OPEN CELLULAR PUMP FILTER ELEMENT

Abstract: An open cellular pump filter element (27) which is utilized in an oil filter (25) interposed between a sump (ll) and an oil pump (l3) for an automatic transmission wherein the cellular element breaks up large congregated air bubbles (2l) that normally form on a filter screen type mesh and are subsequently released into the suction fluid passage of the pump. An open cellular block of a foam-like material is placed in the filter body after the filter screen.

Description: The present invention relates to an improved filter for oil flow from the sump of a transmission to the oil pump supplying oil to an automatic transmission. Presently utilized oil filters consist of a fine mesh strainer or bag extending across a filter housing with a housing input from the oil sump on one side of the strainer and a housing outlet on the opposite side communicating with the suction fluid passage leading to a transmission oil pump. As air is entrained in the oil circulating through the automatic or continuously variable transmission, air bubbles tend to form along the fine mesh screen in the filter due to re­ duced pressure therein resulting from the suction side of the oil pump. The bubble size increases as vacuum in­ creases and these large air bubbles pass through the screen and are released into the suction passage leading to the pump mixed with the oil. Large air bubbles create a condition that is most critical in variable displacement vane pumps running at minimum displacement, but the condition is present in all automatic transmission systems using an enclosed filtration system. Where the large air bubbles are released and pass through the variable displacement pump under minimum displacement, such as occurs in the minimum ratio range of a continuously variable transmission or in the top ratio range of an automatic transmission, a periodic release of the hydraulically-actuated drive system is experienced causing a neutral condition due to premature hydraulic element release. The present invention overcomes this problem. The present invention relates to an improved oil filter construction that acts to ensure a homogeneous supply of aerate oil without large air bubbles entrained in the oil flow. The pump filter interposed between the source of oil and the suction passage of the transmission oil pump includes upper and lower housing portions having a fine mesh strainer or filter screen extending across the filter at the juncture between the two housing portions. An inlet is formed in the lower housing portion and an outlet in the upper portion, and the upper housing portion above the filter screen is substantially completely filled with an open cellular foam material acting to homogenize air bubble size. Further objects are to provide a construction of maximum simplicity, efficiency, economy and ease of assembly and operation, and such further objects, ad­ vantages and capabilities as will later more fully appear and are inherently possessed thereby. Figure l is an elevational view partially in cross section, of a conventional transmission oil filter. Figure 2 is an elevational view, partially in cross section, similar to Figure l, of the present invention showing the addition of an open cellular material. Figure 3 is a cross sectional view through an alternative embodiment of oil filter. Referring more particularly to the disclosure in the drawings wherein is shown an illustrative embodiment of the present invention, Figure l discloses a conventional oil filter l0 interposed between the source or sump ll for the oil for the transmission (not shown) and the suction fluid passage l2 leading to an oil pump l3, such as a variable displacement vane pump or gear pump, for an automatic transmission or continuously variable transmission. The oil filter l0 consists of a housing l4 formed of a lower dish-like member l5 and an upper inverted dish-like member l6 which are suitably sealingly joined together along an intermediate seam or joint l7. A fine mesh stainer or filter screen l8, formed of a plastic material and/or metal wire mesh material, extends across the housing l4 and is secured therein at the joint l7 between the members to screen out and retain any foreign particles or impurities present in the oil from the source ll. In an enclosed filtration system, air becomes entrained in the oil during flow through the transmission system. As the oil reaches the filter screen l8, large air bubbles 2l form in the oil-air mixture l9 due to reduced pressure created by operation of the pump l3 and the surface tension of the air bubble. The bubble size increases as vacuum increases in relation to the surface tension and the vacuum in which it exists due to pump suction, and the air bubbles 2l above the filter screen l8 are released into the suction intake passage l2 leading to the pump. When the large air bubbles pass through the pump under minimum displacement, such as for the minimum ratio range of a continuously variable transmission or the top ratio range of a conventional automatic transmission, a periodic release of the hydraulically actuated drive system is experienced resulting in a neutral condition due to premature hydraulic element release. Figure 2 discloses the improved oil filter 25 of the present invention wherein identical elements will be denoted by the same reference numerals with the addition of a script a. This filter includes a housing l4a formed of a lower member l5a, an upper member l6a, and a filter screen l8a extending centrally across the housing. The housing chamber 26 above the filter screen l8a is filled with an open cellular homogenization material 27, such as a commercially available industrial foam material impervious to oil and high temperatures. The block of foam material has approximately ten pores per inch and sufficient thick­ ness so as to provide approximately ten levels of non-aligned openings with the dimensions of a single opening being approximately 0.l87 inch. Such a foam material is available from the Foam Division of the Scott Paper Company and is characterized as a reticulated, fully "open pore" flexible, ester type of polyurethane foam. Thus, large air bubbles 2la which form in the oil-air mixture l9a in the lower chamber 28 due to reduced pressure and pass through the filter screen l8a into the open cellular foam 27 are broken up and dispersed due to the open cellular foam 27 to provide a homogeneous mixture of oil and small bubbles 29 of a size smaller than the size of any single opening in material 27, which air-oil mixture will not provide problems either in the pump or in the hydraulically actuated drive system. Although the Scott industrial foam has been disclosed for use in the filter, obviously other similar materials will also provide the same result in the oil filter. Figure 3 discloses an alternative filter structure where the filter 3l is built into a recess 33 formed in a cast housing 32, such as the transmission housing. A lower filter housing member l5b has a circumferential mounting flange 34 with openings 35 to receive bolts 36 to secure the member to the cast housing 32. A suitably configured screen l8b is located in the member l5b with its periphery 37 clamped between the housing 32 and flange 34; a suitable sealing ring (not shown) being positioned to be clamped by the housing flange 34. A block of cellular foam 27b is positioned to substantially fill the upper chamber 26b defined by the recess 33 and the screen l8b. An inlet from the sump llb in the lower member l5b communicates with the lower chamber 28b, and the suction fluid passage l2b to the pump l3b is formed in the cast housing 32. This arrangement operates in the same manner as the embodiment of Figure 2.

Claims: 1. An oil filter (25,3l) for an oil pump (l3) of an automatic transmission interposed between a source of oil (ll) and the oil pump, comprising a filter housing (l4a,32) having an inlet communicating with the source of oil (ll) and an outlet communicating with a suction fluid passage (l2) leading to the oil pump (l3) and a filter screen (l8a,l8b) in said housing dividing the filter into an inlet chamber (28,28b) and an outlet chamber (26,26b), the improvement comprising an open cellular filter element (27,27b) substantially completely filling said outlet chamber (26,26b) to break up large air bubbles (2la) forming in said filter. 2. An oil filter (25,3l) as set forth in Claim l, wherein said open cellular filter element (27,27b) is formed of a flexible polyurethane foam having approximately ten pores to the inch. 3. An oil filter (25,3l) as set forth in Claim 2, in which said pores in the foam material have an opening size of approximately 0.l87 inch. 4. An oil filter as set forth in Claim 3, in which said foam material is impervious to oil and temperature.

Inventors: SCHNEIDER, KARL FRIEDRICH
Applicants: BORG-WARNER AUTOMOTIVE, INC.
Application year: 1987
Main classification: F16N39
IPC codes: B01D35, F16N39, F16H57, F01M11, B01D29, B01D19