Winding – tensioning – or guiding – Reeling device – With spring motor
Patent
1996-02-08
1997-08-05
Darling, John P.
Winding, tensioning, or guiding
Reeling device
With spring motor
B65H 7548, A62B 3500
Patent
active
056533985
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a drive device for a belt pretensioner adapted to act on the belt drum of a belt retractor, comprising a housing fitted laterally to the belt retractor and in which a cylinder space is formed, a generally circular disk-like rotor rotatably and eccentrically mounted in such cylinder space and having lamellas arranged in radial slots, and a compressed gas source adapted to be a activated in a manner responsive to the vehicle, for pressurizing chambers formed between the lamellas, the rotor and the wall of the housing via an inlet.
A drive device of this type has already been disclosed in the German patent publication 2,814,487 C. Since the rotor of this drive device, which may be termed a lamella motor, can be directly coupled with the belt drum of the belt retractor, there is an efficient use of the energy made available by the compressed gas source as compared with other designs of belt pretensioner drives, in the case of which linear motion must firstly be converted into a rotary movement. In said drive device the compressed gas source, a pyrotechnic gas generator, does not however directly pressurize the chambers formed between the lamellas of the rotor, but rather using a liquid drive means such as water, since it had not been possible to sufficiently seal off the rotor in the housing. In the case of conventional lamella motors the lamellas thereof are thrust by compression springs radially outward to be in sealing engagement with the housing wall. On an increase in the speed of rotation of the rotor the lamellas are additionally thrust by centrifugal force against the housing wall. However in the case of a drive device for a belt pretensioner the rotor must turn through 1 to 2 and preferably 1.5 revolutions within only approximately 6 to 10 ms, something corresponding to a mean speed of rotation of 10,000 to 20,000 rpm. With the sudden increase in pressure required for this after activation of the gas generator the lamellas are also put under pressure at their outer end surfaces, which are to make sealing engagement with the housing wall, this meaning that massively dimensioned springs, which are to hold the lamellas in sealing engagement with the housing wall, are overridden so that ultimately there is no sealing action or only an insufficient one and the gases will escape at the outlet of the housing without having performed any work. By arranging a liquid working medium, such as water, in between there is admittedly an improved conversion of the energy released by the gas generator into mechanical drive work, since owing to the viscosity of such medium, which is higher than that of gases, leakage at the rotor is less significant, but the use of such a medium gives rise to problems for a number of different reasons. On the one hand the liquid working medium must be accommodated in an efficiently sealed supply space and be constantly kept available so that a complex structure with a larger volume and weight is called for. On the other hand measures must be adopted to prevent undesired effects due to escape of working medium at the outlet of the housing during activation of the belt pretensioner drive.
The invention is to provide a drive device of the lamella motor type, which makes do without a liquid working medium while nevertheless ensuring optimum conversion of the energy released by the gas generator into mechanical drive work. In accordance with the invention the radial slots of the rotor, in which the lamellas run, are respectively connected at inner ends thereof by a flow duct with a chamber placed in the direction of the rotation of the rotor before the respective lamella. By having such a flow duct there will be pressure equalization between the pressurized chamber and the radially inner end of each slot so that the radial forces produced by the application of pressure at each lamella will compensate one another. It is now only necessary to ensure that at the start of pressurization the lamellas are either already in sealing engagement with the housing wall or howeve
REFERENCES:
patent: 1539728 (1925-05-01), Ensign
patent: 4230288 (1980-10-01), Fohl
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