JP5040928B2 - Accumulator and method for manufacturing the same - Google Patents

Description

  The present invention relates to a pressure accumulator that stores fuel injected from an injector into an internal combustion engine in a high pressure state, and a method for manufacturing the same.

  In a conventional accumulator, a fuel chamber extending in the axial direction and a communication hole extending in the radial direction are formed in a cylindrical main body, and a screw into which a fuel pipe is screwed is formed on the outer peripheral side of the main body. In response to the pressure of the fuel, a stress is generated in the main body, and in particular, a high stress is generated at the opening edge of the communication hole in the fuel chamber side (hereinafter referred to as a hole intersection). May occur.

Therefore, in order to ensure the strength of the hole intersection, the hardness of the main body is increased or residual compressive stress is applied. For example, the main body is processed by the following methods (1) to (3). ing.
(1) After increasing the hardness by heat treatment, a screw or the like is formed by cutting.
(2) After forming a screw or the like by cutting, the hardness is increased by heat treatment.
(3) A residual compressive stress is applied to the main body by auto-frettage processing, burnishing, or the like (see, for example, Patent Document 1).

JP-A-10-141172

  Incidentally, in recent years, in diesel engines, the injection system pressure has been increased. For this reason, it is required to further increase the strength of the hole intersection.

  However, in the main body processing method of (1), since the cutting is performed after the heat treatment, the hardness is limited to a level at which cutting is possible (about HRC30) or less, and therefore the hardness cannot be further increased.

  In the main body processing method of (2), since heat treatment is performed after cutting, the hardness can be made higher than that of the processing method of (1), but from the viewpoint of preventing delayed screw failure, the hardness should be extremely high. Cannot be done (about HRC40). Moreover, in the main body processing method of (2), for example, the screw accuracy may deteriorate due to distortion caused by heat treatment, and assembly failure may occur.

  In the main body processing method of (3), a strength equal to or higher than that of the main body processing method of (2) is expected in order to give residual compressive stress. However, since it is limited below the possible level, the hardness cannot be further increased.

  In view of the above points, an object of the present invention is to increase the strength of a hole intersection while avoiding delayed fracture of a screw and deterioration of accuracy.

In order to achieve the above object, according to the first aspect of the present invention, a cylindrical main body (10) in which a main body center hole (100) extending in the axial direction is formed, and has a higher hardness than the main body (10) and the center of the main body. A cylindrical inner pipe (12) inserted into the hole (100), a screw (104) disposed on the outer peripheral side and screwed into the fuel pipe (2), and a fuel A communication hole (105) for communicating the pipe (2) and the main body center hole (100) is formed, and the inner pipe (12) has a fuel chamber (120) extending in the axial direction and storing high-pressure fuel; An orifice (121) having a smaller diameter than the communication hole (105) and connecting the communication hole (105) and the fuel chamber (120), and a diameter located around the orifice (121) on the outer peripheral surface of the inner pipe (12). protruding portion protruding outward (122) and is formed, the protruding portion (122) A rounded relief shape surrounding the orifice (121), the inner tube (12) and body (10) is characterized in that it is joined by shrinkage fitting.

  According to this, since the inner pipe (12) does not have the screw (104), there is no need to consider delayed fracture or deterioration of accuracy of the screw (104), and therefore the hardness of the inner pipe (12) can be increased. . Further, residual compressive stress is applied to the inner tube (12) by shrink fitting. High stress is generated at the opening edge of the orifice (121) on the fuel chamber (120) side (hereinafter referred to as the orifice hole intersection), but the hardness of the inner pipe (12) in which the orifice (121) is formed is reduced. The strength of the orifice hole intersection can be increased in combination with the fact that it can be increased and the residual compressive stress is applied to the inner pipe (12), so that the orifice hole intersection can be prevented from being damaged. .

  Furthermore, since the inner peripheral surface forming the main body central hole (100) in the main body (10) is covered with the inner tube (12), the opening edge (hereinafter referred to as the main body central hole (100) side) in the communication hole (105). The stress generated at the intersection of communication holes) is smaller than the stress generated at the intersection of orifice holes. Moreover, since a residual compressive stress is given to a main body (10) by shrink fitting, the intensity | strength of a communicating hole crossing part can be raised. Thus, since the stress which generate | occur | produces in a communicating hole crossing part is small, and a residual compressive stress is provided to a main body (10), it can prevent the failure | damage of a communicating hole crossing part. It is not necessary to increase the hardness of the main body (10). Therefore, the hardness of the main body (10) on which the screw (104) is formed can be made lower than the hardness of the inner tube (12), and delayed fracture and accuracy deterioration of the screw (104) can be avoided.

Moreover, since the protrusion part (122) is provided in the circumference | surroundings of the orifice (121) in the outer peripheral surface of an inner pipe (12), the residual compression higher than another site | part in the vicinity of an orifice (121) and a communicating hole (105). Stress can be applied.

According to a second aspect of the present invention, in the pressure accumulator according to the first aspect , the projecting portion (122) extends to the outside of the opening edge portion on the main body center hole (100) side in the communication hole (105). It is characterized by that.

  According to this, a residual compressive stress can be reliably given to a communicating hole crossing part (105a).

According to a third aspect of the present invention, there is provided a method for manufacturing the pressure accumulator according to the first or second aspect , wherein the main body central hole (100), the screw (104), and the communication hole (105) are formed. (10) The main body machining step and the inner pipe machining step for forming the inner pipe (12) by performing a process for increasing the hardness after forming the protrusion (122), the fuel chamber (120) and the orifice (121). And the inner peripheral surface forming the main body center hole (100) in the main body (10) is covered with the inner pipe (12), and the main body (10) and the inner pipe (12) are joined by shrink fitting. And a fitting process.

  The pressure accumulator manufactured in this way can obtain the same effect as that of the invention of claim 1.

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

It is a figure which shows the whole structure of a fuel-injection apparatus provided with the pressure accumulator which concerns on one Embodiment of this invention. (A) is sectional drawing of the pressure accumulator of FIG. 1, (b) is sectional drawing which follows the AA line of (a). (A) is sectional drawing of the main body in the pressure accumulator of FIG. 2, (b) is sectional drawing of the inner tube | pipe in the pressure accumulator of FIG. It is an expanded sectional view of the B section of FIG. FIG. 3 is a perspective view of an inner tube in the pressure accumulator of FIG. 2. It is sectional drawing which shows the shrink fitting process of the pressure accumulator of FIG. It is an expanded sectional view of the C section of Drawing 6 (b). It is a perspective view of the inner pipe which shows the reference example of an accumulator . It is sectional drawing of the inner pipe | tube of FIG. It is sectional drawing of the inner pipe which shows the other reference example of an accumulator . It is a sectional view showing a modification type example of the accumulator according to one embodiment.

  As shown in FIG. 1, the fuel injection device includes a pressure accumulator 1 that stores high-pressure fuel, and a plurality of injectors 3 are connected to the pressure accumulator 1 via a fuel pipe 2. The injector 3 is controlled by a control device (hereinafter referred to as an ECU) 4 to open a valve at a predetermined time for a predetermined period, and to supply high-pressure fuel supplied from the pressure accumulator 1 to each cylinder of a diesel engine (not shown). To spray.

  High-pressure fuel stored in the pressure accumulator 1 is supplied from a supply pump 5 via a fuel pipe 2. The supply pump 5 pressurizes the fuel and discharges it to the accumulator 1, the low-pressure pump 52 that supplies the fuel sucked from the fuel tank 6 through the filter 7 to the high-pressure pump 51, and the low-pressure pump 52 A metering valve 53 for adjusting the flow rate of the fuel supplied to the high-pressure pump 51 is provided. The high-pressure pump 51 is a pump of a type in which the fuel discharge amount is adjusted by adjusting the fuel intake amount by the metering valve 53. The high pressure pump 51 and the low pressure pump 52 are driven by the engine.

  The ECU 4 includes a known microcomputer including a CPU, a ROM, a RAM, and the like (not shown), and performs arithmetic processing according to a program stored in the microcomputer. Various information such as a signal regarding the fuel pressure (so-called common rail pressure) in the pressure accumulator 1 (so-called common rail pressure), engine speed, accelerator opening, and the like is input to the ECU 4 from time to time.

  The ECU 4 calculates the optimal injection timing and injection amount (injection period) according to the operating conditions of the engine and the vehicle, and controls the valve opening timing and valve opening period of each injector 3. Further, the ECU 4 calculates the target discharge amount of the supply pump 5, outputs a control signal to the metering valve 53, and controls the discharge amount of the supply pump 5, thereby controlling the fuel pressure in the pressure accumulator 1.

  As shown in FIGS. 2 to 4, the pressure accumulator 1 includes a cylindrical main body 10 and a cylindrical inner tube 12 that is inserted into the main body 10 and arranged coaxially. The accumulator 1 detects the fuel pressure in the accumulator 1 and outputs it to the ECU 4 (see FIG. 1), and opens when the fuel pressure in the accumulator 1 exceeds a predetermined value. A relief valve 9 for escaping the fuel in the vessel 1 to the fuel tank 6 (see FIG. 1) is mounted.

  The main body 10 is made of a metal (for example, chromium molybdenum steel), and is formed in a predetermined shape and given a predetermined hardness in the main body processing step. Specifically, in the main body machining step, the hardness is such that cutting is possible by heat treatment or aging treatment (about HRC30), and after the heat treatment or aging treatment, it is formed into a predetermined shape as described below by cutting or the like. .

  A columnar main body center hole 100 extending in the axial direction of the main body 10 and the inner tube 12 (hereinafter referred to as the axial direction) is formed inside the main body 10. A sensor female screw 101 to which the pressure sensor 8 is screwed is formed on one end side in the axial direction of the main body 10, and a female screw for relief valve 102 to which the relief valve 9 is screwed is formed on the other axial end side of the main body 10. Is formed.

  Five pipe protrusions 103 for connecting the fuel pipe 2 (see FIG. 1) are formed on the outer peripheral side of the main body 10. A pipe male thread 104 into which the fuel pipe 2 is screwed is formed on the outer peripheral side of the pipe protrusion 103, and the fuel pipe 2 and the main body center hole 100 are communicated with each other on the inner peripheral side of the pipe protrusion 103. A communication hole 105 is formed. The communication hole 105 extends substantially in the radial direction. Further, two flanges 106 for assembling the pressure accumulator 1 to the engine are formed on the outer peripheral side of the main body 10. A bolt through hole 107 is formed in the flange portion 106.

  The inner pipe 12 uses a pipe material made of metal (for example, low carbon steel or high speed steel) having a thickness of about 2 mm. The inner tube 12 is formed in a predetermined shape and given a predetermined hardness in the inner tube processing step. Specifically, in the inner tube processing step, the hardness is about twice that of the main body 10 (approximately HRC 60) by carburizing or quenching and tempering, and the predetermined shape as described below is formed by cutting or the like. It should be noted that at least cutting among the processes for forming the shape is performed before carburizing or quenching and tempering.

  A fuel chamber 120 that is a cylindrical space extending in the axial direction is formed in the inner tube 12 by cutting. The inner pipe 12 has the same number of orifices 121 (five in this example) as the piping projections 103 that allow the communication hole 105 and the fuel chamber 120 to communicate with each other. The orifice 121 is for reducing pressure pulsation in the fuel chamber 120, and has a smaller diameter than the communication hole 105.

The orifice 121 is first roughed by cutting, and then the inner peripheral surface of the orifice 121 is finished by cutting or fluid polishing. Further, the orifice hole intersection 121a which is the opening edge of the orifice 121 on the fuel chamber 120 side is deburred or rounded by cutting, fluid polishing after heat treatment, electrolytic processing, or the like. As shown in FIG. 5, a protruding portion 122 that protrudes radially outward is formed around the orifice 121 on the outer peripheral surface of the inner tube 12. In other words, the protruding portion 122 has a round raised shape surrounding the orifice 121. In addition, the site | part in which the protrusion part 122 is not formed among the inner tubes 12, ie, the site | part 123 where the outer diameter dimension is constant is hereafter called a base part.

  As described above, the main body 10 processed by the main body processing step and the inner tube 12 processed by the inner tube processing step are joined by shrink fitting in the shrink fitting step described below. First, as shown in FIG. 6, the main body 10 is heated and expanded in a temperature range below the transformation point (see FIG. 6A). Subsequently, the normal temperature inner tube 12 is inserted into the main body central hole 100 of the heated main body 10 (see FIG. 6B). Subsequently, by cooling the main body 10, the main body 10 contracts and the main body 10 and the inner tube 12 are coupled, and the inner peripheral surface forming the main body center hole 100 in the main body 10 is covered with the inner tube 12 (FIG. 6 ( c)).

  As shown in FIG. 2, the main body 10 and the inner tube 12 are positioned and coupled so that the communication hole 105 and the orifice 121 are coaxial. The communication hole 105 and the orifice 121 are eccentric with respect to the main body center hole 100. In other words, when viewed along the axial direction, the axes of the communication hole 105 and the orifice 121 do not intersect with the axis of the main body center hole 100 (see FIG. 2B).

  In order to generate residual compressive stress in the main body 10 and the inner pipe 12 by this shrink fitting, the dimensions of the respective parts of the main body 10 and the inner pipe 12 are set as follows.

  Here, as shown in FIG. 7, the inner diameter of the main body center hole 100 in the main body 10 (hereinafter referred to as the main body central hole inner diameter) is d1, and the inner diameter of the communication hole 105 in the main body 10 (hereinafter referred to as the communication hole inner diameter) is d2. To do. Further, the outer diameter of the base portion 123 (hereinafter referred to as the base portion outer diameter) in the inner tube 12 is d3, the width of the protruding portion 122 in the inner tube 12 (hereinafter referred to as the protruding portion width) is e, and the protruding portion in the inner tube 12 The maximum protrusion amount 122 (hereinafter referred to as a protrusion protrusion amount) is assumed to be f.

When the body 10 has a linear expansion coefficient of about 10 × 10 ⁻⁶ and the body center hole inner diameter d1 is about 10 mm, the body center hole inner diameter d1 expands by about 50 μm when the body 10 is heated to about 500 ° C. below the transformation point. To do. Therefore, when the main body center hole inner diameter d1 is about 10 mm, the base portion outer diameter d3 and the main body center hole inner diameter d1 are set so that the base portion outer diameter d3 is several tens of micrometers larger than the main body center hole inner diameter d1 at room temperature. The difference between the base part outer diameter d3 and the main body center hole inner diameter d1 at room temperature is a margin.

  Thus, after shrink fitting, residual compressive stress is applied to the main body 10 and the inner tube 12, and more specifically, the orifice hole intersection 121a and the opening edge of the communication hole 105 on the main body center hole 100 side. Residual compressive stress is also applied to the communication hole intersection 105a (see FIG. 7). Therefore, the strength of the orifice hole intersection 121a and the communication hole intersection 105a is increased. Incidentally, a relatively high residual compressive stress is applied to the inner tube 12 having a lower hardness than the main body 10.

  In addition, after shrink fitting, the inner peripheral surface forming the main body center hole 100 in the main body 10 and the outer peripheral surface of the inner tube 12 are in close contact (hereinafter, this close contact portion is referred to as a shrink fit surface). Fuel leakage from the surface can be prevented or reduced. In order to improve the sealability of the shrink-fitting surface, it is desirable that the surface roughness of the inner peripheral surface of the main body 10 and the outer peripheral surface of the inner tube 12 be 6.3z or more. However, since both ends of the main body center hole 100 are closed by the pressure sensor 8 and the relief valve 9, even if there is a fuel leak from the shrink fit surface, it does not leak out of the accumulator 1.

  On the other hand, the protrusion part protrusion amount f is set to 20 to 30 μm. Further, by setting the protruding portion width e to be larger than the communication hole inner diameter d2, the protruding portion 122 extends to the outside of the communication hole intersecting portion 105a. Thereby, the protrusion 122 can bite into the main body 10 after shrink fitting, and a higher residual compressive stress can be applied in the vicinity of the orifice 121 and the communication hole 105 than in other portions. In addition, by eliminating the sagging of the opening edge portion on the communication hole 105 side in the orifice 121 and eliminating the sagging of the communication hole intersecting portion 105a, a high residual compressive stress can be reliably applied to the communicating hole intersecting portion 105a.

  As described above, in the pressure accumulator 1 of the present embodiment, the inner tube 12 does not have a screw, so there is no need to consider delayed fracture of the screw or deterioration of accuracy, and therefore the hardness of the inner tube 12 is increased. Can do. Further, residual compressive stress is applied to the inner tube 12 by shrink fitting. And although high stress is generated in the orifice hole intersection 121a, combined with the fact that the hardness of the inner tube 12 formed with the orifice 121 can be increased and the residual compressive stress is applied to the inner tube 12, Since the strength of the orifice hole intersection 121a can be increased, the orifice hole intersection 121a can be prevented from being damaged.

  Furthermore, since the inner peripheral surface forming the main body center hole 100 in the main body 10 is covered with the inner tube 12, the stress generated in the communication hole intersecting portion 105a is smaller than the stress generated in the orifice hole intersecting portion 121a. Further, since the residual compressive stress is applied to the main body 10 by shrink fitting, the strength of the communication hole intersection 105a can be increased. As described above, since the stress generated in the communication hole intersection 105a is small and the residual compressive stress is applied to the main body 10, the communication hole intersection 105a can be prevented from being damaged. It is not necessary to increase the hardness of the main body 10. Therefore, the hardness of the main body 10 on which the screws 101, 102, and 104 are formed can be made lower than the hardness of the inner tube 12, and delayed fracture and deterioration of accuracy of the screws 101, 102, and 104 can be avoided.

In the above embodiment, the protruding portion 122 has a round relief shape, but the protruding portion 122 may be formed over the entire circumference with a predetermined width as in the reference examples shown in FIGS. . In other words, the protrusion 122 may be formed continuously along the circumferential direction with a predetermined width. According to this, when forming the protrusion part 122 by cutting, for example, it can form more easily than the case where the protrusion part 122 is formed only in a part of circumferential direction.

Further, as in another reference example shown in FIG. 10, the protruding portion 122 may be formed over the entire circumference with a predetermined width by bulge forming.

Further, in the above embodiment, the communication hole 105 and the orifice 121, but is decentered with respect to the body central bore 100, as shown be variable type example in FIG. 11, the communication hole 105 and the orifice 121, the body center It is not necessary to be eccentric with respect to the hole 100. In other words, the axial lines of the communication hole 105 and the orifice 121 may intersect the axial line of the main body center hole 100 when viewed along the axial direction. According to this, processing of the communication hole 105 and the orifice 121 becomes easy.

2 Fuel piping 10 Main body 12 Inner pipe 100 Main body central hole 104 Screw 105 Communication hole 120 Fuel chamber 121 Orifice

Claims (3)

A pressure accumulator for storing fuel injected from an injector (3) into an internal combustion engine in a high pressure state;
A cylindrical main body (10) in which a main body center hole (100) extending in the axial direction is formed, and a cylindrical inner pipe (higher hardness than the main body (10) inserted into the main body center hole (100) ( 12)
The main body (10) is connected to a screw (104) arranged on the outer peripheral side and screwed into the fuel pipe (2), and a communication hole for communicating the fuel pipe (2) and the main body center hole (100). (105) is formed,
The inner pipe (12) includes a fuel chamber (120) extending in the axial direction and storing high-pressure fuel, and the communication hole (105) and the fuel chamber (120) having a smaller diameter than the communication hole (105). An orifice (121) that communicates with each other, and a projecting portion (122) that is located around the orifice (121) on the outer peripheral surface of the inner pipe (12) and projects radially outward ,
The protrusion (122) has a round raised shape surrounding the orifice (121),
The pressure accumulator characterized in that the main body (10) and the inner pipe (12) are coupled by shrink fitting. 2. The pressure accumulator according to claim 1 , wherein the protruding portion (122) extends outward from an opening edge portion on the main body center hole (100) side of the communication hole (105). A method for producing the pressure accumulator according to claim 1 , comprising:
A main body processing step of forming the main body (10) by forming the main body center hole (100), the screw (104), and the communication hole (105);
An inner pipe processing step of forming the inner pipe (12) by performing a process of increasing hardness after forming the protrusion (122), the fuel chamber (120) and the orifice (121);
An inner peripheral surface forming the main body center hole (100) in the main body (10) is covered with the inner pipe (12), and the main body (10) and the inner pipe (12) are shrink-fitted. A pressure accumulator manufacturing method comprising: a shrink fitting process to be combined.

Images