Internal combustion engine valve actuation and adjustable lift and timing

A cam can rotate on a camshaft of an internal combustion engine. A rocker arm that actuates a valve of the internal combustion engine can include a rocker pivot connection point located on a distal side of a valve component from a proximate end of the rocker arm that is deflected by action of the cam. The rocker arm can include a contact point located between the rocker pivot point and the proximate end. The contact point can act on the valve component to actuate the valve. The rocker pivot connection point can be translated such that it is closer to or further from the cam. This translation can be used to vary valve lift and/or valve timing. The cam can have a three-dimensional profile to provide different actuation distance of the rocker arm. Systems, methods, and articles of manufacture consistent with one or more of these features are described.

TECHNICAL FIELD

The subject matter described herein relates generally to internal combustion engines and in particular to operation of valves controlling inlet and/or exhaust ports in such engines.

BACKGROUND

Internal combustion engines generally include one or more pistons that move in a reciprocal motion within each of one or more cylinders defined by an engine block or other engine structure. Air and/or fuel are delivered to a combustion chamber within each cylinder by one or more inlet ports and exhaust gases are removed from the combustion chamber within each cylinder by one or more exhaust ports. Control over the opening and closing of inlet and exhaust ports is generally provided by one or more valves, which can be reciprocating poppet valves, sleeve valves, or the like.

Poppet valves include a tapered valve head that plugs a hole and a valve stem extending from the valve head to guide and/or actuate motion of the valve head for opening and closing of the valve. In internal combustion engines with a single piston per cylinder, two or more poppet valves positioned in the cylinder head opposite the piston crown are commonly used to control opening and closing of intake and exhaust ports. Some single piston per cylinder engine configurations, for example those described in co-owned and co-pending international application no. PCT/US2011/055457 include sleeve valves, as do opposed piston engines such as those described in co-owned U.S. Pat. No. 7,559,298.

A sleeve valve typically forms all or a portion of the cylinder wall. In some variations, the sleeve valve reciprocates back and forth along its axis to open and close intake and exhaust ports at appropriate times to introduce air or fuel/air mixture into the combustion chamber and to exhaust combustion products from the chamber. In other variations, the sleeve valve can rotate about its axis to open and close the intake and exhaust ports.

SUMMARY

In one aspect, a system includes a cam that rotates on a camshaft of an internal combustion engine and a rocker arm that actuates a valve of the internal combustion engine. The rocker arm includes a rocker pivot connection point located on a distal side of a valve component from a proximate end of the rocker arm that is deflected by action of the cam. The rocker arm includes a contact point located between the rocker pivot point and the proximate end. The contact point acting on the valve component to actuate the valve.

In an interrelated aspect, a method includes rotating a cam of an internal combustion engine by causing rotation of a camshaft upon which the cam is mounted, and actuating a valve of the internal combustion engine by motion of a rocker arm. The rocker arm includes a rocker pivot connection point located on a distal side of a valve component from a proximate end of the rocker arm that is deflected by action of the cam. The rocker arm further includes a contact point located between the rocker pivot point and the proximate end. The contact point acts on the valve component to actuate the valve.

In some variations one or more of the following features can optionally be included in any feasible combination. A pivot connection point translation system can optionally be included to cause the pivot connection point to move closer to or farther from the cam according to a throttle input received from a throttle control device. Moving the pivot connection point closer to the cam can optionally result in reducing an amount of lift experienced by the valve off a valve seat under actuation by the rocker arm, and moving can optionally result in the pivot connection point farther from the cam results in increasing the amount of lift experienced by the valve off the valve seat under actuation by the rocker arm. Moving the pivot connection point closer to the cam can optionally result in an earlier actuation of the valve under actuation by the rocker arm and moving the pivot connection point farther from the cam can optionally result in a delayed actuation of the valve under actuation by the rocker arm. The cam can optionally include a three-dimensional cam profile that can include at least two cam profiles that result in differing deflection distances of the proximate end of the rocker arm. The three-dimensional cam profile can optionally further include a continuously variable cam profile. The proximate end of the rocker arm can optionally include a rotatable follower that rotates relative to the rocker arm in response to interacting with the at least two cam profiles. The proximate end of the rocker arm can optionally include a follower that interacts with the cam. The valve can optionally include a sleeve valve or a poppet valve.

DETAILED DESCRIPTION

Regardless of the valve type used in an internal combustion engine and also largely independent of the type of engine, some form of reciprocating valve that is moved between an opened and a closed position in a reciprocating motion is generally used open and close intake and exhaust ports at appropriate times during the engine cycle. Commonly used valve actuation systems typically rely on a camshaft for valve opening and a spring for valve closure. Yet other systems utilize hydraulic or pneumatic systems for valve actuation. Regardless of what type of valve actuation system an engine uses, opening and closing intake and exhaust valves presents a number of challenges to provide desirable characteristics of timing, lift, duration, sealing, producibility, serviceability, etc.

A cam is a rotating or sliding piece in a mechanical linkage that transforms rotary motion (e.g. of a camshaft) into linear motion or vice-versa. A cam is generally part of a part of a rotating wheel (e.g. an eccentric wheel) or a camshaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path. A cam follower, also known as a track follower, is a specialized type of roller or needle bearing designed to follow cams. In internal combustion engines with pistons, one or more camshafts can be used to operate intake and exhaust valves that conduct combustion fluids (e.g., air and/or fuel) and exhaust gases to and from the combustion chamber or chambers of an engine. The cams force the valves open by pressing on the valve, or on some intermediate mechanism (e.g. a rocker or rocker arm) as they rotate.

A rocker or rocker arm is generally a reciprocating lever that conveys radial movement from a cam lobe into linear movement at a valve to open and/or close it. One end of a rocker arm is raised and lowered by a rotating lobe or lobes of the camshaft (either directly or via a tappet or lifter and pushrod) while the other end acts on the valve. When the cam lobe raises the outside of the arm, the inside presses on the valve, thereby opening the valve. When the outside of the arm is permitted to return due to rotation of the camshaft, the inside rises, allowing the valve spring to close the valve. The effective leverage of the arm (and thus the force it can exert on the valve) is determined by the rocker arm ratio, the ratio of the distance from the center of rotation of the rocker arm to the tip divided by the distance from the center of rotation to the point acted on by the camshaft or pushrod.

FIG. 1shows a partially cut away isometric view of an internal combustion engine100having a pair of opposing pistons that includes a first piston102and a second piston104. The first piston102is operably coupled to a first crankshaft106by a first connecting rod110and the second piston104is operably coupled to a second crankshaft112by a second connecting rod114. As shown inFIG. 1, the first crankshaft106is operably coupled to the second crankshaft112by a series of gears that synchronize or otherwise control motion of the first piston102and second piston104. During engine operation, the first piston102and the second piston104reciprocate toward and away from each other in coaxially aligned cylindrical bores formed by corresponding sleeve valves. More specifically, the first piston102reciprocates back and forth in an exhaust sleeve valve116, while the second piston104reciprocates back and forth in a corresponding intake sleeve valve120. The exhaust sleeve valve116and the intake sleeve valve120can also reciprocate back and forth to open and close a corresponding exhaust port122and inlet port124, respectively, at appropriate times during the engine cycle to deliver air and/or fuel to a combustion chamber126defined at least in part by the bodies of the exhaust and intake sleeve valves116,120and the heads of the first and second pistons102,104.

FIG. 2shows a cross-sectional view200of the internal combustion engine100ofFIG. 1. As further illustrated inFIG. 2, a first pivoting rocker arm230(also referred to as a “rocker”230), which has a proximal end portion in operational contact with a corresponding first cam lobe232and a distal end portion operably coupled to the exhaust sleeve valve116, opens the exhaust sleeve valve116, for example by moving a sealing edge of the exhaust sleeve valve116away from its corresponding first valve seat234. Similarly, a pivoting rocker arm236(also referred to as a “rocker”240), which has a proximal end portion in operational contact with a second cam lobe240and a distal end portion operably coupled to the intake sleeve valve120, opens the intake sleeve valve120, for example by moving a sealing edge of the intake sleeve valve120away from its corresponding second valve seat242.

The first cam lobe232can be carried on a suitable first camshaft that can be operably coupled to a corresponding crankshaft by one or more gears. On the exhaust side, for example, rotation of the first cam lobe232can drive the proximal end portion of the first rocker230in one direction (e.g., from left to right), which in turn causes a distal end portion of the first rocker230to drive the exhaust sleeve valve116in an opposite direction (e.g., from right to left) to thereby open the exhaust port122. A similar action can occur on the intake side, where rotation of the second cam lobe240can drive the proximal end portion of the second rocker236in one direction (e.g., from right to left), which in turn causes a distal end portion of the second rocker236to drive the intake sleeve valve120in an opposite direction (e.g., from left to right) to thereby open the inlet port124.

Each of the exhaust sleeve valve116and the intake sleeve valve120is urged into a closed position by a corresponding biasing member, such as for example a first large coil spring244and a second large coil spring246, each of which is compressed between a flange on the bottom portion of the corresponding sleeve valve and an opposing surface fixed to the corresponding crankcase. The first biasing member244urges the exhaust sleeve valve116from left to right to close the exhaust port122as controlled by the first cam lobe232, and the second biasing member246urges the intake sleeve valve120from right to left to close the intake port124as controlled by the second cam lobe240.

During operation of the engine100, gas pressure acting directly on at least a portion of the annular sealing edges of the exhaust sleeve valve116and the intake sleeve valve120, and also piston side loads resulting from the piston connecting rod angle relative to the cylinder axis, can tend to tilt or otherwise lift the exhaust sleeve valve116and the intake sleeve valve120off their respective first valve seat234and second valve seat242, respectively. If the exhaust sleeve valve116and the intake sleeve valve120do not seal sufficiently, a number of undesirable consequences can result, including burnt valves, loss of power, poor fuel economy, accelerated wear, etc.

The tilting force caused by the piston connecting rod angle, as well as the lifting force from combustion gas pressure, can tend to increase as the cylinder bore diameter increases. Accordingly, larger bore engines typically require larger biasing members (e.g. springs) to counteract tilting/lifting forces during operation. Larger springs tend to have lower natural frequencies, which can limit the operating speed range for a particular engine design. Alternatively, other systems for actuating sleeve valves, such as hydraulic systems, may be relatively costly to implement or may add undesirable complexity to the manufacture and assembly of such engines.

As noted above, conventional piston engines (e.g. those that do not use opposed pistons), can use poppet valves, sleeve valves, or a combination of poppet and sleeve valves to open and close intake and exhaust ports serving a combustion chamber.FIG. 3shows an example of an engine300having two poppet valves302and304positioned in a cylinder head306that is opposite a reciprocating piston310. The first poppet valve302controls opening and closing of an intake port120, and the second poppet valve304controls opening and closing of an exhaust port124. A first cam312rotating on a first camshaft314causes deflection of a first rocker316that actuates the first poppet valve to cause opening of the intake port120, and a second cam320rotating on a second camshaft322causes deflection of a second rocker324that actuates the first poppet valve to cause opening of the exhaust port122.

One or more implementations of the current subject matter provide methods, systems, articles or manufacture, and the like that can, among other possible advantages, provide features relating to lift and/or timing of valve actuation in internal combustion engines. These features, which can be used in any feasible combination, can optimize air intake rates according to current engine operating conditions for example by allowing dynamic variation of valve lift and/or timing from one cycle of an internal combustion engine to a later cycle of the internal combustion engine.

By positioning the pivot point for the rocker arm on the far side of the cylinder from the cam, the forces acting on the pivot can be reduced by approximately half relative to the the force on the valve, because both the cam force and the pivot force act in the same direction, opposite the force generated by the spring and the inertia of the valve. The cam needs to be larger to generate the same valve motion, but the forces are reduced. In some implementations, the reduction in forces can be sufficient to minimize or even eliminate the need for roller followers.

Consistent with one or more implementations, a stamped, forged, cast, etc. rocker arm can include a socket on one end to mate with an adjustable ball attached to the engine block. In the middle of the rocker arm a hole can be provided to allow a sleeve vale or valve stem of a poppet valve to pass through and contact patches to engage the actuation shoulder on the sleeve valve or valve stem. The opposite end of the rocker arm can include a roller follower, a precision sliding surface to contact the cam, etc.

In one implementation, an example of which is illustrated inFIG. 4a pivot point of a rocker can be repositioned on a side of a valve opposite from the point of action of the cam on the rocker instead of between the cam and the valve. The loads at the cam and the pivot can thereby be reduced in exchange for a longer path of action from the cam. This repositioning can provide the option of dynamically adjusting the position of the rocker pivot point to alter valve lift.FIG. 4illustrates a system400for dynamically adjusting the position of the rocker pivot point to alter valve lift in this manner. The position402of the rocker pivot point404, the contact point of the distal end of the rocker with the base circle406of the cam, and the contact of the distal end of the rocker with the nose410of the cam can define a triangle representing the extents of the rocker centerline. Very little displacement occurs at the pivot end of the triangle, and maximum displacement occurs at the cam centerline position412. The position of the valve centerline414can be disposed at a non-fixed distance from the cam axis position412. Moving the rocker pivot position402closer to the valve can shorten the triangle by decreasing the distance between the valve centerline position414and pivot position402, thereby resulting in a lower valve lift condition416than occurs at a neutral condition of the rocker pivot position402that provides a medium lift condition420. Conversely, moving the pivot position402further away from the valve centerline414can increase the valve lift by moving the line of action toward the maximum displacement end of the cam/rocker triangle, thereby creating larger valve lift condition422than occurs at the neutral, medium lift condition420.

As shown in the system500ofFIG. 5, moving the current location502of the rocker pivot position402can also involve varying the point of action or contact point504of the cam upon a roller follower506. As the current location502of the rocker pivot position402is moved toward or away from the cam axis position412, the contact point504between the cam and the roller follower506moves as well. This movement can have the effect of changing the cam phasing, as the acting portion (e.g. the cam nose410) of the cam profile occurs earlier510, later512, or unchanged514from a neutral condition in the rotation of the cam depending on the current location502of the rocker pivot position402. This phasing effect can optionally be used in combination with the lift adjustment described above in reference toFIG. 4, or avoided by use of a flat follower with sufficient reach to contact the cam over the length of the adjustment of the pivot point position402.

A phasing effect can also or alternatively be achieved using a curved stamped follower instead of a roller follower to reduce costs. Such a configuration can be achieved using a convex follower contact profile, so that it wraps around the cam base circle. The geometry of a rocker consistent with the current subject matter can be either flat or curved. In some implementations, a flat geometry can be simple and effective if the displacement of the rocker pivot position402is parallel to the line defined by the rocker pivot point404and the contact point504between the base circle406of the cam and the cam follower506.

In another implementation, a three dimensional (3D) or variable profile cam can be used in which the cam profile changes with axial position as well as angular position. A 3D cam profile can be impractical in some engines due to high contact stresses resulting from point contact between the cam and the follower. However, the lower actuation forces of an opposed pivot point such as is described above can allow the advantageous use of such a configuration.

FIG. 6A,FIG. 6B, andFIG. 6Cshow side vies of a valve opening rocker600, a valve closing rocker602, and a desmodromic rocker combination700for use with sleeve valves consistent with implementations of the current subject matter.FIG. 7shows a top view of the desmodromic rocker combination700. As shown, the cam604can be set up to be perpendicular to the axis of motion of the sleeve valve606and positioned with its centerline over the sleeve actuation shoulder610at mid lift. The pivot point404for each rocker can be on the opposite (e.g. distal) side of the valve from the cam location. An open cam lobe410can be offset to one side of the cylinder centerline and a close cam lobe612(e.g. inFIG. 6BandFIG. 6C) can be offset to the other side of the cylinder centerline. As shown inFIG. 7, the desmodromic rocker combination700can be formed as a forked closing rocker702having two cam followers704overlaid with an opening rocker706having only one follower710that is positioned within the fork of the two cam followers704on the forked closing rocker702. A desmodromic rocker combination700can actuate a valve in both directions, which can in some implementations provide a faster closing response as well as additional positive closing force for the valve than a spring.

A 3D cam can, in some variations, be composed of layers of narrow 2D profiles802with an equal base circle arranged in series on a camshaft804, such as for example as shown in the system800ofFIG. 8. A single follower506of width equal to or less than the profile width of each of the narrow 2D profiles802can track the cam. The rocker can optionally be shaped like a stirrup806in such a configuration, with the valve810passing through the center of the stirrup806to provide two pivot points810for the rocker to stabilize the single follower506. The single follower506can thus track one layer802of the cam stack, according to the axial position of the cam, and the cam position can be adjusted from one indexed location of a to another during the unloaded base circle portion of the cam rotation to shift from one 2D cam profile802to another. Several different 2D cam profiles802can thus be accessed with relatively low actuating forces. Depending on the width of the individual cam layers802, a modified follower506can be used to ensure retention. Such a modified follower506can optionally include a flanged follower. This configuration can require modifications to the cam profile, as the follower rides on the flanges during a base circle segment of the cam and shifts to the center portion of the follower506during the actuation phase.

The follower506can also be a narrow finger follower, contact loads permitting. This configuration can reduce the required width of the each cam layer. As shown inFIG. 8, each 2D profile layer802can advantageously be wider than the follower wheel506plus the bracket arms, plus some margin. A finger follower implementation can in some variations employ cam layers of nearly the same width as the follower506.

Such a layered cam can include indexing features on the cam translation mechanism so that the cam settles only at points where a specific 2D layer802of the cam and the follower506are aligned. Such a feature can take the form of a series of grooves in the camshaft804, for example with a spring loaded detaining element. Alternatively, an indexing barrel form can be used, in the fashion of a motorcycle sequential shift system, where a groove in the surface of a cylindrical element positions a shift fork to determine cam position. If the shift drum is biased in one direction by engine speed (e.g. by centrifugal actuation or oil pressure) or by engine vacuum, and return biased by a spring, then a continuum of pressure balances can be translated into definite steps of the cam position.

For a continuous 3D cam, with a continuum of intermediate profiles from one limit to the other, a flat finger follower902on a pivot point904can be employed to reduce contact loads. If the cam profile is designed such that a flat to mildly convex surface profile is maintained across the cam surfaces, a flat follower with mild freedom to rotate can approximate a line contact over a narrow width as shown in the system900ofFIG. 9AandFIG. 9B, instead of a point contact.

FIG. 10shows a system1000illustrating an example of a continuous 3D cam with a range of rotating finger oscillation. The cross sectional views1002,1004, and1006show the effective cam nose410displacement at each of three sections A, B, and C along the axis of a continuously variable 3D cam feature1010rotating on a camshaft804.

FIG. 11A,FIG. 11B, andFIG. 11Cshow views of a system1100that illustrates features of interactions of a rotatable finger follower1102with changes in location cam pitch.FIG. 11Ashows a side view along the axis of the camshaft804in which a rotatable finger follower1102is associated with a rocker arm1104secured by a pivot point404and interacting with a shoulder feature1106of a valve or valve component1110(e.g. either a sleeve valve body or a valve stem of a poppet valve). The rotatable finger follower1102can freely rotate relative to the rocker arm1104about an axle or other rotatably connective feature1112. As shown inFIG. 11B, the rotatable finger follower1102is not rotated about the axle1112when interacting with the base circle part of the cam. However, during interaction with the variable 3D cam feature810, the rotatable finger follower1102oscillates about the axle1112that is in the plane of the view ofFIG. 11Ain response to the varying profile of the variable 3D cam feature810rotating on the camshaft804.

The tip1202of the finger follower1102can be curved slightly, for example as shown in the view1200ofFIG. 12. The curve finger follower tip can approximate the surface of a roller follower and thereby allow cam event phasing by shifting the rocker pivot point, for example in a manner as described above.

The rocker can optionally be formed by machining, stamping, or other methods of preparing such elements of an engine. Consistent with one or more implementations of the current subject matter, a rocker can include a folded side or flange formed in the rocker near its contact area with a valve. This folded material or flange can provide additional stiffness to the structure of the rocker and can extend all the way out to the end of the rocker on either or both ends to provide a desired level of stiffness. Optionally, the folded side can include material to hold the axle of a roller follower or the sides of a socket that mates with the ball end. The ball end can optionally be adjustable to provide valve lash adjustment.FIG. 13AandFIG. 13Bshow top and bottom isometric views, respectively, of a rocker1300consistent with such an implementation. The rocker1300can include a first or proximal end portion1302having a clevis portion1304with a corresponding shaft1306configured to carry a cam follower506. The rocker1300can also include a second or distal end portion1310having first and second arms1312,1314that can extend around opposite sides of the sleeve valve or poppet valve stem. The first and second arms1312,1314can include recesses1316,1318(e.g., cylindrical recesses) and/or other suitable features (e.g., axel pins) to pivotally support one or more sliders or other valve actuation components. As shown inFIG. 13B, each of the first and second arms1312,1314can include a corresponding flange1320,1322shaped and/or sized to provide additional stiffness to the rocker1300to reduce or minimize unwanted deflection during operation. As this view also shows, the underside of the rocker1300can include a hemispherical or similarly shaped recess1324configured to receive the crown of a corresponding rocker pivot.

A continuous 3D cam also provide potential advantages in actuation, for example by permitting the elimination of a conventional throttle valve entirely and directly actuating cam position with the accelerator control to vary valve lift. Operator demand for more or less torque can translate into allowing a larger or smaller combustion charge (e.g. a mixture of air and fuel) into the engine, in much the same fashion as a conventional throttle valve.

Lower cam loads provided by an opposed rocker pivot point can also allow for simpler cam construction, particularly in small engines with low valve loads. A polymer cam, or a cam with polymer lobes molded onto a tubular shaft, or a cam with sintered lobes pressed onto a solid or tubular shaft, can in some implementations be produced at a lower cost compared to a conventional cam. Alternative manufacturing processes can particularly benefit a 3D cam, whose surfaces can be more difficult to grind or otherwise form according to conventional methods. In some variations, the basic lobe form can be injection molded in a durable polymer resin, either left raw or with a hard coating applied (for example by sputtering or the like), or formed using powder metallurgy and surface hardened. A chemical etch, a media blast, a polishing process, or the like can optionally be applied for surface smoothing, which can have the benefit of eliminating the need for grinding. Another potential approach to preparing a 3D cam can include stamping or powder-forming the external surface of the lobe and then attaching the external form of the lobe to a shaft using a polymer binder, for example as shown inFIG. 14in which a polymer 3D cam1400is formed on a camshaft804as a lightweight, low-cost core1402coated by a hard, more resistant outer surface1404.

FIG. 15shows a process flow chart1500illustrating method features consistent with one or more implementations of the current subject matter. At1502, a cam of an internal combustion engine is rotated by causing rotation of a camshaft upon which the cam is mounted. A valve of the internal combustion engine is actuated at1504by motion of a rocker arm that includes a rocker pivot connection point located on a distal side of a valve component from a proximate end of the rocker arm that is deflected by action of the cam. The rocker arm also includes a contact point located between the rocker pivot point and the proximate end. The contact point acts on the valve component to actuate the valve. Optionally at1506, the pivot connection point is translated, for example by a pivot connection point translation system, to move the pivot connection point closer to or farther from the cam. The motion can be in response to a throttle input received from a throttle control device of the internal combustion engine. Also optionally at1510, deflection of the proximate end of the rocker arm can be varied using a cam having a three-dimensional cam profile.