Patent Publication Number: US-7915772-B2

Title: Motor for vehicle door lock

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 200810065085.6 filed in The People&#39;s Republic of China on Jan. 18, 2008. 
     FIELD OF THE INVENTION 
     The present invention relates to electric motors and in particular, to a motor with a built-in rotation detector or position sensor for vehicle door locks. 
     BACKGROUND OF THE INVENTION 
     For vehicles, the door lock is a major item of concern for safety issues. Before driving or leaving a vehicle unattended, drivers usually need to confirm whether or not the doors are locked. 
     In a vehicle door lock device of conventional art, an additional micro motor is used to confirming whether the vehicle door lock is in the locked or unlock position. However, this additional motor raises the cost of the vehicle door lock. 
     Hence, there is a desire for a motor for a door lock which can provide feedback about the state of the lock or which at least provides the public with a useful choice 
     SUMMARY OF THE INVENTION 
     Hence there is a desire for a motor for a door lock which can verify its position. 
     Accordingly, in one aspect thereof, the present invention provides a motor for a vehicle door lock comprising: a motor housing; an end cap fixed to the motor housing; and a rotation detector, the motor housing accommodating an armature including a motor shaft, a rotor core and a commutator, wherein a sensor magnet is fixed to the motor shaft and the rotation detector comprises a circuit board fixed to an inner part of the end cap, a rotation sensor fixed to the circuit board and adjacent the sensor magnet for sensing rotation of the magnet to produce a corresponding signal, and a sensor connector fixed to the circuit board and being electrically connected with the rotation sensor, the sensor connector being arranged to be connected to signal wires to transfer the signal to a microprocessor of the vehicle. 
     Preferably, sensor connector comprises a pair of terminals, each terminal having at least one spring plate, and the terminals contact a respective connector of the signal wire by the spring plates. 
     Preferably, the end cap is provided with a first pair of through holes for connectors of the signal wires to pass through from outside of the end cap, to make contact with the sensor connector. 
     Preferably, the end cap is provided with a second pair of through holes for connectors of power supply wires to pass through from outside of the end cap to supply power to the motor, the second pair of through holes is axially spaced from the first pair of through holes. 
     Preferably, the end cap comprises multiple resilient terminal links to connect the power supply to brushes of the motor and to the rotation detector. 
     Preferably, the rotation sensor is a Hall sensor, and the rotation detector also comprises a current-limiting resistor fixed to the circuit board and being electrically connected with the Hall sensor. 
     Preferably, the end cap is provided with a pair of slots for slidably receiving two sides of the circuit board. 
     Preferably, an edge of the circuit board is provided with an opening, and the end cap is provided with a resilient catch or hook which engages the opening to prevent accidental removal of the circuit board from the slots of the end cap. 
     Preferably, the sensor magnet is a plastic magnet keyed to at least one axially extending projection provided on an axial end of the commutator adjacent the sensor magnet. 
     Preferably, the motor for door lock also comprises an oil slinger pressed on to the shaft and located adjacent the sensor magnet on the side remote from the commutator, the outer diameter of the oil slinger being bigger than or equal to the outer diameter of the sensor magnet. 
     Advantages of embodiments of the present invention include a saving in cost o the overall vehicle door lock system. When the motor is rotating, the Hall sensor detects the changes of the magnetic poles of the magnet to produce a voltage signal which changes between high and low potential. A microprocessor processing the signal, counts the changes in polarity to calculate the number of turns of the armature to determine whether or not the vehicle door is correctly locked. Compared with conventional systems, a motor can be saved, reducing the overall cost of the door lock. By mounting the position sensor in the end cap of the motor, the position sensor occupies little space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
         FIG. 1  is a side elevation of a motor for a vehicle door lock according to the preferred embodiment of the present invention; 
         FIG. 2  is an isometric view of the inside of an end cap of the motor of  FIG. 1  showing a rotation detector; 
         FIG. 3  is an isometric view of the rotation detector of  FIG. 2 ; 
         FIG. 4  is an isometric view from a different angle of the rotation detector of  FIG. 3 ; 
         FIG. 5  is a schematic diagram illustrating the arrangement of the rotation detector; 
         FIG. 6  is a sectional view of a part of the motor of  FIG. 1 ; and 
         FIG. 7  is a graph showing the waveform of a voltage signal produced by the rotation detector. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The motor for a vehicle door lock according to the preferred embodiment of the present invention, as shown in  FIGS. 1 to 6 , comprises a motor housing  10 , an end cap  30 , and a rotation detector  50  fixed to the end cap  30 . 
     As shown in  FIG. 5 , the motor housing  10  comprises an armature  12  having a shaft  11 , a commutator  13 , a sensor magnet  14  fixed to the shaft  11  adjacent the commutator  13 , and an oil slinger  16  fixed to the shaft  11  adjacent the sensor magnet  14 . Multiple axial projections  18  are provided on an axial end face of the commutator  13 . The sensor magnet  14  is a the plastic cylinder shape magnet which is pressed on to the shaft  11  and has axial recesses which tightly engage the axial projection  18  to key the magnet to the armature to prevent relative rotational movement there between. The sensor magnet  14  has a pair of south and north poles. 
     The shaft  11  is journalled in bearings in the end cap and motor housing. The oil slinger  16  is arranged to stop oil migrating along the shaft from the bearing in the end cap and contaminating the commutator  13 . Ideally, the outer diameter of the oil slinger  16  is bigger than or equal to the outer diameter of the sensor magnet  14 . 
     Referring to  FIG. 2 , the end cap  30  is made of a plastics material and has a central through hole  31  for accommodating the shaft  11  of the motor. A pair of slots  32  is provided on the inside surface of the end cap  30  adjacent the central through hole  31 , for mounting the rotation detector  50 . The end cap  30  is also provided with a resilient catch  34  to retain the rotation detector  50  in the slots  32 . Terminal links  35  connect brush gear of the motor with an external power supply. The end cap  30  is also provided with two pairs of through holes  36 ,  38  (as shown in  FIG. 1 ), of which one pair  36  is for connectors of the signal wires, and the other pair  38  is for the power supply connectors. 
     Referring to  FIG. 3  and  FIG. 4 , the rotation detector  50  comprises a circuit board  52 , a current-limiting resistor  54 , a Hall sensor  56 , and a sensor connector  58 . The current-limiting resistor  54  and the Hall sensor  56  are fixed at one side of the circuit board  52  by soldering, preferably using a surface mounting technique (SMT). The current-limiting resistor  54  is electrically connected in series with the Hall sensor  56  to protect the Hall sensor  56  from over current. One edge of the circuit board  52  is provided with an opening  52   a . The sensor connector  58  comprises two terminals  582 ,  584 , and each terminal comprises two spring plates  582   a ,  584   b . Connecting feet  582   b ,  584   b  extend from each spring plate. The connecting feet  582   b ,  584   b  are each inserted through and soldered to corresponding holes  52   b  of the circuit board  52 . Each spring plate of one terminal  582  is located opposite to the corresponding spring plate of the other terminal  584 . The sensor connector is thus electrically connected to the Hall sensor  56  via the circuit board  52 . 
     After rotation detector  50  is inserted into the slots  32  of the end cap  30 , the resilient catch  34  of the end cap  30  is located in the opening  52   a  of the circuit board  52  (as shown in  FIG. 2 ,  FIG. 6 ), so as to prevent the rotation detector  50  from accidentally separating from the end cap  30 . Connectors of the signal wires pass through the first pair of through holes  36  of the end cap  30  to electrically connect with the terminals of the sensor connector  58  of the rotation detector  50 , and the other end of the signal wires are connected to the control panel of the vehicle. Connectors of the power supply wires connected to an external power supply pass through the second pair of through holes  38  of the end cap  30  and connect with terminal links  35  of the end cap  30  to supply power to the brush gear. Should the circuit board  52  require power, it may be connected to the connectors of the power supply wires either directly or by the terminal links  35 . The motor shaft  11  passes through the through hole  31  of the end cap  30  and the end cap  30  is fixed to the motor housing  10 . Thus the Hall sensor  56  is located adjacent the sensor magnet  14  (as shown in  FIG. 5  and  FIG. 6 ). 
     When user locks a vehicle door, the armature  12  will rotate for multiple turns. In each turn the armature  12  rotates, the Hall sensor  56  will be influenced by each of the North and South poles of the sensor magnet  14  for one time, so as to produce a voltage signal with changes of high and low potential. When the armature  12  rotates for multiple turns, the Hall sensor  56  will produce a voltage signal with continuous changes of high and low potential as shown in  FIG. 7 . The signal is sent to the microprocessor of the vehicle control panel via the signal wires, and the microprocessor processes the signal to determine the number of revolutions made by the armature  12  and accordingly, determines whether or not the vehicle door is locked. Thus compared with conventional art, the total cost of the vehicle door lock is reduced by reducing the number of motors in each assembly. Also, as the rotation detector  50  is inserted in the slots on the inside of the end cap  30 , it occupies little space. 
     In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
     Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow. For example, the sensor magnet may have more than one pair of magnetic poles and thus each full turn of the armature will produce a corresponding number of pulses in the signal from the Hall sensor.