Abstract:
A vehicle including an active front steer system including a locking mechanism having a solenoid actuated locking pin and a spring for biasing the pin toward an extended or locked position for engaging a locking disc of the active front steer system wherein the active front steer system further includes a current sensor for sensing the motion of the pin of the solenoid when the engine of the vehicle is shut down and pulse width modulated current to the solenoid is reduced and when the pin movement is sensed, the pulse width modulated current is increased (fed forward duty cycle) to reduce the movement of the pin to reduce the noise made when the metal pin makes when contacting the metal locking disc. The end of the pin and/or the locking disc may also include an insulating material to further reduce any remaining noise made when the metal pin makes when contacting the metal locking disc.

Description:
BACKGROUND 
       [0001]    It is generally known to provide a vehicle including an active front steering system and including a solenoid for locking the front steering system. It is also generally known to provide a vehicle including a locking solenoid of an active front steering system that makes an objectionable “click” noise every time the vehicle is shut down. The active front steering (AFS) system may add and subtract angle between the driver steering wheel input and the steering gear input shaft. The active front steering system consists of an electronic control unit (ECU), a motor, a gear and a locking device all integrated into the steering wheel. The locking unit may provide a mechanical connection between the steering wheel and wheels during power-off of the AFS system (i.e., before and/or after shutting down the engine) and it may provide a means to lock the actuator in case of a severe failure in the AFS system. The locking unit may include a solenoid attached to the steering wheel armature, a pin having a spring for biasing the pin in a direction toward a locked position and a locking disc connected to the motor shaft, the disc including pockets or spaces for receiving the end of the pin and for locking the AFS system. 
         [0002]    The active front steering (AFS) system can add and subtract angle between the driver steering wheel input and the steering gear input shaft. In one known embodiment, the AFS system consists of an electronic control unit (ECU), a motor, a gear and a locking device all integrated into the steering wheel. The locking unit may provide a mechanical connection between the steering wheel and the wheels of the vehicle during power-off of the system (i.e., after shutting down of the engine). The locking unit may also provide a lock of the AFS system in case of a severe failure in the AFS system or some other input. 
         [0003]    While it is known to use a solenoid and locking pin as a lock actuator for an AFS system, it generates objectionable noise when contacting the locking disc. When the current is removed from the solenoid coil, the solenoid pin begins to accelerate from the force of the coil spring of the solenoid which biases the locking pin toward the locked position. When the moving solenoid pin makes contact with the lock plate, an objectionable “click” noise or sound is produced. In one known application, the locking solenoid of the active front steering system makes a noise every time the vehicle is shut down. Despite this long known problem with such systems, there remains a very significant need for an effective solution to eliminate the noise of such systems and yet be operable in the unique operating environment of the AFS system. 
     
    
     
       DRAWINGS 
         [0004]      FIG. 1  is a graphic view of a vehicle including an active front steering (AFS) system including a quiet operating AFS lock according to an exemplary embodiment of the present disclosure. 
           [0005]      FIG. 2  is a partial, perspective graphic view of the AFS system components of the vehicle of  FIG. 1 . 
           [0006]      FIG. 3  is a partial graphic view of the AFS lock and solenoid components of the AFS system of the vehicle of  FIG. 1 . 
           [0007]      FIG. 4  is a graph of the known current control duty cycle versus time and the measured current versus time during shutdown according to the AFS system of the vehicle of  FIG. 1 . 
           [0008]      FIG. 5  is a graph of the current control duty cycle versus time and the measured current versus time during shutdown to the AFS system of the vehicle of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    To meet certain customer, industry and regulatory requirements for passenger vehicles, automotive manufacturers are challenged to design vehicles using understood and predictable methods and materials. In one exemplary embodiment of the present disclosure, there is disclosed a vehicle  1  including an active front steering (AFS) system  200 . The vehicle may further include a steering wheel  21  and a steering column  22  for adjusting the direction of the front wheels of the vehicle  1 . The AFS system  200  can add and subtract angle between the operator&#39;s input to the driver steering wheel  21  and the steering column  22  to provide various affects to driving. 
         [0010]    In an exemplary embodiment of the present disclosure, the active front steering system  200  may also include an electronic control unit  65  (ECU) that may be dedicated to controlling the AFS system  200 . In an alternate exemplary embodiment of the present disclosure, the AFS system  200  may include an engine control module  75  (or other control module of the vehicle) that may include the ECU  65  or may alternatively provide the function of the ECU  65  such that it is unitary with the engine control module  75 , as best shown in  FIG. 3 . In an exemplary embodiment of the present disclosure, the active front steering system  200  may also include a motor  85  coupled to rotate a gear  95  for providing the AFS system  200  input to the steering column  22 . 
         [0011]    The AFS system  200  may include a locking unit solenoid  210  for locking the AFS system upon shutdown of the vehicle  1 . In one exemplary embodiment, the AFS system  200  may include a solenoid  220  attached to a steering wheel armature  23 . For locking the AFS system  200 , a pin  221  has an end extending from the armature  23  and aligned with a locking disc  224  of the system  200 , which disc is operated by rotation by a motor shaft  223  operated by the motor  85 . The pin  221  is biased toward the locked position (as best shown in  FIG. 3 ) by a spring  226  constantly biases the pin  221  so the end of the pin  221  is located in a recess of pocket  225  of the disc  224 . 
         [0012]    The AFS system  200  includes a locking solenoid  210  including a solenoid coil  220  for controlling the location of the pin  221  against the force of the spring  226  using a pulse width modulation (PWM) signal  66  generated by the ECU  65  of the AFS system  200 . 
         [0013]    In one exemplary embodiment of the present disclosure, the AFS system  200  may include a current sensor  67  for monitoring the current of the solenoid coil  220  of the solenoid  210 . The current sensor  67  produces a signal that is connected to the ECU  65  (or alternatively the module  75 ) that provides effective feedback to the ECU  65  for determining movement of the pin  221  during a shutdown of the AFS system  200 , such as during shutdown of the vehicle  1 . 
         [0014]    During normal AFS operation, the pin  221  may be retracted into the locking solenoid  210  when the ECU  65  of the AFS system  200  supplies the PWM signal  66  to the solenoid coil  220  which may use supplied power (not shown) to generate a magnetic force that overcomes the spring force of the spring  226  acting on the pin  221  and locating the end of the pin  221  in the recess  225 . 
         [0015]    In one exemplary embodiment of the present disclosure, the AFS system  200  may include a PWM signal  66  having a duty cycle between 0 and 1 where a 0 duty cycle has no current and a duty cycle of 1 has means the PWM current signal  66  is always on to the solenoid coil  220 . To unlock the AFS system  200 , the ECU controller  65  (or alternatively the ECM  75 ) adjusts the PWM signal  66  to have a duty cycle of 1 applied to the solenoid coil  220  for approximately between 300 and 500 milliseconds to insure the pin  221  is fully retracted from the recess  225  of the locking disc  224 . After the AFS system  200  is unlocked, to maintain the pin  221  retracted in the locking solenoid  210  and the AFS system  200  in an unlocked state, the ECU controller  65  adjusts the PWM signal  66  to have a duty cycle of approximately 0.4 (+/−0.1) while the vehicle  1  is operational (i.e., the engine of the vehicle  1  is not shut down), which particular duty cycle may vary depending upon the particular specifications of the solenoid  210 . As should be understood, the above is accomplished using a current control loop (meaning the current applied to the solenoid coil  220  is controlled by adjusting the PWM signal  66  accordingly), as the PWM signal  66  needed to maintain the pin  221  in an unlocked position may change with variations in temperature. It should be understood that the above duty cycle numbers are specific for a given solenoid  210 , including its associated voltage (not shown), although the numbers give (from a shape point of view) a good general approximation for other solenoids as well. 
         [0016]    Referring in particular to  FIG. 4 , it may be observed on the graph, that upon shutdown of the vehicle  1 , the ECU  65  begins ramping down the PWM current signal or duty cycle  66  being supplied to the solenoid coil  220  toward zero and thereby reduces the magnetic force biasing the pin  221  in the unlocked position against the spring force of the spring  226 . When this occurs, when the magnetic force of the solenoid coil  220  is sufficiently reduced to substantially match the biasing force of the spring  226 , the pin  221  will accelerate and begin to move under the biasing force of the spring  226  from the open position and toward the closed or locked position. When the end of the pin  221  is in the recess or pocket  225  of the locking disc  224 , the AFS system  200  is mechanically locked as best shown in  FIG. 3 . 
         [0017]    In one exemplary embodiment of the present disclosure, the AFS system  200  is controlled using the ECU  65  to ramp down the PWM duty cycle at a rate of approximately fifty percent (50%) or instead of immediately shutting off the PWM signal as best shown in  FIG. 4 . As the PWM current signal  66  to the solenoid coil  220  is ramped down, the current sensor  67  is used to monitor the current in the locking system solenoid  210  and provides the detected current information to the ECU  65  to identify the point in time when the pin  221  begins to move from the open position and toward the closed position. The movement of the pin  221  may be seen as a short “spike” in the measured current detected by the current sensor  67  as best shown in the charts of  FIGS. 4 and 5 . The current spike is created by the movement of the pin  221  through the magnetic field of the solenoid coil  220  under the biasing force of the spring  226 . 
         [0018]    In one exemplary embodiment of the present disclosure, upon the sensing of the movement of the pin  221  as represented by the spike in the detected current from the current sensor  67 , the PWM current signal  66  is immediately increased to increase the PWM duty cycle back toward 1, and to increase the current supplied to the solenoid coil  220 , at a rate of between approximately sixty-six percent (66%) and eighty percent (80%) for a period of approximately one hundred (100) milliseconds, to temporarily generate an additional magnetic counter force in the solenoid coil  220  of the locking solenoid  210  of the AFS system  200  to cause the locking pin  221  to decelerate before the end of the pin  221  lands in the recess  225  of the locking disc  224  thereby reducing, if not eliminating, the noise typically associated with the end of the metal pin  221  contacting the metal locking disc  224 . It should be appreciated that it is possible to use a lookup table for defining the various PWM signal  66  settings mentioned herein for operating the locking solenoid  210  to obtain the quiet function features of the present invention. It should be further appreciated that the lookup table settings may be adjusted using the current sensor  67  feedback until the locking solenoid  210  is correctly decelerated to obtain the quiet function features of the present invention. 
         [0019]    In one alternate exemplary embodiment of the present disclosure, in addition to the improved AFS locking system  200  and its improved locking unit  210 , a sound-deadening or insulating material  230  (as shown in  FIG. 3 ), such as a rubberized coating, may be incorporated or applied on any or all of the recess  225 , the locking disc  224  and/or the end of the pin  221  to further reduce the noise of the locking unit of the AFS system  200 . 
         [0020]    Any numerical values recited herein or in the figures are intended to include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.00011, 0,001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. As can be seen, the teaching of amounts expressed as “parts by weight” herein also contemplates the same ranges expressed in terms of percent by weight. Thus, an expression in the Detailed Description of the Invention of a range in terms of at “‘x’ parts by weight of the resulting polymeric blend composition” also contemplates a teaching of ranges of same recited amount of “x” in percent by weight of the resulting polymeric blend composition.” 
         [0021]    Unless expressly stated, all ranges are intended to include both endpoints and all numbers between the endpoints. The use of “about” or “approximately” in connection with a range applies to both ends of the range. Thus, “about 20 to 30” is intended to cover “about 20 to about 30”, inclusive of at least the specified endpoints. 
         [0022]    The use of the term “consisting essentially of” to describe a combination shall include the elements, ingredients, components or steps identified, and such other elements ingredients, components or steps that do not materially affect the basic and novel characteristics of the combination. The use of the terms “comprising” or “including” to describe combinations of elements, ingredients, components or steps herein also contemplates embodiments that consist essentially of the elements, ingredients, components or steps. By use of the term “may” herein, it is intended that any described attributes that “may” be included are optional. 
         [0023]    The disclosure of “a” or “one” to describe an element, ingredient, component or step is not intended to foreclose additional elements, ingredients, components or steps. Plural elements, ingredients, components or steps can be provided by a single integrated element, ingredient, component or step. Alternatively, a single integrated element, ingredient, component or step might be divided into separate plural elements, ingredients, components or steps. 
         [0024]    It is understood that the present description is intended to be illustrative and not restrictive. Many embodiments as well as many applications besides the examples provided will be apparent to those of skill in the art upon understanding. the present disclosure. The scope of the claimed invention should, therefore, not be determined with limiting reference to the description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which the claims are entitled. Any disclosure of an article or reference, including patent applications and publications, is incorporated by reference herein for all purposes. Any omission in the following claims of any aspect of subject matter disclosed herein is not a disclaimer of such subject matter.