JPH0568638B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a fuel injection valve for an internal combustion engine.

[Conventional technology]

A fuel injection valve using a piezoelectric element is known to perform fuel injection control with good response in an internal combustion engine, especially a diesel engine (Japanese Patent Laid-Open No. 1983-1992).
(See Publication No. 17250 or Japanese Patent Application Laid-open No. 1369/1983). A piezoelectric element expands in the axial direction when voltage is applied, and the time from application of voltage to expansion is extremely short, from 50 μsec to 100 μsec, so utilizing the elongation action of the piezoelectric element can improve the response. Fuel injection control becomes possible. Therefore, in the fuel injection valve described in Japanese Patent Application Laid-Open No. 60-17250, the fuel pressure of high-pressure fuel acting on the pressure receiving surface of the needle is increased by the expansion action of the piezoelectric element to open the needle, thereby injecting fuel. I try to do this. On the other hand, in the fuel injection valve described in JP-A-60-1369, the fuel pressure of high-pressure fuel is applied to the needle end face on the opposite side from the nozzle hole.
The contracting action of the piezoelectric element lowers the fuel pressure of high-pressure fuel acting on the end face of the needle, opening the needle, thereby injecting fuel.

[Problem that the invention seeks to solve]

By the way, in these fuel injection valves, high fuel pressure is applied to the pressure receiving surface of the needle to apply a force in the valve opening direction to the needle, and high pressure fuel pressure is applied to the needle end face to apply a force in the valve closing direction to the needle to cause the needle to open. The needle is held in the valve-closed state by the difference in force acting on the needle pressure-receiving surface and the needle end surface without using a spring that biases the valve in the valve-closing direction. However, if you try to keep the needle closed using the fuel pressure acting on the needle pressure-receiving surface and the needle end face, the force that urges the needle in the valve-closing direction will weaken when the fuel pressure becomes low. There is a problem that the liquid leaks from the nozzle hole.

In addition, these fuel injection valves have a structure in which high fuel pressure acts directly on the piezoelectric element, so a large piezoelectric element is required to withstand the high fuel pressure, resulting in an increase in power consumption. There is a problem in that the amount increases.

Furthermore, the fuel injection valve described in JP-A-60-1369 introduces high-pressure fuel onto the end face of the needle through the vicinity of the needle, and temporarily lowers the pressure of this high-pressure fuel. This allows the needle to open. However, as the fuel pressure increases, as soon as the fuel pressure acting on the needle end surface decreases, the high pressure fuel is guided onto the needle end surface through the vicinity of the needle, so the needle closes immediately after opening. Therefore, there is a problem in that, in practice, when the fuel becomes high pressure, fuel injection control cannot be performed.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a fuel injection valve having a pressure receiving surface where the needle is spring-biased in the valve closing direction and receives fuel pressure in the needle valve opening direction. By applying fuel pressure to the end face of the control rod opposite to the needle and transmitting the fuel pressure to the needle via the control rod, a force is applied to the needle in the valve-closing direction, and the control rod is applied in the needle valve-opening direction. A piezoelectric element is provided for generating a control hydraulic pressure that provides a force, and the control hydraulic pressure is controlled by the piezoelectric element regardless of the fuel pressure.

〔Example〕

Referring to Figures 3 and 4, 1 is the diesel engine body, 2 is the cylinder block, 3 is the cylinder head, 4 is the piston, 5 is the combustion chamber, 6 is the intake valve, 7 is the exhaust valve, and 8 is the combustion chamber. The fuel injection valves 5 and 9 each represent an intake manifold, and the inlet portion of the intake manifold 9 is connected below the supercharger. 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 accumulator pipe 11 has a pressure accumulator chamber 12 with a constant volume inside thereof, and the fuel in this pressure accumulator chamber 12 is supplied to the fuel injection valve 8 via the fuel supply pipe 10. On the other hand, the pressure accumulation chamber 12 is connected via a fuel supply pipe 13 to a discharge port of a fuel supply pump 14 whose discharge pressure can be controlled. A suction port of the fuel supply pump 14 is connected to a discharge port of a fuel pump 15, and a suction port of the fuel pump 15 is connected to a fuel reservoir tank 16. Each fuel injection valve 8 is also 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, the fuel will be fed into the fuel supply pump 14. pump 15
There is no need to specifically provide this. On the other hand, the fuel supply pump 14 is provided to discharge high-pressure fuel, and the high-pressure fuel discharged from the fuel supply pump 14 is accumulated in the pressure accumulation chamber 12.

FIG. 1 shows a side sectional view of the fuel injection valve 8. Referring to FIG. 1, 20 is a fuel injection valve main body, 21
22 is a nozzle, 22 is a spacer, 23 is a nozzle holder for fixing the nozzle 21 and spacer 22 to the fuel injection valve body 20, 24 is a fuel inlet, 25
1 and 2 show nozzle holes formed at the tip of the nozzle 23, respectively. Fuel injection valve body 20, spacer 22,
A control rod 26, a pressure pin 27 and a needle 28 are slidably inserted into the nozzle 21 and are arranged in series with each other. A fuel chamber 29 is formed above the control rod 26, and this fuel chamber 29 is connected to a pressure accumulation chamber (FIG. 4) via a fuel inlet 24 and a fuel supply pipe 10. Therefore, the fuel pressure in the pressure accumulator 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 30, and a needle pressurizing chamber 30 is formed around this pressure receiving surface 30.
is formed. The needle pressurizing chamber 31 is connected to the fuel chamber 29 via a fuel passage 32 on the one hand, and to the nozzle hole 25 via an annular fuel passage 33 formed around the needle 28 on the other hand. A compression spring 34 that biases the pressure pin 27 downward is inserted into the fuel injection valve body 20, and the needle 28 is pressed downward by the bias spring 34. The control rod 26 has a conical pressure receiving surface 35 in its middle portion, and a control rod pressurizing chamber 36 is formed around this pressure receiving surface 35. The pressurizing chamber 36 is communicated with a cylinder 37 formed within the fuel injection valve body 20, and a hydraulic piston 38 is slidably inserted into the cylinder 37. An O-ring 39 is attached to this hydraulic piston 38.

On the other hand, a hydraulic piston 3 is provided in the fuel injection valve body 20.
A drive device 40 for driving 8 is attached. This drive device 40 includes a casing 41 fixed to the fuel injection valve body 20, and a piezoelectric element 4 inserted between the piston 38 and the casing 40.
Consists of 2. This piezoelectric element 42 has a laminated structure in which a large number of thin plate-shaped piezoelectric elements are laminated, and when a voltage is applied to this piezoelectric element 42, the piezoelectric element 42 generates longitudinal strain due to an electrostrictive effect. , i.e. extending in the longitudinal direction. Although the amount of elongation is a small amount, for example, about 50 μm, the response is extremely good, and the response time from application of voltage to elongation is about 80 μsec. When the voltage application is stopped, the piezoelectric element 42 immediately contracts. As shown in FIG. 1, a disc spring 43 is inserted between the hydraulic piston 38 and the fuel injection valve body 20, and the spring force of the disc spring 43 pushes the hydraulic piston 38 toward the piezoelectric element 42. Ru. As shown in FIG. 2, there is a fuel passage 4 inside the hydraulic piston 38.
A check valve 4 is formed in the fuel passage 44.
5 is inserted. Fuel is circulated between the casing 41 and the piezoelectric element 42 by a device (not shown) in order to cool the piezoelectric element 42, and if the fuel in the control rod pressurizing chamber 36, that is, the control oil leaks, the inside of the casing 41 of fuel is supplied into the control rod pressurizing chamber 36 via the fuel passage 44 and the check valve 45.

When the fuel in the control rod pressurizing chamber 36, that is, the control oil, is not pressurized, the needle 28 receives a downward force acting on the upper surface of the control rod 26, a downward force due to the compression spring 34, and the needle 28. An upward force acting on the pressure receiving surface 30 is applied. At this time, the diameter of the control rod 26 and the compression spring 34 are adjusted so that the total downward force is slightly larger than the upward force.
The spring force and the area of the pressure receiving surface 30 of the needle 28 are set. Therefore, a downward force is acting on the normal needle 28, and the normal needle 28 thus closes the nozzle hole 25. Next, when a voltage is applied to the piezoelectric element 42, the piezoelectric element 42 expands, causing the hydraulic piston 38 to move to the left, and as a result, the control hydraulic pressure in the control rod pressurizing chamber 36 increases. At this time, an upward force acts on the pressure receiving surface 35 of the control rod 26, causing the control rod 26 to rise, and thus the needle 28 to rise, so that fuel is injected from the nozzle hole 25.
As mentioned above, the response at this time is approximately 80 μsec, which is extremely fast. On the other hand, the piezoelectric element 42
When the voltage is removed from the piezoelectric element 42, the piezoelectric element 42 contracts, so that the control rod pressure chamber 36
The control rod 26 and needle 28 are lowered to stop fuel injection. At this time, the response time is approximately 80 μsec, which is extremely fast. As mentioned above, the control rod is adjusted so that the sum of the downward forces acting on the needle 28 when the fuel in the control rod pressurizing chamber 36, that is, the control oil, is not pressurized is slightly larger than the upward force. 26, the spring force of the compression spring 34, and the area of the pressure receiving surface 30 of the needle 28 are determined. Therefore, by applying a small upward force to the pressure receiving surface 35 of the control rod 26, the needle 28 can be raised. That is, the control hydraulic pressure in the control rod pressurizing chamber 36 to be increased in order to raise the needle 28 is small, and thus the piezoelectric element 4
Only a small amount of power is required for 2.

FIGS. 5 and 6 show an example of a fuel supply pump 14 whose discharge pressure can be controlled. Referring to FIG. 5, the fuel supply pump 14 is slidably attached to the pump casing 50 via a fixed shaft 51 fixedly supported by the pump casing 50, a rotor 52 rotating around the fixed shaft 51, and a pivot pin 53. a stator 54 and a ring 56 rotatably supported within the stator 54 via a bearing 55.
and has. The rotor 52 includes a plurality of radial pistons 57 arranged radially, and a shoe 58 that rotates together with the radial pistons 57 is inserted between each radial piston 57 and a ring 56. When the rotor 52 rotates, the radial piston 57 also rotates, and at this time the shoe 5
8 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, and the suction port 59 is connected to the fuel pump 15 (FIG. 3).
The discharge ports 60 are respectively connected to the pressure accumulation chamber 12 (FIG. 3). The cylinder chamber 61 of each radial piston 57 communicates with the suction port 59 and the discharge port 60 alternately. When the cylinder chamber 61 communicates with the suction port 59, the radial piston 57 moves radially outward, so that fuel is sucked into the cylinder chamber 61;
When the cylinder chamber 61 communicates with the discharge port 60, compressed fuel is discharged from the cylinder chamber 61 to the discharge port 60. The pressure of the 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, by swinging the stator 54 around the pivot pin 53, the discharge pressure of the fuel supply pump 14 can be controlled.

Referring to FIGS. 5 and 6, a control lever 62 that is slidable in the axial direction of the fixed shaft 51 is arranged at the bottom of the pump casing 50. This control lever 62 has a long groove 63 inclined with respect to the axis of the control lever 62, and the stator 5 is inserted into this long groove 63.
An arm 64 formed at the bottom of 4 is slidably inserted. Therefore, when the control lever 62 is moved in its axial direction, the stator 54 swings, thereby controlling the discharge pressure of the fuel supply pump 14.
The control lever 62 is connected to a drive device 66 via a speed reduction mechanism 65. In this embodiment, the drive device 66
is formed from a step motor, but it is not necessary to use a step motor. For example, a linear solenoid or other means may be used as the drive device 66. The drive device 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. 3, an electronic control unit 70 is provided for controlling the fuel injector 8 and drive 66. This electronic control unit 70 consists of a digital computer, and includes a ROM (read-on memory) 72, a RAM (random access memory) 73, a CPU (microprocessor) 74, and an input port that are interconnected by a bidirectional bus 71. 75 and an output port 76.

As shown in FIG. 3, a fuel pressure sensor 80 for detecting the fuel pressure within the pressure accumulation chamber 12 is attached to the end of the fuel pressure accumulation pipe 11. The fuel pressure sensor 80 generates an output voltage proportional to the fuel pressure within the accumulator chamber 12;
This fuel pressure sensor 80 is connected to the input port 75 via an AD converter 81. On the other hand, a boost pressure sensor 82 is installed inside the intake manifold 9 to detect the boost pressure inside the intake manifold 9. The boost pressure sensor 82 generates an output voltage proportional to the pressure inside the intake manifold 9.
It is connected to input port 75 via converter 83 . Further, a water temperature sensor 84 is attached to the engine body 1 to detect the engine cooling water temperature. Water temperature sensor 8
4 generates an output voltage proportional to the engine cooling water temperature,
This water temperature sensor 84 is connected to the input port 75 via an 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 . This load sensor 87 is connected to the input port 75 via an AD converter 88. In addition, a pair of disks 89 and 90 are installed on the engine crankshaft.
A pair of crank angle sensors 91,
92 is placed. One crank angle sensor 91
For example, it generates an output pulse indicating that the No. 1 cylinder is at the intake top dead center, and therefore it can be determined from the output pulse of this crank angle sensor 91 which cylinder's fuel injection valve 8 is to be operated. .
The other crank angle sensor 92 generates an output pulse every time the crankshaft rotates by a certain angle,
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 input port 75. On the other hand, the output port 76 is connected via a drive circuit 93 to a drive device 66 consisting of a step motor, and via a drive circuit 94 to the piezoelectric element 42 of the corresponding fuel injection valve 8 .

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

FIG. 7 shows the main routine, which is executed by an interrupt at every fixed crank angle. Referring to FIG. 7, first, at step 100, the output signal of the crank angle sensor 92 representing the engine speed N, the output signal of the load sensor 87 representing the amount of depression L of the accelerator pedal, and the supercharging pressure representing the supercharging pressure B. The output signal of the sensor 82, the output signal of the water temperature sensor 84 representing the engine cooling water temperature T, and the fuel pressure P in the pressure accumulator 12 are shown. The output signals of the fuel pressure sensor 80 are sequentially input into the CPU 74, and the engine speed N is calculated from the output signal of the crank angle sensor 92. These engine speed N, accelerator pedal depression amount L, supercharging pressure B, water temperature T, and 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, and in step 400, the fuel pressure P is controlled. The calculation of the injection amount τ in step 200 is shown in FIG. 8, the calculation of the injection timing in step 300 is shown in FIG. 9, and the control of the fuel pressure P in step 400 is shown in FIG.

FIG. 8 shows a flowchart for calculating the fuel injection amount τ. Referring to FIG. 8, first, in step 201, the basic fuel injection amount τ ₀ is calculated from the amount of depression of the accelerator pedal, that is, the load L. FIG. 11a shows the relationship between the basic fuel injection amount τ ₀ and the load L, and this relationship is determined in advance by the ROM 72.
stored within. Next, in step 202, a supercharging correction coefficient _K1 is calculated from the supercharging pressure P. As shown in FIG. 11b, the supercharging correction coefficient _K1 increases as the supercharging pressure P increases. The relationship shown in FIG. 11b is stored in the ROM 72 in advance.
Next, in step 203, the injection amount τ=K ₁ ·τ ₀ is calculated. Next, in step 204, the maximum injection amount MAX is calculated from the water temperature T. As shown in Figure 11c, the maximum injection amount is required to prevent the generation of white smoke.
MAX becomes smaller as the water temperature T becomes higher.
Next, in step 205, the injection amount τ is set to the maximum injection amount.
It is determined whether or not it is larger than MAX. τ＞
If it is MAX, proceed to step 206 and τ=
It is said to be 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, in step 301, the engine speed N and the load L are determined.
The injection start timing τ _a is calculated from . As shown in Fig. 11d, the relationship between the injection start timing τ ₁₁ ...τ _no , the engine speed N, and the load L is determined in advance in the form of a map in the ROM 7.
2, and the injection start time τ _a is calculated from this map. Next, in step 302, a water temperature correction coefficient _K2 is calculated from the water temperature T. The water temperature correction coefficient K ₂ is determined by the water temperature T as shown in Figure 11f.
The relationship shown in FIG. 11f is stored in the ROM 72 in advance. Next, in step 303, the supercharging correction coefficient _K3 is calculated from the supercharging pressure P.
is calculated. The supercharging correction coefficient _K3 increases as the supercharging pressure P increases as shown in FIG. 11e, and the relationship shown in FIG. 11e is stored in the ROM 72 in advance. Then, in step 304, step 3
The correction _coefficient K ₂ ,
K ₃ is added to determine the actual injection start time τ _a . The actual injection start timing τ _a increases, that is, becomes faster, as K ₂ and K ₃ increase. Next, in step 305, the injection amount τ calculated in the routine shown in FIG. 8 and the actual injection start timing τ _a
The injection completion time τ _b is calculated from . The injection start time τ _a and injection completion time τ _b thus obtained are outputted to the output port 76 in step 306.
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, in step 401, a reference fuel pressure _P0 is calculated from the engine speed N and the load L. As shown in Fig. 11g, the relationship between the reference fuel pressure _P11 ...P _no , the engine speed N, and the load L is determined in advance by ROM in the form of a map.
72, and the reference fuel pressure P ₀ is calculated from this map. Next, in step 402, a water temperature correction coefficient _K4 is calculated from the water temperature T. The water temperature correction coefficient _K4 is determined by the water temperature T as shown in Figure 11i.
The relationship shown in FIG. 11i is stored in the ROM 72 in advance. Next, in step 403, a boost pressure correction coefficient _K5 is calculated from the boost pressure P. The boost pressure correction coefficient _K5 is the first
As shown in Fig. 1h, the boost pressure increases as the boost pressure P increases, and the relationship shown in Fig. 11h is determined in advance by the ROM 7.
It is stored in 2. Next, in step 404, the target reference fuel pressure _P0, that is, the target fuel pressure _P0 , is determined by multiplying the reference fuel pressure _P0 determined in step 401 by the correction coefficients _K4 and _K5 . This target fuel pressure P ₀ increases as the water temperature T increases, and as the supercharging pressure P increases, the target fuel pressure P 0 increases. Next, in step 405, it is determined whether 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 process advances to step 406, where it is determined whether P>P ₀ . When P>P ₀ , the program proceeds to step 407, where a fixed number of steps A is subtracted from the step position ST of the drive device 66, that is, the step motor 66. 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 fuel pressure within the pressure accumulator chamber 12 immediately decreases. On the other hand, when P≦P ₀ , the routine proceeds to step 408, where a predetermined number of steps 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 within the pressure accumulation chamber 12 immediately increases. on the other hand,
If it is determined in step 405 that |P ₀ -P|<ΔP, the processing routine is completed, and the step motor 66 is held stationary at this time. In this way, the fuel pressure P in the pressure accumulator chamber 12 is maintained at the target fuel pressure _P0 .

〔Effect of the invention〕

Since a spring is provided that always biases the needle in the valve-closing direction, a valve-closing force above a certain pressure is always applied to the needle regardless of the magnitude of the fuel pressure, and in this way, when the needle closes, the nozzle hole There is no risk of fuel leaking from the In addition, fuel pressure does not directly act on the piezoelectric element, and the needle opens by slightly increasing the control oil pressure acting on the control rod, allowing the use of a small piezoelectric element, reducing power consumption. can do.

[Brief explanation of drawings]

Figure 1 is a side sectional view of a fuel injection valve, Figure 2 is an enlarged plan sectional view of the hydraulic piston in Figure 1, Figure 3 is a schematic plan view of a diesel engine, and Figure 4 is a diagram of a diesel engine. 5 is a side sectional view of the fuel supply pump, FIG. 6 is a plan view of the control lever of FIG. 5 and its driving device, FIG. 7 is a flowchart showing the main routine, and FIG. Flowchart for performing quantity calculations, No. 9
This figure is a flowchart for calculating the injection period, FIG. 10 is a flowchart for controlling fuel pressure, and FIG. 11 is a diagram showing correction coefficients and the like. 8... Fuel injection valve, 10, 13... Fuel supply pipe, 12... Pressure accumulation chamber, 14... Fuel supply pump,
26...control rod, 28...needle, 30,
35...Pressure receiving surface, 34...Compression spring, 38...Hydraulic piston, 42...Piezoelectric element.

Claims (1)

[Claims] 1. A fuel injection valve having a pressure receiving surface in which a needle biased by a spring in the valve closing direction receives fuel pressure in the needle valve opening direction, comprising a control rod disposed in series with the needle, and a control rod on the opposite side of the needle. To generate control hydraulic pressure that applies fuel pressure to the end face and transmits the fuel pressure to the needle via the control rod to apply a force in the valve closing direction to the needle and to apply a force in the needle valve opening direction to the control rod. 1. A fuel injection valve for an internal combustion engine, comprising a piezoelectric element, the control oil pressure being controlled by the piezoelectric element independently of the fuel pressure.