Abstract:
A hydrodynamic machine for producing a braking torque, the hydrodynamic machine comprising: a toroidal working chamber including a first bladed wheel and a second bladed wheel arranged concentrically with the first bladed wheel; and a hydraulic system including an open loop and closed loop control unit, a working medium accumulator, a line system, a pump operable to produce a volume flow circulation of a working medium through the line system and the toroidal working chamber, a heat exchanger, and a pressure control valve operable to control or adjust the baking performance or the braking torque.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of PCT application No. PCT/EP2014/070590, entitled “HYDRAULIC SYSTEM FOR A HYDRODYNAMIC MACHINE”, filed Sep. 26, 2014, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a hydrodynamic machine, in particular a hydrodynamic retarder to produce a braking torque by way of a fluid. 
         [0004]    2. Description of the Related Art 
         [0005]    Hydrodynamic machines or hydrodynamic retarders generally include a housing in which a first bladed wheel, in particular a rotor and a second bladed wheel, in particular a stator arranged concentrically thereto which together form a toroidal chamber, and that are grouped about a common axis of rotation are arranged. 
         [0006]    Retarders or hydrodynamic brakes can be arranged in a drive train on the motor side or respectively gear box side. The fill level of the retarder with a working fluid, for example oil or water with or without additives, determines the “rotor braking torque”. When operating the retarder, oil for example is pumped into the working chamber. During braking operation, the driven rotor accelerates this oil and transfers it on the outside diameter of the working chamber to the stator. There, the oil is slowed and returned via the inside diameter of the working chamber back into the rotor. Due to the generally known interaction between rotor and stator the braking torque develops. 
         [0007]    A hydraulic system ensures that in the non-braking operation and/or in the braking operation the working chamber is supplied or respectively filled with the appropriate working medium. It is thereby of special consideration that the heat that is generated in both operational modes is removed from the working chamber by way of the working medium and is returned for cooling to a cooling circuit in a cooler. It is particularly necessary in the non-braking operation that a minimum volume is routed through the working chamber in order to cool the retarder also in the non-braking operation. 
         [0008]    The working chamber is connected to a working fluid circuit via the fluid supply and the fluid discharge, wherein said circuit consists essentially of a working fluid accumulator, a cooler, a pump and several valves. An open loop and closed loop control unit is connected with the components of a hydraulic system in such a manner that the braking torque and/or working medium flow can be controlled or respectively regulated. 
         [0009]    A hydraulic system of this type is known for example from DE 10 2006 030 791 A1. In this hydraulic system the objective is essentially to direct the working medium in all operational modes through a cooler in order to achieve optimum temperature control. The working medium is an oil that at the same time is used for gear lubrication. For adaptation of the volume flow it is provided to control the pump of the hydraulic system. 
         [0010]    It is the objective of the current invention to suggest an improved hydraulic system for a hydrodynamic machine. In particular, with the objective to improve the electro-hydraulic system in regard to the adjustability of the braking performance. 
       SUMMARY OF THE INVENTION 
       [0011]    The invention includes a hydrodynamic machine or a retarder, in particular a hydrodynamic retarder, comprising a first bladed wheel, in particular a rotor and a second bladed wheel arranged concentrically thereto, in particular a stator that together form a toroidal working chamber. The hydrodynamic machine moreover includes an electrohydraulic system including an open loop and closed loop control unit, a pump, a heat exchanger, a working medium accumulator, a valve and a line system, wherein a volume flow circulation of the working medium can be generated by the pump through the line system and the working chamber. The electrohydraulic system is characterized in that the valve is a pressure control valve by means of which the braking performance or respectively the braking torque can be controlled/adjusted. 
         [0012]    By using a pressure control valve, the system pressure can be advantageously controlled proportionally to the torque or respectively braking torque. The pressure control valve may be a 3/3 directional valve or a 3/2 directional valve. 
         [0013]    The electrohydraulic system for control/adjustment of the pressure control valve can moreover include a pressure differential control. In the sense of the invention, the pressure differential control comprises at least one proportional valve and the open loop and closed loop control unit. 
         [0014]    In addition, a sensor can be coupled for torque measurement with the open loop and closed loop control unit so that torque measurement values can also be used for the pressure differential control. 
         [0015]    The pump is moreover integrated into the hydraulic system in such a manner that the pump can be switched in two operational states: a first operational state, the non-braking state; and a second operational state, the braking state; wherein the line system is designed in such a manner that a volume flow circulation can be pumped through the working chamber in both operational states. 
         [0016]    By using a pump in combination with a switching valve in order to secure supply of the working chamber with working medium in all operational situations, the complexity of the line system or respectively the hydraulic system can be reduced. This results in reduced hydraulic resistances, as well as advantages in regard to system safety, maintenance and economic efficiency. 
         [0017]    The pump can be a Gerotor pump that is coupled or non-rotatably connected with the rotor. 
         [0018]    In a first embodiment, the switching valve for switching of the operational state can moreover be located at the pressure side of the pump, wherein a bypass line is provided for bypassing the switching valve and the pump, back into the working medium accumulator is provided. In this arrangement the substantial control of the working medium volume occurs on the pressure side of the pump, in particular through the downstream hydraulic- or line system. Non-essential working medium is returned into the working medium accumulator before and/or after the valve. 
         [0019]    In a second embodiment, the switching valve for switching of the operational state can be arranged on the suction side of the pump, whereby in this arrangement a bypass line is provided to bypass the valve and through which the working medium can be sucked by the pump. 
         [0020]    A second bypass line is provided, so that working medium or a partial volume flow can be pumped in the first operating state, the non-braking operation, into the working chamber also in this embodiment. A working medium filter can be provided in this bypass line. 
         [0021]    In this design a proportional valve by way of which the first pressure control valve is controlled/adjusted can moreover be coupled advantageously after the working medium filter with the bypass line. This has two advantages. In the first instance, only a small amount of working medium needs to be filtered, thus considerably reducing the costs for the “filter” function. The proportional valve is moreover kept ready for operation at all times due to the coupling with the bypass line, since there is always a certain working medium pressure present. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    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: 
           [0023]      FIG. 1  illustrates a sectional view of a retarder according to the invention; 
           [0024]      FIG. 2  illustrates a first embodiment for the design of a hydraulic system; and 
           [0025]      FIG. 3  illustrates a second embodiment for the design of a hydraulic system. 
       
    
    
       [0026]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    With additional reference to  FIG. 2 ,  FIG. 1  is a sectional view of an exemplary retarder that is used in particular in buses and commercial vehicles. The retarder includes a housing consisting of several housing parts, a rotor  1  and a stator  2  that together form a toroidal annulus or working chamber  4 . 
         [0028]    The retarder is driven by a working medium, in particular an oil that is pumped by way of pump  11  via a line system into intake channel  6  or respectively spiral channel. From intake channel  6  the oil arrives through separating gap  3  into working chamber  4 . During the braking operation, a circulatory flow forms in working chamber  4 . Driven rotor  1  accelerates the oil and transfers it at the outside diameter into stator  2 . There, the oil impacts on the stationary stator blades and is slowed down. On the inside diameter the oil flows again to rotor  2 . The resulting braking energy is converted predominantly into heat, so that it is necessary to cool part of the oil permanently by way of a heat exchanger  19 . This part of the oil is drained from the circulatory flow through the fluid outlet or outlet channel  7 . The drained oil is then pumped through a heat exchanger  19  and subsequently—depending on the operational condition—back into working chamber  4 , so that a circulatory flow is created. In non-braking operation the oil is pumped back into working medium accumulator  10 . 
         [0029]      FIG. 2 , with continued reference to  FIG. 1 , illustrates a first embodiment for the design of the hydraulic system. A substantial characteristic of this design is the positioning of pump  11  before valve  9 . The valve is herein illustrated in the non-braking operational position. As soon as the pump is driven, oil is pumped from the working medium accumulator  10  via the valve  9  into bypass lines  27 ,  28 . A throttle  14  is installed in bypass line  27  that can be adjusted in such a manner that a small part of the working medium is pumped into working chamber  4 . The volume flow is to be selected large enough that sufficient heat removal out of the working chamber is ensured. Moreover, it may not be so large as to create an increased no-load resistance. From working chamber  4 , the oil is pumped through heat exchanger  19  back into working medium accumulator  10 . Thus, a small amount of oil is continuously being cooled in the non-braking operation by way of heat exchanger  19 . 
         [0030]    Second bypass line  28  feeds the remaining, substantially larger volume flow directly back into working medium accumulator  10 . Pump  11  thus runs virtually in a no-load mode as a result of which the losses in the non-braking operation can be minimized without having to adjust the pump  11 . A Gerotor pump can hereby be used that is driven directly by the rotor shaft. 
         [0031]    For the braking operation—position not indicated—valves  9 ,  16  and  20  are switched. As soon as switching valve  9  that is located on the pressure side of pump  11  switches, the working medium gets into working chamber  4  via working medium limes  30 ,  31  and valve  16 . 
         [0032]    Valve  16  is a pressure compensator that is switched into the appropriate switching position via the pressure measured in working chamber  4  and the pressure predefined by proportional valve  21 . A pressure compensator is a differential pressure valve or a pressure control valve that can regulate a differential pressure between an externally fed measuring location and an actual pressure at the valve. Valve  16  can be designed as a 3/3 directional valve as illustrated herein, or also as a 2/3 directional valve. The system pressure in working chamber  4  can be regulated proportionally to the desired braking torque at the rotor shaft by way of the pressure compensator. A torque sensor can be provided for this purpose, for example on the rotor shaft. In this switching, proportional valve  21  is supplied with system pressure only when switching into the braking position. A filter  13  is provided for the protection of proportional valve  21  that filters the entire working medium necessary for the braking operation. 
         [0033]    As a result of switching valve  20 , a closed loop between working chamber  4  and cooler  19  is formed, wherein the system pressure is adjusted through control of the pressure compensator. 
         [0034]      FIG. 3 , with continued reference to  FIG. 1 , illustrates a second embodiment of the structure of the hydraulic system. This differs substantially from the first embodiment, wherein also in this embodiment in the non-braking operation, a certain volume of working medium is pumped into working chamber  4  by way of pump  11 . In this design, valve  9  is located on the suction side of pump  11 . 
         [0035]    In the non-braking operation working medium is continuously sucked by pump  11  via bypass line  26  that is throttled by way of a suction throttle  17  from working medium accumulator  10 , and is pumped via bypass  27  into working chamber  4 . Bypass line  27  thereby ends in inlet channel  6  in such a way that the working medium is essentially pumped through working chamber  4  into outlet channel  7 . 
         [0036]    An additional throttle  14  is installed in bypass  27 , and before the same, a proportional valve  21  is connected with valve  25  to bypass line  27  for control of the pressure compensator. In this way it is ensured that there is always sufficient system pressure available at proportional valve  21 , and that therefore always a quick delay-free adjustment of the braking effect is facilitated. Moreover, a filter  13 , in particular a fine filter is installed in bypass line  27  before proportional valve  21 . As a result, only the relatively small volume that is necessary for the non-braking operation and for control of proportional valve  21  is filtered. 
         [0037]    For the braking operation—position not illustrated—valves  9 ,  20  and  25  are switched. The oil gets into working chamber  4  via working lines  30 ,  31  and valve  25 . Valve  25  is a pressure compensator that is switched into the appropriate switching position according to the pressure that is measured in working chamber  4  and the pressure that is predefined by proportional valve  21 . Valve  25  can be designed as a 2/3 directional valve as indicated in this example, or alternatively as a 3/3 directional valve. By way of the pressure compensator the system pressure in working chamber  4  can be adjusted proportionally to the desired braking torque at the rotor shaft. For this purpose, a torque sensor may for example by provided on the rotor shaft. 
         [0038]    A Gerotor pump  11  is provided as the pump and is connected non-rotatably with the rotor shaft. Both embodiments ensure that the pump resistance in the non-braking operation is very low and supports the braking action in the braking operation. 
         [0039]    Generally, the filters and return lines into the working medium accumulator  10  illustrated in the drawings, and the throttles or check valves that are installed in the lines, are indeed necessary for the overall function but are routinely used by the expert. 
         [0040]    While this invention has been described with respect to at least one embodiment, 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 LIST 
       [0000]    
       
           1  rotor 
           2  stator 
           3  separation gap 
           4  working chamber 
           5  axis of rotation 
           6  inlet channel 
           7  outlet channel 
           8  electrohydraulic system 
           9  valve 
           10  working medium accumulator 
           11  pump 
           12  pressure relief valve 
           13  oil strainer/filter 
           14  throttle 
           15  check valve 
           16  pressure differential valve 3/3 directional valve 
           17  suction throttle 
           18  pressure relief valve 
           19  heat exchanger 
           20  switching valve 
           21  proportional valve 
           22  open loop and closed loop control unit 
           23  control line 
           24  control line 
           25  pressure differential valve 
           26 - 29  bypass line 
           30 - 31  working line 
           32  line to cooler