Patent Publication Number: US-11035265-B2

Title: Methods and system for an engine lubrication system with a three-stage oil cooler bypass valve

Description:
FIELD 
     The present description relates generally to methods and systems for controlling a flow of oil through or around an oil cooler by way of a three-stage oil cooler bypass valve as a function of oil pressure from an oil pump. 
     BACKGROUND/SUMMARY 
     A vehicle engine includes a multitude of moving parts. For example, pistons inside engine cylinders move in an upward and downward fashion corresponding to different strokes of the engine. Accordingly, it is imperative that engine systems be properly lubricated to prevent undesirable noise, vibration and harshness (NVH), and for purposes of reducing engine degradation. 
     An engine lubrication system may include a sump filled with engine oil and an oil pump that may draw oil from the sump. Oil drawn from the sump may be drawn through a strainer, and may then be directed through an oil filter to engine main bearings and an oil pressure gauge. From the main bearings, the oil passes into drilled passages in a crankshaft and big-end bearings of a connecting rod. Oil fling dispersed by the rotating crankshaft may lubricate engine cylinder walls and pinto-pin bearings. Excess oil may be scraped off by scraper rings on a piston. Engine oil may also lubricate camshaft bearings and the timing chain or gears on the camshaft drive. Excess engine oil in the system then drains back to the sump. 
     In some examples, a heat exchanger (also referred to herein as an oil cooler) may be positioned between the oil pump and the oil filter. The engine oil cooler may be configured to cool or heat engine oil during engine operation. For example, an oil cooler may enable a more even temperature throughout the engine, which may reduce chances of engine degradation, may increase engine power, and may improve fuel economy. 
     However, there are certain vehicle operating conditions where it may be desirable to bypass the engine oil cooler. Towards this end, U.S. Pat. No. 9,896,979 discloses a system for controlling a temperature of oil in an engine, where the system includes a heat exchanger configured to receive oil from the engine, modify temperature of the oil, and return the modified temperature oil to the engine. The system includes a valve configured to direct the oil through the heat-exchanger during a warm-up operation of the engine such that the oil temperature is increased. The valve is configured to direct the oil to bypass the heat-exchanger during a low-load operation of the engine such that the temperature of the oil is increased. Furthermore, the valve is configured to direct the oil through the heat-exchanger during a high load operation of the engine such that the temperature of the oil is decreased. 
     However, the inventors herein have recognized potential issues with such a system. Specifically, the valve operates based on an oil pressure differential that is a function of oil viscosity, temperature, and flow rate, and thus it may be challenging to develop a spring for the valve that responds as desired under a wide range of oil viscosity, temperature and flow rates. Furthermore, the valve includes an additional actuator (e.g. wax thermostat or electro-magnetic solenoid valve) for directing oil to bypass the heat exchanger under high load conditions. 
     Thus, the inventors herein have developed systems and methods to at least partially address the above-mentioned issues. In one example, a method comprises controlling an oil pump to pump an oil for lubricating an engine at a first pressure, a second pressure or a third pressure to bias an oil cooler bypass valve to a first position, a second position or a third position, respectively, as a function of engine operating conditions, to selectively route the oil through or around an oil cooler. In this way, a controller of a vehicle may command a variable flow oil pump to pump oil at varying pressures in line with particular engine operation conditions, and the bypass valve will passively adjust to the varying pressures to control whether the oil bypasses the oil cooler or is routed through the oil cooler. Such methodology may improve fuel economy by reducing a load on the oil pump when operating conditions are such that oil cooler can be bypassed. 
     In a first example of the method, the first position is a first open position where the oil is routed around the oil cooler, the second position is a closed position where oil is prevented from being routed around the oil cooler, and the third position is a second open position where the oil is routed around the oil cooler. The first pressure may be greater than the second pressure, and the second pressure may in turn be greater than the third pressure. For example, the first pressure may be greater than 500 kPa, the second pressure may be between 250 and 400 kPa, and the third pressure may be between 100-200 kPa. 
     As another example, the method may include biasing the oil cooler bypass valve to the first position at a cold-start event of the engine where a temperature of the oil is greater than a threshold below a predetermined oil temperature and where a circuit that receives the oil is below a predetermined circuit pressure. The method may include biasing the oil cooler bypass valve to the second position to control the temperature of the oil to within the threshold of the predetermined oil temperature. The method may still further include biasing the oil cooler bypass valve to the third position when the temperature of the oil is within the threshold of the predetermined oil temperature. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an engine; 
         FIG. 2  is a schematic illustration of an engine lubrication system; 
         FIGS. 3A-3C  depict different states that an oil cooler bypass valve of the present disclosure can adopt; 
         FIG. 4  describes an example method for controlling a flow of engine oil under varying vehicle operating conditions. 
         FIG. 5  depicts a prophetic example for controlling oil pump output pressure in order to bias an oil cooler bypass valve to desired positions as a function of vehicle operating conditions. 
         FIG. 6  depicts an example method for determining whether the bypass valve of  FIGS. 3A-3C  is degraded or is functioning as expected. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for controlling an engine lubrication system that includes a passively actuatable bypass valve that regulates a flow of engine oil through or around an oil cooler. Specifically, the bypass valve may respond to changes in oil pressure output from an oil pump for which oil pressure output can be actively controlled. Accordingly,  FIG. 1  depicts an engine coupled to an oil pump, and  FIG. 2  shows an example lubrication system of the present disclosure that includes the oil pump, engine, oil cooler and passively actuatable oil cooler bypass valve.  FIGS. 3A-3C  depict how oil pressure may act on the bypass valve to bias the bypass valve to different configurations. A method for controlling oil pump output pressure as a function of vehicle operating conditions to selectively route oil around the oil cooler or through the oil cooler is shown at  FIG. 4 . A prophetic example of how the oil pump may be controlled (thereby regulating flow of the oil through or around the oil cooler) based on varying vehicle operating conditions is depicted at  FIG. 5 . An example diagnostic method for determining whether the bypass valve is degraded or is functioning as expected, is depicted at  FIG. 6 . 
       FIG. 1  is a schematic diagram showing one cylinder of multi-cylinder engine  10 , which may be included in a propulsion system of an automobile. Engine  10  may be controlled at least partially by a control system including controller  12  and by input from a vehicle operator  132  via an input device  130 . In this example, input device  130  includes an accelerator pedal and a pedal position sensor  134  for generating a proportional pedal position signal PP. Combustion chamber (i.e., cylinder)  30  of engine  10  may include combustion chamber walls  32  with piston  36  positioned therein. Piston  36  may be coupled to crankshaft  40  so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft  40  may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system. Further, a starter motor may be coupled to crankshaft  40  via a flywheel to enable a starting operation of engine  10 . 
     Combustion chamber  30  may receive intake air from intake manifold  44  via intake passage  42  and may exhaust combustion gases via exhaust passage  48 . Intake manifold  44  and exhaust passage  48  can selectively communicate with combustion chamber  30  via respective intake valve  52  and exhaust valve  54 . In some embodiments, combustion chamber  30  may include two or more intake valves and/or two or more exhaust valves. 
     In this example, intake valve  52  and exhaust valves  54  may be controlled by cam actuation via respective cam actuation systems  51  and  53 . Cam actuation systems  51  and  53  may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller  12  to vary valve operation. For example, valve operation may be varied as part of pre-ignition abatement or engine knock abatement operations. The position of intake valve  52  and exhaust valve  54  may be determined by position sensors  55  and  57 , respectively. In alternative embodiments, intake valve  52  and/or exhaust valve  54  may be controlled by electric valve actuation. For example, cylinder  30  may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. 
     In one example, cam actuation systems  51  and  53  are variable cam timing systems that include cam phasers  186  and  187  that are hydraulically actuated via oil from a variable flow oil pump  180 . Variable flow oil pump may also be referred to herein as variable displacement oil pump  180 . Under some conditions, an output flow rate of variable flow oil pump  180  may be varied to control a response time for cam phasers  186  and  187  to change a position of the cams based on operating conditions. For example, under high engine loads, the output flow rate of the variable flow oil pump  180  may be increased, so that the cam phasers  186  and  187  change position more quickly and correspondingly change a position of the cams more quickly than under low engine loads. 
     Engine  10  may further include a compression device such as a turbocharger or supercharger including at least a compressor  162  arranged along intake manifold  44 . For a turbocharger, compressor  162  may be at least partially driven by a turbine  164  (e.g. via a shaft) arranged along exhaust passage  48 . For a supercharger, compressor  162  may be at least partially driven by the engine and/or an electric machine, and may not include a turbine. Thus, the amount of compression provided to one or more cylinders of the engine via a turbocharger or supercharger may be varied by controller  12 . A boost sensor  123  may be positioned downstream of the compressor in intake manifold  44  to provide a boost pressure (Boost) signal to controller  12 . 
     Fuel injector  66  is shown coupled directly to combustion chamber  30  for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller  12  via electronic driver  68 . In this manner, fuel injector  66  provides what is known as direct injection of fuel into combustion chamber  30 . The fuel injector may be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example. Fuel may be delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber  30  may alternatively or additionally include a fuel injector arranged in intake manifold  44  in a configuration that provides what is known as port injection of fuel into the intake port upstream of combustion chamber  30 . Fuel injector  66  may be controlled to vary fuel injection in different cylinder according operating conditions. For example, controller  12  may command fuel injection to be stopped in one or more cylinders as part of pre-ignition abatement operations so that combustion chamber  30  is allowed to cool. Further, intake valve  52  and/or exhaust valve  53  may be opened in conjunction with the stoppage of fuel injection to provide intake air for additional cooling. 
     Intake passage  42  may include a throttle  62  having a throttle plate  64 . In this particular example, the position of throttle plate  64  may be varied by controller  12  via a signal provided to an electric motor or actuator included with throttle  62 , a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle  62  may be operated to vary the intake air provided to combustion chamber  30  among other engine cylinders. The position of throttle plate  64  may be provided to controller  12  by throttle position signal TP. Intake passage  42  may include a mass air flow sensor  120  and a manifold air pressure sensor  122  for providing respective signals MAF and MAP to controller  12 . 
     Ignition system  88  can provide an ignition spark to combustion chamber  30  via spark plug  92  in response to spark advance signal SA from controller  12 , under select operating modes. Controller  12  may vary signal SA based on operating conditions. For example, controller may retard signal SA in order to retard spark in response to an indication of engine knock as part of engine knock abatement operations. Though spark ignition components are shown, in some embodiments, combustion chamber  30  or one or more other combustion chambers of engine  10  may be operated in a compression ignition mode, with or without an ignition spark. 
     Variable flow oil pump  180  can be coupled to crankshaft  40  to provide rotary power to operate the variable flow oil pump  180 . In one example, the variable flow oil pump  180  includes a plurality of internal rotors (not shown) that are eccentrically mounted. At least one of the internal rotors can be controlled by controller  12  to change the position of that rotor relative to one or more other rotors to adjust an output flow rate of the variable flow oil pump  180  and thereby adjust the oil pressure. For example, the electronically controlled rotor may be coupled to a rack and pinion assembly that is adjusted via the controller  12  to change the position of the rotor. The variable flow oil pump  180  may selectively provide oil to various regions and/or components of engine  10  to provide cooling and lubrication. The output flow rate or oil pressure of the variable flow oil pump  180  can be adjusted by the controller  12  to accommodate varying operating conditions to provide varying levels of cooling and/or lubrication. Further, the oil pressure output from the variable flow oil pump  180  may be adjusted to reduce oil consumption and/or reduce energy consumption by the variable flow oil pump  180 . 
     It will be appreciated that any suitable variable flow oil pump configuration may be implemented to vary the oil pressure and/or oil output flow rate. In some embodiments, instead of being coupled to the crankshaft  40  the variable flow oil pump  180  may be coupled to a camshaft, or may be powered by a different power source, such as a motor or the like. Furthermore, in some examples, the variable flow oil pump may be a vane-type pump where pressure output is regulated via a solenoid valve, as will be discussed in further detail below. 
     Engine oil users  185  may receive oil from variable flow oil pump  180 . Discussed herein, engine oil users  185  may include any and all locations or galleries in an engine system that receive oil. As an example, oil injector  184  may be coupled downstream of an output of the variable flow oil pump  180  to selectively receive oil from the variable flow oil pump  180 . In some additional or alternative embodiments, the oil injector  184  may be omitted, or it may be incorporated into the combustion chamber walls  32  of the engine cylinder and may receive oil from galleries formed in the walls. The oil injector  184  may be operable to inject oil from the variable flow oil pump  180  onto an underside of piston  36 . The oil injected by oil injector  184  may provide cooling effects to the piston  36 . Furthermore, through reciprocation of piston  36 , oil may be drawn up into combustion chamber  30  to provide cooling effects to walls of the combustion chamber  30 . Moreover, oil injector  184  may provide oil for lubrication of an interface between piston  36  and combustion chamber  30 . 
     An oil pump valve  182  may be positioned between the output of the variable flow oil pump  180  and the oil injector  184  to control flow of oil to the oil injector  184  and other oil users (e.g. oil users  185 ). In some examples, oil pump valve  182  may be used to regulate a pressure of oil that flows to oil injector  184  and oil users  185 . As one such example, when the oil pump valve  182  is commanded fully closed, a greater output pressure from variable flow oil pump  180  may be communicated to oil injector  184  and oil users  185  as compared to when the valve is fully open. Thus, in such an example, when the valve is closed pump displacement may be increased as compared to when the valve is opened. Alternatively, in another embodiment, the output pressure from the variable flow oil pump  180  may increase under circumstances where oil pump valve  182  is in a fully open position as compared to a fully closed positon. In such an example, when the valve is commanded fully open, pump displacement may be increased as compared to when oil pump valve  182  is commanded to a fully closed position. In other words, depending on the type of pump, the oil pump valve may be differentially controlled so as to exert control over pressure of oil emanating from variable flow oil pump  180 . In some embodiments, the oil pump valve  182  may be an electronically actuatable valve (e.g. solenoid valve) that is controlled by controller  12 . As one example, the oil pump valve is a proportional solenoid valve that may vary a flow of oil from the pump by adjusting a size of a restriction that the oil passes through. While not explicitly illustrated at  FIG. 1 , it may be understood that there may be an oil cooler, an oil filter and an engine cooler bypass valve positioned between the output of the variable flow oil pump  180  and the oil injector  184 . Such components will be discussed in further detail below with regard to  FIGS. 2 and 3A-3C . 
     Oil pump valve  182  may have a default pressure regulation set point under conditions where the solenoid valve is de-energized. In other words, when the oil pump valve is de-energized, for example, oil pressure may be regulated to the default pressure regulation set point. This default pressure may be higher than a maximum oil pressure requirement of the engine at all conditions, for example. In other examples, the opposite may be true, for example when the oil pump valve is energized, oil pressure may be regulated to the default pressure regulation set point, depending on the type of pump associated with oil pump valve  182  and how pressure output is controlled for such a valve. It may be understood that the controller  12  may send an electric signal to the oil pump valve (e.g. solenoid valve) in order to control the oil pressure to a target pressure anywhere between the default high pressure regulation set point and a minimum value limited by the oil pump. The target pressure may depend on one or more of engine load and/or engine speed, oil temperature, engine temperature, coolant temperature, ambient temperature, etc. Desired oil pressure may be lower at mild engine conditions, and may be higher at higher load and speed conditions. 
     Exhaust gas sensor  126  is shown coupled to exhaust passage  48  upstream of emission control device  70 . Sensor  126  may be any suitable sensor for providing an indication of exhaust gas air-fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. Emission control device  70  is shown arranged along exhaust passage  48  downstream of exhaust gas sensor  126 . Device  70  may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof. In some embodiments, during operation of engine  10 , emission control device  70  may be periodically reset by operating at least one cylinder of the engine within a particular air-fuel ratio. 
     Controller  12  is shown in  FIG. 1  as a microcomputer, including microprocessor unit  102 , input/output ports  104 , an electronic storage medium for executable programs and calibration values shown as read only memory chip  106  in this particular example, random access memory  108 , keep alive memory  110 , and a data bus. Controller  12  may receive various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor  120 ; a profile ignition pickup signal (PIP) from Hall effect sensor  118  (or other type) coupled to crankshaft  40 ; throttle position (TP) from throttle position sensor  189 ; and absolute manifold pressure signal, MAP, from sensor  122 . Engine speed signal, RPM, may be generated by controller  12  from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Note that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor can give an indication of engine torque. Further, this sensor, along with the detected engine speed, can provide an estimate of charge (including air) inducted into the cylinder. In one example, sensor  118 , which is also used as an engine speed sensor, may produce a predetermined number of equally spaced pulses every revolution of the crankshaft. Moreover, these sensors may be used to derive an indication of engine load. 
     Furthermore, controller  12  may receive signals that may be indicative of various temperatures related to the engine  10 . For example, engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114  may be sent to controller  12 . In some embodiments, sensor  126  may provide an indication of exhaust temperature to controller  12 . Sensor  181  may provide an indication of oil temperature and/or oil viscosity to controller  12 . One or more of these sensors may provide an indication of an engine temperature that may be used by controller  12  to control operation of the oil injector  184 . Controller  12  may receive signals indicative of an ambient temperature from sensor  190 . 
     Further, controller  12  may receive an indication of oil pressure from pressure sensor  188  positioned downstream of an output of variable flow oil pump  180 . The oil pressure indication may be used by the controller  12  to control adjustment of oil pressure by varying an output flow rate of variable flow oil pump  180 . 
     Oil pressure and oil flow rates output by variable flow oil pump  180  may in some examples be functions of engine oil viscosity. Engine oil viscosity may be based on engine oil temperature and an engine oil viscosity index. The engine oil viscosity index may be different for different engine oil formulas, and may change over time as engine oil is used within an internal combustion engine. 
     In some examples, engine  10  may be included in a hybrid electric vehicle (HEV) or plug-in HEV (PHEV), with multiple sources of torque available to one or more vehicle wheels  198 . In the example shown, vehicle system  100  may include an electric machine  195 . Electric machine  195  may be a motor or a motor/generator. Crankshaft  40  of engine  10  and electric machine  195  are connected via a transmission  197  to vehicle wheels  198  when one or more clutches  194  are engaged. In the depicted example, a first clutch is provided between crankshaft  199  and electric machine  195 , and a second clutch is provided between electric machine  195  and transmission  197 . Controller  12  may send a signal to an actuator of each clutch  194  to engage or disengage the clutch, so as to connect or disconnect crankshaft  40  from electric machine  195  and the components connected thereto, and/or connect or disconnect electric machine  195  from transmission  197  and the components connected thereto. Transmission  197  may be a gearbox, a planetary gear system, or another type of transmission. The powertrain may be configured in various manners including as a parallel, a series, or a series-parallel hybrid vehicle. 
     Electric machine  195  may receive electrical power from a traction battery  196  to provide torque to vehicle wheels  198 . Electric machine  195  may also be operated as a generator to provide electrical power to charge traction battery  196 , for example during a braking operation. 
     Turning now to  FIG. 2 , an example engine lubrication system  200  is depicted. Engine lubrication system  200  includes engine  10 , controller  12 , oil pump  180 , and oil pump valve  182  as discussed above with regard to  FIG. 1  above. Engine lubrication system  200  further includes oil cooler  220 , oil filter  225 , and oil sump  240 . Also depicted is coolant system  250 . Heat energy generated by engine operation may be reduced via circulating heat transfer fluid or coolant (not shown) through the engine and other coolant conduits via a fluid or coolant pump  251 . Coolant may be a solution of a suitable organic chemical (e.g. ethylene glycol, diethylene glycol, or propylene glycol) in water. Coolant may be routed to oil cooler  220  along first coolant conduit  253 , and may exit oil cooler  220  via second coolant conduit  255 . First coolant conduit  253  may include a first temperature sensor  252  and second coolant conduit may include a second temperature sensor  254 . Thus, it may be understood that oil cooler  220  may operate as a coolant-to-oil radiator. Oil cooler  220  may transfer heat energy between the coolant and the oil, depending on relative temperatures of each of the coolant and the oil. For example, when oil temperature is greater than that of the coolant, the oil cooler may enable the coolant to absorb heat energy from the oil to thus cool the oil. Alternatively, when coolant temperature is greater than that of the oil, the oil cooler may enable the coolant to transfer heat energy to the oil, to thereby raise the temperature of the oil. Thus, the coolant pump  251  may be configured to circulate coolant through oil cooler  220  in order to modify the temperature of the oil. 
     A flow of oil via engine lubrication system  200  will now be discussed. Oil sump  240  houses oil for engine lubrication system  200 . Oil pump  180  draws oil from oil sump  240  as depicted via arrow  202 . Output of the pump and/or the oil pressure may be under control of controller  12  through oil pump valve  182 , as discussed above and as depicted via arrow  204 . Controller  12  may determine output instructions based on querying lookup table  205 , as depicted via arrow  207 . Lookup table  205  may include input parameters and output parameters. Input parameters may include but are not limited to temperature of the oil, engine speed (RPM) and engine load. The output parameter may correspond to oil pressure (e.g. kPa). Oil temperature may range from a minimum (e.g. −40° C.) to a maximum (unspecified value), engine speed may range from a minimum (e.g. idle speed) to a maximum (unspecified value), and engine load may range from a minimum (e.g. 0%) to a maximum (e.g. 100%). While specific values are not shown for oil pressure output, it may be understood that individual values may be retrieved as a function of one or more variables including but not limited to oil temperature, engine speed and engine load. 
     Output from oil pump  180  may be regulated via oil pump valve  182 , under control of controller  12 . As an example, a pulse-width modulation (PWM) signal sent to oil pump valve  182  may be controlled so as to achieve the desired output oil pressure as retrieved from lookup table  205 . 
     Output from oil pump  180  may be directed to a first conduit (represented by arrow  206 ) that fluidically couples oil pump  180  and oil cooler  220 . A second conduit (represented by arrow  210 ) may stem from the first conduit, and may include an oil cooler bypass valve  235 . Bypass valve  235  may comprise a passively actuatable valve, as will be discussed in greater detail with regard to  FIGS. 3A-3C . Under conditions where bypass valve  235  is open, oil may be directed around oil cooler  220 , as depicted via arrow  210 . Alternatively, under conditions where bypass valve  235  is closed, the oil may be directed through oil cooler  220 , as depicted via arrow  206 . In some examples, an oil temperature sensor  209  may be included in the second conduit. There may be more than one open configuration corresponding to bypass valve  235  (e.g. first open position and second open position), and a single closed configuration (e.g. closed position or first closed position), which will be elaborated below. Circumstances where oil is prevented from flowing through bypass valve  235  and around oil cooler  220 , and instead is directed to flow through oil cooler  220 , may be referred to as oil flow through a first path. Alternatively, under circumstances where oil is allowed to flow around the oil cooler, oil flow may be referred to as flowing along a second path. Thus, discussed herein the first path refers to oil flow through the oil cooler and the second path refers to oil flow around the oil cooler. In some examples, the second path may include oil both bypassing the oil cooler and some amount of oil flowing through the oil cooler. 
     Whether oil flow is via the first path or the second path, oil flow continues to flow through oil filter  225 , as indicated via arrow  212 . Arrow  212  may represent a third conduit, for example. In some examples, an oil temperature sensor  213  may be included in the conduit (e.g. third conduit) between the oil cooler and oil filter  225 . Oil filter  225  may function to clean the oil entering the engine. Once oil has passed through oil filter  225 , the oil may be delivered to engine  10  as depicted via arrow  214 . Arrow  214  may represent a fourth conduit, for example. After oil has been delivered to engine  10 , excess engine oil may then drain back to sump  240  as depicted via arrow  216 . In some examples arrow  216  may be a fifth conduit. Additionally or alternatively, arrow  216  may simply represent engine oil draining from the engine back to the sump in absence of a physical conduit for the transfer of oil back to the sump. 
     Thus, based on the above, it may be understood that the engine lubrication system  200  may include a variable displacement or variable pressure oil pump, of which an output oil flow (e.g. output pressure in kPa) may be regulated via an electro-mechanical actuator (e.g. solenoid valve) under control of the controller and as a function of a number of operating parameters including but not limited to oil temperature, engine speed (RPM) and engine load. Oil pressure output from the oil pump may passively actuate the bypass valve  235 , for directing oil to flow either through or around the oil cooler. Accordingly, the controller may control pressure of oil output from the oil pump differentially depending on whether it is desirable to route oil through the oil cooler where it may be cooled, or around the oil cooler to avoid being cooled, as a function of engine operating conditions. Examples of how the passive bypass valve is actuated are discussed in detail below with regard to  FIGS. 3A-3C . 
     Turning now to  FIGS. 3A-3C , they depict example illustrations ( 305 ,  340  and  380 ) of various positions or configurations that the bypass valve may adopt, along with an indication of where oil flow is directed depending on the various positions or configurations. 
     At  FIG. 3A , the bypass valve  235  is shown in a first open position. Bypass valve  235  includes body  310 , plunger  308 , and spring  312 . Bypass valve  235  further includes a first channel  315 , and a second channel  318 . The first channel may receive oil for biasing the position of plunger  308 , while second channel  318  may be a channel that selectively allows or prevents oil from bypassing the oil cooler. In some examples, the first channel is perpendicular to the second channel. Spring  312  biases plunger  308  in the direction of arrow  320 , whereas pressure of oil output from the oil pump (e.g. oil pump  180  at  FIG. 2 ) flowing into first channel  315  provides a counter force to spring  312  in the direction of arrow  322 . Thus, it may be understood that oil flow through the first channel  315  acts on plunger  308  to counter the bias of spring  312 . Plunger  308  includes three thick regions and two thin regions. Specifically, plunger  308  includes first thick region  326 , second thick region  328  and third thick region  330 . It may be understood that each of the first thick region  326 , second thick region  328 , and third thick region  330  may sealingly engage with inner walls  336  of bypass valve  235 . In other words, a circumference of the first, second and third thick regions may be similar to an inner circumference of bypass valve  235  defined by inner walls  336  so that the thick regions sealingly engage with the inner walls of bypass valve  235 . Said another way, the thick regions may refer to regions where the thickness of the plunger is equal to or substantially similar to (e.g. within 1-2% of) an inner circumference of the bypass valve. 
     First thin region  332  may couple first thick region  326  to second thick region  328 , and second thin region  334  may couple second thick region  328  to third thick region  330 . It may be understood that the first thin region and the second thin region may not sealingly engage with the inner walls  336  of the bypass valve. The thin regions may refer to regions where the thickness of the plunger is less than the inner circumference of the bypass valve. 
     Operation of the bypass valve as depicted at  FIG. 3A  will now be discussed. Oil flow from the oil pump may flow through first channel  315 , and the pressure of the oil may act on plunger  308  in the direction of arrow  322 . At  FIG. 3A , oil pressure is such that the oil pressure overcomes the force of spring  312 , thus aligning the second channel  318  with first thin region  332 . With second channel  318  aligned with first thin region  332 , oil may flow through the bypass valve as depicted via arrow  323 , thus bypassing the oil cooler (refer to the X along arrow  321  which indicates that flow through the oil cooler is significantly reduced (or prevented). Accordingly,  FIG. 3A  depicts bypass valve  235  in the first open position as discussed. It may be understood that bypass valve  235  is passive in the sense that the controller does not specifically command the bypass valve to a particular position, but instead indirectly controls the position that the bypass valve adopts by regulating pressure output from the oil pump. 
     Proceeding to  FIG. 3B , it depicts the same bypass valve  235  as that depicted at  FIG. 3A , and thus not all numerals at  FIG. 3B  are replicated for clarity and brevity.  FIG. 3B  depicts bypass valve  235  in the closed configuration. Specifically, oil flow from the pump is not of a high enough pressure to fully overcome the force of spring  312 . Instead, the combination of the force of spring  312  acting in the direction of arrow  320  and the force imparted against the spring by plunger  308  in the direction of arrow  322  are such that the second thick region  328  aligns with the second channel  318 , thereby completely blocking off the second channel and preventing oil flow through the bypass valve via the second channel. Accordingly, flow through the bypass valve to bypass the oil cooler is prevented, as indicated via the “X” over arrow  323 . With flow through the bypass valve blocked via the second thick region preventing oil flow through the second channel  318 , oil flows through the oil cooler as indicated via arrow  321 . 
     Proceeding to  FIG. 3C , it depicts the same bypass valve  235  as that depicted at  FIG. 3A  and  FIG. 3B , and thus not all numerals at  FIG. 3C  are replicated for clarity and brevity.  FIG. 3C  depicts bypass valve  235  in a fuel economy mode of operation, as the oil cooler is bypassed to reduce a load on the oil pump, which may thereby improve fuel economy.  FIG. 3C  depicts bypass valve  235  in the second open position. Specifically, oil flow from the pump is not of a high enough pressure (refer to arrow  322 ) to overcome the force of spring  312  (refer to arrow  320 ), and thus the second thin region  334  of plunger  308  aligns with second channel  318 . Accordingly, flow through the bypass valve to bypass the oil cooler is enabled, as illustrated by arrow  323 . With the flow through the bypass valve by way of the second channel enabled, oil flow through the oil cooler is reduced (or prevented), as indicated via the “X” along arrow  321 . 
     With regard to  FIGS. 3A-3C , it may be understood that the bypass valve (e.g. bypass valve  235  at  FIG. 2 ) may be biased to the first open position when oil pressure acting on the plunger is of a first pressure range. In one example, the first pressure range may include pressure greater than 5 bar (&gt;500 kPa). It may be further understood that the bypass valve may be biased to the closed position when oil pressure acting on the plunger is within a second pressure range. As an example, the second pressure range may include pressure of 2.5-4 bar (250-400 kPa). Furthermore, it may be understood that the bypass valve may be biased to the second open position when oil pressure acting on the plunger is within a third pressure range. As an example, the third pressure range may include pressure of 1-2 bar (100-200 kPa). Accordingly, it may be understood that the bypass valve may be in the first open position at a high oil pressure, may be in the closed position at a medium oil pressure, and may be in the second open position at a low oil pressure. As mentioned above with regard to  FIG. 1 , the oil pump valve (e.g. oil pump valve  182  at  FIG. 1 ) may have a default pressure regulation set point that is higher than the maximum oil pressure requirement of the engine at all conditions. The default pressure regulation set point may be such that the bypass valve is in the first open position at the default pressure regulation set point. 
     Thus, discussed herein, a system for a vehicle may include a variable flow oil pump that provides an oil to an engine for lubrication purposes by way of an oil circuit, and oil cooler, and an oil cooler bypass valve. The system may further include a controller with computer readable instructions stored on non-transitory memory that when executed, cause the controller to determine an operating condition of the engine, and command the variable flow oil pump to pump the oil at a determined pressure that includes one of a first pressure, a second pressure or a third pressure as a function of the operating condition of the engine. The determined pressure may passively adjust a position of the oil cooler bypass valve so as to prevent or enable the oil to bypass the oil cooler. 
     For such a system, the oil cooler bypass valve may be a three-state valve that adopts a first open position when the determined pressure is the first pressure, adopts a closed position when the determined pressure is the second pressure, and adopts a second open position when the determined pressure is the third pressure. The first pressure may be greater than the second pressure, which is in turn may be greater than the third pressure. The oil may be prevented from bypassing the oil cooler when the oil cooler bypass valve is in the closed position, but may be allowed to bypass the oil cooler when the oil cooler bypass valve is in the first open position and the second open position. 
     For such a system, the system may further comprise a coolant system that flows a coolant through the oil cooler to allow heat transfer between the oil and the coolant. 
     For such a system, the controller may store further instructions to first command the variable flow oil pump to pump the oil at the first pressure at a cold-start event of the engine until the oil circuit is pressurized to above a predetermined oil circuit pressure, then command the variable flow oil pump to pump the oil at the second pressure to raise a temperature of the oil to within a threshold of a predetermined oil temperature. Responsive to the temperature of the oil being within the threshold of the predetermined oil temperature, the instructions may include commanding the variable flow oil pump to pump the oil at the third pressure. In such a system, the controller may store further instructions to determine whether the temperature of the oil has reached a threshold oil temperature that is greater than the predetermined oil temperature while the variable flow oil pump is commanded to pump the oil at the third pressure. The controller may store further instructions to command the variable flow oil pump to pump the oil at the second pressure to lower the temperature of the oil to within the threshold of the predetermined oil temperature in response to the temperature of the oil reaching the threshold oil temperature while the variable flow oil pump is commanded to pump the oil at the third pressure. 
     Turning now to  FIG. 4 , an example method  400  for controlling oil pressure that in turn biases a flow of oil through the oil cooler or around (e.g. bypassing) the oil cooler is shown. Specifically, method  400  depicts example methodology for controlling an oil pressure by controlling the oil pump (e.g.  180 ) and/or oil pump valve (e.g. oil pump valve  182  at  FIG. 1 ), which in turn causes the oil cooler bypass valve (e.g. oil cooler bypass valve  235  at  FIG. 2 ) to adopt various configurations which either result in oil being routed through the oil cooler or bypassing the oil cooler. The controlling of the oil pressure may be based on vehicle operating conditions, as will be elaborated below. 
     Method  400  will be described with reference to the systems and components described herein and shown in  FIGS. 1-3C , though it will be appreciated that similar methods may be applied to other systems and components without departing from the scope of this disclosure. Instructions for carrying out method  400  and the rest of the methods included herein may be executed by a controller, such as controller  12  at  FIG. 1 , based on instructions stored in non-transitory memory, and in conjunction with signals received from sensors of the engine system and vehicle powertrain as discussed with regard to  FIGS. 1-2 . The controller may employ actuators such as the oil pump valve (e.g. oil pump valve  182  at  FIG. 1 ), oil pump (e.g. oil pump  180  at  FIG. 1 ) etc., to alter state of devices in the physical world according to the methods depicted below. 
     Method  400  begins at  405  and includes estimating and/or measuring vehicle operating conditions. Operating conditions may be estimated, measured, and/or inferred, and may include one or more vehicle conditions, such as vehicle speed, vehicle location, etc., various engine conditions, such as engine status, engine temperature, engine oil temperature, coolant temperature, engine load, engine speed, A/F ratio, manifold air pressure, etc., various fuel system conditions, such as fuel level, fuel type, fuel temperature, etc., as well as various ambient conditions, such as ambient temperature, humidity, barometric pressure, etc. 
     Proceeding to  410 , method  400  includes indicating whether cold-start conditions are met for starting the engine. In other words, at  410 , method  400  includes indicating whether an engine start is being requested, and whether that engine start event qualifies as a cold-start of the engine. Cold-start conditions being met may include one or more of an engine temperature below a threshold engine temperature, a coolant temperature below a threshold coolant temperature, ambient temperature below a threshold ambient temperature, exhaust catalyst temperature below a threshold exhaust catalyst temperature, etc. 
     If, at  410 , cold-start conditions are not indicated to be met, method  400  may proceed to  415 . At  415 , method  400  includes maintaining current operating conditions. For example, if the vehicle is already in operation with the engine combusting air and fuel, then the variable flow oil pump may be continued to be controlled as a function of current operating conditions. For example, if engine oil temperature is already within a threshold of a desired engine oil temperature and engine operating conditions are mild (e.g. engine load below a threshold engine load, engine speed below a threshold engine speed, etc.), then method  400  may include commanding a low output pressure from the oil pump (e.g. 100-200 kPa) to control or maintain the bypass valve (e.g. bypass valve  235  at  FIG. 2 ) in the second open position (refer to  FIG. 3C ). Commanding the low output pressure may include controlling a PWM signal of the oil pump valve (e.g. oil pump valve  182 ) to achieve the low output pressure from the oil pump, in one example. With the bypass valve in the second open position, the oil cooler (e.g. oil cooler  220  at  FIG. 2 ) may be bypassed which may reduce pressure loss through the oil cooler and thus reduce the oil pump power consumption, thereby improving fuel economy. In such an example, if engine operating conditions change, then it may be understood that the controller may command a different output pressure from the oil pump in order to control the oil cooler bypass valve to a desired state, as will be discussed in further detail below. Method  400  may then end. In some examples, it may be understood that method  400  may end in response to a vehicle-off event where the engine is deactivated. 
     Returning to  410 , in response to cold-start conditions being met, method  400  proceeds to  420 . At  420 , method  400  includes controlling output pressure of oil from the oil pump to the first pressure range. As discussed above, the first pressure range may include pressure greater than 500 kPa, and the oil pump valve (e.g. oil pump valve  182  at  FIG. 1 ) may have a default pressure regulation set point under conditions where the solenoid valve is de-energized. The default pressure may be higher than a maximum oil pressure requirement of the engine at all conditions, and may be greater than 500 kPa. Thus, controlling the oil pump valve at step  420  may include de-energizing the oil-pump valve so the oil pump outputs the default pressure which corresponds to a pressure greater than 500 kPa. With the oil pump outputting the default pressure, it may be understood that the oil cooler bypass valve (e.g. bypass valve  235  at  FIG. 2 ) may adopt the first open position (see  FIG. 3A ). Accordingly, with the bypass valve in the first position, the oil cooler may be bypassed. This may enable rapid pressurization of the engine oil circuits, which may be advantageous over methods which route oil through the oil cooler initially upon a cold-start request. It may be understood that oil circuits as discussed above may refer to any conduits, lines, etc., that receive oil. Thus, by controlling output pressure of the oil pump to the first pressure range (e.g. &gt;500 kPa), the oil pressure acting on the bypass valve serves to force the bypass valve to the first open position which thereby routes the oil around the oil cooler. Because the output pressure is high, engine oil circuits may rapidly pressurize as compared to methodology where oil is routed through the oil cooler. 
     Accordingly, proceeding to  425 , method  400  includes monitoring oil pressure in the oil circuits. For example, the oil pressure sensor (e.g. pressure sensor  188  at  FIG. 1 ) may be relied upon for monitoring oil pressure in the oil circuits. Based on the information regarding oil pressure in the oil circuits obtained at  425 , method  400  continues to  430  where method  400  judges whether a desired oil pressure in the oil pressure circuits has been reached or attained. The desired oil pressure may be a preset oil pressure, for example, stored at the controller. If, at  430 , the desired oil pressure is indicated to have been reached or exceeded, then method  400  may proceed to  435 . Alternatively, if the desired oil pressure has not been reached at  430 , then method  400  returns to  420  where the oil pump valve is continued to be controlled in a manner so as to regulate output pressure from the oil pump to the first pressure range. 
     In response to the desired oil pressure being reached or exceeded at  430 , method  400  proceeds to  435 . At  435 , method  400  includes commanding the oil pump valve to control oil pressure to the second oil pressure range. As discussed above, the second oil pressure range may include pressure of 250-400 kPa. Again, control over the output oil pressure from the oil pump may be regulated by the controller controlling an operational state of the oil pump valve. For example, the controller may control a PWM signal for current sent to the oil pump valve to control the output oil pressure to 250-400 kPa. As discussed above, with oil pressure output from the oil pump corresponding to the second oil pressure range, the force of the oil acting on the oil cooler bypass valve may be lower than when the oil pressure output is of the first pressure range, which may cause the bypass valve to adopt the closed position (see  FIG. 3B ). With the bypass valve in the closed position, oil is prevented from bypassing the oil cooler, and thus flows through the oil cooler. An advantage of routing the oil through the oil cooler is that the oil may be warmed due to the fact that engine coolant warms faster than oil. Specifically, when coolant temperature is greater than that of the oil flowing through the oil cooler, the warmer coolant may transfer heat energy to the oil, thereby raising the temperature of the oil. Raising the temperature of the oil in such a fashion during a cold-start may serve an advantage in that fuel economy may be improved as compared to a situation where it takes a longer period of time to raise the temperature of the engine oil. 
     Accordingly, with oil flowing through the oil cooler due to the output pressure from the oil pump being controlled to the second pressure range thereby causing the bypass valve to close, method  400  proceeds to  440 . At  440 , method  400  includes monitoring engine oil temperature. Engine oil temperature may be monitored post-oil cooler, for example via an engine oil temperature sensor (e.g. engine oil temperature sensor  213  at  FIG. 2 ). Proceeding to  445 , method  400  may include judging whether oil temperature is within a threshold of (e.g. within 5% or less of) a desired or predetermined engine oil temperature. The predetermined engine oil temperature may be stored at the controller, for example. If the oil temperature is not within the threshold of the predetermined engine oil temperature, then method  400  may return to step  435  where the controller may continue to exert control over the oil pump valve to control output pressure to the second pressure range such that the engine oil may be raised to within the threshold of the desired temperature. 
     In response to the oil temperature being within the threshold of the desired temperature, method  400  proceeds to  450 . At  450 , method  400  includes commanding the oil pump valve to control the output oil pressure from the oil pump to the third pressure range. As discussed above, the third pressure range may include a pressure of 100-200 kPa. When the output oil pressure from the oil pump is within the third pressure range, the oil pressure may not be high enough to overcome the force of the spring (e.g. spring  312  at  FIG. 3C ), and thus the bypass valve may adopt the second open configuration (refer to  FIG. 3C ). When in the second open configuration, the oil cooler may again be bypassed. In other words, after the engine oil has been heated to within the threshold of the desired temperature, it may be desirable to bypass the engine oil cooler to reduce the load on the pump, which may thereby improve fuel economy. It may be understood that the oil pressure output from the oil pump being controlled to the third pressure range may be in response to engine oil temperature becoming within the threshold of the desired engine temperature and further in response to an indication of mild engine operating conditions, where mild engine operating conditions may define most customer drive cycles where engine load is below a threshold engine load and engine speed is below a threshold engine speed. 
     While the output oil pressure from the oil pump is controlled to the third pressure range such that the engine oil flow bypasses the oil cooler, method  400  may proceed to  455  where engine oil temperature is continued to be monitored. Again, engine oil temperature may be monitored via an engine oil temperature sensor (e.g. engine oil temperature sensor  213  at  FIG. 2 ). Proceeding to  460 , method  400  includes indicating whether conditions are met for cooling the oil. For example, engine oil temperature above a second engine oil temperature threshold that is greater than the desired engine oil temperature, may be an indication that oil cooling is needed. Additionally or alternatively, engine load above the threshold engine load and/or engine speed above the threshold engine speed may be indicative of a need for cooling the engine oil. In other words, a transition from mild to more aggressive engine operating conditions may correspond to a situation where conditions are met for cooling the engine oil. 
     If, at  460 , conditions are met for engine oil cooling, then method  400  may return to step  435  where the output oil pressure is commanded to be within the second pressure range such that the bypass valve closes. With the bypass valve closed, engine oil may be directed through the oil cooler. In a case where engine oil is above the second engine oil temperature threshold, it may be understood that the coolant circulating through the oil cooler may be at a temperature lower than that of the oil. As such the oil cooler may enable the coolant to absorb heat energy from the oil to thereby cool the oil. With the oil pump valve commanded in a manner so as to control the output pressure of the oil pump to the second range, method  400  may continue to monitor the temperature of the circulating oil. Once the oil temperature is within the threshold of the desired temperature, the oil pump output pressure may again be controlled to the third pressure range so as to bypass the oil cooler. 
     Returning to  460 , in response to an indication that conditions are not met for oil cooling, method  400  may proceed to  465 . At  465 , method  400  includes indicating whether vehicle operation has been discontinued. Specifically, at step  465 , method  400  judges whether a vehicle-off event is occurring where the engine is being shut down. If so, then method  400  may end. Alternatively, method  400  may return to  450  where oil pump output pressure is continued to be controlled to the third pressure range. 
     Thus, discussed herein, a method may include controlling an oil pump to pump an oil for lubricating an engine at a first pressure, a second pressure or a third pressure to bias an oil cooler bypass valve to a first position, a second position or a third position, respectively, as a function of engine operating conditions, to selectively route the oil through or around an oil cooler. 
     For such a method, the first position may be a first open position where the oil is routed around the oil cooler, where the second position may be a closed position where oil is prevented from being routed around the oil cooler, and where the third position may be a second open position where the oil is routed around the oil cooler. 
     For such a method, the first pressure may be greater than the second pressure, which may in turn be greater than the third pressure. 
     For such a method, the oil cooler bypass valve may passively respond to pressure of the oil in order to adopt the first position, the second position and/or the third position. 
     For such a method, the oil pump may be a variable displacement oil pump. 
     For such a method, controlling the oil pump may include adjusting a position of a solenoid valve of the oil pump based on a command from a controller. In such an example, the oil cooler bypass valve may not be communicably coupled to the controller. 
     For such a method, the first pressure may be greater than 500 kPa, the second pressure may be between 250-400 kPa, and the third pressure may be between 100-200 kPa. 
     For such a method, the oil cooler may be a coolant-to-oil heat exchanger where heat energy is transferred between a coolant circulating through the oil cooler and the oil. 
     For such a method, the method may further comprise biasing the oil cooler bypass valve to the first position at a cold-start event of the engine where a temperature of the oil is more than a threshold below a predetermined oil temperature and where a circuit that receives the oil is below a predetermined circuit pressure. The method may further include biasing the oil cooler bypass valve to the second position to control the temperature of the oil to within the threshold of the predetermined oil temperature. The method may still further include biasing the oil cooler bypass valve to the third position when the temperature of the oil is within the threshold of the predetermined oil temperature. 
     Another example of a method may include controlling whether an oil used for lubricating an engine is routed through or around an oil cooler solely by adjusting a pressure of the oil emanating from an oil pump to bias an oil cooler bypass valve to a first open position under a first operating condition, to a closed position under a second operating condition, and a second open position under a third operating condition. 
     For such a method, the first operating condition may include a cold-start of the engine where pressure of an oil circuit that receives the oil is below a threshold circuit pressure and a temperature of the oil is not within a threshold of a predetermined oil temperature. The second operating condition may include the oil circuit pressurized to above the threshold circuit pressure and where the temperature of the oil is not within the threshold of the predetermined temperature. The third operating condition may include the oil circuit pressurized to above the threshold pressure and the temperature of the oil within the threshold of the predetermined temperature. 
     For such a method, biasing the oil cooler bypass valve to the first position may allow the oil to bypass the oil cooler. Further, biasing the oil cooler bypass valve to the closed position may prevent the oil from bypassing the oil cooler. Biasing the oil cooler bypass valve to the second open position may additionally allow the oil to bypass the oil cooler. 
     For such a method, the oil cooler may additionally receive a coolant from a coolant system. Heat may be transferred from the oil to the coolant or vice versa with the oil cooler bypass valve closed under the second operating condition. 
     For such a method, the oil pump may be a variable flow oil pump. The pressure of the oil emanating from the oil pump may be adjusted based on a command from a controller to a valve associated with the oil pump. 
     Turning now to  FIG. 5 , an example timeline  500  depicts a prophetic example of how oil pump output pressure may be controlled in order to bias the oil cooler bypass valve to desired positions depending on vehicle operating conditions. Timeline  500  includes plot  505 , indicating whether cold-start conditions are indicated to be met (yes or no), over time. Timeline  500  further includes plot  510 , indicating oil pump output pressure, over time. As discussed above with regard to  FIGS. 3A-4 , oil pump output pressure may be controlled to a first pressure range ( 1 ), a second pressure range ( 2 ), a third pressure range ( 3 ), or the pump may be off. Timeline  500  further includes plot  515 , indicating a position of the oil cooler bypass valve (e.g. bypass valve  235  at  FIG. 2 ), over time. As discussed above with regard to  FIGS. 3A-4 , the oil cooler bypass valve may be in a first open position (refer to  FIG. 3A ), a closed position (refer to  FIG. 3B ), or a second open position (refer to  FIG. 3C ). Timeline  500  further includes plot  520 , indicating whether a circuit or circuits (e.g. conduits, oil injector(s), lines, etc.) that receive oil from the oil pump (e.g. oil pump  180  at  FIG. 1 ) are pressurized to a desired level (yes or no), over time. Timeline  500  further includes plot  525 , indicating a temperature of the oil, over time. The engine oil may increase (+) or decrease (−) in temperature over time. 
     At time t0 it may be understood that the engine is off and the vehicle is stationary. There is no request for an engine startup, and thus cold-start conditions are not yet met (plot  505 ). With the vehicle off, there is no oil pump output pressure (plot  510 ). The bypass valve (plot  515 ) is in the second open position (refer to  FIG. 3C ) because there is no oil pressure to overcome the force of the spring (e.g. spring  312  at  FIG. 3C ) associated with the bypass valve. With the vehicle off, oil circuits that receive oil from the oil pump are not pressurized (plot  520 ), and oil temperature is low (plot  525 ). 
     At time t1, cold-start conditions are indicated to be met. For example, at time t1 there is a request for an engine startup (e.g. remote start request, driver turning a key to initiate engine operation, driver pressing a button on the vehicle dash to initiate engine operation, etc.), and it is indicated that the request is a cold-start request. As discussed above at step  410  of method  400 , cold-start conditions may be met when one or more of engine temperature is below a threshold engine temperature, temperature of coolant is below a threshold coolant temperature, ambient temperature is below a threshold ambient temperature, exhaust catalyst temperature is below a threshold exhaust catalyst temperature, etc. 
     With an engine cold-start indicated, at time t1 the oil pump (e.g. oil pump  180  at  FIG. 1 ) is controlled in a manner so as to produce an output oil pressure within the first pressure range (e.g. &gt;500 kPa). As discussed above, oil pump output pressure may be regulated via a solenoid valve (e.g. oil pump valve  182  at  FIGS. 1-2 ) under control of the controller (e.g. controller  12  at  FIG. 1 ). The oil pump valve may have a default pressure regulation set point under conditions where the solenoid valve is de-energized, and the default pressure may be greater than a maximum oil pressure requirement of the engine at all conditions, and thus the default pressure may be greater than 500 kPa. Thus, at time t1, controlling the oil pump output pressure to the first pressure range may include de-energizing or maintaining de-energized the oil pump valve. Accordingly, between time t1 and t2 oil pump output pressure rises to the first pressure range. As the oil pump output is controlled to the first pressure range, the bypass valve passively adopts the first open position (refer to  FIG. 3A ) at time t2, whereby the oil cooler is bypassed. 
     As discussed above, the high pressure output (e.g. pressure output in the first pressure range) of the oil pump may serve to pressurize the oil circuit(s). By regulating the bypass valve to the first open position, the restrictive oil cooler may be bypassed, which may enable rapid pressurization of the oil circuits in a manner faster than if the oil were directing through the oil cooler. For determining whether the oil circuits are pressurized to a desired level, an oil pressure sensor (e.g. oil pressure sensor  188  at  FIG. 1 ) may be relied upon for communicating oil pressure in the oil circuits to the controller. At time t3, it is indicated that the oil circuits are sufficiently pressurized (plot  520 ). In response to the indication that the oil circuits are sufficiently pressurized, the oil pump output pressure is controlled to the second pressure range (e.g. 250-400 kPa) (plot  510 ) between time t3 and t4. With the oil pump output pressure controlled to the second pressure range, the bypass valve passively responds to the change in oil pump output pressure, to adopt the closed position (refer to  FIG. 3B ) at time t4. As discussed above, the closed position of the bypass valve thus directs the oil emanating from the oil pump through the oil cooler. It may be beneficial to direct the oil through the oil cooler at time t4 due to a temperature of the coolant (not shown) being greater than a temperature of the oil (plot  525 ), because coolant increases in temperature at a cold-start faster than engine oil. Thus, transfer of heat from the coolant to the engine oil that takes place in the oil cooler may increase temperature of the oil faster than if the oil cooler were continued to be bypassed once the oil circuits are pressurized. 
     Thus, prior to time t4 it can be seen at timeline  500  that oil temperature rises at a slower rate than between time t4 and t5. In other words, the rate of increase in oil temperature is greater between time t4 and t5 than prior to time t4, due to the oil being directed through the oil cooler between time t4 and t5. 
     At time t5, temperature of the oil becomes within a threshold (line  526 ) of the desired or predetermined engine oil temperature (represented by line  527 ). Accordingly, cold-start conditions are no longer indicated (plot  505 ), and the oil pump is controlled to output oil pressure within the third pressure range (e.g. 100-200 kPa). While not explicitly illustrated, it may be understood that the operating conditions are mild (e.g. engine speed below the engine speed threshold and engine load below the engine load threshold), thus it is desirable to control the oil pump to output oil pressure to within the third pressure range. Between time t5 and t6, oil pump output pressure is controlled (via controlling the oil pump valve) to within the third pressure range (plot  510 ). As the pressure decreases from the second pressure range to the third pressure range, the oil cooler bypass valve (plot  515 ) passively adopts the second open position (refer to  FIG. 3C ) at time t6. Thus, with the bypass valve in the second open position the oil cooler is once again bypassed. Bypassing the oil cooler under mild engine operating conditions may serve to reduce oil pressure losses compared to if the oil flow was continued to be directed through the oil cooler. Reducing the pressure loss through the oil cooler may reduce oil pump power consumption, thereby improving fuel economy. 
     Some amount of time passes between time t6 and t7. At time t7, engine oil temperature rises to above the second oil temperature threshold (line  528 ), and thus there is a request for engine oil cooling. Accordingly, between time t8 and t9, the oil pump output pressure is controlled back to the second pressure range (plot  510 ). Increasing the output pressure from the oil pump results in the bypass valve passively adopting the closed position (plot  515 ) at time t9. With the bypass valve in the closed position, oil emanating from the oil pump is once again directed through the oil cooler. While not explicitly illustrated, it may be understood that at time t9 oil temperature is greater than the temperature of the coolant. Thus, transfer of heat from the oil to the coolant occurs between time t9 and t10, thereby cooling the oil. At time t10, engine oil temperature is once again within the threshold (refer to line  526 ) of the desired or predetermined oil temperature (line  527 ). With the engine oil temperature having sufficiently cooled at time t10, oil pump output pressure is once again controlled to the third pressure range (plot  510 ) between time t10 and t11, and at t11 the bypass valve passively adopts the second open position (plot  515 ). After time t11 oil temperature remains within the threshold of the desired oil temperature, oil pump output pressure is continued to be controlled to the third pressure range, and the bypass valve is maintained in the second open position where the oil cooler is bypassed to improve fuel economy. 
     Turning now to  FIG. 6 , a high-level example method  600  is shown for determining whether the oil cooler bypass valve (e.g. bypass valve  235  at  FIG. 2 ) is degraded or is functioning as desired or expected. Specifically, method  600  may be used under conditions where switching from bypassing the oil cooler (e.g. oil cooler  220 ) to routing oil through the oil cooler is expected to result in a change in oil temperature due to a difference in temperature between the engine oil and the coolant. If the expected change is not observed, then the bypass valve may be degraded. 
     Method  600  will be described with reference to the systems and components described herein and shown in  FIGS. 1-3C , though it will be appreciated that similar methods may be applied to other systems and components without departing from the scope of this disclosure. Instructions for carrying out method  600  and the rest of the methods included herein may be executed by a controller, such as controller  12  at  FIG. 1 , based on instructions stored in non-transitory memory, and in conjunction with signals received from sensors of the engine system and vehicle powertrain as discussed with regard to  FIGS. 1-2 . The controller may employ actuators such as the oil pump valve (e.g. oil pump valve  182  at  FIG. 1 ), etc., to alter state of devices in the physical world according to the methods depicted below. 
     Method  600  begins at  605  and includes indicating whether conditions are met for determining potential bypass valve degradation. Conditions may be met based on one or more of the following examples. In one example, conditions may be met when there is a request to switch from bypassing oil flow through the oil cooler to directing the oil flow through the oil cooler. Conditions may be met when a temperature of engine oil is greater than that of coolant by a predetermined threshold difference, in an example. In another example, conditions may be met when temperature of engine oil is less than that of coolant by another predetermined threshold difference. Conditions may be met under circumstances where there is not any inferred degradation of the oil cooler, coolant system, engine oil pump, oil pump valve, engine oil temperature sensors, coolant temperature sensors, etc. 
     If, at  605 , conditions are not indicated to be met for determining bypass valve degradation, then method  600  may proceed to  610  where current operating conditions may be maintained. For example, if the oil cooler is bypassed, then such conditions may be maintained in an absence of a request to route oil through the oil cooler. In another example, if the oil cooler is not bypassed, then such conditions may be maintained in an absence of a request to bypass the oil cooler. In some examples where the difference between coolant temperature and engine temperature is not greater than the predetermined threshold difference, but where a switch from bypassing the oil cooler to routing oil through the oil cooler (or vice versa) is requested, then the switch may be carried out as discussed above but the degradation test may not be conducted due to potential signal-to-noise issues. Method  600  may then end. 
     Alternatively, in response to conditions being met for determining bypass valve degradation, method  600  proceeds to  615 . At  615 , method  600  includes conducting the switch from bypassing the oil cooler to routing oil through the oil cooler. In one example, conducting the switch may include controlling the output pressure of the oil pump from the first pressure range to the second pressure range. As another example, conducting the switch may include controlling the output pressure of the oil pump from the third pressure range to the second pressure range. Said another way, conducting the switch may include controlling the oil pump in a manner to bias the bypass valve from the first open position (refer to  FIG. 3A ) to the closed position (refer to  FIG. 3B ), or controlling the oil pump in a manner to bias the bypass valve from the second open position (refer to  FIG. 3C ) to the closed position (refer to  FIG. 3B ). It may be understood that prior to making the switch both engine oil temperature and coolant temperature may be retrieved from respective sensors and stored at the controller. 
     In response to the switch being conducted, method  600  proceeds to  620 . At  620 , method  600  includes monitoring engine oil temperature. While not explicitly illustrated, it may be understood that coolant temperature may additionally or alternatively be monitored. 
     Proceeding to  625 , method  600  includes determining whether a change in the engine oil temperature (e.g. difference in the temperature of oil prior to the switch and after the switch) is within a threshold (e.g. within 5% of, within 10% of, within 20% of, within 50% of etc.) of an expected engine oil temperature change. For example, if engine oil temperature was greater than the coolant temperature prior to the switch, then it may be expected that engine oil temperature may cool in response to the switch. Alternatively, if engine oil temperature was less than the coolant temperature prior to the switch, then it may be expected that engine oil temperature may rise in response to the switch. The expected difference may be determined via the controller, and may be a function of variables including but not limited to ambient temperature, coolant flow rate, engine oil flow rate, engine oil volume, etc. 
     If, at  625 , it is determined that the change in engine oil temperature is not within the threshold of the expected engine oil temperature change, then method  600  proceeds to  630  where bypass valve degradation is indicated. For example, because the change in oil temperature was not within the threshold of the expected temperature change, the bypass valve may not be functioning as desired. Specifically, the bypass valve may be stuck in any one of the first open position, the second open position, or closed position such that when the switch is commanded the bypass valve does not respond as expected and, as a result, engine oil temperature does not undergo the expected change in temperature. 
     Proceeding to  635 , method  600  includes updating vehicle operating conditions. Updating vehicle operating conditions may include storing the results of the test at the controller, setting diagnostic trouble code (DTC) and illuminating a malfunction indicator light (MIL) at the vehicle dash to alert the vehicle operator of a request to have the vehicle serviced. Method  600  may then end. 
     Returning to  625 , responsive to an indication that the change in engine oil temperature is within the threshold of the expected temperature change, method  600  proceeds to  640 . At  640 , method  600  includes indicating that the bypass valve is functioning as desired or expected. Proceeding to  635 , the passing result may be stored at the controller. Method  600  may then end. 
     While the above discussion with regard to method  600  centered on engine oil temperature changes, coolant temperature changes may additionally or alternatively be monitored in similar fashion to infer whether the bypass valve is functioning as desired. For example, if coolant temperature is lower than engine oil temperature before a switch from bypassing the oil cooler to routing engine oil through the oil cooler, then it may be expected that coolant temperature may increase by a predetermined amount. If the coolant temperature does not increase to within a threshold of the predetermined amount, then degradation of the bypass valve may be inferred. As another example, if coolant temperature is greater than engine oil temperature before a switch from bypassing the oil cooler to routing engine oil through the oil cooler, then it may be expected that coolant temperature may decrease by another predetermined amount. If the coolant temperature does not decrease to within a threshold of the other predetermined amount, then degradation of the bypass valve may be inferred. 
     Furthermore, while the above discussion with regard to method  600  centered on the switch being from bypassing the oil cooler to routing engine oil through the oil cooler, similar methodology may be utilized for a switch from routing engine oil through the oil cooler to bypassing the engine oil cooler without departing from the scope of this disclosure. 
     In this way, under mild driving conditions where vehicles tend to spend most of their time, an oil cooler may be bypassed which may improve fuel economy by reducing a load on the oil pump. Additionally, bypassing the oil pump initially at a cold-start event may enable faster time-to-desired oil pressure as opposed to other methods that route oil through the oil cooler initially at cold-start events. 
     The technical effect of combining a passive three-state oil cooler bypass valve and a variable flow oil pump is to enable a change in oil pressure as commanded via a controller to influence whether the oil cooler is bypassed or not. Specifically, low, medium and high oil pressure set points for controlling the bypass valve position may be designed such that oil pressure requirements for the engine are met at each different pressure set point, and the bypass valve will automatically (e.g. passively) adopt the appropriate position for routing oil either around the oil cooler or through the oil cooler such that oil temperature can be maintained at a temperature appropriate for different engine operational conditions. In this way, reliance on additional actuators including but not limited to wax thermostat of electro-magnetic solenoid valves for bypassing the oil cooler may be avoided, thus removing sources of potential degradation. 
     The systems discussed herein and with regard to  FIGS. 1-3C , along with the methods discussed herein and with regard to  FIG. 4  and  FIG. 6 , may enable one or more systems and one or more methods. In one example, a method comprises controlling an oil pump to pump an oil for lubricating an engine at a first pressure, a second pressure or a third pressure to bias an oil cooler bypass valve to a first position, a second position or a third position, respectively, as a function of engine operating conditions, to selectively route the oil through or around an oil cooler. In a first example of the method, the method further includes wherein the first position is a first open position where the oil is routed around the oil cooler, where the second position is a closed position where oil is prevented from being routed around the oil cooler, and where the third position is a second open position where the oil is routed around the oil cooler. A second example of the method optionally includes the first example, and further includes wherein the first pressure is greater than the second pressure, which is in turn greater than the third pressure. A third example of the method optionally includes any one or more or each of the first through second examples, and further includes wherein the oil cooler bypass valve passively responds to pressure of the oil to adopt the first position, the second position or the third position. A fourth example of the method optionally includes any one or more or each of the first through third examples, and further includes wherein the oil pump is a variable displacement oil pump. A fifth example of the method optionally includes any one or more or each of the first through fourth examples, and further includes wherein controlling the oil pump includes adjusting a position of a solenoid valve of the oil pump based on a command from a controller. A sixth example of the method optionally includes any one or more or each of the first through fifth examples, and further includes wherein the oil cooler bypass valve is not communicably coupled to the controller. A seventh example of the method optionally includes any one or more or each of the first through sixth examples, and further includes wherein the first pressure is greater than 500 kPa, wherein the second pressure is between 250-400 kPa, and where the third pressure is between 100-200 kPa. An eighth example of the method optionally includes any one or more or each of the first through seventh examples, and further includes wherein the oil cooler is a coolant-to-oil heat exchanger where heat energy is transferred between a coolant circulating through the oil cooler and the oil. A ninth example of the method optionally includes any one or more or each of the first through eighth examples, and further comprises biasing the oil cooler bypass valve to the first position at a cold-start event of the engine where a temperature of the oil is more than a threshold below a predetermined oil temperature and where a circuit that receives the oil is below a predetermined circuit pressure; biasing the oil cooler bypass valve to the second position to control the temperature of the oil to within the threshold of the predetermined oil temperature; and biasing the oil cooler bypass valve to the third position when the temperature of the oil is within the threshold of the predetermined oil temperature. 
     Another example of a method comprises controlling whether an oil used for lubricating an engine is routed through or around an oil cooler solely by adjusting a pressure of the oil emanating from an oil pump to bias an oil cooler bypass valve to a first open position under a first operating condition, to a closed position under a second operating condition, and a second open position under a third operating condition. In a first example of the method, the method further includes wherein the first operating condition includes a cold-start of the engine where pressure of an oil circuit that receives the oil is below a threshold circuit pressure and a temperature of the oil is not within a threshold of a predetermined oil temperature; where the second operating condition includes the oil circuit pressurized to above the threshold circuit pressure and where the temperature of the oil is not within the threshold of the predetermined temperature; and where the third operating condition includes the oil circuit pressurized to above the threshold pressure and the temperature of the oil within the threshold of the predetermined temperature. A second example of the method optionally includes the first example, and further includes wherein biasing the oil cooler bypass valve to the first position allows the oil to bypass the oil cooler, where biasing the oil cooler bypass valve to the closed position prevents the oil from bypassing the oil cooler, and where biasing the oil cooler bypass valve to the second open position allows the oil to bypass the oil cooler. A third example of the method optionally includes any one or more or each of the first through second examples, and further includes wherein the oil cooler additionally receives a coolant from a coolant system; and wherein heat is transferred from the oil to the coolant or vice versa with the oil cooler bypass valve closed under the second operating condition. A fourth example of the method optionally includes any one or more or each of the first through third examples, and further includes wherein the oil pump is a variable flow oil pump; and wherein the pressure of the oil emanating from the oil pump is adjusted based on a command from a controller to a valve associated with the oil pump. 
     An example of a system for a vehicle comprises a variable flow oil pump that provides an oil to an engine for lubrication purposes by way of an oil circuit; an oil cooler; an oil cooler bypass valve; and a controller with computer readable instructions stored on non-transitory memory that when executed, cause the controller to: determine an operating condition of the engine; command the variable flow oil pump to pump the oil at a determined pressure that includes one of a first pressure, a second pressure or a third pressure as a function of the operating condition of the engine, where the determined pressure passively adjusts a position of the oil cooler bypass valve so as to prevent or enable the oil to bypass the oil cooler. In a first example of the system, the system further includes wherein the oil cooler bypass valve is a three-state valve that adopts a first open position when the determined pressure is the first pressure, adopts a closed position when the determined pressure is the second pressure, and adopts a second open position when the determined pressure is the third pressure, where the first pressure is greater than the second pressure which is in turn greater than the third pressure; and wherein the oil is prevented from bypassing the oil cooler when the oil cooler bypass valve is in the closed position, but where oil is allowed to bypass the oil cooler when the oil cooler bypass valve is in the first open position and the second open position. A second example of the system optionally includes the first example, and further comprises a coolant system that flows a coolant through the oil cooler to allow heat transfer between the oil and the coolant. A third example of the system optionally includes any one or more or each of the first through second examples, and further includes wherein the controller stores further instructions to first command the variable flow oil pump to pump the oil at the first pressure at a cold-start event of the engine until the oil circuit is pressurized to above a predetermined oil circuit pressure, then command the variable flow oil pump to pump the oil at the second pressure to raise a temperature of the oil to within a threshold of a predetermined oil temperature; and responsive to the temperature of the oil being within the threshold of the predetermined oil temperature, command the variable flow oil pump to pump the oil at the third pressure. A fourth example of the system optionally includes any one or more or each of the first through third examples, and further includes wherein the controller stores further instructions to determine whether the temperature of the oil has reached a threshold oil temperature that is greater than the predetermined oil temperature while the variable flow oil pump is commanded to pump the oil at the third pressure; and command the variable flow oil pump to pump the oil at the second pressure to lower the temperature of the oil to within the threshold of the predetermined oil temperature in response to the temperature of the oil reaching the threshold oil temperature while the variable flow oil pump is commanded to pump the oil at the third pressure. 
     In another representation, a method comprises in response to conditions being met for determining whether a passive three-state oil cooler bypass valve is degraded, controlling an output pressure of a variable flow oil pump to bias the bypass valve to switch from routing a flow of oil around an oil cooler to through the oil cooler, and monitoring a temperature change of the oil. In a first example of the method, the method includes indicating degradation of the bypass valve in response to the temperature change of the oil not being within a threshold of an expected temperature change. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described 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 actions, operations, and/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 of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations, and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations, and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     As used herein, the term “approximately” is construed to mean plus or minus five percent of the range unless otherwise specified. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. 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 sub-combinations of the disclosed features, functions, elements, 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.