Abstract:
The invention relates to a rotor for a centrifuge for cleaning a liquid, in particular the lubricating oil of an internal combustion engine, wherein the rotor is designed in two parts, namely, on the one hand, a drive part and, on the other hand, a dirt-collecting part comprising a dirt collection area, wherein the dirt-collecting part can be connected to the drive part to the rotor, and wherein the dirt-collecting part can be detached, for disposal or cleaning, by being pulled off axially from the drive part. The rotor according to the invention is characterized in that the drive part and the dirt-collecting part are provided with an interacting connection arrangement which, when the dirt-collecting part is connected to the drive part, secures the dirt-collecting part against axial withdrawal relative to the drive part, and in that the dirt-collecting part is provided with an unlocking arrangement which interacts with the connection arrangement and which includes at least one gripping and actuating element that protrudes upward above the dirt-collecting part.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a rotor for a centrifuge for cleaning a liquid, in particular the lubricant oil of an internal combustion engine, the rotor having a two-part construction, having on the one hand a drive part and on the other hand a dirt-catching part that has a dirt collection area, the dirt-catching part being connectable to the drive part at the rotor, and the dirt-catching part being capable of being separated from the drive part by pulling it off axially, in order to dispose of it or clean it. Moreover, the present invention relates to a centrifuge having a rotor of the type named above. 
   Rotors of centrifuges are parts that must be exchanged or cleaned at certain intervals. At the time of the exchange or the cleaning, the rotors are wetted by the fluid cleaned in the centrifuge. In order to avoid frictional losses that would reduce their rotational speed, standard rotors have smooth outer surfaces, making manual grasping of the rotor in order to remove it from the centrifuge housing difficult. If the rotor is a part of a centrifuge for cleaning lubricant oil, a further difficulty is that the surface of the rotor is wetted by oil, which makes grasping it significantly more difficult than it already is due to the smooth outer surface. This problem exists both in one-part rotors, which are exchanged as a whole, and also in two-part rotors as mentioned above, which consist of a drive part that standardly remains in the centrifuge and a dirt-catching part detachably connected thereto, which is standardly an exchangeable part. In two-part rotors, it is important that during operation of the centrifuge the dirt-catching part be secured on the drive part both against undesired movements in the axial direction and also against relative movements in the circumferential direction. At the same time, however, it must remain possible to exchange the dirt-catching part as needed by pulling it off the drive part. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is therefore to create a rotor of the type named above in which on the one hand it is ensured that the dirt-catching part is reliably secured in its position on the drive part during operation of the centrifuge, and that on the other hand the dirt-catching part is capable of being removed from the drive part quickly and easily for the purpose of maintenance of the centrifuge, in order to replace it with a new or cleaned dirt-catching part. In addition, a centrifuge that is particularly suitable for such a rotor is to be created. 
   The solution of the part of this problem relating to the rotor is achieved according to the present invention by a rotor of the type named above that is characterized in that on the drive part and on the dirt-catching part, cooperating, connecting means are provided that secure the dirt-catching part, in the state in which it is connected to the drive part, against being pulled off axially relative to the drive part, and that on the dirt-catching part unlocking means that cooperate with the connecting means are provided that comprise at least one grasping and actuating element that protrudes upward past the dirt-catching part. 
   In the rotor according to the present invention, it is advantageously ensured that the dirt-catching part is reliably secured in its position on the drive part, and in particular that it cannot by itself move undesirably far in the axial direction on the drive part. A certain degree of slight movement play can be useful here, in order for example to permit accommodation of varying thermal expansions. At the same time, in the rotor according to the present invention it is ensured that as needed, in particular during maintenance of the centrifuge, the dirt-catching part can easily be removed from the drive part; for this purpose, the grasping and actuating elements can be grasped by an operator either manually or using a simple tool. Advantageously, the unlocking of the connecting means and the pulling off of the dirt-catching part from the drive part take place together via the at least one grasping and actuating element; in this way, a particularly simple and ergonomic handling is achieved. Of course, the grasping and actuating element is formed in such a way that it can still be securely grasped and actuated even when it is wetted with a liquid, e.g. oil. 
   In another embodiment, it is preferably provided that the connecting means are constructed as locking connecting means that automatically enter into connecting engagement with one another when the dirt-catching part is connected to the drive part by axially plugging the dirt-catching part onto the drive part. In this way, it is ensured that when a fresh dirt-catching part is installed, a simple axial plugging onto the drive part is sufficient to bring the connecting means into connecting engagement. Installation errors that could result in an error in the effective connection in the axial direction between the drive part and the dirt-catching part are practically excluded in this way. 
   In addition, the present invention proposes that the connecting means comprise one or more snap hooks that, in the connected state of the drive part and the dirt-catching part, engage in one or more openings situated on the drive part. Such snap hooks are simple in the design and reliable in their functioning. The snap hooks can easily be configured such that they automatically enter into engagement in the direction of installation of the dirt-catching part, but block movement in the opposite direction of the dirt-catching part as long as the unlocking means are not actuated. The openings that cooperate with the snap hooks are also very easy to manufacture, which permits overall an economical manufacture of the rotor according to the present invention. 
   A development of the present invention provides that the connecting means at the side of the dirt-catching part are situated on two flexible arms that are situated opposite one another and that run essentially parallel to an axis of rotation of the rotor, and that the arms have, as unlocking means, arm ends that protrude upward past the rest of the dirt-catching part, these arms forming two grasping and actuating elements. Preferably, the arms are themselves flexible, or, if this is not the case, they are equipped with a spring element, the spring force holding the arms in their locking position if no external actuating forces are exerted on them. In this embodiment, the connecting means and the unlocking means are constructively combined, requiring a lower manufacturing expense and providing an additional contribution to lower manufacturing costs. 
   In a concrete development, the snap hooks on the arms point radially outward, and the arms can be pivoted radially inward towards one another for unlocking. In this embodiment, the unlocking is particularly simple, because here it is sufficient to use for example the thumb and index finger to press the two arms inward in the radial direction, against their own spring force or their spring element, and then, in this compressed state of the arms, to pull the dirt-catching part off the drive part using the two arms and the grasping and actuating elements formed by the ends of the arms. 
   In an alternative embodiment of the rotor, it is proposed that the connecting means at the dirt-catching part are situated on a ring that is flexible in the radial direction and is situated essentially in a radial plane concentric to an axis of rotation of the rotor, and that the ring protrudes upwards, past the rest of the dirt-catching part, as a whole or with two ring segments situated opposite one another as unlocking means. This ring forms, as do the arms mentioned above, a flexible and resilient element that permits the desired automatic engagement of the connecting means as well as the unlocking, which can be brought about by an unlocking action executed against the spring force exerted by the ring itself or by a spring element allocated to the ring. 
   In a concrete development, for this purpose it is provided that the snap hooks on the ring are situated opposite one another and point radially inward, and that for the unlocking the ring can be pressed inward radially at two areas situated between the snap hooks, simultaneously forcing the snap hooks to move radially outward. In this embodiment, the effect is exploited that a flexible ring having a constant circumference that is pressed inward radially at two opposite points will necessarily move outward in the radial direction at two additional points situated between these first two points in the circumferential direction, because the circumference of the ring does not change. The ring can initially have a round shape, and can then be deformed to an ellipse or an oval through the exertion of a radially inward-directed force at two force application points situated opposite one another. Alternatively, the ring may also already have an elliptical or oval initial shape which is then further deformed by the exerted force; depending on the construction of the ring, the deformation can go either in the direction of a “flatter” ellipse or oval shape or in the direction towards a circular shape. 
   For all above-described embodiments of the rotor, it is preferably provided that the dirt-catching part is an injection-molded part made of plastic, and that the connecting means at the dirt-catching part and the unlocking means are constructed in one piece with the rest of the dirt-catching part. In this way, the dirt-catching part becomes an economically manufacturable mass part that does not require any additional working steps for the attachment of the connecting means. 
   In addition to the above-described rotor, the present invention also relates to a centrifuge having such a rotor, the centrifuge comprising a housing that accommodates the rotor and that has a removable lid. According to the present invention, for the centrifuge it is provided that the lid has on its underside facing the rotor at least one blocking element that cooperates with the unlocking means and that, when the lid is in place, prevents the unlocking means from being displaced in the unlocking direction. In this way, it is ensured with a particularly high degree of security that an undesired self-displacement of the unlocking means in the unlocking direction cannot take place during operation of the centrifuge. 
   With regard to this, a development provides that the blocking element is a projection that extends in the axial direction into an area of movement of the unlocking means when the lid is put into place; when the lid is in place, this projection is situated radially inside or radially outside the unlocking means, and blocks a radially inward or radially outward unlocking movement of the unlocking means. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, two exemplary embodiments of the present invention are explained on the basis of a drawing. 
       FIG. 1  shows a centrifuge having a rotor, in longitudinal section, 
       FIG. 2  shows a segment of the upper central area of the centrifuge in  FIG. 1 , also in longitudinal section, in an enlarged view, 
       FIG. 3  shows the segment according to  FIG. 2 , in this case shown without a drive part of the rotor, also in longitudinal section, 
       FIG. 4  shows a segment of the upper central area of a dirt-catching part that forms a part of the rotor, in longitudinal section, 
       FIG. 5  shows the dirt-catching part of the rotor according to  FIGS. 1 to 4 , in a top view, 
       FIG. 6  shows a second exemplary embodiment, also in a longitudinal section through a central upper area of a centrifuge, and 
       FIG. 7  shows a dirt-catching part of the rotor of the centrifuge from  FIG. 6 , in a top view. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The exemplary embodiment shown in  FIG. 1  of a centrifuge  1  comprises a rotor  10  that is rotatably mounted on an axle  12 . Axle  12  is connected at its lower end to a part of a housing  11 , hereby a screw connection. Upwardly, housing  11  is closed during operation of centrifuge  1  by a screw-on lid  13 . Screw-on lid  13  stands in screwed engagement with another part of housing  11  that is not shown in  FIG. 1  and that extends further downward from the lower area of lid  13  and surrounds the depicted part of housing  11 . 
   Here, rotor  10  has a two-part construction, and comprises a drive part  2  and a dirt-catching part  3 . Drive part  2  comprises a central hollow element  20  from whose lower end area two nozzle arms  21  extend outward and downward obliquely in the radial direction. At the free end of each nozzle arm  21  there is situated a respective jet nozzle  22  through which a liquid jet can be ejected in order to set drive part  2  into rotation via the reaction principle. For the rotatable mounting of drive part  2  on axle  12 , a lower plain bearing  24  and an upper roller bearing  25  are used. 
   Dirt-catching part  3  is connected in rotationally fixed manner to drive part  2 , so that dirt-catching part  3  also executes all rotational movement of drive part  2 . Drive part  2  is usefully a permanent component that remains in centrifuge  1  over the entire lifetime of use of the centrifuge, while dirt-catching part  3  is an exchangeable part that can be pulled upward off drive part  2  in the axial direction for the purpose of maintenance, after removal of lid  13 , and replaced by a fresh dirt-catching part  3 . 
   In order to secure dirt-catching part  3  in the axial direction against undesired displacements relative to drive part  2 , cooperating connecting means  23  and  33  are provided in the upper area of drive part  2  and dirt-catching part  3 . 
   In the exemplary embodiment shown in  FIG. 1 , connecting means  23  at drive part  2  are made up of two recesses or openings on the radially inward-pointing side of the upper end of central hollow element  20  of drive part  2 . In the assembled state of rotor  10  shown in  FIG. 1 , connecting means  33  at the dirt-catching part, in the form of two locking noses or locking hooks, engage in connecting means  23 . The connecting means  33  formed by the locking noses or locking hooks are integrally formed on opposite-situated arms  34 , on their radially outward-pointing side. 
   In section, as shown in  FIG. 1 , arms  34  are approximately U-shaped, and arms  34  are fashioned in materially unified fashion with the rest of the dirt-catching part, and are made of plastic. This gives arms  34  sufficient flexibility and spring force to perform their function. Connecting means  23  and  33 , which engage with one another according to  FIG. 1 , ensure that dirt-catching part  3  cannot move in the axial direction, i.e. parallel to an axis of rotation  19  of rotor  10 , relative to drive part  2 . 
   The two arms  34  have unlocking means  35  that extend upward past a covering wall  31  of dirt-catching part  3 . These unlocking means  35  are used to detach dirt-catching part  3  by disengaging connecting means  23  and  33 , so that dirt-catching part  3  can be pulled off of drive part  2 . For this purpose, lid  13  is removed, and unlocking means  35  are moved inwardly toward one another in the radial direction, e.g. by the thumb and index finger of an operator, causing connecting means  33  at dirt-catching part  3  to move inward in the radial direction far enough that they move out of engagement with connecting means  23  of drive part  2 . In this position of connecting means  33 , dirt-catching part  3  can then be pulled off of drive part  2  upward in the axial direction, and can be replaced by a new dirt-catching part  3 . When installing new dirt-catching part  3 , it is sufficient to push this part from the top downward onto drive part  2  in the axial direction, such that at the end of this plugging movement connecting means  23  and  33  automatically enter into locking engagement with one another. 
   In order to prevent undesired unlocking of connecting means  23  and  33  during operation of centrifuge  1 , lid  13  has on its underside a blocking element  15 . This blocking element has the form of a sleeve whose outer circumference is conical, and whose diameter becomes smaller from the top towards the bottom. When lid  13  is attached, this blocking element  15  moves downward in the axial direction into the area of movement of connecting means  33  and of unlocking means  35 , and blocks these against movement inward in the radial direction, i.e. the detaching direction. Because dirt-catching part  3  forms together with drive part  2  the rotor  10  that rotates during operation of centrifuge  1 , while lid  13  remains stationary, a sufficient movement gap must of course remain open between blocking element  15  on the one hand and connecting means  33  and unlocking means  35  on the other hand, so that disturbing friction does not occur. 
   In addition, in the exemplary embodiment of centrifuge  1  shown here, the upper end of axle  12  is supported and held in centering fashion in lid  13 . 
   Finally,  FIG. 1  also shows, in the interior of dirt-catching part  3 , guide and dividing walls  32 , situated precisely in the plane of the section, that run in the radial direction and that subdivide dirt-catching part  3  into a plurality of chambers situated next to one another in the circumferential direction. 
     FIG. 2  shows the area of centrifuge  1  having connecting means  23  and  33  in an enlarged detail view, also in longitudinal section; in the right half of  FIG. 2 , the position of the section is pivoted somewhat in the circumferential direction relative to  FIG. 1 . In the center of  FIG. 2  there runs axle  12 , on which the drive part, of which only an upper part of central hollow element  20  is visible here, is mounted. For this mounting, inter alia the roller bearing  25  visible in  FIG. 2  is used that is situated between the outer circumference of axle  12  and the inner circumference of central hollow element  20 . 
   In the left half of  FIG. 2 , one of the recesses that forms connecting means  23  is visible at the upper end of central hollow element  20 , on the radially inward-pointing side of hollow element  20 . In the right half of  FIG. 2 , the sectional plane runs differently than in  FIG. 1 , such that in the right half of  FIG. 2  an area of central hollow element  20  is sectioned that is situated outside connecting means  23 , seen in the circumferential direction. 
   In  FIG. 2 , the U shape of arms  34 , connected radially inwardly and at the top to the rest of dirt-catching part  3 , can be seen particularly clearly. From here, arms  34  run at first approximately downward in the axial direction, and then each bend radially outward and then upward in a U-shape. Close to the upper end of central hollow element  20 , connecting means  33  at the dirt-catching part, in the form of radially outward-pointing locking noses or locking hooks, are situated opposite connecting means  23  of element  20 . Arms  34  then continue upward as unlocking means  35 , each terminating in a grasping and actuating element  36 . 
   In the state of drive part  2  and dirt-catching part  3  shown in  FIG. 2 , their connecting means  23  and  33  are engaged with one another, thus preventing a movement of dirt-protecting part  3  in the axial direction relative to drive part  2 . 
   Blocking element  15  on the underside of lid  13  prevents an undesired self-detachment of connecting means  23  and  33 . In the assembled state of the lid, this blocking element  15  is situated in the movement area of arms  34 , directed radially inward, thus blocking an unlocking movement. In order to avoid disturbing friction between unlocking means  35  and blocking element  15 , a sufficiently large movement gap is left open between them. 
   It can also be seen in  FIG. 2  that the upper end of axle  12  is supported and held in the center of lid  13  in centering fashion. 
   It can also be seen in  FIG. 2  that dirt-catching part  3  has in its covering wall  31  two through-openings  30  in each of which there engages a part of the upper end area of central hollow element  20  of drive part  2 , and through which unlocking means  35  protrude upward. In this way, it is possible simultaneously to provide a rotationally fixed connection between drive part  2  and dirt-catching part  3 , and to prevent the relative movements of drive part  2  and dirt-catching part  3  in the circumferential direction during operation of the centrifuge. 
   If lid  13  is removed in order to perform maintenance, blocking element  15  is removed from the area of movement of unlocking means  35 . Moreover, grasping and actuating element  36  of unlocking means  35  are then available for manual grasping by an operator. In this way, it is then very easy to actuate unlocking means  35  via grasping and actuating elements  36 , for example using the thumb and index finger. For the unlocking, grasping and actuating elements  36  are pressed inward towards one another in the radial direction, causing connecting means  33  at the dirt-catching part, on arms  34 , to move out of engagement with connecting means  23  on drive part  2 . In this position, dirt-catching part  3  can then be pulled off of drive part  2  upward in the axial direction, held by grasping and actuating elements  36 . 
   When placing a new dirt-catching part  3  onto drive part  2 , connecting means  23  and  33  automatically move into locking engagement with one another, so that an actuation of unlocking means  35  is then not required. 
   Due to the position of the longitudinal section in the right half of  FIG. 2 , which is changed in  FIG. 2  relative to  FIG. 1 , in the left half of  FIG. 2  one of the guide and dividing walls  32  is again visible in section, while in the right half of  FIG. 2  the view is now into one of the chambers inside dirt-catching part  3 . 
     FIG. 3  shows the same segment as does  FIG. 2 , but in  FIG. 3 , in order to illustrate the construction of dirt-catching part  3 , drive part  2  (here its central hollow element  20 ) has been omitted. 
   In the center of  FIG. 3 , there is situated axle  12  on which upper roller bearing  25  is situated. Axle  12  is surrounded by dirt-catching part  3 , of which one of guide and dividing walls  32  is again visible in section in the left half of  FIG. 3 , while in the right half of  FIG. 3  the view is into one of the chambers inside dirt-catching part  3 . Upwardly, dirt-catching part  3  is essentially sealed by covering wall  31 , and through-openings  30  are situated in the central part of covering wall  31 . 
   On covering wall  31  of dirt-catching part  3 , arms  34  are integrally formed radially inwardly in one piece therewith; these arms are U-shaped and flexible. One of connecting means  33  at the dirt-catching part is integrally formed on each arm  34  in the form of radially outward-pointing locking noses or locking hooks. Further upward, arms  34  go over into unlocking means  35  with the respective grasping and actuating element  36 . When lid  13  is in place, as is shown in  FIG. 3 , blocking element  15  on the underside of lid  13  prevents unlocking means  35  from moving radially inward, i.e. in the unlocking direction. 
     FIG. 4  shows another segment, here a vertical section only through the upper central area of dirt-catching part  3 . Here it can be seen particularly clearly that when the lid is removed, unlocking means  35  protrude upward with their grasping and actuating elements  36  far enough past covering wall  31  of dirt-catching part  3  to enable problem-free manual grasping and unlocking. This is easily possible even when the surfaces are oily, as in, for example, lubricant oil centrifuges. 
     FIG. 5  shows dirt-catching part  3  from  FIGS. 1 to 4  in a top view. Thus, here covering wall  31  of dirt-catching part  3  is visible, and through-openings  30  are situated in covering wall  31  to the left and to the right of the midpoint. Through through-openings  30 , arms  34  protrude from the interior of dirt-catching part  3  upward, i.e. in the direction toward the viewer of  FIG. 5 . From each arm  34  one of connecting means  33  protrudes outward in the radial direction, in the form of the locking nose or locking hook. Radially externally thereto, in  FIG. 5  unlocking means  35  are visible with their grasping and actuating elements  36 . If a force is exerted on grasping and actuating elements  36  in the direction of arrows F according to  FIG. 5 , arms  34  move inward in the radial direction against their own spring force, causing connecting means  33  also to move inward in the radial direction, and in this way to move out of engagement with the connecting means on the drive part (which is not shown here). In this state, it is then possible to lift dirt-catching part  3  off the drive part by exerting a tensile force, oriented upward in the axial direction, on grasping and actuating elements  36 . 
     FIGS. 6 and 7  show, in section and in a top view, a modified exemplary embodiment of centrifuge  1 , in which connecting means  23  on drive part  2  and connecting means  33  on dirt-catching part  3  have a different construction. 
   In the section shown in  FIG. 6 , in the center axle  12  can be seen on which drive part  2 , together with dirt-catching part  3 , is rotatably mounted as a rotor about axis of rotation  19 . Two bearings are used for the mounting, of which here upper bearing  25 , in the form of a roller bearing, is visible. Bearing  25  is situated between the outer circumference of axle  12  and the inner circumference of a hollow element  20  that forms a part of drive part  2 . Above bearing  25 , central hollow element  20  runs further upward, and has there, at two areas situated opposite one another, grooves that open outwardly and that form connecting means  23  at the drive part. 
   Here as well, dirt-catching part  3  is upwardly limited by a covering wall  31  that has in its center a through-opening  30  through which the upper end of central hollow element  20  protrudes upward. In its central area, covering wall  31  has two wall segments  31 ′ that run upward in the axial direction and are situated opposite one another and that run parallel to the upper end area of central hollow element  20  having connecting means  23  provided there. Wall segments  31 ′ each bear one of connecting means  33 , which here are present in the form of locking noses or locking hooks pointing inward in the radial direction, and which, in the assembled state of drive part  2  and dirt-catching part  3  shown in  FIG. 6 , engage with drive-part-side connecting means  23 . 
   Upwardly, wall segments  31 ′ go over into a ring  34 ′ that runs approximately concentrically around axle  12 , and that, like wall segments  31 ′, is fashioned in a materially unified manner and in one piece with covering wall  31  and with the rest of dirt-catching part  3 . Dirt-catching part  3  is made of plastic, which means that ring  34 ′ and wall segments  31 ′ are flexible and have resilient properties. In a basic state in which no external forces are exerted on ring  34 ′, ring  34 ′ and wall segments  31 ′ have the shape and position shown in  FIG. 6 , in which connecting means  33  engage with connecting means  23 . Thus, in this state dirt-catching part  3  is sufficiently secured against an axial displacement relative to drive part  2 . A certain amount of movement play is allowed here in order to enable differing thermal expansions to be accommodated. Here, this is concretely achieved in that the grooves that form connecting means  23  are longer in the axial direction than the axial height of the locking noses and locking hooks that form connecting means  33 . 
   Ring  34 ′ that circumferentially connects wall segments  31 ′ simultaneously acts as unlocking means  35  and as grasping and actuating element  36  in order to bring connecting means  33  and  23  out of engagement with one another and then to pull dirt-catching part  3  off of drive part  2  once lid  13  has been removed. 
   This function is illustrated in  FIG. 7 , which shows a top view of dirt-catching part  3  from  FIG. 6 . In the center of  FIG. 7  there is situated axle  12 , here sectioned in its upper end. Running centrally through axle  12  is axis of rotation  19  for dirt-catching part  3  and for the associated drive part (not shown here), which together form the rotor of the centrifuge. 
   Around axle  12  runs ring  34 ′, which is shown here in a state in which a force is exerted on it in the direction of arrows F. At the points at which force arrows F make contact, the force causes a radially inward displacement of the force-charged areas of ring  34 ′. Because the ring is flexible and does not change its circumference, the exertion of force F necessarily results in a broadening of ring  34 ′ outward in the radial direction, between the force contact points regarded in the circumferential direction; this broadening is shown by the two movement arrows drawn in at left and at right in  FIG. 7 . In this way, connecting means  33  situated there of dirt-catching part  3  move out of engagement with connecting means  23  of the drive part. In this unlocked state, dirt-catching part  3  on ring  34 ′ can be lifted off upwardly from the drive part, i.e. perpendicular to the plane of the drawing, towards the viewer. 
   Radially externally from axle  12 , upper roller bearing  25  is visible through central through-opening  30  in covering wall  31  of dirt-catching part  3 . Through the radially external area of through-opening  30 , the upper end of central hollow element  20  of the drive part is visible, on which drive-part-side connecting means  23  are provided. 
   Thus, in this embodiment ring  34 ′ bears at its area pointing to the left and to the right in  FIG. 7  the dirt-catching-part-side connecting means  33 , while its areas situated at the top and at the bottom in  FIG. 7  respectively form unlocking means  35  and grasping and actuating elements  36 . 
   As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.