JPH0552130A - Controller of diesel engine - Google Patents

Abstract

PURPOSE:To decrease a discharge quantity of NOx in a low-speed/middle-load range in which delay control in a fuel injection timing, and/or EGR control are limited, in a diesel engine equipped with a fuel injection valve which injects fuel in multi-stages. CONSTITUTION:There are provided a variable valve timing mechanism 44 which varies the opening/closing timing of an intake valve, a means 41 which detects the operational condition of an engine, a means 42 which discriminates a operational range in which a fuel quantity injected at an initial lift position of a needle is comparatively large, and a control means 43 which delays the opening/ closing timing of the intake valve via the variable value timing mechanism 44 in the operational range.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine control device.

2. Description of the Related Art There is a fuel injection valve that performs fuel injection in stages in order to reduce ignition delay of a diesel engine and realize smooth combustion. This fuel injection valve has a first spring and a second spring interposed in parallel to urge the needle of the fuel injection nozzle to close the valve, and the first spring works when the needle initially lifts, and when the initial lift position is exceeded. In addition to this, by operating the second spring, the needle is lifted step by step with respect to the fuel injection pressure, and a large amount of main injection is performed after the initial injection fuel is ignited, and there is little ignition delay, and therefore vibration and noise Stable and smooth combustion is ensured. Even in a diesel engine equipped with such a fuel injection valve that injects fuel in multiple stages, NOx
As a means for reducing the amount of exhaust gas, control for delaying the fuel injection timing or EG for recirculating a part of the exhaust gas to the intake system
There is no change in that it is extremely effective to reduce the maximum temperature and pressure during combustion by the R control (see, for example, JP-A-61-55358). However, in the low-speed medium-load range where the rotation speed of the fuel injection pump is low, the period during which the needle lift remains at the initial lift is relatively long, and the injection period of one cycle is longer than in the high-speed range. When it is attempted to reduce NOx by delaying the amount, in the vicinity of the end of injection, the piston falls too much, the cylinder pressure is low, and the amount of smoke and HC discharged increases. Therefore, there is a problem that the allowable amount for delaying the fuel injection timing is small in the low speed and medium load range. Further, since the excess air ratio is high in the low load region, a large amount of exhaust gas recirculation can be performed, but in the medium load region, the exhaust gas recirculation amount is limited because the excess air ratio is relatively low, and the fuel injection timing is Contrary to the limitation, the NOx emission amount tended to increase in the low speed and medium load range as shown in FIG. The present invention focuses on the above points, and in a diesel engine including a fuel injection valve that injects fuel in multiple stages, fuel injection timing control and EGR
It is intended to reduce the NOx emission amount in the low speed medium load range where the control is limited.

As shown in FIG. 1, the present invention comprises a fuel injection valve for injecting fuel in multiple stages by gradually lifting a needle in accordance with the fuel pressure fed from a fuel injection pump. In a diesel engine, a variable valve timing mechanism 44 for changing the opening / closing timing of an intake valve
A means 41 for detecting the operating state of the engine, a means 42 for determining an operating range in which the amount of fuel injected at the initial lift position of the needle is relatively large, and a variable valve timing mechanism 44 in this operating range. The control means 43 for delaying the opening / closing timing of the intake valve is provided.

In the low-speed medium-load region, the fuel injection pressure does not rise so much due to the low number of revolutions of the fuel injection pump, so the period during which the needle stays in the initial lift becomes relatively long,
Although the injection period of one cycle is longer than that in the high speed range, the present invention reduces the effective compression stroke and delays the pressure in the combustion chamber by delaying the closing timing of the intake valve in this low speed and medium load range. As a result, the combustion temperature decreases and N
Reduce Ox emissions. By lowering the compression ratio,
An increase in the fuel injection amount during the ignition delay period with respect to the entire injection period leads to an increase in the NOx emission amount, but in the low speed and medium load range, the needle stays in the initial lift position for a long period of time, so The amount of fuel injected during the ignition delay period is small and NOx is reduced even if the actual compression ratio is lowered to some extent.
The increase in the amount is suppressed to a small level, and the effect of lowering the combustion pressure during a long injection period after ignition lowers the combustion temperature, and the total NOx emission amount can be reduced. Furthermore, in the low-speed and medium-load range, the valve closing timing of each intake valve is delayed, reducing the valve overlap in which the intake valve opens at the same time as the exhaust valve near the top dead center of the piston. By increasing the gas amount (internal EGR amount),
The effect of increasing the specific heat of the combustion gas while maintaining the gas temperature in the cylinder at the time of ignition high is obtained.

Embodiments of the present invention will be described below with reference to the accompanying drawings. 2 and 3, 10 is a syrin head,
Reference numeral 2 is a cylinder, 3 is a piston, and a cavity 4 is formed at the top of the piston 3 to define a combustion chamber 5. A fuel injection valve 6 is attached to the cylinder head 10, and an injection nozzle 7 of the fuel injection valve 6 is provided facing the center of the combustion chamber 5. 4 shows an example of the fuel injection valve 6, a needle 22 is arranged inside the nozzle holder 21, and the needle 22 has a first spring 23 and a second spring 24.
Is urged in the valve closing direction by. The fuel pressure sent from a fuel injection pump (not shown) is applied to the needle 22,
When the fuel pressure increases above a predetermined value, the needle 22 lifts by the initial lift amount L ₁ while compressing the first spring 23 via the push rod 26. This is the initial injection, and this state is maintained until the fuel pressure exceeds the initial spring load (second stage valve opening pressure) of the second spring 24. Next, while compressing the second spring 24 via the spring seat 27, the needle 22 lifts up to the total lift amount L ₂ , the main injection for supplying a large amount of fuel starts, and the stepwise fuel injection is performed.
Two intake ports 33 and two exhaust ports 34 are formed in the cylinder head 10 around the injection nozzle 7 so as to face each other. The intake valves 8 and the exhaust valves 9 are provided on the cylinder heads 10 on the respective camshafts 11 and 12.
The rotation of the cams 11a and 12a, the respective valve springs 15 and 1
It is opened and closed against 6. Each camshaft 11, 12
The cam pulleys 35 and 36 are coupled to the front ends of the respective gears, and a timing belt 37 is wound around the cam pulleys 35 and 36 and a crank pulley (not shown) to rotate in synchronization with the engine rotation. The intake-side camshaft 11 that drives the intake valves 8 to open and close is provided with a variable valve timing mechanism 44 that makes the rotational phase thereof variable. The variable valve timing mechanism 44 includes the intake side camshaft 11
It is composed of an actuator that changes the rotational phase between the cam pulley 35 and the cam pulley 35 by hydraulic pressure. The opening / closing timing of each intake valve 8 is adjusted by changing the rotational phase between the cam shaft 11 and the cam pulley 35 by the actuator. In the present invention, the point is to delay the opening / closing timing of each intake valve 8 by operating the variable valve timing mechanism 44 in an operating range in which the amount of fuel injected at the initial lift position of the needle 22 is relatively large. Are controlled by the controller 30. The controller 30 is composed of a microcomputer including a CPU of a calculation part, a RAM of a storage part, a ROM, and an I / O of an input / output part. A detection signal from an engine speed sensor 31 and a lever opening sensor 32 that detects the control lever opening of the fuel injection pump on behalf of the engine load is input to the controller 30 and preset as shown in FIG. Based on the map, the operating range in which the amount of fuel injected at the initial lift position of the needle 22 is relatively large is determined, and the opening / closing timing of each intake valve 8 is delayed in this operating range as shown by the broken line in FIG. Then, the variable valve timing mechanism 44 is operated. Next, the operation will be described. FIG. 7 shows the lift characteristic of the needle 22 which changes according to the engine speed and the load in the lower part of each masu, and the fuel injection rate characteristic in the upper part of each masu. Characteristics of fuel injection rate The arrow shown above represents the ignition timing, and the black portion in front of this arrow corresponds to the amount of fuel injected during the ignition delay period. FIG. 5
In the low speed medium load range corresponding to the delay control range shown in (1), the fuel injection pressure does not rise so much due to the low rotation speed of the fuel injection pump, so that the period in which the needle 22 stays in the initial lift position becomes relatively long, and The injection period of the cycle is longer than the high speed range. In the present invention, by delaying the closing timing of each intake valve 8 in the low speed and medium load range, the effective compression stroke is reduced and the pressure in the combustion chamber is lowered as shown in FIG. As a result, the combustion temperature is lowered and the NOx emission amount can be reduced. When the fuel injection amount during the ignition delay period is increased with respect to the entire injection period by lowering the compression ratio, the NOx amount is rather increased, but the needle 22 stays in the initial lift position for a long period in the low speed and medium load region. Therefore, the amount of fuel injected during the ignition delay period is small with respect to the entire injection period, and even if the actual compression ratio is lowered to some extent, the increase in the NOx amount is suppressed to be small, and the combustion pressure during the long injection period after ignition is reduced. As a result, the combustion temperature is lowered, and the total NOx emission amount can be reduced. further,
In the low speed medium load region, the valve closing timing of each intake valve 8 is delayed, so that the valve overlap in which the intake valve 8 opens simultaneously with each exhaust valve 9 near the piston top dead center (TDC) is reduced, and the in-cylinder Burned gas remaining in the engine (internal EGR
Amount is increased, and the effect of increasing the specific heat of the combustion gas while maintaining the gas temperature in the cylinder at the time of ignition high is obtained. In the low speed and low load region, the opening timing of each intake valve 8 is returned to the normal timing, but since the excess air ratio is high, a large amount of exhaust gas recirculation can be performed, and the NOx emission amount can be sufficiently suppressed. Even at the time of starting, the opening / closing timing of each intake valve 8 is returned to the normal timing, thereby increasing the actual compression ratio and ensuring good startability. In the low speed and high load range,
By returning the opening timing of each intake valve 8 to the normal timing, the efficiency of filling fresh air is increased and the amount of smoke discharged is reduced. In this low speed and high load range, the NOx emission amount can be effectively reduced by delaying the fuel injection timing. In the high speed and low load range, the rotation speed of the fuel injection pump is high,
Since the amount of fuel injection is small, the amount of fuel injected during the ignition delay period increases, so by increasing the exhaust gas recirculation amount or delaying the fuel injection timing without delaying the closing timing of the intake valve, NOx emissions can be reduced. Next, as another embodiment, a means for detecting the lift amount of the needle 22 is provided, and an operating range in which the initial lift period exceeds a predetermined value is discriminated based on this detection signal to perform highly accurate control. It is possible. In this case, as a lift detecting means of the needle 22, a piezoelectric element 28 is interposed between the spring seat 27 of the second spring 24 and the spacer 29 in FIG. The output voltage of the piezoelectric element 28 changes according to the pressure acting on the piezoelectric element 28, and as the lift amount of the needle 22 lifts beyond the initial lift amount L ₁ , the second spring 2 moves.
When the spring seat 27 of No. 4 separates from the piezoelectric element 28, the output changes, and it can be detected whether or not the needle 22 is in the initial lift position. Further, the lift detecting means for the needle 22 does not necessarily have to be provided for all cylinders in a multi-cylinder engine.

INDUSTRIAL APPLICABILITY As described above, the present invention provides an intake valve in a diesel engine equipped with a fuel injection valve in which a needle is lifted stepwise in response to fuel pressure fed from a fuel injection pump to inject fuel in multiple stages. A variable valve timing mechanism for varying the opening and closing timing of the engine, means for detecting the operating state of the engine, means for determining an operating range in which the amount of fuel injected at the initial lift position of the needle is relatively large, Since the control means for delaying the opening / closing timing of the intake valve via the variable valve timing mechanism is provided, the NOx emission is compatible with HC and smoke in the low speed medium load range where the delay control of the fuel injection timing and the EGR control are limited. Emissions can be effectively reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is a vertical sectional view of an engine showing an embodiment of the present invention.

FIG. 3 is a plan view of a cylinder head of the same.

FIG. 4 is a vertical sectional view of a fuel injection valve of the same.

FIG. 5 is a control characteristic diagram of the same.

FIG. 6 is a valve lift characteristic diagram of the same.

FIG. 7 is a diagram showing a fuel injection rate and a lift characteristic of a needle.

FIG. 8 is a characteristic diagram of pressure in the combustion chamber.

FIG. 9 is a characteristic diagram of NOx emission amount of a conventional device.

[Explanation of symbols]

 41 operating state detecting means 42 operating range determining means 43 control means 44 variable valve timing mechanism

Claims (1)

[Claims] 1. A diesel engine equipped with a fuel injection valve, in which needles are lifted in stages according to fuel pressure fed from a fuel injection pump to inject fuel in multiple stages,
A variable valve timing mechanism for varying the opening / closing timing of the intake valve, a means for detecting the operating state of the engine, a means for determining an operating range in which the amount of fuel injected at the initial lift position of the needle is relatively large, and A control device for a diesel engine, comprising: a control means that delays the opening / closing timing of an intake valve by operating a variable valve timing mechanism in an operating range.