DEVICE FOR ACCURATE TIME CONTROL OF A LOCKING MEANS IN A VEHICLE SAFETY BELT

Abstract: In a device for accurate time control of a locking means (14) in a vehicle safety belt having an extractable band which causes a rotatably mounted shaft (10) to rotate during the extraction, the shaft is provided with a sequence of marks (21) arranged to be read by a reading head (23) during the rotation of the shaft. The shaft (10) is provided with a number of stop teeth (13) adapted to co-operate with the locking means (14) to lock the shaft, so that the band of the safety belt cannot be extracted. The reading head (23) is connected to an electric circuit (18) arranged to enable activation of the locking means (14) only at the times when the point where the locking means is to be entered into the travelling path of the stop teeth (13) is situated in a space between two stop teeth. In this way, the locking means will always be entered into a space between two teeth, so that the risk that the locking means during the entering will hit a tooth and bounce outwardly is eliminated. This will make the operation of the locking device more reliable and faster. The shaft is also provided with further marks (24) arranged to be read by a reading head (26) which is also connected to the electric circuit (18) and intended to make it possible to determine the rotary speed or acceleration of the shaft (10). The marks (21, 24) are provided on a disk (11) attached to the shaft (10) or directly on the shaft, and the electric circuit controls the locking means (14) over a control means (16) depending upon the signals from the reading heads (23, 26).

Description: Device for accurate time control of a locking means in a vehicle safety belt Technical Field The present invention is related to a device for accu¬ rate time control of a locking means in a vehicle safety belt having an extractable band which causes a rotatably mounted shaft to rotate during the extraction. The shaft is provided with a number of evenly spaced stop teeth, and the locking means is adapted to be guided into the travelling path of the stop teeth, depending upon the operation of a band or vehicle sensitive means, to come into engagement with a stop teeth of the shaft to lock the shaft, so that the band of the safety belt can not be extracted. Background Art Vehicle safety belts in which a band of the safety belt is arranged to be automatically coiled on a rotatably mounted shaft when the safety belt is not used, and to be uncoiled from the shaft when the seat belt is fastened be¬ long to the prior art. In devices of this type the shaft on which the band is coiled must be locked in case of danger, so that the safety belt can provide the person embraced by the belt with the intended protection. The locking is gene¬ rally provided by means of a tooth wheel rigidly attached to the shaft and a movable locking means arranged to be moved into the travelling path of the teeth to come into engagement with the teeth, so that the rotation of the shaft is prevented. The engagement of the locking means is then generally controlled by a band or vehicle sensitive inertia means, so that the locking is provided when the band is extracted rapidly or the vehicle is subject to a rather large change of speed or direction. In order to make the locking as efficacious and fast as possible, the lock¬ ing means must be entered into a space between two teeth of the wheel. If the locking means is entered in such a way that it comes into contact with a tooth before the locking means has reached its locking position, there is a conside¬ rable risk that the locking means will bounce outwardly, thus delaying the locking operation. If the locking means repeatedly bounces against the teeth of the wheel, the loc- king may be delayed to such an extent that the safety belt does not provide the intended protection. Therefore, it is necessary to co-ordinate the movement of the locking means with the movement of the teeth, so that the locking means always is entered into a space between two successive teeth. Many mechanical devices are known in which the move¬ ments of the locking means are synchronized. However, in these devices generally primary locking means designed to take up the forces appearing during the locking operation, and secondary locking means only intended to bring the pri- mary locking means into engagement, are used. The secondary locking means normally provide only a clutch between the rotatably mounted shaft and the primary locking means, so that the shaft, when turned in the extraction direction of the band, forces the locking means to the engagement posi- tion. The secondary locking means generally comprise a tooth wheel that can be turned on the rotatably mounted shaft and that can be actuated by a band and/or vehicle sensitive inertia means, as has been disclosed in the Swe¬ dish Patent Application No. 8206364-5. Generally, also in the secondary locking operation a locking means is used which has to be brought into engagement with a tooth of a rotating tooth wheel, and also in this case there is a risk that the locking means bounces against the teeth, so that the locking is delayed. No device for synchronization of the secondary locking is in use to-day, but several designs have been suggested. However, these designs have been dif¬ ficult or expensive to realize. Disclosure of Invention The main object of the invention is to provide a devi- ce for accurate time control of a locking means in a safety belt of the type set forth in the beginning, so that a pri¬ mary locking means can be synchronized with stop teeth on the rotatably mounted shaft in an easy way. This object is achieved according to the invention by giving the device the features set forth in the claims. Due to the fact that the rotatably mounted shaft is provided with a sequence of marks equally spaced from each other along a circle concentric with the shaft, the marks being arranged to be read by a reading head during the rotation of the shaft, it is possible to synchronize the locking means with the stop teeth of the shaft in an easy and efficacious way, so that the locking means always is entered into a space between two successive stop teeth. This will make the locking operation more reliable and fas¬ ter, so that only a minor length of band is extracted from the shaft, before the shaft is locked. This means that the safety belt will become more reliable. Due to the fact that the reading head delivers signals to an electric circuit, the locking means can be directly controlled in an electric way, so that no secondary locking is required. This means that fewer mechanical parts are required and that leads to less mechanical friction and, thus, to a more reliable ope¬ ration at fixed limit values. Due to the fact that fewer mechanical parts are required, the outer size of the device can be made smaller and the sound level can possibly be kept lower. Due to the fact that the marks are provided on the shaft or on a disk attached to the shaft, the device can also be used for sensing the rotary speed and/or the acce¬ leration of the shaft, so that the device prefarably also can be used for controlling the locking means depending upon the extraction of the band. However, in the last men¬ tioned case it is preferable to use two types of marks. Brief Description of Drawing One embodiment of the device according to the inven¬ tion will now be further described below with reference to the accompanying drawing which schematically shows a rota¬ tably mounted shaft with a disk provided with marks and a locking device for the shaft. Best Mode for Carrying Out the Invention The device shown in the Figure comprises a rotatably mounted shaft 10 upon which a band of the safety belt can be coiled automatically. The band of the safety belt and the mechanical means for the automatical coiling of the band on the shaft have been omitted, because these parts are of a conventional type and do not belong to the inven¬ tion. A control disk 11 and a tooth wheel 12 are rigidly attached to the shaft 10 and thus adapted to rotate togeth- er with the shaft, when band is extracted from or coiled on the shaft. The tooth wheel 12 is of a conventional type and is provided with a number of teeth 13 which are equally spaced from each other along the rim of the wheel. A pivo¬ ted latch 14 is positioned adjacent the tooth wheel and its tip 15 is designed to co-operate with the teeth 13 of the wheel for locking the shaft 10. The latch is controlled by means of a solenoid 16 adapted to keep the latch in a neut¬ ral position in which the tip 15 of the latch is outside the travelling path of the teeth 13 of the wheel, when cur- rent flows through the solenoid. The latch is provided with a spring 17 adapted to move the latch towards the teeth of the wheel, when no current flows through the solenoid, so that the tooth wheel 12 and, consequently, the shaft 10 are locked, when no current is supplied to the solenoid. The solenoid is controlled by means of an electric circuit 18, the operation of which will be further explained below. The electric circuit 18 is connected to a control means 19 comprising an inertia body 20 which senses the movements of the vehicle in which the safety belt is fitted and which can be either in a neutral position or in a lock¬ ing position. The vehicle sensitive inertia body 20 may be of a conventional type and adapted to control an electric contact or of the type that is shown in the copending Swe¬ dish Patent Application 8402093-2 and that is provided with optical sensing means 20A and 20B for indication of the position of the inertia body. The disk 11, which Is rigidly attached to the shaft 10 as mentioned above, is provided with a number of marks 21 which are equally spaced from each other along a circle 22 concentric with the shaft 10. The marks 21 are arranged to be read by a reading head 23, when the shaft 10 and the disk 11 rotate during the extraction of band from the shaft. The reading head 23 is positioned adjacent the tra¬ velling path of the marks and is connected to the electric circuit 18. The number of marks 21 is equal to the number of teeth 13 of the wheel 12. The marks are arranged to indicate the position of the teeth on the wheel. The disk 11 is further provided with a number of marks 24 equally spaced from each other along a circle 25 which is concentric with the shaft 10 and has a larger diameter than the circle 22. The marks are arranged to be read by a reading head 26, when the disk 11 rotates. The reading head 26 is positioned adjacent the travelling path of the marks 24 and is connected to the electric circuit 18. The marks 24 are thin and positioned close to each other along the circle 25, so that the number of marks 24 is several times larger than the number of teeth 13 on the wheel 12. Thus, several marks 24 correspond to each space between two teeth on the wheel. The number of marks 24 is a multiple of the number of teeth, so that each space between two teeth on the wheel corresponds to the same number of full marks. The marks 21 and 24 are formed by optically or magne¬ tically readable surfaces or lines. The disclosed device operates in the following way. When the band of the safety belt coiled on the shaft 10 is extracted, the disk 11 rotates, so that the marks 21 pass the reading head 23. The reading head delivers a sig¬ nal to the electric circuit 18 for each mark passing the reading head. These signals indicate the position of the teeth on the wheel in relation to the point where the latch 14 with the tip 15 enters into the travelling path of the teeth. The electric circuit 18 is designed to interrupt the supply of current to the solenoid 16, so that the spring 17 can move the latch 14 with the tip 15 Into the travelling path of the teeth 13 to lock the shaft 10 at a moment when the point of entering the latch into the travelling path of the stop teeth lies in a space between two teeth of the wheel, provided that .the vehicle sensitive inertia body is in its locking position. In this way, the activated latch will always be entered in a space between two successive teeth, so that the risk that the entering latch will hit the top of a tooth and bounce back outwardly is completely eliminated. Such a bouncing will cause a delay in the lock¬ ing of the shaft, so that a longer length of band will be uncoiled from the shaft, thus reducing the security for the person embraced by the safety belt. Also the reading head 26 will deliver signals to the electric circuit 18, when the disk 11 rotates. The reading head delivers a signal to the electric circuit for each mark 24 passing the reading head. The time interval between two successive signals from the reading head indicates the rotary speed of the shaft and is consequently a measure of the speed of extraction of the band. The difference between two successive time intervals indicates whether the band is being accelerated or retarded. The time intervals and the differences between them can easily be determined in the electric circuit 18. The circuit can be provided with electronical and logical circuits to indicate that the speed or the acceleration of the band has reached a value above a predetermined limit value and that the shaft has to be locked as rapidly as possible. The supply of current to the solenoid 16 can then be interrupted by the electric circuit, as soon as the point where the latch is to be entered into the travelling path of the teeth is situated in a space between two successive teeth. The electric circuit 18 can be designed by persons skilled in the art on the basis of given specifications and has therefore not been shown in detail on the drawwing. While only one embodiment has been described above and shown, it is obvious that many variations and modifications are possible within the scope of the invention. The syn¬ chronization marks can preferably be designed in such a way that they indicate the beginning as well as the end of a space at the point where the locking means is to be entered into the travelling path of the stop teeth. This can be achieved by two separate marks or by one mark which is so shaped that the reading head senses the beginning as well as the end of the mark. There is no need to place the marks on a separate disk attached to the shaft, and the marks may as well be placed directly on the shaft or on a separate sleeve which is then attached to the sha t. All the marks can also be positioned on the same circle, so that the same reading head can be used for reading marks of different types, i. e. synchronization marks as well as speed and acceleration marks, so that the required space is reduced. Also marks readable by non-optical or non-magnetical meth¬ ods can be used. The marks can also be arranged to be read with a lead time corresponding to the time required for activating the locking means and moving its engaging end to the travelling path of the stop teeth, so that the locking means can be entered into the travelling path of the stop teeth at any time during the whole space interval between two stop teeth.

Claims: Claims 1. Device for accurate time control of a locking means (14) in a vehicle safety belt having an extractable band which causes a rotatably mounted shaft (10) to rotate during the extraction of the band, the shaft being provided with a number of evenly spaced stop teeth (13) and the locking means (14) being adapted to be moved into the travelling path of the stop teeth depending upon the operation of a band and/or vehicle sensitive means (20) to engage with one of the stop teeth of the shaft for locking the shaft, so that the band of the safety belt can not be extracted, cha¬ racterized in that the rotatably mounted shaft (10) is pro¬ vided with a sequence of marks (21) which are equally spa¬ ced from each other along a circle (22) concentric with the shaft (10) and which are arranged to be read by a reading head (23) during the rotation of the shaft, and that an electric circuit (18) is adapted to receive signals from the reading head (23) to enable activation of the locking means only at the times when the point where the locking means is to be entered into the travelling path of the stop teeth (13) lies in a space between two stop teeth, so that the locking means (14) when activated always is entered into a space between two successive stop teeth (13). 2. Device according to claim 1, characterized in that the shaft (10) is provided with at least one mark (21) for each space between the stop teeth (13) of the shaft. 3. Device according to claim 2, characterized in that the shaft (10) for each space between the stop teeth (13) of the shaft is provided with a mark indicating when the beginning of the space passes the point where the locking means (14) is to be entered into the travelling path of the stop teeth and a mark indicating when the end of the space passes the entering point. 4. Device according to any of claims 1-3, characterized in that the marks (21) are arranged on a disk (11) rigidly attached to the rotatably mounted shaft (10). 5. Device according to any of claims 1-3, characterized in that the marks are provided on the rotatably mounted shaft. 6. Device according to claim 1, characterized in that the marks (21) are formed by areas having permanent magnetiza¬ tion. 7. Device according to claim 1, characterized in that the marks (21) are formed by areas that are optically readable. 8. Device according to claim 6 or 7, characterized in that the marks (21) have an extention along the travelling path corresponding to the space between two adjacent stop teeth (13) and that the reading head (23) is arranged to sense the beginning and the end of the marks. 9. Device according to claim 1, characterized in that the marks (21) are arranged to be read with a time lead corres¬ ponding to the time required to activate the locking means (14) and to move its engagement end (15) to the travelling path of the stop teeth (13), so that the locking means (14) can be entered into the travelling path of the stop teeth at any time during the space interval between two stop teeth (13). 10. Device according to claim 1, characterized in that the rotatably mounted shaft (10) is provided with further marks (24) arranged to be read by a reading head (26) for indica- tion of the rotary speed and/or acceleration of the rota¬ tably mounted shaft (10).

Inventors: ANDERSSON TOMMY, ANDERSSON, TOMMY
Applicants: AUTOLIV DEV, AUTOLIV DEVELOPMENT AKTIEBOLAG
Application year: 1985
Main classification: B60R22
IPC codes: B60R22