Low drag failsafe brake

A brake adapted to be rotationally coupled with a shaft and in communication with a fluid source and a negative pressure source, the brake including a housing defining a chamber therein. A disc assembly is positioned within the chamber and includes a plurality of stationary discs carried by the housing and a plurality of rotating discs carried by the shaft. The rotatable discs and stationary discs are positioned for engagement. A piston is movable to cause the stationary discs to engage the rotatable discs. A first fluid input is in communication with the fluid source, providing a constant supply of fluid to the chamber. A second fluid input is in communication with the fluid source, providing fluid when the stationary and rotating discs are caused to engage.

TECHNICAL FIELD

This invention relates to a brake provided with coolant. More specifically, this invention relates to such a brake wherein the coolant is provided upon actuation of the brake.

BACKGROUND ART

Many forms of heavy industrial equipment require disc braking systems which, during operation, generate a significant amount of heat. Further, such systems often require a steady supply of lubrication to ensure efficient operation and long life. One method for dispersing the generated heat and providing lubrication is by supplying fluid directly to the disc assembly within the brake housing. The fluid used in such brakes provides both the cooling and lubricating functions and is often an oil based product. Such brakes are often referred to as “wet” brakes because of the constant supply of fluid to the interior chamber of the brake.

While the continuous provision of fluids to the brake chamber is effective in cooling and lubricating the brake, other problems could exist in such a design. Specifically, fluid accumulates and pools within the brake and the rotating discs experience significant drag as they rotate therethrough. This drag creates a measurable torque and effects drive-train efficiency.

In view of these problems, it is evident that the need exists for a brake which provides sufficient cooling and lubrication but reduces the drag upon the disc assembly.

DISCLOSURE OF THE INVENTION

It is thus an object of the present invention to provide a brake for machinery or the like, which provides coolant to the disc assembly.

It is a further object of the present invention to provide a brake, as above, which provides additional coolant upon actuation of the brake.

These and other objects of the present invention, as well as the advantages thereof over existing prior art forms, which will become apparent from the description to follow, are accomplished by the improvements hereinafter described and claimed.

In general a brake in accordance with the present invention includes a housing defining a chamber, a disc assembly positioned within the chamber including a plurality of stationary discs carried by the housing and a plurality of rotating discs carried by the shaft, the rotatable discs and the stationary discs being positioned for engagement with each other. A piston is movable to cause the stationary discs to engage the rotatable discs. A first fluid input may be in communication with the fluid source and provide a constant supply of fluid to the chamber. A second fluid input may be in communication with the fluid source and provide fluid when the stationary and the rotating discs are caused to engage.

In accordance with another aspect of the present invention, a brake includes a housing having a chamber therein. A disc assembly is positioned within the chamber and includes a plurality of stationary discs carried by the housing and a plurality of rotating discs carried by the shaft, the rotatable discs and the stationary discs being axially movable and positioned for engagement with each other. A first orifice is adapted to communicate a constant supply of fluid to the chamber and a second orifice is adapted to variably provide fluid to the chamber. A braking force is applied to the shaft when a compressive force is applied to the disc assembly. The second orifice is unobstructed when the compressive force is applied and obstructed when no compressive force is applied.

In accordance with yet another aspect of the present invention, a brake includes a housing having a chamber therein, a disc assembly is positioned within the chamber and includes a plurality of stationary discs carried by the housing and a plurality of rotatable discs carried by the shaft. The rotatable discs and the stationary discs being axially movable and positioned for engagement. A fluid input is operatively interconnected with the disc assembly. Wherein a braking torque is provided to the shaft when the disc assembly is axially moved and compressed against the housing, the fluid input providing fluid upon the axial movement.

A preferred exemplary low drag failsafe brake according to the concepts of the present invention is shown by way of example in the accompanying drawings without attempting to show all the various forms and modifications in which the invention might be embodied, the invention being measured by the appended claims and not by the details of the specification.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

A brake made in accordance with the present invention is indicated generally by the numeral10and includes a housing assembly11which contains and protects the working components of brake10, in addition to providing the means to mount the brake10to a piece of equipment, machinery or the like. Referring toFIGS. 1-3, housing assembly11includes a main housing12and a power plate13. Main housing12is generally cylindrical and cup-shaped in configuration, having an open end. Power plate13is coupled to main housing12at the open end by a plurality of bolts14. Thus configured, main housing12and power plate13define a sealed chamber15which retains the working brake components as will be hereinafter discussed. A gasket16may be provided between a portion of the mating surface of main housing12and power plate13, thereby preventing contamination of the lubricants within chamber15. Gasket16also prevents escape of the lubricants within chamber15. Main housing12and power plate13further include a plurality of mounting bores17(seeFIG. 2) which are aligned and extend through housing assembly11. Mounting bores17provide a means to attach brake10to a machine or other device in need of brakes. For example, bolts may be inserted through bores17and engage threaded holes in a machine frame (not shown), thereby securing housing assembly11thereto.

Referring toFIGS. 3 and 4, power plate13is generally disc shaped and includes an interior surface20which faces chamber15. An annular channel21is provided which may be centered about a central axis18and which extends inwardly from interior surface20. Annular channel21is configured as a circumferential groove having a generally square cross-section and is adapted to receive an annular piston22therein. Annular channel21thereby serves as a piston housing, and to that end, when annular piston22is so inserted, a sealed reservoir23is created. Annular piston22includes a pair of circumferential grooves24aand24balong the inner and outer radial surface thereof. Grooves24each receive an o-ring25which sealingly contacts piston22and channel21. Grooves24may each also receive a backup ring26proximate to o-ring25on the cavity side of grooves24. Backup rings26sealingly contact piston22and channel21, ensuring that pressurized fluid within reservoir23is not transmitted to cavity15. One or more ports27may be provided to communicate pressurized fluid from an external pressure source to the reservoir23, thus selectively actuating the piston22. One or more of the ports27may be provided with a screw bleeder valve28which may selectively be employed to empty the reservoir23of pressurized fluids. Still further, one or more of the ports27may be in communication with a pressure exhaust line which may return the pressurized fluid to a source when piston22is un-actuated. The present embodiment discloses three ports27positioned 120 degrees apart. Each port27may selectively receive a bleeder valve, plug or connector for a fluid pressure line depending upon end-user requirements and the orientation of the brake within the machinery. Providing multiple ports in various locations creates flexibility for end-users and aids in installation.

Piston22is further provided with four curved fingers29, separated by slots30, which project from the radially outer periphery of piston22and extend axially into cavity15, toward main housing12. It should be appreciated that, while the present embodiment discloses four curved fingers, more or less may be employed.

As shown inFIG. 4, power plate13includes four axially oriented torque pin holes31which are positioned equidistant from axis18and spaced 90 degrees apart. Torque pin holes31are each adapted to receive a torque pin32(seeFIG. 1) and are axially aligned with a pair of matching torque pin holes33(seeFIG. 5) on main housing12. When main housing12and power plate13are assembled, torque pins32span chamber15and are securedly positioned within torque pin holes31and33.

Power plate13further includes a central bore40which is concentric with axis18. Bore40allows a shaft41to project therethrough and includes three distinct surfaces. A bearing surface42is located adjacent to the end of bore40proximate to the exterior of power plate13. Bearing surface42may be provided with a circumferential groove43which is adapted to receive a retaining ring44. A seal surface45is positioned adjacent to, and has a smaller diameter than bearing surface42. Seal surface45may also be provided with a circumferential groove46which is adapted to receive a retaining ring47. A stop surface48is positioned adjacent to seal surface45. Stop surface48has a smaller diameter than seal surface45and terminates at interior surface20, proximate to chamber15.

Shaft41is generally cylindrical and includes several distinct outer surfaces. A first bearing surface50is located adjacent to bearing surface42of bore40. A seal surface51is provided adjacent to, and has a larger diameter than, bearing surface50. A disc surface52is provided adjacent to, and has a larger diameter than, seal surface51. Disc surface52is positioned within chamber15and includes a plurality of radially projecting splines (not shown) along the axial length thereof. A second bearing surface53is provided proximate to an interior end54of shaft41. Second bearing surface53has a diameter that is smaller than the diameter of disc surface52.

Shaft41further includes a central hole55which extends axially inward from the interior end54of shaft41. Central hole55is in fluid communication with a plurality of shaft oil ports56, which extend radially from central hole55and terminate at disc surface52. As will be hereinafter described in more detail, central hole55and shaft oil ports56communicate a fluid into chamber15. It should be appreciated that the fluid may be a coolant and/or a lubricant. Typically, the fluid is oil based which provides desired lubrication, corrosion prevention and heat transfer functions.

Shaft41is rotatable within chamber15. To provide for reduced rotational friction, a first bearing58is provided between shaft first bearing surface50and power plate bearing surface42. Bearing58is restrained from axial movement by retaining ring43and by the steps created by seal surfaces45and51. A lip seal59is provided between seal surfaces45and51to prevent contaminates from entering chamber15, while maintaining fluids within chamber15. Lip seal59is restrained from axial movement by retaining ring47and by the step created by stop surface48. A second bearing60is provided between shaft second bearing surface53and a circumferential bearing surface61provided in main housing12. In this manner shaft41is rotatable within housing11. In the present embodiment, bearing58is positioned outside chamber15and second bearing60is positioned inside chamber15. Thus, fluids provided within chamber15contact second bearing60but not first bearing58. It should be appreciated, however, that in other embodiments, first bearing58may reside within chamber15.

Referring now toFIGS. 3 and 5, a first fluid input generally indicated by the numeral57may be provided which supplies a constant flow of fluid into chamber15. First fluid input57includes a first orifice62, which may be located on main housing12, aligned with central axis18. First orifice62extends from the exterior of main housing12to chamber15and is configured to receive an orifice adapter63therein. Orifice adapter63may include a threaded outer surface which engages matching threads within first orifice62. A gasket64may be provided between the mating surface of orifice adapter63and first orifice62, which promotes a proper seal therebetween. Orifice adapter63provides a connection site for an external fluid source to couple to brake10and provide fluid to chamber15. Orifice adapter63includes a stepped central bore65which includes a first portion66proximate to the exterior of brake10and a second portion67proximate to first portion66and terminating at the interior of brake10. Second portion67has a diameter which is larger than first portion66and is adapted to receive a plug68therein. Plug68includes a bore69which permits fluid flow therethrough. Plug68is selectively removable and may be replaced with plugs having larger or smaller diameter bores, depending upon a desired fluid flow rate. Thus it should be evident that an external fluid source may be coupled to orifice adapter63and that fluid may be provided through first portion66, bore69, and finally first orifice62. Thereafter fluid may travel to second bearing60to provide cooling and lubricating functions. Further, fluid may flow into central hole55of shaft41and consequently through oil ports56and into chamber15.

Main housing13includes one or more drain ports70. The present embodiment provides three ports70located at the radially outer wall of main housing12and equidistant from one another. It should be appreciated that more or less drain ports70may be employed. Typically, one or more coolant drain ports are sealed by a plug71. The plurality of drain ports70are provided to enable easy and flexible installation steps. One or more drain ports70are interconnected to a negative pressure source (not shown) which, as will be hereinafter described in more detail, continuously draws fluid out of chamber15. In other words, negative pressure source draws a negative pressure on chamber15, causing fluid to exit via a drain port70.

Main housing13includes a stop surface72which may be generally annular and faces chamber15. A plurality of piston bores73are provided on stop surface72, which extend axially inwardly and are each adapted to receive a piston74therein. Each piston bore73thereby serves as a piston housing, and to that end, when piston74is so inserted, a sealed reservoir75is created. Piston74includes a body76which is cylindrical and adapted to fit within a piston bore73. A circumferential groove77is provided around body76which may receive an o-ring78which sealingly contacts piston74and bore73. Groove77may also receive a backup ring79proximate to o-ring78on the chamber side of grooves77. Backup rings79sealingly contacts piston74and bore73, ensuring that pressurized fluid within reservoir75is not transmitted to chamber15. Piston74further includes an extension80which is generally cylindrical and has a smaller diameter than body76. Extension80extends out of bore73into chamber15where it interacts with a disc assembly90which will be hereinafter described in more detail. The present embodiment includes three piston bores73with corresponding pistons74, though it should be appreciated that any number of pistons74may be employed. It is advantageous, however, to position the pistons in a manner which distributes the loads equally about axis18. Thus, in the present embodiment, piston bores73are arranged in a triangular pattern, being equidistant from axis18and approximately 120 degrees apart. It should, however, be appreciated that other piston configurations may be used. For example, the plurality of pocket pistons may be replaced with a single annular piston, similar to piston22. Still further, it should be appreciated that, though the present embodiments discloses piston22on an opposed side of chamber15from pistons74, both pistons may be positioned on the same side of chamber15.

Referring now toFIGS. 3,6and7, bores73are in fluid communication with each other through a plurality of interconnecting channels81within main housing12. At least one inlet channel82is provided which may communicate with an outside pressure source to selectively pressurize reservoirs75. Because the reservoirs75are interconnected, approximately the same pressure is realized within each reservoir75and consequently each piston74exerts approximately the same piston force when pressurized fluid is provided via inlet channel82.

Main housing12further includes a plurality of spring recesses83which extend inwardly from stop surface72. The present embodiment includes thirteen spring recesses, though, more or less may be included. Each spring recess83is adapted to receive one or more compression springs84. As shown inFIG. 3, compression springs84interact with a disc assembly generally indicated by the numeral90in a manner which will be hereinafter described.

Disc assembly90includes a plurality of rotating discs91and a plurality of stationary discs92. Rotating discs91and stationary discs92are stacked in an alternating manner within chamber15as shown inFIG. 3. In the present embodiment seven rotating and seven stationary discs are shown, but it should be appreciated that any number may be employed. Rotating discs91are provided with a radially inner surface93which is splined to engage the splines of disc surface52of shaft41. In this manner, as shaft41rotates, rotating discs91rotate therewith. While rotating discs91are rotationally coupled to shaft41, they are free to slide axially thereon. Stationary discs92have a radially inner surface94which fits over, but is not engaged by, the splined disc surface52of shaft41. Thus, stationary discs92will not rotate with shaft41.

As best shown inFIGS. 1 and 8, stationary discs92are provided with diametrically opposed ears95extending radially outwardly therefrom. Ears95are adapted to extend radially through slots30of annular piston22and slidingly engage pins32which are positioned radially outward of fingers29. To that end, each ear95is provided with a groove96which is adapted to slidingly receive pin32therein. In this manner, stationary discs92are coupled to housing assembly11, and thus prevented from rotating. The stationary discs92are, however, free to slide axially along pins32. Therefore, when an axial force is applied to one end of disc assembly90, stationary discs92are caused to slide axially and compress against rotating discs91, creating a frictional interface. As is known in the art, when these discs are caused to engage each other, a braking torque is applied to shaft41due to the friction created between rotating discs91and stationary discs92which are prevented from rotating by pins32.

Referring toFIGS. 3 and 9, disc assembly90may further include a primary disc generally indicated by the numeral97which is positioned on the end of disc assembly90proximate to stop surface72. Primary disc97is annular, with an inner surface98which fits over but does not engage shaft41. As is evident fromFIG. 3, the outside diameter of primary disc97is relatively larger than that of stationary discs92. This allows fingers29of annular piston22to bypass rotating discs91and stationary discs92and contact a first surface99of primary disc97, which faces chamber15. A second surface101of primary disc97is opposed from first surface99and contacts springs84. Primary disc97is provided with a pair of diametrically opposed ears102which extend radially outward therefrom. Ears102are adapted to slidingly engage pins32. To that end, each ear is provided with a groove103, each of which slidingly receives a pin32therein. In this manner, primary disc97is coupled to the housing, and thus prevented from rotating. The primary disc97is however, free to slide axially along pins32. Primary disc97further includes a first set of bores104, which are adapted to allow extension80of pistons74to project therethrough and contact a secondary disc110. A second set of bores105are also provided on primary disc97which are each adapted to receive an orifice pin106therethrough. Thus, pistons74and pins106may interact with secondary disc110uninhibited by primary disc97, which operates independently therefrom.

Secondary disc110is positioned between primary disc97and the stationary disc92closest to primary disc97. As shown inFIGS. 10 and 11, secondary disc110is annular, with an inner surface111which fits over but does not engage shaft41. A plurality of threaded holes112are provided and aligned with bores105of primary disc97. Each hole112is adapted to receive matching threaded portions107of orifice pins106. Thus, in this manner, pins106are secured to secondary disc110wherein axial movement of secondary disc110causes corresponding axial movement of pins106. Secondary disc110is also provided with a pair of diametrically opposed ears113which extend radially outward therefrom. Ears113are adapted to slidingly engage pins32. To that end, each ear is provided with a groove114, each of which slidingly receives a pin32therein. In this manner, secondary disc110is coupled to the housing, and thus prevented from rotating. Secondary disc110is however, free to slide axially along pins32. Further, as shown inFIG. 8, ears113are positioned on a different pair of pins32than stationary discs92and primary disc97. In other words, the ears of stationary discs92and primary disc97are aligned and received on a first pair of pins32a, and the ears of secondary disc110are offset 90 degrees, thereby residing separately on a second pair of pins32b. As shown inFIGS. 8 and 12, return springs115may be received on second pair32bbetween power plate13and secondary disc110. Thus, secondary disc110is biased toward main housing12by return springs115.

Referring now toFIGS. 5,6,13and14, a second fluid input116may be provided which variably supplies fluid to chamber15. Second fluid input116provides fluid to chamber15when disc assembly90engages and a braking torque is applied to shaft41. In other words, second fluid input116provides fluid to chamber15during movement of primary or secondary disc movement toward the disc stack. In this manner additional cooling and lubrication is provided during high heat generation periods, that is, braking. Second fluid input116includes a second orifice117which extends from the outer surface of main housing12and communicates with chamber15. Second orifice117may include a threaded portion118which is adapted to receive the threaded portion of a fitting119. Fitting119is adapted to provide easy coupling to an external fluid source (not shown). The external fluid source may be the same as that which provides fluid to first orifice62or may be a separate, independent source. In any event, the external fluid source provides fluid at a predetermined pressure to second orifice117. An o-ring120may be provided at the area of intersection between main housing12and fitting119to promote a sealed fit therebetween. A circumferential step121may be located on bore117which receives a lip seal122therein. Pin106is adapted to selectively engage bore117. To that end, an angled lip123may be provided which is adapted to engage bore117, and particularly lip seal122. As will become apparent, when secondary disc110moves axially away from main housing12, pins106correspondingly move away. When pins106move away from main housing12, angled lip123disengages from lip seal122. In other words, when brake10is not engaged and rotating discs91spin freely, pin106obstructs orifice117, preventing fluid flow therethrough. When brake10is engaged, pin106is drawn out of orifice117and fluid may flow from external fluid source into chamber15. The present embodiment discloses a pair of second fluid inputs116but it should be appreciated that more or less may be employed. Though the above disclosed arrangement may be advantageous, other methods of varying the fluid supplied to the chamber may be employed. For example, in one embodiment, a valve may be externally controlled such that, during brake actuation, it opens to provide additional fluid to the chamber. In another embodiment, brake actuation energizes a fluid pump that supplies chamber15with fluid.

As shown inFIG. 15, main housing12includes a wear indicator125which indicates the relative position of primary disc97, and consequently the level of disc wear, without the need to disassemble brake10. Wear indicator125includes an indicator bore126which extends from the exterior of main housing12to chamber15. A modified hex head plug127is secured within indicator bore126and includes a central hole which receives an indicator shaft128. Indicator shaft128is an elongated pin which is long enough to contact primary disc97. A circumferential groove129is located near the end of shaft128proximate to primary disc97. A retaining ring130is received in groove129. A spring131is positioned around shaft128and between ring130and main housing12. Thus, indicator shaft128is biased toward contact with primary disc97and will move axially with disc as it moves. As a result, the portion of indicator shaft128which is visible outside main housing indicates to an operator the relative position of primary disc97.

As assembled, brake10is engaged when no hydraulic fluid is supplied to it. In other words, when no hydraulic fluid is supplied to annular piston reservoir23or piston reservoirs75, disc assembly90is compressed against interior surface20of power plate13causing a braking torque to be applied to shaft41. In this orientation, springs84supply the actuating force to engage the brake by pushing primary disc97axially away from main housing12and toward power plate13. Because disc assembly90is free to slide axially, springs84press against the second surface101of primary disc97causing it to move axially toward power plate13. This in turn causes the rotating discs91, stationary discs92, and secondary disc110to slide axially towards power plate13. When the disc assembly90contacts interior surface20of power plate13, springs84compress the disc assembly90against power plate13. In this condition, friction between the rotating discs91and the stationary and secondary discs92and110applies a torque to the stationary discs92and secondary disc110urging them to rotate. However, because ears95and109are confined by pins32, stationary discs92and secondary disc110will not rotate and a braking torque is applied to the shaft. This type of brake actuation is commonly referred to as a failsafe mechanism, because the brake is engaged when no power is applied to the system. The brake10will prevent unwanted and often times dangerous shaft movement when the equipment is not operating.

When the machine is turned on, fluid under pressure, such as oil, may be supplied to the annular channel21either automatically or by operator control. As hydraulic fluid under pressure is received in reservoir23, the fluid acts on piston22pushing it axially away from the power plate13toward main housing12. Fingers29transfer the piston force to primary disc97, countering the force of springs84. If sufficient pressure is supplied within reservoir23, the force of piston22will overcome the spring force, thereby moving primary disc97axially toward main housing12and against stop surface72. This in turn eliminates the compressive force on disc assembly90and the disc assembly disengages, allowing the free rotation of rotatable discs91. It should be appreciated that, even when disc assembly90is disengaged and no compressive force is applied thereto, some contact may occur between rotating and stationary discs91and92. Such contact is inherent in such brake designs, and the resulting frictional forces are minimal compared to those generated when disc assembly is engaged by compression.

With the failsafe brake disengaged, the machinery may operate normally, allowing rotating discs91to spin freely within chamber15. During normal operation, it may be desirous to provide service braking. Service braking occurs when an operator wishes to apply a braking torque to shaft41during normal operation, to selectively slow or stop rotation. Service braking provides more operator control and command than the failsafe brake. The service braking function is provided by service pistons74. Extensions80of service pistons74extend through primary disc97and contact secondary disc110. Ordinarily, springs115hold secondary disc110securely against primary disc97, enabling rotating discs91to rotate freely. When fluid under pressure, such as oil, is supplied to reservoirs75, the fluid acts on pistons74, pushing them axially away from main housing12toward power plate13. Extensions80transfer piston force to secondary disc110countering the force of return springs115. If sufficient pressure is supplied within reservoirs75, the force of pistons74will overcome the force of springs115, thereby moving secondary disc110axially toward power plate13. Consequently rotating and stationary discs91and92are pressed against interior surface20. Pistons74thereafter cause stationary and secondary discs91,92and110to engage by compressing them against power plate13. In this condition, friction between the rotating discs91and the stationary and secondary discs92and110applies a torque to the stationary discs92and secondary disc110urging them to rotate. However, because ears95and113are confined by pins32, stationary discs92and secondary disc110will not rotate and a braking torque is applied to the shaft. This type of brake actuation is commonly referred to as a service brake, because the failsafe is disengaged and the service brake is used during normal operation to slow or stop shaft41.

This type of brake generally requires a fluid to be circulated therethrough which provides lubricating and cooling functions. Typically an oil based fluid is used, although other fluids may be employed. Lubrication is necessary, primarily to ensure that second bearing60functions with minimum friction. Also, lubrication is necessary to ensure that, when disengaged, the rotating and stationary discs91and92spin freely and any incidental contact friction therebetween is minimized by the presence of at least a small amount of coolant/lubrication. This ensures long bearing life and efficient machine operation. The cooling function is required because, when brake10is engaged, either via the failsafe method or the service method, heat is generated by the frictional contact between rotatable and stationary discs91and92respectively. Further, heat is generated by second bearing60during rotation. Thus, it should be evident that during normal non-engaged operation, a minimal amount of fluid is required, in particular to provide lubrication to second bearing60. Yet when the disc assembly90is compressed, by either the failsafe function or service brake function, more fluid is necessary to remove excess heat buildup caused by the frictional contact between disc assembly90. Thus, the present invention provides a first amount of fluid during normal, non-engaged operation, and additional fluid is provided automatically during braking as will be hereinafter described.

As described earlier, fluid is constantly provided through first orifice62via orifice adapter63. Plug68is provided to selectively restrict the amount of fluid provided through first orifice62. Typically a relatively small amount of fluid is provided through plug68which communicates with second bearing60and through ports56in shaft41. Additionally, at least one drain port70is coupled to an negative pressure source which continuously draws fluid out of chamber15. Thus, when operating under non-braking conditions, very little excess fluid remains within chamber15because drain port70draws out fluid as fast or faster than orifice adapter63provides it. As a result, little drag is realized by the rotating discs91, as compared to prior art methods. Significantly, because no excess fluid resides within chamber15during normal operation, rotating discs91are not forced to spin through this excess fluid which would significantly increase drag and reduce efficiency.

Upon actuation of failsafe brake, as previously described, springs84push primary disc97axially away from main housing12. Because the disc assembly90is free to slide axially, springs84press against the second surface101of primary disc97causing it to move axially toward power plate13. This in turn causes the rotating discs91, stationary discs92, and secondary disc110to slide axially toward power plate13. When the disc assembly90contacts interior surface20, springs84compress the disc assembly90against power plate13. Because pins106are coupled to secondary disc110, pins106will also move axially towards power plate13. This movement draws angled lip123away from lip seal122, allowing additional fluid to flow from the external fluid source, through fitting119and into chamber15.

Similarly, the actuation of service brake function will also cause additional fluid to flow into chamber15. As previously described, the service braking function is provided by service pistons74. Fluid under pressure is supplied to reservoirs75and pushes pistons74axially away from main housing12toward power plate13. Extensions80transfer piston force to secondary disc110countering the force of return springs115. When sufficient pressure is supplied to reservoirs75, pistons74will overcome the force of springs115and move secondary disc110axially toward power plate13, compressing rotating and stationary discs91and92, respectively, against interior surface20. Because pins106are coupled to secondary disc110, pins106will also move axially toward power plate13. This movement draws angled lip123away from lip seal122, allowing additional fluid to flow from the external fluid source, through fitting119and into chamber15.

Thus, the present invention provides a reduced amount of coolant to the brake during normal, non-braking operation. This reduced amount of coolant is drawn out via drain port70at the same, or faster rate than is introduced so that very little excess coolant remains inside cavity during non-braking operation. This results in improved efficiency, because rotating discs91spin primarily through air instead of a fluid, which would produce increased drag. When increased heat removal is necessary, during either failsafe or service braking, additional fluid is provided to remove the heat. Once braking is accomplished, the brake returns to normal non-braking operation, and the additional fluid is drawn out of chamber15by drain ports70. Because drain ports70draw out fluid faster than is provided by first fluid input57, excess fluid is eventually removed providing for reduced drag operation. Further, the variation of coolant disclosed in the present invention is not limited to failsafe braking applications, but may be used in any brake configuration that would benefit from low drag during non-braking operation and increased coolant during brake actuation.

In view of the foregoing, it should thus be evident that a brake as described herein accomplishes the objects of the present invention and otherwise substantially improves the art.