Device for tightening a screw joint

A device for tightening screw joints, comprising a pressure fluid motor, an overload friction type slip clutch, a pressure fluid shut off valve and a release mechanism for initiating closing of said shut off valve at slipping of said overload clutch. The release mechanism comprises a female member associated with one of the slip clutch halves and a male member associated with the other of the slip clutch halves, and when aligned with said female member receivable thereinto. The release mechanism also comprises a guide means for urging against a biasing means said male member into alignment with said female member upon relative rotation of the slip clutch halves.

This invention relates to a device for tightening screw joints. In 
particular the invention relates to a pressure fluid powered device for 
tightening screw joints, comprising a friction type slip clutch. 
A problem concerned with screw tightening devices of the above kind is how 
to obtain an automatic shut off of the pressure fluid supply as the 
friction slip clutch starts slipping. An important fact to consider is 
that a friction slip clutch may occupy when reengaging any position as it 
is reengaged after release, which means that there is no predetermined 
relative position or positions in which the clutch halves tend to 
reengage. This means in turn that a shut off means intended for a clutch 
of this type has to work properly whatever the actual relative position of 
the clutch halves may be. 
The invention intends to solve the above problem, which is accomplished by 
the device defined in the claims.

DETAILED DESCRIPTION 
In FIG. 1, 10 designates the housing of the nut runner. The housing 
encloses a pneumatic motor (not shown) to which is connected a driving 
clutch half 11 of a torque responsive slip clutch 12. The slip clutch 
further comprises a driven clutch half 13 connected to an output shaft 14 
and a coil type friction spring 15 which is arranged to transmit torque 
from the driving clutch half 11 to the driven clutch half 13. 
For that purpose, the axially extending rear endpart 17 of the friction 
spring 15 is positively connected to the driving clutch half 11 via a 
recess 18 in the latter. The driven clutch half 13 has an external 
cylindrical friction surface 19 for cooperation with the internal surface 
of the friction spring 15. The latter transmits torque by means of its 
friction grip on the friction surface 19, which grip is accomplished by 
pre-tensioning of the spring 15. The characteristc feature of such a 
spring is that its friction grip is practically independent of the 
friction coefficient provided several windings of the spring are in 
engagement with the friction surface. 
To make the friction spring 15 act as a slip clutch its rear end 17 has to 
be driven in the unwinding direction of the spring. 
The nut runner comprises an auxiliary spring 20 which has rear and forward 
axially extending ends 21 and 22, respectively. The rear end 21 of the 
auxiliary spring 20 is received in a bore 24 in a setting ring 25 which is 
rotatively supported on the driving clutch half 11. The setting ring 25 is 
rotatable relative to the driving clutch half 11 by means of a screw which 
engages a thread 29 on the outer periphery of the driving clutch half 11 
thereby constituting a worm gear. Stop screws 27 and 28 are provided to 
limit the rotation movement of the setting ring 25 relative to the driving 
clutch half 11. 
The forward end 22 of the auxiliary spring 20 is positively connected to a 
coupling sleeve 30 via an axial bore 31 in the latter. The coupling sleeve 
30 is journalled on the driven clutch half 13 so as to be able to rotate 
freely relative thereto. The coupling sleeve 30 further comprises a recess 
32 in which is received the forward end 33 of the friction spring 15. 
According to the above described arrangement, the auxiliary spring 20 is 
connected in parallel relationship to the friction spring 15 and acts 
between the ends 17 and 33 of the latter. This means that a torsion load 
is appliable on the friction spring 15 in order to increase or decrease 
the friction grip of the latter. 
The auxiliary spring 20 can be arranged either to act in the winding 
direction of the friction spring 15, thereby increasing the pre-tensioning 
and the friction grip of the latter, or to act in the unwinding direction 
of the friction spring 15, thereby neutralizing to some extent the 
pre-tensioning and the friction grip of the latter. The direction of 
action as well as the pre-tensioning magnitude of the auxiliary spring 20 
can be set by rotating the setting ring 25 by turning the screw 26. 
The slip clutch 12 is covered by a protection tube 34 which is supported on 
the outer periphery of the setting ring 25 and the sleeve 30. As the slip 
torque level of this type of clutch is practically independent of the 
friction coefficient, the friction spring 15 may very well be lubricated 
with grease to avoid a too hard wear. The protection tube 34 prevents 
grease from being spread in the nut runner housing 10. 
The nut runner shown in the drawing figures also comprises a pressure air 
supply valve 36 and an automatic shut off device. The shut off device 
comprises a release mechanism 37 and a shut off valve 38 operated by the 
release mechanism 37. The release mechanism comprises an axially extending 
bore 40 in the driving clutch half 11 in which is movably guided a cup 41. 
The latter is open toward the driven clutch half 13 and has an external, 
longitudinal groove 42 for cooperation with a key pin 43 secured in the 
driving clutch half 11, thereby preventing the cup 41 from rotating 
relative to the latter. 
The cup 41 is biased rearwardly by a spring 44 acting between the forward 
end of the cup 41 and the rear end of the driven clutch half 13. A 
maneuver rod 46 connects the cup 41 with the shut off valve 38 which in 
turn is biased forwardly by a spring 47. Spring 47 is in the shown 
embodiment weaker than spring 44 but is supported by the air pressure to 
accomplish a closing force exceeding the load of spring 44. 
The release mechanism 37 further comprises a release rod 48 the rear end of 
which is received in the cup 41, whereas the forward end thereof is 
arranged to cooperate with the rear end of the driven clutch half 13. The 
release rod 48 is pivotably mounted on a transverse pin 50 in the cup 41, 
and a spring 49 is also supported on the transverse pin 50 so as to act 
between the release rod 48 and the inner wall of the cup 41. The release 
pin 48 is thereby biased toward one side of the cup 41 and the bore 40. 
The driven clutch half 13 is in its rear end provided with a concentric 
bore 51 the diameter of which is slightly larger than the diameter of the 
forward end of release rod 48. In its rear end the driven clutch half 13 
is also provided with circular recesses 52 and 53 of which recess 52 is 
coaxial with bore 51 and the driven clutch half 13 while recess 53 is 
excentrically located. Recess 53 is of such a diameter and is so located 
as to constitute a circular tangent to recess 52 as well as to bore 51. 
See FIG. 3. 
During tightening of a screw joint supply valve 36 as well as shut off 
valve 38 are open. The forward directed load upon the maneuver rod 46 from 
spring 47 and the motive air pressure exceeds backward directed force 
exerted by spring 44, which means that cup 41 and release rod 48 are urged 
forwardly. Due to the action of spring 49 the forward end of release rod 
48 is brought into a lateral position in recess 52 and is prevented from 
moving forwards in that it abuts against the bottom of recess 52 or recess 
53. 
When reaching the slip torque level of the slip clutch 12 a relative 
rotation takes place between driving clutch half 11 and driven clutch half 
13. Release rod 48 is then rotated relative to recesses 52 and 53 in that 
the cup 41 is locked as regards relative rotation to the driving clutch 
half 11. At first, the forward end of release pin 48 will follow the inner 
contour of the concentric recess 52, and, when reaching the tangent point 
between recess 52 and excentric recess 53 the release rod 48 is moved 
forwards to abut against the bottom of recess 53. Now, rod 48 will follow 
the inner contour of recess 53 until it reaches the tangent point between 
recess 53 and the bore 51. At this moment the forward end of release rod 
48 falls down into bore 51, and the cup 41, the maneuver rod 46 and shut 
off valve 38 are displaced forwards. The shut off valve 38 is closed. This 
position is illustrated in FIG. 2. 
The release mechanism is re-set in that the supply valve 36 is closed. The 
spring 47 then looses its support from the pressure air and is not able to 
withstand the load of spring 44 and maintain valve 38 in closed position. 
The cup 41, release rod 48, maneuver rod 46 and shut off valve 38 is then 
reclosed, and the release rod 48 is pivoted into a tilted position by 
means of spring 49. 
The characteristic features of the release mechanism 37 as regards 
operation are specifically related to the characteristic of the above 
described slip clutch 12. The latter is characterized in that, after a 
completed tightening operation, including slippage at the desired maximum 
torque level, it stops in any position and does not tend to seek for any 
specific reengagement position defined by a certain angular relationship 
between the driving and driven clutch halves. This means that the release 
mechanism of the automatic shut off device has to work properly whichever 
the angular relationship between the clutch halves is. The release 
mechanism described above and shown in the figures releases within a 
relative rotation between the clutch halves of 11/2 revolution from the 
start of the overload slippage, no matter what the relative start position 
might be. 
The embodiments of the invention are not limited to the shown and described 
example but can be freely varied within the scope of the invention as it 
is defined in the claims.