Abstract:
To control one clutch ( 2 ) in a hydrodynamic torque converter, the pressure acting upon one first piston area ( 4 ) is supplied to a control unit which, depending on the pressure, adjusts the pressure acting upon a second piston area ( 5 ). It is possible to exactly adjust the piston force acting upon a clutch ( 2 ) even in the presence of changing pressure ratios within the hydrodynamic torque converter.

Description:
This application claims priority from German Application Serial No. 103 14 335.1 filed Mar. 28, 2003. 
   FIELD OF THE INVENTION 
   The invention relates to a hydrodynamic torque converter. 
   BACKGROUND OF THE INVENTION 
   Generic hydrodynamic torque converters comprise a housing connectable via a clutch with a pump impeller and while rotating said pump impeller conveys pressure fluid to a turbine wheel connected with one output of the hydrodynamic torque converter which preferably forms the drive mechanism of a powershift transmission. The hydraulic pressure within the converter housing changes depending on the state of operation of the hydrodynamic converter. In generic converters the housing, in order to cool the converter, is flown through with pressure fluid conveyed by a hydraulic pump. The hydraulic pump is often connected with the prime mover whereby the flow rate varies depending on the input rotational speed of the hydraulic pump. The variation of the flow rate additionally influences the hydraulic pressure in the converter housing. 
   DE 195 21 458 A1 discloses a hydrodynamic torque converter where a prime mover can be connected via a clutch with the pump impeller. 
   The problem on which this invention is based is to provide a hydrodynamic torque converter with one clutch within the converter housing where the clutch can be controlled with precision. 
   SUMMARY OF THE INVENTION 
   The inventive hydrodynamic torque converter comprises one housing connected with a prime mover, the housing being connectable via at least one clutch with other parts of the converter. The actuation device of the clutch has at least one piston which comprises one first piston area directly loaded with the pressure fluid located in the interior of the housing. The converter inner pressure, which varies as result of the operating conditions of the converter and the rotational speed of the hydraulic pump, thus acts upon said first piston area. The second area of the piston of the actuation device forms one side of a space which can be loaded with pressure fluid by a supply line. If the clutch is purposefully brought to slip, then a defined piston force is needed which acts upon the clutch. Since the hydraulic pressure acting upon the first piston area steadily varies, the hydraulic pressure acting upon the second area likewise has to be steadily changed in order that the piston exerts a defined force upon the clutch. Therefore, according to the invention, the hydraulic pressure acting upon the second piston area changes according to the hydraulic pressure acting upon the first piston area. In a first embodiment, the pressure acting upon the first piston area, is directly or indirectly measured by a pressure sensor which relays this pressure signal to an electronic control unit which adjusts the pressure acting upon the second piston area according to a nominal value setting and according to the measured pressure acting upon the first piston area so that the piston exerts a defined force upon the clutch. The pressure sensor can be situated here in the direct proximity of the first piston area, but it is possible to deliver the pressure at one other place, via a connection, such as a line or hole in a shaft, the pressure fluid acting upon the first piston area having to communicate with the delivery place. It is possible to also make use of correction factors depending, for example, on rotational speed or pressure medium temperatures. Here a hole is preferably used in the non-rotatable shaft connected with the stator for transmitting the pressure. 
   In another embodiment, there exists a connection to the pressure medium acting upon the first piston area to a valve unit whose pressure medium supply is the pressure medium acting upon the first piston area and which according to a nominal value setting guides this pressure medium to the second piston area. The same pressure thus acts upon the first and the second piston areas when the valve unit is fully open whereby the clutch is In opening direction and transmits no torque. By reducing the pressure upon the second piston area, the pressure of the first piston area prevails and the clutch is actuated in closing direction. Depending on the variation of the pressure acting upon the first piston area and the nominal value setting, the pressure acting upon the second piston area is adjusted by the valve unit. In one other embodiment, a connection exists between the pressure medium acting upon the first piston area and a valve unit, said pressure medium and thus the pressure assuming a pure control function of the valve unit. The second piston area is supplied with pressure medium by a source which can be, for example, a hydraulic pump, in addition, which assumes the through flow of the hydrodynamic torque converter or a lubrication pump of a powershift transmission. The valve unit guides pressure medium from said hydraulic pump according to the pressure acting upon the first piston area and the nominal value setting in the space formed with the second piston area. In another embodiment, the valve units described can be combined with the electronic control unit and, in addition, it is possible to issue the output signal of the electronic control unit to a proportional valve which then adjusts the clutch pressure acting upon the second piston area. In another embodiment, it is possible In the electronic control unit to process together correction factors like, for example, the rotational speed of the prime mover, the rotational speed of the pump impeller, the rotational speed of the turbine impeller, one characteristic of the hydrodynamic converter, the rotational speed on one output or measured torque on parts of the hydrodynamic converter or on parts of the transmission. 
   By the inventive solution, it is thus possible to control a clutch exactly within a hydrodynamic torque converter and purposefully keep it in a defined slip state. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  is a diagram of a hydrodynamic torque converter with one valve unit having its pressure medium supply connected with the pressure medium acting upon the first piston area; 
       FIG. 2  is a hydrodynamic torque converter with a valve unit having its pressure medium supply connected with a hydraulic pump; 
       FIG. 3  is a hydrodynamic torque converter with an electronic control unit which processes signals from a pressure sensor; 
       FIG. 4  is a sectional drawing of a hydrodynamic torque converter with a converter bridge clutch; and 
       FIG. 5  is a sectional drawing of a hydrodynamic torque converter with a converter ridge clutch and a primary clutch. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 : 
   A prime mover (not shown) drives a converter housing  1  connected with a primary clutch  2 . One piston  3  has a first piston area  4  and a second piston area  5 . If the hydraulic pressure prevails upon the piston area  4 , the clutch  2  is actuated in closing direction and connects the converter housing  1  with a pump impeller  6  of the hydrodynamic converter. By rotation of the pump impeller  6  pressure medium within the converter housing  1  is conveyed to a turbine impeller  7  which thereby produces a torque. In order to cool the parts within the converter housing  1 , the pressure medium flows steadily via a pressure medium supply line  8  through the hydrodynamic converter. This pressure medium is preferably conveyed by a hydraulic pump that communicates with the prime mover. By changing the rotational speed of the prime mover, the pressure within the housing  1  changes and thus the pressure upon the first piston area  4 . A space  10  is connected with a valve unit  11  via a line  9 . If the valve unit  11  is now adjusted by a nominal value setting  12  which can be, for example, a pedal or also a setting of an electronic control unit, the pressure medium flows via the line  9  and the valve unit  11  to a line  13  and from there into a space  14 . The piston  3  actuates the clutch  2  with the force from the differential pressure which acts upon the first piston area  4  and upon the second piston area  5  and actuates the clutch  2  in closing direction. If the pressure acting upon the first piston area  4  changes, the pressure in the line  9  and a line  15  changes whereby the valve unit  9 , likewise, changes the pressure in the line  13  and the differential pressure acting upon the piston  3  remains the same. The clutch  2  is thus actuated with an unchanged closing force. 
     FIG. 2 : 
   The mode of operation of the hydrodynamic torque converter corresponds to the mode of operation such as disclosed in  FIG. 1  and can be understood from the description of  FIG. 1 . 
   The hydrodynamic torque converter of  FIG. 2  differs from the representation of  FIG. 1  in the supply of the pressure medium to the valve unit  11 . The valve unit  11  is supplied with pressure medium via a line  16  which is connected with a pressure medium source of a hydraulic pump such as from a rear-mounted powershift transmission. The space  14  is accordingly loaded with pressure medium from the hydraulic pump (not shown) of the transmission. The valve unit  11  is adjusted in a manner analogous to  FIG. 1  via the pressure medium, which reaches the valve unit  11  via the line  15 . 
     FIG. 3 : 
   The mode of operation of the hydrodynamic torque converter of  FIG. 3  corresponds to the mode of operation of the hydrodynamic torque converter of  FIGS. 1 and 2 . 
   Unlike the design described in  FIG. 1 and 2 , the torque converter in  FIG. 3  contains one pressure sensor  17  which determines the pressure acting upon the first piston area  4  and supplies it to an electronic control unit  18 . The electronic control unit issues a signal to a proportional valve  19  and controls it according to a single rotational speed sensor  20  and nominal value settings  21  and correction factors  22 . The proportional valve  19  supplies the space  14  with pressure medium and pressurizes the second piston area  5  in order to apply to the clutch  2  a defined force via the piston  3 . 
     FIG. 4 : 
   The converter housing  1  is connected with a prime mover (not shown) and driven. The primary clutch  2  connects the housing  1  with the pump impeller  6 . The turbine impeller  7  can be connected, via a converter bridge clutch  23 , with the housing  1 . Upon the first piston area  4  acts the variable pressure within the housing which depends on the operational parameters and the operational state of the converter. The first piston area  4  and the space  10  are connected via the line  9  with a valve or control unit  11 . The pressure of the space  10  can be detected via the line  9 . While pressure medium is passed into the space  14 , via the line  13 , hydraulic pressure acts upon the second piston area  5 . The resulting differential pressure from the pressure upon the first piston area  4  and the second piston area  5  actuates the piston  3 . In order to supply the clutch  2  in the open state with lubricant, there is located in the piston  3  at least one aperture  24  through which lubricant can be passed through the discs of the clutch  2 . It is possible to seal the space  14  by sealing elements  25 . The outer discs of the clutch  2  are non-rotatably connected with the pump impeller  6 , the inner discs of the clutch  2  being non-rotatably connected with the housing  1 . 
     FIG. 5 : 
   The construction of the hydrodynamic torque converter corresponds to the hydrodynamic torque converter of  FIG. 4 , the inner rotating discs being non-rotatably connected with the pump impeller  6  and the outer rotating discs of the clutch  2  non-rotatably connected with the housing  1 . It is hereby possible to enlarge the area of the piston  3 . 
   REFERENCE NUMERALS 
   
       
         1  converter housing 
         2  primary clutch 
         3  piston 
         4  first piston area 
         5  second piston area 
         6  pump impeller 
         7  turbine impeller 
         8  pressure medium supply line 
         9  line 
         10  space 
         11  valve unit 
         12  nominal value setting 
         13  line 
         14  space 
         15  line 
         16  line 
         17  pressure sensor 
         18  electronic control unit 
         19  proportional valve 
         20  rotational speed sensor 
         21  nominal value setting 
         22  correction factor 
         23  converter bridge clutch 
         24  aperture 
         25  sealing elements