Force Sensing Device

Abstract

A force sensing device has a monolithic metal housing with a rigid upper housing part and a rigid lower housing part, which are interconnected via U-shaped spring elements while being movable in a springy manner towards each other along an axis of movement when a force is applied thereto. The spring elements are disposed symmetrically to one another relative to a cross-sectional area that runs parallel to the axis of movement. A deflection sensor is disposed between the upper and lower rigid housing parts for detecting their movement relative to one another. The unitary housing is produced in metal injection molding (MIM) technology.

Description

Advantageous embodiments of inventive devices are described in the description of the Figures given below. The Figures show:

FIG. 1 a first exemplary embodiment for an inventive force sensing device in cross-section,

FIG. 2 the force sensing device depicted in FIG. 1 in a perspective view,

FIG. 3 the force sensing device depicted in FIG. 1 in an overhead view,

FIG. 4 the force sensing device from FIG. 1 in a cross-sectional view along cross section A-A,

FIG. 5 an enlarged part view of FIG. 4

FIG. 6 a second exemplary embodiment for an inventive force sensing device shown in cross section through area A-A as in FIG. 1 and

FIG. 7 an enlarged part section from FIG. 6.

Elements which are constructed or which function in the same way are identified by the same reference symbol in all figures.

FIG. 1 shows an advantageous embodiment of an inventive force sensing device 1, consisting of a monolithic housing 2 produced in Metal Injection Molding (MIM) technology. The housing has a top housing part 25 and a bottom housing part 26, embodied as rigid parts by comparison with the U-shaped spring elements 21 and 22 joining these two housing parts 25, 26 and so that the two rigid housing parts 25 and 26, although they can move towards each other and away from each other under the influence of a weight force, ideally do not themselves deform. A deflection sensor 6 is mounted between the two rigid housing parts 25 and 26, which detects a relative movement of the two housing parts 25, 26 in relation to one another and can convert this into an electrical signal, which is fed via a cable connection not shown via a connector 5 to an electronic evaluation unit or is further processed in the evaluation electronics in the connector 5. This signal is also supplied to an occupant protection device not shown in the diagram and is available there as information about the weight acting on the force sensing device 1, on the basis of which the triggering of an occupant restraint means is adapted if necessary.

In the interests of the desired low mechanical stresses in the housing 22 mentioned at the start, even if a force is acting on it, which is applied by a means of introducing a force 3 from a vehicle seat onto the top rigid housing part 25 and thereby onto the force sensing device 1, the arms of the two spring elements 22 and 21 form an acute angle α.

Furthermore in the interests of a largely even distribution of the stress in the overall housing 2 of the force sensing device 1 each of the spring elements tapers, starting from the top rigid housing part 25 continuously until it reaches a narrowest wall thickness at the beginning of the bend to the U-section. From this point onwards the wall thickness increases again around the bending point of the U-section, reduces again after the bending point and remains constant until the transition into the bottom rigid housing part 26. Since the cross-section A-A represents a plane of symmetry of the spring element, the passage of the wall thickness d along the spring element is the same as that of the spring element 22.

Furthermore the housing 1 shown features, as two integrated components behind each of the two spring bends 21 and 22 shown, an attachment bracket 4 in each case, with the aid of which the force sensing device 1 is connected rigidly in its installed state via two screws 7 to the vehicle chassis. Instead of screws, other means of attachment can also be used, for example rivets or similar.

FIG. 2 shows a perspective view of the force sensing device depicted in FIG. 1. It can be seen that behind the two attachment means 4 with the associated screws 7 there is a further pair of U-shaped spring elements 24 and 25 arranged symmetrically around the two rigid housing parts 25 and 26. This diagram shows particularly clearly how, with the aid of the option of a very filigree embodiment of the housing 2 in MIM technology, the four spring bends shown 21, 22, 23, 24 can be produced narrow enough for the attachment points of the force sensing device 1 to be arranged within the same surface area, which is occupied by the entire housing 2 including spring elements 21, 22, 23 and 24. This surface area is shown once again in FIG. 3 in an overhead view.

FIG. 4 shows a cross-section through the housing 2 of the force sensing device 1 already shown, along cross-section A-A of FIG. 1. The method of operation of the additional overload protection elements 8, 9 will be explained with reference to this cross-sectional diagram, said elements having already been shown in the two FIGS. 2 and 3 in the overhead view of the housing 2. The two overload protection elements 8, 9 are fixed to the top rigid housing part 25, for example by means of a screw connection.

In the direction towards the bottom rigid housing part 26, the diameter of each of the two overload protection elements 8 and 9 increases in steps. The two overload protection elements 8, 9 are each spaced from the bottom rigid housing part 26 by a narrow air gap which remains approximately the same.

To clarify the geometrical design of the two overload protection elements 8, 9, an area of the force sensing device 1 highlighted in FIG. 4 by a black outline is enlarged in FIG. 5.

The two overload protection elements 8 and 9 emerge from the housing 2 as soon as a force acts via the force introduction means 3 in the direction of the bottom rigid housing part 26. A further deflection of the two rigid housing parts 25 and 26 towards one another for a further increase in the force exerted is only prevented if the two overload protection elements 8 and 9 have emerged far enough out of the housing 2 to form a close fit with the motor vehicle chassis.

With a force acting in the reverse direction, the two rigid housing parts 25 and 26 are deflected towards each other, provided the gap between the bottom rigid housing part 26 and the step in each of the two overload protection elements 8, 9 is closed.

FIG. 6 shows a further advantageous embodiment of an inventive force sensing device 1 in a diagram similar to FIG. 1 in cross-section. Unlike in FIG. 1, the top force introduction means 3 is not embodied as a screw with an external thread; instead the top rigid housing part 25 has an internal thread into which the screw is screwed, which is also routed above the top rigid housing part 25 through a cutout of the vehicle seat 10 or of a part rigidly connected with the vehicle seat. In this way the force sensing device 1 is rigidly connected to the vehicle seat 10.

In a further difference from the diagram in FIG. 1, a cross section through one of the two attachment screws 7 is shown. The screw 7 shown in the cross-sectional diagram appears from its highlighted presentation in cross-section to lie in front of spring bend 21; it is however actually arranged behind this bend 21, similar to the other attachment screw 7 shown behind the spring bend 22.

To facilitate understanding of the mechanical design and the subsequent explanation of the advantages produced by this mechanical design, the section through the screw 7 in FIG. 7 is enlarged once again.

A force sensing device 1 in the installed state is shown, meaning that in the present case: Two screws 7 are inserted from the direction of the top rigid housing part 25 through cutouts in the bottom rigid housing part 26 and are screwed to the motor vehicle chassis with their screw thread on the side of the force sensing device 1 facing away from the vehicle seat. In this case, in the exemplary embodiment shown, there is a close-fitting contact surface of a partial area of the screw 7 with the corresponding attachment brackets 4, which are a component of the bottom rigid housing part 26. Instead of a close-fitting contact surface, one or more mechanical stops points can also serve for example to allow a rigid attachment of the force sensing device.

The top rigid housing part 25 rests in the installed state of the force sensing device 1 on neither one nor the other attachment means 7 shown, but is held under a force effect to allow movement against the lower rigid housing part 26. As soon as a compression force in the direction of the vehicle chassis or a tension force in the opposite direction (along the movement axis 60) acts on the force sensing device 1 the two housing parts 25 and 26 consequently move towards each other or away from each other from their rest position.

In the advantageous embodiment of the invention in accordance with FIG. 6 a partial area 25′ of the top rigid housing part 25 engages below the head of screw 7, so that the partial area 25′ is arranged between the screw head of the screw 7 and the bottom rigid housing part 26. On the one hand this causes a gap a to be produced in the direction of movement 60 between the screw head of the screw 7 and partial area 25′ engaging below it; On the other hand a further gap b is produced between the underlying partial area 25′ and the bottom rigid housing part 26; thirdly a further gap (not indicated) is produced perpendicular to the movement axis 60 between the screw and the partial area 25′.

This arrangement of the partial area 25′ enables force to be applied to the force sensing device 1 in the direction of the movement axis 60 on the one hand until such time as the gap b closes through the deflection of the top rigid housing part 25. This creates a mechanical stop in this direction of deflection which prevents a mechanical overextension of the force sensing device 1. On the other hand a mechanical overload with an extension of the force sensing device 1 directed in the opposite direction is prevented by a mechanical stop of the partial area 25′ on the bottom rigid housing part 26, whereby the gap a is closed. The mechanical stop surface shown here could also be reduced to only one stop point if this appears expedient.

The arrangement of the underlying partial area 25′ in relation to the screw 7 has only been explained as an example with reference to the screw 7 shown in the part cross-section depicted in FIGS. 6 and 7. In the example shown in FIG. 6 there is an arrangement similar to this of a further partial area of the top rigid housing part 25 and a second screw 7 symmetrical to the movement direction axis 60. Such a symmetrical arrangement is to be preferred, since it means that the compression or tension forces act symmetrically on the force sensing device 1. In principle the symmetrical arrangement is consequently to be preferred, however an unsymmetrical arrangement could be selected which has functionally the same effect as the overload protection depicted in FIG. 6.

Claims

1-7. (canceled)

8. A force sensing device, comprising: a metal-injection molded, monolithic metal housing formed with a rigid upper housing part, a rigid lower housing part, and U-shaped spring elements interconnecting said upper and lower housing parts and allowing said upper and lower housing parts to move in a springy manner towards each other along an axis of movement when a force is applied thereto;said spring elements being disposed symmetrically to one another relative to a cross-sectional area extending parallel to said axis of movement; anda deflection sensor disposed between said upper and lower housing parts for detecting a relative movement therebetween.

9. The force sensing device according to claim 8, wherein each of said U-shaped spring elements is formed with legs enclosing an acute angle.

10. The force sensing device according to claim 8, wherein said spring elements have a defined wall thickness initially decreasing from a start at said rigid upper housing part, and once more increasing towards an apex of said spring element.

11. The force sensing device according to claim 8, wherein said lower housing part includes at least one attachment bracket for rigidly attaching the force sensing device to a chassis of a motor vehicle.

12. The force sensing device according to claim 11, wherein said attachment bracket is formed to be bolted to the motor vehicle chassis.

13. The force sensing device according to claim 8, wherein said housing includes at least four U-shaped spring elements, with two said spring elements projecting in a common direction from said cross-sectional area in each case.

14. The force sensing device according to claim 13, wherein said lower housing part includes two attachment brackets, respectively disposed between two said spring elements, for rigidly attaching the force sensing device to a chassis of a motor vehicle

15. The force sensing device according to claim 11, wherein said upper housing part is formed with a flange engaging below attachment means attaching said lower housing part to the motor vehicle chassis, such that, with said lower housing part rigidly connected to the motor vehicle chassis and a suitably large tension force acting on said upper housing part, a deflection of said upper and lower housing parts relative to one another is limited.