Abstract:
An air valve assembly is provided for a power piston in a vacuum brake booster including an input element with a hollow axial extension. The hollow axial extension includes a retaining portion. An output element is provided that includes an input extension slidably positioned within the hollow axial extension. The input extension includes an outer groove formed thereon and a ring member is disposed in the outer groove, the ring positioned adjacent the retaining portion to prevent separation of the input element and outer element.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/186,271, filed Mar. 1, 2000. 
    
    
     TECHNICAL FIELD 
     The present invention and is related to power brake boosters of the differential pressure type. In particular, the power brake booster of the present invention includes a simplified mechanical panic assist air valve assembly and a method of assembling such an air valve. 
     BACKGROUND OF THE INVENTION 
     Power brake boosters of the differential pressure type using engine vacuum are well known in the motor vehicle industry. A brake booster of this type has a diaphragm separating a vacuum chamber open to a source of vacuum, such as created in an engine intake passage, and a working chamber normally provided with vacuum or atmospheric air by a valve apparatus responsive to input brake pedal actuation to provide brake assist force as required through a power piston fixed to the diaphragm and coupled to the booster output. 
     The valve apparatus in a standard vacuum booster is a double or bipartite valve arrangement. The valve may have a vacuum valve seat on the power piston that is engageable with a floating control valve as well as an air valve that also has a seat engageable with the same side of the floating control valve and is coupled to a brake input rod. In the rest position (no brake apply) the air valve is engaged with the floating control valve, and the vacuum valve is slightly separated therefrom to guarantee vacuum on both sides of the diaphragm and thus no brake boost assist. A brake input to the air valve moves the air valve seat axially past the vacuum valve seat, whereupon the floating control valve moves against the vacuum valve seat to shut off the flow of vacuum into the working chamber and allow the air valve seat to disengage and admit air at atmospheric pressure into the working chamber. The increase in air pressure in the working chamber produces a differential pressure across the diaphragm to move it axially; and the power piston moves with it to provide an assist force to the brake fluid in the master cylinder. Movement of the power piston allows the floating control valve to move toward the air valve seat; and the level of boost assist is thus matched to the driver&#39;s input force. The opening of the air valve is calibrated to provide smooth brake apply in normal and typical driving situations. 
     Occasionally a driver may wish or need to stop the vehicle as quickly as possible. In such a situation, it might be possible to provide quicker brake application by admitting air into the working chamber of the brake booster at a faster rate. But this faster air admittance should not be provided except in such situations, since it would not produce appropriate braking behavior in normal driving. Linear solenoid and rotary motors have been used beneficially to provide dual rate actuation and control of brake boosters. However, the significant complexity of these systems can be a disadvantage in cost and reliability terms. Other brake boosters have been disclosed with the capability to provide a dual reaction ratio as a function of the input force using a dual rate spring-biased double valve. When the input force exceeds a predetermined force, the spring biasing force acting on the double valve is exceeded resulting in a collapse of the valve. Thus, this collapse causes an increased opening through the air valve seat providing a greater rate of airflow therethrough than during normal operation of the valve. The output gain of the booster is accordingly provided at an increased amount. 
     However, the attachment feature of the input and output portions of a prior art two-part valve can have some disadvantages. The attachment feature can be a screw attachment. There exists a potential for the screw attachment to unscrew, which affects the dimensional stack height of the valve and the function thereof and thus, the reliability of the valve. The attachment can be a pin. The integrity of the attachment and the alignment thereof can be compromised by an improper joining of the two-part valve as a result of a cross-threaded join of the two parts, or improper alignment before or after pinning or the like. 
     It would therefore be advantageous to provide a simple means for providing an input and an output portion of a valve for a brake booster using a minimum of robust parts that reduce or eliminate component misalignment and improper stack height in a reliable assembly that is easy to assemble. 
     SUMMARY OF THE INVENTION 
     The present apparatus provides a braking speed of application enhancement by increasing the air valve opening in a vacuum brake booster when a vehicle operator applies braking force quickly and forcefully. This is accomplished with a two-part air valve which is normally expanded axially to a normal length by an internal spring, but which may be shortened to open air valve by a greater amount when the brake pedal input force is sufficient to move the air valve axially against another spring into contact with a shoulder of the power piston. The internal spring has a much higher preload than the other spring so that the booster operates with a fully axially expanded air valve in normal, low force brake activation. Once the air valve axially engages the power piston, however, the increase in air valve opening is immediate and substantial with any further increase in braking force. 
     One aspect of the present invention provides an air valve assembly for a power piston in a vacuum brake booster including an input element with a hollow axial extension. The hollow axial extension includes a retaining portion. An output element is provided that includes an input extension slidably positioned within the hollow axial extension. The input extension includes an outer groove formed thereon and a ring member is disposed in the outer groove, the ring member positioned adjacent the retaining portion to prevent separation of the input element and outer element. 
     Another aspect of the present invention provides an assembly wherein the ring member extends outwardly from the outer groove to engage the retaining portion. The ring member can be a circlip. 
     The retaining portion of the input element can include an inwardly extending notch positioned at an open axial end of the hollow axial extension, an inwardly extending radial retention surface, an inwardly extending catch and an internal groove. 
     The groove can allow the clip to move axially with respect to the hollow axial extension. The hollow axial extension can include an open axial end. The open axial end can include a plurality of axial slots formed therein, the slots allowing portions of the open axial end defined thereby to be spread apart. The open axial end can include four slots formed in the open axial end. The open axial end can include a beveled surface to guide insertion of the input extension. 
     Other aspects of the present invention can include a flange formed on the input element. The flange includes a shoulder portion. A spring seat portion is formed on the output element and a spring is disposed between the flange and the spring seat to bias the input element and the output element apart from each other. The spring is provided with a predetermined load resistance above which the air valve assembly collapses by allowing the input element and output element to move axially toward each other. The valve assembly can include a pair of springs, the pair of springs compressing at different predetermined loads. 
     Another aspect of the present invention provides a method of assembling an air valve for a vacuum brake power booster. The air valve includes an input element and an output element. The method includes retaining a clip on an input extension of the output element. An axial extension of the input element is spread over the clip. The input extension of the output element is inserted into the axial extension of the input element and the input extension is retained to the axial extension. A spring is provided between the input member and the output member before the input extension is inserted into the axial extension. 
     Another aspect of the invention provides a vacuum brake power booster assembly including an air valve including a means for retaining a clip on an input extension of an output element of the air valve, a means for spreading an axial extension of an input element of the air valve over the clip, a means for inserting the input extension of the output element into the axial extension of the input element and a means for retaining the input extension to the axial extension. The assembly can further include a means for biasing apart the input element and output element. The biasing means compresses at a predetermined apply force to permit collapse of the air valve. 
     The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a section view of one embodiment of the air valve assembly for a brake booster. 
     FIG. 2 is an enlargement of FIG.  1 . 
     FIG. 3 is a section view along lines  3 — 3  of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This apparatus shows a “drop-in” replacement air valve assembly for a standard vacuum brake booster to provide a braking speed of application enhancement described above. Referring to FIG. 1, air valve assembly  120  comprises two main parts: air valve input element  130  and air valve output element  140 . Each of these parts may be made of a metal, plastic or other suitable material. 
     Air valve seat input element  130  can be provided with an axially raised rim  122  comprising an air valve seat at the input (right, in FIG. 1) end  131  thereof, rim  122  being engageable with the floating control valve, (not shown), in the normal manner. Rim  122  can also define an opening for a deeply concave receptacle  132  in input end  131  adapted to receive an input rod, (not shown), that transfers input brake force from a brake pedal axially to air valve input element  130  in the normal manner. Air valve input element  130  also can define a shoulder  133 , which forms a spring seat facing in the output direction, away from input end  131 . Between air valve seat  122  and shoulder  133  a pair of annular flanges  136 ,  137  can project radially outward from axial end  131  of air valve input member  130  with outer cylindrical surfaces for supporting axial end  131  of air valve input element  130  within a power piston  114 . A spring seat  138  can be also defined on annular flange  136  facing in the output direction, spring seat  138  being located radially outward from shoulder  133 . 
     Air valve input element  130  also can include an axial extension  135  extending in the output direction (left in FIG. 1) from shoulder  133  and having a reduced outer diameter compared with axial end  131 . Output extension  135  can be essentially tubular in shape and has an open axial end  139  and an essentially cylindrical internal surface  162  provided with an axially extending, circumferential notch or groove  164 . As seen most clearly in FIG. 2, which is an enlarged view of a portion of FIG. 1, notch  164  defines adjacent end  139 , a retention surface  166 , comprising an annular portion of essentially radial plane; and a portion  168  of internal surface  162  adjacent output end  139  of output extension  135  is tapered as shown. It will be understood that the retention surface  166  can be provided on any feature suitable for retaining a cooperating feature provided on the output member. In other words, the surface  166  can be a portion of a channel, notch, groove, tooth, flange or catch, or the like which includes an effective retaining, substantially radial surface. 
     As shown in FIG. 3, one or more axial slots  176  are provided in output extension  135  from output end  139  inward to separate a substantial portion of output extension  135  from output end  139  inward into a plurality of tangs facilitating limited, resilient outward spreading or expansion of output end  139 . 
     Air valve output element  140  can include a radially extending flange  142  that provides an axial spring seat  150  on the input (right, in the figure) side thereof and a stop  152  on the output (left) side thereof. On the output end of flange  142 , a plunger portion  148  has an outer cylindrical supporting surface  143 . On the input side of flange  142  is an input extension  144  having an outer cylindrical surface  145  and adapted for insertion within output extension  135  of air valve input element  130 . A circumferential groove  146  contains a retention ring  147 , a portion of which extends radially outward from groove  146  beyond surface  145 . The ring can be a circlip, or the like, that cooperates with surface  166  to retain the output member input extension  148  within axial extension  135 . It should also be noted that extension  148  is slidable with respect to extension  135  even after the ring or clip  147  is engaged by surface  166 . The axial length of groove  164  allows the ring  147  to reciprocate within groove  164 , and thus the output member with respect to the input member. Also, a portion of the length of extension  144  may contact the input element  130  and prevent further collapse of the valve assembly  120 . 
     To assemble air valve assembly  120 , a compression spring  154  is inserted over axial extension  135  of air valve input member  130  abutting shoulder  133 . Retention ring  147  is seated in groove  146 . Input extension  144  is axially inserted into axial opening  160  of air valve input element  130 . As air valve element  130  and  140  are moved toward each other during insertion, spring  154  is compressed between shoulder  133  of air valve input element  130  and spring seat  150  on flange  142  of air valve output element  140  to exert a separating bias between the elements  130 ,  140 . In addition, the tangs of output end  139  (defined by slots  176 ) are pushed radially and resiliently outwardly by retention ring  147  until the latter passes retention surface  166  of notch  164 . At this point, the tangs of end  139  are no longer pushed outward and resiliently return inward. The insertion force is withdrawn, and the separate bias exerted by spring  154  between air valve input element  130  and air valve output element  140  causes axial expansion of air valve assembly  120  to the maximum axial length permitted by retention ring  147  locked in groove  146  and engaging retention surface  166  of notch  164 . Air valve assembly  120  can be then installed in the power piston  114  with an air valve spring  170  compressed between spring seat  138  on air valve input element of air valve assembly  120  and the cooperating spring seat on a shoulder  172  in the power piston to bias air valve assembly  120  in the input direction. 
     In braking operation, if normal braking forces are applied to air valve assembly  120  by the vehicle operator, the relatively greater strength of compression spring  154  keeps air valve elements  130  and  140  fully separated in a constant axial relationship; and normal brake booster operation results. But if a large, sudden braking force is applied to air valve assembly  120  sufficient to engage stop  152  on the output face of flange  142  with shoulder  172  of power piston  114 , compression spring  154  is temporarily compressed to allow air valve input element  130  to move axially toward air valve output element  140 . It will be understood that the spring  154  will compress at a predetermined force that coincides to a panic apply force. Since air valve seat  122  is carried on air valve input element  130 , it provides a greater than normal opening relative to the floating control valve, which is limited in leftward movement by power piston  114 , for airflow into the booster working chamber. This results in faster booster response and quicker increase in braking force at the wheels. 
     While the embodiment of the invention disclosed herein is presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.