Closest prior art: the Multiair (or UniAir, or TwinAir) system of Fiat, U.S. Pat. No. 6,918,364 etc, an electronically controlled hydraulic VVA currently in mass production, wherein an “oil push rod” is interposed between the valve and the cam; the cam pushes the “oil push rod” and the “oil push rod” pushes the valve; at the right moment a solenoid valve opens, the “oil push rod” collapses and the valve closes under the restoring action of the valve spring; a “hydraulic braking mechanism” smoothes the landing of the valve. A Hydraulic Desmodromic valve train, the HyDesmo, is here disclosed.
A valve 1 comprises a valve piston 2 and a valve stem 3, the valve piston 2 is secured to the valve stem 3;
the one end of the valve piston 2 is slidably fitted and seals one side of an opening oil chamber 4;
the other end of the valve piston 2 is slidably fitted and seals one side of a closing oil chamber 5;
a cam 6 actuates an oil piston 7;
the oil piston 7 is slidably fitted and seals one side of an oil chamber 8;
the cam 6 moves in synchronization to the engine and forces the oil piston 7 to perform an actuating motion wherein the oil piston displaces oil out of the oil chamber 8;
an oil reservoir 11, the cam 6 controls the oil piston 7 restoring motion wherein oil from the oil reservoir 11 enters into the oil chamber 8;
by control means 71, 10, and channels 9, the oil chamber 8 and the oil reservoir 11 are connected controllably with the opening oil chamber 4 and with the closing oil chamber 5,
the actuating motion of the oil piston comprises an initial part wherein the oil from the oil chamber is directed, according the state of the control means, either to the opening oil chamber and displaces the valve to open positively, or to the closing oil chamber and displaces the valve to close positively,
the actuating motion of the oil piston comprises a final part wherein the oil from the oil chamber is directed to the closing oil chamber and displaces the valve to close positively,
the final part of the actuating motion is adequately long to guarantee that, at all operational conditions, at the end of the actuating motion of the oil piston the valve will be closed.
The cam 6 pushes “downwards” the oil piston 7 during the valve opening and during valve closing, providing the necessary force, and power, to cause the valve motion, so that the valve 1 opens positively and closes positively, so that the HyDesmo is a desmodromic valve train.
In a first embodiment,
The niches and the galleries of the oil piston 7, and the ports of the oil chamber 8, are such that, no matter what the angular displacement of the oil piston 7 relative to the oil chamber 8 is, for as long as oil from the oil chamber 8 goes to the opening oil chamber 4, the closing oil chamber 5 communicates with the oil reservoir 11, and for as long as oil from the oil chamber 8 goes to the closing oil chamber 5, the opening oil chamber 4 communicates with the oil reservoir 11. I.e. besides displacing oil, the oil piston serves also as the control means: in synchronization to the crankshaft of the engine the oil piston permits and forbids the communication of the opening oil chamber 4 and of the closing oil chamber 5 with the oil chamber 8 and with the oil reservoir 11. During the valve closing and until the moment the valve is finally closed, the oil piston niches and galleries, in cooperation with the oil chamber ports, direct the oil from the oil chamber 8 to the closing oil chamber 5; after the valve closing, the oil piston niches and galleries, in cooperation with the oil chamber ports, direct the oil from the oil chamber 8 to the oil reservoir 11.
With more than half of the downwards motion of the oil piston dedicated, at all possible modes of operation, to the valve closing, the hydraulic-mechanical system guarantees that at the end of the actuating motion of the oil piston 7, the valve 1 will always be closed.
Having a single opening ramp of a rotating cam to cause both, the opening and the closing of the valve, and having a single part, the oil piston, to control the communication between the various oil chambers, the system becomes as accurate, as simple and as reliable as it gets.
The roller of the rocker arm,
The duration of the opening ramp of the cam lobe, i.e. the duration of the “valve opening or closing” section plus the duration of the “valve closing” section,
An auxiliary/safety spring 18 holds the valve from “dropping” towards the combustion chamber during engine's stall.
A hydraulic lash adjuster (spring 19, one way valve 20) controls the valve lash.
An auxiliary piston 21 is slidably fitted to, and seals, one side of the closing oil chamber 5; together with its supporting spring 22, it serves as an oil pressure surge compensation means: during the pressure surging, the piston 21 moves slightly outwards of the closing oil chamber 5 dumping the pressure surge; when the pressure drops, the piston 21 moves, by the supporting spring 22, slightly inwards the closing oil chamber 5 to compensate any oil leakage and to keep, this way, the valve firmly closed until the next valve opening.
As shown in
By angularly displacing the oil piston relative to the oil chamber, the duration and the lift of the valve vary. The system can offer a continuous range of valve lifts starting from zero, enabling the throttling by the intake valves, i.e. enabling the throttle-less operation. The pure mechanical control is an option: in a HyDesmo motorcycle, for instance, the driver can rotate, by the grip and the gas-cable, the oil piston relative to the oil chamber, just like he controls the throttle valve in a conventional engine. The fuel system can align the quantity of the fuel with the air entering the cylinder (oil piston angular displacement sensor, rev sensor, lambda sensor, loop control etc).
The electronic control is another option. With servomotors controlled by the ECU, the angles of the oil pistons of different oil chambers are micro-aligned (fine tuning) in order to balance the operation of different cylinders based on lambda sensors, on the feedback control etc. This fine-tuning needs not the high-power instant-response solenoid electromagnetic valves of the MultiAir system. The ECU can complete the micro alignment in a few rotations of the crankshaft. In case the ECU fails to control the servomotors, the engine continues to operate based on the mechanical control.
In another embodiment,
In
In
In
Near its middle stroke the oil piston covers the oil chamber port wherein the one way valve 14 resides; for the rest of the downward motion of the oil piston, the oil from the oil chamber is directed to the closing oil chamber 5 through the one way valve 13; this way the hydraulic-mechanical system guarantees that at the end of the downwards motion of the oil piston 7, the valve 1 will always be closed.
When the piston starts its upward motion, oil enters through the one-way valve 12 into the oil chamber; the other two one-way valves 13 and 14 prevent oil leakage from the closing oil chamber 5, keeping the valve firmly closed.
Without valve restoring springs, this embodiment realizes all the “strategies” of the MultiAir system of Fiat, as
late valve opening (for an initial part of the downward motion of the oil piston the electromagnetic valve is off);
multi-lift (the electromagnetic valve is activated and deactivated more than once during the downward motion of the oil piston);
late opening—early closing (the electromagnetic valve turns on after an initial part of the downward motion of the oil piston, the electromagnetic valve turns off before the valve lift is maximized);
full valve lift (the electromagnetic valve stays on from the beginning of the downward motion of the oil piston until the moment the valve starts closing);
valve deactivation (the electromagnetic valve is off for the entire cycle).
The MultiAir operates according the “Ingoing Air Control”, as explained in the US2011/214632 patent application publication that also discloses the necessary modifications to enable the MultiAir to operate either according the “Ingoing Air Control” of Fiat or according the “Outgoing Air Control”. In a similar way, a cam of adequately long duration (for instance 400 crankshaft degrees) enables the HyDesmo to operate according all the strategies of the MultiAir and according the “Outgoing Air Control” strategy; for 400 crankshaft degrees valve duration, the duration of the opening ramp of the cam needs to be 200 cam degrees, leaving another 160 cam degrees for the “oil chamber refill” section and for the “base circle” section.
In comparison to the MultiAir system, in this embodiment the restoring motion of the valve is independent on the restoring force of a restoring valve spring and on the characteristics (viscosity etc) of the hydraulic liquid (oil); in the HyDesmo the cam defines the valve motion during the valve opening and during the valve closing.
Without restoring valve springs to compress and to accelerate, the hydraulic circuit pressure (and energy consumption) of the HyDesmo is less, in comparison to MultiAir; the reduced mass of the valve assembly enables higher rev limit. The shorter valves and the absence of valve springs enable a lighter, cheaper and shorter engine.
The HyDesmo is applicable to all poppet valve reciprocating piston engines and pumps.
In the embodiment of
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.
Number | Date | Country | Kind |
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GB 1115137.0 | Sep 2011 | GB | national |