Patent Application
20170089223
The present disclosure is directed to a valve actuation system and, more particularly, to a system for actuating gas exchange valves of an engine.
Each cylinder of an internal combustion engine is equipped with one or more gas exchange valves (e.g., intake and exhaust valves) that are cyclically opened during normal operation to allow fuel and air into the engine and to discharge exhaust from the engine. In a conventional engine, the valves are opened by way of a camshaft/rocker arm arrangement. The camshaft includes one or more lobes oriented at particular angles corresponding to desired lift timings and amounts of the associated valves. The cam lobes are connected to stem ends of the associated valves by way of the rocker arm and associated pushrod linkage. As the camshaft rotates, the cam lobes come into contact with a first pivoting end of the rocker arm, thereby forcing a second pivoting end of the rocker arm against the stem ends of the valves. This pivoting motion causes the valves to lift or open against a spring bias. As the cam lobes rotate away from the rocker arm, the valves are released and allowed to return to their closed positions. An exemplary system for moving the gas exchange valves is disclosed in U.S. Pat. No. 8,210,144 of Langewisch that published on Jul. 3, 2012.
Most diesel engines manufactured today can be classified as one of several common types, for example a common rail engine, a HEUI (Hydraulically operated Electronically actuated Unit Injector) engine, a MUI (Mechanically operated Unit Injector) engine, or a MEUI (Mechanically operated Electronicaly actuated Unit Injector). These engines are classified based on the type of fuel injector and fuel system used in the engine. Due to differences between these types of engines, the space inside each cylinder head and valve actuation requirements may be different for each engine. Accordingly, each of these types of engines has historically had a unique valve actuation system.
Although the unique valve actuation systems described above may function adequately for their intended applications, they can also be problematic. In particular, many different parts must be designed, stocked, and distributed for each of the different systems, which can be costly. In addition, it may be difficult to keep track of and maintain the different systems. Accordingly, resources may be limited for use in pursuing new or improved designs.
The valve actuation system of the present disclosure is directed towards overcoming one or more of the problems set forth above and/or other problems of the prior art.
One aspect of the present disclosure is directed to a valve actuation system. The valve actuation system may include a rocker shaft, a rocker arm pivotally mounted on the rocker shaft and having a first end and a second end, at least one cam follower, and a pushrod connecting the at least one cam follower to the first end of the rocker arm. The valve actuation system may also include a plurality of gas exchange valves, and a bridge connecting the second end of the rocker arm to the plurality of gas exchange valves. The valve actuation system may further include at least one spring disposed around each of the plurality of gas exchange valves and configured to bias each of the plurality of gas exchange valves toward closed positions, and a rotocoil configured to rotatably connect the at least one spring to each of the plurality of gas exchange valves. The rotocoil may have an internal chamfer at a bridge end with an angle of about 26-28° measured relative to a center axis of the rotocoil. The at least one spring may have an assembled load of about 750-850 N.
Another aspect of the present disclosure is directed to another valve actuation system. This valve actuation system may include a rocker shaft, a rocker arm pivotally mounted on the rocker shaft and having a first end and a second end, at least one cam follower, and a pushrod connecting the at least one cam follower to the first end of the rocker arm. The valve actuation system may also include a plurality of gas exchange valves, and a bridge connecting the second end of the rocker arm to the plurality of gas exchange valves. The valve actuation system may further include an outer spring disposed around each of the plurality of gas exchange valves and configured to bias each of the plurality of gas exchange valves toward closed positions, and an inner spring disposed inside the outer spring. The outer spring may have an assembled load of about 500-550 N. The inner spring may have an assembled load of about 250-300 N.
Yet another aspect of the present disclosure is directed to another valve actuation system. This valve actuation system may include a rocker shaft, a rocker arm pivotally mounted on the rocker shaft and having a first end and a second end, at least one cam follower, and a pushrod connecting the at least one cam follower to the first end of the rocker arm. The valve actuation system may also include a plurality of gas exchange valves, and a bridge connecting the second end of the rocker arm to the plurality of gas exchange valves. The valve actuation system may further include at least one spring disposed around each of the plurality of gas exchange valves and configured to bias each of the plurality of gas exchange valves toward closed positions, and a rotocoil configured to rotatably connect the at least one spring to each of the plurality of gas exchange valves. The rotocoil may have an internal chamfer at a bridge end with an angle of about 27.5° measured relative to a center axis of the rotocoil. The valve actuation system may additionally include a seat disposed around each of the plurality of gas exchange valves and having abase end with a removal tool engagement surface that tapers conically outward, a sealing surface oriented opposite the base end adjacent a head of each of the plurality of gas exchange valves, and an inner cylindrical surface that joins with the removal tool engagement surface at an intersection. A radial length dimension of the removal tool engagement surface is about 3.4-3.7 mm. A bevel located at the intersection has an angle of about 28-32° measured relative to a center axis of the seat.
Engine 10 may include an engine block 14 that at least partially defines one or more cylinders 16. A piston (not shown) and a cylinder head 18 may be associated with each cylinder 16 to form a combustion chamber. Specifically, the piston may be slidably disposed within each cylinder 16 to reciprocate between a top-dead-center (MC) position and a bottom-dead-center (BDC) position, and cylinder head 18 may be positioned to cap off an end of cylinder 16, thereby forming the combustion chamber. Engine 10 may include any number of combustion chambers; and the combustion chambers may be disposed in an “in-line” configuration, in a “V” configuration, in an opposing-piston configuration, or in any other suitable configuration.
Engine 10 may also include a crankshaft (not shown) that is rotatably disposed within engine block 14. A connecting rod (not shown) may connect each piston to the crankshaft so that a sliding motion of the piston between the TDC and BDC positions within each respective cylinder 16 results in a rotation of the crankshaft. Similarly, a rotation of the crankshaft may result in a sliding motion of the piston between the TDC and BDC positions. In a four-stroke engine, the piston may reciprocate between the TDC and BDC positions through an intake stroke, a compression stroke, a power stroke, and an exhaust stroke.
Cylinder head 18 may define one or more fluid passages (e.g., intake and exhaust passages not shown) associated with each combustion chamber that are configured to direct gas (e.g., air and/or exhaust) or a mixture of gas and fluid (e.g., fuel) into or out of the associated chamber. The intake passage(s) may be configured to deliver compressed air and/or an air and fuel mixture into a top end of the combustion chamber. The exhaust passage(s) may be configured to direct exhaust and residual gases from the top end of the combustion chamber to the atmosphere.
System 12 may include a plurality of gas exchange valves (e.g., intake valves 20 and exhaust valves 22) positioned within the passages of cylinder head 18 to selectively engage corresponding seats 24 that are pressed into (or otherwise formed inside of) cylinder head 18. Each of the valves may be movable between a first position at which seat 24 is engaged to inhibit a flow of fluid through the corresponding passage, and a second position at which seat 24 is not engaged (i.e., at which the corresponding valve is lifted) and thereby allows a flow of fluid through the passage. The timing at which the valves are lifted, as well as a lift profile of the valves, may have an effect on the operation of the engine. For example, the lift timing and profile may affect production of emissions, production of power, fuel consumption, efficiency, temperature, pressure, etc. At least one spring 26 may be associated with each valve and configured to bias the valve toward the first position and against seat 24. A spring retainer 28 (also known as a rotocoil) may connect spring(s) 26 to a stem end of each valve.
System 12 may be mounted inside a base 30 that is operatively engaged with cylinder head 18, and consist of elements that move intake and exhaust valves 20, 20 against the biases of springs 26 from their first positions toward their second positions at desired timings. These elements of valve actuation system 12 may include, among other things, a plurality of cam followers (e.g., an intake follower 32 and an exhaust follower 34) configured to ride along a common camshaft (not shown) of engine 10, a pushrod 36 engaged with each cam follower, and a rocker arm (e.g., an intake arm 38 and an exhaust arm 40) configured to translate follower motion to the corresponding valves. Each rocker arm may be mounted to base 30 via a shaft 42, and connected to the corresponding valves by way of a bridge (e.g., an intake bridge 44 and an exhaust bridge 46).
In the disclosed embodiment, valve actuation system also includes an injector follower 48 located between intake and exhaust followers 32, 34. Injector follower 48 may be configured to ride along the common camshaft of engine 10, and a pushrod 50 may connect injector follower 48 to an injector arm 52 that is pivotally mounted to shaft 42 at a location between intake and exhaust arms 38, 40. A spring 54 may function to maintain contact between injector follower 48 and the camshaft. It is contemplated that injector follower 48, pushrod 50, injector arm 52, and spring 54 could be omitted, if desired.
The camshaft of engine 10 may operatively engage the crankshaft in any manner readily apparent to one skilled in the art, such that a rotation of the crankshaft results in a corresponding rotation of the camshaft. At least one cam lobe (not shown) may be formed on the camshaft and configured to drive a reciprocating motion of each of the associated followers as the camshaft rotates. With this configuration, an outer profile of any intake and exhaust cam lobes may determine, at least in part, the lift timing and profile of intake and exhaust valves 20, 22, respectively. Similarly, an outer profile of any injector cam lobe(s) may determine, at least in part, an injection timing and profile of an associated fuel injector (not shown for clarity) that is co-located inside base 30 and cylinder head 18.
An end of each of pushrods 36 may reside inside one of cam followers 32, 34 and move in accordance with the profile of the cam lobes as the camshaft rotates, thereby transferring a corresponding reciprocating motion to a first pivoting end of an associated rocker arm 38, 40. This reciprocating motion imparted to rocker arms 38, 40 may cause rocker arms 38, 40 to pivot about shaft 42, thereby creating a corresponding reciprocating motion at an opposing second end that lifts and releases intake and exhaust valves 20, 22, respectively. Thus, the rotation of the camshaft may cause intake and exhaust valves 20, 22 to move from the first position to the second position to create a specific lift pattern corresponding to the profile of the cam lobes.
Rocker arms 38, 40 may be connected to intake and exhaust valves 20, 22 by way of valve bridges 44, 46, respectively. Specifically, each of rocker arms 38, 40 may include a pin 56 that is received within the second ends of rocker arms 38, 40. A button-end of pin 56 may be able to swivel somewhat relative to the associated bridge 44 or 46, and includes a generally flat bottom surface that is configured to slide along a corresponding upper surface of the bridge 44 or bridge 46. The ability of the button-end of pin 56 to swivel and slide may allow rocker arms 38, 40 to transmit primarily vertical (i.e., axial) forces into valve bridges 44, 46. The only horizontal (i.e., transverse) forces transmitted between rocker arms 38, 40 and valve bridges 44, 46 may be relatively low and due only to friction at the sliding interface between pin 56 and bridges 44, 46. This interface may be lubricated and/or polished to reduce the associated friction.
In some applications, valve actuation system 12 may further include one or more lash adjusters 58 disposed within an upper end of pushrods 36, and an adjusting screw 60 located within the first end of rocker arms 38, 40. Lash adjusters 58 may be configured to automatically adjust a clearance between a corresponding intake or exhaust valve 20, 22 and its associated seat 24 (and/or between other valve train components) when the cam lobe is rotated away from pushrods 36. Adjusting screws 60 may be configured to connect rocker arms 38, 40 with pushrods 36 in a manually adjustable manner.
An exemplary valve arrangement 62 is illustrated in
Each of intake and exhaust valves 20, 22 may include a tip 66 received within a pocket of the corresponding bridge 44 or 46, a head 68 located opposite tip 66, and a stem 70 connecting tip 66 to head 68. Stem 70 may join head 68 at a neck 72. One or more grooves 74 may be located at tip 66 and configured to receive inward annular protrusions of a keeper 76, which retains rotocoil 28 and springs 26 in their axial positions on the valve. The valve may have a stem diameter d1, an overal length l1, a length l2 that extends from tip 66 to a closest one of keeper grooves 74, and a length l3 that extends from a face of head 68 to a gauge plane 77. The dimensions d1, l1, l2, and/or length l3 may be the same or different for intake and exhaust valves 20, 22. In one specific embodiment, intake valve 20 has d1about equal to 11 mm, l1 about equal to 218-219 mm (e.g., about equal to 218,86 mm), l2 about equal to 16-17 mm (e.g., about 16.8 mm), and length l3 about equal to 4.5-5 mm (about 4.72 mm). In this same embodiment, exhaust valve 22 has d1 about equal to 12-13 mm (e.g., about 12.5 mm), l1 about equal to 218-219 mm (e.g., about equal to 218.9 mm), 12 about equal to 18.5-19 mm (e.g., about 18.9 mm), and length l3 about equal to 3.5-4 mm (e.g., about 3.7 mm). In this same embodiment, intake valve 20 has multiple (e.g., two) keeper grooves 74, while exhaust valve 22 has a single keeper groove 74. It should be noted that, for the purposes of this disclosure, the term “about”, when used in reference to a dimension, may be interpreted as “within manufacturing tolerances”.
Seat 24 may be a replaceable wear component pressed into an existing recess in cylinder head 18. Seat 24 may be generally ring-like, with an internal conical sealing surface 78 located at an external end that is configured to be engaged by valves 20, 22 when valves 20, 22 are moved to their flow-blocking positions. To remove seat 24 from cylinder head 18, a tool (not shown) may be inserted through sealing surface 78 to engage a base end of seat 24. To facilitate this engagement, seat 24 may taper outward at the base end (i.e., the internal surface of seat 24 at the base end may have a conical surface 80), allowing a radially protruding wedge portion of the tool to fit into a void 82 created by the taper. An outward force may then be applied to the tool, causing the wedge portion to engage surface 80 and urge seat 24 out of the recess of cylinder head 18. Surface 80 may have a radial length dimension l4, and an intersection of surface 80 and an inner cylindrical surface 86 of seat 24 may include a bevel 88 oriented at an angle β. In one specific embodiment, l4 is about 3-4 mm (e.g., about 3.4-3.7 mm) resulting in a contact pressure with the tool of about 65-80 MPa. In this same embodiment, β is about 28-32° when measured relative to a center axis of seat 24. It is contemplated that bevel 88 may be omitted or replaced with around, if desired. By omitting bevel 88, l4 may become greater, allowing for reduced contact pressure between the tool and surface 80.
Springs 26 may be designed to provide for desired operation of intake and exhaust valves 20, 22. In particular, each spring 26 may have an assembled length ls, a free length l6 (not shown), an outer diameter d2, a wire diameter d3, and an assembled load L1 (not shown). The dimensions l5, l6, d2, d3 and/or length L1 may be the same or different when springs 26 are used with intake and exhaust valves 20, 22. In one specific embodiment, inner spring 26a has length l5 about equal to 55-60 mm (e.g., about 57.5 mm), a free length ls about equal to 70-75 mm (e.g., about 73 mm), an outer diameter d2 about equal to 30-31 mm (e.g., about 30.4 mm), a wire diameter d3 about equal to 3.75-4.25 mm (e.g., about 4 mm), and an assembled load L1 about equal to 250-300 N (e.g., about 275 N). In this same embodiment, outer spring 26b has length l5 about equal to 58-62 mm (e.g., about 60.29 mm), a free length l6 about equal to 75-80 mm (e.g., about 77.07 mm), an outer diameter d2 about equal to 43-44 mm (e.g., about 43.47 mm), a wire diameter d3 about equal to 5-6 mm (e.g., about 5.54 mm), and an assembled load L1 about equal to 500-550 N (e.g., about 510 N). Thus, in this embodiment, a combined assembled load L1 from both inner and outer springs may be about 750-850 N (e.g., about 785 N).
Rotocoil 28 may fulfill at least two functions. First, rotocoil 28 may function as a spring retainer, keeping springs 26 in compression at their desired locations around the corresponding valve. Second rotocoil 28 may function to rotate the corresponding valve somewhat during each opening/closing event, thereby inhibiting burning of the valve through even distribution of heat loads across the face of the valve. And while performing the first and second functions described above, rotocoil 28 should avoid engagement with valve bridges 44, 46. Rotocoil 28 may have a generally cylindrical body 79 with a narrow diameter portion configured to reside inside inner spring 26a, an outer housing 81 configured to rest on an axial end of inner and outer springs 26a, 26b, and a spiral spring 83 disposed within a channel between body 79 and housing 81. In one embodiment, the spring or distal end (i.e., the end inside of inner spring 26a) of body 79 may be blunt (i.e., without piloting features), and rotocoil 28 may have an overall axial length l7, an outer diameter d4, and an internal chamfer having an angle α at a bridge or base end. The dimensions l7, and d4 may be the same or different when rotocoils 28 are used with intake and exhaust valves 20, 22. In one specific embodiment, when rotocoil 28 is intended for use with intake valve 20, l7 is about 15.75-16.25 mm (e.g., about 16 mm), d4 is about 43-44 mm (e.g., about 43.765 mm), and α is about 21-24° (e.g., about 22.5°) when measured relative to a center axis of rotocoil 28. In another specific embodiment, when rotocoil 28 is intended for use with exhaust valve 22, l7 is about 17.5-18 mm (e.g., about 17.73 mm), d4 is about 43-44 mm (e.g., about 43.765 mm), and α is about 26-28° (e.g., about 27.5°).
Guides 64 may function to guide intake and exhaust valves 20, 22 during their reciprocating motions. Each guide 64 may be generally cylindrical and hollow, extending in an axial direction of stem 70. At least a portion (e.g., a bottom end portion) of guide 64 may be pressed into a recess of cylinder head 18, thereby securing guide 64 in place. In one embodiment, a stem seal 84 may be placed over the free portion (i.e., the portion not pressed into cylinder head 18) and configured to engage outer surfaces stem 70 in order to inhibit oil leakage through cylinder head 18 at the associated valve. In the example depicted in
Two or more internal supports 92 may be integrally formed at opposing side walls 85 of base 30, and configured to receive posts or inserts (removed from
An injector spring pad (“pad”) 98 may be formed at the end wall 87 closest to supports 92 (i.e., at the end wall 87 located in the same half of base 30 as supports 92), and configured to provide reaction support for injector spring 54 (referring to
The areas inside base 30 that are located to the sides of pad 98 (i.e., between pad 98 and side walls 85) may be left open to accommodate valve pushrods 36. In embodiments having lash-adjusters 58, more space may be required in these areas than in other embodiments that do not have lash adjusters 58. In order to accommodate both embodiments, the sides of pad 98 at these areas may curve inward. That is, the sides of pad 98 may be generally concave in order to maintain clearance around lash adjusters 58, and recess 102 may be truncated at these concave sides. The clearance around lash adjusters 58 at the concave areas of pad 98 may have a radius r1, such that the concave sides of pad 98 have a width w1. In one embodiment, r1 is about 18-20 mm (e.g., about 19 mm), and w1 is about 7-8 mm (e.g., about 7.5 mm).
Because pad 98 may be concave at its sides, a strength of pad 98 may be reduced. In some instances, this reduction could result in overloading of pad 98 by injector spring 54. In order to provide for the required reaction support and stiffness, one or more ribs 104 may be integrally formed in base 30 that extend from side walls 85 to pad 98. As shown in the embodiment of
As shown in
In order to ensure adequate strength of pad 98, one or more processes may be performed on base 30 after fabrication of pad 98. For example, a shot-peening process may be performed at an intersection of pad 98 with ribs 104 and/or at an intersection of pad 98 and wall 87. In the disclosed embodiment, the shot-peening process may include using S230 cast shot, with an intensity of about .25-.36 mm. This process may result in a residual stress at these areas of about 110 N.
When system 12 is used with an electrically-actuated injector, a wiring harness 106 may need to be routed to the injector. This routing, in one embodiment, may pass through one or both ribs 104. For example, one or both ribs 104 may include a recess 108 located within the bottom surface. Wiring harness 106 may be positioned within recess 108, and a retention mechanism (not shown) may be placed over wiring harness 106 to keep wiring harness 106 inside of recess 108.
In some embodiments, additional means of retention may be necessary to properly position wiring harness 106 relative to base 30. In these embodiments, a tab 110 may protrude from pad 98 toward the center of base 30; a through-hole 112 may be formed within tab 110; and a retention member (e.g., a fire-tree-not shown) may be placed (snap-fit or threaded) into through-hole 112. The retention member may wrap around wiring harness 106 to position wiring harness 106 against tab 110. After passing over tab 110 and through recess 108, wiring harness may be run the length of base 30, within a groove (not shown) formed in bottom 89 at side wall 85.
The disclosed valve actuation system may have applicability with internal combustion engines. In particular, the disclosed valve actuation system may be used to lift one or more gas exchange valves of an engine, while maintaining a desired valve clearance during operation of the engine. The disclosed rocker base may provide clearance for the different components of the valve actuation system, while still maintaining a necessary strength and stiffness.
Several advantages may be associated with the disclosed valve actuation system. In particular, the number of different parts that must be designed, stocked, and distributed for each type of engine used in conjunction with the disclosed valve actuation system may be low, which can reduce a cost of the system. In addition, it may be simple to keep track of and maintain the disclosed system. Accordingly, resources may be freed for use in pursuing new or improved designs.
It will be apparent to those skilled in the art that various modifications and variations can be made to the valve actuation system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.
