JP2704890B2 - Fuel injection control device for diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection control device for a diesel engine for an automobile.

(Prior Art) Generally, in a diesel engine that performs compression ignition, fuel injected into a combustion chamber explosively burns due to ignition delay, resulting in combustion noise and nitrogen oxides (NO _X ) in exhaust gas.
May increase.

In response to this, there is a concept that a small amount of fuel is pilot-injected before the main injection of fuel, and the pilot injection is used as the kind of main injection fuel. Conventionally, as a fuel injection system for performing such pilot injection, for example, those described in JP-A-59-165856 and JP-A-62-659 are known. In this system, a fuel injection pump for main injection and a fuel injection pump for pilot injection are provided, and both fuel injection pumps are controlled according to engine operating conditions.

(Problems to be solved by the invention) By the way, combustion noise of a diesel engine is generally
It tends to increase as the maximum value of the in-cylinder pressure rise rate increases. This in-cylinder pressure rise rate is, as shown in FIG.
It usually shows a maximum value before the top dead center (TDC) of the piston when transitioning from the compression stroke to the expansion stroke. Therefore, when pilot fuel is injected near this maximum value (for example, in the range of 20 ° to 5 ° before TDC), the combustion pressure generated by its combustion follows the mechanical air compression pressure by the piston, As shown by the two-dot chain line in the figure, there is a concern that the maximum value of the in-cylinder pressure rise rate is further increased and the noise performance is deteriorated.

In response to this, it is conceivable to inject the pilot fuel later than the above-mentioned noise-deteriorated region.
In the worst case, there is a risk that the engine will stop.

The present invention addresses the above-described situation in a diesel engine in which pilot injection is performed prior to main injection of fuel, and an object of the present invention is to achieve both combustion performance and noise performance particularly when the engine is cold.

(Means for Solving the Problems) The present invention relates to a fuel injection control device for a diesel engine having fuel injection means a capable of performing pilot injection prior to main injection of fuel, as shown in FIG. An injection timing variable means b for changing the injection timing of the pilot injection, and when the engine temperature is lower than a predetermined value, the injection timing of the pilot injection is shifted by a predetermined angle from the piston top dead center when shifting from the compression stroke to the expansion stroke. When the engine temperature is set to the preceding advance side and the engine temperature is higher than a predetermined value, the injection timing is extended from the advance side more than the predetermined angle to the crank angle on the piston top dead center side beyond the predetermined crank angle width at a stroke. Control means c for controlling the injection timing variable means b so as to retard is provided.

(Operation) According to the above configuration, when the engine temperature is low and equal to or lower than the predetermined value, the control means c controls the injection timing variable means b so that the injection timing of the pilot injection is at least a predetermined angle before the piston top dead center. Set to the advance side of. And
When the engine temperature is higher than the predetermined temperature, the control means c controls the injection timing variable means b so that the injection start timing of the pilot injection is retarded at a stroke beyond the predetermined crank angle width to the vicinity of the piston top dead center. Let it. As a result, the pilot fuel is injected from the fuel injection means a before and after the noise deterioration area.

(Examples) Hereinafter, examples of the present invention will be described. In the embodiment, the present invention is applied to a four-cylinder diesel engine for an automobile.

As shown in FIG. 2, the fuel injection pump 1 according to the present invention
Has a feed pump 3 driven to rotate by a drive shaft 2 linked to an engine output shaft, and a plunger 6 rotatably reciprocated by the drive shaft 2 via an engagement mechanism 4 and a cam mechanism 5. . A suction groove 8 communicating with the pressure feed chamber 7 is provided near the tip of the plunger 6, and an oil feed path 9 having one end opened to the pressure feed chamber 7 is provided in the axial longitudinal direction. The other end of the passage 9 communicates with a distribution groove 10 formed on the side wall surface of the plunger 6, and the distribution groove 10 communicates with the delivery valve 11 at a predetermined timing according to the rotation of the drive shaft 2. The communication with the distribution passage 12 is enabled. Then, the fuel flowing from the fuel tank (not shown) into the suction chamber 3a is introduced into the pump chamber 13 by the rotation of the feed pump 3, whereby the internal pressure of the pump chamber 13 is increased and the plunger 6 is driven by the drive shaft. By reciprocating while rotating in conjunction with 2, the suction groove 8 communicates with the fuel introduction passage 14 leading to the pump chamber 13, and the distribution groove 10 communicates with the distribution passage 12 leading to the delivery valve 11. Has become.

In this case, as shown in FIGS. 2 and 3, the cam mechanism 5 has a cam disk 14 fixed to one end of the plunger 6 and a coaxial core opposed to the cam disk 14. It is composed of a roller ring 15 and rollers 16... 16 arranged in a circumferential direction of the roller ring 15 so as to correspond to the projections 14 a.
In this case, the projecting portions 14a are formed in a mountain shape as shown in FIG. 4, and the projecting portions 14a are spaced apart from each other in accordance with the number of cylinders of the engine. The cam disk 14 protrudes from the cam disk 14, and when the protruding portion 14a rides on the roller 16, the cam disk 14 is lifted, whereby the plunger 6 is lifted to further pressurize the fuel in the pumping chamber 7, and this pressurization is performed. Fuel distribution groove 10
Is connected to the distribution passage 12, the delivery valve 11 is opened to inject. An electromagnetically driven high-speed spill valve 17 is provided between the pumping chamber 7 and the pump chamber 13. By opening the high-speed spill valve 17, fuel in the pumping chamber 7 is rapidly discharged. The fuel injection from the delivery valve 11 is instantaneously interrupted by being spilled.

The roller ring 15 is rotatably held on the same axis as the cam disk 14 and has a timer device.
The movement is controlled to an arbitrary position in the circumferential direction by 18. The timer device 18 includes a timer housing 19
A timer piston 20 slidably inserted into, and a high-pressure chamber 21a formed facing one end of the timer piston 20,
A low-pressure chamber 21b also formed facing the other end of the timer piston 20, and a timer spring arranged in the low-pressure chamber 21b
22, an electromagnetically driven timer control valve 23 also disposed between the low-pressure chamber 21b and the high-pressure chamber 21a, and a timer position sensor 24 for detecting the position of the timer piston 20. In this case, the suction chamber 3a of the feed pump 3 communicates with the low-pressure chamber 21b, and the pump chamber 13 communicates with the high-pressure chamber 21a. A timer pin 25 fixed to the roller ring 15 is engaged with the timer piston 20.For example, when the drain amount by the timer control valve 23 is increased, the timer piston 20 moves in the A direction, thereby The roller ring 15 rotates in the direction B opposite to the rotation direction of the plunger 6 via the timer pin 25, and the lift timing of the plunger 6 changes in the retard direction with respect to the crank angle. On the other hand, when the timer piston 20 is moved in the opposite direction by the timer control valve 23,
The lift timing of the plunger 6 changes in the advance direction with respect to the crank angle.

By the way, in the present embodiment, the cam disk 14
Has a non-uniform cam shape, for example, a constant acceleration cam shape. In the cam disk 14 having such a uniform acceleration cam shape, the cam lift and the cam speed change as shown in FIG. 5 with respect to the cam angle based on the starting end of an arbitrary protrusion 14a. That is, the cam speed curve initially changes in an upward slope as the cam angle increases, and then reverses at a point beyond the inflection point of the cam lift curve, and then changes downward in a slope, and becomes zero at the top of the cam lift curve. Then, it shifts to the negative area. In this case, when the region (I) before and after including the apex of the cam speed curve is used, the lift speed of the plunger 6 is increased and the fuel in the pumping chamber 7 is pressurized at a high speed. It will be injected at a rate. And the lower angle side area (II)
Is used, the lift speed of the plunger 6 is reduced by the lower cam speed, so that the fuel is injected at a low injection rate.

When the fuel is injected at a low injection rate, a higher angle side (III) than the area (II) may be used.

Next, a fuel injection system for a diesel engine using the fuel injection pump 1 having such a structure will be described with reference to FIG. 6. In the fuel injection pump 1, a fuel injection valve 27 is provided via a high-pressure pipe 26. While connected, the timer piston position signal from the timer position sensor 24 of the timer device 18 is input to the control unit 28. The control unit 28 includes an accelerator opening signal from an accelerator opening sensor 29 and an engine speed sensor.
The engine speed signal from the engine 30, the crank angle signal from the crank angle sensor 31, the intake pressure signal from the intake pressure sensor 32 disposed in the intake passage downstream of the supercharger (not shown), and the intake An air temperature signal, a water temperature signal from a water temperature sensor 34 for detecting engine water temperature, an atmospheric pressure signal from an atmospheric pressure sensor 35 for detecting atmospheric pressure, and a vehicle speed signal from a vehicle speed sensor 36 are input, respectively. On the other hand, from the control unit 28, the timer control valve 23 and the high-speed spill valve
Control signals will be output to 17 respectively.

Next, the operation of this embodiment will be described more specifically with reference to the flowchart of the fuel injection control shown in FIG.

That is, the control unit 28 performs system initialization by performing the first step S ₁ after startup, and then inputs various sensor signals in step S _2. Then, the control unit 28 performs a basic control operation for high-speed spill valve 17 and the timer control valve 23 based on the engine speed and the accelerator opening degree for example, in step S _3. In this case, the memory of the control unit 28 stores in advance the injection start timing of the pilot injection, the fuel injection rate and the fuel duration, and the injection start timing of the main injection, the fuel injection rate and the injection duration corresponding to the engine load state. The control unit 28 looks up the values, and makes a high injection rate such that the pilot injection and the main injection are set to a low injection rate at a low load and the pilot injection is reduced to a high injection rate at a high load. The control target values for the spill valve 17 and the timer control valve 23 are calculated. In this embodiment, the control configuration is such that the injection start timing of the pilot injection approaches the injection start timing of the main injection as the load becomes higher.

Then, the control unit 28, step S ₄ to S ₈
Determination process performed, after performing the appropriate correction operation, if necessary, outputs a control signal to the high-speed spill valve 17 and the timer control valve 23 executes step S _9.

Hereinafter, each determination processing in step S ₄ to S _8, correction control for based thereon will be described.

Determination processing for high altitude correction control is performed in the first step S _4. That is, at high altitudes, the air density is lower than that on flat terrain, and when fuel is injected with the same injection amount when using on flat terrain, the air-fuel ratio decreases, and smoke is more likely to occur. Therefore, the control unit 28, step S when the atmospheric pressure as Figure 8 is first set atmospheric pressure p ₁ or less
₁₀ is executed to perform a predetermined high altitude correction. In this embodiment, when the atmospheric pressure falls below the first set atmospheric pressure p _1, the fuel injection rate with increasing linearly until it reaches the second set atmospheric pressure p _2, reaches the second set atmospheric pressure p ₂ Control is performed so that the fuel injection rate becomes constant from the time point. This prevents the generation of smoke due to a decrease in atmospheric pressure and ensures the output performance on flat ground.

Determination processing for cold cold start correction control is performed in the second step S _5. That is, the control unit 28, as shown in FIG. 9, if it is determined that the water temperature detected by the water temperature sensor 34 is lower than the first set temperature t _1, the predetermined cold cold start executes step S ₁₁ Make corrections. In this case, the control unit 28
Is performed, the time interval between the pilot injection and the main injection is increased within the effective cam area of the cam disk 14, the injection start timing of the pilot injection is set to a low injection rate, and the main injection Correction calculation is performed on the high-speed spill valve 17 so that the injection start timing is set to a high injection rate. As a result, as shown in FIG. 10, the pilot injection is performed early at a low injection rate, and a lean air-fuel mixture is formed in the combustion chamber, thereby increasing the ambient temperature in the compression stroke. Since the vaporization of the pilot injection is promoted and a preflame reaction occurs,
A radicalized atmosphere is created in the combustion chamber. Since the main injection fuel atomized at a high injection rate is injected there, the main injection fuel is reliably burned, and good starting performance is obtained.

Then, in the third step S _6, the determination process for the warm-up operation correction control according to the present embodiment is performed. That is, in the diesel engine, the region where the combustion noise is deteriorated when the pilot injection is performed as described above is located before the piston top dead center at which the transition from the compression stroke to the expansion stroke occurs. Therefore, as shown in FIG. 11, when the control unit 28 determines that the water temperature is equal to or lower than the second set water temperature t ₂ (for example, 50 ° C.), the control unit 28 sets the injection start timing of the pilot injection to the combustion deterioration region at the crank angle. a correction operation is performed so as to set the advance side than the ban corresponding to (step S _12). As a result, during the warm-up operation, as shown in FIG. 12, pilot injection is performed on the advance side of the noise deterioration region near the maximum in-cylinder pressure value before the top dead center (TDC), Combustion noise can be reduced while preventing misfiring. Then, the control unit 28 determines that the water temperature has reached the second set temperature t _2, is once advanced until the piston on the vicinity of dead center past the ban the injection start timing of the pilot injection. As a result, as shown in FIG. 13, the pilot fuel is injected while avoiding the noise deterioration area. Incidentally, the water temperature in the present embodiment is adapted to reduce to a third predetermined temperature t ₃ lower than the second set temperature t _2, the fuel injection rate with temperature decrease linearly.

Determination processing for the acceleration correction control is performed in the fourth step S _7.

That is, as shown in FIG. 14, when the change in the accelerator opening per unit time, that is, the rate of change in the accelerator opening shows a value equal to or greater than the set value α, the control unit 28 determines that acceleration is in progress and performs pilot injection. simultaneously with the stop to set the main injection at a high injection rate of the cam disc 14 (step S _13). Therefore, as shown in FIG.
Since the main injection fuel is injected in a single shot at a high speed, not only the amount of smoke generated is reduced, but also the acceleration performance is improved.

Determination processing for the boost pressure correction control is performed in the fifth step S _8. That is, when the supercharging pressure generated by the supercharger rises to some extent, the strong vortex generated thereby causes the pilot spray to flow, whereby the air-fuel mixture becomes over lean and the hydrocarbon (HC) in the exhaust gas is exhausted. ) May be increased. In this case, since the ignitability of the fuel by increasing the supercharging pressure is maintained well, even by shortening the time interval of the pilot injection and the main injection is considered to be significantly affect the combustion noise and NO _X. Therefore, the control unit 28
As shown in FIG. 16, when the intake pressure becomes larger than the first set boost pressure p ₃ (for example, 300 mmHg), the time interval between the two is linearly adjusted so that the injection start timing of the pilot injection approaches the injection start timing of the main injection. is changed to control so as to stop the intake pressure reaches a second predetermined boost pressure p ₄ pilot injection (step S _14). Therefore, for example, at an arbitrary intake pressure p _X , the position of the pilot injection changes from the state of the two-dot chain line corresponding to the first set boost pressure p ₃ to the state of the solid line as shown in FIG. become. In this case, the first and second set boost pressures p ₃ and p ₄ may be changed according to the engine speed.

Further, in addition to the above correction, the pilot injection amount may be decreased according to an increase in the supercharging pressure, or the injection rate may be increased according to an increase in the supercharging pressure, and the injection timing may be retarded. good.

The correction conditions may be mapped in advance, and the boost pressure correction control may be performed based on the map.

When not performing the above-described correction control, the control unit 28 controls the timer device 18 and the high-speed spill valve.
17 is controlled as follows according to the engine load.

First, at the time of low load, as shown in FIG. 18, the timer device 18 is set to the retard side, and a small amount of pilot fuel is injected in the region (II) where the cam speed is low, especially in the low injection rate side. The main injection fuel is injected in a region (II) where the crank angle is retarded by a predetermined amount. Therefore, the ignitability of the main injection fuel is favorably maintained by using the pilot fuel as an ignition source, thereby not only reducing the combustion noise and the NO _X amount in the exhaust gas, but also
Since the main injection fuel is also injected at a low injection rate, the fuel spray is not excessively diffused and the increase in the HC amount is suppressed.

In addition, at the time of medium load, as shown in FIG. 19, the timer device 18 is advanced slightly more than at the time of low load,
In an intermediate portion in the low cam speed region (II), pilot injection is performed near the main injection.

And, at the time of high load, as shown in FIG.
The timer device 18 is further advanced, and only the main injection is performed in the region (I) where the cam speed is high. As described above, when the load is high, the main injection fuel is injected at a high injection rate, so that the atomization of the fuel spray is improved and the penetration force is increased, whereby the fuel spray may be locally excessively concentrated. Therefore, even if the injection start crank angle of the main injection is retarded by Δθ from the low load,
The generation of smoke is prevented, and the combustion is performed efficiently, thereby improving fuel efficiency.

(Effect of the Invention) As described above, according to the present invention, in the process of shifting from the compression stroke to the expansion stroke in this kind of diesel engine, the pilot engine avoids the mechanical noise deterioration area which can be generated just before the piston top dead center. Since the injection is performed, the effect that low noise can be realized while preventing the deterioration of the combustion performance due to the misfire is obtained. Particularly, by applying the present invention to a sub-compartment type engine with low compression, there is an advantage that excellent quietness can be obtained.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of the present invention. Figures 2 to 20
Fig. 2 shows an embodiment of the present invention. Fig. 2 is a partially cutaway side view showing the internal structure of the fuel injection pump according to the embodiment partially expanded, and Fig. 3 is III- FIG. 4 is a partial exploded view of the cam disk, FIG. 5 is a cam speed diagram of the same cam disk, FIG. 6 is a fuel injection system diagram, and FIG. 7 is a control unit. Flow chart of the fuel injection control to be executed, FIG. 8 is an explanatory diagram of a map used for high altitude correction, FIG. 9 is an explanatory diagram of a map used for cold start correction, and FIG. 10 is an injection rate characteristic at the time of cold start correction FIG. 11 is an explanatory diagram of a map used for warm-up correction,
FIG. 12 is a characteristic diagram of the in-cylinder pressure increase rate and the injection rate during the warm-up correction, FIG. 13 is a characteristic diagram of the in-cylinder pressure increase rate and the injection rate after the completion of the warm-up, and FIG. 14 is used for the acceleration correction. Illustration of the map,
FIG. 15 is an injection rate characteristic diagram at the time of acceleration correction, FIG. 16 is an explanatory diagram of a map used for boost pressure correction, FIG. 17 is an injection rate characteristic diagram at the time of boost pressure correction, and FIG. FIG. 19 is an injection rate characteristic diagram at a medium load, and FIG. 20 is an injection rate characteristic diagram at a high load. FIG. 21 is a characteristic diagram showing a change in an in-cylinder pressure rise rate with respect to a crank angle showing a conventional problem. 17 ... fuel injection means, injection timing variable means (high-speed spill valve), 28 ... control means (control unit).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication F02M 45/06 F02M 45/06 A (56) References JP-A-62-659 (JP, A) JP-A-62-55436 (JP, A) JP-A-62-58034 (JP, A) JP-A-62-150053 (JP, A) JP-A-61-275532 (JP, A) JP-A-62-55458 (JP, A) JP-A-63-147956 (JP, A) JP-A-2-95742 (JP, A) JP-A-62-17343 (JP, A)

Claims (1)

(57) [Claims] 1. A fuel injection control device for a diesel engine having fuel injection means capable of performing pilot injection prior to main fuel injection, comprising: an injection timing variable means for changing an injection timing of the pilot injection; Is lower than a predetermined value, the injection timing of the pilot injection is set to an advance side which is a predetermined angle or more before the piston top dead center when shifting from the compression stroke to the expansion stroke, and the engine temperature exceeds a predetermined value. Sometimes control means is provided for controlling the injection timing variable means so as to retard the injection timing from the advance side, which is at least the predetermined angle before, to the crank angle on the piston top dead center side beyond the predetermined crank angle width at a stroke. A fuel injection control device for a diesel engine.