Abstract:
An oil-flooded single-plate or multi-plate lockup clutch is provided in a torque transfer device. The torque transfer device may, for example, be a converter, a dual clutch, a starting clutch, a manual shifter or power shifting clutch, having a piston to engage the clutch and a damper. In accordance with the present disclosure, the piston together with a housing of the torque transfer device forms a closed pressure chamber when the clutch is engaged and at least one oil flow opening is provided in the piston in an area outside of the pressure chamber. The torque transfer device preferably has a damper and the piston of the clutch forms a part of the damper and may be designed as a retainer for springs of the damper.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from German Patent Application No. 10 2015 213 079.7, filed Jul. 13, 2015, which application is incorporated herein by reference in its entirety. 
       FIELD 
       [0002]    The present disclosure relates to an oil-flooded single-plate or multi-plate clutch in a torque transfer device such as a converter, a dual clutch, a starting clutch, a manual shifter or power shifting clutch, having a piston to engage the clutch and a damper, wherein the piston of the clutch is at the same time also designed as part of the damper, and where the piston, together with a housing of the torque transfer device, forms a closed pressure chamber when the clutch is engaged. 
       BACKGROUND 
       [0003]    A clutch is a mechanical device that engages and disengages the power transmission, especially from the driving shaft to the driven shaft. Clutches are used whenever the transmission of power or motion must be controlled either in amount or over time. Clutches control transmission of engine power to the wheels. In an oil-flooded single-plate or multi-plate clutch in a torque transfer device such as a converter, a dual clutch, a starting clutch, a manual shifter or power shifting clutch, having a piston to engage the clutch and a damper, the piston of the clutch may, at the same time, may also be designed as part of the damper, and where the piston, together with a housing of the torque transfer device, forms a closed pressure chamber when the clutch is engaged. Single-plate clutches of this type are used in some converter constructions so as to use the piston of the torque converter lockup clutch simultaneously in particular as a retainer damper to save a lot of space. 
         [0004]    Unfortunately, during an engagement of the lockup clutch of this type, a slippage occurs between the piston and the housing, because of the differences in speed of rotation existing at this time, which are not reduced until operation is free of slip. These rotational speed differences result in hydraulic fluid pressures. This causes flows to develop in the converter to equalize the pressure. To this end, in single-plate clutches whose piston is designed as a retainer bowl, the flow must stream around the retainer bowl. Avoidance of this pressure difference or compensatory flow is possible only with difficulty. 
         [0005]    It therefore is an object of the present disclosure to provide an oil-flooded single-plate or multi-plate clutch of the above type having improved adjustability and to avoid the problems of differences in hydraulic fluid pressure. This object is fulfilled according to the disclosure by an oil-flooded single-plate or multi-plate clutch having the features above and below described. These and other objects, features, and advantages of the present disclosure will become readily apparent upon a review of the following detailed description of the disclosure, in view of the drawings and appended claims. 
       SUMMARY 
       [0006]    In accordance with the disclosure, an oil-flooded single-plate or multi-plate lockup clutch is provided in a torque transfer device. The torque transfer device may, for example, be a converter, a dual clutch, a starting clutch, a manual shifter or power shifting clutch, having a piston to engage the clutch and a damper. In accordance with the present disclosure, the piston together with a housing of the torque transfer device forms a closed pressure chamber when the clutch is engaged and at least one oil flow opening is provided in the piston in an area outside of the pressure chamber. The torque transfer device preferably has a damper and the piston of the clutch forms a part of the damper and may be designed as a retainer for springs of the damper. 
         [0007]    The oil-flooded single-plate or multi-plate clutch may be provided with a friction lining which is positioned on a motor-side lateral surface of the piston and is provided to rest against an opposite inner surface of the housing when the piston is displaced axially, in order to engage the lockup clutch and the oil flow opening is provided outside of the friction lining. Further, the piston may extend radially beyond the pressure chamber and the oil flow opening may be present radially outside of the pressure chamber. The oil flow opening may be in the form of a drilled hole. The one or more oil flow openings thus permit pressure equalization between a first and a second axial side of the piston. The present invention is usable in particular for oil-flooded single-plate clutches having a piston, in particular with a combined retainer piston in 2-channel torque converters. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Various embodiments are disclosed, by way of example only, with reference to the accompanying drawings in which corresponding reference symbols indicate corresponding parts, in which: 
           [0009]      FIG. 1  shows a cross sectional view of a two-channel torque converter having an oil-flooded single-plate clutch with a combined retainer piston, 
           [0010]      FIG. 2  is a schematic depiction of a two-channel converter having a retainer piston and oil flow openings in accordance with the disclosure in the combined retainer piston, and 
           [0011]      FIG. 3  is a top view of a retainer piston having oil flow openings. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements. It is to be understood that the claims are not limited to the disclosed aspects. 
         [0013]    Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the claims. 
         [0014]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure pertains. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the example embodiments. The assembly of the present disclosure could be driven by hydraulics, electronics, and/or pneumatics. 
         [0015]    It should be appreciated that the term “substantially” is synonymous with terms such as “nearly,” “very nearly,” “about,” “approximately,” “around,” “bordering on,” “close to,” “essentially,” “in the neighborhood of,” “in the vicinity of,” etc., and such terms may be used interchangeably as appearing in the specification and claims. It should be appreciated that the term “proximate” is synonymous with terms such as “nearby,” “close,” “adjacent,” “neighboring,” “immediate,” “adjoining,” etc., and such terms may be used interchangeably as appearing in the specification and claims. The term “approximately” is intended to mean values within ten percent of the specified value. 
         [0016]    As depicted in the sectional view according to  FIG. 1 , in this embodiment a torque converter that serves as a hydraulic transmission unit has: an impeller  11  that is attached to a housing  10 , a turbine rotor  12  that faces the impeller  11  and is positioned rotatably in the housing  10 , a stator  2  that is positioned between the impeller  11  and the turbine rotor  12 , and a freewheeling clutch  3 . The freewheeling clutch  3  is positioned radially in the stator  2  and has an inner raceway  4 , an outer raceway  5  and a sprag  6  positioned between them. The stator  2  and the outer raceway  5  of the freewheeling clutch  3  are fixed against rotary motion and are positioned concentrically with each other. 
         [0017]    In the present case, the stator  2  and the outer raceway  5  are engaged through a spline profile section A and a centering section B, which are offset from each other axially and radially. As depicted in  FIG. 2 , the spline profile section A has an inner spline profile  21  and an outer spline profile  51 . 
         [0018]    The freewheeling clutch  3  is provided with a front ring plate  7  and a rear ring plate  2   a,  so that the outer raceway  5  is centered in relation to the inner raceway  4 . The axial positioning of the sprag  6  by means of a cage is likewise fixed. In this embodiment, the stator  2  has an elongated section which extends radially inward from the centering section B, and this elongated section functions as the rear ring plate  2   a  for positioning the freewheeling clutch  3 . That is, the stator  2  is formed in a single piece with the rear ring plate  2   a  of the freewheeling clutch. As a result, the stator  2  is centered in relation to the inner raceway  4  through engagement between a stepped internal circumferential surface of the rear ring plate  2   a,  which is formed in a single piece with it, and the external circumferential surface of the inner raceway  4 . 
         [0019]    The front ring plate  7 , which is conventionally designed as a separate element, is centered in relation to the inner raceway  4  through engagement of its stepped internal circumferential surface with the external circumferential surface and front edge of the inner raceway  4 . The stepped external circumferential surface of the front ring plate  7  is positioned on the internal circumferential surface of the outer raceway  5 , and is axially positioned and fastened in relation to the outer raceway  5  by a splining  50 . The splining  50  is located in a position that overlaps the position of the snap ring  22  radially. As a result, although the front side of the stator  2  is centered in relation to the inner raceway  4  in the conventional way by means of the outer raceway  5  and the front ring plate  7 , its back side is centered in relation to the inner raceway  4  directly in a single stage by means of the rear ring plate  2   a,  which is designed in a single piece with the stator  2 . 
         [0020]    The stator  2 , the outer raceway  5 , the front ring plate  7  and the inner raceway  4 , which are centered and axially positioned as described above, are supported in the housing  10  by means of a pair of thrust bearings, i.e., a front thrust bearing  8  and a rear thrust bearing  9 . The rear thrust bearing  9  is positioned axially opposite the outer raceway  5 , namely on the other side of the rear ring plate  2   a,  which is formed in a single piece with the stator  2 . A spline profile C is formed on the inner circumference of the raceway  91  of the bearing  9  to prevent relative rotary motion between the bearing raceway  91  and the rear ring plate  2   a,  and is positioned radially inside the bearing  9  and axially behind the sprag  6 . 
         [0021]    The front thrust bearing  8  is positioned between the front ring plate  7  and the turbine rotor  12 . A hub  13 , which also serves as the hub of a lockup clutch  14 , is supported in the housing  10  by means of a thrust bearing  15 . 
         [0022]    Since a fluid flows in the direction of the arrow in  FIG. 1 , as described above, when there is a large difference in the rotary motion between the impeller  11  and the turbine rotor  12  (especially if the turbine rotor  12  is braked because of excessive vehicle loading or the like), in the region of the converter an axial force acting from front to rear is exerted on the stator  2  of the torque converter, which load is transferred via the stator  2  to the rear ring plate  2   a  and is finally received and absorbed by the bearing  9 . Since, in this embodiment, the bending force that acts on the rear ring plate  2   a  and results from the axial load is transferred directly to the bearing  9 , the rear ring plate  2   a  is thereby protected against deformation. 
         [0023]    Also shown in  FIG. 1  is a friction lining  100 , which is positioned on the motor-side lateral surface of the combined piston retainer and is provided to rest against the opposite inner surface of the housing  101  when the piston  14  is displaced axially, in order to engage the lockup clutch. So as to enable a certain flow of cooling oil even when the converter lockup clutch is engaged, an orifice plate  102  is provided in the piston  14 , by which a certain exchange of oil between the opposite sides of the piston  14  is enabled. 
         [0024]    During an engagement of the lockup clutch, a slippage occurs between the piston and the housing. Because of the differences in speed of rotation existing at this time, which are not reduced until operation is free of slip. These rotational speed differences result in hydraulic fluid pressures. This causes flows to develop in the converter to equalize the pressure. To this end, in single-plate clutches whose piston is designed as a retainer bowl, the flow must stream around the retainer bowl. To avoid this compensatory flow, which is possible only with difficulty, the openings  104  in the schematic depiction shown in  FIG. 2  are made in the retainer piston  108  radially outside of the friction lining  100  and radially inside of the rounding of the retainer  106 , which serve as oil flow openings for free oil circulation; that is, the oil does not have to run around the edge of the retainer. These oil openings  104  are preferably located in immediate proximity to the friction lining  100 . As a rule, certainly, the larger the openings  104  and the more (elongated) holes, slits, etc. are provided, the greater the benefit. But, at the same time, the available space requirement and the necessary rigidity of the component  108  must be taken into account, so that an optimization is achieved between oil flow cross section and space requirement/rigidity. 
         [0025]    If the piston  108  with the retainer bowl  106  is designed with the oil flow openings  104  provided outside of the friction linings, improved adjustability of the clutch results, especially if the pressure equalization holes or oil openings  104  are made in a section  110  of the piston  108  located radially outside of the pressure chamber  112 , and particularly immediately outside of the friction lining  100  (since the retainer pistons must be pressure-tight, it is possible to position the holes/openings only radially outside of the friction lining). Through these holes/openings  104  the oil can drain away (preferably radially) directly at the back of the piston, and does not have to first flow a long way around the retainer edge and springs. This is of decisive benefit to the sequence in the transition from clutch disengaged to clutch engaged, when even very small oil gaps and flow paths are relevant. 
         [0026]      FIG. 3  shows a top view of the retainer piston  108  having a large number of such oil flow openings  104  located in the radial section  110  and radially outside of the friction lining (for example, 50 holes with a diameter of 3 mm), shown in top view. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           2  Stator 
           2   a  Rear Ring Plate 
           3  Clutch 
           4  Inner raceway 
           5  Outer Raceway 
           6  Sprag 
           7  Front Ring Plate 
           8  Front Thrust Bearing 
           9  Rear Thrust Bearing 
           14  Piston 
           21  Inner Spline Profile 
           22  Snap Ring 
           50  Spline 
           51  Outer Spline Profile 
           91  Inner Circumference Raceway of Bearing  9   
           100  Friction Lining 
           101  Inner Surface 
           102  Orifice Plate 
           104  Oil Openings 
           104  Retainer 
           108  Retainer Piston 
           110  Piston Section 
           112  Pressure Chamber 
         A Spline Profile Section 
         B Centering Section 
         C Spline Profile