Abstract:
A control module including a traffic determination module that determines when a vehicle is in traffic and that selectively generates a traffic signal. The control module also having a creep enable module that generates a creep enable signal based on the traffic signal. The control module further including a power control module that selectively generates an internal combustion engine (ICE) disable signal. The power control module also commands a motor generator unit to produce power based on the creep enable signal as a driver reduces brake pedal pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/105,605, filed on Oct. 1, 2008. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to electric machines, and more particularly to control systems and methods for a motor generator unit in a hybrid vehicle. 
       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]    Hybrid powertrains typically include a first torque generator, such as an internal combustion (ICE), and a second torque generator, such as an electric machine (EM). Both may provide torque to a driveline to propel a vehicle. In a full hybrid powertrain, the EM may drive the drivetrain directly, without transferring torque through a component of the ICE. In a mild hybrid powertrain, the EM may be coupled with the ICE through the accessory drive, and torque generated by the EM is transferred to the drivetrain through the ICE. An exemplary mild hybrid powertrain includes a belt alternator starter (BAS) system. In the BAS system, the EM is coupled to the ICE via a belt and pulleys. Other accessory components, such as pumps and compressors, may be powered by the belt or additional belts attached to one of the pulleys. Alternatively, the other accessory components may be driven by electric power. 
         [0005]    Referring now to  FIG. 1 , a functional block diagram of a hybrid powertrain of a vehicle is presented. The hybrid powertrain includes an internal combustion engine (ICE)  102 , a motor generator unit (MGU)  104 , an inverter  106 , a hybrid battery  108 , and an accessory power module (APM)  110 . The APM  110  provides power to a 12V battery  114  and 12V vehicle loads  116 . 
         [0006]    The inverter  106  converts power between the DC voltage of the hybrid battery  108  and the electrical power produced by the MGU  104 . The DC voltage of the hybrid battery  108  may be 42 volts in the current hybrid systems and may be 118 volts in the next generation of BAS hybrids. The APM  110  converts power from the DC voltage of the hybrid battery  108  into a standard vehicle voltage, such as 12 volts. By using the APM  110 , the 12V vehicle loads  116  do not need to be redesigned to work with the higher voltage of the hybrid battery  108 . 
         [0007]    The ICE  102  and the MGU  104  may be coupled via a belt  120  encircling pulleys  122  and  124  of the ICE  102  and the MGU  104 , respectively. The combined torque of the ICE  102  and the MGU  104  propel the vehicle. When more propulsion torque is desired than the ICE  102  is currently producing, the MGU  104  may be used as a motor to provide additional torque. 
         [0008]    At times when the ICE  102  is producing more torque than is required, the MGU  104  may function as a generator, providing power to the hybrid battery  108 . In addition, during regenerative braking, the MGU  104  may function as a generator, slowing the vehicle while providing electrical power to the hybrid battery  108 . 
       SUMMARY 
       [0009]    A control module including a traffic determination module that determines when a vehicle is in traffic and that selectively generates a traffic signal. The control module also having a creep enable module that generates a creep enable signal based on the traffic signal. The control module further includes a power control module that selectively generates an internal combustion engine (ICE) disable signal. The power control module also commands a motor generator unit to produce power based on the creep enable signal as a driver reduces brake pedal pressure. 
         [0010]    A method including the steps of determining when a vehicle is in traffic and selectively generating a traffic signal, generating a creep enable signal based on the traffic signal, and selectively generating an internal combustion engine (ICE) disable signal and commanding a motor generator unit to produce power based on the creep enable signal as a driver reduces brake pedal pressure. 
         [0011]    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 are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a functional block diagram of a hybrid powertrain of a vehicle according to the prior art; 
           [0014]      FIG. 2  is a functional block diagram of an exemplary hybrid powertrain that operates a motor generator unit according to the principles of the present disclosure; 
           [0015]      FIG. 3  is a functional block diagram of an exemplary hybrid control module according to the principles of the present disclosure; and 
           [0016]      FIG. 4  is a flow diagram depicting exemplary steps performed by the hybrid control module according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    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. 
         [0018]    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. 
         [0019]    When a driver applies the brakes and comes to a stop in a mild hybrid vehicle, the ICE normally shuts off. A motor generator unit (MGU) operates on battery power and provides power to the vehicle accessories when it recieves power and rotates at a predetermined speed. When the driver reduces the brake pedal pressure, the MGU restarts the ICE to allow the vehicle to accelerate. 
         [0020]    A hybrid control module may determine when a vehicle is in heavy traffic. For example only, the hybrid control module may determine that the vehicle is in heavy traffic based on a number of successive stop-starts within a predetermined period. When the hybrid control module determines that the vehicle is in heavy traffic, a creep mode may be enabled. When the creep mode is enabled and the driver reduces the brake pedal pressure, the vehicle may be propelled by the MGU rather than the ICE. The ICE may remain off, which may reduce emissions and increase fuel economy. If the driver presses the accelerator pedal, the ICE may be restarted by the MGU and the creep mode may be disabled. 
         [0021]    When the creep mode is enabled, the hybrid control module may command the torque converter clutch to lock, making the transmission input shaft rotate at the same speed as the crankshaft in the ICE. Locking the torque converter clutch prevents power losses that occur when the impeller and the turbine inside of the torque converter are allowed to slip. 
         [0022]    In the creep mode, the hybrid control module may also shift the transmission from a first gear to a second higher gear. This shift may be performed while the vehicle is stopped. By engaging the second higher gear, the speed of the MGU necessary to achieve a given vehicle speed may be reduced. Reducing the speed of the MGU may reduce the amount of power consumed by the MGU. To effectuate shifts without the ICE running, an auxiliary transmission oil pump may be used to provide hydraulic pressure. 
         [0023]    When the driver reduces the brake pedal pressure, the hybrid control module may command the MGU to accelerate up to a predetermined speed to propel the vehicle. The MGU may increase in speed at a predetermined rate to provide smooth acceleration. For example only, the MGU speed increase may mimic the acceleration of an ICE with an automatic transmission as the driver removes pressure from the brake pedal. 
         [0024]    Referring now to  FIG. 2 , a functional block diagram of an exemplary hybrid powertrain is presented. The hybrid powertrain includes a hybrid control module  202  that controls the MGU  104 . The hybrid control module  202  may be included in or in communication with an engine control module (ECM)  206 . The ECM  206  may control various operating parameters of the ICE  102 . Similarly, a transmission control module (TCM)  208  may control various operating parameters of an automatic transmission  210  and an auxiliary transmission pump  212 . 
         [0025]    The hybrid control module  202  controls the MGU  104  using an MGU power signal. When the MGU power signal is positive, the MGU  104  may operate as a motor, providing positive torque to the ICE  102 . The MGU  104  is powered via the inverter  106  by the hybrid battery  108 . The inverter  106  may also selectively control operation of the MGU  104 . When the MGU power signal is negative, the MGU  104  operates as a generator, converting rotational torque into electric power. The inverter  106  outputs the electric power to the hybrid battery  108 . 
         [0026]    The hybrid control module  202  may control operation of the MGU  104  based on multiple signals. For example only, the hybrid control module  202  may receive a steering wheel position signal from a steering wheel position module  204 . The hybrid control module  202  may receive a brake pedal position (BPP) signal from a brake pedal position module  214  to determine when brake pedal pressure is changing. The hybrid control module  202  may receive an accelerator pedal position (APP) signal from an accelerator pedal position module  216 . The hybrid control module  202  may also receive a state of charge signal from the hybrid battery  108 , an MGU temperature signal from the MGU  104 , and a vehicle speed signal from the ECM  206 . 
         [0027]    With reference to  FIG. 3 , a functional block diagram of an exemplary hybrid control module is presented. The hybrid control module  202  may include a power control module  302 , a timer module  304 , a traffic determination module  306 , and a creep enable module  308 . The traffic determination module  306  may selectively receive a signal from the ECM  206  when the ICE  102  is turned off. The timer module  304  may enable a timer (not shown) when the traffic determination module  306  receives the signal from the ECM  206 . 
         [0028]    If the traffic determination module  306  determines that the ICE  102  has been turned off and on a predetermined number of times within a predetermined period, a traffic signal may be selectively generated. The traffic determination module  306  may also selectively generate the traffic signal based on a percentage of time that the vehicle is stopped. When the percentage is within a predetermined range, the traffic signal may be generated, for example only. 
         [0029]    Alternatively, the traffic determination module  306  may selectively generate the traffic signal based on an adaptive cruise control signal from the ECM  206 . For example only, the adaptive cruise control signal may provide information that may be used by the traffic determination module  306  to determine the distance from other vehicles on a road. When the distance is less than a predetermined threshold for a predetermined period, the traffic signal may be selectively generated. 
         [0030]    The creep enable module  308  may evaluate additional signals to determine whether the creep mode may be enabled when the traffic signal is received. For example only, the creep enable module  308  may determine whether the steering wheel angle is less than a predetermined angle based on a signal from the steering wheel position module  204 . The creep enable module  308  may determine whether the hybrid battery  108  charge is sufficient to propel the vehicle. The creep enable module  308  may also determine whether a temperature of the MGU  104  and a temperature of the hybrid battery  108  are within a predetermined range. After the additional signals have been evaluated, the creep enable module  308  may selectively generate a creep enable signal. The creep enable signal may be selectively canceled when a speed of the vehicle exceeds a threshold speed, for example only. 
         [0031]    The power control module  302  may receive the creep enable signal and selectively disable the ICE. The power control module  302  may selectively generate an MGU power signal based on the creep enable signal when the driver begins to release the brake pedal. The power control module  302  may selectively cancel the MGU power signal when the accelerator pedal is depressed. The power control module  302  may cancel the ICE disable signal when the accelerator is depressed, allowing the ICE  102  to restart. 
         [0032]    The power control module  302  may also selectively generate a torque converter clutch (TCC) lock signal and a transmission shift signal when the creep enable signal is generated. Based on the TCC lock signal, the TCM  208  may command the TCC (not shown) to lock. Locking the TCC makes the transmission input shaft rotate at the same speed as the crankshaft (not shown) in the ICE. Locking the TCC may prevent power losses that occur when the impeller and the turbine inside of the torque converter are allowed to slip. 
         [0033]    Based on the transmission shift signal, the TCM  208  may command the transmission  212  to shift from a first gear to a second higher gear. By engaging the second higher gear, the speed of the MGU  104  necessary to achieve a given vehicle speed may be reduced. Reducing the speed of the MGU  104  may reduce the amount of power consumed by the MGU  104 . To effectuate the shift with the ICE  102  off, the TCM  208  may command the auxiliary transmission pump  212  to provide hydraulic pressure to clutches (not shown) inside of the transmission  210 . 
         [0034]    The ECM  206  may prevent the ICE  102  from starting based on the ICE disable signal from the power control module  302  to allow the MGU  104  to propel the vehicle as the driver releases the brake pedal. The ICE  102  may be prevented from starting by continuing not to deliver fuel and spark to the ICE  102 , for example only. By disabling the ICE  102  while the MGU  104  propels the vehicle, emissions may be reduced and fuel economy may be increased. 
         [0035]    With reference to  FIG. 4 , a flow diagram depicting exemplary steps performed by the hybrid control module is presented. In step  410 , control determines whether a predetermined number of stop-start events have occurred within a predetermined time. If so, continues in step  412 . If not, control remains in step  410 . In step  412 , control determines whether the brake pedal is pressed. If so, control continues to step  414 . If not, control returns to step  410 . 
         [0036]    In step  414 , control determines whether the vehicle steering wheel is centered. If not, control returns to step  410 . If so, control continues in step  416 . In step  416 , control determines if the hybrid battery charge is greater than a predetermined level. If so, control continues in step  418 . If not, control returns to step  410 . In step  418 , control determines whether the MGU temperature is within predetermined limits. If so, control continues in step  420 . If not, control returns to step  410 . 
         [0037]    In step  420 , control enables the creep mode. In step  422 , control disables the ICE. In step  424 , control determines whether the brake pedal is being released. If so, control continues in step  426 . If not, control remains in step  424 . In step  426 , control commands the transmission to engage a desired gear. In step  428 , control commands the MGU to a predetermined speed to propel the vehicle. In step  430 , control determines whether the brake pedal is being pressed. If so, control continues in step  424 . If not, control continues in step  432 . 
         [0038]    In step  432 , control determines whether the accelerator pedal is being pressed. If so, control continues in step  434 . If not, control remains in step  432 . In step  434 , control enables the ICE. In step  436 , control commands the MGU off. In step  438 , control determines whether the vehicle speed is greater than a threshold speed. If so, control continues in step  440 . If not, control remains in step  438 . In step  440 , control disables the creep mode and control ends. 
         [0039]    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.