Patent Application
20110214633
This invention relates to a hydro-mechanical variable valve actuation (or VVA) system that controllably extends the valve duration.
The closest prior art is the multiair system of Fiat, U.S. Pat. No. 6,918,364, a lost motion hydro-mechanical VVA currently in mass production, wherein a cam opens the valve indirectly by means of a fluid interposed “in series” between the valve and the cam: the cam by a plunger displaces the fluid, and the fluid displaces the valve. A solenoid valve is opened the right moment allowing the fluid to escape and the valve to close, reducing either the duration or the duration and the lift. The inherent elasticity and play of the “hydraulic” system, the high loads it undergoes, the sensitivity to leakage, the need of additional means for the smooth landing of the valves, the need for additional restoring springs are some of the problems of the prior art.
In the present invention the valve opens up mechanically/conventionally to the maximum lift, under the action of a cam of a camshaft. The hydraulic part of the system controllably retards the closing of the valve, and takes part only during the valve-closing. The opening of the valve causes the displacement of a plunger slidably fitted into an oil-chamber. Oil enters into the oil-chamber through a one-way-valve or other type of valve. During the valve closing, the pressure of the oil into the oil-chamber increases. The trapped oil reacts to the force from the valve spring to the valve and to the plunger, disengaging the valve from the cam. The valve closes later, under the restoring action of the valve spring, dew to the damping action of the oil escaping out of the oil-chamber. A release-valve, for instance a solenoid on-off valve, opens at the right moment (i.e. at the right crank angle) to allow the quick escape of oil from the oil-chamber. With the release-valve open, the valve restores quickly under the action of the valve spring, pressing the oil out the oil-chamber. The conventional lubrication system is adequate to feed the oil chamber with oil.
For the smooth “landing” of the valve on the valve seat, the damping action of the oil escaping from the oil-chamber increases a little before the landing of the valve, as much as necessary; for instance by the progressive covering of the discharge port by the plunger. The shape of the discharge port can be properly designed to match with the desirable landing characteristics (acceleration, jerk etc) and to compensate for fabrication etc inaccuracies. I.e. the system has a simple and effective built-in ability to smooth out the landing of the valve.
The valve duration is equal or longer than the duration defined by the cam. With a cam having 220 degrees duration, the actual duration of the valve opening can be anything over 220 degrees, i.e. the system controllably extends the valve duration without effecting the valve lift.
With reference to
The system enables the engine to get rid of the conventional throttle valve.
The breathing of the engine depends on the timing of the release-valve, i.e. on the duration of the suction cycle. The suction cycle starts at the moment the intake valves of the cylinder open and ends at the moment the intake valves of the cylinder close, where the actual compression begins.
An early actuation of the release-valve, for instance 50 degrees after BDC, increases the quantity of air trapped into the cylinder. A late actuation of the release-valve, for instance 140 degrees after BDC, allows a part of the air originally suctioned into the cylinder to return back to the intake manifold, thereby reducing the pumping loss. The increased turbulence and swirl of the charge entering and leaving the cylinder enables faster, cleaner and more efficient combustion.
For example, the suction cycle can continue until 140 degrees after BDC enabling the engine to idle at 600 rpm. This is because most of the charge suctioned into the cylinder through the wide open intake valves is pushed out of the cylinder as the piston moves towards the TDC with the intake valves still open. The duration of the suction cycle is the key parameter for the control of the engine. With the suction cycle ending earlier, for instance at 90 degrees after BDC, a good part of the working medium is trapped into the cylinder and the engine operates at medium load. With the suction cycle ending even earlier, for instance at 30 degrees after BDC at 2000 rpm or at 70 degrees after BDC at 7000 rpm, the engine makes its peak torque at the specific revs.
The same system is applicable on the exhaust valves, too, if desirable. The cam opens the exhaust valve in the conventional way, while the oil-chamber with the release-valve control the closing of the valve. Because of the heavy forces during the opening of the exhaust valve, dew to the pressure into the cylinder, most of the state-of-the-art VVAs (mechanical, electromagnetic, hydraulic etc) avoid or fail to deal with the exhaust valves, limiting themselves exclusively to the intake valves. The present hydro-mechanical system, which is not sensitive to leakage, can control the exhaust valves too, because its “hydraulic” part deals exclusively with the control of the valve closing, thereby the strong force necessary to start opening the exhaust valve does not act on the hydraulic system.
The ECU (electronic control unit) of the engine triggers each release-valve independently. Without a signal from the ECU, the release-valve stays open allowing the oil to escape quickly from the oil-chamber, i.e. the default or “safety” mode for a release-valve is “open”. This protects the engine in case of ECU (or other) failure: the system operates in the pure mechanical way, with the cam controlling not only the opening but also the closing of the valves. Each release-valve receives a pulse from the ECU. The release-valve closes at the beginning of the pulse and stays closed till the end of the pulse. In the simplest case, the ECU generates, per release-valve and per two rotations of the crankshaft, a pair of time values T1 and T2 and feeds the release-valve with a pulse starting at T1 and ending at T2. The independent control of each release-valve by the ECU allows a simpler, yet precise and effective control over the engine. Even in case there are differences from cylinder to cylinder (for instance because of a different flow capacity of the release-valves or because of a poor valve lash adjustment) the engine can still operate clean and smooth because the ECU aligns independently, based on the feedback it receives, the pulses to the release-valves.
Instead of fighting with the accuracy of the constituent parts, the ECU has the potential to rectify the operation. The old, difficult and expensive mechanical control turns to an easy and cheap digital control.
With the system proposed, an engine can operate either according the over-expansion Atkinson/Miller cycle for economy/low emissions, or it can operate according the conventional cycle for high specific torque. When combined with a Variable Compression Ratio system, like those disclosed in the U.S. Ser. No. 12/553,975, U.S. Ser. No. 12/546,714 and U.S. Ser. No. 12/404,355, the overall result is an actually variable capacity engine capable to constantly operate at optimum thermodynamic efficiency.
Applied on a Diesel engine, this system enhances the volumetric efficiency when it is advantageous, controls the actual compression ratio, controls the overlap by the retardation of the exhaust valve closing, enables the controllable exhaust gas recirculation, etc.
In a first preferred embodiment,
In a second preferred embodiment,
In a third preferred embodiment,
In a fourth preferred embodiment,
In a fifth preferred embodiment,
The release valves can be of any type of the state of the art, for instance on-off solenoid valves. The loads the release-valves of this invention undergo and their flow capacity are smaller in comparison with the loads and the flow capacity of the release-valves of the closest prior art, i.e. the existing mass production solenoid on-off valves are more than adequate for the realization of the present invention.
Although the invention has been described and illustrated in detail, the spirit and scope of the present invention are to be limited only by the terms of the appended claims.
