A theft prevention device for use in the mounting of automotive audio equipment, such as a two-way radio to a secure structure, such as a "U" bracket or trunnion. The invention is a generally conical-shaped mounting knob that threadably attaches the audio equipment to the mounting bracket. Attached to one end of the knob enclosure is a key lock and attached to the opposite end is a threaded stud that is able to rotate about the longitudinal axis of the enclosure. In operation, the knob, in its unlocked position, is rotated clockwise until the threaded stud is securely attached to its threaded counterpart on the radio. In this position, the lock assembly rotates a cam plate so that an engaging disc engages both the knob enclosure and a stud plate allowing torque applied to the enclosure to be transferred to the threaded stud. The knob is then locked. In this position, the lock assembly rotates the cam plate so that the engaging disc does not engage the stud plate, and a compression spring forcibly separates the engaging disc and stud plate. Torque is not transferred from the enclosure to the stud plate. The knob will rotate freely in either the clockwise or counterclockwise direction, but the stud will not loosen or tighten, thus preventing removal of the radio from the vehicle.

BACKGROUND OF THE INVENTION 
a. Field of the Invention 
This invention relates to theft prevention devices for automotive radios 
and accessories, and more particularly, to a theft deterrent locking knob 
for mounting radios and accessories. 
b. Description of Related Art 
Theft of radios and other audio accessories from automobiles is, 
unfortunately, a common occurrence. Accordingly, numerous types of 
security devices exist to discourage or prevent such theft. Types of 
security devices include guards that cover or encase the equipment or 
devices that disguise the underlying expensive equipment. For example, 
U.S. Pat. Nos. 4,553,414 to Caputo, 4,248,069 to Burbank and 3,699,787 to 
Corrado involve the use of lockable covers that can be secured over the 
face of the audio equipment. U.S. Pat. No. 4,365,280 to Crosetti discloses 
a false front that simply slides into place over the equipment. U.S. Pat. 
No. 4,211,995 to Smith discloses encasing the equipment in a special 
container and wiring the container to an electric alarm system. 
U.S. Pat. No. 4,962,651 to Gibbs discloses a theft prevention device for 
use on the mounting bolts of automotive audio equipment. The device 
includes a pair of uniquely designed nuts that can not be effectively 
gripped with a wrench or other conventional turning tool in order to 
remove the audio equipment from the automobile. 
The present invention offers a simple and inexpensive way to mount 
automotive equipment in such a way to deter thefts of such equipment. In 
accordance with the present invention, the audio equipment can be 
initially secured in place on the dashboard or floorboard and thereafter 
securely held in place without the need for the owner to constantly lock 
and unlock the device or manipulate any parts each time the owner exits 
the vehicle. The invention also offers a locking device that is easily 
removable and is capable of being used on other pieces of equipment. 
SUMMARY OF THE INVENTION 
According to the present invention, the foregoing and other objects are 
attained by a theft prevention device for use in mounting automotive audio 
equipment, such as a two-way radio, to a secured structure, such as a 
mounting bracket or trunnion, attached to the floorboard or dashboard. The 
invention is a generally conical-shaped mounting knob that threadably 
attaches the audio equipment to the mounting bracket. Attached to one end 
of the knob enclosure is a key lock and attached to the opposite end is a 
fastening means, such as a threaded stud, that is able to rotate about the 
longitudinal axis of the enclosure. A cam-function engaging means attaches 
to the lock assembly. Torque applied to the enclosure is transmitted by 
the engaging means to the fastening means when the lock is in the unlocked 
position. When the lock is in the locked position, torque applied to the 
enclosure is not transmitted by the engaging means to the fastening means. 
Therefore, in the locked position the knob will simply rotate about the 
fastening means and prevent the removal of the audio equipment from the 
secured structure. 
In operation, the knob, in its unlocked position, is rotated clockwise 
until the threaded stud is securely attached to its threaded counterpart 
on the radio. In this position, the lock assembly rotates a cam plate so 
that an engaging disc engages both the knob enclosure and a stud plate 
allowing torque applied to the enclosure to be transferred to the threaded 
stud. The knob is then locked. In this position, the lock assembly rotates 
the cam plate so that the engaging disc does not engage the stud plate, 
and a compression spring forcibly separates the engaging disc and the stud 
plate. Torque is not transferred from the enclosure to the stud plate. The 
knob will then rotate freely in either the clockwise or counterclockwise 
direction, but the stud will not loosen or tighten, thus preventing 
removal of the radio from the vehicle. To remove the knob, the knob must 
be unlocked using a special key. In this position, any loosening or 
tightening torque applied to the enclosure will be transmitted to the 
stud. 
Additional objects, advantages and novel features of the invention will be 
set forth in part in the description which follows, and in part will 
become apparent to those skilled in the art upon examination of the 
following or may be learned by practice of the invention. The objects and 
advantages of the invention may be realized and attained by means of the 
instrumentalities and combinations particularly pointed out in the 
appended claims. 
The following detailed description, which describes only the preferred 
embodiment of the invention, is understood only to be an illustration of 
the best mode contemplated of carrying out the invention. As will be 
realized, the invention is capable of other and different embodiments and 
applications, and its several details are capable of modifications in 
various obvious respects, all without departing from the invention. 
Accordingly, the drawings and description are to be regarded as 
illustrative in nature, and not as restrictive.

DETAILED DESCRIPTION OF THE INVENTION 
The theft prevention device of the present invention is primarily intended 
for mounting or attaching radio and accessory equipment within vehicles. 
The invention has a more specific use for mounting audio equipment, such 
as a two-way radio, on a dashboard using a conventional "U"-shaped 
mounting bracket or trunnion. The invention, however, has broad 
applications whether in an automobile, at home, or wherever there is a 
need to discourage theft of property. The following description makes 
reference to mounting a mobile radio to a dashboard or a floorboard only 
as a means to illustrate the use of the invention, but in no means is 
intended to limit the applications of the invention. 
The invention provides an anti-theft fastening device for mounting or 
attaching a mobile radio to a dashboard or floorboard that prevents the 
fastening means from being unfastened by unauthorized personnel. Referring 
to FIG. 1, the invention is a substantially conical-shaped mounting knob 
20 having a lock assembly 26 mounted to a first end and a threaded stud 28 
attached to a second end. Generally, the threaded stud 28 passes through a 
mounting bracket (fixed to the vehicle) and engages a threaded counterpart 
on the radio as shown in FIG. 2. The knob 20, in its unlocked position, is 
rotated clockwise until tight, then locked. In the locked position, the 
knob will rotate freely in either direction, but will not loosen, thus 
preventing removal of the radio from the vehicle. To remove the knob, the 
knob must be unlocked using a special key and rotated in a 
counterclockwise direction. The invention can be manufactured of any 
suitable material strong enough to withstand attempts to forcibly remove 
it. 
FIG. 3 illustrates the internal construction of the invention. 
Specifically, mounting knob 20 comprises a generally conical-shaped 
enclosure 22, shown in more detail in FIG. 4, having a first open end 56 
and a hex-shaped second open end 58. Enclosure 22 further defines cavity 
60 in which other elements of the invention are located. 
Lock assembly 26 inserts into cavity 60 through opening 56 and securely 
fastens to enclosure 22 by means of nut 32 tightened against annular 
flange 64. Lock assembly 26 may be any miniature cam lock, such as 
miniature cam lock number C520 S, manufactured by Illinois Lock Co. of 
Wheeling Ill. As shown in FIG. 5A, lock 26 comprises a rotatable member 66 
and an arcuate-shaped fixed member 67. Rotatable member 66 undergoes a 
rotational motion in response to the key position of lock 26 changing from 
the locked to unlocked position and vice versa. 
Referring to FIGS. 3 and 5, cam plate 34 comprises cam openings 68 and 68A, 
an arcuate-shaped slotted opening 70 and a center opening 72. Referring 
again to FIG. 5A, slotted opening 70 interfaces with fixed member 67 and 
acts as a stop to limit the rotational motion of cam plate 34, as is 
discussed below. Center opening 72 is sized to slidably attach to 
rotatable member 66. Accordingly, cam plate rotates in response to the key 
position of lock 26. Cam openings 68 and 68A accept cams 74 and 74A, 
respectively. Preferably, cams 74 and 74A are solid 1/8" steel round head 
rivets. Cams 74 and 74A are inserted so that the round head interfaces the 
engagement disc 44. Alternatively, other types of cam configurations, such 
as rails having varying depths, may be used for the cam function and 
modified accordingly for this application as would be known to those 
skilled in the art. 
Referring to FIGS. 6 and 6A, engagement disc 44 is a hex-shaped plate 
comprising two cam slots 76 and 76A, a center opening 78 and an annular 
depression 80. Cam slots 76 and 76A are configured so that at one end the 
slots are deep enough to accept cams 74 and 74A. The remaining portion of 
the cam slots are configured so that the depth decreases uniformly. The 
sweep of cams 74 and 74A within slots 76 and 76A is dependent upon the 
rotational motion of cam plate 34 as determined by the length of slotted 
opening 70, the range of motion of rotational element 66 from its unlocked 
to locked position and the size of fixed member 67 in relation to slotted 
opening 70. That is, in the locked position, cams 74 and 74A are 
positioned within the bulbous portion of slots 76 and 76A. Moving from the 
locked position to the unlocked position, cams 74 and 74A rotate through 
cam slots 76 and 76A and come to rest at the opposite end of slots 76 and 
76A or on the engagement disc surface. The rotation of cam plate 34 from 
the locked to the unlocked position causes disc 44 to move axially within 
the second open end 58. The total travel in this axial direction is 0.10 
inches. Disc 44 is, however, prevented from rotating about the 
longitudinal axis of enclosure 22 since the second open end 58 is 
hex-shaped or "keyed" to correspond in shape with the hex shape of disc 
44. 
Referring to FIGS. 7 and 7A, stud plate 30 is a three-tiered member that 
aligns with and seals the second open end 58. Stud plate 30, however, does 
not fixedly attach to enclosure 22. Extending outwardly from stud plate 30 
is the threaded stud 28 that threadably engages a threaded interface on a 
radio. The second tier 86 comprises an annular slot 87 in which an annular 
compression spring 52 rests. Compression spring 52 also engages annular 
depression 80. Compression spring 52 forcibly separates disc 44 from stud 
plate 30 when lock 26 is in the locked position, as is discussed below. 
Alternate means may be used to separate these two elements, such as 
magnetic forces. The third tier 88 comprises a hex recess 90 sized to 
accept disc 44 and an annular groove 92 that accepts a pair of spring 
washers 54. 
Referring to FIGS. 3, 8 and 8A, stud plate 30 and the other internal 
elements of the invention discussed above are secured in a cooperating 
relationship within cavity 60 by base 24. The circumferences of enclosure 
22 and base 24 comprise interlocking surfaces and are fixedly attached by 
any conventional means such as an adhesive or ultrasonic weld. The 
attachment means must be made permanent to prevent tampering or opening of 
the assembly. Base 24 comprises a central opening 94 through which 
threaded stud 28 passes. Stud plate 30 does not fixedly engage base 24, 
but rather is able to freely rotate about the inner circumference of base 
24. Preferably, the outer circumference of base 24 is textured in such a 
way that allows an individual to grasp the base 24 when rotating knob 20. 
In operation, knob 20 has two functional positions, unlocked and locked. In 
the unlocked position, shown in FIG. 3, the lock assembly 26 is 
key-operated to position cams 74 and 74A on top of engagement disc 44. In 
this position, disc 44 is fixedly engaged with both enclosure 22 and stud 
plate 30. Rotating knob 20 will allow tightening or loosening of threaded 
stud 28. The torque from the outer shell 22/24 is transferred to stud 
plate 30 through hex disc 44. Disc 44 is securely held in this downward 
position by cams 74 and 74A. When the key is turned to rotate lock 26 to 
the locked position, cams 74 and 74A rotate to engage the bulbous areas of 
slots 76 and 76A respectively. Disc 44 is forcibly disengaged from stud 
plate 30 by compression spring 52. Disc 44 now engages only enclosure 22. 
Therefore, if knob 20 is rotated to remove it, it will only rotate because 
torque is not transmitted to stud plate 30. Therefore, threaded stud 28 
will not loosen or tighten. 
To remove the knob, the lock is moved to the unlocked position, cam plate 
34 rotates and forces disc 44 to engage stud plate 30 and compresses 
spring 52. While in the locked position, enclosure 22 and disc 44 may have 
been rotated independently of plate 30, therefore, disc 44 and hex recess 
90 may not line up exactly. If not lined up, spring washer 54 compresses 
because plate 30 and disc 44 move together away from cam plate 34. As knob 
20 is rotated, it will rotate only as far as needed to align disc 44 with 
plate 30, then both will snap into engagement. Torque will now transfer to 
plate 30 and knob 20 may be loosen or tightened. 
It will be understood that the particular embodiments described above are 
only illustrative of the principles of the present invention, and that 
various modifications could be made by those skilled in the art without 
departing from the scope and spirit of the present invention, which is 
limited only by the claims that follow.