Patent Application
20150275782
The present invention relates to a control device for an engine equipped with a supercharger in which scavenging occurs in a supercharging region.
In an engine equipped with a supercharger, in a supercharging region where supercharging pressure becomes higher than exhaust pressure, scavenging with air blowing through the inside of a cylinder from an intake passage to an exhaust passage occurs. In the engine equipped with a supercharger, supercharging performance can be improved by positive use of the scavenging. This is because if the amount of air blowing through the inside of the cylinder (hereinafter, a scavenging amount) is increased by scavenging, the total amount of the gas which flows into the turbine of a turbocharger increases, and supercharging of air by a compressor is accelerated by increase in the revolution speed of the turbine. Therefore, from the viewpoint of supercharging performance, the scavenging amount is desired to be made as large as possible.
However, increasing the scavenging amount is accompanied by a harmful effect. Since the air flowing into the exhaust passage by scavenging contains a large amount of oxygen, the reaction of unburned fuel and oxygen on the catalyst becomes active as the scavenging amount increases, and heat of the reaction increases the temperature of the catalyst. Subsequently, excessive increase of the catalyst temperature deteriorates the catalyst. Therefore, from the viewpoint of protection of the catalyst, the scavenging amount is desired to be prevented from being excessively large.
In the light of the demand as above, it is understandable that an accurate grasp of the scavenging amount is important in control of the engine equipped with a supercharger. The scavenging amount can be changed by adjusting a valve overlap time period between the exhaust valve and the intake valve. Therefore, if an accurate grasp of the scavenging amount is possible, it becomes possible to control the scavenging amount actively by adjustment of the valve overlap time period so as to enhance the supercharging performance to the maximum within the range where overheating of the catalyst is not caused.
Further, an accurate grasp of the scavenging amount is also useful in air-fuel ratio control. When the scavenging amount becomes large, the cylinder air-fuel ratio becomes richer than the target air-fuel ratio correspondingly to decrease of the air remaining in the cylinder. Therefore, depending on the value of the target air-fuel ratio which is set, there is a fear of occurrence of a misfire by the cylinder air-fuel ratio becoming excessively rich following scavenging. However, if the accurate scavenging amount can be grasped, the rich limit of the target air-fuel ratio is set in accordance with the estimated scavenging amount, and the target air-fuel ratio can be guarded with the rich limit.
As described above, an accurate grasp of the scavenging amount is an important task in the control of the engine equipped with a supercharger. However, the scavenging amount cannot be directly measured by using a sensor such as a flow sensor. Therefore, in order to grasp the scavenging amount, only thing to do is to estimate the scavenging amount indirectly by calculation using engine information relating to scavenging. The scavenging amount is one state amount of the engine, and in estimation of the state amount, a physical model obtained by modeling the engine can be used. For example, Patent Literature 1 described as follows discloses the method for estimating the in-cylinder air amount by using a physical model. However, the method for accurately estimating the scavenging amount is not disclosed in Patent Literature 1 as follows, and is not found in other prior art literatures, either.
Patent Literature 1: Japanese Patent Laid-Open No. 2008-291830
The present invention is made in the light of the aforementioned problem, and has an object to provide a control device for an engine equipped with a supercharger that can accurately calculate an estimated value of a scavenging amount.
The control device for an engine equipped with a supercharger according to the present invention includes three calculation units that will be described as follows. The following three calculation units may be respectively configured by separate computers, or one computer may be caused to function as the following three calculation units by software.
A first calculation unit is programmed to calculate an estimated value of an intake valve passing air amount. The intake valve passing air amount is an amount of air that is passed through an intake valve, and the first calculation unit calculates the estimated value of the intake valve passing air amount based on a measured value of an intake air amount. The intake air amount is an amount of air that is taken into an intake passage, and can be measured by using a flow sensor such as an air flow meter.
A second calculation unit is programmed to calculate an estimated value of an in-cylinder air amount. The in-cylinder air amount is an amount of air that is subjected to combustion in a cylinder, and the second calculation unit calculates the estimated value of the in-cylinder air amount based on a measured value or an estimated value of intake pipe pressure. The intake pipe pressure can be measured by an intake pipe pressure sensor. Further, the intake pipe pressure also can be estimated from a measured value of a supercharging pressure by a supercharging pressure sensor.
However, the second calculation means preferably calculates the estimated value of the intake pipe pressure based on the measured value of the intake air amount, and calculates the estimated value of the in-cylinder air amount based on the estimated value of the intake pipe pressure. That is to say, just as the measured value of the intake air amount is set as a basis of the calculation of the estimated value of the intake valve passing air amount in the first calculation unit, the measured value of the intake air amount is set as a basis of the calculation of the estimated value of the in-cylinder air amount in the second calculation unit. This means that both the intake valve passing air amount and the in-cylinder air amount are estimated by using the common sensor output value.
More preferably, the second calculation unit uses the estimated value of the intake valve passing air amount calculated by the first calculation unit as a basis of calculation of the estimated value of the in-cylinder air amount. In this case, the estimated value of the intake valve passing air amount can be converted into the estimated value of the intake pipe pressure by using a first map in which the intake valve passing air amount and the intake pipe pressure are associated with each other by using a plurality of parameters. Further, the estimated value of the intake pipe pressure can be converted into the estimated value of the in-cylinder air amount by using a second map in which the intake pipe pressure and the in-cylinder air amount are associated with each other by using a plurality of parameters.
A third calculation unit is programmed to calculate an estimated value of a scavenging amount. The scavenging amount is an amount of air blowing through an inside of the cylinder, and the third calculation unit calculates the estimated value of the scavenging amount from a difference between the estimated value of the intake valve passing air amount calculated by the first calculation unit, and the estimated value of the in-cylinder air amount calculated by the second calculation unit. Note that a unit of each of the intake valve passing air amount, the in-cylinder air amount and the scavenging amount may be a mass per time, or may be a mass per cycle. Alternatively, each unit may be made dimensionless with a predetermined air amount, for example, a maximum in-cylinder air amount as a reference.
By including the three calculation units as above, according to the control device for an engine equipped with a supercharger according to the present invention, the estimated value of the scavenging amount can be accurately calculated. Especially when both the intake valve passing air amount and the in-cylinder air amount are estimated by using the common sensor output value, the influence which the variations of the output characteristics of the sensors gives on estimation precision of the scavenging amount can be restrained as compared with the case of estimating the intake valve passing air amount and the in-cylinder air amount by using separate sensor output values.
Hereinafter, embodiment 1 of the present invention will be described with reference to the drawings.
An operation of an engine equipped with a supercharger to which a control device according to the present embodiment is applied is controlled by operations of a plurality of actuators. Various actuators such as a wastegate valve that changes a supercharging characteristic of the supercharger, an electronically controlled throttle, an intake side variable valve timing mechanism that changes valve timing of an intake valve, and an exhaust side variable valve timing mechanism that changes valve timing of an exhaust valve are mounted to the present engine.
The operation of the present engine is controlled by an on-vehicle ECU (Electronic Control Unit). The control device according to the present embodiment is realized as a part of a function included by the ECU. Various kinds of information relating to an operation state and operation conditions of the engine are inputted to the ECU from various sensors including an air flow meter, an intake pipe pressure sensor, an atmospheric pressure sensor, an intercooler temperature sensor, an accelerator position sensor, and a crank angle sensor. When the ECU functions as the control device according to the present embodiment, the ECU cooperatively operates actuators relating to the air amount, that is, the throttle, the intake side variable valve timing mechanism, the exhaust side variable valve timing mechanism, and the wastegate valve in accordance with a control program for air amount control that is stored in a memory.
The control device 100 according to the present embodiment is configured by an intake valve passing air amount calculation unit 10, an in-cylinder air amount calculation unit 12, an in-cylinder air amount map parameter calculation unit 14, and a scavenging amount calculation unit 16. The calculation units 10, 12, 14 and 16 are realized through software by the air amount control program being executed in the ECU.
The intake valve passing air amount calculation unit 10 calculates an estimated value KL of an intake valve passing air amount that is an amount of air that passes through the intake valve from the measured value AFM of the intake air amount. The intake air amount and the intake valve passing air amount coincide with each other at a time of a steady state operation of the engine. However, in a transient state such as a time of an acceleration operation and a time of a deceleration operation, a deviation occurs between the intake air amount and the intake valve passing air amount due to a response delay of air. Therefore, the intake valve passing air amount calculation unit 10 calculates the intake valve passing air amount from the intake air amount, by using a physical model that is a result of modeling a response characteristic of the air in the engine equipped with a supercharger.
The in-cylinder air amount calculation unit 12 calculates an estimated value KLCYL of an in-cylinder air amount that is an amount of air subjected to combustion in the cylinder from the measured value PM of the intake pipe pressure. Conditions other than the intake pipe pressure, which influence the in-cylinder air amount, are fixed, a correlation is established between the intake pipe pressure and the in-cylinder air amount. The in-cylinder air amount calculation unit 12 converts the intake pipe pressure into the in-cylinder air amount by using an in-cylinder air amount map in which the correlation is mapped.
The in-cylinder air amount map parameter calculation unit 14 calculates a value of a parameter of the in-cylinder air amount map from the conditions other than the intake pipe pressure, which influence the in-cylinder air amount, and sets the calculated value to the in-cylinder air amount calculation unit 12. The conditions which influence the in-cylinder air amount are more specifically, an engine speed NE, valve timing INVT of the intake valve, valve timing EXVT of the exhaust valve, an opening degree WGV of the wastegate valve, an intercooler temperature THIC, an atmospheric pressure PA and the like. Information relating to these conditions is supplied to the in-cylinder air amount map parameter calculation unit 14 from sensors and actuators relating to the information of them.
The scavenge amount calculation unit 16 calculates a difference between the estimated value KL of the intake valve passing air amount calculated in the intake valve passing air amount calculation unit 10, and the estimated value KLCYL of the in-cylinder air mount calculated in the in-cylinder air amount calculation unit 12. The difference is the scavenging amount, that is, an estimated value KLSCA of the amount of air blowing through the inside of the cylinder. The estimated value KLSCA of the scavenging amount calculated in the scavenging amount calculation unit 16 is used in estimation of a catalyst temperature. The catalyst temperature constitutes a constraint that specifies an upper limit of a turbine flow rate or the supercharging pressure in the supercharging pressure control. Further, the estimated value KLSCA of the scavenging amount is also used in calculation of a guard value that specifies a rich limit of the target air-fuel ratio in air-fuel ratio control.
The control device 100 calculates the estimated value KLCYL of the in-cylinder air amount by substituting the measured value PM of the intake pipe pressure into the in-cylinder air amount map. The graph shows a line of the estimated value KL of the intake valve passing air amount, and when scavenging occurs, the estimated value KL of the intake valve passing air amount is larger than the estimated value KLCYL of the in-cylinder air amount as in the graph. By calculating the difference between the estimated value KLCYL and the estimated value KL, the estimated value KLSCA of the scavenging amount can be obtained. Note that though not illustrated in the graph, the estimated value KL of the intake valve passing air amount becomes smaller than the estimated value KLCYL of the in-cylinder air amount, depending on the operation state of the engine. In that case, the difference between the estimated values expresses an amount of combustion gas remaining in the cylinder, that is, an internal EGR amount.
In the present embodiment, the intake valve passing air amount calculation unit 10 corresponds to “first calculation means” in the present invention. The in-cylinder air amount calculation unit 12 corresponds to “second calculation means” in the present invention. The scavenge amount calculation unit 16 corresponds to “third calculation means” in the present invention.
Next, embodiment 2 of the present invention will be described with reference to the drawings.
As described in embodiment 1, a number of sensors are used in control of the engine. These sensors cannot always obtain fixed output characteristics in all individuals. Due to individual differences at the time of manufacture, or due to a secular change with use, variations in the output characteristics exist among the individuals of the sensors. In the control device 100 according to embodiment 1, the output value from the air flow meter 2 and the output value from the intake pipe pressure sensor 4 are used in estimation of the scavenging amount, and there is a possibility that deviations of the output characteristics occur in these sensors 2 and 4. The deviation of the output characteristic of the air flow meter 2 influences estimation precision of the intake valve passing air amount, and the deviation of the output characteristic of the intake pipe pressure sensor 4 influences measurement precision of the intake pipe pressure. A problem in the case like this will be described with use of
The estimated value KL of the intake valve passing air amount, and the measured value PM of the intake pipe pressure in a graph shown in
As above, the control device 100 according to embodiment 1 has the problem of being susceptible to the variations of the output characteristics of the air flow meter 2 and the intake pipe pressure sensor 4.
A control device according to embodiment 2 has a configuration in which a countermeasure against the above described problem is taken.
A difference of the control device 200 according to the present embodiment from embodiment 1 is that the output value from the intake pipe pressure sensor is not used in estimation of the scavenging amount. The control device 200 according to the present embodiment calculates the estimated value KLCYL of the in-cylinder intake air amount based on the measured value AFM of the intake air amount obtained by the air flow meter 2. In order to realize the function, the control device 200 according to the present embodiment includes an intake pipe pressure calculation unit 20 and an ab map parameter calculation unit 22, in addition to the calculation units 10, 12, 14 and 16 common to embodiment 1.
The intake pipe pressure calculation unit 20 calculates the estimated value PM of the intake pipe pressure from the estimated value KL of the intake valve passing air amount. The estimated value KL of the intake valve passing air amount is calculated from the measured value AFM of the intake air amount by the intake valve passing air amount calculation unit 10. When the conditions other than the intake pipe pressure, which influence the intake valve passing air amount, are fixed, a correlation is established between the intake valve passing air amount and the intake pipe pressure. The intake pipe pressure calculation unit 20 converts the intake valve passing air amount into the intake pipe pressure by using a so-called ab map in which the correlation is mapped. The estimated value PM of the intake pipe pressure calculated in the intake pipe pressure calculation unit 20 is inputted to the in-cylinder air amount calculation unit 12. The in-cylinder air amount calculation unit 12 calculates the estimated value KLCYL of the in-cylinder air amount from the estimated value PM of the intake pipe pressure.
The ab map parameter calculation unit 22 calculates the value of the parameter of the ab map from the conditions other than the intake pipe pressure, which influence the intake valve passing air amount, and sets the calculated value to the intake pipe pressure calculation unit 20. The conditions which influence the intake valve passing air amount are more specifically the engine speed NE, the valve timing INVT of the intake valve, the valve timing EXVT of the exhaust valve, the opening degree WGV of the wastegate valve, the intercooler temperature THIC, and the atmospheric pressure PA. Information relating to these conditions is supplied to the ab map parameter calculation unit 22 from the sensors and actuators relating to the information of them.
The control device 200 according to the present embodiment first calculates the estimated value KL of the intake valve passing air amount from the measured value AFM of the intake air amount, substitutes the estimated value KL of the intake valve passing air amount into the ab map (the first map), and thereby calculates the estimated value PM of the intake pipe pressure. Next, the control device 200 substitutes the estimated value PM of the intake pipe pressure into an in-cylinder air amount map (a second map), and thereby calculates the estimated value KLCYL of the in-cylinder air amount. Subsequently, the control device 200 calculates the difference between the estimated value KL of the intake valve passing air amount and the estimated value KLCYL of the in-cylinder air amount, and thereby calculates the estimated value KLSCA of the scavenging amount. As above, according to the control device 200 according to the present embodiment, the estimated value KLSCA of the scavenging amount is calculated by using only the measured value AFM of the intake air amount which is obtained by the air flow meter 2.
As is understandable from the above example, the configuration which is included by the control device 200 according to the present embodiment has higher robustness to variations of the output characteristics of the sensors as compared with the configuration included by the control device 100 according to embodiment 1. Therefore, according to the control device 200 according to the present embodiment, the estimated value of the scavenging amount can be accurately calculated without being influenced by the variations of the output characteristics of the sensors.
Note that in the present embodiment, the intake valve passing air amount calculation unit 10 corresponds to “the first calculation means” in the present invention. A combination of the intake pipe pressure calculation unit 20 and the in-cylinder air amount calculation unit 12 corresponds to “the second calculation means” in the present invention. The scavenging amount calculation unit 16 corresponds to “the third calculation means” in the present invention.
The present invention is not limited to the aforementioned embodiments, and can be carried out by being variously modified within the range without departing from the gist of the present invention. For example, in embodiment 1, the intake pipe pressure is measured by the intake pipe pressure sensor, but when the supercharging pressure sensor is included upstream of the throttle, the intake pipe pressure also can be estimated by using a physical model of the throttle based on the output value from the supercharging pressure sensor.
The control device according to the present invention also can be applied to the engine equipped with a supercharger which does not include an actuator that changes a supercharging characteristic of the supercharger, such as a wastegate valve and a variable nozzle. The supercharger may be a turbocharger or may be a mechanical supercharger. Further, in the engine equipped with a supercharger to which the control device according to the present invention is applied, the intake side variable valve timing mechanism and the exhaust side variable valve timing mechanism are not indispensable. Further, the type of the engine equipped with a supercharger may be a diesel engine or may be a gasoline engine.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2012/080940 | 11/29/2012 | WO | 00 |
