Gas damped acceleration switch

#This invention relates to vehicle crash-sensing switches and, more particularly, to a gas damped acceleration switch.

#With the development of the air bag as a safety device for automobiles and other passenger vehicles, there has developed a need for a crash-sensing device for actuating the air bag inflater in a crash situation. This requires a detection device mounted on the vehicle for sensing a rapid change of velocity of the vehicle and actuating a switch when the deceleration is greater than a threshold amount. To be most effective, a crash-sensing device is preferably mounted at the front of a vehicle, such as on the front bumper where the change in velocity is most abrupt and acts with the minimum of time delay following the onset of a crash. At such locations, however, the device is exposed to other forces not connected with a crash situation but which may still be relatively large in magnitude. Thus the device must be direction sensitive, must be extremely rugged in construction, and must be able to discriminate both against high accelerations of very short duration to which the front of the vehicle is normally subjected, and discriminate against large velocity changes which nevertheless take place over a relatively long period of time, such as are experienced in emergency braking of the vehicle.

#Crash-sensing devices using an inertial mass are known in the art. See, for example, U.S. Pat. Nos. 3,556,556 and 3,750,100. Inertial switches of the same general type have also been proposed which utilize the movement of an inertial mass under an acceleration or deceleration force. Such known devices have been used to sense acceleration but also, by means of fluid damping, have been used as velocimeters to respond to the integral of the acceleration. Fluid damping has been provided by enclosing the inertial mass in a closed chamber, the inertial mass acting as a piston dividing the chamber into two volumes. Any force acting on the piston is damped by the transfer of fluid from the decreasing volume side of the moving piston to the increasing volume side of the piston, as through a space around the piston or through a tubular passage between the two volumes. See U.S. Pat. Nos. 3,632,920 and 3,300,603.

#For a better understanding of the invention, reference should be made to the accompanying drawings, wherein:

#FIG. 1 is a top view partially cut away of the preferred embodiment of the present invention;

#FIG. 2 is a sectional view taken substantially on the line 2--2 of FIG. 1;

#Referring to the drawings in detail, the numeral 10 indicates a base made of molded plastic or other rigid or nonconductive material. Supported on the base 10 is a cylindrical cup-shaped cover 12 similarly molded of a suitable plastic or other rigid nonconductive material. The base may be attached or anchored to a vertical, forward-facing surface on an automobile or other vehicle when the unit is used as a crash-sensing device.

#Secured to the open end of the cup-shaped cover 12 is a spiral spring 14. As seen in FIG. 1, the disk-shaped spring has two arms 15 and 15' which spiral inwardly to a center portion 16. A central rod 18 has a flange 20 which is secured to the center section 16 of the spring 14. The outer end of the rod 18 slidably engages an oversized bore 22 in the end wall of the cup-shaped cover 12. The spiral spring 14 allows the rod to move along its axis, the flange moving to the dotted position indicated at 20'. The spring applies a restoring force to the rod 18, which resists the movement of the rod 18 and urges the rod back to its normal at-rest position. The rod 18 acts as an inertial mass which moves relative to the base 10 when the base 10 is accelerated or decelerated in a direction parallel to the axis of the rod 18. The spiral spring, in addition to providing a restoring force, operates as a centering means for maintaining axial alignment of the rod 18 with the base 10.

#Movement of the rod 18 to the right, as viewed in FIG. 2, brings the end of the rod 18 into engagement with a spring contact leaf 26. The contact leaf is supported by a flat flexible metal terminal 28. A portion of the terminal is cut out to form a tab 29 that is folded over on top of the leaf 26 to clamp the leaf in place. An opening 31 in the terminal 28 permits the rod 18 to pass through the terminal into contact with the leaf 26. The terminal 28 is molded to the base 10 with one end 28' projecting outside the base to provide an external electrical connection. The other end of the terminal 28 is cantilevered so as to be movable by a calibrating set screw 30 which can be adjusted to deflect the contact leaf 26 toward the end of the rod 18 to reduce the gap between the end of the rod 18 when in its normal position. Thus the distance the rod 18 must move axially to close the gap and make contact with the contact leaf 26 is made adjustable by the set screw 30. A second external contact 32, which is integral with the spiral spring 14, provides an external connection to the rod 18. Thus when the rod 18 comes into contact with the contact leaf 26, an electrical circuit is closed between the external connections 28' and 32. Preferably a piece of foam material, indicated at 34, acts as a dampening material for the contact leaf 26 to eliminate or reduce contact bounce when the rod 18 moves into contact with the contact leaf 26.