Abstract:
A vehicle may include a sensor configured to detect a rearward approaching object and at least one controller configured to cause the vehicle to accelerate in response to the sensor detecting a rearward approaching object while the vehicle is moving forward.

Description:
BACKGROUND 
     Cruise control (sometimes known as speed control or autocruise) is a feature that may automatically control the speed of a motor vehicle. Cruise control systems control throttle to maintain a steady speed as set by the driver. 
     SUMMARY 
     An automotive vehicle may include a powertrain and at least one controller configured to command the powertrain to accelerate the vehicle in response to information about an object approaching the vehicle from the rear if a speed of the vehicle is less than a target cruise control speed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an automotive vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Certain vehicles have adaptive cruise control (ACC) systems, which may improve cruise control functionality via automatic braking or dynamic set-speed controls. Automatic braking controls may use, for example, a radar or lidar arrangement to allow the vehicle to keep pace with the car it is following, slow when closing in on the vehicle in front, and accelerate again to the preset speed when traffic allows (referred to herein as ACC resume acceleration). The ACC resume acceleration may, for example, be based on vehicle type, whether it is raining (as determined, for example, based on information from a windshield wiper sensor), whether it is nighttime (as determined, for example, based on information from a headlamp sensor), whether the vehicle is cornering (as determined, for example, based on information from a steering angle sensor or yaw rate sensor), and/or whether a turn indicator is active. Dynamic set-speed controls may use the GPS position of the vehicle and a map database with speed limit information or information from speed limit signs to adjust the cruise set-speed accordingly. 
     A driver of an active ACC vehicle may choose to change lanes after automatically being slowed (from 65 mph to 45 mph for example) to pass a vehicle that it had been closing in on. Once in the new lane, the ACC system may then cause the vehicle to accelerate until the preset speed (65 mph in this example) is reached. The ACC resume acceleration, as discussed above, may be based on vehicle type and/or driving conditions. These factors may result, for example, in a nominal acceleration of approximately 1 m/sec 2 . If another vehicle (travelling at 65 mph for example) closes in on the vehicle with active ACC too quickly from behind (because the acceleration of 1 m/sec 2  set by the ACC is not sufficient to keep the vehicles adequately spaced apart), the driver of the vehicle with active ACC may need to intervene by stepping on the accelerator pedal to increase the acceleration of the vehicle. This may cause driver dissatisfaction with the ACC system. Hence, embodiments contemplated herein may consider, for example, the speed of an object approaching from the rear in determining the ACC resume command. 
     Referring to  FIG. 1 , an automotive vehicle  10  may include a powertrain  12  (e.g., engine, transmission, brakes, etc.), a forward sensor  14  (e.g., radar, lidar, camera, etc.), a rearward sensor  16  (e.g., radar, lidar, camera, etc.), a plurality of other vehicle sensors  18  (e.g., wiper sensor, headlamp status sensor, steering wheel sensor, etc.) and one or more controllers  20 . The sensors  14 ,  16 ,  18  are in communication with the controllers  20 . (Other sensor arrangements are, of course, also contemplated.) The powertrain  12  is in communication with/under the control of the controllers  20 . 
     The forward sensor  14  may detect the distance or range to (and/or the velocity/acceleration/range rate of) another vehicle in front of the vehicle  10 . Likewise, the rearward sensor  16  may detect the distance or range to (and/or the velocity/acceleration/range rate of) another object/vehicle behind the vehicle  10 . The sensors  18  may detect a variety of information regarding the operating state of the vehicle  10  (such as whether the headlamps are on, whether the windshield wipers are on, the steering angle at any given instant, etc.) and the ambient conditions (e.g., temperature, humidity, etc.) in the vicinity of the vehicle  10 . 
     As discussed above, information from the sensors  14 ,  18  may be used to determine, in a known fashion, an ACC resume acceleration. This ACC resume acceleration, however, may not be sufficient to keep the vehicle  10  adequately spaced apart from another object approaching from its rear. Hence, information from the sensor  16 , as discussed below, may be used by the controllers  20  to modify/determine the ACC resume acceleration. 
     To maintain at least a timed headway distance, T r  (sec), to a rearward approaching vehicle, the required vehicle acceleration, a h , may be found from the relations 
                   min   t     ⁢       d   r     ⁡     (   t   )         =         min   t     ⁢     (         ∫   0   t     ⁢       (       υ   h     +       a   h     ·   τ       )     ⁢     ⅆ   τ         +     d     r   ⁢           ⁢   0       -       υ   r     ·   t       )       ≥       υ   r     ·     T   r           ,     t   ≥   0           
where
 
d r (t)=distance to the rear vehicle, d r0 =distance to the rear vehicle at lane change,
 
v r =rear vehicle speed at lane change, T r =rear vehicle&#39;s headway time (sec) (tunable),
 
v h =host vehicle speed at lane change, a h =host vehicle acceleration, and assuming d r0 &gt;v r ·T r  and v r ≧v h  
 
Hence, a h  should be greater than or equal to
 
                 (       υ   r     -     υ   h       )     2       2   ⁢     (       d     r   ⁢           ⁢   0       -       υ   r     ·     T   r         )             
T r  is given, v r  and d r0  are determined in a known fashion or obtained from the sensor  16 , and v h  is known. The controllers  20  may solve for a h  and compare this acceleration with the ACC resume acceleration determined based on information from the sensors  14 ,  18 . The controllers  20  may then apply the maximum of these accelerations.
 
     A look-up table accessible by the controllers  20  and populated with parameters such as those discussed above (or other suitable parameters) may be mapped with various ACC resume acceleration values. As an example, inputs to the look-up table may include approaching vehicle speed, wiper status, yaw rate, etc. A nominal ACC resume acceleration may thus be identified based on the values of the input parameters. As another example, inputs to the look-up table may include those parameters identified in the paragraph above. Hence, a h  need not be solved for but rather selected based on the values of the input parameters. 
     The ACC resume acceleration determined from the information from the sensors  14 ,  18  may be modified by a gain factor that depends on, for example, a speed of (and/or the distance to, etc.) the rearward approaching vehicle. If, for example, the controllers  20  determine a nominal ACC resume acceleration of 1.3 m/s 2  via a look-up table based on information from the sensors  14 ,  18 , the controllers  20  may then modify (e.g., multiply) this ACC resume acceleration by a factor (generally greater than 1) that depends on approaching vehicle speed. This factor may be equal to, for example, 1.3 if the approaching vehicle speed is 50 mph, and may be equal to, for example, 1.7 if the approaching vehicle speed is 70 mph, etc. The gain factor may also be fixed. Other scenarios and modification strategies are also contemplated. 
     Alternatively, the controllers  20  may assign a value to a parameter (e.g. a flag) representing whether the sensor  16  detects a reward approaching vehicle. That is, if the sensor  16  detects a rearward approaching vehicle, the controllers  20  set the flag to “1.” Otherwise, the controllers  20  set the flag to “0.” The controllers  20  may command the powertrain  12  to accelerate the vehicle  10  if the controllers  20  determine the flag to be “1” and the speed of vehicle  10  to be less than the cruise speed set point. The acceleration rate may simply be a fixed value or determined based on factors and techniques similar to those described above. 
     In addition, a turn indicator may be used to trigger an increase in the acceleration request. This acceleration request may be scaled as a function of rear vehicle speed, distance and/or acceleration. A more complex algorithm may use turn signal application to activate this feature, which then scales the acceleration gain as a function of offset relative to the lead vehicle and/or lane markings. An example sequence may be as follows: (1) driver applies left turn signal=&gt;acceleration request=0.1·a h ; (2) driver turns wheel and vehicle begins to change lanes to pass=&gt;acceleration request=a h ·lead vehicle lateral offset·scaling factor; (3) lead vehicle is fully out of path=&gt;acceleration request=a h ; (4) if the host vehicle does not change lanes within a specified timeout period or the range to the lead vehicle is too small=&gt;acceleration request=acceleration necessary to follow lead vehicle. 
     The ACC resume acceleration (or acceleration rate) may be bounded by a maximum threshold value. This value may be fixed (e.g., 2 m/s 2 ) or depend on information from the sensors  14 ,  18  or other data sources. As an example, the controllers  20  may calculate/identify a h , as described above, to be 2.3 m/s 2 . Such a rate of acceleration may be precluded and instead limited to 1.9 m/s 2  if, for example, the sensor  14  detects another vehicle 50 m away. 
     Suitable/known vehicle communications technology may be used to acquire information on approaching vehicles. Hence, sensors need not be used to obtain information regarding approaching vehicles. A host vehicle, for example, may receive speed and/or location information from a rearward approaching vehicle. Based on this (as well as other information similarly received), the controllers  20  may determine/identify a suitable ACC resume acceleration as described herein. Other arrangements are also possible. 
     The controllers  20  may periodically/continuously monitor the speed of the vehicle  10  versus the cruise speed set point to determine when to discontinue the ACC resume acceleration. That is, when the speed of the vehicle  10  meets or exceeds the cruise speed set point, the controllers  20  cease to issue the ACC resume acceleration command as known in the art. 
     The controllers  20  may instead use torque and/or speed commands to cause the vehicle  10  to accelerate during ACC resume. That is, one of ordinary skill will recognize that there are kinematic equivalent techniques to those described above to represent the change in vehicle speed necessary to achieve the cruise speed set point. As an example, a look-up table may map various input parameters with an ACC resume engine (or wheel) torque instead of an ACC resume acceleration, etc. 
     The algorithms disclosed herein may be deliverable to/implemented by a processing device, such as the controllers  20 , 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. 
     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.