Belt retractor having a device for detecting belt strap extension length

Abstract

To provide a belt retractor having a device that allows for sensing the extended length of a belt strap with improved resolution. [Solution] This relates to a belt retractor (1) having a frame (3) that can be fixedly attached to a vehicle, and a belt shaft (2) that is rotatably mounted within the frame (3) and onto which a safety belt can be wound, a device for detecting the extension length has a first rotary encoder (16) and a first rotational angle sensor (6), a reduction gear unit (23) is provided that reduces the rotation of the belt shaft (2) to a rotation of the first rotary encoder (16) at a lower speed, a second rotary encoder (15) and a second rotational angle sensor (5) are provided, and the second rotary encoder (15) is driven by the belt shaft (2) at a speed higher than the speed of the first rotary encoder (16).

Description

[Technical field]

[0001] The invention relates to a belt retractor having a device for detecting the extended length of a belt strap having the features set forth in the preamble of claim 1. [Background technology]

[0002] Belt retractors are used, for example, in safety belt systems in motor vehicles to restrain occupants in the event of an accident and prevent them from colliding with a hard surface, such as the windscreen, and thus suffering serious injuries. Furthermore, in modern motor vehicles, such belt retractors are equipped with irreversible or reversible belt tensioners, which remove the slack in the seat belt system in the event of an accident or in the pre-accident stage, thereby further improving the coupling of the occupant to the vehicle. In particular, in the case of reversible belt tensioners, which have, for example, an electric motor driving the belt shaft in the winding direction, the belt force generated can be controlled so that different belt forces can be generated depending on the type of occupant, the seating position or the extension length of the belt strap. Here, the extension length of the belt strap is of particular importance, since the determined extension length of the belt strap can also be used to detect certain states of the seat belt system, such as "the occupant has just fastened the belt" or "the occupant has just loosened the belt". In the aforementioned cases, it may be useful to increase the belt force for a short period of time in order to wind the belt into a standby position or to remove any slack created when tightening the belt. Furthermore, belt retractors are known that have pyrotechnic pretensioning devices that are only intended to be triggered in the event of an accident when the belt is fastened. In this case too, it is important to determine the state of the seat belt.

[0003] Another problem with belt retractors is that they can be blocked unintentionally if the belt is retracted too quickly. To overcome this problem, various systems are known which switch off the sensor system when the belt is fed in depending on whether the extension length of the belt strap falls below a predefined value. Even in belt retractors with ELR / ALR functionality, the switch from ELR to ALR operation occurs depending on whether a predefined extension length of the belt strap is exceeded. Furthermore, modern belt retractors are known which have two or more force limiting levels, which can be switched depending on the extended extension length of the belt strap.

[0004] Therefore, it may be useful to sense the extension length of the belt strap for a variety of reasons, whereby sensing accuracy is particularly important since the belt retractor is a safety-related component and inaccurate control can lead to serious damage.

[0005] For example, from German patent No. 4132876 (C2) a belt retractor is known which has a mechanical device for detecting a predefined extension length of the belt strap and for switching the belt retractor from ELR to ALR operation when the extension length of the belt strap is exceeded. This device comprises a mechanical counting gear which mechanically switches the belt retractor via a rocker switch when a predefined switching point is exceeded. Since this solution is a mechanical device with various interlocking parts, an increase in the detection accuracy can only be achieved by a complex and very high level of manufacturing precision. Furthermore, with this solution a switching cam must be provided to detect each extension length of the belt strap, so that an infinite number of extension lengths of the belt strap cannot be detected and it is a design effort to detect each extension length of the belt strap.

[0006] From DE 10 2018 113 582 A1 a safety belt system with a belt retractor is known, in which the belt retractor is provided with a belt spool angle sensor with a rotary encoder, a rotation angle sensor and a multi-stage reduction gear. Due to the reduction gear, the rotational movement of the belt shaft is reduced to the lower speed of the rotary encoder, so that it is possible to detect the absolute extension length of the seat belt. Summary of the Invention

[0007] Against this background, it is an object of the present invention to provide a belt retractor having a device for detecting the extended length of a belt strap, which makes it possible to detect the extended length of the belt strap with improved resolution.

[0008] To achieve the object, a seat belt retractor is proposed having the features of claim 1. Further advantageous developments of the invention can be taken from the dependent claims, the drawings and the associated description.

[0009] According to the basic concept of the invention, it is proposed to provide a second rotary encoder and a second rotation angle sensor, the second rotary encoder being driven by the belt shaft at a speed higher than that of the first rotary encoder. The proposed additional second rotary encoder and rotation angle sensor and their higher speed provide a second additional signal, which allows a higher resolution of the rotational movement of the belt shaft. The signals from the two rotation angle sensors can be combined with each other, i.e. the extension length is determined based on the signal from the first rotation angle sensor, while the signal from the second rotation angle sensor allows to derive a decision on the rotational angle position of the belt shaft due to the higher speed of the second rotary encoder. The higher the speed of the second rotary encoder, the higher the resolution of the rotational angle position of the belt shaft.

[0010] It is further proposed that a second rotary encoder is arranged on a gear of the reduction gear. The reduction gear is designed to reduce the rotational movement of the belt shaft of the first rotation angle sensor. In order to achieve a cost-efficient and compact design, this reduction gear, already provided in some way here, is also used to arrange the second rotary encoder. The different speed of the second rotary encoder can be realized very easily by arranging a second rotary encoder on a gear of the reduction gear, which is arranged between the first rotary encoder and the belt shaft and rotates at a higher speed than the first rotary encoder.

[0011] A particularly large and easy to realize speed difference between the second rotary encoder and the first rotary encoder can be achieved in that the gear of the reduction gear on which the second rotary encoder is arranged is the drive gear of the reduction gear which is connected in a rotationally fixed manner to the belt shaft, so that the second rotary encoder rotates at the same speed as the belt shaft, and so the signal from the second rotary encoder directly correlates with and reproduces 1:1 the rotational movement of the belt shaft.

[0012] It is further proposed that the reduction gear has a rotatably mounted output gear which is fixedly arranged on the belt retractor and the first rotary encoder is arranged on the output gear. Due to the proposed further development, the first rotary angle encoder does not perform any further movement apart from its rotation about its rotation axis and the rotary angle sensor can be arranged in a fixed position relative to the first rotary encoder. This makes it possible to realize a simplified and compact design while still accurately detecting the rotary movement of the first rotary encoder.

[0013] It is further proposed that an intermediate gear is provided, which is arranged between the drive gear and the output gear, and which is formed by a two-stage gear having two toothings with different diameters and different numbers of teeth, the intermediate gear meshing with the toothing of the drive gear with the toothing having the greater number of teeth and with the toothing of the output gear with the toothing having the lesser number of teeth. The intermediate gear thus forms a two-stage reduction of the rotational movement of the drive gear relative to the output gear, with a very compact design.

[0014] It is further proposed that the belt retractor has a first housing cap held on the frame, and the reduction gear has at least one gear rotatably mounted on a bearing journal of the housing cap. This can be a drive gear, an output gear, or even a third intermediate gear, depending on how many gears the reduction gear has and how it is constructed. By mounting the gear on the housing cap fixed to the frame, the gear is rotatably mounted and at the same time fixed to the frame in a certain spatial relationship with respect to the belt shaft and to the parts that interact with the belt shaft, such as the extension for driving its drive wheel.

[0015] It is further proposed that a second housing cap is provided, which covers the reduction gear from the outside and to which the first and / or second rotation angle sensor is fixed. The second housing cap covers the reduction gear from the outside and thus protects it from external influences, and at the same time serves to fix the rotation angle sensor to the reduction gear and the rotary encoder held thereon by fixing the first and / or second rotation angle sensor.

[0016] It is further proposed that the second housing cap has at least one opening, which exposes the first and / or second rotary encoder and is covered by the first and / or second rotary angle sensor. The opening exposes the respective rotary encoder so that it can be freely accessed from the outside. The opening is then covered again by the respective rotary angle sensor, so that there is no wall between the rotary encoder and the rotary angle sensor that would impair the signal, and the rotary encoder and the rotary angle sensor directly interact with each other in terms of signal transmission.

[0017] It is further proposed that the opening is designed as a slotted hole. A slotted hole opening is advantageous since it makes it possible to compensate for manufacturing errors.

[0018] The second housing cap may preferably be attached to the first housing cap or to a part rigidly connected to the first housing cap, and thus, using the fixed chain of the first and second housing caps, a constant spatial relationship of the rotational angle sensor to the rotary encoder may be achieved, so that after assembly, the rotational angle sensor is aligned with the rotary encoder held on the first housing cap by simply fastening the rotary encoder to the second housing cap, without the need for additional adjustment or alignment of the rotary encoder.

[0019] It is further proposed that the reduction gear reduces the rotational movement of the belt shaft to such an extent that the first rotary encoder rotates less than one revolution about its axis of rotation from the rotational angular position of the belt shaft when the safety belt is fully retracted to the rotational angular position of the belt shaft when the safety belt is fully extended. The proposed solution allows for an unambiguous detection of the extension length of the seat belt, since each rotational angular position of the rotary encoder can be associated with exactly one extension length of the seat belt.

[0020] For this purpose, the reduction gear may preferably have a reduction ratio of at least 1:5, so that the belt shaft makes at least 5 revolutions while the rotary encoder makes one revolution, which corresponds to a seat belt extension length of at least 750 mm, which corresponds to the minimum seat belt extension length that the occupant will pull out on average while fastening the belt. [Brief description of the drawings]

[0021] The present invention will be described below based on preferred embodiments with reference to the accompanying drawings, in which: [Figure 1] 1 shows a perspective view of a seat belt retractor according to the invention according to a first second exemplary embodiment; [Diagram 2] 6 shows a cross-sectional view of the belt retractor of FIG. 5 in the cross-sectional direction AA. [Diagram 3] FIG. 2 shows a front view of a first housing cap having a reduction gear of the belt retractor of FIG. 1; [Figure 4] FIG. 2 shows a perspective view of a first housing cap having a reduction gear of the belt retractor of FIG. 1; [Diagram 5] 2 shows the belt retractor of FIG. 1 without a rotation angle sensor. [Figure 6] 2 shows a belt retractor according to the invention according to a second embodiment. [Figure 7] FIG. 7 shows a signal diagram of the belt retractor of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 1 reveals a belt retractor 1 according to the invention, which comprises a frame 3 which can be fixedly secured to the vehicle and a belt shaft 2 rotatably mounted therein. A safety belt (not shown) can be wound onto the belt shaft 2, as has long been known in the art. Furthermore, a reversible belt tensioner 4 and an irreversible pyrotechnic belt tensioner 8 are provided in the belt retractor 1.

[0023] Furthermore, the belt retractor 1 is covered on one side to the outside by a second housing cap 7 on which the first rotation angle sensor 6 and the second rotation angle sensor 5 are held, both of which are designed as Hall sensors, as will be explained in more detail below.

[0024] In Fig. 2 the same belt retractor 1 can be seen in an enlarged cross-section along the cross-sectional direction AA shown in Fig. 5. The irreversible belt tensioner 8 has a drive wheel 10 connected in a rotationally fixed manner to one end of a torsion bar 9, which in turn is connected in a rotationally fixed manner at the other end to the belt shaft 2. The drive wheel 10, the torsion bar 9 and the belt shaft 2 form a rotationally fixed connection, i.e. a unit, until the torsion bar 9 is activated. Furthermore, a blocking pawl and a control disk 13 are mounted on the drive wheel 10 and together form a blocking device of the belt retractor 1. The drive wheel 10 of the irreversible belt tensioner 8 together with the drive unit are covered towards the outside by a tensioner housing 26, which is fixedly attached to the frame 3 of the belt retractor 1. The control disc 13, rotatably mounted on the drive wheel 10, is covered to the outside by a first housing cap 11, which is in turn attached to the tensioner housing 26 of the irreversible belt tensioner 8 and thus fixed to the frame.

[0025] An axial extension 12 is provided on the drive wheel 10, which may also be considered as a rotationally fixed extension 12 of the belt shaft 2 due to the rotationally fixed connection therewith explained above. The extension 12 is arranged coaxially on the axis of rotation of the belt shaft 2 and passes through a central opening of the first housing cap 11.

[0026] The drive gear 14 of the reduction gear 23, which can be seen enlarged in Figures 3 and 4, is held in a rotationally fixed manner at the end of the extension 12 which passes through the first housing cap 11. In addition to the drive gear 14, the reduction gear 23 comprises an intermediate gear 17 and an output gear 18. The intermediate gear 17 and the output gear 18 are rotatably mounted on bearing journals 24 and 25, respectively, in the first housing cap 11 and are fixed in place (see Figures 2 and 3).

[0027] The drive gear 14 has a toothing 22, while the intermediate gear 17 has two toothings 19 and 20, so that the output gear 18 has a toothing 21. The intermediate gear 17 thus has a two-stage toothing with a toothing 19 having 28 teeth at the larger outer diameter and a toothing 20 having 8 teeth at the smaller diameter. The toothing 22 of the drive gear 14 has 8 teeth, and the toothing 21 of the output gear 18 has 28 teeth. The toothing 22 of the drive gear 14 has the same number of teeth and the same diameter as the toothing 20 of the intermediate gear 17, which has a smaller number of teeth. The toothing 21 of the output gear 18 has the same number of teeth and the same diameter as the toothing 19 of the intermediate gear 17, which has a larger number of teeth.

[0028] The drive gear 14 meshes with its toothing 22 of the toothing 19 of the intermediate gear 17 having the greater number of teeth, while the output gear 18 meshes with its toothing 21 of the toothing 20 of the intermediate gear 17 having the lesser number of teeth. This results in a double reduction of the rotational motion of the belt shaft 2, first the intermediate gear 17 is reduced in a first stage with a reduction ratio of 8 / 28, and then the output gear 18 is further reduced in a second stage, again with a reduction ratio of 8 / 28. This results in a total reduction of the rotational motion from the belt shaft 2 to the output gear 18 in a ratio of 1 / 12.25. In other words, the output gear 18 completes one rotation when the belt shaft completes 12.25 rotations.

[0029] The output gear 18 is provided with a first rotary encoder 16 in the form of a two-pole magnet which, due to its fixed arrangement on the output gear 18, performs an identical rotational movement during the rotational movement of the output gear 18, i.e. also one rotation during 12.25 revolutions of the belt shaft 2. Furthermore, on the drive gear 14, a second rotary encoder 15 in the form of a two-pole magnet is likewise held in a rotationally fixed manner, which due to the rotationally fixed connection performs an identical rotational movement to that of the drive gear 14, which rotational movement corresponds to that of the belt shaft 2 due to the rotationally fixed connection of the drive gear 14 to the belt shaft 2 described above. The first rotary encoder 16 and the second rotary encoder 15 are preferably identical. Furthermore, the toothings 22 and 20 with the smaller number of teeth and the toothings 19 and 21 with the larger number of teeth are also identical. The first rotary encoder 16 is connected to the output gear 18 in a rotationally fixed manner and for this purpose is rotationally fixed in a correspondingly shaped recess. For this purpose, the first rotary encoder 16 can be fixed in a rotationally fixed manner by gluing, positively connecting, press-fitting into the recess or even by an injection molding process of the output gear 18. Similarly, the second rotary encoder 15 can also be fixed in a recess of the drive gear 14.

[0030] Furthermore, the second housing cap 7 is fixed to a frame on the tensioner housing 26 and supports the first rotation angle sensor 6 and the second rotation angle sensor 5. The first rotation angle sensor 6 is positioned by a bracket on the second housing cap 7 in such a way that its sensor face faces the first rotary encoder 16, so that the rotational movement of the first rotary encoder 16 leads to the signal of the first rotation angle sensor 6. The second rotation angle sensor 5 is also positioned by a bracket in such a way that its sensor face faces the second rotary encoder 15, so that the rotational movement of the second rotary encoder 15 leads to the signal of the second rotation angle sensor 5. For mounting the rotation angle sensors 5 and 6, the second housing cap 7 is provided with two receptacles, in which the rotation angle sensors 5 and 6 are mounted by their brackets.

[0031] Since the second rotary encoder 15 is arranged on the drive gear 14, which is arranged coaxially to the axis of rotation of the belt shaft 2, the second rotation angle sensor 5 is also arranged centered, i.e. centrally, on the second housing cap 7, overlapping the axis of rotation of the belt shaft 2. The tensioner housing 26 is rigidly held on the frame 3 of the belt retractor 1 and forms a fastening surface for the first housing cap 11. The tensioner housing 26 simultaneously also forms a fastening surface for the second housing cap 7. This means that both the first housing cap 11 and the second housing cap 7 are rigidly attached to the frame. Furthermore, since both the two housing caps 11 and 7 are attached to the same part, i.e. to the tensioner housing 26, the housing caps are fixed in a constant spatial relationship to each other and the tensioner housing 26 forms a common base. Since the output gear 18 on which the first rotary encoder 16 is arranged is held on the bearing journal 25 of the first housing cap 11 and the first rotation angle sensor 6 is held on the second housing cap 7, the first rotation angle sensor 6 is in a fixed spatial allocation with respect to the first rotary encoder 16 simply by fastening the second housing cap 7. Furthermore, the belt shaft 2 is mounted in a frame 3 to which the second housing cap 7 is also indirectly attached via a tensioner housing 26. The belt shaft 2 with the extension 12 including the drive wheel 10 and the drive gear 14 and the second rotation angle sensor 15 arranged thereon is therefore in a fixed spatial relationship with respect to the second housing cap 7 and the second rotation angle sensor 5 held thereon.

[0032] Due to the different association of the two rotary encoders 15 and 16 with the reduction gear 23, they perform different rotational movements. The first rotary encoder 16 performs the reduced rotational movement, starting from a fully wound seat belt, with a maximum of one revolution until the seat belt is fully unwound. The first rotational angle sensor 6 therefore generates a signal directly correlated to the extension length of the seat belt. The second rotary encoder 15 is held on the drive gear 14 and therefore rotates with an unreduced rotational movement identical to the rotational movement of the belt shaft 2. Since the second angle sensor 15 therefore rotates significantly faster and at a higher speed than the first angle sensor 16, the second rotational angle sensor 5 delivers a second signal with a higher resolution of the rotational movement of the belt shaft 2, which, in combination with the signal of the first rotational angle sensor 6, makes it possible not only to detect the extension length, but also to detect the rotational angle of the belt shaft 2 more accurately. In this case, the second rotary encoder 15 also rotates at the same speed as the belt shaft 2 , so that the signal of the second rotation angle sensor 5 also directly maps the 1:1 rotational movement of the belt shaft 2 .

[0033] In Fig. 5 one can see the belt retractor 1 according to the invention shown in Fig. 1 without the rotation angle sensors 5 and 6. The second housing cap 7 is provided with two slotted hole openings 27 and 28, which are positioned such that they are located in the receptacles for the brackets of the rotation angle sensors 5 and 6 and also expose the rotary encoders 15 and 16 arranged thereunder. Furthermore, the slotted hole openings 27 and 28 of the receptacles of the second housing cap 7 are aligned with their longitudinal axis in the direction of the insertion direction of the rotation angle sensors 5 and 6, so that the rotation angle sensors 5 and 6 as well as the rotary encoders 15 and 16 are not separated from each other by the walls of the second housing cap 7 due to inaccurate manufacturing of the brackets of the rotation angle sensors 5 and 6, the receptacles of the second housing cap 7, the shape of the second housing cap 7 and the fastening of the second housing cap 7.

[0034] FIG. 6 shows a belt retractor 1 according to the invention according to a second embodiment. The belt shaft 2 is here connected in a rotationally fixed manner to a drive gear 14, which with its toothing 22 meshes with the toothing 21 of two output gears 18. The output gears 18 have different outer diameters with different numbers of teeth in the toothing 21 and are therefore driven at different speeds by the drive gears 14. The output gears 18 simultaneously carry markings, magnets, etc. and therefore also act at the same time as rotary encoders 15 and 16. Opposite the rotary encoders 15 and 16 are arranged rotation angle sensors 5 and 6, respectively, which generate the signals shown in FIG. 7 when the belt shaft 2 and the output gears 18 are rotated by being driven. The reduction gear 23 is here realized by the rotational connection of the drive gear 14 with the output gear 18, which can also rotate at a higher speed than the drive gear 14 and the belt shaft 2.

[0035] The left output gear 18 in this figure has a larger outer diameter and its toothing 21 has a larger number of teeth than the right output gear 18. The left output gear 18 is therefore driven by the drive gear 14 to rotate at a lower speed than the right output gear 18. The left output gear 18 therefore corresponds to the first rotary encoder 16 according to the invention, while the right output gear 18 corresponds to the second rotary encoder 15 according to the invention, which is driven at a higher speed. The two rotation angle sensors 5 and 5 each generate a sinusoidal signal with a different frequency during the rotational movement of the belt shaft 2. The different frequencies result in a change of the phase shift of the signals relative to each other, which allows a higher resolution in determining the rotational angular position of the belt shaft 2. The absolute extension length of the belt can be determined simply by evaluating one of the signals from the rotation angle sensors 5 or 6, taking into account the reduction ratio.

[0036] Basically, the transmission of the rotational motion from the drive gear 14 to the output gear 18 by the reduction gear 23, in particular by the toothings 21 and 22, is described. However, if different rotational speeds of the drive gear 14 and the output gear 18 are realized during the rotational motion of the belt shaft 2, it is easily possible to transmit the rotational motion simply via a frictional connection or another type of power transmission.

Claims

1. A belt retractor (1) having a device for detecting the extension length of a safety belt, - the belt retractor (1) comprises a frame (3) that can be fixed to the vehicle and a belt shaft (2) that is rotatably mounted in the frame (3) and onto which the safety belt can be wound, - the device for detecting the extension length comprises a first rotary encoder (16) and a first rotation angle sensor (6); - a reduction gear unit (23) is provided which reduces the rotational movement of said belt shaft (2) to the rotational movement of said first rotary encoder (16) at a slower rotational speed; a second rotary encoder (15) and a second rotary angle sensor (5) are provided; - said second rotary encoder (15) is driven by said belt shaft (2) at a rotational speed higher than that of said first rotary encoder (16); Belt retractor (1).

2. A belt retractor (1) according to claim 1, characterized in that the second rotary encoder (15) is arranged on a gear of the reduction gear unit (23).

3. A belt retractor (1) according to claim 2, characterized in that said gear is a drive gear (14) of said reduction gear unit (23) which is connected to rotate in unison with said belt shaft (2).

4. - said reduction gear unit (23) has a rotatably mounted output gear (18) arranged in a fixed position on said belt retractor (1); A belt retractor (1) according to claim 3, wherein said first rotary encoder (16) is arranged on said output gear (18).

5. - an intermediate gear (17) is provided, arranged between said drive gear (14) and said output gear (18); the intermediate gear (17) is formed by a two-stage gear having two toothings (19, 20) with different diameters and different numbers of teeth, the toothing (19) with the greater number of teeth meshing with the toothing (22) of the drive gear (14) and the toothing (20) with the lesser number of teeth meshing with the toothing (21) of the output gear (18); A belt retractor (1) according to claim 4.

6. - said belt retractor (1) has a first housing cap (11) held on said frame (3); - said reduction gear unit (23) comprises at least one gear rotatably mounted on a bearing journal (24) of said first housing cap (11); A belt retractor (1) according to claim 1.

7. - a second housing cap (7) is provided which externally covers the reduction gear unit (23); - the first and / or second rotation angle sensor (5, 6) is fixed to the second housing cap (7), A belt retractor (1) according to claim 6.

8. - said second housing cap (7) has at least one opening, - the opening exposes the first rotary encoder (16) and / or the second rotary encoder (15) and is covered by the first and / or second rotation angle sensor (5, 6); A belt retractor (1) according to claim 7.

9. - Belt retractor (1) according to claim 8, wherein said openings are designed as slot openings (27, 28).

10. A belt retractor (1) according to claim 7, characterized in that the second housing cap (7) is fixed to the first housing cap (11) or to a part fixedly connected to the first housing cap (11).

11. 2. The belt retractor (1) according to claim 1, wherein the reduction gear unit (23) reduces the rotational movement of the belt shaft (2) from a rotational angular position of the belt shaft (2) when the safety belt is fully retracted to the rotational angular position of the belt shaft (2) when the safety belt is fully extended to such an extent that the first rotary encoder (16) rotates less than one revolution around its axis of rotation.

12. - Belt retractor (1) according to claim 1, characterized in that said reduction gear unit (23) has a reduction ratio of at least 1:5.

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