US 3417699 A
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Dec. 24, 1968 w. M. PIPER ET AL CONTACT FUZE Filed May 28, 1956 mwww m m m w w. RB R .m 0 .00 T .mwm wh United States Patent 3,417,699 CONTACT FUZE William M. Piper, McLean, Va., Jacob Rabinow, Takoma Park, and Ralph B. Rizer, Forest Heights, Md., as-
signors to the United States of America as represented by the Secretary of the Army Filed May 28, 1956, Ser. No. 587,909 2 Claims. (Cl. 102-70.2)
The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.
This invention relates to ordnance fuzes and more particularly to the placing of piezoelectric impact detecting elements in these fuzes.
In ordnance projectiles it is often desirable to obtain a signal at the instant of contact. For example, with a shaped explosive charge it is necessary that the explosion be initiated while the shaped charge is an exact distance from the target; or for internal explosions in aircraft elements it is necessary that the explosion occur at a certain short interval of time after contact is first made. Piezoelectric elements are used in fuzes for the purpose of giving an electrical pulse the instant of contact. Conventionally the piezoelectrical element is placed at the nose of the projectile so that it is pressed by contact with the target. This pressure creates an electrical impulse which is conducted to the detonator in the rear of the projectile in a shaped charge round. There are two undesirable aspects to this arrangement: first, the fuze is separated into two partsi.e., the detecting part at the front and the detonator at the rear; and second, the detecting part is not sensitive to grazei.e., contact with the target at an angle to the axis of the projectile.
An object of this invention is to provide a complete fuze at the rear of the projectile which is sensitive to contact with the target at any angle.
Another object is to provide a fuze in a single container at the rear of the projectile.
A further object is to provide a piezoelectric element at the rear of the projectile which is compatible with fuzes and projectiles now in use.
A still further object is to achieve the above with a device that is sturdy, simple, and reliable, yet cheap and easy to manufacture.
The specific nature of the invention as well as other objects, uses, and advantages thereof will clearly appear from the following description and from the accompanying drawing in which:
FIG. 1 is a partial axial sectional view of a projectile in accordance with this invention.
FIG. 2 is a schematic representation of the essential elements in the electrical detecting and firing circuit.
FIG. 3 is a partial axial sectional view of another form of this invention.
The practice of the invention entails placing a piezoelectric or other electro-mechanical transducer element at a point on a projectile remote from the point which impacts the target and stressing it by audio shock waves resulting from impact with a target. These shock waves travel in metals at speeds15,00() feet per second is representative-that are much higher than usual of sufiicient magnitude to produce an electrical pulse from a correctly positioned piezoelectric element. This electrical pulse may be used to initiate explosion directly, in which case the explosion will typically occur some 60 microseconds after contact. This time is short enough for use with relatively slow-moving projectiles such as mortar, bomb, or bazooka rounds. Alternatively the explosion may be delayed some set time after the generation of the pulse. Because the pulse will occur at an exact time after contact the explosion may be set to occur some exact time after contact.
In a device according to this invention as represented in FIG. 1, the piezoelectric detecting element 10 is ring shaped and located near base 12 of projectile 14. The projectile has an explosive charge 16 shaped by cone 18 all in a case 20. The rear end of case 20 has a planesurfaced annular step 22 around a threaded cylindrical extension 24. Tail boom 26 (with fins, etc., not shown) screws on these threads and forms the base of the projectile. Threaded extension 24 has a coaxial bore 28 which, with boom 26, forms a cavity for fuze 30. The fuze is conventional with safety-and-arming devices, electrical detonator, tetral lead, booster, etc.
The detecting element 10 itself comprises two identical Washers 32 and 33 of piezoelectric material with an electrically conductive washer 34 between them. A short insulating annular band 36 fits snugly over extension 24 against step 22. The washers 32, 33 and 34 fit snugly over the insulating band with washer 32 contacting the step 22. Edge 38 of boom 26 contacts washer 33. Thus the washers are concentric with and generally aligned with the projectile case 20. An electrical lead 40 passes through hole 42 in band 36 and makes electrical connection with contact 44 on the fuze. The extension 24 has slot 46 for use when the parts are assembled. As can be seen the detecting element 10 may be selectively prestressed by the torque on boom 26.
The electrical schematic equivalent circuit is shown in FIG. 2. The piezoelectric washers 32 and 33 are so polarized that their pulses add. When a shock wave arrives at step 22 it stresses the washers 32 and 33 and they produce a pulse of electrical energy which is conducted through lead 40 to detonator 48. The other side of the detonator is grounded as are the washers 32 and 33 by contact with the step 22 and edge 38.
The device described above is a complete fuze located at the base of a projectile with no connections, either electrical or mechanical, to the nose except the projectile case itself. By machining edge 38 of boom 26, it may be used with existing fuzes and projectiles. The device is sensitive to graze because impact anywhere on the projec' tile case will result in shock waves which will be transmitted to the piezoelectric element.
An embodiment shown in FIG. 3 and described below is a single-package fuze located in the base of the projectile. The case 50 of the projectile is formed with a cavity 51 containing explosive material 53. At the rear of case 50 there is a plane-surfaced annular step 54. The rear section 52 of the cavity 51 is frusto-conic in shape. The apex angle of the cone of this frusto-conic section 52 is smalli.e., about or lessto form a natural path for shock waves down the base 50 to the step 54. On the outside of the case in the region of the conic section 52 is a threaded section 56 of reduced diameter. Threaded to this section is cup 58 having a cylindrical cavity 60.
Within cavity 60 is a fuze 62 housed in a metal container 64 having a booster 66 affixed to one end thereof and extending into the conic section 52.. The piezoelectric detecting element is ring shaped and comprises washer 70 of piezoelectric material, conducting washer 72, flanged insulating washer 74 and tubular weight 76. The washer 70 is attached by an electrically conductive bond 71 to the forward portion 78 of the container 64. Conducting washer 72 is bonded by cement 73 to the other side of washer 70, and insulation washer 74 is attached to the other side of washer 72. The weight 76 is attached to washer 74 and is free to move relative to the container 64. The container 64 is compressed between cup 58 and step 54 so that the forward portion 78 is firmly seated on step 54 for optimum transmittal of shock waves. The weight 76 is free to move so that it will stress the washer 70 in response to projectile deceleration, should the shock waves fail to produce a sutficient electrical pulse.
Although detonator 80 could be connected directly to conducting washer 72 similar to the embodiment shown in FIG. 2, we prefer to use an electronic amplifier 82 to increase sensitivity. The amplifier is of conventional design and set to a sensitivity just below the noise level of the projectile in flight.
Since the conventional safety-and-arming devices, such as delay timers, switches, shutters, form no part of this invention, they have not been shown or described.
It Will be apparent that the embodiments shown are only exemplary and that various modifications can be of the invention as defined in the appended claims.
We clairnz 1. In an ordnance projectile having an explosive charge, improved means for detonating said explosive charge in response to impact of said projectile, said improved means comprising in combination: a projectile case having a plane-surfaced annular step therein located near the base of said projectile, a ring-shaped piezoelectric detecting element disposed in said step so as to intercept the shockwaves generated in said case upon impact, said piezoelectric detecting element comprising two washers of piezoelectric material and an electrically conductive washer therebetween, said washers being concentric and snugly fitted in said step, one side of each piezoremade in construction and arrangement within the scope electric washer being in contact with a side of said conductive washer and the other sides of said piezoelectric washers being in contact with said case at opposite sides of said step, means insulating said conductive washer from said case, detonator means within said case adapted to detonate said explosive charge in response to the electrical pulse generated between said conductive washer and said case upon impact of said projectile, and means connecting said detonator means to said conductive Washer to transfer said electrical pulse therebetween.
2. The invention in accordance with claim 1, wherein the portion of said case to the rear of said step is threadably attached to said projectile so as to make the width of said step adjustable, thereby permitting said piezoelectric'washers to be'sle' ctively pre'stressed.
References Cited UNITED STATES PATENTS 2,514,297 7/ 1950 Smith et al. 102-702 2,688,921 9/ 1954 Meister 10270.2 2,764,091 9/ 1956 Hudson 102-70.2 2,796,025 6/ 1957 Ruppel 10270.2
FOREIGN PATENTS 277,052 11/ 1951 Switzerland. 240,195 11/ 1955 Sweden.
VERLIN R. PENDEGRASS, Primary Examiner.