US3493056A

US3493056A - Fluid operated tool

Info

Publication number: US3493056A
Application number: US729607A
Authority: US
Inventors: James H Boeger; William Workman Jr
Original assignee: Gardner Denver Inc
Current assignee: Gardner Denver Inc
Priority date: 1968-05-16
Filing date: 1968-05-16
Publication date: 1970-02-03
Anticipated expiration: 1987-02-03
Also published as: DE1924352A1; SE380755C; GB1194653A; FR1590801A; SE380755B; BE732016A

Description

Feb. 3-; 19-70 J, H. BOEG-ER M FLUID OPERATED TOOL;

Filed May 16, 1968 R m M R V E N G R 00 SW H M S A EH. H MW ATTORNEY United States Patent I US. Cl. 173-12 8 Claims ABSTRACT OF THE DISCLOSURE A valve mechanism for shutting off the supply of motive fluid to a fluid operated power tool such as a nutsetter, screwdriver, or the like for eliminating adverse torque reaction forces on the tool operator. The valve senses pressure at the tool motor to operate to interrupt the supply of motive fluid when a predetermined pressure value is reached. A fluid supply pressure dependent compensating feature operates to prevent premature shutoff action during the tool operating cycle, and also provides for control of the maximum torque produced by the tool.

BACKGROUND OF THE INVENTION In the design and application of pressure fluid power tools such as nutsetters, screwdrivers and similar devices producing a torque effort, it is desirable to regulate the supply of motive fluid, e.g. compressed air or hydraulic fluid, to control the torque produced by the tool. Control of tool output torque is required not only to assure properly tightened joints employing threaded fasteners but also it is particularly important that reaction forces caused by the tool torque output be minimized to prevent injury to tool operators.

In fluid operated tools of the type mentioned, it has been determined that motive fluid pressure at or near the tool motor inlet is proportional to the torque being produced by the tool. Accordingly, devices sensing motive fluid pressure have been developed that operate to interrupt the supply of fluid to the tool motor and are desirable to be used in power tools in view of their simplicity and efficiency when compared to the more conventional mechanical clutch devices known in the prior art.

An example of a fluid pressure responsive control valve for motive fluid shutoff is disclosed in US. Patent 3,373,824 to H. L. Whitehouse. In the Whitehouse patent a spring biased open valve is operable to interrupt the supply of motive fluid to the tool motor when pressure of the fluid supply flowing through the valve and acting on a surface to oppose the spring bias force reaches a value sufficiently great to overcome the force of the spring and close the valve thereby shutting off the supply of fluid to the tool motor. However, in the embodiment of Whitehouse if the fluid supply pressure is not adequate to overcome the preset spring force, the valve will not operate and the tool will reach a stall condition without shutoff thereby producing a sustained torque reaction which may injure the tool operator. Even at reduced supply pressures the more powerful tools designed to be hand held can produce torque reactions sufliciently great to cause disabling injuries to operating personnel. However, it has been determined that instantaneous peak torques greater than that which an operator could normally tolerate can be safely handled for very short increments of time provided a very rapid response valve shuts olf the motive fluid to the motor so that the inertia of the tool itself resists and absorbs the torque reaction force of the tool. Accordingly, it is desirable that, upon reaching a predetermined motor pressure condition and commensurate output torque, a valve be operable regardless of the absolute pressure value of the fluid supply to shut off the tool instantane- 3,493,056 Patented Feb. 3, 1970 ously thereby obviating a prolonged torque reaction against the tool operators hands and arms. Furthermore, it is desirable that a pressure fluid responsive device, such as described herein, be independent of the tools main motive fluid supply conduit so that no throttling of the motive fluid supply is required as the means to prevent premature shutoff action as is the case in certain prior art tool shutoff means.

SUMMARY OF THE INVENTION The present invention provides a motive fluid control valve for torque producing power tools which is operable to interrupt the supply of motive fluid to the tool when maximum torque output has been reached regardless of variations in motive fluid supply line pressure. By utilizing the tool motive fluid as the source of a compensating or opposing pressure to the pressure produced at the tool motor inlet, the control valve device of the present invention automatically compensates itself for variations in supply line pressures over a range of values greater than normally encountered in pneumatic or hydraulic fluid distribution systems.

A particularly advantageous aspect of the invention resides in the provision of a control valve which is not in line with the main motive fluid supply circuit of the tool and thereby does not require any restrictive orifices contributing to the throttling of the motive fluid supply. The present invention contemplates a control valve operable in conjunction with a pilot valve to operate a motive fluid supply valve of ample size to assure minimal pressure loss upstream of the tool motor thereby providing a tool of greater efficiency than heretofore known.

Yet another advantage of the present invention is the provision of a motive fluid shutoff control valve which is compact and mechanically simple permitting containment within the normal tool profile.

A further advantage of the disclosed invention is the quick response characteristic of the control valve to minimize the time in which the operator must physically resist torque reaction forces of the tool.

A still further advantage is a shutoff valve which senses motive fluid pressure within or closely adjacent the motor inlet port for greater accuracy in control of the desired shutoff pressure.

Other advantages and objects of the invention will be better understood upon reading the detailed description of the preferred embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary view partly in section of a typical pneumatic power tool illustrating details of the motive fluid shutoff control valve mechanism.

FIG. 2 is a schematic representation of the complete shutoif control valve mechanism in the position taken with motive fluid supplied to the tool proper but before actuation of the pilot valve.

FIG. 3 is a view similar to FIG. 2 but illustrating the pilot valve in the actuated position to start the tool.

FIG. 4 is a view similar to FIG. 3 illustrating the position of the shutoff control valve after actuation by the motor inlet pressure to shut off the motive fluid supply to the tool motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 a fluid operated tool is partially shown and designated by the numeral 10. The tool illustrated is typical of the pneumatically powered type used extensively in industry for tightening threaded fasteners. The tool housing comprises a casing 12 and handle portion 14. A rotary fluid operated motor 16 is mounted in the casing 12 and is rotatably supported on bearings 18 housed in the motor end plate 20. Pressure fluid such as compressed air'is conducted to the tool by a hose or other suitable supply line, not shown, connected to casing 12 by a fitting 22 having a hollow interior24 for conducting pressure fluid into the interior assage area 26 of the tool casing. A generally cylindrical insert 28 sealably housed in the casing 12 forms a chamber 30 for slidably receiving a fluid supply valve body 32 having a head portion 34 and a resilient sealing element 36 for seating the valve body in the closed position shown in FIG. 1. The opposite end of the valve body 32 includes a valve operating piston 38 forming with the insert 28 a chamber 40 which is in communication with a to be described source of pressure fluid by way of the passage 42. The valve piston 38 and chamber40 form a fluid pressure operator responsive to the admission of pressure fluid to thechamber 40 to move the valve 32 to an open position permitting fluid flow from space 26 into the chamber 30 and through the opening 44 into the passage 46 to the space 48 and through a motor inlet port 50 into the motor 16. The passage 46 is contained within the casing 12 but for simplicity and clarity of illustration is schematically shown in FIG. 1. The valve operator piston 38 also houses a spring 52 which assists in opening the valve 32.

The tool is energized by the manual actuation of a trigger 54 threadedly connected to a pilot valve 56 slidably housed in a cylinder housing 58 the latter being retained in a transverse bore 60 formed in the insert 28 by a retaining ring 62.

The transversely disposed valve housing 58 slidably journals a spool shaped control valve element 64 in a bore 66. The valve element 64 includes a cuplike pressure surface 67 forming with the housing 58 a first pressure cavity 68. The other end surface 70 of the spool element 64 coacts with valve housing 58 and handle 14 to define a second pressure cavity 72. The reduced diameter intermediate portion of the valve element 64 forms with the housing 58 an annular flow passage 74. In communication with the first pressure cavity 68 is a conduit 76 leading to a pressure regulating needle valve 78 threadedly disposed in the insert 28. A vent passage 80 leads from the regulating valve 78 into the annular space 81 surrounding the pilot valve 56 which communicates through passage 82 with the space 84 in the cylindrical insert 28. The space 84 is in flow communication with the motor exhaust port, not shown, or other suitable means vented to atmosphere.

Near the bottom of the bore 60 in the insert 28 a small passage 85 having a ball check valve 86 disposed therein is in flow communication with the second pressure cavity 72 and the space 48 thereby permitting a pressure signal from the motor inlet port 50 to be transmitted to the second pressure cavity 72 except, of course, under conditions when the pressure in the cavity 72 exceeds the pressure at the motor inlet port 50 to close the check valve 86.

Additional passages and conduits for conducting pressure fluid to and from the pilotvalve 56 and the control valve 64 are contained Within the tool casing but are more easily shown by the schematic views of FIGS. 2 through 4 which also illustrate the operating positions of the valves. Referring to FIG. 2, a passage 88 leads to the first pressure cavity 68 and a branch portion 90. The passage 88 also is in communication with the area 26 so that when the tool 10 is connected to a compressed air supply pressure air is always conducted to the first pressure cavity 68. Also shown schematically in FIGS. 2 through 4 is a pilot valve conduit 92 leading from a chamber 94 formed by the pilot valve 56 to the intermediate flow passage 74. A control valve augmenting conduit 96 is in communication with the second pressure cavity 72 depending on the position of the control valve 64. I

The control valve element 64 is operable to shift from the position of FIG. 2 to the position shown in FIG. 4 in response to the pressure at the motor inlet port and hence the cavity 72 exceeding the pressure in the first cavity 68. Since the effective areas of the

surfaces

67 and 70 are equal the unequal pressures will cause a resultant pressure force to shift the valve 64. The shifting of the control valve 64 from the position of FIG. 2 to the position of FIG. 4 is effective to shut off the air supply to the tool motor as will be described below. The control of the shutoff pressure yalue present at the motor inlet port may be achieved by regulating the pressure in the cavity 68 by the needle valve 78. The size of the passage 98 is determined to be less than the

vent passages

76, 80 and 82 so that compressed air from the tool inlet entering the cavity 68 may be controlled by adjusting the valve 78 to bleed air out of the cavity 68 at a greater rate than it is entering and thereby control the pressure therein.

The pressure in cavity 68 is desirably set to a value slightly less than the pressure at the motor inlet port 50 and the second cavity 72 which in turn corresponds to a value slightly less than the tool stall torque pressure. In this way the valve 64 will actuate to shut olf the motive air supply to the tool motor rapidly at a predetermined pressure condition to avoid adverse and sustained torque reaction forces being transmitted from the tool to the operator. A particularly advantageous aspect of the present invention is that, regardless of the supply pressure to the tool and hence to the cavity 68, a pressure force differential is exerted on the valve 64 slightly before the tool motor stalls which causes the valve 64 to shift to shut off motive air to the tool motor. In fact, it has been determined that by setting the regulating valve 78 to cause the valve 64 to operate satisfactorily for a supply pressure of 60 p.s.i.g. that a virtually linear proportionality between supply pressure and the pressure in the cavity 68 can be retained for line pressures as low as 10 p.s.i.g. or as high as 110 p.s.i.g., thereby serving to control the tool with precision within these limits of supply line pressure.

With a pressure air source connected to the tool 10, air will flow into the area 26 (FIG. 1) and act on the head 34 of the supply valve 32 to overcome the bias of the spring 52 and close the valve thereby preventing the flow of motive air to the tool motor 16. As supply pressure air flows from the area 26 through the passage 88 to the cavity 68, the control valve will be forced to the posi tion of FIG.- 2 and pressure in the cavity 68 will act on the flange 100 on the pilot valve 56 to force it into the position shown closing the

vent passages

80 and 82 and blocking the pilot branch 90 from communication with the pilot conduit 92 by way of the chamber 94. With the control valve in the position shown in FIG. 2, the valve operator chamber 40 is vented through the passage 42, the intermediate passage 74, pilot conduit 92, chamber 94 and vent branch 102 to the vent passage 82. As the tool operator depresses theitrigger to the position of FIG. 3 overcoming the pressure acting on the flange 100, the pilot branch portion 90 will now conduct pressure fluid at essentially supply pressure through the chamber 94, the

conduit

92 and 74, and passage 42 to the operator chamber 40 to'act on'the supply valve operator piston 38 which, with assistance 'from'the spring 52', will open the motive fluid supply valve 32. Motive fluidmay now flow from the passage area 26, through the opening 44in the valve chamber 30,. and the passage 46 to the motor inlet port 50. During the relatively free run-down period of a typical threaded fastener, the tool motor 16 will be operating at a speed-to permit a relatively high rate of motive fluid flow such that the pressure at the port 50 and the space 48 willbe considerably less than the supply pressure in the area 26. Consequently, the pressure in the second cavity 72 will be less than the regulated pressure set by the needle valve 78 which, as shown in the condition of FIG. 3, is bleeding the cavity 68 through passage 76 past the valve 78 and through the passage 80, space 81, passage 82 and eventually to the motor exhaust port. However, as the tool motor slows down in response to the torsional resistance of the fastener being tightened, the pressure of the motive fluid in response to reduced flow through the motor will rise to approach the predetermined desired shutoff value which, as previously men tioned, is desirably set at an incremental value less than the stalled motor inlet pressure. This predetermined shutoff pressure is sensed in the second cavity 72 and being greater than the preset regulated pressure present in cavity 68 will operate on the pressure surface 70, which is irregular enough to permit full area contact with the fluid even in the position shown in FIGS. 2 and 3, to shift the control valve 64 from the position shown in FIG. 3 to that shown in FIG. 4. As the valve 64 moves upward past the control valve augmenting conduit 96, fluid at essentially supply pressure may enter the cavity 72 to accelerate the valve 64 in its movement toward the position of FIG. 4 and maintain the valve in that position as long as the trigger 54 is depressed. In the position of FIG. 4, the control valve 64 has shifted to cause the supply valve operator chamber 40 to be shut off from receiving pressure fluid through the pilot conduit 92. The valve operator chamber 40 is instead vented through the passage 42, intermediate conduit 74 and the vent branch 104 to the main vent passage 82. The supply valve 32 will immediately close in response to pressure acting on the head 34 shutting off the motive fluid supply to the tool and preventing the stall torque reaction from being transmitted to the operator. The tool motor cannot be restarted until release of the trigger 54 causes pressure fluid in the cavity 68 to reset the trigger to the position of FIG. 2 whereupon the second cavity 72 may be vented through the augmenting conduit 96, the pilot conduit 92, chamber "94 and vent branch 102 to the vent passage 82. Leakage around the control valve diameter 106 will permit full return to the position of FIG. 2.

As may be appreciated from the foregoing, the invention has the particular advantage of rapid and positive shutoff action to prevent adverse torque reactions from stall type tools without requiring any adjustment or compensation for variations in fluid supply pressure. Furthermore, the regulating va ve can be set to control the maximum torque output of a given tool over a considerable range making the control more versatile than heretofore known shutoff devices. By removing the shutoff control valve from the main fluid supply circuit the valve element itself can to a degree be miniaturized to thereby make possible a more compact overall tool envelope and provide a control valve with low inertia to facilitate quick response to operating pressures.

It may also be appreciated that various alternations could be made in the design of the valve control shutoff without departing from the scope of the invention. For example, rather than utilizing equal pressure surfaces and regulating the supply pressure, it would be possible to design the control valve element with unequal pressure surfaces to determine the desired pressure force necessary to shitf the valve, and thereby use fluid at supply pressure in the first pressure cavity. Also, the shutoff control valve could be enlarged and placed directly in the main supply fluid circuit to the motor at a sacrifice, however, in operating speed and supply passage flow area.

What is claimed is:

1. In a fluid operated tool comprising:

a casing having fluid connection means thereon for connection to a pressure fluid supply;

a fluid operated motor in said casing, said motor including a fluid inlet port; and

fluid passage means in said casing in communication with said pressure fluid supply and said motor inlet port, the improvement comprising:

pressure fluid supply valve means including pressure fluid operator means interposed in said passage means between said motor inlet port and said pressure fluid supply, said supply valve means being operable to be in an open fluid flow condition in response to supplying pressure fluid to said operator and to be in a closed fluid shutoff condition in response to venting pressure fluid from said operator; and,

control means comprising a movable element having first and second opposed pressure surfaces subject to fluid pressure forces from said pressure fluid supply and said motor inlet port, respectively, and said control means is operable in response to said pressure fluid forces acting thereon to alternatively effect pressurization and venting of said operator means. The invention according to claim 1 together with:

a pilot valve in communication with said pressure fluid supply and being operable to admit pilot valve controlled pressure fluid through a pilot-fluid conduit to pressurize said fluid supply valve operator means and to vent pressure fluid from said valve operator means.

The invention according to claim 2 wherein:

said control means is interposed in said pilot fluid conduit and is operable in response to pressure fluid acting on said first pressure surface to shift to a position providing for flow of pilot fluid from said pilot valve to said fluid supply valve operator means to open said fluid supply valve, said control means also being operable in response to a predetermined pressure at said motor inlet port and acting on said second pressure surface to shift to a position whereby pilot pressure fluid is vented from said fluid supply valve operator to close said fluid supply valve.

The invention according to claim 3 wherein:

said control means comprises valve housing means having a hollow chamber for movably receiving said shiftable element and said element forms with said chamber a fluid passage intermediate said first and second pressure surfaces whereby in response to a fluid pressure force acting on said first pressure surface said element shifts to provide for fluid flow from said pilot fluid conduit through said intermediate passage to said supply valve operator, and in response to a predetermined fluid pressure force on said second pressure surface said element shifts to vent said valve operator through said intermediate passage.

The invention according to claim 4 together with:

pressure fluid augmenting means comprising conduit fluid passage means in said casing in communication with said pressure fluid supply and said motor inlet port, the improvement comprising; control means in communication with said motor inlet port, said control means including a movable element having opposed surfaces subject to fluid pressure forces;

said element is operable to be biased in a first position by a pressure fluid force from said pressure fluid supply operating on one of said opposed surfaces, and said element is operable to move to a second position to effect the shutoff of pressure fluid to said motor in response to a pressure fluid force from said motor inlet port operating on the other surface in opposition to said pressure fluid force operating on said one surface.

7. The invention according to claim 6 together with:

pressure regulating means operable to regulate the pressure of said fluid operating on said one pressure surface.

8. The invention according to claim 6 together with:

pressure fluid supply valve means interposed in said passage means between said motor inlet port and said pressure fluid supply, and operable to be in an open fluid flow condition and a closed fluid shutoff condition, and said control means is operable in response to said fluid pressure forces operating thereon to provide for opening and closing said supply valve means.

References Cited UNITED STATES PATENTS 1,414,222 4/1922 Slater 91-59 2,397,893 4/1946 Van Sittert et a1. l3746l 3,373,824 3/1968 Whitehouse 17312 ERNEST R. PURSER, Primary Examiner US. Cl. X.R.