US2017287A - Distributing valve for pneumatic tools - Google Patents

Description

0%. E5, 1935. M NELL 2,917,287

DISTRIBUTING VALVE FOR PNEUMATIC TOOLS Filed May '7, 1935 TILE? E1 INVENTOR ATTORNEY Patented Oct. 15, 1935 UNITED STATES PATENT. OFFICE DISTRIBUTING VALVE FOR PNEUMATIC TOOLS Application May 7, 1935, Serial No. 20,122

2 Claims.

This invention relates to automatic distributing valve mechanism for pneumatic hammer tools, and particularly to valves arranged to be moved in one direction by live pressure fluid and in the opposite direction by fluid compressed by the piston.

Among the objects are to secure maximum number of blows per minute, maximum intensity of blow and minimum motive fluid consumption.

In the case of valves arranged to be tripped by motive fluid under control of a relatively light free moving piston, it is very essential that the valve begin moving in exact timed relation to the piston, complete its movement from one position to the other in the very least possible time, and yet be forcibly held in each of its extreme positions. It can be shown mathematically that the variation of piston velocity from reversal tocompletion of its stroke is far greater in the case of a free moving relatively light piston than in the case of a piston imparting its power to a crankshaft and flywheel. Furthermore the maximum instantaneous velocity occurs just at the time that the valve is caused to trip. Again, in

the type of fluid motor having a central exhaust uncovered by the piston, and on the forward or working stroke, admitting pressure fluid from the cylinder chamber through a passageway to a valve tripping area, the valve must be completely tripped in an exceedingly short interval of time,

as otherwise this passageway is put into communication with the central exhaust, allowing the fluid pressure therein and on the valve tripping area to drop abruptly and so interfere with the rapidity of the valve movement. This is particularly true of the herein described type of fluid motor, wherein the valve is placed in back of the rear cylinder chamber, thereby necessarily elongating the trip passageway and hence increasing the time required for building up suflicient fluid pressure on the valve tripping area.

In this art there are no practicable means when in operation of indicating relative valve and piston positions with diagrams of actual fluid pressures in cylinder chambers. Consequently, what appears to be a more or less obvious development after disclosure, in reality requires a great deal of experimentation and inventive effort.

5 One embodiment of the invention, in which the foregoing objects are attained and the abovementioned problems overcome, is shown in the accompanying drawing in which:

Fig. 1 is a fragmentary longitudinal sectional 55 view of a rock drill having a fluid pressure motor of the hammer piston type, the piston being shown at the start of the forward stroke; and

Fig. 2 is a similar view indicating the positions of the valve and piston when the latter is at the start of its return stroke. 5

In the illustrative embodiment of the invention, the drill comprises a cylinder '4, providing a cylinder chamber 5 in which reciprocates a hammer piston 6, the machine being provided with conventional rotation mechanism for stepping piston 10 6 around during a part of its reciprocating movement. Such mechanism may comprise a rifle nut (not shown) mounted in a recess in the piston to receive a rifle bar 8. A ratchet head 9 on the rifle bar cooperates in the usual manner with a ratchet 15 ring Ill screwed into the backhead l l which is connected to the cylinder 4.

The cylinder has a counterbore l3 which re-. ceives a valve chest I 4 and a portion of the backhead H. The valve chest is composed of two 20 parts, namely a valve case I 5 and a valve cap H5. The valve cap has an annular projection or sleeve l1, forming a bearing for the rifie bar 8 and surrounded by the valve case l5. The valve case has two external annular grooves 13 and [9, the for- 25 mer exhausting through ports :29 to atmosphere, and the latter being connected by passageway El to the front end of the cylinder chamber 5. The interior of the valve case I5 is recessed to provide an annular chamber 22, an annular exhaust 30 groove 23 and an annular inlet 'groovez l. Groove 23 is constantly connected to exhaust through ports '25 and external :groove 18, while groove 24 has connections, such as passages 21, leading to an annular distributing chamber 29 in the backhead H for supplying live motive fluid to said inlet groove. The front end of the projection I1 is so positioned as to provide an annular passageway 30 between said projection and the front end of the valve case l5, said passageway being adapted at 40 times to connect the inlet groove 24 with the rear end of the cylinder chamber '5.

An annular distributing valve 32 surrounds the projection l7 and is adapted to slide back and forth thereon. The internal surface of the valve comprises portions 32a and 32b of difierent diameters, separated by an annular shoulder 33. The projection H is of correspondingly stepped formation to fit both portions 32a and 32b and provides an annular groove 34 of variable length between the projection I1 and the valve 32. The groove 34 communicates with the shoulder 33 and is connected by passages 35 with annular distributing chamber 29. The latter is supplied with pressure fluid, such as compressed air, by a under constant pressure.

between the live air groove 24 and the rear cylinder chamber.

The valve has an exterior annular groove 39 cooperating with a series of radial ports 40 in the valve case, which ports register with. the valve chest external groove 19. 5 The valve groove 39 controls the flow of air to and from the front end of the cylinder chamber by alternately connecting groove I9 with live air groove 24 and exhaust groove 23.

At or near the rear end of the valve is a flange 42 situated in the chamber 22. The front face of the flange is connected to exhaust through ports 43 while thefrear face is subjected to air pressure under control of the piston, which is transmitted through elongated passageway 45.

The operation of the device will now be described. Assume that the parts are as shown in Fig. 1 with the piston B and. valve 32 in their rearward positions. Live motive fluid, such as compressed air, admitted by the throttle valve 31 passes through passage. 36 to the rear annular distributing chamber 29, thence through passages 21 to valve case internal groove 24 and then through annular opening 30 to the rear cylinder chamber, causing the piston to be moved forwardly.

At the time that the piston starts its forward movement, live air pressure acting on the internal shoulder 33, and tending to move thevalve forward, is ineffective to overcome pressure against the larger area on the front face 41 of the valve which holds thevalve in its rearward position. At this time, fluid from the front cylinder chamber passes out to atmosphere through exhaust port 48. After the piston in its forward travel has closed the exhaust port 48, the air in the front cylinder chamber 5 is forced out through passageways 2 I, external valve chest groove I9, radial ports 40, around external valve groove 39 to internal valve chest groove 23, through a series of passages 25 to external valve chest groove l8 and then through ports 20 to atmosphere.

During its forward travel, piston B uncovers passageway 45 thereby allowing motive fluid from the rear cylinder chamber to enter said passageway and pass to the annular chamber 22 in the valve chest l4, where it acts on the rear face of the valve flange 42. The combined area of the rear face of the flange 42 and of the shoulder 33 is considerably greater than the front area 4! and consequently the valve trips'forward to the Fig. 2 position. Passage 49, leading to atmosphere through groove l8 and port 20, is small relative to passage 45 but is of sufficient diameter to vent fluid from the chamber 22 before the opposite compression stroke of the valve takes place.

After the valve has been tripped to the Fig. 2 position, live air is supplied by the internal valve chest groove 24 around valve groove 39 through radial ports 40 to the annular chamber l9 and longitudinal passageways 2| to force the piston rearwardly. In its rearward travel, piston 6 will cover'main exhaust 48 and, after cutting off passageways 45, will compress the residue fluidin the rear end of the cylinder chamber 5. The

shoulder 33 and trip the valve to the Fig. 1 posi- 5 tion, thus completing the cycle of operation.

An important, feature of the above described construction resides in the arrangement of the internal shoulder 33 and the connections including passages 35 and live air chamber 29 for main- 10 taining a constant pressure on said shoulder. It has been found by extensive experiment that one of the defects of prior valve constructions which employed a holding area acting in opposition to a compression area resided in the fact that the 15 holding area secured its fluid pressure from a source where motive fluid fluctuations are great.

To illustrate the effect of a variable holding pressure such as exists in prior devices, let it be assumed, for example, that the holding area pres- 20 sure fluid is taken from the vicinity of the annular valve chest groove nearest the cylinder chamber, corresponding to groove 24 in the present disclosure. During the forward stroke of the piston, pressure in annular groove 24 is at a minimum 25 value due to the flow of air through annular open- 1 ing 30 to the cylinder chamber'5. A corresponding reduction in pressure would take place on the holding area 33, thereby preventing rapid shifting.

On the return stroke, the pressure in the annular 30.

in the opposite direction. 40..

It will be observed that the internal shoulder 33 on the valve is situated slightly rearwardly of the annular external groove 39 so that the groove 39 and the counterbore 32a do not overlap. As a result of this arrangement it is possible to reduce the weight of the valve to a minimum without sacrificing strength.

From the above description it will be seen that the invention takes advantage of the discovery that by utilizing a fluid pressure source where fluctuations are a minimum, the holding area opposed to the compression tripping area can be made relatively smaller and, supplemented by the uniform pressure on this holding area, the other valve surfaces can be better proportioned so as 55 to produce more uniform results and quicker and more positive valve movements. Furthermore, with a given space and valve areas, the total valve weight is reduced and there is a corresponding increase in the ratio of tripping areas to weight 60 in the particular valve design illustrated herein.

What is claimed is:

1. In a fluid pressure motor, a cylinder having a reciprocable piston therein and providing a front cylinder chamber and a rear cylinder cham- 65 her, a valve chest supported by the cylinder and situated in the rear of the rear cylinder chamber, said valve chest comprising a valve case and a valve cap acting as a closure for the rear end of the case, said valve cap having an extension 70' passages arranged to supply pressure fluid to said front and rear cylinder chambers and exhaust fluid from said front cylinder chamber, said cylinder having an atmospheric exhaust port located centrally between said cylinder chambers, said valve having a first area in communication with said rear cylinder chamber and intermittently exposed to pressure fluid and air compressed by rearward movement of said piston for the purpose of moving said valve rearwardly, a second area opposed to said first area and of larger extent and intermittently exposed to pressure fluid under control of said piston for the purpose of moving said valve forwardly, a third area of less extent than and opposed to said first area and continuously exposed to live pressure fluid under constant pressure for the purpose of assisting in the forward movement of the valve and holding it in its forward position when fluid pressure on the second area becomes relatively low, said valve having a flange on its rearward end, the rear face of which provides said second area, said valve having a counterbore at its rearward end which cooperates with the extension on the valve chest cap to form a chamber adjacent said third area, said valve having an external annular groove on its forward end so arranged that said groove is located wholly forwardly and said counterbore wholly rearwardly of a plane normal to the longitudinal axis of said valve for the purpose of decreasing the weight of said valve without decreasing its thinnest section and consequently its relative strength between the said counterbore and groove.

2. In a fluid pressure motor, a cylinder having a reciprocable piston therein and providing a front cylinder chamber and a rear cylinder chamber, a valve chest supported by the cylinder and situated in the rear of the rear cylinder chamber, said valve chest comprising a valve case and a valve cap acting as a closure for the rear end of the case, said valve cap having an extension projecting within the valve case, a fluid pressure distributing chamber located rearwardly of the valve chest, a tubular valve within said valve chest, said valve encircling the extension and having a sliding fit thereon and being adapted to move forwardly and rearwardly, passages arranged to supply pressure fluid to said front 5 and rear cylinder chambers and exhaust fluid from said front cylinder chamber, said cylinder having an atmospheric exhaust port located centrally between said cylinder chambers, said valve having a first area in communication with said rear cylinder chamber and intermittently exposed to pressure fluid and air compressed by rearward movement of said piston for the purpose of moving said valve rearwardly, a second area opposed to said first area and of larger extent and intermittently exposed to pressure fluid under control of said piston for the purpose of moving said valve forwardly, a third area of less extent than and opposed to said first area and continuously exposed to live pressure fluid under constant pressure for the purpose of assisting in the forward movement of the valve and holding it in its forward position when fluid pressure on the second area becomes relatively low, said valve having a flange on its rearward end, the rear face of which provides said second area, said valve having a counterbore at its rearward end which cooperates with the extension on the valve chest cap to form a chamber adjacent to said third area, said last-mentioned chamber being connected by passages in the valve cap leading directly to the fluid pressure distributing chamber in the rear of the valve chest, said valve having an external annular groove on its forward end so arranged that said groove is located groove.

GUSTAVE M. NELL.

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