Abstract:
A vehicle system is disclosed. The system include a engine capable of disabling and enabling at least one cylinder; a motor coupled to said engine capable of absorbing torque and providing torque; and a controller for disabling and enabling said at least one cylinder, and during at least one of disabling and enabling, varying torque of said motor to compensate for transient changes in engine output torque caused by said one of disabling and enabling.

Description:
FIELD 
   The present application relates to variable displacement engines coupled in hybrid powetrains of vehicles. 
   BACKGROUND AND SUMMARY 
   Variable displacement engine have been used where one or more cylinder is deactivated (e.g., by closing intake and exhaust valves). In this way, increased fuel economy can be obtained during engine operating conditions that do not require full cylinder operation. 
   Vehicle system with variable displacement capabilities have also been described having hybrid powertrains. For example, US 2004/0035113 describes an approach where cylinder deactivation operation can be extended by providing additional torque from an electric motor. Further, activation/deactivation transitions are described using changes in throttle position with motor assist require before, during, and after the transition. 
   The inventors herein have recognized a disadvantage with such an approach. In particular, US 2004/0035113 generally requires consistent application of torque from the motor during cylinder deactivation conditions; however, this can continually drain the battery, especially during vehicle towing conditions or during long vehicle climbs. Furthermore, the inventors herein have also recognized that the transitions according to US 2004/0035113 may also result in degraded vehicle feel since a substantially constant motor torque is used, relying on rapid throttle changes to handle the torque disturbance. Specifically, even rapid throttle changes may be inadequate to provide acceptable vibration and drive feel during the transition. 
   In one example, at least some of the above disadvantages may be overcome by a vehicle system, comprising: a engine capable of disabling and enabling at least one cylinder; a motor coupled to said engine capable of absorbing torque and providing torque; and a controller for disabling and enabling said at least one cylinder, and during at least one of disabling and enabling, varying torque of said motor to compensate for transient changes in engine output torque caused by said one of disabling and enabling. 
   In this way, it may be possible to provide improved torque control during variation in the number of cylinders carrying out combustion. Further, such transitions may be performed with less energy loss due to spark retard. Further still, such transitions may be performed to increase stored energy. Finally, such transitions may be performed based on battery status to provide improved hybrid vehicle performance. 
   Note that there may be various approaches to disabling cylinders, including disabling intake and exhaust valves, disabling fuel injection (without disabling valves), or others. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of an engine in an example hybrid powertrain; 
       FIG. 2  is a schematic diagram of an engine, intake system, and exhaust system; 
       FIGS. 3–6  are graphs showing example operation according to various example embodiments; and 
       FIGS. 7–8  are high level flowcharts showing an example embodiment of operation. 
   

   DETAILED DESCRIPTION 
   The present disclosure relates to electric vehicles and, more particularly, hybrid electric vehicles (HEVs).  FIG. 1  demonstrates just one possible configuration, specifically a parallel/series hybrid electric vehicle (split) configuration. 
   In an HEV, a planetary gear set  20  mechanically couples a carrier gear  22  to an engine  24  via a one way clutch  26 . The planetary gear set  20  also mechanically couples a sun gear  28  to a generator motor  30  and a ring (output) gear  32 . The generator motor  30  also mechanically links to a generator brake  34  and is electrically linked to a battery  36 . A traction motor  38  is mechanically coupled to the ring gear  32  of the planetary gear set  20  via a second gear set  40  and is electrically linked to the battery  36 . The ring gear  32  of the planetary gear set  20  and the traction motor  38  are mechanically coupled to drive wheels  42  via an output shaft  44 . 
   The planetary gear set  20 , splits the engine  24  output energy into a series path from the engine  24  to the generator motor  30  and a parallel path from the engine  24  to the drive wheels  42 . Engine  24  speed can be controlled by varying the split to the series path while maintaining the mechanical connection through the parallel path. The traction motor  38  augments the engine  24  power to the drive wheels  42  on the parallel path through the second gear set  40 . The traction motor  38  also provides the opportunity to use energy directly from the series path, essentially running off power created by the generator motor  30 . This reduces losses associated with converting energy into and out of chemical energy in the battery  36  and allows all engine  24  energy, minus conversion losses, to reach the drive wheels  42 . 
   A vehicle system controller (VSC)  46  controls many components in this HEV configuration by connecting to each component&#39;s controller. An engine control unit (ECU)  48  connects to the Engine  24  via a hardwire interface (see further details in  FIG. 2 ). In one example, the ECU  48  and VSC  46  can be placed in the same unit, but are actually separate controllers. Alternatively, they may be the same controller, or placed in separate units. The VSC  46  communicates with the ECU  48 , as well as a battery control unit (BCU)  45  and a transaxle management unit (TMU)  49  through a communication network such as a controller area network (CAN)  33 . The BCU  45  connects to the battery  36  via a hardware interface. The TMU  52  controls the generator motor  30  and the traction motor  38  via a hardwire interface. The control units  46 ,  48 ,  45  and  49 , and controller area network  33  can include one or more microprocessors, computers, or central processing units; one or more computer readable storage devices; one or more memory management units; and one or more input/output devices for communicating with various sensors, actuators and control circuits. 
     FIG. 2  shows an example engine and exhaust system that may be used as engine  24 . Internal combustion engine  24 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 2 , is controlled by electronic engine controller  48 . Engine  24  includes combustion chamber  29  and cylinder walls  31  with piston  35  positioned therein and connected to crankshaft  39 . Combustion chamber  29  is shown communicating with intake manifold  43  and exhaust manifold  47  via respective intake valve  52  an exhaust valve  54 . Each intake and exhaust valve is operated by an electromechanically controlled valve coil and armature assembly  53 . Armature temperature is determined by temperature sensor  51 . Valve position is determined by position sensor  50 . In an alternative example, each of valves actuators for valves  52  and  54  has a position sensor and a temperature sensor. In an alternative embodiment, cam actuated valves may be used with or without variable cam timing or variable valve lift. 
   Intake manifold  43  is also shown having fuel injector  65  coupled thereto for delivering liquid fuel in proportion to the pulse width of signal FPW from controller  48 . Fuel is delivered to fuel injector  65  by fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Alternatively, the engine may be configured such that the fuel is injected directly into the engine cylinder, which is known to those skilled in the art as direct injection. In addition, intake manifold  43  is shown communicating with optional electronic throttle  125 . 
   Distributorless ignition system  88  provides ignition spark to combustion chamber  30  via spark plug  92  in response to controller  48 . Universal Exhaust Gas Oxygen (UEGO) sensor  76  is shown coupled to exhaust manifold  47  upstream of catalytic converter  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  76 . Two-state exhaust gas oxygen sensor  98  is shown coupled to exhaust manifold  47  downstream of catalytic converter  70 . Alternatively, sensor  98  can also be a UEGO sensor. Catalytic converter temperature is measured by temperature sensor  77 , and/or estimated based on operating conditions such as engine speed, load, air temperature, engine temperature, and/or airflow, or combinations thereof. Converter  70  can include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple bricks, can be used. Converter  70  can be a three-way type catalyst in one example. 
   Controller  48  is shown in  FIG. 2  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , and read-only memory  106 , random access memory  108 ,  110  keep alive memory, and a conventional data bus. Controller  48  is shown receiving various signals from sensors coupled to engine  24 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  119  coupled to a accelerator pedal; a measurement of engine manifold pressure (MAP) from pressure sensor  122  coupled to intake manifold  44 ; a measurement (ACT) of engine air amount temperature or manifold temperature from temperature sensor  117 ; and a engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position. In one aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. 
   In an alternative embodiment, a direct injection type engine can be used where injector  66  is positioned in combustion chamber  29 , either in the cylinder head similar to spark plug  92 , or on the side of the combustion chamber. 
   In one example, engine  24  can operate in a variable displacement mode where one or more cylinder operates with deactivated valves. For example, both the intake and exhaust valves can be held closed for one or more cycles of the cylinder or engine. In the example of cam actuated valves, a deactivation mechanism may be used which is electro-hydraulically controlled. For example, deactivators may be used in lifters or in portions of an overhead cam assembly. Alternatively, cylinder deactivation may include continuing valve operation and disabling fuel injection (e.g., fuel-cut operation). 
   As noted above, any number of different engine types may be used. While the description below relates to a V-8 engine capable of deactivating four cylinders (e.g., 4 cylinder valve-deactivation mode and 8 cylinder non-valve-deactivation mode), various other engine configurations may be used. The examples described herein equally apply to an engine with 4, 6, 10, 12 or other number of cylinders. Additionally, these examples can easily be extended to systems where multiple valve deactivation modes are available (i.e. 2, 4, or 6 cylinder operation for a V8 engine). 
   One approach to managing mode transitions utilizes coordination of ignition timing retard and throttle position. When running in valve deactivation mode, the manifold pressure is increased to maintain substantially equivalent torque. Since throttle position may not immediately change airflow into the VDE engine (due to throttle response lag and manifold filling), spark retard may be used to reduce engine torque while increasing manifold pressure to the new desired set point (see  FIG. 3 ). While spark is one variable that may be used to reduce engine output of oncoming (or off going) cylinders, any combination of spark, enleanment, or injector cutout could be used to reduce torque during this transition. As can be seen from  FIG. 3 , such an approach may result in a energy loss (and thereby degrade fuel economy) during these transitions. In other words, spark retard is able to rapidly reduce torque, but results in inefficient use of the injected fuel. Note that  FIG. 3  shows spark retard/advance from a nominal value, which may be maximum torque for best torque (MBT). 
   Another approach to managing mode transitions incorporates adjustment a secondary torque source, such as a motor used in a hybrid powertrain. Various other types of secondary torque sources may be used, such as, for example, a starter-alternator or transaxle motor. In this example, the secondary torque source provides another option for managing engine torque during VDE transitions. Torque adjustments (to reduce or increase torque) can be achieved via the secondary torque source instead of, or in addition to, spark retard. In this way, numerous options are available to manage the transition in the number of active cylinders. These include:
         Absorbing torque in the secondary torque source before deactivating activated cylinders;   Absorbing torque in the secondary torque source after activating deactivated cylinders;   Providing torque in the secondary torque source after deactivating activated cylinders;   Providing torque in the secondary torque source before activating deactivated cylinders; and/or   Combinations thereof, including varying the levels of absorbing/providing torque during any one transition (or between multiple transitions), such as based on battery state of charge and/or other operating conditions.       

   By using any one or more of the above options, it can be possible to manage energy flow while providing the desired engine torque control during VDE mode transitions. 
   Referring now to  FIGS. 4–6 , various examples are shown illustrating different mode transition control strategies (4-&gt;8 and 8-&gt;4 transitions with energy recovery/negative secondary torque and energy usage/positive secondary torque). In these examples, an electric motor is given as an example secondary torque source.  FIG. 4  shows an example in which energy is absorbed through the electric motor during both the activation and deactivation of cylinders. The absorbed energy may then be available to be stored, such as in a battery. In particular,  FIG. 4  shows that the increased engine output (from increasing manifold pressure via, e.g., adjustment of throttle position) during 8-cylinder operation can be used absorbed by the motor/battery electrical system. Then, when disabling cylinders (and thus removing the increased engine output), the motor/battery system can likewise be adjusted to reduce its energy storage. The enablement transition follows a similar approach in which energy is stored via the motor/battery system during the decrease in manifold pressure. In this way, engine torque during the transition can be controlled. While not shown in this example, further adjustments to ignition timing may be used, if desired. 
   While the approach of  FIG. 4  provides efficient use of the temporary engine output increase, additional factors can determine the amount of motor torque absorption/storage, such as, for example, battery state of charge (SOC). For example, energy absorption via the motor may be advantageous during low battery state of charge conditions. Also, as noted above, ignition timing adjustments may be used, some combination of negative motor torque and spark retard may be used, or positive motor torque may be used (see below), or combinations thereof. 
   Referring now to  FIG. 5 , an example transition is shown in which energy may be provided through the electric motor during both the activation and deactivation of cylinders. In this example, the torque deficiency that may otherwise be present due to the increasing (or decreasing) of manifold pressure is made up through the motor. In other words,  FIG. 5  shows that the engine output torque deficiency during 4-cylinder operation can be compensated for by the motor/battery electrical system. In this way, engine torque during the transition can be controlled. Such an approach may be used when there is a surplus of charge (e.g., high battery SOC), or when there may be motor torque limitations (e.g. maximum negative torque limits or dynamic response limits). Also, while not shown in this example, further adjustments to ignition timing may be used, if desired. Such an approach may be particularly useful in a starter-alternator/VDE combination where the starter-alternator may have less torque capability and less energy storage capability within the battery. 
   Note that other parameters may also influence whether the motor is used to supply or absorb energy, whether ignition timing retard is used, or whether to use the motor at all, or whether to select from combinations thereof. For example, ignition timing retard may affect catalyst temperature and emissions, and thus such factors may be used to select the transition compensation strategy. For example, in  FIG. 6 , the motor both supplies and absorbs torque during the transition. The amount of supply/absorption can be adjusted (based on operating conditions such as battery state of charge, motor torque capability, desired engine torque, etc.), or can be selected to be energy neutral. An energy neutral transition can be one in which the amount of energy supplied by the motor approximately equals the amount of energy stored. Alternatively, by changing the actual VDE transition point relative to the transition of the manifold absolute pressure (MAP) from one mode to the other, it can be possible to adjust the net energy flow from full absorption, to neutral, to full torque supply. 
   Note that in the preceding cases, for illustrative purposes, the nominal secondary engine torque condition is shown to be zero. However, the approaches can be applied to other conditions, such as non-zero nominal torque (e.g., the case both the VDE and transaxle motor produce positive torque). In such a case, the motor may provide less positive torque (less energy) during a transition rather than actually recovering energy as shown in the above examples. 
   Referring now to  FIGS. 7–8 , example routines are described for controlling VDE transitions. As shown above, several different examples are described for maintaining the desired engine torque during a VDE transition (4-&gt;8 or 8-&gt;4). As described below, the approach used to maintain torque during the transition can vary depending on battery SOC, secondary motor torque capacity, secondary motor dynamic torque response, and/or other relevant system conditions. 
   The flow chart of  FIG. 7  begins with an indication from other portions of a powertrain control strategy that a VDE mode transition is desired. The first step ( 710 ) is to determine the effective constraints of the HEV motor and battery to absorb or add torque to the system. The next step ( 712 ) is to select a combination of ignition timing retard, throttle adjustment (before, after, and/or during the transition), and motor torque adjustment (absorption, supply, or combinations thereof) (before, after, and/or during the transition). For example, step  712  may determine whether energy should be stored, spent, or maintained substantially neutral. This determination can be based on conditions such as battery SOC. However, conditions such as a high battery SOC may result in the selection of still another mode (see below). In one approach, energy recovery is nominally selected, except when battery SOC is above a threshold or the system is unable to absorb the required energy. In another approach, the routine has a preset map of the type of compensation to use depending on engine speed/load/torque conditions to minimize engine torque disturbances irrespective of engine storage/release. 
   Continuing with  FIG. 7 , in step  714  the mode transition method determined in step  712  is activated and the desired torque contribution from the HEV motor and engine (valve activation/deactivation timing, ETC MAP control, and/or spark retard, if necessary) is determined. Further, additional adjustments may be added to account for various system limitations (both steady state and dynamic). 
   Referring now to  FIG. 8 , a routine is shown providing an example approach that can be used in place of step  712 . In this example, the amount of motor torque supplied/absorbed (and optionally the timing of motor torque adjustments) can be varied as the batter SOC varies. First, in step  810 , the routine determines whether battery SOC is below a minimum threshold. If so, then the routine continues to maximize the energy recovery (absorb engine torque) in  812 . Otherwise, in step  814 , the routine determines whether battery SOC is greater than a maximum threshold. If so, then the routine continues to step  816  to expend energy during the VDE transition (supply motor torque). Otherwise, in step  818  the routine determines if the battery SOC is within a desired steady state operating conditions. If so, a neutral energy VDE transition mode is selected in step  820 . Otherwise, a default response where the amount of torque supplies/absorbed is may be used to control the battery SOC to a desired value in step  822 . 
   As will be appreciated that the routines described in  FIGS. 7–8  and elsewhere herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages described herein, but are provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. 
   The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the valve operating patters, cylinder operating patterns, cylinder stroke variations, valve timing variations, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure. 
   This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the disclosure. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in diesel, natural gas, gasoline, or alternative fuel configurations could be used to advantage.