US2345974A - Power transmission - Google Patents

Description

April 4, 11944..'V F. fr. HARRINGTON 2,345,974

POWER TRANSMISSION Filed oct, 11, 19'41 u l 727 y l v 28 l FERRIS T. HARRINGTON Patented Apr. 4, 1944 A POWER TRANSMISSIGN Ferris T. Harrington, Detroit, Mich., assignor to Vickers Incorporated,v Detroit, Mich., a corporation o! Michigan Application october 11,l 1941, serial 10,414,555

(ci. so-szi 4 Claims.

This invention relates to power transmissions, particularly to those of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor. l

The invention is more particularly concerned with a power transmission system of the type incorporating what is termed a metering-in, flow rate control valve comprising an adjustable throttle together with a pressure responsive compensating valve for maintaining a constant pressure .drop through the throttle. Valves of this conduit I4, for withdrawing fluid from a tank i6, and a delivery conduit I8. A relief valve 28,.

on pump I0. is adapted to pass uid to tank I6 character are customarily used in power transmission systems for producing 'a reduced feed rate' of a machine tool slide or similar device which is hydraulically operated.

It has been found that, where the flow rate regulating valve is placed on the inlet sideof the circuit, some difiiculty has been experienced at the time the slide is started into a feeding movement from rest. This diiiculty lies in the inability of the compensated ow control valve to immediately assume its normal regulating position. During the time interval that this ref of the 'cutting tool. -This 'difficulty has been avoided in the past only by continued caution on the part of the operator to remember that when stopping the slide in the middle of a cut lie must first back the tool away from the work .slightly before resuming the feeding movement.l

It is an Aobject of the present invention to provide an improved circuit which overcomes this diillculty.

A further object is to provide in a power transmission system of this character a'bypass valve ahead of the flow rate controlling valve which is so controlled as to maintain flow through the now rate'regulating valve even while the motor is stopped and thus cause the flow rate regulating valve to maintain its normal regulating position. l

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the .accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing:

The single figure is a diagrammatic viewf-of a power transmission system incorporating a preferred form of the present invention.

There is indicated at I8 a pump adapted to 'be driven by a suitable prime mover such as an through a conduit 22 whenevera predetermined maximum pressure is exceeded in the pump.

The conduit I8 extends through a bypass valve 24 and a hydrostatic ow control valve 26 to a six-way directional valve 28 where it opens into a valve bore 30 through an annular pressure port 32. vSpaced along bore 30 to the right of port 32 are three annular ports 34, 3B and 38, while to the left of port 32 are corresponding ports 48, 42 and 44. A valve spool-46 mounted in bore 30,'and slidable between five positions, has 'formed thereon three lands 41, 48 and 50 for controlling communication between the various ports. When in the position shown, lands 41, 48 and 58 blockports 42, 32 and 36, respectively. However, the pressure port 32 is open to the ports 38 and 44. which constitute tank ports. through passages 52 in valve spool 46. lA hand lever 54 is connected to the left end of'spool 48 for shifting it between its ve positions. An end cap 56, on the-right end of valve 28, h as therein a spring-pressed detent 58 for releasably retain' ing spool 46 in each of three centermost positions. The right end of spool 48 carries a spring device 60, enclosed by end cap 56, which is adapted to shift the valve spool from either extreme position to the next adjacent position upon release of lever 54.

The ports 34 and 40 of valve 28 constitute cylinder ports and are connected by conduits 62 and 64 to the head and rod ends, respectively, of a cylinder 68. A piston 88 reciprocably mounted in cylinder 66 has a rod 18 ,which may be operatively connected to the worlicarrying slide of a machine tool. The two tank ports 38 and 44 are connected by a conduit 12 to tank I 6;

The purpose of flow control valve 28 is toA provide a constant rate of flow through conduit I8 available for cylinder 66 when it is desired to operate piston 68 at a slow feeding rate. Valve 26 includes an adjustable throttle 14 and a hydrostatic valve 16. A control piston 18 of the latter is mounted in a cylinder 88 from which two passages 82 and 84 extend, one from each end, to opposite sides of throttle 14. A light spring 85 tends to move valve 16 to its open po-l sition. Thus vit will be seen that hydrostatic valve 18 regulates fluid iiow to throttle 14 in accordance with the pressure drop across the port 88. A valve spool 98, slidable in bore 86, is adapted to open or close port 88 to an annular bypass port 92 spaced to theleft of port 68. A pilot piston 94, smaller in diameter than spool 98 and mountedin a bore 96 in an end cap 98 on the right end of valve 24, is in axial alignment with and abuts spool 98. Piston 94 is subjected to fluid pressure from port 88 through a passage |88 extending therefrom to bore 96. The left end of bore 66 is also in communication with port'86 but through a restricted passage |82. A tank port |84 opening into bore 86 near the leftend thereof is opened when spool 98 is in its righthand position, as shown, and blocked when shifted to the left. Port |84 is connected to tank I6 through a conduit I 86l and a resiste ance valve |88 which is adapted to open only after a predetermined low pressure is exceeded at sure diiferential between passages 82 and 84, to

' ltle 14.

port |84. The bypass port 92 is connected by a l conduit |I8 to that portion of conduit I8 between ow control valve 26 and directional valve 28. An end cap ||2 of valve 24 provides a fluid connection for the left end of bore 86 from which a conduit |I4 extends to the ports 36 and 42 of valve 28. A check valve ||3 may be interposed in conduit ||8 to prevent any back flow which might occur during feed by leakage at valve 24.

A drain conduit |I6.is provided for throttle 14 of, valve 26 which connects to the tank conduit 12. 'I'he right end of bore 86 of valve 24 is open to'tank through a conduit ||8 to insure free shifting of spool 98.

In operation, with the parts in the positions shown and thermotor I2 driving pump I8, fluid is withdrawn from tank I6 through conduit -I4 and delivered by conduit I8 to the pressure port 32 of directional valve 26. From there the uid is passed to tank I6 through passages 52 in valve spool 46, ports 38 and 44 and conduit 12.

Fluid in port 88 of valve 24 bleeds through restricted passage |82 toV the left end of bore 86 where it acts over the full end area of spool 98. Passage |88 directs fluid from port 88 tothe small bore 96 where it acts on piston 94. The end area of spool 98, however, is greater than that of piston 94 so valve spool 98 will be held to the right, as shown. Fluid in the left end of bore 86 cannot escape through connection ||2 and conduit ||4 as the latter is blocked at ports 36 and 42 of valve 28 by lands 58 and 41 nor can iiuid escape to tank in suilicient quantity through port |84.and conduit |86, because of resistance valve |88, to permit spool 98 to be shifted to the left by pilot piston 94.

It will be noted that the resistance valve |86 is not necessary to maintain the valve 24 closed at this time since, if it were not present, then the fluid bleeding into the left end of bore 66 would escape to tank freely through port |84. 'Ihis will permit spool- 98 to shift to the left sufficiently to almost close port |84 and thus build up pressure on the left end of spool 98 and prevent it from moving farther to the left. In this way the spool 98 may be held just slightly away from its righthand position without, however, opening up port 92.

Accordingly, the bypass port 92 is blocked by spool 98| and the pump delivery must be directed to pressure port 32 of yvalve 26 through ow control valve 26. Anyexcess over that which the ow control'will pass is bypassed to tank through the relief valve 28.

The hydrostatic valve 16 of valve 28 is under maintain a constant rate of flow through throt- Thus, it will be seen that, even though the machine is at rest,piluid is metered to the pressure port 32, and the'hydrostatic valve 16 is maintained in regulating position as distinguished from its wide-open position which it assumes when flow through the valve 26 as a whole is stopped.

' To perform a feeding stroke to the left, the lever 54 of valve 28 is moved to its feed left position to shift spool 46 to the left. Land 48 opens port 32 to cylinder port 34 and directs the metered ilow from valve 26 through conduit 62 to the head end of cylinder 66 causing piston 68 and rod 18 to move to the left at a feed rate to perform the work. When spool 46 was shifted,

Iland 41 opened port 42 to cylinder port 48. This opens a path for uid exhausting from the rod end of'cylinder 66 through conduit 64, valve 28, conduit II4 and connection 2 to the left end of bore 86 in valve 24. From there the exhaust iuid passes through port |84, conduit |86 and4 resistance valve |88 to tank I6. Valve |86 lmaintains a low back pressure in bore 86 to hold valve spool 98 to the right. The restricted passage |82 bleeds a small amount of fluid from port 88 to supplement the cylinder exhaust fluid for holding spool 98 in this position.

Thus, it will be seen that piston 66 moves to the left at a constant feed rate, as determined by the setting of throttle 14, regardless of variations in resistance offered by the work, because of the constant pressure drop held by hydrostatic valve 16 across throttle 14. It will also be noted that the rate of flow from' valve 26 at this time is exactly the same as before valve 28 was shifted control of its piston 16, as effected by the presto start piston 68 on a feed stroke. Thus, there is no jumping ahead as the piston 18 is started into feed which would otherwise occur due to the momentary increased rate of flow which occurs whenever iiow is initiated through valve 26, and is due to the small but appreciable time interval required for valve 16 to move from its wide-open position to its regulating position.

` If, for any reason, it becomes necessary to stop the machine during any portion of a work stroke, the lever 54 is shifted to return spool 46 to the position shown in the 'drawing The resulting condition is the same as that rst described.

When it is desired to continue -the work stroke, lever 54 is again shifted to its `ufeed left position. The constantly available metered iiow from valve 26 will again be directed to the head end of cylinder. 66, and the piston 68 will resume its feed rate from the same point at which it was stopped without racing or jumping. The necessity of backing the work away from the cutting tool before restarting to prevent breakage of the latter is completely eliminated.

When the feed stroke to the left is completed, piston 68 may be returned to the right on another feed stroke. To accomplish this, lever 64 is moved to its feed right position which shifts spool 46 to the right causing land 48 to open port- 32 to'cylinder port 48, and land 58'to open port 36'to cylinder port 34. The operation is the same as when feeding to the left except thatl the metered flow from valve 26 is directed through' ports 32 and 48 and conduit 64 to the rod end i stroke, lever 64 'is moved to the right to its rapid return position. This shifts spool 46 to its extreme right position Where land 41 opens port 42 to port 44. The rest of the connections through valve 28 remain the same `as last described. In this position, exhaust uid from the head end of cylinder 66 passes through conduit 62, ports 34 and 36, conduit H4, ports 42 and 44 and conduit 'l2 directly to tank I6. As conduit H4 is connected to tank, pressure iluid in the left end of bore 86 of valve- 24'is exhausted. The restricted passage |02 merely bleeds off to tank a small amountl of fluid from port 88. Pressure in port 88 is transmitted through passage |60 to bore 96 causing pilot piston 94 to shift valve spool 90 to the left. Accordingly, port 88 is opened to port 92 and the pump delivery is bypassed around ilow control valve 25 through conduit H0, ports 32 and 40 of valve 28 andconduit 64 to the rod end of cylinder 66. With valve 26 bypassed, piston 68 will return to the right at full speed and there `stopped by returning lever 54 to the position shown in the drawing.

A rapid traverse movement to the left may be obtained in a similar manner by shifting the valve 28 to its extreme left-hand position. It will be noted that during'rapid movements in either direction, flow is maintained through flow control valve 26 since valve 24 maintains a preference, so to speak, for flow through valve 26. It is only the excess of the pump delivery over and Vbeyond, the amount accepted by valve 26, which is bypassed around the valve 26 through port 92 and conduit l i0. Whenever piston 68 is stopped, whether in feed or rapid return, valve spool 90 of valve 24 will be retained in or shifted to its righthand position'to direct the pump delivery through flow control valve 26. Thus it will be seen that the ing fluid to and from the motor for either direction of operation thereof at either of two different speeds and having a neutral position in which ow from the'source is bypassed around the motor, fluid supply and return conduits connecting the source to the motor with the directional valve therebetween, a flow rate control valve interposed in the supply conduit' for producing a governed flow rate therein to obtain one of said speeds and having a compensating valve therein of the type said bypass valve for maintaining it closed while the directional valve is in neutral position whereby flow is maintained through the rate control valve and the compensating valve is prevented from moving fully open.

3. In a hydraulic power transmission the combination of a pressure fluid source, a iiuid motor, a directional control valve for selectively directing fluid to and-from the motor for either direction of operation thereof at either of two different speeds and having a'neutral position in which flow from the source is bypassed around the motor, uid supply and return conduits connecting the source to the motor with the directional valve therebetween, a flow rate control valve interposed in the supply conduit for producing a governed flow rate therein to obtain' one of said speeds and having a compensating Valve therein' of the type which opens fully whenever the flow through the rate control valve is interrupted, a supply pressure responsive bypass valve ahead of the rate control valve and connected when open to conduct fluid around the rate control valve to obtain the other piston 68 may be started from any stopping point at a feed rate, regardless of its previous action, without racing or jumping.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms fluid to and from the motor for either directionof operation thereof and having a neutral position in which now from the source is bypassed around the motor, uid supply and return conduits connecting the source to the motor with the directional valve therebetween, a ow rate control 'valve interposed in the supply conduit for producing a governed flow rate therein and having a compensating valve therein of the type which opens fully whenever the ow through the rate control valve is interrupted, a supply pressure responsive bypass valve ahead of the rate control valve and connected 'when open to conduct iiuid around the rate control valve, and means associated with said bypass valve for maintaining it closedy while the directional valve is in neutral position whereby flow is maintained-through the rate control valve and the compensating valve is prevented from moving fully open.'

2. In a hydraulic power transmission thecombination of a pressure 4iiuid source, a fluid motor, a directional control valve for selectively directof said speeds, and means including a connectioni from the exhaust side of the motor during slow speed movement for maintaining said bypass valve closed against the tendency of the supply pressure to open the bypass valve during slow speed movement of the motor.

4. In a hydraulic power transmission the combination of a pressure iluid source, a fluid motor, a directional control valve for selectively directing fluid to and from the motor for either direcwhich opens fully Whenever the flow through the rate control valve is interrupted, a supply pressure responsive bypass valve ahead of the rate control valve and connected when open to con-

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