JPH0641736B2 - Fuel injection control device for diesel engine - Google Patents

Description

The present invention relates to a fuel injection control device for a diesel engine.

[Conventional technology]

In a diesel engine, when the temperature of the engine is low as when starting the engine, the ignition delay period becomes long because the ambient temperature in the combustion chamber is low, and therefore the injection start timing is advanced at the time of starting the normal engine (for example, Kaisho
56-162232 gazette). In other words, the injection start timing is delayed as the engine temperature rises.

[Problems to be solved by the invention]

However, in the conventional diesel engine, the fuel injection pressure is maintained almost constant even when the engine temperature rises. Therefore, if the injection start timing is delayed as the engine temperature rises, the injection completion timing also delays accordingly. Will end up.
However, there is a problem that white smoke is generated when the injection completion timing is delayed.

Therefore, in the present invention, the fuel injection pressure is increased as the engine temperature increases so that the injection completion timing will not be delayed in response to the engine completion temperature being delayed and the injection completion timing being delayed. In this case, it is determined that the fuel injection pressure needs to be increased by about 10% as the engine temperature rises by 10 ° C. in order to prevent the injection completion timing from being delayed even if the engine temperature rises.

By the way, in the conventional plunger type fuel pump, when the engine temperature rises and the fuel temperature rises, the viscosity of the fuel decreases, so the leaked fuel from the plunger increases, and as a result, the fuel injection pressure increases even if the engine temperature rises. It won't be expensive. Therefore, in the conventional plunger type fuel pump, the fuel injection pressure cannot naturally increase as the engine temperature rises.

[Means for solving problems]

According to the present invention, in order to solve the above problems, the fuel discharged from the fuel supply pump whose discharge amount can be controlled is supplied to the electrically controlled fuel injection valve through the fuel supply passage, and the engine temperature increases. In a diesel engine in which the injection start timing is delayed as a result, a pressure sensor for detecting the fuel pressure in the fuel supply passage and a temperature sensor for detecting the temperature of the engine are provided. And a fuel pressure control means for controlling the discharge amount of the fuel supply pump so that the fuel pressure in the fuel supply passage becomes a target fuel pressure that increases as the engine temperature rises.

〔Example〕

Referring to FIGS. 1 and 2, 1 is a diesel engine body, 2 is a cylinder block, 3 is a cylinder head, 4
Is a piston, 5 is a combustion chamber, 6 is an intake valve, 7 is an exhaust valve, 8
Is a fuel injection valve arranged in the combustion chamber 5, 9 is an intake manifold, and the intake manifold 9 has a supercharger T at the inlet.
Connected to. The fuel injection valve 8 is connected via a fuel supply pipe 10 to a fuel pressure accumulation pipe 11 common to each cylinder. The fuel pressure accumulating pipe 11 has a pressure accumulating chamber 12 having a constant volume therein, and the fuel in the pressure accumulating chamber 12 is supplied to the fuel injection valve 8 via the fuel supply pipe 10. On the other hand, the pressure accumulator 12 has a fuel supply pipe 13
Is connected to the discharge port of the fuel supply pump 14 whose discharge pressure can be controlled. The suction port of the fuel supply pump 14 is connected to the discharge port of the fuel pump 15, and the suction port of the fuel pump 15 is connected to the fuel reservoir tank 16. Further, each fuel injection valve 8 is connected to a fuel reservoir tank 16 via a fuel return conduit 17. The fuel pump 15 is provided to feed the fuel in the fuel reservoir tank 16 into the fuel supply pump 14, and if the fuel can be sucked into the fuel supply pump 14 without the fuel pump 15, It is not necessary to provide the pump 15 in particular. On the other hand, the fuel supply pump 14 is provided for discharging high-pressure fuel, and the high-pressure fuel discharged from the fuel supply pump 14 is accumulated in the pressure accumulating chamber 12.

FIG. 3 shows a side sectional view of the fuel injection valve 8. Referring to FIG. 3, 20 is a fuel injection valve main body, 21 is a nozzle, 22
Is a spacer, 23 is a nozzle holder for fixing the nozzle 21 and the spacer 22 to the fuel injection valve main body 20, and 24
Is a fuel inlet, and 25 is a nozzle hole formed at the tip of the nozzle 21. Fuel injection valve body 20, spacer 2
2. A control rod 26, a pressure pin 27 and a needle 28 which are arranged in series in the nozzle 23 are slidably inserted. A fuel chamber 29 is formed above the control rod 26, and the fuel chamber 29 is connected to the pressure accumulating chamber 12 (FIG. 2) via the fuel inlet 24 and the fuel supply pipe 10. Therefore, the fuel pressure in the pressure accumulating chamber 29 is applied to the fuel chamber 29, and the fuel pressure in the fuel chamber 29 acts on the upper surface of the control rod 26. The needle 28 has a conical pressure receiving surface 3
0, and the needle pressure chamber 31 is provided around the pressure receiving surface 30.
Is formed. The needle pressurizing chamber 31 is connected to the fuel chamber 29 via the fuel passage 32 on the one hand, and is connected to the nozzle hole 25 via the annular fuel passage 33 formed around the needle 28 on the other hand. A compression spring 34 that urges the pressure pin 27 downward is inserted in the fuel injection valve body 20, and the needle 28 is pressed downward by the compression spring 34. The control rod 26 has a pressure receiving surface 35 having a conical shape in the middle thereof, and a control rod pressurizing chamber 36 is formed around the pressure receiving surface 35. The pressurizing chamber 36 is communicated with a cylinder 37 formed in the fuel injection valve main body 20, and a hydraulic piston 38 is slidably inserted in the cylinder 37. This hydraulic piston 38 has an O-ring 3
9 is attached.

On the other hand, a drive device 40 for driving the hydraulic piston 38 is attached to the fuel injection valve body 20. The drive device 40 includes a casing 41 fixed to the fuel injection valve body 20.
And a piezoelectric element 42 inserted between the piston 38 and the casing 40. This piezo piezoelectric element 42
Has a laminated structure in which a large number of thin plate piezoelectric elements are laminated, and when a voltage is applied to the piezoelectric element 42, the piezoelectric element 42 is distorted in the longitudinal direction due to the electrostrictive effect. That is, it extends in the longitudinal direction. This elongation is, for example, 50μ
Although it is a small amount of about m, the response is extremely good, and the response time from application of voltage to extension is about 80 μsec. When the voltage application is stopped, the piezoelectric element 42 contracts immediately. As shown in FIG. 3, the hydraulic piston 3
8, a disc spring 43 is inserted between the fuel injection valve body 20 and
The spring force of the disc spring 43 presses the hydraulic piston 38 toward the piezoelectric element 43. As shown in FIG. 4, a fuel passage 44 is formed in the hydraulic piston 38,
A check valve 45 is inserted in the fuel passage 44. Fuel is circulated between the casing 41 and the piezoelectric element 42 by a device (not shown) for cooling the piezoelectric element 42. When the fuel in the control rod pressurizing chamber 36 leaks, the fuel in the casing 41 is replaced by the fuel passage 44. Further, the pressure is replenished into the control rod pressurizing chamber 36 via the check valve 45.

When the fuel in the control rod pressurizing chamber 36 is not pressurized, the needle 28 has a downward force acting on the upper surface of the control rod 26, a downward force of the compression spring 34, and a pressure receiving surface 30 of the needle 28. An upward force acting on is applied.
At this time, the diameter of the control rod 26, the spring force of the compression spring 34, and the area of the pressure receiving surface 30 of the needle 28 are set so that the total of the downward force is slightly larger than the upward force. Therefore, a downward force acts on the normal needle 28, so that the normal needle 28 closes the nozzle hole 25. Next, when a voltage is applied to the piezoelectric element 42, the piezoelectric element 42 expands, so that the hydraulic piston 3
8 moves to the left, and as a result, the pressure in the control rod pressurizing chamber 36 increases. At this time, the pressure receiving surface 35 of the control rod 26
The control rod 26 rises due to the upward force acting on the nozzle hole 25 and thus the needle 28 rises.
Fuel is injected from. At this time, the response is about 80 μsec, which is extremely fast, as described above. On the other hand, when the voltage application to the piezoelectric element 42 is stopped, the piezoelectric element 42 contracts, and as a result, the control rod pressurizing chamber 36
Since the fuel pressure in the inside decreases, the control rod 26 and the needle 28 descend and the fuel injection is stopped. The response at this time is about 80 μsec, which is extremely fast. As described above, when the fuel in the control rod pressurizing chamber 36 is not pressurized, the diameter of the control rod 26 is adjusted so that the total downward force acting on the needle 28 is slightly larger than the upward force. The spring force of the compression spring 34 and the area of the pressure receiving surface 30 of the needle 28 are defined. Therefore, the needle 28 can be raised by applying a small upward force to the pressure receiving surface 35 of the control rod 26. That is, the fuel pressure in the control rod pressurizing chamber 36 to be raised in order to raise the needle 28 can be small, and thus the electric power to be applied to the piezoelectric element 42 can be small.

5 and 6 show an example of the fuel supply pump 14 whose discharge pressure can be controlled. Referring to FIG. 5, the fuel supply pump 14 is swingably attached to the pump casing 50 via a fixed shaft 51 fixedly supported by a pump casing 50, a rotor 52 rotating around the fixed shaft 51, and a pivot pin 53. And a ring 56 rotatably supported in the stator 54 via a bearing 55.
Have and. The rotor 52 includes a large number of radial pistons 57 arranged in a radial pattern.
A shoe 58 that rotates together with the radial piston 57 is inserted between the ring 7 and the ring 7. When the rotor 52 rotates, the radial piston 57 also rotates accordingly. At this time, the shoe 58 slides on the inner peripheral surface of the ring 56, and the ring 56 also rotates due to the frictional force with the shoe 58. A suction port 59 and a discharge port 60 are formed in the fixed shaft 51, the suction port 59 is connected to the fuel pump 15 (FIG. 1), and the discharge port 60 is connected to the pressure accumulating chamber 12 (FIG. 1). The cylinder chamber 61 of each radial piston 57 communicates with the suction port 59 and the discharge port 60 alternately. Since the radial piston 57 moves radially outward when the cylinder chamber 61 communicates with the suction port 59, fuel is sucked into the cylinder chamber 61 and compressed when the cylinder chamber 61 communicates with the discharge port 60. The fuel is discharged from the cylinder chamber 61 to the discharge port 60. The amount of fuel discharged to the discharge port 60 depends on the stroke of the radial piston 57, and the stroke of the radial piston 57 is determined by the position of the stator 54. Therefore, the discharge amount of the fuel supply pump 14 can be controlled by swinging the stator 54 around the pivot pin 53, and thereby the discharge pressure of the fuel supply pump 14 is controlled.

Referring to FIGS. 5 and 6, the pump casing 50
A control lever 62 that is slidable in the axial direction of the fixed shaft 51 is disposed in the lower part of the. The control lever 62 has a long groove 63 inclined with respect to the axis of the control lever 62, and an arm 64 formed in the lower portion of the stator 54 is slidably inserted into the long groove 63. Therefore, when the control lever 62 is moved in its axial direction, the stator 54 swings, and thereby the discharge pressure of the fuel supply pump 14 is controlled. The control lever 62 is connected to a drive device 66 via a speed reduction mechanism 65. In this embodiment, the driving device 66 is formed of a step motor, but it is not always necessary to use the step motor, and for example, a linear solenoid or other means can be used as the driving device 66. The drive lever 66 causes the control lever 62 to move in its axial direction, so that the discharge pressure of the fuel supply pump 14 is controlled by the drive device 66.

Referring again to FIG. 1, an electronic control unit 70 for controlling the fuel injection valve 8 and the drive device 66 is provided. The electronic control unit 70 is composed of a digital computer, and a ROM (read-on memory) 72, a RAM (random access memory) 73, a CPU (microprocessor) which are mutually connected by a bidirectional bus 71.
74, an input port 75 and an output port 76.

As shown in FIG. 1, a fuel pressure sensor 80 for detecting the fuel pressure in the pressure accumulating chamber 12 is attached to the end of the fuel pressure accumulating pipe 11. The fuel pressure sensor 80 generates an output voltage proportional to the fuel pressure in the pressure accumulating chamber 12, and the fuel pressure sensor 80 has an AD voltage.
It is connected to the input port 75 via the converter 81. On the other hand, a supercharging pressure sensor 82 for detecting a supercharging pressure in the intake manifold 9 is attached in the intake manifold 9. The supercharging pressure sensor 82 generates an output voltage proportional to the pressure in the intake manifold 9, and the supercharging pressure sensor 82 is an AD converter 83.
Is connected to the input port 75 via. A water temperature sensor 84 for detecting the engine cooling water temperature is attached to the engine body 1. The water temperature sensor 84 generates an output voltage proportional to the engine cooling water temperature, and the water temperature sensor 84 is connected to the input port 75 via the AD converter 85. Further, a load sensor 87 that generates an output voltage proportional to the amount of depression of the accelerator pedal 86 is attached to the accelerator pedal 86. The load sensor 87 is connected to the input port 85 via the AD converter 88. A pair of discs 89 and 90 are attached to the engine crankshaft.
A pair of crank angle sensors 91 facing the toothed outer peripheral surface of 90,
92 is arranged. One crank angle sensor 91, for example, generates an output pulse indicating that the first cylinder is at the intake top dead center. Therefore, it is determined which cylinder the fuel injection valve 8 should be operated from based on the output pulse of the crank angle sensor 91. You can decide. The other crank angle sensor 92 generates an output pulse each time the crankshaft rotates by a certain angle, and therefore the engine speed can be calculated from the output pulse of the crank angle sensor 92. These crank angle sensors 91 and 92 are connected to the input port 75. On the other hand, the output port 76 is connected via a drive circuit 93 to a drive device 66 composed of a step motor, and connected via a drive circuit 94 to the corresponding piezoelectric element 42 of the fuel injection valve 8.

Next, the operation of the fuel injection control device according to the present invention will be described with reference to FIGS. 7 to 11.

FIG. 7 shows a main routine, and this main routine is executed by interruption every fixed crank angle. Referring to FIG. 7, first, at step 100, the output signal of the crank angle sensor 92 indicating the engine speed N and the load sensor 8 indicating the depression amount L of the accelerator pedal.
7 output signal, the output signal of the supercharging pressure sensor 82 representing the supercharging pressure B, the output signal of the water temperature sensor 84 representing the engine cooling water temperature T, and the fuel pressure sensor 80 representing the fuel pressure P in the accumulator 12. Output signals are sequentially input into the CPU 74, and the engine speed N is calculated from the output signal of the crank angle sensor 92. The engine speed N, the accelerator pedal depression amount L, the boost pressure B, the water temperature T and the fuel pressure P are stored in the RAM 73. Next, in step 200, the injection amount τ is calculated, in step 300 the injection timing is calculated,
In step 400, the fuel pressure is controlled. Step
The calculation of the injection amount τ at 200 is shown in FIG. 8, the calculation of the injection timing at step 300 is shown in FIG. 9, and the control of the fuel pressure P at step 400 is shown in FIG.

FIG. 8 shows a flowchart for calculating the fuel injection amount τ. Referring to FIG. 8, first step 201
At, the basic fuel injection amount τ ₀ is calculated from the accelerator pedal depression amount, that is, the load L. FIG. 11 (a) shows the relationship between the basic fuel injection amount τ ₀ and the load L, and this relationship is stored in the ROM 72 in advance. Then step 202
Then, the supercharging correction coefficient K ₁ is calculated from the supercharging pressure P. First
As shown in FIG. 1 (b), the supercharging correction coefficient K ₁ increases as the supercharging pressure B increases. The relationship shown in FIG. 11 (b) is stored in the ROM 72 in advance. Next, at step 203, the injection amount τ = K ₁ · τ ₀ is calculated. Then step
At 204, the maximum injection amount MAX is calculated from the water temperature T. First
As shown in FIG. 1 (c), the maximum injection amount MAX becomes smaller as the water temperature T becomes higher in order to prevent the generation of white smoke. Next, at step 205, it is judged if the injection amount τ is larger than the maximum injection amount MAX. If τ> MAX, the routine proceeds to step 206, where τ = MAX. Therefore, the maximum injection amount MAX is limited by the water temperature T.

FIG. 9 shows a flowchart for calculating the fuel injection period. Referring to FIG. 9, first step 301
At, the injection start timing τ _a is calculated from the engine speed N and the load L. As shown in FIG. 11 (d), the injection start timing τ
_11, ... tau _mn and the engine speed N, the relationship between the load L is pre-ROM 72 in the storage in the form of a map, the injection start timing tau _a is calculated from this map. Next, at step 302, the water temperature correction coefficient K ₂ is calculated from the water temperature T. The water temperature correction coefficient K ₂ decreases as the water temperature T increases as shown in FIG. 11 (f), and the relationship shown in FIG. 11 (f) is stored in the ROM 72 in advance. Next, at step 303, the supercharging correction coefficient K ₃ is calculated from the supercharging pressure B. The supercharging pressure correction coefficient K ₃ increases as the supercharging pressure B increases as shown in FIG. 11 (e), and the relationship shown in FIG. 11 (e) is stored in the ROM 72 in advance. Next, at step 304, the correction factors K _{2 and} K ₃ are added to the injection start timing τ _a obtained at step 301 to obtain the actual injection start timing τ _a . The actual injection start timing τ _a becomes larger as K _{2 and} K ₃ increase.
That is, it is accelerated. A calculated injection amount tau in the routine shown in FIG. 8 in step 305 and then, the injection completion timing tau _b is calculated from the actual injection start timing tau _a. That is,
The injection completion timing τb is calculated from the injection period determined from the injection amount τ and the injection start timing τa. In this case, when the injection amount τ is determined, the injection period becomes shorter as the fuel pressure P in the pressure accumulating chamber 12 becomes higher. Therefore, the time from the start of injection to the completion of injection becomes shorter as the fuel pressure P in the pressure accumulating chamber 12 becomes higher. Become. The injection start timing τ _a and the injection completion timing τ _b thus obtained are output to the output port 76 in step 306, and the injection control of each fuel injection valve 8 is performed according to these τ _a and τ _b .

FIG. 10 shows a flowchart for controlling the fuel pressure P. Referring to FIG. 10, first step
At 401, the reference fuel pressure P ₀ is calculated from the engine speed N and the load L.
Is calculated. As shown in FIG. 11 (g), the reference fuel pressure P
₁₁ ... P _mn , the engine speed N, and the load L are stored in advance in the ROM 72 in the form of a map, and the reference fuel pressure P ₀ is calculated from this map. Next, at step 402, a water temperature correction coefficient K ₄ is calculated from the water temperature T. Water temperature correction coefficient K
₄ increases as the water temperature T increases as shown in FIG. 11 (i), and the relationship shown in FIG.
Stored in 2. Next, at step 403, the boost pressure correction coefficient K ₅ is calculated from the boost pressure B. The supercharging pressure correction coefficient K ₅ increases as the supercharging pressure B increases as shown in FIG. 11 (h), and the relationship shown in FIG.
It is stored in 72. Next, at step 404, the reference fuel pressure P ₀ obtained at step 401 is added to the correction coefficient K ₄ ,
The target reference fuel pressure P ₀ by multiplying K ₅ ,
That is, the target fuel pressure P ₀ is obtained. This target fuel pressure P ₀
Becomes larger as the water temperature T becomes higher, and becomes larger as the supercharging pressure P becomes higher. In this case, actually, when the water temperature T rises by 10 ° C., the target fuel pressure P ₀ is increased by about 10%. Next, at step 405, it is judged if the absolute value of the difference between the target fuel pressure P ₀ and the current fuel pressure P is smaller than ΔP. When | P ₀ −P | ≧ ΔP, the routine proceeds to step 406, where it is judged if P> P ₀ . When P> P _0, the routine proceeds to step 407, where a constant step number A from the step position ST of the driving device 66, that is, the step motor 66.
Is subtracted. As a result, the control lever 62 (FIGS. 5 and 6) of the fuel supply pump 14 is moved in the direction of decreasing the discharge pressure of the fuel supply pump 14, so that the pressure accumulating chamber 12
The fuel pressure inside immediately decreases. On the other hand, when P ≦ P _0, the routine proceeds to step 408, where the constant step number A is added to the step position ST of the step motor 66. As a result, the control lever 62 of the fuel supply pump 14 is moved in the direction of increasing the discharge pressure of the fuel supply pump 14, so that the fuel pressure in the pressure accumulating chamber 12 immediately rises. On the other hand, if it is determined in step 405 that | P ₀ −P | <ΔP, the processing routine is completed, and at this time, the step motor 66 is held stationary. In this way, the fuel pressure P in the pressure accumulating chamber 12 is maintained at the target fuel pressure P ₀ .

〔The invention's effect〕

As the engine temperature increases, the fuel pressure supplied to the fuel injection valve is increased, so that the fuel injection period is shortened.
Therefore, even if the engine temperature rises and the injection start timing is delayed, the injection completion timing is not delayed, so that white smoke can be prevented from being generated.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing a diesel engine, and FIG.
FIG. 3 is a side sectional view of a diesel engine, FIG. 3 is a side sectional view of a fuel injection valve, FIG. 4 is an enlarged plan sectional view of a hydraulic piston of FIG. 3, and FIG. 5 is a side sectional view of a fuel supply pump. 6
The figure is a plan view of the control lever and its drive unit of FIG.
FIG. 7 is a flow chart showing the main routine, FIG. 8 is a flow chart for executing the calculation of the injection amount, and FIG.
The figure shows a flow chart for performing the calculation of the injection period,
FIG. 10 is a flow chart for executing fuel pressure control, and FIG. 11 is a diagram showing correction factors and the like. 8 ... Fuel injection valve, 10, 13 ... Fuel supply pipe, 12 ... Accumulation chamber, 14 ... Fuel supply pump,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location F02D 43/00 G 7536-3G F02M 51/06 N 9248-3G

Claims (1)

[Claims] 1. A fuel supply pump capable of controlling a discharge amount supplies fuel to an electrically controlled fuel injection valve via a fuel supply passage, so that the injection start timing is delayed as the engine temperature rises. The diesel engine comprises a pressure sensor for detecting the fuel pressure in the fuel supply passage and a temperature sensor for detecting the temperature of the engine, and the fuel supply passage is based on the output signals of the temperature sensor and the pressure sensor. A fuel injection control device for a diesel engine, comprising fuel pressure control means for controlling the discharge amount of a fuel supply pump so that the internal fuel pressure becomes a target fuel pressure that increases as the engine temperature rises.