Piston-cylinder unit, method for operating and method for producing such a piston-cylinder unit and vehicle-integrated personal safety system

Abstract

Piston-cylinder unit (2) with a cylinder (4) and a piston (12) mounted in the cylinder (4) so ​​as to be displaceable in an axial direction (A) from an initial position to an end position, wherein the cylinder (4) has a stop (34) for defining the end position of the piston (12), and the piston (12) comprises a damping region (26) for braking the piston (12) before reaching the end position, at which the piston (12) is deformed in its end position, wherein the piston (12) is displaceable in the end position towards the initial position, characterized in that the piston (12) is a hollow piston (12), and an annular component (22) is displaceable relative to the piston (12) and / or the cylinder (4) and is designed and arranged to deform the piston (12) in the region of the end position of the piston (12).wherein the damping region (26) is formed by a conically widened end region of the hollow piston (12) and the conically widened end region of the hollow piston (12) is deformable at least in sections along a longitudinal axis of the piston (12).

Description

[0001] The invention relates to a piston-cylinder unit, a method for operating it, and a method for manufacturing such a piston-cylinder unit, comprising a cylinder and a piston mounted in the cylinder so as to be displaceable in an axial direction from an initial position to an end position. Furthermore, the invention relates to a vehicle-integrated personal safety system comprising such a piston-cylinder unit.

[0002] Piston-cylinder units are used in many areas of vehicle safety technology. One area of ​​application is systems that actively improve the safety of pedestrians or cyclists. In this context, a piston-cylinder unit is used to cushion the impact of a pedestrian on the hood of a vehicle by increasing the potential deformation of the hood. To do this, the vehicle's hood is raised by a defined distance shortly before impact, which can be achieved using a piston-cylinder unit. Piston-cylinder units are also used in seat belt tensioners and serve to limit the forward displacement of the occupants by tightening the seat belt. Piston-cylinder units are also used in convertible vehicles for roll bars, which can be extended using the piston-cylinder unit if the vehicle rolls over.

[0003] In the case of state-of-the-art piston-cylinder units, it is important to prevent the unfavorable forces that could act on the piston in the event of misuse when the piston is moved to its end position. Such a misuse could occur, for example, if the piston-cylinder unit is triggered while removed or—if it is installed in the hinge of a hood to improve pedestrian safety—when the hinge is open. For this scenario, the existing piston-cylinder units are extremely robust and complex, particularly with regard to material thickness.

[0004] From the document FR 2 931 910 A1 a piston-cylinder unit is known, comprising a cylinder and a piston mounted in the cylinder so as to be displaceable in an axial direction from an initial position to an end position, wherein the cylinder has a stop for defining the end position of the piston and the piston comprises a damping region for braking the piston before reaching the end position, at which the piston is deformed in its end position, wherein the piston is displaceable in the end position towards the initial position.

[0005] The object of the invention is to provide a simplified piston-cylinder unit, an improved method for operating and producing such a piston-cylinder unit, and an improved vehicle-integrated personal safety system.

[0006] The piston-cylinder unit according to the invention has a cylinder and a piston mounted in the cylinder so as to be displaceable in an axial direction from an initial position to an end position. The cylinder has a stop for defining the end position of the piston. The piston has a damping region for braking the piston before it reaches the end position and is deformed in its end position and, in the end position, is displaceable towards the initial position. The piston is a hollow piston and an annular component is designed and arranged so as to be displaceable relative to the piston and / or the cylinder, to deform the piston in the region of the end position of the piston. The damping region is formed by a conically widened end region of the hollow piston and the conically widened end region of the hollow piston is deformable at least in sections along a longitudinal axis of the piston. During the deformation orDeformation of the piston can be plastic or elastic. This deformation results in less abrupt deceleration of the piston as it moves toward its end position. The impact force of the piston in the end position is thus reduced. These measures reduce the load on the piston and cylinder, especially when the piston extends without any counterforce.

[0007] Since the damping area is advantageously part of the piston itself, no additional components such as damping elements are required. In addition to reduced assembly effort due to the elimination of loose parts, this simplifies and reduces costs in the production of the piston-cylinder unit.

[0008] The use of a hollow piston allows for a compact design of the piston-cylinder unit. The reduced size in the longitudinal direction is achieved through the synergistic combination of a hollow piston with an integrated damping area.

[0009] Furthermore, according to one embodiment, the piston-cylinder unit can be pyrotechnically driven. For this purpose, the piston has an expansion chamber for compressed gas in its interior. In particular, in the initial position, an igniter and a combustion chamber filled with pyrotechnic material can protrude into the interior of the piston. These measures also contribute to a particularly compact design of the piston-cylinder unit, which is particularly advantageous for applications in the automotive sector. Alternatively, a compressed gas chamber can also be accommodated in the piston.

[0010] The piston-cylinder unit can have an annular component, in particular a seal carrier. The annular component is designed to be displaceable relative to the piston and / or the cylinder. In particular, the annular component is designed and arranged to deform the piston in the region of the piston's end position. In this case, the piston, in its end position, can be drawn into the annular component, so to speak, or pulled through it in sections, i.e. regions of the piston which have a larger outer diameter than the inner diameter of the annular component are reduced by deformation to at least the size of the inner diameter of the annular component.

[0011] According to a further embodiment, the cylinder stop is formed by a tapered portion in one of its end regions. This measure is particularly advantageous with regard to the manufacturing costs of the cylinder. A tapered portion can easily be formed in the cylinder during the manufacture of the piston-cylinder unit, e.g., by cold forming.

[0012] Advantageously, the conically widened end region of the hollow piston can be deformable along the longitudinal axis of the piston by reducing an outer circumference of the section of the end region.

[0013] According to one embodiment, the hollow piston can have an opening in an end face adjoining the conically widening end region. The piston can preferably be a formed tube open at least on one side toward the igniter. Advantageously, the strength or rigidity of the deformation region can be adjusted by the size of the opening. A rim on the end face surrounding the opening can also contribute to stiffening. For example, the extent of the radial rim can influence the strength or deformability of the deformation region.

[0014] According to a further embodiment, the hollow piston can have a flanged collar in the damping area, preferably at its axial end. This collar can advantageously serve as additional reinforcement. However, it is generally not necessary for the damping area of ​​the piston to extend so far into the cylinder stop that the collar interacts with the cylinder-side stop. The provided collar therefore preferably serves as additional security.

[0015] Another preferred piston-cylinder unit has a seal, particularly on the piston side, between an outer side of the piston and an inner side of the cylinder. The seal can preferably consist of an O-ring and a seal carrier, wherein the O-ring can be inserted into a radially circumferential groove of the seal carrier.

[0016] In addition, the piston can have a reduced cross-section to accommodate the seal carrier. This allows the seal carrier to be held in a form-fitting manner on the piston in the longitudinal direction, at least toward the end position. The seal or its seal carrier can rest axially against the cylinder-side stop in the piston's end position. The seal carrier can be moved into the piston's damping area under plastic deformation, whereby plastic deformation of the seal carrier is also tolerated for additional damping.

[0017] According to a further aspect of the invention, a vehicle-integrated personal safety system, in particular a pedestrian safety system, belt tensioner, or roll bar, is specified, which comprises a piston-cylinder unit according to at least one of the preceding embodiments as a drive unit. The personal safety system is preferably a pedestrian protection system in which the hood of a motor vehicle is raised with the aid of the piston-cylinder unit shortly before a collision with a pedestrian. Another preferred personal safety system is a belt tensioner, which is operated with the aid of the piston-cylinder unit, so that forward displacement of the occupants can be effectively limited. Another preferred personal safety system is an extendable roll bar, which can be extended by the piston-cylinder unit in the event of a convertible vehicle rollover.

[0018] Preferably, the vehicle-integrated personal safety system comprises a sensor and an electronic control unit by means of which the piston-cylinder unit can be activated when a triggering situation occurs.

[0019] The invention further provides a method for operating a piston-cylinder unit. This comprises a cylinder and a piston mounted in the cylinder so as to be displaceable in an axial direction from an initial position to an end position. The cylinder has a stop for defining the end position of the piston. The piston comprises a damping region which is deformed to brake the piston before it reaches the end position. In its end position, the piston is displaceable towards the initial position and is a hollow piston, wherein an annular component is displaced relative to the piston and / or the cylinder and deforms the piston in the region of the end position of the piston. The damping region is formed by a conically widened end region of the hollow piston, and the conically widened end region of the hollow piston is deformed at least in sections along a longitudinal axis of the piston.Such a piston reset capability is advantageous, for example, in a pedestrian protection system in which the bonnet of a motor vehicle can be raised shortly before a collision with a pedestrian using the piston-cylinder unit, since after the collision the bonnet can be reset to its original position, for example to enable a subsequent trip to the workshop.

[0020] The same or similar advantages as those already mentioned with regard to the piston-cylinder unit according to embodiments of the invention also apply to the vehicle-integrated personal safety system and to the method for operating the piston-cylinder unit and therefore require no further explanation.

[0021] According to a further aspect of the invention, a method for producing a piston-cylinder unit according to the invention is specified. During the production of such a piston-cylinder unit, the piston is conically expanded and flanged to create a damping area or a collar. The deformation area is deformed by the cylinder before reaching the end position. Furthermore, the piston is displaceable in the end position towards the starting position. With the aforementioned production method, the integration of additional damping elements, which serve to brake the piston before reaching its end position, can be dispensed with. The production method is therefore particularly simple and cost-effective to implement.

[0022] The invention is explained in more detail below with reference to the figures. They show: Fig. 1 a perspective sectional view of a piston-cylinder unit according to the invention according to an embodiment as part of the personal safety system according to the invention, Fig. 2 a detailed sectional view of this piston-cylinder unit in the area of ​​the igniter-side end, with the piston in its initial position, Fig. 3 a further detailed sectional view of this piston-cylinder unit in the area of ​​the igniter-side end, where the piston is close to its end position, and Fig. 4 a detailed sectional view of the igniter-side piston end, in which the piston of the piston-cylinder unit according to the invention is in its end position.

[0023] Fig. Figure 1 shows a simplified perspective sectional view of a piston-cylinder unit 2 of a vehicle-integrated personal safety system. The unit comprises a cylinder 4, which is provided with a closure cap 6 on its front end. A plug receptacle 8 is provided on the rear end of the cylinder 4 or the piston-cylinder unit 2, which has pin-shaped contacts 10 of an igniter 18.

[0024] Located inside cylinder 4 is a piston 12 designed as a hollow piston. For the sake of clarity, this will be referred to hereinafter simply as piston 12; however, a hollow piston is always meant.

[0025] The piston 12 is closed on one side and contains an expansion chamber 14 for receiving compressed gas. The pressure required to extend the piston 12 is Fig. 1. The pyrotechnic drive comprises a combustion chamber 16 that extends into the expansion chamber 14 of the piston 12. The combustion chamber 16 contains pyrotechnic material or a compressed gas cartridge. The pyrotechnic material can be activated using the igniter 18. Predetermined breaking points 20 on the front side of the combustion chamber 16 allow the generated or released compressed gas to expand into the expansion chamber 14, so that the piston 12 can move out of the cylinder 4 in an axial direction A. During this movement, the closure cap 6 is pierced or removed.

[0026] The expansion chamber 14 is sealed from the annular space 21 between the inside of the cylinder 4 and the outside of the piston 12 spaced therefrom by a seal. This seal comprises a seal carrier 22 designed as an annular component and an O-ring 24 inserted into a radially circumferential groove of this seal carrier 22. The seal located at the igniter-side end of the piston 4 moves—when the piston-cylinder unit 2 is activated—together with the piston 12 in the axial direction A and seals the combustion-chamber-side high-pressure section in the cylinder from the annular space 21.

[0027] Fig. 2 shows the end region of the piston-cylinder unit 2 comprising the plug receptacle 8 in a detailed sectional view. The piston 12 comprises, at its igniter-side end, a damping region 26 formed by a cone 28 present at the end of the piston 12 and produced by forming the piston wall. Furthermore, the piston 12 comprises a collar 30 which adjoins the cone 28, delimits the piston 12 at its end face, and can be introduced into the piston 12, for example, by flanging. Furthermore, a radially inwardly extending edge 32 is present on the end face, which adjoins the collar 30 and forms part of the end face of the piston 12. The edge 32 encloses an opening 36 present in the end face of the piston (cf. Fig. 3 and Fig. 4). Fig. 2 shows that the seal carrier is axially supported between the beginning of the cone 28 and a small shoulder 31 of the piston wall, which is produced by plastic forming.

[0028] If the piston-cylinder unit 2 is activated by igniting the pyrotechnic charge, the piston 12 extends in the axial direction A. Fig. 3 shows the extended piston 12 shortly before reaching its end position in a detailed sectional view of the front end of the cylinder 2. The seal carrier 22, which is fixed in the axial direction A to the hollow piston 12 by the fact that the latter has a groove-like recess in the region of the seal carrier 22, strikes a stop 34 of the cylinder 4 in this position of the piston 12. This stop 34 is preferably achieved by a tapering of the cylinder 4, which is produced by plastically deforming the tubular cylinder wall.

[0029] In order to brake the piston 12 to its end position, the seal carrier 22, or the seal consisting of the seal carrier 22 and the O-ring 24, slides onto the cone 28 of the piston 12, whereby the damping region 26 of the piston 12, designed as a cone 28, is plastically or elastically deformed. The seal carrier 22 is supported on the stop 34 of the cylinder 4. The strength or rigidity of the damping region 26 of the piston 12 can be determined in particular by the size of the opening 36 present on the end face or by the radial extent of the edge 32. The seal carrier is therefore displaceable, specifically relative to the piston 12 and / or the cylinder 4, and is designed and arranged in such a way as to deform the piston 12 in the region of the end position of the piston 12.

[0030] This is evident from another sectional view, as Fig. 4. The damping area 26 of the piston 12 is deformed radially inward, whereby the collar 30 is displaced and the edge 32 is deformed in the axial direction A. The piston 12 is additionally secured by the collar 30, which abuts the seal carrier 22 in this piston position.

[0031] The cone 28 of the piston 12 can be designed in such a way that when the piston-cylinder unit 2 is operating as intended, i.e. when a corresponding counterforce is applied to the piston 12, the forces occurring in the piston-cylinder unit 2 push the seal carrier 22 via the cone 28 into the Fig. 4. If the piston-cylinder unit 2 is triggered without counterforce in the event of misuse, the braking effect of the damping area 26 significantly slows down the movement of the piston 12 in the axial direction A. In the position shown in Fig. 4, the piston 12 is still in the direction of its initial position (cf. Fig. 1) movable. This is important, for example, to Fig. 1 indicated engine hood 40 can be lowered again after a false triggering.

[0032] The piston-cylinder unit 2 according to the Fig.1 to 4 has a particularly compact design. This is achieved in particular by the fact that no additional damping element is used, but rather the damping of the piston 12 is achieved by the damping region 26 integrated therein. The compact design, which has not been achieved so far in the prior art, qualifies the piston-cylinder unit 2 in particular for vehicle-integrated personal safety systems, e.g. for pedestrian protection systems, in which the hood 40 is raised by a certain distance before the pedestrian impacts the hood, so that a corresponding crumple zone is available when the pedestrian impacts and contact with the engine block below can be effectively prevented. In addition, the compact piston-cylinder unit 2 is suitable for belt tensioner systems, but also as part of a drive unit for an extendable roll bar, for example in a convertible vehicle.

[0033] The piston-cylinder unit 2 can also be manufactured particularly effectively because the cone 28 serving as the damping area 26 can be manufactured in a single, easily integrated step, namely by conically widening the piston 12, which in the simplest case is a tube open toward the igniter 18. In a subsequent step, the collar 30 serving as a safety feature can be inserted into the piston 12, for example, by flanging.

Claims

[1] Piston-cylinder unit (2) with a cylinder (4) and a piston (12) mounted in the cylinder (4) so ​​as to be displaceable in an axial direction (A) from an initial position to an end position, wherein the cylinder (4) has a stop (34) for defining the end position of the piston (12) and the piston (12) comprises a damping region (26) for braking the piston (12) before reaching the end position, at which the piston (12) is deformed in its end position, wherein the piston (12) is displaceable in the end position towards the initial position, characterized byin that the piston (12) is a hollow piston (12), and an annular component (22) is designed and arranged to be displaceable relative to the piston (12) and / or the cylinder (4) in order to deform the piston (12) in the region of the end position of the piston (12), wherein the damping region (26) is formed by a conically widened end region of the hollow piston (12) and the conically widened end region of the hollow piston (12) is deformable at least in sections along a longitudinal axis of the piston (12). [2] Piston-cylinder unit (2) according to claim 1, characterized by that it is pyrotechnically driven and the hollow piston (12) has an expansion chamber (14) for compressed gas in its interior. [3] Piston-cylinder unit (2) according to claim 2, characterized by that in the initial position an igniter (18) and a combustion chamber (16) filled with pyrotechnic material protrude into the interior. [4] Piston-cylinder unit (2) according to at least one of the preceding claims, characterized by that the stop (34) is formed by a taper of the cylinder (4) in one of its end regions. [5] Piston-cylinder unit (2) according to at least one of the preceding claims, characterized by that the conically widened end region of the hollow piston (12) is deformable by reducing an outer circumference of the section of the end region. [6] Piston-cylinder unit (2) according to at least one of the preceding claims, characterized by that the hollow piston (12) has an opening (36) in an end face adjoining the conically widened end region. [7] Piston-cylinder unit (2) according to at least one of the preceding claims, characterized by that the hollow piston (12) has a collar (30) in the damping area (26). [8] Piston-cylinder unit (2) according to at least one of the preceding claims, wherein a seal (22, 24) is arranged between an outer side of the piston (12) and an inner side of the cylinder (4). [9] Vehicle-integrated personal safety system with a piston-cylinder unit (2) according to at least one of the preceding claims as a drive unit. [10] Vehicle-integrated personal safety system according to claim 9, comprising a sensor and an electronic control unit by means of which the piston-cylinder unit (2) can be activated when a triggering situation occurs. [11] Method for operating a piston-cylinder unit (2) with a cylinder (4) and a piston (12) mounted in the cylinder (4) so ​​as to be displaceable in an axial direction (A) from an initial position to an end position, wherein the cylinder (4) has a stop (34) for defining the end position of the piston (12), wherein the piston (12) comprises a damping region (26) which is deformed to brake the piston (12) before reaching the end position, and the piston (12) is displaceable in its end position in the direction of the initial position, characterized bythat the piston (12) is a hollow piston (12), and an annular component (22) is displaced relative to the piston (12) and / or the cylinder (4) and carries out a deformation of the piston (12) in the region of the end position of the piston (12), wherein the damping region (26) is formed by a conically widened end region of the hollow piston (12) and the conically widened end region of the hollow piston (12) is deformed at least in sections along a longitudinal axis of the piston (12). [12] Method for producing a piston-cylinder unit (2) with a cylinder (4) and a piston (12) mounted in the cylinder (4) so ​​as to be displaceable in an axial direction (A) from an initial position to an end position, wherein the cylinder (4) has a stop (34) for defining the end position of the piston (12), characterized bythat the piston (12) is conically widened and flanged to create a damping area (26) which can be deformed by the cylinder (4) before the end position of the piston (12) is reached.

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