Variable cam control during engine shutdown and start-up

Abstract

Method for controlling an actuator for variable cam timing (VCT), comprising the following: during engine shutdown (10, 200), adjusting a camshaft (214, 216) by means of the VCT actuator (224, 226) to a target initial position and applying a first holding level to the VCT actuator (224, 226) to maintain the target initial position, and increasing the holding level applied to the VCT actuator (224, 226) from the first holding level to a third holding level, which is greater than the first holding level, in order to compensate for inertial transition loads of a valve train during engine shutdown (10, 200); and During engine start-up (10, 200), before camshaft position feedback becomes available, a second hold level is applied to the VCT actuator (224, 226) to maintain the target initial position; wherein the VCT actuator (224, 226) is an electric VCT actuator and the first hold level is a first current, the second hold level is a second current, and the third hold level is a third current; and where the first current is smaller than the second current.

Description

[0001] Variable cam timing (VCT) systems can be implemented in an engine to adjust a camshaft position, thereby advancing or retarding the camshaft timing. By controlling the camshaft, the VCT system can vary the timing of the intake and exhaust valves according to engine operating conditions, such as engine load and engine speed. This variable timing allows for increased engine power, reduced emissions, and improved fuel efficiency compared to engines with fixed camshafts.

[0002] More specifically, electric VCT systems provide a camshaft positioning function while the engine is cranking and no firings are taking place. In other words, an electric VCT system can move a camshaft to a desired position for an initial ignition event during engine cranking. For example, the electric VCT system adjusts the camshaft position based on closed-loop feedback calculated from crankshaft position and camshaft profile ignition pickup (PIP) signals. These signals may not be available and / or reliable until the engine speed has reached a minimum threshold. Accordingly, closed-loop control of the camshaft is not available until the engine speed has reached a minimum threshold.One way to avoid this problem is to move the camshaft to the desired position for the first ignition cycle before shutting down the engine. This allows the camshaft to be in the desired position when the engine is started. Such a method is known, for example, from DE 10 2008 008 117 A1.

[0003] However, the present inventors have identified potential problems with such an approach. For example, the VCT system may not include detent pins to hold the camshaft in the desired position when the VCT system is de-energized. In such cases, no control loop feedback is available when the engine speed drops below a certain threshold during engine shutdown and before the engine speed rises above another threshold during engine startup. Therefore, the camshaft position may be shifted to a retarded position due to frictional braking effects during the uncontrolled phases and would therefore not be held in the desired position for the initial engine firing.

[0004] Thus, for example, the problem described above can be partially solved by a method for controlling an electric VCT actuator. The method includes, during engine shutdown, adjusting a camshaft with an electric VCT actuator to a desired initial position, applying a first current to the electric VCT actuator to maintain the desired initial position, and during engine startup, before camshaft feedback is available, applying a second current to the electric VCT actuator to maintain the desired initial position. The first current can be a fixed current level regardless of conditions, or it can be adjusted to different levels depending on the conditions.Similarly, the second current may also be a fixed current level regardless of the conditions, or it may be adjusted to different levels depending on the conditions, but it is nevertheless different from the first current for a particular engine starting procedure.

[0005] For example, by supplying the assigned currents to the VCT actuator when camshaft measurement is unavailable during engine shutdown and startup, the camshaft can be substantially prevented from drifting from the desired initial position. In some embodiments, the current applied to the VCT actuator may differ between engine shutdown and startup because the valvetrain torque applied to the camshaft during engine shutdown and startup may be different. Furthermore, when camshaft position feedback becomes available, the accuracy of the camshaft position relative to the desired initial position can be confirmed.In the event that the camshaft position is not at the desired initial position, the electric VCT actuator can be triggered to quickly adjust the camshaft position to the desired initial position, since the camshaft is likely close to the desired initial position. Thus, the time required for the camshaft to reach the desired initial position after feedback control is restored can be significantly reduced, or ideally even reduced to zero, compared to an electric VCT system that does not use different current levels for different conditions when camshaft position feedback is unavailable.

[0006] It should be understood that the above summary of the invention is intended only to briefly introduce, in simplified form, a selection of concepts that are further elaborated upon in the following detailed description. It is not intended to point out core or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome disadvantages addressed above or in any other part of this disclosure.

[0007] The figures show: Fig. 1 shows an embodiment of an engine system according to the present description. Fig. 2 shows an embodiment of an electrical “Variable Cam Timing” (VCT) system according to the present description. Fig. 3 shows an embodiment of a method for adjusting a camshaft position with a variable cam timing actuator. Fig. Figure 4 shows a graph showing characteristics of the current applied to an electric VCT actuator during different operating conditions.

[0008] Methods and systems are provided for adjusting a position of a camshaft of an engine (such as the one shown in Fig. 1) is provided with an electric “Variable Cam Timing” (VCT) system. More specifically, the camshaft position may be adjusted to a desired initial position during engine shutdown in preparation for a first ignition event of a subsequent engine start. Furthermore, the camshaft may be maintained at the desired initial position, for example, within a degree range of the desired timing (such as 5 degrees or less), if camshaft position feedback is not available during engine shutdown and subsequent engine start. For example, the camshaft may be maintained at the desired initial position if camshaft feedback is not available by applying a preset current to an electric VCT actuator (such as the one shown in Fig. 2) to compensate for the valve train torque applied to the camshaft during engine shutdown and engine startup. A control unit may be configured to execute a control routine, such as the routine of Fig. 3, to maintain a camshaft position at a desired initial position when camshaft position feedback is not available during engine shutdown and startup. The camshaft position can be maintained at the desired initial position by applying preset currents (such as those in Fig. 4) are applied to the electric VCT actuator. This can prevent the camshaft from drifting from the desired initial position when camshaft position feedback is not available during engine shutdown and engine start-up.

[0009] Fig. 1 is a diagram illustrating one cylinder of a multi-cylinder engine 10, which may be included in a propulsion system of an automobile. The engine 10 may be controlled at least in part by a control system including a control unit 12 and by commands 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. The combustion chamber (also referred to as a cylinder) 30 of the engine 10 includes combustion chamber walls 32 with a piston 36 located therein. The piston 36 is coupled to the crankshaft 40 such that reciprocating motion of the piston is translated into rotary motion of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel of a vehicle via an intermediate powertrain system.Furthermore, a starter may be coupled to the crankshaft 40 via a flywheel to enable the engine 10 to be started.

[0010] Combustion chamber 30 may receive intake air from an intake manifold 46 via an intake port 42 and may expel combustion gases via an exhaust port 48. The intake manifold 46 and the exhaust port 48 may be selectively fluidly connected to the combustion chamber 30 via an intake valve 52 and an exhaust valve 54. In some embodiments, the combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0011] In this example, intake valve 52 and exhaust valve 54 may be controlled by cam actuation via cam actuation systems 51 and 53, respectively. Cam actuation systems 51 and 53 may each include one or more cams and may utilize a cam profile switching (CPS) system and / or variable cam timing (VCT) and / or variable valve timing (VVT) and / or variable valve lift (VVL), which may be actuated by control unit 12 to vary valve operation. The cam actuation system used to vary valve operation is described in Fig. 2. The position of intake valve 52 and exhaust valve 54 may be determined by position sensors 55 and 57, respectively. In alternative embodiments, intake valve 52 and / or exhaust valve 54 may be controlled by electric valve actuation. For example, cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation using a CPS and / or VCT system.

[0012] An injector 66 is shown coupled directly to the combustion chamber 30 for directly injecting fuel proportional to the pulse width of the signal FPW received from the control unit 12 via the electronic control unit 68. In this way, the injector 66 performs what is known as direct injection of fuel into the combustion chamber 30. The injector may, for example, be mounted in one side of the combustion chamber or in the upper part of the combustion chamber. Fuel may be supplied to the injector 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, the combustion chamber 30 may alternatively or additionally include an injector disposed in the intake manifold 46 in a configuration that performs what is known as port injection of fuel into the intake port upstream of the combustion chamber 30.

[0013] 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 control unit 12 via a signal provided to an electric motor or actuator included in the throttle 62, a configuration commonly referred to as electronic throttle control (ETC). In this manner, the throttle 62 may be actuated to vary the intake air introduced into the combustion chamber 30 between other engine cylinders. The position of the throttle plate 64 may be communicated to the control unit 12 via a throttle position (TP) signal. The intake passage 42 may include a mass air flow sensor 120 and an intake manifold absolute pressure sensor 122 to communicate MAF and MAP signals, respectively, to the control unit 12.

[0014] The ignition system 88 can generate an ignition spark in the combustion chamber 30 via the spark plug 92 in response to the spark advance (SA) signal from the control unit 12 during 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 can be operated in a compression ignition mode, with or without an ignition spark.

[0015] An exhaust gas sensor 126 is shown coupled to the exhaust passage 48 upstream of the exhaust aftertreatment device 70. The sensor 126 may be any suitable sensor capable of providing an indication of the air-fuel ratio in the exhaust gas, such as a linear oxygen sensor or UEGO (Universal or Wide-Range Exhaust Gas Oxygen), a dual-state oxygen sensor or EGO, a HEGO (Heated EGO), a NOx, HC, or CO sensor. The exhaust aftertreatment device 70 may be a three-way catalyst (TWC), a NOx trap, various other exhaust aftertreatment devices, or combinations thereof. In some embodiments, the exhaust aftertreatment 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.

[0016] The engine 10 may further include a boosting device, such as a turbocharger or a supercharger, including at least one compressor 162 disposed along a compressor passage 44, which may include a sensor 123 for measuring air pressure. In a turbocharger, the compressor 162 may be driven at least partially by a turbine 164 (e.g., via a shaft) disposed along the exhaust passage 48. In the case of a supercharger, the compressor 162 may be driven at least partially by the internal combustion engine and / or an electric motor. Thus, the amount of boost provided to one or more cylinders of the engine via a turbocharger or a supercharger may be varied by the control unit 12.

[0017] Furthermore, in the disclosed embodiments, an exhaust gas recirculation (EGR) system (not shown) may direct a desired portion of the exhaust gas from the exhaust passage 48 via an EGR passage to the charge air passage 44 and / or intake passage 42. The amount of EGR introduced into the charge air passage 44 and / or intake passage 42 may be varied by the control unit 12 via an EGR valve. Furthermore, an EGR sensor may be disposed within the EGR passage and may provide an indication of the pressure, temperature, and / or exhaust gas concentration.

[0018] The control unit 12 is in Fig. 1 as a microcomputer including a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values ​​(shown in this particular example as a read-only memory chip 106), a random access memory 108, a keep-alive memory 110, and a data bus. The storage medium of the read-only memory 106 can be programmed with computer-readable data representing instructions executable by the processor 102 to perform the methods described below, as well as other variations that are implicitly included but not explicitly stated.

[0019] In addition to the signals previously discussed, control unit 12 may receive various signals from sensors coupled to engine 10, including measurements of the incoming mass air flow (MAF) from mass air flow sensor 120; engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a profile ignition pickup (PIP) signal from Hall effect sensor 118 (or other type) coupled to crankshaft 40; throttle position (TP) from a throttle position sensor; and the manifold absolute pressure (MAP) signal from sensor 122. The engine speed (revolutions per minute, RPM) signal may be generated by control unit 12 from the PIP signal. The intake manifold pressure MAP signal from an intake manifold pressure sensor can be used to obtain an indication of the vacuum or pressure in the intake manifold.It should be noted that various combinations of the above-mentioned sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. In some circumstances, the MAP sensor may provide an indication of engine torque. Furthermore, this sensor, along with the detected engine speed and other signals, may provide an estimate of the charge (including air) introduced into the cylinder. For example, sensor 118, which is also used as an engine speed sensor, may output a predetermined number of evenly spaced pulses per crankshaft revolution.

[0020] As described above, Fig. 1 only a single cylinder of a multi-cylinder engine, and each cylinder can equally contain its own groups of intake / exhaust valves, fuel injector, spark plug, etc. However, some or all cylinders may also share some components, such as camshafts for controlling valve operation. In this way, a common camshaft can be used to control valve operation for two or more cylinders.

[0021] Fig. 2 shows an embodiment of an engine 200 including an electric VCT system 201 configured to adjust a camshaft position of one or more camshafts of the engine. The engine 200, in this illustration, includes an intake manifold 204 configured to direct intake air and / or fuel to a plurality of cylinders 202 and an exhaust manifold 206 configured to exhaust the combustion products from the plurality of cylinders. Ambient air may flow into the intake system through intake passage 208. The flow rate of intake air to the intake manifold 204 may be controlled at least in part by a main throttle (not shown) disposed within the intake passage 208. The plurality of cylinders 202 may each be served by one or more valves. In the example discussed herein, each cylinder includes a corresponding intake valve 210 and an exhaust valve 212.As will be explained in more detail below, the engine 200 includes one or more camshafts 214 and 216, each of which can be actuated to actuate intake and / or exhaust valves of a plurality of cylinders coupled to a common camshaft.

[0022] Each intake valve 210 may be actuated between an open position allowing intake air into the corresponding cylinder and a closed position substantially blocking intake air to the cylinder. The intake valves 210 of the plurality of cylinders 202 may be actuated by a common intake camshaft 214. The intake camshaft 214 includes intake cams 218 having a cam nose profile for opening the intake valves 210 for a predetermined intake duration. In some embodiments (not shown), the camshaft may include additional intake cams with an alternative cam nose profile that allows the intake valves 210 to be opened for an alternative duration (also referred to herein as a cam profile switching system). Based on the nose profile of the additional cam, the alternative duration may be longer or shorter than the predetermined intake duration of the intake cam 218.The lobe profile can affect cam lift, cam duration, and / or cam timing. A control unit 220 can be configured to change intake valve duration by longitudinally translating the intake camshaft 214 and switching between cam profiles. For example, the control unit 220 is the same as the control unit 12 of FIG. Fig. 1.

[0023] In the same way, each exhaust valve 212 can be actuated between an open position that allows exhaust gas to flow out of the corresponding cylinder and a closed position that substantially retains the gas within the cylinder. The exhaust valves 212 of the plurality of cylinders 202 can be actuated by a common exhaust camshaft 216. The exhaust camshaft 216 includes exhaust lobes 222 having a cam nose profile to open the exhaust valves 212 for a predetermined exhaust duration. In some embodiments (not shown), the camshaft can include additional exhaust lobes with an alternative cam nose profile that can open the exhaust valves 212 for an alternative duration. Based on the nose profile of the additional cam, the alternative duration can be longer or shorter than the predetermined exhaust duration of the exhaust cam 222.The lobe profile may affect cam lift, cam duration, and / or cam timing. Controller 220 may be configured to vary exhaust valve duration by shifting exhaust camshaft 216 longitudinally and switching between cam profiles.

[0024] It should be understood that while the example shown illustrates a common intake camshaft 214 coupled to the intake valves 210 of each cylinder and a common exhaust camshaft 216 coupled to the exhaust valves 212 of each cylinder, in alternative embodiments, the camshafts may also be coupled to subsets of the cylinders and that multiple intake and / or exhaust camshafts may be present. For example, a first intake camshaft may be coupled to the intake valves of a first subset of cylinders, while a second intake camshaft may be coupled to the intake valves of a second subset of cylinders. Similarly, a first exhaust camshaft may be coupled to the exhaust valves of a first subset of cylinders, while a second exhaust camshaft may be coupled to the exhaust valves of a second subset of cylinders.Furthermore, one or more intake valves and exhaust valves may be coupled to each camshaft. The subset of cylinders coupled to the camshaft may depend on their position along the engine block, their firing order, the engine configuration, etc.

[0025] In some embodiments, the camshafts and related components may further cooperate with pushrods, rocker arms, cam followers, etc., to actuate the intake / exhaust valves. Such devices and features may control the actuation of the intake valves 210 and the exhaust valves 212 by converting the rotational motion of the cams into translational motion of the valves. As previously discussed, the valves may also be actuated via additional cam lobe profiles on the camshafts, where the cam lobe profiles may provide varying cam lift, cam duration, and / or cam timing between different valves. However, alternative camshaft arrangements (overhead and / or pushrod) could also be used, if desired. Furthermore, for example, the plurality of cylinders 202 may each have more than one exhaust valve and / or intake valve.For example, each of the exhaust valves and intake valves of one or more cylinders may be actuated by a common camshaft. Furthermore, some of the intake valves and / or exhaust valves may be actuated by their own independent camshaft or other actuating device.

[0026] The electric VCT system 201 includes an electric VCT intake actuator 224 operatively connected to the intake camshaft 214 and an electric VCT exhaust actuator 226 operatively connected to the exhaust camshaft 216. A position of the intake camshaft 214 can be adjusted by the intake actuator 224 via the control unit 220. Similarly, a position of the exhaust camshaft 216 can be adjusted by the exhaust actuator 226 via the control unit 220. The electric VCT system 201 can be configured to advance or retard valve timing by accelerating or retarding cam timing and can be controlled by the control unit 220 via signal lines.

[0027] In some embodiments, the electric VCT system 201 may be an independent, variable twin camshaft timing system to independently control intake valve timing and exhaust valve timing. For example, the electric VCT system 201 may be configured to rotate the intake camshaft 214 and / or the exhaust camshaft 216 independently of the crankshaft to advance or retard valve timing. In some embodiments, the electric VCT system 201 may be a cam torque-actuated device configured to quickly vary cam timing. In some embodiments, valve timing, such as intake valve closing (IVC) and exhaust valve closing (EVC), may be varied by continuously variable valve lift (CVVL).

[0028] The valve and cam timing devices and systems described above may be electrically operated, although in some implementations, at least one camshaft may be adjusted via an electric actuator and another camshaft may be adjusted via a hydraulic actuator. For example, a camshaft position may be varied via cam phasing of an electric actuator (e.g., an electrically actuated cam phaser) with an accuracy exceeding that of most hydraulically actuated cam phasers. The signal lines may send control signals to the electrical VCT system 201 and receive a cam timing and / or cam selection measurement from the electrical VCT system 201.

[0029] The controller 220 may control a camshaft position for a particular camshaft based on closed-loop feedback. For example, the camshaft position feedback may be determined based on a crankshaft position signal and a camshaft PIP signal for that camshaft. For example, the electrical VCT system 201 may be configured to adjust a camshaft position based on camshaft position feedback and operating conditions to open a first valve for a first duration during a first operating mode. In a specific example, the first operating mode occurs at an engine load below a part-load threshold. Further, the electrical VCT system may be configured to open the first valve for a second duration, shorter than the first duration, during a second operating mode.In a concrete example, the second operating mode occurs when the engine load is above a load threshold and the engine speed is below an engine speed threshold (for example, during low to medium engine speeds).

[0030] Such closed-loop control may not be possible until the engine speed has reached a minimum speed threshold. Furthermore, the update rate and resolution of the feedback signal may not be reliable at such low speeds. For example, a 4-tooth PIP wheel allows for an updated cam position every 180 degrees of crank angle, which is 150 ms at 200 rpm. However, in some cases, the electrical VCT system 201 is required to move the camshaft to a desired position within 500 ms. The lack of camshaft position feedback at low engine speeds can make camshaft position control particularly difficult during engine shutdown and engine start-up. Furthermore, the controller 220 may be configured to adjust a camshaft position using the electrical VCT system 201 to a desired initial position for a first ignition event upon engine start-up.In particular, a camshaft position may be adjusted from an initial position to a state other than an end-stop position in order to reduce feed gas (FG) emissions during a first ignition event.

[0031] It should be noted that because the electric VCT system 201 is powered by electricity, the electric VCT system 201 can adjust a camshaft position at low engine speeds (for example, during engine shutdown), while a hydraulically actuated VCT system would not be capable of such adjustment.

[0032] For example, the control unit 220 is configured to adjust a camshaft position to a desired initial position during engine shutdown based on camshaft position feedback in preparation for the next engine start. In this way, the camshaft can be precisely positioned at the desired initial position based on camshaft position feedback when the engine starts. However, the present inventors have discovered that because various adjustment devices may not have locking pins to hold the camshaft in place when no power is flowing to the electric VCT actuator, the camshaft position could be shifted toward a retarded position due to friction braking effects during the uncontrolled phases and would not be maintained at the desired initial position for the first engine firing.In other words, the camshaft position may drift from the desired starting position during periods when no camshaft feedback is available for closed-loop control of the electric VCT actuator of the electric VCT system (for example, at low engine speeds).

[0033] For example, the control unit 220 includes a processor 228 and a computer-readable medium 230 having instructions that, when executed by the processor during engine shutdown, adjust the camshaft position via an electric VCT actuator to a desired initial position, apply a first current to the electric VCT actuator to maintain the desired initial position, and during engine startup, before camshaft position feedback becomes available, apply a second current to the electric VCT actuator to maintain the desired initial position.By applying currents to the electric VCT actuator when camshaft position feedback is unavailable for closed-loop control, the VCT actuator can be adjusted to counteract the valvetrain friction torque acting on the camshaft during such uncontrolled phases of engine shutdown and engine start-up. This can prevent the camshaft position from drifting from a desired initial position when camshaft position feedback is unavailable.

[0034] In some embodiments, the first and second currents are preset currents that can be preset for a particular engine configuration by measuring valvetrain torque at low engine speeds and by knowing the cranking and shutting down engine speed profiles and VCT inertia loads. In other words, the first current can be set to a fixed current level regardless of conditions, and the second current can be set to a fixed current level regardless of conditions.

[0035] In other embodiments, the first and / or second currents may be varied from one shutdown and startup event to the next. For example, once camshaft position feedback becomes available during engine startup, if the camshaft position is farther from the desired initial position than a threshold, one or both of the holding current levels may be adjusted for the next engine shutdown to maintain the camshaft position closer to the desired initial position. In other words, the holding currents may be adaptively learned from one shutdown / start event to the next. For example, one or both of the holding currents may be corrected as a function of coolant temperature during engine shutdown and startup. For example, one or both of the holding currents may be corrected as a function of oil temperature during engine shutdown and startup.In particular, the adaptive learning of the holding currents can be a function of the motor temperatures both at engine shutdown and engine start-up, because the temperatures can be different depending on the duration between engine shutdown and the next engine start-up.

[0036] In some embodiments, the first and second currents may be determined experimentally by controlling the engine to preset low-speed conditions and minimum torque to avoid retardation, and controlling the engine to maximum torque to avoid camshaft advance. In some embodiments, the first current is smaller than the second current because the moment of inertia acting on the camshaft during engine startup is greater than the torque acting during engine shutdown.

[0037] In some embodiments, the first current may be applied in response to the camshaft position feedback no longer being available while the engine is still rotating during engine shutdown. In some embodiments, the desired initial position may be based on a camshaft position signal derived from a crankshaft position and a camshaft PIP signal.

[0038] Note that the second current may be applied first before, during, or immediately after the motor begins to rotate to start the engine. Furthermore, in some embodiments, the second current may be maintained until the feedback sensors reach a level suitable for closed-loop control.

[0039] Furthermore, in some embodiments, the computer-readable medium 230 of the control unit 220 includes instructions that, when executed by the processor 228, increase the current applied to the electric VCT actuator from the first current to a third current greater than the first current to compensate for transient inertia loads of the valvetrain during engine shutdown. Stated another way, the preset current may be increased by a secondary margin to compensate for transient inertia loads that occur at a point between a commanded engine stop and the point at which the engine stops rotating. It should be understood that the current may be increased in any suitable manner without departing from the scope of the present disclosure. For example, the current may be increased incrementally from the first current to the second current.As another example, the current may be gradually increased from the first current to the second current. Furthermore, it should be understood that the current may be adjusted at any suitable time between a commanded motor shutdown and motor stop without departing from the scope of the present disclosure.

[0040] Furthermore, in some embodiments, the computer-readable medium 230 of the control unit 220 includes instructions that, when executed by the processor 228, in response to the camshaft position feedback becoming available after engine start, confirm the position of the camshaft and adjust the camshaft position to the desired initial position using the electric VCT actuator if the camshaft is not at the desired initial position. In other words, when the camshaft position feedback first becomes available during engine start (e.g., when the engine speed becomes greater than a speed threshold), the accuracy of the camshaft position relative to the desired initial position can be confirmed.In the event that the camshaft is not at the desired initial position or within a predefined tolerance, the closed-loop VCT controller can quickly adjust the camshaft position to the desired initial position, since the camshaft is likely close to the desired initial position. Thus, the time to reach the desired initial position after resuming feedback control can be significantly reduced, or ideally, reduced to zero, compared to approaches that do not apply preset currents to the VCT actuators during periods when no camshaft position feedback is available.

[0041] In some embodiments, the computer-readable medium 230 of the control unit 220 further includes instructions that, when executed by the processor 228, apply different current levels to the electric VCT actuator during different conditions of non-combustion engine operation, including shutdown and immediately following cranking and starting, while no camshaft position feedback is available. For example, the different camshaft holding currents may include a first current level during cranking down and a second, different, current level during cranking. In some implementations, the different current levels may be preset and fixed regardless of the operating conditions. In some implementations, the different current levels may be changed in response to the engine cranking down to or cranking up from the rest state.In some implementations, the various current levels can be changed in response to operating conditions. For example, the current levels can be adaptively learned or adjusted from one engine shutdown or startup event to the next. For example, the current levels can be adjusted based on temperatures during engine shutdown and startup or another suitable operating parameter.

[0042] As described above, Fig. 2 shows a non-limiting example of an internal combustion engine and the associated intake and exhaust systems. It should be understood that in some embodiments, the engine may have, among other things, more or fewer combustion cylinders, control valves, throttles, and compression devices. Example engines may have cylinders arranged in a "V" configuration. Further, a first common camshaft may control the valves for a first group of cylinders in a first block, while a second camshaft may control the intake valves for a second group of cylinders in a second block. That is, a common camshaft of a cam actuation system (e.g., an electric VCT system) may be used to control the valve operation of a group of cylinders. Further, the electric VCT system may control a position of one or more camshafts of the engine.

[0043] The configurations illustrated above enable various methods for controlling an electrical VCT system to maintain a camshaft in a desired initial target position for a first ignition event after engine start-up. Accordingly, some such methods will now be described by way of example and with continued reference to the configurations set forth above. However, it should be understood that these methods and others fully within the scope of the present disclosure may also be practiced via other configurations.

[0044] Fig. 3 shows an embodiment of a method 300 for controlling a camshaft position using an electric VCT actuator of an electric VCT system. For example, the method may be performed by the control unit 12 in Fig. 1 or the control unit 220 of Fig. 2 are executed.

[0045] At 302, method 300 includes determining operating conditions. Determining operating conditions may include, for example, camshaft position, crankshaft position, engine speed, torque demand, vehicle speed, ambient conditions, engine temperature, exhaust catalyst temperature, MAP, MAF, etc.

[0046] At 304, method 300 includes determining whether engine shutdown is commanded. If engine shutdown is commanded, method 300 proceeds to 306. Otherwise, method 300 returns to other operations.

[0047] At 306, method 300 includes adjusting the camshaft to a desired initial position using the electric VCT actuator. For example, the camshaft position may be adjusted in a closed-loop manner based on camshaft position feedback including a crankshaft position and a camshaft position. For example, the desired initial position is based on a camshaft position signal.

[0048] At 308, method 300 includes determining whether camshaft position feedback is unavailable and the engine is rotating. For example, the determination may be made based on an engine speed becoming less than a speed threshold. If camshaft position feedback is unavailable and the engine is rotating, method 300 proceeds to 310. Otherwise, method 300 returns to 308.

[0049] At 310, method 300 includes applying a first current to the electric VCT actuator to maintain the camshaft at the desired initial position. For example, the first current may be applied in response to camshaft position feedback becoming unavailable while the engine is rotating during shutdown. In some embodiments, the first current may be applied until the engine stops.

[0050] In some embodiments, method 300 includes, at 312, increasing the current applied to the electric VCT actuator from the first current to a third current greater than the first current to compensate for transient inertia loads of a valvetrain during engine shutdown. For example, the second current may be a preset current that may be predetermined for a particular engine configuration by measuring valvetrain torque at low engine speeds and knowing a shutdown engine speed profile and the inertia loads of the VCT system. In some embodiments, the second current may be applied temporarily, and the current may be decreased to the first current. In some embodiments, the second current may be applied until engine shutdown.

[0051] At 314, method 300 includes determining whether engine start is commanded. If engine start is commanded, method 300 proceeds to 316. Otherwise, method 300 returns to 314.

[0052] At 316, method 300 includes applying a second current to the electric VCT actuator to maintain the camshaft at the desired initial position. In some embodiments, the second current may be applied before the engine begins to rotate for cranking. In some embodiments, the second current may be applied after the engine begins to rotate for cranking. In some embodiments, the first and second currents are the same. In some embodiments, the first current is different from the second current. In some embodiments, the first current is less than the second current.

[0053] At 318, method 300 includes determining whether camshaft position feedback is available. For example, the determination may be made based on an engine speed becoming greater than a speed threshold. If camshaft position feedback is available, method 300 proceeds to 320. Otherwise, method 300 returns to 318.

[0054] At 320, method 300 includes confirming the position of the camshaft using camshaft position feedback.

[0055] At 322, method 300 includes determining whether the camshaft is at the desired starting position. If the camshaft is not at the desired starting position, method 300 proceeds to 324. Otherwise, method 300 returns to other operations.

[0056] At 324, method 300 includes determining whether the camshaft position is farther from the desired starting position than a threshold. If the camshaft position is farther from the desired starting position than the threshold, method 300 proceeds to 326. Otherwise, method 300 proceeds to 328.

[0057] At 326, method 300 includes adjusting the first and / or second holding currents for the next engine shutdown or startup event. The holding currents may be adjusted via adaptive learning to maintain the camshaft at the desired initial position with greater precision during the next engine shutdown or startup event. For example, the holding current correction may be based on a function of the coolant temperature (or oil temperature) during engine shutdown and engine startup. The function may track the temperature during both engine startup and shutdown because temperatures may differ depending on the duration between engine shutdown and the next startup.

[0058] At 328, method 300 includes adjusting the camshaft position to the desired initial position using the electric VCT actuator. By applying a preset current to the VCT actuator during conditions where camshaft position feedback is unavailable, the likelihood of the camshaft drifting from the desired position may be reduced. Furthermore, in the event that the position is not at the desired position or within an assigned tolerance and closed-loop VCT control is again available, the camshaft may be quickly adjusted to the desired position because the camshaft is likely close to the desired position.Thus, the time to position the camshaft at the desired position after resuming feedback control can be significantly reduced, or ideally reduced to zero, compared to approaches that do not apply current to the VCT actuators during conditions where no camshaft position feedback is available.

[0059] In another embodiment, the method includes applying different current levels to an electric VCT actuator of an engine during different conditions of non-combustion engine operation, including a shutdown followed immediately by a cranking and starting, while no camshaft position feedback is available. For example, the different current levels include a first current level during engine shutdown, where the engine is cranking down to rest, and a second, different, current level during engine cranking, where the engine is cranking up to the first ignition event. In some embodiments, the different current levels may be varied in response to the engine cranking down to rest or cranking up from rest because different moments of inertia act on the camshaft during each event.

[0060] In another embodiment, the method for controlling a VCT actuator includes, during engine shutdown, adjusting a camshaft using the VCT actuator to a desired initial position, applying a first hold level to the VCT actuator to maintain the desired initial position, and during engine startup, before camshaft position feedback becomes available, applying a second hold level to the VCT actuator to maintain the desired initial position. In some implementations, the hold level may be preset. In some implementations, the hold level may be adjusted based on operating conditions. For example, the VCT actuator is an electric VCT actuator, and the first hold level is a first current and the second hold level is a second current.For example, the VCT actuator is hydraulically actuated, and the first hold level is a first hydraulic pressure, and the second hold level is a second hold pressure. It should be understood that the hold levels may represent any suitable VCT operating parameter without departing from the scope of the present disclosure.

[0061] Fig.4 shows a graph 400 with characteristics of the current applied to an electric VCT actuator under different operating conditions. The graph 400 plots the current applied to the VCT actuator to control camshaft position versus time. It should be noted that if camshaft feedback is available, closed-loop control of the camshaft position may be used. Furthermore, it should be understood that the illustrated closed-loop control is merely an example and may be of a different type without departing from the scope of the present invention.

[0062] At time T1, engine shutdown is commanded. At time T2, camshaft position feedback is no longer available because the engine speed drops during deceleration. At some point between T1 and T2, the camshaft position is adjusted to the desired starting position using the electric VCT actuator. In response to camshaft position feedback no longer being available, a first current is applied to the electric VCT actuator to compensate for valvetrain torque and maintain the desired starting position. In some embodiments, the first current is applied until engine shutdown at time T4. In some embodiments, at time T3, the current is increased from the first current to the second current to compensate for inertial transient loads. In some embodiments, the second current is applied until engine shutdown at time T4.At time T5, engine cranking is commanded, and a third current is applied to the VCT actuator to maintain the desired initial position. In the illustrated example, the third current is greater than the first current, although it should be understood that in some embodiments, the third current may be equal to the first current or the second current, or less than the first current or the second current. In some embodiments, the third current is applied until camshaft position feedback becomes available at time T6. Once camshaft position feedback becomes available again at time T6, closed-loop control of the camshaft resumes. Note that camshaft position feedback is unavailable for the duration between times T2 and T6.

[0063] It should be noted that the illustrated first, second, and third holding currents are merely examples and may vary without departing from the scope of the present disclosure. Furthermore, the holding currents may vary from one engine shutdown or start-up event to the next. Furthermore, in some implementations, one or more of the currents need not be constant currents as shown. For example, the third current may be varied to compensate for inertia during engine cranking.

[0064] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments should not be considered limiting, as numerous variations are possible. For example, the technology described above can be applied to V6 engines, inline four-cylinder engines, inline six-cylinder engines, V12 engines, horizontally opposed four-cylinder 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.

[0065] The following claims expressly point out certain combinations and sub-combinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalents of such language. Such claims are to be construed as encompassing the incorporation of one or more such elements without requiring or excluding two or more such elements. Other combinations and sub-combinations 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, equal, or different in scope than or equal to the first element, are to be construed as if they were not intended to be amended or modified in any way.as the original claims are also considered to be within the subject matter of the present disclosure.

Claims

[1] A method for controlling a variable cam timing (VCT) actuator, comprising: during shutdown of the engine (10, 200), adjusting a camshaft (214, 216) by means of the VCT actuator (224, 226) to a desired initial position and applying a first hold level to the VCT actuator (224, 226) to maintain the desired initial position, and increasing the hold level applied to the VCT actuator (224, 226) from the first hold level to a third hold level greater than the first hold level to compensate for inertial transient loads of a valve train during shutdown of the engine (10, 200); and during engine start-up (10, 200), before camshaft position feedback becomes available, applying a second hold level to the VCT actuator (224, 226) to maintain the desired initial position; wherein the VCT actuator (224, 226) is an electric VCT actuator and the first hold level is a first current, the second hold level is a second current, and the third hold level is a third current; and where the first current is smaller than the second current. [2] The method of claim 1, further comprising: Increasing the current applied to the electric VCT actuator (224, 226) from the first current to a third current greater than the first current to compensate for inertial transient loads of a valve train during shutdown of the engine (10, 200). [3] The method of claim 1, further comprising: in response to the camshaft position feedback becoming available after starting the engine (10, 200), confirming a camshaft position; and Adjusting the camshaft position by means of the electric VCT actuator (224, 226) to the desired starting position if the camshaft (214, 216) is not at the desired starting position. [4] The method of claim 3, further comprising: in response to the camshaft position being farther than a threshold from the desired starting position, adjusting at least one of the first current and the second current applied to the electric VCT actuator (224, 226) to maintain the camshaft (214, 216) at a desired starting position for a next start of the engine (10, 200). [5] The method of claim 1, wherein the first current is applied in response to the camshaft position feedback no longer being available while the engine (10, 200) is rotating during shutdown. [6] The method of claim 1, wherein the first current is set to a fixed current level regardless of conditions and the second current is set to a fixed current level regardless of conditions. [7] System comprising: an engine (10, 200) including at least one cylinder (30, 202); a camshaft (214, 216) coupled to the at least one cylinder (30, 202), the camshaft (214, 216) being adapted to actuate an intake valve (52, 210) and / or exhaust valve (54, 212) of the at least one cylinder (30, 202); an electric VCT actuator (224, 226) operatively connected to the camshaft (214, 216), the electric VCT actuator (224, 226) being adapted to position the camshaft (214, 216); and a control unit (12, 220) including a processor (102, 228) and a computer-readable medium (106, 230) having instructions that, when executed by the processor (102, 228): while the engine (10, 200) is switched off, adjust the camshaft position to a desired initial position by means of an electric VCT actuator (224, 226); apply a first current to the electric VCT actuator (224, 226) to maintain the desired initial position and increase the current applied to the electric VCT actuator (224, 226) from the first current to a third current greater than the first current to compensate for inertial transient loads of a valve train during shutdown of the engine (10, 200); and during engine start-up (10, 200), before camshaft position feedback becomes available, apply a second current to the electric VCT actuator (224, 226) to maintain the desired initial position; where the first current is smaller than the second current. [8] The system of claim 7, wherein the computer-readable medium (106, 230) further includes instructions that, when executed by the processor (102, 228): in response to the camshaft position feedback becoming available after starting the engine (10, 200), confirm the position of the camshaft (214, 216); and adjust the camshaft position to the desired starting position by means of the electric VCT actuator (224, 226) if the camshaft (214, 216) is not at the desired starting position. [9] The system of claim 8, wherein the computer-readable medium (106, 230) further includes instructions that, when executed by the processor (102, 228): in response to the camshaft position being farther than a threshold from the desired starting position, adjust the first current and / or the second current applied to the electric VCT actuator (224, 226) to maintain the camshaft (214, 216) at a desired starting position for a next start of the engine (10, 200). [10] The system of claim 7, wherein the first current is applied in response to the camshaft position feedback no longer being available while the engine (10, 200) is rotating during shutdown. [11] The system of claim 7, wherein the first current is set to a fixed current level regardless of conditions and the second current is set to a fixed current level regardless of conditions.

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