Abstract:
A steering lock for ensuring an unlock state when it is imperative that the steering lock remain in the unlock state. The steering lock includes a motor for generating drive force that engages and locks a lock bar with a steering shaft. The steering lock includes an ECU. When shifting the steering lock to the unlock state from a lock state, the ECU controls the motor to generate drive force acting in a direction to urge the lock bar to disengage from the steering shaft. The ECU continuously controls the motor to generate drive force acting in the direction to urge the lock bar to disengage from the steering shaft even after the lock bar has moved to the unlock position.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a steering lock that locks a steering shaft with a lock bar.  
         [0002]     Electronic steering locks for use in an automobile have been proposed in recent years. Such an electronic steering lock includes an electronic control unit (ECU) and a motor. The ECU controls the motor to produce torque used to move a lock bar so that the lock bar engages with or disengages from a steering shaft. The lock bar locks the steering shaft when engaged with the steering shaft and unlocks the steering shaft when disengaged from the steering shaft.  
         [0003]     In an electronic steering lock, electric noise may cause the ECU to erroneously function and drive the motor in an unintended manner. Therefore, electronic steering locks are configured so that they do not lock the steering shaft when the vehicle is traveling. For example, Japanese Laid-Open Patent Publication No. 2003-063354 describes a steering lock provided with a power line, which includes a relay and a plurality of field effect transistors (FETs), for supplying the motor with power. The FETs are series-connected to the relay, which is connected to the motor. In this steering lock, the relay and the FETs must all be activated to drive the motor. This prevents the steering lock from locking the steering shaft when the vehicle is traveling even if electric noise causes the ECU to function erroneously.  
         [0004]     Nevertheless, with the structure in which the FETs are series-connected to the relay, there still is a possibility of the motor being driven in an erroneous manner.  
       SUMMARY OF THE INVENTION  
       [0005]     It is an object of the present invention to provide a steering lock that ensures a steering shaft remains unlocked under circumstances in which it is imperative that the steering shaft remains unlocked.  
         [0006]     One aspect of the present invention is a steering lock for locking a steering shaft of a vehicle. The steering lock includes an actuator. A lock member is driven by the actuator to engage and lock the steering shaft. A control unit controls the actuator. The control unit controls the actuator to generate drive force acting in a direction to urge the lock member to move from a lock position in which the lock member engages the steering shaft to an unlock position in which the lock member is disengaged from the steering shaft. The control unit uses the drive force to move the lock member from the lock position to the unlock position. Further, the control unit controls the actuator to continuously generate the drive force acting in said direction to urge the lock member to move to the unlock position even after the lock member has moved to the unlock position.  
         [0007]     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0009]      FIG. 1  is a schematic diagram showing a steering lock according to a preferred embodiment of the present invention; and  
         [0010]      FIG. 2  is an electric circuit diagram of the steering lock shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]     A steering lock  1  according to a preferred embodiment of the present invention will now be described. The steering lock  1  is for use in an automobile.  
         [0012]     Referring to  FIG. 1 , the steering lock  1 , which is of an electronic type, uses the drive force, or torque, produced by a motor  10  to lock a steering shaft  20  with a lock bar  30 . The structure of the steering lock  1  will now be discussed.  
         [0013]     As shown in  FIG. 1 , the steering lock  1  includes the motor  10 , a worm  11 , a spur gear  12 , the lock bar  30 , and an ECU  40 . The motor  10  functions as an actuator for producing torque used to move the lock bar  30  so that the lock bar  30  engages with and disengages from the steering shaft  20 . The motor  10  is a DC motor that rotates its output shaft in forward and reverse directions. The output shaft of the motor  10  is fixed to the worm  11 . The worm  11  is mated with the spur gear  12 , which is further mated with a rack  31  formed on the lock bar  30 .  
         [0014]     When the motor  10  is driven, the torque of the motor  10  is transmitted to the rack  31  of the lock bar  30  by the worm  11  and the spur gear  12 . That is, the rotating motion produced by the motor  10  is converted to the linear motion of the lock bar  30  by a gear mechanism, which includes the worm  11 , the spur gear  12 , and the rack  31 . The worm  11  and the spur gear  12  form a reduction gear that reduces the rotation speed of the motor output shaft. Thus, the rotation speed of the drive shaft, or the output shaft of the motor  10 , is reduced in comparison to that of the driven shaft, or the rotary shaft to which the spur gear  12  is attached.  
         [0015]     The steering lock  1  is in a lock state when the lock bar  30  is engaged with the steering shaft  20 . The steering lock  1  is in an unlock state when the lock bar  30  is disengaged from the steering shaft  20 . When a driver performs an operation for starting the engine, the steering lock  1  is in the lock state. Thus, the ECU  40  controls the motor  10  to rotate its output shaft in the forward direction so that the lock bar  30  moves in the direction indicated by arrow A in  FIG. 1 . This moves the lock bar  30  out of a lock groove  21 , which is formed in the steering shaft  20 . As a result, the steering lock  1  shifts from the lock state to the unlock state. Accordingly, when an engine starting operation is performed, the ECU  40  executes unlock control so that the motor  10  performs an unlock operation and rotates its output shaft in the forward direction. During the unlock operation, the motor  10  produces unlocking force applied to the lock bar  30  in the direction in which the lock bar  30  disengages the lock groove  21  of the steering shaft  20 .  
         [0016]     After the engine is stopped and the vehicle occupant opens and closes the door to leave the vehicle, the steering lock  1  is in the unlock state. Thus, the ECU  40  controls the motor  10  to rotate its output shaft in the reverse direction so that the lock bar  30  moves in the direction indicated by arrow B in  FIG. 1 . This moves the lock bar  30  into the lock groove  21  of the steering shaft  20  and shifts the steering lock  1  from the unlock state to the lock state. Accordingly, when the vehicle door is opened and closed after the engine is stopped, the ECU  40  executes lock control so that the motor  10  performs a lock operation and rotates its output shaft in the reverse direction. During the lock operation, the motor  10  produces locking force applied to the lock bar  30  in the direction in which the lock bar  30  engages the lock groove  21  of the steering shaft  20 .  
         [0017]     The lock bar  30  is movable between a lock position and an unlock position. In the lock position, the lock bar  30  is engaged with the lock groove  21  of the steering shaft  20 . In the unlock position, the lock bar  30  is disengaged from the lock groove  21 .  
         [0018]     The steering lock  1  is provided with an unlock detection switch  41  and a lock detection switch  42 . The unlock detection switch  41  closes and goes on when the lock bar  30  moves to the unlock position. This sends a signal having a high level, which indicates that the steering lock  1  is in the unlock state, to the ECU  40  from the unlock detection switch  41 . As a result, the ECU  40  determines that the steering lock  1  is in the unlock state and enables the execution of various controls that requires the steering shaft  20  to be unlocked.  
         [0019]     The lock detection switch  42  closes and goes on when the lock bar  30  moves to the lock position. This sends a signal having a high level, which indicates that the steering lock  1  is in the lock state, to the ECU  40  from the lock detection switch  42 . As a result, the ECU  40  determines that the steering lock  1  is in the lock state and controls the motor  10  to stop rotating its output shaft in the reverse direction.  
         [0020]     The configuration of the ECU  40  will now be described. As shown in  FIG. 2 , the ECU  40  includes a microcomputer  60 , transistors TR 1  and TR 2 , and relays  70  and  80 . The microcomputer  60  includes a central processing unit (CPU), a read-only memory (ROM), a random-access memory (RAM), and a timer. The microcomputer  60  is powered by a vehicle battery via a DC-DC converter (not shown) to perform various controls.  
         [0021]     The transistors TR 1  and TR 2  are each activated when receiving a signal having a high level from the microcomputer  60 . The relay  70  includes a coil  71 , a movable contact  72 , a fixed negative contact  73 , and a fixed positive contact  74 . Further, the relay  80  includes a coil  81 , a movable contact  82 , a fixed negative contact  83 , and a fixed positive contact  84 . Activation of the transistor TR 1  excites the coil  71  and switches the relay  70  from a state in which the movable contact  72  is electrically connected to the fixed negative contact  73  to a state in which the movable contact  72  is electrically connected to the fixed positive contact  74 . Activation of the transistor TR 2  excites the coil  81  and switches the relay  80  from a state in which the movable contact  82  is electrically connected to the fixed negative contact  83  to a state in which the movable contact  82  is electrically connected to the fixed positive contact  84 . The motor  10  is electrically connected between the movable contact  72  of the relay  70  and the movable contact  82  of the relay  80 .  
         [0022]     When executing the unlock control, the microcomputer  60  sends a signal having a high level to the transistor TR 1  while sending a signal having a low level to the transistor TR 2 . This activates the transistor TR 1  and inactivates the transistor TR 2 . Thus, the coil  71  of the relay  70  is excited, and the coil  81  of the relay  80  is de-excited. As a result, during the unlock control, current flows from a positive terminal of the vehicle battery to a negative terminal of the vehicle battery via the fixed positive contact  74  and movable contact  72  of the relay  70 , the motor  10 , and the movable contact  82  and fixed negative contact  83  of the relay  80 . Accordingly, an unlock power route extends from the positive terminal of the vehicle battery to the negative terminal of the vehicle battery via the fixed positive contact  74  and movable contact  72  of the relay  70 , the motor  10 , and the movable contact  82  and fixed negative contact of the relay  80 . In this manner, the microcomputer  60  activates only the transistor TR 1  during the execution of the unlock control so that the motor  10  rotates its output shaft in the forward direction.  
         [0023]     During the execution of the unlock control, the microcomputer  60  determines that the steering lock  1  is in the unlock state when receiving a signal from the unlock detection switch  41  indicating that the lock bar  30  a located at the unlock position. If it becomes necessary to stop the motor  10  under such circumstance, the microcomputer  60  sends a signal having a low level to the transistor TR 1  and a signal having a low level to the transistor TR 2 . This inactivates both of the transistors TR 1  and TR 2  and de-excites the coil  71  of the relay  70  and the coil  81  of the relay  80 . Thus, current does not flow through the motor  10 . As a result, the motor  10  stops rotating its output shaft in the forward direction.  
         [0024]     When executing the lock control, the microcomputer  60  outputs a signal instructing locking. That is, the microcomputer  60  sends a signal having a high level to the transistor TR 2  while sending a signal having a low level to the transistor TR 1 . This activates the transistor TR 2  and inactivates the transistor TR 1 . Thus, the coil  81  of the relay  80  is excited, and the coil  71  of the relay  70  is de-excited. As a result, during the lock control, current flows from the positive terminal of the vehicle battery to the negative terminal of the vehicle battery via the fixed positive contact  84  and movable contact  82  of the relay  70 , the motor  10 , and the movable contact  82  and fixed negative contact  73  of the relay  70 . Accordingly, a lock power route extends from the positive terminal of the vehicle battery to the negative terminal of the vehicle battery via the fixed positive contact  84  and movable contact  82  of the relay  80 , the motor  10 , and the movable contact  72  and fixed negative contact  73  of the relay  70 . In this manner, the microcomputer  60  activates only the transistor TR 2  during the execution of the lock control so that the motor  10  rotates its output shaft in the reverse direction.  
         [0025]     During the execution of the lock control, if the microcomputer  60  receives from the lock detection switch  42  a signal indicating that the steering lock  1  is in the lock state, the microcomputer  60  sends a signal having a low level to the transistor TR 1  and a signal having a low level to the transistor TR 2 . This inactivates both of the transistors TR 1  and TR 2  and de-excites the coil  71  of the relay  70  and the coil  81  of the relay  80 . Thus, current does not flow through the motor  10 . As a result, the motor  10  stops rotating its output shaft in the reverse direction. In this manner, the microcomputer  60  has the motor  10  stop rotating its output shaft in the reverse direction when determining that the steering lock  1  is in the lock state.  
         [0026]     The features of the steering lock  1  will now be discussed. Referring to  FIG. 2 , the microcomputer  60  of the ECU  40  is electrically connected to a vehicle velocity sensor  91 , an ignition relay  92 , and a parking brake switch  93 . The vehicle velocity sensor  91  generates a pulse signal in cycles corresponding to the velocity of the vehicle and sends the pulse signal to the microcomputer  60 . The microcomputer  60  determines the vehicle velocity based on the pulse signal from the vehicle velocity sensor  91 . When the vehicle velocity is not zero (i.e., when the vehicle is traveling), the microcomputer  60  causes the motor  10  to rotate its output shaft in the forward direction so as to perform the unlock operation.  
         [0027]     Activation of the ignition relay  92  activates the ignition system of the vehicle. In this state, the ignition relay  92  sends a signal having a high level to the microcomputer  60 . When the ignition relay  92  inactivates the ignition system, the ignition relay  92  sends a signal having a low level to the microcomputer  60 . The microcomputer  60  determines whether or not the ignition system is activated based on the signal from the ignition relay  92 . When the ignition system is activated, this indicates that the vehicle is in a state in which it may be driven. Thus, the microcomputer  60  controls the motor  10  to rotate its output shaft in the forward direction so as to perform the unlock operation.  
         [0028]     When a parking brake is activated, the parking brake switch  93  sends a signal having a high level to the microcomputer  60 . When the parking brake is inactivated, the parking brake switch  93  sends a signal having a low level to the microcomputer  60 . The microcomputer  60  determines whether or not the parking brake is activated based on the signal from the parking brake switch  93 . When the parking brake is inactivated (released), this indicates that the vehicle is in a state in which it may be driven. Thus, the microcomputer  60  controls the motor  10  to rotate its output shaft in the forward direction so as to perform the unlock operation.  
         [0029]     The microcomputer  60  monitors the voltage level at a node N between the coil  81  of the relay  80  and the transistor TR 2 . The voltage level at the node N is high when the motor  10  is performing the unlock operation, that is, when the transistor TR 2  is inactivated. The voltage level at the node N is low when the motor  10  is performing the lock operation, that is, when the transistor TR 2  is activated. If the voltage level at the node N shows a decrease even though the microcomputer  60  is not executing the lock control, that is, even though the microcomputer  60  is not outputting a signal instructing locking, the microcomputer  60  controls the voltage level so that the motor  10  performs the unlock operation and rotates its output shaft in the forward direction.  
         [0030]     Accordingly, even after the execution of the unlock control shifts the steering lock  1  to the unlock state, the microcomputer  60  continues controlling the motor  10  to rotate its output shaft in the forward direction so as to perform the unlock operation.  
         [0031]     The preferred embodiment has the advantages described below.  
         [0032]     (1) Even after the execution of the unlock control shifts the steering lock  1  to the unlock state, the microcomputer  60  continues controlling the motor  10  to perform the unlock operation. Thus, under a condition in which the steering lock  1  must remain in the unlock state, the motor  10  is prevented from performing the lock operation. This keeps the steering lock  1  in the unlock state.  
         [0033]     (2) When the vehicle is traveling, the motor  10  is controlled to perform the unlock operation so as to keep the steering lock  1  in the unlock state. Further, audible noise produced by the motor  10  is offset by the audible noise produced when the vehicle travels. Thus, such noise would not cause the vehicle occupant to feel uncomfortable.  
         [0034]     (3) When the vehicle is in a state in which it may be driven, the motor  10  is controlled to perform the unlock operation so as to keep the steering lock  1  in the unlock state. Thus, the steering lock  1  is in the unlock state even before the vehicle is driven.  
         [0035]     (4) As long as the lock control is not executed, the motor  10  is forced to continuously perform the unlock operation even if there is a factor such as electric noise that would cause the motor  10  to erroneously perform the lock operation. This prevents the steering lock  1  from locking the steering shaft  20  when locking must be avoided.  
         [0036]     (5) Unlike the steering lock of the prior art, FETs do not have to be connected in series to the relay  80  to keep the steering lock  1  in the unlock state. This reduces the cost of the steering lock  1 .  
         [0037]     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.  
         [0038]     The microcomputer  60  may control the motor  10  so that after the unlock control shifts the steering lock  1  to the unlock state, the unlock operation is performed with the current flowing through the motor  10  being smaller than that when the motor  10  is actually moving the lock bar  30 . This reduces power consumption. For example, instead of the relays  70  and  80  and the transistors TR 1  and TR 2 , four FETs may be employed to configure a full bridge, and the microcomputer  60  may execute pulse width modulation (PWM) control with the FETs. In this case, after the steering lock  1  shifts to the lock state, the microcomputer  60  may execute PWM control with an ON duty ratio that is smaller than that during the execution of the unlock control. In this case, however, it is preferred that the microcomputer  60  execute the PWM control at an ON duty ratio of 100% when the motor  10  attempts to perform the lock operation even though the lock control is not being executed.  
         [0039]     After the engine is stopped, the motor  10  may be controlled to perform the unlock operation until the vehicle occupant opens and closes the vehicle door to leave the vehicle.  
         [0040]     In the lock power route, switches such as FETs may be connected in series to the relay  80 .  
         [0041]     The actuator is not limited to the motor  10  and may be any type of motor.  
         [0042]     The concavo-convexo relationship of the steering shaft  20  and the lock bar  30  may be reversed.  
         [0043]     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.