Abstract:
A power booster for a brake system including a housing having an interior and a pair of diaphragms separating the interior of the housing into three chambers. A power piston assembly is coupled for movement with the diaphragms and includes an output member. A reaction member is coupled to the power piston assembly, and an input member is adapted to be coupled to a movable brake pedal. An air valve assembly moves between open and closed positions to selectively admit atmospheric air into selected ones of the chambers. This induces an output force on the diaphragm that is transferred to the output member of the power piston assembly. The triple booster adds an additional working chamber with an added approximately 45% increase in power boost. The triple power booster retains many of the same components as prior dual or tandem boosters to provide an economical solution to increase booster output without the need for new tuning procedures or added booster diameter.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to power boosters for brake systems, such as those used in automobiles, for intensifying the input force between a brake pedal and a master cylinder. 
     BACKGROUND OF THE INVENTION 
     Brake power boosters generally utilize fluid pressure, or differentials thereof, to provide a power assist in applying force to the master cylinder of the brake system. Upon application of an input force on the brake pedal, an input member such as a pushrod activates the power booster. The power booster intensifies the force by a calibrated amount and transfers the force to a power piston which then moves the master cylinder to apply the brakes at each wheel. 
     In conventional power boosters, an air valve assembly is opened upon depression of the brake pedal by the operator to admit atmospheric air to at least a first chamber of the power booster housing. This creates a pressure differential across a diaphragm separating the first chamber from a second chamber of the housing. The diaphragm is coupled to the power piston and transmits a force resulting from the pressure differential to the power piston and, ultimately, to the master cylinder. 
     The force generated by the power booster is a function in large part to the volume of the working chambers of the power booster housing. As a result, the use of vacuum boosters of this type have been limited by physical space constraints, particularly with respect to the booster diameter. Larger and/or heavier vehicles such as trucks and the like require substantially more output force to adequately stop the vehicle. Known vacuum boosters have not been able to deliver the required output force within the available physical size constraints. Therefore, typically a hydraulic booster is employed in larger and/or heavier vehicles to produce sufficient output force to adequately stop such vehicles. 
     For these general reasons, it would be desirable to provide a vacuum power booster that delivers a high output force to the master cylinder for larger and/or heavier vehicles such as trucks and the like without exceeding the physical space constraints that are available, particularly with respect to booster diameter. Moreover, due to the relatively large number of parts required for a typical power booster and the wide range and styles of automobiles utilizing such systems, the inventory, assembly, repair and related requirements place significant demands on the brake system manufacturer and repair technician. Therefore, it would be highly desirable to provide such a power booster without significantly adding to the inventory, assembly and service demands of such a system. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides a vacuum power booster for a brake system with an air valve assembly having the ability to deliver a high output force within limited available space. The present invention could be used for vehicles where a larger vacuum booster is needed, but there is a constraint on booster diameter. Furthermore, the invention offers these advantages while minimizing the number of unique parts and assembly or service demands. 
     In one embodiment, this invention is a triple vacuum booster in which an additional working chamber is added to known dual chamber vacuum booster. The invention increases output force by approximately 45% over known vacuum boosters having a comparable booster diameter. The present invention utilizes many of the same components of known tandem boosters and as such provides a very economical solution to increase booster output without adding significantly to production costs, inventories and support requirements. 
     Generally, the power booster of this invention includes a housing having an interior and a number of diaphragms and associated plates separating the interior of the housing into at least three chambers. A two-piece power piston is coupled for movement with the diaphragms and includes an output rod. An input member is adapted to be coupled to a movable brake pedal and is coupled to an air valve assembly. The input member moves the air valve assembly between open and closed positions to selectively admit atmospheric air into at least one of the chambers to induce an output force on the diaphragms which is transferred to the output rod of the power piston. 
     In accordance with the invention, the vacuum booster includes first, second and third chambers in which the first and second chambers are of comparable size and design with respect to known tandem boosters. The third chamber similarly sized with respect to the first and second chambers or may have a reduced size booster for applications where additional boost is required over a comparable tandem booster, but packaging limitations dictate a reduced size third chamber. Advantageously, the assembly of the triple booster utilizes a number of identical components for the multiple chambers thereby minimizing inventory complexities. Moreover, the installation of the diaphragms entails a retaining ring or similar member to both seal the diaphragm to the power piston and secure the multi-component power piston assembly together. 
     Testing of the triple booster according to this invention has shown that input/output force plots are substantially identical with respect to tandem booster designs with the exception of an increase in overall output force on the order of about 45%. This offers a significant benefit in braking force without the need for new calibration and tuning procedures typically required for new booster designs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various objectives, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings. 
     FIG. 1 is fragmentary cross sectional view of a power booster constructed in accordance with one embodiment of the invention and shown with no applied input force; 
     FIG. 2 is a view similar to FIG. 1 but of an alternative embodiment of the invention; and 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG. 1 showing a retaining ring according to one embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIG. 1, a power booster  10  is shown as a triple diaphragm vacuum operated booster in this exemplary embodiment utilizing vacuum and atmospheric pressure differentials to boost input forces F I , generating intensified output forces F O . However, the present invention is also applicable to systems with a higher order diaphragm vacuum booster and with power boosters operating with other power sources. Power booster  10  has a substantially open internal cavity which is formed by a mating front housing  12 , an intermediate housing  14  and a rear housing  16 . The housings  12 ,  14 ,  16  are formed from a substantially rigid conventional material such as metal or plastic. Intermediate and rear housings  14 ,  16  each include an axially extending flange  18 ,  20  respectively. Axially extending flanges  18 ,  20  mate with outer turned flange  22 ,  24  of front and intermediate housing  12 ,  14 , respectively, locking the housings  12 ,  14 ,  16  together. An inner edge  26  of rear housing  16  carries a seal  28 . The end of rear housing  16  is enclosed by boot  30  which is received over the inner edge  26 . Another seal  32  seals the area at an inner edge  34  of front housing  12 . The seal  32  is secured between the rearward end of an associated master cylinder  36  of the type well known in the art and the front housing  12 . 
     Housing dividers  38 ,  40  separate the internal cavity into front, intermediate and rear chambers  42 ,  44  and  46 , respectively. Housing dividers  38 ,  40  each include an outer peripheral flange  48 ,  50  which is engaged between the associated and adjacent housings  12 ,  14 ,  16 . Housing dividers  38 ,  40  also each include an inner edge which carries an annular seal  52 ,  54 , respectively. A power piston assembly  56  extends through annular seals  28 ,  52 ,  54 . The power piston assembly  56  is slidable forwardly and rearwardly within the annular seals  28 ,  52 ,  54  with the annular seals  28 ,  52 ,  54  acting as bearings for supporting the power piston assembly  56  in the lateral direction. 
     Power piston assembly  56  includes first and second power piston members  58 ,  60  that are concentrically mounted one upon another with the second power piston member  60  mounted around a reduced diameter portion  62  of the first power piston member  58 . The first power piston member  58  extends across the rear and intermediate chambers  46 ,  44  and into the front chamber  42 . 
     Power piston assembly  56  includes a rearwardly directed annular abutment flange  64  on the first member  58  against which support plate  66  supports diaphragm  68 . Diaphragm  68  includes an integral inner annular seal  70  that engages the first member  58  of the power piston assembly  56 . Diaphragm  68  separates front chamber  42  into a constant pressure control volume  42   a  and a variable pressure control volume  42   b.  The inner circumference of the diaphragm  68  is secured in sealing engagement to the power piston assembly  56  to form the seal  70  by a retaining member  72  (FIG.  3 ). The retaining member  72  is pressed onto the power piston assembly  56  to capture the seal  70  and an inner portion of plate  66  against the abutment flange  64 . The retaining member  72  in one embodiment is a ring with a number of spaced tabs  74  around the inner circumference that deflect and bend to bite into the power piston assembly  56  when the ring  72  is pressed onto it. 
     Power piston assembly  56  also includes a rearwardly directed abutment flange  76  on the second member  60  against which support plate  78  supports diaphragm  80 . Diaphragm  80  includes an integral inner annular seal  82  formed once again by a retaining ring  72  that engages the power piston assembly  56 . Diaphragm  80  separates intermediate chamber  44  into a constant pressure control volume  44   a  and a variable pressure control volume  44   b.    
     Power piston assembly  56  also includes a rearwardly directed annular abutment flange  84  on a proximal end of first power piston member  58  against which support plate  86  supports diaphragm  88 . Diaphragm  88  includes an integral inner annular seal  90  formed by a retaining ring  72  that engages the power piston assembly  56  (FIG.  3 ). Diaphragm  88  separates rear chamber  46  into control volume  46   a  and control volume  46   b.    
     The first and second power piston members  58 ,  60  are concentrically mounted together. The first member  58  includes a step  92  on its outer surface to mate with an annular notch  94  on the distal end of the second member  60 . As a result of the step  92 , the first member  58  has a larger diameter portion  96  and the smaller diameter portion  62 . The step  92  and notch  94  engage each other and in combination with the associated retaining ring  72  of the intermediate chamber  44 , the first and second power piston members  58 ,  60  are fixed together and prevented from translating relative to each other. 
     The diaphragms  68 ,  80 ,  88  and their respective support plates  66 ,  78 ,  86 , are operable such that a vacuum pressure exists in control volumes  42   a,    44   a,    46   a.  This vacuum pressure is generated therein through a vacuum check valve  98 . A variable pressure exists in control volumes  42   b,    44   b,    46   b  for selectively moving power piston assembly  56  forward in response to pressure differentials created by the introduction of atmospheric air through an air valve assembly  130 . The variable pressure in control volumes  42   b,    44   b,    46   b  selectively creates a force on the respective diaphragms  68 ,  80 ,  88 . The support plates  66 ,  78 ,  86  apply the force of the diaphragms to the respective rearwardly directed abutment flanges  64 ,  76 ,  84  of power piston assembly  56 . In response, power piston assembly  56  compresses a return spring  102 , causing power piston assembly  56  to slide within annular seals  28 ,  52 ,  54  forcing output support body  104  to apply force to the associated master cylinder  36 . The variable pressure in control volumes  42   b,    44   b,    46   b  is increased through operation of the air valve assembly  130 . 
     Referring to FIG. 2, an alternate embodiment of a triple power booster  10  according to this invention is shown in which the front chamber  43  has a reduced diameter compared to the intermediate and rear chambers  44 ,  46 . This embodiment is particularly useful when additional boost is required over a tandem booster, but packaging limitations prevent the use of the triple booster of FIG.  1 . Components which are similar between the embodiments of FIGS. 1 and 2 and similarly numbered. 
     In FIGS. 1 and 2, air valve assembly  130  is illustrated in the closed position against its mating component floating control valve  108 . When opened, air valve assembly  130  allows atmospheric pressure to enter the control volumes  42   b,    44   b,    46   b  and thus creates a pressure differential across the diaphragms  68 ,  80 ,  88 . The maximum pressure differential between constant pressure control volumes  42   a,    42   a,    46   a  on one hand and variable pressure control volumes  42   b,    44   b,    46   b  on the other hand, is the difference between generated vacuum and atmospheric. Typically, the vacuum pressure is generated by an internal combustion engine or by another form of air pump. 
     Referring to FIGS. 1 and 2, atmospheric air entering the power booster  10  travels through a filter  110  and the vacuum drawn from the power booster  10  exits through vacuum check valve  98  which is received in the front housing  12 . Power piston assembly  56  includes a plurality of air passages  112  through which flow is directed in a conventional manner. When the pressure in control volumes  42   b,    44   b,    46   b  reaches atmospheric, no further additional pressure differential increase is possible. The power piston assembly  56  transmits power assisted force from the annular wall  114  through the annular reaction body  116  and the reaction disc  118  to a rod assembly designated as output support body  104  and therethrough, to the master cylinder  36 . The output force F O  is applied to the master cylinder  36  by the output support body  104 , which is of a two piece construction in the present embodiment, but can also be formed as one piece. The output force OF  results in an equal and opposite opposing force designated as total reaction force F R  that is applied to the output support body  104 . The total reaction force F R  is apportioned by the reaction mechanism of the power booster  10  through a pushrod  120 , which is transmitted to the driver&#39;s foot on the brake pedal. 
     When the brakes are applied, feedback in the form of a counteracting total reaction force F R  from the master cylinder  36 , is applied to the output support body  104  and therethrough to the reaction disc  118 . The resiliency of the reaction disc  118  permits deformation thereof into the annular reaction body  116  so that engagement is established with the extension of reaction piston rod  122 . This total reaction force F R  is transmitted back through the reaction disc  118  to the annular reaction body  116  in the known manner. The reaction disc  118  biases the reaction piston rod  122  rearwardly providing a feedback force through piston rod  122  ultimately to the brake pedal (not illustrated) coupled with pushrod  120 . 
     The design of the triple booster  10  of this invention offers significant advantages over other triple booster designs while still providing a substantial increase in power. The respective diaphragms  68 ,  80  support plates  66 ,  78  and retaining rings  72 ,  72  of the front and intermediate chambers  42 ,  44  of FIG. 1 are identical components thereby minimizing the inventory requirements for unique components in the system. Moreover, the retaining member, particularly the retaining ring  72  for the intermediate chamber  44  serves the added function of securing the first and second power piston members  58 ,  60  together when installed. 
     While the present invention has been illustrated by a description of a preferred embodiment and while this embodiment has been described in some detail, it is not the intention of the Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user. This has been a description of the present invention, along with the preferred methods of practicing the present invention as currently known.