JP4618257B2 - Fuel injection valve - Google Patents

Description

  The present invention relates to a fuel injection valve for injecting fuel into a heat engine.

In the fuel injection valve proposed in Patent Document 1, a sliding shaft portion (piston portion) of a nozzle needle that opens and closes an injection hole is slidably inserted into a pressure compartment sliding component (cylindrical member). Also, by making this pressure compartment sliding part a separate part from the nozzle body, the sliding part clearance between the sliding shaft part and the pressure compartment sliding part expands at high pressure, increasing the amount of leakage from the sliding part clearance. I try to suppress it.
JP 2005-256759 A

  However, in the conventional fuel injection valve, the amount of leakage from the sliding portion clearance produces a temperature characteristic due to the temperature dependence of the viscosity of the fluid flowing through the sliding portion clearance, and thus the temperature characteristic of the fuel injection amount.

  In view of the above points, an object of the present invention is to suppress the amount of leakage from the sliding portion clearance from changing according to temperature.

In the present invention, a seat portion (21b) that opens and closes a nozzle hole (24) by contacting and separating from a valve seat (25) is formed on one end side, and a columnar shape inserted into a cylindrical nozzle sleeve (23) A nozzle needle (21) having a piston portion (21a) provided on the other end side, a nozzle body (1) for accommodating the nozzle needle (21) and the nozzle sleeve (23), and an inner periphery of the nozzle sleeve (23) A control chamber (26) formed by the surface and the piston portion (21a) for applying fuel pressure to the surface on the other end side of the nozzle needle (21), and the nozzle needle (21) on the nozzle hole (24) side. And a nozzle spring (22) for urging the nozzle sleeve (23) in the direction opposite to the nozzle hole (24), and controlling the fuel pressure in the control chamber (26) to make the nozzle needle (21) A fuel injection valve for controlling the opening and closing valve operation, the linear expansion coefficient of the nozzle sleeve (23) [alpha] 1, when the linear expansion coefficient of the nozzle needle (21) and the [alpha] 2, characterized in that it is a [alpha] 1 <[alpha] 2 .

In this case, since the change in the leak amount from the sliding portion clearance between the nozzle sleeve (23) and the piston portion (21a) is suppressed, the pressure change in the control chamber (26) when the on-off valve of the nozzle needle (21) is operated. It is suppressed that a speed changes according to temperature. As a result, it is possible to prevent the fuel injection characteristic from changing due to the opening / closing valve speed of the nozzle needle (21) changing according to the temperature.

  In addition, the code | symbol in the bracket | parenthesis of each means described in a claim and this column shows the correspondence with the specific means as described in embodiment mentioned later.

  An embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing the overall configuration of a fuel injection device including a fuel injection valve according to an embodiment of the present invention, and FIG.

  The fuel injection valve is mounted on a cylinder head of an internal combustion engine (more specifically, a diesel engine, not shown) and injects high-pressure fuel stored in a pressure accumulator (not shown) into the cylinder of the internal combustion engine. It is.

  As shown in FIGS. 1 and 2, the nozzle body 1 of the fuel injection valve includes a fuel inlet portion 11 into which high-pressure fuel from the pressure accumulator is introduced, and a fuel that causes the fuel inside the fuel injection valve to flow out toward the fuel tank 100. And an outlet 12.

  A nozzle 2 that injects fuel when the valve is opened is disposed on one end side in the axial direction of the nozzle body 1. The nozzle 2 includes a nozzle needle 21 that is slidably held on the nozzle body 1, a nozzle spring 22 that urges the nozzle needle 21 in a valve closing direction, and a cylindrical portion into which a piston portion 21a of the nozzle needle 21 is inserted. And a nozzle sleeve 23. The nozzle sleeve 23 corresponds to the cylindrical member of the present invention.

  At one end in the axial direction of the nozzle body 1, an injection hole 24 communicating with the fuel inlet 11 through the high-pressure fuel passage 13 is formed, and high-pressure fuel is injected from the injection hole 24 into the cylinder of the internal combustion engine. Yes. The nozzle body 1 is formed with a tapered valve seat 25 on the upstream side of the nozzle hole 24, and the nozzle needle 21 is formed with a seat portion 21 b on the side opposite to the piston portion, and this seat portion 21 b contacts the valve seat 25. The nozzle hole 24 is opened and closed by separating.

  The cylindrical piston portion 21a is slidably and liquid-tightly inserted into the nozzle sleeve 23, and the control chamber 26 in which the internal fuel pressure is switched between high pressure and low pressure by the piston portion 21a and the nozzle sleeve 23. Is formed. The nozzle needle 21 is urged in the valve closing direction by the fuel pressure in the control chamber 26 and is opened by the high pressure fuel guided from the fuel inlet 11 to the nozzle hole 24 side through the high pressure fuel passage 13. Be energized by.

  Here, the linear expansion coefficient α1 of the nozzle sleeve 23 is set so that the sliding portion clearance between the nozzle needle 21 and the nozzle sleeve 23 (hereinafter simply referred to as sliding portion clearance) is large at low temperatures and small at high temperatures. The linear expansion coefficient α2 of the needle 21 is made smaller. In other words, the linear expansion coefficient ratio λ (where λ = α1 / α2) between the nozzle needle 21 and the nozzle sleeve 23 is λ <1.

Specifically, for example, the material of the nozzle sleeve 23 is an Fe-36Ni alloy (α1 = 2 × 10 ⁻⁶ / ° C.), and the material of the nozzle needle 21 is a high-speed tool steel (SKH material, α2 = 10.7 ×). 10 ⁻⁶ / ° C.). In this case, λ≈0.19.

  A valve chamber 14 in which the control valve 3 for controlling the pressure in the control chamber 26 is accommodated is formed in the intermediate portion in the axial direction of the nozzle body 1. The control chamber 26 is always in communication with the valve chamber 14 via the communication passage 15.

  The valve chamber 14 is connected to the fuel inlet 11 through the high-pressure fuel passage 13. Further, the valve chamber 14 is connected to the fuel outlet portion 12 through a low pressure fuel passage 16.

  The control valve 3 opens and closes between the valve chamber 14 and the low pressure fuel passage 16 by contacting and separating from the low pressure seat portion 33, and opens and closes between the valve chamber 14 and the high pressure fuel passage 13 by contacting and separating from the high pressure seat portion 34. And a valve spring 32 that biases the valve body 31 in such a direction that the space between the valve chamber 14 and the high-pressure fuel passage 13 is opened and the space between the valve chamber 14 and the low-pressure fuel passage 16 is closed. is doing.

  An actuator chamber 17 in which the actuator 4 that drives the control valve 3 is housed is formed on the other end side in the axial direction of the nozzle body 1. The actuator chamber 17 is connected to the low pressure fuel passage 16 via the low pressure communication passage 16a.

  The actuator 4 includes a piezo stack 41 in which a large number of piezo elements are stacked and expands and contracts due to charge and discharge, and a transmission unit that transmits the expansion and contraction displacement of the piezo stack 41 to the valve body 31 of the control valve 3.

  The transmission unit is configured as follows. A first piston 43 and a second piston 44 are slidably and liquid-tightly inserted into the actuator sleeve 42, and a liquid chamber filled with fuel is provided between the first piston 43 and the second piston 44. 45 is formed.

  The first piston 43 is urged toward the piezo stack 41 by a first spring 46 and is directly driven by the piezo stack 41. When the piezo stack 41 is extended, the pressure of the liquid chamber 45 is increased by the first piston 43.

  The second piston 44 is urged toward the valve body 31 side of the control valve 3 by the second spring 47 and is actuated by receiving the pressure of the liquid chamber 45 to drive the valve body 31. When the piezo stack 41 is extended, the second piston 44 operates by receiving the pressure of the liquid chamber 45 that has been increased in pressure, thereby closing the space between the valve chamber 14 and the high-pressure fuel passage 13 and the valve chamber 14. The valve body 31 is driven to a position where the space between the low pressure fuel passage 16 is opened. On the other hand, when the piezo stack 41 contracts, that is, when the pressure in the liquid chamber 45 is low, the second piston 44 is pushed back toward the first piston 43 by the valve spring 32 of the control valve 3 against the second spring 47.

  A back pressure valve 120 that controls the pressure on the low pressure fuel passage 16 side is disposed in the return path 110 that connects the fuel tank 100 and the fuel outlet portion 12. Incidentally, while the pressure of the high pressure fuel stored in the pressure accumulator is 100 MPa or more, the back pressure valve 120 controls the pressure on the low pressure fuel passage 16 side to about 1 MPa.

  Electric power is supplied to the piezo stack 41 via the piezo drive circuit 130. In the piezo drive circuit 130, the energization timing to the piezo stack 41 is controlled by an electronic control circuit (hereinafter referred to as ECU) 140.

  The ECU 140 includes a well-known microcomputer including a CPU, ROM, EEPROM, RAM, and the like (not shown), and performs arithmetic processing according to a program stored in the microcomputer. The ECU 140 receives signals from various sensors (not shown) that detect the intake air amount, the accelerator pedal depression amount, the internal combustion engine speed, the fuel pressure in the accumulator, and the like.

  Next, the operation of the fuel injection valve will be described. When the piezo stack 41 is energized, the piezo stack 41 extends and the first piston 43 is driven, and the pressure of the liquid chamber 45 is increased by the first piston 43. The second piston 44 is driven toward the valve body 31 side of the control valve 3 by the pressure of the liquid chamber 45 that has been increased in pressure.

  Then, when the valve body 31 is driven by the second piston 44, the valve body 31 comes into contact with the high pressure seat portion 34 and the space between the valve chamber 14 and the high pressure fuel passage 13 is closed. The valve chamber 14 and the low pressure fuel passage 16 are opened apart from the low pressure seat portion 33. Therefore, the fuel in the control chamber 26 is returned to the fuel tank 100 through the communication passage 15, the valve chamber 14, and the low pressure fuel passage 16.

  As a result, the pressure in the control chamber 26 decreases and the force for urging the nozzle needle 21 in the valve closing direction decreases, so that the nozzle needle 21 moves in the valve opening direction and the seat portion 21b moves away from the valve seat 25. The nozzle hole 24 is opened, and fuel is injected from the nozzle hole 24 into the cylinder of the internal combustion engine.

  During this valve opening operation, the pressure in the control chamber 26 decreases, so that fuel leaks from the high-pressure fuel passage 13 side to the control chamber 26 via the sliding portion clearance. Here, when the temperature of the fuel, the nozzle needle 21 and the nozzle sleeve 23 (hereinafter simply referred to as the fuel temperature) increases, the viscosity of the fuel decreases, and λ <1 as in this embodiment. The sliding part clearance becomes smaller.

  A decrease in the viscosity of the fuel increases the amount of leakage from the sliding portion clearance (hereinafter simply referred to as the sliding portion leakage amount), whereas a decrease in the sliding portion clearance reduces the sliding portion leakage amount. It becomes a factor to decrease. Therefore, it is possible to suppress a change in the sliding portion leak amount accompanying the temperature change. For this reason, it is suppressed that the pressure change speed of the control chamber 26 at the time of valve opening operation | movement changes according to temperature. As a result, it is suppressed that the valve opening speed of the nozzle needle 21 changes according to temperature, and a fuel injection characteristic changes.

  Thereafter, when energization to the piezo stack 41 is stopped, the piezo stack 41 contracts, and the first piston 43 is returned to the piezo stack 41 side by the first spring 46. Further, the valve body 31 and the second piston 44 are returned to the first piston 43 side by the valve spring 32.

  As a result, the valve body 31 is separated from the high-pressure seat portion 34 to open the valve chamber 14 and the high-pressure fuel passage 13, and the valve body 31 contacts the low-pressure seat portion 33 so as to contact the valve chamber 14 and the low-pressure fuel passage 16. Is closed. Therefore, the high pressure fuel from the pressure accumulator is introduced into the control chamber 26 through the high pressure fuel passage 13, the valve chamber 14, and the communication passage 15.

  As a result, the pressure in the control chamber 26 rises and the force for urging the nozzle needle 21 in the valve closing direction increases, so that the nozzle needle 21 moves in the valve closing direction and the seat portion 21b sits on the valve seat 25. Thus, the nozzle hole 24 is closed and the fuel injection is completed.

  Even during this valve closing operation, fuel leaks from the high-pressure fuel passage 13 side to the control chamber 26 through the sliding portion clearance. For the same reason as during the valve opening operation, the pressure change in the control chamber 26 during the valve closing operation It is suppressed that a speed changes according to temperature. As a result, it is suppressed that the valve closing speed of the nozzle needle 21 changes according to temperature and the fuel injection characteristics change.

  FIG. 3 shows the analysis result of the relationship between the fuel temperature and the sliding portion leakage amount, using the linear expansion coefficient ratio λ of the nozzle needle 21 and the nozzle sleeve 23 as a parameter in the fuel injection valve of the present embodiment. . Here, the range of −30 ° C. to 120 ° C., which is a practical operating temperature range of the fuel injection valve, is analyzed.

  The horizontal axis in FIG. 3 is the fuel isothermal temperature, and the vertical axis is the ratio of the sliding part leak amount at each fuel isothermal temperature to the sliding part leak amount when the fuel isothermal temperature is 0 ° C.

  In this analysis, the outer diameter of the piston portion 21a of the nozzle needle 21 and the inner diameter of the nozzle sleeve 23 are set to φ3.5 mm, and the sliding portion clearance when the temperature of fuel etc. is 0 ° C. is the standard in the fuel injection valve. The typical value is set to 8 μm. The fuel is light oil.

  As shown in FIG. 3, in the case of λ = 1, the sliding portion leak amount increases rapidly in a quadratic curve as the temperature rises. In the case of λ = 0.5, the sliding portion leakage amount gradually increases linearly with increasing temperature. In the case of λ = 0.2 or λ = 0.1, the sliding part leak amount gradually increases as the temperature rises, and then the sliding part leak amount gradually increases as the temperature rises from a certain temperature range. Decrease.

  As described above, when λ <1, the sliding part clearance is large when the temperature is low and small when the temperature is high, so that the change in the sliding part leakage due to the temperature change can be suppressed. When λ ≦ 0.2, the amount of leakage at the sliding portion tends to gradually increase after the temperature rises, and then gradually decreases, and the change in the amount of leakage at the sliding portion due to temperature change is further reduced. be able to. In particular, when λ ≦ 0.1, the change in the sliding portion leakage amount in the practical operating temperature range is reduced to about 10% when λ = 1.

(Other embodiments)
In the above embodiment, the nozzle sleeve 23 is made of Fe-36Ni alloy and the nozzle needle 21 is made of high-speed tool steel. However, these materials can be appropriately changed.

  In the above embodiment, an example in which the nozzle sleeve 23 is a separate part from the nozzle body 1 has been described. However, the present invention is also applicable to a fuel injection valve having a configuration in which the nozzle sleeve 23 is integrated with the nozzle body 1. Can do.

It is sectional drawing which shows the whole structure of a fuel-injection apparatus provided with the fuel-injection valve which concerns on one Embodiment of this invention. It is an expanded sectional view of the A section of FIG. It is a figure which shows the analysis result of the relationship between the temperature and sliding part leak amount in the fuel injection valve of this embodiment.

Explanation of symbols

  21 ... Nozzle needle, 23 ... Nozzle sleeve (tubular member), 24 ... Injection hole.

Claims (1)

A seat portion (21b ) that opens and closes the nozzle hole (24 ) in contact with and away from the valve seat (25) is formed on one end side, and a columnar piston portion (21a) inserted into the cylindrical nozzle sleeve (23). ) Is provided on the other end side of the nozzle needle (21) ,
A nozzle body (1) for accommodating the nozzle needle (21) and the nozzle sleeve (23) therein;
A control chamber (26) formed by the inner peripheral surface of the nozzle sleeve (23) and the piston portion (21a), and for applying fuel pressure to the other end surface of the nozzle needle (21);
A nozzle spring (22) for urging the nozzle needle (21) in the direction toward the nozzle hole (24) and urging the nozzle sleeve (23) in a direction opposite to the nozzle hole (24); With
A fuel injection valve for controlling the fuel pressure in the control chamber (26) to control the on-off valve operation of the nozzle needle (21) ;
A fuel injection valve characterized in that α1 <α2 where α1 is a linear expansion coefficient of the nozzle sleeve (23) and α2 is a linear expansion coefficient of the nozzle needle (21).

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