Reservoir for power steering system

A reservoir is provided having an upper reservoir body connected to a lower reservoir body. The reservoir includes and inlet port and an outlet port that are separated by a filter, which filters fluid flowing from the inlet to the outlet. In addition, a re-circulating cover is provided to separate fluid returning through the inlet port from the fluid in the main reservoir chamber. A re-circulating cover is provided that defines a re-circulating chamber. Fluid communication between the main reservoir chamber and the re-circulating chamber is restricted by the re-circulating cover until the main reservoir fluid reaches a predetermined temperature threshold. Accordingly, a given quantity of fluid is re-circulated from the inlet port to the outlet port and is continuously warmed before mixing with main reservoir fluid. Such a reservoir design helps to eliminate cold start up noises.

FIELD OF THE INVENTION
 The present invention relates to reservoirs for power steering systems and
 more particularly, to reservoirs having fluid flow control features for
 cold temperature environments.
 BACKGROUND OF THE INVENTION
 A reservoir is provided in a power steering system to hold a predetermined
 quantity of hydraulic fluid. Typically, the reservoir has an outlet port
 that communicates fluid to a power steering pump and an inlet port that
 returns fluid from a power steering gear back into the reservoir. It is
 also known to provide a filter inside the reservoir to filter the fluid as
 it flows from the inlet port to the outlet port.
 However, one draw back of such known reservoirs is that hydraulic fluid
 does not flow fast enough through the filter during cold temperature
 operation. The colder the hydraulic fluid, the greater the resistance to
 flow. Such increased viscosity greatly reduces the ability of the fluid to
 pass through the filter. As a result, an insufficient amount of fluid is
 supplied to the pump. The insufficient amount of fluid causes cavitation
 within the pump, which produces undesirable noise and sound.
 One known reservoir design has attempted to diminish cold weather effects.
 The known reservoir utilizes a relatively complex series of angled guide
 members and a series of filter elements to control the directional flow of
 fluid returning from the inlet port to the outlet port. However, the
 elaborate guide system is costly to manufacture and has an unnecessarily
 large number of parts.
 SUMMARY OF THE INVENTION
 The present invention is directed to a reservoir for a power steering
 system having an upper reservoir body connected to a lower reservoir body
 and has a removable cap for accessing the interior of the reservoir. A
 filter is disposed within the reservoir at a location to filter fluid
 entering from an inlet port and exiting through an outlet port. In
 addition, a re-circulating cover is provided having first and second
 passages that limit communication between fluid in a main reservoir
 chamber and fluid in a re-circulating chamber.
 In operation, relatively warm fluid from the inlet port flows into the
 re-circulating chamber and passes through the filter before traveling
 through the outlet port to a pump. During cold weather operation, the same
 fluid from the inlet port is continuously re-circulated through the
 re-circulating chamber to the outlet port, resulting in warming of the
 fluid as it passes through the power steering system. The re-circulating
 cover includes venturi slots having predetermined configurations that
 limit the flow of relatively cold hydraulic fluid in the main reservoir
 chamber into the re-circulating chamber. Further, at least one orifice is
 provided in the re-circulating cover that allows flow of warm fluid in the
 re-circulating chamber into the relatively colder fluid contained in the
 main reservoir chamber.
 According to another embodiment of the present invention, a re-circulating
 cover is provided having spiral or vortex shaped channels for efficiently
 delivering re-circulating fluid from the inlet port to the filter, and
 ultimately to the outlet port and pump.
 Therefore, according to the present invention, a sufficient amount of fluid
 is supplied to the steering pump, even during initial cold weather
 operation, to greatly reduce, minimize or eliminate unwanted noise.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 FIG. 1 shows a reservoir 10 for use in a hydraulic system, such as a power
 steering system (not shown). Reservoir 10 includes an upper reservoir body
 12 connected to a lower reservoir body 14. A cap 16 is releaseably
 connected to upper reservoir body 12 to allow introduction of hydraulic
 fluid 18 into reservoir 10. A filter 20 is attached to a lower reservoir
 body 14, upstream from an outlet port 22 that communicates fluid to a pump
 (not shown). A re-circulating cover 24 separates fluid in a main reservoir
 chamber 26 from fluid in a re-circulating chamber 28. Re-circulating cover
 24 is illustrated having a generally hat shaped cross-section, however,
 any suitable shape can be utilized. Re-circulating cover 24 includes an
 outer flange 30 that engages both an outer periphery of filter 20 and a
 shoulder 32 of reservoir 10. Re-circulating chamber 28 receives fluid from
 an inlet port 34, which is shown in FIG. 2.
 As shown in FIG. 2, re-circulating cover 24 includes a plurality of
 circumferentially spaced apart venturi slots 36 located on generally
 cylindrical outer side wall 38. Venturi slots 36 have predetermined
 configurations including predetermined size and shape to control fluid
 flow from main reservoir chamber 26 to re-circulating chamber 28. A top 40
 of cover 24 is connected to side wall 38 and is predominately solid except
 for a plurality of orifices 42 that are sized and configured to restrict
 fluid flow from re-circulating chamber 28 to main reservoir chamber 26
 below a predetermined temperature level. Therefore, re-circulating cover
 24 creates a physical barrier between main reservoir chamber 26 and
 re-circulating chamber 28, except for very limited fluid communication
 paths.
 As shown in FIG. 3, inlet port 34 delivers fluid into re-circulating
 chamber 28 at a position vertically above filter 20. Outlet port 22
 receives filtered fluid from re-circulating chamber 28 for communicating
 to a pump (not shown).
 Next, the operation of the reservoir 10 in a cold weather environment will
 be described. During initial cold weather operation of, for example, a
 steering system utilizing the present invention, fluid is removed from
 reservoir 10 via outlet port 22 and returned to reservoir 10 through inlet
 port 34. Incoming fluid from inlet port 34 flows into re-circulating
 chamber 28 and is separated from fluid in main reservoir chamber 26 by
 re-circulating cover 24. The re-circulating fluid then passes through
 filter 20 and is re-circulated to outlet port 22 to re-supply the pump. As
 the re-circulating fluid continues to pass through the steering system, it
 tends to warm up by virtue of frictional heat produced within the system.
 When the re-circulating fluid reaches a predetermined threshold
 temperature or viscosity, some of the warm fluid in re-circulating chamber
 28 is allowed to flow through orifices 42 in top 40 of re-circulating
 cover 24. Consequently, some of the warm re-circulating fluid mixes with
 the relatively colder fluid in main reservoir chamber 26. Orifices 42 have
 a size and profile that prevents the relatively colder main reservoir
 fluid 26 from flowing into re-circulating cover 24 until fluid in main
 reservoir chamber 26 reaches a predetermined threshold temperature or
 viscosity.
 The only way in which cold fluid in main reservoir chamber 26 is allowed to
 enter re-circulating cover 24 is through venturi slots 36 located on the
 side wall 38 of re-circulating cover 24. Again, because of higher
 viscosity of the cold main reservoir fluid 26, flow through venturi slots
 36 is restricted only to fluid having at least a second predetermined
 temperature or viscosity.
 As re-circulating fluid continues to increase in temperature and mix with
 fluid in main reservoir chamber 26 via flow through orifices 42, fluid in
 main reservoir chamber 26 also warms. In addition, heat is conducted from
 the warmer re-circulating cover 24 to the colder fluid in main reservoir
 chamber 26 that immediately surrounds cover 24. When fluid in reservoir
 chamber 26 reaches the predetermined threshold temperature, a desired
 viscosity level is obtained. The viscosity level corresponds to the
 threshold temperature/viscosity level of orifices 42 and allows free,
 bi-directional flow of fluid through orifices 42. Such a free flow of
 fluid helps to maintain a relatively constant flow of fluid to the pump
 and therefore minimizes cavitation. Thus, unwanted cold start noise is
 greatly minimized or eliminated.
 Another embodiment of the present invention is shown in FIGS. 4-6. FIGS.
 4-6 show a reservoir 110 having most of the same features as reservoir 10
 described above. However, the re-circulating cover 124 has a different
 design. The re-circulating cover 124 has an outer periphery 126 connected
 to a raised central portion 128 by a spiral or vortex shaped portion 130.
 The outer periphery 126 includes an arcuate inlet tunnel 132 for
 communication with an inlet port 134. The raised central portion 128
 includes a plurality of orifices 142, similar to orifices 42, described
 above, and has a generally constant height.
 The vortex shaped portion 130 changes in height and/or shape in a clockwise
 direction in FIG. 5. The vortex shaped portion 130 has a greatest height
 adjacent the inlet tunnel 132 and decreases consistently in height in a
 clockwise, circumferential direction. As shown in FIG. 5, the vortex
 shaped portion 130 extends approximately 270 degrees around the raised
 central portion 128. However, the vortex portion 130 can extend any
 suitable arcuate amount. For purposes of description, the raised central
 portion 128 includes the additional approximately 90 degree portion 140
 having generally the same height as the portion containing the orifices
 142.
 Similar to re-circulating cover 24, the re-circulating cover 124 of the
 second embodiment includes venturi slots 136 spaced circumferentially
 about a side wall 144 of the re-circulating cover 124. The venturi slots
 136, like the orifices 142, perform identical functions as in the first
 embodiment.
 As shown in FIG. 6, the leftmost side of the re-circulating cover 124 shows
 the inlet tunnel 132 connected to the raised central portion 128. The
 rightmost side of FIG. 6 shows a reduced height vortex portion 130 that
 also tapers downwardly in a radially outward direction. The purpose of the
 vortex design is for efficiently delivering re-circulating fluid from the
 inlet port 134 to the filter, and ultimately to the outlet port 122 and
 pump.
 Preferred embodiments of the present invention have been disclosed. A
 person of ordinary skill in the art would realize, however, that certain
 modifications would come within the teachings of this invention. For
 example, the venturi slots may be replaced by other venturi-type elements
 that provide the same restriction of flow between colder fluid and warmer
 fluid. Likewise, the orifices may take any form or profile that produces a
 restrictive flow between warmer fluid and colder fluid. Further, the
 location of the venturis and orifices can be changed.