A DEVICE FOR SENSING THE POSITION OF A MOVABLE INERTIA BODY IN A VEHICLE SAFETY SYSTEM

Abstract: A device for sensing the position of a movable inertia body in a vehicule safety system comprises a radiation emitting means (20) and a radiation detecting means (21) adapted to receive at least a portion of the emitted radiation. The inertia body (23) can be either in a neutral position in which the body does not activate the safety system, or in at least one working position in which the body activates the safety system, and is adapted to influence the radiation received by the detecting means (21) depending on its position, so that the radiation received by the detecting means indicates the position of the inertia body. The radiation emitting means (20) and the radiation detecting means (21) are positioned on opposite sides of the inertia means, and the radiation can be, for example, light passing through a hole (22) in the inertia body. Due to the fact that the radiation passes through a hole in the inertia body, a reliable indication of the position of the inertia body is obtained.

Description: A device for sensing the position of a movable inertia body in a vehicle safety system Technical Field The present invention is related to a device for sens¬ ing the position of a movable inertia body in a vehicle sa¬ fety system in which the inertia body can be either in a 5 neutral position, in which the body does not activate the safety system, or in at least one working position, in which the body activates" the safety system. The device is primarily intended to be used in connection with standing, tiltable inertia bodies but can also be used in connection 10 with movable inertia bodies of other types in vehicle safe¬ ty systems. Such safety systems can comprise for example safety belts, inflatable air cushions and belt stretchers. Background Art It is previously known to sense the position of movab- 15 le inertia bodies used in locking devices for vehicle safe¬ ty belts by means of displaceable bars or pivoting arms abutting against the inertia bodies and operated by the mo¬ vements of the bodies. One example of such a device is dis¬ closed in the British Patent Specification No. 1 351 642. 20 One disadvantage of this type of sensing device is that the sensing means by its friction and mechanical inertia impe¬ des the movements of the inertia body, so that the sensiti¬ vity of the locking device is influenced and can vary with¬ in rather wide limits. A particular disadvantage in connec- 25 tion with standing, tiltable inertia means intended to give the locking device the same sensitivity irrespective of the direction of the appearing force is that said sensitivity can be lost, because the sensing means may influence the inertia body differently in different moving directions of 30 the inertia body. Furthermore, through the German Patent Specification No. 26 30 553 it is previously known to use light rays or radiation from other radiating sources to sense or detect the position or the movements of inertia bodies in locking devices for vehicle safety belts. It is particularly pre¬ viously known to use light rays that can be reflected by a surface of an inertia body, for example a pendulum, and detected by a light sensitive means. When the inertia body changes position, the output from the light sensitive means is changed, and this output is used for controlling the locking device. One disadvantage of this type of sensing device is that the light radiating means and the light detecting means must be positioned with a high degree of accuracy in relation to the reflecting surface of the iner¬ tia body to provide a reliable operation. This is particu¬ larly difficult to achieve, when the inertia body is a standing, tiltable inertia means. Disclosure of Invention The main object of the invention is to provide a sens¬ ing device for a movable inertia body in a vehicle safety system which does not influence the operation of the iner¬ tia body and which gives a strong and reliable indication signal without requiring a very high degree of accuracy in assembling the device. According to the invention, this object is achieved by giving the sensing device the featu¬ res set forth in the claims. Brief Description of Drawings The sensing device according to the invention will now be furher described below with reference to the accompany¬ ing drawings. Fig. 1 is a schematical view of one embodiment of the sensing means in the device according to the invention. Fig. 2 is an example of an electric circuit in which a sensing means according to the invention can be connec¬ ted. Best Mode for Carrying Out the Invention The sensing means shown in Fig. 1 comprises a light emitting means 20 and a light receiving means 21. The iner¬ tia body, the position of which is to be detected, is shown as a standing body 23, provided with a thin circular- cylindrical foot 23A and a thicker, upwardly tapering head portion 23B having the shape of a truncated cone. In this case, the light emitting means 20 is positioned above the inertia body 23 and the light receiving means 21 is posi- tioned below the inertia body. The inertia body is provided with a cylindrical through hole 22 running along the verti¬ cal central axis. The means 20 and 21 are so positioned that a light ray from the means 20 passes through the hole 22 in the inertia body 23 and hits the means 21, when the inertia body is in its upright position. This position is indicated with full lines in Fig. 1 and is the neutral position of the inertia body. When the vehicle is accelerated or retarded above a certain limit value, the inertia body will tilt to the position indicated with broken lines in Fig. 1, so that the light ray from the means 20 no longer can pass through the hole 22 in the inertia body and, therefore, does not hit the means 21. Thus, an indication that the inertia body has left its neutral position and that the safety system is to be activated is obtained due to the fact that the light ray from the light emitting means no longer hits the light receiving means. In the embodiment according to Fig. 1 the light emit¬ ting means 20 may be a light emitting diode and the light receiving means 21 may be a photo transistor. The embodiment shown in Fig. 1 has the advantage that no high degree of assembling accuracy is required and that a strong and reliable indication signal to the light recei¬ ving means 21 is obtained. Furthermore, in this embodiment it is possible to determine the limit value of the accele¬ ration or retardation at which the inertia body has to change position by changing the diameter of the hole 22 along a portion or the full length of the hole. Thus, it will be easy to manufacture inertia bodies having different sensibility. The embodiment has the disadvantage, however, that the light emitting means 20 and the light receiving means 21 must be mounted on either side of the inertia body, i. e. in different places in the safety system. Fig. 2 shows an example of an electric circuit in which the light emitting and light receiving means used in the embodiment according to Fig. 1 can be connected for controlling the activation of the safety system. The circuit shown in Fig. 2 comprises a solenoid 30 for enabling or disabling a control means in a safety sys¬ tem, for example a locking means in a locking device for a safety belt. The solenoid is controlled by a Darlington- transistor 31, i. e. a Darlington-connected pair of tran¬ sistors. This circuit is used to obtain a higher current amplification factor. The Darlington-transistor 31 is cont¬ rolled by the phototransistor 21 which is connected in the base circuit of the Darlington-transistor and which is controlled by the light ray from the light emitting diode 20. The circuit further comprises coupling resistors 32, 33, 34 and a diode 35, connected in parallel with the sole¬ noid to prevent high reverse voltages over the solenoid when the Darlington-transistor is switched off. The circuit has a 12 volt direct current voltage supply. When the light ray between the light emitting diode 20 and the phototransistor 21 is interrupted, the current through the phototransistor 21 decreases. The Darlington- transistor becomes non-conductive and the solenoid 30 is switched off, so that the control means in the safety sys¬ tem is connected and activates the safety system. While only one embodiment of the sensing device accor¬ ding to the invention has been described above and shown on the drawings, it is obvious that many modifications and variations are possible within the scope of the invention. The through hole must not necessarily be cylindrical and can have a cross section area that varies along the length of the hole. The hole can for example have the shape of a cone having the base turned downwardly. This will provide a better sensitivity in detecting the movements of the iner¬ tia means, as the entrance area for the light ray is small. Furthermore, a conical hole provides the advantage that the centre of gravity of the inertia means is moved upwardly. This fact makes the inertia means still more sensitive to the movements of the vehicle. A conical hole also provides the advantage that all the light passing through the ent- ranee area of the inertia means can hit the light detecting means without being reflected by the walls of the hole. If the entrance area is small and the hole is cylindrical, a large portion of the incident light will be reflected and absorbed by the walls of the hole, thus reducing the possi- • bility of the light detecting means to give a reliable indication of a change of position of the inertia means. Furthermore, the light emitting means can be positioned be¬ low the inertia body and the light detecting means above the inertia body, at least when the hole through the iner- tia body is substantially cylindrical. Alternatively, the means can be positioned horizontally on either side of the inertia body. This may be preferable in case the inertia body is a pivoting body, for example a pendulum. In stead of light rays any other type of rays can be used which can be controlled and detected, for example jets, sound waves, magnetic fields, etc. The detection and operation can also be reversed, i. e. so that the radiation passes through the hole and is detected only when the inertia body is in its working position.

Claims: Claims 1. Device for sensing the position of a movable inertia body in a vehicle safety system, in which the inertia body (23) can be either in a neutral position in which the body does not activate the safety system, or in at least one working position in which the body activates the safety system, comprising a radiation emitting means (20) and a radiation detecting means (21) adapted to be able to recei¬ ve at least a portion of the radiation, the inertia body (23) being arranged to influence the radiation received by the detecting means (21) depending on its position, so that the radiation received by the detecting means provides an indication of the position of the inertia body, characteri¬ zed in that the inertia body (23) is provided with a through hole (22) and in that the radiation emitting means (20) and the detecting means (21) are positioned on either side of the inertia body (23) in such a way that the radia¬ tion can pass through the through hole (22) for indication of the position of the inertia body. 2. Device according to claim 1, characterized in that the through hole (22) in the inertia body (23) is so arranged that the radiation passes through the hole, when the iner¬ tia body is in its neutral position, and is interrupted, when the inertia body is in its working position. 3. Device according to claim 2, the inertia body being a standing, tiltable body (23), characterized in that the two means (20,21) are positioned above and below, respectively, the inertia body (23) and that the through hole (22) runs along a vertical axis of the inertia body (23). 4. Device according to claim 3, characterized in that the through hole (22) runs along the central axis of the iner¬ tia body (23). 5. Device according to claim 4, characterized in that the through hole (22) in the inertia body (23) has a cross sec¬ tion area varying along the length of the hole. 6. Device according to claim 5, characterized in that the through hole (22) in the inertia body (23) has the shape of a cone. 7. Device according to claim 6, characterized in that the cone has the base downwardly. 8. Device according to claim 7, characterized in that the radiation emitting means (20) is positioned above the iner¬ tia body (23) .

Inventors: ANDERSSON TOMMY, ANDERSSON, TOMMY
Applicants: AUTOLIV DEV, AUTOLIV DEVELOPMENT AKTIEBOLAG
Application year: 1985
Main classification: B60R21
IPC codes: B60R21, B60R22, G01P15