JP4387851B2 - Diesel engine start control device - Google Patents

Description

  The present invention relates to a start control device for a diesel engine that controls and accumulates fuel pressure to a target value and injects the accumulated fuel into a cylinder via an injector.

  Generally, a diesel engine is a compression ignition engine that compresses intake air, raises its temperature, and self-ignites by injecting fuel into the compressed high-temperature and high-pressure air. In comparison with the above, at the time of cold start or the like, the temperature rise of the compressed air is slow and the time to complete explosion tends to be long.

  For this reason, various techniques for improving the startability of a diesel engine have been proposed in the past. For example, in Patent Document 1, when at least one of a cooling water temperature and a fuel temperature is lower than a predetermined temperature, the start from the start is started. A technique for improving low-temperature startability is disclosed by performing split injection control in which a necessary fuel injection amount is divided into a plurality of times and injected until a complete explosion occurs.

Further, in Patent Document 2, the basic start fuel injection amount calculated according to the engine coolant temperature and the cranking rotation speed is decreased according to the elapsed time from the end of cranking to the complete explosion, so that A technique for preventing over-rich and improving startability by accelerating engine start-up is disclosed.
JP 11-1332078 A JP 2001-173490 A

  Patent Document 1 and Patent Document 2 described above all attempt to improve the startability by optimizing the fuel injection amount at the time of starting. However, in order to optimize the fuel injection amount, the fuel pressure is appropriate. It is necessary to assume that

  In general, the fuel pressure is preset to an optimum value for engine conditions such as engine speed, cooling water temperature, intake air temperature, etc. The value set in advance is not always the optimum value due to conditions such as variations and the properties of fuel and oil.

  In particular, at an extremely low temperature, since the setting range of the optimum fuel pressure capable of starting the engine is narrowed, slight variations in various parameters greatly affect the startability, which may make starting difficult. For example, as shown in FIG. 5, even when the actual fuel pressure is within the allowable range of the preset pressure value, the actual fuel pressure is outside the required fuel pressure, which is the optimum fuel pressure for starting the engine. In this case, after cranking is started at time T0, there is a possibility that the engine speed may rise and fall at a low speed equal to or lower than the complete explosion speed, and the complete explosion may not be achieved.

  The present invention has been made in view of the above circumstances, and provides a start control device for a diesel engine capable of improving startability by using the fuel pressure at the time of engine start as an optimum fuel pressure corresponding to the engine state. It is aimed.

  In order to achieve the above object, a diesel engine start control device according to the present invention controls a fuel pressure to a target value and accumulates the accumulated pressure, and injects the accumulated fuel into a cylinder via an injector. In the above, at the time of starting the engine, a means for detecting a violent explosion state in which the engine rotational speed continues below the set rotational speed for a set time before reaching the complete engine explosion state, and when the violent explosion state is detected, And means for gradually increasing or decreasing the pressure control target value in accordance with a change in the engine speed until the engine is completely detonated.

  The start control device for a diesel engine according to the present invention detects the target value of the fuel pressure when the engine is started, and when the engine speed is detected to be in a state where the engine speed remains below the set speed for a set time or longer. Until the explosion occurs, the fuel pressure is gradually increased or decreased according to the change in the engine speed, so that the optimum fuel pressure corresponding to the engine state can be obtained and the startability can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 relate to an embodiment of the present invention, FIG. 1 is an overall view of an engine control system, FIG. 2 is a flowchart of control processing at start-up, FIG. 3 is an explanatory diagram of a difference in average rotational speed, and FIG. These are time charts showing changes in rail pressure and engine speed when the engine is started.

  In FIG. 1, reference numeral 1 denotes a diesel engine (hereinafter simply referred to as “engine”). As an intake and exhaust system of the engine 1, an intake passage is connected to a combustion chamber 2 via an intake valve 3 and an exhaust valve 4. 5, the exhaust passage 6 is communicated.

  The intake passage 5 is bifurcated in the vicinity of the intake valve 3, and a vortex flow such as a swirl flow (lateral swirl flow) or a tumble flow (vertical swirl flow) is generated in one branch passage to cause gas flow in the cylinder. And an intake control valve 7 for intervening in order to stabilize combustion. A negative pressure operation type actuator 8 is connected to the intake control valve 7, and a negative pressure switching electromagnetic valve 9 controlled by an engine control unit (ECU) 50 is connected to the pressure introduction pipe of the actuator 8. ing. The negative pressure switching electromagnetic valve 9 switches the pressure introduced into the actuator 8 between a negative pressure from a negative pressure source (not shown) and atmospheric pressure, and the opening / closing operation of the intake control valve 7 is controlled.

  A throttle valve 10 is interposed upstream of the intake passage 5 where the branch passages are gathered. The throttle valve 10 is adjusted by the control signal from the ECU 50 to adjust the amount of intake air. An intake actuator 11 to be controlled is continuously provided. An intercooler 12 is interposed upstream of the throttle valve 10, and a compressor 13 a of the turbocharger 13 is interposed upstream of the intercooler 12. Further, an air cleaner 14 is interposed upstream of the compressor 13 a of the turbocharger 13, and an air flow meter 16 including an intake air temperature sensor 15 for detecting the intake air temperature is interposed downstream of the air cleaner 14. Yes.

  On the other hand, a turbine 13b of the turbocharger 13 is interposed in the exhaust passage 6 of the engine 1, and the exhaust gas that has passed through the turbine 13b is purified by a catalyst (not shown) and discharged. The exhaust passage 6 on the upstream side of the turbine 13b is connected to the intake passage 5 on the downstream side of the throttle valve 10 via an exhaust gas recirculation (EGR) passage 17, and the EGR amount is supplied to the EGR passage 17 by a control signal from the ECU 50. An EGR control valve 18 for controlling and an EGR cooler 19 for cooling the EGR gas are interposed.

  The turbocharger 13 is a variable nozzle turbocharger, for example, and the nozzle opening degree of the exhaust gas introduced into the turbine side is varied by the negative pressure actuated actuator 20. A negative pressure control electromagnetic valve 21 controlled by the ECU 50 is connected to the pressure introduction pipe of the actuator 20, and negative pressure from a negative pressure source (not shown) is regulated by the negative pressure control electromagnetic valve 21 to be supplied to the actuator 20. be introduced. Thereby, the nozzle opening on the turbine side of the turbocharger 13 is varied, the turbine rotational speed is varied, and the supercharging pressure is controlled.

  Next, the fuel injection system of the engine 1 will be described. The engine 1 employs a well-known common rail type fuel injection system, and an injector 25 controlled by the ECU 50 faces the combustion chamber 2. A glow plug 26 whose energization is controlled by a glow controller 27 is exposed near the injection nozzle of the injector 25 in the combustion chamber 2.

  The injector 25 is connected to a common rail 29 via a fuel pipe 28 branched to each cylinder, and a supply pump 30 that sucks up and pressurizes fuel from a fuel tank (not shown) is connected to the common rail 29. The fuel boosted to a high pressure by the supply pump 30 is accumulated in the common rail 29, and the high-pressure fuel is supplied to the injector 25 of each cylinder via the fuel pipe 28 to each cylinder.

  The supply pump 30 is provided with, for example, an inner cam type pressure feeding system and an intake amount adjustment method using an electromagnetic valve, and an intake adjustment electromagnetic valve 31 for adjusting the intake amount, and a fuel temperature sensor 32 for detecting a fuel temperature are provided in the main body. It is built in. A signal from the fuel temperature sensor 32 of the supply pump 30 is input to the ECU 50 together with a signal from the fuel pressure sensor 33 that detects the fuel pressure (rail pressure) in the common rail 29, and is processed together with signals from other sensors. . Then, the ECU 50 feedback-controls the discharge pressure of the supply pump 30, that is, the fuel pressure of the common rail 29, for example, to an optimum value according to the engine speed and load via the intake metering solenoid valve 31.

  Next, an electronic control system centering on the ECU 50 will be described. The ECU 50 includes a microcomputer and peripheral circuits. The ECU 50 faces the above-described intake air temperature sensor 15, air flow meter 16, fuel temperature sensor 32, fuel pressure sensor 33, and water jacket of the engine 1 to detect the temperature of the cooling water. A water temperature sensor 34, a crank angle sensor 35 for detecting the rotational position of the crankshaft 1a, an accelerator pedal sensor 36 for detecting the depression amount of the accelerator pedal, and other various sensors and switches (not shown) are input. Based on signals from these sensors and switches, the ECU 50 executes various engine controls such as fuel pressure control, fuel injection control, intake air control, supercharging pressure control, EGR control, etc., and determines the operating state of the engine 1. Maintain optimal condition.

  Further, the ECU 50 monitors the increase in the engine speed accompanying cranking at the time of engine start, and through the supply pump 30 so that the rail pressure of the common rail 29 becomes the required rail pressure that is the optimum fuel pressure for engine start. The rail pressure of the common rail 29 is controlled. Specifically, in a process in which the engine is cranked and the engine speed increases, a state in which the engine speed is equal to or lower than a set speed (for example, 300 rpm) continues for a set time (for example, 10 sec) (hereinafter, “turbulence”). The fuel pressure control target value is changed from the value stored in the ECU 50 in advance and the engine speed is changed according to the change in the engine speed. Gradually increase or decrease the set value.

  The process for controlling the fuel pressure at the time of starting is performed in the program process of the ECU 50 shown in FIG. Hereinafter, description will be made based on the flowchart of FIG.

  The start time control process shown in FIG. 2 is a process that is executed at the time of engine start until the engine is completely exploded through cranking. First, in step S1, it is determined whether or not a starter signal from a starter switch (not shown) is ON, and it is determined whether or not an engine start state has been detected.

  As a result, if the starter signal is OFF and the engine is stopped before starting the engine, or if the engine is already in a normal operation state after complete explosion, the system waits in step S1, and if the starter signal is ON, that is, If the engine is cranked and is in the starting state, the process proceeds to step S2. In step S2, it is checked whether or not the engine speed is a set explosion speed (for example, 300 rpm) or less in a turbulent state that continues for a set time (for example, 10 seconds). Returning to S1, when it is a violent explosion state, the process proceeds to step S3.

  In step S3, the control target value (target rail pressure) for the rail pressure of the common rail 29 stored in the ECU 50 is increased in advance by a set value (for example, 2 MPa). With this increase in the target rail pressure, the control command value for the intake metering solenoid valve 31 of the supply pump 30 is changed so that the actual rail pressure of the common rail 29 detected by the fuel pressure sensor 33 becomes the target rail pressure, and the rail pressure increases. Head in the direction.

  Then, after the target rail pressure is increased, the process proceeds to step S4, and the change in the engine speed for a certain time is examined. As shown in FIG. 3, the change in the engine speed uses a difference ΔAv.NE of the average value of the engine speed NE over a certain period of time, thereby eliminating the influence of local rotational fluctuations in a short time. Thus, it is possible to accurately grasp the increase or decrease in the engine speed.

  When the engine speed increases steadily due to the increase in the target rail pressure and ΔAv.NE ≧ 0 rpm, the process proceeds from step S4 to step S5, where the engine speed NE reaches the complete explosion speed Ns (for example, 700 rpm). ) Check whether or not the above has been reached, and determine whether a complete explosion has been detected. As a result, if NE <Ns, the process returns to step S3 to repeat the process of increasing the target rail pressure so that the rail pressure matches the required rail pressure. When NE ≧ Ns and the complete explosion is reached, the process is performed. Complete.

  On the other hand, if ΔAv.NE <0 rpm in step S4 and the engine speed is not increasing smoothly, the process branches from step S4 to step S6, and the target rail pressure is decreased by a set value (for example, 2 Mpa). Then, in step S7, the increase / decrease in the engine speed is examined again using the difference ΔAv.NE of the average value of the engine speed NE for a predetermined time.

  In step S7, if ΔAv.NE <0 rpm and the engine speed continues to decrease, the process returns to step S3 to increase the target rail pressure, and ΔAv.NE ≧ 0 rpm. When the rotational speed starts to increase, the routine proceeds from step S7 to step S8, where it is determined whether or not the engine rotational speed NE has increased to the complete explosion rotational speed Ns (for example, 700 rpm) or more, and the complete explosion state detection is determined. As a result, if NE <Ns, the process returns to step S6, and the target rail pressure is decreased again by the set value. Then, the process of increasing / decreasing the target rail pressure is repeated, and when NE ≧ Ns is reached in step S8 and the complete explosion is reached, the process is completed.

  Changes in rail pressure and engine speed due to the above processing will be described with reference to FIG. When cranking is started at time T0, the ECU 50 monitors the increase in the engine speed NE due to cranking. In spite of the fact that the actual rail pressure of the common rail 29 is a pressure that matches a preset target rail pressure, the engine speed NE does not increase smoothly, and the up-and-down movement is repeated at a low speed and balanced. When the state is reached, a violent explosion state is detected by the ECU 50 at time T1, and the target rail pressure is increased or decreased by a set value (in FIG. 4, an increase in the target rail pressure is indicated).

  The target rail pressure is increased or decreased according to the increase or decrease of the average engine speed. By repeating the increase or decrease of the target rail pressure, the actual rail pressure can be increased to the required rail optimal for engine start. . As a result, as shown by the broken line in FIG. 4, even if the actual rail pressure is set in advance and conforms to the target rail pressure stored in the ECU 50, the complete explosion without exiting the violent explosion state is achieved. It is possible to avoid a situation where the engine does not reach the limit and complete the engine explosion.

  As described above, in the present embodiment, the increase in the engine speed due to cranking at the start of the engine is monitored, and when a violent explosion state is detected, the control target value of the fuel pressure is determined from a preset value. Control for gradually increasing or decreasing the set value in accordance with the change in the rotational speed is performed, so that the startability can be improved by setting the fuel pressure at the start of the engine as the optimum fuel pressure corresponding to the engine state.

Overall view of engine control system Flow chart of control process at start Explanatory diagram of difference in average rotation speed Time chart showing changes in rail pressure and engine speed at engine start Time chart showing changes in rail pressure and engine speed when starting the engine

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 25 Injector 29 Common rail 30 Supply pump 31 Suction metering solenoid valve 33 Fuel pressure sensor 50 Engine control device NE Engine speed (DELTA) Av.NE Difference of the average value of engine speed in fixed time
Agent Patent Attorney Susumu Ito

Claims (2)

In a start control device for a diesel engine that controls and accumulates fuel pressure to a target value, and injects the accumulated fuel into a cylinder via an injector,
Means for detecting a violent explosion state in which the engine speed is kept below the set speed before the engine complete explosion state at the time of starting the engine for a set time or more;
And a means for gradually increasing or decreasing the control target value of the fuel pressure according to a change in the engine speed until the complete explosion of the engine when the violent explosion state is detected. Diesel engine start control device.   2. The diesel engine start control device according to claim 1, wherein the change in the engine speed is a difference between the average values of the engine speed over a predetermined time.

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