Abstract:
A mechanism for selectively locking and unlocking a vehicle door latch, comprising a rheological fluid in operable connection with an output and an input, the fluid acting so as to in a first state prevent actuation of the output upon actuation of the input and in a second state permit such actuation.

Description:
This application claims priority to Great Britain patent application number GB 0113542.5 filed on Jun. 5, 2001. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a vehicle locking mechanism that utilizes a rheological fluid in its operation. 
   Conventional locking systems require a number of moving parts whose operation may be compromised by dust ingress and wear, for example. Such locks are often relatively noisy in operation and may be relatively slow to change between locked and unlocked states. A further problem with know locking systems is that they do not interface well with electrically operated passive entry systems. 
   Passive entry systems replace conventional vehicle unlocking devices such as keys or “plip” type devices with sole form of transponder device that is carried by a vehicle user and that is remotely interrogated by a reader associated with the vehicle. If entry permission is granted, the system will signal the unlocking of the vehicle locks. However, as locking mechanisms are essentially mechanical in operation, one or more electrical motors must be fitted to a locking mechanism so as to convert the signals from the passive entry system to operate the locking mechanism. 
   SUMMARY OF THE INVENTION 
   The present invention seeks to overcome, or at least mitigate, the problems with the prior art. 
   Accordingly one aspect of the present invention provides a mechanism for selectively locking and unlocking a vehicle door latch, comprising a rheological fluid in operable connection with an output and in input, the fluid acting so as to in a first state prevent actuation of the output and in a second state permit such actuation. 
   A second aspect of the present invention provides a vehicle door latch comprising a locking mechanism having a rheological fluid, an output of the locking mechanism being operably connected to a door release mechanism of the latch and an input of the locking mechanism being suitable for operable connection to a door handle, the fluid acting so as to in a first state prevent actuation of the output upon actuation of the input and in a second sate permit such actuation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention are now described, by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  is a schematic diagram of a vehicle locking mechanism according to one embodiment of the invention. 
       FIG. 2  illustrates the tensile operation of the mechanism of  FIG. 1  when in a locked condition; and 
       FIG. 3  illustrates the mechanism of  FIG. 1  in an unlocked condition. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , there is shown generally at  10  a locking mechanism comprising a motion control device  12  and a linkage arrangement  14  mounted in a vehicle door (not shown) so as to lock the door when in a closed position relative to an associated vehicle. 
   The motion control device  12  comprises a cylinder  18  containing a magneto-rheological (hereinafter referred to as MR) fluid  16 . A perforated piston  20  is securely mounted on a ram  27 , the piston being axially slidable within cylinder  16 . 
   In this embodiment, the piston  20  is shaped such that movement from right to left in the Figures requires less force than movement left to right. This may act to damp the return of a door handle  31  to which the mechanism is attached. In other embodiments, the piston design may be altered to reverse this, or to make the required force equal in both directions in accordance with the particular requirement of the mechanism or components with which the mechanism interacts. 
   The cylinder  18  is at least partially surrounded by an electromagnet  22  connected by a circuit  24  to electrical power source  34  such as the vehicle battery. A switch  26  is provided to enable the circuit to be energised, such that when the switch is closed, a magnetic field is induced in the MR fluid by the electromagnet  22 . Magnetic shielding (not shown) is preferably provided to ensure that the MR fluid  16  is not influenced by external magnetic fields. 
   Magneto-rheological fluids are suspensions of small magnetisable particles in a liquid such as oil. MR fluids are normally free flowing and have a viscosity similar to that of motor oil. However, once a magnetic field is applied across the fluid, the fluid consistency becomes almost instantly more viscous. The increase in viscosity is proportional to the magnitude of the magnetic field applied. Electro-rheological fluids (hereinafter ER fluids) function in a similar manner upon application of a potential difference across the fluid. 
   In this embodiment, the linkage  14  comprises an input arm  30  which in this embodiment is connected to an internal and/or external door handle  31  of the associated vehicle door, and an output member  32  connected to an input of a latching mechanism  33  of the vehicle. Ram  27  and input arm  30  are pivotally interconnected by a connecting arm  28  at the distal ends of ram  27 , arm  30  and connecting arm  28 . Output arm  32  is pivotally connected to the connecting arm  28  at a position intermediate the ends of connecting arm  28 . 
   When the locking mechanism is in a first, locked state, the potential difference is not applied to electromagnet  22 . Therefore, the MR fluid is this first state has a low viscosity such that the fluid may pass through the perforations in the piston and piston  20  may move along cylinder  18  in a relatively unhindered manner. 
   Thus, when arm  30  is caused to moved in a direction X shown in  FIG. 2  by operation of the handle  31  connected thereto, the force required to displace the piston  20  is lower than the force required to cause arm  32  to unlatch the latching mechanism  33 . Movement of arm  30  in a direction X merely causes a corresponding movement of piston  20  and ram  27  in the direction Y, with substantially no movement of arm  32 , resulting in the latching mechanism  33  remaining latched. 
   Referring now to  FIG. 3 , it can be seen that switch  26  is now closed, thus energising the electromagnet  22 . This causes the viscosity of MR fluid  16  to increase so that movement of arm  30  by the door handle  31  in the direction X in turn causes arm  32  to move in a direction Z because in this second unlocked state, the force required to unlatch the latching system  33  is lower than the force required to displace the piston  20 . 
   It is therefore apparent that the locking mechanism of the present invention requires fewer moving parts than prior art devices, and is particularly suited to use with passive/keyless entry systems that are by their very nature electrically controlled. For this reason, the locking mechanism of the present invention may be easily integrated into such a passive entry system by causing switch  26  to be under its control. If the passive entry system determines that a particular person should be permitted entry to the vehicle switch  26  is closed. Otherwise, switch  26  remains open and the door remains locked. A particular advantage of this arrangement is that the locking mechanism consumes no power when in the locked state. 
   Vehicle door latches, typically have a number of operating modes. For a latch having an override unlocking function, these may include locked (when pulling on an outside door handle will not release the latch but pulling on an inside handle may override the locked state, superlocked (when pulling on both the inside and outside handle will not release the door) and child safety (in which the latch can be unlocked by the inside door handle but not released). To provide these modes, latches may comprise separate mechanisms of the present invention in the transmission path from the inside and outside door handles. The mechanisms may be individually controlled by a controller to provide the above described modes as appropriate. 
   It should be understood that numerous changes may be made within the scope of the present invention. In particular, it should be understood that the linkage described is for illustrative purposes only, and that the mechanism may be altered as required. In alternative embodiments, an ER fluid may be used rather than an MR fluid. Furthermore, appropriate alterations may be made to the electrical circuit  24  and/or the design of the cylinder and piston so that the mechanism may be adjusted to take into account changes in the viscosity of the fluid used and in the unlatching load of a particular latch mechanism. In particular, the resistance displacement of the piston may be adjusted to provide differing resistance in either direction of travel as required for the overall function of the mechanism. The mechanism may be fitted to a door surround portion of a vehicle rather than the door itself. It should be apparent that the mechanism may have applications in other fields such as locking mechanisms in buildings. 
   The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred examples of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.