FIELD OF THE INVENTION
The present invention relates to a valve actuator assembly for controlling axial motion of a valve.
BACKGROUND
Typically valves in an internal combustion engine are opened and closed by the action of a camshaft lobe upon some type of valve lifter or rocker arm assembly. FIG. 1 shows a typical type of prior art valve actuator with a cam lobe 1 acting directly upon a bucket lifter 2 which then transmits this motion to the valve 3. Another type of prior art valve actuator is shown in FIG. 2, where the cam lobe 1 acts upon a roller finger follower 2A which pivots on a hydraulic lash adjuster 4 to open and close the valve 3. It is often desirable to vary the timing of when the valve opens and the duration it remains open. These typical valve actuators make it difficult to control the timing and duration of the opening of the valve.
SUMMARY
In one embodiment, a valve actuator assembly includes an axially movable valve in an internal combustion engine and a ramp roller thrust drive. The ramp roller thrust drive includes at least first and second opposed thrust plates, each plate including one or more ramps. At least one roller is positioned between corresponding opposed plate ramps, and a rotation of one of the thrust plates relative to the other thrust plate causes the plates to move axially relative to one another such that axial motion is imparted to the valve. A plate actuating mechanism is configured to rotate one of the plates relative to the other plate.
A method for actuating an axially movable valve includes providing a ramp roller thrust drive including at least first and second opposed thrust plates, each plate including one or more ramps, and further including at least one roller positioned between corresponding opposed plate ramps. The method also includes rotating one of the thrust plates relative to the other thrust plate to impart axial motion to the valve.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are side elevation schematic views of prior art valve actuators;
FIGS. 3 and 3A are perspective, exploded views of roller ramp thrust drives of the present invention;
FIGS. 4 and 5 are side elevation views of roller ramp thrust drives of the present invention;
FIG. 6 is a side elevation view of a first embodiment of a valve ramp actuator assembly;
FIG. 6A is a side elevation view of a second embodiment of a valve ramp actuator assembly;
FIG. 7 is a side elevation view of a valve ramp actuator assembly along with an illustrative plate actuating mechanism;
FIG. 8 is a side elevation view of a valve ramp actuator assembly along with an alternative plate actuating mechanism;
FIGS. 9A-9C are a top plan view, a side cross sectional view and a graph, respectively, illustrating the valve lift in conjunction with a moderate oscillation angle;
FIGS. 10A-10C are a top plan view, a side cross sectional view and a graph, respectively, illustrating the valve lift in conjunction with a maximum oscillation angle;
FIGS. 11A-11C are a top plan view, a side cross sectional view and a graph, respectively, illustrating the valve lift in conjunction with a minimum oscillation angle;
FIG. 12 is a side elevation view of a third embodiment of a valve ramp actuator assembly;
FIG. 13 is a side elevation view of a fourth embodiment of a valve ramp actuator assembly; and
FIG. 14 is a side elevation view of a fifth embodiment of a valve ramp actuator assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Certain terminology, for example, “top”, “bottom”, “right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and “rearward”, is used in the following description for relative descriptive clarity only and is not intended to be limiting.
Referring to FIG. 3, a valve ramp actuator such as roller ramp thrust drive 45 is operable to convert rotary input motion into axial motion that is transmitted to a valve 3 (shown in FIGS. 6-8 and 12-14) in an internal combustion engine. Ramp thrust drive 45 includes a first plate 5 and a second plate 6, each of which have one or more specially shaped, radially oriented recesses or ramps 7 which act as cam surfaces. Rollers 8, which can be cylindrical or tapered in shape, are placed in corresponding recesses and may be held in correct relative positions by a separator 9. A central pin 10 is used to keep the plates 5, 6 and separator 9 in the proper relationship to one another.
In order to prevent the rollers 8 from moving out of position due to slipping on the ramps 7, FIG. 3A shows the use of a plurality of rollers 8A with gear teeth 49 formed on the ends, which mesh with gear teeth 49 formed in the ramps 7A, for example on the outer periphery of plates 5A, 6A. The gear teeth could also be formed elsewhere on the rollers and plates.
FIG. 4 shows the operation of the roller ramp thrust drive 45 of FIG. 3. A plate actuating mechanism 53 (such as that shown in FIGS. 7 and 8) provides relative rotative motion between the plates 5, 6. For example, as depicted in FIG. 4 the plate 6 is stationary while plate 5 is rotated in the direction of the arrow. This action causes the rollers 8 to ride up the ramps 7 to cause an increase in the height H of the roller ramp thrust drive 45. The ramps 7 can be shaped in such a way that a desired change in height is achieved for a given movement of a plate (or relative movement between plates). In general, the distance D the plate 5 is moved is greater than the increase in height ΔH of thrust drive 45. The result is a multiplication of the input force which is useful to overcome the forces holding a valve closed.
In cases where a greater increase in height for a given input movement is necessary, it is possible to stack ramp thrust drives in series to multiply the effect. For example, FIG. 5 shows such a double ramp thrust drive 46 wherein an upper plate 14 and a lower plate 15 are stationary and a center plate 16 rotates relative to the upper and lower plates 14, 15. One benefit of the double ramp thrust drive 46 is that for a given amount of input movement and needed valve lift, the ramp angles can be made shallower to reduce contact stresses and improve the mechanical efficiency of the unit.
FIG. 6 illustrates an embodiment of a valve ramp actuator assembly 48 including a double ramp thrust drive 46 that is used to actuate a valve 3 in an internal combustion engine. Valve 3 is axially movable between a closed position and an open position and can be an intake valve for allowing air to be drawn into a combustion chamber or an exhaust valve for allowing products of combustion to be removed from the combustion chamber. Valve 3 can be normally biased in a closed position by spring 51 having a spring retainer 37. Guide 40 provides proper guidance for the axially movable valve 3.
FIG. 6 illustrates details of the spring retainer 37 and valve keeper 39 which is composed of two halves. In FIG. 6, the spring retainer 37 has been pushed downward, compressing the valve spring 51. Although not shown in the exploded view of FIG. 6, the upper end of valve stem 38 is meant to be positioned within a bore 42 in the plate 15. A tapered inner diameter of retainer 37 engages the tapered outer diameters of the valve keeper 39, forcing them inward to engage a groove 47 on the valve stem 38. When this occurs, the valve 3, retainer 37 and valve keeper 39 will be locked together and move as one unit if a force is applied to the upper end of the valve stem 38 via the movement of plate 15. Note that for simplification, central pin 10 of FIG. 5 is not shown in FIG. 6.
Thus, the lower plate 15 acts directly on the valve 3 while the upper plate 14 reacts against a ground plane 17 connected to the primary structure of the engine. In the example shown, this ground plane 17 includes a hydraulic lash adjuster 18 which also helps insure proper seating of the valve 3 in the closed position. Input motion is applied to the center plate 16. In this example, rotation of the upper plate 14 is prevented by a pin 19 which is fixed to the ground plane 17. A slotted clip 20 is attached to the upper plate 14 and engages a pin 21 on the lower plate 15 to also prevent rotation of the lower plate 15. Pin 21 can move axially as necessary in the slot of clip 20. When plate 16 is rotated relative to the other plates 14, 15, the plates 15, 16 move axially relative to plate 14 and axial motion is imparted to the valve 3, thereby opening the valve 3.
In some cases, the timing of the valve opening can also be varied. As explained below, by altering the position of the clip 20 with respect to the plate 16 (and thus the ramps 7), the valve opening can occur at different times relative to a constant oscillating input motion.
FIG. 6A illustrates an embodiment of a valve ramp actuator assembly 48A including a double ramp thrust drive 46A that is used to actuate valve 3 in an internal combustion engine. In this embodiment, double roller ramp thrust drive 46A includes anti-slipping gear teeth 49 on rollers 8A and plates 14A, 15A, 16A. FIG. 6A also illustrates valve 3 in a closed position.
Input motion, preferably oscillating input motion, can be provided to a plate in a variety of ways. As illustrated in FIG. 7, input motion is provided to center plate 16 of double roller ramp thrust drive 46 by a plate actuating mechanism 53. In this case, plate actuating mechanism includes an auxiliary rotating crankshaft 22 and connecting rod 23 which oscillates the center plate 16 through an oscillation angle 25 of the double roller ramp thrust drive 46. Input motion can also be provided by a variety of other mechanical, hydraulic, electromechanical, electromagnetic, or similar devices.
For example, FIG. 8 shows the same ramp thrust drive 46 as in FIG. 7, wherein plate actuating mechanism 53 provides oscillating input motion and includes a linear electromechanical actuator 27. Actuators of this type can accurately control position, but are limited in their ability to control velocity. The double roller ramp thrust drive 46 provides the proper valve lift, velocity and acceleration for a given input displacement. The mechanical advantage provided by the double roller ramp thrust drive 46 means that a relatively low-power plate actuating mechanism 53 can be used to provide input motion to achieve a desired amount of valve lift.
To improve the efficiency and performance of an internal combustion engine, it is often desirable to alter the valve opening cycle for specific operating conditions. There are various ways to accomplish this. For example, with reference to FIG. 7, altering the throw T of the crankshaft 22 will increase or decrease the oscillation angle 25 of the center plate 16 about a midpoint. This alters the amount of cam surface of the ramps 7 available to provide valve lift. In this same example, altering the length L of the connecting rod 23 will change the midpoint of the input oscillation towards one end of the cam surface or the other. An advantage of the thrust drive 46 is that the amount of valve lift for a given position of plate 16 is a direct function of the height of the cam surface or ramp 7 and an indirect function of the plate position. Having these two functions related, but separate, offers significant advantages in controlling valve motion.
FIGS. 9A-9C, 10A-10C, and 11A-11C show how alterations in the oscillation angle and/or center point of rotation can use different parts of the cam surface for different operating conditions. For example, FIGS. 9A-9C demonstrate a moderate oscillation angle 28 which results in roller movement over range 29 of the cam surface. The resulting valve lift 30 is sufficient to produce moderate engine power for normal operation. In FIGS. 10A-10C, the oscillation angle 31 has been increased, resulting in roller movement over range 32 of the cam surface. The resulting valve lift 33 is both higher and broader, which can be used to allow an engine to develop maximum power. The oscillation angle 34 in FIGS. 11A-11C has been reduced and its midpoint shifted toward the flatter area of the cam surface. This results in roller movement over range 35 of the cam surface and minimal valve lift 36, allowing an engine to operate with great efficiency under low load conditions such as idling.
Another manner in which the valve motion can be modified is by changing the hydraulic characteristics of the lash adjuster 18. Since the ramp thrust drive reacts against force of the lash adjuster 18 to open the valve 3, a reduction in stiffness of this member will allow some of the increase in ramp thrust drive height to be absorbed as “lost motion” by the lash adjuster 18. This can be accomplished by venting a portion of the fluid from a high pressure chamber of the lash adjuster 18 to a low pressure side for operating conditions that do not require full mechanical valve motion. An alternative to using the lash adjuster 18 to achieve modified valve motion would be to incorporate a position indicator and a feedback loop into the control system for the thrust drive 46. Therefore, the hydraulic lash adjuster 18 need not be used in the illustrated valve actuator assemblies.
Another embodiment of a valve actuator assembly 48B is shown in FIG. 12, which shows a cross section of a double roller ramp thrust drive 46B not including the rollers 8 and ramps 7. In this embodiment, the lower plate 15B of the drive 46B is modified to include a valve spring seat 50 so that lower plate 15B can function as the upper seat for valve spring 51B. This eliminates separate valve spring retainer 37, such as is shown in FIG. 6, and significantly reduces the reciprocating mass that must be accelerated as a function of opening the valve. This improves the performance and efficiency of the valve actuator assembly 48B.
Further, the valve 3B is modified by lengthening valve stem 38B so that it extends into the ramp thrust drive 46B, thereby eliminating the separate central pin 10 that is shown in FIGS. 3, 3A, and 5. Two snap rings 44 engage grooves in the valve stem 38B above and below plate 15B. Elements 3B, 15B, and 44 then move as one unit against the valve spring 51B, with the motion being provided by the axial movement of the ramp thrust drive 46B. A central bore 54 in the middle plate 16B allows for a slip fit on the valve stem 38B, and relative movement between the middle plate 16B and valve stem 38B equal to half the valve lift. A central recess 55 in the upper plate 14B provides a slip fit with the stem 38B like the middle plate, however in this case the relative motion between the two is equal to the full extent of the valve lift. For this reason, it may be necessary to increase the thickness of the upper plate 14B to have sufficient piloting length for the valve stem 38B. Because the upper plate 14B is stationary, this additional material is not detrimental to the performance of the valve assembly.
A distinct advantage of the arrangement illustrated in FIG. 12 concerns the guidance of the valve 3B. In current internal combustion engines this function is accomplished entirely by the valve guide 40. In this embodiment, the valve stem 38B is also guided in the upper plate 14B which is biased, in this example, by the lash adjuster 18. The fact that the valve is now guided in two places, and that these are widely separated, means that the alignment of the valve 3B relative to its seat is significantly improved. This also means that the valve guide 40 can be made shorter or otherwise modified to reduce its size or improve the performance of the engine.
In addition to directly coupling the ramp thrust drive 46 and the valve 3, various coupling mechanisms can be used instead. For example, FIG. 13 shows how the ramp thrust drive 46 can be used to replace the conventional cam lobe in the arrangement shown in FIG. 2. The axial movement of the ramp thrust drive 46 causes a roller finger follower 52, which pivots on hydraulic lash adjuster 18A, to open and close the valve 3. In this case, all of the advantages of the ramp thrust drive 46 still apply, however in this case the roller finger follower 52 can be used to multiply the amount of lift created by the ramp thrust drive 46.
FIG. 14 shows another coupling mechanism that can multiply the lift generated by the ramp thrust drive 46. In this case a center pivot rocker arm 43 is used to perform this function. A lash adjuster 18B can be used to compensate for excess clearance in the system.
Patent Application
20060196457
