GB2315665A

GB2315665A - Collision detection device

Info

Publication number: GB2315665A
Application number: GB9715757A
Authority: GB
Inventors: Takashi Inoue; Sadayuki Kuwahara; Seiichi Narita
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 1996-07-31
Filing date: 1997-07-28
Publication date: 1998-02-11
Anticipated expiration: 2017-07-28
Also published as: GB2315665A8; GB2315665B; GB9715757D0; DE19733172B8; JPH1097823A; DE19733172B4; JP3728876B2; DE19733172A1

Abstract

A collision detection device (100) designed to have arbitrary operational characteristics has a weight (3), which consists of an eccentric mass (32) which determines the eccentric mass moment of the weight and a metallic plate (31) which determines the moment of inertia of the weight without varying the eccentric mass moment. The weight is pivoted by a shaft (2) at a position eccentric from the mass barycenter to have a prescribed swing velocity and frequency response. A rotor (6) having a first and second cams (61, 62) is fixed to the weight, and leaf springs (4, 5) having contacts (41, 51) are provided to stand on a base (8), with their ends exerting a resilient force to the cams. The weight is pressed by the springs in the b-direction to come in contact with the inner wall of a housing (7). When the acceleration caused by the impact of collision acts on the weight in the A-direction, it swings in the a-direction against the spring force, and bounces on a stopper (16) to swing back in the b-direction. The rotor which swings together with the weight causes the contacts on the springs to close at a certain swing angle, producing a collision detection signal.

Description

2315665 COLLISION DETECTION DEVICE HAVING ECCENTRIC MASS AND INERTIAL MASS

The present invention relates to a collision detection device which is designed to detect collision of a moving body based on the detection of acceleration above a certain level acting on the device. This collision detection device is used, for example, to trigger the activation timing device of the air bag system or seat belt tensioner which protects passengers in the vehicle in the event of collision.

Among conventional mechanical-type collision detection devices used for activating air bags, there is known a vehicle collision detection device described in Japanese patent publication JP-A 8-264088, which includes a pendulum (termed as "weight" hereinafter) pivoted at a position eccentric from its mass barycenter so that it swings in response to the acceleration above a certain level actiang on it in a certain direction, and a cam rotor which turns together with the weight operates to close associated electrical contacts, thereby producing a collision detection signal.

This collision detection device is designed to exert a force of a leaf spring to the weight against the swing motion caused by the impact of collision thereby to establish the threshold of detection and preclude the weight from swinging when the vehicle does not actually collide, thereby preventing the erroneous detection. A stopper is provided on the path of swing motion of the weight so that the swing motion at the impact of collision is limited thereby.

The above-mentioned mechanical-type collision detection device is mainly used as a redundant safety sensor to back up an active electronic acceleration sensor, and in this case it is-designed to have a weight of a large eccentric mass moment and a small moment of inertia enough to swing at the incident of collision.

However, the conventional collision detection device of the abovementioned structure may not meet the demand satisfactorily in some cases. For example, in case the collision detection device is installed in the vehicle crash zone or used to detect the incident of side collision, the weight with a large eccentric mass moment and small moment of inertia will have a large swing velocity and thus have a large bouncing force by undergoing the impact of high-frequency, large-amplitude acceleration when it hits the stopper. The resulting reciprocating motion of the weight induces the chattering of electric contacts and produces an unstable pulsative collision detection signal.

Particularly, in an air bag system where a collision detection signal is subjected to logical-product gating with other sensor signals in triggering an inflator, the unstable collision detection signal can possibly fail to inflate the air bag.

In order to preclude the reciprocating motion of the weight when it undergoes the impact of high-frequency, large-amplitude acceleration, it must be designed to have a large moment of inertia which depends on its shape. The amplitude and frequency of acceleration caused by the impact of collision varies depending on the type of vehicle, device installation location, and direction of collision. Therefore, in order to provide a proper moment of inertia for the weight to meet individual functional conditions, it needs to be designed on a trial-and-error basis, resulting in a high manufacturing cost.

Accordingly, an object of the present invention is to provide a collision detection device which enables easy setting of the moment of inertia of a weight without varying an eccentric mass moment so that a stable collision detection signal is produced under various operational conditions including vehicle types, device installation locations, and collision sensing directions, the optimal design of the weight is made easy, and the manufacturing cost is reduced.

A collision detection device of the invention includes a weight which is pivoted at a position eccentric from its mass barycenter so that it swings in response to an acceleration above a certain level acting on it, with the conduction state of contacts being varied by the swing motion, thereby producing a collision detection signal. The collision detection device is based on the scheme of providing an intended moment of inertia for the weight without varying the eccentric mass moment, thereby determining the swing velocity and frequency response of the weight arbitrarily while retaining the threshold of detection.

In order to achieve the above objective, a collision detection device of the present invention includes a weight which consists of an eccentric section and an inertial section, with the eccentric section having a swing axis eccentric from its mass barycenter and functioning to determine th e eccentric mass moment of the weight. The inertial section which swings together with the eccentric section functions to determine the moment of inertia about the swing shaft of the weight without varying the eccentric mass moment of the weight. Accordingly, it is possible to determine an intended moment of inertia of the weight without varying the eccentric mass moment and thus determine the swing characteristics of the weight arbitrarily while retaining the threshold of detection. By providing a large moment of inertia for the weight so as to be suited for a crash sensor and for the detection of side collision, for example, in which cases the impact of high-frequency, large-amplitude acceleration acts on the device, the swing velocity of the weight can be made smaller, the bouncing force of the weight produced when it hits the swing limiting member can be made smaller, and the reciprocating motion of the weight between the swing limiting members can be suppressed, whereby the chattering of contacts can be prevented and a stable collision detection signal can be produced. Based on the alteration of only the moment of inertia of the inertial section, the weight has its moment of inertia adjusted easily at the time of prototype manufacturing to meet various operational conditions including the use for an active crash sensor or backup safety sensor, type of vehicle, device installation location, and collision sensitive direction, instead of having to alter the weight design to meet individual conditions, whereby the manufacturing cost of the collision detection device can be reduced.

Preferably, the inertial section of the weight has a larger specific gravity than the eccentric section, thereby being capable of readily performing an active crash sensor. The weight can have a smaller inertial section, and a compact collision detection device can be accomplished. More preferably, the eccentric section is made of resin and the inertial section is made of metal.

Preferably, the inertial section has its moment of inertia to, determine the moment of inertia of the weight, thereby allowing the arbitrary setting of the frequency response to the acceleration of the weight adapted to each operational condition. more preferably, the the weight has its moment of inertia to determine the lower limit of the period of acceleration at which the conduction state of the contacts is varied, thereby precluding the weight from swinging by undergoing the acceleration below a certain period.

Preferably, the inertial section is made or shaped to determine the moment of inertia thereof about the swing shaft, thereby allowing the arbitrary setting of the moment of inertia of the whole weight. More preferably, the inertial section has a shape of plate and with its span, thickness or specific gravity to allow the easy and arbitrary setting of the moment of inertia of the weight. More preferably, the inertial section has a shape of disc so as to achieve the largest moment of inertia at smallest dimensions, thereby contributing to the compact design of the.collision detection device.

Preferably, the inertial section is insert- molded with the eccentric section made of resin, thereby accomplishing a steady mechanical connection of the eccentric and inertial sections to complete the weight.

Preferably, the inertial section and the eccentric section are separate parts, and the inertial section is fixed to a swing shaft which swings together with the eccentric section so that the inertial section swings together with the eccentric section.

other objects, features and advantages of the present invention will be made more apparent by the following detailed description with reference to the accompanying drawings, in which:

Figs. l(a) and 1(b) are cross-sectional views showing internal structures of a collision detection device according to an embodiment of this invention; Fig. 2 is an exploded view showing an assembly of component parts of the collision detection device of this embodiment; Figs. 3(a) and 3(b) are cross-sectional views of the collision detection device according to this embodiment, showing its actuated state; Figs. 4(a) and 4(b) are charts showing along thetime axis the swing angle of a weight and the contact conduction state of the collision detection device according to this embodiment; and Fig. 5 is a chart showing the actuation region of the collision detection device of this embodiment in terms of the relation between the amplitude and period of acceleration acting on the device.

A specific embodiment of this invention will be explained with reference to the drawings.

Figs. 1(a) and 1(b) are front and side cross-sectional views of a collision detection device 100 based on this invention, with its contacts 41 and 51 being open in the absence of acceleration above a certain level. The collision detection device 100 has a collision sensitive direction indicated by the arrow A, and has its weight 3 swingable about a swing axis (swing shaft) 2 in the direction indicated by the arrow a in response to the impact of collision. Fig. 2 shows the assembly of the component parts of the collision detection device 100.

The collision detection device 100 has a cover 9 made of resin, a flat base 8, and a housing 7. The base 8 is press-fitted to the housing 7, and the housing 7 is press-fitted to the cover 9. Adhesive 11 is applied to the bottom of the base 8 in order to keep the hermetic sealing of the collision detection device 100.

The housing 7 has a base section 72 and a pair of confronting stem sections 70a and 70b, which have the formation of cuts 71a and 71b at the top. The shaft 2 is fixed at its both ends to the cuts 71a and 71b of the stems 70a and 70b and adapted to support the weight 3 swingably about its swing axis which is eccentric from the mass barycenter.

The weight 3 comprises a metallic plate (inertial section) 31 which is made of Al, Cu, W or the like and machined to have a disc shape and centered by the mass barycenter, and an eccentric mass (eccentric section) 32 which is made of resin. These sections are joined mechanically based on resin insert molding. The eccentric mass 32 has on both sides thereof the formation of recesses 33, by which a prescribed value of eccentric mass moment is provided for the weight 3.

The weight 3 has its eccentric mass moment MRT and moment of inertia IT expressed by the following formulas (1) and (2) in terms of the eccentric mass moment mr and moment of inertia i of the eccentric mass 32 and the moment of inertia I of the metallic plate 31. The metallic plate 31 has no eccentric mass moment since its swing axis is not eccentric from the mass barycenter.

MRT = mr ( 1) IT = i+I (2) As explained by the formulaes (1) and (2), it is possible for the weight 3 with the metallic plate 31 to have its moment of inertia IT increased by the amount of the moment of inertia I of the metallic plate 31 without varying the eccentric mass moment MRT.

Formed on the weight 3 is a rotor 6 of resin mold, which has a first cam 61 and second cam 62 and shares the shaft 2 with the weight 3. Accordingly, the rotor 6 swings together with the weight 3 about the shaft 2. The first and second cams 61 and 62 have their profiles 42 and 52 shaped such that the distance of contacts 41 and 52 formed on flat contact springs 4 and 5 (explained below) decreases as the weight 3 swings.

The contact springs 4 and 5 having the respective contacts 41 and 51 are f ixed to stand on the base 8. The contact 41 is formed at a flat section of the spring 4, while the contact 51 is formed at a section of the spring 5 which is bent to protrude toward the contact 41. The contact springs 4 and 5 exert a resilient force to the rotor 6 in the direction opposite to the action of acceleration, i.e., the direction indicated by the arrow B, so that their ends 42 and 52 are in contact with the profile of the first and second cams 61 and 62, respectively.

The resilient force of the contact springs 4 and 5 on the rotor 6 acts indirectly on the weight 3 so that it is normally in contact with the inner wall 73 of the housing 7 and is precluded from swinging in the direction indicated by the arrow b. Based on this arrangement, the weight 3 and rotor 6 are restricted from swinging in the direction indicated by the arrow a by undergoing the acceleration attributable to hard braking of the vehicle or running on a rough road surface.

The contact spring 5 has the formation of a cut 53 extending in the longitudinal direction from its approximate center to the end 52, thereby having split end sections...The contact spring 5 with the cut 53 enables the reliable electrical contact between the contacts 41 and 51.

The contact springs 4 and 5 are fixed by resin insert molding to the base 8, while being connected electrically with external output terminals 12 and 13, respectively. The external terminals 12 and 13 protrude outwardly from the bottom of the base 8, and the conduction state of the contacts 41 and 51 is led out as a collision detection signal.

Further provided on the base 8 by resin insert molding is a fixing lug 14, by which the collision detection device 100 is mounted on a circuit boad or the like (not shown).

on the path of swing motion of the weight 3, a stopper 16 is press-fitted to the inner wall of the cover 9. The weight 3 which hits the stopper 16 following a swing in the a-direction is precluded from swinging beyond a prescribed swing angle.

Next, the operation of the collision detection device 100 will be explained.

When the collision detection device 100 does not undergo the acceleration above a prescribed level in the A-direction, the contact springs 4 and 5 exert the resilient force on the rotor 6 in the B-direction, causing the weight 3 which is integrated with the rotor 6 to stay in contact with the inner wall 73 of the housing 7 by being pressed in the b-direction as shown in Fig. 1(b). That is, the weight 3 is precluded from swinging in the a-direction by the resilient force of the contact springs 4 and 5 and also in,. the b-direction by the inner wall 73 of the housing 7.

Accordingly, in the absence of acceleration above a prescribed level in the A-direction, the weight 3 does not swing and the rotor 6 does not swing either, causing the contacts 41 and 51 to keep the open state. Consequently, the contacts 41 and 51 are not closed in the presence of acceleration caused by hard braking or the vibration of the vehicle during a run, and the reliability of the collision detection device 100 is ensured.

If, on the other hand, the collision detection device 100 undergoes the acceleration above the prescribed level in the A-direction, the contacts 41 and 51 are closed, as will be explained with reference to Figs. 3(a) and 3(b) and Figs. 4(a) and 4(b). Figs. 3(a) and 3(b) show the state of the collision detection device 100, with its weight 3 swinging in the adirection by undergoing the acceleration and coming in contact with the stopper 16. Fig. 4(a) shows along the time axis the swing angle of the weight 3 in the a-direction in response to the acceleration, and Fig. 4(b) shows the conduction state of the contacts 41 and 51 along the time axis. Shown by the dashed line in Figs. 4(a) and 4(b) is the behavior of the conventional collision detection device.

When the acceleration of a significant level acts on the weight 3 in the A-direction due to the event of side collision or the like at time point tO, the moment acting on the mass barycenter of the weight 3 causes the weight 3 and rotor 6 to start to swing in the a-direction about the shaft 2 against the resilient force of the contact springs 4 and 5. The weight 3 has the greater moment of inertia IT as compared with the conventional counterpart, and therefore it swings slower than the conventional case (less steep slope of the swing rate curve in Fig. 4(a)).

The rotor 6 which swings together with the weight 3 causes its first and second cams 61 and 62 to warp the contact springs 4 and 5, thereby narrowing the distance of the contacts 41 and 51.

When the swing of the weight 3 reaches a prescribed angle eth at time point t2, the rotor 6 closes the contacts 41 and 51 and the current conduction through the output terminals 12 and 13 is detected as a collision detection signal. The weight 3 continues to swing beyond the angle eth in the a-direction until it hits the stopper 16 at the maximum swing angle emax at time point t5.

The weight 3 bounces on the stopper 16 and swings back in the b-direction toward the original position by being aided by the resilient force of the contact springs 4 and 5. In this case, the weight 3 having a lower swing velocity as compared with the conventional case when it hits the stopper 16 produces a smaller bouncing force, and therefore it swings back slower than the conventional case in the b-direction (less steep slope of the swing rate curve in Fig. 4(a)).

When the weight 3 swings back up to the angle e th at time point t6, the contacts 41 and 51 open, and it further swings back to the original position to come in contact.,with the inner wall 73 of the housing 7 at time point t7.

The acceleration acting on the collision detection device 100 varies in its amplitude and frequency depending on the location of device installation and the direction of collision, and therefore the weight 3 needs to have characteristics that meet individual conditions. For example, in case the collision detection device is installed in the vehicle crash zone or used to detect the incident of side collision, the acceleration of collision acting on the device will have a high frequency and large amplitude, and therefore the weight 3 needs to have a larger moment of inertia IT in order to produce a stable collision detection signal. otherwise, in case the collision detection device 100 is installed in other location than the vehicle crash zone, the acceleration of collision acting on the device will be relatively small, and the weight 3 suffices to have a smaller moment of inertia IT. Therefore, the weight 3 needs to have a moment of inertia IT determined arbitrarily to meet individual conditions.

Conventionally, it has been necessary to design the weight by determining the moment of inertia to meet each condition, whereas the weight 3 according to this embodiment allows the easy and arbitrary setting of the moment of inertia ITtO meet individual conditions without varying the eccentric mass moment MRT based on the provision of the metallic plate (inertial section) 31. The metallic plate 31 of this embodiment is a disc, and its moment of inertia I is expressed by the following formula (3) in terms of the specific gravity r, radius r and plate thickness T.

I = (l/2)(7rr 4 Tr) (3) That is, the moment of inertia I of the metallic plate 31 is dependent on the specific gravity r, radius r and thickness T, and by designing only the metallic plate 31 by choosing these values properly, it is fairly possible to obtain a weight 3 having the intended moment of inertia IT given by the formula (2). The conventional weight having no metallic plate and thus having a smaller moment of inertia behaves to swing faster (steeper slope of the swing rate curve) and produces a shorter duration of closed state of the contacts (f rom time point tl to t4) as shown by the dashed line in Fig.4(a). In contrast, the weight 3 of this embodiment having the metallic plate 31 and thus having a larger moment of inertia IT can swing slower and can produce a longer duration of closed state of the contacts 41 and 51 (from time point t2 to t6). Moreover, the conventional weight swinging faster produces a larger bouncing force when it hits the stopper, and the resulting reciprocating motion between the stoppers can possibly cause the chattering of collision detection signal and produce an unstable collision detection signal. In contrast, the weight 3 of this embodiment of the invention which behaves to swing slower can reduce the bouncing force on the stopper 16 and inner wall 73, suppressing the reciprocating motion between the stopper 16 and inner wall 73, reducing the chattering of collision detection signal, and producing a stable collision detection signal. By varying the moment of inertia IT Of the weight 3, it is possible to alter the slope of the swing rate curve arbitrarily at least between the solid curve and dashed curve shown in Fig. 4(a). It is not necessary to design and fabricate the whole weight 3 at each alteration of the moment of inertia, and consequently the collision detection device 100 can be manufactured at a lower cost.

It is possible to provide intended characteristics for the collision detection device 100 by properly setting the moment of inertia IT Of the weight 3. The spring force produced by the contact springs 4 and 5 is a function of the swing angle 0, i.e., F( 19), of the weight 3, and the following equation (4) holds during a swinging period of the swinging weight 3., d' e /dt' = (MRT G - F( e) rf) / IT (4) where rf is the distance between the acting position of the spring force F( 19) and the swing axis of the weight 3, and G is the acceleration acting on the weight 3.

The equation (4) reveals that the angular acceleration d'O/dt' of the weight 3 is a function of the ratio of the eccentric mass moment MRT to the moment of inertia IT, and accordingly the operational characteristics of the collision detection device 100 are dependent on the value of MRT/IT.

Fig. 5 shows the actuation region (conduction state of the contacts 41 and 51) of the collision detection device 100 in terms of the relation between the amplitude and period (reciplocal of frequency) of the acceleration acting on the device. The area above the amplitude/ period curve is the operative region and the area below the curve is the inoperative region. The amplitude/period curve having a vertical asymptotic line at acceleration period DO and a horizontal asymptotic line at acceleration amplitude GO represents the operation threshold characteristics. The DO is the lower limit of acceleration period needed to close the contacts, and it depends on the ratio of the eccentric mass moment MRT to the moment of inertia IT, i.e., MRT/IT, of the weight 3.

The point DO moves to the left as the value of 14RT/IT increases on the chart of Fig. 5. Since the eccentric mass moment MRT of the weight 3 is unvarying irrespective of the addition of the metallic plate 31, the value of DO is solely dependent on the moment of inertia IT Of the weight 3. That is, the DO moves to the left as the moment of inertia IT is decreased, and it moves to the right as the IT is increased.

Accordingly, it is possible to set the operational characteristics (frequency response) of the weight 3 arbitrarily to meet the condition of use by setting the moment of inertia 1 of the metallic plate 31 properly so that the weight 3 is prevented from swinging in the presence of acceleration below the prescribed period. Particularly, by providing the weight 3 with a relatively large moment of inertia IT and a relatively small eccentric mass moment MRT, it becomes possible to use the collision detection device 100 as a crash sensor which detects the incident of collision directly.

The point GO which gives the horizontal asymptotic line of the chart of Fig. 5 represents the acceleration in static equilibrium. Setting d 2 19 Mt2 = 0 in equation (4) gives GO= F( e) rf /ERT, and accordingly it reveals that the GO is dependent on the eccentric mass moment MRT and spring force F( e). The acceleration GO of static equilibrium signifies the threshold of detection, and it is determined in advance from the required performance of the collision detection device 100. The acceleration GO of static equilibrium is unvarying irrespective of the value of moment of inertia I of the metallic plate 31, and it is possible for the collision detection device 100 of this embodiment to have its operational characteristics altered while retaining a constant threshold of detection. That is, by adjusting the moment of inertia I of the metallic plate 31 so as to set the intended moment of inertia ITwithout varying the eccentric mass moment MRT of the weight 3, it is possible to accomplish the intended operational characteristics of the collision detection device 100 at the time of prototype manufacturing.

Although the weight 3 of the foregoing embodiment is designed to lower the swing velocity by increasing the moment of inertia I of the metallic plate 31, demands of quick response can be met by reducing the moment of inertia I of the metallic plate 31 thereby to provide a smaller moment of inertia IT for the weight 3.

In providing the metallic plate 31 of the foregoing embodiment with an arbitrary moment of inertia I by choosing its specific gravity r, radius r or thickness T, through a number of metallic plates of the same shape (radius r and thickness T) are used but different materials (different specific gravity r) may be used, thereby allowing selective use for individual purposes.

Although the metallic plate 31- of the foregoing embodiment is formed of a unitary member, it may consist of multiple detachable divisions. For example, the metallic plate 31 is formed of a certain number of ringshaped divisions assembled coaxially, thereby amounting to an intended moment of inertia I.

Although the metallic plate 31 of the foregoing embodiment.is made of metal, it may be of other material such as resin.

Although the metallic plate 31 of the foregoing embodiment is a discshaped plate, it may be a square plate, rectangular plate or elongated circular plate, provided that its swing axis is coincident with the mass barycenter.

Although the eccentric mass 32 of the foregoing embodiment is made of resin, it may be formed of other material, provided that its swing axis is eccentric from the mass barycenter.

Although the metallic plate 31 and eccentric mass 32 of the foregoing embodiment are joined by resin insert molding, these parts may be joined by other manner such as calking or bonding - Although the weight 3 and rotor 6 of the foregoing embodiment are supported to swing freely about the shaft 2, an alternative structure is to fix the weight 3 and rotor 6 to the shaft 2, which is supported rotatably by bearings provided on the housing 7.

Although the metallic plate 31 and eccentric mass 32 of the foregoing embodiment are joined by resin insert molding, an alternative structure is to fix these parts separately to the shaft 2, which is supported rotatably by bearings provided on the housing 7.

Although the contacts 41 and 51 of the foregoing embodiment are integral parts of the contact springs 4 and 5, respectively, an alternative structure is to arrange the contacts separately from the contact springs, with the conduction state of the contacts being varied by the movement of the contact springs.

Although the weight 3 of the foregoing embodiment is rendered the exertion of the resilient force of the leaf springs 4 and 5, an alternative structure is to exert a resilient force of a coil spring or the like to the weight 3 against the swing motion caused by the impact of collision, with a contact being f ormed on the surf ace of the weight 3 against a fixed contact so that these contacts make or break the conduction by sliding.

Although the contacts of the foregoing embodiment are normally open andthey close in response to the acceleration above a certain level, the contacts may be of normally-closed type so that they open in response to the acceleration above a certain level.

As described above, the collision detection device according to the present invention has its pendulum formed of an eccentric section having an eccentric mass moment and an inertial section having no eccentric mass moment joined together mechanically, allowing the easy setting of the moment of inertia of the pendulum by the adjustment of the moment of inertia of the inertial section, while leaving the eccentric mass moment of the whole pendulum unvarying, thereby to be adapted to various operational conditions including the type of vehicle, device installation location, and collision sensitive direction, whereby it is capable of producing a stable collision detection signal and enabling the cost reduction.

Claims

CLAIMS:

1. A collision detection device for a moving body comprising a weight which is pivoted at a position eccentric from a mass barycenter thereof and adapted to swing in a certain direction in response to an acceleration acting thereon against a bias force exerted thereon, and contacts having their conduction state varied by swing motion of said weight, thereby detecting the incident of collision of said moving body, wherein said weight includes:

an eccentric section which has a swing axis eccentric from the mass barycenter thereof and functions to determine the eccentric mass moment of said weight; and an. inertial section which swings together with said eccentric section and functions to determine the moment of inertia of said weight about a swing shaft thereof.

2. A collision detection device according to claim 1, wherein said inertial section of said weight has a greater specific gravity than said eccentric section.

3. A collision detection device according to claim 2, wherein said eccentric section of said weight is made of resin and said inertial section is made of metal.

4. A collision detection device according to any one of claims 1 through 3, wherein said inertial section of said weight has its moment of inertia about said swing shaft determined thereby to determine the moment of inertia of said weight, thereby allowing the arbitrary setting of the frequency response to acceleration of said weight.

5. A collision detection device according to claim 4, wherein said weight has its moment of inertia determined, thereby allowing the setting of the lower limit of a period of acceleration at which the conduction state of said contacts is varied.

6. A collision detection device according to any one of claims 1 through 5, wherein said inertial section of said weight has its material or shape determined thereby to determine its moment of inertia, thereby allowing the arbitrary setting of the moment of inertia of said weight.

7. A collision detection device according to claim 6, wherein said inertial section of said weight has a shape of plate, with its span, thickness or specific gravity being determined thereby to determine the moment of inertia thereof, thereby allowing the arbitrary setting of the moment of inertia of said weight.

8. A collision detection device according to claim 7, wherein said inertial section of said weight has a shape of disc.

9. A collision detection device according to any one of claims 1 through 8, wherein said inertial section is f itted by insert molding to said eccentric section thereby to complete said weight.

10. A collision detection device according to any one of claims 1 through 8, wherein said inertial section and eccentric section of said weight are separate parts, with said inertial section being fixed to the swing shaft which swings together with said eccentric section.

11. A collision detection device substantially as described herein with reference to the accompanying drawings.