Abstract:
An electric vacuum cleaner is equipped with a dust collection unit ( 20 ) that can be detachably installed in the air passage en route from a suction unit to an electric fan of the cleaner. The dust collection unit ( 20 ) comprises a dust collecting case ( 21 ) for accumulating dust sucked in, a lid member ( 32 ) that can be opened to discharge the accumulated dust; and a lock mechanism (clamp lever) ( 33 ) for locking the lid member  32  tightly closed. The dust collection unit ( 20 ) is further provided with a hand grip ( 24 ), arranged to face said user, thereby facilitating a user to hold the dust collection unit when discharging dust from the bottom of the dust collecting case. Further, a hinge ( 31 ) is arranged at a position which is adjacent to said bottom ( 32 ) of said dust collecting case ( 21 ) facing the user holding the hand grip. Furthermore, a lock mechanism ( 33 ) is arranged near the periphery of the lid member ( 32 ) and at a position opposite to the hinge.

Description:
FIELD OF THE INVENTION 
   The invention relates to an electric vacuum cleaner equipped with a dust collection unit, installed in a suction passage en route from a suction unit to an electric fan, the dust collection unit having a dust collecting case that can be opened by opening a lid member thereof to discharge the accumulated dust, and a lock mechanism for tightly locking the closed lid member. 
   BACKGROUND OF THE INVENTION 
   Some of conventional electric vacuum cleaners, especially upright (or vertical type) vacuum cleaners are equipped with a dust collecting case, detachably installed in a suction passage, for accumulating dust in a cylindrical filter fitted in the dust collecting case. The accumulated dust is removed by opening a lid of the dust collection unit. Such dust collection unit is economical as compared with a disposable paper bag in that the unit can be used semipermanently. 
   An example of this type of vacuum cleaners is disclosed in Japanese Patent Application Early Publication 2000-342492 (A47L 9/10). 
   In this cleaner, the lid of a dust collecting case is configured to be opened by the weight of the dust itself accumulated in the dust collecting case when a clamp hook locking the lid is unlocked. 
   This type of dust collection unit is provided with a packing for sealing the periphery of the lid to prevent leakage of dust. In order to enhance the sealing, the sealing pressure of the packing must be raised. However, if the sealing pressure is raised, movement of the lid will become heavy. Furthermore, as the amount of dust accumulated in the dust collecting case increases, the dust will be compacted on the inner wall of the dust collecting case, thereby failing to weigh on the lid. For these reasons, the lid will not always open by itself if the lid is unlocked by releasing the clamp hook, and, in that event, it must be forcibly opened by hand. This work is tedious and unsanitary. Moreover, the conventional apparatuses show an unsanitary phase that they do not have special consideration for the detachment of dust collection unit and discharge of dust in the dust collecting case. 
   SUMMARY OF THE INVENTION 
   In view of the problem pertinent to the prior art as mentioned above, the invention is directed to an improved dust collection unit. It is an object of the invention to provide an electric vacuum cleaner equipped with a dust collection unit in which the dust collection unit can be detached and the dust in the dust collecting case can be discharged in a sanitary way, without difficulty and without any manual operation, the invention thereby allowing the user to avoid unsanitary job. 
   In accordance with an object of the invention above, there is provided an electric vacuum cleaner equipped with a dust collection unit detachably installed in the air suction passage of the cleaner en route from a suction unit to an electric fan thereof, said dust collection unit comprising: 
   a dust collecting case for accumulating dust sucked in said suction unit; 
   a hand grip formed on the upper portion of said dust collection unit; 
   a lid member rotatably engaged with one end of said dust collecting case to serve as the bottom of said dust collecting case; 
   an outlet for discharging the dust accumulated in said dust collecting case when said lid member is released; 
   a lock mechanism for sealably locking said lid; and 
   an unlock mechanism for unlocking said lock mechanism; wherein 
   said hand grip facilitating a user to hold said dust collection unit when discharging dust from said outlet, said hand grip arranged to face said user, 
   said hinge arranged at a position which is adjacent to said bottom of said dust collecting case facing said user holding said hand grip, and 
   said lock mechanism arranged near the periphery of said lid member and at a position opposite to said hinge. 
   In this arrangement, the user can avoid a troublesome and unsanitary job of opening the lid by hand. The lid can be opened without difficulty in a simple procedure. In addition, as the hand grip is arranged to face the user, it can be gripped easily. Moreover, as the lock member is arranged to be released toward the opposite side of the user, it may prevent the dust to be discharged toward the user holding the hand grip, thereby preventing the trouble that the user would be covered with the dust. In such ways, the sanitary can be kept. 
   In the inventive electric vacuum cleaner, the dust collecting case shall have an inclined upper surface, so that the dust collecting case can be easily attached to and detached from the body of the electric vacuum cleaner. 
   In addition, the dust collecting case shall be made of a transparent resin and have a cylindrical filter inside the dust collecting case, so that the state of the accumulated dust can be seen and checked visually. 
   The dust collection unit is provided with a stick for unlocking the lock mechanism, and the stick is arranged outside the dust collecting case and at the position opposite to the hinge. This prevents the trouble that the user would be covered with the dust. The lock member can be opened easily. 
   The dust collection unit shall be provided with a biasing member for biasing the lid member in the direction in which the lid member is released from the outlet. The biasing member is adapted to forcibly release the lid member from the outlet by a biasing force when the lock mechanism is unlocked by the unlock mechanism. Thereby, even though the lid member is adhered to the dust case, it can be opened easily. 
   Inside the case, the air and dust taken from a suction port into the dust collecting case are whirled, then only the dust is remained inside. The air filtered free of the dust in the dust collection unit is taken into an electric blower after it is let out of the dust collecting case and discharged out of the body of the vacuum cleaner through an exhaust filter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of an upright electric vacuum cleaner according to the invention, which is equipped with a detachable dust collection unit mounted in the suction passage en route from a suction unit to an electric fan. 
       FIG. 2  is a side view of the upright electric vacuum cleaner shown in  FIG. 1 . 
       FIG. 3  shows a sectional side elevation of a dust collection unit for use with the upright electric vacuum cleaner of the invention. 
       FIG. 4  is an enlarged sectional view of a main part of the lock mechanism and unlocking mechanism for use with the lid member of the dust collection unit shown in  FIG. 3 . 
       FIG. 5  is an enlarged sectional view of a main part of the lock mechanism and unlock mechanism shown in  FIG. 4 . 
       FIG. 6  shows a sectional side elevation of the clamp hook of the dust collecting case of the dust collection unit shown in  FIG. 3 , showing a condition that the clamp hook is unhooked. 
       FIG. 7  shows an enlarged sectional view of a main part of the lock mechanism shown in  FIG. 6 . 
       FIG. 8  shows a sectional side elevation of the dust collection unit of  FIG. 3  with the lid member of the dust collection unit opened. 
       FIG. 9  shows an enlarged sectional side elevation of a main part of the lid member shown in  FIG. 8 . 
       FIG. 10  shows a sectional side elevation of another dust collection unit for use with the upright electric vacuum cleaner of the invention. 
       FIG. 11  is an enlarged sectional view of the dust collection unit of  FIG. 10 , showing in detail a main part of the lock mechanism and unlock mechanism. 
       FIG. 12  is a rear view of the dust collection unit shown in  FIG. 10 . 
       FIG. 13  is an enlarged rear view of a main part of the dust collection unit shown in  FIG. 12 . 
       FIG. 14  shows a cross section taken along line A-A of  FIG. 13 . 
       FIG. 15  shows a sectional side elevation of the dust collection unit of  FIG. 10  when the clamp hook is disengaged and the lid opening lever starts opening the lid member. 
       FIG. 16  is a rear view of the dust collection unit in the same condition as shown in  FIG. 15 . 
       FIG. 17  is an enlarged sectional view of a main part of the dust collection unit shown in  FIG. 15 . 
       FIG. 18  shows a rear view of the dust collection unit of  FIG. 15 , with the lid member further opened. 
       FIG. 19  shows an enlarged rear view of the dust collection unit shown in  FIG. 18 , showing in detail the main part of the dust collection unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1-9 , a first preferred embodiment of the invention will now be described in detail below. The first embodiment of the invention is an upright electric vacuum cleaner as shown in  FIGS. 1 and 2 . In this embodiment, the cleaner has a main body  1 , a suction unit  2  provided beneath the main body  1  for sweeping a floor, and a manipulation handle  3  provided on top of the main body  1  for maneuvering the main body. The manipulation handle  3  extends upward from the back of the main body  1 , and is provided at the top end thereof with a generally triangular grip section  3   a , which protrudes forward. 
   The suction unit  2  has a suction port  4  facing the floor, and a rotary brush  5  facing the suction port  4 . The rotary brush  5  is installed in the lower section of the main body  1 , and operably connected to the shaft of a built-in electric fan (not shown) by means of a belt for example. Mounted on the opposite sides of the front end of the suction unit  2  are a pair of right and left front wheels  7 , and on the rear of the lower end of the main body  1  are a pair of right and left rear wheels  8 . 
   Formed on one side of the back of the suction unit  2  is a hose connector  9  that communicates at the lower end thereof with the suction port  4 . One end of a hose  10  is detachably connected to the hose connector  9 . The hose  10  extends over the back of the main body  1 , via a holder section  11  provided on the back of the manipulation handle  3 , to a suction cylinder  12  provided on one side of the back of the main body  1 . 
   On the other hand, a dust collection unit  20  of the invention is detachably mounted on the central front section of the main body  1 . 
   The dust collection unit  20  includes a cylindrical pre-filter  22  installed inside a cylindrical dust collecting case  21  made of a transparent resin, and a generally cylindrical main filter  23  inside the pre-filter  22  as sown in  FIG. 3 . 
   The dust collecting case  21  has an upper end which is inclined forward, i.e. facing the user, when the dust collecting case  21  is installed on the main body  1 . Formed on the inclined upper end of the dust collecting case  21 , and below the manipulation handle  3 , is an arcuate hand grip  24  as shown in  FIGS. 1 and 2 . 
   On the back of the dust collection unit  20  is a rotary handle  26  for rotating the pre-filter  22 . In the example shown herein, the rotary handle  26  has a form of a cap and is hidden and cannot be seen or touched from outside when the unit  20  is mounted on the main body  1  so that the handle  26  cannot be unintentionally operated by children. 
   The dust collecting case  21  is provided with a suction port (not shown), which, when mounted on the main body  1 , communicates to an opening of a suction cylinder  12  via a packing or a seal. The suction cylinder is mounted on the back of the main body  1 , offset to one side of the back. (This suction port is shown in the second embodiment by a reference numeral  30 .) Because the suction port of the dust collecting case  21  is offset from the center of the dust collecting case  21 , dust-containing air sucked from the suction port is set in a whirlpool motion inside the dust collecting case  21 . 
   Rotatably mounted on the bottom of the dust collecting case  21  is a lid member  32  via a hinge  31  (or a fulcrum  31  for opening and closing the lid member). A clamp lever  33  is formed on the lower section of the dust collecting case  21 . The closed lid member  32  can be locked by hooking up the clamp hook  33   a  formed on the lower end of the clamp lever  33  on an extended peripheral portion  32   a  of the lid member  32 . 
   The clamp lever  33  has a fulcrum  33   b  which is rotatably mounted on two ribs  34  formed on the opposite sides of the clamp lever  33 . Mounted at the upper end of the fulcrum  33   b  is a coil spring  33   c  for urging a hook  33   a  at the lower end of the fulcrum  33   b  towards the lid member  32 . 
   In the embodiment shown herein, a lid opening stick  35  is slidably mounted between the clamp lever  33  and the dust collecting case  21  so that it can be freely moved in the vertical direction. A coil spring  35   b  is mounted at an upper manipulatory section  35   a  of the lid opening stick  35  to urge the lid opening stick  35  upward. The lid opening stick  35  is provided with a vertically elongated hole  35   c  formed at a position of the coil spring  33   c  such that the lid opening stick  35  will not abut on the coil spring  33   c  while moving up and down. 
   Formed below the fulcrum  33   b  of the clamp lever  33  is an outward protrusion  35   d  in correspondence with an inwardly inclined facet  33   d  formed on the clamp lever  33 , so that when the lid opening stick  35  is pushed downward, outward protrusion  35   d  abuts on the inwardly inclined facet  33   d  of the clamp lever  33  to push the inclined facet  33   d  downward, thereby disengaging a clamp hook  33   a  from the extended portion  32   a  of the lid member. 
   The leading end  35   e  of the lid opening stick  35 , when pushed down, abuts on the extended portion  32   a  of the lid member  32 , thereby pushing it down, and forcibly opens the lid member  32  to thereby liberate it from the clamp hook  33   a . This causes the dust outlet  36  of the dust collecting case  21  to be opened as shown in  FIG. 8 . The extended portion  32   a  of the lid member  32  has an upper inclined facet  32   b  in correspondence with the inclined facet  33   e  of the clamp hook  33   a  so that the lid member  32  can be closed without manipulating the clamp lever  33 . When the outward protrusion  35   d  is pushed down, it is inwardly pushed by the clamp lever  33 , the leading end  35   e  of the lid opening stick  35  pushes down the extended portion  32   a  without sliding on the inclined facet  32   b  of the extended portion  32   a.    
   Mounted on the periphery of the lid member  32  is a packing  37  to seal the opening of the dust collecting case  21 . Formed on the upper face of the lid member  32  is a protruding section  38  that can fit in the inner periphery of the lower opening of the pre-filter  22  so as to prevent transverse vibrations of the pre-filter  22 . A packing  39  is provided on the open end of the pre-filter  22  for keeping the open end of the pre-filter  22  in tight contact with the upper surface of the lid member  32 . 
   A suction port  41  is formed inside the top end of the protruding section  38  of the lid member  32 . The suction port  41  is connected to the lower end of a cylindrical member  40 , which forms an air passage for directing air from the main filter  23  to the exterior of the dust collecting case  21 . A packing  42  is mounted on the inner periphery of the suction port  41  to keep the open end of suction port  41  and the cylindrical member  40  of the main filter  23  in sealing contact. 
   The main filter  23  is mounted on the top plate  43  of the dust collecting case  21  by means of a mounting shaft  44  that protrudes from the center of the main filter  23 . A cylindrical hollow shaft  45  of the pre-filter  22  is mounted on the mounting shaft  44 , extending between the top plate  43  of the dust collecting case  21  and the main filter  23 . 
   Mounted on the upper end of the cylindrical hollow shaft  45  of the pre-filter  22  is an annular gear  47  that engages with an disk-shaped gear  46  mounted on the rotary shaft  27  of the rotary handle  26 . Thus, rotation of the pre-filter  22  will cause the rotation of the rotary handle  26  in a predetermined direction. By forming a simple mechanism for rotating the pre-filter (the mechanism hereinafter referred to as pre-filter rotating mechanism) in this way, the pre-filter  22  can be firmly rotated. Mounted on the outer peripheries of the upper ends of the pre-filter  22  and the main filter  23  are packings  48  and  49 , respectively, to keep the pre-filter  22  in tight contact with an upper partition plate  22   a  and the main filter  23  in tight contact with the top plate  43  of the dust collecting case  21 , so as to prevent dust from entering the pre-filter rotating mechanism described above. 
   Resilient protrusions  50  are formed under the cylindrical hollow shaft  45  of the pre-filter  22 . The resilient protrusions  50  abut on the plait tips formed on the inside of the main filter  23  as described later. With this arrangement, the resilient protrusions  50  are rotated together with the cylindrical hollow shaft  45  to prick the plait tips of the main filter  23 , facilitating efficient removal of dust from the filter. 
   The lower section  51  of the pre-filter  22  is meshed for filtering larger pieces of dust. Because the meshed filter  51  is provided in the lower section of the dust collecting case  21 , dust sucked in together with the air from a suction port (not shown) provided at an upper section of the dust collecting case  21  is forced to whirl downward at a high speed, and compacted on the bottom of the dust collecting case  21 . 
   Formed on the external circumference of the pre-filter  22  are spiral ribs  52  that generally extend in the vertical direction. The ribs  52  are configured to push the dust accumulated and compacted in the dust collecting case  21  towards the dust outlet  36  of the lid member  32  when the rotary handle  26  is turned in the clockwise direction. 
   The main filter  23  is a plaited cylindrical paper filter surrounding the cylindrical member  40  serving as an air passage for the filtered air. The mounting shaft  44  fixed on the upper central section of the main filter  23  is fitted in a mounting bore  53  formed in the top plate  43  of the dust collecting case  21  in such a way that the mounting shaft  44  will not be rotated with the rotary pre-filter  22 . 
   The tips of the plait inside the main filter  23  are covered with a plastic resin member  54  to prevent them from being worn by the friction with the rotating resilient protrusions  50  formed on the lower section of the cylindrical hollow shaft  45  of the pre-filter  22 . 
   The clean air filtered by the dust collection unit  20  is discharged from the suction port  41  (of the dust collecting case  21 ) located below the cylindrical member  40  of the main filter  23 . The air is then sucked into an electric fan (not shown), and exhausted, via an exhaust filter (not shown), from an outlet  58  formed in the lower front end of the main body  1 . 
   In the upright vacuum cleaner of the invention as described above, dust on the floor is scratched by the rotary brush  5  of the suction unit  2  and enters the dust collecting case  21  through the hose  10  and the suction cylinder  12  positioned offset from the center of back of the main body  1 . The dust is whirled downward along the inner wall of the dust collecting case  21 . Larger pieces of dust accumulate on the bottom of the dust collecting case  21 . 
   Since the mesh  51  of the pre-filter  22  is located in the lower section of the dust collecting case  21 , dust sucked together with the air from the upper suction port is forcibly whirled downward, causing the dust to be accumulated and compacted on the bottom of the lid member  32  of the dust collecting case  21 , as previously described. This compaction effect is significant especially when dust is cotton refuse. The compression rate is larger several fold, as compared with a conventional cyclone type separator. Because of such large compaction rate, the dust collection unit of the invention is capable of collecting a large amount of dust per unit volume. 
   On the other hand, fine dust enters inside the pre-filter  22  via the mesh  51  provided below the pre-filter  22 , and is filtered by the plaited main filter  23 . As a consequence, only clean filtered air is passed down to the electric fan and exhausted from the outlet  58 . 
   As described above, in the dust collection unit  20  of the invention, the cylindrical pre-filter  22  is provided with resilient protrusions  50  formed at the lower end of the cylindrical hollow shaft  45  so as to prick the tips of the plait inside the main filter  23 . In addition, spiral ribs  52  are provided on the exterior of the pre-filter  22 . The cylindrical hollow shaft  45  of the pre-filter  22  is operably connected to the rotary handle  26  via the gears  46  and  47 . 
   Consequently, when the rotary handle  26  is rotated in one (arbitrary) direction, the pre-filter  22  is rotated in a corresponding direction by means of the gears  46  and  47  and the cylindrical hollow shaft  45 . As the pre-filter  22  is rotated, the resilient protrusions  50  located on the lower section of the shaft  45  prick the tips of the plait (resin member  54 ) inside the main filter  23 , causing vibrations therein, which in turn causes fine dust accumulating on the surface of the main filter  23  to fall off. Large-sized pieces accumulating in a compacted form in the dust collecting case  21  sweep fine dust which is sticking to the outer surface of the pre-filter  22 . Accordingly, lowering of dust collecting efficiency of the dust collection unit caused by accumulation of dust on the main filter  23  and pre-filter  22  may be effectively prevented. 
   As the large-sized dust pieces or trash accumulates in the dust collecting case  21 , the mesh  51  formed below the pre-filter  22  can be gradually clogged. In the event that clogging has taken place, the dust collection unit  20  is once disengaged from the vacuum cleaner, and by rotating the rotary handle  26 , and hence the pre-filter  22 , to move the spiral ribs  52  formed thereon up and down, gaps (air passage) can be formed between the mesh  51  and the trash, that prevents lowering of dust collection efficiency of the filter. 
   On the other hand, to remove the dust accumulated in the dust collecting case  21 , the hand grip  24  of the dust collecting case  21  is withdrawn by hand while pressing the button  28  provided on the hand grip  24 . This permits the dust collecting case  21  to be disconnected from the main body  1 . At this time, the dust collecting case  21  can be detached from the body of the vacuum cleaner very easily, as the hand grip  24  is arranged to face the user. 
   If the manipulatory section  35   a  of the lid opening stick  35  is forced down as shown in  FIGS. 6 and 7 , the outward protrusion  35   d  formed on the lower end of the lid opening stick  35  abuts against the inwardly inclined facet  33   d  of the clamp lever  33 , causing the inwardly inclined facet  33   d  to recede outward, thereby rotating the clamp lever  33  away from the extended portion  32   a  of the lid member  32  and disconnecting the clamp hook  33   a  of the clamp lever  33  from the extended portion  32   a . If the manipulatory section  35   a  is further forced down, the leading end  35   e  of the stick  35  abuts on the extended portion  32   a  and pushes it down, causing the lid member  32  to be forcibly opened as shown in  FIG. 8 . Now, the dust accumulated in the dust collecting case  21  can be removed from the dust collecting case  21 . 
   Thus, if the sealing pressure of the packing  37  is increased to enhance sealability of the lid member  32  or if the compacted dust in the dust collecting case  21  sticks to the inner wall of the dust collecting case  21 , not weighing on the lid member  32 , the lid member  32  can be easily and securely opened without manually opening it by hand, thereby permitting the user to avoid laborious and unsanitary operations of opening the lid member  32 . 
   It is noted that although the lid member  32  can be easily opened, cotton refuse in particular does not come off the inner wall of the dust collecting case  21  when it is compacted on the wall. In this case, the spiral ribs  52  provided on the exterior of the pre-filter  22  may be operated to push the compacted dust such as cotton refuse outward. This facilitates easier removal of the sticking dust. This can be done by turning the rotary handle  26  to rotate the pre-filter  22  in a predetermined direction (right in the example shown). 
   Since the hinge  31  of the lid member  32  (or fulcrum for opening the lid member) is provided on the same side as the hand grip  24  of the dust collecting case  21 , the lid member  32  can prevent removed dust from coming unexpectedly close to the user or splashing to the user when the hand grip  24  is held and the lid member  32  is opened ( FIG. 8 ). 
   Every time dust is removed, dust cleaning function of the pre-filter is executed by the rotation of the pre-filter  22 , so that lowering of dust collecting efficiency of the filter is prevented if the user is not cognizant of cleaning the filter. 
   As described above, a vacuum cleaner in accordance with the embodiment described above provides an economic advantage that, unlike conventional cleaners, it can be used semipermanently without any replacement of disposable paper bag. In addition, the usability of the dust collection unit is greatly improved to that of a disposable type unit or more than that. 
   The upright dust collection unit  20  may have a sufficient inner volume that it is especially suitable for a heavy duty upright vacuum cleaner. 
   An upright vacuum cleaner of the invention is provided with a generally triangular protruding grip  3   a  formed on top of the manipulation handle  3  that extends upward from the back of the main body  1 , as shown in  FIG. 3 . Hence, the grip section  3   a  provides the user with convenience that he needs not to stoop over the cleaner while cleaning, for example, the floor under a bed if he inclines the cleaner through a large angle, since he can then keep the grip section  3   a  at a convenient height. 
     FIGS. 10-19  show further embodiments of the invention, in which the same reference numerals refer to the same components as before. The main body  1  is the same as the preceding one shown in  FIGS. 2 and 3 . The dust collecting case  21  is provided in the back thereof with a suction port  30  offset to one side of the back as shown in rear views of  FIGS. 12 ,  16 , and  18 . The suction port  30  communicates to the suction cylinder  12  of the main body  1  when they are air-tightly connected together. 
   A unique feature of this embodiment is that the lid member  32  has a special opening mechanism. The rest of the features of the embodiment are the same as those of the preceding ones. 
   As compared with the preceding lid opening mechanism in which the lid opening stick  35  is formed on the dust collecting case  21 , this lid opening lever  60  is provided on the lid member  32 . 
   The lock mechanism has a clamp lever  33  attached to one side of the dust collecting case  21  opposite the hinge  31  of the lid member  32  (or fulcrum for opening the lid member), and having a hook  33   a  to be hooked on the extended portion  32   a  formed on the fringe of the lid member  32 , like a preceding embodiment. However, the lid opening mechanism is provided with a lid opening lever  60  which is mounted on the underside of the lid member  32  in correspondence with the clamp lever  33 , opposite the hinge  31 , and is urged to push the underside of the dust collecting case  21 . 
   The lid opening lever  60  is provided at one end thereof with pushing sections  60   a  that protrude from the opposite sides of said one end to push the lower ends of the ribs  34  supporting the fulcrum  33   b  of the clamp lever  33 , as shown in  FIGS. 12-14 . The lid opening lever  60  is urged by a coil spring  60   c  mounted on the other end of the fulcrum  60   b  of the lever  60  so as to push the lower ends of the ribs  34  against the upper pushing sections  60   a.    
   In addition, the lid opening lever  60  is provided at the tip thereof with a protrusion  60   d  located between the two ribs  34 . The facet  60   e  of the protrusion  60   d  facing an inclined facet  33   e  of the clamp hook  33   a  is correspondingly inclined so as not to hinder locking operation of the clamp hook  33   a , as shown enlarged in  FIG. 11 . 
   In the arrangement described above, in order to discharge the accumulated dust from the dust collecting case  21 , the upper section  33   f  of the clamp lever  33  is pushed to disengage the clamp hook  33   a  at the lower end thereof from the extended portion  32   a  of the lid member  32  as shown in  FIGS. 15-17 . 
   When the lid member  32  is unlocked from the clamp hook  33   a , a downward force acts on the lid member  32  as a consequence of the reaction of pushing the undersides of the ribs  34  of the dust collecting case  21  by the pushing section  60   a  of the lid opening lever  60 . The downward force will cause the lid member  32  to be opened to the position as shown in  FIGS. 15-17 . As the lid member  32  is opened like this, the packing  37  is also disengaged from the open end of the dust collecting case  21 , allowing the lid member  32  to open by the weight of its own as shown in  FIGS. 18-19 . The dust accumulated in the dust collecting case  21  is thus discharged from the case  21 . 
   In this way, as in the preceding embodiments, manual operations of the lid member  32  are not necessary to open the lid member if the weight of the compacted dust does not facilitate the disengagement of the lid member due to the fact that the dust is compacted in the dust collecting case  21  and sticks to the inner wall of the case  21 . Thus, the user can avoid unsanitary job of opening the lid member  32  to remove the dust by hand. 
   In this embodiment, the two ribs  34  supporting the shaft  33   b  of the clamp lever  33  are utilized advantageously to create a reaction force to disengage the lid member from the dust collecting case, and no additional element is required on the dust collecting case  21  for liberating the lid member. Thus, the dust collection unit can be manufactured at no extra cost. The unit can be operated like a conventional one. 
   The protrusion  60   d  formed between the two ribs  34  facilitates correct positioning of the lid member  32  following the removal of dust.