Mechanical device for varying the phase between a drive shaft and a camshaft of an internal combustion engine

Abstract: In a mechanical device for varying the phase between a drive shaft and a camshaft (3) of an internal combustion engine, in which the phase variation is achieved by varying the angular position of a body (5), connected kinematically to the drive shaft, relative to that of a shaft (2), connected kinematically to the camshaft (3), by the movement of a piston (4) interposed between the body and the shaft to each of which it is connected by toothed portions (15 17), there are provided stop means (30) for stopping the relative rotation of the body and the shaft, causing the piston (4) to be stopped by engagement in the toothed portions (16, 18) of the shaft (2) and of the body (5) in the stop positions. At least one of those toothed portions has at least one gap (36, 38, 40) in the axial profile of the respective sides of the toothed portions (16, 18), which gap is in a position such that it straddles the edge (19, 20) of the piston (4) in the corresponding stop position. The gap extends for a distance adjacent to the toothed portion (15, 17) of the piston (4) and for a further distance beyond that toothed portion in the direction of further travel beyond the stop position.

Description: The present invention relates to a mechanical device for varying the phase between a drive shaft and a camshaft of an internal combustion engine according to the preamble of the main claim. A device having the above characteristics is known from EP-A-742 350 of the same Applicant. In devices of the type indicated, it is provided that the piston member is stopped in the stop positions by engaging in the toothed portions of the coaxial components in such a manner as to eliminate the play existing between the mutually coupled toothed portions and consequently to limit the noise induced by the relative movement of the coupled toothed portions. That movement is the result of the reversal of the load acting on the camshaft brought about principally by the timing dynamics. As the hours of operation of those devices increase, a certain wear occurs on the coupled toothed portions and consequently, in order to recover the play between the toothed portions, the piston member has to assume more advanced positions in the stop positions. In addition, the pressure forces between the sides of the mutually contacting toothed portions, which are generated by the engaging action of the piston member, may cause the formation of small localised impressions on the sides of the toothed portions of the coaxial components. As wear increases, those impressions may reach depths sufficient to form a step on the sides of the toothed portions which impedes, to the extent of preventing, the sliding of the piston member relative to the coupled coaxial component. If the advance of the piston member is prevented, the play between the toothed portions can no longer be recovered by the movement of the piston member and there is consequently an undesired increase in the noise of the device. The problem underlying the present invention is to provide a mechanical device for varying the phase between a drive shaft and a camshaft of an internal combustion engine, which device has structural and functional characteristics such as to overcome the disadvantages discussed with reference to the mentioned prior art. The problem is solved by the invention by means of a mechanical device for varying the phase between a drive shaft and a camshaft of an internal combustion engine, which device is produced in accordance with the claims which follow. The characteristics and advantages of the invention will become clear from the following detailed description of some of its preferred embodiments which are illustrated by way of non-limiting example with reference to the appended drawings in which: Figures 1 and 2 are diagrammatic cross-sectional views of a mechanical device according to the present invention in two different operative positions, Figure 3 is a partial view, in section and on an enlarged scale, of a detail of the device of the previous Figures, Figure 4 is a diagrammatic view in partial section on the line IV-IV of Figure 3, Figure 5 is a partial view of a detail of the device of the previous Figures in a variant of the invention, Figure 6 is a diagrammatic cross-sectional view of a further variant of the device of the invention. With reference to Figure 1, a mechanical device according to the invention for varying the phase between the drive shaft and a camshaft 3 of an internal combustion engine is generally indicated 1. The device 1 is of the type described in patent application no. PD95A000094, the content of which is incorporated in the present description by reference. The present invention will be described with reference to one of the embodiments referred to in the above-mentioned patent application, it being understood, however, that the invention can also relate in principle to the other embodiments described. The mechanical device 1 comprises a first component constituted by a hollow annular body 5, a second component constituted by a hollow shaft 2 which is rotatably supported in coaxial manner in the body 5, and an annular piston member 4 which is interposed between the body 5 and the shaft 2 and which is likewise coaxial with the body 5. The body 5 is formed by an inner semi-body and an outer semi-body which are indicated 5a and 5b, respectively, and which are fixedly joined to one another by means of a screw and nut coupling. The outer semi-body 5b has a flange 7 formed on it for securing, by means of screws, a toothed wheel (not shown in the drawing) designed to be connected to the drive shaft by means of a toothed belt drive. One end 8a of the body 5 has an inner shoulder 9 and the opposite end 8b has a base 10 welded to the body 5. The base 10 comprises a cover 11 which is connected thereto by a screw and nut coupling. One end 2a of the shaft 2 has a flange 12 which is supported against the shoulder 9, while the opposite end 2b is supported on the base 10 of the body 5. A tie rod 13 connects the shaft 2 axially to the camshaft 3, thus rendering them integral in rotation. The tie rod 13 comprises a shank inserted in the central hole of the shaft 2 and in a central hole of the camshaft, a head accommodated in a cylindrical seat of the shaft 2 and a threaded end 13a connected to a corresponding threaded portion of the central hole of the camshaft 3. The shank of the tie rod 13 has a smaller diameter than that of the holes in which it is inserted, so that an annular duct 14 is defined inside the camshaft 3 and the shaft 2. The piston member 4 comprises, on the outside, a helicoidal toothed portion 15 in engagement with a corresponding inner toothed portion 16 of the inner semi-body 5a, and, on the inside, a toothed portion 17, preferably of the rectilinear type, in engagement with a corresponding outer toothed portion 18 of the shaft 2. The toothed portions 15, 17 are defined between axially opposing end edges 19, 20 of the piston 4 (with reference to a hypothetical axial section through the piston). At one end facing the end 8a of the body 5, the piston 4 has a head 21 having a front surface of larger diameter than that of the remaining portion having the helicoidal toothed portion 15. The head 21 constitutes an axially mobile baffle which divides an annular chamber 22, defined inside the mechanical device 1 by the inner semi-body 5a, by the outer semi-body 5b and by the shaft 2, into a first and a second half-chamber facing the base 10 and the end 8a of the body 5, respectively. The volume of the above-mentioned half-chambers is a function of the position of the head 21 in the annular chamber 22. A helical spring 24 is arranged in the above-mentioned first half-chamber and acts on the head 21 of the piston, urging the piston towards the end 2a of the shaft 2. A plurality of radial ducts 25 formed in the shaft 2 bring the first half-chamber into fluid communication with the annular duct 14 which is in turn in fluid communication with a first pressurised fluid hydraulic circuit of the camshaft 3. A further duct 26 formed in the shaft 2 brings the second half-chamber into fluid communication with a duct 27 which is in turn in fluid communication with a second pressurised fluid hydraulic circuit of the camshaft 3. A solenoid valve, known per se and not shown in the drawing, is controllable from an electronic control unit to pass from a first operating position, in which it brings the first hydraulic circuit into fluid communication with a main pressurised fluid circuit of the engine and at the same time discharges the second hydraulic circuit, to a second operating position in which it discharges the first hydraulic circuit and at the same time brings the second hydraulic circuit into fluid communication with the main circuit. The mechanical device 1 also comprises an auxiliary annular element 30 interposed coaxially between the body 5 and the shaft 2 and having, like the piston 4, an outer helicoidal toothed portion 31 in engagement with the corresponding toothed portion 16 of the inner half-body 5a and an inner rectilinear toothed portion 32 in engagement with the corresponding toothed portion 18 of the shaft 2. The auxiliary annular element 30 is arranged axially between the base 10 and the piston 4, at a predetermined distance from the latter. The mechanical device 1 also comprises a plurality of pins 33 interposed between the auxiliary annular element 30 and the piston 4 and arranged circumferentially with uniform spacing around the shaft 2. The pins 33 are preferably accommodated in seats formed axially in the piston 4. An axial shoulder 34 which limits the axial sliding of the pins 33 towards the end 2a of the shaft 2 is formed in the shaft 2. When the solenoid valve is in its first operating position, the pressurised fluid flows into the second half-chamber, causing a sliding of the piston 4 and the auxiliary annular element 30 towards the base 10 counter to the action of the spring 24, and also a relative angular rotation of the components 2, 5. The sliding causes the auxiliary annular element 30 to abut the base 10 in a first stop position (Figure 1), causing the piston 4 to stop by engagement in the toothed portions 16 and 18, which prevents further relative rotation of the components 2, 5. In that first stop position, the pins 33 are axially free to move between the piston 4 and the auxiliary element 30. When, conversely, the solenoid valve is in its second operating position, the action of the pressurised fluid which flows into the first half-chamber, together with the resilient force of the spring 24 and the discharge action of the fluid from the second half-chamber, cause the piston 4 and the auxiliary annular element 30 to slide towards the end 2a of the shaft 2. During the sliding movement, the pins 33 are pushed by the auxiliary annular element 30 and caused to slide towards the end 2a of the shaft 2 until they abut the axial shoulder 34 of the shaft 2 (Figure 2). As a result, the auxiliary annular element 30 is caused to stop against the pins 33 in a second stop position and the piston 4 is caused to stop by becoming engaged in the toothed portions 16 and 18. During passage from one of the above-mentioned stop positions to the other, for an axial sliding of the piston 4 on the rectilinear toothed portion 18 of the shaft 2 there is a corresponding rotation of the body 5 relative to the shaft 2 which is due to the helicoidal toothed portion coupling between the piston 4 and the body 5, which brings about the variation in the timing system. The relative rotation in turn involves axial sliding of the auxiliary annular element 30 on the rectilinear toothed portion 18 of the shaft 2. This sliding is the same as that of the piston 4 since the annular element is also in engagement with the helicoidal toothed portion 16 of the body 2. In both of the above-mentioned stop positions, the engagement of the piston 4 enables the coupled toothed portions to be kept in close contact, eliminating the continuous reciprocating movement between them and consequently reducing the noise of the device. According to a further characteristic of the present invention, a gap is provided in the axial profile of the sides of the toothed portions 16 and 18, respectively, of the body 5 and the shaft 2. In accordance with a first embodiment of the invention, the above-mentioned gap comprises a first and a second groove 36, 38. The grooves are formed circumferentially on the body 5 and on the shaft 2 in such a manner that they affect each tooth of the toothed portions 16 and 18. With reference to Figure 3, the first and the second groove 36, 38 are formed in a position such that they straddle the edge 19 of the piston 4 when the piston is in the first stop position. Relative to that position, each groove 36, 38 extends axially for a distance adjacent to the respective toothed portion 15, 17 of the piston and for a further distance beyond the toothed portion 15, 17 in the direction of further travel beyond the first stop position (in the direction towards the base 10). For each tooth of the respective toothed portions 16 and 18, the grooves 36, 38 are defined by surfaces 36a, b and 38a, b which face one another and which extend from the base of the corresponding groove. Preferably, each surface 36b, 38b, that is to say, that adjacent to the toothed portion of the piston in the first stop position, extends from the groove base, diverging from the other surface 36a, 38a. The inclined surfaces 36b, 38b facilitate the fitting of the toothed portions 31, 32 of the auxiliary element 30 in the respective toothed portions 16, 18 during the actuating stroke of the auxiliary element. The above-mentioned gap in the toothed portions also comprises a third groove 40 formed in a position such that it straddles the edge 20 of the piston when the piston is in the second stop position. Advantageously, the third groove 40 may be constituted by the discharge groove provided for the production of the toothed portion of the shaft 2 in the area of the shoulder 34. In a manner analogous to that described for the first and second groove 36, 38, the third groove 40 also extends, relative to the second stop position of the piston, for a distance adjacent to the toothed portion 17 of the piston and for a further distance beyond that toothed portion 17 in the direction of further travel beyond the second stop position (in the direction towards the shoulder 34). In operation, the piston is locked in each stop position by engagement in the toothed portions 16 and 18, as described above. The pressure forces exerted between the sides of the mutually contacting toothed portions are such that, as the hours of operation increase, they can cause wear on the sides of the toothed portions with the formation of small cavities or impressions, especially along the sides of the toothed portions 16 and 18. As a result, the play between the coupled toothed portions tends to increase owing to the wear and the piston 4 is urged to move axially beyond the corresponding end position in order to recover the above-mentioned play. That axial movement is not impeded by any cavities or steps, caused by wear and present on the side of the toothed portions 16, 18, because the corresponding edge 19, 20 of the piston is not in contact with the side of the toothed portions 16, 18 but straddles the corresponding groove 36, 38, 40. The edge 19, 20 is therefore not impeded in its axial movement and the piston 4 can be moved axially, under the action of the pressurised fluid (and of the spring 24 in the second stop position), beyond the corresponding stop position in order to recover the play and to be locked again by engagement in the toothed portions 16 and 18. In accordance with a second embodiment of the invention, the gap in the axial profile of the sides of the toothed portions 16 and 18 is in the form of an impression 41 obtained by a reduction in height of the side of the toothed portion, as shown in Figure 5. It will be appreciated that in the presence both of the grooves 36, 38, 40 and of the impressions 41 which reduce the height of the axial toothed portion profile, the axial extent of the gap portion extending adjacent to the toothed portions 15, 17 of the piston (relative to the stop positions) is smaller than the axial extent of the toothed portions of the piston, so that the sides of the toothed portions 15, 17 of the piston are always in contact with the respective sides of the coupled toothed portions 16, 18 without ever falling into the grooves 36, 38, 40 or the impressions 41. Figure 6 shows a further variant of the invention which differs from the preceding examples in that the third groove 40 is not provided as a discharge groove in the production of the toothed portion 18 of the shaft 2. The shaft 2 is in this case produced in two portions 2c, 2d of which the portion 2c having the toothed portion 18 is forced onto the flange portion 2d and the production of the toothed portion is carried out before the operation of forcing the portions 2c, 2d one onto the other, the provision of a discharge groove therefore being dispensed with. Consequently the groove 40 should be appropriately formed for the purposes of the invention.

Claims: A mechanical device for varying the phase between a drive shaft and a camshaft (3) of an internal combustion engine, of the type comprising a first component (5) and a second component (2) which are coaxial with one another and which are connected kinematically to the drive shaft and the camshaft (3), respectively, a piston member (4) interposed between the components (2, 5) and having two toothed portions (15, 17), of which one has a screwing angle relative to the other and which are in engagement with a toothed portion (16) of the first component (5) and with a toothed portion (18) of the second component, respectively, the toothed portions (15, 17) of the piston member (4) having axially opposing end edges (19, 20), the piston member being movable relative to those components under the action of a pressurised fluid between two opposite stop positions in order to vary the angular position between the first (5) and the second (2) component and consequently the phase between the drive shaft and the camshaft, and stop means (30) interposed between said components to stop the relative rotation of the components and to stop the piston member (4) by the engagement thereof in the toothed portions (16, 18) of the components in each of the stop positions, characterised in that it comprises, on at least one of the toothed portions (16, 18) of the components (5, 2), at least one gap (36, 38, 40) in the axial profile of the respective toothed portion sides, the at least one gap being in a position such that it straddles the edge (19, 20) of the piston member (4) in the corresponding end position, the gap extending for a distance adjacent to the toothed portion (15, 17) of the piston member and for a further distance beyond the toothed portion (15, 17) in the direction of further travel beyond the stop position, the extent of the portion adjacent to the toothed portion of the piston being smaller than the axial extent of the toothed portion of the piston. A device according to claim 1, wherein the gap comprises, for each tooth of the toothed portion (16, 18) of the at least one component (2, 5), a respective groove (36, 38), the grooves being aligned circumferentially on said component. A device according to claim 2, wherein each of the grooves (36, 38) is defined by opposing lateral surfaces (36a, b; 38a, b) extending from the base of the groove, at least one of the surfaces (36b, 38b) diverging from the other of the surfaces (36a, 38a), starting from the base of the groove. A device according to claim 1, wherein the gap in the profile of the toothed portion (16, 18) comprises at least one impression (41) formed on the corresponding side of the toothed portion (16, 18) of the at least one component (5, 2).

Inventors: TORTUL RENZO, TORTUL, RENZO
Applicants: CARRARO SPA, CARRARO S.P.A.
Application year: 1998
Main classification: F01L1
IPC codes: F01L1