Abstract:
A hydrostatically operated clutch system having a hydrostatic clutch actuator for hydrostatically operating a clutch, in particular a pulse separation clutch of a hybrid drive, such that the hydrostatic clutch actuator is combined with a valve arrangement which is to be opened actively and enables the clutch to be engaged rapidly.

Description:
BACKGROUND 
       [0001]    The invention relates to a hydrostatically operated clutch system comprising a hydrostatic clutch actuator for the hydrostatic operation of a clutch, particularly a pulse separation clutch of a hybrid drive. The invention further relates to a method for operating such a hydrostatically operated clutch system. 
         [0002]    A method and a device for adjusting a clutch characteristic of an automatically operated friction clutch is known from the German publication DE 10 2013 207 263 A1, comprising a clutch actuator with an actuating device comprising a fluid column between the master cylinder and a slave cylinder, with the clutch actuator comprising an air opening. A method for controlling an actuator system is known from the German patent publication DE 10 2013 205 237 A1 for the hydraulic activation of a clutch in which the actuator system comprises a master cylinder with a master piston, a return-flow container for receiving hydraulic fluid, a connecting opening between the return-flow container and the master cylinder, a hydrostatic actuator for controlling a position of the master piston, and a control device for controlling the hydrostatic actuator. 
       SUMMARY 
       [0003]    The objective of the invention is to simplify the hydrostatic operation of a clutch, particularly a pulse separation clutch of a hybrid drive. 
         [0004]    The objective is attained in a hydrostatically operated clutch system comprising a hydrostatic clutch actuator for the hydrostatic operation of a clutch, particularly a pulse separation clutch of a hybrid drive, in that the hydrostatic clutch actuator is combined with a valve device that can actively be opened, allowing a rapid closing of the clutch. The hybrid drive represents a drive which comprises a secondary drive, for example an electric machine, in addition to the primary drive, for example an internal combustion engine. The primary drive and the secondary drive may be used together or each alone for driving the motor vehicle equipped with said hybrid drive. The motor vehicle with the hybrid drive is also called a hybrid vehicle. The clutch is preferably arranged in the hybrid vehicle between the primary drive and the secondary drive. The primary drive can be separated from the drive train by opening the clutch. When the hybrid vehicle is driven exclusively by the secondary drive, within the scope of the so-called pulse start it is possible to add the primary drive while driving. By the valve device actively to be opened here advantageously a very rapid closing of the clutch is possible. 
         [0005]    A preferred exemplary embodiment of the hydrostatically operated clutch system is characterized in that the clutch is embodied as a separating clutch with a pulse start function. The separating clutch is embodied as a normally closed clutch, which is closed in the idle state and is opened by the hydrostatic clutch actuator. 
         [0006]    Another preferred exemplary embodiment of the hydrostatically operated clutch system is characterized in that the clutch is closed in an idle state by a spring device, particularly a disk spring device, and can be opened by a hydrostatic clutch actuator. The hydrostatic clutch actuator has proven advantageous within the scope of the present invention with regards to the structural space available in a hybrid vehicle. However, within the scope of the present invention it has also shown that the hydrostatic clutch actuator cannot close the clutch quickly enough. By the alleged disadvantage of an additional valve device the rapid closing of the clutch can be possible using a hydrostatic clutch actuator. By the combination according to the invention of the hydrostatic clutch actuator with the valve device actively to be opened the clutch can be closed completely in an extremely rapid fashion, for example within a few hundred milliseconds. 
         [0007]    Another preferred exemplary embodiment of the hydrostatically operated clutch system is characterized in that the valve device is embodied and arranged such that the valve device allows a rapid pressure reduction at the master side. For example, a master cylinder with a master piston is arranged on the master side, which can be moved by an electric motor via a transmission and a piston rod assembly in the master cylinder. The master cylinder is connected via a hydrostatic path to a slave cylinder, in which a slave piston is arranged. The clutch can be actuated via the slave piston, particularly opened. The valve device to be opened actively is allocated for example to the master cylinder at the master side. The pressure in the master cylinder can rapidly be reduced by the valve device to be opened actively. 
         [0008]    Another preferred exemplary embodiment of the hydrostatically operated clutch system is characterized in that the valve device comprises a clutch pressure connection and a tank connection, allowing a rapid pressure reduction for opening the clutch. The tank connection is connected to a reservoir, for example. The reservoir contains a hydraulic medium, for example impinged with ambient pressure. 
         [0009]    Another preferred exemplary embodiment of the hydrostatically operated clutch system is characterized in that the clutch pressure connection and the tank connection of the valve device are closed by a valve piston in a closed position of the valve device. The valve piston is pre-stressed by a pre-stressing spring into its closed position, for example. By an electromagnetic operation, for example the valve piston can be moved out of its closed position into an opening position, in which the clutch pressure connection is connected to the tank connection. 
         [0010]    Another preferred exemplary embodiment of the hydrostatically operated clutch system is characterized in that the valve piston limits an annular chamber radially at the inside, which annular chamber in the axial direction is limited by two seals and which is radially at the outside limited by a valve housing with a tank connection. The connections of the valve device are preferably embodied like or similar to an air hole in conventional clutch master cylinders. This way the pressure at the master side, particularly in the master cylinder, can be rapidly reduced via the opened valve device. Furthermore, the valve device according to the invention can perform diagnostics and shows very low leakage. Compared to valve devices according to the invention, simple and low-cost slide valves frequently show high leakage due to soiling. If necessary, pressure can develop in the master cylinder due to a motion of said master piston, which is then released in a targeted fashion by the valve device actively opened, which can be sensed for diagnostic purposes. This “diagnosing process” can be used for example to provide a signal when the system is activated that the clutch is available, particularly the pulse separation clutch. 
         [0011]    In a method for operating an above-described hydrostatically operated clutch system, the above-stated objective is alternatively or additionally attained in that the opened clutch is closed rapidly by an active opening of the valve device. Here, for the active closing of the clutch intentionally the hydrostatical clutch actuator is not used, because it is too slow. 
         [0012]    A preferred exemplary embodiment of the invention is characterized in that during the closing of the clutch a master cylinder is moved in the direction of a minimal position by the active opening of the valve device. The minimal position of the master piston is equivalent to the end position of the master piston. 
         [0013]    Another preferred exemplary embodiment of the method is characterized in that the valve device remains open until the master piston has reached its minimal position. Only then the system regains full functionality. By keeping the valve device open it is advantageously prevented that a vacuum develops inside the master cylinder or erroneously air penetrates into the master cylinder, passing the seals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Additional advantages, features, and details of the invention are discernible from the following description, in which various exemplary embodiments are described in detail with reference to the drawings. Shown are: 
           [0015]      FIG. 1  a schematic illustration of a hydrostatic clutch system with a valve device to be opened actively, 
           [0016]      FIG. 2  a detailed illustration of the valve device of  FIG. 1  to be actively opened in a closed position, and 
           [0017]      FIG. 3  a valve device of  FIG. 2  in its opened position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]      FIG. 1  shows schematically the design of the hydraulic clutch system  1  using the example of a schematically shown hydraulic, hydrostatic clutch actuator (HCA). A cylinder  4 , also called master cylinder, is arranged on the master side  15  with a piston or master piston  19 . 
         [0019]    The hydraulic clutch system  1  comprises at the master side  15  a control device  2  as the control unit, which controls an actuator  3 . When changing the position of the actuator  3  with respect to the output element of the actuator and thus the piston  19  in the cylinder  4  along the actuator path towards the right, the volume of the cylinder  4  is changed, causing a pressure P to be generated in the cylinder  4 , which is transferred by pressure medium  7  via a hydraulic line  9  to the slave side  16  of the hydraulic clutch system  1 . 
         [0020]    The hydraulic line  9  is adjusted with regards to its length and shape to the situation of the structural space of the vehicle. At the slave side  16 , the pressure P of the pressure medium (fluid)  7  results in a change of the path in a cylinder  4 , which is also called the slave cylinder, of the piston position of a piston of slave piston  22  in the slave cylinder, which is transferred via an actuation bearing  24  to a clutch  8 , in order to actuate it. The pressure P in the cylinder  4  at the master side  15  of the hydraulic clutch system  1  can be determined via a first sensor  5 . The first sensor  5  preferably represents a pressure sensor. 
         [0021]    The path traveled by the actuator  3  and/or the piston of the master cylinder along the actuator path is determined via a second sensor  6 . The second sensor  6  can either represent a path sensor, which determines the path traveled by the actuator compared to a reference position, or preferably a sensor which determines the number of rotations of the actuator drive, which may represents an electric motor  10 , for example, and determines therefrom the actuator path. 
         [0022]    The cross-section of an air opening  18  for volume compensation is advantageously embodied with as little flow resistance as possible. The clutch  8  is embodied as a separating clutch and thus the spring device  20 , particularly a disk spring device, is pre-stressed into its closed position. 
         [0023]    A valve device  40  is allocated to the master cylinder  4 . The valve device  40  is embodied as a pressure reduction valve  42 , which allows rapid pressure reduction in the master cylinder  4  when needed. For this purpose, the pressure reduction valve  42  has a pressure reduction opening  44 , which is also called the tank connection. 
         [0024]    The pressure reduction valve  42  is connected via the pressure reduction opening  44  to the reservoir  17 . Via an inlet opening  46  which is also called the clutch pressure connection, the pressure reduction valve  42  is connected to the master cylinder  4 . The pressure reduction valve  42  is operated via an actuator  60 . 
         [0025]    In a closed condition of the pressure reduction valve  42  the connection is interrupted between the master cylinder  4  and the reservoir  17 . In a state of the pressure reduction valve  42  operated by the actuator  60  the connection is released by the pressure reduction valve  42  between the input opening and/or the pressure connection or the clutch pressure connection  46  and the pressure reduction opening and/or the tank connection  44 . 
         [0026]    In the open state of the pressure reduction valve  42 , in order to provide a rapid pressure reduction in the hydraulic cylinder  4 , pressure medium or hydraulic medium  7  reaches from the master cylinder  4  via the inlet opening  46  and the pressure reduction opening  44  of the pressure reduction valve  42  into the reservoir  17 . This way the clutch  8  can be closed most rapidly, for example within fifty milliseconds, with the help of a disk spring device  20 . 
         [0027]      FIGS. 2 and 3  show in a simplified fashion the valve device  40  with a pressure reduction valve  42  for implementing an additional pressure reducing function. The pressure reduction valve  42  comprises a pressure reduction opening  44  in a valve housing  45  of the valve device  40 . 
         [0028]    The pressure can be reduced via the pressure reduction opening  44  into a low pressure area or into a hydraulic medium reservoir ( 17  in  FIG. 1 ), which is impinged with low pressure or ambient pressure. The valve housing  45  further comprises an inlet opening  46 , which is also called clutch pressure connection. 
         [0029]    The valve housing  45  comprises a receiving chamber space  48 , in which a valve piston  50  is accepted, capable to move back and forth. Two seals  51 ,  52  are allocated to the valve piston  50  in a similar fashion as in a master cylinder with an air hole. The seals  51 ,  52  are axially fixed in the valve housing  45 . 
         [0030]    Here, the seals  51 ,  52  are embodied as annular seals, which show radially at the inside a sealing lip, which as discernible in  FIGS. 2 and 3  contacts the valve piston  50 . The seals  51 ,  52  limit an annular chamber  53  in the axial direction, which is limited radially at the inside by the valve piston  50 . Radially at the outside the annular chamber  53  is limited by the valve housing  45 . A pressure reduction opening  44  extends from the annular chamber  53 . 
         [0031]    The valve piston  50  is pre-stressed by a closing spring  55  into its closed position shown in  FIG. 2 . In the closed position shown in  FIGS. 2 and 3  the valve piston  50  impinges with its upper end a closing stop  56 , which is embodied at the valve housing  45 . Here, the closing spring  55  rests on an opening stop  58  which is also provided at the valve housing  45 . The valve piston  50  can move back and forth in the axial direction between the two stops  56  and  58 , thus in  FIGS. 2 and 3  upwards and downwards. 
         [0032]    In the closed position shown in  FIG. 2  the valve piston  50  closes the pressure reduction opening  44 . In  FIG. 3  the valve piston  50  is shown in its opened position. In the opened position, the valve piston releases a connection between the inlet opening  46  and the pressure reduction opening  44 , so that pressure can be reduced via the pressure reduction opening  44  as indicated in  FIG. 3  by an arrow  59 . 
         [0033]    The valve piston  50  is actuated electrically by an actuator  60 . When electrifying the actuator  60 , a force is applied by the actuator  60  upon the valve piston  50 , directed downwards in  FIGS. 2 and 3 . This force acts opposite the closing force of the closing spring  55 . 
         [0034]    When the actuator  60  is switched to a non-energized state, the actuator  60  applies no pressure upon the valve piston  50 . In the non-energized state of the actuator  60 , the valve piston  50  is pre-stressed by the closing spring  55  into its closed position. 
         [0035]    In  FIG. 2  the pressure reduction valve  42  is closed. The closing spring  55  also called pre-stressing spring keeps the non-energized pressure reduction valve  42  in the closed state. When the pressure reduction valve  42  is electrified, a force acts upon the actuator  60  and/or a piston rod assembly upon the valve piston  50  such that the pressure reduction valve  42  is opened. 
         [0036]      FIG. 3  shows the pressure reduction valve  42  in its open position. An arrow  59  indicates how pressurized hydraulic medium is released from the master cylinder through the inlet opening  46 , passing the open valve piston  50 , through the pressure reduction opening  44  into the reservoir. 
         [0037]    During operation, the function of the pressure reduction valve  42  can be checked easily. For example, via the hydrostatic clutch actuator  3  and the master piston  19  a pressure can be generated in the master cylinder  4  for diagnostics purposes, which is then released by the pressure reduction valve  42 . 
         [0038]    Here, the actuator  60  is switched to a non-energized state for diagnostics purposes, in order to check if the pressure in the master cylinder  4  is reduced immediately, as expected, via the pressure reduction opening  44 . 
         [0039]    If that is the case, this information can be used for example when starting up the system in order to generate a signal “pulse separation clutch available”. In case of the valve piston  50  being stuck, this can be saved and indicated in an error memory of the control device ( 2  in  FIG. 1 ). Independent from the diagnostics function which is optional the pressure reduction valve  42  shows very low leakage. 
         [0040]    When an error occurs, i.e. when the hydrostatic clutch actuator  3  is defective because the transmission or the spindle cannot move any more, the clutch shall remain in its present position. In particular, the clutch shall not be closed again. In case of such an error, the master piston  19  is located in the position necessary for the maximum opening of the clutch. The slave piston  22  is then also in the position necessary for the maximum opening of the clutch. 
         [0041]    By an active opening of the pressure reduction valve  42  the hydraulic medium  7  can be drained from the master cylinder  4  into the reservoir  17 . The slave cylinder  22  is pressed by the retention force of the disk spring into its minimal position. The master piston  19  is still in its maximum position. 
         [0042]    After the pressure in the master cylinder  4  has dropped, the pressure reduction valve  42  must remain open in order to allow the exchange of hydraulic medium with the reservoir  17  when the master cylinder  19  is displaced from the maximum to the minimum position, the master cylinder  4  must now be filled with hydraulic medium. If the pressure reduction valve  42  was not opened, a vacuum would develop in the master cylinder  4  or erroneously air would enter past the seals, which is undesired. 
       LIST OF REFERENCE CHARACTERS 
       [0000]    
       
           1  hydrostatically operated clutch system 
           2  control device 
           3  hydrostatic clutch actuator 
           4  cylinder 
           5  first sensor 
           6  second sensor 
           7  pressure medium 
           8  clutch 
           9  hydraulic line 
           10  electric motor 
         
           11 
         
         
           12 
         
         
           13 
         
         
           14 
         
           15  master side 
           16  slave side 
           17  reservoir 
           18  air opening 
           19  master piston 
           20  disk spring device 
         
           21 
         
           22  slave piston 
         
           23 
         
           24  actuator bearing 
         
           25 
         
         
           26 
         
         
           27 
         
         
           28 
         
         
           29 
         
         
           30 
         
         
           31 
         
         
           32 
         
         
           33 
         
         
           34 
         
         
           35 
         
         
           36 
         
         
           37 
         
         
           38 
         
         
           39 
         
           40  valve device 
         
           41 
         
           42  Pressure reduction valve 
         
           43 
         
           44  Pressure reduction opening 
           45  Valve housing 
           46  Inlet opening 
         
           47 
         
           48  receiving space 
         
           49 
         
           50  valve piston 
           51  seal 
           52  seal 
           53  annular chamber 
         
           54 
         
           55  closing spring 
           56  closing stop 
         
           57 
         
           58  opening stop 
           59  arrow 
           60  actuator