Piezoelectric Charging Device

In the past, some missiles have used a complicated and fairly expensive thermal battery circuit to charge a capacitor before flight of the missile in order to provide an energy source for a detonator of the warhead. These systems are too expensive and require more sophisticated circuitry than is desirable.

Therefore, it is an object of this invention to provide a simple piezoelectric charging device that utilizes pressure from the rocket motor to cause a piezoelectric crystal to produce sufficient energy to charge a capacitor that can be used to cause detonation of a detonator for a warhead.

Another object of this invention is to provide a simple device that utilizes a simple bridge circuit in causing the energy to be stored in a capacitor.

Still another object of this invention is to provide for detonator safety in that the system of applicant's allows the detonator power supply to be physically isolated from other power supplies.

Yet another object of this invention is to provide a charging arrangement that eliminates the need for costly charging circuits.

A further object of this invention is to provide a system that has few components in the charging circuit and therefore less chance of failure.

Other objects and advantages of this invention will be obvious to those skilled in this art.

In accordance with this invention, a piezoelectric charging device is provided and includes a housing with a piezoelectric crystal mounted therein with electrical leads mounted at opposite sides of the piezoelectric crystal with pressure applying means at one end and in communication with the gas pressure from a rocket motor casing to apply pressure to the crystal when the rocket motor is ignited and cause an output to be produced at the electrical leads for the crystal and applying the output leads to a bridge circuit that has a capacitor connected thereacross and utilizing the energy stored in the capacitor as a power supply for setting off the detonator for a warhead.

FIG. 1 is a sectional view with a portion of the rocket cut-way and schematically illustrating the piezoelectric charging device in accordance with this invention,

FIG. 2 is a sectional view of a structure illustrating the mounting of the piezoelectric crystal with the application of force thereto and leads connected to an electric circuit from the piezoelectric crystal,

FIG. 3 is a graph illustrating pressure versus time,

FIG. 4 is a graph illustrating current versus time, and

FIG. 5 is a graph illustrating voltage versus time.

Referring now to the drawings, rocket 10 includes a conventional rocket motor 12 with piezoelectric unit 14 secured to front end 16 of rocket 12 in a conventional manner such as by threads 17 on member 16 and threads 18 on piezoelectric unit 14. Piezoelectric unit 14 includes an outer housing 20 and inner mounting structure 22 that is made of insulating material. A threaded insulating plug 24 and threads 25 at end 26 of housing structure 22 are threaded together to hold insulating structure 22 in place in housing 20. Insulating structure 22 has a bore 28 at one end thereof and piezoelectric crystal 30 is mounted in bore 28 with metal plates 32 and 34 at opposite ends of piezoelectric crystal 30. Plate 34 has electrical lead 36 connected thereto and extends out through plug structure 24 as illustrated and plate 32 has lead 38 connected thereto and extends through plug 24 as illustrated. A piston 40 with an O-ring type seal 42 is slidably and sealably mounted in bore 44 at one end of housing structure 20. Lead 36 is connected to one terminal of full wave bridge rectifier circuit 46 and lead 38 is connected to an opposite terminal of full wave bridge circuit 46 as illustrated. The other two terminals of full wave bridge circuit 46 are connected by leads 48 and 50 across capacitor 52 and output leads 54 and 56 from capacitor 52 are connected to a detonator and warhead structure 58. Lead 56 has a conventional crush type switch 60 connected therein for completing the circuit to warhead 58 upon the missile arriving at the target.

In operation, when it is desired to launch rocket 10, motor 12 is ignited in a conventional manner to propel rocket 10 toward a desired target and when rocket motor 12 is ignited, fluid pressure from the rocket motor is communicated to piston 40 which exerts pressure on plates 32 and 34 to squeeze crystal 30 and cause an output to be produced across leads 36 and 38 to full wave rectifier 46 and from full wave rectifier 46 to leads 48 and 50 to capacitor 52 to store the produced energy in capacitor 52. Capacitor 52 then becomes a power supply source for an explosive charge detonator of warhead 58 to set warhead 58 off at the target. Switch 60 is closed when the rocket strikes the target and completes the circuit to the explosive charge detonator and causes warhead 58 to be set off. When rocket motor 12 is ignited, the pressure first rises and then falls therein at burn out in relation to time as illustrated in FIG. 3, current from crystal 30 is produced as illustrated in FIG. 4 in relation to the rise and fall of the pressure in rocket motor 12, full wave bridge recitifier circuit 46 causes energy as illustrated in FIG. 5 to be stored in capacitor 52 as a power supply, and switch 60 is closed upon contacting the target to cause the stored energy in capacitor 52 to be connected across the explosive charge detonator to set off warhead 58.