FR2821891A1 - CYLINDER HEAD OF THERMAL ENGINE INCLUDING AN UPPER ELEMENT, FORMING A CYLINDER HEAD COVER, WHICH SUPPORTS THE CAMSHAFT - Google Patents

Abstract

The invention provides a cylinder head for a heat engine, in particular for a motor vehicle, comprising a main part or cylinder head body (10) intended to be mounted on a cylinder block of the engine and capped by a cylinder head cover (30), type in which the cylinder head has a recess (28) which is intended to receive actuating elements (18 ') of the engine valves and which opens into an upper face (32) of the cylinder head body (10), on which is fixed to said cylinder head cover (30), the valve actuating elements comprising a camshaft (18 ') fixed by means of bearings (34a, 34b) each consisting substantially of a fixed half (34a) in the cylinder head and of an attached half in the form of a bearing cap (34b), characterized in that said fixed bearing halves (34a) are formed in the cylinder head cover (30).

Description

according to any of claims 1 to 13.

  "Heat engine cylinder head comprising an upper element, forming a cylinder head cover, which carries the camshaft" The invention relates to a heat engine cylinder head,

  especially for a motor vehicle.

  The invention relates more particularly to a cylinder head of a combustion engine, in particular for a motor vehicle, comprising a main part, forming a body of a tire, intended to be mounted on a cylinder block of the engine and comprising an upper part, forming a cylinder head cover, of the type in which the cylinder head has a recess which is intended to receive valve actuating elements of the engine and which opens into an upper face of the body of the cylinder, on which the cover is fixed cylinder head, the valve actuating elements comprising a camshaft fixed by means of bearings each consisting substantially of a fixed half in the cylinder head and of an attached half in the form of a

bearing cap.

  In an internal combustion engine cylinder head, the admission of the air / fuel mixture and the discharge of the burnt gases are controlled by respective valves, actuated by a camshaft, ie a single camshaft,

either by two camshafts.

  In most vehicles of recent production, the camshaft (s) are mounted "at the head", that is to say the closest

  possible valves, so in the cylinder head.

  Each camshaft is positioned and rotatably mounted in the cylinder head by means of plain bearings, generally made of aluminum or aluminum alloy, each of which consists of a bearing half, called the "fixed" half, formed directly in the cylinder head and completed by an attached bearing cap, or a part that incorporates this function, which should therefore be fixed on the

cylinder head.

  To provide the necessary lubrication between the camshaft, usually made of steel, and the aluminum of the bearings, oil supply pipes are practiced in the cylinder head,

  so as to lead to the right of the landings.

  This results in a number of constraints for the design and construction of the cylinder head. In particular, the "fixed" half bearings produced at the level of the cylinder head are obtained during the manufacture of the latter by molding. Therefore, their shapes and positions depend on the constraints of production of the cylinder head, namely that it must have on the one hand adequate passages for the elements of the distribution, as well as

  passages for the bolts fixing the cylinder head to the block

engine cylinders.

  In particular, it is sought to place the camshaft bearings as much as possible in the middle between two successive engine cylinders, but the cylinder head must also be fixed lS on the engine cylinder block precisely in the same intermediate region between the cylinders, so that practically in the same transverse plane of the cylinder head four or six vertical bores, two for fixing the cylinder head to the cylinder block of the engine and two or four for fixing the

  or bearing caps. This is not always possible.

  Furthermore, taking into account the orientation of the fixed half-bearings formed in the cylinder head, almost all of the forces which develop between the camshaft and the valves are precisely directed in the opposite direction to these fixed half-bearings, so that they must be collected by the bearing caps added. It should therefore be taken into account when designing and producing these bearing caps, as well as their

  fixing on the rest of the cylinder head.

  In a very compact architecture, as is the case with small displacement engines, the installation of these fixed half-bearings becomes an important problem, and one may have to opt for non-optimal technical solutions, which it is cost, mass, or technical performance. By way of example, it may indeed be necessary to choose a spacing, considered in the axial direction of the camshaft, greater than necessary between the bearings, with the corollary that it will then be necessary to make the stiffer camshaft, therefore more

heavy and bulkier.

  Another solution could consist in decoupling the "fixed" half bearings from the rest of the cylinder head, but with the consequence that an interface is added between the cylinder head and each half bearing, that is to say also manufacturing operations additional, and then a

  tightness at this interface.

  Finally, the numerous conduits, channels, recesses and bores thus formed in the cylinder head, and very particularly in the cylinder head body, significantly reduce its rigidity, and it is therefore frequently necessary to provide that the cylinder head cover fixed on the upper face of the breech body has a rigidity of its own to give the assembly formed by the breech body and the breech cover sufficient rig id ity. Fixing this cylinder head cover also requires corresponding tapped holes

dants for fixing screws.

  The object of the invention is therefore to propose a cylinder head in which the mounting of the camshaft, or of the camshafts, does not have the abovementioned drawbacks, without however increasing the complexity of the production of the cylinder head,

  nor increase production costs.

  According to the invention, this objective is achieved with a cylinder head of the type indicated in the introduction, characterized in that said fixed halves of bearings are produced in the

weary cover.

  According to other characteristics of the invention: - the fixed halves of bearings made in the cylinder head cover have an orientation capable of absorbing substantially all of the stresses under operation by the camshaft;

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  - The cylinder head cover is made in the form of a beam having a rigidity suitable for supplementing that of the cylinder head body; - The bearing caps are fixed under the underside of the cylinder head cover which is itself supported on the upper face of the cylinder head body; - two threads formed in the cylinder head cover for screws for fixing a bearing cap and two holes formed in the cylinder head body for screws for fixing the cylinder head are arranged substantially in the same axial plane of the engine, between two cylinders thereof; The camshaft has a central bore for the distribution of lubricant to the bearings of the camshaft; - each bearing cap has through holes for fixing screws, and the cylinder head cover has threads for the screws; - Each bearing cap has a projecting positioning finger, which is housed during mounting in a hole of corresponding shape in the underside of the

weary beam cover.

  Other characteristics 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 appended drawings, in which: - Figure 1 is a fragmentary schematic sectional view, through a vertical axial plane parallel to the axes of the cylinders, of a first cylinder head according to the prior art; - Figure 2a is a sectional view of a second cylinder head according to the prior art, taken along line 2a-2a of Figure 2b; - Figure 2b is a partial elevational view of the cylinder head of Figure 2a from above;

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  - Figure 3a is a sectional view of a cylinder head according to the invention, taken along line 3a-3a of Figure 3b, in a representation similar to that of Figure 2a; and - Figure 3b is a partial elevation view from above of the cylinder head of Figure 3a. Throughout the figures, the same references have been used to designate elements which are identical or fulfill the same functions, if appropriate accompanied by an index

  (a, b, etc.), or of the sign ['] (prime) or ["] (second).

  In addition, in the present description, the expressions

  "vertical", "below", etc., refer to the orientation of the elements of a heat engine as shown in

figures.

  In FIG. 1, there is seen a vertical section of a cylinder head according to the state of the art, comprising a main part or body of the cylinder head 10, the lower face 12 of which is intended to be fixed to a cylinder block (not shown) of a heat engine, which is therefore arranged below the cylinder head in the

representation of figure 1.

  In the lower region of the cylinder head body 10 are provided intake (or exhaust) passages 14 intended for the flow of the admitted air / fuel mixture to the engine cylinders, or respectively for the flow of gases.

  burns which escape from the cylinders.

  These passages 14 are controlled by valves 16, and these are actuated by at least one camshaft 18, of which only the cross section can be seen, which extends in the longitudinal direction of the engine, here perpendicular to the plane of the figure. The camshaft 18 carries cams 20, only one of which is visible here, distributed along its length and each associated with one

  engine intake or exhaust valves 16.

  As is well known, the profile of the cams 20 and their respective angular positions around the shaft 18 are chosen in the desired manner to obtain the temporal succession

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  adequate valve openings / closings that match the engine operating cycles

  (intake - compression - expansion - exhaust).

  The cams 20 serve only to control the downward movement of the valves 16, by pressing the valve stems 22 directed upwards. The return of the valves 16 upwards in the closed position is ensured by means of springs 24 trapped between the cylinder head body 10 and cups 26 fixed on the valve stems 22 l0The camshaft 18-20 is housed in a longitudinal recess 28 provided in the upper face 32 formed in the top of the cylinder head body 10, which is capped by an upper part forming a cylinder head cover 30, the latter being fixed by pressing its lower face 33 on the upper face 32 of the cylinder head body 10. The camshaft 18 is mounted in the cylinder head by bearings, each of which is designated as a whole by the reference 34, composed of a lower half-bearing 34a "fixed" integrally formed with the cylinder head body itself, and an attached upper half-bearing 34b, known as a "bearing cap", fixed to the cylinder head body in correspondence with the lower fixed half-bearing 34a by screws 36, thereby completing the bearings 34 For the passenger e of screws 36, the bearing cap

has holes 37.

  Figure 1 shows that the production of the cylinder head is complex, especially since it must still house passages for the flow of engine coolant, threaded housings for fixing the spark plugs (engines with petrol) or glow plugs (diesel engines) or injectors (injection engine), as well as passages and pipes for the lubricant supplied to

  bearings 34 of the camshaft 18-20.

  We also see in this figure that the cylinder head cover 30 is not only a simple "cover" intended to close the upper recess of the cylinder head body 10, but that it is

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  brought to fulfill an important stiffening function of the cylinder head body which no longer has the proper rig id ity required, taking into account the multiple recesses and passages mentioned passing through it. It is also clear that the lower half-bearings 34a take almost no effort in operation, but that the upper half-bearings 34b take almost all the efforts, mainly due to the return springs 24. It is therefore necessary to take them into account for their dimensioning, and that of their fixing. On the other hand, the apparently satisfactory aspect for those skilled in the art, it is here that the production of the lower half-bearings directly coming from material in the body of the tire during its molding appears to be the most suitable solution.

simpler and less expensive.

  Now observing Figures 2a and 2b, we realize

  that this solution often leads to difficult technical choices.

  Indeed, it is here a cylinder head which carries two camshafts (not themselves represented in the figure, but symbolized by their axes 18 ′ and 18 ″), as is becoming usual in modern engines, in particular small displacement engines

  which we seek to obtain the greatest possible power.

  In the section of FIG. 2a, the lower half-bearings 34a 'and 34a "are displaced relatively far upwards and outwards, if one refers to a median longitudinal and vertical plane, symbolized by the line LL in the elevation view of FIG. 2b. Correspondingly, the upper half bearings 34b ′ and 34b ″ are made integrally

  with a common component which also forms the cylinder head cover 30.

  This solution has in this respect at least the advantage that the integration of the upper half-bearings 34b 'and 34b "in the

  cylinder head cover is homogeneous with its stiffening function.

  On the other hand, the geometric constraints are such that, as shown in FIG. 2b, the threads 38 intended for the screws

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  36 for fixing the upper half-bearings must be advanced axially (that is to say in the direction L-L) so far that they are almost at the same level as an engine cylinder (C). The intermediate zones between the cylinders are in fact reserved for the holes 40 intended for the bolts for fixing the cylinder head to the cylinder block, which can in no case be placed elsewhere since they are essential for the sealing of

the cylinder head on the cylinder block.

  Referring now to Figures 3a and 3b which show a cylinder head according to the present invention,

  new in section and partial elevation.

  Here, the cylinder head body 10 itself no longer directly performs the mounting function of the camshaft (symbolized by its axis 18 '). This function is taken up by the upper part forming a cylinder head cover 30, practically performed here

  in the form of a "beam" in which the half-pieces are formed

  "fixed" upper bearings 34a, with the necessary rigidity taking into account the forces they take, and here also in a way which is well compatible with the stiffening function devolved to the

cylinder head beam 30.

  The lower half-bearings 34b are added parts, fixed under the cylinder head cover beam 30. Since they take almost no effort in operation, they can be dimensioned as closely as possible, just like their fixing screws,

  to simply close the corresponding bearing 34.

  The advantages of this solution are manifold. First, because it is no longer necessary to provide fixed half-bearings formed in the cylinder head body, there is greater freedom for its design. It is also not necessary to provide holes in the cylinder head body for fixing the bearing caps, which also leads to a more

great freedom of design.

  In this regard, since the threads 38 'for the fixing screws 36' of the bearing caps 34b are provided in the

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  cylinder head cover 30 and no longer in the cylinder head body 10, there is no obstacle to providing that these threads 38 'formed in the beam and the holes 40 formed in the cylinder head body 10 for the screws cylinder head fixing on the cylinder block are arranged substantially in the same axial plane

  of the engine, between two cylinders thereof.

  It is of course necessary to provide in the cylinder head threads 42 for fixing screws 44 of the cylinder head cover beam 30 on the cylinder head body 10. Thanks to the inherent rigidity of the beam 30, it will be possible to provide these threads 42 to practically any locations, in which they do not interfere with other elements of the cylinder head or the mechanical assembly

camshaft / valves.

  In particular, when there is enough material, it is possible to spare the threads 42 also substantially in the same plane as the fastening screws of the thickened, that is to say between

  two successive engine cylinders (C).

  For the lubrication of the bearings 34, nothing prevents the provision in the cylinder head body 10, and / or in the cylinder head cover 30, of lubricant distribution conduits, such as for example the same lubricant which is used for the mechanical elements of the motor, these conduits leading to the upper half-bearings 34a. However, it may be wise to provide lubrication through the center of the camshaft. In this case, it has an axial bore (not shown) closed at both ends, which extends over the entire length concerned by the bearings, and radial holes at each of the bearings. The axial drilling is supplied with lubricant under pressure via a bearing at the end of the camshaft, leaving a shallow groove and holes in the periphery of the camshaft.

  radial which make it communicate with the axial bore.

  It should also be noted that the fact of providing the “fixed” bearing half-bearings on the cylinder head cover beam does not

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  does not lead, during assembly, to possible cu m uis of harmful tolerances between the camshaft - which depends on the cylinder head cover on the one hand, and the rest of the mechanism

  valves - which depends on the cylinder head body - on the other hand.

  Indeed, the bearing spans are machined at the final dimensions "in situ". That is to say that we proceed to the blank mounting of the bearing caps on the beam and then the beam on the cylinder head body, and we take advantage of the fact that it exists at the end of the cylinder head (according to the axial direction) in any case an opening for the subsequent passage of the end of the camshaft which is to be connected to its drive mechanism (chain, gear, or toothed belt), to introduce the final machining tool in

  axial direction and make it pass successively through the bearings.

  The very small clearances which can then result from disassembly and then reassembly are immaterial. The only clearances which cannot be completely overcome are the axial clearances, that is to say in the direction of the length of the camshaft. These games, however, remain here in the range of those found in cylinder heads of conventional construction and do not

represent no discomfort.

  As an option, each bearing cap 34b has a positioning finger 50 in sail lie, which is housed during mounting in a hole 52 of corresponding shape in the face

  lower 33 of the cylinder head cover beam 30.

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Claims (8)

  1. Cylinder head (10) of an engine, in particular for a motor vehicle, comprising a main part or body of cylinder head (10) intended to be mounted on a cylinder block of the engine and covered by a cylinder head cover (30), type in which the cylinder head has a recess (28) which is intended to receive actuating elements (18-20) of engine valves and which opens into an upper face (32) of the cylinder head body (10), on which is fixed said cylinder head cover (30), the valve actuating elements comprising a camshaft (18) fixed by means of bearings (34) each consisting substantially of a fixed half (34a) in the cylinder head and an attached half in the form of a bearing cap (34b), characterized in that said fixed bearing halves   (34a) are made in the cylinder head cover (30).   2. Cylinder head according to claim 1, characterized in that the bearing halves (34a) produced in the cylinder head cover (30) have an orientation capable of absorbing substantially all of the forces undergone by operation by led it a rb re à cams (18).   3. Cylinder head according to either of claims 1 and 2,   characterized in that the cylinder head cover (30) is produced in the form of a beam having a rigidity suitable for supplementing that of the cylinder head body (10).   4. Cylinder head according to any one of claims 1 to   3, characterized in that the fixing of the bearing caps (34b)   is performed under the underside (33) of the cylinder head cover (30).   5. Cylinder head according to any one of claims 1 to   4, characterized in that two threads (38 ') formed in the cylinder head cover (30) for fixing screws (36') of a bearing cap (34b) and two holes (40) formed in the cylinder head body ( 10) for cylinder head fixing screws are arranged substantially in the same axial plane of the engine, between two cylinders of it. i2 2821891   6. Cylinder head according to any one of claims 1 to   , characterized in that the camshaft has a central bore for distribution of lubricant to the bearings of the cams (18).   7. Cylinder head according to any one of claims 1 to   6, characterized in that each bearing cap (34b) has through holes (37) for fixing screws (36 '), and the cylinder head cover (30) has internal threads (38') for said screws (36 ').   8. Cylinder head according to any one of claims 1 to   7, characterized in that each bearing cap (34b) has a sail lie positioning finger (50), which is accommodated during mounting in a hole (52) of corresponding shape   in the lower face (33) of the cylinder head cover beam (30).