US 3710873 A
A pneumatically operated hand-held impact wrench or screwdriver having a hammer member which reciprocates against the action of a spring, said spring being adjustable to vary the value of maximum torque at which the tool operates.
Description (OCR text may contain errors)
O Umted States Patent 1 [111 3,710,873 Allen [451 Jan. 16, 1973 I  IMPACT WRENCH OR SCREWDRIVER  References Cited  Inventor: Michael George Allen, North Wat- UNITED STATES PATENTS ford, England 3,515,225 6/1970 States ..173/12  Assignee: Desoutter Brothers Limited, Lon- 3 313 390 5/19 7 n at don, England 2,814,277 11/1957 Jimerson ..173/l2  Flled: 1970 Primary ExaminerJames A. Leppink  Appl. No.2 95,772 Attorney-Maxon & Weiner  Foreign Application Priority Data  ABSTRACT A pneumatically operated hand-held impact wrench Dec. 8, 1969 Great Britain ..59,836/69 or Screwdriver having a hammer member which reciprocates against the action of a spring, said spring  US. Cl ..l73/l2, 173/93.6 being adjustable to vary the value of maximum torque  Int. Cl. at which the tool operates  ,Field of Search ..173/12,93,93.5,93.6
3 Claims, 1 Drawing Figure PATENTEUJAN 16 I975 INVENTOR MICHAEL GEORQE ALLEN L" W//Jn..',a
AI IOHNEY IMPACT WRENCH OR SCREWDRIVER The invention relates to impact wrenches or screwdrivers of the kind having a hammer member which is supported upon a driving shaft for reciprocating movement against the action of a compression spring to cause cyclic engagement and disengagement of hammers upon the hammer member with anvils associated with a driven shaft.
It is known to provide an arrangement associated with the hammer and anvil mechanism of an impact wrench or screwdriver whereby as the reciprocating movement of the hammer becomes of such amplitude as the torque developed by the tool reaches a predetermined maximum value it is utilized to operate a valve controlling the supply of air to a pneumatic motor driving the tool, to stop the latter, and thus prevent said predetermined maximum value of torque from being exceeded.
In a form of construction previously proposed to cause reciprocating movement of the hammer member there are provided ramped grooves between the hammer member and its supporting driving shaft, which contain balls, so that with relative rotational movement between the hammer member and the driving shaft the balls run up and down the grooves and the hammer member reciprocates.
The spring is usually a helical spring surrounding the driving shaft, and disposed within a recess in the hammer member, abutting the latter at one end and resting against an abutment on the driving shaft at the other end. The driving shaft rotates at a substantially constant speed, and immediately upon impact the hammer is decelerated with a resultant relative rotational movement between the latter and the driving shaft with consequent movement of the hammer member longitudinally of the shaft and compression of the spring. This movement is sufficient to allow disengagement of the hammers and anvils and for the hammer member to accelerate and overrun the anvils to become re-engaged to make further impact, and soon cyclically.
lt has also previously been proposed to associate rotationally resilient means either with the hammer member or the driven shaft, whereby to influence the degree of bounce of the hammers from the anvils at the instance of impact, and thus to influence the amount of relative rotational movement between the hammer member and the driving shaft and the consequent extent of reciprocating movement for a particular value of torque developed by the tool.
Some of the energy imparted by the hammers is absorbed in the rotationally resilient means, which energy is released immediately after impact with a consequent increase of bounce of the hammers from the anvils, followed by an increased longitudinal movement of the hammer member. As previously mentioned, this increased longitudinal movement is used to operate a valve controlling the supply of air to the motor of the tool.
It is known to provide a torsion bar type driven shaft as the rotationally resilient means associated with the anvils, and to provide detachable torsion bars of different resilient characteristics which can be substituted for one another to change the valve of maximum torque when the supply of air to the tool is interrupted.
The object of the present invention is to provide a pneumatically driven impact wrench or screwdriver, of the kind referred to, and in which the supply of air to the tool is interrupted at a predetermined and adjustable maximum value of torque, which is simpler to, but cheaper to manufacture that such tools heretofore proposed.
The invention consists in a pneumatically operated hand-held impact wrench or screwdriver comprising a hammer member which is supported upon adriving shaft for reciprocating movement against the action of a compression spring to cause cyclic engagement and disengagement of hammers upon the hammer member with anvils associated with the driven shaft, and in which, when the amplitude of reciprocating movement becomes increased, as the torque developed by the tool reaches a predetermined maximum value of torque, operates a valve which interrupts the supply of air to a motor driving the tool, to stop the latter, to prevent a predetermined maximum valve of torque being exceeded, characterized in that means are provided for varying the force exerted by the compression spring to vary the valve of torque at which the valve is operated.
The invention further consists in an impact wrench or screwdriver as set forth in the preceding paragraph in which the compression spring is a helical spring which surrounds the driving shaft and engages, either directly or indirectly, at one end the hammer member and at the other end a ring having an internal thread which cooperates with the corresponding thread upon the driving shaft.
The invention still further consists in an impact wrench or screwdriver as set forth in the preceding paragraph in which the ring has a bevel gear thereon which is engageable with a bevel gear on a key insertable from the exterior of the tool to rotate said ring to adjust the value of torque at which the valve is operated.
The accompanying drawing shows in longitudinal section, by way of example only, an impact wrench or screwdriver constructed in accordance with the invention and comprising a casing constructed in two parts, 1 and 2 within which are housed a vaned pneumatic motor 3, a planetary gear 4, a hammer and anvil mechanism 5, and a tool holder 6. v
The motor 3 comprises a rotor 7, a radial blade 8, which is one of a plurality of such blades, and a cylinder 9, which is formed as a sleeve housed in a recess in the part 1 of the casing and which is mounted eccentrically with respect to the center line of the rotor. Air leaves the cylinder by way of the exhaust ports 10 at the top thereof, and passing into the cavity 11 enters the bore 12 and thence passes to the annular space 13 around the gear 4 and leaves below the gear, and is discharged to the atmosphere by way ofthe silencer 14.
The rotor shaft 15 drives the driving shaft 16 of the hammer mechanism 5 by way of the planetary gear 4. Upon the shaft 16 there is mounted a hammer member 17 which is urged to the left as viewed in the figure by the helical spring 18, to cause engagement of the hammers 19 with the anvils 20 on the driven shaft 21.
Due to relative rotational movement between the shaft 16 and the hammer member 17, the balls 22 are caused to run along the sloping grooves in the surface of the shaft 16, in a known manner, and cause a longitudinal disengaging movement of the hammers from the anvils once each half revolution against the action of the spring 18. The greater the torque developed by the tool the greater the longitudinal movement of the hammer member 17 at each hammer blow.
This longitudinal movement is utilized to operate the valve 23 by means of a pin 23a being hit by the hammer member 17 when its longitudinal movement exceeds a predetermined value. The purpose and operation of this valve will be described later.
The driven shaft 21 has a tool holder 6 for receiving a variety of tools.
The rear part of the casing has a pistol-grip type handle 24 which houses a pair of double start and direction determining valves 25 and 26, operated alternatively by the rocker lever 27. The upper valve 25 is for counterclockwise rotation of the tool, and the valve 26 for clockwise rotation of the tool. The valves 25 and 26 are in two parts, forward valves 25a and 26a respectively, and rear valves 25b and 26b respectively, the rear valves for feeding the supply of air to appropriate inlet port of the motor for the direction of rotation required, while the forward valves are for connecting the inlet port not at that instant in use as such to the atmosphere to relieve pressure in front of the blades.
The valves 25 and 26 comprise sleeve 25c and26c, respectively, fitting in bores 25d and 26d, respectively. Annular grooves 25e and 26:: are formed in the bores and act to connect ports in the sleeves 25c and 26c with substantially vertical bores, one on each side of the valves, not shown, connecting with the clockwise and anti-clockwise inlet ports of the motor, respectively.
The inlet pressure air cavities 31 and 32 of the valves 25b and 26b are connected together and to the master control valve 33 by the passageway 34. The purpose and action of the valve 33 is described hereinafter. When, for example, valve 25 is operated, pressurized air enters the cavity 35 and passes to the annular grooves 25e and thus to the motor inlet port to give a counter-clockwise direction or rotation. Simultaneously, the inlet port of the motor for clockwise direction of rotation is connected to the atmosphere by the valve 25a, the air passing from the motor to the ports 36 to cavity 37, through the valve to cavity 38, passages 39 to the silencer 14 and thence to the atmosphere.
The operation of the valve 26 is similar in respect of valves 26a and 26b but gives the other direction of rotation.
The master control valve 33 comprises a plunger 40 having a valve head 41 at one end and a light helical spring 43 at the other, which initially holds open the valve. When air is supplied to the tool air passes down the annular space 47 and entering the spring chamber 44 balances the pressure on the head of the valve, and the valve remains open. When however the valve 23 is triggered and the spring chamber 44 is connected to the atmosphere the pressure drops and the valve closes, and will not open again to restart the motor until a finger is removed from the direction determining valve 26, and pressure allowed to build up in the spring chamber 44 by way of the leakage passages 45 and 46 and the valve is again opened. Thus, air passes to the passageway 34 by way of the annular space 47 and the valve 33, and is available for driving the motor 3 when either of the valves 25 or 26 is again operated.
Pressure in the chamber 44 is relieved by the valve 23 when operated by the hammer member 17 when the torque developed by the tool reaches a predetermined maximum value. When valve 23 opens the air in the chamber 44 passes out to atmosphere by way of the bore 48, and as a result the valve 33 closes and the motor stops.
it will, however, be observed that there is a bore 49 between the bore 48 opposite the end of valve 26b which is normally open, but is closed by the valve head 26g when the valve 26 is pressed. This bore 49 leads to the pressure cavity 32, so that when the bore is opened the action of the valve 23 to relieve the pressure in the spring chamber 44 is nullified, and the valve 33 remains open. When valve 26 is pressed, the bore 49 is closed and the valve 23 becomes operative to close the valve 33. This arrangement is necessary to ensure maximum torque output from the tool without automatic cut-off when the tool is used for retaining a fastener.
A portion of the driving shaft 16 of the hammer and anvil mechanism 5 is provided with a thread 50, which corresponds to the internal thread 51 on a maximum torque adjusting ring 52. The shaft 16 is also provided with splines 53 on which there is slidably fitted a collar 54. The spring 18 bears against a thrust ring 55, shaped, together with the collar 54, to receive the thrust balls 56. The collar 54 is provided with a spring and ball catch 57, which engages in one of a number of circumferentially spaced recesses in the side of the ring 52, so that the latter is retained in any one of a number of different circumferential positions as it is rotated on the thread on the shaft 16.
A key 58, which may be inserted through an aperture 59, is provided with bevel teeth 60, which engage with teeth 61, on the ring 52, to rotate the latter to its alternative position, to change the degree of compression of the spring 18. As the spring is tightened up the value of torque required to cause longitudinal movement of the hammer member 17 of sufficient amplitude to strike the pin 23a of the valve 23 is increased, and vice versa.
By fitting springs of different strength to different tools during manufacture, they can be adapted to cover different ranges. For example, with a lighter spring the tool may be used in the range of 30-60 pound feet and with a heavier spring the range 50pound feet.
The bounce of the hammers from the anvils immediately following impact is caused by resilience in the structures associated with the hammers and anvils respectively, and in particular to the torsional resilience of the driver shaft 21 and its connection with the nut or screw being driven. It is therefore proposed to provide an extension to the shaft 21, which has a tool holder, and by .use of which the resilience may be increased and consequently a further range of torque values can be added to that provided by the shaft 21 alone. This is a convenient way of changing the range of the tool in a matter of a few seconds.
lt is to be understood that the above description is by way of example only, and that details for carrying the invention into effect may be varied without departing from the scope of the invention.
1. A pneumatically operated hand-held impact wrench or screwdriver comprising a hammer member which is supported upon a driving shaft for reciprocating movement against the action of a compression spring to cause cyclic engagement and disengagement of hammers upon the hammer member with anvils associated with the driven shaft, and which, when the amplitude of reciprocating movement becomes increased as the torque developed by the tool reaches a predetermined maximum value of torque, operates a valve which interrupts the supply of air to a motor driving the tool, to stop the latter, to prevent a predetermined maximum value of torque being exceeded, characterized in that means are provided for varying the force exerted by said compression spring to vary the value of torque at which the valve is operated when torque is applied by the tool to a fastener by means of a torsion bar attached to the output shaft of the tool.
2. An impact wrench or screwdriver as claimed in claim 1 in which the compression spring is a helical spring which surrounds the driving shaft and engages either directly or indirectly at one end the hammer member and at the other end a ring having an internal thread which cooperates with the corresponding thread upon the driving shaft.
3. An impact wrench or screwdriver as claimed in claim 2 in which the ring has a bevel gear thereon which is engageable with a bevel gear on a key insertable from the exterior of the tool to rotate said ring to adjust the value of torque at which the value is operated.