Patent Publication Number: US-2005116535-A1

Title: Fluid accumulator and brake bias system incorporating fluid accumulator

Description:
RELATED INVENTION  
      The present invention claims priority to U.S. Provisional Patent Application Ser. No. 60/526,167 filed Dec. 1, 2003. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to brake systems. More particularly, the invention relates to a brake system including a fluid accumulator and fluid accumulators for brake systems.  
     BACKGROUND OF THE INVENTION  
      Hydraulic brake systems in high performance or race vehicles often utilize dual master cylinders or a production-style tandem master cylinder. Tandem master cylinders use one cylinder bore with two pressure ports and pistons. They are designed so that if pressure is lost in either port, the other port maintains its pressure. Dual master cylinder set-ups completely isolate the two hydraulic systems. One system connects to the front wheels, while the other connects to the rear wheels.  
      Dual master cylinder systems allow braking force to be varied between the front and rear wheels. Selection of the applied braking force in such systems, including the braking force applied by the front as compared to the rear wheels (which may be referred to as “brake bias”), can be very important. In a racing environment, it is particularly important to control braking to maximize braking effect, but prevent wheel lock-up.  
      Among other things, as a car decelerates or enters a corner, weight is transferred from the rear to the front tires. The exact amount of weight shift depends on the speed of the car, track, corner, and how much brake is applied upon entry. This weight transfer reduces the amount of braking force the rear tires can produce.  
      The driver maybe permitted to adjust the brake system before, after or during a race, or practice sessions, to change the precise adjustment of the front to rear bias setting, allowing for changing track conditions or to optimize brake performance. The correct front brake bias setting depends on the driver&#39;s driving style and how hard or how much the brakes are used when entering a corner. Since this will vary with each corner at each track, it is important to find the right balance as not to upset the chassis when the brakes are applied while cornering.  
      Unfortunately, adjustments in the brake bias may actually contribute to brake lock. For example, in order to counter the loss in braking force at the rear wheels associated with weight shift, the applied braking force to the rear wheels is generally increased. When the brakes are applied suddenly, however, the rear brake bias often results in excessive braking force, causing rear wheel lock-up and associated loss of traction and control.  
      Some attempts have been made to address this lock-up issue, but these attempts have been unsuccessful in resolving the problem. Commonly, proportioning valves are utilized in these types of brake systems. These proportioning valves serve to reduce line pressure downstream of the valve relative to the pressure upstream of the valve, generally in the form of a percentage pressure reduction. While these valves can be relatively effective in preventing brake lock when brakes are applied slowly, they are not effective in preventing brake lock when brakes are applied quickly with high force. In those situations, a very high line pressure is generated by the quick, hard application of the brakes. The proportioning valve reduces the downstream line pressure, but that reduction, being only a percentage reduction, is relatively small compared to the total line pressure, such that the downstream pressure is still very high, causing the brakes to lock.  
      An improved braking system which overcomes these disadvantages is desired.  
     SUMMARY OF THE INVENTION  
      The present invention is a fluid accumulator for a brake system and a brake system including at least one fluid accumulator.  
      A vehicle braking system comprises a first master cylinder and at least one first fluid line leading from that first master cylinder to at least one first fluid-actuated braking mechanism. The braking system includes a second master cylinder and at least one second fluid line leading from that second master cylinder to at least one second fluid-actuated braking mechanism.  
      In one embodiment, the first master cylinder provides fluid to braking mechanisms associated with the front wheels of a vehicle. The second master cylinder provides fluid to braking mechanisms associated with the rear wheels of the vehicle.  
      The braking system includes an actuating member for actuating the first and second master cylinders to cause the first and second master cylinders to dispense fluid into the at least one first and at least one second fluid lines, respectively. Preferably, the position of the actuating member is adjustable so that the amount of fluid dispensed by the first and second master cylinders relative to one another may be adjusted.  
      In one embodiment, the actuating member includes a brake pedal linked to a balance bar, the balance bar configured to activate the first and second master cylinders via a pair of links or arms. The position of the balance bar may be changed so that the force applied to each link via the brake pedal, and thus the master cylinders, varies.  
      The brake system further includes at least one fluid accumulator associated with the at least one second fluid line, the accumulator configured to selectively accumulate fluid which is dispensed into the at least one second fluid line by the second master cylinder.  
      In one embodiment, the brake system is associated with a race car. The balance bar is utilized to bias the braking force to the rear wheels. The accumulator is associated with the fluid line leading to the rear wheel braking mechanisms for accumulating brake fluid to prevent rear wheel lock-up.  
      Various embodiments of the invention comprise a fluid accumulator, such as for use with the brake system of the invention.  
      In one embodiment, the fluid accumulator includes a housing defining an interior space. A body, preferably in the form of a piston, is movably mounted in the interior space and cooperates with the housing to define a fluid chamber. The accumulator includes at least one port through the housing leading to the fluid chamber through which fluid may pass to and from a fluid line or other fluid source.  
      At least one member generates a biasing force which is applied to the body, causing the body to move to a position wherein the size of said fluid chamber is reduced. In one embodiment, this member comprises a spring mounted in the housing which engages the piston.  
      Preferably, the accumulator includes a means for adjusting the biasing force generated by the bias generating member. In one embodiment, one end of the spring is mounted to a spring mount. The spring mount is movable with a rod which is connected to the housing. Movement of the rod changes the position of the spring mount, and thus the position of one end of the spring relative to the other end of the spring which engages the piston, thus changing the bias force.  
      Various objects, features, and advantages of the present invention over the prior art will become apparent from the detailed description of the drawings which follows, when considered with the attached figures.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of a fluid accumulator for a brake system in accordance with one embodiment of the invention;  
       FIG. 2  is a cross-sectional view of a fluid accumulator for a brake system in accordance with another embodiment of the invention; and  
       FIG. 3  schematically illustrates a balance bar brake bias system having a fluid accumulator in accordance with an embodiment of the invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The invention comprises a fluid accumulator for a hydraulic braking system and a brake system including an accumulator. In the following description, numerous specific details are set forth in order to provide a more thorough description of the present invention. It will be apparent, however, to one skilled in the art, that the present invention maybe practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention.  
      In general, the invention comprises a fluid accumulator for a hydraulic brake system. Another embodiment of the invention comprises an adjustable hydraulic brake system including a fluid accumulator.  
      The fluid accumulator of the invention has particular applicability to brake systems utilized on vehicles, and most preferably, vehicles having both at least one front and rear wheel. Such vehicles include cars and trucks, including passenger and racing vehicles, as well as karts/go-karts, motorcycles, airplanes, trains and other moving bodies.  
      The accumulator of the invention is useful with brake systems in which braking force is generated by moving two bodies into contact with one another. In one embodiment, movement is effectuated with a hydraulic force, such as applied fluid.  
       FIG. 1  illustrates one embodiment of a fluid accumulator  20  in accordance with the present invention. The accumulator  20  includes a housing  22  or body. In one embodiment, the housing  22  is generally cylindrical in shape and has a first end  24  and a second end  26 . The first end  24  is generally open and leads to an interior space  28  defined by the housing  22 . As illustrated, the interior space  28  is also generally cylindrical in shape, thus having a circular cross-sectional shape.  
      Preferably, an end cap  30  selectively closes the first end  24  of the housing  22 . In one embodiment, the end cap  30  has threads on at least a portion of the exterior thereof for engaging mating threads provided on the housing  22 . In this manner, the end cap  30  maybe connected and disconnected from the housing  22 , thus providing access to the interior  28  of the housing  22 , such as during assembly.  
      In one embodiment, at least one seal  32  is provided between the end cap  30  and the housing  22  to provide a fluid seal. When the housing  22  is cylindrical in shape, the seal  32  maybe circular in shape. The seal  32  may be, for example, an “O”-ring or the like.  
      A body is movably mounted in the housing  22 . In a preferred embodiment, the body is a piston  34  mounted in the interior  28  of the housing  22 . As illustrated, the piston  34  comprises a generally open cylindrical member having an internal dividing wall or member  36 . Preferably, the piston  34  is sized so that its outer surface is closely spaced to the inside of the housing  22 , but yet still permits the piston  34  to move inside of the housing  22  relative to the housing  22 .  
      As illustrated, the dividing wall  36  of the piston  34  effectively divides the interior  28  of the housing  22  into a first chamber  31  and a second chamber  32 . The first chamber  31  is located between the dividing wall  36  of the piston  34  and the second end  26  of the housing  22 . The second chamber  32  is located between the dividing wall  36  of the piston  34  and the end cap  30 .  
      In a preferred embodiment, these two chambers  31 , 32  are in fluid isolation. At least one seal  38  maybe provided between the housing  22  and the piston  34  for this purpose. As illustrated, the seal  38  is an O-ring which is mounted to the housing  22 , such as in a channel formed in the housing. Again, when the housing  22  is cylindrical in shape, the seal  38  may be circular in shape.  
      Means are preferably provided for biasing the piston  34  in the direction of the second end  26  of the housing  22 . In one embodiment, as illustrated, this means comprises a spring  40 . In a preferred embodiment, the spring  40  is a conical coil spring.  
      In one embodiment, a spring mount  42  is connected to the end cap  30 . In particular, as illustrated, the end cap  30  has a first end which is located inside of the housing  22  when it is connected to the housing  22 . That end includes a mount  44  comprising a generally cylindrical open wall. The spring mount  42  comprises a generally cylindrical body having a first end which engages the mount  44 . Of course, the mount  42  might also be integrally formed with the cap  30 .  
      As illustrated, a second end of the mount  44  is configured to accept one end of the spring  40 . As illustrated, a first end of the spring  40  may seat on a cylindrical extension of the mount  44 . The second end of the spring  40  preferably engages the piston  34 . As illustrated, the second end of the spring  40  engages the dividing wall  36  of the piston. In this configuration, the spring  40  biases or presses the piston  34  towards the second end  26  of the housing  22 .  
      The housing  22  includes a port or passage  46  leading to the first chamber  31 . In one embodiment, the passage  46  is defined through the second end  26  of the housing  22 . As illustrated, an interior of the passage  46  maybe threaded for accepting a fitting. Preferably, the fitting is configured to connected to a fluid line of a hydraulic brake system.  
      In one embodiment, the housing  22  also includes a bleed port or passage  48 . Preferably, the bleed passage  48  also leads to the first chamber  31 . As illustrated, the bleed passage  48  is defined through the second end  26  of the housing  22 . The bleed passage  48  maybe similarly threaded to engage a bleed fitting.  
      Operation of this embodiment accumulator  20  is as follows. The accumulator  20  is located along a fluid path so that fluid may flow into and out of the first chamber  31  through the fluid port  46 . In one embodiment, a “T” fitting maybe located along a fluid line, with one end of the “T” connected to the fluid port  46 .  
      Once connected, the first chamber  31  is preferably filled with fluid. Air within the chamber  31  is preferably bled out of the chamber via the bleed port  48 , such as by opening a bleed fitting connected thereto.  
      Under normal operating pressures, the piston  34  is biased towards the second end  26  of the housing  20 , reducing the size of the first chamber  31 . In response to the introduction of additional fluid into the brake system, such as via a master cylinder, and the associated high fluid pressure resulting therefrom, fluid flows into the first chamber  31 . In particular, the pressure of the fluid causes the piston  34  to move against the spring  40  towards the first end  24  of the housing  22 . As this occurs, the size of the first chamber  31  increases, allowing fluid to accumulate in the first chamber  31 . When the fluid pressure in the line decreases, the piston  34  forces fluid back out of the first chamber  31  as the size of the chamber is reduced when the piston  34  is biased back towards the second end  26  of the housing  22 . Movement of the piston  34  towards the second end  26  of the housing  22  is limited by contact of the piston  34  with the housing  22 . Movement of the piston  34  towards the first end  24  of the housing  22  maybe limited in high pressure situations by contact with the spring mount  42 , which also serves as a piston stop.  
       FIG. 2  illustrates another embodiment of a fluid accumulator  120  in accordance with the invention. Once again, the accumulator  120  includes a housing  122  having a first end  124 , second end  126  and interior  128 . An end cap  130  is located at the first end  124  of the housing  122 , the end cap  130  sealed to the housing  122  with one or more seals  132 .  
      A piston  134  or other body is again movably located in the housing  122 . The piston  134  again includes a divider portion  136 . One or more seals  138  preferably seal the piston  134  and the housing  122 , thus dividing the interior of the housing into a first chamber  131  and a second chamber  132 . First and second ports  146 , 148  or passages are again provided through the housing  122  to the second chamber  132 . These ports  146 , 148  have the same purpose as the ports  46 , 48  described above.  
      Once again, means are preferably provided for biasing the piston  134  towards the second end  126  of the housing  122 . In one embodiment, this means again comprises a spring  140 .  
      Preferably, in this embodiment, means are provided for selecting or adjusting the biasing force which is applied to the piston  134 . In the embodiment illustrated, this means comprises a means for changing the position of a spring mount.  
      As illustrated, the end cap  130  defines a passage  150  there through. A rod  152  extends through the passage  150 . In a preferred embodiment, at least a portion of the passage  150  is threaded for engagement with threads on the exterior of the rod  152 . In this manner, the relative position of the rod  152  to the end cap  130  maybe adjusted. In one embodiment, to maintain a fluid seal, at least one seal  156  may be located between the rod  152  and end cap  130 .  
      As illustrated, the rod  152  has a generally circular cross-sectional shape, as does the passage  150 . The passage  150  and rod  152  preferably extend along a centerline of the housing  122  extending through the first and second ends  124 , 126  of the housing  122 .  
      The rod  152  has a first end and a second end. In one embodiment, the first end of the rod  152  defines a spring mount  154 . A head or knob  158  is preferably located at the second end of the rod  152 . In one embodiment, the knob  158  maybe detached from the rod  152 . As illustrated, the knob  158  defines a passage  160  for accepting the second end of the rod  152 . A set screw  162  preferably extends through a counter-passage  164  in the knob  158  into selective engagement with the rod  152 . When tightened, the set screw  152  secures the knob  158  to the rod  152 .  
      The knob  158  maybe knurled on its exterior surface for gripping by a user. The set screw  162  maybe configured to extend from the knob  158  to provide a visual indicator of the relative rotational position of the rod  152  to the housing  122 . Other such indicators might be provided, however, such as surface etchings or markings provided on the knob  158  and/or housing  122 .  
      Operation of this embodiment accumulator  120  is similar to that illustrated in  FIG. 1  and described above. In this embodiment, however, the force applied by the spring  140  to the piston  134  may be varied. In particular, by moving the rod  152  outwardly of the end cap  130  (such as by rotating it in a counter-clockwise direction), the spring mount  154  is moved towards the first end  124  of the housing  122 . In this position, the distance between the mount  154  and the piston  134  is maximized, and the spring  140  is relatively uncompressed, lessening the force it applies to the piston  134 .  
      On the other hand, by moving the rod  152  inwardly relative to the end cap  130 , the spring mount  154  moves and compresses the spring  140 . This causes the spring  140  to generate a higher biasing force as applied to the piston  134 .  
      By changing the bias force which is generated by the spring  134 , the fluid pressure which is necessary to move the piston  134  and thus cause fluid accumulation, is changed. As described below, this has numerous advantages.  
      The components of the accumulators of the invention maybe constructed of a wide variety of materials. In one embodiment, the housing, end cap, piston and knob maybe constructed of aluminum, while the set screw, rod and spring maybe constructed of steel. Seals maybe constructed of a variety of materials, including Buna N elastomer material.  
      One embodiment of the invention is a brake or braking system including a fluid accumulator. Referring to  FIG. 3 , in a preferred embodiment, the brake system  220  includes a first brake master cylinder  222  and a second brake master cylinder  224 . In one embodiment, the first master cylinder  222  provides fluid to one or more front wheel brake mechanisms of a vehicle, and the second master cylinder  224  provides fluid to one or more rear wheel brake mechanisms.  
      The system  220  includes means for controlling or adjusting the actuation of the first and second master cylinders  222 , 224  relative to one another. In one embodiment, this means includes a threaded adjustable brake bias rod or bar  226 . As illustrated, the brake bias rod  226  actuates the first or front and second or rear brake master cylinders  222 , 224 .  
      In a preferred embodiment, the brake system  220  includes a brake pedal  232 . The brake pedal  232  actuates the brake bias rod  226  via a connecting arm or lever. In turn, the brake bias rod  226  acts upon the front and rear brake master cylinders  222 , 224  via first and second rods, levers, arms or other connections  223 , 225  at first and second connections  227 , 229 .  
      A point of activation  234  of the brake bias rod  226  by the brake pedal  232  is preferably adjustable. In particular, the location of the point of activation  234  can be changed via rotation of the brake bias rod with a cable  228 , as actuated by a knob  230 . Preferably, the knob  230  is located inside a driver compartment of the vehicle, and thus is accessible to the driver. Other means to change the location of the point of activation  234  may also be utilized.  
      When the knob  230  is turned by the driver, the driver changes the brake bias between the front and rear brakes of the race car. In particular, as the knob  230  is turned, the bias rod  226  rotates, changing its position. As the position of the brake bias rod  226  changes, so does the point of activation  234 . As the point of activation  234  changes, so does the length of the brake bias bar  226  on each side of the point of activation. In particular, as illustrated, the brake bias bar  226  has a first portion  236  located between the point of activation  234  and the front brake master cylinder  222 , and a second portion  238  which is located between the point of activation  234  and the rear brake master cylinder  224 .  
      It will be appreciated that if the length of both portions  236 , 238  of the brake bias rod  226  is the same, then the amount of force which is applied to the front and rear brake master cylinders  222 , 224  via the brake pedal  232 , is equal. If the length of the first portion  236  is greater than the length of the second portion  238 , then there is a decreased mechanical advantage and a lesser force applied to the front brake master cylinder  222  than the rear brake master cylinder  224 . In this arrangement, the hydraulic pressure used to actuate the front brakes is less than that used to actuate the rear brakes. Alternatively, if the length of the second portion  238  is greater than the length of the first portion  236 , then there is a decreased mechanical advantage and a lesser force applied to the rear brake master cylinder  224 . In this arrangement, the hydraulic pressure used to actuate the rear brakes is less than that used to actuate the front brakes.  
      The front brake master cylinder  222  is connected by at least one fluid line  240  to a right front brake caliper  242  and a left front brake caliper  244 . These calipers  242 , 244  are preferably associated with braking mechanisms for the right and left front wheels of the vehicle.  
      Similarly, the rear brake master cylinder  224  is connected by at least one fluid line  246  to a right rear brake caliper  248  and a left rear brake caliper  250 . These calipers  248 , 250  are preferably associated with braking mechanisms for the right and left rear wheels of the vehicle.  
      As indicated, a wheel braking mechanism is preferably associated with one or more of the wheels of the vehicle. When the braking mechanism is activated, such as via hydraulic pressure transitted by fluid through the brake lines, the braking mechanism is configured to impede the rotation of the wheel. In one embodiment, each wheel braking mechanism is a disc-type braking system which includes a caliper, a rotor and at least one pad. The pad is mounted to the caliper. The pad is mounted for movement towards and away from the rotor in response to hydraulic pressure. When the pad moves towards the rotor under applied hydraulic pressure, the pad presses upon the rotor. The rotor is preferably mounted to the wheel or a support for the wheel, such that braking of the rotor results in braking of the wheel.  
      It will be appreciated that other means or configurations may be provided for selectively controlling the actuation of the first and second master cylinders relative to one another. For example, in a “drive by wire” configuration, two solenoids might move master cylinder actuating levers in response to the actuation of the brake pedal. The amount of actuation of the solenoids might be controlled differently, so that the amount of braking force generated at the front and rear portions of the braking system varies.  
      The brake system  220  includes a fluid accumulator  252 . Preferably, the fluid accumulator  252  comprises accumulator  20  illustrated in  FIG. 1  or accumulator  120  illustrated in  FIG. 2 , both described above. The accumulator may be of other types, however.  
      In a preferred embodiment, the accumulator  252  is associated with the rear wheel braking system(s). As illustrated, the accumulator  252  is located between the rear wheel master cylinder  224  and the rear wheel braking mechanisms  248 , 250 . Preferably, the accumulator  252  is located along the fluid line  246  or path through which fluid is provided from the rear wheel master cylinder  224  and the rear wheel braking mechanisms.  
      As indicated above, in one embodiment, a “T” fitting maybe provided along that line. One port of the “T” fitting maybe connected to the fluid port of the fluid accumulator  252 , permitting fluid to flow into and out of the accumulator.  
      As described, the front and rear wheel braking mechanism may include calipers. These calipers maybe configured to move brake pads into and out of engagement with a rotor or “disc” located at each wheel. The brake system, however, may include “drum” type braking mechanisms, rather than “disc” 0  type braking mechanisms.  
      During normal operation of the brake system  220 , fluid pressure within the system, including fluid line  246 , is relatively low. When the brakes are applied very quickly, as when a driver applies the brakes when entering a turn of a race-course, fluid pressure in the system increases via actuation of the front and rear master cylinders  222 , 224 . The fluid pressure increases due to the front and rear master cylinders  222 , 224  pushing fluid into the fluid lines  240 , 246 . Because the volume of fluid is increased within the otherwise fixed volume of the lines  240 , 246  and associated front and rear brake mechanisms, the fluid pressure increases.  
      In accordance with the invention, when the fluid pressure in the fluid line  246  increases, the fluid pressure causes the accumulator to accumulate fluid. As indicated above, in the embodiment accumulators  20 , 120  of the invention, the increase in fluid pressure causes the piston  34 , 134  of the accumulators  20 , 120  to move, enlarging a chamber within the accumulator, thus providing space for accommodating fluid.  
      The increased fluid pressure in the lines  240 , 246  is transmitted to the front and rear brake mechanisms  242 , 244 , 248 , 250 , which affects actuation of those mechanisms. In accordance with the invention, however, the accumulator  252  temporarily accumulates some of the fluid which is transmitted into the system, thus preventing the fluid pressure from rising to such an extent that the braking force becomes excessive and causes the braking mechanisms to lock the wheels.  
      The brake system  220  has particular utility in racing vehicles. Without the accumulator of the invention, such a system may have to be adjusted with maximum front brake bias in order to prevent rear wheel lock-up during braking. With the inclusion of the accumulator as described, the system  220  can be configured with a rear brake bias. For example, the system  220  can be configured with more rear brake bias, thus permitting the rear wheels to provide significantly more braking force to the vehicle, without the rear wheels locking during braking.  
      In a preferred embodiment, the brake system  220  includes an accumulator such as illustrated in  FIG. 2  and described above. In that configuration, the user may adjust the operation of the accumulator.  
      The adjustable accumulator  120  has many advantages over other accumulators of the prior art. As described, in an adjustable brake system, the amount of brake bias maybe frequently adjusted based upon a number of conditions, including track conditions, size of brake calipers and other factors. In that situation, the accumulator  120  of the invention can be adjusted to match changes in the brake system settings. For example, if the brake bias is changed to increase rear braking force, the accumulator  120  may be adjusted to accumulate more fluid to prevent rear brake lock when the brakes are applied. In the case where fixed or “non-variable” accumulators are utilized, this eliminates the need to replace the accumulator each time the brake system is adjusted.  
      The brake system including an accumulator in accordance with the present overcomes the problem of brake lock which is not effectively addressed by proportioning valves. In accordance with the present invention, the accumulator of the brake system is effective in temporarily accumulating an excessive volume of brake fluid in the brake system when brakes are applied quickly with force. Control over the volume of brake fluid in the brake line addresses the underlying cause of pressure spikes, and thus brake lock. This is a significant advantage over proportioning valves, which only reduce the size of such spikes, still permitting such spikes, and associated brake lock, to occur.  
      The braking system of the invention may vary from that described. For example, the mechanism for controlling the amount of pressure applied/generated by the master cylinders may vary, and need not comprise the brake bias rod configuration specifically described. In some situations, it may be found beneficial for the brake system to include a fluid accumulator associated with the front wheel braking system (such as along line  240  of the system illustrated in  FIG. 3 ), or a system where an accumulator is associated with both the front and rear wheel braking mechanisms.  
      Various alternate configurations of the accumulators are contemplated and, as described below, a variety of different types of accumulators may be utilized with the braking system of the invention, other than those specifically described above. In one embodiment, the accumulator which is utilized with the braking system may be of other configurations.  
      The means for biasing the piston of the accumulator maybe other than a spring. For example, such biasing maybe provided by a resilient closed-cell sponge, resilient heavy-walled elastomeric bag (such as pre-charged with a pressurized gas) and/or a solid elastomeric member. In one or more embodiments, the piston and biasing mechanism may be unitary, with the piston comprising a resilient member. For example, the piston may simply comprise a resilient elastomeric body which is positioned in the interior of the housing.  
      The accumulator may have other porting arrangements. For example, one port may lead into the accumulator and one port may lead out of the accumulator.  
      Other means may be provided for selectively changing the bias of the piston or other member located inside of the accumulator. For example, in an embodiment where the piston or biasing member associated with the piston comprises an elastomeric bag, means maybe provided for changing the charging pressure of the bag. In an embodiment where the piston or the biasing member associated with the piston comprises a resilient elastomeric member, the member maybe formed as rings, the number of which may be changed to change the total biasing force.  
      It is noted that the embodiment accumulator  20  illustrated in  FIG. 1  maybe configured to be adjustable. For example, shims maybe placed between the spring  40  and the dividing wall  36  or between the spring  40  and the spring mount  42  as a means for selecting or adjusting the biasing force which is applied to the piston  34 .  
      The configuration of the accumulators may vary. For example, the piston might be a closed head member, rather than an open cylinder with a dividing wall. The housing and associated components might vary in shape, such as by being oval in configuration.  
      In one embodiment, a vent maybe provided from the second chamber  32 , 132  to the exterior of the housing to permit air behind the piston  34 , 134  to exit the housing when the piston is compressed rearwardly, thus reducing air pressure behind the piston and associated counter-acting force. In another embodiment, that chamber might be evacuated of air.  
      It will be appreciated that while the accumulators of the invention have particular utility to the brake system described and illustrated, the accumulators of the invention maybe used with other brake systems. Such systems may comprise brake systems which do not include a balance bar or multiple master cylinders.  
      It will be understood that the above described arrangements of apparatus and the method there from are merely illustrative of applications of the principles of this invention and many other embodiments and modifications maybe made without departing from the spirit and scope of the invention as defined in the claims.