DE10042612A1 - Internal grinding method for fuel injection nozzle, involves simultaneous grinding and pressing of non-conductive film provided on bonded surface of grinding wheel during contact with workpiece - Google Patents

Abstract

A grinding process and a dressing process are simultaneously carried out when a workpiece (1) comes in contact with a metal bonded grinding wheel (10). A weak non-conducting film is formed or removed on grinding particles bonding surface of the grinding wheel based on contact with the workpiece having electric conductivity. A voltage is applied between the metal bonded grinding wheel and the workpiece. A grinding lubricant having electric conductivity is supplied between the grinding wheel and the workpiece by a grinding lubricant supply device (14). Independent claims are also included for the following: (a) Internal grinding apparatus; (b) Fuel injection nozzle

Description

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method and a device for grinding an inner surface with which an inner surface of a deep and fine holes such as B. a fuel injector, is sanded and on the fuel injector.

Description of the related art

In recent years, the emissions regulations for Motor vehicles became stricter due to environmental problems the, with a fuel injection pump of a die selmotors the increase in pressure of fuel injection tion has been advanced to remove the particles in the exhaust to diminish.

Figs. 1A, 1B show an example of a conventional fuel injector (in this example, a nozzle-shaped lochför). The fuel injection nozzle injects a pump-fed and high-pressure fuel in a spraying state into a combustion chamber of an engine with a needle valve 2 movably inserted in the axial direction in the center of a nozzle main body 1 and down by a spring (not shown) is pressed. In a pointed end of the nozzle main body 1 (lower end in the drawing), a nozzle hole 1 a, a conical layer surface 1 b and a cylindrical guide surface 1 c are arranged, and a pointed end 2 a of the needle nozzle 2 with the layer surface 1 b connected and a middle section 2 b is guided through the guide surface 1 c, at the same time sealing a gap. When the high pressure beauf budgeted fuel from the pump between the layer surface 1 b and the guide surface 1 c is promoted, this pressure lifts the needle nozzle 2 against the spring, wherein the fuel through the nozzle hole 1 a through the gap between the film surface 1 b and the pointed end 2 a of the needle nozzle 2 is injected. The injection reduces an internal pressure, the spring presses the needle nozzle 2 on the layer surface 1 b, and the injection ends.

In the above-mentioned fuel injector, the adaptation to the combustion z. B. by selecting the number of nozzle holes, the diameter of the nozzle holes and the injection direction. In addition, to reduce the "subsequent drip" that generates hydrocarbon (HC) in the exhaust as shown in FIG. 1C, a stratified hole nozzle or the like is used in which a volume of the fuel reservoir of the nozzle hole portion is reduced.

As described above, the layer surface 1 b and the guide surface 1 c of the nozzle main body 1 must touch the needle valve 2 , seal the gap and guide the valve for the fuel injection nozzle. Therefore, the layer surface 1 b and the guide surface 1 c must be processed with a high precision and with a high quality.

However, because the guide surface 1 c defines a fine hole, e.g. B. with an inner diameter of about 4 mm, and because the layer surface 1 b is arranged on the underside of the fine hole, it has been difficult to machine the guide and layer surfaces.

With a conventional technique, me mechanical processing of the guide and shift surface using free abrasive grains for the how repetition of the lapping (especially for the shift surface lapping tool) and fer ner, if necessary, by performing a run-in operation these inner surfaces smoothed to the desired one Maintain surface roughness. Even if the lapping is repeated using free abrasive grains, however, the surface roughness Rz is of the order of magnitude voltage from 0.8 to 1.2 µm, whereby to get more surface roughness to get the enema for a long time Time is necessary. That is why in the conventional Technology is not just a lot of work for the Reini conditions, which is accompanied by the lapping, son because it’s also a long time for lapping that Clean and the enema operation required, the The problem is that productivity is low.

On the other hand, the applicant u. a. an electrolytic grinding process with dressing during loading processing (hereinafter referred to as the ELID grinding process is drawn) as an abrasive for performing a highly efficient and extra fine grinding of Mirror surfaces that with a conventional grinding technology is impossible, developed and published. The ELID grinding involves dissolving a conductive gene binding portion of a metal bond loop by electrolytic dressing around the dressing and grinding at the same time. According to the Grinding process is through the metal bond grinding disc that contains fine abrasive grains, an efficient Processing of mirror surfaces with reference to a be particularly hard material possible, being the feature sits that a highly efficient, extra fine Bear  processing is realized.

Because the grinding wheel while the elec Trolysis is exposed to the ELID grinding move a space to install an elec trode in a section that is different from the machining cut is different, essential. That is why it is at the guide and layer surfaces of the fuel spray nozzle and another inner surface of a deep and fine hole impossible to put the electrode in the Environment of the grinding wheel processing surface to install.

To solve the problem, the inventor developed, among other things, an "Electrolytic Interval Dressing Grinding Method" and filed an application (Japanese Patent Application Laid-Open No. 115867/1992). As shown schematically in FIG. 2, this method comprises arranging an electrode 5 at a distance from the material 1 to be ground (workpiece), the reciprocating / driving a conductive grinding wheel 4 , between the workpiece 1 and the A voltage is applied to electrode 5 , the introduction of a conductive grinding fluid between the conductive grinding wheel 4 and the electrode 5 , and the alternating execution of the electrolytic dressing and grinding.

Because in this process electrolytic dressing and the grinding is carried out alternately is the Efficiency of grinding, however, being low is possible, the procedure especially on the bottom the deep and fine hole, such as B. the upper layer area of the fuel injector.

In addition, the inventor developed, among others, "Energizing Dresden Grinding Method and Apparatus" and filed an application (Japanese Patent Application No. 45437/1998, not disclosed). As shown schematically in Fig. 3, this device comprises a semi-permanent grinding wheel 6 , which is formed from abrasive grains and a semiconducting binding portion for fastening the grains, a device 7 for applying a voltage between the grinding wheel and the conductive workpiece 1 and a grinding fluid delivery device 8 for delivering a conductive grinding fluid between the grinding wheel and the workpiece. The United driving involves bringing the grinding wheel 6 into contact with the workpiece 1 , dressing the binding portion of the grinding wheel in a contact point by electro lysis, and simultaneously grinding the workpiece with the grinding wheel. In addition, 7 a in Fig. 3 denotes a voltage source, 7 b a voltage supply and 8 a a nozzle.

Because the grinding wheel 6 is formed from the grinding grains and the semiconducting binding portion for fixing the grains, the grinding wheel can be brought into direct contact with the machining surface of the workpiece 1 and can be electrolytically dressed. However, because the grinding wheel has a low mechanical strength and is heavily worn, changes in the application to the device on the deep and fine hole, such as. B. the fuel injector, the diameter of the grinding wheel largely due to the wear of the grinding wheel, the problem being that the high precision can not be maintained.

SUMMARY OF THE INVENTION

The present invention has been developed to achieve the solve the above-mentioned problems. More specifically, it is an up  Object of the present invention, a method and - Device for grinding an inner surface, at those inner surfaces of a deep and fine hole, such as B. the guide and layer surfaces of one Fuel injector, with high precision, with high Quality and high efficiency without executing one Lapping or running-in operation ground for a long time can be, as well as a fuel injector create.

According to the present invention, there is provided a method of grinding an inner surface comprising the steps of: applying a voltage between a bond bond grinding wheel ( 10 ) formed of abrasive grains and a conductive bond portion for attaching the abrasive grains and a workpiece ( 1 ) that is conductive; Providing a conductive grinding fluid between the grinding wheel and the workpiece to form a non-conductive film on the surface of the conductive bond portion of the grinding wheel; then bringing the grinding wheel into contact with the workpiece to remove a portion of the surface layer of the non-conductive film at a contact point; Dressing the conductive bond portion containing the non-conductive film by weak electrolysis; and simultaneous grinding of the workpiece with the grinding wheel.

In addition, according to the present invention, there is provided an inner surface grinding apparatus comprising: a metal bond grinding wheel ( 10 ) formed of abrasive grains and a conductive bond portion for fixing the abrasive grains; means ( 12 ) for applying a voltage between the grinding wheel and a conductive workpiece ( 1 ); and abrasive fluid delivery means ( 14 ) for delivering a conductive abrasive fluid between the grinding wheel and the workpiece, forming a non-conductive film on the surface of the conductive bonding portion, the grinding wheel is subsequently brought into contact with the workpiece to form a portion of the Remove surface layer of the non-conductive film at a contact point, and the conductive bonding portion containing the non-conductive film is dressed by weak electrolysis; while simultaneously grinding the workpiece with the grinding wheel.

Because according to the method and the device of the present Invention of the non-conductive film on the surface surface of the conductive bond portion of the grinding wheel is formed, the grinding wheel subsequently in contact brought with the workpiece to the section of the Surface layer of the non-conductive film in a con tact point to remove, and the conductive binding cut containing the non-conductive film through which weak electrolysis is prevented non-conductive film that a spark between the bond section of the grinding wheel and the workpiece , the binding portion of the grinding wheel in the contact point is dressed by electrolysis where where the grinding wheel can be dressed. Therefore can the grinding wheel in unchanged with the workpiece Be brought in contact, at the same time the plant piece can be ground.

Furthermore, according to the present invention, a Surface roughness of a conical and / or cylindrical inner surface machined to Rz 0.5 µm or less. In addition, the layer surface and / or the Guide surface of a fuel injector edited this procedure. The surface roughness has  so far even when using free abrasive grains to to repeat the lapping, in the order of margin 0.8 to 1.2 microns, but by the present Ver can drive through the ELID grinding an outstanding Mirror surface can be obtained. By grinding the layer surface and / or the guide surface ELID grinding can not only be used on a mirror surface preserve surface with high precision and high quality but it can also increase the sharpness of the grinding disc with a small machining resistance for be held for a long time, also shows the grinding disc a little wear, which is why grinding run with high efficiency for a long time can, with productivity being increasingly improved can.

Other tasks and advantageous features of the present the invention will be apparent from the following Be description with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

Figs. 1A, 1B, 1C are explanatory views of a fuel injector.

Figure 2 is a schematic view of applicant's prior art, among others

Figure 3 is a schematic view of applicant's other prior art, among others

FIGS. 4A, 4B, 4C are schematic views showing a structure of a surface-grinding apparatus for an internal upper show according to the present invention.

Fig. 5 is a graph showing a relationship between an abrasive grain size and the roughness of the machining surface.

Fig. 6 is a diagram showing a relation between a grit size and a grinding ratio.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following a preferred embodiment of the present invention with reference to the drawing be wrote. In addition, ge are in the respective figures common parts with the same reference numerals, redundant description is omitted.

FIGS. 4A, 4B, 4C are schematic views of the structure of a grinding apparatus for an inner upper surface according to the present invention. In the drawing, Fig. 4A is a sectional view of a material to be ground (workpiece). In this example, a workpiece 1 is a nozzle main body of a fuel injection nozzle, where a conical layer surface 1 b and a cylindrical guide surface 1 c are used as inner surfaces of a deep and fine hole located in the center of the nozzle main body 1 as the machining surfaces become. The guide surface 1 c is a fine hole, z. B. with an inner diameter of approximately 4 mm, while the layer surface 1 b is a beveled surface, which is arranged in the underside of the fine salmon.

Fig. 4B shows a grinding device for an inner surface for processing the guide surface 1 c, while Fig. 4C shows a grinding device for an inner surface for processing the layer surface 1 b. In addition, FIGS. 4B and 4C are the same except for the grinding wheel, part of FIG. 4C being omitted.

As shown in FIGS . 4B and 4C, the inner surface grinding device of the present invention is provided with a metal bond grinding wheel 10 , a voltage applying device 12, and a grinding liquid supply device 14 .

The metal bond grinding wheel 10 comprises a shaft section 10 a of the grinding wheel made of a highly conductive metal and a grinding wheel section 10 b, which is arranged at a pointed end of the shaft section (left end of the drawing). The shaft portion 10 a of the grinding wheel is rotated / driven by a drive device (not shown) around an axial center, where it moves back and forth along the machining surface.

The grinding wheel section 10 b comprises abrasive grains (e.g. diamond or CBN) and a conductive binding section (metal binding section) for fastening the grains. The metal bond portion can be formed by melting and solidifying cast iron, bronze, and other metals. In the example of FIG. 4B, the grinding wheel section 10 b is formed in a cylindrical upper surface which has a diameter which is a little smaller than an inner diameter (approximately 4 mm) of the cylindrical guide surface 1 c. In addition, in the example of FIG. 4C, the grinding wheel portion has a conical surface that has an inclination angle that is equal to that of the conical layer surface 1 b, and a maximum diameter that is a little smaller than that of the layer surface 1 b , having.

The device 12 for applying a voltage is provided with a voltage source 12 a, a brush 12 b and a power line 12 c for electrically connecting the workpiece 1 and the shaft section 10 a of the grinding wheel to the voltage source, with a voltage between the grinding wheel 10 and the workpiece 1 is created. For the voltage source 12 a, a constant current type ELID voltage source is preferred, which can supply a pulsed DC voltage. In this example, the brush 12 b directly touches the outer surface of the shaft section 10 a of the grinding wheel in order to apply + to the grinding wheel 10 and - to the workpiece 1 . In addition, the workpiece 1 is rotated / driven about its axial center by the drive device (not shown).

The grinding fluid delivery device 14 is provided with a nozzle 14 a, which is positioned in the direction of a contact section of the grinding wheel 10 and the workpiece 1 , and a grinding fluid line 14 b for supplying a conductive grinding fluid to the nozzle 14 a, the conductive one abrasive liquid to the Kon clock section of the grinding wheel 10 (ie, the abrasive disk portion 10 b) and is supplied to the workpiece. 1

According to the present invention using the above-mentioned inner surface grinder, the inner surface grinding method includes: applying the tension between the metal bond grinding wheel 10 and the conductive workpiece 1 ; further providing the conductive abrasive liquid between the grinding wheel and the workpiece to form a non-conductive film on the surface of the grinding wheel; Forming the non-conductive film on the surface of the conductive bond portion; then bringing the abrasive layer to remove the non-conductive film; Starting the conductive bond portion containing the non-conductive film by weak electrolysis; and simultaneously grinding the workpiece with the grinding wheel. The non-conductive film prevents a spark from being generated between the bond portion of the grinding wheel and the workpiece, the bond portion of the grinding wheel being dressed in the contact point by electrolysis, whereby the grinding wheel can be dressed. Therefore, the grinding wheel can be brought into contact with the workpiece unchanged, whereby the workpiece can be ground simultaneously.

Examples

Experiments were carried out using a disc-shaped copper electrode, initial dressing and the ELID grinding of the present invention in the order of discharge dressing. For the ELID grinding of the present invention, the processing was carried out in three patterns of only # 325, # 325 → # 1200 and # 325 → # 1200 → # 4000. In view of the fact that an influence of a previously machined surface is eliminated and a wear amount of the grinding wheel can be clearly measured, a machining tolerance has been increased. In order to prevent the discharge spark between the grinding wheel and the workpiece during the ELID grinding of the present invention, the voltage was applied between the metal bond grinding wheel 10 and the conductive workpiece 1 , where the conductive grinding fluid was supplied between the grinding wheel and the workpiece so that the non-conductive film was previously formed on the surface of the grinding wheel. In addition, to bring the grinding wheel into contact with the workpiece and to dress the bonding portion of the grinding wheel in the contact point by weak electrolysis to such an extent that the non-conductive film remains normal, the peak current Ip was set to 1 A, which is half or was less of the current during normal ELID grinding. An experimental system is shown in Table 1, while the processing conditions are shown in Table 2.

Table 1

Experimental system

Table 2

Processing conditions

A diameter of the grinding wheel and an inner diameter of the workpiece were measured before and after machining, while an amount of wear of the grinding wheel and an amount of removal of the workpiece were calculated from the measurement results, whereby a grinding ratio was obtained. Fig. 5 is a diagram showing a relationship between an obtained abrasive grain size and a roughness of the machining surface, while Fig. 6 is a diagram showing a relationship between an abrasive grain size and a grinding ratio.

During the processing, no discharge spark between between the grinding wheel and the workpiece, being even after on the surface of the grinding wheel no special deviation was found during processing has been. That was why even the cast iron bound  Grinding wheel by forming a non-conductive Films on the surface of the grinding wheel and the opti machining conditions, the ELID grinding of the present invention possible. For the roughness of the Bear processing surface after # 4000 machining became a very satisfactory roughness of Rz 0.1 µm or less ger received. Because the deformation after the material hardness was large, the grinding ratio was low for # 325 just deteriorated. Because the grinding ratio has deteriorated quickly is for the ## 4000 grinding was confirmed that it is preferable to use the Be to minimize work tolerance.

As described above, the method and the device for grinding an inner surface and the fuel injector of the present invention the outstanding effects that the inner Surfaces of a deep and fine hole, such as B. the Fuel injection guide and layer surfaces nozzle, with high precision, high quality and high We Degree of efficiency without execution of the lapping or the infeed ration can be ground for a long time.

In addition, the present invention is not limited to that above-mentioned embodiments or examples limits, of course they are different can be modified in an area not covered by the Scope of the present invention differs. In the example mentioned above is e.g. B. editing the Fuel injector has been described in detail however, the present invention is not so limited limits, rather it can generally be grinded an inner surface of the deep and fine hole be turned.

Claims (4)

A method for grinding an inner surface, comprising the steps of: applying a voltage between a metal bond grinding wheel ( 10 ) made of abrasive grains and a conductive bond portion for fixing the abrasive grains, and a conductive workpiece ( 1 ); Providing a conductive abrasive liquid between the grinding wheel and the workpiece to form a non-conductive film on the surface of the conductive bond portion of the grinding wheel; then bringing the grinding wheel into contact with the workpiece to remove a portion of the surface layer of the non-conductive film at a contact point; Dressing the conductive bond portion containing the non-conductive film by weak electrolysis; and simultaneously grinding the workpiece with the grinding wheel. 2. Method of grinding an inner surface according to claim 1, wherein a surface roughness of a conical and / or cylindrical inner surface Rz 0.5 µm or less is processed. 3. A device for grinding an inner surface, comprising: a metal bond grinding wheel ( 10 ) which is formed from abrasive grains and a conductive bond portion for attaching the abrasive grains; means ( 12 ) for applying a voltage between the grinding wheel and a conductive workpiece ( 1 ); and abrasive fluid delivery means ( 14 ) for delivering a conductive abrasive fluid between the grinding wheel and the workpiece, forming a non-conductive film on the surface of the conductive bonding portion, and then bringing the grinding wheel into contact with the workpiece around a portion remove the surface layer of the non-conductive film at a contact point, and the conductive bonding portion containing the non-conductive film is dressed by weak electrolysis; while simultaneously grinding the workpiece with the grinding wheel. 4. Fuel injector, at one Layer surface and / or a guide surface the method according to claim 2 are processed.