Abstract:
A latch arrangement including an electric motor operable to open a latch and at least one switch that is closeable by operation of an associated manually operable element. The switch is connected in series with the motor so that a release current passing through both the first switch and the motor can release the latch. The switch ensures that electrical disturbances in the motor do not inadvertently release the latch.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority to United Kingdom (GB) Patent Application Number 0118685.7 filed on Aug. 1, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a latch arrangement, and more particularly to a latch arrangement for a vehicle door.  
           [0003]    Door latches are known wherein a latch bolt of the latch can releasably retain a striker, attached to fixed structure of a vehicle, in order to allow an associated door to open. Typically the latch bolt is retained in a closed or first safety position by a pawl.  
           [0004]    Known door latches further include an electric motor operable to move the pawl so as to enable the latch to be power released.  
           [0005]    However a problem of such devices is that it is possible to inadvertently actuate the motor, either as a result of electrical malfunction or as a result of EMC disturbances, resulting in the door opening unexpectedly.  
           [0006]    An object of the present invention is to provide an improved form of latch arrangement that prevents inadvertent release of the latch when the motor is actuated due to malfunctions or disturbances.  
         SUMMARY OF THE INVENTION  
         [0007]    Accordingly, one embodiment of the invention is directed to a latch arrangement comprising a motor that releases a latch, a switch connected in series with the motor and a manually operable element that can close the switch. The motor releases the latch if the switch forms a circuit that allows a release current to pass through the switch and the motor. By requiring the release current to travel through both the motor and the switch before releasing the latch, the invention prevents inadvertent release of the latch. The switch acts as a safeguard to ensure that the latch release is truly due to manual operation of the operable element.  
           [0008]    Other embodiments of the inventive system include circuits that have more than one switch.  
           [0009]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic view of a latch arrangement according to the present invention.  
         [0011]    [0011]FIG. 2 is a schematic view of a further latch arrangement according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    With reference to FIG. 1, there is shown a latch arrangement  10  including a latch power releasable by a motor M. The latch arrangement further includes a handle switch  12  (also known as a first switch) closeable by operation of an associated inside handle IH. The latch arrangement further includes a second switch  14  which typically might be a relay or a semiconductor device. A power source  16  is provided and it can be seen that the motor M, handle switch  12  and second switch  14  are all provided in series.  
         [0013]    A control device in the form of a microprocessor  18  controls operation of the second switch  14  and is connected via a resistor  20  to a power cable  22 B.  
         [0014]    A power cable  22  comprises portions  22 A,  22 B,  22 C,  22 D and  22 E, which connect the various components.  
         [0015]    Microprocessor  18  is capable of receiving input signals  36  which define the state of the latch. Thus the latch can be unlocked, locked (wherein operation of an outside handle does not open a latch but operation of an inside handle does open a latch), superlocked (wherein operation of an outside or inside handle does not open the latch), or child safety (wherein in the “child safety on” condition, operation of an inside handle does not open a latch, but the latch may or may not be opened from an outside handle depending upon whether the latch is unlocked or locked).  
         [0016]    The microprocessor is connected at the junction of power cable  22 C and  22 B via signal cable  24 , and is also connected to second switch  14  by signal cable  26 . It should be noted that the current required for the motor to operate latch L is typically 8-10 amps with a peak current of typically 16 amps. This should be contrasted with the currents traveling through signal cables  24  and  26  which typically would be fractions of an amp.  
         [0017]    Operation of the latch arrangement is as follows.  
         [0018]    Resistor  20  is used to connect the handle switch  12  to an input of the microprocessor  18 , to enable the microprocessor to read the status of the handle switch  12 . In the event that handle switch  12  is closed, then the microprocessor then signals second switch  14  to either remain open or to close depending upon the status of the latch  10 .  
         [0019]    Thus, consider the case where input signals  36  to the microprocessor  18  have indicated that the latch  10  is in an unlocked condition. With the inside handle in its rest position, both handle switch  12  and second switch  14  are in an open condition.  
         [0020]    When it is required to open the latch, the inside handle IH is operated which in turn closes the handle switch  12 . The microprocessor  18  can determine (from signals via signal line  24 ) that the first switch  12  is closed. Since an earlier signal  36  to the microprocessor has indicated that the latch is in an unlocked condition, the microprocessor  18  then signals for second switch  14  to close.  
         [0021]    This results in a release current (typically 8-10 amps with a peak of typically 16 amps) passing through first handle switch  12 , motor M and second switch  14 , since these components are in series. In particular it should be noted that first switch  12  and second switch  14  should be designed to withstand such high current loads.  
         [0022]    It can be seen that should the microprocessor suffer any EMC disturbance causing second switch  14  to inadvertently close, the motor will not cause the latch to release since the handle switch  12  is still open, preventing the formation of a complete circuit.  
         [0023]    With reference to FIG. 2 there is shown a further embodiment of the present invention which in this case includes an inside handle switch  30  closeable by inside handle IH, an outside handle switch  32  closeable by outside handle OH, and an additional switch  34  closeable by an additional handle FH.  
         [0024]    In this case each handle switch has an associated diode D 1 , D 2  and D 3  positioned such that the microprocessor can read the individual status of each handle switch.  
         [0025]    Thus with the latch in a locked condition, operation of the outside handle will cause the outside handle switch  32  to close, but the microprocessor  118  will not close the second switch  114 , preventing the latch from unlocking. However, operation of an inside handle will cause the inside switch  30  to close; in this case, the microprocessor  118  does close the second switch  114 , thus allowing the door to open.  
         [0026]    It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.