JP2017125444A - Engine combustion chamber structure - Google Patents

Abstract

[PROBLEMS] To effectively suppress an increase in cost while improving sealing performance with a simple configuration. A first cylinder part 11 formed in a cylinder block 10, a piston 30 capable of reciprocating in the first cylinder part 11, a cylinder head 20 above the cylinder block 10, and a piston 30 A second cylinder portion 21 capable of receiving at least a part of the top land portion 31 of the piston 30 at the top dead center, the second cylinder portion 21 being formed with a smaller diameter than the first cylinder portion 11, 2 At least a part of the inner periphery of the cylinder portion 21 is caused to function as a carbon scraper that scrapes off carbon adhering to the top land portion 31. [Selection] Figure 1

Description

  The present invention relates to a combustion chamber structure of an engine.

  A general combustion chamber structure of an engine includes a cylinder liner provided in a cylinder block, a lower surface of a cylinder head arranged at the upper part of the cylinder block, and a top surface (cavity) of a piston accommodated in the cylinder so as to be reciprocally movable. (See, for example, Patent Document 1).

JP 2003-83157 A

  In the conventional combustion chamber structure, the gap between the cylinder head and the cylinder block is sealed with a head gasket that is sandwiched between the cylinder head lower surface and the cylinder block upper surface. According to such a seal structure, even when the piston reaches the compression top dead center, the head gasket (seal part) is positioned above the piston. That is, since the head gasket is in communication with the combustion chamber at the compression top dead center of the piston where the combustion chamber reaches the maximum cylinder pressure, the maximum cylinder pressure directly acts on the head gasket to affect the sealing performance. May give.

  Further, in the conventional combustion chamber structure, an annular step portion is provided on the inner periphery on the upper end side of the cylinder liner, and a carbon scraper ring for scraping off carbon adhering to the top land portion of the piston is fitted to the annular step portion. ing. That is, since the cylinder liner and the carbon scraper ring are provided separately, there is a possibility that the cost increases, such as an increase in the number of parts and assembly man-hours.

  An object of the disclosed combustion chamber structure is to effectively suppress an increase in cost while improving sealing performance with a simple configuration.

  The disclosed combustion chamber structure is formed in a first cylinder part formed in a cylinder block, a piston capable of reciprocating in the first cylinder part, a cylinder head above the cylinder block, and a top dead center of the piston. A second cylinder part capable of receiving at least a part of the top land part of the piston, and the second cylinder part is formed with a smaller diameter than the first cylinder part, and the second cylinder It is characterized in that at least a part of the inner periphery of the portion functions as a carbon scraper that scrapes off carbon adhering to the top land portion.

  You may further provide the gasket provided between the upper surface of the said cylinder block, and the lower surface of the said cylinder head, and the opening diameter was formed in the same diameter as the internal diameter of the said 1st cylinder part.

  It is preferable that the gasket is provided between the upper surface of the cylinder block and the lower surface of the cylinder head so that the opening edge thereof coincides with the inner peripheral edge of the upper end of the first cylinder portion.

  According to the disclosed combustion chamber structure, it is possible to effectively suppress an increase in cost while improving the sealing performance with a simple configuration.

It is a typical longitudinal cross-sectional view which shows the combustion chamber structure of the engine which concerns on one Embodiment of this invention. In FIG. 1, it is a typical longitudinal cross-sectional view which shows the state which has a piston in the vicinity of a top dead center. It is a typical longitudinal cross-sectional view which shows the combustion chamber structure of the engine which concerns on other embodiment. It is a typical longitudinal cross-sectional view which shows a part of conventional combustion chamber structure.

  Hereinafter, an engine combustion chamber structure according to an embodiment of the present invention will be described with reference to the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, the combustion chamber structure of the engine of this embodiment includes a first cylinder portion 11 provided in the cylinder block 10, and a second cylinder portion 21 provided in a cylinder head 20 above the cylinder block 10. The piston 30 is capable of reciprocating in the first and second cylinder parts 11 and 21, and the gasket 40 is used to seal the gap between the cylinder block 10 and the cylinder head 20.

  The cylinder head 20 includes an intake port 23, an exhaust port 24, an intake valve 25 that introduces fresh air into the combustion chamber from the intake port 23 by an opening / closing operation, and an exhaust valve 26 that guides exhaust gas from the combustion chamber to the exhaust port 24 by an opening / closing operation. An injector 27 for directly injecting fuel is provided in the combustion chamber.

  A plurality of ring grooves 32 </ b> A to 32 </ b> C extending in the circumferential direction are recessed in the outer periphery of the top land portion 31 of the piston 30. Piston rings 33A to 33C are mounted in the plurality of ring grooves 32A to 32C, respectively. Further, a step portion 31 </ b> A having a diameter smaller than that of the skirt portion 34 is provided above the top ring groove 33 </ b> A of the top land portion 31.

  The first cylinder portion 11 has an inner diameter D1 that is substantially the same as the outer diameter of each piston ring 33A to 33C. The outer peripheral surface of the slidably moves.

  The second cylinder portion 21 has an inner diameter D2 slightly larger than the outer diameter of the step portion 31A of the top land portion 31. Further, the second cylinder portion 21 is formed such that its axial length (height) is longer than the axial length (height) of the step portion 31 </ b> A of the top land portion 31.

  That is, as shown in FIG. 2, when the piston 30 reaches the vicinity of the top dead center, the step portion 31 </ b> A of the top land portion 31 is received in the second cylinder 21, and a minute clearance is formed between the inner peripheral surface of the second cylinder 21. By being close to each other, the inner cylinder surface of the second cylinder 21 functions as a carbon scraper that scrapes off the carbon adhering to the side surface of the top land portion 31. Further, when the piston 30 reaches the vicinity of the compression top dead center, the step portion 31A of the top land portion 31 is received in the second cylinder 31 so that the head gasket 40 is positioned below the top surface of the piston 30. It has become so.

  The head gasket 40 is sandwiched between the upper surface of the cylinder block 10 and the lower surface of the cylinder head 20 to seal the gap between the cylinder block 10 and the cylinder head 20. In this embodiment, the opening diameter of the head gasket 40 is formed to be substantially the same as the inner diameter D1 of the first cylinder portion 11, and the inner peripheral edge 41 of the opening is substantially the same as the upper edge of the inner peripheral surface of the first cylinder portion 11. Mounted to match.

  That is, the opening inner peripheral edge 41 of the head gasket 40 is substantially coincident with the upper edge of the inner peripheral surface of the first cylinder portion 11, so that the lower surface of the cylinder head 200 and the carbon scraper ring 500 of the conventional structure shown in FIG. A space S that does not contribute to combustion defined by the upper surface and the inner peripheral edge 400A of the head gasket 400 (hereinafter, the space is referred to as a waste volume) is eliminated.

  As described above in detail, in the combustion chamber structure of the engine of the present embodiment, when the piston 30 reaches near the top dead center, at least a part of the top land portion 31 of the piston 30 is received in the second cylinder 21, The inner peripheral surface of the second cylinder 21 functions as a carbon scraper that scrapes off carbon adhering to the side surface of the top land portion 31. Thereby, compared with the conventional structure which equips a carbon scraper ring with another body, it becomes possible to reduce a number of parts and an assembly man-hour, and can suppress an increase in cost effectively.

  Further, the head that seals the gap between the cylinder head 20 and the cylinder block 10 by at least a part of the top land portion 31 being received in the second cylinder 21 due to the difference in which the piston 30 reaches the vicinity of the compression top dead center. The gasket 40 is positioned below the top surface of the piston 30 at the maximum in-cylinder pressure so as not to communicate directly with the combustion chamber. As a result, it is possible to effectively prevent the maximum in-cylinder pressure from acting on the head gasket 40 at the compression top dead center of the piston 30, and the sealing performance can be reliably improved.

  In addition, since the inner peripheral surface of the second cylinder portion 21 has an integral structure that functions as a carbon scraper, the head gasket 40 is placed outside the carbon scraper ring in order to ensure sealing performance as in the conventional structure shown in FIG. There is no need to offset it. That is, there is no waste volume S (see FIG. 4) between the upper surface of the cylinder block 10 and the lower surface of the cylinder head 20, and deterioration of wrinkles and the like can be effectively prevented. Further, since it is not necessary to offset the head gasket 40 to the outside, it is possible to shorten the separation distance between the cylinders, so that it is possible to effectively reduce the engine downsizing and weight.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, in the above-described embodiment, the step portion 31A is provided in the top land portion 31 of the piston 30, but the step portion 31A may be omitted as shown in FIG. Also in this case, the inner diameter D2 of the second cylinder portion 21 is formed to be smaller than the inner diameter D1 of the first cylinder portion 11, and the inner peripheral surface of the second cylinder portion 21 functions as a carbon scraper. An effect can be produced.

DESCRIPTION OF SYMBOLS 10 Cylinder block 11 1st cylinder part 20 Cylinder head 21 2nd cylinder part 23 Intake port 24 Exhaust port 25 Intake valve 26 Exhaust valve 27 Injector 30 Piston 31 Topland part 31A Step part 32A-C Ring groove 33A-C Piston ring 34 Skirt 40 Head gasket

Claims (3)

A first cylinder part formed in the cylinder block;
A piston capable of reciprocating in the first cylinder part;
A second cylinder part formed on a cylinder head at the top of the cylinder block and capable of receiving at least a part of a top land part of the piston at a top dead center of the piston;
Forming the second cylinder part with a smaller diameter than the first cylinder part, and causing at least a part of the inner periphery of the second cylinder part to function as a carbon scraper that scrapes off carbon adhering to the top land part. Characteristic engine combustion chamber structure. The engine combustion chamber according to claim 1, further comprising a gasket provided between an upper surface of the cylinder block and a lower surface of the cylinder head, the opening diameter of which is the same as the inner diameter of the first cylinder portion. Construction. The combustion chamber structure for an engine according to claim 2, wherein the gasket is provided between an upper surface of the cylinder block and a lower surface of the cylinder head with an opening edge thereof coinciding with an inner peripheral edge of an upper end of the first cylinder portion.

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