Abstract:
A method according to an exemplary aspect of the present disclosure includes, among other things, periodically adjusting powertrain operation of an electrified vehicle equipped with an internal combustion engine to progressively influence oil quality of oil of the internal combustion engine.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to an oil maintenance strategy for an electrified vehicle. Powertrain operation of the electrified vehicle may be periodically adjusted to progressively influence oil quality of engine oil. 
       BACKGROUND 
       [0002]    The need to reduce automotive fuel consumption and emissions is well known. Therefore, vehicles are being developed that reduce or completely eliminate reliance on internal combustion engines. Electrified vehicles are one type of vehicle currently being developed for this purpose. In general, electrified vehicles differ from conventional motor vehicles because they are selectively driven by one or more battery powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on the internal combustion engine to drive the vehicle. 
         [0003]    Contaminants such as oil, gas and water must be periodically removed from the oil of an internal combustion engine to achieve efficient operation and for engine protection. Electrified vehicles equipped with internal combustion engines, such as hybrid vehicles, typically include a passive oil minder feature that forces the internal combustion engine into high power operation to help evaporate the contaminants. This is referred to as a forced engine pull-up. Such forced engine operation, which only occurs after the oil quality has deteriorated below a threshold value, may be undesirable to many electrified vehicle operators. 
       SUMMARY 
       [0004]    A method according to an exemplary aspect of the present disclosure includes, among other things, periodically adjusting powertrain operation of an electrified vehicle equipped with an internal combustion engine to progressively influence oil quality of oil of the internal combustion engine. 
         [0005]    In a further non-limiting embodiment of the foregoing method, the method includes determining a measured oil quality number of the oil. 
         [0006]    In a further non-limiting embodiment of either of the foregoing methods, determining the measured oil quality number includes estimating the measured oil quality number based on at least one operating parameter of the internal combustion engine. 
         [0007]    In a further non-limiting embodiment of any of the foregoing methods, the at least one operating parameter is a number of cold starts of the internal combustion engine. 
         [0008]    In a further non-limiting embodiment of any of the foregoing methods, the method includes comparing the measured oil quality number to an oil quality target value. 
         [0009]    In a further non-limiting embodiment of any of the foregoing methods, the method includes continuing to actively monitor the measured oil quality number if the measured oil quality number exceeds the oil quality target value. 
         [0010]    In a further non-limiting embodiment of any of the foregoing methods, the method includes determining a normalized oil quality number if the measured oil quality number is below the oil quality target value. 
         [0011]    In a further non-limiting embodiment of any of the foregoing methods, the normalized oil quality number is a scaled value derived from the measured oil quality number. 
         [0012]    In a further non-limiting embodiment of any of the foregoing methods, adjusting the powertrain operation includes adjusting the powertrain operation by a calibratable value that is based on the normalized oil quality number. 
         [0013]    In a further non-limiting embodiment of any of the foregoing methods, adjusting the powertrain operation includes modifying engine speed. 
         [0014]    In a further non-limiting embodiment of any of the foregoing methods, adjusting the powertrain operation includes applying an engine pull-up threshold modifier. 
         [0015]    In a further non-limiting embodiment of any of the foregoing methods, adjusting the powertrain operation includes applying a battery charge modifier. 
         [0016]    In a further non-limiting embodiment of any of the foregoing methods, adjusting the powertrain operation includes increasing a temperature of the oil gradually over time and without requiring a forced engine pull-up. 
         [0017]    In a further non-limiting embodiment of any of the foregoing methods, adjusting the powertrain operation is performed automatically without any required input from an operator of the electrified vehicle. 
         [0018]    In a further non-limiting embodiment of any of the foregoing methods, adjusting the powertrain operation occurs without requiring any forced engine pull-ups. 
         [0019]    An electrified vehicle according to another exemplary aspect of the present disclosure includes, among other things, a set of drive wheels, a battery pack configured to selectively power the drive wheels, an engine configured to selectively power the drive wheels, and a control system configured to influence an oil quality number of oil of the engine without requiring a forced pull-up of the engine. 
         [0020]    In a further non-limiting embodiment of the foregoing electrified vehicle, the control system is configured to measure the oil quality number, normalize the oil quality number and adjust powertrain operation of the electrified vehicle based on a normalized oil quality number. 
         [0021]    In a further non-limiting embodiment of either of the foregoing electrified vehicles, at least one look-up table is stored in a memory device of the control system. 
         [0022]    In a further non-limiting embodiment of any of the foregoing electrified vehicles, the control system is configured to apply a calibratable offset to a parameter of the engine to influence the oil quality number. 
         [0023]    In a further non-limiting embodiment of any of the foregoing electrified vehicles, the control system is configured to apply a calibratable offset to a parameter of the battery pack to influence the oil quality number. 
         [0024]    The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
         [0025]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
           [0027]      FIG. 2  schematically illustrates a control strategy for actively influencing the oil quality of the oil used by an internal combustion engine of an electrified vehicle. 
           [0028]      FIG. 3  is a graphical representation of an engine oil quality measurement. 
           [0029]      FIG. 4  is a graphical representation of an engine oil quality normalization strategy. 
           [0030]      FIGS. 5A, 5B and 5C  are graphical representations of powertrain operation modifiers for increasing engine oil quality in an active, progressive manner. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    This disclosure details an oil maintenance strategy for electrified vehicles. Powertrain operation of an electrified vehicle equipped with an internal combustion engine may be periodically adjusted to actively and progressively influence the oil quality of engine oil. The oil maintenance strategy may include measuring or inferring an oil quality number, normalizing the oil quality number, and adjusting the powertrain operation based on the normalized value. These and other features are discussed in greater detail in the following paragraphs of this detailed description. 
         [0032]      FIG. 1  schematically illustrates a powertrain  10  for an electrified vehicle  12 . Although generally depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to HEV&#39;s and could extend to other electrified vehicles, including, but not limited to, plug-in hybrid electric vehicles (PHEV&#39;s) or any other electrified vehicle equipped with an internal combustion engine. 
         [0033]    In one non-limiting embodiment, the powertrain  10  is a power-split powertrain system that employs a first drive system and a second drive system. The first drive system includes a combination of an engine  14  and a generator  18  (i.e., a first electric machine). The second drive system includes at least a motor  22  (i.e., a second electric machine), the generator  18 , and a battery pack  24 . In this example, the second drive system is considered an electric drive system of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  28  of the electrified vehicle  12 . Non-power-split architectures may also benefit from the teachings of this disclosure. 
         [0034]    The engine  14 , which in one embodiment is an internal combustion engine, and the generator  18  may be connected through a power transfer unit  30 , such as a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  18 . In one non-limiting embodiment, the power transfer unit  30  is a planetary gear set that includes a ring gear  32 , a sun gear  34 , and a carrier assembly  36 . 
         [0035]    The generator  18  can be driven by the engine  14  through the power transfer unit  30  to convert kinetic energy to electrical energy. The generator  18  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  38  connected to the power transfer unit  30 . Because the generator  18  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  18 . 
         [0036]    The ring gear  32  of the power transfer unit  30  may be connected to a shaft  40 , which is connected to vehicle drive wheels  28  through a second power transfer unit  44 . The second power transfer unit  44  may include a gear set having a plurality of gears  46 . Other power transfer units may also be suitable. The gears  46  transfer torque from the engine  14  to a differential  48  to ultimately provide traction to the vehicle drive wheels  28 . The differential  48  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  28 . In one embodiment, the second power transfer unit  44  is mechanically coupled to an axle  50  through the differential  48  to distribute torque to the vehicle drive wheels  28 . 
         [0037]    The motor  22  can also be employed to drive the vehicle drive wheels  28  by outputting torque to a shaft  52  that is also connected to the second power transfer unit  44 . In one embodiment, the motor  22  and the generator  18  cooperate as part of a regenerative braking system in which both the motor  22  and the generator  18  can be employed as motors to output torque. For example, the motor  22  and the generator  18  can each output electrical power to the battery pack  24 . 
         [0038]    The battery pack  24  is an exemplary electrified vehicle battery. The battery pack  24  may be a high voltage traction battery pack that includes a plurality of battery assemblies  25  (i.e., battery arrays or groupings of battery cells) capable of outputting electrical power to operate the motor  22 , the generator  18  and/or other electrical loads of the electrified vehicle  12 . Other types of energy storage devices and/or output devices can also be used to electrically power the electrified vehicle  12 . 
         [0039]    In one non-limiting PHEV embodiment of the electrified vehicle  12 , the battery pack  24  may be recharged or partially recharged using a charger module  54  that is connectable to a charging station or power outlet powered by an external power source, such as an electrical grid, a solar panel, or the like. 
         [0040]    The powertrain  10  may additionally include a control system  56  for monitoring and/or controlling various aspects of the electrified vehicle  12 . For example, the control system  56  may communicate with the engine  14 , the battery pack  24 , the motor  22  and other vehicle components to monitor the electrified vehicle  12 , control the electrified vehicle  12 , or both. In another non-limiting embodiment, as further discussed below, the control system  56  is configured to monitor and adjust the oil quality of the oil of the engine  14 . A controller area network (CAN)  58  allows the control system  56  to communicate with the various components of the electrified vehicle  12 . 
         [0041]    The control system  56  may include electronics, software, or both to perform the necessary control functions for controlling the electrified vehicle  12 . In one non-limiting embodiment, the control system  56  is a combination vehicle system controller (VSC) and powertrain control module. Although shown as a single hardware device, the control system  56  may include multiple controllers in the form of multiple hardware devices, or multiple software controllers within one or more hardware devices. In another non-limiting embodiment, each of the engine  14  and the battery pack  24  may include individual control modules, and these control modules may communicate with one another and with the control system  56  over the CAN  58  to influence oil quality within the engine  14 . 
         [0042]    In one non-limiting embodiment, the electrified vehicle  12  includes at least two basic operating modes. The electrified vehicle  12  may operate in an Electric Vehicle (EV) mode where the motor  22  is used (generally without assistance from the engine  14 ) for vehicle propulsion, thereby depleting the battery pack  24  state of charge up to its maximum allowable discharging rate under certain driving patterns/cycles. The EV mode is an example of a charge depleting mode of operation for the electrified vehicle  12 . During EV mode, the state of charge of the battery pack  24  may increase in some circumstances, for example due to a period of regenerative braking. The engine  14  is generally OFF under a default EV mode but could be operated as necessary based on a vehicle system state or as permitted by the operator. 
         [0043]    The electrified vehicle  12  may additionally operate in a Hybrid (HEV) mode in which the engine  14  and the motor  22  are both used for vehicle propulsion. The HEV mode is an example of a charge sustaining mode of operation for the electrified vehicle  12 . During the HEV mode, the electrified vehicle  12  may reduce the motor  22  propulsion usage in order to maintain the state of charge of the battery pack  24  at a constant or approximately constant level by increasing the engine  14  propulsion. The electrified vehicle  12  may be operated in other operating modes in addition to the EV and HEV modes within the scope of this disclosure. 
         [0044]    Over time, the quality of the oil used by the engine  14  may deteriorate because of the accumulation of contaminants such as oil, gas and/or water. These contaminants must be removed from the oil to improve performance of the engine  14 . An oil maintenance strategy, which may also be referred to as an oil minder feature, is described below for progressively restoring oil quality. 
         [0045]      FIG. 2 , with continued reference to  FIG. 1 , schematically illustrates a control strategy  100  for actively and progressively influencing the oil quality of the oil used by the engine  14  of the electrified vehicle  12 . The oil quality is “progressively” influenced in that it is gradually improved over time as opposed to waiting until after the oil quality has fallen below a threshold value such that forced engine pull-ups are necessary to remove oil contaminants. The exemplary control strategy  100  may include actively monitoring an oil quality number and then adjusting powertrain operating parameters to avoid forced engine pull-ups based on the monitored oil quality number. Of course, the electrified vehicle  12  is capable of implementing and executing other control strategies within the scope of this disclosure. In one non-limiting embodiment, the control system  56  is programmed with one or more algorithms adapted to execute the control strategy  100 , or any other control strategy. The control strategy  100  may be stored as executable instructions in the non-transitory memory of the control system  56 , in one non-limiting embodiment. 
         [0046]    As shown in  FIG. 2 , the control strategy  100  begins at block  102 . At block  104 , the control strategy  100  may determine an oil quality target value Q target . The oil quality target value Q target  represents the threshold against which a measured oil quality number Q meas  is compared to determine whether the oil quality of the oil of the engine  14  has deteriorated to such a level that a corrective action is required. In one non-limiting embodiment, the oil quality target value Q target  is a quantitative value that can be expressed generically as an integer between the numbers 1 and 10. The oil quality target value Q target  may be set at any value and is a design specific parameter of the control strategy  100 . In one non-limiting embodiment, the oil quality target value Q target  is stored in the memory of the control system  56 , such as within a look-up table. In another embodiment, the oil quality target value Q target  is a variable value that could change based on ambient temperatures, vehicle speed, etc. 
         [0047]    Next, at block  106 , the measured oil quality number Q meas  associated with the oil used by the engine  14  may be measured or inferred. The measured oil quality number Q meas  can be expressed generically as an integer between 0 and 10 and represents an estimate of the amount of contaminants within the engine oil, with ‘0’ representing relatively poor oil quality and ‘10’ representing relatively good oil quality, for example. The measured oil quality number Q meas  may be estimated based on one or more operating parameters of the engine  14 . In one non-limiting embodiment, the operating parameter is the number of cold starts of the engine  14  (i.e., the number of times the engine  14  is forced into operation). The measured oil quality number Q meas  could be estimated based on a single engine parameter or a combination of engine parameters within the scope of this disclosure. 
         [0048]    An exemplary plot  60  of the measured oil quality number Q meas  is shown in  FIG. 3 . As illustrated, the measured oil quality number Q meas  (shown on the X-axis) may be a function of the number of engine cold starts (shown on the Y-axis). As also indicated by the plot  60 , the measured oil quality number Q meas  decreases as the number of cold starts increases. In other words, the measured oil quality number Q meas  is inversely related to the number of engine cold starts. 
         [0049]    Referring again to  FIG. 2 , the measured oil quality number Q meas  is next compared against the oil quality target value Q target  at block  108 . If the measured oil quality number Q meas  exceeds the oil quality target value Q target , the control strategy  100  returns to block  106  and actively continues to monitor the measured oil quality number Q meas . If, however, the measured oil quality number Q meas  is determined to be less than the oil quality target value Q target , indicating that the oil quality is below a desired threshold of quality, the control strategy  100  may proceed to block  110  by normalizing the measured oil quality number Q meas . In one non-limiting embodiment, a normalized engine oil quality number Q norm  may be derived from logic stored in a look-up table stored in the memory of the control system  56 . 
         [0050]    An exemplary plot  70  of the normalized oil quality number Q norm  is shown in  FIG. 4 . The normalized oil quality number Q norm  (shown on Y-axis) is calculated as a function of the measured oil quality number Q meas  (shown on the X-axis), and in its simplest form is a simple adjustment of the measured oil quality number Q meas  to a different scale. In one non-limiting embodiment, the normalized engine oil quality number Q norm  may be expressed as a value between 0 and 1. The normalized engine oil quality number Q norm  may level off near the point of the plot  70  at which the measured oil quality number Q meas  reaches the oil quality target value Q target . 
         [0051]    Finally, as shown in block  112  of  FIG. 2 , a corrective action may be taken, based on the normalized engine oil quality number Q norm , to influence the oil quality number of the engine oil. In one non-limiting embodiment, powertrain operation of the electrified vehicle  12  is adjusted to influence the oil quality number. The powertrain operation adjustment may be a function of the normalized engine oil quality number Q norm . Adjusting powertrain operation may include, but is not limited to, modifying engine speed, modifying engine torque, modifying spark retard, modifying how often the engine runs, etc. to increase oil/coolant temperatures, and thereby influence the oil quality number. 
         [0052]      FIGS. 5A, 5B and 5C  provide graphical illustrations of several example powertrain operation adjustments for influencing the oil quality number of engine oil. Referring first to  FIG. 5A , an exemplary plot  80 A is shown for adjusting powertrain operation using an engine pull-up threshold modifier. The plot  80 A graphs the driver demanded power threshold for engine start (shown on Y-axis) versus a vehicle parameter (e.g., vehicle speed, pedal position, etc., shown on X-axis) based on the normalized engine oil quality number Q norm . As shown by the plot  80 A, the amount of demanded power necessary for the engine  14  to be started decreases as the normalized oil quality number Q norm  decreases toward 0. 
         [0053]    In one non-limiting embodiment, the value of the engine pull-up threshold modifier may be derived from logic stored in a look-up table saved in the memory of the control system  56 . The plot  80 A is a simple graphical representation of the type of information that may be stored in the look-up table. The engine pull-up threshold modifier represents a calibratable value by which the engine  14  can be forced to run more frequently to achieve higher oil/coolant temperatures, thereby influencing the oil quality number. 
         [0054]    Plot  80 B of  FIG. 5B  illustrates an engine speed modifier for adjusting powertrain operation to influence the oil quality. The plot  80 B graphs an engine speed schedule (shown on the Y-axis) versus a vehicle parameter (e.g., vehicle speed, pedal position, etc., shown on X-axis) based on the normalized engine oil quality number Q norm . As shown by the plot  80 B, the engine speed modifier increases as the normalized oil quality number Q norm  decreases. In one non-limiting embodiment, the value of the engine speed modifier may be derived from logic stored in a look-up table saved in the memory of the control system  56 . The plot  80 B is a simple graphical representation of the type of information that may be stored in the look-up table. The engine speed modifier may be a calibratable value by which the engine speed may be increased to achieve higher oil/coolant temperatures, thereby actively influencing the oil quality number. In one non-limiting embodiment, the engine speed modifier is a calibratable offset applied to engine speed tables that are stored within the memory of the control system  56 . 
         [0055]    Finally, plot  80 C of  FIG. 5C  illustrates a battery charge modifier for adjusting powertrain operation to actively influence the oil quality. The plot  80 C graphs the battery charge rate (shown on Y-axis) versus a vehicle parameter (e.g., vehicle speed, pedal position, driver demanded power, etc., shown on X-axis) based on the normalized engine oil quality number Q norm . As shown by the plot  80 C, the battery charge modifier increases as the normalized oil quality number Q norm  decreases, thus indicating that higher engine powers can be achieved by using the engine  14  to charge the battery pack  24  (in addition to providing propulsion) when oil quality is poor. In one non-limiting embodiment, the value of the battery charge modifier may be derived from logic stored in a look-up table saved in the memory of the control system  56 . The plot  80 C is a simple graphical representation of the type of information that may be stored in the look-up table. The battery charge modifier may be a calibratable value for scheduling charging of the battery pack  24  in a manner that increases engine usage and reduces battery usage, thereby actively influencing the oil quality number. In one non-limiting embodiment, the battery charge modifier is a calibratable offset applied to battery charge tables that are stored within the memory of the control system  56 . The excess energy created by the engine  14  in this type of situation may be stored in the battery pack  24  for later use. 
         [0056]    Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
         [0057]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
         [0058]    The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.