Patent Application
20160341298
This disclosure relates to the field of transmission systems. More particularly, the disclosure pertains to a filter assembly with improved pressure relief functionality.
Automatic transmission fluid serves many functions in a modern automatic transmission. Pressurized fluid may be used engage friction clutches in order to establish a power flow path with a desired speed ratio. Fluid lubricates gears and bearings. Excess heat is removed by fluid flowing over various components. When the fluid contain contaminants, it may be less effective in these functions and may cause failures such as stuck valves. Therefore, transmissions often include fluid filters.
The filter media 30 provides some resistance to the flow. Consequently, the pressure at inlet port 14 must be greater than the pressure at outlet port 16 when fluid is flowing. The magnitude of this pressure difference depends upon the flow rate, the level of contamination in the filter media, and the fluid viscosity. When the temperature of the fluid is very cold, such as shortly after starting the vehicle during the winter, the viscosity can be very high causing the pressure drop across the filter to be excessive. When the pressure drop across the filter is excessive, relief valve 34 opens permitting fluid to bypass the filter media 30 to limit the pressure difference. Since contaminant usually enter the fluid only gradually, it is normally acceptable to periodically send unfiltered fluid to the outlet port. However, since the fluid passes close to the filter media on its way to the relief valve, some of the previously captured contaminant may re-enter the fluid. Consequently, the fluid leaving the outlet port 16 may actually have substantially more contamination than the fluid entering inlet port 14.
A transmission includes a hydraulic pump, a control system, a housing defining a filter chamber, a filter cartridge, and a spring biasing the filter cartridge toward a first position within the filter chamber. The pump draws fluid from a sump and supplies the fluid at increased pressure to a pump outlet circuit. The control system routes fluid from a line pressure circuit to transmission clutches. The filter chamber includes an inlet port connected to the pump outlet circuit and an outlet port connected to the line pressure circuit. When the filter is in the first position within the filter chamber, fluid is constrained to flow through filter media in the filter cartridge. If the pressure difference between the pump outlet circuit and the line pressure circuit exceeds a threshold, the filter cartridge slides within the filter chamber to a second position in which fluid may bypass the filter media. The transmission may also include a removable cover which provides access to replace the filter cartridge when the filter media is saturated with contaminants. In the first position, a face seal between the filter cartridge and the chamber may prevent bypass flow. Two sets of axially spaced tabs position the filter cartridge radially within the filter chamber while permitting circumferential flow around the cartridge.
A transmission oil filter includes a housing defining a filter chamber and a filter cartridge containing filter media configured to slide within the filter chamber. In a first position, fluid flowing from an inlet port to an outlet port of the chamber is constrained to flow through the filter media. In a second position, fluid may bypass the filter media. A spring may bias the filter cartridge toward the first position. For example, the spring may be a compression spring retained between the cartridge and a removable cover. A pressure difference between the inlet port and the outlet port may bias the cartridge toward the second position. Two sets of axially spaced tabs position the filter cartridge radially within the filter chamber while permitting circumferential flow around the cartridge.
An oil filter cartridge includes a perforated side wall, filter media, a bottom cap, and a top cap defining an inlet and having an exterior sealing surface. A plurality of tabs extend from each of the caps to locate the filter cartridge radially within a filter chamber while permitting the filter cartridge to slide axially with respect to the chamber. The bottom cap may be impervious to fluid flow at all pressure differences encountered in operation of a transmission, including at least 100 psi. The filter cartridge may also include a compression spring fixed to the bottom cap.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
When fluid is flowing through the filter media, the pressure at inlet port 14 exceeds the pressure at outlet port 16. This differential pressure acts on an area equal to the area enclosed by face seal 72 tending to push the cartridge downward. During ordinary operation, the spring force exceeds the force generated by differential pressure and the cartridge remains in the position shown in
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
