Patent Publication Number: US-9421675-B2

Title: Adjustable torque screwdriver

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This utility patent application is a U.S. National Phase of PCT/2012/080945, filed Sep. 4, 2012, which claims priority from CN 201210082515.1, filed Mar. 26, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to an adjustable torque screwdriver, and pertains to the field of manual tools. 
     BACKGROUND OF THE INVENTION 
     Generally, the output torque of an ordinary screwdriver is not adjustable, relying merely on the user&#39;s experience to control the torque applied. So when the torque needs to be controlled precisely, as in the case of interconnections between various parts of precise instruments, or in the case of brittle or easily damaged fastening and/or fastened parts, excessive force or too large an exerted torque may damage the parts. In such a case, experience of the operator is the sole reliance, and therefore there is a certain prerequisite for the user, for example, he/she needs to be a skilled mechanic. 
     SUMMARY OF THE INVENTION 
     In light of the foregoing limitations of an ordinary screwdriver, the present invention provides an adjustable torque screwdriver of which the size of output torque can be adjusted according to the needs of users, thus allowing multi-stage adjustment of the output torque. When the torque exerted by the user is larger than the set torque, the torque output shaft of the screwdriver slips, thereby shutting off the output of torque. 
     In light of the defects of the prior art, the invention aims to solve the technical problem by providing an adjustable torque screwdriver. 
     To this end, the invention provides an adjustable torque screwdriver, including a torque input assembly and a torque output assembly, and further including a ratchet pair, which comprises a first ratchet and a second ratchet, respectively having circular teeth. The torque input assembly transmits the torque to the first ratchet, and the second ratchet then transmits the torque to the torque output assembly, and the circular teeth are arranged to enable the ratchet pair to slip either clockwise or counterclockwise, but not to slip in the respective opposite direction. The adjustable torque screwdriver also includes an adjusting assembly and an elastic assembly, the elastic assembly exerting pressure to the ratchet to tightly fit the ratchet pair, the adjusting assembly loading and unloading the elastic assembly, thereby adjusting the exerted pressure and the in-between fitting tightness of the ratchet pair, thus adjusting the torque for the ratchet pair to slip. 
     In a preferred embodiment of the invention, the elastic assembly is a spring group which includes a plurality of springs approximately concentrically disposed, each of the springs having respectively a specific free height and an elastic modulus. 
     In a further preferred embodiment of the present invention, the spring group includes a first spring and a second spring; the free height of the first spring is larger than that of the second spring, and the elastic modulus of the second spring is larger than that of the first spring. 
     In another preferred embodiment of the invention, the adjusting assembly is an outer casing with an internal thread and an interior ring with an external thread. The interior ring matches with the outer casing through the threads, and not allowed to rotate about the axis of the screwdriver; when the outer casing revolves about the axis of the screwdriver relative to the interior ring, the interior ring translates relative to the elastic assembly under the effect of the thread pair, thus loading or unloading the elastic assembly. 
     In another preferred embodiment of the invention, the embodiment also includes a flange rotating together with the outer casing, a plurality of round holes arranged on the flange, and a bead mating with the round holes and the grading spring biasing the bead. 
     In another preferred embodiment of the invention, the outer casing is disposed in the head part of the adjustable torque screwdriver, and the ratchet pair and the elastic assembly are disposed in the outer casing. 
     In another preferred embodiment of the invention, the elastic assembly is disposed on the side of the first ratchet. 
     In another preferred embodiment of the invention, the outer casing is rotatably connected to the handle about the axis of the adjustable torque screwdriver. 
     In another preferred embodiment of the invention, the handle has a cavity, to be used for storing screwdriver blades mountable on the screwdriver. 
     In another preferred embodiment of the invention, the handle has a rear cover. 
     In another preferred embodiment of the invention, grading marks are arranged on the outer casing, and an indication arrow is arranged on the handle. 
     The adjustable torque screwdriver according to the invention can set maximum output torque thereof in a set direction in order to produce a more accurate output torque; when the torque exceeds the set grade, the output shaft automatically slips so as to avoid damage to the fastening/fastened pieces and the bit of the screwdriver, not relying on the operating skill of the user, thus there is no specific requirement for the user. 
     Further, the invention adopts a spring group composed of multi-stage springs to adjust the maximum output torque of the screwdriver, achieving a wider range of output torque, a more precise setting in particular in the low range of torque, and a longer service life than that of a single spring. 
     In addition, as the ratchet pair and the elastic assembly are disposed in the outer casing of the head part of the screwdriver, the center of gravity of the screwdriver is closer to the output shaft of the screwdriver, and therefore the screwdriver works more stably, and the vibrations of the bit of the screwdriver is weaker when slipping occurs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referencing now to the figures, the conception, detailed structure and induced technical effect of the present invention will be expounded for due understanding of the purpose, characterizations and effects of the present invention: 
         FIG. 1  is a front view of an adjustable torque screwdriver of a preferred embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of an adjustable torque screwdriver of a preferred embodiment of the present invention; 
         FIG. 3  is an exploded perspective view of an adjustable torque screwdriver of a preferred embodiment of the present invention; 
         FIG. 4  is a perspective view of a hexagonal sleeve of an adjustable torque screwdriver of a preferred embodiment of the present invention; 
         FIG. 5  is a perspective view of a hexagonal drive rod of an adjustable torque screwdriver of a preferred embodiment of the present invention; 
         FIG. 6  is a perspective view of a ratchet pair of an adjustable torque screwdriver of a preferred embodiment of the present invention; 
         FIG. 7  is a perspective view of an outer casing of an adjustable torque screwdriver of a preferred embodiment of the present invention; 
         FIG. 8( a )  and  FIG. 8( b )  are perspective views of an interior ring of an adjustable torque screwdriver of a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a preferred embodiment of an adjustable torque screwdriver  100  according to the invention, the screwdriver  100  having a torque input assembly, a torque output assembly and a torque control assembly. And it is one main object of the present invention to output the torque by the torque output assembly, which is exerted by the user from the torque input assembly and transmitted through the torque control assembly, so as to realize the maximum output torque control of the screwdriver  100  in a single direction (usually the clockwise direction for tightening the screw). 
     As shown in  FIG. 1-3 , the torque input assembly includes a handle  2  which is arranged with a cavity  19  therein, and one end of which is arranged with a rear cover  1 . The first hexagonal hole  20  and the axially extended periphery  21  are disposed at the other end of the handle  2 , where a first connection hole  22  is arranged at the bottom of the first hexagonal hole  20 , being in communication with cavity  19 . The torque input assembly also includes a hexagonal sleeve  4  as shown in  FIG. 4 . As shown in the figure, the structure of the hexagonal sleeve  4  includes an outer hexagonal column  23 , a second hexagonal hole  24  and a convex edge  25 , and a second connection hole  26  is arranged at the bottom of the hexagonal hole  24 . As shown in  FIG. 5 , the torque input assembly also includes a hexagonal drive rod  5  having an hexagonal contour, and a third connection hole  27  with an internal thread is arranged at an end thereof. During assembly, the hexagonal column  23  of hexagonal sleeve  4  is inserted into and fits the first hexagonal hole  20  of handle  2 , and the end of hexagonal drive rod  5  arranged with a third connection hole  27  is inserted into and fits the second hexagonal hole  24  of the hexagonal sleeve  4 , where the first, second and third connection holes  22 ,  26  and  27  are axially aligned and of the same diameter, and through the cavity  19  of handle  2 , screw  3  is screwed into the first, second and third connection holes  22 ,  26  and  27  to draw the axial engagement of handle  2 , hexagonal sleeve  4  and hexagonal drive rod  5 . In addition, through the connections between handle  2  and hexagonal sleeve  4 , and between hexagonal sleeve  4  and hexagonal drive rod  5  via the fitness of a column with an angular periphery and a polygonal hole, the torque exerted on handle  2  is transmitted to hexagonal sleeve  4  and hexagonal drive rod  5 , and then is transmitted to the torque control assembly in this embodiment. 
     The aforementioned is only a specific description of a torque transmission method, the object of which is to realize torque input in the adjustable torque screwdriver  100  of the invention. It should be understood by the technicians in the field that, other torque transmission means in the prior art are also adaptable to, but are not intended to be restricted by, the present invention. 
     Now further description of the torque control assembly of the embodiment of the invention will be expounded, as shown in  FIG. 2 . The torque control assembly includes a ratchet pair  14 , as seen in  FIG. 3  and  FIG. 6 , which includes a first ratchet  28  and a second ratchet  29 , and the first ratchet  28  and the second ratchet  29  have, on their opposing end surfaces, respectively circular teeth  30 ,  31 , matching with each other. Thus the first ratchet  28  and the second ratchet  29  overcome a certain axial force under the effect of the input torque and slip in the pre-set direction of clockwise or counterclockwise, but are not allowed to slip in the opposite direction. And the axial force determines the difficulty of slip or the required input torque causing slip. Thus, the limit of the input torque causing slip can be controlled by controlling the axial force between ratchet  28  and ratchet  29 ; when the input torque in the set direction exceeds this limit, slip occurs between ratchets  28  and  29 , thereby cutting off the rotation and torque output. Generally, this embodiment included, ratchets  28 ,  29  is set to slip in the clockwise direction for screw tightening. In addition, hexagonal through holes  34  and  35  are arranged axially in ratchets  28  and  29 , and hexagonal drive rod  5  is inserted into the first hexagonal through hole  34  so as to transmit the torque to ratchet  28 . 
     The axial force between the ratchets  28  and  29  is usually provided by the elastic assembly, engaging one of the ratchets  28 ,  29 , on the opposite side to the side of the teeth. The larger the pressure imposed on ratchet pair  14  is, the greater the fitting tightness between the ratchet pair. The elastic assembly may be a single spring or a spring group configured in accordance to their different free height and elastic modulus, as shown in  FIG. 2  and  FIG. 3 . In this embodiment, the elastic assembly is composed of springs  11 ,  12  disposed approximately concentrically encircling hexagonal drive rod  5 . The free height H 0  of the first spring  11  is larger than the free height H 0 ′ of the second spring  12 , while the elastic modulus E 2  of the second spring  12  is larger than the elastic modulus E 1  of the first spring  11 . At least one end of spring  11  and spring  12  engages on the side of ratchet  28  to fit ratchet  28  tightly with ratchet  29  by the elastic force in the axial direction, so that the clockwise input torque on the ratchets  28 ,  29  need to overcome the elastic force of the spring to enable ratchets  28 ,  29  to slide on each other. And the elastic force of springs  11 ,  12  is proportional to the amount of its compression, thus, by setting the compression of springs  11 ,  12 , the maximum output torque on the ratchets  28  and  29  in the clockwise direction can be adjusted and controlled. 
     The torque control assembly also includes an adjusting assembly which is mainly used for adjustment of the compression of springs  11 ,  12 , as shown in  FIG. 2 , and a flange  8  arranged between handle  2  and hexagonal sleeve  4 , which is connected to outer casing  13  by multiple small screws  9  disposed on the convex edge thereof. In this embodiment, outer casing  13  is also the outer casing of the screwdriver  100  head, an opening end of which rotatablly fits the periphery  21  of handle  2 , as shown in  FIG. 7 , and internal thread  40  is arranged on the inside of outer casing  13 , ratchets  28 ,  29  and springs  11 ,  12  all disposed in outer casing  13 . The torque control assembly also include, as is shown in  FIG. 8 , an interior ring  10  matching inside the outer casing  13 , the external side of which is arranged with external thread  41  matching with internal thread  40  of outer casing  13 , and a third hexagonal through hole  32  and concave stage  33  are arranged inside for the axial passing through of hexagonal drive rod  5 , as seen in  FIGS. 8( a ) and 8( b ) . One end of each springs  11 , 12  is engaged on the side of the first ratchet  28  and the other ends are engaged on the concave stage  33  inside interior ring  10 . When the user revolves outer casing  13  about the axial of the screwdriver  100  relative to handle  2 , interior ring  10  is not enabled to revolve about the axial of the screwdriver  100 , as the hexagonal through hole  32  thereof is constrained by hexagonal drive rod  5  in the circumferential direction, so that interior ring  10  is only enabled to translate along hexagonal drive rod  5  under the effect of the thread pair, which deforms springs  11 ,  12  to adjust the axial force thereof exerted on ratchet  28 , and as the free height of the first spring  11  H 0  is larger than the free height H 0 ′ of the second spring  12 , in the starting stage the first spring  11  is firstly compressed and deforms, ratchet  28  then only receives exerted force from spring  11 , and when spring  11  deforms to a certain degree, the translation of interior ring consequently causes the second spring  12  to deform, ratchet  28  then receives both elastic forces from springs  11 ,  12 , and as the elastic modulus E 2  of the second spring  12  is larger than the elastic modulus E 1  of the first spring  11 , thus the accelerating rate of elastic force received by ratchet  28  increases. The arrangement of the double-stage springs as adopted by the embodiment, on one hand, enables a broader range of torque adjustment, especially in a low torque region, and on the other hand, prolongs the service life of the second spring  12  which has a large elastic modulus E 2 . It should be understood by technicians of the field that the spring group can further include multiple springs having different free heights and elastic modulus so as to form a multi-stage arrangement. 
     Further, as shown in the figure, handle  2  is arranged with a grading spring  6  and bead  7 , and accordingly flange  8  is arranged with a plurality of round holes  36 . When the outer casing  13  rotates, the flange  8  rotates along with it, so that the bead in turn falls into the round holes on the flange  36  by the elastic biasing force of the grading spring. In addition, as shown in the figure, outer casing  13  is arranged with grading marks corresponding to the locations of round holes  36  with indication arrow arranged on handle  2 , so that users can revolve outer casing  13  to set the output torque of the screwdriver  100  to a required grade. 
     Torque output assembly includes a torque output shaft  18 , having a hexagonal contour at one end of it, and can be inserted into and fit the second hexagon hole  35  of the second ratchet  29 . Further, as shown in the figure, a blind hole is disposed on the surface of the shaft end. Accordingly, a convex boss extends from the end of hexagonal drive rod  5  inserted in the first hexagon hole  34  of the first ratchet  28 . During assembly, the convex boss is connected into the blind hole. The other end of the torque output shaft, through sleeve  17 , flat gasket  16 , and shaft retaining ring  15 , extends from the opening  37  of outer casing  13 , and mounting holes are arranged in the other end surface to mount all kinds of screwdriver bits. 
     The foregoing disclosure is only a specific description of a torque transmission method, the object of which is to realize torque input in the adjustable torque screwdriver  100  of the invention. It should be understood by the technicians in the field that, other torque transmission means of the prior art are adaptable to, but are not intended to be restricted by, the present invention. 
     The foregoing description details the preferred embodiments of the invention. It should be understood that with the general technique of this field, no inventive work is necessary as to make multiple amendments and changes according to the conception of this invention. Therefore, all the technical schemes gained from logical analysis, deductions or limited experimentation based on the conception of the present invention by technicians in this field, should be considered within the protection range asserted in the Claims.