FR2730065A1 - ACCELEROMETER - Google Patents

Abstract

The invention relates to an accelerometer comprising a mobile sensitive mass, mounted on a support (3) and of which a given displacement trajectory forms a triggering threshold, the sensitive mass consisting of two masses (1) and (2), of which the first (1) is guided and can oscillate on the support (3), and the second (2) is mounted and can oscillate on the first (1).

Description

Accelerometer. The present invention relates to an accelerometer comprising

  a mobile sensitive mass, mounted on a support and of which a given displacement trajectory forms a triggering threshold.

  Such a mechanical accelerometer constitutes a detection system.

  inertial latching, for example for locking. Mechanical type drive systems (pressure or tension springs), pneumatic type (compressed gas)

  or hydraulic, can be unlocked by unlocking-

  ge. Unlocking occurs above a given triggering threshold, from a force exerted from the outside and transmitted to the support, for example. The trigger threshold is characterized by a given trajectory of the displacement of the sensitive mass, caused by the transmitted force. The trigger threshold is opposed to the effects of

  external forces, impulses in particular, located

  below this threshold, provoke an accelerometer response

  tre and the subsequent unlocking, for example of a locking

  full. In this regard, it must be taken into account that all

  force effects, located below the trigger threshold

  cannot elicit an accelerometer response

  be and the sensor only responds when the force effect

  rises above the above threshold.

  The invention aims to create an accelerometer of the type mentioned in the introduction, which makes it possible to obtain a behavior of

improved response.

  On an accelerometer of the type mentioned in the introduction, this objective is achieved, in accordance with the invention, by the fact that the sensitive mass consists of two masses, the first of which is guided and can oscillate on the support, and

  whose second is mounted and can oscillate on the first.

  The two masses are preferably coupled to one another so that, with an external force in the form of a pulse, transmitted via the support, a force is transmitted by the second mass displaced to the first mass, displaced from its rest position, this force

  opposing, for a given period, a return of the first

  mass in its rest position. Under the effect of several successive impulses and / or effects of forces in

  form of pulses, acting from the outside and located above

  below the triggering threshold, the first mass conti-

  naked to move from an initial position, which is already outside the rest position, when

  the arrival of the second and subsequent pulses

  so that getting the trigger

  implies the course of a trajectory of displacement, inferior

  lower than the trajectory corresponding to the trigger threshold

  due to the external force required to

reach this threshold.

  On motor vehicles in particular, pulses are exerted at the start of an accident (crash), during

  first 20 to 30 milliseconds for example, on an accelerated

  rometer provided on the vehicle, these pulses being located

  below the trigger threshold of the sensor. These impulses

  resulting from deformations on the vehicle,

  which are produced when deformable areas are pre-

  views on the latter. A force, which exceeds the threshold of

  triggering of the accelerometer, therefore acts on this

  deny it with considerable delay. Security systems,

  provided on the vehicle, in particular restraint systems

  tying, such as air bags, belt winders, or accelerator pedal safety systems, are started too late with a response too late

  of the accelerometer, so that they exercise only insufficiently

  their security function.

  But since an addition of the displacement trajectories

  cement of the sensitive mass, produced by the impulses

  initial force even below the trigger threshold

  ment, is obtained using the two masses coupled together, a considerable shortening of the accelerometer response is obtained, before the force exerted

  does not reach the trigger threshold. Individual impulses

  dual "untimely", called "misuse" in English, not produced by an accidental event and located below the triggering threshold, therefore cause no response

  of the accelerometer. But in the event of an accident, the sensor

  lays before the external force exerted reaches the threshold

above.

  Each of the two masses preferably has a degree of freedom, the degrees of freedom of the two masses being

  in a plan. A coupling of the two masses is thus preferred.

  essentially obtained, so that the addition explained above

  above the external pulses below the threshold

  trigger, which are initially exerted on the accelerated

  rometer in case of accidental event, provokes a response

sensor early.

  It is advantageous for the first mass to be part of an oscillating spring mass system, mounted on the support, and for the second mass to be produced in the form of a pendulum.

  physics, the oscillation axis of which lies at the cross

  dirty in the direction of movement of the first mass.

  Preferably, the mass-spring system of the first mass performs a linear movement. The first one

  mass then performs a parallel movement and / or transla-

tion in relation to the support.

  The displacement added to the first mass can be used to unlock a locking device, a stopper

  applying to this mass, for example.

  But it is also possible to use the displacement of the second mass to release a locking. The

  locking can then also form a limit of

placement for the second mass.

  The first mass is preferably mounted without rubbing-

  on the support by means of transverse swing arms

  saux. For support without friction, the swinging arms are preferably made in one piece with the first mass. They can be made in the form of springs (leaf springs or bars). Arms

  oscillating transverse are fixed on the support and articulated

  strips with the first mass, so that the latter can execute the preferential translational movement relative to the support. The swinging arms can be fixed in the support or be made in one piece with the latter. In a preferred form of construction, the locking has a stop lever which is applied to the first mass, along a trajectory corresponding to the triggering threshold. The stop lever is then applied to the first mass with minimal support force,

  which acts in the direction of unlocking the lock.

  Finally, it is advantageous for the bearing force to be formed by

  a driving force, blocked by the locking.

  The invention will be further detailed using the drawings anne-

  xés, which correspond to: Figure 1: a schematic representation of an example of construction of the accelerometer, Figure 2: a diagram corresponding to the force exerted in

  a vehicle on the accelerometer, in the event of an

accidentally,

  Figures 3A - E: an example of construction of the accelerometer

be coupled to a lock.

  The example of construction of an accelerometer, reproduced on

  FIG. 1 shows a first mass 1, mounted and for

  before oscillating on a support 3 by means of transverse oscillating arms 7, 8, produced in the form of

  springs. A second mass 2, produced in the form of a pen-

  physical dule, mounted on the first mass 1 with a

  possibility of pivoting around an axis of oscillation 4.

  The two masses 1 and 2 form the sensitive mass of the acces-

  Lerometer. The support 3 can be fixed to a vehicle or to another device, controlled for the effects of external forces. For support without friction of the mass 1, the transverse oscillating arms 7 and 8 are made in one piece with the mass 1. In the construction example

  shown, the swing arms 7 and 8 are also reali-

  in one piece with support 3. But it is also

  ment possible to fix the lower ends of the arms 7 and 8 in the support 3. It is also possible to provide hinges with reduced friction hinges at the transition points between the transverse oscillating arms 7 and 8 and the mass 1, c ' that is to say on the upper ends of the swinging arms. An oscillating support on the support 3 is thus provided for the mass 1. Under the effect of a force

  external, mass 1 executes a limited oscillation movement

  nary compared to support-3. In this example

  a movement of translation (parallel) back and forth.

  Furthermore, the second mass 2, produced in the form of a physical pendulum, performs an oscillation on mass 1

  rotating around axis 4. The two masses 1 and 2 present

  try different inertial forces. The degree of freedom (linear displacement) of mass 1 and the degree of freedom (rotation) of mass 2 lie in a common plane. The coupling between the two masses 1 and 2 and the different inertias means that, under the effect of an external force transmitted by the support 3, in the form of a pulse in particular, the first mass 1 performs a linear movement with respect to to the support 3 from its rest position, against the spring force exerted by the transverse oscillating arms 7 and 8, which can be produced

  in the form of leaf or bar springs, and optionally

  against the force of an additional spring, not shown

  smelled. After the effect of the impulse, the system mass-

  spring, of which mass 1 is a part, tends to return mass 1 to its rest position. But given that the accelerated movement of mass 1 gives the physical pendulum of mass 2 a consecutive pendulum movement in the same plane as the plane of movement, and that this pendulum movement, following in time, is supported on mass 1 , the mass 2 exerts a force on the mass 1 which opposes the immediate return of the mass 1 in its rest position after the impulse has faded. The amplitude of

  pendulum oscillations of mass 2 causes persistence

  tance of mass 1 in its deflection position and / or a

  delayed return movement to the initial position.

  This behavior of the accelerometer, reproduced in FIG. 1, can be used in particular when recording a

  vehicle accident (crash). This possibility will be

  core detailed using figure 2.

  When a vehicle is involved in an accident and frontal forces are exerted, iL results in a diagram

  forces on the accelerometer roughly in the form repro-

  taken by the curve of figure 2. Time, in milLisecon-

  des, for example, is plotted on the abscissa of the figure, the force and / or acceleration being plotted on the ordinate. The force and / or acceleration, corresponding to the trigger threshold of the sensor, is reproduced in phantom. At the start of the accident, the external frontal force was not exerted

  not totally, but results in relative impulses-

  low, which are below the trigger threshold

  dearly. It is only after a period of 40 to 50 millis-

  condes that the force exerted exceeds the trigger threshold

  is lying. This means that the accelerometer, if carried out in the conventional sense, does not respond until very late. A frequent recourse until then consisted in fixing at a relatively low value the triggering threshold of the sensor, but with the risk that this threshold is exceeded as a result of individual shocks, not caused by an accident, and that an erroneous "untimely triggering" "ou" misuse "in English de

the accelerometer occurs.

  O20 Under the effect of a force, such as that reproduced in FIG. 2 or of an analogous effect, the accelerometer according to the invention operates as follows: By the first pulse, the mass 1 is displaced from its rest position for a given trajectory, which has not yet reached the trigger threshold. With this

  displacement, the mass 2 is animated by a hanging movement-

  laire, during which mass 1 is subjected to a force

  who opposes his return to the rest position and / or slowed down

  tit back to rest position. When the second pulse is exerted from the outside, mass 1 is deviated from a given trajectory from its rest position, so that the still missing trajectory of mass 1 is traversed from the second pulse, to reach

  and / or exceed the trigger threshold.

  The force exerted on the mass 1 by the oscillating mass 2 is then reflected when the mass 2 oscillates in the direction,

  in which mass 1 has already been moved.

  A locking device, in particular a locking pawl, such as that still explained with the aid of the construction example of FIG. 3, is released by the displacement of the mass 1. But it is also possible to release a locking device 6 (Figure 1), or others, by the pendulum movement of the mass 2. Furthermore, the locking 6 then acts as a displacement limit for the pendulum movement of the mass 2. But it is also possible to provide on the mass 1 a stopper, which limits the movement

pendulum of mass 2.

  An example of application of the invention will be further detailed with the aid of FIGS. 3A - E. An accelerometer according to the invention, the first mass 1 and one of the two transverse oscillating arms 7, 8 of which are reproduced, is shown in Figure 3 in competition

  with a lock, produced in the form of a ratchet.

  The lock 5 engages in an ignition system of a gas generator 9. The ignition system has a striker 13, subjected to the initial tension of a percussion spring 10. The lock 5, produced in the form of

  stop pawl, engages in a recess of the striker 13.

  On the support 3 made in the form of a housing, the stop pawl has a knife support 14. The stop pawl also applies to a bearing surface 15 of the

  first mass 1 of the accelerometer. In the direction of displacement

  cement (arrow 16 in Figure 3B) of mass 1, the over-

  contact face between the bearing surface 15 and the locking device 5 has an extension, which corresponds to the trajectory of movement of the sensitive mass, forming the triggering threshold. The displacement of the mass 1 can occur against the force of an additional spring 12, which can have the function of a sensor spring. But the property of such a spring can also be conferred by the transverse oscillating arms 7, 8. The locking 5

  has the form of a stop lever, the part of which

  quet, as already described, engages in a recess of the striker 13. The striker 13 forms an element which can be driven by the percussion spring 10. The spring 10 acts as a drive spring. A closure 11, produced in the form of an adjustment screw, allows fine adjustment of the force of the spring 10. The axis of rotation of the stop lever is formed by the knife holder 14. By the force of the spring 10, the locking stop lever 5 is prestressed in a pivoting position, characterized by an arrow 17 in FIG. 3C. As a result of the high transmission ratio, the stop lever is only applied to the bearing surface 15 with minimal force (approximately 3 N). This high ratio is obtained by a short lever arm between the point of engagement of the lock 5 in the element to be driven (striker 13) and the rotary support (knife support 14) of the stop lever, and by the large lever arm between the rotary support of the lever and the support surface

  on mass 1. In the construction example shown

  tee, the supporting force is transmitted by the spring

  cussion 10, which serves as a drive spring.

  With the vehicle slowing down, greater than 5 g for example, the mass 1 begins to move in the direction of arrow 16 in FIG. 3B. This direction of movement can

  preferably match the direction of travel of the vehicle.

  Return forces in the mass-spring system, including

  is part of mass 1, can also be exercised in the

against this sense.

  During this movement, the overlap between the lock 5 and the bearing surface 15 on the mass 1 is reduced, to an amount for example, reduced relative to the

  overlap in rest position (Figure 3B). If the slowdown

  vehicle spin was caused by an impulse

  external individual, and if this impulse is located

  below the triggering threshold (figure 2), the lock

  ge 5 is not unlocked. As a result of the pendulum movement of mass 2, not visible in Figure 3, because it is located below or inside mass 1, mass 1

  stays in the overlap position for some time

  ment reduced, to finally return to its original position,

  due to elastic restoring forces.

  But if the first impulse is followed by other impulses-

  sions, as in the case of an accident, the pulse and / or the following pulses, which are still below the triggering threshold, are exerted so that the mass 1 is still displaced, from the overlap reduced u, until there is no overlap and the mass i has moved, relative to the support 3 and / or to the locking device 5, from the path corresponding to the triggering threshold. The lock 5 is then released from the bearing surface 15, and pivots around the knife support 14 in the direction of arrow 17, that is to say in the direction of unlocking the lock. The engagement of the locking pawl 5 in the element to be driven, that is to say in the striker, is then released, so that the striker is moved on the ignition system of the gas generator 9, by continuation of the driving effect of the spring 10 (figure

  3D). The gas generator 9 is thus primed (FIG. 3E).

  The spring 10 can also be used for training other elements to be driven. Spring 10 can be

  used, for example, for mechanical drive of

  elements to be moved in a vehicle, such as towing cable

  tion of a seat belt retractor, or others.

  The fuel gas from generator 9 can be used for inflating an air bag. But it can also be used as a training agent for a belt tensioner, 1 1

driven by a propellant.

Claims (14)

Claims.   1. Accelerometer comprising a mobile sentient mass, mounted on a support and of which a given movement trajectory forms a triggering threshold, characterized in that the sensitive mass consists of two masses (1, 2), the first of which (1) is guided and can oscillate on a support (3), and the second (2) of which is mounted and can oscillate on the first (1).   2. Accelerometer according to claim 1, characterized in that each of the two masses (1, 2) has a degree of freedom, the degrees of freedom of the two masses (1, 2) are situating in a plane.   3. Accelerometer according to one of claims 1 or 2,   characterized in that the first mass (1) is part of an oscillating mass-spring system, mounted on the support (3), the second mass (2) being produced in the form of a pendulum   physics, whose axis of oscillation (4) is located at the trans-   the direction of movement of the first mass (1).   4. Accelerometer according to one of claims 1 to 3,   characterized in that the two masses (1, 2) are coupled together so that, under the effect of an external force in the form of an impulse, transmitted via the support (3), a force is transmitted by the second mass (2) displaced to the first mass (1) displaced from its rest position, this force opposing the return of the   first mass (1) in its rest position.   5. Accelerometer according to one of claims 1 to 4,   characterized in that the mass-spring system of the pre-   mass (1) performs a linear movement.   6. Accelerometer according to one of claims 1 to 5,   characterized in that a lock (5) can be released   by The first mass (1) displaced.   7. Accelerometer according to one of claims 1 to 5,   characterized in that a lock [Lage (6) can be released by the second mass (2) moved. 8. Accelerometer according to claim 7, characterized in that the locking (6) forms a displacement limit of the second mass (2).   9. Accelerometer according to one of claims 1 to 6,   characterized in that the first mass (1) is mounted without friction on the support (3) by means of oscillating arms transverse (7, 8).   10. Accelerometer according to claim 9, characterized in that the transverse oscillating arms (7, 8) are made in the form of springs and are made in one piece with the first mass (1).   11. Accelerometer according to one of claims 9 or 10,   characterized in that the transverse swing arms (7, 8) are fixed in the support (3).   12. Accelerometer according to claim 7, characterized in that the lock (5) has a stop lever, which   applies to the first mass (1) along a path   roof corresponding to the trigger threshold.   13. Accelerometer according to claim 12, characterized in that the stop lever is applied to the first mass (1) by a minimal pressing force, acting in the direction of release of the lock (5).   14. Accelerometer according to claim 13, characterized   in that the supporting force is formed by an en-   dragged, blocked by the lock (5).