US3037354A - Hydraulic apparatus for variable load systems - Google Patents

Description

June 5, 1962 F. H. TENNIS 3,

HYDRAULIC APPARATUS FOR VARIABLE LOAD SYSTEMS Filed May 2, 1961 3 Sheets-Sheet 1 RESERVOHZ ind/MW June 5, 1962 F. H. TENNIS Filed May 2, 1961 3 Sheets-Sheet 2 434440 16 9 f 29 20 4 a g J4 r 25 7 Z 4:;

52 80 55 f: 1": 55 5E E 54 59 E Trina; 15. 71 222215 June 5, 1962 F. H. TENNIS HYDRAULIC APPARATUS FOR VARIABLE LOAD SYSTEMS Filed May 2, 1961 3 Sheets-Sheet 3 United States Patent 3,037,354 HYDRAULIC APPARATUS FOR VARIABLE LOAD SYSTEMS Francis H. Tennis, Milwaukee, Wis., assign'or to Hydraulic Unit Specialties Company, Pewaukee, Wis., a corpora tion of Wisconsin Filed May 2, 1961, Ser. No. 107,253 12 Claims. (Cl. 6052) This invention relates ot control means for hydraulic apparatus, and refers more particularly to means for increasing the cycle of speed of hydraulic apparatus of the type which normally encounters substantially varying load forces during its working cycle.

In certain types of equipment, such as front end loaders, power shovels and the like, a large force must be exerted during one part of the working stroke or cycle of the apparatus, while the remainder of the stroke requires the exertion of substantially less force but is desirably accomplished at relatively high speed. For example, in the case of a power shovel or the like, the earth engaging imple ment must often exert a large force at the beginning of its cycle, when it is breaking dirt loose from a compacted pile, but after break out a much smaller force is usually re quired to lift or move the loosened dirt, and it then be comes desirable for the earth engaging implement to operate at a comparatively high speed in order to minimize the cycle time and expedite the work. Where such a machine incorporates hydraulic control and actuating apparatus, as is now commonly the case, a cycle of this type requires that during the initial phase of the cycle, when the ground is being broken loose, pressure fluid be supplied to the hydraulic motor which powers the ground engaging implement at a relatively high pressure but at a relatively slow rate, and that during the remainder of the cycle, when the loosened ground is being lifted or moved, the hydraulic motor receives fluid at a relatively high flow rate, though not necessarily at as high a pressure.

Usually the hydraulic apparatus in such a machine is powered by a single prime mover, such as an internal combustion engine, and heretofore it has been conventional to have this prime mover drivingly connected to a single hydraulic pump which supplied pressure fluid to the hydraulic apparatus. If the pump afforded a relatively high flow rate of pressure fluid, so as to insure comparatively fast movement of the hydraulic motor or motors driven thereby, then the necessary pressure could not be obtained for driving the hydraulic motor at a slow speed against a heavy load, and it was possible for the prime mover to be stalled when a heavy load was imposed upon the hydraulic motor, as during break out of compacted dirt. On the other hand if the pump provided a low flow rate, so as to insure adequate pressure for slow speed working of heavy loads, then the entire operation of the apparatus took place at low speed, with a proportionately long work cycle time.

With the foregoing in mind it is an object of this invention to provide hydraulic apparatus of the type having a hydraulic motor or motors to which hydraulic fluid under pressure is supplied from pump means driven by a single prime mover, which apparatus includes means for automatically reducing the rate of flow of pressure fluid to the hydraulic motor at times when a heavy load is imposed upon the motor, and for supplying pressure fluid to the hydraulic motor at a normal high rate at times when the motor is working against a lighter load, to thus insure that the hydraulic motor is capable of exerting a large force for break out but is nevertheless capable of moving comparatively rapidly at other times, thereby affording a very short working cycle despite the high force available for break out.

Another object of this invention resides in the provision of hydraulic apparatus of the character described which enables the power output of a single prime mover to be very advantageously utilized in automatically effecting slow movement of a hydraulic motor when the same is heavily loaded and rapid movement of the motor when it is lightly loaded.

It is also an object of this invention toprovide hydraulic apparatus whereby the above stated objects can be obtained, and which apparatus is nevertheless very simple, inexpensive and dependable.

Still another object of this invention is to provide a hydraulic apparatus of the type which comprises pump means driven by a prime mover, a hydraulic motor, and a control valve of the open center type for directing hydraulic pressure fluid from the pump means either to the hydraulic motor, for actuation of the same, or to a reservoir or the like at times when operation of the motor is not desired, which apparatus incorporates two pumps that are driven by the prime mover, one of which is at all times connected with the control valve and the other of which is connected with the control valve only at times when the hydraulic motor is lightly loaded, so as to supplement the output of the first pump at such times and thus cause faster operation of the motor.

A further object of this invention is to provide a simple and inexpensive pilot operated unloading valve for hydraulic apparatus of the character described, having a body with an inlet and a pair of outlets and incorporating pressure responsive valve means for directing pressure fluid from the inlet to one of the outlets when the pressure at said one outlet is below a predetermined value, and for directing such fluid to the other outlet when fluid pressure at the firs-t designated outlet exceeds said predetermined value.

In this connection it is another and more specific object of this invention to provide an unloading valve of the character described having a pressure responsive main valve member which is movable between normal and unloading positions and is yieldingly biased toward its normal position, and wherein a pilot valve is provided which prevents hunting of the main valve member and which assures that the main valve member will not move out of its normal position at fluid pressures below said predetermined value, said pilot valve being adjustable to provide for regulation of the pressure at which it permits shifting of the main valve member from one of its positions to the other.

Another specific object of this invention is to provide a simple, dependable and inexpensive unloading valve of the character described having a body which can be readily formed from a single casting.

It is also a specific object of this invention to provide an unloading valve having in its body an inlet, a high pressure outlet, and an exhaust outlet, and having means for communicating the inlet either with the high pressure outlet or with the exhaust outlet, depending upon the pressure which obtains at the high pressure outlet, and which valve also incorporates means for effectively preventing back flow of pressure fluid from the high pressure outlet to both the inlet and the exhaust outlet, without iniposing back pressure on a pump connected with its in et. a

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate several complete examples of the physical embodiments of the invention U constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

FIGURE 1 is a diagrammatic view of a hydraulic apparatus which embodies the present invention;

FIGURE 2 is a sectional view of an unloading valve of this invention shown in its normal position;

FIGURE 3 is a view similar to FIGURE 2 but showing the unloading valve in its relief or unloading position;

FIGURE 4 is a view similar to FIGURE 2 but illustrating a modified form of unloading valve embodying the principles of this invention, shown in its normal position; and

FIGURE 5 is a view similar to FIGURE 4, but showing the modified valve in its relief or unloading position.

Referring now more particularly to the accompanying drawings, in which like reference characters designate like parts throughout the several views, the numeral 5 designates generally a hydraulic motor, the operation of which is governed by a control valve 6 and which is connected for actuation by pressure fluid from pump means, generally designated 7, driven by a prime mover 8. The hydraulic motor 5 is in this case shown as comprising a double acting cylinder, adapted to actuate the ground engaging implement (not shown) of an excavating shovel, a front end loader or the like, or to drive a similar load which at times requires the hydraulic motor to exert a large force at very low speed and at other times requires the motor to exert substantially less force but, desirably, to move at a relatively fast speed.

The control valve 6 is preferably of the well known open center type, and has a spool 9 that is axially manually shiftable between a neutral position and a pair of operating positions spaced to opposite sides of neutral. When the spool is in the neutral position, pressure fluid is locked in both ends of the cylinder 5 while fluid from the pump means is allowed to pass substantially unimpeded through the control valve and to a reservoir 10 or other unpressurized source of fluid, by way of an exhaust duct 11 connected between the control valve and the reservoir. When the spool 9 of the control valve is shifted to one of its operating positions, it communicates one end of the cylinder with the pump means via a duct 12, and connects the other end of the cylinder with the exhaust duct 11 via a duct 13 to effect movement of the work performing element of the cylinder in one direction. When the spool 9 is shifted to its other operative position, the duct 13 supplies pump fluid to said other end of the cylinder, to eifect movement of its work performing element in the opposite direction; and the fluid then being expelled from the cylinder flows to the exhaust duct 11 via the duct 12 and the passages in the control valve.

Those skilled in the art will understand that the control valve 6 can comprise a bank of open center valves, each of which is connected with a hydraulic motor to etfect control thereof, and that the principles of this invention are as well applicable to apparatus comprising a plurality of control valves and motors as to a system having only a single motor and control valve. It will also be understood that the double-acting hydraulic cylinder 5 shown in FIGURE 1 is merely illustrative of any of a wide variety of hydraulic motor types that can be used with the apparatus.

It is a feature of the apparatus of this invention that the pump means 7 comprises two pumps P-1 and P-2, both of which are driven by the same prime mover 5. The inlets of both pumps are connected, as by duct means 14, with the hydraulic fluid reservoir It}, but the high pressure outlet of the pump P1 is connected directly with the control valve 6 by means of a duct 15, while the high pressure outlet of the other pump P-2 is connected, via a duct 16, with an unloading valve 17.

When pressure in the system comprising the duct 15 and the hydraulic motor 5 is below a predetermined value,

the unloading valve 17 allows the output of the pump P2 to be fed to the control valve by way of a duct 18 which connects the unloading valve with the duct 15, and consequently at such times the motor 5 receives hydraulic fluid at a high rate of flow, equal to the combined output volumes of both pumps.

However, when the motor 5 is heavily loaded, causing the pressure in the ducts 15 and 18 to rise above said predetermined value, the unloading valve 17 dumps the output of pump P-2 into the reservoir 10 by way of a duct 19 which is connected between the unloading valve and the exhaust duct 11. Under such conditions of heavy load on the hydraulic motor the pump P2 consumes only a negligible amount of power from the prime mover, since its output flows substantially unimpeded to the reservoir 1t), and consequently substantially all of the power of the prime mover is available to drive the pump P-l. Hence the hydraulic motor 5 is driven by hydraulic fiuid at a high pressure and low flow rate dring break out or other heavy load conditions,

When the load upon the hydraulic motor 5 is reduced, as when a load of earth breaks loose from a pile, and the unloading valve connects the outlet of pump P-2 into the pressure system by way of the duct 18, to feed the combined outputs of the two pumps to the hydraulic motor, each of the pumps absorbs its respective share of the power produced by the prime mover.

It is naturally important that the pump P-l be rated for the maximum pressure for which the system is designed, as limited by the displacement of pump P-1 and the horsepower rating of the prime mover. However, it will be understood that the two pumps need not be of equal displacements. Thus if there is a substantial variation between the maximum expected load and the normal load, and rapid operation of the hydraulic motor is desired at times when it is lightly loaded, the pump P-Z may have a larger displacement than the pump P-l. Obviously the pump P2 can be rated for a lower pressure than pump P1, since maximum system pressure is never applied by pump P-2.

The unloading valve 17 of this invention has a body 20 that can be formed as a single block-like casting, and has a bore 21 extending therethrough and three passages 22, 23 and 24 transverse to the bore that open to it at spaced intervals along it length and extend to the exterior of the body. The opposite end portions of the bore 21 are counterbored and closed by plugs 25 and 26 which are threaded into the counterbores. The intermediate portion of the bore accommodates an axially slidable pressure responsive main valve member or spool 27.

The passage 22 is an inlet passage which communicates the medial portion of the bore with an inlet port 28 that opens to one side of the body and is adapted to be connected with the high pressure outlet of a pump corresponding to the pump P-2, as by means of a duct corresponding to the duct 16. The passage 23 is a high pressure outlet passage which communicates the bore 21 with a high pressure port 29 that is located at the side of the valve body opposite to that to which the inlet port 28 opens, The port 29 is adapted to be connected with a duct, corresponding to the duct 18, in which hydraulic system pressure is manifested. The passage 24 is an exhaust outlet passage which opens to an exhaust port 30 that is located at the same side of the body as the outlet port 29 and is connectable to a reservoir or other unpressurized fluid source.

It will be noted that the several passages 22, 23 and 24 open to enlarged diameter portions of the bore, and that the inlet passage 22 communicates with the bore at a zone intermediate the zones at which the bore is respectively communicated with the high pressure outlet passage 23 and the exhaust outlet passage 24.

The main valve member or spool 27 is biased to a normal position in which an axially elongated land 31 thereon blocks communication between the inlet passage 22 and the exhaust passage 24, but in which the spool permits communication through the bore 21 between the inlet passage and the high pressure outlet passage 23. Such bias toward its normal position is imparted to the main valve member by means of a coiled compression spring 32 in the counterbored end portion 21 of the bore that is nearer the exhaust outlet passage 24, and which spring reacts between the plug 26 and the axially outer end of the land 31 on the main valve member. A smaller diameter projecting end portion 33 of the spool, adjacent to the land 31, serves as a pilot for the spring 32, and the spring is further guided by having its axially outer portion received in an inwardly opening well in the plug 26.

The body also has a feed back passage 35, controlled by a pilot poppet 36, through which pressure fluid can flow from the high pressure outlet passage 23 into the counterbored end portion 34 of the bore remote from the spring 32 whenever fluid pressure in the outlet passage 23 exceeds a predetermined unloading value. When pressure fluid is thus introduced into the bore the main valve member is moved thereby against the bias of the spring 32 to an unloading position in which a land 37 on the spool blocks communication between the inlet passage 22 and the high pressure outlet passage 23, and in which the land 31 is out of the restricted portion of the bore between the inlet passage ad the exhaust passage 24, so that the output of a pump connected with the inlet passage is directed through the bore to the exhaust passage 24.

The feed back passage 35 is provided by a bore 39 in the valve body which extends parallel to the main bore 21 and which communicates with the high pressure outlet passage 23, a coaxial counterbore 44 in which the pilot poppet 36 is axially slidable, and an obliquely inclined passage portion 41, which can be drilled from the end portion of the bore 21 before the same is closed by the plug 25, and which communicates the counterbores 4t) and 34. The shoulder defined by the junction of the bore 39 with the counterbore 40 provides an outwardly facing valve seat toward which the pilot poppet 36 is biased by a coiled compression spring 42 that surrounds a reduced diameter coaxial stem 43 on the pilot poppet and reacts against a plug 44 threaded into the mouth of the counterbore.

It will be apparent to those skilled in the art that the biasing force of the spring 42 can be regulated by adjustment of the axial depth to which the plug 44 is threaded into the counterbore 40, and consequently the pilot poppet affords accurate control of the fluid pressure value at which the main valve member or spool 27 is moved to its unloading position. Lock or jam nuts 45 threaded onto the outer end portion of the plug 44 hold the latter against displacement out of any position of adjustment in which it may be set.

At its end adjacent to the plug 25, the main valve member has a reduced diameter end portion 46 which serves as a stop abutment that engages the plug 25 to define the normal position toward which the main valve member 27 is biased by the spring 32.

The axially outer end of the land 37 on the spool serves as a piston which receives the thrust due to hydraulic pressure fluid in the cylinder comprising the counterbored end portion 34 of the bore. Since such fluid cannot escape back to the high pressure outlet passage 23 when the pilot poppet 36 closes, the spool is provided with a coaxial bleed passage 47 by which such entrapped fluid can be conducted to the exhaust outlet passage 24 upon closure of the pilot poppet, to allow the spool to be returned to its normal position by the biasing force of the spring 32. To this end the spool has a radial bore 48 which opens from the bleed passage 47 to the surface of the land 31 and which is so located along the length of the spool as to be in register at all times with the exhaust outlet passage 24. The bleed passage 47 also includes a throttling restriction 49 which allows fluid pressure in the end portion 34 of the bore to build up more rapidly, when the pilot poppet 36 is open, than it can escape through the bleed passage.

It is well known that a pressure responsive poppet such as the pilot poppet 36 tends to open slightly, or crack, at fluid pressure values below that at which it is intended to respond. It will be noted that the bleed passage 47 allows fluid that leaks past the pilot poppet, due to its cracking, to be conducted out of the end portion 34 of the bore before the spool can be displaced by such fluid. However, when the pilot poppet 36 is fully open, the restriction 49 prevents the full flow of fluid into the bore from passing through the bleed passage, so that under those circumstances the spool is moved to its unloading position. The bleed passage 47, with its restriction 49, thus cooperates with the pilot poppet 36 in providing for stable and accurate operation of the main valve member, insuring that it will shift to its unloading position at exactly a predetermined pressure value, with no tendency to hunt.

The bleed passage 47 opens axially to the end portion 21' of the bore in which the spring 32 is located, so that leakage fluid cannot be trapped in said end portion of the bore to interfere with movement of the spool to its unloading position, and so that a vacuum cannot be drawn there when the spring shifts the spool to its normal position.

The spool may also be provided with a radial bore 50 which opens from the bleed passage to a circumferential groove 51 in the spool, so located along the length of the elongated land 37 as to be at all times situated between the high pressure outlet passage 23 and the end portion 34 of the bore. Fluid which leaks along the bore from the high pressure outlet passage is intercepted at the groove 51 and conducted to the exhaust outlet passage 24 by way of the radial bore 50, the bleed passage 47, and the radial bore 48, so that such fluid cannot enter the end portion 34 of the bore and tend to shift the spool toward its unloading position or prevent it from returning to its normal position.

It is important to prevent any flow of pressure fluid from the high pressure outlet passage 23 to the exhaust outlet passage 24 when the spool shifts from one of its positions to another, since such flow could produce ,an undesirable pressure drop in the hydraulic system connected with the high pressure outlet 23. The lands 31 and 37 on the spool are therefore so located and spaced apart on the spool 27 that as the spool shifts from its normal to its unloading position, and vice versa, it passes through a transition or intermediate position in which the land 37 blocks communication through the bore between the inlet passage 22 and the high pressure outlet passage 23 while the land 31 blocks communication through the bore between the inlet passage and the exhaust outlet passage 24. To prevent injury to a pump connected with the inlet passage, due to the back pressure upon the pump that might result from such dead ending of the inlet passage, the unloading valve of this invention includes a passage 53 in the valve body through which pressure fluid can flow from the inlet passage to the high pressure outlet passage, and a check valve 54 in said passage 53 which blocks flow of such fluid in the reverse direction.

The check valve controlled passage 53 comprises a bore 55 which is parallel to the bore 21 and which intersects the inlet passage intermediate the bore 21 and the inlet port 28, a coaxial outwardly opening counterbore 56 in which the check valve 54 is slidable, and a passage section 57 which communicates the bore 21 with the counterbore 56. The passage section 57 comprise-s, in effect, a coaxial inward extension of the high pressure outlet passage 23. The mouth of the counterbore 56 is closed by a plug 58 which also serves to receive the reaction of a coiled compression spring 59 by which the check valve 34 is urged toward a closed position engaging the seat provided by the junction of the bore 55 and counterbore :1 56. The check valve preferably comprises an elongated poppet which is slidable in the counterbore 56 and which has an outwardly opening coaxial well 60 therein in which a substantial portion of the spring 59 is guidingly received.

In the embodiment of the unloading valve illustrated in FIGURES 2 and 3, the check valve 54 is intended to open only at times when the main spool is in its intermediate or transition position blocking all communication through the bore between the three passages 22, 23 and 24 which open thereto. In the embodiment of the invention illustrated in FIGURES 4 and 5 the land 37 on the spool 27 is of such length that it always blocks communication through the bore between the inlet passage 22 and the high pressure outlet passage 23. Hence the spool 27 does not have a transition or intermediate position, since pressure fluid entering the inlet passage 22 must flow to the high pressure outlet passage by way of the passage 53 controlled by the check valve 54 at all times that the land 31 blocks flow of such fluid through the bore 21 to the exhaust passage 24. In all other respects the unloading valve illustrated in FIGURES 4 and 5 can be identical to that shown in FIGURES 2 and 3.

The modified form of unloading valve illustrated in FEGURES 4 and 5 has the advantage of a simplified construction of the main valve member, as compared with the FIGURES 2 and 3 version of the valve, but has the disadvantage that it provides a slightly less eflicient system because of the back pressure which the relief or check valve 54 imposes upon a pump connected with its inlet passage 22.

From the foregoing description taken together with the accompanying drawings it will be apparent that this invention provides hydraulic apparatus of the type comprising a hydraulic motor, an open center control valve by which the motor is controlled, and pump means driven by a prime mover, whereby the power developed by the prime mover can be most advantageously utilized to provide for operation of the motor with fluid at high pressure and a low flow rate when the motor is heavily loaded and with lower pressure fluid at a higher flow rate when the motor is more lightly loaded. It will be further apparent that this invention also provides a simple, inexpensive and dependable unloading valve by which pressure fluid from a source thereof is directed to a pressurized hydraulic system when pressure in the system is below a predetermined value, but whereby such pressure fluid is dumped to an unpressurized reservoir or the like when pressure in the hydraulic system exceeds said value.

What is claimed as my invention is:

1. An unloading valve for directing pressure fluid from a hydraulic pump to a pressurized hydraulic system when pressure of fluid in the system is below a predetermined value and for diverting pressure fluid from the pump away from said hydraulic system when pressure of fluid in the system exceeds said value, said unloading valve comprising: a valve body having a bore therein which is adapted to receive a slidable valve element and the ends of which are closed, and having high pressure and low pressure outlet passages which intersect said bore at zones that are spaced lengthwise of the bore axis from one another and from one end of the bore, and which respectively open to a high pressure port in the valve body that is connectable with a pressurized hydraulic system, and a low pressure port in the valve body that is connectable with a fluid reservoir, said valve body also having an inlet passage therein which intersects the bore at a zone spaced lengthwise of the bore axis from said end of the bore and from the zones of intersection of said outlet passages with the bore, a feed back passage communicating with said end portion of the bore and with the high pressure outlet passage intermediate the bore and the high pressure port, and a check valve passage which communicates with the inlet passage and the high pressure outlet passage; a main valve element in said bore in the body movable axially back. and forth between a first position blocking communication through the bore between the inlet passage and both outlet passages, and a second position allowing communication through the bore between the inlet passage and the low pressure outlet passage but blocking communication through the bore between the inlet passage and the high pressure outlet passage, said main valve element being responsive to the pressure of fluid in said end portion of the bore to be moved thereby toward its said second position; biasing means in the valve body reacting against the main valve element to hold the same out of its said second position as long as pressure of fluid in said end portion of the bore does not exceed a value corresponding to said predetermined value of pressure in the hydraulic system; and check valve means in the check valve passage for blocking flow of fluid from the high pressure outlet passage to the inlet passage, but responsive to fluid pressure in the inlet passage which is higher than that in the high pressure outlet passage to allow fluid to flow from the inlet passage to the high pressure outlet passage through the check valve passage when the main valve element is in its said first position.

2. The unloading valve of claim 1, further characterized by: a pressure responsive valve element in said feed back assage normally blocking flow of fluid therethrough from the high pressure outlet passage to said one end portion of the bore, but arranged to open in response to fluid pressure in the high pressure outlet passage which is in excess of said predetermined value to permit such flow of fluid through the feed back passage.

3. The unloading valve of claim 1, further characterized by: the fact that the valve body has a second bore therein which opens to one side thereof and provides a portion of said feed back passage, and has means at the inner end of said second bore defining a valve seat; a pressure responsive pilot poppet in said second bore slidable toward and from engagement with said valve seat; a plug axially adjustably t readed into the outer end portion of said second bore; and a spring reacting between said plug and the pilot poppet to bias the latter toward said valve seat with a force depending upon the'position of axial adjustment of said plug, so that adjustment of the plug regulates the value of pressure in the high pressure outlet passage at which the main valve element is moved to its said second position.

4. The unloading valve of claim 1, further characterized by the fact that: the high pressure outlet passage and the inlet passage open to opposite sides of the valve body, and their axes are substantially parallel to one another; further characterized by the fact that a portion of the check valve passage extends from the bore toward the side of the valve body to which the inlet passage opens, and is coaxial with the high pressure outlet passage; further characterized by the fact that another portion of the check valve passage extends substantially parallel to the bore, is intersected by the first designated portion of the check valve passage, and intersects the inlet passage intermediate the bore and the side of the valve body to which the inlet passage opens; and further characterized by the fact that the check valve comprises an elongated poppet which is axially slidable in said other portion of the check valve passage.

5. The unloading valve of claim 1, further characterized by the fact that the main valve element is movable to a third position axially remote from said second position, and in which the main valve element blocks communication through the bore between the inlet passage and the low pressure outlet passage but allows communication through the bore between the inlet passage and the high pressure outlet passage, so that when the main valve element is in said third position pressure fluid need not unseat the check valve and hence does 9 not have back pressure imposed upon it by the check valve, said biasing means in the valve body normally maintaining the main valve element in its said third position.

6. The unloading valve of claim 2, further characterized by the fact that the main valve element has a restricted bleed passage extending axially therein and which in all positions of the main valve element communicates said end portion of the bore with the low pressure outlet passage, said bleed passage providing for drainage of pressure fluid out of said end portion of the bore at substantially the same rate that such fluid accumulates therein when the pilot poppet is partially unseated but by reason of its restriction preventing such fluid from leaving said end portion of the bore at the rate that it enters the same when the pilot poppet is fully open.

7. An unloading valve for directing pressure fluid from a hydraulic pump to a pressurized hydraulic system when pressure of fluid in the system is below a predetermined value and for diverting pressure fluid from the pump away from said hydraulic system when pressure of fluid in the system exceeds said value, said unloading valve comprising: a valve body having an inlet passage opening to one side of the body and adapted to be connected with a pump, a high pressure outlet passage parallel to and spaced in one direction from the inlet passage opening to the opposite side of the body and connectable with a pressurized hydraulic system, an exhaust outlet passage parallel to and spaced in the opposite direction from the inlet passage, opening to said opposite side of the body and connectable with a fluid reservoir, and a main bore extending through the body normal to said passages and to which said passages open at their inner ends, said body also having a feed back bore parallel to said main bore and opening to the high pressure outlet passage, a first counterbore coaxial with the feed back bore and opening to a third side of the body nearer the high pressure outlet passage than the exhaust outlet passage, and a feed back passage portion communicating said counterbore with the end portion of the main bore nearer said third side of the body, said body further having a check valve bore parallel to the main bore and communicating with the inlet passage, a second counterbore coaxial with the check valve bore and opening to said third side of the body, and a passage portion coaxial with the high pressure outlet passage communicating the latter with said second counterbore through the main bore; a main valve member slidable axially in the main bore to a first position blocking communication through the main bore between the inlet passage and both outlet passages while permitting communication between the inlet passage and the high pressure outlet passage through the second counterbore and said passage portion, and to a second position permitting communica tion through the main bore between the inlet passage and the exhaust outlet passage, said main valve member having a restricted bleed passage therein which at all times provides limited communication between said end of the main bore and the exhaust outlet passage; 21 pair of plugs, one in each end of the main bore; a spring in the other end portion of the main bore reacting between the ad jacent plug and the main valve member to bias the latter away from its said second position; a pilot poppet axially slidable in the first counterbore to and from a seated position blocking the feed back bore and responsive to fluid pressure in the high pressure outlet passage to be moved out of said position; a third plug closing the mouth of the first counterbore; a spring reacting between the third plug and the pilot poppet to bias the latter toward its seated position; a check poppet in the second counterbore axially slidable to and from a seated position blocking the check valve bore and arranged to move out of said position in response to fluid pressure in the inlet passage which is greater than that in the high pressure outlet passage; a fourth plug closing the mouth of the second counterbore; and a spring reacting between 10 the fourth plug and the check poppet to bias the latter toward its seated position.

8. In a hydraulic system of the type which is driven by a prime mover and which includes a hydraulic motor and a control valve having an inlet for hydraulic fluid under pressure and by which such fluid can be directed either to the hydraulic motor, for actuating the same, or to an unpressurizedreservoir or the like, means for supplying hydraulic fluid under pressure to the motor at a low rate of flow at times when the motor is heavily loaded and at a high rate of flow at times when the motor is lightly loaded, so that the motor moves fastest when least lightly loaded and thus advantageously utilizes the power available from the prime mover, said means comprising: a pair of hydraulic pumps connected with the prime mover to be driven thereby; means connecting the inlet of each of said pumps with -a source of unpressurized hydraulic fluid; means connecting the outlet of one of said pumps with the inlet of the control valve so that pressurized fluid from said one pump is at all times available to the control valve and hence to the hydraulic motor; an unloading valve body having an inlet and a pair of outlets and having passage means through which the inlet is communicable with both outlets; means communicating the inlet in the unloading valve body with the other hydraulic pump; pressure responsive valve means in said passage means in the unloading valve body biased to a normal position blocking communication between the inlet and one outlet while allowing communication between the inlet and the other outlet, but shiftable against its bias, in response to fluid pressure at said other outlet in excess of a predetermined value, to an unloading position at which said valve means blocks communication between the inlet and said other outlet while allowing communication be tween the inlet and the first designated outlet; means communicating said other outlet in the unloading valve body with the inlet of the control valve so that pressurized fluid from said other outlet is normally available to the control valve, and hence to the hydraulic motor, to supplement the volume of fluid supplied by the first hydraulic pump; and means communicating said first designated outlet in the unloading valve body with a source of unpressurized hydraulic fluid, so that only fluid from said one hydraulic pump is supplied to the control valve, and hence to the hydraulic motor, at times when pressure of fluid at said other outlet exceeds said predetermined value.

9. In a hydraulic system of the type which is driven by a prime mover and which includes a hydraulic motor and a control valve having an inlet for hydraulic fluid under pressure and by which such fluid can be directed either to the hydraulic motor, for actuating the same, or to an unpressurized reservoir or the like, means for supplying hydraulic fluid under pressure to the motor at a low rate of flow at times when the motor is heavily loaded and at a high rate of flow at times when the motor is lightly loaded, so that the motor moves fastest when least lightly loaded and thus advantageously utilizes the power available from the prime mover, said means comprising: an unloading valve of the type having an inlet and a pair of outlets and comprising pressure responsive valve means by which fluid is directed from the inlet to one of said outlets so long as pressure of fluid at said one outlet is below a predetermined value, and by which fluid from the inlet is directed to the other outlet when pressure of fluid at the first designated outlet exceeds said predetermined value; a pair of pumps driven by the prime mover, each of said pumps having a high pressure outlet and an inlet connected with a source of hydraulic fluid; means connecting the high pressure outlet of one of said pumps with the inlet of the control valve so that fluid under pressure from said one pump is at all times available to the control valve and hence to the hydraulic motor; means connecting the high pressure outlet of the other pump with the inlet of the unloading valve; and means connecting the first designated outlet of the unloading 1 1 valve with the inlet of the control valve so that fluid under pressure of said other pump is available to the control valve, and hence to the hydraulic motor, to supplement the fluid from the first designated pump, at times when fluid at said first designated outlet of the unloading valve is below said predetermined value.

10. An unloading valve for hydraulic systems comprising: a body having an inlet port connectible with a source of fluid under pressure, a service port connectible with a hydraulic motor, and an exhaust port; first passage means in the body for communicating the inlet and service ports; a check valve in said first passage means arranged to block flow of fluid therethrough in the direction from the service port to the inlet port, but to allow flow of fluid in the opposite direction through said first passage means; second passage means in the body for communicating the inlet and exhaust ports; a valve element movable in the body between a pair of positions, and adapted to cooperate with said second passage means at one of said positions to block communication between the inlet and the exhaust ports while allowing fluid to flow through said first passage means from the inlet port to the service port, said valve element in the other of its positions being adapted to allow communication through said second passage means between the inlet and the exhaust ports; means in the valve body yieldingly biasing the valve element toward its said one position; and means in the valve body responsive to pressure at the service port and operable to effect movement of the valve element from its said one position to its said other position when pres sure at the service port rises above a predetermined value.

11. An unloading valve for hydraulic systems comprising: a body having an inlet port conncctible with a source of fluid under pressure, a service port connectible with a hydraulic motor, and an exhaust port; first passage means in the body for communicating the inlet and service ports; second passage means in the body for communicating the inlet and exhaust ports; a valve element movabl in the body between a pair of positions, and adapted to cooperate with said second passage means at one of said positions to block communication between the inlet and the exhaust ports while allowing fluid to flow through said first passage means from the inlet port to the service port, said valve element in the other of its positions being adapted to allow communication through said second passage means between the inlet and the exhaust ports; means in the valve body yieldingly biasing the valve element toward its said one position; means in the body providing a cylinder having a restricted outlet communicating with the exhaust port and a pressure responsive piston movable back and forth in said cylinder and having a motion transmitting connection with the valve element by which the valve element can be moved to said other position thereof in consequence of the admission of pressure fluid into the cylin- 5 der; third passage means in the valve body for communicating said cylinder with the service port; and pressure responsive pilot valve means in said third passage means, arranged to allow fluid to flow through said third passage means from the service port to said cylinder, at a rate faster than such fluid can flow out of said restricted outlet,

when pressure at the service port rises above a predetermined value, to thus cause the piston to effect movement of the valve element from its said one position to its said other position.

12. An unloading valve for hydraulic systems comprising: body having an inlet port connectible with a source of fluid under pressure, a service port connectible with a hydraulic motor, and an exhaust port; first passage means in the body for communicating the inlet and service ports; second passage means in the body for communicating the inlet and exhaust ports; a valve element movable in the body between a pair of positions, and adapted to cooperate with said second passage means at one of said positions to block communication between the inlet and the exhaust ports while allowing fluid to flow through said first passage means from the inlet port to the service port, said valve element in the other of its positions being adapted to allow communication through said second passage means between the inlet and the exhaust ports; means in the valve body yieldingly biasing the valve element toward its said one position; means in the body providing a fluid pressure responsive operator for shifting the valve element toward its said other position, comprising a pressure chamher having a restricted outlet which leads to the exterior of the body, and a fluid pressure responsive member movable in one direction to effect such shifting of the valve element in consequence of admission of pressure fluid into the pressure chamber at a rate faster than it can flow out of said outlet; third passage means in the valve body for communicating said pressure chamber with the service port; and pressure responsive pilot valve means in said third passage means, arranged to allow fluid to flow through said third passage means from the service port to said pressure chamber, at a rate faster than such fluid can flow out of said restricted outlet, when pressure at the service port rises above a predetermined value, to thus ettect movement of the valve element from its said one position to its said other position.

No references cited.

Disclaimer 3,037,354.Fmn0is H. Tenn is, Milwaukee, Wis. HYDRAULIC APPARATUS FOR VARIABLE LOAD SYSTEMS. Patent dated June 5, 1962. Disclaimer filed Aug. 5, 1963, by the assignee, Hydraulic Um't Specialties Company. Hereby enters this disclaimer to claims 9 and 10 of said patent.

[Official Gazette October 29, 1.963.]

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