This invention has to do with improvements in hydrostatic journal bearings. More particularly, the invention relates to provision of added damping and stiffness in longer stroke hydrostatic journal bearings such as those used to support and guide slip plates in vibration testing of parts and assemblies for reliability and optimization of design and manufacture. Background of the Invention

Hydrostatic journal bearings typically comprise a pillow block or housing and a shaft, and means connecting the housing or shaft to a moving element which is to be guided or supported by the bearing. Such apparatus has been used in vibration testing equipment for a number of years. In a typical arrangement, the housing was connected to the slip plate or other workpiece and the shaft journaled in the housing was supported by stationary blocks affixed to a reference base. Summary of the Invention

As compared with past devices, the present apparatus provides higher static load capability, higher dynamic load capability, increased stroke length with no reduction and actually an increase in the oil film damped area for improved dynamic response at high frequencies of vibration, absence of internal oil flow porting of slip plates and its expense and potential for interfering with test article

attachment, avoidance of external hoses between the oil supply and the slip plate/table interface to create the oil film, increased pitch, yaw and roll dynamic overturning moments, freedom from O-ring seals at the bearing housing slip/plate interface for oil feed so that minimum slip plate size is no longer a consideration, and ready alinement, adjustment and replacement of the apparatus.

It is accordingly an object of the invention to provide apparatus having the foregoing features.

In general, the invention provides in vibration test apparatus a hydrostatic journal bearing in which the pillow block or housing is not connected to the slip plate as formerly, but is positioned in spaced relation to the slip plate and spaced from the base, so as to define a damping enhancing oil film at the slip plate. The slip plate is fixed to carriage blocks which in turn are fixed to the bearing shaft, so that the carriage blocks, and not the housing move with the slip plate. The housing surface thus can carry an oil film and enhance the damping of the slip plate vibration. The stroke of the bearing can be increased since the aperture necessary to accommodate the greater stroke while larger is not lost area for purposes of damping, the housing surface within the aperture being available for damping as noted. The mounting of the housing to the base is adjustable in height and uniquely variable so as to have either one or two degrees of freedom in the bearing. Thus in addition to the usual degree of freedom in

the axial direction of the shaft, another, second degree of freedom, normal to the first is available, to accommodate thermal expansion of the slip plate for example. The feeding of oil to the slip plate granite block interface by hoses passed upwardly from a pressurized oil supply, and thence to a long bore in the slip plate for distribution to the surface area and to the bearings which has caused problems is past designs is avoided by keeping the oil path within the apparatus, by first feeding the housing bore and then feeding oil from there upward to the housing surface and thence to the slip plate without use of external hoses. Other features are identified below.

In particular the improvements in accordance with the invention are realized in vibration test apparatus having an extended stroke and improved stiffness for use with a plate mounting a test article for vibration testing, wherein the apparatus comprises a hydrostatic journal bearing plate guide having a housing mounted on a base, a shaft shiftable axially in the housing, carriage block means for connecting the shaft to the plate for movement relative to the housing in a plane including the shaft axis, and oil film means for operatively coupling the plate and a surface of the housing in vibration damping relation.

In this embodiment there is further provided an oil- pressurized bore in the housing in which the shaft is shiftable; a pressurized oil supply, and passage means for pressurized oil to the housing surface; the carriage block

means comprises carriage blocks on either side of the housing, disposed normally to the plane of the oil fed housing surface; the shaft is preferably tubular chrome- plated steel? the housing surface is preferably cast iron having a higher porosity to oil than the plate? the carriage block means is free of attachment to the base, the housing is free of attachment to the plate, and the apparatus having first and second degrees of freedom; the axial shifting of the shaft defines the apparatus first degree of freedom, and there is also included selectively deflectable means mounting the housing to the base for movement of the apparatus in a direction normal to the axial shifting of the shaft as a second degree of freedom for the apparatus; there is further included a series of elongated bolts mounting the housing to the base in spaced relation for accommodating the second degree of freedom as a function of the flexibility in the bolts; and means selectively tensioning the bolts in bolt flexibility decreasing relation.

In this and like embodiments there is also included a housing oil feed passage from the bore to the housing surface.

In a preferred embodiment there is provided a vibration test apparatus comprising a granite block having at least one journal bearing receiving aperture and a smooth surface surrounding the aperture, the surface being adapted to support a slip plate in sliding relation coupled to a vibration source, a base supporting the granite block, at

least one hydrostatic journal bearing in an aperture of the granite, the hydrostatic journal bearing being smaller than the aperture to define therewith an aperture clearance and comprising a pillow block housing defining a bore and a surface opposite the slip plate, a shaft journaled in the bore, an oil supply adapted to supply oil under pressure to the bore, an oil passage through the housing between the bore and the housing surface, the passage eing adapted to convey oil at reduced rates of flow from the bore to the housing surface; carriage blocks at either side of the housing fixed to the shaft at a predetermined combined clearance relative to the housing of not less than 2.5 inches, the carriage blocks being fixed to the slip plate in a manner elevating the slip plate slightly above the granite block, the housing surface being lower than the height of the slip plate to define a gap, a continuously flowing oil film filling the gap with oil from the passage, the oil film operatively coupling the housing and the slip to damp the slip plate vibration at the housing surface, a pair of oil transferring webs carried by the housing in sliding contact with the granite block surface opposite the slip plate for transferring oil flowing on the housing surface across the aperture clearance to the granite in slip plate movement facilitating relation, longitudinally extended trough means in the housing surface, grooving in the slip plate surface opposite, the trough and grooving being continuously in registration for movement of flowing oil from the trough to

the slip plate grooving in web supported relation across the aperture clearance to damp the slip plate beyond the apertures; the housing being mounted to the base in spaced relation to the slip plate by a series of mounting bolts adapted to adjust the gap width, the mounting bolts being flexible over their exposed length between housing and base to permit transverse shifting of the housing within the aperture as well as axial motion of the shaft within the aperture, whereby the bearing has two degrees of freedom, and means to block the transverse motion by tensioning the bolts. The Drawing

The invention will be further described as to an illustrative embodiment in conjunction with the attached drawing in which:

Fig. 1 is a top plan view of vibration test equipment havin the invention hydrostatic journal bearings installed;

Fig. 2 is a side elevation of the equipment shown in Fig. 1, partly broken away to show underlying parts;

Fig. 3 is a top plan view of the invention hydrostatic journal bearing, installed in a granite table aperture;

Fig. 4 is a side elevation view of the bearing shown in Fig. 3, partly broken away to show underlying parts;

Fig. 5 is a view like Fig. 4 of a mofified form of the invention;

Fig. 6 is a fragmentary detail view, greatly enlarged of the housing passage and housing surface oil film; and.

Fig. 7 is a fragmentary detail view like that of Fig. 4, of an alternate form of the invention.

Preferred Modes

A signal feature of the invention apparatus applied to use in vibration equipment is the operative coupling of the slip plate to the housing surface by a continuously formed oil film, such that these elements interact with each other, the effect being a damping of the slip plate in the area of the granite aperture which heretofore has been a void and undamped, with the result that as a vibration test device, the invention provides better dynamic response of the slip plate at high frequencies and better high load support at low frequencies.

A further feature is the availability of first and second degrees of freedom, a result of the mounting technique for the housing which permits lateral deflection under Such influences as thermal expansion or contraction of ^" the slip plate, as a function of relatively flexible or inflexible set screws cooperating with the housing mounting bolts.

Yet another feature is an increased stroke without loss of damped area, and the available use of an increased diameter shaft for better stiffness in the bearing. Heretofore largex shafts were often infeasible because the commensurate enlargement of the housing bore left the housing walls too frail for the high pressures in the bore

needed to hydrostatically balance the shaft in the bore. The housing walls could not be increased in thickness without increasing the size of the granite apertures, and thus again the amount of undamped area under the slip plate. The present design retains the needed wall thickness without undue loss of damped area by virtue of the housing surface oil film.

With reference now to the drawings in detail, in Figs. 1 and 2 a source of vibration shown schematically as electrodynamic shaker S is connected by conventional means not shown, such as a driver bar, to a slip plate 10, typically made of magnesium or aluminum. A test article 12 which may be of any suitable configuration is mounted on the slip plate 10. The slip plate 10 is supported statically and dynamically by a granite table 14 having a smoothly polished surface 16 and a series of hydrostatic journal bearings 18 distributed as shown beneath the slip plate in ovoid apertures 20 formed in the granite. The granite table 14 is supported on bosses 22 above a mass or base 24, suitably comprising concrete sheathed in steel. Oil falling from the edge of the granite table 14 is captured in the granite-base gap 26 and recirculated from a sump not shown by pump means comprising the pressurized oil supply represented schematically.

The hydrostatic journal bearing 18, best shown in Figs. 3 and 6, includes a housing 28 which is preferably formed of cast iron so as to be relatively porous for oil assimilation

on its surfaces in its bore 30 and opposite the slip plate 10 as will be seen, shaft 32 which is preferably formed of tubular steel for strength and chrome plated for minimum friction in the housing bore. The housing 28 defines the pillow block of the bearing 18 and journals the shaft 32 for axial, longitudinal motion in guiding relation to the slip plate 10 which is subject to large forces on a reciprocating basis from the shaker S and is restrained from spurious motion by the bearing by means of the connection of the slip plate to the bearing shaft 32 by carriage blocks 34. Carriage blocks 34 are used in pairs as shown on opposite sides of the housing 28, their relative spacing determining the bearing stroke. As noted elsewhere, the present bearing 18 has preferably a minimum 2.5 inch stroke where the shaker S makes such a long stroke available. Carriage blocks 34 are split blocks which are joined beneath the shaft 32 by bolt fastener 36. The upper end of carriage blocks 34 is flat for lying flush against the underside of the slip plate 10, as shown, and tapped for receiving a pair of fastening bolts 38 extending through the slip plate 10 and into tapped holes 40. The slip plate 10 is thus attached to the bearing 18 by threaded connection via bolts 38 to the carriage blocks 34, which are in turn fixed to the shaft 32 by fastener 26 for transmitting the loading on the carriage blocks to the housing 28 via bore 30.

The bore 30 is oil pressurized by the pressurized oil supply, shown schematically, by feeding pressurized oil at

pressures in excess of 2000 pounds per square inch typically, through interior hose 42 which is in open comunication with bore 30. With reference to Fig. 6, particularly, the oil from hose 42 fills the annulus 44 which is centrally located in the bore 30, and flows thence to the shaft surface-bore wall interspace 46 which is a mechanical clearance. The bore annulus 44 is in open communication with the housing passage 46, for purposes to appear.

The housing 28 transmits the load imposed on it to the base 24 to which the housing is mounted. Uniquely in the invention design, the housing 28 is elevated above the base 24 and carried stilt-like on four elongated bolts 50 at the corners of the generally rectangular housing. The bolts 50 are threaded through holes 52 in the housing 28, and extend from the housing at a tapered portion thereof at 54, to enter tapped holes 56 in the base 24 into which they are threaded more or less depending on the elevation desired for the housing for purposes of varying the oil film between the slip plate 10 and the housing surface 58 as will be later described.

The bolts 50 while rigid have enough flexibility to permit the housing to deflect laterally, i.e. normal to the direction of movement of shaft 32, providing a second degree of freedom in the bearing beyond the shaft-axis freedom. With reference to Fig. 1, the importance of this feature will be explained. In Fig. 1 seven bearings are shown.

three on the center line of the slip plate and two each on the left and right hand sides of the slip plate. Lateral loads such as can be caused by the expansion of the slip plate 10 are different for the outer bearings than for the center bearings but can be taken up by the slight deflection of the outer bearings by movement of the housings 28 on their bolt supports. The movement is demand responsive and no more than necessary to accommodate the lateral loading, and left or right direction is immaterial.

Typically the bolts 50 are tensioned by relatively flexible set screws 59 (Fig. 4) which have enough flexibility to permit deflection of the housing 28, screws

59 being provided on two sides of the housing threaded into housing hole 61 and extending to the surface 58 of the housing for ease of adjustment.

In situations where for test reasons no deflection is desired, the bolts 50 can be rigidified by tensioning them with another feature of the invention. With reference to Fig. 7, a relatively inflexible tensioning set screw 60 is shown threaded into housing hole 62 and extending to the surface 58 of the housing for ease of adjustment. Set srews

60 are provided on two sides of the housing, between the mounting bolts 50. A seat 64 is provided opposite set screws 59, 60 to preserve the base from damage as necessary. As will be evident, threaded adjustment downward of the set screws 59, 60 pushes the housing 28 upwardly, as the bolts 50 are holding it, resulting in a tensioning of the bolts

50, rigidifying them and controlling, indeed blocking deflection of the housing 28 in the case of the inflexible set screws 60, and making the bearing 18 a single degree of freedom bearing.

With reference to Figs. 3, 4 and 6, the formation of the oil film under the slip plate will be described. Initially, it will be recalled that the housing bore 30 is fed high pressure oil via hose 42. The bore annulus 44 is hydraulically filled as shown in Fig. 6. The housing passage 46 extends through the housing 28 from the annulus 44 to the surface 58 of the housing, the upper terminus of the passage defining a port 64, such that the housing surface is open to the bore 30 and the oil therein. Because the very high f-lows in the bearing bore 30 are not necessary at the housing surface 58, a flow restrietor 66 is mounted in the passage 46.

The oil 70 from the bore annulus 44 flows up the passage 46 and emerges from port 64 whence it spreads out over the housing surface 58. The slip plate 10 is spaced above the housing surface 58 by a gap 72 which in turn is determined by the height adjustment of the housing 28 on mounting bolts 50, and the relative height of carriage blocks 34 to the housing surface 58. In general the gap 72 is such as will allow formation of an oil film sufficient to operatively couple the housing surface 58 and the slip plate. This height is usually such as will put the housing surface 58 at approximately the height of the granite

surface 16, which height permits an oil film between the slip plate and the granite surface.

A noted feature of the present invention is the absence of external hose lines and the absence of bores in the slip plate, both having previously been used to get oil to the granite surface 16. The use of bores in the slip plate means having to be careful about placing test article supporting inserts so as to not breach the bore. In addition, the drilling of long, small bore holes is expensive and may lead to excessive scrappage in production. A further disadvantage of feeding oil from the slip plate to the granite is the necessity of having 0-ring sealed ports to the bearings which had to register with the oil flow bore for all different sizes of slip plates. Moreover, the previously used hoses get in the way of workers, are hazardous, and are often too lengthy for the job at hand because they must be usable an all sizes of slip plates, including those not requiring long hoses.

In the present invention, the oil 70 is fed from the bore annulus 44; no external hoses are used; no sealing to the bearings is required; and, no gundrilled bores through the slip plate are needed.

These advantages flow from using the housing surface 58 to receive all the oil and transporting the oil from that locus to the granite by the bridging the clearance 78 between the bearing housing 28 and the adjoining granite of aperture 20. With reference to Fig. 3, a pair of oil

impervious e.g. suitably oil resistant plastic, webs 80 are shown cantilevered from the housing surface 58 to be in sliding contact with the surrounding granite. The webs 80 may be above, at or slightly below the granite surface 16, provided the oil 70 flowing from the port 64 bridges the clearance 78 thereon. Of course other forms of oil delivery to the granite may be used.

The spreading of the oil 70 over the granite surface 16 is readily accomplished by providing grooving 82 in the underside of the slip plate. The exact configuration of the grooving 82 is not critical, but should be such as will distribute oil evenly and widely. For purposes of facilitating registration of the grooving 82 with the port 64, a trough 84 is advantageously provided in effect elongating the port and enabling continual open communication between the port and the grooving. See Fig. 6.

In the embodiment shown in Fig. 5, wherein like numbers to the other F gs, indicate like parts, noncommunicating left and right hand patterns of grooving 82R, 82L are shown each communicating with its respective ports 64R, 64L and troughs 84R, 84L only, an arrangement enabling closer control of oil flow to the respective sides of the slip plate.

In operation, the slip plate 10 resting on granite 14 is fixed to the carriage blocks 34 which are fixed to the shaft 32 journaled in the housing 28 already positioned on

the base 24 by bolts 50 to be a t the desired height. Oil 70 is circulated to the bore 30 and thence to the housing surface 58 via passage 46 where a film is developed between the housing surface and the underside of slip plate 10. Additional oil 70 is passed to the surface 16 of the granite table 14 via webs 80. Movement of the slip plate 10 by the shaker S is guided by the bearing 18, and the slip plate damped by both the granite surface 16 oil film and the housing surface 58 oil film, whereby less area than heretofore is undamped, and less in fact than the area under the slip plate ^" defined by the granite apertures 20.