EGR device

Abstract

To provide an EGR device which can make an EGR gas properly return to an intake passage while removing deposits around an EGR valve.SOLUTION: An EGR device comprises: a butterfly-type EGR valve for opening and closing an EGR passage while turning around a prescribed axis; an EGR valve drive unit for turn-driving the EGR valve; and a control device for setting a target opening being a target value of an opening of the EGR valve on the basis of an operation state of an engine, valve-opening the EGR valve at the establishment of a prescribed EGR execution condition, and controlling the EGR valve drive unit so that the opening of the EGR valve reaches the target EGR opening. The EGR device performs overturn control for driving the EGR valve in an open direction up until the opening of the EGR valve reaches the target EGR opening after driving the EGR valve in a close direction from a full-opened position by the EGR valve drive unit when the EGR valve is valve-opened accompanied by the establishment of the EGR execution condition.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an EGR device. [Background technology]

[0002] In some automotive engines, an EGR passage that connects the exhaust passage and the intake passage and an EGR valve that opens and closes the EGR passage are provided to return a portion of the exhaust gas flowing through the exhaust passage to the intake passage as EGR gas in order to improve exhaust performance, etc. However, the EGR gas contains soot and other particles, which may adhere and stick between the EGR valve and the inner circumferential surface of the EGR passage, preventing the EGR valve from opening and closing properly.

[0003] To address the above problem, for example, Patent Document 1 discloses a configuration in which, for an engine equipped with a butterfly-type EGR valve, the engine has two operating modes: a normal mode in which the EGR valve is opened to a degree corresponding to the engine's operating state, and a cleaning mode in which the EGR valve is repeatedly rotated in an opening direction and a closing direction around a fully closed position. In this way, by rotating the EGR valve in an opening direction and a closing direction around a fully closed position, deposits that have adhered between the EGR valve and the inner circumferential surface of the EGR passage can be scraped off and removed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4526468 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, when the cleaning mode is activated, the EGR valve passes through the fully closed position multiple times. This may cause EGR gas to pulsate in the EGR passage. Pulsating EGR gas may result in an inappropriate amount of EGR gas being recirculated to the intake passage. Furthermore, in the configuration of Patent Document 1, a cleaning mode is set in addition to a normal mode, which adjusts the EGR valve opening to a value corresponding to the engine's operating conditions. However, when the cleaning mode is activated, the EGR valve opening is not adjusted to a value corresponding to the engine's operating conditions, which may result in an inappropriate amount of EGR gas being released into the engine.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide an EGR device that can properly recirculate EGR gas to the intake passage while removing deposits around the EGR valve. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides an EGR device provided in an engine having an engine body formed with cylinders, an intake passage through which intake air introduced into the cylinders flows, and an exhaust passage through which exhaust gas discharged from the cylinders flows, the EGR device comprising: an EGR passage that connects the exhaust passage and the intake passage and through which EGR gas flows, a butterfly-type EGR valve that rotates about a predetermined axis to open and close the EGR passage; an EGR valve drive device that rotationally drives the EGR valve; and a control device that sets a target EGR opening that is a target value for the opening of the EGR valve based on an operating state of the engine, and controls the EGR valve drive device so that the EGR valve opens and the opening of the EGR valve becomes the target EGR opening when a predetermined EGR execution condition is met, and when the direction in which the EGR valve rotates from a fully closed position to a fully open position is defined as an opening direction and the opposite direction is defined as a closing direction, the control device The target EGR opening is set to an angle rotated in the opening direction from a fully closed position of the EGR valve, EGR execution condition Since it is not true Established Switching to Along with In the fully closed position The EGR valve Towards the target EGR openingWhen opening the valve, the EGR valve drive device drives the EGR valve from a fully closed position in the closing direction, and then executes overturn control to drive the EGR valve in the opening direction until the opening of the EGR valve reaches the target EGR opening.

[0008] According to this configuration, the over-turn control rotates the EGR valve in both the closing and opening directions around the fully closed position, scraping off and removing deposits that have accumulated between the EGR valve and the EGR passage. Moreover, this configuration performs the over-turn control when the EGR execution condition is met, i.e., when EGR gas recirculation to the intake passage is required. This prevents unnecessary EGR gas from being introduced into the intake passage, unlike when the over-turn control is performed when the EGR execution condition is not met. Furthermore, this configuration limits the number of times the EGR valve passes the fully closed position to one, and performs the over-turn control with almost no EGR gas flow in the EGR passage. This more reliably suppresses EGR gas pulsation in the EGR passage. Therefore, this configuration allows EGR gas to be appropriately recirculated to the intake passage while removing deposits around the EGR valve.

[0009] In the above configuration, it is preferable that the engine further comprises a turbocharger including a compressor provided in the intake passage for supercharging the intake air, and a turbine provided in the exhaust passage for receiving energy from the exhaust to drive the compressor, and the EGR passage communicates between the exhaust passage upstream of the turbine and the intake passage downstream of the compressor (claim 2).

[0010] The pressure in the exhaust passage upstream of the turbine is relatively high. Therefore, in a configuration in which the EGR passage is connected to the exhaust passage upstream of the turbine, pulsation of the EGR gas is likely to occur due to the opening and closing of the EGR valve. In contrast, as described above, the present invention suppresses EGR gas pulsation when over-turn control is performed, so that over-turn control can be performed to remove deposits and more appropriately return EGR gas to the intake passage at a more appropriate timing.

[0011] In the above configuration, preferably, the control device determines whether or not a predetermined high exhaust energy condition, in which the exhaust energy is high, is established based on the operating state of the engine, and prohibits the execution of the over-turn control if the high exhaust energy condition is established (claim 3).

[0012] When the exhaust energy is high, pulsation of the exhaust and EGR gas is likely to occur as the EGR valve opens and closes. In contrast, with this configuration, execution of overturn control is prohibited when a high exhaust energy condition is met, ensuring an appropriate amount of EGR gas is recirculated to the intake passage.

[0013] In the above configuration, the high exhaust energy conditions include a condition that the engine speed is higher than a predetermined judgment speed, a condition that the engine load is higher than a predetermined judgment load, a condition that the exhaust pressure, which is the pressure of the exhaust, is higher than a predetermined judgment pressure, and a condition that the exhaust temperature, which is the temperature of the exhaust, is higher than a predetermined judgment temperature, and if any one of these conditions is met, it is determined that the high exhaust energy condition is met (Claim 4).

[0014] In the above configuration, the control device preferably prohibits the execution of the over-turn control when the exhaust O2 concentration, which is the oxygen concentration in the exhaust passage, is lower than a predetermined determination concentration (claim 5).

[0015] When the exhaust O2 concentration is excessively low, the amount of EGR gas recirculated to the intake passage and the engine body increases, which tends to result in excessive soot generation. Furthermore, if the EGR gas pulsates, the amount of EGR gas recirculated to the intake passage may increase. In contrast, with this configuration, when the exhaust O2 concentration is lower than a predetermined concentration, the execution of overturn control, which may cause EGR gas pulsation, is prohibited, thereby reliably preventing the amount of EGR gas recirculated from increasing and resulting in excessive soot generation.

[0016] In the above configuration, preferably, the control device prohibits the execution of the over-turn control when the engine speed is lower than a predetermined lower limit speed (claim 6).

[0017] With this configuration, when the engine speed is low and the amount of EGR gas recirculated to the intake passage and engine body tends to fluctuate, the over-turn control, which may cause the EGR gas to pulsate and increase or decrease the amount of EGR gas recirculated, is prohibited, thereby ensuring good exhaust performance, combustion noise, and the like when the engine speed is low. [Effects of the Invention]

[0018] As described above, the EGR device of the present invention provides an exhaust structure that can properly recirculate EGR gas to the intake passage while removing deposits around the EGR valve. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a system diagram showing a schematic configuration of an engine according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing the periphery of an HP-EGR valve. [Figure 3] FIG. 2 is a block diagram showing a control system of the engine. [Figure 4] 3 is a flowchart showing a control procedure of the HP-EGR valve. [Figure 5]5A and 5B are cross-sectional views showing the state of the EGR valve when overturn control is being executed, with (a) and (b) showing the state at each time. [Figure 6] 4 is a time chart showing a target EGR rate and an EGR opening degree during normal valve opening control. [Figure 7] 4 is a time chart showing a target EGR rate and an EGR opening degree when overturn control is performed. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Overall engine configuration) An embodiment of an EGR device according to the present invention will be described in detail below with reference to the drawings. In this embodiment, an example in which the EGR device is applied to a diesel engine will be described. First, the overall configuration of the engine E will be described with reference to FIG. 1. The engine E shown in FIG. 1 is a four-stroke diesel engine mounted on a vehicle as a power source for driving the vehicle. The engine E includes an engine body 1 having multiple cylinders 2 and driven by a supply of fuel primarily composed of diesel fuel; an intake passage 30 through which intake air introduced into the engine body 1 flows; an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows; and an HP-EGR device 44 and an LP-EGR device 50 that recirculate EGR gas, which is part of the exhaust gas flowing through the exhaust passage 40, back to the intake passage 30. The engine system also includes a turbocharger 46 that includes a compressor 47 disposed on the intake passage 30 side and a turbine 48 disposed in the exhaust passage 40, and that supercharges the intake air with exhaust gas passing through the exhaust passage 40.

[0021] The engine body 1 has a plurality of cylinders 2 (only one of which is shown in FIG. 1) lined up in a direction perpendicular to the plane of the paper on which FIG. 1 is drawn. The engine body 1 has a cylinder block 3 in which the cylinders 2 are formed, and a cylinder head 4 attached to the upper surface of the cylinder block 3. A piston 5 is housed in each cylinder 2 so that it can slide back and forth, and is connected to a crankshaft 7 via a connecting rod 8. The crankshaft 7 rotates around its central axis in response to the reciprocating motion of the piston 5. A combustion chamber 6 is defined above the piston 5.

[0022] The cylinder head 4 is formed with intake ports 9 and exhaust ports 10 that communicate with each combustion chamber 6, and is fitted with intake valves 11 that open and close each intake port 9 and exhaust valves 12 that open and close each exhaust port 10. The intake valves 11 and exhaust valves 12 are driven to open and close by valve trains 13 and 14 provided in the cylinder head 4. The cylinder head 4 is fitted with one injector 15 for each cylinder 2, which injects fuel from its tip into the combustion chamber 6. The injector 15 injects fuel supplied through a fuel supply pipe (not shown) into the combustion chamber 6. The fuel injected from the injector 15 mixes with air in the combustion chamber 6. The fuel-air mixture combusts in the combustion chamber 6, and the piston 5 is pushed down by the expansion force caused by the combustion of the mixture, causing it to reciprocate up and down.

[0023] A crank angle sensor SN1 that detects the rotation speed of the crankshaft 7, i.e., the engine speed, is attached to the cylinder block 3. A water temperature sensor SN2 that detects the coolant temperature, which is the temperature of the coolant flowing inside the engine body 1, is attached to the cylinder head 4. That is, a water jacket W through which the coolant flows is formed in the cylinder block 3 and the cylinder head 4, and the water temperature sensor SN2 detects the temperature of the coolant flowing through the water jacket W.

[0024] The intake passage 30 is connected to one side of the engine body 1 so as to communicate with each intake port 9. In the intake passage 30, an air cleaner 31, a compressor 47 of a turbocharger 46, a throttle valve 32, an intercooler 33, and a surge tank 34 are arranged in this order from the upstream side.

[0025] The air cleaner 31 removes foreign matter from the intake air to purify it. The throttle valve 32 opens and closes the intake passage 30 to adjust the flow rate of intake air in the intake passage 30. The compressor 47 compresses the intake air and sends it out downstream of the intake passage 30. The intercooler 33 cools the intake air compressed by the compressor 47. The surge tank 34 is located immediately upstream of the intake manifold connected to the intake port 9, and is a tank that provides space for evenly distributing the intake air to the multiple cylinders 2.

[0026] An air flow sensor SN3 is attached to the intake passage 30 to detect the intake air volume, which is the flow rate of intake air that flows through the intake passage 30 and is introduced into the engine body 1. The air flow sensor SN3 is disposed between the air cleaner 31 and the compressor 47, and detects the flow rate of intake air passing through these parts.

[0027] The exhaust passage 40 is connected to the other side of the cylinder head 4 so as to communicate with the exhaust port 10. In the exhaust passage 40, a turbine 48 of a turbocharger 46, an oxidation catalyst 41, and a DPF (diesel particulate filter) 42 are arranged in this order from the upstream side.

[0028] The turbine 48 is connected to the compressor 47 so as to be rotatable together with the compressor 47. The turbine 48 rotates by receiving energy from the exhaust gas flowing through the exhaust passage 40, thereby rotating the compressor 47. The oxidation catalyst 41 is a catalytic device that oxidizes harmful components (CO and HC) contained in the exhaust gas to make them harmless. The DPF 42 is a filter that collects particulate matter contained in the exhaust gas.

[0029] The exhaust passage 40 is fitted with an exhaust pressure sensor SN4 that detects the exhaust pressure, which is the pressure of the exhaust gas flowing through the exhaust passage 40, an exhaust temperature sensor SN5 that detects the exhaust temperature, which is the temperature of the exhaust gas, and an air-fuel ratio sensor SN6 that detects the air-fuel ratio of the exhaust gas. The exhaust pressure sensor SN4 is located upstream of the turbine 48 near the connection between the exhaust passage 40 and an HP-EGR passage 44A, which will be described later, and detects the pressure of the exhaust gas passing through this section. The exhaust temperature sensor SN5 is located between the turbine 48 and the oxidation catalyst 41 and detects the temperature of the exhaust gas passing through this section. The air-fuel ratio sensor SN6 is located between the connection between the exhaust passage 40 and an LP-EGR passage 51, which will be described later, and the DPF 42, and detects the air-fuel ratio of the exhaust gas passing through this section.

[0030] The HP-EGR device 44 includes an HP-EGR passage 44A that connects the exhaust passage 40 and the intake passage 30, and an HP-EGR valve 45 provided in the HP-EGR passage 44A. The HP-EGR passage 44A connects a portion of the exhaust passage 40 upstream of the turbine 48 with a portion of the intake passage 30 between the intercooler 33 and the surge tank 34 and downstream of the compressor 47. The HP-EGR valve 45 is driven by an HP-EGR motor 45M to open and close the HP-EGR passage 44A. The amount of EGR gas recirculated to the intake passage 30 via the HP-EGR passage 44A is changed depending on the opening degree of the HP-EGR valve 45. The detailed structure of the HP-EGR valve 45 will be described later.

[0031] The LP-EGR device 50 includes an LP-EGR passage 51 that connects the exhaust passage 40 and the intake passage 30, an EGR cooler 52 that is provided in the LP-EGR passage 51, and an LP-EGR valve 53 that is provided in the LP-EGR passage 51. The LP-EGR passage 51 connects a portion of the exhaust passage 40 downstream of the DPF 43 with a portion of the intake passage 30 between the air cleaner 31 and the compressor 47. The LP-EGR valve 53 is driven by an LP-EGR motor 53M to open and close the LP-EGR passage 51. The amount of EGR gas that recirculates to the intake passage 30 via the LP-EGR passage 51 is changed depending on the opening degree of the LP-EGR valve 53. The EGR cooler 52 is a heat exchanger that cools the EGR gas flowing through the LP-EGR passage 51 by heat exchange.

[0032] As described above, the upstream end of the LP-EGR passage 51 is connected to a portion of the exhaust passage 40 that is downstream of the DPF 43. The upstream end of the HP-EGR passage 44A is connected to a portion of the exhaust passage 40 that is upstream of the turbine 48. In other words, the HP-EGR passage 44A is connected to a portion that is upstream of the LP-EGR passage 51. As a result, high-temperature, high-pressure exhaust gas (EGR gas) before particulates are trapped by the DPF 52 is recirculated to the intake passage 30 through the HP-EGR passage 44A, and low-temperature, low-pressure gas (EGR gas) after particulates are trapped by the DPF 52 is recirculated through the LP-EGR passage 51.

[0033] Hereinafter, the exhaust gas (EGR gas) recirculated to the intake passage 30 through the HP-EGR passage 44A will be referred to as high-pressure EGR gas where appropriate. In this embodiment, of the HP-EGR valve 45 and the LP-EGR valve 53, the HP-EGR valve 45 corresponds to the "EGR valve" in the claims. Also, of the HP-EGR passage 44A and the LP-EGR passage 51, the HP-EGR passage 44A corresponds to the "EGR passage" in the claims. Also, of the HP-EGR motor 45M and the LP-EGR motor 53M, the HP-EGR motor 45M corresponds to the "EGR valve drive device" in the claims.

[0034] (HP-EGR valve configuration) 2 is a schematic cross-sectional view showing the periphery of the HP-EGR valve 45. The HP-EGR valve 45 is a butterfly-type valve that rotates about a predetermined axis to open and close the HP-EGR passage 44A. The HP-EGR valve 45 has a substantially disk-shaped valve body 150 that opens and closes the HP-EGR passage 44A, a seal member 160 attached to the circumferential surface of the valve body 150, and a valve stem 155 connected to the valve body 150 so as to be rotatable integrally therewith.

[0035] The valve stem 155 is rod-shaped and attached to the HP-EGR passage 44A in an orientation extending substantially perpendicular to the flow direction of the high-pressure EGR gas in the HP-EGR passage 44A. The HP-EGR motor 45M rotates the valve stem 155 about its central axis X, thereby rotating the valve body 150 about the central axis X of the valve stem 155. Hereinafter, the central axis X of the valve stem 155, which is also the rotational axis of the valve body 150, will be referred to as the rotation axis X.

[0036] 2 indicates the flow direction of high-pressure EGR gas when the HP-EGR valve 45 is open, and the upper side of FIG. 2 is the upstream side in the flow direction of high-pressure EGR gas. As shown in FIG. 2, in this embodiment, the valve body 150 has a generally hat-shaped cross section with its center convex toward the upstream side.

[0037] The HP-EGR valve 45 is supported by the HP-EGR passage 44A so that it can rotate both clockwise (as indicated by arrow Y1) and counterclockwise (as indicated by arrow Y2) from a fully closed position shown in Fig. 2, i.e., a position perpendicular to the flow direction of high-pressure EGR gas. However, the direction in which the HP-EGR valve 45 rotates from the fully closed position to the fully open position is limited to one of the clockwise and counterclockwise directions. Except during execution of the overturn control described below, the HP-EGR valve 45 opens when rotated in one of the directions from the fully closed position, and returns to the fully closed position when rotated in the opposite direction from the open position. Hereinafter, the opening direction of the HP-EGR valve 45, which rotates from the fully closed position to the fully open position except during execution of the overturn control, will be simply referred to as the "opening direction," and the opposite direction will be simply referred to as the "closing direction." The fully closed position of the HP-EGR valve 45 is the minimum position at which the flow rate of the high-pressure EGR gas (the amount flowing through the HP-EGR passage 44A) is the smallest, and is not limited to a position extending perpendicular to the flow direction of the high-pressure EGR gas as described above. The fully open position of the HP-EGR valve 45 is the maximum position at which the flow rate of the high-pressure EGR gas is the largest. In this embodiment, the fully open position is the position at which the HP-EGR valve 45 extends along the flow direction of the high-pressure EGR gas, as shown in FIG. 5(d).

[0038] (Control system) The control configuration of the engine system will be described with reference to the block diagram in Figure 3. The engine system is comprehensively controlled by an ECU (Engine Control Unit) 100. The ECU 100 is composed of a CPU, ROM, RAM, etc. The ECU 100 corresponds to the "control device" in the claims.

[0039] The ECU 100 sequentially receives various types of information detected by the sensors SN1 to SN6 described above, such as engine speed, coolant temperature, intake air volume, exhaust pressure, exhaust temperature, and exhaust air-fuel ratio. The ECU 100 controls each part of the engine system while executing various determinations and calculations based on the above information. That is, the ECU 100 is electrically connected to the injector 15, the throttle valve 32 (a drive device that drives the throttle valve 32), the HP-EGR motor 45M (HP-EGR valve 45), the LP-EGR motor 53M (LP-EGR valve 53), and the like, and outputs control signals to these devices based on the results of the above calculations, etc.

[0040] (HP-EGR valve control) Next, a description will be given of the control of the HP-EGR valve 45, which is a characteristic feature of the present invention.

[0041] First, the ECU 100 reads various information (step S1). Specifically, the ECU 100 reads information such as the engine speed, coolant temperature, intake air volume, exhaust pressure, exhaust temperature, and exhaust air-fuel ratio detected by the above-mentioned sensors SN1 to SN6. The ECU 100 also reads an exhaust O2 concentration, which is the oxygen concentration in the exhaust gas, calculated separately. Specifically, the ECU 100 estimates the intake O2 concentration, which is the oxygen concentration of the intake air flowing into the combustion chamber 6, based on the opening of the HP-EGR valve 45 and the LP-EGR valve 53, and estimates the exhaust O2 concentration based on the intake O2 concentration, the intake air volume, and the amount of fuel injected from the injector 15, and corrects this based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor SN6.

[0042] Next, the ECU 100 determines whether a condition for executing HP-EGR, that is, an EGR execution condition for recirculating high-pressure EGR gas to the intake passage 30, is satisfied (step S2). The condition for executing HP-EGR is preset and stored in the ECU 100. In this embodiment, the EGR execution condition is set to a condition that the engine is operating in a preset HP-EGR execution region within the engine operating region defined by the engine load, i.e., the required engine torque, which is the torque required of the engine, and the engine speed. The ECU 100 determines whether the current operating point of the engine is within the HP-EGR execution region based on the engine speed detected by the crank angle sensor SN1 and the calculated required engine torque. The ECU 100 then determines that the EGR execution condition is satisfied if the current operating point of the engine is within the HP-EGR execution region, and determines that the EGR execution condition is not satisfied if the current operating point of the engine is outside the HP-EGR execution region. The ECU 100 calculates the required engine torque based on the opening of an accelerator pedal provided on the vehicle and the engine speed. For example, the HP-EGR execution region is set to a low-speed, low-load region where the engine speed is equal to or lower than a predetermined value and the required engine torque (engine load) is equal to or lower than a predetermined value.

[0043] If the determination in step S2 is NO and the EGR execution condition is not satisfied, the ECU 100 fully closes the HP-EGR valve 45 and ends the process (step S30).

[0044] On the other hand, if the determination in step S2 is YES and the EGR execution condition is satisfied, the ECU 100 sets a target EGR rate, which is a target value of the EGR rate. The EGR rate is the ratio of the weight of high-pressure EGR gas in the combustion chamber 6 to the total weight of gas in the combustion chamber 6. The target EGR rate is set in advance for each engine operating point and stored in the ECU 100. The ECU 100 extracts a value corresponding to the current engine operating point from this stored information and sets it as the target EGR rate. For example, the target EGR rate is stored in a map of engine speed and required engine torque, and the ECU 100 extracts a value corresponding to the current engine speed and required engine torque from this map and sets it as the target EGR rate. Note that step S3 is a step that is executed when the EGR execution condition is satisfied, and the target EGR rate is set to a value greater than 0.

[0045] Next, the ECU 100 determines whether the number of times the over-turn control is performed is equal to or less than a predetermined number of times (step S4). The number of times the over-turn control is performed is the number of times the over-turn control, which will be described later, is executed. The number of times the over-turn control is performed is set to 0 while the engine E is stopped, and is counted up each time the over-turn control is executed after the engine E is started, as will be described later. The above-mentioned number of times of determination is preset to a value greater than 1 and stored in the ECU 100. For example, the number of times of determination is set to 4.

[0046] If the determination in step S4 is NO and the number of times of over-turn control is greater than the determination number, that is, after the over-turn control has been executed the determined number of times after the start of the engine E, the ECU 100 executes normal valve opening control on the HP-EGR valve 45 (step S20). Specifically, the ECU 100 sets a target EGR opening, which is the opening of the HP-EGR valve 45 that achieves the target EGR rate set in step S3, and drives the HP-EGR motor 45M so that the opening of the HP-EGR valve 45 (the rotation angle in the opening direction relative to the fully closed position) becomes this target EGR opening. Note that the target EGR opening is set to an opening greater than 0°. After step S4, the ECU 100 ends the process (returns to step S1).

[0047] Returning to step S4, if the number of overturn control times is equal to or less than the determination number, the ECU 100 next determines whether the EGR condition is satisfied with the HP-EGR valve 45 in a fully closed state (a state in a fully closed position). That is, it determines whether the timing has come immediately after the EGR execution condition has switched from not being satisfied to being satisfied, and therefore it is time to start opening the HP-EGR valve 45 in response to the satisfaction of the EGR execution condition (step S5). Specifically, the ECU 100 determines whether the EGR execution condition in the previous calculation cycle was not satisfied.

[0048] If the determination in step S5 is NO and the EGR condition is met when the HP-EGR valve 45 is not in the fully closed position (if the EGR execution condition has not just changed from not met to met), ECU 100 proceeds to step S20 and executes normal valve opening control for the HP-EGR valve 45.

[0049] On the other hand, if the determination in step S5 is YES and the EGR condition is met with the HP-EGR valve 45 in the fully closed position (immediately after the EGR execution condition has switched from not being met to being met), the ECU 100 determines whether the high exhaust gas energy condition is not met. The high exhaust gas energy condition is met when the exhaust energy is high and is not met when the exhaust energy is low. Specifically, it is determined that the high exhaust gas energy condition is met when any of the following conditions 1 to 4 is met. Condition 1: The engine load is equal to or greater than a predetermined judgment load. Condition 2: The exhaust pressure is equal to or greater than a predetermined judgment pressure. Condition 3: The exhaust temperature is equal to or higher than a predetermined judgment temperature. Condition 4: The engine speed is equal to or greater than a predetermined determination speed.

[0050] The ECU 100 determines that the condition 1 is met when the separately calculated required engine torque is equal to or greater than a predetermined judgment torque. The ECU 100 determines whether the above condition 2 is met based on the exhaust pressure detected by the exhaust pressure sensor SN4. The ECU 100 determines whether the above condition 3 is met based on the exhaust temperature detected by the exhaust temperature sensor SN5. The ECU 100 determines whether the above condition 4 is met based on the engine speed detected by the crank angle sensor SN1. The above judgment torque (judgment load), judgment pressure, judgment temperature, and first judgment speed are set in advance and stored in the ECU 100.

[0051] If the determination in step S5 is NO and the high exhaust gas energy condition is met due to the satisfaction of any one of the above conditions 1 to 4, the ECU 100 proceeds to step S20 and executes normal valve opening control on the HP-EGR valve 45.

[0052] On the other hand, if the determination in step S5 is YES and the high exhaust gas energy condition is not satisfied due to the non-satisfaction of any of the above conditions 1 to 4, the ECU 100 proceeds to step S7. In step S7, the ECU 100 determines whether the engine speed is equal to or higher than a predetermined lower limit speed. The lower limit speed is preset to a value lower than the above-mentioned determination speed and is stored in the ECU 100.

[0053] If the determination in step S7 is NO, that is, the engine speed is lower than the lower limit speed, the ECU 100 proceeds to step S20 and executes normal valve opening control on the HP-EGR valve 45.

[0054] On the other hand, if the determination in step S7 is YES and the engine speed is equal to or higher than the lower limit speed, the ECU 100 determines whether the excess concentration of the exhaust O2 concentration, which is the oxygen concentration of the exhaust, relative to the smoke guard is equal to or higher than a predetermined determination amount (step S8). That is, the ECU 100 determines whether the exhaust O2 concentration is equal to or higher than the value obtained by adding the determination amount to the smoke guard. The smoke guard is a lower limit value of the exhaust O2 concentration for reducing the smoke (soot) emitted from the engine body 1 to a predetermined value or less, and is set in advance and stored in the ECU 100. The ECU 100 calculates the excess concentration relative to the smoke guard by subtracting the smoke guard from the exhaust O2 concentration read in step S1, and determines whether this value is equal to or higher than the determination amount. The determination concentration is set in advance to a value greater than 0 and stored in the ECU 100. Here, the value obtained by adding the determination amount to the smoke guard corresponds to the "determined concentration" in the claims.

[0055] If the determination in step S8 is NO, that is, the excess concentration for the smoke guard is lower than the determination concentration, the ECU 100 proceeds to step S20 and executes normal valve opening control on the HP-EGR valve 45.

[0056] On the other hand, if the determination in step S8 is YES, that is, if the excess concentration for the smoke guard is equal to or greater than the determination amount, the ECU 100 executes the over-turn control (step S9).

[0057] Overturn control is a control for removing deposits from the periphery Z (FIG. 2) of the HP-EGR valve 45 to ensure proper opening and closing of the HP-EGR valve 45. When the HP-EGR valve 45 is fully closed, soot and other particles contained in the high-pressure EGR gas adhere to the periphery Z of the HP-EGR valve 45. If this soot and other particles become stuck, it becomes difficult for the HP-EGR valve 45 to open properly. Therefore, in this engine, overturn control is performed to remove deposits such as soot from the periphery Z (FIG. 2) of the HP-EGR valve 45.

[0058] FIG. 5 is a diagram showing the state of the HP-EGR valve 45 when overturn control is being executed. In FIG. 5, the arrow Y2 indicates the closing direction, and the arrow Y1 indicates the opening direction. The process proceeds to step S9, where the overturn control is executed, when the determination in step S5 is YES and the EGR execution condition is met with the HP-EGR valve 45 in the fully closed position. As a result, just before the overturn control is executed, the HP-EGR valve 45 is in the fully closed position, as shown in FIG. 5(a). When the overturn control is being executed, the ECU 100 rotates the HP-EGR valve 45 from the fully closed position shown in FIG. 5(a) in the closing direction Y2 as shown in FIG. 5(b) (by driving the HP-EGR motor 44M to rotate in the closing direction Y2) to open the HP-EGR valve 45. Thereafter, as shown in FIG. 5(c), the ECU 100 rotates the HP-EGR valve 45 in the opening direction Y1 (by driving the HP-EGR motor 44M to rotate in the opening direction Y1) and returns it to the fully closed position, and then, as shown in FIG. 5(d), rotates it further in the opening direction Y1 to set the opening degree of the HP-EGR valve 45 to an opening degree that achieves the target EGR rate set in step S3.

[0059] Thus, in the overturn control, the ECU 100 first rotates the HP-EGR valve 45 in the closing direction from the fully closed position to open the valve, and then rotates it in the opening direction to an opening degree that achieves the target EGR rate set in step S3. Specifically, the ECU 100 drives the HP-EGR motor 45M so that the opening degree of the HP-EGR valve 45 in the closing direction becomes the closing-side opening degree that is set and stored in advance. Also, as in step S20, the ECU 100 sets a target EGR opening degree, which is the opening degree of the HP-EGR valve 45 that achieves the target EGR rate set in step S3, and after rotating the HP-EGR valve 45 in the closing direction, drives the HP-EGR motor 45M so that the opening degree of the HP-EGR valve 45 becomes this target EGR opening degree.

[0060] After the overturn control is executed, the ECU 100 counts up the number of times of overturn control (adds 1 to the number of times of overturn control), and returns to the step S1 where the control is ended.

[0061] (Changes in EGR opening over time) FIG. 6 is a schematic diagram showing the time changes of the target EGR rate and EGR opening degree when normal valve opening control is executed. FIG. 7 is a schematic diagram showing the time changes of the target EGR rate and EGR opening degree when overturn control is executed. In the EGR opening graphs of FIG. 6 and FIG. 7, the solid line indicates the actual EGR opening degree, which is the actual EGR opening degree, and the dashed line indicates the target EGR opening degree. FIG. 6 shows an example in which the EGR execution condition is satisfied around time t1 and the target EGR rate increases at time t1. The figure also shows an example in which the EGR execution condition switches from not being satisfied to being satisfied at time t10, and the target EGR rate increases from 0 at time t10.

[0062] As shown in Fig. 6, when normal valve opening control is being performed, if the target EGR rate increases at time t1, the HP-EGR valve 45 is not rotated in the closing direction but is rotated in the opening direction toward the target EGR opening. In contrast, as shown in Fig. 7, when overturn control is being performed, the HP-EGR valve 45 is first rotated in the closing direction at time t10. Then, at time t11, when the opening degree of the HP-EGR valve 45 (opening degree in the closing direction) reaches the closing-side opening degree, the HP-EGR valve 45 is then rotated in the opening direction. Specifically, even after the opening degree of the HP-EGR valve 45 becomes 0 at time t12 and the HP-EGR valve 45 returns to the fully closed position, the HP-EGR valve 45 continues to be rotated in the opening direction toward the target EGR opening.

[0063] (action, etc.) As described above, in the above embodiment, when the EGR execution condition is satisfied while the HP-EGR valve 45 is in the fully closed position, and the HP-EGR valve 45 is opened when the EGR execution condition changes from not satisfied to satisfied, the HP-EGR valve 45 is rotated from the fully closed position in the closing direction to open, and then the HP-EGR valve 45 is rotated in the opening direction until the opening degree reaches the target EGR opening degree. Specifically, the HP-EGR valve 45 is rotated from the fully closed position in the closing direction, returned to the fully closed position, and then rotated in the opening direction toward the target EGR opening degree. This allows deposits around the HP-EGR valve 45 to be scraped off and removed by the periphery of the HP-EGR valve 45 or the inner circumferential surface of the HP-EGR passage 44A. This ensures proper opening and closing of the HP-EGR valve 45.

[0064] Moreover, in the above-described over-turn control, the number of times that the HP-EGR valve 45 passes through the fully closed position is limited to one. Therefore, the execution of the over-turn control can suppress pulsation of the high-pressure EGR gas in the HP-EGR passage 44A, and the high-pressure EGR gas can be appropriately introduced into the intake passage 30 and the combustion chamber 6.

[0065] Furthermore, since the over-turn control is performed when the EGR execution condition is satisfied, it is possible to prevent unnecessary high-pressure EGR gas from being introduced into the intake passage. Specifically, if the over-turn control is performed to open the HP-EGR valve 45 when the EGR execution condition is not satisfied, high-pressure EGR gas will be introduced into the intake passage 30 and the combustion chamber 6, causing the gas composition in the combustion chamber 6 to deviate from the appropriate composition. In contrast, if the over-turn control is performed when the EGR execution condition is satisfied and it is desired to introduce high-pressure EGR gas into the intake passage and the combustion chamber 6, it is possible to prevent the gas composition in the combustion chamber 6 from deviating from the appropriate composition.

[0066] Furthermore, since the overturn control is performed when the EGR execution condition is satisfied with the HP-EGR valve 45 in the fully closed position, pulsation of high-pressure EGR gas in the HP-EGR passage 44A can be more reliably suppressed. Specifically, when the HP-EGR valve 45 is open due to the satisfaction of the EGR execution condition and high-pressure EGR gas is flowing through the HP-EGR passage 44A, if the HP-EGR valve 45 is rotated past the fully closed position, the flow of high-pressure EGR gas is temporarily stopped, which increases pulsation of the high-pressure EGR gas. In contrast, when the HP-EGR valve 45 is in the fully closed position, high-pressure EGR gas does not flow through the HP-EGR passage 44A, so by performing the overturn control at the above timing, pulsation of the high-pressure EGR gas can be suppressed.

[0067] When the exhaust energy is high, pulsation of the exhaust gas and high-pressure EGR gas is likely to occur as the HP-EGR valve 45 opens and closes. In contrast, in the above embodiment, even when the EGR execution condition is met with the HP-EGR valve 45 in the fully closed position, normal valve opening control is executed for the HP-EGR valve 45 if the exhaust energy is high enough to meet the high exhaust gas energy condition. In other words, when the high exhaust gas energy condition is met, overturn control is prohibited. This more reliably prevents pulsation of the high-pressure EGR gas.

[0068] Furthermore, when the exhaust O2 concentration is low, the amount of soot generated tends to become excessive as the amount of high-pressure EGR gas introduced into the combustion chamber 6 increases. In contrast, in the above embodiment, when the excess exhaust O2 concentration relative to the smoke guard is lower than the determination amount and the exhaust O2 concentration is lower than the value obtained by adding the determination amount to the smoke guard, normal valve opening control is executed for the HP-EGR valve 45. In other words, when the excess exhaust O2 concentration relative to the smoke guard is lower than the determination amount, overturn control is prohibited. Therefore, in the above case, it is possible to reliably prevent the high-pressure EGR gas from pulsating and increasing the amount of high-pressure EGR gas introduced into the combustion chamber 6, and it is possible to reliably prevent the amount of gas soot generated from becoming excessive.

[0069] Furthermore, when the engine speed is low, exhaust performance, combustion noise, and the like are likely to fluctuate as the amount of high-pressure EGR gas introduced into the combustion chamber 6 increases or decreases. In contrast, in the above embodiment, when the engine speed is lower than the lower limit speed, normal valve opening control is executed for the HP-EGR valve 45, that is, the over-turn control is prohibited, and a situation in which the high-pressure EGR gas pulsates and the amount of high-pressure EGR gas introduced into the combustion chamber 6 increases or decreases is avoided. Therefore, when the engine speed is low, it is possible to reliably prevent the exhaust performance, combustion noise, and the like from deteriorating due to the influence of the over-turn control.

[0070] Furthermore, the HP-EGR device 44 reduces the travel distance of EGR gas from the exhaust passage 40 to the intake passage 30 compared to the LP-EGR device 50. Therefore, according to the above embodiment, by including the HP-EGR device 44, an appropriate amount of EGR gas can be recirculated to the intake passage at more appropriate timing. However, the HP-EGR passage 44A is connected to the exhaust passage 40 upstream of the turbine 48, and the pressure in the exhaust passage 40 upstream of the turbine 48 is relatively high. Therefore, in the HP-EGR device 44, pulsation of EGR gas (high-pressure EGR gas) is likely to occur when the HP-EGR valve 45 is opened and closed. In contrast, in the above embodiment, pulsation of high-pressure EGR gas is suppressed when the overturn control is performed, as described above. Therefore, according to the above embodiment, the overturn control is performed to remove deposits from the HP-EGR valve 45, and high-pressure EGR gas can be recirculated to the intake passage at more appropriate timing.

[0071] (Variation) In the above embodiment, the case where the target of the over-turn control is the HP-EGR valve 45 has been described. However, the above control may be applied to an engine that does not have the HP-EGR device 44, and the target of the over-turn control may be the LP-EGR valve 53.

[0072] In the above embodiment, the condition 1 included in the high exhaust gas energy condition is that the engine load (required engine torque) is equal to or greater than the judged load (judgement torque), but instead, the condition that the amount of fuel injected by the injector 15 is equal to or greater than a predetermined value may be used.

[0073] Furthermore, the high exhaust gas energy conditions are not limited to the above conditions 1 to 4, and other conditions may also be applied.

[0074] Furthermore, the specific configuration of the engine is not limited to that described above. For example, the number of cylinders of the engine is not limited to that described above. Furthermore, the engine is not limited to a diesel engine. [Explanation of symbols]

[0075] 10 Engine body 30 intake passage 44 HP-EGR device 44A HP-EGR passage 45 HP-EGR valve (EGR valve) 45M HP-EGR motor (EGR valve drive unit) 100 ECU (control unit) E-Engine

Claims

1. An EGR device provided in an engine including an engine body having cylinders formed therein, an intake passage through which intake air introduced into the cylinders flows, and an exhaust passage through which exhaust gas discharged from the cylinders flows, an EGR passage that communicates the exhaust passage and the intake passage and through which EGR gas flows; a butterfly-type EGR valve that rotates about a predetermined axis to open and close the EGR passage; an EGR valve drive device that rotationally drives the EGR valve; a control device that sets a target EGR opening, which is a target value of the opening of the EGR valve, based on an operating state of the engine, and controls the EGR valve drive device so that the EGR valve opens and the opening of the EGR valve becomes the target EGR opening when a predetermined EGR execution condition is met, When the direction in which the EGR valve rotates from the fully closed position to the fully open position is defined as an opening direction, and the opposite direction is defined as a closing direction, The control device The target EGR opening is set to an angle rotated in the opening direction from a fully closed position of the EGR valve, an EGR device characterized in that, when the EGR valve, which is in a fully closed position, is opened toward the target EGR opening degree as the EGR execution condition switches from not being satisfied to being satisfied, the EGR valve drive device first drives the EGR valve from the fully closed position in the closing direction, and then performs overturn control to drive the EGR valve in the opening direction until the opening degree of the EGR valve reaches the target EGR opening degree.

2. The EGR device according to claim 1, The engine further comprises a turbocharger including a compressor provided in the intake passage for supercharging intake air, and a turbine provided in the exhaust passage for receiving energy of the exhaust gas to drive the compressor, The EGR device is characterized in that the EGR passage communicates the exhaust passage upstream of the turbine with the intake passage downstream of the compressor.

3. The EGR device according to claim 1, The control device determines whether a predetermined high exhaust energy condition, in which the exhaust energy becomes high, is met based on the operating state of the engine, and prohibits the execution of the over-turn control if the high exhaust energy condition is met.

4. The EGR device according to claim 3, The control device determines that the high exhaust energy condition is met when one of the following conditions is met: the engine speed is higher than a predetermined judgment speed; the engine load is higher than a predetermined judgment load; the exhaust pressure, which is the pressure of the exhaust, is higher than a predetermined judgment pressure; or the exhaust temperature, which is the temperature of the exhaust, is higher than a predetermined judgment temperature.

5. The EGR device according to claim 1, The EGR device is characterized in that the control device prohibits execution of the over-turn control when an exhaust O2 concentration, which is an oxygen concentration in the exhaust passage, is lower than a predetermined judgment concentration.

6. The EGR device according to any one of claims 1 to 5, The EGR device is characterized in that the control device prohibits execution of the over-turn control when the engine speed is lower than a predetermined lower limit speed.

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