JPS61212624A - Shaping of combustion chamber of piston for diesel engine - Google Patents

Abstract

PURPOSE:To reduce production cost and answer to the massive demand by shaping a combustion chamber which has a fundamental shape of twisted multipetal shape and is further applied with useful correction, by utilizing a turning apparatus. CONSTITUTION:On the upper surface 12 of a piston, an arbitrary part of the shaft center line of a mushroom-shaped cutting tool is allowed to accord with the center A of a circular petal part 14a, and cutting is carried-out by revolving the tool, lowering by the depth H1 in parallel to the center line O. Then, the cutting is carried-out by lowering the tool by the depth H2 in parallel to the center line O, shifting the tool up to the time when the tool reaches the B point over the desired center angle alpha along the arc having the radius OA. Through the quite similar procedure, the partial circular petal parts 14b-14d are worked. The protrusion having the fundamental shape of twisted multipetal and a deep visor form, i.e., a reentrant part 24 is formed. The jetting out of the fuel mist jetted into a combustion chamber 14 and flame onto the upper surface 12 of the piston can be prevented by the reentrant part 24.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a combustion chamber cavity recessed from the upper surface of a piston into the interior of the piston in a diesel engine, particularly a direct injection diesel engine.

The present applicant previously proposed that the planar shape of the opening edge on the upper surface of the piston has a multi-petal shape with a plurality of partially circular petals, and that the multi-petal shape is rotated around a center line parallel to the piston axis. He devised a combustion chamber for a piston for a diesel engine whose basic shape was a twisted petal-shaped cavity that was formed by moving the cavity downward along the same center line, and applied for registration as a utility model in 1932.
It was proposed in No. 8, No. 180419 (filed on November 22, 1982). According to this previously proposed device, by associating the above-mentioned specially shaped twisted petal-shaped cavity with the direction of the swirl flow, it is possible to improve the mixing of fuel spray and air and improve combustion, thereby reducing fuel consumption and exhaust gas. Although it was possible to improve performance and further reduce noise, there were problems with the processing of the combustion chamber.

In other words, conventionally, the combustion chamber was formed by electric discharge machining using an electrode that had the same shape as the multi-petal planar shape of the combustion chamber at the opening edge of the upper surface of the piston, but the machining time was long and productivity was extremely high. Due to the low price, the manufacturing cost was extremely high and there were defects that made it unsuitable for mass production.

Therefore, the present invention does not rely on the conventional electric discharge machining method described above, but utilizes a highly productive turning machine to create a combustion chamber having the above-mentioned twisted, multi-petaled basic shape and with beneficial modifications made thereto. It is an object of the present invention to provide a method for forming a combustion chamber of a piston for a diesel engine, which can significantly reduce manufacturing costs and meet large-scale demand by making molding possible. In order to achieve the above object, the method of the present invention provides a method for forming a combustion chamber comprising a cavity whose opening edge on the upper surface of the piston has a multi-petal shape with a plurality of partially circular petals. A shaft handle that is gripped and rotated by the device, and a disc-shaped part fixed to the coaxial handle and having a diameter substantially the same as the diameter of the partial circular petal part, and a curved outer peripheral part of the bottom part of the combustion chamber on the outer peripheral part of the lower surface thereof. A cutting tool consisting of a cutting part forming a curved surface corresponding to the above is lowered to a desired depth along a straight line passing through the center of the partial circular petal part and parallel to the piston axis, and then placed on the center line of the combustion chamber. Cutting is performed by moving circumferentially over a desired central angle along an arc that has a center and passes through the center of the partial circular petal portion, and further descends to a desired depth to perform cutting. The present invention is characterized in that the combustion chamber is removed by repeating the same number of times.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. First, in FIG. 1, reference numeral 10 generally indicates a piston of a diesel engine (not shown), and the piston is provided with a cavity 14 opening at its upper surface 12, and the cavity constitutes a combustion chamber. The cavity 14 has a plurality of partially circular petal portions 14m, 14b, 14c, and a plurality of (four in the illustrated embodiment, but may also be three, five, or six) opening edges on the piston top surface 12. 14
d, and this multi-petal shape is defined by an axis O parallel to the piston axis (in the illustrated example, for convenience, the case where both axes coincide, that is, the distance between the two axes is zero is shown) (Of course, there are cases where both axes are parallel to each other with a short distance between them.) While rotating at the same angular velocity by an angle α around the periphery of the coaxial line 0, it is formed by moving it downward to the desired depth. The basic shape is a special rotating body, with some modifications described in detail later.

For forming the cavity 14, a mushroom-shaped cutting tool 16 as shown in FIG. 2 is used. The tool 16 includes a shaft handle 18 that is gripped and rotated by a turning device (not shown);
The cutting part 20 has a disc shape having a diameter substantially equal to the diameter of the partially circular petal part, and the combustion chamber cavity 14 is formed in the outer peripheral part continuous with the lower surface of the cutting part 20. A rotating curved surface with a radius R corresponding to the outer peripheral curved surface of the bottom part is provided, and cutting edges 22 are provided on the lower surface and the outer peripheral curved surface portion, respectively.
It is equipped with When molding the cavity 14 using such a tool 16, first align the center line of the shaft handle 18 with the center AK of any partial circular petal part 14a, and align it parallel to the center line O of the combustion chamber cavity. In Figure 2, H
Cutting is performed by rotating the tool 16 while lowering it by a depth indicated by l. Next, while moving the tool 16 circumferentially around the center A of the combustion chamber cavity 14 along an arc of radius OA over a desired center angle α, that is, until it reaches point B, Cutting is performed by descending by a depth indicated by H2 in FIG. As a result, one partial circular petal portion 14m is initially aligned with the center line of the combustion chamber cavity.
Then, a partial cavity twisted around the concentric line is formed, and a curved surface with a radius R is formed on the outer peripheral surface of the bottom. Therefore, the tool 16 is moved in the opposite direction to the above and pulled out from the partial cavity that has already been cut.
The partial circular petal parts 14b to 14d are successively processed in exactly the same manner. In this way, all partial circular petal parts 1
When the machining of 4m to 14d is completed, the planar shape is approximately triangular, as shown in Fig. 1, between the adjacent partial circular petals.
A deep eave-like protrusion that forms a step, that is, a reentrant portion 24
is formed. Then, without first lowering the tool 16 by a depth Hl parallel to the combustion chamber center line 0, the tool 16 is moved circumferentially from the beginning along an arc AB with the same center angle α to the same depth H=H, - 1-H, to form the twisted petal-shaped combustion chamber as the basic shape, the first
A reentrant 1 portion having a small protrusion is formed, as shown by a dashed line 26 in the figure. Therefore, according to the method of the present invention, the combustion chamber 14 having the end runt portion 24 is formed by widening the basic twisted petal-shaped combustion chamber by the dimension indicated by the symbol S in FIG. becomes. By expanding the endrunt portion 24 in this way, it is possible to more effectively prevent the fuel spray and flame injected into the combustion chamber 14 from blowing out onto the upper surface of the piston 10, and thus suppress the generation of black smoke. In addition, the twisted petal-shaped combustion chamber has the advantage of reducing noise.

In addition, in the previously proposed device, as mentioned in the specification, the partial petals 14a to 14d do not necessarily need to be provided at equal intervals, but may be provided at unequal intervals in relation to the nozzle orifice of the fuel injection nozzle. Although it is possible to arrange them at intervals,
In this case as well, there is no change in the combustion chamber forming method itself. In the case of an automobile diesel engine, the four-petal combustion chamber shown in the diagram is usually appropriate, but depending on the size of the piston diameter and the number of injection holes in the injection nozzle, it may be possible to use a three-petal, five-petal, or A multi-hole valve-shaped combustion chamber with six petals, etc.
It is also clear that it can be processed in a manner similar to that described above. Even in the case of the above-mentioned side deviation, the machining time for forming the combustion chamber 14 inside the piston 10 using the mushroom-shaped cutting tool 16 is much shorter than that of forming using the conventional electrical discharge machining method. Therefore, it has the advantage of low production cost and the ability to easily meet a large amount of demand.

As described in the paper, the method for forming a combustion chamber of a piston for a diesel engine according to the present invention involves forming a combustion chamber consisting of a cavity whose opening edge on the upper surface of the piston has a multi-petal shape with a plurality of partially circular petals. The method comprises: a shaft handle that is gripped and rotated by a turning device; and a disc-shaped shaft that is fixed to the coaxial handle and has a diameter substantially the same as the diameter of the partially circular petal portion, and the burner is attached to the outer periphery of the lower surface of the shaft handle. A cutting tool consisting of a cutting part having a curved surface corresponding to the outer circumferential curved part of the chamber bottom is lowered to a desired depth along a straight line passing through the center of the partial circular petal part and parallel to the piston axis, and then Cutting is performed by moving in the circular direction over a desired central angle along an arc having a center on the center line of the combustion chamber and passing through the center of the partial circular petal portion, and further descending to a desired depth. The combustion chamber is cut by repeating the same number of partial circular petals as the number of partial circular petals, and a special twisted petal-shaped combustion chamber can be quickly and easily made using a normal turning device and a simple tool. This method has the advantage of being able to be produced at low cost, and the combustion chamber made by this method has the effect of effectively suppressing the generation of black smoke and reducing noise.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a piston showing an embodiment of the molding method of the present invention, and FIG. 2 is a side view of a cutting tool used for molding the combustion chamber of FIG. 1, and a developed trajectory of the tool. 10...Piston 14a-14d...
・Partial circular petal portion 12...Piston top surface 16...
・Cutting tool 14... combustion chamber

Claims (1)

[Claims] A method for forming a combustion chamber consisting of a cavity whose opening edge on the upper surface of a piston has a multi-petal shape with a plurality of partially circular petals, the method comprising: a shaft handle that is gripped and rotated by a turning device; and a coaxial handle. a cutting tool which is fixed to a disk and has a disk shape having a diameter substantially the same as the diameter of the partial circular petal portion, and has a curved surface corresponding to the outer peripheral curved surface of the bottom of the combustion chamber on the outer peripheral portion of the lower surface thereof; is lowered to a desired depth along a straight line passing through the center of the partial circular petal portion and parallel to the piston axis, and then forming an arc having its center on the center line of the combustion chamber and passing through the center of the partial circular petal portion. The combustion chamber is cut by moving the combustion chamber along the circumferential direction over a desired central angle and further lowering it to a desired depth for cutting, and repeating this process by the number of partial petals. Characteristic method for forming combustion chambers of pistons for diesel engines.