EP1898438A1 - Inertia sensor without curling effect - Google Patents

Abstract

The switch (10) has a force guide (12) for a mass body (18), which is movable along a longitudinal axis of the guide between a rest position and an end position with a preset radial play. The body actuates a switch contact (22), when the body reaches the end position, where the shape of the body is a sphere and a cross-sectional shape of the guide is a polygon. The guide cross-section and the body are formed in proportion to each other, such that the body moves along an edge of the cross section parallel to a guide longitudinal axis (16), when a transverse acceleration acts on the switch.

Description

The present invention relates to a switch with a mass body, with a positive guide for the mass body, wherein the positive guide has a predetermined radial cross-sectional shape and the mass body with predetermined radial play along a longitudinal axis of the positive guide between a rest position and an end position is movable, with a retaining element for Biasing the mass body in the rest position, and with an operable by the mass body when reaching the end position switching contact.

A switch of the type mentioned above is from the document DE 195 18 824 C1 known.

More particularly, the present invention relates to switches that serve as a threshold threshold acceleration or deceleration sensor for deploying occupant protection systems in automobiles. Such switches are intended to detect a collision and / or overturning of the motor vehicle and, given a corresponding severity of the accident, trigger protective systems, for example an occupant restraint system (belt tensioner), an airbag system, a roll bar and the like. Switches for this application include a mass body which, in the event of an accident, moves relative to a vehicle-fixed reference system of the switch and actuates a switch connected to the reference system. In order for the triggering process to take place only in the event of a serious accident, the mass body is normally operated by means of a retaining device which defines a threshold value, i. with a certain bias, kept in a rest position.

The physical quantities acceleration and deceleration (= negative acceleration) are hereinafter referred to uniformly by the term "acceleration".

Many known switches of this type work on the spring-mass-action principle. In the spring-mass-action principle of the inert mass representing mass body relative to the reference system must be accelerated or persist that in the manner already mentioned, a force exerted by the spring biasing force is overcome to actuate a switching element. The energy required for this purpose is provided by the kinetic energy or the inertia of the mass of the mass body.

Such switches can actively switch the electrical ignition circuit of an actuator needed to inflate, for example, an airbag, to tighten a seatbelt, to extend a crash-active headrest or safety bar. In these arrangements, as already mentioned, in order to distinguish between a dangerous and a harmless accident, it is ensured that the protection system is activated only when a sufficiently high acceleration prevails for a predetermined minimum period of time, ie when, in fact, one for the Occupant dangerous situation exists. To detect this as quickly and safely as possible, the switches must have correspondingly short response times.

At the international level, corresponding assessment standards have been defined in the so-called NCAP test conditions. For example, the Euro-NCAP (European New Cars Assessment Program) stands for a crash test project supported by the European Commission, European governments, consumer associations and automobile clubs. The aim of the Euro-NCAP is to specify uniform test conditions. Such a crash test is in four parts: frontal crash with 64 km / h against a deformable barrier, side crash at 48 km / h also against a deformable barrier, pile tests at 30 km / h against a steel column at the level of the driver and collision with a pedestrian dummy at 40 km /H. Similar NCAP test conditions exist, for example, in the USA, Australia and Japan.

A collision usually does not take place exactly in the direction of the longitudinal axis of a motor vehicle, in particular in the case of accidents in which the motor vehicle is slammed sideways obliquely by another motor vehicle. If the direction of action of the switch in this case is parallel to the longitudinal axis of the motor vehicle, then in addition to an acceleration component in the direction of the vehicle longitudinal axis, an acceleration component transverse to the vehicle longitudinal axis additionally acts on the switch, which is referred to below as "lateral acceleration".

High lateral accelerations cause in switches of the type described above radial collisions of the mass body with the forced operation, which can lead to a slowing down of the movement of the mass body and thereby cause an undesirable ignition delay of the safety device. In the context of the present invention, it has been found for this purpose that in the case of spherical mass bodies which run in a hollow cylindrical positive guide with a radial clearance necessary for their movement, an effect occurs which can be termed the "curling effect". When a lateral acceleration occurs, the ball is namely deflected from its path in the radial direction and strikes the guide wall the positive guidance, so on the hollow cylindrical inner surface. On the one hand, this leads to impacts on opposite walls with a repetition frequency, which depends inter alia on the amplitude curve of the acting lateral acceleration and which can be in the kilohertz range. These multiple impacts result in energy loss due to the elastic deformation at each impact to a loss of kinetic energy of the ball and thus to a slowing down of the movement, ie to a life extension. On the other hand, on the other hand, that the ball performs a circular motion as a result of the shocks, which overlaps with their longitudinal movement to a helical path (curling), which is longer than the ideally linear trajectory. This curling has therefore a further significant slowdown of the ball and thus an additional term extension.

One from the document mentioned above DE 195 18 824 C1 Known switch has a cylindrical guide tube, in which a rotationally symmetrical, in particular cylindrical mass body is slidably mounted along the tube axis. The mass body is held by a tension spring in an end position of the guide tube, which corresponds to its rest position, under prestress. When the switch acts on a delay whose component in the direction of the tube axis and from the rest position exceeds a predetermined by the tension spring threshold, the mass body overcomes the retaining force of the tension spring and moves away from the rest position until it is in an opposite end position, a switching element actuated.

A disadvantage of this known switch is that due to the sliding movement of cylindrical surfaces already a relatively high friction occurs, which leads to a deceleration of the mass body. Furthermore, when a transverse acceleration occurs, the triggering may be delayed because the mass body then laterally strikes the inner wall of the guide tube as a result of the radial play required for its sliding movement in the guide tube, thereby causing a rotational movement, if not even at particularly high transverse accelerations a tilting occurs.

From the document GB 2 238 170 A another such switch is known. This switch has a spherical mass body which is movable in a cylindrical tube-shaped positive guide. In a rest position at one end of the positive guide, in which the ball is held by a coil spring, the ball pushes with its uppermost point a free end of a first contact tongue of a switching contact away from a second contact tongue, so that the switching contact always in the rest position of the mass body is open. As soon as the ball moves out of the rest position as a result of an acting acceleration, the free end of the first contact tongue slides down and lies down on the second contact tongue, with the result that the switching contact is closed. The Schalkontakt is therefore actuated immediately after the onset of movement of the ball and the further movement of the ball has no influence on the switching function. In the inner cylindrical surface of the positive guidance axially extending grooves are incorporated in this switch, which should prevent that a movement inhibiting air cushion builds up in front of the ball when the ball moves from its rest position to the end position.

In this switch is disadvantageous that, depending on the positioning of the first contact tongue on the ball even small movements of the ball lead to a response of the switching contact. In fact, the helical spring is a system with a zero-going spring characteristic, which means that each applied force causes a certain movement, with the result that even small accelerations can lead to a response of the switch. The threshold of this switch is therefore not exactly definable.

One in the document DE 41 60 691 A1 described switch also uses a spherical mass body which runs down on a channel-shaped path and whose movement is damped by a spring abutting the top of him.

In this switch, although a rotational movement of the ball is prevented when a lateral acceleration occurs, but this at the price of one through the spring blade even stronger deceleration of the ball and thus a delay of the triggering process.

The document US 4,948,929 describes another such switch, in which inter alia, a cuboid mass body is used, which runs in a rectangular tube.

As a result of this shaping, there is the risk of tilting when a lateral acceleration occurs in the case of this switch.

In the document US 4 210 789 discloses a switch with an inner guide, the mass body runs with an axially continuous thread on an axial screw body and therefore rotates when moving about the longitudinal axis.

Due to its design, this switch is not suitable for realizing short response times.

The document US Pat. No. 6,635,835 B2 Finally, describes an acceleration sensor for the same application with a cube-shaped mass body. The mass body is provided with an axial passage opening. It is slidably mounted with this passage opening on a guide rod. The through hole is circular in radial sections in embodiments of this sensor and the guide rod elliptical or triangular. In other embodiments, conversely, the passage opening in the radial section is elliptical or triangular and the guide rod is circular. There is some radial play between the passage opening and the guide bar to allow the axial sliding movement. In order to avoid that the mass body in an oblique impact of the vehicle as a result of irregular friction of the guide rod at the passage opening into rotation and rattling, is provided in this known sensor that the guide rod rests with the passage opening at two or more points.

This sensor has the disadvantage that due to the axially long guidance of the mass body on the guide rod also threatens to tilt. Even with tilt-free guidance is a sliding friction along two contact lines, which extend along the passage opening. This sliding friction is significant and contributes to the deceleration of the mass body and thus to a delay in the tripping process. Next is a disadvantage that the mass body requires an external guide, because he can otherwise rotate freely on the guide rod. However, this external guidance is also associated with friction losses.

In contrast, the invention has the object, a switch of the type mentioned in such a way that the above-mentioned disadvantages are avoided. In particular, a switch is to be created, which allows shortest response times even when acting on a lateral acceleration. This should preferably apply to delay curves, as are typical in motor vehicle accidents.

This object is achieved with a switch of the type mentioned above in that the mass body is a ball, that the cross-sectional shape of the positive guide is configured as a polygon, and that the polygon and the mass body in relation to each other are formed such that the mass body substantially moves with two points of contact along a corner of the polygon parallel to the longitudinal axis of the positive guide when a lateral acceleration acts on the switch.

The object underlying the invention is completely solved in this way.

By selecting a ball as a mass body and by forming the polygon and the ball in relation to each other in the above-mentioned manner, the number of shocks of the mass body is reduced with the wall of the positive guidance at the occurrence of a lateral acceleration, thereby preventing the curling. The otherwise three-dimensional movement of the mass body is thus focused in a corner of the polygon and converted into a substantially one-dimensional movement, wherein the one-dimensional movement is oriented along the effective direction axis of the switch.

Each corner of the polygon has two wedge-forming boundary surfaces, between which the mass body is trapped when a lateral acceleration occurs after a few reflections in the corresponding corner. The mass body then no longer rotates about the longitudinal axis of the forced operation. He only moves along the edge catching him.

In order to optimize the movement sequence of the spherical mass body in the polygonal radial guidance in the radial section, in embodiments of the invention at least two optimization variants are available, which can be used alternatively or with each other:

In a first group of embodiments, the polygon is formed as a uniform polygon and the number of corners is optimized.

This measure has the advantage that it can be determined for each individual case on the basis of tests which are easy to carry out, which number of corners is optimal, since significantly different results result for polygons with different number of corners under otherwise identical test conditions.

It is preferred if the number of corners is four.

This dimensioning has proved in practical trials for most applications over other numbers of corners than superior.

In a second group of embodiments, however, the radial clearance is optimized such that the mass body moves within a predetermined frequency range of the transverse acceleration along the positive guide in abutment at the two points of contact.

This measure has the advantage that a significant optimization to a frequency range is possible, which is typical for accidents of motor vehicles. In that regard, it must be considered as the merit of the inventor to have realized that the frequency in the acceleration spectrum, from which a detachment of the ball from its path along a corner takes place, depends on the set radial clearance. Since at frequencies which are higher than this Ablösefrequenz using the curling described above, which leads to a delay of the triggering process, so the Ablösefrequenz can be chosen by adjusting the radial clearance so that the frequencies of typical accidents happen to motor vehicles below.

dimensioniert, wobei a_t0 die Amplitude der Querbeschleunigung ist.In a practical embodiment of the aforesaid procedure in which the frequency range is from zero to a predetermined separation frequency f _c , the radial clearance S is of the formula $$\mathrm{S}\mathrm{=}{\mathrm{a}}_{\mathrm{t}\mathrm{0}}\mathrm{/}{\left(\mathrm{2}{\mathrm{\pi f}}_{\mathrm{c}}\right)}^{\mathrm{2}}$$

dimensioned, where a _{t0 is} the amplitude of the lateral acceleration.

This measure has the advantage that the radial clearance can be determined and adjusted with a simple formula.

In a preferred development, the removal frequency is in the range between 50 and 300 Hz, preferably between 100 and 200 Hz.

These are the frequency ranges of accident occurrences in which motor vehicles are involved, but of course the invention is not limited to this frequency range.

Although the invention has been presented above with reference to the application example of sensors for determining a serious accident, it is understood that it is not limited to this application. A switch of the type mentioned above can namely with advantage also as a position sensor, tilt sensor, inertial sensor, Use an acceleration sensor or as a safety switch, eg in robotics.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Fig. 1

einen Längsschnitt durch einen Schalter gemäß der vorliegenden Erfindung;

Fig. 2

in vergrößertem Maßstab eine radiale Schnittansicht von Führungsflächen des Schalters von Figur 1 in einer Ebene II-II;

Fig. 3a

in verkleinertem Maßstab eine äußerst schematisierte radiale Schnittansicht einer im Radialschnitt kreisförmigen Zwangsführung ;

Fig. 3b-3e

Darstellungen wie in Fig. 3a, jedoch für Ausführungsbeispiele der Erfindung mit im Radialschnitt vieleckigen Zwangsführung gemäß der vorliegenden Erfindung;

Fig. 4

einen Versuchsaufbau zur Ermittlung optimierter Parameter des Schalters gemäß der vorliegenden Erfindung;

Fig. 5

ein erstes Laufzeit-Frequenz-Diagramm für die vier verschiedenen Querschnittsformen der Fig. 3b-3e, das unter Verwendung einer Versuchsanordnung gemäß Fig. 4 bei einer ersten Querbeschleunigung aufgenommen wurde;

Fig. 6

ein zweites Laufzeit-Frequenz-Diagramm wie in Fig. 6, jedoch bei einer zweiten, erhöhten Querbeschleunigung; und

Fig. 7

ein drittes Laufzeit-Frequenz-Diagramm wie in Fig. 6, jedoch bei einer dritten, noch höheren Querbeschleunigung.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

Fig. 1

a longitudinal section through a switch according to the present invention;

Fig. 2

on an enlarged scale, a radial sectional view of guide surfaces of the switch of Figure 1 in a plane II-II;

Fig. 3a

on a reduced scale, an extremely schematic radial sectional view of a circular guide in a circular forced operation;

Fig. 3b-3e

Representations as in Fig. 3a, but for embodiments of the invention with in radial section polygonal forced guidance according to the present invention;

Fig. 4

a test setup for determining optimized parameters of the switch according to the present invention;

Fig. 5

a first transit time-frequency diagram for the four different cross-sectional shapes of FIGS. 3b-3e taken at a first lateral acceleration using an experimental arrangement according to FIG. 4;

Fig. 6

a second transit time-frequency diagram as in FIG. 6, but at a second, increased lateral acceleration; and

Fig. 7

a third transit time-frequency diagram as in Fig. 6, but at a third, even higher lateral acceleration.

Fig. 1 shows a sectional view through a switch or acceleration sensor 10 according to the present invention. The drawing plane of FIG. 1 lies in the x-z plane of an imaginary Cartesian coordinate system.

The switch 10 has a housing 11. In the housing 11, a tubular positive guide 12 is formed with an inner wall 14. A longitudinal axis 16 of the positive guide 12 lies in the x-z plane. A spherical mass body 18 is movably mounted in the positive guide 12 along the longitudinal axis 16. Thus, the mass body 18 can move along the positive guide 12, a predetermined radial clearance S between mass body 18 and inner wall 14 is set, which is designated in an enlarged section 19 in Fig. 1 with S. Otherwise, the representation of the guidance of the mass body 18 on the inner wall 14 is to be understood only schematically. Details will be explained below with reference to FIG.

The mass body 18 is biased in normal operation by means of a retaining device, here by means of a spring system 20 in a rest position. In Figure 1, the mass body 18 is in this rest position, in which it rests against a radial wall 21 at the left end of the forced operation 12.

In the extension of the longitudinal axis 16, a switching contact 22 is arranged on a front wall 26 of the housing 11. The switching contact 22 is actuated when the mass body 18 moves along the longitudinal axis 16, as indicated by a direction of action 24, and after passing through a certain distance on the switching contact 22 impinges.

In a practical embodiment, the spherical mass body 18 has a diameter of 7 mm and a mass of 1.4 g. The path of the mass body 18 between the rest position and the end position is 0.6 mm. The retention force of the spring system 20 is 0.016 N. The radial clearance S is set at a few 1/100 mm, as will be explained below.

It is assumed that the switch 10 is installed in a motor vehicle, such that the longitudinal axis 16 is parallel to the vehicle longitudinal axis and consequently the direction of action 24 coincides with the direction of travel of the motor vehicle when driving straight ahead. An oblique side impact on the vehicle is symbolized by an arrow 27 in FIG. The side impact causes an acceleration of the vehicle in Fig. 1 to the left, wherein the acceleration of a longitudinal component a _x and a transverse component a _t , hereinafter referred to as lateral acceleration having.

The longitudinal acceleration a _x is directed opposite to the direction of action 24. Due to the inertia of the mass of the mass body 18, this moves relative to the positive guide 12 in Fig. 1 to the right in the direction of the switching contact 22. For this, the inertial force must be greater than the biasing force of the spring system 20, which acts as a threshold. Only in a serious accident, the inertia overcomes this threshold. The mass body 18 then moves into a right end position, not shown in FIG. In this end position, the mass body 18 encounters the switch contact 22 and thus triggers a signal, which in turn is used to more activate a safety system, for example an occupant restraint system, an airbag, a roll bar or the like.

The lateral acceleration a _t does not have an immediate effect on the procedure explained above. From a physical point of view, the lateral acceleration a _{t occurs} in the time domain in a pulse shape. This pulse shape in the time domain corresponds in the frequency domain a sum of individual frequencies, which can be determined for example with a Fourier analysis from the time domain. In typical accident events of motor vehicles, these frequencies are in a range below 1,000 Hz, usually below 300 Hz.

This property of the transverse acceleration a _t has the consequence that the spherical mass body 18 during its longitudinal movement in the direction of action 24 is additionally accelerated laterally, ie in the radial direction relative to the longitudinal axis 16 of the positive guide 12. This results in inelastic multiple collisions at opposite points of the inner wall 14 and in a spin of the mass body 18. As a result, the mass body 18 is braked both by friction and energy conversion due to elastic deformation at each reflection as well as by the additional motion components. Namely, the mass body 18 moves along a helical path around the longitudinal axis 16 which is longer than the ideally straight trajectory.

This effect is referred to in the context of the present application as "curling". The curling leads to a delay in triggering the safety systems due to the slowing down of the movement of the mass body 18 and is therefore highly undesirable.

According to the invention, therefore, measures are provided to reduce this undesirable effect as much as possible.

A first, essential measure consists in providing a polygonal cross-section, preferably in the form of a regular polygon, instead of the hollow cylindrical positive guide 12, that is to say a circular radial cross section of the inner wall 14. The aim of this measure is to run the spherical mass body 18 along a corner of the polygon, so that rotation of the mass body 18 is prevented by punctiform contact of the mass body 18 at the two forming the corner straight wall sections.

FIG. 2 shows a corner 28 of a polygonal cross-section of a longitudinal guide 12 'provided according to the invention in a greatly enlarged scale in order to explain the aforementioned measure. The illustrated cross-section is a regular hexagon in which the corner 28 has an opening angle of 120 °. Of the Spherical mass body 18, which is indicated in Fig. 2 by a dashed circular arc, is in abutment with the corner 28. The ball center is designated 30. The mass body 18 contacts the corner 28 at two points 32 and 34 on the straight wall sections 14a and 14b forming the corner 28.

For the corner angle applies: $$a_n=\pi \left(1-\frac{2}{n}\right)$$

A so-called capture angle Φ _{n is} determined as follows: $${\phi }_n=\frac{2\pi }{n}$$

The trapping process for the mass body 18 in the corner 28 proceeds as follows:

The mass body 18 overcomes the retention force of the spring system 20 immediately after a severe collision of the vehicle with an oblique impact. As a result of the lateral acceleration, it first executes some uncontrolled multiple collisions at arbitrary sections of the inner wall 14 of the forced guidance 12 'and thereby becomes self-rotating, ie in the undesired state of curling. If it then impinges on one of the wedge-forming surfaces 14a or 14b at an angle within the incident cone φ _n , it is trapped by these subsequent surfaces 14a and 14b in the corner 28 by subsequent multiple reflection. The curling is interrupted.

If the direction of incidence is outside the capture cone φ _n , then the mass body 18 moves to the next (adjacent) corner (not shown) and is finally caught there. The curling is prevented at the latest in the following corner.

In any case, the mass body 18 then moves with appropriate longitudinal acceleration only along the trapping corner 28 in the direction of action 24, i. in Fig. 2 in the plane.

Ideally, with negligible lateral acceleration, the mass body 18 would only move along one of the surfaces (eg 14a or 14b) in the direction of the end position, so that the friction occurring in this case would be due to an (idealized) point contact between mass body 18 and one of the surfaces. However, as the mass body 18 according to the present invention moves along the corner 28 towards the end position, as described, two points of contact 32 and 34 occur. This increases the friction. One measure to express this friction is the so-called wedge friction coefficient μ _n . $${\mu }_n={\left(\frac{2}{1-\cos {\alpha }_n}\right)}^{\frac{1}{2}}$$

The wedge friction inhibits the movement of the mass body 18 along the corner 28, so that the travel time reduction is partially compensated by the capture of the mass body 18 in the corner 28 and thus the elimination of curling due to increased wedge friction. The dimensionless wedge friction coefficient μ _n is greater than 1 and indicates the extent to which the wedge friction outweighs the simple punctiform friction between the mass body 18 and the surface.

In order to optimize the movement sequence of the spherical mass body 18 in the polygonal radial guidance 12, two optimization measures are provided:

With a first optimization measure, the number of corners n of the polygon is selected such that the largest possible capture angles Φ _n are produced, while the wedge friction coefficient μ _{n is} as small as possible. These two prescriptions are conflicting Requirements, so that a compromise must be found by varying the number of corners.

This is illustrated in FIG. 3 on the basis of several examples.

Fig. 3a illustrates the positive guide 12a of Fig. 1 having a circular cross section. A circle is a polygon with an infinite number of vertices, so the number of vertices is n = ∞.

Figures 3b to 3e show various constraining guides 12b to 12e according to the present invention. Fig. 3b shows a hexagonal positive guide 12b, Fig. 3c shows a pentagonal positive guide 12c, Fig. 3d shows a quadrangular (square) positive guide 12d, and Fig. 3e shows a triangular constraint 12e. For simplicity, the polygons are assumed to be regular polygons, but this is not absolutely necessary.

As can already be seen from the given values for Φ and μ, the configuration of FIG. 3d with quadratic, quadratic cross-section of the forced guidance 12d with Φ ₄ = 90 ° and μ ₄ = 1. 41 represents a good compromise between these variables.

By way of example, in this preferred square positive guide 12d in FIG. 3d, the radial ball play S is shown, which of course is also present in all other embodiments.

The radial ball clearance S is, as mentioned, required so that the spherical mass body 18 can move freely along the positive guide 12 after overcoming the retention force of the spring system 20. As noted in the present invention, a second optimization measure is to adjust the radial clearance S so that the desired, curling-free movement of the mass body 18 along the corner 28 within a predetermined frequency range of lateral acceleration succeeds that which occurs in practice Frequency range corresponds. Namely, if the radial clearance is incorrectly dimensioned, then the mass body 18 detaches from the corner when the lateral acceleration a _t contains high frequency components.

In order to be able to carry out these optimization measures, tests are necessary. An experimental setup for determining the optimum corner number n and the optimal radial clearance S will now be described with reference to FIG.

FIG. 4 shows by way of example the preferred constrained guide 12d with a square cross-section. It goes without saying that test setups with the positive guides 12b, 12c and 12e according to FIGS. 3b, 3c and 3e are required for optimizing the number of corners n (not shown, but results are shown in FIGS. 5 to 7) ).

The positive guide 12d in Figure 4 is inclined according to the principle of the inclined plane by an angle α, in particular 30 °, relative to the horizontal. The mass body 18 moves due to the slope force with a longitudinal acceleration a _x , which is 0.5 g, along the longitudinal axis 16 of the forced operation 12d. The transit time of the mass body 18 is then measured with a simultaneously acting sinusoidal transverse acceleration a _t , which is impressed on the forced operation 12d at different oscillation amplitudes a _to and oscillation frequencies f by means of an excitation device (not shown).

The criticality of the external acceleration is evaluated by the ratio (a _t / a _x ) _eff . This measure quantifies the lateral acceleration a _t ratiometrically to the longitudinal acceleration a _x in a time average over the period of oscillation. The lateral acceleration a _t is subcritical if the ratio <1. It is considered critical if the measure is slightly larger than 1. The measure is supercritical for values significantly greater than 1.

In FIGS. 5 to 7, for these three cases, the characteristic number and for the forced guides 12a (circle, n = ∞), 12b (hexagon, n = 6), 12d (square, n = 4), and 12e (triangle, n = 3) the transit times of the mass body 18 in the frequency range of the transverse acceleration a _t of 10 to 1000 Hz shown.

With regard to the optimization of the number of corners n, FIGS. 5 to 7 initially show the expected result that, particularly in the case of critical and supercritical lateral acceleration a _t, the polygonal profiles provided according to the invention provide significantly shorter running times compared with the circular profile. Within the variants of the number of corners n, the forced guidance with a square cross-section (n = 4) gives optimum results in comparison to other numbers of vertices (n = 3 and n = 6).

Above a certain frequency f _c , the so-called detachment frequency, the transit times abruptly return to very low values because virtually no wall contact of the mass body 18 takes place here. The frequency range in which the curling effect is effectively suppressed, therefore, extends from 0 to this Ablußfrequenz f _c , which is typically at about 50 to 300 Hz, in particular at 100 to 200 Hz. This frequency range is typical with high amplitude proportions for real collision processes in motor vehicles.

in der a_t0 die Amplitude der Querbeschleunigung ist.In the context of the present invention, it has now been found that the detachment frequency f _c depends on the radial play S and is therefore optimized by suitable dimensioning of the radial clearance S, ie can be placed at the upper limit of the frequency range occurring in real accident occurrences of motor vehicles. This is done according to the invention at least approximately by the formula: $$\mathrm{S}\mathrm{=}{\mathrm{a}}_{\mathrm{t}\mathrm{0}}\mathrm{/}{\left(\mathrm{2}{\mathrm{\pi f}}_{\mathrm{c}}\right)}^{\mathrm{2}}.$$

where a _{t0 is} the amplitude of the lateral acceleration.

If, for example, the amplitude of the lateral acceleration a _{t0 is} assumed to be 10 times the acceleration due to gravity (10 g = 981 m / s ² ) and the detachment frequency is to be 200 Hz, then the radial clearance S results in S = 0.065 mm. At a _to = 1.5 g and f _c = 90 Hz, S = 0.046 mm.

Claims (6)

Switch (10) with a mass body (18), with a positive guide (12) for the mass body (18), wherein the positive guide has a predetermined radial cross-sectional shape and the mass body (18) with a predetermined radial play (S) along a longitudinal axis (16 ) the positive guide (12) between a rest position and an end position is movable, with a retaining element (20) for biasing the mass body (18) in the rest position, and with a from the mass body (18) when reaching the end position operable switch contact (22), characterized in that the mass body (18) is a ball, that the cross-sectional shape (36) of the positive guide (12) is configured as a polygon, and that the polygon and the mass body (18) in relation to each other are formed such that the mass body (18) moves substantially at two points of contact (32, 34) along a corner (28) of the polygon parallel to the longitudinal axis (16) of the positive guide (12) when a Que R acceleration (a _t ) on the switch (10) acts. Switch according to claim 1, characterized in that the polygon is formed as a uniform polygon and that the number (n) of the corners (28) is optimized. Switch according to claim 2, characterized in that the number (n) of the corners (28) is four. Switch according to one or more of claims 1 to 3, characterized in that the radial clearance (S) is dimensioned such that the mass body (18) within a predetermined frequency range (0 - f _c ) of the transverse acceleration (a _t ) along the Forced operation (12) moved in contact with the two points of contact (32, 34). A switch according to claim 4, characterized in that the frequency range is from zero to a predetermined separation frequency (f _c ) and that the radial clearance (S) is given by the formula $$\mathrm{S}\mathrm{=}{\mathrm{a}}_{\mathrm{t}\mathrm{0}}\mathrm{/}{\left(\mathrm{2}{\mathrm{\pi f}}_{\mathrm{c}}\right)}^{\mathrm{2}}$$

is dimensioned, where a _{t0 is} the amplitude of the lateral acceleration (a _t ). Switch according to Claim 5, characterized in that the removal frequency is in the range between 50 and 300 Hz, preferably between 100 and 200 Hz.

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