JP2767959B2 - Diesel engine fuel injection system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection device for a diesel engine, and more particularly to a fuel injection device in which fuel is injected at a low injection rate in the early stage of injection.

(Prior art) If more fuel is injected than at the beginning of the injection, the ignition delay will increase, increasing NOx and generating combustion noise. An apparatus has been proposed (see Japanese Utility Model Application Laid-Open No. 61-65269).

Referring to FIG. 13, the plunger barrel 2 formed integrally with the unit injector body 1 is provided with a plunger 3 for pressure-feeding fuel, which is slidable in the vertical direction in FIG. The pressure chamber 4 is formed by partitioning.

The pressurizing chamber 4 is connected to a fuel supply port 8 and a discharge port 9 via a supply port 6 and a discharge port 7, respectively.
A solenoid valve 10 for opening and closing the port 7 is interposed in the middle of the process. The fuel supply port 8 is connected to a discharge port of a feed pump via a pipe, and the fuel discharge port 9 is connected to a fuel tank via a pipe.

A nozzle needle 13 slidable up and down is provided on a nozzle body 12 of the injection nozzle 11 located below in the figure, and the needle 13 is urged downward by a nozzle spring 14. Reference numeral 15 denotes a seat for the nozzle spring 14, and reference numeral 16 denotes a valve opening pressure adjusting shim which also serves as a spring seat. The nozzle needle 13 closes the injection hole 17 opened at the lower end of the nozzle body 12 by the urging force of the nozzle spring 14.

The pressurizing chamber 4 is provided in the oil sump chamber 18 partitioned toward the nozzle needle 13 via fuel passages 21 to 23 provided in the nozzle body 12, the distance piece 19 and the cage 20, respectively.
Is communicated to. The nozzle body 12, the distance piece 19 and the cage 20 are fixed to the injector body 1 by a retaining nut 24.

A stepped central plunger 26 is slidably provided on a cylinder 25 formed along the axis of the cylindrical cage 20 and having an upper part communicating with the pressurizing chamber 4, and the plunger 26 is moved to a lower limit position by its own weight. At some point (as shown), an initial lift gap is formed between the lower end surface of the small diameter portion 26a extending downward and the upper end surface of the spring seat 15 in the valve closed state.
We are opposed to each other at the L _1. Further, between the upper end face and lower end face of the distance piece 19 of the nozzle needle 13 in the closed state, and it is opposed at a total lifting gap L _2.

The spring chamber 27 containing the nozzle spring 14 is provided in a return passage provided in the injector body 1 and the cage 20.
It communicates with the supply port 6 via 28 and 29.

A cylindrical portion 31 protruding above the injector body 1
A cylindrical member 32 is slidably provided on the inner peripheral surface of the member. While this member 32 is urged upward by a return spring 33, a plate cam (not shown) slides on its upper end surface. Touched. Numeral 34 denotes a spring seat which simultaneously connects the cylindrical member 32 of the plunger 3.

The plate cam (not shown) rotates in synchronization with the crankshaft of the engine.
Reciprocates, fuel is sucked into the pressurizing chamber 4 from the supply port 8 during the rising stroke, the supply port 6 is closed on the peripheral wall surface of the plunger 3 during the descending stroke, and the discharge port 7 is discharged.
Is shut off by closing the solenoid valve 10, the sucked fuel is pressurized, and the high-pressure fuel is sent to the oil reservoir 18 via the fuel passages 23 to 21.

This increases the pressure in the oil reservoir chamber 18, this pressure reaches valve opening pressure determined by the nozzle spring 14, the nozzle needle 13 upward against the initial lift gap L ₁ only nozzle spring 14. With this rise, the injection hole 17 opens and fuel is injected at a low injection rate.

When the fuel pressure in the pressurizing chamber 4 rises and the pressure in the oil sump chamber 18 rises and drops to the full valve opening pressure, the central plunger 26
Pressure receiving area Ac on the upper end surface of the nozzle and pressure receiving area Ad of the nozzle needle 13
The force corresponding to the difference (Ac-Ad) exceeds the urging force of the nozzle spring 14, and the nozzle needle 13 further rises by the force, and finally, the lift gap L ₂ from the valve-closed state.
Rise by a minute. Fuel region exceeding the initial lifting gap L ₁ is are injected at a high injection rate.

When the valve opening pressure of the nozzle needle 13 becomes two stages in this manner, the injection rate characteristics show that fuel is injected at a low injection rate at the beginning of injection as shown by the solid line in FIG. Fuel consumption and smoke are improved with less.

When the solenoid valve 10 is opened, the pressure in the pressurizing chamber 4 is released from the discharge port 7 and the discharge port 9 to the fuel tank.
Is again urged by the nozzle spring 14 to close the injection hole 17. This terminates the fuel injection.

The control unit controls the opening / closing timing of the solenoid valve 10, based on various data signals such as engine speed, engine load, cooling water temperature and exhaust temperature, and the injection quantity and injection timing most suitable for the operating state of the engine. Is determined, and is converted into a predetermined pulse and output to the electromagnetic valve 10.

(Problems to be Solved by the Invention) By the way, in such an apparatus, the initial lift gap L ₁
Since the order required is a very small value of several tens of μm, there is a limit in the accuracy control, and there is inevitably variation among cylinders. Due to such variations among the cylinders, the emission levels of NOx and HC deteriorate, and the combustion noise also increases.

The present invention has been made in view of such conventional problems, the initial lifting gap L ₁ estimates the cylinder from the injection pulse width during idling, by controlling so that optimal spacing, cylinder It is an object of the present invention to provide an apparatus for preventing a variation in the injection rate from occurring for each of them.

(Means for Solving the Problems) A first invention is a nozzle needle (13) for opening and closing an injection hole in a nozzle body (12), and the nozzle needle (1).
3) a first spring (55) for biasing the valve in the valve closing direction;
In the closed state at the nozzle needle (13) and the initial lifting gap L ₁ slidably arranged push rod (5
7) and a second nozzle (51) for urging the push rod (57) in the valve closing direction (51).
In a diesel engine fuel injection device comprising:
As shown in FIG. 1, a piezoelectric actuator 102 to the initial lifting gap L ₁ provided by the cylinder may be changed in accordance with the supply voltage, and means for determining 103 whether the idle stable state in cylinder idle Means 10 for detecting the injection pulse width of the injection nozzle (51) for each cylinder in a stable state
4 and the required injection pulse width (for example, Avi for the i-th cylinder) is a required value (for example, required injection pulse width Avs).
Means 105 for calculating the amount of voltage correction to the piezoelectric actuator 102 for each cylinder so as to match the reference supply voltage (Vv) based on the amount of voltage correction (for example, ΔVi for the i-th cylinder). Means 106 for deciding the supply voltage to each cylinder, and means 107 for supplying the determined supply voltage (for example, Vi for the i-th cylinder) to the piezoelectric actuator 102 of the corresponding cylinder.

According to a second aspect of the present invention, a plunger (3) for reciprocating in a plunger barrel (2) to pump fuel and a nozzle needle (1) for opening and closing an injection hole (17) in a nozzle body (12).
3), a nozzle spring (14) for urging the nozzle needle (13) in the valve closing direction, and a lifter provided between the plunger (3) and the nozzle needle (13). The fuel pressure during the plunger (3) pumping stroke acts, and the lower end face of the plunger (3) and the nozzle lift (13) in the closed state are separated from the initial lift gap L _1.
The fuel injection system for a diesel engine comprising a unit injector consisting a central plunger which faces (26) at a, as shown in FIG. 1, in accordance with the supply voltage the initial lifting gap L ₁ formed by the cylinder A piezoelectric actuator 102 that can be changed, a means 103 for determining whether the engine is in an idle stable state for each cylinder, a means 104 for detecting the injection pulse width of the unit injector in the idle stable state for each cylinder, and an injection pulse for each cylinder. Means 105 for calculating the amount of voltage correction to the piezoelectric actuator 102 for each cylinder so that the width (for example, Avi for the i-th cylinder) matches the required value (for example, the required injection pulse width Avs), and this voltage correction amount (for example, i The reference supply voltage (Vv) is corrected for cylinder No. ΔVi) and the supply voltage to the piezoelectric actuator 102 is determined for each cylinder. Determining means 106
And means 107 for supplying the determined supply voltage (for example, Vi for the i-th cylinder) to the piezoelectric actuator 102 of the corresponding cylinder.

(Operation) According to the present invention, so that the actual injection pulse width matches the required value, for example, the actual for injection pulse width is the smaller cylinder than the required value is the estimated initial lifting gap L ₁ is a broad , the supply voltage to the piezoelectric actuator 102 for cylinder is controlled, the initial lifting gap L ₁ is narrowed by this.

Since the initial lift gap L ₁ is estimated to narrow the larger cylinder than the required value Avs vice versa, is widely initial lift gap L ₁ of the cylinder, the gap L ₁ for the initial lift of each cylinder
Is adjusted to an optimum value.

(Embodiment) FIG. 2 is a sectional view of a distribution type fuel injection pump according to an embodiment of the first invention, and FIG. 3 is a sectional view of an injection nozzle 51 through which high-pressure fuel is guided from this pump.

In the injection pump, as shown in FIG. 2, two pumps are provided in a pump housing 41, a feed pump 42 that rotates in synchronization with the engine rotation, and a plunger pump 43 that pumps the fuel in the high-pressure chamber 45 to the injection nozzle. A drive pulse from the control unit is received in a fuel return passage 47 that communicates the low-pressure pump chamber 46 formed on the discharge side of the feed pump 42 with the high-pressure chamber 45, and the passage 47 is connected to the plunger pump 43. A high-speed responsive solenoid valve 48 that opens and closes during the pressurization process is interposed.

When the solenoid valve 48 is closed during the compression stroke of the plunger 44, the injection of fuel from an injection nozzle 51 described later is started,
When the electromagnetic valve 48 is opened after a predetermined period, the injection ends. That is, when the solenoid valve 48 closes, the fuel injection start timing becomes
The injection amount is controlled according to the valve closing period.

The injection nozzle 51 shown in FIG. 3 is configured such that both two-stage valve opening pressures are set by the elastic force of the spring, and the injection nozzle 51 is provided for each cylinder. For example, an oil sump chamber (not shown) from a fuel inlet 53 through a fuel passage 54
When the pressure of the fuel guided to the first reaches the first stage valve opening pressure determined by the elastic force of the first spring 55, the nozzle needle 13 moves the spring seat 15 and the spindle 56 upward in the figure against the first spring 55. The initial lift gap L ₁ between the spindle 56 and the spindle receiver (push rod) 57
Just rise and stop.

When the fuel pressure guided to the oil sump further increases and reaches a set pressure (second stage valve opening pressure) determined by the combined force of the first spring 55 and the second spring 58, the second spring 58
Pushes the spindle receiver 57 up against the nozzle needle 13
Rises.

Numerals 59 and 60 denote shims for adjusting the first-stage valve opening pressure and the second-stage valve opening pressure, respectively, and 61 denotes a sleeve for guiding the spindle 56.

62 is a piezoelectric actuator is interposed between the sleeve 61 and the spindle receiving 57, the initial lifting gap L ₁ is determined by the thickness of the actuator 62. This actuator
Reference numeral 62 denotes a piezoelectric element having a property of causing distortion when a voltage is applied, and is configured so that the thickness changes vertically in the figure due to the distortion. Here, Yes it made to be thick as the thickness voltage applied is high, it is possible to change the initial lifting gap L ₁ in accordance with the magnitude of the voltage applied.

Since the initial lift gap L ₁ is managed on the order of several tens of [mu] m, At the same order or an order of magnitude smaller orders piezoelectric material that varies (e.g. BaTiO _3, PZ
T, PbTiO ₃ etc.).

FIG. 4 is a block diagram of a control system. The control unit is composed of a microcomputer including an input / output circuit (I / O) 81, a ROM 82, a RAM 83, and a CPU 84.

The input / output circuit 81 includes only one pulse (reference pulse) 71 per revolution of the injection pump 71, 36 pulses (scale pulse) 72 per revolution, and a sensor 73 that detects an accelerator opening as an engine load. Instead, signals from sensors for detecting other operating conditions (fuel temperature sensor 74, water temperature sensor 75, idle switch 74, etc.) are input.

Reference numeral 77 denotes a sensor for detecting the valve closing timing and the valve opening timing of the solenoid valve 48, and is provided for the solenoid valve 48, for example, as shown in FIGS. 5 (A) and 5 (B). The opening / closing timing sensor 77 is formed by applying an insulating coating 48c to the outer periphery of a needle valve 48b that slides in the housing 48a, so that the needle valve 48b and the needle valve 48b are opened as shown in FIG. 5 (A). The housing 48a (both conductors) is insulated and the two are short-circuited when the needle valve 48b is seated as shown in FIG. 5 (B). A detection resistor (R) is connected in parallel to both. connection,
When a current i is applied to this, sensor outputs shown in FIG. 6 are obtained at both ends of R. In this case, the illustrated valve closing period corresponds to the fuel injection pulse width. The signal from the sensor 48 is also input to the input / output circuit 81.

The CPU 84 takes in information from the input / output circuit 81 in accordance with a program stored in the ROM 82, performs various arithmetic processing, and controls data (injection start time and injection end time) for the solenoid valve 48 and the piezoelectric actuator 62. Is set in the input / output circuit 81.

In this case, regarding the fuel injection control, the optimum injection timing and injection amount corresponding to various engine conditions such as engine speed, accelerator opening, cooling water temperature, fuel temperature, etc. are stored in the ROM 72. Reference pulse 71
And the scale pulse 72, the engine speed is calculated, and the basic injection timing and the basic injection amount are read out and read in accordance with the engine speed and the accelerator opening, and further considering the cooling water temperature and the fuel temperature. A drive pulse is generated from the information and output to the solenoid valve 48.

FIG. 7 is a routine for determining the supply voltage to the piezoelectric actuator 62, which is performed for each cylinder. However, in the figure, the cylinder number i (in the case of a four-cylinder engine, i takes an integer of 1 to 4) is represented.

S1 is a part that fulfills the function of the idling stable state determining means 103 in FIG. 1. Here, it is determined whether or not the i-th cylinder is in the idling stable state. For example, a difference ΔN (= N _SET −Ni) between a predetermined target idle speed N _SET and an actual idle speed Ni for the i-th cylinder is determined, and if the difference ΔN is equal to or less than a set value, a stable state is established. Judge that there is, and proceed to S2. Conversely, if the set value is exceeded, it is determined that the vehicle is not in a stable state and the control is terminated. The idle switch 76
Is ON, it is determined that the vehicle is idling.

S2 is a part that performs the function of the injection pulse width detecting means 104 in FIG. 1 together with the opening / closing timing sensor 77. The output signal of the opening / closing timing sensor 77 is input to calculate the actual injection pulse width Avi for the i-th cylinder. And read the calculated value.

In S3, the engine cooling water temperature Tw is read, and this water temperature Tw is read.
The idle required injection pulse width Avs common to all cylinders is determined in accordance with the above. For example, the characteristics as shown in FIG. 8 are stored as a map in the ROM 82, and the map is looked up. In FIG. 8, the reason why Avs is increased at a low water temperature is to stabilize combustion.

S4 and S5 are portions that fulfill the function of the voltage correction amount calculation means 105 in FIG.

In S4, a difference ΔAvi (= Avi−Avs) between the required injection pulse width Avs and the actual injection pulse width Avi read in S3 is calculated.

In S5, a voltage correction amount ΔVi for the i-th cylinder is obtained by looking up a map from the difference ΔAvi.

S6 is a part which fulfills the function of the supply voltage determining means 106 in FIG. 1. Here, a value obtained by adding this correction amount ΔVi to a reference supply voltage Vv common to each cylinder is supplied to the piezoelectric actuator 62 of the i-th cylinder. Determined as voltage Vi. This is represented by the following equation.

Vi = Vv + ΔVi FIG. 9 shows the map contents of the voltage correction amount ΔVi. ΔAvi
> 0, that is, if Avi> Avs, i corresponds to ΔAvi
Initial lifting gap L ₁ turn cylinder is estimated to narrow. In this case, it is necessary to increase the initial lifting gap L ₁ of the i-th cylinder. For that purpose, the piezoelectric actuator of the i-th cylinder
What is necessary is just to increase the voltage applied to 62. Therefore, ΔAvi
If> 0, the voltage correction amount ΔVi is given as a positive value. In contrast, since DerutaAvi <initial lifting gap L ₁ for the i-th cylinder in the case of 0 is estimated to broad, initial lift gap
L As ₁ becomes smaller, giving a negative value [Delta] Vi. The map having the contents shown in FIG. 9 is stored in the ROM 82.

In S7, the supply voltage Vi determined in S6 is stored at a predetermined address in the RAM.

 Here, the operation of this example will be described.

In this example, the feedback control by increasing or decreasing the thickness of the piezoelectric actuator 62 is performed for each cylinder so that the actual injection pulse width matches the required value. For example, the smaller cylinder than the actual injection pulse width required value Avs, for initial lifting gap L ₁ is narrowed by lowering the supply voltage to the piezoelectric actuator 62 for that cylinder. The larger cylinder than the required value Avs vice versa, the initial lifting gap L ₁ of the cylinder is wider.

As a result, the initial lifting gap L ₁ is set substantially close to the required value for any of the cylinders, the variation in the injection rate for each cylinder is suppressed, greatly improve each performance of the exhaust and noise Can be.

In contrast, in the conventional example, there is a limit to the quality control of the shim 16 for adjusting the initial lifting gap L _1, it is just the could not prevent the variation in the injection rate for each cylinder occurs .

Incidentally, what small provided the initial lifting gap L ₁ is
But in order to improve each performance of the exhaust and noise during low-speed low load, reducing the initial lifting gap L ₁ to a high load, as shown in FIG. 11 and affected, since the injection period prolonged However, it is not preferable from the viewpoint of measures against smoke, which becomes a problem at low speed and high load.

Therefore, by the time of low-speed high-load be greater than the low speed low load the initial lifting gap L ₁ by increasing the 62 supply voltage to the piezoelectric actuator, it is possible to make the smoke does not increase, this at this It is possible to achieve both output in the operating range and exhaust performance. FIGS. 10 and 11 show injection characteristics at low speed and low load and at low speed and high load.

FIG. 12 shows another embodiment applied to a unit injector using a so-called central plunger 26. In this embodiment, a piezoelectric actuator 91 is superimposed on a shim (also serving as a spring seat) 16 for adjusting the first-stage valve opening pressure. Is provided. The same parts as those in FIG. 13 are denoted by the same reference numerals.

In this example, the same operation and effect as those of the previous embodiment are obtained, but the piezoelectric actuator 91 is
Since it acts in the opposite direction to 62, it is necessary to reverse the sign of the correction amount ΔVi.

Finally, it goes without saying that the injection pump may be provided with a timer mechanism capable of adjusting the injection timing.

(Effects of the Invention) As described above, in the present invention, instead of the shim for adjusting the initial lift gap, a piezoelectric actuator capable of changing the gap is mounted for each cylinder, and each cylinder in the idle stable state is mounted. By driving the actuator so that the injection pulse width matches the required value and changing the initial lift gap, the variation in the injection rate of each cylinder can be reduced without using an initial lift gap measurement sensor or the like. It is possible to significantly reduce exhaust and noise performance.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of each invention, FIGS. 2 and 3 are cross-sectional views of a fuel injection pump and an injection nozzle of one embodiment of the first invention, and FIG. 4 is a control unit of this embodiment. 5 (A) and 5 (B) are block diagrams of the open / close timing sensor in the open and closed states of the solenoid valve 48 of this embodiment, and FIG. 6 is an output characteristic diagram of the sensor. 7, FIG. 7 is a flow chart for explaining the control operation of this embodiment, FIGS. 8 and 9 are characteristic diagrams showing the contents of each map used in the control operation of FIG. 7, and FIGS. figure characteristic diagram showing the injection rate and injection period when changing the initial lifting gap L ₁ during low-speed low load and low speed, high load, respectively, FIG. 12 second
FIG. 2 is a sectional view of a unit injector according to an embodiment of the present invention. FIG. 13 is a cross-sectional view of a conventional unit injector, and FIG. 14 is an injection characteristic diagram of a conventional example. 1 Unit injector body 2 Plunger barrel 3 Plunger 12 Nozzle body 13
... Nozzle needle, 14 ... Nozzle spring, 17 ... Injection hole, 26 ... Central plunger, 42 ... Feed pump, 43 ... Plunger pump, 45 ... High pressure chamber, 46 ...
Pump chamber, 47… Fuel return passage, 48… Solenoid valve, 51…
Injection nozzle, 55: first spring, 56: spindle, 57: spindle receiver (push rod), 58: second spring, 62: piezoelectric actuator, 71: reference pulse, 72: scale Pulse, 73: Accelerator opening sensor, 75: Water temperature sensor, 76: Idle switch, 77: Open / close timing sensor, 81: Input / output interface, 82: ROM, 83: RAM, 84: CPU , 91 ……
Piezoelectric actuator, 102 ... Piezoelectric actuator, 103
... Idle stable state determining means 104, injection pulse width detecting means 105, voltage correction amount calculating means 106, supply voltage determining means 107, energizing means

Claims (2)

(57) [Claims] 1. A nozzle needle for opening and closing an injection hole in a nozzle body, a first spring for urging the nozzle needle in a valve closing direction, and a gap for initial lift with the nozzle needle in a valve closed state. In a fuel injection device for a diesel engine including an injection nozzle including a push rod slidably disposed and a second spring for urging the push rod in a valve closing direction, the initial lift clearance provided for each cylinder is provided. , A means for determining whether the engine is in an idle stable state for each cylinder, a means for detecting the injection pulse width of the injection nozzle for each cylinder in a stable and idle state, Means for calculating the amount of voltage correction to the piezoelectric actuator for each cylinder so that the injection pulse width of Means for correcting the reference supply voltage with the pressure correction amount to determine the supply voltage to the piezoelectric actuator for each cylinder, and means for supplying the determined supply voltage to the piezoelectric actuator of the corresponding cylinder. Diesel engine fuel injection device. 2. A plunger for reciprocating in a plunger barrel to feed fuel, a nozzle needle for opening and closing an injection hole in a nozzle body, a nozzle spring for urging the nozzle needle in a valve closing direction, and the plunger. Between the nozzle needle and the nozzle needle. The upper end face of the plunger receives the fuel pressure during the pressure feeding stroke, and the lower end face of the plunger faces the nozzle needle in the closed state with a gap for the initial lift. In a diesel engine fuel injection device having a unit injector comprising a central plunger, a piezoelectric actuator provided for each cylinder and capable of changing the initial lift gap in accordance with a supply voltage, and determining whether or not the engine is in an idle stable state for each cylinder. Means for determining, and the unit Means for detecting the injection pulse width of the injector for each cylinder, means for calculating the voltage correction amount to the piezoelectric actuator for each cylinder such that the injection pulse width for each cylinder matches the required value, and A diesel engine comprising: means for correcting a reference supply voltage to determine a supply voltage to the piezoelectric actuator for each cylinder; and means for supplying the determined supply voltage to the piezoelectric actuator of the corresponding cylinder. Fuel injection device.