Variable overhead valve control for engines

A valve control mechanism is provided for an overhead valve, internal combustion engine having a camshaft moving a pushrod to move a rocker arm that in turn moves the valve. Three aligned rollers are fastened to the end of the pushrod adjacent the rocker arm. The outer two rollers roll along parallel profiled surfaces that control at least the valve lift and ramp. The middle roller rolls along an engaging surface on the rocker to move the rocker arm in a motion determined by the configuration and location of the profiled surfaces and the engaging first and second rollers. The outer rollers rotate in a direction opposite the middle roller.

BACKGROUND

This document describes a mechanism for a variable valve control of overhead-valve (OHV) internal combustion piston engines. An OHV engine is typically defined as an engine that has poppet type intake and/or exhaust valves located in the engine cylinder head, one or more camshafts located in the cylinder block, and with the valves being actuated via lifters, pushrods and rocker arms. OHV engines may be of various cylinder configurations such as vee, in-line or opposed. The OHV engine architecture is widely used because it is economical to manufacture, provides a compact physical package size and is reliable in service

Variable valve control is a very desirable feature in an engine because it can reduce exhaust emissions, reduce fuel consumption and improve power output characteristics. There are several known methods of variable valve control, such as electromagnetic (U.S. Pat. No. 4,777,915) or hydraulic (U.S. Pat. No. 6,739,293). However, these systems typically require complex and expensive control systems and tend to be unreliable in service. There are also mechanical systems (U.S. Pat. No. 6,792,903) but these typically require an overhead cam type engine architecture, which can be expensive to manufacture. Therefore, what is needed is a mechanical variable valve control device that can be incorporated into an OHV type engine.

SUMMARY

A valve control mechanism is provided for an overhead valve, internal combustion engine having a camshaft moving a pushrod to move a rocker arm that in turn moves the valve. The mechanism preferably includes a first and second roller each rollably connected to the end of the pushrod that is opposite the camshaft and adjacent the rocker. A roller guide is provided and has a first profiled surface, with the first roller and roller guide positioned so the first roller rolls along the first profiled surface. The first profiled surface is configured to achieve a desired valve movement, such as valve closed, ramp and lift. An engaging surface is provided on the rocker arm with the rocker arm and second roller positioned so the second roller rolls along the engaging surface of the rocker arm to rotate the rocker arm as the first roller rolls along the first profiled surface. Ideally the first roller rolls in one direction along the profiles surface while the second roller rolls in an opposite direction against the engaging surface to move the rocker arm according to the first profiled surface.

In further variations, the roller guide is positionable along a first axis which is preferably, but optionally parallel to the engaging surface. Further, there is preferably, but optionally a third roller rollably connected to the end of the pushrod opposite the camshaft, with the first and third rollers being on opposing sides of the second roller, and with the roller guide having a second profiled surface spaced apart from the first profiled surface but configured the same as the first profiled surface and located to engage the second roller.

The third roller is preferably rollably connected to the end of the pushrod opposite the camshaft, with the first and third rollers being on opposing sides of the second roller, ideally with the first and third rollers being of smaller diameter than the second roller. Thus, ideally, the first and third rollers roll in one direction against the profiled surfaces while the second roller rolls in an opposing direction against the engaging surface.

The engaging surface on the rocker arm is preferably straight and parallel to a portion of the first profiled surface, and ideally that straight portion controls the valve closed position. But the engaging portion could be inclined, or profiled to further vary the valve operation in a way that differs from having a straight engaging surface parallel to a portion of the profiled surface.

The roller guide is preferably positionable along a first axis to vary the valve operation, and is positionable by a rotating cam which moves the roller guide along that first axis, with a spring resiliently urging the roller guide against that rotating cam. Control of the roller guide could also be provided by incremental rotation of a setting shaft by, for example, an electric motor or a hydraulic actuator either directly, or through various intermediate drive systems such as gears, belts or chains.

Preferably, the profiled surface has a first portion parallel to the engaging surface to alter the valve closed duration, and also has a second middle portion configured to alter valve ramp, with a third portion configured to alter valve lift, as the first roller moves along these three portions of the first profiled surface.

The valve control mechanism also includes a roller guide having at least one, and preferably two similarly profiled surfaces configured to control the valve closed, ramp and valve lift. The profiled surfaces are spaced apart with a slot between them. Three rollers are rollably connected to the end of the pushrod that is opposite the camshaft, with two of the rollers each abutting a different one of the profiled surfaces and the third roller fitting in the slot. A rocker arm surface is formed on one arm of the rocker arm so the rocker arm surface is located opposite the profiled surfaces with the third roller rolling on the rocker arm surface in a direction opposite the other two rollers. Thus, movement of the two rollers along the profiled surface moves the third roller and rocker arm in a corresponding motion.

Preferably, but optionally, the roller guide moves along a first axis generally parallel to a portion of the profiled surface. More preferably, a cammed surface abuts the roller guide to move the roller guide along the first axis in order to alter at least one of the magnitude or duration of the valve lift, ramp or valve closed position and/or duration.

As to the valve lifter, the engaging surface is again preferably a straight surface, but could vary and could include a profiled surface that is not straight. As before, the three rollers preferably, but optionally rotate about parallel axes or rotate about a common axis. Ideally, the third roller that abuts the engaging surface is larger in diameter than the other two rollers.

The control mechanism can also be considered as including a pushrod having a first and second roller rotatably mounted at one end of the pushrod, where the first roller rolls against a profiled surface in a first direction and the second roller rolls against an engaging surface on the rocker arm in an opposing direction to move the rocker arm in a motion defined by the shape of the profiled surface. The profiled surface is preferably on a roller guide that in turn is movable along a first axis located to shift the profiled surface and vary the magnitude of the valve lift, or the valve ramp, or the timing or duration of the valve closed position. Preferably, the roller guide is resiliently urged against a setting camshaft, the rotation of which moves the roller guide along the first axis.

In this embodiment the engaging surface is also preferably a straight surface, and more preferably is generally parallel to a portion of the profiled surface when the valve is closed, and is ideally parallel to the portion of the profiled surface that affects the valve closed duration and/or timing.

In any of the above valve control mechanisms, there is preferably, but optionally a swivel mount on the pushrod and the swivel mount is configured to permit the one end of the pushrod to rotate at least a few degrees. That rotation helps accommodate lateral movement of the rollers which rotate against two different surfaces, surfaces which preferably face or oppose each other.

Moreover, a lifter spring is preferably used to resiliently urge a lifter against the camshaft, with the lifter spring engaging a lifter perch. Preferably, but optionally, the lifter perch abuts a stop on the engine where the stop is located to limit motion of the perch and spring toward the camshaft. Limiting the spring movement limits the force with which the spring urges the lifter against the camshaft, and that can be sued to reduce wear on the non-lifting portions of the camshaft.

There is also provided a method for controlling the operation of a valve in an overhead valve, internal combustion engine having a camshaft moving a pushrod to move a rocker arm that in turn moves the valve. The method includes rolling a first roller connected to the pushrod along and in engagement with a first profiled surface that is configured to control at least the lift and ramp of the valve. The method also includes moving a second roller connected to the pushrod along but not in engagement with the first profiled surface. Further, the method includes rolling the second roller along an engaging surface on the rocker arm and in a direction opposite the first roller. Finally, the method includes pivoting the rocker arm in a motion that results from movement of the first roller along the first profile.

The method also preferably, but optionally has the two rolling steps use rollers that have different diameters. Preferably, the method also includes rolling a third roller connected to the pushrod along and in engagement with a second profiled surface having the same profile as the first profiled surface, and ideally the first and third rollers are on opposite sides of the second roller. The method also optionally includes aligning the rotational axes of these various rollers.

Further, the method also preferably, but optionally includes moving the first profiled surface along an axis generally parallel with a portion of the profiled surface, and doing so to vary at least one of the valve ramp, valve lift or valve closed duration and/or timing. Moreover, the method preferably includes repeatedly cycling the first profiled surface along that axis, and more preferably that axis is generally parallel with a portion of the profiled surface, and ideally that axis is parallel to a portion of the profiled surface that affects the timing and/or duration of the valve closed position.

There is also provided a mechanism for reducing wear on a camshaft of an overhead valve, internal combustion engine where the camshaft moves a pushrod to move a rocker arm that in turn moves the valve. The pushrod has one end engaging a lifter which is resiliently urged against the camshaft by a lifter spring which engages a lifter perch. A stop is formed on the engine and located so that the lifter perch abuts the stop and limits movement of the spring toward the camshaft. That limit stop limits the force with which the lifter is urged against the camshaft in the non-lift positions, thus reducing wear.

A method is also provided for limiting camshaft wear on such an internal combustion engine. The method includes placing a stop on the engine and locating the stop relative to the perch to limit the movement of the spring toward the camshaft.

The various features can be used alone, or in combination with each other, and a number of such combinations are described above. These control mechanisms and methods are preferably used on intake and exhaust valves, each of which is separately controlled by moving the roller guide along the defined axis ad describe above and explained in more detail herein.

DETAILED DESCRIPTION

A brief overview is given first. Referring toFIGS. 1-10, and especiallyFIGS. 6-7, a camshaft2rotates with its cammed surface2acontrolling the axial motion of pushrod8. The camshaft2contacts a lifter4connected to the pushrod8through spring swivel9and spring perch10which allow rotational movement about one and preferably about two orthogonal axes, with lifter spring11maintaining these parts in contact during operation. The end of the pushrod8opposite the camshaft2has a roller assembly5that includes two outer rollers18and one middle roller19(FIG. 8) that is larger in diameter than the outer rollers. Thus, the pushrod8has a first roller18abutting a profiled surface21and a second roller19abutting the rocker arm6so the rocker arm motion (and valve motion) derives from the shape profiled surface21. The rollers18,19all rotate about parallel axes and preferably, but optionally rotate about a common shaft and common axis. The middle roller19rotates in a direction opposite outer rollers18. The middle roller19rolls against engaging surface20on rocker arm6. The rollers18roll against surface21on roller guide3which is constrained to move along a predetermined axis shown as a generally vertical axis inFIG. 2, but the orientation can vary. Rotatable cammed surface1aon the setting shaft1adjusts the position of the roller guide3and its profiled surface21relative to the rollers18and pushrod8.

The setting shaft1is rotated so that the profiled surface1apositions the roller guide3to a desired location. Because rollers18roll against surfaces21a,21b,21con the roller guide3, movement of the roller guide3this adjusts the duration of the valve ramp, lift and closed positions as described below.

The two outer rollers18roll against two different, but similarly profiled surfaces on the roller guide3in order to control the motion of the engine valve7. The rollers19roll against engaging portion20on a first arm6aof rocker arm6, so that the profile of the surfaces21thus controls motion of the rocker arm6. The rocker arm6has a second arm6bwhich abuts an end7aof the valve stem7bto control motion of the valve7and its valve head7c. The rocker arm6is located on a rocker stud13and positionable along the length of that stud by nut15.

The setting shaft1is rotated so that the profiled surface1apositions the roller guide3to a desired location. Because rollers18roll against surfaces21a,21b,21con the roller guide3, movement of the roller guide3this adjusts the duration of the valve ramp, lift and closed positions as described below.

In more detail, and referring to FIGS.2and6-7, the setting shaft1preferably comprises a rotatable cylindrical shaft1having an eccentric lobe1awith various profiles configured to position the roller guide3. The setting shaft1is rotated when a change in valve operation is desired, such as altering the start, duration or end of the lift, ramp or closed positions.

The camshaft2is similar in design and function to a conventional camshaft. However, the profile of the cam lobes2awill be optimized with regards to kinematics of the overall mechanism. Ways to optimize the design of cam lobes2aare known in the art and not described in detail herein.

Roller guide3is constrained to move along an axis and is positioned axially by the setting shaft1. The roller guide3is shown as a generally cylindrical part in a cylindrical sleeve contained in housing16. But the configuration of the roller guide3can vary, as can its mounting. The roller guide3is preloaded against the lobe1aon the setting shaft1by springs14which preferably, but optionally comprise coil springs parallel to the axis along which roller guide3is constrained to move. The piston-like shape of the roller guide3thus encircles and encloses the spring14. Advantageously there are two springs14, one on each side of the roller guide3and adjacent each of the two profiled surfaces21. The springs14resiliently urge the roller guide3against the cammed surface1aon rotary positionable setting shaft1.

By adjusting the rotational position of setting shaft1and its cam or profiled surface1a, the axial position of roller guide3relative to rollers18and pushrod8is adjusted and set. As discussed later regardingFIG. 10, the roller guide3has a profiled surface21that constrains the movement of the pushrod rollers5which abut this profiled surface, so the setting shaft1adjusts the movement of the pushrod rollers5by positioning the intermediate roller guide3. The pushrod rollers5in turn control movement of the rocker arm6and valve7.

The lifter4is of conventional design and function, and may optionally incorporate hydraulic adjustment as desired. The lifter4abuts the cam shaft2because it is periodically actuated by rotation of the lobed or cammed surface2aon the cam shaft2, with the motion of the lifter4and pushrod8being determined by and controlled by the shape of the cammed surface on cam shaft2.

As best seen in FIGS.2and6-8, the pushrod roller5is provided with three circular rollers18,19centered on a common rotational axis so there are two outer rollers18and one central or middle roller19. The middle roller19rolls against the engaging surface20of rocker arm6while the outer rollers18roll against a profiled or cammed surface21on the roller guide3to control movement of the rocker arm. The engaging surface20is preferably a flat, straight surface on the rocker arm6a.

The rocker arm6rocks about a pivot axis and has two arms, usually on opposing sides of that axis. One arm6aof rocker arm6has engaging surface20against which the pushrod roller19bears in order to control motion of the rocker arm. The other arm6bof the rocker arm6bears against an end7aor tip of the valve stem7bin order to control motion of the valve. The rocker arm6transfers the motion of the pushrod roller5into movement of the valve7, because the roller5moves one arm6aof the rocker arm6so the other arm6bof the rocker arm moves the valve stem7bof valve7.

The valve7is preferably a poppet valve assembly of conventional design and function having a valve stem7band valve head7cconfigured to engage a valve seat in the engine. The valve head7cmoves to allow exhaust gas or air to enter the combustion chamber of an engine and/or to exit the combustion chamber. The valve stem7bis connected to the head7c, with the distal end or tip7aof the valve stem abutting the rocker arm6. A valve spring11, usually a coil spring, resiliently urges the valve stem7band end7atoward the rocker arm6, so the parts remain in contact and so that movement of the rocker arm controls motion of the valve7.

The pushrod8transmits the motion produced by the camshaft2and lifter4to the pushrod rollers5(18and19inFIG. 8) affixed to the opposite end of the pushrod8. The pushrod8has a hemispherical surface8aon one end to mate with the lifter4, allowing it to swivel relative to the lifter4. Because alignment of the surfaces21and20will likely cause the pushrod8to rotate, the pushrod is configured to swivel. A swivel of a few degrees is believed suitable, with movement of 1-3 degrees believed suitable for most applications. But the amount of rotation will vary with the design.

Preferably, but optionally, swiveling of the pushrod is also allowed by a hemispherical shaped spring swivel9which allows angular movement between the pushrod8and spring perch10. The spring swivel9has a threaded connection to pushrod8, which allows for adjustment at assembly by rotating the swivel9to move it along the length of the threaded segment of the pushrod8. The spring perch10has a recess configured to receive and mate with swivel9. A lifter spring11, preferably a coil spring, encircles the pushrod8, with a first end of the spring11adjustably positioned along the length of the pushrod8by various means known in the art. For example, a spring plate12is shown with the pushrod extending through a hole in the plate12so the plate restrains axial movement of one end of the lifter spring11. The function of the spring plate11may be incorporated into the design of the cylinder head by providing a stop serving the same purpose as the spring plate. The second end of the lifter spring11abuts the lifter perch10, and transmits the lifter spring force such that the pushrod8and lifter4maintain contact with the camshaft2during operation. Advantageously a centering flange10aextends from the lifter perch10on the inside of the lifter spring11to help position the spring and maintain alignment and contact between the spring and perch. The lifter spring11is thus positioned along the pushrod8to resiliently urge the lifter4against the camshaft2.

The spring perch10preferably, but optionally has a stop surface10bthat bears against the engine block30. This stop surface10bprevents the lifter spring force from being transmitted through the camshaft/lifter interface when the lifter is working against the camshaft's base circle (i.e. the portion of the camshaft profile that does not produce any lift). This stop surface10bhelps minimize friction loss in the mechanism because it prevents the lifter spring11from resiliently urging the lifter4against the cam2aand camshaft2during portions of the cam rotation which do not activate the lifter4and pushrod8.

The rocker arm6typically includes a rocker arm stud13and rocker arm nut15. The stud13and nut15attach the rocker arm to the engine, typically by attaching to the cylinder head. The rocker arm stud13is preferably aligned along an axis that passes through the rocker arm pivot axis, with the rocker arm6positioned along the stud and abutting the nut15, yet free to rotate or rock. Rotation of the rocker arm nut15moves the nut along the length of the rocker arm stud13and that adjustably positions the rocker arm6along the rocker arm stud13, thereby adjusting the location of the rocker arm pivot axis along the length of the rocker arm stud13. Alternatively, a plurality of the rocker arms4may be mounted on a common shaft and some of the supporting studs13omitted.

The mechanism housing16is preferably provided to enclose the adjustable valve mechanism. The shape of housing16will vary according to the engine design and the design of the valve mechanism. The mechanism housing16is shown as being a separate component from the cylinder head. However, the mechanism housing16maybe incorporated into the configuration of the cylinder head if desired. The mechanism housing16contains the cylinder within which the roller guide3moves axially, and the housing16also provides a rotational support for the rotational setting shaft1, but these support functions could be implemented by separate structure apart from the housing16.

As shown inFIG. 8, the pushrod rollers18and19are of different diameter. The center roller19has a larger diameter the outer rollers18. The center roller19bears against the engaging portion20of rocker arm6and the two outer rollers18bear against an opposing surface21on the roller guide3. The engaging surface20of rocker arm6and the profiled surfaces21face each other in the depicted embodiment. Having differing roller diameters allows the inner and outer rollers (19,18respectively) to bear against these opposing surfaces and still roll in opposite directions. They preferably roll along a common axis and about a common shaft, thus minimizing friction losses and reducing the parts.

The rollers18,19preferably roll along a common axis and more preferably use a common axle. Thus, the end of pushrod8has a two pronged yoke with axially aligned holes in each yoke, and a shaft extending through those holes so one roller19is mounted between the two yokes and the outer rollers18are cantilevered on an outer side of each yoke. If desired, the end of the pushrod8could have four yokes, with each of the two outer rollers18and the middle roller19mounted between two adjacent yokes for a more sturdy support.

The configuration of the roller guide3is shown inFIG. 10. The roller guide is generally cylindrical in shape. The center of the roller guide contains inclined surface22, which is typically a groove between profiled or cammed surfaces21in order to provide clearance for center roller19which extends into that groove. The inclined surface22is shown as extending through the diameter of the guide3, from one side to the other side in order to provide clearance for center roller19. The shape of surface22can vary as long as clearance with center roller19is provided. The center pushrod roller19is located adjacent this inclined surface22but does not abut it. The inclined surface22is thus preferably recessed relative to cammed surfaces21in order to provide clearance for the center pushrod roller19as well as serving as a position limit and/or guide for the pushrod body8.

On opposing sides of this (optionally) flat, inclined surface22are profiled or cammed surfaces21which preferably, but optionally do not extend more than half way through the diameter of the roller guide3. But the shape of the profiled surface21will vary. The two cammed surfaces21each have the same profile, and each outer pushrod roller18abuts one of these cammed surfaces21.

Because the center roller19is on the same axis as outer rollers18the centers of rollers18,19have the same motion, and center roller19will thus track the motion of rollers18along the profiled surface21. Because center roller19abuts engaging surface20of rocker arm6a, the roller19causes the rocker arm to move according to the profiled surface21. The rollers18,19rotate in different directions, but about the same axis.

The roller guide3thus has profiled surfaces21designed to guide the outer pushrod rollers18along the profiled surface21, with the center roller19transferring that predetermined motion to the rocker arm6which in turn operates the valve7to move with a predicted motion that is a variation of that predetermined motion of rollers18,19and profiled surface21. The motion of rocker arm6is thus determined by the configuration and location of profiled surface21.

Referring toFIGS. 2 and 10, the roller guide surface21has three regions. First region21ais a portion of the guide surface21that is essentially parallel to the engaging surface20of the rocker arm6, and that is preferably, but optionally generally parallel to the axis along which the roller guide moves. This first region21ais the region most distant from the setting shaft1as shown inFIG. 10. As the pushrod rollers18pass along this portion21a, the rollers18(and roller19) do not move any closer to engaging surface20on the rocker arm6a, and thus do not result in any rocker arm movement or valve lift. Because the rollers18are rolling on a surface21awhich is parallel to the rocker arm engaging surface20, there is no relative movement between the rollers18and the rocker arm engaging surface20. By adjusting the length of this parallel portion21aand the time which the rollers18abut this parallel portion21a, the duration which the valve is closed can be adjusted. This initial portion21aof the guide surface21ais called the “closed” portion, because it adjusts the time the valve remains in the closed position at the beginning and end of each valve cycle.

Middle region21bis a portion of the guide surface21that moves very gradually towards the engaging surface20of the rocker arm6, and thus produces a very gradual initial/final movement of the rocker arm and valve. As the rollers18roll along surface21bthe rollers move toward the engaging surface20and thus the middle roller19moves toward rocker arm surface20and rotates the rocker arm6which in turn moves valve7. In conventional camshaft terminology, this is referred to as the opening/closing “ramp” and this portion21bis referred to as the ramp portion. The ramp is necessary to minimize and control the impact velocities between the valve and its valve seat. High impact velocities can create abnormal valve wear and noise. The profile of the middle ramp portion21bwill vary with the engine and valve design.

Region21cis a portion of the guide surface21that moves more aggressively towards the engaging surface20of the rocker arm6. Region21cis located on the portion of guide surface21that is closest to the setting shaft1as shown inFIG. 2. The rollers18thus cause the rocker arm to move according to the profile of portion21cand thus aggressively pivot the rocker arm6which moves the valve7. This region21cis the portion of the guide surface21that produces the majority of the rocker motion and valve lift and is called the lift portion21c. The shape of this lift profile is designed to work in conjunction with the shape of the profile of camshaft2, to produce the desired kinematic characteristics within the overall mechanism.

The motion of rollers18along profiled surface21is cyclic, going first one direction to open the valve, and retracing the path in the opposite direction to close the valve. In operation, the valve lift and duration is initially adjusted by placing setting shaft1and roller guide3in positions or orientations that produce a desired valve operation relative to the movement resulting from profile21.

FIG. 3shows the setting shaft1and roller guide3in their respective positions that produce maximum valve lift and duration, as indicated by dimension17b. In this position cam2ais positioned to move pushrod8to its most distant position from camshaft2. In this position the contact portion10bon the spring perch10is not in contact with the engine block30. More importantly, the profiled surface1ais positioned to move roller guide3to a position that is more distant from shaft1, with outer rollers18abutting portion21cof the profiled surface21on the roller guide, and with

FIG. 4shows the setting shaft1and roller guide3in their respective positions that produce a medium valve lift and duration, as indicated by dimension17c. The profiled surface1ais positioned to move roller guide3to a position closer to shaft1but intermediate the extreme positions, so that outer rollers18abut portion21cof the profiled surface21on the roller guide do not extend along surface21cas much as in the maximum lift position, and thus the rocker arm6is not rotated as much.

FIG. 5shows the setting shaft1and roller3in their respective positions that produce minimum valve lift and duration, as indicated by dimension17d. In the example shown, the minimum valve lift and duration values are both zero. The profiled surface1ais positioned to move roller guide3to its position closest to shaft1, with outer rollers18abutting portion21aof the profiled surface21on the roller guide. The position of cam2aand pushrod8are as before.

The valve lift and duration is infinitely variable between the maximum (FIG. 3) and minimum (FIG. 5) settings of the valve adjustment mechanism. The profile surface21varies the rate of valve movement as the valve passes through the valve closed, ramp and lift cycles, while the position of the profile surface21relative to the rollers18(via setting shaft1and cam1a) varies the maximum valve lift and cycle duration as discussed later regardingFIGS. 12-13. The shape of the ramp portion21bcan be varied to achieve different ramp rates and forces. Positioning the rollers18along the profiled surface21(by setting cam shaft1a), allows selecting various portions of the profile21and its associated motions of the rocker arm6and valve7.

The position of setting shaft1can be releasably fastened in position by various means, such as screws, clamps or other devices for a long term fixed setting. But preferably the movement of shaft1is dynamically or actively controlled by cables, belts, gears, linkages, chain drives, stepper motors, hydraulic motors and/or controls, or other control mechanisms. The movement can also be variably controlled using input from sensors detecting various engine parameters such as speed, fuel, oxygen, engine temperature or combustion constituents, or detecting various environmental parameters such as humidity and temperature. Thus, for example, the valve operation can be adjusted for engine start-up, for cold weather, for hot weather, for fuel efficiency, for desired power output, for speed, etc. Other mechanisms could be used to position the roller guide, including a threaded projection abutting or connected to a portion of the roller guide3to position the guide along its axis.

Referring toFIG. 1, the cammed surface1aon setting shaft1on the left side is larger than the cammed surface1aon the right side. The left side is shown as the intake and the right illustrates the exhaust, and typically the valve lift on the intake is larger than on the exhaust, thus, the cammed surface1ais larger on the intake than on the exhaust. As indicated byFIG. 1, the valve adjust mechanism can vary between the intake and exhaust valves7.

Further, while a simpler construction is provided by having setting shaft1acommon for all intake valves and a different setting shaft1afor all exhaust valves, it is preferable for each valve to be separately controlled, or for sub-groups of valves to be separately controlled. If each valve7is separately controlled, then each valve can be separately adjusted to optimize various engine parameters, such as power, fuel efficiency, or emission control. Further, by moving the setting shaft1to provide a minimum valve open position, fewer than all cylinders could be selectively operated. Thus, for example, six of eight cylinders in an engine could be provided with fuel and air while two cylinders have the intake valves remaining shut or slightly open to prevent vacuum conditions, with a slight exhaust opening to ensure the shut-off cylinders are cleared of any gases and to guard against vacuum conditions. Thus, it is preferable that one valve adjustment mechanism be provided for the intake valve or valves7on a particular cylinder, and that a separate mechanism be provided for the exhaust valve(s) on that particular cylinder, with each adjustment mechanism being separately controlled to achieve a desired control of one or more engine parameters, including such engine parameters as fuel consumption, power, or emissions.

Referring toFIG. 11, an illustrative graph of the valve operation resulting from a profiled surface21is shown. The valve lift is shown on the vertical axis and time is on the horizontal axis. Because the rollers18travel the profiled surface21for each cycle of the pushrod8, the curve is symmetric. By altering the profile21and the length and shape of the profile portions21a,21b,21c, the shape of the curve shown inFIG. 11can be altered and the duration of the various lift, ramp and closed portions can be changed.

Using the same profile21but altering the beginning and ending portions by positioning roller guide3using cam1a, the general shape of the motion curve remains the same but it is shifted on the vertical, motion axis. This is shown inFIG. 12, which shows the valve motion sequence for maximum valve lift17bas described inFIG. 3, and also shows the valve motion for a medium lift17cas described inFIG. 4. The same profiled surface21is used for both valve motions so the curves are symmetric, but vertically shifted on the graph.

Referring toFIG. 13, the longer the valves remain open or closed, the longer the overlap in operation of the valves on the intake and exhaust. The valve overlap can affect emissions in complex ways since less overlap allows a longer power stroke, more complete combustion and less hydrocarbons but may increase nitrogen oxides, while more overlap allows a shorter power stroke, but less complete combustion and possibly fewer nitrogen oxides. By varying the valve timing, the power of the engine can be varied, as can emissions. The valve adjustment can thus be used to vary engine power and performance in conjunction with the fuel provided to the engine.

The variable valve control mechanism described herein can be adapted to any OHV engine configuration. The mechanism may be applied to just the intake valves, just the exhaust valves, or it may be applied to both intake and exhaust valves. The mechanism can be used to vary valve lift, duration of valve opening, and overlap of intake and exhaust valve open periods. The mechanism provides infinite adjustment of valve lift and valve open duration, within the range of its design parameters.

Further variation is provided by using separate camshafts for the intake and exhaust to allow more variation in the valve overlap characteristics. There are several known methods for varying camshaft phasing that may be employed, one of which is described in U.S. Pat. No. 6,883,480, the complete contents of which are incorporated herein by reference.

The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein, including various ways of arranging the profiled surfaces described herein to achieve various sequences of valve operation. Further, while three rollers18,19are used, it is believed possible to use only two rollers, or to use more than three rollers. While the rollers18,19are preferably on the same or parallel axes it is believed possible to offset the rotational axes of the roller(s)18and19and/or to incline the rotation axes relative to each other. While the rollers18,19are of different diameter, by correct positioning approximately the same sized rollers could be used, or by putting the engaging surface20on a protruding rib the middle roller19could be smaller diameter than the outer rollers. Moreover, the engaging surface20on rocker arm could be inclined and straight, or it could be curved or otherwise profiled to further adjust the movement of the valve7. Additionally, the outer rollers18could rotate about profiled surfaces21that are inclined relative to each other rather than being parallel as illustrated, in order to further center the roller guide3. But the complexity of maintaining contact with such inclined surfaces is undesirable. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.