Abstract:
A hydrodynamic braking system with a retarder including a rotor arranged in a rotor housing and a stator arranged in a stator housing, whereby the rotor and the stator together form a working space. The rotor is axially movable relative to the stator, from a first position (braking operating position) to a second position (non-braking operating position), and vice versa. The axial distance between the rotor and the stator in the non-braking operating position is a multiple of the distance separating them in the braking operating position. According to one aspect of the present invention the rotor housing includes an outlet that is located at a distance from the axis of rotation of the rotor and is open toward the rotor in the non-braking operating position such that the operating medium collected by the rotor is conveyed outside the working space through the outlet.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention pertains to a hydrodynamic braking system with a retarder, and, more particularly, to a hydrodynamic braking system with a secondary retarder.  
         [0003]     2. Description of the Related Art  
         [0004]     WO 00/40872 describes a retarder that, for the purpose of targeted emptying of the retarder to a predetermined level, is equipped with an outlet located on the back wall of the stator housing that discharges into an outlet chamber. A pressure impulse cylinder is connected to the outlet chamber whose piston accelerates excess operating medium and moves it against internal resistance until an optimum power loss operation is achieved.  
         [0005]     A disadvantage of this design is that additional energy is required in order to effect the return transportation of excess operating medium from the retarder. In addition, the construction is complicated and its operation associated with additional mechanical losses.  
         [0006]     What is needed in the art is a hydrodynamic braking system with a retarder whereby the return transportation of excess operating medium from the retarder is to be more effective when compared with the current state of the art. Specifically, what is needed is a hydrodynamic braking system with a retarder whereby a particularly effective evacuation of the retarder in the non-braking position to a predetermined level can be achieved so that the evacuation should occur automatically, that is independently.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides a retarder with a movable rotor meaning that, in a non-braking operational condition it assumes a so-called “second position”, whereby moving the rotor into this “second, or non-braking position” the power loss, in particular the air power loss of the retarder is low.  
         [0008]     The invention comprises, in one form thereof, a hydrodynamic braking system with a retarder including a rotor arranged in a rotor housing and a stator arranged in a stator housing, whereby the rotor and the stator together form a working space. The rotor is axially movable relative to the stator, from a first position (braking operating position) to a second position (non-braking operating position), and vice versa. The axial distance between the rotor and the stator in the non-braking operating position is a multiple of the distance separating them in the braking operating position. According to the present invention the rotor housing includes an outlet that is located at a distance from the axis of rotation of the rotor and is open toward the rotor in the non-braking operating position such that the operating medium collected by the rotor is conveyed outside the working space through the outlet.  
         [0009]     Thereby the centrifugal force being exerted upon the operating medium in the rotating rotor is utilized in order to transport the operating medium through the outlet. The outlet is therefore provided at a location in the rotor housing, especially so that it is arranged radially internally opposite to the direction of the centrifugal force. The desired residual operating medium volume that is to remain in the retarder work space during non-braking operation can be adjusted through the radial position of the outlet.  
         [0010]     In the so-called “first position” during the braking operation the rotor is located relatively closely to the stator. The gap between the rotor and the stator blade tips is preferably only a few millimeters. In the non-braking position the gap width is many times greater than the gap width of the braking position.  
         [0011]     The axial movement of the rotor relative to the stator from a close position in the braking position to a more distant position in the non-braking operating position allows for a considerable reduction of retarder losses in the non-brake position compared to non-movable rotors.  
         [0012]     During non-braking operation the retarder is largely emptied in order to prevent ventilation losses due to air and residual operating medium remaining in the work space. On the other hand, a certain residual volume of operating medium should remain for the purpose of achieving an optimum power loss value that is, a minimal ventilation loss, and especially for achieving heat removal.  
         [0013]     Advantageously, the hydrodynamic braking system includes an external operating medium loop, especially for cooling of the operating medium that is heated during braking operation. The operating medium loop includes an equalizing reservoir with an operating medium discharge below the liquid level of the operating medium in the equalizing reservoir in order to compensate for leakages or volume differentials in the loop. The operating medium discharge in the equalizing reservoir is connected to at least one supply connection of the retarder via at least one supply line so that the operating medium can be fed into the working space from the equalizing reservoir. In one advantageous embodiment of the invention the outlet of the rotor housing is connected at least indirectly with the equalizing reservoir through a discharge line. This discharge line can discharge directly into the equalizing reservoir whereby the outlet is located below the liquid level in the equalizing reservoir. In another variation it can also discharge into a line section below the equalizing reservoir, between the equalizing reservoir and the supply line to the retarder.  
         [0014]     In the event of an indirect connection of the outlet of the rotor housing with the equalizing reservoir an additional atmospherically linked reservoir can advantageously be provided in the external loop. This atmospherically linked reservoir is positioned at a geodetic height above the liquid level in the equalizing reservoir.  
         [0015]     The atmospherically linked reservoir is connected via a line with the equalizing reservoir, and the discharge line that is connected to the outlet of the rotor housing discharges into the atmospherically linked reservoir. This has the advantage that the operating medium that is brought by way of the rotor in the non-braking operating position through the outlet in the rotor housing into the atmospherically linked reservoir, flows back into the equalizing reservoir due to gravitational force. This allows an especially low flow resistance to be achieved against which the operating medium is transported by way of the rotor through the outlet in the rotor housing. Since the discharge line flows into an atmospherically linked reservoir it is advantageous to provide a valve in the discharge line behind the outlet in the rotor housing, so that this line can be shut off securely during braking operation. It is especially advantageous if this valve is located directly on, or behind the outlet in the rotor housing. For example, shut-off valves or check valves are suitable.  
         [0016]     If the discharge line discharges directly into the equalizing reservoir below the liquid level, or into a line below the equalizing reservoir, a throttle may be installed in the discharge line instead of the described valve. This throttle is preferably dimensioned so that the braking operation is not be negatively influenced however, at the same time achieving the desired discharge via the outlet in the non-braking operation.  
         [0017]     In order to achieve sufficient cooling of the retarder, especially in non-braking operation, a continuous minimum mass flow of operating medium can advantageously be supplied through the retarder. This mass flow of operating medium that is referred to as cooling mass flow enters the retarder working through the supply line via a supply connection and exits it through the outlet in the rotor housing. It is advantageous to incorporate a pressure reducing element into the supply line whereby the reducing element has a continuously opened minimum flow cross section. On the one hand the pressure reducing element can be in the form of an adjustment device with a minimum flow cross section. On the other hand it may be in the form of an adjustment or shut-off element, that can especially be shut-off completely, whereby then parallel to this adjustment or shut-off element a throttle having a minimum flow cross section, especially a fixed cross section, is installed.  
         [0018]     Likewise, a throttle element having a continuously opened flow cross section may be installed in the discharge line, whereby a particularly low flow resistance is achieved if a single pressure reducing element is provided. Particularly if the entire external operating medium loop is free of external energy supply, that is if no driven pumps or hydraulic pistons are provided, emptying of the retarder to a desired residual operating medium volume, or cooling in non-braking operation can be done especially effectively. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0020]      FIG. 1  is a schematic view of an embodiment of a control diagram of a hydrodynamic braking system in accordance with the present invention, in non-braking operational condition, with a supply of the operating medium that is discharged from the retarder into an atmospherically linked reservoir;  
         [0021]      FIG. 2  is a schematic view of an embodiment of a control diagram of a hydrodynamic braking system with a retarder in accordance with the present invention, whereby the operating medium that is discharged from the retarder is fed directly into an equalizing reservoir;  
         [0022]      FIG. 3  is a schematic view of an embodiment of a control diagram of a hydrodynamic braking system with a retarder in accordance with the present invention, whereby the operating medium that is discharged from the retarder is fed directly into an equalizing reservoir having a minimum opening cross section in the discharge line;  
         [0023]      FIG. 4  is a schematic view of an embodiment of a control diagram of a hydrodynamic braking system with a retarder in accordance with the present invention, whereby a continuous cooling flow occurs through the retarder and the discharged operating medium is fed into an atmospherically linked reservoir;  
         [0024]      FIG. 5  is a schematic view of an embodiment of a control diagram of a hydrodynamic braking system with a retarder in accordance with the present invention, whereby a continuous cooling flow occurs and the discharged operating medium is fed into an equalizing reservoir;  
         [0025]      FIG. 6  is a schematic view of an embodiment of a control diagram of a hydrodynamic braking system with a retarder in accordance with the present invention, whereby a continuous cooling flow occurs and a throttle is installed in the discharge line; and  
         [0026]      FIG. 7  is a partially cross-sectional and partially schematic view of an embodiment of a retarder with an external loop in accordance with the present invention. 
     
    
       [0027]     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     Referring now to the drawings, and more particularly to  FIG. 1  there is shown a schematic illustration of retarder  1 , including rotor  1 . 1  and stator  1 . 2 .  FIG. 1  further illustrates rotor housing  1 . 3  and stator housing  1 . 4 . The non-braking operational condition is illustrated, that is, rotor  1 . 1  has been moved from stator  1 . 2  in axial direction, the direction of the axis of rotation  2  of the rotor, into a position of a greater distance, in order to avoid ventilation losses.  
         [0029]     Outlet  4  is located in rotor housing  1 . 3  at a defined distance from the axis of rotation of the rotor. In this example the direction of the outlet is aligned radially, that is vertical to the rotor&#39;s axis of rotation. As indicated, projections, or a pipe section protrude radially in direction of rotor  1 . 1  beyond the inner surface of rotor housing  1 . 3 . The height of this protrusion determines the residual operating medium that remains in the retarder housing. It is also possible to arrange the outlet in axial direction that is parallel to the rotor&#39;s axis of rotation  2 , at a defined position, at a distance from the axis of rotation of rotor  2 , whereby this defined radial position determines the volume of the residual operating medium remaining in the retarder housing.  
         [0030]     Check-valve  16  is located near outlet  4  in rotor housing  1 . 3 . Due to the motion of rotation of rotor  1 . 1 , the excess operating medium is captured by rotor  1 . 1  and transported through outlet  4  via opened check-valve  16  and discharge line  13  into an atmospherically linked reservoir  15 .  
         [0031]     As illustrated, outlet  4  serves to empty retarder  1  completely or to the level of a defined residual operating medium volume. The cross section of outlet  4  and discharge line  13  is therefore relatively small when compared with the cross sections of the lines or flow elements in external loop  10  that have through-flow during braking operation. During braking operation the operating medium is fed into working space  3  of retarder  1  through supply line  12  and supply connection  5 . In addition the operating medium is discharged from retarder I via outlet  6 , following throttle  21  and check-valve  22  into line  23  to heat exchanger  27 . From heat exchanger  27 , where the heat volume that was supplied to the operating medium in retarder  1 , is again evacuated, the operating medium flows back into retarder  1  through supply line  12  that is equipped with check-valve  24  and throttle  25 .  
         [0032]     An equalizing reservoir is provided in external loop  10 . The equalizing reservoir includes an operating medium outlet  11 . 1  below the liquid level of the operating medium in equalizing reservoir  11 . Line  14  is connected to operating medium outlet  11 . 1 , that is positioned essentially vertically, or almost vertically, which connects operating medium outlet  11 . 1  with supply line  12 . With the assistance of the operating medium in equalizing reservoir  11  leakages, for example, and volume differences that occur especially during the transition from the non-braking operational position to the braking operational position and vice versa in the retarder, or the external operating medium loop, can be equalized.  
         [0033]     The atmospherically linked reservoir  15  into which the operating medium that is captured by rotor  1 . 1  in the non-braking operating position and transported through outlet  4  from retarder  1  is fed, is positioned at a geodetic height above equalizing reservoir  11 . The atmospherically linked reservoir  15  is connected with equalizing reservoir  11  through line  19  with valve  20  which is designed as a gravity dependent check-valve so that the operating medium can flow from the atmospherically linked reservoir  15  back into equalizing reservoir  11 , conditional upon gravity. At a time when the pressure in equalizing reservoir  11  exceeds a predetermined pressure value valve  20  closes.  
         [0034]     Since discharge line  13  in this example feeds into the atmospherically linked reservoir  15 , line  13  is shut off by check-valve  16  during braking operation. As illustrated in the control diagram, check-valve  16  is designed so that it closes due to the braking operating pressure in retarder  1  and is opened by a spring element against the lesser pressure in retarder  1  during non-braking operation, so that the operating medium can flow into reservoir  15 .  
         [0035]     The pressure in equalizing reservoir  11  through which the braking torque of retarder  1  in the braking operating position is controlled, is adjusted by way of the 3/2 directional control valve  26  that is designed as a continuously changeable proportional valve. In the illustrated example the control medium with which the 3/2 directional control valve  26  is supplied (with the pressure P v ,) is separated from the operational medium. This is however, not imperative. A control valve that is supplied with operating medium can also be utilized to control the pressure in equalizing reservoir  11 .  
         [0036]      FIG. 2  illustrates another embodiment of a hydrodynamic braking system with retarder  1 .  
         [0037]     Identical references are assigned to identical elements. In this example, discharge line  13  that is connected to outlet  4  of rotor housing  1 . 3  feeds into the equalizing reservoir  11  below the operating medium level. The distance between the operating medium level and the opening of discharge line  13  is designated h. Essentially the same function mode as described in the first example ( FIG. 1 ) results. It is however, also be feasible to let discharge line  13  flow into line  14  below equalizing reservoir  11 .  
         [0038]      FIG. 3  illustrates an additional design example. Here too, discharge line  13  discharges below the operating medium level in equalizing reservoir  11 . In this example throttle  17  instead of check valve  16  is incorporated into discharge line  13  after outlet  4  of rotor housing  1 . 3 .  
         [0039]     Throttle  17  provides a continuously open cross section. The cross section is selected so that no adverse effects occur in the braking operation and that at the same time in the non-braking operation, the desired operating medium volume which is captured by rotor  1 . 1  is discharged through outlet  4 .  
         [0040]      FIG. 4  is a control diagram of an additional design example. In this design example discharge line  13  discharges, as in  FIG. 1 , into an atmospherically linked reservoir  15  that is located at a geodetic level above equalizing reservoir  11  and from which the operating medium discharges through line  19  and valve  20  due to gravity into equalizing reservoir  11 . A constant, but throttled line connection exists between equalizing reservoir  11  and supply connection  5  of retarder  1 . Line  14  is connected to outlet  11 .  1  of equalizing reservoir  11 , below the operating medium level. The line progresses essentially vertically or almost vertically and connects equalizing reservoir  11  through supply line  12 .  
         [0041]     An additional line  29  is connected to equalizing reservoir  11  that connects the equalizing reservoir with the line segment prior to heat exchanger  27 . Throttle element  30  and check-valve  28  that opens through the force of gravity are installed in line  29 . In the braking position check-valve  28  is closed due to the dynamic pressure. The flow connection through line  14  on the other hand, is essentially only effective during braking.  
         [0042]     In the further flow progression, supply line  12  splits into two parallel line branches  12 . 1  and  12 . 2 . Line branches  12 . 1  and  12 . 2  are brought together again prior to supply connection  5 . It is however, also feasible to have these line branches flow separately into different supply connections in retarder  1 . Supply branch  12 . 2  based on the location of check-valve  24  in-line with throttle  25  is consistent with supply line  12  of the previously cited examples. In this design example, however, line branch  12 . 1  with throttle  18  that has a continuously open minimum cross section, or a fixed cross section is installed parallel to line branch  12 . 2 . This opening cross section is preferably very small relative to, for example, throttle  25 . This line branch  12 . 1  with throttle  18  ensures the continuous line connection from equalizing reservoir  11  to supply connection  5 , and thereby into retarder operating chamber  3 . Instead of, or in addition to, parallel line branch  12 . 1  it is also feasible to equip check-valve  24  with a continuously open minimum flow cross section, or to replace it with another suitable valve.  
         [0043]     The dimension of throttle  18  in line branch  12 . 1  is selected so that an uninhibited braking operation is ensured. With the line connection from outlet  4  in rotor housing  1 . 3  through check-valve  16 , discharge line  13  to the atmospherically linked reservoir  15  a low pressure return flow of the discharged operating medium is possible. This operating medium flows due to the force of gravity from the atmospherically linked reservoir  15  into equalizing reservoir  11 . The gradient height h that results from the difference between the geodetic height between operating medium level in equalizing reservoir  11  and the geodetic height of supply connection  5 , whereby the operating medium level in equalizing reservoir  11  is positioned above supply connection  5 , ensures a continuous return flow of the operating medium into retarder  1 , with rotating rotor  1 . 1 . Since at the same time rotating rotor  1 . 1  transports an appropriate volume of operating medium through outlet  4 , a reliable heat elimination is provided through this continuous operating medium flow rate. The desired coolant flow rate can be adjusted through adjustment of the gradient height h and selection of the suitable pressure reducing flow elements in the flow lines. In this manner, a reliable cooling operation without the introduction of external energy, for example in pumps or hydraulic pistons, is achieved especially effectively in the entire external operating medium loop  10 .  
         [0044]     In addition to the cooling function the throughput operating medium volume also fulfills the function in the non-braking operating position of lubricating the rotating retarder components, so that the flow rate is established especially also in dependence of a defined, necessary lubricant volume.  
         [0045]      FIG. 5  illustrates a control diagram of another embodiment of the present invention. In contrast to  FIG. 4 , discharge line  13  is connected below the operating medium level in equalizing reservoir  11 , the same as in  FIGS. 2 and 3 .  
         [0046]      FIG. 6  illustrates another embodiment of the present invention. Here too, the discharge line flows into equalizing reservoir  1   1 , below the operating medium level. In this example, check-valve  16  in discharge line  13  according to the example in  FIG. 3  is replaced by throttle  17  with a continuously open flow cross section. Here too, as in the example illustrated in  FIG. 5 , a flow of operating medium results from equalizing reservoir  11  due to the geodetic height difference h between the operating medium level in equalizing reservoir  11  and supply connection  5  of retarder  1 , into working space  3  of retarder  1 . At the same time the portion of the operating medium that is captured by rotating rotor  1 . 1  is transported through outlet  4 , throttle  17  and discharge line  13  into equalizing reservoir  11 . This ensures a continuous cooling flow and especially also a lubricant flow whose volume flow can be regulated by way of the flow elements that are installed in the line connections, and the height difference h. The entire operating medium circuit is free of external energy supply, with the exception of the energy supplied to rotor  1 . 1 .  
         [0047]     In braking operation a flow cycle occurs from retarder  1  through line  23 , heat exchanger  27 , lines  12  and  12 . 2  into retarder  1 . In non-braking operation a cooling/lubrication cycle occurs from retarder  1  through line  13 , equalizing reservoir  11 , line  29 , heat exchanger  27 , lines  12  and  12 . 1  into retarder  1 . Line  14  serves essentially to fill retarder  1 .  
         [0048]     In the inventive hydrodynamic braking system all types of retarder can be utilized. Cited examples are primary retarder, secondary retarder, oil operated retarder, retarder operated with the operating medium of the vehicle cooling system (cooling water circulating pump retarder) retarder without bearings (over-mounted retarder) and retarder with (integrated) bearing assembly.  
         [0049]      FIG. 7  illustrates an additional embodiment of the present invention that essentially is consistent with the schematic depiction in  FIG. 6 , however, in larger constructive detail. Same components are designated with the same references. Again, the flow in non-braking operation that serves the retention of a cooling and lubrication circuit is indicated by the unbroken arrow lines  31 . This flow exits the retarder through outlet  4  and is returned to it again through supply connection  5 .  
         [0050]     In addition, the progression of the flow in braking operation is indicated by dot-dash line  32 . As can be seen, this flow is partially in opposite direction to the progression of the flow in the non-braking operation. This permits a flow through heat exchanger  27  in opposite direction, and also the supply and discharge lines that are connected to the heat exchanger. In general all lines or channels through which medium flows exclusively in the non-braking operating position have a smaller cross section than the lines or channels through which operating medium flows exclusively or additionally in the braking operating position, since the volume flow of the operating medium during braking operation is clearly greater than the throughput lubricant/coolant volume in non-braking operation.  
         [0051]     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.  
       Component Identification  
       [0052]    
       
           1  Retarder  
           1 . 1  Rotor  
           1 . 2  Stator  
           1 . 3  Rotor housing  
           1 . 4  Stator housing  
           2  Axis of rotation of rotor  
           3  Working space  
           4  Outlet  
           5  Supply connection  
           6  Outlet  
           10  Operating medium loop  
           11  Equalizing reservoir  
           11 . 1  Operating medium discharge  
           12  Supply line  
           12 . 1 ,  12 . 2  Line branches  
           13  Discharge line  
           14  Line  
           15  Atmospherically linked reservoir  
           16  Check-valve  
           17  Throttle  
           18  Pressure reducing element  
           19  Line  
           20  Valve  
           21  Throttle  
           22  Check-valve  
           23  Line  
           24  Check valve  
           25  Throttle  
           26  3/2 directional valve  
           27  Heat exchanger  
           28  Check-valve  
           29  Line  
           30  Throttle element  
           31  Flow progression in non-braking operation  
           32  Flow progression in braking operation