US3415057A - Hydraulic free-wheeling means for the hydraulic drives of conveyors and the like - Google Patents

Description

e/llcL INVENTOR )IARRY RUSENBERG HYDRAULIC FREE-WHEELING MEANS FOR THE HYDRAULIC` DRIVES OF CONVEYORS AND THE LIKE Dec. 10, 1968 United States Patent O 31 10 Claims. (Cl. 60-53) ABSTRACT F THE DISCLOSURE Hydraulic drive arrangement including hydraulic drive means having `main working iiow line means and main return ow line means operatively How-connected therewith for hydraulic actuation thereof, short-circuit ow line means disposed correspondingly in such short-circuit ow return ilow line means to bypass such drive imeans, a pair of independently openable operatively opposed check valve means disposed correspondingly in such short-circuit flow line `means to permit when open short-circuit bypass ilow therethrough, and control means operatively connected with such check valve means to open the check valve means independently of one another, such control means including, for example, hydraulic control valve means and control flow line means operatively ow connecting the control valve rneans with the check valve means to open hydraulically each check valve means independently, the control valve `means being Imanually or automatically operable.

The present invention relates to hydraulic drive arrangements, and 4more particularly to such arrangements coritemplating free-wheeling means whereby to achieve under varying pressure conditions free-wheeling of the hydraulic drive system especially in connection with multi-motor hydraulic drives for conveyors, and the like.

In hydraulic drives of the kind in question, especially where a pair of such drives is used for driving a conveyor system, one such drive may sometimes practically overtake the other. In the motor or drive that is overtaken in speed, a reversal of its function is produced in that it operates `as a pump since both drives are coupled together by the hydraulic fluid system utilized. In particular, such hydraulic drives are provided in the form of rotary vane machines or rotary piston machines, i.e. rotary iluid machines, which transmit hydraulic power into mechanical l power in one direction of operation (performing as a motor) `and mechanical ypower into hydraulic power in the other direction of operation (performing as a pump). In connection with the foregoing, as a result of the overtaking of one such hydraulic drive by the other, a drop in pressure develops in the pressure output line unless the hydraulic drive acting as a pump is able to put out suicient iluid -to make up the deficiency. More precisely, the input pressure of the overtaken hydraulic drive is reduced to the level of the output pressure thereof, and thereafter the above-noted eifect takes place whereupon the output pressure exceeds the input pressure. In the extreme case the faster running drive means may use up all its power in dragging along the slower running drive means since the latter acts as a pump rather than `a motor.

3,415,057 Patented lDec. 10, 1968 ice It is true that the foregoing disadvantageous eifect can be mitigated -by the use of known power regulators or governors customarily employed for such purposes. Nevertheless, a -certain energy loss will result because of the necessity of balancing the speed of the two or more hydraulic drive means operatively coupled together, for example, with a conveyor system to be driven thereby. Specifically, such energy losses will occur in any case until the threshold response pressure of the power regulator associated with the faster running drive is reached` However, at extreme loads, a reciprocal build-up of counter-pressures in the drive means may be produced by oscillating effects in the endless conveyor chain or belt system and/ or by diiierent speeds of response of the power valves necessary for the hydraulic energizing of the two or more drive means. Only at no-load speeds which are very accurately attuned to one another as between the two or more drive means utilized, and only when such drive means have the same characteristic with respect 'to the delivery rate, and furthermore operate with approximately equal losses and/ or eiciency, can quick balancing of the speeds be achieved. In practice, this set of conditions is seldom attained and, therefore, the problem of overtake with respect to two or more hydraulic iluid operated drive machines, or the like, arranged for conjoint output at the same speed cannot be overcome.

It is an object of the present invention to overcome the foregoing drawbacks and to provide hydraulic drive arrangements for use in conjoint operation of a co-mmon drivable system to be driven thereby without overtake in speed of one drive means with respect to the other.

It is another object of the present invention to provide `an arrangement of the `foregoing type in which hydraulic free-wheeling means are included whereby to achieve under varying pressure conditions free-wheeling of the hydraulic drive system especially in connection with `multimotor hydraulic drives for conveyors, and the like.

It is a further object of the present invention to provide an arrangement of the foregoing type with respect to a given rotary fluid machine wherein the hydraulic input line to such `machine and the hydraulic output line from such machine are provided with a Ifree-wheeling system or neutral operating condition system analogous to that applied heretofore in mechanical drives, whereby a shortcircuit cycle connection between such input and output lines is employed together with control means for permitting pressure flow communication between such inlet and outlet lines to equalize the pressure therebetween and thus permit an idle or neutral condition of operation to exist with respect to such drive and thereby avoid energy loss in a second such drive means operated conjointly therewith at a diierent speed.

It is a still further object to provide only one such arrangement, e.g. where such drive must avoid operating as a brake for its associated drivable system.

Other and further objects of the present invention will become apparent from :a study of the within specification and accompanying drawings in which the figure shown illustrates schematically an arrangement of two such hydraulic drive means conjointly arranged for driving an endless conveyor system, with each such hydraulic drive means having a short-circuit ow system provided between the corresponding inlet `and outlet flow lines thereof, in accordance with the present invention.

It has been found in accordance with the present invention that a hydraulic drive arrangement may now be provided to overcome the foregoing disadvantages. Such arrangement comprises hydraulic drive means having main working ow line means and main return ow line means operatively dow-connected therewith for the hydraulic actuation thereof, short-circuit flow line means correspondingly interconnecting said working and return flow line means to by-pass said drive means, a pair of independently openable operatively opposed check valve means disposed correspondingly in said short-circuit flow line means to per-mit when opened short-circuit by-pass ilow therethrough, and control means operatively connected with said check valve means to open said check valve means independently of one another.

Preferably, the control means include hydraulic control v alve `means and control flow line means operatively flow-connecting said control valve means with said check valve means .to open hydraulically each check valve means independently. Such control valve means may be manually operable or automatically operated in conjunction with a programmed system.

In accordance with one specic feature of the present invention, at least two separate hydraulic drive means of the foregoing type are provided in independent operative association with a common drivable system to be driven cooperatively the-reby, each said drive means having a separate set of said working land return flow line means operatively How-connected therewith and a separate said short-circuit ow line means correspondingly interconnecting said working and return flow line means to bypass the particular drive means as well as a pair of said check valve means disposed correspondingly in the particular short-circuit ow line means, with said control means being operatively connected with said check valve means to open said check valve means independently of one another. In this regard, each pair of check valve means is provided preferably with a separate control means operated independently of the other.

The hydraulic drive -means in each case may conveniently take the form of a hydraulically operated rotary drive machine and the com-mon drivable system may be a conveyor system such as a chain scraper conveyor system utilized in mining operations, or a mining planer traction cable, etc.

Advantageously, the pair of check valve means should be disposed in series flow relation in the short-circuit How line means and normally maintained closed by .the corresponding normally existing positive hydraulic pressure exerted thereagainst through the appropriate m-ain ow line means and the corresponding portion of said shortcircuit flow line means flow-communicating therewith.

Referring to the drawing, the figure illustrates diagrammatically a hydraulic drive system, for use with an endless conveying chain, belt, or the like, which may be, for example, the chain used to drive a mining machine, such as a coal planer, back and forth along a mine face or a scraper chain of a mining conveyor used to convey mineral, such as coal, away from the site of mineral winning from a mine Iface. Such mining machines and mining conveyors are normally used in longwall mining operations, such as in the winning of coal.

Conveyor 1 which may take the form of a conveyor belt is mounted on a pair of spaced apart driving wheels or drums 2, 3 which are coupled via the corresponding clutches 4, 5 with the appropriate hydraulic drive 6, as the case may be.

Such hydraulic drive 6 may be in the form of a rotary fluid machine normally disposed to function as a hydraulic motor under positive hydraulic pressure provided through the hydraulic system 7 in each instance.

Describing the operation of the hydraulic system 7 used to drive the hydraulic motor 6 coupled via clutch 4 with drum 2, it will be seen that the main working ilow line 8 under hydraulic pressure generated by pump Cil 10 or similar means is fed to the motor 6 to cause such motor to rotate and thus transmit lrotary motion via clutch 4 to drum 2 to cause in turn travel of endless conveyor 1 in the direction shown by the arrow. The spent hydraulic fluid passes via the main return flow line 9 back to the pump 1li or the like. Pump 10 is normally positioned at a convenient distance from motor 6 and the main flow lines 8 and 9 may be of any appropriate length. Pump 10 may be replaced by other means which will provide under normal operation a higher working pressure in line 8 than in line 9, yet the pressure in lines 8 and 9 will normally be positive pressure.

In accordance with the present invention, the main flow lines S and 9 are interconnected by means of a by-pass or short-circuit line 11 in which are disposed in series flow connection the operatively opposed check valves 12 and 13. Check valves 12 and 13 may be of any convenient design which permit under normal operation unilateral back low when the valve body 12a or 13a is displaced away from the valve seat 12b or 13b, as the case may be. Thus, when valve body 12a is displaced from valve seat 12b, the working pressure in line 8 will be exerted upon valve body 13a to force such valve body away from the valve seat 13b. In the same way, when valve body 13a is displaced from valve seat 13b, the working pressure in line 9 will be exerted upon valve body 12a to force such valve body away from the valve seat 12b. In accordance with the present invention, the displacing of valve body 12a and valve body 13a away from the appropriate valve seat is carried out by auxiliary control means 16. Auxiliary control means 16 may take the form of an auxiliary hydraulic uid system, including control flow line 14 to one side 11a of the check cylinder 11C containing the check piston 11d with the ram 11e operatively positioned at valve body 12a of check valve 12 and control line 1S to the other side 11b of the check cylinder 11e` with the other piston ram 11f operatively positioned at valve body 13a of check valve 13, coupled with the control valve 17, the portion of short-circuit line 11 between valve seats 12b and 13b being shown in dash line and actually how-connecting valves 12 and 13. Because of their length, rams 11e and 11f when piston 11d is in idle or neutral position will not prevent valve body 12a nor valve body 13a from normal closed seating against valve seats 12b and 13b respectively but will only disturb this relationship when piston 11d is actuated to the left or right. Control valve 17 is connectable to a source (not shown) of hydraulic fluid, or `the like, via the pressure line 18 and via the return line 19. Valve 17 is provided with three possible valve positions 20, 21 and 22. Valve 17 is displaceable laterally against the spring force of springs 23 and 24 which normally maintain valve 17 in the neutral or idle position 20 which permits flow communication between control lines 14 and 15. During the normal operation of motor 6, the pressure in line 8 will understandably be higher than the pressure in line 9, and the pressure in both main lines 8 and 9 will be positive pressure sufficient to maintain valve bodies 12a and 13a in closed position against valve seats 12b and 13b, as the case may be. During this time, the pressure in control lines 14 and 15 will not operate to change the closed disposition of check valves 12 and 13. Upon displacement of valve 17 to the right as viewed in the drawing so that valve position 22 is aligned with the pressure and return lines 18 and 19, the pressure in line 18 communicates with control line 14 to cause valve body 13a to be displaced away rom valve seat 13b, thus opening check valve 13.

Even so, since the pressure in line 8 is normally higher than that in line 9, the pressure exerted through shortcircuit line 11 via line 9 and valve 13 will not be suflicient to displace the valve body 12a from valve seat 12b. However, upon change in the pressure condition in the hydraulic system 7 such that the pressure in line 9 exceeds that in line 8, when valve 17 is in position 22, excess pressure in line 9 will be short-circuited through line 11 to cause valve body 12a to be displaced as aforesaid, whereupon the pressure in line 8 and line 9 will be eqpalized. Under such conditions, motor 6 will be in freewheeling or neutral or idle position despite the working pressure of pump 10.

On the other hand, upon displacing valve 17 in a direction toward the left as shown in the drawing to the position 21, then pressure line 18 will communicate with control line and return line 19 will communicate with control line 14. In this instance, the opposite actuation will take place, i.e. the hydraulic pressure through line 18 and control line 15 will displace valve body 12a from valve seat 12b to open check valve 12. Thence, the pressure in line 8 when the same exceeds that in line 9 will cause the displacement of valve body 13a from valve seat 13b to efrect the opening of check valve 13 and the equalization of the pressure in line 8 and line 9 as aforesaid.

It will be appreciated that under a versatile arrangement as may be provided in accordance with the present invention, pump 10 or the like may be reversed in its operation to provide higher pressure in line 8 than in line 9, or higher pressure in line 9 than in line 8. When the pressure in line 8 is higher, then motor 6 will rotate in clockwise direction whereas when the pressure in line 9 is higher, then motor 6 will rotate in icounterclockwise direction, In this way, advantageously, the appropriate rotary motion may be exerted via clutch 4 to drum 2 to rotate such drum in the appropriate direction so as to cause the travel in turn of the conveyor 1 in the appropriate direction. This is especially applicable to the operating of a mining machine, such as a mining planer, back and forth along a mine face reciprocally. For example, drum 2 may be located at one end of the portion of the mine face being worked and drum 3 at the other end of the portion thereof and by appropriately changing the direction of pressure flow through the pumps 10, or the like, in both arrangements 7, the two motors 6 may first operate in clockwise direction and thence in counterclockwise direction to achieve the reciprocal movement of the conveyor 1 which may be a cable to be attached to the mining machine to be reciprocated along the mine face.

Of course, the construction and operation of the hydraulic system 7 associated with that motor 6 coupled with clutch 5 to transmit rotary motion to drum 3 will be the same as that described hereinabove in connection with the imparting of rotary motion in the 'desired direction to drum 2.

In normal operation, both motors 6 are meant to rotate in the same functional direction to cause rotary motion to be transmitted through clutches 4 and 5 to the appropriate drums 2 and 3 so as to attain a conjoint additive rotation of such drums under the combined power of both motors 6. In practical operation, however, both motors 6 do not always rotate the appropriate drums at the exact same speed under approximately the same efficiency and, therefore, one motor 6 may overtake the other and cause the corresponding drum of the overtaking motor to rotate at a higher speed than the other drum. Assuming, for instance, that motor 6 coupled via clutch 5 to drum 3 operates at a higher speed than the motor 6 coupled through clutch 4 to drum 2, then the latter motor will eventually be dragged along in its functional operation because of the conjoint connection of the motor outputs via the conveyor 1. This will mean that the dragging motor 6 associated with drum 2 will be rotated via the connection provided by conveyor 1, drum 2, and clutch 4, faster than the pressure in line 8 of its hydraulic system 7 would normally operate such motor. As a result, hydraulic fluid is taken from the ycorresponding line 8 into the dragging motor 6 under an induced suction and discharged into the corresponding line 9 under a higher pressure than the normal pressure, causing the dragging motor 6 to act as a pump rather than a motor. If, in accordance with the present invention, control valve 17 is in position 22 which will serve to maintain check valve 13 open, then such excess pressure in line 9 will be short-circuited through line 11 to cause check valve 12 to open in the above-described manner so as to equalize the pressure in lines 8 and 9 and permit the dragging motor 6 or pump to reach a free-wheeling or neutral or idle position so as not to detract from the eticiency of the faster running motor connected via clutch 5 with drum 3.

In the opposite direction of rotation, the same freewheeling effect can be attained by displacing valve 17 to position 21 whereby excess pressure in line 8, now a return iline, may be equalized via short-circuit line 11 with t'he pressure in line 9 now a working line.

In the event the motor 6 associated via clutch 5 with drum 3 is the dragging motor, then the reverse operation may be carried out by suitable displacement of the appropriate valve 17 associated with that hydraulic system 7 connected with said motor 6 associated with drum 3.

Advantageously, in accordance with the present invention, check valves 12 and 13 are normally maintained in closed position by the positive pressure ow via lines 8 and 9, and each check valve is connected operatively with control valve 17 to permit independently opening of check valves 12 and 13 with respect to one another and indeedwith respect to the existing pressure in either or both of lines 8 or 9. The construction of check valves 12 and 13 is conventional and the operative connection of valve 17 therewith to provide independent actuation of such check valves to open the same despite the pressure in lines 8 and 9 is also conventional (cf. U.S. Patents 2,467,508 and 3,135,087, and German Patent 1,045,202). Of course, any valve means may be utilized as valves 12 and 13 herein so long as such valves are functionally opposed in operative connection in the short-circuit line or by-pass line 11 and openable independently of one another by a control system not related to the hydraulic pressure in line 8 and line 9, yet with each valve 12 and 13 being unilaterally operated in the sense that the appropriate positive pressure directly now-communicated therewith by line 8 or line 9, as the case may be, will normally maintain the particular check valve 12 or 13 in closed position under the attendant hydraulic pressure exerted thereagainst, yet displaceab-le despite such attendant pressure by independent actuation caused by control means such as control valve 17, or the like.

It will be appreciated that more than two such by-pass lines may be provided in any such hydraulic system 7, each having appropriately disposed therein a pair of functionally opposed check valves 12 and 13 of the type contemplated with control means operatively connected with both such check valves to control the opening thereof independently of the pressure in the hydraulic system 7. Also, while two motors 6 are shown in the embodiment of the drawing, it will be appreciated that any number of motors 6 may be provided in conjoint operative association to produce an additive resultant power for running a given device, wherein it is desirable to operate such device under rotary |motion of the individual motors 6 at the same speed in the interests of over-all eciency. By using a system of the type shown, instead of intricate gearing arrangements, the reversal of rotation of drums 2 and 3, or the like, may be achieved by simply changing the direction of working pressure and return pressure in the hydraulic systems 7 via the appropriate directional operation ofthe pump 10, or the like.

It will be further realized that but one such motor 6 associated with a given hydraulic system 7 may be provided where it is desired to provide rotary motion at a constant speed or at least at a minimum speed for a drivable system. In the case of a lminirnum speed, it will be realized that by providing the instant by-p'ass arrangement in the hydraulic system 7, motor 6 will not act as a brake under any circumstances since when the speed of the rotary motion through the appropriate clutch 4, for

instance, exceeds that supplied by the corresponding motor 6, instead of 'a braking effect, motor 6 will assume a neutral or idle free-running state until the speed of motor 6 once more exceeds that through clutch 4, whereupon positive rotation of motor 6 will once again be undertaken. This will lbe true since the pressure in the working line 8 will once again exceed that in return line 9 so as to cause the closing of check valve 12 under the existing pressure in line 8 which is higher than the pressure in line 9 communicating via open check Valve 13 and shortcircuit line 11 with valve 12.

Valve 17 may be in the form of a manually operated valve having the three stated positions, with springs 23 and 24 normally biasing such valve in the neutral or idle position 20, yet which permit in the position 22 the independent opening of valve 13 and in the position 21 the independent opening of valve 12 to achieve the results described hereinabove, depending upon whether motor 6 is operating in clockwise or counterclockwise direction and in turn whether the hydraulic pressure in line 8 is meant to exceed normally that in line 9, or vice versa. Additionally, valve 17 may be a magnetically controlled threeway valve of the aforementioned type which may be operated electromagnetically by conventional control systems (not shown) including servo motors, etc., causing displacement, for example, between the nonmal, neutral or idle position 20 and, on the one hand, position 21 and, on the other hand, position 22. Such automatic control means may be coupled with the control for operating pump in the desired direction whereby when pump 10 operates in a direction causing working pressure in line 8 and return pressure in line 9, valve 17 will correspondingly assume position 22, and when pump 10 is operated in the reverse manner, valve 17 will automatically assume the position 21. Of course, hydraulic control means may be utilized as well for operating control valve 17 which may again tbe coupled with the control means for operating pump 10 in the given direction, or other remote control means may be applied to operate valve 17 or to operate check valves 12 and 13 independently of one another to open such check valves in dependence upon the normal disposition of pressure in line 8 and line 9 and the normal direction of rotation of lmotor 6 associated therewith.

Therefore, by utilizing the by-pass short-circuit flow line in the hydraulic system 7 in accordance with the present invention in which the two functionally opposed check valves are normally kept closed, by appropriate independent opening of a given check valve to achieve a balance of hydraulic pressure in lines 8 and 9 of a given hydraulic system 7, hydraulic circulation takes place under the pumping force of motor 6 through return line 9, short-circuit line 11 including lopen check Valves 13 Iand 12, and working line 8, whereby approximate mechanical free-wheeling or idle running of motor 6 will be attained to offset such pumping action and balance the ra-te of rotation of mot-or 6 with that associated therewith through clutch 4 or clutch 5, as the case may be. It will be realized as aforesaid that one or more such by-pass shortcircuit lines may be provided with an appropriate control means to open the check valves thereof independently of one another and independently of the hydraulic pressure of the system. and it will be further realized that the present invention is not meant to be limited to the means and the arrangement herein shown in the specific embodiment of the drawing, but instead also systems operated by other pressure-fluid medium, such as compressed air, pneumatic drives, or the like. Indeed, any machine capable of being energized to produce work or power in mechanical form and operated by pressure-fluid medium in two opposing resultant rotary directions may be employed in accordance with the present invention since the crux of the invention is in coupling the working pressure or fluid pressure to the machine to be energized with the return pressure or exhaust pressure of such machine whereby to attain under all operating conditions at least a minimum speed of rotation, be it a result of the pressure energizing in the desired direction of the uid motor or of freewheeling idle running thereof at a higher speed than that achievable under the existing working working pressure due to the mechanical coupling of such motor with means meant to operate at a minimum speed.

Advantageously, the instant invention may be practiced in Huid motor installations with very little additional equipment to prevent reliably and more or less completely those energy losses which have occurred heretofore. In this regard, unnecessary increases in temperature in the pressure iiuid, such as hydraulic liquid, are avoided since the losses which have heretofore occurred took the form of dissipated heat whereas at most only very slight losses are entailed where one drive means is overtaken in speed by another in an arrangement of the present type. This is true since a simple pressure medium circulation flow, e.g. hydraulic circulation, is all that takes place in the system by reason of the by-pass of the present invention, and such circulation will only lead to negligible temperature increase and heat dissipation loss.

Desirably, a separate control system should be associated with each direction of drive of the particular fluid machine. Specifically, a separate control system should be provided for each of the two contrarily disposed check valves in the by-pass line of each drive or fluid motor so that the opening of the desired check valve may be carried out independently. Where an automatic control system for the selection of the opening for the correct check valve is concerned, the controlling mechanism may be coupled to operate conjointly with that controlling the direction of rotation of the pump 10 or with other controlling means which in turn control that control mechanism used for determining the direction of rotation of such pump 10, or the like.

In this regard, the reversal of the direction of rotation of the drive means or hydraulic motors in the case of traction cable means for displacement of a coal planer or other coal winning apparatus is usually accomplished automatically by limit switches which operate when the full amplitude in the particular direction of the coal planer, or the like, has been attained and reverse operation is necessary to displace such coal planer to the opposite end of the mine face area being worked. The application of the present invention to such a system which will permit reverse rotation of the rotary uid machines and/or idle disposition during normal operation in one or the other direction will be readily apparent. On the other hand, where a system such as that contemplated herein is used with a mining conveyor or the like, the rotary fluid machines in accordance with the present invention associated therewith will normally operate in the same direction of rotation and reversal in such instance will normally be carried out manually since reversal occurs only infrequently.

Nevertheless, the arrangement of the present invention may be utilized advantageously in all cases in which a plurality of the hydraulic drive means are employed conjointly to drive a common system thereby and in special cases, as aforesaid, it is possible to use the instant arrangement where only a single hydraulic drive means or rotary fluid machine is contemplated yet where the freewheeling state is found necessary under certain conditions, such as where the hydraulic drive 'means must avoid acting as a brake for the system driven thereby.

The simplicity of the by-pass circuit of the present invention represents a distinct advantage as well as the freedom from malfunctioning. Indeed, the conservation of power in operating rotary uid machines utilizing the instant arrangement is considerable whereas the modilications necessary to provide the instant arrangement are inexpensive to carry out.

Thus, the crux of the present invention is in providing a pair of check valve means in direct series ow relation with each other in a short-circuit llow line means interconnecting the main working ilow line means and the main return ow line means such that one said check valve m'eans is separately exposed via one corresponding portion of the short-circuit ow line means to the normally existing positive hydraulicv pressure in the working flow line means exerted thereagainst to maintain such one check valve means normally closed, and the other said check valve means is separately exposed via the other corresponding portion of the short-circuit ow means to the normally existing positive hydraulic pressure in said return flow line means exerted thereagainst to maintain such other check valve means normally closed, control means being operatively connected with the check valve means to open the same independently of one another and independently of the existing hydraulic pressure in the main ow line' means and short-circuit llow line, means. In this way when such other check valve means has been opened by the control means against the existing positive pressure in the return ow line means to permit such return ilow line means pressure to be flow-communicated therethrough and in turn to be exerted against said one check valve means, then upon variation of the relative pressures in the main flow line means such that the existing pressure in the working ow line means is exceeded by the pressure in the return flow line means, such excess return ow line means pressure will open the one check valve means to permit direct llow communication through both of the open check valve means between the return flow line means and the working flow line means to equalize the pressure therebetween until said working ow line means pressure exceeds the return ow line means pressure and causes said one check valve means to close once again.

Naturally, where various constructional parts have been defined in terms of means in the instant specification, such means have been illustrated in the accompanying drawing as specific elements, but in accordance with the present invention such means contemplate any and all elements usable to achieve the combination of the shortcircuit by-pass arrangement in the hydraulic system of a rotary fluid machine or the like, and any and all such constructional elements are contemplated herein just as if prolix enumeration thereof were set forth in detail herein.

It will be appreciated that the instant specification and drawing are set forth by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention which is to be limited only by the scope of the appended claims.

What is claimed is:

1. Hydraulic drive arrangement which comprises hydraulic drive means having main working flow line means and main return ow line means operatively ow connected therewith for the hydraulic actuation thereof, shortcircuit flow line means correspondingly interconnecting said working and return flow line means to by-pass said drive means, a pair of independently openable operatively opposed check valve means disposed correspondingly in said short-circuit ow line means to permit when opened short-circuit by-pass ow therethrough, and control means operatively connected with said check valve means to open said check valve means independently of one another.

2. Arangement according to claim 1 wherein said control means include hydraulic control valve means and control ow line means operatively ll-ow connecting said control valve means with said check valve means to open hydraulically each check valve means independently.

3. Arrangement according to claim 2 wherein said oontrol valve means are manually operable.

4. Arrangement according to claim 1 wherein at least two separate said hydraulic drive means are provided in independent operative association with a common drivable system to be driven cooperatively thereby, each said drive means having a separate set of said working and return flow line means operatively flow connected therewith and a separate said short-circuit ow line means correspondingly interconnecting said working and return ow line means to by-pass the particular drive means as well as a pair of said check valve means disposed correspondingly in the particular short-circuit ilow line means, and said control means being operatively connected with said check valve means to open said check valve means independently of one another.

5. Arrangement according to claim 4 wherein each said pair of check valve means is provided with a separate said control means operable independently ot the other.

6. Arrangement according to claim 5 wherein said hydraulic drive means are hydraulically operated rotary drive machines and said common drivable system is a conveyor system.

7. Arrangement according to claim ll wherein said pair of check valve means are in series low relation in said short-circuit ilow line means and normally maintained closed by the corresponding normally existing positive hydranlic pressure exerted thereagainst through the appropriate main ow line means and the corresponding portion of said short-circuit ow line means llow communicating therewith.

8. Arrangement according to claim 1 wherein said pair of check valve means are in direct series tlow relation with each other in said short-circuit flow line means, one said check valve means being separately exposed via one corresponding portion of said short-circuit tlow means to the normally existing positive hydraulic pressure in said working llow line means exterted thereagainst to maintain such one check valve means normally closed and the other said check valve means being separately exposed via the other corresponding portion of said short-circuit ow means to the normally existing positive hydraulic pressure in said return flow line means exerted thereagainst to maintain such other check valve means normally closed, said control means being operatively connected with said check valve means to open said check valve means independently of one another and independently of the existing hydraulic pressure in said main llow line means and said short-circuit ow line means, whereby when said other check valve means has been opened by said control means against the existing positive pressure in said return flow line means to permit such return flow line means pressure to be flow communicated therethrough and in turn be exerted against said one check valve means, then upon variation of the relative pressures in said main ilow line means such that the existing pressure in said working flow line means is exceeded by the pressure in said return -ow line means such excess return ow line means pressure will open said one check valve means to permit direct ilow communication through both of the open check valve means between said return ow line means and said working flow line means to equalize the pressure therebetween until the working tlow line means pressure exceeds the return ow line means pressure and causes said one check valve means to close once again.

9. Arrangement according to claim 8 wherein two separate said hydraulic drive means are provided in independent operative association with a common drivable system to be driven cooperatively thereby, each said drive means having a separate set of said working and return flow line means operatively ow connected therewith and a separate said short-circuit ilow line means correspondingly interconnecting said working and return ow line means to by-pass the particular drive means as well as a pair of said check valve means disposed correspondingly in the particular short-circuit ilow line means and said control means being operatively connected with said check valve means to open said check valve means independently of one another and independently of the existig hydraulic pressure in each of the corresponding main tlow line means and short-circuit ow line means.

10. Arrangement according to claim. 9 wherein said hydraulic drive means are hydraulically operated rotary drive 1 1 1 2 machines and said comon drivable system is a conveyor FOREIGN PATENTS System 1,045,202 11/1958 Germany.

References Cited I UNITED STATES PATENTS 5 EDGAR W. GEOGHEGAN, Przmary Exammer. 2,467,508 4/ 1949 Trautman 60-52 US Cl- X-R 3,135,087 6/1964 Ebert 60-53XR 9116, 437

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