Abstract:
An intake system for the combustion air of a motor of a hand held implement is provided. The system includes an air filter and a centrifugal separator. The air filter has a dirt chamber and a clean chamber that is separated therefrom by a filter medium. The clean chamber is fluidically connected with a carburetor of the motor to convey combustion air to the motor. The centrifugal separator splits the air stream into a core flow having low particle density and a peripheral flow having high particle density. The centrifugal separator includes at least two cyclones, wherein the discharged flows from the cyclones are respectively combined in pairs and open out into a common suction tube.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to a suction or intake system for the combustion air of the motor of a hand-held power tool, especially a disc cutter or cut-off machine. An intake system for the motor of a hover lawnmower is known from patent specification DE 25 50 165 C3 and has a centrifugal separator. Pre-cleaned air is delivered from the core flow of the centrifugal separator to the air filter disposed downstream of the centrifugal separator.  
           [0002]    The underlying objective of the invention is to propose an intake suction system of the aforementioned general type, which is efficient at sucking up dirt and can be readily integrated in a portable power tool.  
         SUMMARY OF THE INVENTION  
         [0003]    This objective is inventively realized by an intake system having an air filter with a dirt chamber and a clean chamber that is separated from the dirt chamber by a filter medium, wherein the dirt chamber is fluidically connected with the carburetor of the motor; a centrifugal separator that splits an incoming air stream into core flows having a low particle density, and peripheral flows having a high particle density, wherein one of the flows is conveyed to the dirt chamber of the air filter, and the other of the flows is discharged, wherein the centrifugal separator includes at least two cyclones, and wherein discharge flows from the cyclones are respectively combined in pairs; and a suction tube, wherein the paired discharge flows open out into the suction tube.  
           [0004]    The discharged airflows are fed into a common suction tube. This saves on mounting space compared with a system where a separate suction tube is provided for every cyclone. At the same time, fewer components are needed. However, using the common suction tube does mean that suction paths from the individual cyclones will necessarily be of differing lengths. When the airflows are remerged with one another, significant pressure differences are generated as a result, which can considerably reduce the suction power and hence the separating efficiency. In order to guarantee that dirt is sucked away efficiently, a system is therefore proposed whereby the airflows from the cyclones are merged again in respective pairs. Remerging the airflows in respective pairs reduces the resultant pressure differences. As a result, the same vacuum pressure and mass flow can be obtained at every cyclone.  
           [0005]    The intake system advantageously has a dirt collector with a dirt collection chamber into which the part-flows are fed. In particular, the dirt collection chamber has passages, in which the part-flows are merged. Efficient dirt suction can be achieved if a part-flow is fed out of a cyclone through a discharge spiral. Manufacture is facilitated if the discharge spirals from the cyclones are designed as an integral part of the dirt collector. In order to ensure efficient dirt suction in all the cyclones, the cross section and the length of the passages are selected so that approximately the same vacuum pressure prevails in the discharge spirals of all cyclones. This ensures that the same mass flow is fed through each passage. In this respect, the choice of cross section relative to the length of every passage is decisive. The distribution of pressure across the passages can be controlled by means of the cross section. A simple layout of passages is obtained by providing a dividing wall between two passages in the dirt collection chamber. The dividing wall may be designed as an integral part of the dirt collector.  
           [0006]    For practical purposes, the dirt collection chamber has a flow-connection to the peripheral flow leaving the cyclones, which has a high particle density. At least one cyclone advantageously has an immersion tube, provided on the end of the main body remote from the intake element, through which the core flow leaves the cyclone. In particular, the immersion tubes for all cyclones are provided as an integral part of the dirt collector. This therefore dispenses with the need for any other separate components. The fact that the immersion tubes are an integral part of the dirt collector makes for a compact construction. The dirt collection chamber in the dirt collector advantageously extends substantially transversely to the longitudinal axis of the cyclone.  
           [0007]    Every cyclone advantageously has a main body with an intake element adjoining it. The intake element is specifically provided as a separate part. The intake element can therefore be manufactured separately. This duly simplifies the component geometries to be manufactured. Particularly in the case of centrifugal separators made from plastic, production can be simplified by using an injection molding process. However, it may also be of advantage to make the intake element as an integral part of the main body. To make the centrifugal separator easy to retrofit in existing housings, it is proposed that the centrifugal separator should have at least two, in particular at least three, cyclones. This enables a sufficient throughput of combustion air to be generated without the need for a large contiguous construction volume. In order to obtain efficient intake, the intake element has an inlet funnel.  
           [0008]    The intake element is advantageously joined to the main body in a snap-fit connection. This makes for a simple assembly system. In particular, a catch connection is provided between intake element and main body. The intake elements may also be fixed onto the main body by additional means, such as welding for example. The number of parts is kept low if the intake elements for all cyclones are of an identical design. This makes production and warehouse storage less complex. However, it may also be expedient to design the intake elements as an integral part of the main bodies of the cyclones. The number of parts needed can also be reduced if the air filter is disposed in an air filter housing and the main bodies of the cyclones constitute a common component in conjunction with a first housing part of the air filter housing. This enables the cyclones to be produced in a single process step together with the air filter housing. This is easily done by providing the intake elements separately and manufacturing them by an injection molding process in particular. One particularly advantageous embodiment can be obtained by incorporating the dirt chamber of the air filter in the first housing part of the air filter housing.  
           [0009]    For the purpose of emptying the dirt collection chamber, the intake system incorporates a fan and a suction tube, in which case the suction tube provides a flow connection between the dirt collection chamber and the bladed rear face of the fan directed towards the motor. To this end, the suction tube is arranged on a suction side of the fan in particular and therefore sucks the dirt and debris which has accumulated in the dirt collection chamber, together with the airflow, out of the dirt collection chamber. For practical purposes, the cross section of the suction tube becomes larger towards the fan. This produces conducive flow conditions, thereby obtaining efficient suction. The suction tube opens in particular in the region of the rotation axis of the fan.  
           [0010]    In order to prevent dirt from accumulating in the suction tube, the suction tube approximately coincides with the direction of gravitational force when the power tool is in the normal operating position. A particularly conducive arrangement is one in which the dirt collection chamber is disposed above the air filter by reference to the direction of gravitational force when the power tool is in the normal operating position. The dirt collector is specifically attached to a housing part of the air filter housing, in particular to the first housing part. The dirt chamber of the air filter is specifically closed off from the outside environment by an air filter cover. This being the case, the air filter cover expediently locates in a sealing groove provided on the first housing part of the air filter housing. It is of a continuous and flat design to ensure efficient sealing. The air filter cover locates at least partially around the cyclone and at least partially, in particular totally, around the dirt collector. As viewed in the direction of the longitudinal axis of the cyclones, the dirt collector is disposed between the air filter cover and the cyclones.  
           [0011]    Advantageously, the main bodies of the cyclones are approximately cylindrical, in particular slightly conical. Opting for a slightly conical design will facilitate mold release of the main body after the injection molding process. An advantageous arrangement can be obtained if the longitudinal axes of the cyclones extend parallel with one another and form a plane. By reference to the direction of gravitational force, the intake elements specifically draw in combustion air from above the carburetor. In this region, the air is charged with a low proportion of particles, which means that the main flow leaving the cyclones contains few particles, ensuring that the air filter will have a long service life. In one particularly advantageous embodiment, the intake system proposed by the invention is used in a disc grinder. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Other features will become clear from the following description and the exemplary embodiment illustrated in the accompanying schematic drawings, in which:  
         [0013]    [0013]FIG. 1 is a schematic diagram showing a cutaway view in section through a disc cutter,  
         [0014]    [0014]FIG. 2 is a schematic diagram showing a section along line II-II indicated in FIG. 1,  
         [0015]    [0015]FIG. 3 is an exploded diagram of an intake system,  
         [0016]    [0016]FIG. 4 is a section through the intake system illustrated in FIG. 3,  
         [0017]    [0017]FIG. 5 is a perspective diagram of a dirt collector,  
         [0018]    [0018]FIG. 6 is a perspective view of an intake element,  
         [0019]    [0019]FIG. 7 is a perspective view of another intake element, and  
         [0020]    [0020]FIG. 8 shows a different perspective view of the intake element illustrated in FIG. 7. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    [0021]FIG. 1 is a cutaway view in longitudinal section illustrating a portable, hand-held power tool, namely a cut-off machine or disc grinder  1 . The disc grinder  1  has a motor  8 , which drives the cutting disc  43  shown in section in FIG. 2. The motor  8  is supplied with a fuel/air mixture via the carburetor  7 . The fuel/air mixture is admitted to the motor  8  in the region of the top dead center position of the piston  45  via an inlet  44  into the crankcase  46 . After combustion, the exhaust gases leave the combustion chamber  47  via the outlet  48 , which opens into the exhaust muffler  26 . Upstream of the carburetor  7  and disposed in the flow path is an air filter  3 . The clean chamber  6  downstream of the air filter  3  is connected to the carburetor  7 . The dirt chamber  5  upstream of the air filter  3  is linked by a flow-connection to a centrifugal separator  4 . The dirt chamber  5  is separated from the clean chamber  6  by a filter medium  27  disposed in an air filter housing  19  (FIG. 4).  
         [0022]    The centrifugal separator  4  has at least two, in particular at least three, cyclones  11 , one of which is illustrated in section in FIG. 1. The cyclones are of a tangential cyclone design, i.e. the inlet to the cyclone is essentially at a tangent to the circumference of the cyclone. However, it may be of advantage to use axial cyclones. The inlet to the cyclone  11  is disposed in an intake element  13 . The intake element  13  sucks or draws in combustion airfrom a region between the air filter  3  and the motor  8 , which region lies above the carburetor  7  by reference to the direction  25  of gravitational force.  
         [0023]    As illustrated in the section shown in FIG. 2, a fan  22  is provided at one end of the crankshaft  57  of the motor  8 . The fan  22  has blades both on the front face  23  remote from the motor  8  and on the rear face  24  directed towards the motor  8 . The purpose of the fan  22  is to generate a cool airflow to cool the motor  8 . Opening onto the rear face  24  of the fan  22  is a discharge pipe or suction tube  21 , which is connected to the centrifugal separator  4 . The suction tube  21  opens onto a suction area at the rear face  24  of the fan  22 . The orifice of the suction tube  21  is expediently disposed in the region of the rotation axis  33  of the fan  22 . A substantially pointed opening orifice of the suction tube  21  is advantageous. The orifice may have an aperture which widens the small cross-section of the pointed outlet towards the fan  22 . As a result, the pointed flow is distributed uniformly around the circumference in the region of the rotation axis of the fan.  
         [0024]    In order to operate the disc grinder  1 , a handle  32  is provided, partially illustrated in FIGS. 1 and 2, which spans the disc grinder  1  when in the normal operating position illustrated.  
         [0025]    [0025]FIG. 3 is an exploded diagram of the intake system  2 , which incorporates the air filter  3  and the centrifugal separator  4 . The centrifugal separator  4  has four cyclones  11 , each of which consists of a main body  12 , an intake element  13 , an immersion tube  14  and a discharge screw or spiral  42 . The four cyclones  11  are disposed parallel with one another in the airflow and form a cyclone battery. The intake elements  13  are each made as a single piece. A separate intake element  13  is provided for each cyclone  11 . The intake elements  13  each have a cyclone inlet  49  through which the combustion air is drawn into the cyclone  11 . The cyclone inlet  49  extends substantially at a tangent to the circumference of the main body  12  of the cyclone  11 . At the end directed towards the main body  12 , the intake elements  13  each have a collar  37 , the circumference of which is bigger than the main body  12 . By means of the collar  37 , the intake element  13  locates over the end  28  of the main body  12  of the cyclone  11  directed towards the intake element. The collar  37  has a slot  39 , which co-operates with a matching nose  38  on the main body  12 . Provided at the end  28  of the main body  12  is a continuous raised area  50 , which locates in a continuous groove  51  provided on the internal periphery of the intake elements  13 . In the located position, the nose  38  sits in the slot  39 . However, the intake elements  13  may be fixed to the main bodies  12  by any other method, for example by welding, bonding or by screws. The intake elements may also be made as an integral part of the main body  12 .  
         [0026]    The main bodies  12  of the cyclones  11  are approximately cylindrical, in particular slightly conical in design, the cone advantageously tapering towards the intake elements  13 . The longitudinal axes  20  of the cyclones  11  extend parallel with one another and in particular lie in a common plane. At the end  29  remote from the intake element  13 , the main bodies  12  are fixed to a first housing part  18  of the air filter housing  19 . The main bodies  12  form a common unit with the air filter housing  19 . In particular, they are designed as an integral part of the first housing part  18  of the air filter housing  19 . The end  40  of the suction tube  21  is fixed to a discharge or suction section  41  in the region of the main bodies  12  of the cyclones  11 . The discharge section  41  is disposed in the first housing part  18  of the air filter housing  19 . The discharge section  41  advantageously extends substantially parallel with the cyclone bodies  12 . However, the direction of flow is the opposite of that through the cyclones  11 . The cross-section of the suction tube  21  decreases from the end  40  to the end  67  directed towards the fan  22 .  
         [0027]    As illustrated in FIG. 4, the suction tube  21  coincides with the direction  25  of gravitational force in a region between its ends  40 ,  67  when the power tool is in its normal operating position.  
         [0028]    In the first housing part  18  of the air filter housing  19 , a continuous sealing groove  34  is provided on the face remote from the main bodies  12  of the cyclones  11 . A seating  35  for a dirt collector  16  is provided inside the sealing groove  34 . The dirt collector  16  is attached to the first housing part  18  of the air filter housing  19  by means of fixing screws  36 . However, the dirt collector  16  may also be connected to the first housing part by any other type of connection, for example by a bonded or welded joint. The dirt collector  16  may also be joined to the first housing part  18  by a snap-in connection. As illustrated in the section of FIG. 4, the dirt collector  16  sits entirely in the seating or receiving means  35 . The immersion tubes  14  provided on the dirt collector  16  therefore project respectively into a main body  12  of a cyclone  11 . The discharge spiral  42  provided on the outer periphery of each immersion tube  14  sits in a tight seal against the main body  12  of the respective cyclone  11 . As illustrated in FIG. 3, the discharge spirals  42  open into a dirt collection chamber  17  in the dirt collector  16 . The dirt collection chamber  17  extends substantially transversely to the longitudinal axis  20  of the cyclones. In particular, the dirt collection chamber  17  extends substantially parallel with the plane formed by the longitudinal axes  20  of the cyclones  11 . An air filter cover  15  is removably screwed by a butterfly screw  31  in the screw mount  53  provided in the first housing part  18  of the air filter housing  19 .  
         [0029]    As illustrated in FIG. 4, when the air filter cover  15  is tightly screwed on, a rim  54  integral with the air filter cover  15  projects into the sealing groove  34  provided on the first housing part  18  of the air filter housing  19 . As a result, the dirt chamber  5  upstream of the air filter  3  is sealed off from the outside environment. One or more resilient sealing elements may be arranged in the sealing groove  34  to improve the seal. The filter medium  27  disposed in the air filter  3  is sealed off from the air filter housing  19  so that a flow connection via the filter medium  27  exists only between the clean chamber  6  and dirt chamber  5 . Orifices or openings  55  are provided in the first housing part  18  of the air filter housing  19  through which a flow connection is established from the filter medium  27  to the interior  56  of the air filter cover  15  and hence to the centrifugal separator  4  opening into the interior  56 .  
         [0030]    The dirt collector  16  is disposed in the seating  35  so that a rim  30  of the first housing part  18  of the air filter housing  19  extends around it. The rim  30  is an integral part of the cyclone main bodies  12  and the first housing part  18 . As viewed in the direction of the longitudinal axis  20  of the cyclone  11 , the dirt collector  16  is disposed between the main body  12  of the cyclones  11  and the air filter cover  15 . The air filter cover  15  completely encases the dirt collector  16  in an area outside of the interior  56  closed off by the sealing groove  34  in the direction of the cyclone longitudinal axis  20 . The cyclones  11  are also partially encased by the air filter cover  15  in a region of their longitudinal extension.  
         [0031]    The combustion air passes through the cyclone inlet  49  into an intake element  13 . The radial inlet generates an airflow in the circumferential direction of the cyclone main body  12 . As a result of the centrifugal forces, the particles contained in the airflow accumulate in the outer peripheral flow  10 . The peripheral flow  10  thus has a higher particle density than the core flow  9  in the interior in the region of the longitudinal axis  20 . The core flow  9  passes through the immersion tube  14  out to the interior  56 , while the peripheral flow  10  is directed through the discharge spiral  42  to the dirt collection chamber  17 . However, it may also be expedient to direct an airflow with a defined particle density out of the peripheral flow to the air filter. From the dirt collection chamber  17 , the airflow together with the debris is sucked through the suction tube  21  by the bladed rear face of the fan  22 .  
         [0032]    [0032]FIG. 5 provides a perspective diagram of a dirt collector  16 . Together with the dirt collector  16 , the discharge spirals  42  of the four cyclones  11  as well as the immersion tubes  14  of the cyclones  11  are designed as an integral unit. Two fixing orifices  68  are provided in the dirt collector  16 , through with the screws  36  illustrated in FIG. 3 extend in order to attach the dirt collector  16  to the housing  19  of the air filter. The peripheral flow  10  containing a high density of particles, illustrated in FIG. 4, flows into the discharge spirals  42  of the cyclones  11 . The part-flows flowing into the dirt collector  16  are fed into the dirt collection chamber  17 . Accordingly, each part-flow is fed through a passage  59 ,  60 ,  61 ,  62  in the dirt collection chamber  17 .  
         [0033]    The individual part-flows directed into the passages merge with one another again in pairs in the dirt collection chamber  17 . Dividing walls or partitions  65 ,  66  are duly provided for this purpose. Dividing wall  65  is disposed between the passages  59  and  60  and extends more or less as far as center of the dust collection chamber  17 . The part-flows fed into the passages  59  and  60  from two adjacent cyclones  11  therefore merge with one another more or less at the center of the dirt collection chamber  17 . Passages  59  and  60  therefore open into a passage  63 . The part-flows from the other two adjacent cyclones  11  are directed into the dirt collection chamber  17  through passages  61  and  62 , which open into a passage  64  in which the part-flows merge. Passages  61  and  62  are separated by a dividing wall  66 , which also separates passage  60  from passage  61 . The passages  63  and  64  directing the respective part-flows out from the cyclones merge in the region of the tongue  71 , disposed on the dividing wall  66  more or less in the region of the discharge section  69 . From the discharge section  69 , the airflow is fed into the suction tube  21 , the start of which is indicated by the circle  70 . The tongue  71  is designed so that the cross-section in passage  64  is smaller than that of passage  63 . Passage  61  and passage  64  are separated from passage  63  by the dividing wall  66 . The cross-sections of passages  59  to  64  are selected by reference to the respective length of the passages so that a more or less uniform vacuum pressure and mass flow is established at every discharge spiral  42 . This ensures that the dirt is efficiently carried out of all the cyclones.  
         [0034]    FIGS.  6  to  8  illustrate exemplary embodiments of intake elements  13 . The intake element  13  illustrated in FIG. 6 has an inlet funnel  58  in the region of the inlet orifice  49  through which the airflow is drawn in. A dividing wall  72  is provided in the main body  73  in the region where the intake base or connector  75  opens and forms an extension of the side wall  74  of the intake base  75  directed towards the cyclone main body  12 . The dividing wall  72  prevents the airflow from being able to pass out from the intake base  75  directly into an immersion tube  14  located at the opposite end of the cyclone  11 . The air drawn in is simultaneously forced into a rotating motion.  
         [0035]    [0035]FIGS. 7 and 8 illustrate a front and rear view of an intake element  13 . The inflow geometry may be tangential to the flat base and/or, as illustrated in FIG. 6, with an axial pitch, in other words in the form of a helix. The additional or alternative embodiment with a radial spiral, in other words radially pitched, may also be of advantage (FIGS. 7 and 8). With these embodiments, the airflow is forced into a rotating motion. It may be of advantage if the cross-section in the intake base  75  decreases more or less up to a region  76 . The reduced cross-section will accelerate the flow.  
         [0036]    In order to produce efficient separation with a low flow resistance, it is of advantage if a length of the intake base  75  is approximately 10 mm. The length l of the intake base is the area more or less up to the periphery of the main body  12  of the cyclone, as indicated in FIG. 8. The length in the cyclone inlet  49  is expediently twice the width in the cyclone inlet. This imparts sufficient impetus to the flow to produce efficient separation.  
         [0037]    The immersion tubes  14  are designed as an integral part of the dirt collector  16 , and are so in particular for all cyclones  11 . However, it may be more practical instead to provide individual covers which enclose the immersion tube and/or discharge spiral. The intake elements  13  are expediently joined to the main bodies  12  of the cyclones in a push-fit connection. All the intake elements  13  are specifically of the same design. As illustrated in FIG. 4, the dirt collection chamber  17  is disposed substantially above the air filter  3  by reference to the direction  25  of gravitational force. In particular, the dirt collector  16  is entirely disposed above the air filter  3 . The cyclones  11  are also disposed above the air filter  3 , as illustrated in FIG. 4.  
         [0038]    The specification incorporates by reference the disclosure of German priority document DE 102 35 761.7 filed Aug. 5, 2002.  
         [0039]    The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.