US3587752A

US3587752A - Fluidic governor for air tools

Info

Publication number: US3587752A
Authority: US
Inventors: Stanley K Smith
Original assignee: Black and Decker Manufacturing Co
Current assignee: Master Power Inc
Priority date: 1969-06-02
Filing date: 1969-06-02
Publication date: 1971-06-28
Anticipated expiration: 1988-06-28

Abstract

AN OVERSPEED GOVERNOR FOR ROTATING AIR MOTORS INCLUDING SPEED SENSING MEANS FOR PROVIDING A SIGNAL CORRESPONDING TO THE SPEED OF THE MOTOR, VALVE MEANS LOCATED IN THE PATH OF THE AIR SUPPLY TO THE MOTOR, AND FLUIDIC MEANS RESPONSIVE TO THE SPEED SIGNAL FOR CONTROLLING THE OPERATION OF THE VALVE. THE SYSTEM IS PREFERABLY SEALED FROM THE INLET SUPPLY BUT EXERCISES CONTROL OVER A PORTION OF THE INLET SUPPLY PRESSURE WHICH IS USED TO ACTUATE THE VALVE. THE VALVE IS BIASED CLOSED AND MOTOR SPEED ABOVE A SELECTED LEVEL SWITCHES THE CONTROL PRESSURE AWAY FROM THE ACTUATION MEANS SO THAT THE VALVE CLOSES.

Description

United States Patent inventor Appl. No.

Filed Patented Assignee Stanley K. Smith Baltimore, Md.

June 2, 1969 June 28, 1971 The Black and Decker Manufacturing Company Towson, Md.

FLUIDIC GOVERNOR FOR AIR TOOLS 37 Claims, 6 Drawing Figs.

US. Cl 173/12,

137/815 Int. Cl. B24b 23/00 Field of Search 173/12;

[56] References Cited UNITED STATES PATENTS 2,897,832 8/1959 Jimerson 173/12X 3,410,287 11/1968 Van Der Heyden et a1... l37/81.5X

Primary Examiner- Ernest R. Purser An0rneys Leonard Bloom, Joseph R. Slotnik and Edward D.

Murphy ABSTRACT: An overspeed governor for rotating air motors including speed sensing means for providing a signal corresponding to the speed of the motor, valve means located in the path of the air supply to the motor, and fluidic means responsive to the speed signal for controlling the operation of the valve. The system is preferably sealed from the inlet supply but exercises control over a portion of the inlet supply pressure which is used to actuate the valve. The valve is biased closed and motor speed above a selected level switches the control pressure away from the actuation means so that the valve closes.

PATENTEU JUN28 1971 SHEET 1 0? 3 AIR SUPPLY 1 SPEED REGL JLATOR FIG 2 VALVE CONTROL 0N OFF VALVE BYPASS VALVE I GOVERNOR TOOL MOTOR SPEED SENSO? STARTING INVENTOR STANLEY K. SMITH ATTORNEY PATENTEnJunaelsn 3587752 sum 2 OF 3 INVENTOR STANLEY K. SMITH BY Maya/ 4 ATTORNEY PATENTEDJUN28|9H 3587.752

SHEET 3 F 3 FIG. 5

FIG. 6 95\ 97 Q \m\\\\\\ &\\\ 78 I INVENTOR STANLEY. K. SMITH ATTORNEY FLUIDIC GOVERNOR FOR AIR TOOLS This invention relates to the field of air powered rotary tools, particularly of the pneumatic grinder class and is specifically directed to rotary air tools including safety devices for preventing overspeed.

Portable air tools using rotary air motors, particularly those classed as grinders and sanders, are widely used in industrial, shop and field applications where they are subjected to hard use and frequent shocks, even in normal use. These tools are normally found in environments such as garages, machine shops, factory floors, etc. where they encounter frequent vibration, dirty atmospheres, and high ambient temperatures. Frequently, these conditions are generated by the use of the tool itself. Accordingly, the tools and the operating elements thereof must be constructed so as to withstand such severe treatment.

In addition, however, such tools may be subjected to various excessive stresses due to improper operation, careless application of the tool to workpieces, etc., particularly in the hands of unskilled operators. Under these conditions, it can become difficult for the overspeed preventing device, or tool governor to maintain the proper output speed of the driven elements. For example, wide variations in speed can occur when the load is changed or removed so abruptly that presently available governors cannot respond in time. Also, the governors now used which are small enough and sufficiently light in weight for use in portable tools are subject to hunting; that is, oscillation of the motor speed above and below the rated speed for a period of time immediately after a change.

Another difficulty which can be produced by careless or abusive handling of air tools is damage to the governor mechanism. The shocks to which these tools can be subjected in this manner may break or weaken the operativeness of many mechanical governors presently used. The governor mechanism may then break during use or it may be inoperative when the air supply to the motor is turned on. Similarly, the governor may become inoperative due to lack of, or improper maintenance. If this happens, the large volume of air, which must be available to maintain rated speed when the tool element is loaded, becomes uncontrolled and can drive the element to a speed farin excess of its rated value when it is removed from the load. Either the tool element or the motor itself can then be subjected to stresses in excess of their rated values and'they may explode, with consequent danger to the operator and to others in the area.

Fluid-operated governors have been proposed to avoid these difficulties and provide tools which can safely be handled in a careless manner but these devices have not been successful. A basic problem is that it has not previously been possible to obtain sufficient power to operate a governing valve without using the compressed air supply and this air is so impure that it can block the fluidic system and cause it to fail. In addition, these devices are still subject to the difficulties of slow response and hunting" above and below the selected speed value.

It is accordingly the purpose of the present invention to provide a fluidic overspeed governor for use with air tools, particularly of the portable type, and specifically for grinding tools, which overcomes the disadvantages of both the prior mechanical and fluidic governors described above and which normally operates to maintain the motor accurately at the selected speed and which, in the event of failure of the governor, causes the motor to be shut down. The governor is also adapted to maintain the tool in an off condition if the governor becomes inoperative while the tool is shut off.

Accordingly, it is an object of this invention to provide a new and improved fluidic overspeed governor for pneumatic motors.

Another object of this invention is the provision of a new and improved regulating speed governor for air tools.

It is also an object of this invention to provide an overspeed governor for air motors which prevents'the motor from starting if the governor is not operative.

It is also an object of this invention to provide an improved governor for air motors which is not sensitive to mechanical shock.

Another object is the provision of an air tool governor having improved response.

Another object of this invention is the provision of an overspeed governor for air motors which is of increased sensitivity to speed changes.

A further object of this invention is the provision of an improved air tool having an effective overspeed control.

Another object of this invention is the provision of new and improved portable air tools of increased safety.

It is also an object to provide a new and improved overspeed control which can be incorporated into a portable air tool.

Briefly, in accord with this invention, I provide an overspeed governor for rotating air motorswhich includes speed sensing means associated with the rotor for providing a signal corresponding to the speed of the rotor, valve means located in the supply path of air to the motor for regulating the air supply, and fluidic means responsive to the speed signal for controlling the operation of the valve so that an overspeed produces a corrective reduction of the air supply. In a specific embodiment, the speed sensing means preferably includes a rotating member attached to the shaft which provides a speed signal such as fluid pressure. This signal is both the source of energy and the control signal for the fluidic control means which maintains the governor valve open so that either failure of the speed sensor or an overspeed signal causes shut down. The valve is operated by the air supply pressure, under the control of the fluidic means. The valve is preferably biased in the closed direction so that failure of the governor produces shut down of the motor.

Further objects and advantages of this invention will become apparent as the description and illustration thereof proceed. The invention itself may best be understood by a consideration of the following description, in conjunction with the accompanying FIGS. in which:

FIG. 1 is a perspective view of an operator using a portable grinding tool;

FIG. 2 is a schematic view of a preferred embodiment in accord with the present invention;

FIG. 3 is a plan view, partially in cross section of a specific embodiment of this invention;

FIG. 4 is a plan view of an element of the system shown in FIG. 2;

FIG. 5 is a schematic view of an alternative embodiment of this invention; and

FIG. 6 is a schematic view of a further alternative embodiment of the present invention.

A typical application of a portable air-driven grinder is illustrated in FIG. 1 wherein an operator is shown applying the tool to grind smooth a welded seam. In such use, the tool is subject to the varying degree of operator pressure which may be applied, the self-generated heat and metallic dust and other severe conditions during use, as previously described. While present governors are constructed to withstand these conditions, improper or abusive use, handling or maintenance of the tool, such as might occur if the operator left the tool on the workpiece and it was knocked to the floor, can cause the difficulties previously mentioned.

To overcome these potential difficulties, the present invention proposes a system, a preferred form of which is shown schematically in FIG. 2. This system includes an air motor 5 of an air-powered tool coupled to a source of compressed air (not shown) through a governor valve 6 and an on-off valve 7. The motor is coupled through a shaft 8 to a working device such as a grinding wheel 9.

Also coupled to the motor 5 is a speed sensing unit 10 which is shown schematically. This element represents any appropriate transducer which produces an output signal indicative of the speed of the motor. A primary feature of air-driven grinders is that of safety since no electrical power is required, thus eliminating the danger of shock. Accordingly, a particular feature of the present invention is that of providing a sensing unit which produces its output as a parameter of a fluidic system, thus maintaining the safety aspect of air-driven grinders. Specifically, it is preferred that the fluidic signal be the pressure output of a small fan or a compressor which rotates with the air motor.

In accord with a further feature of this invention, the pressure output of the speed sensing device is used as both the source and the control in the speed regulating unit 11, as indicated by the

connective lines

12 and 13 respectively. The speed regulator comprises means for controlling the output stream from the speed sensor according to its pressure so as to transmit an "open" or closed instruction to the valve control unit 14 by means of the pressure of the stream from the sensor. Specifically, for overspeed regulation, the speed regulator 11 transmits the open" instruction until the selected maximum value for the speed signal is reached, at which time the instruction changes to close," which closes the governor valve.

In further accord with the present invention, the valve control 14 comprises means for utilizing a portion of the supply air to control the governor valve; specifically, to open the valve when the open" instruction is received. By means of this arrangement, sufficient amplification is achieved to enable the fluidic system to control the governor valve. This control is illustrated by the connection 15 to the air supply line and the dotted connection 16 to the governor valve 6.

As an additional feature of this invention, the governor valve is biased closed when the motor is shut down. This protects the operator against possible failure of the governor system when the motor is being started for the first time after an extended period without use. With the valve biased closed, the motor will not start if some portion of the governor mechanism has become broken, blocked or frozen due to corrosion, etc. To enable starting of the motor in this case, a bypass tube 17 is provided around the governor.

To operate the motor with the above described governor system, the on-off valve 7 is operated and a small supply of air produces an initial rotation of the motor via bypass tube 17. The speed sensor 10 produces a small output which enables the valve control 14 to open the governor valve 6. As soon as the valve is open, the increased air supply brings the motor up to speed. If the motor is not fully loaded, the air supply attempts to drive the motor into an overspeed condition. This is immediately sensed by the speed regulator 11 and the valve control 14 responds by shutting down the governor valve. Depending on the exact choice of elements of the system, the governor valve may be maintained in a partially opened condition or it may alternate between its full-open and full-closed positions in a duty cycle which maintains the motor in a speed range very close to its rated speed.

Thus, the system of this invention provides improved response to speed changes and is not subject to mechanical failure due to careless treatment. In addition, a particular advantage of this system is the fact that the governor uses a fluidic control over a portion of the air supply to control the governing valve, thus enabling a low power speed signal to control the operation of the governor valve. Further features include the use of a pressure-generating speed sensor and the provision of a fluidic system which has no moving parts and therefore is not subject to wear or corrosion. Also, since the valve is biased closed, the failure of the speed sensor and the consequent lack of a speed signal at the fluidic controller causes shutdown. As previously noted, the closed bias applied to the governor valve prevents failure of the governor mechanism if corrosion occurs during an idle period.

In FIG. 3, a preferred embodiment of this invention is illustrated which, in addition to the above-noted features, is compact and packaged within the housing of the device. This is required for practical use in portable devices. The particular device shown is a portable grinding tool 19 which includes a handle 20 adapted to be grasped by an operator, an air motor 5 and a rotating element 9 which comprises a grinding wheel.

An inlet for the driving air, controlled by an appropriate onoff valve in the external supply line or in a portion of the ham dle, extends via conduit 21 through handle 20, through a governor valve indicated generally at 6 and through an inlet passage 22 in the motor housing 23 which directs it to the motor to produce rotation. The illustrated motor includes a rotor 24, a stationary cylinder 25 supported in the housing 23 and a plurality of vanes 26 which are slidably mounted within the rotor. The rotor is eccentrically mounted with respect to the cylinder so that introduction of the pressurized air into a confined region defined by the rotor, the cylinder and the vanes causes rotation as the air expands.

The rotor is mounted on a shaft 8 which rotates in bearings 27, supported by a member 28 which is suitably affixed to housing 23. In accord with the present invention, the shaft is provided with an extension 29 to drive the speed sensing means 10. in this embodiment, the speed sensor comprises a small fan or compressor which includes a rotor 30 mounted on the shaft extension 29, a stationary cylinder 31 and a plurality of vanes 32 slidably mounted in the rotor. The cylinder is mounted within an end housing 33-which is suitably affixed to motor housing 23. The compressor is enclosed between bottom plate 34 and top plate 35. A chamber 36, containing air or other appropriate fluid, is defined by the housing 33 and communication with the inlet region of the compressor is provided by a passage 37. The chamber may be in communication with the atmosphere through means such as a porous plug 38 which acts as a filter to prevent entry of dust, etc. and it is sealed from the dirty air passing through the motor by bearing support member 28. Due to eccentric mounting of the rotor 30 with respect to the cylinder 31, the compressor produces a pressure at its outlet 39 which corresponds to the speed of the motor 5.

The compressed air produced by the compressor 30 is, in this embodiment, used as the supply air for the fluidic system. A fluidic gating member 40 is mounted at the top of the housing 33 between gaskets 41 and is held in place by a cover plate 42 and a plurality of bolts, not shown. A plan view of the gating member 40 is shown in FIG. 4. The compressor outlet 39 communicates through passage 43 to an inlet port 44. In accord with the normal action of fluidic gates, the air supplied at the inlet port passes through the fluidic member and exits through one or the other of

outlet ports

45 or 46. A unique definition of the air path from the inlet port 44 to one or the other of the outlet ports is provided by the differential pressure between the

control ports

47 and 48; that is, the existence of a higher pressure at one of the control ports pushes the supply air stream against the opposite wall and, due to the phenomenon of wall attachment, the supply stream passes only to the corresponding outlet port. Thus if the pressure at control port 47 is higher than that at control port 48, the supply air passes entirely to outlet port 45. If the pressure at control port 48 increases to a higher level than that at control port 47, the air stream is switched to the other wall and it is entirely directed to outlet port 46.

Vents

49 and 50 are connected through passages, not shown, to chamber 36 and insure that the attachment of the stream to the respective walls is maintained despite loading on

outlet ports

45 and 46.

In accord with the present invention, the selection of one or the other or both of the

outlet ports

45, 46 is used to control the governor valve. Specifically, outlet port 45 communicates through passage 51 with the governor valve 6 so as to cause it to open. The other outlet port 46 communicates through passage 52 to the chamber 36, thus returning the compressor air to its reservoir. The

control ports

47 and 48 are arranged so as to direct the air stream to outlet port 45 and maintain the governor valve open until an overspeed signal is received at which time the air supply is switched to the outlet port 46 so that the bias of the governor valve causes it to close. To ac complish this, control port 47 is connected through a passage 53 to the chamber 36 which the control port 48 is connected through a passage 54 including a check valve to the compressor outlet passage 43. The check valve, which includes a diaphragm 55, a spring 56, and an adjusting screw 57, which biases the diaphragm closed until a predetermined pressure is received from the compressor. Thus, in normal operation, no pressure is received at control port 48 while the control port 47 is connected to the atmospheric pressure in chamber 36. Therefore, vacuum switching causes the air stream from supply port 44 to be diverted to outlet port 45 and the governor valve is opened. When an overspeed condition is reached, the compressor pressure exceeds the force of spring 56 and opens the diaphragm, thus exposing control port 48 to the full compressor pressure. Since this is higher than the pressure in chamber 36, the air stream is diverted to the opposite wall and now exits through outlet port 46. Since the compressor pres sure is no longer supplied to the governor valve, the governor closes, thus shutting down the motor. As the driving pressure to the motor falls due to closure of the governor valve, the overspeed pressure no longer exists, the check valve closes and the governor is opened by switching of the supply stream. Thus, the motor is maintained at its rated speed.

The governor valve 6 as shown in detail in FIG. 3, is

mounted in the

housings

23 and 33, and comprises a body 58 and

end caps

59 and 60. The body includes a bore 61 in which is mounted a valve member 62. In the upper position illustrated, the member blocks communication between the air inlet conduit 21 and internal passage 22 except for the small bleeder passage 63 which provides sufficient air to permit the motor to start. The valve member is biased into the closed position by means of aspring 64 and further upward travel is prevented by any suitable stop 65. The air passing through the bleeder passage 63 produces a pressure in the internal passage 22 and also in the region 66 of the bore around the valve stem 67. A small bleeder passage 68 communicates by one or more outlets 69 with this region and also with an enclosed chamber 70 above an upper member 71 on the valve stem 67. Other air communication is prevented by means of the valve guide 72 and O-ring seals 73.

The enclosed chamber 70 communicates through a rigid upper wall 74 through a tube 75 into a vented chamber 76. The vent is through an outlet 77.

When the air supply to the motor is turned on, the inlet pressure is communicated via bleeder passage 63 to the internal passage 22. This air starts an initial, low speed rotation of the motor while simultaneously supplying a pressure through internal region 66, bleeder passage 68, and enclosed chamber 70 to vented chamber 76. As the motor starts to turn, the compressor also turns and generates a supply stream which, due to the atmospheric pressure from chamber 36 and control port 47, passes through outlet 45 and passage 51 into an upper enclosed chamber 78 in the governor valve bore. The enclosed chamber 78 is separated from the vented chamber 76 by a flexible diaphragm 79. As the compressor pressure enters the upper chamber 78, the diaphragm 79 is forced against the tube 75, thus breaking the communication between the enclosed chamber 70 and the outlet 77. Since the supply air pressure continues to build up in the enclosed chamber 70, this pressure now acts against the upper valve member 71, thus moving the valve against the force of spring 64 and opening it to allow full communication between the air inlet and the internal region 66. The bleeder passages 68 are sized so that, with the air supply passing normally through internal passage 22 to the motor, the pressure in chamber 70 does not overcome the pressure supplied by the compressor to the upper chamber 78. Thus, as long as the normal motor speed is not exceeded, the governor valve is maintained in the open position. As previously described, if an overspeed condition occurs, the compressor pressure is switched to outlet port 46, and the pressure at port 45 and consequently in chamber 78 falls to zero. Thus, the diaphragm is released from the tube 75 and chamber 70 is connected to the vent 77. As the pressure in chamber 70 is reduced, the spring 64 closes the governor valve.

In a preferred embodiment of this invention, the check valve is designed to have a very high sensitivity and speed of response. Thus, this valve operates very rapidly for a very slight change in inlet pressure due to movement of the governor valve member 62. Thus, the valve member would pulsate about a nearly stable position while the check valve alternated rapidly between open and fully closed. In this manner, the operation of the motor appears to be nearly continuous and the small variation is not noticeable to the operator. Of course other methods of accomplishing this result which are familiar to those skilled in the art may be used instead.

FIG. 5 is a schematic illustration of an embodiment similar to that of FIG. 3 except that the fluidic system uses filtered air from the motor supply. In this embodiment, the supply conduit 22 is modified as illustrated by the expanded region 80 to deliver a portion of the inlet air to inlet port 44 through passage 81. Since the quantity of dirt, oil, etc. contained in the supply air is quite high, the use of a filter 82 is required. Preferably, this is a five micron filter; that is, a filter which will not permit the passage of any particle greater than five microns in diameter.

Since the speed signal is no longer used as the pressurized control stream in the fluidic device, the compressor can be replaced by fan 83, which, with the check valve in passage 54, produces an overspeed signal. The remainder of the apparatus illustrated in this FIG. is the same as the of FIG. 3 except that the illustration is in a schematic form for convenience. This view also includes an illustration of the connections between the various ports of the fluidic member and the other parts of the apparatus, as previously described in connection with FIG. 3

FIG. 6 is a schematic illustration of a further alternative embodiment of this invention. In this FIG., the motor 5, the inlet path and the lower portion of the governor valve 6 have been omitted since these are similar to those shown in FIG. 3. The speed signal in this embodiment is produced by a fan which is mounted on the extension 29 of the motor shaft. The fan produces its output signal adjacent the tips ofits blades while a low pressure exists in the region of the shaft. The outlet 91 accordingly is positioned at the outer periphery of the fan 90 and the air flow is directed through passage 92 into a force balancing device 93. This device includes a flexible diaphragm 94 which is biased by spring 95 to seal the diaphragm against the opening into a return passage 96. The degree of force exerted by this spring is adjustable by means of set screw 97. A long as the output pressure of the fan does not exceed the spring pressure, the air flow enters a chamber 98 and is directed through passage 99 into the upper enclosed chamber 78 of the governor valve. As previously described, this forces the flexible diaphragm 79 to close against the tube 75, thus producing a build up of pressure in chamber 70 and opening the governor valve. If an overspeed condition is reached, the pressure through passage 92 exceeds the spring bias of spring 95, thus opening the passage 96. Since this passage communicates with the center of the fan, it is returned to the low pressure region and the air flow passes through it rather than into the closed chamber 78. Thus, this releases the pressure on the diaphragm 79 which in turn opens the chamber 70 to the vent 77 and this permits the governor valve to close.

As in the previous embodiments, this system incorporates the advantages ofa fluidic control coupled with automatic closure of the governor valve in the event of failure of the pressure required to open the valve. In the embodiment of FIG. 6, the fluid amplifier, comprising the chambers and diaphragm in the upper end of the governor valve, is designed to be very sensitive so that the output pressure of the fan is sufficient to cause the governor valve to open, thus eliminating the need for a positive displacement compressor.

While several specific embodiments have been shown and described, it is clear that further modifications will occur to those skilled in the art. For example, in addition to the regulator described above, hydraulic or AC fluidic means could be used; also, means such as a sonic generator driven by the motor couldgenerate the speed signal. Accordingly, it is intended that the appended claims cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. An air-driven power tool comprising:

a housing;

an air-driven motor within said housing;

conduit means for supplying air to said motor;

a tool element coupled to said motor and arranged to be driven thereby; and

fluidic speed governing means for said motor including:

valve means disposed in said conduit;

biassing means urging said valve means to its closed position;

speed-sensing means coupled to said motor for providing a signal corresponding to the speed of said motor; and

means responsive to said speed signal for opening said valve means against said biassing means and for enabling closure of said valve means in the event that said motor reaches a speed in excess of a selected value.

2. An air-driven power tool as claimed in claim 1 wherein said tool element comprises a grinding wheel.

3. An air-driven power tool as claimed in claim 1 wherein biasing means are provided to close said valve means in the absence of a signal from said speed-sensing means.

4. An air-driven power tool as claimed in claim 3 wherein said speed-sensing means provides an output signal only when said motor is running and is at a speed below a selected value.

5. An air-driven power tool as claimed in claim 4 which includes a low-capacity bypass around said valve means to permit starting of said motor.

6. An air-driven power tool as claimed in claim 1 wherein said speed governing means comprises a fluidic system; and wherein said tool includes means isolating said system from the air supplied to said motor.

7. An air-driven power tool as claimed in claim 1 wherein said speed governing means comprises a fluidic system; and wherein said speed sensing means comprises compressing means for pressurizing the fluid according to the speed of said motor.

8. An air-driven power tool as claimed in claim 7 wherein said speed signal responsive means comprises check valve means biased closed against said pressurized fluid whereby said pressure opens said check valve only when said pressure is excessive.

9. An air-driven power tool as claimed in claim 8 wherein means are included for adjusting the bias level applied to said check valve.

10. An air-driven power tool as claimed in claim 1 wherein:

said valve means is pressure-actuated; and wherein:

said valve-opening means comprises a connection to said air supply pressure and means for enabling and disabling pressure at said valve means according to the speed of said motor whereby said valve means is opened by the pressure of the air supply.

11. An air-driven power tool as claimed in claim 10 wherein:

said speed governing means comprises a fluidic system;

said tool includes means sealing said system from said inlet air; said speed-sensing means comprises means for pressurizing said systemaccording to the speed of said motor; and

biasing means are provided for closing said valve means unless a signal causing said valve to open is received from said governing means.

12. An air-driven power tool as claimed in claim 1 wherein said means responsive to said speed signal includes means establishing a reference value to which said signal is com pared.

13. A fluidic speed governor for an air motor comprising:

an inlet conduit for connecting a supply of pressurized air to said motor;

valve means disposed in said conduit for controlling the quantity of air supplied to said motor;

biassing means urging said valve means to its closed position;

an actuating member for said valve means;

speed-sensing means coupled to said motor for providing a fluid pressure signal corresponding to the speed of said motor;

fluidic means responsive to said speed signal for coupling the pressure of said air supply to said actuating member to overcome said biassing means in a normal speed range to control the operation of said valve means and for decoupling said pressure upon the occurrence of an overspeed condition whereby the speed of said motor is prevented from exceeding a selected valve.

14. A speed governor as claimed in claim 13 wherein said speed responsive means regulates said valve means to maintain said motor substantially at said selected speed.

15. A speed governor as claimed in claim 13 wherein said speed responsive means comprises means applying the full pressure of said supply to said actuating member when said motor is below said selected speed and disconnecting said pressure from said member when said motor exceeds said selected speed.

16. A speed governor as claimed in claim 15 wherein the response time of said valve means is substantially greater than that of said pressure applying means whereby said valve means is maintained at an intermediate position while said pressure applying means alternates between extreme positions.

17. A speed governor as claimed in claim 13 wherein means are provided to bias said valve means toward the closed position and wherein said pressure applying means applies said pressure to open said valve means only when said motor is running and is below the selected speed, whereby said valve means is closed when an overspeed signal is produced and when no speed signal is produced.

18. A speed governor as claimed in claim 17 wherein said pressure applying means comprises:

a chamber adjacent said actuating member;

means connecting said inlet pressure to said chamber;

means venting said chamber; and

means breaking the connection between said connecting means and said vent in response to an overspeed signal from said motor.

19. A speed governor as claimed in claim 18 wherein said connection-breaking means comprises a flexible diaphragm adjacent said chamber and arranged to move in response to said speed signal.

20. A speed governor as claim in claim 13 wherein said speed-sensing means comprises means for controlling a selected parameter of a fluid; said fluid being sealed from the air supply to said motor.

21. A speed governor as claimed in claim 20 wherein said speed-sensing means comprises means controlling the pressure of said fluid.

22. A speed governor as claimed in claim 13 wherein said speed-sensing means comprises means for controlling a selected parameter of a fluid; and wherein said governor includes a passage for obtaining fluid from said motor supply; and filter means in said passage for cleaning said fluid.

23. A speed governor as claimed in claim 13 wherein said speed-sensing means comprises compressing means driven by said motor for controlling the pressure of a fluid according to the speed of said motor.

24. A speed governor as claimed in claim 23 wherein means are provided to bias said valve means toward the closed position.

25. A speed governor as claimed in claim 24 wherein said speed-sensing means is sealed from said inlet air supply.

26. A portable air tool comprising:

a housing;

handle means affixed to said housing adapted to be grasped by an operator;

an air-powered rotary motor within said housing;

conduit means for delivering compressed air to said motor;

a tool element driven by said motor and arranged to be applied to a workpiece by the operator; and

fluidic speed governing means disposed in said housing for preventing overspeed of said tool, said governing means comprising:

governor value means disposed in said conduit for controlling the supply of air to said motor;

biassing means urging said governor valve to its closed position;

speed-sensing means mounted adjacent said motor and driven thereby to provide a speed signal dependent on the speed of said motor; and

actuator means responsive to said speed signal for controlling said governor valve;

said actuator means being arranged to release said governor valve upon occurrence of a speed signal in excess of a predetermined value whereby said biassing means closes said governor valve.

27. A portable air tool as claimed in claim 26 wherein said actuator means comprises a connection to said compressed air supply for applying supply pressure to operate said governor valve.

28. A portable air tool as claimed in claim 26 wherein said governing means comprises biasing means for closing said governor valve in the absence of a normal speed indication from said speed-sensing means.

29. A portable air tool as claimed in claim 26 wherein said governing means comprises a fluidic system and wherein said tool includes means sealing said system from said motor air supply.

30. A portable air tool as claimed in claim 26 wherein said speed governing means comprises a fluidic system and wherein said speed-sensing means comprises means for pressurizing the fluid in said system.

31. A portable air tool as claimed in claim 26 wherein:

said motor includes a shaft having an extension within said housing; and

said speed-sensing means comprises a rotary device mounted on said extension.

32. A portable air tool as claimed in claim 31 wherein said rotary device comprises a compressor.

33. A portable air tool as claimed in claim 26 wherein:

said governor valve means comprises a valve member in said conduit having a valve stem extending from said member out of said conduit; and wherein:

said actuator means comprises an actuating piston attached to said stem;

a chamber partially defined by said piston;

means for conducting the supply pressure to said chamber;

and

means controlled by said speed signal for connecting said chamber to a vent.

34. A portable air tool as claimed in claim 33 wherein said means for conducting the supply pressure to said chamber comprises a low-capacity passage through said valve stem.

35. A portable air tool as claimed in claim 33 wherein said controlled vent connection means comprises a vented chamber, a passage from said piston chamber to said vented chamber and flexible closure means for said passage, said closure means being controlled by said speed signal.

36. A portable air tool as claimed inclaim 35 wherein said speed sensing means comprises a compressor driven by said motor, and said flexible closure means is closed by the output of said compressor.

37. A portable air tool as claimed in claim 36 wherein said governing means includes means for disconnecting said compressor output from said flexible means if the motor speed exceeds a selected value.