Pyrotechnical linear actuating means for a belt tensioner

A pyrotechnical linear actuating means for a belt tensioner, comprises a piston/cylinder unit having a piston and a cylinder, a multi-stage gas generator having several propellants separated from each other for actuating the piston, and an ignition unit for activating the propellants of the gas generator. Each of the propellants being activatable separately individually or at the same time.

TECHNICAL FIELD 
The invention relates to a pyrotechnical linear actuating means for a belt 
tensioner. 
BACKGROUND OF THE INVENTION 
In conventional pyrotechnical linear actuating means the pyrotechnical 
propellant is dimensioned for vehicle occupants of average body weight, 
this being the reason why the belt is tautened with the same force for 
small, tall, lightweight or heavy occupants. The intention in optimizing 
belt tensioning is to involve the vehicle occupant as early as possible in 
the deceleration of the vehicle in a crash situation. However, in the case 
of smaller persons of low weight this object may already be achieved by a 
tensioning force which is smaller than that of persons of average or 
higher body weight. 
BRIEF DESCRIPTION OF THE INVENTION 
The invention provides a pyrotechnical linear actuating means for a belt 
tensioner, the actuating energy of which is made available in several 
stages to ensure belt tensioning optimally adapted to such parameters as 
stature, weight of the occupant, seating position or intensity of 
collision. The pyrotechnical linear actuating means according to the 
present invention comprises a piston/cylinder unit having a piston and a 
cylinder, a multi-stage gas generator having several propellants separated 
from each other for actuating the piston, and an ignition unit for 
activating the propellants of the gas generator. Each of the propellants 
being activatable separately individually or at the same time. The gas 
generator constitutes a unit of its own in which the propellants are 
arranged separate from each other. Accordingly, there is no need to 
incorporate several gas generators, each having its own propellant in the 
linear actuating means, thus simplifying assembly. 
Preferably two propellants having differing actuating capacities are 
contained in the gas generator so that three different actuating 
capacities are achievable, namely that of each individual propellant and, 
on simultaneous activation of both propellants the sum of the individual 
actuating capacities, the ratio of the actuating capacities being 
preferably in the ratio of roughly 1 to 2. 
The linear actuating means according to the invention is assigned at least 
one sensor for sensing the vehicle occupant, vehicle or vehicular 
environment parameters and an activator connected thereto which controls 
activation of one or more propellants as a function of the sensed 
parameters. The parameters which can be sensed thereby are e.g. seat 
occupancy, body weight, stature or seating position of vehicle occupants 
as well as collision intensity, vehicular indoor or outdoor temperature. 
Including the last two parameters in sensing the actuating capacity to be 
generated is based on the following reasoning: at low outdoor temperatures 
and low temperatures in the vehicle interior, e.g. in winter, it is to be 
assumed that a vehicle occupant wears heavier clothing so that a seat belt 
is not in close contact with the body of the vehicle occupant and that the 
vehicle occupant needs to be moved far in case of a collision due to the 
thick layers of pliant clothing until he is restrained by the seat belt. 
In such a case a belt tensioner needs to have a higher actuating capacity 
so as to quickly bring the seat belt to bear on the body of the occupant. 
In one preferred embodiment the gas generator, is a circular ring-shaped 
body adjoining the cylinder wall in the interior of the cylinder, a 
parting wall being provided between the propellants in the interior of the 
gas generator, the parting wall being all-in-all oriented axially. Each 
propellant is separated by a face end cover from the working space and 
protected from being activated on igniting of the other propellant.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Shown in FIG. 1 is a pyrotechnical linear actuating means 1 for a belt 
tensioner featuring a unit comprising an actuatable piston (not shown) and 
a cylinder 3. A piston rod 5 extends outwardly from the piston through an 
opening at the face end 7 of the cylinder 3 where it is connected to a 
means for sensing the seat belt. In the interior of the cylinder 3, 
adjoining the face end 7, a circular ring-shaped gas generator 9 
surrounding the piston rod 5 is provided, the gas generator including a 
thin circular ring-shaped housing i1. In the interior of the gas generator 
9 two propellants located spatially separate from each other, namely a 
first propellant 13 and a second propellant 15 are provided. The ratio of 
the actuating capacities of the two propellants 13, 15 is roughly 1 to 2. 
The two propellants 13, 15 are separated from each other by a rotationally 
symmetrical wall 17 having an L-shaped cross-section. The parting wall 17 
is arranged so that both propellants 13, 15 are in connection with a 
working space 18 in the interior of the cylinder 3. Each propellant 13, 15 
is separated, however, by a face end cover 19, 20 from the working space 
18.in the non-actuated condition of the linear actuating means 1. 
Each of the two through-openings 21, 23 at the generated surface of the 
cylinder 3 is in connection with a propellant 13 and 15, respectively, the 
housing 11 of the gas generator 9 being recessed in the region of the 
through-openings 21, 23. A common ignition unit 25 is secured by a 
clamping ring 26 to the generated surface of the cylinder 3 and primers 27 
and 29 extending from the ignition unit 25 protrude partly into the 
through-openings 21 and 23, respectively. 
The ignition unit 25 is connected via a cable 39 to an electronic activator 
31 to which in turn several sensors are connected, of which only one 
sensor 33 is illustrated. The sensors provided being a crash sensor, a 
sensor for sensing collision intensity, a sensor for sensing seat 
occupancy, a sensor for sensing the body weight of a vehicle occupant and 
a sensor for sensing the outdoor temperature. 
The activators 31 and sensors 33 provided in the case of the embodiment as 
shown in FIGS. 2 through 4 are not illustrated. 
In the case of the embodiment shown in FIG. 2 the gas generator 9' is 
slightly modified with respect to the gas generator 9 shown in FIG. 1, by 
the parting wall 17' being conically tapered within the gas generator 9' 
towards the piston. The two covers 19, 20 shown in FIG. 1 are combined to 
a common cover 34. Furthermore, the through-opening 21' is provided at the 
face end 7 and the through-opening 23 again in the generated surface of 
the cylinder 3, this being the reason why the common ignition unit 35 
extends up to the face end 7. The multi-core cable 39 connected to the 
activator 31 extends into the interior of the ignition unit 35 and is 
connected to a high-frequency choke 37, following which the cable 39 is 
branched off by individual cores leading to the primers 27, 29. The common 
high-frequency choke 37 is arranged in the common ground lead of the 
primers 27, 29. 
The embodiment shown in FIG. 3 differs from that shown in FIG. 1 by the 
ignition unit 45, which is similar to ignition unit 35 shown in FIG. 2, 
being configured as an elongated body adjoining the generated surface of 
the cylinder 3 and not standing off therefrom as is evident from FIG. 1. 
Both through-openings 21, 23 are, however, the same as in the embodiment 
shown in FIG. 1 provided in the generated surface of the cylinder 3. The 
housing 11 is closed in the regions 57, 58 of the through-openings 21, 23 
but e.g. weakened by an annular groove or by a perforation to facilitate 
breaking through the housing 11 on igniting. Furthermore, each primer 27, 
29 is surrounded by a shell 55, 56 of a pyrotechnical material for 
boosting ignition which in the embodiment shown in FIG. 3 protrudes into 
the corresponding through-opening 21, 23. 
In the case of the embodiment of the linear actuating means 1 shown in FIG. 
4, to each propellant 13, 15 is assigned its own ignition unit 49 and 51, 
respectively, each of the ignition units 49, 51 being configured as a plug 
connection. The plug connection has a projection 53 of small cross-section 
which is inserted into through-openings 21, 23 of correspondingly larger 
cross-section in the generated surface of the cylinder 3 by a press-fit. 
The functioning of the linear actuating means 1 will now be explained with 
respect to FIG. 1. When the vehicle is involved in a collision, a 
corresponding signal is applied by a crash sensor to the activator 31. The 
latter initiates, depending on whether a seat is occupied or not, 
depending on the body weight of the vehicle occupant, stature and seat 
position, activation of one or both propellants 13, 15 via the ignition 
unit 25. If the sensors sense that the linear actuating means 1 needs to 
be activated for a small, lightweight vehicle occupant, only the first 
propellant 13 is activated by the primer 27, and gas flows into the 
working space 18, the cover 19 thereby being penetrated. The cover 20 at 
the face end not destroyed by the gas pressure prevents activation of the 
propellant 15 which is not required to be ignited by the ignited 
propellant 13. In the case of only one propellant being ignited only the 
region of the cover 34 assigned to the activated propellant is destroyed 
in the embodiments shown in FIGS. 2 and 3. 
In the case of a vehicle occupant of average constitution only the second 
propellant 15 is ignited. In the case of heavy, tall vehicle occupants, 
especially when the outdoor temperature is very low, a high actuating 
capacity of the linear actuating means 1 is required so that, in a crash 
situation both, propellants 13, 15 are activated independently of each 
other, but at the same time.