A debris removal device features structural support from an exterior housing that allows more space for debris collection. The debris enters the collection volume from the top to eliminate debris from having to go through a valve. The screen in the device is disposed internally to protect it during handling and running. A variety of external flow diverters are used to direct debris laden fluid into the tool and to keep debris out of an annular space around the tool that could interfere with its removal. The diverters can be actuated by relative movement in the tool or applied pressure to a piston which can inflate a sleeve or orient or misalign paths through brushes for selective bypassing of fluid exterior to the tool.

FIELD OF THE INVENTION 
     The field of the invention is downhole devices that separate cuttings from fluid that was previously pumped through the device to a mill or tool below and return the cuttings-laden fluid up an annular space to pass through the tool again for debris removal. 
     BACKGROUND OF THE INVENTION 
     Milling downhole components generates debris that needs to be removed from circulating fluid. Fluid circulation systems featuring flow in different directions have been tried. One design involves reverse circulation where the clean fluid comes down a surrounding annulus to a mill and goes through rather large ports in the mill to take the developed cuttings into the mill to a cuttings separator such as the VACS tool sold by Baker Oil Tools. Tools like the VACS cannot be used above a mud motor that drives the mill and can only be used below a mud motor when using a rotary shoe. Apart from these limitations the mill design that requires large debris return passages that are centrally located forces the cutting structure to be mainly at the outer periphery and limits the application of such a system to specific applications. 
     The more common system involves pumping fluid through a mandrel in the cuttings catcher so that it can go down to the mill and return up the surrounding annular space to a discrete passage in the debris catcher. Usually there is an exterior diverter that directs the debris laden flow into the removal tool. These designs typically had valves of various types to keep the debris in the tool if circulation were stopped. These valves were problem areas because captured debris passing through would at times cling to the valve member either holding it open or closed. The designs incorporated a screen to remove fine cuttings but the screen was placed on the exterior of the tool putting it in harms way during handling at the surface or while running it into position downhole. These designs focused on making the mandrel the main structural member in the device which resulted in limiting the cross-sectional area and the volume available to catch and store debris. This feature made these devices more prone to fill before the milling was finished. In the prior designs, despite the existence of a screen in the flow stream through the tool, some fines would get through and collect in the surrounding annulus. The fixed debris barriers could get stuck when the tool was being removed. In some designs the solution was to removably mount the debris barrier to the tool housing or to let the debris barrier shift to open a bypass. In the prior designs that used cup seals looking uphole for example, if the screen in the tool plugged as the tool was removed the well could experience a vacuum or swabbing if a bypass around the cup seal were not to open. 
     Typical of the latter type of designs is U.S. Pat. No. 6,250,387. It accepts debris in FIG. 3 at 11 and all the debris has to clear the ball 12 that acts as a one way valve to retain debris if the circulation is stopped. Debris plugs this valve. The screen 6 is on the tool exterior and is subject to damage in handling at the surface or running it into the well. That screen filters fluid entering at 7 as the tool is removed. It has an emergency bypass 20 if the screen 6 clogs during removal operations. It relies on a large mandrel having a passage 3 which limits the volume available for capturing debris. By design, the cup 5 is always extended. 
     U.S. Pat. No. 7,188,675 again has a large mandrel passage 305 and takes debris laden fluid in at 301 at the bottom of FIG. 4. It uses internal pivoting valve members 203 shown closed in FIG. 5a and open in FIG. 5b. These valves can foul with debris. It has an exterior screen 303 than can be damaged during handling or running in. Its diverter 330 is fixed. 
     Finally U.S. Pat. No. 6,776,231 has externally exposed screen material 4 and a debris valve 20 shown in FIG. 3 that can clog with debris. It does show a retractable barrier 9 that requires a support for a part of the tool 7 in the wellbore and setting down weight. However, this barrier when in contact with casing has passages to try to pass debris laden flow and these passages can clog. 
     Well cleanup tools with barriers that function when movement is in one direction and separate when the tool is moved in the opposite direction are shown in Palmer US Application 2008/0029263. Other articulated barriers are illustrated in U.S. Pat. No. 6,607,031 using set down weight and U.S. Pat. No. 7,322,408 using an inflatable and a pressure actuated shifting sleeve that uncovers a compressed ring to let it expand and become a diverter. 
     The present invention features one or more of an internal screen, an outer housing for structural support to allow a smaller mandrel and more volume for debris collection, top entry of the debris into the collection volume to eliminate valves that can clog with debris and articulated diverters or diverter to direct debris laden fluid into the tool at the bottom and/or at the top to keep debris from falling into an annular space around the exterior of the tool that may have gotten through the screen or was for some other reason in the wellbore. These and other features of the present invention will be more apparent to those skilled in the art from a review of the description of the various embodiments and the associated drawings with the understanding that the full scope of the invention is given by the claims. 
     SUMMARY OF THE INVENTION 
     A debris removal device features structural support from an exterior housing that allows more space for debris collection. The debris enters the collection volume from the top to eliminate debris from having to go through a valve. The screen in the device is disposed internally to protect it during handling and running. A variety of external flow diverters are used to direct debris laden fluid into the tool and to keep debris out of an annular space around the tool that could interfere with its removal. The diverters can be actuated by relative movement in the tool or applied pressure to a piston which can inflate a sleeve or orient or misalign paths through brushes for selective bypassing of fluid exterior to the tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of an embodiment of the present invention during run in; 
         FIG. 2  is the view of  FIG. 1  shown during a milling operation with circulation; 
         FIG. 3  is an alternative embodiment with an articulated diverter in the retracted position during run in; 
         FIG. 4  is the view of  FIG. 3  with increased circulation that extends the debris barrier; 
         FIG. 5  shows a detail of an articulated diverter that operates on set down weight in the retracted position for run in; 
         FIG. 6  is another articulated diverter design shown in section and where flow can pass through its brushes; 
         FIG. 7  is the view of  FIG. 6  showing in more detail the clutch assembly, which can be used to close the flow paths that are shown in an open position; and 
         FIG. 8  is an exterior view of the brush sections pushed together so that their flow paths through the brushes are misaligned by the clutch; 
         FIG. 9  is an alternative embodiment to  FIG. 6  involving translation and putting a cover over the spring to keep dirt out of it; 
         FIG. 10  is an exterior view of the embodiment of  FIG. 9  in the open flow position; and 
         FIG. 11  is the view of  FIG. 10  in the blocked flow position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A top sub  10  is connected to a string (not shown) that extends from the surface. A bottom sub  12  is connected to more string and perhaps a downhole motor to a mill at the bottom (all not shown) as the focus of the present invention is the debris removal tool T that is connected to the string and subs  10  and  12 . A flow tube  14  is sealed at seal  16  to bottom sub  12  and is sealed at seals  18  to top sub  10 . Passage  20  that extends through the flow tube  14  allows fluid from the surface to go through the tool T and down to the mill at the bottom to cool the mill and to remove cuttings and bring them back uphole to inlets  22 . 
     Housing  24  is secured at opposed ends to top sub  10  and bottom sub  12 . The hanging weight of the string (not shown) that is attached to bottom sub  12  is transferred through the housing  24  to top sub  10  and the balance of the string (not shown) that is located above top sub  10 . Notice that there is no tension in the flow tube  14  from string weight by design. Instead, the flow tube  14  is simply a spacer sealed at opposed ends with seals  16  and  18 . Since the flow tube  14  is not structural, it can be made fairly small and its size is determined by the surface pumping equipment, the needed circulation rates for the mill and the length of the string. However, using a small diameter flow tube leaves more room around it to use to catch debris without filling the debris retention volume, as will be later explained. This design feature is one of the aspects of the present invention. 
     The debris laden fluid enters annular passage  26  through inlets  24  and then flows through diverter tube(s)  28  as indicated by arrows  30  in  FIG. 2 . This happens because there is an external diverter  32  sitting above a stabilizer  34 . As will be explained below, the diverter  32  can be mounted on bearings such as shown for example in  FIG. 5  so that the external diverter  32  can remain stationary while the tool T is rotated by the string to turn the mill below. 
     Referring back to  FIG. 1 , the diverter tube(s)  28  end at  36  above the top of the lower debris retention basket  38 . The reduction in fluid velocity allows the heavier debris indicated by arrow  40  to fall into lower basket  38 , as shown in  FIG. 2 . The remaining debris continues and preferably makes a turn to promote additional debris to drop into the basket  38  before the stream continues into an upper diverter tube(s)  42  that run through the bottom of the upper debris retention basket  44  and terminates at end  46 . Here again due to the velocity reduction, additional debris indicated by arrow  48  drops into upper basket  44 . While two baskets with tubes that come through their sealed bottoms are illustrated with an offset in the flow path between the baskets, those skilled in the art will appreciate that only one basket can be used or more than two baskets with or without offsets in the flow path among them. What should be noted is that the design with a sealed bottom and a diverter tube extending through the closed bottom takes away the need for valves to keep debris in the baskets when circulation is shut off. It is just such valves in the prior art that had to pass debris that gave operational trouble in the past as the debris hung the valves up in the open or the closed positions. The illustrated preferred embodiment eliminates these valves for a system with no moving parts or small passages that can clog with debris. 
     As seen in  FIG. 2  the flow stream represented by arrow  52  now enters an annular passage  50  that is defined on the inside by screen  54  and on the outside by housing  24 . The lower end of the inside of screen  54  is sealed to the exterior of the flow tube  14  at seal  56  while the upper end is open inside the screen  54  to outlets  58 . From outlets  58  the fluid stream  60  continues in the annulus  62  to the surface. Solids that failed to pass the screen  54  remain in passage  50  on the outer screen face, as long as circulation continues. Once the circulation is cut off those retained cuttings on screen  54  or in space  50  fall down into basket  44 . The flow stream  60  heads up the annulus  62  because an upper diverter  64  sitting close to an upper stabilizer  66  prevent flow back down into annular space  68  between the tool T and the surrounding tubular or casing C. Although two diverters  32  and  64  are shown, those skilled in the art will appreciate that only one will also work. The diverters  32  and  64  can be articulated so that they can be selectively retracted or they can be of the type that are always extended such as brushes or brush segments. Even when brushes are used they can selectively have passages through them that can be opened or closed as will be explained below. The diverters are preferably bearing mounted to allow the tool T to turn while the diverters are stationary. 
     One of the features to be noted at this point is the placement of the screen  54  inside of housing  24  so as to protect the screen  54  from impacts during surface handling or while tripping into and out of the well. The prior designs that used screens located them on the outside of the tool making the screen in those tools more prone to such damage. 
     In another aspect of the present invention, the external flow diverter or diverters that span the surrounding annulus  68  are articulated as opposed to the fixed deflectors used in the designs of the past. A fixed external flow deflector can cause formation damage either going into the well or coming out of the well. For example, a fixed cup seal looking downhole can build pressure on the formation when running in while if the cup seal is looking uphole it can reduce the formation pressure when the tool is pulled out of the hole to the point where the well actually comes in at the wrong time. While some past designs have incorporated bypasses for such diverters if flow through the tool is blocked when pulling the tool out, for example, there still remains a risk of adversely affecting the formation if such backup features do not fully perform. An articulated diverter as is proposed for the preferred embodiment eliminates this risk when moving in both directions as it can be placed in external bypass mode for running in and for coming out of the well and can also be energized for milling. The various embodiments of the diverter on the outside of the tool will now be described in conjunction with also describing an alternative embodiment for the internals of the tool. 
       FIG. 3  illustrates a tool that has a top sub  70  secured to a bottom sub  72  by a housing  74 . Housing  74  has an inlet  76  although the inlet can optionally come through the bottom sub  72 . Adjacent the inlet  76  is a projecting diverter  78  that leaves a gap  80  from the surrounding tubular C′. Optionally one or more offset and preferably spiral paths  82  can extend through the diverter  78  with such paths  82  leading into inlet  76 . Entering debris goes up passage  84  and due to velocity reduction falls into debris retention volume  86 . The remaining debris continues in a flowing stream to screen  88  where additional debris is stopped. After the screen  88  the fluid exits through passages  90  to go uphole in the manner described before. Housing  74  has an inflatable  92  that is mounted on bearings  94  and  96 . Flow tube  98  has a lateral passage  100  leading to piston  102  whose movement actuates the inflatable  92  as shown in  FIG. 4 . Note that flow in the flow tube  98  that is represented by arrow  104  has to go past a restriction  106  so as to build back pressure to passage  100  to set the inflatable  92 . The flow  104  continues down to the mill (not shown) and comes back up with cuttings to inlets  76 . Note that for run in, there may be flow  104  but at a low enough rate so as not to set the inflatable  92 . Even though the diverter  78  presents some restriction to flow around the outside of the tool as it is run into or out of the hole, the gap  80  is designed to be sufficiently large and the rate of going in or coming out of the hole sufficiently controlled so as to avoid adverse impacts on the formation. Indeed, the diverter  78  can be eliminated so that with the inflatable  92  in the retracted position of  FIG. 3  there is no added resistance to flow  108  in the surrounding annular space when the tool is run into the whole. The same thing happens when the tool is removed from the hole with the inflatable  92  retracted. Increasing the flow rate when the mill lands on the object to be milled actuates the inflatable  92  so that it can serve as a diverter whether located as shown or anywhere on the housing  74  above the inlets  76 . 
     Those skilled in the art will also appreciate that some of the benefits of the present invention of the  FIGS. 1 and 2  embodiment are also in  FIGS. 3 and 4 . The screen  88  is internally mounted and protected. The outer housing  74  takes the tensile forces of string weight as opposed to the flow tube  98  to allow the flow tube  98  to be made smaller and thus making a greater volume within the housing  74  available for debris retention. There are no valves that debris laden fluid has to go through that can clog and get stuck. The diverter  92  is articulated and in this embodiment automatically extended when flow rates for milling are maintained. Running in or out of the well with the diverter  92  fully retracted removes or at least minimizes the potential for damaging the formation during such operations. 
     Referring to  FIG. 5  an articulated diverter  110  comprises a sleeve  112  that is on bearings  114  and  116 . An upper sub  118  is movable with set down weight on mandrel  120  to axially compress the sleeve  112  and urge it out radially to close a surrounding gap and act as an articulated diverter. A ball  122  in a track  124  prevents relative rotation between sub  118  and housing  120 . These two components can also be shaped with a hex that interlocks them so that they transmit torque while moving in tandem for rotation. Only the diverter  110  is the focus of  FIG. 5  with the other FIGS. previously discussed providing the details of the debris catcher operation. Weight is set down when the mill (not shown) lands on the object to be milled and that in turn articulates the sleeve  112  to move out radially. For running in or out the string weight keeps the sleeve  112  extended. 
       FIGS. 6-8  illustrate another embodiment of an articulated diverter.  FIG. 6  is a section view and  FIG. 7  is an exterior view.  FIG. 8  illustrates the flow paths through the brush assemblies in the obstructed position. While brush arrays are preferred, arrays of solid shapes made of a variety of materials such as metal or plastic for example can also be used as long as the shapes define flow paths that can be selectively obstructed to get the diversion of flow effect. Sleeves  200  and  202  have brush arrays  204  and  206  extending radially out. Bearings  208  and  210  support the sleeves  200  and  202  such that the housing or a sub  212  can rotate as the brush arrays  204  and  206  are in contact with a surrounding tubular (not shown). A passage  214  extends to a piston  216  that when actuated pushes the sleeves  200  and  202  together by moving sleeve  202 . A spring  218  biases the sleeves  200  and  202  apart until piston  216  overcomes the bias of spring  218 . Sleeve  200  has a series of end serrations  220  seen in both  FIGS. 6 and 7 . Sleeve  202  has serrations  222  seen only in  FIG. 7  because they are recessed under sleeve  202 . Serrations  220  and  222  are a matched pair and self align when forced together with piston  216 . When the sleeves  200  and  202  are apart as shown in  FIG. 7  there are spiral flow paths  224  and  226  that allow a continuous flow stream represented by arrows  228  to pass through the brush arrays  204  and  206  with minimal resistance. However, when piston  216  is actuated to bring serrations  220  and  222  together while overpowering spring  218  the flow paths  224  and  226  misalign at the point  230  where they are pushed together. With the flow paths so misaligned the brush arrays  204  and  206  act as a diverter. These  FIGS. 6-8  illustrate yet another embodiment of an articulated diverter having the advantages described before. As before it actuates automatically when the flow rate is stepped up to levels needed for mill operation. 
       FIGS. 9-11  are an alternative embodiment again showing sleeves  300  and  302  with sleeve  300  movable biased apart by spring  304  which is covered by sleeve  306  to prevent entry of debris. In the open position of  FIG. 10  the paths  308  and  310  are spaced apart forming a gap  312 . Flow can go through as represented by arrow  314 . Sleeves  300  and  302  can be splined so they can translate axially without relative rotation. Since paths  308  and  310  are misaligned, translation of the sleeves  300  and  302  urged by piston  316  in effect creates dead ends  318  that block flow. This can be done by simply abutting the arrays or nesting them with mating notch patterns as shown in  FIGS. 10 and 11 . As before bearings  320  and  322  allow relative rotation so that the arrays that define paths  308  and  310  can remain still while other parts of the tool rotate. As before, while brush arrays are preferred arrays made of solid shapes that define paths can also be used in a variety of materials compatible with downhole conditions. 
     While the present invention can be used in a string for milling it can also be used with other downhole tools that for example jet sand away from the top of a packer and remove it in tool T of the present invention. 
     The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.