Patent Description:
A typical DEF system includes a DEF storage tank or reservoir, a filter, a pump, such as a positive displacement pump, and an injector. The DEF should be injected into the exhaust stream of the diesel engine as a fine mist. In order to produce the fine mist, the positive displacement pump draws DEF fluid from the reservoir to deliver DEF to the injector at high pressure. These pumps are prone to failure from debris as small as <NUM> microns. For this reason, a DEF filter rated at <NUM> microns or better is typically included on the suction side of the pump between the reservoir and the pump.

Experience in the laboratory and the field has shown that DEF tends to absorb or otherwise trap air in the fluid (see for example <CIT>).

The air may be trapped in the fluid in the form of nano-bubbles, or be dissolved in the DEF according to Henry's Law. Without limiting the invention to any particular theory of how air may be entrained in DEF, it is believed that air may be dissolved into fluid and/or air bubbles created while filing the DEF reservoir, or though agitation while the vehicle is under way, during a purge event, or entrained.

through other means. This entrained air may be released at very inopportune times. Certain environmental conditions can expedite the release of air from DEF. These conditions include, but are not limited to, an increase temperature or a decrease in absolute pressure. A pressure decrease will occur when there is an increase in altitude or when the DEF is being drawn by the suction side of a pump. The released air may then accumulate until a large bubble of air is withdrawn, for example, from the filter assembly, disrupting injection pressure in the DEF system.

The scope of the invention is defined by the independent claim <NUM>.

An aqueous fluid filter assembly according to one example of the present invention includes a cap, a bowl engaging the cap and defining a filter volume, and a filter element disposed within the filter volume. The bowl and filter element may be combined into a spin-on filter cartridge. The filter element is sealed against an interior of the cap and an interior of the bowl to provide an unfiltered volume and a filtered volume. An inlet is in fluid communication with the unfiltered volume and an outlet is in fluid communication with the filtered volume via a pickup section. The pickup section has a pick-up section inlet extending into the filtered volume and an air-metering orifice, wherein the air-metering orifice has a diameter less than <NUM>% of the diameter of the pick-up section inlet and the pick-up section inlet is located below the air-metering orifice. The diameter of the air-metering orifice is <NUM> to <NUM>.

The filter element may be cylindrical. The filtered volume is defined at least in part by an interior volume of the filter element. The pick-up section has a length sufficient to locate the pick-up section inlet within the interior volume of the filter element to allow for accumulation of separated air above the pick-up section inlet. A portion of the filtered volume defined by the interior volume of the cap may provide a space for air to accumulate above the pick-up section inlet.

In some examples, the interior volume of the cap includes a recess to allow for collection of separated air. The air-metering orifice may be located in the recess where separated air collects.

In some examples, the fluid filter assembly may further include a heater element. In one such example, the pick-up section inlet is located alongside the heater element. In another such example, the pick-up section inlet coaxially encloses the heater element.

In some examples, the fluid filter assembly further includes a compressible member inside the filtered volume to provide for protection against freeze damage.

In another example, an aqueous fluid filter assembly includes a cap, a bowl engaging the cap and defining a filter volume, and a filter element disposed in the filter volume, the filter element having an interior volume, the filter element being sealed against an interior of the cap and interior of the bowl, the bowl and an outer surface of the filter element cooperating to provide an outer unfiltered volume and the interior volume of the filter element and cap cooperating to provide an inner filtered volume. An inlet is in fluid communication with the outer unfiltered volume and an outlet is in fluid communication with the inner filtered volume via a pickup section. The pickup section includes a pick-up section inlet extending into the filtered volume and an air-metering orifice, wherein a diameter of the air-metering orifice is less than <NUM>% of a diameter of the pick-up section inlet and the pick-up section inlet is located below the air-metering orifice.

A known filter assembly <NUM> typical of those installed on the suction side of a DEF pump is illustrated in Figure Ia, with additional detail shown in <FIG>. The filter <NUM> has a cap <NUM>, bowl <NUM>, filter element <NUM>, heater <NUM>, inlet <NUM> and outlet <NUM>. The filter element is typically cylindrical with a hollow cylindrical interior. The ends of the filter element are sealed against the cap and bottom of the bowl. The bowl and outer cylindrical surface of the filter element <NUM> cooperate to provide an outer, unfiltered volume <NUM>. The interior cylindrical volume of the filter element, bottom of the bowl and interior of the cap cooperate to provide an inner filtered volume <NUM>. Fluid enters the inlet and flows into the outer unfiltered volume. The fluid passes through the filter element membrane and into the inner filtered volume. The outlet is in fluid communication with the top of the filtered volume by way of a tube, or an aperture in the tube sufficient for fluid flow, within the portion of filtered volume defined by the inside of the cap <NUM>.

A filter as illustrated in <FIG> maybe prone to air problems for at least two reasons. First, the membrane of the filter element may act as an air barrier. Filter elements are typically rated by particle sizes that they are capable of removing from the fluid. For example, a <NUM> micron filter element will remove particles of <NUM> microns and larger from the fluid being filtered. However, the membranes of <NUM> micron filter elements may also prevent entrained air from passing through the filter element. When this happens, the air accumulates in the outer unfiltered volume, typically at the top of the filter bowl. The air continues to accumulate until some, or all, of it is released around the filter element into the filtered volume, typically in a large "slug" or bubble. The "slug" of air travels to the top of the filtered volume and is withdrawn through the filter outlet tube. Once at the "slug" of air reaches the pump, the fluid pressure at the output of the pump drops, affecting injector operation, which may adversely impact emission system performance.

Second, because the filter is on the suction side of the pump, pressure within the fluid is lower than ambient pressure, especially in the inner filtered volume on the "clean" side of the filter element. Lower than ambient pressure promotes the release of air out of the liquid. Additionally, operation of the heater element in cold operating conditions may release additional dissolved air. Once the air is separated from the DEF, it tends to rise and collect at the upper sections <NUM> of the filtered volume in the cap. A large aperture in the outlet tube allows for proper fluid flow, but also allows air pockets to be re-introduced into the outlet flow as large "slugs" of air. The large slugs of air disrupt the pressure output and volume flow of the dosing pump. If the disruptions occur frequently enough the system may register a fault and cause reduced vehicle performance.

An improved aqueous DEF Fluid Filter Assembly <NUM> is illustrated in <FIG>, <FIG> and <FIG>. The Fluid Filter Assembly <NUM> comprises a cap <NUM>, bowl <NUM>, filter element <NUM>, heater element <NUM>, inlet <NUM> and outlet <NUM>. The filter element <NUM> and bowl <NUM> may be combined in a spin-on filter cartridge. As in known DEF filters, the filter element <NUM> may be cylindrical with a hollow cylindrical interior volume. The ends of the filter element are sealed against the cap <NUM> and the bowl <NUM>. Ends of the filter element <NUM> may seal against planar portions of the cap <NUM> and bowl <NUM>. Additionally, or in lieu of engaging the ends of filter element <NUM>, raised features 114a may engage and seal against side walls of filter element <NUM>. The bowl and outer cylindrical surface of the filter element cooperate to provide an outer unfiltered volume <NUM>. The interior cylindrical volume of the filter element, bottom of the bowl and interior volume of cap cooperate to provide an inner filtered volume <NUM>. Fluid enters the inlet and flows into the unfiltered volume. The fluid passes through the filter element membrane and into the filtered volume.

A portion of filtered volume <NUM> is occupied by a compressible member <NUM> to provide for protection against freeze damage. As freezing DEF expands, the compressible member <NUM> compresses reducing expansion stresses on the cap <NUM>, bowl <NUM>, and filter element <NUM>.

The outlet <NUM> is coupled to the filtered volume by an air-metering pick-up section <NUM>. Pick-up section <NUM> may comprise a pick-up section inlet <NUM> extending into the filtered volume, preferably into a portion of the filtered volume defined by the interior cylindrical volume of the filter element. The pick-up section <NUM> has a length dimensioned to allow for accumulation of separated air above the pick-up section inlet <NUM>, in the portion of the filtered volume defined by the interior volume of the cap and above filter element <NUM> filtered volume. The pick-up section <NUM> incorporates an air-metering orifice <NUM> above the pick-up section inlet <NUM> preferably in the portion of the filtered volume defined by the interior volume of the cap, to remove any air that accumulates in the interior volume of the cap at a slow, controlled rate.

The removal of air via an air-metering orifice <NUM> having a small diameter opening relative to the pick-up section inlet <NUM>, at a location in the interior volume that is above the inlet of the pick-up section inlet <NUM>, significantly reduces the potential for a "slug" of air large enough to disrupt DEF injector performance to accumulate in the filtered volume or be passed along to the injector pump. To achieve this, the air metering orifice <NUM> should be of a diameter insufficient for the fluid flow requirements for the DEF. According to the invention, the diameter of the air metering orifice <NUM> is less than <NUM>% of the pick-up section inlet <NUM>. In one example, the air-metering orifice <NUM> is a <NUM> to <NUM> (<NUM> to <NUM> inch) diameter aperture in pick up section <NUM>. Because features in the range of tens of a mm are not readily reproducible at the scale of the drawings, the air metering orifice <NUM> is not illustrated in <FIG>, and as illustrated in <FIG>, is not to scale to improve the visibility of the feature.

Also illustrated in <FIG> is a recess <NUM> in filter cap <NUM> to provide a high point at the top of the filtered volume. Air-metering orifice <NUM> is located in this recess. Any separated air in the filtered volume rises and accumulates in the recess, and therefore in the vicinity of the air-metering orifice <NUM>. This promotes metered removal of the separated air.

The example of <FIG> illustrates that outlet <NUM> and pick up section <NUM> may compromise a unitary tube shaped with an elbow to turn the pick up section inlet <NUM> into the filtered volume. Alternatively, the flow path from pick-up section <NUM> to outlet <NUM> may be constructed from multiple components. Pick up section <NUM> may be located adjacent to heater element <NUM>. Additionally, a portion of inlet <NUM> may extend toward heater element <NUM> to improve thermal coupling.

Another example is illustrated in <FIG>. The embodiment of <FIG> does not fall under the scope of the invention but is useful for understanding the invention. Elements in common with <FIG> and <FIG> have the same reference characters and the same description applies. In the example of <FIG>, the air-metering pick-up section <NUM> comprises a larger diameter pick-up section inlet 132a that is mounted coaxially with the heater element <NUM>. Air metering orifice <NUM> is located on a smaller diameter tube leading to outlet <NUM>. As in prior examples, air metering orifice <NUM> is much smaller in diameter than pick-up section inlet 132a. To enhance visibility, the air metering orifice <NUM> illustrated in <FIG> is not to scale.

In view of the foregoing, an improved fluid filter may comprise a cap, a bowl engaging the cap and defining a filter volume, a filter element disposed in the filter volume, the filter element being cylindrical with a hollow interior volume, the ends of the filter element being sealed against an interior of the cap and bottom interior of the bowl. The bowl and outer cylindrical surface of the filter element cooperate to provide an outer unfiltered volume. An interior cylindrical volume of the filter element, bottom of the bowl and interior volume of cap cooperate to provide an inner filtered volume. An inlet is in fluid communication with the unfiltered volume, and an outlet is in fluid communication with the filtered volume via a pickup section comprising a pick-up section inlet extending into the filtered volume and an air-metering orifice, wherein the air-metering orifice is less than <NUM>% of the diameter of an inlet of the pick-up section and the pick-up section inlet is located below the air-metering orifice. The diameter of the air-metering orifice is <NUM> to <NUM>.

The length of the pick-up section may be of a length sufficient to allow for accumulation of separated air above the pick-up section inlet, in a portion of the filtered volume defined by the interior volume of the cap and cylindrical interior volume of the filter element. The interior volume of the cap may include a recess to allow for collection of separated air. The air-metering orifice may be located in the recess.

Claim 1:
An aqueous fluid filter assembly, comprising:
a bowl (<NUM>) defining a filter volume;
a filter element (<NUM>) disposed in the filter volume, the filter element (<NUM>) sealed against an interior of the bowl (<NUM>) to provide an unfiltered volume (<NUM>) and a filtered volume (<NUM>);
an inlet (<NUM>) in fluid communication with the unfiltered volume (<NUM>);
an outlet (<NUM>) in fluid communication with the filtered volume (<NUM>) via a pickup section (<NUM>);
the pickup section (<NUM>) comprising a pick-up section inlet (<NUM>) extending into the filtered volume (<NUM>) and an air-metering orifice (<NUM>) and the pick-up section inlet (<NUM>) is located below the air-metering orifice (<NUM>);
characterized in, a compressible member (<NUM>) inside the filtered volume (<NUM>), wherein the compressible member (<NUM>) is configured to compress upon expansion of freezing diesel exhaust fluid reducing expansion stress on at least one of the bowl (<NUM>) and filter element (<NUM>), wherein a diameter of the air-metering orifice (<NUM>) is less than <NUM>% of a diameter of the pick-up section inlet (<NUM>) and wherein the air-metering orifice (<NUM>) is configured to remove air at the top of the filtered volume.