More specifically, this lock includes: -a fixed barrel with a cylinder mounted for selective rotation therein, -a member for operating a bolt, and -an intermediate member mounted for rotation inside the barrel and rotatable by a distal end of the cylinder.

In the prior art, such an intermediate member is secured to the operating member. In the case of a forced opening, which is usually carried out by removing the cylinder, the perpetrator can therefore act directly on the intermediate member-which, in the absence of the cylinder, is accessible from the outside-to move the operating member and open the bolt.

The object of the present invention is to provide an improved lock compared to the ones of the prior art, with regard in particular to increasing its ability to withstand attempts to force it.

This object is achieved according to the invention by providing a lock with the characteristics specifically claimed in the Claims which follow.

Advantages and characteristics of the invention will become apparent from the detailed description which follows, with reference to the appended drawings, provided purely by way of non-limitative example, and in which: Figure 1 is a sectioned side-elevation view of a lock of the invention, and Figures 2-4 are sections view taken on the lines II-II, III-III and IV-IV respectively of Figure 1.

A lock, in particular for a door of a motor vehicle, includes: a fixed barrel 10 with a cylinder 12 mounted for selective rotation therein, an element 14 for operating a bolt (not shown in the drawings), an intermediate member 16, also mounted for rotation inside the barrel 10, and a security device 18.

The cylinder 12 is of a known per se type and, once the appropriate key is inserted into the keyhole, is rotatable inside the barrel 10. These operating characteristics and associated structural details are well known to those skilled in the art and, being substantially transparent in the context of the present invention, are not described in detail.

The intermediate member 16 is substantially cylindrical and has a first closed end 20, intended to face the cylinder 12, with a polygonal aperture 22, which can be square for example, its outline being complementary with that of a protuberance 24 projecting from the distal end of the cylinder 12.

The intermediate member 16 has a second, open, end 26 operable to engage a proximal end 28 of the operating member 14 and a central cross member 30 with a hole 32 aligned with the axis 34 of the cylinder 12. A window 36 is also formed in a portion of the side surface of the intermediate member 16.

The security member 18 includes a"roof portion"38 of a shape substantially complementary to that of the window 36 in the side of the intermediate member 16, with two pairs of legs, a distal pair 40 and a proximal pair 42 extending from the corners thereof.

The distal legs 40 are engageable between the cross member 30 and the open end 26 of the intermediate member 16, securing this for rotation with the operating member 14. The proximal legs 42 are engageable between the cross member 30 and the closed end 20 of the intermediate member 16 and their ends furthest from the roof 38 are linked by a transverse bar 44 so as to form an opening 46 at the site of the axis 34 of the cylinder 12, for the protuberance 24 of the cylinder 12 to pass through.

The proximal legs 42 are hollow and house respective coil springs 48 (see Figure 3) able to react against an inner portion of the side of the intermediate member 16.

The operating member 14 has a proximal portion 28 secured to a distal portion 50, in the form of a rod.

The proximal portion 28 includes a flange 52 and a cylindrical portion 54 containing a cavity 56 which extends coaxially of the axis 34 of the cylinder 12 and faces it, with two diametrically opposed flat surfaces 58 formed on the outer surface of the cylindrical portion 54 (see Figures 2 and 4).

A pin 60 is slidable within the cavity 56, with means for preventing it from sliding out completely. These means include an enlarged head 62 on the distal end of the pin and an annular seal 64, with an inner diameter smaller than the cross section of the cavity 56, fixed to the mouth of the cavity 56 so as to act as a stop for the head 62.

In the normal operating configuration of the lock shown in the drawings, the protuberance 24 of the cylinder 12 passes through the aperture 22 in the end 20 of the intermediate member 16, the aperture 46 in the security device 18 and the hole 32 in the cross member 30 of the intermediate member 16.

The security device 18 is thus secured to the intermediate member 16 and to the cylinder 12. Meanwhile, the distal legs 40 of the security device 18 engage the flat surfaces 58 of the operating element 14, thereby securing it to the security device 18.

The cylinder 12, intermediate member 16, security device 18 and operating element 14 together constitute an integral assembly, rotatable as a unit when the key is inserted into the keyhole in the cylinder 12, in substantially the same way as a conventional lock.

However, if the cylinder 12 is removed from the lock in an attempt to force it, this assembly is no longer integral. As soon as the protuberance 24 of the cylinder 12 no longer engages the aperture 46 in the security device 18, this latter is expelled through the window 36 in the member 16 under the resilient force of the springs 48, which is no longer contained (see the position of the device 18 shown by a dotted line in Figure 1).

The expulsion of the security device 18 breaks the connection between the operating element 14 and the intermediate member 16. Any manipulation of the latter-which is the only component accessible from the outside through the cavity in the barrel 10 left open by the removal of the cylinder 12- will fail to move the operating element 14. Once the connection with the distal legs 40 of the security device 18 is broken, the element 14 rotates freely, without engaging the intermediate member 16.

The lock of the invention is thus clearly better able to resist attempts at forcing it, especially since a perpetrator is unable to act on the element 14 which operates the bolt simply by removing the cylinder 12.

As shown in Figure 1, the protuberance 24 of the cylinder 12 inserted into the aperture 32 in the cross member 30 holds the pin 60 pressed against the bottom of the cavity 56. The pin 60 plays a specific role in the assembly of the lock, which is completed by inserting the cylinder 12 into the barrel 10.

At this time the security device 18 needs to be secured to the other components of the lock during the various operations which take place before the cylinder 12 is inserted into the barrel 10. This problems is resolved by making the pin 60 protrude from the cavity 56 in such a way that it engages the aperture 46 in the security member 18, thereby holding it in the barrel 10. When the cylinder 12 is inserted into the barrel 10 to finish assembling the lock, the protuberance 24 pushes the pin 60 towards the end of the cavity (see Figure 1) where it plays no further role either in the normal operation of the lock or in the case of the security device 18 being expelled. Naturally, the principle of the invention remaining unchanged, manufacturing details and embodiments may vary widely from those described purely by way of non-limitative example, without departing thereby from the scope of the invention.