Variable valve timing actuator

Details Variable valve timing actuator Variable valve timing actuator

2000-04-13

2001-11-13

Lee, Kevin (Department: 3754)

Valves and valve actuation

Fluid actuated or retarded

Pilot or servo type motor

C251S032000, C123S090120

Reexamination Certificate

active

06315265

ABSTRACT:

FIELD OF THE INVENTION
This disclosure concerns an invention relating generally to valve actuators, and more specifically to valve actuators which are actuated hydraulically or electrically without use of cams.
BACKGROUND OF THE INVENTION
Usually valves in automobiles (cylinder intake and exhaust valves) are operated by cams driven from the engine's crankshaft. The cams are designed to provide valve behavior characteristics that result in desired engine economy and performance. There are three primary characteristics that define the behavior of a valve. First, valve timing refers to the engine piston or crankshaft position at which the valve begins to open. Second, duration refers to the amount of time a valve is open during each engine cycle (with dwell referring to the time that the valve is closed); these are generally determined by the cam profile. Finally, lift is the distance that the valve opens (typically around 0.4 inches/1 centimeter). Owing to the relationship between the valves, the cams, and the crankshaft, valve duration/dwell (when measured in seconds) will vary directly with engine speed, but timing (when measured as a function of crankshaft angle) and lift will tend to stay constant regardless of engine speed.
Unfortunately, valve timing, lift, and dwell/duration for optimal engine performance changes between low and high engine speeds and engine loading. As a result, varying the relationship between the crankshaft and camshaft may allow gains in performance at one speed and load, but these will generally lead to decreased economy at another speed and load, and vice versa. For example, a so-called “hot” cam would provide poor fuel economy and excessive emissions for idling and everyday driving, but the car would exhibit sporty high-power performance at higher speeds.
Auto manufacturers have therefore expressed great interest in developing means for adapting valve behavior during vehicle operation so as to allow changes in a vehicle's economy and performance. As an example, systems have been introduced wherein cam rotation is changed depending on the engine speed. Unfortunately, the systems achieve valve timing changes without a commensurate change in dwell/duration; for example, when the valve opens early, it also closes early, even though it is generally desirable to also keep the valve open for a longer time.
Other auto manufacturers have focused on the development of camless designs so as to decouple valve operation from crank operation—in other words, to allow the engine valves to open and close at different times with respect to the crankshaft position, a condition known as Variable Valve Timing (or VVT). Unfortunately, prior VVT schemes have also been largely unsuccessful. For example, electrical actuators (e.g., solenoids which actuate the valves) have thus far met with limited success because the components to be actuated have substantial inertia, and thus substantial energy demands.
SUMMARY OF THE INVENTION
The invention involves a variable valve timing actuator that allows the opening and closing of engine valves to be variably and individually controlled without using a camshaft. The ability to vary the lift, duration/dwell, and timing of each intake and exhaust valve provides for more efficient internal combustion engines, with attendant improvement in fuel economy and the opportunity to reduce harmful emissions. The invention utilizes energy regeneration so that energy delivered to a valve while accelerating it (less any friction or other losses) is recovered while it is decelerating. The losses are made up by adding energy to the actuator while the valve is stationary (or nearly so) in an open or closed state. The valves are maintained stationary by a latch (e.g., a one-way clutch) which is disengaged when the valve is to begin opening or closing. The one-way nature of this latch allows it to automatically lock the valve in its open (or closed) position without the need for a control input. Furthermore, no energy is required to hold the valves in their open (or closed) position, and only a small amount of energy is required to disengage the latch.
Regeneration is preferably provided by potential energy storage devices such as springs. The most preferred version of the invention utilizes an opposing spring design wherein springs impose an opening force on the valve, and once the valve is open, the opposing springs impose a closing force on the valve (as illustrated, e.g., in the accompanying FIGS.
1
(
a
) and
1
(
c
) by the springs
143
/
154
versus the valve
159
). Since losses from valve exhaust forces, spring hysteresis, mechanical friction, etc. will not allow the opposing springs to open and close the valves in this manner unless make-up energy is added, make-up potential energy is input by (1) moving the spring seats in relation to the valve, thereby charging the springs against the valve (as illustrated by the exemplary variable valve timing actuator
100
of FIGS.
1
(
a
)-
1
(
e
), discussed below), and/or by (2) moving the valve with respect to the spring seats to charge the springs (as illustrated by the exemplary variable valve timing actuator
300
of FIGS.
3
(
a
)-
3
(
d
), discussed below). These acts are done after the potential energy within the springs has already been expended. To hold the valves into their open and closed positions when desired, latches (such as the sprag sets A and B shown throughout the various Figures) are used to releasably fix the valves in place.
The invention may be better understood if characteristics of preferred versions of the invention are briefly described. Turning, for example, to the versions of the invention exemplified by FIGS.
2
(
a
)-
2
(
e
) (and also
FIG. 5
, though the following discussion will primarily reference FIG.
2
), the valve actuator is seen to include a valve housing (
201
); a valve (
259
) having a valve head and a valve stem, with the valve being movable within the valve housing (as can be best visualized by comparing the FIGS.
2
(
a
)-
2
(
e
)); one or more springs (
243
/
254
), each spring being situated between the valve and a spring charger assembly (
253
) which is movable with respect to the valve, wherein the spring(s) may urge the valve along the valve motion axis; and a latching assembly (
202
) which is also movable with respect to the valve, and which includes one or more latches (
208
), each latch being actuatable to selectively restrain the valve from motion in one direction along the valve motion axis (while allowing motion in the opposite direction along the valve motion axis). Preferably, the spring charger assembly is actuated to move with respect to the valve housing by fluid pressure in an adjacent spring charger assembly chamber (
241
); similarly, the latching assembly is actuated to move with respect to the valve by fluid pressure in an adjacent latching assembly chamber (
233
). The valve stem preferably has a valve switching cavity (
277
) defined therein so that motion of the valve stem selectively ports fluid to the spring charger assembly chamber, thereby altering the fluid pressure therein. In the embodiment of
FIG. 2
, this is done by defining a bridge cavity (
249
) within the spring charger assembly, the bridge cavity being in fluid communication with the spring charger assembly chamber, and also defining at least one spring charger assembly switching cavity (
244
/
251
) within the spring charger assembly, with each spring charger assembly switching cavity being in fluid communication with a pressurized fluid supply. When the valve moves, the valve switching cavity may connect the spring charger assembly switching cavity and the bridge cavity, thereby porting fluid from the spring charger assembly switching cavity to the spring charger assembly chamber and moving the spring charger assembly. Also in the embodiment of
FIG. 2
, the spring charger assembly chamber and the latching assembly chamber are in fluid communication via a bridging passage (
237
).
As a result of the foregoing arrangement, it can be seen from a compar

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