The invention provides an on-board electric
wrench, comprising a
flywheel, an output shaft, a lug boss and an
impact block. A pin shaft which is used for positioning the
impact block is sheathed with a
torsion spring; two forcing ends of the
torsion spring are respectively positioned on a position limit
retaining pin and the
impact block; the distance between the center of the positioning hole of a
steel ball and the center of the pin shaft complies with the requirement that the chord length corresponding to the motion track of the
steel ball is more than the
radius of the positioning hole of the
steel ball. The invention replaces a pulling spring with the
torsion spring, changes the adjusting position, leads the adjustment of the impact force and the
recovery force of the impact block to be realized by the rigidity of the torsion spring and the steel ball supporting spring respectively, solves the contradiction that adjustment of the impact force and the
recovery force of the impact block is integrated into a whole on the pulling spring, meets the impact force of the
wrench design, leads the
recovery of the impact block to be slow, leads the engagement surface of the impact block can always push through the forcing surface of the convex block and convex shoulder before the screw is screwed or after the screw is loosened so as to achieve the
continuous operation, and has the advantages of fully
automation of loosening and tightening the screw, complete engagement of the impact block and the root of the convex block, and long service life.