PATENT ABSTRACT
A rotary power tool according to the invention includes a manual ratchet mechanism having a driveshaft driven by a motor, an output shaft, a disengageable shaft coupling element for mechanically coupling the driveshaft to the output shaft, and a disengageable ratchet element for blocking rotation of the output shaft unidirectionally. The invention provides that one of the coupling element and the ratchet element is engaged, the other one is disengaged.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on EP Application No. 08104538.7 filed Jun. 25, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ratchet mechanism that permits a rotary power tool to be used in a manual ratchet mode for alternatively tightening or loosening a screw. 
     2. Description of the Prior Art 
     DE 4128651 A1 describes an electric screwdriver with a ratchet and pawl arrangement to permit manual screwdriving when the motor is inoperative. The tool operates in four distinct modes: forward and reverse power drill/driving modes plus forward and reverse manual ratchet modes. One of the four modes is conveniently selected via a rotating switch. In both of the manual ratchet modes, the motor is electrically decoupled via movement of electrical contacts that are mechanically coupled to the rotating switch. A problem with this design is that if the motor is inadvertently activated while the tool is in a ratchet mode, the motor could jam and possibly be damaged. It would be useful to have a rotary power tool with the manual ratchet functionality but without the associated risks to the motor. 
     ADVANTAGES OF THE INVENTION 
     A rotary power tool having a manual ratchet mechanism includes a driveshaft driven by a motor, an output shaft, a disengageable shaft coupling element for mechanically coupling the driveshaft to the output shaft, and a disengageable ratchet element for blocking rotation of the output shaft unidirectionally. When one of the coupling element and the ratchet element is engaged, the other one is disengaged. This design has the advantage that the motor is mechanically uncoupled from the output shaft when the ratchet element is operational, so that there is no possibility of damage to the motor should it be inadvertently activated. 
     The shaft coupling element can be conveniently engaged or disengaged by movement axially along a rotary axis of the tool. A preferred or default position can be established by providing a biasing member such as a coil spring to urge the shaft coupling element to move into either the engaged or the disengaged position. 
     The shaft coupling element is advantageously positioned between a transmission that modulates the output of the motor and the ratchet element. This allows an adjustment device in the form of a compact adjustment collar to access both the ratchet element and the shaft coupling element. 
     If the shaft coupling element is generally ring-shaped and at least partially surrounds the driveshaft and/or output shaft, then it can be conveniently positioned without a separate element for positioning it within the tool. Such an arrangement also facilitates implementation of the invention into existing power tool designs without requiring extensive redesign of the internal components. 
     By providing the shaft coupling element with splines for coupling with the driveshaft and/or the output shaft, rotational coupling is conveniently achieved while preserving freedom of movement in the axial direction. 
     Since the motor is provided with a motor housing which is mechanically coupled with the ratchet element and also unitary with the tool handle, the ratchet element is conveniently utilized to provide a screwdriving function to the tool by the user. 
     In its simplest form, ratchet action can be achieved by providing a ratchet element that includes a ratchet shaft interacting with at least one locking plate. 
     A mechanism for adjusting the operational mode of the rotary tool is mechanically coupled to the shaft coupling element and the ratchet element for adjusting each into either an engaged or a disengaged position. The adjustment mechanism therefore provide the basis for linking selection of the operational mode (drill/driving mode or ratchet mode) with the power state of the tool (powered or unpowered/manual). 
     Less parts are necessary and the design is more compact if the same adjustment mechanism that determine whether the tool operates in powered drill/driving mode or manual ratchet mode can also be used to determine the direction of unidirectional blocking by the ratchet element in manual ratchet mode. 
     A device for interfacing with the ratchet element and the shaft coupling element are conveniently adapted to the adjustment collar in the form of inner protrusions that contact the ratchet element and an inner cam surface for adjusting the shaft coupling element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in further detail below in conjunction with the drawings, in which: 
         FIG. 1  is a schematic view of a power tool according to a first embodiment of the invention. Internal components are illustrated with dashed lines; 
         FIG. 2  is a partial section view of a power tool in powered drill/driving mode; 
         FIG. 3  is a partial section view of a power tool in manual ratchet mode; 
         FIG. 4A  is a partial perspective view of a power tool in powered drill/driving mode wherein the adjustment collar is shown in dashed lines; 
         FIG. 4B  is a partial perspective view of a power tool in manual ratchet mode wherein the adjustment collar is shown in dashed lines; 
         FIG. 5A  is a section view taken along line A-A in  FIG. 2  when the power tool is in powered drill/driving mode; 
         FIG. 5B  is a section view taken along line B-B in  FIG. 2  when the power tool is in reverse manual ratchet mode; and 
         FIG. 5C  is a section view taken along line B-B in  FIG. 2  when the power tool is in forward manual ratchet mode. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A rotary power tool  10  of the type used for power drilling or driving is shown in  FIG. 1 . The working end of the tool is configured with a tool holder  12  for securing drill or driver bits or the like. A rotatable adjustment collar  14  permits the user to select from a variety of operating modes. A gearbox housing  16  and a motor housing  18  secure a planetary gear transmission  20  and a motor  22 , respectively. Alternatively the gearbox housing  16  and the motor housing  18  can be of unitary construction. The motor housing forms a portion of a larger tool shell that also includes a handle  24  for gripping the tool  10 . 
     The working end of the tool  10  is illustrated in more detail in  FIG. 2 . A motor pinion  26  which is the output shaft of the tool motor  22  ( FIG. 1 ) engages the planetary gear transmission  20  to drive a spindle  28 . An air gap  30  separates the spindle  28  from a ratchet shaft  32 , but they are both symmetrical about the same tool axis of rotation  34 . The ratchet shaft  32  is mechanically coupled with a tool bit holder  12  via a pin  36  which can be omitted if the ratchet shaft  32  and tool bit holder  12  are instead constructed of unitary design. 
     For the purpose of the description that follows, rotating parts that are always rotationally coupled with the motor  22  will be considered to be a “driveshaft.” Rotating parts that are always rotationally coupled with a tool (not shown) secured by the tool holder  12  are considered an “output shaft.” In the preferred embodiment illustrated in the figures, the motor pinion  26  and the spindle  28  are always driveshafts, and the ratchet shaft  32  and tool bit holder  12  are each always output shafts. 
     A mechanical coupling between a driveshaft and output shaft can be established in certain circumstances so that rotation of a driveshaft will drive an output shaft. In the illustrated embodiment, a bushing  38  serves as shaft coupling means for this purpose. It is configured with internal splines  40  which are capable of cooperating with corresponding recesses  42  on the spindle  28  and/or recesses  44  on the ratchet shaft  32 . Other manners of complementary part profiles are also possible so long as when the parts overlap axially, rotation of the bushing  38  is sufficient to drive the spindle  28  or the ratchet shaft  32  and vice versa. 
     In the power drill/driving mode illustrated in  FIG. 2 , the bushing  38  is mechanically coupled with both the spindle  28  and ratchet shaft  32 . In other words, in this mode, rotation of a driveshaft will through this coupling rotate an output shaft. However, in the ratcheting mode of  FIG. 3 , the bushing  38  is in a different axial position, so that it is not in contact with the ratchet shaft  32 . Rotation of a driveshaft in this mode will not rotate an output shaft. 
     The bushing  38  is normally biased into the position illustrated in  FIG. 2  by a coil spring  46 . However, rotation of the adjustment collar  14  can urge the bushing  38  to move into the position illustrated in  FIG. 3 . The coupling between the adjustment collar  14  and the bushing  38  is mediated by an adjustment ring  48  which contacts both parts. 
     The adjustment ring  48  is provided with two projections  50  that cooperate with cam surfaces  52  on the inner portion of the adjustment collar  14  (see  FIGS. 4A and 4B ). Since the adjustment ring  48  is mechanically coupled with the bushing  38 , the projections  50  are urged by the force of spring  46  into contact with the cam surfaces  52 . The drill/driving mode illustrated in  FIG. 4A . If the adjustment collar  14  is rotated in the direction of arrow  54 , the cam surfaces  52  urge the adjustment ring  48  to move against the force of the spring  46 , resulting in the position illustrated in  FIG. 4B . Here the adjustment ring  48  has moved axially and the mechanically coupled bushing  38  has also moved axially so that it is in the position illustrated in  FIG. 2 . 
       FIGS. 5A ,  5 B and  5 C are cross sectional views taken from the perspective of the working end of the tool and illustrate components of a ratchet means along with means for engaging or disengaging the ratchet mechanism. 
     The periphery of the ratchet shaft  32  is configured with fins  56 . Mounted in close radial proximity to these fins  56  are two lock plates  58  which pivot around pins  60 . So that the lock plates  58  have some flexibility in their movement, each is in contact with a deformable spring  62 . The lock plates take on different positions relative to the pivot points depending on rotation of the adjustment collar  14 . This coupling is mediated by protrusions  64  projecting from the inner surface of the adjustment collar  14  which in certain positions press against the springs  62  which abut the lock plates  58 . 
       FIG. 5A  illustrates that the protrusions  64  do not contact the springs  62  when the tool is operated in power drill/driving mode. As such, the lock plates  58  do not contact the fins  56  of the ratchet shaft  32 . However, in a reverse manual ratchet mode illustrated in  FIG. 5B , the protrusions  64  tend to contact portions of the springs  62  so that the lock plates  58  pivot about the pins  60 . As such, one of the two arms  66  of each respective lock plate  58  contacts a slot  68  between the fins  56  of the ratchet shaft  32 . However, since the springs  62  are flexible, the lock plates  58  are able to move out of these slots  68  to permit the ratchet shaft  32  to rotate in the direction indicated by arrow  70 . Rotation allows the aims  66  to return into contact with the slots  68  under the force of the springs  62 . This creates the well-known ratchet sound when the ratchet shaft  32  is engaged in this fashion. 
     Rotation of the ratchet shaft  32  in the opposite direction, however, drives the arms  66  of the lock plates  58  further into the slots  68 , so that the ratchet shaft  32  is not able to rotate. Hence the ratchet shaft  32  and any other output shaft rotationally coupled is only capable of unidirectional rotation. 
       FIG. 5C  illustrates a forward manual ratchet ode which functions analogously to the reverse manual ratchet mode. The only difference is the direction of rotation permitted by the ratchet means. Switching between the three possible operational modes is mediated by rotation of the adjustment collar  14 , as is illustrated by comparing  FIG. 4A  with  FIG. 4B . When the collar  14  is orientated so that the tool  10  is operating in forward or reverse ratchet mode, the adjustment ring  48  is in such a position that the spindle  28  is definitively de-coupled from the ratchet shaft  32 . 
     In this case, the user may use the tool  10  much as it were simply an unpowered screwdriving device by rotating the handle  24 . Since the handle  24  is coupled with the motor housing  18  and the motor housing  18  is coupled with the gearbox housing  16  and the gearbox housing  16  is rotationally coupled to the lock plates  58  via the pins  60  (see  FIG. 3 ). Therefore, rotation of the handle  24  in one direction will be such that the lock plates  58  drive the ratchet shaft  32  and therefore the output shaft. Rotation in the other direction will simply cause the lock plates  58  to rotate around the ratchet shaft  32  creating a typical ratchet sound. In this way, conventional ratchet action is achieved. 
     In an alternate construction, the coupling means are positioned instead between the motor pinion  26  and the planetary gear transmission  20 . The adjustment collar  14  can in this case be enlarged so that it can still couple with both the ratchet means and the shaft coupling means. 
     The foregoing relates to the preferred exemplary embodiment 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.