The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate two preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
The benefits and advantages of a VVA system in accordance with the present invention may be better appreciated by first considering a relevant prior art WA system for varying valve opening timing, valve closing timing, and valve lift.
Referring to
As noted above, two significant shortcomings of the just-described prior art invention are a) an inability to keep a constant valve opening timing while varying the valve closing timing, and b) an inability to vary the duration of a fully open valve lift. In addition, this prior art does not permit total valve deactivation-via lost motion as may be desired.
The present invention comprises a new VVA mechanism that provides increased functionality and a simpler, more cost-effective actuator system.
Functionality of this mechanism makes it suitable to either gasoline or Diesel applications. Gasoline engines require variation in intake valve lift and duration to control the amount of air entering a cylinder during an intake event; whereas, Diesel engines utilizing HCCI require variation in intake valve opening duration with fixed (full) lift to vary the effective compression ratio of the engine during an intake event. The intake valve opening position remains fixed (no inherent phasing) for all lift/duration and duration only variations; however, peak lift advances when the mechanism is used to vary both lift and duration (as for gasoline engine operation). This is an engine requirement for Diesel operation to avoid piston/valve interference.
Gasoline engine control strategy is simplified in that the intake cam phaser control algorithm does not need to compensate for intake valve opening variation with changes in lift.
Phasing in the present invention may take advantage of inexpensive prior art employing an electric or hydraulic cam phaser, rather than a DC motor/worm and worm gear arrangement.
It will be seen that in any arrangement employing a single cam for both opening and closing a valve, the timing of the opening cannot be separated from the timing of the closing because the opening cam flank and the closing cam flank are in fixed relationship on the same cam lobe. The only way to separate the two functions and provide independent control is to provide two cams for each valve (or valve pair): an opening cam and a closing cam. Thus, as described below, a VVA system in accordance with the present invention includes dual dwell camshafts for the opening and the closing. This means that there are two constant radius sections per camshaft: a base radius and a peak nose radius. The duration of the respective radii and the angular relationship between the two camshafts has a significant impact on the performance and function of the device and on an engine thus equipped.
Referring to
A conventional combustion valve 202 is seated in a valve seat 204 by a valve return spring 206. Valve 202 is actuated by a conventional roller finger follower 208 pivotably mounted conventionally on a hydraulic lash adjuster (not shown). These elements define a prior art valvetrain 209.
A valve opening cam 210 and a valve closing cam 212 are spaced apart from each other and from roller finger follower 208. Each cam 210,212 comprises a base circle portion 211, 213 respectively, having a minimum radius, and a working portion 215,217, respectively having a larger radius which may be variable. Each cam 210,212 further comprises respective ramp portions 219,221 between their respective base circle and working portions.
A novel oscillating rocker arm 214 comprises a first or intermediate roller 226 defining a first working element that engages valve closing cam 212; a second or outer roller 228 defining a second working element that engages valve opening cam 210; and a rocker cam surface 220 defining a third working element having a base radius portion 222 and a working cam portion 224 that engages the roller 216 of roller finger follower 208. Oscillating rocker arm 214 thus floats among valve opening cam 210, valve closing cam 212, and roller finger follower 208, and is urged into continuous contact therewith by a lost motion spring 232. A guide block 230 includes a surface for guiding the motion of oscillating rocker arm 214 along a predetermined path.
The oscillating rocker arm 214 is similar in function to those found in some other prior art continuously variable valve train mechanisms. A novel feature of the present oscillating rocker arm 214 is the use of a constant radius base radius portion 222 extending into a working curve of working cam portion 224. This type of curve is determined typically by kinematics from the desired lift profile. The present system, however, does not require such a curve: a simpler more linear contour will also work but provides less satisfactory kinematics/dynamics for the system. The constant radius base radius portion is important in that it is the feature providing lost motion for the device. Its duration is determined by the amount of angular stroke of the oscillating rocker cam (see discussion below respecting
Many internal combustion engines are provided with dual intake valves and dual exhaust valves. Thus, a mechanism in accordance with the invention is also adaptable for use with such dually-provided valve sets, as is now described.
Referring to
Referring to
The benefits of a continuously variable valve actuation system in accordance with the invention are apparent in
Referring now to
In Stages 12a and 12b, closing cam 212 is on its working portion 217. This is required for a lift event to occur because the closing cam governs the position in space of pivot axis 239 about which opening roller 228 and rocker cam surface 220 must pivot.
In Stage 12a, opening cam 210 is on its base circle portion 211 and rocker cam surface 220 is on its base circle portion 222, so the valve remains closed.
In Stage 12b, the cams have each rotated approximately 60° from Stage 12a, such that opening cam 210 is now on its working portion 215. The position of pivot axis 239 is unchanged because closing cam 212 is still on its working portion 217. Oscillating rocker arm 214 is thus pivoted about axis 239, causing rocker cam surface 220 to be moved along roller 216 on working cam portion 224 of rocker cam surface 220, thus causing the valve to be opened.
In Stage 12c, the cams have each rotated approximately 60° from Stage 12b, such that closing cam 212 is now entering its base circle portion 213. Although opening cam lobe 210 is still on its working portion 215, the rotation of closing cam 212 to its base circle portion 213 has caused pivot axis 239 to be moved such that the opening cam 210 can no longer open the valve. Variable lift curves such as those shown in
Stages 12a and 12c demonstrate a fundamental property of the system which is both unique and practical. In both stages, the oscillating rocker's cam profile is contacting the roller finger follower roller 216 at the very end of base radius (lost motion) portion 222, or alternatively just before the working portion 224 of the rocker cam surface 220. In Stage 12a, closing cam 212 is contacting on its working portion 217 and opening cam 210 is contacting on its base circle portion 211. For the mechanism to function properly, the same must be true in Stage 12c wherein the opening cam 210 is on its working portion 215 and the closing cam 212 is on its base circle portion 213. This is essentially what provides the lost motion for the mechanism and allows both cams to stay in contact with the oscillating rocker arm at all times.
In Stage 12d, the cams 210,212 continue to rotate, opening cam 210 moving to its base circle portion 211 in lost motion. The cams will continue to rotate through another approximately 180°, with the valve remaining closed, to return to Stage 12a and the beginning of another valve opening event.
By judicious placement of the lengths and phases of the working portions in opening and closing cams 210,212, and by providing a phasing device 278 having a larger range of authority, for example, 60 cam degrees or greater, it is possible by phasing the closing cam to provide complete valve deactivation as may be useful in, for example, engine braking of a vehicle.
Referring now to
A-valve opening cam 510 and a valve closing cam 512 disposed respectively on camshafts 562, 564 are spaced apart from each other and from roller finger follower 208 (prior art valvetrain 209 is unchanged). Each cam 510, 512 comprises a base circle portion 511, 513 respectively, having a minimum radius, and a working portion 515, 517, respectively having a larger radius which may be variable.
An oscillating rocker arm 514 engages the roller 216 of roller finger follower 208 and includes a rocker cam surface 520 having a base radius portion 522 and a working cam portion 524. An intermediate link 540 comprises a first roller 526 disposed on a first arm 527 engaging valve opening cam 510, and-a second roller 528 disposed on a second arm 529 engaging valve closing cam 512. Intermediate link 540 pivots on an intermediate pivot shaft 590, and both oscillating rocker arm 514 and intermediate pivot shaft 590 rotate about a fixed pivot shaft 592 having a pivot axis 539, in contact with valve opening cam 510, valve closing cam 512, and roller finger follower 208, and is urged into continuous contact therewith by a lost motion spring 532.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
This present invention relates to provisional application Ser. No. 60/847,784, filed on Sep. 28, 2006.
The present invention was supported in part by a U.S. Government Contract, No. FC26-05NT42483. The United States Government may have rights in the present invention.
Number | Date | Country | |
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60847784 | Sep 2006 | US |