Method for detecting heater core isolation valve status

Methods and systems are provided for a vehicle coolant circuit. In one example, the coolant circuit includes a heater core isolation valve (HCIV) where a status of the HCIV may be diagnosed by intrusively activating a positive temperature coefficient heater in a cooling loop in which the HCIV is arranged. A response of coolant temperature to heater activation may be used to determine a position of the HCIV.

FIELD

The present description relates generally to methods and systems for a coolant circuit of a vehicle propulsion system.

A plug-in hybrid electric vehicle (PHEV) may include more than one method for providing passenger cabin heating to accommodate an operating mode of the PHEV. For example, the PHEV may have a primary coolant circuit that flows coolant through both an engine cooling loop and a heating loop when the PHEV is energized by fuel combustion, utilizing waste heat from an engine system of the PHEV to warm the passenger cabin. The secondary coolant circuit may include circulating coolant through the heating loop and not the engine cooling loop and a path of coolant flow may be controlled by a heater core isolation valve (HCIV). The HCIV may be adjustable between coupling the engine cooling loop and the heating loop or a isolating the engine cooling loop from the heating loop.

In some examples, an exhaust gas recirculation (EGR) cooler may be included in the engine cooling loop. The EGR cooler may receive a portion of a flow of coolant that has circulated through the engine block and utilize heat extraction provided by the coolant to reduce a temperature of EGR gases before the gases are delivered to the engine block for combustion. When the engine cooling loop is coupled to the heating loop, coolant may flow from the EGR cooler to the heating loop where heat absorbed by the coolant is exchanged at a heater core and used to warm the passenger cabin. When the engine cooling loop is decoupled from the heating loop, coolant may instead flow from the EGR cooler to a degas bottle configured to de-aerate the coolant before the coolant is recirculated to the engine.

In some instances, the HCIV may become stuck in a position that isolates the engine cooling loop from the heating loop. As a result, heated coolant from the EGR cooler may not be cooled by heat exchange in the heating loop. An ability of the EGR cooler to cool EGR gases may degrade, leading to termination of EGR flow. Stopping EGR flow may cause an undesirable increase in levels of carbon monoxide, nitrogen oxides, particulate matter, and non-methane hydrocarbons in the exhaust gases released to the atmosphere from the vehicle's exhaust system. Thus, detecting when the HCIV is degraded and stuck in one position may circumvent halting of EGR flow. However, monitoring of a status of the HCIV is obfuscated by a lack of a position feedback mechanism.

One example attempt to detect a position of a HCIV is shown by Porras in U.S. Pub. No. 2014/0110081. Therein, a fault in a HCIV of a PHEV, when the HCIV is actuated to a position coupling a primary cooling circuit of an engine to a secondary cooling circuit, is detected by monitoring responses of temperature sensors to a position of the HCIV and a status of a vehicle heating system. A valve system of a vehicle selectively directs coolant from an engine to a heat exchanger and is configured to detect a position of the HCIV based on a comparison of coolant temperature entering the heat exchanger to coolant temperature exiting the engine.

However, the inventors herein have recognized potential issues with such systems. As one example, the method of Porras may be incorporated into an emission diagnostic trouble code and add to a warranty cost of the vehicle. Furthermore, the diagnosis may not mitigate heating of coolant by an EGR cooler and delivery of the heated coolant to a degas bottle. Thermal degradation of EGR system components may occur, leading to costly repairs.

In one example, the issues described above may be addressed by a method for a vehicle, including transferring heat from an EGR cooler of an engine cooling loop to a heater core of a heating loop by flowing coolant through both the engine cooling loop and the heating loop, the engine cooling loop coupled to the heating loop by a valve arranged in the heating loop, commanding the valve to a first position based on generation of torque at the engine, activating a positive temperature coefficient (PTC) heater in the heating loop following commanding of the valve to the first position, inferring an actual position of the valve responsive to coolant temperature in the heating loop following heater activation, and indicating valve degradation based on the actual position being different from the commanded position. In this way, a degraded HCIV may be detected before degradation of engine cooling loop components occurs.

As one example, a temperature of the coolant flowing through the heating loop may spike above a threshold temperature when the heater is activated intrusively while the valve is in the second position. The temperature spike may be indicative of an inability of the HCIV to be adjusted to the first position to fluidly couple the heating loop to the engine cooling loop. Responsive to determination of HCIV degradation, mitigating actions may be performed, such as, for example, reducing EGR flow to circumvent thermal fatigue of an EGR cooler arranged in the engine cooling loop, as well as displaying an alert. In this way, repair and/or replacement of the HCIV may be implemented before engine components degrade and emission of undesirable combustion byproducts increases.

DETAILED DESCRIPTION

The following description relates to systems and methods for determining a status of a heater core isolation valve (HCIV). Determining the status of the HCIV includes diagnosing a position of the HCIV, adjustable between a first position that directs coolant flow through a primary circuit and a second position that directs coolant flow through a secondary circuit. The HCIV may be included in a plug-in hybrid electric vehicle (PHEV), relying on both a traction battery and an internal combustion engine to propel the vehicle. An example of an engine system that may be implemented in the PHEV is shown inFIG. 1. The engine system may be cooled by a portion of a coolant system that forms an engine cooling loop, configured to circulate a coolant through various components of the engine system. The primary circuit may include both the engine cooling loop and a heating loop, the loops fluidly coupled to one another. As the coolant flows through the primary circuit when the PHEV engine is operating, heat is extracted from the engine block, a temperature of EGR gases is reduced, and heat is removed from the coolant as the coolant flows through the heating loop. The coolant system may also have a secondary circuit that flows the coolant solely through the heating loop when the PHEV is operating in an electric mode. The engine cooling loop and the heating loop may be linked by an HCIV, as shown in a schematic diagram of the coolant system inFIG. 2. An example of an HCIV is shown inFIGS. 3 and 4, alternating between a first position and a second position, the positions controlling flow of coolant through either the primary circuit or the secondary circuit. During events where the HCIV becomes stuck in a position, e.g., the second position, that isolates the engine cooling loop from the heating loop, a status of the HCIV may be detected by intrusively activating a positive temperature coefficient (PTC) heater in the heating loop and monitoring an engine coolant temperature (ECT) in response to heating by the PTC heater. A response of the ECT to activation of the PTC heater when the HCIV is stuck in the second position is illustrated in exemplary plots inFIG. 5, depicting an effect of PTC heater activation on ECT relative to time. An example of a method for determining the position of the HCIV is shown inFIG. 6.

In a PHEV, heating of a passenger cabin may not rely solely on waste heat from an engine system components, such as an engine and/or an EGR cooler, due to frequent operation of the PHEV in an electric mode, without the engine running. When the PHEV is in the electric mode, the PHEV may utilize a heating loop that forms a secondary circuit of coolant flow. The heating loop may also be included in a primary circuit where the heating loop is fluidly coupled to an engine cooling loop that extracts heat from the engine and cools EGR gases. The heating loop includes, amongst other components, a PTC heater that operates based on electrical energy. The PTC heater may be a heat source for the heating loop, converting electrical energy to thermal energy that is transferred to coolant flowing through the heating loop. The heat absorbed by the coolant is exchanged at a heater core and used to heat the passenger cabin.

The PTC heater may be a self-regulating heater that does not rely on an external diagnostic controls and provides faster and more uniform heating than conventional wire or coil-based heaters. The PTC heater may be formed of a material that increasingly resists current as a temperature of the PTC heater rises, thereby reducing a potential for overheating. Implementation of the PTC heater in the heating loop may be leveraged to provide feedback regarding a position of an HCIV in the circuit, e.g., a direction of flow through the HCIV, allowing efficient diagnosis of an operating condition of the HCIV. Details of a method for detecting the position of the HCIV, thereby decreasing a likelihood of thermal degradation of engine components such as an EGR cooler, is provided further below, with reference toFIGS. 2-6.

Turning now to the figures,FIG. 1depicts an example of a cylinder14of an internal combustion engine10, which may be included in a vehicle5. Engine10may be controlled at least partially by a control system, including a controller12, and by input from a vehicle operator130via an input device132. In this example, input device132includes an accelerator pedal and a pedal position sensor134for generating a proportional pedal position signal PP. Cylinder (herein, also “combustion chamber”)14of engine10may include combustion chamber walls136with a piston138positioned therein. Piston138may be coupled to a crankshaft140so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft140may be coupled to at least one vehicle wheel55via a transmission54, as further described below. Further, a starter motor (not shown) may be coupled to crankshaft140via a flywheel to enable a starting operation of engine10.

Cylinder14may be cooled by a cooling sleeve118that circumferentially surrounds cylinder14and flows a coolant therethrough. The cooling sleeve118may be included in a coolant system that circulates coolant through various components of the engine10to provide cooling and heat exchange and may regulate engine temperature and utilization of waste heat. An example of a coolant system which may be coupled to the engine10is shown inFIG. 2and described further below.

In some examples, vehicle5may be a hybrid vehicle, such as a plug-in hybrid electric vehicle (PHEV), with multiple sources of torque available to one or more vehicle wheels55. In other examples, vehicle5is a conventional vehicle with only an engine or an electric vehicle with only an electric machine(s). In the example shown, vehicle5includes engine10and an electric machine52. Electric machine52may be a motor or a motor/generator. Crankshaft140of engine10and electric machine52are connected via transmission54to vehicle wheels55when one or more clutches56are engaged. In the depicted example, a first clutch56is provided between crankshaft140and electric machine52, and a second clutch56is provided between electric machine52and transmission54. Controller12may send a signal to an actuator of each clutch56to engage or disengage the clutch, so as to connect or disconnect crankshaft140from electric machine52and the components connected thereto, and/or connect or disconnect electric machine52from transmission54and the components connected thereto. Transmission54may 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. In electric vehicle embodiments, a system battery58may be a traction battery that delivers electrical power to electric machine52to provide torque to vehicle wheels55. In some embodiments, electric machine52may also be operated as a generator to provide electrical power to charge system battery58, for example, during a braking operation. It will be appreciated that in other embodiments, including non-electric vehicle embodiments, system battery58may be a typical starting, lighting, ignition (SLI) battery coupled to an alternator46.

Alternator46may be configured to charge system battery58using engine torque via crankshaft140during engine running. In addition, alternator46may power one or more electrical systems of the engine, such as one or more auxiliary systems including a heating, ventilation, and air conditioning (HVAC) system, vehicle lights, an on-board entertainment system, and other auxiliary systems based on their corresponding electrical demands. In one example, a current drawn on the alternator may continually vary based on each of an operator cabin cooling demand, a battery charging requirement, other auxiliary vehicle system demands, and motor torque. A voltage regulator may be coupled to alternator46in order to regulate the power output of the alternator based upon system usage requirements, including auxiliary system demands.

Cylinder14of engine10can receive intake air via a series of intake passages142and144and an intake manifold146. Intake manifold146can communicate with other cylinders of engine10in addition to cylinder14. One or more of the intake passages may include one or more boosting devices, such as a turbocharger or a supercharger. For example,FIG. 1shows engine10configured with a turbocharger, including a compressor174arranged between intake passages142and144and an exhaust turbine176arranged along an exhaust passage135. Compressor174may be at least partially powered by exhaust turbine176via a shaft180when the boosting device is configured as a turbocharger. However, in other examples, such as when engine10is provided with a supercharger, compressor174may be powered by mechanical input from a motor or the engine and exhaust turbine176may be optionally omitted.

A throttle162including a throttle plate164may be provided in the engine intake passages for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle162may be positioned downstream of compressor174, as shown inFIG. 1, or may be alternatively provided upstream of compressor174.

An exhaust system145is coupled to cylinder14via a poppet valve156. The exhaust system includes an exhaust manifold148, an emission control device178, and exhaust tail pipe179. Exhaust manifold148can receive exhaust gases from other cylinders of engine10in addition to cylinder14. An exhaust gas sensor126is shown coupled to exhaust manifold148upstream of an emission control device178. Exhaust gas sensor126may be selected from among various suitable sensors for providing an indication of an exhaust gas air/fuel ratio (AFR), 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, a HC, or a CO sensor, for example. In the example ofFIG. 1, exhaust gas sensor126is a UEGO. Emission control device178may be a three-way catalyst, a NOxtrap, various other emission control devices, or combinations thereof.

Engine10may further include one or more exhaust gas recirculation passages for recirculating a portion of exhaust gas from the engine exhaust to the engine intake. As such, by recirculating some exhaust gas, an engine dilution may be affected which may improve engine performance by reducing engine knock, peak cylinder combustion temperatures and pressures, throttling losses, and NOxemissions. In the depicted embodiment, exhaust gas may be recirculated from exhaust manifold148to intake passage144via EGR passage141. The amount of EGR provided to intake passage144may be varied by controller12via EGR valve143. In other examples, engine10may be configured to also provide low pressure EGR (not shown inFIG. 1) being provided via an LP-EGR passage coupled between the engine intake upstream of the turbocharger compressor174and the engine exhaust downstream of the turbine176.

Furthermore, when the engine10is operating and generating exhaust gas, heat from the EGR gases may be extracted through an EGR cooler149, arranged in the EGR passage141in a path of gas flow. The EGR cooler140may be a heat exchanger, utilizing cooling by air-to-liquid heat exchange, as an example. Coolant may flow through the EGR cooler149, absorbing heat from the hot gases and flowing to a heater core where the heat is extracted from the coolant via liquid-to-air heat exchange and directed to a passenger cabin to heat the cabin. Heat transfer between the EGR gases and an engine coolant system is described further below with reference toFIG. 2. It will be appreciated that while the EGR cooler149is shown inFIG. 1upstream of the EGR valve143, other examples may include the EGR cooler149arranged downstream of the EGR valve143or in another region of the EGR passage141.

Each cylinder of engine10may include one or more intake valves and one or more exhaust valves. For example, cylinder14is shown including at least one intake poppet valve150and at least one exhaust poppet valve156located at an upper region of cylinder14. In some examples, each cylinder of engine10, including cylinder14, may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder. Intake valve150may be controlled by controller12via an actuator152. Similarly, exhaust valve156may be controlled by controller12via an actuator154. The positions of intake valve150and exhaust valve156may be determined by respective valve position sensors (not shown).

During some conditions, controller12may vary the signals provided to actuators152and154to control the opening and closing of the respective intake and exhaust valves. The valve actuators may be of an electric valve actuation type, a cam actuation type, or a combination thereof. The intake and exhaust valve timing may be controlled concurrently, or any of a possibility of variable intake cam timing, variable exhaust cam timing, dual independent variable cam timing, or fixed cam timing may be used.

Cylinder14can have a compression ratio, which is a ratio of volumes when piston138is at bottom dead center (BDC) to top dead center (TDC). In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may happen, for example, when higher octane fuels or fuels with higher latent enthalpy of vaporization are used. The compression ratio may also be increased if direct injection is used due to its effect on engine knock.

Each cylinder of engine10may include a spark plug192for initiating combustion. An ignition system190can provide an ignition spark to combustion chamber14via spark plug192in response to a spark advance signal SA from controller12, under select operating modes. A timing of signal SA may be adjusted based on engine operating conditions and driver torque demand. For example, spark may be provided at maximum brake torque (MBT) timing to maximize engine power and efficiency. Controller12may input engine operating conditions, including engine speed, engine load, and exhaust gas AFR, into a look-up table and output the corresponding MBT timing for the input engine operating conditions. In other examples, spark may be retarded from MBT, such as to expedite catalyst warm-up during engine start or to reduce an occurrence of engine knock.

In some examples, each cylinder of engine10may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder14is shown including a fuel injector166. Fuel injector166may be configured to deliver fuel received from a fuel system8. Fuel system8may include one or more fuel tanks, fuel pumps, and fuel rails. Fuel injector166is shown coupled directly to cylinder14for injecting fuel directly therein in proportion to a pulse width of a signal FPW received from controller12via an electronic driver168. In this manner, fuel injector166provides what is known as direct injection (hereafter also referred to as “DI”) of fuel into cylinder14. WhileFIG. 1shows fuel injector166positioned to one side of cylinder14, fuel injector166may alternatively be located overhead of the piston, such as near the position of spark plug192. Such a position may increase mixing and combustion when operating the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to increase mixing. Fuel may be delivered to fuel injector166from a fuel tank of fuel system8via a high pressure fuel pump and a fuel rail. Further, the fuel tank may have a pressure transducer providing a signal to controller12.

In an alternate example, fuel injector166may be arranged in an intake passage rather than coupled directly to cylinder14in a configuration that provides what is known as port injection of fuel (hereafter also referred to as “PFI”) into an intake port upstream of cylinder14. In yet other examples, cylinder14may include multiple injectors, which may be configured as direct fuel injectors, port fuel injectors, or a combination thereof. As such, it should be appreciated that the fuel systems described herein should not be limited by the particular fuel injector configurations described herein by way of example.

Fuel injector166may be configured to receive different fuels from fuel system8in varying relative amounts as a fuel mixture and further configured to inject this fuel mixture directly into cylinder. Further, fuel may be delivered to cylinder14during different strokes of a single cycle of the cylinder. For example, directly injected fuel may be delivered at least partially during a previous exhaust stroke, during an intake stroke, and/or during a compression stroke. As such, for a single combustion event, one or multiple injections of fuel may be performed per cycle. The multiple injections may be performed during the compression stroke, intake stroke, or any appropriate combination thereof in what is referred to as split fuel injection.

Controller12is shown inFIG. 1as a microcomputer, including a microprocessor unit106, input/output ports108, an electronic storage medium for executable programs (e.g., executable instructions) and calibration values shown as non-transitory read-only memory chip110in this particular example, random access memory112, keep alive memory114, and a data bus. Controller12may receive various signals from sensors coupled to engine10, including signals previously discussed and additionally including a measurement of inducted mass air flow (MAF) from a mass air flow sensor122; an engine coolant temperature (ECT) from a temperature sensor116coupled to the cooling sleeve118; an exhaust gas temperature from a temperature sensor158coupled to exhaust passage135; a profile ignition pickup signal (PIP) from a Hall effect sensor120(or other type) coupled to crankshaft140; throttle position (TP) from a throttle position sensor; signal UEGO from exhaust gas sensor126, which may be used by controller12to determine the AFR of the exhaust gas; and an absolute manifold pressure signal (MAP) from a MAP sensor124. An engine speed signal, RPM, may be generated by controller12from signal PIP. The manifold pressure signal MAP from MAP sensor124may be used to provide an indication of vacuum or pressure in the intake manifold. Controller12may infer an engine temperature based on the engine coolant temperature and infer a temperature of emission control device178based on the signal received from temperature sensor158.

Controller12receives signals from the various sensors ofFIG. 1and employs the various actuators ofFIG. 1to adjust engine operation based on the received signals and instructions stored on a memory of the controller. For example, the controller may obtain the ECT from the temperature sensor116and adjust a flow of coolant circulating through the cooling sleeve118based on the ECT.

As described above,FIG. 1shows only one cylinder of a multi-cylinder engine. As such, each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plug, etc. It will be appreciated that engine10may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each of these cylinders can include some or all of the various components described and depicted byFIG. 1with reference to cylinder14.

When the engine10ofFIG. 1is implemented in a PHEV, the PHEV may operate as a hybrid electric vehicle with an ability to connect to an external electric grid. The PHEV may be driven over a range propelled by the electric machine52, powered by the battery58, and switch to the engine10when the battery58is depleted below a threshold power level. When the engine10is not operating, heat is not generated and as a result passenger cabin heating may not be obtained through waste heat from the engine10or from the EGR cooler149. As an alternative, the PHEV may have a coolant system that includes a primary circuit where an engine cooling loop and a heating loop are fluidly coupled through an HCIV, providing cabin heating by using waste heat from the engine, and a secondary circuit, where the engine cooling loop and the heating loop are isolated from one another and cabin heating is enabled by an electric heater. An example of such a coolant system is shown inFIG. 2.

InFIG. 2, a schematic diagram of a coolant system200of a PHEV is depicted. The coolant system may be coupled to an engine202, such as the engine10ofFIG. 1, and may provide cooling to combustion chambers of the engine202by flowing a coolant through a water jacket or cooling sleeve, such as the cooling sleeve118ofFIG. 1. The coolant may be glycol, an aqueous glycol solution, or some other type of coolant with a lower freezing point than water. The coolant system200has two distinct circuits: a primary circuit204that flows coolant through both an engine cooling loop201and a heating loop230and a secondary circuit250formed exclusively of the heating loop230. The engine cooling loop201includes components such as the engine202, an engine oil cooler206, an EGR cooler208, and a radiator210and the heating loop230includes a PTC heater232, a heater core234, and a HCIV236. The primary circuit204may be configured to both cool the engine202and provide heating to a passenger cabin of the PHEV when heating is requested and the engine202is operating. The secondary circuit250may provide heating to the passenger cabin when the engine is not running and the PHEV is operating in an electric mode.

The engine cooling loop201includes a main pump212that drives coolant flow through the primary circuit204as indicated by arrows214. The main pump212may be mechanically or electrically driven. For example, the coolant may flow from the pump to the engine202. After circulating through the engine202and extracting heat from the engine202, the flow may be directed to a first three-way junction216that splits the flow of heated coolant. A first portion of coolant flow may be directed to the radiator210, as indicated by arrows214, and a second portion directed to the EGR cooler208, as indicated by arrow218.

The first portion of the coolant flow may flow through the radiator210where heat from the coolant may be transferred to the radiator210. In some examples, the heat absorbed by the radiator may be channeled to the passenger cabin to assist in warming the cabin. The first portion of the coolant flow may flow from the radiator210to a degas bottle220where the coolant may be de-aerated before returning to the main pump212.

The second portion of the coolant flow may flow from the first three-way junction216to the EGR cooler208and extract heat from EGR gases flowing therethrough. When the PHEV is operating with the engine202running and flowing coolant through the primary coolant circuit204, the second portion of the coolant flow may continue from the EGR cooler208to the heating loop230, as indicated by arrow222. The coolant enters the heating loop230at a second three-way junction238and flows along a path indicated by arrows240.

An auxiliary pump242may be positioned downstream of the second three-way junction238, driving coolant flow through the heating loop230. The auxiliary pump242may be electrically or mechanically driven. Coolant is pumped to the PTC heater232, which, as described above, may be an electric, self-regulating heater. When the PHEV engine202is operating and coolant is flowing through the primary circuit204, passenger cabin heating may be provided by heat extracted from the EGR gases at the EGR cooler208. The coolant is already heated upon arrival at the PTC heater232and the PTC heater232is not activated. However, during engine cold starts, when the engine202is operating and coolant is flowing through the primary circuit204, the engine202may not be sufficiently warm to provide passenger cabin heating. The PTC heater232may be turned on to heat the coolant in the heating loop230until the engine202reaches a threshold operating temperature, enabling the PTC heater232to be deactivated.

The coolant flows from the PTC heater232to the heater core234. An ECT sensor244may be arranged in the path of coolant flow between the PTC heater232and the heater core234to monitor a temperature of the coolant prior to interaction with the heater core234. The heater core234may be a heat exchange device that extracts heat from the coolant, transfers the heat to air, and directs the absorbed heat to the passenger cabin. For example, a blower may be arranged adjacent to the heater core234, utilizing liquid-to-air heat exchange across the heater core234to funnel heated air into the passenger cabin. A temperature of the coolant emerging from the heater core234is therefore reduced relative to the coolant entering the heater core234.

The cooled coolant flows from the heater core234to the HCIV236. The HCIV236may be a three-way valve that may be varied between at least two positions. For example, a non-limiting example of the HCIV236ofFIG. 2is shown inFIGS. 3 and 4by an HCIV302arranged in a first position300inFIG. 3and a second position400inFIG. 4. The HCIV302may be implemented in the coolant system200ofFIG. 2and configured to alternate between directing coolant flow through the primary circuit204and the secondary circuit250ofFIG. 2. The HCIV302has a pivotable partition304that rotates about a hinge306. Adjustment of the partition304between the first position300and the second position400may be actuated by an electric, electromagnetic, or hydraulic device, or some other type of actuating mechanism.

In the first position300shown inFIG. 3, the partition304is oriented so that flow from the heater core234ofFIG. 2passes through the HCIV302, as indicated by arrow308, along a continuous path that fluidly couples the heating loop230to the engine cooling loop201ofFIG. 2, thereby flowing coolant through the primary circuit204. The position of the partition304interrupts flow around the heating loop230so that coolant is forced to divert along the direction indicated by arrow246to circulate through the engine cooling loop201ofFIG. 2before returning to the heating loop230. In the second position400shown inFIG. 4, the partition304is pivoted in a clockwise direction, blocking flow from the heater core234to the engine cooling loop201. Instead, coolant flows through the HCIV302as indicated by arrow310to continue circulating through the heating loop230, e.g., through the secondary circuit250.

Returning toFIG. 2, when the HCIV236is adjusted to a first position, e.g., the first position300ofFIG. 3, coolant may flow from the heater core234, through the HCIV236and to the engine oil cooler206via arrows246while blocking flow between the heater core234and the second three-way junction238. Coolant flow may be driven by operation of the main pump212and the auxiliary pump242may be deactivated unless a speed of the main pump212drops below a threshold speed, e.g., the main pump212becomes degraded. Thus the coolant is forced to flow from the heating loop230to the engine cooling loop201via arrows246and from the engine cooling loop201to the heating loop230via arrow222. The first position allows the engine cooling loop201and the heating loop230to be combined and fluidly coupled. Alternatively, when adjusted to a second position, e.g, the second position400ofFIG. 4, coolant flow between the heater core234and the engine oil cooler206is inhibited and coolant instead flows through the HCIV236to the second three-way junction238, as indicated by arrow248, confining coolant circulation within the heating loop230, as indicated by arrows240. In this position, the heating loop230is isolated from the engine cooling loop201and coolant is circulated through the secondary circuit250while the PHEV is operating in the electric mode and the engine202is not running.

During electric mode operation of the PHEV, cooling of the engine202and of EGR gases at the EGR cooler208may not be demanded or may be at least reduced. Flow between the EGR cooler208and the heating loop230may therefore be discontinued without resulting in an increase in coolant temperature that may lead to thermal degradation of components of the engine cooling loop201. The second portion of coolant, flowing from the engine202through the first three-way junction216and to the EGR cooler208, may flow to the degas bottle220, as indicated by arrow215, instead of to the heating loop230, as indicated by arrow222, when the HCIV236is in the second position.

As elaborated above, the HCIV236may be adjusted to the second position during electric mode operation, isolating the heating loop230from the engine cooling loop201. Flow through the heating loop230is driven by operation of the auxiliary pump242. The PTC heater232may be activated to heat the coolant as the coolant passes through. The heated transferred to the coolant from the PTC heater232is extracted from the coolant at the heater core234, providing heat for warming the passenger cabin. In this way, the heating loop230may heat the passenger cabin without relying on waste heat from the engine cooling loop201.

If the HCIV236is degraded and becomes stuck in the second position, blocking coolant flow between the engine cooling loop201and the heating loop230during engine operation when engine cooling is desired, the engine cooling loop201and the heating loop230may remain isolated from one another. Without detection of a status of the HCIV236, heated coolant may be forced to flow from the EGR cooler208to the degas bottle220, as indicated by arrow215, which may alter a pressure of the degas bottle220and adversely affect an ability of the degas bottle220to maintain an air-free volume of coolant within the coolant system200.

Furthermore, if the HCIV236is stuck in the second position, isolating the engine cooling loop201from the heating loop230, coolant circulating through the EGR cooler208may increase in temperature, reducing a capacity to cool EGR gases. Detection of insufficient cooling of EGR gases, by, for example a rise in intake manifold temperature, may lead to termination of EGR flow and an increase in carbon monoxide, nitrogen oxides, particulate matter, and non-methane hydrocarbon emissions of the PHEV. Additionally, lack of heat extraction from the coolant via the heating loop230may result in local boiling within the engine cooling loop201that may impose thermal stress on the EGR cooler208. A position of the HCIV236, e.g., whether the HCIV236is in the first or second position when coolant flow through the primary circuit204, e.g., when the heating loop230and the engine cooling loop201are combined, is requested, may be assessed by a method including briefly activating the PTC heater232and monitoring an effect of the activation on a coolant temperature in the heating loop230. When the HCIV236is in a commanded position for circulation through the primary circuit204, e.g., the first position300ofFIG. 3which enables coolant to flow through both the engine cooling loop201and the heating loop230, turning the PTC heater232on for a short time duration, such as between 10-30 seconds, may not cause a detectable change in coolant temperature in the heating loop230, as measured by the ECT sensor244. Changes in coolant temperature due to activation of the PTC heater232may not be detected until the PTC heater232is heating coolant flowing therethrough for greater than, for example, one minute, due to coolant inertia as the coolant circulates through the primary circuit, as well as a hysteresis effect on coolant temperature as the coolant flows through more than one heat exchanger.

However, if the HCIV236is in the second position, interrupting coolant flow between the engine cooling loop201and the heating loop230, in spite of active engine operation and a command to adjust the HCIV236to the first position, the auxiliary pump242may be inactive. As a result, the coolant in the isolated heating loop230may become stagnant. The coolant in the heating loop230does not receive heated coolant from the EGR cooler208and does not flow through more than one heat exchanger. Coolant inertia is reduced due to confinement within the heating loop230and lack of pumping.

During operation with the HCIV236in the first position, the PTC heater232may be maintained off when coolant flows through the primary circuit204(except during cold engine starts when passenger cabin heating is requested, as described above). However, intrusively activating the PTC heater232, e.g., turning on the PTC heater232even though coolant heating by the PTC heater232is not requested, for 30 seconds or less may rapidly generate a detectable spike in the coolant temperature as measured by the ECT sensor244when the auxiliary pump242is not operating.

Even during instances where the PTC heater232is commanded to turn on to provide passenger cabin heating, such as during cold engine starts where the engine is not yet warm enough, while the coolant is flowing through the primary circuit204, a position of the HCIV236may be quickly assessed. As described above, a change in coolant temperature that persists beyond a threshold period of time, such as beyond 60 seconds, may be delayed for at least a minute when the coolant is circulating through the primary circuit204. However, if the HCIV236is stuck in the second position, e.g., the second position400ofFIG. 4, and the coolant is instead circulating through the secondary circuit250, a sharp increase in temperature may be observed within 30-60 seconds of the PTC heater232activation.

As an example, stacked plots500and550are shown inFIG. 5. Plot500depicts a coolant temperature in a heating loop of a coolant system, such as the heating loop230ofFIG. 2, as detected by a temperature sensor, such as the ECT sensor244, positioned immediately downstream of a PTC heater, such as the PTC heater232ofFIG. 2. Plot550illustrates a status of the PTC heater, alternating between turning on and heating coolant and turning off. Both plots500and550are plotted against time along the x-axis.

A response of coolant temperature to PTC heater activity is shown at, for example, a first activation pulse502of the PTC heater in plot550where the PTC heater is turned on and turned off after a preset period of time. The first activation pulse502may occur over a first interval of time t1 such as 10 seconds or 20 seconds, or between 5 to 30 seconds. By the end of the first activation pulse502, e.g., at the end of t1, the coolant temperature begins to rise, increasing rapidly and reaching a first peak504after a second interval of time t2. The second interval of time t2, beginning when the PTC heater is turned on at the start of t1 and overlapping with t1, may be longer than t1 by, for example, two or three times. The second interval of time t2 may be a time period of 20 to 60 seconds. However, the sharp rise in temperature begins by the end of t1, thus detection of the rise in coolant temperature may be detected part-way through t2 and before the end of t2. For example, confirmation of the rise in coolant temperature may be achieved in less than one minute. The coolant temperature response to the activation pulse502may be a spike in temperature, reaching a maximum for a brief period time, such as 1-5 seconds, and immediately decreasing in temperature at a similar rate as the rise in temperature.

By intrusively activating a PTC heater in a heating loop, fluidly coupled to an engine cooling loop via a primary circuit when an engine of a PHEV is operating, a position of an HCIV in the heating loop, configured to control coolant flow through either the primary circuit or a secondary circuit, may be determined efficiently. The secondary circuit is formed from the heating loop, isolated from the engine cooling loop by the HCIV, and flow of coolant through the secondary circuit instead of the primary circuit when the engine is operating may lead to degradation of an EGR cooler, flow of heated coolant to a degas bottle, and termination of EGR flow. A status of the HCIV when flow through the primary circuit is requested may be detected by turning on the PTC heater in short bursts, allowing identification of the HCIV being stuck in a position that decouples the heating loop from the engine cooling loop before degradation of the EGR cooler occurs.

An example of a method600for evaluating a position of the HCIV is shown inFIG. 6. Method600may be implemented in a coolant system of a PHEV such as the coolant system200ofFIG. 2, where coolant flows through a primary circuit when the engine is operating and providing torque and an HCIV is actuated to a first position, such as the first position300shown inFIG. 3. The coolant flows through a secondary circuit when the PHEV is operating in an electric mode, not utilizing engine torque, and the HCIV is actuated to a second position, such as the second position400shown inFIG. 4. The primary circuit may include both an engine cooling loop and a heating loop, the loops coupled to one another by the HCIV adjusted to the first position. A PTC heater is included in the heating loop. The secondary circuit may include the heating loop and not the engine cooling loop, the loops decoupled from one another by adjustment of the HCIV to the second position. In some instances the HCIV may not be able to adjust to the first position when flow through primary circuit is demanded due to degradation of the HCIV. Method600may be conducted routinely to evaluate a performance of the HCIV. For example, method600may be implemented each time the HCIV is instructed to switch from the second position to the first position. Instructions for carrying out method600and the rest of the methods included herein may be executed by a controller based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference toFIGS. 1 and 2. For example, the controller may receive information from an engine coolant temperature (ECT) sensor positioned in the heating loop, such as the ECT sensor244shown inFIG. 2. The controller may employ engine actuators of the engine system to adjust engine operation, according to the methods described below.

Prior to602, the PHEV is operating, e.g., the engine is not keyed off and a battery of the PHEV is actively powering electrical components of the PHEV. The PHEV may be propelled by engine torque or by electrical energy. For example, the PHEV may be idling or in transit, e.g., travelling and may alternate between operating in an electric mode or a fuel combustion mode. At602, the method includes determining if the PHEV engine is operating, e.g., actively providing torque. Engine operation may be detected via data received from a MAP sensor to measure a pressure at an intake manifold, from an intake manifold temperature, or from an exhaust sensor to measure an AFR (or lack thereof), etc. If the engine is not determined to be operating, the method continues to604to determine if passenger cabin heating is requested. A request for passenger cabin heating may be implemented by an operator turning on a switch or dial at a passenger control console of the PHEV.

If heating is not requested, the method proceeds to606to continue operating the PHEV under current operating conditions, e.g., in electric mode, without passenger cabin heating, and with the HCIV in the second position. The method returns to the start. However, if heating is requested at604, the method continues to608to activate the PTC heater in the heating loop to warm coolant flowing through the heating loop, the heat absorbed by the coolant transferred at a downstream heater core to air flowing to the passenger cabin. The method returns to the start.

Returning to602, responsive to detection of engine operation, the method continues to610to initiate a test to diagnose a status of the HCIV by initiating an HCIV test. In order to enable efficient engine and EGR gas cooling, the HCIV is commanded to the first position to flow coolant through the primary circuit when the engine is operating. However, degradation of the HCIV may occur and result in retention of the HCIV in the second position, circulating coolant through the secondary circuit, in spite of the command to adjust the HCIV to the first position. The HCIV test may thus evaluate a condition of the HCIV, e.g., whether the HCIV is able to respond to the command to adjust its position or if the HCIV is stuck in the second position.

Initiating the HCIV test includes activating the PTC heater at612for a brief period of time, such as 30 seconds or less, followed by deactivation. In other words, the PTC heater may be pulsed at least one time. In examples, the PTC heater may be pulsed for a preset number of pulse cycles to provide a minimum statistical level of confidence in a status of the HCIV. The preset number of pulse cycles may three cycles, or five cycles, and may be performed at uniform intervals or varying intervals of time. Initiating the HCIV test further includes monitoring the ECT at the ECT sensor at614. The controller may query the ECT sensor continuously as the PTC heater is pulsed to collect continuous data from the ECT sensor regarding the ECT response to PTC heater pulsing.

At616, the method includes determining if the time elapsed since initiating the HCIV test reaches or passes a first threshold. The first threshold may be a duration of time that includes both a pulse duration of the PTC heater as well as a period of time to allow an effect of the pulse on ECT to be observable. For example, an inertia and heat capacity of the coolant may result in a hysteresis effect, delaying a detectable change in ECT. The first threshold may therefore be a total of 35, 40, 45 seconds, or a period of time between 30 and 55 seconds, depending on a composition of the coolant. If the elapsed time does not reach the first threshold, the method returns to616to continue comparing the elapsed time to the first threshold.

If the elapsed time reaches the first threshold, the method continues to618to determine if the ECT reaches or surpasses a second threshold. The second threshold may be a coolant temperature higher than a reference ECT when the PTC heater is not operating. The second threshold may be an elevated temperature that, when attained within the first threshold of time, is indicative of a spike in ECT resulting from the HCIV being stuck in the second position. The second threshold may be, for example, a 20, 40, 50% rise in temperature relative to the reference ECT. The reference ECT may a coolant temperature in the heating loop prior to PTC heater activation, e.g., an ambient coolant temperature in the heating loop. The reference ECT may vary depending on operating conditions of the PHEV, therefore the second threshold may also vary accordingly. When stuck in the second position but commanded to the first position, the HCIV blocks coolant circulation between the engine cooling loop and heating loop while an auxiliary pump in the heating loop is deactivated, enabling ECT to rapidly rise in response to operation of the PTC heater. In contrast, when the HCIV is in the first position when commanded to the first position and the PTC heater is activated, a large hysteresis effect and coolant inertia resulting from flow through the primary circuit may delay a change in the ECT for a longer period of time than the first threshold, such as, for example, more than one minute.

If the ECT does not reach the second threshold, the HCIV is determined to not be degraded and successfully commanded to the first position. The method continues operation of the PHEV at620under current operating conditions, such as utilizing fuel combustion for vehicle propulsion and passenger cabin heating (if requested), with the HCIV in the first position. The method returns to the start. Responsive to a determination that the ECT reaches the second threshold and the HCIV is stuck in the second position, the method proceeds to622to perform mitigating actions. The mitigating actions may include sending an alert to notify an operator of the status of the HCIV. For example, an alert may be displayed at624at a display panel in the passenger cabin. At626, EGR flow may be reduced or halted to reduce heat transfer from EGR gases to the coolant that may lead to thermal stress at an EGR cooler. Engine operations may be adjusted to compensate for the reduced or lack of EGR flow to maintain emissions below a threshold level of emissions. The threshold level of emissions may be a preset concentration of substances such as CO, NOx, etc., as detected by corresponding sensors in an exhaust manifold of the PHEV. The PTC heater may be activated to provide passenger cabin heating, if heating is requested, to compensate for reduced heat transfer from the EGR gases. The mitigating actions may be continued until the controller is notified that the HCIV is repaired or replaced.

In this way, a status of a heater core isolation valve (HCIV) of a PHEV may be diagnosed by intrusively activating a positive temperature coefficient (PTC) heater. The HCIV may control coolant flow between an engine cooling loop and a heating loop, adjustable between a first position that couples the loops and a second position that decouples the loops. During instances when the HCIV is stuck in the second position while an engine of the PHEV is operating and engine cooling is requested, diagnosis of the HCIV status may be achieved by activating the PTC heater for a brief period of time and observing the engine coolant temperature (ECT) in the heating loop for a spike in the ECT. Generation of the temperature spike may indicate a degraded condition of the HCIV, enabling further mitigating actions, such as alerting and operator, reducing EGR flow, etc., to be performed. Release of undesirable exhaust emissions when the HCIV is stuck as well as thermal degradation of an EGR cooler is reduced.

The technical effect of diagnosing the HCIV status by intrusive activation of the PTC heater is that a likelihood of increased carbon monoxide, nitrogen oxides, particulate matter, and hydrocarbon emission is reduced when the HCIV is degraded and EGR gas cooling is not provided.

In a first embodiment, a method includes while flowing coolant through an engine coolant system, the engine coolant system including a heating loop coupled to a cooling loop via a valve, activating a heater coupled to the heating loop for a duration responsive to a command to adjust the valve to a first position to flow coolant through both the heating loop and the cooling loop, and indicating an actual position of the valve based on a change in coolant temperature in the heating loop following the activating. In a first example of the method, flowing coolant through the engine coolant system includes flowing coolant selectively through the heating loop where coolant flows through the heater, a temperature sensor, and a heater core while bypassing the cooling loop when the valve is commanded to adjust to a second position, different from the first position. A second example of the method optionally includes the first example, and further includes wherein indicating the actual position of the valve includes indicating that the valve is stuck in the second position, following the command to adjust the valve to the first position, responsive to a higher than threshold rise in coolant temperature in the heating loop. A third example of the method optionally includes one or more of the first and second examples, and further includes, wherein the threshold rise in coolant temperature is a predetermined increase in temperature above a temperature of the coolant prior to activating the heater. A fourth example of the method optionally includes one or more of the first through third examples, and further includes, wherein responsive to determining that the HCIV is stuck in the second position, reducing EGR flow to the engine and notifying a vehicle operator.

In another embodiment, a method includes transferring heat from an EGR cooler of an engine cooling loop to a heater core of a heating loop by flowing coolant through both the engine cooling loop and the heating loop, the engine cooling loop coupled to the heating loop by a valve arranged in the heating loop, commanding the valve to a first position based on generation of torque at the engine, activating a positive temperature coefficient (PTC) heater in the heating loop following commanding of the valve to the first position, inferring an actual position of the valve responsive to coolant temperature in the heating loop following heater activation, and indicating valve degradation based on the actual position being different from the commanded position. In a first example of the method, commanding the valve to the first position responsive to using torque generated at the engine to flow coolant through both the engine cooling loop and the heating loop, and commanding the valve to a second position, different from the first position, responsive to using torque generated by an electric motor to flow coolant through only the heating loop. A second example of the method optionally includes the first example, and further includes, wherein commanding the valve to the second position includes flowing coolant from the EGR cooler to a degas bottle in the engine cooling loop and circulating coolant through the heating loop isolated from the cooling loop. A third example of the method optionally includes one or more of the first and second examples, and further includes, wherein indicating valve degradation includes indicating the valve is in the second position responsive to a higher than threshold rise in coolant temperature upon activating the PTC heater following commanding the valve to the first position. A fourth example of the method optionally includes one or more of the first through third examples, and further includes, wherein activating the heater includes heating coolant in the heating loop for less than a threshold duration of time, the threshold duration of time being less than a period of time for a coolant temperature to respond to the heater activation when coolant flows through both the engine cooling loop and the heating loop. A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes, wherein inferring the actual position of the valve includes measuring coolant temperature at a temperature sensor positioned downstream of the PTC heater in the heating loop.

In yet another embodiment, a hybrid vehicle system includes vehicle wheels propelled using torque from one or more of an engine and an electric motor, a coolant system for circulating coolant through the engine, the coolant system including a cooling loop coupled to a heating loop when a valve of the heating loop is in a first position and separated from the heating loop when the valve is in a second position, a positive temperature coefficient (PTC) heater arranged in the heating loop, a temperature sensor arranged downstream of the PTC heater in the heating loop, and a controller with computer readable instruction stored on non-transitory memory that, when executed, cause the controller to activate the PTC heater responsive to a command to adjust the valve to the first position, monitor a change in coolant temperature in the heating loop following heater activation, and diagnose an actual position of the valve based on the monitored change in coolant temperature. In a first example of the system, the cooling loop includes an engine, a radiator, a degas bottle, an engine oil cooler, and an EGR cooler. A second example of the system optionally includes the first example, and further includes wherein the heating loop includes the valve, the PTC heater, the temperature sensor, a heater core downstream of the temperature sensor, and a three-way junction between the valve and the PTC heater. A third example of the system optionally includes one or more of the first and second examples, and further includes, wherein the controller includes further instructions to operate the coolant system in a first mode with the valve in the first position responsive to the wheels using torque from the engine and operate the coolant system in a second mode with the valve in the second position responsive to the wheels using torque from the electric motor. A fourth example of the system optionally includes one or more of the first through third examples, and further includes, wherein when in the first mode, the coolant system is configured to flow coolant from the EGR cooler of the cooling loop to the valve of the heating loop and flow coolant from the three-way junction of the heating loop to the engine oil cooler of the cooling loop. A fifth example of the system optionally includes one or more of the first through fourth examples, and further includes, wherein when in the second mode, the coolant system is configured to circulate coolant within the heating loop, separate from the cooling loop, and flow coolant from the EGR cooler to the degas bottle in the cooling loop. A sixth example of the system optionally includes one or more of the first through fifth examples, and further includes, wherein the controller includes further instructions to diagnose the actual position of the valve responsive to a measurement of coolant temperature in the heating loop above a threshold temperature. A seventh example of the system optionally includes one or more of the first through sixth examples, and further includes, wherein the controller includes further instructions to indicate that the valve is stuck in the first position following measurement of the coolant temperature above the threshold temperature. An eighth example of the system optionally includes one or more of the first through seventh examples, and further includes, wherein the hybrid vehicle is a plug-in hybrid electric vehicle.

In another representation, an engine method includes, during heater core isolation valve diagnostics, activating a positive temperature coefficient heater, and in response to a higher than threshold spike in coolant temperature, indicate valve degradation. In a first example of the method, the positive temperature coefficient heater is activated to provide heating to a passenger cabin with the valve is determined to be degraded.