internal combustion engine

Abstract

To further reduce a cooling loss generated in a cylinder block of an internal combustion engine.SOLUTION: An internal combustion engine 1 controls a flow of cooling water so that the temperature of cooling water circulating in a cylinder head 12 forming a ceiling portion of a combustion chamber of a cylinder in which a piston provided with a heat shielding film on a surface moves forward / backward becomes lower than the temperature of cooling water circulating in a cylinder block 11 containing a cylinder bore of the cylinder. Therefore, the temperature of the cooling water circulating in the cylinder block 11 can be made higher than the temperature of the cooling water circulating in the cylinder head 12, and a cooling loss generated in the cylinder block 11 can be further reduced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-cooled (or liquid-cooled) internal combustion engine that is mounted on a vehicle or the like as a power source. [Background technology]

[0002] Internal combustion engines installed in vehicles, especially four-wheeled automobiles, are generally water-cooled. Today, the coolant (or coolant) used in water-cooled internal combustion engines is made by mixing water with LLC (Long Life Coolant), which is primarily composed of ethylene glycol, and anti-rust additives. LLC lowers the freezing point and raises the boiling point of the coolant. Anti-rust additives inhibit rust on the metals that make up the internal combustion engine components.

[0003] To further explain the cooling water system of an internal combustion engine, the cooling water drawn in and discharged by the cooling water pump first flows into the cylinder block containing the cylinder bores, where it cools various parts of the cylinder block, particularly the areas around the cylinder bores. The cooling water then flows into the cylinder head, which forms the ceiling of the combustion chamber, and cools various parts of the cylinder head, particularly the ceiling of the combustion chamber and the areas around the intake and exhaust ports connected to it. After cooling the cylinder block and cylinder head, the cooling water flows down toward the cooling water pump and is sucked back into the pump.

[0004] When the coolant receives heat and becomes significantly hot, the coolant is forced to flow into a heat exchanger for cooling, typically a radiator that exchanges heat with outside air, to actively lower its temperature. The cylinder head is provided with a shunt passage that communicates with the radiator, and a thermostat that opens and closes the shunt passage. When the temperature of the coolant flowing through the cylinder head exceeds a set temperature, the thermostat opens, allowing the coolant to flow through the radiator. When the temperature of the coolant flowing through the cylinder head falls below the set temperature, the thermostat closes, and the coolant stops flowing through the radiator (see, for example, Patent Document 1 below).

[0005] Among the various losses in an internal combustion engine, cooling loss (heat loss), in which thermal energy is taken from the combustion gas to the wall of the combustion chamber, including the top surface of the piston, during the expansion stroke, accounts for a large proportion.In an attempt to reduce this cooling loss, recent attempts have been made to use a piston with a heat-shielding film formed on the surface that reciprocates within the cylinder (see, for example, Patent Document 2 below). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-133869 [Patent Document 2] Japanese Patent Publication No. 2020-101141 Summary of the Invention [Problem to be solved by the invention]

[0007] By covering the piston with a heat-shielding film, the amount of heat escaping from the combustion chamber of the cylinder to the piston can be reduced, but on the other hand, the temperature inside the combustion chamber of the cylinder increases, resulting in a trade-off: more heat is escaping to the cylinder block via the inner wall surface of the cylinder bore.

[0008] The heat that escapes to the cylinder block is absorbed by the coolant flowing through the cylinder block, raising its temperature. The coolant then flows into the cylinder head, where it receives heat and is further heated. This causes the thermostat attached to the cylinder head to open, allowing the coolant to flow into the heat exchanger, or radiator. This essentially means that the cylinder bore absorbs thermal energy from the combustion gases and then wastefully discards that heat energy outside via the radiator.

[0009] The present invention has been made in view of the above points, and has as its intended object to further reduce the cooling loss that occurs in the cylinder block of an internal combustion engine. [Means for solving the problem]

[0010] In this invention, the cooling water discharged from the cooling water pump is branched, and a portion of it flows into a cylinder block containing the cylinder bore of a cylinder in which a piston with a heat insulating film on the surface moves back and forth, and the remainder flows into a cylinder head forming the ceiling of the combustion chamber of the cylinder without passing through various parts in the cylinder block, and a thermostat is provided on a flow path in which the cooling water that has circulated in the cylinder block returns to the cooling water pump via a radiator, and another thermostat is provided on a flow path in which the cooling water that has circulated in the cylinder head returns to the cooling water pump via the radiator, The temperature at which the latter thermostat opens is set to be approximately the same as the temperature at which the former thermostat opens, This created an internal combustion engine in which the latter thermostat opened before the former thermostat. [Effects of the Invention]

[0011] According to the present invention, it is possible to further reduce the cooling loss occurring in the cylinder block of an internal combustion engine. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram schematically illustrating the configuration of a cooling water system of an internal combustion engine according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described with reference to the drawings. The internal combustion engine 1 of this embodiment is a water-cooled four-stroke reciprocating engine that is mounted on a vehicle or the like as a power source, and its basic structure follows that of a known internal combustion engine.

[0014] FIG. 1 shows a schematic diagram of the cooling water passages of an internal combustion engine 1 according to this embodiment. In the drawing, the flow of cooling water is indicated by arrows. The cooling water pump 15, which draws in, discharges, and circulates cooling water, may be a mechanical (non-electric) pump that operates by receiving rotational driving force from the crankshaft, which is the output shaft of the internal combustion engine 1, or may be an electric pump that is rotationally driven by an electric motor. If the cooling water pump 15 is mechanical, its rotation speed will be proportional to the rotation speed of the internal combustion engine 1.

[0015] The cooling water discharged from the cooling water pump 15 is first branched, with one part heading toward the cylinder block 11 containing the cylinder bores of the multiple cylinders of the internal combustion engine 1, and the other part heading toward the cylinder head 12, which forms the ceiling of the combustion chamber and the intake and exhaust ports of each cylinder 1. The latter flow of cooling water flows directly into the cylinder head 12 without passing through various parts within the cylinder block 11. In other words, the latter flow of cooling water does not significantly cool the cylinder block 11, and does not receive much heat from the cylinder block 11.

[0016] The cooling water that flows into the cylinder block 11, circulates within the cylinder block 11, and cools various parts of the cylinder block 11 flows down toward the cooling water pump through the return path 18, and is again sucked into the cooling water pump 15. This return path 18 is provided with a path that communicates with a radiator 16, which is a heat exchanger located outside the internal combustion engine 1, and a thermostat 13 that opens and closes this path. The thermostat 13 opens when the temperature of the cooling water flowing within the cylinder block 11 reaches a predetermined value, for example, a high temperature of 90°C to 100°C or higher, and closes when the temperature of the cooling water falls below the predetermined value.

[0017] When the thermostat 13 is open, at least a part of the cooling water that has flowed through the cylinder block 11 flows into the radiator 16. 6The coolant exchanges heat with the outside air in the cooling water circulator 13, where it is cooled, and then merges with the return path 18, through which it is returned to the coolant pump 15. When the thermostat 13 is closed, the coolant that has circulated through the cylinder block 11 does not flow into the radiator 16, but instead flows back to the coolant pump 15 through the return path 18.

[0018] The cooling water that flows into the cylinder head 12, circulates within the cylinder head 12, and cools various parts of the cylinder head 12 flows down through a return flow path 19 toward the cooling water pump 15, and is again sucked into the cooling water pump 15. This return flow path 19 is provided with a flow path that communicates with the radiator 16, and a thermostat 14 that opens and closes this flow path. The thermostat 14 opens when the temperature of the cooling water flowing within the cylinder head 12 reaches a predetermined value, for example, a high temperature of 90°C or 100°C or higher, and closes when the temperature of the cooling water falls below the predetermined value.

[0019] When the thermostat 14 is open, at least a portion of the coolant that has circulated inside the cylinder head 12 flows into the radiator 16. The coolant exchanges heat with outside air in the radiator 16 to be cooled, then joins the return path 19 and flows back to the coolant pump 15 through the return path 19. When the thermostat 14 is closed, the coolant that has circulated inside the cylinder head 12 does not flow into the radiator 16, but flows back to the coolant pump through the return path 19.

[0020] Incidentally, a portion of the coolant that has circulated inside the cylinder block 11 or the cylinder head 12 may flow through a heat exchanger 17 other than the radiator 16 before being returned to the coolant pump 15. Specific examples of the heat exchanger 17 include a heater core for heating the vehicle interior, an EGR cooler that lowers the temperature of EGR gas that is returned from the exhaust passage to the intake passage by an exhaust gas recirculation device of the internal combustion engine 1, and a warmer that warms the working fluid (automatic transmission fluid, continuous variable transmission fluid) used in the transmission of the vehicle's drive system.

[0021] In conventional internal combustion engine coolant systems, the coolant discharged from a coolant pump first flows through the cylinder block to cool the cylinder block, then flows through the cylinder head to cool the cylinder head, and then flows into the radiator. The coolant supplied to the cylinder head is already heated by the cylinder block. In other words, the temperature of the coolant flowing through the cylinder head is higher than that of the coolant flowing through the cylinder head itself, and the thermostat located between the cylinder head and the radiator senses the temperature of the heated coolant and opens and closes accordingly.

[0022] Abnormal combustion, such as knocking, is likely to occur near the ceiling of the combustion chamber in the cylinder, i.e., near the cylinder head. Therefore, to prevent abnormal combustion, it is necessary to reliably cool the cylinder head. However, in the conventional cooling water system described above, an attempt to suppress the temperature of the cooling water flowing through the cylinder head results in the temperature of the cooling water flowing through the cylinder block being lower than the temperature of the cooling water flowing through the cylinder head, which raises concerns about an unnecessary increase in the amount of heat absorbed by the cylinder bore from the combustion gases.

[0023] On the other hand, in the coolant system of the internal combustion engine of this embodiment, the coolant discharged from the coolant pump 15 is divided into two, one of which is supplied to the cylinder block 11, while the other is supplied directly to the cylinder head 12. This allows the temperature of the coolant flowing through the cylinder head 12 to be lower than the temperature of the coolant flowing through the cylinder block 11. Conversely, the temperature of the coolant flowing through the cylinder block 11 can be higher than the temperature of the coolant flowing through the cylinder head 12.

[0024] Therefore, even if a heat-shielding film is formed on the surface of the piston that reciprocates within the cylinder of the internal combustion engine 1, the amount of heat that the cylinder bore of the cylinder contained in the cylinder block 11 removes from the combustion gas is reduced compared to conventional methods. As a result, the cooling loss that occurs in the cylinder block 11 can be further reduced. In addition, as a side effect of keeping the cylinder block 11 warm, the temperature of the lubricating oil (engine oil) supplied to the sliding parts of the piston (piston rings) and piston oil jets, as well as the cylinder bore, is appropriately increased, which is expected to reduce friction loss.

[0025] Furthermore, the temperature of the ceiling of the combustion chamber of the cylinder contained within the cylinder head 12 can be kept sufficiently low, which reliably reduces the risk of abnormal combustion such as knocking. If abnormal combustion is less likely to occur, it becomes possible to advance the spark ignition timing for the air-fuel mixture filled in the cylinder and bring it closer to MBT (Minimum Advance for Best Torque), improving the thermomechanical conversion efficiency of the internal combustion engine 1.

[0026] In this embodiment, the temperature at which the thermostat 13 on the cylinder block 11 side opens and the temperature at which the thermostat 14 on the cylinder head 12 side opens are set to be approximately the same. Nevertheless, the latter thermostat 14 is likely to open before the former thermostat 13. However, the temperature at which the former thermostat 13 opens may be set to a temperature range higher than the temperature at which the latter thermostat 14 opens.

[0027] When both the thermostat 13 and the thermostat 14 are open, the flow rate of the cooling water flowing through the cylinder head 12 becomes greater than the flow rate of the cooling water flowing through the cylinder block 11 .

[0028] The present invention is not limited to the above-described embodiment. For example, a flow path that directly connects the cylinder block 11 and the radiator 16, which is a heat exchanger, and a thermostat 11 that opens and closes the flow path may be provided. 3can be abolished.

[0029] In addition, the specific configuration of each part can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0030] 1...Internal combustion engine 11...Cylinder block 12...Cylinder head 13, 14...Thermostat 15...Cooling water pump 16...Heat exchanger (radiator)

Claims

[Claim 1] The cooling water discharged from the cooling water pump is branched, and a portion of the branched water flows into a cylinder block containing a cylinder bore in which a piston with a heat insulating film on its surface moves back and forth, and the remaining portion flows into a cylinder head that forms the ceiling of the combustion chamber of the cylinder without passing through various parts of the cylinder block. a thermostat is provided on a flow path through which the cooling water that has flowed through the cylinder block returns to the cooling water pump via a radiator, and another thermostat is provided on a flow path through which the cooling water that has flowed through the cylinder head returns to the cooling water pump via the radiator, An internal combustion engine in which the temperature at which the latter thermostat opens is set to be approximately the same as the temperature at which the former thermostat opens, and the latter thermostat opens before the former thermostat.

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