Patent Publication Number: US-2009229402-A1

Title: Brake system for hybrid vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a brake system suited for use with a hybrid vehicle having both regenerative and friction braking on one or more axles. 
     2. Disclosure Information 
     Hybrid vehicles, whether powered by an internal combustion engine or otherwise, and using electric, hydraulic, or compressed gas or another energy storage medium, typically utilize regenerative and friction braking on one or more axles. Regenerative braking is a fixture of hybrid vehicles simply because energy which is usually lost during the braking process may be recovered and used for powering the vehicle. Because, however, regenerative braking is not available at times, due to, for example, the lack of storage capacity in a traction battery or pump storage reservoir, or during certain operating modes, it is necessary to provide hybrid vehicles with not only regenerative braking, but also friction braking. 
     When a vehicle is being braked regeneratively, it is desirable for the brake pedal travel and effort to be, to the extent possible, equivalent to the travel and effort necessary to achieve a given level of braking during operation solely with friction brakes. In order to achieve the desired transparency needed of operation both with and without regenerative capability, it is required that the vehicle&#39;s brake pedal be displaceable by the motorist, during regenerative braking, without resistance from the master cylinder used to apply the friction brakes. This requirement of non-interaction from the master cylinder may be satisfied by the accommodation of lost motion between the master cylinder push rod and the arm to which the brake pedal is attached. Known attachments between the brake cylinder push rod and brake pedal arm are very complex and difficult to assemble. Moreover, known devices use a drive pin centered by the outer surfaces of a clevis attached to the master cylinder, and this causes friction to develop between the drive pin&#39;s head and the clevis surfaces. 
     It would be desirable to provide a brake pedal and master cylinder arrangement allowing rapid and relatively effortless coupling of the brake booster/master cylinder push rod to the brake pedal arm, using a structure which minimizes annoying vibration and noise during operation of the vehicle. 
     It would further be desirable to employ a drive pin and pedal arm combination which center the drive pin through its interaction with the pedal arm, rather than through interaction of the drive pin with a clevis attached to the master cylinder or brake booster. In this manner, friction between the head of the drive pin and adjoining surfaces of the clevis is eliminated. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a brake system for a hybrid vehicle includes a master cylinder connected with a number of wheel cylinders, and a brake pedal mounted upon a pivoted brake pedal arm which is adapted for mounting within the passenger compartment of the vehicle. The brake pedal arm has a bore extending therethrough. A compliance device extends between the brake pedal arm and the master cylinder. The compliance device includes a push rod having a first end attached to a master cylinder and a second, free end. A clevis is attached to the second end of the push rod. The clevis has a base engaging the push rod. A pair of opposing connecting members are integral with the clevis base. In a first embodiment, the opposing connection members each have a linear aperture extending generally parallel to a longitudinal axis of the push rod. A composite drive pin extends through the linear apertures and through the bore formed in the brake pedal arm in a direction generally perpendicular to the push rod. The composite drive pin includes a metallic core and a resin sheath applied to the core. The resin sheath has a generally cylindrical outer surface adapted to engage with both the bore formed in the brake pedal arm, and with the linear apertures. The resin sheath has a number of axial location abutments including at least one abutment which is radially displaceable so as to permit the drive pin to be readily assembled to the clevis and the brake pedal arm. 
     The composite drive pin preferably includes an anti-rotation cam extending radially outward from a portion of the generally cylindrical outer surface of the resin sheath. The anti-rotation cam is adapted to fit within a non-circular portion formed in the brake pedal arm bore. 
     In a first embodiment of the present invention, the opposing connecting members incorporated in the clevis are generally planar and configured such that the linear apertures in the connecting members have major axes which extend generally parallel to the longitudinal axis of the push rod. This is shown in  FIGS. 5 and 6 . 
     According to another aspect of the present invention, a master cylinder used with the present brake system is preferably configured as an active booster master cylinder, with the compliance device allowing the brake pedal to be depressed for a fraction of its normal travel, without applying the hydraulic brake system. This allows the use of regenerative braking in conjunction with friction braking in a manner which is transparent to the driver of the vehicle. 
     According to another aspect of the present invention, the axial location abutments formed on the resin sheath of the composite drive pin include a number of abutments positioned between the brake pedal arm and each of the opposing connecting members of the clevis. The axial location abutments are formed integrally with the resin sheath and are preferably created when the resin sheath is molded in place upon a metallic core. The abutments are preferably configured as radial displaceable sprags which are cantilevered to the resin sheath so as to normally project from the outer cylindrical surface of the resin sheath, with each sprag having a selectively retracted position enabling insertion of the composite drive pin within the clevis and bore formed in the brake pedal arm. 
     According to another aspect of the present invention, the axial abutments of the installed composite drive pin may be positioned within an internal annular groove formed within the bore of the brake pedal arm. As an alternative, the axial abutments may include an abutment positioned within an internal annulus defined by an outer surface of the composite drive pin and a bore formed within a doubler applied to the brake pedal arm such that the bore formed within the doubler is concentric with the bore formed in the brake pedal arm. 
     According to another aspect of the present invention, a brake system includes an active booster master cylinder connected with a number of wheel cylinders, with a brake pedal having a linear aperture extending through a brake pedal arm. A clevis has opposing connecting members which each have a generally cylindrical bore extending therethrough in a direction generally perpendicular to a push rod having a first end attached to the master cylinder and a second free end which is attached to the clevis. A composite drive pin extends through the bores formed in the connecting members and through the linear aperture formed in the brake pedal arm. 
     It is an advantage of a system according to the present invention that compliance may be provided between a brake pedal and an active booster master cylinder, with a minimum number of components in the compliance device, while avoiding undesirable noise, vibration and harshness from the connection between the master cylinder push rod and the brake pedal arm. 
     It is yet another advantage of a brake system according to the present invention that a connection may be made up between a brake pedal arm and a master cylinder push rod without the need for attaching threaded fasteners under the dash of a vehicle during the final assembly process. 
     It is yet another advantage of a brake system according to the present invention that necessary compliance between a brake pedal and a master cylinder is provided with minimal tooling cost. 
     It is an advantage of a system according to the present invention that compliance may be provided between a brake pedal and an active booster master cylinder with a minimum amount of friction within the compliance device. 
     Other advantages, as well as features of the present invention, will become apparent to the reader of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation of a brake system according to the present invention. 
         FIG. 2  is a side elevation similar to  FIG. 1 , but having a number of components removed for clarity of reading. 
         FIG. 3  is a perspective view showing insertion of a composite drive pin according to one aspect of the present invention. 
         FIG. 4  is a perspective view of a composite drive pin according to an aspect of the present invention. 
         FIG. 5  is a plan view of an embodiment according to one aspect of the present invention. 
         FIG. 6  is similar to  FIG. 5 , but shows another embodiment according to an aspect of the present invention. 
         FIG. 7  is similar to  FIGS. 5 and 6 , but shows yet another embodiment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , active booster master cylinder  24  is connected with a number of wheel cylinders,  26 . Master cylinder  24  is driven by push rod  32 , having a first end attached to master cylinder  24  and a second end attached to clevis base  37 , which is part of slotted clevis  36 . Opposed connecting members  38   a  and  b  (shown with particularity in  FIGS. 3 ,  5  and  6 ) have linear apertures, commonly termed “slots”,  40   a  and  40   b,  extending therethrough. Linear apertures  40   a  and  40   b,  are shown in  FIGS. 5 and 6  as having major axes which extend generally parallel to the longitudinal axis, A, of push rod  32 . A brake pedal travel sensor,  28 , is coupled to brake pedal shaft  22  shown in  FIG. 2 . 
     A brake pedal,  14 , is attached to a brake pedal arm,  18 , which is mounted to a bracket,  20 , by means of a pivot shaft  22 .  FIG. 2  also shows with particularity a bore,  44 , through brake pedal arm  18 , with bore  44  having an anti-rotation cam slot illustrated as non-circular segment,  44   a.  Both bore  44  and non-circular segment  44   a  are engaged, as described below, by composite drive pin  64 , which is shown with particularity in  FIGS. 3 and 4 . 
       FIGS. 3 and 4  show the external surfaces of drive pin  64 . These external surfaces include a bar handle,  82 , which is formed in external resin sheath,  72 . Sheath  72  also includes an anti-rotation cam,  86 , which is intended to slidingly fit within non-circular bore segment  44   a  of pedal arm  18 . As shown in  FIGS. 5-7 , resin sheath  72  is preferably molded in place over metallic core  68 . In a preferred embodiment, core  68  is configured from steel. 
     Composite drive pin  64  further includes at least one fixed abutment,  80 , and at least one cantilevered, radially displaceable abutment or sprag,  84 . As shown in  FIG. 4 , sprag  84  is cantilevered from, and formed integrally with, resin sheath  72  of composite drive pin  64 . 
     Composite drive pin  64  is inserted, as shown in  FIG. 3 , by axially moving the composite drive pin through linear apertures  40   a  and  b  formed in opposing connecting members  38   a  and  38   b,  as well as through bore  44  formed in pedal arm  18 . As composite drive pin  64  is inserted axially through these components, sprags  84  are at first compressed radially to allow passage through bore  44 , and then the sprags move from their selectively retracted position to a normally extended position for retaining composite pin  64  centered within bore  44  of pedal arm  18 . 
     In the embodiment shown in  FIG. 3 , composite drive pin  64  has fixed abutments  80 , and sprags  84 , all of which come to rest on either side of pedal arm  18  when composite drive pin  64  has been inserted into its fully installed position. In the embodiment of  FIG. 5 , however, one or more sprags  90 , are employed at the midpoint of composite drive pin  64 . Sprags  90  register with an internal annular groove,  48 , formed in the aperture  44  of brake pedal arm  18 . In each case, drive pin  64  is retained in a predetermined axial position in which only external sheath  72  contacts connecting members  38   a  and  38   b.  Essentially, drive pin  64  is locked axially upon pedal arm  18 . 
     In the embodiment of  FIG. 6 , a doubler,  52 , is applied to brake pedal arm  18 , and a bore,  56 , formed in doubler  52 , combines with the outer cylindrical surface of composite drive pin  64  to define an annulus in which one or more cantilevered radially displaceable abutments, or sprags,  90  may be located when composite drive pin  64  is mounted in the fully installed location. As is further shown in  FIG. 6 , one or more cantilevered radially displaceable sprags  91  may be mounted at an end of composite drive pin  64  opposite bar handle  82 . 
     In the embodiment of  FIG. 7 , opposing connecting members  38   a  and  38   b  have bores  34  formed therein. These bores  34  allow composite drive pin  64  to be securely mounted within clevis  43 , so as to permit composite drive pin  64  to move reciprocally within slot  30  formed in brake pedal arm  18 . As before, the presence of resin sheath  72  as the outer surface of composite drive pin  64  prevents unwanted noise, vibration, and harshness from being generated as the result of interaction of composite pin  64  with either clevis  43 , or brake pedal arm  18 . At least two radially displaceable abutments or sprags  91  are preferably located at the lead end of composite drive pin  64  in the configuration of  FIG. 7 . 
     Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.