JPH0128300Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a fuel injection detection device for a diesel engine using a piezoelectric element.

<Prior art> A piezoelectric element directly receives a spring attached to a spring seat on the needle valve, and the piezoelectric element is distorted by changes in stress on the pressure-receiving surface due to its elasticity and contraction, producing an output that is synchronized with the injection timing. An injection detection device for a fuel injection device that extracts the fuel is known as disclosed in Japanese Patent Laid-Open No. 113044/1983.

<Problem to be solved by the invention> However, the above-mentioned known structure causes strain in the piezoelectric element due to stress changes caused by the elasticity and contraction of the spring, and since transmission by the spring causes a delay, the structure shown in FIG. As shown in Figure 4, there is a difference of about 400 μsec a between the generation timing of the output signal from the piezoelectric element and the actual fuel injection timing (the rise of the rectangular wave in Figure 4 A).
This resulted in the inability to accurately detect fuel injection timing.

The present invention aims to eliminate the above drawbacks.

<Means for Solving the Problems> The present invention uses a needle valve slidably mounted in the injection housing to close the injection port by the force of a spring attached to the needle valve, thereby reducing the fuel pressure. In a fuel injection device for a diesel engine that moves the needle valve against a spring to open the injection port intermittently as the needle valve rises, a sealed working chamber is provided in a spring seat attached to the needle valve. , a diaphragm that curves due to inertia as the needle valve moves up and down is supported in the working chamber so that its thickness direction coincides with the direction of movement of the needle valve, and a main surface of the diaphragm is This is characterized in that the piezoelectric element is fixed and the signal extraction lead wire connected to the electrode of the piezoelectric element is led out of the injection casing.

<Operation> As the needle valve moves, the diaphragm bends due to its inertial force. The bending causes distortion in the piezoelectric element, which causes the piezoelectric element to generate an output signal that is synchronized with the fuel injection of the diesel engine.

Therefore, the output signal can be extracted from the lead wire directly by raising and lowering the needle valve without depending on stress changes caused by elastic contraction of the spring.

<Example> In Fig. 1, 1 is a hollow nozzle holder 2
This is a well-known injection housing consisting of a nozzle body 4 connected to the lower part of the holder 2 by a nozzle nut 3, and a nozzle cap 5 screwed to the upper part of the holder 2. A lower needle valve guide hole 8 communicating with the injection port 6 at the lower end of the nozzle body 4 and a fitting hole 9 having a slightly smaller diameter than the guide hole 8.
A communication hole 12 is formed in which the fitting hole 9 and the upper spring mounting hole 11 communicate with each other via the tapered support surface 10.

A pipe connecting beak 13 is attached to the side of the nozzle holder 2.
from the fuel supply pipe 14 connected to the connecting beak 13 through the fuel passage 16 formed in the nozzle holder 2 and the nozzle body 4 between the needle valve guide hole 8 and the injection hole 6 at the lower end of the nozzle body 4. Fuel oil is supplied to the supply circumferential hole 7 of.

A needle valve 15 having a tapered surface 15a at the bottom facing the supply peripheral hole 7 is inserted into the needle valve guide hole 8,
A spring seat 2 is mounted on the needle valve 15 by a connecting pin 21.
0 are connected, and a spring 17 attached between the lower surface of the nozzle cap 5 and the spring seat 20 causes the inclined lower surface 21a of the spring seat 20 to be connected to the tapered support surface 1.
Close contact with 0. In the center of nozzle cap 5,
A communication bolt 18 having an insertion hole 18a is screwed in from above.

Further, a connecting beak 19 is screwed onto the side surface of the nozzle holder 2 to communicate with the spring mounting hole 11 and to discharge leaked oil from the hole 11.

FIG. 2 shows an embodiment of the spring seat 20, which includes a base body 23 which has a locking surface 22 projecting on the circumferential side to receive the spring 17, and on which the connecting pin 21 is fitted, and the base body 23. The outer casing is formed by a cylinder 26 that is externally fitted and fixed to a fitting end 24 formed on the upper surface, and an insulator 28 that is fitted from below into a fitting hole 27 provided in the upper wall of the cylinder 26. A working chamber 30 is formed by the groove 25 provided on the upper surface of the base body 23 and the inside of the cylindrical body 26 .

31 is a plate-shaped piezoelectric element having an output side electrode 32a on the upper surface and a ground side electrode 32b on the lower surface, and a diaphragm 33 having an outer diameter equal to the inner diameter of the cylinder 26 is fixed to the lower surface. Further, the piezoelectric element 3
1 is mounted on the open groove 25 of the working chamber 30 by mounting and fixing the diaphragm 33 on the fitting end 24. Thus, the piezoelectric element 31 and the diaphragm 33
A sensing member is configured.

The output side electrode 32a is electrically connected to an external control device by a signal extraction lead wire 35. That is, the conductor of the lead wire 35 is connected to the output side electrode 32a, the conductor is passed through the insertion tube 29 fitted in the center of the insulator 28, and then the conductor of the lead wire 35 is connected to the output side electrode 32a.
is passed through the spring mounting hole 11 and pulled out from the insertion hole 18a of the communicating bolt 18. At this time, the outer end of the insertion tube 29 and the insertion end of the lead wire 35 are held insulatively by an insulating resin material 36.

The operation of the above embodiment will be explained.

When the fuel oil supply pressure is increased by driving a plunger pump or the like, an axial force is applied by the tapered surface 15a, causing the needle valve 15 to rise at high speed against the elastic force of the spring 17. For this reason, the injection hole 6 is opened and fuel oil is injected. At this time, the piezoelectric element 31 installed in the spring seat 20 is such that even if the spring seat 20 rises rapidly, the diaphragm 33 has flexibility.
Due to inertia, the vibration plate 33 moves slowly as shown in Figure 3.
At the same time, it curves downward and causes distortion.

Therefore, as shown in FIG. 4B, an output signal is generated from the piezoelectric element 31 in synchronization with the injection start timing (the rising timing of the rectangular wave in FIG. 4A).

In order to increase the inertial force, a weight 34 may be attached to the lower surface of the diaphragm 33, and in this case,
The sensitivity of the piezoelectric element 31 becomes even better.

Further, in this embodiment, the diaphragm 33 is attached to the fitting end 24 to hold the periphery, but the center of the diaphragm 33 is fixed to the base 23, and the periphery is made vertically swingable, so that the inertia The piezoelectric element 31 may be distorted by curving its periphery, and in this case, the weight 34 is fixed to the periphery of the diaphragm 33.

<Effects> As clarified from the above explanation, the present invention includes a diaphragm 33 which is curved by the inertial force accompanying the elevation of the needle valve 15 in the spring seat 20 attached to the needle valve 15. is provided, and the piezoelectric element 31 is fixed to the vibration plate 33 to constitute a sensing member, and by the inertial force,
Since the piezoelectric element 31 is made to generate a signal output, the injection timing can be accurately detected without causing a delay in response, unlike the piezoelectric element 31 which is distorted due to stress changes caused by elastic contraction of the spring 17. There are excellent effects that can be achieved.

[Brief explanation of the drawing]

The accompanying drawings show embodiments of the invention, and FIG.
Vertical side view of the fuel injection device, Figure 2 shows the spring seat 20
FIG. 3 is a vertical side view showing the operating state. FIG. 4 is a response correspondence diagram with the conventional device, in which FIG. 4A shows the movement of the needle valve 15, FIG. 4B shows the output signal timing of the device of the present invention, and
Figure C shows the output signal timing of the conventional device. 15... needle valve, 17... spring, 20... spring seat, 30... working chamber, 31... piezoelectric element, 33...
...Diaphragm, 35...Lead wire.

Claims (1)

[Scope of Claim for Utility Model Registration] A needle valve slidably mounted in the injection casing closes the injection port by the force of a spring attached to the needle valve, and as the fuel pressure increases. In a diesel engine fuel injection device in which the needle valve is moved against a spring to intermittently open an injection port, a sealed working chamber is provided in a spring seat attached to the needle valve, and a sealed working chamber is provided inside the working chamber. A piezoelectric element is fixed to the main surface of the diaphragm by supporting a diaphragm that curves due to inertia as the needle valve moves up and down so that its thickness direction coincides with the direction of movement of the needle valve. A fuel injection detection device for a diesel engine, characterized in that a signal extraction lead wire connected to the electrode of the piezoelectric element is led out of the injection casing.