EP2268912A2

EP2268912A2 - Egr valve for exhaust gas recirculation to the intake manifold of internal combustion engines

Info

Publication number: EP2268912A2
Application number: EP09723562A
Authority: EP
Inventors: Pierluigi Dell'orto; Mario Marchetti; Salvatore Iovino
Original assignee: Dell Orto SpA
Current assignee: Dell Orto SpA
Priority date: 2008-03-17
Filing date: 2009-03-16
Publication date: 2011-01-05
Also published as: WO2009115975A2; ITMI20080450A1; WO2009115975A3

Abstract

The invention concerns a valve assembly for the recirculation of the exhaust gases of an internal combustion engine, to an intake manifold of the engine, through a by-pass or respectively through a cooling device. The valve assembly comprises means for the deviation of an adjusted amount of exhaust gases, from a single inlet of exhaust gases (Gsc) to two outlets (13b, 14b), controlled by two distinct closing valves (13, 14), pushed by respective spring means (16). A single actuation means (21; 20, 36, 37; 42; 47; 20, 48, 49; 51) controls alternatively either one of said valves (13, 14), under the control of a single electric actuator (19, 25), controlled by an electronic central control unit, in association with a single position sensor (22, 30). The actuation means comprises a single rotary shaft (20, 43, 46, 52), whereon a rocker arm (21, 42, 47,51) is keyed, or a pair of cams (36,37; 48, 49) having angularly offset profiles, the two arms of the rocker arm, or the two cams, respectively, being apt to act on either one, respectively, of said valves.

Description

"EGR VALVE FOR EXHAUST GAS RECIRCULATION TO THE INTAKE MANIFOLD OF INTERNAL COMBUSTION ENGINES"

*o*oOo*o* DESCRIPTION FIELD OF THE INVENTION

The present invention refers to a valve (so-called EGR valve) apt to control the recirculation of exhaust gases to the intake manifold of internal combustion engines,- more in particular, it is a valve which allows to deviate the recirculation of gases through a by-pass or alternatively through a cooling device. BACKGROUND ART

The problem linked to the need to reduce the emissions of polluting agents in exhaust gases of internal combustion engines has been known for some time: in order to meet anti-pollution regulations, which become ever more stringent in the automotive sector, exhaust gas recirculation systems have been developed which, by transferring to the combustion chamber (through the same intake manifold) the desired percentage of burnt gases, dilute the charge of incoming fresh air. This brings a two-fold advantage in the reduction of the polluting agents released by the engine: firstly, by subtracting part of the flow rate from exhaust gases, the mass of unburnt gases released into the atmosphere is reduced; secondly, the dilution of the charge of fresh air implies a dramatic reduction of the concentration of nitrogen oxides (NOx) at the exhaust, and this due both to the lower temperatures reached in the cylinder, and to the reduced presence of oxygen in the chamber at the time of combustion.

In internal combustion engines these systems provide a pipe for the recirculation of burnt gases, which draws these gases at the exhaust and transfers them to the entry of the combustion chamber. Along such pipe a valve is arranged, electrically driven by an electronic central unit; the opening of the valve is driven so as to adjust the quantity of burnt gases one wants to recirculate. A valve of this type is disclosed for example in document W02006/097884-A1 in the name of the same Applicant, reference whereto can be made for a better understanding of the function and of the building features of valves of this type. It is a structure with a mushroom-shaped valve, which is displaced axially, from a closed position to a more or less markedly open position, under the actuation of an electric actuator driven by a central electronic control unit.

More recently, the development of the exhaust gas recirculation techniques has highlighted the need for controlling not only the recirculated amount of exhaust gases, but also the temperature thereof. As a result, relatively more complex recirculation systems have been developed, wherein the exhaust gas, upstream or downstream the EGR valve, is caused to flow through temperature adjustment means. This adjustment is effected by causing the exhaust gases to flow through a circuit specially apt to perform this function, a diagram whereof is shown in fig.l herewith enclosed: it comprises an engine M with an intake manifold 1 and an outlet manifold 2, as well as an EGR valve 3 which draws a dosed amount of exhaust gas from manifold 2 and transfers it to the intake manifold 1. On the transfer path - and in this case downstream of the EGR valve - a cooling device 4 and a by-pass 5 are provided; control means (not shown) determine if said dosed amount of exhaust air must be transferred to the intake manifold directly, i.e. through bypass 5, or through cooling device 4. In documents DE-34.33.569, DE-101.33.182, EP-I.746.263 , and EP-I.468.184 valves are disclosed apt to perform this function of deviation of the exhaust gases to a cooling device or to a by-pass, respectively. All these known devices use a shutter which is capable of opening fully the passage of gases to cooling, closing the one to by-pass, or viceversa, or even of taking up an intermediate position for distributing the exhaust gas flow to both the cooling pipes and the by-pass pipes.

As can be understood, in such a system two control means must be provided, and precisely first motor means, which control the adjustment system of the opening of EGR valve 3 (adjustment of the amount of recycled gas) , and second motor means, which control the deviation of the flow of exhaust gases to the cooling device 4 or respectively to by-pass 5 (adjustment of the temperature of the recycled gas) . This solution evidently has the disadvantage of being relatively bulky and costly. The object of the present invention is therefore to propose a system which groups in a single building unit the two functions indicated above, using a single control actuator. In actual fact, an arrangement of this type is already proposed in document EP-O .994.247, where a single shutter can be brought to close both a valve seat of a pipe to a cooling device, and a valve seat of a pipe to a by-pass, or to close one thereof and to open the other one or viceversa. The object of the present invention is hence, more in detail, to propose a device which accomplishes this same function, but with simpler and better controllable means. This object, and further advantages, are obtained by a valve having the features described in claim 1.

Further features and advantages of the present invention are in any case more evident from the following detailed description of a preferred embodiment, given purely as a non-limiting example and shown in the accompanying drawings, wherein: fig. 1 is a diagrammatic view of circuit for the recirculation of burnt gases according to the known art, as described above; fig. 2 is a very diagrammatic vertical section of a first embodiment of a burnt gas recirculation valve according to the invention, provided with two valves, one for the recirculation to the by-pass and the other one for the recirculation to the cooling device, both in a closed position; fig. 3 is a perspective view of the same valve of fig.l, showing in a diagram the motion transmission for valve control; figs. 4 and 5 are views similar to that of fig. 2, with an open valve to the by-pass and respectively with an open valve to the cooling device; figs. 6 and 7 are section views, fully similar to those of figs. 2 and 4, of a different embodiment with a position sensor; figs. 8, 9, 10 are section views fully similar to that of fig. 2, but concerning some further embodiment variants of the recirculation valve according to the invention; figs. 11 and 12 are section views of a variant, similar to that of fig. 8, with both valves closed and respectively with one of the two valves open,- figs. 13 and 14 show, in a partial section and in a perspective view, respectively, another embodiment, with planetary gear set actuation; figs. 15, 16 and 17 show another embodiment variant again, with rotating-cam, desmodromic actuation, in a longitudinal section, in a transversal section and in a perspective view, respectively; figs. 18, 19 and 20 show another embodiment variant again, with desmodromic actuation having an oscillating driving sector, in a longitudinal section with two closed valves, in section with an open valve and in a perspective view, respectively;

As schematised more in detail in figs. 2 and 3, the recirculation valve assembly according to the invention consists of a lower part 11 and of an upper part 12. In the lower part there are provided the seats for two mushroom-shaped valves 13 and 14, each one associated with a respective spring means 16; said means acts through a cap 17, fastened to the upper end of the stem of each one of valves 13, 14. The action of springs 16 is such as to push valves 13, 14 upwards (with respect to the drawing) and to close the respective seats 13a, 14a.

These seats 13a and 14a represent two distinct openings for the entry of the exhaust gases coming from an exhaust pipe of engine M. This exhaust pipe is not shown in these drawings but rather in drawings 6 and 9, where it is referred to by Gsc. The opening of the one or the other valve 13 or 14 allows to channel said exhaust gases to either one of two outlets 13b (visible on the side of body 11) and 14b (provided on the back of body 11) , connected to two respective manifolds (not shown) to the by-pass or to the cooling device (also not shown) , respectively. In the upper part 2 the actuation members of the valve assembly are housed, i.e. an electric actuator 19 (for example a DC motor or a stepping motor, of a known type, placed under the control of an electronic central control unit) , which, according to the main feature of the invention, acts on the two valves 13, 14 through a shared actuation means . This actuation means consists - according to a first embodiment of the invention, shown in figures 2 to 5 - of a shaft 20, whereon a rocker arm 21 is keyed on. Shaft 20 is driven into rotation, by means of gear transmission 23, by actuator 19, electrically connected, through a connector 18, to said electronic control unit (not shown, since fully known per se) . The unit controls precisely the angle of rotation of actuator 19, and consequently that of rocker arm 21, based on a position signal of the same rocker arm. Such a position signal is provided by a rotational position sensor 22 (schematised in fig. 3), for example a Hall-effect sensor,- this sensor 22 is arranged in the proximity of an end of shaft 20, with which a magnetic element is associated. Figure 3 gives only a very schematic representation of this sensor, devoid of the corresponding support; this is to be understood as supported in a fixed position, for example fastened to the inner wall of a carter (not shown) .

The operation of this valve assembly occurs in the following way: a) the position shown in fig. 2 corresponds to the closed one of the EGR valve EGR, i.e. when no exhaust gas recirculation is required. In this case, both valves 13, 14 are pushed upwards by respective springs lβ and they rest on and close respective seats 13a, 14a,- rocker arm 21 lies in the horizontal position shown, wherein its two ends rest pressureless on the top of the valve stems, i.e. of caps 17, or they have a short play with respect to this top area; b) the position shown in fig. 4 corresponds to the open one of valve 13 , for the deviation of the exhaust gas recirculation flow to the by-pass ; this is the position which ensures that the EGR system send into recirculation the hot exhaust gases, as taken from outlet manifold 2. It can be clearly detected from fig. 4 that rocker arm 21 is in such a position that one of its arms - and precisely arm 21a, on the right hand side, with respect to the drawing - pushes valve 13 into an open position, against the action of respective spring 16; at the same time, arm 21b on the left hand side remains lifted from cap 17 of valve 14, so that said valve remains closed. It is understood that said actuator 19, or better, its electronic central control unit, is capable of moving more or less arm 21a, and consequently of opening more or less valve 13, depending on the amount of hot gases which one intends to send to engine M; c) the position shown in fig. 5 corresponds to the open one of valve 14, for the deviation of the exhaust gas recirculation flow to cooling device 4; this is the position which ensures that the EGR system sends into recirculation the cooled exhaust gases. Here too, it is clearly detectable from fig. 5 that rocker arm 21 is in such a position that its arm 21b (and precisely the left hand side arm, with respect to the drawing) pushes valve 14 into an open position, against the action of respective spring 16; at the same time, the right hand side arm 21a is raised from cap 17 of valve 13, so that said valve remains closed. The central control unit of said actuator 19 will be capable of displacing more or less arm 21b, and consequently of opening more or less valve 14, depending on the amount of cooled gases which one intends to send to engine M. Figures 6 and 7 show an embodiment variant wherein - instead of a rotational sensor 22 - a linear position sensor 30 is employed, which is capable of providing at any time, in an obviously much more direct way, as better described in the following, the exact open or closed position of valves 13 and 14, as well as of any other intermediate position; as said also above, this position indication is essential for the electronic central control unit of the EGR valve to be able to perform its function correctly.

Sensor 30 is arranged centrally between the two valves 13, 14 and has a rod 31, whereon a spring is arranged (not shown in the drawing, since it is inside the sensor itself) ,- such spring imparts such a force as to determine, in any operation condition, the contact between rod 31 and a matching block 32. Said block is driven - always in a central position between the two' valves - by a shaft 33, with which it is integral, and is pushed upwards, with respect to the drawing, by an own spring 34.

Both caps 17 at the top of springs 16 have an appendix 17a shaped as an enlarged edge; against the two opposite appendixes a matching block 32 rests from below, under the thrust of spring 34.

In the position shown in fig. 6 both valves 13 and 14 are closed, pushed upwards by the respective springs 16. Also matching block 32 is raised, under the thrust of respective spring 34, and rests against the opposite edges of both caps 17. Rod 31 is hence fully raised and the sensor shows in this case a position of zero.

In the position shown in figure 7, only valve 14 is closed, while valve 13 is open; in its descending movement into an open position - driven by end 21a of rocker arm 21 - appendix 17a of cap 17 of valve 13 rests against the edge of matching block 32 and drags it downwards, compressing the spring 34 thereof. Rod 31 in turn is displaced downwards, so that the sensor shows a position other than zero. It is clear that, the further open valve 13 is, the further downwards rod 31 will be dragged; sensor 30 will hence be able to provide an indication of the position of valve 13 at any time.

The position wherein valve 13 is closed and valve 14 is open is not shown, but such position is symmetrical and for a person skilled in the field it is perfectly understandable how matching block 32 can be pushed downwards by the thrust of end 21b of rocker arm 21 through the cap 17 associated with valve 14, instead of by the cap end 21a under the thrust of end 21b associated with valve 13.

Linear sensor 30 will in any case be able to determine the width of the opening movement of either one of valves 13, 14, based on the position of matching block 32. At the same time, the determination of which one of the valves is in an opening phase will be made based on the position of rocker arm 21, i.e. on the sense of rotation of the electric motor, which is decided by the electronic central control unit. In other words, the displacement detected by the sensor will be associated with the valve which the central electronic unit orders to open defining the sense or rotation of the motor.

Fig. 8, as already mentioned, concerns a further embodiment of the EGR valve assembly according to the invention. The arrangement of valves 13 and 14, as well as that of rocker arm 21, is identical to the arrangement in drawings 2 and 4. The variant consists mainly in the fact that actuator assembly 25 - replacing motor 19 - is mounted on the top of part 12 of the valve assembly and in that the outlet thereof is in the shape of an axially slidable rod 26.

This rod 26 acts directly on one of the arms of rocker arm 21, in the case shown on the end 21b of arm 21, substantially in correspondence of the resting point thereof on valve 14; a downward pushing action drives the opening of valve 14 and respectively an upward pulling action drives the opening of valve 13.

In order to avoid forcing in the actuation movement of rocker arm 21, it can be provided for rod 26 to be manufactured as an articulated lever, or - as shown in fig. 8 - so that the pin 28 for the articulation of rod 26 on the arm 21b of the rocker arm operates with play in a slot-shaped hole 27.

Fig. 9 concerns still another embodiment variant of the EGR valve assembly according to the invention. The arrangement of valves 13 and 14 is identical to the arrangement of figures 2 and 4. The variant consists in the fact that rotating actuator 19 no longer drives a rocker arm 21, but the shaft 20 thereof is mounted coaxially to the driving shaft of actuator 19 and a pair of cams 36 and 37 is keyed thereon; these cams, which act on mushroom-shaped valves 13 and 14, respectively, are angularly offset so as to drive the opening of the valves one alternatively to the other, as described above in connection with the other embodiment variants .

This arrangement with a two-cam shaft might, at least theoretically, allow four different positions of the two valves, namely: both closed valves, one open valve towards the by-pass and the other one closed towards the cooling device, or viceversa, or both valves at least partially open.

Figures 11 and 12 show a further embodiment variant, similar to the one of fig. 8 in the sense that it uses an actuator 25, the outlet of which is shaped as a rod 41 slidable with a rectilinear movement. Rocker arm 42 is pivoted in a fixed point 43 of upper body 12 and the two ends thereof are shaped as a pin supporting two respective resting rollers 42a and 42b; these are intended to promote the actuation of the stems of valves 13 and 14, by directly resting on the upper heads thereof. Again for the purpose of promoting the actuation, rocker arm 42 extends into an appendix which in turn carries a guiding roller 42c, which is apt to engage with a groove 41a formed in the rod 41 of actuator 25.

Figure 11 shows the valve assembly with both valves 13 and 14 closed, while figure 12 shows rocker arm 42 rotated in an anticlockwise direction to bring valve 13 into an open position.

Figures 13 and 14 show still a further embodiment variant, wherein the output shaft of motor 19 actuates an epicycloid wheelwork 45, the output whereof engages directly with the rotatable shaft 46 of a rocker arm 47 very similar to the rocker arm 42 of the variant according to figures 11 and 12; as in said last figure, the opposite ends of the rocker arm carry two support and sliding rollers 47a and 47b, which act directly on the heads of the stems of valves 13 and 14. Figure 13 is a vertical section running through the axis of actuating motor 19, which in turn is transversal to the alignment of valves 13 and 14. Figure 14 is instead a partial perspective view, relative to the sole head of the valves for the sake of the simplification of the drawing. Figures 15 to 17 show still another embodiment variant, similar to the one of figures 13 and 14 due to the fact that it uses a motor 19 with an epicycloid wheelwork outlet, but also similar to that of figure 9 due to the fact that it comprises a driving shaft 20, arranged parallel to the alignment of valves 13 and 14. Figures 15 and 16 are vertical-section views, along the axis of shaft 20 and in a crosswise direction to this axis, respectively, while fig. 17 is a diagrammatic perspective view.

The main difference over the other variants lies in the fact that the motion transmission from shaft 20 to valves 13, 14 occurs through desmodromic actuation by means of cams 48 and 49. Each of these cams, which in actual fact are integral with shaft 20, is provided with a groove 48a and 49a, having a shaped profile, with which a guiding roller 13c, 14c engages, carried at the upper end of the stems of cams 13 and 14.

When shaft 20 rotates, and cams 48 and 49 with it, the engagement of rollers 13c and 14c with grooves 48a and 49a causes the stems of cams 13 and 14 to be forced to rise and fall, with a motion law which is determined by the profile of grooves 48a and 49a. Springs 16 do not have a true recall function of valves 13, 14 in a closed position, since this function is already performed by the desmodromic drive of cams 48 and 49. However, when the position of cams 48 and 49 is in correspondence of that of the closure of valves 13 and 14, a certain play is obtained between rollers 13c and 14c and grooves 48a and 49a; then, the closure of valves 13 and 14 on the respective valve seats 13a, 14a is ensured precisely by springs 16, so that the gas-proof seal thereof is also guaranteed.

Finally, figures 18, 19 and 20 show another embodiment variant, wherein the actuation of the valves occurs through the combination of an oscillating rocker arm 51 with a central cam- like actuation. Rocker arm 51 oscillates on a fixed-axis shaft 52 and carries an extension appendix 51a, at the free end of which there is pivoted a guiding roller 51b.

The cam actuation is accomplished with an oscillating driving sector 53 which is keyed on a shaft 54, which is displaced by an actuator such as the one shown in figures 14 and 17, i.e. consisting of a motor 19 and of an epicycloid wheelwork 45, the outlet of which engages directly with rotating shaft 54. On driving sector 53 there is formed a shaped groove 53a, with a cam profile, with which the roller 51b of rocker arm 51 engages. The arrangement of rocker arm 51 and driving sector 53 is substantially similar to that of the embodiment variant according to figs. 13 and 14, however, with the opportunity of better adjusting the motion law, precisely by means of cam 53a.

It must be notice that, for the purpose of a correct actuation, the cooperation between rocker arm 51 and driving sector 53 occurs by means of roller 51b, engaged with the shaped groove 53a of the same driving sector 53 - shown in fig. 18 in a closed position of both valves 13, 14, and in fig. 19 in an open position of sole valve 13 - with a slackless cooperation, as visible in figure 20. The innovative configurations shown above, with reference to the figures from 1 to 9 and from 11 to 20 - which, it must be repeated, are shown only in an extremely diagrammatic way, and hence without the arrangement of the parts and their sizing having any pretence of matching a real exemplifying embodiment - show self-enclosed assemblies, which can be employed in supply systems of internal combustion engines M in the ways deemed most suitable by the designer.

Figure 10 provides instead an indication of the opportunity of accomplishing the EGR valve as part of a larger assembly. In particular, fig. 10 shows the EGR valve in a configuration wherein lower body 11 also embeds, for example, cooling system 4, schematised here by chambers 40, wherein a cooling liquid of the valve assembly circulates. The same liquid further circulates, for example, in the heat exchanger (not shown) which serves to the cooling of exhaust gases,- these gases enter the pipe Gsc through opening 39, run through either one of valves 13 or 14 and exit through opening 13b towards by-pass 5 (not shown in detail) or through opening 14b towards the heat exchanger 4 for cooling, respectively. Figure 10 also shows, very diagrammatically, that other components of engine M (not specifically indicated) can be part of the integrated assembly shown here.

As is immediately understandable, the valve assembly according to the invention implies at least the following advantages : in a single structural component the EGR functionality is accomplished, with double valve, towards the cooling device and towards the by-pass, allowing a remarkable reduction of the bulk, of the weight and of the cost; the use of a single actuator (electric motor) and of a single actuation for the two valves allows a simplification both in the mechanical structure of the valve, and in the electronic control system of the exhaust gas flow rates; also the use of a single position sensor for the two valves allows a simplification both on a building level and in the verification system of the exhaust gas flow rate;

However, it is understood that the invention must not be considered limited to the peculiar arrangements illustrated above, which represent merely preferred embodiments thereof, but that different variants are possible, all within the reach of a person skilled in the field, without departing from the scope of protection defined by the following claims.

Number References M engine

1 intake manifold

2 intake manifold 3 EGR valve

4 cooling device

5 by-pass

11 lower part of EGR valve

12 upper part of EGR valve 13 mushroom-shaped valve

13a valve seat 13b valve outlet opening 14 mushroom-shaped valve 14a valve seat 14b valve outlet opening

16 spring of the mushroom-shaped valves

17 cap of the mushroom-shaped valves

18 connector

19 actuator 20 rocker arm shaft

21 rocker arm 21

22 rotational position sensor

23 gear transmission

25 rectilinear actuator 26 rod of the rectilinear actuator 28 pin for rod 26 27 slot for pin 28

30 linear position sensor 31 rod of the linear sensor 32 matching block

33 shaft

34 shaft spring 36 cam

37 cam 39 opening for the entry of exhaust gases 40 chamber of the cooling circuit 41 rod of the rectilinear actuator

42 rocker arm

42a, 42b support rollers 42c appendix with guiding roller 43 fixed pin of the rocker arm

45 epicycloid wheelwork

46 rotatable shaft

47 rocker arm

47a sliding roller 47b sliding roller

48 cam

48a cam groove

49 cam

49a cam groove 50 spring

51 rocker arm

51a rocker arm appendix 51b guiding roller

52 rocker arm shaft 53 driving sector

53a cam-shaped groove of the driving sector 54 shaft of the driving sector Gsc entry pipe of exhaust gases

Claims

1) Exhaust gas recirculation (EGR) valve assembly of an internal combustion engine (M) , comprising means for the deviation of an adjusted amount of exhaust gases, taken from the engine outlet manifold (2) , to an engine intake manifold (1) , through a by-pass or through a cooling device, respectively, characterised in that said deviation means comprise an exhaust gas inlet (Gsc) and two outlets (13b, 14b), two distinct closing valves (13, 14) of said two outlets, spring means (16) associated with each of said valves to push them towards the respective closed position and a single actuation means (21; 20, 36, 37; 42; 47; 20, 48, 49; 51) for alternatively driving either one of said valves (13, 14) towards the open position, and in that with said actuation means there is associated a single position sensor (22, 30), said actuation means being put under the control of a single electric actuator (19, 25) , controlled by an electronic central control unit based on the signals coming from said single position sensor (22, 30).

2) Valve assembly as claimed in claim 1, characterised in that said actuation means consists of a rocker arm (21, 42, 47, 51) keyed on a rotatable shaft (20, 43, 46, 52) , arranged between said two valves (13, 14) and having rotation axis perpendicular to the plane running through the axes of the valves, the free ends (21a, 21b; 42a, 42b; 47a, 47b) of the two arms of the rocker arm acting on one and the other, respectively, of said valves, to push them alternatively into an open position.

3) Valve assembly as claimed in claim 2, characterised in that said rocker arm (21, 47, 51) is displaced by a rotatable electric actuator (19) , by means of a motion transmission.

4) Valve assembly as claimed in claim 3) , characterised in that said motion transmission is a reduction gear (23) transmission, the inlet gear of which is integral with the shaft of the electric actuator (19) and the outlet gear of which is integral with the shaft (20, 46, 52) of said rocker arm.

5) Valve assembly as claimed in claim 4) , characterised in that said gear transmission consists of an epicycloid gearwork mechanism (45) .

6) Valve assembly as claimed in claim 3), characterised in that said motion transmission comprises cam means (36, 37; 48, 49), acting directly on valves (13, 14).

7) Valve assembly as claimed in claim 3) , characterised in that said motion transmission comprises cam means (53, 53a), acting on an appendix (51a, 51b) of said rocker arm (51) .

8) Valve assembly as claimed in claim 7) , characterised in that said cam means (53, 53a) comprise an oscillating drive sector (53) , integral with the outlet shaft of said motion transmission (45) and provided with a cam-shaped groove (53a) , and a guiding roller (51b) integral with said rocker arm appendix (51a) .

9) Valve assembly as claimed in claim 2) , characterised in that said rocker arm (21, 42) is displaced by an electric actuator (25) with a rectilinear movement, the outlet rod of which (26, 41) acts on an appendix (21b, 42c) of said rocker arm.

10) Valve assembly as claimed in claim 9) , characterised in that said rocker arm appendix consists of the end (21b) of one of the arms of the same rocker arm (21) , connected to the outlet of said electric actuator through an articulated lever.

11) Valve assembly as claimed in claim 10) , characterised in that said articulated lever is rod-shaped (26) , the end of which acts directly on one of the arms of the rocker arm through a pin connection (28) and slot-shaped hole (27) .

12) Valve assembly as claimed in claim 9) , characterised in that said appendix of the rocker arm is arm-shaped, carrying at one end thereof a guiding roller (42c) , which engages with a groove (41a) of the outlet rod (41) of the rectilinear actuator (25) .

13) Valve assembly as claimed in claim 1) , characterised in that said actuation means consists of a driving shaft (20) , driven into rotation by said electric actuator (19) , the axis of said shaft lying in the plane of axes of said two closing valves (13, 14) and being oriented perpendicularly to these axes, on said shaft two cams (36, 37; 48, 49) being further keyed, each one acting directly on a respective closing valve (13, 14) .

14) Valve assembly as claimed in claim 13), characterised in that said two cams (36, 37; 48, 49) have identical profiles and are keyed on said driving shaft angularly offset from each other.

15) Valve assembly as claimed in claim 13 or 14) , characterised in that said two cams (36, 37) act directly on the valve heads with their outer edge.

16) Valve assembly as claimed in claim 13 or 14) , characterised in that said two cams (48, 49) are provided with a driving profile in the shape of a groove (48a, 49a) having a shaped edge, with which a guiding roller (13c, 14c) engages, carried at the end of upper appendixes of the stems of the respective cams (13 and 14) . 17) Valve assembly as claimed in any one of the preceding claims, characterised in that said position sensor is a rotational sensor (22) , such as a Hall-effect sensor, arranged near a magnetic element integral in rotation with the outlet shaft (20, 46, 52) of said rotary electric actuator. 18) Valve assembly as claimed in any one of the preceding claims, characterised in that said position sensor is a linear movement sensor, the sensor rod of which is displaced directly by the valve actuated on each occasion by said electric actuator. 19) Valve assembly as claimed in claim 18) , characterised in that said linear movement sensor is mounted in a central position between the two valves, and is displaced by either one, respectively, of two opposite appendixes, carried by the two valves . 20) Valve assembly as claimed in claim 19) , characterised in that said opposite appendixes are part of two stopping caps of the valve springs .

21) Valve assembly as claimed in any one of the preceding claims, characterised in that said electric actuator is a continuous current motor or a stepper motor.