JP4229819B2 - Engine control system for construction machinery - Google Patents

Description

  The present invention relates to an engine control system for a construction machine such as a hydraulic excavator, and more particularly to a construction machine that can meet exhaust gas regulations by reducing NOx (nitrogen oxide), PM (particulate suspended matter), and black smoke. The present invention relates to an engine control system.

  In general, a hydraulic excavator is equipped with a diesel engine as a power source, and a boom, an arm, a bucket, and the like are operated using a hydraulic pump mounted on the diesel engine as a drive source to perform various operations.

Diesel engines are concerned with the emission of harmful components into the air, and while regulations on exhaust emissions are being strengthened, various regulations-compliant technologies have been adopted. As one of the techniques, a so-called EGR (Exhaust Gas Recirculation) system is known in which inactive exhaust gas is recirculated to the intake pipe in order to suppress generation of NOx that is a harmful component in exhaust gas ( For example, see Patent Document 1).
JP-A-6-147024.

  The EGR system as found in the invention described in Patent Document 1 is employed for the purpose of lowering the combustion temperature in order to reduce NOx. Since NOx is generated more in a state where the combustion temperature is high, EGR control is considered to be effective in a steady load state (a load state generally found in a vehicle) in which the load on the engine is high and stably applied.

  However, in a construction machine in which the load on the engine is constantly changing rapidly, EGR control is accompanied by a deterioration in combustion efficiency, so that NOx is replaced and PM and black smoke are forced to increase. In other words, when the combustion temperature is high (close to complete combustion), the amount of NOx is large and the amount of PM / black smoke is small. Conversely, when the combustion temperature is low (incomplete combustion), the amount of NOx is small and the amount of PM / black smoke increases. Thus, there is a so-called trade-off relationship in which if one is pursued, the other must be sacrificed.

  Therefore, a technical problem to be solved in order to eliminate the trade-off relationship between NOx and PM / black smoke in the engine arises, and the present invention aims to solve this problem.

The present invention has been proposed to achieve the above object, and the present invention relates to an engine, a hydraulic pump driven by the engine, a hydraulic actuator driven by a discharge pressure from the hydraulic pump, EGR means for recirculating the exhaust gas to the combustion chamber, the EGR means detects a load change of the engine, and the engine rapidly increases from a no-load idle operation to a state of low load operation and medium load operation. When switching to load operation, or when suddenly exceeding the state of medium load operation from low load operation to high load operation, the amount of exhaust gas fed into the combustion chamber is gradually increased to a steady amount. on the contrary, when switched to a state of low load operation beyond the state of the middle load operation from the high load operation, off some have the exhaust gas fed into the combustion chamber to instantaneously sounds in low flow In the construction machine of the engine control system to control in this way,
There is provided an engine control system for a construction machine, wherein the EGR means is configured to detect a load fluctuation of the engine from a discharge pressure of the hydraulic pump.

  According to this configuration, when the engine load fluctuation is easily detected from the discharge pressure of the hydraulic pump, the combustion chamber has a high combustion temperature. By sending exhaust gas, generation of NOx can be suppressed. On the other hand, when the combustion temperature is low and NOx is small, but PM and graphite are exhausted, a sudden load change (low load to high load) causes exhaust gas to be gradually fed into the combustion chamber.・ The discharge of graphite can be reduced.

Since the present invention can easily detect engine load fluctuations from the discharge pressure of the hydraulic pump, it can reduce both NOx generated when the combustion temperature is high and PM / graphite generated during sudden load fluctuations. Can do.

In order to achieve the purpose of eliminating the trade-off relationship between NOx and PM / black smoke in an engine, an engine, a hydraulic pump driven by the engine, and a hydraulic actuator driven by discharge pressure from the hydraulic pump, EGR means for recirculating the exhaust gas of the engine to the combustion chamber, the EGR means detects a load fluctuation of the engine, and the engine exceeds a state of low load operation and medium load operation from no-load idle operation When the engine is suddenly switched to high-load operation, or when it suddenly exceeds the state of medium-load operation from low-load operation and becomes high-load operation, the amount of the exhaust gas fed into the combustion chamber is reduced to a steady amount. When the exhaust gas gradually increases and conversely switches from the high load operation to the low load operation state beyond the medium load operation state, the exhaust gas fed into the combustion chamber is reduced. Sometimes off some stomach In a construction machine engine control system for controlling so that the low flow rate,
This is realized by providing an engine control system for a construction machine, wherein the EGR means is configured to detect a load fluctuation of the engine from a discharge pressure of the hydraulic pump.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The technical matters related to the present invention will be described at the same time. FIG. 1 shows a hydraulic excavator as a construction machine to which the present invention is applied. In the hydraulic excavator 10, an upper swing body 13 is rotatably mounted on a lower traveling body 11 via a swing mechanism 12. The upper swing body 13 is provided with a cab 14 on one front side thereof, and a boom 15 is attached to the front center portion so as to be able to be raised and lowered. An arm 16 is attached to the tip of the boom 15 so as to be rotatable up and down, and a bucket 17 is attached to the tip of the arm 16.

  FIG. 2 is a configuration block diagram of an engine control system applicable to the hydraulic excavator 10 of FIG. 2, the engine control system of the present embodiment includes an engine 21 that drives the excavator 10, a hydraulic pump 22 that is connected to the power line of the engine 21, an EGR control unit 23, and an actual rotational speed sensor. 26, a supercharging pressure sensor 27, and a pump discharge pressure sensor 28.

  The engine 21 is a diesel engine in this embodiment, and the excavator 10 travels using the engine 21 as a drive source. Although not shown, the engine 21 is provided with a turbocharger.

  The hydraulic pump 22 drives an actuator (not shown) including hydraulic cylinders that operate the boom 15, the arm, and the bucket 17, and operates under the driving force of the engine 21.

  The EGR control unit 23 functions as a control calculation unit including a microcomputer (commonly called “microcomputer”), and includes an engine controller 24 that controls the drive of the engine 21 and an excavator controller 25 that controls the hydraulic system. The EGR control unit 23 receives a pump discharge pressure signal from the pump discharge sensor 28, an engine actual speed signal from the actual speed sensor 26, and a turbo boost pressure signal from the boost pressure sensor 27. The engine controller 24 and the excavator controller 25 are each caused to perform predetermined control in accordance with a control procedure programmed in advance.

The EGR control by the EGR control unit 23 detects a load change of the engine 21 and the engine 21 is suddenly switched from a no-load idle operation to a low load operation and a medium load operation to a high load operation. Or when the load changes from low load operation to high load operation that suddenly exceeds the state of medium load operation, gradually increase the amount of exhaust gas sent to the combustion chamber to a steady amount, and conversely, high load operation when switched to the state of low load operation beyond the state of the middle load operation from the off some have the exhaust gas fed into the combustion chamber to instantaneously so that the low flow rate, by controlling in accordance with the load, The trade-off relationship between NOx generated when the combustion temperature is high and PM / graphite generated during a sudden load change is eliminated.

  Hereinafter, a specific example of EGR control by the EGR control unit 23 will be described with reference to FIGS.

(Specific example 1: See FIG. 3)
Specific example 1 is a case where the EGR control unit 23 detects the state of engine load fluctuation from a pump discharge pressure signal obtained from the pump discharge pressure sensor 28. FIG. 3 shows the signal waveform of the hydraulic pump 22 in correspondence with the waveform of the EGR amount. The horizontal axis of (a) is the time t, the vertical axis is the change in the pump discharge pressure P with the time t, The horizontal axis of (b) shows time t, and the vertical axis shows the change in the EGR amount Q with time t.

In FIG. 3, the EGR control unit 23 reads the pump discharge pressure P of the hydraulic pump 22 from the pump discharge pressure signal, and compares it with the pressure preset in S1 in FIG. When the pressure exceeds the set pressure S1, it is determined that the vehicle is under a high load operation state, and steady-state EGR control is performed. On the other hand, when the pressure is lower than the set pressure S1, it is determined that the high load operation is switched to the low load operation, and the EGR control is instantaneously turned off (off) to stop sending exhaust gas into the combustion chamber of the engine 21. When the set pressure S1 or less exceeds the set pressure S1, it is determined that the low load operation is switched to the high load operation state, and the EGR amount (exhaust gas amount) is gradually increased to a steady amount.

That is, in FIG. 3, in the time regions T1, T3, and T5, the pump discharge pressure P is in a low load state, that is, a state equal to or lower than the set pressure S1, and therefore the EGR control is OFF. Further, FIG. 3B shows that EGR (exhaust gas) is instantaneously turned off when entering the state of high load operation to low load operation (see time regions T3 and T5). Conversely, when entering the state of high load operation from low load operation, it can be seen that EGR gradually increases and returns to the steady EGR amount (time region T2, T2).
(See T4).

  Therefore, when EGR is controlled as in the first specific example, both NOx generated when the combustion temperature is high and PM / graphite generated when the combustion temperature is low and sudden load can be reduced.

(Specific example 2: see Fig. 4)
Specific example 2 is a case where the EGR control unit 23 detects the engine load fluctuation state from the turbo boost pressure signal obtained from the boost pressure sensor 27 and the pump discharge pressure signal obtained from the pump discharge pressure sensor 28. . FIG. 4 shows the signal waveform of the hydraulic pump 22, the signal waveform of the turbocharger (not shown), and the waveform of the EGR amount in correspondence with each other. Is the change in pump discharge pressure P with time t, the horizontal axis of (b) is time t, the vertical axis is the change of turbocharge pressure P with time t, and the horizontal axis of (c) is time t. The vertical axis represents the change in EGR amount with time t.

  In FIG. 4, the EGR control unit 23 reads the pump discharge pressure P from the pump discharge pressure signal and also reads the turbo boost pressure P from the turbo boost pressure signal, and is set as indicated by S2 in FIG. 4B. Compare with the pressure. When the pressure exceeds the set pressure S2, it is determined that the vehicle is in a high load operation state, and a steady amount of EGR control is performed. On the other hand, when the pressure becomes lower than the set pressure S2, it is determined that the high load operation has been switched to the low load operation state, and the EGR control is instantaneously turned off (off) to stop sending exhaust gas into the combustion chamber of the engine 21. When the set pressure S2 or less is exceeded and the set pressure S2 is exceeded, it is determined that the low load operation is switched to the high load operation state, and the EGR amount is gradually increased to the steady amount.

  That is, in FIG. 4, in the time regions T1, T3, T5, the pump discharge pressure P is in a low load, that is, a state equal to or lower than the set pressure S2, and therefore the EGR control is OFF. Also, from FIG. 4C, it can be seen that EGR is turned off instantaneously when entering the state of high load operation to low load operation (see time regions T3 and T5). On the contrary, when entering the state of high load operation from low load operation, it can be seen that EGR gradually increases and returns to the steady EGR amount (see time regions T2 and T4).

  Therefore, when EGR is controlled as in Example 2, both NOx generated when the combustion temperature is high and PM / graphite generated when the combustion temperature is low and sudden load are reduced as in Example 1. be able to.

(Specific example 3: See FIG. 5)
Specific example 3 is a case where the EGR control unit 23 detects the engine load fluctuation state from the pump discharge pressure signal and the actual engine speed obtained from the actual engine speed sensor 26. FIG. 5 shows the signal waveform of the hydraulic pump 22, the signal waveform of the engine speed, and the waveform of the EGR amount in correspondence with each other. The horizontal axis of (a) is time t and the vertical axis is time t. Changes in pump discharge pressure P, time t on the horizontal axis of (b), change in engine speed N with time t on the vertical axis, time t on the horizontal axis of (c), time t on the vertical axis The change of the EGR amount accompanying the is shown, respectively. In the engine speed (b), a target speed N0 is provided, and a set speed S3 obtained by subtracting a certain speed α from the target speed N0 is provided.

  Then, in FIG. 5, the EGR control unit 23 reads the pump discharge pressure P from the pump discharge pressure signal, and also reads the actual engine speed N1 of the engine 21 from the engine actual engine speed signal, and compares it with the set engine speed S3. . When the set rotational speed S3 is exceeded, it is determined that the engine is in a high-load operation state, and steady-state EGR control is performed. On the other hand, when the rotation speed is lower than the set speed S3, it is determined that the high load operation is switched to the low load operation state, and the EGR control is instantaneously turned off to stop sending exhaust gas into the combustion chamber of the engine 21. . When the set rotational speed S3 is exceeded, it is determined that the low load operation is switched to the high load operation state, and the EGR amount is gradually increased to the steady amount. In FIG. 5, the time regions T0 and T5 are in a no-load state such as idling. Therefore, in this example, the EGR is set to be OFF even when there is no load.

In FIG. 5, in the time regions T1 and T3, the pump discharge pressure P is in a state of sudden load, that is, the set rotational speed S3 or less, and therefore the EGR control is OFF. Further, FIG. 5 (c) shows that EGR is instantaneously turned off when the low load operation state is entered from the high load operation (see time regions T3 and T5). On the contrary, when entering the state of high load operation from low load operation, it can be seen that EGR gradually increases and returns to the steady EGR amount (see time regions T2 and T4).

  Therefore, when the EGR is controlled as in the specific example 3, both NOx generated when the combustion temperature is high and PM / graphite generated when the combustion temperature is low and sudden load is applied as in the case of the specific examples 1 and 2. Can be reduced.

  It should be noted that the present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

The figure shows an embodiment of the present invention.
1 is an overall configuration diagram of a hydraulic excavator to which an engine control system according to the present invention is applied. The block diagram of a structure of an engine control system same as the above. A specific example 1 of EGR control in the system of the present invention is shown. (A) is a waveform diagram showing a change in pump discharge pressure in correspondence with time, and (b) a change in EGR amount in correspondence with time. Waveform diagram. FIG. 2 shows a specific example 2 of EGR control in the system of the present invention, where (a) is a waveform diagram showing a change in pump discharge pressure in correspondence with time, and (b) is a turbocharger pressure of a turbocharger. The waveform diagram which shows a change corresponding to time, (c) The waveform diagram which shows the change of the EGR amount corresponding to time. FIG. 3 shows a specific example 3 of EGR control in the system of the present invention, where (a) is a waveform diagram showing a change in the discharge pressure of the hydraulic pump in correspondence with time, and (b) is a change in the actual engine speed. FIG. 4 is a waveform diagram showing the time corresponding to the time, and (c) a waveform diagram showing the change in the EGR amount corresponding to the time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Engine 22 Hydraulic pump 23 EGR control part 24 Engine controller 25 Excavator controller 26 Actual rotation speed sensor 27 Supercharging pressure sensor 28 Pump discharge pressure sensor

Claims (1)

An engine, a hydraulic pump driven by the engine, a hydraulic actuator driven by a discharge pressure from the hydraulic pump, and an EGR means for returning the exhaust gas of the engine to a combustion chamber, wherein the EGR means When a load change is detected and the engine is suddenly switched from a no-load idle operation to a low-load operation and a medium-load operation to a high-load operation, or from a low-load operation to a medium-load operation When the engine is in a high load operation over the range, the amount of the exhaust gas fed into the combustion chamber is gradually increased to a steady amount, and conversely, the state of the low load operation is exceeded from the high load operation to the medium load operation state. to when switched, the off certain have the exhaust gas instantaneously feeding into the combustion chamber at the construction machine engine control system for controlling so that the low flow rate,
An engine control system for a construction machine, wherein the EGR means is configured to detect a load fluctuation of the engine from a discharge pressure of the hydraulic pump.

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