US2532735A - Hydraulic press with auxiliary pump in cooling by-pass - Google Patents

Description

GwlcK WITH AUXILIARY COOLING BY-PASS a May 6, 1949 PUMP R. K. 5 HYDRAULIC PRE Dec. 5, 1950 IN VEN TOR.

w W WM 1 5 M 1 PM @atented Dec. 5, 1950 UN'KTED STATES PAINT O FFECE 3 Claims.

This invention relates to'hydraulic circuits and more particularly to the cooling of a variable delivery, reversible discharge pump adapted'to alternately discharge fluid into anddraw-fluid from apair of hydraulic lines or chambers, andadapted in holding position to deliver substantially no fluid except for such volume as may be necessary to compensate for loss. of fluid from one line or chamber.

In circuits such as above described, the oil in the pump may be heated as the result of continuous operation thereof in holding position, inasmuch as substantially no fluid passestherethrough to remove heat from the pump, and it will be understood thatsuch operation may resuit in rapid pump deterioration. Inasmuchas it may be advisable under certain conditions to operate the pump in holdingposition for substantial time periods, a primary object of the present invention is to permit suchcon'tinued operation, while accommodating a substantial flow of a predetermined volume of fluid through the pump to prevent over-heating thereof.

A more specific object of the invention is to devise a circuit suchas above described: wherein a predetermined pressure is maintained by the pump in holding position thereof, to retain an hydraulic ram in a predetermined position.

The foregoing and other objectsandadvantages of the invention will become apparent from a consideration of the following specification and the accompanying drawing, wherein:

Figure l is a side. view of an hydraulic press embodying the invention, portions of the press being shown in elevation and other portions being shown in vertical section; and

Figure 2 is a reduced sectional view on the line 2-2 of Figure 1.

Describing the invention in detail, the press comprises a main cylinder casting, generally designated 2, containing a ram 4 with a head 6 defining a main or full .pressure advance chamber 8 and a return or pullback chamber Ill within the cylinder casting 2. The ram lis provided with a central bore or passage I2 connected to the pullback chamber it as by radial ports l4 and containing a pullback tube slidably fitted in a restricted portion [8 of the passage [2 in substantially fluid-tight engagement with: said portion at the upper end of the passage.

The cylinder casting 2 supports a tank or reservoir adapted to contain a suitable supply of low pressure hydraulic fluid such as, for example, oil. The cylinder also supports a bracket 22 carrying a conventional variable discharge; re-

versible delivery pump-24. The-bracket 2:2 isconnected in any suitable manner, as by cap'screws (not shown), to the cylinder casting and is provided with advance and pullback ports 2-8 and 28 respectively, connected with advance and pullback lines 30 and 32 extending through the cyl indercasting, the'line 38 being connected to the mainchamberu and the line 32 being connected to the pullbacktube IS. The bracketZZ supports amotorv 34 having an armature shaftsfi. operably connected to the pump 2d. shaft 35 also connected to a pump 31 mounted'on the tank- 20, the suction side of the pump iii being connected by a line 39 to the pullbackpassage 28. The discharge side of the pump 3'1 is connected through a cooler ll: and a filter at to the tank 28. The'pump 3-? is preferably an inexpensive fixed-stroke pump having a capacity considerably less than-that-of the pump 2d on advance err-e turn strokeunder actuation by theshaftfib; For

example the capacity of pump 3? may be ofthe order of three gallons per minute while the capacity of pump t ion advance or return stroke thereof maybe ofthe order offifty gallonsper minute.

It will be understood that in operation of the device, as. hereinafter discussed in detail, the pump ZiaIternateIy delivers pressure fluid to and exhausts pressure fluid from the respective lines 3i) and 32 in-such manner that the line at delivers. pressure fluid when the line 32 is exhaustedand vice versa.

The cylinder casting 2 also supports a prefill valve body 38' containing a cylindrical preflll valve chamber Ml having a smaller diameter portion t2 adapted to communicate through apassage it with a port or passage 36 connected to the chamber 8. A hollow prefill valve stem 55 reciprocates within the chamber to and comprises a smaller diameter portion 5c adapted to close the port it in the closed position of thestem. The stem portion 59 comprises ports 52 con nected to the passage id and other ports 54 connected to the larger diameter portion: of the chamber 46 beneath the larger diameterportion of the stem Q8 which defines an annular chamber 56 connected to a passage 58 which isinturn connected by a passage 69 to the upper end of the pullback tube It.

The prefill valve stem it comprises a cylindrical chamber or bore 82 having a smaller diameter portion 64 receiving a smaller diameter portion 66 of a hollow valve stem 61 having a larger diameter portion 68 fitted into the larger diameter portion of theabore 621- The valve stem Ell-is spring-pressed by a spring to its closed position whereat the ports 52 are closed from communication with the ports 54 and the annular chamber 55.

Sleeved over the portion 50 of the prefill valve stem 58 is an annular valve .plate 12 adapted to close ports l6 connecting the chamber 56 with the passage 44.

It may be noted that each stem 38 and 6'! is formed with a larger diameter portion and a smaller diameter portion whereby, as hereinafter described in connection with the operation of the press, the development of pressing tonnage in the chamber 8 acting against the relatively great pressure area of the stem 48 thrusts the latter downwardly to closed position and also thrusts the valve stem 67 downwardly to open position against the resistance of spring 10, inasmuch as the stem 51 comprises a longitudinal passage H accomodating flow of fluid from the passage 26 to the top of the chamber 40, whereby pressure in passage 45 acts on the top surfaces of the stems i8 and 61.

The top of valve chamber 40 is connected to a conventional relief valve 78 adapted to discharge into the reservoir to maintain a predetermined maximum pressure value within the chamber 8, and the passage 60 is connected by a passage 18 to a similar relief valve 80 adapted to prevent excessive pressure in the pullback chamber and associated conduits in the pullback phase of the operating cycle.

In the operation of the press, the operator initiates the rapid advance phase of the cycle by actuating the pump 2:? to the advance position thereof whereat fluid is drawn to the suction side of the pumps from the pullback passage 32 and is delivered from the discharge side of the pump 24 to the advance passage 35. The pump 24 draws fluid from the passage 32 at a rate less than that which fluid is supplied thereto from the chamber Iii, due to the weight of the descending ram 4, which ordinarily maintains a pressure of the order of several hundred pounds per square inch on the fluid in chamber [0, whereby this pressure is transmitted to the chamber 56 aflording an opening pressure against the stem the top and bottom areas of which are under atmospheric pressure, inasmuch as the stem .78 is in open position at the start of the advance stroke of the ram Under these conditions the ram desecends toward the work, forcing fluid from the pullback chamber H3 through the pullback tube !ii into the passage 32 and into the annular passage 55 holding the prefill valve stem :33 in the open position thereof accommodating flow of fluid from the hydraulic reservoir 20 into the chamber 8 as the ram Q moves on its rapid advance stroke toward the work.

As the ram encounters resistance of the work,

the advance movement of the ram is checked, diminishing the flow of fluid from the pullback chamber 50 to the passage 68 and the pullback passage 32. This causes a rapid drop in the pressure within the annular chamber 56 causing the preflll valve stem 48 to be urged to the closed position shown in Figure 1 and sucking the annular valve plate 52 to its open position to accommodate supply of hydarulic fluid to the pullback passage 32 which is, under these conditions, delivering fluid to the suction side of the pumps. With the valve stem 38 closed, pressure rapidly builds up in the chamber 8 acting on the larger diameter portion of the stem 48 to maintain it in tightly closed position and acting on the larger diameter portion 58 of the valve stem 61 to force the latter downwardly to the open position shown in Figure l whereat fluid is supplied from the reservoir 20 through the passage 44, the ports 52 and 54 to the annular chamber 56 which is in communication with the pullback line 32 thus insuring an adequate supply of fluid for the pump 24, while the latter is on the full pressure advance stroke thereof. Because this adequate supply of fluid is afforded for the pump 24, it will be apparent that the combined suction rates of the pumps 23 and 31 do not exceed the rate at which fluid is delivered thereto when the valve stem 61 is in open position.

The pullback phase of the cycle is initiated by reversing the pump 24. Under these conditions the pump directs pressure fluid to the pullback passage 32 and draws fluid from the advance passage 30. The fluid in the pullback passage 32 is exhausted through the passages es and 58 and the annular chamber 56 into the ports 54 and thence through ports 52 into the reservoir 20. When pressure within the advance chamber 8 is relieved sufiiciently to accommodate closing of the stem 67, the pressure of the fluid trapped within the annular chamber 56 urges the stem E8 to its open position whereat fluid from the advance chamber 8 is expelled through the passages 46 and 4 3 into the reservoir 20 as the ram moves on its pullback stroke preparatory to initiation of another cycle.

At the end of the pullback stroke of the ram 4, the pump 24 is actuated to a substantially neutral position whereat a relatively small volume of fluid at least sufiicient to satisfy the capacit of pump 3'1 and such additional volume as is necessary to compensate for leakage, is delivered to the passage 32 by the pump 2d. Under these conditions the pressure in passage 32 which as above noted is considerably greater than atmospheric, generally of the order of several hundred pounds per square inch, is efiective to overdrive the pump 31 or in other words tends to drive pump 3'! faster than the shaft 35 would actuate it at atmospheric pressure in line 39, whereupon driving torque is transmitted from the pump 3'! to the shaft 35. Thus sufiicient pressure is maintained within the passage 32 to hold the ram i in pullback position without wasting energy by blowing the output of pump 24 through a throttle valve.

It will be understood that in the arrangement illustrated, the amperage necessary to drive the motor at a predetermined rate with the pump 24 in holding position is considerably less than that which would be necessar to drive fluid from line 39 through a throttle valve and then into the cooler 4|.

Thus a constant flow of fluid is ensured through the cooler 4| with the expenditure of a minimum amount of power and a simple and economical method of cooling the fluid in the system has been devised.

I claim:

1. In an hydraulic circuit comprising advance and return chamber means, ram means therein,

a reservoir of low pressure fluid, prefill Valve means adapted to open the reservoir to said advance chamber means during rapid advance and pullback strokes of said ram means and adapted to restrict flow of fluid between the reservoir and said advance chamber means on working advance stroke of said ram means; the combination of valve means having an opening area acted on by fluid pressure in the advance chamber means and having a closing area acted on by pressure in the return chamber means, said last-mentioned valve means being adapted when open to connect the reservoir to the return chamber means and being adapted when closed to cut on communication between the reservoir and the return chamber means, a variable discharge, reversible delivery pump having opposite sides connected to respective chamber means, said pump being adapted on advance and pullback stroke thereof to deliver fluid at a predetermined rate and being adapted in holding position to deliver fluid to the pullback chamber means at less than the first-mentioned rate, and an electric motor having an armature shaft connected to the pump, another pump connected to said shaft, said other pump having its suction side connected to said pullback chamber means and said other pump having its discharge side connected to the reservoir, the delivery rate of said other .pump under actuation by said shaft being not greater than that of the second-mentioned rate, and a cooler connected to the discharge side of said other pump, the combined suction rates of said pumps being no greater than the delivery rate of said last-mentioned valve means when open.

2. In an hydraulic circuit for an hydraulic device having advance and pullback chambers and ram means therein, said circuit including a reservoir of low pressure fluid, prefill valve means adapted to open the reservoir to communication with the advance chamber means during rapid advance and pullback strokes of the ram means and adapted to cut ofi said communication on working advance stroke of said ram means; the combination of valve means having an opening area acted on by fluid pressure in the advance chamber and having a closing area acted on by fluid pressure in the pullback chamber, said second-mentioned valve means being adapted when open to connect the reservoir to the pullback chamber and being adapted when closed to cut off communication between the reservoir and the pullback chamber, a reversible pump having opposite sides thereof connected to respective chamber means and being adapted in holding position to deliver fluid to the return chamber means, and an electric driving motor connected to the pump, an hydraulic pump connected to the driving motor and having its intake side connected to the pullback chamber means, the output side of said last-mentioned pump being connected to the reservoir, means for cooling fluid delivered by the last-mentioned pump from the pullback chamber means to the reservoir, said last-mentioned pump having a delivery rate not exceeding that of said reversible pump, the combined intake rates of said pumps being no greater than the delivery rate of said last-mentioned valve means when open.

3. In an hydraulic circuit for an hydraulic motor having advance and pullback chamber means containing ram means, said circuit comprising valve means having an opening area acted on by fluid pressure in the advance chamber means and having a closing area acted on by fluid pressure in the pullback chamber means, said valve means being adapted when open to connect an associated reservoir of low pressure fluid to the pullback chamber means and being adapted when closed to cut off communication between the reservoir and the pullback chamber means, a reversible pump with opposite sides thereof connected to respective chamber means, and a motor operatively connected to the pump for driving the same, a second pump connected to the motor, the suction side of the second pump having a connection to the pullback chamber means, and a connection between the second pump and said circuit independent of the pullback chamber means, and means for treating fluid flowing through the second pump, the combined suction rates of said pumps being no greater than that at which fluid is delivered thereto by said valve means when open.

ROBERT K. SE-DGWICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,769,671 Bjerregaard July 1, 1930 1,892,568 Ernst Dec. 27, 1932 1,978,856 Briggs Oct. 30, 1934 2,042,247 Blood May 26, 1936 2,358,353 Stacy Sept. 19, 1944 2,406,965 Orr Sept. 3, 1946 2,460,058 I Brodeur Jan. 25, 1949 FOREIGN PATENTS Number Country Date 601,902 France Dec. 11, 1925

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