JP3254145B2 - piston - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine having internal hardware.

[0002]

2. Description of the Related Art FIG. 13 is a sectional view of a main part of a piston for a large diesel engine having an internal hardware. In FIG. 13, 1 is a piston crown, 2 is an internal hardware housed on the cooling side of the piston crown 1, 3 is a piston skirt,
Is a piston rod.

On the upper surface on the center side and the upper surface on the outer peripheral side of the internal hardware 2, projections 5a and 5b for promoting cooling are provided on the cylinder axis 50.
The cooling liquid passages 51 and 52 having a minute gap are formed between the projections 5a and 5b and the cooling surfaces 1a and 1b of the piston crown 1 opposed thereto.

The coolant enters the internal hardware 2 through a coolant inlet passage 53 provided at the center of the piston rod 4, passes through the coolant passage 51 having a minute width at the center, and passes through the center of the piston crown 1. After cooling the vicinity, the gas flows into the outer peripheral portion, passes through the cooling liquid passage 52 having a minute width on the outer peripheral side, cools the outer peripheral shoulder portion of the piston crown 1 and the vicinity of the piston ring groove 54, and is discharged to the outside.

[0005]

In the conventional piston as shown in FIG. 13, when the piston is cooled by cooling oil, the tip of the projection 5a or 5b and the tip of the projection 5a or 5b are required to obtain a desired cooling promoting effect. The minimum clearance between the cooling surface 1a and the cooling surface 1b of the piston crown 1 opposed to the piston crown 1 is formed as extremely small as about 2 mm. This is because the thickness of the temperature boundary layer, which affects heat transfer, becomes extremely thin because oil is used as the cooling liquid.

[0006] However, when the clearance is reduced as described above, the cooling promoting effect is increased, but the pressure loss of the cooling liquid is increased, thereby increasing the capacity of the cooling liquid supply pump and increasing the cost. There is.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a piston in which a cooling effect is promoted without increasing pressure loss.

[0008]

According to the present invention, a coolant passage is formed between a cooling surface of a piston crown and a surface of an internal hardware housed in the piston crown. In the piston, a plurality of annular wave peaks concentric with the cylinder axis are continuously provided on a surface of the internal hardware, which faces the cooling surface of the piston crown across the coolant passage, and each of the wave peaks is A top portion projecting into the coolant passage to form a minimum gap of the coolant passage;
Connected to the top, from the top toward the downstream side of the coolant flow
A face-like state such that the gap of the coolant passage expands or
A widened portion that is inclined in a curved shape, and connected to the next top portion from the widened portion.
Curved surface reduction in which the clearance of the coolant passage is reduced
A piston characterized by having a portion is proposed.

The plurality of wave peaks may be formed in one or both of an outer peripheral coolant passage forming portion located on the outer peripheral side of the piston crown and a central coolant passage forming portion located in the center of the piston. Is preferably provided.

According to this invention, the flow rate of the coolant flowing through the coolant passage between the cooling surface of the piston crown and the wave peak of the internal hardware increases at the minimum gap at the top of the wave peak, thereby increasing the heat transfer coefficient. After the passage, the separation of the flow and the frictional force are suppressed at the expanded portion where the passage is expanded, the pressure loss is suppressed, and the fluid flows into the top of the next crest.

Therefore, the heat transfer coefficient of the cooling liquid at the top increases, the cooling effect is increased, and then the increase in the pressure loss at the expanding portion is suppressed. The cooling effect is improved, and piston cooling with reduced pressure loss is performed.

In the piston, it is preferable that a wave crest of the internal hardware and a coolant passage are configured as follows.

That is, the minimum clearance (C) of the coolant passage of the wave crest forming portion is set to 1.5 mm on the outer peripheral side.
To a 2 mm, to not C = 3 mm at the center side and 4 mm, The pitch of the wave crests in the outer peripheral side and the center side (a) a = 30mm or less, the height of the wave crests and (b) and b = 3 mm to 10 mm I do.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a main part of a piston according to an embodiment of the present invention (a sectional view along a cylinder axis), FIG. 2 is an enlarged sectional view of an outer peripheral side cooling section, and FIG. The enlarged sectional views are respectively shown.

1 to 3, reference numeral 1 denotes a piston crown, 2 denotes an internal hardware housed inside the cooling side of the piston crown 1, and 53 denotes a coolant inlet passage.

Cooling surface 1 at the center of piston crown 1
a and the cooling liquid passages 51 and 52 of minute clearances between the outer cooling surface 1 b and the surface (cooling liquid surface) of the internal hardware 2.
And cooling fluid passages 55 and 57 having a large gap. Reference numeral 56 denotes a coolant communication passage that communicates the coolant passage 55 with the coolant passage 52 in the minute gap.

The surface facing the coolant passage 51 in the minute gap on the center side of the internal hardware 2 and the surface of the internal hardware 2
A plurality of annular ridges 7 are formed concentrically with the cylinder axis 50 on the surface of the minute gap on the outer peripheral side facing the coolant passage 52.

FIGS. 2 and 3 show the detailed shape of the wave crest 7, FIG. 2 showing a portion facing the coolant passage 52 on the outer peripheral side, and FIG. 3 showing a portion facing the coolant passage 51 on the center side. Is shown.

A plurality of the wave peaks 7 are formed on the outer peripheral side and the center side along the direction of the flow Z of the coolant at a pitch a. The wave crest 7 has a top portion 7a from the upstream side of the flow Z of the coolant, and a surface shape or a curved surface shape in which the passage area of the coolant from the top portion 7a is widened (shown in FIGS. 2 and 3). ) Is formed by a widened portion 7b and a curved reduced portion 7c connected to the next top portion 7a from the widened portion 7b to reduce the passage area.

The pitch a of the wave peak 7 is set to be large in a range where the change of the heat transfer coefficient α does not become large in the direction of the flow Z of the coolant. This is because when the pitch a is large, the number of the tops 7a is reduced and the pressure loss is reduced.

The height b of the wave crest 7 and the minimum gap c between the piston crown 1 and the cooling surface 1a are selected in relation to the heat transfer coefficient α and the pressure loss P. In this embodiment, preferred examples of the pitch a, the crest height b, and the gap c were obtained by a heat-fluid experiment shown in Examples described later.

During operation of the diesel engine equipped with the piston according to the above configuration, a coolant pump (not shown)
The coolant (oil) sent from the piston rod spreads outward from the coolant inlet passage 53 of the piston rod, and its flow velocity is increased in the coolant passage 51 on the center side to cool the center of the piston crown 1. The cooling fluid flows out into the cooling passage 55 having a large area, is decelerated, and flows out through the cooling fluid communication passage 56 into the cooling fluid passage 52 on the outer peripheral side.

Further, the flow rate of the coolant is increased in the coolant passage 52 on the outer peripheral side to cool the shoulder of the outer periphery of the piston crown 1 and forms a swirling flow in the coolant passage 57 on the outermost periphery. After cooling the shoulder, ring groove, etc., it is discharged to the outside.

FIG. 5 shows a temperature distribution of the coolant near the wave peak 7. In FIG. 5, when the coolant flows through the coolant passage 51 (52) between the internal hardware 2 provided with the wave peak 7 and the cooling surface 1a of the piston crown 1, the coolant passage 5
A wall jet is formed in the minimum gap c of 1 (52) (see FIGS. 2 and 3).

By selecting the minimum gap c at which the wall jet is generated to an optimum value, the temperature boundary layer near the wall can be thinned to promote cooling. However, when the minimum gap c is reduced, the pressure loss increases.

This pressure loss is roughly classified into the following two. (A) Enlargement and reduction of the passage at Namiyama 7. (A) Wall surface between the wave peaks 7 (the cooling surface of the piston crown 1 and the wave peaks 7 of the internal hardware 2) due to friction loss. The friction loss has a large influence on the internal hardware 2 side, that is, on the wave peak 7 side.

However, in the embodiment of the present invention, FIG.
(A) As shown in (B), after the flow rate is increased by narrowing the coolant passage at the top 7a of the wave crest 7, the passage area is expanded at the angle θ in the expansion portion 7b. As shown by the arrow, the fluid flows while expanding at the expanding portion 7b. After the separation of the flow and the wall friction force are suppressed, the pressure rise is suppressed, and then the flow flows to the next top portion 7a, where the flow velocity is increased. . This increases the heat transfer coefficient.

A large diesel engine having a cylinder diameter of 850 mm was operated using the above piston, and the optimum shape of the wave peak 7 having a large cooling effect and a small pressure loss was obtained by a heat flow analysis as follows. is there. Pitch a = 20mm, wave height b = 5mm, minimum gap c
= 1.5 mm.

FIG. 6 shows a heat flow analysis of the pressure loss P and the heat transfer coefficient α at the wave peak 7 forming portion based on the position (distance) U from the lowest wave peak 7 as shown in FIG. Is shown.

In FIG. 6, P1 and α1 are conventional ones without a crest, P2 and α2 are provided with a crest according to the embodiment of the present invention, and P3 and α3 are expanded to a minimum gap C = 5 mm and incorporated into an actual machine. Each of them.

As is apparent from FIG. 6, the pressure loss P and the heat transfer coefficient α of the above-described embodiment of the present invention indicated by P2 and α2 are smaller than those of the prior art indicated by P1 and α1 in FIG.
And the cooling effect is improved.

FIG. 7 shows the relationship between the pitch a of the wave peak 7 and the heat transfer coefficient α. In FIG. 7, α11 is the wave peak 7
When the pitch a is small, α12 indicates a case where the pitch a is twice as large as when α11 is α11. As is clear from the figure, when the pitch a is increased, the heat transfer coefficient α is reduced, the cooling effect is reduced, and uniform cooling becomes difficult.

FIG. 12 shows a coolant passage 51 facing the wave peak 7.
The relationship between the maximum flow velocity V in (52), the pressure loss and the heat transfer coefficient α is shown.

As is apparent from FIG. 12, the pressure loss P is
Although it tends to increase monotonically with the flow velocity V, the heat transfer coefficient α has a transition region. This indicates that there is a limit value of the jet velocity contributing to the thinning of the boundary layer because the temperature boundary layer thickness is extremely thin.

FIGS. 8 and 9 show the internal hardware of the heat transfer coefficient α (FIG. 8) and the pressure loss (FIG. 9) on the outer peripheral side (the coolant passage 52 side) when the pitch a of the wave peak 7 is changed in four ways. The change situation based on the position U (see FIG. 4) is shown. In both figures, the subscript 21 has the smallest pitch a, and the subscript 22,
23 and 24 increase in order.

As apparent from FIGS. 8 and 9, the pressure loss P decreases as the pitch a increases, but the heat transfer coefficient α also decreases, and the cooling effect decreases. (This is also shown in FIG. 7).

FIGS. 10 and 11 show the heat transfer coefficient α (FIG. 10) and the pressure loss P (FIG. 11) when the minimum clearance c of the coolant passage 52 on the outer peripheral side of the portion where the wave peak 7 is formed is changed in four ways. 5 shows a change situation based on the position U. In both figures, the subscript 31 has the smallest minimum gap c and the subscript 3
2, 33, and 34 in that order.

As is apparent from FIGS. 10 to 11, the gap c
Is small, the heat transfer coefficient α increases, but the pressure loss P sharply increases.

According to the experimental results based on the heat flow analysis described above, the following numerical values are suitable for the shape of the wave peak 7 formed on the cooling surface of the internal hardware 2 and the shape of the coolant passages 51 and 52 facing the wave peak 7. is there.

(1) Peripheral coolant passage 52 side (part shown in FIG. 2) Pitch of wave peak 7 a = 30 mm or less Height b = 3 mm to 10 mm Minimum gap c = 1.5 mm to 2 mm

(2) Central coolant passage 51 side (part shown in FIG. 3) In this part, since it is located at a radius position which is about 外 周 the radius of the outer peripheral part, the size of the wave crest 7 is defined as the outer peripheral part. If they are the same, the flow velocity will be doubled and the pressure loss will increase, so the dimensions are determined so that the flow velocity is the same as the outer peripheral part. Therefore, the pitch a and the height b of the wave crest are the same as the outer peripheral portion, and the minimum gap c is 3 mm to 4 mm.

[0043]

As described above, according to the present invention, the cooling effect is increased by increasing the heat transfer coefficient on the coolant side at the wave crest, and the pressure of the coolant is then increased at the expanding portion. The increase in loss is suppressed, and the cooling effect is improved with a high heat transfer coefficient, and the piston can be cooled with reduced pressure loss.

As a result, it is possible to obtain a highly durable piston in which the rise in the temperature of the piston is suppressed, the destruction of thermal stress and the occurrence of burning are prevented, and the capacity of the coolant supply pump can be reduced. .

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a piston according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of an outer peripheral side cooling unit in the embodiment.

FIG. 3 is an enlarged cross-sectional view of a central cooling unit in the embodiment.

FIG. 4 is an explanatory diagram showing a position of a piston cooling unit.

FIGS. 5A and 5B are explanatory diagrams showing the flow of a coolant wave crest in the embodiment.

FIG. 6 is a diagram showing changes in pressure loss and heat transfer coefficient in the embodiment.

FIG. 7 is a diagram showing a relationship between a pitch of a wave peak and a heat transfer coefficient in the embodiment.

FIG. 8 is a diagram showing a relationship between a pitch of a crest and a heat transfer coefficient in the embodiment.

FIG. 9 is a diagram showing a relationship between a wave peak pitch and a pressure loss.

FIG. 10 is a diagram showing a relationship between a minimum clearance of a coolant passage and a heat transfer coefficient.

FIG. 11 is a diagram showing a relationship between a minimum gap of a coolant passage and a pressure loss.

FIG. 12 is a diagram showing a relationship between a maximum flow rate of a coolant passage, a heat transfer coefficient, and a pressure loss.

FIG. 13 is a longitudinal sectional view showing a conventional piston.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston crown 1a, 1b Cooling surface 2 Internal hardware 7 Wave peak 7a Top 7b Expanded portion 7c Reduced portion 51, 52 Coolant passage

Claims (3)

(57) [Claims] 1. A cooling surface of a piston crown and a piston
Between the surface of the internal hardware housed inside the ton crown
A cooling fluid passage formed in the piston, wherein a cooling surface of the piston crown of the internal hardware is provided.ofThe cold
On the opposite surface across the liquid passage,
Multiple annular wave peaksContinuous installationThe wave peaks protrude into the coolant passage, and the
With the top forming a minimum gap,  Connected to the top, from the top toward the downstream side of the coolant flow
SaidSo that the gap in the coolant passage expandsFace or
CurvedWith a sloping expansionFrom the expanded portion to the next top
Curved surface reduction in which the clearance of the coolant passage is reduced
DepartmentA piston comprising: The method according to claim 2 wherein said plurality of said wave crests, the outer peripheral side cooling fluid passage forming portion located on the outer peripheral side of the piston crown or piston either center-side coolant passage forming portion located at the center side of the or It is characterized by being provided on both sides
The piston according to claim 1, wherein that. Wherein said at said outer peripheral side <br/> the minimum gap (c) of the coolant passage forming part of the wave crests, c = 1.5 mm
To a 2 mm, and 4mm to no c = 3 mm at the center side, also, the pitch of the wave crests in the outer peripheral side and the center side (a) a = 30mm or less, the height of the wave crests and (b) b = 3
3. The piston according to claim 2, wherein the piston has a diameter of 10 mm to 10 mm.