Abstract:
A device has a unit for determining a clamping pressure of a wrap belt in a stepless wrap gear mechanism. The unit is provided for processing at least one sensor signal, which contains a first characteristic variable for the clamping pressure. The unit is provided for the purpose of processing at least a second characteristic variable for checking the plausibility of the sensor signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     Applicant claims priority under 35 U.S.C. §119 of German Application No. 10 2004 017 991.3 filed Apr. 14, 2004.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a device having a unit for determining a clamping pressure of a wrap belt in a stepless wrap gear mechanism, wherein the unit is provided for processing at least one sensor signal which contains a first characteristic variable for the clamping pressure.  
         [0004]     2. The Prior Art  
         [0005]     A device having a unit for determining and regulating a clamping pressure of a wrap belt of a stepless wrap gear mechanism is known from DE 195 22 674 A1. The unit is intended to process a sensor signal generated by a pressure sensor, which signal is suitable as a characteristic variable for the clamping pressure.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention aims at making available a device by means of which a particularly reliable determination of the clamping pressure can be achieved. In addition, it is an object of the invention to provide a device by means of which the plausibility errors of the sensor signal, which can be attributable to a malfunction of a sensor, can be advantageously recognized.  
         [0007]     The invention proceeds from a device having a unit for determining a clamping pressure of a wrap belt in a stepless wrap gear mechanism. The unit is provided for processing at least one sensor signal, which contains a first characteristic variable for the clamping pressure.  
         [0008]     According to one aspect of the invention, the unit is provided for the purpose of processing at least a second characteristic variable for checking the plausibility of the sensor signal. It can advantageously be achieved that a plausibility error of the sensor signal becomes apparent from the second characteristic variable, so that a particularly reliable determination of the clamping pressure can be achieved. In this connection, the unit can generate a correction signal for automatic correction of an error that has been recognized, if a plausibility error is recognized, and/or it can generate a warning signal to warn a driver, and/or it can switch into an emergency mode.  
         [0009]     In this connection, “provided” should also be understood to mean “designed” and “equipped.” The second characteristic variable can generate a redundancy and check the plausibility of the sensor signals by means of a comparison of the first and the second characteristic variable. The second characteristic variable can also represent a characteristic variable that is at least partially independent of the first characteristic variable, thereby making it possible to achieve an independent check of the plausibility of the first characteristic variable.  
         [0010]     Furthermore, in accordance with another aspect, the sensor signal is at least dependent on a signal of a pressure sensor for detecting a pressure that generates the clamping pressure. In this way, an advantageously direct determination of the clamping pressure can be achieved, and error sources in longer signal chains can be avoided.  
         [0011]     If the unit is provided to trigger a switching signal for activating an emergency mode when a plausibility error is recognized, damage to the wrap gear mechanism resulting from an incorrectly determined clamping pressure can be advantageously avoided. In this connection, the emergency mode can either relate to the entire motor vehicle, in that a torque that can be transferred by way of the wrap gear mechanism is restricted, for example, or only to an activation of the wrap gear mechanism, in that a safety clamping pressure that is not optimal with regard to a friction loss at the wrap gear mechanism is selected, for example.  
         [0012]     If the unit is provided for processing a characteristic variable for an activity of a pump for hydraulic generation of the clamping pressure, an independent check of the plausibility of the sensor signal can be achieved. The characteristic variable for the pump activity may be determined by means of a pump speed of rotation, an energy consumption of the pump, or another characteristic variable that appears practical to a person skilled in the art. If the sensor signal indicates a high clamping pressure at low pump activity, or vice versa, then there is a plausibility error that can be recognized by the unit.  
         [0013]     A particular gain in reliability and convenience can be achieved if the unit is provided to trigger a warning signal to an operator, i.e. driver upon recognition of a plausibility error. This warning signal can be structured to be acoustical or optical, or can be made up of an error message to a maintenance technician, for example by way of an error memory.  
         [0014]     If the unit is provided to equalize at least one time delay between the first characteristic variable and the second characteristic variable, incorrect recognition of an apparent plausibility error by the unit can be avoided. Such apparent plausibility error may be attributable to a deviation between the information from the first characteristic variable and the second characteristic variable, caused by the time delay.  
         [0015]     In addition, in a further aspect, a method is provided for determining the clamping pressure of a wrap belt in a stepless wrap gear mechanism, which is dependent on at least one characteristic variable for the clamping pressure.  
         [0016]     In accordance with this aspect, at least a second characteristic variable is used to check the plausibility of the first characteristic variable. In this way, the result can be achieved that a particularly reliable determination of the clamping pressure can be achieved, and that plausibility errors of the sensor signal can be advantageously detected. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.  
         [0018]     The claims, the figures, and the description contain several characteristics in combination. A person skilled in the art will also consider these characteristics individually, and will combine them into practical further combinations.  
         [0019]     In the drawings:  
         [0020]      FIG. 1  shows a device having a wrap gear mechanism and having a unit for determining a clamping pressure of a wrap belt of the wrap gear mechanism,  
         [0021]      FIG. 2  is a flow chart for recognition of a first plausibility error by the unit, and  
         [0022]      FIG. 3  is a flow chart for recognition of a second plausibility error by the unit. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]     Referring now to the drawings,  FIG. 1  shows a device having a unit  10  that is configured as a computer unit having several control outputs and regulation inputs. Unit  10  is connected via a communication line  18  with a controller area network (CAN) bus of a motor vehicle that includes the device. By way of this bus, the unit can query all variables detected in the motor vehicle. In particular, unit  10  can query, via a connection  20 , a characteristic variable n that is detected by a speed of rotation sensor  19  and determined by the motor speed of rotation. In this connection, the characteristic variable n is, at the same time, an input speed of rotation of a wrap gear mechanism  13 . Furthermore, unit  10  is connected, by way of a control line  21 , with a pump  17  that is directly driven by a motor  23 , by way of a shaft  22 . A pressure sensor  14  detects a pressure generated by the pump, in a pressure line  24 , whereby the pressure determined by the sensor is detected by pressure sensor  14  as a characteristic variable P S  for a clamping pressure  11 , by way of a sensor line  25 . The pressure in pressure line  24  propagates itself by means of a hydraulic medium in the pressure line  24 , up to a cuff  26  around an input shaft  27 . By means of a bore in cuff  26 , the pressure propagates itself into a circumferential groove  28  and from there through an axial interior bore  29  in input shaft  27  into a pressure chamber  30  of the wrap gear mechanism, in order to generate a pressure P K  there.  
         [0024]     A wall surface that delimits the pressure chamber  30  in the direction of a wrap belt  12  is formed by means of a surface, facing away from wrap belt  12 , of a conical body  31  movably mounted, in the axial direction, on input shaft  27 . The surface of body  31 , facing wrap belt  12 , is provided to support the body and forms a segment of a conical surface whose axis coincides with an axis of input shaft  27 . A second surface, forming a segment of a conical surface, for supporting wrap belt  12  at an opposite edge, is rigidly connected with input shaft  27 , whereby the two surfaces form an intermediate space  34  to accommodate wrap belt  12 , which widens in the radial direction about input shaft  27 .  
         [0025]     An output shaft  38  of wrap gear mechanism  13  has an arrangement analogous to the arrangement described above, having a second conical body  32 , an intermediate space  35 , and a second pressure chamber  33 , to which a control pressure P K2  can be applied by unit  10  by way of a pump and pressure lines not shown here. If the pressure P K  is increased and, at the same time, the control pressure P K2  is reduced, intermediate space  34  becomes narrower, and intermediate space  35  becomes wider, which results in a change in a translation of wrap gear mechanism  13 .  
         [0026]     In order to prevent slipping of wrap belt  12  on the surfaces that delimit intermediate spaces  34 ,  35 , wrap belt  12  is constantly under tension and exerts a force on conical bodies  31 ,  32  that drives the conical bodies  31 ,  32  in the direction of pressure chambers  33 ,  30 , in each instance. The counter-force of this force is determined by clamping pressure  11 , which is generated by the pressure P K  and the control pressure P K2 , respectively. Unit  10  can increase clamping pressure  11  by way of an increase in the pressure P K , which can be triggered by way of control line  21 , while the control pressure P K2  remains the same. In this way, the pressure P K  is directly determined by the pressure detected by pressure sensor  14 , which pressure can be detected and processed by unit  10  by way of sensor line  25 , as a characteristic variable P S . In this connection, the pressure generated by pump  17  is essentially determined by the motor speed of rotation, and can merely be corrected by way of control line  25 .  
         [0027]     A program that includes functions for recognizing plausibility errors of the sensor signal of pressure sensor  14 , i.e. of the characteristic variable P S  formed by this sensor signal, is implemented in unit  10 .  
         [0028]      FIG. 2  shows a first function for recognizing a first plausibility error. The input variables are the characteristic variables P S  and n. Since the characteristic variable P S  follows the characteristic variable n, which is dependent on the pump speed of rotation, with a time delay δt of several milliseconds, if the device is functioning properly, the characteristic variable n is passed through a delay filter  37  that can be selected by a time measurement unit  39 , in order to compensate the time delay δt. If the characteristic variable P S  is less than a value P min , and, at the same time, the characteristic variable n is greater than a value n min , unit  10  recognizes that there is a plausibility error of the sensor signal. This error is recognized because pump  17  works and produces a pressure that is greater than the pressure determined by pressure sensor  14 , at a speed of rotation that is greater than the value n min . In a step  36 , a check takes place to determine whether a global, standard error exists, which could be responsible for this contradiction. If no global, standard error exists, unit  10  triggers a switching signal  15  to switch over into an emergency mode, and generates a warning signal P low  on the display of the motor vehicle. A warning message then appears on the display, which informs the driver of an error in a hydraulic plate or in pressure sensor  14 .  
         [0029]     Unit  10  detects the value of a variable t, which indicates how long the motor  23  is shut off, from the CAN bus ( FIG. 3 ). If variable t has a value greater than a value t 0 , the pump  17  is inactive for a corresponding period of time, and a pressure in the pressure line  24  should have dropped to a value close to zero. If the characteristic variable P S  nevertheless has a value greater than the value P min , unit  10  recognizes a plausibility error of the sensor signal of pressure sensor  14 . To check the plausibility error, the function simultaneously demands, with the two aforementioned conditions, that the characteristic variable n must be less than a maximal value n max . If all conditions are met, unit  10  confirms a malfunction of pressure sensor  14 . Unit  10  also generates a switching signal  16  for switching into the emergency mode, and for generating a warning signal P f , which informs the driver of the malfunction of pressure sensor  14 .  
         [0030]     Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention as defined in the appended claims.