A valve lifter is activated selectively by one of a plurality of cams, either via displaceable rollers or via tappets having rotatable grooves on top, to provide discrete or stepwise multimode operation and deactivation.
The pure mechanical control is adequate.
The closest prior art is the PCT/GR04/000043 patent application.
In the continuously variable valve lift systems a unique cam lobe, in cooperation with a control member, controls the motion of a valve depending on the position of the control member. Although the number of the valve lift curves is infinite, it is not necessarily the desirable.
In the discrete or stepwise multimode systems, on the other hand, the complexity of the valve lifters, the hydraulic control, the impact transition from mode to mode and the inertia loads of the idle parts are disadvantages which are solved with this invention.
As shown in FIGS. 1 to 5, a typical roller finger follower with hydraulic lash adjuster is actuated by cam lobes of different profiles, mounted on the same camshaft. The cam lobes are not in direct contact to the roller of the valve lifter. A first free roller is trapped inside a properly machined groove on a first engaging member, while a second free roller is trapped inside a second engaging member.
In FIG. 2 the two engaging members are in the deactivation positions, i.e. as the camshaft rotates, the two free rollers are idle, not loading the system with their inertia and friction. The valve is deactivated.
In FIG. 3, the left engaging member with its free roller has come in its activation position and the soft cam lobe profile activates the valve.
In FIG. 4, both engaging members with their free rollers have come in their actuation positions, but only the wild cam lobe can activate the valve.
In FIG. 5, the finger follower is shown in section view and the wild cam engaging member is at a secondary activation position, compared to its activation position shown in FIG. 4, for providing a different valve lift profile. Only the right engaging member is in activation position. The left engaging member is in deactivation position, idle. Here the mild cam lobe can provide duration and timing not limited by the respective values of the wild cam lobe. When both engaging members are in their activation position, as shown in FIG. 4, the wild cam lobe must provide higher lift and sooner opening and later closing of the valve. The engaging member can be mounted on the engine pivotally or slidably or with any other known way in order to move from its activation position(s) to its deactivation position.
The use of a free roller seems the simplest, strongest and lightest solution. Nevertheless, as shown in FIG. 6, the right roller is held on the engaging member by a pivotally mounted rocker arm. The control here is hydraulic, i.e. oil is pressed into the back side of a small cylinder displacing the rocker arm and the roller till the activation position. Here the lash adjustment can be accomplished by the oil of the cylinder without the need of conventional lash adjuster.
It must be noted that the transition from deactivation to mild mode and then to wild mode is progressive and may even last for a few cycles of the engine in comparison to the impact/instant transition.
In FIG. 7 it is shown another realization, even simpler, but without deactivation capability. Here the soft cam lobes act directly on the roller of the roller finger follower while the wild cam lobe is selectively engaged depending on the position of the engaging member.
In FIG. 8 it is shown the case where the valve lifter is a bucket lifter.
It is obvious that the system can use more that the two or the three steps described. Additional modes can be added easily because when a cam is deactivated, the relevant engaging member and the roller stay aside idle without adding their inertia.
The valve lifter may activate more than one valves.
The valve lifter can be a rocker arm pivotally mounted on a pivot shaft.
The control of the system is easy because there is no need for complicated oil passages inside the valve lifters, no need for locking pins, no need for extreme accuracy etc. Here the control is applied only on stationary like components.
In another embodiment, a valve operating system includes a tappet cam follower combined with high lift and low lift or no lift cams.
The tappet comprises grooves at its surface facing the cams.
At one mode of operation the grooves are at a direction that provides space to the high lift cam(s) to rotate without displacing the tappet, so the tappet is actuated by the low lift or the no lift cam(s).
At a second mode of operation the grooves are at a direction that cancels the disengagement of the high lift cam(s), so the tappet is actuated by the high lift cam(s).
The proper geometry of the system, including the tappet, the grooves and the cams, provides smooth/continuous control of the valve at all modes. The application is similar to the overhead camshaft engines and to the side camshaft engines with pushrods.
The profiles of the associated cams can be different from valve to valve, to provide additional modes of engine operation, like valve deactivation, cylinder deactivation etc.
The grooves can be machined directly on the top surface of the tappet or on its lash adjuster.
Hydraulic or mechanical lash adjusters can be incorporated as in conventional tappets.
The control of the system can be mechanical, hydraulic etc. The objective of the control is to rotate and keep at the right direction the grooves. Compared to the prior art two mode tappet, the present is simpler, because it is nothing more than a conventional tappet with some slots on it, it is lighter, permitting higher revs and lower friction, it does not need extreme construction accuracy or special materials, it is easily controlled even mechanically, it is space effective permitting direct application on existing engines as retrofit, etc.
In FIG. 9 it is shown the camshaft having three cams, a central low lift cam and two high lift cams mounted at the two sides of the central cam. In FIG. 10 the camshaft has been removed, in FIG. 11 the tappet guide, i.e. the slider of the tappet, has been removed and the tappet has been sliced.
In FIG. 12 when the tappet is rotated for about 180 degrees, as shown at right side, the high lift cam is disengaged from the tappet and the valve is displaced under the camming action of the low lift cam, which in the case shown in FIG. 12, is a no lift cam providing deactivation. In the general case the tappet shown in FIG. 12 provides two different valve lift profiles.
In FIGS. 13 and 14 the tappet is at low lift mode.
In FIGS. 15 and 16 the tappet is at high lift mode. Compared to FIGS. 13 and 14 the only difference is that the tappet is rotated for about 50 degrees to cancel the disengagement of the high lift cams. Provided that the camshaft at FIG. 14 and FIG. 16 is at the same angular position, the difference of the valve lift is obvious.
In case the low lift cam lobe is a no lift cam, at low lift mode the valve is deactivated.
FIG. 17 shows the valve lift for three different camshaft angles, with the tappet at low lift mode.
FIG. 18 shows the valve lift for the same three cam shaft angle, with the tappet at high lift mode.
In FIG. 19 it is shown the camshaft and the tappet. The parallel dash lines define the slide ways, i.e. the paths of contact, of the wild cam lobes along the tappet. The hatched areas is where the relevant high lift cam completely loses contact with the tappet. The geometry of the tappet, cams and grooves was selected to provide permanent contact of at least one of the two high lift cams during high lift mode. It is obvious that more cams could be used, for instance three high lift cams with two low lift cams between them. It is also evident that the exact angle of the tappet at high lift mode is not critical.
The transition from high lift mode to low lift mode can be done no matter what the camshaft angle is, but the transition from the low lift mode to the high lift mode takes place with the valve closed, otherwise the high lift cams that move inside the grooves do not allow the tappet to rotate.
In FIG. 20 it is shown a way to control hydraulically the rotation angle of the tappet. The tappet has a slot parallel to its axis. The tappet guide or slider has a proper groove. Inside the groove is displaced a “piston” that holds the tappet angularly, at its slot. The “piston” is displaced along the tappet guide groove via pressurized oil, shifting angularly the tappet.
In FIG. 21 it is shown a way for mechanical control. Here the tappet has slots at its lower end, while a guide member has reverse slots permitting the free reciprocation of the tappet and providing, when necessary, the required torque to rotate the tappet to the other mode or to keep the tappet at its present mode. To apply the mechanical control in a row of tappets, what is necessary is a rod or shaft connected elastically to each one of the tappets of the row. The elastic connection, via springs, etc, is necessary due to the fact that the transition from the low lift mode to the high lift mode can be done only when the valve is closed. Another simple way to rotate the guide member is by pressurized oil, pistons, cylinders etc.
In FIG. 22 it is shown the case of a three mode tappet. The camshaft has a short lift central cam located between two high lift cams, while two more medium lift cams are located outside the two high lift cams. The parallel dash lines mark the slide ways, or paths of contact, of the cams along the tappet. At bottom left it is shown the tappet at short lift mode. In this the grooves on the top of the tappet disengage the high lift and the medium lift cams. At bottom centre it is shown the medium lift mode. In this case another set of grooves disengage the high lift cams. At bottom right it is shown the tappet at high lift mode. In a similar way additional modes can be added. In case that the short lift cam is replaced by a no lift cam, the short lift mode becomes a deactivation mode.
It is obvious that cams of the same maximum valve lift, but providing different valve lift profiles, can be used.
Patent Application
20060196459
