JPS61277827A - Fuel injector for diesel engine - Google Patents

Abstract

PURPOSE:To improve safety when an electric strain actuator is broken, by installing a stopper between a casing and a piston which forms a variable capacity chamber communicating to a pump chamber. CONSTITUTION:An electric strain actuator 21 and a piston 22 are accommodated into a casing 20, and a variable capacity chamber 26 whose capacity is varied by the movement of the piston 22 is allowed to communicate to a pump chamber 2. A stopper 50 having the less diameter than the outside diameter of the piston 22 is formed onto the inner peripheral surface of the casing 20. Therefore, even if the electric strain actuator 21 is broken, the piston contacts with the stopper after shifting by a prescribed distance, and safety is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fuel injection device for a diesel engine that controls the fuel injection rate of a fuel injection pump in a diesel engine.

(Prior Art) Conventionally, when fuel is injected into a diesel engine, the initial injection rate is reduced. Alternatively, pilot injection (preliminary injection before main injection) was known to have the effect of reducing diesel engine noise and harmful waste gases, as well as improving fuel efficiency.

However, the above-mentioned control of the injection rate has the problem of producing the opposite effect unless it is performed with high precision, and has not been carried out in reality.

On the other hand, systems have also been devised that attempt to optimally control the fuel injection rate in response to changes in engine operating conditions such as accelerator pedal travel and engine rotation. (For example, Japanese Patent Application Laid-Open No. 59-18249) This is equipped with a pressure chamber that communicates with the main injection pump chamber and houses a piston that is displaced according to the voltage applied to the piezo stack, and injects fuel according to the operating conditions of the engine. This method adjusts the rate, but it has the following problems. In other words, in order to drive a piezo stack (an electrostrictive actuator in which a large number of piezoelectric element thin plates are stacked, hereinafter referred to as an electrostrictive actuator), it is necessary to apply a high voltage from the outside, and the power supply circuit is particularly weak under in-vehicle conditions. It becomes complicated and expensive.

(Problems to be Solved by the Invention) The present invention has been made in view of the above points, and an object of the present invention is to operate an electrostrictive actuator without using a high-voltage power source.

On the other hand, there is a prior art (Japanese Patent Application No. 59-147788, etc.) in order to solve the above problem due to the present application, and this prior technology discharges the electric charge generated in the electrostrictive actuator when a compressive load is applied. This paper focuses on a new phenomenon in which an electrostrictive actuator contracts due to this phenomenon, and its basic principles and examples are disclosed. The present invention is based on the technology of the prior application described above, and further includes technical improvements.

A further object of the present invention is to ensure at least the same original injection as in the prior art even if the contraction control becomes impossible for some reason when contracting the electrostrictive actuator.

(Means for Solving the Problems) The present invention, as a technical solution to achieve the above object, introduces fuel into a pump chamber formed by a cylinder bore and a plunger manually fitted into the cylinder bore. In addition, in a diesel engine fuel injection device that changes the volume of a pump chamber to pressurize fuel and inject it from an injection valve, an electrostrictive actuator and a piston that responds to expansion and contraction of the electrostrictive actuator are housed in a casing. A variable volume chamber whose volume changes according to the movement of the piston is communicated with the pump chamber, and the injection rate of the fuel injected from the injection valve is controlled by expansion and contraction of the electrostrictive actuator, and the The present invention is characterized in that a stopper is provided that restricts the piston from moving beyond a predetermined distance in the direction in which the electrostrictive actuator expands and contracts.

(Function) According to the present invention, even if a part of the electrostrictive actuator is broken due to breakage or the like and its total length is shortened, the piston can still absorb the pressure received from the pump chamber and the variable volume chamber. After the electrostrictive actuator moves a predetermined distance in the direction of contraction, it comes into contact with the stopper and its movement is restricted. Therefore, since the volume of the variable volume chamber does not increase any further, the same fuel injection as before is ensured.

The configuration of a first embodiment of the present invention will be described based on FIG.

FIG. 1 is a partial sectional view in which the present invention is applied to a distribution type fuel injection pump. A feature of this configuration is that an injection rate control device 3 is provided directly connected to the pump chamber 2 of the distributed fuel injection pump.

First, the fuel injection pump l will be explained. Casing 4
A plunger 6 is slidably supported in the cylinder bore of
performs a rotational reciprocating motion in synchronization with 1/2 of the engine speed. That is, the rotation of the engine is transmitted to a drive shaft (not shown) via gears or a timing belt, and the plunger 6 is rotationally driven coaxially by this drive shaft, and the face cam 7 is engaged with the roller 8. This causes a reciprocating movement. The face cam 7 is always biased to the left in the figure by a spring (not shown) and is engaged with a roller 8. This is done by following the shape of the surface. The plunger 6 has one distribution boat 9 and the same number of suction boats 10a110b as the number of engine cylinders formed on its outer periphery,
A pump chamber 2 is formed between the tip surface of the plunger 6 and the cylinder bore 5.

The casing 4 is formed with a low pressure chamber 11, an intake passage 12 that communicates the low pressure chamber 11 with the cylinder bore 5, and a distribution passage 14 that allows each external injection valve 13 to communicate with the cylinder bore 5. The same number of distribution passages 14 as the number of engine cylinders are provided, and a delivery valve 15 is provided in each of them. The delivery valve 15 can be opened against the force of the spring 16, and has a function as a check valve and a suction valve. When the plunger 6 moves to the left and the pump chamber 2 expands, one of the suction boats 10 is connected to the suction passage 12 and the fuel in the low pressure chamber 11 is sucked into the pump chamber 2;
When the plunger 6 moves to the right and the pump chamber 2 is pressurized, the distribution port 9 is connected to one of the distribution passages 14, and the fuel in the pump chamber 2 is delivered to the outside. Fuel delivery begins when plunger 6 starts moving to the right, and
The flow ends when the flow moves to the right and the spill port 17 opens into the low pressure chamber 11 from the right end surface of the spill ring 18. Here, the spill port 17 is an opening provided in the plunger 6 for communicating between the pump chamber 2 and the low pressure chamber 11, etc. The spill ring 18 has a short cylindrical shape, and the inner hole of the spill ring 18 is an opening provided in the plunger 6. It is something that slides. spill ring 18
can be changed to its fixed position by the lever 19, and the discharge amount of the pump chamber 2 can be changed by the position of the spill ring 18. The lever 19 is indirectly linked to the accelerator lever.

Next, an injection rate control device according to the present invention will be explained.

The injection rate control device 3 includes, from the right in the figure, an electrostrictive actuator 21, a piston 22, a disc spring 23,
It is configured to house a distance piece 24. The casing 20 has a cylindrical shape with a bottom, and is fixedly attached to the injection pump 1 by a male thread 29 at its open end. An O-ring 28 is disposed around the outer periphery of the piston 22 to prevent the pressure in the pump chamber 2 from leaking through the piston 22 to the electrostrictive actuator 21 side.

A stopper 50 is formed in the casing 20 on the side where the electrostrictive actuator 21 is housed, which restricts the movement of the piston 22 to the right in the figure. The stopper 50 is the piston 2
The casing 21 has an annular contact surface that is formed on the inner circumferential surface of the casing 21 so as to have a smaller diameter than the outer diameter of the piston 2, and that the piston 22 contacts.

A notch 51 having a partial plane is provided on the outer peripheral surface of the piston 22 along the longitudinal direction of the piston 22. A locking bolt 53 is inserted from the outside of the casing 20 into a gap 52 formed by the notch 51 of the piston 22 and the inner peripheral sliding surface of the casing 20 . Note that the tip of the locking bolt 53 is connected to the piston 22.
It protrudes from the inner circumferential surface of the casing 20 to restrict rotation of the notch 51 and the retaining piston 22 to such an extent that it does not come into contact with the flat surface of the notch 51 .

The electrostrictive actuator 21 has a thin disc shape (φ15XtO
, 5) are laminated in approximately 50 layers to form a cylindrical shape. This electrostrictive element is a ceramic material called PZT, and its main component is lead zirconate titanate.
When a voltage of about 500V is applied in the thickness direction, the thickness becomes 1μm.
It stretches to some extent. If 50 of these elements are stacked and 500V is applied in the thickness direction of each element, a total elongation of 50 μm can be obtained. If this voltage is removed or a slight negative voltage is applied, the film will shrink by 50 μm and return to its original length. Further, when an axial compressive load is applied to the electrostrictive actuator 21, a voltage and a charge proportional to the load are generated in each electrostrictive element 5. For example, 500V with a 500kg load
voltage is generated.

The properties of these electrostrictive elements and electrostrictive cutuators are known.

Next, when the electric charge generated in proportion to this load is short-circuited or shot and released, the entire electrostrictive actuator 21 is shrunk in the axial direction. That is, 50 to the piston 22
Shooting the electrostrictive actuator 21 with a load of 0 kg causes a contraction of 50 μm, and a major feature of the present invention is that it utilizes this property. Operations such as applying a voltage to the electrostrictive actuator 21 at a predetermined time, short-circuiting, opening, etc. are performed using an external device via the lead wire 25 based on the pressure detected by the voltage generated in the electrostrictive actuator 21. It is controlled by a controller 100 which is a control circuit. The expansion and contraction action of the electrostrictive actuator 21 is transmitted to the piston 22, thereby expanding or contracting the volume of the pump chamber 2.

The operation of the injection rate control device will be explained.

When no external voltage is applied to the electrostrictive actuator 21 and no chute is applied, that is, when the electrostrictive actuator 21 is electrically open, the pressure in the pump chamber 2 is as shown in the curve labeled "Conventional" in Fig. 2. Become. The convex part shown in the figure is the discharge stroke, that is, when the plunger 6 is moving to the right and the spill port 17 is covered by the spill ring 18. Among these, the injection valve 13 is opened. The part higher than the pressure is the part that contributes to injection. That is, during this period, the injection valve 13
is open and its opening lift is proportional to its pressure. Therefore, the injection amount is also roughly proportional to the pressure.

Further, an electric charge proportional to the pressure in the pump chamber 2 is generated in the electrostrictive actuator 21, and a voltage is generated. .

The voltage generated by the electrostrictive actuator 21 at the start of injection is 400V. In addition, the controller 100 further increases the voltage generated in the electrostrictive actuator 21 and
When the voltage reaches 0■, that is, at a predetermined time immediately after the injection valve 13 starts injection, the electrostrictive actuator 21 is short-circuited to reduce the generated voltage to OV. At this time, the electrostrictive actuator 21 causes a contraction of 50 μm, so the piston 22 moves to the right and the volume of the variable volume chamber 26 expands, so that the pressure in the pump chamber 2 decreases and the injection valve 1
The injection valve from 3 is lowered and the pressure in the pump chamber 2 becomes the curve marked ``control'' in FIG. In this case, the injection valve 1
The injection from No. 3 can be temporarily interrupted to realize a form of pilot injection. However, in this case, the piston 22
does not come into contact with the stopper 50.

By the way, let us consider a case where the electrostrictive actuator 21 is damaged for some reason, that is, an abnormality in which the electrostrictive element is broken and the overall length of the electrostrictive actuator 21 is shortened. At this time, if the stopper 50 is not formed in the casing 21, when the plunger 6 is turned to the right and the pump chamber 2 is pressurized, the piston 22 of the injection rate control device 3 will move to the right in response to the pressure. Since the moving distance during the rightward movement is larger than that in the normal case, the volume of the variable volume chamber 26 is expanded, which is the same as that of the pump chamber 2, so that the pressure in the pump chamber 2 becomes difficult to rise. Here, if the pressure does not reach the valve opening pressure of the injection valve 13, no injection will occur, or if it is not high enough for the valve opening pressure, the injection amount will be extremely reduced compared to the normal case. On the other hand, when the stop horn 50 is formed in the piston 21, even in the case of the above-mentioned abnormality, the piston 22 moves to the right by a predetermined distance and comes into contact with the stopper 50. Since the abnormal movement to the right is regulated, there is no possibility that the injection amount will be drastically reduced or that the injection will not be possible.

In addition, when the piston 22 attempts to rotate, the rotation stopper bolt 53 that is inserted from the outside of the casing 20 collides with the rotation stopper bolt 53, so that the rotation can be suppressed. This can be done by preventing twisting of the lead wire 21 and also preventing the problem of wire breakage due to force being applied to the connection between the lead wire 25 and the electrostrictive actuator 21.

Next, a second embodiment will be explained based on FIG.

The difference from the first embodiment is that the stop collar 50 of the first embodiment is provided as a stopper 60 separately from the casing 20,
Furthermore, the material used for the stopper 60 has approximately the same longitudinal elastic modulus as that of the electrostrictive actuator.

In general, the longitudinal elastic modulus of an electrostrictive actuator is smaller than that of metal such as steel used for the casing 2o, and when the piston 22 hits the stopper 50 in the first embodiment, the contraction obtained in the electrostrictive actuator 21 Because there is no
In some cases, the injection amount may actually increase. On the other hand, by using a material for the stopper 60 that has almost the same modulus of longitudinal elasticity as the electrostrictive actuator 2, when the piston 22 hits the stopper 60, the same contraction as that of the electrostrictive actuator 21 can be obtained. A similar injection amount can be achieved.

A third embodiment will be described based on FIG. 4. Third
The feature of this embodiment is that the piston 2 is attached to the locking bolt 53.
The purpose is to have it also serve as the stopper function of 2. That is,
The distance from the left end of the notch 51 provided in the piston 22 to the locking bolt 53 is made equal to the predetermined distance between the piston 22 and the stopper 50 in the first embodiment. With the above structure, there is no need to separately provide a part of the stopper, and the stopper function and rotation prevention function can be fulfilled. Here, when the locking bolt 53 acts as a stopper, a large shear force is applied to the locking bolt 53, so the locking bolt 53 must have a material and shape that can sufficiently withstand it. Needless to say.

In the embodiments described above, a bolt was used to prevent the piston from rotating, but a bolt fixed to the casing using a pin or the like may also perform the same function.

(Effects of the Invention) As described above, even if the overall length of the electrostrictive actuator is shortened due to damage etc., the electrostrictive actuator will not be affected by the pressure that the piston receives from the pump chamber and the variable volume chamber. After the actuator moves a predetermined distance in the direction of contraction, it comes into contact with a stopper and is regulated. Therefore, since the volume of the variable volume chamber does not increase beyond a certain volume, at least fuel injection similar to that of a conventional fuel injection device in which the pump chamber does not communicate with the variable volume chamber is ensured.
The authenticity and safety of the device of the present invention can be improved.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a diesel engine fuel injection device showing a first embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the present invention in detail, and FIGS. FIG. 7 is a partial cross-sectional view showing second and third embodiments of the invention. 1...Fuel injection pump, 2...Pump chamber, 3...
Fuel injection rate control device, 4...Casing, 5...Cylinder bore, 6...Plunger, 13...Injection valve,
20... Casing, 21... Electrostrictive actuator, 22... Piston, 26... Variable volume chamber, 50.
60... Stopper, 51... Notch, 53... Bolt. Representative Patent Attorney Takashi Okabe Figure 2

Claims (2)

[Claims] (1) Fuel is introduced into a pump chamber formed by a cylinder bore and a plunger manually fitted into the cylinder bore, and the volume of the pump chamber is changed to pressurize the fuel and inject it from the injection valve. In a fuel injection device for a diesel engine, an electrostrictive actuator and a piston that responds to expansion and contraction of the electrostrictive actuator are housed in a casing, and a variable volume chamber whose volume changes depending on the movement of the piston is communicated with the pump chamber, a stopper that controls the injection rate of fuel injected from the injection valve by expansion and contraction of the electrostrictive actuator, and restricts the piston from moving more than a predetermined distance in the direction in which the electrostrictive actuator expands and contracts within the casing; A fuel injection device for a diesel engine, characterized in that it is provided with. (2) A notch having a plane extending in the longitudinal direction of the piston is formed on the outer periphery of the piston, and a rotation regulating member that engages with the notch to restrict rotation of the piston is provided. A fuel injection device for a diesel engine according to claim 1.