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Title:
VALVETRAIN WITH VARIABLE VALVE ACTUATION
Document Type and Number:
WIPO Patent Application WO/2015/181264
Kind Code:
A1
Abstract:
The invention relates to a valvetrain assembly comprising: - 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; - a latch arranged on the respective main rocker arm for locking the auxiliary cam follower in the first position; and - at least one auxiliary camshaft with a selector cam for each latch to control said latch.

Inventors:
RAIMONDI, Emanuele (Via Diani 33, San Francesco Al Campo, I-10070, IT)
Application Number:
EP2015/061768
Publication Date:
December 03, 2015
Filing Date:
May 27, 2015
Export Citation:
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Assignee:
EATON SRL (Via Orvieto 19, Torino, I-10149, IT)
International Classes:
F01L13/00; F01L1/18
Domestic Patent References:
WO1994028288A21994-12-08
Foreign References:
US20120067309A12012-03-22
US6314928B12001-11-13
DE19700316A11997-07-17
EP2653673A12013-10-23
US4656977A1987-04-14
EP0267696A11988-05-18
EP0462853A11991-12-27
EP1544422A12005-06-22
Attorney, Agent or Firm:
EATON IP GROUP EMEA (Route de la Longeraie 7, Morges, CH-1110, CH)
Download PDF:
Claims:
Claims

1. Valvetrain assembly comprising:

- 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;

characterized by

- 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;

- a latch arranged on the respective main rocker arm for locking the auxiliary cam follower in the first position; and

- at least one auxiliary camshaft with a selector cam for each latch to control said latch.

2. Valvetrain assembly according to claim 1, wherein the auxiliary cam follower is arranged on a free end of an auxiliary rocker arm, which is pivotable arranged with the opposite end to the main rocker arm. 3. Valvetrain assembly according to claim 2, wherein spring means are arranged between the auxiliary rocker arm and the main rocker arm for urging the auxiliary cam follower to the first position.

4. Valvetrain assembly according to any of the preceding claims, wherein 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 selector cam on the auxiliary cam shaft.

5. Valvetrain assembly according to any of the preceding claims, wherein the valve stem actuation portion is arranged on end of the rocker arm, the pivot axis is arranged on the other end of the rocker arm, and the main cam follower is arranged between the valve stem actuation portion and the pivot axis.

6. Valvetrain assembly according to claim 5, wherein the latch is arranged adjacent to the pivot axis.

7. Valvetrain assembly according to any of the preceding claims, comprising electric drive means for driving the auxiliary cam shaft.

8. Valvetrain assembly according to any of the preceding claims, comprising at least a first and a second valve both corresponding to a single cylinder of a combustion engine, wherein a first selector cam for the first valve has a profile different from the profile of the second selector cam for the second valve.

9. Valvetrain assembly according to any of the preceding claims, wherein a main cam comprises two identical, disc like, cam portions, wherein the corresponding auxiliary cam is arranged between the two identical cam portions, and wherein the main rocker arm has two main cam followers mirror-symmetrically arranged with respect to the length of the rocker arm.

Description:
Valvetrain with variable valve actuation The invention relates to a valvetrain assembly comprising:

- 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; Such a valvetrain assembly is commonly known and used in combustion engines to ensure that the valves are opened en closed in synchronization with the movement of the pistons in the cylinders.

The timing and lift of the valves is determined by the profile of the cam corresponding to the specific valve. However, the profile is static and cannot be changed, so the profile is a compromise between for example fuel consumption, power and emissions.

It is further known in the prior art to provide a variable valve actuation to change the timing and lift of the valves while running the engine. Numerous techniques are used to achieve this.

One technique is providing two differently shaped cams on the cam shaft for each valve and shifting the camshaft axially while running the engine. This allows one to use two different valve timing profiles. For example, one profile to have high power, but also high fuel consumption and emissions, and the other profile for less power, but better fuel consumption and lower emission. Another technique is to change the phase of the camshaft, such that the lifting of the valves is advanced or delayed. By for example delaying the closing of the exhaust valve, will ensure that more burned fuel is driven out of the cylinder, such that more fuel can be burned in the next stroke.

Also electro-hydraulic systems are used in which a body is arranged between the cam and the valve, which can either transmit the actuation by the cam or absorb the actuation. To this end, the body is telescopic and filled with hydraulic fluid. When a drain opening is closed by an electric valve, the body is stiff and cannot collapse and the valve is actuated by the cam. However, when the drain opening is opened, the hydraulic fluid can be pushed out and the body can be compressed, such that the actuation of the cam is absorbed and the valve stays in a closed position.

Now by electronically controlling the electric valve one can change the profile of the cam and therefor the timing and lift of the valve. If the full profile of the cam is to be used, the valve remains closed, but if only part of the valve lift is desired, the electric valve is opened during the actuation of the valve by the cam.

However, the temperature, the pressure and the viscosity of the hydraulic oil influences the characteristics of electro-hydraulic variable valve actuation.

It is furthermore known to operate the valves without the use of cams, for example by a solenoid type of actuation system. However, such systems are complex and with high costs, as such an actuator is needed for each valve of a combustion engine.

It is an object of the invention to provide a valvetrain system according to the preamble, in which the above mentioned disadvantages are reduced or even removed.

This object is achieved with a valvetrain system according to the invention, which is characterized by

- 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;

- a latch arranged on the respective main rocker arm for locking the auxiliary cam follower in the first position; and

- at least one auxiliary camshaft with a selector cam for each latch to control said latch.

With the valvetrain according to the invention, an auxiliary cam is provided on the main cam shaft, which can be switched on and switched off by controlling the latch. This latch is controlled by an auxiliary cam shaft, which makes it possible to turn on or off a number of latches of adjacent valves simply by rotating the auxiliary cam shaft in the desired position.

When the latch is locked, the auxiliary cam will either alter the profile of the main cam or even fully replace the profile of the main cam. When the latch is unlocked, the auxiliary cam follower can freely move between the first and second position, such that the auxiliary cam is in fact disabled. Only the main cam will impose its profile onto the valve.

With the valve train system according to the invention, it is possible to provide all valves with two different profiles for lift and timing, but is also possible to only provide a selected number of valves with this functionality. For example, only the first intake valve of each cylinder can be provided with a double profile. It would also be possible to provide switch- off functionality to an engine with a large number of cylinders. With this functionality some of the cylinders can be turned off, when the engine produces only part of its maximum power. In a preferred embodiment of the valvetrain assembly according to the invention the auxiliary cam follower is arranged on a free end of an auxiliary rocker arm, which is pivotable arranged with the opposite end to the main rocker arm.

With an auxiliary rocker arm one can achieve a large stroke of the auxiliary cam follower between the first and second position. This stroke can for example be larger than the height of the main rocker arm. Preferably, spring means are arranged between the auxiliary rocker arm and the main rocker arm for urging the auxiliary cam follower to the first position. The spring means also ensure that the auxiliary cam follower will not jump around when in unlocked state due to the vibrations of the engine.

In a further preferred embodiment of the valvetrain 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 selector cam on the auxiliary cam shaft.

When the auxiliary rocker arm is more of less aligned with the main rocker arm, the auxiliary rocker arm can easily be locked just by sliding the pin into a hole in the auxiliary rocker arm. This will require virtually no force, such that rotation of the auxiliary cam shaft can be performed quickly. By arranging a spring between the selector cam and the sliding pin, it is ensured that the selector cam can be rotated at any time, while the sliding pin will slide into the auxiliary rocker arm as soon as the auxiliary rocker arm is aligned with the main rocker arm.

In yet a further embodiment of the valvetrain assembly according to the invention the valve stem actuation portion is arranged on end of the rocker arm, the pivot axis is arranged on the other end of the rocker arm, and the main cam follower is arranged between the valve stem actuation portion and the pivot axis.

By providing the pivot axis at the other end of the rocker arm, a nearly stationary portion of the rocker arm is easily accessible. It is accordingly preferred to arrange the latch adjacent to the pivot axis, such that it can be easily controlled by the selector cam. Yet another embodiment of the valvetrain assembly according to the invention comprises electric drive means for driving the auxiliary cam shaft. These electric drive means can be a stepper motor directly coupled to the auxiliary cam shaft or another electric drive means coupled to the cam shaft via a gear transmission.

Yet another preferred embodiment of the valvetrain assembly according to the invention comprises at least a first and a second valve both corresponding to a single cylinder of a combustion engine, wherein a first selector cam for the first valve has a profile different from the profile of the second selector cam for the second valve.

With this embodiment it is for example possible to select whether a first intake valve, a second intake valve or both intake valves are provided with an alternative lift and timing profile.

In still a further embodiment of the valvetrain assembly according to the invention a main cam comprises two identical, disc like, cam portions, wherein the corresponding auxiliary cam is arranged between the two identical cam portions, and wherein the main rocker arm has two main cam followers mirror- symmetrically arranged with respect to the length of the rocker arm.

By designing the main rocker arm, auxiliary rocker arm and corresponding cams mirror- symmetrically, it is ensured that the forces on the components of the valvetrain are minimized and no undesired moments are present within the valvetrain.

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

Figure 1 shows a perspective view of an embodiment of the valvetrain assembly according to the invention.

Figure 2 shows an enlarged perspective view partially in cross section of the valvetrain assembly of figure 1. Figure 3A - 3C show a cross sectional view of the valvetrain assembly of figure 1 in three positions with unlocked latch.

Figure 4A - 4C show a cross sectional view of the valvetrain assembly of figure 1 in three positions with locked latch.

Figure 1 shows a perspective view of an embodiment of the valvetrain assembly 1 according to the invention.

The figure 1 shows two valves 2, 3, for example intake valves of a single cylinder. The respective valve stems 4, 5 are actuated by main rocker arms 6, 7. Each rocker arm 6, 7 has two main cam followers 8, 9, 10 , 11 arranged in the center of each rocker arm 6, 7. The main rocker arms 6, 7 have each at the pivot axis end a latch 12, 13 respectively. These latches 12, 13 are operated by their respective selector cam 14, 15 arranged on an auxiliary cam shaft 16. The auxiliary cam shaft 16 is rotated by an electric motor 17 coupled to the cam shaft 16 via gears 18, 19. Figure 2 shows an enlarged perspective view partially in cross section of the valvetrain assembly 1 of figure 1. In this figure 2 also a main cam shaft 20 is depicted having main cams 21, 22 and auxiliary cams 23, 24.

Each main rocker arm 6, 7 has an auxiliary rocker arm 25 pivotable around an axle 26. A spring 27 is arranged around the axle 26 and attached to the auxiliary rocker arm 25 to urge the arm 25 upwardly. The auxiliary rocker arm 25 is furthermore provided with an auxiliary cam follower 28, which follows the profile of the auxiliary cam 23.

The latch 12 operated by the selector cam 14 on the auxiliary cam shaft 16 has a pin 29, which is movable in the length of the main rocker arm 6. Springs 30 urge the pin 29 against the selector cam 14. The other end of the pin can be shifted into the auxiliary rocker arm 25 to lock the auxiliary rocker arm 25 to the main rocker arm 6. The springs 32 arranged between the pin 29 and the selector cam 14 ensure that the selector cam 14 can be rotated at any time, even when the auxiliary rocker arm is 25 is not yet aligned with the main rocker arm 6.

Figures 3A - 3C show a cross sectional view of the valvetrain assembly 1 of figure 1 in three positions of the main cam shaft 20 with unlocked latch 12.

In figure 3A, the valve 4 is in closed position. The main rocker arm 6 is in substantial horizontal position. The pivot axis of the main rocker arm 6 is shown as a sphere shaped support 31. The selector cam 14 is in a position in which the pin 29 is out of engagement with the auxiliary rocker arm 25. This allows the rocker arm 25 to pivot freely around the axle 26.

Furthermore figure 3 A shows that the main cam followers 8, 9 are in contact with the main cam 21, while the auxiliary cam follower 29 is in contact with the auxiliary cam 23.

In figure 3B, the main cam shaft 20 is rotated such that the cam lobe of the main cam 21 pushes the main cam followers 8, 9 down, such that the main rocker arm 6 is tilted and the valve 4 is lifted over a distance x . In this position the auxiliary cam follower 28 is out of contact with the auxiliary cam 23.

In figure 3C, the main cam shaft is rotated further, such that the cam lobe of the main cam 21 is again out of contact with the main cam followers 8, 9 and the main rocker arm 6 is again tilted back to its horizontal position and the valve 4 is closed again.

In this shown position of the main cam shaft 20, the lobe of the auxiliary cam 23 is in contact with the auxiliary cam follower 28. As the auxiliary rocker arm 25 is in unlocked state, the auxiliary rocker arm 25 is pivoted down within the main rocker arm 6 without having an effect on the valve 4. All cam followers 8, 9, 28 are in contact with their respective cam 21, 23 on the main cam shaft 20. Figure 4A - 4C show a cross sectional view of the valvetrain assembly 1 of figure 1 in the same three positions as shown in the figures 3A - 3C, however with locked latch 12.

In order to lock latch 12, the auxiliary cam shaft 16 is rotated, such that the lobe of the selector cam 14 shifts the pin 29 in longitudinal direction of the main rocker arm 6, and such that the pin 29 is inserted into the auxiliary rocker arm 25.

Figure 4A shows again the horizontal rest position, similar to figure 3A in which the cam followers 8, 9, 28 are in contact with their respective cams 21, 23.

In figure 4B, the main cam shaft is rotated such that the lobe of the main cam 21 is in contact with the cam followers 8, 9, which causes the main rocker arm 6 to tilt and the valve 4 to lift over a distance x 1 ; again similar to figure 3B. In figure 4C, the main cam shaft 20 is rotated further, such that the lobe of the auxiliary cam 23 is in contact with the auxiliary cam follower 28. In contrast to figure 3C, the auxiliary rocker arm 25 can not pivot down, as it is locked to the main rocker arm 6 by the pin 29. So, as a result, the main rocker arm 6 will be pivoted by the profile of the auxiliary cam 23, such that the valve 4 is still lifted over a distance x 2 . In this position, the main cam followers 8, 9 will no longer be in contact with the main cam 21 , and only the auxiliary cam follower 28 will have direct contact with the auxiliary cam 23.

By selecting a suitable profile for both the main cam 21 and the auxiliary cam 23, one can provide a desired valve lift and timing for the locked state and the unlocked state.

As the latch 12, 13 of each valve 2, 3, 4, 5 is controlled by a separate selector cam 14, 15 one can also provide a desired locking and unlocking pattern by providing the correct profile to the selector cams 14, 15.

In figure 1 and 2, the cam 14 is shown with a substantially sector shaped profile, while cam 15 has a substantially oval profile. As a result, one can obtain the following states by rotating the auxiliary cam shaft 16 in steps of 90°: both valves 2, 3 unlocked; valve 2 unlocked, valve 3 locked; valve 2 locked, valve 3 unlocked; both valves 2, 3 locked.