JPS60156956A - Piston and processing method thereof - Google Patents

Abstract

PURPOSE:To enhance the anti-seizure property of a piston, by shaping the skirt of the piston as a barrel, and providing the peripheral surface of the skirt with streaks extending in the circumferential direction. CONSTITUTION:A piston 1 consists of a head 4 having a piston ring groove 2 and an oil ring groove 3, and a skirt 5 extending down from the head 4. The peripheral surface of the skirt 5 of the piston 1 is shaped as a barrel so that the vertically central portion of the peripheral surface is expanded outwards in the radial direction. The peripheral surface of the skirt 5 is provided with streaks extending in the circumferential direction. This results in enhancing the anti- seizure property of the piston 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a piston with improved seizure resistance and a method for processing the piston.

Prior Art Conventionally, piston skirts have been treated with different ellipticity or taper degree, or with surface Sn plating or striation finishing in order to prevent seizure. However, with these methods, it was difficult to say that the initial familiarization with the bore was short. In other words, the ellipticity and taper amount simulate the shape of the piston when it is thermally deformed, but the surface that causes seizure problems remains as it has been machined, and does not fit into the bore. Similarly, in the case of Sn plating, the treated film becomes thin and cannot be said to be sufficient against seizure.

In the case of a striation finish, there are grooves to retain oil, but the part that contacts the bore is made up of protrusions, so there is a risk of the oil film breaking and seizing.

OBJECTS OF THE INVENTION An object of the present invention is to improve the seizure resistance between the piston and the cylinder bore in order to solve the above-mentioned problems with the conventional piston.

Structure of the Invention In order to achieve this object, in the piston of the present invention, the piston skirt portion is shaped like a barrel, and the shape of the trapezoidal portion between the striations of the piston skirt portion is similar to that of the piston skirt. - The trapezoidal parts at the upper and lower ends of the upper part have a larger trapezoid top area than the trapezoidal part at the center.

Furthermore, in the piston processing method of the present invention, the piston skirt section is preferably formed into a straight cylindrical state with striations, and then a sleeve having the same diameter as the cylinder bore of the actual engine to which the piston is installed is formed. The piston is machined by the step of barreling up the piston within the machine.

Effect of the Invention In the piston formed as described above and the piston processed by the above method, the trapezoidal top area of the trapezoidal part between the grooves is larger at the upper and lower ends of the piston skirt than at the center, so that initial break-in is difficult. It is possible to reduce the sliding surface pressure between the upper and lower ends of the piston skirt and the cylinder bore, which is a problem, and is very effective in preventing seizure.

In addition, in the above processing method, by performing normal striation processing and then barreling up, it is possible to naturally form a striation-interval shaped portion having a trapezoidal top area larger at the upper and lower ends than at the center of the piston skirt. can. Further, since the trapezoidal shape between the grooves obtained by wrapping inside the sleeve follows the shape of the cylinder bore of the actual machine, it is also advantageous in terms of seizure resistance.

Effects of the Invention Various effects of the piston and its processing method of the present invention described above can be obtained.

First, the 7-tube barrel inside the sleeve eliminates the need for barrel processing using a special cam, which was previously required.
Processing is facilitated.

Second, since the surface pressure at the upper and lower ends of the screw scars 1 to 1, which tend to cause seizure problems, is reduced, seizure and scuffing are prevented.

Thirdly, unlike the conventional case in which the grooves are formed on the barrel-shaped piston force part, the present invention allows the barrel to be raised after forming the grooves on a straight cylinder. The depth of the grooves at the upper and lower ends of the piston skirt is shallower than that at the center, which prevents the oil that retains the grooves from seeping out and improves lubricity, which tends to occur when the grooves are too deep. The effect of preventing burning is promoted.

Fourthly, since the barrel processing is performed using a sleeve with the same dimensions as the actual engine bore, the piston after barrel processing can be installed directly into the actual engine without having to adjust it to the cylinder bore of the actual engine.

EXAMPLES Below, preferred examples of the piston of the present invention and its processing method will be described with reference to the drawings.

1 to 4 show a piston according to an embodiment of the present invention. The piston 1 includes a piston top 4 in which a screw I-ring groove 2 and an oil ring groove 3 are formed;
It consists of a piston force section 5 that continues below it. The outer circumferential surface of the piston skirt portion 5, which appears in a cross section including the piston center axis, is formed in a barrel shape in which the center portion in the vertical direction bulges outward in the radial direction. The outer circumferential surface is usually formed in an elliptical shape.

The outer peripheral surface of the piston skirt portion 5 is provided with grooves 6 extending in the circumferential direction. As shown in FIGS. 2 to 4, a trapezoidal portion 7 is formed between the grooves 6. The area of the top 7a of the trapezoidal part 7 is the area of the piston skirt part 5.
The upper portion 5b-1 and the lower portion 5c are larger than the central portion 5a. The depth of the striations 6 is shallower in the upper and lower portions 5b and 5c of the piston skirt portion 5 than in the central portion 5a.

FIG. 5 shows a conventional piston 1- for comparison with the pistons of FIGS. 1 to 4 according to the present invention. The grooves 6- of the conventional piston 1- have the same depth over the entire length of the piston scars 1 to 5, and the trapezoidal portion 7 between the grooves 6-
The top area of - is also the same over the entire length of the piston skirt portion 5.

The piston 1 of the present invention described above can be formed by the following processing method.

First, the piston skirt portion 5 is formed into a straight cylindrical shape by forming grooves. The striations 6 at this time are formed at equal intervals and at the same depth from the surface of the straight cylinder.

Next, the part 5 of the straight cylindrical piston scar 1 on which the grooves 6 have been formed is placed in a sleeve having the same diameter as the cylinder bore of the actual engine, and barrel-processed with an abrasive. Barrel machining is carried out by piston 1 inside the sleeve.
This can be done by pressing and rotating the swash plate from above and below. By this barrel processing, the outer peripheral surfaces of the upper and lower parts 5b and 5c of the piston skirt portion 5 are polished. By this barrel machining, the top area of the trapezoidal part 7 between the grooves 6 is
The piston 1 is finished in a shape that is wider than a and in which the depth of the grooves 6 is shallower in the upper and lower parts 5b and 5c of the piston skirt part than in the central part 5a, and the piston 1 described above is obtained.

In the piston machining method, the piston skirt portion 5 may be made into a barrel shape by polishing or grinding in advance, and then striations may be formed thereon, and finally the barrel may be raised by rubbing within the sleeve.

The piston and piston processing method described above provide the following effects.

First, since barrel processing is naturally performed on the piston skirt portion 5 by raising the barrel within the sleeve, a special cam device required in conventional piston barrel processing becomes unnecessary.

Further, since the top area of the trapezoidal part 7 is increased at the upper and lower parts 5b and 5c of the piston skirt part, the surface pressure between the piston 1 and the cylinder bore is reduced when installed in an actual machine, and scuffing and seizure are prevented.

Furthermore, although the striations 6 have the effect of retaining oil, if the depth of the striations 6 is too deep, oil will come out to the surface, causing seizure. However, in the piston 1 of the present invention, the upper and lower parts 5b of the piston skirt portion 5, which are subject to particularly severe loads,
Since the depth of the grooves 6 at 5c is shallow, the oil seeps out smoothly from the grooves, and the space between the piston 1 and the cylinder bore is well lubricated and seizure is prevented.

Furthermore, since barrel-up is carried out in a sleeve with the same diameter as the cylinder bore of the actual machine, the piston 1 after barrel processing can be installed in the actual machine as is, eliminating the need for old alignments that were previously required, and reducing the machining process. reduction can be achieved.

[Brief explanation of the drawing]

1 is a front view of a piston according to an embodiment of the present invention, FIG. 2 is a partial sectional view of a part of the upper part of the piston skirt 1 of the piston of FIG. 1, and FIG. 3 is a piston skirt of the piston of FIG. 1. FIG. 4 is a partial sectional view of the lower part of the piston skirt of the piston shown in FIG. 1. FIG. 5 is a partial sectional view of the piston skirt of the conventional piston. 1... Piston 5... Piston skirt portion 5a... Piston force -1~ part center portion 5b...
...Piston skirt part upper part 5C...Piston force -i~ part lower part 6...Striation 7...Trapezoid part 7a...Top part of trapezoid part Patent applicant: Toyota Motor Corporation Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] <1) The piston skirt portion is barrel-shaped, and the shape of the trapezoidal portion between the striations of the piston skirt portion is such that the trapezoidal portions at the upper and lower ends of the piston skirt portion are trapezoidal at the center portion. A piston characterized by having a trapezoidal shape in which the area of the top of the trapezoid is larger than that of the piston. (2) A method for machining a piston, which comprises forming grooves on the piston skirt, and then barreling up the piston within a sleeve having the same diameter as the cylinder bore of the actual machine.