Systems and methods for engine oil temperature estimation

Abstract

The present application relates to systems and methods for estimating engine oil temperature, and discloses methods and systems for estimating engine oil temperature during conditions in which a sensor for measuring engine oil temperature is inoperative or unreliable. The zero duty cycle of a solenoid spool valve of a variable cam timing mechanism is estimated. Then, when an existing sensor for calculating engine oil temperature becomes unreliable, the calibration relationship between the duty cycle, the angular velocity of the associated cam, and the engine oil temperature is used to estimate the engine oil temperature.

Description

Technical Field

[0001] This specification generally relates to methods and systems for estimating engine oil temperature in an engine system configured with a hydraulically actuated VCT mechanism. Background Art

[0002] Engine control systems use multiple variables for adjusting various engine operations. For example, an estimated engine oil temperature (EOT) value can be used to calculate total friction and pumping losses at the engine, which are in turn used for torque control. As another example, EOT is used for powertrain limitations, where engine idle speed and maximum and minimum allowable engine speeds are limited to protect the engine from extreme temperature conditions (such as may occur when EOT is too high or too low). The EOT value can also be used to adjust variable camshaft timing, control crankcase ventilation, and monitor engine oil life.

[0003] Various methods have been developed for EOT estimation. Some methods rely on direct EOT estimation via a temperature sensor coupled to the engine oil pan. Still other methods rely on (indirect) EOT inference logic, where signals from various engine sensors (such as an engine coolant temperature (ECT) sensor, a mass air flow (MAF) sensor, an intake air temperature (ACT) sensor, etc.) are combined with the last inferred EOT value stored in the memory of the engine controller (e.g., in a keepalive memory or KAM) to generate an inferred value during engine operation.

[0004] However, the inventors herein have recognized potential problems with such methods. As an example, in a direct estimation method, deterioration of the temperature sensor may cause the EOT measurement to become inaccurate. As another example, in an indirect estimation method, deterioration of any one of the KAM, ECT sensor, MAF sensor, and ACT sensor (or any other such sensor used in the EOT inference logic) may cause the inferred EOT value to be unreliable. Even when the sensors are functioning, there may be situations where the input from one or more sensors is unreliable for EOT estimation. As an example, during a hot engine start, the engine coolant may be significantly hotter than the engine oil. The engine controller may utilize the hot soak time (i.e., the total amount of time elapsed since the engine was shut off), the engine coolant temperature estimated via the ECT sensor, and the last estimated EOT value before engine shutdown to calculate an initial EOT estimate for the EOT inference logic during subsequent engine starts. However, if the hot soak time or the last estimated EOT value is corrupt due to a KAM error, the initial EOT estimate may be inaccurate, at least for the first few minutes of vehicle operation. Thus, inaccuracies in EOT estimation may result in sub-optimal engine performance. Additionally, overheating of the engine oil may cause engine component deterioration and reduced engine life. SUMMARY OF THE INVENTION

[0005] The inventors herein have recognized that the temperature dependence of the oil control valve (OCV) of a variable camshaft timing (VCT) mechanism can be advantageously utilized for reliable EOT estimation. For example, this relationship can be used to infer EOT when the sensors used in EOT estimation deteriorate and / or when engine conditions render the sensor outputs less reliable. In one example, an engine oil temperature may be estimated by a method for an engine that includes adjusting an engine torque actuator in response to the engine oil temperature, the engine oil temperature being formed based on a mapping of the camshaft solenoid valve duty cycle of a variable camshaft timing device and the camshaft angular velocity stored in a memory.

[0006] As an example, the engine may be configured with a hydraulically actuated VCT device actuated by a solenoid oil control valve (OCV). The VCT device may include an intake cam and an exhaust cam. In response to meeting the EOT estimation conditions and setting one or more EOT faults, EOT estimation may be applied via a mapped relationship between the camshaft solenoid duty cycle and the camshaft angular velocity. One or more EOT faults may include degradation of sensors for measuring EOT, such as an EOT sensor, an ECT sensor, an ACT sensor, etc. One or more EOT faults may alternatively include conditions where the sensor output is unreliable, such as when the KAM is damaged or during a hot engine start. During such conditions, the controller may apply an excitation pulse to one of the intake cam and the exhaust cam. For example, the controller may pass a current with a defined duty cycle pulse width through the solenoid that controls the OCV of the cam. The duty cycle may be selected such that the spool valve moves to a position that directs engine oil to the cam pressure chamber, thereby rotating the cam relative to the camshaft (in the advance direction or the retard direction, depending on the need for the selected timing). The controller may measure the change in the camshaft speed or velocity corresponding to the applied duty cycle (e.g., via a camshaft position sensor) and estimate the null duty cycle of the OCV based on this. Based on the estimated null duty cycle, and further based on the mapping and calibration relationship between the angular velocity of the camshaft and the solenoid duty cycle (e.g., via an inverse model mapping), the controller may infer the EOT. Then, the estimated EOT may be used to reliably estimate the engine torque and actuate one or more torque actuators.

[0007] In this way, a reliable EOT estimate value can be provided during conditions where sensors conventionally used to measure or estimate EOT are degraded, or the outputs of these sensors are unreliable. The technical effect of relying on the mapped relationship between the duty cycle applied to the oil control valve (OCV) of the hydraulically actuated VCT and the angular velocity of the cam actuated by the OCV is that a more robust EOT estimation method can be provided. By utilizing the temperature dependence of the OCV resistance when estimating the EOT, the need for dedicated sensors is reduced, thereby providing a reduction in components and improving the robustness of the method against various EOT faults. By more reliably estimating the EOT, the torque estimation accuracy and the engine torque limit for temperature protection are improved.

[0008] It should be understood that the above summary is provided to introduce in a simplified form a selection of concepts that are further described in the detailed description. This is not meant to identify the key or essential features of the claimed subject matter, the scope of which is defined solely by the appended claims. Additionally, 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

[0009] Figure 1 An exemplary engine system having a variable camshaft timing (VCT) device is shown.

[0010] Figure 2 An exemplary oil control valve (OCV) for the VCT is depicted.

[0011] Figure 3 An exemplary VCT phaser system is depicted.

[0012] Figure 4 An advanced flowchart for estimating engine oil temperature is shown.

[0013] Figure 5 An exemplary zero duty cycle determination for the OCV is depicted.

[0014] Figure 6 An exemplary map depicting the relationship between zero duty cycle and EOT is shown.

[0015] Figures 7 - 10 An exemplary EOT estimation result is depicted. DETAILED DESCRIPTION

[0016] The following description relates to systems and methods for controlling a vehicle engine having a variable cam timing (VCT) device actuated using oil pressure via an oil control valve, as Figures 1 - 2 shown. The engine controller may be configured to execute control routines (such as Figure 4 exemplary routines) to estimate engine oil temperature (EOT) in situations where the default EOT estimation method is unreliable (such as due to sensor degradation or due to unreliable sensor output). The controller may apply a pulse width signal to determine the zero duty cycle of the oil control valve ( Figure 5 ) and then infer the EOT based on the mapping relationship between the VCT duty cycle and the EOT ( Figure 6 ). Reference Figures 7 - 10 to the example shows an exemplary EOT estimation.

[0017] Figure 1 An exemplary embodiment of a combustion chamber or cylinder of an internal combustion engine 10 is depicted. Figure 1It is shown that the engine 10 can receive control parameters from a control system including a controller 12 and receive inputs from a vehicle operator 190 via an input device 192. In this example, the input device 192 includes an accelerator pedal and a pedal position sensor 194 for generating a proportional pedal position signal PP.

[0018] The cylinder (also “combustion chamber” herein) 30 of the engine 10 can include combustion chamber walls 32 within which a piston 36 is positioned. The piston 36 can be coupled to a crankshaft 40 such that the reciprocating motion of the piston is converted into rotational motion of the crankshaft. The crankshaft 40 can be coupled to at least one drive wheel of a passenger vehicle via a transmission system. Additionally, a starter motor can be coupled to the crankshaft 40 via a flywheel to enable starting operation of the engine 10. A housing 136 is hydraulically coupled to the crankshaft 40 via a timing chain or belt (not shown).

[0019] The cylinder 30 can receive intake air via an intake manifold or air passage 44. In addition to the cylinder 30, the intake passage 44 can also communicate with other cylinders of the engine 10. In some embodiments, one or more intake passages can include a boosting device (such as a turbocharger or a supercharger). A throttle valve system including a throttle plate 62 can be provided along the intake passage of the engine to change the flow rate and / or pressure of the intake air supplied to the engine cylinders. In this particular example, the throttle plate 62 is coupled to an electric motor 94 such that the controller 12 controls the position of the oval throttle plate 62 via the electric motor 94. This configuration can be referred to as electronic throttle control (ETC), which can also be used during idle speed control.

[0020] The combustion chamber 30 is shown to communicate with the intake manifold 44 and the exhaust manifold 48 via respective intake valves 52a and 52b (not shown) and exhaust valves 54a and 54b (not shown). Thus, while four valves per cylinder can be used, in another example, a single intake valve and a single exhaust valve per cylinder can also be used. In yet another example, two intake valves and one exhaust valve per cylinder can be used.

[0021] In addition to the cylinder 30, the exhaust manifold 48 can also receive exhaust from other cylinders of the engine 10. An exhaust sensor 76 is shown to be coupled to the exhaust manifold 48 upstream of a catalytic converter 70 (where the sensor 76 can correspond to various different sensors). For example, the sensor 76 can be any of a number of known sensors for providing an indication of the air / fuel ratio of the exhaust, such as a linear oxygen sensor, UEGO, bistable oxygen sensor, EGO, HEGO, or an HC or CO sensor. An emissions control device 72 is shown to be located downstream of the catalytic converter 70. The emissions control device 72 can be a three-way catalyst, a NOx trap, various other emissions control devices, or a combination thereof.

[0022] In some embodiments, each cylinder of the engine 10 may include a spark plug 92 for initiating combustion. In a selected operating mode, the ignition system 88 may provide an ignition spark to the combustion chamber 30 through the spark plug 92 in response to a spark advance signal SA from the controller 12. However, in some embodiments, the spark plug 92 may be omitted, such as in cases where the engine 10 may initiate combustion by auto-ignition or by injecting fuel (as in some diesel engines).

[0023] In some embodiments, each cylinder of the engine 10 may be configured to have one or more fuel injectors for supplying fuel thereto. As a non-limiting example, the fuel injector 66A is shown directly coupled to the cylinder 30 for directly injecting fuel therein that is proportional to the pulse width of a signal dfpw received from the controller 12 via the electronic driver 68. In this manner, the fuel injector 66A provides so-called direct injection of fuel (hereinafter also referred to as "DI") into the cylinder 30. For example, the fuel injector may be mounted in the side (as shown) of the combustion chamber or in the top of the combustion chamber (near the spark plug). Fuel may be delivered to the fuel injector 66A through a fuel system including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, alternatively or additionally, the combustion chamber 30 may include a fuel injector disposed in the intake manifold 44, which is configured to provide so-called port injection of fuel into the intake port upstream of the combustion chamber 30.

[0024] The controller 12 is shown as a microcomputer that includes a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values (shown as a read-only memory chip 106 in this particular example), a random access memory 108, a non-volatile memory 110, and a data bus. In addition to the signals previously discussed, the controller 12 is shown as receiving various signals from sensors coupled to the engine 10, including the following measurements: intake mass air flow (MAF) from a mass air flow sensor 100 coupled to the throttle 20; engine coolant temperature (ECT) from a temperature sensor 112 coupled to the coolant jacket 114; a surface ignition sensing signal (PIP) from a Hall effect sensor 118 coupled to the crankshaft 40; and throttle position TP from the throttle position sensor 20; an absolute manifold pressure signal MAP from the sensor 122; a knock indication from the knock sensor 182; and an absolute or relative ambient humidity indication from the sensor 180. The controller 12 generates an engine speed signal RPM in a conventional manner based on the signal PIP, and the manifold pressure signal MAP from the manifold pressure sensor provides an indication of the vacuum or pressure in the intake manifold. During stoichiometric operation, this sensor can give an indication of engine load. Additionally, this sensor together with the engine speed can provide an estimate of the charge (including air) introduced into the cylinders. In one example, the sensor 118, which also serves as an engine speed sensor, generates a predetermined number of equally spaced pulses during each revolution of the crankshaft.

[0025] In this particular example, the temperature Tcat1 of the catalytic converter 70 is provided by the temperature sensor 124, and the temperature Tcat2 of the emissions control device 72 is provided by the temperature sensor 126. In alternative embodiments, the temperatures Tcat1 and Tcat2 can be inferred from engine operation.

[0026] Continuing to refer to Figure 1, shows a variable camshaft timing (VCT) system 19. In this example, an overhead cam system is shown, but other methods may be used. Specifically, the camshaft 130 of the engine 10 is shown in communication with rocker arms 132 and 134 for actuating intake valves 52a, 52b and exhaust valves 54a, 54b. In the depicted example, the VCT system 19 is oil pressure actuated (OPA), where actuation of the camshaft phaser of the VCT system is enabled via oil pressure from an oil flow through a spool valve. In an alternative example, the VCT system 19 may be cam torque actuated (CTA), where actuation of the camshaft phaser is enabled via cam torque pulses. By adjusting a plurality of hydraulic valves to thereby direct hydraulic fluid (specifically engine oil) into cavities of the camshaft phaser, such as an advance chamber or a retard chamber, the valve timing can be changed, i.e., advanced or retarded. As described in further detail herein, the operation of the hydraulic control valve may be controlled by a corresponding control solenoid. Specifically, the engine controller may transmit a signal to the solenoid to move a spool valve (also referred to herein as an oil control valve, OCV) that regulates the oil flow through the phaser cavity. As used herein, advance and retard of cam timing refer to relative cam timing, since a fully advanced position may still provide a retarded intake valve opening with respect to top dead center, by way of example only. Refer to Figures 2 - 3 Shows an example of the operation of the OCV of the VCT system 19.

[0027] The camshaft 130 is hydraulically coupled to a housing 136. The housing 136 forms a toothed rim wheel having a plurality of teeth 138. In an exemplary embodiment, the housing 136 is mechanically coupled to the crankshaft 40 via a timing chain or belt (not shown). Thus, the housing 136 and the camshaft 130 rotate at substantially equal speeds with respect to each other and in synchronism with the crankshaft. In an alternative embodiment, such as in a four-stroke engine, the housing 136 and the crankshaft 40 may be mechanically coupled to the camshaft 130 such that the housing 136 and the crankshaft 40 may rotate in synchronism at different speeds with respect to the camshaft 130 (e.g., a ratio of 2:1, where the crankshaft rotates at twice the speed of the camshaft). In an alternative embodiment, the teeth 138 may be mechanically coupled to the camshaft 130. By manipulating the hydraulic coupler as described herein, the relative position of the camshaft 130 with respect to the crankshaft 40 can be changed by the hydraulic pressure in the retard chamber 142 and the advance chamber 144. By allowing high-pressure hydraulic fluid to enter the retard chamber 142, the relative relationship between the camshaft 130 and the crankshaft 40 is retarded. Thus, the intake valves 52a, 52b and the exhaust valves 54a, 54b open and close at a time later than normal with respect to the crankshaft 40. Similarly, by allowing high-pressure hydraulic fluid to enter the advance chamber 144, the relative relationship between the camshaft 130 and the crankshaft 40 is advanced. Thus, the intake valves 52a, 52b and the exhaust valves 54a, 54b open and close at a time earlier than normal with respect to the crankshaft 40.

[0028] While this example shows a system where intake and exhaust valve timing are both controlled, variable intake cam timing, variable exhaust cam timing, dual independent variable cam timing, dual equal variable cam timing, or other variable cam timing can be used. Additionally, variable valve lift can be used. Further, a cam profile switching system can be used to provide different cam profiles under different operating conditions. Still further, the valve train mechanism can be a roller finger follower, a direct acting mechanical piston, an electro-hydraulic, or other alternatives to a rocker arm.

[0029] Continuing the discussion of the variable cam timing system, the teeth 138 that rotate synchronously with the camshaft 130 allow the relative cam position to be measured via the cam timing sensor 150 that supplies the signal VCT to the controller 12. Teeth 1, 2, 3, and 4 can be used to measure cam timing and are equally spaced (e.g., in a V-8 dual bank engine, 90 degrees apart from each other), while tooth 5 can be used for cylinder identification. Additionally, the controller 12 sends control signals (LACT, RACT) to conventional solenoid valves (not shown) to control the flow of hydraulic fluid into the retard chamber 142, the advance chamber 144, or no flow into either.

[0030] The relative cam timing can be measured in various ways. Generally, the time or rotational angle between the rising edge of the PIP signal and the receipt of a signal from one of the multiple teeth 138 on the housing 136 gives a measurement of the relative cam timing. For a specific example of a V-8 engine, in the case of a wheel with two cylinder banks and five teeth, the cam timing of a particular bank is measured four times within each revolution, with an additional signal for cylinder identification.

[0031] As described above, Figure 1 only one cylinder of a multi-cylinder engine is shown, and each cylinder has its own intake valve / exhaust valve set, fuel injector, spark plug, etc.

[0032] Figure 2 is shown Figure 1Exemplary oil control valve (OCV) 200 of the VCT system 19. The OCV 200 is configured as a spool valve having a spool valve core 212 positioned within a housing 210 (and may be referred to herein as a spool valve). As shown, the spool valve core 212 is spring-loaded within the housing 210 via a spring 216. The engine controller adjusts the position of the spool valve by sending a PWM duty cycle command 202 to a drive circuit 219 that is placed between a battery 218 providing a power supply voltage and a solenoid 214. The drive circuit applies a PWM voltage to the solenoid 214, thereby driving a current through the solenoid 214, and the solenoid applies an external force to the spool valve, where the magnitude of the force is proportional to the magnitude of the current passing through the solenoid 214. Thus, the magnitude of the current and thus the force applied to the spool valve depends on the resistance of the solenoid, the power supply voltage, and the commanded PWM duty cycle. Therefore, the position of the spool valve is controlled by adjusting the PWM duty cycle, since the resistance of the solenoid and the power supply voltage are non-adjustable quantities.

[0033] By changing the position of the spool valve, oil is directed to or from a pressure chamber that drives a cam to rotate in a retard or advance direction, and thereby the rotational speed of the cam is proportional to the oil pressure in the chamber. For example, by adjusting the position of the spool valve, oil can be supplied to the advance chamber 220 and oil can be discharged from the retard chamber 222 via an oil supply 204 and an oil passage 232, respectively, to advance the valve timing. As another example, by adjusting the position of the spool valve, oil can be directed from the oil supply 204 into the retard chamber 222 and oil can be discharged from the advance chamber 220 via an oil passage 230 to retard the valve timing. Finally, by adjusting the position of the spool valve, the oil passages 230, 232 leading to the advance chamber and the retard chamber can be blocked so that the valve timing remains fixed. The duty cycle required to hold the spool valve in this position is referred to as the zero duty cycle.

[0034] Figure 3 The VCT phaser 300 is shown in the advance position. In one example, the VCT phaser 300 may include Figure 1 the VCT phaser 19. Figure 3 Also depicted is a solenoid-operated spool valve 309 coupled to the VCT phaser 300. As a non-limiting example, the spool valve 309 is shown positioned in the advance region of the spool valve. It should be understood that the spool valve can have an infinite number of intermediate positions, such as positions located in the advance region, zero region, and retard region of the spool valve (as described in detail below). The position of the spool valve can not only control the direction of VCT phaser movement, but also control the rate of VCT phaser movement depending on the discrete spool valve position.

[0035] Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft to improve engine performance or reduce emissions. Most of these variable camshaft timing (VCT) mechanisms use one or more "vane phasers" located on the engine camshaft (or multiple camshafts in a multi-camshaft engine), such as the VCT phaser 300. The VCT phaser 300 can have a rotor 305 with one or more vanes 304, which is mounted to the end of the camshaft 326 and is surrounded by a housing assembly 340 that has vane chambers into which the vanes fit. In an alternative example, the vanes 304 can be mounted to the housing assembly 340, and the chambers can be mounted in the rotor assembly 305. The outer circumference 301 of the housing forms a sprocket, pulley, or gear that receives driving force, typically from the crankshaft or from another camshaft in a multi-cam engine, via a chain, belt, or gear.

[0036] The VCT phaser 300 is depicted as a hydraulically actuated phaser. In this case, hydraulic pressure is applied to the camshaft via pressure chambers 302 and 303 to move the vanes 304. The advance chamber 302 and the retard chamber 303 are arranged to resist pressure pulses on the camshaft 326 and are alternately pressurized by hydraulic pressure pulses. Depending on the desired direction of movement, the spool valve 309 allows the vanes 304 in the phaser to move by permitting fluid flow from the advance chamber 302 to the retard chamber 303 or vice versa. For example, when the desired direction of movement is in the advance direction, the spool valve 309 allows the vanes to move by permitting fluid flow from the retard chamber to the advance chamber. In contrast, when the desired direction of movement is in the retard direction, the spool valve 309 allows the vanes to move by permitting fluid flow from the advance chamber to the retard chamber.

[0037] The housing assembly 340 of the VCT phaser 300 has an outer circumference 301 for receiving a driving force. The rotor assembly 305 is connected to the camshaft 326 and is coaxially positioned inside the housing assembly 340. The rotor assembly 305 has vanes 304 that divide the chamber formed between the housing assembly 340 and the rotor assembly 305 into an advance chamber 302 and a retard chamber 303. The vanes 304 are rotatable to shift the relative angular position of the housing assembly 340 and the rotor assembly 305. Additionally, there are a hydraulic braking circuit 333 and a locking pin circuit 323. The hydraulic braking circuit 333 and the locking pin circuit 323 are fluidly coupled such that they function substantially as one circuit as described above, but will be discussed separately for simplicity and to better distinguish their different functions. The hydraulic braking circuit 333 includes: a spring 331 loaded pilot valve 330; an advance braking line 328 that connects the advance chamber 302 to the pilot valve 330 and a common line 314; and a retard braking line 334 that connects the retard chamber 303 to the pilot valve 330 and the common line 314. The advance braking line 328 and the retard braking line 334 are a predetermined distance or length away from the vanes 304. The pilot valve 330 is located in the rotor assembly 305 and is fluidly connected to the locking pin circuit 323 and a supply line 319a through a connecting line 332. The locking pin circuit 323 includes a locking pin 325, a connecting line 332, a pilot valve 330, a supply line 319a, and an exhaust line 322.

[0038] The pilot valve can be actuated between two positions, namely a first position corresponding to a closed or off position and a second position corresponding to an open or on position. The pilot valve can be commanded to these positions by a spool valve. In the first position, the pilot valve is pressurized by the engine-generated oil pressure in line 332, which positions the pilot valve such that it blocks the flow of fluid through the pilot valve and the braking circuit 333 between the advance chamber and the retard chamber. In the second position, there is no engine-generated oil pressure in line 332. The absence of pressure in line 332 allows the spring 331 to position the pilot valve such that it permits the flow of fluid through the pilot valve and the common line between the braking line from the advance chamber and the braking line from the retard chamber, thereby causing the rotor assembly to move to and remain in a locked position.

[0039] The locking pin 325 is slidably received in a hole in the rotor assembly 305 and has an end that is biased by a spring 324 towards and fits into a recess 327 in the housing assembly 340. Alternatively, the locking pin 325 can be received in the housing assembly 340, and the spring 324 can be biased towards the recess 327 in the rotor assembly 305. The opening and closing of the hydraulic braking circuit 333 and the pressurization of the locking pin circuit 323 are controlled by the switching / movement of the spool valve 309.

[0040] The spool valve 309 includes a hole in the rotor 305 and a spool valve core 311 within a pilot in the camshaft 326, the spool valve core 311 having cylindrical shoulders 311a, 311b, and 311c that are slidably received within a sleeve 316. One end of the spool valve core contacts a spring 315, and the opposite end of the spool valve core contacts a pulse-width modulated variable force solenoid (NTS) 307. The solenoid 307 can also be linearly controlled by varying the duty cycle, current, voltage, or other suitable methods. Additionally, the opposite end of the spool valve core 311 can contact and be affected by a motor or other actuator.

[0041] The position of the spool valve 311 is affected by the spring 315 and the solenoid 307 controlled by the controller 12. Additional details regarding the control of the phaser are discussed below. The position of the spool valve 311 controls the movement of the phaser, including the direction and rate of movement. For example, the position of the spool valve determines whether the phaser moves towards the advanced position, towards the hold position, or towards the retarded position. Additionally, the position of the spool valve determines whether the lock pin circuit 323 and the hydraulic brake circuit 333 are open (energized) or closed (de-energized). In other words, the position of the spool valve 311 actively controls the pilot valve 330. The spool valve 309 has an advance mode, a retard mode, a zero mode, and a brake mode. These control modes can be directly associated with positioning regions. Thus, a specific region of the spool valve stroke can allow the spool valve to operate in the advance mode, the retard mode, the zero mode, and the brake mode. In the advance mode, the spool valve 311 moves to a position located in the spool valve advance region, whereby fluid is enabled to flow from the retard chamber 303 through the spool valve 311 to the advance chamber 302 while preventing fluid from leaving the advance chamber 302. Additionally, the brake circuit 333 remains de-energized or closed. In the retard mode, the spool valve 311 moves to a position located in the spool valve retard region, whereby fluid is enabled to flow from the advance chamber 302 through the spool valve 311 to the retard chamber 303 while preventing fluid from leaving the retard chamber 303. Additionally, the brake circuit 333 remains de-energized or closed. In the zero mode, the spool valve 311 moves to a position located in the spool valve zero region, whereby fluid is prevented from leaving each of the advance chamber 302 and the retard chamber 303 while the brake circuit 333 continues to remain de-energized or closed. In the brake mode, the spool valve moves to a position located in the brake region. In the brake mode, three functions occur simultaneously. The first function in the brake mode is that the spool valve 311 moves to a position where the spool valve shoulder 311b prevents fluid flow from the line 312 from entering any other line and the line 313 when between the spool valve shoulders 311a and 311b, thereby effectively removing the control of the phaser from the spool valve 309. The second function in the brake mode is the opening or energizing of the brake circuit 333. Thus, the brake circuit 333 has full control over the movement of the phase shifter to the advance position or the retard position until the vane 304 reaches the intermediate phase angle position. The third function in the brake mode is to bleed the lock pin circuit 323, thereby allowing the lock pin 325 to engage in the recess 327. The intermediate phase angle position (also referred to herein as the intermediate lock position and also as the lock position) is defined as the position where the vane 304 is located between the advance wall 302a and the retard wall 303a, the walls defining the chamber between the housing assembly 340 and the rotor assembly 305. The lock position can be any position between the advance wall 302a and the retard wall 303a and is determined by the position of the brake channels 328 and 334 relative to the vane 304.Specifically, the positions of the brake channels 328 and 334 relative to the vane 304 define positions where neither channel can be exposed to the propulsion chamber 302 and the delay chamber 303, such that when the pilot valve is in the second position and the phasing loop is disabled, the communication between the two chambers is completely disabled. Commanding the spool valve to the braking region can also be referred to as commanding a "hard lock" or "hard locking" of the cam phaser by referencing the engagement of the hardware component (locking pin) involved in the locking cam phaser in the intermediate locking position.

[0042] Based on the duty cycle of the pulse-width modulated variable force solenoid 307, the spool valve core 311 moves along its stroke to a corresponding position. In one example, when the duty cycle of the variable force solenoid 307 is approximately 30%, 50%, or 100%, the spool valve core 311 moves to positions corresponding to the delay mode, zero mode, and advance mode, respectively, and the pilot valve 330 is pressurized and moves from the second position to the first position, while the hydraulic brake circuit 333 closes and the locking pin 325 is pressurized and released. As another example, when the duty cycle of the variable force solenoid 307 is set to 0%, the spool valve core 311 moves to the braking mode, such that the pilot valve 330 is vented and moves to the second position, the hydraulic brake circuit 333 opens, and the locking pin 325 is vented and engages with the recess 327. By selecting 0% duty cycle as the limit position along the spool valve core stroke to open the hydraulic brake circuit 333, vent the pilot valve 330, vent the locking pin 325, and engage with the recess 327, in the event of a power or control loss, the phaser can default to the locked position, thereby improving the certainty of the cam phaser position. It should be noted that the duty cycle percentages listed above are provided as non-limiting examples, and in alternative embodiments, different duty cycles can be used to move the spool valve core of the spool valve between different spool valve core regions. For example, at 100% duty cycle, the hydraulic brake circuit 333 can alternatively be opened, the pilot valve 330 can be vented, and the locking pin 325 can be vented and engage with the recess 327. In this example, the braking region of the spool valve can be adjacent to the advance region rather than the delay region. In another example, the braking mode can be at 0% duty cycle, and duty cycles of approximately 30%, 50%, and 100% can cause the spool valve core 311 to move to positions corresponding to the advance mode, zero mode, and delay mode. Also in this example, the advance region of the spool valve is adjacent to the braking region.

[0043] During the selected condition, the controller can map one or more regions of the spool valve spool by varying the duty cycle of the command to the spool valve and correlating the corresponding change with a change in phaser position. For example, the transition region between the braking region and the retard region of the spool valve spool (also referred to herein as the "forbidden zone") can be mapped by correlating the movement of the spool valve out of the braking region into the retard region with the movement of the phaser from the intermediate locked position toward the retard position.

[0044] Figure 3 The phaser 300 is shown moving toward the advance position. To move the phaser toward the advance position, the duty cycle of the spool valve is increased to greater than 50%, and optionally up to 100%. Accordingly, the force exerted by the solenoid 307 on the spool valve spool 311 increases, and the spool valve spool 311 moves to the right, toward the advance region, and operates in the advance mode until the force of the spring 315 balances the force of the solenoid 307. In the illustrated advance mode, the spool valve shoulder 311a blocks the line 312, while the lines 313 and 314 are open. In this case, the oil pressure pulse pressurizes the retard chamber 303, causing fluid to move from the retard chamber 303 into the advance chamber 302, thereby causing the vane 304 to move in the direction shown by the arrow 345. The hydraulic fluid exits the retard chamber 303 through the line 313 to the spool valve 309, between the spool valve shoulders 311a and 311b, and recirculates back to the central line 314 and the line 312 leading to the advance chamber 302. The pilot valve remains in the first position, blocking the brake lines 328 and 334.

[0045] In an alternative example, to move the phaser toward the retard position, the duty cycle of the spool valve is decreased to less than 50%, and optionally down to 30%. Accordingly, the force exerted by the solenoid 307 on the spool valve spool 311 decreases, and the spool valve spool 311 moves to the left, toward the retard region, and operates in the retard mode until the force of the spring 315 balances the force of the solenoid 307. In the retard mode, the spool valve shoulder 311b blocks the line 313, while the lines 312 and 314 are open. In this case, the oil pressure pulse pressurizes the advance chamber 302, causing fluid to move from the advance chamber 302 into the retard chamber 303, and thereby causing the vane 304 to move in a direction opposite to the direction shown by the arrow 345. The hydraulic fluid exits the advance chamber 302 through the line 312 to the spool valve 309, between the spool valve shoulders 311a and 311b, and recirculates back to the central line 314 and the line 313 leading to the retard chamber 303. The pilot valve remains in the first position, blocking the brake lines 328 and 334.

[0046] In this way, Figures 1 - 3The components implement an engine system that includes: a variable cam timing device including a cam, a hydraulically actuated phaser, a camshaft, a spool valve, and a solenoid; a cam position sensor coupled to the cam; a battery; an engine coolant temperature sensor; an intake charge temperature sensor; a mass air flow sensor; and a controller. The controller may include computer-readable instructions stored on a non-transitory memory for the following operations: in response to at least one diagnostic flag set related to an engine oil temperature estimate, applying an excitation pulse to the solenoid to move the spool valve, the duty cycle of the excitation pulse being adjusted to move the cam beyond a hard-stop region; measuring, via the cam position sensor, the angular velocity of the camshaft after the application; estimating a zero duty cycle of the spool valve based on the applied duty cycle; and estimating the engine oil temperature based on a mapping relationship between the estimated zero duty cycle and the measured angular velocity. The controller may include additional instructions for the following operations: limiting each of an upper engine speed threshold and a lower engine speed threshold based on the estimated engine oil temperature, the upper engine speed threshold decreasing and the lower engine speed threshold increasing when the estimated engine oil temperature exceeds a threshold temperature. At least one diagnostic flag related to the engine oil temperature estimate may be set in response to one of the following: degradation of the engine coolant temperature sensor, degradation of the intake charge temperature sensor, degradation of the mass air flow sensor, corruption of the memory, and an engine hot start condition. In one example, the mapping relationship is stored in the memory and uses the last estimated engine oil temperature, the estimated zero duty cycle, and the measured angular velocity as inputs. Additionally, the cam may be one of an intake cam and an exhaust cam, and the controller includes additional instructions for the following operations: selecting the intake cam when the engine controller provides an intake cam switching command; and selecting the exhaust cam when the controller provides an exhaust cam switching instruction. The zero duty cycle may include the amount of duty cycle that results in a zero angular velocity of the VCT device outside of a hard stop or pin locked position. Additionally, the controller may include additional instructions for the following operation: in response to a diagnostic flag related to the engine oil temperature estimate not being set, estimating the engine oil temperature based on an output of one or more of the engine coolant temperature sensor, the intake charge temperature sensor, and the mass air flow sensor.

[0047] Now turning to Figure 4 , an exemplary routine 400 for estimating EOT via a mapping relationship between a commanded solenoid duty cycle and an engine oil temperature is described. Under an EOT estimation entry condition when the amount of EOT measured or inferred via existing engine sensors may be unreliable, routine 400 may be performed by an engine controller such as Figures 1 - 3executed by the controller 12).

[0048] At 402, the routine includes estimating and / or measuring engine operating conditions. For example, these engine operating conditions can include: determining whether the engine is off or running, and measuring parameters such as engine speed, engine temperature, ambient conditions (ambient temperature, pressure, humidity, etc.), torque demand, manifold pressure, manifold air flow, exhaust catalyst condition, oil temperature, oil pressure, hot start time (time elapsed since the engine was last turned off), etc.

[0049] At 404, it can be determined whether the EOT estimation condition has been met. In one example, the EOT estimation can be triggered in response to engine start. In another example, the EOT estimation can be performed when the engine is running, such as when a threshold time (or duration) of vehicle travel has elapsed since the last EOT estimation. Thus, when the engine is running, or immediately before (or at) engine start, EOT estimation may be required for (actual) torque estimation, boost control, determining variable camshaft (or valve) timing, scheduling and estimating crankcase forced ventilation, oil life monitoring, powertrain limiting, and powertrain protection. For example, in response to the engine controller needing to calculate the total friction and pumping torque losses of the engine, the EOT estimation can be triggered, and then the total friction and pumping torque losses can be used to calculate the total crankshaft torque loss, and thereafter the engine torque output can be calculated. As another example, the EOT estimation can be triggered after a threshold duration of engine operation, so as to be used for powertrain limiting and protection to reduce overheating or underheating of the powertrain.

[0050] If the EOT estimation condition is not met, then at 406, the engine controller does not measure or infer the EOT. For example, if the engine is off, the engine remains off. Similarly, if the engine is running, the engine continues to run without updating the last EOT estimation value stored in the memory of the engine controller. Additionally, the engine controller continues to adjust the engine actuators based on the last estimated EOT stored in the controller's memory. For example, torque output and powertrain limiting can be performed based on the last estimated EOT.

[0051] If the EOT estimation conditions are met, at 408, the controller monitors various fault flags generated by relevant features of the engine system, where the fault flags indicate whether the (last) measured / inferred EOT value is reliable. For example, the controller can retrieve all diagnostic codes and flags that have been set and determine whether any of them are related to EOT estimation. In this way, the EOT can be directly measured via an EOT sensor connected to the engine oil pan. However, such EOT sensors can be expensive and prone to deterioration. Therefore, in some engine systems, the EOT can be indirectly inferred via one or more other engine sensors, such as an intake charge temperature (ACT) sensor and / or an engine coolant temperature (ECT) sensor and / or an intake mass air flow (MAF) sensor. Among them, the EOT can be inferred based on the output of one or more of the following: the ACT sensor, the ECT sensor, the MAF sensor, and the last EOT estimated value stored in the controller's memory (such as in the KAM).

[0052] Estimating the EOT based on one or more of the ACT sensor, the ECT sensor, and the MAF sensor includes.

[0053] As an example, the retrieved fault flags can include a KAM error fault flag, which indicates that the non-volatile memory of the controller (e.g., the KAM) has been damaged and thus any variables stored in the KAM are unreliable. In some other examples, the fault flags can indicate a fault condition in the engine's electronic control module (which is not limited to non-failing memory).

[0054] As another example, the fault flags can include deterioration of a sensor for directly or indirectly measuring the engine oil temperature. For example, an ACT sensor fault flag can be retrieved, which indicates that the charge temperature (ACT) sensor connected to the engine intake passage has deteriorated, the output of the ACT sensor has been damaged, or the engine operating conditions are such that the EOT estimated based on the output of the ACT sensor is unreliable. The ACT can be used as an input to a thermal model for inferring the EOT, where the ACT serves as a substitute for the ambient temperature. If the ACT sensor deteriorates or fails, or the data transmission between the ACT sensor and the PCM is impaired (such as due to KAM damage), the ACT value may be unreliable. In one example, the engine operating conditions can be such that the output of the ACT sensor is reliable for ACT estimation but unreliable for EOT estimation.

[0055] As another example, a fault flag can include an ECT sensor fault flag that indicates that the engine coolant temperature (ECT) sensor coupled to the engine coolant system has deteriorated, the output of the ECT sensor has been corrupted, or the engine operating conditions are such that the EOT estimated based on the output of the ECT sensor is unreliable. In one example, the engine operating conditions can be such that the output of the ECT sensor is reliable for ECT estimation (such as for estimating engine temperature) but unreliable for EOT estimation. As an example, the output of the ECT sensor may not be reliable during a hot engine start condition but may be reliable during a cold engine start condition. For example, the ECT value estimated during vehicle start-up may not be transmitted to the controller quickly enough, and thus, the EOT inference logic can be initialized with a default ECT value (such as a default value of 60 degrees Celsius). While this does not affect a cold engine start, during a hot start where the actual ECT value is significantly higher than the default value (e.g., the actual ECT value is at or above 190 degrees Celsius), the estimated EOT may deviate from its true value by approximately 50% because the initial / default value of the ECT is used to initialize the inferred EOT thermal model (instead of the actual ECT value).

[0056] As another example, a fault flag can include a MAF sensor fault flag that indicates that the mass air flow (MAF) sensor coupled to the engine intake has deteriorated, the output of the MAF sensor has been corrupted, or the engine operating conditions are such that the EOT estimated based on the output of the MAF sensor is unreliable. In one example, the engine operating conditions can be such that the output of the MAF sensor is reliable for MAF estimation (such as for estimating intake charge or flow) but unreliable for EOT estimation.

[0057] In yet another example where the vehicle is equipped with an EOT sensor, a fault flag can include an EOT sensor fault flag that indicates that the EOT sensor coupled to the engine oil pan has deteriorated or the output of the EOT sensor has been corrupted.

[0058] In one example, during engine startup, the engine controller may use a combination of the hot start time, the measured engine coolant temperature, and the last EOT sample before engine shutdown stored in the KAM to calculate an initial estimate of the EOT inference logic. If the last EOT value or the hot start time value is corrupted due to a KAM error, if the ECT sensor deteriorates, or if the engine coolant is significantly warmer than the engine oil (as may occur during a hot engine startup), the initial EOT estimate may be incorrect. This can result in an inaccurate inferred EOT value during the first few minutes of vehicle operation. A KAM error can also have the same effect. For example, if the battery is disconnected from the PCM such that the KAM is reset, the hot start timer will be reset, and the initialization of the inferred EOT depending on the hot start time will be inaccurate. In still some other examples, at 410, it may be determined whether there is an engine hot start condition.

[0059] If no EOT fault is detected, such as a condition that may occur when no fault flag related to the EOT estimate is retrieved (or if the engine hot start condition is not confirmed), then at 412, the routine includes estimating or measuring the EOT via any one or more default EOT estimation methods. For example, the EOT can be directly measured based on the output of the EOT sensor. As another example, the EOT can be inferred from the measured ACT or the measured ECT or the measured MAF. The thermal model for the EOT inference logic can be summarized by the following equation:

[0060] EOT = EOT_ss + k_ect * (ect - 200) + k_amb * (act - 100) (1)

[0061] where EOT_ss is the adjusted steady-state value of the EOT calculated based on the engine speed and engine load (via a 2-D lookup table). The EOT is then low-pass filtered to obtain the final value EOT_filt to be used by the powertrain characteristics. The time constant of this low-pass filter also depends on the engine speed. Thus, in addition to the ECT and ACT during normal operation, the EOT inference calculation depends on the engine speed in multiple ways.

[0062] Then, at 414, the controller may adjust one or more engine torque actuators based on the estimated EOT. For example, the controller may compare the estimated EOT to an upper threshold and a lower threshold, and based on the comparison, the controller may select an engine torque actuator and the amount and direction of adjustment of the selected torque actuator. As an example, in response to the estimated EOT being higher than the upper threshold, engine output may be limited, boost pressure may be limited, and / or the engine torque provided in response to an operator torque demand may be limited. As another example, engine idle speed may be limited to reduce engine overheating and for engine oil temperature low protection. As yet another example, if the EOT is too low (e.g., below the lower threshold) or too high (e.g., above the upper threshold), the upper engine speed threshold and the lower engine speed threshold of the allowable engine speed range may be limited (e.g., by reducing the upper engine speed threshold and / or increasing the lower engine speed threshold) to protect the engine from extreme temperature conditions.

[0063] Returning to 410, if an EOT fault is detected, such as when a flag or diagnostic code corresponding to the EOT estimate is set (or if a hot start condition is confirmed), it may be inferred that the relevant memory and / or sensor signals in the calculation of the EOT are corrupted and unreliable. During such conditions, an alternative method may be used to infer the EOT in order to enable engine torque and powertrain temperature control. As detailed hereinbelow, the inventors have recognized that during such conditions, the temperature dependence of the oil control valve (OCV) of a variable camshaft timing (VCT) system (which is configured as a solenoid valve) can be utilized to use the OCV as an EOT sensor.

[0064] It should be understood that while the described routine illustrates EOT estimation via using the OCV of the VCT system as a sensor, in other examples, the EOT estimation method may be used as the primary tool for estimating engine oil temperature. Alternatively, the method may be used in combination with existing tools as an auxiliary method to serve as an additional EOT source, which may be used in cases where the EOT value provided by a sensor is unreliable, or where the EOT value provided by an existing tool may be unreliable.

[0065] If any EOT fault is detected, at 416, the method includes applying an excitation characteristic curve (such as an excitation signal or excitation pulse in the form of a cam position command, voltage, current, or duty cycle of pulse width modulation) to the intake or exhaust cam of the VCT device. Specifically, an excitation signal is applied to a variable camshaft timing solenoid valve coupled to the intake or exhaust cam. The applied excitation characteristic curve or pulse can include amplitude, frequency, and application duration. The controller can use a battery coupled to the engine or driveline (such as a battery of an alternator coupled to the engine, or a battery of an electric motor coupled to the engine) as a power source to apply a pulse width modulation (PWM) duty cycle to the solenoid of the oil control valve (spool valve) of the (VCT device), and the PWM duty cycle drives the current through the solenoid to change the position of the spool valve. The PWM duty cycle can be selected such that a zero duty cycle of the OCV can be determined. Specifically, the applied duty cycle moves one of the intake and exhaust cams beyond a hard stop (or pin lock) position. As used herein, the zero duty cycle refers to the amount of duty cycle that results in a zero angular velocity of the VCT device beyond the hard stop or pin lock position. For example, a cam position reference command can be provided to a closed-loop VCT controller such that the cam position is maintained at a predetermined set point. Then, the VCT controller can determine the zero duty cycle based on the PWM duty cycle applied to the solenoid in order to maintain the cam position at the set point position. In this way, applying the excitation signal can include applying a reference angular position command via a closed-loop controller to change the angular velocity of the camshaft of the VCT device. Then, the controller can measure the camshaft angular velocity and the duty cycle (or voltage or current of the excitation signal) applied to the solenoid via the closed-loop controller. In another example, the PWM duty cycle can be directly adjusted without using a closed-loop controller in order to determine the zero duty cycle. A duty cycle pulse with an incremental increase value can be applied to the solenoid valve control valve over a fixed time period, and the measured cam position signal can be monitored to determine the zero duty cycle. Further, applying the excitation signal can include applying an incrementally increasing duty cycle, voltage, or current to the solenoid of the spool valve, and measuring the camshaft angular velocity after each incremental increase.

[0066] In one example, the applied excitation characteristic curve (which can be applied as a duty cycle, voltage, or current) can depend on the particular method or parameter intended to be used to infer EOT. For example, for a zero-duty-cycle-based method, the excitation characteristic curve can be a step reference command, as detailed in the example of reference Figure 5 (at 504). The excitation characteristic curve can be a ramp command with a specific commanded cam speed. Among them, the zero-duty-cycle method can be a limitation or special case of the following situation: where a particular ramp command has a commanded cam speed of 0 degrees / second.

[0067] In one example, the controller can select between an intake cam and an exhaust cam to apply an excitation profile based on the ability to apply the excitation profile in a non-invasive manner. That is, instead of applying an excitation pulse (which disturbs the VCT system for a short period of time), the VCT command profile inherent to normal engine operation is used. In this case, if the engine requests intake cam movement, the controller can select the intake cam, and if the engine controller requests exhaust cam movement, the exhaust cam is selected.

[0068] The inventors have recognized herein that there is a relationship or defined mapping between the PWM duty cycle (DC) applied to the solenoid of the spool valve and the angular velocity of the cam. Additionally, the mapping can be characterized by applying a known PWM duty cycle signal and measuring the resulting cam angular velocity, assuming a constant solenoid resistance and a known battery voltage. Specifically, the PWM duty cycle changes the position of the spool valve, which in turn adjusts the oil pressure in the pressure chamber of the OCV, thereby driving the angular velocity of the cam relative to the camshaft. Then, the angular velocity of the cam can be measured by using a cam position sensor. Since the solenoid resistance varies with the solenoid temperature, the solenoid resistance is not a constant term but varies with the solenoid temperature. Additionally, since the engine oil is close to the solenoid, the solenoid resistance is largely driven by the engine oil temperature near the OCV. Thus, through the mapping relationship, the EOT can be reliably inferred without the need for any default sensors (such as an EOT sensor, an ECT sensor, or an ACT sensor). Specifically, after applying an excitation signal to the solenoid valve of the VCT device, the EOT can be estimated according to the mapping relationship stored in the non-volatile memory, which associates the camshaft solenoid valve duty cycle and the camshaft angular velocity of the VCT device with the engine oil temperature. The mapping relationship also includes mapping the relationship between the EOT and the zero duty cycle of the OCV.

[0069] At 417, the method includes determining the cam position and / or cam speed when applying the PWM duty cycle. For example, the controller can reference the output of a cam position sensor coupled to the excited intake cam or exhaust cam to determine the position change of the cam from the initial position before applying the excitation PWM duty cycle to the final position of the cam after applying the excitation pulse. In another example, the output of the cam position sensor can be used to determine the direction of cam movement and the rate of change of the cam position (such as the rate of change of the cam position towards the retarded position or the advanced position). Further still, the cam position sensor can be used to measure the camshaft angular velocity.

[0070] At 418, the method includes determining a zero duty cycle corresponding to the OCV based on the PWM duty cycle applied to the solenoid. The zero duty cycle is the duty cycle that needs to be applied to the solenoid to hold the cam position at a constant position (excluding the pin lock positions (such as 0 degrees) or intermediate lock positions where the locking mechanism holds the cam position constant without a duty cycle input). The zero duty cycle determination can be performed by one of a variety of methods. For example, at 420, the zero duty cycle is determined via low-pass filtering of the applied PWM duty cycle. As another example, at 422, the zero duty cycle is determined via Kalman filtering of the PWM duty cycle (also referred to herein as recursive least squares). Generally, the controller calculates the zero duty cycle, or the duty cycle required to achieve the commanded rate of change of the cam position.

[0071] At 420, determining the zero duty cycle via low-pass filtering of the PWM duty cycle includes applying a stepped cam position reference command to the cam such that the cam is commanded to a position different from the hard stop position or the intermediate lock position (such as a 10 - 30 degree advanced position). The cam position and / or cam speed can be monitored during movement, such as via a cam position sensor coupled to the cam, and when the cam position and / or cam speed reach a threshold, a low-pass filter acting on the PWM duty cycle can be activated. Alternatively, a timer can be used to activate the low-pass filter. However, if a timer is started, the timer threshold can be conservatively selected to ensure that the cam is in a stationary position when the filter is activated. As a non-limiting example, the low-pass filter can be an average filter, a moving average (FIR) filter, or an IIR filter. The low-pass filter can filter out the high-frequency components of the signal and can have a unity DC gain. Other types of filters can also be used. After a predetermined amount of filtering time that may depend on the type and time constant of the selected filter (e.g., if an IIR filter is used, the filtering time can be as low as 100 ms, or if an FIR filter is used, the filtering time can be 1 second or higher), the output of the low-pass filter can be retrieved and used as an input to estimate the zero duty cycle value (DC_null value), which is inserted into a model, look-up table, or algorithm to infer the estimated EOT (EOT_est), as described in detail below.

[0072] At 422, determining the zero duty cycle via a Kalman filter includes applying a recursive least squares (RLS) estimate to fit the PWM duty cycle and cam speed measurements via a look-up table operator, and estimating the DC_null value via a look-up table. An RLS estimator can be used to obtain a 1-D look-up table that maps cam speed to PWM duty cycle. The look-up table can have at least two input breakpoints, and the input domain can cover zero cam speed. As a non-limiting example, the input breakpoints can be selected as [-23 0 10.5], in units of [deg / s], such that the input domain covers zero cam speed. In this case, the RLS estimator can use a stepped cam position command similar to that in the low-pass filtering method of (420) to estimate the look-up table entries, and the entry corresponding to zero cam speed can provide an accurate estimate of the DC_null value, which can be used to infer EOT_est.

[0073] At 424, the method includes using the mapping between the determined zero duty cycle and EOT to estimate EOT. Wherein, passing the calculated zero duty cycle through a mapping function to estimate EOT, and the mapping function can be a look-up table-based mapping or another functional relationship. As described below, the mapping between the zero duty cycle and EOT can be pre-calibrated. The mapping can be a pre-calibrated mapping that uses the estimated zero duty cycle as an input and produces the estimated EOT as an output. In one example, the mapping relationship between the camshaft duty cycle, camshaft angular velocity, and engine oil temperature over the entire operating range of the engine can be obtained from a pre-calibration procedure performed in a test vehicle or test bench environment where accurate engine oil temperature measurements are available, and the mapping relationship is presented in the form of a query table or another mathematical relationship.

[0074] As previously mentioned, the two independent variables that control the angular velocity of the cam are the PWM voltage applied to the solenoid of the oil control valve (OCV), and the solenoid resistance. However, since the battery voltage is known and the solenoid resistance is mainly driven by EOT, we can consider the duty cycle (DC) of the PWM and EOT as independent variables and form a mapping relationship to characterize the actuator according to Equation (1):

[0075] CAM SPEED = F(EOT,DC). (1)

[0076] Next, characterize the inverse model with respect to EOT, since the angular velocity of the cam is measurable via a cam position sensor and the PWM DC applied to the solenoid is known. The inverse model can be used to calculate EOT using the applied PWM DC and the measured angular cam speed according to Equation (2) below:

[0077] EOT est = F -1 (CAM SPEED,DC) (2)

[0078] where EOT est is the estimated EOT, and F -1 is the inverse model applied relative to the EOT.

[0079] In one example, to simplify the calculations and make them more practical, the EOT estimation can be performed at a predetermined cam speed. For example, when the cam speed is equal to zero, the estimation can be reduced to Equation (3) below:

[0080]

[0081] where and DC null is the zero duty cycle (i.e., the duty cycle that produces zero camshaft angular velocity). It should be understood that although the Figure 4 method maps the EOT to the zero duty cycle and zero cam speed based on the mapping relationship, in alternative examples, for any cam speed value within the cam position sensor bandwidth, the mapping can be similarly adapted (by adapting the relevant Equations (1)–(3)). In other words, Equation (3) can be generalized to include cam speeds other than zero within the cam position sensor bandwidth.

[0082] Figure 5 The determination of the zero duty cycle is shown at graph 500. Specifically, curves 502 - 508 of graph 500 depict the determination of the zero duty cycle via the Figure 4 low-pass filtering and Kalman methods discussed at (422 and 424) in order to obtain the DC_null value on a 2014 Ford KA test vehicle with a 1.5L PFI Sigma engine operating at an engine speed of 1500 rpm. The duty cycle applied to the intake cam during the excitation pulse is shown at curve 502. The corresponding change in the cam angle is shown at curve 504. The zero duty cycle estimate based on the applied duty cycle and the measured cam angle change is shown at curve 506. The EOT inferred via the defined mapping based on the estimated zero duty cycle is shown at curve 508.

[0083] In the example of the graph 500, referring to curves 502 - 508, near t = 17 s, a - 10 - degree step reference command is applied to the intake cam, and near t = 25 s, the low - pass filter and the RLS algorithm are enabled. A simple moving average filter is used for the low - pass filter algorithm. For the RLS algorithm, a forgetting factor of 0.995 is used, and the initial covariance matrix is 10 * I, where I is a 3×3 identity matrix. Five seconds after the step reference command is applied, both algorithms are enabled and the estimated values of the DC_null values from each algorithm are retrieved. In the depicted example, the DC_null values estimated via the low - pass filtering method and the Kalman filtering method converge to 0.363. The mapped EOT estimate is approximately 91 degrees Fahrenheit.

[0084] Focusing on the zero - duty - cycle method without loss of generality, from Equation (3), it can be derived that with real - time knowledge of using the inverse model and zero - duty - cycle DC null , the controller can calculate the EOT at any time during engine operation. est .

[0085] The controller can model the inverse function of the map via various methods. Regardless of the method applied, it can be modeled as a look - up table stored in the controller's memory (such as in the KAM) to simplify its implementation into the embedded hardware.

[0086] Various methods for mapping the inverse function include a first method that relies on an existing calibration map in the controller's memory. For example, the first mapping relationship "fnvct_rate2dc_base" can be an existing calibration map in the controller's memory that maps EOT and cam angular velocity (or "rate") into PWM duty cycle, where the cam rate is the same as the cam speed. This map may have been used to determine the cam response time and to infer whether the cam is operating normally or deteriorating during diagnostic routines. Additionally, this map is also used as a characteristic table for the feed - forward VCT controller to calculate the feed - forward duty cycle. Among them, in response to a reference cam position command, the VCT control characteristic uses this map to calculate the feed - forward VCT duty cycle. The inputs to this table are the requested VCT offset rate (or cam speed) and EOT calculated based on the difference between the actual cam position and the reference cam position; the output is the feed - forward duty cycle applied to the solenoid.

[0087] This map can also be used to obtain Assuming that fnvct_rate2dc_base is accurately calibrated and represents the actual actuator response, the entries of this map can be used to construct a model that accurately represents the EOT relationship depicted in Equation (3).

[0088] Briefly turn to Figure 6 which shows a non - limiting example of using an existing mapping to build a model. Consider the smaller - scale "fnvct_rate2dc_base" look - up table 600 depicted in Figure 6 which is assumed to have been calibrated for optimizing VCT control features. The DC entries in the column associated with the 0 cam rate (highlighted by the dashed box 602) can be used to build a query table as shown in Table 620, which can be used for EOT estimation in the range of [120, 180] degrees Fahrenheit. As an example, during vehicle operation, if the DC null is estimated to be 0.41, then according to Table 620, the estimated EOT is inferred to be 126 degrees Fahrenheit by interpolating between adjacent table entries as indicated by well - known look - up table algebra.

[0089] One advantage of modeling the inverse function using an existing mapping is that it can be computationally less intensive and thus easier to implement. Since this method uses the calibration work that has already been done to build the reference mapping (here "fnvct_rate2dc_base"), this method requires little calibration work. However, it relies on the assumption that the calibration of fnvct_rate2dc_base accurately represents the OCV, and further, it relies on the more stringent assumption that fnvct_rate2dc_base originally exists in the powertrain strategy. There may be situations or cases where the reference mapping is unavailable, inaccessible, or unreliable.

[0090] Now discuss an alternative data - driven method for building a look - up table model without using fnvct_rate2dc_base from the VCT features. The data - driven method can be applied during the calibration phase of the vehicle (when calibrating other vehicle software). Additionally or optionally, the alternative method can be extended to adaptively (e.g., in real - time) build the look - up table during vehicle operation to correct for initial calibration errors and changes over time. The only required assumption for the data - driven method is that the EOT is accurately measured or inferred during the acquisition of the data that will be used to build the . That is, it can be first confirmed that during the calibration of the , no failure modes that corrupt the EOT measurement (such as the EOT fault detected at 410) are applied. For example, it can be confirmed that ECT sensor faults, ACT sensor faults, and KAM controller faults do not corrupt the EOT measurement during calibration. If this assumption holds, then the null can be performed by selecting one or more DC Construction. Based on an optimization routine that provides the best lookup table fit to the collected data points, one or more DC null breakpoints and the lookup table entries corresponding to these breakpoints can be selected, where the data points include the measured EOT values provided by the above EOT measurement / inference methods, and the DC null values that can be determined by using the low-pass filtering method or the RLS method as described above.

[0091] Reference Figure 10 Graph 1000 shows an example of selecting one or more breakpoints.

[0092] As an example, if 0.363 is selected as the DC null breakpoint, then the characteristic curve depicted in Figure 5 can be used to fill the lookup table entry corresponding to 0.363, which will result in the entry being selected as 91 degrees Celsius, as both the low-pass filtering method and the RLS method indicate. Similar characteristic curves can be applied at different EOTs to fill the lookup table that covers a wide range of EOTs, and the lookup table can later be used in Equation (3) for EOT estimation. It should be understood that the input to this table is zero duty cycle (such as zero duty cycle breakpoints), and the output is the estimated EOT.

[0093] Reference Figure 6 , at Table 630 shows the lookup table model obtained by applying EOT breakpoints. The breakpoints are selected as [100 120 140 160 175 185 190 195] degrees Fahrenheit. The vehicle is idled at a crank speed of 1500 rpm for about 30 minutes, and a step command excitation characteristic curve similar to the Figure 5 shown is applied near the breakpoint temperature to obtain the corresponding DC_null entries.

[0094] Return Figure 4, at 426, the controller may adjust one or more engine torque actuators based on the estimated EOT. For example, the controller may compare the estimated EOT with an upper threshold and a lower threshold, and based on the comparison, the controller may select an engine torque actuator and the amount and direction of adjustment of the selected torque actuator. As an example, in response to the estimated EOT being higher than the upper threshold, engine output may be limited, boost pressure may be limited, and / or engine torque provided in response to an operator torque demand may be limited. As another example, engine idle speed may be limited to reduce engine overheating. As yet another example, if the EOT is too low or too high, the upper engine speed threshold and the lower engine speed threshold of the allowable engine speed range may be limited (e.g., by reducing the upper engine speed threshold and / or increasing the lower engine speed threshold) to protect the engine from extreme temperature conditions.

[0095] Next, at 428, it may be determined whether a one-time estimate of the EOT is required, or whether continuous EOT monitoring is required. This may be based on an EOT fault that triggers an alternative EOT estimate, and on engine parameters controlled based on the EOT estimate. As an example, a one-time estimate of the EOT may be required to provide robustness against potential signal loss due to a KAM error (e.g., KAM corruption), or due to low reliability of a functional ECT sensor during a hot start condition. In this case, the controller may execute the Figure 4 method only once after a hot start of the engine, where there may be a significant temperature difference between the ECT temperature and the EOT temperature. As another example, continuous estimation of the EOT may be required to provide robustness against potential sensor signal loss during vehicle operation due to a permanent sensor error (such as due to an ACT sensor or ACT sensor degradation, or KAM degradation). In this case, as long as the corresponding sensor error (or EOT fault flag) is set, the controller may continuously or repeatedly execute the method.

[0096] If a one-time estimate is required, at 430, the controller may update the EOT estimate value and then the routine ends. If an EOT estimate is required and an EOT fault is determined, only another iteration of the routine may be triggered, as discussed previously at 404 and 410.

[0097] If continuous estimation is required, the controller may continuously execute the routine and keep updating the EOT estimate value after each iteration of the routine.

[0098] Since the excitation profile applied to the intake or exhaust cam may interfere with VCT operation (even for a short period of time), at 432, when in continuous mode, the controller may pause the program and start a timer. By starting the timer, the routine can be paused for only a predetermined period of time. The length of this pause can be defined by a predetermined time threshold. At 434, it can be determined whether the predetermined time threshold has elapsed since the timer was started. If not, the controller can wait for the predetermined time threshold to elapse. Otherwise, if the predetermined time threshold has elapsed on the timer, the routine returns to 408 and begins monitoring the relevant fault flag indicating an EOT fault. Then the program iterates repeatedly.

[0099] In this way, a more reliable EOT estimate can be provided, especially when a selected error code is set. Specifically, since the EOT estimate determined based on the mapping relationship between the solenoid duty cycle and the cam movement does not depend on sensors (such as the ECT sensor, MAF sensor, ACT sensor) or any variables stored in the KAM, this method may be more robust against sensor errors, KAM corruption, and unreliability during hot engine start conditions.

[0100] It should be understood that although Figure 4 the method depicted estimates EOT via the mapping relationship between the VCT solenoid valve duty cycle, VCT angular velocity, and engine oil temperature in response to a fault flag (indicating a fault at the EOT sensor, MAF sensor, ECT sensor, ACT sensor, and / or KAM), this is not meant to be limiting. In additional examples, EOT can be estimated via the mapping relationship in response to a fault in any engine component typically used in EOT estimation. Additionally, the EOT estimate via the mapping relationship can be used as the primary or default method for EOT estimation, thereby reducing the dependence on sensors (e.g., reducing the need for an EOT sensor). In still other examples, the EOT estimate via the mapping relationship can be used to confirm a sensor-based EOT estimate, or vice versa, where the mapping relationship is the default method for EOT estimation, a sensor-based EOT estimate can be used to confirm the mapping-based method. In yet other examples, both a sensor-based EOT estimate and a mapping-based estimate can be used, with the weight of each method varying based on engine operating conditions. For example, the weight of the sensor-based method can be increased during cold engine start, while the weight of the mapping-based method can be increased during hot engine start.

[0101] Figure 7EOT estimation during a cold engine start is shown at graph 700. Specifically, curves 702-708 of graph 700 depict zero duty cycle determination via Kalman filtering, which is used to obtain a DC_null value on a test vehicle having a 1.5L PFI engine. The duty cycle applied to the intake cam during the excitation pulse is shown at curve 702 (the actual duty cycle depicted at line 710 is compared to the reference command depicted at line 712). The corresponding change in cam angle is shown at curve 704. The zero duty cycle estimate based on the applied duty cycle and the measured cam angle change is shown at curve 706. The EOT inferred via a defined map based on the estimated zero duty cycle is shown at curve 708.

[0102] In the example of graph 700, the vehicle is cold started and operated at idle speed for approximately 10 minutes until the EOT reaches approximately 125 degrees Fahrenheit. Data is then recorded while a -10 degree step reference command is applied to the intake cam, as shown in reference curve 702. Approximately 10 seconds after the step reference command, the RLS zero duty cycle estimation algorithm is turned on and the EOT estimate is then determined by applying equation (3). For the RLS algorithm, a forgetting factor of 0.995 is used and the initial covariance matrix is 10*I, where I is a 3×3 identity matrix. Five seconds after applying the algorithm, an estimate of the DC_null value is retrieved. Also generated is the value previously reported in Figure 6 630 descriptions of Lookup table. Referring to curve 708, the estimated EOT at a hot start (solid / red line) as determined via the sensorless, filtered, and data-driven approach discussed above converges to the inferred EOT (dashed / blue line) determined via EOT inference logic that uses the KAM variables for initialization and, after initialization, the onboard ACT and ECT sensors.

[0103] Figure 8 Map 800 illustrates EOT estimation during a hot engine start. Specifically, plots 802-808 of map 800 depict zero duty cycle determination via Kalman filtering, which was used to obtain a DC_null value on a test vehicle with a 1.5L PFI engine. Plot 802 illustrates the duty cycle applied to the intake cam during an excitation pulse. Plot 804 illustrates the corresponding change in cam angle. Plot 806 illustrates an estimate of zero duty cycle based on the applied duty cycle and the measured change in cam angle. Plot 808 illustrates the estimated EOT based on the estimated zero duty cycle, via a defined map.

[0104] follow Figure 7The mapping shown shuts down the engine for approximately 5 minutes before restart. During restart, a KAM error is determined to have occurred, which triggers an EOT fault code that causes the inferred EOT calculation logic to start with an incorrect initial condition. This causes the inferred EOT value to be approximately 77 degrees Fahrenheit when the vehicle restarts. This value is inaccurate because the engine oil temperature cannot cool by more than 50 degrees Fahrenheit within 5 minutes (the outside vehicle temperature is approximately 65 degrees Fahrenheit). Additionally, since the engine coolant temperature was measured at 196 degrees Fahrenheit when the engine was shut down and 188 degrees Fahrenheit when the engine was restarted, it is expected that the EOT should actually increase during the first few minutes of the engine shutdown period. Referring to curves 802 - 808, approximately 10 seconds after the vehicle restarts, a 10-degree step reference command is applied to the VCT intake cam, and shortly thereafter the EOT estimation algorithm is enabled. The estimated EOT converges near 143 degrees within approximately 5 seconds, which is a likely true value because in an environment where the engine coolant temperature is approximately 190 degrees Fahrenheit, an oil temperature increase of approximately 10 degrees is expected within 5 minutes. This example provides validation of the inferred-based method and demonstrates the potential use of the algorithm to replace the initial value of the inferred EOT logic with an estimated value determined from the EOT map during a hot start by running a fast estimation characteristic curve during the first few seconds of the idle time after engine start. Referring to curve 808, the solid (blue) curve is the inferred EOT, which is the existing EOT signal generated by the ACT sensor and the ECT sensor.

[0105] Specifically, the engine is restarted approximately 5 minutes after the engine warm-up time, and during restart, an error in the non-volatile memory (KAM) causes the controller to start the EOT inference logic with an incorrect initial condition. For this reason, the inferred EOT value is approximately 80 degrees Fahrenheit throughout the operation. Since the last inferred EOT before engine shutdown was 130 degrees Fahrenheit and the engine coolant temperature is approximately 190 degrees Fahrenheit, an increase in EOT is actually expected during a short engine warm-up time. The current EOT estimation algorithm produces an estimated EOT of 143 degrees Fahrenheit after the engine is turned on, which is as expected.

[0106] Continuing the experiment, at Figure 9Compare the EOT estimation algorithm of the present invention with traditional / existing EOT inference algorithms at the graph 900. Specifically, the recorded EOT data is shown at curves 902 - 906. Data is collected at the moments corresponding to the square symbols. The lines between the squares are generated by linear interpolation and do not correspond to actual data readings. Allow the engine to idle for a few minutes until the inferred EOT reaches 100°F (which corresponds to t = 0). Then, collect EOT estimates at discrete time points using the mapping-based method discussed herein until approximately t = 200 seconds. Then, turn off the engine and allow it to cool for about 510 seconds, and then restart it. After restarting, resume collecting the estimated and inferred EOT values and the measured ECT values. During engine restart, the same / above KAM error causes the traditional / existing inferred EOT algorithm to start from a faulty initial value of about 80°F. As used herein, the inferred EOT refers to the existing original EOT algorithm representing the traditional EOT algorithm operating in the test vehicle. It is called inferred because it uses ACT / ECT sensors (instead of an EOT sensor) to calculate the EOT value. On the other hand, the estimated EOT refers to the EOT estimated via the mapping of the present disclosure. It can be observed that the inferred EOT and the estimated EOT are almost equal until the engine is turned off. After restarting, due to the KAM error, the difference between the estimated EOT and the inferred EOT is large. Due to the KAM error, the existing EOT inference algorithm malfunctions. However, based on the engine-off time (or warm-up time), the EOT value before engine shutdown, and the ECT values before and after engine shutdown, the EOT estimates provided by the mapping of the present disclosure remain plausible, thus demonstrating the accuracy of the mapping. Specifically, since the EOT estimation via the mapping does not require KAM parameters and ECT / ACT sensors, the estimation is not affected by any type of failure mode occurring in these components, which is verified for the Figure 9 specific KAM failure mode in. In addition, since the impact of the initialization error on the existing EOT inference logic decreases over time, the inferred EOT algorithm becomes more accurate over time, and the mapped EOT estimation algorithm and the traditional EOT inference algorithm seem to converge near each other over time, as Figure 9 shown.

[0107] In this way, during an engine cold start condition, the engine controller can estimate the engine oil temperature based on each of the measured engine coolant temperature, the measured ambient temperature, and the measured intake air temperature (or directly measure the engine oil temperature via a dedicated sensor). In contrast, during an engine hot start condition, the controller can estimate the engine oil temperature based on the mapping relationship between the solenoid duty cycle of the spool valve of the variable cam timing device, the angular velocity of the cam actuated by the spool valve, and the engine oil temperature. For example, during an engine hot start condition, the engine oil temperature can be estimated based on the mapping relationship within a first duration since the first combustion event of the engine hot start, and after the first duration, it can be switched to estimating the engine oil temperature based on each of the measured engine coolant temperature, the measured ambient temperature, and the measured intake air temperature. Within the first duration, the engine oil temperature can be estimated independently of each of the measured engine coolant temperature, the measured ambient temperature, and the measured intake air temperature. Additionally, during a hot start condition, the controller can adjust the solenoid duty cycle applied to the spool valve to move the cam from the current position to a final position outside the hard lock position, and measure the angular velocity via a position sensor coupled to the cam after applying the solenoid duty cycle. As an example, the mapping during a hot start can include: estimating the zero duty cycle of the spool valve based on the adjusted solenoid valve duty cycle and the measured angular velocity; and estimating the engine oil temperature by passing the estimated zero duty cycle value through the mapping relationship between the zero duty cycle and the engine oil temperature. In this way, the accuracy of EOT estimation can be improved by reducing the dependence on existing sensors. The technical effect of the engine oil temperature dependence of the solenoid resistance of the VCT spool valve (or OCV) is that the defined mapping between the PWM duty cycle (DC) applied to the solenoid of the spool valve and the cam angular velocity can be known. By characterizing the mapping by applying a known PWM duty cycle signal and measuring the resulting cam angular velocity, the EOT can be inferred without the need for a dedicated sensor. By relying on the mapping relationship, the EOT estimation can be performed even when the default EOT estimation sensors (such as the ECT sensor, the ACT sensor, or the EOT sensor) deteriorate, and during conditions where the sensor output is unreliable (such as during an engine warm start) and the controller memory is damaged. By improving the EOT estimation, the engine torque control is improved.

[0108] An exemplary engine method includes: adjusting an engine torque actuator based on an engine oil temperature estimated by applying an excitation signal to a solenoid valve of a variable camshaft timing device, the excitation signal including one of a pulse width modulated duty cycle, voltage, and current; and using a mapping stored in a non-volatile memory that correlates a camshaft solenoid duty cycle and a camshaft angular velocity of the device with the engine oil temperature. In a previous example, additionally or optionally, the adjustment is responsive to one of a degradation of a sensor for directly or indirectly measuring the engine oil temperature and a corruption of the non-volatile memory, the non-volatile memory including a non-failing memory of an engine controller, the sensor including one or more of an engine oil temperature sensor coupled to an oil pan, an engine coolant temperature sensor, an intake air temperature sensor, and a mass air flow sensor. In any one or all of the previous examples, additionally or optionally, the adjustment is responsive to an engine hot start condition. In any one or all of the previous examples, additionally or optionally, the applied pulse width modulated duty cycle moves one of the intake and exhaust cams beyond a hard stop position. In any one or all of the previous examples, additionally or optionally, estimating the engine oil temperature further includes: estimating a zero duty cycle of a solenoid of a spool valve by low pass filtering or Kalman filtering the applied duty cycle, where the zero duty cycle includes an amount of duty cycle that results in a zero angular velocity of the VCT device beyond a hard stop or pin lock position; and estimating the engine oil temperature via a pre-calibrated mapping that uses the estimated zero duty cycle as an input and produces the estimated engine oil temperature as an output. In any one or all of the previous examples, additionally or optionally, applying the excitation signal includes: applying an incrementally increasing duty cycle, voltage, or current to the solenoid and measuring the camshaft angular velocity after each incremental increase. In any one or all of the previous examples, additionally or optionally, applying the excitation signal includes: applying a reference angular position command via a closed loop controller to change the angular velocity of a camshaft of the device and measuring the camshaft angular velocity and one of a duty cycle, voltage, and current applied to the solenoid by the closed loop controller. In any one or all of the previous examples, additionally or optionally, adjusting the engine torque actuator based on the estimated engine oil temperature includes restricting one or more of an engine torque, engine speed, and boost pressure output of the engine in response to the inferred engine oil temperature being higher than a threshold temperature. In any one or all of the previous examples, additionally or optionally, the variable camshaft timing device uses a solenoid oil control actuator.

[0109] Another exemplary method includes: estimating engine oil temperature based on a measured engine coolant temperature, a measured ambient temperature, and a measured charge air temperature during an engine cold start condition; and estimating the engine oil temperature during an engine hot start condition based on a mapping relationship between a solenoid duty cycle of a spool valve of a variable cam timing device, an angular velocity of a cam actuated by the spool valve, and the engine oil temperature. In the previous example, additionally or optionally, during the engine hot start condition, the engine oil temperature is estimated based on the mapping relationship within a first duration since the first combustion event since the engine hot start, and after the first duration, the engine oil temperature is estimated based on each of the measured engine coolant temperature, the measured ambient temperature, and the measured charge air temperature. In any one or all of the previous examples, additionally or optionally, during the first duration, the engine oil temperature is estimated independently of the measured engine coolant temperature, the measured ambient temperature, and the measured charge air temperature. In any one or all of the previous examples, additionally or optionally, the method further includes, during the hot start condition: adjusting the solenoid duty cycle applied to the spool valve to move the cam from a current position to a final position outside a hard lock position; and measuring the angular velocity via a position sensor coupled to the cam after applying the solenoid duty cycle. In any one or all of the previous examples, additionally or optionally, the mapping during the hot start includes: estimating a zero duty cycle of the spool valve based on the adjusted solenoid valve duty cycle and the measured angular velocity; and estimating the engine oil temperature by passing the estimated zero duty cycle value through the mapping relationship between the zero duty cycle and the engine oil temperature.

[0110] An exemplary engine system may include: a variable cam timing (VCT) device including a cam, a camshaft phaser, a camshaft, a spool valve, and a solenoid; a cam position sensor coupled to the cam; a battery; an engine coolant temperature sensor; an intake charge temperature sensor; a mass air flow sensor; and a controller. The controller may include computer-readable instructions stored on a non-transitory memory for operations including: in response to at least one diagnostic flag related to engine oil temperature estimation being set, applying an excitation pulse to the solenoid to move the spool valve, where the duty cycle of the excitation pulse is adjusted to move the cam beyond a hard stop region; measuring an angular velocity of the camshaft via the cam position sensor after the application; estimating a zero duty cycle of the spool valve based on the applied duty cycle; and estimating the engine oil temperature based on a mapping relationship between the estimated zero duty cycle and the measured angular velocity. In the previous example, additionally or optionally, the controller may include additional instructions for operations including: limiting each of an upper engine speed threshold and a lower engine speed threshold based on the estimated engine oil temperature, where the upper engine speed threshold is decreased and the lower engine speed threshold is increased when the estimated engine oil temperature exceeds a threshold temperature. In any one or all of the previous examples, additionally or optionally, at least one diagnostic flag related to engine oil temperature estimation is set in response to one of: degradation of the engine coolant temperature sensor, degradation of the intake charge temperature sensor, degradation of the mass air flow sensor, corruption of the memory, and an engine hot start condition. In any one or all of the previous examples, additionally or optionally, the mapping relationship is stored in the memory and uses the last estimated engine oil temperature, the estimated zero duty cycle, and the measured angular velocity as inputs. In any one or all of the previous examples, additionally or optionally, the cam is one of an intake cam and an exhaust cam, the memory is a non-failing memory, and the zero duty cycle includes an amount of duty cycle that results in a zero angular velocity of the VCT device outside of a hard stop or pin lock position. In any one or all of the previous examples, additionally or optionally, the controller includes additional instructions for operations including: estimating the engine oil temperature based on an output of one or more of the engine coolant temperature sensor, the intake charge temperature sensor, and the mass air flow sensor in response to no diagnostic flag related to engine oil temperature estimation being set.

[0111] In another representation, a method for an engine includes: applying an excitation signal to a solenoid valve of a variable camshaft timing (VCT) device; estimating engine oil temperature according to a mapping stored in a non-volatile memory, the mapping correlating camshaft solenoid duty cycle and camshaft angular velocity of the VCT device with the engine oil temperature; and adjusting an engine torque actuator based on the estimated engine oil temperature. In the previous example, additionally or optionally, the VCT device is hydraulically actuated. In yet another representation, the engine is coupled in a hybrid electric vehicle system.

[0112] It should be noted that the exemplary control and estimation routines included herein can be used with a variety of engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. Accordingly, the various actions, operations, and / or functions shown can be executed in the order shown, can be executed in parallel, or can be omitted in some cases. Likewise, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations, and / or functions shown can be repeatedly executed depending on the particular strategy used. Additionally, the actions, operations, and / or functions described can graphically represent code to be programmed into the non-transitory memory of a computer-readable storage medium of an engine control system, wherein the described actions are executed by executing instructions in a system including various engine hardware components in combination with an electronic controller.

[0113] It should be understood that the configurations and routines disclosed herein are exemplary in nature and these specific embodiments should not be considered limiting as many variations are possible. For example, the above techniques can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, 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.

[0114] The following claims particularly point out certain combinations and subcombinations that are regarded as novel and non - obvious. These claims may refer to "a" element or "the first" element or their equivalents. Such claims should be understood to cover the incorporation of one or more such elements, neither requiring nor precluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by modifying these claims or by presenting new claims in this application or a related application. Such claims, whether broader, narrower, equal, or different in scope compared to the original claims, are also regarded as included within the subject matter of this disclosure.

Claims

1. An engine method, comprising: Adjusting an engine torque actuator based on an estimated engine oil temperature by applying an excitation signal to a solenoid valve of a variable camshaft timing device, the excitation signal including one of a pulse width modulated duty cycle, voltage, and current; And using a mapping relationship stored in a non-volatile memory to associate a camshaft solenoid duty cycle and a camshaft angular velocity of the device with the engine oil temperature, wherein the adjustment is responsive to one of a degradation of a sensor for directly or indirectly measuring the engine oil temperature and a corruption of the non-volatile memory, the non-volatile memory including a non-failing memory of an engine controller, and the sensor including one or more of an engine oil temperature sensor coupled to an oil pan, an engine coolant temperature sensor, an intake air temperature sensor, and a mass air flow sensor.

2. The method according to claim 1, wherein the adjustment is responsive to an engine hot start condition.

3. The method according to claim 1, wherein the applied duty cycle moves one of an intake cam and an exhaust cam beyond a hard stop position.

4. The method according to claim 1, wherein estimating the engine oil temperature further comprises: Estimating a zero duty cycle of the solenoid valve via low-pass filtering or Kalman filtering of the applied duty cycle, wherein the zero duty cycle includes an amount of duty cycle that results in a zero angular velocity of the variable camshaft timing device beyond a hard stop or pin lock position; And Estimating the engine oil temperature via a pre-calibrated mapping that uses the estimated zero duty cycle as an input and produces the estimated engine oil temperature as an output.

5. The method according to claim 1, wherein applying the excitation signal comprises: Applying an incrementally increasing duty cycle, voltage, or current to the solenoid valve and measuring the camshaft angular velocity after each incremental increase.

6. The method according to claim 1, wherein applying the excitation signal comprises: Applying a reference angular position command via a closed-loop controller to change the angular velocity of the camshaft and measuring the camshaft angular velocity and one of a duty cycle, voltage, and current applied to the solenoid valve by the closed-loop controller.

7. The method according to claim 1, wherein adjusting the engine torque actuator based on the estimated engine oil temperature comprises restricting one or more of an engine torque, an engine speed, and a boost pressure output of the engine in response to an inferred engine oil temperature being higher than a threshold temperature.

8. The method according to claim 1, wherein the variable camshaft timing device uses a solenoid oil control actuator.

9. An engine system, comprising: A variable cam timing device, i.e., a VCT device, including a cam, a camshaft phaser, a camshaft, a spool valve, and a solenoid; A cam position sensor coupled to the cam; A battery; An engine coolant temperature sensor; An intake air temperature sensor; A mass air flow sensor; And A controller including computer-readable instructions stored on a non-transitory memory, the instructions for: In response to at least one diagnostic flag related to engine oil temperature estimation being set, an excitation pulse is applied to the solenoid to move the spool valve, and the duty cycle of the excitation pulse is adjusted to move the cam beyond the hard stop region; after the application, the angular velocity of the camshaft is measured via the cam position sensor; estimate the zero duty cycle of the spool valve based on the applied duty cycle; and estimate the engine oil temperature based on the mapping relationship between the estimated zero duty cycle and the measured angular velocity.

10. The system according to claim 9, wherein the controller includes additional instructions for: Based on each of the estimated engine oil temperature-limited upper engine speed threshold and lower engine speed threshold, when the estimated engine oil temperature exceeds the threshold temperature, the upper engine speed threshold is reduced and the lower engine speed threshold is increased.

11. The system according to claim 9, wherein at least one diagnostic flag related to engine oil temperature estimation is set in response to one of the following: deterioration of the engine coolant temperature sensor, deterioration of the intake charge temperature sensor, deterioration of the mass air flow sensor, damage to the memory, and engine hot start condition.

12. The system according to claim 9, wherein the mapping relationship is stored in a memory and uses the last estimated engine oil temperature, the estimated zero duty cycle, and the measured angular velocity as inputs.

13. The system according to claim 9, wherein the cam is one of an intake cam and an exhaust cam, the memory is a non-volatile memory, and the zero duty cycle includes the amount of duty cycle that results in a zero angular velocity of the VCT device outside the hard stop or pin lock position.

14. The system according to claim 9, wherein the controller includes additional instructions for: In response to a diagnostic flag related to engine oil temperature estimation not being set, estimate the engine oil temperature based on the output of one or more of the engine coolant temperature sensor, the intake charge temperature sensor, and the mass air flow sensor.

Images