Servo valve for ultra-fast pressure regulation with controlled system damping

• US 4,506,861 A
• Filed: 01/10/1983
• Issued: 03/26/1985
• Est. Priority Date: 01/10/1983
• Status: Expired due to Fees

• Current Assignee: Anatech BV (Anatech Holding BV)
• Original Assignee: Automotive Engine Associates
• Inventors: Showalter, Merle R.
• Primary Examiner(s): Nilson, Robert G.
• Application Number:
  US06/456,718
• Time in Patent Office: 806 Days
• Field of Search: 251/139, 251/141, 137/527, 137/855-858
• US Class Current: 251/129.16
• CPC Class Codes: F16K 15/03 with a hinged closure member or with a pivoted closure member
• CPC Class Codes: F16K 15/162 with limit stop
• CPC Class Codes: F16K 31/0651 the fluid passing through the solenoid coil
• CPC Class Codes: F16K 31/0655 Lift valves
• CPC Class Codes: Y10T 137/7892 With stop
• CPC Class Codes: Y10T 137/7898 Pivoted valves

Abstract

A liquid flow control servo valve where the flow controlling element is a magnetically loaded hydrostatic step bearing. An electromagnet has a central liquid passage 3 through it, and flow from this passage 3 is closed off by a magnetically permeable flat plate which has a planar surface matching a corresponding planar surface of the electromagnet. Pressure from passage 3 floats the plate on a thin liquid film in the manner of a hydrostatic step bearing, and the film thickness of this liquid film rapidly adjusts until the hydrostatic bearing pressure force W balances the magnetic forces on the plate. This variation in film thickness adjusts flow rate past the plate. The flow and pressure drop across the hydrostatic bearing plate rapidly adjusts to coil current in the low hysteresis electromagnet, so that P across the plate varies nearly in proportion to coil current I. The geometry of the hydrostatic bearing can be tailored to produce a wide range of viscous damping characterization using conventional squeeze film equations. So long as flow in the step bearing is laminar, the ratio of critical damping produced by the valve in a particular installation is invariant over a wide operating range of flows and fluid viscosities.

Claims

1. A pressure differential controlling servo valve wherein the pressure differential across the valve is a simple and smooth function of electric current, said valve comprising a housing having a centrally positioned inlet and an outlet, a ferrite electromagnet positioned within the housing in flow communication with the inlet, said ferrite electromagnet comprising a torroidal ferrite body with a core of coiled wire within said torroidal body, said wire core being potted in said torroidal body by a gasoline resistant substance, the central opening formed by the torroidal body surrounding the housing inlet, the ferrite electromagnet having a top and a bottom, the top of the electromagnet having a smooth planar surface perpendicular to the housing inlet,

a ferrite disk having a top and a bottom surface and sized to be coextensive with the electromagnet body, a magnetically impermeable film secured to the bottom surface of said ferrite disk and generally coextensive therewith, said film having a tongue extending outwardly beyond the edge of the ferrite disk, said disk being positioned on the top planar surface of the electromagnet with the film in confronting relation thereto, clamping means for securing the film tongue to the housing to hingedly retain the disk in position for back and forth movement with respect to the top planar surface of the electromagnet.

said housing having an outlet chamber in flow communication with the outlet and adapted to receive flow from the inlet when the ferrite disk is raised away from the top planar surface of the electromagnet, and whereby the fluid in the inlet passes between the film and the top planar surface of the electromagnet to provide a hydrostatic full film bearing so that the hydrostatic full film pressure forces balance the magnetic forces and thereby insures nonimpaired and smooth response to current flow into the electromagnet.

2. A fluid flow control servo valve where the flow controlling element is a magnetically loaded hydrostatic step bearing constructed as follows:

an electromagnet has a central fluid passage through it, and the outlet of said central passage is on a flat planar electromagnet surface which forms one surface of a hydrostatic step bearing

a magnetically permeable closure element which has a flat planar closure surface corresponding to said planar electromagnet surface, where said closure element is stiff so as to maintain said closure surface truly flat under the magnetic and pressure forces to which said closure element is subjected, and where said closure element is mounted elastically so that it can move to increase or decrease the distance between said closure surface and said electromagnet surface

wherein the magnetic forces between said electromagnet and said closure element act to force said closure surface directly against said electromagnet surface and wherein the pressure differential between the central fluid passage and the periphery of said closure surface causes a sheet of fluid to flow between said closure surface and said electromagnet surface separating the surfaces whereby said closure surface floats on said fluid as a magnetically loaded hydrostatic step bearing and the force balance and flow relations of fluid flow between said surfaces are dominated by viscous drag

wherein the film thickness of the fluid film between said electromagnet surface and said closure element surface rapidly adjusts to establish a force balance between the hydrostatic bearing pressure W and the force from the electromagnet on said plate.

3. The invention as stated in claim 2 and wherein said electromagnet and said magnetically permeable closure element are constructed of very low magnetic hysteresis materials such as ferrite for rapid electromagnetic response.

4. The invention as stated in claim 2 and wherein said closure element is held in position to operate in hydrostatic bearing mode by a relatively floppy and flexible elastic mounting characterized by negligible mechanical hysteresis, so that mechanical hysteresis of said servo valve can be eliminated.

5. The invention as stated in claim 2 and wherein a thin spacer film of magnetically impermeable material is placed between the planar surfaces of said closure element and said electromagnet so as to flatten the magnetic force versus distance curve on which the servo valve operates.

6. The invention as stated in claim 2 and wherein the maximum film thickness h of said closures element is constrained by a mechanical stop limiting travel of said plate away from said electromagnet.

7. The invention as described in claim 2, and wherein the geometrical planes of said closure element and said electromagnet which form the hydrostatic step bearing have sufficient surface roughness that they do not lock together excessively due to residual magnetism during shut down periods.

8. The invention as stated in claim 2 and wherein the flat planar surfaces of said electromagnet and said closure element are arranged so that the sheet of fluid flowing between said surfaces is in the form of a circular disk and wherein the outlet of the fluid passage in said electromagnet is central with respect to said fluid disk.

9. The invention as stated in claim 8 and wherein the flat planar surfaces of said electromagnet and said closure element are arranged so that the absolute value of the fluid disk radius produces a specified degree of squeeze film damping of the motion of said closure element to produce damping of the fluid control system of which the fluid flow control servo valve is a part.

10. The invention as described in claim 2 and wherein the geometrical planes of said closure element and said electromagnet which form the hydrostatic step bearing have surface roughness in excess of 4 microinches.