Abstract:
A control valve arrangement having a clutch regulation valve ( 3 ), which pressurizes a device to actuate the clutch, and a valve that produces a controlled pilot pressure (P_VST 3 ). An electronic control unit (ECU) controls a valve to supply a control valve with the pressure (P_VST 3 ). The arrangement further having a hydraulic system which, if the ECU fails and the pressure (P_VST 3 ) ceases, the last shift condition of the clutch actuation device, prior to the ECU failure, can be maintained in an emergency. The arrangement includes a valve, which delivers an activation pressure (P_A), depending on an engine-speed-dependent control pressure (P_D), to an actuation valve ( 2 ), which then delivers the pressure (P_A) to the valve ( 3 ) to prevent the emergency function initiation despite a lack of pressure (P_VST 3 ) and existance of the pressure (P_D) sufficiently high to initiate the emergency function.

Description:
[0001]    This application is a national stage completion of PCT/EP2006/009903 filed Oct. 13, 2006, which claims priority from German Application Serial No. 10 2005 050 489.2 filed Oct. 21, 2005. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns a control valve arrangement for controlling a starting clutch of an automatic transmission of a motor vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    In automatic transmissions with an automated wet starting clutch, in order to activate a mechanical emergency transmission operation function, for example in the event that a transmission control unit has failed, it is usual for the force-flow linkage in the transmission to be eliminated by virtue of the fact that when not energized, the starting clutch is shifted to its disengaged condition. Especially in vehicle conditions typical of flowing traffic, this strategy can lead to critical situations, since the vehicle can only coast forward without any positive propulsion drive. 
         [0004]    For technical reasons related to safety, engaging the wet starting clutch in such a driving situation is also not possible, since the force-flow linkage can only be obtained by way of a hydraulic clutch actuation pressure. Inasmuch as when the speed of the vehicle is reduced with the clutch engaged, the vehicle&#39;s engine will stall, there still remains some residual vehicle speed, but some important auxiliary aggregates, such as braking force enhancers or steering assistance pumps normally driven by the engine, can no longer be sufficiently powered. 
         [0005]    In automatic transmissions with a dry starting clutch, when the mechanical emergency operation function is activated, this clutch is engaged so that the vehicle&#39;s drive output remains in driving connection with the engine until the vehicle comes to rest. Although no critical driving situations arise because of this, once the vehicle has stopped, it can no longer be moved or pushed out of the way. 
         [0006]    Consequently, there is need for a control device for a starting clutch of an automatic transmission of a motor vehicle which, depending on the engine speed and/or the drive output speed of the transmission, interrupts the force-flow linkage in the drivetrain only when the engine speed or transmission output speed falls below a certain value so that the vehicle&#39;s engine does not stall, the auxiliary aggregates remain powered and it is still possible for the driver to drive safely away from any danger area that there may be. In addition, such behavior also allows the vehicle to be moved after coming to rest, since the force flow, between the engine and the transmission, is then interrupted. 
         [0007]    Against this background, a hydraulic emergency control system for a belt-type transmission is known from DE 199 43 939 A1 in which a clutch, associated with the transmission, can be disengaged or engaged, depending on the speed of a vehicle drive engine. In this way, in the event of a failure repeated stalling of the drive engine, when the engine speed falls below a certain limit value, can be avoided and starting when the speed rises above a certain value is made possible. Depending on the design of this emergency control system, the engine-speed-dependent control signal can be produced and used as a hydraulic pressure, a pneumatic pressure or an electric voltage. 
         [0008]    In addition, a method for controlling an emergency shift program for an automatic transmission with a starting clutch is known from DE 102 38 104 A1, which is especially designed to enable emergency running, even when the vehicle is at rest, and to prevent the engine speed from falling below a stalling threshold. In this method, it is provided that the emergency shift program is actuated by a signal that depends on the vehicle&#39;s speed and/or its engine speed. The signal is processed by a valve logic system and has the effect that in thrust operation the force linkage to the engine is interrupted in time to prevent stalling of the vehicle&#39;s engine. 
         [0009]    Furthermore, a dual-clutch transmission is known from DE 103 38 355 A1, which has a first and a second clutch such that for normal operation to engage/disengage the first clutch, a first hydraulic system and to engage/disengage the second clutch, a second hydraulic system controlled by an electronic system are present. In addition, a status-maintaining hydraulic system is provided to which status signals corresponding to the momentary shift condition of the first and second clutches are passed, via a first and a second hydraulic line, and which is connected by hydraulic control lines to the first and second hydraulic systems. If the electronic system should fail, the status-maintaining hydraulic system controls the first and second hydraulic systems in such a manner that at least in many shift conditions of the two clutches, the shift condition of the clutches that existed immediately before the electronic failure is maintained. 
         [0010]    Finally, from DE10 2004 020 569,8 which was not published before the filing date of the present patent application, a control valve arrangement for controlling a starting clutch of an automatic transmission is known with which, in a simple, inexpensively produced and reliable manner, in an emergency control situation the starting clutch can be disengaged if the engine speed and/or the drive output speed of the transmission or the driving speed of the vehicle fall below a predetermined value. 
         [0011]    This control valve arrangement comprises a clutch control valve for controlling at least one clutch actuation device which, during normal operation of the transmission, converts a supply pressure delivered to it as a function of a pilot pressure or an electric pilot signal, into a clutch actuation pressure to control the clutch actuation device. The control valve arrangement is also characterized in that to realize emergency transmission operation, if the pilot pressure or the electric pilot signal should fail then, as a function of the engine speed and/or the drive output speed, an activation pressure can be delivered to the clutch control valve or directly to the clutch actuation device, where the clutch is kept in the engaged position so long as the speed remains above a predetermined limiting speed value. 
         [0012]    This valve arrangement provides a control device for the emergency driving operation of a vehicle with an automatic transmission that can be produced inexpensively and operated reliably and which is activated, for example when an electronic transmission control unit and/or an electrically actuated clutch control valve fails. The engine-speed-dependent and/or transmission-output-speed-dependent control pressure then ensures that a starting clutch of the automatic transmission remains engaged in order to transmit torque through the transmission so long as the driving speed and thus the speed of the drive engine does not fall below a stalling speed at which the engine&#39;s function as a combustion engine would cease. 
         [0013]    During such emergency driving operation, if the driving speed falls so much that there is a risk of stalling if the starting clutch remains engaged, then by way of the speed-coupled control pressure, the known control valve arrangement disengages the starting clutch which was until then transmitting torque. This advantageously avoids stalling of the engine so that important auxiliary vehicle aggregates, such as a braking force enhancer and a steering assistance pump, can still be powered by the engine without problems. 
         [0014]    Although this known control valve arrangement works very well, it has nevertheless been found that in some operating situations its function is disadvantageous and, therefore, requires improvement. For example, an operating situation of a vehicle can arise in which it has first been moved in a forward or reverse gear with an engine speed above the limiting speed value. In this type of operation, a self-holding valve of the control valve arrangement to be improved will have been actuated by the speed-dependent pressure as described. 
         [0015]    Now when starting from this driving operation mode, the vehicle is stopped but the engine speed is still kept above the limiting speed value, the self-holding valve remains in a position such that if the pilot pressure fails, emergency operation with a starting clutch then to be engaged is enabled. However, this system behavior persists when the starting clutch is disengaged by a corresponding selector lever actuation from the forward drive selector lever setting D or from the reverse drive selector lever setting R to the transmission selector lever setting neutral or the parking setting P and in the transmission the most recently used gear remains engaged. 
         [0016]    Inasmuch as in such a situation the pilot pressure is absent, the known control valve arrangement engages the starting clutch and the vehicle starts off with a jerk, because of the comparatively high engine speed, although since the selector lever position is at neutral, the vehicle&#39;s driver is not prepared for this. For safety reasons, such behavior of the known control valve arrangement should be prevented. 
         [0017]    Accordingly, the purpose of the invention is to propose a control valve arrangement of the type in question with which unintentional initiation of an emergency operating function can be avoided. 
       SUMMARY OF THE INVENTION 
       [0018]    According to the claims, the starting point of the invention is a control valve arrangement for controlling the actuation of at least one starting clutch of an automatic transmission of a motor vehicle, in each case having a clutch control valve through which a supply pressure can be passed into a pressure chamber of the respective clutch actuation device, with a pressure regulation valve that produces a controlled pilot pressure, that can be actuated by an electronic control unit and supplies a control valve of the control valve arrangement with the pilot pressure, and with a self-holding hydraulic system with whose help, if the electronic control unit fails and the pilot pressure is therefore absent, the shift condition of the at least one clutch actuation device that existed before the failure of the electronic control unit is maintained in the sense of an emergency operating function, at least in many operating situations. 
         [0019]    To solve the technical problem described, in this control valve arrangement according to the invention, it is first provided that the self-holding hydraulic system for realizing the emergency operating function comprises a self-holding valve and an actuation valve. The self-holding valve is designed to be suitable for passing on to the actuation valve an actuation pressure as a function of an engine-speed-dependent control pressure and the actuation valve is capable of passing the actuation pressure to the at least one clutch control valve. Moreover, the control valve arrangement is provided with means whereby, in certain operating situations, activation of the emergency operating function can be prevented despite the absence of the pilot pressure and the presence of an engine-speed-dependent control pressure sufficiently high to produce the emergency operation function. 
         [0020]    This control valve arrangement according to the invention, therefore, activates an emergency operation mode of the vehicle in the event that an associated electronic control unit fails, or prevents such activation, in a manner appropriate for the vehicle&#39;s operating situation at the time. 
         [0021]    A particular operating situation in which, according to the invention, despite a failure of the electronic control unit or absence of the pilot pressure for the valves, and despite a drive engine speed that is above an established limiting value, the at least one starting clutch is not engaged, exists when the motor vehicle is first driven normally forward or in reverse in drive settings D or R with its starting clutch engaged or slipping and the vehicle is then stopped and the starting clutch has been disengaged by moving the transmission selector lever to the neutral or parking position P of the selector lever while a gear is engaged in the automatic transmission. In this way, if a gear is still engaged and the starting clutch is disengaged, the latter is prevented from automatically engaging and taking the driver by surprise. 
         [0022]    According to a further preferred development of the invention, the control valve arrangement is designed such that if the particular operating situation exists, then to prevent activation of the emergency operating function, a hydraulic connection for the actuation pressure, between the self-holding valve and the actuation valve, is engaged. 
         [0023]    In a concrete structural embodiment, it can be provided that the actuation valve, formed in a so-termed valve casing of an electro-hydraulic transmission control unit, can be acted upon by a neutralizing pressure which, in the absence of the pilot pressure, can be passed from the actuation valve to the self-holding valve in such a manner that the self-holding valve blocks the onward passage of the actuation pressure to the actuation valve. 
         [0024]    The neutralizing pressure is provided by an electro-mechanically actuated valve that can be controlled by the electronic control unit. If the electronic control unit has failed, but the aforesaid critical operating situation is not present, activation of the emergency operating function in which the starting clutch is or remains engaged may be desired. Since failure of the electronic control unit also means that the electro-mechanically actuated valve that produces the neutralizing pressure is no longer controlled by it. There is also no neutralizing pressure at the actuation valve. Thus, in the presence of a sufficiently high engine-speed-dependent control pressure, i.e., under the control of the self-holding and the actuation valves, pressure medium can get to the clutch actuation device via the clutch regulation valve and the starting clutch can be engaged. 
         [0025]    In an advantageous design, it can be provided that the neutralizing pressure can be passed into a pressure chamber of the self-holding valve delimited by an axially movable control piston by way of which the onward passage of the actuation pressure, between the self-holding valve and the actuation valve, can be interrupted. In this case, the pressure chamber is preferably that in which a restoring spring of the self-holding valve that acts upon this control piston is located. 
         [0026]    According to another embodiment of the invention, the control valve arrangement comprises a cut-off valve by way of which the pressure medium at the speed-dependent control pressure can be drained into a pressure medium tank when the neutralizing pressure acts on the cut-off valve. 
         [0027]    In a concrete embodiment of this second embodiment of the invention, it is provided that the neutralizing pressure can be passed into the pressure chamber of the cut-off valve that is remote from the restoring spring, where this neutralizing pressure can act upon a servo-piston of the control valve-slide of the cut-off valve. In addition, it is provided that the speed-dependent control pressure is passed, via a line, from the self-holding valve to another pressure chamber of the cut-off valve. Finally, the control valve-slide of the cut-off valve comprises a servo-piston which, when the neutralizing pressure acts on the valve-slide, opens a connection between a pressure chamber of the cut-off valve that can be drained and the pressure chamber of the cut-off valve that is acted upon by the speed-dependent pressure. 
         [0028]    Furthermore, in another embodiment it can be provided that the cut-off valve has a pressure chamber in which a restoring spring that acts on the control valve-slide is arranged, that this pressure chamber is connected, via a line, to the pressure medium tank; that a one-way valve, which blocks in the direction toward the cut-off valve, is arranged in the line and that a hydraulic throttle is arranged in a line whose flow bridges across the one-way valve. 
         [0029]    This structure with a one-way restrictor makes it possible to prolong the time taken to restore the control valve-slide of the cut-off valve to its spring-loaded starting position and to reduce the time to a minimum during which the neutralizing pressure has to be applied to the cut-off valve. Thus, to de-activate the emergency operation function or the hydraulic emergency actuation of the starting clutch, only a short pressure pulse at the neutralizing pressure input of the cut-off valve is needed. 
         [0030]    According to a further embodiment of a control valve arrangement constructed in accordance with the invention, it is provided that the pressure chamber of the self-holding valve, remote from the restoring spring, can be acted upon by a pilot pressure, by way of which the control valve-slide of the self-holding valve, once its self-holding function has been de-activated, can be displaced against the restoring force of the restoring spring of the self-holding valve for enough to allow the speed-dependent pressure to act axially upon a servo-position of the control valve-slide. 
         [0031]    Moreover, it is preferably provided that the pressure chamber of the at least one clutch regulation valve, remote from the restoring spring, can be acted upon by another or by the same pilot pressure. With the help of this pilot pressure, after de-activation of the self-holding function of the self-holding valve, a servo-piston of the clutch regulation valve can be displaced against the restoring force of a restoring spring that acts upon this control valve-slide far enough to allow a supply pressure, delivered to the clutch regulation valve as the clutch actuation pressure, to be passed on to at least one clutch actuation device. 
         [0032]    According to another embodiment of the control valve arrangement, it can be provided that the neutralizing pressure can be delivered to the pressure chamber of the cut-off valve, remote from the restoring spring, and that a pilot pressure P_V 2  can be delivered, via a line, to a central pressure chamber of the cut-off valve and from there, in a manner that can be blocked by the control valve-slide of the cut-off valve, via a line, to the pressure chamber of the self-holding valve on the restoring spring side. 
         [0033]    In addition the control valve arrangement of the invention can be constructed such that the already mentioned pilot pressure P_VST 3  can be delivered to the pressure chamber of the cut-off valve remote from the restoring spring and the pilot pressure P_V 2  can be delivered, via a line, to the control pressure chamber of the cut-off valve and from there, in a manner that can be blocked by the control valve-slide of the cut-off valve, via a line, to the pressure chamber of the self-holding valve on the restoring spring side. 
         [0034]    According to a last embodiment of the control valve arrangement of the invention, it is provided that the neutralizing pressure can be delivered, via a line, to the pressure chamber of the self-holding valve on the restoring spring side and, via another line, to a pressure chamber of the actuation valve. The latter pressure chamber is formed in the area of the end face, remote from the restoring spring, of the central servo-piston of a three-piston control valve-slide of the actuation valve; that the actuation pressure can be passed from the associated pressure chamber of the self-holding valve, via a line, to a pressure chamber of the actuation valve; that close to this latter pressure chamber, a further pressure chamber is formed in the actuation valve, which is connected with an actuation pressure line that leads to the pressure chamber of the clutch regulation valve remote from the spring and that, by way of the central servo-piston of the control valve-slide of the actuation valve, a connection between the two pressure chambers of the actuation valve close to one another can be blocked. 
         [0035]    Let it be said here that with regard to passing on the actuation pressure to the at least one clutch regulation valve, the control valve arrangement can be designed differently with the same effect. As opposed to the embodiments described above, it can also be provided that the actuation pressure is delivered first to the actuation valve, from there to the self-holding valve, and from the latter to the at least one clutch regulation valve. 
         [0036]    Finally, it should be pointed out that the control valve arrangement, according to the invention, can be used to good effect not only for vehicle drivetrains with only one starting clutch, but also advantageously for dual-clutch transmissions. In the case of dual-clutch transmissions, however, it must be ensured that to realize the emergency operation mode described, only one of the two starting clutches need be or remain closed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0037]    The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
           [0038]      FIG. 1  is a control valve arrangement with a self-holding hydraulic system and means for the de-activation of a self-holding function; 
           [0039]      FIG. 2  is a control valve arrangement as in  FIG. 1 , but with a cut-off valve for de-activating the self-holding function; 
           [0040]      FIG. 3  is a control valve arrangement as in  FIG. 2 , but with a ball-type one-way restrictor on the cut-off valve; 
           [0041]      FIG. 4  is another embodiment of the control valve arrangement, similar to that shown in  FIG. 2 ; 
           [0042]      FIG. 5  is another control valve arrangement, similar to that of  FIG. 4 ; 
           [0043]      FIG. 6  is a diagram of various operating functions of the control valve arrangement shown in  FIG. 5 , and 
           [0044]      FIG. 7  is a last embodiment of the control valve arrangement according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]    The control valve arrangement, shown in  FIG. 1 , comprises a self-holding valve  1 , an emergency operation actuation valve  2  (called the actuation valve in what follows), a clutch regulation valve  3  and a clutch actuation device  4 . The clutch actuation device  4  comprises a cylinder  5  in which a piston  6  is surrounded co-axially in the area of its piston rod by a restoring spring  7  that acts in opposition to a clutch actuation pressure P_K and which, when its end face, remote from the spring is acted upon by pressure, can be moved in a closing direction in such a manner that a starting clutch of an automatic transmission is engaged such that torque is transmitted. 
         [0046]    The starting clutch (not shown here), but known to those with knowledge of the field, is part of an automatic transmission which can be made as a variable-speed automatic gearbox based on a planetary transmission, a gearbox that changes its transmission ratio continuously or an automated change-under-load gear shift transmission. When the control valve arrangement is intended for a dual-clutch transmission, two clutch regulation valves and two clutch actuation devices are used. 
         [0047]    The valves  1 ,  2  and  3  are arranged in a valve casing (not shown) of an electro-hydraulic control unit for the transmission, each valve having at least one control valve-slide which can be moved axially by hydraulic pressures and/or restoring spring forces to open, connect and/or close pressure chambers. 
         [0048]    The self-holding valve  1  has a control valve-slide  30  arranged to move axially in a valve bore  36 . The control valve-slide  30  has three spaced apart servo-pistons  20 ,  21  and  22 . An end face of the servo-piston  20  is acted upon with a restoring force by a restoring spring  31 , which is arranged in a pressure space  71  of the self-holding valve  1 . 
         [0049]    The axially opposite end of the control valve-slide  30  is acted upon, when necessary, by a pilot pressure P_VST 1  which can be delivered, via a pressure line  8 , to a pressure chamber  38  of the self-holding valve  1 . The pilot pressure P_VST 1  is also delivered by a line  10  to a pressure chamber  74  of the clutch regulation valve  3 , which serves to exert pressure on the free end faces of two control valve-slides  19 ,  34  of the clutch regulation valve  3 , whose function will be described below in due course. 
         [0050]    The pilot pressure P_VST 1  is provided by a pressure regulation valve  168  from the main pressure of the pressure medium generated by an oil pump (not shown). For this purpose the pressure regulation valve  168  can be controlled by an electronic control unit not shown here, preferably a transmission control unit. 
         [0051]    Another pilot pressure P_VST 3  is provided from the main pressure by a pressure regulation valve  166 , which can also be controlled by the electronic control unit. This pilot pressure P_VST 3  is delivered to a pressure chamber  78  of the actuation valve  2  remote from the restoring spring, wherein it can act on the end face of a servo-piston  23  of a control valve-slide  29  of the actuation valve  2 . 
         [0052]    In addition, via a line  11 , a control pressure P_D is delivered to a pressure chamber  39  of the self-holding valve  1 , between the servo-pistons  21  and  22 . The level of this pressure depends on the speed of the vehicle&#39;s drive engine. 
         [0053]    Furthermore, via a line  12 , an actuation pressure P_A is delivered to a pressure chamber  70  of the self-holding valve  1 , located between the servo-pistons  20  and  21  which, during emergency operation of the transmission after a failure of the electronic control unit, ensures that a torque-transmitting clutch of the transmission remains engaged in a speed-dependent manner. 
         [0054]    With regard to the structure of the actuation valve  2 , it should be mentioned that its control valve-slide  29  has three spaced apart servo-pistons  23 ,  148  and  24  that are arranged to move axially in a bore  63  of the valve casing. An end face of the servo-piston  24  is acted upon by the force of a restoring spring  32 . 
         [0055]    The pilot pressure P_VST 3  already mentioned can be delivered by a line  9  to a pressure chamber  78  at the axially opposite end of the control valve-slide  29 . Also, a line  14  connects the pressure chamber  70  or  143  of the self-holding valve  1  to a pressure chamber  72  of the actuation valve  2 , so that this pressure chamber  72  can be closed by way of the servo-piston  23  remote from the restoring spring or, if the pilot pressure P_VST 3  is absent, connected hydraulically to a pressure chamber  73  of the actuation valve  2 . 
         [0056]    By way of the central servo-piston  148 , a pressure chamber  149  of the actuation valve  2 , connected to a line  150 , can be engaged or, when the pilot pressure P_VST 3  is absent, connected to a pressure chamber  147  of the actuation valve. In certain critical operating situations of the motor vehicle or its automatic transmission, the line  150  carries a hydraulic neutralizing pressure P_Lösch, which is provided by a switching valve  167  that can be actuated by the electronic control unit. The pressure chamber  147  is connected by a line  151  to the pressure chamber  71  of the already mentioned self-holding valve  1 . 
         [0057]    The clutch regulation valve  3  comprises an axially longer control valve-slide  19  with three servo-pistons  26 ,  27  and  28  and the axially shorter control valve-slide  34 , which are held and able to move axially in bores  64  and  65  of the valve casing. At one end of the servo-piston  28 , the axially longer control valve-slide  19  is acted upon by a restoring force of a restoring spring  33 . 
         [0058]    The axially shorter control valve-slide  34  comprises a servo-piston  25  whose end facing toward the other control valve-slide  19  can be acted upon by the already mentioned pilot pressure P_VST 1 . For this, the pressure chamber  74  of the clutch regulation valve  3  is connected, via lines  10  and  152 , to a pressure regulation valve  168  that produces the pilot pressure P_VST 1 . The actuation pressure P_A can be delivered, via a line  15 , to the opposite end face of the piston  25  in a pressure chamber  80 , which is connected to a pressure chamber  73  of the actuation valve  2 . 
         [0059]    The axially longer control valve-slide  19  of the clutch regulation valve  3  has three servo-pistons  26 ,  27  and  28 . The two pistons  26  and  27  are arranged axially directly adjacent to one another. The free end of the servo-piston  26 , opposite the axially shorter control valve-slide  34 , can also be acted upon, via the pressure chamber  74 , by the pilot pressure P_VST 1 , while the end of the servo-piston  28 , remote from the restoring spring, is associated with a pressure chamber  75  to which a system or supply pressure P_V 1  can be delivered. 
         [0060]    During normal operation, this pressure chamber  75  can be connected with an adjacent pressure chamber  76  by actuating the clutch control valve  3  by way of the pilot pressure P_VST 1  so that a controlled clutch actuation pressure P_K, produced by the servo-piston  28 , can act in the pressure chamber  76 . In addition, the pressure chamber  76  is connected by a line  16  to the cylinder  5  of the clutch actuation device  4  and to a pressure chamber  77  of the clutch regulation valve  3  that also accommodates its restoring spring  33 . 
         [0061]    The mode of operation of the control valve arrangement shown in  FIG. 1 , is now as follows: 
         [0062]    During normal driving operation the pilot pressure P_VST 1  is set such that the control valve-slide  30  of the self-holding valve  1  is pushed axially against the force of the spring  31  such that the servo-piston  20  is axially displaced far enough to open a path for the supply pressure P_A from the pressure chamber  70 , via a pressure chamber  143  and a line  14 , to a pressure chamber  72  of the actuation valve  2 . 
         [0063]    In addition, during normal driving operation, the pilot pressure P_VST 3  acts within the pressure chamber  78  of the actuation valve  2  in such a manner that the latter&#39;s control valve-slide  29  is pushed axially within the bore  63  against the force of the restoring spring  32  far enough for the pressure chamber  73  to be separated from the pressure chamber  72  by the servo-piston  23 . This prevents the passage of the actuation pressure P_A from the actuation valve  2 , via a line  15 , to the clutch regulation valve  3 . 
         [0064]    Furthermore, via line  10 , the axially longer control valve-slide  19  of the clutch regulation valve  3  is acted upon by the pilot pressure P_VST 1  in such a manner that a control edge of the servo-piston  28  opens up the pressure chamber  75  of the clutch regulation valve  3  to a greater or lesser extent. In this way, as a function of the pilot pressure P_VST 1 , the supply pressure P_V 1  can be adjusted to the clutch actuation pressure P_K such that the clutch actuation device  4  can ultimately be brought to a position that disengages or engages the clutch. Of course, intermediate positions can also be set in which the clutch is operated in a slipping mode. 
         [0065]    In  FIG. 1 , it can also be seen that the end of the servo-piston  28  of the clutch regulation valve  3  facing the restoring spring  33  can also be acted upon by the controlled clutch actuation pressure P_K or by the actuation pressure P_A, via the pressure chamber  76  and lines  16  and  17 . 
         [0066]    For example, if a fault or failure of the transmission control unit results in an absence, or at least a large decrease of the pilot pressure P_VST 1  and P_VST 3 , the speed-dependent pressure P_D in the pressure chamber  39  of the self-holding valve  1  becomes effective for actuation. If the speed of the vehicle&#39;s drive engine is high enough such that stalling of the engine is not to be feared, this control pressure P_D will also be high enough to be able to keep the control valve-slide  30  of the self-holding valve  1  positioned such that the supply pressure P_A is delivered, via the pressure chambers  70  and  143  and via line  14 , to the pressure chamber  72  of the actuation valve  2 . 
         [0067]    The self-holding function of the self-holding valve  1  ceases when the speed-dependent control pressure P_D falls below a predetermined value. This limiting pressure value characterizes the stalling speed of the engine. In such a case, the control valve-slide  30  is pushed axially by the force of the restoring spring  31  in the direction toward the pressure chamber  38  so that the actuation pressure supply P_A of the actuation valve  2  is cut off. The starting clutch is therefore disengaged. 
         [0068]    In an emergency operating situation, the pilot pressure P_VST 3  is also absent or greatly reduced in the pressure chamber  78  of the actuation valve  2 , so that its control valve-slide  29  is pushed axially by the force of the restoring spring  32  in the direction toward the pressure chamber  78  in such a manner that the pressure chambers  72  and  73  are connected to one another. Consequently, the actuation pressure P_A is also delivered, via line  15 , to the pressure chamber  80  of the clutch regulation valve  3 , where it acts upon the axially shorter control valve-slide  34 . As a result, the control valve-slide  34  pushes against the free end of the piston  26  of the axially longer control valve-slide  19 , so that the latter is pushed axially against the force of the restoring spring  33 . Thereby, despite the absence of the pilot pressure P_VST 1 , the connection between the pressure chambers  75  and  76  is kept disengaged. 
         [0069]    Thanks to this mode of action, even if the pilot pressure P_VST 1  or P_VST 3  is absent, a clutch actuation pressure P_K can be delivered via a line  18 , the pressure chambers  75 ,  76  and line  16  to the clutch actuation device  4  to hold it in its disengaging position. 
         [0070]    If the engine speed falls so much that there is a risk of stalling, then the speed-dependent pressure P_D will also have a correspondingly low value. This ultimately leads to an interruption of the emergency operation of the transmission, since the force of the restoring spring  31  in the self-holding valve  1  will then be sufficient to push its control valve-slide  30  axially far enough to cut off the actuation pressure connection between the pressure chamber  70  of the self-holding valve  1  and the pressure line  14 . 
         [0071]    As a result of this, the short control valve-slide  34  of the clutch regulation valve  3  will also no longer be acted upon by the actuation pressure P_A so that the longer control valve-slide  19 , driven by the force of the restoring spring  33 , is moved to a position such that the connection, between the pressure chambers  75  and  76 , is cut off. Consequently, the clutch actuation pressure in the cylinder  5  of the clutch actuation device  4  also falls so that its piston  6 , driven by the force of the restoring spring  7 , is pushed to its disengaged position. 
         [0072]    As  FIG. 1  makes clear, if the speed-dependent control pressure P_D again increases after an emergency operation phase, the clutch actuation device  4  at first can not be restored to its engaging position, giving the advantage from a standpoint of safety that the engine speed can be run up in a repair workshop for test purposes without the resultant increase of the speed-dependent pressure P_D then automatically establishing a force flow in the automatic transmission. 
         [0073]    With the control valve arrangement described, according to the invention, a further operating mode is possible in which, in certain critical operating situations of the motor vehicle or the automatic transmission, triggering of the emergency operation function described, i.e., when the starting clutch is engaged or kept disengaged in an engine-speed-dependent manner in the event of the electronic control unit failure, is prevented. 
         [0074]    For example, an operating situation of a motor vehicle is possible, in which it has first been moving in a forward or a reverse gear with an engine speed above the limiting speed value. During such operation, the self-holding valve  1  of the control valve arrangement has, as described, been activated by the speed-dependent pressure P_D and the control valve-slide  30  has, therefore, been pushed against the force of the restoring spring  31 , far enough for pressure medium at the pressure P_D to reach the pressure chamber  39  of the self-holding valve  1 . 
         [0075]    Starting from such driving operation, when the vehicle is stopped, but the engine speed remains above the limiting speed value, the self-holding valve  1  remains in the position described which enables emergency operation with the starting clutch to be engaged in the absence of the pilot pressure P_VST 1 , P_VST 3 . This system behavior persists even when the starting clutch is disengaged by actuation of the selector lever to the transmission selector positions neutral or parking P. 
         [0076]    Now prevent the possibility that in such a situation with a gear engaged, the starting clutch disengaged, the transmission selector lever at neutral or parking P and an engine speed above the limiting value, the starting clutch is then automatically engaged by virtue of a failure of the electronic control unit and thus an absence of the pilot pressure P_VST 1 , P_VST 3 , such autonomous engaging of the starting clutch can be prevented by the prompt application of the neutralizing pressure. 
         [0077]    To do this, the electro-hydraulic valve  167 , shown in  FIG. 1 , is actuated so that a hydraulic neutralizing pressure P_Lösch is present in line  150 , leading to the pressure chamber  149  of the actuation valve  2 . Inasmuch as the pilot pressure P_VST 3  is present in line  9 , this acts via the pressure chamber  78  of the actuation valve  2  on the free end of the servo-piston  23  of the control valve-slide  29  in the actuation valve  2  so that the control valve-slide  29  is pushed against the force of the restoring spring  32 . Thereby, when the electronic control unit is functional the pressure chamber  149  is closed by the servo-piston  148  and the connection, between the pressure chambers  72  and  73 , is cut off. 
         [0078]    Now, if the pilot pressures P_VST 1  and P_VST 3  cease to act, then as already explained, and if the speed-dependent pressure P_D were high enough, the control valve-slide  30  of the self-holding valve  1  would remain in its position, shown in  FIG. 1 , while the control valve-slide  29  of the actuation valve  2 , driven by the restoring spring  32 , would be moved in the direction toward the pressure chamber  78  so that the pressure chambers  73  and  74  would be connected. This would enable the actuation pressure P_A to reach the clutch regulation valve  3  and there push the smaller control valve-slide  34  in such a manner that, by virtue of the large control valve-slide  19 , pressure medium at the supply pressure P_V 1  could be delivered to the clutch actuation device  4  for engaging the starting clutch. 
         [0079]    However, thanks to the delivery of the neutralizing pressure P_Lösch to the actuation valve  2 , according to the invention, if the pilot pressure P_VST 3  is absent then pressure medium at the neutralizing pressure P_Lösch passes from the pressure chamber  149  into the pressure chamber  147  and from there, via line  151 , to the pressure chamber  71  at the foot of the self-holding valve  1 . Here, the neutralizing pressure P_Lösch pushes from below and assists the restoring spring  31  in biasing the servo-piston  20  so that the control valve-slide  30  moves against the speed-dependent pressure P_D in the direction toward the pressure chamber  38 . This blocks the delivery of actuation pressure P_A to the pressure chamber  70  byway of the servo-piston  20 , with the consequence that the actuation valve  2  and the clutch regulation valve  3  are not supplied with this actuation pressure P_A and the starting clutch is disengaged or remains disengaged due to the force of the restoring spring  7  in the clutch actuation device  4 . 
         [0080]    The neutralizing pressure P_Lösch is delivered by actuation of the electro-hydraulic valve  167  when the electronic control unit is functioning and the critical operating situation of the vehicle occurs (described above). If the electronic control unit then fails, the emergency operation function of the hydraulic control arrangement could not be activated. When the critical operating situation is no longer present and the electronic control unit is still working correctly, the latter switches off the neutralizing pressure P_Lösch by de-energizing the valve  167  so that the control valve-slide  30  of the self-holding valve  1 , under the action of the pilot pressure P_VST 1  applied there, is displaced against the force of the restoring spring  31  for the speed-dependent pressure P_D to fill the pressure chamber  39  at the end of the servo-piston  21  remote from the restoring spring. 
         [0081]    Although the control valve arrangement according to  FIG. 1  as such, has a very advantageous structure, in order to initiate its neutralizing function, i.e., to prevent activation of the emergency operation function, the hydraulic emergency operating function has to be activated by briefly cutting off the pilot pressure P_VST 3 . Because of this a perceptible though short engaging of the starting clutch cannot be completely excluded. The following embodiments of the control valve arrangement, according to the invention, avoid the possible occurrence of this disadvantage. 
         [0082]    The control valve arrangement, according to the invention shown in  FIG. 2 , differs from the example embodiment just explained mainly in that it comprises a separate cut-off valve  153 , while the actuation valve  2  has only two servo-pistons  23  and  148 . The cut-off valve  153  has a control valve-slide  159  with two servo-pistons  154  and  155  a distance apart, which can be pushed to its starting position by the restoring spring  166  a pressure chamber  156  is formed. At the end of the cut-off valve  153 , remote from the restoring spring, can be pressurized, via line  150 , with the neutralizing pressure P_Lösch. Between the two servo-pistons  154 ,  155  is formed a pressure chamber  157  that can be drained into a pressure medium tank. This pressure chamber  157  can be connected by axial displacement of the servo-piston  155  against the force of a restoring spring  142  to a pressure chamber  158 , which is connected via a line  146  to line  11  that carries the engine-speed-dependent control pressure P_D in the area of the pressure chamber  39  of the self-holding valve  1 . 
         [0083]    To suppress the emergency operation function of the control valve arrangement, according to  FIG. 2 , in the critical vehicle operation situation outlined above, the pressure chamber  156  of the cut-off valve  153  is pressurized with the neutralizing pressure P_Lösch so that its control valve-slide  159  is moved against the force of the restoring spring  142 . This causes the servo-piston  155 , with its control edge, to open the pressure chamber  158  so that pressure medium at the speed-dependent pressure P_D passes from line  11  or the pressure chamber  39  of the self-holding valve  1 , via a line  146 , and the pressure chamber  158  into the pressure chamber  157 . From there, the pressure medium passes into a pressure medium tank  165  so the pressure in the pressure chamber  39  of the self-holding valve  1  falls until its control valve-slide  30  is moved by the force of the restoring spring  31 . The servo-piston  20  of the control valve-slide  30  then cuts off the pressure chamber  70  from the pressure chamber  143  so that the actuation pressure P_A can no longer pass from the self-holding valve  1  to the actuation valve  2 . Thus, the self-holding function for emergency operation of the drivetrain, if an electronic control unit failure occurs, cannot at first be activated. 
         [0084]    As soon as the critical vehicle operation situation outlined has disappeared, the neutralizing pressure P_Lösch is received by the pressure chamber  156  of the cut-off valve  153  so that the drainable pressure chamber  157  is no longer acted upon by pressure medium at the pressure P_D which, instead, again passes into the pressure chamber  39  of the self-holding valve  1 . Since the pilot pressure P_VST 1  is acting in the pressure chamber  38  of the self-holding valve  1 , the control valve-slide  30  of the self-holding valve  1  is again pushed against the force of the restoring spring  31  so that, even if the pilot pressure P_VST 1  should subsequently disappear, pressure medium at the pressure P_A can still pass from the self-holding valve  1  to the actuation valve  2  when the speed-dependent pressure P_D is high enough. 
         [0085]    In the two embodiments of the control valve arrangement described so far, it is necessarily the case that the discharge of the pressure medium at the speed-dependent pressure P_D into a pressure medium tank  165  and the return of the control valve-slide  30  of the self-holding valve  1  to its starting position take up a certain time. Furthermore, during this the neutralizing pressure P_Lösch must be applied continually. To design this working behavior in a different way, the control valve arrangement, according to  FIG. 3 , is equipped with a one-way restrictor ball in the cut-off valve, which prolongs the restoration duration of the return of the control valve-slide  30  of the self-holding valve  1  and shortens the time during which the neutralizing pressure P_Lösch must be applied to the cut-off valve  153  to the point where, to de-activate the emergency operation property of the control valve arrangement, only a short pressure pulse P_Lösch is needed. 
         [0086]    As can be seen in  FIG. 3 , the control valve arrangement is largely identical to that of  FIG. 2 . As a supplement thereto, a pressure chamber  160  in which the restoring spring  142  of the cut-off valve  153  is located, is connected to a line  164  which disengages into the pressure medium tank  165 . Integrated in this line is a spring-loaded one-way ball valve  163  which blocks in the direction toward the cut-off valve  153 , which can be bridged across by a line  161  that has a hydraulic throttle  162 . 
         [0087]    With regard to its structure and mode of operation, the embodiment of the control valve arrangement, according to  FIG. 4 , corresponds largely to the embodiment shown in  FIG. 2 , so that in what follows essentially only the differences will be explained. Whereas the neutralizing pressure P_Lösch can be delivered by line  150  to the pressure chamber  156  of the cut-off valve  153 , its pressure chamber  158  can be acted upon, via a line  81 , by a control pressure P_V 2 . For example, the two pressures P_Lösch and P_V 2  can be the main pressure of the hydraulic system produced by the pressure medium pump or a reduced pressure of the hydraulic system, which can preferably be switched on by way of electromagnetically actuated valves  90  or  167  respectively. In addition, a line  82  runs from the pressure chamber  158  of the cut-off valve  153  to the pressure chamber  71  of the self-holding valve  1 . 
         [0088]    During normal operation of the vehicle, the restoring spring  142  pushes the control valve-slide  159  of the cut-off valve  153  to its home position, so that the pressure chamber  158  is closed by the servo-piston  155 . In the critical operating situation already mentioned, the pilot pressure P_VST 1  is no longer applied at the level required in the pressure chamber  38  of the self-holding valve  1 , but the speed-dependent pressure P_D is high enough to move the servo-piston  21  of the self-holding valve  1  against the force of the restoring spring  31  far enough for pressure medium at the actuation pressure P_A to be delivered to the clutch regulation valve  3  in order to realize an emergency operation function. 
         [0089]    Now, to prevent the activation of the hydraulic emergency operation, the neutralizing pressure P_Lösch is delivered to the pressure chamber  156 . This moves the control valve-slide  159  against the force of the restoring spring  142  so that pressure medium at the pilot pressure P_V 2  passes into the pressure chamber  71  of the self-holding valve  1  on the spring side, via line  81 , the pressure chamber  158  and line  82 . The pilot pressure P_V 2 , supported by the force of the restoring spring  31 , then pushes the control valve-slide  30  to its home position so that, although the speed-dependent control pressure P_D is high enough for emergency operation, no actuation pressure can get from the self-holding valve  1  to the actuation valve  2 . 
         [0090]    A further embodiment, similar to the control valve arrangement according to  FIG. 4 , is shown in  FIG. 5 . Advantageously, in this case the delivery of the separate neutralizing pressure P_Lösch is dispensed with. Rather, the pilot pressure P_VST 3  is not only passed to the actuation valve  2 , via line  9 , but also via a line  83 , to the pressure chamber  156  of the cut-off valve  153 . By a different switching point design of the cut-off valve  153  and the actuation valve  2 , this pilot pressure P_VSR 3  can be used to actuate both valves  2 ,  153 , as will be explained below with reference to  FIGS. 5 and 6 . 
         [0091]    During normal operation of the vehicle, the pilot pressure P_VST 3  acts both in the pressure chamber  78  of the actuation valve  2  and in the pressure chamber  156  of the cut-off valve  153 . Accordingly, the servo-piston  23  of the actuation valve  2  blocks the delivery of the actuation pressure P_A to the clutch regulation valve  3 , so that the emergency operation function is de-activated. By designing the switching points of the actuation valve  2  and the cut-off valve  153  differently, in normal operation the pilot pressure P_VST 3  can be set between the two switching points S 1  and S 2  in  FIG. 6  so that the piston  155  of the cut-off valve  153  remains in its home position, the pressure chamber  71  of the self-holding valve  1  on the spring side is drained into the pressure medium tank, and when the pilot pressure P_VST 1  in the pressure chamber  38  and/or the speed-dependent pressure P_D in the pressure chamber  39  is high enough, the valve piston  21  of the self-holding valve  1  is held in its pushed-over position against the force of the restoring spring and the emergency operation function can therefore be activated. The emergency operation function is de-activated by increasing the pilot pressure P_VST 3  above the switching threshold S 2  in  FIG. 6 , where the valve piston  155  of the cut-off valve  153  is pushed away from its rest position against the restoring spring force and the pilot pressure P_V 2  in the pressure chamber  158  is passed via pressure line  82  into the pressure chamber  71  of the self-holding valve  1  on the spring side so that the valve piston  21  of the self-holding valve  1  is pushed back with spring support to its home position against the pilot pressure P_VST 1  that may be present in the pressure chamber  38  and the speed-dependent pressure P_D that may be present in the pressure chamber  39  so that the connection, between the actuation pressure P_A in the pressure chamber  70  and pressure line  14  leading to the actuation valve  2 , is interrupted. 
         [0092]    Finally,  FIG. 7  shows a control valve arrangement, according to the invention, in which described activation of the emergency operation function can be prevented by pushing the self-holding valve  1  on the spring chamber side to its home position by the action of the neutralizing pressure P_Lösch and, at the same time, bringing the actuation valve  2 , against the force of its restoring spring, to a position in which a servo-piston of the actuation valve  2  prevents the further transmission of the actuation pressure P_A. 
         [0093]    For this, according to  FIG. 7  a control valve arrangement is provided, which is largely the same as that shown in  FIG. 1 , since the actuation valve  2  is made with three servo-pistons  23 ,  24  and  148 . In addition, the neutralizing pressure P_Lösch can be delivered, via a line  83 , to the pressure chamber  71  of the self-holding valve  1  on the restoring spring side and to a pressure chamber  86  of the actuation valve  2 , via a line  85 , which is arranged axially between the two servo-pistons  23  and  148  remote from the restoring spring. The actuation pressure P_A can be delivered by the self-holding valve  1 , via a line  84 , to a pressure chamber  87  which can be blocked off by the servo-piston  148  of the actuation valve  2 . Between the servo-pistons  148  and  24 , a pressure chamber  88  in the actuation valve  2  is formed, which can be connected to the pressure chamber  87  when the control valve-slide  29  is appropriately positioned and thus enables the actuation pressure P_A to be passed on via a line  84  to the pressure chamber  80  of the clutch regulation valve  3 . 
         [0094]    With this control valve arrangement according to  FIG. 7 , in order to prevent activation of the emergency operation function, if the pilot pressure P_VST 3  disappears, the neutralizing pressure P_Lösch is passed both to the pressure chamber  71  of the self-holding valve  1  on the spring side and also to the pressure chamber  86  of the actuation valve  2 . Thereby, the control valve-slide  30  of the self-holding valve  1  is pushed to its non-spring-loaded home position against a possibly sufficiently high speed-dependent control pressure P_D. In addition, this neutralizing pressure P_Lösch in the pressure chamber  86  of the actuation valve  2  pushes its control valve-slide  29  against the force of the restoring spring  32  far enough for the middle servo-piston  148  to prevent the further transmission of the actuation pressure P_A via the pressure chambers  87  and  88 . 
       REFERENCE NUMERALS 
       [0000]    
       
           1  self-holding valve 
           2  actuation valve 
           3  clutch regulation valve 
           4  clutch actuation device 
           5  cylinder 
           6  clutch piston 
           7  restoring spring 
           8  line carrying the pilot pressure P_VST 1   
           9  line carrying the pilot pressure P_VST 3   
           10  line carrying the pilot pressure P_VST 1   
           11  line carrying the speed-dependent pressure P_D 
           12  line carrying the actuation pressure P_A to the self-holding valve 
           14  connection line self-holding valve to actuation valve 
           15  connection line actuation valve to clutch regulation valve 
           16  connection line clutch regulation valve to clutch actuation device 
           17  connection line clutch regulation valve to clutch actuation device 
           19  line carrying the supply pressure 
           19  control valve-slide in the clutch regulation valve 
           20  servo-piston on the control valve-slide in the self-holding valve 
           21  servo-piston on the control valve-slide in the self-holding valve 
           22  servo piston on the control valve-slide in the self-holding valve 
           23  servo-piston on the control valve-slide in the actuation valve 
           24  servo-piston on the control valve-slide in the actuation valve 
           25  servo-piston on the control valve-slide in the clutch regulation valve 
           26  servo-piston on the control valve-slide in the clutch regulation valve 
           27  servo-piston on the control valve-slide in the clutch regulation valve 
           28  servo-piston on the control valve-slide in the clutch regulation valve 
           29  control valve-slide in the actuation valve 
           30  control valve-slide in the self-holding valve 
           31  restoring spring in the self-holding valve 
           32  restoring spring in the actuation valve 
           33  restoring spring in the clutch regulation valve 
           34  short control valve-slide in the clutch regulation valve 
           36  valve bore in the self-holding valve 
           38  pressure chamber in the self-holding valve 
           39  pressure chamber in the self-holding valve 
           63  bore for the control valve-slide in the actuation valve 
           64  bore for the long control valve-slide in the clutch regulation valve 
           65  bore for the short control valve-slide in the clutch regulation valve 
           70  pressure chamber in the self-holding valve 
           71  pressure chamber in the self-holding valve 
           72  pressure chamber in the actuation valve 
           73  pressure chamber in the actuation valve 
           74  pressure chamber in the clutch regulation valve 
           75  pressure chamber in the clutch regulation valve 
           76  pressure chamber in the clutch regulation valve 
           77  pressure chamber in the clutch regulation valve 
           78  pressure chamber in the actuation valve 
           80  pressure chamber in the clutch regulation valve 
           81  line 
           82  line 
           83  line 
           84  line 
           85  line 
           86  pressure chamber 
           87  pressure chamber 
           88  pressure chamber 
           90  electromagnetically actuated valve 
           142  restoring spring of the cut-off valve 
           143  pressure chamber in the self-holding valve 
           146  line 
           147  drainable pressure chamber in the self-holding valve 
           148  servo-piston in the self-holding valve 
           149  pressure chamber carrying the neutralizing pressure 
           150  line carrying the neutralizing pressure 
           151  line 
           152  line carrying P_VST 1   
           153  cut-off valve 
           154  servo-piston 
           155  servo-piston 
           156  pressure chamber 
           157  pressure chamber that can be drained 
           158  pressure chamber 
           159  control valve-slide of the actuation valve 
           160  pressure chamber of the actuation valve 
           161  line 
           162  throttle 
           163  one-way valve 
           164  line 
           165  pressure medium tank 
           166  electromagnetically actuated valve 
           167  electromagnetically actuated valve 
           168  electromagnetically actuated valve 
         I_VST 3  control current for valve  166   
         P_A actuation pressure 
         P_D speed-dependent control pressure 
         P_K clutch actuation pressure 
         P_Lösch neutralizing pressure 
         P_V 1  supply pressure 
         P_V 2  pilot pressure 
         P_VST 1  pilot pressure 
         P_VST 3  pilot pressure 
         S 1  switching point of actuation valve 
         S 2  switching point of cut-off valve