JP2012132364A - Control system of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control system capable of preventing an engine from being damaged by condensate produced in an intercooler while such a problem as the deterioration of exhaust gas etc. is suppressed.SOLUTION: On the basis of the rate of a flow of a suction air which passes through the intercooler, the limit value of the relative humidity of the suction air at the intercooler outlet is set larger than 1.0 and to such a value as increasing with an incremental rate of a flow of the suction air which passes through the intercooler, and the suction air is made to flow into the intercooler so that the relative humidity of the suction air does not exceed the set limit value.

Description

  The present invention relates to an engine control apparatus including an intercooler for cooling intake air pressurized by a supercharger.

  An engine including a supercharger (such as a turbocharger) generally includes an intercooler in an intake passage for cooling the intake air pressurized by the supercharger. Some engines equipped with a supercharger include an exhaust gas recirculation (EGR) device that recirculates a part of exhaust gas to an intake passage and reburns it with fresh air.

  In the engine having such a configuration, when the intake air is cooled in the intercooler, moisture is condensed and condensed water is generated. The EGR gas supplied to the intake passage by the exhaust gas recirculation has a relatively high temperature and contains a relatively large amount of moisture as water vapor. For this reason, in the case of intake air including EGR gas, condensed water tends to be generated particularly in the intercooler. If this condensed water flows into the combustion chamber at once, there is a risk that the engine may be damaged due to the occurrence of a so-called water hammer phenomenon. For this reason, it is preferable that the amount of condensed water generated in the intercooler is as small as possible.

  In order to suppress the generation of condensed water, for example, an EGR cooler is provided in an EGR passage for circulating a part of exhaust gas to cool the EGR gas, and the amount of water in the EGR gas passing through the EGR cooler The temperature and amount of the EGR gas flowing out from the EGR cooler are adjusted so that the maximum amount that can exist in the state is smaller than the maximum amount that can exist in the state of water vapor in the EGR gas that passes through the intercooler. (See Patent Document 1).

  Theoretically, when the relative humidity of the intake air at the intercooler outlet exceeds 1.0, condensed water starts to be generated. Therefore, in order to prevent the condensed water from being generated in the intercooler, it is theoretically necessary that the relative humidity of the intake air at the intercooler outlet be less than 1.0. For example, in the invention according to Patent Document 1, it is considered that the temperature and amount of EGR gas are controlled such that the relative humidity of the intake air at the intercooler outlet is less than 1.0. Thus, if the temperature and amount of EGR gas are controlled, the generation of condensed water can be prevented.

JP 2009-52486 A

  In order to make the relative humidity of the intake air less than 1.0 as described above, for example, it is conceivable to significantly reduce the amount of EGR gas. Thereby, the production | generation of condensed water can be prevented. However, since NOx emission increases accordingly, it is desirable to limit the limit of EGR gas to a minimum. Further, for example, the relative humidity of the intake air can be suppressed by significantly reducing the cooling efficiency of the intercooler. However, there is a possibility that problems such as deterioration of exhaust gas due to temperature rise in the intake manifold and reduction in output due to reduction in intercooler capacity may occur.

  Therefore, it is preferable that the relative humidity of the intake air at the intercooler outlet is maintained as high as possible so that condensed water is not generated.

  Here, the inventors of the present application have conducted sincere research on the generation of condensed water in the intercooler. As a result, if the relative humidity of the intake air at the intercooler outlet exceeds 1.0, the condensed water It was found that water droplets were not generated. That is, if the relative humidity exceeds 1.0 and is within a predetermined range, condensed water is not generated, or even if it is generated, it is a trace amount that does not form water droplets (so that it does not accumulate in the intercooler). I found out that there was. Furthermore, the inventor of the present application has found that the predetermined range in which condensed water is not generated as water droplets changes according to the flow rate (flow velocity) of intake air when passing through the intercooler.

  The present invention has been made based on such knowledge, and it is possible to prevent engine damage due to condensed water generated in the intercooler while suppressing problems such as deterioration of exhaust gas. The purpose is to provide.

  A first aspect of the present invention that solves the above problem is an engine control device that controls an engine including an intercooler provided in an intake passage downstream of a supercharger that supercharges intake air. Relative humidity calculation means for calculating the relative humidity of the intake air based on the water vapor pressure of the intake air at the cooler outlet, and droplets of condensed water are generated in the intercooler based on the flow rate of the intake air passing through the intercooler. Limit value setting means for setting a limit value of the relative humidity, which is a starting value, and the relative humidity calculated by the relative humidity calculation means so as not to exceed the limit value of the relative humidity set by the limit value setting means. Intake control means for causing intake air to flow into the intercooler, wherein the limit value of the relative humidity is greater than 1.0, and the intercooler is The control apparatus for an engine, wherein the flow rate of intake air over that is larger value with the increase.

  In the first aspect, the generation of condensed water in the intercooler can be substantially prevented even when the relative humidity of the intake air is set to a value larger than 1.0. Therefore, it is possible to prevent engine damage due to condensed water while suppressing problems such as deterioration of exhaust gas.

  A second aspect of the present invention includes an EGR flow path that connects an exhaust passage downstream of the supercharger and the intake passage upstream of the supercharger, and the intake control means includes: The engine control apparatus according to the first aspect is characterized in that the amount of EGR gas supplied from the EGR flow path to the intake passage is changed so that the relative humidity does not exceed the limit value.

  In the second aspect, it is possible to more reliably and efficiently suppress the generation of condensed water in the intercooler by changing the amount of EGR gas.

  According to a third aspect of the present invention, in the engine according to the first or second aspect, the intake air control means changes the cooling efficiency of the intercooler so that the relative humidity does not exceed the limit value. In the control unit.

  In this 3rd aspect, the production | generation of the condensed water in an intercooler can be suppressed more reliably and efficiently by changing the cooling efficiency of an intercooler.

  In this invention, even if the relative humidity of the intake air at the intercooler outlet is set to a value larger than 1.0, the generation of condensed water in the intercooler can be substantially prevented. That is, it is possible to substantially prevent the generation of condensed water while maintaining the relative humidity of the intake air higher than in the past. Therefore, it is possible to prevent engine damage due to condensed water while suppressing problems such as deterioration of exhaust gas.

It is a figure showing a schematic structure of an engine system concerning one embodiment of the present invention. It is a block diagram which shows schematic structure of the control apparatus which concerns on one Embodiment of this invention. It is a figure which shows an example of the map which prescribes | regulates the relationship between the flow volume of intake air, and saturated water vapor pressure. It is a figure which shows an example of the map which prescribed | regulated the relationship between the flow volume of intake air, and the relative humidity which the water droplet of condensed water begins to produce | generate. It is a flowchart which shows an example of the condensed water suppression control which concerns on one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, an engine system 10 according to the present embodiment includes an in-line four-cylinder diesel engine (hereinafter simply referred to as “engine”) 12 including four cylinders (combustion chambers) 11 arranged in series. . An intake manifold (not shown) of each cylinder 11 is connected to an intake manifold 13, and an intake pipe (intake passage) 14 is connected to the intake manifold 13. On the other hand, an exhaust manifold (not shown) of each cylinder 11 is connected to an exhaust manifold 15, and an exhaust pipe (exhaust passage) 16 is connected to the exhaust manifold 15.

  In addition, an injector (fuel injection valve) 17 for injecting fuel is provided corresponding to each cylinder 11, and each injector 17 is connected to a common rail 18. The common rail 18 is connected to a fuel tank via a supply pump (high pressure pump) (not shown). Fuel is pumped from the fuel tank by the supply pump, and high-pressure fuel in the common rail 18 is injected from the injector 17 into each cylinder 11.

  A turbocharger (supercharger) 19 is provided in the middle of the intake pipe 14 and the exhaust pipe 16. In the turbocharger 19, when exhaust gas flows from the engine 12, the turbine rotates by the flow of exhaust gas, and the compressor rotates as the turbine rotates, and air is sucked into the turbocharger 19 from the intake pipe 14 and pressurized. It has come to be.

  The intake pipe 14 on the upstream side of the turbocharger 19 is provided with an air cleaner 20 and a first throttle valve 21. The air cleaner 20 is provided with a humidity sensor 22 that detects the humidity of the intake air. The first throttle valve 21 adjusts the amount of fresh air that has passed through the air cleaner 20 (fresh air amount), and by this adjustment, the amount of exhaust gas introduced into the intake pipe 14 via the low-pressure EGR pipe (described later) ( The low-pressure EGR gas amount) is indirectly adjusted. An air flow sensor 23 for detecting the intake air flow rate is provided on the downstream side of the air cleaner 20. In this embodiment, the air flow sensor 23 has a temperature detection function, and detects the intake air temperature together with the intake air flow rate.

  An intake pipe 14 on the downstream side of the turbocharger 19 is provided with an intercooler 24 that cools the intake air whose temperature has risen due to pressurization by the turbocharger 19. In the vicinity of the outlet of the intercooler 24, a temperature sensor 25 that is a temperature detecting means for detecting the temperature of the intake air is provided. The intake pipe 14 on the downstream side of the intercooler 24 is provided with a second throttle valve 26 that opens and closes the intake pipe 14 by driving an electric actuator.

  The second throttle valve 26 adjusts the amount of intake air that has passed through the intercooler 24 (fresh air amount + low pressure EGR gas amount), and is introduced into the intake pipe 14 via a high pressure EGR pipe described later by this adjustment. The amount of exhaust gas (high pressure EGR gas amount) is indirectly adjusted.

  One end of a high-pressure EGR pipe 27 through which high-pressure exhaust gas (high-pressure EGR gas) circulates is connected to the intake pipe 14 downstream of the second throttle valve 26. The other end of the high pressure EGR pipe 27 is connected to the upstream side of the turbocharger 19 of the exhaust pipe 16. A high pressure EGR cooler 28 is provided in the high pressure EGR pipe 27, and a high pressure EGR valve 29 is provided in a connection portion of the high pressure EGR pipe 27 with the intake pipe 14. By opening the high pressure EGR valve 29, a part of the high pressure exhaust gas flowing upstream of the turbocharger 19 of the exhaust pipe 16 flows into the high pressure EGR pipe 27 and is cooled by the high pressure EGR cooler 28, and then the intake air It is supplied to the pipe 14.

  A linear air-fuel ratio sensor (LAFS) 30 that is an air-fuel ratio detecting means for detecting the air-fuel ratio of the intake air is provided downstream of the high-pressure EGR pipe 27 of the intake pipe 14. The intake manifold 13 is provided with a boost pressure sensor 31 that is a pressure detection means for detecting the pressure inside the intake manifold 13.

  Further, on the downstream side of the turbocharger 19 of the exhaust pipe 16, a diesel oxidation catalyst (hereinafter simply referred to as “oxidation catalyst”) 32 as an exhaust purification catalyst and a diesel particulate filter (DPF: DPF: exhaust purification filter). Diesel Particulate Filter (hereinafter referred to as “DPF”) 33 is arranged in order from the upstream side.

  One end of a low-pressure EGR pipe 34 through which a part of the low-pressure exhaust gas (low-pressure EGR gas) circulates is connected downstream of the turbocharger 19 of the exhaust pipe 16, in this embodiment, downstream of the DPF 33. The other end of the low pressure EGR pipe 34 is connected to the intake pipe 14 between the turbocharger 19 and the throttle valve 21. As with the high pressure EGR pipe 27, the low pressure EGR pipe 34 is provided with a low pressure EGR cooler 35 and a low pressure EGR valve 36. When the low pressure EGR valve 36 is opened, a part of the low pressure exhaust gas (low pressure EGR gas) flowing downstream from the turbocharger 19 of the exhaust pipe 16 is cooled by the low pressure EGR cooler 35 and supplied to the intake pipe 14. It has come to be.

  Further, differential pressure sensors 37 as differential pressure detection means are provided at both ends of the low pressure EGR pipe 34. The differential pressure sensor 37 detects the differential pressure between the pressure upstream of the turbocharger 19 in the intake pipe 14 and the pressure downstream of the turbocharger 19 in the exhaust pipe 16. That is, the flow rate and flow rate of the low pressure EGR gas flowing through the low pressure EGR pipe 34 are obtained from the detection result of the differential pressure sensor 37.

  The engine 12 of the engine system 10 is controlled by an ECU (Electronic Control Unit) 40. The ECU 40 includes an input / output device, a storage device (ROM, RAM, etc.), a central processing unit (CPU), a timer counter, and the like, and performs overall control of the engine 12 based on signals from the various sensors. That is, the control device for the engine 12 according to the present embodiment is configured by such an ECU 40 and various sensors.

  On the input side of the ECU 40, various sensors such as a crank angle sensor that detects the crank angle of the engine 12 in addition to the air flow sensor 23, LAFS 30, boost pressure sensor 31, humidity sensor 22, temperature sensor 25, and differential pressure sensor 37 described above. Are connected, and detection information from these sensors is input. On the other hand, various output devices such as the injector 17, the first and second throttle valves 21 and 26, the high pressure EGR valve 29, and the low pressure EGR valve 36 are connected to the output side of the ECU 40. These various output devices output various information such as the fuel injection amount and valve opening calculated by the ECU 40 based on the detection information detected by the various sensors as described above.

  In the engine control apparatus according to the present embodiment configured by such an ECU 40 and various sensors, the valve opening timing of the injector 17 is set so that the desired air-fuel ratio according to the operating state of the engine 12 is obtained. As well as controlling, the operation of the first and second throttle valves 21 and 26 and the high-pressure and low-pressure EGR valves 29 and 36 are appropriately controlled, so that the condensed water in the intercooler 24 is controlled. Generation is efficiently suppressed.

  Hereinafter, the control (condensed water suppression control) which suppresses the production | generation of the condensed water in the intercooler by the control apparatus of the engine which concerns on this embodiment is demonstrated. As shown in FIG. 2, the ECU 40 includes air-fuel ratio control means 41, relative humidity calculation means 42, limit value setting means 43, and intake air control means 44.

  The air-fuel ratio control means 41 controls the fuel injection valve amount so that the air-fuel ratio of the intake air becomes a predetermined value. In the present embodiment, the air-fuel ratio control means 41 sets the target air-fuel ratio of the intake air according to the operating state of the engine 12, and based on the detection result of the LAFS 30, the actual air-fuel ratio of the intake air becomes the target air-fuel ratio. The amount of fuel injected from the injector 17 is appropriately controlled.

  The relative humidity calculating means 42 calculates the relative humidity of the intake air near the outlet of the intercooler 24. The relative humidity of the intake air is a value represented by the ratio (Y / X) of the water vapor pressure (Y) contained in the intake air near the outlet of the intercooler 24 and the saturated water vapor pressure (X).

  Here, an example of a method for calculating the relative humidity (Y / X) of the intake air will be described.

  First, the saturated water vapor pressure (X) is obtained based on the detection result of the temperature sensor 25, for example, from a predetermined map that defines the relationship between the temperature and the saturated water vapor pressure as shown in FIG.

On the other hand, the water vapor pressure (Y = P _{H2O_IC} ) includes the intercooler passage water amount (M _{H2O_IC} [mg / st]), the intercooler gas amount (M _IC [mg / st]), and the intake manifold pressure (P _IM [ kPa]) and the following equation (1). In this embodiment, the molar mass (G _H2O ) of water is 18 [g / mol], and the molar mass (G _AIR ) of outside air (air) is 28.8 [g / mol].
P _{H2O_IC} = (M _{H2O_IC} / 18) / (M _IC /28.8)×P _IM (1)

Here, the intake manifold pressure (P _IM ) is detected by the boost pressure sensor 31. In addition, the intercooler passing water amount (M _{H2O_IC} [mg / st]) is determined based on the moisture content of the outside air (air) (M _{H2O_AIR} [mg / st]) and the moisture content of the low pressure EGR gas (M (n) _{H2O_EGR} [mg / st]. ] Is calculated from the following equation (2).
M _{H2O_IC} = M _{H2O_AIR} + M (n) _{H2O_EGR} (2)

The moisture content of the outside air (M _{H2O_AIR} ) includes the density of air (outside air) (ρ _a [kg / m ³ ]), the density of saturated water vapor (ρ _ws [kg / m ³ ]), and the relative humidity of the outside air (RH [RH [ %]) And the intake air amount (M _AIR [mg / st]).
M _{H2O_AIR} = (ρ _ws / ρ _a ) × (RH / 100) × M _AIR (3)

The density (ρ _ws ) of the saturated water vapor is calculated from a predetermined map or the like based on the detection result (outside air temperature) of the air flow sensor 23. Further, the outside air relative humidity (RH) is detected by the humidity sensor 22, and the intake air amount (M _AIR ) is detected by the air flow sensor 23.

The moisture content of the low-pressure EGR gas (M (n) _{H2O_EGR} [mg / st]) is _{calculated from} the moisture mass ratio (R _{H2O_EX} ) in the exhaust gas and the total low-pressure EGR gas mass (M _EGR [mg / st]) as _follows : Calculated by equation (4).
M (n) _{H2O_EGR} = R _{H2O_EX} × M _EGR (4)

The moisture mass ratio (R _{H2O_EX} ) in the exhaust gas is _{calculated from} the moisture content of the exhaust gas (M _{H2O_EX} [mg / st]) and the mass of the exhaust gas (M _EX [mg / st]) by the following equation (5). The
R _{H2O_EX} = M _{H2O_EX} / M _EX (5)

The moisture content of the exhaust gas (M _{H2O_EX} ) includes the moisture content of the low-pressure EGR gas calculated previously (M (n−1) _{H 2 O_EGR} ), the moisture content of the outside air (M _{H2O_AIR} ), and moisture generated during combustion in the cylinder. This is a value obtained by summing the amount (combustion water content: M _{H2O_BURN} ), and is represented by the following formula (6).
M _{H2O_EX} = M (n-1) _{H2O_EGR} + M _{H2O_AIR} + M _{H2O_BURN} (6)

The mass of the exhaust gas (M _EX ) is the sum of the amount of intake air (M _AIR ), the amount of injected fuel (M _FUEL ) introduced into each cylinder from the injector 17, and the mass of low-pressure EGR gas (M _EGR ) It is a value and is represented by the following formula (7).
M _EX = M _AIR + M _FUEL + M _EGR (7)

The intake air amount (M _AIR ) is detected by the air flow sensor 23, the input fuel amount (M _FUEL ) is the target fuel injection amount set by the air-fuel ratio control means 41, and the mass of the low pressure EGR gas (M _EGR ) Is calculated by the following equation (8).
M _EGR = [S × (2 × ΔP × ρ _a ) ^ 0.5] / (2 × Ne) (8)
(S: equivalent opening area according to low-pressure EGR valve opening, ΔP: differential pressure (detection result of differential pressure sensor), ρ _a : air density, Ne: engine speed)

From the above formulas (4) to (7), the water content (M (n) _{H2O_EGR} ) of the low-pressure EGR gas is represented by the following formula (9).
M (n) _{H2O_EGR} = [(M _{H2O_AIR} + M _{H2O_BURN} ) / (M _AIR + M _FUEL )] × M _EGR (9)

Further, the amount of combustion generated water (M _{H2O_BURN} ) is calculated by the following formula (10) assuming that the fuel used is C ₁₆ H ₃₀ with a CH ratio of 1.875. The molar mass (G _C16H30 ) of the fuel used is 222 [g / mol], and the molar mass of water (G _H2O ) is 18 [g / mol]. This value may be appropriately changed according to the fuel properties to be used.
M _{H2O_BURN} = 15 × (G _H2O / G _C16H30 ) × M _FUEL (10)

Then, the water vapor pressure (Y = P _{H2O_IC} ) included in the intake air near the outlet of the intercooler 24 is calculated by the above formulas (1) to (10), the calculated water vapor pressure (Y), and saturated water vapor From the pressure (X), the relative humidity (Y / X) near the outlet of the intercooler 24 is calculated.

  The limit value setting means 43 sets a limit value of relative humidity (Y / X) at which condensed water droplets start to be generated in the intercooler 24 based on the flow rate of the intake air passing through the intercooler 24. In other words, the limit value setting means 43 sets an upper limit value in a range where water droplets of condensed water are not generated. Note that the fact that condensed water droplets are not generated means that the condensed water is not generated, or even if it is generated, it is a minute amount that does not form water droplets (so that it does not accumulate in the intercooler).

  Further, the limit value of the relative humidity set by the limit value setting means 43 is a value that is larger than 1.0 and increases as the flow rate of the intake air passing through the intercooler 24 increases.

  Theoretically, condensed water should be generated when the relative humidity of the intake air becomes higher than 1.0. However, the inventor of the present application has the relative humidity of the intake air at the outlet of the intercooler 24 exceeding 1.0. However, if it was in the predetermined range, it discovered that condensed water was not produced | generated as a water droplet. The present invention is based on such knowledge and is completely new, which is different from the prior art.

  The relative humidity limit value is set based on the detection result of the air flow sensor 23, the flow rate of the intake air passing through the intercooler 24 as shown in FIG. 4 and the generation of condensed water droplets in the intercooler 24, for example. This is performed based on a predetermined map that defines the relationship with the relative humidity.

  The intake air control unit 44 causes the intake air to flow into the intercooler 24 so that the relative humidity (Y / X) calculated by the relative humidity calculation unit 42 does not exceed the limit value set by the limit value setting unit 43. For example, the intake control means 44 according to the present embodiment performs control to change the amount of low-pressure EGR gas that is circulated to the intake pipe 14 via the low-pressure EGR pipe 34, so that the relative humidity (Y / X) is a limit value. Intake air is allowed to flow into the intercooler 24 so as not to exceed.

  In this way, by causing the intake air to flow into the intercooler 24 so as not to exceed the limit value of the relative humidity, the generation of condensed water in the intercooler can be efficiently prevented. That is, even if the relative humidity of the intake air at the outlet of the intercooler 24 is set to a value larger than 1.0 by appropriately adjusting the flow rate (flow velocity) of the intake air flowing into the intercooler 24 according to the limit value of the relative humidity, the intercooler The generation of condensed water in can be substantially prevented. Therefore, it is possible to prevent engine damage due to condensed water while suppressing problems such as deterioration of exhaust gas.

  The intake air control means 44 may perform control for changing the cooling efficiency of the intercooler 24 in addition to the control of the low pressure EGR gas amount or instead of the control of the low pressure EGR gas amount. That is, the intake air control unit 44 may increase the cooling efficiency of the intercooler 24 so that the relative humidity does not exceed the limit value. The method for changing the cooling efficiency of the intercooler 24 is not particularly limited. For example, a shutter for changing the area of the heat exchanger is provided in the intercooler 24, and the cooling efficiency is changed by opening and closing the shutter. be able to.

  Hereinafter, the condensed water suppression control in the intercooler according to the present embodiment will be further described with reference to the flowchart of FIG.

  As shown in FIG. 5, when the engine 12 is first started, the outside air humidity is detected by the humidity sensor 22 provided in the air cleaner 20 in step S1. In step S2, the intake air temperature is detected, and in step S3, the fresh air flow rate is detected. In the present embodiment, since the air flow sensor 23 has a temperature detection function, the air flow sensor 23 detects the intake air temperature and the fresh air flow rate.

Next, in step S4, the amount of moisture in the intake air (M _{H2O_AIR} ) is calculated. Specifically, first, the saturated water vapor pressure M _{ST_AIR} is calculated based on the map as shown in FIG. 3 as described above from the intake air temperature detected in step S2. Then, from this saturated water vapor pressure M _{ST_AIR} , the intake air flow rate M _AIR detected in step S3, and the outside air humidity RH detected in step S1, the intake water amount (M _{H2O_AIR} ) is calculated by the above equation (3). The

  In step S5, the fuel injection amount is detected. The fuel injection amount detected here is the target fuel injection amount set by the air-fuel ratio control means 41 as described above. The fuel injection amount injected from the injector 17 is feedback-controlled according to the operating state of the engine 12, and the target fuel injection amount is a value set in this feedback control.

  In step S6, the low pressure EGR gas amount is calculated by the above equation (8). In step S7, the temperature of the intake air near the outlet of the intercooler 24 is detected by the temperature sensor 25. In step S8, the boost pressure sensor 31 detects the pressure in the intake manifold 13 (intake manifold pressure). The method of detecting the intake air temperature is not limited to the method of directly detecting by the temperature sensor 25, and may be a method of estimating based on the temperature of the outside air, the temperature of the exhaust gas, or the like.

  In step S9, the saturated water vapor pressure (X) of the intake air near the outlet of the intercooler 24 is calculated, and in step S10, the water vapor pressure (Y) of the intake air near the outlet of the intercooler 24 is calculated. In step S11, the relative humidity (Y / X) of the intake air near the outlet of the intercooler 24 is calculated based on the calculation results in steps S9 and S10. The saturated water vapor pressure (X) is obtained from the detection result of the temperature sensor 25 (the intake air temperature near the outlet of the intercooler 24) based on a predetermined map as described above, and the water vapor pressure (Y) is calculated by the above-described formula Is calculated based on

  Next, in step S12, based on the flow rate (velocity) of the intake air passing through the intercooler 24, a limit value of relative humidity (Y / X) at which water droplets of condensed water start to be generated in the intercooler 24 is set. This limit value is set based on the map shown in FIG. 4 as described above.

  Here, the limit value is a value larger than 1.0 and increases as the flow velocity of the intake air passing through the intercooler 24 increases. For example, in the present embodiment, the limit value setting unit 43 sets the limit value to a value of about 1.3 to 1.4 according to the flow rate of the intake air passing through the intercooler 24.

  In step S13, it is determined whether or not the relative humidity (Y / X) is smaller than a set limit value. Here, when the relative humidity has reached the limit value (step S13: NO), it is determined that water droplets of condensed water are generated in the intercooler 24 so that the amount of low-pressure EGR gas decreases. The low pressure EGR valve 36 is controlled (step S14). That is, the low pressure EGR valve 36 is controlled so that the relative humidity (Y / X) becomes smaller than the limit value. On the other hand, when the relative humidity has not reached the limit value (step S13: Yes), it is determined that water droplets of condensed water are not generated in the intercooler 24, and without changing the amount of low-pressure EGR gas, A series of condensed water suppression control ends.

  If the relative humidity has not reached the limit value, the amount of the low pressure EGR gas is increased so that the relative humidity does not exceed the limit value by controlling the opening degree of the low pressure EGR valve 36 as necessary. Also good. Thereby, the production | generation of the condensed water in an intercooler can be suppressed still more efficiently.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this Embodiment, A various change is possible in the range which does not deviate from the main point of invention.

  For example, in the above-described embodiment, the present invention has been described by exemplifying a configuration including an EGR device that circulates EGR gas through the EGR flow path. However, the EGR device is not necessarily provided. In that case, the relative humidity of the intake air may be prevented from exceeding the limit value by changing the cooling efficiency of the intercooler.

DESCRIPTION OF SYMBOLS 10 Engine system 11 Cylinder 12 Engine 13 Intake manifold 14 Intake pipe 15 Exhaust manifold 16 Exhaust pipe 17 Injector 18 Common rail 19 Turbocharger 20 Air cleaner 21 First throttle valve 22 Humidity sensor 23 Air flow sensor 24 Intercooler 25 Temperature sensor 26 Second sensor Throttle valve 27 High pressure EGR pipe 28 High pressure EGR cooler 29 High pressure EGR valve 31 Boost pressure sensor 34 Low pressure EGR pipe 35 Low pressure EGR cooler 36 Low pressure EGR valve 37 Differential pressure sensor

Claims (3)

An engine control device that controls an engine including an intercooler provided in an intake passage downstream of a supercharger that supercharges intake air,
Relative humidity calculating means for calculating the relative humidity of the intake air based on the water vapor pressure of the intake air at the intercooler outlet;
Limit value setting means for setting the limit value of the relative humidity, which is a value at which condensed water droplets start to be generated in the intercooler, based on the flow rate of the intake air passing through the intercooler;
An intake control means for causing intake air to flow into the intercooler so that the relative humidity calculated by the relative humidity calculation means does not exceed the limit value of the relative humidity set by the limit value setting means;
With
The engine control device according to claim 1, wherein the limit value of the relative humidity is greater than 1.0 and increases as the flow rate of the intake air passing through the intercooler increases. An EGR flow path connecting the exhaust passage downstream of the supercharger and the intake passage upstream of the supercharger;
2. The engine control according to claim 1, wherein the intake air control unit changes an amount of EGR gas supplied from the EGR flow path to the intake air passage so that the relative humidity does not exceed the limit value. apparatus.   3. The engine control device according to claim 1, wherein the intake air control unit changes the cooling efficiency of the intercooler so that the relative humidity does not exceed the limit value. 4.

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