Electrical anti-theft security system, especially for a motor vehicle

An electrical anti-theft security system for a motor vehicle includes an immobilising device for inhibiting power supply to the starter of the vehicle so long as the motor, incorporated in the anti-theft system and arranged to drive a blocking member, such as a steering lock, has not reached the unlocked position. The immobilising device is also arranged to prevent the system from being locked unless the vehicle is at rest.

FIELD OF THE INVENTION 
The present invention relates to anti-theft security systems, in particular 
for a motor vehicle. 
BACKGROUND OF THE INVENTION 
It has previously been proposed to provide apparatus which enables the 
doors or other opening parts of something that is capable of being broken 
into by unauthorised persons, and in particular a motor vehicle, to be 
unlocked by remote control, and therefore without any contact, either 
electrical or mechanical, with the doors or other opening parts. In 
particular, keyless access techniques have been developed which enable 
access to be gained to a vehicle without the need to find a mechanical 
key, or the equivalent of a key, in order to gain access. 
Such a system is very attractive from the comfort or convenience point of 
view and also because it offers various possibilities for obtaining access 
using modern information technology. 
In the application of this concept to the locking and unlocking of opening 
parts, such as doors, for example those of a motor vehicle, or the locking 
and unlocking of an anti-theft security system for a vehicle, such as that 
which involves locking the steering column or the output shaft of the 
gearbox of a vehicle, mechanical systems have been proposed in these 
contexts which employ electrical actuating devices, for example a rotary 
electric motor or an electromagnet. 
When the system for obtaining access recognises that a right of access 
exists, and that an unauthorised demand for access also exists, a control 
member produces a command for actuation of the system which excites the 
electrical actuating device. The anti-theft system and/or the lock changes 
state by passing from the locked condition to the unlocked condition. When 
the user leaves the vehicle, and/or when it is desired to activate the 
anti-theft system, a similar sequence takes place in reverse. 
In one known design, which is described and shown in the specification of 
French patent application No. 93 11671 of 30 Sep. 1993, it was proposed to 
provide a method of control for an anti-theft system for a motor vehicle, 
in particular with a remote control access system, which, in particular, 
employs a switch for controlling starting of the vehicle, and the supply 
of electrical power to various electrical circuits of the vehicle. 
In that method, during a phase of deactivation of the anti-theft system, 
contact is made with the vehicle by means of, for example, a telecontrol 
unit. An anti-theft security switch is then operated, which reproduces the 
manipulation of the conventional mechanical keys, and a predetermined 
position of the security switch is detected so as to set up an 
interrogation procedure in order to identify the demand to unlock the 
anti-theft system. In response to this, a command or order for actuation 
of successive positions of the security switch, and finally a command to 
unlock the anti-theft system, are produced. 
In an activating phase of the anti-theft system, the step in which the 
anti-theft system is activated by operation of the security switch is 
detected. This operation of the switch reproduces the conventional 
manipulations of mechanical keys. Once this step is completed, the system 
is activated, and the successive positions of the security switch are 
deactivated. 
In order to realise such a procedure in practice, it is necessary to 
provide an electrical anti-theft security system of the type comprising: 
an anti-theft security switch for controlling starting of the engine of the 
vehicle and the power supply to various electrical circuits of the 
vehicle; 
a motorised security device comprising a blocking member, such as a 
steering column lock, and an electric motor for moving the blocking member 
between a locked position and an unlocked position; 
and a central anti-theft unit which is connected to the elements mentioned 
above for the purpose of implementing a procedure in which the anti-theft 
system is armed or disarmed. 
This system is also of the type in which the anti-theft security switch 
comprises: 
a key interruptor for detecting simulation of the introduction of a key 
into the anti-theft switch; 
and a multiple position control interruptor for controlling, in sequence, 
the power supply for a plurality of electrical circuits of the vehicle and 
for the starter, this control interruptor comprising a movable control 
contact which is connected to one polarity of an electrical power supply 
source, and a set of fixed contacts with which the movable contact makes 
successive contact during operation of the security switch with a view to 
enabling the vehicle to be started, the said fixed contact with which the 
movable contact engages in the succession being connected to the starter, 
and the control interruptor being unable to be actuated except in the 
presence of a key; and 
an immobilising device, for inhibiting the control interruptor, which 
device prevents the movable control contact from making contact with the 
fixed contact associated with the starter so long as the anti-theft system 
is not in its unlocked condition, and which, in response to a release 
signal from the central anti-theft unit, enables the movable contact to 
come into contact with the fixed contact associated with the starter. 
Such a system will be referred to as a system of the kind specified. 
DISCUSSION OF THE INVENTION 
An object of the present invention is to propose an electrical anti-theft 
system of the kind specified, which includes an immobilising device in the 
control interruptor, for example, an electromagnet and which prevents any 
starting of the vehicle so long as the blocking member of the said 
motorised security device is not in its unlocked condition, and which also 
prevents any possibility of the anti-theft system becoming activated into 
its locked condition unless the vehicle is stationary. 
According to the invention, an electrical anti-theft system of the kind 
specified is characterised in that: 
the immobilising device comprises a power supply unit which is connected 
directly to the electrical power supply source, and which is connected to 
the central anti-theft unit; 
in that it includes means for detecting the unlocked condition of the 
system, these detecting means being such as to deliver a corresponding 
signal to the central anti-theft unit; and 
in that the central anti-theft unit is unable to transmit a release signal 
to the immobilising device except when the central anti-theft unit has 
received an unlocking signal from the detecting means. 
According to a preferred feature of the invention, the drive motor of the 
motorised security device is connected to the power supply source through 
the key interruptor in the absence of a key, and, when a key is 
introduced, is connected thereto through a power supply line connected to 
a fixed contact, corresponding to the unlocked condition of the system and 
being part of the control interruptor, and with which the movable control 
contact cooperates at the beginning of its course of travel during 
operation of the control switch with a view to starting the engine, and, 
in an inhibiting position, an inhibiting member of the immobilising device 
is interposed between the fixed contact corresponding to the unlocked 
condition of the system and the fixed contact connected to the starter. 
The detecting means preferably comprise at least one interruptor for 
detection of the unlocked state of the system and comprising a movable 
contact permanently connected to the central anti-theft unit and connected 
to the power supply source when a key is introduced, and which is arranged 
to cooperate with a first fixed contact, connected to the central 
anti-theft unit, when the system is in its unlocked condition, and with a 
second fixed contact connected to the central anti-theft unit and to the 
drive motor of the motorised security device when the latter is in its 
locked condition. 
Preferably, the anti-theft system includes an immobiliser interruptor 
interposed between the central anti-theft unit and the power supply unit 
for the immobilising device, such as to interrupt the said line when the 
system is not in its unlocked condition. 
The immobiliser interruptor preferably has a movable contact which is 
linked in tandem to the movable contact of the interruptor for detection 
of the unlocked condition of the system. 
According to another preferred feature of the invention, the anti-theft 
system includes an interruptor for detecting the locked condition of the 
system, which comprises a movable contact connected to the electrical 
supply source in the absence of a key, and which is arranged to cooperate 
with a first fixed contact connected to the central anti-theft unit when 
the system is in its locked condition, and with a second fixed contact 
permanently connected to the central anti-theft unit, to the drive motor 
of the motorised security device, and to the second fixed contact of the 
interruptor for detecting the unlocked state of the system, when the 
system is in its unlocked condition. 
In another embodiment of the invention, the detecting means comprise at 
least one sensor for detecting the position of the drive motor, or that of 
the blocking member of the security device, in the unlocked condition of 
the system, the said sensor being connected to the central anti-theft 
unit. 
The central anti-theft unit preferably transmits a release signal to the 
immobilising device only when it has received an unlocking signal from the 
position sensor. 
The detecting means may include a sensor for detecting the position of the 
drive motor or the blocking member of the security device, in the locked 
condition of the system, the said sensor being connected to the central 
anti-theft unit. 
The anti-theft security switch may be of the rotary type. 
The key interruptor preferably includes a movable contact which is 
connected to the power supply source, and which is arranged to cooperate 
with the first fixed contact connected to the drive motor of the motorised 
security device in the absence of a key, and a second fixed contact 
connected to the central anti-theft unit in the presence of a key which 
has been introduced, so as to transmit to the central unit a signal 
representing a demand for unlocking or locking of the system. 
The drive motor is preferably connected electrically to the key interruptor 
and to the fixed contact corresponding to the unlocked condition, through 
a power supply unit which receives signals from the central anti-theft 
unit for controlling locking or unlocking of the system. 
The immobilising device is preferably in the form of an electromagnet, the 
core of which is biased resiliently towards an inhibiting position, and 
which is put into a retracted position when the coil of the electromagnet 
is energised. 
Further features and advantages of the invention will appear more clearly 
on a reading of the following detailed description of preferred 
embodiments of the invention, given by way of example only and with 
reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
The electrical anti-theft security system shown diagrammatically in FIG. 1 
includes a key 10, or a "false key", which is adapted to be introduced 
into the key barrel, or into a "false" key barrel, of an anti-theft 
security switch 12. 
The switch 12 is arranged to be mounted on the fascia of the vehicle, and 
its design is of a substantially similar type to that of the ignition 
switch of a vehicle in a conventional form. The user operates the contact 
key 10, or an ignition ring which simulates such an operation. The contact 
key 10 is in fact, in this example, a false key, and it does not 
necessarily operate on a mechanical lock, even though an actual key of 
this kind does afford an additional degree of safety by adding a 
supplementary locking or unlocking means in series with the general design 
of an electrical anti-theft system. 
The security switch 12 comprises a key interruptor 14 which is adapted to 
detect the absence of the key 10 or the presence of the latter in position 
when it has been introduced. The switch 12 also includes a multiple 
position control interruptor 16, for controlling the starting of the 
engine of the vehicle and for controlling the power supply to various 
electrical circuits of the vehicle. 
The key interruptor 14 is connected through a line 18 to one input of an 
electronic central anti-theft unit 20, while the control interruptor 16 is 
connected through a line 22 to another input of the central anti-theft 
unit 20. 
The central anti-theft unit includes an analysis circuit which is, in 
particular, capable of reading the positions, or states, of the 
interruptors 14 and 16 in the switch 12. For example, the anti-theft unit 
20 may include a microcontroller such as an INTEL 8051 circuit. This 
circuit contains a programme for reading the input ports so as to inform 
the central anti-theft unit of the positions of the various interruptors 
of the switch 12, as will be explained later herein. 
In accordance with a known design, and through another input and a line 23, 
the central anti-theft unit is able to exchange signals with an 
interrogation and receiving station 24, which in turn exchanges, through 
further lines 26 and 28, signals with, for example, a badge 30 carried by 
the user for giving keyless access to the vehicle. 
Depending on these exchanges of signals with the central anti-theft unit 
20, the latter produces, on a connecting line 32, a command signal for 
energising, in one direction or the other, an anti-theft motor 34 which 
acts on a blocking member 36 for mechanically locking the steering column 
of the vehicle or the output shaft of the gearbox. The motor 34 and 
blocking member 36 together constitute a motorised security device. 
In FIG. 1, the motor 34 is referred to as a "system motor", for reasons 
that will become apparent later herein. 
In addition, if the user overlooks the radio frequency badge 30 inside the 
vehicle by mistake, or if he omits to operate the key 10 in order to 
initiate a sequence for locking the anti-theft system, or if he leaves his 
badge 30 in the vehicle by mistake, the central anti-theft unit 20 sets 
off a reminder alarm 38. 
A first embodiment of an electrical anti-theft security system in 
accordance with the invention will now be described with reference to FIG. 
2, in which those components which are identical or similar to those in 
FIG. 1 are designated by the same reference signs. 
The key interruptor 14 includes a pivoting movable contact 42 which is 
permanently connected to the positive terminal +BAT of the battery of the 
vehicle. The free end of the contact 42 cooperates with a fixed contact 44 
in the absence of the key, or with a fixed contact 46 when the key 10 is 
introduced into the anti-theft security switch 12. 
The fixed contact 44 is connected through a line 48 to the power supply 
input 49 of an electrical power supply unit 50 for supplying power to the 
motor 34. The power supply unit 50 receives command signals for the 
locking and unlocking of the system, over lines 32V and 32D, which are 
connected to output ports LOC and UNL respectively of the central 
anti-theft unit 20. 
The fixed contact 46 of the key interruptor 14 is permanently connected 
through the line 18 to a "DEMAND" input port of the central anti-theft 
unit 20, so that the latter is able to set in train a sequence of steps 
for identification of the demand for unlocking of the anti-theft system, 
or the demand for locking of the anti-theft system. 
The multiple position control interruptor 16 is an interruptor of the 
rotary type which includes a movable control contact 52, which is 
connected permanently to the positive terminal +BAT of the battery of the 
vehicle. 
The movable control contact 52 is arranged to occupy a plurality of 
successive positions which are offset from each other in the direction of 
rotation of the contact 56. These positions are designated "O", "ACC", "R" 
and "S" in the drawings. In these successive positions, namely a stop 
position (O), a position for supplying power to electrical accessories of 
the vehicle (ACC), a running position (R), and a position for starting the 
engine of the vehicle (S), the rotary control contact 52 is arranged to 
cooperate with one or more conductive strips 54, 56, 58, 60 which are 
arranged in an arc of a circle and which constitute the fixed contacts of 
the interruptor 16. 
When the movable contact 52 is in the ACC position, it cooperates with the 
fixed strip 54, which is connected electrically to the power supply 
circuit ACC for the accessories of the vehicle. 
When the movable control contact 52 is in the "R" position, it is 
simultaneously in contact with the contact strip 54 and also with the 
further contact strip 56, which is connected to the ignition circuit +IGN 
of the engine of the vehicle. 
When the movable control contact 52 is in the "S" position, it is in 
contact with the fixed contact strip 56 and with the fixed contact strip 
58. 
The contact strip 58 is the fixed contact connected through an output STA 
to the starter circuit of the internal combustion engine (not shown) of 
the vehicle. The output STA is connected to the starter in a manner which 
will be described in greater detail later herein. 
When the movable control contact 52 is in contact with the leading end of 
the contact strip which constitutes the fixed contact 54, starting from 
the stop position "O", it comes simultaneously into contact with an 
arcuate contact strip 60 which is the fixed contact for the purpose of 
unlocking the system (in the sense of the term used in the present 
invention). The arrangement of the contact strip 60 with respect to the 
contact strip 54 is such that the movable contact 52 is in simultaneous 
contact with both of the strips 54 and 60 over part of its angular travel 
during the course of which it travels over the contact strip 54. This part 
of the travel is delimited by an immobilising device 64 which, in this 
embodiment, is shown in the form of an electromagnet. 
The electromagnet 64 includes a plunger or core 66, which is resiliently 
biased permanently by a spring into its extended position shown in FIG. 2, 
in which it projects outside the housing 68. In this position, the plunger 
or core 66 lies, adjacent to the end of the unlocking contact strip 60, 
across the path of travel of the movable control contact 52, so as to 
prevent any angular travel of the latter beyond the contact strip 60 
towards the ignition contact strip 56 and the starter contact strip 58. 
This situation exists so long as the immobilising electromagnet 64 has not 
been energised electrically in such a way as to retract the movable core 
or plunger 66 of the electromagnet into the housing 68 of the latter. 
From the operating point of view, and having regard to the rotation of the 
movable contact 52 in the anticlockwise direction (with reference to FIG. 
2), the immobilising device 64 is therefore disposed downstream of the 
unlocking contact strip 60 and upstream of the ignition contact strip 56 
and starter contact strip 58. 
The immobilising electromagnet 64 is supplied with electrical energy 
through a power supply unit 70 which is connected directly to the positive 
pole +BAT of the battery through a line 72, and which receives the command 
signals for release of the immobilising device, that is to say the signal 
for energising the coil of the electromagnet 64, through a line 74 which 
is connected to an output port EM of the central anti-theft unit 20. 
So long as the power supply unit 70 has not received any command from the 
central anti-theft unit 20, and starting from the locked position shown in 
FIG. 2, it is impossible for the movable control contact 52 to reach the 
contact strips 56 and 58. 
The disabling module 76, shown in the lower part of FIG. 2 within a box of 
phantom lines, will now be described in greater detail. The disabling 
module 76 includes means 78 for detecting the locked or unlocked condition 
of the anti-theft system. These detecting means 78 deliver a corresponding 
signal to the central anti-theft unit 20. 
In the first embodiment which is shown in FIGS. 2 to 5, the detecting means 
78 consist of two detecting interruptors 80 and 82, each of which is of 
the changeover type having two positions. The interruptor 80 which detects 
the unlocked condition of the system comprises a swinging movable contact 
element 84, which is permanently connected through the line 18 to the 
fixed contact 46 of the key interruptor 14. The movable contact 84 is also 
permanently connected to the "DEMAND" input of the central anti-theft unit 
20. The movable contact element 84 is arranged for cooperation with a 
first fixed contact 86 when the system is in its unlocked position. The 
fixed contact 86 is connected through a line 87 to an input port M2U of 
the central anti-theft unit 20, for detection of the unlocked condition. 
When the anti-theft system is in the locked condition shown in FIG. 2, the 
movable contact 84 is in contact with a second fixed contact 88 of the 
interruptor 80. This contact 88 is connected to the electrical power 
supply input 49 of the power supply unit 50 for the motor 34. It is also 
connected to the central anti-theft unit 20 through the interruptor 82 for 
detection of the locked condition of the system. 
The movable contact 84 of the interruptor 80 is coupled in rotation to the 
motor 34. The drawings show diagrammatically a movable finger 90 which is 
coupled in rotation to the motor 34, for movement through an arc between 
two end stop positions in which it meets a respective one of two 
mechanical end stop elements 94 and 92, which correspond to the locked and 
unlocked states of the system respectively. 
The design of the interruptor 80 for detection of the unlocked condition is 
such that the movable contact 84 comes into engagement with the fixed 
contact 86 before the movable finger 90 reaches the end stop 92 
corresponding to the unlocked state. 
The interruptor 82 for detection of the locked condition of the system 
comprises a movable contact element 96 which is permanently connected 
through the line 48 to the fixed contact 44 of the key interruptor 14. In 
the locked condition shown in FIG. 2, the movable contact 96 cooperates 
with a fixed contact 98, which is connected directly through a line 99 to 
an input port M1L of the central anti-theft unit 20, for detection of the 
locked condition of the system. The movable contact element 96 is also 
arranged to cooperate with a second fixed contact 100 which is permanently 
connected to an inlet port L/U of the central anti-theft unit 20, and is 
also connected to the power supply inlet 49 of the power supply unit 50 
for the motor 34, and to the second fixed contact 88 of the interruptor 80 
for detection of the unlocked condition. 
Finally, the electrical anti-theft system includes an immobiliser 
interruptor 102 which is interposed in the line 74 between the central 
anti-theft unit 20 and the electrical power supply unit 70 for the 
immobilising electromagnet 64. The interruptor 102 has a movable contact 
element 104 which is coupled mechanically to the movable contact element 
84 of the interruptor 80 for detecting the unlocked condition of the 
system, in such a way that the movable contacts 104 and 84 move in tandem. 
This mechanical coupling is indicated diagrammatically in the drawings by 
a broken line 106. 
The movable contact element 104 is in contact, when the anti-theft system 
is in its locked condition, with a fixed dead contact 108, and it is 
arranged to make electrical contact with a fixed contact 110 when the 
system is in its unlocked condition, that is to say when the movable 
element 84 of the interruptor 80 for detecting the unlocked condition 
reaches its unlocked condition in contact with the fixed contact 86. 
The operation of the electrical anti-theft system shown in FIGS. 2 to 5 
will now be described. In its locked condition shown in FIG. 2, the finger 
90 of the motor 34 is in contact with the mechanical end stop 94 
corresponding to the locked condition, and the movable contact 42 of the 
interruptor 14 is in contact with the fixed contact 44, while the movable 
control member 52 is in its stop position "O". 
When the driver introduces the key 10 into the anti-theft security switch 
12, this, at first, causes the key interruptor 14 to change state by 
passing from the condition shown in FIG. 2 to the condition shown in FIG. 
3. In this new position, the movable contact member 42 is in contact with 
the fixed contact 46, and transmits a demand for unlocking of the system, 
over the line 18 to the "DEMAND" inlet port of the central anti-theft unit 
20. 
The change of state of the key interruptor 14 also has the effect of 
causing the power supply unit 50 for the motor 34 to be itself supplied 
with power through the line 18 and through the interruptor 80 for 
detection of the unlocked condition, the fixed contact 88 of the 
interruptor 80 being connected to the power supply input 49. 
The driver then rotates the multiple contact control interruptor 16, in 
such a way that its movable control element 52 can pivot into its 
immediately adjacent angular position ACC, in which it is in simultaneous 
contact with the fixed contact strips 54 and 60. 
The central anti-theft unit 20 transmits to the power supply unit 50, 
through its output port LOC, a command for unlocking of the system, as a 
result of which the motor 34 is energised and rotates to an intermediate 
position which is shown in FIG. 3. In this intermediate position, the 
interruptor 82 for detection of the locked condition has already changed 
its position, so causing a change of state to occur at the input port M1L 
of the central anti-theft unit 20. 
Rotation of the motor 34 continues until the system is in its unlocked 
condition. The electrical power supply of the unit 50 is maintained up to 
the end of the unlocking operation, by the contact 60 and the movable 
element 84 in contact with the fixed contact 86. 
At the end of this change of condition of the anti-theft system, the motor 
34 is arrested by the movable finger 90 coming into engagement with the 
end stop 92 corresponding to the unlocked state, and the interruptor 80 
for detection of the unlocked state reaches the position shown in FIG. 4, 
and at the same time causes the immobiliser interruptor 102 to change its 
state. 
When the movable contact element 84 of the interruptor 80 for detection of 
the unlocked condition is in its "unlocked" position, the movable element 
104 of the immobiliser interruptor 102 has put the central anti-theft unit 
20 into communication, via the line 74, with the power supply unit 70 for 
the electromagnet 64. A signal is thus passed to the electromagnet 64 so 
as to cause the plunger 66 to be retracted into the housing 68 of the 
electromagnet, so releasing the contact element 52. 
It is now possible for the driver to continue operating the multiple 
position interruptor 16, in particular towards its "run" position "R" and 
its "start engine" position "S", thus enabling the engine of the vehicle 
to be started and the vehicle then used. 
In the normal "run" position R, the movable contact 52 is in simultaneous 
contact with the fixed contact 54, supplying power to the accessories ACC, 
and with the fixed contact 56 which supplies power to the ignition circuit 
IGN. 
When the driver stops the vehicle and desires to lock the anti-theft 
system, he first returns the movable contact 52 of the multiple position 
16 to the stop position "O", as is shown in FIG. 5. In this position it is 
no longer in contact with any of the fixed contact strips 54 to 60. At the 
end of this rotation, the driver removes the false key 10, the effect of 
which is to return the key interruptor 14 to its position shown in FIG. 2 
to 5, in which the movable contact 42 connects the positive battery 
terminal +BAT directly to the fixed contact 44 and to the line 48. 
The return of the key contact from its active position shown in FIG. 4 to 
its rest, or parked, position (shown in FIG. 5) also has the effect of 
supplying electrical energy to the input 49 of the power supply being 
transmitted to the "DEMAND" input port of the central anti-theft unit 20, 
the state of which has changed; and a signal is transmitted to the input 
port L/U. 
The central anti-theft unit 20 then transmits an order for locking of the 
system over the line 32D, to the power supply unit 50 and to the motor 34. 
The motor then leaves its "unlocked" position in which the movable finger 
90 is in contact with the end stop 92 moving to the "locked" position set 
by the end stop The various components are then restored to their 
respective position shown in FIG. 2. 
In this connection, during the rotation of the m the "locked" position, the 
interruptor 80 for the unlocked condition changes state; and 
simultaneously, the immobiliser interruptor 102 changes state so as once 
again to interrupt the connection between the central anti-theft unit 20 
and the power supply unit 70 for the electromagnet 64. This causes the 
plunger 66 of the electromagnet to be deployed, so as then once again to 
prevent the movable control contact element 52 from gaining access to the 
fixed contact strips 56 and 58 of the switch 16. 
It can now easily be understood that, so long as the driver has not 
withdrawn the false key, that is to say he has not caused any change of 
state to occur in the key interruptor 14 from the position occupied by the 
latter in FIG. 4, it is not possible for the power supply unit 50, under 
the control of the central anti-theft unit 20, to cause the system to 
become locked, because the power supply unit 50 is not supplied with any 
electrical power. 
Reference is now made to FIGS. 6 to 9 showing a second embodiment of the 
invention. In FIGS. 6 to 9 those elements which are identical or similar 
to those in FIGS. 1 to 5 are indicated by the same references. 
In this embodiment, the detecting means 78 consist of two Hall effect 
sensors 80 and 82, which are connected to the input ports H2L and H1U of 
the central anti-theft unit 20, via lines 87 and 99 respectively. The 
movable finger 90 coupled in rotation to the motor 34, apart from its 
cooperation with the mechanical end stops 94 and 92 corresponding to the 
locked and unlocked conditions of the system respectively, also cooperates 
with the sensors 80 and 82 so as to act on these two sensors according to 
the position which it occupies with respect to them. The control line 74 
for the power supply unit 70 for the electromagnet 64 is connected in this 
example directly to the output port EM of the central anti-theft unit 20. 
The fixed contact 44 of the key interruptor 14 is connected directly to 
the power supply input 49 of the motor power supply unit 50, which is also 
connected directly to the "unlocked" fixed contact strip 60 of the control 
interruptor 16. Finally, the fixed contact 46 of the key interruptor 14 is 
connected directly to the "DEMAND" input port of the central anti-theft 
unit 20. 
The operation of this second embodiment of the electrical anti-theft system 
in accordance with the invention will now be described with reference to 
FIGS. 6 to 9. 
In the locked condition shown in FIG. 6, the system is in its locked 
condition, with the key interruptor 14 and the control interruptor 16 in 
their respective parked positions. When the driver introduces a key 10 
into the security switch 12, and causes the movable control contact 52 to 
rotate into the ACC position, it simultaneously causes the motor power 
supply unit 50 to be supplied with electrical power, and it transmits a 
demand for unlocking of the system to the "DEMAND" input port of the 
central anti-theft unit 20 over the line 18. 
The central anti-theft unit 20 transmits an order over the line 32D to the 
power supply unit 50, which causes the motor 34 to rotate. At the 
beginning of this rotation, after the finger 90 has left contact with the 
"locked" end stop 94, the movable finger 90 passes in front of the sensor 
82, which transmits a change of state signal to the input port H1U of the 
central anti-theft unit 20. 
So long as the system is not in its unlocked condition, that is to say so 
long as the element 90 has not passed in front of the "unlocking" sensor 
80, the immobiliser electromagnet 64 remains in its position shown in 
FIGS. 6 and 7, in which it prevents the movable control element 52 of the 
interruptor 16 from gaining access to the fixed contact strips 56 and 58. 
At this stage, it is therefore impossible to start the engine. 
When the motor 34 reaches its "unlocked" position, that is to say when the 
steering lock 36 (FIG. 1) is released, and as is shown in FIG. 8, the 
central anti-theft unit 20, which has received an unlocking signal at its 
input port H2U from the sensor 80, transmits over the line 74 an order to 
the power supply unit 70 for the electromagnet 60, such as to cause the 
plunger 66 of the latter to be retracted. The driver can then continue to 
operate the multiple position switch 16, in particular into the ignition 
or run position R and the starting position S. 
When the driver stops the vehicle, and as is shown in FIG. 9, he returns 
the multiple position switch 16 and the key interruptor 14 into their 
parked positions shown in FIG. 9. This causes a demand signal for locking 
of the system to be given, and this signal is passed over the line 18 to 
the "DEMAND" input port of the central anti-theft unit 20, which 
accordingly changes its state. 
When the central anti-theft unit 20 receives from the sensor 82 a signal 
that indicates to it that the system has been locked, it sends over the 
line 74, to the power supply unit 70 for the electromagnet 64, a signal 
for interrupting the power supply of the latter and causing the plunger 66 
to be deployed. Thus any further operation of the vehicle is no longer 
possible because the anti-theft system will no longer be in its unlocked 
condition. 
As in the case of the first embodiment, it will be understood that it is 
impossible to operate the starter so long as the security device 34, 36 is 
not in its unlocked condition, and that it is equally impossible to cause 
any accidental locking of the system, and in particular the steering 
column lock, when the vehicle, or at least its engine, is moving, due to 
the energisation of the power supply unit 50 for the motor 34. 
The invention is not limited to the embodiments described above. In 
particular, it is not limited to an arrangement in which the key 
interruptor 14 is in the form of an electrical interruptor controlled by a 
false key. This function may be replaced by any other type of electrical 
interruptor which is controlled directly or indirectly by the driver. 
Similarly, the multiple position interruptor is not necessarily of the 
rotary kind.