US2433220A - Pressure control for pumps - Google Patents

Description

De.23,.1947.' v M. w.-HUBER v 2,433,220

PRESSURE CONTROL FOR PUMPS Fil ed Oct. 20, 1944 L Fial Jnnentor Mafihew W; Huber Gttomegs Patented Dec. 23, 1941 PRESSURE cosmos ron PUMPS Matthew W. Huber, Watertown, N. Y., assignor to The New York Air Brake Company, a. corporation of New Jersey Application October 20, 1944, Serial No. 559,593

4 Claims.

i This invention relates to pressure control devices for high pressure hydraulic pumps, and particularly to a mechanism of this class built into the head of a continuously operating pump, and capable of operating in a hydraulic pressure system having no accumulator. The absence of an accumulator requires a very sensitive pressure control. It must respond instantly when pressure rises above the set value. It must be such as to permit the pump to continue in operation without damage to itself.

The control device belongs to that known class in which a pressure responsive piston shifts a valve against Spring resistance first to cut off the supply of liquid to the pump at the desired limiting pressure, and also to vent the discharge line.

Important features of thepresent invention are that venting occurs directly from the discharge manifold of the pump, and in response to pressure in that manifold; the pressure piston itself acts as the vent valve, and some fluid is continually circulating through the pump. The port controlling part of the pressure piston is shouldered,

so that it operates in two phases. In the first phase (which occurs just before the inlet ports are completely closed), the discharge is vented at a very restricted rate. The Second phase is reached after the inlet ports are completely closed and in this phase venting occurs at a rate which increases to the full output of the pump if the pressure rises high enough.

Since the hydraulic liquid in this type of system is oil, and since the pumped liquid furnishes the only lubrication which the pump receives, complete stoppage of the inflow of liquid to the pump would in time be attended with damage to the pump. Consequently a fixed by-pass leads around the inlet-controlling valve to supply a metered quantity of oil sufficient to cool and lubricate the pump. The oil so drawn into the pump is vented by the valve action of the pressure piston above mentioned.

The invention will now be described as applied to a. pump of the type described and claimed in my pending application Ser. No. 506,091, filed October 13, 1943', now patent No. 2,385,990, October 2, 1945. No claim is made in the present application to the pump mechanism nor will its details be elaborated.

In the drawing:

Figure l is an axial section through a parallel cylinder pump and through a control mechanism mounted in the head of said pump.

Figure 2 is a fragmentary view of the control mechanism showing its full venting position.

Figure 3 is a. section through the valve seat bushing and pressure cylinder insert on the line 3-3 of Figure 2.

Figure 4 is an elevation of the combined pressure piston and vent valve.

Nora-Figure 3 shows the actual arrangemen of the ports in the control cylinder insert, whereas Figures 1 and 2 are diagrammatic to the extent that one of the two Sump ports and one of the two discharge pressure ports are drawn as if they lay in the same plane. Actually and as indicated in Figure 3 they lie in planes at to each other. This diagrammatic showing permits all flows to be traced on Figures 1 and 2. The actual location of the two sets of ports is not significant from a functional standpoint so long as they do not intersect.

Referring first to Figure 1, the pump has a tubular drive shaft 6 on which is mounted a swash plate I. The swash plate is sustained by a thrust bearing assembly generally indicated at 8 and reacts through creep plate 9 and a plurality of ball thrust members ll upon a plurality of parallel plungers l2, one of which is shown in section, and another in elevation on Figure 1, Coil compression springs l3 urge the plungers towards the swash plate. The plungers l2 (commonly nine in number) reciprocate in bores formed in a cylinder block I 4.

The inlet flow to each cylinder is through the hollow bore of the Shaft 6, thence through a radial passage 15 formed in the swash plate, thence through an L-Shaped passage l6 formed in the cylinder block I4. The passage It comprises two intersecting drilled ports, one of which intersects the bore of the cylinder as indicated at H. Thus when the plunger I2 is fully retracted (see the lower plunger in Figure 1) the end of the plunger exposes the port H. The axial passage l8 drilled in the plunger is a lubricating port.

The discharge valves l9 are cup-shaped poppet valves mounted in the cylinder head 2| and urged closed by individual springs 22. The discharge manifold of the pump is the continuous annular passage 23. Provision is made for connecting a discharge line to manifold 23, but this detail being conventional is not illustrated.

Formed on the cylinder head 2| is a transverse generally cylindrical hollow housing 24 closed at its ends by screw plugs 25 and 26. These are sealed by ring gaskets of rubber-like material clearly shown in the drawing. Received in a seat in the housing 24 is a valve seat bushing 21. This overlies an annular intake passage 28 to which the Supply connection of the pump (not shown) 3 leads. Where the bushing 21 overlies the annular passage 28 it is provided with two series of through ports 29 and 3|,

Fitting withinbushing 21 and having a flange which engages the end of the bushing 21 is the pressure cylinder element 32. The plug 25 engages cylinder element 32 and holds it and bushing 21 tightly in place. Element 32 has an axial bore, which is closed at the lower end by a plug 33 pressed to place, and receives the pressure piston 34 which makes a close but free sliding fit in the bore of the cylinder. The bushing 21 has a peripheral groove 35 which is connected by a passage 36 with the discharge manifold 23 of the pump. From the groove 35 lead a plurality of radial passages 31. These communicate with a peripheral groove 38 formed in the cylinder element .22. Sealing gaskets (sometimes called rings) seal the joint between the bushing 21 and the housing 24 on each side of the groove 35. Similar O-rings seal the joint between the cylinder element 32 and the bushing 21 on both sides of the groove 38.

Leading from the groove 38 to the cylinder bore in element 32 are radial ports 39, only one of which is visible in Figures 1 and 2. Actually there are two as shown in Figure 3. A cross port 4| is drilled through the reduced upper portion of the cylinder element 32 to intersect the cylinder bore. Its ends are closed by a sleeve 42 which is pressed over the reduced end of the cylinder element 32. Two axial ports 43, only one of which is shown in Figures 1 and 2 connect the cross port 4| with the space below the cylinder body 32. The location of these ports is shown in Figure 3.

A pipe (not shown) screwed into the threaded socket 44 in plug 26 is used to conduct oil venting through the passage 43 to the sump or oil supply (not shown).

Mounted in the bushing 21 is the valve element which is of the grid piston type and controls the ports 29 and 3|. The ports 29 are controlled by the cup-shaped portion 45 of the valve and the ports 3| by a spaced ring portion 45. By making the portion 45 cup-shaped along guiding surface is secured, without making the mechanism unduly long, since the cup-shaped member 45 telescopes over the end of the cylinder body 32.

A thrust stem 41 reacts against the valve just mentioned, the lower end, as viewed in Figure 1, being socketed in the valve. The upper end 48 is guided in a tubular guide 49 which forms part of a spring seat threaded into the housing 24 beneath the cap 25. A coil compression spring 52 reacts between the spring seat 5| and a second spring seat 53 formed as an enlargement of the rod 41. Guiding head 48 does not exercise any very marked dash pot effect, since there is a port 54 in the spring seat 5|.

It will be observed that the piston 34 has a reduced shouldered end at 55 and that there is a by-pass port 56 of limited dimension which leads from the annular space 28 to the inlet path of the pump.

The dimensions of the parts Just mentioned are quite important. The by-pass port 56 is of such size that it will pass approximately one gallon of oil per minutewhen the valve controlling inlet.

flow to the pump is closed.

The position of the shoulder on the plunger 34 and the amount the diameter of the plunger.is reduced at the shoulder are both important. The reduction of diameter assuming a plunger 0.218" in diameter is of the order of 0.0035" n 011$ Q 1?!- mercial embodiment which operates at 300 p. s. i. The position of the shoulder is such that the shoulder will start to expose the cross port 4| before the ports 29 and 3| are completely closed.

The position was originally determined by trial as follows. When the ports 29 and 3| are fully open the suction pressure in the passage leading to the hollow shaft 6 is approximately equivalent to 29" of mercury (absolute). When the ports 29 and 3| have been closed sufficiently to reduce this suction pressure to 15 of mercury absolute) the shoulder should commence to expose the cross port 4|. Careful tests have indicated that this timing gives very smooth action without any tendency of the valve to vibrate. The effect is believed to be attributable to restricted flow in the annular passage that is initiall opened between the reduced end of the plunger and the wall of the cylinder.

Operation The pressure at which the constantly running I pump is to be unloaded is determined by adjustment of spring seat 5|. This determines the initial loading of spring 52. When the discharge pressure in manifold 23 reaches the value determined by the spring load, the inflow to the pump will be throttled to the extent mentioned and the shoulder at 55 will expose port 4| and initiate a very restricted venting action.

The timing of the events just mentioned is very important. Throttling of the inlet ports 29 and 3| restricts the feed of oil to the cylinders, and when the throttling becomes substantial the delivery of the pump is irregular and there is a tendency for pressure fluctuations to occur. Unless eliminated these pressure fiuctuations cause erratic performance of the pressure control device. Elimination of these fluctuations is the function of the reduced portion 55 on the pressure piston 34.

The shoulder is so located that when ports 29 and 3| are throttled to an extent which would cause fluctuations of discharge pressure, the shoulder permits a definite restricted flow through passages 36, 31, 39, past the shouldered end of plunger 34 and thence through passages 4| and 43 to the sump connection. The arrangement is such that a substantially uniform venting rate is established when the shoulder on the piston 34 reaches the port 4|, and this venting flow is maintained at this approximately uniform rate until the ports 29 and 3| are completely closed and the supply flow is restricted to the capacity of by-pass 56.

The shouldered arrangement is believed to be the simplest way of securing a metered venting flow through a considerable range of motion of the plunger 34. Other arrangements are, however, possible and could be substituted provided they give the functional characteristics above set forth.

If the discharge pressure continues to rise, and it may do so because of flow through the port 56, the piston 34 will move further until a state of equilibrium is reached. The position shown in Figure 2 is believed to be the extreme limit of motion of the plunger 34 under pressure (upward with reference to Figure 2).

The head 48 on the stem 4'! probably exercises some motion damping effect but reliance is placed chiefly on a dash pot action produced by the cup-like portion of the valve. At any rate the valve is sensitive and very stable. It will operate in systems having no accumulator and will maintain pressure within very close limits. Precise action is attributed partly to the fact that the port 56 permits at least a minimum flow to occur. It is believed, however, that the shouldered end on the piston'and the dash pot effect of the cupped end 45 of the valve are vital factors in the precise functioning of the device.

While the embodiment illustrated is preferred modifications within the scope of the claims is contemplated.

What is claimed is:

1. The combination of a continuously running hydraulic pump having a suction passage and a discharge passage; a, cylinder in communication at one end with said discharge passage, said cylinder having a lateral vent port; a combined valve and piston slidable in said cylinder, the chant the pistonsubject to pressure from the discharge passage being formed to alIord a flow restricting passage leading to a control edge on the piston, said control edge coacting with the control edge of said lateral vent port in such manner the flow hydraulic pump having a suction passage and a discharge passage; a cylinder in communication at one end with said discharge passage, said cylinder having a lateral vent port; a combined valve and piston slidable in said cylinder, the

end of the piston subject-to pressure from the restricting passage imposes a secondary throttling action as said edges overtravel in an opening direction; a valve arranged to be moved in a closing direction, by said piston as the piston moves in a vent opening direction under the urge of discharge pressure, said valve controlling flow through said suction passage; and yielding means loading said valve and piston in opposition to discharge pressure, the parts being so dimensioned that said control edge starts, to expose said vent port when the suction valve commences materialiv to throttle flow in the suction passage and the vent port is fully exposed by the piston after the suction valve is closed.

2. The combination of a continuously running hydraulic pump having a suction passage and a discharge passage; a cylinder in communication atone end with said discharge passage, said cylinder having a lateral vent port; a combined valve and piston slidable in said cylinder, the end of the piston subject to pressure from the discharge passage being reduced in diameter to form an annular flow passage having a marked and approximately uniform throttling effect and leading to an annular control edge on the piston, said control edge coacting with the control edge of said lateral vent port in such manner the flow passage imposes a secondary throttling action as said edges overtravel in an opening direction; a valve arranged to be moved in a, closing direction by said piston as the piston moves in a vent opening direction under the urge of discharge pressure, saidvalve controlling flow through said suction passage; and yielding means loading said valve and piston in opposition to discharge pressure, the parts being so dimensioned that said control edge starts to expose said vent port when the suction valve commences materially to throttle flow in the suction passage and the vent port is fully exposed by the piston after the suction discharge-passage being formed'to afiord a flow restricting passage leading to a control edge 'on the piston, said control edge coacting with the control edge of said lateral vent port in such manner the flow retricting passage imposes a-secondary throttling action as said edges overtravei in an opening direction; a valve arranged to be moved in a closing direction by said piston as the piston moves in a vent opening direction un-. der the urge of discharge pressure, said valve controlling fiow'through said suction passage; means forming a metering by-pass around the last named valve; and yielding means loading said valve and piston in opposition to discharge pressure, the parts'being so dimensioned that said control edge starts to expose said vent port when the suction valve commences materially to throttlefiow in the suction passage and the vent port is fully exposed by the piston after the suction valve .is closed.

4. The combination of a continuously running hydraulic pump having a suction passage and a discharge passage; a cylinder in communication at one end with said discharge passage, said cylinder having a lateral vent port; a combined valve and piston slidable in said cylinder, the end of the piston subject to pressure from the discharge passage being formed to afford a flow restrictin passage leading to a control edge on the piston, said control edge coacting with the control edge of said lateral vent port in such manner the flow restricting passage imposes a secondary throttling action as said edges overtravel in an opening direction; a valve arranged to be moved in a closing direction by said piston as the piston moves in a vent opening direction under the urge of discharge pressure, said valve controlling flow REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Number Name Date 2,123,815 Tweedell July. 12, 1938 Dick -sjMar. 11, 1941

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