Patent Publication Number: US-9402522-B2

Title: Cyclonic separation device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of United Kingdom Patent Application No. 1404229.5 filed Mar. 11, 2014, which application is incorporated herein in its entirety by this reference. 
     This application is also related to co-pending U.S. application Ser. No. 14/644,042, being filed concurrently herewith by the same inventors, of same title, which claims the benefit of United Kingdom Patent Application No. 1404237.8 filed Mar. 11, 2014, which applications are incorporated herein in their entirety by this reference. 
     BACKGROUND 
     This invention relates to a cyclonic separation device and more particularly but not solely to a cyclonic separation device for a vacuum cleaner. 
     Cyclonic separation devices are widely used in vacuum cleaners to separate dirt and dust from the airflow. Typically such vacuum cleaners incorporate a single upstream cyclonic separator which is relatively large in diameter and which is suited to separating heavy dirt and dust particles as well as coarse and fibrous matter from the airflow. Such large diameter cyclonic separators are unable to separate lighter dirt and dust particles and hence a further separation stage is needed downstream of the cyclonic separator. 
     It is well known to provide vacuum cleaners having a downstream stage which comprises a plurality of smaller diameter cyclonic separators connected fluidly in parallel with each other. Whilst smaller diameter cyclonic separators act to restrict airflow, the number of cyclonic separators is chosen so as not to impede the airflow due to the fact that each cyclonic separator takes a proportion of the airflow from the upstream device. 
     One such vacuum cleaner is disclosed in GB2490693 in which each cyclonic separator of the second stage comprises a cyclone chamber having a frusto-conical side wall. An air inlet is directed tangentially into the first and widest end of the chamber through the side wall thereof. An air outlet extends axially from an end wall which closes the first end of the cyclone chamber. The second end of the cyclone chamber is open. In some cyclonic separators, the side wall may be parallel or reverse-tapered, although cyclone chambers having a frusto-conical side wall are more suited to separating lighter dust particles. 
     In use, air enters the cyclone chamber through the inlet and rotates in a vertical manner around the cyclone axis inside the frusto-conical side wall towards the second end of the cyclone chamber. The dust particles in the rotating airflow are forced radially outwardly against the side wall under centrifugal action. The volume of rotating airflow slowly diminishes towards the second end of the cyclone chamber as air is drawn radially inwardly and axially towards the outlet at the first end of the cyclone chamber. However, the dust particles that are forced radially outwardly against the frusto-conical side wall are disposed in a boundary layer and slowly migrate towards the open second end of the cyclone chamber, whereupon they pass out of the cyclone chamber into a collection chamber. 
     A disadvantage of the above-mentioned arrangement is that dust particles in the boundary layer can become re-entrained in the airflow, particularly if the airflow is heavily laden with dust or if there is a drop in airflow. Also, the speed at which the dust particles migrate is slow and hence the risk of re-entrainment is increased, partly because the volume of dust in the boundary layer is so great that it forms a layer which is too wide to remain inside the boundary layer. 
     Clearly the separation efficiency can be improved by using a high powered motor to drive the fan, which causes a higher rate of airflow through the cleaner. However, legislation is being introduced which limits the power that vacuum cleaners can consume with the result that the separation efficiency will be detrimental. 
     We have now devised a cyclonic separation device having an improved efficiency. 
     SUMMARY 
     In accordance with the present invention there is provided a cyclonic separation device comprising a plurality of cyclonic separators fluidly arranged in parallel with each other, each cyclonic separator comprising a chamber having a circular-section side wall, a fluid inlet and a fluid outlet disposed at one end of the cyclone chamber, and an opening at the second end of the cyclone chamber through which separated matter passes out of the chamber for collection, said cyclonic separators being arranged in a rotatable body such that their respective cyclone axes are outwardly inclined relative to an axis of rotation of the body and such that the second end of each cyclone chamber is disposed radially outwardly of its first end with respect to said axis of rotation, the device further comprising a motor for rotating the body about its axis of rotation. 
     In use, the body is rotated and the cyclonic separators operate as hereinbefore described. However, the rotation of the body about its axis of rotation applies additional forces to the dust particles in the cyclone chamber, which act to force the dust particles radially outwardly of the axis of rotation of the body and hence axially of the inclined cyclone chamber towards the opening at the second end thereof. In this manner the separation efficiency is improved because the additional force acts to increase the speed at which the dust particles in the boundary layer migrate towards the outlet. 
     When utilized in a vacuum cleaner, a cyclonic separation device in accordance with the present invention enables a lower power motor to be used without detrimenting the separation efficiency. 
     The longitudinal cyclone axis of each cyclonic separator may extend substantially radially of the axis of rotation of the body (i.e., at substantially 90° thereto) or it may lie at an angle of preferably greater than 30° to the axis of rotation. 
     Preferably each cyclonic separator comprises a frusto-conical side wall. 
     Preferably the body comprises at least four cyclonic separators arranged fluidly in parallel. 
     Preferably the cyclonic separators are equally spaced circumferentially around the body. 
     Preferably the body is disposed inside a housing defining a collection chamber for separated matter. 
     Preferably the collection chamber comprises an annular wall which extends around the body in front of the outlets of the cyclone chambers. 
     Preferably the motor is arranged to rotate the body at rotational speeds of 1500-5000 rpm. The motor may be also arranged to drive a fan which creates the airflow through the device. 
     Preferably the cyclonic separators in the body form a downstream separation stage of the device, the device further comprising an upstream separation stage. The upstream stage may comprise a single cyclonic separator or a plurality of cyclonic separators fluidly connected in series and/or parallel. 
     Preferably the upstream stage comprises a cyclonic separator having a cyclone axis which co-extends with the axis of rotation of the body. 
     Preferably the cyclonic separator of the upstream stage comprises a fluid outlet at one end which connects to a fluid inlet of the second stage, a cylindrical shroud being disposed around the outlet inside a cyclone chamber of the cyclonic separator of the first stage, the longitudinal axis of the shroud co-extending with the axis of rotation of the body. 
     A problem with such shrouds is that the apertures therein can become blocked with dirt and dust. Another problem is that the rotational airflow inside the cyclone chamber of the first stage has to decelerate and turn radially inwardly to pass through the apertures, thereby causing a pressure drop. 
     In order to solve the above-mentioned problems, co-pending UK patent application no. 1404237.8 filed Mar. 11, 2014, discloses a cyclonic separation device having a shroud which is rotated at or near the rotational airflow speed inside the cyclonic separator in which it is provided. Therefore, the shroud is preferably also rotated by said motor. 
     The motor can be positioned inside the shroud or outside the shroud, for example in a dust collection receptacle of the device. In the former case, providing the motor within the shroud increases the capacity of the dust collection receptacle of the device and reduces the noise emanating from the motor. 
     Preferably the above-mentioned collection chamber comprises a portion which extends around the cyclone chamber of said first stage. 
     Preferably the shroud and body form a unitary member. 
     Preferably the shroud extends through an end wall of the cyclone chamber of the first separation stage, a seal preferably being provided for sealing the end wall of the chamber to the shroud. 
     Also in accordance with the present invention, there is provided a vacuum cleaner having a cyclonic separation device as hereinbefore defined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention will now be described by way of an example only and with reference to the accompanying drawing, the single FIGURE of which is a sectional view through a cyclonic separation device of a vacuum cleaner in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects, features and advantages of exemplary embodiments of the present invention will become better understood with regard to the following description in connection with the accompanying drawing(s). It should be apparent to those skilled in the art that the described embodiments of the present invention provided herein are illustrative only and not limiting, having been presented by way of example only. All features disclosed in this description may be replaced by alternative features serving the same or similar purpose, unless expressly stated otherwise. Therefore, numerous other embodiments of the modifications thereof are contemplated as falling within the scope of the present invention as defined herein and equivalents thereto. Hence, use of absolute terms, such as, for example, “will,” “will not,” “shall,” “shall not,” “must,” and “must not,” are not meant to limit the scope of the present invention as the embodiments disclosed herein are merely exemplary. 
     Referring to the drawing, the cyclonic separation device comprises an air inlet  10  which leads tangentially into the upper end of a cyclone chamber  11  of a first separation stage through a cylindrical side wall  12  thereof The upper end of the cyclone chamber  11  is closed by an end wall  13  which defines a circular air outlet of the first stage. 
     A cylindrical shroud  14  is mounted concentrically inside the cyclone chamber  11  at the upper end thereof The shroud  14  comprises a bottom wall which is supported on the shaft of a motor  15  disposed at the bottom of the cyclone chamber  11 . The shroud  14  extends upwardly through the circular air outlet in the end wall  13  and is rotationally sealed thereto by an annular seal  16 . 
     The lower end of the shroud  14  comprises a plurality of apertures which fluidly communicate the interior of the cyclone chamber  11  with the interior of the shroud  14 . The upper end of the shroud  14  is rigidly connected to the body  17  of a second separation stage. The body  17  comprises six outwardly-inclined cyclonic separators which are circumferentially arranged about an axis A of rotation of the shroud  14  and body  17 . Each cyclonic separator comprises a cyclone chamber  18  having a cyclone axis B which extends radially outwardly of the rotational axis A. 
     Each cyclone chamber  18  is defined by a frusto-conical side wall  19  which tapers inwardly towards its radially outer end, the latter being open to define a dust outlet of the cyclone chamber  18 . 
     The radially inner end of each cyclone chamber  18  comprises an inlet  20  which extends tangentially through its frusto-conical side wall  19 . The inlets  20  communicate directly with the interior of the upper end of the shroud  14 . The combined cross-sectional area of the inlets  20  is substantially equal to the cross-sectional area of the inlet  10  of the first separation stage. 
     The radially inner end of each cyclone chamber  18  also comprises a tubular outlet or so-called vortex finder  21  which extends axially of the cyclone chamber  18  from its inner end wall. The vortex finders  21  lead into a manifold chamber  22  at the upper end of the body  17 . 
     The first and second separation stages are enclosed within a housing having a tubular side wall  23 , an openable bottom wall  24  and a top wall  25 . A tubular air outlet  26  extends axially upwardly from the manifold  22  to a tubular duct  27  provided on the upper surface of the top wall  25 , the outlet  26  being rotationally journalled thereto by an annular seal  28 . 
     In use, a negative pressure is applied to the outlet duct  27  by a motor and fan unit (not shown) disposed downstream thereof. The motor  15  is actuated to cause the shroud  14  and body  17  to rotate about the axis A at a rotational speed of between 1500 and 5000 rpm. The negative pressure draws dirt and dust laden air tangentially into the cyclone chamber  11  through the inlet  10  from a cleaning head of the cleaner. The motor  15  is arranged to rotate the shroud  14  and body  17  in the same direction as the air flows around the shroud  14  inside the cyclone chamber  11 . The dirt and dust particles in the rotating airflow are forced radially outwardly against the side wall  12  of the cyclone chamber  11  under centrifugal action. The negative pressure draws the rotating airflow radially inwardly through the apertures in the shroud  14 . However, since the shroud  14  is rotating at or near the rotational speed of the airflow, the air does not need to decelerate to pass through the apertures into the interior of the shroud  14 . Any dirt and dust particles that accumulate on the exterior of the shroud  14  are thrown radially outwardly under centrifugal action and therefore the risk of blockage of the apertures is avoided. 
     The diameter of the cyclone chamber  11  is such that the airflow leaving the cyclone chamber is not fully cleaned and hence lighter dust particles pass through the apertures into the interior of the shroud  14 . 
     The dirt and dust particles that are forced against the tubular side wall  12  of the cyclone chamber  11  slowly migrate downwardly in a boundary layer towards the bottom end of the cyclone chamber  11 , whereupon they accumulate for collection. 
     The air entering the shroud  14  flows axially upwardly to the bottom wall of the body  17  where it is equally divided and flows tangentially into a respective cyclone chambers  18  through the inlets  20  thereof. The air inside each cyclone chamber  18  flows around the frusto-conical side wall  19  thereof towards the radially outer end of the cyclone chamber  18 . The lighter dust particles in the rotating airflow are forced radially outwardly against the side wall  19  under centrifugal action. The volume of rotating airflow slowly diminishes towards the radially outer end of the cyclone chamber  18  as air is drawn inwardly and axially towards the vortex finder  21 . However, the dust particles that are forced outwardly against the frusto-conical side wall move in a boundary layer towards the radially outer open end of the cyclone chamber  18 . It will be appreciated that the dust particles in the boundary layer are rapidly forced radially outwardly along the cyclone axis B by virtue of the centrifugal action of the rotating body  17 . 
     Dust particles leaving the cyclone chamber  18  are thrown radially outwardly against the tubular side wall  23  of the housing, whereupon they fall downwardly towards the bottom of the device. The bottom wall  24  can be removed to allow the separated dirt and dust particles to be removed from both the first and second stages of the device. 
     A vacuum cleaner in accordance with the present invention has a greatly improved separation efficiency compared with vacuum cleaners of the kind disclosed in GB2490693 even when the overall power consumption of the vacuum cleaner is reduced to comply with legislation. 
     While the preferred embodiment of the invention has been shown and described, it will be understood by those skilled in the art that changes of modifications may be made thereto without departing from the true spirit and scope of the invention.