Abstract:
The invention relates generally to a disk brake system for a hydraulic disk brake retractor system that maximizes running clearance while still effectively providing for manual braking in a power-down condition. The invention uses a simple spring-loaded brake retractor system comprised of a brake piston, a brake spring, and a retractor shaft.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a disk brake system in a moving vehicle. More specifically, it relates to a hydraulic disk brake retractor system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Brake assemblies are generally used to stop the movement of motor vehicles, such as an agricultural tractor. As shown in U.S. Pat. No. 6,002,976, the driveline of a typical agricultural tractor, for example a tractor in the John Deere 6000 series, includes an engine, a shifted multi-speed transmission, a reversing unit, a drive clutch, an optional creeper transmission, a shifted range transmission, and a rear axle differential gear which drives the rear wheels. As shown in U.S. Pat. No. 5,197,574, a brake may also be provided between the transmission housing and the rear axle differential gear. Due to low operating speeds, large mass and high torque under which agricultural tractors operate, these brakes are often configured so the brake disks are submerged in oil. The oil serves to lubricate and carry heat away from the brake disks when the brakes are applied by a tractor operator. 
         [0003]    When the brakes are initially assembled, an optimal running clearance is set between a brake piston, the brake disks, separator plates (if applicable) and a brake cover. Ideally, a very small running clearance between brake disks is desired to allow for fast brake engagement and a short pedal throw. However, if the clearance is too small, windage effect may prevent sufficient oil flow between the braking surfaces, interfering with the lubrication and cooling of the brake disks. In addition, the small amount of oil between the braking surfaces may become entrapped. As a result, even when the brake is not engaged, significant heat may be generated between the braking surfaces and the entrapped oil, causing damage to the brake assembly. 
         [0004]    In most of today&#39;s brake system design, there is usually a compromise between having as much running clearance as possible to reduce drag, and improve system efficiency, while at the same time, keeping this running clearance small to meet manual braking stopping distance versus time requirement per regulation. 
         [0005]    To minimize windage loss through brake disks, it is therefore desirable to maximize the running clearance between brake disks. Alternatively, it is also desirable to minimize running clearance between brake disks in order to maximize braking performance, especially in the power-down condition, where hydraulic power to brake valve is lost, and the operator must make an emergency brake stop with only the limited available flow volume from the brake valve. 
         [0006]    For the reasons listed above, it has been a challenge for the industry to provide a brake design with more running clearance for improved efficiency, and yet, still be able to meet the regulated requirement for manual brake stopping distance versus time. 
       SUMMARY OF THE INVENTION 
       [0007]    In light of the above background information, an improved spring-loaded brake retractor system is proposed. This spring-loaded brake retractor system uses the system&#39;s hydraulic power to retract the brake piston to provide desired running clearance between disks. In the power-down condition, the spring will provide the force to position the brake piston against brake disk pack to eliminate the piston “travel” that is normally required to bring brake piston and brake disks to a near contact position. 
         [0008]    The proposed invention improves brake system efficiency by allowing increased running clearance between brake disks. Additionally, the invention minimizes the distance the piston has to travel, and the corresponding volume of oil required from brake valve, to engage the brake in power-down condition. 
         [0009]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-section view of a brake assembly with a brake retractor system according to an embodiment of the present invention. 
           [0011]      FIG. 2  is a cross-section view of a brake assembly with a brake retractor system in an embodiment of the present invention engaging a pair of friction disks and moving axially to eliminate running clearance. 
           [0012]      FIG. 3  is a cross-section view of a brake assembly with a brake retractor system in an embodiment of the present invention fully engaging a pair of friction disks and eliminating running clearance. 
           [0013]      FIG. 4  is an expanded view of the brake retractor system according to an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    In general, the present invention is directed to a spring-loaded brake retractor system  36 ,  FIGS. 1-4 , comprising a retractor shaft  14 , brake spring  22  and retractor piston  18 . 
         [0015]    Reference is made to  FIG. 1 , which shows a brake assembly designated at  10 , generally embodying the principles of the present invention. As its primary components, the brake assembly  10  includes a retractor shaft  14  mounted inside a brake housing cavity  32 , having a first end  14   a  and a second end  14   b ; a retractor piston  18  attached to the first end of retractor shaft  14   a ; a brake piston  20  attached to the second end of the retractor shaft  14   b  that prevents the brake piston  20  from rotating, and to facilitate the axial movement of the brake piston  20  during the engaged or disengaged modes; a retractor piston  18  adjacently located next to a brake spring  22 , which utilizes a source of hydraulic pressure or fluid flowing through a passage  24  to disengage the brake and retract the brake piston  20  in a second direction opposite the first; a brake spring  22  situated between a retaining device such as a snap ring  12  that enables a retractor piston  18  and retractor shaft  14  to move in a first direction to engage the brake piston  20 . At least one separator plate  28  is fixedly splined onto a rotating hub  42 . Also fixedly splined into a stationary brake housing cavity  32  is at least a first and second friction disk  26  for engaging separator disk  28  that is splined onto hub  42  that rotates within brake housing cavity  32 . With at least a first and second friction disk  26  separator plate  28  fits in between the at least first and second friction disks  26  to hold them together. 
         [0016]    As shown in  FIG. 1 , during normal tractor operation, brake (not shown) is deenergized, oil pressure in annular passage  38  is zero and hydraulic pressure is supplied to retractor piston cavity  54  through passage  24 . This hydraulic pressure in cavity  54  acts to move retractor piston  18  against spring  22 , the movement of the retractor piston  18  also moves the retractor shaft  14 , and the brake piston  20  in the second direction within the brake housing cavity  32 . Under this condition, the brake piston  20  is disengaged, and the running clearance  30  is created and or realized. 
         [0017]    As shown in  FIG. 2 , during normal braking, brake valve (not shown) is energized, which sends pressured oil to brake piston annular passage  38  via passage  50 , this pressurized oil moves the brake piston  20  within the brake housing cavity  32 , closing the running clearances  30  on each side of the at least first and second friction disks  26  and resulting in frictional engagement of the at least first and second rotating friction disks  26  between brake piston  20  and brake housing cavity  32 . 
         [0018]    When brake is deenergized, as shown in  FIGS. 1 and 4 , the source of hydraulic pressure or oil pressure in annular passage  38  is vented, and the retractor system  36  returns the brake piston  20  in a second direction opposite the first to its initial position, disengaging brake piston  20  from the at least first and second friction disks  26 . 
         [0019]    The actual running clearance of the brake assembly  10  equals the distance the brake piston  20  must travel in order to clamp the at least first and second friction disks  26  equal to the sum of the running clearances  30 . The desired running clearance is based on various factors including at least a first and second friction disk  26 , separator plates  28 , the required response time of the brake assembly  10 , the brake retractor system  36  and the cooling requirements for a particular application. In addition, windage effects may generate additional heat and prevent sufficient hydraulic pressure from flowing between the at least first and second friction disks  26 . These factors may cause damage to brake assembly  10  having very small running clearance  30 . Thus, running clearance  30  utilizing a brake retractor system  36  eliminates the risk of the damage, while still keeping the response time and pedal throw to a minimum. 
         [0020]    The invention is carried out when the system  36  is in a power on condition, pressurized hydraulic pressure or fluid in a passage  24  to cavity  54  is used to retract the brake piston  20  in a second direction opposite the first, and apply a disengagement force against a brake spring  22 . This retraction then provides a desired running clearance  30  between disks  26  and separator plate  28 ,  FIGS. 1 and 4 . 
         [0021]    In the power down condition, as shown in  FIG. 3 , with system hydraulic pressure in passage  24 , to cavity  54  being zero, the brake spring  22  will provide proper force in a first direction to position brake piston  20  against the at least first and second friction disks  26  to minimize the piston travel and bring brake piston  20  to a point called the kiss-up position. Due to the size of brake spring  22 , brake spring  22  will only close the clearance gap  30  up to the kiss-up position. To reach full engagement, it is necessary for the operator to push the brake pedal to come to an immediate stop. The kiss-up position may also be referred to as a near contact position and essentially means there is not enough torque capacity in a power-down condition to completely engage the brake therefore less than full brake engagement occurs. Less that full engagement may also be considered as the point just prior to full engagement. Additionally, in the power down condition, the source of hydraulic pressure or fluid to the brake valve (not shown) is lost and limited flow volume from the brake valve exists therefore making it difficult to stop the vehicle. To accommodate this problem and reach full brake engagement, the brake pedal is pushed by operator to eliminate the remaining running clearance. If the running clearance  30  is eliminated, the flow volume of hydraulic pressure or fluid in passage  24  from the brake valve during an emergency stop will move the brake piston  20  to fully engage the at least first and second friction disks  26 . 
         [0022]    This invention is being shown and claimed with one brake retractor. However, a preferred alternative embodiment can be designed to accommodate three brake retractors. The three brake retractors are positioned on the outer edge of the brake piston. By locating the brake retractors on the outer edge of the brake piston, the entire system has a tendency to be more balanced than a system that positions its brake retractors near the center of axis of the brake piston. Passage  60  is used to supply oil pressure to all three brake retractors. Additionally, the further away each brake retractor is from the center of axis of the brake piston the more torque carrying capacity. 
         [0023]    As the person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.