WO2009148893A1 - Passive pressure-responsive engine valve unseating - Google Patents

Abstract

A method of engine valve timing, and products and engines using same.

Description

PASSIVE PRESSURE-RESPONSIVE ENGINE VALVE UNSEATING

This application claims the benefit of U.S. Provisional Application No. 61/057,903 filed June 2, 2008.

TECHNICAL FIELD

The field to which the disclosure generally relates includes power plants or engines and, more particularly, to operating mechanisms for poppet valves of internal combustion engines.

BACKGROUND

An internal combustion engine includes intake and exhaust poppet valves to respectively admit a combustible charge of fuel to and expel combustion gases from a combustion chamber of the engine. Conventional mechanical valvetrains of internal combustion engines include valve springs to bias the poppet valves toward a closed position, a camshaft with lobes and coupled to a crankshaft of the engine, and cam- follower devices coupled between the camshaft and the poppet valves. The camshaft rotates in synchronicity with the crankshaft so that rotation of the camshaft lobes actively opens the valves against the bias force of the valve springs. Recent valvetrains include variable camshaft timing (VCT) devices operably coupled between the camshaft and the crankshaft to adjust an angular position of the camshaft (cam angle) relative to an angular position of the crankshaft (crank angle) to vary valve timing. Such devices are particularly useful for overlapping the opening of the intake and exhaust valves to achieve internal exhaust gas recirculation (EGR) for reduced exhaust emissions. Some VCT devices also include camshafts with three-dimensionally profiled cam lobes, wherein the camshafts are axially shifted to traverse the profiled cam lobes over a poppet valve to additionally vary valve lift. More recent valvetrains do not include camshafts and instead include variable valve actuation (VVA) devices directly coupled to the poppet valves to individually control valve timing and lift. According to generally accepted wisdom in the art, VCT and Vλ^A devices use crank- angle-based valve timing to actively vary valve opening and closing relative to the engine's operating cycle. But in multi-cylinder engines such timing may not provide repeatabie cylinder-to-cylinder or cycle-to-cycle cylinder filling or EGR residual gas content because of pressure variations in the cylinders and in the engine intake and exhaust manifolds. This is particularly true at engine speeds and loads where acoustic waves in the manifolds are not in phase with the engine operating cycle.

SUMMARY OF EXEMPLARY EMBODIMENTS

One exemplary embodiment includes an internal combustion engine including a cylinder block including a cylinder and carrying a crankshaft, and a piston disposed in the cylinder of the cylinder block. The engine also includes a cylinder head coupled to the cylinder block and including a valve seat and a fluid passage, and a manifold in fluid communication with the fluid passage of the cylinder head. The engine further includes a valve carried by the cylinder head in communication with the cylinder and seated against the valve seat of the cylinder head at least during an ignition event, which at least partially produces a cylinder pressure that results in a cylinder force on the valve tending to seat the valve against a manifold force on the valve imposed by manifold pressure in the fluid passage of the cylinder head. The engine additionally includes a variable valve actuator coupled to the valve to apply a variable force on the valve to actively open the valve with respect to an angular position of the crankshaft, after applying a set force on the valve such that the valve unseats when the set force exceeds a predetermined level of a net force on the valve resulting from the cylinder force and the manifold force and irrespective of crank-angle-based valve timing.

Another exemplary embodiment includes a product for an internal combustion engine, w^rhich includes a crankshaft, and a valve in communication with a cylinder. The product includes a variable valve actuator coupleable to the valve to apply a set force on the valve such that the valve is passively allowed to unseat as a direct function of a relative decrease in cylinder pressure and irrespective of crank-angle-based valve timing.

A further exemplary embodiment includes a method of engine valve timing for an engine including a crankshaft, and a valve in communication with a cylinder of the engine. The method includes applying a set force on the valve such that the valve is passively allowed to unseat as a direct function of a relative decrease in cylinder pressure and irrespective of crank- angle-based valve timing. Other exemplary embodiments will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments, are intended for purposes of illustration only and are not intended to limit the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWTNGS

Exemplary embodiments will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is cross-sectional schematic view of an exemplary embodiment of an internal combustion engine including variable valve actuators to actuate exhaust and intake valves;

FIG. 2 is a cross-sectional schematic view of an exemplary embodiment of the variable valve actuators of FiG. 1;

FIG. 3 is a cross-sectional schematic view of another exemplary embodiment of the variable valve actuators of FIG. 1 ; FIG. 4 is a graphical plot of an exemplary embodiment of exhaust and intake valve timing and lift for the engine of FIG. 1 ; and

FIG. 5 is a graphical plot of an exemplary embodiment of engine cylinder pressure that produces a cylinder force on the exhaust and intake valves of FIG. 1

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description of the exemplary embodiment(s) is merely exemplary in nature and is in no way intended to limit the claims, their application, or uses.

An exemplary operating environment is illustrated in FIG. 1 , and may be used to implement a presently disclosed method of controlling valve timing. The method generally may include engine valve timing wherein a valve becomes unseated in a passive, pressure- responsive manner. More specifically, the method may include applying a set force on the valve such that the valve is allowed to unseat as a direct function of a relative decrease in cylinder pressure and irrespective of crank-angle-based valve timing.

The method may be carried out using any suitable engine and, more specifically, may be carried out in conjunction with an internal combustion engine such as engine 10. The following engine description simply provides a brief overview' of a portion of one exemplary engine, but other engines and components not shown here could also support the presently disclosed method. In general, the engine 10 may include a block assembly 12, a head assembly 14 coupled to the block assembly 12 in any suitable manner, intake and exhaust manifolds 16, 18, and a controller 20 to control at least some operation of the engine 10. The engine 10 may be a gasoline or diesel engine, a turbocharged or naturally-aspirated engine, a single or multiple cylinder engine, a two, three, or four valve-per-cylinder engine, or any other type of engine.

The block assembly 12 may include a block 22 that defines a cylinder 24 and a crankcase 26 and partially defines a combustion chamber 28. The block assembly 12 may further include a piston 30 disposed in the cylinder 24, and a crankshaft 32 disposed in the crankcase 26 and coupled to the piston 30 by a connecting rod 34. The block assembly 12 may also include a position sensor 36 that may be carried by the block 22 and cooperative with crank angle features 38 that may be provided on the crankshaft 32 itself or on some other component coupled to the crankshaft 32.

The head assembly 14 may include a cylinder head 40 that partially defines the combustion chamber 28 and has intake and exhaust passages 42, 44, a spark plug 46 (or glow^r plug for diesel applications) carried by the head 40, and intake and exhaust valves 48, 50 carried by the head 40 and including valve heads 52, 54 partially defining the combustion chamber 28 at least when closed. The head assembly 14 may also include one or more variable valve actuators 58 that are operatively coupleable to the controller and to the valves 48, 50 to open and close the valves according to variable timing and/or lift. The actuators 58 may be electro-mechanical devices, for example, electro-hydraulic devices, and/or electromagnetic devices like solenoids as one example. Any suitable quantity of valves 48, 50 and actuators 58 may be used, for example, one actuator 58 for each valve 48. 50.

The induction or intake manifold 16 may be coupled to the cylinder head 40 in any suitable manner and may convey air or other induction gas to the combustion chamber 28 via the intake passage 42 of the cylinder head 40. The intake manifold 16 may also carry a fuel injector 56 upstream of the intake valve 48 to inject fuel into the combustion chamber 28 via the intake passage 42 of the cylinder head 40. The fuel injector 56 may also or instead be carried by the head 40 or the block 22 for direct injection to the combustion chamber 28. The exhaust manifold 18 may be coupled to the cylinder head 40 in any suitable manner and may convey combustion or exhaust gases to a downstream exhaust system (not shown) via the exhaust passage 44 of the cylinder head 40. Instead of being separate components, the intake and exhaust manifolds 16, 18 may be partially or entirely integrated with the cylinder head 40.

In general, the controller 20 may receive input from various devices associated with the engine 10, for example, the crankshaft position sensor 36, a throttle position sensor 37a, an intake manifold pressure sensor 37b, an air temperature sensor 37c, and/or an engine temperature sensor 37d. The controller 20 may process this input in light of stored instructions and/or data, and may transmit output signals to other devices associated with the engine 10, for example, the variable valve actuators 58. The controller 20 may be, for example, an electrical circuit, an electronic circuit or chip, and/or a computing device. In the computing device embodiment, the controller 20 generally may include a processor (not shown), memory coupled to the processor (not shown), and one or more interfaces to couple the controller to one or more other devices (not shown). The processor may execute instructions that provide at least some of the functionality for the engine 10. As used herein, the term instructions may include, for example, control logic, computer software and/or firmware, programmable instructions, or other suitable instructions executable by the processor. The processor may include, for example, one or more microprocessors, microcontrollers, application specific integrated circuits, and/or any other suitable type of processing device. Also, the memory may be configured to provide storage for data received by or loaded to the engine controller 20, and/or for processor-executable instructions. The data and/or instructions may be stored, for example, as look-up tables, formulas, algorithms, maps, models, and/or any other suitable format. The memory may include, for example, RAM, ROM, EPROM, and/or any other suitable type of storage device. Finally, the interfaces may include, for example, analog/digital converters, signal conditioners, other electronics or software modules, and/or any other suitable interfaces. The interfaces may conform to, for example. RS-232, parallel, small computer system interface, universal serial bus, CAN, MOST, LIN, FlexRay, and/or any other suitable protocol(s). The interfaces may include circuits, software, firmware, or any other device to assist or enable the controller 20 in communicating with other devices.

FIGS. 2 and 3 illustrate two examples of electromagnetic actuators that may be used for the variable valve actuators 58 of FIG. 1. Referring first to FlG. 2, an exemplary variable valve actuator 158 may include an axial-attraction arrangement that may include a housing 160 that may carry a first electromagnetic coil 162 to close a valve 150 and a second electromagnet coil 164 to open the valve 150. The actuator 158 may also include a plate-like armature 166 between the coils 162, 164, and first and second springs 168, 170 to bias the armature 166 to any desired position, for example, a neutral position as shown. A position sensor 172 may be coupled to the controller 20 and used to detect positioning of the valve 150 and may include, for example, a proximity sensor, a displacement transducer, and/or any other suitable device to detect one or more positions of the valve 150.

Referring now to FIG. 3, another exemplary variable valve actuator 258 may include a radial-attraction arrangement that may include a housing 260 that may carry a first electromagnetic coil 262 to close a valve 250 and a second electromagnet coil 264 to open the valve 250. The actuator 258 may also include a cylinder-like armature 266 between the coils 262, 264, and first and second springs 268, 270 to bias the armature 266 to any desired position, for example, a neutral position as shown. A position sensor 272 may be coupled to the controller 20 and used to detect positioning of the valve 250 and may include, for example, a proximity sensor, a displacement transducer, and/or any other suitable device to detect one or more positions of the valve 250. Referring to FIGS. 2 and 3, the armatures 166, 266 may be coupled to the valves 150,

250 to advance and retract the valves 150, 250 so as to open the valves 150. 250 into an engine cylinder 128, 228 and close the valves 150, 250 against valve seats 141, 241 of cylinder heads 140, 240. The springs 168, 170, 268, 270 may be, for example, compression or tension springs to push or pull the armatures 166, 266. The coils 162, 164 and 262, 264 may be coupled to and powered in any suitable manner, for example, by a vehicle battery, one or more capacitors, and/or any other suitable device(s) (not shown). The coils 162, 164 and 262, 264 may be coupled to and controlled in any suitable manner, for example, by the controller 20 and/or any other suitable device(s).

In operation, and according to an embodiment of the method, the method may be at least partially carried out as one or more computer programs within the engine 10 operating environment described above. Those skilled in the art will also recognize that a method according to any number of embodiments may be carried out using other engines within other operating environments. As the description of the method progresses, reference will be made to the exemplary engine 10 of FIG. 1, the exemplary actuators 158, 258 of FIGS. 2 and 3, and the exemplary plots of FIGS. 4 and 5.

FIG. 4 illustrates a graphical representation of engine cylinder pressure along a Y axis and an exemplary engine operating cycle along an X axis. The engine operating cycle may include a compression stroke from -180 degrees of crankshaft angle at bottom dead center (BDC) to 0 degrees top dead center firing (TDCF) of the piston 30 in the engine cylinder 24, a combustion or power stroke from TDCF to 180 degrees BDC, an exhaust stroke from BDC to 360 degrees TDC, and an expansion or intake stroke from TDC to 540 degrees BDC.

According to the exemplary method, a mixture of fuel and induction gases may be supplied to the engine cylinder 24, for example, during the intake stroke. Then, the fuel and induction gas mixture may be compressed by the piston 30, for example, during the compression stroke. According to an exemplary pressure trace T of FIG. 4, cylinder pressure rapidly increases during the compression stroke as the piston 30 moves toward the cylinder head 40 to define the combustion chamber 28. Thereafter, the compressed fuel and induction gas mixture may be ignited by an ignition event, for example, by activation of the spark plug 46 or by diesel auto-ignition during the power stroke. The ignition event may further produce cylinder pressure, which results in a cylinder force on the valve 48 or 50 tending to seat the valve 48 or 50 against the cylinder head 40. In the illustrated example, ignition of fuel and induction gases in the combustion chamber 28 may occur slightly after TDCF and cylinder pressure may peak at about 35 degrees after TDCF. Cylinder pressure may rapidly decrease during the power stroke as the piston 30 is displaced toward the crankcase 26 to rotate the crankshaft 32.

Subsequently, the exhaust valve 50 may passively open as a direct function of a decrease in cylinder pressure below a predetermined cylinder pressure level. As shown in FIG. 4, an exemplary predetermined cylinder pressure level may be about 12.5 bar. But, any predetermined pressure level(s) may be used. Cylinder pressure may decrease less rapidly over the exhaust stroke as exhaust gases are expelled from the cylinder 24.

Similarly, the intake valve 48 may passively open as a direct function of a further decrease in cylinder pressure below another predetermined cylinder pressure level. As shown in FIG. 4, an exemplary other predetermined cylinder pressure level may be about 3.5 bar. But, any predetermined pressure level(s) may be used. Cylinder pressure may more or less flatten and minimize over the intake stroke as induction gases are drawn into the cylinder 24. Given the relatively small pressure differential over the expansion stroke, the actuator 56 used to actuate the intake valve 48 may be more precise or resolute in its operation compared to the actuator 56 used to actuate the exhaust valve 50.

At least during the power stroke, cylinder pressure imposes a cylinder force on the valve 48 or 50 in the direction of seating the valve 48 or 50, and manifold pressure in the fluid passage 42 or 44 of the cylinder head 40 may also impose a manifold force on the valve 48 or 50 in the direction of unseating the valve 48 or 50. More specifically, the cylinder force may be a function of cylinder pressure acting on a relevant area of the valve 48 or 50 facing the combustion chamber 28, and the manifold force may be a function of manifold pressure acting on another relevant area of the valve 48 or 50 facing the fluid passage 42 or 44 of the cylinder head 40. In any event, a net force on the valve 48 or 50 results from the cylinder force and the manifold force in the direction of seating the valve 48 or 50, at least during the power stroke.

According to the exemplary method, the actuator 56 applies a set force on the valve 48 or 50, such that the valve 48 or 50 is allowed to unseat as a direct function of a relative decrease in cylinder pressure. As used herein, the term "direct" is used in contrast to a situation wherein an actuator varies application of force to a valve to unseat the valve in indirect response via a cylinder pressure sensor reading. In a specific example, the actuator 56 may apply the set force on the valve 48 or 50, such that the valve 48 or 50 is passively allowed to unseat when the set force exceeds a predetermined level of the net force on the valve 48 or 50 resulting from the cylinder force and the manifold force and irrespective of crank-angle-based valve timing. In other words, when the net force on the valve 48, or 50 is exceeded by the set force on the valve 48 or 50, the valve 48 or 50 will open. The valve opening timing is passively controlled because the decrease in cylinder pressure or the decrease in the net force on the valve 48 or 50 is the agency that allows or activates the valve opening. The set force may be applied within an appropriate stroke of the engine cycle, for example, during a latter portion of the power stroke or an earlier portion of the exhaust stroke for an exhaust valve, and during a latter portion of the exhaust stroke or an earlier portion of an intake stroke for an intake valve. Although crankshaft position may be referenced in this regard, crank-angle-based timing need not be used. Referring to FIGS. 4 and 5, the set force may be provided by energizing a coil, for example, the first electromagnetic coil 162, 262. Also, the set force may be provided or supplemented by selection of a suitable spring, for example, the first springs 168, 268. In this embodiment, no separate cylinder pressure sensors need be used as input to energize the actuator 158, 258 because the actuator itself senses cylinder pressure and the valve becomes unseated as a direct function of a decrease in cylinder pressure below a predetermined level.

Also according to the exemplary method, after the valve 150, 250 unseats or is displaced from the valve seat 141, 241 of the cylinder head 140, 240, valve timing may be actively controlled with respect to crank-angle-based timing and/or regardless of cylinder pressure. For example, a crank-angle-based timing map may be stored in the memory and executed by the processor of the controller 20 in conjunction with data received from the position sensor 36 to output control signals to the actuator(s) 58, 158, 258. This step may be triggered by a signal from the valve position sensor 172, 272 or in any other suitable manner. In a specific example, the controller 20 may receive a signal from the valve position sensor 172, 272 that indicates that valve 150, 250 has been unseated. Thereafter, the controller 20 may vary a supply of electrical current to the variable valve actuator 158, 258 to apply a variable force to the valve 150, 250 according to a crank-angle-based valve timing stored in the controller 20. In other words, the controller 20 controls the actuator 158, 258 to actively set the timing of the valve 150, 250. Because there is no significant pressure difference after the valve 150, 250 has been unseated, switching to a conventional crank-angle-based valve timing scheme may assist in achieving a consistent valve opening duration and a low valve seating velocity.

Tn a running engine, the presently disclosed exemplary method may result in some scatter in valve timing relative to crankshaft position. But an initial gas exchange, for example between a manifold and an engine cylinder, may be more consistent, because fluid flow conditions across a valve will be substantially proportional to the difference in pressure across the valve. The result may include more consistent cycle-to-cycle engine breathing.

The above description of embodiments is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the claims.

Claims

CLAIMSWhat is claimed is:

1. An internal combustion engine comprising; a cylinder block including a cylinder and carrying a crankshaft; a piston disposed in the cylinder of the cylinder block; a cylinder head coupled to the cylinder block and including a valve seat and a fluid passage; a manifold in fluid communication with the fluid passage of the cylinder head; a valve carried by the cylinder head in communication with the cylinder and seated against the valve seat of the cylinder head at least during an ignition event, which at least partially produces a cylinder pressure that results in a cylinder force on the valve tending to seat the valve against a manifold force on the valve imposed by manifold pressure in the fluid passage of the cylinder head; and a variable valve actuator coupled to the valve to apply a variable force on the valve to actively open the valve with respect to an angular position of the crankshaft, after applying a set force on the valve such that the valve unseats when the set force exceeds a predetermined level of a net force on the valve resulting from the cylinder force and the manifold force and irrespective of crank-angle-based valve timing.

2. The engine as set forth in claim 1 wherein the valve is an exhaust valve.

3. The engine as set forth in claim 1 w^rherein the valve is an intake valve.

4. A product for an internal combustion engine, which includes a crankshaft, and a valve in communication with a cylinder, the product comprising a variable valve actuator coupleable to the valve to apply a set force on the valve such that the valve is passively allowed to unseat as a direct function of a relative decrease in cylinder pressure and irrespective of crank- angle-based valve timing.

5. The product of claim 4 such that the valve becomes unseated when the set force exceeds a predetermined level of a net force on the valve resulting from a cylinder force and manifold force on the valve.

6. The product of claim 4 wherein the variable valve actuator applies a variable force on the valve to actively open the valve with respect to the angular position of the crankshaft, after the valve unseats.

7. The product of claim 6 further comprising a controller coupled to the variable valve actuator to vary a supply of electrical current to the variable valve actuator to apply the variable force according to crank-angle-based valve timing stored in the controller.

8. A method of engine valve timing for an engine including a crankshaft, and a valve in communication with a cylinder of the engine, the method comprising applying a set force on the valve such that the valve is passively allowed to unseat as a direct function of a relative decrease in cylinder pressure and irrespective of crank-angle-based valve timing.

9. The method of claim 8, further comprising applying a variable force on the valve to actively open the valve with respect to the angular position of the crankshaft, after the valve unseats.