FR2652906A1 - SPEED CHANGE DETECTOR WITH ADJUSTMENT SCREW. - Google Patents

Abstract

An accelerometer for operating a passenger restraint system in a motor vehicle, comprising a housing (112) with a passage defining a path of movement and an inertial member (116) moving in that path. Either a mechanical element or a magnetic element (134) can be used to bias the inertial element towards a preset position. This preset position is defined by a preset element (122) which can be set so that the accelerometer responds to collisions with a tolerance of + - 1.6 km / h. As the inertial element moves away from the preset position in a collision, it makes electrical contact with blades (118, 120) to deploy the passenger restraint system.

Description

The present invention relates to a speed change detector or

  accelerometer used in motor vehicles to detect sudden speed changes and to actuate a passenger restraint, such as an airbag, in response. More particularly, this device comprises an element which moves to a preselected position in response to a sudden deceleration to close an electrical contact, this device also having adjustment means for predetermining a position of this element in order to increase

the sensitivity of the detector.

  Studies indicate that injuries caused by motor vehicle accidents, especially at high speed, can be significantly reduced or eliminated by the use of passenger restraint systems (the term "passengers" is used to also cover the driver of the vehicle). These systems include an inflatable balloon, usually called an "air bag", which is normally stored in the dashboard or the steering wheel. When the motor vehicle is subjected to a sudden deceleration, the airbag is inflated and deploys automatically in a condition which cushions the passengers, limits their movement and prevents any contact between them and the interior of the automobile, for example - breeze, steering wheel, dashboard, etc. Of course, a crucial element of all these systems is the speed change detector or accelerometer which triggers the inflation and deployment of the airbags. The movement of the motor vehicle must be carefully and precisely controlled so that the air bags can deploy very quickly,

  before passengers could be injured.

  US Patent No. 4,329,549, issued to the present Applicant, describes a speed change detector. This detector comprises a tubular ring surrounding a metal case, a metal ball and a magnet recalling the ball in the direction of a first end of the case. Two electrical contact blades are arranged at the second end of the case. The sensor is arranged in the motor vehicle with its orientation so that when the

  vehicle decelerates beyond a predetermined level-

  mined, the ball moves from the first end towards

  tion of the second end, establishing contact with the two blades. Because the blades and the ball are made of an electrically conductive material, when the ball comes into contact with the blades, an electrical path is established between the two blades. This electrical path is used to trigger a signal for the deployment of

pneumatic cushions.

  The accuracy of the detector described in US Patent No. 4,329,549 depends on the correct alignment of the two electrical contact blades. The sensitivity, i.e. the minimum deceleration that triggers the detector, is determined by

  the strength of the magnet and the initial position of the ball.

  It has been found that, due to dimensional variations of the detector during manufacture, the detector has a tolerance of approximately 3 km / h. In practice, this tolerance is unacceptable in the industry because, if the detector triggers for a deceleration which is too low, a retaining cushion can be deployed when the vehicle is not involved in a collision (i.e. - say 13 km / h)

  and the driver risks losing control of his vehicle.

  If the sensor is set to trigger only when the vehicle experiences a very high deceleration (for example, a collision above 20 km / h), it may fail to trigger in an actual collision and would fail

  to its task of protecting passengers.

  Given the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a restraint system in which the sensitivity, i.e. the deceleration for which the passenger restraint system deploys, can be set to a

precise value.

  Another object is to provide a restraint system with a speed sensor in which a movable member has a preset initial position so as to reduce tolerances. Another object is to provide a detector which is easy and inexpensive to manufacture and in which the critical elements do not need to be manufactured with great precision since the sensitivity of the detector can be adjusted

  for each unit after assembly.

  Other objects and advantages of the invention will become apparent from

  reading the following description.

  In a first aspect, the invention provides an accelerometer for detecting speed changes, comprising a

  housing with a cavity for determining a travel path

  lied an inertial element disposed in the housing and able to move along this path between a first position and a second position, return means for returning the inertial element towards the first position, and presetting means arranged at the level of the first end and can be adjusted to modify the first position. Advantageously, the return means are constituted

  by spring means. In another embodiment, the element

  the inertial material is made of a permeable magnetic material and the return means are constituted by a magnet producing

a magnetic field.

  The presetting means consist of a presetting screw extending from the housing to the path

of the inertial element.

  According to another aspect of the invention, there is provided a passenger restraint system for protecting passengers in motor vehicles in the event of a collision, this assembly comprising a passenger restraint system arranged in the vehicle, an accelerometer arranged in the vehicle for

  operate the passenger restraint system, this accelerator

  meter being made as described above. In summary, an accelerometer produced according to the invention comprises a housing with contact blades and a contact element which establishes an electrical path between the blades when it

  has detected a deceleration above a threshold level.

  An adjustment element is also provided for presetting the position of the contact element. This presetting element is adjusted after assembly of the detector to take account of variations in its components and variations in the intensity of the field of the magnet, in case there is one. As a result, it has been found that detectors can be manufactured which can be adjusted to trigger a section of the restraint system in response to a collision resulting in a given deceleration, the detector being able to be preset with precision of

1.6 km / h.

  The invention will be better understood on reading the description.

  detailed tion, given below by way of example only, of preferred embodiments of the invention, in conjunction with the accompanying drawing in which: - Figure 1 is a side elevational view of a first accelerometer made according to the invention and arranged in a housing; - Figure 2 is a side sectional view of another embodiment of the accelerometer of Figure 1; and - Figure 3 is a cross-sectional view of a second

  accelerometer produced according to the invention.

  The detector shown in Figure 1 has a housing 12 with an interior chamber 14 in which is located

  a ball 16. Chamber 14 determines a movement path

  ment between a first end wall 24 and a second end wall 26 of the chamber 14 containing the ball 16 and a leaf spring 18 is used to return the ball towards the end wall 24 and keep it in abutment against this wall, as is see in Figure 1. The detector is arranged in a motor vehicle so that, if the vehicle collides at a predetermined minimum speed, the ball, under the influence of the deceleration resulting from the collision, overcomes the force return of the leaf spring 18 and begins to move on the path defined by the chamber 14 in the direction of the opposite end wall 26. As the ball moves on this path, it rotates the leaf spring 18. When this spring 18 strikes a second leaf 20, an electrical contact is closed and is used to produce an electrical signal and send it to a control unit to trigger a passenger restraint system, t and a pneumatic cushion

(not shown).

  An important characteristic of the invention is the presence of a pr <adjustment screw 22 screwed into the end wall 24 and passing through it, its head 28 being disposed outside the housing 12 and its proximal end 30 being in contact

  with ball 16 in the rest position, as shown

felt in figure 1.

  The response of the detector depends on a number of factors, namely the weight of the ball, the dimensions of the detector, the elastic constant of the blade 18, etc. By varying these parameters, the detector can be constructed so that it detects and responds to a predetermined deceleration. For example, the parameters can be chosen so that the detector activates the passenger restraint system when a collision is detected at a nominal speed of 16 km / h. However, due to variations in these parameters occurring during manufacture, the detector

  has a characteristic tolerance of 3 km / h. As above

  As mentioned, this tolerance may be unacceptable.

  However, it has been found that in a detector constructed in accordance with this invention, this tolerance can be reduced considerably. In particular, the rest position of the ball 16 can be adjusted with the presetting screw 22. By advancing the screw, the ball is moved slightly away from the end wall 24. By unscrewing the screw, it is moved slightly the ball 16 to bring it closer to the wall 24. In this way, it is possible to preset, with a

  precision or tolerance of 1.6 km / h, the pre-

  detector set, i.e. the speed at which a collision triggers the restraint system

passengers by the detector.

  In the embodiment of FIG. 1, the presetting screw

  22 abuts directly on the ball 16 with its end

  mite 30. In order to increase the contact area between the screw and the ball, it is possible to fix a disc 32 on the end of the screw, as seen in FIG. 2. In this way, the wear and erosion between the screw and the ball. The disc is even more efficient

  if it is rotatably attached to screw 22.

  Figure 3 shows a different type of detector 110. This detector, similar to the detector described in US Patent No. 4,329,549, has a housing 112 with an inner sleeve 114 of magnetically permeable material. The housing 112 has two opposite end walls 124,126. The wall 126 carries two blades 118, 120 which, in this configuration,

  have similar shapes and dimensions. A permanent magnet

  nent 134 is arranged outside the housing 112. The housing

  112 also contains a ball 116 having a slight diameter-

  ment lower than the sleeve 114. The ball is also made of a magnetically permeable material. The sleeve 114, the ball 116 and the magnet 134 are produced and arranged so that the magnetic field produced by the magnet returns the ball to its rest position shown in the figure

  3. When the detector is placed in a motor vehicle

  tor in such a way that, in a collision at a speed greater than a preselected value, the ball moves in the direction of the wall 126. When it comes into contact with the blades 118, 120, an electrical signal is produced by well known means in the technique. The signal is sent, for example, over conductors 136,138 to a

  passenger restraint system 140 for operating the latter.

  Furthermore, without the presetting screw 122, the detector would have a tolerance of approximately 3 km / h. This tolerance is reduced to approximately 1.6 km / h by adjusting the screw 122 to move the ball 116, ie in the direction of the wall.

  124, either in the opposite direction.

  Of course, many modifications can be made.

  tees to the invention, without departing from its scope as it

  is defined in the appended claims.

Claims (14)

Claims   1.- Accelerometer (10) for detecting changes in speed, characterized in that it comprises (a) a boot (12) with a cavity (14) to determine a movement path, (b) an inertial element (16) arranged in the housing   and being able to move along this path between a first   first position (24) and a second position, (c) return means for returning this inertial element in the direction of the first position (24) and (d) presetting means arranged at the first end and which can be   set to change the first position.   2. An accelerometer according to claim 1, characterized   in that the return means comprise a spring (18).   3.- Accelerometer according to claim 1, characterized   in that the inertial element is made of a magnetic material-   permeable and in that the return means include   a magnet (134) for producing a magnetic field.   4. Accelerometer according to claim 1, characterized in that the presetting means comprise a presetting screw (22) extending from the housing in the path of the inertial element.   5.- Accelerometer (110) for actuating a passenger restraint system in a motor vehicle, characterized in that   that it comprises: (a) a housing (112) with an internal passage   laughter defining a path of movement, (b) an inertial element disposed in the housing to move along this path (c), return means for recalling the inertial element towards a first position, (d) presetting means for defining this first position and which can be adjusted from outside the housing, and (e) contact means arranged on the path at the second position at a predetermined distance from the first position, these means contact being arranged to detect the instant when the inertial element has moved into this second position and actuate the passenger restraint system. 6. Accelerometer according to claim 5, characterized   in that the inertia element is a ball (116).   7. Accelerometer according to claim 6, characterized in that the boot (112) contains a cylindrical sleeve (114) having a diameter substantially equal to the diameter of the ball, and in that the sleeve and the ball are in one   magnetically permeable material.   8.- Accelerometer according to claim 7, characterized   in that the return means comprise a permanent magnet   nent (134) arranged and produced to produce a magnetic field tick to remind the ball.   9. Accelerometer according to claim 5, characterized   in that the return means comprise a spring.   10.- Passenger restraint assembly for protecting passengers in a motor vehicle in the event of a collision, characterized in that it comprises: (a) a passenger restraint system (140) disposed in the motor vehicle, ( b) an accelerometer (110) arranged in the motor vehicle   to operate the passenger restraint system and   both: (i) a shoemaker (112) with a passage defining a path, (ii) an inertial element (116) arranged in the housing to move along this path, (iii)   recall means for recalling the inertial element directly   tion of a first position, and (iv) means of pre-   adjustment arranged at one end of the passage and can be adjusted from outside the housing to define this first position.   11.- passenger restraint system according to claim, characterized in that the accelerometer further comprises (v) contact means (118,120) disposed at a second position distant from the first position on the path, these contact means detecting the instant when the inertial element has moved from the first position to the second position so as to then send a signal to the passenger restraint.   12.- passenger restraint assembly according to claim   , characterized in that the presetting means include   There is a screw (122) extending from the case through it. 13. Passenger restraint system according to claim, characterized in that the return means comprise a spring for pushing the inertial element towards from the first position.   14.- passenger restraint system according to claim, characterized in that the return means comprise a magnet (134) to produce a magnetic field recalling   the inertial element towards the first position.