Abstract:
A vehicular system including an electrical sub-system, an engine generating a first torque to drive a crankshaft, an electric machine applying a second torque to the crankshaft, and a mechanical accessory sub-system applying a third torque to the crankshaft. The vehicular system also includes a control sub-system having a processor and a tangible, non-transitory computer-readable medium, storing instructions that, when executed by the processor, cause the processor to (i) during idle operation of the vehicle, select a mode operation, of a plurality of system modes including a charge mode and a discharge mode, to stabilize a net torque being a sum of the first, second, and third torques, and (ii) control operation of at least one of the electric machine and the engine according to the selected mode.

Description:
TECHNICAL FIELD 
       [0001]    The technical field is generally systems and methods for controlling engine torque, including responding to loads on the engine. 
       BACKGROUND 
       [0002]    During idle operation of a vehicle, loads may be intermittently and quickly applied to the vehicle&#39;s power system and draw from power supplied by the internal combustion engine. Loads include various electrical loads, mechanical loads, and those caused by environmental conditions. For example, loads are applied when the vehicle accelerates from idle (such when the vehicle accelerates from being stopped or from a constant speed), when an air conditioning compressor coupled to the engine is enabled or when an alternator responds to an increase in electrical power usage. During idle operation, the engine alone needs a relatively constant specific amount of energy to run the engine (e.g., to compensate for heat loss and frictional loss) and maintain a constant idle speed. However, to compensate for intermittent loads applied to the engine while maintaining constant idle speed operation, different approaches have been developed. 
         [0003]    One approach is to control airflow into the engine with the throttle. However, the throttle provides a torque response that is often too slow to meet the demands of intermittently applied loads. Another approach is to control spark timing. Spark timing is measured with respect to crankshaft rotation for a spark ignited internal combustion engine, with Top Dead Center (TDC) of the piston compression stoke being considered 0 degrees. Advancing spark refers to igniting the spark device earlier in the piston rotation cycle. Retarding spark refers to igniting the spark later in the rotation cycle. 
         [0004]    Ideally the spark timing commanded during idle operation is the spark advance that provides maximum brake torque timing (referred to as MBT timing). This provides the highest energy output of the engine for the given operating conditions and the amount of fuel used. Retarding spark timing from MBT timing reduces the power output from the engine. This has the effect of reducing the efficiency of the engine and requires more airflow and fuel to provide a given torque; but, it also has the effect of creating a torque reserve that can be used to meet the demands of quickly increasing loads on the engine via spark control by advancing spark on the next combustion cycle. However, as provided, retarding spark timing results in increased fuel consumption and a concomitant reduction in fuel economy. 
         [0005]    In vehicles such as hybrid vehicles, one or more electric machine may work in conjunction with the internal combustion engine and may be used to respond to intermittent load demands. The electric machine can respond much more quickly to torque commands than throttle generated torque commands for the internal combustion engine. Consequently, the electric machine represents a torque actuator that may be used in place of spark retard generated torque reserve. Additionally, when a load is removed from the engine and less torque is required, the electric machine can quickly provide negative torque that can be used to charge an electrical energy storage device. This operation removes the necessity to even further retard spark for decreasing torque requests. 
         [0006]    The electric machine may be powered by batteries or other electric energy sources (such as supercaps or fuel cells) and also has the ability to generate and store electrical energy. When the electric machine draws electrical energy, it provides positive torque, when the electrical machine generates and stores electrical energy, it provides negative torque. 
       SUMMARY 
       [0007]    The various embodiments provide an engine control system configured to provide idle torque reserve, to reduce spark retard losses during engine idle, to improve combustion stability at idle, to significantly lower or eliminate battery voltage fluctuations on an LV bus, and problems associated therewith. 
         [0008]    In one embodiment, the disclosure refers to a vehicular system including a crankshaft and an internal combustion engine connected to the crankshaft, and generating a first, engine torque T 1  to drive the crankshaft. The vehicular system further includes an electric machine coupled to the crankshaft, and applying a second torque T 2  to the crankshaft and a mechanical accessory sub-system, including at least one mechanical accessory, coupled to the crankshaft, and applying a third, accessory torque T 3  to the crankshaft. The vehicular system also includes a control sub-system having a processor and a tangible, non-transitory computer-readable medium, storing instructions that, when executed by the processor, cause the processor to (i) during idle operation of the vehicle, select a mode operation, of a plurality of system modes including a charge mode and a discharge mode, to stabilize a net torque T 4  being a sum of the first, second, and third torques (T 4 =T 1 +T 2 +T 3 ), and (ii) control operation of at least one of the electric machine and the engine according to the selected mode, thereby limiting voltage fluctuations in the electrical sub-system (e.g., on an LV bus). 
         [0009]    In another embodiment, the disclosure refers to a method implemented by a computerized system of a vehicle having a crankshaft, an internal combustion engine connected to the crankshaft, and generating a first, engine torque T 1  to drive the crankshaft, an electric machine coupled to the crankshaft, and applying a second torque T 2  to the crankshaft, and a mechanical accessory sub-system coupled to the crankshaft, and applying a third, accessory torque T 3  to the crankshaft. The method includes, (1) during idle operation of the vehicle, selecting a mode operation, of a plurality of system modes including a charge mode and a discharge mode, to stabilize a net torque T 4  being a sum of the first, second, and third torques (T 4 =T 1 +T 2 +T 3 ) and (2) controlling operation of at least one of the electric machine and the engine according to the selected mode, thereby limiting voltage fluctuations in the electrical sub-system (e.g., fluctuations on the LV bus). 
         [0010]    In one embodiment, the disclosure relates to a tangible, non-transitory computer-readable medium storing instructions that, when executed by a computer processor, cause the processor to perform a method for controlling select operations of a vehicle having an electrical sub-system, a crankshaft, an internal combustion engine connected to the crankshaft, and generating a first, engine torque T 1  to drive the crankshaft, an electric machine coupled to the crankshaft, and applying a second torque T 2  to the crankshaft, and a mechanical accessory sub-system coupled to the crankshaft, and applying a third, accessory torque T 3  to the crankshaft. The includes (a) during idle operation of the vehicle, selecting a mode of operation, of a plurality of system modes including a charge mode and a discharge mode, to stabilize a net torque T 4  being a sum of the first, second, and third torques (T 4 =T 1 +T 2 +T 3 ), and (b) controlling operation of at least one of the electric machine and the engine according to the selected mode, thereby limiting voltage fluctuations in the electrical sub-system (e.g., fluctuations on the LV bus). 
         [0011]    The foregoing has broadly outlined some of the aspects and features of the various embodiments, which should be construed to be merely illustrative of various potential applications. Other beneficial results can be obtained by applying the disclosed information in a different manner or by combining various aspects of the disclosed embodiments. Other aspects and a more comprehensive understanding may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings, in addition to the scope defined by the claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic illustration of vehicle with a system configured to respond to loads, according to an exemplary embodiment. 
           [0013]      FIGS. 2 and 3  are graphical illustrations of torques associated with a charge mode of operation of the system of  FIG. 1 . 
           [0014]      FIGS. 4 and 5  are graphical illustrations of torques associated with a discharge mode of operation of the system of  FIG. 1 . 
           [0015]      FIG. 6  is a graphical illustration of state of charge associated with a sub-system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    As required, detailed embodiments are disclosed herein. It must be understood that the disclosed embodiments are merely exemplary of and may be embodied in various and alternative forms, and combinations thereof. As used herein, the word “exemplary” is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. In other instances, well-known components, systems, materials, or methods that are known to those having ordinary skill in the art have not been described in detail in order to avoid obscuring the present disclosure. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art. 
         [0017]    Idle Operation 
         [0018]    Exemplary embodiments of a vehicle are described in the context of idle operation. Generally, idle operation occurs when loads of the internal combustion engine are limited to auxiliary system loads and internal engine losses, such as when the vehicle is stopped. Generally, during idle operation, the driver is not requesting any operation that would result in changes of engine speed. Idle operation could also include any operating mode in which it is necessary to maintain a torque reserve via spark retard to meet the torque demand requirements for intermittent loads while maintaining smooth engine operation. 
         [0019]    Loads 
         [0020]    Systems and methods described herein are configured to respond to loads that are intermittently and quickly applied to the vehicle&#39;s power system (e.g., engine) during idle operation of the vehicle. Such loads include mechanical loads, electrical loads, loads due to environmental conditions, and the like. For example, load changes occur whenever mechanical devices directly coupled to the rotational output of the internal combustion engine change their torque demands. Examples of such mechanical devices are: air conditioning compressors, alternators, pumps, etc. Additionally, the vehicle transmission represents a load on the engine even at idle. Manual transmission loads, when the clutch is disengaged, provide additional frictional drag. Automatic transmission loads include frictional drag, but also include additional, varying loads required to drive the hydraulic pump in the transmission. 
         [0021]    Referring to  FIG. 1 , a vehicle  100  includes an internal combustion engine  110 , an electric machine  112 , other mechanical accessory systems  114 , and a control system  116 . The electric machine  112  may be an electric motor and/or generator, and in one embodiment is preferably the combined electric motor/generator. 
         [0022]    The engine  110  drives a crankshaft  120 , and the electric machine  112  and the mechanical accessory systems  114  are coupled to the crankshaft  120 . In certain embodiments, the electric machine  112  is selectively coupled to the engine  110 . For example, the electric machine can be connected via a clutch, a belt drive, or a gear drive. 
         [0023]    The engine  110  includes a throttle  122  that controls airflow to the engine  110  and a spark control (not shown in detail) that controls spark timing. The throttle  122  and the spark control are electronically controlled by the control system  116 . The engine  110  generates an engine torque T 1 , which is applied to the crankshaft  120  as a function of the amount of air that enters the engine  110  and a setting of the spark timing. The spark timing can be advanced or retarded to change engine torque T 1 . However, the control system  116  generally maintains the spark timing generally at about MBT timing to optimize fuel efficiency. 
         [0024]    The electric machine  112  is configured to apply a torque T 2  (positive, negative, or zero) to the crankshaft  120 . The electric machine  112  applies a negative torque T 2  to use power generated by the engine  110  or applies a positive torque T 2  to add to power output by the engine  110 . As described further below, during idle operation, engine torque T 1  and torque T 2  are controlled to stabilize a net torque. As such, the electric machine  112  is configured to support the idling operation of the internal combustion engine  110 . 
         [0025]    The mechanical accessory systems  114  are configured to apply an accessory torque T 3  to the crankshaft  120 . The mechanical accessory systems  114  apply no accessory torque T 3  or apply negative accessory torque T 3  to use power generated by the engine  110 . Exemplary accessory systems include transmissions (e.g., with respect to spin loss), steering systems, brake systems, heating, ventilating, and air conditioning (HVAC) systems, other mechanical systems, combinations thereof, and the like. 
         [0026]    Referring to  FIGS. 1-5 , the sum of the engine torque T 1 , the torque T 2 , and the accessory torque T 3  is referred to as a net torque T 4 . In general, the net torque T 4  is sufficient to overcome friction (e.g., friction in the engine and/or other parts of the system associated with the engine  110  in the vehicle  100 ) during idle operation and maintain a desired idle speed. 
         [0027]    Continuing with  FIG. 1 , the vehicle  100  further includes a high-voltage (HV) battery  124  connected to a low-voltage (LV) battery  128  (e.g., 12V battery) by way of a DC/DC converter  126 . The HV battery  124  is configured to power and be charged by the electric machine  112 . The HV battery  124  powers the electric machine  112  when the electric machine  112  applies a positive load (e.g., positive torque T 2 ) and is charged by the electric machine  112  when the electric machine  112  applies a negative load (e.g., negative torque T 2 ). The HV battery  124  is also configured to recharge the LV battery  128 . The DC/DC converter  126  converts the output of the HV battery  124  into an input to charge the LV battery  128 . Typically, the LV battery  128  provides electrical power for low-voltage vehicle sub-systems  129  such as lights, radio, and the like. 
         [0028]    The control system  116  is now described in further detail. The control system  116  includes a control unit  130  that is configured to control the throttle  122 , the spark timing, and the electric machine  112 . 
         [0029]    In some embodiments, the control system  116  is connected to the mechanical accessories  114 , such as in cases in which it is needed to activate an AC compressor clutch or some other actuator. 
         [0030]    It will be appreciated that the control unit  130  may in practice communicate with various other automotive systems, and that the system shown in  FIG. 1  is simplified for clarity. Furthermore, while the systems shown in the drawings are incorporated into an automotive vehicle, the system is not so limited, and may be incorporated into an aircraft, a marine vessel, or any other application in which an internal combustion engine may be used. 
         [0031]    The control unit  130  includes a processor  140 , a computer-readable medium (e.g., memory  142 ), and program modules represented by program module  144 . The program module  144  includes computer-executable instructions that are stored in the memory  142  and, when executed by the processor  140 , cause the control unit  130  to perform methods described herein. 
         [0032]    While the methods described herein may, at times, be described in a general context of computer-executable instructions, the methods of the present disclosure can also be implemented in combination with other program modules and/or as a combination of hardware and software. The term program module, or variants thereof, is used expansively herein to include routines, applications, programs, components, data structures, algorithms, and the like. Program modules can be implemented on various system configurations, including servers, network systems, single-processor or multiprocessor systems, minicomputers, mainframe computers, personal computers, hand-held computing devices, mobile devices, microprocessor-based, programmable consumer electronics, combinations thereof, and the like. 
         [0033]    Computer-readable media includes, for example, volatile media, non-volatile media, removable media, and non-removable media. The term computer-readable media and variants thereof, as used in the specification and claims, refer to storage media. In some embodiments, storage media includes volatile and/or non-volatile, removable, and/or non-removable media, such as, for example, random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), solid state memory or other memory technology, CD ROM, DVD, BLU-RAY, or other optical disk storage, magnetic tape, magnetic disk storage or other magnetic storage devices. 
         [0034]    In one contemplated embodiment, the control system  116  further includes a virtual torque sensor  150  determining net torque T 4  from the crankshaft  120 . Though a feedback loop  152  is shown connecting the virtual torque sensor  150  to the control system  116 , for providing the net torque T 4  to the control system  116 , the virtual torque sensor  150  may be a component of the control system  116 . The virtual torque sensor  150  uses various engine and driveline measurements to determine the net torque T 4 . 
         [0035]    In a primary embodiment, the control system  116  includes an RPM sensor (not shown) that is configured to measure the speed of the crankshaft  120 . 
         [0036]    In one contemplated embodiment, the control system  116  further includes a virtual state-of-charge sensor  160  determining the state of charge of the (HV) battery  124  and providing it to the control unit  130 . By virtual sensor is meant a computing module that estimates state-of-charge. The virtual sensor  160  estimates the state-of-charge using measured variables, such as battery voltage, current, and temperature and mathematical models (i.e., battery mathematical models). 
         [0037]    The program module  144  includes computer executable instructions that, when executed by the processor  140 , cause the control unit  130  to control the engine  110  and the electric machine  112  and thereby control engine torque T 1  and torque T 2 . In general, during idle operation, engine torque T 1  and torque T 2  are controlled to stabilize net torque T 4 . 
         [0038]    Referring to  FIGS. 2-5 , the control system  116  operates in one of two modes, referred to as a “charge mode” and a “discharge mode,” to stabilize the net torque T 4 .  FIGS. 2 and 3  represent the charge mode and  FIGS. 4 and 5  represent the discharge mode. The net torques T 4  shown in  FIGS. 3 and 5  are substantially the same.  FIG. 3  shows net torque T 4 , being the sum of the torques T 1 , T 2 , T 3  of  FIG. 2 , and  FIG. 5  is net torque T 4  that represents the sum of torques T 1 , T 2 , T 3  of  FIG. 4 . 
         [0039]    Referring to  FIGS. 2 and 3 , in the charge mode, the control system  116  controls the electric machine  112  to apply a negative torque T 2 , and therein charge the HV battery  124 . The control system  116  increases or decreases the torque T 2  as needed to respond to an accessory torque T 3 , with an increase being shown in  FIGS. 2 and 4 . 
         [0040]    Regarding increasing torque T 2 , in some cases the control system  116  reduces the absolute magnitude of a negative (or resistance) torque, as shown in  FIG. 2 . In other words, the numerical value of the torque is increased toward zero, though the increased torque may not actually reach zero, as the magnitude of charging torque only need be sufficiently reduced to compensate for intermittent accessory loads. 
         [0041]    Further, in the charge mode, the control system  116  operates the engine  110  at a higher engine torque T 1  to compensate for the negative torque T 2 . 
         [0042]    Referring to  FIGS. 4 and 5 , in the discharge mode, the control system  116  operates the electric machine  112  to apply second torque T 2  of about zero in order to minimize the engine torque T 1  required to obtain a target net torque T 4 . And, as provided, the control system  116  increases the torque T 2  as needed to respond to accessory torque T 3 , as shown in  FIG. 4 . 
         [0043]    The memory  142  stores parameters that are used to determine non-interrupted values for the engine torque T 1  and the torque T 2 . The parameters include a target value for net torque T 4  and a maximum value for accessory torque T 3 . The target value for net torque T 4  is determined so as to be large enough to overcome engine internal losses, such as mechanical friction, at idle. 
         [0044]    Referring to  FIG. 6 , in one embodiment, according to the computer-readable instructions of the program module  144 , the control unit  130  chooses a mode of operation as a function of, for example, the state of charge (SOC) of the HV battery  124 . As previously provided, the vehicle  100  includes a virtual state-of-charge sensor  160  providing a state-of-charge to the control unit  130 . 
         [0045]    If the state of charge is less than a minimum state of charge  602 , the control unit  130  operates in charge mode  604 . Although the minimum state of charge  602  is shown being generally at a level of zero state of charge in  FIG. 6 , the minimum state of charge  602  is not necessarily zero. If the state of charge is greater than a maximum state of charge  606 , the control unit  130  operates in discharge mode  608 . As such, the HV battery  124  remains at least partially charged, and is not charged when it is full. In other contemplated embodiments, the control unit  130 , executing the instructions, chooses the mode of operation as a function of other variables, such that the mode is most energy efficient for the vehicle  100 . 
         [0046]    In some embodiments, a minimum state of charge threshold, or lower threshold  610 , shown in  FIG. 6 , is set according to one or more factors, such as a determined minimum amount of charge needed to enable application of maximum accessory load (e.g., accessory electrical load). And in some embodiments, a maximum state of charge threshold, or upper threshold  612 , also shown in  FIG. 6 , is set according to one or more factors, such as a determined optimal state of charge. 
         [0047]    Having one or both of these two thresholds  610 ,  612 , which are shown in  FIG. 6 , places a safety band providing sufficient buffer before physical limits of the HV battery,  602 , and/or  606  are reached. In cases in which these threshold bands are used, the bands could vary, such as depending on the total battery capacity. For instance, a larger battery capacity could correlate with a smaller SOC safety band. 
         [0048]    It should be appreciated that electrical charging energy in hybrid electric vehicles (HEVs) comes entirely or at least partially from onboard fuel energy. Thus, when operating between the thresholds  610 ,  612  (shown in  FIG. 6  as “ 604  or  608 ”), and making the decision to operate in the charge or discharge mode, it would generally be effective to charge the battery, in the charge mode, while the vehicle is at idle, when the battery can be charged with sufficiently high fuel-to-electricity system conversion efficiency and otherwise discharge the battery, in the discharge mode. For example, a relatively high torque, e.g., torque T 1  in  FIG. 2 , consumes fuel at a relatively high rate m 1     —     HIGH , and a relatively low torque, e.g., T 1  in  FIG. 4 , consumes fuel at a relatively low rate m 1     —     LOW . 
         [0049]    By way of example, with T 2     —     CHG  representing an electric motor charging torque, w 2  representing an electric motor speed, eff 2  representing an electric motor energy conversion efficiency (or charging efficiency), and Q LHV  representing a lower heating value of fuel, the following relationship can be used to describe the efficiency of converting additional fuel to electricity at the electric generator output, between the relatively low rate of fuel consumption m 1     —     LOW  and the relatively high rate of fuel consumption m 1     —     HIGH : 
         [0000]        P   batt     —     in   /P   fuel =( T   2     —     CHG   ×w   2   ×eff   2 )/(( m   1     —     HIGH   −m   1     —     LOW )× Q   LHV )
 
         [0050]    The processor  140 , implementing the instructions stored in the memory  142 , compares this efficiency (P batt     —     in /P fuel ) to a pre-determined energy conversion efficiency value. The energy conversion efficiency value is pre-calculated by the processor  140  and stored in the memory  142  or, in a contemplated embodiment, external to the vehicle and stored in the memory  142  in an initial or updating data upload, such as during vehicle manufacture or maintenance. The pre-determined energy conversion efficiency value is set so that when the evaluated efficiency (P batt     —     in /P fuel ) exceeds the pre-determined efficiency during idle vehicle operation, it would be best to charge the battery. Likewise, when the evaluated efficiency (P batt     —     in /P fuel ) does not exceed the pre-determined efficiency during idle vehicle operation, it would be best to discharge the battery, and the system may identify a more efficient charging opportunity later during the driving cycle. In one embodiment, the pre-determined energy conversion efficiency value is a peak energy conversion efficiency possible for the system. By way of a single non-limiting example, in one implementation, peak energy conversion is about 35% peak engine efficiency and about 85% generator efficiency. 
         [0051]    One goal of the present technology is to rapidly counteract torque disturbances on the engine shaft while maintaining a high-energy conversion efficiency (e.g., fuel and electricity combined). Presence of the HV system and the DC/DC converter makes it possible to partially isolate the LV bus from potential voltage fluctuations occurring on the HV bus. 
         [0052]    The above-described embodiments are merely exemplary illustrations of implementations that are set forth for a clear understanding of the principles of the invention. Variations, modifications, and combinations associated with the above-described embodiments may be made without departing from the scope of the claims. All such variations, modifications, and combinations are included herein by the scope of this disclosure and the following claims.