JPH0529781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piston for a high-power diesel engine.

[Conventional technology]

Recent high-performance diesel engines have a remarkable tendency toward lower fuel consumption and higher output. Therefore, on the one hand, the in-cylinder pressure in the combustion chamber increases, and on the other hand, the temperature distribution increases as the amount of heat generated in the combustion chamber increases. That is, as the in-cylinder pressure increases, the stress due to gas pressure increases, and in order to withstand high cycle fatigue, the thickness of the main part of the piston must be increased. If the plate thickness is increased, the temperature distribution of the piston will become higher, and the thermal stress will increase, resulting in insufficient thermal fatigue life due to engine starts and stops, or the cylinder liner will suffer from excessive thermal deformation and high temperature itself. Lubrication problems may occur. Therefore, the plate thickness with respect to gas pressure and the plate thickness with respect to temperature distribution are under contradictory conditions. Recently, in order to solve these technical problems, a piston of the outside diameter supported type shown in FIG. 3a has been replaced with an internally supported type piston shown in FIG. 3b or a pore cool type piston shown in FIG. 3c.

[Problem to be solved by the invention]

However, the current in-cylinder pressure is 110 to 130 kg/cm ² in recent high-performance engines, and in the near future
It is about to reach 180Kg/cm ² . Furthermore, the larger the engine diameter is, the more difficult it is to solve the above technical problems, and it is becoming increasingly difficult to achieve structures such as those shown in Figures 3b and 3c unless high-quality materials are used. .

An object of the present invention is to solve the problems of the conventional device and provide a piston that is most suitable for high-performance diesel engines that are expected to appear in the near future.

[Means and actions for solving the problem]

The internal pressure balanced piston of the present invention reduces the heat load on the piston by making the wall thickness as thin as possible.
In order to create a piston that can withstand gas pressure, the piston has a structure that automatically creates an internal pressure that is almost in balance with the cylinder pressure, and applies this internal pressure to the inside of the piston crown. As a result, the explosive gas pressure acting on the piston generates an even liquid pressure inside the piston that is approximately balanced with this gas pressure, so the piston can have a thin wall structure.
Note that since the hydraulic oil at this time also serves as cooling oil, the piston is sufficiently cooled and seizure of the piston can be prevented.

〔Example〕

One embodiment of the present invention will be described below with reference to FIGS. 1 and 2. 1 is a piston crown;
is an internal piston integrally formed at the upper end of the piston rod 12, 3 is a spring, 4 is a ring land,
5 is an internal liner fixed to the lower end of the piston crown 1, 6 is a spool slidably fitted into the inner circumference of the internal piston, and 7 and 8 are cooling oil inlets drilled into the spool 6 and the internal piston 2, respectively. port,
Reference numerals 9 and 10 denote cooling oil discharge ports formed around the inner liner 5 and the inner piston 2, respectively; 11 a cooling oil discharge control valve; and 13 a pressurized fluid chamber formed inside the piston crown 1.

In Fig. 1, a combustion pressure Po acts on the outer circumference of the piston crown 1, and an internal pressure Pi is created inside the piston crown 1 by the internal piston 2 and the internal liner 5, and this Pi depends on the engine output. I try to keep it almost balanced with the determined Po.
The strength of the difference between Po and Pi is the piston crown 1
The strength is ensured by supplementing with the spring 3. One purpose of installing spring 3 is to ensure safety in case something goes wrong with the balance of Po and Pi (assuming when Pi is 0), and only piston crown 1, spring 3, and internal piston 2 are installed. It is designed to withstand an output of 50 to 70% of the engine output.

When the engine is operating normally, the above-mentioned balance is maintained.
Since the piston crown 1 and spring 3 only need to be strong enough to withstand Po-Pi gas pressure fluctuations, the thickness of the main part of the piston can be made extremely thin, which is extremely advantageous in terms of durability against heat loads. be. In addition, with this piston, the abnormal deformation that occurs in conventional pistons is eliminated, and the abnormal deformation that caused abnormal wear of the ring and cylinder liner and breakage of the ring is smoothed out by the action of the even piston internal pressure Pi. By making the modification, the above-mentioned trouble can be solved.

In addition, the above-mentioned hydraulic oil serves not only for pressure balancing but also for cooling the piston, and the arrows in the figure indicate the flow direction of the oil. A downward extension of the internal piston 2 is integrated with the piston rod 12 and is connected to the crankshaft via a crosshead (not shown). This internal piston 2 is hollow, and the cooling oil that has passed through this hollow part is sent to the cooling oil inlet port 7 formed in the spool 6 and the cooling oil on the side of the internal piston 2 that slides on the exterior of the spool 6. Cooling oil flows into the piston crown 1 only at the timing when it communicates with the oil inflow port 8. After this cooling oil fulfills the function of generating hydraulic pressure Pi and the function of a cooling medium, it passes between the outer circumferential side of the internal liner 5, and further passes through the cooling oil discharge port 9 and the cooling oil discharge port 1 on the internal piston 2 side.
After passing through 0 and being controlled by the cooling oil discharge control valve 11, the oil returns to the lubricating oil reservoir in the engine body (not shown), where it is boosted again by the lubricating oil pump and the above circulation is repeated. Note that it is appropriate to use lubricating oil as the above-mentioned hydraulic oil.

Next, in the above embodiment, the cooling oil inflow port 7,
8 and the opening/closing timing of the cooling discharge ports 9 and 10 will be explained.

In Figure 2, A is the crank angle and cylinder pressure.
It is a relationship diagram of Po. When the piston passes a little after TDC, the fuel burns and the cylinder pressure Po reaches its maximum. At BDC near a crank angle of 180°, the scavenging port opens, so the Po drops to the scavenging pressure.

Next, B shows the internal piston displacement with respect to the spool 6. As shown in FIG. 1, since the piston crown 1 and the spring 3 are provided in series, this displacement and the cylinder pressure Po are approximately proportional. The movement of the internal piston 2 also determines the conduction of the cooling oil inlet ports 7 and 8 and the cooling oil outlet ports 9 and 10.

This timing is shown by a hatched straight line parallel to the horizontal axis in FIG. 2, where the horizontal axis is the crank angle and the vertical axis is the internal piston displacement. D to E indicate the opening range of the cooling oil discharge ports 9 and 10, and D to F indicate the opening range of the cooling oil inlet ports 7 and 8.
Indicates the opening timing. For safety reasons, as an example, the oil inlet ports 7 and 8 are opened at a wide range of timings.

Note that boost pressure is applied to the cooling oil at the positions of the cooling oil inflow ports 7 and 8.

Next, a step-by-step explanation will be given with reference to FIGS. 1 and 2.

To explain with reference to Fig. 1A in the region of Fig. 2B-, when the crank angle exceeds 0° (TDC) and Po reaches the maximum, the internal piston is displaced the most, and the inlet ports 7, 8 and the discharge ports 9, 10 Both are closed (corresponding to the compressibility of oil and the elasticity of spring 3).
At this time, Pi also reaches its maximum, and Po and Pi are almost balanced between the outside and the inside. Therefore, piston crown 1
The wall thickness of the main part is thin, so the temperature distribution is sufficiently low and can be controlled to a reasonable temperature. Then D ₁ ~
Referring to FIG. 1B, the region shown in FIG. 2 when the crank angle reaches E ₁ will be explained with reference to FIG. It is then discharged.
That is, the oil that has finished cooling the piston crown 1 is discharged. At the same time, the cooling oil inflow ports 7 and 8 are also opened, and low-temperature cooling oil flows into the piston crown 1 due to the cooling oil boost pressure and the volume increase due to the restoration of the crown and spring. Then E ₁ ~
E ₂ , that is, in the region of FIG. 2, as shown in FIG. 1, here the cooling oil discharge ports 9, 10 are closed, while the inflow ports 7, 8 are still open,
As Po decreases, low-temperature oil continues to flow in by the amount of change in the crown internal volume due to the restoration of the piston crown 1 and spring 3.

Next, in Figure 2 E ₂ ~ D ₂ , that is, in the area of the same figure, 1B
To explain with a diagram, here the piston is on its upward stroke, the scavenging port is closed, the cylinder pressure rises, and when the internal piston 2 reaches the position _E2 ,
Although the inflow ports 7 and 8 are still open, the discharge ports 9 and 10 are also open, and hot oil is discharged by the amount corresponding to the reduced volume of the fluid chamber 13.

Next, when the crank angle further advances and reaches D ₂ in FIG. 2, that is, in the area shown in FIG. From then on, as the crank angle advances, the displacement of the internal piston 2 increases,
The oil confined in the pressurized fluid chamber 13 generates an internal pressure Pi relative to Po determined by the load, and operates as an internal pressure balance piston.

〔Effect of the invention〕

As described above, the internal pressure balanced piston of the present invention has a mechanism that balances external pressure with internal pressure, so it is ideal for high-performance diesel engines, has a thin wall thickness, is light in weight, and has low thermal stress. We can provide high performance pistons.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main parts of the internal pressure balance piston according to the present invention, FIGS. 1A and 1B are action explanatory diagrams,
Figure 2 is an explanatory diagram of the functions of various ports of the same piston,
Figures 3a-3c are cross-sectional views of conventional piston crowns. 1... Piston crown, 2... Internal piston, 3... Spring, 5... Internal liner, 6...
...Spool, 7, 8...Cooling oil inflow port, 9,
10... Cooling oil discharge port, 13... Pressurized fluid chamber.

Claims (1)

[Claims] 1. In a crosshead type piston oil-cooled engine; an internal liner 5 formed integrally with the skirt portion of the piston crown 1; an internal piston 2 fitted on the inner periphery of the liner and formed integrally with the piston rod; A spool 6 that is fitted into the center hole that also serves as an oil passage of the internal piston and whose top surface abuts the ceiling of the piston crown; and a spool 6 that is fitted externally into the spool and whose bottom surface abuts the internal piston 2 and whose top surface abuts the piston crown ceiling. A dish-shaped spring 3 provided with
a pressurized fluid chamber 13 formed by the piston crown 1, the internal liner 5, the internal piston 2, and the spool 6; cooling oil inlet ports 7 and 8 provided in the spool 6 and the internal piston 2, respectively; 2 and cooling water discharge ports 9 and 10 provided in an internal liner 5, respectively.