Hydrodynamic retarder
BACKGROUND OF THE INVENTION 
     The present invention relates to a hydrodynamic retarder including a rotor on a shaft, a stator, and a toroidal work chamber, in which the rotor and the stator are hydrodynamically coupled by respective blade wheels on the rotor and the stator located in the work chamber. The invention particularly relates to means for filling and emptying the work chamber. 
     Particularly when the hydrodynamic retarders are used in automotive vehicles or in systems with strongly varying operation, such retarders are connected and disconnected by filling and emptying the work chamber. For this purpose, working liquid is fed through suitable channels and past a prior control device to the work chamber or work space of the retarder. Removal of the working liquid from the work chamber is preferably radially outward via a slot located between the rotor and stator blade wheels. 
     Federal Republic of Germany Patent No. 35 11 795 discloses a hydrodynamic retarder in which the working liquid is introduced through channels in the blades of the stator directly into the so-called core ring of the retarder. There the lowest pressure prevails within the flow. As a rule, there is a hollow space that is not filled by the working liquid in the core ring even during operation, so that the retarder can be filled from a filling pump with only a slight expenditure of energy. The channels necessary for filling the work space are either cast directly into the blading or are subsequently welded therein. In either case, a channel path through the blades is connected, producing a sensitive local thickening of the blades in question. This leads to a considerable disturbance in the flow through the blading. 
     A hydrodynamic retarder is known from U.S. Pat. No. 2,126,751 in which feeding of the work liquid is effected via plates which are provided with slots, and the plates are arranged turnably on both sides of the stator blade wheel. The slots are of different widths. Depending upon the position of rotation of the plates, the slots come into alignment with channels which are cast into the blading of the stator blade wheel. However, these are control slots for dosaging the amount of working liquid flowing to the retarder and are not working liquid inlet or outlet slots. 
     Federal Republic of Germany Application DE-OS 16 75 246 discloses a retarder having blades which are also free of channels for the filling or emptying of the work space. The working liquid passes through an annular slot formed between the blade wheels and into the work space, and the liquid emerges from the work space via a similar slot arranged radially on the outside. The passage of the flow from one blade wheel to the other thus results in a considerable disturbance in the flow. 
     One skilled in the art knows that even in the case of a retarder whose flow is completely converted into heat by eddying, the power that is absorbed and the braking torque that is developed can be increased if the blading results in a flow which is as free of surges and is as undisturbed as possible. In the case of cast channels, this means careful rounding out of the differences in the thickness of the blades, and that in turn means an increased expense for material and a greater weight. In the case of welded channels, a flow favorable development within the thickness of the blade can be obtained only at a very particularly high manufacturing expense. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to improve the known hydrodynamic retarder in such a manner than an even higher braking power can be obtained, together with the possibility of simpler manufacture. 
     A further object is to improve the entrance and exit of working liquid in the working chamber of the hydrodynamic retarder. 
     The invention comprises a hydrodynamic retarder. As conventional, it includes a housing defining a torus shaped work chamber. A stator blade wheel with blades extending into the work chamber is supported in the housing. A rotor blade wheel is also supported in the housing. It includes blades in the work chamber which extend toward the blades of the stator blade wheel. The rotor blade wheel is supported for rotating on a shaft. The invention particularly concerns the openings through which the work chamber is filled and from which the work chamber is emptied. 
     For filling and emptying the work chamber, elongated working liquid inlet slots and working liquid outlet slots are provided on at least one of the two blade wheels, and preferably on the rotor blade wheel. The inlet or filling slots are located in the radially inner region of the respective blade wheel. The outlet or emptying slots are located in the radially outer region of the same blade wheel. The slots or openings are permanently open. In this way, the blades are free of the blade thickenings that result from the prior art filling or emptying channels, as these thickenings affect the flow of the liquid over the blades. The blade wheels have their full cross-sectional profiles opposite each other, so that the flow can pass, as free of surges as possible, from one blade wheel to the other. 
     The present invention reduces disturbances like those experienced with the retarder of the German Application DE OS 16 75 246 to a minimum and assures the development of optimal braking power. This is because the rear torus shaped surface of the chambers formed by two blades is not interrupted by slots or, for instance, circular holes. The slot like development of the inlet or filling openings and the outlet or emptying openings of the invention disturbs the flow rushing between two adjacent blades on the one slotted wheel only minimally, namely, only in that circumferential region which corresponds to the circumferential width of the slots. 
     The filling and emptying slots are preferably arranged on the rotor blade wheel. The inlet or filling slots are arranged behind or trailing the corresponding blades, as seen in the direction or rotation, on the radially inner region of the work chamber, while the outlet or emptying slots are arranged in front of or leading the corresponding blades, as seen in the direction of rotation, in the radially outer region of the work chamber. The slots, in this connection, follow in each case the orientation direction of the blades and are directed substantially radially. The blades themselves are at an inclined orientation with respect to the axis of the work chamber and the axis of the retarder, and the rotor blades are inclined in the leading direction leading the motion of the rotor wheel. 
     The number of inlet or filling slots depends primarily on how fast the retarder is to be filled, while the number of outlet or emptying slots depends on the braking power to be developed, i.e., on the liquid throughput necessary for the removal of the braking heat developed. A favorable distribution of the slots is obtained if a filling and an emptying slot are respectively arranged behind and in front of each second blade (that is, alternate blades) of the rotor wheel. There are preferred angular regions for the arrangement of the slots within the profile cross-section of the rotor blade wheel, and preferred ratios between the radial length of the profile cross-section, the thickness of the blade, and the width of the slots. 
     A labyrinth packing which is free of contact with the retarder housing is arranged on the rear side of the rotor blade wheel facing the retarder housing, in the circumferential region between the filling and emptying slots. In this way, passage of working liquid from the radially inner region to the radially outer region of the rotor blade wheel on the outside of the rotor blade wheel is to be prevented. 
     Other objects and features of the invention are described with reference to an embodiment shown in the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a digrammatic longitudinal section through part of a hydrodynamic retarder, including the invention; 
     FIG. 2 is a longitudinal section through part of the rotor blade wheel of the retarder; and 
     FIG. 3 is a cylindrical section through the blading of the rotor blade wheel, along the line III in FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a hydrodynamic retarder including a housing 1 having a torus shaped stator blade wheel 2 fixed in the housing 1 against rotation. There are blades on the stator blade wheel which extend over the full radial height of the torus shape and extend axially out from the axial outside of the wheel toward the rotor blade wheel. Opposite the stator blade wheel in the housing 1 of the retarder, there is a torus shaped rotor blade wheel 3 which is fastened on a retarder shaft 4. There are blades on the rotor blade wheel which extend over the full radial height of the torus shape and extend axially out from the axial outside of the wheel toward the stator blade wheel. 
     The two blade wheels and their blades are shaped to together substantially fill a torus-shaped work space or work chamber 10 in which both blade wheels are disposed. The blades extend near to each other, but do not interfere with their passage past each other. Each blade wheel terminates at an axial normal plane defined by the face side or edge of all of its blades. 
     The working liquid is first fed to the retarder through a feed channel 5 via a control device (not shown) in a radially inward, annular distributor space 6 wrapped around the shaft 4. From the space 6, the liquid passes through the work chamber 10, and then is removed through an outlet channel 7. On the rotor blade wheel 3, there are inlet or filling slots 8 in the radially inner region close to the distributor space 6, and there are outlet or emptying slots 9 in the radially outer region. Each of those slots extends over a given angular region. As seen in FIG. 3, each slot is obliquely inclined to the axis of the retarder to follow the direction of the rotor blades 11. The torus shaped work chamber or space 10 between the rotor blade wheel 3 and the stator blade wheel 2 is filled and emptied via the filling and emptying slots 8 and 9. 
     FIGS. 2 and 3 show the rotor wheel in a longitudinal section and in a cylindrical section. The rotor blade wheel can be viewed as a hollow, half torus shaped shell with an array of angled blades, as seen in FIG. 3, spaced around the shell, and each blade extends completely across the half torus shaped shell. As seen in FIG. 3, the blades 11 are inclined to the axis of the retarder, and particularly inclined in a leading direction, that is they are directed toward the direction in which the rotor blade wheel moves, that is down in FIG. 3, and away from the axial outer side of the rotor blade wheel. 
     The slots 8 and 9 are openings through the shell of the rotor blade wheel. The filling slots 8 commence after an angle a of between 15° and 30° from the radial bottom of the rotor at the open face side of the rotor blade wheel 3. The slots 8 have an angular length over an arc of an angle b which is between 30° and 60°. Similarly, the outlet or emptying slots 9 arranged in the radially outer profile region start after an angle c of between 10° and 20° from the radial top of the rotor at the open face side. The slots 9 have an angular length over an arc of an angle d between 30° and 60°. The filling slots 8 are each cast behind or trailing a rotor blade 11, while the emptying slots 9 are each cast in front of or leading a blade 11, in each case seen in the direction of rotation. 
     The width f of each of the filling and the emptying slots 8 and 9 is about one to three times the thickness s of the rotor blade 11. The ratio of the blade thickness s to its radial profile height h, that is, its height in the radial direction of the retarder, is between 1:30 and 1:35, and preferably 1:32. The radial profile height h is formed of a radially outer arcuate region m, a radially inner arcuate region n, and a flat intermediate region e. The ratio of the height of region e to the total profile height h is about 1:20. A labyrinth packing arrangement is indicated at 12, which is arranged around the circumference of the axially outer surface of the rotor blade wheel, between the inlet openings and the outlet openings, and extends from the rotor blade wheel to form a labyrinthine arrangement with the housing while being free of contact with the housing. The labyrinth packing prevents passage of working liquid from the radially inner region to the radially outer region around the outside of the rotor blade wheel. 
     Although the present invention has been described in connection with a preferred embodiment thereof, many other variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.