GB2510469A

GB2510469A - Combustion engine with gasket clamped between cylinder head and engine block

Info

Publication number: GB2510469A
Application number: GB201321396A
Authority: GB
Inventors: Arun Krishnamurthy; Hartwig Renninger
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2013-12-04
Filing date: 2013-12-04
Publication date: 2014-08-06
Also published as: GB201321396D0

Abstract

The invention relates to a combustion engine 1 for a motor vehicle, the combustion engine comprising an engine block 2, which is separated from a cylinder head 3 by a gasket, which is clamped between the engine block 2 and the cylinder head 3 by means of fixing elements 4 which are arranged in bores 5, 6 in the cylinder head 3 and the engine block 2 and which exert a clamping force 13 upon the gasket. In an area 8 around at least one of the bores 5, 6 at least one gap 9 is arranged, by means of which a peak 7 of the clamping force 13 is circumferentially spaced apart from the at least one of the bores 5, 6 of the fixing elements 4. The gap 9 may be a countersunk bore or a slotted hole. The gap may extend from one fixing bore 5,6 to another.

Description

A Combustion Engine for a Motor Vehicle The invention relates to a combustion engine for a motor vehicle according to the preamble of claim 1.

A combustion engine for a motor vehicle with the feature of the preamble of claim 1 is known from US 2010/0072687 Al. The combustion engine described in this document comprises a dummy head (a jig for processing a cylinder block) having a dummy head body deforming a cylinder bore by assembling into a mounting surface of the cylinder block by bolt fastening. During the finish processing of the cylinder bore, a boss having a contact surface contacting a peripheral portion of the cylinder bore on the head mounting surface is provided on a mounting surface side for the cylinder block of the dummy head body. This boss is designed as a material accumulation surrounding the cylinder bores whereat by means of this boss gases from the combustion in the combustion engine can be prevented from leaking from the combustion engine due to the fact that the boss exerts a clamping force to seal the contact surface between the boss and the cylinder block. The boss in this document comprises a circumferential grooving, which is adapted to the contour of the successively arranged cylinder liners. Due to the fact that the boss is arranged at least partially circumferentially around the cylinder liners this material accumulation (the boss) has to be manufactured precisely along a large area and therefore with especially great effort.

It is the object of the present invention to provide a combustion engine for a motor vehicle of the initially mentioned kind, by means of which the combustion gases can be prevented from leaking from the combustion engine in an especially-efficient and easy manner.

According to the invention, this object is solved by a combustion engine for a motor vehicle having the features of claim 1. Advantages, configurations with convenient developments of the invention are specified in the remaining claims.

In order to provide a combustion engine of the initially mentioned kind, by means of which the combustion gases can be prevented from leaking from the combustion engine in an especially inexpensive and particularly easy manner, it is provided according to the invention that in an area around at least one of the bores at least one gap is arranged, by means of which a peak of the clamping force is circumferentially apart from the at least one of the bores of the fixing elements.

The contact pressure to seal the combustion chamber of the combustion engine against combustion gas leakage depends on both the clamping force, which is exerted by means of the fixing element (e.g. bolts, screws) and the contact area of the parting plane between the cylinder head and the engine block. By means of the gap this contact area of the parting plane can be reduced and thus the contact pressure can be increased, by means of which also the tightness of the combustion chamber against combustion gas leakage can be increased. The gap corresponds to a material cut-out, which is arranged around at least one of the bores so that the clamping force and especially the peak of the clamping force is circumferentially spaced apart from the bores according to the contour of the gap. In other words, by means of the gap the contact area of the parting plane between the cylinder head and the engine block is restricted whereat if the size of the gap is enlarged the contact area of the parting plane is reduced accordingly and thus the contact pressure between the cylinder head and the engine block increases. In other words, by reducing the contact area on the parting plane a higher contact pressure between the cylinder head and the engine block can be achieved with the same or even less pretension of the fixing elements. By modifying the contour of the gap around at least one of the bores the contact pressure between the fixing elements can be distributed in a favourable manner thus increasing the overall tightness of the combustion engine. The contact pressure P is defined as: P0 = clamping force/contact area.

The following example shall illustrate this fact: Under the simplified assumption that the contact area of the parting plane between the cylinder head and the cylinder block is rectangular having the width B and the length L and also having a bore with the diameter d of the contact area Ad can be calculated as follows: = (L B) -d2/4) Assuming now that for the sake of simplicity a circular gap with the diameter d' is arranged in an area around the bore with the diameter d, a new contact area Ad can be calculated as follows: = (L B) -(u d'214) Due to the fact that the circular gap comprises a bigger area than the bore, and thus d' > d, hence it applies to the corresponding contact areas: Ad' .c Ad. Thus it is clear that by arranging the gap with a bigger area than the bore the contact area of the parting plane is reduced corresponding to the area of the gap. Whilst the cylinder head was previously rested upon the edge of the bore in the cylinder block, the cylinder head is now rested upon the edge of the gap in the cylinder block, wherein the peak of the clamping force between the cylinder block and the cylinder head passes through the edge of the gap. In other words and compared to the force flow in the conventional bore, by means of the gap the force flow is now redirected according to the edge of the gap and thus spaced apart from the bore.

By means of such a gap a high contact pressure can be achieved with less pretension of the fixing elements (e.g. bolts, screws, studs) and thus the fatigue life of the fixing elements is increased. By means of such a gap a leak-proof joint between the engine block and the cylinder head can be achieved, since the manufacturing of the gap is accompanied by a material cut-out, a weight reduction on the combustion engine can also be achieved. Since the contact area between the cylinder head and the engine block is reduced by means of the gap, also the material usage of the gasket between the engine block and cylinder head can be reduced. The gap can be manufactured especially easily, wherein the modification of the combustion engine can be achieved with little effort.

Further advantages, features and details of the invention are apparent from the following description of a preferred embodiment as well as by way of reference to the drawings.

They show in: Fig. 1 a a schematic sectional view of a portion of a combustion engine, wherein a combustion chamber of the combustion engine is built by an engine block

and a cylinder head according to the prior art;

Fig. lb a schematic view of a portion of the combustion engine according to a section D, which is marked with dashed lines in Fig. 1 a; Fig. ic a schematic isometric view of a section of the engine black comprising bores with threads by means of which the cylinder head can be mounted on the engine block using fixing elements; Fig. id a schematic sectional view of the bores inside the engine block and the cylinder head, wherein the clamping force, which is caused by one of the fixing elements, passes along the bores in both the engine block and the cylinder head; Fig. le a schematic top view of the parting plane of the engine block, wherein the contact area between the engine block and the cylinder head is defined by a length L, a width B, and the bore with the diameter d in the engine block; Fig. 2a an isometric view of the portion of the engine block, wherein circular gaps are arranged around the bores; Fig. 2b a schematic top view of the portion of the engine block shown in Fig. 2a; Fig. 2c a schematic top view of a portion of the engine block shown in Fig. 2a, wherein the contact area according to the parting plane between the engine block and the cylinder head is reduced by the gap; Fig. 2d a schematic sectional view on a portion of the engine block shown in Fig. 2a, wherein the gap has a height h; Fig. 2e a schematic sectional view of the engine block shown in Fig. 2a, wherein a peak of the clamping force is circumferentially spaced apart from the bore in the engine block; Fig. 3a an isometric view of the engine block, wherein the gap extends from one bore to another, adjacent bore of the engine block; Fig. 3b a schematic top view of the engine block shown in Fig. 3a; and in Fig. 3c a schematic sectional view of the engine block shown in Fig. 3a.

Fig. 1 a shows a schematic sectional view of a combustion engine 1 according to the prior art. A combustion chamber 10 of the combustion engine 1 is restricted by an engine block 2 and a cylinder head 3. The engine block 2 comprises a bore 5 with a thread 11 and the cylinder head 3 comprises a bore 6, wherein the bore 6 is designed as a through-bore hole, which is at least substantially aligned with the bore 5. By means of a fixing element 4, which is designed e.g. as a bolt, a stud, or a screw and engages the thread 11, the cylinder head 3 is fixed to the engine block 2 wherein by means of the fixing element 4 a clamping force 13 (which is not illustrated in Fig. la) is exerted upon a gasket, which is also not shown.

Fig. lb shows a detailed view of a portion D, which is marked with dashed lines in Fig. la.

Fig. lb shows that the engine block 2 and the cylinder head 3 at least substantially share a parting plane 12 with a contact area between the engine block 2 and the cylinder head 3. It is clear that usually the engine block 2 is in contact with an underside of the gasket (not shown) and the cylinder head 3 is in contact with an upper side of the gasket, but for the sake of simplicity the engine block 2 and the cylinder head 3 share the contact area according to the parting plane 12.

Fig. lc to Fig. le -like Fig. la and Fig. lb -also show different views of a portion of the engine block 2. If the fixing element 4 is designed as a bolt an engaged with the thread 11, by means of the fixing element 4 a clamping force 13 is exerted upon the gasket (not shown) and thus both upon the cylinder head 3 and the engine block 2. The clamping force 13 is induced by the pretension of the fixing element 4, wherein a head (not shown) of the fixing element 4 rests upon a bolt head area 16 when the fixing element 4 is engaged with the thread 11 in the engine block 2. The clamping force 13 extends from the bolt head area 16 to a thread end 15 of the thread 11. In other words, the force flow of the clamping force 13 terminates in the thread end 15 of the thread 11 in the bore 5. The thread end 15 corresponds to an area where an end of the fixing element 4, which comprises a corresponding thread at this end is engaged with the thread 11. A peak 7 of the clamping force 13 passes both through the cylinder head 3 and the engine block 2 along the bore 6 and the bore 5, wherein the clamping force 13 as well as the peak 7 of the clamping force 13 terminates in the thread end 15 of the thread 11. Both the peak 7 and the clamping force 13 are illustrated as slightly curved lines extending from the bolt head area 16 to the thread 11. When the fixing element 4 is tightened and thus engaged with the thread 11 by means of a tightening torque, the fixing element 4, the cylinder head 3, and the engine block 2 are at least slightly deformed. This deformation results in the peak 7 of the clamping force 13 in the cylinder head 3 and the engine block 2 respectively, and close to the fixing element 4 (along the bores 5, 6) wherein the peak 7 is equivalent to the maximum value of the clamping force 13. As a consequence, in regions of both the cylinder head 3 and the engine block 2, which are spaced from the bores 5, 6, the value of the clamping force 13 decreases due to the deformations. The larger the distance from the fixing element 4, and accordingly from the bores 5, 6. the smaller is the clamping force 13 exerted by the fixing element 4. The reduction of the clamping force 13 is carried out with increasing distance from the bores 5, 6 in a radial direction corresponding to a decrease direction 14, which is illustrated by arrows in Fig. 1 d. It is clear that the quality of the tightness decreases with the decreasing of the clamping force 13 according to the decrease direction 14 and thus in radial distance to the bores 5, 6. If another, adjacent fixing element 4 is arranged in too wide a distance from this fixing element 4, this can lead to leaks in the region of the parting plane 12, since the clamping force 13 between the adjacent fixing elements 4 is too low to maintain a high sealing quality.

The contact pressure P is influenced by both the clamping force 13 and the contact area according to the parting plane 12. Based on Fig. 1 e, and according to the prior art as well as Fig. lc and Fig ld, one can calculate the contact area Ad between the engine block and the cylinder head 3 as follows: Ad = (L B) -(rr d2/4) Since the contact pressure P0 is defined as P0 = clamping force/contact area, it can be seen that the contact pressure P0 increases with decreasing contact area.

Fig. 2a to Fig. 2e show different views of portions of the engine block 2, wherein in an areaS around each of the shown bores 5 a gap 9 is arranged. The gap 9 has a height h and adiarneterd', wherein: > d.

In other words, the diameter d' of the gap 9 is larger than the diameter d of the bore 5 in the engine block 2. To achieve an easy manufacturing, the gap 9 is designed as a countersunk bore and thus the gap 9 is arranged centrally with respect to the bore 5.

Since the diameter d' of the gap 9 is larger than the diameter d of the bore 5, the contact area Ad', which is defined as Ad = (L B) -(u d'214) is smaller than the contact area Ad without the gap 9 and thus Ad' c Ad.

In other words, by means of the gap 9, which is arranged in a circumferential area 8 around the bore 5 at present, the contact area between the engine block 2 and the cylinder head 3 is decreased and thus the contact pressure between the engine block 2 and the cylinder head 3 is increased. By means of the gap 9 also the peak 7 of the clamping force 13 is circumferentially spaced apart from the bore 5 of the fixing element 4. Alternatively or in addition, a further gap could be arranged around the bore 6 in the cylinder head 3. by means of which the peak 7 of the clamping force 13 can also be spaced apart from the bore S of the fixing element 4. This further gap could be arranged in the cylinder head 3 as an alternative or in addition to the gap 9 in the engine block. By means of the gap 9 the peak 7 of the clamping force 13 is spaced apart from the bore 5 of the fixing element 4, as can be seen in Fig. 2e. Thus, the force flow of the peak 7 of the clamping 13 extends along the bore 6, which is formed as a through-bore hole in the cylinder head 3 and is then deflected in accordance with the contour of the hole 9 and depending on the diameter d' and the height h of the gap 9 around the bore 5 in the cylinder block 2, respectively. The force flow of the clamping force 13 terminates in the thread end 15 of the thread 11 in the bore 5. By means of the gap 9 the clamping force and especially the peak 7 of the clamping force 13 is spaced apart from the bore 5 according to the respective decrease direction 14 of the clamping force 13. The decrease direction 14 of an adjacent bolting has an opposite direction and thus the clamping forces 13 of the two adjacent boltings are closer to each other and thus distributed over a larger portion of the contact area than without the gap 9. In other words, by means of the gap 9 also in an area between the boltings the clamping force is large to ensure a high quality of the sealing.

Fig. 3a to Fig. 3c show another embodiment of the gap 9, wherein the gap 9 is designed as a slotted hole. The gap 9 extends from one bore 5 to another adjacent bore 5 of the engine block 2. In addition or as an alternative, the gap 9 could also be arranged within

S

the cylinder head 3 and thus extend from one bore 6 to another, adjacent bore. It the gap 9 is designed as a slotted hole, the contact area between the engine block 2 and the cylinder head 3 is reduced in a particularly extensive manner and thus the contact pressure P0 can be further increased in comparison to the gap 9 shown in Fig. 2a to Fig. 2e, in which the gap 9 is designed as a countersunk bore.

List of reference signs 1 combustion engine 2 engine block 3 cylinder head 4 fixing element bore 6 bore 7 peak S area 9 gap combustion chamber 11 thread 12 parting plane 13 clamping force 14 decrease direction thread end 16 bolt head area

Claims

Claims A combustion engine (1) for a motor vehicle, the combustion engine (1) comprising an engine block (2) which is separated from a cylinder head (3) by a gasket, which is clamped between the engine block (2) and the cylinder head (3) by means of fixing elements (4) which are arranged in bores (5, 6) in the cylinder head (3) and the engine block (2) and which exert a clamping force (13) upon the gasket, characterized in that, in an area (8) around at least one of the bores (5, 6) at least one gap (9) is arranged, by means of which a peak (7) of the clamping force (13) is circumferentially spaced apart from the at least one of the bores (5, 6) of the fixing elements (4).
2. The combustion engine (1) according to claim 1 characterized in that, the gap (9) is designed as a countersunk bore.
3. The combustion engine (1) according to claim 1 characterized in that, the gap (9) is designed as a slotted hole.
4. The combustion engine (1) according to claim 3 characterized in that, the gap (9) extends from one bore (5, 6) to another, adjacent bore (5, 6) of the engine block (2) and/or of the cylinder head (3).
5. The combustion engine (1) according to any one of claims 1 to 4 characterized in that, the bores (6) in the cylinder head (3) are designed as through bore-holes.
6. The combustion engine according to any one of claims 1 to 4 characterized in that, the bores (5) in the engine block (2) each comprise a thread.