Abstract:
A ratchet screwdriver includes a ratchet wheel; a pawl base assembly, for inserting into the ratchet wheel, and a plurality of pawl pieces for engaging with teeth, the rear end of the pawl base assembly connecting to a handle of a screwdriver while the front end connecting to a head of the screwdriver; a rings assembly adjustably mounted on the ratchet wheel; the pawl base assembly includes a center rod and a pedestal, the rear part of the center rod is provided with a first positioning slot, the center rod passes through the center hole of the pedestal, the center rod is clamped at the first positioning slot by a first clamping member. Compared with the prior art, the overall structure is more rational and practical, and is safer and more reliable in use, and is capable of loosening or tighten a screw quickly.

Description:
RELATE APPLICATIONS 
       [0001]    This application claims the benefit of Chinese Utility Model Application 201320642437.6, filed on Oct. 17, 2013, the specification of which is incorporated herein by this reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a screwdriver and particularly to a ratchet screwdriver. 
       DESCRIPTION OF THE PRIOR ART 
       [0003]    As one of the common hardware tools, screwdrivers are used for loosening or tightening screws. A common screwdriver generally includes a handle, a toolbar and a head. Users rotate the handle of the screwdriver to drive the toolbar and the head of the screwdriver to rotate, so that the head drives a screw to rotate in order to loosen or tighten the screw. A common screwdriver rotates totally depending on manpower, so it is strenuous to use the screwdriver and difficult to control its direction. It is likely to cause convolution during the rotation, so that the use efficiency is relatively low. Therefore, some ratchet screwdrivers capable of realizing one-way idling are designed, for example, a Chinese Patent CN2307658Y (Patent No.: ZL 97235059.4), titled “Hidden Ratchet Screwdriver” and a Chinese Patent CN2900088Y (Patent No.: ZL200620103975.8), titled “Combined Ratchet Screwdriver”. The Chinese Patent CN2307658Y discloses that the ratchet screwdriver comprises a spring, an extension rod, a transmission rod, a ratchet set consisting of a positioning ratchet, a leftward ratchet and a rightward ratchet, a positioning lug and other components. The Chinese Patent CN2900088Y discloses that the ratchet screwdriver comprises a connecting base, a ring, a brake block, an arc sliding sleeve and other structures. Although both the two ratchet screwdrivers can realize the one-way rotation of the ratchet screwdriver, they are complicated in structure, large in size and relatively complicated in assembling and manufacturing. Furthermore, it is likely to result in the failure of the screwdrivers due to the damage or missing of a small component. 
         [0004]    In practical applications, ratchet screwdrivers also have the following disadvantages: on one hand, due to the positioning of a pawl base and a ratchet, the rotation of a ratchet screwdriver is realized by hexagonal connection, so the torsion can not meet the requirements in use, which is likely to result in slipping; on the other hand, during the installation of the toothed plates, the rectangular plates are directly fitted with rectangular grooves on the pawl base, in this case, although the normal functions of the ratchet may be realized, such assembly goes against good positioning and the toothed plates are easy to slip off, as a result, the installation is inconvenient and the accurate fitting between the toothed plates and the external teeth is thus influenced. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to provide a ratchet screwdriver having improved torsion and safer and more reliable use. 
         [0006]    For achieving this object, the ratchet screwdriver, comprises: a ratchet wheel having an inner surface with a tooth ring; a pawl base assembly, for inserting into the ratchet wheel, having a front end, a rear end, and a plurality of pawl pieces for engaging with teeth on the tooth ring, the rear end of the pawl base assembly connecting to a handle of a screwdriver while the front end connecting to a head of the screwdriver; and a rings assembly adjustably mounted on the ratchet wheel; wherein the pawl base assembly includes a center rod with a front end, a middle section, and a rear part and a pedestal with a center hole and a rear end, the rear part of the center rod passes through the center hole of the pedestal, the middle section has a circular periphery, the pedestal has a circular periphery, the circular periphery of the middle section of the center rod is provided with a plurality of protrusions, and the inner surface at a front end of the ratchet wheel is provided with a plurality of limiting recesses for receiving the plurality of protrusions, the rear end of the pedestal connects to the handle of the screwdriver, and the head of the screwdriver inserts into the front end of the center rod, a first groove, a second groove, a third groove and a fourth groove are provided on the circular periphery of the pedestal, four grooves each along the axis of the center rod, and a first pawl piece, a second pawl piece, a third pawl piece and a fourth pawl piece are respectively rotatably inserted into each of the four grooves, each pawl piece has a tooth-shape outer end for engaging with the teeth of the tooth ring, two elastic elements are respectively resisted between the first pawl piece and the fourth pawl piece, and between the second pawl piece and the third pawl piece, for pushing the first pawl piece away from the fourth pawl piece, and pushing the second pawl piece away from the third pawl piece, and the rings assembly is provided therein with a plurality of push portions for engaging the pawl pieces and selectively disconnecting the pawl pieces from the teeth of the tooth ring to rotate the pawl base assembly. 
         [0007]    Preferably, the rear part of the center rod is provided with a first positioning slot, the center rod is clamped at the first positioning slot by a first clamping member to limit displacement of the pedestal. 
         [0008]    Preferably, there are four protrusions distributed on the circular periphery of the center rod, correspondingly, and there are also four limiting recesses on the front end of the ratchet wheel 
         [0009]    Preferably, the end of each groove is an arc groove with a C-shape, inner ends of the pawl pieces have arc surfaces, and the inner ends of the pawl pieces are rotatably disposed in the arc grooves. 
         [0010]    In the existing ratchet screwdrivers, matching of the rectangular pawl pieces and the rectangular grooves of the pedestal results in poor positioning effect. As a result, the pawl pieces are easy to slip off from the grooves and the installation is inconvenient, so that accurate matching between the pawl pieces and an external tooth ring is influenced. In the present invention, the rear ends of the pawl pieces are cylinders having a lager diameter than that of the front ends of the pawl pieces, and the pedestal is provided thereon with cylindrical grooves correspondingly, so that the matching of cylinders and grooves makes the pawl pieces slip off hardly. The axes of the rear ends of the pawl pieces rotate around the axes of the grooves of the pedestal, so the better matching precision of the pawl pieces and the tooth ring are ensured, and the stability and safety in use of the product can be greatly improved. 
         [0011]    Preferably, the rings assembly includes a ring and a ring release with an inner surface and an outer surface, the ring release is disposed inside the ring, the ring drives the ring release to rotate, the ratchet wheel is located between the ring release and the ring, four push portions are provided on the inner surface of the ring release, recesses for receiving the push portions are provided on an outer surface of the pedestal at corresponding positions to the grooves. 
         [0012]    Preferably, a side, in contact with the pawl pieces, of each push portion has a beveled edge with a gradient matched with a gradient of side walls of the pawl pieces, and side edges of the push portions are designed to be beveled edges matched with the pawl pieces, a force exerted by the push portions onto the pawl pieces is dispersed uniformly. 
         [0013]    Preferably, the front part of the center rod is reduced to form an insertion portion, with a front circumference, on which a first spring is sheathed, that the first spring pushing against an connecting portion, the front circumference of the insertion portion is provided with a second positioning slot in which a second clamping member is clamped to limit displacement of the connecting portion, in a position where the center rod gets close to the second positioning slot, a first hole is provided behind the second positioning slot, a first steel ball, embedded in the center rod, protrudes from the first hole and presses against an inward-convex conical surface of a front segment of the connecting portion. 
         [0014]    Preferably, the outer surface of the ring release is provided with a clamping bulge, and correspondingly, an inner surface of the ring is provided with a clamping slot, matching of the clamping bulge and the clamping slot enables the ring to drive the ring release to rotate. 
         [0015]    Preferably, any two adjacent grooves among the four grooves are symmetrical relative to a center line of the pedestal, and any two spaced-apart grooves are symmetrical relative to a center axis of the pedestal. 
         [0016]    Preferably, outside of a middle part of the pedestal is provided with a bulge ring for engaging the ring, a side of the bulge ring is provided with a second blind hole with a second spring and a second steel ball placed on top of the second spring, the second spring pushes the second steel ball, the second steel ball, embedded in the pedestal, protrudes from the second blind hole and pushes against the inner surface of the ring release, a left positioning hole, a middle positioning hole and a right positioning hole matching the second steel ball are provided on the inner surface of the ring release, when the second steel ball is located in the middle positioning hole, the pawl pieces are just all meshed, and the pawl base assembly does not rotate, when the ring drives the ring release to rotate and the second steel ball is located in the left or right positioning hole, the pawl base assembly performs one-way rotation. 
         [0017]    Preferably, the elastic elements are double-ring torsion springs, which have higher elasticity than straight springs, so the pawl pieces can rebound or retract to the corresponding positions completely, resulting in reliable performance when in use. The double-ring torsion springs are more applicable to the above technical solution to effectively improve the assembling efficiency. 
         [0018]    Preferably, the connecting portion is a sleeve made of iron, an outer surface of the connecting portion is distributed with concave and convex grid texture. In the present invention, taking iron instead of conventional aluminum that the cost is reduced and the intensity and service life of the connecting portion are enhanced under the premise of rust resistance. 
         [0019]    Preferably, the center rod is a hollow rod made of zinc alloy. Under the premise of ensuring the intensity, one-step molding reduces the machining procedures, improves the precision of a single product and the production efficiency of the whole product, and thus reduces the cost. 
         [0020]    Compared with the prior art, in the present invention, the positioning of the tooth ring on the center rod is achieved by the protrusions of the center rod, so that the torsion and torque are strengthened substantially, and the use safety of the ratchet screwdriver is better ensured; the cross-sections of the bottom of the grooves are arc grooves with a C-shape, and inner ends of the pawl pieces have arc surfaces correspondingly, so that the pawl pieces may be prevented from slipping off from the arc grooves, and the matching precision of the pawl pieces and the teeth are further ensured; finally, the rear end of the center rod is provided with a positioning slot, and the rear end of the center rod is provided with a ring after passing through a center hole of the pedestal, so that the longitudinal motion of the center rod is fixed without influencing its rotation. Therefore, the overall structure is more rational and practical, and is safer and more reliable in use. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is an exploded perspective view of a ratchet screwdriver in accordance with an embodiment of the present invention; 
           [0022]      FIG. 2  is a partial view of the ratchet screwdriver in accordance with the embodiment of the present invention; 
           [0023]      FIG. 3  is a sectional view of line A-A of  FIG. 2 ; 
           [0024]      FIG. 4  is a sectional view of line B-B of  FIG. 2 ; 
           [0025]      FIG. 5  is a sectional view of the crisscross protrusions disposed on the front end face of the ratchet wheel in accordance with the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    To enable a further understanding of the innovative and technological content of the invention herein, refer to the detailed description of the invention and the accompanying drawings below: 
         [0027]    As shown in  FIG. 1  to  FIG. 4 , in this embodiment, a ratchet screwdriver, comprises: a ratchet wheel  100  having an inner surface with a tooth ring  5 ; a pawl base assembly  200 , for inserting into the ratchet wheel  100 , having a front end, a rear end, and a plurality of pawl pieces for engaging with teeth on the tooth ring  5 , the rear end of the pawl base assembly  200  connecting to a handle of a screwdriver while the front end connecting to a head of the screwdriver; and a rings assembly  300  adjustably mounted on the ratchet wheel  100 . 
         [0028]    In this embodiment, the pawl base assembly  200  includes a center rod  8  with a front end, a middle section, and a rear part and a pedestal  13  with a center hole and a rear end, the rear end of the pedestal  13  connects to the handle of the screwdriver, and the head of the screwdriver inserts into the front end of the center rod  8 ; the center rod  8  is a hollow rod made of zinc alloy, so that, under the premise of ensuring the intensity, one-step molding reduces the machining procedures, improves the precision of a single product and the production efficiency of the whole product, and thus reduces the cost. The rear part of the center rod  8  is provided with a first positioning slot  83 , the center rod  8  passes through the center hole of the pedestal  13 , and the center rod  8  is clamped at the first positioning slot  83  by a first clamping member  14  to limit displacement of the pedestal  13 . There are four protrusions  81  distributed on the circular periphery of the center rod  8 , correspondingly, and there are also four limiting recesses  51  on the front end of the ratchet wheel  100 , as shown in  FIG. 5 , so that the center rod  8  can be rotated together with the ratchet wheel  100 . 
         [0029]    The front part of the center rod  8  is reduced to form an insertion portion  84 , with a front circumference, on which a first spring  3  is sheathed, the inner end of the first spring  3  presses against the inner annular surface of the insertion portion  84  and annular surface of the insertion portion  84  is pressed against the inward-convex ring of the connecting portion  1 , for pushing the connecting portion  1  away from the insertion portion  84 , the front circumference of the insertion portion  84  is provided with a second positioning slot  82  in which a second clamping member  2  is clamped to limit displacement of the connecting portion  1  matching with the inner annular surface of the insertion portion  84 , in a position where the center rod  8  gets close to the second positioning slot  82 , a first hole  85  is provided behind the second positioning slot  82 , a first steel ball  7 , embedded in the center rod, protrudes from the first hole  85  and presses against an inward-convex conical surface  1   a  of a front segment of the connecting portion  1 . The connecting portion  1  is a sleeve made of iron, an outer surface of the connecting portion  1  is distributed with concave and convex grid texture, in this embodiment, taking iron instead of conventional aluminum that the cost is reduced and the intensity and service life of the connecting portion are enhanced under the premise of rust resistance. The connecting portion  1 , the first spring  3  and the first steel ball  7  and etc form a quick locking mechanism for quickly locking the head of the screwdriver inserted into the front end of the center rod  8 . When the connecting portion  1  is pushed backward, the first steel ball  7  may protrude to be movable. In this way, the head of the screwdriver may be conveniently inserted into the front end of the center rod  8 . Then, the connecting portion  1  moves forward under the push of the first spring  3 , and the first steel ball  7  is pressed by the inward-convex conical surface  1   a  of the front segment of the connecting portion  1 , so that the head of the screwdriver is locked again. 
         [0030]    The rear end of the pedestal  13  of the pawl base assembly  200  connects to the handle of the screwdriver. a first groove  95 , a second groove  96 , a third groove  97  and a fourth groove  98  are provided on the circular periphery of the pedestal  13 , four grooves each along the axis of the center rod  8 , any two adjacent grooves among the four grooves are symmetrical relative to a center line of the pedestal  13 , and any two spaced-apart grooves are symmetrical relative to a center axis of the pedestal  13 ; and a first pawl piece  91 , a second pawl piece  92 , a third pawl piece  93  and a fourth pawl piece  94  are respectively rotatably inserted into each of the four grooves, each pawl piece has a tooth-shape outer end for engaging with the teeth of the tooth ring  5 , two elastic elements  10  are respectively resisted between the first pawl piece  91  and the fourth pawl piece  94 , and between the second pawl piece  92  and the third pawl piece  93 , in the embodiment, the elastic elements  10  are double-ring torsion springs, which push the first pawl piece  91  away from the fourth pawl piece  94 , and push the second pawl piece  92  away from the third pawl piece  93 . To prevent the pawl pieces from slipping off from the grooves, the degree of opening of the four grooves increases gradually, the end of each groove is an arc groove with a C-shape, inner ends of the pawl pieces have arc surfaces, and the inner ends of the pawl pieces are rotatably disposed in the arc grooves. Outside of a middle part of the pedestal  13  is provided with a bulge ring  15  for engaging the ring  4 , a side of the bulge ring  15  is provided with a second blind hole  16  with a second spring  11  and a second steel ball  12  placed on top of the second spring  11 , the second spring  11  pushes the second steel ball, the second steel ball  12 , embedded in the pedestal, protrudes from the second blind hole  16  and pushes against the inner surface of the ring release  6 , a plurality of positioning holes  63  matching the second steel ball  12  are provided on the inner surface of the ring release  6 . 
         [0031]    In this embodiment, there are left, middle and right positioning holes  63 . when the second steel ball  12  is located in the middle positioning hole  63 , the pawl pieces are just all meshed, and the pawl base assembly  200  does not rotate, when the ring  4  drives the ring release  6  to rotate and the second steel ball  12  is located in the left or right positioning hole  63 , the pawl base assembly  200  performs one-way rotation. 
         [0032]    In this embodiment, the rings assembly  300  includes a ring  4  and a ring release  6  with an inner surface and an outer surface, the ring release  6  is disposed inside the ring  4 , the outer surface of the ring release  6  is provided with a clamping bulge  61 , and correspondingly, an inner surface of the ring  4  is provided with a clamping slot  41 , matching of the clamping bulge  61  and the clamping slot  41  enables the ring  4  to drive the ring release  6  to rotate, the ratchet wheel  100  is located between the ring release  6  and the ring  4 , the inner surface of the ring release  6  is provided with a plurality of push portions  62  for engaging the pawl pieces and selectively disconnecting the pawl pieces from the teeth of the tooth ring  5  to rotate the pawl base assembly  200 , there are four push portions  62 , each engages a pawl piece, arc recesses  131  for receiving the push portions  62  are provided on an outer surface of the pedestal  13  at corresponding positions to the grooves, and inner ends of the push portions  62  also have arc surfaces relative to arc recesses  131 . The ring release  6  passes through the rear end of the pedestal  13  to be sheathed on the pedestal  13 , the push portions  62  of the inner surface of the ring release  6  respectively inserts into the corresponding recesses for engaging the outer ends of the pawl pieces, when the ring  4  drives the ring release  6  to rotate, the pawl pieces is driven to engage and disconnect the teeth of the tooth ring  5 , then the pawl base assembly  200  performs one-way rotation relative to the ring  4 . 
         [0033]    This embodiment employs a universal external member, i.e., the ring  4 , which is a ratchet structure rotating while the pawl pieces are inserted into or pushed away from the tooth grooves by a predetermined rotation. Referring to  FIG. 4 , when the second steel ball  12  is located in the middle positioning hole  63 , the four pawl pieces are just all meshed under the action of the elastic members  10 , and the pawl base assembly  200  does not rotate. In this case, when the handle of the screwdriver is rotated clockwise, the handle drives the pedestal  13  to rotate clockwise. The pedestal  13  drives the ratchet  100  to rotate clockwise as the pawl pieces are engaged with the teeth of the tooth ring  5 , and the ratchet  100  drives the center rod  8  to rotate clockwise under the action of the limiting recesses  51 . Finally, the center rod  8  drives the head of the screwdriver to rotate clockwise. At this time, the head of the screwdriver is in a clockwise operating state. If the handle of the screwdriver is rotated anticlockwise, the head of the screwdriver is in an anticlockwise operating state. When the ring  4  is rotated anticlockwise under the action of an external force and the second steel ball  12  is located in the right positioning hole  63 , the push portions  62  push the fourth pawl piece  94  and the second pawl piece  92  to generate deflection against the elasticity of the elastic elements  10 , so that the fourth pawl piece  94  and the second pawl piece  92  are disconnected from the teeth while the first pawl piece  91  and the third pawl piece  93  are engaged with the teeth of the tooth ring  5 . Therefore, the pawl base assembly  200  can perform one-way anticlockwise rotation to rotate by a certain angle, while the ratchet  100  may rotate clockwise relative to the ring  4 . Meanwhile, the ratchet  100  may drive the center rod  8  to rotate clockwise, and the center rod  8  drives the head of the screwdriver to rotate clockwise. At this time, if the handle of the screwdriver is rotated clockwise, the handle drives the pedestal  13  to rotate clockwise. As the pawl pieces are engaged with the teeth, the ratchet  100  drives the center rod  8  to rotate clockwise simultaneously; as a result, the clockwise working force of the head of the screwdriver is further strengthened. When the ring  4  is rotated clockwise and the second steel ball  12  is located in the left positioning hole  63 , the push portions  62  push the first pawl piece  91  and the third pawl piece  93  to generate deflection against the elasticity of the elastic elements  10 , so that the first pawl piece  91  and the third pawl piece  93  are disconnected from the teeth while the fourth pawl piece  94  and the second pawl piece  92  are engaged with the teeth. Therefore, the pawl base assembly  200  can perform one-way clockwise rotation to rotate by a certain angle, while the ratchet  100  may rotate anticlockwise relative to the ring  4 . Meanwhile, the ratchet  100  may drive the center rod  8  to rotate anticlockwise, and the center rod  8  drives the head of the screwdriver to rotate anticlockwise. At this time, if the handle of the screwdriver is rotated anticlockwise, the handle drives the pedestal  13  to rotate anticlockwise. As the pawl pieces are engaged with the teeth, the ratchet  100  drives the center rod  8  to rotate anticlockwise simultaneously; as a result, the anticlockwise working force of the screwdriver bit is further strengthened. 
         [0034]    The working principle of the ratchet screwdriver in this embodiment is as follows: when the ring  4  rotates in a certain direction, the pawl pieces are engaged with or disconnected from the teeth under the external force of the push portions  62 , and the pawl base assembly  200  rotates towards the same direction; and when the ring  4  does not rotate, the pawl pieces are all engaged with the teeth, and the pawl base assembly  200  cannot rotate and stays in an idle state.