JP2000087117A - Method for joining valve shaft of solenoid valve to sintered movable iron core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the sintering of a green compact and its joining to a valve shaft by a single process, to reduce the size and weight of a movable iron core, and to improve the responsiveness of a solenoid valve by compacting a powder of ferromagnetic material excellent in soft magnetic properties or a powder mixture of equivalent composition into the required shape and size of a movable iron core, fitting the resultant green compact in the prescribed position of a valve shaft, and carrying out sintering. SOLUTION: It is preferable that the material of a sintered movable iron core is composed of any of pure iron, Fe-P-alloy, Fe-Si alloy, Fe-Si-P alloy, Permalloy (R) alloy, Permendur (R) alloy, and electrical stainless steel materials, and further, as for a fit tolerance between the inside diameter of a green compact and the valve shaft, running fit of <=5 μm clearance or close fit of <=60 μm interference is preferred. Moreover, the valve shaft is composed preferably of a non-magnetic material of <=100 magnetic permeability. Because no allowance for machining is necessary for attachment to the valve shaft in this method, the movable iron core can be reduced in size and weight. Further, the amount of expansion of the green compact, in the high temperature region where sintering proceeds, is smaller than that of the valve shaft composed of melted material, and the valve shaft can be held tight by the green compact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solenoid valve which is operated by a solenoid widely used for controlling a hydraulic pump, a fuel injection device of an automobile engine and other fluids, and more particularly to a movable iron core of a sintered alloy on a shaft of the solenoid valve. And a method for joining them together.

[0002]

2. Description of the Related Art A non-magnetic material such as stainless steel SUS304 is used for a shaft (valve shaft) of an electromagnetic valve. In general, a movable iron core is provided, and when an electric pulse is applied to a solenoid coil, the movable iron core moves to open a valve. For convenience of assembly and other reasons, there is also a type in which the valve shaft is divided between the valve body and the movable core, and the valve shaft on the valve body side is pushed and moved by the valve shaft on the movable core side, but the valve shaft in this specification is in both cases Contains.

[0003]

Heretofore, press-fitting, caulking, or some form of plastic working has been used for attaching the movable iron core to the valve shaft. Therefore, the material of the movable iron core is limited to a material that can be plastically deformed, high dimensional accuracy is required for finishing the inner diameter, cost is high, and a certain amount of machining allowance is required for plastic working. There were various restrictions on the material, shape, manufacturing process, and the like of the iron core, such as the limitations on miniaturization and weight reduction. SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive method suitable for mass production for integrally joining a movable core to a valve shaft without being restricted by the material of the movable core and other restrictions.

[0004]

SUMMARY OF THE INVENTION According to the present invention, a powder of a ferromagnetic material or a mixed powder of the composition thereof having good soft magnetic properties and suitable for a movable core is compression-molded into a required shape and size of the movable core. The essence is to complete the sintering of the green compact and joining to the valve shaft in one step by fitting the body into a predetermined position of the valve shaft and sintering. In this case, ferromagnetic materials suitable for use include pure iron, Fe-P, and Fe-Si.
System, Fe-Si-P system, permalloy system, permendur system alloy, and electromagnetic stainless material such as SUS410. The material of the valve shaft has a magnetic permeability of 100.
The following is preferred. In this method, no machining margin is required for attachment to the valve shaft, so that the movable iron core can be reduced in size and weight.

[0005] When a movable iron core (compact powder) is fitted to a valve shaft and sintered and joined, not only a simple mechanical shrink fitting but also a joining surface of both members is required to obtain high joining strength. It is necessary to achieve bonding by solid-phase diffusion of alloy components by sintering in a state where they are sufficiently adhered. Regarding this point, all of the above-mentioned materials below pure iron are in a high temperature range where sintering proceeds as described later (about 8 in the case of iron-based sintered alloys).
This is extremely convenient because the dimensional change (expansion) at (at least 00 ° C.) is smaller than that of the valve shaft of the ingot material, and sintering proceeds with the compact compacting the valve shaft.

[0006] Further, a fitting dimensional difference in fitting the two members (difference between the inner diameter of the hole of the green compact and the outer diameter of the valve shaft).
It is also important that the valve shaft is set to be thicker (tight fit) and press-fitted into the hole of the green compact. The larger the interference, the higher the degree of adhesion between the two. However, in order to avoid breakage of the low-strength green compact due to tensile stress, it is necessary to stop the interference within 30 μm, preferably at most 60 μm. Even in the case of choosing a straight fit, the smaller the gap, the better, and should be kept below 5 μm.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, stainless steel (SU
S304) is based on the case where a green compact of Fe-0.6P (green compact density: 7.0 g / cm ³ ) is used for the movable core material.
The state of thermal expansion due to each heating will be described. The measurement conditions were as follows: SUS304 in vacuum, green compact in nitrogen gas,
Each was heated to 1130 ° C at a rate of 10 ° C per minute,
After holding for 20 minutes, the temperature is lowered at the same rate. In addition, the percentages related to the composition and the like in this specification are% by weight unless otherwise specified.

[0008] Since SUS304 already exhibits an austenite phase at room temperature, no allotropic transformation occurs upon heating and cooling. It is merely a dimensional change due to heat and shows uniform expansion and contraction as the temperature rises and falls. When the temperature returns to room temperature, the dimensions return to the original dimensions. On the other hand, in the case of the Fe-0.6P green compact, the allotrope transformation (shrinkage due to the α-γ transformation) and the dimensional change due to heat during the heating process are the same as in the case of the ingot material. As a phenomenon peculiar to a sintered alloy, pores in powder particles are densified (shrinkage) due to disappearance of pores in a process of sintering from a green compact, and these shrinkages reduce the amount of expansion due to heat. As a result, the thermal expansion of the green compact in the high temperature region of about 800 ° C. or higher where diffusion bonding proceeds is much smaller than that of SUS304. Therefore, when both are fitted and sintered, the movable iron core is brought into close contact with the valve shaft. The sintering in the pressed state is reliably performed.

[0009] Next, a compact of permalloy (Fe-47Ni) (also having a compact density of 7.1 g / cm) which is also suitable for a movable iron core
About ³ ), 1200 ° C at a rate of 10 ° C per minute in vacuum
The state of thermal expansion in the case where the temperature is raised to and maintained for 20 minutes and then returned to room temperature at the same speed will be described in comparison with SUS304.

[0010] The permalloy green compact expands slowly up to around 550 ° C during the heating process, and thereafter the gradient of expansion becomes somewhat larger, but the expansion amount is always smaller than that of SUS304.
At a temperature of 1170 ° C. or higher, shrinkage due to sintering is observed, and this shrinkage continues even during the step of maintaining the sintering temperature. When the temperature returns to room temperature, the size of SUS304 returns to the original size, whereas the permalloy sintered body shrinks more than the green compact before heating, as in the case of Fe-0.6P.

Therefore, if the movable core made of the appropriate ferromagnetic material is compression-molded by powder metallurgy and the green compact is fitted with a valve shaft made of a non-magnetic material and sintered, the green compact becomes a valve. Sintering proceeds while the shaft is tightened, and both can be firmly integrated.

(Example 1) First, for a movable iron core, a cylindrical green compact having a composition of Fe-0.6P (inner diameter 4 mm, outer diameter 10 mm, length 12 mm, green compact density 7.0 g / cm ³ )
Was prepared using 0.5% of Acurawax (trade name) as a powder lubricant. The outer periphery of the cylinder is provided with several grooves in the longitudinal direction as a fluid passage, but this is not the gist of the present invention. On the other hand, a non-magnetic stainless steel SUS304 was used for the valve stem to produce a valve stem having a diameter of 4 mm. Next, the green compact is fitted to a predetermined position of the valve shaft by press-fitting with a closing margin of 20 μm,
By sintering at 60 ° C. for 60 minutes, sintering of the movable iron core and joining to the valve shaft were performed in one step.

The product was subjected to a destructive test in which the movable core was fixed and the valve shaft was pushed out. As a result, the valve shaft was deformed when the load reached 350 kg before the joint surface was broken. This is because the joining strength of both members was superior to the compressive yield strength of the valve shaft, and it is evaluated that sufficient joining as a component of the solenoid valve was achieved. By the way, conventionally, the movable iron core is caulked to the annular groove provided on the outer circumference of the valve shaft,
Since the standard at that time is 180 kg of the withstand load, the method of the present invention is far beyond.

(Embodiment 2) The valve shaft is the same as that of Embodiment 1, and the material of the compact for the movable core is permalloy (Fe-
47Ni; compact density was 7.1 g / cm ³ ). The two are fitted together by press-fitting with a 20 μm interference, and
After sintering at 200 ° C. for 60 minutes, the strength of the obtained product was measured in the same manner as in Example 1, and the result was the same as that in Example 1. Therefore, this is also evaluated as having reached sufficient bonding as a component of the solenoid valve.

[0015]

As described above in detail, according to the present invention using a sintered alloy, unlike the conventional method in which the movable core formed from the ingot material is fixed to the valve shaft by plastic working or the like. The size and weight can be reduced as compared with the conventional case, and the responsiveness of the solenoid valve is improved. Furthermore, since the sintering of the movable core and the joining to the valve shaft are completed in one step, it is economically excellent.

Claims (4)

[Claims] 1. A powder of a ferromagnetic material having excellent soft magnetic properties or a mixed powder of the composition thereof is compression-molded into a required shape and size of a movable iron core, and the compact is fitted into a predetermined position of a valve shaft. A method for joining a valve shaft and a sintered movable iron core in an electromagnetic valve, wherein sintering of the green compact and joining to a valve shaft are completed in one step by sintering. 2. The sintered movable iron core is made of pure iron, Fe-P
The valve shaft and the sintering movable of the solenoid valve according to claim 1, wherein the valve shaft is any one of a system alloy, a Fe-Si system alloy, a Fe-Si-P system alloy, a permalloy system alloy, a permendur system alloy, and an electromagnetic stainless steel material. Iron core joining method. 3. The solenoid valve according to claim 1, wherein the fitting dimension difference between the inner diameter of the green compact and the valve shaft is a fitting with a gap of 5 μm or less or a fitting with a fitting margin of 60 μm or less. A method of joining the valve shaft and the sintered movable iron core. 4. The method according to claim 1, wherein the valve shaft is made of a non-magnetic material having a magnetic permeability of 100 or less.