Abstract:
The disclosed apparatus relates to a liquid cooled brake apparatus comprising: a housing, a brake cooling pump mounted to said housing, a braking force actuator mounted to said housing, said actuator being driven by a first driven member; and a braking force applicator in operable communication with said braking force actuator and a brake rotor, the rotor rotationally fixed to said first or a second driven member. The disclosed method relates to a method of retarding a driven member comprising: driving a braking force actuator with a first driven member, actuating a braking force applicator; and retarding the rotation of a rotor rotationally fixed to said first or a second driven member.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The disclosed invention relates to an apparatus and method for retarding a driven member. This invention has applications in transportation, dynamometers, conveyor systems and mining to name a few. In transportation, for example, when a truck is descending down a long grade the vehicle&#39;s air-cooled original equipment manufacturer brakes can overheat, this overheating condition is exacerbated when the truck is carrying a heavy load. The heat generated by the friction of the brake pads against the disc, for disc brakes, or brake shoes against the drums, for drum brakes, can reduce braking efficiency.  
         [0002]     Accordingly there is a need in the art for an improved frictional braking system.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0003]     The disclosed apparatus relates to a liquid cooled brake apparatus comprising: a housing, a brake cooling pump mounted to said housing, a braking force actuator mounted to said housing, said actuator being driven by a first driven member; and a braking force applicator in operable communication with said braking force actuator and a brake rotor, the rotor rotationally fixed to said first or a second driven member.  
         [0004]     The disclosed method relates to a method of retarding a driven member comprising: driving a braking force actuator with a first driven member, actuating a braking force applicator; and retarding the rotation of a rotor rotationally fixed to said first or a second driven member. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:  
         [0006]      FIG. 1  depicts a cross sectional view of a brake apparatus of an embodiment of the invention;  
         [0007]      FIG. 2  depicts an exploded perspective view of the chain and sprocket assembly shown in  FIG. 1 ;  
         [0008]      FIG. 3  depicts an exploded perspective view of a brake rotor of an embodiment of the invention;  
         [0009]      FIG. 4  depicts a cross sectional view of a brake rotor and stator assembly with the stator assembly in the opened fluid flow path position according to an embodiment of the invention;  
         [0010]      FIG. 5  depicts a cross sectional view of the brake rotor and stator assembly of  FIG. 4  with the stator assembly in the closed fluid flow path position;  
         [0011]      FIG. 6  depicts a partial cross sectional view of  FIG. 1  at a larger scale;  
         [0012]      FIG. 7  depicts a hydraulic schematic of an embodiment of the invention;  
         [0013]      FIG. 8  depicts a partial cross sectional view of a gear pump and housing of an embodiment of the invention;  
         [0014]      FIG. 9  depicts a partial cross sectional view of the gear pump and housing shown in  FIG. 8 ;  
         [0015]      FIG. 10  depicts a cross sectional view of a needle valve of an embodiment of the invention; and  
         [0016]      FIG. 11  depicts a block diagram of a control system of an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     A detailed description of several embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.  
         [0018]     Referring to  FIGS. 1 and 2 , a brake assembly  14  comprising: a brake housing  18 , a rear chain case  22 , a front chain case  26 , an outlet housing  106  and a tail housing  30  are sealedly attached to one another to generally form a structure for supporting the components that comprise a friction brake apparatus  10 . Studs  32  fasten the brake housing  18 , rear chain case  22  and front chain case  26  together, while band clamp  33  attaches the tail housing  30  to the front chain case  26 . A first driven member, illustrated in one embodiment as a universal joint coupling (or yoke or slip yoke)  34 , is rotationally fixed to a drive sprocket  38  that rotates within the brake assembly  14  on bearings  42 . Alternately, a second driven member, illustrated in one embodiment as a tail shaft  36 , may be rotationally fixed to the universal joint coupling  34 , which is rotationally fixed to the drive sprocket  34 , or it may be rotationally fixed to the drive sprocket  38  directly, while allowing axial movement. A chain  46  engaged with drive sprocket  38  drives a rotor sprocket  50  on bearings  54 . The rotor sprocket  50  is rotationally fixed to a brake rotor  300  through a brake shaft  62 . Through the above-described linkages the brake rotor  300  is rotationally fixed to either the first or the second driven member. It should be appreciated by one skilled in the art that the chain  46 , as described herein, is only an exemplary embodiment for rotationally fixing the brake rotor  300  with the driven member and other embodiments such as a belt or gear set, for example, may also be utilized.  
         [0019]     The frictional brake apparatus  10  hinders the rotation of the universal joint coupling  34  by hindering the rotation of the brake rotor  300  that is rotationally fixed to the universal joint coupling  34  as described above. A braking force applicator illustrated in one embodiment here as pistons  66 , brake pad plates  70  and brake pads  74 , apply a braking force to the brake rotor  300 . The brake rotor  300  has opposing outside axial brake surfaces  330  and  334  that are engaged by the brake pads  74  that are attached to the brake pad plates  70 . The brake pads  74  are urged against the brake surfaces  330 ,  334  by pistons  66 . The urging force of the pistons  66  results from hydraulic pressure generated in a braking force actuator  110 . The actuator utilizes hydraulic force as a function of pressure to move the pistons  66  to apply the braking (retarding) force. The braking force actuator is illustrated in one embodiment here as a gear pump  500  that will be described in more detail with reference to  FIGS. 7-9 . It should be appreciated by those skilled in the art, that alternate embodiments such as a gerotor or piston pump, for example, may be used as the braking force actuator while remaining within the scope of the invention.  
         [0020]     The brake pad plates  70  are slidably engaged with the brake assembly  14  to substantially limit the travel of the brake pad plates  70  to a direction parallel to the axis of the brake rotor  300 . It should be appreciated, by one skilled in the art, that pistons urging brake shoes against a drum type rotor could also be employed in other embodiments of the invention. The portion of the system described above is similar to the types of frictional braking systems, the drawbacks of such are identified in the background section of this application. The system herein described however, further includes a brake surface cooling pump operatively communicated with the system. In one illustrated embodiment of the invention the cooling pump resides within the brake rotor  300 . The pump includes internal pumping blades that are described in greater detail with reference to  FIGS. 3-5 . The purpose for the cooling pump is to circulate a fluid in conductive communication with the brake rotor friction surface to remove heat from the brake rotor  300  and surrounding components generated by the friction of the brake pads  74  against the brake surfaces  330 ,  334 . The cooling pump pumps cooling liquid, to and from the brake apparatus  10 , through inlet nipple  98 , and outlet nipple  102  formed in the outlet housing  106 . The cooling fluid may be routed through a vehicle radiator (not shown) or other heat-exchanging device (not shown) located near, on or remotely from the brake apparatus  10  of the invention.  
         [0021]     Referring now to  FIG. 3 , an exploded view of the brake rotor  300 , shows details of the internal cooling pump. Pumping of cooling fluid is facilitated by the rotation of several components within the brake rotor  300 ; the rotor sprocket  50  driven by the chain  46  provides the driving force for this rotation. The brake shaft  62  is rotationally fixed to the rotor sprocket  50  by a spline  304  located on one end of the brake shaft  62 . A flange  316  on the rotor side of the brake shaft  62  is rotationally fixed to a drive plate  308  by two axially protruding posts  312  that engage with bottom cylindrical recesses (not shown) in the drive plate  308 . A button head bolt  320  and o-ring  324  fix the drive plate  308  to the brake shaft  62  axially. Through the above arrangement the drive plate  308  is rotationally fixed to the rotor sprocket  50 .  
         [0022]     Several other components within the brake rotor  300  are also rotationally fixed to the drive plate  308 . The drive plate  308  has an outer peripheral surface  328  that extends axially beyond the drive plate brake surface  330  and has outer diameter threads  326  thereon. A seal plate  336  has an outer peripheral surface  338  that extends axially beyond the seal plate brake surface  334  and has inner diameter threads  332 , thereon, that thread into the outer diameter threads  326  of the drive plate  308 . An o-ring  340  diametrically seals the drive plate  308  to the seal plate  336 .  
         [0023]     Referring now to  FIGS. 3 through 5  sandwiched between the drive plate  308  and the seal plate  336  is a rotor disc  344 , and a stator assembly  356  comprising a stator flange  348  and a stator blade plate  372 . The rotor disc  344  bisects the rotor cavity  354  into a first cavity  358  and a second cavity  362 . The rotor disc  344  is rotationally locked to, and therefore, rotates with the plates  308  and  336 , while the stator assembly  356  is not locked to the plates  308 ,  336  and therefore does not rotate with the plates  308  and  336 . A rotor disc bearing  352  positions the stator assembly  356  concentric to the rotor disc  344  as the rotor disc  344  rotates relative to the stator assembly  356 . An o-ring  365  seals a ceramic face seal  361  to the seal plate  336  in a center hole therethrough. The ceramic face seal  361  seals dynamically to a carbon face seal  363  that is rotationally fixed to the outlet housing  106  and sealed to the outlet housing  106  by o-ring  359 . A wave spring  366  urges the carbon face seal  363  against the ceramic face seal  361  to maintain the face-to-face contact required for the seal. The smoothness of the ceramic face seal  361  against the low friction, highly durable surface of the carbon face seal  363  establishes a low torque long life seal design. Other materials having appropriate properties to substitute for the ceramic for the seal  361  include but are not limited to tungsten carbide, silicon carbide or heat-treated steel for example.  
         [0024]     The cooling fluid pumping action is generated by the rotation of the rotor disc  344  and more specifically a set of first blades  360  and a set of second blades  364  formed on opposing sides of the rotor disc  344 . The cooling fluid is propelled radially outward in the first cavity  358  by the first blades  360 , axially around the outer diameter of the rotor disc  344 , radially inward in the second cavity  362  by the second blades  364  and radially inward into channels  370  of the stator assembly  356 . The channels  370  of the stator assembly  356  are formed by the axial space between the stator blade plate  372  and the stator flange  348 , and by stator blades  368  formed on the stator blade plate  372 . The cooling fluid flows axially from the channels  370  into an annular flow path  376  formed by the radial clearance between the stator flange  348  and the stator blade plate  372 . This fluid is contained by the sliding seal of the ceramic face seal  361  to the carbon face seal  363 , described above, and is ported to the outlet nipple  102  of the outlet housing  106 . Thus, the pumping action pumps fluid along surfaces  331  and  333  which are the surfaces just opposite the drive plate brake surface  330  and the seal plate brake surface  334  respectively, thereby carrying away heat from the plates  308 ,  336  in the process.  
         [0025]     An embodiment of the invention ports the inlet cooling fluid along the axis of the rotor within the stator flange  348  and ports the outlet cooling fluid coaxial with the inlet fluid along an external portion of stator flange  348 . This construction permits an internal dynamic seal to be formed by the rotor disc bearing  352 , which seals the rotating rotor disc  344  to the stationary stator flange  348 . The sealing integrity of this seal is not critical since any leakage is still contained completely internal to the fluid flow paths, thus the designation as “internal dynamic seal.” Conversely, the other dynamic seal, the one created by the ceramic face seal  361  to the carbon face seal  363 , described above, is not contained within the fluid flow paths and is therefore described as an “external dynamic seal” and any leakage by it will allow coolant to escape the closed cooling system of the vehicle, a condition that should be avoided. The construction of this embodiment, specifically having the inlet flow along the axis of the rotor, allows for a single external dynamic seal to be used. Whereas alternate constructions, that do not port either the inlet or the outlet flow along the axis of rotation, require at least two external dynamic seals; one between each stationary flow nipple and the rotating, coolant filled, rotor assembly.  
         [0026]     The cooling fluid enters the brake apparatus  10  ( FIG. 1 ) through the inlet nipple  98 . For assembly purposes the inlet nipple  98  is threadably attached to the stator flange  348  and sealed thereto with o-ring  384 . A hole  388  formed in the stator flange  348  accepts a pin  392  through a hole  394  in the outlet housing  106  that prevents the stator flange  348  from rotating while the inlet nipple  98  is threaded onto the stator flange  348  via a hex shape  398  on its perimeter. After assembly the pin  392  is removed and the hole  394  in the outlet housing  106  is plugged with a plug  402 .  
         [0027]     As with any pumping mechanism, the work performed during the pumping operation consumes energy. One exemplary embodiment of the invention permits reduction in the energy consumption of the brake apparatus  10  ( FIG. 1 ), by stopping or reducing the pumping of cooling fluid during times when cooling is not necessary, such as when the brake apparatus  10  is not engaged in a braking action. To enable or disable the pumping action, the stator assembly  356  is repositionable relative to the brake assembly  14  and the drive plate  308  in an axial direction. A cooling fluid flow path  440  is formed by the axial clearance between the stator flange  348  and the drive disc  308 . When the stator assembly  356  moves towards the drive disc  308 , into a first position, the flow path  440  is blocked, thereby stopping the pumping action. When the stator assembly  356  moves away from the drive disc  308 , into a second position, the flow path  440  is opened and the pumping action is allowed.  
         [0028]     To permit the repositioning of the stator assembly  356 , a compression stator spring  406  is housed between the inlet nipple  98  and a hex plate  410 . The hex plate  410  is attached to the outlet housing  106  with bolts  414 . The stator spring  406  urges the stator assembly  356  towards the drive disc  308  until a stator flange shoulder  418  bottoms out against the outlet housing  106 . Conversely, the stator assembly  356  is axially movable in the opposite direction, a direction away from the drive disc  308 , until the stator blade plate  372  contacts the outlet housing  106 . The force to move the stator assembly  356  away from the drive plate  308  is generated by hydraulic oil pressure in a pressure chamber  426 . (The pressure is ported to the pressure chamber  426  through seventh pressure port  442  and sixth pressure port  446  that fluidically connect a piston cavity  454  with stator pressure cavity  426 , as will be described in more detail with reference to  FIGS. 7-9 ). The pressure in stator pressure chamber  426  causes the stator assembly  356  to move axially, thereby opening coolant flow path  440 , as was described above. The pressure chamber  426  is formed in an annular cavity between the outlet housing  106  and the stator flange  348  that are sealed to each other by o-ring  436 . The inlet nipple  98 , which is sealed to the outlet housing  106  by o-ring  432 , and to the stator flange  348  by o-ring  384 , caps the end of the pressure chamber  426 . O-rings (or other radial seals)  436  and  432  create sliding seals between the stator assembly  356  and the outlet housing  106  and also provide alignment of the stator assembly  356  within the brake assembly  14  on one end of the stator assembly  356 . The stator flange  348  riding within an inner diameter of the rotor disc bearing  352  aligns the other end of the stator assembly  356 . Thus, cooling fluid flow path  440  is closed due to the stator spring  406  urging the stator assembly  356  towards the drive disc  308  in response to a drop in oil pressure in pressure chamber  426 . And conversely, the fluid flow path  440  is opened in response to an increase in oil pressure in pressure chamber  426 , compressing the stator spring  406  while moving the stator assembly  356  away from the drive disc  308 . It should be understood by those skilled in the art, that alternate embodiments such as a solenoid, for example, may be used to actuate the movement of the stator assembly  356  to open and close the fluid flow path  440  while remaining within the scope of the invention.  
         [0029]     Referring now to  FIG. 6 , the hydraulic pressure that pressurizes the pressure chamber  426  is generated by gear pump  500  attached to the front chain case  26 . This gear pump  500  also provides the hydraulic oil to the pistons  66  described above. The gear pump  500  is a positive displacement pump housed within a gear plate  934  that is attached to the front chain case  26 . A drive gear  130  meshes with and drives a driven gear  132 . The driving force for the drive gear  130  is provided by the brake shaft  62  through a slotted bolt  118  threadably attached to the brake shaft  62 . A protruding tab  122  on a drive gear shaft  126  engages a drive slot  114  in the slotted bolt  118 . Thus, the drive gear  130  is rotationally fixed to the brake shaft  62 , which is rotationally fixed to the universal joint coupling  34 , and thus pumps hydraulic oil whenever the universal joint coupling  34  is rotating. Through the above linkage, the braking force actuator, illustrated here as the gear pump  500  is driven by the first driven member, illustrated here as the universal joint coupling  34 . It should be appreciated, by one skilled in the art, that the braking force actuator may be driven by the first driven member and the brake rotor rotationally fixed to the second driven member, or it may be driven by an external source such as an electric motor or as an accessory driven off a prime mover, while still remaining within the scope of the invention.  
         [0030]     Referring now to  FIG. 7 , a schematic for a hydraulic system of an embodiment of the invention will be reviewed. The positive displacement gear pump  500  generates low pressure in suction port  502  connecting the pump  500  to an oil sump  504  through a filter  508  thereby drawing filtered oil into the pump  500 . The outlet of the pump  500  is connected in parallel through pressure port  512  to the pistons cavities  454 , the stator pressure chamber  426 , and to a needle valve  700 .  
         [0031]     Referring to  FIGS. 8 and 9 , partial cross sectional views of the brake apparatus  10  show the hydraulic fluid porting of  FIG. 7  in further detail. The oil filter  508  is positioned relative to the chain cases  22  and  26 , such that the oil filter  508  is located near the bottom of the oil sump  504 , and therefore is submerged in oil due to gravity. The filter  508  is sealed to the front chain case  26  by gasket  510  that is compressed by spring  511 . A first suction port  516  in the front chain case  26  ports oil from the filter  508  towards the gear pump  500 , it is then ported through a second suction port  520 , which is perpendicular to the first suction port  516 , and is connected to a third suction port  524  formed in a needle housing  528 . The third suction port  524  connects to a forth suction port  532  that forms the inlet to the gear pump  500 . Thus, the suction port  502  of  FIG. 7  comprises: first suction port  516 , second suction port  520 , third suction port  524  and forth suction port  532 . As the drive gear  130  of the gear pump  500  is rotated it meshes with and drives the driven gear  132  thereby generating an increasing volume that draws oil in from the forth suction port  532  and a decreasing volume that forces oil out through a first pressure port  540 . The first pressure port  540  connects the outlet of the gear pump  500  in parallel to the needle valve  700 , piston cavities  454  and the stator pressure cavity  426 . Thus, the pressure port  512  of  FIG. 7  comprises: first pressure port  540 , second pressure port  544 , third pressure port  548 , forth pressure port  552 , fifth pressure port  556 , sixth pressure port  446 , seventh pressure port  442  and a needle pressure port  712 . Plugs  560  are used to prevent oil leakage from through holes drilled in the various housings, and plug  564  plugs the access hole for the filter  508 .  
         [0032]     Since the gear pump  500  is continuously pumping oil, whenever the driven members are rotating, all of the outlet flow of the gear pump  500  is ported to oil sump  504  when there is no braking action. Thus, no pressure is generated or supplied to either the piston cavities  454  or the stator pressure chamber  426 . With no pressure supplied to the piston cavities  454  the brake pads  74  are not urged against the braking surfaces  330 ,  334  and no braking action is initiated. Additionally, with no pressure supplied to stator pressure chamber  426 , the stator spring  406  extends urging the stator assembly  356  towards the drive plate  308  to close off the cooling fluid flow path  440 , thereby not permitting the cooling fluid to be pumped. Conversely, when braking action is initiated, the needle valve  700  ( FIG. 10 ), ported in parallel with the piston cavities  454  and the stator pressure chamber  426 , moves toward a closed position, which generates pressure in the pressure port  512 .  
         [0033]     Referring now to  FIGS. 8 through 10 , oil flows into the needle valve  700  through inlet needle pressure port  712 , which is connected to the outlet of the gear pump  500  ( FIG. 8 ) via the first pressure port  540  ( FIG. 9 ), the second pressure port  544  ( FIG. 9 ) and third pressure port  548 . The needle pressure port  712  is connected to a needle cavity  716  in the needle housing  528 . A seat insert  714  is sealed to the lower portion of the needle cavity  716  with O-ring  718 . An outside diameter  734  of the needle  722  slidably and sealingly engages an inside diameter  738  of the seat insert  714 . A needle drain port  740  connects the inside diameter  738  to the oil sump  504  to vent the needle  722  within the insert  714  and needle housing  528 . Cross-holes  742  in the seat insert  714  connect the inside diameter  738  to a needle sump port  746  that connects to the oil sump  504 . A tapered needle seat  750  ramps the outside diameter  734  of the needle  722  to a neck  754  of a smaller diameter. Thus, with the needle valve  700  in the opened positions, oil is free to flow; in through the needle pressure port  712 , to the cavity  716 , through the inside diameter  738 , through the cross holes  742 , to the needle sump port  746 , and out to the oil sump. Therefore, the needle valve  700  is fully opened when the needle seat  750  is below the cross-holes  742  of the seat insert  714  such that oil is able to freely flow from the cavity  716  to the oil sump  504  resulting in no backpressure to the gear pump  500 .  
         [0034]     A solenoid  704 , attached to the needle valve  700 , is used to partially close the needle valve  700  resulting in an increase of the oil pressure of the system. The needle  722 , is suspended from a plunger  730 , of the solenoid  704 , by a head  726 . The plunger  730  that captures the needle head  726  is free to move, in a direction parallel to the axis of the needle  722 , within a plunger tube  758 . A hole  760  in the plunger  730  allows oil and air to flow therethrough, pressure balancing the plunger  730  within the plunger tube  758 . The plunger tube  758  is threadably attached to the needle housing  528  and is sealed to the needle housing  528  with an O-ring  762 . A coil  776  of the solenoid  704  abuts the needle housing  528  and circumferentially encases the plunger tube  758 . A nut  770  threadably engaged to the plunger tube  758  retains the coil  776  to the needle valve  700 .  
         [0035]     Energizing the coil  776  in the solenoid  704  generates a magnetic field that attracts the metal of the plunger  730 , which is normally positioned substantially below the coil  776  because of gravity and oil pressure acting over the area of the needle seat  750 . The magnetic attraction causes the plunger  730  to lift and move axially towards the center of the coil  766 . Oil pressurized by the gear pump  500  acts against the tapered needle seat  750  in a direction opposite that of the magnetic force on the plunger  730 . As the magnetic force on the plunger  730  increases, so does the pressure in the pressure port  512 . Thus, by controlling the strength of the magnetic field, the braking force is controlled. This embodiment has a fail-safe condition, in which, a failure of the electrical signal to the solenoid will result in the brake not braking at all. Additionally, this embodiment allows for limiting the maximum braking force that may be applied, by setting the maximum force of the solenoid  704  relative to the force due to pressure acting on the tapered seat  750  of the needle  722 . In this instance the solenoid serves as a hydraulic fluid pressure relief valve.  
         [0036]     Referring to  FIG. 11 , a control system  900  is used to control the electrical power supplied to the solenoid, thereby controlling the braking performed by the brake apparatus  10 . The heart of the control system  900  is a control circuit  904  which may be, for example, a microprocessor. The control circuit  904  may have several inputs  908  including; electrical power  912  supplied from the vehicle&#39;s power system, a driven member speed input  914  which may be supplied from the vehicle&#39;s computer or it may be supplied as pulses from a pick up such as a magneto or hall effect device attached to the brake apparatus  10  (of  FIG. 1 ) (this option will be discussed in more detail below) and an operator input  918 . The operator input  918  may provide a signal proportional to the level of braking desired by the vehicle operator through an input device such as a manually activated lever or through tapping into a brake pedal position sensor (not shown) for example. An output  922  of the control circuit  904  may be an electronic pulse width modulated (PWM) signal, for example. Such a signal to the solenoid  704  may generate a magnetic field strength, and a corresponding braking force, that varies depending on the duty cycle of the PWM signal. It should be appreciated by those skilled in the art, that alternate embodiments such as a voltage controller, for example, may be used to control the solenoid  704  while remaining within the scope of the invention.  
         [0037]     The driven member speed input  914  permits the control circuit  904  to adjust the braking force through the PWM output based on feedback received by the driven member speed input  914 . For example, a setting for maintaining a specific and constant drive member speed could be inputted by the operator. This constant speed mode would permit the operator to set a desired driven member speed to be maintained during a condition when the driver of the driven member is attempting to increase the speed of the driven member. Such a constant speed mode may be useful, when descending a grade, and instead of the operator manually adjusting the brake pedal to maintain a constant vehicle speed, the brake apparatus  10  would automatically adjust the braking force, thus creating a braking ‘cruise control’. This constant speed mode requires the control system  900  to receive an input  908  of the speed of the driven member  914  and in response send a PWM signal to the solenoid  704  to maintain the specified driven member speed.  
         [0038]     Referring back to  FIG. 6 , an embodiment of the invention showing one possible location for a driven member speed pick up is shown. One or more magnets  926 , attached to the axial end of the rotor sprocket  50 , will rotate with the rotational speed of the universal joint coupling  34  of  FIG. 1 . A magnetic field sensor  930 , attached to a the gear plate  934 , may be positioned to pick up the magnetic field of the magnet  926 , as it passes in proximity to the sensor  930 , during each revolution of the rotor sprocket  50  thereby creating a drive member speed input  914 . The magnetic field sensor  930  may be a Hall effect circuit or a magneto coil, for example, or any other magnetic field detecting sensor. Referring to  FIG. 11 , the control circuit  904  may use the output of the sensor  930  as feedback to control the rotational speed of the universal joint coupling  34  through control of the brake apparatus  10  of  FIG. 1 .  
         [0039]     By having the drive member speed input device  908  integrated into the brake apparatus  10  an embodiment of the invention may be attached to an existing vehicle without having to tap into the vehicle&#39;s electrical system to acquire a drive member speed input  908 . It may be desirable to attach the brake apparatus  10  to existing vehicles with little or no changes required of the vehicle hardware. The offset axis arrangement defined by having the axis of the brake rotor  300  offset from the axis of the vehicle&#39;s tail shaft  36 , allows the application of the brake apparatus  10  to the vehicle without requiring modifications to the vehicle&#39;s drive-shaft (not shown). Accordingly, the universal joint coupling  34  attaches directly to the vehicle&#39;s drive shaft universal joint (not shown). Additionally, the bolt hole pattern of the tail housing  30  is designed to match the bolt hole pattern of the vehicle&#39;s transmission (not shown) from which the tail shaft  36  protrudes. The band clamp  33  fixes the tail housing  30  relative to the front chain case  26  in any rotational orientation. This angular adjustability allows for installation variations without requiring additional customization during the installation process.  
         [0040]     Various embodiments of the invention may have some of the following advantages: a frictional braking apparatus that does not overheat, on board cooling fluid pump, on board hydraulic fluid pump, on board pressure control valve, automatic activation and deactivation of cooling fluid pump, braking force control system, constant driven member speed control system, a non-braking failsafe condition for any electrical system failure, an integrated hydraulic pressure relief feature, inherently pressure limited, and a closed hydraulic system with all in housing hydraulic porting (no hydraulic hoses), an offset drive configuration, allowing an aftermarket installation in a driveline of certain vehicles, without requiring driveshaft modification, and enhanced serviceability of rotor and seal components.  
         [0041]     While the embodiments of the disclosed method and apparatus have been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the embodiments of the disclosed method and apparatus. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the embodiments of the disclosed method and apparatus without departing from the essential scope thereof. Therefore, it is intended that the embodiments of the disclosed method and apparatus not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the embodiments of the disclosed method and apparatus, but that the embodiments of the disclosed method and apparatus will include all embodiments falling within the scope of the appended claims.