HYDRAULIC FLUID CASE AND PILOT DRAIN FILTRATION

1 . A hydraulic tank, comprising

at least one side wall comprising an inlet for receiving hydraulic fluid from a hydraulic actuation circuit, an outlet for providing hydraulic fluid to the hydraulic actuation circuit, and a drain line inlet;

a port plate comprising at least one drain port, the port plate being attached to the at least one side wall over the drain line inlet;

a filter disc comprising a filter media, the filter disc being disposed between the port plate and the drain line inlet; and

a gasket positioned around the filter disc and disposed between the port plate and the at least one side wall;

wherein the filter media is spaced apart from the port plate.

2 . The hydraulic tank of claim 1 , wherein the filter media comprises a first flow area, the at least one drain port comprises a second flow area, and the first flow area is greater than the second flow area.

3 . The hydraulic tank of claim 2 , wherein the at least one drain port comprises a plurality of drain ports.

4 . The hydraulic tank of claim 3 , wherein the plurality of drain ports comprises a combined flow area and wherein the first flow area is greater than the combined flow area.

5 . The hydraulic tank of claim 1 , further comprising a positioning ring disposed within the gasket that spaces the filter media apart from the port plate.

6 . The hydraulic tank of claim 1 , wherein the port plate and the at least one side wall are separated by a distance D and wherein the filter media is spaced apart from the port plate by a first spacing S1 in a range 0D<S1≤1D.

7 . The hydraulic tank of claim 1 , further comprising a supporting disc disposed between the filter media and the drain line inlet.

8 . The hydraulic tank of claim 7 , wherein the supporting disc spaces the filter media from the at least one side wall by a second spacing S2 in a range 0D<S2<1D.

9 . The hydraulic tank of claim 7 , wherein the supporting disc comprises an outer ring and a plurality of inwardly extending fingers configured to support the filter media.

10 . The hydraulic tank of claim 9 , wherein the supporting disc further comprises an inner ring concentric with the outer ring, the fingers extending from the outer ring to the inner ring.

11 . The hydraulic tank of claim 1 , wherein the filter media comprises a mesh screen.

12 . The hydraulic tank of claim 11 , wherein the mesh screen has a size in a range from 20 mesh to 250 mesh (or 840 microns to 62 microns).

13 . The hydraulic tank of claim 1 , wherein the drain line inlet comprises a plurality of substantially parallel slits, a semicircular aperture, or a circular aperture.

14 . The hydraulic tank of claim 13 , wherein the at least one side wall further comprises at least one bleed hole disposed above the drain line inlet, each of the at least one bleed hole being covered by the port plate.

15 . A hydraulic system, comprising:

the hydraulic tank of claim 1 containing hydraulic fluid;

at least one actuator;

a pump configured to draw the hydraulic fluid from the outlet of the hydraulic tank and pressurize the hydraulic fluid for actuation of the at least one actuator, the actuation causing return of hydraulic fluid to the inlet of the hydraulic tank;

wherein a first portion of the hydraulic fluid flowing through the pump lubricates the pump, the first portion of the hydraulic fluid being returned to the hydraulic tank through a first drain line in fluid communication with the at least one drain port.

16 . The hydraulic system of claim 15 , wherein the at least one actuator comprises a hydraulic motor, wherein a second portion of hydraulic fluid flowing through the motor lubricates the motor, and wherein the second portion of the hydraulic fluid is returned to the hydraulic tank through a second drain line in fluid communication with the at least one drain port.

17 . A method for filtering hydraulic fluid on a drain line, comprising:

drawing the hydraulic fluid from a hydraulic tank through a pump;

using a first portion of the hydraulic fluid to lubricate the pump;

pressurizing, using the pump, a second portion of the hydraulic fluid for use by at least one actuator;

returning the first portion of the hydraulic fluid from the pump to the hydraulic tank through the drain line;

filtering the first portion of the hydraulic fluid as the first portion of the hydraulic fluid flows into a drain line inlet of the hydraulic tank by passing the first portion of the hydraulic fluid through a filter media disposed over the drain line inlet;

wherein the drain line terminates at a port plate attached to the hydraulic tank and wherein the filter media is positioned between the port plate and the drain line inlet.

18 . The method of claim 17 , wherein the filter media is positioned between the port plate and the drain line inlet using a positioning ring and a supporting disc, the positioning ring being disposed between the port plate and the filter media and the supporting disc being disposed between the filter media and the drain line inlet.

19 . The method of claim 17 , wherein the at least one actuator comprises a motor, wherein the second portion of the hydraulic fluid comprises a third portion of the hydraulic fluid, and wherein the method further comprises:

using the third portion of the hydraulic fluid to lubricate the motor;

returning the third portion of the hydraulic fluid from the motor to the hydraulic tank through a second drain line;

filtering the third portion of the hydraulic fluid as the third portion of hydraulic fluid flows into the drain line inlet of the hydraulic tank by passing the third portion of hydraulic fluid through the filter media disposed over the drain line inlet;

wherein the second drain line terminates at the port plate attached to the hydraulic tank.

20 . The method of claim 19 , wherein the drain line and the second drain line terminate at a first drain port and a second drain port, respectively, of the port plate; and

wherein the filter media comprises a first flow area, the first and second drain ports together comprise a second flow area, and the first flow area is greater than the second flow area.