintaining unit  11   c  includes a connection energizing time control unit  11   h  and a separated state maintaining unit  11   e  includes a separation energizing time control unit  11   i.    
   When the movable intake pipes  30  are stationary in the coupled position Y, the connection energizing time control unit  11   h  detects an engine rotating speed on the basis of a signal input from the crank angle sensor  57  to determine a time interval at which the actuator  21  is driven based on the engine rotating speed. That is, stoppage time (referred to herein as connection energizing stoppage time) existing between a coupling direction energizing time, during which the actuator  21  is driven, and a subsequent coupling direction energizing time is determined. The processing by the connection energizing time control unit  11   h  is executed, for example, in the following manner. 
   A table (referred to herein as connection energizing control table), which illustrates a relationship between connection energizing stoppage time and an engine rotating speed, is stored in the memory of a storage unit  12 . The connection energizing time control unit  11   h  detects an engine rotating speed in a predetermined sampling cycle to refer to the connection energizing control table every detection to acquire that connection energizing stoppage time, which corresponds to the engine rotating speed.  FIG. 11  illustrates an example of the connection energizing control table stored in the storage unit  12 . In this table, an upper row indicates an engine rotating speed, a lower row indicates connection energizing stoppage time, and the connection energizing stoppage time is shortened as an engine rotating speed increases. 
   In addition, the processing by the connection energizing time control unit  11   h  is not limited thereto. For example, connection energizing stoppage time may be calculated by substituting engine rotating speed, which is detected by the crank angle sensor  57 , with an equation indicative of the relationship between an engine rotating speed and connection energizing stoppage time. 
   The coupled state maintaining unit  11   c  drives the actuator  21  for the coupling direction energizing time to energize the movable intake pipes  30 , and then stops driving of the actuator  21  for the connection energizing stoppage time acquired by the connection energizing time control unit  11   h . Thereafter, the actuator  21  is again driven for the coupling direction energizing time, and then driving of the actuator  21  is again stopped for the connection energizing stoppage time. In this manner, the coupled state maintaining unit  11   c  repeats such driving and stoppage of the actuator  21 . 
   In the same manner as the processing of the connection energizing time control unit  11   h , when the movable intake pipes  30  are stationary in the separated position X, the separation energizing time control unit  11   i  determines a time interval at which the actuator  21  is driven on the basis of an engine rotating speed detected by the crank angle sensor  57 . That is, stoppage time (referred to herein as separation energizing stoppage time) existing between a separating direction energizing time, during which the actuator  21  is driven, and a subsequent separating direction energizing time is determined. For example, a table (referred to herein as separation energizing control table), which provides a relationship between separation energizing stoppage time and an engine rotating speed, is stored in the memory of the storage unit  12 . The separation energizing time control unit  11   i  refers to the separation energizing control table to acquire that separation energizing stoppage time that corresponds to the engine rotating speed.  FIG. 12  is a view illustrating an example of the separation energizing control table. In this table, an upper row indicates an engine rotating speed, a lower row indicates separation energizing stoppage time, and the separation energizing stoppage time becomes shorter as an engine rotating speed increases. 
   In addition, like the connection energizing time control unit  11   h , the separation energizing time control unit  11   i  may substitute the engine rotating speed, which is detected by the crank angle sensor  57 , into an equation indicative of the relationship between an engine rotating speed and separation energizing stoppage time to calculate separation energizing stoppage time. 
   The separated state maintaining unit  11   e  drives the actuator  21  for the separating direction energizing time to energize the movable intake pipes  30 , and then stops driving of the actuator  21  for the separation energizing stoppage time acquired by the separation energizing time control unit  11   i . Thereafter, the actuator  21  is again driven for the separating direction energizing time, and then driving of the actuator  21  is again stopped for the separation energizing stoppage time. In this manner, the separated state maintaining unit  11   e  repeats such driving and stoppage of the actuator  21 . 
   In addition, a time during which the coupled state maintaining unit  11   c  drives the actuator  21  may be made longer than a time during which the separated state maintaining unit  11   e  drives the actuator  21 . That is, connection energizing stoppage time may be shorter than separation energizing stoppage time. For example, as illustrated in the connection energizing control table in  FIG. 11  and the separation energizing control table in  FIG. 12 , the respective connection energizing stoppage times may be set to be shorter than separation energizing stoppage time, which is caused to correspond to an engine rotating speed equal thereto. Thereby, positions of the movable intake pipes  30  in the coupled position Y are stably maintained as compared with the case where the movable intake pipes  30  are present in the separated position X. Consequently, in the case where the movable intake pipes  30  are present in the coupled position Y, clearances between the movable intake pipes  30  and the stationary intake pipes  40  are sealed. 
   With reference to  FIG. 13 , a description is provided of a preferred control process flow executed by the coupled state maintaining unit  11   c  and the separated state maintaining unit  11   e .  FIG. 13  is a flowchart illustrating an example of the processing executed by the coupled state maintaining unit  11   c  and illustrates examples of control processes in S 102  and S 110  in the flowchart of  FIG. 9 .  FIG. 14  is a flowchart illustrating an example of the processing executed by the separated state maintaining unit  11   e  and illustrates an example of processing in S 106  in the flowchart of  FIG. 9 . 
   Initially, a description of the processing executed by the coupled state maintaining unit  11   c  is provided. The coupled state maintaining unit  11   c  drives the actuator  21  for the coupling direction energizing time to energize the movable intake pipes  30  in the coupling direction (S 201 ). Also, the connection energizing time control unit  11   h  detects an engine rotating speed (S 202 ) to refer to the connection energizing control table stored in the storage unit  12  to acquire that connection energizing stoppage time, which corresponds to the engine rotating speed (S 203 ). 
   Thereafter, the coupled state maintaining unit  11   c  stops driving of the actuator  21  for the connection energizing stoppage time acquired by the connection energizing time control unit  11   h  (S 204 ). The coupled state maintaining unit  11   c  repeats the above processing until the separating operation unit  11   d  determines that the separating operation starting condition is met. 
   Next, a processing of the separated state maintaining unit  11   e  is described. The separated state maintaining unit  11   e  drives the actuator  21  for the separating direction energizing time to energize the movable intake pipes  30  in the separation direction (S 301 ). Also, the separation energizing time control unit  11   i  detects an engine rotating speed to refer to the separation energizing control table stored in the storage unit  12  (S 302 ) to acquire that separation energizing stoppage time, which corresponds to the engine rotating speed (S 303 ). Thereafter, the separated state maintaining unit  11   e  stops driving of the actuator  21  for the separation energizing stoppage time acquired by the separation energizing time control unit  11   i  (S 304 ). The separated state maintaining unit  11   e  repeats the above processing until the coupling operation unit  11   f  determines that the coupling operation starting condition is met. 
   In addition, while it has been described that a relationship is given between an engine rotating speed and connection energizing stoppage time in the connection energizing control table, for example, coupling direction energizing time may be caused to correspond to an engine rotating speed. In this case, it may be set so that the higher an engine rotating speed, the longer coupling direction energizing time, and the coupling direction energizing time may be constant. Likewise, it may be set in the connection and separation energizing control tables so that separating direction energizing time is caused to correspond to an engine rotating speed and the higher an engine rotating speed, the longer separating direction energizing time. 
   Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In particular, while the present intake control system has been described in the context of particularly preferred embodiments, the skilled artisan will appreciate, in view of the present disclosure, that certain advantages, features and aspects of the system may be realized in a variety of other applications, many of which have been noted above. Additionally, it is contemplated that various aspects and features of the invention described can be practiced separately, combined together, or substituted for one another, and that a variety of combination and subcombinations of the features and aspects can be made and still fall within the scope of the invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims.