JP2015175320A - Cooling device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure sufficient cooling efficiency in a cooling device of an internal combustion engine even when the concentration of an antifreezing solution varies.SOLUTION: In a cooling device 1, 5 of an internal combustion engine EG, cooling water containing an antifreezing solution is circulated in paths α, β, which include a jacket part 12 arranged in the internal combustion engine EG, to perform cooling. The cooling device comprises: flow rate detection means 21, 30 detecting the flow rate Q of the cooling water in the paths α, β; temperature detection means 22 detecting the temperature θ of the cooling water in the paths α, β; concentration detection means 23 detecting the concentration C of the antifreezing solution of the cooling water; and pressure control means 17, 18, 30 controlling the pressure P of the cooling water in the paths α, β on the basis of the flow rate Q and the temperature θ of the cooling water and the concentration C of the antifreezing solution in the paths α, β.

Description

  The present invention relates to a cooling device for an internal combustion engine, and more particularly to a cooling device for a water-cooled internal combustion engine.

  In a vehicle using an internal combustion engine (engine) as a power source, a water-cooled type is generally used as an engine cooling device. In a water-cooled cooling device, cooling water is used as a refrigerant, and a coolant obtained by diluting a glycol-based liquid agent (antifreeze) with water for rust prevention and freezing prevention is widely used.

  In such a cooling device, by adjusting the concentration and pressure of the antifreeze of the cooling water, bubbles are continuously generated by the cooling water boiled on the wall surface of the cooling water passage (water jacket) (subcooled boiling), and due to the latent heat of evaporation. Heat can be removed efficiently. The bubbles are cooled by the surrounding cooling water and returned to the liquid again.

  In such a cooling device using subcooled boiling, if the concentration of the antifreeze is increased too much, the boiling point of the cooling water rises and subcooled boiling does not occur, so that efficient heat removal as described above cannot be performed. Moreover, when the pressurization to cooling water is not enough, or when the density | concentration of an antifreeze is low, the boiling point of cooling water falls, it boils excessively, the quantity of steam | vapor increases, and cooling efficiency falls.

  In addition, when sudden high load operation is performed immediately after engine startup or cold, the temperature and pressure of the cooling water in the system are both low, and the cooling water temperature rises locally (for example, near the turbine housing or EGR cooler). And partially boil. Since the vapor of this portion cannot be returned to the liquid and the cooling efficiency is lowered, the parts to be cooled cannot be sufficiently cooled.

  Therefore, in the cooling device of Patent Document 1, the pressure of the cooling system is adjusted based on the temperature of the cooling water and the engine speed, and the subcooling degree (the difference between the saturation temperature and the actual cooling temperature) is controlled.

  Further, in the apparatus of Patent Document 2, the boiling point temperature of cooling water is determined based on the LLC (antifreeze) concentration and the pressure of the cooling system, and whether or not the temperature of the cooling water is in an overheated state based on this boiling point temperature is determined. If it is determined, and an overheat state is determined, an alarm is issued.

JP-A-5-106435 Japanese Patent Laid-Open No. 7-71252

  However, the cooling device of Patent Document 1 does not control the cooling system pressure based on the cooling water component, and cannot cope with changes in the boiling point and subcooling degree of the cooling water accompanying the change in the cooling water component.

  Moreover, in the apparatus of patent document 2, there is no apparatus which adjusts the pressure of cooling water, and there is no means for preventing an overheat state based on detected data.

  Accordingly, an object of the present invention is to ensure sufficient cooling efficiency in a cooling device for an internal combustion engine even if the concentration of the antifreeze in the cooling water changes.

  In order to achieve the above object, the present invention provides a cooling apparatus for an internal combustion engine that performs cooling by circulating cooling water containing antifreeze liquid in a path including a jacket portion disposed in the internal combustion engine. A flow rate detecting means for detecting a flow rate of the cooling water in the passage, a temperature detecting means for detecting the temperature of the cooling water in the passage, a concentration detecting means for detecting the concentration of the antifreeze liquid in the cooling water, A cooling device for an internal combustion engine, comprising: pressure control means for controlling a pressure of the cooling water in the path based on a flow rate of cooling water, a temperature, and a concentration of the antifreeze.

  The pressure control means may control the pressure of the cooling water in the path so that the cooling water in the path does not saturate and the cooling water is in a subcooled boiling state in the jacket portion.

  The pressure control means may control the pressure of the cooling water based on a function having variables of the flow rate, temperature, and concentration of the antifreeze liquid.

  The pressure control means may control the pressure of the cooling water so as to be within a predetermined range from the value of the function.

  A temperature difference estimating means for estimating a temperature difference between the temperature of the inner wall of the jacket portion and the temperature of the cooling water from the operating state of the internal combustion engine, and the pressure control means is further configured based on the temperature difference. The pressure of the cooling water may be controlled.

  According to the present invention, in the cooling device for an internal combustion engine, sufficient cooling efficiency can be ensured even if the concentration of the antifreeze of the cooling water changes.

It is the figure which showed the cooling device which concerns on one Embodiment of this invention. It is the figure which showed the change of the heat flux with respect to the temperature difference of a cooling water and a water jacket wall surface. It is the figure which showed the state figure (vapor pressure curve) of the cooling water. It is a flowchart which shows an example of the pressure control of a cooling water. It is the figure which showed the cooling device which concerns on the modification of the apparatus structure which concerns on one Embodiment of this invention. It is a flowchart which shows another example of the pressure control of a cooling water.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same components are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

<Configuration of cooling device>
FIG. 1 is a view showing a cooling device 1 according to an embodiment of the present invention. In the figure, the upper side is the vehicle upper side, and the left side is the vehicle front. The configuration shown in the drawing is merely an example of a typical configuration of the present embodiment, and is not limited to the configuration shown here as long as the intended operation and effect can be obtained in the present embodiment.

  In this embodiment, the cooling device 1 is mounted on a vehicle (not shown) that uses an internal combustion engine (engine) EG as a power source, and cools the engine EG by circulating cooling water in the path. . The cooling water is obtained by diluting an antifreeze liquid with water. In this embodiment, the antifreeze liquid is a long life coolant (hereinafter, LLC), which is a liquid agent mainly composed of ethylene glycol.

  The cooling device 1 includes a pump 11, a water jacket 12, a thermostat 13, a radiator 14, a pressure cap 15, a reserve tank 16, a compressor 17, a pressure regulating valve 18, an engine speed sensor 21, a temperature sensor 22, a concentration sensor 23, and a pressure sensor. 24 and controller 30. There are two circulation paths for the cooling water of the cooling device 1, α and β. In the path α, the cooling water exiting the water jacket 12 passes through the passage C1, the thermostat 13, the passage C2, the radiator 14, the passages C3 and C4, and returns to the water jacket 12 again. In the path β, the cooling water exiting the water jacket 12 passes through the passage C1, the thermostat 13, the passages C5 (bypass) and C4, and returns to the water jacket 12 again. That is, the path β is a path that does not pass through the radiator 14. Hereinafter, the paths α and β are collectively referred to as a circulation path.

  The pump 11 is arranged near the inlet of the water jacket 12 and circulates cooling water. In the present embodiment, the pump 11 has an impeller that rotates when engine power is transmitted. Therefore, the rotational speed of the impeller increases as the rotational speed of the engine EG increases, and the flow rate Q of the circulating cooling water increases. The pump 11 may be an electric type. In this case, the pump 11 is electrically connected to the controller 30, and the flow rate Q of the cooling water is controlled by controlling the rotation speed of the impeller in accordance with a command from the controller 30.

  The water jacket 12 is arranged in the engine EG, and the engine EG is cooled by the cooling water flowing through the water jacket 12. The relationship between the state of the cooling water in the water jacket 12 and the cooling efficiency of the engine EG will be described later.

  The thermostat 13 is a device that switches the path of the cooling water from the water jacket 12. The thermostat 13 shuts off the passages C1 and C2 when the temperature is equal to or lower than the predetermined temperature, and connects the passages C1 and C2 when the temperature exceeds the predetermined temperature. Therefore, for example, immediately after the engine EG is started, when the cooling water is not sufficiently warmed (below the predetermined temperature), the cooling water does not pass through the radiator 14 and circulates only through the path β, thereby efficiently cooling the cooling water. Increase temperature. When the predetermined temperature is exceeded, the cooling water circulates through the paths α and β.

  The radiator 14 is a device for cooling the cooling water by exchanging heat with outside air. In the present embodiment, the radiator 14 is disposed in front of the vehicle. The outside air is guided from the front of the vehicle to the radiator 14 by a fan (not shown) attached to the rotation shaft of the engine EG. Further, the upper portion of the radiator 14 is connected to a passage C 6 that leads to the pressure cap 15. Further, the passage C6 has a branch that leads to the passage C8 in the middle thereof.

  The pressure cap 15 is a component for setting the pressure in the cooling device 1 within a predetermined range, and is disposed between the passage C6 and the passage C7 leading to the reserve tank 16. The pressure cap 15 includes a pressurizing valve and a negative pressure valve. When at least one of these valves is open, the passages C6 and C7 communicate with each other, and when both of them are closed, the passage C6 and It is blocked from C7.

  When the pressure on the circulation path side exceeds a predetermined upper limit, the pressurization valve is opened and the pressure is released via the passage C7. When the pressure on the circulation path side falls within a predetermined range, the pressurization valve is closed.

  On the other hand, when the temperature of the cooling water in the circulation path decreases due to the stop of the engine EG or the like, the cooling water contracts and the pressure decreases. When the pressure on the circulation path side falls below a predetermined lower limit, the negative pressure valve is opened, cooling water flows from the reserve tank 16 side to the circulation path side, and if the pressure on the circulation path side is within a predetermined range, the negative pressure valve is Closed.

  In the cooling water pressure control described later, the pressure is controlled within a range in which the pressurization valve and the negative pressure valve are not opened.

  The reserve tank 16 stores cooling water supplied into the circulation path via the pressure cap 15 or discharged from the circulation path. A water supply port 161 is provided in the upper part of the reserve tank 16, and the water supply port 161 is closed by a lid 162 except during water supply.

  The compressor 17 is a device for pressurizing the circulating cooling water by supplying pressurized air through the pressure regulating valve 18 and the passage C8. The compressor 17 is electrically connected to the controller 30 and operates according to a signal from the controller 30.

  The pressure regulating valve 18 is in a pressurized state that allows passage between the passage C8 and the compressor 17, an air release state that shuts off the passage C8 and the compressor 17 and allows passage between the passage C8 and the outside of the cooling device 1 (hereinafter referred to as an open state), and The pressure is controlled during a pressure holding state in which the passage 8 is shut off between the compressor 17 and the outside (atmosphere). In the present embodiment, the pressure regulating valve 18 is driven by an electric actuator. The pressure regulating valve 18 is electrically connected to the controller 30, and an actuator is operated by a signal from the controller 30.

  The engine speed sensor 21 detects the speed of the engine EG. The engine speed sensor 21 is electrically connected to the controller 30 and transmits the detected engine speed data of the engine EG as a signal to the controller 30. As described above, the rotation speed of the impeller of the pump 11 is related to the rotation speed of the engine EG, the viscosity and the concentration of the cooling water. Therefore, the controller 30 calculates the flow rate Q of the cooling water flowing through the paths α and β (water jacket 12) based on the rotational speed of the engine EG, the temperature θ of the cooling water described later, and the concentration C of the antifreeze.

  The temperature sensor 22 detects the temperature θ of the circulating cooling water. The temperature sensor 22 is electrically connected to the controller 30 and transmits data of the detected temperature θ of the cooling water to the controller 30 as a signal. In the present embodiment, the temperature sensor 22 is provided in the thermostat 13. Therefore, the temperature close to the temperature of the cooling water in the water jacket 12 can be detected by detecting the temperature θ of the cooling water exiting the water jacket 12. Also, with this arrangement, the temperature θ of the circulating cooling water can be detected regardless of the state of the thermostat 13 (cooling water temperature). The location of the temperature sensor 22 is not limited to the location of the thermostat 13, and the same effect can be obtained as long as it is any location in the passage C <b> 1.

  The concentration sensor 23 detects the concentration C of the antifreeze of the cooling water by detecting the refractive index of the cooling water. The concentration sensor 23 is electrically connected to the controller 30 and transmits the detected concentration C data of the antifreeze liquid as a signal to the controller 30. The location where the concentration sensor 23 is disposed is preferably a location where fine bubbles or the like are not generated in the cooling water, that is, outside the circulation path. In this embodiment, the concentration sensor 23 is disposed in the reserve tank 16. Note that the detection method of the concentration sensor 23 is not limited to this, and may be one that detects specific gravity or viscosity, and may be one that detects color (darkness) if the antifreeze is colored.

  The pressure sensor 24 detects the pressure P of the cooling water. The pressure sensor 24 is electrically connected to the controller 30 and transmits data of the detected cooling water pressure P as a signal to the controller 30. In order to measure the pressure P of the cooling water in the circulation path, the pressure sensor 24 needs to be arranged on the circulation path side with respect to the pressure cap 15 and the pressure regulating valve 18. In the present embodiment, the pressure sensor 24 is provided in the passage C6 that is outside the circulation path, and therefore pressure data that is less influenced by the flow of the cooling water is obtained.

  The controller 30 is, for example, an ECU, a conversion unit 31 for converting an analog input signal such as an A / D converter into a digital signal, a calculation unit 32 such as a CPU or MPU, and a storage unit 33 such as a ROM or RAM. including. The controller 30 receives data obtained from various sensors as a signal, and operates various electrically connected devices based on these data.

<Saturated boiling>
FIG. 2 is a diagram showing a state diagram (steam pressure curve) of cooling water. In the figure, the horizontal axis represents the cooling water temperature θ, and the vertical axis represents the value of the cooling water pressure pV flowing through the water jacket 12. The vapor pressure curve (solid line) of the pure solvent (water) is represented by pV = 10 (k1−k2 / (θ + k3)), and the upper left side of the curve is the liquid phase and the lower right side is the gas phase. Note that k1, k2, and k3 are constants, and in the case of water, k1 = 8.07544, k2 = 1705.616, and k3 = 231.405. When the state of the cooling water crosses the vapor pressure curve from the liquid phase to the gas phase, the cooling water boils (saturated boiling), and the cooling efficiency of the engine EG is significantly impaired.

  When a solute (LLC) is contained in the solvent (water), the vapor pressure decreases (vapor pressure drop), and a vapor pressure curve such as a dotted line is obtained. For this reason, when the pressure pV is constant, the boiling point of the cooling water rises, but this amount of rise (molar boiling point rise) θm is calculated using the mass molar concentration m (mol / kg) of solute (LLC) as θm = kb. M (kb: constant (0.515 (K · kg / mol) when the solvent is water)) That is, the molar boiling point increase θm is expressed by a function f (C) (f (C) ≧ 0 and ∂f (C) / ∂C> 0) of the concentration C detected by the concentration sensor 23.

From this, the vapor pressure curve at the concentration C is expressed as pV = 10 (k1−k2 / (θ−f (C) + k3)). The relationship between the pressure pV of the cooling water flowing in the water jacket 12 and the detected pressure P is expressed as pV = P− (1/2) ρV2 (ρ: water density) using the cooling water flow velocity V. (Bernoulli's theorem). The flow velocity V is expressed as a function of the flow rate Q, such as V = Q / A (A: cross-sectional area of the passage). Therefore, P = 10 (k1−k2 / (θ−f (C) + k3)) + (1/2) ρ {V (Q)} 2. _Assuming that the pressure of the cooling water on this curve is P = P _BOIL (θ, Q, C) (hereinafter also _referred to as P _BOIL ), the detected pressure P of the cooling water is _higher than P _BOIL. If it is large (P> P _BOIL ), the cooling water will not boil.

<Subcool boiling>
Subcooled boiling refers to a state in which, although saturation boiling has not occurred, cooling water is overheated in the vicinity of the heat transfer surface, here, the wall surface of the water jacket 12, and bubbles are generated in the vicinity of the wall surface. In this state, when the cooling water boils in the vicinity of the wall surface, it takes a large amount of heat from the wall surface, and when it reaches the part that has not reached the boiling point away from the wall surface, it is cooled by the surrounding cooling water and returned to the liquid again. Pressure subcooled boiling begins is higher than the pressure of saturated boiling begins, therefore, when the pressure subcooled boiling begins and P = P _SUB, the P _SUB> P _BOIL.

  FIG. 3 is a diagram showing the change of the heat flux q with respect to the difference Δθ between the temperature of the wall surface of the water jacket 12 and the temperature θ of the cooling water. In the figure, the horizontal axis represents the temperature difference Δθ, and the vertical axis represents the value of the heat flux q. The lines L1 to L3 are in a state where the cooling water is not subcooled boiling (hereinafter referred to as a non-subcooled boiling state, and these lines are collectively referred to as a line L). Like L3, the rate of increase in heat flux increases. The lines S1 to S3 indicate the pressure of the cooling water flowing through the water jacket 12 in a state where the cooling water is boiling in a subcooled state (hereinafter referred to as a subcooled boiling state, and these lines are collectively referred to as a line S). As pV (detected pressure P) and antifreeze concentration C increase, the line moves to the right from S1 to S3.

  As can be seen from the figure, the heat flux q increases as the difference Δθ between the temperature of the wall surface of the water jacket 12 and the temperature θ of the cooling water increases. Further, as can be seen by comparing L1 to L3 and S1 to S3, it can be seen that the heat flux q is much larger in the subcooled boiling state than in the non-subcooled boiling state, and the engine EG can be efficiently cooled.

  The intersection of each line in the figure is the point at which subcooled boiling of the cooling water begins. For example, in the flow velocity that becomes L1, the pressure that becomes S1, and the concentration of the antifreeze, the right side from the intersection of L1 and S1 is in the subcooled boiling state, and the left side is in the non-subcooled boiling state.

<Cooling water pressure control>
From the above, if the pressure P of the cooling water in the circulation path is P _BOIL <P <P _SUB , the cooling water in the water jacket 12 can be kept in a subcooled boiling state, and the engine EG can be efficiently _operated. Can be cooled. In this embodiment, P _BOIL (θ, Q, C) + ΔP ₁ <P <P _BOIL (θ, Q, C) + ΔP ₂ (<P _SUB ), that is, based on the pressure at which saturation boiling occurs. The pressure P of the cooling water in the circulation path is controlled. Note that ΔP ₁ is a value that allows for a margin with respect to the pressure at which saturation boiling starts, and ΔP ₂ is a value that is experimentally obtained as a condition for subcooled boiling in the range of use. The functions P _BOIL (θ, Q, C), ΔP ₁ and ΔP ₂ are stored in the storage unit 33.

FIG. 4 is a flowchart showing an example of cooling water pressure control. This control is executed by the controller 30. Here, P _BOIL (θ, Q, C) + ΔP _{1 is set} to P _LWR , and P _BOIL (θ, Q, C) + ΔP _{2 is set} to P _UPR .

  In S401, the flow rate Q calculated based on the signal from the engine speed sensor 21, the temperature θ of the cooling water detected by the temperature sensor 22, the concentration C of the LLC of cooling water detected by the concentration sensor 23, and the pressure sensor The cooling water pressure P detected by 24 is acquired.

In S402, P _LWR and P _UPR are calculated based on θ, Q, and C. First, in S403, the cooling water pressure P and P _LWR are compared. If P <P _LWR (No in S403), in S404, the controller 30 sends a signal, pressurizes the pressure regulating valve 18, operates the compressor 17, pressurizes the circulation path, and proceeds to S401. Return.

If P ≧ _PLWR (Yes in S403), the cooling water pressure P and _PUPR are compared in S405. If P> _PUPR (No in S405), in S406, the controller 30 transmits a signal to stop the compressor 17, open the pressure regulating valve 18, reduce the pressure in the circulation path, and return to S401. Note that the processing order of S403 and S405 may be reversed.

If P ≦ _PUPR (Yes in S405), in S407, the controller 30 transmits a signal, stops the compressor 17, sets the pressure regulating valve 18 to the pressure maintaining state, maintains the pressure in the circulation path, and again The process returns to S401 (RETURN).

  In S406 and S407, the compressor 17 is stopped, but the passage C8 and the compressor 17 are shut off in any control (when the pressure regulating valve 18 is in the open state and the pressure holding state). Therefore, the compressor 17 may be operated. However, by stopping the compressor 17 when there is no need for pressurization as in this embodiment, the burden on the engine EG can be reduced, and effects such as improved fuel efficiency can be obtained.

By this processing, the pressure P of the cooling water can be controlled based on the temperature θ, the flow rate Q, and the concentration C, and the cooling water in the water jacket 12 can be brought into a subcooled boiling state. In addition to this example, a control range of the pressure P with respect to the temperature θ, the flow rate Q, and the concentration C is mapped, or a table that defines the upper limit value P _UPR and the lower limit value P _LWR is stored in the storage unit 33. The pressure P may be controlled by the calculation unit 32 reading.

<Effect of this embodiment>
According to this embodiment, the pressure in the circulation path is set so that the cooling water in the water jacket 12 is in the subcooled boiling state based on the temperature θ of the cooling water, the flow rate Q, and the concentration C of the antifreeze liquid detected by various sensors. P is controlled. Therefore, even if the concentration C of the antifreeze liquid changes, the pressure P can be maintained in an appropriate range, and the cooling water can be maintained in the subcooled boiling state in the water jacket 12. As described above, if the cooling water is in the subcooled boiling state, the engine EG can be efficiently cooled.

  Therefore, according to the present embodiment, sufficient cooling efficiency can be ensured in the cooling device 1 of the engine EG even if the concentration C of the antifreeze of the cooling water changes.

<Modified example of apparatus configuration of this embodiment>
FIG. 5 is a view showing a cooling device 5 according to a modification of the device configuration according to the embodiment of the present invention. Here, the description of the same configuration as that of the cooling device 1 of FIG. 1 is omitted.

  In this configuration, the pressure cap 15 is provided on the upper portion of the reserve tank 16. Therefore, the pressure in the reserve tank 16 is also maintained (pressurized) at the same pressure as in the circulation path. When at least one of the pressure valve and the negative pressure valve is open, the pressure cap 15 communicates between the reserve tank 16 and the outside (atmospheric release). Therefore, when the pressure in the reserve tank 16 exceeds or falls below a predetermined range, the reserve tank 16 is opened to the atmosphere.

  Moreover, the pressure sensor 24 can be provided in the reserve tank 16 by arranging in this way. By disposing the pressure sensor 24 away from the circulation path and avoiding the narrow passage, the influence of the flow of the cooling water on the pressure data is further smaller than in the case of FIG.

  The compressor 17 and the pressure regulating valve 18 are arranged so as to communicate with the inside of the reserve tank 16 through the passage C9, but may be branched from any place between the reserve tank 16 and the radiator 14.

  The water supply port 161 and its lid 162 communicate with the radiator 14 via the passage C6. The water supply port 161 is provided at a position higher than the water surface of the reserve tank 16. This is to prevent the cooling water from being ejected from the water supply port 161 when the lid 162 is opened.

<Modification of pressure control of this embodiment>
Hereinafter, modified examples of the pressure control of the present embodiment will be described. This modification may be applied to any of the devices shown in FIGS.

  Refer to FIG. 3 again. From this figure, it can be seen that the position of the intersection of L and S (value of Δθ) is determined by the pressure pV of the cooling water flowing in the water jacket 12, the flow velocity V, and the concentration C of the antifreeze. Therefore, since the values of Δθ, V, pV, and C are related to each other, it can be said that the pressure pV at the intersection depends on Δθ, V, and C. Δθ can be estimated from the value of θ and the operating state of the engine EG (rotation speed, load, air-fuel ratio, supercharging pressure, etc.). Further, the higher the temperature θ of the cooling water, the higher the temperature of the cooling water on the wall surface, and the subcooled boiling tends to occur even at a high pressure. For this reason, the position (intersection point) at which the subcooled boiling starts also changes depending on the temperature θ of the cooling water. Therefore, in a state where Δθ, θ, V, and C are determined, the position of the intersection can be moved by changing the value of pV. Moreover, since P = pV + (1/2) ρV2, by performing control based on the pressure P detected by the pressure sensor 24, the cooling water can be controlled to the subcooled boiling state.

Therefore, the pressure detected by the pressure sensor 24 when the cooling water starts subcooling boiling is represented by P _SUB (Δθ, θ, V, C) (hereinafter also referred to as P _SUB ). Since the flow velocity V is a function of the flow rate Q, it is also expressed as P _SUB (Δθ, θ, Q, C). If the pressure P of the cooling water is smaller than P _SUB (P <P _SUB ), the cooling water is in a subcooled boiling state. The function P _SUB (Δθ, θ, Q, C) varies depending on the shape of the cooling water path, the state of the wall surface, and the like. In addition, it turns out that there exists the following tendency about the increase / decrease in _PSUB with respect to the increase / decrease in (DELTA) (theta), (theta), Q, C.

FIG. 3 shows that Δθ at the intersection is higher as the cooling water pressure P is higher. This is because boiling of the wall surface of the water jacket 12 is more likely to occur as the temperature of the wall surface of the water jacket 12 is higher than the temperature θ of the cooling water. Therefore, ∂P _SUB / ∂Δθ> 0.

As described above, the higher the temperature θ of the cooling water, the easier the subcooled boiling occurs even at a higher pressure. Therefore, ∂P _SUB / ∂θ> 0.

Considering from FIG. 3, when the intersection is taken on a predetermined Δθ (on a line parallel to the vertical axis), the faster the cooling water flow velocity V (as it moves from L1 to L3), the line S becomes the left side. The pressure _PSUB decreases as the line S goes to the left. That is, the pressure P _SUB starting the subcooled boiling higher flow velocity V is high becomes low. Therefore, ∂P _SUB / ∂V <0. Furthermore, since it is ∂V / ∂Q> 0, the ∂P _SUB / ∂Q <0. This can also be predicted from the fact that the faster the flow velocity V (the larger the flow rate Q), the shorter the time that the cooling water stays on the wall surface, and it is necessary to lower the pressure P to promote boiling on the wall surface.

When the flow velocity V is fixed, if the concentration C is increased, the line S moves to the right, so that the temperature difference Δθ at the intersection increases. Therefore, in order to make the temperature difference Δθ at the intersection point constant even when the concentration C increases, the line S must be moved to the left by the amount moved by increasing the concentration C by decreasing the pressure P. Therefore, under conditions where the flow velocity V and the temperature difference Δθ are constant, the higher the concentration C, the lower the pressure P _SUB that starts subcool boiling. Therefore, ∂P _SUB / ∂C <0. This can be predicted from the fact that when the concentration C of the solute (LLC) is high, the solvent (cooling water) is less likely to boil, and it is necessary to lower the pressure P to promote boiling on the wall surface.

From the above, a function P _ST (Δθ, θ,...) Such that P _BOIL (θ, Q, C) <P _ST (Δθ, θ, Q, C) <P _SUB (Δθ, θ, Q, C) is satisfied. Q, C) is determined, and the cooling water pressure P is controlled so that the cooling water pressure P falls within a predetermined range (allowable range value ΔP ₃ ) from this value (P _ST (Δθ, θ, Q, C) −ΔP ₃ > P _BOIL (θ, Q, C), P _ST (Δθ, θ, Q, C) + ΔP ₃ <P _SUB (Δθ, θ, Q, C)). In the case of this embodiment, the functions P _ST (Δθ, θ, Q, C) and ΔP ₃ are P _BOIL (θ, Q, C) and P _SUB (Δθ, θ, Q, C) obtained by experiment. Although it is determined based on this, it may be determined based on analysis such as computer simulation. The function P _ST (Δθ, θ, Q, C) and the allowable range value ΔP ₃ are stored in the storage unit 33.

FIG. 6 is a flowchart showing another example of the cooling water pressure control. This control is executed by the controller 30. Here, P _ST (Δθ, θ, Q, C) −ΔP ₃ is P _LWR , and P _ST (Δθ, θ, Q, C) + ΔP ₃ is P _UPR .

  In S601, the flow rate Q calculated based on the signal from the engine speed sensor 21, the coolant temperature θ detected by the temperature sensor 22, the LLC concentration C of the coolant detected by the concentration sensor 23, and the pressure sensor. The cooling water pressure P detected by 24 is acquired. Subsequently, in S602, Δθ is estimated based on θ and the operating state of the engine EG.

In S603, P _LWR and P _UPR are calculated based on Δθ, θ, Q, and C. First, in S604, the pressure P of the cooling water and P _LWR are compared. If P <P _LWR (No in S604), in S605, the controller 30 transmits a signal, pressurizes the pressure regulating valve 18, operates the compressor 17, pressurizes the circulation path, and proceeds to S601. Return.

If P ≧ P _LWR (Yes in S604), the pressure P of the cooling water and P _UPR are compared in S606. If P> _PUPR (No in S606), in S607, the controller 30 transmits a signal to stop the compressor 17, open the pressure regulating valve 18, reduce the pressure in the circulation path, and return to S601. Note that the processing order of S604 and S606 may be reversed.

If P ≦ _PUPR (Yes in S606), in S608, the controller 30 transmits a signal, stops the compressor 17, sets the pressure regulating valve 18 to the pressure maintaining state, maintains the pressure in the circulation path, and again The process returns to S601 (RETURN).

By this processing, the pressure P of the cooling water can be controlled within a predetermined range (P _{LWR to} P _UPR ) based on the function P _ST (Δθ, θ, Q, C), and the cooling water in the water jacket 12 can be controlled. Can be brought into a subcooled boiling state. Moreover, since Δθ is estimated from the operating state of the engine EG, it is possible to appropriately cope with a change in the operating state of the engine EG. In particular, if the configuration is such that the parameter of the operating state of the engine EG is obtained based on a command value from the ECU, feedforward control is incorporated, and it is possible to cope with a sudden change in the operating state of the engine EG.

EG Engine 1, 5 Cooling device α, β Circulation path 12 Water jacket 17 Compressor 18 Pressure regulating valve 21 Engine speed sensor 22 Temperature sensor 23 Concentration sensor 30 Controller

Claims (5)

A cooling device for an internal combustion engine that performs cooling by circulating cooling water containing antifreeze liquid in a path including a jacket portion disposed in the internal combustion engine,
Flow rate detection means for detecting the flow rate of cooling water in the path;
Temperature detecting means for detecting the temperature of the cooling water in the path;
Concentration detecting means for detecting the concentration of the antifreeze in the cooling water;
A cooling device for an internal combustion engine, comprising: pressure control means for controlling the pressure of the cooling water in the path based on the flow rate, temperature, and concentration of the antifreeze liquid in the path.   The pressure control means controls the pressure of the cooling water in the path so that the cooling water in the path does not saturate and the cooling water is in a subcooled boiling state in the jacket portion. The cooling device for an internal combustion engine according to claim 1.   3. The internal combustion engine according to claim 1, wherein the pressure control unit controls the pressure of the cooling water based on a function having variables of the flow rate, the temperature, and the concentration of the antifreeze liquid. Engine cooling system.   The cooling apparatus for an internal combustion engine according to claim 3, wherein the pressure control means controls the pressure of the cooling water so as to be within a predetermined range from the value of the function. A temperature difference estimating means for estimating a temperature difference between the temperature of the inner wall of the jacket portion and the temperature of the cooling water from the operating state of the internal combustion engine;
The cooling apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the pressure control means further controls the pressure of the cooling water based on the temperature difference.

Images