U.S. patent number 3,703,933 [Application Number 05/133,647] was granted by the patent office on 1972-11-28 for impact wrench with torque control means.
This patent grant is currently assigned to Atlas Copco Aktiebolag. Invention is credited to Knut Christian Schoeps.
United States Patent |
3,703,933 |
Schoeps |
November 28, 1972 |
IMPACT WRENCH WITH TORQUE CONTROL MEANS
Abstract
In an impact wrench provided with torque control means, a
cut-off for the wrench drive motor is activated at attainment in an
adding mechanism of a predetermined sum total of the lengths of
displacement of a body which in response to rotational resistance
at each impact is displaced against the action of a return
force.
Inventors: |
Schoeps; Knut Christian (Nacka,
SW) |
Assignee: |
Atlas Copco Aktiebolag (Nacka,
SW)
|
Family
ID: |
20267131 |
Appl.
No.: |
05/133,647 |
Filed: |
April 13, 1971 |
Foreign Application Priority Data
Current U.S.
Class: |
173/178;
173/93.5 |
Current CPC
Class: |
B25B
23/1453 (20130101) |
Current International
Class: |
B25B
23/14 (20060101); B25B 23/145 (20060101); B25b
021/02 () |
Field of
Search: |
;173/12,93,93.5
;81/52.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Leppink; James A.
Claims
What I claim is:
1. An impact wrench with torque control means comprising a housing,
a drive motor in said housing, cut-off means for said motor in said
housing, a drive shaft in said motor, an anvil rotatably journalled
in said housing and adapted to be connected to a workpiece, a
rotary impact motor in said housing operatively interconnected
between said drive shaft and said anvil for applying a succession
of rotational impacts against said anvil and thereby to said
workpiece, a body in said housing operatively associated with said
drive shaft for being displaced at each impact relative thereto in
response to rotational resistance of said anvil, means for
producing a return force active against said body to cancel the
displacements thereof, an adding mechanism in said housing for
adding the lengths of displacement of said body, and means in said
housing associated with said adding mechanism for activating said
cut-off means at attainment in said adding mechanism of a
predetermined sum total of said lengths of displacement.
2. An impact wrench according to claim 1 in which said body is an
inertial body axially displaceably mounted on said drive shaft,
axial cam means between said drive shaft and said body for rotating
the latter conjointly with said drive shaft and for displacing said
body at retardation of said shaft by way of inertia axially of said
shaft, said adding mechanism including an adding shaft, a driving
member between said body and said adding shaft, and means for
transforming the axial displacements of said body and driving
member into uni-directional turning movement of said adding
shaft.
3. An impact wrench according to claim 2 in which said transforming
means include a pair of free-wheel-mechanisms, one between said
driving member and said adding shaft and the other between said
adding shaft and said housing.
4. An impact wrench according to claim 2 in which said activating
means comprises a setting drum rotatably mounted in said housing, a
base portion on said setting drum, means for adjusting and affixing
said base portion angularly with respect to said housing, a drum
portion on said setting drum connectable to said adding shaft for
being turned thereby relative to said base portion, spring means
interposed between said base and drum portions for counteracting
such turning movement of said drum portion, and a member on said
drum portion for activating said cut-off means upon appropriate
turning movement of said drum portion.
5. An impact wrench according to claim 4 in which a clutch is
provided for connecting said drum portion to said adding shaft, and
means for disengaging said clutch at activation of said cut-off
means to permit resetting of said drum portion relative to said
base portion under the action of said spring means.
6. An impact wrench according to claim 5 in which there are
provided manually actuatable starting means in said housing for
said motor, and means in said housing for engaging said clutch in
response to actuation of said starting means.
7. An impact wrench according to claim 4 in which said motor is
actuated pneumatically, a passage in said housing for supplying
compressed air to said motor, said cut-off means being a normally
open cut-off valve in said passage, means for biasing said valve to
the cut-off portion thereof, a locking arm pivotally mounted in
said housing and cooperating with said cut-off valve to releasably
arrest said cut-off valve in the open position thereof, and said
member on said drum portion cooperating with said locking arm for
releasing movement of said cut-off valve to the cut-off position
thereof.
8. An impact wrench according to claim 6 in which said motor is
actuated pneumatically, a passage in said housing for supplying
compressed air to said motor, a throttle valve in said passage
providing said starting means, and said clutch engaging means being
a pneumatically actuated servo piston means controlled by said
throttle valve and operatively connected to said clutch.
9. An impact wrench according to claim 2 in which said turning
movement of said adding shaft is arranged to be generated by said
return force.
Description
The invention relates to impact wrenches incorporating torque
control means for controlling the tightening of threaded fasteners,
for example screws and nuts, by means of such power driven tools.
More particularly the invention relates to impact wrenches with
torque control means of the type incorporating a drive motor, a
cut-off means for the motor, a drive shaft in the motor, and a body
operatively associated with the drive shaft which body in response
to rotational resistance at each impact is displaced against the
action of a return force. In such devices the body is subjected to
inertial forces or rebound forces when impacting occurs. These
forces increase with increasing rotational resistance and are
conventionally employed for controlling the torque by releasing the
motor cut-off when the individual successively increasing length of
displacement of the body finally reaches a predetermined selective
value. A difficulty in this connection is that the first impact
often tends to be stronger than the following producing an
excessively long first displacement which tends to activate the
motor cut-off too early before the desired final torque has been
reached in the fastener to be tightened. It is an object of the
invention to provide an impact wrench with torque control means of
the aforementioned type in which the risk for such too early a
release of the motor cut-off is eliminated.
For the above and other purposes there is according to the
invention provided an impact wrench with torque control means
comprising a housing, a drive motor in said housing, cut-off means
for said motor in said housing, a drive shaft in said motor, an
anvil rotatably journalled in said housing and adapted to be
connected to a workpiece, a rotary impact motor in said housing
operatively interconnected between said drive shaft and said anvil
for applying a succession of rotational impacts against said anvil
and thereby to said workpiece, a body in said housing operatively
associated with said drive shaft for being displaced at each impact
relative thereto in response to rotational resistance of said
anvil, means for producing a return force active against said body
to cancel the displacements thereof, an adding mechanism in said
housing for adding the lengths of displacement of said body, and
means in said housing associated with said adding mechanism for
activating said cut-off means at attainment in said adding
mechanism of a predetermined sum total of said lengths of
displacement.
The above and other purposes of the invention will become obvious
from the following description and from the accompanying drawings
in which an embodiment of the invention is illustrated by way of
example. It should be understood that this embodiment is only
illustrative of the invention and that various modifications
thereof may be made within the scope of the claims following
hereinafter.
In the drawings FIG. 1 shows a fragmentary side view drawn partly
in section of a wrench embodying the invention. FIG. 2 is a cross
section on the line 2--2 in FIG. 1. FIG. 3 is a cross section on
the line 3--3 in FIG. 1 FIG. 4 is a fragmentary section on the line
4--4 in FIG. 3. FIG. 5 shows a fragmentary section on the line 5--5
in FIG. 3 and illustrates by broken lines an operating position of
the elements covered by the section. FIGS. 6 and 7 correspond to
FIGS. 4 and 5 but show an alternative position of the elements
involved. FIG. 8 is a section on line 8--8 in FIG. 3. FIG. 9 is a
rear end view drawn partly in section and seen on the line 9--9 in
FIG. 1. FIG. 10 is a section on the line 10--10 in FIG. 1. FIG. 11
is a section on the line 11--11 in FIG. 1. FIG. 12 shows an
enlarged partial view of FIG. 8. FIG. 13 is a section on the line
13--13 in FIG. 10.
rotor
As an example for the description has been chosen an application of
the invention to a pneumatically driven impact wrench but the
invention may also be applied with advantage in connection with
electrically or hydraulically driven impact wrenches. The pneumatic
impact wrench in FIG. 1 includes a housing 20 in which is
journalled the rotor 21 of a motor preferably made as a vane motor.
Within a front piece 22 the rotor 21 drives a conventional rotary
impact motor, not shown, the anvil 23 of which projects from the
front portion with a square end 24 intended for taking up a socket
wrench. The socket wrench, not shown, is brought into engagement
with a workpiece such as a nut to be tightened and the motor
housing 20 is directed and held by way of a handle 25.
The motor housing 20 carries a backhead 26 having a cover 27, these
parts enclosing the torque control means. The main parts of the
latter are formed by an inertial or flywheel body 28, FIGS. 1,2,5,
and 7, an adding shaft 29, FIGS. 3-8, a clutch shaft 30, FIGS. 8
and 12, a setting drum 31, 65. FIGS. 10, 11, and a motor cut-off
means 32, FIG. 13.
The inertial or flywheel body 28 encloses in cap-like manner the
rear end of the rotor 21 which is provided with cam means in the
form of oblique grooves 34 into which are inserted cam balls 35.
The outer halves of the cam balls 35 project into internal oblique
grooves in the inner portion of the inertial body 28 radially
around the rear end of the rotor 21. A piston 37 is axially
slidably supported in the backhead 26 and abuts under the load of a
helical spring 38 in axial direction against the outer side of the
inertial body 28, producing a return force active to but the
inertial body 28 against the end face of the rotor 21 whereby the
cam balls 35 are caused to take inner positions in the respective
oblique grooves 34, 36, FIG. 7. Normally the inertial body rotates
conjointly with the rotor 21 occupying the position illustrated in
FIG. 7. However, as soon as the impact motor disposed within the
front piece 22 delivers an impact against the anvil 23, the rotor
21 is momentarily retarded by the rotational resistance while the
inertial body 28 in response to such resistance persists in its
rotational movement and forces the cam balls 35 to roll outwardly
in the oblique grooves 34 and 36, respectively, to the position
illustrated in FIG. 5. As a result thereof the inertial body 28 is
displaced axially relative to the rotor 21 a distance increasing
with the increased rotational resistance at impact and under
compression of the helical spring 38 of the piston 37 and axial
retraction of the latter. During the acceleration phase of the
impact motor prior to the next impact thereof, the piston 37 is
returned by the spring 38 towards the rotor 21 and the inertial
body 28 and the cam balls 35 are simultaneously returned to the
position in FIG. 7.
The adding shaft 29 is journalled in the backhead 26 on suitable
ball bearings in a plane perpendicular to the rotational axis of
the rotor 21. The adding shaft 29 is associated with means for
transforming the axial movements of the inertial body 28 to
unidirectional angular movement of the adding shaft 29, which means
are provided by a pair of free-wheel-mechanisms 39,40 each
comprising rollers or needle bodies 41 which at rotation in one
direction are pressed by an outer ring 42 provided with cam
surfaces into non-rotary engagement with the adding shaft and at
rotation in the opposite direction through the intermediary of a
needle holder provided with resilient elements allow free rotation
of the outer ring 42 relative to the adding shaft 29. The outer
ring 42 of the free-wheel-mechanism 39 is carried non-rotatably by
a ring shaped hub or driving member 43 which by means of a tooth 44
is in engagement with a ring groove 45 on the piston 37. The other
free-wheel-mechanism 40 is received at the outer ring 42 thereof
non-rotatably in a ring shaped hub 46 which by a locking plug 47 is
non-rotatably locked in the backhead 26. The locking direction of
the two free-wheel-mechanisms 39, 40 is chosen such, FIGS. 4,5 and
6,7, respectively, that during movement of the inertial body 28
axially away from the rotor 21, FIG. 5, the ring hub 43 will rotate
freely in counter-clockwise direction with respect to the adding
shaft which by the free-wheel-mechanism 40 is locked against
rotation in counter-clockwise direction. At return of the inertial
body 28 under the action of the return force of spring 38 and the
piston 37, the groove 45 entrains the tooth 44 and the ring hub 43
in clockwise direction. The free-wheel-mechanism 39 now locks
against the adding shaft 29 and entrains the latter in its
movement, FIG. 7, simultaneously with the free-wheel-mechanism 40
allowing such movement by free-wheeling relative to the adding
shaft 29. As a result of this function the adding shaft 29 at each
return movement of the piston 37 will be turned uni-directionally
an angle increasing step by step.
The adding shaft 29 is by means of a bevel gear 48 in engagement
with a bevel gear 49 on a clutch shaft 30 which is supported on
suitable ball bearings in the backhead 26 and the cover 27 thereof.
On the clutch shaft 30 is freely rotatably journalled a gear 50 the
hub of which is formed as one half 51 of a conical friction clutch.
The cooperating other half 52 is carried slidably in axial
direction on the clutch shaft 30 and is non-rotatably fixed thereto
by a cross pin 53 traversing the clutch half 52 and the shaft 30,
and being slidable axially in an axial groove 54 formed in the
clutch shaft 30. Furthermore the clutch shaft is made hollow and
carries a helical spring 55 bearing against the cross pin 53 and
the cover 27 and striving to move the cross pin 53 and thus the
clutch half 52 to such a position in the groove 54 as to release
the clutch half 52 from the clutch half 51 of the gear 50. In the
clutch shaft 30 is furthermore slidably supported an axial pin 56
for actuating the cross pin 53 which axial pin for purposes of
engaging the clutch halves 52, 51 is actuatable by actuating means
in response to actuation of the main control means of the impact
wrench for the drive motor thereof. In electrically driven wrenches
such actuation will be attained by application of a suitable
solenoid. In pressure fluid actuated wrenches such as in the
present example a servo piston motor including a servo piston 57
affixed to the axial pin 56 is applied , the servo piston 57
striving under the force bias of annular springs 58 to move the
axial pin 56 to inactivated position in which the cross pin 53 is
unaffected. When pressure fluid is supplied via a passage 59 to the
cylinder 60 of the servo piston 57, the clutch halves 52, 51 are
caused to engage by the axial pin 56 applying a thrust against the
cross pin 53. The passage 59 is pressurized or can be exhausted,
respectively, by means of the reversing valve 61 of the wrench ,
diagrammatically illustrated in FIGS. 1,9, in the two alternative
positions of said valve 61, the reversing valve 61 being arranged
in usual manner downstream of the throttle valve 62. The gear 50
driven via the clutch halves 52, 51 by the coupling shaft 30 is in
engagement with a peripheral gear rim 63 on the setting drum 31,
FIG. 10.
The setting drum 31, 65 includes a drum portion 31 which is
rotatably journalled on a base portion 65, FIG. 1, in its turn
rotatably supported in a bore in the cover 27 coaxially with the
piston 37. A bore 66 in the base portion 65 facing the piston 37
receives the helical spring 38 of the piston 37. In an annular
cavity between the base portion 65 and the drum portion 31 a
clockwork spring 67 is tensioned between a groove 68 in the base
portion 65 and a pin 69 in the drum portion 31, FIG. 10. The
clockwork spring 67 is pre-stressed striving to but a pin 70 on the
drum portion 31 against a tooth 64, FIG. 10, arranged on the base
portion 65 on the rim of a flange thereon. The base portion 65 is
adjustably affixed to the cover 27 in a manner to prevent rotation
between these parts . To this end a cogwheel-shaped locking plate
71 is axially slidably but non-rotatably mounted in the base
portion 65 on a cross pin 72 engaging an axial groove 73 in the
locking plate 71 and is depressable against the action of helical
springs 74 which are inserted between the base portion 65 and the
interior of the locking plate 71 to urge the latter outwardly into
locking position, FIG. 1. In the locking position the locking plate
71 mates with a toothed ring 75 which by means of screws is affixed
to the cover 27, FIG. 9. When the locking plate is depressed
axially towards the base portion 65, it will be released from the
toothed ring 75 so that the locking plate 71 by a suitable tool
insertable into axial bores 76 in the plate 71 may be turned
together with the base portion 65 and the drum portion 31 to the
desired angular position in the cover 27, whereupon the plate 71 is
permitted to spring out into locking engagement with the toothed
ring 75, the base portion 65 thus becoming locked in the desired
angular position. The drum portion 31 carries an abutment embodied
by a release pin 77 for activating the motor cut-off means 32.
In the exemplary wrench intended to be driven by compressed air,
the motor cut-off 32 is formed by a cut-off valve provided with a
closing head which is slidable in a bore 80 in the backhead 26
through the intermediary of a base shaped as a piston 79 of equal
size with the head 32. A helical spring 81 is inserted between the
cover 27 and the piston 79 and strives to move the cut-off 32 in a
direction away from the cover 27 to but against the bottom 82 of
the bore 80 in which position both faces of the closing head of the
cut-off 32 are pressurized. A bell crank lever 84 is pivotally
journalled on a pivot 83 adjacent the piston 79 between the cover
27 and the backhead 26 and is actuated by a turning spring 85 to
latch in the bottom butting position of the cut-off 32 under the
action of the turning spring 85 behind an annular shoulder 86 on
the piston 79, thus locking the cut-off 32 in inactivated position
between the lever 84 and the shoulder 82, FIG. 13. The bore 80 is
supplied with pressure fluid from the reversing valve 61 via a
passage 87 and the pressure fluid flows from the bore 80 past the
cut-off 32 via a passage 88 to the motor inlet 89 in the motor
housing 20, FIG. 1. By pressure in the bore 80 acting against the
piston 79, the cut-off 32 is biased in the direction of the cover
27. The release pin 77 of the setting drum 31 cooperates with the
lever 84 and is capable of applying a thrust against the arm 90
thereof remote from the shoulder 86 whereby the lever 84 is turned
against the action of the turning spring 85 away from the ring
shoulder 86. At such instant the pressure in the bore 80 will
displace the piston 79 towards the cover 27 so that the head of the
cut-off 32 engages the central part of the bore 80 thus closing off
the supply of pressure fluid from the passage 87 to the passage 88
whereby the drive motor of the wrench is stopped.
In electrically driven wrenches the cut-off preferably will be
embodied by a conventional solenoid-actuated switch for the main
current with the solenoid striving to displace the switch member
past the lever 84 when the latter is released by the release pin 77
acting against the arm 90.
By axial depression and turning of the locking plate 71 the base
portion 65 of the setting drum 31, 65 is first adjusted to the
desired angular starting position in the backhead 26. This means
that one selects by way of adjustment of the base portion 65 the
desired angular starting position of the release pin 77, FIG. 11,
and of the tooth 64 of the base portion 65, against which the pin
70 is butted by the clockwork spring 67 in the starting position.
Thereupon the locking plate 21 is allowed to spring out into
locking engagement with the toothed ring 75 so that the position of
the base portion 65 is fixed. The wrench is connected to a suitable
pressure fluid supply, for example to a source of compressed air.
Upon the socket wrench having been placed on a nut to be tightened,
the throttle valve 62 of the handle 25 is depressed so that the
reversing valve 61, set to cause clockwise rotation of the motor 21
when the tool is viewed from the rear in FIG. 1, is pressurized as
is the case with the passages 87,59.
From the passage 59 the pressure fluid enters the cylinder 60
actuating the servo piston 57 to bring the clutch halves 52, 51 of
the clutch shaft 30 into frictional engagement. The pressure fluid
passes through the passage 87 and the bore 80 past the motor
cut-off 32 and thence to the passage 88 and to the motor inlet 89
to rotate the rotor 21 in clockwise direction. The screw rotates
until it has been driven down against the workpiece whereupon the
anvil 23 stops and the rotary impact motor starts impacting. Prior
to each impact the inertial or flywheel body 28 is in the state of
rapid rotation and when the anvil 29 at impact causes the rotor 21
to stop, the inertial body 28 will continue its rotation
performing, by reason of the oblique grooves 34, 36 and the cam
balls 35, an axial rearwardly directed stroke for each impact
delivered. Thus the piston 37 for each impact delivered is firstly
displaced freely rearwardly, FIG. 5, and thereafter returned in
forward direction under the bias of the spring 38 entraining the
adding shaft 29. The uni-directional angular movements of the
adding shaft 29 are transmitted directly to the clutch shaft 30 and
via the clutch halves 52, 51 to the gear 50. As a result of each
reciprocation of the inertial body 28 the adding shaft 29 sums up
the length of displacement by uni-directional rotation and turning
of the gear 50, the rotation of the latter being transmitted via
the gear rim 63 to the drum portion 31. The turning motion forces
the pin 70 of the setting drum 31 to leave the tooth 64 and as the
increment lengths of the displacements generate turning movement of
the adding shaft 29 and the setting drum 31, the pin 77 will be
successively displaced towards the arm 90. After a sufficient
number of impacts the release pin 77 hits the arm 90 , the lever 84
is unlatched and the motor cut-off is released so that it can fall
into the middle portion of the bore 80 thus closing the air supply
to the motor inlet 89. Upon cut-off the operator has to release the
throttle valve 62, the latter being preferably made such as to
exhaust in the released position thereof the passages 87 and 59 and
the reversing valve 61 via the throttle valve 62. When the pressure
is relieved in the passage 87, the closing bias acting against the
piston 79 disappears and the spring 81 of the cut-off 32 is thus in
the position to return the cut-off to open position supported
against the bottom of the hole 82. Relief of the passage 59
relieves the servo piston 57 and the annular springs 58 thereof
displace the axial pin 56 away from the cross pin 53. This permits
the helical spring 55 to move the cross pin 53 and the clutch half
52 away from the clutch half 51, the gear 50 thus becoming released
for free rotation on the clutch shaft 30. This allows the tensioned
clockwork spring 67 to return the setting drum back to the starting
position, the pin 70 thus being returned against the tooth 64 and
the release pin 77 to its starting position.
When a series of screws are to be tightened under similar
conditions, substantially the same tightening torque will be
reached in the screws provided they have received the same number
of impacts from the wrench up to cut-off of the latter, such
condition in the above described device meaning that the angular
distance between the starting position of the release pin 77 and
the arm 90 during each tightening operation must remain unchanged.
During pressure variations in the pressure fluid line a variable
number of impacts will be generated up to cut-off. Within pressure
variation limits occuring in practice, however, the final torque
will tend to be constant since a lower pressure gives an increased
number of somewhat smaller angular increments to be totaled while a
higher pressure gives fewer but somewhat larger angular increments.
If it is desired to change the final torque in the screw, another
angular starting position will be chosen for the release pin 77 by
adjustment of the locking plate 71 to a different angular position
relative to the toothed ring 75. For more easy adjustment the
toothed ring 75 is provided with suitable marking with
numerals.
When the wrench is set for reverse rotation, the passage 59 is
exhausted directly via the reversing valve 61 so that the clutch
halves 52, 51 do not engage. Simultaneously, during impacting in
counter-clockwise direction the inertial body 28 is locked by the
cam balls 35 against continued rotation at the moment of impact and
thus the inertial body 28 will not perform any axial displacements
and leaves the adding shaft 29 unaffected.
As obvious from the foregoing, the first impact in the exemplary
embodiment only represents a fraction of the total turning movement
of the adding shaft up to activation of the cut-off, and an
excessively long first displacement of the inertial or flywheel
body, therefore, will be unable to have any adverse effects on the
resulting final torque.
* * * * *