Abstract:
A hydraulic pump [ 10 ] for use in a power steering system includes a power steering fluid chamber [ 24 ] for receiving power steering fluid from a fluid source. The power steering fluid chamber [ 24 ] is in fluid communication with a fluid passageway [ 26 ] which transfers fluid to a pressure wave attenuator [ 46 ] for receiving power steering fluid from the power steering fluid chamber [ 24 ] such that fluid borne noise in the power steering system is minimized.

Description:
TECHNICAL FIELD 
     The present invention relates generally to hydraulic pumps. More particularly, the present invention relates to an apparatus for reducing fluid borne noise in a hydraulic pump. 
     BACKGROUND ART 
     The use of hydraulic pumps, such as power steering pumps, is well known in the automotive industry. Conventional hydraulic pumps, such as those used in power steering systems, are positive displacement pumps. Positive displacement pumps, such as gear pumps, have a pumping action that creates a pressure fluctuation in the pump discharge flow. Any variations in this pump discharge flow are converted to pressure pulsations when they encounter circuit resistance. This conversion is referred to in the art as pressure ripple. 
     The pressure pulsations transmitted through the fluid can cause resonating of the system components downstream of the pump, which is known in the art as fluid borne noise. This pressure fluctuation can also excite structure in the pumping circuit causing them to vibrate and generate additional objectionable noise. 
     Typical pumps generate the majority of their noise energy at the fundamental or pumping frequency (shaft speed x the number of pumping chambers). Typical pumps also can generate appreciable noise energy in multiples of harmonics of the fundamental frequency. The sound level of the noise energy generated by typical pumps generally decreases at higher frequencies, but even fourth and fifth harmonics can have enough energy to cause noise. 
     Additionally, the configuration of these prior pumps is such that they require the use of hoses for fluid transfer. The hoses are typically located between the outlet of the pump and the steering gear. By adding a pressure pulse attenuator as a separate part downstream of the pump, the size of the power steering gear pack and the cost of the power steering system are increased. 
     It would therefore be desirable to provide a pump for use in a power steering system that is able to reduce the amount of fluid borne noise and is also compact. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an apparatus for reducing the fluid borne noise in a power steering system. 
     It is a further object of the present invention to provide a pressure pulse attenuator that is integral with the pump housing. 
     In accordance with one aspect of the invention, an apparatus for reducing the fluid borne noise in a power steering system is provided. The apparatus includes a hydraulic pump for use in a power steering system. The hydraulic pump has a pump housing with a power steering fluid inlet port formed in the pump housing. The inlet port is in fluid communication with a power steering fluid reservoir to transfer power steering fluid to a power steering fluid chamber formed in the pump housing. A fluid conduit is formed in the pump housing and has an inlet opening and an exit opening. The fluid conduit inlet opening is in fluid communication with the power steering fluid chamber to receive power steering fluid therethrough. The fluid conduit exit opening is in fluid communication with a pressure wave attenuator to transfer power steering fluid thereto. The pressure wave attenuator is in fluid communication with an outlet port to convey the power steering fluid to a steering gear. 
     Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a gear pump and associated motor housing in accordance with a preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, which is a cross-sectional illustration of a preferred hydraulic pump  10  in accordance with the present invention. The pump  10  has a pump housing  12  which is mounted to a motor  14  by a mounting apparatus  16 , such as a bracket or the like. The hydraulic pump  10  is preferably a positive displacement pump, such as a gear pump, however any other positive displacement pump may be utilized. The disclosed hydraulic pump  10  is preferably for use in a vehicle power steering system, but may be utilized in a variety of other systems, including non-automotive applications. 
     The pump housing  12  has an outer wall portion  18  and an end cap  20 . The outer wall portion  18  preferably has an inlet port  22  formed therein to allow the transfer of fluid from a fluid reservoir (not shown) into the pump housing  12 . The preferred fluid is a power steering fluid, however, other fluids may be utilized depending upon the application for the pump  10 . The inlet port  22  may obviously be formed through other portions of the pump housing  12 , including the end cap  20 . 
     A power steering fluid chamber  24  is formed within the pump housing  12  to receive the power steering fluid transferred thereto by the inlet port  22 . The power steering fluid chamber  24  is in fluid communication with a fluid passageway  26  formed in a gear housing  28  disposed within the pump housing  12 . The power steering fluid chamber  24  is defined by the outer wall portion  18 , the end cap  20 , and the mounting apparatus  16 . A seal  30  is preferably disposed at the junction between the mounting apparatus  16  and the outer wall portion  18  of the pump housing  12  in order to prevent any leakage of power steering fluid from the power steering fluid chamber  24  to the motor  14 . 
     As shown in FIG. 1, a drive gear  32  is housed within the gear housing  28  and is in rotational communication with a drive shaft  34  to operate the hydraulic pump  10 . The drive shaft  34  is coupled to the motor  14  by a drive coupling  36  to drive the shaft  34 . The motor  14  is preferably an electric motor, however, a variety of other motors may be utilized. The drive shaft  34  is also in rotational communication with a bearing plate  38 , which is disposed in the gear housing  28 . A seal  39  is preferably disposed around the drive shaft  34  to prevent the fluid leakage from the fluid chamber  24  to the motor  14 . 
     The fluid passageway  26  is in fluid communication with a fluid conduit  40 . The fluid conduit  40  has a fluid inlet opening  42  in communication with the fluid passageway  26  and a fluid outlet opening  44  in communication with a pressure wave attenuator  46 . The pressure wave attenuator  46  is preferably formed between the mounting apparatus  16  and a motor end plate  48  which is secured to the motor  14  around the motor output  50 . The pressure wave attenuator  46  is in fluid communication with an output passage  52 . The pressure wave attenuator  46  allows the fluid from the fluid passageway  26  to flow therein allowing for the addition of a fluid volume to the flow circuit to allow for the reduction in fluid borne noise. It should be understood that the location of the pressure wave attenuator  46  may be varied. However, in accordance with the present invention, it is preferred that the pressure wave attenuator  46  is formed integral with the pump housing  12 . 
     The first fluid conduit  40  preferably has a backup passage  54  that is in communication with a pressure relief valve  56 . The pressure relief valve  56  allows excess pressure in the pump  10  to be relieved by allowing fluid to exit the first fluid conduit through the valve and reenter the power steering fluid chamber  24 . 
     By positioning the pressure wave attenuator  46  in the mount  16  between the pump  10  and the motor  14 , the amount of fluid borne noise can be reduced due to phase tuning. Further, the mounting apparatus  16  and the motor end cover  48  serve as expansion chamber walls, which decrease the cost and size of the pump by eliminating the requirement for a separate part. This configuration also eliminates the requirement for hose tuning which results in substantial cost savings. 
     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.