GB2240632A

GB2240632A - Torque impulse unit

Info

Publication number: GB2240632A
Application number: GB9002565A
Authority: GB
Inventors: Christopher John Dudden
Original assignee: Desoutter Ltd
Current assignee: Air Compressors and Tools Ltd
Priority date: 1990-02-06
Filing date: 1990-02-06
Publication date: 1991-08-07
Anticipated expiration: 2010-02-06
Also published as: GB9002565D0; GB2240632B

Abstract

An inertial mass 6 carried by an input member 2 of a hydraulic impulse clutch 1 is subjected to an accelerating force in the frame of reference of the input member 2 during transmission of a torque impulse to an output member 3. When a bit coupled to output shaft 23 is located on a nut or screw to be tightened a spring 24 is compressed and a push rod 19 which is engaged with the abutment surface 21 of a latch plate 17 causes the motor to start. The clutch 1 is rotated in the direction of arrow a and the screw or nut is tightened until the resistance to tightening causes output shaft 23 to slow down or stop, whereupon input member 2 is disconnected from output member 3 of shaft and the input member 2 accelerates. After one revolution member 2 abruptly reconnects to member 3 and applies a torque impulse to output shaft 23. Repeated impulses are applied until the deceleration of member 2 is such that the acceleration force applied to inertial mass 6 is sufficient to cause its arm 6b to push a ball 13 back against adjustable spring 12 and move latch plate 17 against spring 16 so that the abutment surface 21 is released from the push rod 19. The push rod moves through an aperture 27 in latch plate 17 and causes the motor to stop at the required torque value. <IMAGE>

Description

TORQUE IMPULSE UNIT This invention relates to a torque impulse unit, e.g.

for a power tool, such as a screwdriver or a nut runner, driven by an air motor or other motive source.

Conventional torque impulse units comprise an input member which is to be driven in rotation about an axis, an output member rotatable about the said axis relative to the input member, and means for transmitting torque impulses from the input member to the output member. The torque impulse transmitting means may be mechanical or hydraulic.

The present invention provides a unit including an inertial mass which is carried by the input member and which is subjected to an accelerating force in the frame of reference of the input member during transmission of a torque impulse, and means for producing a signal in response to the said force.

The signal produced may be an all-or-nothing signal indicating whether or not a given (fixed or variable) maximum torque has been reached, or it may be a signal which varies (continuously or step-wise) as a function of the said force.

The signal may be electrical, electromagnetic, pneumatic, hydraulic, or mechanical, or it may be used to monitor the torque output of the unit or to control the driving of the input member.

Preferred and optional features are set forth in claims 2 et seq.

The signal producing means may comprise a spring acting in opposition to the said accelerating force, or a pressure sensor (e.g. a load cell or a piezo-electric element). The inertial mass may be pivotably or slidably mounted on the input member.

The invention also provides a power tool including a torque impulse unit as described above and drive means for rotating the input member, the drive means being controlled by the said signal.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a part-sectional side view of a torque impulse unit on a power tool when running; Figure 2 is a section on line II-II in Figure 1; Figure 3 is a similar view to Figure 1, when the required torque is reached; Figure 4 is a section in line IV-IV in Figure 3; Figure 5 is a part-sectional side view of another embodiment of torque impulse unit as a power tool; Figue 6 schematically shows the relationship of various parts of the unit of Figure 5; Figure 7 schematically shows part of the unit of Figure 5; and Figures 8 and 9 schematically illustrate how a slot is made in part of the unit of Figure 5.

The torque impulse unit illustrated in Figures 1 to 4 comprises a hydraulic impulse clutch 1 (well-known in itself) having an input member 2 and an output member 3 rotatable about a common axis 4. The input member 2 carries a generally L-shaped inertial mass 6 movably mounted in a similarly shaped recess 7. One arm 6a of the mass 6 is pivoted on a pin 8 and its free end 9 is adapted to abut against the face 11 of the recess 7 to define a rest position of the mass 6 relative to the input member 2. The mass 6 is urged into the rest position by a spring 12 pushing a ball 13 against the other arm 6b of the mass.

The spring force acting on the ball 13 is adjustable by a screw 14.

Urged into contact with the arm 6b of the mass 6 (with a lower contact force than the ball 13) by a spring 16 is a latch plate 17 having a recess 18 receiving the arm 6b.

A push rod 19 for controlling the on/off device of an air motor (not shown) of the power tool is urged against an abutment surface 21 on the latch plate 17 by a spring or other urging means (not shown). The input member 2 has an input shaft 22 which is rotated by the motor via a gearbox (not shown). An output shaft 23 in the output member 3 is coupled to a bit holder (not shown), the bit being a screwdriver or a nut runner socket.

The impulse clutch 1 is urged to a forward datum position by a spring 24 acting between an abutment surface 26 on the input member 2 and an abutment surface (not shown) of a part rotated by the gearbox output of the power tool.

The power tool is operated as follows: The bit is located on a screw or nut to be tightened and the tool is pushed forwards (to the right in Figure 1).

Since the axial positions of the clutch 1 is fixed at this time, the spring 24 is compressed and the push rod 19 (which is held up by the abutment surface 21 of the latch plate 17) operates the on/off device of the forwardly moving motor so as to start the motor.

The motor then rotates the hydraulic clutch 1 in the direction of arrow a (Figure 2). The output shaft 23 consequently rotates to tighten the screw or nut until sufficient resistance to tightening occurs to cause the output shaft 23 to slow down or stop, whereupon the clutch 1 disconnects the output member 3 from the input member 2. The input member 2 is thereupon accelerated by the motor and, after one revolution, is abruptly re-connected to the output member 3 so that its kinetic energy is transmitted to the output shaft 23 as a torque impulse while the input member 2 decelerates to near zero speed, whereupon the clutch 1 again disconnects and the cycle is repeated.

As the screw or nut is tightened the rate of deceleration of the input member 2 increases. Thus, in the frame of reference of the input member 2, the mass 6 is subjected to an accelerating force which increases as the tightness of the screw or nut increases. The kinetic energy of the mass 6 is imparted to the input member 2 via the ball 13 and spring 12.

When the accelerating force on the mass 6 in the frame of reference of the input member 2 reaches a predetermined value (set by adjustment of the spring force by the screw 14) the arm 6b of the mass 6 will push the ball 13 back against the spring 12, at the same time pushing the latch plate 17 back against the spring 16, thereby releasing the abutment surface 21 from the end of the push rod 19. The push rod 19 (constantly urged forwards, as described above) moves forwards to the position shown in Figure 3 through an aperture 27 in the latch plate 17, thereby transmitting to the on/off device a mechanical signal which stops the motor.

When the power tool is moved backwards to withdraw the bit from the screw or nut which has been tightened, the impulse clutch 1 is returned to its datum position by the spring 24 while the rod 19 is pulled back through the aperture 27 in the latch plate 17, which is thereupon reset to its latching position (Figures 1 and 2) by the spring 16.

During undoing of a screw or nut, when the clutch rotates in the reverse direction to arrow a, the mass 6 is prevented from moving by the abutment of its end 9 against the surface 11 of the recess 7 in the input member 2.

Figures 5 to 9 illustrate an alternative embodiment in which parts similar to those shown in Figures 1 to 4 are given the same reference numerals. In this embodiment the input member 2 carries a coaxial annular inertial mass 56 which acts on the latch plate 17 via a latch ball 55 which is captive in the latch plate and which is received by a groove 58 in the inside of the annular mass 56 when the mass is in its rest position (as illustrated).

The annular mass 56 is urged towards the output end of the hydraulic impulse clutch 1 by a compression spring 62 abutting against an adjustment ring 64 screwed onto the input member 2. Three balls 63 are arranged between the mass 56 and the input member 2 and are received in slanting slots 65 in the mass 56 and member 2.

Means (not shown) are provided for restricting the rotation of the mass 56 so that the balls 63 cannot leave the slots 65. The way in which a slot 65 is drilled by a drill bit 66 is shown in Figure 8.

The power tool with the clutch in the embodiment of Figures 5 to 9 is started by applying the bit (on the output shaft 23) to the screw or nut to be thightened, in the same way as described with reference to Figures 1 to 4. As the screw or nut is tightened, the annular mass 56 is subjected to an accelerating force (in the frame of reference of the input member 2) which increases as the tightness of the screw or nut increases. The kinetic energy of the mass 56 is imparted to the input member 2 via the balls 63. When the accelerating force in the mass 56 in the frame of reference of the input member 2 reaches a predetermined value (set by adjustment of the force of the spring 62 by the screw ring 64) the balls 63 ride up the slanting slots 65 and the annular mass 56 turns so that the latch ball 55 leaves the groove 58 in the mass and is forced radially inwards, pushing the latch plate 17 back against the spring 16, thereby releasing the push rod 19 which transmits to the on/off device a mechanical signal stopping the motor.

In the two embodiments described above, the moment of inertia of the inertial mass 6 or 56 is small in relation to that of the input member 2. However, the moment of inertia of the inertial mass could be made greater than that of the input member, which would be of advantage if the screw or nut tightened abruptly.

Claims

Claims.

1. A torque impulse unit comprising an input member which is to be driven in rotation about an axis, an output member rotatable about the said axis relative to the input member, means for transmitting torque impulses from the input member to the output member, an inertial mass which is carried by the input member and which is subjected to an accelerating force in the frame of reference of the input member during transmission of a torque impulse, and means for producing a signal in response to the said force.

2. A unit as claimed in claim 1, including means for maintaining the mass is a rest position relative to the input member against the action of the said force, the maintaining means allowing the mass to move away from the rest position when the said force exceeds a given value.

3. A unit as claimed in claim 2, in which the said given value is variable.

4. A unit as claimed in claim 2 or 3, in which the maintaining means comprises a spring.

5. A unit as claimed in any of claims 2 to 4, in which the signal producing means comprises an element which is movably mounted on the input member and which is kinematically connected to the mass so as to be moved when the mass moves away from its rest position.

6. A unit as claimed in claim 5, in which the said element is a latch member which is movable against the action of urging means tending to restore it to a latching position.

7. A unit as claimed in claim 6, including a push rod which is to be urged into abutment with the latch member in the latching position, the abutment being released when the latch member moves away from the latching position to a sufficient extent.

8. A unit as claimed in any preceding claim, in which the mass is pivoted on the input member.

9. A torque impulse unit substantially as described with reference to, and as shown, in Figures 1 to 4 or Figures 5 to 9 of the accompanying drawings.

10. A power tool including a torque impulse unit according to any preceding claim and drive means for rotating the input member, the drive means being controlled by the said signal.

11. A power tool as claimed in claim 10, in which the said signal stops the rotation of the input member by the drive means when the said accelerating force reaches a given value.