reference is now made to fig1 showing the upright vacuum cleaner 10 of the present invention . the upright vacuum cleaner 10 includes a nozzle assembly 14 and a canister assembly 16 . the canister assembly 16 further includes a control handle 18 and a hand grip 20 . a control switch 22 is provided for turning the vacuum cleaner on and off . of course , electrical power is supplied to the vacuum cleaner 10 from a standard electrical wall outlet through a cord ( not shown ). as is known in the art , sets of front and rear wheels ( not shown ) are provided , respectively , on the nozzle assembly 14 and canister assembly 16 to support the weight of the vacuum cleaner 10 . together , these two sets of wheels allow the vacuum cleaner 10 to roll smoothly across the surface being cleaned . to allow for convenient storage of the vacuum cleaner 10 , a foot latch 30 functions to lock the canister assembly 16 in an upright position as shown in fig1 . when the foot latch 30 is released , the canister assembly 16 may be pivoted relative to the nozzle assembly 14 as the vacuum cleaner 10 is manipulated back - and - forth to clean the floor . the canister assembly 16 includes a cavity 32 adapted to receive and hold a dirt collection vessel or dust bag 12 . alternatively , the vacuum cleaner 10 could be equipped with a dust collection cup such as found on cyclonic type models if desired . additionally , the canister assembly 16 carries a suction fan 34 and suction fan drive motor 35 . together , the suction fan 34 and its cooperating drive motor 35 function to generate a vacuum airstream for drawing dirt and debris from the surface to be cleaned . while the suction fan 34 and suction fan drive motor 35 are illustrated as being carried on the canister assembly 16 , it should be appreciated that they could likewise be carried on the nozzle assembly 14 if desired . the nozzle assembly 14 includes a nozzle and agitator cavity 36 that houses a pair of rotating agitator brushes 38 a , 38 b . the agitator brushes 38 a , 38 b shown are rotatably driven by the drive motor 35 through a cooperating belt and gear drive ( not shown ). in the illustrated vacuum cleaner 10 , the scrubbing action of the rotary agitator brushes 38 a , 38 b and the negative air pressure created by the suction fan 34 and drive motor 35 cooperate to brush and beat dirt and dust from the nap of the carpet being cleaned and then draw the dirt and dust laden air from the agitator cavity 36 to the dust bag 12 . specifically , the dirt and dust laden air passes serially through one of the hoses 46 and an integrally molded conduit in the nozzle assembly 14 and / or canister assembly 16 as is known in the art . next , it is delivered into the dust bag 12 which serves to trap the suspended dirt , dust and other particles inside while allowing the now clean air to pass freely through to the suction fan 34 , a final filtration cartridge ( not shown ) and ultimately to the environment through the exhaust port ( not shown ). as best shown in fig2 a and 2 b , the nozzle assembly 14 includes a hollow stub shaft 52 at one side thereof . this stub shaft 52 is received and nests in a cooperating groove 54 provided in the canister assembly 16 . for clarity of illustration both portions of the canister assembly 16 are shown in fig3 a . only the rear portion is shown in fig3 b , 3 c and 4 . the two portions of the canister assembly 16 mate along the centerline of the groove 54 to aid in the overall assembly of the vacuum cleaner 10 . while not shown , it should be appreciated that a similar structural configuration may be provided on the other side of the vacuum cleaner 10 to provide the same function . the two stub shafts or trunnions 52 are aligned to provide a single axis about which the nozzle assembly 14 pivots relative to the canister assembly 16 during vacuum cleaner operation . as further illustrated , a biaser , in the form of a torsion spring 56 , is partially received in the stub shaft 52 . more specifically , the coiled portion 58 of the spring 56 is positioned in the stub shaft 52 . a first end 60 of the spring is received in an aperture 62 in the metal reinforcing plate 64 of the nozzle assembly 14 . a second end 66 of the spring 56 extends through a slot 68 in the wall of the stub shaft 52 downwardly into a channel 70 formed by a box rib 72 on the wall 74 of the canister assembly 16 . when the canister assembly 16 is in the full down position ( see fig3 a ) forming an included angle with the nozzle assembly 14 of approximately 170 °- 178 °, the second end 66 of the spring 56 projects downwardly just inside the forward edge 76 of the groove 68 and provides the necessary spring force to urge the nozzle assembly downwardly into engagement with the surface being cleaned . as the control handle 18 and canister assembly 16 are pivoted upwardly to an included working angle of approximately 135 ° with the nozzle assembly 14 , ( i . e . into an angular orientation commonly employed during use of the vacuum cleaner by the operator ) shown in fig3 b , the forward wall 78 of the box rib 72 partially winds the torsion spring 56 . this further increases the downforce on the forward end of the nozzle assembly 14 so as to better insure that the nozzle assembly 14 stays down in engagement with the ground as the vacuum cleaner is moved back - and - forth by means of the handle . as the handle 18 and canister assembly 16 are pivoted still further with respect to the nozzle assembly 14 toward the upright position , further winding of the torsion spring 56 occurs ( see fig3 c ). it should be appreciated that the slot 68 cut in the stub shaft 52 provides sufficient clearance to allow free passage of the end 66 of the spring 56 into the channel 70 in all the various angular orientations that the canister assembly 16 may assume with the nozzle assembly 14 . thus the spring 56 provides in all operating positions between about 1 . 2 and about 3 . 2 and more typically between about 2 . 0 and about 2 . 4 lbs / sq . in . of preload . this converts to between about 0 . 2 and 3 . 0 lbs / sq . in . of downforce on the forward end of the nozzle assembly 14 . thus , when the canister assembly 16 is positioned at about a 135 ° working angle with the nozzle assembly 14 ( see fig3 b ), the spring may provide a downforce of between about 0 . 8 and about 1 . 6 lbs / sq . in . and more typically about 1 . 2 lbs / sq . in . on the forward end of the nozzle assembly 14 . these specific ranges are , of course , only mentioned to be illustrative of the invention and are not to be considered restrictive . numerous benefits result from employing the concepts of the present invention . the downforce the spring 56 exerts on the nozzle assembly 14 serves a dual function . first , it resists any tendency of the nozzle assembly 14 to be lifted from the floor being cleaned as the vacuum cleaner 10 is manipulated or pushed and pulled back - and - forth by the operator . as a consequence , the agitators 38 a and 38 b are better maintained in contact with the floor . this promotes more efficient and effective cleaning . second , it has a tendency to dampen any vibration resulting from the engagement of the agitators 38 a , 38 b or the brushes , beater bars or other cleaning structures carried thereon with the surface being cleaned . this advantageously reduces or eliminates this operator annoyance which may otherwise become very pronounced when the vacuum cleaner is operated on surfaces having particular physical characteristics . further , it should be appreciated that these benefits are also provided and are even more pronounced when the vacuum cleaner is constructed from lightweight materials . such vacuum cleaners are user friendly since they are easier and more convenient to move and manipulate . the foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description . it is not intended to be exhaustive or to limit the invention to the precise form disclosed . obvious modifications or variations are possible in light of the above teachings . for example , while a vacuum cleaner with dual agitators is illustrated , the invention is equally applicable to a vacuum cleaner with one agitator or more than two agitators . the embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated . all such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly , legally and equitably entitled .
an upright vacuum cleaner includes a nozzle assembly , a canister assembly pivotally mounted to said nozzle assembly , a suction fan and motor and a biaser . the biaser has a first end that engages the nozzle assembly and a second end that engages the canister assembly . the biaser provides a positive downforce urging the forward end of the nozzle assembly toward the surface being cleaned .