US2918879A

US2918879A - Plunger-controlled inlet port for pumps

Info

Publication number: US2918879A
Application number: US659824A
Authority: US
Inventors: Gordon A Cervo
Original assignee: New York Air Brake LLC
Current assignee: New York Air Brake LLC
Priority date: 1957-05-17
Filing date: 1957-05-17
Publication date: 1959-12-29
Anticipated expiration: 1976-12-29

Description

Dec. 29, 1959 G. A. CERVO PLUNGER-CONTROLLED INLET PORT FOR PUMPS 2 Sheets-Sheet 1 Filed May 17, 1957 INVENTOR GordonACeruo ATTORNEYS Dec. 29, 1959 G. A. CERVO 2,918,879

PLUNGER-CONTROLLED INLET PORT FOR PUMPS Filed May 17, 1957 2 Sheets-Sheet 2 INVENTOR Gordon A.Cruo

BY ma ggfdm.

- ATTORNEYS United States Patent '0 PLUNGER-CONTROLLED INLET PORT FOR PUMPS Gordon A. Cervo, Watertown, N.Y., assignor to The New York Air Brake Company, a corporation of New Jersey Application May 17, 1957, SerialNo. 659,824

4 Claims. (Cl. 103-173),

This invention relates to swash-plate-actuated pumps of the parallel plunger type generally similar to that shown in the patent to Huber 2,433,222,. December 13, 1947, and the improvement relates to the plunger-controlled inlet ports. The Huber patent above identified includes means to vary pump delivery by the use of spillback sleeve valves which are adjusted in the direction of the plunger axes to vary the effective stroke, but the present invention is capable of use regardless of the presence or absence of spill-back valves, and will be shown embodied in a pump devoid of such valves.

To secure large inlet port area and consequent high charging efliciency, applicants assignee has heretofore used inlet ports each of which was an annular groove completely encircling the cylinder bore. Since, in such pumps, the rear ends of the plungers necessarily project from the cylinders and are subject to lateral as well as axial thrust by the plunger actuator, usually a swash plate, there is a tendency for the forward or inner ends of the plungers to be deflected laterally. This tendency makes it desirableto provide a continuous guiding surface for the inner ends of the plungers (not possible with a bore encircling groove), and since a swash plate is indifferent to its direction of rotation and sois likely to be driven in either direction, opposed. continuous guiding surfaces are quite desirable.

The invention substitutes two diametrically opposite and favorably located port recesses for each continuous annular port, and so shapes the two opposed recesses that they can be produced by simple machining operations. The direction of flows to these two port recesses so favors unidirectional inlet flow that. loading losses are minimized. -Another and very important advantage is that the new porting produces a more rigid cylinder block, so that pistons may be fitted more closely than has been possible with encircling groove ports. The blocks of the former design, unless made undesirably thick, were subject to appreciable distortion by the head pressure, and this distortion was suflicient to cause very closely fitted pistons to bind. Closer fitting of the pistons affords increased volumetric efficiency and makes it possible to attain higher operating pressures.

A successful embodiment of the invention will now be described by reference to the accompanying drawing.

In the drawing:

Fig. 1 is an axial section of a known type of pump modified by inclusion of the improved porting.

Fig. 2 is a fragmentary section through a portion of i the cylinder block, on the same plane as Fig. 1, but on a larger scale, and showing the cylinder bore without the plunger.

Fig. 3 is a fragmentary diagram showing one cylinder bore and its two loading ports as they would appear on a section through the bore normal to the axis of the bore. Broken lines are used as a basis for explaining principles involved in the design.

Refer first to Fig. 1. The pump housing comprises a body portion 6 and a cap 7, the body portion having the "ice threaded inlet connection 8 and the cap having the threaded dischargeconnection 9. The cap is held to the body by machine screws, one of which appears at 11. A gasket 12 is interposed.

The cylinder block 13 is clamped between

shoulders

14, 15 on body and cap. It is sealed to the body by a toric ring 16,v and to the cap by two toric rings 17,.18 each with an annular anti-extrusion follower, as shown. A dowel 19 fixes the assembled positions.

A spherical support 21 for the nutating plate 22 is formed on the head of a bolt-like member 23 threaded at 24 to cylinder block 13. Flutes 25 and spline ring 26 function as a nut lock to preserve the adjustment of. sup-v port 21. The toric seal ring 27 and washer 28 seal the assembly. The end portion of bolt 23 is reduced in diameter and threaded to receive a nut 29 which seats on a washer clearly shown in Fig. 1 and clamps the cylinder block.13 and the nutating plate support 21 to cap 7.

The cylinder block has. parallel cylinder bores, one of which appears at. 31. These bores are commonly nine in number, are all parallel with the common axis of the pump and its drive shaft and, are arranged in circular order around said axis. All the bores open into an an: nular passage 32 between the cylinder block and cap. This passage 32 communicates with connection 9 through one or more drilled ports 33. Discharge valves 34 of conventional form biased to close by springs 35, are provided, one for each cylinder bore.

Each bore 31 contains a reciprocable plunger 36 having a cupped end 37 with universally tiltable slipper 38 which engages the swash plate 39 and universally tiitable sliding ring 41 which engages the nutating plate 22, all according to a construction familiar in the art.

The swash plate 39 has a journal 42 which, in conjunction with bearing ring 43 and annular discs 44, 45, affords a combined radial and thrust bearing for the swash plate. A dowel 46. positions ring 43. A removable plate 47 held by cap screws, as shown, confines a shaft seal assembly 48 of known form. A conventional spline drive member 49 is used to rotate the swash plate.

No novelty is here claimed for the structure so far described. It is. in commercial use and is simply one typical environment in which the invention may be used.

As in the Huber pump above identified, the reciprocating plungers are used to control inlet flow to the cylinders. According to the invention, there are two port recesses 51 which are exposed at least partially as the plunger approaches complete retraction. The retracted position is shown for that plunger 36 which is fully visible in Fig. 1.

It is convenient to form these two port recesses by a milling operation, and when so formed they have the crescent-shaped contour clearly shown in Fig. 3. Flo-w to the port recesses 51 is afforded by the passages 52, one leading to each recess 51 and each directed toward that end of the cylinder bore which is closed by its discharge valve 34. Thus each passage 52 is at an acute angle to the axis of the cylinder bore so as to afford the least practicable change of flow direction.

At the end of its displacement stroke each plunger 36 is nearly in contact with the corresponding valve 34, so that when the end of the plunger reaches the edges of the port recesses 51 on its suction stroke, there is nearly a vacuum in the cylinder bore. At this time the plunger is slowing to reverse its motion, after which its displacing motion gradually accelerates. In the small fractions of a second during which the inlet ports are open at high pump speeds, such as 3000 r.p.m. and higher, the working space must receive its charge of oil. Tests have demonstrated that though the arcuate extent of the port recesses in the new construction is about one half the circumference of the bore, the favorable angle of the approach-passages 52 more than compensates for the reduction of arcuate extent, so there is no impairment of loading efficiency.

-At this point, it will clarify matters to explain how the extent of port recesses '51 can be determined. In Fig. 3, the axis of rotation of swash plate 31 is at A and the periphery of the cylinder bore is the circle B. Diameters CC and DD are normal to tangent lines AC and AD and so intersect at an angle equal to CAD. The arcuate interval between port recesses 51 is more than twice the shorter arc CD in the example illustrated. This disparity could be reduced somewhat by shortening the radius of the circle on which the centers of the bores are spaced or by other modifications, but within the design range permissible in a pump of this type, it will be found that the angular interval W between recesses 51 measured about the axis of the bore materially exceeds the angle M subtended by the bore about the axis of rotation of the swash plate.

Thus a significant design objective is so to limit port recesses 51 that they lie wholly between two planes each passing through the axis of rotation of the swash plate and the respectively tangent to opposite sides of the bore.

Both of the above relationships appear in Fig. 3 and each allows a moderate margin of safety.

The forward ends of the plungers when closely guided can be devoid of fillets and the plunger fit can be uniform to the very ends.

Since the two port recesses 51 are respectively inward and outward radially, the interval between adjacent bores is not narrowed at the inlet ports in applicants design. It is narrowed by twice the depth of the port where as heretofore complete annular grooves are used. Strict comparative tests using pumps identical except as to the inlet ports show that with the new construction and the same head pressures, the plungers can be fitted more closely using the new porting without binding.

The difference in plunger diameter is a few tenths of a thousandth of an inch, but the improvement is commercially significant both as to performance and production costs, and can readily be availed of by the precision methods used in this field.

What is claimed is:

1. In an expansible chamber pump, the combination of a rotary shaft; a swash plate turning therewith; means defining a plurality of fixed pump cylinder bores, each substantially parallel with the axis of rotation of said shaft and arranged in a circular series around said axis; plungers reciprocable in said cylinder bores and operatively engaged by said swash plate, the inlet path to each of said cylinder bores comprising a corresponding pair of diametrically opposed arcuate port recesses formed in the wall of respective bores, each pair of recesses subtending, in the aggregate, more than half the circumference of the bore, the arcuate recesses of each pair being centered on a plane substantially radial to said axis of rotation, and said recesses being spaced apart by an angular interval measured about the bore which materially exceeds the angle subtended by the bore about said axis of rotation; and discharge means for each cylinder bore.

2. The combination defined in claim 1 in which said arcuate port recesses approximate segments of cylinders whose axes are substantially parallel with the axis of the bore and whose radius is shorter than the radius of the bore.

3. The combination defined in claim 2 in which each arcuate recess is supplied by an approach passage extending at an acute angle to the axis of the bore and leading to the corresponding recess in the general direction of displacing motion of the plunger.

4. In an expansible chamber pump, the combination of a rotary shaft; a swash plate turning therewith; means defining a plurality of fixed pump cylinder bores whose axes are substantially parallel wtih the axis of rotation of said shaft and arranged in a circular series substantially centered on said shaft axis; and single-acting plungers each projecting at its rear end from a corresponding cylinder bore into engagement with the swash plate, said plungers being reciprocable in said bores by the rotation of said swash plate, the inlet path to each of said bores comprising a corresponding pair of diametrically opposed arcuate port recesses which are cyclically exposed and blanked by the forward end of the corresponding plunger, each pair of port recesses being formed in the wall of a bore and substantially centered on a plane radial to said axis of rotation, said port recesses nearly but not quite subtending the angle between two planes which are radial to the axis of rotation of the swash plate and tangent respectively to opposite sides of the corresponding bore.

References Cited in the file of this patent UNITED STATES PATENTS 1,078,889 Woerner Nov. 18, 1913 2,417,137 Smith Mar. 11, 1947 2,688,286 Friedlander Sept. 7, 1954 FOREIGN PATENTS 7 27,057 Great Britain Nov. 22, 1909 674,892 Great Britain July 2, 1952