US2227814A - Control for hydraulic transmissions - Google Patents

Description

Jan. 7, 1941. R YL 2,227,814

CONTROL FOR HYDRAULIC TRANSMISSIONS Filed Oct. 10, 1938 2 Sheets-Sheet l 36 INVENTOR. HANsm M T YLE R BY WW ATTORNEY- Jan. 7, 1941. R YL I 2,227,814

CONTROL FOR HYDRAULIC TRANSMISSIONS Filed Oct. 10, 1938 2 Sheets-Sheet 2 INVENTOR- 59 HANSEIM TYLER BY W ATTORNEY.

Patented Jan. 7, 1941 CONTROL FOR HYDRAULIC TRANSMISSIONS Ransom Tyler, Greenfield, Wis., assignor to The oilgear Company, Milwaukee, Wis., a corporation of Wisconsin Application October 10, 1938, Serial No. 234,171

12 Claims.

This invention relates to controls for hydraulic transmissions of the type in which reversal of the motor is effected by reversing the pump discharge.

5 An object of the invention is to provide a con trol which is positive and precise in operation.

Another object is to provide a control which is operable from a remote point.

Other objects and advantages will appear from the following description of the controls shown schematically in the accompanying drawings in which the views are as follows:

Fig. 1 is a diagrammatic view showing a hydraulic transmission provided with a control in which the invention is embodied and which causes the transmission to be reversed in response to an element moved by the transmission reaching a predetermined point.

Fig. 2 is a vertical transverse section through the pump shown in Fig. 1.

Fig. 3-is a view showing on a larger scale a part of the pump control mechanism shown in Fig. 2.

Fig. 4 is a view showing a control valve in a position different from that shown in Fig. 1.

Fig. 5 is aview similar to Fig. l but showing a control which will cause the pump to be reversed in response to pump pressure exceeding a predetermined maximum.

FIGS. 1 To 3 The transmission shown in Fig. 1 includes a hydraulic motor, which has a piston l fitted in a stationary cylinder 2 and connected to a rod or ram 3, and a reversible pump 4 which is connected by channels and 6 to the opposite ends of cylinder 2.

Any suitable type of pump may be employed but, for the purpose of illustration, pump 4 has been shown as being of the rolling piston type which is f lly illustrated and described in Patent No. 2,074,068. It is deemed suflicient to state herein that pump 4 has its pistons and cylinders arranged radially in a cylinder barrel 1 which rotates upon a stationary valve shaft or pintle 8 having formed therein ports and passages through which liquid flows to and from the cylinders, that the outer ends of the pistons react against an annular reaction surface 9 which in practice is formed in a separate rotatable thrust member carried by a slide block ill but which has been shown as being formed in slide block lil, that pump 4 will discharge liquid in a direction and at a rate depending upon the direc- 55 tion and the distance the axis of reaction surface 9 is offset from the axis of cylinder barrel 1. and that slide block I0 is arranged in a casing H which permits it to be moved transversely of pintle 3 but prevents it from moving in any other direction. 5

Channels 5 and B are connected to pump 4 in communication with the passages formed in pintle 8 so that, if cylinder barrel 1 is rotated in a clockwise direction as viewed in Fig. 2, pump 4 will discharge liquid into channel 6. and have 10 liquid returned to it through channel 5 when slide block ill is shifted toward the right from its central position, and it will discharge liquid into channel 5 and have liquid returned to it through channel 6 when slide block I0 is shifted toward the left from its central position. When slide block I!) is in its central or neutral position, at which time reaction surface 9 is concentric with cylinder barrel 1, pump 4 is at zero stroke and no liquid will be delivered thereby.

In order to compensate for leakage losses and for the difference in volume delivered by pump 4 and the volume returned thereto from motor |2, pump 4 is provided with a reservoir I! for liquid and means are provided to permit liquid returned to the pump in excess of pump requirements to be discharged lntoreservoir l2 and, when the volume returned to the pump is less than pump requirements, to either permit the pump to draw the additional liquid required from reservoir l2 or to be supplied therefrom by a gear pump l5 which has been shown in Fig. 2 as a separate pump but which is ordinarily driven in unison with the main pump and arranged in the casing thereof according to the common practice.

As shown, communication between pump 4 and reservoir 12 is controlled by an automatic valve I6 having two spaced apart heads or pistons H and I8 arranged thereon and closely fitted in a bore l9 formed in a valve casing 20 which is arranged below slide block in and has a part thereof extending into the liquid in reservoir 12. Piston heads I! and I8 on valve I6 control communication between bore l9 and two channels 2i and 22 which connect the channels 5 and 6 with bore H at two points spaced from the opposite ends thereof. The extreme left end of bore 19 is connected by a channel 23 to channel 2| intermediate the ends thereof, and the so extreme right end of bore I8 is connected by a channel 24 to channel 22 intermediate the ends thereof.

That part of bore l9 between channels 2| and 2,2 communicates with a chamber 25 formed in the lower part of valve casing 28 and communicating with reservoir l2 through a check valve 26 which permits pump 4 to draw liquid freely from reservoir |2 but prevents liquid from being expelled from chamber 25 except through a low pressure relief valve 21 having its inlet connected to chamber 25.

Gear pump l5 draws liquid from reservoir l2 and discharges it into a low pressure supply channel 28 having connected thereto the inlet of a relief valve 29 the outlet of which is connected to chamber 25 by a channel 30.

A part of the liquid discharged by gear pump I5 is used for control purposes, as will presently appear, and the remainder is exhausted through relief valve 29 into chamber 25. The liquid discharged by gear pump |5 into chamber 25 in excess of the volume required to supercharge pump 4 is exhausted through relief valve 21 so that, except when pump 4 is drawing liquid from reservoir 2 through check valve 26, gear pump I5 is enabled to maintain in chamber 25 a pressure equal to the resistance of relief valve 21 and to maintain in channel 28 a pressure equal to the sum of the resistances of relief valves 21 and 29.

The arrangement is such that, when pump 4 starts to deliver liquid into channel 5, pressure extends from channel 5 through channels 2| and 23 to the left end of bore l9 and shifts valve l6 toward the right so that channel 2| is blocked by piston l1 and channel 22 is opened to chamber 25 through bore i9, and, when pump 4 starts to deliver liquid into channel 6, pressure extends from channel 8 through channels 22 and 24 to the right end of bore 9 and shifts valve l5 toward the left to the position shown so that channel 22 is blocked by piston l8 and channel 2| is opened to chamber 25 through bore l9.

Valve I8 thus operates to automatically block the pressure side of the pump from chamber 25 and to open the return side of the pump to chamber 25 in either direction of pump delivery so that pump 4 can at no time discharge freely into reservoir l2, liquid returned to the pump in excess of a pump requirements can at all times be discharged through channels 2| or 22, bore I9,

chamber 25 and relief valve 21 into reservoir 12,- and any deficiency in the liquid returned to the pump from an external circuit can be made up by liquid supplied by gear pump l5 or by liquid drawn by pump 4 through check valve 26 from reservoir l2.

Pump 4 is caused to deliver liquid in one direction or the other by shifting slide block ID in one direction or other from a central or neutral position. This is accomplished by hydraulically actuated means operated by liquid supplied thereto from gear pump |5 partly under the control of a valve which controls the rate, direction and extent of movement of slide block l and partly under the control of a second valve which renders the first valve eifective or ineffective.

As shown in Fig. 2, slide block 18 is constantly urged toward the right by a hydraulic servomotor consisting of a cylinder 35, which is formed integral with or connected to pump casing II, and a piston 36 which abuts or is connected to the left side of slide block l8 and fitted in cylinder 35. Supply channel 28 is connected to cylinder 35 so that piston 38 is subjected at all times to gear pump pressure.

Slide block I0 is adapted to be moved toward the left by a hydraulic servo-motor consisting of a piston 31, which has a larger effective prespiston 31.

sure area than piston 38 and abuts or is connected to the right side of slide block I, and a cylinder 38 which is formed integral with or connected to pump casing II and has piston 31 fitted therein.

Cylinder 38 is closed at its outer end by a head 33 having a bore 40 (Fig. 3) formed therein in axial alinement with an axial bore 4| which extends through piston 31 and through an extension or hub formed upon the outer face of piston 31. The inner end of bore 4| communicates at all times with the interior of pump casing II as by means of one or more radial passages 42 formed in the inner end of piston 31.

Liquid for operating servo-motor 3138 is supplied to cylinder 38 by gear pump I under the control of a rotary follow-up valve 43 which is closely fitted in bores 48 and 4| and provided at its outer end with a lever 44 for rotating it and for restraining it from axial movement.

Valve 43 is provided with an internal passage 45 having one end thereof in communication at all times with an annular groove 48 which is formed in the wall of bore 49 and adapted to be supplied with motive liquid from gear pump l5 as will presently be explained.

The other end of passage 45 opens into a spiral groove 41 which is formed in the peripheral surface of valve 43 adjacent a port 48 formed in the hub of piston 31. Port 48 is adapted, upon rotation of valve 43 in one direction or the other, to provide communication between the interior of cylinder 38 and either groove 41 or a spiral groove 49 which is formed'in the peripheral surface of valve 43 and opens into the inner end of bore 4|.

The arrangement is such that, when liquid is supplied to groove 48 from gear pump l5 and port 48 isin registry with groove 41, liquid will flow from groove 48 through passage 45, groove 41 and port 48 into cylinder 38 and act upon Since the effective pressure area of piston 31 is greater than that of piston 38, the liquid entering cylinder 38 will cause piston 31 to move slide block l0 toward the left and piston 38 will expel liquid from cylinder 35 through relief valves 29 and 21. When port 48 registers with groove 49, cylinder 38 is open to drain and the liquid constantly supplied to cylinder 35 will cause piston 35 to move slide block Ill toward the right and cause piston 31 to expel liquid from cylinder 38 through port 48, groove 49, the inner end of bore 4| and passage 42 into pump casing Port 48 and grooves 41 and 43 are so proportioned that, when valve 43 is stationary, opposite edges or corners of port 48 aline with adjacent edges of grooves 41 and 49 so that the slightest relative movement between port 48 and grooves 41 and 49 axially of valve 43 will open communication between port 48 and one or the other of grooves 41 and 49.

Communication between port 48 and one or the other of grooves 41 and 49 may be established by rotating valve 43 in one direction or the other to thereby cause slide block ill to be moved in one direction or the other. Since port 48 is formed in a part of piston 31 so that it moves therewith and with slide block l0, valve 43 and piston 31 constitute a follow-up valve mechanism which permits liquid to flow to or from cylinder 31 only while valve 43 is rotating. Consequently, movement of slide block l8 ceases at substantially the same instant that valve 43 ceases to rotate.

Valve 43 is adapted tobe rotated manually by means of foot lever 58 which is pivoted intermediate its ends and has one of its ends connected to the free end of lever 44 by a link 5|, suitable stops being provided on opposite sides of lever 53 to prevent valve 43 from being rotated beyond its eifective range.

By depressing the free end of lever 58, valve 43 will be rotated in a direction to open cylinder 38 to'drain' and permit servo-motor -43 to move slide block it toward the right so that pump 4 will deliver liquid to the upper end of cylinder 2 and cause piston l to move ram 3 downward as previously explained and, by raising'the free end of lever 50, valve 43 will be rotated in a direction to permit gear pump liquid to enter cylinder 38 and cause piston 31 to move slide block it toward the left so that pump 4 will deliver liquid to the lower end of cylinder 2 and cause piston l to move ram 3 upward as previously explained.

In order that the transmission may operate semi-automatically, valve 43 is rotated to its neutral position in response to piston i reaching the limit of its up stroke and it is rotated in a direction to open communication between groove 46 and cylinder 38 in response to piston l starting its down stroke.

As shown, a spring 52 is arranged beneath lever 50, the free end of lever 44 is connected to one end of a rod 53 which extends loosely through a collar 54 fixed upon ram 3, and a nut 53* is arranged upon the upper end of rod 53 to be engaged by collar 54 as .piston l approaches the end of its up stroke.

Servo-motor 31-38 is also controlled by a valve 55 (Figs. 1 and 4) arranged in a-valve casing 56 and controlling communication between two ports 51 and 58, which are formed in the wall of casing 56, and between port 51 and a drain channel 59 which is connected to both ends of valve casing 56 and discharges into reservoir l2.

Valve 55 is urged by a spring 68 toward the position shown in Fig. 1, and it is adapted to be moved to the position shown in Fig. 4 by a solenoid 6i which has its core connected to the stem of valve 55.

Port 51 is connected to groove by a channel 62, and. port 58 is connected by a channel 63 (Figs. 1 and 2) to supply channel 28 so that groove 46 (Fig. 3) is supplied with motive liquid by gear pump i5 when valve is in the position shown in Fig. 1. I

Channel 62 communicates intermediate its ends with the outlet of a check valve 64 which has its inlet connected to one end of a channel 65 the other end of which is connected to cylinder head 39 and communicates with the interior of cylinder 38.

The arrangement is such that, when valve 55 is in the .position shown in Fig. 1, no liquid can enter cylinder 38 except under the control of rotary valve 43 and, when valve 55 is in the posi-' tion shown in Fig. 4, it blocks communication between ports 51 and 58, to thereby prevent the delivery of any liquid to cylinder 38, and port 51 is open to drain channel 53 so that liquid can escape from cylinder 38. Consequently, when valve 55 is in the position shown in Fig. 4, servo-motor 35-36 will move slide block l8 toward the right and cause piston 31 to expel liquid from cylinder 38 through channel 55, check valve.64, channel 62, valve casing 58, and channel 53 into reservoir l2.

Solenoid Si is adapted to be energized by current supplied thereto from a power line 18 under the control of a magnetic switch ll the electromagnet 12 of which is controlled by a normally open push button switch 13, a normally closed push button switch I4 and a normally closed limit switch 15 the actuating member of which is arranged in the .path of an actuator 15 carried by collar 54, switch 15 being so positioned and actuator I5 being so adjusted that actuator 16 will open switch 15 when ram 3 reaches the end of its down stroke.

The circuit connecting the power line, the sole- ,noid and the several switches has been simplified in the drawing from which it will be obvious that, when push button switch 13 is closed, magnet 12 will be energized and close switch H and a circuit will be completed through solenoid 5| to energize it and a circuit will be completed through magnet I2 to energize it so that it will hold switch ll closed after which push button switch I3 is released. It will also be obvious that, when push button switch 14 or limit switch I5 is opened, the circuit through magnet 12 will be broken so that magnet 12 will be deenerglzed and switch II will open and deenergize solenoid 5i.

Operation Assuming that motor [-2 and ram 3 are parts of a hydraulic press, that pumps 4 and I5 are running and that the several .parts are in the positions shown in Fig. 1, the press will operate as follows:

When switch 13 is closed, magnet 12 will be energized and close switch II to energize solenoid 5| which will shift valve 55 toward the right to the position shown in Fig. 4 so that cylinder 38 is connected to drain and servo-motor 35-45 permitted to shift slide block ill toward the right to cause pump 4 to deliver liquid through channel 5 to the upper end of cylinder 2, thereby causing piston I to move ram 3 downward.

Downward movement of ram 3 from its upper limit permits spring 52 to swing the outer end of lever 44 downward and thereby rotate valve 43 in a direction to move groove 41 into registry with port 48 so that gear pump liquid may be supplied to cylinder 38 as soon as valve 55 is returned .to the position shown in Fig. 1.

Switch 13 may be opened immediately after it was closed as magnetl! will hold switch ll closed until ram 3 reaches-a predetermined point in its downward movement at which time actuator 16 will open limit switch 15, thereby deenergizing magnet 12 and permitting switch H to open and deenergize solenoid 5| so that spring may then shift valve 55 to the position shown in Fig. l.

Liquid from gear pump l5 may then flow through channel 63, valve casing 56, channel 62, groove 45, passage 45, groove 41 and port 48 to cylinder 38 and shift slide block [8 toward the left to cause pump 4 to deliver liquid through channel 5 to the lower end of cylinder 3 and thereby cause piston l to move ram 3 upward.

As ram 3 approaches the limit of its upward movement, collar 54 will engage nut 53 and raise rod 53 and the outer end of lever 44, thereby rotating valve 43 in a direction to move groove 45 into registry with port 48 so that liquid can escape from cylinder 38 and servo-motor 35-35 can move slide block l8 toward the right.

Rotation of valve 43 and movement of slide block it toward the right will continue until slide block l8 reaches its neutral position at which time further movement will cease and the press will come to rest with the parts thereof in the positions shown in Fig. 1.

FIG. 5

The transmission shown in this figure is exactly the same as the transmission shown in Fig. 1 except that it is reversed in response to the fluid pressure exceeding a predetermined maximum instead of in response to an element being moved to a predetermined point. Consequently, like parts have been indicated by like reference numerals and no further description thereof will be iven.

g As shown, reversal is obtained by means of a normally closed pressure responsive switch 15 which corresponds to limit switch 15 and is connected into the electric circuit in exactly the same manner. Pressure switch 15 is subjected to a pressure proportional to the pressure created by the pump when the motor is performing useful work.

In order that the pressure at which the transmission is reversed may be varied through a wide range, pressure switch 15 is adapted to operate at a predetermined low pressure and an adjustable resistance valve is connected between it and the pressure side of the pump. As shown, the pressure inlet of switch 15* is connected by a channel 80 to the outlet of an adjustable resistance valve 8| the inlet of which is subjected to pump pressure as by being connected to the upper end of cylinder 2 by a channel 82, and a check valve 83 is connected in parallel with resistance valve BI and opens in the opposite direction to permit the pressure in channel 80 to fall as soon as the pump has been reversed so that pressure switch 15 can close. Also, in order to prevent possible damage to pressure switch 15, a safety relief valve 84 is ordinarily connected to channel 80 and adjusted to open at a pressure but slightly higher than the pressure required to open pressure switch 75.

A cycle of operation is started by closing switch 13 as previously explained. Ram 3 will advance until it is exerting sufiicient force upon the work to cause pump pressure to rise high enough to open resistance valve 8| and then operate pressure switch 15 which will deenergize magnet 12 to efiect reversal of pump l. Otherwise, the transmission operates in exactly the same manner as the transmission shown in Fig. 1 operates.

It is obvious that the controls shown in Figs. 1 and 5 could be combined so that the pump could be reversed either on distance or on pressure. as desired. For example, the control shown in Fig. 5 could have a limit switch such as switch 15 connected in series with pressure switch 15 and ram 3 could be provided with an actuator such as actuator 18 for operating the limit switch. Then, by proper adjustments of actuator l6 and resistance valve 8|, the pump could be reversed either in response to ram 3 reaching a predetermined point in its advance movement or in response to pump pressure exceeding a predetermined maximum.

The invention herein set forth is susceptible of various modifications and adaptations without departing from the scope thereof as hereafter claimed. I

The invention is hereby claimed as follows:

1. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor for supplying liquid thereto to energize the same and having a displacement varying member shiftable in one direction or the other to one or the other of two predetermined positions in the first of which said pump delivers liquid in a direction to cause said motor to advance said element and in the second of which said pump delivers liquid in a direction to cause said motor to retract said element, said member being also shiftable to an intermediate I neutral position to reduce pump delivery to zero,

means including a fluid actuated servo-motor for shifting said member, means for supplying motive fluid to said servo-motor, and a. first valve for controlling operation of said member shifting means, of a second valve for controlling said member shifting means connected in series with said first valve, said second valve being shiftable to two positions in the first of which it renders said first valve effective and in the second of which it renders said first valve ineffective and causes said member shifting means to shift said member to its first position whereby said pump delivers liquid in a direction to cause said motor to advance said element, means for moving said first valve to a position in which when effective it will cause said member shifting means to shift said member toward its second position, and means operable at the end of the advance movement of said element for shifting said second valve to its first position.

2. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor for supplying liquid thereto to energize the same and having a displacement varying member shiftable in one direction or the other to one or the other of two predetermined positions in the first of which said pump delivers liquid in a direction to cause said motor to advance said element and in the second of which said pump delivers liquid in a direction to cause said motor to retract said element, said member being also shiftable to an intermediate neutral position to reduce pump delivery to zero, means including a fluid actuated servo-motor for shifting said member, means for supplying motive fluid to said servo-motor, and a first valve for controlling operation of said member shifting means, of a second valve for controlling said member shifting means connected in series with said first valve, said second valve being shiftable to two positions in the first 'of which it renders said first valve effective and in the second of which it renders said first valve ineffective and causes said member shifting means to shift said member to its first position whereby said pump delivers liquid in a. direction to cause said motor to advance said element, means operable in response to said element starting its advance movement for moving said first valve to a position in which when effective it will cause said member shifting means to shift said member toward its second position, means operable at the end of the advance movement of saldelement for shifting said second valve to its first position to thereby cause said motor to retract said element, and means operable by said element as it nears the end of its retraction movement for so adjusting said first valve as to cause said member shifting means to move said member to its neutral position.

3. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor for supplying liquid thereto to energize the same and having a displacement varying member shiftable in one direction or the other to one or the other of two predetermined positions in the first of which said pump delivers liquid in a direction to cause said motor to advance said element and in the second or which said pump delivers liquid in a direction to cause said motor to retract said element, said member being also shiitable to an intermediate neutral position to reduce pump delivery to am, means including a fluid actuated servomiotor for shifting said member, means for supplying motive fluid to said servo-motor, and a first valve for controlling operation of said member shifting means, of a second valve for controlling said member shifting means connected in series with said first valve, said second valve being shiitable to two positions in the first of which it renders said first valve effective and in the second of which it renders said first valve ineffective and causes said member shifting means to shift said member to its first position whereby said pump delivers liquid in a direction to cause said motor to advance said element, means for moving said first valve to a position in which when effective it will cause said member shifting means to shift said member toward its second position, means for shifting said second valve,

means operated by said element at the end of its advance movement for causing said valve shifting means to shift said second valve to its first position and thereby cause said element to be retracted, and means responsive to said element approaching a given point in its retraction movement for so adjusting said first valve as to cause said member shifting means to move said member to its neutral position.

4. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor for supplying liquid thereto to energize the same and having a displacement varying member shiftable in one direction or the other to one or the other of two predetermined positions in the first of which said pump delivers liquid in a direction to cause said motor to advance said element and in the second of whichsaid pump delivers liquid in a direction to cause said motor to retract said element, said member being also shiftable to an intermediate neutral position to reduce pump delivery to zero, means including a fluid actuated servo-motor for shifting said member, means for supplying motive fluid to said servo-motor, and a first valve for controlling operation 01' said member shifting means, of a second valve for controlling said member shifting means connected in series with said first valve, said second valve being shiftable to two positions in the first of which it renders said first valve effective and in the second of which it renders said first valve inefiective and causes said member shifting means to shift said member to its first position whereby said pump delivers liquid in a direction to cause said motor to advance said element, means for moving said first valve to a position in which when efiective it will cause said member shifting means to shift said member toward its second position, means fo shifting said second valve, means responsive to the pressure in said motor exceeding a predetermined maximum for causing said valve shitting means to shift said second valve to its first position and thereby cause said element to be retracted, and means responsive to said element approaching a given point in its retraction movement for so adjusting said first valve as to cause said member shifting means to move said member to its neutral position.

5. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor for supplying liquid thereto to energize the same and having a displacement varying member shiftable in one direction or the other to one or the other of two predetermined positions in the first of which said pump delivers liquid in a direction to cause said motor to advance said element and in the second of which said pump delivers liquid in a direction to cause said motor to retract said element, said member being also shiftabie to an intermediate neutral position to reduce pump delivery to zero, means including a fluid actuated servo-motor for shifting said member, means for supplying motive fluid to said servo-motor, and a first valve for controlling operation of said member shifting means, of a second valve for controlling said member sifting means connected in series with said first valve, said second valve being shiftabie to two positions in the first of which it renders said first valve effective and in the second of which it renders said first valve inefiective and causes said member shifting means to shift said member to its first position whereby said pump delivers liquid in a direction to cause said motor to advance said element, means for moving said first valve in one direction to a position in which when eiiective it will cause said member shifting means to shift said member toward its second position, means operated by said element near the end of its retraction movement for moving said valve in the opposite direction to thereby cause said member shifting means to move said member to its neutral position, means including an electro-magnet for operating said second valve, means including a manual switch for energizing said magnet, and means including a limit switch operable by said element at the end of its advance movement for deenergizing said magnet.

6. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor for supplying liquid thereto to energize the same and having a displacement varying member shiftable in one direction or the other to one or the other of two predetermined positions in the first of which said pump delivers liquid in a direction to cause said motor to advance said element and in the second of which said pump delivers liquid in a direction to cause said motor to retract said element, said member being also shiftable to an intermediate neutral position to reduce pump delivery to zero, means including a fluid actuated servo-motor for shifting said member, means for supplying motive fluid to said servo-motor, and a first valve for controlling operation of said member shifting means, of a second valve for controlling said member shifting means connected in series with said first valve, said second valve being shiftable to two positions in'the first of which it renv ders said first valve effective and in the second of which it renders said first valve inefiective and causes said member shifting means to shift said member to its first position whereby said pump delivers liquid in a direction to cause said motor to advance said element, means for moving said first valve to a position in which when effective it will cause said member shifting means to shift said member toward its second position, means operated by said element near the end of its retraction movement for moving said valve in the opposite direction to thereby cause said member shitting means to move said member to its neutral position, means including an electromagnet tor operating said second valve, means including a manual switch for energizing said magnet, and means including a pressure switch responsive to the pressure in said motor exceeding a predetermined maximum for deenerglzing said magnet.

7. The combination, with a reciprocable ele- ,ment, a hydraulic motor *for reciprocating said element, a reversible pump connected in series with said motor and having a displacement varying member shiltable to one side or the other or a neutral position to cause said pump to deliver liquid in one direction or the other and thereby cause said motor to move said element in one direction or the other, yieldable means for constantly urging said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to advance said element, a fluid servo-motor adapted when energized to move said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to retract said element, a source or motive fluid, and means for connecting said servo-motor to said source including a first valve adapted to direct liquid from said source to said servo-motor to energize it during movement of said valve in a given direction and to connect said servo-motor to drain to deenergize it during movement of said valve in the opposite direction, of a second valve shiftable to two positions in the first of which it directs fluid from said source to said first valve and in the second of which it connects said servo-motor to drain and blocks communication between said source and said first valve, means for shifting said second valve to its second position to thereby permit said yieldable means to shift said member and thereby cause said motor to advance said element, means operable in response to said element advancing for moving said first valve in said given direction, and means operable at the end of the advance movement of said element for causing said second valve to be shifted to its first position.

8. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor and having a displacement varying member shifita'ble to one side or the other of a neutral position to cause said pump to deliver liquid in one direction or the other and thereby cause said motor to move said element in one direction or the other, yieldable means for con stantly urging said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to advance said element, a fluid servomotor adapted when energized to move said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to retract said element, a source of motive fluid, and means for connecting said servo-motor to said source including a first valve adapted to direct liquid from said source to said servo-motor to energize it during movement of said valve in a given direction and to connect said servo-motor to drain to deenergize it during movement of said valve in the opposite direction, of a second valve shiftable to two positions in the first of which it directs fluid from said source to said first valve and in the second of which it connects said servomotor to drain and blocks communication between said source and said first valve, means for shifting said second valve to its second position to thereby permit said yieldable means to shift said member and thereby cause said motor to advance said element, means operable in response to said element advancing for moving said first valve in said given direction, means operable at the end of the advance movement of said element for causing said second valve to be shifted to its first position and thereby cause said pump to be reversed and cause said motor to retract said element, and means operable by said element as it nears the end of its retraction movement for moving said first valve in said opposite direction to thereby permit said yieldable means to move said displacement varying member to its neutral position.

9. The combination, with a reciprocable element, a. hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor and having a displacement varying member shifltable to one side or the other of a neutral position to cause said pump to deliver liquid in one direction or the other and thereby cause said motor to move said element in one direction or the other, yieldable means for constantly urgingsaid member in a direction to cause said pump to deliver liquid in a direction to cause said motor to advance said element, a fluid servomotor adapted when energized to move said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to retract said element, a source of motive fluid, and means for connecting said servo-motor to said source including a first valve adapted to direct liquid from said source to said servo-motor to energize it during movement of said valve in a given direction and to connect said servo-motor to drain to deenergize it during movement of said valve in the opposite direction, of a second valve shiftable to two positions in the first of which it directs fluid from said source to said first valve and in the second of which it connects said servomotor to drain and blocks communication between said source and said first valve, means for shifting said second valve to its second position to thereby permit said yieldable means to shift said member and thereby cause said motor to advance said element, means operable in response to said element advancing for moving said first valve in said given direction, other means for shifting said second valve, means operated by said element at the end of its advance movement for causing said other valve shifting means to shift said second valve to its first position and thereby cause said element to be retracted, and means responsive to said element approaching a given point in its retraction movement for moving said first valve in said opposite direction to thereby permit said yieldable means to move ,said displacement varying member .to its neutral position.

10. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor and having a displacement varying member shiftable to one side or the other of a neutral position to cause said pump to deliver liquid in one direction or the other and thereby cause said motor to move said element in one direction or the other, yieldable means for constantly urging said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to advance said element, a fluid servo-motor adapted when energized to move said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to retract said element, a source of motive fluid,

and means for connecting said servo-motor to said source including a first valve adapted to direct liquid from said source to said servo-motor to energize it during movement of said valve in a given direction andto connect said servo-motor to drain to deenergize it during movement of said valve in the opposite direction, '01 a second valve shiitable to two positions in the first of which it directs fluid irom said source to said first valve and in the second of which it connects said servo-motor to drain and blocks communication between said source and said first valve, means for shifting said second valve to its second position to thereby permit said yieldable means to shift said member and thereby cause said motor to advance said element, means operable in response to said element advancing for moving said first valve in said given direction, other means for shifting said second valve, means responsive to the pressure in said motor exceeding a predetermined maximum for causing said other valve shifting means to shift said second valve to its first position and thereby cause said element to be retracted, and means responsive to said element approaching a given point in its retraction movement for moving said first valve in said opposite direction to thereby permit said yieldable means to move said displacement varying member to its neutral position.

11. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor and having a displacement varying'member shiftable to one side or the other of a neutral position to cause said pump to deliver liquid in one direction or the other and thereby cause said motor to move said element in one direction or the other, yieldable means for constantly urging said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to advance said element, a fluid servomotor adapted when energized to move said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to retract said element, a source of motive fluid, and means for connecting said servo-motor to said source including a first valve adapted to direct liquid from said source to said servo-motor to energize it during movement of said valve in a given direction and to connect said servo-motor to drain to deenergize it during movement of said valve in the opposite direction, of a second valve shlitable to two positions in the flrst 0! which it directs fluid from said source to said first valve and in the second oi which it connects said servomotor to drain and blocks communication between said source and said first valve, valve actuating means for urging said second valve to its first position, an electro-magnet for shifting said second valve to its second position to thereby permit said yieldable means to shiit said member to cause said motor to advance said element, means operable in response to said element advancinz for moving said first valve in said given direction, means including a limit switch operable by said element at the end of its advance movement for deenergizing said magnet to permit said valve actuating means to shift said second valve to its flrst position and thereby eflect reversal of said pump and retraction of said element, and means operated by said element near the end of its retraction'movement for moving said first valve in said opposite direction to thereby permit said yieldable means to move said member to neutral position.

12. The combination, with a reciprocable element, a hydraulic motor for reciprocating said element, a reversible pump connected in series with said motor and having a displacement varying member shiftable to one side or the other oi a neutral position to cause said pump to deliver liquid in one direction or the other and thereby cause said motor to move said element in one direction or the other, yieldable'means for constantly urging said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to advance said element, a fluid servo-motor adapted when energized to move said member in a direction to cause said pump to deliver liquid in a direction to cause said motor to retract said element, a source of motive fluid, and means for connecting said servomotor to said source including a first valve adapted to direct liquid from said source to said servo-motor to energize it during movement of said valve in a given direction and to connect said servo-motor to drain to deenergize it during movement of said valve in the oDPosite direction, of a second valve shiitable to two positions in the first of which it directs fluid from said source to said first valve and in the second of which it connects said servo-motor to drain and blocks communication between said source and said first valve, valve actuating means for urging said second valve to its first position, an electro-magnet for shifting said second valve to its second position to thereby permit said yieldable means to shift said member to cause said motor to advance said element, means operable in response to said element advancing for moving said first valve in RANBOM TYLER.

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