Abstract
A switchable rocker arm to control the lift of a valve bridge or of a single valve of a valve train group of an internal combustion engine; the switchable rocker arm being able to rotate around a first axis and comprising: a cam body, which is configured to be rotated by a cam; a valve body, which is configured to act upon the valve bridge or the single valve; wherein the switchable rocker arm can selectively be switched between a first configuration, in which the rotation of the cam body around the axis generates a movement of the valve body, and a second configuration, in which the rotation of the cam body around the axis does not generate any movement of the valve body.
Claims
1. A switchable rocker arm for controlling the lift of a valve bridge or of a single valve of a valve train group of an internal combustion engine; the switchable rocker arm being rotatable around a first axis and comprising: a cam body configured to be driven in rotation by a cam about the first axis; a valve body configured to act on the valve bridge or on the single valve; wherein the switchable rocker arm is selectively switchable between a first configuration, in which the rotation of the cam body about the first axis generates a movement of the valve body about the first axis; and a second configuration in which the rotation of the cam body about the first axis it does not generate any movement of the valve body; characterized in that inside the cam body or the valve body a cylinder is obtained for housing a sliding shaped piston movable between a first position and a second position; the switchable rocker arm comprising a locking device which cooperates with the shaped piston and configured in such a way that: in the first position of the piston the locking device acts simultaneously on the cam body and on the valve body so as to constrain the switchable rocker arm in the first configuration; in the second position of the piston the locking device enters the cylinder so that the switchable rocker arm is in the second configuration.
2. The switchable rocker arm as claimed in claim 1, wherein the locking device comprises two balls movable along a second axis parallel to the first axis depending on the position of the piston for moving from the first position, wherein the balls act simultaneously on the cam body and on the valve body to constrain the switchable rocker into the first configuration, to a second position wherein the balls penetrate inside the cylinder so that the switchable rocker is in the second configuration and vice-versa.
3. The switchable rocker as claimed in claim 1, wherein the locking device comprises a pin having a second axis parallel to the first axis.
4. The switchable rocker as claimed in claim 2, wherein the cam body comprises a roller having a third axis parallel to the first axis and in contact with the cam; the distance between the first axis and the second axis being more than 0.75 times the distance between the first axis and the third axis.
5. The switchable rocker arm as claimed in claim 1, wherein the shaped piston is hydraulically actuated, a spring configured to force the piston into the first position being provided.
6. The switchable rocker arm as claimed in claim 1, wherein inside the cylinder a mobile collar is provided around a steam of the piston; the piston and the collar being configured so that for passing from a first to a second position the piston prior performs a first movement forced by the movement hydraulically driven of the collar and after it performs a second movement with the collar fixed forced by the penetration of the locking device inside the cylinder.
7. The switchable rocker as claimed in claim 6, wherein the collar comprises a bottom configured for acting on a lip of the piston during the oil supply inside the cylinder for pushing the piston during the first movement.
8. The switchable rocker as claimed in claim 7, wherein inside the cylinder an end-stop for the collar is provided in a position so that, at the end of the stroke of the collar, the shaped portion of the piston is only in part facing the locking device, the locking device penetrating inside the cylinder generating the second movement of the piston.
9. The switchable rocker arm as claimed in claim 1, between the cam body and the valve body a spring is provided and configured to force the switchable rocker arm in the first configuration.
10. A valve train group for controlling the valve lift of an internal combustion engine, the valve train group comprising: a camshaft; a plurality of rocker arms driven by the camshaft to control the valve lift; wherein at least one of the rocker arms is a switchable rocker according to claim 1.
11. Valve train assembly as claimed in claim 10, wherein the valve train assembly comprises a plurality of inlet valve bridges and a plurality of exhaust valve bridges; at least one switchable rocker arm being provided coupled to an exhaust valve bridge.
12. Valve train assembly as claimed in claim 1, wherein the valve train assembly comprises at least one switchable rocker arm coupled to an intake valve bridge.
13. Valve train assembly as claimed in claim 1, wherein the valve train assembly comprises at least one engine brake rocker arm coupled to an exhaust valve.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Further features and advantages of the invention will be best understood upon perusal of the following description of a non-limiting embodiment thereof, with reference to the accompanying drawings, wherein:
[0027] FIG. 1 shows an example of a valve train group comprising a plurality of switchable rocker arms according to the invention;
[0028] FIG. 2 shows an enlarged portion of the valve train assembly of FIG. 1;
[0029] FIG. 3 shows a first example of a switchable rocker arm according to the invention;
[0030] FIG. 4 shows an exploded view of the switchable rocker arm of FIG. 3;
[0031] FIGS. 5 and 6 shown two cross sections of the switchable rocker arm of FIG. 3;
[0032] FIG. 7 shows a second example of a switchable rocker arm according to the invention;
[0033] FIG. 8 shows a sectional view of the switchable rocker arm of FIG. 7;
[0034] FIGS. 9 and 10 show the sectional view of FIG. 8 in two different use configurations;
[0035] FIG. 11 shows a third example of a switchable rocker arm according to the invention;
[0036] FIG. 12 shows a sectional view of the switchable rocker arm of FIG. 11;
[0037] FIG. 13 shows a side view of a rocker arm of the type of FIG. 3, in which a geometric/mechanical condition required by the invention is shown;
[0038] FIGS. 14 and 15 show a novel piston device which can be used in cooperation with the locking balls or pin, said novel piston device needing a smaller oil volume for the deactivation of the rocker arm;
[0039] FIGS. 16 and 17 show a comparison of the oil volume needed for the deactivation of the rocker arm with a known and with a novel piston device.
BEST MODE FOR CARRYING OUT THE INVENTION
[0040] With reference, in detail, to the figures listed above, FIG. 1 shows an example of a valve train group (indicated, as a whole, with number 1) comprising a plurality of switchable rocker arms according to the invention. Said valve train group 1 is configured to control the lift of the valves of an internal combustion engine, which are partly visible in FIG. 1. In particular, FIG. 1 shows a cylinder head 2 of the engine, where there are obtained six in-line cylinders, which house, on the inside, movable pistons. The way in which an internal combustion engine works is very well known and, therefore, no further details are needed. In the example of FIG. 1, each cylinder is provided with two intake valves and with two exhaust valves. The lift cycles of these valves are traditional cycles of a 4-stroke engine and, in general, said lifts are operated by suitable rocker arms, which, in turn, are operated by a camshaft. The general operation of these rocker arms is known as well. In FIG. 1, number 3 indicates the exhaust valve bridges, each supporting two exhaust valves 4. Number 5 indicates the intake valve bridges, each supporting two intake valves 6. An exhaust rocker arm 7 acts upon each exhaust valve bridge 3. Even though FIG. 1 does not show details, each one of said exhaust rocker arms 7 is a switchable rocker arm according to the invention. An intake rocker arm 8 acts upon each intake valve bridge 5. In the example shown herein, the three intake rocker arms on the left are switchable rocker arms according to the invention, whereas the three remaining intake rocker arms on the right are known, non-switchable rocker arms. In the example of FIG. 1, the valve train group 1 further comprises 6 engine brake rocker arms 9, each acting upon an exhaust valve 4 of a cylinder. As already mentioned above, the example of FIG. 1 is just an example of the many possible combinations included in the invention. Indeed, the only condition the valve train group 1 has to fulfil is that of comprising a switchable rocker arm according to the invention, regardless of whether it is an exhaust or intake rocker arm or whether it acts upon a valve bridge or a single valve. The presence of engine brake rocker arms is not necessary either. However, the example shown herein proves to be very effective because, as it is known, it enables double braking phases per cycle and allows the engine cycles to be controlled in a very refined manner. Finally, number 10 of FIG. 1 indicates three oil supply valves. Said three valves, when needed, supply oil to the engine brake rocker arms and to the switchable rocker arms in a coordinated manner based on the needs of the manufacturer. A peculiar aspect of the invention concerning the three valves 10 lies in the fact that said valves are structurally identical to one another and the relative supply of oil to the different rocker arms only depends on the presence or absence of possible ducts obtained in the rocker arms. Indeed, where one of the different holes of the valve faces an inner duct of a rocker arm, the supply can take place, whereas, where there is no coupling, the supply cannot take place due to the lack of a duct on the inside of the rocker arm. By mere way of example, the left valve 10 supplies the three switchable intake rocker arms, the intermediate valve 10 supplies the three switchable exhaust rocker arms on the left, the right valve 10 supplies the three switchable exhaust rocker arms on the right and the six engine brake rocker arms. By operating the right valve and the intermediate valve, a control logic is activated; by operating the left valve and the intermediate valve, a different control logic is activated.
[0041] FIG. 2 shows an enlarged portion of a portion of FIG. 1, namely the rocker arms associated with the left cylinder. This figure shows constructive details of a sub-assembly of FIG. 1, in which both the exhaust rocker arm 7 and the intake rocker arms 8 are switchable rocker arms according to the invention. Both rocker arms as well as the engine brake rocker arm 9 can rotate around the common axis A1, which is parallel to the axis of the camshaft.
[0042] FIGS. 3-6 show a first example of a switchable rocker arm according to the invention. Even though said rocker arm can be the rocker arm indicated with numbers 7 or 8 in the preceding figures, hereinafter, for the sake simplicity, number 11 will always be used for each switchable rocker arm according to the invention. The numbers indicated above were only used to highlight the multiple possible applications of the invention in a valve train group. In the example of FIGS. 3-6—and in general in the invention—the switchable rocker arm 11 comprises two bodies, a valve body 12 and a cam body 13 respectively, which cooperate with a valve or bridge valve and with a cam respectively. Like in known switchable rocker arms, the two bodies 12 and 13 are coupled to one another so as to assume two different configurations. In the first configuration, the rotation transmitted by the cam to the cam body 13 around the axis A1, namely around the axis of the shaft supporting the rocker arm, generates a movement or rotation of the valve body 12 around the axis A1 and, consequently, the lift of the valve or valve bridge is operated based on the profile of the cam. In the second configuration, the rotation transmitted to the cam by the cam body 13 around the axis A1 does not generate any movement of the valve body 12 and, hence, the lift of the valve or of the valve bridge is not operated based on the profile of the cam (actually, the lift is not operated at all). In a standard or non-switchable rocker arm, the two bodies 12 and 13 are always integral to one another or even manufactured as one single piece. For the purposes of this invention, the term “body” does not necessarily mean one single mechanical body, but it can also identify a plurality of components, which, however, once they are assembled, are always integral to one another. In that sense, FIG. 4 shows how, in this example, the cam body 13 is manufactured by joining two half-shells 14, whereas the valve body substantially is one single piece with the sole addition of a contact tip 15, which comes into contact with the valve or the valve bridge. Numbers 16 and 17 indicate the roller (having a third axis A3 parallel to the axis A1) coming into contact with the cam and a rotation bearing of the rocker arm, both of them being known elements. On the other hand, peculiar elements of the invention are indicated with numbers 18, 19, 20 and 21. According to FIGS. 5 and 6, number 19 indicates a movable piston, which is housed inside a cylinder 22 obtained in the valve body 12. The position of the cylinder 22 can change based on constructive needs. Said piston is hydraulically operated by the oil supplied by the valve 10 and, hence, is movable in the cylinder between a first and a second position. An inventive piston, or piston device, will be described below. The spring 20 forces the piston 19 in the first position, so that, in the absence of oil, the piston always is in said first position. Number 21 indicates 2 balls arranged in opposite positions relative to the piston 19. According to FIG. 6, which shows the first position of the piston 19, in this configuration the balls 21 are housed between the bodies 12 and 13 and are held in this position, on one side, by the piston 19 and, on the other side, by a semi-spherical seat 23 obtained in the cam body 13. Hence, when the piston 19 is in said position, the balls 21 are locked as shown in the figure and act as structural bridge between the bodies 12 and 13, so that the rotation of the cam body 13 operated by the cam generates, through dragging, a movement of the valve body 12. There are no further mechanical bridge elements between the two bodies, besides the aforesaid balls 21. When the piston 19 is lifted (namely, when the valve 10 is activated so as to supply oil into the cylinder), the latter moves so as to allow a portion with a reduced thickness 23 to reach the area of the balls 21. Said reduced thickness 23 is configured so as to allow the balls 21 to penetrate the cylinder 22. In this configuration, the balls 21 move along the axis A2 (shown in FIG. 6), which is parallel to the axis A1, towards the inside of the cylinder and do not cooperate any longer with the cam body 13 in order to transmit the motion to the valve body 12. In this condition, the rotation of the cam body 13 due to the cam, which takes place around the axis A1, does not generate a corresponding movement of the valve body 12. Finally, number 18 indicates a spring, which is designed to hold the two bodies 12 and 13 assembled together.
[0043] FIGS. 7-10 show a second example of a switchable rocker arm according to the invention. This example uses the same reference numbers used in the description of the preceding example, as the mechanical components are the same. The difference between the two examples solely lies in the profile of the bodies, due to different mechanical side conditions, and in the space arrangement of the spring 18, of the piston 19 and of the balls 21. However, the operation of this example is exactly the same as the one of the preceding example. FIG. 10 further shows the second configuration with the balls 21 housed in the cylinder 22, which was not shown in the preceding example. Number 24 indicates the channel supplying oil to the cylinder 22.
[0044] FIGS. 11 and 12 show a third embodiment of the invention. In this example, which is structurally similar to the preceding example, the balls 21 are no longer present and are replaced by a pin 25 with an axis orthogonal to the one of the piston 19 and integral to the cam body 13. In this example, again, in the first configuration (visible in detail in FIG. 12), the pin 25 is at an opening of the cylinder 22 striking against the piston 19 so that, like the balls, it can act as mechanical bridge between the bodies 12, 13 and, hence, the rotation of the cam body generates a movement of the valve body. In this example, again, the piston 19 has a portion with a reduced thickness. In particular, in this case, the portion with a reduced thickness creates a C-shaped seat housing the pin 25, so that, in the second position of the piston 19, the pin is housed in the cylinder 22 and, like the balls, does not drag the valve body 12 during the rotation of the cam body 13.
[0045] FIG. 13 shows a side view of a rocker arm of the type of FIG. 3, in which a geometric/mechanical condition required by the invention is shown. The condition set by the invention is that the distance A between the first axis A1 (only rotation axis of the rocker arm) and the second axis A2 (movement axis of the balls or of the pin) is greater than 0.75 times the distance B between the first axis A1 and the third axis A3 of the roller 16. This condition ensures that the stress affecting the balls or the pin in the active rocker arm configuration does not exceed threshold values, which could lead to a damaging of the device itself.
[0046] FIGS. 14 and 15 show a novel piston device, which can be used in cooperation with the locking balls 21 or pin 25. As mentioned above, the shaped piston 19 is movable between a first position (FIG. 14) and a second position (FIG. 15), in which it holds the balls 21 (or the pin) in the activation position or deactivation position of the rocker arm, respectively. The inventive aspect introduced thereby concerns the activation of the movement of the piston 19. As mentioned above, there is a spring 20, which forces the piston 19 in the activation position and the activation is hydraulic, namely oil under pressure is introduced into the cylinder 22 in order to force the movement thereof. According to the invention, the piston 19 of FIG. 5 becomes a “piston device” and, in an inventive manner, it is manufactured in two pieces, namely in the cylinder 22 there is a movable collar 30, which is cup-shaped and is fitted on the rod of the piston 19. The piston 19, at first, is dragged by the collar 30 and, then, can slide relative to the collar 30 in the following manner. The collar 30 comprises a bottom 31, which, when operated by the oil introduced into the cylinder 22, acts so as to strike against a lip 32 of the piston 19. On the opposite side (the one facing the balls 21), the collar 30 is open so as to enable a relative movement of the piston 19 allowing it to get closer to the balls 21. The starting position (FIG. 14) of the collar 30 and of the piston 19 is maintained by the spring 20. In order to deactivate the rocker arm, oil under pressure is introduced into the cylinder 22 upstream of the collar 30 (in the chamber indicated with 33 in FIG. 15, on the opposite side relative to the balls). Said oil under pressure generates the movement of the collar 30 towards the balls 21 and, as a consequence, a first movement (which is a dragging movement, due to the oil) of the piston 19. The piston 19 can slide relative to the collar towards the balls and the shaped seat of the piston simply needs to face the balls 21 penetrating the cylinder 22 in order to generate a second movement of the piston 19 (which is dragging movement, due to the balls) when the collar 30 is standing still. A suitable end stop element 34 is provided in order to stop the stroke of the collar as indicated above. Hence, the second part of the movement of piston is not due to a further oil volume introduced, but is generated by the balls (or by the locking device in general) after the first initial movement caused by the short movement of the collar 30. In order to re-activate the rocker arm, oil simply needs to be removed upstream of the collar 30. In the absence of this hydraulic thrust, the spring 20, at first, causes the piston 19 to strike again against the bottom 31 of the collar 30 and, then, drags both bodies 19, 30 to their original position in which the balls 21 are out of cylinder 22 activate the rocker arm.
[0047] FIGS. 16 and 17 show a comparison of the oil volume needed for the deactivation of the rocker arm with a one-piece piston and with a novel piston device with sequential sliding or with two pieces. Evidently, the oil volume needed (references 35 and 36 in FIGS. 16 and 17) with the novel piston device does not correspond to the one needed in the absence of collar and is much smaller than that. In the example shown herein, the improved version of the piston device needs approximately ⅓ of the oil needed by the one-piece piston in the same conditions, namely the volume to be filled with oil in the cylinder is circa ⅓ of the original volume.
[0048] Finally, it is clear that the invention described herein can be subjected to changes and variations, without for this reason going beyond the scope of protection of the appended claims. As a matter of fact, the main aspect shared by all the examples of the invention is the presence of one single rotation axis of the rocker arm A1, of the geometric condition setting a ratio between the distance of the axes A1-A2 and A1-A3 and of the movable piston (preferably of the novel two-piece piston device), which is housed inside only one of the bodies and, when operated, allows a locking element or mechanical bridge (preferably, in the form of balls or pin as shown herein) to penetrate the cylinder. Preferably, and for safety reasons, the system is configured so that, in the absence of oil, it steadily is in the first configuration (integral bodies). The rocker arm according to the invention can have multiple applications in a valve train group. In the example shown herein, with six in-line cylinders, all the exhaust rocker arms and three intake rocker arms are switchable rocker arms according to the invention and cooperate with six engine brake rocker arms. In order to allow for many different applications without multiplying costs, the invention also entails using oil supply valves that are all the same and each time intercept different supply channels depending on the nature of the rocker arms.
