Power wrench for tightening screw joints

• US 5,155,421 A
• Filed: 11/05/1991
• Issued: 10/13/1992
• Est. Priority Date: 06/12/1989
• Status: Expired due to Fees

• Current Assignee: Atlas Copco Tools AB (Atlas Copco AB)
• Original Assignee: Atlas Copco Tools AB (Atlas Copco AB)
• Inventors: Hansson, Gunnar C.
• Primary Examiner(s): SALATA, ANTHONY J
• Application Number:
  US07/789,428
• Time in Patent Office: 343 Days
• Field of Search: 318/434, 318/432, 318/280-286, 318/264-266, 318/272, 318/275, 318/367, 318/369, 318/462, 318/465, 318/467-469, 318/470, 318/475, 318/476, 318/482, 81/55, 81/57.11, 81/57.14, 81/57.18, 81/57.22, 81/467, 81/469, 81/477, 81/429, 81/DIG. 3, 361/23, 361/31, 388/937
• US Class Current: 318/434
• CPC Class Codes: B25B 21/008 with automatic change-over from high speed-low torque mode to low speed-high torque mode
• CPC Class Codes: B25B 23/147 specially adapted for electrically operated wrenches or screwdrivers

Abstract

A power wrench for two-step tightening of screw joints, has a housing (13), an electric motor (10) including a rotor (25), an output shaft (24) coupled to the rotor (25), and a power supply. The power supply includes a power converter (11) with a variable frequency and voltage output and a current responsive power shut-off device. A retardation responsive inertia device (28) is coupled to the motor rotor (25) via a spring (32) and a cam (29, 30) for corotation with the motor rotor (25) and for activation of a switch (12) as a certain predetermined retardation magnitude in the motor rotor (25) is exceeded. The latter is used for obtaining a fast torque interruption of the initial tightening step of the two-step tightening process, whereas the final tightening step is discontinued automatically as a predetermined current magnitude in the power supply is reached.

Claims

1. A power wrench for two-step tightening of a screw joint, the first step of said two steps comprising an initial tightening to a predetermined torque snug level and the second step of said two steps comprising a final tightening from said predetermined torque snug level to a desired final torque level,

said power wrench comprising:

a housing (13);

an electric motor (10) having a rotor (25), and an output shaft (24) drivingly coupled to said rotor (25); and

a power supply means (11) including a variable voltage and frequency output power converter for supplying power to said motor;

said power supply means comprising;

a current responsive power shut-off means for interrupting the power supply to said motor (10) at attainment of said final torque level; and

a torque overshoot protective retardation responsive switch means (12,

     28) associated with said rotor (25) for delivering an electrical shut-off signal to said power converter to stop the supply of power to said motor at attainment of a predetermined retardation magnitude during said first tightening step, said torque overshoot protective retardation responsive switch means being located completely out of contact with the screw joint, a screw joint engaging protruding spindle or a base surface surrounding the screw joint.

2. The power wrench of claim 1, wherein said retardation responsive switch means (12, 28) comprises:

a switch;

an inertia member (28) coaxially disposed relative to said rotor (25); and

a cam means (29,

     30) drivingly coupling said inertia member (28) to said rotor (25) for providing a switch actuating movement to said switch at a certain retardation magnitude of said rotor (25) for delivering said electrical shut-off signal via said switch.