Safety system for a motor vehicle steering lock

Claim 1

In a motor vehicle anti-theft steering lock device of the type incorporated with the motor vehicle ignition switch having a key operated ignition switch lock including a rotatable cylinder, said steering lock including a steering lock bolt displaceable between an extended position in which it engages the steering column of the vehicle and a retracted position in which it is spaced from the steering column, resilient biasing means urging said steering lock bolt towards said extended position, a rotatable cam rigidly connected to said rotatable cylinder of said ignition switch lock holding said steering lock bolt in said retracted position against the action of said resilient biasing means when said key is in position in said ignition switch lock, safety means operable to allow displacement of said steering lock bolt from said retracted position to said extended position thereof only upon withdrawal of said key from said ignition switch lock when said rotatable cylinder thereof is in a position where the ignition switch is turned off, further safety means comprising: detector means for sensing whether the vehicle is in motion or is stationary, said detector means operating to provide a first output electrical signal when the vehicle is in motion and a second output electrical signal when the vehicle is stationary, an electronic circuit connected to the output of said detector means and operating in response to said first and second output signals to provide at its output a control voltage when the vehicle is in motion, and electromagnetic locking means connected to the output of said electronic circuit and operating in response to said control voltage to prevent the displacement of said steering lock bolt from said retracted position thereof to said extended position thereof whenever the vehicle is in motion, wherein the said electronic circuit comprises: an input terminal, a capacitor connected between said input terminal of said circuit and ground, a voltage source, an electrolytic capacitor connected between said voltage source and ground, a Zener diode connected by one terminal to said voltage source and by the other terminal to ground, a first NOR gate having two inputs, which are both connected to said input terminal of said circuit, a second NOR gate having two inputs one of which is connected through an RC unit, constituted by a capacitor and a grounded resistor, to the output of said first NOR gate, a third NOR gate having two inputs which are connected together and to a capacitor which is connected to the output of said second NOR gate, the output of said third NOR gate being connected to the other input of said second NOR gate, a resistor connected between the input of said third NOR gate and the non-grounded terminal of said Zener diode, a fourth NOR gate having two inputs one of which is connected, through a unit constituted by a diode in parallel with a resistor, to the output of said second NOR gate, and the other of which is connected to a junction point between two resistors one of which is grounded and the other of which is connected to control terminal of the circuit, an electrolytic capacitor connected between said one input of said fourth NOR gate and the non-grounded terminal of said Zener diode, and a transistor the base of which is connected through a resistor to the output of said fourth NOR gate, the emittor of which is connected to ground, and the collector of which is connected to said voltage source through a diode, said collector constituting the output of said circuit.