Abstract:
A automotive braking system for use on a vehicle for emergency stopping and parking comprising a mechanical brake caliper which exerts frictional stopping force on a brake rotor, the caliper being designed so as to provide a means of transferring mechanical force to the caliper pistons by means of a lever which transfers mechanical force to the piston through one or more apertures in the piston cylinders. The lever is operated by an actuator rod, which is engaged by a spring chamber having a heavy duty parking spring with and opposing force created by a variable pressure means, typically air or hydraulic. The system fails to a safe-mode mode wherein a loss of pressure opposing the parking spring results in the engagement of the braking system, bringing a moving vehicle to rest within a reasonable distance and holding a vehicle parked until such time the pressure can be restored.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/378,828, filed on May 9, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates to automotive brake systems. Specifically, the invention relates to hydraulic disc brake systems on light/medium duty vehicles. 
   BACKGROUND OF THE INVENTION 
   Light/medium duty vehicles equipped with hydraulic disc brakes have a significant safety issue related to their ability to stop when the hydraulic or power assist system fails. This problem is presently shared by nearly every make and model numbering in the millions. The problem is that the emergency braking capabilities of these vehicles are not adequate. While the current hydraulic braking systems are relatively safe through redundancy, the possibility for complete failure exists and is not too improbable to overlook. 
   The most commonly used braking system for light/medium duty vehicles is a hydraulic braking system. This system generates its braking fluid pressure by means of a master cylinder, power assistance provided by the power steering pump that is mounted on and powered by the engine. In the event of an engine failure, the engine mounted hydraulic pump will cease to function. Generally a back up electric powered hydraulic pump is used to supply hydraulic-assist pressure to the service brake. However, a safety issue arises when there is a complete failure of the vehicle&#39;s electrical system, in that a failure will disable the engine. Further, the back-up electric hydraulic-assist pump will not receive power and will fail to operate when braking is needed. The drive line mounted parking brake, at best, will hold a vehicle parked. However, it is completely incapable of bringing the vehicle to a safe stop within a reasonable distance. This existing system rests in the released position and requires input energy generally by means of a cable to apply. 
   A large majority of medium duty vehicles, including school buses employ the above-mentioned system. Current parking brakes on medium duty vehicles are prone to failure and do not provide enough holding power. Furthermore, current parking brake systems consist of a manually operated drum brake that is installed somewhere on the drive shaft. Being mounted on the drive shaft, this system is insufficient due to the properties of spider gears in the differential. An example is one rear wheel on a slick surface or in the event a driveline failure occurs. Another type of braking system available for medium duty vehicles is an air braking system. Air brakes do not have the above-mentioned problem because they fail to a safe mode. That is, failure of an air brake system by design will allow spring force to apply the brakes. However, air brakes are much more expensive than hydraulic systems and fall under heavy federal mandates to include required commercial drivers license and strict, frequent maintenance measures. 
   Thus there is a need for an emergency brake/parking brake system that is completely independent of the service brake system and can be easily and immediately employed on medium duty vehicles to include but not limited to new production and retrofit. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an emergency/parking brake system that can easily be installed on current and future production light/medium duty vehicles; is simple and easy to maintain; does not modify or rely upon existing service brake systems; and will fail to the safe mode. 
   It is another object of the present invention to provide an emergency/parking brake system that requires actuator input energy for release, but does not require actuator input energy for application. 
   It is another object of a the present invention to provide an emergency/parking brake system that requires little maintenance or adjustment. 
   In a further embodiment, it is an object of the present invention to provide an emergency/parking brake system that has independent brake assemblies on each rear wheel. 
   These and other objects are achieved by providing an automotive braking system for use on a vehicle for emergency stopping and parking comprising a mechanical brake caliper which exerts frictional stopping force on a brake rotor, the caliper being designed so as to provide a means of transferring mechanical force to the caliper pistons by means of a lever which transfers mechanical force to the piston through one or more apertures in the piston cylinders. The calipers are fully floating and receive no torque, in which they only force pads against the brake rotors, allowing the brake system anchor plate to receive the torque from the brake pads. The lever is operated by an actuator rod, which is engaged by a spring chamber having a heavy duty parking spring with and opposing force created by a variable pressure means, typically air or hydraulic. 
   The present invention provides completely independent parking and service brake systems, and fails to a safe-mode mode wherein a loss of pressure opposing the parking spring results in the engagement of the braking system, bringing a moving vehicle to rest within a reasonable distance and holding a vehicle parked until such time the pressure can be restored. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a perspective overview view of the brake system attached to the rear axle of a vehicle. 
       FIG. 2A  is a partial-sectional view of the brake system attached to the rear axle of a vehicle with the brake mounting frame omitted, illustrating the engaged position of the brake. 
       FIG. 2B  is a partial-sectional view of the brake system attached to the rear axle of a vehicle with the brake mounting frame omitted, illustrating the disengaged position of the brake. 
       FIG. 3  illustrates an isolated sectional view of the spring chamber operating the lever linkage of the braking system. 
       FIG. 4  illustrates a perspective view of the Siamese anchor plate for mounting both a hydraulic service brake and a mechanical parking/emergency on the same brake rotor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   The present invention can be obtained by providing a mechanically operated brake caliper. As shown in the figures, the invention employs a simple lever system connected to an air/spring chamber which actuate the caliper pistons, depressing the brake pads against the brake rotors. As an emergency/parking brake system, the brakes should not have enough power to “lock up” during emergency dynamic braking so that maximum control of the vehicle is still possible. Parking brakes are not dynamic and require less application power than dynamic braking, as is evident by existing parking brake systems. The system disclosed herein is well within the scope needed for successful operation. 
   The emergency/parking caliper utilizes mechanical input versus hydraulic input, as shown in  FIGS. 2A and 2B . To achieve this, the back of the caliper is drilled out to expose the rear surface of the pistons. Service brake calipers subject the back of the pistons to hydraulic pressure, whereby the preferred embodiment of the present invention employs a bridging means which connects the pistons and allows a mechanical input to actuate them. The bridge bears the necessary force applied by the lever system, and evenly distributes the force to the pistons in a controlled and sate manner. Typical hydraulic operation does not subject the pistons to lateral forces. A lever system could produce lateral forces, causing possible piston and cylinder scoring. To prevent this, the lever system makes contact with the piston bridge by means of a roller. The roller is not able to transmit any significant lateral forces to the piston bridge by design. 
   The lever system is designed in a manner that facilitates the required “Fail to Safe” concept, in that when the actuating chamber is relieved of air or fluid pressure, a maximum braking force is developed that will stop and park the vehicle. Furthermore, the system does not hinder the “floating caliper” design, which allows the caliper to receive input from only one side of the rotor, and apply the supplied forces evenly on both faces of the rotor to prevent warping and uneven wear. Thus, the lever system is integral to the caliper, and in a preferred embodiment, dual calipers are utilized on a single brake rotor, mounted to a siamese anchor plate as shown in  FIG. 4 . This configuration provides mounting for the hydraulic service brake caliper and the mechanically actuated emergency/parking caliper, as shown in  FIG. 1 . Finally, the system is suitably made to fit into the space available on light/medium duty vehicles. 
   Referring now to the figures, specifically  FIG. 1 , the preferred embodiment of the invention is shown, attached to the rear axle of a vehicle, comprising the linkage system  60  attached to the caliper  50  having a spring chamber  30  for engagement/disengagement of the caliper  50  without affecting the normally employed hydraulic service brake system. 
   Best illustrated in  FIGS. 3 and 4 , there is shown an example of the spring chamber  30  mechanism of the present invention. Known to those skilled in the art, this provides the force of the present invention through controlled air pressure within chambers  34  and  36  releasing a parking brake spring  35  acting upon plunger  37 . Designed to fail to the safe mode, when there is no increased air pressure present, the brake spring  35  is engaged. The spring brake chamber  34  which is charged with air pressure to compress a heavy-duty parking brake spring  35 . 
   The fail-to-safe mode, common on most air brake systems, provides that in the event air pressure is lost (vented) the spring  35  will apply longitudinal force to the actuator rod  38  through the actuator plate  77  and thus causing the emergency brake to stop the vehicle if in motion, or to park the vehicle once stationary. To disengage the braking system  10  and thereby allowing the vehicle to move, the spring chamber  30  must once again be subjected to an increase in air pressure. 
   Referring now to  FIGS. 1 ,  2 A and  2 B, The brake pads  53  and  54  utilized in the preferred embodiment provide a frictional surface on the rotor  26  to retard vehicle movement, and are readily obtainable and known by those skilled in the art. The caliper  50  shown, is unique in that it adapts to the means of mechanical braking utilized in the present invention. In service brake applications, the caliper  50  converts hydraulic fluid pressure to mechanical output that is directly applied to a set of brake pads, wherein the present invention, the pistons  52  of the caliper  50  are operated by the mechanical means described below. The caliper  50  is mounted to the Siamese anchor plate  22  adjacent to the brake rotor  26  by an anchoring means  24 , the anchor plate  22 , attaching to the axle housing  20 . In a preferred embodiment, the anchor plate  22  has dual mounting locations  25  and  27  as mentioned, for utilizing both a normal, hydraulically operated service brake caliper  28 , and the mechanical emergency/parking brake caliper  50  of the present invention upon the same rotor  26 . 
   The anchoring means  24  in the preferred method of attaching the caliper  50  to the anchor plate  22  comprises two floating pins  29 . The caliper  50  is machined so as to bore two holes in the back of the piston cylinders, which allow external mechanical coupling of the pistons  52 , comprising the emergency braking system. To maximize reliability and functionality, each piston  52  is subjected to forces that do not exceed those produced in hydraulic applications. To accomplish this, the force produced is applied to the entire back surface area of each piston, by designing the piston coupler  56  interface to have equal surface area to that of the piston  52 . 
   In the preferred embodiment, the coupler  56  is then attached to the piston  52  and a bridging means  55  through the center of each coupler  56 , maintaining a solid interface with the piston  52  and bridging means  55 . The bridging means  55  delivers and distributes the force to actuate two pistons in a multiple piston caliper application, commonly know in the art. 
   The lever system is fastened using bolts  64  and  65  at the pivot points. Since large forces are generated in this system, known design methods and techniques are used to account for these forces, and determine which bolt properties and geometries are necessary for reliability. With the primary stresses observed being a shear stress, the preferred embodiment utilized bolts of ¾ inch diameter. 
   To best illustrate the leverage linking system,  FIG. 1  is referred to, showing the various components comprising the system. The linkage  60  is comprised of three individual elements; a mounting frame  61 , the lever linkage  62  and the yoke linkage  63 . The mounting frame  61  provides a means of attaching the spring chamber  30  to the caliper  50 . The lever linkage  62  comprises the lever arm  2 , for applying force to the piston couplers  56  via the bridging means  55 , and further connects to the spring actuator rod  38  via the pivotal actuator linkage  63 , so as to provide the force for engagement of the braking system  10 . 
   The mounting frame  61 , attaching the system to the caliper  50 , is generally constructed from a pair of parallel angled, square steel arms  66  and  67  with a mounting plate  68  at one end for attaching the spring chamber  30 . The mounting plate provides a means, generally an aperture there through, allowing the actuator rod  38  to engage the lever linkage  62 . The opposite end of arms  66  and  67  in the preferred embodiment are attached to the caliper  50  body and is braced, for reinforcing the brake system components. 
   As shown, the lever linkage  62  is pivotally attached to the mounting frame  61  at a first end positioned between the parallel arms  66  and  67  by a pivotal axis bolt  65 , shown in  FIG. 2A . This pivotal axis provides the lever means for transferring the force applied to the second end of the lever linkage  62  by the pivotally attached actuator linkage  63  attaching to the spring chamber actuator rod  38 . A roller  51  is rotatably attached to the lever linkage  62  by bolt  59 , and in a preferred embodiment, two rollers are utilized providing a more uniform distribution of force to the bridge  55 . The roller  51  transfers force applied to the second end of lever linkage  62  to the bridging means  55 , which distributes the force evenly to the caliper piston couplers  56 , without inducing lateral force or causing binding of the pistons within the cylinders. 
   The actuator linkage  63  provides for the pivotal attachment of the spring chamber actuator rod  38  to the lever linkage  62 , and is fabricated so as to withstand the required force necessary to actuate the braking system. 
   The brake system  60  is normally engaged, until such time that air pressure above ambient is introduced into the spring brake chamber  34 . While engaged, the actuator arm  38  is extended creating a force on the lever linkage  62  through the actuator linkage  63 . This force is carried on to the roller  51 , and translates to a longitudinal force upon the bridging means for forcing the plurality of pistons to engage the brake pads  53  and  54  with the rotor  26 . Once air pressure is introduced to the spring brake chamber  34 , the pressure creates a force upon the actuator plate  77  which compresses the parking spring  35  and retracts the actuator rod  38  into the spring chamber  30 . This results in the release of the force upon the lever linkage  62 , and in turn the force applied to the pistons  50  through the couplers  56 , thereby releasing the brake pads  53  and  54  from the rotor  26 . 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.