VALVE TRAIN WITH VARIABLE VALVE ACTUATION

A valve train assembly includes valves having a valve stem; a main camshaft having main cams corresponding to the valves; main rocker arms corresponding to the valves; an auxiliary cam arranged on the main camshaft; at an auxiliary cam follower following the auxiliary cam, the auxiliary cam follower being movably arranged on a main rocker arm between a first and second position; and a latch on a main rocker arm for locking the auxiliary cam follower in the first position. A rotatable control rod controlling the latch is between the first and the second positions. The control rod includes a transmission element configured to convert torque in the control rod into a control force to control movement of the latch.

FIELD

The present invention relates to a valve train with a variable valve actuation.

BACKGROUND

A valve train assembly can include: a number of valves each having a valve stem; at least one main camshaft with a number of main cams, at least one main cam corresponding to each valve; a number of main rocker arms, each main rocker arm corresponding to a valve and having a valve stem actuation portion, a pivot axis parallel to the main cam shaft and a main cam follower for following the corresponding main cam, wherein the valve stem actuation portion, the pivot axis and the main cam follower are arranged along the length of the main rocker arm and at a distance from each other; at least one auxiliary cam arranged on the main camshaft; at least one auxiliary cam follower for each auxiliary cam and for following said auxiliary cam, wherein each auxiliary cam follower is movable arranged on one of the main rocker arms between a first and a second position; and a latch arranged on the respective main rocker arm for locking the auxiliary cam follower in the first position.

By way of example, a valve train assembly is described in the earlier patent application PCT/EP2015/061768 of the applicant.

In this valve train, a latch is controlled by an auxiliary camshaft with a selector cam, which is in contact with the latch. The control force exerted by the selector cam on the latch is in radial direction to the auxiliary camshaft. As a result, it is required, that the auxiliary camshaft is positioned close to the rocker arms, in which the latches are mounted.

If this valve train assembly is to be mounted on an existing cylinder head of a combustion engine, the inventors have recognized that modifications need to be done to the cylinder head and even the cylinder head might have to be redesigned to provide space for the auxiliary camshaft.

Also, the auxiliary camshaft needs to be actuated to put the latches in the correct positions depending on the conditions of the engine. This actuation of the auxiliary camshaft is typically performed by an electric motor or the like, which needs to be coupled to the auxiliary camshaft. With the above valve train, the inventors have recognized that coupling of a motor to the camshaft proves difficult and requires further modification of the cylinder head, as the auxiliary camshaft is typically positioned deep in the cylinder head, directly adjacent of the rocker arms.

So, with the above-described valve train the inventors have recognized that substantial modifications need to be made to the cylinder head of an existing combustion engine, when such a valve train is to be mounted to cylinder head.

SUMMARY

In an embodiment, the present invention provides a valve train assembly that includes a plurality of valves each having a valve stem; at least one main camshaft with a plurality of main cams—at least one main cam corresponding to each of the valves; a plurality of main rocker arms—each of the main rocker arms corresponding to one of the valves and having a valve stem actuation portion, a pivot axis parallel to the at least one main cam shaft and a main cam follower for following the corresponding one of the main cams, the valve stem actuation portion, the pivot axis and the main cam follower being arranged along a length of a corresponding one of the main rocker arms and at a distance from each other; at least one auxiliary cam arranged on the at least one main camshaft; at least one auxiliary cam follower for each of the at least one auxiliary cam and for following the at least one auxiliary cam, the respective at least one auxiliary cam follower being movably arranged on one of the main rocker arms between a first position and a second position; and a latch arranged on a respective one of the main rocker arms for locking the at least one auxiliary cam follower in the first position. At least one rotatable control rod for controlling the respective latch between the first position and the second position. The at least one control rod includes for the respective latch a transmission element, the transmission element configured to convert torque in the at least one control rod into a control force tangential to the at least one control rod to control movement of the latch between the first and second position.

DETAILED DESCRIPTION

Embodiments of the invention reduce or even remove the above-mentioned disadvantages of valve train assemblies.

Embodiments reduce or remove those disadvantages by providing a valve train assembly having at least one rotatable control rod for controlling the latches between the first and second position, wherein the at least one control rod includes for each latch a transmission element, which transmission element converts the torque in the at least one control rod into a control force tangential to the control rod to control movement of the latch between the first and second position.

With the valve train according to embodiments of the invention, a transmission element is provided for each latch, such that a control force tangential to the control rod can be exerted on to the latch. As a result, the distance between the control rod and the latches, arranged in the rocker arms, can be larger and there is no need to have the control rod in line with the latches, as is the case with known valve train assemblies. Accordingly, the control rod can be positioned more freely within the cylinder head, such that the number of modifications of the cylinder head can be substantially reduced or even be prevented.

The main rocker arm can be manufactured from sheet steel, but more preferably, the rocker arm is a cast metal object. By casting the rocker arm, the manufacturing costs for a large number of rocker arm can be kept low as a limited finishing operations are required. Furthermore, a cast metal rocker arm is able to better transfer the forces from the cam shafts and valves, enabling to minimize the weight of the rocker arms.

While cast metal rocker arms are preferred for the valve train assembly of the invention, such cast metal rocker arms could also be applied on the valve train assembly from PCT/EP2015/061768.

In a preferred embodiment of the valve train assembly according to the invention, the transmission element is an elongate element arranged with one end to the control rod and wherein the other end of the elongate element engages the latch. Preferably, the control rod extends substantially in radial direction.

The elongate element, such as a small beam, provides a lever, with which the rotation of the control rod is converted into a tangential force, with which the latch can be controlled between the first and second position. This allows for a position of the control rod at a distance from the latches and rocker arms, in which the latches are arranged. This position of the control rod can be selected more freely and the elongate elements can be shaped such that the existing design and components of the cylinder head are circumvented by the elongate elements and the torque of the control rod is transferred to the latches.

In a further embodiment of the valve train assembly according to the invention a substantially U-shaped or R-shaped leaf spring is arranged between the other end of the elongate element and the latch, wherein the leaf spring is arranged with one free end to the latch.

With the known valve train assembly, a compliance spring in the form of a coil spring is arranged on the latch pin. This compliance spring ensures that the control cam can be rotated from a position in which the latch is unlocked to a position for locking the latch position, even when the latch is not yet registered with a latch opening.

The substantially U-shaped or R-shaped leaf spring provides the same compliance spring function, while a U-shaped or R-shaped leaf spring is more easily mounted to the latch and provides a simple design, than the coil spring used in the known valve train assembly. Such a leaf spring could also be used in the known valve train assembly, where at least one auxiliary camshaft with a selector cam for each latch is provided to control said latch.

Another preferred embodiment of the valve train assembly according to the invention further comprises a camshaft carrier for accommodating the main camshaft, wherein the transmission element comprises a control cam arranged on the control rod and a curved leaf spring arranged between the control cam and latch, wherein one free end of the curved spring leaf is arranged to the camshaft carrier.

With the known valve train assembly, the auxiliary camshaft needs to be positioned close or adjacent the rocker arms, which are provided with the latches. With the invention, the control rod with the control cams can be placed more freely in the cylinder head, for example on top of the mounting of the main camshaft. By using transmission elements, which are in this embodiment curved leaf springs, the torque in the control rod is converted via the control cams and the curved lead springs into a control force for operating the latches. A free end of the curved leaf spring needs to be fixedly mounted, in particular to the camshaft carrier, such that the control cam can tilt the curved spring around the fixation point, while the other free end of the spring can act on the latch to control it between the first and second position. On top of that, the curved leaf spring also acts as a compliance spring, such that the latch no longer needs to be provided with such an additional compliance spring.

Preferably, the curved leaf spring is substantially C-shaped, wherein the control cam engages on the curved leaf spring at a distance from the attachment of the one free end to the camshaft carrier and wherein the other free end of the curved leaf spring engages the latch.

In yet another embodiment of the valve train assembly according to the invention, the control rod is rotatable between two angles and the control rod is provided with bends to accommodate components of a cylinder head on which the valve train assembly is to be mounted.

As the control rod only needs to rotate between two angles to control the latch between two positions, and the control rod does not need to be rotated over a full revolution, the control rod can be provided with bends in order to circumvent components or the shape of the cylinder head. For example it is possible to circumvent a timing wheel of the timing belt, by providing a U-shaped bend in the control rod.

In still another embodiment of the valve train assembly according to the invention, the curved leaf spring is being bent from a M-shaped starting shape, wherein the leaf spring comprises a bridge portion from which three legs extend parallel to each other, wherein the two outer legs are arranged to the camshaft carrier and wherein the free end of the middle leg engages the latch.

This curved leaf spring is easily bent out of a flat piece of spring steel having an M-shape. As both outer legs are attached to the camshaft carrier, which is typically arranged to the cylinder head, a pivot support is provided for the middle leg. Furthermore, as the middle leg is supported on both sides by the attached outer legs, the control cam will cause the middle leg to pivot in a defined and predictable manner to control the latch.

Preferably, the outer legs of the curved leaf spring extend on opposite sides of control cam. This provides for symmetry, such that the force exerted by the control cam is evenly distributed along the leaf spring and that torsions in the leaf spring is minimized.

Furthermore, it is preferred if the outer legs are provided with U-shaped free ends. The U-shaped free ends provide for additional spring action and contribute to the compliance spring function enabling the control cam to be rotated at any time, irrespective of alignment of auxiliary and main camshaft.

In yet another embodiment of the valve train assembly according to the invention, the latch comprises a pin movable in the length of the main rocker arm, wherein one end of the pin is engagable on the auxiliary rocker arm and wherein the pin is urged with the other end in contact with the transmission element.

The control force, which is tangential to the control rod and is generated from a torque in the control rod via the transmission element, will be substantially coaxial with the pin of the latch.

The invention also relates to a combination of a cylinder head for a combustion engine and a valve train assembly according to the invention, wherein the valve train assembly is mounted on the cylinder head.

An embodiment of the combination according to the invention further comprises an actuator, such as an electric motor, arranged on a side of the cylinder head, which actuator is coupled to the control rod for rotating said control rod.

Because the control rod can be positioned more freely within the cylinder head, the position of the actuator, which is typically mounted on the outside of the cylinder head, can also be chosen more freely.

Preferably the actuator is coupled to an end of the control rod or the actuator is coupled to a midsection of the control rod via a worm drive.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

FIG. 1shows an enlarged perspective view partially in cross section of a valve train assembly1according to patent application PCT/EP2015/061768 of the applicant. InFIG. 1, a main cam shaft20is depicted having main cams21,22and auxiliary cams23,24. The main rocker arms6rests with one end on a valve stem4to operate the corresponding valve.

Each main rocker arm6has an auxiliary rocker arm25pivotable around an axle26. A spring27is arranged around the axle26and attached to the auxiliary rocker arm25to urge the arm25upwardly. The auxiliary rocker arm25is furthermore provided with an auxiliary cam follower28, which follows the profile of the auxiliary cam23, while a main cam follower9is provided to follow the profile of the main cams21,22.

The latch12operated by the selector cam14on the auxiliary cam shaft16has a pin29, which is movable in the length of the main rocker arm6. Springs30urges the pin29against the selector cam14. The other end of the pin can be shifted into the auxiliary rocker arm25to lock the auxiliary rocker arm25to the main rocker arm6. The springs32arranged between the pin29and the selector cam14ensure that the selector cam14can be rotated at any time, even when the auxiliary rocker arm is25is not yet aligned with the main rocker arm6.

As will be clear, the selector cam14exerts a control force F on the latch29, which force F is radial to the auxiliary cam shaft16. This requires for the auxiliary cam shaft16to be close to the rocker arm6,7and for the axis of the auxiliary cam shaft16to be coplanar with the axis of the latch29.

FIG. 2shows a partial perspective view of a combination50according to the invention. The combination50has a cylinder head51with inlet openings52and outlet openings53. A main cam shaft54is provided having main cams55and auxiliary cams56, similar to the embodiment ofFIG. 1.

The main cam shaft54is mounted to a camshaft carrier57by brackets58. These brackets58also comprise through holes along which a control rod59extends. The control rod59has elongate elements60for controlling latches, as explained in detail withFIGS. 3A and 3B.

The control rod59is provided with a U-shaped bend portion61to circumvent a timing belt wheel62. Furthermore the control rod59is coupled to an electric motor63, which is arranged on the outside of the cylinder head51.

FIGS. 3A and 3Bshow a first embodiment of the valve train70assembly according to the invention. Similar to the valve train assembly1ofFIG. 1, this valve train assembly70has a main rocker arm71, which is with one end supported on a fixed pivot72and with the other end on a valve stem73. The main rocker arm71has an auxiliary rocker arm74with an auxiliary cam follower75hingedly arranged to the main rocker arm71. The auxiliary cam follower74is in contact with an auxiliary cam56on the camshaft54.

A latch pin76is arranged in the main rocker arm71to lock the auxiliary rocker arm74(as shown inFIG. 3A) or in unlocked position (as shown inFIG. 3B).

The latch pin76is operated by the control rod59and the elongate element60, which is in contact with a U-shaped leave spring77. This U-shaped leave spring77is arranged with one free end78to the latch pin76. This U-shaped spring77provides the same functionality as the spring32of the embodiment shown inFIG. 1.

By using an elongate element60, the torque in the control rod59can be converted to a tangential force F, which is arranged at a radius R from the control rod59. As a result, the control rod59can be positioned more freely in the cylinder head and does not need to be adjacent the main rocker arm71, such as in the embodiment shown inFIG. 1.

FIGS. 4A and 4Bshow a second embodiment80of the valve train assembly according to the invention. This embodiment80is largely similar to the embodiment70and corresponding element are provided with the same reference signs.

Instead of a control rod59with elongate elements60and a U-shaped spring77, this embodiment80is provided with a control rod81, on which control cams82are arranged. The cam82is in contact with a curved leaf spring83, which is arranged with one end84to the cylinder head85, for example to the camshaft carrier.

The curved leaf spring83has another free end86, which can be brought in contact with the latch pin76. InFIG. 4A, the lobe of the cam82contacts the leaf spring83, such that the other free end86is pressed against the latch76coupling the auxiliary rocker arm74with the main rocker arm71.

When the control rod81is rotated, the lobe of the cam82is brought out of contact with the curved leaf spring83, such that the latch76can be moved by the spring87to a position, in which the auxiliary rocker arm74can freely rotate in the main rocker arm71(seeFIG. 4B)

FIG. 5shows an embodiment of cast metal rocker arm90for the valve train assembly of the invention. This rocker arm90has a cast metal main rocker arm91, in which an auxiliary rocker arm92is arranged pivotable around the pivot axis93.

The main rocker arm91is provided with two cam followers94, while the auxiliary rocker arm is provided with a single cam follower95. A spring96urges the auxiliary rocker arm92into the shown position, while a latch pin97enables locking or unlocking of the auxiliary rocker arm92to the main rocker arm91.

The latch pin97is provided with an R-shaped leave spring98, which ensures that a force can be applied to the latch97, even when the auxiliary rocker arm is92is not yet aligned with the main rocker arm91.

This rocker arm90cannot only be applied to the valve train assembly according to the invention, but also to the valve train assembly according to the patent application PCT/EP2015/061768.

FIGS. 6, 7A and 7Bshow a third embodiment100of a valve train assembly according to the invention. This embodiment100is partially similar to the second embodiment80and corresponding parts are designated with the same reference signs.

FIG. 6shows schematically a control rod101with a control cam102, which actuates a leaf spring103. InFIG. 6, two leaf springs103are shown besides each other with the control rod101cut away for one of the leaf springs103.

Each leaf spring103is arranged to a part104of the cylinder head on which the valve train assembly100is arranged. Each leaf spring103has an M-shaped starting shape having a bridge portion105from which three legs106,107,108extend. The outer legs106,108are bent into a U-shape, such that the free ends of the outer legs106,108are perpendicular to the bridge part105. The free ends of the outer legs106,108are attached to the part104.

The middle leg107provides a lever, which is actuated by the control cam102and with which the latch pin76is actuated. The free end of the middle leg107is folded into a U-shape to provide an additional spring, which can act as a compliance spring.

As the middle leg107is attached to the part104of the cylinder head via both outer legs106,108via the U-shaped ends, the middle leg107can pivot along a resiliently suspended pivot axis, which contributes to the compliance spring function: So even when the auxiliary rocker arm is74is not yet aligned with the main rocker arm71, the control cam102can be rotated to the position shown inFIG. 7A, which is facilitated by the deformation of the U-shape in the outer legs106,108, the U-shape in the middle leg107as well as bending of the middle leg107. As soon as the auxiliary rocker arm74and main rocker arm71align, the latch pin76can be shifted to lock both rocker arms71,74to each other.