JP2841443B2 - Diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in a diesel engine for the purpose of improving startability and reducing a compression ratio.

(Prior Art) Generally, a diesel engine is of a direct injection type in which combustion is started by fuel directly injected and supplied to a combustion chamber, and a sub chamber such as a vortex chamber provided separately from the main combustion chamber. There is a sub-chamber type in which fuel is supplied to the sub-chamber and the combustion gas whose combustion is started in the sub-chamber is ejected to the main combustion chamber. In small engines for passenger cars and the like, a swirl chamber type, which mainly uses air well and has excellent combustibility, is often used.

By the way, in the vortex chamber type, in the process of compressing the air sucked into the cylinder, a thermal loss occurs when the compressed air flows into the vortex chamber through the injection hole. A phenomenon occurs in which the temperature rise slows down. If the air temperature in the vortex chamber is not sufficiently raised, the self-ignition of the fuel will not cause self-ignition, and the startability will deteriorate. It tends to emit vibration and noise.

For this reason, in a swirl chamber type engine, generally, a glow plug is desired in the swirl chamber, and measures are taken to raise the temperature of the combustion chamber in advance before starting.

(Problems to be Solved by the Invention) However, even if the combustion chamber is preheated in this way, a high compression ratio such as 21 to 23 is required in order to secure a sufficient compressed air temperature by the vortex chamber type. Is done. In contrast, the direct injection type with low heat loss has a low compression ratio.
Since it is about 16 to 18, the vortex chamber type requires a large mechanical load to secure the self-ignition temperature.

That is, in this way the compression ratio is high after warm-up becomes too high actual compression ratio, the maximum combustion pressure for operating conditions exceeding 100 kg / cm ² is generated, such a high combustion It is necessary to use a piston structure, a connecting rod, and a crank system that can withstand the pressure, and the engine becomes heavier. Also, as the weight of the moving part is heavy and the friction increases at a high compression ratio, the torque loss accompanying the rotation of the engine increases, so that a spark ignition type engine of the same class can be used up to 7000 rpm or more In contrast, a diesel engine has a rotation limit of 5000
The rpm must be set as low as about rpm, so that the usable rotation range becomes very narrow. (A well-known document concerning this kind of technology is, for example, “Automotive Engineering Complete Book 5 Diesel Engine” published by Sankaido Co., Ltd. in March 1980.
See pages 127-133. The present invention has been made in view of such a problem peculiar to a diesel engine. In addition to obtaining a required self-ignition temperature at a low compression ratio, a low-load operation that tends to increase with a low compression ratio is performed. The purpose is to suppress combustion noise at the time.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, a throttle valve opening control means for variably controlling the opening of a throttle valve provided in the middle of an engine intake passage; Overlap control means for variably controlling the valve overlap, start detection means for detecting an engine start condition, and throttle valve opening control means for driving the throttle valve opening control means at the time of starting based on the output of the start detection means to reduce the throttle valve opening. And a drive control means for driving the overlap control means to increase the valve overlap, and wherein the drive control means operates the valve overlap and the throttle valve at the time of the start in a low load operation state after the complete explosion of the start. It was configured to maintain the opening.

(Operation) If the throttle valve opening is reduced at the time of starting, a strong negative pressure is generated in the intake pipe downstream of the throttle valve. At this time, if the overlap between the intake and exhaust valves is increased, a strong negative pressure acts in the cylinder to reduce the exhaust action, so that the residual gas amount in the cylinder increases accordingly. Since the residual gas has become hot in the immediately preceding compression stroke, if cranking is continued for several cycles with such a large amount of residual gas, the air temperature in the combustion chamber rises and quickly reaches the self-ignition temperature of the fuel. Since the fuel injected during this time is activated at high temperatures, the engine easily explodes. On the other hand, since the amount of heat held by the residual gas contributes to the increase in the temperature of the combustion chamber in this way, the amount of temperature increase depending on the compression action can be reduced, and the compression ratio can be reduced accordingly.

In addition, even after the complete explosion of the start, the throttle valve opening and the valve overlap are controlled in the low load operation state in the same way as at the start, so that
When the compression ratio is reduced, the combustion chamber temperature can be maintained high by the residual gas in a low load operation state where the noise tends to increase due to the decrease in the combustion chamber temperature. Can be reliably reduced.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the overall configuration of a diesel engine including a control system. In the figure, 1 is a swirl chamber type diesel engine, 2 is an intake passage, 3 is a fuel injection nozzle, 4 is a fuel injection pump, 5 is a glow plug, 6 is a glow relay,
7 is a glow lamp, 8 is a rotation sensor, 9 is a water temperature sensor,
Reference numeral 10 denotes a power supply battery, 11 denotes an ignition switch, and 12 denotes a starter switch. Reference numeral 13 denotes a throttle valve opening control means provided in the middle of the intake passage 2, reference numeral 14 denotes overlap control means for variably controlling the intake / exhaust valve overlap of the engine 1,
Is drive control means for driving the control means 13 and 14.

The drive control means 15 is configured as a general control device including a microcomputer or the like, and includes an engine rotation speed signal N from the rotation sensor 8, a water temperature signal Tw from the water temperature sensor 9,
A fuel injection amount Q and an injection timing IT are determined according to a required load signal Acc and a fuel temperature signal Tf from a load sensor (not shown) to control the fuel injection pump 4 and correspond to a start detection means in this embodiment. The start condition is determined from the start signal Ss issued by turning on the starter switch 12, and the throttle valve opening control means 13 and the overlap control means are determined so that the throttle valve opening decreases and the valve overlap increases. Drive 14 During a cold start with a low engine coolant temperature, the glow plug 7 is rapidly heated via the glow relay 6 to promote an increase in the temperature of the combustion chamber.

2 and 3 show the details of the throttle valve opening control means 13 and the overlap control means 14, respectively.

As shown in FIG. 2, the throttle valve opening control means 13 includes a throttle valve 20 provided in the middle of the intake passage 2 and a step motor 21 for changing the opening thereof in accordance with a signal from the control means 15. Consists of

Further, in this case, the overlap control means 14 advances the phase of the intake valve drive cam more than usual, corresponding to a so-called DOHC type cylinder head in which cams for driving the intake valve and the exhaust valve are individually provided. It is configured to enlarge the overlap. More specifically, as shown in FIG. 3, a cam pulley 25 is attached to one end of a cam shaft 23 for driving an intake valve with an annular piston 24 interposed therebetween.
The piston 24 slides in the axial direction between the cam pulley 25 and the camshaft 23 according to the balance between the hydraulic pressure acting on one end surface of the piston 24 and the tension of the return spring 26. The inside and the outside of the piston 24 are engaged with the camshaft 23 and the cam pulley 25 via helical splines 27A and B having different pressure angles, and the relative movement of the cam pulley 25 and the camshaft 23 is restricted in the axial direction. As described above, when the piston 24 moves in the axial direction as described above, the camshaft 23 relatively rotates around the cam pulley 25 to move the phase forward and backward. As a hydraulic source for driving the piston 24, a hydraulic pump of the engine is used, and by opening and closing a control valve 29 via a solenoid 28 responsive to a signal from the control means 15, the control hydraulic pressure is adjusted. Has become. FIG. 4 shows a change in the phase of the intake valve cam controlled in this way and a change in the overlap therewith. At the time of starting, the cam phase is advanced compared to the normal operation after the starting. The period during which the intake valve is open is constant, but the overlap increases.

Next, the control operation of the drive control means 15 in the above configuration and the operation associated therewith will be described with reference to the flowchart shown in FIG. FIG. 6 shows temporal changes of various control amounts accompanying this control.

First, in step 51, as information necessary for various subsequent controls, rotation speed N,
Load Acc, cooling water temperature Tw, fuel temperature Tf, starter signal Ss
Read. Next, in step 52, it is detected whether or not the starter signal Ss is on.If the starter signal Ss is on, it is determined that the starting cranking is being performed, and the process proceeds to the starting control of step 53 and subsequent steps.
If it is off, the control moves to step 57 and subsequent steps after the start is completed.

In the starting control after step 53, it is first determined whether or not a complete explosion has occurred. This is determined, for example, by optically monitoring the combustion state with an ignition sensor 16 provided facing the combustion chamber of the engine 1. When the engine is started, the rotation speed is increased more rapidly than at the time of cranking. Therefore, it is possible to detect the increase in the rotation based on a signal from the rotation sensor 8 to determine the complete explosion of the engine. If it is determined in that step that the explosion is complete, the control moves to step 57 and the subsequent steps after the completion of the start.

When it is determined in step 53 that the explosion has not been completed, in step 54, a drive signal is output to the throttle valve opening control means 13 so as to decrease the throttle valve opening, and at the same time, the valve overlap increases. A drive signal is output to the overlap control means 14 so as to perform the operation. After that, in step 55, the cumulative number of revolutions of the crankshaft by cranking is calculated, and as shown in FIG. 6, the fuel injection amount is reduced during several revolutions after the start cranking is started, and the fuel amount becomes excessive before the complete explosion. I try not to be. The starting fuel injection amount at this time
The Qs and the injection timing Its are based on basic values that are predetermined as amounts suitable for starting, respectively, the cooling water temperature Tw and the fuel temperature Tf.
This is obtained by correcting with. Then, in the next step 56, the aforementioned Qs and Its are set as the final fuel injection amount Q and the fuel injection timing IT, respectively. In step 60, these signals are output to the fuel injection pump 4 to
The control routine is ended. In this start control, the start operation is continued when the starter signal Ss is on, and
It is repeated while it is determined that the explosion is not completed in 53.

On the other hand, if it is determined in step 52 or 53 that the engine is after the complete explosion, then it is determined in step 57 whether the engine is in a predetermined low-load operation state including idling, for example, by referring to the load Acc. It is determined by At this time, if the engine is in the low load operation state, the throttle valve opening is made small and the valve overlap is kept large in the same manner as at the start in step 57a.
On the other hand, if a large load is required due to starting or the like after the complete explosion of the engine, the throttle valve opening is increased and the valve overlap is reduced in step 57b, so that operation performance suitable for operation in a normal range is achieved. To secure. Next, in step 58, the fuel injection amount Qa after the start and the injection timing ITa are calculated, and these are set as the final appropriate fuel injection amount Q and the injection timing IT in step 59. And proceed. Note that Qa and ITa at this time are the rotational speed N and the load A, respectively.
The basic value obtained by a search process of a table formed to give a predetermined value from cc or a calculation process of a calculation formula is corrected by the coolant temperature Tw and the fuel temperature Tf.

According to such control, the negative pressure in the intake pipe increases due to the effect of the throttle valve at the start of cranking, and the ratio of residual gas increases due to the enlarged valve overlap. During this time, since the residual gas is an unburned gas mixture, the fuel injection amount is reduced to some extent based on the integration of the cranking rotation as described above so as not to be supplied excessively. When the fuel contained in the residual gas undergoes compression and expansion, it is chemically activated at a high temperature, and when the proportion of the residual gas increases, the amount of the activated fuel that is compressed again increases, leading to self-ignition in several cycles. As a result, the overall temperature of the compressed intake air increases, so that the injected fuel also ignites and completely explodes.

When the complete explosion is started in this way, the unburned air-fuel mixture in the cylinder decreases at the same time as the complete explosion, and the next time the residual gas is occupied mostly by burned gas.
In 58, the engine speed is increased by increasing the fuel injection amount.

On the other hand, when the engine is in a low-load operation state such as idling even after the start-up complete explosion, the throttle valve opening is small and the valve overlap is kept large as at start-up, so the residual gas increases the combustion chamber temperature. It is possible to keep. As a result, it is possible to avoid a rise in combustion noise due to an increase in the premixed combustion ratio due to a decrease in the temperature of the combustion chamber, which tends to occur particularly when the compression ratio is reduced, and to perform a quiet operation.

Also, as explained earlier, the loss of compressed air temperature in a diesel engine is remarkable mainly in a swirl chamber type engine. Even if the present invention is applied to a direct injection type engine, a great effect can be obtained.

(Effects of the Invention) As described above, according to the present invention, it is possible to reduce the compression ratio of a diesel engine, so that the weight and friction loss of the moving parts of the engine are reduced, and various performances such as output, fuel consumption, and rotation limit are performed. Can be comprehensively improved. In addition, since the maximum combustion pressure is reduced by reducing the compression ratio, excellent exhaust emission performance with less generation of NOx is obtained, and the combustion noise during low load operation, which tends to increase with the reduction of the compression ratio, is suppressed. be able to.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of one embodiment of the present invention, FIG. 2 is a detailed view of the throttle valve control means, and FIG. 3 is a detailed view of the overlap control means. FIG. 4 is an explanatory diagram for explaining a change in the overlap, FIG. 5 is a flowchart showing the operation contents of the control system of the embodiment, and FIG. 6 is a diagram showing changes in various control amounts accompanying the operation of the control system. 5 is a timing chart showing a relationship with rotation. 1 ... Diesel engine, 2 ... Intake passage, 3 ... Injection nozzle, 4 ... Fuel injection pump, 8 ... Rotation sensor, 9 ...
... water temperature sensor, 12 ... starter switch, 13 ... throttle valve opening control means, 14 ... overlap control means, 15 ... drive control means.

Claims (1)

(57) [Claims] A throttle valve opening control means for variably controlling an opening of a throttle valve disposed in the middle of an engine intake passage; an overlap control means for variably controlling a valve overlap of intake and exhaust valves; Start detection means for detecting a condition, and the throttle valve opening control means is driven at the time of starting based on the output of the start detection means to reduce the throttle valve opening degree and to drive the overlap control means to enlarge the valve overlap. A drive control unit, and wherein the drive control unit is configured to maintain the valve overlap and the opening of the throttle valve at the time of the start in a low-load operation state after a complete combustion of the start. organ.