Abstract:
A generator brake is controlled such that a powersplit hybrid powertrain enters and exits a parallel mode of operation. The generator brake may be an electrically controlled one-way clutch. The one-way clutch is controlled as a function of an acceleration request to determine whether the parallel mode is to be entered or exited.

Description:
BACKGROUND OF INVENTION 
     The present invention relates to a method of controlling an automotive powertrain and in particular to entering and exiting a parallel mode of operation for a powersplit powertrain. 
     An automotive vehicle may use a powersplit hybrid electric powertrain. Included in the powersplit powertrain is an electric generator, which may also alternatively operate as an electric motor. The powersplit powertrain may be operated in a plurality of modes, including negative powersplit, positive powersplit, and parallel modes. In the positive powersplit mode the generator charges a battery. In the negative powersplit mode the generator operates as a traction motor producing a torque to propel the vehicle. In the parallel mode the generator is braked from rotating, which allows the vehicle to be propelled by a combined torque produced by the engine and a second electric motor. A clutch may be used to brake the generator so that the powertrain may operate in the parallel mode. 
     However, entering the parallel mode requires the clutch to brake the generator from rotating and exiting the parallel mode requires the clutch to release the generator to rotate. 
     SUMMARY OF INVENTION 
     An embodiment contemplates a method of controlling a powersplit hybrid vehicle powertrain. An acceleration command is received for a vehicle. A parallel mode of operating an electric motor, a generator, and an engine is determined to be needed to meet the received acceleration command. A selectively actuatable one-way clutch, rotationally fixed to the generator to prevent rotation in an engagement direction, is electronically actuated to enter the parallel mode. 
     Another embodiment contemplates a method of controlling a powersplit hybrid vehicle powertrain of a vehicle. An electric motor, a generator, and an engine are operated in a parallel mode when an acceleration command for the vehicle is received. The parallel mode is determined to not be required to meet the received acceleration command. When the parallel mode is determined to not be required, the parallel mode is exited by electronically deactivating a selectively actuatable one-way clutch coupled to the generator to allow for generator rotation in first and second, opposite, directions. 
     An advantage of an embodiment is providing a control methodology for the one-way clutch. This improves operation of the powertrain when entering and exiting the parallel mode. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a hybrid electric powertrain. 
         FIG. 2  is a schematic, perspective view of a one-way clutch. 
         FIG. 3  is a schematic view of a portion of the one-way clutch. 
         FIGS. 4A and 4B  are a flow chart of a control routine for a hybrid electric powertrain. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a powersplit type hybrid electric powertrain  10  for an automotive vehicle  12 . The powertrain  10  is merely exemplary, and may take other forms, such as front wheel drive, rear wheel drive, and all wheel drive types of powertrains. 
     The powertrain  10  includes an internal combustion engine  14  powering a crankshaft  16 . The crankshaft  16  transmits torque from the engine  14  to a planetary gear set  18 . Also connected to transmit torque to and from the planetary gear set  18 , via a generator shaft  20 , is a generator  22 . The planetary gear set  18  comprises a sun gear, ring gear, and carrier assembly, which can be conventional and so the specifics of this gear set are omitted from  FIG. 1  for clarity. The crankshaft  16  connects to the carrier assembly and the generator shaft  20  connects to the sun gear. The ring gear transmits torque, via a first gearing input  24 , to a gearing  26 . Also connected to the gearing  26 , via a second gearing input  28 , is an electric motor  30 . The generator  22  and the motor  30  are connected via a high voltage bus  32  to a battery  34 . The generator  22  is also connected via a brake shaft  36  to a selectively actuatable one-way clutch (OWC)  38 . The gearing  26  transmits torque via a gearing output  40  to a differential  42 . The differential  42  transmits torque, via first and second axles  44  and  46 , respectively, to rotate first and second wheels  48  and  50 , respectively. Operation of the powertrain  10 , including the engine  14 , generator  22 , motor  30 , and one-way clutch  38 , is controlled by a controller  52 . The controller  52  may be a vehicle speed controller (VSC), which controls the powertrain  10  to regulate a speed of the vehicle  12 . 
     As described, the powertrain  10  may operate in a positive powersplit mode in which the generator  22  operates to charge the battery  34 . Alternatively, the powertrain  10  may operate in a negative powersplit or parallel mode. In the negative powersplit mode the generator  22  is powered by the battery  34  to rotate and produce a generator torque that propels the vehicle  12 . The powertrain  10  operates in a parallel mode when the one-way clutch  38  brakes the generator  22  from rotating. Once braked from rotating, the generator  22  may be turned off. In the parallel mode, torque is supplied to the gearing  26  from the engine  14  and the motor  30 . The parallel mode allows both the engine  14  and the motor  30  to propel the vehicle  12 . 
       FIG. 2  illustrates the one-way clutch  38 . The one-way clutch  38  comprises a rocker plate  100  having pockets  108  that each contain a corresponding rocker  102 , which are pivotally hinged within the pockets  108 . The clutch  38  also includes a cam plate  104 , which has a plurality of notches  112  that define teeth. The teeth can selectively catch fingers extending from the rockers when the rockers  102  are pivoted to extend the fingers radially inward. The rocker plate  100  is connected to and rotates with the brake shaft  36 , and the cam plate  104  is secured to the vehicle  12  to prevent rotation of the cam plate  104 . For example, the cam plate  104  may be bolted to a casing for the clutch  38 . 
     The cam plate  104  contains a coil  106  that may be selectively electrified to produce a magnetic force. As illustrated in  FIG. 2 , the clutch  38  is in a deactivated state, in which the fingers of the rockers  102  are pivoted to a radially outer position in the rocker plate recesses and thus the fingers do not engage the teeth of the cam plate  104 . When the clutch  38  is in the deactivated state, the rockers  102  fit within the pockets  108  without protruding beyond a radially inside face  110  of the rocker plate  100 . The rockers are biased by a spring  120  to remain within the pockets  108  without protruding (a bias in a counterclockwise direction as illustrated in  FIGS. 2 and 3 ). When the clutch  38  is deactivated (i.e., the coil  106  is not electrified), no torque is transferred between the rocker and cam plates  100  and  104 , respectively. The clutch  38  is activated by electrifying the coil  106 . The magnetic force that results from electrifying the coil  106  pivots the fingers of the rockers  102  out of the pockets  108 , against the bias of the spring  120 , such that the fingers protrude beyond the radially inside face  110  of the rocker plate  100 . 
     As understood by one skilled in the art, the rockers  102  may alternatively be hinged from the cam plate  104 , the pockets  108  correspondingly located in the cam plate  104 , the notches  112  located in the rocker plate  100 , and the coil  106  located in the rocker plate  100 . 
       FIG. 3  illustrates the clutch  38  in an activated state. The fingers of the rockers  102  extend beyond the inside surface  110  of the rocker plate  100  and are pivotally biased towards the notch  112  of the cam plate  104 . As discussed, the clutch  38  is a selectively actuatable one-way clutch. When the clutch  38  is activated and the rocker plate  100  rotates in a disengagement direction  114 , the fingers of the rockers  102  will be cammed outward by the teeth and so will not engage with the teeth to prevent rotation. Rather, as the rocker plate  100  rotates, a plurality of first cam surfaces  116  deflect the fingers of the rockers  102  toward the pockets  108 . 
     Alternatively, when the clutch  38  is activated and the rocker plate  100  attempts to rotate in an engagement direction  122 , opposite the disengagement direction  114 , the fingers of the rockers  102  engage with a second engagement surface  118  of the teeth and the clutch  38  is engaged. The mechanical engagement between the cam and rocker plates  104  and  100 , respectively, prevents rotation of the rocker plate  100 . The mechanical engagement is sufficient such that, if the coil  106  of the clutch  38  is deactivated, the clutch  38  remains engaged to prevent rotation. De-energizing the coil  106  once the clutch  38  is engaged, which deactivates the rockers  102 , reduces discharge of the battery  34  while still preventing rotation of the rocker plate  100 . Since the rocker plate  100  is rotationally fixed to the generator  22 , braking the rocker plate  100  from rotating also prevents the generator  22  from rotating. 
     Rotation of the rocker plate  100  may be changed from the disengagement direction  114  to the engagement direction  122  by slowing rotation in the disengagement direction  114  to a second stop before commencing rotation in the engagement direction  122 . Rotation in the engagement direction  122  may then be accelerated from the second stop to the desired speed. Rotation of the rocker plate  100  may be changed from the engagement direction  122  to the disengagement direction  114  by slowing rotation in the engagement direction  122  to a stop before commencing rotation in the disengagement direction  114 . Similarly, rotation in the disengagement direction  114  may then be accelerated from the stop to a desired speed. A time period between stopping and commencing rotation of the rocker plate  100  may vary and may be minimized so as to be imperceptible to a driver of the vehicle  12 . 
     The engaged clutch  38  may be disengaged by rotating the rocker plate  100  in the disengagement direction  114 . With or without the coil  106  of the clutch  38  being activated, when the rocker plate  100  is rotated in the disengagement direction  114 , no engagement occurs between the rocker and cam plates  100  and  104 , respectively, thus allowing the rocker plate  100  to freely rotate. When the coil  106  of the clutch  38  is deactivated, allowing the springs to pivot the fingers away from engagement with the teeth, the rocker plate  100  may be freely rotated in the disengagement direction  114  and engagement direction  122 . 
       FIGS. 4A and 4B  will now be discussed with reference to  FIGS. 1-3 .  FIGS. 4A and 4B  illustrate a control routine  200  for the clutch  38  when the powertrain  10  enters and exits the parallel mode. 
     In a step  202  an acceleration command is received, and whether the parallel mode is active is determined in a step  204 . When the parallel mode is inactive, the control routine  200  proceeds to a step  206 . Otherwise, when the parallel mode is active, the control routine  200  proceeds to a step  228 . 
     In the step  206 , the control routine  200  determines whether the acceleration command is a constant acceleration command. For example, a constant acceleration command may be made when the driver is accelerating the vehicle  12 . If the acceleration command is not the constant acceleration command, then in a step  208 , the parallel mode remains inactive and the control routine  200  returns to the step  202 . If the acceleration command is the constant acceleration command, then in a step  210 , whether the parallel mode should be activated is determined. The parallel mode may need to be activated when a required torque to meet the acceleration command exceeds an available torque produced by the powertrain  10  with the parallel mode inactive. If the parallel mode is not needed to meet the acceleration command, then the control routine  200  maintains the parallel mode inactive in the step  208  before returning to the step  202 . 
     If the parallel mode is to be activated, then in a step  212 , the control routine  200  determines whether the constant acceleration command has been altered to a reduced acceleration command. For example, the reduced acceleration command may be made once the vehicle  12  reaches a cruising speed to maintain the cruising speed. The reduced acceleration command is less than the constant acceleration command but greater than a zero acceleration command. If the constant acceleration command has not been altered to the reduced acceleration command, then the control routine  200  proceeds to a step  214 . Otherwise, if the constant acceleration command has been altered to the reduced acceleration command, then in a step  216  the generator  22  rotates to slow the engine  14 , via the planetary gear set  18 , before the control routine  200  proceeds to the step  214 . For example, the engine  14  may be slowed by the generator  22  rotating in the engagement direction  122 . 
     In the step  214  the generator  22  is commanded to overrun the clutch  38  by rotating the rocker plate  100  in the disengagement direction  114 . In a step  218 , while the generator  22  is overrunning the clutch  38 , the clutch  38  is activated by electrifying the coil  106 . As discussed, when the clutch  38  is activated, the rockers  102  pivot, causing the fingers to protrude beyond the inside surface  110 . The clutch  38  is then engaged in a step  220  by rotating the rocker plate  100  a short distance in the engagement direction  122 , which mechanically engages the rockers  102  with the second engagement surfaces  118  of the teeth. Once the clutch  38  is engaged, torque being carried by the generator  22 , from the engine  14 , is smoothly transferred to the clutch  38  until the generator  22  is carrying no torque. 
     In a step  222 , the control routine  200  determines whether the acceleration command has been altered to the zero acceleration command. If the acceleration command has been altered to the zero acceleration command, then in a step  224  the generator  22  is operated in a regenerative mode. In the regenerative mode, as understood by one skilled in the art, the generator  22  operates to brake the vehicle  12  while charging the battery  34 . Following operating the generator  22  in the regenerative mode, the control routine  200  returns to the step  202 . If the acceleration command is not altered to the zero acceleration command, then the generator  22  is turned off in the step  226  before the control routine  200  returns to the step  202 . Prior to turning off the generator  22 , in the step  220 , engine torque carried by the generator  22  has been transferred to the clutch  38 . Turning off the generator  22  conserves charge of the battery  34 . 
     As discussed, if the parallel mode is not active in the step  204 , the control routine  200  proceeds to the step  228 . In the step  228 , the control routine  200  determines whether a decreased acceleration command has been made. For example, a decreased acceleration command may be made when the driver desires the vehicle  12  to slow from the cruising speed. If the decreased acceleration command has been made, then in a step  230 , the control routine  200  determines whether the parallel mode should be deactivated. The parallel mode may be deactivated when the required torque to meet the acceleration command is available from the powertrain  10  with the parallel mode inactive. If, in the step  230 , the parallel mode should remain inactive, then in a step  232  the parallel mode is maintained active and the control routine  200  returns to the step  202 . If the parallel mode should be deactivated, then the control routine  200  proceeds to a step  234 . 
     In the step  234 , the generator  22  is turned on. The generator  22  may be turned on while the clutch  38  is activated and engaged. In a step  236  the generator  22  is commanded to overrun the clutch  38  by rotating the rocker plate  100  in the disengagement direction  114 . In a step  238  the clutch  38  is disengaged when the rockers  102  separate from the second engagement surfaces  118  due to the cam surfaces  116  of the teeth camming the fingers radially outward. In a step  240  the clutch  38  is deactivated while overrunning. In a step  242  the generator  22  operates in the regenerative mode. 
     In a step  244 , the control routine  200  determines if there has also been a brake command. For example, a brake command may be made by the driver when a rapid slowing of the vehicle  12  is desired. If the brake command has been made, then in a step  246  the vehicle  12  is braked. If a magnitude of the braking force required to meet the brake command exceeds a regenerative braking capacity of the generator  22 , then additional braking is applied. For example, the additional braking may be from a conventional hydraulic brake system or operating the motor  30  in the regenerative mode. Following braking of the vehicle  12 , the control routine  200  returns to the step  202 . Otherwise, if the brake command has not been made in the step  244 , the control routine  200  proceeds to the step  202 . 
     If, in the step  228 , a decreased acceleration command is not received, then in a step  248  the control routine  200  determines whether an increased acceleration command has been received. For example, an increased acceleration command may be made when the driver desires the speed of the vehicle  12  increase from a cruising speed. The increased acceleration command may be the result of the driver increasing the speed of the vehicle  12  or due to an increased road grade or other driving condition that requires the increased acceleration command to maintain the vehicle  12  at a constant speed. If the increased acceleration command is received, then in a step  250  the control routine  200  determines whether to deactivate the parallel mode. If the parallel mode is to remain active, then the control routine  200  continues to the step  202  via the step  232 . If the parallel mode is to be deactivated, then the generator  22  is turned on in a step  252 , the generator  22  is commanded to overrun the clutch  38  in a step  254 , and the clutch  38  is disengaged in a step  256 . The generator  22  may be turned on while the clutch  38  is activated and engaged. In a step  258  the clutch  38  is deactivated (de-energizing the coil  106 ) while overrunning. In a step  260 , control of the generator  22  and the clutch  38  are given to the vehicle speed controller before the control routine  200  returns to the step  202 . If, in the step  248 , the increased acceleration command is not received, then the control routine  200  proceeds to the step  232  before returning to the step  202 . If, in the step  250 , the control routine  200  decides to keep the parallel mode active, then the control routine  200  proceeds to steps  232  and  202 . 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.