Seat belt system for a motor vehicle

Abstract

Seat belt device (10) for a motor vehicle comprising a belt shaft (11), a gearbox (12) and an electric motor (13), wherein the gearbox (12) and the electric motor (13) are configured for pre-tensioning a seat belt on the belt shaft (11), wherein the gearbox (12) comprises at least one planetary gear (14), wherein the planetary gear (14) comprises at least one ring gear (15), at least one sun gear (16) and a plurality of planet gears (17, 18), characterized in that the planetary gear (14) has first planet gears (17) with a toothing (19) made of plastic and second planet gears (18) with a toothing (19) made of metal.

Description

The present invention relates to a seat belt device according to the preamble of claim 1.Modern seat belt devices are provided with electric motors which drive the belt shaft in the winding direction, for example, when a reversible pretensioning of the seat belt is activated in an incident phase. Furthermore, it is known in such seat belt devices that a transmission is arranged between the belt shaft and the electric motor, which transmission converts the rotational speed of the electric motor into a provided rotational speed of the belt shaft. The use of the transmission also makes it possible to use an electric motor of the smallest possible construction with a high rotational speed. The use of a planetary gear in a seat belt device is known, for example, from DE 199 27 731 C2.Furthermore, for example, pyrotechnic belt tensioners are known, which are triggered in the event of a crash. These belt tensioning devices or also power tensioning devices have a significantly higher force level during belt tensioning than is provided for reversible pretensioning of the seat belt with an electric motor. An electrically driven belt tensioner, which can also be used as a power tensioner, must therefore apply significantly higher forces than is usually the case with electric pretensioners for the incident phase. At the same time, the installation space available for the seat belt device is limited in motor vehicles and cannot be increased as desired, even for design reasons. Furthermore, the acoustic behavior of the transmission is also relevant, since the seat belt device with the transmission is regularly arranged in the vicinity of a head of an occupant and is thus acoustically perceptible.WO 2021 / 105 159 A1 discloses a belt retractor having a belt reel, wherein an electric motor is provided to drive the belt reel. Furthermore, a gear is provided which transmits the rotational movement of the electric motor to the belt reel.EP 1 391 637 A2 discloses a gear wheel arrangement for a transmission which is as quiet as possible and which nevertheless can be subjected to heavy load.Furthermore, EP 0 074 241 A1 discloses a metal-plastic composite gearwheel and a method for producing the gearwheel.DE 199 27 731 C2 discloses a belt retractor having a belt reel mounted on a frame, wherein a switchable clutch is provided which, in dependence on a signal, transmits a torque supplied by an electric motor to the belt reel for pretensioning a seat belt.Against this background, the object of the invention is to specify a seat belt device which enables electrical pre-tensioning of the seat belt with power tensioning for an accident phase and at the same time achieves a limited installation space requirement and an acceptable acoustic behavior.To achieve the object, a seat belt device having the features of claim 1 is proposed. Further preferred further developments of the invention can be taken from the dependent claims, the figures and the associated description.A seat belt device for a motor vehicle having a belt shaft, a transmission and an electric motor is proposed, wherein the transmission and the electric motor are configured for pre-tensioning a seat belt on the belt shaft, wherein the transmission comprises at least one planetary transmission, wherein the planetary transmission comprises at least one ring gear, at least one sun gear and a plurality of planetary gears. It is proposed that the planetary gear has first planetary gears with a toothing made of plastic and second planetary gears with a toothing made of metal.The proposed seat belt device can be used for a power tightening of the seat belt and can therefore also be referred to as a power tightening device, wherein the proposed seat belt device can also be used for a belt winding, reversible pre-tightening or also pre-pre-tightening. The forces in the planetary gearing that occur during pre-tensioning during the accident phase (power tensioning) are so great that, with limited installation space for the seat belt device, the planetary gears must be made of metal. The same also applies to the ring gear and / or sun gear. In this way, sufficient strength of the planetary gearing can be achieved in order to translate the drive torque of the electric motor to a corresponding torque of the belt shaft for pre-tensioning. The metal-metal contact occurring in this case in the planetary transmission, which is necessary for achieving sufficient strength with a given installation space, however, inevitably leads to loud noises in normal operation, which are undesirable, for example, in the case of an electric belt winding, a reversible pre-tensioning or even pre-pre-tensioning in a pre-crash phase. The use of planet gears with a toothing of plastic reduces the number of metal-metal contacts in favor of plastic-metal contacts in the transmission and thus the noise level.A metal in this sense may be a pure metal or a metal alloy. The first and second planetary gears are preferably arranged on a common planetary carrier. Furthermore, the first and second planetary gears are preferably rotatably supported on an identical diameter.According to a further development, it is proposed that the first planetary gears with a toothing made of plastic are larger than the second planetary gears with a toothing made of metal. The second planetary gears are therefore preferably slightly rearward in the planetary gear in comparison to the first planetary gears.This leads to a significantly improved acoustic behavior. At lower loads or lower torques on the belt reel, for example during belt winding or pre-pre-tensioning of the seat belt in an incident phase, the loads can be transmitted via the somewhat larger first planetary gears with a toothing made of plastic. At higher loads in the case of power tensioning, as are necessary for pre-tensioning the seat belt in an accident phase, the larger first planetary gears, preferably elastically, in particular the teeth, made of plastic, deform so significantly that the second planetary gears, which are somewhat smaller, with a toothing made of metal, which is significantly more rigid and stronger, take over the load transmission. The safety belt device is therefore significantly less in the event of pre-tensioning in an incident phase, since the load path runs over the first planetary gears, which do not have a metal-metal contact, at these comparatively low loads. Thus, the loads on metal-to-metal contacts may be reduced or entirely avoided. This significantly reduces acoustic emissions from the transmission. Only in the case of pre-tensioning of the seat belt in an emergency situation or accident phase does there occur a high noise emission through the metal-metal contacts and the correspondingly high rotational speed of the electric motor or the high transmission ratio. In this situation, however, the acoustic properties of the seat belt device are negligible. Therefore, an advantageous seatbelt device having low operating behavior of the transmission in normal operation in pre-pre-tensioning and effective pre-tensioning in an emergency can be achieved in a small installation space.It is further proposed that the first planetary gears with a toothing made of plastic have a greater tooth thickness, preferably a greater tooth thickness in the pitch circle and / or pitch circle, than the second planetary gears with a toothing made of metal. In advantageous embodiments, the tooth thickness in the pitch circle and / or pitch circle differs by preferably more than 0.3 mm, for example 0.4 mm or 0.5 mm. Further preferably, the tooth thickness in the pitch circle and / or pitch circle differs in a range between 0.4 mm and 0.6 mm, for example 0.6 mm. In further possible exemplary embodiments, the tooth thickness in the pitch circle and / or pitch circle can also differ by more than 0.6 mm.This improves the acoustic behavior above all at lower loads, since the first gearwheels with a toothing made of plastic in the planetary transmission transmit the loads and the second planetary gearwheels made of metal can travel with them largely free of load, so that the acoustic emissions can be significantly reduced. The teeth of the second planetary gears made of metal are thus preferably smaller or narrower than the teeth of the first planetary gears made of plastic. Preferably, the first planet gears are engaged in plastic before the second planet gears engage. However, the first planetary gears with at least one toothing made of plastic have, due to the material, a lower modulus of elasticity than the second planetary gears made of metal, so that the first planetary gears deform more toward higher loads, as in the pre-tensioning, and the second planetary gears, which are more rigid due to the material, then abut on the tooth flanks of the ring gear and / or of the sun gear, which take over loads and additionally have sufficient strength.In possible embodiments, the tooth width for the first and second planetary gears may be different.According to a further development, it is proposed that the first planetary gears with a toothing made of plastic have a greater backlash with the sun gear and / or the ring gear than the second planetary gears with a toothing made of metal. In advantageous embodiments, the first planetary gears with their toothing abut with minimal play on the toothing of the ring gear and / or of the sun gear during normal operation.This improves the running for the second planetary gears made of metal at low loads, since the first planetary gears made of plastic transmit the main part of the loads due to the lower backlash at low loads and thus with a resulting small deformation of the first planetary gears. The second planet gears are thus subjected to very low stress at low transmission loads, which significantly reduces the acoustic emissions due to metal-metal contacts of the second planet gears with the ring gear and / or the sun gear in this operating state. As the load on the transmission increases, as occurs during pre-tensioning, the first planetary gears, in particular the teeth of the first planetary gears made of plastic, deform under the load, so that the second planetary gears made of metal take over the main loads. Any increased transmission noise is irrelevant in the case of belt tightening in an emergency situation.It is further proposed that the first planetary gears with a toothing made of plastic have a larger tip circle diameter than the second planetary gears with a toothing made of metal. The tip diameter of the first planetary gears is preferably at least 0.2 mm, for example 0.4 mm, larger than the tip diameter of the second planetary gears.The larger tip circle diameter of the first planetary gears made of plastic supports the largely load-free operation of the second planetary gears made of metal at low transmission loads with a comparatively low torque on the belt shaft, such as, for example, during pre-tensioning.Preferably, the ring gear and / or the sun gear is made of metal. In the typical transmission ratios from a small electric motor with a high rotational speed to a lower rotational speed with a high torque of the belt shaft for belt tensioning, high loads occur in the toothing of the sun wheel and / or of the ring wheel, which can be absorbed accordingly.According to a further development, it is proposed that the number of first planetary gears and the number of second planetary gears be the same. For example, in a planetary gear of the seat belt device, three first planetary gears with a toothing of plastic and three second planetary gears with a toothing of metal can be arranged. The first and second planetary gears are preferably arranged alternately, so that an optimum load distribution can be achieved. As a result, the most uniform possible load distribution can be achieved for low and high loads in the planetary transmission.In advantageous embodiments, the transmission is a two-speed transmission. This allows, for example, an electric belt winding with low tensile forces and a low rotational speed of the electric motor in a first transmission ratio and a pretensioning of the seat belt with high tensile forces or high torque on the belt shaft and a high rotational speed of the electric motor in a second transmission ratio.In an advantageous embodiment, the first planetary gears are made entirely of plastic. This enables a particularly cost-effective production of the seat belt device.Preferably, the toothing of the first planetary gears is made of polyoxymethylene (POM) or the first planetary gears are made entirely of polyoxymethylene (POM).It is furthermore proposed that the second planetary gears are completely made of metal. This allows a high transferability of loads to be achieved.The toothing of the second planetary gears made of metal or the complete second planetary gears made of metal are made of sintered steel, for example D39, in preferred embodiments.In advantageous embodiments, the transmission of the seat belt device has two or three planetary transmissions connected in series.The invention is explained below with reference to preferred embodiments with reference to the attached figures. This shows FIG. 1 shows a seat belt device with a planetary gear; FIG. 2 shows a detail of a planetary gear of a seat belt device; FIG. 3 is a planetary gear of a seat belt device; FIG. 4 shows a detailed view of a planetary gear mechanism with a first and second planetary gear in comparison, FIG. 5 shows a schematic illustration of the transmission in a first gear; and FIG. 6 shows a schematic illustration of the transmission in a second gear.FIG. 1 shows an exemplary embodiment of a seat belt device 10 for a motor vehicle in a schematic illustration. The seat belt device 10 has a belt shaft 11 which is connected to an electric motor 13 via a transmission 12. In this exemplary embodiment, the transmission 12 has a planetary transmission 14, which reduces the rotational speed of the electric motor 13 with the further stages of the transmission 12 for driving the belt shaft 11. In this advantageous exemplary embodiment, a two-stage planetary transmission 14 is involved, it also being possible in alternative exemplary embodiments to use single-stage, three-stage or generally multistage planetary transmissions 14. The seat belt device 10 can be used as an electric belt retractor, as a reversible pre-tensioner in an incident phase (pre-pre-tensioning) and also as a power tensioner, and for this purpose has two gears in this advantageous exemplary embodiment, which is explained with reference to FIGS. 5 and 6.FIG. 2 shows a schematic sectional view of a planetary gear 14 with a sun gear 16 and a ring gear 15, between which the planetary gears 17, 18 are arranged. In this exemplary embodiment, three first planetary gears 17 with a toothing 19 made of plastic, for example of POM, and three second planetary gears 18 with a toothing 19 made of metal, for example sintered steel, are arranged in each case alternately. In this advantageous embodiment, the first planetary gears 17 are made entirely of plastic, e.g. POM, and the second planetary gears 18 are made entirely of metal.FIG. 3 shows a detailed view of the two-stage planetary gear mechanism 14 of FIG. 1 in a detailed view. In this view, it can be seen that the first and second planetary gears 17, 18 are arranged on a common planetary carrier 25, wherein the first and second planetary gears 17, 18 are rotatably mounted on the identical diameter of the planetary carrier 25 in advantageous exemplary embodiments.FIG. 4 shows a detailed view of a planetary gear 14 with the first and second planetary gears 17, 18 in comparison with a ring gear 15. The first planetary gears 17 with a toothing 19 made of plastic are shown in dotted lines and superimposed with the toothing 19 made of metal of the second planetary gears 18, which is shown with a solid line.The first planetary gears 17 are clearly larger than the second planetary gears 18. Furthermore, the toothing 19 of the first planetary gears 17 has a greater tooth thickness 20 in the pitch circle 21 than the toothing 19 of the second planetary gears 18. In this advantageous exemplary embodiment, the tooth thickness 20 is also greater outside the pitch circle 21. The second planetary gears 18 therefore have a greater backlash with the ring gear 15 and with the sun gear 16 than the first planetary gears 17. At low loads, as in the case of pre-pre-tensioning, the transmission of the mechanical loads thus takes place substantially via the first planetary gears 17 with the toothing 19 made of plastic, so that a quiet operating behavior can be achieved. With increasing loads, as in the case of belt tensioning in an accident phase, the toothing 19 of the first planetary gears 17 yields to such an extent that the load path changes over to the second planetary gears 18, which are more rigid and have a higher strength. At high loads, therefore, metal-metal contacts with the sun gear 16 and / or the ring gear 15 with a loud operating behavior occur in the load path, which can be neglected in the case of power tightening in an accident, however. The very high loads during power tightening can thus be transmitted via the second planetary gears 18 for a given installation space, wherein in the case of pre-tightening, for example for a warning function, the planetary gear 14 causes only a slight noise generation.FIGS. 5 and 6 schematically show the seat belt device 10 of FIG. 1, the function of the transmission 12 of the seat belt device 10 being described below.The electric motor 13 drives the sun gear 16 of the planetary gearing 14 via a pinion 23 and a further gearwheel 24. The electric motor 13 can be operated at different speeds according to the desired function. The electric motor 13 can be operated, for example, at a speed of 5000 min -1 during regular winding of a seat belt or, for example, at a speed of 50000 min -1 during power tensioning.The planetary transmission 14 is designed in two stages and can be shifted into two gears. The planetary gears 17, 18 of the two stages of the planetary gear 14 are connected to one another in a rotationally fixed manner and can in particular be embodied in one piece. In this case, tandem planetary gears can also be referred to, whereby the same number and positioning of first and second planetary gears 17, 18 on the planetary carrier 25 results in the first and second stage. The left ring gear 15 is the output of the planetary gearing 14 and drives the belt shaft 11 via the further gearwheels 26, 27, 28.In FIG. 5, the planetary gear 14 is in a first gear, in which the planetary carrier 25 is braked or blocked. Accordingly, the right ring gear 15 is not loaded and both ring gears 15 rotate in the same direction. In advantageous exemplary embodiments, the transmission ratio of the transmission 12 is, for example, approximately 10.3 in the first gear. With this transmission ratio, for example, an electrical winding of a loosened seatbelt on the belt shaft 11 can be carried out, wherein the rotational speed of the electric motor 13 can be, for example, 5000 min -1. This winding can be carried out with a low level of noise, since only a comparatively low torque is transmitted to the belt shaft 11.The braking or blocking of the planetary carrier 25 takes place with a control device 30, The control device 30 is furthermore configured to brake or block the right-hand, drive-side ring gear 15 of the planetary transmission 14 in addition to the planetary carrier 25, wherein in each case either the planetary carrier 25 or alternatively the ring gear 15 can be blocked or blocked or braked by the control device 30.FIG. 6 shows the planetary transmission 14 in a second gear, with which a transmission ratio of approximately 124 is achieved in advantageous exemplary embodiments. The right-hand, drive-side ring gear 15 is braked or blocked for this purpose and the planet carrier 25 is released. The electric motor 13 can be operated at a speed of 50000 min -1 for example, for belt tensioning. In this case, the planet carrier 25 reaches a very high rotational speed and a high torque can be brought about on the belt reel 11.

Claims

Seat belt device (10) for a motor vehicle having a belt shaft (11), a transmission (12) and an electric motor (13), wherein the transmission (12) and the electric motor (13) are configured for pre-tensioning a seat belt on the belt shaft (11), wherein the transmission (12) comprises at least one planetary transmission (14), wherein the planetary transmission (14) comprises at least one ring gear (15), at least one sun gear (16) and a plurality of planetary gears (17, 18), characterized in that the planetary transmission (14) has first planetary gears (17) with a toothing (19) made of plastic and second planetary gears (18) with a toothing (19) made of metal.Seat belt device (10) according to Claim 1, characterized in that the first planet gears (17) with a toothing (19) made of plastic are larger than the second planet gears (18) with a toothing (19) made of metal.Seat belt device (10) according to Claim 1 or 2, characterized in that the first planet gears (17) with a toothing (19) made of plastic have a greater tooth thickness (20), preferably a greater tooth thickness (20) in the pitch circle (21), than the second planet gears (18) with a toothing (19) made of metal.Seat belt device (10) according to one of Claims 1 to 3, characterized in that the first planet wheels (17) with a toothing (19) made of plastic have a greater backlash with the sun wheel (16) and / or the ring wheel (15) than the second planet wheels (18) with a toothing (19) made of metal.Seat belt device (10) according to one of Claims 1 to 4, characterized in that the first planet wheels (17) with a toothing (19) made of plastic have a greater tip circle diameter (22) than the second planet wheels (18) with a toothing (19) made of metal.Seat belt device (10) according to one of Claims 1 to 5, characterized in that the ring gear (15) and / or the sun gear (16) is made of metal.Seat belt device (10) according to one of Claims 1 to 6, characterized in that the number of first planet wheels (17) and the number of second planet wheels (18) are the same.Seat belt device (10) according to one of Claims 1 to 7, characterized in that the transmission (14) is a two-speed transmission.Seat belt device (10) according to one of Claims 1 to 8, characterized in that the first planet wheels (17) are made completely from plastic.Seat belt device (10) according to one of Claims 1 to 9, characterized in that the second planet wheels (18) are completely made of metal.

Images