US2562615A - Hydraulic control system responsive to pressure and flow rate - Google Patents

Description

.Buy 3l, 1951 M. w. HUBER HYDRAULIC CONTROL SYSTEM RESPONSIVE TO PRESSURE AND FLOW RATE F'lled DeC 6 1948 I H f A m wm E \\0 A Q Snventors Machew W. Huber (Ittornegs Patented July 31, 1951 HYDRAULIC CONTROL SYSTEM RESPON- SIVE T PRESSURE AND FLOW RATE Matthew W. Huber, Watertown, N. Y.,` assignor to The New York Air Brake Company, a corporation of New Jersey Application December 6, 1948, Serial No. 63,724'

7 Claims.

f This invention relates to hydraulic circuitsy and to a Variable displacement pumpr intended for usel inY such circuits.

In the patent of Matthew W. Huber No. 2,512,799, June 27, 1950, issued on an application filed June 13, 1947, there is described a pump of this general type with the control mechanism so arrangedthat it operates to maintain a low pressure, say 200 pounds per square inch in the discharge line when no flow is permitted to occur through the discharge line but sets itself to maintain a higher pressure, say 3,000 pounds per square inch immediately that ow is permitted to occur through the discharge line.

In the arrangement of said Huber patent the flow responsive element was a spring-loaded valve which opened in response to flow and closed upon termination of ow. The object of the present invention is to secure a similar result by means which offer the minimum practicable absorption of energy. Very generally stated the change of control is eiected in response to the reduction of pressure head in the throat of a Venturi tube when flow occurs. While the scheme is probably not suited to use under all conditions that could be imagined, it offers desirable operative characteristics in those cases in which it is available.

The invention will now be described by reference to the accompanying drawings in which:

Fig. lis an axial section of so much of a parall'el cylinder, swash-plate actuated pump as is necessary to illustrate the discharge control mechanism.

Fig'. 2 is a diagram of such a pump connected in circuit with one motor and a motor controlling valve.

Fig. 3 is a View illustrating a modication of the mechanism shown in Fig. 1.

Refer to Fig. 1. Statements of direction used in the following description refer to the pump as positioned in Fig. 1.

I'he housing ofthe pump comprises a body 5 and a cap E. The cap has an inlet passage 1 and a discharge passage 8, each threaded to receive connections hereinafter described.

Housed in the body and clamped between the body and cap is an assembly made up of the cylinder block 9 and the guide block Il. These are annular in form and enclose between them a chamber I2 which communicates with the inlet passage 1 bya passage I3. The two blocks are rigidly connected together by a dowel and screws, not visible on the drawing.

The outer periphery of the cylinder block 9 is channeled to receive the ring gasket I4 Which seals the joints between the body 5, cap 6 an cylinder block 9. Another annular channel receives the ring gasket I5 which seals the joint;

between the cap and cylinder block 9 at the inner margin of the latter. Thus the annular discharge passage IB, formed in. cap 6' is isolated. It communicates with discharge passage 8 by way of drilled passage I 1.

'I'he two blocks 9 and II have alined bores of' the same size, those in block 9 forming the cylinders I8 and those in block II serving as guides for the plungers I9. `In the pump chosen for illustration there are' nine plungers, ,but the number is a matter of design.

The cylinder bores I8 are each encircled by a groove 2| which is the inlet port, controlled by the end of the corresponding plunger. Drilled passages 22 connect the inlet ports with the pump inlet passage 1. There is a discharge valvef 23 for each cylinder. These valves are mountedv in passage IB and each valve is guided by a stem 24. and seated by a coil compression spring 25. The valves seat on cylinder block 9 in areas encircling the corresponding cylinder bore.

The various plungers i9 extend, each through the guidel bore inblock Il, across chamber I2l and into its cylinder I8, and each is reciprocated so as to overtravel inlet port 2l and at its limit; of motion to approach valve 23 closely. The plungers have counterbores 26 leading from their ends. Radial drilled ports 2'!v lead from the counterbore 26, and are so positioned that they are always within the limits of chamber I2 as the plungers reciprocate.

The mechanism which reciprocates the plungers is not illustrated but generally conforms to the structure of the plunger-actuating mechanism shown in Huber Patent 2,385,990 of October 2, 1945. Briefly, a drive shaft 28 carries a swashplate (not shown) and this reacts on the ends-of the plungers I 9 through creep plates and universally tiltable thrust heads (not shown), the

latter mounted on the plungers. The plungers are reciprocated with harmonic motion in a maintained phase relation, as will readily be understood.

Pressed into the central aperture in cylinder block 9 is a bushing 29, which forms the cylinder of the regulatory motor. At its left end it is bored to t stem 3l and at its right end it is bored to t piston head 32 which is slightly larger.

Both are lapped fits so as to be substantially leakproof under the high discharge pressures developed by the pump. To the right of bushing 29 stem 3I terminates in a thrust head 33..

At mid-length, the bore of bushing 29 is enlarged and to this enlarged portion a port 34 leads from an encircling groove. To this groove a port 35 leads from discharge passage I6. A choke 36 is interposed in passage 35 to damp out pressure surges.

Stem 3| carries a ported spider 31 which engages in grooves encircling the sleeve-like spillback valves 38. There is one such valve encircling each plunger I9 and controlling the ports 21. The arrangement is such that when spider 31 is to the left, all the way, as shown, ports 21 will be closed by valve 38 just before the end of the plunger overtravels inlet port 2|. As the spider moves the valves further and further to the right, ports 21 are closed later and later in the plunger stroke until at the right hand limit of the spiders motion the ports are not closed at all.

Since discharge pressure urges piston head 32 to the right the stem 3| is spring biased t0 the left. Since the discharge pressures are high and it is desired that the piston move full stroke near the upper `pressure limit (say, for example, between 2800 and 3000 pounds per square inch discharge pressure) it is desirable to use a piston 32 of very small effective area, so that the loading spring may be light and of low scale "Scale is defined as the rate at which spring resistance rises per unit of deilection.

The spring assembly comprises a spring seat 39 seated on head 33 and connected with an opposed spring seat 4| by a guide bolt 42. Slidable on bolt 42 is an intermediate spring seat 43 between which and respective seats 39 and 4| the springs 44 and 45 are mounted. The bolt guides the intermediate seat and holds the parts together for convenience in assembly. The arrangement affords a rather long spring unit protected against lateral deilection.

A tubular iitting 46 is threaded in cap 6 and is coaxial with stem 3|. The threaded joint has a sealing gasket clearly shown in the drawing. Adjustably threaded into tting 46 is a cylinder bushing 41 having a stop shoulder 48. The bushing 41 is sealed in the fitting by a ring gasket 49, and its adjustment changes the position of shoulder 48.

Slidable in bushing 41 is an elongated piston having an enlarged head 52 which engages shoulder 48 to limit the leftward (inward) motion of the piston. A bleed port 53 allows restricted flow of pressure liquid from the outer (right hand) side of piston 5| to inlet passage 1. Spring-seat 4| is mounted on the left hand end of rpiston 5|. A cap 54 is threaded onto the projecting end of cylinder bushing 41 and is sealed to fitting 46 by ring gasket 55. A comparatively light spring 56 urges piston 5| inward (to the left).

When the space to the right of piston 5| is under pump discharge pressure the piston is held in the position shown in Fig. 1, in which springs 44, 45 load piston 32 and set the pump controller to maintain the high pressure here assumed to be 3000 pounds per square inch. Under such conditions spider 31 will start to move to the right when discharge pressure reaches, say, 2800 pounds per square inch.

When the space to the right of piston 5| is vented springs 44, 45 elongate to the limit set by bolt 42, and the control is transferred to spring 56 which will allow spider 31 to move all the way to the right under a pressure of say 100 pounds per square inch. Any desired low pres- 4 sure may be used provided it is sumcient to move piston 5| to the left (preferably full stroke) against the urge of springs 44, 45.

The structure so far described is identical with that disclosed in the Huber Patent No. 2,512,799. The novelty in the present application resides primarily in the means used to control the supply of ypressure fluid admitted to the right of Threaded into the outlet connection 8 is a Venturi fitting 51, i. e. a fitting in which the cross-sectional area of the flow path gradually decreases to a minimum and then gradually increases so as to merge into the bore of the discharge line indicated at 58. A connection 59 leads from the iiow passage at the entrance end of the venturi. A similar connection 6| leads from the interior of the throat of the venturi, i. e. from a point at which the velocity head of the flowing liquid is high. These connections are used to develop opposing pressures on the motor and that motor controls a valve regulating flow from the connection 59 to the space at the right of piston 5|.

In Fig. l the motor in question is indicated as of the diaphragm type. The diaphragm 62 is clamped at its periphery between the valve housing 63 and cap 64. The cap 64 is of such a conguration as to limit the deflection to the right of the diaphragm 62. It also limits similar motion of the hub 65 on which the pin valve 66 is carried. A spring 61 biases the pin valve and the diaphragm to the left, i. e. in a direction to seat the pin valve 66 on the seat 68. The seat member 68 is connected rigidly by pipe or tube 69 with a needle valve housing 1| which is threaded into a port at the outer end of the cap 54. The needle valve is indicated at 12 and is provided for the purpose of limiting the 'maximum flow to a value only slightly greater than the venting capacity of the port 53. A cap 13 seals the needle valve against leakage.

Instead of using a diaphragm and a needle valve the same resultv can be secured by substituting a piston operated valve arranged to duplicate'the functions of the diaphragm ac` `cylinder |63 with an end closure |64. In this case the combined piston and valve is indicated at |66, the valve being biased to the left by a coil compression spring |61. A side port |68 which is closed by the .piston valve |66 when the latter is in its left-hand position and exposed by said piston when the latter is forced to the right leads to a connection |69 which is a direct analogue of the pipe 69 shown in Fig. 1.

Various other types of valve are possible and the purpose of illustrating two is to indicate that the essential thing is a valve which will open when there is a differential of pressure and close when such differential disappears or substantially disappears.

Considered in its broadest aspects let us assume that flow through the discharge lline 58 is controlled by a valve. If the valve is closed the pressure head developed by the pump will be effective in both connections 59 and 6|. Under such 4conditions the valve 66 or |66 as the case may be will be closed by the spring 61 or |61. However, if the valve controlling the discharge line 58 is open so that flow occurs, the pressure in the connection 6| will drop because a large part of the total head in the constricted part of the venturi will! befvelcc-ity'headf? According to the well-known Bernou-illi theorem there. will be a substantial pressure differential4 between con-- nections 59. and 6|. Thus, with either type of valve, that illustrated in Fig. 1 or that illustrated in Fig. 3', the pressure differential functions to operi the valve and admit pressure uid flowing through the'connections- 59 and 69, pastneedle valve12 to the space at the right of piston 52. The needle valve is soadjusted that this flow will slightly exceed the venting ilow through the port 53.

It follows that when a flow occurs through the discharge connection 58, the head 52 of piston 5| will be held against shoulder 48 and the springs 44, 45 will load the piston 32. This establishes the high pressure controlling action at which the pump will deliver against the head between 2800 to 3000 pounds per square inch. However, if the valve 66 or |68 closes, venting flow through the port 53 will dissipate the pressure acting on piston 5|. When this happens the springs 44, 45 which are mounted under stress function as a substantially rigid element and the light spring 56 becomes the regulating spring and maintains a relatively low pressure, say 200 pounds per square inch.

The arrangements in Figs. 1 and 3 may be used precisely as proposed in Patent No. 2,512,799. A very simple installation is illustrated in Fig. 2. Here the discharge line 58 leads to a valve 8|. This valve has a plug 82 whose porting is indicated in the drawing and has the form of the letter H. 83 represents a rotary motor of the expansible chamber type which may be reversed by interchanging its supply and discharge. One of the interchangeable supply and discharge connections is indicated at 84 and the other at 85. 88 is an exhaust connection leading from the valve body 8| to a sump 81. The pump draws liquid from the sump 81 through a suction line 88 which is connected with the pump intake With the valve 82 in the position shown the motor 83 is supposed to be running forward. If the plug be turned 90 counter-clockwise from the position shown, the motor would run backwards. If the plug be turned 45 counter-clockwise from the position shown, the motor would be stopped. Observe that in stopped position the discharge connection 58 would be completely closed and this, according to the general principles of operation above described, would cause the pump to set for a low discharge pressure, here assumed to be 200 pounds per square inch.

Assume now that the valve is in one of the motor-operating positions, say the one shown in Fig. 2 and assume that the motor 83 is overloaded and stalls. The small cross port 89 in the valve plug 82 is provided to permit suicient by-passing flow from supply to exhaust to keep the pump in a high pressure setting despite stall- 'ing of the motor 83.

Everything that has been described with particular reference to Fig. 2 is fully disclosed in the Huber Patent No. 2,512,799 and is repeated here merely to make clear the fact that the present invention affords similar possibilities. The port 89 is to be used only in cases where protection against stalling eifects is required. While only one motor is shown in Fig. 2, it is obvious that according to the principle disclosed in the earlier Huber application, a plurality of motors each with its own controlling valve can be connected in parallel.

The principle of the invention can be availed 6 ofwith different types of variable displacement: pumps and as explained. with referencey to Figs. 1 and 3, the exact type ofv pressure responsive valve is a matter of choice.

I claimed:

1. The combination of a pump; a controller.v shiftable to vary the displacement of said pump: between zero and full displacement; a regulatoryJ motor of the expansible chamber type, subject to discharge pressure developed by said pump, and connectedto move said controller in response to risingV discharge pressure in the direction to reduce pump displacement; loading means resisting such motion of said regulatory motor and controller; means for adjusting said loading means to vary the resistance oiered thereby; a Venturi connection through which said pump discharges, said connection including a restricted throat; means located at a point in the discharge path beyond said throat for alternatively permitting and substantially inhibiting discharge flow through said throat; and means serving to control said adjusting means in response to changes of pressure head in said throat.

2. The combination defined in claim 1 in which the means serving to control the loading-adjusting means comprises a movable abutment responsive to the differential between the pressure head in said throat and the pressure head developed by the pump.

3. The combination deflned in claim 1 in which the means serving to control the loading-adjusting means comprises a valve arranged to be opened and closed by a movable abutment which is subject to the pressure diierential between the pressure head in said throat and the pressure head developed by the pump.

4. The combination of a pump; a controller shiftable to vary the displacement of said pump progressively between zero and full displacement; a Venturi connection having a restricted throat through which said pump discharges; rst regulatory means responsive to the discharge pressure developed by operation of said pump and serving in response to rising discharge pressure to shift said controller in the direction to reduce displacement; second regulatory means responsive at least in part to variations of pressure head in said Venturi throat and serving to modify the action of said first regulatory means; and nowcontrolling -valve means located in the flow path beyond said Venturi throat.

5. The combination of a pump; a controller shiftable to vary the displacement of said pump progressively between zero and full displacement; a Venturi connection having ya restricted throat through which said pump discharges; iirst regulatory means responsive to the discharge pressure developed by operation of said pump and serving in response to rising discharge pressure to shift said controller in the direction to reduce displacement; second regulatory means responsive to variations of the differential between said discharge pressure and the pressure in said throat and serving to modify the action of said first regulatory means; and now-controlling valve means located in the flow path beyond said Venturi throat.

6. The combination defined in claim 5 in which the second regulatory means is so biased as to respond only when said differential approaches zero, and then serves suddenly to increase the response of the rst regulatory means to discharge pressure.

7. The combination of a pump including disanemia motor means arranged to actuate said controlling 5 means; `and means for subjecting said motor means to the action of two opposed pressures, one of which is pump-discharge pressure acting continuously in a direction to reduce pump displacement and the other of which is created as l0 an incident to the existence of a, velocity head in said throat above a predetermined low value.

- MATTHEW W. HUBER.

Emmons crrnn The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,284,897 Harrington June 2, 1942 2,304,831 Kendrick Dec. 15, 1942 2,385,990 Huber Oct. 2, 1945 2,512,799 Huber June 2-7, 1950

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