CRASH SENSOR WITH IMPROVED ACTIVATION FOR STABBING PRIMER

Abstract: A crash sensor (10) for automobiles of the type including a ball (20) moving against viscous damping in a closed cylinder (27) for releasing a firing pin (72) for initiating a pyrotechnic sequence has an improved release mechanism (40). When the ball (20) moves a predetermined distance from its normal or resting position during an automobile crash a release mechanism (40) releases a belleville spring (64) maintained under stress. The belleville spring (64) thereupon initiates movement of a firing pin (72) towards a stab primer (122). The release mechanism is a single piece of spring material having multiple levers (42) extending radially inward from a torsionally elastic ring (41) each lever (42) having a detent and pivot (48). The firing pin (72) is mounted on and driven by a snap disk (20) which is normally in its position of higher energy equilibrium and is released to go to its position of lower energy equilibrium by pressure applied by the belleville spring (64).

Description: CRASH SENSOR WITH IMPROVED ACTIVATION FOR STABBING PRIMER FIELD OF THE INVENTION This invention relates to mechanisms that release a firing pin upon frontal collision of auto¬ mobiles for initiating deployment of air bags. BACKGROUND OF THE INVENTION Air bags are inflatable bags that remain folded and out of sight in readiness for a frontal col¬ lision. During a collision, chemical reaction of a material typically containing sodium azide produces gaseous products which inflate the bag and interpose it between the driver and the steering wheel or the front seat occupant and the dashboard. A sensor of the type to which this invention is applicable is marketed by Breed Automotive Corp. It has a metallic ball free to move in a sealed cylinder. Air flow around the ball causes a pressure differen¬ tial. The pressure differential causes a force propor- tional to and opposite the relative velocity of the ball with respect to the cylinder. The proportionality of force to velocity makes the sensor an acceleration integrator that initiates a chemical reaction upon achievement of a predetermined velocity change. The variation of air viscosity with temperature is compen¬ sated by making the cylinder and ball of materials of different thermal expansion coefficients thereby caus¬ ing the gap between the ball and cylinder to change with temperature as required to maintain the perform- ance of the sensor over a wide temperature range. A firing mechanism for initiating combustion of a stab primer includes a pin propelled by a first spring into the stab primer. A release means for the firing mech¬ anism includes a trigger lever in the form of a metal rod extending perpendicular to a pivoted shaft having a ' "D" shaped cross section. The trigger lever is moved by the ball to its firing position during a crash. A second spring urges the trigger lever away from the firing position thereby causing the trigger lever to maintain the ball in a normal or resting position dur¬ ing normal operation of the vehicle. The force the trigger lever applies to the ball modifies the pure velocity change character of the sensor so that the velocity change required for release of the firing pin increases with the duration of the deceleration pulse of the crash. Movement of the ball during a crash rotates the trigger lever until the flat portion of the D-shaft releases the firing pin which is thereupon driven by the spring into a stab primer. Ignition of the stab primer initiates combustion of larger amounts of propellent material that generates gas for filling the air bag. Two complete sensor and firing mechanisms are combined into one package to enhance reliability by providing two units each capable of initiating combus- tion of the propellant. This sensor is expensive to manufacture and one reason for the high cost is the large number of complex parts and the precision required in the trigger mechanism. Great care is required to make each part so as to insure minimum friction and maximum precision during the life of the sensor. A belleville spring is a washer shaped piece of elastic material bent so that in its relaxed shape its inner circumference is in a plane offset from the plane of its outer circumference. Under pressure applied to its inner circumference the spring flattens and, under greater pressure, its inner circumference moves to the opposite side of the outer circumference. When released it returns to its initial relaxed shape. A belleville spring has two characteristics that are used to advantage in this invention. The first is that it can exhibit a negative spring rate over much of its operating range. In a typical case the spring force will rise from zero as the spring is deformed from its relaxed shape to a peak force at a first deflection and then, as the spring is additionally deformed, diminish to a minimum of perhaps one fifth of the peak force at a second deflection before resuming its increase. A second characteristic is that the inner and outer circumference of a belleville spring can be made to high accuracy. The high accuracy obtainable at acceptable cost allows a design to be dependent upon achieving high accuracy for purposes such as accurately determining the velocity at which the sensor will be actuated. A snap disk resembles a belleville spring without the inner hole. A snap disk is a piece of spring material that has a normal relaxed shape approx¬ imating a section of a sphere. In this shape its po¬ tential energy is at its lowest value. It is also in equilibrium, or will also remain indefinitely in a sec¬ ond shape in which it is dished in the opposite direc¬ tion. In its second shape it has greater potential en¬ ergy than in its normal relaxed shape and will energet¬ ically snap into its relaxed position when it is urged in that direction by force applied to its center. A general object of this invention is to provide a crash sensor for automotive vehicles which also overcomes certain disadvantages of the prior art. SUMMARY OF THE INVENTION The present invention provides a crash sen- sor of the type having a viscously damped ball movable in a sealed cylinder with trigger lever means to sense movement of the ball and initiate movement of a firing pin when the ball has reached a firing position. The invention discloses a system of the aforementioned type which is highly reliable, compact, light in weight, and economical to manufacture. The trigger mechanism is a novel design that minimizes the number of components and their manufacturing cost. Further, in accordance with this invention, there is a spring having a negative spring rate and linked with the trigger lever for release thereby so the force of the spring at the position from which it is released is less than at other positions thereby maximizing the energy released relative to the friction force at the time of release. Further, in accordance with this invention, all precision fitting of parts is done at surfaces having circular symmetry thereby achieving high preci¬ sion using inexpensive production methods. Further, in accordance with this invention, the axial symmetry of the sensor and its components simplifies the manufacture because many of the components do not require rotational orientation during assembly. Further, in accordance with this invention, the force of the spring before it is released by the trigger urges the trigger lever and ball towards their normal resting positions thereby eliminating need for a second spring to return the trigger lever and ball. Further, in accordance with this invention, the entire sensor and stabbing mechanism is a self contained unit having structural integrity. By con¬ trast, known mechanical crash sensing and primer stab¬ bing systems rely on the structure supporting the stab primer for structural integrity. Therefore, the two sensor and primer stabbing systems of the known system must be manufactured and assembled at the same time as each other and at the same time as the entire sensor. This has the disadvantage that the if there is an error or defect in manufacturing one of the two crash sensing and primer stabbing systems there is a higher than random probability that the same cause will affect the other of the two units. Two units of the design dis¬ closed herein can be chosen from independently manufac- tured lots and combined in the same occupant protection system whereby the probability of system failure is re¬ duced to a greater extent than if both units are manu¬ factured simultaneously. A complete understanding of this invention may be obtained from the description that follows taken with the accompanying drawings. DESCRIPTION OF THE DRAWINGS FIGURE 1 shows a complete sensor of the invention with certain parts shown in section and the ball in its normal or resting position; FIGURE 2 shows the sensor as illustrated in Figure 1 but with the ball in its firing position just prior to releasing the belleville spring for initiating movement of the firing pin. FIGURE 3 shows the sensor as illustrated in Figure 1 but with the trigger levers and ball in their relaxed positions and the movement of the belleville spring and firing pin complete. FIGURE 4 shows a top view of the trigger levers and unitary torsionally elastic ring. BEST MODE FOR CARRYING Referring now to the drawings, an illustra¬ tive embodiment of the invention is shown in a crash sensor 10. The crash sensor comprises a ball in a sealed cylinder for sensing a deceleration pulse indic¬ ative of a crash. During a crash the ball moves trig¬ ger levers to a position where a firing mechanism is released. A firing pin is adapted for piercing a stab primer (not illustrated) for initiating a chemical reaction that generates gas that causes deployment of an air bag. It will be appreciated as the description proceeds that the invention may be implemented in dif¬ ferent embodiments. Referring now to FIGURES 1 through 4, the crash sensor 10 comprises a ball 20 movable in cylinder 22 between stops 26 and 28. Cylinder 22 fits loosely in cavity 32 in cylinder housing 34. Sealing ring 36 in groove 38 of cylinder 22 prevents movement of air around cylinder 22 while allowing cylinder 22 to move slightly within cavity 32. Trigger levers 42 extend inwardly from support ridge 44 of foundation 50 to ball 20. At their outward extremity trigger levers 42 have triangular pawls 46 for engaging the inner edge 62 of belleville spring 64. Each trigger lever 42 has a pivot 48 which fit in a mating groove 52 in support ridge 44 and posi¬ tions trigger lever assembly 40 (illustrated in Figure 4) with respect to support ridge 44. Collar 54 retains trigger lever assembly 40 and belleville spring 64 on foundation 50. Rods 56 are slideably positioned in holes 58 in foundation 50. Snap disk 70 is positioned for energetically snapping between the position illustrated in Figure 1 and the position illustrated in Figure 3 when urged by rods 56. Firing pin 72 is attached to the center of snap disk 70. The entire assembly is held together by outer cylindrical housing 74. During normal operation of the vehicle any play that might exist between cylinder housing 34, collar 54 and foundation 50 is taken up by movement resulting from the force applied by center 76 of snap disk 70 to foun¬ dation 50. Extensions 59 of rods 56 extend through holes in snap disk 70 and provide means for applying pressure through rods 56 to belleville spring 64 for setting the sensor to its armed state. No counterbalance for trigger levers 42 has been described or illustrated. This is because it is believed that the best design is to not counterbalance the levers. If it should be required to counterbalance the levers to reduce sensitivity to shock then counter¬ balance weights may be added to trigger levers 42 by extending trigger levers 42 outward into cavity 78 defined by belleville spring 64 and collar 54. Trigger lever assembly 40 is illustrated in Figure 4. It comprises trigger levers 42 connected by torsionally elastic ring 41 at the radius of and incor¬ porating pivots 48. It is a unitary structure formed from a sheet of spring material. In its relaxed condi¬ tion the trigger levers 42 and ring 41 are coplanar. The orientation of the trigger levers 42 illustrated in Figure 1 is the result of force applied by belleville spring 64. In some embodiments of the invention it may be desirable to provide walls 43 which are extensions of support ridge 44 which form channels confining ring 41. Walls 43 limit the radial movement of ring 41 at all points on its circumference other than at the trig¬ ger levers 42. Four trigger levers 42 are illustrated in Figure 4. Any other number of trigger levers may also be used. The operation of the invention will now be described with reference to FIGURES 1 through 4. In operation of the system, ball 20 is nor¬ mally urged against stop 26 by the trigger levers 42. When a deceleration much greater than one g is applied to the sensor, as would happen during an automobile crash, the inertia of the ball 20 causes it to move away from the stop 26 and toward stop 28. For this movement to happen it is necessary for some of the air in chamber 25 to pass through the annular gap between ball 20 and cylinder 22 into the chamber 27. The move¬ ment of the air between the ball and cylinder is resis¬ ted by the viscosity of the air thereby causing a pres¬ sure differential with the pressure in chamber 25 being greater than the pressure in chamber 27. This pressure differential opposes the movement of ball 20 toward stop 28 so that a predetermined movement required to initiate movement of the firing pin 72 is not achieved until a predetermined velocity change has occurred. At lower ambient temperatures the clearance between ball 20 and cylinder 22 decreases because the thermal coefficient of expansion of the cylinder 22 is greater than that of the ball 20. This increases the viscous resistance to the movement of air through the annular gap and compensates for the reduced viscosity of air at lower temperatures. At higher temperatures the clearance increases thereby also compensating for the higher viscosity of air at higher temperatures. The diameters of the ball and cylinder bore are chosen so that the temperature compensation is correct for the materials of which the ball and cylinder are made. As the ball 20 moves toward stop 28 trigger levers 42 rotate about their respective pivots 48. As triangular pawls 46 rotate their outer ends move upward and inward. This additionally stresses belleville spring 64. This continues until triangular pawls 46 move inward to a release position illustrated in Figure 2 where their outer extremities align with the inner diameter of belleville spring 64. Ideally, the release position is where the force of belleville spring 64 is near its minimum both because it is desirable to mini¬ mize friction force at the point of release and because it is desirable for the force applied by trigger levers 42 to ball 20 to diminish as the ball travels farther from its normal resting position. When the pawls 46 have moved to the positions where their outer extremit¬ ies are in alignment with the inner diameter of belle- ville spring 64, the belleville spring 64 is no longer supported and it snaps toward its relaxed position. As belleville spring 64 moves toward its relaxed position it encounters rods 56. By this time the force it is capable of applying has increased by a substantial factor, such as five, since its release and this force combined with the force resulting from the inertia of belleville spring 64 is applied through rods 56 to snap disk 70. This force starts the snap disk in its movement toward its relaxed position illustrated in Figure 3. As snap disk 70 and firing pin 72 move, belleville spring 64 continues to apply force through rods 56 thereby further adding energy to enhance the penetration of the stab primer (not illustrated) by firing pin 72. When the crash sensor 10 is in the unarmed state illustrated in Figure 3 it is armed by applying force to the extensions 59 of rods 56 while urging snap disk 70 into its position of higher energy equilibrium. As belleville spring 64 is bent toward the armed posi¬ tion illustrated in Figure 1 it contacts triangular pawls 46 of trigger levers 42 and moves them to the right or toward cylinder 22 and inward toward the center of the sensor. This causes trigger levers 42 to rotate about pivots 48 until the outer extremities of trigger levers 42 are aligned with the inner diameter of belleville spring 64. The triangular pawls will then slip past belleville spring 64 and trigger lever assembly 40 will revert to its relaxed planar condi¬ tion. Extensions 59 of pins 56 are then released to cause the inner edge 62 of belleville spring 64 to engage pawls 46 and urge them into the position illustrated in Figure 1. A mechanism for preventing accidental firing when the system is not installed in a vehicle is normally included in complete systems of the type that would includes sensors 10. Sensor 10 can be made safe against accidental firing by incorporating a means in the complete system for holding pins 56 against belleville spring 64 at those times that the system is not installed in a vehicle. Although the description of this invention has been given with reference to a particular embodi¬ ment, it is not to be construed in a limiting sense. Many variations and modifications will now occur to those skilled in the art. For a definition of the invention reference is made to the appended claims.

Claims: What is claimed is: 1. In a crash sensor of the type compris¬ ing a first resilient means for storing energy, an ele¬ ment movable in response to deceleration forces during a crash, and release means adapted to release the ener¬ gy stored in said first resilient means upon movement of said element to a predetermined position, the im¬ provement comprising: said first resilient means having a negative spring rate for some range of stored energy. 2. The invention as defined by Claim 1 wherein said movable element is a ball movable in a cylinder. 3. The invention as defined by Claim 1 wherein said first resilient means is a belleville spring. 4. The invention as defined by Claim 1 in- eluding a second resilient means for storing energy and means linking said second resilient means with said first resilient means for releasing energy stored in said second resilient means upon release of said energy stored in said first resilient means. 5. The invention as defined by Claim 4 wherein said second resilient means comprises a snap disk. 6. In a crash sensor of the type compris¬ ing a first resilient means for storing energy, an ele¬ ment movable in response to deceleration forces during a crash, and release means adapted to release the ener- gy stored in said first resilient means upon movement of said element to a predetermined position, the im¬ provement comprising: said release means comprising a ring having trigger levers extending inward. 7. The invention as defined by Claim 6 wherein said ring and said trigger levers are made of a single piece of material. 8. The invention as defined by Claim 6 wherein there is a foundation supporting said ring and said foundation comprises an annular groove adapted to support said ring and to retain said ring in a pre- cisely determined position. 9. The invention as defined by Claim 8 wherein said groove is also linked with said trigger levers and positions said trigger levers for rotation about said groove. 10. In a crash sensor of the type compris¬ ing a first resilient means for storing energy, an ele¬ ment movable in response to deceleration forces during a crash, and release means adapted to release the ener¬ gy stored in said first resilient means upon movement of said element to a predetermined position, the im¬ provement comprising: said release means comprising trigger means linked with said first resilient means for move¬ ment therewith and wherein, said trigger means is adapted to util- ize energy stored in said first resilient means to urge said movable element away from said predetermined posi¬ tion. 11. The invention as defined by Claim 1 wherein two or more independently manufactured sensors are placed within one airbag system, and wherein each of said sensors has its own stab primer and each of said stab primers is by itself capable of initiating deployment of the air bag, whereby the probability of the system failing to operate in the event of a crash requiring an air bag is reduced. 12. In an occupant protection system of an automotive vehicle of the type comprising multiple crash sensors located near each other and each adapted to pierce a stab primer and initiate a chemical reac¬ tion in response to deceleration forces during a crash, the improvement comprising: each of said crash sensors being a unitary structure adapted to be placed in an occupant protec¬ tion system, said crash sensors being grouped in groups the elements of which have one or more manufacturing circumstances in common, each sensor of said multiple crash sensors being drawn from a different one of said groups. 13. The invention as defined by Claim 12 wherein said different groups from which said multiple crash sensors are drawn are selected to maximize the differences in the manufacturing circumstances. 14. In a crash sensor of the type compris¬ ing a resilient means for storing energy, an element movable in response to deceleration forces during a crash, and release means adapted to release the energy stored in said resilient means upon movement of said element to a predetermined position, the improvement comprising: said resilient means having a normal relaxed state in which its stored energy is at its lowest value, said resilient means also having a second state in which it will remain indefinitely and in which it has greater stored energy than it has when it is in said normal relaxed state, and said release means being adapted to release said resilient means to change from said second state to said normal relaxed state. 15. The invention as defined by Claim 14 wherein said resilient means is a snap disk.

Inventors: NORTON PETER, NORTON, PETER
Applicants: NORTON PETER, NORTON, PETER
Application year: 1990
Main classification: B60R21
IPC codes: B60R21, F42C1, G01P15