Abstract:
A rotary power tool having a tool housing, an internal housing within the tool housing, and a switch assembly that is substantially within the tool housing. According to the invention, the switch assembly is supported by the internal housing and is movable between at least two positions for selecting between at least two tool operational modes. The internal housing is embodied by at least one blocking element that extends towards the tool housing and limits the overall range of motion of the switch assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on European Patent Application 09169001.6 filed Aug. 31, 2009. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotary power tool with a rotating switch for determining its operational mode. In particular it relates to improved ways for retaining the switch in defined positions corresponding to respective operational modes. 
     2. Description of the Prior Art 
     EP 1 050 381 A2 discloses a rotary tool with a switch for changing between impact operation and drill operation modes. An operation member accessible at the top of the external tool housing is slidable by the user in a back-and-forth manner. The external tool housing limits the range of motion of the operation member by providing discrete stops corresponding to operational modes. This design has the disadvantage that it limits freedom in designing the appearance of the switch and the external tool housing. If there are stresses on the switch due to coupling with internal tool components, excessive wear of the external housing may result. Furthermore, the potential for stack-up errors resulting from necessary cooperation between the switch and the external tool housing may add to the expense of the design. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     A rotary power tool is described having a tool housing, an internal housing within the tool housing, and a switch assembly that is substantially within the tool housing, wherein the switch assembly is supported by the internal housing and movable between at least two positions for selecting between at least two tool operational modes. The internal housing has at least one blocking element that extends towards the tool housing and limits the overall range of motion of the switch assembly. A switch assembly involved in selecting tool operational modes is preferably coupled with a gear assembly in order to change speeds, for example. As such it is often necessary to provide a blocking element in order to prevent overshifting of the switch assembly which might damage the gear assembly. Positioning of the blocking element on the same component on which the switch assembly is supported has the advantage that less accumulated stack-up error would need to be considered when designing components. 
     The internal housing may comprise a plurality of gears, as would, for example, the housing of a gear assembly or “gear box”. If so, the blocking element can be incorporated on a stand-alone gear assembly that can be incorporated within the tool housing. Since the blocking element is not positioned on the external tool housing, no switch assembly stop surface needs to be present on the external housing. This allows greater freedom of design for the switch assembly, allowing cosmetic aspects rather than mechanical aspects to dictate the design. Since the switch assembly does not rely on the external housing as a stop surface, there is likely to be reduced wear on the external housing. If the switch assembly operates completely independently from the tool housing and is a component of a stand-alone assembly, any modifications to the gear assembly will have less of a design impact on the housing, and therefore may be less costly. 
     The tool gear assembly may include a gear housing that is generally cylindrically shaped. It would be advantageous under these conditions for the switch assembly to be substantially ring-shaped and rotatable with respect to the gear housing and therefore the tool axis of rotation. In this way the gear housing would support the switch assembly. 
     Since the switch assembly takes on at least two positions and quite possibly additional positions between extreme positions, at least two limit stops are required for limiting the range of motion of the switch assembly. This can be accomplished if the internal housing (which may be the gear housing) has a second blocking element that extends towards the tool housing and limits the overall range of motion of the switch assembly. Preferably the second blocking element is at a distance from the first blocking element to permit a range of movement for the switch assembly. Together the first and second blocking elements delimit the overall range of movement for the switch. As discussed above, separating the limit stops for the switch assembly from the external tool housing is advantageous. A second blocking element can be readily incorporated onto the internal housing. Since they extend in the direction of the tool housing, the same elements that are provided as limit stops for limiting the range of movement of the switch assembly can advantageously be used for positioning the internal housing within the tool housing. The tool design advantageously incorporates corresponding structures such as ribs on the internal surface of the tool external housing which can cooperate with the structures that include blocking elements for positioning and securing the gear housing within the external tool housing. 
     Especially if the switch assembly is substantially ring-shaped, interaction with limit stops on the housing can conveniently be mediated by an extension of the switch assembly that extends in a direction of the axis of rotation of the tool so that it is positionable between the blocking elements. 
     It is desirable for the power tool to incorporate blocking elements that limit the overall range of motion of the switch assembly. In order to select tool operational modes with accuracy, the power tool is preferably provided with an element for retaining the switch assembly in particular positions corresponding to the tool operational modes. One way of accomplishing this is with a switch assembly that has flexibility so that it can be readily overcome retaining features such as a nearby detent when the switch assembly is being moved, but can engage nevertheless with the retaining features once the switch assembly takes on a desired position. This configuration can be advantageously achieved with a switch assembly that has two portions, a switch outer portion having a substantially fixed shape and a switch inner portion that is flexible and which changes shape when the switch assembly is moving between the at least two positions. For example, the inner portion may change shape in a way that provides additional clearance for adjusting the switch assembly. This clearance can be mediated by a flexible switch inner portion is substantially ring-shaped and has at least one ring diameter which increases when the switch assembly is moving between respective positions. 
     For retaining the switch assembly, the internal housing which supports the switch assembly is advantageously provided with retaining features in addition to the movement limiting features. For example, the switch assembly can be simply retained in one position if the internal housing includes a detent that cooperates with at least one recess on the switch assembly. 
     If there are features for limiting the range of movement of the switch assembly, it would be advantageous to include features that retain the switch assembly in a defined position at the very same switch assembly positions where the switch assembly reaches a limit stop. Therefore it is preferable if a detent on the internal housing cooperates with at least one recess on the switch assembly when the extension of the switch assembly is in contact with the blocking element. 
     As a mechanism for disengaging the recess from the detent on the tool housing without causing wear or potentially damaging the detent, the recess is advantageously able to be moved in a direction away from the detent. This is readily accomplished by incorporating the recess within the flexible switch inner portion. When the switch inner portion changes shape by increasing its effective diameter, clearance is created for moving the recess away from the detent without contacting the detent. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in detail below in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a top left perspective view of a cordless impact driver; 
         FIG. 2  is a bottom right perspective view of the gear, impact and switch assemblies; 
         FIG. 3  is an exploded top left perspective view of the switch assembly; and 
         FIG. 4  is a section view of the gear assembly, impact assembly, and switch assembly at the position indicated by arc A-A in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A perspective view of a hand-held rotary tool  10 , in particular a cordless impact driver, is illustrated in  FIG. 1 . The speed and torque of the rotary output of a motor (not shown) is modulated by a gear assembly  12  and transmitted to an impact assembly  14 . Construction details of impact assembly  14  are not shown since it comprises components well understood by those familiar with impact drivers, such as a striker, spring, and anvil for providing high torque impacts within a preferably metal impact assembly housing  16 . An output shaft having a tool holder  18  extends from impact assembly housing  16 . The motor, gear assembly  12 , and at least a portion of impact assembly  14  are mounted within a preferably plastic tool housing  20  which extends to form a handle  22  and a base  24  for inserting a removable DC battery pack  26  to power the motor. Battery pack  26  is preferably rechargeable and based on lithium ion chemistry. The tool may alternatively include an intrinsic (i.e., non-removable) rechargeable DC battery pack. While a cordless tool is described, power to drive the motor may alternatively be provided by an electrical cord for drawing AC power. 
     Exemplary components of gear assembly  12  are seen clearly in the cross sectional view of  FIG. 4 . Within a gear housing  28  are several stages of epicyclic gears, of which ring gear  30 , sun gear  32 , and planetary gears  34  are illustrated. Those skilled in the art will appreciate how enabling or disabling one or more of the stages of gear reduction can readily modify the output speed and torque output by gear assembly  12 . 
     The user controls the speed output of gear assembly  12  by rotating a switch assembly that is mounted around the gear housing  28 . The switch assembly may comprise one unitary part, or it may be separated into more that one part as is illustrated in  FIG. 3 . In the preferred embodiment, the external part of the switch assembly is a mode switcher  36  which is provided with a switch button  38  having a substantially flat but arc-shaped top surface  40  as well as two sloped side surfaces  42  which are provided with multiple ridges  44  to facilitate manual rotation of mode switcher  36 . Indication means such as arrow  46  are provided on top surface  40  for cooperating with corresponding indication means such as mode indicators  48  on tool housing  20 . Switch button  38  is accessible through a generally rectangular slot  50  in tool housing  20  but is otherwise obscured by tool housing  20  (see  FIG. 1 ). As such, the switch assembly is substantially within tool housing  20 , in so far as the majority portion, but not necessarily all portions of the switch assembly fall within a fictive perimeter delineated by the outer surfaces of tool housing  20 . 
     Mode switcher  36  interlocks with and serves as a substantially rigid outer sleeve for permitting the user to rotate a flexible switching ring  52  which comprises a second inner portion of the switch assembly (See  FIG. 3 ). Switching ring  52  is provided with structural features that underlie changes in operational modes. For example, slots  54  are provided for translating rotation of switching ring  52  into axial movement of other parts, such as epicyclic gear components (not shown) along tool axis  56  in order to modulate rotary speed and torque. Sloped perimeter surfaces  58  are also shaped for translating rotation into axial movement of distinct parts (not shown) which mediate an impact on-off mechanism for switching the impact driver into a pure drilling (non-impact) mode. Therefore via switching ring  52 , mode switcher  36  is involved in modifying multiple types of user modes. For reasons of balance, slots  54  and sloped perimeter surfaces  58  are arranged symmetrically around switching ring  52 . 
     While a switch assembly having a distinct mode switcher  36  and switching ring  52  has been described, these two components may be integrated into a single part of unitary construction, wherein the solitary switch would retain each of the described features. However certain functionalities of the switch assembly that are described in the text that follows are preferably implemented by having mode switcher  36  and switching ring  52  as separate parts. 
     In the illustrated example, control is provided for three operational modes, although the invention is suitable for tools having additional modes. For each mode, there is a corresponding groove  60  provided on the inner face of switching ring  52 . As switching ring  52  is rotated, the respective grooves  60  cooperate with a detent  62  provided on the outer surface of gear housing  28  (see  FIG. 4 ). Neither the grooves  60  nor the detent  62  need to extend across the full axial width  64  of switching ring  52 . Because of a fixed coupling with impact assembly  14  as well as other tool portions, gear housing  28  is fixed in position with respect to the tool  10 . The detent-groove coupling is sufficient to retain switching ring  52  in a defined position relative to gear housing  28  even under conditions of heavy vibration when tool  10  is operating. 
     To switch between different modes the user manually rotates mode switcher  36 . Switching ring  52  is not a true ring. It is ring-shaped and preferably formed of a flexible material such as plastic so that it may flex to increase the size of gap  66  thereby increasing its effective diameter. In doing so, it changes shape, but since it is flexible, it is resilient and if permitted to do so, will return to its original shape. A representative effective diameter  68  is shown in  FIG. 3 . Neck portions  70  near gap  66  interlock with the inner portion of switch button  38 , but do not form a tight fit. When mode switcher  36  is rotated by the user, rib  72  presses against one of the neck portions  70 , but because of gaps  74  provided between the neck portions  70  and inner wall  76 , gap  66  will tend to increase whenever mode switcher is rotated. The increased diameter  68  will allow grooves  60  to separate from detent  62  so that switching ring  52  may rotate to bring detent  62  into alignment with an adjacent groove  60 . Releasing mode switcher  36  when detent  62  is positioned within one of the grooves  60  allows switching ring  52  to return to its original position with reduced diameter  68 . Mode switcher  36  has a substantially fixed shape, but if it is thinly constructed, it may also deform slightly when switching ring  52  enlarges its diameter  68 . 
     Opposite from switch button  38 , mode switcher  36  is provided with an extension  78  that creates a significantly larger width  80  of mode switcher  36  and thereby establishes shoulders  82 . This extension  78  extends axially to overlap an end cap  84  of gear housing  28  which has radially-extending protrusions  86  for positioning the gear assembly  12  within the tool housing  20 . End cap  84  may be constructed separately from the remainder of gear housing  28  or it may formed or molded as one continuous housing. Like the rest of gear housing  28 , it contributes to enclosing and protecting the epicyclic gears from other tool components. 
     Since the extension  78  of mode switcher  36  lies between these two protrusions  86  (see  FIG. 2 ), the overall range of motion of mode switcher  36  is restricted when it is rotated. That is, each protrusion  86  acts as a blocking element and partially limits the overall range of motion, but together the two protrusions  86  define and delimit the overall range of motion. Depending on the direction of rotation, each of its shoulders  82  will ultimately come into contact with one or the other corresponding protrusion  86  as illustrated in  FIG. 2 . The position of extension  78  is selected so that it corresponds with the positions wherein detent  62  is in alignment with one of the outermost grooves  60 . Alignment of detent  62  with one of the grooves  60  may somewhat restrict motion of the switch assembly, but detent  62  does not itself act as a limit stop, i.e., it does not limit the overall range of motion of the switch assembly. 
     The alignment of detent  62  with respective grooves  60  for positioning the switch assembly need not be coupled with means for limiting the range of motion of the switch assembly. For example, in alternate embodiments, the switch assembly may be free to rotate 360 degrees and therefore not require any sort of limit stops. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.