Pyrotechnic drive unit and method for producing a pyrotechnic drive unit

Abstract

The invention relates to a pyrotechnic drive unit (10), in particular for an engine hood prop or an active head support. The pyrotechnic drive unit (10) has a housing (12) which has a cavity (14) in which a piston (16) is displacably mounted from an idle position to an activation position. The pyrotechnic drive unit (10) furthermore comprises a pyrotechnic unit (20) with an igniter (22) at an end (24) of the housing (12), said pyrotechnic unit being able to displace the piston (16) in its activation position. The housing (12) is closed by a closure element (38) on an end face at an end (32) opposite the pyrotechnic unit (20). The pyrotechnic drive unit (10) furthermore comprises a retaining element (36) for the vehicle-side fastening of the pyrotechnic drive unit (10), wherein the closure element (38) connects the housing (12) to the retaining element (36). The invention also relates to a method for producing such a pyrotechnic drive unit (10).

Description

[0001] Pyrotechnic drive unit and method for producing a pyrotechnic drive unit

[0002] The invention relates to a pyrotechnic drive unit, in particular for a hood divider or an active headrest, and to a method for producing such a pyrotechnic drive unit.

[0003] It has been observed that when a pedestrian strikes a motor vehicle, the motor vehicle often pulls the pedestrian's legs out from under them in the direction of travel due to contact with the bumper. As a result, the pedestrian's upper body is pushed onto the hood of the vehicle and, depending on the severity of the impact, towards the windshield. To minimize pedestrian injuries, modern cars are equipped with hood lifts that raise the rear part of the hood, i.e. the part of the hood closest to the windshield. This prevents the pedestrian's upper body and head from hitting the engine block in the event of an impact. Unlike the engine block, the hood is a flexible structure that can absorb some of the impact energy.Furthermore, raising the hood reduces the speed of pedestrians before they hit the windshield, which can limit the severity of injuries. Consequently, using a hood lifter helps reduce the risk of injury to a pedestrian struck by a motor vehicle.

[0004] Active head restraints, on the other hand, are designed to protect vehicle occupants in the event of a rear-end collision. Such active head restraints are activated, for example, in the event of a rear-end collision and follow the occupant's head as quickly as possible to reduce pressure on the cervical spine during an impact. This ensures that a vehicle occupant's head does not suddenly and sharply collapse backward, which can lead to whiplash. Both bonnet deployers and active head restraints often contain very small pyrotechnic drive units. These are activated by a pyrotechnic drive medium, which causes a piston within the pyrotechnic drive unit to be pressurized and moved into its activated position. The movement of the piston either raises the bonnet or moves the head restraint forward.

[0005] Typically, actuators are enclosed in separate parts to protect the internal components of the pyrotechnic actuator. A cap is often used, the preload of which serves to secure the piston inside the pyrotechnic drive unit. However, the piston often still has a certain amount of play within the housing, which can lead to noise.

[0006] Furthermore, such pyrotechnic propulsion units often have a flange at one end, which is used to attach them to the vehicle. However, the flange process damages the paint on the corresponding housing area of ​​the pyrotechnic propulsion unit, which can lead to rust damage at the flanged area.

[0007] Consequently, it is an object of the invention to provide a pyrotechnic drive unit that is better protected against external influences and minimizes noise.

[0008] This object is achieved according to the invention by a pyrotechnic drive unit, in particular for a hood stay or an active headrest. The pyrotechnic drive unit has a housing having a cavity in which a piston is mounted so as to be displaceable from a rest position to an activation position. Furthermore, the pyrotechnic drive unit comprises a pyrotechnic unit with an igniter at one end of the housing, which can displace the piston into its activation position. At an end opposite the pyrotechnic unit, the housing is closed at the front by a closure element. The pyrotechnic drive unit further comprises a retaining element for securing the pyrotechnic drive unit to the vehicle, the closure element connecting the housing to the retaining element.In other words, the sealing element serves to secure the retaining element to the housing of the pyrotechnic drive unit while simultaneously protecting the pyrotechnic drive unit from external influences such as moisture. Such a seal is particularly important in applications such as a hood popper, as the pyrotechnic drive unit may come into contact with cleaning fluids, splash water, or similar substances. If liquid enters the housing of the pyrotechnic drive unit in cold outside temperatures, this can impair its functionality, so a secure seal increases the functional reliability of the pyrotechnic drive unit.

[0009] The closure element is preferably made of a plastic injection-molded onto the housing, in particular a thermoplastic or thermosetting plastic. Further preferably, the closure element is made of a polyamide that expands during injection molding. The expanding polyamide can expand either physically or chemically. Using injection-molded plastic can increase moisture protection for the pyrotechnic drive unit, as can the closure element being precisely molded onto the pyrotechnic drive unit. This also reduces production tolerances, which are important when using a separate cap for the pyrotechnic drive unit. By injection-molded plastic, the closure element becomes part of the housing, eliminating the need for a separate closure element.

[0010] The end element is preferably manufactured using a known plastic injection molding process. This can, in particular, be a thermoplastic foam injection molding process.

[0011] According to one embodiment, the piston comprises a tube that is open on both ends and closed at one end by the closure element. Thus, the closure element closes both the housing of the pyrotechnic drive unit and the tube of the piston, thereby securing the piston to the housing.

[0012] Preferably, the closure element is molded onto the tube end and simultaneously onto the end of the housing to close both. Thus, the closure element enables a positive connection between the piston and the housing of the pyrotechnic drive unit, preventing or at least reducing noise.

[0013] The piston tube can have at least one radially inwardly extending projection, in particular a radially inwardly extending annular projection, at its end opposite the pyrotechnic unit, which is positively embedded in the closure element. In other words, the closure element extends into the piston tube, with the radially inwardly extending projection ensuring that the piston is guided in the housing.

[0014] According to a further embodiment, the piston is a tube provided with an end wall and closed at one end. The end wall adjoins the closure element, and the closure element is molded onto the housing, particularly if a piston is present. The closure element preferably adjoins the end of the housing opposite the pyrotechnic unit, radially inward and radially outward. In this embodiment, too, the piston is connected to the housing of the pyrotechnic drive unit by a positive fit, thus preventing or reducing noise. In addition, the pyrotechnic drive unit is thus effectively protected from moisture.

[0015] According to a preferred embodiment, the retaining element surrounds the end of the housing opposite the pyrotechnic unit and projects into a radially inwardly extending, in particular annular, circumferential recess in the housing. The recess serves as a guide for the piston, particularly in the deactivated and / or activated state. The recess ensures that the retaining element cannot slip, thus securing the vehicle-mounted attachment of the pyrotechnic drive element. At the same time, the recess prevents the piston from jamming with the housing of the pyrotechnic drive unit, thus ensuring proper functioning of the pyrotechnic drive unit.

[0016] Preferably, the end element also extends from the outside of the housing into the recess and, in particular, at least partially fills it. Thus, the end element provides additional corrosion protection, as the recess, in particular, is prone to rust formation. Especially if the recess is created by flanging, this can damage the protective paint in the corresponding area of ​​the pyrotechnic drive unit. The sprayed-on end element prevents rust formation even if the paint is damaged.

[0017] According to a preferred embodiment, the closure element is designed such that it is destroyed by the piston upon ignition of the pyrotechnic unit and / or detaches from the housing to release piston movement. Alternatively, the closure element can also break at a desired location, ensuring that the closure element continues to close the piston tube when the piston tube is open on both sides.

[0018] Preferably, the retaining element has at least one opening through which the plastic of the closure element extends. This provides improved corrosion protection and additionally secures the retaining element by a positive fit between the retaining element and the housing provided by the closure element.

[0019] The object is further achieved by a method for producing a pyrotechnic drive unit, as described above. The closure element is injection-molded onto the pyrotechnic unit using a plastic injection molding process before it has been assembled. As already mentioned, this is preferably a thermoplastic foam injection molding process, in which an expanding polyamide is injection-molded onto the housing of the pyrotechnic drive unit. Using a plastic injection molding process allows both the housing of the pyrotechnic drive unit and the piston to be designed flexibly, as the closure element adapts to the corresponding shape.

[0020] Preferably, when the piston is open at its end opposite the pyrotechnic unit, a counterholder is pushed into the piston prior to and during injection molding to shape the closure element. After injection molding, the counterholder is removed. By using a counterholder, the end section of the closure element can be flexibly determined and / or designed. Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. In the drawings:

[0021] Figure 1 is a cross-section of a pyrotechnic drive unit according to the invention according to a first embodiment; and

[0022] Figure 2 is a cross-section of one end of a second embodiment of the pyrotechnic drive unit.

[0023] Figure 1 shows a pyrotechnic drive unit 10, in particular for a hood lifter or an active headrest. The pyrotechnic drive unit 10 comprises a housing 12 having a cavity 14.

[0024] A piston 16 is mounted in the cavity 14, and the piston 16 can be moved from a rest position to an activated position. The piston 16 comprises a tube 18, which is open on both sides.

[0025] In order to move the piston 16 from its rest position to its activation position, the pyrotechnic drive unit 10 comprises a pyrotechnic unit 20 with an igniter 22. The pyrotechnic unit 20 is arranged at a first end 24 of the housing 12.

[0026] The pyrotechnic unit 20 shown in Figure 1 is an electrically actuated actuator, so that the igniter 22 has two electrical connections 26.

[0027] The pyrotechnic unit 20 not only closes the first end 24 of the housing 12, but in the initial state also a first end 28 of the tube 18. In order to prevent moisture from entering the cavity 14 of the pyrotechnic drive unit 10, a sealing element 30 is arranged between the pyrotechnic unit 20 and the housing 12.

[0028] At a second end 32 opposite the pyrotechnic unit 20, the housing 12 has a radially inwardly extending, in particular annular, recess 34. The recess 34 can be created, for example, by flanging. A retaining element 36, which surrounds the housing 12, projects into the recess 34. The retaining element 36 is preferably a flange and serves for the vehicle-mounted fastening or positioning of the pyrotechnic drive unit 10.

[0029] As can also be seen in Figure 1, the retaining element 36 is connected to the housing 12 by crimping. Optionally, the retaining element 36 can also be welded to the housing 12 at this point, i.e., in the recess 34.

[0030] At the second end 32 opposite the pyrotechnic unit 20, the housing 12 is closed by a closure element 38. The closure element 38 consists of a plastic injection-molded onto the housing 12.

[0031] The plastic is preferably a thermoplastic or thermosetting plastic, in particular an expanding polyamide. The expansion of the polyamide can occur physically or chemically.

[0032] In addition, the end element 38 also connects, ie secures, the holding element 36 to the housing 12. For this purpose, the end element 38 protrudes from the outside of the housing 12, like the holding element 36, into the recess 34. Preferably, the end element 38 at least partially fills the recess 34.

[0033] As shown in Figure 2, the retaining element 36 can have at least one opening 40, so that the plastic of the end element 38 extends through the retaining element 36 and fills the entire recess 34, creating a form-fit connection on all sides between the end element 38 and the retaining element 36. The recess 34 creates a radially inwardly projecting, circumferential annular projection.

[0034] As already mentioned, the embodiment shown in Figure 1 is a piston 16 with a tube 18 that is open at both ends. In this embodiment, the closing element 38 is simultaneously injection-molded onto the second end 32 of the housing 12 and a second end 42 of the tube 18, so that the closing element 38 closes both the tube 18 and the housing 12 at the respective second end 32, 42 opposite the pyrotechnic unit 20.

[0035] The second end 42 of the piston 16 rests against the recess 34 of the housing 12 or has a slight clearance relative to the recess 34, so that the recess 34 forms a guide for the piston 16 in the activated state.

[0036] The positive embedding of the recess 34 of the housing 12 into the end element 38 prevents the generation of noise despite a slight clearance. This is due to the fact that the end element 38 is not only positively connected to the recess 34, but also to the second end 32 of the housing 12.

[0037] When the pyrotechnic unit 20 is ignited, the end element 38 is destroyed at the edge by the piston 16 and detached from the housing 12. This releases the piston movement and enables activation of the safety function.

[0038] For a piston 16 with an open second end 42, the closure element 38 is released from the housing 12 such that the piston 16 remains closed. Preferably, the closure element 38 breaks at a point outside the housing diameter.

[0039] To produce the embodiment of the pyrotechnic drive unit 10 shown in Figure 1, the closure element 38 is injection-molded onto the housing 12 using a plastic injection molding process before the pyrotechnic unit 20 is mounted. To limit the closure element 38, a counterholder 44 is inserted into the housing 12 prior to the plastic injection molding process. This counterholder determines the inward shape of the closure element 38. The counterholder 44 is left in the housing 12 for the duration of the injection molding process and is not removed until the injection molding process is complete.

[0040] The injection molding process is preferably a thermoplastic foam injection molding process using an expanding polyamide. The overmolded, reshaped end of the housing 12 creates an undercut that is filled with the plastic, thereby improving the seal.

[0041] Figure 2 shows a second embodiment of the pyrotechnic drive unit 10. The general structure of the pyrotechnic drive unit 10 is the same, so only the differences will be discussed below.

[0042] In this embodiment, the piston 16 also comprises a tube 18, wherein the tube 18 is provided with an end wall 46, so that it is a tube 18 closed on one side.

[0043] Here, the end wall 46 borders the end element 38 and lies in the area of ​​the recess 34, so that this again acts as a guide for the piston 16. Consequently, tilting of the piston 16 in the cavity 14 of the housing 12 is avoided.

[0044] In the embodiment according to Figure 2, the end element 38 adjoins the end wall 46 and encompasses the end of the housing 12, so that the generation of disturbing noises can be prevented here as well.

[0045] The end member 38 extends into the housing 12 to the point where the piston 16 comes into contact with the recess 34.

[0046] Such a pyrotechnic drive unit 10 can be used, for example, in a hood lifter.

[0047] The pyrotechnic unit 20 ignites when a pedestrian comes into contact with the car in a rear-end collision. When the pyrotechnic unit 20 is ignited, the piston 16 is partially shot out of the housing 12, causing the hood to lift at its rear, i.e., the part closest to the windshield. This prevents the hood from denting all the way to the engine block when a pedestrian hits it. Thus, a hood deployer can reduce the risk of injury to a person struck by a vehicle. Alternatively, the pyrotechnic drive unit 10 can be used in an active headrest. In this case, the pyrotechnic unit 20 is activated in a rear-end collision, causing the headrest to move forward toward the head. Accordingly, the travel distance to impact is reduced, thus also reducing the pressure on the cervical spine.Accordingly, the risk of whiplash is reduced.

[0048] Of course, the pyrotechnic drive unit 10 can also be installed in other areas of application, such as for tightening a safety belt.

Claims

Patent claims 1. Pyrotechnic drive unit (10), in particular for a hood divider or an active headrest, with a housing (12) which has a cavity (14) in which a piston (16) is mounted so as to be displaceable from a rest position into an activation position, a pyrotechnic unit (20) with an igniter (22) at one end (24) of the housing (12), which can displace the piston (16) into its activation position, wherein the housing (12) is closed at an end (32) opposite the pyrotechnic unit (20) by a closure element (38), and with a holding element (36) for fastening the pyrotechnic drive unit (10) to the vehicle, wherein the closure element (38) connects the housing (12) to the holding element (36).

2. Pyrotechnic drive unit (10) according to claim 1, characterized in that the end element (38) consists of a plastic injection-molded onto the housing (12), in particular of a thermoplastic or thermosetting plastic, more preferably of a polyamide which expands during injection molding.

3. Pyrotechnic drive unit (10) according to one of claims 1 or 2, characterized in that the piston (16) comprises a tube (18) which is open on both sides and is closed on one side by the closure element (38).

4. Pyrotechnic drive unit (10) according to 3, characterized in that the closing element (38) is injection-molded onto a tube end (42) and at the same time onto the end (32) of the housing (12) in order to close both.

5. Pyrotechnic drive unit (10) according to claim 3 or 4, characterized in that the tube (18) has at its end (42) opposite the pyrotechnic unit (20) at least one radially inwardly extending projection, in particular a radially inwardly extending annular projection, which is positively embedded in the end element (38).

6. Pyrotechnic drive unit (10) according to one of claims 1 or 2, characterized in that the piston (16) is a tube (18) provided with an end wall (46) and closed on one side, wherein the end wall (46) is the closure element (38) is adjacent and the closure element (38) is injection-molded onto the housing (12), in particular when a piston (16) is present, and, preferably, is adjacent to its end (32) opposite the pyrotechnic unit (20) on the radial inside and radial outside.

7. Pyrotechnic drive unit (10) according to one of the preceding claims, characterized in that the holding element (36) surrounds the end (32) of the housing (12) opposite the pyrotechnic unit (20) and projects into a radially inwardly extending, in particular annular, recess (34) of the housing (12), in particular wherein the recess (34) is a guide for the piston (16) in the non-activated and / or activated state.

8. Pyrotechnic drive unit (10) according to claim 7, characterized in that the closing element (38) preferably also projects from the outside of the housing (12) into the indentation (34), in particular at least partially filling it.

9. Pyrotechnic drive unit (10) according to one of the preceding claims, characterized in that the closure element (38) is designed such that when the pyrotechnic unit (20) is ignited it is destroyed by the piston (16) and / or detaches from the housing (12) in order to release a piston movement.

10. Pyrotechnic drive unit (10) according to one of the preceding claims, characterized in that the holding element (36) has at least one opening (40) through which the plastic of the end element (38) extends.

11. Method for producing a pyrotechnic drive unit (10) according to one of the preceding claims, characterized in that, when the pyrotechnic unit (20) is not yet assembled, the end element (38) is injection-molded by a plastic injection-mold process.

12. Method according to claim 10, characterized in that the piston (16) is open at its end (42) opposite the pyrotechnic unit (20), wherein a counterholder is inserted into the piston before and for the injection molding (16) is pushed for shaping the end element (38), wherein the counterholder is removed again after injection molding.

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