Description

The present invention relates to a rotary valvetrain system, with a curved valve control stem, for opening and closing valves in a four-stroke internal combustion engine, and to a related four-stroke internal combustion engine, with a related cylinder head structure.

As it is known, in the current four-stroke internal combustion engines, the valvetrain system is positioned on top of cylinder and above the intake and exhaust ducts. It is constituted at least by a camshaft, acting on a row of valves aligned on the engine head, which, by means of cams with suitable shape and thanks to some motion elements, allows to open and close the valves by transfer along the axis of the valve stem, so as to allow to intake the mixture of fuel and combustion agent through the intake ducts and to discharge the exhaust gases through the exhaust ducts, in the related engine operating steps.

An example of rotary valvetrain system and with curved stems is described in the US patent N. 4, 036, 185 A, wherein such system, however, is deprived of a backlash- recovering system integrated in the valve itself.

Another example of rotary valvetrain system and with curved stems, similar to the previous one, is described in the Japanese patent application N. JP 2006 183,560 A.

The British patent N. GB 784,974 describes a distribution valve equipped with a return and closure system controlled by a swivelling lever. A valve similar to this one is described in the US patent N. 2,831,470 A.

Other examples of valvetrain systems are described in the German patent application N. DE 102 60 986 Al and in the International patent application N. WO 2014/068, 365 Al .

In the valvetrain systems, some parameters such as the loading and trapping coefficient are particularly critical to optimize the performance of the internal combustion engine.

In the known solutions, the load losses and the dissipations concentrated in the distribution elements allow such optimization which affects the engine consumption. Furthermore, the proposed solutions have not the required compactness in the design of cylinder heads for internal combustion engines.

The technical problem underlying the present invention is to provide a valvetrain system allowing to obviate the drawback mentioned with reference to the known art.

Such problem is solved by a valvetrain system as specified above, which is defined in the enclosed claim 1.

Additional features and accessory details are mentioned in the enclosed depending claims.

In accordance with the designated goals, according to the present invention an internal combustion engine head is implemented having a valvetrain system comprising the ducts for intaking the mixture, the ducts for discharging the exhaust gases, the compartments for housing the distribution elements for intake and exhaust, and the housing for transmitting the actuation of the distribution elements, such as valves and related camshafts .

In particular, the proposed solution provides the use of a valvetrain system comprising one or more valves with curved stem, the purpose thereof is to allow to adjust the passage of the mixture, by further guaranteeing to keep the valves closed during the various engine operation steps. The valves are engaged in respective one or more valve seats, allowing the correct coupling between valve and ducts in the cylinder head, thus by guaranteeing to keep the valve closed. The valvetrain system further comprises one or more rocker arms, in relation to the number of valves, with the purpose of giving a rotatory motion to the valves, around the respective rotation axis, on a spindle which has the purpose of constraining the rocker arm in the rotation around the axis thereof.

Moreover, two pins are provided which, apart from fixing the valve to the rocker arm, allow the valve to move along the pin direction by recovering the possible backlash; two cam disks playing the function of transmitting the cam motion to the rocker arm and to the valve; two plates for the backlash recovery interposed between the cam disk and the rocker arm, with the purpose of recovering the backlash between cam and cam disk; one or more guides for the valve stem, depending upon the number of adopted valves, housed inside the distribution compartment with the purpose of guiding the valve in the motion thereof and avoiding that the gases in the duct could enter the compartment; and at last, a return spring for rocker arm, with the purpose of guaranteeing the valve sealing when it closes the duct.

This scheme can be used both for the intake valves and for the exhaust valves, which are alternatively opened and closed and they are arranged on a respective row or rows on the engine head, in order to be controlled by a camshaft for each raw, with a plurality of cams.

It is further to be meant that such solution can be applied independently from the number of intake valves existing for each cylinder, and analogously for the exhaust valves.

The main advantage of the valvetrain system according to the present invention lies in the fact of allowing a decrease in the dissipations and load losses, with the maximum compactness of the system.

The present invention will be described hereinafter according to a preferred embodiment thereof, provided by way of example and not for limitative purposes by referring to the enclosed drawings wherein:

• figure 1 is a section view of a cylinder head of a four-stroke combustion engine, integrating a rotary valvetrain system according to the present invention;

• figure 2 is an isometric view of how the cylinder head of figure 1 appears, with removed portions for sake of clarity, constituted by exhaust and intake ducts, the distribution compartments and the transmission compartment ;

• figure 3A is a view of the single components related to the intake valve and the motion thereof, of the valvetrain system of figure 1;

· figure 3B is a view of the single components related to the exhaust valve and to the motion thereof, of the valvetrain system of figure 1;

• figures 4A and 4B show schematically a base representation of the valvetrain system, showing the key references for implementing the whole system;

• figure 5 is a section view between the cam closing profile, the rocker arm, the backlash-recovering plate, the cam disk and the spindle of the valvetrain system of figure 1; and

· figure 6 is a section view between the cam opening profile, the rocker arm, the backlash-recovering plate, the cam disk, the valve pins, the valve and the spindle of the valvetrain system of figure 1.

By referring to the figures, a cylinder head of a four- stroke internal combustion engine is designated as a whole with 1; it has an intake duct 2, therethrough the mixture of fuel and combustion agent is conveyed towards a combustion chamber, an exhaust duct 3, therethrough the exhaust gases are expelled, a compartment of the intake distribution elements 4 and a compartment of the exhaust distribution elements 5, inside thereof the cylinder head distribution elements, that is of the herein described valvetrain system, are arranged and the transmission compartment 6, therethrough it is possible to access the components for the motion of the distributions (figure 2) .

More in details for the intake side and by referring to figures 1, 3A and 3B, the valvetrain system comprises an intake valve 7, in particular a valve of mushroom-like type with an intake plug 32 inserted in a first valve seat 8, a curved intake stem 30, inserted in a first guide of intake valve 14, and a first actuation head 31, at the end of the stem 30 opposite to the intake plug 32. The first guide of intake valve 14 is inserted in a first guide seat la obtained in the cylinder head 1 at the intake duct 2.

The valvetrain system further comprises, on the intake side, a first camshaft 25 having cams with two distinct profiles: a first opening cam 25a and a first closing cam 25b, placed in direct contact with a respective first disk-like cam follower 12, which has the task of following the course of the cam profiles, having a first contact head shaped like a disk, with a bent surface, thereon the respective cam presses, and a first shank which is inserted in a corresponding first recess. The first cam follower 12 transmits such motion to a first rocker arm 9, constrained on a first spindle 10, which transfers the motion to the intake valve 7 the first actuating head thereof 31 is constrained to the first rocker arm 9 by means of a pair of first axial pins 11.

The first rocker arm 9 comprises a first arm 9a, whereon said opening cam 25a acts, which has an axial extension 9b, thereto the actuating head 31 is constrained at first pin axial seats 9f wherein the first axial pins 11 are inserted, with a first recess 9d wherein the respective shank of the first cam follower 12 is inserted.

The first rocker arm 9 further comprises a second arm 9c whereon said first closing cam 25b acts and which has a second recess 9e wherein the shank of the respective first cam follower 12 is inserted.

Between the disk-like contact head of the first cam follower 12 and the seat thereof a respective first backlash—recovering plate 13 with predetermined thickness is provided, which is responsible for the correct positioning of the first disk-like cam followers 12.

Therefore, for each intake valve, there are two first disk-like cam followers 12 and two respective backlash- recovering plates 13 with predetermined thickness.

The first axial pins 11, apart from fastening the intake valve 7 to the first rocker arm 9, allow the intake valve 7 to move along the direction defined by the first pins 11, by giving a freedom degree in the recovery of possible backlash.

The opening of the intake valve 7, apart from being conditioned by the first rocker arm 9 in a rotation motion around the axis of the spindle 10, is controlled by the valve guide 14 which, apart from helping the intake valve 7 in the motion thereof, does not allow the mixture to pass from the intake duct 2 to the compartment of the intake distribution elements 4.

The correct sealing of the intake valve 7, during the steps for the engine compression and combustion, is guaranteed by the coupling with the first valve seat 8 and by the action of a first sealing spring 15 (figure 3A) acting on the first spindle 10 of the first rocker arm 9, by guaranteeing the correct force to keep the intake valve 7 in closed position.

By referring to the exhaust side of the valvetrain system, it comprises an exhaust valve 16, in particular a valve of the mushroom-like type with an exhaust plug 33 inserted in a second valve seat 17, a curved exhaust stem 34, inserted in a second exhaust valve guide 23, and a second actuating head 35, at the end of the stem 34 opposite to the exhaust plug 33.

The second valve guide 23 is inserted in a second guide seat lb obtained in the cylinder head 1 at the exhaust duct 3.

The valvetrain system further comprises, on the exhaust side, a second camshaft 26 having cams with two distinct profiles: a second opening cam 26a and a second closing cam 26b, placed at direct contact with a respective second disk-like cam follower 21, which has the task of following the course of the cam profiles, which has a second contact head shaped like a disk, with a bent surface, whereon the respective cam presses, and a second shank which is inserted in a recess. The second cam follower 21 transmits such motion to a second rocker arm 18, constrained on a second spindle 19, which transfers the motion to the exhaust valve 16 the actuating head 35 thereof is constrained to the second rocker arm 18 by means of a pair of second axial pins 20.

The second rocker arm 18 has a structure wholly analogous to that of the first rocker arm 9, which then is not further described.

Between the second disk-like contact head of the second cam follower 21 and the seat thereof a respective second backlash-recovering plate 22 with predetermined thickness is provided, which is responsible for the correct positioning of the first disk-like cam followers 21.

Therefore, for each valve, there are two disk-like cam followers 12 and two respective backlash-recovering plates 22 with predetermined thickness.

Again, the second axial pins 20, apart from fastening the exhaust valve 16 7 to the second rocker arm 18, allow the exhaust valve 16 to move along a direction defined by the pair of second pins 20 by providing a freedom degree in the recovery of possible backlash.

The opening of the exhaust valve 18, apart from being conditioned by the second rocker arm 18 in a rotation motion around the axis of the second spindle 19, is controlled by the second valve guide 23 which, apart from helping the exhaust valve 16 in the motion thereof, does not allow the exhaust gases to pass from the exhaust duct 3 to the compartment of the exhaust distribution elements 5.

The correct sealing of the exhaust valve 16, during the steps of the engine compression and combustion, is guaranteed by the coupling with the second valve seat 17 and by the action of a second sealing spring 24 (figure 3B) acting on the second spindle 19 of the second rocker arm 18, by guaranteeing the correct force to keep the exhaust valve 16 in closed position.

During the engine intake step, step wherein the mixture enters the combustion chamber, the intake valve 7 is opened to allow the passage of the mixture in the combustion chamber. The opening of the intake valve takes place with the rotation of the same valve around an axis determined by the curvature of the intake stem 30.

In fact, by using said first camshaft 25 with two cam profiles, one for the opening and the other one for the closing, placed in direct contact with the disk-like cam followers 12 for following the course of the profiles, they transmit the motion to the first rocker arm 9; the latter, constrained on the respective first spindle 10, is put into rotation and transfers its own motion to the intake valve 7 which, constrained to the first rocker arm between the two first pins 11, opens, by allowing the mixture to enter the combustion chamber. By referring to figure 1 and 3B, during the engine exhaust step, step wherein the exhaust gases are expelled from the combustion chamber, the exhaust valve 16 is opened .

Even in this case, by using the second camshaft 26 with two cam profiles, one for the opening and the other one for the closing, placed in direct contact with the respective second disk-like cam followers 21, with the purpose of following the course of the corresponding cam profile, they transmit the motion to the second rocker arm; the latter, constrained on the second spindle, which is placed in rotation and transfers its own motion to the exhaust valve 16 which, constrained to the second rocker arm 18 transmits said two second pins, opens by allowing the exhaust gases to be expelled.

The following represents a description of schematic type of the valvetrain system the ownership thereof is wanted to be claimed. It provides guidelines for the implementation thereof and the key elements constituting it in its uniqueness. Furthermore, the following represents a not limiting generalization as it can be applied for the motion of any valve which has to rotate around an axis and the portions constituting this scheme can be implemented with any shape provided that the schematic reference is the one described hereinafter.

Hereinafter the kinematic behaviour is described as a result of the structure of the above-described valvetrain system: the following then is valid both for the intake valve and for the exhaust valve.

By referring to figures 4A and 4B, the valve is schematically constituted by a stem (s) and by a head (t) ; the stem (s) is represented by a circumference arc, with suitable length, with centre (c) and radius (rv) .

The curve (a) represents the trajectory which the valve head (t), during its motion, describes by going from the position of closed valve (t) to opened valve (tl) . The motion of the valve head (t) is a rotation around an axis (ar) passing through the centre of the valve stem (c) and normal to the rotation plane (p) of the valve. Exactly the centre (c) represents the key element of the system as it is the heart of the mechanism and its position in the space determines the way in which the valve opens.

The rocker arm is schematically constituted by an opening disk (da) , lying on the rotation plane (p) of the valve and connected to the rocker arm body (b) by means of a main arm (ba) , and by an opening disk (dc) , on the plane (q) parallel to the rotation plane (p) of the valve and connected to the rocker arm body (b) by means of a secondary arm (be) , having an opening angle (h) suitably selected therebetween.

The valve rotation around the centre (c) takes place as it is constrained to the rocker arm by means of an anchoring arm (bv) , which, in turn, can rotate around the rotation axis (ar) .

The cam disks (da and dc) , which represent the base profile of the cam followers 12, 21, have suitable radius (ra and rc) and they are in contact with the primitive (pa) of the profile for opening the valve, of the camshaft, and the primitive (pc) of the profile for closing the valve, of the camshaft.

To what described above a person skilled in the art, with the purpose of satisfying additional and contingent needs, could introduce several additional modifications and variants, all however comprised within the protective scope of the present invention, as defined by the enclosed claims.