Patent Publication Number: US-9415489-B2

Title: Impact mechanism for an electric tool

Description:
This is a U.S. national stage application of PCT Application No. PCT/CN2011/081767 under 35 U.S.C. 371, filed Nov. 4, 2011 in Chinese, claiming the priority benefit of Chinese Application No. 201020612631.6, filed Nov. 9, 2010, which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The invention relates to the field of electric tools, in particular to an impact mechanism for an electric tool. 
     BACKGROUND OF THE INVENTION 
     Electric wrenches are tools powered by power supplies or batteries and used for tightening bolts. The electric wrenches mainly include impact wrenches, shear wrenches, constant torque wrenches, torque angle wrenches, angle wrenches, hydraulic wrenches, torque wrenches, rechargeable electric wrenches and the like. The electric wrenches have the characteristics of convenient operation and time and labor conservation. As they are mainly used for mounting high-strength bolts of steel structures in the steel structure installation industry, high demands are proposed on the torque of the wrenches. 
     In the prior art, the work of an electric wrench generally involves a motor connected with a power supply and a transmission mechanism driven by the motor. Energy is transferred to a whip block by the transmission mechanism, and the work task is accomplished by means of striking a working head by the whip block. 
     However, the impact mechanism of such structure is provided with only one whip block which, when working, causes quite a few separations in the housing. As such, the output efficiency is reduced and the toque is low. In addition, in order to achieve periodic striking, an eccentric wheel or an asymmetric structure are usually adopted as the structure of the whip block, so dynamic balance of the whip block during the operation cannot be ensured. 
     SUMMARY OF THE INVENTION 
     The technical problem to be solved by the invention is to provide, in view of the prior art, an impact mechanism for an electric tool, which has a large toque and good dynamic balance. 
     The following technical solution is adopted in the invention to solve the aforesaid technical problem: the impact mechanism for an electric tool comprises a transmission mechanism arranged in a housing and driven by a motor, whip blocks and a power output member; the whip blocks are driven by the transmission mechanism, and are connected to and drive an output shaft, wherein the transmission mechanism comprises a transmission wheel, the motor is connected to and drives the transmission shaft of the transmission wheel, two grooves are symmetrically arranged on the peripheral wall of the transmission wheel, tail portions of the two whip blocks are mounted in the two grooves through wrist pins, respectively; head portions of the two whip blocks are connected to the power output member; a first axial hole and a second axial hole are arranged at an interval on the transmission shaft corresponding to the head portions and the tail portions of the whip blocks, a spring is received in the first axial hole, two ends of the spring abut against the tail portions of the two whip blocks, respectively, and a magnet is arranged in the second axial hole, such that the two whip blocks are whipped at the same time. 
     The transmission wheel is connected with the motor by a clutch. 
     The clutch comprises a driving wheel connected with the output shaft of the motor and a driven wheel sleeved on the exterior of the driving wheel. The peripheral wall of the driving wheel is provided with small grooves symmetrical to each other and steel balls are arranged in each of the groove. A gap is arranged between the inner wall of the driven wheel and the outer wall of the driving wheel, and the driven wheel is connected with the transmission shaft. 
     The inner peripheral wall of the driven wheel is uneven. 
     The power output member is a rotatable power output shaft, the tail portion of the power output shaft is provided with a receiving groove, an opening of which faces the transmission wheel, and the head portions of the whip blocks are received in the receiving groove and the transmission shaft is connected onto a bottom surface of the receiving groove. 
     Compared with the prior art, the impact mechanism for an electric wrench is provided with two whip blocks. It stores energy by using the spring and whips the two whip blocks at the same time by using the magnet, so that a large output power can be achieved when the motor operates at a low power. Besides, as the two whip blocks are symmetrically arranged, a dynamic balance can be ensured during operation. The arrangement of the clutch between the transmission wheel and the motor allows the impact mechanism to operate more stably. The steel balls are used as engaging members for the clutch, thus achieving the advantages of long service life, low cost, low temperature rise during the operation, among other things. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of an assembled structure of embodiments of the invention; 
         FIG. 2  to  FIG. 4  are schematic plans of the transmission wheel in the embodiments of the invention; 
         FIG. 5  to  FIG. 7  are schematic plans of the output shaft in the embodiments of the invention; 
         FIG. 8  to  FIG. 10  are schematic plans of the driven wheel in the embodiments of the invention; 
         FIG. 11  to  FIG. 13  are schematic plans of the driving wheel in the embodiments of the invention; and 
         FIG. 14  and  FIG. 15  are schematic plans of the whip blocks in the embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be further described in details below with reference to drawings and embodiments. 
     As shown in  FIG. 1  to  FIG. 15 , the impact mechanism for an electric wrench comprises the following components arranged in a housing (not shown in the figures): 
     a motor  2 , located at a tail portion of the housing, serving as a driving device for the electric wrench and capable of being connected with an external power supply through a conductive wire or a battery; 
     a clutch  3 , comprising a driving wheel  31 , steel balls  32  and a driven wheel  33 ; wherein the driving wheel  31  is fixedly connected with an output shaft  21  of the motor  2 , a peripheral wall of the driving wheel  31  is provided with two small grooves  311  symmetrical to each other, and there may be more small grooves  311  as needed; the two steel balls  32  are received in each of the small grooves  311 , respectively; the driven wheel  33  is U-shaped, a wheel concave  331  in the middle of the driven wheel  33  is sleeved on the exterior of the driving wheel  31 , the inner diameter of the wheel concave  331  is larger than the outer diameter of the driving wheel  31 , a gap is arranged between the wheel concave  331  and the driving wheel  31 , the inner wall of the wheel concave  331  is uneven, and such structure can be achieved by disposing a plurality of shallow grooves on the inner wall of the wheel concave  331 ; 
     a transmission wheel  4 , comprising a wheel body  41  and a transmission shaft  42  arranged at the axis of the wheel body; wherein, one end of the transmission shaft  42  is coaxially connected with the driven wheel  33 , and the abutted portion between the transmission shaft  42  and the driven wheel  33  is arranged on a first bearing  9  for purpose of improving the operation stability and prolonging the service life of components; and the other end of the transmission shaft  42  is operatively connected with an output shaft  8  mentioned below; a first axial hole  421  and a second axial hole  422  are arranged at an interval on the head portion and the tail portion of the transmission shaft along a direction perpendicular to the axis of the transmission shaft; a spring  5  is received in the first axial hole  421 , and a magnet  6  is arranged in the second axial hole  422 ; two grooves  411  are symmetrically arranged on the peripheral wall of the wheel body  41  so that the wheel body  41  is separated into two half wheel bodies symmetrical to each other; two pin shafts  71  are arranged in the two grooves  411 , respectively, and two ends of each pin shaft  71  are fixed on the two half wheel bodies, respectively; and the tail portions of the two whip blocks  7  are respectively connected onto corresponding pin shafts  71  through wrist pins; 
     two whip blocks  7 , the tail portions of each one of which are mounted in the two grooves  411  through the pin shafts  71 , respectively; wherein two ends of the spring  5  abut against the tail portions of the two whip blocks  7 , respectively, and two ends of the magnet  6  are aligned with the head portions of the two whip blocks  7 ; and 
     an output shaft  8 , arranged between the transmission wheel and a working head (not shown in the figures) and transferring kinetic energy of the impact mechanism onto the working head for operation; wherein the tail portion of the output shaft  8  is provided with a receiving groove  81 , the opening of which faces the transmission wheel  4 , and the head portions of the two whip blocks  7  are received in the receiving groove; the other end of the transmission shaft  42  is operatively connected onto a bottom surface of the receiving groove  81 ; and the head portion of the output shaft  8  is arranged on a second bearing  1 . 
     When energized, the motor  2  drives the driving wheel  31  to rotate. The steel balls  32  located in the small grooves  311  move outwards under a centrifugal force and generate certain pressure to squeeze the driven wheel when contacting the inner wall of the wheel concave  331 , so that a friction force is generated to drive the driven wheel. As the inner wall of the wheel concave  331  is designed to be of an uneven structure, the friction between the steel balls and the driven wheel  33  can be greatly increased so that the driven wheel can rotate quickly. As the driven wheel  33  is fixedly connected with the transmission wheel  4  to drive the transmission wheel to rotate, after a certain time, the transmission wheel reaches a certain rotational speed, the two whip blocks  7  arranged on the transmission wheel overcome the pressure of the spring  5  and the attraction of the magnet  6 , whip heads rotate outwards instantaneously, the head portions of the whip blocks  7  immediately strike the output shaft  8  to generate a great torque instantaneously and further to bring the working head to work at a great acting force.