Torque impulse tool with automatic power shut-off comprising two

Details Torque impulse tool with automatic power shut-off comprising two Torque impulse tool with automatic power shut-off comprising two

1999-06-15

2000-12-05

Vo, Peter

Tool driving or impacting

Automatic control of power operated means

Drive means responsive to torque or speed condition

173178, B23Q 500

Patent

active

061553557

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a torque impulse tool for tightening screw joints and including an automatic power shut-off means. In particular, the invention concerns a torque impulse tool of the type comprising a housing, a hydraulic impulse generator, a pneumatic motor with a rotor drivingly coupled to the impulse generator, wherein the shut-off means includes an air inlet valve communicating with the motor and shiftable between an open condition and a closed condition, and a retardation responsive activation means corotative with the rotor and including an inertia actuator, and a connection member coupling the inlet valve to the activation means for shifting the inlet valve from the open condition to the closed condition when activated by the activation means as a predetermined maximum retardation magnitude level is reached.


BACKGROUND OF THE INVENTION

A previously known torque impulse tool of this type is described in U.S. Pat. No. 5,082,066.
A problem concerned with this type of tools is that the very first delivered torque impulse tends to be powerful enough to cause a premature shut-off of the tool. This is due to the fact that in many cases the rotation speed during running down of the screw joint is very high and, accordingly, the kinetic energy of the impulse unit and the motor is very high. This kinetic energy produces a powerful first torque impulse which is strong enough to activate the retardation responsive actuation means and make the inlet valve close. The risk for a premature shut-off is particularly great when tightening so called stiff joints, i.e. screw joints having a steep torque growth characteristic per unit angle of rotation, because in such cases the first impulse is amplified by a very quick and abrupt growing torque resistance in the joint.
At screw joints with a steep torque growth characteristic, there is also a risk that the very first generated torque impulse becomes so powerful that the desired target torque level for the screw joint is passed and an undesirable torque overshoot is caused.
In the above referred U.S. Pat. No. 5,082,066, there is disclosed a speed responsive mechanism for blocking the inertia actuator at rotation speeds above a certain level. This means that the actuating means is prevented from being activated at the first torque impulse, and that the problem of having a premature power shut-off is overcome. At the impulses generated after the first one, the rotation speed and the kinetic energy of the rotating parts of the tool is considerably smaller and, consequently, the energy per impulse is much smaller too. Therefore, the blocking mechanism is deactivated and the inertia actuator is free to initiate power shut-off.
However, the problem of getting too powerful a first impulse and a subsequent undesireable torque overshoot is not overcome by this known device. There is no means provided to reduce the energy of the very first torque impulse.


OBJECT OF THE INVENTION

The main object of the invention is to provide a torque impulse tool comprising means for obtaining a reduced motor speed and power output during the initial stage of each tightening process, thereby reducing the kinetic energy of the motor and impulse generator at the first torque impulse such that an undesireable torque overshoot and/or a premature power shut-off is avoided.
Further objects and advantages of the invention will appear from the following specification and claims.
A preferred embodiment of the invention is hereinbelow described in detail with reference to the accompanying drawings.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a torque impulse tool according to the invention.
FIG. 2a shows a longitudinal section through the power control section of the tool in FIG. 1, illustrating a partial flow condition of the air inlet valve.
FIG. 2b shows the same section as FIG. 2a, but illustrates an open condition of the air inlet valve.
FIG. 2c shows the same section as FIG. 2a, but illustrates a closed condition of the air inlet valve.
FIG.

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patent: 5082066 (1992-01-01), Schoeps
patent: 5492185 (1996-02-01), Schoeps et al.

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