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Title:
ELECTRO-MECHANICAL ACCELEROMETER
Document Type and Number:
WIPO Patent Application WO/1998/029888
Kind Code:
A1
Abstract:
An accelerometer (10) includes housing (16) retaining an actuator (28) movable between three positions partially disposed therein in the first position and an assembly including a first element (48) movable between three positions engaging and retaining the actuator (28) when in the first position, a second element (50) spaced from the actuator (28) and the first element (48) when each is in the first position to engage the first element (48) when the actuator moves from the first position to the second position when the acceleration greater than a first level is exerted on the accelerometer to close a first circuit, and a third element (52) spaced from the actuator (28) and the first and second elements (48 and 50) when each is in the first or second positions to engage the second element (50) when the actuator (28) moves from the first position to the third position when the acceleration greater than a second level is exerted on the accelerometer to close a second circuit.

Inventors:
HUSBY HARALD SNORRE
GROSSI CARL THOMAS III
Application Number:
PCT/US1997/020562
Publication Date:
July 09, 1998
Filing Date:
November 13, 1997
Export Citation:
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Assignee:
BREED AUTOMOTIVE TECH (US)
International Classes:
G01P15/135; H01H35/14; (IPC1-7): H01H35/14
Foreign References:
US5031931A1991-07-16
US5059751A1991-10-22
US5178410A1993-01-12
US5237134A1993-08-17
Attorney, Agent or Firm:
Drayer, Lonnie R. (Inc. P.O. Box 3305, Lakeland FL, US)
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Claims:
CLAIMS :
1. An electromechanical accelerometer (10) comprising a hollow housing (16) assembled with an actuator assembly (18) including a substantially tubular member (22) having an aperture (40) formed therein to selectively receive an actuator (28) therein and a chamber (75) cooperatively formed by said hollow housing and said substantially tubular member wherein said actuator assembly is selectively operable in first, second and third actuator configurations such that said actuator is at least partially disposed in said housing when in said first actuator configuration and disposed in said chamber when in said second and third actuator configurations and a switch assembly (20) including a first conductive e switch element (48) movable between first, second and third positions disposed to engage said actuator in said first position, a second conductive switch element (50) movable between first, second and third positions disposed in spaced relationship relative to said actuator assembly and said first conductive switch element in said first position and disposed to engage said first flexible conductive switch element in said second position when a lateral acceleration force greater than a first predetermined threshold level is exerted on the electromechanical accelerometer to close said first electric circuit and a third conductive switch element (52) movable between first and second positions disposed in spaced relationship relative to the second conductive switch element in said first position and to engage the second conductive switch element in said second position when a lateral acceleration force greater than a second predetermined threshold level is exerted on the electromechanical accelerometer to close said second electric circuit.
2. The electromechanical accelerometer (10) of claim 1 wherein said substantially tubular member (22) includes a recess (32) formed therein to house said actuator assembly (18) comprising an actuator damping mechanism (24) with said aperture formed therethrough to operatively retain said actuator (28) therein when in said first position.
3. The electromechanical accelerometer (10) of claim 2 wherein said actuator assembly (18) further comprises an actuator adjustment mechanism (26) to longitudinally adjust the position of said actuator (28) within said substantially tubular member (22) when said actuator (28) is in said first position.
4. The electromechanical accelerometer (10) of claim 1 wherein said actuator (28) comprises a substantially spherical member movable between first, second and third positions having a diameter substantially equal to the diameter of said aperture (40) to minimize oscillation or lateral movement of said actuator (28) within said aperture.
5. The electromechanical accelerometer (10) of claim 2 wherein said substantially tubular member (22) comprises an inner end portion (30) having said recess (32) formed therein to retain said actuator damping mechanism (24) therein and an outer end portion (34) having a substantially cylindrical channel (36) formed therein to retain said actuator adjustment mechanism (26) therein.
6. The electromechanical accelerometer (10) of claim 5 wherein said actuator damping mechanism (24) comprises a substantially annular damping member (38) securely disposed within said recess (32) of said inner end portion (30) of said substantially tubular member (22).
7. The electromechanical accelerometer (10) of claim 3 wherein said actuator adjustment mechanism (26) comprises an actuator seat member (42) to engage said actuator (28) when in said first position.
8. The electromechanical accelerometer (10) of claim 7 wherein the actuator seat member includes a concave seat (44) which engages the actuator (28) when in said first position.
9. The electromechanical accelerometer (10) of claim 1 wherein said chamber (75) has a diameter greater than the diameter of said aperture (40) of said substantially tubular member (22).
10. The electromechanical accelerometer (10) of claim 9 wherein the longitudinal axis of said aperture (40) of said substantially tubular member (22) is misaligned with the center of said actuator (28) when said actuator is in said second and third positions.
Description:
ELECTRO-MECHANICALACCELEROMETER The present invention relates to an electro- mechanical accelerometer to detect sudden changes in the lateral acceleration of a motor vehicle and actuate a motor vehicle safety device when the rate of change in the lateral velocity of the motor vehicle exceeds a predetermined threshold level.

Airbag passive restraint systems for protecting vehicle occupants in frontal collisions have been incorporated into most new vehicles by manufacturers.

These airbag systems are primarily designed to protect occupants in frontal impacts. Many people, however, are killed or seriously injured in side-impacts, which typically involve one vehicle running into the side of a second vehicle. Since airbags have been largely successful in alleviating injuries from frontal impacts, it is important now to focus on the next greatest danger, side-impacts. The prior art is seriously deficient in its ability to effectively sense lateral acceleration force in side-impact collisions. The present invention provides an inexpensive, reliable accelerometer appropriate for detecting lateral acceleration of vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a vehicle equipped with the electro-mechanical accelerometer of the present invention.

Fig. 2 is a partial detailed perspective view of the interior of the vehicle with the electro- mechanical accelerometer of the present invention.

Fig. 3 is a cross-sectional side view of the electro-mechanical accelerometer of the present invention in the first configuration with an open circuit.

Fig. 4 is a cross-sectional side view of the electro-mechanical accelerometer of the present invention in the second configuration with a closed circuit.

Fig. 5 is a cross-sectional side view of the electro-mechanical accelerometer of the present invention in the third configuration with a closed circuit.

Fig. 6 is a cross-sectional side view of another embodiment of the electro-mechanical accelerometer of the present invention in the first configuration with an open circuit.

Fig. 7 is a cross-sectional side view of another embodiment of the electro-mechanical accelerometer of the present invention in the second configuration with a closed circuit.

Fig. 8 is a cross-sectional side view of another embodiment of the electro-mechanical accelerometer of the present invention in the third configuration with a closed circuit.

DETAILED DESCRIPTION OF THE INVENTION An accelerometer used to sense a side-impact is typically placed as close to the impact zone as possible to provide for optimal sensing and airbag deployment capability. To design an accelerometer for side-impacts, the side-intrusion characteristics of a vehicle must be fully analyzed. The physical reaction of a side door panel in response to a collision is critical in determining the desired characteristics and placement of an accelerometer. The velocity of the side door panel of a struck vehicle increases immediately after the impact to a maximum velocity comparable to the velocity of the colliding vehicle.

This rapid rise in velocity can happen within five to ten milliseconds (ms). The passenger compartment experiences a relatively small velocity change during this initial stage of the crash. The difference in velocity between the side door and the passenger compartment manifests itself in the crush of the struck vehicle. As the side of the vehicle stiffens in the deep post-buckling stage, the resistance force increases and starts to decelerate the side door panel until finally the side-panel and the passenger compartment reach a common velocity. The critical limitation to gauge in the design of an accelerometer for detecting a side-impact is the time when the occupant is hit by the side door inner panel. The deciding factors that influence this time are the stiffness and weights of the vehicles, the angle and location of the impact, the speed of the vehicles, and the distance between the occupant and the side-panel in the struck vehicle. An accelerometer must trigger

the airbag and the airbag must deploy before the occupant is hit by the side door panel.

Considering all critical limitations and variables, an accelerometer for sensing side-impacts must be placed on the side door panels to be effective. This location is essential since it is sensing the velocity change of the portion of the vehicle which will eventually strike the occupant. To ensure the effectiveness of sensing, it is reasonable that more than one sensor be used for side-impact sensing. By utilizing multiple accelerometers, inadvertent deployment of an airbag can be avoided while assuring that for all side crashes in which the protection apparatus is needed, the airbag will deploy. For instance, the sensing system can be implemented in such a manner that the airbag will not deploy without a concurrent electric signal from at least two accelerometers. Minor collisions that directly impact one accelerometer will therefore not deploy the airbag. However, if the side door is not hit directly but deployment of an airbag is nonetheless desirable, the electro-mechanical accelerometer must have the ability to sense delayed and stretched pulses propagated to the side door by the collision in addition to pulses generated in a direct side door impact. In order to produce concurrent electrical signals for non-direct lateral collisions, the electro-mechanical accelerometer must be more sensitive to these longer, stretched pulses and have longer contact dwell times.

For added sensitivity, it is desirable for an accelerometer to include a safing level and a discriminating level. For frontal impact detection, velocity-type low-bias accelerometers located in the

passenger compartment are used for safing purposes.

In side-impact crashes, however, the crash pulse in the passenger compartment does not provide sufficient data at the time when an accelerometer is required to trigger. Therefore, it is difficult to use a passenger-compartment safing sensor for a side-impact sensing system. By strategically utilizing multiple accelerometers each with safing and discriminating ability, inadvertent deployment can be avoided while assuring reliability. Additionally, the lower threshold for initiation of the safing electrical signal will provide for detection pulse waves from non-direct side-impacts. The side-impact system can be organized in such a manner that an airbag will deploy only upon the concurrent receipt of at least a safing electrical signal and a discriminating electrical signal.

As shown in Fig. 1, the present invention relates to an electro-mechanical accelerometer 10 capable of sensing a side-impact employed to selectively actuate at least one safety device 12 such as an airbag installed in a vehicle 14. As shown in Fig. 2, at least one accelerometer 10 is strategically placed in every side door panel and side door beam. The safety device 12 is stored for example in the side door beam, the passenger seat backrest or any other suitable location. Upon the accelerometer sensing a lateral acceleration greater than a predetermined threshold level, the safety device 12 deploys and prohibits the vehicle occupant from coming into contact with the intruding side door panel. As described more fully hereinafter, the electro-mechanical accelerometer 10 may comprise a damped ball-in-cylinder embodiment or a non-damped ball-on-track embodiment.

A damped ball-in-cylinder embodiment is shown in Figs. 3,4 and 5. Specifically, the electro- mechanical accelerometer 10 comprises an outer hollow housing 16 configured to maintain an actuator assembly 18 in operative relationship relative to a switch assembly 20 therein. As discussed more fully hereinafter, the actuator assembly 18 is selectively operative in a first, second and third actuator configurations and the switch assembly 20 selectively operative in a first, second and third switch configuration cooperate to supply an electrical signal from an external electrical source (not shown) to actuate at least one safety device 12 when the actuator assembly 18 and the switch assembly 20 are in the second or third actuator configurations and the second or third switch configurations respectively.

The actuator assembly 18 comprises a substantially tubular member 22 which contains an actuator damping mechanism and an actuator adjustment mechanism 24 and 26 respectively and an actuator 28 movable between a first, second and third position in operative relationship relative to the actuator damping mechanism 24 and the actuator adjustment mechanism 26 when in the first position. The substantially tubular member 22 comprises an inner end portion 30 having a substantially annular recess 32 formed therein to retain the actuator damping mechanism 24 and an outer end portion 34 having a substantially cylindrical channel 36 formed therein to retain the actuator adjustment mechanism 26 therein.

The actuator damping mechanism 24 comprises a substantially annular damping member 38 securely disposed within the substantially annular recess 32 of the inner end portion 30 of the substantially tubular

member 22 having a substantially annular damping aperture 40 formed therethrough to receive at least a portion of the actuator 28 therein when the actuator 28 is in the first position. The actuator adjustment mechanism 26 is preferably a stopper comprising an actuator seat member 42 including a concave seat 44 disposed to engage the actuator 28 when in the first position and longitudinally adjustable within the substantially cylindrical channel 36 to adjust the distance of travel of the actuator 28 from the first position to the second position and from the second position to the third position to control the actuation time or time between a collision and the actuation of the safety device 12 for any particular G force exerted on the vehicle 14. The actuator 28 comprises a substantially spherical member 46 having a diameter substantially equal to the diameter of the substantially annular damping aperture 40 to minimize oscillation or lateral movement of the actuator 28 within the substantially annular damping aperture 40.

The switch assembly 20 comprises first, second and third flexible conductive switch elements 48,50 and 52 respectively held in operative position relative to each other by a switch mounting bracket 54 disposed within the outer hollow housing 16. The first flexible conductive switch element 48 movable between a first, second, and third position comprises a first proximal substantially horizontal conductive section 56 held in operative position by switch mounting bracket 54 and electrically connected to an external electrical source (not shown) and a first distal substantially straight flexible substantially vertical conductive section 58 extending between the switch mounting bracket 54 and the actuator 28

terminating in camming contact section 60 followed by an arcuate or concave contact element 62. The first distal substantially straight flexible substantially vertical conductive section 58 physically guides the actuator 28 between the first and second positions.

The second flexible conductive switch element 50 movable between a first, second and third position comprises a second proximal substantially horizontal conductive section 64 held in operative relationship by switch mounting bracket 54 and electrically connected to the external electrical source (not shown) and a second distal substantially straight flexible substantially vertical conductive section 70 disposed in spaced relationship relative to the arcuate or concave contact element 62 of the first flexible conductive switch element 48 and the actuator 28 when each is in the first position to form an open circuit. The end portion 72 of the second distal substantially straight flexible substantially vertical conductive section 70 engages a first stop or limit 74 formed on the inside of the housing 16. The third flexible conductive switch element 52 comprises a third proximal substantially horizontal conductive section 76 held in operative relationship by switch mounting bracket 54 and electrically connected to the external electrical source (not shown) and a third distal substantially straight flexible substantially vertical conductive section 78 including an arcuate or convex contact element 80 normally disposed in spaced relationship relative to the second distal substantially straight flexible substantially vertical conductive section 70. The end portion 82 of the third distal substantially straight flexible substantially vertical conductive section 78 engages a

second stop or limit 84 formed on the inner end portion 30 of the substantially tubular member 22.

As shown in Fig. 3, the camming contact section 60 of the first distal substantially straight flexible substantially vertical conductive section 58 of the first flexible conductive switch element 48 normally biases the actuator 28 against the actuator adjustment mechanism 26 or concave seat 44 of the actuator seat member 42 to maintain the actuator 28 in the first position. As shown in Fig. 4, the substantially arcuate or concave contact element 62 of the first distal substantially straight flexible substantially vertical conductive section 58 of the first flexible conductive switch element 48 engages the second distal substantially straight flexible substantially vertical conductive section 70 of the second flexible conductive switch element 50 when the actuator 28 and the first flexible conductive switch element 48 is each in the second position to complete an electric circuit.

As shown in Fig. 5, the substantially arcuate or concave contact element 62 of the first distal substantially straight flexible substantially vertical conductive section 60 and the second distal substantially straight flexible substantially vertical conductive section 70 of the second flexible conductive switch element 50 engages the substantially arcuate or convex element 80 of the third flexible conductive switch element 52 when the actuator 28 and the first flexible conductive switch element 48 is each in the third position to complete an electric circuit.

As previously described, the actuator 28 is normally biased in the first position by the first

flexible conductive switch element 48 with the second flexible conductive switch element 50 engaging the first stop or limit 74 and the third flexible conductive switch element 51 engaging the second stop or limit 84. So positioned, the electro-mechanical accelerometer 10 is in the first configuration with the actuator 28 and the switch assembly 20 in the first actuator configuration and first switch configuration respectively. The position of the actuator 28 within the substantially tubular member 22 of the actuator assembly 18 when in the first position is set by adjusting the actuator adjustment mechanism 26 longitudinally relative to the substantially tubular member 22.

The inner end portion 30 of the substantially tubular member 22 and the outer hollow housing 16 cooperatively form an actuation chamber 75 therebetween having a diameter greater than the diameter of the damping aperture 40 and an actuator retention member or retention shoulder 77 to engage and retain the actuator 28 therein when in the second and third positions.

When the electro-mechanical accelerometer 10 senses a lateral acceleration G force exceeding a first predetermined threshold level such as 7 Gs, the force due to the resulting deceleration causes the actuator 28 to move from the first position to the second position moving the first flexible conductive switch element 48 to the second position to contact with the second flexible conductive switch element 50 as shown in Fig. 4. As the actuator 28 moves from the first position (Fig. 3) to the second position (Fig. 4) outside the substantially annular damping aperture 40 or the substantially tubular member 22,

camming contact section 60 and the arcuate or concave contact element 62 of the first flexible conductive switch element 48 guide the actuator 28 against the retention shoulder 77. Retention of the actuator 28 within the actuator chamber 75 by the retention shoulder 77 and the first conductive switch element 48 increases the dwell time or the time in which the electrical circuit is complete during high G force collisions. This increased dwell time allows for a stronger electrical current to be produced resulting in a more reliable electro-mechanical accelerometer 10 during high G force collisions. So positioned, the electro-mechanical accelerometer 10 is in the second configuration with the actuator assembly 18 and the switch assembly 20 in the second actuator configuration and second switch configuration respectively, with the first and second proximal substantially horizontal conduction sections 56 and 64 connected to the electric power source (not shown) to complete an electric circuit.

When the vehicle 14 is involved in a crash resulting in a deceleration G force exceeding a second predetermined threshold level such as 12 Gs, the force due to the resulting deceleration causes the actuator 28 to move from the first position to the third position moving the first and second flexible conductive switch elements 48 and 50 to their third positions to contact with the third flexible conductive switch element 52 as shown in Fig. 5. As the actuator 28 moves from the first position (Fig. 3) to the third position (Fig. 5) outside the substantially annular damping aperture 40 or the substantially tubular member 22, the camming contact section 60 and the arcuate or concave contact

element 62 guide the actuator 28 against the retention shoulder 77. Retention of the actuator 28 within the actuator chamber 75 by the retention shoulder 77 and the first flexible switch element 48 increases the dwell time or the time in which the electrical circuit is complete during high G force collisions. This increased dwell time allows for a stronger electrical current to be produced resulting in a more reliable electro-mechanical accelerometer 10 during high G force collisions. So positioned, the electro- mechanical accelerometer 10 is in the third configuration with the actuator assembly 18 and the switch assembly 20 in the third actuator configuration and third switch configuration respectively, with the second and third proximal substantially horizontal conductive sections 64 and 76 connected to the electric power source (not shown) to complete another electric circuit.

With the improved geometric design, the damped ball-in-cylinder electro-mechanical accelerometer can obtain a minimum dwell time of 5.0 ms at 300 Gs in response to a 5.0 ms pulse as compared to prior art accelerometers which can obtain dwell times of 1.0 ms.

A non-damped ball-on-track embodiment is shown in Figs. 6,7 and 8. The difference between the damped ball-in-cylinder embodiment and the non-damped ball-on-track embodiment is that the substantially tubular member 22 which contains the actuator dampening mechanism 24 and the actuator adjustment mechanism 26 is replaced by a track guiding 90. In all other respects, the basic functionality of the two embodiments are similar.

More specifically, the electro-mechanical accelerometer 10 in its non-damped ball-on-track

embodiment comprises an outer hollow housing indicated as 16 configured to maintain an actuator assembly 18 in operative relationship relative to a switch assembly 20 therein. As discussed more fully hereinafter, the actuator assembly 18 selectively operative in a first, second and third actuator configuration and the switch assembly 20 selectively operative in a first, second and third switch configuration cooperate to supply an electrical signal from an external electrical source (not shown) to actuate at least one safety device 12 when the actuator assembly 18 and the switch assembly 20 are in the second or third actuator configurations and the second or third switch configurations respectively.

The actuator assembly 18 comprises an actuator 28 movable between a first, second and third position and a track guiding 90 which contains a body 92 having an inner end portion 93 wherein a recess 94 is formed to retain a track 96 therein to guide the actuator 28 when moving from the first position to the second and third positions. The track 96 includes a substantially vertical seat 98 disposed to engage the actuator 28 when in the first position and a substantially annular travel aperture 99 to receive at least a portion of the actuator 28 when in the second position. The length of the track 96 can be longitudinally varied within the recess 94 to adjust the distance of travel of the actuator 28 from the first position to the second position and from the first position to the third position to control the actuation time or time between a collision and the actuation of the safety device 12 for any particular G force exerted on the vehicle 14. Similar to the damped ball-in-cylinder embodiment, the actuator 28

comprises a substantially spherical member 46 having a diameter substantially equal to the diameter of the substantially annular travel aperture 99 to minimize oscillation or lateral movement of the actuator 28 within the substantially annular travel aperture 99.

The switch assembly 20 comprises a first, second and third flexible conductive switch element 48,50 and 52 respectively held in operative position relative to each other by a switch mounting bracket 54 disposed within the outer hollow housing 16. The first flexible conductive switch element 48 movable between a first, second and third position comprises a first proximal substantially horizontal conductive section 56 held in operative position by switch mounting bracket 54 and electrically connected to an external electrical source (not shown) and a first distal substantially straight flexible substantially vertical conductive section 58 extending between the switch mounting bracket 54 and the actuator 28 terminating in camming contact section 60 followed by an arcuate or concave contact element 62. The first distal substantially straight flexible substantially vertical conductive section 58 physically directs the actuator 28 along the track 96 between the first and second positions.

The second flexible conductive switch element 50 movable between a first, second and third position comprises a second proximal substantially horizontal conductive section 64 held in operative relationship by switch mounting bracket 54 and electrically connected to the external electrical source (not shown) and a second distal substantially straight flexible substantially vertical conductive section 70 movable between a first, second and third position

disposed in spaced relationship relative to the arcuate or concave contact element 62 of the first flexible conductive switch element 48 and the actuator 28 when each is in the first position to form an open circuit. The end portion 72 of the second distal substantially straight flexible substantially vertical conductive section 70 engages a first stop or limit 100 formed on the inner end portion 93 of the body 92 of the track guiding mechanism 90.

The third flexible conductive switch element 52 comprises a third proximal substantially horizontal conductive section 76 held in operative relationship by switch mounting bracket 54 and electrically connected to the external electrical source (not shown) and a third distal substantially straight flexible substantially vertical conductive section 78 including an arcuate or convex contact element 80 normally disposed in spaced relationship relative to the second distal substantially straight flexible substantially vertical conductive section 70. The end portion 82 of the third distal substantially straight flexible substantially vertical conductive section 78 engages a second stop or limit 103 formed on the inner end portion 93 of the body 92 of the track guiding mechanism 90.

As shown in Fig. 6, the camming contact section 60 of the first distal substantially straight flexible substantially vertical conductive section 58 of the first flexible conductive switch element 48 normally biases the actuator 28 against the substantially vertical seat 98 of the track 96 to maintain the actuator 28 in the first position. As shown in Fig. 7, the substantially arcuate or concave contact element 62 of the first distal substantially

straight flexible substantially vertical conductive section 58 of the first flexible conductive switch element 48 engages the second distal substantially straight flexible substantially vertical conductive section 70 of the second flexible conductive switch element 50 when the actuator 28 and the first flexible conductive switch element 48 is each in the second position to complete an electric circuit.

As shown in Fig. 8, the substantially arcuate or concave contact element 62 of the first distal substantially straight flexible substantially vertical conductive section 58 and the second distal substantially straight flexible substantially vertical conductive section 70 of the second flexible conductive switch element 50 engages the substantially arcuate or convex element 80 of the third flexible conductive switch element 52 when the actuator 28 and the first flexible conductive switch element 48 is each in the third position to complete an electric circuit.

As previously described, the actuator 28 is normally biased in the first position by the first flexible conductive switch element 48 with the second flexible conductive switch element 52 engaging the first stop or limit 100 and the third flexible conductive switch element 52 engaging the second stop or limit 103. So positioned, the electro-mechanical accelerometer 10 is in the first configuration with the actuator 28 and the switch assembly 20 in the first actuator configuration and first switch configuration respectively. The position of the actuator 28 on the track 96 of the actuator assembly 18 when in the first position is dependent upon the length of the track 96.

The inner end portion 93 of the body 92 of the track guiding mechanism 90 and the outer hollow housing 16 cooperatively form an actuation chamber 75 therebetween having a diameter greater than the diameter of the substantially annular travel aperture 99. The first stop or limit 100 serves as a retention shoulder 104 to receive and momentarily retain the actuator 28 within the actuation chamber 75 when in the second and third positions.

When the accelerometer 10 senses a lateral acceleration G force exceeding a first predetermined threshold level such as 7 Gs, the force due to the resulting deceleration causes the actuator 28 to move from the first position to the second position moving the arcuate of concave contact element 62 of the first distal substantially straight flexible substantially vertical conductive section 58 of the first flexible conductive switch element 48 to the second position to contact with the second distal substantially straight flexible substantially vertical conductive section 70 of the second flexible conductive switch element 50 as shown in Fig. 7. As the actuator 28 moves from the first position (Fig. 6) to the second position (Fig. 7), the camming contact section 60 and the arcuate and concave contact element 62 of the first flexible conductive switch element 48 guide the actuator 28 against the retention shoulder 104.

Retention of the actuator 28 within the actuator chamber 75 by the retention shoulder 104 and the first flexible conductive switch element 48 increases the dwell time or the time in which the electrical circuit is complete during high G force collisions. This increased dwell time allows for a stronger electrical current to be produced resulting in a more reliable

electro-mechanical accelerometer 10 during high G force collisions. So positioned, the electro- mechanical accelerometer 10 is in the second configuration with the actuator assembly 18 and the switch assembly 20 in the second actuator configuration and second switch configuration respectively, with the first and second proximal substantially horizontal conduction sections 56 and 64 connected to the electric power source (not shown) to complete an electric circuit.

When the vehicle 14 is involved in a crash resulting in a deceleration G force exceeding a second predetermined threshold level such as 12 Gs, the force due to the resulting deceleration causes the actuator 28 to move from the first position to the third position moving the first and second flexible conductive switch elements 48 and 50 to their third positions to contact with the third flexible conductive switch element 52 as shown in Fig. 8. As the actuator 28 moves from the first position (Fig. 6) to the third position (Fig. 8), the camming contact section 60 and the arcuate and concave contact element 62 of the first flexible conductive switch element 48 guide the actuator 28 against the retention shoulder 104. Retention of the actuator 28 within the actuator chamber 75 by the retention shoulder 104 and the first flexible switch element 48 increases the dwell time or the time in which the electrical circuit is complete during high G force collisions. This increased dwell time allows for a stronger electrical current to be produced resulting in a more reliable electro-mechanical accelerometer 10 during high G force collisions. So positioned, the electro- mechanical accelerometer 10 is in the third

configuration with the actuator assembly 18 and the switch assembly 20 in the third actuator configuration and third switch configuration respectively, with the second and third proximal substantially horizontal conductive sections 64 and 76 connected to the electric power source (not shown) to complete another electric circuit.

With the improved geometric design, the non- damped ball-on-track electro-mechanical accelerometer can obtain a minimum dwell time of 5.0 ms at 300 Gs in response to a 5.0 ms pulse as compared to prior art accelerometers which can obtain dwell times of 1.0 ms.

The dual-threshold design of the invention in either embodiment provides for a more discriminating accelerometer 10 such that inadvertent or minor collisions will not actuate the safety device 12.

Because safety devices such as airbags are single use mechanisms and must be replaced upon each use, it is extremely cost beneficial to prevent inadvertent actuation upon low-impact collisions. The dual threshold design provides for actuation of the safety device 12 only upon detection of a discriminating or second predetermined threshold level. Consequently, direct impacts upon the accelerometer 10 by a shopping cart or extending vehicle side door will at most produce a safing electrical signal which by itself will not deploy the safety device 12. In addition, the dual threshold embodiment allows for multiple uses of the signals produced by the first and second electric circuits of the accelerometer 10. For instance, at each predetermined threshold level, a different safety mechanism can be actuated depending upon the force of the collision and the desired passenger protection. Additionally, the strategic

arrangement of multiple accelerometers 10 may provide for additional security in that the control device (not shown) can be programmed such that it will actuate the safety device 12 only upon the detection of a safing electrical signal in conjunction with a discriminating electrical signal.

The enhanced closure dwell time of the accelerometer allows for the receipt by the control device (not shown) of two concurrent signals from at least two accelerometers 10. For instance, the enhanced closure dwell time allows a first accelerometer to produce a discriminating electrical signal of sufficient strength such that a second accelerometer can produce a concurrent safing or discriminating electrical signal in response to delayed crash wave pulses.

For an integrated side-impact detection system, three accelerometers 10 are strategically positioned on each side of the vehicle 14. Each accelerometer 10 is mounted just inside the sheet metal skin of the vehicle, and attached to a beam or support member.

The three accelerometers are wired in parallel. In order for the airbag 12 to be deployed, at least one safing signal and one discriminating signal must be concurrently received by the control device (not shown).

The components of the electro-mechanical accelerometer 10 are insert molded which provide for a minimal amount of components. Unlike in the prior art, the hollow housing 16 is an integrated component of the accelerometer 10 in that it provides a cavity for receiving the actuator 24 upon a collision. The ball-on-track embodiment of Fig. 6 has the additional benefit of having a hollow housing 16 which is

plastic. The ability to make the accelerometer largely from plastic with the exception of the conductive switch elements and the actuator makes this accelerometer easy to manufacture and inexpensive to produce. To ensure that the ball-in-cylinder accelerometer 10 of Fig. 3 is hermetically sealed, the metallic parts can first be coated by a bonding mate- rial which adheres to both the contacts and the plastic. It is known that the contacts and the plastic have different thermal expansion coefficients and thus, if they are not treated, they could separate when the temperature changes, resulting in leaks.

Another important feature of the disclosed invention is the specific material and shape of the contact blade terminals. The contact blade terminals are bi-metallic thus allowing for each to be crimped onto the output terminals (not shown). This added feature alleviates the need for a pigtail mechanism to connect the contact blade terminals to the output terminals 32. By doing so, this reduces the need for an additional connection thus reducing the possibility of electrical failure.