Abstract:
A method for controlling a drivetrain including an automatically shifted starting clutch and gear-shift clutch and a transmission, with a non self-locking clutch actuator, a gear actuator for engaging and disengaging transmission gears and a control unit which generates control commands for the clutch actuator and gear actuator and transmits such commands to the actuators such that, when the vehicle is at rest and a gear is engaged and if the clutch actuator fails, the clutch does not inadvertently engage. When a transmission gear is engaged, a control command is generated and sent for the clutch actuator to disengage the clutch. Thereafter, the vehicle speed is determined and if the speed is essentially zero and the clutch begins to engage, a control command is sent to the gear actuator to shift the transmission to its neutral position.

Description:
This application is a National Stage completion of PCT/EP2006/002389 filed Mar. 15, 2006, which in turn claims priority from German patent application serial no. 10 2005 012 261.2 filed Mar. 17, 2005. 
     FIELD OF THE INVENTION 
     The invention concerns a method and device for controlling a motor vehicle drivetrain with an automatic gear-shift transmission and an automated starting and gear-shift clutch. 
     BACKGROUND OF THE INVENTION 
     As is known, a motor vehicle drivetrain comprises a starting and gear-shift clutch between a drive engine and a transmission. Particularly in the case of drivetrains with automatically shifting transmissions, the starting and gear-shift clutch is usually also made to be actuated automatically, so that a driver of the vehicle is largely relieved of the need to actuate the gear shifts and the clutch. To actuate such a clutch, an actuator that can be controlled by a control unit is used, which in most applications is actuated by a pressure medium but can also be made to be actuated electrically. 
     Pressure-medium-actuated clutch actuators consist, in the simplest case, of a cylinder in which a piston is fitted and able to move axially. The piston is connected by a piston rod to a clutch element which, when moved axially, keeps the friction linings of the clutch separated against the restoring force of springs or brings them together, thereby engaging or disengaging the clutch. In relation to this axial movement, the clutch actuator is not made self-locking, so if there is a pressure drop its piston allows the clutch to move back to its starting position, thereby engaging it. 
     To actuate pressure-medium-actuated clutch actuators, electromagnetic switching valves are usually used, which can be controlled by a control unit on the basis of information from sensors and control programs. Depending on their switch position these switching valves provide, for at least one pressure space of the clutch actuation cylinder, a pressure medium connection to a pressure delivery line, the seal the cylinder space relative to the outside, or enable it to be drained into a pressure medium tank. By virtue of these control functions the piston of the clutch actuation cylinder is axially displaced or maintained in a particular position, so that the starting and gear-shift clutch can be disengaged, engaged or operated in slipping mode. 
     As is known from DE 101 61 742 A1, certain hydraulic, electro-hydraulic or electric components of a motor vehicle even such as switching valves and adjusting motors are, for reasons of cost among others, not designed to last for very long times, so that to avoid damaging such components a maximum permissible duration of operation within a reference time period should not be exceeded. 
     Now, if a switching valve for a clutch actuation cylinder or a pressure medium line that connects this switching valve to the clutch actuation cylinder has a leak, in order to open the clutch, and depending on the size of the leak, the switching valve must be actuated until the control unit has determined, on the basis of sensor information, that the clutch has disengaged to the desired extent, whereupon it transmits an engaging command or at any rate no further disengaging commands to the switching valve in question. If the leak is comparatively large this can result with the switching valve remaining actuated for a very long time in order to keep the clutch disengaged. Such a long an actuation time can be damaging for the life of the switching valve and may even lead to its sudden failure. In addition, situations must be avoided in which, for example, when a gear is engaged and the starting and gear-shift clutch is disengaged, a leak results in the undesired driving circumstance that the clutch engages inadvertently because of the leak. 
     This operating behavior of the starting and gear-shift clutch can also occur with clutch actuators which are not actuated by pressure medium and therefore have no switching valves. For example, in the case of a clutch actuator based on a spindle drive powered by an electric motor and not designed to be self-locking, it must be ensured that if a component fails or if the electric voltage supply is briefly interrupted, for example because of a loose contact, no driving situation arises in which the starting and gear-shift clutch engages inadvertently while a gear is engaged. 
     SUMMARY OF THE INVENTION 
     With this as a background, the purpose of the present invention is to propose a method and device with which the above problems can be solved. In particular, the possibility should be prevented that if there is a leak in a pressure line leading to a clutch actuator which, in relation to its actuation movement, is not of self-locking design, in the actuator itself, or in a clutch switching valve associated therewith, the component fails because it is sometimes required to operate for long periods and the clutch engages inadvertently. If the non self-locking clutch actuator is made to be actuated electrically, then in the event of a drive component failure or if the electric voltage supply is interrupted, no driving situation must arise such that the starting and gear-shift clutch engages inadvertently. 
     The invention is based on the realization that the objective is achieved if the fault is detected by a control unit, which then generates and emits a switching command to a transmission actuator which ensures that the transmission is shifted to its neutral position, in which it can transmit no torque. This measure ensures that engaging of the starting and gear-shift clutch as a result of a fault does not lead to an undesired driving situation. 
     Thus the invention concerns in the first place a method for controlling a drivetrain with an automatically actuated starting and gear-shift clutch and an automatic transmission, with a clutch actuator not designed to be self-locking in relation to its actuation movement, with a gear actuator for engaging and disengaging transmission gears, and with a control unit which, with the aid of information received from sensors and control programs, generates control commands for the clutch actuator and the gear actuator and sends them to the actuators. To achieve the stated objective the following process steps are envisaged: 
     a) when a gear is engaged, a control command is generated and sent to at least one actuating means for the clutch actuator to disengage the clutch, 
     b) the speed of the vehicle is determined, 
     c) when the vehicle speed is zero or nearly so and the beginning of an undesired clutch engagement is detected, a control command is generated and sent to at least one actuation means of the gear actuator to shift the transmission to its neutral position. 
     These measures reliably ensure that after some event such as a short interruption of the electric voltage supply to an electro-mechanical clutch actuator, or for example if there is a leak in a pressure medium line leading to a clutch actuator which is actuated by a pressure medium, inadvertent engagement of the starting and gear-shift clutch does not lead to an undesired vehicle operating situation, such as undesired starting thereof. In addition this operating behavior ensures that the clutch actuator actuating means are not damaged by an otherwise excessively long period of operation 
     According to a particular embodiment variant of this method it is provided that an undesired engagement of the clutch due to abnormal operation of the actuation means for the clutch actuator, the clutch actuator itself and/or due to a leak, is detected by determining the actuation duration of the actuation means. 
     In addition, in this connection it can be provided that the actuation duration determined for the actuation means of the clutch actuator, is compared with a predetermined maximum value of the actuation duration, and if this maximum value is exceeded, it can be concluded that there is a defective function of the actuation means, the clutch actuator and/or that there is a leak in a pressure line connected to the clutch actuator or in the clutch actuator itself. It is understood that a defective function of the actuation means for the clutch actuator also includes a disturbance of the voltage supply to an electric motor for an electro-mechanical or electromagnetic clutch actuator. 
     According to a further aspect of the invention, the process step (c) is only carried out when a maximum actuation duration of the actuation means for the clutch actuator for disengaging the clutch is exceeded within a specified time period. 
     To determine the actuation duration of the actuation means, the time for which it has been active can be measured or estimated, or its active time intervals can be summed. Suitable ways of doing this are known from DE 101 61 742 A1. 
     In particular, in this connection it can be provided to measure the actuation duration of an electro-hydraulic or electro-pneumatic switching valve through which the clutch actuator can be supplied with a pressure medium pressure that disengages the clutch. 
     In the case when the clutch actuator is made as an electric motor which, for example, drives a positioning spindle of an electro-mechanical clutch actuator, the actuation duration of this electric motor can be determined. 
     In another embodiment of the method according to the invention, the beginning of the undesired engagement of the starting and gear-shift clutch is detected by measuring the movement path of the moving portion of the clutch actuator. 
     According to another variant, however, the beginning of the undesired engagement of the clutch is detected by measuring a pressure drop compared with a nominal pressure in a pressure space of the clutch actuator that can be actuated by a pressure medium, or in a line leading to the pressure space. 
     In particular, in this connection it can be provided that the process step (c) is only carried out if, when the switching valves which block a line that delivers pressure medium pressure to the clutch actuation cylinder or its pressure space are closed, the pressure therein falls below a specified nominal pressure value. 
     The invention also concerns a device for controlling a drivetrain with an automatically engaged starting and gear-shift clutch and an automatic transmission, with a clutch actuator not designed to be self-locking in relation to its actuating movement, with a gear actuator for engaging and disengaging transmission gears, and with a control unit which, with the aid of information received from sensors and control programs, generates control commands for the at least one clutch actuator and the gear actuator and sends them to the actuators. 
     According to the invention this device also comprises means for determining the beginning of an undesired engaging movement of the clutch actuator when a gear is engaged, the means being designed to co-operate with the control unit in such manner that when the speed of the vehicle is zero or nearly so, the control unit can act upon actuation means for the gear actuator so that the transmission can be shifted to its neutral setting. 
     A further development of this device provides that the at least one means for determining the beginning of an undesired engaging movement of the clutch actuator consist of a pressure sensor in the area of the clutch actuation cylinder of a clutch actuator, a path sensor and/or a device which determines active time. 
     According to the invention, the pressure sensor is arranged in the pressure space of the clutch actuation cylinder or in the pressure line leading thereto. 
     In a preferred variant this pressure line is arranged between two electro-mechanical switching valves by means of which the pressure space of the clutch actuation cylinder can be filled with pressure medium or drained of pressure medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, the invention is explained in more detail with reference to a drawing in which: 
         FIG. 1  is a schematic view of an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The single FIGURE shows at the top a drivetrain of a motor vehicle, with an internal combustion engine  45 , an automatically actuated starting and gear-shift clutch  43  and an automatic transmission  46 . In this known structure the crankshaft  41  of the combustion engine  45  is connected in a rotationally fixed manner with the input side  39  of the clutch  43 , while the output side  40  of the clutch  43  is connected in a rotationally fixed manner to the transmission input shaft  42  of the automatic transmission  46 . In addition, the output side  40  of the clutch is made axially movable relative to its input side  39 , and a clutch-engagement spring  37  engages the clutch  43  without being actuated. Furthermore, the output side  40  of the clutch  43  is acted upon by a clutch actuator  4  by means of which the clutch  43  can be disengaged against the restoring force of the clutch-engagement spring  37 . 
       FIG. 1  also shows a control scheme  1  of a hydraulic control device, according to the invention for the above-mentioned starting and gear-shift clutch  43  and for the automatic transmission  46 , which is divided into four functional blocks. 
     The first functional block  2  is formed by the already mentioned actuator  4  for the starting and gear-shift clutch  43 . In this case the actuator  4  is made as a hydraulic clutch actuation cylinder  4  with a simple and not self-locking action, whose piston  5  can act against the restoring force of the clutch-engagement spring  37 . The clutch-engagement spring  37  ensures that, in a manner known as such, the clutch  43  is engaged unless it is actuated. The piston rod  5  of the clutch actuator  4 , in a concrete, mounted situation in a motor vehicle, is in active connection with a disengaging fork (not shown here) of a clutch-disengaging mechanism. 
     The movement path of the piston rod  5  is determined by a path sensor  25  and transmitted to a control unit  31 , so that the movement of the piston rod  5  can be controlled or regulated as necessary. The control unit  31  is in signal-exchange connection with the relevant sensors and actuators via sensor paths or control paths  32 . 
     The second functional block  3  of this control scheme  1  is formed by two dual-action hydraulic actuators for actuating the transmission. Here, a transmission actuator is made as a gate operating cylinder  6  whose piston separates two pressure spaces within the operating cylinder  6  from one another in a pressure-tight way. The piston rod  9  emerging from the operating cylinder  6  is connected to a transmission actuating device and serves for the selective choice of shift gates. A path sensor  27  communicates to the control unit  31  the exact position of the piston rod  9 . 
     The second hydraulic transmission actuator  8  is constructed in the same way as the first transmission actuator  6 , but in this case serves to engage and disengage transmission gears. For that purpose its piston rod  7  is connected to a related transmission actuation device. The position of this piston rod  7  is detected by a path sensor  26  and transmitted to the control unit  31 . 
     The third functional block  10  of the control scheme  1  comprises the hydraulic control system for the operating cylinders  4 ,  6  and  8 , the clutch  43  and the transmission  46 . Its structure and mode of operation will be described below. 
     The fourth functional block  11  is formed by the control unit  31  and other components. These include a speed sensor  33  connected to the control unit  31  by a sensor lead  34 , which serves to detect the speed of the vehicle.  FIG. 1  also shows a device  35  for determining the active time, connected to the control device  31  by a data lead  36 . However, the active time determination device  35  can also be an integral part of the control unit  31  and can be operated in the manner already known from the document DE 101 61 742 A1 mentioned earlier. The control and sensor leads  32  represented in  FIG. 1  as a lightning symbol connect to the respective sensors and switching valves, but wireless signal transmission paths are also conceivable. 
     The hydraulic control system in the functional block  10  comprises, first, pressure generation, pressure storage and pressure medium line components known as such. These include an electric motor  44  that drives a pressure medium pump  12 , a pressure reservoir  13 , pressure lines  29  leading to the operating cylinders  4 ,  6  and  8 , and unpressurized or drainage lines  30  leading away from them, a pressure-limiting valve  23  between the two lines  29  and  30 , and a pressure medium tank  24  into which the drainage line  29  opens and from which the pump  12  draws the pressure medium. 
     To effect the actuation movement of its piston, the clutch actuation cylinder  4  is associated with three electromagnetic 2/2-way valves  14 ,  15  and  16 . In the switch position shown all these associated switching valves  14 ,  15  and  16  are closed, so that a definite volume of pressure medium from a previous valve switching process is enclosed at a definite pressure in the single pressure space  49  of the clutch operating cylinder  4 . In this case the piston rod  5  is shown in a position in which the starting and gear-shift clutch  43  is engaged. 
     To disengage the clutch  43 , the switching valve  14  is brought to its open position so that more of the pressure medium can pass into the pressure space  49  of the clutch operating cylinder  4  through the line  29 . With the switching valves  15  and  16  still closed, the piston and piston rod  5  move to the right against the force of the clutch-engagement spring  37  and the clutch  43  disengages. Now the switching valve  14  is closed again, so that the pressure of the pressure medium enclosed in the pressure space  49  of the clutch operating cylinder  4  keeps the clutch disengaged. 
     If the clutch  43  is then to be engaged again, the switching valve  14  is still kept closed and the switching valve  15  is opened. This allows pressure medium to flow out of the pressure space  49  of the clutch operating cylinder  4  into the drainage line  30 , whereupon the clutch-engagement spring  37  brings about the restoring movement of the piston and piston rod  5 . 
     With the aid of the switching valve  16  and the throttle  22  arranged downstream from it, the engagement of the starting and gear-shift clutch  43  can take place more comfortably than with the switching valve  15 . It is preferably used to engage the clutch during starting processes. 
     The switching valves  17  to  20  associated with the transmission operating cylinders  6  and  8  are made as 3/2-way valves, which can also be actuated electromagnetically on the basis of control commands from the control unit  31 . With these valves  17  to  20  the two pressure spaces of the respective operating cylinders  6 ,  8  are connected alternatively to the pressure line  29  or the drainage line  30 . 
     By virtue of its two possible switch positions in combination with a pressure sensor  28 , a further electromagnetically actuated 2/2-way valve  21  makes it possible, when the switching valves  17 ,  18  and  21  are in appropriate switch positions, for the pressure medium pressure in the right- or left-hand pressure space of the gear-operating cylinder  8  or in the pressure line  29  to be measured, and for the pressure medium pressure to be maintained in one of the two pressure spaces of the gear-operating cylinder  8 . 
     In the case of such a control device or one similar to it, the normal operating sequence in the area of the clutch control can be disturbed if a leak  38  occurs from the clutch actuation cylinder  4  or the line leading to it. If the leak  38  exceeds a certain volume flow per unit time, when the clutch  43  is disengaged, even with the valves  15  and  16  closed and the valve  14  open, although pressure medium passes into the pressure space  49  of the clutch operating cylinder  4 , at the same time the disengagement time or sum of partial disengaging times that suffices for the normal operation of the switching valve  14  will not be enough to compensate for the pressure medium loss through the leakage point  38 . 
     Now, when an operating situation arises in which the vehicle is at rest and a gear is engaged, it must always be guaranteed that a disengaged clutch  43  remains disengaged, because otherwise the vehicle would start off on its own without the driver wanting or expecting that to happen. In such a case the control unit  31  would therefore continue actuating the switching valve  14  in its operating direction, but this could lead to overheating and subsequent damage thereof. 
     To avoid this, in one variant of the method according to the invention the actual active time of the switching valve  14  is determined, the active time is compared with a stored maximum value of the switched-on time, and when the maximum value has been exceeded, the transmission  46  is brought to its neutral position. This procedure, on the one hand, ensures that the switching valve  14  for admitting pressure medium to the clutch operating cylinder  4  is not damaged, but, on the other hand, reliably prevents the vehicle from starting up inadvertently because the starting and gear-shift clutch  43  has engaged because of a leak. 
     As  FIG. 1  also shows, the control function can also be triggered if a pressure sensor  47  is used to measure the pressure in the line  48  that leads to the clutch actuation cylinder  4 . If this pressure falls below a specified nominal value while the shift valves  14 ,  15  and  16  are closed, it can be assumed that the clutch will engage inadvertently, for example because of the leak  38 . This then causes the control unit  31  to bring the transmission  46  to its neutral position as described. 
     To achieve this control behavior, the gear operation cylinder is brought by actuation of at least one of the switching valves  17  and/or  18 , to such an actuation position (neutral) that the transmission cannot any longer transmit any torque. 
     The invention is not limited to control devices with pressure-medium-actuated clutch actuators, but includes any control device in which, in relation to its regulating movement, the clutch actuator is not made to be self-locking. Thus, for example, such a clutch actuator could be a non self-locking, electric motor powered spindle drive, such that in the event of a failure or short interruption of the voltage supply to its electric drive motor, there would be a risk that the clutch  43  would be restored in the direction of its engaged position by its clutch-engagement spring  37 . 
     With such electric motor powered or even electromagnetic clutch actuators, application of the method according to the invention results in a desired operating behavior such that the electric or electromagnetic clutch actuation mechanism does not sustain any damage, while at the same time it is ensured that the vehicle will not start off on its own. This is achieved by shifting the transmission to neutral when the defective functioning of a component that is important for keeping the clutch disengaged is found or has already been detected. 
     INDEXES 
     
         
           1  Clutch and transmission control scheme 
           2  Clutch actuation block 
           3  Transmission actuation block 
           4  Clutch operating cylinder, clutch actuator 
           5  Piston rod 
           6  Gate operation cylinder, gate operator 
           7  Piston rod 
           8  Gear actuation cylinder, gear actuator 
           9  Piston rod 
           10  Hydraulic control device block 
           11  Electronic control device block 
           12  Pump 
           13  Pressure reservoir 
           14  First 2/2-way valve, clutch 
           15  Second 2/2-way valve, clutch 
           16  Third 2/2-way valve, clutch 
           17  First 3/2-way actuating cylinder, gear 
           18  Second 3/2-way actuating cylinder, gear 
           19  Third 3/2-way actuating cylinder, gate 
           20  Fourth 3/2-way actuating cylinder, gate 
           21  2/2-way valve, gear 
           22  Throttle 
           23  Pressure-limiting valve 
           24  Tank 
           25  Path sensor, clutch 
           26  Path sensor, gear 
           27  Path sensor, gate 
           28  Pressure sensor 
           29  Pressure line 
           30  Drainage line 
           31  Control unit 
           32  Control and sensor lines 
           33  Speed sensor 
           34  Sensor lead 
           35  Device for determining active time 
           36  Data lead 
           37  Clutch-engagement spring 
           38  Leak, leak point 
           39  Clutch input side 
           40  Clutch output side 
           41  Crankshaft 
           42  Transmission input shaft 
           43  Clutch, starting and gear-shift clutch 
           44  Electric motor 
           45  Internal combustion engine 
           46  Automatic transmission 
           47  Pressure sensor 
           48  Pressure line 
           49  Pressure space