WO1988008613A1

WO1988008613A1 - Acceleration switch

Info

Publication number: WO1988008613A1
Application number: PCT/DE1988/000233
Authority: WO
Inventors: Rudolf Hopt; Hans-Jochen Rapp; Gebhard Birkle
Original assignee: Ddm Hopt + Schuler Gmbh & Co. Kg
Priority date: 1987-04-24
Filing date: 1988-04-16
Publication date: 1988-11-03
Also published as: DE3713698C1; EP0356444A1

Abstract

An electric switch is actuated by means of an inertial mass movably accommodated in a housing by at least one spring when the acceleration exceeds a predetermined valve. For this purpose, a steel spring ribbon curved about its longitudinal axis and attached to the inertial mass (3) acts as a leaf spring (4).

Description

Acceleration switch

The invention relates to an electrical switch which contains an inertial mass which is movably held in a housing by at least one spring, by means of which the switch is actuated when the acceleration exceeds a predetermined value. Such switches, installed in motor vehicles, can, for example in the event of a motor vehicle colliding with an obstacle, close a circuit which triggers a safety device, for example an air cushion which can be inflated in front of the driver. The switching frequency of such switches is very low; on the other hand, the switching time and the switching reliability must be very high. So far, mercury switches have also been used as acceleration switches, the tube containing the mercury being mounted obliquely to the direction of acceleration. However, efforts are being made to replace mercury switches with mechanical switches wherever possible, since if these switches are thrown away the environment is polluted with considerable amounts of mercury.

From DE-PS 26 06 790 an acceleration switch has become known in which the inertial mass is held in its rest position by two intersecting spring rods. If the acceleration exceeds a predetermined value, the body serving as an inertial mass pushes the spring rods back against their pederic force until the body connects two contact loops and thus closes the circuit. These switches have a complicated structure and their production is relatively complex. Another disadvantage is that the spring force, which counteracts the movement of the inertial mass, is the smallest in the rest position of the inertial mass, but then increases very considerably up to the end point of the displacement, in which the inertial mass closes the contact. However, this leads to the fact that the speed at which the inertial body travels through the switching path becomes increasingly smaller with increasing distance from its rest position, i.e. the switching time becomes relatively long due to the decrease in the speed of movement of the inertial mass, which is very important for some applications of the switch is undesirable.

The invention is therefore based on the object of developing an easy-to-produce inertia switch, the one high switching reliability and a very short switching time.

This object is achieved according to the invention in that a steel strip acting as a leaf spring acts on the inertial mass and is curved around its longitudinal axis. Steel tapes curved around their longitudinal axis are known for their use as tape measures. They are therefore curved around their longitudinal axis in order to give the steel strip a certain stiffness after it has been pulled off the roll. These steel strips, which are curved around their longitudinal axis, are relatively stiff when an attempt is made to bend them outwards with respect to the curvature about an axis running transversely to the longitudinal axis. However, once this bend has taken place, that is to say the curvature has been removed at the kink, that is to say straightened, the steel band only provides a relatively small spring resistance to an increase in the bend. If you bend the curved steel band inwards about the aforementioned transverse axis with respect to the curvature, the resistance to this bend is considerably smaller than the resistance which arises when the steel band is bent outwards with respect to the curvature, but here, too, the resistance to further bending decreases the moment at which the curvature leveled off at the kink, and then rose again slightly when turning further. After the curvature has disappeared at the kink, the spring force counteracting the further bending of the band runs through approximately the same characteristic curve as the spring force counteracting the bending of a non-curved steel band, increasing somewhat with increasing bending, or is slightly greater than this. In any case, the spring force which occurs after the curvature has equalized at the kink point of the band is small compared to the force which is required to bend the arched band at the kink point. This effect known from measuring tapes is used in the switch according to the invention. The force with which the inertial mass is held in its rest position is relatively high. If this force threshold and thus the acceleration threshold is exceeded and the spring steel strip is kinked, the already kinked band no longer offers any significant resistance to the inertial mass, so that the inertial mass practically brakes the switching path, i.e. extremely short with high initial resistance to movement from the rest position Time switches arise.

By choosing a suitable curvature of the steel strip serving as a leaf spring, the resistance that the leaf spring opposes to the movement of the inertial mass from its rest position can be selected with the same material dimensions and material properties. This resistance can also be influenced by the distance of the kink from the clamping point.

In order to. determine at which point the leaf spring should buckle, a predetermined kink can be specified in that in one embodiment of the invention the leaf spring has a recess at this point. This recess can either be provided in the middle between the two lateral edges of the leaf spring, or else the predetermined kink can be marked by two notches recessed on the lateral edges.

The above principle cannot only be applied if the inertial body unites at the end of its movement Contact closes, which triggers another process, but also when the inertial body in its rest position closes a circuit that triggers another process when this normally closed contact is opened. In the latter case, it is advantageous that the inertial mass is retained in its rest position with a relatively high force, that is to say the normally closed contact is kept closed with high force, but the spring force drops immediately after the contact has opened, i.e. immediately after leaving the rest position no significant restoring force acts on the movable switching element when it has opened the contact. The switching reliability is very high.

If the process which is to be initiated by the switch is only triggered by closing a make contact after passing through the switching path, the switch according to the invention has the above-mentioned advantage that its switching time and also the bounce time are very short.

In one embodiment of the invention, the inertial mass is still held by a second leaf spring. This leaf spring or the inertial body are designed so that after passing through the switching path, the inertial mass comes into contact with a part forming a contact half on this second spring at a distance from the spring end which is permanently connected to the inertial mass. In this case, the second spring forms the other contact half of the working contact or else it carries a contact rivet or the like at the point at which the inertial mass lies against it. The end of the second spring is connected to the inertial mass via insulating material. This embodiment of the invention can be further developed in such a way that the position defined by the application of the inertial mass to the second spring is followed by a second distance of the inertial mass which takes place against a restoring force of the second spring. Since the second spring is fastened at one end in the housing and with its other end on the side of the contact point facing away from the spring end fastened in the housing, the inertial mass moves against this force against a force caused by the deformation the spring attached on both sides is created. This force in turn depends on the distance of the contact point from the ends of the leaf spring and on whether the leaf spring is rigidly clamped at the ends or is movably attached to one or both ends. Finally, by means of a suitable shaping of this second spring, it can be achieved that the contact-making surfaces rub against one another during the passage of this second distance and thus the safety of the contact is increased.

The switch according to the invention is not only suitable as a safety switch in the event of an impact in a motor vehicle, but also for triggering safety devices in the event of explosions or the like in which high accelerations occur.

Embodiments of the invention are shown in the drawing. Show it:

1 shows a cross section through the acceleration switch in the rest position. Figure 2 shows the switch in the working position.

3 shows a section through an embodiment of the curved leaf spring;

Fig. 4 shows a spring characteristic of the curved leaf spring;

5 shows the combined spring characteristic of the two springs;

6 shows the formation of a predetermined kink in one embodiment of the invention;

7 shows a predetermined kink in another embodiment;

Fig. 8 shows another embodiment of a spring in section along the line VIII-VIII of Fig. 1;

FIG. 9 shows the embodiment according to FIG. 8 in a representation corresponding to FIG. 1.

In the embodiment of the invention shown in the drawing, an inertial mass 3 is suspended from two standing springs 4 and 5 in a housing consisting of a housing base 1 made of insulated material and a hood-shaped upper housing part 2 such that the inertial mass 3 is in the manner of a parallelogram can be moved. The springs 4 and 5 are injected into the housing base 1 and have two soldering lugs 6 which are led out downward from the housing base 1 and which are perpendicular to the plane of the drawing in FIG. 1 and 2 are arranged one behind the other. The inertia mass 3 has on its underside a recess 7 into which a cam 8 molded onto the housing base 1 engages. The switching movement of the inertial mass 3 is limited by the contact of the side surfaces of the cam 8 on the flanks of the recess 7.

The spring 4 has a cross-section shown as an example in FIG. 3, arched about its longitudinal axis or, for example, also kinked. From a certain threshold value of an acceleration acting in the direction of arrow 9 or a deceleration acting against arrow 9, this spring kinks and releases the lateral displacement of the inertial mass 3 in the drawing to the right. The arched spring has the property that after the buckling when the threshold value of the acceleration is exceeded, it only opposes further bending or bending with an insignificantly large spring force. The spring 4 also serves as an electrical connecting element between one of the two soldering lugs 6 and the inertia mass 3. The spring 5 has no curvature, it is designed as a leaf spring, its upper end is bent and injected into a plastic part 10, which is in the vicinity of the the upper edge of the inertial mass facing away from the housing base 1 is fastened in this. The spring 5 essentially serves only to guide the inertial mass 3, its spring force is small compared to the force required to bend the spring 4.

In the rest position of the inertial mass 3 shown in FIG. 1, the spring 5 runs at a distance from the right edge of the inertial mass 3. This edge is at 11 angled back slightly. If the inertial mass 3 moves to the right in the drawing after the spring 4 has been bent, the rounded region 11 of the inertial mass 3 rests on the spring 5, as shown in FIG. 2, and therefore closes the contact between the inertial mass 3 and the spring 5. The area 11 and the corresponding contact point of the spring 5 are covered with non-corrosive contact material.

From the moment in which the area 11 bears against the spring 5, the inertial mass 3 continues to move against the resistance of the spring 5 clamped on both sides, which increases sharply with increasing distance. The area 11 is in contact with the spring 5 before the point at which the movement of the inertial mass 3 directed to the right in the drawing comes to a standstill in that the left side flank of the recess 7 in the drawing on the opposite side surface of the cam 8 Facility is coming.

Fig. 4 shows the spring characteristic of the curved spring 4, namely the restoring spring force F as a function of the deflection s. K denotes the deflection s at which the spring 4 buckles. 5 shows the overall characteristic of the two springs 4 and 5, SK denotes the deflection in which the region 11 of the inertial mass 3 bears against the spring 5.

The spring 4 has a predetermined kink 15, which is formed either according to FIG. 6 in that the spring has a central recess 16 at the point at which it is intended to buckle or, according to FIG. 7, has two notches 17 cut out on the lateral edges . In the embodiment shown in FIGS. 8 and 9, a tongue 12 is cut out in the spring 5, at the free end of which a contact rivet 13 is fastened. As shown in FIG. 9, the contact rivet 13 protrudes a little on the surface of the tongue 12 facing the inertial mass 3, so that this contact rivet comes into contact with the inertial mass 3 before the lower right corner 14 of the inertial mass in FIG. 9 3 applied to the spring 5. This results in further options for the contact pressure and the switching mechanism of the working contact formed between the contact 13 and the inertial mass 3.

The kinetic energy stored in the springs at the end of the movement of the inertial mass (see FIG. 5), after the acceleration or deceleration has ended, throws the inertial mass 3 back into its starting position shown in FIG Fig. 1 right flank of the recess 7 on the cams 8 is ended. The spring 4 springs back into its straight position, it bulges around its longitudinal axis again at your kink.

The spring 4 can be curved so that the inner surface of its curvature faces the inertial mass 3 about its longitudinal axis. However, the spring 4 can also be fastened in the housing with an opposite curvature, namely in such a way that the inner surface of the curvature lies about the longitudinal axis of the spring on the side of the spring facing away from the inertial mass 3.

The inertial mass 3 can have a recess on its side facing the spring 5, into which the spring 5 enters when the inertial mass 3 moves into its end position shown in FIG. 2.

Claims

1. Electrical switch which responds with the aid of an inertial mass held movably by at least one spring in a housing when an acceleration is greater than a predetermined value, characterized in that an inertial mass (3) attached, acting as a leaf spring (4) Steel spring band is arched around its longitudinal axis.

2. Switch according to claim 1, characterized in that the leaf spring (4) has a predetermined kink (15) which is formed by weakening the material, in particular at least one recess (16, 17) in the leaf spring (4).

3. Switch according to claim 2, characterized in that the predetermined kink (15) is formed by two recesses on the lateral edges notches (17).

4. Switch according to one of the preceding claims, characterized in that the inertial mass (3) is held by two springs (4, 5), of which the first has the curved cross section.

5. Switch according to claim 4, characterized in that the inertial mass (3) is additionally held by a second spring (5), and that the inertial mass (3) with a part forming a contact (11) on this second spring (5) comes into contact in the working position of the switch at a distance from the end of the spring (5) which is permanently connected to the inertial mass (3).

6. Switch according to claim 5, characterized in that from the position defined by the application of the inertial mass (3) to the spring (5), a second distance of the inertial mass (3) is connected, which counter to the action of the second spring (5 ) he follows.

7. Switch according to claim 5 or 6, characterized in that in the second spring (5) a tongue (12) is cut out, the end of which forms one half of a working contact, on which the inertial mass (3) comes to rest.