DE102022133637A1 - Belt tensioner for a seat belt system - Google Patents

Abstract

A belt tensioner (40) for a safety belt system comprising a belt retractor (32) and a gear, wherein the gear is a switchable planetary gear (10) and has a sun gear (12), two ring gears (22, 26) and a planetary gear carrier (18) with at least one stepped planetary gear (16). The planetary gear (10) is characterized in that a first stage (20) of the planetary gear (16) meshes with the first ring gear (22) and a second stage (24) of the planetary gear (16) meshes with the second ring gear (26).

Description

The invention relates to a belt tensioner for a safety belt system and a method for tightening a safety belt.

Belt tensioners are used to reduce certain influences that have a negative effect on the restraint of vehicle occupants in a restraint situation before the vehicle occupant is moved forward and, if necessary, a force limiting device is used. These influences include the so-called film reel effect and belt slack. The belt tensioner reduces these influences within a very short time, for example by winding a belt strap onto a belt reel of a belt retractor and tightening it in the process. This ensures that the vehicle occupant can participate in the vehicle deceleration at an early stage. It also improves the conditions for the subsequent use of a force limiting device.

Pyrotechnically powered belt tensioners are usually used in vehicles. These make it possible to provide the high forces required to tighten the belt in a sufficiently short time. After the belt tensioner has been triggered, it must be exchanged and replaced either as a whole or at least in parts. Alternatively, there are reversible belt tensioners that are driven by an electric motor. To tighten the belt, the electric motor must provide a high torque at a high speed in order to be able to tighten the belt with sufficient force and speed. Reversible belt tensioners have the advantage that they do not have to be replaced after they have been triggered.

However, the high-power electric motors used in belt tensioners are large, heavy and expensive to manufacture.

The object of the invention is to provide a belt tensioner which replaces the pyrotechnic tightening with an electromechanical tightening and thereby enables the installation of a lighter, more compact and cheaper electric motor.

The object is achieved according to the invention by a belt tensioner for a safety belt system comprising a belt retractor and a gear, wherein the gear is a switchable planetary gear and has a sun gear, two ring gears and a planet gear carrier with at least one stepped planet gear, characterized in that a first stage of the planet gear meshes in the first ring gear and a second stage of the planet gear meshes in the second ring gear.

The planetary gear has a particularly compact design, which makes it particularly suitable for installation in belt retractors. At the same time, the switchability of the gear means that large torques can be transferred to the belt retractor and high gear ratios can be achieved, which in turn result in high tensioning forces on the belt webbing. Lower tensioning forces are required in belt retractors, particularly for comfortable tensioning of the belt webbing. A high tensioning force, on the other hand, is required in the event of an accident in order to optimally protect the vehicle occupants.

The inventive design of the planetary gear with the stepped planetary gear and two ring gears makes it possible to freely select and individually adjust the gear ratio jump between the two states. This allows the tensioning force to be optimally adjusted in both states.

The use of a planetary gear allows less powerful electric motors to be installed in the belt retractor. These are usually lighter and more compact, resulting in a lighter and more compact belt retractor.

The invention makes it possible to retain the previous functions of a reversible belt retractor, for example reducing belt slack and installing haptic warning signals.

According to the invention, the belt tensioner has a switching mechanism which, in a first state, supports the planetary gear carrier in a rotationally fixed manner and, in a second state, supports the second ring gear in a rotationally fixed manner.

By non-rotatably supporting either the planetary gear carrier or the second ring gear, different gear ratios and different torques are realized within the planetary gear.

In one aspect of the invention, the belt tensioner has an electrical actuator with which the switching mechanism can be switched from one state to another state.

The electromechanical actuator can have a lifting magnet or a gas generator and a piston. In the belt retractor, the electromechanical actuator is supplied with power via an external power source.

Furthermore, the sun gear is axially fixed on an input shaft, at least one planet gear is axially fixed on the planet gear carrier and the ring gears are also axially fixed.

This is the prerequisite for the switching mechanism to be able to reliably fix the ring gear or the planet gear carrier in a rotationally fixed manner and for torques to continue to be transmitted within the planetary gear. The axially fixed fixation of the sun gear, the planet gear and the ring gears ensures that all parts of the planetary gear mesh reliably with one another.

In a further aspect of the invention, the sun gear is mounted directly on the input shaft of a motor and kinematically coupled to the motor via the input shaft.

This is advantageous because the sun gear is directly coupled to the motor. As soon as the motor is switched on and rotates, the torque is transferred directly to the sun gear and thus to the planetary gear. In a particularly advantageous way, the sun gear alone drives the planetary gear, which also saves installation space.

The ring gears of the planetary gear are arranged next to each other and have different numbers of teeth.

The second ring gear is arranged between the first ring gear and the planetary gear carrier. The switching mechanism only switches between the planetary gear carrier and the adjacent second ring gear, which means that a particularly space-saving switching mechanism can be used. This design also reduces the weight of the planetary gear.

Advantageously, the first ring gear has a larger number of teeth than the second ring gear. This allows different gear ratios to be achieved on the first ring gear and the second ring gear.

Furthermore, the first ring gear has an output, both in the first state and in the second state. The output on the first ring gear represents the only output of the planetary gear. Since only the first ring gear of the planetary gear has an output, the planetary gear is arranged in a particularly space-saving manner.

According to the invention, the first ring gear is coupled, for example via an intermediate gear, to a clutch, which in turn is coupled to a belt reel.

On one side of the planetary gear, the drive of the planetary gear is arranged and on the side of the planetary gear facing away from the drive, the planet gear carrier is arranged, with the first ring gear, the intermediate gear and the clutch being arranged on the drive side.

This creates a particularly space-saving arrangement, which results in a smaller belt retractor overall.

According to the invention, the seat belt with a belt tensioner has a method for switching the planetary gear, wherein in the first state the planet gear carrier is supported in a rotationally fixed manner and the two ring gears are driven via the sun gear and the planet gears and the output is transmitted to the coupling via the intermediate gear, so that a belt webbing is retracted onto the belt webbing spool of the belt retractor with less tension and higher speed compared to the second state. In the second state, the second ring gear is supported in a rotationally fixed manner, wherein the planet gear carrier is driven together with the first ring gear via the sun gear and the planet gears and a higher torque than in the first state is transmitted to the coupling via the intermediate gear, so that the belt webbing is retracted with a higher tension compared to the first state.

Due to the high torque transmitted to the belt retractor in the second state, the tightening performance is comparable to pyrotechnic tightening.

By installing the belt tensioner according to the invention with the planetary gear, it is therefore no longer necessary to install pyrotechnics in the belt tensioner. As a result, known disadvantages of pyrotechnically driven belt tensioners are avoided, in particular that a pyrotechnic belt tensioner can only be triggered once or that injuries can occur when rescuing vehicle occupants after an accident if the pyrotechnics of the belt tensioner are accidentally ignited.

• - 1 eine schematische Ansicht eines erfindungsgemäßen schaltbaren Planetengetriebes;
• - 2 eine schematische Ansicht eines schaltbaren Planetengetriebes in einem ersten Zustand, das an einem Gurtaufroller angebracht ist;
• - 3 eine schematische Ansicht des schaltbaren Planetengetriebes aus 2 in einem zweiten Zustand, das an einem Gurtaufroller angebracht ist;

Further features and advantages of the invention will become apparent from the following description and from the following drawings, to which reference is made. In the drawings:

• - 1 a schematic view of a switchable planetary gear according to the invention;
• - 2 a schematic view of a switchable planetary gear in a first state, which is attached to a belt retractor;
• - 3 a schematic view of the switchable planetary gear from 2 in a second state, attached to a belt retractor;

The 1 shows a schematic view of a switchable planetary gear 10.

In the 1 There is a sun gear 12 in the center of the planetary gear 10. The sun gear 12 is mounted on an input shaft 14 and represents a drive 15 of the planetary gear 10.

The sun gear 12 meshes with a planet gear 16, which is rotatably mounted on a planet gear carrier 18. The planet gear carrier 18 is located in the 1 sketched structure on the same side as the drive 15 of the planetary gear 10. However, it is also possible to connect the drive on the side of the ring gear 22.

The planet gear 16 is a stepped planet gear with two stages (stepped gear). A first stage 20 of the planet gear 16 meshes with the sun gear 12 and a first ring gear 22, a second stage 24 of the planet gear 16 meshes with a second ring gear 26.

The first stage 20 of the planetary gear 16 is arranged on the side of the planetary gear 10 facing away from the planetary gear carrier 18, and the second stage 24 is arranged on the side of the planetary gear 10 facing the planetary gear carrier 18.

The diameter of the planet gear 16 (more precisely the pitch circle diameter) at the first stage 20 is larger than at the second stage 24.

Each stage of the planetary gear 16 has teeth. The number of teeth in the first stage 20 is higher than that in the second stage 24. Due to the different number of teeth in both stages, different gear ratios can be achieved in the planetary gear 10. The exact number and the ratio of the number of teeth in the first stage 20 to the second stage 24 can be freely selected.

The planetary gear 10 further comprises two ring gears. The first ring gear 22 is located on the side of the sun gear 12, and the second ring gear 26 is arranged on the side of the planet gear carrier 18.

The first ring gear 22 meshes with the first stage 20 of the planetary gear 16, the second ring gear 26 meshes with the second stage 24 of the planetary gear 16.

In the planetary gear 10, the first ring gear 22 has a larger pitch circle diameter of the teeth than the second ring gear 26.

Both ring gears have internal teeth, with the first ring gear 22 having more teeth than the second ring gear 26. Accordingly, the gear ratio of the first stage 20 of the planetary gear and the first ring gear 22 is different from the gear ratio of the second stage 24 of the planetary gear and the second ring gear 26. The exact gear ratio depends on the ratio of the teeth of the respective stage of the planetary gear 16 to the number of teeth of the ring gear interacting with this stage and can be freely selected.

The planetary gear 10 also has an output 27. The output 27 always occurs through the first ring gear 22. Neither the second ring gear 26 nor the planet gear carrier 18 serve as the output of the gear.

Furthermore, the planetary gear 10 has a switching mechanism 28.

The switching mechanism 28 serves to firmly support one of the two ring gears (or possibly neither) on a housing 30 of the planetary gear 10.

The switching mechanism 28 can be in two states, whereby it either supports the planetary gear carrier 18 or the second ring gear 26 of the planetary gear 10 in a rotationally fixed manner. The switching mechanism 28 can act like a brake or a clutch, for example a positive coupling with a switching sleeve or claw, on the components and fix them in a rotationally fixed manner.

In a first state, the switching mechanism 28 contacts the planetary gear carrier 18 and supports it in a rotationally fixed manner. In this case, a rotationally fixed connection is established between the planetary gear carrier 18 and the housing 30 via the switching mechanism 28.

In a second state, the switching mechanism 28 contacts the second ring gear 26 and supports it in a rotationally fixed manner, whereby a rotationally fixed connection is established between the second ring gear 26 and the housing 30.

In the embodiment shown here, the switching mechanism 28 can only ever contact one of the two planetary gear parts and It is not possible to support several transmission parts at the same time.

However, in alternative applications or design concepts it would be possible to block the transmission if both planetary gear parts were blocked. Freewheeling or idle running can also be enabled by releasing or opening on both sides. The switching mechanism 28 can be switched to one of the two states as often as desired and in any order.

During the switching process of the switching mechanism 28 from one state to the other state, the switching mechanism 28 is adjustable relative to the housing 30. As soon as the switching process is completed, the switching mechanism 28 remains in its position so that either the second ring gear 26 or the planet gear carrier 18 is supported in a rotationally fixed manner.

The 2 and 3 show another possible embodiment of the switchable planetary gear 10. The switchable planetary gear 10 is attached to a belt retractor 32.

The sun gear 12 of the planetary gear 10 is located in the center of the planetary gear 10 and is coupled to a motor 34 via an input shaft 14. The motor 34 is arranged here on the side of the first ring gear 22 and thus on the side facing away from the planet gear carrier 18.

The motor 34 can in particular be an electric motor.

The planetary gear 10 has two stepped planet gears 16. However, it is possible without any problems for the planetary gear 10 to have more than two stepped planet gears.

The first stage 20 of the planetary gear 16, which is located on the side of the drive 15 of the planetary gear 10, meshes with the sun gear 12.

The first stage 20 of the planetary gear 16 meshes with the first ring gear 22 and the second stage 24 of the planetary gear 16 meshes with the second ring gear 26.

The planet gears 16 are rotatably mounted on the planet gear carrier 18. The planet gear carrier 18 is located on the side of the planetary gear 10 facing away from the drive 15.

Furthermore, the planetary gear 10 has the switching mechanism 28. The switching process of the switching mechanism 28 is controlled via an electromechanical actuator 35. The electromechanical actuator 35 must be connected to a power source 36, in particular via a vehicle plug located on a vehicle.

The electromechanical actuator 35 is, for example, an electromagnet, in particular a lifting magnet, or contains electrically ignitable pyrotechnics. The electromechanical actuator 35 switches the switching mechanism 28 from one state, preferably the first state, to the other state, preferably the second state, after it has received a corresponding signal.

If an electromagnet is used as the electromechanical actuator 35, the switching process of the switching mechanism 28 is reversible and can be repeated as often as desired. If the electromechanical actuator 35 is pyrotechnic, it can only switch the switching mechanism 28 from the first state to the second state once. After switching, the electromechanical actuator must be replaced.

The planetary gear 10 is connected via an intermediate gear 38 to a belt tensioner 40 of the belt retractor 32.

The belt retractor 32 has a belt retractor housing 42, a belt spool 44 mounted in the belt retractor housing 42 so as to be rotatable about an axis, and the belt tensioner 40.

The belt spool 44 of the belt retractor 32 serves to wind and unwind a belt strap 46. The belt spool 44 can be rotated in two directions.

At least one end of the belt strap 46 is fixed to the belt spool 44 and wound around it.

The belt retractor has a force limiter. In the embodiment shown, the force limiter is a torsion bar 48 which is mounted in the belt reel 44 and is firmly connected to the belt reel 44 on one side. On the other side, the torsion bar 48 is firmly connected to a locking component 50.

The belt reel 44 is spring-loaded on the side opposite the locking component 50 in the winding direction of the belt webbing 46 via a drive spring 52. The drive spring 52 is supported on the belt retractor housing 42 so that the drive spring 52 is tensioned when the belt webbing 46 is unrolled. This ensures that the belt webbing 46 is automatically wound onto the belt reel 44 after it has been removed.

On the side of the belt reel 44 opposite the mainspring 52, the belt reel 44 is rotatable firmly connected to an output side of a clutch 54 of the belt tensioner 40. The drive side of the clutch is coupled to the output 27 of the planetary gear via the intermediate gear 38.

The clutch 54 is open in the normal state so that the belt reel can rotate freely. When the drive side of the clutch is driven, the clutch closes so that a torque-transmitting connection is established between the planetary gear 10 and the belt tensioner 40. The motor 34 is thus connected to the belt retractor 32 via the planetary gear 10 and the belt tensioner 40.

Any coupling that is suitable for use in a belt tensioner can be used as coupling 54.

When no more torque is transmitted via the clutch, it opens automatically so that the belt spool can rotate freely again.

Alternatively, it would be conceivable to completely open the circuit 28 instead of the clutch.

2 shows the first state of the planetary gear 10. This state is used to drive the belt reel at high speed but low torque in the winding direction of the seat belt. This can be used to pre-tighten or comfort tighten the belt.

If the planetary gear 10 is not in the first state when pre-tightening is to be carried out, the electromechanical actuator 35 is used to bring it into the first state.

In the first state, the planetary gear carrier 18 is supported in a rotationally fixed manner by the switching mechanism 28. Therefore, the planetary gear carrier 18 is firmly connected to the housing 30, i.e. held in a rotationally fixed manner.

When the motor 34 is operated, it generates a torque that is transmitted to the sun gear 12 via the input shaft 14. The torque is transmitted to the two ring gears 22 and 26 via the stepped planet gear 16. The planet gear carrier 18 is fixed in a rotationally fixed manner via the switching mechanism 28.

Due to the different gear ratios within the planetary gear 10, the output 27 transmits a low torque. In other words, the output 27 provides engine power with a high rotational speed but low torque.

Via the output 27 on the first ring gear 22, the torque is transmitted via the intermediate gear 38 to the clutch 54, which closes and drives the belt reel.

When the seat belt force increased by pre-tensioning is no longer required, the motor 34 can be operated in the opposite direction to release the previously wound-up belt webbing.

When there is no longer any torque, the clutch 54 opens automatically so that the belt spool can rotate freely again.

In 3 the second state of the planetary gear 10 is shown. This state is used when the seat belt has to be tightened considerably before an accident (so-called power tightening).

For this purpose, the switching mechanism 28 is switched from the first state to the second state via the electromechanical actuator 35. In the second state, the belt webbing is wound up with a high force, comparable to a pyrotechnic belt tensioner.

In the second state, the second ring gear 26 is supported in a rotationally fixed manner by the switching mechanism 28. Therefore, the second ring gear 26 is firmly connected to the housing 30, i.e., is fixed in a rotationally fixed manner.

The sun gear 12 is driven by the motor 34 and transmits a torque to the planet gear 16. The torque is transmitted to the first ring gear 22 and the planet gear carrier 18. No rotation can be transmitted to the second ring gear 26 because it is fixed in a rotationally fixed manner to the housing 30.

Due to the different gear ratios within the planetary gear 10, the output 27 provides a lower rotational speed in the second state while maintaining the same engine power, but a higher torque than in the first state.

The torque is transmitted to the clutch 54 via the output 27 on the first ring gear 22 via the intermediate gear 38.

The clutch 54 closes and transmits the torque to the belt spool 44, which is rotated in the winding direction.

Claims (10)

Belt tensioner (40) for a safety belt system comprising a belt retractor (32) and a Transmission, wherein the transmission is a switchable planetary transmission (10) and has a sun gear (12), two ring gears (22, 26) and a planet gear carrier (18) with at least one stepped planet gear (16), characterized in that a first stage (20) of the planet gear (16) meshes in the first ring gear (22) and a second stage (24) of the planet gear (16) meshes in the second ring gear (26). Belt tensioner (40) after Claim 1 , characterized in that the belt tensioner (40) has a switching mechanism (28) which, in a first state, supports the planetary gear carrier (18) in a rotationally fixed manner and, in a second state, supports the second ring gear (26) in a rotationally fixed manner. Belt tensioner (40) according to one of the preceding claims, characterized in that the belt tensioner (40) has an electrical actuator (35) with which the switching mechanism (28) can be switched from one state to another state. Belt tensioner (40) according to one of the preceding claims, characterized in that the sun gear (12) is mounted axially fixed on an input shaft (14), the at least one planet gear (16) is mounted axially fixed on the planet gear carrier (18) and the ring gears (22, 26) are mounted axially fixed. Belt tensioner (40) according to one of the preceding claims, characterized in that the sun gear (12) is mounted directly on the input shaft (14) of a motor (34) and is kinematically coupled to the motor (34) via the input shaft (14). Belt tensioner (40) according to one of the preceding claims, characterized in that the ring gears (22, 26) are arranged next to one another and have different numbers of teeth. Belt tensioner (40) according to one of the preceding claims, characterized in that the first ring gear (22) has an output (27). Belt tensioner (40) according to one of the preceding claims, characterized in that the first ring gear (22) is coupled via an intermediate gear (38) to a clutch (54) which is coupled to a belt spool (44). Belt tensioner (40) according to one of the preceding claims, characterized in that the drive (15) is arranged on one side of the planetary gear (10) and the planet gear carrier (18) is arranged on the side facing away from the drive (15), wherein the first ring gear (22), the intermediate gear (38) and the clutch (54) are arranged on the side of the drive (15). Method for tightening a safety belt with a belt tensioner (40) according to one of the preceding claims, characterized in that in the first state the planetary gear carrier (18) is supported in a rotationally fixed manner and the two ring gears (22, 26) are driven via the sun gear (12) and the planetary gears (16), the output (27) is transmitted via the intermediate gear (38) to the clutch (54) so that a belt webbing (46) on the belt spool (44) of the belt retractor (32) is drawn in with a lower tensioning force and a higher speed compared to the second state and in the second state the second ring gear (26) is supported in a rotationally fixed manner, wherein the planetary gear carrier (18) is driven together with the first ring gear (22) via the sun gear (12) and the planetary gears (16) and a higher torque than in the first state is transmitted via the intermediate gear (38) to the clutch (54) so that the belt webbing (46) is drawn in with a higher tightening force compared to the first state.

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