INTERNAL COMBUSTION ENGINE WITH IMPROVED THERMAL EFFICIENCY

Abstract

An internal combustion engine includes a piston adapted to reciprocate in a cylinder. The piston includes a first portion, a second portion, and a third portion. The first portion of the piston forms a crown surface of the piston, the second portion of the piston forms a piston ring groove of the piston with the piston ring groove arranged and configured to receive a piston ring, and the third portion of the piston forms a crankcase side surface of the piston with the crankcase side surface facing a crankcase of the engine. The second portion of the piston is formed of a material having a higher thermal conductivity than a material forming the first portion of the piston and a material forming a third portion of the piston.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Various examples of objects, features and attendant advantages of an embodiment of the present invention will become fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein:

FIG. 1 shows a variable compression-ratio mechanism.

FIG. 2A and FIG. 2B show a mechanism for adjusting the stroke of a piston at the time of top dead center in the variable compression-ratio mechanism.

FIG. 3 is a chart that shows piston stroke characteristics obtained in a multi-link piston stroke mechanism and in a single-link piston stroke mechanism.

FIG. 4 is a chart that shows the relationship between compression ratio and thermal efficiency when the compression ratio is increased.

FIG. 5 shows a sectional view of the main part of a thermal insulating piston.

FIG. 6 is a chart that shows the change in the thermal insulation of a combustion chamber when the compression ratio is increased.

FIG. 7 shows a configuration of a control system according to an embodiment of the present invention.

FIG. 8A and FIG. 8B are charts showing compression-ratio control characteristics in relation to varying engine operating conditions.

FIG. 9 is a set of charts showing transient characteristics of a compression-ratio control and of an ignition advance control when knocking occurs.

FIG. 10 shows a sectional view of a part related to a piston and a cylinder liner.

Claims

1. A piston adapted to reciprocate in a cylinder of an internal combustion engine, comprising: a first portion formed at least in part of a first material;a second portion formed at least in part of a second material; anda third portion formed at least in part of a third material,wherein the first portion forms a crown surface of the piston, the second portion forms a piston ring groove of the piston with the piston ring groove arranged and configured to receive a piston ring, and the third portion forms a crankcase side surface of the piston with the crankcase side surface facing a crankcase of the engine, andwherein the second material has a higher thermal conductivity than that of the first material and the third material.

2. The piston in accordance with claim 1, wherein the first portion is joined to the third portion with the second portion sandwiched therebetween.

3. The piston in accordance with claim 1, wherein the first portion and the third portion are jointed and formed in layers through the second portion.

4. The piston in accordance with claim 1, wherein the third material is lighter in weight than the second material.

5. The piston in accordance with claim 1, wherein the third material is a non-metric material.

6. The piston in accordance with claim 1, wherein the entirety of the third portion of the piston is formed of the third material.

7. The piston in accordance with claim 1, wherein the third portion is formed with an oil ring groove configured and arranged to receive an oil ring.

8. An internal combustion engine, comprising: a cylinder block having a cylinder with a top dead center side portion of the cylinder is formed of a top dead center material having a lower thermal conductivity than a bottom dead center material forming a bottom dead center side portion of the cylinder; anda piston as set forth in claim 1.

9. The internal combustion engine in accordance with claim 8, wherein the piston adapted to reciprocate in the cylinder is configured and arranged such that the piston ring is in contact with the bottom dead center material of the cylinder at a bottom dead center position of the piston.

10. The piston in accordance with claim 1, wherein the second material forming the piston ring groove has a thermal conductivity lower than or equal to that of the piston ring received therein.

11. An internal combustion engine, comprising: a variable compression-ratio mechanism adapted to vary an engine compression ratio on the basis of an operating condition of the internal combustion engine, the compression ratio being reduced during low speed and high load operating condition as compared to that during high speed and low load operating condition, anda piston as set forth in claim 1.

12. The internal combustion engine in accordance with claim 11, further comprises a knocking sensor, and wherein the compression ratio is controlled to reduce when a signal from the knocking sensor is greater than or equal to a predetermined value.

13. The internal combustion engine in accordance with claim 11, wherein the variable compression-ratio mechanism comprises: a first link having one end connected with a piston pin of the piston;a second link having one end connected with a second end of the first link, the second link being rotatably mounted on a crank shaft;a third link having one end connected with a second end of the second link; anda control shaft having an eccentric shaft portion eccentric from a rotational center axis of the control shaft, the eccentric shaft portion being rotatably connected with a second end of the third link, andwherein the compression ratio being varied by rotating the control shaft based on the operating condition of the internal combustion engine with moving the eccentric shaft portion in up and down directions and varying a top dead center position of the piston.

14. The internal combustion engine in accordance with claim 13, wherein a link configuration of the first link, the second link, and the third link cases a stroke characteristic of the piston to be substantially simple harmonic motion.

15. An internal combustion engine, comprising: a piston adapted to reciprocate in a cylinder, the piston having a first portion that forms a crown surface of the piston, a second portion that at least forms a piston ring groove adapted to receive a piston ring, a third portion that forms a crankcase side surface of the piston, and wherein the second portion is formed of a second material having a thermal conductivity higher than a first material forming the first portion and a third material forming the third portion.