US2925089A

US2925089A - Pneumatic tool

Info

Publication number: US2925089A
Application number: US562377A
Authority: US
Inventors: Robert M Conklin; Albert M Rockwood; James W Smelker; Linsker Eugene
Original assignee: BUCKEYE TOOLS CORP
Current assignee: BUCKEYE TOOLS Corp
Priority date: 1956-01-31
Filing date: 1956-01-31
Publication date: 1960-02-16
Anticipated expiration: 1977-02-16

Description

United States Patent PNEUMATIC TOOL Robert M. Conklin, Albert M. Rockwood, and James W. Smelker, Columbus, and Eugene Linsker, Dayton, Ohio, assignors, by direct and mesne assignments, to Buckeyeogiools Corporation, Dayton, Ohio, a corporation 0 0 Application January 31, 1956, Serial No. 562,377

3 Claims. (Cl. 137-33) This invention relates to pneumatically driven power tools and, more particularly, to a speed responsive governing valve for controlling the admission of driving air in power tools having a pneumatic motor.

In pneumatic driven rotary power tools, it is important to provide a speed responsive governing device or throttle valve for the air inlet to provide protection against pos sible damage of the tool due to overspeeding of the motor with fluctuations in load, to assure idling at a safe speed, and to limit air consumption during idling in use. If a socalled fiy-ball or centrifugal governor is provided as the speed responsive device for actuating a throttle valve to control the air input to the pneumatic motor, the device must be sufficiently large and with sufficient fiy-ball weight to close the throttling valve against such opposed forces as spring means biasing the throttling valve open andany components of force against the valve caused by the inrush of driving air to be throttled.

If a throttling valve is provided in which the inrushing air impinges directly against the valve itself tending to force the valve open, greater force is needed from the speed responsive device to close the valve. Also, in such a construction, the sensitivity of the valve may be reduced and, if the inlet air flow impinges directly on. the closing valve, a substantial reduction of output horsepower may result at speeds approaching the governed speed. Furthermore, if the inlet air to be throttled impinges directly upon the valve itself, pneumatic forces caused thereby and acting to urge the valve open must be overcome by the speed responsive mechanism before theair can be throttled, and such pneumatic forces, being a function of inlet pressure, also may afiect the speed range in which the governor will operate.

According to this invention, however, a speed responsive governing valve is provided to throttle the inlet air flow into the pneumatic motor of a'pneumatically driven rotary tool so that a predetermined operating speedwill be effectively maintained despite fluctuations in driving air pressure or sudden relaxation of the load on the tool. Such structure includes a sleeve type throttling valve disposed with respect to the air inlet so that the inrushing driving air does not impinge directly upon the valve in a manner to oppose closing the valve, yet, since the valve sleeve is correlated in size and positioning with respect to the air inlet, a continuously open and unobstructed air admission control port is maintained. With a structure according to this invention a conveniently compact speed responsive throttling or governing valve is provided with enhanced sensitivity and is substantially independent of air inlet pressures in a manner to provide properly controlled output horsepower maintained at speeds closely appreaching the predetermined governed speed. 3

It is one object of this invention to provide in a pneumatic tool ofthe character described a speed responsive governing valve for throttling the driving air input at a predetermined speed with a sleeve type valveoperating with respect to the air inlet to vary the area of a continuously open and unobstructed air inlet control port to maintain such a predetermined speed effectively under changes in load and pressure of the air supply.

A further object of this invention is to provide in a tool of the character described a sleeve-type throttling valve disposed and correlated with an air inlet so as to provide throttling through a continuous annular control port and yet avoid the impinging of inrushing air on the valve memher in a manner to oppose closing of the valve.

Another object of this invention is to provide in a device of the character described a speed responsive governing or throttling valve which may be compactly constructed and mounted in the device on a rotating shaft therein yet without rotating engagement of the valve members with stationary parts of the device such as might cause wear and inaccuracy of the valve.

Still another object of this invention is to provide in a device of the character described a speed responsive governing valve for throttling input air into the device by varying the size of a single input control port which is maintained at all times continuously open and unobstructed for uninterrupted air fiow therethrough.

Other objects and advantages of this invention will be apparent from the following description, the accompanying drawing and the appended claims.

in the drawings,

Fig. l is a view partly in section of a pneumatic too of the character described having the invention applied thereto;

Fig. 2 is a sectional view on an enlarged scale of a speed responsive governing or throttling device embodying the invention; I

Fig. 3 is a view'partly in section along the line 3-3 of Fig. 2;

Fig. 4 is a view partly in section alongthe line 4 -4 of Fig. 2; and v i Fig. 5 is a transverse section along the line 5-5.

In the drawing, in which like reference characters refer to like parts throughout the several views thereof, a pneumatically driven grinding tool is shown generally in Fig. 1 as having a handle member 10 at one end of which is a fitting 11 to receive an air hose (not shown) to provide driving air to the tool. The air enters the tool through fitting 11, a filter or screen 12, and an air passage 13 where droplets of lubricating oil are entrained in :the air from Wick 14 fed from a lubricating oil reservoir 15 in handle 10. The admission of air is controlled by an off on valve indicated generally at 16 and operated by a trigger member 17. Valve 16 admits driving air through a bushing or sleeve 19, having air inlet passage 20 and a discharge end 21, into chamber 22. From chamber- 22 the driving air passes through admission passages 31 through plate 23 and cylinder 32 to impinge upon the vanes 24 of rotor 25 mounted on main shaft 26 within the eccentric bore 33 of cylinder 32 and coupled to shaft 26 as by keys 27, thereby rotatably driving rotor 25 and shaft 26 in the well-known manner of operationbf pneuan abrasive grinding wheel or the like, also in knowni ll m. in.

sleeve, 45 respectively, :thereby .urging-sleeve 45 '20terminates Wi'thits discharge en having a "free and open cross section surrounded by a flange surface substantially normal to the direction of flow of the air through passage 20 as indicated by the arrow in Fig. 2. Spaced from the discharge end 21 of air inlet passage 20 and coaxially aligned therewith is a spindle coupled to one end of main shaft 26 by the threaded member 36 and mounted ffor rotation with shaft 26 in suitable, bearings 37. At oneenjd of spindle 35 is mounted 'for rotation therewith a centrifugally operatedspeed responsive device including cross bars 40 afiixed to spindle 35 and'carrying at opposite ends thereof weights or fly- .balls 41, each of whichis pivotally mounted between cross bars 40 by pins '42.

' 'Also mounted on. spindle 35 ,butfree to-slide axially with respect thereto is valve sleeve '45 having a throttling end "46 spaced from arid-aligned with the discharge end '21 of air inlet passage 20. "The inner diameter of valve sleeve is preferably substantially the same or at least as'large as the inner-diameter of discharge end 21 of airinletpassage20,,and end 46 of valve sleeve 45 defines withfflange surfaces 30 ofinlet passage 21 an annplar continuously open control port 50 through which anguninterrupted ,flow of. air is maintained from air inlet passage 20 intochamber 22 and thence to the ,.air notor 24, 25, etc. during operation of the tool.

' Twoannulan'slots '55 areprovidedin valve sleeve 45 intermediate .the ends thereof, and a retainingring 56 is provided around valve sleeve'45. Retaining ring 56 is axiallypositioned on spindle 35 by annular keys 57 received in keyways 5.8 in spindle 35 through slots in sleeve 45. Adjusting shims 59 of various thicknesses mayQbe provided-between-keys 57 and retaining ring 56 for accurately adjusting the positioning of 'ring 56 along ispindle 35 and of the preload on spring 61 referredto beow. t

' The end of vvalve sleeve .45 opposite to throttlingend '46 is provided with a flange or shoulder portion 60 of enlarged diametenr anda. compression spring 61 is mounted around .valv'e sleeve 45 with the opposite ends of spring 61 abutting against retaining ring 56 and flange60'of I axially along spindle 35 away from discharge end 21 of air inlet passage 20.(i.e., to the.,r ight in Fig. 2). The arrangement of keys 57 and retaining ring 56 also provides for readily and quicklydisassemblingand/or replacing the entireassembly of parts on "spindle 35 when repairyreplacement oraadjustment of the governing deviceis desired, as wellas maintaining ring 56 centered about sleeve 45 to avoid ,friction or ,binding therebetween.

that, when apredetermined desired maximumspeed of rotation "is reached, -the centrifugal force"ten'ding to cause fiy-balls 41 to fly radially outwardly will have moved arms 65 thereof sufiiciently to force sleeve 45 enough to the left in Fig. 2 to diminish the size of'control port 50 and throttle the inlet air admitted to vanes 24 of rotor 25 so that the speed of rotation will not increase beyond the predetermined maximum desired. Conversely, as the speed of rotation decreases, the lessened centrifugal force acting uponifly-balls 41 permits spring 61 to force sleeve .45 toward the right.in Fig. 2, thereby enlarging the annular area of control port 50 to admit into chamber zz, and thence to vanes 24, a greater driving force of air.

As will 'be understood from the foregoing, theinrushingair through passage 20 'does'not impinge directly upon the throttling valve, but is directed against the end'66 of spindle :35 to be deflected, radially outwardly through control port 50 into chamber 22. .Since control port 50 is open and unobstructedthroughout its entire annular area, subdivision of the airflow radially deflected from the rotating end 66 of spindle 35 is avoided, as compared with ,a situation where the 'air flow, after-having been deflected from the rotatingspindle, is interrupted by a plurality of individual radially positioned ports.

Furthermore the force of air entering through passage 20 does not impinge directly upon movable parts of the throttling valve in a manner or direction substantially opposing closing of the valve thereby avoiding dynamic pneumatic effects from this cause .from the'inflowing air from the governing-system. Also adverse static pneumatic eifectsfrom pressure differences inside and'outside sleeve 45 are minimized by the reduced valve surface area 46. Thus, a construction embodying the invention avoids not only loss of available horsepower from interrupting air flow through a number oftbafiled control ports and fromhaving incoming air flow opposetthe clos- ,;-As will be understoodfrom ,theforegoing, asthe incoming. driving :-air causes rotor'25 and shaft 26 to; rotate by impinging-upon'the vanes 24, spindle and Haassociated ,parts also rotate. :As the speed of rotation, increases, centrifugal 'force causes fiy-balls 41 to "pivot vradially outwardly about pins 42, thereby causing arms ,65onfiy-balls 41 to bear against'flange .on sleeve 45 ;and .force it toward the leftin Fig. 2 against the con trary biasing ,action of;spring :61,-thereby diminishing the annular-area;of;control port50 between throttling end 46 of :sleeve 45 and flange surfaces 30 of'the'discharge end 21 of airinle't passage 20. The limits of axial slidinggmovement'of sleeve 45 alongspindle 35 toward and away from air inlet passage 20 are defined by the axial width of slots:55 through which keys 57 engage keyways spring 61 which must be overcome'by centrifugal force (and, hence, the speed-at which the governing device will operate) maybe-accurately 'adjustedby varying the thickness "of shims '59 between keys 57 and retainingring 56. -The-weight and dimensioning of fly-balls 41 as wellas the off-eenteriplacement of pins'42 with respect thereto, are correlated =-with the '-length of the cross bars 40 and the strength and adjustment of compr ssi n spring'fl so 58 in spindle F35, and thebiasing force of compression ,ing of a throttling valve by the Lairwdriven motor,.butalso the accuracy and sensitivityof the throttling valve is:- enhanced and madesubstantiallyindependent of'inlet 'air pressure,-and, to agreater extent than -heretofore, ofboth the ,static and dynamic pneumatic effects of prior constructions, and asmore compact arrangement is provided.

Also, rotating bearing engagement between stationary and'rotating-partsof the throttling mechanism is avoided.

While the vform of apparatus herein described constitutes :a, preferred embodiment of vthe invention, it'is to be understood that the invention'is not limited ftothis precise formofapparatugand that changesmaybemade therein without departing from the scope of the invention which is'defined in theappended claims.

.1. Incombination-with a pressure fluid driven'motor having a casing and a fluid driven rotor mounted.for.rotation insaid casingza .control chamber in'said casing having 1 connections to supply motive 'fluid to said rotor, means for admittingfluid into said chamber including an inlet'nozzle having a throughpassa'ge coaxially withthe axis of rotation .of saidirotor, a spindle inr'said chamber mounted to:rotate with said rotor and terminating'at one about said one end o f said spindle, a biasing=spring sur-,

rounding s'aid"sleeve and acting thereon to urge said sleeveno'rma'lly away fromsai'd nozzle "for fully opening said annularfpassage, fly=weights pivotally mounted on said 'sp'indleand acting'up'on'saidsleeve in opposition to. said spring for restrigting said annular passagewhen the rotational speed of said motor attains a predetermined limit, and means for mounting said fly-weights radially externally of both said valve sleeve and said biasing spring. 2. Apparatus as defined in claim 1 including means limiting movement of said valve sleeve to prevent contact thereof with said nozzle and other stationary parts within said casing.

3. Apparatus as defined in claim 1 including adjustable means coacting between said valve sleeve and said biasing References Cited in the file of this patent must be overcome by said fiy-weights.

UNITED STATES PATENTS Pottle May 20, 1879 Van Sittert Mar. 7, 1939 Mitchell July 2, 1946 Sturrock Oct. 18, 1949 Jones Sept. 26, 1950 Karlen Apr. 6, 1954 Palmenberg May 28, 1957