BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an air intake device of an engine. 
         [0003]    2. Description of the Related Art 
         [0004]    A conventional structure includes an idle number-of-revolutions control device that is fitted to a throttle body and controls an idle number of revolutions of an engine to a target number of revolutions according to the state of the engine. For example, an idle number-of-revolutions control device disclosed in Japanese Unexamined Patent Publication No. 9-42119 has a water collection portion formed therein and can temporarily store dew condensed in the throttle body and water droplets from air cleaner piping in the water collection portion. 
         [0005]    In the device disclosed in Japanese Unexamined Patent Publication No. 9-42119, the water collection portion is arranged on the downstream side of the idle number-of-revolutions control device. The idle number-of-revolutions control device has a valve body built in an air flow passage extending from an air cleaner, the valve body being operated by a proportion type solenoid. Thus, there is a possibility that moisture from the air cleaner will adhere to the valve body and will freeze up, and in that case, a problem is caused in that the idle number-of-revolutions control device will not smoothly operate. 
       SUMMARY OF THE INVENTION 
       [0006]    In order to overcome the problems described above, preferred embodiments of the present invention provide an air intake device for an engine that ensures smooth operation of an idle number-of-revolutions control device. 
         [0007]    According to a preferred embodiment of the present invention, an air intake device includes a throttle body disposed in an intake passage of an engine, a bypass passage that connects an upstream side and a downstream side of a throttle valve disposed in the throttle body, an idle number-of-revolutions control device that is disposed in the bypass passage and that is arranged to control the quantity of air passing through the bypass passage and flowing into the downstream side of the throttle valve according to the state of the engine, and a water collection portion that is disposed on the upstream side of the idle number-of-revolutions control device in the bypass passage and that includes a connection portion arranged to connect to the bypass passage. 
         [0008]    According to a preferred embodiment of the present invention, the water collection portion is arranged on the upstream side of the idle number-of-revolutions control device, so that water in the bypass passage is collected before the idle number-of-revolutions control device. Thus, the water collection portion is arranged to prevent moisture from being frozen to the idle number-of-revolutions control device in cold weather. 
         [0009]    Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a front view illustrating an entire layout of an air intake device according to a first preferred embodiment of the present invention. 
           [0011]      FIG. 2  is a section view illustrating an idle number-of-revolutions control device. 
           [0012]      FIG. 3  is a section view of a measurement portion. 
           [0013]      FIG. 4  is a section view of a main portion in a second preferred embodiment of the present invention. 
           [0014]      FIG. 5  is a section view of a main portion in a third preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Preferred Embodiment 
       [0015]    A first preferred embodiment of the present invention will be described with reference to  FIG. 1  to  FIG. 3 .  FIG. 1  shows the main portion of an air intake device for use in, for example, an engine of a snowmobile. A vehicle of this preferred embodiment is preferably mounted with a four-cylinder engine E arranged in parallel to a direction perpendicular to the surface of  FIG. 1 . One end side of each intake pipe  2  is connected to the cylinder head  1  of each cylinder, and the other end side of each intake pipe  2  is connected to an air cleaner  3  arranged forward of the engine E. The entire engine including the air cleaner  3  is housed in an engine department and is covered with a bonnet B (cover) that can be opened and closed from above. 
         [0016]    The air cleaner  3  has its interior partitioned into two chambers by a filter element  4 . One chamber is a dirty side chamber  5  into which outside air is taken, and the other chamber is a clean side chamber  6  into which clean air filtered through the filter element  4  is introduced, and the end portion of the intake pipe  2  is connected to the clean side chamber  6  in a protruding manner. A connection pipe  7  protrudes from the side surface, to which the intake pipe  2  is connected, of the bottom portion of this clean side chamber  6  and has the upstream end portion of a bypass pipe  9  connected thereto, the bypass pipe  9  defining a portion of a bypass passage  8 . 
         [0017]    A throttle body  10  is interposed in the middle of the intake pipe  2  and defines a portion of an intake passage  10 A extending from the air cleaner  3  to the engine E. The throttle body  10  is arranged in a position slightly inclined downward and rearward with respect to a front and rear direction of the vehicle. In the interior of the throttle body  10 , a throttle valve  11  is fitted to a support shaft  11 A so as to be turned around the support shaft  11 A, and can open and close the intake passage  10 A in the interior in association with the operation of the throttle. Although not shown in the drawing, the opening of the throttle valve  11  is detected by a throttle opening sensor and its detection signal is inputted to an engine control unit (ECU) (not shown). 
         [0018]    The throttle body  10  is preferably provided for each cylinder in this preferred embodiment. The throttle bodies  10  are preferably constructed to have the following unit structure: two throttle bodies  10  integrally formed as one set of throttle bodies  10 , and two sets of throttle bodies  10  coupled to each other by a joining member (not shown); thus, a unit structure is produced in which four throttle bodies  10  are arranged in parallel or substantially parallel as a whole. 
         [0019]    One of the two sets of throttle bodies  10  is provided with an idle number-of-revolutions control device  12 . A lower housing  13  is formed integrally with a portion bridging between the throttle bodies  10  in this one set of throttle bodies  10 , and the idle number-of-revolutions control device  12  is fitted in the lower housing  13  in a position protruding in a direction perpendicular or substantially perpendicular to the axial line of the throttle body  10 , in other words, in an upward position slightly inclined rearward with respect to the front and rear direction of the vehicle. 
         [0020]    The idle number-of-revolutions control device  12  introduces air from the air cleaner  3  to the downstream side of the throttle valve  11  in each of the throttle bodies  10  so as to bypass the intake pipe  2 , thereby optimizing the quantity of air corresponding to the state of the engine at the time of the idle operation and of supplying the air to each cylinder. 
         [0021]    The idle number-of-revolutions control device  12  has an upper housing  14  having a substantially circular cylinder shape and has a flange portion  14 A integrally provided at its lower end in a projecting manner, the flange portion  14 A being fitted to the lower housing  13 . The flange portion  14 A has a seal ring  15  fitted in the lower surface thereof, and when the idle number-of-revolutions control device  12  is fitted to the lower housing  13  with screws, for example, the sealing performance between the flange portion  14 A and the lower housing  13  can be ensured by the seal ring  15 . A fitting hole  16  is formed in the upper housing  14  along an axial direction thereof so as to pass to the outside. The upper housing  14  has an inflow pipe  17  fitted thereto in a manner protruding outward in the radial direction of the fitting hole  16 , and the inflow pipe  17  has the downstream end portion of the bypass piping  9  connected thereto. The inflow pipe  17  connects with the interior of the fitting hole  16  and can introduce the clean air (bypass air) from the air cleaner  3  into the idle number-of-revolutions control device  12  through the bypass piping  9 . 
         [0022]    The upper housing  14  preferably has four outflow passages  19 , for example, formed therethrough so as to extend in the radial direction from the through hole  16 , the four outflow passages  19  preferably being arranged at intervals of nearly 90 degrees, for example, and connecting with the downstream sides of the throttle valves  11  in the bores of the corresponding throttle bodies  10 . In this manner, the bypass passage  8  for supplying the bypass air from the air cleaner  3  to the downstream side of the throttle valve  11  in the throttle body  10  is defined by a route passing the bypass piping  9 , the inflow pipe  17 , the fitting hole  16 , and the respective outflow passages  19  and extending to the downstream side of the throttle valve  11  in the throttle valve  10 . 
         [0023]    The upper housing  14  has an idle number of revolutions control valve (hereinafter referred to as an “ISC valve  21 ”) fitted thereinto from the upper end side of the fitting hole  16 . This ISC valve  21  has a plunger  22  arranged to be moved along the axial direction of the fitting hole  16  by a stepping motor, for example. The position of the plunger  22  is controlled by the stepping motor and hence the opening of each of the respective outflow passages  19  is controlled, whereby the quantity of air to be supplied to the downstream side of each throttle valve  11  at the time of an idle operation can be controlled. Here, the stepping motor of the ISC valve  21  has its motion controlled by the engine control unit. 
         [0024]    The lower housing  13  fitted with the idle number-of-revolutions control device  12  has a water collection portion  23  disposed coaxially with the fitting hole  16 . The water collection portion  23 , in this preferred embodiment, is arranged so as to pass through the lower housing  13  along the axial direction and has a plug  24  fitted therein from a lower surface side, thereby being sealed. The position at which the water collection portion  23  is disposed is a position lower in the vertical direction with respect to a portion in which the air entering along the radial direction into the fitting hole  16  from the inflow pipe  17  changes its direction to the axial direction toward the ISC valve  21 . In other words, the water collection portion  23  is constructed so as to be arranged outside a region through which the bypass air passes in a state where the water collection portion  23  connects with the bypass passage  8 . Thus, even if there is caused an event in which water is collected in the bypass passage  8 , the region through which the bypass air passes can be ensured to be free of contact with such collected water. 
         [0025]    In this regard, a portion acting as the water collection portion in this preferred embodiment, as shown in  FIG. 2 , in a strict sense, preferably has an area substantially equal to a depth formed in the lower housing  13  plus a thickness of the flange portion  14 A of the upper housing  14  side. 
         [0026]    The air intake device of the first preferred embodiment is preferably constructed in the manner described above. At the time of idling the engine, the outside air is taken into the air cleaner  3  by a negative pressure produced in the cylinder. The outside air is filtered by the element  4  in the air cleaner  3  and enters the clean side chamber  6 . A portion of the air passes through the bypass passage  8  and has its quantity measured by the ISC valve  21  and then is supplied to each cylinder. The ISC valve  21  displaces the plunger  22  in the axial direction on the basis of the publicly known control technique by the ECU (not shown) to control the opening of each outflow passage  19 . In this manner, the engine is controlled, for example, such that, as the cooling water temperature of the engine decreases, the idle number of revolutions increases, whereby a warming-up time can be made shorter. 
         [0027]    For example, when a vehicle runs on a snow covered path, the stirred-up snow and moisture can enter into the air cleaner. In this case, bypass air containing a large amount of moisture enters into the bypass piping  9  from the clean side chamber  6 . The bypass air enters into the fitting hole  16  of the idle number-of-revolutions control device  12  from the inflow pipe  17 , then changes its direction upward in the axial direction, passes through each outflow passage  19  being in a state where its opening is adjusted, and reaches the corresponding cylinder. 
         [0028]    In this preferred embodiment, when the bypass air enters into the upper housing  14  of the idle number-of-revolutions control device  12 , the bypass air impacts on a side opposite to the opening of the inflow pipe  17  in the hole wall of the fitting hole  16 , such that, along with such a decrease in a flow rate that is caused by the direction change of the bypass air after the impact, water easily tends to adhere to the surface of the wall on which the bypass air impacts. The water adhering to the surface of the wall runs down along the inclination of the impact wall by the action of the gravity and is collected in the water collection portion. Thus, the bypass air has moisture removed in the upstream portion before the bypass air has its quantity measured by the ISC valve  21 . Thus, this can prevent the possibility that the ISC valve  21  will cause an operating malfunction due to the water being frozen. Moreover, the water collection portion is disposed in a way to expand a portion of the bypass passage  8 , so that as long as water is not excessively collected, it is not closed by the water. Thus, the operation of the idle number-of-revolutions control can be ensured. 
         [0029]    Moreover, in this preferred embodiment, the water collection portion  23  is defined by the arrangement of the upper and lower housings  13 ,  14  of the idle number-of-revolutions control device  12 . This eliminates the need for disposing an external member exclusively for collecting water. In particular, the lower housing  13  is formed integrally with the throttle body  10 , which can contribute to a reduction in the number of parts. Further, the water collection portion  23 , in a strict sense, is arranged so as to extend over the lower housing  13  and the flange portion  14 A of the upper housing  14 , which can contribute to an increase in the capacity of the water collection portion  23 . Still further, the water collection portion  23  is arranged coaxially with the fitting hole  16  for fitting the ISC valve  21 , so that the water collection portion  23  can be formed simultaneously at the time of performing the work of forming the fitting hole  16 , and can thus be easily formed. In addition, in this preferred embodiment, the water collection portion  23  is positioned near the upper portion of the engine, so that water collected in the water collection portion  23  can be evaporated by the radiation heat from the engine. As a result, it is possible to reduce the capacity of the water collection portion  23 . In addition, in this preferred embodiment, when the water collection portion  23  is disposed in the engine department covered with the bonnet B, the radiation heat of the engine remains in the engine department and hence facilitates the evaporation action of the water in the water collection portion  23 . Thus, this can more effectively achieve a reduction in the size of the water collection portion  23 . 
       Second Preferred Embodiment 
       [0030]    Next, a second preferred embodiment of the present invention will be described with reference to  FIG. 4 . In the first preferred embodiment, the water collection portion  23  is provided in the housings  13 ,  14  of the idle number-of-revolutions control device  12 , but in the second preferred embodiment, a water collection portion  23 A is disposed outside the idle number-of-revolutions control device  12 . That is, the lower housing  13  has a through hole  25  formed therein coaxially with the fitting hole  16 , and the through hole  25  has an introduction pipe  26  inserted thereinto from below. The introduction pipe  26  protrudes downward from the lower housing  13  and is arranged to bend obliquely from its middle position. 
         [0031]    On the other hand, the bypass piping  9  connected to the clean side chamber  6  of the air cleaner  3  extends obliquely downward and rearward and has air piping  27  connected to its end portion, the air piping  27  having its tip portion branched into two portions. One branch portion  27 A of the air piping  27  is bent to the bent end side of the introduction pipe  26 , and both of the branch portion  27 A and the bent end side are connected to each other by a connection tube  28 . The other branch portion  27 B is directed obliquely downward and rearward and has a water storage tube  29  connected thereto in a nearly longitudinal position, the water storage tube  29  having a water collection portion  23 A formed therein. The water storage tube  29  has a closed end and can be connected to the other branch portion  27 B so as to be freely removed (but may be connected so as not to be removed) The water storage tube  29  is disposed at the lowest position between the connection pipe  7  of the air cleaner  3  and the idle number-of-revolutions control device  12  of the bypass passage  8 . 
         [0032]    The other features are preferably the same as in the first preferred embodiment. According to the second preferred embodiment, the water collection portion  23 A is disposed at the lowest position in the upstream portion of the idle number-of-revolutions control device  12  of the bypass passage  8  and hence can automatically collect water in the bypass passage  8 . Moreover, unlike the first preferred embodiment, the water collection portion  23 A is formed separately from the idle number-of-revolutions control device  12  so as to branch the air piping  27 . Thus, this can provide the advantage that the idle number-of-revolutions control device  12  is not forced to be changed to have a special structure. Further, since the water storage tube  29  can be removed, the water storage tube  29  can be also removed at an appropriate time for draining water. In this case, if the water storage tube  29  is formed of transparent material, the amount of collected water can be visually determined from the outside and hence the water can be drained from the water storage tube  29  at the appropriate time. 
       Third Preferred Embodiment 
       [0033]    Next, a third preferred embodiment of the present invention will be described with reference to  FIG. 5 . In the second preferred embodiment, the water collection portion  23 A is preferably disposed in the water storage tube  29  that is a separate member from the air piping  27 , but in the third preferred embodiment, the water collection portion  23 A is preferably formed integrally with the air piping  27 . A lower end of the other branch portion  27 B in the air piping  27  preferably has a bulged, substantially spherical shape and has a water collection portion  23 B formed therein. This water collection portion  23 B, as in the second preferred embodiment, is also disposed at the lowest position between the connection pipe  7  of the air cleaner  3  and the idle number-of-revolutions control device  12  of the bypass passage  8 . Thus, the water produced in the bypass passage  8  can be automatically collected in the water collection portion  23 B. Here, the water collection portion  23 B is disposed at a position comparatively close to the engine, so that the water in the water collection portion  23 B is evaporated by the radiation heat from the engine. 
       Other Preferred Embodiments 
       [0034]    The present invention is not limited to the preferred embodiments described above and with reference to the drawings, but for example, the following preferred embodiments are included in the technical scope of the present invention. Further, in addition to the following preferred embodiments, the present invention can be variously modified and put into practice without departing from the spirit and scope of the present invention. 
         [0035]    In any one of the preferred embodiments described above, it has been described in which the present invention is preferably applied to the snowmobile, but the present invention can be widely applied to other vehicles such as a motorcycle or any other vehicles. 
         [0036]    In the above preferred embodiments, it has been described in which the present invention is preferably applied to a four-cylinder engine, but it should be noted that the number of cylinders is not limited to four. 
         [0037]    While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
An air intake device of an engine includes a throttle body provided in an intake passage of an engine, a bypass passage arranged to connect an upstream side and a downstream side of a throttle valve disposed in the throttle body, an idle number-of-revolutions control device that is disposed in the bypass passage and that controls the quantity of air passing through the bypass passage and flowing into the downstream side of the throttle valve according to the state of the engine, and a water collection portion that is disposed on the upstream side of the idle number-of-revolutions control device in the bypass passage and that is constructed so as to include a space portion connecting with the bypass passage. This structure enables smooth operation of the idle number-of-revolutions control device and prevents damage thereto caused by water in a bypass passage.