Abstract:
A method and system for controlling the creeping behavior of a vehicle equipped with an automated clutch ( 4 ). According to the method for controlling the creeping behavior of a vehicle equipped with an automated clutch ( 4 ), the actuation of a brake actuation element ( 34 ) is detected. In addition, a creep parameter, which influences creeping and whose magnitude influences the actuation position of the clutch ( 4 ), is modified with an increasing actuation of the brake actuation element ( 34 ) to reduce the creeping behavior.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a continuation of PCT Application No. PCT/DE02/02071, filed Jun. 7, 2002, and claims priority to German Patent Application 101 28 692.1 filed Jun. 13, 2001. Both of these applications are hereby incorporated by reference herein. 
     
    
     
       BACKGROUND INFORMATION  
         [0002]    The present invention relates to a method and a system for controlling the creep behavior of a vehicle equipped with an automated clutch.  
           [0003]    Automated clutches are being increasingly used not only because of the added convenience they provide, but also because of the possible reduction in wear in motor vehicles.  
           [0004]    [0004]FIG. 2 shows a schematic diagram of a power train of a motor vehicle equipped with an automated clutch as an example. The power train includes an internal combustion engine  2 , a clutch  4 , and a transmission  6 , which is connected to driven wheels (not shown) via a drive shaft  8 . Transmission  6  is an automated manual shift transmission, for example, a taper disk belt transmission having a continuously variable transmission ratio, or a conventional automatic transmission having planetary gears. A shifting device  9 , which is controllable from a selector device  10  using a selector lever  12  via a control unit  14  in a known manner, is used to actuate or shift transmission  6 . It is understood that the selector device may also have a different design, for example, as a conventional shift stick (H gate) or as a lever having jog positions for shifting up and down. Clutch  4  is a friction disk clutch, for example, of a design which is known per se, having an actuating device  16 , which may have a hydraulic, electric, electrohydraulic, or other known design.  
           [0005]    The sensors contained in the power train, such as a pressure sensor  18  for detecting the intake pressure of engine  2 , a rotational speed sensor  20  for detecting rotational speed n M  of the engine crankshaft, a sensor  22  for detecting position α of an accelerator pedal  24 , a sensor  26  for detecting the position of selector lever  12 , and an additional rotational speed sensor  28  for detecting the rotational speed of drive shaft  8 , are connected to the inputs of control unit  14 .  
           [0006]    Control unit  14 , having a microprocessor with respective memories  29 , contains characteristic maps and programs in an essentially known manner, which control actuators, such as a load adjustment element  30  for adjusting the load of engine  2 , actuating device  16 , clutch  4 , and shifting device  9  of transmission  6 , and other consumers  31  driven directly or indirectly by the engine such as a generator, a pump, or a heating element, etc. The individual actuators may be designed in such a way that their position is immediately known in control unit  14 , for example, as stepping motors, or additional position transducers, such as position transducer  32  for detecting a parameter relevant to position s K  of clutch  4 , may be provided.  
           [0007]    A brake pedal  34  is connected, via a hydraulic line  35 , to a braking pressure control unit  36 , which is connected to vehicle brakes  38  via additional hydraulic lines. An additional electronic control unit  40 , which is connected to control unit  14  via a data line  42 , is provided for controlling brake pressure control unit  36 . The pressure in hydraulic line  35  generated by the actuation of brake pedal  34  is detected by a pressure sensor  44  connected to control unit  14 . Control unit  40  controls the brakes, for example, in an essentially known manner, in such a way that locking of a wheel is prevented (ABS system) and/or that the vehicle does not skid unintentionally (vehicle stability system). For this purpose, additional sensors (not shown) are provided, whose signals are analyzed in control unit  40 , possibly together with signals delivered by control unit  14 , so that the individual vehicle brakes and, if present, load adjustment element  30 , may be triggered as needed. The distribution of hardware and software between devices  14  and  34 , as well as the connections of the sensors and actuators are adapted to the particular conditions.  
           [0008]    The design and function of the above-described system are essentially known and will therefore not be described in detail. Depending on the driver&#39;s intent communicated via accelerator pedal  24  and the intent of selecting a driving program or a driving direction communicated via selector lever  12 , load adjustment element  30 , actuating device  16 , and shifting device  9  are actuated in a mutually coordinated manner as a function of the signals delivered by the sensors in such a way that comfortable and/or economical driving results.  
           [0009]    A characteristic curve, for example, which determines a setpoint position of clutch  4  set by actuating device  16  as a function of the torque to be transmitted by clutch  4  is stored in the memory of control unit  14  to actuate clutch  4 . For reasons of control quality, clutch wear, and power consumption of the actuating device, the clutch torque to be transmitted at a given time should not exceed the absolutely necessary value. The required torque to be transmitted results from the driver&#39;s intent, i.e., the position of accelerator pedal  24  and, for example, from the load on internal combustion engine  2 , detected by sensor  18 , and possibly from additional operating parameters such as the rotational speed of engine  2 , etc.  
           [0010]    The characteristic curve stored in control unit  14 , which provides the desired path of the clutch&#39;s final control element moved by actuating device  16  as a function of the calculated torque to be transmitted, has a decisive influence on comfortable start and comfortable shifting. The characteristic curve changes in the short-term due to temperature changes, for example, and in the long-term over the lifetime of the clutch due to wear, for example. It is, therefore, constantly updated, i.e., readjusted, according to a wide variety of strategies, to the prevailing operating conditions.  
           [0011]    One important function which is made possible by an automated clutch is the vehicle creep, which makes it possible for the vehicle to move slowly when a forward or reverse gear is selected and the engine is running, without actuating the accelerator pedal. The driver is thus able to maneuver the vehicle more easily by operating only the brake pedal to stop the creeping vehicle. In creeping, the clutch is controlled in general in such a way that it is engaged as long as it transmits a certain creep torque, for example, 10 Nm. This creep torque is controlled, for example, by control unit  14  slowly engaging clutch  4  using actuating device  16  with the transmission in gear and the gas pedal not actuated, while engine  2  is controlled via load adjustment element  30  of engine  2  at, as far as possible, a constant speed of engine  2  in such a way that it generates the predefined torque on the clutch. It is understood that the power consumption of any additional consumers driven by the engine is taken into consideration.  
           [0012]    One peculiar feature of the known creep behavior of vehicles is that the driver is not able to directly influence the creep, which impairs comfort and requires a high degree of skill from the driver when, for example, he must maneuver on a sloping roadway.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    An object of the present invention is to provide a method and a system for controlling the creep behavior of a vehicle equipped with an automated clutch, in which it is possible to further enhance comfort in creep operation.  
           [0014]    The present invention provides a method for controlling the creep behavior of a vehicle equipped with an automated clutch, wherein the actuation of a brake actuating element is detected and a creep parameter influencing the creep, whose magnitude influences the actuating position of the clutch, is modified when the brake actuating element is increasingly actuated in such a way that the extent of creep is reduced.  
           [0015]    Using the method according to the present invention, it is achieved that the driver is able to directly influence the position of the clutch and thus the creep behavior by actuating the brake, so that the creep torque transmitted by the clutch during creep states may vary within broad limits. Furthermore, the clutch is spared, because the creep torque is weakened with increasing actuation of the brake, and the clutch, i.e., the engine, does not work entirely against the actuated brakes.  
           [0016]    The present invention also provides a system for controlling the creep behavior of a vehicle equipped with an automated clutch, containing sensors for detecting operating parameters of a vehicle engine, a sensor for detecting an operating state of a vehicle braking device, a power adjustment actuator for controlling the power output of the engine, a clutch actuator for controlling the clutch, a brake actuating element, and an electronic control device having memory devices and a microprocessor, connected to the sensors and actuators, the control device controlling the actuators according to the analysis of the sensor signals for carrying out the method according to the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The present invention is elucidated below on the basis of the schematic drawing used as an example and further details.  
         [0018]    [0018]FIG. 1 represents a flow chart for elucidating a creep strategy, and  
         [0019]    [0019]FIG. 2 represents a schematic drawing, described previously, of a prior art vehicle power train having a controller. 
     
    
     DETAILED DESCRIPTION  
       [0020]    As an example, the present invention is elucidated below using a power train designed as in FIG. 2 described previously.  
         [0021]    A characteristic curve which provides the setpoint value of a creep parameter KP S  as a function of a brake actuation parameter B, i.e., KP S =f(B), is stored in control unit  14 . Creep parameter KP is a variable which defines the “extent of creep” of the vehicle. Function f is such that KP S  decreases as brake actuation B increases, i.e., when the brake is not being actuated, the vehicle creeps strongly by itself, and the extent of creep diminishes with increased brake actuation in that, for example, the clutch is gradually disengaged or the engine is controlled in such a way that its torque is reduced.  
         [0022]    The measure of brake actuation B may be given, for example, by pressure p detected by sensor  44  or by a force with which the brake pedal is actuated or the path by which the brake pedal is displaced (the corresponding sensors are not shown in the drawing). Taking the force on the brake pedal or the path of actuation of the brake pedal as the variable describing the brake actuation is advantageous in electronic or electric brake systems where, like in electronic gas pedals, actuation of the brake itself is separated from the operation of the brake pedal. The actuation of a hand brake lever, not shown, may also be used as a variable describing the brake actuation.  
         [0023]    The creep parameter describing the creep behavior of the vehicle may be of different types. For example, the creep torque transmitted by clutch  4  may be used as the creep parameter, the engine then being kept at a constant speed using, for example, an idling control device (not shown), and the clutch being controlled by actuating device  16  in such a way that it transmits the torque predefined by the brake actuation. The torque that is transmitted when the brake is not actuated may be defined by a value such that the vehicle creeps forward even if it is standing on an upward slope.  
         [0024]    It is particularly advantageous if the vehicle speed is used as the creep parameter, which, to be measurable with sufficient accuracy even at very low speeds, is advantageously detected by a sensor which detects the rotation of an input shaft of transmission  6 . This rotation is convertible directly into the vehicle speed if the transmission ratio of the transmission is known. Rotational speed sensor  28 , which in FIG. 2 detects the rotational speed of output shaft  8  of the transmission, may then be omitted and is replaced by a corresponding sensor which detects the rotational speed of the input shaft of transmission  6 . Because of the higher speed of the transmission input shaft compared to the rotational speed of the vehicle&#39;s wheels, it is advantageous to detect the speed of the transmission input shaft rather than using the wheel speed sensors usually present in vehicles equipped with ABS systems.  
         [0025]    An example of the creep control by the driver is elucidated on the basis of FIG. 1.  
         [0026]    Initially, it is determined in step  50  whether the vehicle is in the creep mode. The creep mode is defined, for example, by the fact that the engine is running, gas pedal  24  is not being actuated, and the forward gear having the highest transmission ratio or the reverse gear is engaged.  
         [0027]    If the vehicle is in the creep mode, it is determined in step  52  whether clutch  4 , i.e., engine  2 , is controlled in such a way that instantaneous creep parameter KP i  is greater than, for example, setpoint creep parameter KP S  dependent on the actuation of brake pedal  34  (the pressure detected by sensor  44 , for example) plus a value Δ which is advantageous for the control, i.e., whether the condition  
           KP   i   &gt;KP   s +Δ 
         [0028]    is met. If this is the case, in step  54  the clutch is gradually disengaged and/or the engine torque is reduced, so that KP i  is reduced by a predefined value, for example. The system then jumps back to step  50 .  
         [0029]    If it is determined in step  52  that the condition is not met, it is determined, in step  54 , whether the condition KP i &lt;KP s −Δ is met. If this is the case, KP i  is increased in step  56 , and the system jumps to step  50 . If it is determined in step  54  that the condition checked there is not met, engine and/or clutch control is maintained in step  58 , whereupon the system jumps to step  50 . If it is determined in step  50  that the creep mode is no longer present, for example, due to the fact that the accelerator pedal has been actuated, the neutral gear has been selected, or, for example, the brake pedal has been actuated using a force greater than the threshold value, the system jumps to end step  60 , where the creep mode is terminated.  
         [0030]    A simple function KP i =f(B) reads, for example:  
           v   setpoint =(( B   max   −B )/ B   max )× v   max  for  B&lt;B   max  and  
         v setpoint =0 for B&gt;B max .  
         [0031]    Here, v max  is the maximum creep speed (the brakes not being actuated). If brake actuation B exceeds the value B max , the creep speed should be reduced to zero. The torque transmitted via the clutch is controlled by control unit  14  in such a way that the desired speed dependent on the brake actuation is quickly set without control vibrations. In this way, the vehicle exhibits a creep behavior which allows it to maneuver very comfortably under a great variety of conditions.  
         [0032]    The above-mentioned method in which the creep speed is taken as the creep parameter has the following advantages:  
         [0033]    The engine torque available at the clutch, which is difficult to measure accurately, does not need to be determined directly.  
         [0034]    Displacements of the clutch measuring point, which always occur, do not need to be taken into account directly.  
         [0035]    The strategy is easily usable even on an upward slope, as long as the engine is capable of delivering sufficient torque within the controlled range, e.g., at its idling speed. Otherwise, the control range of the engine may be extended by activating not only the idling control system, but also the setting of a load adjustment element.  
         [0036]    The above-described method according to the present invention may be modified in many ways. For example, different characteristic curves, setpoint values, and limiting values may be used for a forward and a reverse gear.