Patent Publication Number: US-2004040595-A1

Title: Power steering pump comprising cartridge flow control assembly

Description:
RELATED APPLICATIONS  
     [0001] The present patent document claims the benefit of the filing date under 35 U.S.C. §119(e) of Provisional U.S. Patent Application Serial No. 60/407,918, filed Sep. 3, 2002, which is hereby incorporated by reference. 
    
    
     
       TECHNICAL FIELD OF THE INVENTION  
       [0002] This invention relates to a power steering pump wherein the fluid output is controlled by recycling a portion of the pumped fluid through a bypass within the pump. More particularly, this invention relates to such power steering pump that includes a cartridge flow control assembly that may be readily installed in the pump housing and includes a pre-set flow control valve for regulating flow through the bypass.  
       BACKGROUND OF THE INVENTION  
       [0003] A power steering system of an automotive vehicle comprises a pump for providing hydraulic fluid under pressure. A typical pump comprises a rotor having retractable vanes and rotating within a cam chamber. During operation, hydraulic fluid is drawn into the cam chamber from a fluid suction passage and pumped out under pressure to a fluid discharge port. The rotor is driven by the engine through a belt and a pulley. As the speed of the engine increases, the volume of fluid pumped by the rotor also increases. However, it is desired that the output from the pump remain relatively constant. This is accomplished by recycling a portion of the pumped fluid through a bypass in the pump housing, so that pumped fluid is diverted from the outlet and returned to the suction passage. At low engine speeds, the bypass is closed so that the entire volume of pumped fluid is outputted from the pump. However, at higher engine speeds, the bypass is open for recycling as much as 90 percent of the pumped fluid.  
       [0004] U.S. Pat. No. 5,887,612, issued to Bleitz et al. in 1999, shows a mechanism for opening and closing a fluid bypass port to regulate the output from the pump. For this purpose, the housing defines a bore that communicates with a fluid discharge port from the pumping chamber and with the fluid bypass port. The outlet from the pump is located at one end of the bore. Within the bore, a flow control valve slides to open and close the bypass port. The valve is biased in the closed position by a spring that is retained by a plug in the end of the bore opposite the outlet. At high engine speeds, the fluid pressure at the fluid discharge port acts upon the valve to contract the spring and open the bypass port.  
       [0005] It is found that deviations in the compression force of the spring as manufactured affects the pressure required for opening of the bypass port by the flow control valve and causes undesirable variations in the performance of the steering system. Because the pump comprises multiple components that are assembled directly into the pump housing, it is difficult to detect variations in performance or make adjustments to the spring force in the final assembly. In addition, the pump housing is typically formed of aluminum metal to reduce weight. Sliding of the relief valve against the aluminum surface of the bore causes wear that shortens the useful life of the pump. Still further, in the event that repair is needed, it is necessary to disassemble and reassemble the several components in the pump, adding significantly to the time and expense required for the repair.  
       [0006] Therefore, a need exists for a flow control assembly that can be readily installed in a power steering pump and provides a predetermined force for opening the bypass port by allowing the force required to open the flow control valve to be measured and adjusted prior to installation in the pump housing. There is also a need for reducing wear of the flow control assembly and thereby extending the useful life of the power steering pump. Still further, it is desired that, in the event that repair becomes necessary, the flow control assembly may be readily removed and replaced as a single component, thereby reducing the time and expense required to effect the repair.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007] In accordance with this invention, a power steering pump is provided that includes a housing defining a bore having an axis, a fluid discharge port communicating with the bore at a first axial location, and a fluid bypass port communicating with the bore at a second axial location. The power steering pump also includes a flow control assembly that is received in the bore. The flow control assembly comprises a cartridge defining a fluid outlet at one end through which pressurized fluid is supplied to the power steering system, and a passage communicating with the outlet. The cartridge includes a first opening communicating with the fluid discharge port for admitting fluid to the passage and a second opening communicating with the fluid bypass port for diverting fluid from the fluid outlet. A flow control valve is disposed within the cartridge and is axially slideable between a closed position wherein the valve closes the fluid bypass port from communication with the fluid discharge port, and an open position when the valve is axially withdrawn to provide fluid communication between the first opening and the second opening, thereby permitting fluid to flow through the passage from the fluid discharge port to the fluid bypass port. A coil spring is disposed within the cartridge for biasing the flow control valve in the closed position. A retainer is secured in the cartridge at a second end opposite the fluid outlet, so that the spring is interposed between the flow control valve and the retainer. It is an advantage of the flow control assembly that the force needed to open the flow control valve may be measured, and the position of the retainer adjusted, prior to securing the retainer in the cartridge. In this manner, the cartridge assembly of this invention compensates for variations in the coil spring and provides a predetermined pump output. After the opening pressure is set and the retainer is secured, the flow control assembly is readily installed in the pump housing as a single component, and, if necessary, replaced as a single component in repairing the pump. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] This invention will be further described with reference to the following drawings wherein:  
     [0009]FIG. 1 is a cross-sectional view partially in schematic of a power steering pump, having a flow control assembly in accordance with this invention; and  
     [0010]FIG. 2 is a cross section of a portion of the power steering pump in FIG. 1, taken along line  2 - 2  in the direction of the arrows; and  
     [0011]FIG. 3 is a cross-sectional view of a portion of the power steering pump in FIG. 1, indicated by circle  3 , showing the elements thereof in an open position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0012] In accordance with the preferred embodiment of this invention, referring to FIGS. 1 and 2, there is depicted a power steering pump  10  for supplying pressurized fluid for a power steering system of an automotive vehicle. Pump  10  comprises a housing  12 , preferably formed of an aluminum alloy. Housing  12  contains pumping elements, shown schematically, that include a rotor  14  that propels retractable vanes  16  within a cam chamber  18 . Housing  12  defines a fluid discharge port  20  that discharges fluid under pressure from cam chamber  18 , as indicated by arrow  22 . The housing also defines a suction passage, indicated by arrow  24 , for delivering fluid to cam chamber  18 . During operation, rotor  14  is driven by the automotive engine via a belt and pulley arrangement. Fluid is pumped under pressure through discharge port  20  and exits through outlet adapter  26 , as output  28 . Outlet adapter  26  is connected through tubing to a rotary valve and steering gear of the power steering system. Fluid is returned to the pump through a return line (not shown) connected to suction passage  24  and is, in turn, drawn into cam chamber  18 .  
     [0013] During operation, it is desired that the fluid output  28  remain at a substantially constant volume despite an increase in volume of pumped fluid resulting from higher engine speeds. For this purpose, a bypass port  30  is provided for recycling a portion of the pumped fluid to the suction passage  24 , as indicated by arrow  32 .  
     [0014] In accordance with this invention, pump  10  includes a flow control assembly  40  for regulating fluid flow through bypass port  30  and thereby regulating fluid output  28  from the pump. Flow control assembly  40  is received in a bore  42  in housing  12  that is symmetrical about an axis  44 . Bore  42  communicates with fluid discharge port  20  at a first location and with bypass port  30  at a second location that is axially spaced from the first location.  
     [0015] Flow control assembly  40  comprises a cartridge  46  that is generally cylindrical about axis  44 . Cartridge  46  comprises a shoulder  48  that engages a circumferential stop in bore  42  to position the flow control assembly within the bore, and is secured at one end  50 , referred to as the outlet end, by outlet adapter  26 . Cartridge  46  defines an axial fluid passage  52  that communicates with fluid discharge port  20  through an opening  54 . Although FIG. 1 depicts opening  54  in registration with fluid discharge port  20 , cartridge  46  includes a circumferential groove  56  to provide fluid communication between the opening and the discharge port regardless of the radial orientation of the cartridge in the bore. At the second location adjacent bypass port  30 , an opening  58  is provided, along with a circumferential groove  60 , for fluid communication between passage  52  and bypass port  30 . At end  50 , cartridge  46  defines an outlet passage  62  that communicates with outlet adapter  26 . A flow control fitting  64  is fitted into end  50  and includes slots  66  for improved fluid flow control through the outlet under low flow conditions.  
     [0016] A flow control valve  70  is slideably disposed within the cartridge and includes a face  72  facing flow control fitting  64 . Valve  70  is slideable between a closed position shown in FIG. 1 wherein valve  70  overlies bypass port  30  to prevent fluid communication with passage  52 , and an open position shown in FIG. 2 wherein valve  70  is axially withdrawn relative to flow control fitting  64  and outlet end  50  to open opening  58  to bypass port  30 . A suitable circumferential seal is provided between cartridge  46  and valve  70  by lands and grooves in the perimeter of the valve. A coil spring  74  extends between valve  70  and a retainer  76  secured in end  78  of cartridge  46  opposite outlet end  50 . Spring  74  biases valve  70  in the closed position shown in FIG. 1. Also, cartridge  46  and retainer  76  cooperate with valve  70  to define a pressure sensing chamber  80  axially opposite valve  70  from fluid passage  52 . Referring to FIG. 2, housing  12  defines a fluid pressure sensing passage  82  that communicates at one end with outlet passage  62  through an orifice  84  and circumferential groove  85 , and at the other end with fluid pressure sensing chamber  80  through an orifice  86  and a circumferential groove  87 .  
     [0017] The power steering system is designed to operate at low engine speeds using an output  28  from pump  10  that is equal to the volume of pumped fluid discharged from cam chamber  18  by rotor  14  and retractable vanes  16 . Under these conditions, valve  70  is biased by spring  74  in the closed position to close bypass port  30 , so that the entire output from the pumping elements flows through outlet passage  62  and outlet adapter  26 . At higher engine speeds, the faster rotation of rotor  14  increases the volume of fluid discharged from cam chamber  18  through fluid discharge port  20  into passage  52  within cartridge  46 . Fluid flow from passage  52  to outlet  28  is restricted by the size of outlet passage  62 . Fluid pressure within chamber  52  increases and acts upon face  72  to contract spring  74  and slide valve  70  into the open position. As the fluid pressure in chamber  52  opens valve  70 , the fluid pressure in chamber  80  is relieved through passage  82 . When valve  70  is retracted, excess fluid flows from chamber  52  through bypass port  30  and into suction passage  24  en route to cam chamber  18 .  
     [0018] It is a main advantage of this invention that valve  70  and spring  74  are assembled in cartridge  46  prior to installation into housing  12 . In a preferred embodiment, retainer  76  is fixed to cartridge  46  by swaging. During the assembly process, valve  70 , spring  74  and retainer  76  are inserted into cartridge  46  through end  78 . Prior to swaging, the force required to compress spring  74  and open valve  70  is measured, and the position of retainer  76  is adjusted to set the opening force at a predetermined value. After the opening force is set, end  78  is swaged to secure retainer  76 . Thereafter, assembly  40  may be readily tested, for example, by installing into a test pump or suitable fixture, to verify the desired opening pressure. Thus, proper operation of flow control assembly  40  may be assured when assembly  40  is installed into a pump for vehicle use. Alternately, the retainer may be threadedly mounted in the cartridge end, or may be adjusted and secured by other joining techniques such as soldering or welding.  
     [0019] It is also an advantage of this invention that flow control assembly  40  is installed into housing  12  as a single component, thereby facilitating the final assembly of the pump and reducing the cost associated therewith. In the event that repair becomes necessary, the flow control assembly may be readily removed and replaced as a single component. Moreover, the cartridge and the valve are preferably formed of steel or other wear resistant metal. This reduces wear due to sliding of the valve against the cartridge, particularly in comparison to a valve sliding against an aluminum surface of the housing, and thereby extends the useful life of the pump.  
     [0020] While this invention has been described in terms of certain embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.