JPS5864523A - Shift fork - Google Patents

Abstract

PURPOSE:To improve wear resistance, baking resistance, and peeling strength by jetting molten Mo to pawl part surfaces of the shift fork of a speed change gear through a plasma torch, and thus forming a melt-spray depositing layer which has a prescribed hole rate and prescribed thickness and also contains molybdenum oxides. CONSTITUTION:Over a pawl part 1a of a fork 1, a plasma torch 2 for spraying molten Mo on a surface of the pawl part 1a is arranged movably to left and right. Then, working gas is heated by arcs generated by high frequency discharge between an anode and a cathode, and part of it is placed in an electrolytic dissociation state to generate a plasma, thereby jetting the plasma 3 from the torch 2 at a high speed. For this purpose, Mo powder having 5-55mum grain size is supplied as a melt-sprayed material into the jet 3, and an adequate amount of air is supplied to and mixed with the jet forcibly. Consequently, the Mo powder forms melt-spray depositing layers 4, which have 1-4% hole rates and 20-100mum thickness and also contain molybdenum oxides, on the pawl part 1a and reverse surface of the fork 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shift fork forming a part of a vehicle transmission, the shift fork having a thermally sprayed molybdenum coating layer having excellent wear resistance and seizure resistance on its surface. .

The pawls of the shift fork of a transmission cannot be brought into sliding contact with the transmission gear of the other party under high pressure, so the sliding contact parts are worn and exposed to a high temperature atmosphere due to frictional heat, which tends to cause damage due to seizure. For this purpose, in the past, the sliding contact parts such as the pawls of the shift fork were plated with hard chrome, or molybdenum wire was melted with oxygen and acetylene flame to form a sprayed film on the surface of the shift fork. I am doing thermal spraying.

However, recently, with the advent of high-output engines such as turbocharged engines, the functional parts that make up transmissions are being used under increasingly harsh conditions.In particular, the pawls of shift forks are subject to shifting under even higher pressure. It has reached the point where it comes into sliding contact with the gear. However, conventional hard chrome or gas spraying cannot sufficiently prevent abrasion and sintering from occurring on the contact surfaces of the shift fork pawl and the transmission gear pawl. Specifically, iJ: When hardness 11 is applied, the hardness of the film is 750 to 900 L.
The wear resistance is long-lived due to its high ImV, but since the melting point of chromium is 1903°C, frictional heat with the transmission gear can cause seizure, which can cause extreme wear of the mating gear and scuffing. The hardness of the molybdenum thermal spray coating is 580~580~ when gas spraying is used.
It has relatively good wear resistance at 620 HmV, and also has good seizure resistance because the melting point of molybdenum is as high as 2620°C. However, since the temperature of the oxygen/acetylene gas flame that melts molybdenum is approximately 3200°C, the melting power is insufficient to melt molybdenum (melting point 2620°C), and therefore the molybdenum particles that fly during thermal spraying are The diameter becomes large, about 100 to 150 microns, and the porosity within the sprayed coating layer becomes large, about 8 to 18%.

As a result, the strength between the sprayed coatings tends to be weak, and the peel strength of the coatings decreases to 260-275. Therefore, there are also problems when using gas spraying.

Furthermore, it is also possible to form a thermal spray coating layer by plasma spraying using molybdenum as a thermal spraying material, but such plasma spraying is generally performed in a non-oxidizing atmosphere, and its hardness is 400 to 450 HmV, making it suitable for shift forks. This method is unsuitable for surface hardening on nails.

In view of the conventional problems as described above, the present inventors have created the present invention in order to effectively solve the problems. 55
Plasma spraying using μ molybdenum as a thermal spraying material results in a thermal spray coating with a porosity of 1 to 4%, a thickness of 20 to 100 μ, and a sufficient amount of molybdenum oxide to ensure a specified hardness. By forming a layer, wear resistance, corrosion resistance,
We would like to offer a shift fork with excellent peel strength.

A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows the main parts of an apparatus for manufacturing a soft fork according to the present invention.
A plasma torch 2 for spraying molten molybdenum onto the surface of the claw portion 1a is disposed above the claw portion 1a so as to be movable in the left-right direction. The torch 2 is equipped with a positive electrode made of copper and a cathode made of tungsten, and has an inlet hole for introducing an inert working gas such as Ar, and an inlet for feeding powdered thermal spray material. It forms a feed hole.

The arc generated by high-frequency discharge between the anode and the cathode heats the working gas (~, and partially ionizes it to generate plasma, which is ejected from the torch 2 at high speed as a plasma jet 3).

Here, a particle size of 5~
Molybdenum powder of 55μ is fed as a thermal spraying material, and an appropriate amount of air, for example -5~
Dry air at 15° C. is forcibly supplied for mixing. Then, the molybdenum powder is melted by the high heat of the plasma jet 3, and a part of it is further oxidized by the forcibly supplied air.

The molten molybdenum particles are then sprayed onto the surface of the claw portion 1a of the shift fork by the plasma jet 3.
A sprayed coating containing molybdenum oxide is formed there. Further, by repeating this process several times, as shown in FIGS. 2 and 3, the pawl portion 1a of the shift fork 1 is
A molybdenum spray coating layer 4 is formed on the front and back surfaces.

The particle size of the thermal spray material particles is set to 5 to 55 microns in order to set the porosity of the pores in the thermal spray coating layer 4 to 1 to 4%. Generally, when the particle size of the thermal spray material is increased, the particles that melt and fly also become larger, and as a result, the structure of the thermal spray coating formed on the surface of the claw portion of the shift fork also becomes coarse. Then, by performing plasma spraying several times, the bonding strength between the sprayed coatings of the thermal sprayed coating layer formed by overlapping a plurality of thermal sprayed coatings becomes weak, resulting in peeling. ! On the other hand, if the particle size of the sprayed particles is too small, the acceleration of the sprayed particles will be reduced and the collision will be weakened, resulting in a decrease in peel strength. Therefore, the porosity is suitably 1 to 4%, and therefore the particle size of the molybdenum powder is preferably 5 to 55μ. By setting the particle size within the above range,
The surface roughness of the thermally sprayed coating is also good, and the product can be manufactured without performing grinding for finishing after thermal spraying.

Further, it is preferable that the thickness of the sprayed coating layer formed on the shift fork pawl is 20 fi to 1001 t.

As is clear from Fig. 5, which will be explained later, the thickness should be 20μ or more in consideration of safety because approximately 15μ of wear occurs when traveling 3000 km, and the thickness should be 20μ or more. This is because if it is -, the roughness will become rough and finishing will be required.

In other words, when thermal spray particles are laminated one layer or two on the base material, the uneven portions gradually grow and the surface roughness becomes rough. Therefore, the thickness of the film layer is preferably 20 to 100 microns.

Next, the amount of air forcibly supplied into the plasma jet is preferably such that the weight percentage of molybdenum oxide mixed in the sprayed coating is 4.0 to 8.0%, as shown in the table below. By mixing a predetermined amount of molybdenum oxide in the film in this way, a film that satisfies hardness and peel strength at the same time can be obtained.

〔table〕

As is clear from this table, when air is forcibly supplied into the plasma jet as in the present invention, both hardness and peel strength are sufficient for practical use, whereas when gas spraying is used, the peel strength is Furthermore, it can be seen that the hardness is insufficient when conventional plasma spraying is performed in a non-oxidizing atmosphere.

Next, we compared the shift fork according to the present invention with a conventional one, specifically one with hard chrome plating, one with gas spraying, and one with conventional plasma spraying, and the results are shown in FIG. It is shown in FIG. In this case, FIG. 4 shows the relationship between the wear depth of the carburized mating gear and the travel distance, and FIG. 5 shows the relationship between the wear thickness of the shift fork and the travel distance. In this case, the shift fork according to the present invention is forged with 348C and then machined into the shape of the shift fork, the pawls are induction hardened, and then subjected to a blast treatment using alumina material, and then subjected to the following process. Plasma spraying was performed according to thermal spraying conditions.

Thermal spraying conditions 1, Plasma spraying machine: Plasmadyne 5G100 gun 2, Working current: 900A 3, Working gas: Argon, hydrogen mixed gas 4, Thermal spraying material: 999% MO powder 5, Air flow rate Near 504/i+ (inner diameter 5φ nozzle 6. Sprayed film thickness: 01 As shown in Figures 4 and 5, the shift fork according to the present invention has dramatically improved durability compared to the conventional one, and the mating gear It can be seen that there is also less wear.

As is clear from the above description, according to the present invention, in the shift fork that constitutes a part of the transmission, at least the surface of the pawl is sprayed with molybdenum with a particle size of 5 to 55 μm by plasma spraying. Porosity is 1-4%, thickness is 20
~100μ and contains a sufficient amount of molybdenum oxide to obtain the specified hardness, a sprayed coating layer is formed that has excellent wear resistance, seizure resistance, peel strength, etc., and is suitable for use in high-output engines such as turbo engines. To the transmission of the vehicle to which it is applied
9- It has many advantages such as being able to be put to practical use even if it is used.

[Brief explanation of drawings]

The drawings show a preferred embodiment of the present invention, and FIG. 1 is a schematic side view of an apparatus for plasma spraying a shift fork according to the present invention, FIG. 2 is a plan view of the shift fork, and FIG. is a longitudinal sectional side view of the same shift fork, Figure 4 is a diagram showing the relationship between the wear depth of the shift fork and the transmission gear that makes sliding contact with the travel distance, and Figure 5 is a diagram showing the relationship between the wear thickness of the shift fork and the travel distance. FIG. In the drawings, 1 is a shift fork, la is a claw portion of the shift fork, and 4 is a thermal spray coating layer. Patent Applicant Hon [[1 Technique 7j Jf Industries Co., Ltd. Agent Patent Attorney 2 111 Akuta Ichiban Patent Attorney Kunihiko Ohashi --' 10- Figure 2 Figure M3

Claims (1)

[Claims] In the shift fork of a transmission, at least the surface of the sliding pawl with the transmission gear is coated with plasma spraying using molybdenum with a particle size of 5 to 55μ as a thermal spraying material to have a porosity of 1 to 4%.
, a shift fork formed with a sprayed coating layer having a thickness of 20 to 100 μm and containing molybdenum oxide.