JP2018204491A - Control system - Google Patents

Abstract

To provide a control system for suppressing the lowering of heat efficiency accompanied by a change of an operation condition while obtaining an effect for improving the heat efficiency by cooling intake air.SOLUTION: A control system (1) is used in an internal combustion engine (10) having a combustion chamber (12) which is defined by a cylinder (11) and a piston (13). The control system comprises: an intake air cooling part (40) for cooling the intake air of the internal combustion engine; a variable compression ratio mechanism part (30) for making a combustion form of the combustion chamber variable; a combustion state acquisition part (21) for acquiring an index of a combustion state of the combustion chamber; and an ECU (20) for controlling the intake air cooling part and the variable compression ratio mechanism part on the basis of an acquisition result by the combustion state acquisition part. The ECU controls the variable compression ratio mechanism part after maximally lowering an intake air temperature by the intake air cooling part at the transition of an operation state of the internal combustion engine.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control system used for an internal combustion engine.

  2. Description of the Related Art Conventionally, a technique for cooling intake air in order to improve thermal efficiency of an internal combustion engine is known. For example, a cooling device for an internal combustion engine described in Patent Document 1 includes a variable compression ratio mechanism in which a mechanical compression ratio is changed by operation of an electric motor, and an intake air cooler that cools intake air that has been compressed by a supercharger and has risen in temperature. And.

Japanese Patent Laid-Open No. 2006-8570

Generally, the lower the intake air temperature, the higher the oxygen concentration and the better the thermal efficiency. However, if the intake air is cooled too much, combustion deterioration or misfire may occur depending on the load level of the internal combustion engine. As a solution to this, it is conceivable to adjust the cooling degree of the intake air cooler.
However, the response of the cooling degree adjustment of the intake air cooler is not so high. Therefore, for example, when the operating condition of the internal combustion engine changes so as to reduce the load, a state in which the degree of cooling is high is maintained for a while. As a result, the in-cylinder temperature excessively decreases, and as a result, the above-described combustion deterioration or misfire occurs, and the thermal efficiency may decrease.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a control system in which a decrease in thermal efficiency due to a change in operating conditions is suppressed while an effect of improving thermal efficiency by cooling the intake air is obtained. is there.

  The control system of the present invention is used in an internal combustion engine (10) having a combustion chamber (12) defined by a cylinder (11) and a piston (13). The control system includes an intake air cooling unit (40) that cools the intake air of the internal combustion engine, a combustion mode variable unit (30) that varies the combustion mode of the combustion chamber, and a combustion state acquisition that acquires an index of the combustion state of the combustion chamber And a control unit (20) for controlling the intake air cooling unit and the combustion form variable unit based on the result obtained by the combustion state obtaining unit. The control unit controls the combustion mode variable unit after the intake air temperature is reduced to the maximum by the intake air cooling unit when the operating state of the internal combustion engine is excessive.

Examples of the “combustion mode” include a compression ratio, a valve timing, an EGR rate, and the like. “Making the combustion mode variable” means that the combustion mode in the combustion chamber can be changed by adjusting each of these elements individually or in plurality.
According to this configuration, the control unit controls the intake air cooling unit and the combustion form variable unit based on the in-cylinder combustion state sequentially obtained by the combustion state obtaining unit. For example, when a variable compression ratio mechanism is provided as the combustion form variable section, the control section feedback-controls the compression ratio as an operation element, and the combustion form is changed. According to this, for example, the in-cylinder temperature rises due to the high compression ratio with respect to the excessive delay of the intake air cooling by the intake air cooling unit, so that the in-cylinder combustion state can be stabilized. That is, it is possible to suppress a decrease in thermal efficiency due to a change in operating conditions while obtaining an effect of improving thermal efficiency by cooling the intake air.

It is a figure which shows notionally the control system of 1st Embodiment of this invention. It is a graph explaining the control by the variable compression ratio mechanism part at the time of load change, Comprising: A continuous line shows transition by 1st Embodiment and a broken line shows transition by a comparison form. It is a flowchart for demonstrating the process which a control part performs. It is a figure which shows transition of the thermal efficiency by the change of intake-air cooling temperature, the graph shown on the left side is based on the time of high load, and the graph shown on the right side is based on the time of medium load. It is a flowchart for demonstrating the process which a control part performs by 2nd Embodiment. It is a flowchart for demonstrating the process which a control part performs by 3rd Embodiment.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings. In the embodiments, substantially the same components are denoted by the same reference numerals and description thereof is omitted.
<First Embodiment>
[Constitution]
The configuration of the first embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the control system 1 of the first embodiment has a function of cooling the intake air of the internal combustion engine 10 of the vehicle (that is, the gas sucked into the combustion chamber 12). The control system 1 includes an electronic control unit (hereinafter referred to as “ECU”) 20 as a control unit, a variable compression ratio mechanism unit 30, an intake air cooling unit 40, a combustion state acquisition unit 21, and the like.

  First, the internal combustion engine 10 and its peripheral configuration will be described. The internal combustion engine 10 is, for example, a diesel engine in which fuel such as light oil is directly injected into the combustion chamber 12. When the fuel injection valve 14 injects fuel in the vicinity of the piston 13 in the cylinder 11 reaching the top dead center, the air-fuel mixture supplied from the intake port 15 self-ignites in the combustion chamber 12 and burns. To do. The piston 13 reciprocates due to the explosive force during combustion, and the reciprocating motion of the piston 13 is converted into rotational motion of the crankshaft 32 via the connecting rod 33. Burned gas generated by the combustion is released into the atmosphere via the exhaust passage 41.

  An intake valve 17 is provided in the intake port 15 of the cylinder head 16 that is the inlet of the combustion chamber 12, and an exhaust valve 19 is provided in the exhaust port 18 of the cylinder head 16 that is the outlet of the combustion chamber 12. Yes. The intake valve 17 and the exhaust valve 19 are driven to open and close by a valve drive mechanism (not shown).

  The ECU 20 is composed of a microcomputer including a CPU, ROM, RAM, input / output ports, and the like, and is provided with various sensors attached to each part of the internal combustion engine 10, such as an in-cylinder pressure sensor 22 that measures the pressure in the combustion chamber 12. A signal is input. The ECU 20 controls the operating state of the internal combustion engine 10 based on detection signals from these various sensors. ECU20 has the combustion state acquisition part 21 which acquires the parameter | index of the combustion state in a cylinder. In the present embodiment, the in-cylinder temperature is employed as an index of the in-cylinder combustion state, and the combustion state acquisition unit 21 estimates the in-cylinder temperature based on the in-cylinder pressure measured by the in-cylinder pressure sensor 22. .

  The variable compression ratio mechanism section 30 corresponds to a “combustion form variable section”, and is a multi-link mechanism section that adjusts the top dead center position of the piston 13 and changes the compression ratio (mechanical compression ratio). The variable compression ratio mechanism 30 connects the piston 13 and the crankshaft 32 via a connecting rod 33 and a lower link 34, and controls the posture of the lower link 34 by a control link 35 to change the compression ratio.

  The control link 35 has one end connected to the lower link 34 and the other end connected to the link drive unit 36. The link drive unit 36 includes a control shaft, a pinion, an electric motor, and the like (not shown). When the control shaft is rotated by the electric motor, the swing center of the control link 35 is changed, the inclination angle between the connecting rod 33 and the lower link 34 is changed, and the top dead center position of the piston 13 is adjusted. Thus, the variable compression ratio mechanism unit 30 adjusts the top dead center position of the piston 13 to vary the compression ratio.

  By having the variable compression ratio mechanism section 30, as shown in FIG. 2, for example, when the load of the operating condition of the internal combustion engine 10 changes so as to increase, the compression ratio is increased to increase the in-cylinder temperature. Therefore, the combustion state can be stabilized as compared with the case where the variable compression ratio mechanism unit 30 is not provided.

  Next, the configuration of the intake air cooling unit 40 will be described. First, the internal combustion engine 10 includes a supercharger 45 including a turbine 42 provided in the exhaust passage 41 and a compressor 44 provided in the intake passage 43. The fresh air compressed by the compressor 44 is sucked into the combustion chamber 12 through the charge cooler 46 and the intake manifold 47.

  An EGR passage 51 is provided between the exhaust passage 41 and the suction passage 43. The EGR passage 51 performs exhaust gas recirculation in which a part of the exhaust gas from the exhaust passage 41 is returned to the suction passage 43 and circulated again. The gas in the EGR passage 51 (hereinafter referred to as EGR gas) is returned to the suction passage 43 through the EGR cooler 52 and the EGR valve 53.

  The suction passage 43 has a first suction passage 54 and a second suction passage 55 that are parallel to each other on the downstream side of the joining point with the EGR passage 51. The first suction passage 54 and the second suction passage 55 are passages that the intake manifold 47 has. A switching valve 56 is provided at a branch point between the first suction passage 54 and the second suction passage 55. The switching valve 56 switches the passage through which the intake air passes between the first suction passage 54 and the second suction passage 55.

  The heat exchanger 61 is provided in the first suction passage 54 on the downstream side of the joining passage with the EGR passage 51 in the suction passage 43. Therefore, the intake air cooled by the intake air cooling unit 40 is a gas in which fresh air and EGR gas are mixed.

  In the exhaust passage 41, a heat exchanger 62 is provided on the downstream side of the turbine 42. The heat exchanger 62 performs heat exchange between the exhaust gas and the hot water. Exhaust becomes a source of heat. The hot water that has absorbed heat from the exhaust is supplied to the refrigeration unit 64 through the hot water pipe 63.

  The freezing unit 64 generates a cold heat source using the heat of hot water. As the refrigeration unit 64, for example, an absorption refrigeration unit, a thermoacoustic refrigeration unit, or the like can be used in addition to an adsorption refrigeration unit. The cooling pipe 65 and the water therein are cooled by the cold heat source generated in the freezing unit 64. The cold water is supplied to the heat exchanger 61 through the cooling pipe 65.

  The intake air cooling unit 40 is configured by each device provided to cool the intake air as described in detail above, and includes the heat exchangers 61 and 62, the freezing unit 64, the charge cooler 46, and these. Various pipes 63 and 65 to be connected, a passage 54 and the like are included.

[Action]
Next, control executed by the ECU 20 in the control system 1 of the present embodiment will be described with reference to FIG. As shown in FIG. 3, first, in step 100 (hereinafter, step is abbreviated as “S”), whether or not the engine coolant temperature is higher than a first predetermined value or the outside air temperature is higher than a second predetermined value. Is judged. When the engine coolant temperature is higher than the first predetermined value or the outside air temperature is higher than the second predetermined value, the intake air cooling unit 40 is controlled to reduce the intake air temperature as much as possible in S200. Specifically, the intake air temperature is controlled by the flow switching control of the intake bypass by the switching valve 56 and the opening control of the EGR valve 53 that adjusts the inflow amount of EGR gas. Note that the determination in S100 is performed to determine a case where the intake air temperature and the in-cylinder temperature are originally low and it is not necessary to cool the intake air, such as when the engine is started or when it is cold in winter.

  Next, in S300, the in-cylinder pressure is measured by the in-cylinder pressure sensor 22. In S400, the in-cylinder temperature Te is estimated based on the in-cylinder pressure. The in-cylinder temperature Te estimated here corresponds to a “combustion state index”. Next, in S500, it is determined whether or not the estimated in-cylinder temperature Te is lower than a preset ideal in-cylinder temperature Ti. That is, in S500, the estimated in-cylinder temperature Te is used as an indicator of the combustion state, and the in-cylinder temperature Te reaches a stable combustion state for ensuring stable combustion set in advance by the in-cylinder temperature Te. It is determined whether or not. The ideal in-cylinder temperature Ti is a temperature for ensuring stable combustion, and is set according to the load of the internal combustion engine 10. The relationship between the load and the ideal in-cylinder temperature Ti is set in advance and is stored, for example, in a ROM or the like included in the ECU 20.

  When the in-cylinder temperature Te, which is an indicator of the combustion state, does not reach the stable combustion state, the variable compression ratio mechanism unit 30 is controlled to increase the compression ratio in S600. The processing of S100 to S600 is repeatedly executed.

[effect]
(1) Generally, the degree of cooling of the intake air is selected so that the intake air temperature is as low as possible within the range allowed by the engine specifications. This is because the lower the intake air temperature, the higher the oxygen concentration, and therefore the thermal efficiency is considered to be better than when the intake air temperature is high.

  However, the response of the cooling degree adjustment of the intake air cooling unit 40 is not so high. Therefore, for example, when the operating condition of the internal combustion engine 10 changes so that the load becomes small, a state where the degree of cooling is higher than necessary is maintained for a while. Here, if the high compression ratio is not increased by the variable compression ratio mechanism 30, the in-cylinder temperature excessively decreases, resulting in deterioration of combustion or misfire, and the right side in FIG. 4 is indicated by a broken line. As such, the engine thermal efficiency decreases.

  On the other hand, the responsiveness of the variable compression ratio mechanism unit 30 is high. In the present embodiment, when the intake air is supercooled when the load fluctuates so as to be reduced, the high compression ratio is rapidly increased by the highly responsive variable compression ratio mechanism 30. With this high compression ratio, as shown in FIG. 4, the same thermal efficiency as that before the load change can be maintained. In other words, with respect to low-response intake air cooling, by executing control by variable response compression ratio with high response so as to compensate for this low responsiveness, the effect of improving the heat efficiency by cooling the intake air is obtained, and accompanying changes in operating conditions A decrease in thermal efficiency can be suppressed.

  (2) In this embodiment, the in-cylinder temperature Te is adopted as an indicator of the combustion state. The in-cylinder temperature Te can be calculated from the measured value by the in-cylinder pressure sensor 22, and an indicator of the combustion state can be obtained with a simple configuration.

  (3) The intake air cooling unit 40 of the present embodiment includes a refrigeration unit 64 that generates a cold heat source, and can obtain high refrigeration efficiency.

Second Embodiment
Next, the control system of 2nd Embodiment of this invention is demonstrated with reference to FIG. In the first embodiment, the variable compression ratio mechanism 30 is used as the combustion mode variable unit, and the combustion mode is variable by changing the compression ratio. However, in the second embodiment, the combustion mode is variable by changing the EGR rate. Is different. That is, in the present embodiment, each device constituting the EGR function such as the EGR passage 51, the EGR cooler 52, and the EGR valve 53 corresponds to the “combustion form variable portion”. In the present embodiment, the variable compression ratio mechanism unit 30 may not be provided.

As shown in FIG. 5, instead of S600 described in detail with reference to FIG. 3 in the first embodiment, in this embodiment, control is performed to increase the EGR rate in S700. That is, by increasing the opening of the EGR valve 53 and increasing the content of the exhaust gas amount, the intake air temperature flowing into the combustion chamber is raised, and the in-cylinder temperature is raised accordingly.
According to this embodiment, the same effect as the first embodiment can be obtained.

<Third Embodiment>
Next, the control system of 3rd Embodiment of this invention is demonstrated with reference to FIG. In the third embodiment, when estimating the in-cylinder temperature employed in the first embodiment, the in-cylinder temperature is determined based on the intake pressure, the intake air amount, the intake air temperature, and the EGR rate of the internal combustion engine 10 in addition to the in-cylinder pressure. The point of estimation is different.

As shown in FIG. 6, after the in-cylinder pressure is measured in S300, the intake pressure, the intake air amount, and the intake air temperature of the internal combustion engine 10 are measured in S301, and the EGR rate is estimated from the opening degree of the EGR valve 53. Is done. In S400, the in-cylinder temperature Te is estimated based on the intake pressure, the intake air amount, the intake air temperature, and the EGR rate in addition to the in-cylinder pressure.
According to this embodiment, the same effect as the first embodiment can be obtained.

<Other embodiments>
In each of the above embodiments, the in-cylinder temperature is estimated based on the pressure measured by the in-cylinder pressure sensor 22, but the in-cylinder temperature may be estimated based on the engine speed and the load.

  In each of the above embodiments, the in-cylinder temperature Te is employed as an indicator of the combustion state, but instead of this, a variation rate COV (Coefficient of Variance) of the indicated mean effective pressure or an estimated thermal efficiency may be used. The COV can be calculated based on the in-cylinder pressure measured by the in-cylinder pressure sensor 22 or the measured value of the acceleration sensor. The estimated thermal efficiency can be estimated based on the pressure measured by the in-cylinder pressure sensor 22 and the injection amount. In this case, when there is a large difference between the current estimated thermal efficiency and the ideal thermal efficiency, it can be determined that the stable combustion state has not been reached.

  In each of the above embodiments, the intake air cooling unit 40 is an exhaust heat recovery refrigeration cycle that uses exhaust gas as a heat source. However, the exhaust air may not be used, and the form of the intake air cooling mechanism is not limited to this. . For example, water intake means may be provided in the intake passage 43 and the intake air may be cooled using latent heat. Further, the refrigeration unit 64 may be shared by a refrigeration cycle of an air conditioning system provided in the vehicle.

  In each of the above embodiments, the variable compression ratio mechanism unit 30 or the EGR mechanism unit has been described as an example of the combustion mode variable unit, but other modes may be used. For example, the combustion mode may be made variable by a variable valve timing mechanism, an injection timing control mechanism using the fuel injection valve 14, a variable valve lift mechanism, or an ignition timing control mechanism using an ignition plug (not shown) in the case of a gasoline engine. These combustion mode changes are all highly responsive when compared with intake air cooling, and the low response of the intake air cooling mechanism can be compensated for by the combustion mode changing unit as in the above embodiments.

  In each of the above embodiments, a step of controlling the ignition timing so as to become a predetermined combustion state or near the combustion limit may be added at the end of the control flow executed by the ECU 20, that is, after S600 or S700. According to this, the response delay of the highly responsive combustion form changing unit can be further compensated by the ignition timing control.

In each of the above embodiments, exhaust gas detection means may be provided in the exhaust passage 41, and the control range of the intake air temperature and the in-cylinder temperature may be limited according to the detection result of the exhaust gas detection means. As the exhaust gas detection means, for example, an O ₂ sensor, an A / F sensor, an exhaust gas temperature sensor, and the like are raised. For example, when O ₂ in the exhaust gas is detected or when the equivalence ratio detected by the A / F sensor exceeds a predetermined value, control that does not cool the intake air may be incorporated.

  In each of the above embodiments, a heat exchanger that exchanges heat between intake air and cold water may be provided directly above the intake port 15 of the intake passage 43 without providing an EGR mechanism.

  Although the internal combustion engine 10 of each said embodiment was demonstrated as a diesel engine, a gasoline engine may be sufficient.

  The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 1 ... Control system 10 ... Internal combustion engine 11 ... Cylinder (cylinder)
12 ... Combustion chamber 13 ... Piston 20 ... ECU (control part)
21 ... Combustion state acquisition unit 30 ... Variable compression ratio mechanism unit (combustion form variable unit)
40 ・ ・ ・ Intake air cooling section

Claims (7)

A control system for use in an internal combustion engine (10) having a combustion chamber (12) defined by a cylinder (11) and a piston (13),
An intake air cooling section (40) for cooling intake air of the internal combustion engine;
A combustion mode variable section (30) for changing the combustion mode of the combustion chamber;
A combustion state acquisition unit (21) for acquiring an indicator of the combustion state of the combustion chamber;
A control unit (20) for controlling the intake air cooling unit and the combustion form variable unit based on an acquisition result by the combustion state acquisition unit;
With
The control unit controls the combustion form variable unit after the intake air temperature is reduced to the maximum by the intake air cooling unit when the operation state of the internal combustion engine is excessive.   The control system according to claim 1, wherein the combustion form variable unit is a variable compression ratio mechanism unit that varies a compression ratio in the cylinder. The controller is
When it is determined that the combustion state index acquired by the combustion state acquisition unit has not reached a stable combustion state for ensuring stable combustion set in advance according to at least the load of the internal combustion engine, The control system according to claim 2, wherein the control is performed so that the compression ratio of the variable compression ratio mechanism is increased.   The said intake air cooling part has a freezing part (64), and cools the intake air of the said internal combustion engine using the cold heat source which the said freezing part produced | generated. Control system.   The control system according to claim 4, wherein the refrigeration unit uses heat recovered from exhaust gas of the internal combustion engine as a heat source.   The control system according to any one of claims 1 to 5, wherein the combustion state acquisition unit estimates an in-cylinder temperature (Te) based on an in-cylinder pressure that is a pressure of the combustion chamber.   The control system according to claim 6, wherein the combustion state acquisition unit estimates the temperature in the cylinder based on an intake pressure, an intake air amount, the intake air temperature, and an EGR rate of the internal combustion engine.

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