US3127776A

US3127776A - Liquid metal floated gyroscope

Info

Publication number: US3127776A
Application number: US39089A
Authority: US
Inventors: Tarasevich Michael; Milan A Telian
Original assignee: American Bosch Arma Corp
Current assignee: Ambac International Corp
Priority date: 1960-06-27
Filing date: 1960-06-27
Publication date: 1964-04-07
Anticipated expiration: 1981-04-07

Description

April 7, 1964 M. TARASEVJCH ETAL 3,127,776

LIQUID METAL FLOATED GYROSCOPE Filed June 27, 1960 X 5 m m m 0 WWW w WM A T m. &A NN A mm MM United States Patent 3,127,776 LIQUID METAL FLOATED GYROSCOPE Michael Tarasevich, Glen Cove, N.Y., and Milan A. Telian, San Diego, Calif., assignors to American Bosch Anna Corporation, a corporation of New York Filed June 27, 1960, Ser. No. 39,089 7 Claims. (Cl. 74-5) The present invention relates to liquid flotation for gyroscopes and has particular reference to liquid metals used therefor.

The concept of flotation of gyros for relieving the load on supporting bearings has received considerable interest during the last decade although the history of floated gyros is much older. However, it is only recently that liquids comprising low melting point metals have been considered, discounting the early uses of mercury.

The present invention proposes the use of an alloy of bismuth, indium and tin, the exact proportions of each being that required to make a eutectic alloy. The metal has many and important advantages over other flotation fluids previously suggested, such as high thermal conductivity, low thermal coefficient of expansion, non-corrosive and so on but most important is the specific gravity of 7.84 compared to a specific gravity of 7.87 for stainless steel at a temperature of 85 C. This extremely close matching permits flexibility in design whereby metal (stainless steel) can be removed from or added to the floating structure without upsetting buoyancy. Also, the eutectic alloy of bismuth, indium, tin is used in preference to other alloys of these elements to preclude Stratification of elements upon cooling. Further advantages are found in the greater resistance to nuclear radiation over organic fluids, high lubricity permitting use of jewel bearings instead of torsion wires, relatively loose temperature control, high angular momentum to volume ratio and relatively low cost.

These and other advantages will be made clear upon reference to the accompanying diagram which shows cross section of a typical gyroscopic device using the flotation principle.

In the diagram, a gyro wheel 10 is supported for rotation in a fluid-tight casing 11 which is suspended in vertical gimbal ring 12 about a horizontal axis by horizontal shafts (not shown) perpendicular to the plane of the paper, while the gimbal ring 12 is adapted for rotation about a vertical axis through

jewelled bearings

13, 14 and

corresponding shafts

15, 16. The

bearings

13, 14 are set into a fluid-tight tank 17. The space between casing 11 and tank 17 is filled with the alloy comprising 32.5% bismuth, 51% indium and 16.5% tin which is the eutectic alloy of these elements. A diaphragm 18 is inserted in the wall of tank 17 to permit expansion of the alloy as it is heated to the operating temperature of about 85 C., the melting point of the alloy being 61 C. The low thermal coefficient of expansion permits use of the diaphragm in place of the usual expansion bellows.

Convection currents are produced by liquid expansion, as well as by thermal unbalances, as the lighter (expanded) liquid rises and the heavier liquid sinks. When the expansion is limited by a low coeflicient of expansion, the magnitude of the convection currents is kept at a small value. Convection currents, of course, apply error producing torques to the gyro, and their reduction is imperative in an accurate gyro.

A decrease of specific gravity occurs with expansion resulting in a change in the buoyancy of the casing 11 and gimbal ring 12 in the liquid. The small expansion experienced by the bismuth-indium-tin alloy permits easier control of the buoyancy by tolerating less rigid temperature controls. The fluid expansion is closely matched 3,127,776 Patented Apr. 7, 1964 "ice by the expansion of the casing material when stainless steel is used.

The high thermal conductivity of the liquid alloy minimizes localized heating due to outside influences and tends to distribute the temperature rise evenly throughout the liquid thereby reducing a major cause of convection currents in the liquid. Also, the high thermal conductivity decreases the warmup time required, conducts heat away from the gyro motor and, all in all, insures a uniform temperature.

The specific gravity of the eutectic alloy of bismuthindium-tin at C. is 7.84 while the specific gravity of stainless steel at 85 C. is 7.87. The significance of this close matching is that when the casing 11 and gimbal ring 12 are made of stainless steel, changes in their design can be made freely without disturbing the buoyancy relationship. Also, the gyro wheel can be made of much heavier metal such as tungsten, for example, without making the specific gravity of the assembly (of the gyro wheel and other components within the casing and the casing itself) greater than the specific gravity of the alloy, 7.84.

The eutectic alloy does not stratify upon cooling; i.e., all the elements solidify at the same temperature. This property is advantageous in starting up the gyro by attaining and maintaining a homogeneous liquid as soon as the metal becomes liquified. Therefore, added warmup time to obtain a proper mixture is not required nor are there present any additional error producing torques during the warmup period which might add to the initial settling time.

Other advantages of this alloy are found in (1) its superior lubricity which permits use of pivot bearings in place of the more intricate wire suspensions; (2) its greater resistance to nuclear radiation than organic flotation liquids; and (3) its non-corrosive reaction to most common structural metals and materials which permits a wider choice of materials for the various parts of the gyroscope which might come in contact with the flotation liquid.

We claim:

1. Means for supporting a gyroscope comprising a tank, a fluid tight casing suspended in a gimbal ring in said tank, said gimbal ring being adapted for rotation about a vertical axis through bearings and a floating medium in said tank between said casing and said tank, said floating medium comprising an alloy of bismuth, indium and tin, and having a specific gravity of approximately 7.84 at a temperature of 85 C.

2. Means for supporting a gyroscope comprising a casing and a floating medium between said gyroscope and said casing to thereby float said gyroscope in said casing, said floating medium comprising an alloy of approximately 32.5% bismuth, approximately 51% indium and approximately 16.5% tin.

3. Means for supporting a gyroscope comprising a casing and a floating medium between said gyroscope and said casing to thereby float said gyroscope in said casing, said floating medium comprising an eutectic alloy of approximately 32.5% bismuth, approximately 51% indium and approximately 16.5% tin.

4. Means for supporting a gyroscope comprising a tank, a fluid tight casing suspended in a gimbal ring in said tank, said gimbal ring being adapted for rotation about a vertical axis through bearings and a floating medium in said tank between said casing and said tank, said floating medium comprising an alloy of approximately 32.5% bismuth, approximately 51% indium and approximately 16.5% tin.

5. Means for supporting a gyroscope comprising a casing with a floating medium between said gyroscope and said casing to thereby float said gyroscope in said casing,

said floating medium comprising an eutectic alloy of bismuth, indium and tin.

6. Means for supporting a gyroscope comprising a casing and a floating medium between said gyroscope and said casing to thereby float said gyroscope in said casing, said floating medium comprising an alloy of bismuth, indium and tin, said alloy having a specific gravity of approximately 7.84.

7. Means for supporting a gyroscope comprising a casing and a floating medium between said gyroscope and 10 2,896,455

said casing to thereby float said gyroscope in said casing, said floating medium comprising an eutectic alloy of bismuth, indium and tin, said alloy having a specific gravity of approximately 7.84.

References Cited in the file of this patent UNITED STATES PATENTS 2,625,045 Brubaker et al Jan. 13, 1953 2,817,974 Muzzey et a1 Dec. 31, 1957 Bishop et a1. July 28, 1959

Claims

1. MEANS FOR SUPPORTING A GYROSCOPE COMPRISING A TANK, A FLUID TIGHT CASING SUSPENDED IN A GIMBAL RING IN SAID TANK, SAID GIMBAL RING BEING ADAPTED FOR ROTATION ABOUT A VERTICAL AXIS THROUGH BEARINGS AND A FLOATING MEDIUM IN SAID TANK BETWEEN SAID CASING AND SAID TANK, SAID FLOATING MEDIUM COMPRISING AN ALLOY OF BISMUTH, INDIUM AND TIN, AND HAVING A SPECIFIC GRAVITY OF APPROXIMATELY 7.84 AT A TEMPERATURE OF 85*C.