JP6323140B2 - EGR control device - Google Patents

Description

  The present invention relates to an EGR control device.

  There is one that discloses an LP-EGR device (see Patent Document 1). The LP-EGR device is provided with an EGR passage that branches from an exhaust pipe downstream of the turbine and joins an intake pipe upstream of the compressor, assuming an engine having a turbocharger having a turbine and a compressor, and an EGR valve is provided in the EGR passage. It is something that is intervened.

JP 2010-216449 A

  By the way, the exhaust temperature changes according to the operating condition of the engine, and the pressure loss of the entire exhaust pipe downstream of the branch portion of the EGR passage changes in response to the change in the exhaust temperature. When the exhaust pressure at the branch portion is significantly larger than the exhaust pressure at the branch portion at the time of adaptation, the actual EGR rate transiently deviates from the target EGR rate. When the actual EGR rate deviates from the target EGR rate, knocking occurs or the drivability deteriorates particularly in a gasoline engine. In order to avoid this, it is prohibited to open the EGR valve even in the EGR region when the exhaust pressure of the branch portion is detected by a pressure sensor and the detected exhaust pressure of the branch portion deviates from a predetermined allowable range. Can be considered. However, the detection accuracy of the pressure sensor tends to decrease due to the influence of the exhaust pulsation, and whether or not the exhaust pressure of the branch portion has deviated from the predetermined allowable range based on the signal from the pressure sensor with poor responsiveness. Is determined, the determination accuracy is poor. In particular, in the LP-EGR device, since the differential pressure across the EGR valve is much smaller than that in the HP-EGR device, the detection error generated in the pressure sensor greatly affects the determination accuracy, and the determination accuracy is further reduced by the amount affected.

  Therefore, the present invention can improve the accuracy of determining whether the flow rate of the LP-EGR valve is within an appropriate range even when the differential pressure across the EGR valve is smaller than that of the LP-EGR device, particularly as in the LP-EGR device. An object is to provide an apparatus.

The EGR control device of the present invention opens and closes an EGR passage that branches from an exhaust pipe of an engine downstream of a turbocharger turbine, bypasses the cylinder, and merges with an intake pipe upstream of the compressor of the turbocharger, and the EGR passage. An EGR valve; and control means for opening the EGR valve in an EGR region and controlling the EGR valve to a fully closed state in a non-EGR region. Furthermore, the EGR control device of the present invention includes downstream exhaust gas temperature detection / estimation means and prohibition means. The downstream exhaust temperature detection / estimation means detects or estimates the exhaust temperature of the branch portion of the EGR passage or the exhaust temperature of the exhaust pipe downstream of the branch portion of the EGR passage. The prohibiting means is configured to prevent the EGR even in the EGR region when the detected or estimated exhaust temperature exceeds an upper limit value of a predetermined allowable range and when the exhaust temperature falls below a lower limit value of the allowable range. Prohibit opening the valve.

  The target EGR valve opening (target EGR valve flow rate) is set so that the target EGR rate is obtained. In this case, the EGR valve flow rate changes according to the differential pressure between the exhaust pressure at the branch portion of the EGR passage and the intake pressure at the junction portion of the EGR passage. For this reason, when the exhaust pressure at the actual branch portion rises above the exhaust pressure at the branch portion at the time of adaptation, the actual EGR valve flow rate becomes larger than the target EGR valve flow rate by the increase in the exhaust pressure, and the actual EGR rate becomes the target It becomes larger than the EGR rate. On the other hand, when the exhaust pressure of the actual branch section is lower than the exhaust pressure of the branch section at the time of adaptation, the actual EGR valve flow rate becomes smaller than the target EGR valve flow rate by the decrease in the exhaust pressure, and the actual EGR rate is the target EGR rate. Decreases from the rate. When the ignition timing is set according to the target EGR rate, if the actual EGR rate deviates from the target EGR rate and becomes large, the combustion state deteriorates and the drivability deteriorates. On the other hand, knocking may occur when the actual EGR rate falls outside the target EGR rate. In order to prevent such a deviation of the actual EGR rate from the target EGR rate, the exhaust pressure of the branch portion is detected, and the EGR valve is turned on even if the detected exhaust pressure is outside the predetermined allowable range even in the EGR region. It is forbidden to open. However, even if a pressure sensor that detects the exhaust pressure is provided at the bifurcation, the pressure sensor is affected by the exhaust pulsation and the response is poor. Therefore, it is possible to determine whether or not the exhaust pressure is out of the predetermined allowable range. Is bad. On the other hand, in the present invention, the exhaust temperature of the branching section and the exhaust temperature downstream of the branching section, which correlate with the exhaust pressure of the branching section, are detected or estimated, and the detected or estimated exhaust temperature of the branching section and the exhaust gas downstream of the branching section are detected. EGR is prohibited when the temperature falls below or exceeds the allowable temperature. Since the temperature sensor that detects the exhaust temperature of the branching section and the exhaust temperature downstream of the branching section is not affected by the pulsation of the exhaust temperature, it is possible to improve the determination accuracy of whether the EGR valve flow rate is in the proper range.

It is a schematic block diagram of the gasoline engine of 1st Embodiment of this invention. It is a driving | operation area | region figure which shows a supercharging area | region and LP-EGR area | region. It is a characteristic figure of a target LP-EGR rate. It is a simple model figure of LP-EGR apparatus. 6 is a timing chart showing changes in exhaust temperature at points A, C, and D with respect to changes in exhaust pressure at point A; It is a flow characteristic figure of LP-EGR valve. It is a flowchart for demonstrating the setting of a LP-EGR permission flag. It is a chart for explaining calculation of a target LP-EGR valve opening. It is a characteristic view of the basic LP-EGR valve opening. It is a characteristic view of a trimming coefficient. It is a characteristic view of the LP-EGR valve differential pressure before and after the intake air amount. It is a characteristic view of the ignition timing with respect to the target LP-EGR rate.

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

(First embodiment)
FIG. 1 is a schematic configuration diagram of a control device for a gasoline engine according to a first embodiment of the present invention.

  The engine 1 is a gasoline engine (hereinafter also simply referred to as “engine”), and is mounted on a vehicle (not shown). The engine 1 includes an intake passage 4 and an exhaust passage 11. The intake passage 4 includes an intake pipe 4a, an intake collector 4b, and an intake manifold 4c.

  The intake pipe 4a immediately upstream of the intake collector 4b is provided with an electronically controlled throttle device that responds to the amount of depression of the accelerator pedal. The throttle device includes a throttle valve 5 and a motor (rotary electric machine) 6 that drives the throttle valve 5. The intake air is metered by the throttle valve 5 through the intake pipe 4a. The metered air is stored in the intake collector 4b, and is distributed and supplied from the intake collector 4b to the cylinders 7 (combustion chambers) of the respective cylinders via the intake manifold 4c. Although the embodiment is an electronically controlled throttle device, the throttle valve and the accelerator pedal may be connected by a wire.

  A fuel injection valve 8 is provided on the intake manifold 4c and a spark plug 9 is provided directly on the cylinder 7, and fuel is injected from the fuel injection valve 8 into the intake manifold 4c (intake port). The injected fuel is mixed with air metered by the throttle valve 5 to form a gas, which is ignited by the spark plug 9 and burned. The burning gas is discharged into the exhaust passage 11 after performing the work of pushing down the piston 10. The position where the fuel injection valve 8 is provided is not limited to the intake manifold. A fuel injection valve may be provided directly facing the cylinder 7.

  The exhaust passage 11 includes an exhaust manifold 11a into which exhaust from the cylinder 7 of each cylinder flows, and an exhaust pipe 11b connected to a collective portion of the exhaust manifold 11a. Since the exhaust contains harmful three components of HC, CO, and NOx, a manifold catalyst 12 is provided at the assembly portion of the exhaust manifold 11a and a main catalyst 13 is provided at the exhaust pipe 11b downstream of the exhaust manifold 11a in order to purify all of them. Yes. The main catalyst 13 is provided, for example, under the floor of the vehicle. Each of these catalysts 12 and 13 is constituted by a three-way catalyst, for example. A muffler 19 is provided at the end of the exhaust pipe 11b.

  The engine 1 further includes a turbocharger 21. The turbocharger 21 includes a turbine 22 provided in the exhaust pipe 11b, a compressor 23 provided in the intake pipe 4a, and a shaft 24 connecting the turbine 22 and the compressor 23. The turbine 22 is rotated by the energy of the exhaust gas flowing through the exhaust pipe 11b, and drives the compressor 23 coaxial with the turbine 22. The compressor 23 compresses the air sucked through the air cleaner 18. The compressed air that is compressed and exceeds the atmospheric pressure is sent to the intake collector 4b. The target supercharging pressure can be obtained by operating the turbocharger 21.

  The turbocharger 21 includes a bypass passage 24 that bypasses the turbine 22 and a normally closed waste gate valve 25 that opens and closes the bypass passage 24. The waste gate valve 25 is driven by a motor (rotating electric machine) 26. For example, when the actual boost pressure detected by the boost pressure sensor 45 becomes higher than the target boost pressure, the waste gate valve 25 is opened by driving the motor 26 and a part of the exhaust flowing into the turbine 22 is removed. The turbine 22 is bypassed to flow. As a result, the turbine rotational speed is decreased from before the waste gate valve 25 is opened, and the compressor rotational speed coaxial with the turbine 22 is also decreased. When the compressor rotational speed decreases, the actual supercharging pressure decreases and matches the target supercharging pressure. The opening degree of the waste gate valve 25 is held at a timing at which the actual boost pressure coincides with the target boost pressure.

  An intercooler 25 is provided in the intake pipe 4 a on the downstream side of the compressor 23. The intercooler 25 is for cooling the air compressed by the compressor 23. The air whose temperature has been increased by the air compression by the compressor 23 is cooled by the intercooler 25, whereby the supercharging efficiency can be increased.

  Now, even in the gasoline engine 1 provided with the turbocharger 21, there is a demand to perform a large amount of EGR (exhaust gas recirculation) in order to suppress knocking in the supercharging region. In order to meet this requirement, in this embodiment, a ropeless loop EGR device 14 is newly provided. The rope pressure loop EGR device 14 includes an EGR passage 15, an EGR cooler 16 interposed in the EGR passage 15, an EGR valve 17 (for example, a butterfly valve) that opens and closes the EGR passage 15, and a motor (rotary electric machine) that drives the EGR valve 17. 18.

  The EGR passage 15 is branched from the exhaust pipe downstream of the turbine 22, specifically, the exhaust pipe 11 b between the manifold catalyst 12 and the main catalyst 13, and merges with the intake pipe 4 a upstream of the compressor 23. Thus, when the EGR passage 15 communicates the exhaust pipe 11b downstream of the turbine 22 and the intake pipe 4a upstream of the compressor 23, the gas is determined by the differential pressure between the exhaust pipe pressure downstream of the turbine and the intake pipe pressure upstream of the compressor. (A part of the exhaust gas) flows through the EGR valve 17. Since the differential pressure between the exhaust pipe pressure downstream of the turbine and the intake pipe pressure upstream of the compressor is as small as about 1 kPa, for example, it is called a ropeless loop EGR (hereinafter referred to as “LP-EGR”) device. Hereinafter, the EGR valve of the LP-EGR device is referred to as “LP-EGR valve”. Further, an operation region in which the LP-EGR valve 17 is opened and LP-EGR is performed is referred to as an “LP-EGR region”, and an operation region in which the LP-EGR valve is fully closed is referred to as a “non-LP-EGR region”. The LP-EGR device itself is known in diesel engines, but in the present embodiment, the LP-EGR device 14 is newly adopted for the gasoline engine 1 provided with the turbocharger 21.

  The EGR cooler 16 is provided in the EGR passage 15 upstream of the LP-EGR valve 17. The EGR cooler 16 cools the gas (a part of the exhaust gas) flowing through the EGR passage 15 until it reaches a certain temperature. For this reason, in the LP-EGR region, the gas cooled to a certain temperature flows through the LP-EGR valve 17.

  Here, the reason why the LP-EGR device 14 is newly adopted in the gasoline engine 1 provided with the turbocharger 21 will be described. There is an EGR device that is applied to a gasoline engine that does not include a turbocharger and that causes a portion of relatively high-temperature exhaust to flow into the intake collector 4b. In this EGR device, the gas flows through the EGR valve with a relatively large differential pressure (negative pressure) between the exhaust passage 11 and the intake collector 4b. Therefore, this EGR device is called a high pressure loop EGR (hereinafter referred to as “HP-EGR”) device. .

  Consider applying the HP-EGR device to a gasoline engine equipped with a turbocharger. First, when not supercharging, a pressure (negative pressure) lower than the atmospheric pressure develops in the intake collector 4b, and the differential pressure from the exhaust pressure increases. Therefore, if the EGR valve is opened, gas (EGR gas) is supplied to the intake collector 4b. Can be inhaled. However, at the start of supercharging by the turbocharger, the pressure of the intake collector 4b increases from negative pressure to atmospheric pressure and from atmospheric pressure to a pressure exceeding atmospheric pressure. When the pressure of the intake collector 4b increases to a pressure exceeding the atmospheric pressure, the differential pressure from the exhaust pressure decreases. The pressure exceeding the atmospheric pressure in the intake collector 4b is a supercharging pressure. The higher the supercharging pressure, the smaller the differential pressure from the exhaust pressure. When the differential pressure from the exhaust pressure becomes small, a large amount of EGR gas cannot be sucked into the intake collector 4b.

  On the other hand, in the LP-EGR device, gas (EGR gas) flows through the LP-EGR valve 17 with a small differential pressure (about 1 kPa) between the relatively low exhaust pipe pressure downstream of the turbine and the intake pipe pressure upstream of the compressor. It is not affected by supercharging pressure. In other words, a configuration in which the LP-EGR device 14 is added to the gasoline engine 1 provided with the turbocharger 21 allows a large amount of EGR gas to be introduced into the intake passage even during supercharging by the turbocharger 21. It became.

  More specifically, FIG. 2 shows the supercharging region and the LP-EGR region of this embodiment in an overlapping manner. In FIG. 2, the case where the pressure of the intake collector 4b is atmospheric pressure is indicated by a broken line. In the present embodiment, a region where the pressure of the intake collector 4b is higher than the atmospheric pressure (region above the broken line) is a supercharging region, and a region where the pressure of the intake collector 4b is equal to or lower than the atmospheric pressure (region below the broken line) is not. It is a supercharged area. On the other hand, the LP-EGR region has a substantially isosceles trapezoidal shape as a whole, and the LP-EGR region is largely generated in the supercharging region in this embodiment.

  For this reason, in this embodiment, the operation region is divided into four regions as follows.

<1> Supercharging region and LP-EGR region (region surrounded by B-C-D-E)
<2> Supercharging region and non-LP-EGR region (region indicated by hatching)
<3> Non-supercharging region and LP-EGR region (region surrounded by ABEF)
<4> Non-supercharging range and non-LP-EGR range

  Here, in FIG. 2, the corners of the isosceles trapezoid are A, C, D, and F, and the points where the isosceles trapezoid and the broken line intersect are B and E. Further, both ends of the broken line are G and J, and the GH-I line is a line at full load. Note that the LP-EGR region is not limited to a substantially isosceles trapezoidal shape as a whole. If the specifications of the engine, turbocharger, and LP-EGR device 14 are different, the shape of the LP-EGR region may be different.

  As shown in FIG. 1, the present embodiment further includes a bypass passage 31 that bypasses the compressor 23. The bypass passage 31 is provided with a recirculation valve 32 driven by a motor (rotating electric machine) 33. This valve 32 recirculates (recirculates) pressurized air confined in the intake pipe 4a from the throttle valve 5 to the compressor 23 upstream of the compressor 23 when the throttle valve 5 is closed for vehicle deceleration. It is for making it happen. On the other hand, when turbocharging is performed by the turbocharger 21 in an operating region other than when the vehicle is decelerating, the valve 32 is basically fully closed and air upstream of the compressor 23 (including EGR gas). ) Are all guided to the compressor 23.

  Here, the reason why the recirculation valve 32 is necessary is that the handling of the throttle valve differs between the diesel engine and the gasoline engine. That is, in a diesel engine, the throttle valve is always open and is closed only when necessary. On the other hand, in a gasoline engine, the throttle valve 5 is provided immediately upstream of the intake collector 4b, and its opening changes in response to the amount of depression of the accelerator pedal.

  Due to such a difference, in the gasoline engine, when the accelerator pedal is returned to decelerate the vehicle from the state of being supercharged by the turbocharger 21, the throttle valve opening is increased by a certain amount in response to this. Become smaller. Due to this sudden decrease in the throttle valve opening, there is no place for the pressurized air existing in the intake pipe 4 a from the throttle valve 5 to the compressor 23. In addition, the pressure of the intake pipe 4a from the throttle valve 5 to the compressor 23 further increases due to the operation of the compressor 23 when the vehicle is decelerated. Then, the air whose pressure is increased downstream of the compressor flows backward toward the compressor 23. Then, when the pressurized air that flows backward passes through the compressor 23 and escapes upstream, noise (noise) is generated from the compressor 23. Such noise generated during vehicle deceleration affects the quietness of the vehicle compartment. Therefore, when the vehicle is decelerated from the supercharging region, the valve 32 is switched from the fully closed state to the open state, and the pressurized air upstream of the compressor is bypassed the compressor 23 and released upstream (recirculation). This prevents the generation of noise during vehicle deceleration.

  Next, assuming that the EGR rate when performing LP-EGR control using the LP-EGR device 14 is referred to as “LP-EGR rate”, the map characteristics of the target LP-EGR rate are as shown in FIG. Yes. That is, as shown in FIG. 3, the substantially isosceles trapezoidal LP-EGR region as a whole is roughly divided into two, 10% in the high load region and 20% in the low load region.

  The reason why the target LP-EGR rate is made smaller in the high load side region than in the low load side region is as follows. That is, if the fresh air can be pushed into the cylinder 7 by the turbocharger even on the high load side, the target LP-EGR rate can be set to 20% on the high load side as well as on the low load side. However, even if fresh air is actually pushed into the cylinder 7 by the turbocharger, the amount of fresh air that can be pushed is limited. On the other hand, it is necessary to generate a larger engine torque on the high load side than on the low load side. Therefore, by reducing the target LP-EGR rate in the range where knocking does not occur on the high load side and in the range where knocking does not occur, the combustion state in the cylinder 7 is improved by that amount, thereby increasing the engine larger than the low load side. Torque is obtained. In FIG. 3, the target LP-EGR rate is set in two stages, but the present invention is not limited to the case where the target LP-EGR ratio is set in two stages. The target LP-EGR rate may be changed in three or more stages or continuously.

  Next, it is necessary to determine the LP-EGR valve opening so that the target LP-EGR rate is obtained. Here, in this embodiment, the LP-EGR rate is a value defined by the following equation.

LP-EGR rate = LP-EGR valve flow rate / (fresh air amount + LP-EGR valve flow rate)
... (1)

  The new air amount in the equation (1) is the amount of air detected by the air flow meter 42, and the LP-EGR valve flow rate in the equation (1) is the amount of gas flowing through the LP-EGR valve 17. The LP-EGR valve flow rate is determined by the LP-EGR valve front-rear differential pressure and the LP-EGR valve opening area Segr. Here, the “LP-EGR valve differential pressure” is the flow resistance of the EGR cooler 16 from the pressure difference between the exhaust pressure at point A shown in FIG. 4 and the intake pressure at point B shown in FIG. This is a value obtained by subtracting the pressure loss due to, that is, a value calculated from

ΔP = (exhaust pressure at point A−intake pressure at point B) −ΔP1 (2)
However, ΔP: LP-EGR valve differential pressure before and after,
ΔP1: Pressure loss due to flow path resistance of EGR cooler,
FIG. 4 is a simplified model diagram of the LP-EGR device 14. In FIG. 4, “Point A” is a point where the EGR passage 15 branches from the exhaust pipe 11b (branch portion of the EGR passage), and “Point B” is a point where the EGR passage 15 joins the intake pipe 4a (EGR passage). The confluence part). In the simplified model diagram of FIG. 4, both the main catalyst 13 and the EGR cooler 16 are elements that become flow path resistances, and thus are described as orifices.

  From the above formulas (1) and (2), the LP-EGR valve opening is set so that the target LP-EGR rate can be obtained with respect to the exhaust pressure at point A at the time of adaptation.

  In this case, since the point B is near the air cleaner 18 further upstream than the throttle valve 5 and the compressor 23, the intake pressure at the point B is near atmospheric pressure and does not change so much. On the other hand, the exhaust pressure at point A changes. This is because the exhaust temperature changes according to the engine operating conditions, and the pressure loss of the entire exhaust pipe 11b downstream of the branch portion of the EGR passage changes in response to the change in the exhaust temperature. This can be explained theoretically as follows. That is, when the ideal gas state equation PV = mRT is solved for P, the following equation is obtained.

P = mRT / V (3)
Where R: gas constant,
m: mass of gas,
From the equation (3), the pressure P is proportional to the temperature T. That is, when the exhaust temperature (T) at point A changes, the exhaust pressure (P) at point A changes.

  For this reason, when the exhaust pressure at point A becomes lower than the exhaust pressure when the LP-EGR valve opening degree is adapted due to the difference in operating conditions, the LP-EGR valve front-rear differential pressure ΔP becomes smaller from the above equation (2). When the LP-EGR valve front-rear differential pressure ΔP is reduced, the LP-EGR valve flow rate is reduced by the reduced amount. When the LP-EGR valve flow rate decreases, the actual LP-EGR rate becomes smaller than the target LP-EGR rate from the above equation (1). Here, in the LP-EGR region, the ignition timing is set so that the ignition timing is advanced as the target LP-EGR rate increases in accordance with the target LP-EGR rate. This is because, as the LP-EGR rate is increased, the combustion state in the cylinder 7 becomes poorer, so that the combustion failure is eliminated by advancing the ignition timing. Thus, when the ignition timing is set according to the target LP-EGR rate, if the actual LP-EGR rate is smaller than the target LP-EGR rate, the ignition timing is excessively advanced and knocking may occur. obtain.

  On the other hand, when the exhaust pressure at point A becomes higher than the exhaust pressure when the LP-EGR valve opening degree is adapted due to the difference in operating conditions, the LP-EGR valve front-rear differential pressure ΔP increases from the above equation (2). When the LP-EGR valve front-rear differential pressure ΔP increases, the LP-EGR valve flow rate increases by the increased amount. When the LP-EGR valve flow rate increases, the actual LP-EGR rate becomes larger than the target LP-EGR rate from the above equation (1). When the ignition timing is set according to the target LP-EGR rate as described above, if the actual LP-EGR rate becomes larger than the target LP-EGR rate, the ignition timing is too late and the combustion in the cylinder 7 is poor. Become. If the combustion in the cylinder 7 deteriorates, the desired engine torque cannot be obtained and the drivability deteriorates.

  As a countermeasure, the exhaust pressure at point A is detected by a pressure sensor, and it is determined that the LP-EGR valve flow rate is within the appropriate range only when the exhaust pressure at point A is within the allowable range. To give permission. On the other hand, when the exhaust pressure at point A is out of the allowable range, it may be considered that the LP-EGR valve flow rate is not within the proper range and LP-EGR is prohibited. However, providing a pressure sensor for detecting the exhaust pressure at point A causes another problem. That is, the pressure sensor is affected by exhaust pulsation and has poor response. In order to eliminate the influence of exhaust pulsation from the detected value of the pressure sensor, advanced filtering technology is required. In the first place, the differential pressure between the exhaust pressure at point A and the intake pressure at point B is as small as about 1 kPa. An expensive pressure sensor is required to accurately detect such a very small differential pressure, and the cost increases in combination with the necessity of the above advanced filtering technique.

  Here, since the pressure change at the point A is a pressure change caused by the temperature change of the exhaust gas, the exhaust temperature strongly correlating with the exhaust pressure at the point A should be in the exhaust pipe 11b downstream from the point A or the point A. The inventors of the present invention thought that there was. Therefore, the inventor of the present invention first takes the exhaust temperature at point A as the exhaust temperature correlated with the exhaust pressure at point A, and when experimented, the exhaust temperature at point A does not necessarily correlate with the exhaust pressure at point A. I understood it. To explain this, as shown in the simplified model diagram of FIG. 4, the points C and D are adopted as the position of the exhaust pipe 11b downstream of the point A. Point C is the outlet of the main catalyst 13 and point D is a point in the muffler 19.

  FIG. 5 is a timing chart showing the results of measuring how the exhaust temperatures at points A, C, and D change with respect to changes in the exhaust pressure at point A. When the exhaust pressure at point A rises from the timing t1 as shown in the upper part of FIG. 5 and settles to a constant value at the timing t2, the change (response) in the exhaust pressure at the point A as shown in the lower part of FIG. A strong correlation was the change (response) in the exhaust temperature at point C, not point A. That is, the exhaust temperature at the point A rises as early as the timing before the timing t1 when the exhaust pressure at the point A starts to change, and the timing before the timing t2 when the exhaust pressure at the point A settles to a constant value. It has settled to a constant value (see the broken line in the lower part of FIG. 5). On the other hand, the exhaust temperature at point D rises at a timing delayed from the timing t1 when the exhaust pressure at point A starts to change, and reaches a constant value at a timing delayed from the timing t2 when the exhaust pressure at point A settles to a constant value. (See the dashed line in the lower part of FIG. 5). In contrast, the exhaust temperature at point C rises at the same timing as t1 when the exhaust pressure at point A starts to change, and is constant at the same timing as t2 when the exhaust pressure at point A settles to a constant value. The value is settled (see the solid line in the lower part of FIG. 5). As described above, it has been newly found from experiments that the change (response) of the exhaust pressure at point A and the change (response) of the exhaust temperature at point C are strongly correlated. This indicates that when the exhaust pipe 11b downstream from the point A has an orifice (13), the exhaust temperature at the point C, which is the outlet of the orifice, can be used as a substitute for the exhaust pressure at the point A. . In this case, there is an advantage that the temperature sensor is less susceptible to the pulsation of the exhaust pressure than the pressure sensor.

  The reason why the change (response) in the exhaust pressure at point A and the change (response) in the exhaust temperature at point C are strongly correlated as described above is as follows. That is, the exhaust flow flowing through the exhaust pipe 11b downstream from the point A is not uniform, and if the exhaust pipe 11 downstream from the point A has an orifice (13), the flow stagnates at that portion (the exhaust flow is regulated by the orifice). ) In the simplified model diagram of FIG. 4, since the main catalyst 13 functions as an orifice, the exhaust temperature at the point C where the exhaust flow stagnates is considered to regulate the temperature of the entire exhaust pipe 11b downstream from the point A. is there.

  Therefore, in the first embodiment of the present invention, the outlet temperature of the main catalyst 13 (the exhaust temperature of the exhaust pipe 11b downstream of the branch portion) is detected by the temperature sensor 46 (see FIG. 1). Then, only when the detected exhaust gas temperature is within the allowable range, it is determined that the LP-EGR valve flow rate is within the appropriate range, and LP-EGR is permitted. On the other hand, if the detected exhaust gas temperature is outside the allowable range, it is determined that the LP-EGR valve flow rate is not within the proper range, and LP-EGR is prohibited.

  In the present embodiment, since the flow rate of the exhaust gas flowing through the exhaust pipe 11b downstream of the point A functions as a factor that determines the main catalyst 13, the main catalyst outlet temperature has been found to have a strong correlation with the exhaust pressure at the point A. . If the configuration of the catalyst or the like disposed in the exhaust pipe 11b downstream of the point A is different, the factors that control the flow rate of the exhaust gas flowing through the exhaust pipe 11b downstream of the point A will be different. For this reason, if the configuration (specifications) of the catalyst or the like disposed in the exhaust 11b downstream of the point A is determined, the exhaust temperature strongly correlating with the exhaust pressure at the point A with respect to the determined configuration is determined as the exhaust pipe downstream of the point A. Search from 11b.

  Further, this embodiment will be described with reference to FIG. 6. FIG. 6 is a flow characteristic diagram of the LP-EGR valve 17. In FIG. 6, the horizontal axis represents the LP-EGR valve opening area, and the vertical axis represents the LP-EGR valve flow rate. It is assumed that the flow rate characteristic when the main catalyst outlet temperature is the reference temperature is a straight line α. Actual LP-EGR valve flow rate characteristics vary due to manufacturing variations of LP-EGR devices such as LP-EGR valve 17. Therefore, an allowable temperature range (allowable range) having a certain width with respect to the reference temperature is provided. When the lower limit value of the allowable range is TA and the upper limit value of the allowable range is TB, the flow characteristics when the main catalyst outlet temperature is the lower limit value TA and the upper limit value TB are β and γ straight lines, respectively.

  Here, it is assumed that the ignition timing is adapted based on the target LP-EGR rate so that knocking does not occur and the combustion state in the cylinder 7 does not deteriorate. For example, as shown in FIG. 12, the ignition timing is set to the advance side as the target LP-EGR rate increases. In this embodiment, since the target LP-EGR rate can only be 10% and 20%, when the target LP-EGR rate is 10%, the ignition timing is set to a predetermined value c, and when the target LP-EGR rate is 20%. The ignition timing becomes a predetermined value d. When spark ignition is performed using the ignition timing shown in FIG. 12 in the LP-EGR region, the above lower limit TA and upper limit TB are set so that knocking does not occur and the combustion state in the cylinder 7 does not deteriorate. It will be determined. If TA and TB are set in this manner, as long as the main catalyst outlet temperature is within the allowable range of not less than the lower limit TA and not more than the upper limit TB, for example, when the LP-EGR valve opening area is the predetermined value S1, -The EGR valve flow rate falls within the appropriate range of Qβ and Qγ. When spark ignition is performed at the ignition timing shown in FIG. 12, knocking does not occur and the combustion state in the cylinder 7 does not deteriorate as long as the LP-EGR valve flow rate is within the appropriate range.

  On the other hand, when the main catalyst outlet temperature is low outside the allowable range, the exhaust pressure at point A is reduced by the temperature drop from the lower limit TA of the allowable range. Then, since the LP-EGR valve flow rate characteristic shifts to a straight line of δ, even if the LP-EGR valve opening area is the same as the predetermined value S1, the LP-EGR valve flow rate becomes Qδ, which is smaller than Qβ. In other words, the actual LP-EGR rate becomes smaller than the target LP-EGR rate by the LP-EGR valve flow rate corresponding to the difference between Qβ and Qδ. As a result, the combustion state in the cylinder 7 is improved by the amount by which the actual LP-EGR rate becomes smaller than the target LP-EGR rate. Therefore, at the ignition timing adapted to the target LP-EGR rate, the over-advance angle And knocking may occur.

  Further, when the main catalyst outlet temperature is high outside the allowable range, the exhaust pressure at point A increases by the temperature increase from the upper limit value TB of the allowable range. Then, since the LP-EGR valve flow rate characteristic moves to a straight line of ε, even if the LP-EGR valve opening area is the same as the predetermined value S1, the LP-EGR valve flow rate becomes Qε, which is larger than Qγ. In other words, the actual LP-EGR rate becomes larger than the target LP-EGR rate by the LP-EGR valve flow rate corresponding to the difference between Qε and Qγ. As a result, the combustion state in the cylinder 7 is deteriorated by the amount by which the actual LP-EGR rate is larger than the target LP-EGR rate. Therefore, at the ignition timing adapted to the target LP-EGR rate, the retarded angle is reduced. Therefore, the combustion state may be further deteriorated and the drivability may be deteriorated.

  Therefore, in the present embodiment, when the main catalyst outlet temperature is out of the predetermined allowable range, the LP-EGR valve 17 is prohibited from being opened even in the LP-EGR region.

  As shown in FIG. 1, in addition to the fuel injection valve 8 and the spark plug 9, an engine controller 41 is provided to control the LP-EGR valve 17, the waste gate valve 25, and the recirculation valve 32. The engine controller 41 is configured as a computer unit including peripheral devices such as a microprocessor, ROM, and RAM. The engine controller 41 receives signals from an air flow meter 42, an accelerator sensor 43, a crank angle sensor 44, a supercharging pressure sensor 45, and a temperature sensor 46. Here, the air flow meter 42 detects the amount of air (mass flow rate) flowing into the intake pipe 4a. The accelerator sensor 43 detects the amount of accelerator pedal depression (accelerator opening) and the amount of change. The crank angle sensor 44 detects the engine rotation speed. The supercharging pressure sensor 45 detects the pressure (actual supercharging pressure) of the intake collector 4b. The temperature sensor 46 detects the outlet temperature of the main catalyst 13.

  The LP-EGR control performed by the engine controller 41 will be described with reference to the following flowchart. First, the flowchart of FIG. 7 is for setting the LP-EGR permission flag. The flow in FIG. 7 is executed at regular time intervals (for example, every 10 ms).

  It is checked whether or not the engine operating point determined from the engine speed Ne and the engine load is in the LP-EGR region shown in FIG. For example, the basic injection pulse width Tp may be used as the engine load. The basic injection pulse width Tp is a basic value for calculating the fuel injection pulse width Ti given to the fuel injection valve 8, and is calculated based on the engine speed Ne and the intake air amount Qa. When the engine operating point is not in the LP-EGR region shown in FIG. 2, the routine proceeds to step 4 where the LP-EGR permission flag (initially set to zero when the engine is started) = 0.

  When the engine operating point is in the LP-EGR region shown in FIG. 2 in step 1, the process proceeds to step 2 to check whether the main catalyst outlet temperature Tmain detected by the temperature sensor 46 is within an allowable range. Here, the lower limit TA of the allowable range and the upper limit TB of the allowable range are determined in advance. If the main catalyst outlet temperature Tmain is not less than the lower limit TA and not more than the upper limit TB (allowable range), it is determined that the LP-EGR valve flow rate is in the proper range. At this time, the process proceeds from step 2 to step 3 to set LP-EGR permission flag = 1.

  In step 2, when the main catalyst outlet temperature Tmain is lower than the lower limit TA or the main catalyst outlet temperature Tmain exceeds the upper limit TB, it is determined that the LP-EGR valve flow rate is not in the proper range. At this time, the process proceeds to step 4 to set LP-EGR permission flag = 0. The value of the LP-EGR permission flag set in this way is stored in the memory.

  In this embodiment, the main catalyst outlet temperature is detected by the temperature sensor 46, but the main catalyst outlet temperature may be obtained by calculation (estimation). A known method may be used to calculate the main catalyst outlet temperature. For example, a temperature sensor (not shown) is provided in the exhaust pipe 11b immediately downstream of the waste gate valve 25 to correct the opening of the waste gate valve 25. If the exhaust temperature changes stepwise at this temperature sensor position, the main catalyst outlet temperature can be considered to change with a first-order response delay with respect to the step-changed exhaust temperature. Therefore, a value obtained by subjecting the exhaust gas temperature detected by the temperature sensor immediately downstream of the waste gate valve 25 to the first-order lag process can be easily obtained as the main catalyst outlet temperature. In this case, the exhaust temperature immediately downstream of the waste gate valve 25 can also be easily obtained by referring to a map using the engine speed Ne and the engine load as parameters. In the above calculation method of the main catalyst outlet temperature, heat dissipation from the exhaust pipe and reduction of exhaust energy due to turbine work are ignored. Actually, after the waste gate valve, the heat of the exhaust is taken away by the heat radiation from the exhaust pipe 11b, the work of the turbine 22, and the passage of the catalysts 12,13. Therefore, the temperature decrease due to heat radiation from the exhaust pipe 11b, the temperature decrease due to the work performed by the turbine 22, and the temperature decrease due to the passage of the catalysts 12 and 13 are individually obtained or set in advance. Then, the main catalyst outlet temperature may be obtained more accurately by adding the respective temperature drop to the exhaust temperature detected by the temperature sensor immediately downstream of the waste gate valve 25.

  Next, the flowchart of FIG. 8 is for calculating the target LP-EGR valve opening. The flow in FIG. 8 is executed following the flow in FIG. 7 at regular time intervals (for example, every 10 ms).

  In step 11, it is checked whether or not the LP-EGR permission flag (set by the flow of FIG. 7) = 1. When the LP-EGR permission flag = 1, the process proceeds to Steps 12 to 15 to perform LP-EGR.

  Steps 12 to 15 are parts for calculating the target LP-EGR valve opening in the LP-EGR region. First, in step 12, a target LP-EGR rate Megr [%] is calculated by searching a map having the contents shown in FIG. 3 from the engine speed Ne and the engine load. As shown in FIG. 3, the target LP-EGR rate is determined in advance on a map having the engine speed Ne and the engine load as parameters.

  In step 13, the basic LP-EGR valve opening voLP-EGR0 is calculated by searching a table having the contents shown in FIG. 9 from the target LP-EGR rate Megr. As shown in FIG. 9, the basic LP-EGR valve opening is a value that increases as the target LP-EGR rate increases. In this embodiment, since the target LP-EGR rate can only be 10% and 20%, when the target LP-EGR rate is 10%, the basic LP-EGR valve opening is set to the predetermined value a, and the target LP-EGR rate Is 20%, the basic LP-EGR valve opening is a predetermined value b.

  In step 14, a trimming coefficient Ktrm [anonymous number] is calculated by searching a map having the contents shown in FIG. 10 from the engine speed Ne and the engine load. The trimming coefficient is a value centered at 1.0. As shown in FIG. 10, in the LP-EGR region, 1.1 is in the region on the low rotational speed and low load side, 0.9 is in the region on the high rotational speed and high load side, and 1.0 is in the remaining region. Is included. When the trimming coefficient exceeds 1.0, the target LP-EGR valve opening is corrected to increase, and when the trimming coefficient is less than 1.0, the target LP-EGR valve opening is decreased.

  In step 15, the basic LP-EGR valve opening voLP-EGR0 is multiplied by the trimming coefficient Ktrm, that is, the target LP-EGR valve opening voLP-EGR is calculated by the following equation.

    voLP-EGR = voLP-EGR0 × Ktrm (4)

  The trimming coefficient Ktrm is for obtaining the target LP-EGR rate even if the intake air amount Qa (engine load) and the engine speed Ne are different.

  The role of the trimming coefficient Ktrm will be specifically described. For example, when the engine speed Ne is constant, as shown in FIG. 11, the differential pressure across the LP-EGR valve changes with respect to the intake air amount Qa. This is because the exhaust temperature increases as the intake air amount Qa increases, and the exhaust pressure at point A increases in a quadratic function as the exhaust temperature increases. From FIG. 11, only a relatively small differential pressure is obtained on the low load side where the intake air amount Qa is relatively small, and a relatively large differential pressure is obtained on the high load side where the intake air amount Qa is relatively large. . This is because the LP-EGR valve flow rate is relatively small on the low load side (EGR gas is less likely to flow through the LP-EGR valve), and the LP-EGR valve flow rate is relatively large on the high load side (LP-EGR valve). The EGR gas can easily flow). Now, an intermediate intake air amount Qa between a low load with a relatively small Qa and a high load with a relatively large Qa is selected as the intake air amount at the time of adaptation, and the intake air amount at the time of adaptation is assumed to be Q1. At this time, on the low load side smaller than the intake air amount Q1 at the time of adaptation, the LP-EGR valve flow rate becomes smaller than the LP-EGR valve flow rate at the time of adaptation. When the LP-EGR valve flow rate decreases, the actual EGR rate deviates from the target EGR rate and decreases. Therefore, as shown in FIG. 10, the actual EGR rate deviates from the target EGR rate even on the low load side by giving a trimming coefficient of 1.1 on the low load side and increasing the LP-EGR valve opening. Avoid getting smaller.

  Further, on the higher load side than the intake air amount Q1 at the time of adaptation, the LP-EGR valve flow rate is larger than the LP-EGR valve flow rate at the time of adaptation. If the LP-EGR valve flow rate increases, the actual EGR rate deviates from the target EGR rate and increases. Therefore, as shown in FIG. 10, by giving a trimming coefficient of 0.9 on the high load side and correcting the decrease in the LP-EGR valve opening, the actual EGR rate deviates from the target EGR rate even on the high load side. Avoid getting bigger.

  In this embodiment, the LP-EGR region is divided into three, and one trimming coefficient is given for each region (that is, three different trimming factors are given stepwise), but this is limited to this case. Not a thing. Four or more different trimming coefficients may be given stepwise, or the trimming coefficient may be given steplessly.

  If the LP-EGR permission flag = 0 in step 11 of FIG. 8, the process proceeds to step 16 to set the target LP-EGR valve opening voLP-EGR to zero. As a result, when the main catalyst outlet temperature Tmain is outside the allowable range, it is determined that the LP-EGR valve flow rate is not within the proper range and LP-EGR is prohibited, so the LP-EGR valve 17 is fully closed.

  In a flow (not shown), a signal is output to the motor 18 which is an LP-EGR valve actuator so that the target LP-EGR valve opening voLP-EGR is obtained.

  Here, the effect of this embodiment is demonstrated.

  The target LP-EGR valve opening (target EGR valve flow rate) is set so that the target LP-EGR rate is obtained. In this case, the LP-EGR valve flow rate depends on the differential pressure between the exhaust pressure at point A (branch portion of the EGR passage) and the intake pressure at point B (merging portion of the EGR passage) as shown in FIG. Change. For this reason, when the actual exhaust pressure at point A rises above the exhaust pressure at point A at the time of adaptation, the actual LP-EGR valve flow rate becomes larger than the target LP-EGR valve flow rate by the increase in the exhaust pressure. The LP-EGR rate becomes larger than the target LP-EGR rate. On the other hand, when the actual exhaust pressure at the point A is lower than the exhaust pressure at the point A at the time of adaptation, the actual LP-EGR valve flow rate becomes smaller than the target LP-EGR valve flow rate by the decrease in the exhaust pressure. -The EGR rate falls outside the target LP-EGR rate. When the ignition timing is set according to the target LP-EGR rate, if the actual LP-EGR rate deviates from the target LP-EGR rate in the LP-EGR region and becomes large, the combustion state in the cylinder 7 deteriorates. The drivability gets worse. Similarly, when the ignition timing is set according to the target LP-EGR rate, knocking may occur when the actual LP-EGR rate falls outside the target LP-EGR rate in the LP-EGR region. In order to prevent such deviation of the actual LP-EGR rate from the target LP-EGR rate, the exhaust pressure at point A is detected, and when the detected exhaust pressure deviates from a predetermined allowable range, the LP-EGR region Even if it exists, it is possible to prohibit opening the LP-EGR valve 17. However, even if a pressure sensor for detecting the exhaust pressure is provided at point A, the pressure sensor is affected by exhaust pulsation and has poor responsiveness. Therefore, it is possible to determine whether or not the exhaust pressure is out of the predetermined allowable range. Is bad. On the other hand, in this embodiment, the exhaust temperature of the exhaust pipe 11b downstream from the point A, which correlates with the exhaust pressure at the point A (branch), is detected, and the detected exhaust temperature of the exhaust pipe 11b downstream of the point A is allowable. LP-EGR is prohibited when the temperature goes down or goes up. Unlike the pressure sensor, the temperature sensor that detects the exhaust temperature of the exhaust pipe 11b downstream of the point A is not affected by exhaust pulsation, and therefore the accuracy of determining whether or not the LP-EGR valve flow rate is within the appropriate range can be improved.

  M in the above equation (3) varies depending on the gas temperature. That is, m is a value corresponding to the state of the gas passing through the LP-EGR valve 17. For this reason, in the relationship between P and T in the above equation (3), P (exhaust pressure at point A) and T (main catalyst outlet) are higher when the gas passing through the LP-EGR valve 17 is at a lower temperature. The correlation of (temperature) becomes higher. If there is no EGR cooler 16 upstream of the LP-EGR valve 17, the gas passing through the LP-EGR valve 17 may become a high temperature. At this time, P (point A in the relationship between P and T in the above equation (3) The exhaust gas pressure) and T (main catalyst outlet temperature) are weakened. On the other hand, in the present embodiment, the EGR passage 15 upstream of the LP-EGR valve is provided with the EGR cooler 16 that cools the gas flowing through the EGR passage 15 so that the LP-EGR valve 17 flows more than the case where the EGR cooler 16 is not provided. The gas is kept at a low temperature. As a result, the correlation between P (exhaust pressure at point A) and T (main catalyst outlet temperature) in the relationship between P and T in the above equation (3) becomes stronger, so is the LP-EGR valve flow rate within an appropriate range? The accuracy of determining whether or not can be further improved.

  When the main catalyst 13 is provided in the exhaust pipe 11b downstream of the point A (branch portion), the main catalyst 13 functions as a flow path resistance in the exhaust pipe 11b downstream of the point A, so that the exhaust temperature at the point A is A The value does not necessarily correlate with the exhaust pressure at the point. Even if the temperature sensor improves the determination accuracy over the pressure sensor, it cannot be said that the determination accuracy improves until the exhaust temperature at point A does not necessarily correlate with the exhaust pressure at point A. On the other hand, the present inventors have newly found that the main catalyst outlet temperature strongly correlates with the exhaust pressure at point A. In the present embodiment, the engine is a gasoline engine, and the exhaust pipe 11 b is provided with a manifold catalyst 12 and a main catalyst 13 in series toward the downstream side, and the EGR passage 15 is an exhaust pipe 11 b between the manifold catalyst 12 and the main catalyst 13. Branch off from. The exhaust temperature of the exhaust pipe 11 b downstream from the point A is the outlet temperature of the main catalyst 13. As a result, even in a gasoline engine including the main catalyst 13 in the exhaust pipe 11b downstream of the point A, it is possible to improve the determination accuracy as to whether or not the LP-EGR valve flow rate is within an appropriate range.

  In the embodiment, since it is assumed that the exhaust pipe 11b downstream of the branch portion of the EGR passage 15 has the main catalyst 13, the exhaust pressure of the branch portion and the exhaust temperature of the branch portion do not correlate strongly, and the main catalyst outlet However, the present invention is not limited to this case. The present invention can also be applied to the premise that the exhaust pipe 11b downstream of the branch portion of the EGR passage 15 does not have the main catalyst 13. When it is assumed that the exhaust pipe 11b downstream of the branch portion of the EGR passage 15 does not have the main catalyst 13, the exhaust pressure of the branch portion and the exhaust temperature of the branch portion are strongly correlated, so the branch portion of the EGR passage What is necessary is just to estimate whether to detect the exhaust temperature.

  In the embodiment, the case where the LP-EGR device is applied to the gasoline engine has been described. However, the present invention is not limited to this case, and the present invention can be applied to the case where the LP-EGR device is applied to the diesel engine.

DESCRIPTION OF SYMBOLS 1 Gasoline engine 4 Intake passage 4a Intake pipe 4b Intake collector 8 Fuel injection valve 9 Spark plug 11 Intake passage 11b Exhaust pipe 12 Manifold catalyst 13 Main catalyst 14 LP-EGR device 15 EGR passage 16 EGR cooler 17 LP-EGR valve 41 Engine controller (Control means, prohibition means)
46 Exhaust temperature sensor

Claims (3)

An EGR passage that branches from the exhaust pipe of the engine downstream of the turbocharger turbine, bypasses the cylinder and joins the intake pipe upstream of the compressor of the turbocharger;
An EGR valve that opens and closes the EGR passage;
An EGR control device comprising: control means for opening the EGR valve in an EGR region and controlling the EGR valve to a fully closed state in a non-EGR region;
Exhaust temperature detection / estimation means for detecting or estimating the exhaust temperature of the branch portion of the EGR passage or the exhaust temperature of the exhaust pipe downstream from the branch portion of the EGR passage;
It is prohibited to open the EGR valve even in the EGR region when the detected or estimated exhaust temperature exceeds the upper limit value of the predetermined allowable range and when the exhaust temperature falls below the lower limit value of the allowable range. An EGR control device, comprising:   The EGR control device according to claim 1, further comprising an EGR cooler that cools a gas flowing through the EGR passage in the EGR passage upstream of the EGR valve. The engine is a gasoline engine;
A turbocharger having a turbine interposed in the exhaust pipe and a compressor interposed in the intake pipe;
A manifold catalyst and a main catalyst are provided in series in the exhaust pipe downstream of the turbine toward the downstream side,
The EGR passage is branched from an exhaust pipe between the manifold catalyst and the main catalyst, and merges with an intake pipe upstream of the compressor,
3. The EGR control device according to claim 1, wherein the exhaust temperature of the exhaust pipe downstream from the branch portion of the EGR passage is an outlet temperature of the main catalyst. 4.

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