The present invention relates to a mechanical variable valve actuation (VVA) system for the control and actuation of the valve of an internal combustion engine. In particular, the present invention relates to a VVA system which allows a 2-stroke engine brake or fired operation.
As it is known, it is possible to control the pistons engines and achieve various functions by means of a valve actuation. In the most simple approach, a variation of cam position is applied to improve volumetric efficiency in the wide open throttle condition. As the intake valve closing event determines the real start compression, thus also the effective compression ration can be influenced. By variation of exhaust valve opening, the exhaust gas energy and consequently catalyst heat up as well as turbocharger performance can be influenced.
In view of the above, it can be easily understood that switching between different dedicated valve lift curves is even more effective in order to influence gas exchange or intake induced charge motion, even cylinder deactivation can be obtained by full valve deactivation.
Moreover, especially fully flexible variable valve actuation systems are considered as dedicated fuel economy concepts. By cam driven mechanical VVA systems, load control can be performed by means of early intake valve closing with minimized throttle losses.
Different VVA systems are already known in the art. For example, it is known to use a cam driven oscillating “profile” rocker to obtain a mechanical VVA. One example of such known systems is shown in
A drawback of this system in
Therefore, it is an object of the present invention to provide a mechanical VVA system suitable to be used in 4-stroke as well as in 2-stroke engine braking or fired operations.
It is a further object of the present invention to provide a mechanical VVA system suitable to reduce the engine fuel consumption and emissions.
Another object is to provide a mechanical system which is highly reliable and relatively easy to manufacture at competitive costs.
The objects above are achieved by a mechanical variable valve actuation system as claimed in claim 1.
Said system, therefore, comprises a control element suitable to control by means of adjustable connection means the lift of the valve of a valve system. The adjustable connection means is a lever connection system suitable to connect said eccentric element with a driven shaft and with an oscillating rocker which engages the valve system. Said oscillating rocker comprises a first and a second lift profiles suitable for engaging said valve system.
Further advantages of the present invention will become evident from the following detailed description of preferred but not exclusive embodiments and from the drawings herewith attached, which are merely illustrative and not limitative of the present invention, wherein:
a represents a schematic representation of the actuation system of the present invention;
As shown in said figures, the system valve 100 comprises at least a valve 104 (exhaust or inlet valve) which is moved by transmission means 101, 102, 103 activated by the profiles 5A,5B of the oscillating rocker 6. These transmission means are known in the art and can comprise an hydraulic lash adjuster 102, a rocker arm 101 connected to the valve 104 and a roller 103. In an alternative embodiment, the latter can be also a follower according to solutions known in the technical field.
According to the invention, the oscillating rocker 6 oscillates around a fixed part 30 in an oscillation range R1, R2, R3 which is established by a corresponding operative configuration of the control element 2. In detail, such an operative configuration is defined by a position of an operative part 10 of the control element 2.
The first lift profile 5A and the second lift profile 5B engage the valve system 100 in function of a relative oscillation range R1, R2, R3 established by the control element 2. That means that each oscillation range R1, R2, R3 corresponds to a specific valve lift characteristic. In other words, it is possible to modify the valve lift characteristic by modifying the position of the operative part 10 of the control element 2.
The control element 2 is preferably an eccentric element (hereinafter indicated with the same reference 2) whose rotation center is indicated in figures as 2a. The adjustable connection means comprises a lever connection system provided with five rods 3a, 3b, 3c, 3d, 3e. Each rod 3a, 3b, 3c, 3d, 3e has two ends. The first end of the first rod 3a corresponds to the operative part 10 of the control element 2. In particular, said operative part 10 can rotate along a circumference having its center in 2a. The position of the operative part 10 could be modified by means of a control element different than said eccentric element. In fact, the operative part 10 could be moved also in linear way by means of a control element comprising a shifting mechanism suitable to move linearly the operative part 10.
The second rod 3b has an end 50 which is connected to the driven shaft 4 by means of a fourth rod 3d. Therefore, a first four pivot system is defined by the four pivots 10, 20, 50 ad 60. The driven shaft 4 moves the pivot part 50 of the second rod 30b in an eccentric way advantageously avoiding the use of a cam.
The valve lift can be modified by means of the shifting of the first end 10 of the first rod 3a. In fact, the second end 20 of first rod 3a moves consequently to the movement of the first end 10. The second end 20 of the first rod 3a is connected by means of the knee joint 5 to the second rod 3b and to the third rod 3c.
The first end of the third rod 3c coincides with the pivot 20 of the knee joint 5, while the second end 40 of the third rod 3c is directly connected to the oscillating rocker 6. Said oscillating rocker 6 is rotatably associated with the pivot 40. A fifth rod 3e is further suitable to connect said pivot part 40 to a fixed pivot part 30. In particular the latter is the center of rotation of the oscillating rocker 6, while the pivot 40 establishes the angular oscillation of the rocker itself. Therefore, a second four pivot system is defined by the four pivots 10, 20, 40, 30.
a is relative to the lever connection system in which the pivot 20 is represented as shifted in the two pivots 20a e 20b in order to better show the two four pivot systems. A first pivot system is defined by the four pivots 10, 20a, 40 and 30, a second pivot system is defined by the four pivots 10, 20b, 50, 60.
A rotation of the eccentric element 2 modifies the valve lift by moving the working range (the oscillating range) of the profile rocker 6 to the left or to the right side by means of the displacement of the rocker pivot 40 caused by the movement of the third rod 3c. When the position of the angular oscillation of the rocker 6 is modified by the third rod 3c, the valve lift results to be modified accordingly by means of more or less engagement of the rocker lift profiles 5A, 5B with the valve roller 103 of the valve system 100.
Always in
A third oscillation range, indicated with reference R3, can be established by a third position of the operative part 10 of the control element 2. The third oscillation range R3 is so that both lift profiles 5A, 5B of the oscillating rocker 6 engage the valve system 100 (in particular the roller 103 shown in
In
According to the invention the VVA system can comprise a cam phaser in order to allow both 2-stroke mode operations and in particular to shift the lift profiles 5A,5B into the right angular position for braking.
It has been shown that the present invention achieves the aim and the objects proposed.
More in detail, it has been shown that the mechanical variable valve actuation system according to the present invention allows to accurately control the valve lift in order to optimize several different operation conditions. In particular the VVA system according to the invention enable both the 2-stroke engine operation or the four-stroke engine operation. With reference to the 2-stroke mode operation, the presence of two lift profiles allow a double valve lift frequency, while by means of the geometric optimization of said profiles it is possible to obtain a specific lift of the inlet and or exhaust valve. That means the VVA system of the invention allows to obtain both two/stroke engine braking and fired operation.
Moreover, the mechanical variable valve actuation system according to the present invention allows to improve the fuel consumption and emissions, especially by means of early inlet valve closing and modification of the valve overlap.
Not last, the variable valve actuation system of the present invention realizes the variation of the valve lift without using a cam in order to rotate the rocker profile which engages the valve, resulting in more accurate control of the valve lift.
It will be apparent to the person skilled in the art that other alternative and equivalent embodiments of the invention can be conceived and reduced to practice without departing from the true spirit of the invention.
From the description set forth above it will be possible for the person skilled in the art to embody the invention without introducing any further construction details.
Number | Date | Country | Kind |
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09179453 | Dec 2009 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/069721 | 12/15/2010 | WO | 00 | 6/5/2012 |
Publishing Document | Publishing Date | Country | Kind |
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WO2011/080076 | 7/7/2011 | WO | A |
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20070209620 | Seethaler et al. | Sep 2007 | A1 |
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20120240889 A1 | Sep 2012 | US |