Pre-filter or shroud with helical stepped wall

Abstract

A vacuum cleaner includes a body. A suction generator and a dirt collection vessel are both carried on the body. The dirt collection vessel includes an arcuate side wall, a tangentially directed inlet, an axially directed outlet, a dirt collection chamber and a shroud provided between the dirt collection chamber and the axially directed outlet. The shroud includes a filter surface having a plurality of air flow apertures and a helical step extending around the shroud through the filter surface.

What is claimed: 
     
         1 . A vacuum cleaner, comprising:
 a body;   a suction generator carried on said body; and   a dirt collection vessel carried on said body, said dirt collection vessel including an arcuate sidewall, a tangentially directed inlet, an axially directed outlet, a dirt collection chamber and a shroud provided between said dirt collection chamber and said axially directed outlet;   said shroud including a filter surface having a plurality of air flow apertures and a helical step extending around said shroud through said filter surface.   
     
     
         2 . The vacuum cleaner of  claim 1 , wherein said shroud includes a lip and a skirt and said filter surface and said helical step extend between said lip and skirt. 
     
     
         3 . The vacuum cleaner of  claim 2 , wherein said helical step has a width of between about 10 and about 16 mm. 
     
     
         4 . The vacuum cleaner of  claim 3  wherein said helical step has a length of between about 210 and about 250 mm. 
     
     
         5 . The vacuum cleaner of  claim 4 , wherein said helical step extends through an arc of between about 180 and about 270 degrees. 
     
     
         6 . The vacuum cleaner of  claim 5 , wherein said helical step engages said lip adjacent said tangentially directed inlet. 
     
     
         7 . The vacuum cleaner of  claim 6 , wherein said skirt and said arcuate sidewall define a continuous gap having a width of between about 9 and about 13 mm. 
     
     
         8 . The vacuum cleaner of  claim 1 , wherein said helical step has a width of between about 10 and about 16 mm. 
     
     
         9 . The vacuum cleaner of  claim 8 , wherein said helical step has a length of between about 210 and about 250. 
     
     
         10 . The vacuum cleaner of  claim 9 , wherein said helical step extends through an arc of between about 180 and about 270 degrees. 
     
     
         11 . The vacuum cleaner of  claim 1 , wherein said plurality of air flow apertures each have a diameter of between about 25 and about 26 mm and define a total surface area of between about 900 mm 2  and about 1400 mm 2 . 
     
     
         12 . The vacuum cleaner of  claim 1 , wherein a first portion of said filter surface is on a first side of said helical step and a second portion of said filter surface remains unrecessed on a second side of said helical step. 
     
     
         13 . The vacuum cleaner of  claim 12 , wherein between about 25 and about 40 percent of said plurality of airflow apertures are provided on said first portion and between about 60 and about 75 percent of said plurality of airflow apertures are provided on said second portion. 
     
     
         14 . The vacuum cleaner of  claim 2 , wherein said skirt includes a hollow adjacent a point where said helical step meets said skirt. 
     
     
         15 . The vacuum cleaner of  claim 14 , wherein said hollow includes an air flow guide wall diverging from said helical step. 
     
     
         16 . The vacuum cleaner of  claim 15 , wherein said air flow guide wall and said helical step define an included angle of between about 38 and about 48 degrees. 
     
     
         17 . The vacuum cleaner of  claim 15 , wherein said air flow guide wall and said helical step define an included angle of about 43 degrees. 
     
     
         18 . The vacuum cleaner of  claim 2 , wherein said arcuate sidewall includes a step provided adjacent said skirt. 
     
     
         19 . The vacuum cleaner of  claim 18 , wherein said arcuate sidewall has a circumference of between about 120 mm and about 135 mm on a first side of said step and a circumference of between about 140 mm and about 150 mm on a second side of said step. 
     
     
         20 . The vacuum cleaner of  claim 2 , wherein said skirt includes a gap adjacent a point where said helical step meets said skirt.