US20030213444A1

US20030213444A1 - Engine valve actuation system

Info

Publication number: US20030213444A1
Application number: US10/309,312
Authority: US
Inventors: Sean Cornell; Scott Leman
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2002-05-14
Filing date: 2002-12-04
Publication date: 2003-11-20

Abstract

An engine valve actuation system that includes an intake valve moveable between a first position that blocks a flow of fluid and a second position that allows a flow of fluid. The system also includes a cam assembly connected to move the intake valve between the first position and the second position and a fluid actuator configured to selectively modify a timing of the intake valve in moving from the second position to the first position. A snubbing valve is configured to restrict a flow of fluid from the fluid actuator so as to reduce a rate of movement of the intake valve to the first position.

Description

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 10/______ (Attorney Docket No. 08350.2153-01), filed on Oct. 30, 2002, of Sean O. Cornell and Scott A. Leman for “Engine Valve Actuation System,” which is a continuation-in-part of U.S. patent application Ser. No. 10/144,062, filed on May 14, 2002.[0001]

TECHNICAL FIELD

The present invention is directed to an engine valve actuation system. More particularly, the present invention is directed to a valve actuation system for an internal combustion engine.

BACKGROUND

The operation of an internal combustion engine, such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions. These emissions, which may include particulates and nitrous oxide (NOx), are generated when fuel is combusted in a combustion chamber of the engine. An exhaust stroke of an engine piston forces exhaust gas, which may include these emissions from the engine. If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.

Research is currently being directed towards decreasing the amount of undesirable emissions that are exhausted to the environment during the operation of an engine. It is expected that improved engine design and improved control over engine operation may lead to a reduction in the generation of undesirable emissions. Many different approaches, such as, for example, engine gas recirculation and aftertreatments, have been found to reduce the amount of emissions generated during the operation of an engine. Unfortunately, the implementation of these emission reduction approaches typically results in a decrease in the overall efficiency of the engine.

Additional efforts are being focused on improving engine efficiency to compensate for the efficiency loss due to the emission reduction systems. One such approach to improving the engine efficiency involves adjusting the actuation timing of the engine valves. For example, the actuation timing of the intake and exhaust valves may be modified to implement a variation on the typical diesel or Otto cycle known as the Miller cycle. In a “late intake” type Miller cycle, the intake valves of the engine are held open during a portion of the compression stroke of the piston.

The engine valves in an internal combustion engine are typically driven by a cam arrangement that is operatively connected to the crankshaft of the engine. The rotation of the crankshaft results in a corresponding rotation of a cam that drives one or more cam followers. The movement of the cam followers results in the actuation of the engine valves. The shape of the cam governs the timing and duration of the valve actuation. As described in U.S. Pat. No. 6,237,551 to Macor et al., issued on May 29, 2001, a “late intake” Miller cycle may be implemented in such a cam arrangement by modifying the shape of the cam to overlap the actuation of the intake valve with the start of the compression stroke of the piston.

In engines capable of implementing a late intake Miller cycle, the intake valves may be spring-loaded to a closed position by a relatively stiff spring. Therefore, when the intake valve is closed, under either a conventional cycle or a late intake cycle, the valve may close and/or open at a high velocity. When closing, the intake valve may impact the valve seat at velocities that can create forces that may eventually erode the valve or the valve seat, or even fracture or break the valve.

Engines implementing a late intake Miller cycle may include a fluid actuator capable of varying the closing timing of mechanically operated intake valve. In such systems, the fluid actuator may also experience impact forces against an actuator chamber wall associated with the closing of the intake valves by the stiff return springs. Therefore, the fluid actuator may also suffer erosion, fracture, and/or breakage.

The intake valve actuation system of the present invention solves one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to an engine valve actuation system that includes an intake valve moveable between a first position that blocks a flow of fluid and a second position that allows a flow of fluid. The system also includes a cam assembly connected to move the intake valve between the first position and the second position and a fluid actuator configured to selectively modify a timing of the intake valve in moving from the second position to the first position. A snubbing valve is configured to restrict a flow of fluid from the fluid actuator so as to reduce a rate of movement of the intake valve to the first position.

In another aspect, the present invention is directed to a method of controlling an engine having a piston moveable through an intake stroke followed by a compression stroke. The method includes cammingly moving an intake valve between a first position that blocks a flow of fluid and a second position that allows a flow of fluid during the intake stroke of the piston. The method also includes directing fluid to a fluid actuator associated with the intake valve when the intake valve is away from the first position and restricting a flow of fluid from the fluid actuator during at least a portion of the compression stroke to reduce a velocity of the intake valve movement to the first position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-sectional view of an exemplary embodiment of an internal combustion engine; [0012]
FIG. 2 is a diagrammatic cross-sectional view of a cylinder and valve actuation assembly in accordance with an exemplary embodiment of the present invention; [0013]
FIG. 3A is a schematic and diagrammatic representation of a fluid supply system for a fluid actuator for an engine valve in accordance with an exemplary embodiment of the present invention; [0014]
FIG. 3B is a schematic and diagrammatic representation of another embodiment of a fluid supply system for a fluid actuator for an engine valve in accordance with an exemplary embodiment of the present invention; [0015]
FIG. 4 is a schematic and diagrammatic representation of a fluid supply system for a fluid actuator in accordance with another exemplary embodiment of the present invention; [0016]
FIG. 5 is a graphic illustration of an exemplary valve actuation as a function of engine crank angle for an engine operating in accordance with the present invention; [0017]
FIG. 6 is a cross-sectional view of an exemplary embodiment of a check valve for a fluid actuator in accordance with an embodiment of the present invention; [0018]
FIG. 7 is a cross-sectional view of an exemplary embodiment of an accumulator for a fluid actuator in accordance with an embodiment of the present invention; [0019]
FIG. 8A is a side sectional view of a fluid actuator and a snubbing valve in accordance with an exemplary embodiment of the present invention; and [0020]
FIG. 8B is a side sectional view of a fluid actuator and a snubbing valve in accordance with another exemplary embodiment of the present invention. [0021]

DETAILED DESCRIPTION

An exemplary embodiment of an [0022] internal combustion engine 20 is illustrated in FIG. 1. For the purposes of the present disclosure, the engine 20 is depicted and described as a four stroke diesel engine. One skilled in the art will recognize, however, that the engine 20 may be any other type of internal combustion engine, such as, for example, a gasoline or natural gas engine.
As illustrated in FIG. 1, the [0023] engine 20 includes an engine block 28 that defines a plurality of cylinders 22. A piston 24 is slidably disposed within each cylinder 22. In the illustrated embodiment, the engine 20 includes six cylinders 22 and six associated pistons 24. One skilled in the art will readily recognize that the engine 20 may include a greater or lesser number of pistons 24 and that the pistons 24 may be disposed in an “in-line” configuration, a “V” configuration, or any other conventional configuration.
As also shown in FIG. 1, the [0024] engine 20 includes a crankshaft 27 that is rotatably disposed within the engine block 28. A connecting rod 26 connects each piston 24 to the crankshaft 27. Each piston 24 is coupled to the crankshaft 27 so that a sliding motion of the piston 24 within the respective cylinder 22 results in a rotation of the crankshaft 27. Similarly, a rotation of the crankshaft 27 will result in a sliding motion of the piston 24.
The [0025] engine 20 also includes a cylinder head 30. The cylinder head 30 defines an intake passageway 41 that leads to at least one intake port 36 for each cylinder 22. The cylinder head 30 may further define two or more intake ports 36 for each cylinder 22.
An [0026] intake valve 32 is disposed within each intake port 36. Each intake valve 32 includes a valve element 40 that is configured to selectively block the respective intake port 36. As described in greater detail below, each intake valve 32 may be actuated to move or “lift” the valve element 40 to thereby open the respective intake port 36. In a cylinder 22 having a pair of intake ports 36 and a pair of intake valves 32, the pair of intake valves 32 may be actuated by a single valve actuation assembly or by a pair of valve actuation assemblies.
The [0027] cylinder head 30 also defines at least one exhaust port 38 for each cylinder 22. Each exhaust port 38 leads from the respective cylinder 22 to an exhaust passageway 43. The cylinder head 30 may further define two or more exhaust ports 38 for each cylinder 22.
An [0028] exhaust valve 34 is disposed within each exhaust port 38. Each exhaust valve 34 includes a valve element 48 that is configured to selectively block the respective exhaust port 38. As described in greater detail below, each exhaust valve 34 may be actuated to move or “lift” valve element 48 to thereby open the respective exhaust port 38. In a cylinder 22 having a pair of exhaust ports 38 and a pair of exhaust valves 34, the pair of exhaust valves 34 may be actuated by a single valve actuation assembly or by a pair of valve actuation assemblies.
FIG. 2 illustrates an exemplary embodiment of one [0029] cylinder 22 of the engine 20. As shown, the cylinder head 30 defines a pair of intake ports 36 connecting the intake passageway 41 to the cylinder 22. Each intake port 36 includes a valve seat 50. One intake valve 32 is disposed within each intake port 36. The valve element 40 of the intake valve 32 is configured to engage the valve seat 50. When the intake valve 32 is in a closed position, the valve element 40 engages the valve seat 50 to close the intake port 36 and block fluid flow relative to the cylinder 22. When the intake valve 32 is lifted from the closed position, the intake valve 32 allows a flow of fluid relative to the cylinder 22.
Similarly, the [0030] cylinder head 30 may define two or more exhaust ports 38 (only one of which is illustrated in FIG. 1) that connect the cylinder 22 with the exhaust passageway 43. One exhaust valve 34 is disposed within each exhaust port 38. A valve element 48 of each exhaust valve 34 is configured to close the exhaust port 38 when the exhaust valve 34 is in a closed position and block fluid flow relative to the cylinder 22. When the exhaust valve 34 is lifted from the closed position, the exhaust valve 32 allows a flow of fluid relative to the cylinder 22.
As also shown in FIG. 2, a [0031] valve actuation assembly 44 is operatively associated with the intake valves 32. The valve actuation assembly 44 includes a bridge 54 that is connected to each valve element 40 through a pair of valve stems 46. A spring 56 may be disposed around each valve stem 46 between the cylinder head 30 and the bridge 54. The spring 56 acts to bias both valve elements 40 into engagement with the respective valve seat 50 to thereby close each intake port 36.
The [0032] valve actuation assembly 44 also includes a rocker arm 64. The rocker arm 64 is configured to pivot about a pivot 66. One end 68 of the rocker arm 64 is connected to the bridge 54. The opposite end of the rocker arm 64 is connected to a cam assembly 52. In the exemplary embodiment of FIG. 2, the cam assembly 52 includes a cam 60 having a cam lobe and mounted on a cam shaft, a push rod 61, and a cam follower 62. One skilled in the art will recognize that the cam assembly 52 may have other configurations, such as, for example, where the cam 60 acts directly on the rocker arm 64.
The [0033] valve actuation assembly 44 may be driven by the cam 60. The cam 60 is connected to the crankshaft 27 so that a rotation of the crankshaft 27 induces a corresponding rotation of the cam 60. The cam 60 may be connected to the crankshaft 27 through any means readily apparent to one skilled in the art, such as, for example, through a gear reduction assembly (not shown). As one skilled in the art will recognize, a rotation of the cam 60 will cause the cam follower 62 and associated push rod 61 to periodically reciprocate between an upper position and a lower position.
The reciprocating movement of the [0034] push rod 61 causes the rocker arm 64 to pivot about the pivot 66. When the push rod 61 moves in the direction indicated by arrow 58, the rocker arm 64 will pivot and move the bridge 54 in the opposite direction. The movement of the bridge 54 causes each intake valve 32 to lift and open the intake ports 36. As the cam 60 continues to rotate, the springs 56 will act on the bridge 54 to return each intake valve 32 to the closed position.
In this manner, the shape and orientation of the [0035] cam 60 controls the timing of the actuation of the intake valves 32. As one skilled in the art will recognize, the cam 60 may be configured to coordinate the actuation of the intake valves 32 with the movement of the piston 24. For example, the intake valves 32 may be actuated to open the intake ports 36 when the piston 24 is withdrawing within the cylinder 22 to allow air to flow from the intake passageway 41 into the cylinder 22.
A similar valve actuation assembly may be connected to the [0036] exhaust valves 34. A second cam (not shown) may be connected to the crankshaft 27 to control the actuation timing of the exhaust valves 34. The exhaust valves 34 may be actuated to open the exhaust ports 38 when the piston 24 is advancing within the cylinder 22 to allow exhaust to flow from the cylinder 22 into the exhaust passageway 43.
As shown in FIG. 2, the [0037] valve actuation assembly 44 also includes a fluid actuator 70. The fluid actuator 70 includes an actuator cylinder 72 that defines an actuator chamber 76. An actuator piston 74 is slidably disposed within the actuator cylinder 72 and is connected to an actuator rod 78. The actuator rod 78 is engageable with an end 68 of the rocker arm 64.
A [0038] fluid line 80 is connected to the actuator chamber 76. Pressurized fluid may be directed through the fluid line 80 and into the actuator chamber 76 to move the actuator piston 74 within the actuator cylinder 72. Movement of the actuator piston 74 causes the actuator rod 78 to engage the end 68 of the rocker arm 64. Fluid may be introduced to the actuator chamber 76 when the intake valves 32 are in the open position to move the actuator rod 78 into engagement with the rocker arm 64 to thereby hold the intake valves 32 in the open position. Alternatively, fluid may be introduced to the actuator chamber 76 when the intake valves 32 are in the closed position to move the actuator rod 78 into engagement with the rocker arm 64 and to pivot the rocker arm 64 about the pivot 66 to thereby open the intake valves 32.
As illustrated in FIGS. 1 and 3, a source of [0039] fluid 84, which is connected to a tank 87, supplies pressurized fluid to the fluid actuator 70. The tank 87 may store any type of fluid readily apparent to one skilled in the art, such as, for example, hydraulic fluid, fuel, or transmission fluid. The source of fluid 84 may be part of a lubrication system, sometimes referred to as a main gallery, such as typically accompanies an internal combustion engine. Such a lubrication system may provide pressurized oil having a pressure of, for example, less than 700 KPa (100 psi) or, more particularly, between about 210 KPa and 620 KPa (30 psi and 90 psi). Alternatively, the source of fluid 84 may be a pump configured to provide oil at a higher pressure, such as, for example, between about 10 MPa and 35 MPa (1450 psi and 5000 psi).
A [0040] fluid supply system 79 connects the source of fluid 84 with the fluid actuator 70. In the exemplary embodiment of FIG. 3A, the source of fluid 84 is connected to a fluid rail 86 through a fluid line 85. As illustrated in FIG. 3A, the fluid rail 86 supplies pressurized fluid from the source of fluid 84 to a series of fluid actuators 70. Each fluid actuator 70 may be associated with either the intake valves 32 or the exhaust valves 34 of a particular engine cylinder 22 (referring to FIG. 1). The fluid lines 80 direct pressurized fluid from fluid rail 86 into the actuator chamber 76 of each fluid actuator 70.
A [0041] directional control valve 88 may be disposed in each fluid line 80. Each directional control valve 88 may be opened to allow pressurized fluid to flow between the fluid rail 86 and the actuator chamber 76. Each directional control valve 88 may be closed to prevent pressurized fluid from flowing between the fluid rail 86 and the actuator chamber 76. The directional control valve 88 may be normally biased into a closed position and actuated to allow fluid to flow through the directional control valve 88. Alternatively, the directional control valve 88 may be normally biased into an open position and actuated to prevent fluid from flowing through the directional control valve 88. One skilled in the art will recognize that the directional control valve 88 may be any type of controllable valve, such as, for example a two coil latching valve.
One skilled in the art will recognize that the [0042] fluid supply system 79 may have a variety of different configurations. For example, as illustrated in FIG. 3B, a restrictive orifice 83 may be positioned in the fluid line 85 between the source of fluid 84 and a first end of the fluid rail 86. A control valve 82 may be connected to an opposite end of the fluid rail 86 and lead to the tank 87. The control valve 82 may be opened to allow a flow of fluid through the restrictive orifice 83 and the fluid rail 86 to the tank 87. The control valve 82 may be closed to allow a build up of pressure in the fluid within the fluid rail 86.
In addition, as illustrated in FIG. 4, the [0043] fluid supply system 79 may include a check valve 94 placed in parallel with the directional control valve 88 between the source of fluid 84 and the fluid actuator 70. The check valve 94 may be configured to allow fluid to flow in the direction from the source of fluid 84 to the fluid actuator 70.
Referring now to FIG. 6, the [0044] check valve 94 may be, for example, a poppet-type check valve, a plate-type check valve, or the like. The exemplary check valve 94 includes a housing 121 that defines an inlet passageway 123 and includes a seat 124. A poppet 122 is disposed proximate the seat 124. A spring 120 acts on the poppet 122 to engage the poppet 122 with the seat 124. The poppet 122 may be disengaged from the seat 124 to create a fluid passage between the inlet passageway 123 and a fluid outlet 125.
The [0045] check valve 94 will open when the poppet 122 is exposed to a pressure differential that is sufficient to overcome the force of the spring 120. The poppet 122 will disengage from the seat 124 when a force exerted by pressurized fluid in the inlet passageway 123 is greater than the combination of a force exerted by fluid in the fluid outlet 125 and the force of the spring 120. If, however, the combination of the force exerted by fluid in the fluid outlet 125 and the force of the spring 120 is greater than the force exerted by the pressurized fluid in the inlet passageway 123, the poppet 122 will remain engaged with the seat 124. In this manner, the check valve 94 may ensure that fluid flows only from the source of fluid 84 to the fluid actuator 70, i.e. from the inlet passageway 123 to the fluid outlet 125. One skilled in the art will recognize that other types of check valves, such as, for example, a ball-type check valve, may also be used.
As also shown in FIG. 4, the [0046] fluid supply system 79 may include an air bleed valve 96. The air bleed valve 96 may be any device readily apparent to one skilled in the art as capable of allowing air to escape a hydraulic system. For example, the air bleed valve 96 may be an air bleed orifice or a spring-biased ball valve that allows air to flow through the valve, but closes when exposed to fluid pressure.
In addition, a snubbing [0047] valve 98, 198 may be disposed in the fluid line 81 leading to the actuator chamber 76. The snubbing valve 98, 198 may be configured to restrict the flow of fluid through fluid line 81, as will be described more fully below with respect to FIGS. 8A and 8B. For example, the snubbing valve 98, 198 may be configured to decrease the rate at which fluid exits the actuator chamber 76 to thereby slow the rate at which the intake valve 32 closes.
The [0048] fluid supply system 79 may also include an accumulator 95. An exemplary embodiment of the accumulator 95 is illustrated in FIG. 7. As shown, the exemplary accumulator 95 includes a housing 126 that defines a chamber 128. A piston 130 is slidably disposed in the chamber 128. A spring 132 is disposed in the housing 126 and acts on the piston 130 to move the piston 130 relative to the housing 126 to minimize the size of the chamber 128. One skilled in the art may recognize that other types of accumulators, such as for example, a bladder-type accumulator, may also be used.
As also shown in FIG. 7. a [0049] restrictive orifice 93 may be disposed in an inlet 134 to the accumulator 95. The restrictive orifice 93 is configured to restrict the rate at which fluid may flow between the accumulator chamber 128 and the inlet 134. As described in greater detail below, the combination of the accumulator 95 and the restrictive orifice 93 may act to dampen pressure oscillations in the actuator chamber 76 and the fluid line 80, which may cause the actuator piston 74 to oscillate.
The components of the [0050] fluid actuator 70 may be contained within a single housing that is mounted on the engine 20 to allow the actuator rod 78 to engage the rocker arm 64. Alternatively, the components of the fluid actuator 70 may be contained in separate housings. One skilled in the art will recognize that space considerations will impact the location of the components of the fluid actuator 70 relative to the engine 20.
Referring now to FIGS. 8A and 8B, the [0051] fluid actuator 70 and the snubbing valve 98, 198 may be housed in a housing 140. The housing 140 includes an inlet 144 having an opening 146 leading to a first fluid passageway 148. The first fluid passageway 148 leads to a second fluid passageway 154, which, in turn, leads to a third fluid passageway 156 that leads to the actuator chamber 76. Referring to the embodiments of FIGS. 3A and 3B, the directional control valve 88 may be opened to allow fluid to flow in either direction through the inlet 144 and the first fluid passageway 148. One skilled in the art will recognize that the inlet 144 may have alternative configurations. For example, the inlet 144 may include multiple openings (not shown) that lead to multiple fluid passageways (not shown). For example, referring to FIG. 4, the check valve 94 and the directional control valve 88 may be opened to allow fluid to flow in either direction through two separate openings that lead to two fluid passageways, which, in turn, lead to the second fluid passageway 154.
The [0052] accumulator 95 may be disposed proximate the second fluid passageway 154 so that the inlet 134 of the accumulator 95 opens to the second fluid passageway 154. This allows fluid from the first fluid passageway 148 to flow through the inlet 134 to the accumulator 95. The restricted orifice 93 (referring to FIG. 7) restricts the amount of fluid that may flow from the second fluid passageway 154 into the accumulator 95.
As illustrated in FIG. 8A, the snubbing [0053] valve 98 may be disposed in the second fluid passageway 154. The second fluid passageway 154 may, at least in part, define a cavity 242 having a first end 244 and a second end 246. The snubbing valve 98 is positioned within the cavity 242 and includes a valving member 248 having a first end 250, a second end 252, and a passage 254 extending between the first and second ends 250, 252. For example, the passage 254 may extend axially through the valving member 248.
The [0054] valving member 248 is movable between a first location, at which the first end 250 of the valving member 248 is against the first end 244 of the cavity 242, and a second location, at which the second end 252 of the valving member 248 is against the second end 246 of the cavity 242.
Referring now to FIG. 8B, the snubbing valve [0055] 198 may be disposed between the third fluid passageway 156 and the fluid actuator 76. The housing 140 may define a first fluid conduit 302, a second fluid conduit 304, and a cavity 342. The cavity 342 may include a first end 344 and a second end 346. The first end 344 of the cavity 342 may be defined, for example, by a washer or other ring-like structure, such as a metal washer. The snubbing valve 198 is positioned within the cavity 342 and includes a valving member 348 having a first end 350, a second end 352, and at least one passage 354 extending between the first and second ends 350, 352. For example, the passages 354 may extend axially through the valving member 348.
The [0056] valving member 348 is movable between a first location, at which the first end 350 of the valving member 348 is against the first end 344 of the cavity 342, and a second location, at which the second end 352 of the valving member 348 is against the second end 346 of the cavity 342.
As shown in FIG. 1, a [0057] controller 100 is connected to each valve actuation assembly 44 and to the control valve 82. The controller 100 may include an electronic control module that has a microprocessor and a memory. As is known to those skilled in the art, the memory is connected to the microprocessor and stores an instruction set and variables. Associated with the microprocessor and part of electronic control module are various other known circuits such as, for example, power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others.
The [0058] controller 100 may be programmed to control one or more aspects of the operation of the engine 20. For example, the controller 100 may be programmed to control the valve actuation assembly, the fuel injection system, and any other function readily apparent to one skilled in the art. The controller 100 may control the engine 20 based on the current operating conditions of the engine and/or instructions received from an operator.
The [0059] controller 100 may be further programmed to receive information from one or more sensors operatively connected with the engine 20. Each of the sensors may be configured to sense one or more operational parameters of the engine 20. For example, with reference to FIG. 3A, a sensor 90 may be connected with the fluid supply system 79 to sense the temperature of the fluid within the fluid supply system 79. One skilled in the art will recognize that many other types of sensors may be used in conjunction with or independently of the sensor 90. For example, the engine 20 may be equipped with sensors configured to sense one or more of the following: the temperature of the engine coolant, the temperature of the engine, the ambient air temperature, the engine speed, the load on the engine, and the intake air pressure.
The [0060] engine 20 may be further equipped with a sensor configured to monitor the crank angle of the crankshaft 27 to thereby determine the position of the pistons 24 within their respective cylinders 22. The crank angle of the crankshaft 27 is also related to actuation timing of the intake valves 32 and the exhaust valves 34. An exemplary graph 102 indicating the relationship between valve actuation timing and crank angle is illustrated in FIG. 5. As shown by the graph 102, exhaust valve actuation 104 is timed to substantially coincide with the exhaust stroke of the piston 24 and intake valve actuation 106 is timed to substantially coincide with the intake stroke of the piston 24.

INDUSTRIAL APPLICABILITY

Based on information provided by the engine sensors, the [0061] controller 100 may operate each valve actuation assembly 44 to selectively implement a late intake Miller cycle for each cylinder 22 of the engine 20. Under normal operating conditions, implementation of the late intake Miller cycle will increase the overall efficiency of the engine 20. Under some operating conditions, such as, for example, when the engine 20 is cold, the controller 100 may operate the engine 20 on a conventional diesel cycle.
The following discussion describes the implementation of a late intake Miller cycle in a [0062] single cylinder 22 of the engine 20. One skilled in the art will recognize that the system of the present invention may be used to selectively implement a late intake Miller cycle in all cylinders of the engine 20 in the same or a similar manner. In addition, the system of the present invention may be used to implement other valve actuation variations on the conventional diesel cycle, such as, for example, an exhaust Miller cycle.
When the [0063] engine 20 is operating under normal operating conditions, the controller 100 implements a late intake Miller cycle by selectively actuating the fluid actuator 70 to hold the intake valve 32 open for a first portion of the compression stroke of the piston 24. This may be accomplished by moving the directional control valve 88 to the open position when the piston 24 starts an intake stroke. (In the embodiment of FIG. 3B, the control valve 82 is closed to implement a late intake Miller cycle.) This allows pressurized fluid to flow from the source of fluid 84 through the fluid rail 86 and into the actuator chamber 76. The force of the fluid entering the actuator chamber 76 moves the actuator piston 74 so that the actuator rod 78 follows the end 68 of the rocker arm 64 as the rocker arm 64 pivots to open the intake valves 32. The distance and rate of movement of the actuator rod 78 will depend upon the configuration of the actuator chamber 76 and the fluid supply system 79. When the actuator chamber 76 is filled with fluid and the rocker arm 64 returns the intake valves 32 from the open position to the closed position, the actuator rod 78 will engage the end 68 of the rocker arm 64.
The [0064] fluid supply system 79 may be configured to supply a flow rate of fluid to the fluid actuator 70 to fill the actuator chamber 76 before the cam 60 returns the intake valves 32 to the closed position. In the embodiment of the fluid supply system 79 illustrated in FIG. 4, pressurized fluid may flow through both the directional control valve 88 and the check valve 94 into the actuator chamber 76. Alternatively, the directional control valve 88 may remain in a closed position and fluid may flow through the check valve 94 into the actuator chamber 76.
When the [0065] actuator chamber 76 is filled with fluid, the controller 100 may close the directional control valve 88, thereby preventing fluid from escaping from the actuator chamber 76. As the cam 60 continues to rotate and the springs 56 urge the intake valves 32 towards the closed position, the actuator rod 78 will engage the end 68 of the rocker arm 64 and prevent the intake valves 32 from closing. As long as the directional control valve 88 remains in the closed position, the trapped fluid in the actuator chamber 76 will prevent the springs 56 from returning the intake valves 32 to the closed position. Thus, the fluid actuator 70 will hold the intake valves 32 in an open position, for example, at least a partially open position, independently of the action of the cam assembly 52.
When the [0066] actuator rod 78 engages the rocker arm 64 to prevent the intake valves 32 from closing, the force of the springs 56 acting through the rocker arm 64 may cause an increase in the pressure of the fluid within the fluid system 79. In response to the increased pressure, a flow of fluid will be throttled through the restricted orifice 93 into the chamber 129 of the accumulator 95 (referring to FIG. 7). The throttling of the fluid through the restricted orifice 93 will dissipate energy from the fluid within the fluid system 79.
The force of the fluid entering the [0067] accumulator 95 will act to compress the spring 132 and move the piston 130 to increase the size of the chamber 128 (referring to FIG. 7). When the pressure within the fluid system 79 decreases, the spring 130 will act on the piston 130 to force the fluid in the chamber 128 back through the restricted orifice 93. The flow of fluid through the restricted orifice 93 into the third fluid passageway 154 will also dissipate energy from the fluid system 79.
The restricted [0068] orifice 93 and the accumulator 95 will therefore dissipate energy from the fluid system 79 as fluid flows into and out of the accumulator 95. In this manner, the restricted orifice 93 and the accumulator 95 may absorb or reduce the impact of pressure fluctuations within the fluid system 79, such as may be caused by the impact of the rocker arm 64 on the actuator rod 78. By absorbing or reducing pressure fluctuations, the restricted orifice 93 and the accumulator 95 may act to inhibit or minimize oscillations in the actuator rod 78.
The [0069] controller 100 may close the intake valves 32 by opening the directional control valve 88. This allows the pressurized fluid to flow out of the actuator chamber 76. The force of the springs 56 forces the fluid from the actuator chamber 76, thereby allowing the actuator piston 74 to move within the actuator cylinder 72. This allows the rocker arm 64 to pivot so that the intake valves 32 are moved to the closed position.
The snubbing [0070] valve 98, 198 may restrict the rate at which fluid exits the actuator chamber 76 to reduce the velocity at which the intake valves 32 are closed. This may prevent the valve elements 40 from being damaged when closing the intake ports 36.
For example, the snubbing [0071] valve 98 may control the rate at which fluid may flow into and out of actuator chamber 76. Referring to FIG. 8A, the snubbing valve 98 may be configured to initially allow a high rate of fluid flow into the actuator chamber 76 when the actuator piston 74 starts to move away from the first, home position. For example, the valving member 248 may initially be in a position such that the second end 252 of the valving member 248 is at or near the second end 246 of the cavity 242. As fluid flows from the first passageway 148 toward the actuator chamber 76, the valving member may move toward the first end 244 of the cavity, thereby initially allowing a high rate of fluid flow to the third passageway 156 and the actuator chamber 76.
Should the [0072] valving member 248 reach a position such that the first end 250 of the valving member 248 contacts the first end 244 of the cavity 242, the only available fluid flow path is through the through the passage 254. Thus, the fluid flow into the actuator chamber 76 is restricted to the lower rate of fluid flow permitted via the passage 254.
Similarly, the snubbing [0073] valve 98 may be configured to initially allow a high rate of fluid flow from the actuator chamber 76 when the actuator piston 74 starts to move toward the first, home position. For example, the valving member 248 may initially be in a position such that the first end 250 of the valving member 248 is at or near the first end 244 of the cavity 242. As fluid flows from the actuator chamber 76 toward the first passageway 148, the valving member 248 may move toward the second end 246 of the cavity, thereby initially allowing a high rate of fluid flow from the third passageway 156 and the actuator chamber 76.
Should the [0074] valving member 248 reach a position such that the second end 252 of the valving member 248 contacts the second end 246 of the cavity 242, the only available fluid flow path is through the passage 254. Thus, the fluid flow from the actuator chamber 76 is restricted to the lower rate of fluid flow permitted via the passage 254.
Referring now to FIG. 8B, the snubbing valve [0075] 198 may slow the rate at which fluid flows from the actuator chamber 76 when the piston 74 approaches the home position during movement from the end position towards the home position. In this manner, the snubbing valve 198 may reduce the impact speed of the piston 74 with the piston stop 142 and the actuator cylinder 72, as well as the impact speed of the intake valve 32 with the valve seat 50 and the cylinder head 30.
The snubbing valve [0076] 198 may be configured to initially allow a high rate of fluid flow into the actuator chamber 76 when the actuator piston 74 starts to move away from the first, home position. For example, the valving member 348 may initially be in a position such that the second end 352 of the valving member 348 is at or near the second end 346 of the cavity 342. As fluid flows from the third passageway 156 toward the actuator chamber 76, the second fluid conduit 304 may be blocked from communication with the actuator chamber 76. Thus, fluid flows to the actuator chamber 76 via the first fluid conduit 302. The valving member 348 is moved away from the second end 346, opening the passages 354 through the valving member 348 and allowing a relatively high rate of fluid flow to the actuator chamber 76. As the actuator piston 74 is moved away from the first, home position, the second fluid conduit 304 is opened, allowing fluid communication between the third passageway 156 and the actuator chamber 76. Thus, a high rate of fluid flow from the third passageway 156 to the actuator chamber 76 is permitted.
When the [0077] actuator piston 74 starts to move toward the first, home position, the snubbing valve 198 may be configured to initially allow a high rate of fluid flow from the actuator chamber 76 through the first fluid conduit 302, via the passages 354, and through the second fluid conduit 304. For example, the valving member 348 may initially be in a position such that the first end 350 of the valving member 348 is at or near the first end 344 of the cavity 342. As fluid flows from the actuator chamber 76 toward the third passageway 156, the valving member 348 may move toward the second end 346 of the cavity 342, thereby initially allowing a high rate of fluid flow from the actuator chamber 76.
When the [0078] valving member 348 reaches a position such that the second fluid conduit 304 is blocked from communication with the actuator chamber 76, the flow rate from the actuator chamber 76 may be reduced. Should the second end 352 of the valving member 348 contact the second end 346 of the cavity 342, the only available fluid flow path is through the center one of the passages 354. Thus, the fluid flow from the actuator chamber 76 is restricted to the lower rate of fluid flow permitted via the passage 354.
An exemplary late intake closing [0079] 108 is illustrated in FIG. 5. As shown, the intake valve actuation 106 is extended into a portion of the compression stroke of the piston 24. This allows some of the air in the cylinder 22 to escape. The amount of air allowed to escape the cylinder 22 may be controlled by adjusting the crank angle at which the directional control valve 88 is opened. The directional control valve 88 may be closed at an earlier crank angle to decrease the amount of escaping air or at a later crank angle to increase the amount of escaping air. The affect of the snubbing valve 98, 198 can be seen from the gradual taper of the late intake closing curve 108 as the compression stroke of the piston 24 approaches top dead center.
As noted previously, certain operating conditions may require that the [0080] engine 20 be operated on a conventional diesel cycle instead of the late intake Miller cycle described above. These types of operating conditions may be experienced, for example, when the engine 20 is first starting or is otherwise operating under cold conditions. The described valve actuation system 44 allows for the selective disengagement of the late intake Miller cycle.
It should be appreciated that the snubbing [0081] valve 98, 198 may reduce the impact velocity of the intake valve 32 and/or the actuator piston 74 regardless of whether the late intake Miller cycle is engaged. For example, the snubbing valve 98, 198 may reduce the impact velocity of the intake valve 32 and/or the actuator piston 74 when the late intake Miller cycle is disabled, for example, during cold start or cold operating conditions. As long as the directional control valve 88 is opened and fluid is available to the fluid actuator 70 without a substantial return path to the tank 87, the snubbing valve 98, 198 may operate to reduce the velocity of the intake valve 32 and/or the actuator piston 74. In such situations, the actuator rod 78 may move substantially with the rocker arm 64, thereby varying the volume of the actuator chamber 76 and allowing fluid to flow into and out of the actuator chamber 76. When the actuator chamber 76 contains fluid and the intake valve 32 is urged closed by the spring 56, the actuator piston 74 is also urged toward a home position. Thus, the volume of the actuator chamber 76 is reduced and fluid is forced out of the actuator chamber 76 as long as the directional control valve 88 is open. The snubbing valve 98, 198 then operates as previously described to reduce the impact velocity of the intake valve 32 and/or the actuator piston 74. It should also be appreciated that the effect of the snubbing valve 98, 198 may be beneficial during engine overspeed conditions, for example, an engine speed over about 2100 rpm.
In the exemplary embodiment of FIG. 3A, the [0082] controller 100 may disengage the late intake Miller cycle by keeping opened the directional control valve 88. The directional control valve 88 may be opened when the controller 100 receives sensory input indicating that the engine 20 is starting or is operating under cold conditions. Opening the directional control valve 88 allows fluid to flow from the actuator chamber 76 to the tank 87 via the fluid rail 86. As long as the directional control valve 88 is not closed, the fluid actuator 70 will not prevent the intake valves 32 from returning to the closed position in response to the force of the springs 56.
Thus, when the [0083] directional control valve 88 is held open, the intake valves 32 will follow a conventional diesel cycle as governed by the cam 60. As shown in FIG. 5, intake valve actuation 106 will follow a conventional closing 110. In the conventional closing 110, the closing of the intake valves 32 may substantially coincide with the end of the intake stroke of the piston 24. When the intake valves 32 close at the end of the intake stroke, no air will be forced from the cylinder 22 during the compression stroke. This results in the piston 24 compressing the fuel and air mixture to a higher pressure, which will facilitate diesel fuel combustion. This is particularly beneficial when the engine 20 is operating in cold conditions.
In the exemplary embodiment of FIG. 3B, the [0084] controller 100 may disengage the Miller cycle by opening the control valve 82. The control valve 82 may be opened when the controller 100 receives sensory input indicating that the engine 20 is starting or is operating under cold conditions. Opening the control valve 82 allows fluid to flow through the restrictive orifice 83 and the fluid rail 86 to the tank 87. Opening the control valve 82 may therefore reduce the pressure of the fluid within the fluid rail 86. The decreased pressure of the fluid within the fluid rail 86 may not generate a force great enough to move the actuator piston 74. Thus, the fluid actuator 70 will not engage the intake valve 32 to prevent the intake valve 32 from closing. Accordingly, the engine 20 will operate on a conventional diesel cycle as governed by the cam 60.
Opening the [0085] control valve 82 may also increase the responsiveness of the valve actuator 70 when the engine 20 is starting or operating under cold conditions. If the fluid within the fluid rail 86 is cold, the fluid will have an increased viscosity. The increased viscosity of the fluid may decrease the rate at which the fluid may flow into and out of the actuator chamber 76 and thereby impact the operation of the valve actuator 70. By opening the control valve 82, the cold fluid may be replaced by warmer fluid from the source of fluid 84. This may decrease the viscosity of the fluid within the fluid rail 86, which may increase the responsiveness of the valve actuator 70 when the control valve 82 is closed to operate the engine 20 on the Miller cycle.
The [0086] restrictive orifice 83 may ensure that the pressure of the fluid upstream of the restrictive orifice 83, i.e. between the source of fluid 84 and the restrictive orifice 83, does not decrease when the control valve 82 is opened. The restrictive orifice 83 may create a smaller opening than is created by the opening of the control valve 82. In other words, the opening of the control valve 82 allows fluid to flow out of the fluid rail 86 at a faster rate than the restrictive orifice 83 allows fluid to flow into the fluid rail 86. This creates a pressure drop over the restrictive orifice 83 where the pressure of the fluid on the upstream side of the restrictive orifice 83 will be greater that the pressure of the fluid in the fluid rail 86. Thus, opening the control valve 82 will not impact the pressure of fluid upstream of the restrictive orifice 83.
As will be apparent from the foregoing description, the present invention provides an engine valve actuation system that may selectively alter the timing of the intake and/or exhaust valve actuation of an internal combustion engine. The actuation of the engine valves may be based on sensed operating conditions of the engine. For example, the engine valve actuation system may implement a late intake Miller cycle when the engine is operating under normal operating conditions. The late intake Miller cycle may be disengaged when the engine is operating under adverse operating conditions, such as when the engine is cold. Thus, the present invention provides a flexible engine valve actuation system that provides for both enhanced cold starting capability and fuel efficiency gains. [0087]
It will be apparent to those skilled in the art that various modifications and variations can be made in the engine valve actuation system of the present invention without departing from the scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents. [0088]

Claims

What is claimed is:

1. An engine valve actuation system, comprising:

an intake valve moveable between a first position that blocks a flow of fluid and a second position that allows a flow of fluid;

a cam assembly connected to move the intake valve between the first position and the second position;

a fluid actuator configured to selectively modify a timing of the intake valve in moving from the second position to the first position; and

a snubbing valve configured to restrict a flow of fluid from the fluid actuator so as to reduce a rate of movement of the intake valve to the first position.

2. The engine valve actuation system of claim 1, further including a source of fluid in selective fluid communication with the fluid actuator.

3. The engine valve actuation system of claim 2, further including:

a fluid rail having a first end and a second end, the fluid rail being configured to supply fluid to the fluid actuator; and

a fluid tank in selective fluid communication with the fluid rail.

4. The engine valve actuation system of claim 3, further including a control valve configured to control a flow of fluid from the fluid rail to the fluid tank, the control valve being moveable between a first position that blocks a flow of fluid from the fluid rail to the fluid tank and a second position that allows a flow of fluid from the fluid rail to the fluid tank.

5. The engine valve actuation system of claim 4, further including a controller configured to move the control valve between the first position and the second position.

6. The engine valve actuation system of claim 3, further including a restrictive orifice disposed between the source of fluid and the fluid rail.

7. The engine valve actuation system of claim 2, further including a directional control valve configured to control a flow of fluid between the source of fluid and the fluid actuator.

8. The engine valve actuation system of claim 7, further including a check valve, wherein the check valve and the directional control valve are disposed in parallel between the fluid actuator and the source of fluid.

9. The engine valve actuation system of claim 8, further including an air bleed valve disposed between the check valve and the fluid actuator.

10. The engine valve actuation system of claim 7, wherein the directional control valve includes a spring urging the directional control valve into a first position that blocks a flow of fluid from the source of fluid to the fluid actuator.

11. The engine valve actuation system of claim 7, wherein the directional control valve includes a spring urging the directional control valve into a second position that allows a flow of fluid from the source of fluid to the fluid actuator.

12. The engine valve actuation system of claim 2, wherein the source of fluid provides fluid having a pressure of between about 210 KPa and 620 KPa to the fluid rail.

13. The engine valve actuation system of claim 1, further including an accumulator and a restricted orifice, the restricted orifice being disposed between the fluid actuator and the accumulator.

14. The engine valve actuation system of claim 1, wherein the fluid actuator includes a piston operatively associated with the intake valve.

15. A method of controlling an engine having a piston moveable through an intake stroke followed by a compression stroke, comprising:

cammingly moving an intake valve between a first position that blocks a flow of fluid and a second position that allows a flow of fluid during the intake stroke of the piston;

directing fluid to a fluid actuator associated with the intake valve when the intake valve is away from the first position; and

restricting a flow of fluid from the fluid actuator during at least a portion of the compression stroke to reduce a velocity of the intake valve movement to the first position.

16. The method of claim 15, further including blocking fluid from flowing from the fluid actuator to modify a timing of movement of the intake valve to the first position during at least a portion of the compression stroke of the piston.

17. The method of claim 16, wherein said restricting occurs after said blocking.

18. The method of claim 15, further including allowing fluid to flow from the fluid actuator to allow the intake valve to move to the first position.

19. An engine, comprising:

an engine having a block defining at least one cylinder and a cylinder head having at least one intake passageway leading to the at least one cylinder;

at least one intake valve moveable between a first position to prevent a flow of fluid through the at least one intake passageway and a second position to allow a flow of fluid through the at least one intake passageway;

a cam assembly connected to the intake valve to move the intake valve between the first position and the second position;

a fluid actuator configured to selectively prevent the intake valve from moving to the first position;

a source of fluid in fluid communication with the fluid actuator;

a directional control valve configured to control a flow of fluid between the source of fluid and the fluid actuator; and

20. The engine of claim 19, wherein the fluid actuator includes a piston operatively associated with the intake valve.