Abstract:
A relief valve for an anti-lock braking system includes a plunger-operated ball and a valve body that defines a seat for receiving the ball thereon. The valve body also defines a relief passageway for relieving hydraulic fluid through the passageway at a rate that is appropriate for prevent brake locking, i.e., skidding. To establish the rate, an orifice is integrally formed on the valve body in the passageway, thereby obviating the need for a separate orifice cup.

Description:
TECHNICAL FIELD 
     The present invention relates generally to anti-lock brake relief solenoid valves, and more particularly to methods and structure for controlling hydraulic fluid flow rate through anti-lock brake relief solenoid valves. 
     BACKGROUND OF THE INVENTION 
     Anti-lock brake systems include solenoid-actuated relief valves that relieve the hydraulic pressure applied to the brakes when the wheels start to skid, i.e., to lock. By relieving the hydraulic braking pressure, the wheels are permitted to roll while nonetheless being slowed by the brakes, which significantly promotes control of the vehicle relative to what is experienced when the brakes lock. 
     Typically, an anti-lock relief valve includes a ball that is attached to a solenoid plunger. The relief valve also includes a valve seat that receives the ball. To relieve pressure in the hydraulic lines, the solenoid is actuated to move the ball away from the seat, thereby opening a relief passageway through which hydraulic fluid can flow back to a brake fluid reservoir. 
     The rate of hydraulic fluid flow through the relief passageway must be established to be sufficiently high to quickly alleviate skidding, but not so high as to cease braking altogether or to cause braking instability. Because the relief passageway itself must be kept sufficiently large to provide an adequate seating surface for the ball at one end of the passageway, conventional relief valves establish the rate of fluid flow by press-fitting an orifice cup into the relief passageway, with the orifice cup being formed with an orifice that is configured to establish the desired fluid flow rate. 
     As recognized herein, however, several disadvantages attend the use of orifice cups. For example, the orifice cup can be unintentionally deformed during the press-fitting process, degrading the performance of the cup. Furthermore, contaminants can enter the hydraulic system during press-fitting. Moreover, occasionally hydraulic fluid can leak between the sides of the orifice cup and the passageway into which it is press-fit. Still further, once installed only the size of the orifice can be easily inspected, not the entire cup. And, the press-fit process is difficult to monitor for installation errors. Apart from the above problems, requiring an orifice cup that is separate from the valve body adds to the number of components and, hence, to the cost of the relief valve. Having recognized these drawbacks, the present invention has provided the below-disclosed solutions to one or more of the prior art deficiencies. 
     SUMMARY OF THE INVENTION 
     A relief valve for an anti-lock brake system includes a valve body that is formed with a relief passageway. The relief passageway terminates at a valve opening that is circumscribed by a valve seat. Per the present invention, the valve body is integrally formed with an orifice in the relief passageway, and the orifice is smaller than the valve opening. A solenoid-actuated valve element is movable between a pressure hold configuration, wherein the valve element contacts the valve seat to prevent fluid flow through the relief passageway, and a pressure relief configuration, wherein the valve element is distanced from the valve seat to permit fluid flow through the passageway. 
     Preferably, the orifice defines a diameter and the valve body defines a length, and the ratio of the length to the diameter (L/D ratio) is established based on a predetermined vehicle type. The LID ratio can be, e.g., between seven (7) and twenty (20). 
     As disclosed in greater detail below, the anti-lock brake system includes a hydraulic fluid line and a valve housing disposed in the line, and the valve body is disposed in the valve housing. In one preferred embodiment, the valve element is a ball. To move the ball, a solenoid plunger is attached to the ball and the plunger is controlled by a solenoid which is actuated by an anti-lock brake system (ABS) processor. 
     In another aspect, a method is disclosed for forming a relief valve for an anti-lock brake system (ABS). The method includes establishing an orifice diameter and a valve seat opening diameter larger than the orifice diameter, and establishing a valve body length bearing a predetermined relationship to the orifice diameter. Moreover, the method includes forming a relief valve body having the valve body length and an orifice having the orifice diameter. The relief valve body is then assembled into an ABS system. 
     In still another aspect, a relief valve system for an ABS system includes a hydraulic fluid line, a valve housing disposed in the line, and a valve body disposed in the valve housing. The valve body is formed with an open valve seat and a relief passageway extends away from the seat. An orifice is in the valve body to establish a predetermined rate of fluid flow through the relief passageway. 
     The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The FIGURE is a side diagram of the present ABS system relief valve in an ABS relief line, schematically showing the control components. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the FIGURE, a pressure relief valve system  10  for an ABS system  12  is shown. As shown, the ABS system  12  includes four wheel sensors  14 ,  16 ,  18 ,  20  for sensing vehicle wheel parameters related to brake lock in accordance with principles known in the art. The sensors  14 - 20  send their signals to an ABS system processor  22 , which controls, among other things, four pressure relief solenoids  24 ,  26 ,  28 ,  30 , one for each wheel. For concise disclosure only the pressure relief system  10  that includes the first solenoid  24  will be discussed, it being understood that each of the other solenoids  26 ,  28 ,  30  control like pressure relief systems. 
     As shown, the system  10  includes at least one hydraulic fluid line  32  that carries hydraulic fluid to and from the brake of the wheel associated with the solenoid  24 . A rigid metal hollow valve housing  34  is disposed in the line  32 . In one embodiment, the housing  34  is engaged with the line  32  by means of an engagement ring  36  in accordance with means known in the art. Also, a radial flange  38  of the housing  34  can abut an end  40  of the line  32  as shown. If desired, an O-ring or other seal  42  can be provided between the flange  38  and a retainer ring  44  of the valve housing  34  to establish a seal between the housing  34  and additional components in accordance with principles known in the art. 
     Having set forth the above structure, attention is now directed to the annulus of the hollow valve housing  34 . A hollow metal unitary valve body  46  is disposed in the valve housing  34  as shown. As intended by the present invention, the valve body  46  is formed with a circular valve seat  48  circumscribing a valve opening  50 . A relief passageway  52  extends longitudinally away from the seat  48 , and an orifice element  53  defining an orifice  54  is formed in the valve body  46 , preferably integrally therewith as shown, to establish a predetermined rate of fluid flow through the relief passageway  50 . It can readily be appreciated in reference to the FIGURE that the diameter D o  of the orifice  54  is less than the diameter D p  of the passageway  52  or valve opening  50 . 
     In accordance with the present invention, the valve body  46  has a length L, and the ratio of the length L to the orifice diameter D o  is established based on a predetermined vehicle type. Stated differently, the valve body length L bears a predetermined relationship to the orifice diameter D o , and the predetermined ratio is tailored to the particular vehicle associated with the system  10 . In one preferred embodiment, the L/D o  ratio is between seven (7) and twenty (20). In particularly preferred embodiments, the following ratios are used, it being understood that other dimensions suitable for other vehicle types may be used: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Length (mm) 
                 Orifice diameter (mm) 
               
               
                   
                   
               
             
             
               
                   
                 5.2 
                 .71 
               
               
                   
                 5.5 
                 .51 
               
               
                   
                 5.9 
                 .39 
               
               
                   
                 6.3 
                 .33 
               
               
                   
                   
               
             
          
         
       
     
     A valve element  56 , preferably a ball as shown, is movable between a pressure hold configuration (shown in the FIGURE), wherein the valve element  56  contacts the valve seat  48  to prevent fluid flow through the relief passageway  52 , and a pressure relief configuration, wherein the valve element  56  is distanced from the valve seat  48  to permit fluid flow through the passageway  52 . The valve element  56  is attached to a solenoid plunger  58 , which in turn is connected to the solenoid  24  for actuation of plunger  58  in response to the solenoid  24  and, hence, in response to the ABS processor  22 . 
     With the above-disclosed combination of structure, the strength of the valve body  46  with orifice  54  surpasses that of conventional orifice cup valves. Furthermore, flow rates do not deviate from design when the valve body  46  is pressed into the housing  34 , in contrast to what might occur when an orifice cup us press-fit into a valve housing. Moreover, the valve body  46  can be 100% airflow tested by the manufacturer, whereas orifice cup valves must first be assembled with their associated valve housings prior to testing. Thus, proper tolerances and flow rates can be ascertained relatively early in the assembly process using the present system  10 , compared to conventional orifice cup systems. 
     Still further, the present system results in the elimination of a component—the orifice cup—heretofore believed to be necessary to ABS systems. This simplifies the present system. Also, since no orifice cup is required, a step in the assembly process, namely, press-fitting an orifice cup into a valve housing, advantageously is eliminated. And, the present flow control system improves dynamic solenoid  24  functioning. The ability to establish the L/D o  ratio promotes flexibility for use in other solenoid applications. 
     While the particular ANTI-LOCK BRAKE RELIEF VALVE WITH INTEGRATED FLOW CONTROL ORIFICE as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C.§112, sixth paragraph, unless the element is expressly recited using the phrase “means for”.