JP4109171B2 - Exhaust gas recirculation control device for work machine engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation control device for an engine of a work machine that is provided in a work machine such as a hydraulic excavator and has an EGR control valve that controls the flow rate of the exhaust gas of the engine.

  As this type of prior art, a pipe that leads fuel supplied from a fuel supply pump to an engine combustion chamber, that is, a supply line, an air supply pipe that leads air to an engine combustion chamber, that is, an air supply line, and exhausted from the engine An exhaust pipe that leads exhaust gas, that is, an exhaust line, and an EGR passage that connects one end to the air supply line and the other end to the exhaust line, and leads part of the exhaust gas guided by the exhaust line to the combustion chamber of the engine, that is, a bypass line And an EGR control valve that controls the flow rate of the exhaust gas flowing through the bypass line.

  In addition, this prior art includes an engine speed detector that detects the engine speed and a throttle opening detector that detects the amount of fuel injected into the engine, and responds to signals output from these detectors. And a control device for outputting a drive control signal for controlling the EGR control valve.

  The control device calculates the current engine load in accordance with the input engine speed and the fuel injection amount, and determines whether the calculated engine load is a high load, a medium load, or a low load. This determination is based on the engine speed, the engine output torque, and the engine horsepower curve. The load applied to the engine is set in a high load region and a medium / low load region on the horsepower curve of the engine and stored in the map.

This prior art also includes a NOx purification device on the exhaust gas discharge line, and a reducing agent supply amount adjusting valve for supplying a reducing agent for reducing NOx on the upstream side of the NOx purification device. When the load is high, the reducing agent supply amount adjustment valve receives a signal from the control device and controls the opening degree to adjust the reducing agent supply amount. At medium and low loads, the EGR control valve receives a signal from the control device. By controlling the opening of the EGR control valve, the flow rate of the exhaust gas recirculated to the bypass line is adjusted. (For example, refer to Patent Document 1).
JP-A-8-121154

  In the above-described prior art, when a load is applied to the engine, the engine speed fluctuates, and an appropriate amount of fuel corresponding to the load is injected by the control device. In the control of the EGR rate, which is the ratio of the exhaust gas flow rate with respect to the total intake amount of the engine, the engine speed and the fuel injection amount are used as control parameters to drive from the control device to an EGR rate suitable for the current engine load state. A control signal is output to the EGR control valve.

That is,
Engine load → Generation of engine speed fluctuation → Fuel injection amount control → EGR control valve control. Since the fuel injection amount control is a time lag, there is a difference between the current engine load state and EGR control valve control. In the meantime, there is a problem that a response delay occurs, and the engine output tends to decrease accordingly.

  In addition, in response to such a delay in response, a NOx purification device, a reducing agent supply amount adjustment valve, and the like are required in order to reduce the NOx component in the exhaust gas. The manufacturing cost of this exhaust gas recirculation control device is required. There is a problem that becomes high.

  The present invention has been made from the state of the prior art described above, and its purpose is an operation capable of realizing the control of the EGR control valve in accordance with the current engine load state without interposing the fuel injection amount control. An object of the present invention is to provide an exhaust gas recirculation control device for a machine engine.

  In order to achieve the above object, the present invention is provided in a work machine having an engine and a hydraulic drive unit including a variable displacement hydraulic pump driven by the engine, and supplies fuel to a combustion chamber of the engine. A line, an air supply line for guiding air to the combustion chamber of the engine, an exhaust line for guiding exhaust gas exhausted from the engine, one end connected to the air supply line, and the other end connected to the exhaust line, Exhaust gas recirculation control for an engine of a work machine comprising a bypass line that leads a part of the exhaust gas led to the exhaust line to the combustion chamber of the engine and an EGR control valve that controls the flow rate of the exhaust gas flowing through the bypass line In the system, the pump torque and engine maximum torque are obtained, and the engine load factor, which is the ratio of these pump torque and engine maximum torque, is obtained. From the relationship between the first calculation means, the preset engine load factor, the EGR rate that is the ratio of the recirculated exhaust gas flow rate to the total intake amount of the engine, and the engine load factor obtained by the first calculation means The second operation means for obtaining the corresponding EGR rate and the output means for outputting a drive control signal corresponding to the EGR rate obtained by the second operation means to the EGR control valve are provided.

  In the present invention configured as described above, a pump torque and an engine maximum torque corresponding to the current engine load are obtained by the first calculation means, and an engine load factor which is a ratio of these pump torque and engine maximum torque. Is required. Next, from the relationship between the engine load factor and the EGR rate set in advance by the second computing means and the engine load factor obtained by the first computing means, the corresponding EGR rate, that is, the current engine load state is obtained. A drive control signal corresponding to the corresponding EGR rate is output from the output means to the EGR control valve. As a result, the EGR control valve adjusts the flow rate of the exhaust gas flowing through the bypass line, that is, the flow rate of the exhaust gas recirculated to the combustion chamber of the engine.

  Therefore, the present invention can realize the control of the EGR control valve according to the current engine load without intervening the fuel injection amount control, and prevent the response delay of the EGR control valve to the current engine load state. Can do.

  According to the present invention, in the above invention, a tilt amount detecting means for detecting a tilt amount of the variable displacement hydraulic pump, a discharge pressure detecting means for detecting a discharge pressure of the variable displacement hydraulic pump, and the engine Control means including rotation speed detection means for detecting the rotation speed, the first calculation means, the second calculation means, and the output means, wherein the first calculation means is the tilt amount detection means. The pump torque is obtained on the basis of the amount of tilt detected at the discharge pressure and the discharge pressure detected by the discharge pressure detection means, and the relationship between the engine speed and the engine maximum torque set in advance is determined by the rotation speed detection means. From the detected engine speed, a corresponding engine maximum torque is obtained.

  According to the present invention, the control of the EGR control valve according to the current engine load state can be realized without intervening the fuel injection amount control, and the response delay of the EGR control valve with respect to the current engine load state can be prevented. As a result, it is possible to suppress a decrease in engine output that has conventionally occurred. In addition, since the response delay can be prevented as described above, the NOx component in the exhaust gas can be effectively reduced, thereby eliminating the need for a NOx purification device, a reducing agent supply amount adjusting valve, and the like that are conventionally required. The production cost of the entire device can be reduced.

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a best mode for carrying out an exhaust gas recirculation control device for an engine of a work machine according to the present invention will be described based on the drawings.

  FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of a control means provided in the embodiment shown in FIG. 1, and FIG. 3 is set in a storage unit of the control means shown in FIG. It is a figure which shows an example of the relationship between the engine load factor performed and an EGR rate.

  The present embodiment is provided in a work machine, for example, a hydraulic excavator. As shown in FIG. 1, the hydraulic excavator includes a hydraulic drive device 19 including an engine 1 and a variable displacement hydraulic pump 20 driven by the engine 1. It has.

  The present embodiment provided in such a hydraulic excavator includes a supply line 3 that leads fuel injected from the fuel injection pump 2 to the combustion chamber of the engine 1, an air supply line 5 that leads air to the combustion chamber of the engine 1, An exhaust line 6 for leading exhaust gas discharged from the engine 1, one end 13 connected to the air supply line 5, the other end 14 connected to the exhaust line 6, and a part 15 of the exhaust gas guided to the exhaust line 6 is connected to the engine 1. And a EGR control valve 17 that controls the flow rate of exhaust gas flowing through the bypass line 12. A cooler 16 that cools the exhaust gas is disposed in the bypass line 12.

  The turbocharger 4 is supercharged with respect to the engine 1, and the turbocharger 4 compresses the air taken in from the outside for supercharging and supplies it to the supply line 5. A centrifugal compressor 7 to be supplied and an exhaust turbine 10 which is disposed in the discharge line 6 and drives the centrifugal compressor 7 are provided. An intercooler 8 for cooling the compressed air is disposed in the air supply line 5. A muffler 11 is disposed on the exhaust line 10 downstream of the exhaust turbine 10.

  In the present embodiment, a discharge pressure detecting means 21 for detecting the discharge pressure 24 of the variable displacement hydraulic pump 20 provided in the hydraulic drive device 19, a tilt amount detecting means 22 for detecting the tilt amount 23 of the hydraulic pump 20, and The engine 1 has a rotation speed detection means 26 and inputs signals from the discharge pressure detection means 21, the tilt amount detection means 22, and the rotation speed detection means 26, and sends a drive control signal 27 to the EGR control valve 17. Control means 25 for outputting is provided.

  As shown in FIG. 2, the control means 25 includes an input means 25a for inputting signals from the detection means 21, 22, 26, an output means 25b for outputting a drive control signal to the EGR control valve 17, and a storage means 25c. And a central processing unit that performs arithmetic processing, that is, a CPU 25d.

  The storage means 25c stores the relationship shown in FIG. 3, that is, the load ratio (Tp / Te) of the engine 1 that is the ratio of the pump torque Tp and the engine maximum torque Te, and the recirculated exhaust gas with respect to the total intake amount (I) of the engine 1. A relationship with the EGR rate (G / I), which is the ratio of the gas flow rate G, is set. This relationship is such that the EGR rate (G / I) decreases as the load factor (Tp / Te) increases, and the EGR rate (G / I) increases as the load factor (Tp / Te) decreases. It has become a relationship. The relationship between the load factor (Tp / Te) and the EGR rate (G / I) of the engine 1 shown in FIG. 3 can be set empirically or experimentally.

  Further, the relationship between the rotational speed of the engine 1 and the engine maximum torque Te is also preset in the storage means 25c.

  The CPU 25d obtains the pump torque Tp based on the discharge pressure 24 detected by the discharge pressure detection means 21 and the tilt amount 23 detected by the tilt amount detection means 22, and the engine 1 stored in the storage means 25c. The engine maximum torque Te is obtained from the relationship between the engine speed and the engine maximum torque Te and the engine speed detected by the engine speed detection means 26, and the ratio between the pump torque Tp and the engine maximum torque Te is obtained. First calculation means 25d1 for obtaining a certain engine load factor (Tp / Te) is provided.

  Further, the CPU 25d is obtained by the relationship between the load factor (Tp / Te) and the EGR rate (G / I) of the engine 1 shown in FIG. 3 stored in the storage unit 25c and the first calculation unit 25d1 described above. The second calculation means 25d2 for obtaining the corresponding EGR rate (G / I) from the engine load factor (Tp / Te).

  A drive control signal corresponding to the EGR rate (G / I) obtained by the second calculating means 25d2 is outputted from the output means 25b to the EGR control valve 17.

  In this embodiment configured as above, the air compressed by the centrifugal compressor 7 is sent to the air supply line 5 by the drive of the turbocharger 4, cooled by the intercooler 8, and then the combustion chamber of the engine 1. To be supplied. Further, the fuel injected by the fuel injection pump 2 is supplied to the combustion chamber of the engine 1 through the supply line 3. The engine 1 is driven by the combustion of fuel in the combustion chamber, the exhaust gas is sent to the exhaust line 6, the exhaust turbine 10 is driven by this exhaust gas, and the exhaust gas is sent to the muffler 11.

  A part 15 of the exhaust gas sent to the discharge line 6 is sent to the bypass line 12, cooled by the cooler 16, and then given to the EGR control valve 17.

  The hydraulic pump 20 is driven by the driving of the engine 1 described above, and, for example, a boom, an arm, and a bucket (not shown) are operated by the pressure oil discharged from the hydraulic pump 20 to perform excavation work and the like.

  As the engine 1 and the hydraulic pump 20 are driven, the rotational speed of the engine 1 is detected by the rotational speed detection means 26, the discharge pressure 24 of the hydraulic pump 20 is detected by the discharge pressure detection means 21, and the hydraulic pump 20 is tilted. The amount 23 is detected by the tilt amount detection means 22 and is input to the input means 25 a of the control means 25.

  Accordingly, the first calculation means 25d1 of the CPU 25d performs a known calculation for obtaining the pump torque Tp based on the input tilt amount 23 and discharge pressure 24 of the hydraulic pump 20. Further, a calculation for obtaining the corresponding maximum engine torque Te is performed from the relationship between the engine speed and the engine maximum torque Te stored in the storage means 25e and the input engine speed. Further, calculation is performed to obtain the load factor (Tp / Te) of the engine 1, which is the ratio of the obtained pump torque Tp to the engine maximum torque Te.

  Subsequently, the second calculation means 25d2 of the CPU 25d determines the relationship between the load factor (Tp / Te) and the EGR rate (G / I) of the engine 1 of FIG. 3 stored in the storage means 25e and the first calculation described above. From the load factor (Tp / Te) of the engine 1 obtained by the means 25d1, an operation for obtaining the corresponding EGR rate (G / I) is performed. A drive control signal corresponding to the obtained EGR rate (G / I) is output to the EGR control valve 17 via the output means 25b.

  Thereby, the opening degree of the EGR control valve 17 is adjusted, and the flow rate of the exhaust gas recirculated to the combustion chamber of the engine 1 is controlled. When the load factor (Tp / Te) of the engine 1 is large, as shown in FIG. 3, the EGR rate (G / I) is small and the opening of the EGR control valve 17 is small, that is, the flow rate of the recirculated exhaust gas. Is controlled to be small. Conversely, when the load factor (Tp / Te) of the engine 1 is small, as shown in FIG. 3, the EGR rate (G / I) is large and the opening degree of the EGR control valve 17 is large, that is, recirculation. The flow rate of the exhaust gas is controlled to increase.

  According to the present embodiment configured as described above, the ratio of the pump torque Tp corresponding to the current load state of the engine 1 and the engine maximum torque Te is set by the first calculation means 25d1 and the second calculation means 25d2 of the CPU 25d. The EGR rate (G / I) corresponding to a certain engine load factor (Tp / Te) is obtained, and the EGR control valve 17 is controlled by a drive control signal corresponding to the EGR rate (G / I). The control of the EGR control valve 17 according to the current engine load state can be realized without interposing the fuel injection amount control. Therefore, a response delay of the EGR control valve 17 with respect to the current engine load state can be prevented, and a decrease in engine output accompanying such a response delay can be suppressed. Moreover, since a response delay can be prevented as described above, the NOx component in the exhaust gas can be effectively reduced. This eliminates the need for a Nox purification device, a reducing agent supply amount adjustment valve, and the like, and can reduce the manufacturing cost of the device.

  In the above embodiment, the relationship between the load factor (Tp / Te) of the engine 1 and the EGR rate (G / I) is stored in the storage means 25c as a linear relationship shown in FIG. Instead of such a linear relationship, a curved relationship may be set. In short, when the load factor (Tp / Te) of the engine 1 is large, the EGR rate (G / I) decreases, and when the load factor (Tp / Te) is small, the EGR rate (G / I) increases. What is necessary is just to set the relationship between the load factor (Tp / Te) of this engine 1 and the EGR rate (G / I) so that it may be maintained.

1 is a circuit diagram showing an embodiment of an exhaust gas recirculation control device for an engine of a work machine according to the present invention. FIG. It is a block diagram which shows the structure of the control means with which one Embodiment shown in FIG. 1 is equipped. It is a figure which shows an example of the relationship between the engine load factor set to the memory | storage part of the control means shown in FIG. 2, and an EGR rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 3 Supply line 5 Supply line 6 Exhaust line 12 Bypass line 13 One end 14 The other end 15 Some 17 EGR control valve 19 Hydraulic drive device 20 Variable displacement hydraulic pump 21 Discharge pressure detection means 22 Inclination amount detection means 23 Inclination Rolling amount 24 Discharge pressure 25 Control means 25a Input means 25b Output means 25c Storage means 25d CPU
25d1 first calculation means 25d2 second calculation means 26 rotational speed detection means 27 drive control signal

Claims (2)

Provided in a work machine having an engine and a hydraulic drive device including a variable displacement hydraulic pump driven by the engine,
A supply line that leads fuel to the combustion chamber of the engine, an air supply line that leads air to the combustion chamber of the engine, a discharge line that leads exhaust gas discharged from the combustion chamber of the engine, and one end of the air supply line A bypass line that is connected to the exhaust line at the other end and leads a part of the exhaust gas led to the exhaust line to the combustion chamber of the engine, and an EGR control valve that controls the flow rate of the exhaust gas flowing through the bypass line In an exhaust gas recirculation control device for an engine of a work machine equipped with
A first computing means for obtaining a pump torque and an engine maximum torque, and obtaining an engine load factor that is a ratio of the pump torque and the engine maximum torque;
From the relationship between the engine load factor set in advance and the EGR rate that is the ratio of the recirculated exhaust gas flow rate to the total intake amount of the engine, and the engine load factor obtained by the first calculation means, the corresponding EGR rate is Second calculating means to be obtained;
An exhaust gas recirculation control device for an engine of a work machine, comprising: output means for outputting a drive control signal corresponding to the EGR rate obtained by the second calculation means to the EGR control valve. In the invention of claim 1,
A tilt amount detecting means for detecting a tilt amount of the variable displacement hydraulic pump;
A discharge pressure detecting means for detecting a discharge pressure of the variable displacement hydraulic pump;
A rotational speed detection means for detecting the rotational speed of the engine;
A control means including the first calculation means, the second calculation means, and the output means;
The first calculation means obtains the pump torque based on the tilt amount detected by the tilt amount detection means and the discharge pressure detected by the discharge pressure detection means,
The exhaust gas recirculation of the engine of the working machine is characterized in that a corresponding engine maximum torque is obtained from the relationship between the engine speed and the engine maximum torque set in advance and the engine speed detected by the speed detecting means. Control device.

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