JPH04296247A - Manufacture of center differential gear case - Google Patents

Abstract

PURPOSE:To promote easiness for operation and reduction in manufacturing cost without entailing any damage to the extent of fatigue strength in a center differential gear case. CONSTITUTION:A soft nitriding process is applied to the whole surface of each of case parts 2a, 2b of a center differential case 2 provided with two spline parts 21, 22 by means of machining a steel material, through which fatigue strength and wear resistance or the like are improvable and simultaneously the surface will in no case be hardened at all, so subsequent finishing operation becomes facilitated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a center differential case, which is a part for an automatic transmission of a four-wheel drive vehicle.

0002

[Prior Art] Center differential 1 built into the automatic transmission of a four-wheel drive vehicle
As shown in Fig. 2, the driving force from the transfer drive gear (not shown), which is the output member of the speed change gear mechanism, is
A transfer driven gear 3 spline-coupled to the center differential case 2, the center differential case 2, a pinion gear 4 pivotally supported within the case, one side gear 5 meshing with the pinion gear (the right side in FIG. 2), and the one side gear. It is transmitted to the rear differential side via the center shaft 6 which is spline-coupled to the front side gear, and is also transmitted to the front differential side via the other side gear 5 (on the left side in FIG. 2) and the front output shaft 7 which is spline-coupled to the other side gear. It is now possible to convey. In addition, 8 is a viscous coupling arranged between the center differential case 2 and the front output shaft 7, and when a difference in rotational speed occurs between the front and rear wheels, it limits the differential movement of the center differential 1 and It controls the distribution of driving force to. The center differential case 2 includes a portion 2a (see FIG. 3) to which the transfer driven gear 3 is connected via a spline portion 21.
and a portion 2b to which the viscous coupling 8 is coupled via the spline portion 22. In the manufacturing method of such a center differential case 2, conventionally, the case portion 2 in which the spline portions 21 and 22 are formed by machining a steel material is used.
a, 2b are formed, and as shown in FIG. 3, only the spline portion 21 of the case portion 2a is subjected to induction hardening using an induction hardening device 10, and then the spline portion 2 is
The parts other than 1 were being finished. The same applies to the case portion 2b.

0003

[Problems to be Solved by the Invention] According to the conventional manufacturing method as described above, there are problems in that it is troublesome to induction harden only the local parts of the case parts 2a and 2b, and the heat treatment cost is high. . In particular, if the base of the spline portion 21 has a recess 23 or a notch, it is difficult to uniformly apply induction hardening. The reason why it was necessary to perform induction hardening only on local parts of the case parts 2a and 2b is that the center differential case 2 has a complex shape, and if the entire surface was carburized and hardened, the surface hardness would be high. This is because finishing processing after heat treatment becomes impossible or difficult. In view of the above-mentioned problems of the conventional technology, the present invention provides a method for manufacturing a center differential case that facilitates work and reduces manufacturing costs without impairing fatigue strength. is intended to provide.

0004

[Means for Solving the Problems] In order to achieve the above-mentioned object, the method for manufacturing a center differential case of the present invention includes forming a spline portion on the entire surface of the case portion of the center differential case in which a spline portion is formed by machining a steel material. It is characterized by performing finishing processing after soft nitriding treatment.

[0005]

[Operation] When the entire surface of the case portion of the molded center differential case is subjected to nitrocarburizing treatment, the fatigue strength of the case portion is enhanced without impairing machinability. Therefore, even after the nitrocarburizing treatment, it is possible to easily finish the case portion by machining.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a center differential case according to the present invention will be described below with reference to the drawings. First, by machining the steel material in the same way as before,
As shown in FIGS. 1 and 2, case portions 2a and 2b of the center differential case 2 are molded. Next, as shown in FIG. 1, the entire case portion 2a is placed in a furnace 11, and the entire surface thereof is subjected to soft nitriding treatment (low-temperature gas instant nitriding treatment). The same applies to the case portion 2b. The nitrocarburizing treatment is preferably performed by the known tuftride method. That is, cyanide such as NaCN or KCN and NaCN
Approximately 520-57 consisting of cyanates such as O or KCNO
Case parts 2a, 2b are treated in a salt bath at 0°C for a relatively short time. When such treatment is applied, the fatigue strength of the case parts 2a and 2b is significantly increased (for example, when the base material is made of low carbon steel, it is approximately 1.8 times that before treatment), and the toughness and wear resistance are increased. , corrosion resistance, etc. are improved, and the surface hardness after treatment is low. In this way, case parts 2a, 2b
Since the surface does not become hard after the treatment, subsequent finishing by machining can be easily performed.

[0007]

[Effects of the Invention] As is clear from the above, according to the method of the present invention, the surface of the case part does not become hard after nitrocarburizing treatment, so finishing can be easily performed even if the entire surface of the case part is treated. , it is possible to solve problems such as the conventional induction hardening method, in which the heat treatment area is limited to a localized area in order to facilitate subsequent finishing processing, which requires complicated work.
Expensive heat treatment equipment such as induction hardening equipment is not required, and heat treatment costs can be significantly reduced. Also,
The center differential case manufactured by the method of the present invention is not strengthened locally as in conventional cases, but has improved fatigue strength and wear resistance of the entire case, and is therefore extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a center differential case portion for explaining one implementation of the method of the present invention.

FIG. 2 is a sectional view of essential parts of an automatic transmission for a four-wheel drive vehicle incorporating a center differential case.

FIG. 3 is a plan view of a center differential case portion for explaining a conventional technique.

[Explanation of symbols]

1 Center differential 2 Center differential case 2a, 2b
Case part 11 Furnace 21, 22 Spline part

Claims (1)

[Claims] [Claim 1] Manufacture of a center differential case characterized in that the entire surface of the case portion of the center differential case in which the spline portion is formed by machining steel material is subjected to soft nitriding treatment, and then finishing processing is performed. Method.