Device for sealing a combustion chamber of a combustion engine

Abstract: Device for sealing a combustion chamber (6) of a combustion engine, which combustion chamber is bounded by a cylinder liner (2), preferably replaceable, surrounded by a cylinder block (1), a piston and a cylinder head (3). A disc-shaped sealing element (5) is pressed in between the cylinder liner (2) and the cylinder head (3), where either the liner (2) or the cylinder head (3) is provided with an annular protruding portion (23) and the other one of them with a corresponding recess (36) into which the sealing element (5) is pressed. The protruding portion (23) has a greater radial width than the recess (36).

Description: The invention relates to an device for sealing a combustion chamber of a combustion engine according to the preamble to claim 1. State of the art. Combustion engines often incorporate a number of combustion chambers arranged in a cylinder block, in which case each combustion chamber is usually bounded radially by a cylinder liner supported with respect to the block, upwards by a cylinder head and downwards by a power-transmitting piston. This arrangement means that there is a gap between, on the one hand, the cylinder head and, on the other hand, the cylinder liner and the cylinder block. This gap has to be sealed to prevent gases from leaking out from the combustion chamber, which might otherwise lead to disturbance of operation and breakdown. This problem is generally greater in diesel engines than in Otto engines, since the former usually have a higher combustion pressure and operate under greater load. One way of solving the problem is to insert a seal in the form of a steel plate disc between the cylinder liner and the cylinder head. This sealing plate is often subjected to deformation by pressing it between labyrinth-forming shoulders and recesses with the object of achieving increased tightness. Such solutions involve having to subject the connection to a large clamping force which may lead to large force stresses and consequently increasing risks of fracture and cracking, e.g. at the support of the cylinder liner in the cylinder block. This applies particularly to engines in which the cylinder liner is supported by a supporting ledge close to the cylinder head, i.e. a so-called "top stop" liner. In engines where the cylinder liner is supported by a supporting ledge situated relatively far from the cylinder head, i.e. a so-called "mid stop" liner, the liner may only be subjected to a certain maximum clamping force, otherwise it risks suffering unfavourable deformation certain maximum clamping force, otherwise it risks suffering unfavourable deformation impairing its interaction with the piston, thereby possibly leading to the moving piston striking the liner, with the consequent possibility of shearing and risk of engine breakdown. US 4 112 907 shows a sealing arrangement between a cylinder liner and a cylinder head of a diesel engine where ribs on top of the cylinder liner abut a lower contact surface of the cylinder head clamping a gasket interposed between the liner and the cylinder head. US 3 661 135 discloses a sealing arrangement between a cylinder liner and a cylinder head of a diesel engine in which a gasket is compressed between an annular rib fitting into a corresponding annular groove. Object of the invention. The object of the invention is to provide a simple arrangement for sealing a combustion chamber of a combustion engine which succeeds in preventing gas leakage from the combustion chamber. This arrangement should as far as possible obviate any need for large clamping forces that might otherwise lead to fracture. The invention is particularly devoted to improving tightness in engines in which the cylinder liner is removable and of the "mid stop" type. Brief description of the invention. The device according to the invention is defined by the features according to claim 1. The fact that the protruding portion is wider than the opposing recess and has a longer radial extent both inwards and outwards means that there are two circular clamping zones in which the sealing element may be compressed and hence prevent gas leakage without unduly large power effects. The arrangement according to the characterising part of claim 2 represents a simple production solution in that the cylinder head may be provided with a flat lower surface in which the recess may thereafter be formed. Using a relatively soft sealing disc with a low yield point according to the characterising part of claim 3 makes it possible to achieve good tightness where the seal fills the recess properly. This solution has advantages in the case of "mid stop" type cylinder liners in that the sealing disc may be deformed sufficiently by relatively small clamping forces. The other dependent claims refer to advantageous dimensioning and detail solutions which, inter alia, ensure clamping zones both radially within and outside the recess. Other features and advantages distinguishing the invention are indicated by the following description of an embodiment, which is described with reference to the attached drawings. List of drawings. Figure 1 shows a vertical section through a combustion engine. Figure 2 shows an enlarged section of area A in Figure 1. Description of embodiment. This description mentions directions as upwards and downwards. These refer only to the drawings, which show a stationary engine. The invention is of course also applicable to engines with other physical orientations. The drawings show a vertical section through a six-cylinder diesel engine of the in-line type intended for a heavy-duty vehicle such as a truck. The engine incorporates inter alia a cylinder block 1, six substantially cylindrical combustion chambers 6 which are each bounded radially by a respective cylinder liner 2 supported in the block 1. Each combustion chamber 6 is bounded axially by a separate cylinder head 3 and a movable piston 4 arranged to transmit power to the driveline. The cylinder liner 2 may advantageously take the form indicated in SE 92 03 933, which refers to a cylinder liner of the so-called "mid stop" type. The liner is supported in the cylinder block by a circular contact surface 26 facing downwards which interacts with a contact surface 11 of the block, which surfaces 11, 26 are arranged in the vicinity of the lower reversing point of the piston 4. The cylinder 2 is surrounded by a number of cooling ducts 12 for cooling its upper hotter section. The liner indicated in SE 92 03 933 is also replaceable, which is of course favourable for the total life of the engine. The engine described here is provided with a separate cylinder head 3 for each combustion chamber 6. The cylinder head 3 is provided in a known manner with inlet and exhaust ducts 31 (only one of which is depicted in the diagrams), cooling ducts 32, recesses 33 for valve bodies and fuel injectors, and holes 34 for bolts for fastening to the cylinder block 1. A disc-shaped sealing element 5, here a metal disc according to the invention with a yield point below 250 MPa, preferably below 150 MPa, is arranged in the gap which is formed between, on the one hand, the cylinder head 3 and, on the other hand, the cylinder block 1 and the cylinder liner 2. The object of the sealing disc 5 is to prevent gas leakage from the combustion chamber 6 to the environment. Such leakage might lead to disturbance of operation or breakdown, because of the possibility of gas reaching the cooling system and the great heat which occurs at the leakage point. The sealing disc 5 has advantageously the same extent as the lower surface 35 of the cylinder head 3. Figure 2 shows an enlarged view of the gas seal arrangement which in all essentials is arranged symmetrically in rotation about the centreline of the combustion chamber 6. The upper axial end portion of the cylinder liner is provided at its radial inner end with a protruding flange 21. The sealing disc 5 is arranged radially outside the protruding flange 21. The sealing disc 5 is pressed against a supporting surface 22 which in the vertical direction projects somewhat above the upper surface 13 of the cylinder block in this area. This is important in that the sealing disc 5 has to be pressed firmly between the cylinder head 3 and the cylinder block 1, otherwise it would not be possible to achieve sufficient tightness. In addition, a sealing ring 25 is arranged between the cylinder liner 2 and the cylinder block 1 with the object of preventing leakage from the upper cooling duct 12. The upper supporting surface 22 is provided with an annular protruding portion 23 according to the invention. Substantially in the middle of this portion 23 the lower surface 35 of the cylinder head 3 is provided with an annular recess 36 with a smaller radial width than the protruding portion 23. The result is the formation of two annular clamping zones 51 where the sealing disc 5 is pressed against the protruding portion 23 but outside the recess 36. The sealing disc 5 is thus deformed so that it substantially fills the recess 36, thereby providing proper tightness in the two clamping zones 51. The radially outer section 24 of the upper surface is somewhat lower than the supporting surface 22. The reason for this is the endeavour to place the power load of the cylinder liner as close to its mean radius as possible in order thereby to achieve favourable deformation of the cylinder liner 2. The endeavour is therefore to achieve substantially the same contact area between the cylinder liner 2 and the sealing disc both outside and within the radially middle part of the projecting portion 23, which may be achieved by suitable choice of radial width for the outer portion 24. "Mid stop" cylinder liners may not be subjected to the same large clamping forces as "top stop" liners. The reason for this was described earlier. If an ordinary plate disc is used as a seal, it is so hard that the maximum forces usable with "mid stop" liners will not deform the disc sufficiently to "fill" the recess 36. Moreover, there would only be line contact in the clamping zones, resulting in great sensitivity to defects and the consequent possibility of insufficient tightness. A softer disc may therefore be used with "mid stop" liners. It is advantageous to use a copper disc or a mild carbon steel disc with a yield point below 150 MPa. The clamping force across the liner should be about 200-400 kN. The clamping force should be increased in cases of increased liner thickness or increased modulus of elasticity of the liner. The force should be reduced correspondingly in cases of reduced thickness or modulus of elasticity. Experiments have shown that reduced clamping forces, due inter alia to softer seals, may be compensated by a larger area of clamping zones. The arrangement according to the invention with two clamping zones with an intermediate "filled" recess also means that leakage in one zone may be tolerated without impairing operation. The fact that the protruding portion 23 and the recess 36 are situated at the same nominal mean distance from the centreline of the combustion chamber 6 minimises the risk of unfortunate tolerances possibly leading to the recess 36 in the fitted position being partly within or outside the projecting portion 23. Experiments with a multi-cylinder diesel engine with a swept volume of 2 litres per cylinder have shown that optimum tightness is achieved if the protruding portion is shelf-like with a height of about 0.2 mm and a radial width of about 1.4 mm whereby the recess is about 0.2 mm deep and about 1.0 mm wide. This results in the respective clamping zone having a radial width of about 0.2 mm. These experiments used a sealing disc 1.0 mm thick. Deviations from the measurements stated above should preferably be not more than one or a few tenths of a millimetre, although the thickness of the sealing disc may be between 0.5 and 2.0 mm depending on the type of engine. In applications on other sizes or types of engines, other dimensions may be preferable but the mutual relationships should substantially correspond to those which may result from the measurements stated above. The radial width of the protruding portion 23 is advantageously not more than twice the radial width of the recess 36. Moreover, the height of the protruding portion 23 should not exceed the depth of the recess 36 nor be less than half of the latter's depth. The embodiment described may be modified in various ways within the scope of the patent claims. Thus the invention may be applied to other combustion engines, not merely diesel engines of the in-line type. A common cylinder head may also be used for two or more combustion chambers. The location of the projecting portion and the recess may also be reversed. This makes no notable operating change but is disadvantageous from the production point of view in that it makes manufacturing the cylinder head more difficult. The change entails no corresponding simplification of cylinder liner manufacture.

Claims: Device sealing a combustion chamber (6) of a combustion engine, which engine incorporates at least one cylinder block (1) with at least one substantially cylindrical combustion chamber (6) bounded by a cylinder liner (2) arranged in the cylinder block (1), by a piston (4) and by a cylinder head (3), with a sealing element (5) pressed in between the cylinder liner (2) and the cylinder head (3), which cylinder liner (2) has an end surface (22) facing towards a lower contact surface (35) of the cylinder head (3), where either the end surface (22) or the contact surface (35) is provided with a shelf-like annular protruding portion (23) and the opposite surface (35; 22) with an annular recess (36) corresponding to the protruding portion (23), the recess and the protruding portion having an inner and outer diameter measured from the cylinder axis, and the sealing element being provided between at least said inner and outer diameters characterised in that the outer diameter of the protruding portion (23) exceeds the outer diameter of the recess (36) and that the inner diameter of the protruding portion (23) is smaller than the inner diameter of the recess (36). Device according to claim 1, characterised in that the end surface (22) is provided with the protruding portion (23) and that the contact surface (35) is provided with the recess (36). Device according to claim 1 or 2, characterised in that the sealing element (5) is substantially disc-shaped with a yield point below 250 MPa, preferably below 150 MPa. Device according to claim 3, characterised in that the sealing element (5) consists of a disc with a thickness of 0.5 - 2.0 mm, preferably 1.0 mm. Device according to any one of claims 1-4, characterised in that the cylinder liner (2) is replaceable and incorporates with respect to the cylinder block (1) an annular contact surface (26) which faces in the opposite direction to the end surface (22) and which is situated in the vicinity of the lower reversing position of the piston (4). Device according to any one of claims 1-5, characterised in that the protruding portion (23) and the recess (36) have substantially the same mean diameter. Device according to any one of claims 1-6, characterised in that substantially the same contact area between the cylinder liner (2) and the sealing disc (5) occurs radially outside as radially within the mean diameter of the protruding portion (23). Device according to any one of claims 1-7, characterised in that the protruding portion (23) is not more than twice as wide as the recess (36), that its height does not exceed the depth of the recess (36) and that its height is not less than half the depth of the recess (36). Device according to any one of claims 1-8, characterised in that the width of the protruding portion (23) is 1.2 - 1.6 mm, preferably 1.4 mm, that its height is 0.15 - 0.25 mm, preferably 0.2 mm, that the width of the recess (36) is 0.8 - 1.2 mm, preferably 1 mm, and that its depth is 0.15 - 0.25 mm, preferably 0.2 mm. Arrangement according to any one of claims 1-8, characterised in that the combustion engine is a diesel engine with a number of combustion chambers (6) accommodated in the cylinder block (1) and that each combustion chamber (6) is bounded by a cylinder liner (2), a piston (4) and a separate cylinder head (3) and is sealed by means of a separate sealing element (5).

Inventors: BERGGREN MARTIN, BERGSTROEM MAGNUS, KARLSSON KARL-ERIK, LANGE PER, MASUS GOERAN, BERGGREN, MARTIN, BERGSTROEM, MAGNUS, KARLSSON, KARL-ERIK, LANGE, PER, MASUS, GOERAN, Bergström, Magnus, Masus, Göran
Applicants: SCANIA CV AB, SCANIA CV AKTIEBOLAG
Application year: 1996
Main classification: F02F11
IPC codes: F16J15, F02F11