FR2988780A1 - HEAT ENGINE CYLINDER HEAD ASSEMBLY - Google Patents

Abstract

The invention relates to a cylinder head assembly (10) for a combustion engine, particularly a motor vehicle engine, said overhead camshaft having a cylinder head (10) receiving in rotation a camshaft (12) which is guided in rotation in said cylinder head (10) via at least two bearings (14), each bearing (14) comprising at least: - an inner cylindrical bearing surface (16) integral with the periphery of the camshaft (12) and, - a bearing base (18) having a lower half-span (20) outer integral with the cylinder head, - a bearing cap (22) having a upper outer half-span (24), adapted to be fixed to the cylinder head (10) to the right of the bearing base (18) for adjusting the lower outer half-span with the upper outer half-span so as to form an outer bearing surface of the bearing, characterized in that at least the outer bearing surface (20, 24) of each bearing (14) is obtained by cold spraying metal powders and / o u ceramics using a gas according to a so-called gaso-dynamic projection process.

Description

The present invention relates to a cylinder head assembly of a heat engine, especially a motor vehicle, said engine having a head cam having a cylinder head receiving in rotation a camshaft which is guided in rotation in said cylinder head. by means of at least two bearings, each bearing comprising at least: an internal cylindrical surface integral with the periphery of the camshaft and a bearing base comprising a lower outer half-surface integral with the cylinder head - a bearing cap, comprising an upper outer half-span, adapted to be fixed to the cylinder head at the level of the bearing base to adjust the lower outer half-span with the upper outer half-span so as to form a bearing external bearing. Numerous examples of yoke assemblies, including yoke assemblies with plain bearings, are known. These plain bearings have the particular disadvantage of being subjected to significant radial forces and high pollution of the oil, especially based on carbonaceous materials or metal particles, which cause wear of the bearings of the cylinder head. This wear is particularly detrimental to the cylinder heads made of soft materials such as aluminum. To reduce friction and further reduce CO2 emissions from the engines, it has been proposed to add bearings on the camshaft bearings. However, because of the shape of the cams, it is not possible to mount a bearing previously assembled on a camshaft after the camshaft has been manufactured. Several solutions therefore consist in reporting on the camshaft and in the cylinder head the various components of the bearing, namely at least one element forming the inner race of the bearing, a cage, and at least one element forming the outer race of the bearing. . Indeed, the cylinder head is generally aluminum, a material whose hardness is reduced, it is not possible to form the outer element or elements of the bearing directly in the cylinder head. It is also not possible to form the inner member (s) of the bearing directly on the camshaft. Indeed, the realization of a running track on a camshaft would involve a treatment thereof to increase its hardness. However, most current camshafts are made using a method in which the cam is threaded onto a tube, which tube is then subjected to a deformation process to immobilize the cam on said tube. This deformation process involves the use of a tube whose hardness is limited to ensure its plastic deformation in the associated cam. The use of a tube of high hardness would make it impossible to mount the cams. In the following description of the process of deformation of the tube of the camshaft we will take as an example the process called "dudgeonnage" but the problem remains the same as other techniques such as hydroforming, hot shrinking or Cold. According to a first known solution of the state of the art, it has been proposed to successively mount a lower half-outer race of the bearing in the cylinder head, then two half-cages carrying needles, rollers or balls on the camshaft, again a top outer half-ring of the bearing, and finally a bearing cap or cylinder head cover.

In addition to a relatively long assembly time of these elements, they may be poorly mounted and cause jamming of the bearing. According to a second known solution of the state of the art, it has been proposed to create rings and split cages that can be discarded and then threaded onto the camshaft. This solution requires complicated assembly because of the location of the bearing which is generally located between two consecutive cams and therefore has only a limited axial space. The assembly must take into account this axial space because it is necessary to set up successively in this restricted space the cage and the outer ring. Moreover, these two solutions are not satisfactory, because the joining of the half-rings or the slot edges of the same ring constitutes a defect on the bearing track considered, a defect which can cause accelerated wear of the rolling elements of the bearing. . The invention overcomes these disadvantages by replacing the rings or half-rings by a thick coating deposited on the bearing surfaces of the cylinder head and / or the camshaft. For this purpose, the invention proposes a heat engine cylinder head assembly of the type described above, characterized in that at least the outer bearing surfaces of each bearing are obtained by cold spraying metal and / or ceramic powders with the aid of a gas according to a so-called gaso-dynamic projection method. According to other features of the invention: the internal bearing of each bearing is also obtained by cold spraying of metal powders and / or ceramics with the aid of a gas according to a so-called gaso-dynamic projection method; the internal cylindrical bearing is mounted directly rotating in the lower and upper outer half-seats; At least one cage provided with rolling elements, in particular needles, rollers or balls, is interposed between the internal cylindrical bearing surface and the lower and upper external half-bearing surfaces; each range obtained by cold spraying of metal and / or ceramic powders using a gas according to a so-called gas-dynamic projection process is of a thickness of 100 to 5000. The invention also relates to a manufacturing method. a breech bearing of the type described above comprising at least: - an internal cylindrical surface secured to the periphery of the camshaft and - a bearing base having a lower outer half-surface secured to the cylinder head, - a bearing cap, having an upper outer half-span, adapted to be fixed to the breech in line with the bearing base to adjust the lower outer half-span with the upper outer half-span so as to form an outer bearing; of the landing. According to a first embodiment of the invention, this process is characterized in that metal and / or ceramic powders which are cold sprayed onto the base and the bearing cap are introduced into a high velocity gas flow. or the periphery of the camshaft so that it plastically deform and consolidate. According to a second embodiment of the invention, this method is characterized in that a chamber filled with an explosive gaseous mixture is introduced into a chamber of metal and / or ceramic powders, and then that detonation is effected in said chamber to project said powders through the barrel on the base and the bearing cap and / or the periphery of the camshaft so that they plastically deform and consolidate therein . Other features and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the accompanying drawings in which: - Figure 1 is a schematic cross-sectional view illustrating the mounting of a camshaft bearing according to a first prior art; FIGS. 2A to 2F are longitudinal views illustrating the mounting of a camshaft bearing according to a second prior art state of the art; - Figure 3 is a cross-sectional view of an outer ring of the bearing of Figure 1; - Figure 4 is a longitudinal sectional view illustrating the manufacture of a camshaft; - Figure 5 is a schematic cross-sectional view of a plain bearing according to the state of the art; FIG. 6 is an exploded longitudinal sectional view showing a bolt assembly according to a first embodiment of the invention; FIG. 7 is an exploded longitudinal sectional view showing a bolt assembly according to a second embodiment of the invention; FIG. 8 is a longitudinal sectional view showing a first gaso-dynamic projection device used in the method according to the invention; - Figure 9 is a longitudinal sectional view showing a second gas-dynamic projection device used in the method according to the invention.

In the remainder of the description, the terms "lower" and "upper" are used in a nonlimiting manner for the purpose of describing the figures and unrelated to the direction of gravity. FIG. 5 shows a portion of a cylinder head assembly of a heat engine (not shown), especially a motor vehicle heat engine, referred to as an overhead camshaft. In known manner, the assembly comprises a yoke 10 receiving in rotation a camshaft 12 which is guided in rotation in said yoke 10 via at least two bearings 14, each bearing 14 comprising at least: - a range internal cylindrical 16 integral with the periphery of the camshaft and - a bearing base 18 having a lower outer half-span 20 secured to the yoke, - a bearing cap 22, having an upper outer half-span 24, adapted to be fixed to the yoke 10 to the right of the bearing base 18 to adjust the lower outer half-span 20 with the upper outer half-span 24 so as to generally form an outer bearing surface of the bearing 18. In a conventional yoke 10 as shown in FIG. 5, the internal cylindrical bearing surface 16 is formed directly on the camshaft 12 and the lower half 20 and upper 24 bearing surfaces are formed directly in the camshaft 12. sse 10, thus forming a smooth bearing 14. Such a sliding bearing 14 has the disadvantage of being subjected to high radial forces and high pollution of the oil, in particular pollution based on carbonaceous materials or metal particles, which cause the wear of the bearing 14 This wear is particularly detrimental to the cylinder heads which are made of soft materials such as aluminum.

To reduce friction and further reduce CO2 emissions from the engines, it has been proposed to add bearings on the camshaft bearings. However, the specificity of the shapes and the methods of mass production of the camshafts do not make it possible to easily mount a bearing between the camshaft and the cylinder head. Thus, because of the shape of the cams, it is not possible to mount a bearing already assembled on a camshaft after the camshaft has been manufactured.

Several solutions therefore consist in reporting on the camshaft and in the cylinder head the various components of the bearing, namely at least one element forming the inner race of the bearing, a cage, and at least one element forming the outer race of the bearing. . These elements forming the inner and outer tracks of the bearing are indeed essential. Indeed, in the case of a cylinder head made of a soft material such as aluminum, whose hardness is reduced, it is not possible to form the outer element or elements of the bearing directly in the cylinder head. It is also not possible to form the inner member (s) of the bearing directly on the camshaft. Indeed, the realization of a running track on a camshaft would involve a prior treatment of it to increase its hardness. However, most of the current camshafts 12 are made using a deformation process, an example of which is the process called "dudonnage", as shown in Figure 4.

According to this method, the cams 26 are threaded onto a tube 28 having a bore 30. The tube 28 is then deformed internally by the introduction into its bore 30 of a tool 32 of diameter greater than the diameter of the bore 30, which plastically deforms the tube 28 to immobilize the cam 26 on said tube 28. This deformation process therefore involves the use of a tube 28 whose hardness is limited to ensure its plastic deformation and the immobilization of the associated cams 26. The use of a tube 28 of high hardness would make it impossible to mount the cams 26 according to this method. Also, to achieve a mounting of a bearing 11 between the cam shaft 12 and the cylinder head 10, it has been proposed according to a first known solution of the state of the art which has been shown in FIG. successively a lower outer half-ring 34 of the bearing in the cylinder head 18, then a half-cage 36, carrier of needles, rollers or balls 40 on the camshaft, another half-cage 42, carrier of needles, rollers or balls 40 on the camshaft 12 and 5 again an upper outer half-ring 44 of the bearing, and finally a bearing cap or cylinder head cover 22. In this configuration the lower outer half-ring 34 of the bearing 11 has the lower half-span 20 and the upper outer half-ring 44 has the upper half-span 24. In addition to a relatively long assembly time of these elements, they may be poorly mounted and cause jamming of the bearing. According to a second known solution of the state of the art which has been shown in FIGS. 2A to 2F, it has been proposed to create a bearing 11 from an outer split ring 46 and a split cage 48 which can be spaced and then threaded on the camshaft 12. According to this design, the slotted cage 48 is first threaded between two cams 26 as shown in FIG. 2A, then the cage is pressed against one of the cams as shown in FIG. 2B. The outer split ring 46 is then introduced into the remaining space by spreading its edges 50 as shown in FIG. 2C and then releasing them as shown in FIG. 2D. The same operation is repeated to arrange the ring 46 on the cage 48, as shown in FIGS. 2E and 2F. This solution requires complicated assembly because of the location of the bearing which is generally located between two consecutive cams 26 and therefore has only a limited space "e" axial. The assembly must take account of this axial space because it is necessary to successively set up in this space "e" restricted the cage 48 and the outer ring 46.

The two previously mentioned solutions are in any case unsatisfactory because the joint 51 of the half-rings 34, 44 shown in Figure 3 or the join of the edges 50 of the same ring slot 46 shown in Figure 2F constitute a defect on the associated track of the associated bearing, a defect which may cause accelerated wear of the rolling elements of the bearing. The invention overcomes these disadvantages by replacing the rings or half-rings of a bearing by a thick coating deposited on the bearing surfaces 16, 20, 24 of the cylinder head 10 and / or the camshaft 12. this purpose, and as illustrated in FIGS. 6 and 7, the invention proposes a heat engine cylinder head assembly 10 of the type described above, characterized in that at least the outer bearing surface 20, 24 of each bearing 14 is obtained by cold spraying of metal powders and / or ceramics using a gas according to a so-called gasodynamic projection process. Advantageously, in the preferred embodiment of the invention, the internal bearing surface 16 of each bearing is also obtained by cold spraying metal and / or ceramic powders using a gas according to a so-called gas-projection method. dynamic. There are two main types of gas-dynamic projection methods. According to a first type of process which has been shown in FIG. 8, metal and / or ceramic powders 53 are introduced into a flow "F" of high-speed gas which are cold-sprayed onto the base 18 and the cap 22 of FIG. bearing and / or the periphery 30 of the camshaft 12 so that it plastically deform and consolidate there. For example, the flow of gas F is created in a chamber 52 which opens into a gun 54 fed with powder 53 through a hopper 56.

According to a second type of process which has been shown in FIG. 9, a gun 62, filled with an explosive gaseous mixture "G", is introduced into a chamber 60, metal and / or ceramic powders 53, and then causes a detonation in said chamber 60 for example by means of a spark plug 64 to project said powders through the barrel on the base 18 and the bearing cap 22 and / or the periphery of the camshaft 12 so that they plastically deform and consolidate.

This method makes it possible to obtain external bearings 20, 24 of bearing 14 which are consolidated by the projection of the metal powders. For this purpose, each span 16, 20 or 24 obtained by cold spraying of metal powders and / or ceramics using a gas according to a so-called gas-dynamic projection process is of a thickness of 100 to 5000 i_tm . The realization of these bearing surfaces 16, 20, 24 is of course carried out on the finished camshaft 12, after the fixing of the cams 26 on the tube 28. According to this general design, several types of bearings can be envisaged. According to a first embodiment of the invention which has been shown in FIG. 7, the internal cylindrical bearing surface 16 is mounted directly rotating in the lower and upper outer half-lands.

According to a first embodiment of the invention which has been shown in FIG. 8, at least one cage 66 provided with rolling elements 68, in particular needles, rollers or balls, is interposed between the internal cylindrical bearing surface 16 and the lower half-outer seats 20 and upper 24.

It will be understood that the cage 66 may be a single split cage or be made up of two half-cages. The invention thus makes it possible in a simple, advantageous and resistant manner to mount a bearing between a camshaft 12 and a cylinder head 10 of a motor vehicle, which makes it possible to increase the longevity of the cylinder heads made of soft materials such as 'aluminum.

Claims (7)

REVENDICATIONS1. A cylinder head assembly (10) for a combustion engine, particularly a motor vehicle, said overhead camshaft having a cylinder head (10) receiving in rotation a camshaft (12) which is rotatably guided in said cylinder head (10) by the intermediate of at least two bearings (14), each bearing (14) comprising at least: - a bearing surface (16) internal cylindrical integral with the periphery of the camshaft (12) and - a bearing base (18) having a lower outer half-span (20) integral with the cylinder head, - a bearing cap (22), having an upper outer half-span (24), adapted to be fixed to the cylinder head (10) in the right of the bearing base (18) for adjusting the lower outer half-span with the upper outer half-span so as to form an outer bearing surface, characterized in that at least the outer bearing surface (20, 24) of each bearing (14) is obtained by cold spraying metal and / or ceramic powders (56) with using a gas according to a so-called gaso-dynamic projection process. 2. Set of engine cylinder head (10) according to the preceding claim, characterized in that the internal bearing (16) of each bearing (14) is also obtained by cold spraying metal and / or ceramic powders (56) to using a gas according to a so-called gaso-dynamic projection process. 3. Engine cylinder head assembly (10) according to the preceding claim, characterized in that the internal cylindrical bearing surface (16) is mounted directly rotating in the lower (20) and upper (24) outer half-bearings. 4. A cylinder head assembly (10) for a heat engine according to one of claims 1 or 2, characterized in that at least one cage (66) provided with rolling element (68), including needles, rollers or balls, is interposed between the internal cylindrical bore (16) and the lower outer half (20) and upper (24). 5. A bolt assembly (10) according to any one of the preceding claims, characterized in that each span (16, 20, 24) obtained by cold spraying metal powders and / or ceramics with a gas according to a so-called gaso-dynamic projection method is of a thickness of 100 to 5000 i_tm. 6. A method of manufacturing a cylinder head bearing (14) according to any one of claims 1 to 5, comprising at least: - a bearing surface (16) internal cylindrical integral with the periphery of the camshaft (12) and, a bearing base (18) having a lower outer half-span (20) integral with the yoke (10), - a bearing cap (22) having an upper outer half-span (24), suitable for be attached to the yoke (10) at the level of the bearing base (18) to adjust the lower outer half-span (20) with the upper outer half-span (24) so as to form an outer bearing surface of the bearing (18); ), characterized in that metal and / or ceramic powders (56) which are cold-sprayed onto the base (18) and the bearing cap (22) are introduced into a high-velocity gas flow (F). or the periphery of the camshaft (12) so that it deforms plastically and consolidate. 7. A method of manufacturing a cylinder head bearing according to any one of claims 1 to 5, comprising at least: - a bearing surface (16) internal cylindrical integral with the periphery of the camshaft (12) and, - a bearing base (18) having a lower outer half-span (20) integral with the cylinder head (10), - a bearing cap (22), having an upper outer half-span (24), which can be fixed to the yoke (10) in line with the bearing base (18) for adjusting the lower outer half-span (20) with the upper outer half-span (24) so as to form an outer bearing surface of the bearing (18), characterized in that a gun (62) filled with an explosive gaseous mixture (G) is introduced into a chamber (60) with metallic and / or ceramic powders (56) and then detonation in said chamber (60) to project said powders (56) through the barrel (62) on the base (18) and the bearing cap (22) and / o u the periphery of the camshaft (12) so that it plastically deforms and consolidates.