Abstract:
A brake assembly ( 30 ) has a plurality of brake fluid actuated pistons. The brake assembly includes a brake inlet port ( 46 ) for receiving brake fluid from a fluid reservoir. The brake assembly includes a plurality of cylinders ( 32, 34, 36, 38, 40, 42 , and  44 ) for actuating a corresponding plurality of pistons. The plurality of cylinders includes at least a first cylinder ( 32 ), a second cylinder ( 44 ), and a third cylinder ( 38 ) for actuating corresponding pistons. The first, second, and third pistons actuate at first, second, and third time intervals. A fluid distribution manifold ( 48 ) is connected in fluid communication with the brake inlet port. A plurality of cylinder manifolds ( 50 ) includes at least a first cylinder manifold connected in fluid communication with the fluid distribution manifold and the first cylinder, a second cylinder manifold connected in fluid communication with the fluid distribution manifold and the second cylinder, and a third cylinder manifold connected in fluid communication with the fluid distribution manifold and the third cylinder. The first, second, and third cylinder manifolds connect the first, second, and third cylinders in parallel fluid flow, and the parallel fluid flow tends to equalize the first, second, and third time intervals.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/388,245, filed Sep. 1, 1999, abandoned as of the filing date of this application, which was a continuation of prior U.S. patent application Ser. No. 08/731,763, filed Oct. 18, 1996, now U.S. Pat. No. 5,971,111. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a brake assembly, and more particularly to a balanced aircraft brake assembly having coincident piston application. 
     BACKGROUND OF THE INVENTION 
     Airplane brake assemblies are well known in the art. FIG. 1 shows a typical prior art brake assembly  2 . The brake assembly  2  includes a brake inlet port  4 . The brake inlet port  4  is typically located at the top of the brake assembly  2  for purging air bubbles that may be present in brake assembly hydraulic fluid. The brake assembly  2  further includes a plurality of piston and cylinder assemblies  6 , a pressure plate  8 , a plurality of rotor and stator assemblies  10 , and a torque tube  12 . As can be seen in FIG. 1, the piston and cylinder assemblies  6  are located in a substantially circular arrangement about the brake assembly  2  for providing an even pressure distribution about the pressure plate  8 . 
     FIG. 2 shows a schematic diagram of a typical brake assembly, such as the brake assembly  2  of FIG.  1 . The brake inlet port  4  is shown at the top of the brake assembly  2 . However, it is well known in the art to locate the inlet port at any position on the brake assembly. The brake inlet port  4  is coupled to a header from a hydraulic fluid reservoir (not shown). The cylinders  14 ,  16 ,  18 ,  19 ,  20 ,  22 , and  24  are connected in series fluid communication via hydraulic manifold sections  26 . The cylinders  14  and  24  are also coupled to the brake inlet port  4  via manifold sections  26 . Flow restrictors  28  may be included in each of the manifold sections  26 . 
     When a pilot applies an aircraft&#39;s brakes, hydraulic fluid flows from the hydraulic reservoir (not shown) through the header to the brake inlet port  4 . When hydraulic fluid is introduced to the brake inlet port  4 , hydraulic fluid first flows to the cylinders  14  and  24  that are coupled to the brake inlet port  4 . Hydraulic fluid pressure increases within the cylinders  14  and  24  as they fill. When the pressure in the cylinders  14  and  24  reaches a predetermined threshold, their associated pistons actuate and press against the pressure plate  8 , which clamps the rotor and stator assemblies  10  against the torque tube  12 . After the cylinders  14  and  24  have filled, hydraulic fluid next flows through the manifold sections  26  to the cylinders  16  and  22 . The cylinders  16  and  22  fill with hydraulic fluid and, in turn, hydraulic fluid flows through the manifold sections  26  to the cylinders  18  and  20 . Finally, after flowing through the above-identified series of cylinders, hydraulic fluid flows to and fills the cylinder  19 . Thus, the pistons associated with the cylinders  14 ,  16 ,  22 , and  24 , located toward the brake inlet  4  at the top of the brake assembly  2 , actuate and clamp the rotor and stator assemblies  10  against the torque tube  12  before the pistons associated with the cylinders  18 ,  19 , and  20 , located toward the bottom of the brake assembly  2  away from the brake inlet port  4 , actuate and clamp against the torque tube  12 . 
     As a result, the rotor and stator assemblies  10  near the brake inlet port  4  at the top of the brake assembly  2  are compressed before the rotor and stator assemblies  10  farther away from the brake inlet port  4  at the bottom of the brake assembly  2 . In some known brake assemblies, the time delay between actuation of piston and cylinder assemblies located closer to the brake inlet port and actuation of piston and cylinder assemblies located farther away from the brake inlet port has been recorded in excess of 50 ms. This time delay causes the torque tube  12  to react through the rotor and stator assemblies  10  at the top of the brake assembly  2  against the piston and cylinder assemblies  6  at the top of the brake assembly  2  while the piston and cylinder assemblies  6  at the bottom of the brake assembly  2  are still compressing against the torque tube  12 . This results in a lateral displacement between the top and bottom regions of the rotor and stator assemblies  10  and the torque tube  12 . When the piston and cylinder assemblies  6  at the bottom of the brake assembly  2  actuate, the bottom of the torque tube  12  reacts through the bottom region of the rotor and stator assemblies  10  against the piston and cylinder assemblies  6  at the top of the brake assembly  2 . This, in combination with a return force from the top region of the torque tube  12  causes the clamping force at the top region of the brake assembly  2  to decrease relative to the clamping force at the bottom of the brake assembly  2 . When the asymmetric clamping cycle and corresponding lateral displacement repeats for a rotating wheel, a vibration of the brake results. The vibration is known as “brake whirl” or “brake wheel vibration.” 
     An imbalance in piston pressure exists across the brake assembly  2  during the time that the pistons are actuating. Piston pressures and torque tube clamping forces are not equalized across the brake assembly  2  during pressure transitions. Each piston actuates as an individual dynamic element within the brake assembly  2 , rather than all the brake pistons actuating together as a single element. The resulting differential pressure between the pistons during braking undesirably reduces overall brake system stiffness. 
     The asymmetric clamping cycle described above can also cause stators to develop a tapered wear pattern. Further, the time delay between actuation of top and bottom region pistons degrades the frequency response of the brake assembly  2 . Because the frequency response of the brake assembly  2  is lower than the frequency response of autobrake and antiskid valves included in aircraft brake systems, degradation in the brake assembly frequency response degrades frequency response of the overall braking system. 
     It would therefore be desirable to minimize time delays between actuation of brake pistons in order to minimize asymmetric clamping. Many prior art brake assemblies  2  include the flow restrictors  28  in the manifold sections  26  in an attempt to reduce brake wheel vibration or brake whirl. As can be appreciated, the flow restrictors  28  instead serve to further increase the time delay between actuation of brake pistons. Therefore, the flow restrictors  28  make brake clamping even more asymmetric and worsen the problems of brake whirl, uneven stator wear, and degraded frequency response. There is thus an unmet need in the art to minimize asymmetric brake clamping. 
     SUMMARY OF THE INVENTION 
     A brake assembly constructed in accordance with the present invention includes a plurality of brake fluid actuated pistons. The brake assembly includes a brake inlet port for receiving brake fluid from a fluid reservoir. A plurality of cylinders actuates a corresponding plurality of pistons, and includes at least a first cylinder, a second cylinder, and a third cylinder for actuating corresponding pistons. A fluid distribution manifold is connected in fluid flow communication with the brake inlet port and the first, second, and third cylinders. The fluid distribution manifold connects the first, second, and third cylinders in parallel fluid flow. 
     The balanced brake assembly of the present invention actuates brake pistons at substantially the same time and minimizes asymmetric brake clamping. Thus, the problems of brake whirl, uneven stator wear patterns, and degraded brake assembly frequency response are minimized. 
     In one embodiment of the present invention, first, second, and third manifold sections couple the first, second, and third cylinders in parallel fluid communication with the fluid distribution manifold. In a further aspect of the present invention, the first and second manifold sections include first and second flow restrictors. 
     In an alternate embodiment, a brake assembly has a plurality of brake fluid actuated pistons. The brake assembly includes a plurality of cylinders for actuating a corresponding plurality of pistons, including at least a first cylinder, a second cylinder, and a third cylinder for actuating corresponding pistons. A brake inlet port receives brake fluid from a fluid reservoir, and is disposed equidistant from each of the cylinders. The brake assembly includes a plurality of manifolds. Each of the manifolds couples the brake inlet port to an associated cylinder and has an equalized length and an equalized volume such that each of the cylinders actuates its corresponding piston at an equalized time interval. 
     According to a further aspect, the plurality of manifolds is disposed radially from the brake inlet port. 
     In another alternate embodiment, the brake assembly has a plurality of brake fluid actuated pistons. The brake assembly includes a brake inlet port for receiving brake fluid from a fluid reservoir. A fluid distribution manifold is connected in fluid communication with the brake inlet port. A first cylinder is provided for actuating a first brake piston. The first cylinder is connected in fluid communication to a first supply segment of the fluid distribution manifold to define a first fluid path distance from the brake inlet port. A second cylinder is provided for actuating a second brake piston. The second cylinder is connected in fluid communication to a second supply segment of the fluid distribution manifold to define a second fluid path distance from the brake inlet port that is greater than the first fluid path distance. The fluid distribution manifold includes a distribution segment coupling the first and second supply segments of the fluid distribution manifold to equalize the supply of brake fluid to the first and second cylinders. 
     In a further aspect, the distribution segment couples the first and second cylinders in parallel fluid communication. 
     In an even further aspect, the distribution segment couples the first and second cylinders in series fluid communication, and the first and second supply segments couple the first and second cylinders in parallel fluid communication. 
     The present invention provides a method of concurrently actuating a plurality of brake fluid actuated pistons of a brake assembly. The brake assembly has a brake inlet port. The brake assembly includes at least a first cylinder for actuating a first piston, a second cylinder for actuating a second piston, and a third cylinder for actuating a third piston. The first cylinder is coupled in fluid communication with the brake inlet port through a first fluid flow path, the second cylinder is coupled in fluid communication with the brake inlet port through a second fluid flow path, and the third cylinder is coupled in fluid communication with the brake inlet port through a third fluid flow path. Brake fluid is applied to the brake inlet port. Brake fluid is supplied from the brake inlet port to the first brake cylinder for actuating the first brake piston and to the second brake cylinder for actuating the second brake piston. Brake fluid is concurrently supplied from the brake inlet port to the third brake cylinder in parallel fluid communication with the brake fluid supplied to the first and second cylinders, such that the first, second, and third brake pistons actuate at an equalized time interval. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective of a prior art brake assembly with a quarter section cut away; 
     FIG. 2 is a schematic diagram of a typical prior art brake assembly; 
     FIG. 3 is a schematic diagram of a brake assembly according to a first embodiment of the present invention; 
     FIG. 4 is a cross-sectional schematic view of a flow restrictor disposed within a manifold branch that supplies hydraulic brake fluid to a cylinder, an end portion of which is shown, for the embodiment of the present invention shown in FIG. 3; 
     FIG. 5 is a schematic diagram of a brake assembly according to another embodiment of the present invention; and 
     FIGS. 6A-6D are corresponding schematic diagrams of other embodiments of a brake assembly of the present invention, utilizing both parallel and series interconnection of brake cylinders. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3 shows a schematic diagram of a brake assembly  30  according to a first embodiment of the present invention. The brake assembly  30  includes cylinders  32 ,  34 ,  36 ,  38 ,  40 ,  42 , and  44 . The brake assembly  30  includes a brake inlet port  46 . The brake inlet port  46  is suitably located at the top of the brake assembly  30  for purging air bubbles that may be present in brake assembly hydraulic fluid. However, the location of a brake inlet port  46  at other than the top of the brake assembly  30  is also acceptable, as is known in the art. The brake inlet port  46  is coupled to a brake system header (not shown) for receiving brake hydraulic fluid for distribution to the plurality of brake cylinders. The brake assembly  30  also includes pistons (not shown), a pressure plate (not shown), rotor and stator assemblies (not shown) and a torque tube (not shown), configured similarly to those components of conventional brake assemblies, such as the previously described brake assembly  2  shown in FIG.  1 . However, the routing of hydraulic brake fluid to the cylinders of the brake assembly  30  of the present invention is distinct from that previously described. 
     In the brake assembly  30 , a parallel distribution manifold  48  is coupled to the brake inlet port  46  and to each of the cylinders  32 ,  34 ,  36 ,  38 ,  40 ,  42 , and  44 . The parallel distribution manifold  48  may be a substantially circular manifold. In such an embodiment, the shape of the parallel distribution manifold  48  corresponds to the arrangement of the plurality of pistons and cylinders about the brake assembly  30 . Manifold sections  50  couple the parallel distribution manifold  48  to each of the cylinders of the brake assembly  30 . An individual manifold section  50  branches radially off of the parallel distribution manifold  48  to supply hydraulic brake fluid to a corresponding cylinder. It is desirable that the manifold sections  50  be as straight and short as practicable in order to minimize hydraulic losses and reduce time delays in filling cylinders with hydraulic fluid. 
     In a further aspect of the brake assembly  30 , a flow restrictor  52  may be included in each of the manifold sections  50  coupled to corresponding cylinders  32 ,  34 ,  36 ,  40 ,  42 , and  44 , as indicated in FIG.  3 . FIG. 4 shows a pictorial view of one embodiment of a flow restrictor  52  mounted within a manifold section  50 , which supplies fluid to a representative cylinder  53  and piston  55 . As seen in FIG. 4, the flow restrictor  52  may be configured as a restrictor check valve. The flow restrictor  52  includes a cylindrical body  54 , which is preferably located at the top of its associated cylinder and is oriented upwardly from horizontal for purging any air bubbles that may be present in the brake hydraulic fluid. The body  54  of the flow restrictor  52  includes a first orifice  56  in the end of the restrictor  52  that is in closest proximity to the manifold section  50 . The flow restrictor  52  includes a floating restrictor piston  58  that includes a second orifice  60  that is smaller than the first orifice  56 . The flow restrictor  52  also includes a low-force return spring  62  that biases the floating piston  58  into sealing engagement with an outlet port  63  of the body  54 . 
     When a cylinder with one of the flow restrictors  52  fills, the restrictor piston  58  is held in sealing engagement against outlet port  63  by hydraulic pressure from the manifold  48  and return spring force, and fluid flows through the second orifice  60  in restrictor piston  58  to its associated cylinder. When brake application has ended, hydraulic pressure within the cylinder causes the restrictor piston  58  to move out of engagement with the outlet port  63  such that the restrictor check valve  54  is held open until differential pressure between the first orifice  56  and the outlet port  63  is less than the return spring  62  force. This provides an outlet port that is large enough so air can readily escape. 
     When the brakes are applied in an aircraft utilizing the brake assembly  30 , hydraulic fluid is supplied to the brake inlet port  46 , as shown in FIG.  3 . Hydraulic fluid flows from the brake inlet port  46  to the parallel distribution manifold  48 . Hydraulic fluid flows in parallel fluid communication from the parallel distribution manifold  48  through the manifold sections  50  to each of the cylinders  32 ,  34 ,  36 ,  38 ,  40 ,  42 , and  44 . Each of the cylinders of the brake assembly  30  fills at substantially the same time, and the pistons of the brake assembly  30  thus actuate substantially simultaneously. 
     It will be appreciated that actuating the various brake pistons substantially simultaneously represents a significant improvement over brake assemblies previously known in the art, such as that illustrated in FIGS. 1 and 2. In the present invention, any time differences in filling the cylinders of the brake assembly  30  are due to some cylinders being located farther away from the brake inlet port  46  than other cylinders. For example, the cylinders  34  and  42  are coupled to the parallel distribution manifold  48  slightly farther away from the brake inlet port  46  than are the cylinders  32  and  44 . Likewise, the cylinders  36  and  40  are coupled to the parallel distribution manifold  48  downstream of the cylinders  34  and  42 . Finally, the cylinder  38  is coupled to the parallel distribution manifold  48  downstream of the cylinders  36  and  40 . The cylinders  32  and  44  may fill with hydraulic fluid shortly before the cylinders  34  and  42  fill. Likewise, the cylinders  36  and  40  may fill just after the cylinders  34  and  42  fill. Finally, the cylinder  38  may fill shortly after the cylinders  36  and  40  fill. However, it will be appreciated that any such time delay is negligible compared to the substantial time delays between piston actuation in series-configured brake assemblies previously known in the art. 
     The use of flow restrictors  52 , such as those illustrated in FIGS. 3 and 4, further minimizes any time delay between the filling of each of the cylinders. As described above, the cylinder  38  fills last because it is farthest from the brake inlet port  46 . Therefore, further restricting the flow of hydraulic fluid to the cylinder  38  by including a flow restrictor in the manifold section  50  coupled to the cylinder  38  is not desirable. The flow restrictors  52  associated with the cylinders  32  and  44  have orifices of a first predetermined diameter to insert a first time delay such that the cylinders  32  and  44  fill at substantially the same time that the cylinder  38  fills. Likewise, the flow restrictors  52  associated with the cylinders  34  and  42  have orifices of a second predetermined diameter, greater than the first predetermined diameter, to insert a second time delay, shorter than the first time delay, such that the cylinders  34  and  42  fill at substantially the same time as the cylinder  38 . Finally, the flow restrictors  52  associated with the cylinders  36  and  40  have a still greater third predetermined diameter to insert a third time delay, shorter than the second time delay, such that the cylinders  36  and  40  fill at substantially the same time as the cylinder  38 . Thus, it is preferred that flow restrictors  52  be included in the brake assembly  30 . However, a brake assembly  30  that does not include flow restrictors  52  presents a major improvement in reducing cylinder actuation time delays. 
     FIG. 5 shows a schematic diagram of a second embodiment of a brake assembly  70  of the present invention. The brake assembly  70  includes cylinders  72 ,  74 ,  76 ,  78 ,  80 ,  82 , and  84 . Each of the cylinders shown in FIG. 5 is associated with a brake piston (not shown) for pressing against a pressure plate (not shown) and clamping brake rotor and stator assemblies (not shown) against a torque tube (not shown) in a known manner. The plurality of cylinders and associated pistons are arranged radially in a substantially circular manner about the brake assembly  70 , as is known. 
     The brake assembly  70  includes a brake inlet port  86 . In this embodiment of the present invention, the brake inlet port  86  is not located at the top of brake assembly  70 . Instead, the brake inlet port  86  is located at a central location within the circular arrangement of cylinders so that the brake inlet port  86  is substantially equidistant from the cylinders. The brake inlet port  86  is coupled to a brake system (not shown) for receiving brake hydraulic fluid for distribution to the plurality of brake cylinders. 
     Manifold sections  88  are provided for coupling the brake inlet port  86  to each of the cylinders. Each manifold section  88  is substantially the same length and has substantially the same volume. Each manifold section  88  should be as short and straight as practicable to minimize hydraulic losses and reduce time delays in filling the cylinders with hydraulic fluid. As can be seen in FIG. 5, the manifold sections  88  extend radially outward from the brake inlet port  86  to the plurality of cylinders. 
     The brake assembly  70  achieves substantially coincident piston application as follows. When the brakes are applied, hydraulic fluid is supplied to the brake inlet port  86 . Hydraulic fluid flows from the brake inlet port  86  through the manifold sections  88  to the plurality of cylinders. Because the manifold sections  88  are substantially the same size, hydraulic fluid is supplied to each of the cylinders at substantially the same time after the hydraulic fluid is supplied to the brake inlet port  86 . 
     FIGS. 6A-6D are schematic diagrams of other embodiments of a brake assembly  90  according to the present invention; each of which uses both parallel and series fluid supply to brake cylinders. In each instance, a brake assembly  90  has a plurality of cylinders  92 ,  94 ,  96 ,  98 ,  100 ,  102 , and  104 . Each of the cylinders is associated with a brake piston (not shown) for pressing against a pressure plate (not shown) to clamp brake rotor and stator assemblies (not shown) against a torque tube (not shown) in a known manner. As is known in the art, the plurality of cylinders and pistons are arranged radially in a circular manner about the brake assembly  90  for providing even clamping pressure. The cylinders  92  and  104  are preferably located near a top region of the brake assembly  90  that is near a brake inlet port  106 , and the cylinder  98  is preferably located near a bottom region of the brake assembly  90  that is farther away from the brake inlet port  106 . The brake assembly  90  includes manifold sections  108  extending between adjacent cylinders. The brake inlet port is suitably located at the top region of the brake assembly  90 , as is well known in the art, but the location of the brake inlet port  106  may be anywhere on the brake assembly  90 . The manifold sections  108  couple the cylinders  92 ,  94 ,  96 ,  98 ,  100 ,  102 , and  104  in series fluid communication with the brake inlet port  106 , as is also known in the art. 
     However, with reference to FIG. 6A, in accordance with the present invention a parallel distribution manifold section  110  also hydraulically couples the lowermost cylinder  98  to the brake inlet port  106 . The cylinders are thus coupled in parallel fluid communication. 
     The embodiment of the present invention shown in FIG. 6A reduces asymmetric clamping of brake assemblies known in the prior art by incorporating a parallel fluid flow path into a brake assembly having a series flow path. The brake assembly  90  operates as follows. When the brakes are applied, hydraulic fluid is initially supplied to the brake inlet port  106 . Hydraulic fluid flows from the brake inlet port  106  through the manifold sections  108  to the cylinders  92  and  104 , as is well known in the art. In accordance with the present invention, hydraulic fluid also flows through the parallel distribution manifold section  110  to the cylinder  98 . The cylinders  92 ,  104 , and  98  therefore fill with hydraulic fluid at substantially the same time. Therefore, the pistons (not shown) associated with the cylinders  92  and  104  located near the top region of the brake assembly  90  actuate substantially coincident with the piston (not shown) associated with the cylinder  98  located near the bottom region of the brake assembly  90 . It has been shown during testing that pressure equalization of cylinders in response to a step input occurred in 25% less time than the pressure equalization time for known brakes having only a series-connected manifold. This represents a major improvement over known brake assemblies that fill cylinders and actuate pistons solely in series. It will be appreciated that the brake assemblies  30  and  70  described above will provide an even more pronounced improvement over known brake assemblies that fill cylinders and actuate pistons solely in series. 
     The brake assembly  90  further reduces asymmetric brake clamping over brake assemblies known in the art. The cylinders  94  and  102  fill with hydraulic fluid after the cylinders  92  and  104  fill with hydraulic fluid, as is known. However, the cylinders  96  and  100  fill with hydraulic fluid after the cylinder  98  fills with hydraulic fluid. Because the cylinder  98  fills with hydraulic fluid at substantially the same time as the cylinders  92  and  104  fill with hydraulic fluid, the cylinders  94  and  102  fill at substantially the same time as the cylinders  96  and  100 . Thus, the brake assembly  90  greatly reduces asymmetry in brake clamping over asymmetric brake clamping inherent in brake assemblies known in the prior art. 
     In the arrangement shown in FIG. 6A, the preferred routing for the parallel distribution manifold section  110  is from the inlet port  106  to an oppositely disposed brake cylinder  98 . However, the brake construction may lend itself to a different routing for the parallel distribution manifold section while still achieving advantages of more nearly coincident and balanced brake application. For example, as represented by broken line  112  in FIG. 6A, the routing may be from the inlet port  106  to a series manifold segment  108 , preferably at the opposite side of the brake assembly from the inlet port. Another possibility, represented by line  114  in FIG. 6A, is routing the parallel distribution manifold section from a series manifold segment  108  near the inlet port  106  to an oppositely disposed brake cylinder  98 ; or, as represented by line  116  in FIG. 6A, from a series segment  108  near the inlet port  106  to a generally oppositely disposed segment  108 . Depending on the number and positions of the brake cylinders, these routings may achieve improved results as compared to a system having only series connected cylinders or, for example, a system having some parallel distribution but with fluid paths of unequal lengths. 
     Similarly, with reference to FIG. 6B, the parallel distribution manifold section  110 ′ can have a first segment  118  extending from the inlet port  106  which branches to other segments  120  and  122  to distribute hydraulic fluid to series manifold sections  108  at generally opposite sides of the brake assembly, with or without an additional segment  124  extending to cylinder  98  or a segment  108  at the opposite side of the assembly from inlet port  106 . As seen in FIG. 6C, the branches  120 ,  122  from the segment  118  may extend directly to brake cylinders at opposite sides of the brake assembly, such as cylinders  94  and  102 , with segment  124  extending to cylinder  98  at the bottom. For the seven cylinder arrangement illustrated, it should be noted that three of the cylinders ( 94 ,  98 , and  102 ) are fed directly from the inlet by way of the parallel manifold segments, in addition to being fed by the series manifold sections  108  from adjacent cylinders, and two cylinders ( 92  and  104 ) are fed directly from the inlet port by way of the series manifold sections  108  extending from the inlet port, as well as by the series manifold sections  108  from cylinders  94  and  102  which are fed by the branches  120 ,  122 . Two of the cylinders ( 96  and  100 ) are fed by series manifold sections  108  from adjacent cylinders, but each of the adjacent series connected cylinders is fed directly from the inlet port. Thus, a more nearly coincident application of braking force is achieved. 
     Another arrangement is illustrated in FIG. 6D where the segments  126 ,  128 ,  130 , and  132  extend from a series manifold section  108  close to the inlet  106  to other sections  108  located approximately equidistant for a uniform and nearly coincident application of braking force. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. For example, a parallel distribution manifold may be incorporated as a retrofit into a conventional brake assembly having cylinders connected in series, rather than filling sequentially through series connections. Accordingly, the invention is not limited except as by the appended claims.