US2925046A

US2925046A - Engine

Info

Publication number: US2925046A
Application number: US656574A
Authority: US
Inventors: Budzich Tadeusz
Original assignee: New York Air Brake LLC
Current assignee: New York Air Brake LLC
Priority date: 1957-05-02
Filing date: 1957-05-02
Publication date: 1960-02-16
Anticipated expiration: 1977-02-16
Also published as: FR1206702A; GB831673A

Description

T. BUDZICH Feb. 16, 1960 ENGINE 3 Sheets-Sheet l Filed May 2. 1957 INVENoR. Tadeuszudmch D 'Sw if? orneys 3 Sheets-Sheet 2 T. BUDZICH ENGINE Feb. 16, 1960 Filed May 2, 1957 INVENTOR.

mr N@ wim? `:11 \\\\\\\\\\\\\\\\\\\\.w\\\\ \\\A. @m wb IJWA- @L L im N wwwa T. BUDZICH Feb. 16, 1960 ENGINE 5 Sheets-Sheet 5 Filed May 2, 195? 25 INVENTOR 14Iadeusz Budzich ATTORNEYS United States Patent() ENGINE Tadeusz Budzich, Watertown, N.Y., assignor to The New York Air Brake Company, a corporation of New Jersey Application May 2, 1957, Serial No. 656,574

13 Claims. (Cl. 10S-162) This invention relates to fluid pressure engines and more particularly to engines of the rotary cylinder barrel longitudinally reciprocating piston type. As used herein, the term engine means a device which is capable of being operated as either a pump or motor.

Engines of the type mentioned are well known in the art and include -a rotatable cylinder barrel containing a plurality of circumferentially spaced longitudinal cylinder bores, a piston slidably received in each bore and having a spherical surface for-med on one of its ends, an inclined cam plate associated with the pistons at their spherical ends for moving them on their discharge strokes, and a valve member for sequentially transmitting uid to and Vfrom the cylinder bores as the barrel rotates. In general, the art teaches the use of two types of cam plate. The first, illustrated by Patent 511,044, issued to Cooper et al. on December 19, 1893, is called the articulated piston type and comprises an annular bearing rotatably mounted on the cam plate and joined to each piston by a connecting rod which is universally mounted in both the annular bearing and the piston. ln this arrangement, the thrust forces transmitted between the cam plate and the pistons act in directions substantially parallel with the axes of the pistons. The second type, illustrated by Patent 1,710,567, issued to Carey on April 23, 1929, and for convenience termed the non-articulated piston type, comprises a cam plate having an uninterrupted surface which bears against the pistons either directly as in Williams Patent 1,539,616, issued May 26, 1925, or indirectly through a piston shoe as in the Carey patent above mentioned. In these devices, the force transmitted to each piston acts in a direction normal to the surface of the cam plate rather than parallel with the axis of the piston. The art discloses two types of valve member; one type comprising a ported cylindrical sleeve coaxial With the cylinder barrel and forming a valving surface in contact with the inner or outer periphery of the barrel. The patent to West, 1,722,832, issued July 30, 1929, is typical of this arrangement. In the other arrangement, the valve member is a ported plate which abuts against an end face of the cylinder barrel. This type is shown in the Cooper et al. patent mentioned above.

The present invention is primarily related to engines of the kind mentioned, which include the non-articulated piston-type cam plate and the axially abutting plate-type valve member. Because of its simplicity, this specific engine is commercially attractive but because of certain inherent difficulties, its usefulness has been limited. As stated above, the force transmitted between the cam plate and each piston acts in a direction normal to the surface of the cam plate and it is apparent that this force can be resolved into two components, one in the direction of the piston axis and the other normal thereto. The firstnamed component moves the pistons on their discharge stroke, but the second tends to cause tilting of the cylinder barrel with respect to the valve plate. When it is remembered that these engines operate at pressures as high as 3000 p.s.i., it can be seen that a relatively small ICC angular misalignment between the cylinder barrel and the valve plate results in intolerable leakage.

Up to the present time, two methods have been used to combat this tilting problem. One approach is to support the cylinder barrel in the housing itself rather than on the shaft and to make the housing walls thick enough and strong enough to resist the tilting tendency. Obviously, this approach results in a large, heavy engine which cannot be used in environments where these considerations are of prime importance. The other approach is to center the splined driving connection between the shaft and the cylinder barrel about the point of intersection of the shaft axis and the plane of the centers of the spherical surfaces on the pistons and to support the cylinder barrel laterally entirely on the spline. In this way, the moments due to the normal components of the thrust force will counterbalance each other about the point of support and the cylinder barrel will experience no tilting tendency. If the shaft should deect under the cumulative load of these normal force components, the cylinder barrel spline can rotate slightly relatively to the shaft spline and maintain the end face of the barrel in contact with the valve plate. This approach has not been altogether satisfactory, because the spline clearances are not sufiicient to permit the required movement and furthermore, since the support also functions as a driving connection, the torque and lateral force loads passing through the support, causing binding of the` spline teeth. The clearance problem has been relieved somewhat by forming the shaft spline teeth with a circular contour in longitudinal cross section, but this solution is of little value as long as the binding problem persists.

The object of this invention is to provide an engine of the type discussed above in which the cylinder barrel is connected to be driven and also laterally supported by the shaft, but in which this driving connection and lateral support permit free longitudinal motion of the cylinder barrel and free rotation of the barel axis with respect to the shaft axis. The invention consists, iirst, in separating spatially the torque transmitting connection and the lateral support so that the latter can be located precisely at the point of zero moment and can be designed to provide the maximum amount of longitudinal and rotational freedom for the cylinder barrel. Preferably, the support comprises a shoulder carried by the shaft and having a` spherical peripheral surface which is centered on the shaft axis, and which is slidably received within a central` cylindrical bore formed in the barrel. Since the cylinder barrel is supported by line contact with the shaft, the optimum support is achieved. While the prior art has approached this type of support, as evidenced by the circular spline mentioned previously, its advantages could not be availed of because of the very presence of the splines.

The second feature of the invention is the provision of a driving connection between the shaft and the cylinder barrel which affords to the barrel the freedom of motion provided by the lateral support while at the same time transmitting the required torque between the barrel and the shaft. This aim is preferably accomplished by use of a torque tube4 located within an annular clearance provided between the barrel and the shaft. The tube is splined to the shaft at one end and to the cylinder barrel at the other end, and is radially spaced from these members except in the regions of the splines.

The prior art has suggested separating the driving connection and the lateral support but little benefit was derived from this arrangement because the driving connection constrained the cylinder barrel. In these engines, the cylinder barrel was splined directly to the shaft and therefore, when the barrel tended to rotate about the lateral support, the mating spline teeth tended to move laterally relatively to each other. Since a spline connection inherently tends to center itself, it is apparent that such movement of the teeth would be resisted and that as a result, the barrel would be constrained against rotational movement about the lateral supporting surface.

In contrast to this, the mating spline`teeth of this invention experience relative rocking motion as the cylinder barrel rotates about the spherical supporting surface and therefore, the self-centering action of the spline does` not constrain the barrel. The reason for this is the fact that as the barrel axis rotates, the cylinder barrel splines, which cannot move laterally relatively to the torque tube splines for the reason just stated, force the torque tube to tilt about its splined connection to the shaft. vThe mating teeth in each connection rotate relatively to each other and hence allow the cylinder barrel to rotate relatively to the shaft axis. It is thus seen that the benefits stemming from the separation of the lateral support and the drive connection can be fully utilized.

A preferred embodiment of the invention will now be described in relation to the accompanying drawings, in which:

Fig. 1 is a View in axial section of a variable displacement engine using the torque tube and lateral support of this invention.

Fig. 2 is an axial section of a simplified xed displacement engine embodying the invention.

Fig. 3 is a view taken on line 3-3 of Fig. 1 showing the porting arrangement on the face of the valve plate.

Fig. 4 is an end view of the spline connection between fthe torque tube and the cylinder barrel; the number of' spline teeth having been greatly reduced for clarity.

Fig. 5 is a top plan view of one of the torque tube spline teeth of Fig. 4.

Fig. 6 is a side elevation of the spline tooth shown in. Fig. 5.

' Fig. 7 is an end view of the spline tooth shown in Fig. 5.

Fig. 8 is an exaggerated schematic diagram of the driving connection between the shaft and the cylinder barrel, showing the positions the parts would assume when the cylinder barrel rotates to accommodate an angular misalignrnent of the valve plate.

Statements of direction refer to the engine positioned as in Fig. 1. Y

Referring to Fig. 1, the engine comprises a housing having two separable sections 11 and 12 formed with mating iianges connected by suitable bolts 13. The right end of the section 12 is bored to receive aconventional valve plate 14 which forms a slip iit therewith. The plate is constrained against rotation by pin 15. As shown in Fig. 3, the valve plate contains inlet and discharge ports '16 and 17, which connect with the exterior of the housing by way of passages 18 and 19, respectively. A two-part drive shaft, having

telescoping sections

21 and 22 joined by splines 23, extends through the housing and is journalled at its left end in the bearing 24 fitted in the housing section 11. The right end of the shaft is keyed to a collar 25 which is supported by the bearing 26 mounted in the valve plate. The right end of the shaft section 22 carries a thrust plate 27 which is located within an axial bore formed in the valve plate and abuts against the end of the housing. As explained and claimed in applicants copending application Serial No. 665,387, filed June 13, 1957, this thrust plate 27 is part of a rigid force-transmitting link which conveys the inertia forces of the pistons to the housing.

A cylinder barrel 28, having an end face 29 in contact with the left face of valve plate 14, encircles the shaft section 22 and is spaced from the shaft by clearance 31. A clearance 32 is also provided between the cylinder barrel and the collar 25. The barrel 28 contains a plurality of circumferentially spaced longitudinal bores 33 which extend through the barrel and slidablyv receive pistons 34. The left end of each piston carries a spherical head 35 having its center 36 located on the axis of the piston. Piston shoes 37 are universally mounted on the spherical heads 35. A longitudinal passage 38 extends through each piston and connects with passages 39 formed in the shoes for hydrostatically balancing the shoes in a well known manner.

The shaft section 22 is formed with an annular shoulder 41 which has a spherical peripheral surface 42 centered at the point 43. The point 43 is located at the intersection of the axis of shaft 22 and the plane 44 (see Fig. 2) which contains the centers 36 of the spherical piston ends. The surface 42 is slidably received within the cylindrical bore 45 formed in the cylinder barrel 28 and forms therewith a lateral support for the barrel.

A variable angle cam plate 46 is supported in the housing by trunnions and yokes (not shown) for angular adjustment about an axis passing through the point 43. Such variable-angle cam plates are known in the art, so further description is needless. The surface 47 of the cam plate is arranged to engage the piston shoes 37 for moving the pistons on their discharge strokes. The pistons are moved on their suction strokes by nutating plate 48 which is supported on the spherical collar 49 carried by the shaft. The forces transmitted to the pistons by the nutating plate pass through bearing Washers 51 carried by the shoes 37.

A torque tube 52, located within the clearance 31, is connected to the cylinder barrel and the shaft by external splines 53 and internal splines 54, respectively. The torque tube itself is radially spaced from the cylinder barrel and from the shaft, except in the regions of the splines, and is axially spaced from collar 25 by clearance 50. A coil spring 55 surrounds the tube 52 and reacts between an adjustable seat 56, secured to the cylinder barrel, and the washer 57 carried by the torque tube. The spring force is transmitted to the cam plate 46 via a path comprising the washer 57, torque tube splines 53, washer 58, shaft shoulders 59 and 61, nutating plate support 49, nutating plate 48, bearing washers 51 and shoes 37. The spring 55 should be stiff enough to provide adequate sealing between the mating surfaces of the cylinder barrel and the valve plate during starting conditions, without producing undue friction at these surfaces.

The lower end of the cam plate 46 pivotally carries an actuator 62 which is universally attached to connecting rods 63 and 64. The other ends of these rods are connected to the spring-biased plunger 65 and the motor piston 66, respectively. The piston 66 is slidably mounted in a cylinder bore 67 which is connected to a conventional control valve 68 by the passage 69.

As shown in Figs. 4 through 7, the connecting splines S3 are of involute shape in transverse cross section and the anks 71 of the torque tube teeth 72 are crowned so that each tooth is thicker at its midpoint than ateither end. This relationship is shown by the

surfaces

73 and 74 in Fig. 7. The top lands of all teeth are beveled as shown at 75 in Fig. 6. It should be noted that this description also applies to the connection 54 between the torque tube and the shaft, except that in this case the flanks of the shaft splines are crowned while the 'flanks of the torque tube splines are straight.

Although this engine may function as either a pump or a motor, its operation will be described as if it were serving in the former capacity. Accordingly, the drive shaft section 21 would be connected to a suitable prime mover (not shown) by spline coupling 76 and the inlet and discharge passages 18 and 19 would be connected with an hydraulicsystem. As the cylinder barrel 28 is rotated by the drive shaft through the torque tube 52, the cylinder bores 33 will sequentially register with the inlet and

discharge ports

16 and 17. In a well known manner, the cam plate 46 and the nutating plate 48 anse Vthe pistons to reciprocate in timed relation With this sequential registration and thereby produce a pump-j ing action. Proper sealing between the matingfacesof the cylinder barrel and valve plate is effected at low speeds and low discharge pressures by the preload force of spring 55 and at high discharge pressure thissealing force 1s supplemented by the hydraulicpressure acting within the cylinder bores 33. Since the cylinder barrel 28 is free to slide in a longitudinal direction, these forces rapidly close any gap existing between the mating members. The stroke of the pump depends on the angle of the cam plate 46 which can be altered by varying the pressure existing in the bore 67. In the common case, the valve 68 vents the cylinder bore until the discharge pressure reaches a predetermined maximum value, and after this point is reached transmitsk discharge fluid to the cylinder to cause the piston 66 to move the cam plate toward its neutral position.

Since the piston shoes 37` are free to move in a direction parallel with the cam plate surface 47, the force transmitted betweenthe cam plate 46 and the pistons34 acts in a direction normal to the surface 47. As shown in Fig. 2, these forces, two of which are indicated at 77, acts through the centers 36 of the spherical piston ends. These thrust forces can be resolved into components 78 and 79 acting, respectively, in directions parallel with and normal to the axes of the pistons. Each of the normal components 79 produces a moment about the cyllnder barrel support, but inasmuch as this support is centered about point 43 in the plane 44, the moments of the .force components to the left of this point counter`- balance the moments of the forces to the right of that point. -It` should be apparent that if the cylinder barrel support were located at any point other than the one specified, the moments would add and tend to tilt the barrel face 29 out of contact with the valve plate 14.

While the momentsof the normal force components are balanced about the cylinder barrel support, the forces are not. The resultant lateral force, indicated at 81 in Fig. 2, acts through the point 43 and is transmitted by the shaft and the bearings 24 and 26 to the housing, as shown by the vectors 82. If the force 81 becomes large enough, the drive shaft will dellect upward. For convenience, the two effects of this deflection will betreated separately, though actually they occur simultaneously. The iirst effect is alateral displacement of the shoulder 41A `and the left end 0f cylinder barrel 28. Since a radial clearance 32 has been provided between the cylinder barrel and the collar 25, the right-hand end of the barrel may also movein a lateral direction, sliding along but not lifting away from the valve plate 14. The second effect of this deection is4 an angular displacement of theV shaft axis which tends to rotate the spherical surface 42 relatively `to the barrel 28. Since the cylinder barrel is" supported by line contact with this surface, it will rock relatively to its and the end face 29 will remain in con-V tact with the valve plate 14. The result of shaft deflection, therefore, is simply lateral displacement of the cylinder barrel.

Turning now to the torque tube, its action during this deflection must be examined to determine whether it imposes restraints on the cylinder barrel which prevent it from moving in the manner just described. As the cylinder barrel moves upward, its spline teeth tend to move laterally with respect tol the spline teeth of the torque tube. self-centering action inherent in spline connections and therefore, the relative lateral positions of mating teeth willrernain fixed. However, since a radial clearance is provided between the torque tube 52 and the shaft section 22', the left end of the tube may move upward c'ausing the tube itself to pivot `about the spline connection 54. Referring to Figs. 4 to 7, and remembering that the spline teeth are of involute contour and that the flanks of the shaft spline teeth are crowned,.it becomes apparent that the contact surface between mating teeth is a point 83. Therefore, this pivoting motion of the This type of motion is resisted by the torque tube produces rocking motion between mating teeth about this point 83. The teeth will assume positions similar to the ones shown in Fig. 8.

The angular` displacement of the shaft axis relatively to the torque tube axis produces a similar effect except that in this case, the tube 52 pivots about the spline connection 53. The net result, therefore, of shaft deflection is a lateral displacement of the cylinder barrel and an angular displacement of the torque tube caused by this motionand the angular displacement of the shaft axis. Itshould now be apparent that this driving connection permits the cylinder barrel to have the freedom provided by its lateral support.

Turning now to Fig. 8, the operation of the invention will be` examined under another set of conditions which require free mounting of the cylinder barrel. In Fig. 8, it has been assumed thatrthe valve plate I4 is displaced angularly from its usual position perpendicular to the shaft axis. This condition could occur either by faulty assembly or by deflections under load during pump operation. In this case, the cylinder barrel will rock upward on the surface 42 until either its end face 29 is in at contact with the valve plate or the right-hand end of the barrel contacts the outer periphery of the collar 25. In Fig. 8 these two conditions occur simultaneously, or in other words,\the maximum rotational movement provided for the cylinder barrel is required to maintain flat contact between the mating surfaces. As the barrel begins to` rock upward, its spline teeth tend to move laterally with respect to the torque tube teeth. As stated before, this type of motion is resisted by the spline and therefore, the torque tube will pivot about the connection S4'to the position shown in Fig. 8. It should be pointed out that this motion of the torque tube is possible only if there is a clearance between the torque tube and the shaft. The mating teeth of the splines will be rotated to the positions shown in Fig. 8 in the manner previously described and the end face 29 of the cylinder barrel will be maintained in contact with the valve plate.

. It should be noted that the spline clearances shown in the drawings, especially in Figs. 4 and 8, are greatly exaggerated. In actual practice, it has been found that splines, having the conventional tolerances specified for sliding movement under load, perform satisfactorily. To illustrate this point and referring to Fig. 2, the radial clearance F between the torque tube 52 and the shaft can be approximately expressed in terms of the clearance D as follows:

When the end of the torque tube 52 has moved this amount F, the axis of the tube will have rotated through an angle 9, whose tangent can be expressed as:

Tan 0:;

Now, the clearance between mating teeth G is related tothe angle 9 as follows:

G=E Tan 6:@

In a typical engine, the labeled dimensions of Fig. 2

would have the following values;

be noted that this arrangement is not though to be critical. One reason for adopting this design is to locate the torque load between the ends of the teeth and to thereby avoid stress concentrations at the edges. This arrangement also reduces the force required to rock the teeth relatively to each other.

As stated above, the drawings and description relate only to a preferred embodiment of the invention and it will be readily apparent to one skilled in the art that many changes can be made in the structure without departing from the inventive concept. Accordingly, the scope of the invention should not be limited in any respect, except in accordance with the`following claims.

What is claimed is:

l. An engine comprising a housing; a drive shaft journalled in the housing; a rotatable cylinder barrel encircling the drive shaft and radially spaced from it; a circumferential series of cylinder bores extending through the barrel; a valve plate located in the housing in abutment with an end face of the cylinder barrel and having inlet and discharge ports which sequentially register with each cylinder bore as the barrel rotates; pistons, one reciprocable in each cylinder bore and having 4a spherical surface at the end remote from the valve plate; means associatedy with the pistons at their spherical ends for causing the pistons to reciprocate in timed relation to the sequential registration of the cylinder bores with the valve plate ports, said means including an inclined cam plate for moving the pistons on their discharge strokes with a force which acts in a direction normal to the surface of the cam plate; support means for laterally but not longitudinally locating one end of the cylinder barrel with respect to the shaft, said means also providing free rotation of the barrel axis about the point of intersection of the shaft axis and thel plane of the centers of the spherical surfaces on the pistons; and a torque tube splined at respective opposite ends to the cylinder barrel and to the shaft and radially spaced from each of these members except in the regions of the splines.

2. The engine defined in claim 1 in which the torque tube is located within the radial clearance between the cylinder barrel and the shaft, and the spline connection between the torque tube andthe cylinder barrel is longitudinally located between the cylinder barrel support means and the spline connection between the torque tube and the shaft.

3. The engine defined in claim 2 in which the Hanks o-f the external spline teeth in both connections are crowned so that the thickness of each tooth is greater at its midpoint than at either end.

4. The engine defined in claim 2 in which the sides of all spline teeth are of involute shape in transverse cross section; and in which the top lands of all teeth and the flanks of the external teeth are crowned.

5. The engine defined in claim 2 in which the support means for the cylinder barrel comprises an annular shoulder carried by the shaft and having a spherical peripheral surface centered at the point of intersection of the shaft axis and a plane passing through the centers of the spherical surfaces on the pistons; and a cylindrical surface formed in the barrel coaxial with the barrel axis and slidably engaging said spherical peripheral surface.

6. An engine comprising a housing; a drive shaft journalled in the housing; a rotary cylinder barrel having an axial bore dimensioned to freely encircle the drive shaft and. having a circumferential series of longitudinal cylinder bores extending through the barrel; a stationary valve plate located in the housing in abutment with an end face of the cylinder barrel and having inlet and discharge ports which sequentially register with each cylinder bore as the barrel rotates; pistons, one reciprocable in each cylinder bore and having a spherical surface at the end remote from the valve plate; means associated with the pistons at their spherical ends for causing the pistons to reciprocate in timed relation to the sequential registration of the cylinder bores with the valve plate ports, said means including an inclined cam plate' for moving the pistons on their discharge strokes with forces which act in directions normal tothe surface of the cam plate; a spherical enlargement carried by the shaft and centered at the point of intersection of the shaft axis'and the plane of the centers of the spherical surfaces on the pistons, said en-` largement being in great circle engagement with said axial bore; and a torque tube splined at respective opposite ends to the cylinder barrel and to the drive shaft but otherwise free of both members.

7. The engine defined in claim 6 in which the torque tube encircles the drive shaft and is located between but radially spaced from the cylinder barrel and the drive shaft.

8. The engine defined in claim 7 in which the splines connecting the cylinder barrel and the torque tube are longitudinally located between the spherical enlargement and the splines connecting the torque tube and the drive shaft.

9. The engine defined in claim 7 in which the splines connecting the cylinder barrel and the torque tube are longitudinally located between the spherical enlargement and the valve plate; and the splines connecting the torque tube and the shaft are longitudinally located between the cylinder barrel-torque tube connection and the valve plate.

10. In an. engine of the type including a drive shaft, a rotary cylinder barrel having an axial bore dimensioned to freely encircle the drive shaft and having a circumferential series of longitudinal cylinder bores extending through the barrel, a stationary valve plate located in abutment with an end face of the cylinder barrel and having inlet and discharge ports which sequentially register with each cylinder bore as the barrel rotates, pistons, one reciprocable in each cylinder bore and having a spherical surface at the end remote from the valve plate, and means associated with the pistons at their spherical ends for causing the pistons to reciprocate in timed relation to said sequential registration, the improvement which comprises a spherical enlargement carried by the shaft and centered at the point of intersection of the shaft axis and the plane of the centers of the spherical surfaces on the pistons, said enlargement being in great circle engagement with said axial bore; and a torque tube splined at respective opposite ends to the cylinder barrel and to the drive shaft but otherwise free of both members.

1l. In an engine of the type including a drive shaft, a rotary cylinder barrel having an axial bore dimensioned to freely encircle the drive shaft and having a circumferential series of longitudinal cylinder bores extending through the barrel, a stationary valve plate located in abutment with an end face of the cylinder barrel and having inlet and discharge ports which sequentially register with each cylinder bore as the barrel rotates, pistons, one reciprocable in each cylinder bore and having a spherical surface at the end remote from the valve plate, and means associated with the pistons at their spherical ends for causing the pistons to reciprocate in timed relation to said sequential registration, the improvement which comprises means supporting the cylinder barrel on the drive shaft for universal movement about the pointV of intersection of the shaft axis and the plane of the centers of the spherical surfaces'on the pistons while providing free longitudinal movement of the barrel; and a torque tube splined at respective opposite ends to the cylinder barrel and the drive shaft but otherwise free of both members.

12. The improvement defined in claim l0 in which the splines connecting the cylinder barrel and the torque tube are longitudinally located between the spherical enlargement andthe splines connecting the torque tube and the drive shaft.

13. The improvementdened in claim l0 in which the torque tube encircles the drive shaft andis locatedbe-` tween but radially spaced from the cylinder barrel and from the drive shaft, and in which the spline connection between the cylinder barrel and toque tube is longitudinally located between the spherical enlargement and the valve plate, while the spline connection between the torque tube and the shaft is longitudinally located between the cylinder barrel-torque tube connection and the valve plate.

References Cited in the le of this patent UNITED STATES PATENTS 925,148 williams June 1s, 1909 1,362,040 Pratt Dec. 14, 1920 10 Carey Apr. 23, 1929 Rayburn et al. Ian. 12, 1932 Hawley et al Jan. 5, 1943 Vickers et al. Mar. 9, 1943 Robinson Dec. 17, 1946 Beaman et al. Jan. 25, 1949 Ruben Feb. 21, 1950 Beaman et al. Aug. 26, 1952 Lauck et al. Mar. 31, 1953 Robinson June 23, 1953 Towler et al. Dec. 8, 1953 Keel Jan. 8, 1957 Badalini Dec. 31, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nos 299251046 February 16Sl 1960 Tadeusz Budzeh It is hereby certified that error appears in the printed specification of' the above numbered patent requiring correction and that the said Letters Patent should read` as corrected below.

Column 5u line 55KL for "to its" read mto it ma; column 7n.

line l"I for "though" read -m thought Signed and sealed this 30th day of August 1960,

( SEAL) Attest:

ERNEST W. SWIDER Attesting Officer ROBERT C. WATSON Commissioner of Patents