Abstract:
The fluid reservoir of a hydraulic system is fitted with a nozzle having a constricted primary discharge opening for directing an accelerated jet stream of hydraulic fluid returned to the reservoir from a pump back to an inlet of the pump. The jet stream aspirates additional fluid from the reservoir to boost the supply to the pump to minimize cavitation for quiet operation. The nozzle includes at least one bleed hole located upstream of the primary discharge opening through which a fraction of the fluid stream escapes into the reservoir and is permitted to dwell for a time sufficient to allow natural separation of entrained gas from the fractional stream before being drawn into the reservoir outlet by the jet stream.

Description:
This application claims the benefit of provisional application 60/178,655 filed Jan. 28, 2000. 
    
    
     TECHNICAL FIELD 
     This invention relates to hydraulic pumps and more particularly to the means of handling of the fluid returned to the hydraulic reservoir used to feed the pump under high flow, high pressure conditions with low noise. 
     BACKGROUND OF THE INVENTION 
     Fixed and/or variable positive displacement hydraulic pumps have numerous applications in many fields, including automotive, aerospace, industrial, agricultural, heavy equipment and the like for performing work. In a typical hydraulic system, return fluid is simply returned into the pump reservoir where it dwells for a time period before being drawn in by the inlet to the pump for recirculation. Under conditions of high load and high flow rate, such hydraulic systems are characteristically unable to keep up with the fluid demand of the pump, leading to cavitation and unacceptable levels of noise. Another inherent disadvantage with such systems is that the kinetic energy of the incoming fluid to the reservoir is lost and not utilized to feed the inlet to the pump, leading to relatively low efficiencies. Such simple single return hydraulic fluid return systems thus have their limits. 
     U.S. Pat. No. 5,802,848 discloses a hydraulic steering system for a motor vehicle having two separate fluid return lines leading to the reservoir. One line is a high return flow which is fed to a nozzle within the reservoir. The outlet of the nozzle is supported adjacent the inlet to the steering pump. The momentum of the return fluid exiting the nozzle creates a venturi action at the reservoir outlet, which has the beneficial effect of aspirating additional volumes of fluid from the reservoir. The momentum of the return fluid together with the addition of the entrained fluid from the reservoir produces a desirable “boost” effect which provides ample feed to the pump under conditions of high flow and high pressure to prevent cavitation attributable to lack of sufficient inflow to the pump. The second return line delivers a fraction of the return fluid to the reservoir. Such fluid is permitted to dwell for a time in the reservoir chamber, during which time any undissolved air or gas bubbles contained in the secondary stream are liberated before the fluid is drawn in by the primary jet stream. Without the secondary return line, the fluid would not be sufficiently deaerated and cavitation and noise would result. 
     One inherent limitation of the above system is that it requires two separate return lines to the reservoir, and thus may not be suitable for all pump applications, and particularly those having only a single high flow return line. The requirement of the secondary line further adds cost, weight and complexity to the construction of the system and particularly the reservoir. 
     SUMMARY OF THE INVENTION 
     A hydraulic system according to the invention includes a hydraulic pump reservoir having a fluid outlet communicating with the inlet to the pump, a single fluid return line having a nozzle within the reservoir adjacent the outlet and operative to direct a high velocity jet flow of fluid from the single return line into the outlet and to thereby aspirate additional volumes of fluid into the inlet to achieve high flow, high pressure operation of the pump. According to a characterizing feature of the invention, the nozzle includes at least one bleed hole through which a fraction of the fluid flow escapes into the reservoir at a location upstream of the nozzle outlet and dwells for a time sufficient to liberate any entrained air or gas bubbles before being drawn into to the pump by the primary flow stream. 
     The invention has the advantage of achieving, with a single return line, high velocity, high flow delivery of fluid to the pump while deaerating the fluid to minimize cavitation and noise. 
     The invention has the further advantage of being readily adaptable to any hydraulic pump system calling for high velocity, high flow delivery of fluid to the pump with low noise, whether the system has a single or multiple return lines. According to the invention, multiple return lines can be converged upstream of the reservoir to provide a single high flow return line leading to the reservoir. Some of the systems contemplated by the invention include, but are not limited to vehicular power steering, transmission, and engine oil applications; industrial; construction; heavy equipment; aerospace, etc. 
     The invention has the further advantage of eliminating the need and thus cost and added weight of a secondary flow return line, as is necessary with system of the above-mentioned &#39;848 prior patent. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Presently preferred embodiments of the invention are disclosed in the following description and in the accompanying drawings, wherein: 
     FIG. 1 is a schematic diagram of a general hydraulic system according to the invention; 
     FIG. 2 is a schematic diagram of a particular hydraulic system according to the invention; 
     FIG. 3 is an elevation view, shown partly in section, of a hydraulic pump fitted with an integrated booster reservoir according to the invention; 
     FIG. 4 is a sectional view taken generally along lines  4 — 4  of FIG. 3; 
     FIG. 5 is a view like FIG. 4 showing a modified intake throat of the pump; 
     FIG. 6 is a fragmentary sectional view illustrating an alternative nozzle construction; 
     FIG. 7 is a view like FIG. 3 but showing a modified bleed hole and baffle arrangement; 
     FIG. 8 is an enlarged fragmentary sectional view showing a further alternative construction of the nozzle; 
     FIG. 9 is a schematic, partly sectional view of a hydraulic pump and remote booster reservoir according to the invention; 
     FIG. 10 is a fragmentary sectioned elevational view of an alternative construction of a booster reservoir according to the invention; 
     FIG. 11 is a schematic elevation view, shown partly in section, of a pump having an integrated reservoir and a pump inlet fitted with an elbow for communicating with the nozzle; 
     FIG. 12 is a fragmentary perspective view of a pump and integrated booster reservoir according to a further embodiment of the invention; and 
     FIG. 13 is a cross-sectional elevational view of an alternative embodiment of a pump. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a schematically represented hydraulic system  10  is shown having a pump  12  and a reservoir  14  having a single return line  76  leading from the pump  12  to the reservoir  14 . The pump  12  may comprise any positive fixed or variable displacement hydraulic pump including motor vehicle steering pumps, oil pumps, transmission pumps, as well as hydraulic pumps used in industrial, agricultural, heavy equipment, rail and aerospace applications, to name a few. The booster reservoir  14  of the invention is thus applicable to working in conjunction with virtually any positive displacement hydraulic pump to achieve high rpm, high displacement and high flow without cavitation and noise. As will become apparent from the description below, the adaptation of the booster reservoir  14  is not limited to pumps having multiple fluid return lines leading to the reservoir, such as is necessary for operation of the return booster reservoir in U.S. Pat. No. 5,802,848. The hydraulic booster reservoir  14  of the present invention operates on and requires only a single return line, which accounts for its ready adaption to virtually any hydraulic pump system, regardless of the number of return lines. 
     FIG. 2 illustrates a schematic diagram of a particular motor vehicle hydraulic system  10  which embodies the subject single return booster reservoir  14  of the invention. The system  10  of FIG. 2 comprises the system disclosed in the aforementioned U.S. Pat. No. 5,802,848, incorporated herein by reference, but modified to include the single return line boost reservoir  14 . Briefly, it will be seen that the slow flow return line  66  no longer extends directly into the reservoir  14  for purposes of deaerating a fraction of the flow, but rather is merged with the high flow return line  76  to provide a single line leading into the reservoir  14  which serves both to feed the pump  12  with a high velocity jet of hydraulic fluid and to deaerate a fraction of the flow within the reservoir  14  as will be described below. 
     Referring to FIGS. 2-4, the illustrated pump  12  of the particular hydraulic system comprises a power steering pump having a stationary housing  20 , an input shaft  22  rotatably supported on the stationary housing  20 , and a rotating group  24  between a non-rotating thrust plate  26  on the housing and non-rotating pressure plate  28  on the housing. The input shaft  22  is rotatably supported on the housing  20  and the pressure plate  26  by a pair of bearings  30 . An end  32  of the input shaft  22  outside of the stationary housing  20  is connected to a motor (not shown) of the vehicle such that the speed of the pump, i.e., the revolutions per minute (RPM&#39;s) of the input shaft  22 , is proportional to the RPM&#39;s of an element, e.g., a crankshaft, of the motor. 
     The rotating group  24  of the power steering pump  12  includes a rotor  33  rigidly attached to the input shaft  22  for rotation therewith and a plurality of radially slideable vanes  34  on the rotor  33  which cooperate with a cam surface  35  on a cam ring  36  non-rotatably secured to the housing  20  around the rotor by a plurality of dowel pins  37  (only one visible in FIG.  4 ), and with the pressure plate  28  and the thrust plate  26  defining a plurality of pump chambers (not shown) which expand and collapse as the rotor rotates with the input shaft  22 . The expanding pump chambers sweep past a fragmentarily illustrated inlet port  38  of the power steering pump and the thrust plate  26 . The collapsing pump chambers sweep past a fragmentarily illustrated discharge port  40  of the pump  12  and the thrust plate  26 . For a more complete description of the structure and operation of the power steering pump  12 , reference may be made to U.S. Pat. No. 4,386,891 the disclosure of which is incorporated herein by reference. 
     Still referring to the particular hydraulic steering system embodiment of FIG. 2, the pump  12  further includes a schematically represented internal control valve  42  which, as illustrated in FIG. 4, is supported in a cylindrical boss  44  of the housing  20 . As described fully in the aforementioned U.S. Pat. No. 4,386,891, the flow control valve  42  is disposed in an internal recirculation passage  46  in the stationary housing  20  between the discharge port  40  and the inlet port  38 . When the flow control valve  42  is closed, all of the fluid expelled into the discharge port  40  is discharged from the power steering pump  12  through a schematically represented high pressure port  47  of the power steering pump connected to the discharge port through an internal branch  48  of the recirculating passage  46 . The flow control valve  42  transitions progressively from closed to fully opened in response to an increasing pressure gradient across a restriction  50  in the internal branch  48 . As the flow control valve  42  opens, progressively more fluid recirculates from the discharge port  40  directly to the inlet port  38  to maintain the flow rate from the high pressure port  47  of the power steering pump substantially constant and to induce subatmospheric pressure at the inlet port  38  to suppress cavitation. When the flow control valve is closed, there is no recirculation to suppress cavitation. A schematically represented internal pressure relief valve  52  of the power steering pump opens only in extraordinary circumstances. 
     The illustrated system  10  of the FIG. 2 embodiment includes a steering assist fluid motor  16  which may be an element of a motor vehicle rack and pinion power steering gear such as described in U.S. Pat. No. 4,454,801. The motor  16  includes a stationary cylinder  54 , a piston  56  dividing the cylinder into a pair of working chambers  58   a,    58   b,  and a rod  60  rigidly attached to the piston and linked to dirigible wheels, not shown, of the motor vehicle such that back and forth linear translation of the rod steers the dirigible wheels. The second fluid motor  18  may have any conventional construction and includes a rotatable output shaft  62  adapted for driving connection to an accessory of the motor vehicle such as a radiator cooling fan. The second fluid motor  18  is disposed in a fluid conduit  64  of the hydraulic system  10  through which flows all of the fluid discharged by the power steering pump  12  through the high pressure port  46  thereof and from which fluid energy is extracted to rotate the output shaft  62 . 
     As further seen in FIG. 2, a second fluid conduit  66  has an upstream end  68  at the second fluid motor  18  and a downstream end  70 . A schematically represented proportional control valve  72  for the steering assist motor  16  is disposed in the second fluid conduit  66  and may have the construction described in the U.S. Pat. No. 4,454,801. In the absence of manual effort at a steering hand wheel  74  of the motor vehicle connected to the proportional control valve  72 , fluid in the second conduit  66  flows with little restriction through the valve. When manual effort is applied to the steering handwheel  74 , the proportional control valve  72  throttles fluid flow in the second conduit  66  to create a steering assist boost pressure and directs the boost pressure to one of the working chambers  58   a,    58   b  of steering assist fluid motor while as the same time maintaining a connection between the other of the working chambers  58   a,    58   b  and a second conduit  66  downstream of the flow control valve. 
     A third fluid conduit  76  of the hydraulic system  10  has an upstream end  78  connected to the second fluid conduit  66  between the second fluid motor  18  and the proportional control valve  72  and a downstream end  80  at the reservoir  14 . A flow control valve  82  of the hydraulic system  10  remote from the power steering pump  12  transitions progressively from closed to filly opened in response to an increasing pressure gradient across a restriction  84  in the second fluid conduit  66  downstream of the third fluid conduit  76 . As the remote flow control valve  82  opens, progressively more fluid bypasses the proportional control valve  72  and flows toward the reservoir  14  through the third fluid conduit  76 . A schematically represented pressure relief valve  86  parallel to the remote flow control valve  82  limits the maximum fluid pressure in the second fluid conduit  66  downstream of the third fluid conduit  76  and opens only in extraordinary circumstances. The fluid flow in the conduit  64  through the second motor  18  consists of the total flow discharged from the power steering pump  12  through the high pressure port  46  thereof. The remote flow control valve  82  is calibrated to divide the fluid flow from the conduit  64  into a constant flow rate fraction in the second fluid conduit  66  downstream of the third fluid conduit  76  and a variable flow rate fraction in the third fluid conduit  76 . The fluid flow rate of the constant flow rate fraction is consistent with the flow requirements of the steering assist fluid motor  16  and is typically about 2.6 gallons per minute. The fluid flow rate of the variable flow rate fraction is constituted by the remainder of the fluid from the high pressure port of the power steering pump and varies with the speed of the input shaft  22  of the power steering pump in the range of input shaft speed when the internal flow control valve  42  of the power steering pump is closed. The fluid flow rate of the variable flow rate fraction typically may range between about 2.6 gallons per minute and 15 gallons per minute. Because the constant flow rate fraction is always substantially less than the variable flow rate fraction, the second conduit  66  constitutes a low flow branch of the hydraulic system  10  and the third conduit  76  constitutes a high flow branch of the hydraulic system. 
     As illustrated in FIG. 2, the schematically illustrated vehicle hydraulic system  10  differs from that disclosed in U.S. Pat. No. 5,802,848 in that the downstream end  70  of the second fluid conduit  66  does not extend directly into the reservoir  14 , but joins the downstream end  80  of the third fluid conduit  76  such that only a single, high flow line enters the reservoir  14 . In other words, the multi-return line hydraulic system of U.S. Pat. No. 5,802,848 has been modified according to the invention and as illustrated in FIG. 2 to provide a single, high flow return line  76  to the reservoir  14 , effectively eliminating the need for a low flow return line into the reservoir  14 . 
     As seen best in FIGS. 3 and 4, the downstream end  80  of the single fluid return line  76  extends into and communicates with an internal chamber  88  through a tubular fitting  90  of the reservoir  14  coupled to a flow-restricting nozzle  92  disposed within the chamber  88  well below the level L of the fluid within the chamber  88 . A fluid discharge tube  94  is submerged in the fluid in the chamber  88  and has a passage  96  therein defining an outlet of the reservoir  14  in flow communication with the inlet  38  of the pump  12 , such that fluid passing through outlet  96  is fed to the pump  12 . 
     The nozzle  92  comprises an elongate tubular member having a fluid-constricting reduced diameter discharge end  98  defining a constricted primary discharge opening  100  in the end thereof communicating with a receiving end  102  of the discharge tube  94 . In the illustrated embodiment, the nozzle  92  and discharge tube  94  are coaxial, although such is not necessary so long as the fluid expelled from the nozzle end  98  is directed into the receiving end  102  of the discharge tube  94 . 
     Upstream of the discharge end  98  of the nozzle  92  there is provided at least one bleed opening  104  through which a fraction of the flow of fluid through the nozzle is discharged into the chamber  88  at a location remote from the receiving end  102  of the discharge tube  94 . 
     In operation, the high velocity fluid entering the nozzle  92  through the single return line  76  is constricted at the discharge end  98 , developing a back pressure within the nozzle  92  which forces a fraction of the flow out of the nozzle  92  through the bleed openingl 04 . The fraction of fluid escaping the bleed port  104  is preferably kept low, on the order of about 2-10% and preferably around 5% of the flow, with the remainder passing through the discharge end  98  and into the discharge tube  94  where it develops a venturi effect producing a negative atmospheric pressure at the receiving end  102  serving to aspirate or draw additional quantities of fluid from the chamber  88  into the discharge tube  94  to effectively boost the inflow of fluid to the pump  12 . For further discussion of the boost effect, reference may be had to the aforementioned U.S. Pat. No. 5,802,848. 
     The small fraction of the fluid flow exiting the bleed port  104  is permitted to dwell for a period within the chamber  88  during which time any entrained gas bubbles are permitted to rise to the surface of the fluid before such fluid is aspirated from the chamber  88  into the discharge tube  94  by the jet stream of return fluid exiting the discharge end  98  of the nozzle  92 . Over time, all of the fluid in the closed system will eventually be discharged through the bleed opening  104  and thus will become deaerated, which has the effect of maintaining the fluid in a substantially deaerated condition to inhibit cavitation which might otherwise result from the feeding of such aerated fluid to the pump  12 . 
     In order to assure that aerated fluid exiting the bleed port  104  has sufficient dwell time before being aspirated into the discharge tube  94 , a partition or baffle  106  is provided to form.a barrier between the bleed port  104  and the receiving end  102  of the tube  94  to prevent the direct flow of the fluid from the bleed port  104  into the tube  94 . The baffle  106  extends at least partially about the nozzle  92  at a location forwardly or downstream with respect to the main fluid flow of the bleed opening  104 . The baffle  106  extends a distance upwardly in the chamber terminating at a free edge  108  below the level L of the fluid within the chamber  88 . As illustrated in FIG. 4, the baffle  106  can extend widthwise across the chamber  88 . The baffle  106  thus partitions the chamber  88  preventing the fraction of fluid exiting the bleed opening  104  from being drawn into the discharge tube  94  until such time as it makes its way around the baffle  106 . The size, location and configuration of the baffle  106  can be adjusted as necessary depending on the conditions of the particular system in which the reservoir  14  is operating. For example, systems in which the hydraulic fluid is prone to high levels of aeration may require a full width, tall baffle  106  to increase the dwell time of the fluid exiting the bleed hole  104 . A fluid-pervious screen  107  may be provided across the partitioned region of the chamber  88  submerged in the fluid in such position that the hydraulic fluid passing up and over the baffle  106  is caused to pass through the screen  107 . Small gas bubbles in the rising fluid encounter the collect on the screen  107 , causing them to coalesce to form larger air bubbles that rise to the surface of the fluid more rapidly and efficiently. 
     FIG. 5 is an alternative embodiment of the reservoir which is identical to that of FIGS. 3 and 4 except that the passage  96  of the discharge tube  94  has a convergent portion  110  at the receiving end  102  and a divergent portion  112  at the opposite end in order to alter the flow characteristics through the discharge tube  94 , if necessary, to achieve the desired aspiration of the fluid in the chamber  88 . 
     FIG. 6 shows still a further embodiment wherein the baffle  106  of the previous embodiment is eliminated. In the FIG. 6 embodiment, the chamber  88  is configured to accommodate a nozzle  92  of sufficient length to permit the bleed hole  104  to be located a sufficient distance from the fluid outlet (i.e., beyond the aspiration zone of the receiving end  102  of the discharge tube  94 ), eliminating the need for the baffle  106 . 
     FIG. 7 is the same as the embodiment of FIGS. 3 and 4, except that the bleed opening  104  is directed upwardly rather than to the side in the chamber  88 . In such case, it may be desirable to provide a deflector  114  on the baffle  106  to restrict the upward flow of the fluid exiting the bleed opening  104 . 
     FIG. 8 shows a further embodiment which is like that of the FIGS. 3 and 4 embodiment, except that the nozzle  92  is provided with a porous section  116  in lieu of a single of multiple bleed hole  104 . The porous section  116  may comprise formed rigid plastic, wove porous tubing of metal or plastics, a perforated metal or plastic tube, etc. providing numerous small openings  104  through which the fluid can flow. 
     FIG. 9 illustrates still a further embodiment in which the reservoir  14  may be constructed and operates in the same manner as any of the embodiments described above, but is remote from the pump  12  rather than being integral therewith. The remotely situated reservoir  14  of FIG. 9 may be coupled by an appropriate fluid line  118  extending from the discharge tube  94  to the intake of the pump  12 . 
     FIGS. 10 and 11 illustrate yet further embodiments in which the passage  96  of the discharge tube  94  is not entirely coaxial with the nozzle  92 . It is thus not essential that the passage  96  of the discharge tube  94  be entirely linear and coaxial with the nozzle. It is permissible to provide a bend or elbow  120  to change the direction of the flow, if necessary, to communicate with the intake  38  of the pump  12 . 
     FIGS. 12 and 13 show a combination pump  12  and reservoir  14  (i.e., integrated) in which the nozzle  92  extends into the chamber  88  and communicates directly with the intake  38  of the pump  12 . The intake  38  has a conical mouth  122  to enlarge the target for the nozzle  92 . The conical mouth  122  may be cast or machined into the body of the pump  12  as appropriate. 
     The disclosed embodiments are representative of a presently preferred form of the invention, but is intended to be illustrative rather than definitive thereof. The invention is defined in the claims.