JP6595851B2 - Engine system - Google Patents

Description

  The present invention relates to an engine system.

  Some marine engine systems include an EGR (Exhaust Gas Recirculation) unit that recirculates exhaust gas discharged from the engine to the engine. By recirculating the exhaust gas (EGR gas) to the engine, the oxygen concentration of the scavenging gas is lowered and the combustion temperature is lowered. As a result, generation of thermal NOx due to the high combustion temperature can be suppressed.

  Increasing the amount of exhaust gas recirculated to the engine (EGR gas flow rate) can reduce NOx emissions, but if the EGR gas flow rate is increased too much, the oxygen concentration of the scavenging gas decreases and the engine The driving condition becomes unstable and in some cases there is a risk of misfire. Therefore, it is necessary to control the EGR gas flow rate so that the oxygen concentration of the scavenging gas becomes an appropriate value.

  Regarding the control of the EGR gas flow rate, the following Patent Document 1 discloses a method of controlling an EGR valve by combining a feedforward process based on engine load (feedforward control) and a feedback process based on oxygen concentration (feedback control). It is disclosed.

JP 2013-170520 A

  However, when the engine load fluctuates, various engine state variables fluctuate or fluctuate behind engine load fluctuations, so feedforward processing based on engine load does not function sufficiently, and in some cases scavenging There is also a risk that the oxygen concentration of the gas rapidly decreases and misfires occur. Even if the correction is performed by feedback processing based on the oxygen concentration, the feedback processing is sufficiently performed in a situation where the oxygen concentration of the scavenging gas rapidly decreases due to the structure of the EGR system, such as it takes time to increase the speed of the turbocharger. It is difficult to function.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine system capable of performing stable operation when the engine load fluctuates when controlling the EGR gas flow rate.

  An engine system according to an aspect of the present invention includes an engine main body to which scavenging gas including EGR gas and fresh air is supplied, and a part of the exhaust gas is taken in, and the taken-in exhaust gas is supplied to the engine main body as EGR gas. And an EGR unit having an EGR gas flow rate adjusting unit for adjusting the EGR gas flow rate, and a supercharger that is driven by the remaining exhaust gas that has not been taken into the EGR unit and boosts fresh air to supply the engine body And an EGR control unit that controls the EGR gas flow rate by transmitting a control signal to the EGR gas flow rate adjustment unit, and the EGR control unit includes a target engine speed, an engine load, a scavenging pressure, and a supercharging A plurality of engine state quantities are acquired from the machine speed, and individually from previously stored map data based on the acquired values of the respective engine state quantities Calculating suitable EGR gas flow rate, respectively, selected to the optimum EGR gas flow rate smallest among the plurality of discrete optimal EGR gas flow rate calculated to generate the control signal based on the optimum EGR gas flow rate chosen was.

  According to this configuration, the EGR gas flow rate is controlled based on the smallest one of the plurality of individual optimum EGR gas flow rates calculated based on each engine state quantity. For this reason, when the engine load fluctuates, the EGR gas flow rate is adjusted to be small in consideration of an engine state quantity that does not synchronize with the engine load fluctuation, such as fluctuating behind the engine load. As a result, the oxygen concentration of the scavenging gas is prevented from rapidly decreasing, and a stable operating state can be maintained even when the engine load fluctuates.

  In the engine system, the EGR control unit calculates a target oxygen concentration of the scavenging gas based on the acquired engine load, and a deviation between the target oxygen concentration and the acquired oxygen concentration of the scavenging gas becomes zero. Alternatively, a correction amount of the EGR gas flow rate approaching zero may be calculated, and the control signal may be generated based on a corrected EGR gas flow rate obtained by adding the correction amount to the optimum EGR gas flow rate.

  According to this configuration, since the feedback process is performed based on the oxygen concentration of the scavenging gas in the control of the EGR gas flow rate, the oxygen concentration can be reflected in the control of the EGR gas flow rate.

  In the engine system described above, the EGR control unit may set a feedback gain for adjusting the magnitude of the correction amount to be smaller than that at the time of engine load set or set to zero when the engine load fluctuates. .

  In the engine system described above, the EGR gas flow rate is controlled so that the oxygen concentration of the scavenging gas can be kept high when the engine load fluctuates. is there. In this case, the operating state may become unstable when the engine load fluctuates. Therefore, if the feedback gain is set to be small or set to zero when the engine load fluctuates as described above, the influence of the feedback processing is weakened and the driving state is prevented from becoming unstable when the engine load fluctuates. Can do.

  In the engine system, the EGR control unit generates the control signal so that the scavenging air pressure is within a predetermined pressure range and the supercharger rotational speed is within a predetermined rotational speed range. May be.

  In the engine system described above, since the supercharger is driven by the remaining exhaust gas that has not been taken into the EGR unit, the flow rate of the exhaust gas supplied to the supercharger also varies as the EGR gas flow rate varies. For example, when the EGR gas flow rate increases, the flow rate of the exhaust gas supplied to the supercharger decreases and the rotational speed of the supercharger decreases. In this case, as a result of not being able to sufficiently increase the fresh air, the scavenging pressure is lowered, the operation state becomes unstable, and in some cases, there is a risk of misfire. On the other hand, when the EGR gas flow rate decreases, the flow rate of the scavenging gas supplied to the supercharger increases, the rotation speed of the supercharger increases, and the scavenging pressure rises. In this case, there is a possibility that the supercharger will be excessively rotated and damaged, and the maximum in-cylinder pressure of the engine body may be increased and the engine body may be damaged. Therefore, as described above, if the control signal is generated so that the scavenging air pressure is within the predetermined pressure range and the supercharger rotational speed is within the predetermined rotational speed range, Misfire, damage to the turbocharger, and damage to the engine body can be prevented.

  As described above, according to the engine system described above, stable operation can be performed when the engine load fluctuates when controlling the EGR gas flow rate.

FIG. 1 is a schematic configuration diagram of the entire engine system. FIG. 2 is a block diagram of a control system of the engine system. FIG. 3 is a flowchart of control by the EGR control unit. FIG. 4 is a schematic configuration diagram of an entire engine system according to a modification.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Below, the same code | symbol is attached | subjected to the element which is the same or it corresponds through all the drawings, and the overlapping description is abbreviate | omitted.

<Overall configuration of engine system>
First, the overall configuration of the engine system 100 will be described. FIG. 1 is a schematic configuration diagram of the entire engine system 100. In FIG. 1, a thick broken line indicates the flow of exhaust gas (EGR gas), and a thick solid line indicates the flow of scavenging gas. The engine system 100 includes an engine main body 10, a scavenging pipe 20, an exhaust pipe 30, a supercharger 40, and an EGR unit 50.

  The engine body 10 of the present embodiment is a main propulsion device for a ship and is a large two-stroke diesel engine. However, the engine body 10 may be a four-stroke engine or a gas engine or a dual fuel engine. Note that “supplying air” in a four-stroke engine is synonymous with “scavenging” in the present invention. The engine body 10 has a plurality of cylinders 11, and the pistons 12 are driven by the explosive combustion of fuel in each cylinder 11. The engine body 10 is provided with a fuel supply device 13 for supplying fuel to the cylinder 11 and an engine tachometer 14 for measuring the engine speed (both are shown in FIG. 2).

  The scavenging pipe 20 temporarily stores the scavenging gas and supplies the stored scavenging gas to each cylinder 11 of the engine body 10. The scavenging pipe 20 is supplied with fresh air from the supercharger 40 and EGR gas from the EGR unit 50 via the scavenging pipe 21. The above-described scavenging gas includes this fresh air and EGR gas. The scavenging tube 20 includes a scavenging pressure gauge 22 that measures scavenging pressure (scavenging gas pressure), and an oxygen concentration meter 23 that measures the oxygen concentration (hereinafter simply referred to as “oxygen concentration”) of the scavenging gas in the scavenging tube 20. Is provided.

  The exhaust pipe 30 temporarily stores the exhaust gas discharged from each cylinder 11 of the engine body 10, and supplies the stored exhaust gas to the turbine 41 and the EGR unit 50 of the supercharger 40 via the exhaust pipe 31. . In the present embodiment, a part of the exhaust gas is taken into the EGR unit 50, and the remaining exhaust gas that has not been taken into the EGR unit 50 is all supplied to the turbine 41 of the supercharger 40.

  The supercharger 40 has a turbine 41 and a blower 42. Exhaust gas is supplied to the turbine 41 via the exhaust pipe 31, and the turbine 41 is rotated by the energy of the exhaust gas. The turbine 41 and the blower 42 are connected by a connecting shaft 43, and the blower 42 rotates as the turbine 41 rotates. When the blower 42 rotates, the air (fresh air) taken from outside is increased in pressure, and the increased new air is supplied to the engine body 10 via the scavenging pipe 21 and the scavenging pipe 20. The supercharger 40 is provided with a supercharger tachometer 44 that measures the rotation speed of the supercharger 40. Further, the scavenging pipe 21 is provided with an air cooler 45 for cooling the boosted fresh air.

  The EGR unit 50 takes in a part of the exhaust gas and supplies the taken-in exhaust gas to the engine body 10 via the scavenging pipe 21 and the scavenging pipe 20. In the following, “EGR gas” means exhaust gas in the EGR unit 50 or exhaust gas that has passed through the EGR unit 50. The EGR unit 50 has an EGR pipe 51 that connects the exhaust pipe 31 and the scavenging pipe 21. In the EGR pipe 51, EGR gas flows from the exhaust pipe 31 toward the scavenging pipe 21. The EGR pipe 51 is provided with a scrubber 52, an EGR gas cooler 53, and an EGR blower 54 in this order from the exhaust pipe 31 side.

  The scrubber 52 is a device for cleaning the exhaust gas taken in. The engine body 10 of the present embodiment uses heavy oil as fuel, and the exhaust gas contains SOx and a large amount of soot. If the taken-in exhaust gas is returned to the engine body 10 without washing, SOx and soot contained in the exhaust gas adversely affect the engine body 10. Therefore, the scrubber 52 removes SOx and soot from the exhaust gas. As a method of cleaning exhaust gas, there are a method of passing exhaust gas in the cleaning water, a method of injecting cleaning water into the exhaust gas, and a method of passing exhaust gas between members soaked with cleaning water. The method may be adopted.

  The EGR gas cooler 53 is a device that cools the exhaust gas taken in. In the present embodiment, the EGR gas cooler 53 is disposed on the upstream side of the EGR blower 54. Therefore, the exhaust gas cooled by the EGR gas cooler 53 has a higher density and a reduced volume flow rate. Thereby, the load of the EGR blower 54 can be reduced. The EGR gas cooler 53 may be disposed on the downstream side of the EGR blower 54 or may be disposed on the upstream side of the scrubber 52. Further, the EGR gas cooler 53 may be disposed at a plurality of locations of the EGR pipe 51.

  The EGR blower 54 is a device that boosts the exhaust gas taken in and adjusts the supply amount (EGR gas flow rate) of EGR gas supplied from the EGR unit 50 to the engine body 10. In the present embodiment, the EGR blower 54 corresponds to the “EGR gas flow rate adjusting unit” of the present invention. The EGR blower 54 of the present embodiment is a positive displacement blower, and the EGR gas flow rate can be adjusted only by controlling the rotational speed of the EGR blower 54.

<Control system configuration>
Next, the configuration of the control system of the engine system 100 will be described. FIG. 2 is a block diagram of a control system of engine system 100. As shown in FIG. 2, the engine system 100 includes a control device 60 that controls the entire engine system 100. The control device 60 is constituted by a CPU, a ROM, a RAM, and the like.

  The control device 60 is electrically connected to a driving operation panel 61, an engine tachometer 14, a scavenging barometer 22, an oxygen concentration meter 23, and a supercharger tachometer 44 that are operated by an operator. Based on the state signals transmitted from these devices, the control device 60 can perform various engine states such as target engine speed, engine speed (actual engine speed), scavenging air pressure, oxygen concentration, and supercharger speed. The amount can be acquired. Furthermore, the control device 60 performs various calculations based on the acquired various engine state quantities, and controls each part of the engine system 100. In the present embodiment, the control device 60 is electrically connected to the fuel supply device 13 and the EGR blower 54, and transmits a control signal to these devices based on the results of various calculations.

  Moreover, the control apparatus 60 has the rotation control part 62 and the EGR control part 63 as a functional structure. Of these, the rotation control unit 62 controls the engine speed. When the driver sets the target engine speed via the driving operation panel 61, the rotation control unit 62 acquires the target engine speed based on the state signal transmitted from the driving operation panel 61. Then, the rotation control unit 62 sends a control signal (fuel injection amount) to the combustion supply device 13 so that the deviation between the target engine speed and the engine speed (actual engine speed) acquired from the engine tachometer 14 becomes zero. ).

  On the other hand, the EGR control unit 63 transmits a control signal to the EGR blower 54 to control the EGR gas flow rate. FIG. 3 is a flowchart showing a flow of control by the EGR control unit 63. The control by the EGR control unit 63 includes a feed forward process, a feedback process, and a limit process. Hereinafter, the control by the EGR control unit 63 will be described with reference to FIG.

<Feed forward processing>
In the feedforward process, the process of feeding back the current oxygen concentration is not performed, and the optimum EGR gas flow rate is estimated based on data stored in advance.

  Steps S1 to S3 shown in FIG. 3 correspond to feedforward processing. When the control is started, the EGR control unit 63 first acquires the engine state quantity (step S1). The “engine state quantity” here is a value indicating the state of the engine system 100, and includes a target engine speed, engine load, scavenging pressure, supercharger speed, and oxygen concentration. The engine load can be calculated (estimated) based on the engine speed and the fuel injection amount, but may be calculated from other engine state amounts.

  Subsequently, the EGR control unit 63 calculates the individual optimum EGR gas flow rate from the map data stored in advance based on the acquired value of each engine state quantity (step S2). The EGR control unit 63 determines the relationship between the individual optimum EGR gas flow rate for each of the target engine speed, engine load, scavenging pressure, and turbocharger speed, excluding the oxygen concentration, from among the plurality of engine state quantities described above. Map data shown is stored. Based on the acquired engine state quantities and the corresponding map data, the individual optimum EGR gas flow rate is calculated.

  The map data can be created based on the operation data of the engine system 100 previously performed. To create the map data, first, at a certain engine load, the EGR gas flow rate is set so that the NOx emission amount is less than or equal to the reference value determined by the environmental standards and the fluctuation width of the engine load is less than or equal to a predetermined value. . Then, the EGR gas flow rate at that time is recorded as the individual optimum EGR gas flow rate, and each engine state quantity is recorded. If this is performed for each engine load, the relationship between each engine state quantity and the individual optimum EGR gas flow rate becomes clear, and map data can be created.

  In addition, since each map data is produced as mentioned above, even if it uses any engine state quantity, it seems that all the calculated individual optimal EGR gas flow rates become the same value. However, when the load applied to the engine main body 10 differs from the measurement time of the engine system 100 due to differences in ambient conditions (for example, atmospheric temperature, atmospheric pressure, sea wind speed, and wave height), or when the engine load fluctuates (for example, a certain engine In the transition period when shifting from a load to another engine load), the timing and rate of change of each engine state quantity do not match each other, and therefore the value of the individual optimum EGR gas quantity calculated for each engine state quantity is Different.

  Subsequently, the EGR control unit 63 selects the smallest one of the plurality of calculated individual optimum EGR gas flow rates as the optimum EGR gas flow rate (step S3). As will be described later, a control signal to be transmitted to the EGR blower 54 is generated based on the optimum EGR gas flow rate selected here, and the EGR gas flow rate is controlled. As described above, if the EGR gas flow rate is controlled based on the smallest one among the individual optimum EGR gas flow rates, the EGR gas flow rate is controlled to decrease when the engine load fluctuates, where the operation state tends to be unstable. Therefore, a high oxygen concentration can be maintained and the operation state can be prevented from becoming unstable.

<Feedback processing>
Next, feedback processing will be described. In the feedback process, correction is made by feeding back the oxygen concentration to the optimum EGR gas flow rate selected in the feedforward process. Note that the feedback process is a process for correcting the optimum EGR gas flow rate to the last, and the control of the EGR flow rate greatly depends on the optimum EGR gas flow rate.

  Steps S4 to S7 in FIG. 3 correspond to feedback processing. In step S4, the EGR control unit 63 calculates a target oxygen concentration. Specifically, the EGR control unit 63 stores map data indicating the relationship between the target oxygen concentration and the engine load, and calculates the target oxygen concentration based on the map data and the acquired engine load. The target oxygen concentration is an oxygen concentration at which the NOx emission amount is equal to or less than a reference value determined by environmental standards, and the engine load fluctuation is equal to or less than a predetermined value. This map data can also be created based on the operation data of the engine system 100 performed in advance.

  Subsequently, the EGR control unit 63 sets a feedback gain (step S5). The feedback gain is a constant for adjusting the magnitude of the correction amount described later. In the present embodiment, the feedback gain is set according to the operating state. Specifically, the feedback gain is set smaller when the engine load fluctuates than when the engine load is set. However, the feedback gain may be set to zero when the engine load fluctuates. “When engine load fluctuates” refers to when the amount of change in engine load per predetermined time is greater than or equal to a predetermined amount, and “when engine load is set” refers to when the amount of change in engine load per predetermined time is less than a predetermined amount. Say time.

  Subsequently, the EGR control unit 63 calculates the correction amount of the optimum EGR gas flow rate (step S6). Specifically, the correction amount of the EGR gas flow rate in which the deviation between the target oxygen concentration calculated in step S4 and the oxygen concentration (actual oxygen concentration) acquired from the oxygen concentration meter 23 becomes zero or approaches zero is set as a feedback gain. Calculate using. For the calculation of the correction amount, a feedback control calculation can be used.

  For example, when a proportional control (P control) calculation is used to calculate the correction amount, a value obtained by multiplying the deviation by a proportional gain can be used as the correction amount. In this case, the proportional gain corresponds to the feedback gain. In addition, when PID control calculation is used, integral gain and differential gain in addition to proportional gain correspond to feedback gain. As described above, since the feedback gain differs between the engine load fluctuation and the engine load settling time, even when the deviation is the same, the calculated correction amount differs between the engine load fluctuation time and the engine load settling time. It will be.

  Subsequently, the EGR control unit 63 adds the correction amount calculated in step S6 (a positive value for the increase amount and a negative value for the decrease amount) to the optimal EGR gas flow rate calculated in step S3, thereby correcting the EGR. A gas flow rate is calculated (step S7). By performing the feedback processing based on the oxygen concentration in this way, the EGR gas flow rate can be controlled to a more optimal value, and as a result, the reduction of NOx emission and the stability of the engine system 100 can both be achieved.

  In the present embodiment, the reason why the feedback gain is set smaller when the engine load varies than when the engine load is set is as follows. That is, in the feedforward process, the EGR gas flow rate is controlled so that the oxygen concentration of the scavenging gas can be secured high when the engine load varies. However, when the feedback process is performed, the oxygen concentration of the scavenging gas may be corrected to be low even when the engine load fluctuates, contrary to the intention of the feedforward process. Therefore, by setting a small feedback gain when the engine load fluctuates, the influence of the feedback processing is weakened, and the operation state is prevented from becoming unstable when the engine load fluctuates.

<Limit processing>
Next, the limit process will be described. In the limit process, the process is performed so that the EGR gas flow rate falls within a predetermined flow rate range.

  Steps S8 to S13 in FIG. 3 correspond to limit processing. In step S8, the EGR control unit 63 calculates an upper limit flow rate and a lower limit flow rate of the EGR gas flow rate. Here, in the present embodiment, all the exhaust gas that has not been taken in by the EGR unit 50 is supplied to the turbine 41 of the supercharger 40, so that the EGR gas flow rate directly affects the rotational speed of the supercharger 40. . For example, when the EGR gas flow rate increases too much, the scavenging pressure decreases due to a decrease in the rotational speed of the supercharger 40. As a result, the operating state becomes unstable and in some cases there is a risk of misfire. Therefore, in this embodiment, an upper limit flow rate of the EGR gas flow rate is provided.

  On the other hand, contrary to the above case, if the EGR gas flow rate becomes too small, the supercharger 40 may over-rotate and be damaged, and the scavenging air pressure rises and the in-cylinder pressure of the engine body 10 increases. There is a risk that the engine body 10 will be excessively raised and damaged. Therefore, in this embodiment, a lower limit flow rate of the EGR gas flow rate is provided. That is, in the present embodiment, the upper limit flow rate and the lower limit flow rate of the EGR gas flow rate are provided so that the scavenging air pressure is within a predetermined pressure range and the supercharger rotational speed is within the predetermined rotational speed range. ing.

  However, since the flow rate of the exhaust gas discharged from the engine body 10 varies depending on the engine load, the upper limit flow rate and the lower limit flow rate of the EGR gas flow rate need to be changed according to the operating conditions. Therefore, in this embodiment, the upper limit flow rate and the lower limit flow rate of the EGR gas flow rate are calculated in step S8. Calculation of the upper limit flow rate and the lower limit flow rate of the EGR gas flow rate can be performed based on previously stored map data and the acquired engine load.

  As a more direct method, the upper limit flow rate and lower limit flow rate of the EGR gas flow rate may be calculated based on scavenging air pressure and supercharger rotation. For example, the upper limit flow rate of the EGR gas flow is calculated based on the map data stored in advance and the acquired scavenging pressure, and the upper limit flow rate of the EGR gas flow is calculated based on the map data stored in advance and the acquired turbocharger rotation speed. The smaller value of the upper limit flow rates of the individually calculated EGR gas flow rates may be employed. Similarly, the lower limit flow rate of the EGR gas flow rate is calculated based on the map data stored in advance and the acquired scavenging pressure, and the lower limit flow rate of the EGR gas flow rate is calculated based on the map data stored in advance and the acquired turbocharger rotation speed. The larger value of the lower limit flow rates of the calculated EGR gas flow rates may be employed.

  Subsequently, the EGR control unit 63 determines whether or not the corrected EGR gas flow rate calculated in step S7 is smaller than the upper limit flow rate calculated in step S8 (step S9). If the EGR control unit 63 determines in step S9 that the corrected EGR gas flow rate is not smaller than the upper limit flow rate (is equal to or higher than the upper limit flow rate) (NO in step S9), the EGR control unit 63 sends a control signal corresponding to the upper limit flow rate to (Step S10). Thereby, the EGR blower 54 rotates at the rotation speed corresponding to the control signal, and the EGR gas flow rate is set to the upper limit flow rate. Therefore, it is possible to avoid an unstable driving state.

  On the other hand, if the EGR control unit 63 determines in step S9 that the corrected EGR gas flow rate is smaller than the upper limit flow rate (YES in step S9), whether or not the corrected EGR gas flow rate is larger than the lower limit flow rate calculated in step S8. Is determined (step S11). If the EGR control unit 63 determines in step S11 that the corrected EGR gas flow rate is not larger than the lower limit flow rate (below the lower limit flow rate) (NO in step S11), the EGR blower 54 sends a control signal corresponding to the lower limit flow rate. (Step S12). Thereby, the EGR blower 54 rotates at the rotation speed corresponding to the control signal, and the EGR gas flow rate is set to the lower limit flow rate. Therefore, damage to the supercharger 40 and the engine body 10 can be avoided.

  On the other hand, if the EGR control unit 63 determines that the corrected EGR gas flow rate is larger than the lower limit flow rate (YES in step S11), the EGR control unit 63 transmits a control signal corresponding to the corrected EGR gas flow rate to the EGR blower 54. As a result, the EGR blower 54 rotates at the rotation speed corresponding to the control signal, and the EGR flow rate is set to the corrected EGR gas flow rate. Since the corrected EGR gas flow rate is calculated as described above, when the engine load is set, the NOx emission amount is not more than the reference value determined by the environmental standards, and the fluctuation width of the engine load is not more than a predetermined value. The operating state is stable when the engine load fluctuates.

  The EGR control unit 63 returns to step S1 again after any of steps S10, S12, and S13, and repeats steps S1 to S13 described above.

<Modification>
In the above, the case where the EGR gas flow rate adjusting unit that adjusts the EGR gas flow rate is configured by the EGR blower 54 has been described. However, the EGR gas flow rate adjusting unit may be configured by equipment other than the EGR blower 54. The EGR gas flow rate adjustment unit may be configured by combining other devices.

  For example, as shown in FIG. 4, a bypass pipe 55 that connects the upstream portion of the EGR gas cooler 53 of the EGR pipe 51 and the downstream portion of the EGR blower 54 is provided, and the EGR gas flow rate adjustment that can adjust the opening degree is provided in the bypass pipe 55. The EGR gas flow rate adjusting unit may be configured by providing the valve 56 and combining the EGR blower 54 and the EGR gas flow rate adjusting valve 56. 4 may be directly provided in the EGR pipe 51 of the engine system 100 shown in FIG. In these cases, a control signal is transmitted from the control device 60 to one or both of the EGR blower 54 and the EGR gas flow rate adjustment valve 56 to control the EGR flow rate.

10 Engine body 40 Supercharger 50 EGR unit 54 EGR blower (EGR gas flow rate adjustment unit)
56 EGR gas flow rate adjustment valve (EGR gas flow rate adjustment part)
63 EGR control unit 100 engine system

Claims (4)

An engine body to which scavenging gas including EGR gas and fresh air is supplied;
An EGR unit that takes in a part of the exhaust gas, supplies the taken exhaust gas to the engine body as EGR gas, and has an EGR gas flow rate adjustment unit that adjusts the EGR gas flow rate;
A supercharger that is driven by the remaining exhaust gas that has not been taken into the EGR unit, boosts fresh air, and supplies it to the engine body;
An EGR control unit that controls the EGR gas flow rate by transmitting a control signal to the EGR gas flow rate adjustment unit,
The EGR control unit acquires a plurality of engine state quantities among a target engine speed, an engine load, a scavenging air pressure, and a supercharger speed, and stores a map stored in advance based on the acquired values of the engine state quantities. The individual optimum EGR gas flow rate is calculated for each engine state quantity from the data, the smallest one of the calculated individual optimum EGR gas flow rates is selected as the optimum EGR gas flow rate, and the above-mentioned based on the selected optimum EGR gas flow rate An engine system that generates control signals.   The EGR control unit calculates a target oxygen concentration of the scavenging gas based on the acquired engine load, and an EGR gas flow rate at which a deviation between the target oxygen concentration and the acquired oxygen concentration of the scavenging gas becomes zero or approaches zero. The engine system according to claim 1, wherein a correction amount is calculated, and the control signal is generated based on a corrected EGR gas flow rate obtained by adding the correction amount to the optimum EGR gas flow rate.   The engine system according to claim 2, wherein the EGR control unit sets a feedback gain that adjusts the magnitude of the correction amount to be smaller than that at the time of engine load stabilization or to zero when the engine load fluctuates.   The said EGR control part produces | generates the said control signal so that scavenging air pressure may be in a predetermined pressure range, and a supercharger rotation speed will be in a predetermined rotation speed range. The engine system according to any one of the items.

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