JP2011256742A - Cooling system for piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the width of temperature change in a top ring, concerning a system for cooling the piston of an internal combustion engine.SOLUTION: A cooling system for a piston includes a cooling channel designed as an annular oil passage embedded in the piston and arranged adjacent to a top ring groove, and an oil jet that supplies oil to the cooling channel. An amount of oil supplied from the oil jet to the cooling channel is made larger when an amount of heat generated in a combustion chamber is large than when the amount of heat generated in the combustion chamber is small.

Description

  The present invention relates to a technique for cooling a piston of an internal combustion engine, and more particularly to a technique for cooling a piston provided with a cooling channel.

  An annular piston ring having a cut (abutment) is attached to the piston of the internal combustion engine. As such a piston ring, one in which an elastic resin is provided on each of two end faces (opposing end faces) facing each other through a joint has been proposed (for example, see Patent Document 1).

JP 2010-031789 A JP 2009-287486 A JP 2009-156186 A

  By the way, a part of the heat generated when the fuel burns in the cylinder (combustion chamber) is transmitted to the piston ring through the piston. Therefore, when the amount of heat generated in the combustion chamber increases, the amount of thermal expansion of the piston ring increases. As a result, the width (gap) of the joint is narrowed, and compression leakage and blow-by gas are reduced.

  However, if the amount of heat generated in the combustion chamber is further increased, the amount of thermal expansion of the piston ring is further increased, so that the opposite end faces of the joint may collide with each other. Such problems that may increase the stress acting on the piston ring or increase the contact load between the piston ring and the cylinder bore wall when the opposite end surfaces abut each other at the joint of the piston ring are caused by the combustion chamber. It becomes prominent in the nearest piston ring (top ring).

  To solve this problem, a method of enlarging the gap at the joint is conceivable. However, when the amount of heat generated in the combustion chamber is small, or when the temperature of the piston is low, the gap at the joint is excessive, causing compression leakage and blow-by gas. The problem arises that increases.

  The present invention has been made in view of the above circumstances, and an object thereof is to reduce the temperature change width of the top ring in a system for cooling a piston of an internal combustion engine.

  In order to solve the above-described problems, the inventor of the present application has found that the temperature of the top ring can be adjusted by using a cooling channel provided in the piston. That is, as a result of earnest experiment and verification, the inventor of the present application makes a cooling channel adjacent to a top ring groove to which a top ring is attached in a piston, and the amount of oil supplied to the cooling channel depends on the amount of heat generated in the combustion chamber. It was found that the temperature change width of the piston ring during the operation of the internal combustion engine is reduced by adjusting the pressure.

Therefore, the piston cooling system of the internal combustion engine of the present invention is
An annular groove provided on the outer peripheral surface of the piston, and a top ring groove to which the top ring is attached;
An annular oil passage provided in the piston, the cooling channel adjacent to the top ring groove;
An oil jet for supplying oil to the cooling channel;
When the amount of heat generated in the combustion chamber is large, a control unit that increases the amount of oil supplied from the oil jet to the cooling channel compared to when the amount of heat is small,
I was prepared to.

  The heat generated in the combustion chamber is transferred to the top surface of the piston. The heat transmitted to the top surface of the piston is transmitted through the piston mainly from the top surface of the piston toward the top ring groove, and is radiated from the top ring groove to the cylinder bore wall surface through the top ring.

  When the amount of heat generated in the combustion chamber is large, the ratio of the amount of heat transmitted from the top ring to the cylinder bore wall surface becomes lower than the amount of heat transmitted from the piston to the top ring. Therefore, when the amount of heat generated in the combustion chamber is large, the amount of temperature rise of the top ring increases.

  On the other hand, when the amount of heat generated in the combustion chamber is small, the ratio of the amount of heat transmitted from the top ring to the cylinder bore wall surface becomes higher than the amount of heat transmitted from the piston to the top ring. Therefore, when the amount of heat generated in the combustion chamber is small, the amount of temperature rise of the top ring is small.

  As described above, the temperature of the top ring greatly varies depending on the amount of heat generated in the combustion chamber. When the temperature of the top ring changes greatly, the size of the abutment gap also changes accordingly. Therefore, when the top ring is formed so that the abutment gap has an appropriate size when the temperature of the top ring is low, a situation occurs in which the opposite end surfaces of the abutment abut each other when the temperature of the top ring becomes high. . On the other hand, when the top ring is formed so that the abutment gap has an appropriate size when the top ring temperature is high, the size of the abutment gap may become excessive when the top ring temperature is low. appear.

  On the other hand, when the cooling channel is disposed adjacent to the top ring groove, particularly when the cooling channel is disposed on the transmission path from the piston top surface to the top ring groove, the piston top surface to the top ring groove. The transmitted heat is lost to the oil in the cooling channel.

  Therefore, if the amount of oil flowing through the cooling channel is increased when the amount of heat generated in the combustion chamber is large, the amount of heat taken away by the oil in the cooling channel increases from the heat toward the top ring groove from the piston top surface. Therefore, it is possible to avoid a situation in which the amount of heat transferred from the piston top surface to the top ring groove becomes excessive. As a result, when the amount of heat generated in the combustion chamber is large, a situation in which the temperature of the top ring becomes excessively high can be avoided.

  On the other hand, when the amount of oil flowing through the cooling channel is reduced when the amount of heat generated in the combustion chamber is small, the amount of heat taken by the oil in the cooling channel is reduced among the heat from the piston top surface toward the top ring groove. Therefore, it is possible to avoid a situation in which the amount of heat transmitted from the piston top surface to the top ring groove is excessively reduced. As a result, it is possible to avoid a situation in which the temperature of the top ring becomes excessively low when the amount of heat generated in the combustion chamber is small.

When the amount of heat generated in the combustion chamber is extremely small (for example, when the internal combustion engine is operated at a low load and low rotation), most of the heat transferred from the combustion chamber to the piston is dissipated to the cylinder bore wall surface. there is a possibility. In such a case, the temperature of the piston and the top ring may decrease after being temporarily increased.

  In contrast, the control unit of the present invention sets the amount of oil supplied from the oil jet to the cooling channel to zero (stops the oil jet) when the amount of heat generated in the combustion chamber is equal to or less than a predetermined lower limit value. May be. The “lower limit value” here is a value that the temperature of the top ring is considered to be lower than the temperature range assumed in advance (the temperature range in which the joint gap of the top ring assumes the assumed size). It is determined by processing.

  When the oil jet is stopped, the amount of heat radiated from the piston to the oil becomes substantially zero. In addition, when the oil jet is stopped, the cooling channel is filled with air. The air in the cooling channel functions as a heat insulating layer that reduces or blocks heat transferred from the top surface of the piston to the top ring groove. Therefore, the amount of heat radiated from the piston to the cylinder bore wall surface is reduced.

  When the amount of heat radiated from the piston to the oil and the amount of heat radiated from the piston to the cylinder bore wall surface are reduced in this way, the temperature drop of the piston (particularly around the top ring groove) is suppressed. When the temperature decrease around the top ring is suppressed, the temperature decrease of the top ring is also suppressed accordingly.

  As described above, when the amount of heat supplied from the oil jet to the cooling channel is adjusted, the temperature of the top ring is maintained at a substantially constant temperature (hereinafter referred to as “appropriate temperature”). As a result, during operation of the internal combustion engine, the size of the top ring joint gap can be kept substantially constant.

  When the size of the joint gap of the top ring is kept substantially constant during the operation of the internal combustion engine, the top ring can be designed so that the joint gap becomes a desired size at the above-described appropriate temperature. As a result, it is possible to reduce compression leakage and blow-by gas as much as possible regardless of the amount of heat generated in the combustion chamber.

  Here, the amount of heat generated in the combustion chamber correlates with the fuel injection amount. Therefore, the control unit may adjust the amount of oil supplied from the oil jet to the cooling channel using the fuel injection amount as a parameter. Further, since the fuel injection amount is determined using the engine load and the engine speed as parameters, the control unit may adjust the amount of oil supplied from the oil jet to the cooling channel using the engine speed and the engine load as parameters. Good.

  By the way, the pressure in the space surrounded by the top ring, the piston, and the cylinder bore (hereinafter referred to as “first space”) changes substantially in synchronization with the pressure change in the combustion chamber. On the other hand, the pressure change in the space surrounded by the top ring, the second ring, the piston and the cylinder bore (hereinafter referred to as “second space”) is slower than the pressure change in the combustion chamber. The time lag at that time increases as the flow rate of blow-by gas flowing into the second space from the joint gap of the top ring decreases. That is, the time lag described above increases as the gap between the top rings becomes smaller.

  Therefore, when the joint gap of the top ring is made as small as possible, the time lag described above becomes large. Therefore, a situation may occur in which the pressure in the second space exceeds the pressure in the first space. In such a case, since the top ring floats in the top ring groove, the sealing performance of the top ring may be reduced.

The phenomenon that the pressure in the second space becomes higher than the pressure in the first space is likely to occur when the amount of heat generated in the combustion chamber is large. This is because when the amount of heat generated in the combustion chamber is large, the outer diameter of the second land (portion between the top ring groove and the second ring groove) in the piston is enlarged, and the volume of the second space is reduced. it is conceivable that.

  Therefore, the cooling channel according to the present invention may be formed adjacent to the second land in addition to the top ring groove. According to such a configuration, when the amount of heat generated in the combustion chamber is large, the heat of the second land is taken away by the oil in the cooling channel. As a result, the temperature rise of the second land is suppressed.

  When the temperature increase of the second land is suppressed, the expansion (thermal expansion) of the outer diameter of the second land is suppressed. As a result, the reduction in the volume of the second space is alleviated. When the reduction in the volume of the second space is alleviated, a phenomenon in which the pressure in the second space becomes higher than the pressure in the first space is less likely to occur.

  In addition, the control unit according to the present invention has a larger amount of oil supplied from the oil jet to the cooling channel when the internal combustion engine is in the warm-up process than after the warm-up is completed in which the engine load and the engine speed are equal. You may control an oil jet so that it may become.

  When the internal combustion engine is in the warm-up process, the temperature difference between the piston and the cylinder bore increases. This is because the piston is directly warmed by the heat generated in the combustion chamber, but the cylinder bore is indirectly warmed by receiving heat released from the piston. Furthermore, since the heat capacity of the cylinder bore is larger than that of the piston, the temperature increase rate of the cylinder bore is slower than that of the piston.

  When the temperature difference between the piston and cylinder bore is large, the piston expands (piston outer diameter is expanded) while the cylinder bore is hardly expanded (cylinder bore inner diameter is not expanded) State). Therefore, the clearance between the piston and the cylinder bore and the clearance between the piston ring and the cylinder bore are reduced. As a result, there is a possibility that the piston, piston ring, cylinder bore, etc. will be worn out and friction will increase.

  On the other hand, if the amount of oil supplied from the oil jet to the cooling channel is increased after the warm-up is completed when the internal combustion engine is in the warm-up process, the thermal expansion of the piston is alleviated. As a result, the occurrence of the above-described problem can be avoided.

  Further, the control unit according to the present invention, when the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined upper limit water temperature, or when the oil temperature (oil temperature) is equal to or higher than a predetermined upper limit oil temperature, The oil jet may continue to operate. In other words, when the cooling water temperature is equal to or higher than the upper limit water temperature, or when the oil temperature is equal to or higher than the upper limit oil temperature, the stop of the oil jet may be prohibited. The “upper limit water temperature” and “upper limit oil temperature” herein are temperatures obtained by subtracting a predetermined margin from a temperature at which the internal combustion engine is considered to be overheated or a temperature at which oil film breakage occurs. When the oil jet is controlled in this way, overheating of the internal combustion engine and oil film breakage of the oil can be prevented.

  ADVANTAGE OF THE INVENTION According to this invention, the temperature change width | variety of a top ring can be made small in the system which cools the piston of an internal combustion engine. Therefore, it becomes possible to maintain the joint gap of the top ring at a suitable interval, and it is possible to reduce compression leakage and blow-by gas as much as possible.

It is a figure which shows schematic structure of the cooling system of the piston in a 1st Example. It is sectional drawing which shows the structure of the piston in a 1st Example. It is a figure which shows the relationship between temperature difference (DELTA) T, engine load Q, and engine speed Ne. In a 1st Example, it is a figure which shows typically the map which prescribed | regulated the relationship between oil injection quantity, the engine load Q, and the engine speed Ne. It is a figure which shows typically the heat transfer path in a piston. It is sectional drawing which shows the structure of the piston in a 2nd Example exception. It is an enlarged view of the clearance gap between a piston and a cylinder bore wall surface. It is a figure which shows the change of the pressure Pv1 of 1st space, and the pressure Pv2 of 2nd space. It is a figure which shows typically the floating phenomenon of a top ring. In a 3rd Example, it is a figure which shows typically the map which prescribed | regulated the relationship between oil injection quantity, the engine load Q, and the engine speed Ne. It is a figure which shows the time-dependent change of cooling water temperature. It is a figure which shows typically the map which prescribed | regulated the relationship between the oil-injection amount, engine load Q, and engine speed Ne at the time of a steady operation in an internal combustion engine. It is a figure which shows typically the map which prescribed | regulated the relationship between the oil injection quantity, engine load Q, and engine speed Ne when an internal combustion engine is medium load and medium rotation operation in a warming-up process. It is a figure which shows typically the map which prescribed | regulated the relationship between the oil injection quantity, engine load Q, and engine speed Ne when an internal combustion engine is operated by high load and high rotation in the warm-up process. FIG. 13 is a diagram schematically showing a map defining a relationship among an oil injection amount, an engine load Q, and an engine speed Ne under a condition where the coolant temperature is lower than that of the example shown in FIG. It is a figure which shows typically the map which prescribed | regulated the relationship between the oil injection quantity in the conditions where cooling water temperature is lower than the example shown in FIG. 13, the engine load Q, and the engine speed Ne. FIG. 15 is a diagram schematically showing a map defining a relationship among an oil injection amount, an engine load Q, and an engine speed Ne under a condition where the coolant temperature is lower than the example shown in FIG. 14.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. FIG. 2 is a cross-sectional view showing the configuration of the piston in this embodiment.

  The internal combustion engine 1 is a compression ignition type internal combustion engine (diesel engine) having a plurality of cylinders 2. In FIG. 1, only one cylinder 2 among the plurality of cylinders 2 is shown. A piston 3 is slidably loaded in each cylinder 2 of the internal combustion engine 1 in the cylinder axial direction. The piston 3 is connected to a crankshaft (not shown) via a connecting rod 4.

A combustion chamber 30 that is recessed in a substantially cylindrical shape is formed on the top surface of the piston 3. Further, three annular grooves 31, 32, 33 are formed on the outer peripheral surface of the piston 3. Of the three annular grooves 31, 32, 33, the annular groove 31 located closest to the top dead center (uppermost in FIG. 2) is a groove for fitting the top ring 5 (hereinafter, annular). The groove 31 is referred to as “top ring groove 31”). Of the three annular grooves 31, 32, 33, the annular groove 32 positioned immediately below the top ring groove 31 is a groove for fitting the second ring 6 (hereinafter, the annular groove 32 is referred to as "second ring groove"). 32 ”). Of the three annular grooves 31, 32, 33, the annular groove 33 located closest to the bottom dead center (the lowest in FIG. 2) is a groove for fitting the oil ring 7 (hereinafter, annular groove 33). Is referred to as “oil ring groove 33”). The top ring 5, the second ring 6, and the oil ring 7 are annular members having a joint.

  The top ring groove 31 is provided on the outer peripheral surface of the wear-resistant ring 300 cast into the piston 3. The wear-resistant ring 300 is an annular member formed of a material (for example, a resist material) having higher hardness and wear resistance than the piston 3.

  In the piston 3, a hollow wear-resistant ring 310 is cast inside the wear-resistant ring 300. The hollow wear-resistant ring 310 is an annular member having a U-shaped cross section having an opening on the outer peripheral side. The outer peripheral side of the hollow wear-resistant ring 310 is in contact with the inner peripheral surface of the wear-resistant ring 300. That is, the U-shaped opening of the hollow wear-resistant ring 310 is closed by the inner peripheral surface of the wear-resistant ring 300. An annular space 34 surrounded by the hollow wear-resistant ring 310 and the wear-resistant ring 300 functions as a passage for oil supplied from an oil jet 8 described later (hereinafter, the space 34 is referred to as “cooling channel 34”).

  In the piston 3, communication passages 35 and 36 are formed for communicating the opening formed in the bottom surface of the piston 3 and the cooling channel 34. One of the communication paths 35, 36 functions as a path for guiding the oil injected from the oil jet 8 to the cooling channel 34 (hereinafter, the communication path 35 is referred to as “introduction path 35”). Of the communication paths 35 and 36, the other communication path 36 functions as a discharge path for discharging oil flowing out from the cooling channel 34 (hereinafter, the communication path 36 is referred to as a “discharge path 36”).

  The internal combustion engine 1 includes an oil jet 8 that injects oil from the bottom dead center side to the top dead center side in the cylinder 2. The oil jet 8 is arranged so as to be positioned below the piston 3 when the piston 3 is positioned at the bottom dead center. Furthermore, the oil jet 8 is arranged and formed so that the oil jetted from the oil jet 8 is directed to the introduction path 35.

  The oil jet 8 communicates with the oil pan 10 through the supply path 9. An oil pump 11 that sucks up the oil in the oil pan 10 is provided in the supply path 9. A flow rate adjusting valve 12 is disposed in the supply path 9 between the oil jet 8 and the oil pump 11. The flow rate adjustment valve 12 is a valve that adjusts the amount of oil flowing in the supply path 9. The flow rate adjusting valve 12 adjusts the oil flow rate in the supply passage 9 so that the oil amount (oil injection amount) injected from the oil jet 8 is increased or decreased.

  As the flow rate adjusting valve 12, an electric valve mechanism in which the ratio between the valve opening time and the valve closing time is duty-controlled, or an electric valve mechanism in which the opening degree can be changed continuously or stepwise is used. be able to. The flow rate adjusting valve 12 may be a valve mechanism including a check valve that opens when the oil pressure is equal to or higher than a certain value, and a pressure adjusting valve that adjusts the oil pressure in the supply passage 9. .

  The supply passage 9 is provided with a return passage 13 that bypasses the oil pump 11. The return passage 13 is a passage for returning excess oil from the supply passage 9 downstream from the oil pump 11 to the supply passage 9 upstream from the oil pump 11. A one-way valve (check valve) 14 that allows only a flow from the supply path 9 downstream from the oil pump 11 to the supply path 9 upstream from the oil pump 11 is disposed in the return path 13.

  The internal combustion engine 1 configured as described above is provided with an ECU 15. The ECU 15 is an electronic control unit that includes a CPU, ROM, RAM, backup RAM, and the like. The ECU 15 is supplied with output signals from various sensors such as a water temperature sensor 16, a crank position sensor 18, an accelerator position sensor 19, and an oil temperature sensor 20.

  The water temperature sensor 16 is a sensor that outputs an electrical signal that correlates with the temperature of the cooling water circulating in the internal combustion engine 1. The crank position sensor 18 is a sensor that outputs an electrical signal correlated with the rotational position of the crankshaft. The accelerator position sensor 19 is a sensor that outputs an electrical signal correlated with the amount of depression of the accelerator pedal (engine load). The oil temperature sensor 20 is a sensor that outputs an electrical signal correlated with the temperature (oil temperature) of the oil circulating in the internal combustion engine 1.

  The ECU 15 controls the amount of oil supplied from the oil jet 8 to the cooling channel 34 (hereinafter referred to as “oil jet control”) in addition to known control such as fuel injection control based on the output signals of the various sensors described above. ) Hereinafter, a method for performing oil jet control will be described. In addition, the control part concerning this invention is implement | achieved when ECU15 performs oil jet control.

  The oil jet control of the present embodiment is control for adjusting the oil injection amount of the oil jet 8 so that the temperature of the top ring 5 becomes a substantially constant temperature. That is, the oil jet control of the present embodiment is control for adjusting the oil injection amount of the oil jet 8 so that the joint gap of the top ring 5 has a substantially constant size.

  The temperature of the top ring 5 changes according to the amount of heat generated in the combustion chamber 30. For example, when the amount of heat generated in the combustion chamber 30 is large, the temperature increase amount of the piston 3 increases, and accordingly, the temperature increase amount of the top ring 5 also increases.

  When the temperature of the top ring 5 is increased, the top ring 5 is thermally expanded, and the joint gap is reduced. When the temperature of the top ring 5 further rises, the opposed end faces of the abutment face each other, and a force is generated to increase the outer diameter of the top ring 5.

  At this time, if the temperature of the inner wall surface (cylinder bore wall surface) of the cylinder 2 is high, the above-described force is offset by the expansion of the inner diameter of the cylinder 2. However, when the temperature of the cylinder bore wall surface is lower than the temperature of the piston 3 and the temperature difference is large, the top ring 5 and the cylinder 2 are tightly fitted, so that the stress acting on the top ring 5 becomes excessive. The contact load between the top ring 5 and the cylinder bore wall surface may become excessive.

  Therefore, when the temperature of the top ring 5 is high and the temperature of the cylinder bore wall surface is low, it is necessary to determine the size of the abutment gap so as not to cause a situation where the opposed end surfaces of the abutment are pressed against each other. However, if the size of the abutment gap is determined by such a method, the abutment gap may become excessive when the temperature of the top ring 5 is low, leading to an increase in compression leakage and blow-by gas.

  Therefore, in the oil jet control of this embodiment, the ECU 15 suppresses the temperature rise of the top ring 5 when the amount of heat generated in the combustion chamber 30 increases (when the temperature difference between the piston 3 and the cylinder bore wall surface increases). When the amount of heat generated in the combustion chamber 30 decreases (when the temperature difference between the piston 3 and the cylinder bore wall surface decreases), the oil injection amount is adjusted so as to suppress the temperature drop of the top ring 5 or to promote the temperature increase. I did it.

  The amount of heat generated in the combustion chamber 30 varies depending on the amount of fuel combusted in the combustion chamber 30, that is, the fuel injection amount. In principle, the fuel injection amount is determined using the load (engine load) Q of the internal combustion engine 1 and the rotational speed (engine rotational speed) Ne of the internal combustion engine 1 as parameters. Therefore, in this embodiment, an example in which the oil injection amount is adjusted using the engine load Q and the engine speed Ne as parameters will be described.

  FIG. 3 is a diagram showing the relationship among the temperature difference ΔT, the engine load Q, and the engine speed Ne. The “temperature difference ΔT” here is the difference between the temperature of the piston 3 (preferably the temperature of the top ring groove 31) and the temperature of the cylinder bore wall surface.

  In FIG. 3, when the engine load Q and the engine speed Ne are low, the amount of heat generated in the combustion chamber 30 is smaller than when it is high. Therefore, the temperature difference ΔT is reduced and the joint gap of the top ring 5 is increased.

  On the other hand, when the engine load Q and the engine speed Ne are high, more heat is generated in the combustion chamber 30 than when the engine load Q is low. For this reason, the temperature difference ΔT increases and the gap between the top rings 5 decreases.

  On the other hand, the ECU 15 controls the flow rate adjusting valve 12 so that the oil injection amount of the oil jet 8 is increased when the amount of heat generated in the combustion chamber 30 is large compared to when the heat amount is small. In other words, the ECU 15 controls the flow rate adjusting valve 12 so that the oil injection amount of the oil jet 8 is larger when the temperature difference ΔT is large than when it is small.

  Specifically, the ECU 15 may control the flow rate adjustment valve 12 according to a map as shown in FIG. The map shown in FIG. 4 is a map that defines the relationship among the engine load Q, the engine speed Ne, and the oil injection amount.

  In FIG. 4, when the engine load Q and the engine speed Ne are high (region A in FIG. 4), the oil injection amount is set to the maximum amount. When the engine load Q and the engine speed Ne are low (region C in FIG. 4), the oil injection amount is made zero (oil jet 8 is stopped). However, oil injection for the purpose of lubrication between the piston 3 and the cylinder bore wall surface or lubrication between the piston 3 and the connecting rod 4 may be performed. Further, when the engine load Q and the engine speed Ne are in an intermediate region (region B in FIG. 4) between region A and region C, the oil injection amount is made smaller than the maximum amount described above. Note that a region C in FIG. 4 is a region where the amount of heat generated in the combustion chamber 30 is equal to or lower than the lower limit value. The “lower limit value” here is a value at which the temperature of the top ring 5 may be lower than an appropriate temperature described later.

  Here, part of the heat generated in the combustion chamber 30 is transmitted from the top surface of the piston 3 toward the top ring groove 31 and is radiated from the top ring groove 31 to the cylinder bore wall surface. Specifically, as shown in FIG. 5, the heat transmitted from the combustion chamber 30 to the piston 3 is mainly directed from the upper edge 30 a of the combustion chamber 30 in the piston 3 toward the top ring groove 31 (the wear-resistant ring 300). (Refer to the arrow in FIG. 5). On the other hand, when the cooling channel 34 is disposed inside the top ring groove 31, the cooling channel 34 is positioned on the above-described heat path. In other words, it can be said that the cooling channel 34 is preferably disposed on the heat path described above.

  Therefore, when the oil injection amount is maximized when the engine load Q and the engine speed Ne are high, most of the heat from the upper edge 30a toward the top ring groove 31 is taken away by the oil in the cooling channel 34. It becomes like this. As a result, the temperature rise of the piston 3 and the top ring groove 31 is suppressed, and the temperature rise of the top ring 5 is also suppressed accordingly.

  If the temperature rise of the top ring 5 is suppressed when the engine load Q and the engine speed Ne are high, it is possible to avoid a situation in which the opposed end face abuts at the joint of the top ring 5. Therefore, it is possible to avoid a situation in which the contact load between the top ring 5 and the cylinder bore wall surface becomes excessive.

  On the other hand, when the oil injection amount is made zero when the engine load Q and the engine speed Ne are low, the cooling channel 34 is filled with air. The air in the cooling channel 34 functions as a heat insulating layer that blocks heat from the upper edge portion 30 a toward the top ring groove 31. Therefore, the amount of heat radiated from the piston 3 to the cylinder bore wall surface is reduced. As a result, the temperature drop of the piston 3 and the top ring 5 groove is suppressed, and the temperature drop of the top ring 5 is also suppressed accordingly.

  If the temperature of the top ring 5 is lowered when the engine load Q and the engine speed Ne are low, a situation in which the joint gap of the top ring 5 becomes excessive can be avoided. Therefore, it is possible to avoid a situation in which compression leakage or blow-by gas increases. Further, when the temperature drop of the top ring groove 31 is suppressed, the atmospheric temperature of the gap (clevis) between the top land of the piston 3 and the cylinder bore wall surface is kept high. When the ambient temperature of the clevis is high, the temperature of the gas passing through the joint gap of the top ring 5 is also higher than when it is low. As a result, the mass of the gas flowing through the joint gap of the top ring 5 is further reduced.

  If the oil injection amount is less than the maximum amount when the engine load Q and the engine speed Ne are in the medium load / medium rotation region, the amount of heat from the upper edge portion 30a toward the top ring groove 31 is A situation in which the amount of heat taken away from the piston 3 to the oil is excessive is avoided. As a result, overcooling of the piston 3 and the top ring groove 31 is suppressed, and accordingly, overcooling of the top ring 5 is also suppressed. Note that the oil injection amount in the region B in FIG. 4 described above may be a fixed amount, or may be an amount that is changed according to the engine load Q and the engine speed Ne. The oil injection amount at that time may be increased when the engine load Q is higher than when the engine load Q is low, and may be increased when the engine speed Ne is higher than when it is low.

  As described above, the ECU 15 performs the oil jet control, so that the temperature of the top ring 5 can be maintained at a substantially constant temperature (appropriate temperature) regardless of the operating state of the internal combustion engine 1. The “appropriate temperature” referred to here is a temperature at which the gap at the abutment becomes the smallest within a range in which the abutment of the opposing end face at the abutment of the top ring 5 does not occur. The top ring 5 is designed so that the joint gap has a desired size at the appropriate temperature.

  Therefore, according to the piston cooling system of the present embodiment, when the amount of heat generated in the combustion chamber 30 is large, the abutment gap of the top ring 5 becomes too small and the opposite end faces of the abutment abut each other, and the combustion chamber 30 It is possible to avoid a situation in which the joint gap of the top ring 5 becomes excessive and the compression leakage and blow-by gas increase when the amount of heat generated in is small.

  In the present embodiment, the example in which the oil jet 8 is stopped when the engine load Q and the engine speed Ne are low is described. However, when the output signal (cooling water temperature) of the water temperature sensor 16 is equal to or higher than the upper limit water temperature. When the output signal (oil temperature) of the oil temperature sensor 20 is equal to or higher than the upper limit oil temperature, the stop of the oil jet 8 may be prohibited. The “upper limit water temperature” and the “upper limit oil temperature” here are temperatures obtained by subtracting a predetermined margin from a temperature at which the internal combustion engine may overheat or a temperature at which oil film breakage may occur. When the stop of the oil jet 8 is prohibited in this way, it is possible to prevent the internal combustion engine 1 from being overheated or the oil film running out.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  The difference between the first embodiment and the present embodiment is the configuration of the cooling channel. In the first embodiment described above, an example in which the cooling channel is arranged so as to cool the top ring groove intensively has been described, but in this embodiment, the cooling channel also cools the second land in addition to the top ring groove. An example of arrangement will be described.

  FIG. 6 is a cross-sectional view showing a configuration of the piston 3 in the present embodiment. In FIG. 6, the same components as those in the first embodiment (see FIG. 2) described above are denoted by the same reference numerals. The wear-resistant ring 300 of this embodiment is formed wider than the first embodiment described above in terms of the length (width) in the cylinder axial direction. Specifically, the wear-resistant ring 300 has a width extending from the top land to the third land of the piston 3.

  In addition to the top ring groove 31, a second ring groove 32 is also formed in the wear-resistant ring 300. As a result, the wear-resistant ring 300 positioned between the top ring groove 31 and the second ring 6 groove also serves as the second land 37.

  A hollow wear-resistant ring 310 having a width substantially equal to that of the wear-resistant ring 300 is cast inside the wear-resistant ring 300 of the piston 3. The hollow wear-resistant ring 310 is an annular member having a U-shaped cross section as in the first embodiment described above. The opening of the hollow wear-resistant ring 310 is closed by the inner peripheral surface of the wear-resistant ring 300. An annular space 34 surrounded by the hollow wear-resistant ring 310 and the wear-resistant ring 300 functions as a cooling channel.

  When the oil jet control similar to that of the first embodiment described above is performed on the piston 3 configured as described above, when the amount of heat generated in the combustion chamber 30 is large (the engine load Q and the engine speed Ne). When the temperature of the top ring 5 is high), the temperature rise of the top ring 5 is suppressed and the temperature rise of the second land 37 is also suppressed.

  Here, the enlarged view of the clearance gap between piston 3 and a cylinder bore wall surface is shown in FIG. V1 in FIG. 7 indicates a space (first space) surrounded by the top ring 5, the piston 3 (top land), and the cylinder bore wall surface. V2 in FIG. 7 indicates a space (second space) surrounded by the top ring 5, the piston 3 (second land 37), the second ring 6, and the cylinder bore wall surface.

  As shown in FIG. 8, the pressure Pv1 in the first space V1 changes substantially in synchronization with the pressure in the combustion chamber 30 (see the solid line in FIG. 8). On the other hand, the pressure Pv2 in the second space V2 changes later than the pressure in the combustion chamber 30 (see the alternate long and short dash line in FIG. 8). The time lag at that time becomes larger as the joint gap of the top ring 5 becomes smaller. Therefore, as described in the first embodiment, when the joint gap of the top ring 5 is made as small as possible, the period in which the pressure Pv2 in the second space V2 is higher than the pressure Pv1 in the first space V1. (See the shaded area in FIG. 8).

  In particular, when the engine load Q and the engine speed Ne are high, in other words, when the temperature difference between the second land 37 and the cylinder bore wall surface becomes large, the volume of the second space V2 is reduced, so the pressure Pv2 of the second space V2 is reduced. Tends to be higher than the pressure Pv1 in the first space V1.

  When the pressure Pv2 in the second space V2 becomes higher than the pressure Pv1 in the first space V1, a phenomenon occurs in which the top ring 5 floats toward the top dead center side in the cylinder axial direction in the top ring groove 31, as shown in FIG. . When the top ring 5 is lifted in this way, blow-by gas may leak from the gap between the top ring 5 and the top ring groove 31.

  On the other hand, when the temperature rise of the second land 37 is suppressed when the engine load Q and the engine speed Ne are high, the expansion of the outer diameter of the second land 37 is suppressed, or the outer diameter of the second land 37 is reduced. The In that case, the reduction of the volume of the second space V2 is suppressed, or the volume of the second space V2 is increased. As a result, the pressure Pv2 in the second space V2 is difficult to increase.

  Moreover, when the temperature rise of the second land 37 is suppressed, the volume expansion of the gas existing in the second space V2 is also suppressed. As a result, the pressure Pv2 in the second space V2 becomes more difficult to increase. Furthermore, since the second ring groove 32 and the second ring 6 are cooled by the oil in the cooling channel 34, the joint gap of the second ring 6 is enlarged. When the joint gap of the second ring 6 is enlarged, the gas in the second space V2 is discharged from the joint gap. As a result, it is possible to more reliably avoid a situation in which the pressure Pv2 in the second space V2 is higher than the pressure Pv1 in the first space V1.

  According to the embodiment described above, a situation in which the pressure Pv2 in the second space V2 becomes higher than the pressure Pv1 in the first space V1 is avoided, so in addition to the same effect as the first embodiment described above, the top ring 5 can be suppressed. As a result, an increase in blow-by gas due to a decrease in the sealing performance of the top ring 5 can be suppressed.

<Example 3>
Next, a third embodiment of the present invention will be described with reference to FIG. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  The difference between the first embodiment and the present embodiment is that the method of executing oil jet control is changed between when the internal combustion engine 1 is in the warming-up process and after the warm-up of the internal combustion engine 1 is completed. . The piston 3 has a smaller heat capacity than the cylinder block. Further, the cylinder bore wall surface indirectly receives the heat of the combustion chamber 30 via the piston 3 and the piston ring, whereas the piston 3 directly receives the heat of the combustion chamber 30. Therefore, when the internal combustion engine 1 is in the warm-up process, the temperature difference ΔT between the piston 3 and the cylinder bore wall surface is likely to be larger than after the warm-up is completed.

  As the temperature difference ΔT between the piston 3 and the cylinder bore wall surface increases, the difference between the amount of expansion of the outer diameter of the top ring 5 and the amount of expansion of the inner diameter of the cylinder 2 increases. As a result, the stress acting on the top ring 5 may be excessive, or the contact load between the top ring 5 and the cylinder bore wall surface may be excessive.

  Therefore, the ECU 15 controls the oil jet 8 so that the oil injection amount is larger when the internal combustion engine 1 is in the warm-up process than after the warm-up is completed. FIG. 10 is a schematic diagram of a map that defines the relationship among the oil injection amount, the engine load Q, and the engine speed Ne. A solid line in FIG. 10 indicates a boundary line between the regions A, B, and C in the warm-up process, and a one-dot chain line in FIG. 10 indicates a boundary line between the regions A, B, and C in the warm-up completion.

  As shown in FIG. 10, when the internal combustion engine 1 is in the warm-up process, each boundary line is shifted to the low load / low rotation side as compared to after the warm-up is completed. Therefore, when the internal combustion engine 1 is in the warm-up process, the oil injection amount of the oil jet 8 is larger than when the warm-up is completed.

  As a result, during the warm-up process of the internal combustion engine 1, a situation where the difference between the expansion amount of the outer diameter of the top ring 5 and the expansion amount of the inner diameter of the cylinder 2 becomes larger than after the warm-up is completed is avoided. Therefore, even when the internal combustion engine 1 is in the warm-up process, the stress acting on the top ring 5 becomes excessive or the contact between the top ring 5 and the cylinder bore wall surface is suppressed while suppressing increase in compression leakage and blow-by gas. It is possible to avoid a situation in which the load is excessive.

<Example 4>
Next, a fourth embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from the above-described third embodiment will be described, and description of the same configuration will be omitted.

  In the third embodiment described above, the execution method of the oil jet control when the internal combustion engine 1 is steadily operated in the warm-up process has been described. However, in this embodiment, the internal-combustion engine 1 is transiently operated in the warm-up process. The execution method of oil jet control is described.

  When the internal combustion engine 1 is transiently operated after cold start, the temperature of the piston 3 rises rapidly, but the temperature of the cylinder bore wall surface (cylinder block) hardly rises. In such a case, the temperature difference ΔT between the piston 3 and the cylinder bore wall surface may become larger. As the temperature difference ΔT between the piston 3 and the cylinder bore wall surface increases, the difference between the amount of expansion of the outer diameter of the top ring 5 and the amount of expansion of the inner diameter of the cylinder 2 increases. As a result, the stress acting on the top ring 5 may be excessive, or the contact load between the top ring 5 and the cylinder bore wall surface may be excessive. Such a problem becomes more prominent as the temperature increase rate (temperature increase rate) of the piston 3 is higher and the temperature of the cylinder bore wall surface is lower.

  Therefore, in this embodiment, the ECU 15 changes the execution method of the oil jet control using the temperature increase rate of the piston 3 and the temperature of the cylinder bore wall surface as parameters. For example, the ECU 15 increases the oil injection amount when the temperature increase rate of the piston 3 is high and the temperature of the cylinder bore wall surface is low, compared to when the temperature increase rate of the piston 3 is low and the temperature of the cylinder bore wall surface is high. The flow control valve 12 is controlled. Here, “when the temperature rise rate of the piston 3 is high and the temperature of the cylinder bore wall surface is low” and “when the temperature rise rate of the piston 3 is low and the temperature of the cylinder bore wall surface is high” means the engine load Q and the engine speed. It is assumed that Ne is equivalent.

  The temperature increase rate of the piston 3 correlates with the temperature increase rate of the cooling water temperature. Therefore, the amount of change in the cooling water temperature per certain time can be used as the temperature increase rate of the piston 3. Further, the temperature of the cylinder bore wall surface is substantially equal to the temperature of the cooling water flowing through the cylinder block. Therefore, the output signal (cooling water temperature) of the water temperature sensor 16 can be used as the temperature of the cylinder bore wall surface.

  FIG. 11 is a diagram showing a change with time of the cooling water temperature. A two-dot chain line X1 in FIG. 11 indicates a change in the coolant temperature when the internal combustion engine 1 is steadily operated during the warm-up process. A one-dot chain line X2 in FIG. 11 indicates a change in the coolant temperature when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process. A solid line X3 in FIG. 11 indicates a change in the coolant temperature when the internal combustion engine 1 is operated at a high load and a high speed during the warm-up process. In FIG. 11, thw0 indicates the cooling water temperature when the oil jet control is executed. ΔP1, ΔP2, and ΔP3 in FIG. 11 indicate the amount of change (temperature increase rate) in the coolant temperature per predetermined time t of X1, X2, and X3.

  As indicated by a two-dot chain line X1 in FIG. 11, when the internal combustion engine 1 is steadily operated in the warm-up process, the ECU 15 controls the oil injection amount according to a map as shown in FIG. The map shown in FIG. 12 is equivalent to the map described in the third embodiment (see FIG. 10), and the boundary lines of the regions A, B, and C are compared with those after the warm-up of the internal combustion engine 1 is completed. Shifted to the low load / low rotation side.

Next, the temperature increase rate ΔP2 when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process is larger than the temperature increase rate ΔP1 when the internal combustion engine 1 is operated idle at the warm-up process. Therefore, when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process, the temperature difference ΔT between the piston 3 and the cylinder block becomes larger than when the internal combustion engine 1 is operated idle during the warm-up process. is expected.

  Therefore, as shown by a one-dot chain line X2 in FIG. 11, when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process, the ECU 15 controls the oil injection amount according to a map as shown in FIG. To do. Note that the solid lines in FIG. 13 indicate the boundary lines of the regions A, B, and C when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process. A one-dot chain line in FIG. 13 indicates the boundary lines of the regions A, B, and C when the internal combustion engine 1 is steadily operated in the warm-up process.

  In FIG. 13, the boundary lines of the regions A, B, and C when the internal combustion engine 1 is operated at a medium load / medium speed in the warm-up process are shown in Compared to the boundary line of B and C, the shift is made to the low load / low rotation side. Therefore, the oil injection amount when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process is larger than the oil injection amount when the internal combustion engine 1 is operated normally during the warm-up process. As a result, the expansion of the temperature difference ΔT between the piston 3 and the cylinder bore wall surface can be suppressed.

  Further, the temperature increase rate ΔP3 when the internal combustion engine 1 is operated at a high load / high rotation speed during the warm-up process is further higher than the temperature increase rate ΔP2 when the internal combustion engine 1 is operated at a medium load / medium rotation speed during the warm-up process. growing. Therefore, when the internal combustion engine 1 is operated at a high load / high speed during the warm-up process, the temperature difference between the piston 3 and the cylinder block is higher than when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process. ΔT is expected to increase further.

  Therefore, as shown by a solid line X3 in FIG. 11, when the internal combustion engine 1 is operated at a high load and a high speed during the warm-up process, the ECU 15 controls the oil injection amount according to a map as shown in FIG. . Note that the solid line in FIG. 14 indicates the boundary line between the regions A and B when the internal combustion engine 1 is operated at a high load and a high speed during the warm-up process. A dashed line in FIG. 14 indicates a boundary line between the regions A and B when the internal combustion engine 1 is operated at a medium load / medium speed in the warm-up process.

  In FIG. 14, the boundary line between regions A and B when the internal combustion engine 1 is operated at a high load / high rotation speed during the warm-up process is a region where the internal combustion engine 1 is operated at a medium load / medium rotation speed during the warm-up process. Compared to the boundary line between A and B, the shift is to the low load / low rotation side. Further, in the map shown in FIG. 14, the stop area of the oil jet 8 (area corresponding to the area C in FIGS. 12 and 13) is deleted. That is, even when the internal combustion engine 1 is shifted from the high load / high rotation operation region to the low load / low rotation operation region, a small amount of oil is injected from the oil jet 8.

  Therefore, the oil injection amount when the internal combustion engine 1 is operated at a high load / high rotation speed during the warm-up process is larger than the oil injection amount when the internal combustion engine 1 is operated at a medium load / medium rotation speed during the warm-up process. . As a result, the expansion of the temperature difference ΔT between the piston 3 and the cylinder bore wall surface can be suppressed.

  When the cooling water temperature (temperature of the cylinder bore wall surface) at the time of executing the oil jet control is lower than thw0 described above, the temperature difference ΔT between the piston 3 and the cylinder bore wall surface becomes larger than when the cooling water temperature is thw0. there is a possibility. Therefore, when the cooling water temperature is lower than thw, it is desirable that the oil injection amount be further increased as compared with the case where the cooling water temperature is thw0.

  For example, when the internal combustion engine 1 is steadily operated during the warm-up process, the ECU 15 controls the oil injection amount according to a map as shown in FIG. In addition, the solid line in FIG. 15 shows the boundary line of area | region A, B, C when a cooling water temperature is lower than thw0, and the dashed-dotted line in FIG. 15 shows area | region A, B, when cooling water temperature is thw0. A boundary line of C (equivalent to the boundary lines of regions A, B, and C in FIG. 12) is shown.

  In FIG. 15, the boundary lines of the regions A, B, and C when the cooling water temperature is lower than thw0 are lower in load and rotation than the boundary lines of the regions A, B, and C when the cooling water temperature is thw0. Shifted to the side. Therefore, the oil injection amount when the internal combustion engine 1 is steadily operated in the warm-up process increases as the coolant temperature decreases. As a result, even when the cooling water temperature (the temperature of the cylinder bore wall surface) is lowered, the expansion of the temperature difference ΔT between the piston 3 and the cylinder bore wall surface is suppressed.

  When the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process, the ECU 15 controls the oil injection amount according to a map as shown in FIG. Note that the solid line in FIG. 16 indicates the boundary line between the regions A and B when the cooling water temperature is lower than thw0, and the alternate long and short dash line in FIG. 16 indicates the boundary line between the regions A and B when the cooling water temperature is thw0. (It is equivalent to the boundary line between the regions A and B in FIG. 13).

  In FIG. 16, the boundary line between the regions A and B when the cooling water temperature is lower than thw0 is shifted to the low load / low rotation side as compared with the boundary line between the regions A and B when the cooling water temperature is thw0. ing. Further, in the map shown in FIG. 16, the stop area of the oil jet 8 (area corresponding to the area C in FIG. 13) is deleted. Therefore, the oil injection amount when the internal combustion engine 1 is operated at a medium load / medium speed during the warm-up process increases as the cooling water temperature decreases. As a result, even when the cooling water temperature (the temperature of the cylinder bore wall surface) is lowered, the expansion of the temperature difference ΔT between the piston 3 and the cylinder bore wall surface is suppressed.

  Further, when the internal combustion engine 1 is operated at a high load / high rotation speed during the warm-up process, the ECU 15 controls the oil injection amount according to a map as shown in FIG. In the map shown in FIG. 17, a region where a small amount of oil is injected from the oil jet 8 (region corresponding to region B in FIG. 14) is deleted. That is, the oil injection amount is set to the maximum amount in all operating regions of the internal combustion engine 1. Therefore, even when the internal combustion engine 1 is in the warm-up process and the temperature of the cylinder bore wall surface is low, even if the internal combustion engine 1 is operated at a high load and a high speed, the expansion of the temperature difference ΔT between the piston 3 and the cylinder bore wall surface is suppressed. be able to.

  According to the embodiment described above, even when the temperature increase rate ΔP of the piston 3 becomes high during the warm-up process of the internal combustion engine 1, the expansion of the temperature difference ΔT between the piston 3 and the cylinder bore wall surface is suppressed. Can do. As a result, the enlargement amount of the outer diameter of the top ring 5 can be suppressed to a small amount. Therefore, it is possible to avoid a situation in which the stress acting on the top ring 5 becomes excessive or the contact load between the top ring 5 and the cylinder bore wall surface becomes excessive.

  In this embodiment, the example in which the map is switched using the cooling water temperature and the temperature increase rate ΔP of the cooling water at the time of executing the oil jet control as parameters is described, but the relationship shown in FIGS. 12 to 17 described above is covered. A functional expression may be used. In other words, the oil injection amount may be determined using a function equation having the cooling water temperature, the temperature increase rate, the engine load Q, and the engine speed Ne as arguments.

  In the present embodiment, the example in which the temperature increase rate of the cooling water temperature is used as the temperature increase rate of the piston 3 has been described. However, there is some time lag before the temperature change of the piston 3 is reflected in the cooling water temperature. May occur.

  Accordingly, the amount of heat transmitted from the combustion chamber 30 to the piston 3 may be calculated using the fuel injection amount as a parameter, and the map may be switched using the calculation result and the temperature of the cylinder bore wall surface (cooling water temperature) as parameters. . At this time, the amount of heat Hq transferred from the combustion chamber 30 to the piston 3 per certain time tinj may be calculated based on the following equation.

  Hq = Hinj × ∫ (ΣFinj) dt / tinj

  In the above equation, Hinj represents the low calorific value (J / g) of the fuel, and ΣFinj represents the sum of the fuel injection amount Finj within the fixed time tinj.

  When the amount of heat Hq obtained by the above equation is large and the cooling water temperature (cylinder bore wall surface temperature) is low, the ECU 15 is less oil than when the amount of heat Hq is small and the cooling water temperature (temperature of the cylinder bore wall surface) is high. The flow rate adjustment valve 12 may be controlled so that the injection amount increases.

  According to such a method, it is possible to execute oil jet control in accordance with the actual temperature of the piston 3.

  The ECU 15 executes in parallel the calculation of the oil injection amount based on the temperature increase rate ΔP of the cooling water temperature and the calculation of the oil injection amount based on the heat amount Hq transmitted from the combustion chamber 30 to the piston 3. The flow rate adjustment valve 12 may be controlled according to whichever of the calculation results is greater. According to this method, the expansion of the temperature difference ΔT between the piston 3 and the cylinder bore wall surface can be more reliably suppressed.

<Example 5>
Next, a fifth embodiment of the present invention will be described. Here, a configuration different from that of the first embodiment described above will be described, and description of equivalent configurations will be omitted.

  In this embodiment, an example will be described in which oil jet control is executed when the cooling system of the internal combustion engine 1 fails, particularly when the cylinder bore wall surface is supercooled, such as when the thermostat valve is stuck in the open state.

  When the thermostat valve is stuck in the open state, the cooling water passes through the radiator even if the cooling water temperature is lower than the valve opening temperature (or valve closing temperature) of the thermostat valve. Therefore, there is a possibility that the cooling water temperature is further lowered. When the cooling water temperature is thus lowered, the cylinder bore wall surface is supercooled.

  If the cylinder bore wall surface is supercooled, the temperature difference ΔT between the piston 3 and the cylinder bore wall surface may increase even if the amount of heat generated in the combustion chamber 30 is small. When the temperature difference ΔT between the piston 3 and the cylinder bore wall surface increases, the amount of expansion of the outer diameter of the top ring 5 may become excessive with respect to the amount of expansion of the inner diameter of the cylinder 2. As a result, even when the amount of heat generated in the combustion chamber 30 is small, there is a possibility that the stress acting on the top ring 5 becomes excessive or the contact load between the top ring 5 and the cylinder bore wall surface becomes excessive. is there.

  On the other hand, in the oil jet control of the present embodiment, when the failure of the cooling system occurs, the ECU 15 operates the internal combustion engine 1 (the engine load Q and the engine speed) as in the map of FIG. Regardless of Ne), the oil injection amount is set to the maximum amount.

Here, as a method of detecting a failure in the cooling system, when the cooling water temperature decrease rate (decrease rate) is larger than a predetermined upper limit decrease rate, or the cooling water temperature decrease amount is a predetermined upper limit decrease. A method of determining that the cooling system has failed when larger than the amount can be used. Here, the “upper limit reduction rate” is a reduction rate when the thermostat valve fails in the open state or a value obtained by subtracting a predetermined margin from the reduction rate. The “upper limit decrease amount” is a temperature decrease amount when the thermostat valve is stuck in the open state, or a value obtained by subtracting a predetermined margin from the temperature decrease amount.

  According to this embodiment, it is possible to avoid a situation in which the temperature difference between the piston 3 and the cylinder bore wall surface increases when the cooling system fails. As a result, expansion of the outer diameter of the top ring 5 is suppressed. Therefore, when the amount of heat generated in the combustion chamber 30 is small, it is possible to avoid a situation in which the stress acting on the top ring 5 becomes excessive or the contact load between the top ring 5 and the cylinder bore wall surface becomes excessive. become.

  Note that at least two or all of the first to fifth embodiments described above can be combined. As a result, in various cases such as when the internal combustion engine 1 is in the warm-up process, when the internal combustion engine 1 is in the warm-up completion state, or when the cooling system of the internal combustion engine 1 is out of order, the joint of the top ring 5 The gap can be maintained at a substantially constant size.

  In the first to fifth embodiments described above, an example in which the cooling channel 34 is configured by a hollow wear-resistant ring has been described. However, as long as the cooling channel 34 is disposed adjacent to the top ring 5 (and the second land 37), Any configuration may be used.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Piston 4 Connecting rod 5 Top ring 6 Second ring 7 Oil ring 8 Oil jet 9 Supply path 10 Oil pan 11 Oil pump 12 Flow control valve 13 Return path 14 One-way valve 15 ECU
16 Water temperature sensor 18 Crank position sensor 19 Accelerator position sensor 20 Oil temperature sensor 30 Combustion chamber 30a Upper edge 31 Top ring groove 32 Second ring groove 33 Oil ring groove 34 Cooling channel 35 Inlet path 36 Discharge path 37 Second land 300 Wear resistant ring 310 Hollow wear-resistant ring

Claims (5)

An annular groove provided on the outer peripheral surface of the piston, and a top ring groove to which the top ring is attached;
An annular oil passage embedded in the piston, the cooling channel adjacent to the top ring groove;
An oil jet for supplying oil to the cooling channel;
When the amount of heat generated in the combustion chamber is large, a control unit that increases the amount of oil supplied from the oil jet to the cooling channel compared to when the amount of heat is small,
Piston cooling system comprising:   2. The piston cooling system according to claim 1, wherein the control unit stops oil supply from the oil jet to the cooling channel when the amount of heat generated in the combustion chamber is equal to or lower than a predetermined lower limit value.   3. The piston cooling system according to claim 1, wherein the cooling channel is formed adjacent to the top ring groove and a second land.   4. The control unit according to claim 1, wherein when the internal combustion engine is in a warm-up process, the control unit performs the cooling from the oil jet compared to after the completion of warm-up when the engine load and the engine speed are equal. Piston cooling system that increases the amount of oil supplied to the channel.   5. The control unit according to claim 1, wherein when the temperature of the cooling water is equal to or higher than a predetermined upper limit water temperature, or when the temperature of the oil is equal to or higher than a predetermined upper limit oil temperature. The piston cooling system prohibits the oil jet from stopping.

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