Method and apparatus for determining the extension length of a webbing wound on a rotatable belt spool

Abstract

A method for determining the extension length of a seat belt webbing wound on a rotatable belt spool, wherein the webbing extension length is determined based on a rotation angle of the belt spool, the rotation angle of the belt spool being detected incrementally or semi-absolutely, characterized in that at least the following parameters are included in the determination of the absolute rotation angle of the belt spool: - a belt buckle status, i.e., information on whether a buckle tongue of the seat belt is inserted into a designated buckle or not; - an absolute difference between a full extension position, i.e., an angular position of the belt spool corresponding to the maximum possible webbing extension, and a minimum extension position, i.e., an angular position of the belt spool corresponding to the minimum possible webbing extension with the buckle tongue not inserted; and - an absolute difference between a ghost position, i.e.,an angular position of the belt spool that corresponds to the smallest possible belt extension with the tongue inserted, and a minimum extension position, i.e. an angular position of the belt spool that corresponds to the smallest possible belt extension with the tongue not inserted.

Description

The invention relates to a method for determining the extended length of a webbing strap wound on a rotatable spool. The invention further relates to a device for determining the extended length of a webbing strap of a safety belt in a motor vehicle, wound on a rotatable spool of a belt retractor. Various devices for determining the length of the seatbelt extension on seatbelt retractors are known. Determining the length of the extension is generally based on measuring the rotational position of the belt spool onto which the webbing is wound. To determine the absolute rotation angle of the belt spool, which can be greater than 360° from a neutral position if the belt spool has completed more than one revolution, it is necessary to measure not only the angular position of the belt spool but also the number of revolutions in both directions. If the belt spool rotation angle is measured using an incremental or semi-absolute measuring device, where only a portion of the total spool rotations is measured absolutely (e.g., the range of one rotation from 0° to 360°) and then summed or incremented, the absolute value of the belt spool rotation angle relative to a fixed reference point, particularly a zero point, is unknown. Furthermore, the previous position information is lost after the measuring control unit is switched off and restarted. It is generally possible, when using such an incrementally or semi-absolutely measuring device, to provide at least one reference point to which the incrementally or semi-absolutely measured belt reel rotation angle can be referenced upon detection. The absolute belt reel rotation angle can then be determined from the total number of belt reel revolutions. The disadvantage of such a reference point is that the measured belt reel rotation angle is not absolutely known until the reference point is detected. German patent DE 101 56 837 A1 describes a method for sensing the belt movement caused by the body of a belted vehicle occupant. This method may include determining a reference value for the belt extension length, particularly after any belt slack has been removed, after the seat belt has been fastened (detected, for example, by an electrical contact when the belt tongue is inserted into the buckle). Based on this reference value, the belt slack occurring during normal driving should be able to be determined at any given time. Furthermore, excessive belt extension, for example, in an out-of-position (OOP) situation of the belted vehicle occupant, should be able to be measured and detected. A seatbelt detection device for a motor vehicle's seatbelt is known from DE 10 2010 023 491 A1. This device includes a belt extension sensor that takes into account the belt's extension length. It determines whether a threshold value for the extension length has been reached or exceeded. This can be done, for example, by detecting an optical marker. Patent application 10 2008 042 399 A1 describes a known method for detecting an ineffective seat belt, which includes interior sensors for determining the current seat belt status. For this purpose, information about the current seat belt extension length and whether the seat belt buckle is engaged is recorded. An evaluation and control unit evaluates the information from the interior sensors (22) to determine the current seating position and combines this information with information about the current seat belt status to detect an ineffective seat belt. The object of the invention is to determine the current belt extension length of a belt retractor as accurately as possible using simple means, i.e. with minimal equipment effort. This problem is solved by a method with the features of claim 1 and by a device with the features of claim 9. Advantageous and expedient embodiments of the method and the device according to the invention are specified in the dependent claims. In the inventive method for determining the extension length of a seat belt webbing wound on a rotatable spool, the webbing extension length is determined based on a rotation angle of the spool, wherein the rotation angle of the spool is measured incrementally or semi-absolutely. At least the following parameters are included in the determination of the absolute rotation angle of the spool: - a buckle status, i.e., information on whether a seat belt tongue is inserted into a designated buckle or not; - an absolute difference between a full extension position, i.e., an angular position of the spool corresponding to the maximum possible webbing extension, and a minimum extension position, i.e., an angular position of the spool corresponding to the minimum possible webbing extension with the tongue not inserted; and - an absolute difference between a ghost position, i.e.,an angular position of the belt spool that corresponds to the smallest possible belt extension with the tongue inserted, and a minimum extension position, i.e. an angular position of the belt spool that corresponds to the smallest possible belt extension with the tongue not inserted. The invention is based on the understanding that the above parameters are unchanging (absolute angular differences between the fully extended and ghost positions of the belt reel) or remain constant during use or non-use of the seat belt (belt buckle status). These parameters thus represent unambiguous framework conditions, the inclusion of which in determining the absolute rotation angle of the belt reel eliminates or at least limits potential misinterpretations. A preferred embodiment of the invention provides that a maximum possible error is assigned to an assumed value of the rotation angle of the belt spool. The error, the determination of which will be explained later, serves to better estimate or assess the first approximation of the absolute rotation angle of the belt spool. The assigned error represents, in a sense, an imprecision that quantitatively captures the remaining uncertainty about the value. According to another perspective, the associated error can be used to determine a "degree of confidence" for the assumed absolute value of the tape reel's rotation angle. This is done by relating the error to the maximum possible absolute change in the tape reel's rotation angle, which is a fixed value. The larger the error, the lower the degree of confidence; conversely, the smaller the error, the higher the degree of confidence. If it is determined that the buckle tongue is not inserted into the designated buckle after the seat belt system has been started, the minimum extension position of the belt spool can initially be assumed as the absolute rotation angle of the belt spool. The absolute difference between the fully extended position and the minimum extension position can then be assigned to this assumed value as the maximum possible error. If, however, it is determined that the buckle tongue is inserted into the designated buckle after the seatbelt system has started, the "ghost position" of the belt spool can be assumed to be the absolute rotation angle of the belt spool. In this case, the absolute difference between the fully extended position and the "ghost position" can be assigned as the maximum possible error to the assumed absolute rotation angle value. Based on these assumptions and error attributions, the method according to the invention, in a preferred embodiment, provides that during use of the safety belt, changes in the rotation angle of the belt spool are incrementally or semi-absolutely detected and included in the determination of the absolute rotation angle of the belt spool, whereby the initially assigned maximum possible error is reduced with the help of the detected changes. The further detected changes in rotation angle then allow for increasingly accurate conclusions to be drawn about the actual absolute rotation angle of the belt spool, since certain error ranges can be gradually eliminated by the additional information. In particular, if the tongue is not inserted, the maximum possible error can be set to zero if the incrementally or semi-absolutely measured change in the belt spool rotation angle corresponds to the absolute difference between the full extension position and the minimum extension position. In other words, if the tongue is not inserted and the rotation angle measurement determines that a belt length has been pulled off that corresponds to the maximum belt length that can be pulled off under these circumstances, then it can only be a full extension. From this point on, the absolute rotation angle of the belt spool is precisely known, so the error can be set to zero, as there is no longer any uncertainty. Accordingly, the confidence level reaches its highest value. The same applies in the case of the inserted tongue. In this case, the maximum possible error can be set to zero if the incrementally or semi-absolutely measured change in the belt spool rotation angle corresponds to the absolute difference between the fully extended position and the ghost position. To improve and / or increase the reliability and robustness of determining the seatbelt extension length, one or more additional pieces of information can be included as further input variables, providing additional parameters and / or exclusion criteria for specific error ranges. These include, in particular, the following information: position of a seatbelt height adjuster; seat position; adjustment range of a seat height adjuster; information about the build of a buckled-up vehicle occupant. The invention also provides a device for determining the extension length of a seat belt webbing wound on a rotatable spool of a belt retractor in a motor vehicle. The device according to the invention comprises a control unit configured to perform the calculations within the framework of the method according to the invention. The control unit of the device according to the invention preferably accesses a data storage device and is in contact with sensors that are arranged in the belt retractor and / or at other suitable locations in the motor vehicle. Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings, to which reference is made. The drawings schematically show: - Fig. 1 a device according to the invention for determining the webbing extension length; and - Fig. 2 a flowchart of the method according to the invention for determining the webbing extension length. Reference is made below to Fig. 1 and Fig. 2, which schematically show certain components of a device or certain steps of a method for determining the extension length of a webbing 12 of a safety belt wound on a rotatable belt spool 10. Starting with the incrementally or semi-absolutely measuring device described above, further measurable or recordable parameters are used to determine the current belt extension length. Using these parameters, a more or less accurate absolute value of the belt spool rotation angle is initially determined, including a maximum possible absolute error f_max and a confidence level of the assumed absolute value, which is defined as the relative ratio of the possible error to the maximum possible absolute change in the belt spool rotation angle. If changes in the belt spool rotation angle are detected during use of the seat belt, the error can be reduced or the confidence level increased. The following essential information, determined by suitable sensors or the like and transmitted to a control unit 14 in the form of data or signals, serves as a parameter: The buckle status indicates whether the buckle tongue 16 of the seat belt is inserted into the designated buckle 18. If this is the case, it can mean two things: Either a certain length of webbing 12 has been extended to secure a vehicle occupant, a child seat, or another object on the corresponding seat 20; or the webbing 12 is only minimally extended, so that the buckle tongue 16 is inserted into the buckle 18, but no person or object has been secured on the corresponding seat 20. The absolute rotation angle of the belt spool 10 corresponding to this minimal extension of the webbing 12 is referred to as the ghost position or, in short, s_ghost. Another essential parameter is the absolute difference between the angular position of the belt spool 10, which corresponds to the maximum possible belt extension (hereinafter referred to as full extension position or s_max for short), and the angular position of the belt spool 10, which corresponds to the smallest possible belt extension with the plug-in tongue 16 not inserted (hereinafter referred to as minimum extension position or s_min for short). The third essential parameter is the absolute difference between the ghost position (s_ghost) and the minimum extension position (s_min). To carry out the procedure described in detail below, a device is provided with a control unit 14 in which the necessary calculations for determining the belt extension length are performed. The control unit 14 can be either part of the belt retractor 26 or a separate unit in the vehicle. The control unit 14 can access fixed values ​​stored in a memory 28 (s_min, s_max, s_ghost, etc.) and receives current values ​​from sensors or the like (belt buckle status, detected change in the belt spool rotation angle, size / weight of the vehicle occupant, etc.) in the form of data or signals as input variables for the currently performed belt extension length determination. The data or signals originate from corresponding sensors or the like, which are arranged in the belt retractor 26 and / or at other suitable locations in the vehicle (in Fig.1 is only symbolically represented as a sensor 30 in the belt winder 26 for detecting the change in the belt spool rotation angle). Determining the current webbing extension length using the parameters mentioned above is based on the fundamental approach explained below. After the system start of the seat belt system (step 100), which usually coincides with the first power supply in the vehicle before or with starting the engine, the values ​​s_max, s_min and s_ghost are read from the memory 28 of the control unit 14 (step 102), and the seat belt buckle status is queried (steps 104, 106). If the tongue 16 is not inserted into the buckle 18 at system startup, the minimum extension position (s_min) is assumed as the absolute belt spool rotation angle or belt extension length s (step 108). The maximum possible absolute error f_max (uncertainty) of this assumption is—as long as no further information is available—the absolute difference between the full extension position and the minimum extension position, i.e., s_max - s_min, since the actual value can lie anywhere in the interval [s_min; s_max]. If, on the other hand, the tongue 16 is inserted into the buckle 18 at system startup, the ghost position (s_ghost) is assumed as the absolute belt spool rotation angle or belt extension length s (step 110). The maximum possible absolute error f_max (uncertainty) in this case is (s_max - s_ghost), since the actual value can lie anywhere in the interval [s_ghost; s_max]. During operation of the seatbelt system, the rotation angle of the belt spool 10, or its changes, is continuously measured by sensors (step 114). The initially relatively large potential errors f_max can be reduced by the measured values ​​obtained during use of the seatbelt, or the confidence level of the currently assumed absolute belt spool rotation angle can be increased (step 116). This will be briefly explained using a concrete example. When the incrementally or semi-absolutely measured change in the belt spool rotation angle reaches its maximum value, i.e., the full extension position (s_max), the maximum possible error f_max (uncertainty) is zero, or the confidence level of this measured value is 100%. Therefore, if the rotation angle measurement detects the maximum belt extension under the given circumstances (especially depending on the belt buckle status), the absolute rotation angle of the belt spool 10 is uniquely known from that point on (namely, the maximum value), so that no uncertainty remains and the error can be set to zero until the next system restart. Further information for more accurately determining the seatbelt extension length can include, for example, the position of the seatbelt height adjuster 22, the seat position, the adjustment range of the seat height adjuster 24, and information about the occupant's build (in particular, classification into specific size / weight categories, such as: small, normal, large; light, medium, heavy). This information, insofar as it is currently available, is incorporated as additional input variables into the algorithm for determining the seatbelt extension length (step 112) and helps to further reduce the error and / or increase the confidence level. Reference symbol list 10 Belt spool 12 Webbing 14 Control unit 16 Plug tongue 18 Belt buckle 20 Seat 22 Belt height adjuster 24 Seat height adjuster 26 Belt retractor 28 Memory

Claims

A method for determining the extension length of a seat belt webbing wound on a rotatable belt spool, wherein the webbing extension length is determined based on a rotation angle of the belt spool, the rotation angle of the belt spool being detected incrementally or semi-absolutely, characterized in that at least the following parameters are included in the determination of the absolute rotation angle of the belt spool: - a belt buckle status, i.e., information on whether a buckle tongue of the seat belt is inserted into a designated buckle or not; - an absolute difference between a full extension position, i.e., an angular position of the belt spool corresponding to the maximum possible webbing extension, and a minimum extension position, i.e., an angular position of the belt spool corresponding to the minimum possible webbing extension with the buckle tongue not inserted; and - an absolute difference between a ghost position, i.e.,an angular position of the belt spool that corresponds to the smallest possible belt extension with the tongue inserted, and a minimum extension position, i.e. an angular position of the belt spool that corresponds to the smallest possible belt extension with the tongue not inserted. Method according to claim 1, characterized in that a maximum possible error is assigned to an assumed value of the rotation angle of the belt spool. Method according to claim 2, characterized in that, after a system start with the safety belt tongue not inserted into the designated belt buckle, the minimum extension position of the belt spool is assumed as the absolute rotation angle of the belt spool, and the absolute difference between the full extension position and the minimum extension position is assigned to this assumed value as the maximum possible error. Method according to claim 2, characterized in that, after a system start with the safety belt tongue inserted into the designated buckle, the absolute difference between the fully extended position and the ghost position is assigned as the largest possible error. Method according to one of claims 2 to 4, characterized in that during use of the safety belt, changes in the rotation angle of the belt spool are detected incrementally or semi-absolutely and included in the determination of the absolute rotation angle of the belt spool, whereby the largest possible error is reduced with the help of the detected changes. Method according to claim 3 and claim 5, characterized in that the maximum possible error is set to zero when the incrementally or partially absolutely detected change in the belt spool rotation angle corresponds to the absolute difference between the full extension position and the minimum extension position. Method according to claim 4 and claim 5, characterized in that the maximum possible error is set to zero when the incrementally or partially absolutely detected change in the belt spool rotation angle corresponds to the absolute difference between the full extension position and the ghost position. Method according to one of the preceding claims, characterized in that at least one of the following information is additionally included in the determination of the belt extension length: position of a belt height adjuster; seat position, adjustment range of a seat height adjuster; information about the stature of a buckled vehicle occupant. Device for determining the extension length of a webbing (12) of a safety belt wound on a rotatable belt spool (10) of a belt winder (26) in a motor vehicle, comprising a control unit (14) which is configured to perform the calculations within the framework of the method according to one of the preceding claims. Device according to claim 9, characterized in that the control unit (14) accesses a data storage device (28) and is in connection with sensors (30) which are arranged in the belt retractor (26) and / or at suitable locations in the motor vehicle.

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