Device for determining the absolute angle of rotation of a belt reel

Abstract

Device for determining the absolute angle of rotation of a belt reel, with a belt reel (10), a first gearbox, and a first rotary element (12) coupled to the belt reel (10) by means of the first gear, wherein the first gear has a gear ratio between the belt reel (10) and the first rotary element (12) which is not equal to 1, and a first measuring device (14) associated with the first rotary element (12) for detecting the angle of rotation of the first rotary element (12), characterized by a second gear and a second rotary element (18) coupled to the belt reel (10) by means of the second gear, wherein the second gear has a transmission ratio between the belt reel (10) and the second rotary element (18) which is unequal to the transmission ratio of the first gear, and a second measuring device (16) associated with the second rotary element (18) for detecting the angle of rotation of the second rotary element (18), and wherein the transmission ratios of the first gear and the second gear are selected such that each combination of rotation angles of the first rotary element (12) and the second rotary element (18) occurs only once over the entire rotation range of the belt reel (10).

Description

[0001] The invention relates to a device for determining the absolute angle of rotation of a belt reel.

[0002] Various methods are known for determining the extended length of a seat belt webbing wound onto a rotating belt spool of a belt retractor in a motor vehicle. Determining the extended length of the webbing is generally based on detecting the rotational position of the belt spool onto which the webbing is wound. In order to determine the absolute angle of rotation of the belt spool, which—starting from an initial position—can be greater than 360° if the belt spool has completed more than one rotation, it is necessary to detect not only the angular position of the belt spool but also the number of rotations of the belt spool in both directions.

[0003] In another context, DE 298 20 086 U1 discloses a belt retractor with a switching disc that is coupled to the belt spool by a reduction gear such that it performs approximately one revolution when the belt spool performs as many revolutions as are required to fully retract the belt webbing wound onto the belt spool. Thus, all revolutions of the belt spool are mapped onto a single revolution of the switching disc. This design has the advantage that certain switching functions, such as a child safety lock function of the belt retractor, in which, after the belt webbing has been fully retracted, it can be wound back onto the belt spool but can no longer be removed in order to reliably secure a child seat to a vehicle seat, or a blocking function for the locking mechanism of the belt retractor, can be implemented without a complex planetary gear system.The switching disc, equipped with projections and recesses, serves exclusively to perform certain switching functions at precisely defined belt extension lengths. The switching disc does not perform any other functions.

[0004] The generic DE 10 2005 042 307 A1 describes a device for determining the absolute angle of rotation of a belt reel, with a belt reel, a first gear, and a first rotary element coupled to the belt reel by means of the first gear, wherein the first gear has a transmission ratio between the belt reel and the first rotary element which is not equal to 1, and a first measuring device assigned to the first rotary element (12) for detecting the angle of rotation of the first rotary element.

[0005] Such generic devices are also known from DE 10 2006 051 969 A1 and DE 199 22 720 A1.

[0006] The object of the invention is to determine the absolute angle of rotation of the belt reel and thus the corresponding belt extension length in a belt retractor with sufficient accuracy using simple means, ie with little equipment complexity.

[0007] This object is achieved by a device having the features of claim 1. Advantageous and expedient embodiments of the device according to the invention are specified in the subclaims.

[0008] The device for determining the absolute angle of rotation of a belt reel comprises a belt reel, a gear, and a rotating element coupled to the belt reel by means of the gear. The gear has a gear ratio between the belt reel and the rotating element that is not equal to 1. The device according to the invention also comprises at least one first measuring device assigned to the rotating element for detecting the angle of rotation of the rotating element.

[0009] The invention is based on the finding that coupling a rotating element to the belt reel, which exhibits a rotational behavior dependent on, but deviating from, the belt reel, opens up various possibilities for determining the absolute rotational angle of the belt reel. The step-up or step-down ratio between the belt reel and the rotating element can be selected such that detecting the rotational angle of the rotating element alone or in combination with detecting the rotational angle of another coupled rotating element or the belt reel itself, within a measuring range of 0° to 360°, provides sufficient information to unambiguously determine the absolute rotational angle of the belt reel, particularly if this angle is greater than 360°.

[0010] In a device according to the invention, the transmission ratio of the first gear is advantageously selected such that the complete rotational range of the belt reel is mapped to no more than one revolution of the first rotating element. Thus, it is sufficient to provide a measuring device that covers a measuring range from 0° to <=360°. Each rotational angle of the first rotating element within this range clearly corresponds to an absolute rotational angle of the belt reel, which, depending on the transmission ratio, can be significantly greater than 360°.

[0011] A further advantage is achieved if a second measuring device is assigned to the belt reel to detect the angle of rotation of the belt reel. Due to the step-up or step-down ratio of the gear, which is not equal to 1, a rotation of the belt reel causes a change in the angle of rotation of the rotating element, which necessarily differs from the corresponding change in the angle of rotation of the belt reel. Each absolute angle of rotation of the belt reel is therefore characterized by a combination of a detected angle of rotation of the belt reel and a detected angle of rotation of the rotating element. From these angle of rotation combinations, the absolute angle of rotation of the belt reel can be deduced, whereby it is sufficient that the two measuring devices only cover a measuring range of 0° to 360° or less.

[0012] Preferably, the transmission ratio of the first gear is selected such that, across the entire rotational range of the belt reel, each combination of rotational angles of the belt reel and the first rotating element occurs only once. This means that, within the (limited) measuring ranges of the measuring devices, each combination of recorded rotational angles does not occur multiple times, but only once. This circumstance makes the determination of the absolute rotational angle of the belt reel unambiguous, so that no further differentiation or exclusion criteria are necessary.

[0013] According to an alternative embodiment of the second aspect of the invention, the first measuring device assigned to the first rotary element can finely resolve a rotation angle range that is smaller than the maximum rotation angle range of the belt reel, in particular 0° to 360°, and the second measuring device assigned to the belt reel can detect at least the number of completed rotations of the belt reel starting from an initial position. This minimum criterion for the second measuring device states that it can at least distinguish between defined absolute rotation angle intervals, e.g., whether the belt reel has completed a total of one, two, three, ... revolutions. A more precise resolution within these intervals is not required, since the second measuring device is provided for this purpose.

[0014] According to the invention, in the device for determining the absolute angle of rotation of the belt reel, in addition to the first rotating element coupled to the belt reel via a first gear, a second rotating element coupled to the belt reel via a second gear is additionally provided. The second gear has a step-up or step-down ratio that is different from the step-up or step-down ratio of the first gear. In addition, a second measuring device assigned to the second rotating element is provided for detecting the angle of rotation of the second rotating element. Due to the different step-up or step-down ratios, a specific combination of angles of rotation of the two rotating elements results for each absolute angle of rotation of the belt reel, which angles are detected by the assigned measuring devices.

[0015] Furthermore, according to the invention, the transmission ratios of the first gear and the second gear are selected such that, across the entire rotational range of the belt reel, each combination of rotational angles of the first rotating element and the second rotating element occurs only once. As already explained above, this ensures that, within the (limited) measuring ranges of the measuring devices, each combination of detected rotational angles does not occur multiple times, but only exactly once, so that no further differentiation or exclusion criteria are necessary for a clear determination of the absolute rotational angle of the belt reel.

[0016] Independently of the above-explained aspects of the invention, a reference point can be provided on the belt webbing to determine the absolute angle of rotation of the belt reel. This reference point marks a unique absolute angle of rotation of the belt reel and can be detected using a suitable stationary device. As soon as the reference point is detected during belt extension, the absolute angle of rotation of the belt reel is known at that moment. The changes in the angle of rotation detected up to that point and subsequently can then be related to the reference point, so that the absolute angle of rotation of the belt reel can be clearly determined.

[0017] Further features and advantages of the invention will become apparent from the following description and the accompanying drawings, to which reference is made. The drawings schematically show: - Fig. 1 a first concept for detecting an absolute angle of rotation of a belt reel; - Fig. 2 a second concept for detecting an absolute angle of rotation of a belt reel; - Fig. 3 a third concept for detecting an absolute rotation angle of a belt reel; and - Fig. 4 a fourth concept for detecting an absolute angle of rotation of a belt reel.

[0018] In the Fig. 1 to 4 show four concepts with which the absolute angle of rotation of a belt reel 10 of a motor vehicle belt retractor can be determined.

[0019] According to the Fig. In the concept shown in Figure 1, the maximum rotational range of the belt reel 10, which may, for example, comprise twelve revolutions, is transmitted by means of a reduction gear to a rotational range of a rotating element 12, e.g., a gear disk, which is no greater than 360°. The reduction ratio i is constant, so that each absolute rotational angle of the belt reel 10, which for twelve revolutions can be in the range from 0° to 4320°, corresponds exactly to a rotational angle of the rotating element 12 between 0° and a maximum of 360°.

[0020] The rotation of the rotating element 12 can be detected by a measuring device 14 assigned to the rotating element 12, the measuring range of which only needs to encompass the maximum rotational range of the rotating element 12 defined above. In particular, the measuring device 14 does not need to have a measuring range extending beyond 360°. The measuring device 14 can detect either only a change in the angle of rotation or also the rotational speed and / or acceleration.

[0021] Another way to determine the absolute angle of rotation of the belt reel 10 is in Fig. 2. The belt reel 10 is in turn coupled to a rotating element 12 via a gear, with the transmission ratio not equal to 1 (i ≠ 1). Both the rotating element 12 and the belt reel 10 are each assigned a measuring device 14 or 16 with a measuring range that is less than or equal to 360°.

[0022] The absolute angle of rotation of the belt spool 10 can be determined from the two recorded angles of rotation, which are both less than 360°. Depending on the step-up or reduction ratio i, it cannot be ruled out that a measured combination of angles of rotation or changes in angle of rotation may occur multiple times within the maximum rotation range of the belt spool 10. In such cases, further criteria would have to be used to determine the absolute angle of rotation in order to obtain an unambiguous result. However, with a suitable selection of the step-up or reduction ratio i, such cases can be completely ruled out, i.e. each absolute angle of rotation of the belt spool 10 is uniquely represented by exactly one combination of angles of rotation of the rotating element 12 and the belt spool 10.

[0023] Another alternative to the absolute angle determination of the belt reel 10 is shown by the Fig. 3. The belt reel 10 is coupled to two different rotating elements 12 and 18 via two different gears. The respective gear ratios i1 and i2 are not equal (i1 ≠ i2). Each of the rotating elements 12 and 18 is assigned a measuring device 14 and 16, respectively, with a measuring range of less than or equal to 360°.

[0024] The absolute angle of rotation of the belt reel 10 can be determined from the detected angles of rotation of the first rotating element 12 and the second rotating element 18, which are both less than 360°. Here, too, it cannot be ruled out that a combination of angles of rotation or changes in the angle of rotation of the two rotating elements 12, 18 occurs multiple times within the maximum rotation range of the belt reel 10. Therefore, the step-up and step-down ratios i1 and i2 are selected such that each absolute angle of rotation of the belt reel 10 is uniquely represented by exactly one combination of angles of rotation of the two rotating elements 12, 18.

[0025] In Fig. 4 shows a combination of two measuring devices 14, 16, of which one measuring device 14 can finely resolve a rotation angle range that is smaller than the maximum possible rotation angle range of the belt reel 10 (e.g. 0° to 360°), and the other measuring device 16 can detect the total number of possible rotations of the belt reel 10 or an end stop or the like that marks the maximum absolute rotation angle of the belt reel 10 or the greatest possible belt webbing extension.

[0026] The fine-resolution measuring device 14 is in the Fig. 4, is assigned to a rotary element 12 which is coupled to the belt reel 10 via a reduction gear (similar to Fig.1), while the other measuring device 16 is directly assigned to the belt reel 10. The reduction ratio i is selected such that, with the aid of the second measuring device 16, a specific interval can be determined in which the absolute angle of rotation of the belt reel 10 lies (e.g., [0°; 360°], [360°; 720°]; [720°; 1080°], etc.). The first measuring device 14 provides a rotation angle within a range that is not larger than the aforementioned individual interval ranges.

[0027] The absolute angle of rotation of the belt reel 10 is then obtained by adding the angle determined by means of the fine-resolution measuring device 14 to the lower limit of the interval determined by means of the other measuring device 16 (e.g. 60° + 360° = 420°).

[0028] Another concept, not specifically shown in the figures, provides for a combination of a measuring device 16 for detecting the angle of rotation of the belt spool 10, which does not have a fixed reference point to an absolute position (e.g., zero or maximum position), with at least one reference point on the belt webbing that marks a unique absolute angle of rotation of the belt spool 10. A suitable reference point, for example, is an absolute angle of rotation of the belt spool 10 that corresponds to a belt webbing extension length that is slightly greater than the minimum belt webbing extension length (with the seat belt tongue not inserted). Such a reference point is initially detected during typical seat belt use as soon as the seat belt is pulled out for the first time. The changes in the angle of rotation detected up to that point and subsequently can then be related to the reference point, so that the absolute angle of rotation of the belt spool 10 can be uniquely determined.To detect the reference point, a suitable device is provided that is fixed relative to the belt extension and detects when the reference point is passed.

[0029] Of course, certain aspects of the embodiments described above can be combined with one another.

[0030] For all embodiments of the invention, it is irrelevant which concrete measuring principle is applied to detect the angle of rotation, i.e. which types of sensors are used. If several measuring devices 14, 16 are used, they can be based on the same or different measuring principles. The signals or measurement data of the measuring devices 14, 16 are fed to a control unit in which the absolute angle of rotation of the belt spool 10 or the change in the angle of rotation and, if applicable, the rotational speed and / or acceleration are determined. From the angle of rotation or the change in the angle of rotation, the belt webbing extension length can be calculated with the help of further known parameters, such as the belt spool diameter. Likewise, the speed of the belt webbing extension or the acceleration of the belt webbing extension can be calculated from the rotational speed and the rotational acceleration.The device according to the invention therefore allows not only the determination of the belt extension length but also the qualitative and quantitative detection of a belt movement. List of reference symbols 10 belt reels 12 first rotating element 14 first measuring device 16 second measuring device 18 second rotating element

Claims

[1] Device for determining the absolute angle of rotation of a belt reel, with a belt reel (10), a first gearbox, and a first rotary element (12) coupled to the belt reel (10) by means of the first gear, wherein the first gear has a transmission ratio between the belt reel (10) and the first rotary element (12) which is not equal to 1, and a first measuring device (14) associated with the first rotary element (12) for detecting the angle of rotation of the first rotary element (12), characterized by a second gear and a second rotary element (18) coupled to the belt reel (10) by means of the second gear, wherein the second gear has a transmission ratio between the belt reel (10) and the second rotary element (18) which is unequal to the transmission ratio of the first gear, and a second measuring device (16) associated with the second rotary element (18) for detecting the angle of rotation of the second rotary element (18), and wherein the transmission ratios of the first gear and the second gear are selected such that each combination of rotation angles of the first rotary element (12) and the second rotary element (18) occurs only once over the entire rotation range of the belt reel (10). [2] Device according to claim 1, characterized by that the transmission ratio of the first gear is selected such that the complete rotational range of the belt reel (10) is mapped to no more than one revolution of the first rotary element (12). [3] Device according to claim 1 or 2, characterized bya second measuring device (16) assigned to the belt reel (10) for detecting the angle of rotation of the belt reel (10). [4] Device according to claim 3, characterized by that the transmission ratio of the first gear is selected such that over the entire rotational range of the belt reel (10) each combination of rotational angles of the belt reel (10) and the first rotary element (12) occurs only once. [5] Device according to claim 3 or 4, characterized by that the first measuring device (14) can finely resolve a rotation angle range which is smaller than the maximum rotation angle range of the belt reel (10), in particular 0° to 360°, and the second measuring device (16) can detect at least the number of completed rotations of the belt reel (10) starting from an initial position. [6] Device according to one of the preceding claims, characterized bya reference point on the belt strap which marks a unique absolute angle of rotation of the belt reel (10) and can be detected by means of a suitable stationary device.

Images