Abstract:
The invention relates to an automotive drive, comprising a cooling circuit with a coolant, a retarder having a rotor and a stator that together form a toroidal working chamber, with the coolant being the working medium of the retarder. The retarder has an inlet for feeding the working medium from the cooling circuit and an outlet for discharging the working medium into the cooling circuit. The present automotive drive is characterized by the following features: the retarder has an additional evacuation outlet, which communicates with the cooling circuit so as to carry the working medium; a leakage pump is interposed in the connection between the evacuation outlet and the cooling circuit.

Description:
BACKGROUND OF THE PRESENT INVENTION 
     1. Field of the Invention 
     The present invention relates to an automotive drive with a water retarder. The invention relates, in particular, to a device and a method for adjusting the optimal residual quantity of working medium in the working chamber of the retarder during non-braking operation. 
     2. Description of the Related Art 
     Retarders have been widely known in the art for a long time. Traditionally, conventional retarders have been operated with oil as the working medium. There has recently been an increasing tendency, however, to place the retarder directly in the cooling circuit of the motor vehicle and to utilize the coolant of the motor vehicle simultaneously as the working medium of the retarder. This is advantageous because it makes it possible to dispense with a separate oil circuit for operating the retarder. The heat that accumulates in the retarder can be dissipated directly via the cooling circuit of the motor vehicle. 
     During non-braking operation, the power loss of the retarder should be kept as low as possible. To this end, the retarder is largely emptied on shifting from braking operation to non-braking operation. Optimally, however, a predetermined residual quantity of working medium remains in the working chamber of the retarder. Up to now, it has been customary to discharge the working medium up to the predetermined residual quantity by means of the pressure produced in the retarder or, optionally, by means of additional, externally imposed pressure impulses. An absolute leak tightness of the sealing elements that seal the working chamber prevents a leakage flow into the working chamber of the retarder and, in this way, the optimal residual quantity of working medium in the working chamber is kept constant during non-braking operation. 
     There are several drawbacks to an absolute leak-tightness of all elements that seal the working chamber, such as the shaft seals or valves arranged in the cooling circuit that close off the branch of the cooling circuit in which the retarder is disposed from the remaining cooling circuit during non-braking operation. Extremely high-grade, precisely manufactured elements, which are expensive, can only be used. In addition, even slight wear after a short period of operation leads to the necessity of replacing these elements. 
     Accordingly, there is a need for a retarder that avoids the above-mentioned disadvantages of currently available systems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a retarder for an automotive system that is integrated into the cooling circuit of the automobile and utilizes the cooling fluid as a working medium. 
     The present invention further provides a retarder that improves on the equipment cost of current retarders by using less expensive parts. 
     The present invention still further provides a long-life retarder whose components do not have to be replaced frequently. 
     These and other objects and advantages of the present invention are provided by an automotive drive comprising a retarder, and a method for adjusting an optimal residual quantity of working medium in the working chamber of such a retarder during non-braking operation. 
     The automotive drive of the invention has a retarder, the working medium of which is the coolant of the motor vehicle. The working medium is fed from the cooling circuit of the motor vehicle via an inlet to the retarder. It then flows into the working chamber of the retarder, which is formed by the rotor blade wheel and the stator blade wheel, and is discharged via an outlet back into the cooling circuit. The retarder has an additional outlet, and evacuation outlet, for discharging the excess residual quantity of working medium from the working chamber of the retarder and into the cooling circuit of the motor vehicle during non-braking operation. The evacuation outlet is therefore connected to the cooling circuit and carries the working medium. 
     In order to ensure that an optimal residual quantity of working medium in the working chamber of the retarder during non-braking operation, a leakage pump is connected to the evacuation outlet and pumps the working medium out of the working chamber via the evacuation outlet into the cooling circuit. This is achieved by setting the tap point of the leakage pump is so that only the excess quantity of working medium is pumped off. The tap point is located in the direction of flow behind outlet holes introduced into the stator of the retarder. An overflow edge can be provided, especially in the direction of flow before the tap point, so that only “overflowing” working medium is pumped off. 
     The arrangement of the leakage pump in the present invention precludes the need for absolutely leak-tight seals and, if need be, valves that seal the working chamber of the retarder. This is especially true for those seals and valves that are impinged on both sides by the coolant of the cooling circuit. Such seals and/or valves include the shaft seals of the retarder rotor, which are lubricated and/or cooled by the coolant of the motor vehicle, and the valves that close off the branch of the cooling circuit in which the retarder is disposed from the remaining cooling circuit of the motor vehicle. 
     With respect to the rotor seals that are exposed to coolant, it is even possible to adjust a predetermined leakage flow into the working chamber of the retarder during non-braking operation, this leakage flow being discharged once again by the leakage pump arranged in accordance with the invention. The retarder and the shaft seal(s) are effectively cooled by this leakage flow, because heat is dissipated via this leakage flow into the cooling circuit of the motor vehicle. Finally, because the leakage pump maintains an optimal residual amount of working medium in the retarder during non-braking operation, power loss of the retarder during idling is reliably prevented, in spite of the lack of tightness of the seals of the working chamber. 
     The shaft seals that seal the retarder against the surroundings are advantageously constructed in an absolutely leak-tight manner in order to prevent an uncontrolled escape of coolant or working medium from the retarder into the ambient surroundings. 
     The leakage pump arranged in accordance with the invention is driven by an electric motor, the retarder shaft, or the compressed air supply of the motor vehicle. Preferably, the leakage pump is disposed directly on the retarder shaft, so that it is possible to dispense with interposed elements that transmit the drive torque. In this way, the leakage pump is driven with particularly low power loss. In an especially preferred embodiment, it is possible to dispense with an additional drive for the leakage pump by constructing the leakage pump as a water-jet pump that is integrated into the cooling circuit of the motor vehicle. In such a construction, the drive work of the leakage pump is performed indirectly by the water pump arranged in the cooling circuit of the motor vehicle. It is also preferred to provide a bypass in order to circumvent the leakage pump during braking operation of the retarder, because working medium can then be discharged from the working chamber of the retarder exclusively via the outlet mentioned for discharging the working medium. 
     The leakage pump can be a piston pump, as a membrane pump, or a centrifugal pump. The present invention also contemplates the use of any other suitable device for the leakage pump. 
     The above described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an embodiment of an automotive driveline of he present invention; and 
         FIG. 2  is a cross-sectional view of a tap point of the leakage pump in of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a cooling circuit  20  of the automotive drive of the present invention is shown. A coolant is circulated by means of a cooling water pump  1  in the cooling circuit. In the shown embodiment, the coolant is water or a water-glycol mixture. However, the present invention contemplates the use of any coolant that would be suitable for such an automotive drive. 
     By means of the coolant, an engine  2  is cooled and simultaneously, during braking operation, a retarder  21  is operated. The coolant in turn is cooled by means of a radiator  10 , which is can be a conventional motor vehicle radiator. A thermostat or a thermostatic valve  8  is disposed in the direction of flow (noted by the directional arrows in  FIG. 1 ) in front of the radiator  10 , and divides the flow of coolant into a line to the radiator  10  and a bypass to radiator  10 . The amount of coolant allowed to pass into radiator  10  and/or the bypass line depends on the amount of cooling required and is controlled by thermostatic valve  8 . For example, all of the coolant can be directed to radiator  10 , through the bypass line, or any mixture thereof. 
     Fluctuations in the coolant flow are compensated for by means of an equalizing tank  9 . An overpressure in the cooling circuit, for example, due to rapid draining of the retarder on shifting from braking operation to non-braking operation can be compensated for by a pressure-limiting valve  12  and the line opening into the equalizing tank  9 . Thus, when pressure-limiting valve  12  detects a coolant pressure that is above a certain value, it can divert some of the coolant into equalizing tank  9 . 
     By means of a 3/2-way valve  3 , it is possible to open up or close off the cooling circuit branch in which the retarder  21  is arranged to or from the remaining cooling circuit  20 . During braking operation, the coolant flows via the line shown (DN  50 ) to an inlet  21 . 1 . Via channels in a stator  23 , the coolant enters a working chamber  24  of the retarder, where it brakes a rotor  22 . Via the outlet holes in the stator  23 , the coolant or working medium is carried into a drainage channel, which is formed in the stator housing, and is discharged via an outlet  21 . 2  from the retarder. Subsequently, it flows through a control valve  7  back into the cooling circuit of the motor vehicle, where, as needed, it is cooled by the radiator  10 . 
     The retarder depicted has an axially adjustable rotor  22 . Rotor  22  is mounted on a rotor shaft  26  by means of an adjustable thread. Accordingly, during braking operation, the rotor  22  can travel to a position that is close against the stator  23  and, during non-braking operation, it can travel to an axial position distant from stator  23  so as to minimize the power loss. It is preferred for this back-and-forth travel to occur automatically. 
     The retarder is mounted in an overhung manner on the rotor shaft  26 , which is carried in a transmission  27 . The shaft seal that seals the working chamber  24  from the surroundings is constructed in two parts. It consists, as depicted, of an absolutely leak-tight, outer sliding ring packing  6  and a special seal  5  that is permeable to the working medium. The space between the two seals  5 ,  6  is impinged by coolant by way of a line  28 , and this coolant flows through the special seal along the rotor  26  to a throttling point, which is constructed as a split ring seal  4 , and then further into the working chamber  24  of the retarder  21 . Furthermore, the coolant can also be carried back via the line  29 , which, as a discharge line, connects the space between the seals  5 ,  6  directly to the cooling circuit  20 . 
     In addition to the outlet  21 . 2 , the retarder  21  further comprises an evacuation outlet  25  for discharging the working medium from the retarder into the cooling circuit  20  during non-braking operation. The evacuation outlet  25  is connected via a line  30  to the cooling circuit  20  at a point that in front of the 3/2-way valve  3  in the direction of coolant flow. Placed in the line  30  is a leakage pump  13  for purposefully pumping off excess working medium out of the working chamber of the retarder during non-braking operation. 
     By means of this leakage pump  13 , working medium that during non-braking operation flows via the shaft seal  5  into the working chamber of the retarder  21  can be pumped off into the cooling circuit  20 , so that the power loss of the retarder  21  is kept optimally low during non-braking operation. Furthermore, lack of tightness between the cooling circuit  20  and the cooling branch in which the retarder  21  is arranged—for example, of the valve  3  or of the valve  7 —can be compensated for by pumping off the leakage flows by means of the pump  13 . 
     Referring to  FIG. 2 , the construction design of the overflow edge  14  in the stator  23  of the retarder  21  is shown. As is discussed above and shown in greater detail in  FIG. 2 , rotor  22  and the stator  23  together form the working chamber  24 . The two are enclosed by a housing  16 . 
     An evacuation channel  11  is formed in this housing on the stator side. The working medium is carried from the working chamber  24  through outlet openings (not shown) in the stator  23  into the evacuation channel  11 . An overflow edge  14  is formed between the evacuation channel  11  and the stator  23 , that is, between the evacuation channel and the walls or shell of the stator  23  that is provided with the outlet holes mentioned. 
     In the shown embodiment, the overflow edge  14  is produced by providing a washer  17 , which is mounted in the housing  16  and is provided with a plurality of holes  15  in the axial direction of the retarder. In the present example, the washer is mounted on its face in the axial direction on two housing projections of the housing  16  and defines the boundary of the evacuation channel  11  in the axial direction. On the one hand, the holes  15  create the overflow edge  14  and, on the other hand, they produce an outlet throttle, the throttling action of which is adjusted by way of the cross section and the number of holes  15 . 
     In place of the holes  15  that are shown, oblong holes or slots—for example, a circumferential slot—could also be provided. 
     As discussed above, the drive of the leakage pump  13  can be constructed in different ways. Preferably, the leakage pump  13  is arranged, for example, on the rotor shaft  26  of the retarder  21  or is driven indirectly by the rotor shaft  26 . The leakage pump  13  need be switched on only during non-braking operation. However, it is also possible to allow the leakage pump  13  to be driven by the rotor shaft  26  during braking operation of the retarder in order to additionally dissipate drive energy from the retarder  21  and thus to increase the braking torque. 
     The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined herein. 
     List of Reference Numbers 
     
         
           1  water pump 
           2  engine 
           3  3/2-way valve 
           4  split ring seal 
           5  special seal 
           6  sliding ring packing 
           7  control valve 
           8  thermostat 
           9  equalizing tank 
           10  radiator 
           11  evacuation channel 
           12  pressure-limiting valve 
           13  leakage pump 
           14  overflow edge 
           15  holes 
           16  housing 
           17  washer 
           20  cooling circuit 
           21  retarder 
           21 . 1  inlet 
           21 . 2  outlet 
           22  rotor 
           23  stator 
           24  working chamber 
           25  evacuation outlet 
           26  rotor shaft 
           27  transmission 
           28  line 
           29  line 
           30  line