EP2003272B1 - Lock cylinder with double locking means - Google Patents

Abstract

The cylinder (10) has two opposite parts (16) with locking blades (28) having a guiding pin (30) mounted between a radial stop unit (18) and a passage path (24). A stator (14) has locking pistons (42) and a rotor has a flat key (26) with coded opposite sides. One of the sides cooperates with the pin when the key is introduced in the path to cause transversal driving of the blades to adjust the notches opposite to the unit (18) and to permit radial movement towards interior of the rotor. Other side drives the pin in translation, where the pin drives the piston outside the rotor.

Description

The present invention relates to a locking cylinder with double locking means adapted to receive a flat key to unlock the locking means.

Known lock cylinders have a stator and a rotor rotatably mounted in said stator, and the rotor has an axial keyway, dividing the rotor into two opposing portions. These opposing portions respectively comprise locking pins and vis-à-vis the drive pins for locking and unlocking the rotating rotor within the stator. The locking pins extend directly protruding from the rotor and inside the stator to lock the rotor in rotation, while on the opposite side, the drive pins are adapted to come pushing locking pistons mounted in the stator and which extend protruding inside the rotor to lock it in rotation. The flat key has two opposite faces grooved and notched to form a code. When the flat key is introduced into the path of the rotor, the two opposite faces, thanks to the grooves and the notches, then cause a radial movement of the pins, so as to unlock the rotor in rotation. For this, the locking pins are then driven inwardly movement of the rotor, while conversely, the drive pins are supported against the locking pistons to drive and chase them outside the rotor. In this way, the rotor is free and unlocked in rotation inside the stator.

We can refer in particular to the document FR 2,534,962 which describes such a lock cylinder.

However, these pin locking mechanisms are well known, and even if the lock cylinders double rows of pins opposed to each other, and having opposite pins opposite operation, make more complex the break-in time, the fact remains that making copies of flat keys or picking these cylinders is still possible.

The document EP 0 103 532 A2 discloses, according to the embodiment shown in FIGS. 9-12, a flat-key lock cylinder, said cylinder comprising a rotor rotatably mounted in a stator, said rotor having an axial key-passing path dividing said rotor in two diametrically opposed parts, said parts comprising radial locking means for locking said rotor in rotation inside said stator, said rotor being adapted to receive a flat key having two opposite coded faces being intended to cause the radial movement of said locking means; radial, when said flat key is introduced into said passageway, so as to unlock said rotor in rotation, the radial locking means of one of said parts comprising a stop member projecting from said rotor in said position locking and inside said rotor in said unlocking position; and on the one hand said one of said opposing portions further comprising cylindrical or square section locking pistons mounted transversely between said stop member and said passage path for locking said stop member in said locking position, said pistons blocking device with a cylindrical or square section having a notch for receiving said stop member and, on the opposite side, a guide pin located in said passage path, and secondly the other of said opposite portion comprising pins for driving mounted sliding in an orifice, while the stator comprises locking pistons slidably mounted in a bore; and one of said coded opposite faces of the key having a sinuous key groove cooperating with said guide pin, when said flat key is introduced into said passageway, to cause the transverse drive of said cylindrical section locking pistons or square so as to adjust said notches opposite said stop member and allow its radial movement inwardly of said rotor, while the other of said coded opposite faces drives in translation said drive pins which come to drive their locking piston outside the rotor.

In addition, the document WO 2005/095738 A2 discloses a reversible flat key for a lock cylinder, said key comprising two axial half-parts symmetrical to each other with respect to a longitudinal key axis which extends between said half-parts, said key having two opposite faces respectively divided into two half-faces coded corresponding to said axial half-portions; and said coded half-faces of said two opposite faces form two pairs of opposite half-faces of each other, one of the two half-faces of a same pair having a sinuous key groove which extends according to an axial direction, while the other half-face has recesses adapted to cooperate with guide lugs and a longitudinal groove guide.

Thus, a problem that arises and that aims to solve the present invention is to provide a more complex lock cylinder that can therefore be more difficult to unlock by breaking, and allowing the introduction of a reversible key.

In order to solve this problem, the present invention proposes, according to a first object, a flat key lock cylinder, said cylinder comprising a rotor rotatably mounted in a stator, said rotor having an axial key passage path, said a passageway dividing said rotor into two diametrically opposed portions, said portions comprising radial locking means for locking said rotor in rotation inside said stator, said rotor being adapted to receive a flat key having two opposite coded faces, said faces coded opposing being intended to cause the radial movement of said radial locking means, when said flat key is introduced into said passage path, so as to unlock said rotor in rotation. The radial blocking means of one of said parts comprises a stop member, said stop member protruding from said rotor in said locking position and inside said rotor in said unlocking position. On the one hand said one of said opposite parts further comprises locking lamellae mounted transversely between said stop member and said passageway for locking said stop member in said locking position, said locking lamellae having a notch of receiving said stop member and opposite, a guide pin located in said passage path and secondly the other of said opposite portion comprises driving pins slidably mounted in an orifice, while the stator comprises locking pistons slidably mounted in a bore; and one of said coded opposite faces cooperates with said guide pin, when said flat key is introduced into said passageway, to cause the transverse drive of said lamellae so as to adjust said notches opposite said stop member and allow its radial movement towards the inside of said rotor, while the other of said coded opposite faces drives in translation said drive pins which drive their locking piston out of the rotor.

According to the invention, said axial keyway is eccentric and has an axial central zone extending longitudinally between said radial locking means of said two diametrically opposite parts, and an axial eccentric zone. Furthermore, and according to the invention, the central and eccentric zones are, according to a cross-section, defined by two symmetrical imprints of each other with respect to an eccentric line extending between the two zones substantially parallel to said rotor. Thus, thanks to these characteristics, a suitable flat key can be reversible, that is to say that it can be introduced into the axial passageway in two different positions, angularly offset by 180 ° one of the other.

Thus, a characteristic of the lock cylinder lies in the dual implementation of locking lamellae on the one hand which are driven in a transverse direction when the key is introduced into the rotor, and which come to release the stop member when their notch is precisely opposite this stop member, and a corresponding system of pins and pistons on the other hand where the pins, unlike the stop member, push their piston outside the rotor. In this way, when the rotor is rotated forcefully in the stator, and to the extent that the relative geometry of the point of contact between the stop member and the stator is in inclined plane, as will be explained hereinafter. after the stop member can be driven in translation towards the inside of the rotor and then escape the stator, while simultaneously and inversely the pistons are pushed towards the outside of the rotor by the pins so as to the contact surface between pins and pistons coincides with the sealing surface between the rotor and the stator. The rotor is then free to rotate inside the stator. As will also be explained below, a plurality of slats are used, respectively with relative positions of the guide pins and notch different, so as to code the lock; this combination of different relative positions must then coincide with the coded surfaces of the flat key. It will be observed that such a dual system using two different operating techniques makes it difficult to break in. In addition, the pin and piston system which is already relatively poorly hooked, makes it more difficult this break.

Advantageously, said indentations of the central and eccentric zones have two parallel impression ribs defining a longitudinal imprint groove between said two impression ribs.

According to a particularly advantageous embodiment of the invention, said stop member comprises a key mounted substantially parallel to said axial keyway, and said key being adapted to cooperate with said lamellae. In this way, the rotor being locked in rotation in the stator until the key is fully retracted inside the rotor, and the key can not be fully retracted unless all the slats have been positioned. so that their notch is opposite the key, we understand the difficulty of unlocking the lock if we do not have the corresponding flat key. And all the more so, that the other of said two diametrically opposite portions of the rotor is also equipped with radial blocking means which operate in a different mode. Indeed, when the flat key is introduced into the path of passage of the rotor, it comes for example, to cooperate with drive pins which themselves radially drive blocking pistons integral with the stator.

Advantageously, said one of said opposite parts has an axial groove which opens out of said rotor, and in which is housed the key. As will be explained below, the key has a substantially rectangular parallelepiped base to be perfectly guided radially in translation in the axial groove, and the opposite, the key has a rounded free edge to cooperate with the stator .

Moreover, said one of said opposite parts has spring means, for example helical springs for exerting a restoring force on said key, said restoring force tending to drive said key into a rest position outside said axial groove, where it locks the rotation of the rotor in the stator. Of course, the rounded free edge of the key abuts inside a recess formed in the stator, while its base remains engaged in the axial groove. The key thus straddling the rotor and the stator prohibits the rotation of the rotor inside the stator.

In addition, and according to a preferred embodiment of the invention, said rotor has transverse slots made in said one of said opposite portions and opening into said axial keyway, said transverse slots being adapted to receive said lamellae blocking to guide them in transverse translation. In this way, the transverse slots also open into the axial groove and thus, the transverse movement of the lamellae in these slots makes it possible to adjust the notches in the axis of the axial groove and thus allow the radial movement of the key towards the groove. inside the rotor. The key then comes to rest in the bottom of the axial groove. In addition, the transverse slots communicating with the passageway, the slats are adjusted so that their guide pin comes to extend precisely in the pathway.

According to a second object, the present invention proposes a flat key adapted to the lock cylinder described above. Said flat key comprises two axial half-portions symmetrical to one another with respect to a longitudinal key axis which extends between said half-parts, said flat key having two opposite faces respectively divided into two coded half-faces corresponding to said axial half-portions; and said coded half-faces of said two opposite faces form two pairs of opposite half-faces of each other. One of the two half-faces of the same pair has on one of the opposite faces, a sinuous key groove being adapted to cooperate with the guide pins and which extends in an axial direction, while the another half-face has, on the other side, two longitudinal key grooves separated by a longitudinal notched key rib being adapted to cooperate with the drive pins to drive the locking pistons. And the two half-faces of the other pair of opposite half faces have, on said other face, the same sinuous groove and on the opposite side, on said one of the opposite faces, the same two longitudinal key grooves separated by the rib. Thanks to these characteristics, the flat key object of the invention is reversible. In addition, thanks to the characteristics of the aforementioned lock, in two diametrically opposed parts and respectively including a device with lamellae and locking member, and a device with pins and pistons, the bit of the flat key object of the invention also, does not requires no lateral notches, and its side edges are straight and parallel to each other. This feature has the dual advantage of reducing the wear of key coding elements and allow to form less prominent edges and therefore less offensive.

Moreover, as will be explained below, when the flat key is introduced into the keyway, the guide pins will engage in the sinuous groove, which will then form a ramp for the pins of guide. In this way, as and when the key into the rotor, the slats will be driven in motion transversely so that their notch is located in alignment with the key. Simultaneously, and opposite, the notched rib cooperates with drive pins to drive locking pistons.

• la Figure 1 est une vue schématique d'une section droite partielle d'un cylindre de serrure à clé plate conforme à l'invention et dans une première position de déverrouillage ;
• la Figure 2 est une vue schématique en perspective montrant un premier élément du cylindre représenté sur la Figure 1 ;
• la Figure 3 est une vue schématique en perspective d'un deuxième élément du cylindre représenté sur la Figure 1 ;
• la Figure 4 est une vue schématique d'une première section selon le plan IV-IV du premier élément représenté sur la Figure 2 ;
• la Figure 5 est une vue schématique d'une seconde section selon le plan V-V du premier élément représenté sur la Figure 2 ;
• la Figure 6 est une vue schématique de faces d'une clé plate conforme à l'invention ;
• la Figure 7 est une vue schématique en coupe selon le plan VII-VII de la clé plate représentée sur la Figure 6 ; et,
• la Figure 8 est une vue schématique en section droite partielle du cylindre tel qu'illustré sur la Figure 1 dans une seconde position de déverrouillage.

Other features and advantages of the invention will emerge on reading the following description of a particular embodiment of the invention, given by way of indication but not limitation, with reference to the accompanying drawings in which:

• the Figure 1 is a schematic view of a partial cross-section of a flat key lock cylinder according to the invention and in a first unlocking position;
• the Figure 2 is a schematic perspective view showing a first element of the cylinder shown in FIG. Figure 1 ;
• the Figure 3 is a schematic perspective view of a second element of the cylinder shown in FIG. Figure 1 ;
• the Figure 4 is a schematic view of a first section according to the plane IV-IV of the first element represented on the Figure 2 ;
• the Figure 5 is a schematic view of a second section along the plane VV of the first element represented on the Figure 2 ;
• the Figure 6 is a schematic view of faces of a flat key according to the invention;
• the Figure 7 is a schematic sectional view along the plane VII-VII of the flat key shown on FIG. Figure 6 ; and,
• the Figure 8 is a schematic view in partial cross-section of the cylinder as illustrated on the Figure 1 in a second unlocking position.

The Figure 1 illustrates a lock cylinder 10 according to the invention. On this Figure 1 some elements are represented in continuous lines in one position and others in dotted lines in other positions. However, we will first focus on describing the elements whose contours are in continuous lines. Thus, the lock cylinder 10 has a rotor 12 of axis of symmetry A rotatably mounted in a stator 14. The rotor of 12 is divided into two diametrically opposed axial parts, a first portion 16 including a key 18 forming a body stopping, and a second portion 20 including drive pins and a single drive pin 22 in solid lines appears on the Figure 1 . The drive pin 22 is slidably mounted transversely in an orifice 21 of the rotor 12. The rotor 12 also has an axial key passageway 24, which extends laterally and longitudinally by separating in half the first and second parts 16, 20. It is here engaged, in the key passageway 24, a coded key 26 which will be detailed in the following description. The rotor 12 also comprises blocking strips, a single blocking strip 28 appearing here in solid lines. This locking blade 28 has, in a bearing edge 29, a guide pin 30 which opens into the passageway 24, and opposite an edge 32 in which is formed a square notch 34. The relative position of the square notch 34 and the guide pin, determines an opening code, only the appropriate key 26 can decode.

The key 18 has a rounded upper edge 36 housed in a rounded axial groove 38 of the stator 14 and opposite a rectangular parallelepiped base 40. Opposite the rounded axial groove 38, and here facing the pin of drive 22 housed in the rotor 12, remains a locking piston 42 slidably mounted in a bore 44 of the stator 14.

We will now detail the rotor 12 shown in perspective on the Figure 2 . It is here rid of the elements described with reference to the Figure 1 . It has a key entry 46 extended by the axial key passage path 24. Moreover, five regularly spaced transverse slots 48 are formed in the first axial portion 16 and are traversed in their middle part by an axial groove 50 of rotor. The five transverse slots 48 are respectively adapted to receive each a locking strip 28, while this axial groove 50 is intended to receive the key 18, above the locking strips 28. The key 18 is shown in perspective on the Figure 3 . It contains its base 40, parallelepiped rectangle and its rounded upper edge 36. This key 18 has a length substantially equivalent to the length of the axial groove 50 shown in FIG. Figure 2 . Moreover, the first axial portion 16 of the rotor 12 shown in this Figure 2 , comprises at each of the ends 52, 54 of the axial groove 50, not shown coil springs for pushing the key 18 outwardly of the rotor 12.

We will refer to the Figure 4 , showing a cross-section of the rotor 12 illustrated on the Figure 2 at the level of one of the transverse slots 48. We then find on this Figure 4 , the axial groove 50 and the axial key passage path 24. Moreover, the transverse slot 48 opens precisely into the axial key passage 24 via a recess 56. This recess 56 allows, as well as will explain below, the passage of the guide pin 30 locking lamellae 28. In addition, the transverse slot 48 forms bearing surfaces 58 of the locking lamellae 28 on each side of the recess 56.

The axial key passageway 24 of the rotor 12 is eccentric and has an axial central zone 60 located in the axis A of the rotor 12 and an axial eccentric zone 62 spaced apart from the axis A of the rotor 12. in the central zone 60, the second rotor portion 12 has two first axial ribs 64, 66 of the passageway 24 and projecting towards the first rotor portion 12, which first ribs 64, 66 define between the two a first axial groove 68 of passageway 24 and form a first impression. In addition, the first rotor portion 12, in the eccentric zone 62, has two axial second ribs 70,72 of the passageway 24 and protrudes towards the second portion 20. The two second axial ribs 70, 72 define between the two a second axial groove 74 of passageway 24 and forms a second imprint; the two impressions being symmetrical to one another with respect to an eccentric line D which extends axially between the two zones 60, 62. As will be explained below, such characteristics make it possible to introduce a suitable flat key in two angularly offset orientations of 180 °.

We will now refer to the Figure 5 , also illustrating a cross-section of the rotor 12 illustrated on the Figure 2 , but here between two transverse slots 48. In addition to the elements not referenced for the clarity of the presentation, we find in this Figure the rotor 12 and its first 16 and second part 20 separated from each other by the passageway 24. There is also the axial groove 50 which opens outwardly of the rotor 12. And opposite this axial groove 50, in the second part 20, there is found the orifice 21 adapted to receive a drive pin, not shown. In contrast, the transverse slot 48 does not appear on this Figure 5 , because in a cross section, the orifices 21 formed in the second portion 20 and opposite the transverse slots 48 in the first rotor portion 12 are alternated. This allows a better distribution of the material to form the rotor 12 and therefore greater rigidity.

We will now refer to the Figure 6 showing a first face 75 of the flat key 26 according to the invention, shown in cross section on the Figure 1 , and for which protection is also sought.

This flat key 26 comprises a bit 76, which has in the Figure a first face divided into two longitudinal and coded half-faces, a first 78 and a second 80, fictitiously separated by a plane P substantially perpendicular to the mean plane defined by the key 24. The first half-face 78 has a sinuous key groove 82 which extends in an axial direction substantially parallel to the plane P. This serpentine key groove 82 has a funnel-shaped inlet flare 84 free end of the bit 76, five parallel portions 86, 88, 90, 92, and 94 at said axial direction and the plane P, and five inclined portions 96, 98, 100, 102 and 104, between the parallel portions 86, 88 , 90, 92, 94 and which will be explained later, form ramps. The five parallel portions 86, 88, 90, 92 and 94 are respectively spaced apart from the second half-face 80 by a predefined distance, different from each other, to constitute a first unique combination.

The second half-face 80 has two longitudinal key grooves, a first 106 located towards the first half-face 78 and a second 108, remote from the second half-face 80. The two longitudinal key grooves 106, 108 are separated from each other by a longitudinal notched key rib 110. This longitudinal notched key rib 110 has six notches 112, 114, 116, 118, 120 and 122, of a predefined depth. Each of these six cuts can be practiced at different depths so that a second combination can be formed unique. The total number of combinations offered is then the product of all the possibilities of the first combination and all the possibilities of the second combination.

We will now refer to the Figure 7 , showing the bit 76 described with reference to the Figure 6 in straight section. We find on this Figure 7 , the first face 75 of the key 26 and also a second face 124. We find on this Figure 7 in the second half face 80 one of the six notches 114 formed in the key ridge 110, and on either side the two longitudinal key grooves 106, 108, while found on the first half face 78, the serpentine key groove 82.

Found on the second face 124, all the elements formed on the first face 75 but in a symmetrical position with respect to a longitudinal axis of key C. Thus these same elements will be referenced by the same reference assigned a prime sign: " '". Opposite the first half-face 78 there is one of the six notches 114 'in the key rib 110', and on either side the two longitudinal key grooves 106 ', 108', while found on the first half-face 78 ', the winding key groove 82'.

Thus, the second half-face 80 'of the second face 124 and the opposite, the first half-face 78 of the first face 75 constitute a pair of half-faces adapted to come to unlock the rotor 12 in rotation, as the second half-face 80 of the first face 75 with the opposite the first half-face 78 'of the second face 124.

In this way, thanks to this symmetry of bit 76 with respect to the longitudinal key axis C, the key 26 is adapted to be introduced into the passageway of the rotor in two key positions angularly offset by 180 ° one the other. Thus, the flat key 26 is reversible.

We will refer again to the Figure 1 , in order to describe the operating mode of the key lock cylinder 10 according to the invention. The rotor 12 is then equipped with five locking strips 28, respectively engaged in the transverse slots 48 and conferring a first part of the coding lock cylinder. One of the five blocking strips 28 appears in continuous lines, while the others appear in broken lines. It will be observed that the square notch 34 has a width equivalent to the width of the base 40 of the keys 18. In addition, the rotor 12 is provided with six drive pins 22, imparting to the lock cylinder a second portion of the coding.

For each of the locking strips 28, the square notch 34 may be formed in the edge 32 in five distinct positions laterally offset; one central, in the axis of the guide pin 30, and two on each side of the guide pin 30. Thus, the relative position of the square notch 34 and the guide pin 30 for each of the locking lamellae 28 confers said first part of the coding of the lock cylinder that only the adapted flat key can decode.

Thus, when the blade 76 of the coded flat key 26 is introduced into the keyway 46, one of the first two half-faces 78, 78 ', in which is formed the sinuous groove 82, 82', will come fit with respect to the first rotor portion 16, while one of the two second half-faces 80, 80 'will fit next to the second rotor portion 12, and this in the axial central area 60.

As the bit 76 is translated into translation in the key passageway 24, the guide pins 30 engage in the sinuous groove 82, 82 ', thanks to the funnel portion 84 while in contrast, the drive pins 22 abut against the key rib 110, 110 '. In addition, the locking strips 28 are driven laterally through the guide pins 30 which successively bear in the inclined portions 96, 98, 100, 102 and 104, the sinuous groove 80,80 ', which form then ramps; and simultaneously the drive pins 22 are successively driven in translation by the notched key rib 110, 110 '.

When the bit 76 is completely housed in the passageway 24, the guide pins 30 of the locking strips 28 are respectively held in a fixed position in the parallel portions 86, 88, 90, 92, and 94 of the sinuous groove 80 , 80 '. In contrast, the drive pins 22 of the rotor 12 are respectively supported in the notches 112, 114, 116, 118, 120 and 122.

If the coded flat key 26 used corresponds to the lock cylinder 10 which is adapted to unlock, then the notches 34 of the locking strips 28 are aligned in the axial groove 50 which opens outwards. rotor 12; and moreover, the drive pins 22 have respectively driven their locking piston 42 out of the rotor 12 so that the sealing surface of the locking pistons 42 and their corresponding pin coincides with the sealing surface of the rotor 12 and the stator 14.

In this way, the key 18 which is held resiliently in the rounded axial groove 38 of the stator 14 will be able to retract into the rotor 12 when the coded flat key 26 is rotated in force, since on the contrary the blocking pistons 42 are pushed back into the stator 14 and that they no longer prohibit the rotation of the rotor 12.

Indeed, the key 18 having its rounded upper edge 36 which is itself housed in the rounded axial groove 38 of the stator 14, when the rotor 12 is rotated by means of the flat key 26, the upper edge rounded 36 of the key 18 is driven in friction against the wall of the rounded axial groove 38, so that the key 18 is driven radially in the bottom of the axial groove 50 towards the inside of the rotor 12 as shown in FIG. Figure 8 .

We find on this Figure 8 elements identical to those illustrated on the Figure 1 , the key 18 now being fully inserted into the axial groove 50, and its base 40 inside the notches 34 of the locking strips 28. The key 18 is then entirely housed inside the rotor 12, just like the pistons 42 are pushed into the stator 14, so that the rotor 12 can be rotated freely in the stator 14 via the coded flat key 26.

Claims (7)

1. A lock cylinder (10) for a flat key, said cylinder comprising a rotor (12) rotatingly mounted within a stator (14), said rotor (12) having an axial key pathway (24), said pathway dividing said rotor (12) into two diametrically opposite parts (16, 20), said parts comprising radial blocking means (18, 50, 22, 21) intended to rotatingly lock said rotor (12) within said stator (14), said rotor (12) being adapted to receive a flat key (26) having two coded opposite faces (78, 80' ; 78', 80), said coded opposite faces (78, 80' ; 78', 80) being intended to cause the radial movement of said radial blocking means (16, 50, 22, 21) when said flat key (26) is introduced into said pathway (24), so as to rotatingly unlock said rotor (12), the radial blocking means (18, 50) of one of said parts comprising a stopping member (18), said stopping member (18) projecting out from said rotor (12) in said locking position and within said rotor (12) in said unlocking position ;
   so that, on the one hand, said one of said opposite parts (16) further comprises blocking plates (28) transversely mounted between said stopping member (18) and said pathway (24) in order to block said stopping member (18) in said locking position, said blocking plates (28) having a receiving notch (34) for said stopping member (18) and at the opposite, a guiding spur (30) located on said pathway (24), and on the other hand, the other of said opposite parts comprises driving pins (22) slidingly mounted within a hole (21), while the stator (14) comprises blocking pistons (42) slidingly mounted within a borehole ; and one of said coded opposite faces (78, 78') cooperating with said guiding spur (30), when said flat key (26) is introduced into said pathway (24), to cause the transversal drive of said blocking plates (28) so as to adjust said notches (34) in front of said stopping member (18) and to allow its radial movement inwards said rotor (12), while the other of said coded opposite faces translates said driving pins (22) which come to drive their blocking piston (42) out of the rotor (12) ;
   and so that said axial key pathway (24) is offset and has an axial central zone (60) which extends longitudinally between said radial blocking means (18, 50, 22, 21) and an axial offset zone (62) ; said central (60) and offset (62) zones being, in a straight cross-section, defined by two imprints symmetrically made the one to the other relative to an offset line (D) which extends between the two zones (60, 62) substantially in parallel to said rotor (12).
2. The lock cylinder according to claim 1, characterized in that said imprints have two parallel imprint ribs (64, 66 ; 70, 72) defining a longitudinal groove imprint (68 ; 74) between said two imprint ribs.
3. The lock cylinder according to claim 1 or 2, characterized in that said stopping member (18) comprises a cotter mounted substantially in parallel to said axial key pathway (24), said cotter cooperating with said plates (28).
4. The lock cylinder according to claim 3, characterized in that said one of said opposite parts (16) has an axial groove (50) opening outside of said rotor (12), said cotter (18) being received into said axial groove (50).
5. The lock cylinder according to claim 4, characterized in that said one of said opposite parts (16) is provided with spring means to exert a back force on said cotter (18), said back force tending to drive said cotter out of said axial groove (50).
6. The lock cylinder according to any of claims 1 to 5, characterized in that said rotor (12) is provided with transversal slits (48) practiced into said one of said opposite parts (16) and opening in said axial key pathway (24), said transverse slits being adapted to receive said blocking plates (28).
7. A flat key (26) for a lock cylinder according to any of claims 1 to 6, said flat key (26) comprising two axial half-parts symmetrically the one to the other relative to a longitudinal key axis (C) which extends between said half-parts, said flat key (26) having two opposite faces (75, 124) respectively divided in two coded half-faces (78, 80 ; 78', 80') corresponding to said axial half-parts ; and said coded half-faces (78, 80 ; 78', 80') of said two opposite faces (75, 124) making two pairs (78, 80' ; 80, 78') of half-faces, the one opposite to the other, one of the two half-faces of a same pair having a sinuous key groove (82 ; 82') being adapted to cooperate with the guiding spurs (30) and which extends in an axial direction, while the other half-face is provided with two longitudinal key grooves (106', 108' ; 106, 108) separated by a longitudinal cut-out key rib (110' ; 110) being adapted to cooperate with the driving pins (22) to drive out the blocking pistons (40).

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