Electricity: circuit makers and breakers – Special application – Change of inclination or of rate of motion responsive
Reexamination Certificate
1996-01-12
2001-11-06
Sterrett, Jeffrey (Department: 2838)
Electricity: circuit makers and breakers
Special application
Change of inclination or of rate of motion responsive
C200S061510, C073S514380
Reexamination Certificate
active
06313418
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to shock sensors in general and to shock sensors used for engaging or deploying automobile safety devices in particular.
BACKGROUND OF THE INVENTION
Shock sensors are used in motor vehicles, including cars and aircraft, to detect vehicle collisions. When such a collision occurs, the shock sensor triggers an electronic circuit for the actuation of one or more safety devices. One type of safety device, the deployable air bag, has found widespread acceptance by consumers as improving the general safety of automobile operation. Air bags have gone from an expensive option to standard equipment in many automobiles. Further, the number of air bags has increased from a single driver's side air bag to passenger air bags with future use of multiple air bags a distinct possibility.
With the ever increasing utilization of air bags, research and development has continued with efforts to make air bags and the electronics and sensors which control their deployment both more reliable and of lower cost. A key aspect of reliability with respect to air bags involves the twin, somewhat conflicting requirements that the air bag deploy in every situation where their deployment would be advantageous to the passengers but, at the same time, not deploy except when actually needed. Reliable deployment of an air bag without unwanted deployments is facilitated by use of multiple sensors in combination with actuation logic which can assess the nature and direction of the crash as it is occurring and, based on preprogrammed logic, make the decision whether or not to deploy the air bag. This increase in reliability tends to lead to a greater number of sensors as well as increased use of electronic logic.
The desire to hold down sensor cost and to keep the sensor integrated with the logic circuits has led to the use of solid state shock sensors. However, solid state shock sensors are prone to losing touch with the real world and may occasionally indicate a crash is occurring due to radio frequency interference, electronic noise, cross-talk within the electronics, etc.
The suitability of mechanical shock sensors as an integral part of bag deployment systems which prevent unnecessary bag deployment has kept up the demand for mechanical shock sensors.
A number of types of shock sensors employing reed switches have been particularly advantageous in combining a mechanical shock sensor with an extremely reliable electronic switch which, through design, can be made to have the necessary dwell times required for reliable operation of vehicle safety equipment. The reed switch designs have also been of a compact nature such that the switches may be readily mounted on particular portions of the vehicle which, in a crash, will experience a representative shock which is indicative of the magnitude and even the direction of the shock inducing crash.
One type of shock sensor, shown in German Patent No. DE 35 09 054, employs a sensing mass mounted on a spring with a second less-rigid spring spaced from the first spring in a glass housing. An acceleration sensing mass of less than three grams is mounted to the less rigid spring.
A need remains, however, for shock sensors having lower cost, high repeatability, and small packaging, which at the same time have the advantages of a mechanical sensor in providing relatively long switch closure or dwell time in combination with insensitivity to electronic noise or interference.
SUMMARY OF THE INVENTION
The shock sensor of this invention has some structural similarities to a reed switch. But, whereas a reed switch, when functioning as part of a shock sensor, requires a moving magnetic mass, the shock sensor of this invention employs a sensing mass mounted on a metallic reed or spring which, under the influence of a crash-induced acceleration, drives the reed against a fixed contact to close an electrical circuit. In order to extend the closure duration to increase the reliability and ease with which a significant event may be detected, a contact surface at the end of the reed and the fixed contact are oriented at an angle 60 degrees out of the plane containing the reed. The 60 degree contact surface on the reed may be formed by twisting a portion of the reed adjacent to the contact end. The sensor is oriented such that the acceleration force is approximately normal to the plane containing the reed. The orientation of the contact area on the reed and the fixed contact allows contact shock to dissipate sufficiently to eliminate most bouncing upon initial closure. The 60 degree contact angle provides a more reliable, less noisy closure signal in the presence of a crash-induced shock. Dwell time of initial contact closure because of the angled contacts is increased five to ten times on even marginal sensor closing events. The dwell time on higher force events is in some instances comparable to magnetically actuated crash-sensing devices. Further, manufacturing imperfections, in achieving alignment of contact interfaces, can actually provide a softer more gradual transition to mating contact The wiping and twisting of the contact surfaces, as they come into full face-to-face contact, increases dwell time.
Closure dwell time can be further enhanced for high shock loads by providing a two stage mass spring system. A second mass is mounted to the first reed or spring by a second reed or spring. The second mass/spring combination is arranged so the motion of the second mass, after the first reed has made electrical contact, is such as to hold the contact closed.
It is a feature of the present invention to provide a shock sensor for use in triggering safety devices within a moving vehicle.
It is another feature of the present invention to utilize the technology for manufacturing reed switches in the construction of a shock sensor.
It is a further feature of the present invention to provide a shock sensor in which all electromechanical components are contained within a hermetically sealed volume.
It is yet another feature of the present invention to provide a mechanical shock sensor having fewer components.
It is a yet further feature of the present invention to provide a reed switch with reduces contact bounce on switch closure.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.
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“Contact bounce in dry reed relays,” R.O. Jenkins, PROC. IEE. vol. 114, No. 11, Nov. 1967.
“Reed Switch Application Manual,” ©1987, Hamlin, Inc., Lake Mills, Wisconsin, 42 pages.
Breed Automotive Technology Inc.
Drayer Lonnie
Steinnon Patrick
Sterrett Jeffrey
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