Abstract:
A Prony brake used as a rotational load absorption unit, or dynamometer, to measure power output of a prime mover includes a cylindrical tube, or drum, disposed within a sealed tank containing coolant water. Disposed within the cylindrical tube in a sealed manner is a fixed stator shaft. The stator shaft is attached to the center of a generally circular, planar stator plate having its outer periphery disposed in closely spaced relation to the tube&#39;s inner surface, with the stator shaft further coupled to a hydraulic control system. Disposed within the stator plate&#39;s outer periphery are plural radially spaced pistons responsive to the hydraulic control system for applying a radially outward friction braking force to the inner surface of the rotating cylindrical tube. The stator shaft is provided with first and second ports and passageways for respectively transporting hydraulic control fluid and lubrication fluid. Also included is a supplemental cooling water supply wherein cooling water is circulated with the Prony brake by the rotating cylindrical tube.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to rotational load absorption devices for precisely measuring the power output of a rotary prime mover, and is more particularly directed to an improved Prony brake-type load absorption device having a reduced number of components, offering simpler parts servicing and replacement, longer power measuring tests, and improved control and lubrication fluid access for servicing or replacement. 
       BACKGROUND OF THE INVENTION 
       [0002]    A Prony brake generally includes a rotating brake drum or disc connected with the output shaft of a prime mover, such as an internal combustion engine, and stationary friction pads, or brake shoes, that are engageable with the drum or disc in applying a retarding force thereto by frictional contact. The degree of retarding action is dictated by the force with which this frictional contact is applied. A Prony brake as described may be used simply as a power absorption device or, in combination with torque measuring means, as a dynamometer for testing the under-load performance characteristics of the prime mover. 
         [0003]    A brake&#39;s reactionary force on a prime mover can be expressed or measured in units of weight, be it pounds or kilograms. Reactionary forces are transferred through the brake&#39;s internal stationary stator section&#39;s shafts. An external extension of the rotary shaft connects to a stationary moment arm or to a fixed torque arm. A torque arm has a defined distance from the centerline of its stationary pivot to a point where the reactionary force is to be measured. This distance can be in inches, feet or in terms of a metric unit. Final measurement of torque is expressed in pounds and feet, i.e., lb/ft, or metric equivalent. Again, a Prony brake only establishes the force or torque reaction to which that force can be measured. 
         [0004]    Once a desired torque load has been obtained and torque values have been observed or recorded, it is at that point in time that the operational speed, or rpm (revolutions per minute), must also be observed. With a known torque load (lb/ft) and the operational speed (rpm), output power, or horsepower, can be calculated. Horsepower is the product of torque (lb/ft)×rpm divided by a constant, i.e., 5252. It is at this point, that the device can be classified as a dynamometer. 
         [0005]    All inherent reactionary forces both internal and external to the device must be measured accurately. These forces can be created by internal viscus oil shear, friction material drag, or external resistance to rotor travel through a cooling medium. Even though these forces may be small, they must be measured and accumulated in order to obtain maximum reaction force accuracy. 
         [0006]    Through the years, Prony brakes have been associated with a brake drum. Brake drums are formed by pouring molten cast iron into a prefabricated sand casting mold. Wooden patterns or aluminum match plates required to make the mold are expensive and require maintenance from time to time. By using this type of casting process, impurities and imperfections are suspended in the casting. Other areas of concern are sand holes, gas holes, and hard spots within the casting. It is the goal that during the machining operations of the brake drum, these impurities and imperfections are removed. Impurities and imperfections at the point of friction can reduce friction material operating lifetime, as well as the life of the brake drum. Brake drums must also be free of porosities which could allow water to penetrate the internal chamber of the brake. Water, oil and friction brakes do not mix very well. Should the brake experience water infiltration, it will go through rapid changes in its coefficient of friction causing the unit to severely vibrate. 
         [0007]    Finally, servicing and repair of Prony brakes over the years has been invasive and time-consuming. The performance of periodic, routine servicing of a typical Prony brake can easily extend over several hours, with multiple rotor brakes each requiring individual, independent servicing. For example, fresh maintenance fluid must be directed through each individual brake drum in cleaning or replenishing the maintenance fliud. The sampling of maintenance fluid currently involves a time consuming, invasive procedure, where the contaminated maintenance fluid typically finds its way to a lower brake drum water tank, and becomes mixed with the cooling water. This mixture of coolant water and used maintenance fluid is typically discharged to a drain or to the ground giving rise to pollution issues. The complex, invasive nature of these types of maintenance procedures gives rise to Prony brake low reliability and failures. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0008]    Accordingly, it is the object of the present invention to reduce dynamic vibration and movement of internal stator components such as encountered in prior art multi-drum Prony brakes, as well as to limit the axial length of the these types of Prony brakes. 
         [0009]    It is another object of the present invention to reduce the number of potential areas for internal hydraulic oil leakage such as encountered in prior art high horsepower, high torque Prony brake, such as where O-ring hydraulic connectors are used at each splined shaft connection in multi-stator Prony brakes. 
         [0010]    A further object of the present invention to reduce the mechanical stress on, the potential wear, and breakage to critical components such as splined and hydraulic connections in high horsepower, high torque Prony brakes. 
         [0011]    A still further object of the present invention is to reduce the extent of heat retained by various components in a Prony brake, particularly in internal pilot bearings located on splined connectors. 
         [0012]    Still another object of the present invention is to substantially reduce or eliminate the number of connecting lids secured by cap screws such as employed in multiple, or compound, brake drums. 
         [0013]    Still another object of the present invention is to reduce the number of required service parts required in high horsepower, high torque Prony brakes. 
         [0014]    Another object of the present invention is to provide increased torque measuring capacity as well as longer output power measuring and evaluation sessions for more accurate determinations. 
         [0015]    A still further object of the present invention is to simplify and shorten the time required for regularly scheduled maintenance of Prony brakes, increase the reliability and operating lifetimes of Prony brakes, and render the operation and servicing of Prony brakes more environmentally clean and safe. 
         [0016]    Briefly, the present invention contemplates a Prony brake having a single tubular stator shaft coupled to a single generally circular and planar stator plate with plural hydraulic piston bodies radially disposed in a spaced manner about its outer periphery to engage the inner surface of a rotating cylindrical tube rotationally displaced by a prime mover for measuring and recording the power output of the prime mover. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The appended claims set forth those novel features which characterize the invention. However, the invention itself, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, where like reference characters identify like elements throughout the various figures, in which: 
           [0018]      FIG. 1  is a longitudinal sectional view of a Prony brake in accordance with the present invention; 
           [0019]      FIG. 2 a    is a plan view of a stator plate used in a preferred embodiment of the present invention; 
           [0020]      FIG. 2 b    is a sectional view of a portion of the stator plate illustrated in  FIG. 2 a    illustrating the hydraulic brake piston used therein; 
           [0021]      FIG. 2 c    is a partial sectional view of the stator plate illustrated in  FIG. 2 a    with various components located therein; 
           [0022]      FIG. 3 a    is a longitudinal sectional view of a stator shaft employed in the Prony brake of the present invention; 
           [0023]      FIG. 3 b    is a plan view of an end of a stator shaft illustrated in  FIG. 3 a   ; 
           [0024]      FIG. 4 a    is a lateral sectional view of output end of the inventive Prony brake; 
           [0025]      FIG. 4 b    is a partially cut-away plan view of the torque arm connection in the inventive Prony brake; 
           [0026]      FIG. 5  is a combination perspective and plan view of the Prony brake system of the present invention incorporating additional cooling water reservoirs in accordance with another aspect of the present invention; and 
           [0027]      FIG. 6  is a top plan view shown partially in phantom of the inventive Prony brake incorporating the additional cooling water reservoirs shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Referring to  FIG. 1 , there is shown a longitudinal sectional view of a Prony brake  10  in accordance with the principles of the present invention. Prony brake  10  includes a single rotor tube  14  preferably comprised of high quality cast iron formed by means of a centrifugal process. During the pouring process, a circular mold turns, or rotates, during the pour. This creates a centrifuge effect allowing impurities to consolidate on the outer nonfunctional diameter of the rotor tube  14 . After machining the internal diameter, the rotor tube  14  is left with high quality material and the correct root means square (RMS) finish required at the point of friction. Using a rotor tube  14  allows for additional capacity expansion by merely cutting, or severing, the tube to a desired length without additional internal or connected external assemblies, where an increase in length allows for additional torque capacity expansion. 
         [0029]    The cylindrical side wall  14   a  of rotor tube  14  is provided with plural spaced radial ribs  15  to facilitate heat transfer from the rotor tube  14  during braking. The open ends of rotor tube  14  are provided with respective first and second machine steel rotor end covers  14   b  and  14   c  secured to the rotor tube&#39;s lateral wall by means of plural cap screws  17 . Each of the first and second rotor tube end covers  14   b ,  14   c  provides a double seal using viton O-rings to ensure retention of internal maintenance fluid and vapor, and to prevent water penetration into rotor rube  14 . The first and second rotor end covers  14   b ,  14   c  are symmetrical in depth design, with the first rotor tube end cover disposed on the input-driven end of the Prony brake  14 , while the second end cover  14   c  provides for retention of a rear rotor seal hub  65 . 
         [0030]    Prony brake  10  is coupled at its input end to a dynamic torque input shaft  30  coupled to a prime mover (not shown for simplicity), the output power of which is to be measured. Prony brake  10  further includes a front input shaft assembly  56  coupled to and engaging the dynamic torque input shaft  30 . The input end of Prony brake  10  also includes a steel tapered rotor hub  19  which is welded to a stator plate  40  and provides a common connection between the stator plate and a stator shaft  18  via a key  28 . Torque, or drive force, is provided through key  28  and stator shaft  18  via a commercially available sure grip bushing and a tapered lock hub  27 . Stator shaft  18  extends through the rotor tube front and rear covers  14   b ,  14   c  and rear rotor seal hub  65 . Further reduction of internal components results from a completely new and unique method of mounting the four hydraulic piston bodies  36   a - 36   d  to the steel stator plate  40  as shown in the sectional view of  FIG. 2 , with each piston body piloted and supported by the stator plate. Located 90° apart, each hydraulic piston body  36   a - 36   d  is cradled between precision machined slots in the stator plate  40  and is secured with cap screws  37 . This arrangement also allows for individual replacement of a respective hydraulic brake piston  32  within each piston body, as shown in  FIG. 2  for the case of piston  32  in piston body  36   d.  The internal working section of the Prony brake  10  requires just four piston bodies to provide approximately the same amount of ram, or hydraulic push, as sixteen hydraulic piston assemblies in the typical prior art Prony brake, or for the same torque and power capacity. 
         [0031]    As shown in  FIG. 2 a   , stator plate  40  is generally circular in shape and includes about its outer periphery four (4) spaced torque drive bar slots  33   a - 33   d  each adapted to receive a respective torque drive bar  39   a - 39   d  and four (4) hydraulic piston slots  31   a - 31   d  each adapted to receive a respective hydraulic piston body  36   a - 36   d.  Also shown in  FIG. 2 a    is one of the slots  45  disposed between the outer surface of stator plate  40  and the inner surface of rotor tube  14 , only a portion of which is shown in  FIG. 2 a   . Disposed on the inner surfaces of rotor tube  14  are plural spaced recessed channels, where one of these channels is shown as element  47  in the figure. Each of the channels  47  permits the flow of the friction material  46  between the rotor tube  14  and the stator plate  40  as shown in  FIGS. 2 b    and  2   c.    
         [0032]    Also as shown in  FIG. 2 c   , the four hydraulic brake pistons  32   a - 32   d  and four hydraulic piston bodies  36   a - 36   d  are disposed in an equally spaced manner about the outer periphery of stator plate  40 . Also shown in  FIG. 2 c    for simplicity are only two torque drive bars  39   a  and  39   b  disposed in stator plate  40 , it being understood that there are a total of four torque drive bars disposed in a spaced manner about the outer periphery of the stator plate. Each of the hydraulic piston bodies  36   a - 36   d  extends inwardly from the stator plate&#39;s outer periphery toward its center as shown in  FIG. 2 . Upon actuation of the Prony brake  10 , each of its four pistons is urged radially outward within stator plate  40  and urges the fluid friction material  46  in each of the four (4) slots  45  disposed about the outer periphery of the stator plate into engagement with the inner surface of the rotating rotor tube  14 . This action results in an outwardly directed braking force being applied to the rotor tube&#39;s circular inner surface. Each of the torque drive bars  39   a - 39   d  provides a respective stationary location for friction material disposed in a respective one of four (4) slots formed between the outer periphery of the stator plate  40  and the inner surface of rotor tube  14 . As a torque load is produced by Prony brake  10 , the reactionary braking force is transferred to each of the four torque drive bars. The force from all four (4) of the torque drive bars accumulates and is transferred to stator plate  40 . 
         [0033]    Referring to  FIGS. 3 a  and 3 b   , there are respectively shown longitudinal sectional and end-on views of the fixed stator shaft  18  disposed within and extending the length of Prony brake  10 . Stator shaft  18  includes first and second deep axial drilled slots  68   a  and  70   a  each having a respective external port  68   b  and  70   b  disposed in an end of the stator shaft. The first and second external ports  68   b ,  70   b  provide external access to the internal portions of the Prony brake  10 . The combination of the first slot  70   a  and first external port  70   b  is used for lubrication inspection, internal vapor pressure reference, and service of internal maintenance fluid. The combination of the second slot  68   a  and second external port  68   b  is adapted to receive hydraulic fluid for activating the brake pistons as discussed above. 
         [0034]    All components of a stationary nature are disposed within rotor tube  14 . Stator plate  40  is securely coupled to fixed stator shaft  18 . These two components are mechanically connected using a tapered hub  27  and a common spline, or key,  28 . Each end of stator shaft  18  is supported by a respective sealed bearing  20   a  and  20   b  disposed in a respective rotor cover plate  14   b  and  14   c.  Sealing of each of these end connections of stator shaft  18  requires a respective O-ring to ensure against the loss of maintenance fluid, as well as to protect against the penetration of water. The outer end of each of the hydraulic brake pistons  32   a - 32   d  receives a respective detent ball  34  as shown in  FIG. 2 c    for establishing a seal between the hydraulic brake piston and an adjacent pusher plate  42  as shown in  FIG. 1 . Pusher plate  42  includes a recessed portion  42   a  for receiving the detent ball  34 . 
         [0035]    A respective formed fabricated metal pusher plate  42  shown in  FIGS. 2 b  and 2 c    is associated with each of the hydraulic brake pistons  32   a - 32   d  and provides distribution of the hydraulic ram or push created by each hydraulic brake piston  32   a  as shown in these two figures as well as in  FIG. 1 . The outer portion of each pusher plate  42  has the same corresponding radius as the inside surface of the formed friction material  46  disposed between the outer surface of the pusher plate and the inner surface of rotor tube  14 . The outside radius of the formed friction material liner  46  also matches the inside radius of rotor tube  14 . Each of the four pusher plates  42  has a respective return spring  44  to return the pusher plate back to a neutral position after hydraulic pressure has been reduced or shut off. 
         [0036]    Each of the hydraulic piston bodies  36   a - 36   d  are disposed in and secured to a respective cylindrical slot disposed in the outer periphery of stator plate  40  as shown in  FIG. 2 . Each hydraulic piston body  36   a - 36   d  contains a respective one of the four hydraulic brake pistons  32   a - 32   d.  In each of the hydraulic piston bodies  36   a - 36   d  are sealed with viton O-rings  38  and pressure back-up rings  41 . Each of the four hydraulic piston bodies  36   a - 36   d  is hydraulically connected to the hydraulic service port within stator shaft  18  to permit the flow of hydraulic fluid required to actuate each of the four brake pistons  32   a - 32   d.    
         [0037]    The hydraulic brake assembly is installed in water tank  12  and is supported at each end of the tank. A stationary rear tank housing  16  provides support for stator shaft  18 . Within rear tank housing  16  are a pair of high pressure water seals  48   a  and  48   b  for confining water within the outer water tank  12 . A torque arm  26  is securely mounted to an end of stator shaft  18  and is attached to a stationary torque arm assembly  24  as supported by a cradle bearing assembly  25 . 
         [0038]    The front input shaft assembly  56  is comprised of dynamic torque input shaft  30  and drive hub  54  and is connected to a brake rotor cover assembly in the form of rotor tube end cover  14   b.  Front tank housing  58  provides a connection from the water tank  12  to a cradle bearing adapter  62 . Front tank housing  58  contains a pair of high pressure water seals  60   a  and  60   b  to retain water in water tank  12 . Also enclosed within the front tank housing  58  is a dynamic bearing  60  required to guide the dynamic torque input shaft  30  through the rotor tube&#39;s first end cover  14   b.  Connected to front tank housing  58  is the cradle bearing adaptor  62  which provides front tank support for the cradle bearing assembly  50 . Cradle bearing adaptor  62  also serves a secondary purpose as the adjustment mechanism required to set the brake assembly into its final operational position within water tank  12 . 
         [0039]    Positioned on the dynamic torque input shaft  30  is a sprocket adaptor (not shown) to drive a chain driven hydraulic pump (also not shown). The sprocket adaptor also provides drive for a toothed magnetic pick-up wheel (also not shown) for magnetic pick-up impulse of rpm, or speed. By driving the hydraulic pump via the dynamic pump input shaft  30 , control of the torque load is provided with a governor effect. This means that as torque load increases, the input speed slows down, and efficiency and oil volume of the hydraulic pump is reduced. This provides a buffer to reduce rapid overload or torque adjustments. 
         [0040]    The hydraulic pressure source used with the present invention can be as simple as a pressure controlled valve, a hydraulic oil reservoir, or a hydraulic pump. A power source for the hydraulic pump can be chain driven by the dynamic torque input shaft  30  for the inventive Prony brake  10 , or the pump may be driven by an electric motor. When the dynamic torque input shaft  30  is used, load control will have a governor loading effect. For example, when torque load is applied or increased, the input speed is reduced, or slows down. As input speed slows down, efficiency and the available oil volume of the pump is reduced. By reducing pump efficiency, hydraulic load control is very smooth and controllable. When the power source of Prony brake  10  is an electric motor, available hydraulic pressure is independent of input speed. This effect provides constant torque load control, with full torque loading starting at zero (0) RPM. Constant torque will work with engine or power take-off work, but is not recommended. Only a few applications, such as stall testing of hydraulic driven mechanical devices or a locked rotor on electric motors use constant torque for load control. 
         [0041]    Braking is a function of controlling hydraulic pressure. Load is applied to achieve a desired amount of torque load against a prime mover. Control of load may also use a desired RPM of the prime mover by which the measurement of torque load at that speed is required. A pair of simple hydraulic needle valves are all that is required to provide control or regulation of pressure. These valves can be positioned in series with each other, with one valve flow used for control and the other valve flow for pressure regulation. Electric options for load control or speed control include PID servo systems and electric proportional hydraulic control valves. These systems are normally closed loop requiring feedback from some type of load cell or strain gauge. Also required is rpm feedback of the prime mover if only speed is to be controlled. 
         [0042]    Hydraulic fluid under pressure is directed through the center of stator shaft  18  as discussed above, ending inside the hydraulic brake assembly, as the four brake pistons  32   a - 32   d  are connected in series with the stator shaft. As hydraulic pressure increases, brake piston push, or ram, increases proportionally to all four hydraulic brake pistons  32   a - 32   d.  The force created by the pistons is then transferred in an equal amount of ram through contact with each of the four (4) pusher plate  42 , which, in turn, pushes on the friction material liner  46  disposed between the pusher plate and the inner surface of rotor tube  14 . The outer radius of pusher plate  42  matches the inner radius of friction material liner  46 . The outer radius of friction material liner  46  is the same as the inner radius of the brake rotor tube  14 . It is very important to have the correct radius of each of the aforementioned mating components. Linear travel of brake piston  32   a  and all mating components is less than 0.125 inch from zero to high pressure. 
         [0043]    The four friction material liners  46  are each contained between a pair of adjacent torque drive bars attached to and extending from the outer surface of stator plate  40  as shown in  FIG. 2 c    for the first and second torque drive bars  39   a  and  39   b.  With each of the formed friction material liners  46  disposed between the outer rotor tube  14  and stator plate  40 , the friction material liners float in the spaces between the rotor tube and stator plate. Thus, friction material liners  46  are not bonded or secured to any other structure. Under dynamic operation, static friction between the friction material liner  46  and an adjacent pusher plate  42  is greater than the dynamic friction between the friction material liner and the rotor tube&#39;s inner friction surface. Depending upon in which direction the rotor tube  14  is turning, the friction material liners  46  will contact either side of each of the torque drive bars  35   a  and  35   b  as shown in  FIG. 2 c   . As working hydraulic pressure increases, the friction increases proportionally against the brake rotor tube  14 . This increase in friction, in turn, creates resistance, or a load, against the prime mover rotationally displacing the rotor tube  14 . This resistance force is transferred through each of the four torque drive bars to stator plate  40 , and thence to stator shaft  18 . Once transferred to the stator shaft  18 , a resistance force, or torque load, can be measured via torque arm  26  as shown in  FIGS. 4 a  and 4 b   . Once torque has been transferred to torque arm assembly  24 , measurement of torque can be used either via a compression or tension type load cell (not shown). Typically these electronic load cells are Z,S beam or candle levered. These types of load cells are positioned at a fixed distance from the centerline of the stator shaft  18  and are mounted to the torque arm assembly  24 . Analog readout of torque can be via a hydraulic pressure gauge, a hydraulic recording cylinder, or a charging supply pump. These measurements can be a direct torque measurement in terms of lb/ft, or as a sliding scale for power. 
         [0044]    The preferred maintenance fluid in the subject invention is a silicon fluid, such as GE SF1153, which replaces prior petroleum synthetic oils. During fluid evaluation, it was discovered that a surplus of fluid would be required to protect the friction material and mating brake drum friction surfaces. It was determined that a dam formed in the lower pusher plate  42  by welding in a gusset allowed friction material fluid to flow to the rotating edge of the brake drum to splash around inside the drum to protect the drum frictional surfaces. The friction material acts as a filter together with some of the maintenance fluid to maintain the friction surfaces clean and free from glazing. The friction material served as the sacrificial component in the operation of the inventive Prony brake  10 , as the friction material is normally a lower cost component. During development of this invention, its coefficient of friction was used as the only guidance as to the brake&#39;s internal condition during dynamic operation. The main success during operation was the fact that the coefficient of friction recovered from hot to cold temperatures. 
         [0045]    Referring to  FIG. 5 , there is shown a partial perspective and partial plan view of a Prony brake in accordance with the present invention incorporating supplemental cooling water reservoirs, which view is also shown partially in phantom. A top plan view of the Prony brake arrangement shown in  FIG. 5  is illustrated in  FIG. 6 . As described above, the Prony brake includes an inner rotor tube  14  disposed within a water tank  12 , which are both shown in  FIG. 5  in dotted line form. Rotor tube  14  includes plural spaced radial ribs, some of which are shown as elements  15  in  FIG. 5 , which are disposed about its outer lateral periphery and are aligned generally perpendicular to the longitudinal axis of the rotor tube.  FIG. 5  also illustrates the input and output cradle bearing assemblies  50  and  25 , as well as a power take-off shield  78  disposed adjacent the front input shaft assembly (not shown in  FIG. 5  for simplicity) for protection purposes. 
         [0046]    Additional Prony brake cooling water is provided by a large water reservoir in the form of a first upper supplemental cooling reservoir  74  and a second larger, lower supplemental cooling reservoir  76 . Water tank  12  is disposed within the upper supplemental cooling reservoir  74  and is connected to the upper supplemental cooling reservoir for receiving cooling water therefrom. These water connections are conventional in design and are not shown herein for simplicity. Upper supplemental cooling reservoir  74  is coupled in a sealed manner to the lower supplemental cooling reservoir  76  by means of first and second flexible rubber boots  72   a  and  72   b.  Depending upon the direction of rotation of rotor tube  14 , water flows from the upper supplemental cooling reservoir  74  via a first one of the flexible rubber boots to the lower supplemental cooling reservoir  76 , and returns from the lower supplemental cooling reservoir to the upper supplemental cooling reservoir via the other flexible rubber boot. The water flows from the upper supplemental cooling reservoir  74  to the lower supplemental cooling reservoir  76  under the influence of gravity. In addition, the high speed rotation of the rotor tube  14  applies an additional force to the downward flow of the water into the lower supplemental cooling reservoir  76  to increase the rate of water circulation. Also, the high speed rotation of the rotor tube  14  exerts another force on the water in the form of drawing the water up through one of the flexible rubber boots from the lower supplemental cooling reservoir  76  to the upper supplemental cooling reservoir  74 . This combination of forces applied to the circulating cooling water by rotor tube  14  increases water flow through the water cooling system and provides increased Prony brake cooling to more fully test the power for a more thorough and complete determination and analysis of the output power of a prime mover. Disposed in a lower portion of the lower supplemental cooling reservoir  76  is a baffle assembly  80  having first and second outer inclined walls  82   a  and  82   b.  Water discharged from one of the flexible rubber boots is incident upon the upper portion of the baffle assembly  80  with the first and second inclined walls  82   a  and  82   b  directing the water discharged into the lower supplemental cooling reservoir in opposite directions to more completely and efficiently circulate the cooling water within the lower supplemental cooling reservoir for enhanced Prony brake cooling. In addition, the weight of the increased water in the upper and lower supplemental cooling reservoirs provides increased ballest to increase the stability of the Prony brake during operation. 
         [0047]    With the rotor tube  14  driven by the prime mover and with the upper supplemental cooling reservoir  74  filled with water, a natural resistance and associated rotational drag on the water are produced by the rotor&#39;s moving outer surface. This rotational drag produces a pumping action of the water as it travels around the outer surface of the rotor tube  14 . Rotational drag in terms of power is a function of rotor speed, such that at 540 rpm the drag is approximately 7 horsepower, while 1,000 rpm produces approximately 25 horsepower. This circulating water power is used in this embodiment of the invention to circulate, or transfer, coolant from the upper supplemental cooling reservoir  74  to the lower supplemental cooling water reservoir, and vice versa. The rotational direction of the rotor tube  14  determines which side of the upper supplemental cooling reservoir  74  is circulated, or transferred, to the lower supplemental cooling reservoir  76  via one of the first or second flexible rubber boots  72   a  or  72   b.  The flexible rubber boot, which does not direct the water downward into the lower reservoir, then draws the water upward into the upper reservoir from the lower reservoir. A key element to increasing Prony brake cooling water efficiency is in the alignment of the centerline of the rotor tube  14  with the center of the coolant transfer ports in the form of the first and second flexible rubber boots  72   a ,  72   b.  This alignment position of the rotor tube  14  with respect to the first and second flexible rubber boots  72   a ,  72   b  also provides maximum rotor cooling at the point of friction, i.e., on the centerline of the above discussed pusher plate  42  relative to the point of highest friction in the friction material liner  46 . The position and orientation of the baffle assembly  80  in the lower portion of the lower supplemental cooling reservoir  76  directs the flow of coolant within the lower supplemental cooling reservoir to achieve more uniform Prony brake cooling. 
         [0048]    While particular embodiments of the present invention have been described, it will be obvious to those skilled in the relevant arts that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications that fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper prospective based on the prior art.