US2284111A - Hydraulic pump or motor - Google Patents

Description

May 26, 1942. H. F. vlcKERs 'HYDRAULIC PUMP oR l11101011 Filed June 28, 19511 vle A JK Q.

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e0 `9. :gf o fu e' I d' m a 9 L \9 0 g Y* l s f O 1 d) m n g 0 u 2 0 w -|NvENTIoR HARRY F. VICKERS i BY ATTORNEY Patented May 26, 1942 mimmo PUMP oa Moron a Harry F. Vickers, Detroit, Mich., assignor to Viclrers Incorporated, Detroit, Mich., a corporation of Michigan Application June 28, 1939, Serial No. 281,648

scisma (c1. -10s-162) 'I'his invention relates to power transmissions and more particularly to those of the type com'- prising two or more fluid pressure energy trans-- lating devices, one of which may function as a pump and another as a fluid motor. In such devices of the type which comprise a revolving cy1- inder barrel having a pluralityI of parallel cylin` der bores therein within which pistons are reciprocated by a swash plate device, it is customary to provide a rotary valving mechanism which is operated by the rotation of the cylinder barrel itself for the purpose of alternately connecting each cylinder bore with the inlet and outlet passages of the device. Many machines of this character utilize a plate type valve formed by a flat Vl5 surface of the cylinder barrel which runs in abutting and in fluid sealing relationship on a stationary fiat `valve plate. The plate type valve may be so constructed that the cylinder barrel is constantly pressed into engagement with the valve plate so that the clearance at the valve is automatically adjusted to take care of variations in oil viscosity and to compensate for wear. This is a distinct advantage and contributes much to the reliability and long life ofl machines employf ing a valve of this character.

It is customary with machines of this characterto` so proportion the size of the distributing ports in the end face of the cylinder barrel relative to the piston area andto the area of the annular 30 surface ofcontact with the valve plate as to provide approximate hydraulic balance between the fluid pressure forces exertedby piston reaction on the end faces of the cylinder bores and the fluid pressure separating forces'exerted in the 35 oil iilm between the cylinder barrel and valve plate. It is, of course, impossible in practice to provide an exact balance between these forces, and since it is necessary to provide some means for holding the barrel in contact with the valve 40 plate while the machine is idle, a spring or other resilient means is usually provided for urging the barrel into contact with the valve plate with a relatively light force at all times It is extremely' diillcult to predetermine with 45 precision the exact amount of hydraulic unbalance which will exist in a given machine since small variations in dimensions which are entirely within normal manufacturing tolerances produce large changes in the hydraulic balance when the f operating pressures are high. If the net unbal-v-A ance is in a direction holding the barrel in contact and is very large,A then the unit bearing pressures at the valve plate are apt to be excessive. On the other hand, if the machine is designed for a very small netV unbalance, it occasionally happens, due to manufacturing variations, that the net unbalance of the hydraulic forces on the barrel is in a direction tending to lift the barrel off from the valve plate, and in such cases the spring is sulcient to maintain the barrel in contact with the valve plate at all operating pressures below a certain maximum. When this maximum is exceeded, however, the

barrel lifts away from the valve plate, and since the valve is thereby rendered ineffective, the power drive through the transmission is completely and suddenly interrupted. This dimcuity can. be extremely troublesome at times, particularly where the transmission is used to operate a device, such as a hoist, which has to overcome a gravity load and in which complete dependence 4upon the transmission is placed for sustaining that load. In such cases it occasionally happens that the critical pressure at which the barrel will blo'w oi is slightly 'above the normal operating pressure` required for lifting the usual loads and that on rare occasions, due to snagging of hoisting lines or some other momentary small overload during hoisting, the criticalpressure is exceeded causing the barrel to lift and resulting in dropping of the load with consequent damage thereto.

It is an object of the present invention to provide a valve plate construction for a fluid pressure energy translating device of the classdescribed in which 'the above problems are avoided l by the provision of means for exerting a variable force tending to hold the barrel on the valve plate and proportional to leakage variations.

Further objects and advantages of the present invention will be apparent from the following delxscription, reference beingr had to the accompanying drawing wherein a preferred form Iof the present invention is clearly shown.

In the drawing the single figure is a longitud? nal cross section of a duid pressure energy translating deviceincorporating a preferred form of the present invention.

The embodiment of the invention selected for illustration comprises a pump of theA same general class as ,that illustrated in the patent to Hans Thoma, No. 1,931,969, and comprises generally a main ring-like frame member I0 having a mounting vflange I2 thereon and provided with bearings Il on which a main shaft i6 is journalled. The shaft I6 isprovided with a socket flange I8 carrying a pluralityof ball sockets l20 in which are mounted ball-'ended connecting rods 22 carrying reciprocating pistons 24.

suitable bolts not shown `are a Rigidly secured to the frame member I8 UY pair of plates 28 provided with bearings 28 and with iluid connections 38. Journalled on the bearings 28 is a swinging yoke generally designated as 32 comprising a valve plate 34 with rigidly attached hollow arms 38 providing trunnions for the yoke and connected to the fluid connection 38 by sealing sleeves 38. Y

'I'he valve plate 34 is provided with an arcuate raised sealing surface 48 against which runs the at end face 42 of a cylinder barrel 44 provided with a plurality of cylinder bores 48 therein. Formed in the valve plate 34 aretwo arcuate fluid distributing ports 48 each of which extends through an arc somewhat less than 180 degrees and communicates with the passages in the hollow arms 38. Formed at the left-hand end of the cylinder bores 48 are a plurality of -.nuld distributing ports 58 opening into the flat face 42 and adapted to alternately register with each of the distributing ports 48. A shaft 52 provided with universal joints 54 at its opposite 'ends con-V nects the barrel 44 to rotate with the shaft I8 in any position of the yoke 32. The parts thus far described are in a broad aspect well known in the art and per se form no part of the present invention.

The hydraulic balance of the cylinder barrel 44 is, of course, determined by suitable proportioning of the radial width of the flat pressure surface 48 relative to the total area of all of4 the ports 58 and the'total area of all of the pistons 24. With the present invention these areas are so proportioned as to produce a net fluid pressure force on the cylinder barrel 44 -tending to lift the barrel out of contact with the surface 48. This unbalance is preferably, though conduit |84 having a predetermined resistance connects the lower end of bore |88 with the tank.

In operation, assumingthat the conduits 38 are connected into a power transmission circuit inthe usual manner so that the upper conduit 38 is the pressure supply connection while the away from the observer each piston 24 will travel to the left during its top-'half revolution and will be withdrawn to the right during its bottomthus withdrawing fluid from the lower port- 48 into the cylinder 48 and discharging it out of them into the upper port 48.

At zero operating pressure in lthe upper port 48 the hydraulic unbalance of the cylinder barrel is likewise zero so that the force of spring 18l transmitted through the bearing 12 to the cylinder barrel'44 is the sole force urging the barrel into contact with the valve plate. As the pressure in the upper port 48 increases and before it reaches the critical pressure at 'which spring 18 can no longer hold barrel 44 against the surface, the spring 18 is able to overcome the 'net hydraulic uibalance of the barrel 44 and hold the same in contact. In increasing to the critical pressure, however, if we assume that the clearance between surfaces 48 and 42 remains constant, the leakage from these not necessarily, made small,`and is, of course,

proportional to the operating pressure.

According to the inve tion, means is provided for imposing an addi ional force tending to urge the barrel into contact with the surface 48,

which force is determined by the amount of leakage ltaking place at the valve plate surface. For this purpose the valve plate is formed with a cylindrical recess 58 in which a cylindrical projection 58 formed integrally with the cylinder barrel 44 is rotatably mounted. A suitable oil seal may be provided at 88. There is thus formed an annular chamber 82 radially inward of the annular valve plate surface 48.

Formed in the valve plate 84 isa cylindrical chamber 88. Slidably mounted in chamberl 88 'is a piston 88 secured to a rod 18. The latter carries Va thrust bearing 12 at its right-hand end whichabuts against a shoulder formed at the left-hand end of a recess 14 in the barrel 44. The left-hand end-of the rod 18 carries an adjustable spring abutment 18 against which is mounted a spring 18 serving as the normal cylinder barrel spring. Cap members 88 and 82 having drain passages 84 and 88 serve to enclose the spring 18 and the left-hand vend of n chamber 88. The right-hand end of chamber 88 is in communication through a passage 88 with a spring-loaded pilot valve u auspicato selectively connect the passage V88 either with a passage 82 leading to the distributing port 48 or a passage 84 leading totank. ,The valve 88 is normally urged down by a spring 88 having an adjusting screw 88. I'he lower end lof the bore |88 within which the valve spool 88 is slidable is in communication with the annular chamber 82 by a conduitv |82 of negligible resistance.. A

surfaces radially inward to the chamber 82 will increase correspondingly. This leakage passes through passage |82 into the lower end of bore |88 and out -through restricted passage |84 to tank. So long as the amount of this leakage is so small as to meet negligible resistance in the restricted passage |84, the pressure in bore |88 tending to lift the valve 88 upwardly will be low.

As soon as the leakage into -chamber 82 increases, however, to a value such that the pressure in the lower end 'of bore |88 is suillcient to overcome spring 88,the valve 88 lifts cutting 'off chamber 88 from the tank connection 84 and admitting pressure fluid from the port 48 through conduits 82 and 88 to the chamber 88. The full pressure existing in port` 48 is thus exerted against the piston 88 in a direction tending to hold the barrel onto the valve plate, thus bringing the barrel 44 into closer contact with the valve plate surface 42- and accordingly decreasing the leakage. 4

It will be noted incidentally that so e pressure is exerted in chamber 82 ten g to lift the cylinder barrel off from the valve plate so that it is accordingly necessaryto provide 'a net 4area at the piston 88 suillcient to overcome this pressure exerted in chamber 82.

While conduit 82 has been shown as connect-- ing with only one of the distributing ports 48, which construction is suitable for devices where the high pressure side of the device is always at the same distributing port and is never reversed, it will be understood -thatwhere either distributing port 48 may be the high pressure' port depending upon operating conditions, that a shuttle valve operating in the well-lmown manner'may be provided for connecting the conduit 82 with whichever of the distributing ports happens to be the high pressure port at any instant.

It will be seen that with the construction shown and described, the total force urging the cylinder barrel into contact with the valve plate is automatically regulated to control the leakage across the valve plate surfaces.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be'adopted, all coming within the scope o! the claims which follow.

What is claimed is as follows: v

1. In a fluid pressure energy translating device having a plurality of cylinders and pistons reciprocable therein; a rotary valve structure comprisingl two relatively rotatable members provided with ilat, annular, sealing surfaces in running engagement and containing fluid distributing ports communicating with said cylinders, one of said members having an area exposed to iiuid pressure from said cylinders tending to urge said member into abutment with torce proportional to said pressure, means forming a chamber for 'A collecting leakage from said va1ve, a restricted conduit for draining said chamber, andy means including a iluid pressure chamber operatively associated with said one member to exert a thrust thereon and a pilot valve responsive to pressure variations in said rst chamber and located in a passage connecting between a source of pressure uid and the second chamber to vary the total force applied to said one member.

2. In a iiuid pressure venergy translating device having a plurality of cylinders andpistons re'- ciprocable therein, a'rotary valve structure comprising two relatively rotatable members provided with dat, annular, sealing surfaces in runy ning engagement and containing iluid distributing ports communicating with said cylinders, one oi' said members having an area exposed to iiuid pressure from said cylinders tending to urge said member into abutment with force proportional to said pressure, resilient means also tending to urge said members into abutment, ,means .forming a chamber for collecting leakage from second chamber to vary the total yforce applied to said one member. 4 y

3. In a iluid pressure energy translating device of the type having a revolving cylinder barrel with a plurality of cylinders therein and pistons reciprocable in the cylinders, a rotary valve structure comprising a stationary valve having a ilat annular surface with fluid distributing ports therein, means forming a ilat annular surface on the cylinderl barrel adapted to abut the valve plate surface. and provided with iluid distributing A ports therein, and means including a fluid pressure chamber operatively associated with the cylinder bari-'el to exert athrust thereon and a pilot valve responsive to leakage `variations at,

the valve plate and located in a e connecting between a source of pressure uid and said chamber to thereby control the clearance between said surfaces.

. HARRY F. VICKERB.

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