This invention relates generally to devices for preventing theft or unauthorized operation of vehicles or machinery powered by internal combustion engines, and more specifically, to devices for preventing automobile thefts by disablement of the fuel supply and ignition or starter systems.
The key-operated ignition switch is the most widely used device for discouraging theft or unauthorized use of motor vehicles. It is well-known that this device suffers from certain deficiencies as a deterrent to automobile theft. The device only acts as an electrical switch for tthe ignition system, and a thief may defeat its purpose simply by connecting a jumper wire directly from the battery to the ignition coil. Furthermore, in many automobiles the ignition key cylinder is notoriously easy to remove from its housing, leaving the electrical switch contacts exposed. These contacts may then be crossed and connected by a metallic foreign object, and the car can be easily driven away. In fact, professional thieves are often known to carry spare key cylinders, and they are able to steal a car very quickly by removing the key cylinder from its housing and substituting a spare cylinder, thereupon driving the car in the normal manner.
A variety of devices supplementing the ignition key switch have been proposed and designed for frustrating the efforts of car thieves. Such devices include electrically or hydraulically actuated solenoids and valves for shutting off the fuel supply or locking the brakes in order to disable the vehicle. These devices sometimes employ a second switch in addition to the ignition switch, the second switch being positioned in a location that is difficult to find or inaccessible. These devices are an inconvenience to the normal user of the vehicle, and the location of the auxiliary switch may be discovered by an experienced thief. Other devices of this type employ an auxiliary switch which is operated with a second key, an electrically coded plastic card, or similar means. Such means are also inconvenient for the normal user, and suffer from the same drawbacks as the ignition key switch. Finally, all these devices may be defeated by appropriate jumper wires to the valves or solenoids and the ignition coil.
Another class of devices involves substantial modification of the ignition key switch itself, and other components of the ignition system, to disable the vehicle. For example, ignition switches have been proposed having internal electric switches or hydraulic valves for shutting off the fuel supply when the key is turned off. Other ignition switches have been designed which employ a special "resistor coded" key, such as the system described in the patent to Schroeder, U.S. Pat. No. 4,148,372. Such devices entail substantial expense and complexity of design, and are not readily adaptable to existing motor vehicles. Their operation may often be thwarted by connecting jumpers or by disconnecting their associated wiring.