Inertial reel assembly for a safety belt

An inertial reel assembly for use with a safety belt. The reel assembly includes a spindle portion rotatably mounted within a housing for take up and pay out of the safety belt. The spindle is formed with plurality of teeth which engage and lock with the plurality of teeth formed within the interior of the housing. The spindle is mounted to move along an arc passing through its center point so that the spindle teeth may lock with the housing teeth. The housing teeth may include a flat section formed at the tips of the housing teeth for preventing the engagement of the spindle teeth with corresponding housing teeth when the spindle teeth are angularly misaligned with respect to the housing teeth.

BACKGROUND OF THE INVENTION 
FIELD OF THE INVENTION 
The invention relates to an inertial reel assembly for a safety belt with a 
rotatably mounted spindle for taking up and paying out the belt which is 
to be drawn out against the force of a spring, comprising at least one 
sensor device, which responds to a rate of vehicle deceleration above a 
certain value, the spindle preferably bearing teeth at both ends and 
performing a translatory or pivotal movement for locking so that the 
spindle teeth engage housing teeth. 
SUMMARY OF THE INVENTION 
Such a safety belt inertial reel assembly is for instance described in the 
German patent publication 3,418,378 A. Tn the case of this known inertial 
reel assembly the base plate of the mechanism is permanently attached to a 
limb of a frame. A journal serves as a pivot for an operating disk. The 
spindle, which is supported in this operating disk, is furthermore 
permanently connected with an operating wheel. If now one of the sensors 
provided is triggered, the operating wheel is latched to the operating 
disk by a pawl. If more belt is paid out, the operating disk will now turn 
with the spindle about the journal and the teeth on the spindle will come 
into engagement with the housing teeth in the limbs of the frame. In the 
case of this known belt take up assembly, angular alignment during 
engagement movement with respect to the teeth connected with the housing 
is ensured owing to the locked state of the operating wheel in relation to 
the operating disk. 
In use it may happen that shortly before an accident the operating wheel is 
in a position in which triggering of a sensor would mean that the 
corresponding pawl would so drop onto the back of a tooth and so engage 
the operating wheel that the spindle has to turn through one tooth pitch 
before the operating wheel is locked. In the case of a sudden, jerked 
paying out of belt as occurs in the case of a crash, the great inertia of 
the spindle will mean that the spindle will be more rapidly jerked upwards 
so than it is turned the corresponding amount. The consequence is angular 
misalignment during engagement with the housing teeth. In this respect it 
may happen that the spindle teeth are not completely in alignment with the 
teeth connected with the housing and in an extreme case, although the 
known reel just keeps to requirements, it only does so marginally. 
Therefore the object of the invention is to achieve a complete overlap of 
the spindle teeth with the housing teeth even in this extreme case of 
angular misalignment of the spindle and thus to provide for the 
transmission of a great force. 
This object is achieved since the housing teeth have flats, which prevent a 
coming into engagement of the spindle teeth in the angularly misaligned 
state. In accordance with a preferred embodiment of the invention the 
spindle is so supported that on coming into engagement with the housing 
teeth it pivots about a point fixed in relation to the housing, which is 
on a circle about the center point of the spindle in its inactive position 
and having a radius equal to the pitch circle diameter. In the case of a 
positioning of the housing teeth wherein the center of the housing teeth 
is located on a line drawn through the center point of the spindle in its 
engaged position, which line itself is perpendicular to the line 
connecting this center point with the pivot point of the spindle, it is 
possible for the part, which bears the teeth, to be largest so that the 
force may best be transmitted from the spindle to the sheet metal frame. 
The first tooth of the set of housing teeth has to be so positioned that 
the spindle is able to turn without obstruction in its neutral condition 
and even in the case of a minimum pivoting angle does not immediately come 
into engagement with the housing teeth. The last housing tooth has to be 
so arranged that the spindle is still able to swing freely into and out of 
engagement. The first third of the housing teeth has a flat. If the 
spindle is jerked upwards in the angularly misaligned state, the spindle 
teeth will land on the flats of the housing teeth and engagement is 
prevented. Were it not for these flats in accordance with the invention 
the spindle would engage even starting from this angularly misaligned 
state and the load would only be transmitted to the last housing teeth. In 
the case of a very high load this may lead to stripping of the last teeth 
and thus to the spindle slipping. However on the other hand in the case of 
the teeth in accordance with the invention the spindle is prevented by the 
flats from making misaligned engagement. In the case of further paying off 
of the belt the spindle teeth will slide so far onto the flats of the 
housing teeth that an angularly aligned position is reached. In order in 
this case as well to prevent the spindle from hooking onto the last 
housing teeth, these teeth as well have flats. When the angularly aligned 
position is reached and the spindle is still under load, it will come into 
complete engagement. The force may now be transmitted over the entire 
teeth from the spindle to the sheet metal frame. 
It is an advantage if the spindle teeth are so designed that they also have 
flats, which are aligned with tip circle of the spindle. This makes it 
possible to effect better sliding on the flats of the housing teeth. This 
is also the possibility of making the angle of the housing teeth smaller 
than the corresponding angle of the housing teeth. This means that during 
engagement there will be some play between the two sets of teeth so that 
the time, which is available for the engagement of the teeth, is 
prolonged. In the case of a particularly advantageous design in accordance 
with the invention the housing teeth are offset by half the tooth pitch on 
the two sides of the sheet metal frame. The sheet metal frame is so 
designed that the teeth or the entire limb may readily deform under toad. 
When, as normally the case, the spindle is lifted at both ends, it will 
come into complete engagement at that end, at which its teeth are nearest 
to the aligned position. On further tension the sheet metal frame or the 
teeth will deform to such an extent that the other end will come into the 
aligned position and will also engage. If however the spindle is unevenly 
lifted, for instance owing to oblique pull on the belt, so that it will 
engage first at one end, in the case of a symmetrical arrangement of the 
housing teeth the spindle teeth on the end with the lag would already be 
past their aligned position and the end with the lead would have to be 
deformed by an entire tooth pitch before the second end could engage. 
Owing to the offset by half the tooth pitch there will be--even in the 
limiting extreme--a deformation by one half of the tooth pitch takes 
place. Therefore engagement at both ends to completely transmit the load 
is ensured.

DESCRIPTION OF THE DRAWINGS 
FIG. 1 serves to show an inertial reel assembly in which a spindle, 20 for 
a coil of safety (not shown) belt is supported for rotation against the 
force of a spring 22 about the pivot point 1. A spindle disk 2 is locked 
in rotation with the spindle 20 and it bears spindle teeth 3. A cutout 5 
is provided in the sheet metal frame or housing 4 having a backwall 4a to 
receive the disk 2 with the teeth 3 thereof so that it may freely rotate 
about its axis 6 in the neutral position. The back wall 4a of the housing 
is at least partially cut away to form limbs 24 and at least one sensor 
device 26 which responds to a rate of deceleration above a certain value 
is cooperatively connected to the assembly in a conventional manner to 
activate the assembly. The teeth 7 of the housing 4 are of conventional 
design. If now the spindle is pivoted with angular misalignment towards 
its locked position it is possible for the condition illustrated in FIG. 1 
to arise. In the part A of the teeth 7 on the housing the spindle teeth 3 
have already moved past the tooth tips. In the part B of the housing teeth 
7, on the other hand, the spindle teeth 3 have not yet reached the tips of 
the housing teeth so that at this instant there is merely one engagement 
at the housing tooth 8. When further safety belt is paid out, which 
compels further movement in the engagement direction of the spindle, the 
spindle tooth 8 will deform to such an extent that in an extreme case the 
two following teeth will engage with the spindle teeth. If now a very high 
load occurs, which is not able to be resisted by the teeth which are in 
the engaged condition, the first thing to happen is that the tooth 8 will 
be stripped. Although then the next tooth will come into engagement with 
the spindle teeth, the load will however only be transmitted by three of 
the housing teeth 7 at the most. As a result of this the teeth on the 
housing will be stripped off one after the other and the spindle not be 
held. 
In the figures the teeth arrangement in accordance with the invention is 
illustrated taking into account the same functional principle as in FIG. 
1. In FIG. 2 the neutral position of the spindle is illustrated. The 
spindle disk 2, which bears the spindle teeth 3', is able to freely rotate 
about its axis 6 when the belt is paid out and taken up. The teeth 11 
through 14 of the housing are in this case provided with flats 15. 
Furthermore each of the spindle teeth 3' are provided with flats 16, the 
flats 16 themselves tangentially aligned with a tip circle 10 radially 
defined from spindle axis 6 to the flats 16 at the tip of each of the 
spindle teeth. 
In FIG. 3 the spindle is shown jerked upwards in the angularly misaligned 
position. In this case it has been pivoted along the circular path 9 about 
the point 1 till the flats 16 of the spindle teeth 3' engage the flats 15 
of the housing teeth 11 and 12. The flats 15 are exactly on the tip circle 
10 shown in broken lines of the spindle teeth 3' in this position. 
Therefore the spindle is prevented from pivoting further about the point 
1. Furthermore the teeth 13 and 14, past which the spindle teeth have not 
yet moved in the illustrated position, are provided with a flat 15 so that 
in this case it is not yet possible for the teeth to engage. The exact 
form of the flat 15 on the teeth 13 and 14 will be seen from FIG. 4. The 
spindle has in this case been further turned to such an extent that the 
part of the spindle teeth, which in FIG. 3 is adjacent to the flats of the 
teeth 11 and 12, has already run past the same and it is possible for the 
spindle to pivot further along the path 9 a small distance. The flats 15 
of the teeth 13 and 14 will now be on the tip circle 10' shown in broken 
lines, of the spindle in this position. On further rotation of the spindle 
in FIG. 5 these flats 15 of the housing teeth 13, 14 are passed by the 
spindle teeth and the spindle will reach its angularly aligned position. 
It is now possible for the spindle to pivot further about the point 1 in 
FIG. 6 for complete engagement with the housing teeth 7'. 
In this condition the load, which acts on the spindle, will be transmitted 
by all teeth to the sheet metal frame. The flanks transmitting the load of 
the spindle and housing teeth are slightly undercut to an angle in a range 
of about 0.degree. to 15.degree. on their locking flanks as shown in FIG. 
6 by numeral 28 in order to prevent the spindle teeth being forced by a 
very high load out of engagement with the housing teeth and on the other 
hand to ensure that on pivoting into the engagement position the spindle 
teeth reliably come into engagement with the housing teeth.