Patent Publication Number: US-10314446-B2

Title: Suction unit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Japan application serial no. 2016-094466, filed on May 10, 2016, and Japan application serial no. 2016-256648, filed on Dec. 28, 2016. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a suction unit for sucking air. 
     2. Description of the Related Art 
     A known electric vacuum cleaner is disclosed in JP-A 2015-192876. This electric vacuum cleaner includes a case including a suction inlet for air and a discharge outlet for air, and further includes an electric blower and a suction unit arranged on an upstream side of the electric blower in the case. 
     A suction passage that connects the suction inlet and a connection opening is defined in the suction unit, and the connection opening is arranged opposite to an air inlet (not shown) of the electric blower. In addition, a filter is arranged between the suction inlet and the connection opening. Left and right drive wheels and a trailer wheel are attached to a bottom surface of the case, and the case is thus able to travel on a floor in a room. 
     If an operation switch of the electric vacuum cleaner having the above-described structure is operated to drive the electric blower, air including waste, such as, for example, dust, is sucked into the suction passage through the suction inlet, and the dust is caught by the filter. Air which has passed through the filter is sucked into the electric blower through the connection opening, and is discharged out of the case through the discharge outlet. The floor is thus cleaned. 
     However, the above suction unit in related art has a problem in that a turbulent flow of air occurs in the vicinity of the connection opening, resulting in reduced suction efficiency of the suction unit. 
     SUMMARY OF THE INVENTION 
     A suction unit according to a preferred embodiment of the present invention is a suction unit to be provided in an electric vacuum cleaner including an electric blower, the suction unit including a suction inlet arranged to extend in a predetermined longitudinal direction, and arranged opposite to a surface to be cleaned; a connection opening to be connected to the electric blower; a suction passage arranged to extend along a center line joining a middle of the suction inlet in the longitudinal direction and a middle of the connection opening in the longitudinal direction to connect the suction inlet and the connection opening; and a plurality of first partition walls each of which is arranged in the suction passage, and is arranged to extend from a side on which the connection opening is defined to a side on which the suction inlet is defined. The suction passage includes a first main passage having the center line of the suction passage passing therethrough; and a plurality of first division passages arranged on both outer sides of the first main passage with respect to the longitudinal direction with one of the first partition walls being arranged between the first main passage and an adjacent one of the first division passages on either side of the first main passage. The first main passage and the first division passages are divided from one another in the longitudinal direction of the suction inlet by the first partition walls. 
     The suction unit according to the above preferred embodiment of the present invention is able to achieve improved suction efficiency. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an electric vacuum cleaner including a suction unit according to a first preferred embodiment of the present invention. 
         FIG. 2  is a bottom view of the electric vacuum cleaner including the suction unit according to the first preferred embodiment of the present invention. 
         FIG. 3  is a side sectional view of the electric vacuum cleaner including the suction unit according to the first preferred embodiment of the present invention. 
         FIG. 4  is a perspective view of the suction unit according to the first preferred embodiment of the present invention. 
         FIG. 5  is a sectional plan view of the suction unit according to the first preferred embodiment of the present invention. 
         FIG. 6  is a graph showing a result of a simulation of an air pressure distribution in a suction inlet of the suction unit according to the first preferred embodiment of the present invention. 
         FIG. 7  is a sectional plan view of a suction unit according to a second preferred embodiment of the present invention. 
         FIG. 8  is a perspective view of a suction unit according to a third preferred embodiment of the present invention. 
         FIG. 9  is a sectional plan view of the suction unit according to the third preferred embodiment of the present invention. 
         FIG. 10  is a sectional plan view of a suction unit according to a modification of the third preferred embodiment of the present invention. 
         FIG. 11  is a sectional plan view of a suction unit according to a fourth preferred embodiment of the present invention. 
         FIG. 12  is a sectional front view of a suction nozzle of a suction unit according to a fifth preferred embodiment of the present invention. 
         FIG. 13  is a sectional front view of a suction nozzle of a suction unit according to a sixth preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is assumed herein that a direction toward a floor F (i.e., a surface to be cleaned) illustrated in  FIG. 3  is a downward direction, while a direction away from the floor F is an upward direction. It is also assumed herein that, with respect to a front-rear direction, a direction leading from an electric blower  7  to a suction inlet  4  is a forward direction, while a direction leading from the suction inlet  4  to the electric blower  7  is a rearward direction. It is also assumed herein that a direction perpendicular to the front-rear direction and parallel to the floor F is a right-left direction (i.e., a longitudinal direction). It is also assumed herein that a surface parallel to the front-rear direction and perpendicular to the right-left direction is referred to as a “side surface”. It is also assumed herein that an upstream side and a downstream side are defined with respect to a direction in which air sucked in through the suction inlet  4  when the electric blower  7  is in operation flows. It is also assumed herein that the wording “the suction inlet  4  arranged opposite to the floor F (i.e., the surface to be cleaned)” and the like can refer to a situation in which the suction inlet  4  and the floor F face each other with another member (e.g., a rotary brush, etc.) arranged therebetween, in addition to a situation in which the suction inlet  4  and the floor F face each other directly with no other member arranged between the suction inlet  4  and the floor F. 
     An electric vacuum cleaner  1  according to a first preferred embodiment of the present invention will be described below.  FIGS. 1, 2, and 3  are a perspective view, a bottom view, and a side sectional view, respectively, of the electric vacuum cleaner  1  according to the first preferred embodiment. The electric vacuum cleaner  1  is a so-called robot-type electric vacuum cleaner, and includes a case  2  which is substantially circular in a horizontal section (i.e., a section parallel to the floor F). 
     A display portion  15  and an operation portion  16  are arranged in an upper surface of the case  2 . The operation portion  16  includes a plurality of buttons (not shown). By operating the operation portion  16 , a user can, for example, issue an instruction to turn on or off the electric vacuum cleaner  1 , issue an instruction to change the rotation rate of the electric blower  7 , which will be described below, or enter a condition, such as, for example, a time at which the electric vacuum cleaner  1  is to start cleaning. The display portion  15  includes, for example, a liquid crystal display panel or the like, and displays, for example, the condition entered with the operation portion  16 . 
     In addition, a position sensor (not shown) is arranged in the upper surface of the case  2 . The position sensor is used to detect the position of the electric vacuum cleaner  1  in a room, for example. 
     The suction inlet  4 , which is arranged to extend in the right-left direction (i.e., a longitudinal direction A), is defined in a bottom surface (i.e., a lower surface) of the case  2 , and a discharge outlet  5 , which is arranged to extend in the right-left direction, is defined in a rear portion of the case  2 . The suction inlet  4  is arranged opposite to the floor F (i.e., the surface to be cleaned) inside the room, and the discharge outlet  5  is arranged to face obliquely rearward and upward from the case  2 . A rotary brush (not shown) is arranged in the vicinity of the suction inlet  4  in a bottom portion of the case  2 . Note that the rotary brush may alternatively be arranged in the suction inlet  4 . 
     An air passage  6 , which connects the suction inlet  4  and the discharge outlet  5 , is arranged inside of the case  2 . The electric blower  7 , which is arranged to produce an air flow, is arranged in the air passage  6 . Once the electric blower  7  is driven, air in the room flows into the air passage  6  through the suction inlet  4  as indicated by arrows S, and is sent out into the room through the discharge outlet  5 . A centrifugal fan is preferably used as the electric blower  7 , but other types of electric blowers, such as, for example, an axial fan, may alternatively be used. 
     In the case  2 , a suction unit  100  is arranged on the upstream side of the electric blower  7 , and the suction unit  100  includes a suction passage  102 , a dust collection portion  8 , and a filter  9 . The suction unit  100  is provided in, for example, the electric vacuum cleaner  1  including the electric blower  7 . 
     The suction passage  102  defines a channel on the upstream side of the electric blower  7  in the air passage  6 , and connects the suction inlet  4  and a connection opening  101 . The connection opening  101  is arranged opposite to an air inlet (not shown) of the electric blower  7 , and air flowing in the suction passage  102  is sucked into the electric blower  7  through the connection opening  101 . That is, the connection opening  101  is connected to the electric blower  7 . The suction passage  102  is divided into a first suction passage  102   a , a second suction passage  102   b , and a third suction passage  102   c , which are arranged in the order named from the upstream side to the downstream side with respect to a direction in which the air flows. 
     The first suction passage  102   a  is defined by a suction nozzle  20 , which is detachably fitted in the case  2 , and the first suction passage  102   a  is arranged to connect the suction inlet  4  and an outlet  22 , which is open at a downstream end of the suction nozzle  20 . The suction inlet  4  is arranged to extend in the predetermined longitudinal direction A, and is arranged opposite to the floor F (i.e., the surface to be cleaned). The width of the outlet  22  measured in the longitudinal direction A is arranged to be smaller than the width of the suction inlet  4  measured in the longitudinal direction A (see  FIG. 5 ). 
     The first suction passage  102   a  is arranged to extend upward from the suction inlet  4  and curve rearward, and is connected to the second suction passage  102   b  through the outlet  22 . 
     The second suction passage  102   b  is arranged on the downstream side of the first suction passage  102   a , and the dust collection portion  8  is arranged below the second suction passage  102   b . An upper side of a front portion of the dust collection portion  8  is covered with the suction nozzle  20 , and an upper side of a rear portion of the dust collection portion  8  is open and in communication with the second suction passage  102   b . That is, the dust collection portion  8  is arranged below the suction passage  102 , and the rear portion of the dust collection portion  8  is arranged to open into a portion of the suction passage  102  on the upper side thereof. 
     The second and third suction passages  102   b  and  102   c  are arranged to be in communication with each other through the filter  9 . The filter  9  is arranged to extend up to a bottom surface of the dust collection portion  8  to cover the entire rear side of the dust collection portion  8 . An airway  108  is arranged below the third suction passage  102   c , and the airway  108  and the dust collection portion  8  are arranged to be in communication with each other through the filter  9 . 
     Each of the third suction passage  102   c  and the airway  108  is arranged to decrease in a channel width (i.e., width in the longitudinal direction A) toward the connection opening  101 , and the connection opening  101  is arranged to face obliquely forward and upward. 
     Dust included in air flowing from the second suction passage  102   b  into the third suction passage  102   c  is caught by the filter  9 , and is collected in the dust collection portion  8 , which is defined in the shape of a container. Air which has flowed from the second suction passage  102   b  into the third suction passage  102   c  through the filter  9 , and air which has flowed from the dust collection portion  8  into the airway  108  through the filter  9 , are sucked into the electric blower  7  through the connection opening  101 . Each of the suction nozzle  20 , the dust collection portion  8 , and the filter  9  is detachably fitted in the case  2 . 
     Left and right drive wheels  19   a  are arranged at left and right end portions of the bottom surface of the case  2 . A trailer wheel  19   b , which is defined by a caster, is arranged at a front end portion of the bottom surface of the case  2 . Each drive wheel  19   a  is connected to a drive motor (not shown). The case  2  is thus able to travel on the floor F. 
     In addition, the electric vacuum cleaner  1  includes a control portion (not shown) which controls various portions of the electric vacuum cleaner  1 . The electric blower  7 , the display portion  15 , the operation portion  16 , the drive motor, the position sensor, a storage portion, and so on are connected to the control portion. The storage portion is arranged to store a control program for the electric vacuum cleaner  1  and, in addition, the condition entered with the operation portion  16  and so on. 
     A power supply portion  11  including a secondary battery and so on is arranged in a front portion of the case  2 . The power supply portion  11  is arranged to supply power to the electric blower  7 , the control portion, the drive motor, and so on, and includes a case-side contact point (not shown) exposed in the bottom surface of the case  2 . The case-side contact point is arranged to make contact with a charger stand-side contact point of a charger stand (not shown) connected to a commercial power supply (not shown). The secondary battery of the power supply portion  11  is thus charged through the charger stand. Before a cleaning operation is started, the electric vacuum cleaner  1  is placed on the charger stand. 
       FIGS. 4 and 5  are a perspective view and a sectional plan view, respectively, of the suction unit  100 . The suction passage  102  is arranged to extend along a center line CT, which joins a middle of the suction inlet  4  in the longitudinal direction A, a middle of the outlet  22  in the longitudinal direction A, and a middle of the connection opening  101  in the longitudinal direction A, to connect the suction inlet  4  and the connection opening  101 . 
     Upper surfaces of the first, second, and third suction passages  102   a ,  102   b , and  102   c  are defined by an upper wall  28   a , and left and right surfaces thereof are defined by a side wall  28   c  and a side wall  28   d , respectively. In addition, a lower surface of the first suction passage  102   a  is defined by a lower wall  28   b . Lower sides of the second and third suction passages  102   b  and  102   c  are not defined by the lower wall  28   b , but are open and in communication with the dust collection portion  8  and the airway  108 , respectively. 
     Each of the upper wall  28   a  and the lower wall  28   b  is arranged to slant in such a manner as to increase in height as the upper wall  28   a  or the lower wall  28   b  extends rearward along the first suction passage  102   a , and air which has flowed into the first suction passage  102   a  through the suction inlet  4  is guided upward and rearward, and passes through the outlet  22 . 
     A bottom surface of the airway  108  is also arranged to slant in such a manner as to increase in height as the bottom surface extends rearward, and the air which has flowed from the dust collection portion  8  into the airway  108  is guided upward and rearward, and is sucked into the connection opening  101 . 
     In the first suction passage  102   a , a plurality of (two in the present preferred embodiment) partition walls (i.e., second partition walls)  25  are arranged side by side in the longitudinal direction A. An upper end and a lower end of each partition wall  25  are arranged to be continuous with the upper wall  28   a  and the lower wall  28   b , respectively, and are arranged to extend from the suction inlet  4  to the outlet  22 . 
     As a result, the first suction passage  102   a  is divided into a main passage (i.e., a second main passage)  21   a  and a plurality of (two in the present preferred embodiment) division passages (i.e., second division passages)  21   b  and  21   c . The main passage  21   a  has the center line CT of the suction passage  102  passing therethrough. The division passages  21   b  and  21   c  are arranged on both outer sides of the main passage  21   a  with respect to the longitudinal direction A with one of the partition walls  25  being arranged between the main passage  21   a  and an adjacent one of the division passages  21   b  and  21   c  on either side of the main passage  21   a.    
     That is, the suction unit  100  includes the plurality of partition walls (i.e., the second partition walls)  25 , each of which is arranged in the suction passage  102  and is arranged to extend from a side on which the suction inlet  4  is defined to a side on which the connection opening  101  is defined, and the suction passage  102  includes the main passage (i.e., the second main passage)  21   a , which has the center line CT of the suction passage  102  passing therethrough, and the plurality of division passages (i.e., the second division passages)  21   b  and  21   c , which are arranged on both outer sides of the main passage  21   a  with respect to the longitudinal direction A with one of the partition walls  25  being arranged between the main passage  21   a  and an adjacent one of the division passages  21   b  and  21   c  on either side of the main passage  21   a , the main passage  21   a  and the division passages  21   b  and  21   c  being divided from one another in the longitudinal direction A of the suction inlet  4  by the partition walls  25 . This prevents a narrowing of a channel on a side closer to the air inlet of the electric blower  7  from causing flows of air sucked in through both end portions of the suction inlet  4  with respect to the longitudinal direction A to abruptly bend toward the center line CT immediately after entering into the first suction passage  102   a , and thus contributes to reducing turbulence in the air. 
     In addition, the suction inlet  4  is divided by the partition walls  25  into suction inlets  4   a ,  4   b , and  4   c . The suction inlets  4   a ,  4   b , and  4   c  are arranged at upstream ends of the main passage  21   a , the division passage  21   b , and the division passage  21   c , respectively. Each of the suction inlets  4   b  and  4   c  is arranged adjacent to the suction inlet  4   a.    
     Each partition wall  25  is arranged to curve in such a direction as to decrease the width of the main passage  21   a  measured in the longitudinal direction A in the vicinity of the suction inlet  4 , and then extend in a direction substantially perpendicular to the longitudinal direction A from the upstream side to the downstream side with respect to the direction in which the air flows. 
     In addition, each of the side walls  28   c  and  28   d  is arranged to curve in such a direction as to decrease the width of the first suction passage  102   a  measured in the longitudinal direction A and extend along an adjacent one of the partition walls  25  in the vicinity of the suction inlet  4  of the first suction passage  102   a , and then extend in a direction substantially perpendicular to the longitudinal direction A from the upstream side to the downstream side with respect to the direction in which the air flows. 
     Thus, upstream portions and downstream portions of the division passages  21   b  and  21   c  are arranged to have equal channel widths. That is, the upstream portions of the division passages (i.e., the second division passages)  21   b  and  21   c  are arranged to have equal channel widths. Note that the term “equal” as used herein includes both “exactly equal” and “substantially equal”. 
     In addition, a width W 20  of the suction passage  102  measured in the longitudinal direction A of the suction inlet  4  is arranged to be smaller than a width W 21  of the dust collection portion  8  measured in the longitudinal direction A of the suction inlet  4 . As a result, a space in which a handle or the like is arranged can be secured above an upper surface of the dust collection portion  8 . 
     In addition, an upstream end of each partition wall  25  is arranged outward of a downstream end thereof with respect to the longitudinal direction A, so that a width W 1  of the main passage  21   a  at the suction inlet  4   a  measured in the longitudinal direction A is greater than a width W 2  of the main passage  21   a  at the outlet  22  measured in the longitudinal direction A. 
     In addition, a width W 3  of the suction inlet  4   b  measured in the longitudinal direction A and a width W 5  of the suction inlet  4   c  measured in the longitudinal direction A are arranged to be substantially equal to each other, and the width W 1  of the suction inlet  4   a  is arranged to be greater than the width W 3  of the suction inlet  4   b  and the width W 5  of the suction inlet  4   c . A width W 4  of the division passage  21   b  at the outlet  22  measured in the longitudinal direction A and a width W 6  of the division passage  21   c  at the outlet  22  measured in the longitudinal direction A are arranged to be substantially equal to each other. In addition, each of the width W 4  of the division passage  21   b  at the outlet  22  and the width W 6  of the division passage  21   c  at the outlet  22  is arranged to be smaller than the width W 2  of the main passage  21   a  at the outlet  22 . 
     In the third suction passage  102   c , a plurality of (two in the present preferred embodiment) partition walls (i.e., first partition walls)  125  are arranged side by side in the longitudinal direction A. An upper end and a lower end of each partition wall  125  are arranged to be continuous with the upper wall  28   a  and the bottom surface of the airway  108 , respectively, and are arranged to extend from the side on which the connection opening  101  is defined to the filter  9 . An upstream end of each partition wall  125  is arranged to be in contact with the filter  9 . That is, the upstream end of each partition wall (i.e., each first partition wall)  125  is arranged on a side of a channel midpoint between the suction inlet  4  and the connection opening  101  in the suction passage  102  closer to the connection opening  101 . In addition, a lower end of the upstream end of each partition wall  125  is arranged at a level lower than that of a lower end of a downstream end of the partition wall  125 . Further, the upstream end of each partition wall (i.e., each first partition wall)  125  and the downstream end of each partition wall (i.e., each second partition wall)  25  are spaced from each other. 
     Thus, the third suction passage  102   c  is divided into a main passage (i.e., a first main passage)  121   a  and a plurality of (two in the present preferred embodiment) division passages (i.e., first division passages)  121   b  and  121   c . The main passage  121   a  has the center line CT of the suction passage  102  passing therethrough. The division passages  121   b  and  121   c  are arranged on both outer sides of the main passage  121   a  with respect to the longitudinal direction A with one of the partition walls  125  being arranged between the main passage  121   a  and an adjacent one of the division passages  121   b  and  121   c  on either side of the main passage  121   a.    
     That is, the suction unit  100  includes the suction passage  102 , which is arranged to extend along the center line CT joining the middle of the suction inlet  4  in the longitudinal direction A and the middle of the connection opening  101  in the longitudinal direction A to connect the suction inlet  4  and the connection opening  101 , and the plurality of partition walls (i.e., the first partition walls)  125 , each of which is arranged in the suction passage  102  and is arranged to extend from the side on which the connection opening  101  is defined to the side on which the suction inlet  4  is defined, and the suction passage  102  includes the main passage (i.e., the first main passage)  121   a , which has the center line CT of the suction passage  102  passing therethrough, and the plurality of division passages (i.e., the first division passages)  121   b  and  121   c , which are arranged on both outer sides of the main passage  121   a  with respect to the longitudinal direction A with one of the partition walls  125  being arranged between the main passage  121   a  and an adjacent one of the division passages  121   b  and  121   c  on either side of the main passage  121   a , the main passage  121   a  and the division passages  121   b  and  121   c  being divided from one another in the longitudinal direction A of the suction inlet  4  by the partition walls  125 . 
     In addition, an edge of the connection opening  101  is divided into connection portions  101   a ,  101   b , and  101   c  by the partition walls  125 . The connection portions  101   a ,  101   b , and  101   c  are arranged at downstream ends of the main passage  121   a  and the division passages  121   b  and  121   c , respectively. Each of the connection portions  101   b  and  101   c  is arranged adjacent to the connection portion  101   a.    
     Each partition wall  125  is arranged to extend from the upstream end thereof in a direction substantially perpendicular to the longitudinal direction A from the upstream side to the downstream side with respect to the direction in which the air flows, and then bend to the side of the center line CT (i.e., inward with respect to the longitudinal direction A) and extend in a straight line toward the connection opening  101 . 
     In addition, at the third suction passage  102   c , each of the side walls  28   c  and  28   d  is arranged to extend in a direction substantially perpendicular to the longitudinal direction A along an adjacent one of the partition walls  125  from the upstream side to the downstream side with respect to the direction in which the air flows, and then bend to the side of the center line CT (i.e., inward with respect to the longitudinal direction A) and extend in a straight line toward the connection opening  101 . 
     Thus, upstream portions and downstream portions of the division passages  121   b  and  121   c  are arranged to have equal channel widths. That is, the upstream portions of the division passages (i.e., the first division passages)  121   b  and  121   c  are arranged to have equal channel widths. Note that the term “equal” as used herein includes both “exactly equal” and “substantially equal”. 
     In addition, the downstream end of each partition wall  125  is arranged inward of the upstream end thereof with respect to the longitudinal direction A, so that a width W 11  of the main passage  121   a  at the downstream end thereof measured in the longitudinal direction A is smaller than a width W 12  of the main passage  121   a  at an upstream end thereof measured in the longitudinal direction A. 
     In addition, a width W 13  of the connection portion  101   b  and a width W 15  of the connection portion  101   c  are arranged to be equal to each other, and the width W 11  of the connection portion  101   a  is arranged to be smaller than the width W 13  of the connection portion  101   b  and the width W 15  of the connection portion  101   c . That is, the width W 11  of the downstream end of the main passage (i.e., the first main passage)  121   a  is different from each of the widths W 13  and W 15  of the downstream ends of the division passages (i.e., the first division passages)  121   b  and  121   c , respectively. A width W 14  of an upstream end of the division passage  121   b  measured in the longitudinal direction A and a width W 16  of an upstream end of the division passage  121   c  measured in the longitudinal direction A are arranged to be equal to each other. In addition, each of the widths W 14  and W 16  of the upstream ends of the division passages  121   b  and  121   c , respectively, is arranged to be smaller than the width W 12  of the upstream end of the main passage  121   a . Note that the term “equal” as used herein includes both “exactly equal” and “substantially equal”. 
     In addition, the width W 12  of the main passage  121   a  at the upstream end thereof measured in the longitudinal direction A is arranged to be equal to the width W 2  of the main passage  21   a  at the outlet  22  measured in the longitudinal direction A. In addition, the widths W 14  and W 16  of the upstream ends of the division passages  121   b  and  121   c , respectively, are arranged to be equal to, respectively, the widths W 4  and W 6  of the division passages  21   b  and  21   c , respectively, at the outlet  22 . Note that the term “equal” as used herein includes both “exactly equal” and “substantially equal”. 
     Note that each of the number of partition walls  25  and the number of partition walls  125  is not limited to two, but may alternatively be an even number equal to or greater than four. In this case, each of the first suction passage  102   a  and the third suction passage  102   c  is divided into one main passage and an even number of division passages, the even number being equal to or greater than four. 
     If a cleaning start time previously stored in the storage portion of the electric vacuum cleaner  1  having the above-described structure comes, the case  2  leaves the charger stand and automatically travels on the floor F. At this time, the electric blower  7  is driven, and the rotary brush is caused to rotate. The cleaning operation of the electric vacuum cleaner  1  is thus started. Air flows including dust on the floor F enter into the main passage  21   a  and the division passages  21   b  and  21   c  through the suction inlets  4   a ,  4   b , and  4   c , respectively, as indicated by arrows S (see  FIG. 5 ). 
     At this time, the upstream portions and the downstream portions of the division passages  21   b  and  21   c  are arranged to have equal channel widths, and this contributes to preventing a suction force in each of the division passages  21   b  and  21   c  from decreasing from the upstream side toward the downstream side with respect to the direction in which the air flows. 
     In addition, the width W 1  of the suction inlet  4   a  of the main passage  21   a , where turbulence does not easily occur, is arranged to be greater than the widths W 3  and W 5  of the suction inlets  4   b  and  4   c , respectively, and this leads to improved suction efficiency of the suction nozzle  20 . 
     In addition, after passing in the main passage  21   a  and the division passages  21   b  and  21   c , the air flows enter into the second suction passage  102   b  through the outlet  22 . A portion of the air flows passing in the second suction passage  102   b  enters into the dust collection portion  8 . Dust D in the air is caught by the filter  9 , and is collected in the dust collection portion  8  (see  FIG. 3 ). 
     At this time, due to the dust collection portion  8  being arranged below the suction passage  102 , and the rear portion of the dust collection portion  8  being arranged to open into the suction passage  102  on the upper side, the suction unit  100  is able to easily achieve improved suction efficiency and cleaning efficiency. 
     In addition, due to the dust collection portion  8  being arranged below the suction passage  102 , the air flows in a laminar state in the suction passage  102 . Accordingly, the dust D can be smoothly sucked in through even the suction inlets  4   b  and  4   c  at both end portions with respect to the longitudinal direction A without an increase in the rotation rate of the electric blower  7 . This contributes to reducing turbulence in the dust collection portion  8 , and preventing the dust D accumulated in the dust collection portion  8  from being rescattered. 
     The air which has flowed from the second suction passage  102   b  into the third suction passage  102   c  through the filter  9  is sucked into the electric blower  7  through the connection opening  101 . In addition, air in the dust collection portion  8  flows into the airway  108  through the filter  9 , and is sucked into the electric blower  7  through the connection opening  101 . The air passes through the electric blower  7 , and is discharged out of the case  2  through the discharge outlet  5 . The floor F is cleaned in the above-described manner. 
     At this time, the partition walls  125 , extending from the connection opening  101  in the third suction passage  102   c , contribute to reducing the likelihood of an occurrence of turbulence in the vicinity of the connection opening  101 . Thus, the air flows can smoothly enter into the connection opening  101  from the main passage  121   a  and the division passages  121   b  and  121   c  resulting in improved suction efficiency of the suction unit  100 . 
     In addition, the upstream end of each partition wall  125  is arranged on the side of the channel midpoint between the suction inlet  4  and the connection opening  101  in the suction passage  102  closer to the connection opening  101 . This contributes to further reducing the likelihood of the occurrence of turbulence in the vicinity of the connection opening  101 , and to a smoother flow of air. 
     In addition, the division passages  121   b  and  121   c  are arranged to have equal channel widths, and the widths W 13  and W 15  of the downstream ends of the division passages  121   b  and  121   c  on the left and right sides, respectively, are equal to each other. This causes suction forces of equivalent magnitude to act in the division passages  121   b  and  121   c , resulting in improved suction efficiency of the suction unit  100 . 
     In addition, the lower end of the upstream end of each partition wall  125  is arranged at a level lower than that of the lower end of the downstream end of the partition wall  125 , and this enables an air flow passing upward and toward the connection opening  101  in the third suction passage  102   c  to smoothly enter into the connection opening  101 . 
     In addition, the upstream end of each partition wall (i.e., each first partition wall)  125  and the downstream end of each partition wall (i.e., each second partition wall)  25  are spaced from each other, and this contributes to reducing the likelihood of an occurrence of an air flow passing upward from the dust collection portion  8  into the second suction passage  102   b , enabling air to flow in the laminar state in the second suction passage  102   b . This leads to improved suction efficiency of the suction unit  100 . 
     In addition, the upstream portions of the division passages (i.e., the first division passages)  121   b  and  121   c  and the downstream portions of the division passages (i.e., the second division passages)  21   b  and  21   c  are arranged to have equal channel widths, and this contributes to preventing suction forces in the upstream portions of the division passages (i.e., the first division passages)  121   b  and  121   c  and the downstream portions of the division passages (i.e., the second division passages)  21   b  and  21   c  from decreasing from the upstream side toward the downstream side with respect to the direction in which the air flows. 
     In addition, the width W 1  of the upstream end of the main passage (i.e., the second main passage)  21   a  measured in the longitudinal direction A is arranged to be greater than the width W 11  of the downstream end of the main passage (i.e., the first main passage)  121   a  measured in the longitudinal direction A. This contributes to increasing suction forces acting in the main passage (i.e., the second main passage)  21   a  and the main passage (i.e., the first main passage)  121   a . This leads to improved suction efficiency of the suction unit  100 . 
     After traveling over the entire floor F while keeping the electric blower  7  in operation, the electric vacuum cleaner  1  returns to the charger stand, and the electric blower  7  is stopped. The cleaning operation of the electric vacuum cleaner  1  is thus completed. 
       FIG. 6  is a graph showing a result of a simulation of an air pressure distribution in the suction inlet  4 . The vertical axis represents the suction force (measured in Pa), while the horizontal axis represents the position in the suction inlet  4  along the longitudinal direction A. A division ranging from 200 to 800 units along the horizontal axis shows an air velocity distribution in the suction inlet  4   a , and a division ranging from 0 to 200 units along the horizontal axis shows an air velocity distribution in the suction inlet  4   b . In addition, a division ranging from 800 to 1000 units along the horizontal axis shows an air velocity distribution in the suction inlet  4   c.    
     A solid line C represents an air velocity distribution of the suction unit  100  according to the present preferred embodiment, while a broken line B represents an air velocity distribution of a suction unit according to a comparative example. In the suction unit according to the comparative example, the upstream portions and the downstream portions of the division passages  21   b  and  21   c  are not arranged to have equal channel widths, and the partition walls  125  are not provided. 
     Compared to the suction unit according to the comparative example, the suction unit  100  according to the present preferred embodiment exhibits an improvement in the suction forces over the entire extent of the suction inlet  4  in the longitudinal direction A. In addition, air velocity distributions were measured at a plurality of positions along the direction in which the air flows in each of the downstream portions of the division passages (i.e., the first division passages)  121   b  and  121   c . This measurement showed that a decrease in the suction force from the upstream side toward the downstream side in each of the division passages  21   b  and  21   c  occurs less easily in the suction unit  100  according to the present preferred embodiment than in the suction unit according to the comparative example. 
     The suction unit  100  according to the present preferred embodiment includes the plurality of partition walls (i.e., the first partition walls)  125 , which are arranged to extend from the connection opening  101  to the side on which the suction inlet  4  is defined in the suction passage  102  connecting the suction inlet  4  and the connection opening  101 , and includes the main passage (i.e., the first main passage)  121   a  having the center line CT of the suction passage  102  passing therethrough, and the plurality of division passages (i.e., the first division passages)  121   b  and  121   c  arranged on both outer sides of the main passage  121   a  with respect to the longitudinal direction A with one of the partition walls  125  being arranged between the main passage  121   a  and an adjacent one of the division passages  121   b  and  121   c  on either side of the main passage  121   a , the main passage  121   a  and the division passages  121   b  and  121   c  being divided from one another in the longitudinal direction A of the suction inlet  4  by the partition walls  125 . 
     Thus, the partition walls  125  extending from the connection opening  101  are arranged in the third suction passage  102   c , and this contributes to reducing the likelihood of the occurrence of turbulence in the vicinity of the connection opening  101 . Thus, the air flows can smoothly enter into the connection opening  101  from the main passage  121   a  and the division passages  121   b  and  121   c , resulting in improved suction efficiency of the suction unit  100 . 
     In addition, the upstream end of each partition wall  125  is arranged on the side of the channel midpoint between the suction inlet  4  and the connection opening  101  in the suction passage  102  closer to the connection opening  101 . This contributes to further reducing the likelihood of the occurrence of turbulence in the vicinity of the connection opening  101 , and to a smoother flow of air. 
     In addition, the width W 11  of the downstream end of the main passage  121   a  is arranged to be different from each of the widths W 13  and W 15  of the downstream ends of the division passages  121   b  and  121   c , respectively, and this leads to improved flexibility in designing the suction unit  100 . 
     In addition, the widths W 13  and W 15  of the downstream ends of the division passages  121   b  and  121   c  on the left and right sides, respectively, are equal to each other, and this causes suction forces of equivalent magnitude to act in the division passages  121   b  and  121   c . This leads to improved suction efficiency of the suction unit  100 . 
     In addition, due to the dust collection portion  8  being arranged below the suction passage  102 , and the rear portion of the dust collection portion  8  being arranged to open into the suction passage  102  on the upper side, the suction unit  100  is able to easily achieve improved suction efficiency and cleaning efficiency. 
     In addition, the lower end of the upstream end of each partition wall  125  is arranged at a level lower than that of the lower end of the downstream end of the partition wall  125 , and this enables an air flow passing upward and toward the connection opening  101  in the suction passage  102  to smoothly enter into the connection opening  101 . 
     In addition, the width W 20  of the suction passage  102  measured in the longitudinal direction A of the suction inlet  4  is arranged to be smaller than the width W 21  of the dust collection portion  8  measured in the longitudinal direction A of the suction inlet  4 , so that the space in which the handle or the like is arranged can be secured above the upper surface of the dust collection portion  8 . Further, the decrease in the width W 20  of the suction passage  102  measured in the longitudinal direction A of the suction inlet  4  results in, for example, a decrease in channel cross-sectional area of the suction passage  102  with decreasing distance from the connection opening  101 , reducing a reduction in pressure in the channel and a reduction in the suction force with decreasing distance from the connection opening  101 . 
     In addition, the suction unit  100  includes the plurality of partition walls (i.e., the second partition walls)  25 , each of which is arranged in the suction passage  102  and is arranged to extend from the suction inlet  4  to the side on which the connection opening  101  is defined, and includes the main passage (i.e., the second main passage)  21   a , which has the center line CT of the suction passage  102  passing therethrough, and the plurality of division passages (i.e., the second division passages)  21   b  and  21   c , which are arranged on both outer sides of the main passage  21   a  with respect to the longitudinal direction A with one of the partition walls  25  being arranged between the main passage  21   a  and an adjacent one of the division passages  21   b  and  21   c  on either side of the main passage  21   a , the main passage  21   a  and the division passages  21   b  and  21   c  being divided from one another in the longitudinal direction A of the suction inlet  4  by the partition walls  25 . 
     This contributes to reducing turbulence in the air in the vicinity of the suction inlet  4 , which is connected to the electric blower  7 . This leads to improved suction efficiency of the suction unit  100 . 
     In addition, the upstream end of each partition wall (i.e., each first partition wall)  125  and the downstream end of each partition wall (i.e., each second partition wall)  25  are spaced from each other, and this enables the air to flow in the laminar state in the suction passage  102 , leading to improved suction efficiency of the suction unit  100 . 
     In addition, the upstream portions of the division passages (i.e., the first division passages)  121   b  and  121   c  and the downstream portions of the division passages (i.e., the second division passages)  21   b  and  21   c  are arranged to have equal channel widths, and this contributes to preventing the suction forces in the upstream portions of the division passages (i.e., the first division passages)  121   b  and  121   c  and the downstream portions of the division passages (i.e., the second division passages)  21   b  and  21   c  from decreasing from the upstream side toward the downstream side with respect to the direction in which the air flows. 
     In addition, the width W 1  of the upstream end of the main passage (i.e., the second main passage)  21   a  measured in the longitudinal direction A is arranged to be greater than the width W 11  of the downstream end of the main passage (i.e., the first main passage)  121   a  measured in the longitudinal direction A. This contributes to increasing the suction forces acting in the main passage (i.e., the second main passage)  21   a  and the main passage (i.e., the first main passage)  121   a . This leads to improved suction efficiency of the suction unit  100 . 
     Next, a second preferred embodiment of the present invention will now be described below.  FIG. 7  is a sectional plan view of a suction unit  100  according to the second preferred embodiment. For the sake of convenience in description, members or portions that have their equivalents in the above-described first preferred embodiment illustrated in  FIGS. 1 to 6  are denoted by the same reference numerals as those of their equivalents in the first preferred embodiment. The second preferred embodiment is different from the first preferred embodiment in the shape of partition walls  125 . The second preferred embodiment is otherwise similar to the first preferred embodiment. 
     Each of division passages  121   b  and  121   c  is arranged to increase in a channel width with decreasing distance from a connection opening  101  in the vicinity of a downstream end thereof. 
     The present preferred embodiment is able to achieve beneficial effects similar to those of the first preferred embodiment. In addition, because each of the division passages  121   b  and  121   c  is arranged to increase in the channel width with decreasing distance from the connection opening  101 , turbulence in the vicinity of the connection opening  101  can be further reduced. Thus, air flows can more smoothly enter into the connection opening  101  from a main passage  121   a  and the division passages  121   b  and  121   c , resulting in improved suction efficiency of the suction unit  100 . 
     Next, a third preferred embodiment of the present invention will now be described below.  FIGS. 8 and 9  are a perspective view and a sectional plan view, respectively, of a suction unit  100  according to the third preferred embodiment. For the sake of convenience in description, members or portions that have their equivalents in the above-described first preferred embodiment illustrated in  FIGS. 1 to 6  are denoted by the same reference numerals as those of their equivalents in the first preferred embodiment. The third preferred embodiment is different from the first preferred embodiment in the shape of partition walls  25 . The third preferred embodiment is otherwise similar to the first preferred embodiment. 
     Each of the partition walls  25  is arranged to extend over both a first suction passage  102   a  and a second suction passage  102   b , with a downstream end of the partition wall  25  being continuous with an upstream end of a corresponding partition wall  125  with a filter  9  therebetween. In the second suction passage  102   b , each partition wall  25  is arranged to extend in a horizontal direction from a downstream end of a lower wall  28   b , and a lower end of the partition wall  25  is arranged above a dust collection portion  8 . That is, the upstream end of each partition wall (i.e., each first partition wall)  125  and the downstream end of the corresponding partition wall (i.e., the corresponding second partition wall)  25  are arranged to be continuous with each other. 
     The present preferred embodiment is able to achieve beneficial effects similar to those of the first preferred embodiment. In addition, the upstream end of each partition wall (i.e., each first partition wall)  125  is arranged to be continuous with the corresponding partition wall (i.e., the corresponding second partition wall)  25 , and this enables air to smoothly flow from a main passage  21   a  and division passages  21   b  and  21   c  into a main passage  121   a  and division passages  121   b  and  121   c , respectively. This contributes to preventing turbulence from occurring between the main passage  21   a  and the division passages  21   b  and  21   c  and, respectively, the main passage  121   a  and the division passages  121   b  and  121   c , and improving suction forces of the suction unit  100 . 
       FIG. 10  is a sectional plan view of a suction unit  100  according to a modification of the present preferred embodiment. Also in the present preferred embodiment, each of the division passages  121   b  and  121   c  may alternatively be arranged to increase in a channel width with decreasing distance from a connection opening  101  in the vicinity of a downstream end thereof, as in the second preferred embodiment. 
     Next, a fourth preferred embodiment of the present invention will now be described below.  FIG. 11  is a sectional plan view of a suction unit  100  according to the fourth preferred embodiment. For the sake of convenience in description, members or portions that have their equivalents in the above-described first preferred embodiment illustrated in  FIGS. 1 to 6  are denoted by the same reference numerals as those of their equivalents in the first preferred embodiment. The fourth preferred embodiment is different from the first preferred embodiment in the shape of partition walls  25  and  125 . The fourth preferred embodiment is otherwise similar to the first preferred embodiment. 
     In a first suction passage  102   a , a plurality of plate-shaped partition walls  25  are arranged side by side in the longitudinal direction A. Each partition wall  25  is arranged to extend over both the first suction passage  102   a  and a second suction passage  102   b , and is arranged to extend in a straight line from a side on which a suction inlet  4  is defined to a side on which a connection opening  101  is defined. 
     Meanwhile, in a third suction passage  102   c , a plurality of plate-shaped partition walls  125  are arranged side by side in the longitudinal direction A. Each partition wall  125  is arranged to extend in a straight line from the side on which the connection opening  101  is defined to the side on which the suction inlet  4  is defined, and a downstream end of each partition wall  25  is arranged to be continuous with an upstream end of a corresponding one of the partition walls  125  with a filter  9  therebetween. 
     Each of the partition walls  25  and  125  is defined by a plate perpendicular to an upper wall  28   a , and the partition walls  25 , which are two in number, and the partition walls  125 , which are also two in number, are arranged to incline in such a manner as to approach each other as they extend away from the suction inlet  4  toward the connection opening  101  in a front view. That is, each of the partition walls (i.e., the first partition walls)  125  and the partition walls (i.e., the second partition walls)  25  is in the shape of a plate, and each partition wall  25  and a corresponding one of the partition walls  125  are arranged to continuously extend in a straight line from the side on which the suction inlet  4  is defined to the side on which the connection opening  101  is defined. 
     The present preferred embodiment is able to achieve beneficial effects similar to those of the third preferred embodiment. In addition, each of the partition walls  25  and  125  is in the shape of a plate, and each partition wall  25  and the corresponding one of the partition walls  125  are arranged to extend in a straight line from the side on which the suction inlet  4  is defined to the side on which the connection opening  101  is defined. This contributes to easily preventing a separation of an air flow passing in each of main passages  21   a  and  121   a  and division passages  21   b ,  21   c ,  121   b , and  121   c  from any of the partition walls  25  and  125 , and further reducing the likelihood of an occurrence of turbulence, which leads to improved suction forces of the suction unit  100 . 
     Next, a fifth preferred embodiment of the present invention will now be described below.  FIG. 12  is a sectional front view of a suction nozzle  20  of a suction unit  100  according to the fifth preferred embodiment. For the sake of convenience in description, members or portions that have their equivalents in the above-described first preferred embodiment illustrated in  FIGS. 1 to 6  are denoted by the same reference numerals as those of their equivalents in the first preferred embodiment. The fifth preferred embodiment is different from the first preferred embodiment in the shape of partition walls  25 . The fifth preferred embodiment is otherwise similar to the first preferred embodiment. 
     Each partition wall  25  includes an upstream vertical portion  25   a , a first curved portion  25   b , a second curved portion  25   c , and a downstream vertical portion  25   d  arranged in the order named from the upstream side to the downstream side with respect to a direction in which air flows. The upstream vertical portion  25   a  is arranged at an upstream end of the partition wall  25 , and is arranged to be substantially perpendicular to the longitudinal direction A. That is, each partition wall  25  includes the upstream vertical portion  25   a , which is substantially perpendicular to the longitudinal direction A, at the upstream end thereof. The first curved portion  25   b  is defined continuously with a downstream side of the upstream vertical portion  25   a , and is arranged to curve so as to be convex away from a center line CT (i.e., outward in the longitudinal direction A). That is, each partition wall  25  includes the first curved portion  25   b , which is defined continuously with the downstream side of the upstream vertical portion  25   a  and is arranged to curve so as to be convex away from the center line CT. The second curved portion  25   c  is defined continuously with a downstream side of the first curved portion  25   b , and is arranged to curve so as to be convex toward the center line CT (i.e., inward in the longitudinal direction A). That is, each partition wall  25  includes the second curved portion  25   c , which is defined continuously with the downstream side of the first curved portion  25   b  and is arranged to curve so as to be convex toward the center line CT. The downstream vertical portion  25   d  is defined continuously with the second curved portion  25   c  at a downstream end, and is arranged to be substantially perpendicular to the longitudinal direction A. That is, each partition wall  25  includes, at the downstream end thereof, the downstream vertical portion  25   d , which is defined continuously with the second curved portion  25   c  and is arranged to be substantially perpendicular to the longitudinal direction A. 
     Thus, the upstream end of each partition wall  25  is arranged outward of the downstream end thereof with respect to the longitudinal direction A, so that a width W 1  of a main passage  21   a  at a suction inlet  4   a  measured in the longitudinal direction A is greater than a width W 2  of the main passage  21   a  at an outlet  22  measured in the longitudinal direction A. A width W 3  of a suction inlet  4   b  measured in the longitudinal direction A is smaller than a width W 4  of a division passage  21   b  at the outlet  22  measured in the longitudinal direction A. A width W 5  of a suction inlet  4   c  measured in the longitudinal direction A is smaller than a width W 6  of a division passage  21   c  at the outlet  22  measured in the longitudinal direction A. 
     The width W 3  of the suction inlet  4   b  and the width W 5  of the suction inlet  4   c  are arranged to be substantially equal to each other, and the width W 1  of the suction inlet  4   a  is arranged to be greater than the width W 3  of the suction inlet  4   b  and the width W 5  of the suction inlet  4   c . The width W 4  of the division passage  21   b  at the outlet  22  and the width W 6  of the division passage  21   c  at the outlet  22  are arranged to be substantially equal to each other. In addition, since each of the division passages  21   b  and  21   c  becomes wider on the downstream side, each of the width W 4  of the division passage  21   b  at the outlet  22  and the width W 6  of the division passage  21   c  at the outlet  22  approaches the width W 2  of the main passage  21   a  at the outlet  22 . In the present preferred embodiment, the width W 2  of the main passage  21   a  at the outlet  22 , the width W 4  of the division passage  21   b  at the outlet  22 , and the width W 6  of the division passage  21   c  at the outlet  22  are arranged to be substantially equal to one another. Note that the width W 3  of the suction inlet  4   b  and the width W 5  of the suction inlet  4   c  may be different from each other. 
     When a cleaning operation of an electric vacuum cleaner  1  is started, and air flows into the main passage  21   a  and the division passages  21   b  and  21   c  through the suction inlets  4   a ,  4   b , and  4   c , respectively, as indicated by arrows S, the upstream vertical portion  25   a  of each partition wall  25  contributes to reducing turbulence in the vicinity of the upstream end of the partition wall  25 . Thus, an air flow smoothly enters into each of the main passage  21   a  and the division passages  21   b  and  21   c . The air which has flowed into each of the main passage  21   a  and the division passages  21   b  and  21   c  flows along the first curved portion  25   b  and then the second curved portion  25   c . Thus, the air which has flowed into each of the division passages  21   b  and  21   c  is smoothly guided toward the center line CT. This contributes to reducing turbulence in the air in each of the division passages  21   b  and  21   c , and causing the air to flow more smoothly therein. 
     In addition, because the widths W 4  and W 6  of the division passages  21   b  and  21   c , respectively, at the outlet  22  approach the width W 2  of the main passage  21   a  at the outlet  22 , suction forces of equivalent magnitude act in the main passage  21   a  and the division passages  21   b  and  21   c . Thus, suction forces are substantially evenly distributed in the longitudinal direction A of a suction inlet  4 . 
     In addition, the width W 1  of the suction inlet  4   a  of the main passage  21   a , where turbulence does not easily occur, is arranged to be greater than the widths W 3  and W 5  of the suction inlets  4   b  and  4   c , respectively, and this leads to improved suction efficiency of the suction nozzle  20 . 
     In addition, the downstream vertical portion  25   d  of each partition wall  25  contributes to causing air which has reached a downstream portion of each of the main passage  21   a  and the division passages  21   b  and  21   c  to be smoothly guided downstream of the outlet  22 . 
     In the present preferred embodiment, the plurality of partition walls (i.e., the second partition walls)  25 , which are arranged to divide a first suction passage  102   a  into the main passage  21   a  and the division passages  21   b  and  21   c  which are divided from one another in the longitudinal direction A of the suction inlet  4 , are provided in the suction nozzle  20 . This prevents a narrowing of a channel on a side closer to an air inlet of an electric blower  7  from causing flows of air sucked in through both end portions of the suction inlet  4  with respect to the longitudinal direction A to abruptly bend toward the center line CT immediately after entering into the first suction passage  102   a , and thus contributes to reducing turbulence in the air. 
     In addition, the width W 1  of the main passage  21   a  at the suction inlet  4  measured in the longitudinal direction A is greater than the width W 2  of the main passage  21   a  at the outlet  22  measured in the longitudinal direction A. This causes each of the widths W 4  and W 6  of the division passages  21   b  and  21   c , respectively, at the outlet  22  to approach the width W 2  of the main passage  21   a  at the outlet  22 , resulting in an increase in the suction force that acts in each of the division passages  21   b  and  21   c . Thus, the suction forces are substantially evenly distributed over the suction inlet  4  in the longitudinal direction A. This leads to improved suction efficiency of the suction nozzle  20 . 
     In addition, each partition wall  25  includes the upstream vertical portion  25   a , which is substantially perpendicular to the longitudinal direction A, at an upstream end of the first suction passage  102   a . This contributes to further reducing the turbulence in the vicinity of the upstream end of the partition wall  25 . 
     In addition, each partition wall  25  includes the first curved portion  25   b , which is defined continuously with the downstream side of the upstream vertical portion  25   a  and is arranged to curve so as to be convex away from the center line CT. This contributes to causing air sucked in through the suction inlets  4   b  and  4   c  at both end portions with respect to the longitudinal direction A to smoothly flow in the division passages  21   b  and  21   c.    
     In addition, each partition wall  25  includes the second curved portion  25   c , which is defined continuously with the downstream side of the first curved portion  25   b  and is arranged to curve so as to be convex toward the center line CT. This contributes to causing the air sucked in through the suction inlets  4   b  and  4   c  at both end portions with respect to the longitudinal direction A to be smoothly guided to a downstream portion of the first suction passage  102   a.    
     In addition, each partition wall  25  includes, at the downstream end thereof, the downstream vertical portion  25   d , which is defined continuously with the second curved portion  25   c  and is arranged to be substantially perpendicular to the longitudinal direction A. This contributes to causing the air flowing in each of the main passage  21   a  and the division passages  21   b  and  21   c  to be smoothly guided to the outlet  22 . 
     In addition, the width W 1  of the main passage  21   a  at the suction inlet  4  measured in the longitudinal direction A is arranged to be greater than each of the widths W 3  and W 5  of the division passages  21   b  and  21   c , respectively, at the suction inlet  4  measured in the longitudinal direction A. This increase in the width W 1  of the main passage  21   a , where turbulence does not easily occur, leads to improved suction efficiency of the suction nozzle  20 . 
     Note that, in the present preferred embodiment, the first curved portion  25   b  may alternatively be arranged to extend from a downstream end of the upstream vertical portion  25   a  to the outlet  22  with the second curved portion  25   c  and the downstream vertical portion  25   d  being omitted. 
     Next, a sixth preferred embodiment of the present invention will now be described below.  FIG. 13  is a sectional front view of a suction nozzle  20  of a suction unit  100  according to the sixth preferred embodiment. For the sake of convenience in description, members or portions that have their equivalents in the above-described first preferred embodiment illustrated in  FIGS. 1 to 6  are denoted by the same reference numerals as those of their equivalents in the first preferred embodiment. The sixth preferred embodiment is different from the first preferred embodiment in the shape of partition walls  25 . The sixth preferred embodiment is otherwise similar to the first preferred embodiment. 
     Each partition wall  25  includes an upstream vertical portion  25   a , a straight portion  25   e , and a downstream vertical portion  25   d  arranged in the order named from the upstream side to the downstream side with respect to a direction in which air flows. In the sixth preferred embodiment, each partition wall  25  includes the downstream vertical portion  25   d , which is arranged to be substantially perpendicular to the longitudinal direction A, at a downstream end thereof. This causes air which has reached a downstream portion of each of a main passage  21   a  and division passages  21   b  and  21   c  to be smoothly guided downstream of an outlet  22 . The straight portion  25   e  is defined continuously with each of a downstream end of the upstream vertical portion  25   a  and an upstream end of the downstream vertical portion  25   d , and is arranged to extend in a straight line. 
     The present preferred embodiment is also able to achieve beneficial effects similar to those of the first preferred embodiment. Note that the upstream vertical portion  25   a  or the downstream vertical portion  25   d  may alternatively be omitted in the present preferred embodiment. 
     Preferred embodiments of the present invention are applicable to suction units and electric vacuum cleaners including suction units. 
     Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises. 
     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 from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.