Procedure for adaptive control of cam profile switching for changes between combustion modes

Abstract

Method for controlling cylinder valve switching between a first valve state and a second valve state for switching between combustion modes of an engine (10), comprising: Adjusting valve timing for switching between valve states based on an oil degradation state determined from measured values ​​of an oil sensor (136), wherein The combustion modes include spark ignition and homogeneous compression ignition, The adjustment involves advancing the valve timing as oil degradation increases and is only carried out if the engine oil has deteriorated beyond an initial threshold of oil degradation, and The switching between valve states is prevented if the engine oil deteriorates beyond a second threshold of oil degradation.

Description

Background and brief presentation

[0001] Vehicles may include engine systems designed to operate in various different combustion modes to improve the vehicle's operating efficiency while meeting speed and load requirements across the engine's operating range. In one example, an engine system may operate in a controlled auto-ignition combustion mode, a homogeneous charge compression ignition (HCCI) combustion mode, to achieve higher thermal efficiency and reduce pumping losses compared to other combustion modes, leading to improvements in fuel economy performance and emission reductions. HCCI combustion may only be desirable or possible above a specific speed / load operating range.To meet requirements outside the operating range of HCCI combustion, the engine system can also be configured to operate in spark ignition (SI) mode. Operating in both HCCI and SI combustion modes can meet speed / load requirements and increase the vehicle's operating efficiency.

[0002] Furthermore, an engine system may switch between combustion modes by changing a valve lift profile along with fuel and ignition commands in one or more cylinders of the engine. In one example, a valve lift profile may be adjusted by actuating a switching tappet of a cylinder valve. The state of the switching tappet may be controlled by an oil circuit. In particular, the oil pressure of the oil circuit may be increased or decreased to change the state of the tappet. A control signal may be sent to the oil circuit to trigger a cam profile switching based on an appropriate switching window of engine operation, for example, based on a desired rotational position of the crankshaft or camshaft.

[0003] A method for controlling the switching of cylinder valves between a first valve state and a second valve state for switching between combustion modes of an engine according to US 2007 / 0240653 A1 includes adjusting the timing of a signal for switching between the valve states in response to information from a combustion sensor, wherein the combustion modes include spark ignition and homogeneous auto-ignition.

[0004] DE 19907743 A1 relates to an oil quality sensor, in particular for testing the quality of engine oils, comprising a sensitive layer having a surface or layer volume specifically adapted to at least one component present in an oil, which, depending on the component's affinity to the layer, is predestined for the specific re-embedding of the component. The aim of the invention is to create an oil quality sensor whose sensitive layer, due to its chemical composition, is particularly suitable for the conditions under which the oil quality sensor is used, in particular in an internal combustion engine. The sensitive layer of the oil quality sensor comprises at least one polyimide or polyamide. The invention further relates to a method for producing the sensitive layer of an oil quality sensor of the aforementioned type.The monomer components are mixed, then the oil of interest is added, and the mixture is heated to at least the temperature needed to initiate the reaction. The sensitive layer of the oil quality sensors according to the invention, comprising a polyimide or polyamide, has proven particularly resistant under the operating conditions of the oil quality sensor.

[0005] However, the inventors of the present disclosure have recognized several problems with the above approach. In particular, during engine operation, engine oil degradation may occur and engine oil temperature may fluctuate, resulting in changes in the oil circuit's response time for executing a cam profile switch. These changes in the oil circuit's response time may cause early or late cam profile switches that occur outside the appropriate switch window of engine operation. These early or late switches may result in torque surges, increased noise, vibration, and harshness (NHV), increased emissions, and reduced fuel economy, among other operating efficiency losses.

[0006] In at least one approach described herein, at least some of the above problems may be addressed by a method of controlling cylinder valve switching between a first valve state and a second valve state to transition between combustion modes of an engine, comprising: adjusting timing of a signal from an oil sensor to switch between the valve states based on an oil degradation state, wherein the combustion modes include spark ignition and homogeneous charge compression ignition.

[0007] By adjusting the cam profile switching signal timing relative to crankshaft and / or camshaft rotation based on oil degradation using an oil sensor, cam profile switching synchronization can be maintained throughout engine operation, even as the engine oil deteriorates. In particular, the oil sensor can provide oil degradation measurements with improved accuracy over predictive algorithms because the oil sensor can measure the condition of the engine oil in real time. This allows cam profile switching to be executed within a suitable operating window, and torque jumps, NVH, emissions, fuel consumption, and other operating efficiency degradations can be mitigated.

[0008] Furthermore, the signal timing of a cam profile switching can be adjusted based on the engine oil temperature measured by the oil sensor, since the viscosity of the engine oil can change at different temperatures, resulting in changes in the response time of the oil circuit. In one specific example, the oil sensor can be configured to measure the temperature of the engine oil directly from rotating components of the engine, such as the oil layer of the rotating camshaft. The oil sensor can provide a more precise reading compared to a temperature measurement of engine coolant, since a temperature delta can exist between the engine coolant and the engine oil based on the transient dynamics of the engine oil temperature, which occurs more quickly than with generic coolant based on engine temperature.By measuring the engine oil temperature using the oil sensor and adjusting the cam profile switching signal based on the oil temperature, control accuracy can be improved. This allows switching between combustion modes to be performed with little or no reduction in operating efficiency. Brief description of the drawings Fig. 1 shows a cylinder of an exemplary engine system. Fig. 2 shows an example of a design of a cam profile switching device used in the engine system of Fig. 1 can be used. Fig. 3 shows an example of a switchable tappet arrangement. Fig. 4 shows an example of an oil circuit for controlling the actuation of switchable tappets of cylinder valves of an engine system. Fig. 5 shows a flowchart corresponding to an exemplary control routine for controlling cam profile switching timing based on a condition of oil degradation. Fig. 6 shows a flowchart corresponding to an exemplary control routine for controlling cam profile switching timing based on oil temperature. Fig. 7 shows a flowchart corresponding to an exemplary control routine for approximating a state of oil degradation. Detailed description

[0009] Fig. 1 is a schematic diagram showing one cylinder of a multi-cylinder engine 10, which may be included in a propulsion system of a motor vehicle. The engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle operator 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. A combustion chamber (i.e., cylinder) 30 of the engine 10 may include combustion chamber walls 32 with a piston 36 positioned therein. The piston 36 may be coupled to a crankshaft 40 such that reciprocating motion of the piston is converted into rotary motion of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel of a vehicle via a gear system disposed therebetween.Furthermore, a starter can be coupled to the crankshaft 40 by means of a flywheel in order to enable starting operation of the engine 10.

[0010] Combustion chamber 30 may receive intake air from an intake manifold 44 via an intake passage 42 and may exhaust combustion gases via an exhaust passage 48. Intake manifold 44 and exhaust passage 48 may be selectively connected to combustion chamber 30 via an intake valve 52 and an exhaust valve 54, respectively. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0011] In this example, an intake valve 52 and exhaust valves 54 may be controlled by cam actuation via respective cam actuation systems 51 and 53. The cam actuation systems 51 and 53 may each include one or more cams. In one example, variable valve lift may be achieved through cam profile switching (CPS). The cam actuation systems 51 and 53 may each include cam profile switching devices 58 and 59, which may be used to switch between different lift profiles of the respective valves based on the different lobes of the cam(s). The cam actuation systems 51 and 53 may be operated by the controller 12 to vary valve operation. In particular, the controller 12 may control the operation of the cam profile switching devices to influence valve lift and / or valve timing.The position of the intake valve 52 and the exhaust valve 54 can be detected by position sensors 55 and 57, respectively. The cam actuation and cam profile switching are described below with reference to FIG. Fig. 2 described in more detail.

[0012] In alternative embodiments, the intake valve 52 and / or the exhaust valve 54 may be controlled by electric valve actuation. For example, the cylinder 30 may alternatively include a cam-actuated intake valve and an electric valve actuated exhaust valve.

[0013] Furthermore, the engine system may include variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems to control valve timing and / or valve lift throughout vehicle operation.

[0014] In some embodiments, an exhaust gas recirculation (EGR) system may direct a desired portion of exhaust gas from the exhaust port 48 to the intake port 44 via an EGR passage. The amount of EGR delivered to the intake port 48 may be varied by the controller 12 via an EGR valve. Further, an EGR sensor may be disposed in the EGR passage and may provide an indication of one or more of: pressure, temperature, and concentration of the exhaust gas. Under some conditions, the EGR system may be used to regulate the temperature of the fuel / air mixture in the combustion chamber, thereby providing a method for controlling spark timing during some combustion modes. Further, during some conditions, a portion of the combustion gases may be retained or trapped in the combustion chamber by controlling exhaust valve timing.

[0015] In some embodiments, the engine 10 may further include a compression device, such as a turbocharger or supercharger, including at least one compressor disposed along the intake manifold 44. With a turbocharger, the compressor may be driven at least partially by a turbine (e.g., via a shaft) disposed along the exhaust passage 48. With a supercharger, a compressor may be driven at least partially by the engine and / or an electric machine and may not include a turbine. Thus, the amount of compression delivered to one or more cylinders of the engine by a turbocharger or supercharger may be varied by the controller 12.

[0016] A fuel injector 66 is shown disposed within intake passage 44 in a configuration providing injection known as port injection of fuel into the intake passage upstream of combustion chamber 30. Fuel injector 66 may inject fuel proportional to the pulse width of a signal FPW received from controller 12 via an electronic driver 68. Fuel may be delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber 30 may alternatively or additionally include a fuel injector directly coupled to combustion chamber 30 for injecting fuel directly therein in a manner known as direct injection.

[0017] The intake passage 42 may include a throttle 62 with a throttle plate 64. In this particular example, the position of the throttle plate 64 may be varied by the controller 12 using a signal provided to an electric motor or actuator included with the throttle 62, a configuration often referred to as electronic throttle control (ETC). In this manner, the throttle 62 may be operated to vary the intake air delivered to the combustion chamber 30, among other engine cylinders. The position of the throttle plate 64 may be provided to the controller 12 by a throttle position signal TP. The intake passage 42 may include an air flow sensor 120 and a manifold air pressure sensor 122 for providing respective MAF and MAP signals to the controller 12.

[0018] The ignition system 88 may provide an ignition spark to the combustion chamber 30 via a spark plug 92 in response to an ignition advance signal SA from the controller 12 under selected operating modes. Although spark-ignition components are shown, in some embodiments, the combustion chamber 30 or one or more other combustion chambers of the engine 10 may be operated in a compression ignition mode with or without an ignition spark.

[0019] An exhaust gas sensor 126 is shown connected to the exhaust passage 48 upstream of an emission control device 70. The sensor 126 may include any suitable sensor for providing an indication of an exhaust air-fuel ratio, such as a linear oxygen sensor or a UEGO (Universal Exhaust Gas Oxygen Sensor), a dual-state oxygen sensor or EGO, a HEGO (Heated EGO), a NOx, HC, or CO sensor. The emission control device 70 is shown disposed along the exhaust passage 48 downstream of the exhaust gas sensor 126. The device 70 may be a three-way catalyst (TWC), a NOx trap, various other emission control devices, or combinations thereof.In some embodiments, the emission control device 70 may be periodically reset during operation of the engine 10 by operating at least one cylinder of the engine within a particular air / fuel ratio.

[0020] The control unit (or control system) 12 is in Fig. 1 as a microcomputer comprising: a microprocessor 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown in this particular example as read-only memory 106, random access memory 108, persistent memory 110, and a data bus. The control module 12 may receive various signals from sensors connected to the engine 10 in addition to those already discussed, including: intake mass air flow (MAF) measurement from a mass air flow sensor 120; engine coolant temperature (ECT) from a temperature sensor 112 connected to a cooling jacket 114; an ignition profile pickup (PIP) signal from a Hall effect sensor 118 (or other type) connected to the crankshaft 40; throttle position (TP) from a throttle position sensor; and a manifold vacuum signal MAP from a sensor 122. An engine speed signal, RPM, may be generated by the controller 12 from the PIP signal.The manifold pressure signal MPA from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold. Note that various combinations of the above sensors may be used, for example, a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor may provide an indication of engine torque. Further, this sensor, along with the detected engine speed, may provide an estimate of the charge (including air) being admitted to the cylinder. In one example, sensor 118, which is also used as an engine speed sensor, may generate a predetermined number of evenly spaced pulses per revolution of the crankshaft.

[0021] Furthermore, the control system 12 may be in communication with the oil sensor 136. In one example, the oil sensor 136 may be a wear sacrificial sensor for directly measuring a wear characteristic of the engine oil to determine a degree of degradation of the engine oil. The sensor may include a sacrificial portion 138 that wears or degrades according to the degradation of the engine oil. The oil sensor 136 may be configured to change the electrical signal (e.g., voltage value) sent to the control system based on the wear of the sacrificial portion to provide the control system with an indication of the degree of oil degradation. Furthermore, the sacrificial portion of the oil sensor may be replaced at regular maintenance intervals (e.g., during scheduled oil changes) to maintain an accurate wear measurement of the engine oil even when the engine oil is replaced with clean engine oil.To facilitate easy replacement of the sacrificial portion of the oil sensor, the oil sensor may be positioned within the engine system to facilitate easy access to the oil sensor. For example, an engine system oil filler cap may be modified to include a robust thermocouple 140 that may encompass the oil sensor 136, so that the sacrificial portion 138 may be accessible and replaced by removing the oil filler cap. The thermocouple 140 may protect the oil sensor 136 from high heat conditions of the engine and oil systems.

[0022] As another example, the oil sensor may be positioned near the camshaft via the robust thermocouple, and the sacrificial portion of the wear sensor may be in contact with a sensor target integral with the rotating camshaft. Furthermore, the sensor target or sacrificial portion may include segments of different materials (metallic and / or non-metallic) and may be configured to operate at different distances or levels of physical contact to simulate the different types and magnitudes of wear behavior from the corrosion and abrasion mechanisms associated with engine oil degradation. The different materials of the sacrificial portion of the oil sensor may wear at different rates, which may correspond to the rates of oil degradation.In one example, wear of the upper section may be due to contaminants in the engine oil interacting with the sacrificial section, causing wear through abrasion or corrosion reactions. Specifically, as the sacrificial section wears, the distance between the sensor target and the sacrificial section may increase, and the sensor may measure the distance between the sensor target and the sacrificial section to generate a degradation reading of the engine oil.

[0023] An alternative arrangement of the oil sensor or sacrificial portion may include, but is not limited to, placement in the oil filter, near an oil drain plug of the oil system, near the oil filler cap, and integral with an oil dipstick. The oil sensor device may be specifically designed to wear at a faster rate than the particular engine components to provide an indication of engine oil degradation. Furthermore, the oil sensor may be placed in a position that facilitates easy replacement of the sacrificial portion. In this way, oil quality problems can be detected in a timely manner, and engine operation can be modified or restricted to account for the condition of the engine oil, and / or the vehicle operator can be alerted.It is understood that multiple oil sensors capable of measuring engine oil degradation and / or engine oil temperature may be placed throughout the engine system and sensor readings may be used to control engine operation.

[0024] It should further be understood that the engine system 10 may operate in various modes, some of which may be triggered based on the temperature of either the engine or the engine oil itself. For example, for HCCI combustion to occur in the engine, the engine must be hot enough. Engine temperature sensors may be implemented to optimize engine mode selection, such as HCCI operation, and these sensors may typically be located on the cylinder head (e.g., thermostat housing) to directly measure engine coolant. However, it should be understood that a temperature delta may exist between the engine coolant and engine oil temperatures. Further, it should be understood that transient dynamics of engine oil temperature based on engine temperature relative to generic coolant may occur rapidly.Thus, under some conditions, control of engine operation based strictly on engine coolant temperature may be inaccurate relative to control based on engine oil temperature.

[0025] Thus, in some embodiments, the oil sensor 136 may be configured to measure and send a temperature reading of the engine oil to the control system 12. As discussed above, the oil sensor 136 may be integrated with the robust thermocouple 140, which can withstand high engine temperatures, and thus the oil sensor may be positioned near the rotating components where an oil temperature measurement may be most accurate. In one particular example, the oil sensor may be positioned near the camshaft, and the oil layer temperature above the rotating camshaft may be measured to provide an accurate measurement of the engine oil temperature. The adapted engine oil sensor may send varying electrical signals to the control system depending on the exact engine oil temperature (ranging from cold to hot oil), which may be used to control engine operation over the full drive cycle.

[0026] In some embodiments, the oil sensor need not include a sacrificial portion, but may instead include a longer-lasting sensing mechanism. Furthermore, in some embodiments, the oil sensor may be integrated into a standalone, robust thermocouple, which may be separate from an oil filler cap, dipstick, or other replaceable oil system component.

[0027] It should be understood that in some embodiments, the oil sensor may be configured to measure both oil temperature and oil degradation. Furthermore, in some embodiments, the robust thermocouple may comprise a sensor that measures oil temperature, and the oil sensor may be used to measure oil degradation, and signals indicating both measurements may be sent to the control system.

[0028] It is understood that the oil sensor and other sensors described above may be connected via wired and / or wireless connection.

[0029] As described above, Fig. 1 only one cylinder of a multi-cylinder engine and that each cylinder can analogously comprise its own set of intake / exhaust valves, fuel injector, spark plug, etc.

[0030] Combustion in engine 10 may be of different types / modes depending on operating conditions. In one example, spark ignition (SI) may be used, where the engine utilizes an ignition device, such as a spark plug installed in the combustion chamber, to control the timing of combustion chamber gas at a predetermined time after top dead center of the power stroke. In one example, during spark ignition operation, the temperature of the air entering the combustion chamber is considerably lower than the temperature required for auto-ignition. While SI combustion may be used over a wide range of engine torque and speed, it may produce elevated levels of NOx and lower fuel efficiency compared to other types of combustion.

[0031] Another type of combustion that may be employed by engine 10 utilizes homogeneous charge compression ignition (HCCI) or controlled auto-ignition (CAI), wherein the auto-ignition of combustion chamber gases occurs at a predetermined point after the compression stroke of the combustion cycle or near compression top dead center. Typically, when compression ignition of a premixed fuel / air charge is utilized, fuel is normally homogeneously premixed with air, as in a port-injected or directly injected spark-ignition engine during an intake stroke, but with a higher proportion of air to fuel. Because the fuel / air mixture is highly diluted by air or residual exhaust gases, resulting in lower peak combustion gas temperatures, NOx production may be reduced compared to levels found with SI combustion.Furthermore, fuel efficiency can be increased when operating in a compression combustion mode by reducing engine pumping loss, which increases the specific heat ratio of the gas, and by utilizing a higher compression ratio.

[0032] In compression-ignition operating mode, it may be desirable to tightly control the auto-ignition timing. The initial intake charge temperature directly influences the auto-ignition timing. The start of ignition is not directly controlled by a process such as fuel injection in a standard diesel engine or spark plug firing in a spark-ignition engine. Furthermore, the heat release rate is neither controlled by the rate nor the duration of the fuel injection process, as in a diesel engine, nor by the time of turbulent flame propagation, as in a spark-ignition engine.

[0033] It should be noted that compression ignition is also a phenomenon that can cause knocking in a spark-ignition engine. Knocking can be undesirable in spark-ignition engines because it increases heat transfer within the cylinder and can burn or damage the piston. In controlled compression-ignition operation with its high air-to-fuel ratio, knocking generally does not cause engine degradation because the diluted charge keeps the rate of pressure rise low and the maximum temperature of the combusted gases relatively low. The lower rate of pressure rise mitigates the damaging pressure fluctuations of spark-ignition knocking.

[0034] Compared to a spark-ignition engine, the charge temperature can typically be raised at the beginning of the compression stroke to achieve auto-ignition conditions at or near the end of the compression stroke. Those skilled in the art will appreciate that numerous other methods can be used to raise the initial charge temperature. Some of these include: heating the intake air (heat exchanger), retaining a portion of the warm combustion products in the cylinder (internal EGR) by adjusting intake and / or exhaust valve timing, compressing the intake charge (turbocharging and boosting), altering the auto-ignition characteristics of the fuel delivered to the engine, and heating the intake air charge (external EGR).

[0035] During HCCI combustion, auto-ignition of the combustion chamber gas can be controlled to occur at a desired piston position or crank angle to produce a desired engine torque, thus eliminating the need to trigger a spark from an ignition mechanism to achieve combustion. However, retarding the spark plug timing after auto-ignition temperature should have been reached can be used as a backup ignition source in the event that auto-ignition does not occur.

[0036] A third type of combustion that may be performed by the engine 10, for example, where an ignition device is included, utilizes the ignition device to initiate (or assist) combustion as the combustion chamber gas temperature approaches an auto-ignition temperature (e.g., reaches a value substantially close to auto-ignition without actually achieving combustion). Such a spark-assisted type of combustion may have improved fuel efficiency and reduce NOx production relative to SI combustion, but may operate in a higher torque range compared to HCCI combustion. Spark assist may also provide an overall larger window for controlling temperature at a given timing in the engine cycle.In other words, without spark assist, a small change in temperature can result in a fairly large change in combustion timing, affecting engine performance and operating behavior. In spark assist mode, it is possible to achieve many of the benefits of HCCI combustion while still relying on spark timing to provide the ultimate energy needed to achieve auto-ignition, allowing for more precise combustion timing control. Thus, in one example, under certain conditions, spark assist can also be used during transitions between SI combustion and HCCI.

[0037] In one embodiment, the spark-assist mode may be operated, delivering a small amount of fuel to the gases near the spark plug. This small cloud of fuel may be used to facilitate flame propagation and create increased pressure in the cylinder, thereby triggering auto-ignition of the remaining fuel / air mixture. Thus, a relatively small cloud of richer gases located near the spark plug may be utilized, which may also be homogeneous, stratified, or somewhat stratified. One approach to providing such operation may be to utilize a second direct fuel injection during the compression stroke.

[0038] An example of an application incorporating at least the three combustion modes presented above may include the use of SI at start-up and / or after engine start-up during an engine warm-up period. Following such engine start-up and warm-up, the combustion process may transition to HCCI combustion via spark-assist combustion for improved fuel economy and emissions. During periods of high engine torque demands, spark-assist may be activated to ensure proper combustion timing. When the engine is returned to a low or moderate torque demand, spark-assist involvement may end to realize the full benefits of HCCI.

[0039] It should be noted that several other parameters can affect both the peak combustion temperature and the required temperature for efficient HCCI combustion. These and any other applicable parameters can be considered in the routines embedded in the engine control module 12 and used to determine optimal operating conditions. For example, as the fuel octane rating increases, the required peak compression temperature may increase because the fuel requires a higher peak compression temperature to achieve ignition. While one or more of the above combustion modes may be used in some examples, other combustion modes may also be utilized, such as stratified operation, either with or without spark-initiated combustion.

[0040] As mentioned herein, in one example of an engine configured for compression or compression-ignition, the intake valve(s) may be actuated by either a low-lift or high-lift cam profile, depending on the selected combustion mode. The low-lift cam profile may be used to retain a high level of residual gas (exhaust gas) in the cylinder. The retained gases, in some examples, promote compression or compression-ignition by raising the initial charge temperature. However, in a spark-ignition mode (either high or low loads), the high-lift cam profile may be used. Such a switchable cam profile may be implemented by various cam and tappet systems, for example, switching between an inner and outer lobe. This switching may be achieved by oil-flow hydraulic actuators. For example, such systems may include a larger number of tappets.

[0041] In another embodiment, instead of using a cylinder with a single intake valve (or multiple switchable intake valves) that switches between different profiles, a cylinder with at least two intake valves may be used, where each of the valves has a different lift profile (at least for that cylinder). During compression or auto-ignition, a higher and / or longer lift intake valve may be deactivated through the use of a collapsible tappet, while a lower and / or shorter lift intake valve remains active. During spark ignition, the higher / longer lift intake valve may operate to increase airflow into the engine, while the lower / shorter lift continues to operate. In other words, the first intake valve may have a lower lift profile, which alone is sufficient to flow sufficient air to operate the engine under compression or auto-ignition.Furthermore, the first intake valve may have valve timing (fixed or adjustable) set for compression or auto-ignition. The second intake valve may have valve lift and / or timing (fixed or adjustable) that provide air balance for spark ignition above and beyond the air required for compression or auto-ignition.

[0042] Active valve operation may refer to valve opening and closing during a cylinder cycle, with deactivated valves being maintained in a closed position throughout a cylinder cycle (or maintained in a fixed position throughout the cycle). It should be understood that the above configurations are examples, and the techniques discussed herein may be applied to a variety of different variable lift profile systems and configurations, such as exhaust systems and systems having more than two intake or two exhaust valves per cylinder.

[0043] Back now to Fig. 2, an example of a design of a cam profile switching device for use with the engine system 10 is shown. The camshaft 212 may include cam lobes 214, 216, 218 that form different lift profiles. Specifically, in this example, the cam lobes 214 and 218 may have identical lift profiles, and the cam lobe 216 may have a different profile. In particular, the cam lobes 214 and 218 may have a high lift profile, and the cam lobe 216 may have a low lift profile. The cam profile switching device 58, 59 may have a Fig. 3, which can interact with a plurality of cam lobes of the camshaft 212. In particular, the cam lobes 214 and 218 can interact with an outer upper surface of the outer portion 222 of the reversible tappet 210, and the cam lobe 216 can interact with a central upper surface of the central portion 224 of the reversible tappet 210. During valve operation, the reversible tappet 210 can be actuated as a unit by cam lobes 214 and 218 to produce a high valve lift profile. Alternatively, the outer portion 222 can be decoupled from the central portion 224, as shown in Fig. 3, and the switchable tappet 210 may be actuated by the cam lobe 216 to generate a low valve lift profile. In some cases, the demand to switch the cylinder valve lift profile may be generated based on a mode change from SI operation to HCCI operation and vice versa.

[0044] While this example shows an overhead camshaft engine with a tappet connected to the valve stems, tappets can also be used with a pushrod engine, and a collapsible tappet can thus be connected to a pushrod.

[0045] Furthermore, the diagram shows Fig. 2 only one cylinder valve of the engine 10, wherein the engine may be a multi-cylinder engine in which each cylinder has several identical, similar or different from the one in Fig. 2. While the above valve system may offer advantages in a compression or compression-ignition engine, it may also be used in other engine combustion systems.

[0046] Fig. 3 shows an example of a reversible tappet 210 in which a locking pin 254 is used to engage or disengage the central portion 224 from the outer portion 222. Thus, when the pin is in the engaged position, the movement caused by contact with the profiles 214 and 218 causes the inner portion to follow the movement, thus actuating the valve stem and the valve coupled to the inner portion. Alternatively, when the pin is in the engaged position, a lost motion spring in the inner portion 256 can cause the outer portion 222 to move separately from the central portion 224. Thus, the central portion can actuate the valve stem and the valve coupled to the inner portion.Furthermore, because the profile 216 in contact with the central portion 224 has a reduced lift profile, the valve lift may be less than during actuation by the cam lobes 214 and 218. In this way, a switchable lifter may be used, in which the manufacturability of the lifter may be improved while still maintaining the desired function. It is understood that other examples of valve actuation may be used as desired. For example, the switchable lifter may be used to deactivate operation of a valve by switching between a first lift profile that produces valve lift and a second lift profile that produces little or no valve lift. Furthermore, the valve may be used in combination with other variable valve lifts to produce the desired lift profile of intake or exhaust valves.

[0047] In one example, pin 254 may be actuated by hydraulic pressure controlled by a hydraulic valve connected to the controller to switch the switchable plunger between the locked position and the unlocked position. Furthermore, an oil circuit configuration may be implemented to control the plunger switching of different cylinder valves. Fig. Figure 4 shows a four-cylinder engine application in which an oil circuit may be implemented to control tappet switching of the valves of each of the cylinders. In the example shown, the oil circuit configuration may include a first hydraulic actuator 410 and a second hydraulic actuator 412, which, as shown, control respective oil pressures to actuators in cylinders 1 through 4. In this example, the engine firing order is 1-3-4-2, although this is only an example. Continue with Fig. 4, the two actuators each utilize separate oil lines for each of the intake and exhaust tappets. This configuration enables independent control of each group of intake and exhaust valves and can provide sufficient switching windows (depending on response time and switching speeds) to achieve a predetermined cylinder switching sequence for both intake and exhaust valves. As shown, with such a system, it is possible to achieve a cylinder switching sequence that is the same for both the intake and exhaust tappets. In other words, since the cam action switching windows required to achieve both acceptable and reliable switching in a predetermined cylinder switching sequence do not overlap between the intake and exhaust sides, separate control for the intake and exhaust valves of multiple cylinders can be used to obtain the desired switching sequence.

[0048] In some embodiments, the oil circuit may include additional actuators for controlling oil pressure in additional oil lines, or for specific groupings of reversible tappets, or for individual reversible tappets. For example, an oil circuit design may include four actuators for controlling oil pressure in four separate oil lines.

[0049] It should be noted that the above procedures can be adapted and / or modified to accommodate alternative firing orders. For example, the oil lines can be reconfigured to achieve the same or a different desired result, for example, by connecting any two consecutive cylinders in the firing order to the same oil line. It should be noted that in the above example, the figures show an engine with a single bank of four cylinders. However, the procedure can be extended to, for example, a V8 engine with two banks, each having four cylinders. In this case, the firing order of the cylinders of the particular bank can be used to configure the oil lines, even if the overall engine firing order may regularly switch between banks.In other words, cylinder 3 may fire consecutively after cylinder 1 among the cylinders in the particular bank shown, even though a cylinder in another bank between cylinders 1 and 3 may fire.

[0050] The oil circuit configurations described above can reduce complexity while providing systems with sufficient repeatability and robustness, as well as sufficient variability to handle a wide range of operating conditions, where the cylinder switching sequence can be predetermined and reliably achieved. Furthermore, it should be understood that the cam profile switching configuration described above is a non-limiting example, and other suitable cam profile switching configurations could be implemented in the engine system.

[0051] During vehicle operation, operating mode switching, and in particular cam profile switching, may be limited to operating windows where switching may have reduced or minimal disruption to engine operation. In one example, a cam profile switching window may be characterized by a range of crank angles over which a signal may be sent to the actuator to trigger a switching of valve operation. The beginning and ending ranges of the windows may be pre-determined by the firing order, the duration of valve opening, etc. With reference to a four-cylinder engine configuration as in Fig. 4, for the exemplary mode switch starting with cylinder number 1, the beginning of the exhaust signal window for cylinders 1 and 3 may be preset to be after the exhaust valve opening angle for cylinder 3, and the end may be before the exhaust valve opening angle of the high lift cam for cylinder 1. In this example, the switch is controlled so that in the last combustion event in the SI mode, the exhaust lift profile is that of the HCCI type and the first combustion event in the HCCI mode uses an intake lift profile of the HCCI type.

[0052] Furthermore, for the example mode switching starting with cylinder number 1, the beginning of the intake signal window for cylinders 1 and 3 may be preset to be after the intake valve opening angle for cylinder 3, and the end may be before the intake valve opening angle of the high-lift cam for cylinder 1. A similar analysis applies to the windows of cylinders 2 and 4, except that the exhaust / intake signal windows for cylinders 2 and 4 may be shifted to correspond to the valve angles of cylinders 2 and 4.

[0053] It should be noted that the window start angles, window end angles, and / or timing may differ from a transition from HCCI to SI. This may be due, for example, to different valve opening times and timing between the different lift profiles. As another example, switchover windows change based on changes in cam timing (e.g., advance or retard) or other appropriate changes in settings by a variable cam timing (VCT) controller or control system component.

[0054] The cam profile switching window may be characterized by a range of crank angles where hydraulic switching occurs via an oil rail. However, as described above, many factors can affect the reliable control of tappet switching timing and switching sequence. In one example, using tappet switching technology with oil rails, each serving multiple cylinders, a tappet switch may occur when an oil pressure threshold is reached. Thus, the location at which each tappet switches may depend on the dynamics of the oil circuit. Furthermore, if a tappet is depressed by a cam lobe when the oil pressure threshold is reached, the tappet will not switch until the next camshaft rotation.

[0055] Furthermore, the present inventors have recognized that the condition of the engine oil in terms of both viscosity and temperature when operating outside of normal operating conditions, i.e., outside temperature conditions and / or outside oil viscosity conditions (due to contamination), can have an effect on the response time of the camshaft profile switching, which, if not taken into account, can result in a camshaft profile switching that may not be synchronized with fuel or ignition, causing torque jumps, increased NVH, increased emissions, and / or reduced fuel economy performance.Specifically, engine oil quality can affect the timing of valve switching relative to the timing of sending a signal to initiate switching in two or more areas, including the low- and high-pressure lines running in or from the engine to the oil converters or reversible lifters, and the reversible lifters themselves. For example, deteriorated oil with a different viscosity can slow or accelerate oil transfer in the lines, as well as slow or accelerate the operation of the reversible lifter's internal locking pin. For example, as engine oil deteriorates, the viscous additives in the oil can break down by shearing, causing the oil to thicken; as the oil deteriorates further, the resulting oil can oxidize and thin.Thus, oil viscosity can change during oil degradation, which in turn can affect the timing of cam profile switching. Furthermore, delays in the electronics and solenoid valves, as well as external conditions, can affect the timing of switching valve operation relative to the timing of sending a signal to initiate the switching. Since precise control of valve profile switching affects the transition of combustion modes, for example, from HCCI to SI or vice versa, and can affect the compression or auto-ignition combustion process, at least some of the factors influencing the switching can be incorporated into various control strategies described herein.

[0056] In one approach, the cam profile (or tappet) switching timing may be adjusted based on a condition of the engine oil or based on engine oil degradation determined from readings from an engine oil sensor. As explained above, the engine oil sensor may be configured to provide electrical signals that vary according to a condition of the engine oil. In particular, the electrical signals from the engine oil sensor may characterize a condition of oil degradation, which may range from fresh, clean oil to dirty or sooty oil. Further, for example, each voltage value of degradation may correspond to a value of oil viscosity, which may be taken into account in the adjustment of the signal timing.

[0057] With reference now to Fig. 5, an example flowchart corresponding to a control routine for adaptively controlling valve lift / tappet switching based on a degradation state of the engine oil is shown. The routine begins at 510, where it may be determined whether a combustion mode switch is requested. For example, the request may be to switch from SI combustion to HCCI combustion. As another example, the request may be to switch from HCCI combustion to SI combustion. Further, the request may include a switch to other suitable modes of combustion or engine operation. As discussed above, the request may be triggered in response to various operating conditions being met. For example, a request to switch to HCCI combustion may be triggered in response to reaching a desired condition of engine speed, load, and temperature.If it is determined that a combustion mode switch is required, the routine moves to 512. Otherwise, the routine returns or ends.

[0058] At 512, the routine may include assessing the operating conditions of the engine, including current, past, and / or future operating conditions. As described above, the operating conditions may include one or more of the following: a state of engine oil degradation, engine oil temperature, engine oil pressure in one or more of the engine oil lines, engine speed, engine load, engine temperature, crankshaft position, cam position, fuel injection quantity and / or timing, ignition timing, ambient conditions such as air temperature and pressure, among other operating conditions of the engine, but are not limited to. In one particular example, assessing the operating conditions may include obtaining a voltage value from an engine oil sensor that corresponds to a state of engine oil degradation, which may be retrieved from a lookup table stored in the memory of the control system.It is understood that the engine oil degradation condition may have any suitable level of granularity or range corresponding to a sensor signal voltage to adjust the signal timing for cam profile switching.

[0059] Next, at 514, the routine may include determining whether the engine oil has deteriorated beyond a first threshold. The determination may include comparing the engine oil sensor readings to a range of oil degradation values. In one example, the first threshold may characterize substantially clean engine oil that does not exhibit a significant change in viscosity due to contamination or degradation. If it is determined that the engine oil has not deteriorated beyond the first threshold, or in this example, that the engine oil is substantially clean, the routine moves to 522, and the cam profile switching or combustion mode switching may be performed without adjusting the signal timing based on the engine oil degradation state. Otherwise, if it is determined that the engine oil has deteriorated beyond the first threshold, the routine moves to 516.

[0060] At 516, the routine may include adjusting the cam profile switching signal timing based on the level of engine oil degradation. In one example, the signal timing may be advanced to account for delays in oil movement due to degradation throughout the oil lines and other lines, which may affect the movement of the locking pin and switching of the tappet. Specifically, contaminants in the degraded oil may change the viscosity of the oil, resulting in faster or slower response times for raising or lowering oil pressure. Thus, the signal timing may be advanced according to the level of engine oil degradation. It should be understood that adjusting the cam profile switching signal timing may include advancing or retarding the signal timing to the appropriate timing based on the condition of the engine oil.Furthermore, adjusting the cam profile switching signal timing may include adjusting the switching window at which cam profile switching can occur. In this way, cam profile switching itself can be synchronized with the commanded fuel and ignition during combustion mode changes. In one example, the switching window and corresponding adjustment of the signal timing may be mapped according to the oil condition, and upon oil degradation, the window and / or signal timing may be remapped or the characteristic curve may be calibrated or switched to account for delays due to degradation. Furthermore, the newly defined characteristic curves may be programmed into the control system's memory and may be generated from dynamometer tests on a range of aged and viscous oils.

[0061] Furthermore, adjusting the signal timing may include adjusting the signal timing for multiple valves. For example, the final SI cycles before a combustion mode switch may utilize a different fuel and ignition strategy than the initial cycles of the HCCI combustion mode, so that both intake and exhaust valves may be switched together to provide the correct environment for either SI or HCCI combustion. Under some conditions, multiple intake valves may be switched in a coordinated manner. Furthermore, under some conditions, multiple exhaust valves may be switched in a coordinated manner. Furthermore, under some conditions, both intake and exhaust valves may be switched in a coordinated manner. In some cases, coordinated valve switching may include simultaneous switching.

[0062] At 518, the control routine may include determining whether the engine oil has deteriorated beyond a second threshold. The determination may include comparing the engine oil sensor readings to a range of oil degradation levels. The second threshold may correspond to a level of severe oil degradation such that switching combustion modes may cause jumps in torque output, increased NVH, increased emissions, and / or increased fuel consumption. Accordingly, if it is determined that the engine oil has deteriorated beyond the second threshold, the routine moves to 520, where the routine may include preventing a cam profile switch and / or a combustion mode switch so that the penalties from an unsynchronized switch may be avoided.Otherwise, if it is determined that the engine oil has not degraded beyond the second threshold, the routine moves to 522, where the routine may include executing the cam profile switching or the combustion mode switching using the adjusted signal timing. By adjusting the cam profile switching signal timing based on the state of oil degradation, a combustion mode switching may be adjusted to maintain synchronization and accuracy throughout engine operation, even with oil degradation. In this way, jumps in torque performance, NVH, emissions, and / or fuel consumption may be reduced.

[0063] It is understood that the thresholds described above may characterize various other predetermined levels of oil degradation than those discussed above. Furthermore, in some embodiments, the routine may include additional thresholds, whereupon, upon reaching the thresholds, a predetermined adjustment of the signal timing may be made to maintain the accuracy and synchronization of the cam profile switching. In some embodiments, the engine oil degradation state may be dynamically updated at the control system based on changes in sensor voltage, and engine operation may be adjusted accordingly.

[0064] In another approach, the timing of the cam profile (or tappet) switching may be adjusted based on an engine oil temperature measured by an engine oil sensor. It is understood that changing engine oil temperature conditions may cause the predetermined cam profile switching windows to move. As a specific example, when the engine oil temperature changes, the viscosity of the oil may change, and in the case of large temperature changes or operating ranges with out-of-range temperatures, the engine oil behavior, i.e., the transmission or response times, may affect the timing of the operating mode switching and, in particular, cam profile switching. As explained above, the engine oil sensor may be configured to provide electrical signals that vary according to an engine oil temperature.Furthermore, the oil sensor can be positioned near a rotating component of the oil system, such as the camshaft, so that an accurate oil temperature can be sent to the control system. The engine oil temperature reading from the oil sensor can have improved accuracy compared to an engine coolant reading and can therefore facilitate more precise switching between HCCI and SI operation.

[0065] With reference now to Fig. 6 shows an example flowchart corresponding to a control routine for adaptively controlling valve lift switching based on an engine oil temperature condition. The routine begins at 610, where it may be determined whether a combustion mode switch is requested. For example, the request may be to switch from SI combustion to HCCI combustion. As another example, the request may be to switch from HCCI combustion to SI combustion. Further, the request may include a switch to other suitable combustion modes or engine operating modes. As discussed above, the request may be triggered in response to various operating conditions being met. For example, a request to switch to HCCI combustion may be triggered in response to a desired engine speed, load, and temperature condition being met.If it is determined that a combustion mode switch is requested, the routine moves to 612. Otherwise, the routine returns or ends.

[0066] At 612, the routine may include assessing the operating conditions of the engine, including current, past, and / or future operating conditions. As described above, the operating conditions may include one or more of the following: a state of engine oil degradation, engine oil temperature, engine oil pressure in one or more of the engine oil lines, engine speed, engine load, engine temperature, crankshaft position, cam position, fuel injection quantity and / or timing, spark timing, ambient conditions such as air temperature and pressure, among other operating conditions of the engine, but are not limited to. In a particular example, assessing the operating conditions may include obtaining a voltage from an engine oil sensor corresponding to a temperature of the engine oil measured directly from the engine oil layer of the rotating camshaft.

[0067] Next, at 614, the routine may include determining whether the engine oil temperature has been reduced above a first threshold. The threshold may be set based on the viscosity of the engine oil and the oil transfer behavior plotted against oil temperature. For example, the threshold temperature may be set at a point where the oil viscosity delays the response time. The threshold may be calibratable and / or may be pre-set based on testing oil response behavior over various engine operating temperatures and may be stored in a lookup table in the control system's memory. Further, the threshold may be set based on the operating temperature range of HCCI combustion. If the oil temperature is below an operating range where HCCI combustion can occur, the mode switch may be adjusted or prevented.If it is determined that the oil temperature received from the oil sensor is not below the threshold temperature, the routine moves to 622. Otherwise, if it is determined that the engine oil temperature has decreased above the first threshold temperature, the routine moves to 616.

[0068] At 616, the routine may include adjusting the cam profile switching signal timing based on the engine oil temperature obtained from the oil sensor. In other words, the signal timing may be adjusted to account for delays in oil movement throughout the oil lines and other lines that may affect locking pin movement and tappet switching. The delays may be due to the higher viscosity of the oil due to a lowered temperature, resulting in slower response times to raise or lower oil pressure. Adjusting the cam profile switching signal timing may include advancing or retarding the signal timing toward the appropriate timing based on temperature.Specifically, the signal timing may be advanced as the engine oil temperature decreases to account for delays, and the signal timing may be retarded as the engine oil temperature increases, as the engine oil viscosity may be lower, resulting in faster movement through the oil passages. Furthermore, adjusting the cam profile switching signal timing may include adjusting the switching window during which a cam profile switching can occur. In this way, the cam profile switching itself can be synchronized with the commanded fuel and ignition during combustion mode changes.In one example, the switching window and corresponding delay of the signal timing can be mapped according to the oil condition. As the oil temperature drops, the window and / or the signal timing can be remapped, or the characteristic curve can be calibrated or switched to account for delays due to oil temperature. Furthermore, the newly defined characteristic curves can be programmed into the control system's memory and can be generated from dynamometer tests on a range of viscous oils at different temperatures.

[0069] Furthermore, adjusting the signal timing may include adjusting the signal timing for just one valve or multiple valves. For example, the final SI cycles before a combustion mode switch may utilize a different fuel and ignition strategy than the first cycles of the HCCI combustion mode, so that both intake and exhaust valves may be switched together to provide the correct environment for either SI or HCCI combustion. Under some conditions, multiple intake valves may be switched in a coordinated manner. Furthermore, under some conditions, multiple exhaust valves may be switched in a coordinated manner. Furthermore, under some conditions, both intake and exhaust valves may be switched in a coordinated manner. In some cases, coordinated valve switching may include simultaneous switching.

[0070] At 618, the control routine may include determining whether the engine oil temperature is less than a second threshold temperature. The determination may include comparing the engine oil sensor readings to a temperature range of HCCI operation. The second threshold may correspond to an oil temperature below the operating range of HCCI combustion, such that switching combustion modes may cause jumps in torque output, increased NVH, increased emissions, and / or increased fuel consumption. Accordingly, if the engine oil temperature is determined to be below the second threshold temperature, the routine moves to 620, where the routine may include preventing a cam profile switch and / or a combustion mode switch so that the penalties due to an unsynchronized switch may be avoided.Otherwise, if it is determined that the engine oil temperature is not less than the second threshold temperature, the routine moves to 624, where the routine may include performing the cam profile switching or the combustion mode switching using the adjusted signal timing.

[0071] Returning to 614, if the engine oil temperature has not decreased below the first threshold, the routine moves to 622. At 622, the routine may include determining whether the engine oil temperature is above a third threshold temperature that is higher than the first and second threshold temperatures. In one example, the third threshold temperature may be a temperature at which auto-ignition combustion or HCCI combustion may not be possible / desirable. If it is determined that the engine oil temperature is at or above the third threshold temperature, the routine moves to 620, where the routine may include preventing a cam profile switch and / or a combustion mode switch so that penalties associated with inappropriate auto-ignition combustion may be avoided.Otherwise, if the engine oil temperature is determined to be lower than the third threshold temperature, the routine moves to 624, where the routine may include performing the cam profile switching or the combustion mode switching without adjusting the signal timing based on the engine oil temperature. By adjusting the cam profile switching signal timing based on oil temperature, a combustion mode switching may be adjusted to maintain synchronization and accuracy throughout engine operation with greater precision than with control based only on engine coolant temperature. In this way, jumps in torque performance, NVH, emissions, and / or fuel consumption may be reduced and / or potentially eliminated.

[0072] It is understood that the thresholds described above may characterize various other predefined temperatures than those discussed above. Furthermore, in some embodiments, the routine may include additional thresholds, after which, upon reaching the thresholds, a predetermined adjustment of the signal timing may be made to maintain the accuracy and synchronization of the cam profile switching.

[0073] In another approach, engine oil degradation can be predicted using a counter cycle algorithm that updates a corrected request for cam profile switching or operating mode switching. Referring now to Fig.7 shows an exemplary flowchart corresponding to a control routine for adaptive control of valve lift switching based on predictive oil degradation. The routine begins at 710, where the routine may include incrementing a counter based on engine speed and engine load. The counter cycle may be initiated and paused based on the crankshaft position sensor. In some embodiments, the counter may be incremented based on alternative or additional operating parameters.

[0074] Next, at 712, the routine may include determining whether the counter is greater than a first threshold. The first threshold may be set according to a predetermined test level generated from dynamometer testing of a range of aged and viscous oils. The first threshold may represent a predicted point at which engine oil degradation may affect signal timing, causing adjustment of the cam profile switching timing. If the counter is greater than the first threshold, the routine moves to 714. Otherwise, the routine loops back to the beginning and does not adjust the cam profile switching signal timing.

[0075] At 714, the routine may include determining whether the counter is greater than a second threshold. The second threshold may be set according to a predicted point at which oil degradation is severe enough that an operating mode switch may cause significant operational degradations such as misfires, NVH (e.g., engine knock), increased emissions, etc. If the counter is greater than the second threshold, the routine moves to 716, where the routine may include preventing a cam profile switch or a combustion mode switch, such as a switch from SI to HCCI operation. Otherwise, the counter is not greater than the second threshold, and the routine moves to 718, where the routine may include adjusting the cam profile switch signal timing to account for the predicted oil degradation.In some embodiments, the cam profile timing may be adjusted by selecting the corrected cam profile switching request from a pre-mapped calibration.

[0076] At 720, the routine may include determining whether the oil has been changed and thus the oil degradation condition has been improved. In some embodiments, the engine oil condition (or counter) may be manually reset in the controller during an oil change, for example, by a mechanic. Further, in some embodiments, the engine oil change may be indicated by an ignition key on / off operation. Further, an indication of an oil change may be generated from an engine oil system sensor in response to detecting the removal of an oil change-related component, such as the oil pan drain or an oil filter. If it is determined that the oil has been changed, the routine moves to 722, where the routine may include resetting the counter. Otherwise, it may be determined that the oil has not been changed, and the routine ends.

[0077] The routine described above can provide appropriate adjustment of the control of operating mode switching by engine operation based on predicted engine oil degradation without using an engine oil sensor. In particular, the routine can adjust the cam profile switching signal timing by adjusting the signal to advance or retard. Furthermore, cam profile switching based on a predicted high level of engine oil degradation can be prevented. By adjusting the cam profile switching signal based on predicted oil degradation, the valve lift and / or timing can be synchronized with fuel and ignition throughout the entire ranges and modes of engine operation. In this way, jumps in torque performance, NVH, emissions, and / or fuel consumption can be reduced.

[0078] It should be understood that various portions of the control routines described above may be combined or omitted to provide appropriate control of engine operation. For example, cam profile switching signal timing may be adjusted based on both an oil degradation condition and an oil temperature condition. Furthermore, an amount of advance or retardation of the signal timing may be increased and / or decreased with respect to both conditions. In one example, the signal timing may be retarded by a predetermined delay due to the engine oil degradation condition; however, the retardation may be advanced or adjusted by a predetermined delay based on a high engine oil temperature. By considering both oil degradation and oil temperature, the accuracy of the signal timing may be improved.In this way, cam profile switching can be synchronized with fuel and ignition during a change between combustion modes across the engine's operating range.

[0079] It should be noted that example control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The specific routines described herein may represent one or more of a variety of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Therefore, various illustrated operations, steps, or functions may be performed in the sequence shown, in parallel, or omitted in some cases. Similarly, the order of processing is not required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for convenience of illustration and description. One or more of the illustrated operations or functions may be performed repeatedly depending on the particular strategy employed.Furthermore, the described operations can graphically represent a code to be programmed into the machine-readable storage medium in the engine control system.

[0080] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered limiting, as numerous modifications are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, horizontally opposed engines, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and configurations, as well as other features, functions, and / or characteristics disclosed herein.

[0081] The following claims particularly point out certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or an equivalent thereof. These claims are to be construed as encompassing the incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims, whether broader, narrower, the same, or different from the scope of the original claims, are also to be considered within the subject matter of the present disclosure.

Claims

[1] A method for controlling cylinder valve switching between a first valve state and a second valve state for switching between combustion modes of an engine (10), comprising: Adjusting control times for switching between the valve states based on an oil degradation state determined from measured values of an oil sensor (136), wherein the combustion modes include spark ignition and homogeneous compression ignition, the adjustment includes adjusting the valve timing to advance as oil degradation increases and is only carried out if the engine oil has deteriorated beyond a first threshold value of the oil degradation state, and switching between the valve states is prevented if the engine oil has deteriorated beyond a second threshold value of the oil degradation state. [2] The method of claim 1, further comprising: Adjusting timing of the signal to switch between the valve states further based on an oil temperature from the oil sensor (136). [3] Method according to claim 1, characterized by that switching between valve states comprises the coordinated switching of the valve lift profiles of intake and exhaust valves (52, 54) of a cylinder (30) of the engine (10). [4] Method according to claim 1, characterized by that the first valve state and the second valve state are different valve lift profiles. [5] Method according to claim 1, characterized byin that switching between the first valve state and the second valve state comprises adapting a lift profile of a valve (52, 54) by switching between a first camshaft lobe (214, 218) and a second camshaft lobe (216) of a common camshaft (212) by actuating a valve tappet (210), wherein the first camshaft lobe (214, 218) has a high lift profile and the second camshaft lobe (216) has a low lift profile. [6] Method according to claim 5, characterized by that the signal triggers a change in the oil pressure of at least one oil line to change a state of the valve tappet (210). [7] Method according to claim 1, characterized bythat switching between the first valve state and the second valve state comprises changing the lift profile of a cylinder (30) comprising at least two intake valves (52) or two exhaust valves (54), and changing the lift profile of the cylinder (30) comprises deactivating the actuation of one of the two intake valves (52) or the two exhaust valves (54) to change the lift profile of the cylinder (30). [8] A system for operating an engine (10) of a vehicle, the engine having at least a first cylinder (30), the system comprising: a camshaft (212) having at least a first lift profile and a second lift profile, wherein the first lift profile differs from the second lift profile; a valve (52, 54) of the cylinder (30) actuated by means of the camshaft (212), the valve having an actuating tappet (210) designed to switch between a first lift state in which the valve lift is based on at least the first profile and a second lift state in which the valve lift is based on at least the second profile; an oil sensor (136) for measuring engine oil degradation; a control unit (12) configured to send a signal to actuate the tappet (210) to switch between the first stroke state and the second stroke state based on a request to switch between spark ignition and homogeneous compression ignition combustion modes, wherein a control time for sending the signal in response to information from the oil sensor (136) is advanced as oil degradation increases when the engine oil has deteriorated beyond a first threshold oil degradation state, and the signal to actuate the tappet (210) is not sent if the engine oil has deteriorated beyond a second threshold value of engine oil degradation. [9] System according to claim 8, characterized by in that the oil sensor (136) comprises a sacrificial portion (138) which wears due to abrasion and corrosive reactions with contaminants in the engine oil, the degradation state being due to the wear of the sacrificial portion (138). [10] System according to claim 9, characterized by that the degradation state is based on a distance measured by the oil sensor (136) between an end of the sacrificial portion (138) and a sensor target. [11] System according to claim 8, characterized by that the information from the oil sensor (136) further includes a temperature of the engine oil. [12] System according to claim 11, characterized bythat the oil sensor (136) comprises a robust thermocouple (140) positioned near the camshaft (212), and the oil sensor (136) is designed to measure the temperature of the oil layer above the camshaft (212). [13] System according to claim 8, characterized by that the oil sensor (136) is integrated with at least one of the vehicle's oil filler cap and oil dipstick. [14] The system of claim 8, further comprising: a second valve (52, 54) actuated by a third cam profile of the camshaft (212), wherein actuation of the tappet (210) deactivates the first valve (52, 54). [15] A method for controlling valve switching for changing between combustion modes of an engine (10), the engine having a plurality of cylinders (30) each having at least a first valve profile and a second valve profile, the cam profiles being changed by switching tappets (210) controlled by an oil circuit, comprising: Obtaining oil temperature and oil degradation information from an oil sensor (136); Adjusting a timing for sending the signal based on the oil temperature and oil degradation information, wherein the adjusting comprises advancing the timing as oil degradation increases and is only performed when the engine oil has deteriorated beyond a first threshold oil degradation state; and Sending a signal to the oil circuit to switch the tappets (210) to change combustion modes, wherein the sending of the signal is prevented when the oil degradation exceeds a second threshold oil degradation state. [16] Method according to claim 15, characterized by that the combustion modes include spark ignition and homogeneous compression ignition. [17] The method of claim 16, further comprising: Prevent combustion mode switching based on oil temperature information. [18] Method according to claim 15, characterized by that adjusting the timing further comprises advancing the signal timing when the engine oil temperature decreases and / or retarding the signal timing when the engine oil temperature increases.

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