High Pressure Sealing Apparatus

The present invention relates to a high pressure seal between the piston rod and cylinder wall of a seismic transducer. While the invention is particularly useful in a transducer, it has application wherever a cylinder is adapted to move along a stationary piston.

High pressure seals for stationary pistons and moving cylinders have been provided in the past with an end plate to seal the space between the sleeve and the piston rod. In addition a plurality of pressure reducing grooves was provided, spaced along the inner wall of the sleeve. The bleeder ports, however, were always attached to the cylinder so that communication was provided at a location near the terminus of the cylinder near to the end plate. The above arrangement, however, necessitated a pipe being attached to a moving element. Such a configuration resulted in several problems, the first being failure of the pipe which connected the bleeder pipe to the low pressure sump and the second being the inability to effectively seal the moving cylinder from the external environment resulting in damage to the hydraulic mechanism from dirt, humidity, etc.

The present invention relates to a means for sealing the piston and cylinder in a seismic transducer. The seal provides an effective means for dropping the pressure as it nears the end plate, thereby providing a simple low pressure seal arrangement between the piston and the sleeve at the end plate. In order to prevent the pressure from building up and thus causing the low pressure seal to fail, a port was formed through the stationary piston rod having an inlet communicating with the space between the outside surface of the piston rod and inside surface of the sleeve. At approximately the midpoint in the stroke of the piston, a bleeder groove is formed having a width substantially identical to the diameter of the port, thus providing a low resistance outlet for hydraulic fluids which are passing from the hydraulic cylinder toward the end plate. Additional bleeder grooves are provided at the maximum stroke position on either side of the center position for the same purpose. The bleeder port outlet is connected to a low pressure sump.

The above arrangement provides an effective means for continually bleeding off the hydraulic fluid as it passes from the cylinder to the end plate, thereby preventing excessive pressure from building up at the low pressure seal. It also permits total enclosure of the hydraulic system, since no external pipes are connected to the moving cylinder or sleeve, while providing adequate lubrication and cooling to the seals and bearings.

This application is related to an application Ser. No. 848,224 entitled "Seismic Transducer Construction" by Delbert W. Fair filed Nov. 3, 1977, which is concurrent with this application.

FIG. 1 is a side elevational view of a seismic transducer for generating seismic shear waves and which incorporates the subject matter of this invention; and

FIG. 2 is a partial cross-sectional view of a portion of FIG. 1 illustrating in detail the high pressure sealing apparatus of this invention.

Referring now to the drawings and in particular to FIGS. 1 and 2, a transducer incorporating the high pressure seal, which is the subject matter of this invention, is indicated generally by the reference number 10. The transducer 10 is comprised of a reaction mass member, indicated generally by the reference numeral 12. A pair of cylinder bores, each indicated generally by the reference numeral 14, extend through the reaction mass member and a piston member, indicated generally by the reference numeral 16, is reciprocally disposed within each such cylinder bore 14. Each piston member 16 is comprised of a piston 18 and opposite extending rods 20 and 22. A frame, indicated generally by the reference numeral 24, interconnects the ends of the rods 20 and 22 which protrude from the cylinder bores 14.

More specifically, the reaction mass member 12 is comprised of a mass block 26 fabricated of a suitable material such as steel and having a desired cross-section, e.g., rectangular. The block 26 has one or more cylindrical bores 28 extending longitudinally therethrough with a first counterbore 30 and a second counterbore 32 in each end of each of the bores 28. A tubular cylinder sleeve 34 is disposed in each of the bores 28 and extends from the bottom of one counterbore 30 to the bottom of the other counterbore 30. The interior wall of each of the tubular cylinder sleeves 34 forms one of the cylinder bores 14 in which one of the pistons 18 is reciprocally disposed, and an inner bronze bearing insert 36 and an outer bronze bearing insert 38 are disposed within each of the one or more counterbores 30 to slidingly receive the piston rods 20 and 22, and also to form the ends of the hydraulic cylinders and thereby form fluid chambers 40 and 42 on either side of each of the pistons 18. As is best shown in FIG. 2, the internal diameters of the bearing inserts 36 and 38 are provided with a plurality of small annular oil grooves 44, which reduce the flow of hydraulic fluid from the high pressure in the cylinders to the low pressure returns. Additionally, each of the inner bearing inserts 36 has a relatively large inner fluid collecting groove 46, and each of the outer bearing inserts 38 has relatively large center and outer fluid collecting grooves 48 and 50 disposed within its internal diameter. The manner of operation and the significance of these fluid collecting grooves are explained hereinafter. Disposed within the internal diameter adjacent the outer face of each of the outer bearing inserts 38 is a groove 52 in which is disposed conventional resilient seal means 54.

A cylinder end cap 56 is disposed within each of the one or more counterbores 32, around each of the piston rods 20 and 22, behind each of the outer bearing inserts 38. Each of the end caps 56 has disposed within its inner face an end cap bearing 58 (FIG. 2). Each of the end caps 56 is held in place by a plurality of suitable high torque bolts 57 extending through the end cap into appropriately threaded bores 59 in the block 26.

A hydraulic fluid bleed-back port 78 is disposed within each remaining end of the piston members 16. Each of the ports 78 communicates with the outer peripheral surfaces of the rod 20 and the rod 22 adjacent the bearing inserts 36 and 38. Each of the ports 78 also communicates with a return port 80 in the end plate 64 that is further connected to the low pressure hydraulic storage. The location of the openings of the bleed-back ports 78 in relation to the fluid collecting grooves 46, 48 and 50 is important.

As is best shown in FIGS. 1 and 2, when the mass member 12 is centered between the end plates 62 and 64, the openings of the bleed-back ports 78 are adjacent the center fluid collecting grooves 48. FIG. 2 shows the mass member 12 in this centered position. This will normally be the stable position of the mass member when the transducer is not being driven by an external signal. As long as there is fluid under pressure in the chambers 40 and 42 there will be a small flow of fluid between the rods and bearing inserts. This fluid will be collected in the grooves 48 and returned to the low pressure side of the hydraulic system via the ports 78. The inner and outer fluid collecting grooves 46 and 50 are located so that when the mass member 12 is at the maximum extent of its travel in either direction the bleed-back ports 78 will be adjacent one of the fluid collecting grooves 46 and 50. In this manner, if the mass member 12 is located at a central position relative to the maximum extent of its reciprocating excursions, or if it is located or becomes lodged at either of the maximum extents of its reciprocating excursions, the fluid will be collected in one of the fluid collecting grooves and returned to the hydraulic system via the ports 78. During normal operation the fluid will collect in the grooves 46, 48 and 50 and as the ports 78 periodically communicate with those grooves the fluid will be returned to the low pressure side of the hydraulic system.

It can be seen from the above that an effective method of sealing a high pressure piston and cylinder system has been described, particularly with respect to a seismic transducer. It is obvious, of course, that the arrangement can be used to seal any system so long as the piston is stationary and the cylinder is moveable, whether it is a seismic transducer or some other unit, and the invention is not so limited as to apply solely to a seismic transducer. The particular number of pressure dropping grooves is determined by the differential in pressure between the cylinder and the end plate seal as well as the length of the sleeve or sleeves necessary to accomplish the reduction in pressure. While several bleeder grooves are illustrated in this invention, it is obvious that, if the stroke is so short that the bleeder port is in contact during the stroke of the piston with the bleeder groove at all times, then no additional bleeder grooves need be required.

It is obvious that numerous changes in the construction and arrangement of parts can be made by those skilled in the art, which changes are encompassed within the spirit and scope of this invention as defined by the appended claims.