The present invention relates to locks and more particularly to "electronic" key locks of the kind where a code is received by the lock from a proper key by way of key locks are relatively well known, at least in the patents literature, as exemplified by DE-2634303, EP-0115747, GB-2158870, GB-2174452, US-4549176, US-4602253 and WO-88/03594. The principle of operation of such devices is that the lock generates an alternating magnetic field in a region into which the key is brought, the key having circuit elements which control an inductive transmission element on the key to modulate or add to the field generated by the lock in such a way as to enable detection by the lock of a code programmed into the key. Preferably, although not essentially, the power for the circuit elements of the key is derived by rectification of the voltage induced by the alternating field of the lock. A particular advantage of this form of code transmission is that it avoids the need for any galvanic contact between the lock and key.
It is recognised that, both in the interests of user acceptance and to maximise the utilisation of standard lock components and furniture, it is desirable that the overall appearance, dimensions and functionality of "electronic" key locks should resemble as far as practicable those of their conventional mechanical counterparts. The present invention is therefore concerned with an "electronic" lock which can resemble a conventional mechanical cylinder lock in that it comprises a housing bearing a rotatable barrel with a keyway, into which the key is inserted and turned in order to retract the associated bolt or other such locking member. A lock of this style operating on the inductive coupling principle, more particularly for vehicle doors, is disclosed in GB-2174452. In this prior art arrangement, the induction elements of both lock and key comprise a respective coil with a soft iron core. The lock coil is mounted longitudinally in a bushing at the end of the barrel, to one side of the keyway, while the key coil is mounted longitudinally in its tip, so that when the key is fully inserted in the barrel the two coils lie side-by-side, with their cores in parallel. It is evident that in an arrangement such as that, however, only a partial inductive coupling between the two coils can be achieved, in the sense that much of the magnetic flux generated by either coil will follow a path which does not pass through the other. In consequence, the total magnetic flux and energising power requirements of the lock are higher than they need be if a more efficient coupling of the inductive elements were achieved. Furthermore, mounting the lock coil in the rotating barrel causes complications for its electrical connection to the rest of the field-generating and processing circuitry. In GB-2174452 this coil is connected by conductors which will be twisted whenever the barrel is turned, and for which there would be an eventual risk of breakage particularly if the barrel was required to describe a large turning angle.
It is particularly desirable in the operation of a lock of this character that its power consumption be minimised, for example so that a usefully long service life can be expected when battery-operated, and because more costly components are required when high power levels must be handled. In addition, current EMC (electromaqnetic compatibility) standards effectively restrict the permissible radiated electromaqnetic power of devices such as electronic locks. Because this radiated power is directly related to the power levels handled in the lock, it is advantageous to keep these levels to a minimum. We believe that these criteria can best be met in an inductively-coupled lock by ensuring that the respective inductive elements are positioned such as to maximise the linkage of magnetic flux between them when reading the code from the key. Accordingly, it is an aim of the invention to provide an inductively-coupled lock of "cylinder" style in which this linkage is maximised, and in particular is improved over the arrangement in GB-2174452.