EP1985816A1

EP1985816A1 - System for continuously varying the lift and the phase of the valves in an internal combustion engine

Info

Publication number: EP1985816A1
Application number: EP08152053A
Authority: EP
Inventors: Giovambattista Vaccaro
Original assignee: Piaggio and C SpA
Current assignee: Piaggio and C SpA
Priority date: 2007-03-05
Filing date: 2008-02-28
Publication date: 2008-10-29
Also published as: CN101260818A; ITMI20070443A1; TW200905062A

Abstract

The invention describes a system for continuously varying the lift and the phase of the valves in an internal combustion engine of the type comprising at least one camshaft (22) provided with at least one pair of cams (26), at least one intake valve (10) and at least one discharge valve (12) each commanded by a rocker arm (14) provided with a roller (16). Each rocker arm (14) is commanded by the respective cam (26) of the camshaft (22) through the interposition of at least one intermediate rocker arm (24). In this way, the system is able to simultaneously and completely mechanically vary both the lift and the phase of the valves of an internal combustion engine.

Description

The present invention refers to a system for continuously varying the lift and the phase of the valves in an alternating internal combustion engine.
As known, in internal combustion engines the opening and closing of the intake and discharge valves of each cylinder is commanded by special eccentrics, known as cams, normally fitted onto a so-called camshaft. The camshaft is actuated by the drive shaft, with respect to which it rotates at half the angular speed and to which it is connected through a chain or a belt or else, more rarely, through a cascade of gears.
The shape of the eccentrics is a defining characteristic for the performance of an engine, since it has an influence both on the opening time, or phase, of each valve, and upon the excursion, expressed in millimetres, of the valve itself. Moreover, the shape of the eccentrics is also a defining characteristic for the noisiness of the engine, since it regulates the impact between the valves and the respective seats.
For the regulation of the phases of each valve known devices have therefore been made like phase variators, which indeed allow the opening time of the valves themselves to be varied. By increasing such an opening time for the valve or the intake valves of each cylinder there is greater filling of the combustion chamber, with a consequent increase in the power delivered. The variation of the discharge phase, on the other hand, allows the crossing over of valves, in other words the phase in which both the intake valves and the discharge valves are open simultaneously after the burning of the mixture, to be increased, so that the unburnt gases are expelled outside of the chamber thanks to the entry of the new mixture. In this delicate phase a small percentage of mixture is lost, but the advantage that is obtained is a good washing of the combustion chamber that thus, at each burn, is always clean and cooled as it should be.
In order to modify the excursion of the valves , on the other hand, it is possible to foresee suitable lift variators that, usually through hydraulic actuation means, are able to increase or decrease the excursion of the valves themselves, thus allowing the power delivered by the engine to be best adjusted.
Such valve control systems, normally made separately and with different technologies, are however expensive and delicate, especially when actuated hydraulically, and therefore are only intended for use on certain high-performance vehicles.
The purpose of the present invention is therefore to make a system that is able to simultaneously and completely mechanically vary both the lift and the phase of the valves of an internal combustion engine.
Another purpose of the invention is to make a system for continuously varying the lift and the phase of the valves in an internal combustion engine that is quick and simple to adjust.
These purposes according to the present invention are accomplished by making a system for continuously varying the lift and the phase of the valves in an internal combustion engine as outlined in claim 1.
Further characteristics of the invention are outlined by the subsequent claims.
The characteristics and advantages of a system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention shall become clearer from the following description, given as a non-limiting example, referring to the attached schematic drawings, in which:

figure 1 is a front view of a first example embodiment of the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention;
figure 2 is a side view of the system shown in figure 1;
figure 3 is a rear view of the system shown in figure 1;
figures 4 to 6 are perspective views of the system shown in figure 1;
figure 7 is a front view of a second example embodiment of the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention;
figure 8 is a side view of the system shown in figure 7;
figure 9 is a rear view of the system shown in figure 7;
figure 10 is a front view of a third example embodiment of the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention;
figure 11 is a side view of the system shown in figure 10;
figure 12 is a rear view of the system shown in figure 10;
figure 13 is a front view of a fourth example embodiment of the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention;
figure 14 is a side view of the system shown in figure 13;
figure 15 is a rear view of the system shown in figure 13; and
figures 16 to 18 are perspective views of the system shown in figure 13.

With reference to figures 1 to 6, a pair of valves belonging to a generic internal combustion engine (not shown) is shown, which can be equipped with one or more cylinders. Such valves 10 and 12, which can be for intake or else discharge, have a first embodiment of the system for continuously varying the lift and phase according to the present invention applied to them.
Each valve 10, 12 is directly commanded by a rocker arm 14, of the so-called finger type, provided or not with a roller 16 for reducing friction. In the example embodiment illustrated, the clearances of each valve 10, 12 can be controlled through a hydraulic recovery mechanism 18. In addition, between each valve 10, 12 and the respective finger rocker arm 14 a capsule or tablet 20 (figure 6) can possibly be arranged for adjusting the clearances.
Each finger rocker arm 14 is in turn commanded by the camshaft 22 through the interposition of a second rocker arm 24, or intermediate rocker arm. In practice, each cam 26 actuates the relative intermediate rocker arm 24 that transmits the motion to the finger rocker arm 14 and, consequently, to the valves 10 and 12.
The intermediate rocker arm 24 has the special characteristic of having the contact surface 28 with the roller 16 of the finger rocker arm 14 equipped with a specific profile. In detail, at least one portion 28a of such a contact surface 28, in other words the portion along which the motion for adjusting/varying the phase and the lift, has its centre of curvature coinciding with the rotation axis C of the camshaft 22, as can be seen in figure 2. A second portion 28b, possibly not present, of the contact surface 28, on the other hand, has a different centre of curvature to the centre C. What has been stated up to now is only valid should the contact between the roller 30 of the intermediate rocker arm 24 and the relative cam 26 of the camshaft 22 take place along the base circle of the cam 26 itself. Should the second portion 28b of the contact surface 28 be present, its curvature can also not be constant.
Each intermediate rocker arm 24 is hinged on a pin 32 supported by a support 34. In turn, the support 34 is hinged on the camshaft 22, with the possibility of rotating with respect to it, and it is formed of a top part 34a and a bottom part 34b, joined together by means of a plurality of screws 36.
The maintaining of the contact between each roller 30 and the relative cam 26 is aided by the action of a spring 38 fixedly connected to each intermediate rocker arm 24. Such a spring 38 has a fixed reaction point on the support 34 and is housed on the support 34 itself. The axial check of the intermediate rocker arm 24 is thus carried out through a washer 40 and a stop ring 42 of the Seeger^® type, both applied in a position opposite that in which the spring 38 is located.
The angular positioning of the support 34 and, consequently, of the intermediate rocker arms 24 is carried out through a control eccentric 44 fixedly connected to a drive shaft 46 supported by the structure of the head (not shown) of the engine. The camshaft 22 and the seats 48 of each valve 10, 12 are also supported, in a conventional manner, on the head. The eccentric 44 is engaged by pressure with a control roller 50 hinged onto the support 34. The contact between the eccentric 44 and the control roller 50 is kept constant thanks to the action of a spring 52, connected to the support 34 and having a fixed reaction point on the head of the engine or on another fixed component.
Therefore, according to the position taken up by the eccentric 44 and, consequently, by the support 34 of the intermediate rocker arms 24, it varies the relative angular position between the camshaft 22 and the intermediate rocker arms 24 themselves. Such a variation in the angular position, during the actuation of each valve 10, 12 and with respect to a predetermined initial position, or start position, shall create a dephasing of the lift law.
In addition, again with respect to the start position, it is possible to obtain a variation of the lever arm with which the intermediate rocker arm 24 actuates the rocker arm 14 for commanding the valves 10 and 12. By virtue of such an arm variation there shall be a lift variation of each valve 10, 12.
The correct sizing of the portions 28a and 28b of each contact surface 28, as well as of the cams 26 and the relative orientation between the pairs of command and intermediate rocker arms 14, 24, shall achieve the desired relationship between the variation in lift and the variation in phase of each valve 10, 12, and without affecting the predetermined maximum and minimum lift range.
Figures 7, 8 and 9 show a second example embodiment of the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention. In this example embodiment, the command rocker arm 14 of each valve 10, 12 lacks the hydraulic clearance recovery mechanism 18. The command rocker arm 14 is thus pivoted on a pin 54, supported by the structure of the head or else by another member that is fixed with respect to the engine. The adjustment of the clearances can be carried out through a suitable calibrated thickness 56 (figure 7) arranged between each valve 10, 12 and the relative command rocker arm 14.
Figures 10, 11 and 12, on the other hand, show a third example embodiment of the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention. In this example embodiment, in which there may or may not be the hydraulic clearance recovery mechanism 18, the angular positioning of the support 34 and of the intermediate rocker arms 24 hinged onto it takes place through a gearwheel sector 58 applied onto the support 34 itself. For controlling the variation system, the gearwheel sector 58 is able to operate both autonomously, and through the interposition of reducing gears.
Finally, figures 13 to 18 show a fourth example embodiment of the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention, intended in particular for being used on racing engines. The system illustrated in such figures is conceptually identical to the previous ones, but it is specifically designed to keep the mass to a bare minimum.
Each valve 10 and 12 is still directly commanded by the finger rocker arm 14, in turn actuated by the intermediate rocker arm 24 that receives the motion from the camshaft 22. Each intermediate rocker arm 24 is thus hinged on the relative pin 32 supported by the support 34.
In this example embodiment, each finger rocker arm 14 is hinged, at an end thereof, on a small shaft 60 fixedly connected to the head of the engine, whereas the support 34 of the intermediate rocker arms 24 is again configured in such a way as to be able to rotate about the camshaft 22. In particular, the support 34 is provided, in addition to the rotation seat on the camshaft 22, with a further circular surface portion or raceway 62 concentric to the rotation axis of the camshaft 22 itself. The support 34 can thus rotate about the camshaft 22 making the raceway 62 slide on the circular portion 44a of the control eccentric 44 that, in this example embodiment, is rigidly fixed, removably or not, onto the small pivoting shaft 60 of the command rocker arms 14. Therefore, in this particular example embodiment, the small shaft 60, free to rotate in its own support seat and with respect to the rocker arms 14, also acts as a drive shaft, thus contributing to reducing the number of components and, therefore, the mass.
The rotation of the small shaft 60 pulls with it the control eccentric 44, which sets the angular position of the support 34 through the effect of the contact of a portion 44b thereof with a roller 64 (figure 18) hinged onto the support 34 itself. Therefore, as the angular position of the control eccentric 44 varies, the support 34 shall take up different positions around the camshaft 22 taking the intermediate rocker arms 24 with it.
The preloading spring 52, hooked to the support 34 and connected to the structure of the head or to another fixed member, shall keep the contact between the roller 64 and the control eccentric 44 constant, thus making the adjustment of the position of the support 34 and, consequently, of the lift and phasing of the valves 10 and 12 stable.
The correct clearance between the base circle of each cam 26 and the relative intermediate rocker arm 24 can be adjusted by the screw system 36 of the support 34 that, in this embodiment, is formed of a single piece and stays in position because it is held by the contact with the roller 64, by the contact between the raceways 62 and the raceways 44a, and with the housing on the cam axis 22.
The system illustrated in figures 13 to 18 can also be made in further configurations, whilst still respecting the same operating principle. For example, the portion 44b of the control eccentric 44 could be replaced by a small gearwheel, without affecting the containment function performed by the circular portion 44a of the control eccentric 44 itself. Such a gearwheel could engage with a toothed sector present on the support 34 instead of the roller 64.
It has thus been seen that the system for continuously varying the lift and the phase of the valves in an internal combustion engine according to the present invention achieves the purposes highlighted previously, being able to simultaneously and completely mechanically vary both the lift and the phase of the valves of an internal combustion engine.
The system for continuously varying the lift and the phase of the valves in an internal combustion engine of the present invention thus conceived can in any case undergo numerous modifications and variants, all of which are covered by the same inventive concept; moreover, all of the details can be replaced by technically equivalent elements. In practice, the materials used, as well as the shapes and sizes, can be whatever according to the technical requirements.
The scope of protection of the invention is therefore defined by the attached claims.

Claims

System for continuously varying the lift and the phase of the valves in an internal combustion engine of the type comprising at least one camshaft (22) provided with at least one pair of cams (26), at least one intake valve (10) and at least one discharge valve (12) each commanded by a rocker arm (14) provided with a roller (16), characterised in that each of said rocker arms (14) is commanded by the respective cam (26) of said camshaft (22) through the interposition of at least one intermediate rocker arm (24).
System according to claim 1, characterised in that at least one first portion (28a) of the contact surface (28) of said intermediate rocker arm (24) with said roller (16) of each rocker arm (14) has a centre of curvature coinciding with the rotation axis (C) of said camshaft (22).
System according to claim 2, characterised in that said contact surface (28) has at least one second portion (28b) having a different centre of curvature to said centre of curvature (C) of said at least one first portion (28a).
System according to claim 1, characterised in that each of said intermediate rocker arms (24) is hinged on a pin (32) supported by a support (34).
System according to claim 4, characterised in that said support (34) is hinged on said camshaft (22), with the possibility of rotating with respect to it.
System according to claim 5, characterised in that said support (34) is formed of a top part (34a) and a bottom part (34b) joined together by means of a plurality of screws (36).
System according to claim 4, characterised in that the maintaining of the contact between the roller (30) of each of said intermediate rocker arms (24) and the relative cam (26) is aided by the action of a spring (38) fixedly connected to each of said intermediate rocker arms (24).
System according to claim 7, characterised in that said spring (38) has a fixed reaction point on said support (34) and is housed on said support (34).
System according to claim 7, characterised in that the axial check of each of said intermediate rocker arms (24) is obtained through at least one washer (40) and at least one stop ring (42).
System according to claim 9, characterised in that said at least one washer (40) and said at least one stop ring (42) are applied in a position opposite that where said spring (38) is located.
System according to claim 4, characterised in that the angular positioning of said support (34) and of said intermediate rocker arms (24) is carried out through at least one control eccentric (44) fixedly connected to a drive shaft (46) supported by the structure of the head of said internal combustion engine.
System according to claim 11, characterised in that said control eccentric (44) is engaged by pressure with a control roller (50) hinged on said support (34).
System according to claim 12, characterised in that the contact between said control eccentric (44) and said control roller (50) is kept constant thanks to the action of a spring (52) connected to said support (34) and having a fixed reaction point on said head of said internal combustion engine.
System according to claim 1, characterised in that the clearances of each of said valves (10, 12) can be controlled through a hydraulic recovery mechanism (18).
System according to claim 14, characterised in that between each of said valves (10, 12) and the respective rocker arm (14) at least one capsule or tablet (20) is arranged to adjust the clearances.
System according to claim 1, characterised in that the clearances of each of said valves (10, 12) can be controlled through a calibrated thickness (56) arranged between each of said valves (10, 12) and the respective rocker arm (14).
System according to claim 4, characterised in that the angular positioning of said support (34) and of said intermediate rocker arms (24) is carried out through at least one gearwheel sector (58) applied onto said support (34).
System according to claim 17, characterised in that said gearwheel sector (58) is able to operate through the interposition of reducing gears.
System according to claim 4, characterised in that each of said rocker arms (14) is hinged, at an end thereof, on a small shaft (60) fixedly connected to the head of said internal combustion engine.
System according to claim 19, characterised in that said support (34) is provided, as well as the rotation seat on said camshaft (22), with a further circular surface portion or raceway (62) concentric to the rotation axis of said camshaft (22).
System according to claim 20, characterised in that said support (34) rotates around said camshaft (22) making said raceway (62) slide on the circular portion (44a) of a control eccentric (44) rigidly fixed on said small shaft (60).
System according to claim 21, characterised in that the rotation of said small shaft (60) pulls said control eccentric (44) with it, which sets the angular position of said support (34) through the effect of the contact of a portion (44b) of said control eccentric (44) with a roller (64) hinged onto said support (34).