Abstract:
A hybrid engine control system comprises a hybrid engine control module and a torque mitigation module. The hybrid engine control module selectively stops an internal combustion engine (ICE). The hybrid engine control module selectively starts the ICE based upon driver inputs and non-driver inputs. The torque mitigation module reduces torque transfer from the ICE to a driveline while the ICE is started based upon the non-driver inputs and maintains torque transfer from the ICE to the driveline while the ICE is started based upon the driver inputs. A method comprises selectively stopping an internal combustion engine (ICE); selectively starting the ICE based upon driver inputs and non-driver inputs; reducing torque transfer from the ICE to a driveline while the ICE is started based upon the non-driver inputs; and maintaining torque transfer from the ICE to the driveline while the ICE is started based upon the driver inputs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/961,547, filed on Jul. 20, 2007. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to hybrid vehicles, and more particularly to smoothing non-driver-commanded engine restarts in hybrid vehicles. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    Referring now to  FIG. 1 , a functional block diagram of a hybrid powertrain of a vehicle is presented. An engine  102  provides torque to a transmission  104 . The transmission  104  transmits torque to a driveline  106 . The engine  102  also drives and is driven by a belt alternator starter (BAS) system  110 . BAS systems may be characterized by a combination motor/generator used in place of a standard alternator and connected to the crankshaft of the engine  102  via the accessory drive belt. 
         [0005]    The BAS  110  converts power from the engine  102  into electrical power, which may be stored in charge storage  112 . When the engine  102  is not running, the BAS  110  may use power from the charge storage  112  to drive the crankshaft of the engine  102 , and thereby propel the vehicle. The BAS  110  and the engine  102  are controlled by a hybrid engine control module (ECM)  120 . The hybrid ECM  120  receives signals from driver inputs  122 , such as an accelerator pedal, a gear shift lever, and/or a brake pedal. 
         [0006]    When the vehicle comes to a stop, the hybrid ECM  120  may instruct the engine  102  to shut off. For example, this may be achieved by stopping fuel delivery and spark to the engine  102 . When the driver desires to start the vehicle from the stop, as indicated by lifting their foot off the brake pedal or pressing the accelerator pedal, the hybrid ECM  120  may command the engine  102  to restart. Also, the engine  102  may be commanded to start by the ECM  120  for reasons not initiated by the driver. When the engine  102  restarts, torque from the engine  102  is transmitted through the transmission  104  to the driveline  106 . If the brakes are applied during the engine  102  start, the driveline  106  is unable to rotate, and the torque is transmitted directly to the frame of the vehicle, which is experienced as a jerk disturbance by the driver. 
       SUMMARY 
       [0007]    A hybrid engine control system comprises a hybrid engine control module and a torque mitigation module. The hybrid engine control module selectively stops an internal combustion engine (ICE). The hybrid engine control module selectively starts the ICE based upon driver inputs and non-driver inputs. The torque mitigation module reduces torque transfer from the ICE to a driveline while the ICE is started based upon the non-driver inputs and maintains torque transfer from the ICE to the driveline while the ICE is started based upon the driver inputs. 
         [0008]    In other features, the torque mitigation module reduces torque transfer by commanding a reduced hydraulic pressure from a pump in a transmission. The reduced hydraulic pressure is a function of transmission oil temperature. The pump is powered by a charge storage module. The torque mitigation module reduces torque transfer by disengaging an electronically-controlled clutch in a transmission. 
         [0009]    In further features, the torque mitigation module reduces torque transfer by selecting a higher gear in a transmission. The non-driver inputs include low state-of-charge of a charge storage module. The non-driver inputs include a demand signal from a heating, ventilation, and air-conditioning module. The driver inputs include signals from an accelerator pedal and a brake pedal. 
         [0010]    A method comprises selectively stopping an internal combustion engine (ICE); selectively starting the ICE based upon driver inputs and non-driver inputs; reducing torque transfer from the ICE to a driveline while the ICE is started based upon the non-driver inputs; and maintaining torque transfer from the ICE to the driveline while the ICE is started based upon the driver inputs. 
         [0011]    In other features, the reducing torque transfer includes commanding a reduced hydraulic pressure from a pump in a transmission. The reduced hydraulic pressure is a function of transmission oil temperature. The reducing torque transfer includes disengaging an electronically-controlled clutch in a transmission. 
         [0012]    In further features, the reducing torque transfer includes selecting a higher gear in a transmission. The non-driver inputs include low state-of-charge of a charge storage module. The non-driver inputs include a demand signal from a heating, ventilation, and air-conditioning module. The driver inputs include signals from an accelerator pedal and a brake pedal. 
         [0013]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a functional block diagram of a hybrid powertrain of a vehicle according to the prior art; 
           [0016]      FIG. 2A  is a functional block diagram of an exemplary hybrid powertrain according to the principles of the present disclosure; 
           [0017]      FIG. 2B  is a functional block diagram of another exemplary hybrid powertrain according to the principles of the present disclosure; 
           [0018]      FIG. 3  is a graphical illustration of auxiliary oil pressure commands during a non-driver-commanded engine restart according to the principles of the present disclosure; 
           [0019]      FIG. 4A  is a flowchart depicting exemplary steps performed in control of the hybrid powertrain of  FIG. 2A  according to the principles of the present disclosure; and 
           [0020]      FIG. 4B  is a flowchart depicting exemplary steps performed in control of the hybrid powertrain of  FIG. 2B  according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0022]    As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0023]    Referring now to  FIG. 2A , a functional block diagram of an exemplary hybrid powertrain is presented. The engine  102  transfers torque to a transmission  202 , which transfers torque to the driveline  106 . The transmission  202  may include a torque converter  204 , which receives torque from the engine  102  and couples the torque to a gearset  206 . 
         [0024]    The gearset  206  transfers torque to the driveline  106 . The transmission  202  includes an oil pump  210 , which may be driven by the input to the torque converter  204 . The transmission  202  also includes an auxiliary pump  212 , which may be powered by a charge storage module  216 . The auxiliary pump  212  and the oil pump  210  provide hydraulic power to friction devices  220  of the transmission  202 . 
         [0025]    For example only, the friction devices  220  may include clutches and/or bands. The friction devices  220  control which gear ratio is selected in the gearset  206 . For example only, the gearset  206  may be a planetary gearset. The friction devices  220  may control which components of the gearset  206  are locked to each other, to a housing of the gearset  206 , and/or to the input or the output of the gearset  206 . This controls the gear ratio of the gearset  206 . 
         [0026]    The belt alternator starter (BAS)  110  converts power from the engine  102  into electrical power, which may be stored in the charge storage module  216 . The BAS  110  may also drive the crankshaft of the engine  102  in order to propel the vehicle when the engine  102  is not running. The BAS  110  and the engine  102  may be coupled via a front end accessory drive (FEAD) belt. 
         [0027]    The FEAD belt may also drive an air-conditioning (A/C) compressor  230 . A heating ventilation and air-conditioning (HVAC) control module  232  controls the A/C compressor  230 . The HVAC control module  232  may control a blower motor for blowing conditioned air into the passenger compartment of the vehicle and may measure a temperature of the engine  102  and/or engine coolant. The HVAC control module  232  may use the A/C compressor  230  to provide cooled and/or dehumidified air and may use heat from the engine  102  to provide heated air. 
         [0028]    A hybrid engine control module (ECM)  240  controls the engine  102  and the BAS  110 . When the vehicle comes to a stop, the hybrid ECM  240  may instruct the engine  102  to shut off, such as by stopping provision of fuel and spark to the engine  102 . When the driver wishes to start the vehicle from the stop, as indicated by the driver inputs  122 , the hybrid ECM  240  may instruct the engine  102  to restart. This is termed a driver-commanded engine restart. 
         [0029]    The auxiliary pump  212  is used to pump oil to provide hydraulic pressure to the transmission  202  when the engine  102  is not running. When vehicle conditions allow, such as zero vehicle speed, brake applied and zero accelerator pedal position, the hybrid ECM  240  may instruct the engine  102  to shut off. The hybrid ECM  240  may instruct the engine  102  to shut off to improve fuel economy. When the speed of the engine  102  falls below a threshold, the hybrid ECM  240  may instruct the auxiliary pump  212  to turn on and produce a predetermined boosted pressure. 
         [0030]    The boosted auxiliary pump pressure minimizes pressure dips during the transition between pressure being provided by the mechanically-driven oil pump  210  and being provided by the electrically-powered auxiliary pump  212 . After shut-off of the engine  102  has begun, the auxiliary pump  212  is directed to produce a steady-state pressure that is less than the boosted pressure. This transition may occur once the engine  102  has stopped rotating. Once the engine  102  is restarted and reaches a certain RPM, pressure from the auxiliary pump  212  may be reduced to zero and the auxiliary pump  212  may be turned off. 
         [0031]    While the engine  102  is shut off, the hybrid ECM  240  may measure state of charge of the charge storage module  216 . If the state of charge of the charge storage module  216  decreases below a threshold level, the hybrid ECM  240  may instruct the engine  102  to restart. This is an example of a non-driver-commanded engine restart. 
         [0032]    Another possible example of a non-driver-commanded engine restart is when the HVAC control module  232  requests that the engine  102  restart. For example, the HVAC control module  232  may require that more heat be generated in the engine  102  to provide heated air. The HVAC control module  232  may require that the A/C compressor  230  be powered to provide chilled and/or dehumidified air. 
         [0033]    When the engine  102  restarts, torque transmitted through the transmission  202  to the driveline  106  may be absorbed by the frame of the vehicle because the wheels of the driveline  106  are not turning. This may be experienced by the driver as a jerk or a bump. This jerk may be expected by the driver during a driver-commanded engine restart. However, a non-driver-commanded engine restart may be surprising to the driver, and may be experienced as a quality issue. 
         [0034]    To mitigate the feeling of jerk, the hybrid ECM  240  may instruct a torque mitigation module  250  to reduce the amount of torque coupled to the driveline  106  by the transmission  202 . In order to reduce torque transfer by the transmission  202 , the torque mitigation module  250  may temporarily allow the friction devices  220  to slip and/or instruct the gearset  206  to temporarily select a lower gear ratio. 
         [0035]    The torque mitigation module  250  may instruct the auxiliary pump  212  to reduce hydraulic line pressure while the engine is restarted in response to a non-driver-commanded restart. With lower line pressure, the friction devices  220  will not be fully engaged and will allow slippage of components of the gearset  206 . The lower line pressure selected may be a function of transmission oil temperature. For example, the friction devices  220  may include a multi-plate wet clutch, whose capacity is affected by oil viscosity, which is a function of temperature. The lower line pressure may also prevent a hydraulic piston from fully engaging a band. 
         [0036]    Once the engine has restarted, pressure from the oil pump  210  takes over and the auxiliary pump  212  can be powered down. Once slack in the driveline  106  is taken up by the gradual torque transfer produced by the torque mitigation module  250 , the friction devices  220  can be operated at full pressure and the gearset  206  can be returned to the desired gear. 
         [0037]    The torque mitigation module  250  may also temporarily instruct the gearset  206  to select a lower gear ratio in order to reduce torque transfer by the transmission  202 . For example, instead of a first gear speed reduction from 3.06 to 1, an overdrive ratio of 0.70 to 1 may be selected. By lowering the gear ratio, the torque mitigation module  250  reduces the torque transferred to the driveline  106 . Once the engine  102  has restarted, the gearset can return to the first gear ratio of 3.06:1. 
         [0038]    Referring now to  FIG. 2B , a functional block diagram of another exemplary hybrid powertrain is presented. A transmission  260  includes the torque converter  204 , the gearset  206 , and the friction devices  220 . The oil pump  210  and the auxiliary pump  212  provide hydraulic power to the friction devices  220 . 
         [0039]    An electronically-controlled clutch  262  selectively couples the gearset  206  to the torque converter  204 . Alternatively, the electronically-controlled clutch  262  may selectively couple the gearset  206  to the driveline  106 . The electronically-controlled clutch  262  is controlled by a torque mitigation module  270 . 
         [0040]    When the hybrid ECM  240  begins a non-driver-commanded engine restart, the torque mitigation module  270  may deactivate the electronically-controlled clutch  262 . This decouples the torque converter  204  from the driveline  106 . After a predetermined delay, during which the engine  102  restarts, the torque mitigation module  270  may reengage the electronically-controlled clutch  262 . In addition, during this predetermined delay, the torque mitigation module  270  may select a lower gear ratio in the gearset  206 . 
         [0041]    Referring now to  FIG. 3 , a graphical illustration of auxiliary oil pump pressure commands during a non-driver-commanded engine restart is illustrated. Plot  302  depicts engine speed in revolutions per minute (RPM) versus time. Using the same time scale, plot  304  depicts the pressure commanded from the auxiliary pump  212  of  FIG. 2A . In plot  302 , the engine RPM is first shown decreasing, indicating that the vehicle is coming to a stop. 
         [0042]    When vehicle conditions allow, such as zero vehicle speed, brake applied, and zero accelerator pedal position, the hybrid ECM  240  may instruct the engine to shut off (prior to time  310 ). As the engine RPM decreases past a threshold, such as at time  310 , the torque mitigation module  250  may instruct the auxiliary pump  212  to provide a boost pressure. At time  312 , after the boost pressure has been applied for a predetermined interval, the torque mitigation module  250  may instruct the auxiliary pump  212  to produce a steady-state pressure, which is lower than the boost pressure. 
         [0043]    The steady-state pressure may be maintained for the remainder of the time that the vehicle is stopped. At time  314 , the hybrid ECM initiates a non-driver-commanded restart. At approximately this time, the torque mitigation module  250  instructs the auxiliary pump  212  to produce a reduced pressure. The torque mitigation module  250  may also select a reduced gear ratio in the gearset  206 . 
         [0044]    The value of the reduced pressure may be a function of transmission oil temperature. The reduced pressure may be calibrated so that it matches or is slightly below the pressure required to maintain clutch plates of one of the friction devices  220  in contact. The clutch therefore remains in mesh, but with little ability to transmit torque. 
         [0045]    After a predetermined delay, such as one second, the engine is restarted at time  316 . The delay allows for the new reduced pressure and/or lower gear to decouple torque-transmitting components of the transmission. The gearset  206  may then be returned to the previously selected gear ratio. Because of the reduced pressure provided to the friction devices  220 , the torque produced by the engine restart will not be transmitted to the driveline  106  as a jerk. As the engine  102  increases in speed, the oil pump  210  will take over providing pressure to the friction devices  220 . Once the oil pump  210  is producing sufficient pressure, the auxiliary pump  212  may be powered off, as shown at time  318 . 
         [0046]    Referring now to  FIG. 4A , a flowchart depicts exemplary steps performed in control of the hybrid powertrain of  FIG. 2A . Control begins in step  402 , where control determines whether an engine shut-off event has been requested. If so, control transfers to step  404 ; otherwise, control remains in step  402 . An engine shut-off may be initiated when vehicle conditions allow, such as zero vehicle speed, brake applied and zero accelerator pedal position. 
         [0047]    In step  404 , as the engine RPM drops below a threshold value, the pressure of the auxiliary pump  212  is commanded to a boost pressure level. Control continues in step  406 , where the engine is turned off. For example, fuel and spark delivery to the engine may be halted. Control continues in step  408 , where pressure of the auxiliary pump  212  is reduced to a steady-state value. 
         [0048]    Control continues in step  410 , where control determines whether an engine restart is desired. If so, control transfers to step  412 ; otherwise, control remains in step  410 . In step  412 , control determines whether the restart was driver-commanded. If so, control transfers to step  414 ; otherwise, control transfers to step  416 . A driver-commanded engine restart may result from the driver releasing the brake pedal or depressing the accelerator pedal. 
         [0049]    In step  416 , pressure of the auxiliary pump  212  is reduced to a reduced pressure level. The reduced pressure level may be a function of transmission oil temperature, and may be determined from a lookup table indexed by transmission oil temperature. Control continues in optional step  418 , where the gear ratio of the gearset  206  is reduced. 
         [0050]    Control continues in step  420 , where control waits for a predetermined delay period. The predetermined delay period may be a function of internal accumulators in the transmission, oil temperature, clutch pack size, and other factors. Control then continues in step  414 . In step  414 , the engine is restarted. 
         [0051]    Control then continues in optional step  422 . In step  422 , the gear ratio of the gearset  206  is restored to the previous gear ratio. For example only, the gear ratio may be restored to first gear. Control then continues in step  424 , where the auxiliary pump is turned off once the oil pump  210  reaches a sufficient pressure. Control then returns to step  402 . 
         [0052]    Referring now to  FIG. 4B , a flowchart depicts exemplary steps performed in control of the hybrid powertrain of  FIG. 2B . Control may be similar to that of  FIG. 4A  until step  412 . In step  412 , control determines whether the engine restart is driver-commanded. If so, control transfers to step  414 ; otherwise, control transfers to step  450 . 
         [0053]    In step  450 , control disengages the electronically-controlled clutch. In this way, the torque converter  204  is decoupled from the driveline  106 . Control transfers to optional step  418 , where control may decrease the gear ratio of the gearset  206 . Control then continues in step  452 , where control waits for a predetermined delay. The predetermined delay period may be determined by the actuation time of the electronically-controlled clutch  262 . 
         [0054]    Control then continues in step  414 , where the engine is restarted. Control then continues in optional step  422 , where the original gear ratio of the gearset  206  is restored. Control continues in step  454 , where the electronically-controlled clutch  262  is re-engaged. For example only, the electronically-controlled clutch  454  may be reengaged gradually so a sudden increase in torque to the driveline  106  does not result. Control continues in step  424 , where control turns off the auxiliary pump  212  once the pressure from the oil pump  210  has reached a sufficient level. Control then returns to step  402 . 
         [0055]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.