Abstract:
An automotive vehicle may include an engine, an electric power steering system and at least one controller. The at least one controller may, during an auto stop event of the engine, reduce at a first rate an available electric power steering system current to a non-zero threshold value before fuel to the engine is shut off and reduce at a second rate different than the first rate the available electric power steering system current from the non-zero threshold value to 0 after fuel to the engine is shut off.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to strategies for controlling electric power steering assist during engine auto stops and engine auto starts. 
       BACKGROUND 
       [0002]    A micro hybrid vehicle may stop its internal combustion engine after coming to a stop. Such a vehicle may also restart its engine before accelerating from the stop. These engine auto stops and auto starts may improve fuel economy by reducing engine idle time (and thus fuel consumption) for a given drive cycle. 
       SUMMARY 
       [0003]    An automotive vehicle may include an engine, an electric power steering system, and at least one controller. The at least one controller, during an auto stop event of the engine, may reduce an available electric power steering system current before fuel to the engine is shut off. 
         [0004]    The available electric power steering system current may be reduced to a non-zero threshold value. 
         [0005]    The at least one controller may further reduce the available electric power steering system current from the non-zero threshold value to 0 after fuel to the engine is shut off. 
         [0006]    The rate at which the available electric power steering system current is reduced before fuel to the engine is shut off may be different than a rate at which the available electric power steering system current is reduced after fuel to the engine is shut off. 
         [0007]    The vehicle may further include a starter. The at least one controller may further, during the auto stop event of the engine, increase from 0 the available electric power steering system current after the starter is disengaged from cranking the engine. 
         [0008]    The available electric power steering system current may be increased to a non-zero threshold value before the engine is running at or above target idle speed. 
         [0009]    The at least one controller may further increase the available electric power steering system current from the non-zero threshold value to a maximum value after the engine is running at or above target idle speed. 
         [0010]    A rate at which the available electric power steering system current is increased from 0 to the non-zero threshold value may be different than a rate at which the available electric power steering system current is increased from the non-zero threshold value to the maximum value. 
         [0011]    The at least one controller may further, during the auto stop event, detect an auto start condition and in response, increase the available electric power steering system current. 
         [0012]    A rate at which the available electric power steering system current is increased before the engine is running at or above target idle speed may be different than a rate at which the available electric power steering system current is increased after the engine is running at or above target idle speed. 
         [0013]    An automotive vehicle may include an engine, an electric power steering system, and at least one controller. The at least one controller may, during an auto stop event of the engine, reduce at a first rate an available electric power steering system current to a non-zero threshold value before fuel to the engine is shut off and reduce at a second rate different than the first rate the available electric power steering system current from the non-zero threshold value to 0 after fuel to the engine is shut off. 
         [0014]    A method for controlling an automotive electric power steering system may include detecting an auto stop event for an engine and in response to detecting the auto stop event for the engine, reducing an available electric power steering system current before fuel to the engine is shut off. 
         [0015]    The available electric power steering system current may be reduced to a non-zero threshold value. 
         [0016]    The method may further include reducing the available electric power steering system current from the non-zero threshold value to 0 after fuel to the engine is shut off. 
         [0017]    A rate at which the available electric power steering system current is reduced before fuel to the engine is shut off may be different than a rate at which the available electric power steering system current is reduced after fuel to the engine is shut off. 
         [0018]    The method may further include increasing from 0 the available electric power steering system current, during the auto stop event of the engine, after a starter is disengaged from cranking the engine. 
         [0019]    The available electric power steering system current may be increased to a non-zero threshold value before the engine is running at or above target idle speed. 
         [0020]    The available electric power steering system current may be increased from the non-zero threshold value to a maximum value after the engine is running at or above target idle speed. 
         [0021]    The rate at which the available electric power steering system current is increased from 0 to the non-zero threshold value may be different than a rate at which the available electric power steering system current is increased from the non-zero threshold value to the maximum value. 
         [0022]    The method may further include, during the auto stop event, detecting an auto start condition and in response, increasing the available electric power steering system current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a block diagram of a micro hybrid vehicle. 
           [0024]      FIG. 2  is a plot illustrating engine status during an auto stop event. 
           [0025]      FIG. 3  is a plot illustrating available electric power steering assist current during the auto stop event of  FIG. 2 . 
           [0026]      FIG. 4  is a plot illustrating engine status during a partial auto stop event. 
           [0027]      FIG. 5  is a plot illustrating available electric power steering assist current during the partial auto stop event of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0029]    Referring to  FIG. 1 , a micro hybrid vehicle  10  may include a starter  11 , an engine  12 , a battery  13 , an alternator  14 , an electric power steering assist system  16 , and a steering system  18  (e.g., steering wheel, etc.) The vehicle  10  may also include an accelerator pedal system  20 , a brake pedal system  22 , and one or more controllers  24 . The starter  11 , engine  12 , battery  13 , steering system  18 , and pedal systems  20 ,  22  are in communication with/under the control of the controllers  24  (as indicated by dashed line). The starter  11  is arranged to mechanically crank the engine  12  (as indicated by heavy line). The engine  12  is arranged to mechanically drive the alternator  14  (as indicated by heavy line) such that the alternator  14  generates electric current. The alternator  14  is electrically connected with the electric power steering assist system  16  (as indicated by light line), which is configured to reduce steering efforts associated with the steering system  18 . As such, the electric power steering assist system  16  may consume current generated by the alternator  14 . The battery  13  is also electrically connected with the electric power steering assist system  16  (as indicated by light line). Hence, the battery  13  may provide electric current for consumption by the electric power steering assist system  16  when, for example, the engine  12  is off. 
         [0030]    The controllers  24  may initiate an auto stop or an auto start of the engine  12 . As the driver engages the brake pedal  22  and the vehicle  10  comes to a stop, for example, the controllers  24  may issue a command to begin the process to stop the engine  12 , thus preventing the engine  12  from powering the electric power steering system  16  via the alternator  14 . As the driver disengages the brake pedal  22  (and/or engages the accelerator pedal  20 ) after an engine stop, the controllers  24  may issue a command to begin the process to start the engine  12 , thus enabling the engine  12  to power the electric power steering assist system  16  via the alternator  14 . 
         [0031]    Sudden changes in steering efforts during engine auto stop events may cause driver dissatisfaction. Hence, the battery  13  may provide electric power for consumption by the electric power steering assist system  16  as mentioned above. The load generated by the electric power steering assist system  16 , however, may exceed the capabilities of the battery  13  if the battery  13  is used to power the electric power steering assist system  16  for the entire duration of the engine auto stop event. 
         [0032]    Referring to  FIG. 2 , an engine auto stop event may include several stages: “auto-stop begin,” which marks the beginning of the engine auto stop event; “preparing for engine auto-stop,” which is the time period during which vehicle systems as well as the engine are prepared for the impending engine stop (if an auto stop inhibit condition is detected during this stage, the preparation for the impending engine stop is discontinued and the vehicle systems and engine are returned to their normal operating modes); “fuel shutoff,” which marks the point at which fuel flow to the engine is stopped; “engine stopping,” which is the time period during which the engine speed is reduced to 0; “below fuel restart,” which marks the point after which if a restart is requested to inhibit the auto stop during the “engine stopping” stage, the starter may need to be engaged to crank the engine (if a restart is requested before “below fuel restart” and during the “engine stopping” stage, the engine may be restarted to inhibit the auto stop by turning the flow of fuel back on); “engine speed=0,” which marks the point at which the engine speed is near or equal to 0; “engine auto-stopped,” which is the time period during which the engine is off; “starter engage,” which marks the point at which the starter starts to crank the engine in an effort to start the engine (in response to detecting an engine auto start condition); “starter cranking engine,” which is the time period during which the engine is unable to crank under its own power; “starter disengage,” which marks the point at which the engine is able to crank under its own power; “engine speed increasing,” which is the time period during which the speed of the engine increases to its running speed; “auto-start end,” which marks the point at which the speed of the engine achieves its running speed (a speed at or above target idle speed). 
         [0033]    Referring to  FIG. 3 , the available electric power steering assist system current (e.g., current available for consumption by the electric power steering system  16 ) may be ramped down around the beginning of an engine auto stop event and ramped up around the end of the engine auto stop event. Such ramping may prevent a driver from experiencing sudden changes in steering efforts, may limit the duration during which the battery  13  is used to power the electric power steering assist system  16 , and/or may limit the adverse effect of additional steering inputs on system voltage during and after the transition from the alternator  14  to the battery  13  as the source of electric power steering assist system current. 
         [0034]    Upon detecting an auto stop event and before beginning to ramp down the available electric power steering assist system current, the controllers  24  may determine whether the current being consumed by the electric power steering assist system  16  is less than a specified threshold (e.g., 40 Amps). If no, the engine auto stop is inhibited. (This check may also be performed during the initial stages of the ramping process. That is, if the current being consumed by the electric power steering assist system  16  exceeds a specified threshold, which may depend on the stage of the auto stop event, the engine auto stop may be inhibited.) This may ensure that the battery  13  is able to handle the current draw during and after the transition from the alternator  14  to the battery  13  as the source of electric power steering assist system current. If yes, during the “preparing for engine auto-stop” stage, the controllers  24  may begin to ramp down the available electric power steering assist system current from a maximum to ASSIST_DOWN using the ramp rate RAMP_DOWN_ 1 . The ASSIST_DOWN level may limit the adverse effect of additional driver steering input on system voltage during and after the transition from the alternator  14  to the battery  13  as the source of electric power steering assist system current. By ramping the assist to this level, the driver may not be impacted since all that is removed is unused assist. Also, the ramp rate may be adjusted such that the driver does not feel this removal of available assist even if they move the steering wheel  18 . 
         [0035]    Once the engine speed is less than a threshold value such that the starter  11  is required for engine restart (that is, after “below fuel restart”), available electric power steering assist system current may be ramped to 0 using the ramp rate RAMP_DOWN_ 2 . This may ensure that in situations in which the engine  12  can be restarted without the use of the starter  11 , a driver&#39;s steering effort or input torque needed to turn the steering wheel  18  is not impacted. Also, this ramp rate may be adjusted such that the driver does not feel a sudden steering wheel kick back and to ensure that the assist is completely ramped out before the earliest point when the starter  11  can be engaged. 
         [0036]    Once the starter  11  is disengaged during engine restart (that is, after “starter disengage”), available electric power steering assist system current may be ramped up using the ramp rate RAMP_UP_ 1  to ASSIST_UP. This may provide the driver a certain level of available assist from battery power while the engine  12  is starting. 
         [0037]    After the alternator  14  is fully operational (that is, after “auto-start end”), available electric power steering assist system current may be ramped to its maximum value using the ramp rate RAMP_UP_ 2 . The system then resumes normal operation. 
         [0038]    Referring to  FIG. 4 , a partial engine auto stop event may include fewer stages than a full engine auto stop event (compare  FIG. 3 ) because the engine  12  is restarted prior to complete shutdown. In the example of  FIG. 4 , the controllers  24  detect an engine auto start condition (e.g., a driver disengaging the brake pedal  22 ) during the “engine stopping” stage (prior to “below fuel restart”). The controllers  24  thus command fuel flow to the engine  12  to resume, which causes the engine  12  to restart. 
         [0039]    Referring to  FIG. 5 , available electric power steering assist system current may be ramped up using the ramp rate RAMP_UP_ 1  once the controllers detect an engine auto start condition in anticipation of further steering inputs from the driver. Available electric power steering assist system current may then be ramped up to its maximum using the ramp rate RAMP_UP_ 2  after the engine begins running (after the engine achieves a speed at or above target idle speed). 
         [0040]    The ramp rates, assist levels (if any), and timing as to when the ramping(s) initiate and/or terminate can be calibrated to provide desired steering performance. As an example, certain ramping algorithms may lack the ASSIST_DOWN and/or ASSIST_UP levels. That is, the available electric power steering assist system current may be ramped from its maximum to 0 and/or vice versa without being held at any intermediary threshold value. Other scenarios are also possible. 
         [0041]    The algorithms disclosed herein may be deliverable to/implemented by a processing device, such as the controllers  24 , which may include any existing electronic control unit or dedicated electronic control unit, in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The algorithms may also be implemented in a software executable object. Alternatively, the algorithms may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
         [0042]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.