Abstract:
The invention relates to switching between 2WD and 4WD of a vehicle. It is suggested to increase output power of an engine ( 106 ) when changing to 4WD. An AWD coupling ( 120 ) is opened, if not already open. To provide 4WD, a PTU clutch ( 108 ) is engaged once engine power has increased. The other couplers are sequentially engaged.

Description:
PRIORITY 
       [0001]    This application claims the benefit of priority of U.S. provisional patent application 61/692,781, filed Aug. 24, 2012, incorporated herein by reference in its entirety. 
     
    
     FIELD  
       [0002]    This application relates to control of All-Wheel Drive (AWD) driveline couplings including control of power transfer during conversion between Two-Wheel Drive (2WD) and AWD. 
       BACKGROUND  
       [0003]    Motor vehicles may include a primary drive axle powered by an engine and transmission. The primary drive axle pushes or pulls the remaining auxiliary axle of the vehicle depending upon whether it is in a Front-Wheel Drive (FWD) or Auxiliary-Wheel Drive (RWD) configuration. Some vehicles can convert to All-Wheel Drive (AWD) by selectively engaging the auxiliary axle and actively powering both the primary and auxiliary axles. 
         [0004]    Prior systems can suffer from deceleration during the conversion to the extent that the driver notices a change in vehicle travelling speed when AWD is engaged. In some circumstances, the change results in unsafe or suboptimal conversion conditions. 
       SUMMARY 
       [0005]    The methods disclosed herein overcome the above disadvantages and improve the art by way of a computer program product comprising a tangible memory device and a program stored on the tangible memory device, the program being readable and executable by a processor. The program comprises instructions for making connections in a vehicle driveline comprising the steps of receiving, at a processor, a request to convert a vehicle from a single drive axle-powered driveline to a two drive axle-powered driveline. The processor may receive sensor data and may process the received sensor data to determine vehicle dynamics including current engine power output. The instructions may determine an additional amount of engine power required to convert the vehicle from the single drive axle-powered driveline to the two drive axle-powered driveline. The processor may send a command to open at least one coupler and a command to increase engine power by the determined additional amount. 
         [0006]    A vehicle driveline may comprise a plurality of sensors and a plurality of actuators with respective connections to an electronic control computer, a primary drive axle, an engine, a power transfer unit, and an auxiliary drive axle. The auxiliary drive axle may comprise a drive shaft, an all-wheel drive coupling, an auxiliary drive unit, a first auxiliary drive axle on a first side of the auxiliary drive unit, and a second auxiliary drive axle on a second side of the auxiliary drive unit. The electronic control computer may comprise a processor and a tangible memory device. The tangible memory device may comprise a stored program, the program being readable and executable by the processor. The program may comprise instructions for making connections in a vehicle driveline. 
         [0007]    The processor may receive a request to convert from a single drive axle-powered driveline to a two drive axle-powered driveline. The processor may receive sensor data. The processor may process the received sensor data to determine vehicle dynamics including current engine power output. The processor may determine an additional amount of engine power required to convert the vehicle from the single drive axle-powered driveline to the two drive axle-powered driveline. The processor may send a command to open at least one coupling in at least one of the power transfer unit, the all-wheel drive coupling, or the auxiliary drive unit. The processor may send a command to increase engine power by the determined additional amount. The at least one coupling may receive the command to open the coupling. The engine may receive the command to increase engine power. At least one of the plurality of actuators opens the at least one coupling and at least another of the plurality of actuators increases the engine power by the determined additional amount. 
         [0008]    The program for the vehicle driveline may comprise instructions for making disconnections in the vehicle driveline comprising the following steps. The processor may receive a request to convert from a two drive axle-powered driveline to a single drive axle-powered driveline. The processor may receive sensor data and may process the received sensor data to determine vehicle dynamics including current engine power. The processor may use the programming to determine whether to suspend or decrease engine power output during a conversion of the vehicle from the two drive axle-powered driveline to the single drive axle-powered driveline. The processor may send a command to open at least one coupling in at least one of the power transfer unit, the all-wheel drive coupling, or the auxiliary drive unit. The processor may send a command to decrease or suspend engine power. The at least one coupling may receive the command to open the coupling. The engine may receive the command to decrease or suspend engine power. At least one of the plurality of actuators opens the at least one coupling and at least another of the plurality of actuators decreases or suspends the engine power output during the conversion. 
         [0009]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic example of a simplified vehicle driveline. 
           [0011]      FIG. 2  is an exemplary flow chart of an AWD engagement process. 
           [0012]      FIG. 3  is a schematic example of a control system for driveline control. 
           [0013]      FIG. 4  is an exemplary flow chart of an AWD disengagement process. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Reference will now be made in detail to the examples which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Directional references such as “left” and “right” are for ease of reference to the figures and are not meant to be limiting. While the disclosure references, in large part, a Front-Wheel Drive (FWD) vehicle and operational mode, the concepts are equally applicable to a Rear-Wheel Drive (RWD) vehicle and operational mode. Because of this, references to “front” and “rear” are, at times, for convenience and consistency and are not meant to exclude the applicability of the disclosure to RWD vehicles. Therefore, a primary drive axle may be the axle of a FWD or RWD operating vehicle that receives power directly from the engine. An auxiliary drive axle may be the pushed or pulled axle of a vehicle operating in FWD or RWD mode. The auxiliary axle becomes a powered axle when AWD is activated and engine power is actively supplied to the auxiliary axle. 
         [0015]      FIG. 1  is a simplified schematic example of a vehicle driveline. A primary drive axle may be a single shaft spanning between wheels, or, as shown, may include left and right half shafts  100 ,  101  and left and right wheels  102 ,  103 . Optional elements include left and right wheel hub disconnects  115 ,  116  and a differential system, which may be centralized or left and right front differentials. A motor  106  generates motive power which is transferred to a transmission  107  for use in the vehicle as torque. Each component may further include a sensor and electronic and or hydraulic actuator. 
         [0016]    The power transfer unit  108  may be a pass-through for the torque, allowing the torque to remain in the primary drive axle  100 ,  101  during an unengaged condition, but transferring the torque during an engaged condition. An engagement feature, such as a synchronizer or clutch pack, in power transfer unit  108  enables a selectable amount of torque to transfer from primary drive axle to drive shaft  109 . Drive shaft  109  can be coupled to, for example, a pinion while the engagement feature couples to a hypoid gear. Drive shaft  109  selectively couples torque to an optional ECC (electronically controlled coupler), or, as illustrated, to an all-wheel drive coupling  120 . The torque may then pass to rear drive unit  110 , which may house an optional rear differential attached to left and right auxiliary half shafts  111 ,  112 . Torque can be selectively coupled to left and right rear wheels  113 ,  114 . 
         [0017]    Torque is controllable in the driveline for such purposes as slip, anti-slip, cornering, braking and other driving purposes. 
         [0018]    The differentials are optional, but otherwise function to selectively couple an amount of torque to left and right front and rear wheels  102 ,  103 ,  112 , and  113 . That is, the differentials comprise coupling members that selectively output all or some of the torque input to the differential. The differentials may comprise, for example, a dog clutch or synchronizer for the selective torque transfer. The differentials may comprise torque vectoring mechanisms, or may be of the “open differential” type. 
         [0019]    In lieu of a rear differential, the rear drive unit  110  may house non-differentiating coupling members to transfer torque to the half-shafts. 
         [0020]    Another optional implementation may include left and right auxiliary wheel hubs  117 ,  118  to selectively couple torque to left and right rear wheels  113 ,  114  via hydraulics and clutch members. The wheel hubs may also be used for such purposes as idling the rotation of the rear half shafts. In some implementations, the auxiliary left and right wheel hubs  117 ,  118  may be linked to the brake system in an actuatable manner. 
         [0021]    The vehicle of  FIG. 1  can operate, in a default state, in FWD mode. All engine power can remain in the primary drive axle so that active torque transfer occurs to left and right front wheels  102 ,  103 . Front differential and primary left and right wheel hubs  115  and  116  can electronically couple to sensors and a CAN of an electronic control system  320  and they can receive commands to open and close their couplings to control vehicle dynamics such as slip, lateral acceleration, longitudinal acceleration, trajectory, yaw, etc. Such coupling control can assist with maintaining safe and low-wear vehicle operation. 
         [0022]    In the default FWD mode, the engagement feature in the PTU is open and no torque is transferred to the hypoid gear or pinion. Thus, the drive shaft  109  and the remainder of the auxiliary driveline do not receive torque. This enables the auxiliary driveline to idle as a passive system. In essence, the primary driveline pulls the auxiliary driveline until the auxiliary driveline is actively powered. If the vehicle were RWD, the primary driveline would essentially push the auxiliary driveline until the auxiliary driveline was to be activated. The idled auxiliary system increases the fuel economy of the vehicle because drag and viscous losses are removed via the decoupling of PTU  108 , drive shaft  109 , rear drive unit  110  with optional differential, and rear half shafts (left and right auxiliary drive axles  111 ,  112 ). Yet, with the auxiliary driveline disconnected from a supply of engine power and torque, all four wheels can rotate without spinning the driveshaft or rear differential. 
         [0023]    Turning to  FIG. 2 , the vehicle can convert from FWD to AWD beginning with a shift request input to the Electronic Control Unit  320  at the start  201 . The shift request can be made through driver request via an actuator such as a toggle, pedal or switch. Or, the vehicle can sense a condition such as wheel slip, a discrepancy between actual and driver-requested trajectory, an unsafe operating condition, etc. and the vehicle can initiate the shift request. 
         [0024]    Next, the current vehicle dynamics are reviewed at step  202  to determine if the vehicle is within a safe range to permit engagement of AWD. Sensors  301  collect data for processing in the ECU  320 . Along with programming stored in the ECU  320 , the data is operated on by a processor in the ECU  320  to determine vehicle conditions relating to one or more of yaw, lateral acceleration, longitudinal acceleration, trajectory, slip, etc., which must be within a particular operating range to proceed. If conditions do not permit the shift, the ECU  320  can loop through the check step  202  until conditions permit proceeding to the calibration threshold check in step  203 . In this step, the ECU  320  determines the absolute value of the front axle speed minus the drive shaft speed. If the absolute value is less than a given calibration threshold, the conversion can proceed, otherwise, return to step  202 . 
         [0025]    If the all-wheel drive (“AWD”) coupling  120  is not already open, AWD coupling  120  is opened in step  204 . The AWD coupling  120  may be a controllable clutch that can control the amount of torque sent to the rear drive unit  110 . 
         [0026]    Engine power is also increased in step  204 . Engine power increases are calculated to convert from FWD to AWD without the driver experiencing deceleration or other adverse operating conditions. Thus, the magnitude of the engine power increase is sufficient to avoid the transfer of kinetic energy to the auxiliary driveline. With sufficient engine power increase, the auxiliary driveline may be connected for AWD operational mode without a lurching sensation and without loss of forward motion. 
         [0027]    The ECU  320  collects sensor data from sensors  301  relating to current engine power and other operational values. The ECU  320  processes the data to determine how much additional engine power is needed to engage the auxiliary driveline without parasitic use of vehicle kinetic energy. The additional engine power can also be based on maintaining safe vehicle conditions. To these ends, the engine power increase may allow the vehicle to experience immediate power supply to the auxiliary wheels  113 ,  114  once the conversion is complete. 
         [0028]    After the AWD coupling is opened, the extra engine power is used to bring the components of the AWD coupling up to speed with the primary driveline. In addition to a one-time power addition, the ECU  320  can control the engine to add power stepwise in proportion to an amount needed for sequential coupling for the AWD conversion. The sequence of  FIG. 4  enables the synchronized locking of the primary driveline with the auxiliary driveline in a manner that is not detectable by the driver. That is, the sequence minimizes the use of vehicle kinetic energy to bring the auxiliary driveline up to speed. The active addition of engine power prevents the deceleration of the vehicle as the auxiliary components come up to speed. The sequential nature can circumvent harsh locking conditions which can cause excessive component wear. And, lastly, the one-time or stepwise additional engine power and sequential coupling can enhance the vehicle stability during engagement and extend the range of operating conditions available for engaging the AWD mode. That is, the vehicle can more safely engage without affecting vehicle handling and can engage AWD without pulling kinetic energy out of the other moving parts of the overall driveline. By checking the vehicle dynamics prior to engagement, the system can also ensure that AWD is engaged at a time when it will not negatively affect vehicle handling or stability. 
         [0029]    At times it may be desirable to use other energy sources in harmony with the increased engine power. At these times, the programming may rely on vehicle kinetic energy to assist with the conversion to AWD. The additional engine power may be calculated to work in synergy with a selected amount of vehicle kinetic energy. Another option is to include a separate torque source in the auxiliary axle, such as one or more motors that can bring the drive shaft  109  or auxiliary half shafts  111  and  112  within a rotational range for coupling with the primary driveline. The increased engine power may be calculated to augment the torque from the separate source. 
         [0030]    In step  205 , the engagement feature of the PTU  108  is engaged so that torque transfers from the primary driveline to the hypoid gear and pinion. The system can first check the rotational speed difference between the driveshaft  109  and the engagement feature to avoid exceeding the power capacity of the engagement feature. 
         [0031]    This same rotational speed difference check may be completed if dog clutches are used in the rear drive unit. In the instance that dog clutches are used for either the engagement feature or in the rear drive unit, too large of a speed difference may cause the dog clutches to ratchet, which can damage not only the clutch, but affiliated synchronizing mechanisms. To remedy the possibility of such damage, the system and method may include an optional additional torque source, as above. Or, the system may first bring the rear differential up to speed by coupling the rear half-shafts to the differential in the rear drive unit  110  and then closing the AWD coupling  120 . If the driveshaft  109  rotates within a range of the primary drive axle, the engagement feature may close to join the primary and auxiliary drivelines. 
         [0032]    Returning to the program outlined in  FIG. 2 , the torque transfer through the PTU  108  brings the driveshaft  109  up to the same rotational speed as the primary driveline. A check of the PTU in step  206  determines if the PTU engagement feature is fully locked. If not, the engagement feature is re-opened and the PTU is re-engaged. If the PTU is locked in step  206 , the process continues the gradual locking of the AWD auxiliary driveline. 
         [0033]    If the PTU is locked, in step  207 , the AWD coupling  120  is engaged. In step  208 , the system checks to ensure that the AWD coupling  120  is locked. If not, the process loops back to step  207  to engage the AWD coupling  120 . The AWD coupling  120  may gradually increase locking torque from 0-100% to help improve shifting smoothness. 
         [0034]    If the AWD coupling is engaged, the rear drive unit (RDU)  110  engages with the AWD coupling  120 . The drive shaft  109  may then bring the rear differential up to speed via the AWD coupling  120 . Then, the differential may lock to the auxiliary half shafts. If the RDU  110  does not lock, as checked in step  210 , the RDU  110  is re-engaged. If the RDU  110  locks, the driveshaft, rear differential and rear half shafts  111 ,  112  will all spin at substantially the same speed. In step  211 , the engine power is returned to normal such that the extra engine power is discontinued in step  211 . In addition, in step  211 , the AWD coupling operation is returned to normal. 
         [0035]    With the shift from FWD to AWD complete in step  212 , normal operation of the AWD coupling may entail electronic or hydraulic regulation to control the torque transferred across an internal clutch. The electronic control unit  320  may comprise a vehicle dynamics controller that determines how much torque should be split between the front and rear drive axles. Control lines and actuators may implement the torque control. 
         [0036]    Normal operation of the engine after shift complete  212  may entail adjustments to engine power based on commands from the vehicle dynamics controller, which may be based on driving conditions such as acceleration, braking, slip, traction control, etc. 
         [0037]    With the vehicle shifted to AWD mode, all four wheels can be actively engaged by the ECU  320  or other vehicle dynamics controller for a variety of purposes such as stability control, traction control, anti-slip, etc. 
         [0038]    The process of  FIG. 2  can be reversed sequentially to shift back to FWD from AWD, or, the couplings may be opened simultaneously, the shift mode depending on current engine power. As shown in  FIG. 4 , a manual or ECU  320  initiated shift request is received at step  401 . The processor executes programming to check if current vehicle dynamics permit disengagement of the AWD driveline in step  402 . If conditions do not permit disengagement, the system can loop back to restart the check. 
         [0039]    If the vehicle dynamics permit disengagement, then in step  403 , the system analyzes the engine power demand. If the driver command is low, or the torque output is within a predetermined range, the system may suspend engine power briefly and simultaneously perform step  404  to unlock the RDU, step  406  to unlock the AWD coupling, and step  408  to unlock the PTU. The brief period may be on the order to 100-200 ms. The system may then check that all scheduled unlocks of the RDU, AWD coupling, and PTU are complete (steps  405 ,  407 , and  409 ). 
         [0040]    If, however, the engine power demand is high, disengagement may be harsh to the clutches or synchronizers. In that high rotation situation, sequential unlocking and unlock checking is performed with either a decrease of engine power or a suspension of engine power 
         [0041]    In order to complete the disclosed processes, the driveline comprises a variety of electronic and hydraulic components that communicate with an electronic control unit (ECU)  320 . Appropriate connective members such as wires, cables, hoses, etc. are supplied along the driveline between the ECU  320  and at least one hydraulic control system and/or electronic control system having motors or solenoids. If necessary, the ECU  320  may comprise several remote computer devices in the vehicle, or the ECU  320  may alternatively comprise remote computing devices that relay communications to each other or a central ECU  320 . 
         [0042]      FIG. 3  shows an exemplary schematic for a vehicle control system. The vehicle control system comprises sensors  301 , ECU  320 , and at least one vehicle bus with associated controller area network (CAN)  319 . The vehicle bus/CAN  319  may connect to at least one hydraulic controller for hydraulically controlled clutches or PTU engagement feature. Vehicle bus/CAN  319  may also connect to actuators for electrical control of devices. In lieu of having separate electrical lines for each sensor and actuator at each driveline component, the CAN may be bidirectional. That is, the CAN may send commands from the ECU  320  and return data from the sensors  301 . 
         [0043]    Sensors  301  are dispersed around the vehicle to collect data for use in observers  310  and controller  314  of ECU  320 . The sensors may comprise one or more of an engine power sensor  300 , steering angle sensor  302 , driveline speed sensor  303 , longitudinal acceleration sensor  304 , lateral acceleration sensor  305 , yaw rate sensor  306 , throttle position sensor  307 , brake pedal sensor  308 , and hydraulic control unit sensor  309 . The sensors shown in  FIG. 3  are exemplary only, and additional or fewer sensors may be used. For example, sensors may be included for any motor or solenoid actuators and rotational sensors may be used to sense the rotational speed of the pinion, auxiliary drive axles  111 ,  112 , primary drive axles  100 ,  101 , drive shaft  109 , differentials, wheel hubs, etc. Sensors may also be implemented to confirm the open or closed status of the PTU engagement feature, AWD coupling  120 , RDU  110 , etc. The sensor data can be supplied to the ECU  320  for observational purposes and for control purposes. 
         [0044]    The sensors  301  forward data to the ECU  320 , which may comprise at least one processor with an associated memory device and stored algorithms. The processor may be part of a computer system or on-board chip system. The memory device may be a FLASH, ROM, RAM or other tangible storage device for storing processor-readable instructions which, when executed by a processing device, cause the processing device to perform the disclosed methods. That is, ECU  320  can receive vehicle operational data from sensors  301  and can process the data to determine vehicle dynamics, engine power needs, thresholds, step timing, completion of commands, etc. ECU  320  can also issue commands to implement each step of the engagement and disengagement processes. And, ECU  320  can compare processed and received data, pull stored predetermined data from the memory device, push received data to the memory device for storage, update stored memory data and instructions, and make determinations of vehicle conditions. 
         [0045]    The processor of the ECU  320  may comprise one or more observers  310 , which may comprise a vehicle model and kinematics observer  311 . The vehicle model and kinematics observer  311  processes the data from sensors  301  according to programmed algorithms and may create data related to a slip angle  312  and vehicle speed  313 . Additional data can also be created by vehicle model and kinematics observer  311 , such as bank angle or roll angle data. In addition, the observers  310  comprise processing capabilities to determine if the absolute value of the primary axle speed minus the drive shaft speed is less than a calibration threshold  321 . This absolute value comparison, together with processing of other vehicle dynamics data, determines if the AWD auxiliary driveline can be engaged or disengaged. If so, an input is sent to the AWD coupling control  317 , which in turn generates signals for control of the engine power, PTU engagement feature, AWD coupling  120 , RDU  110 , and auxiliary drive axles  111 ,  112 . Instead of the centralized AWD coupling control  317 , the controllers  314  may comprise separate controllers for each AWD driveline coupler, such that the AWD coupling  120 , RDU  110 , and PTU  108  each have a dedicated controller. 
         [0046]    As indicated in  FIG. 3 , the sensors  301  may supply data directly to the controllers to enable implementation feedback. The sensors may sense changes in vehicle conditions, which can be processed, observed, and used in the determination of new commands from the controllers  314 . 
         [0047]    The slip angle  312  and vehicle speed  313  data is shared with controller  314 , which also collects data from sensors  301 . Controller  314  may be a part of the processor of the ECU  320  having observers  310 . Or, controller  314  may be an additional processor with associated memory and stored algorithms which cooperate with the processor having observers  310 . A traction and yaw stability control algorithm controller  315  is used to make determinations based upon at least one of the slip angle  312  data, vehicle speed  313  data, sensors  301  data, additional sensors, and additional data. Based on the results of the determinations made by the traction and yaw stability control algorithm controller  315 , commands are sent from the controller via the vehicle bus to CAN  319  for implementation by various vehicle actuators at various locations along the vehicle driveline. The location and function of the vehicle actuators are not shown, but are within the knowledge of one of ordinary skill in the art. The commands from the controller relate to various electronically controlled stability features associated with the vehicle, including but not limited to traction control, anti-lock braking, oversteering control, understeering control, limited slip differential control, and rollover control. 
         [0048]    Results from traction and yaw stability control algorithm controller  315  are also forwarded to torque distribution controller  316 . Torque distribution controller  316  determines how much torque to transfer from the primary drive system to the secondary auxiliary drive system. Commands from torque distribution controller  316  are also forwarded for control of the hydraulics control unit. 
         [0049]    The combination of sensors  301 , ECU  320 , hydraulic and/or electronic control, and actuators allows cooperation, control and observation of moving parts along the driveline. The vehicle control system assists with the synchronous operation of the AWD and FWD systems. The ECU system may determine the extent and timing of mechanical engagement of the various disclosed coupling members of the driveline. The ECU system also assists with the extent and timing of disengagement of the various disclosed coupling members of the driveline for idling of the auxiliary drive system. 
         [0050]    In addition to that shown in  FIG. 3 , the observers  310  and controllers  314  may rely for implementation on programming stored in the ECU  320 . The observers  310  may comprise a dedicated processor and the controllers  314  may comprise a dedicated processor, or a single processor may operate programming for both observers and controllers. 
         [0051]    Other implementations are considered within the scope of the disclosure, such as adjusting the coupling order of the AWD auxiliary driveline. For example, it may be desirable to engage the left and right auxiliary drive axles  112 ,  113  with the auxiliary wheel hubs  117 ,  118  and rear drive unit  110  before engaging the power transfer unit  108  with the drive shaft  109 . It may also be desirable to engage the rear drive unit  110  with the driveshaft  109  before engaging the power transfer unit  108  so that the driveshaft  109  is not idled and is rotating before the power transfer unit  108  is engaged. Such adjustments to coupling order may prevent ratcheting of coupling members when operation speeds are high. 
         [0052]    Other implementations will be apparent to those skilled in the art from consideration of the specification and practice of the examples disclosed herein. It is intended that the specification and examples be considered as exemplary only.