JPH05272404A - Variable compression ratio piston - Google Patents

Abstract

PURPOSE:To increase the compression ratio and swirl ratio of a direct injection type diesel engine at the time of low speed, and reduce respective ratios at the time of high speed. CONSTITUTION:A cylinder groove 22 is provided in the center area of the cavity 21 of a piston 20 to insert therein a variable piston 30 actuated by oil pressure and energized downward by a spring 33. A check valve 50 is provided in a circuit 44 for leading pressure oil into a pressure chamber 34, and relief valves 60, 65 are provided respectively in exhaust circuits 25, 27 for communicating the pressure chamber 34 to the out side. The circuits 25, 26 are closed by the relief valves 60, 65 at the time of low speed, and the variable piston 30 rises by oil pressure to increase compression ratio and swirl ratio. The spool 61 of the relief valve 60 rises near a piston top dead point at the time of high speed by inertia force so as to open the circuit 25. On the other hand the spool 61 of the relief valve 65 falls down near a piston bottom dead point, to open the circuit 27. Oil pressure in the pressure chamber 34 is reduced, and the variable piston 30 falls down to reduce the compression ratio and the swirl ratio.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a piston for a direct injection diesel engine.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view of a piston portion of a diesel engine, in which 1 is a cylinder block, 2 is a cylinder head to which a fuel injection nozzle 80 is attached, and 3 is a cylinder liner. Reference numeral 81 is a piston, which is connected to the connecting rod 5 and the piston pin 7.

On the upper surface of the piston 81, there is a hill portion 83 at the center.
A cavity 82 having a is formed. The air sucked into the cylinder and compressed generates a swirl in the cavity 82 to improve the mixed state of fuel and air.

[0004]

In the above-mentioned conventional piston, the compression ratio and the swirl ratio are always constant. Therefore, there are the following problems. FIG. 1 is a torque performance curve of an engine, where the vertical axis represents torque and the horizontal axis represents rotational speed. In FIG. 1, a low load such as C,
In the low speed rotation, that is, in the vicinity of Li (low idle), a high compression ratio is desirable from the viewpoint of good low-temperature startability and white smoke suppression during cold weather. On the other hand, in the high load region such as E and F, it is desirable to lower the maximum pressure (P _max ) and lower the compression ratio in order to obtain high output. However,
Since both cannot be satisfied, a high compression ratio is set at the expense of output and fuel consumption.

Further, a high swirl ratio is required in order to secure a low speed region such as C and D in FIG. 1, particularly a low velocity region such as D, a smoke countermeasure in a high load region, and a high low speed torque. On the other hand, in the high speed region such as E and F, from the viewpoint of power output, smoke and fuel consumption, it is desirable to reduce the swirl ratio because a high swirl ratio results in an overswirl state. However, since both cannot be satisfied at the same time, an intermediate swirl ratio must be set or the performance of either one must be sacrificed.

The present invention has been made by paying attention to the above problems. A high compression ratio and a high swirl ratio can be obtained in a low speed region of an engine, and a low compression ratio and a low swirl ratio can be obtained in a high speed region. It is intended to provide a variable compression ratio piston.

[0007]

In order to achieve the above object, in a first invention of a variable compression ratio piston according to the present invention, a central hill portion inside a cavity formed on an upper surface of a piston of a direct injection diesel engine. In the second invention, pressure oil for operating the variable piston is introduced into and discharged from the variable piston in order to make the compression ratio variable. It is characterized by the provision of a circuit that
In the third invention, a check valve is provided in the circuit for introducing the pressure oil, and the circuit for discharging the pressure oil is closed when the engine speed is equal to or lower than a predetermined speed.
It is characterized by comprising a relief valve which opens the circuit when the engine speed exceeds the predetermined speed.

[0008]

According to the above construction, a variable piston that is movable up and down for varying the compression ratio is provided in the cavity of the piston, and a check valve is provided in the pressure oil introducing circuit that operates the variable piston. A relief valve was provided in the oil discharge circuit to close the discharge circuit when the engine speed is lower than a predetermined value and open the discharge circuit when the engine speed is higher, so the variable piston rises at low speed. High compression ratio and high swirl ratio, and the variable piston descends at high rotation speed to low compression ratio and low swirl ratio.

[0009]

Embodiments of the variable compression ratio piston according to the present invention will be described below in detail with reference to the drawings. 2 is a cross-sectional view of the engine, 1 is a crankcase, 2 is a cylinder head, 3 is a cylinder liner, 4 is a crankshaft,
Reference numeral 5 is a connecting rod, 6 is a piston, and 7 is a piston pin.

The main journal and the crank journal of the crankshaft 4 are provided with annular grooves 11 and 12 forming a lubricating oil circuit. Lubricating oil is supplied from the gallery 10 to each bearing through a hole 13 provided in the crankcase 1, a hole 14 provided in the crankshaft 4, and a hole 15 provided in the connecting rod 5. Since there are 11 and 12, the lubricating oil of a constant pressure is always supplied to the piston pin 7.

FIG. 3A is a sectional view of the piston portion, and the piston 20 is connected to the connecting rod 5 by the piston pin 7. A cavity 21 is formed on the upper surface of the piston 20, and a cylinder groove 22 is provided in the central portion. A variable piston 30 having a convex upper surface is inserted into the cylinder groove 22 to form a cavity having a hill portion at the center together with the cavity 21. The stem 31 of the variable piston 30 is inserted into a hole 23 formed in the center of the piston 20. A spring seat 32 is attached to the tip of the stem 31, and a spring 33 housed in a spring chamber 24 provided in the piston 20 allows a variable piston 30
Is urged downward. A pressure chamber 34 is formed between the piston 20 and the variable piston 30.

The piston pin 7 has a cylindrical shape having a hole 40, and a lubricating oil hole 15 for the connecting rod 5 is provided at the center thereof.
An annular groove 41 communicating with is provided and is communicated with the hole 42. A hole 43 communicating with the hole 40 is formed at one end of the piston pin 7 and communicates with a pressure oil introducing circuit 44 provided in the piston 20.

The piston 20 has an introduction circuit 44 and a pressure chamber 3
A check valve 50 is provided on the circuit that connects 4 and 4.
The check valve 50 is composed of a valve seat 51, a valve 52 and a spring 53, and allows the oil to flow only from the introduction circuit 44 to the pressure chamber 34.

A relief valve (I) 60 is arranged on the discharge circuit 25 which communicates from the pressure chamber 34 to the outside of the piston 20. The relief valve (I) 60 includes a spool 61 having an annular groove 62 and a spring 64, and is provided with a piston 20.
Is vertically movably inserted into a valve hole 26 formed in the vertical direction. The spool 61 is biased downward by the spring 64, and when the spool 61 is in contact with the plug 67 of the valve hole 26, the flank 63 of the spool 61 closes the discharge circuit 25.

As shown in FIG. 3B, the relief valve (II) is provided on the discharge circuit 27 provided in parallel with the discharge circuit 25.
65 are provided. The relief valve (II) 65 includes a spool 61 and a spring 64, and is vertically movably inserted into a valve hole 28 formed in the piston 20 in the vertical direction. The valve hole 28 is closed by a plug 66.
The spool 61 is biased upward by a spring 64, and the flank 63 closes the discharge circuit 27 in the highest position.

Next, the operation will be described. In the low engine speed region such as A in FIG. 1, the relief valves (I) 60 and (II) 65 are closed as shown in FIGS. From the hole 15 of the connecting rod 5 to the holes 42, 40 of the piston pin 7
Also, the check valve 50 is pushed open by way of the introduction circuit 44 of the piston 20, flows into the pressure chamber 34, and pushes the variable piston 30 upward as shown in FIG. In this state, even if a high pressure is applied to the upper surface of the piston 20, the pressure oil in the pressure chamber 34 will still cause the check valve 50 and the relief valves (I) 60, (I
I) It is closed due to 65 and the variable piston 3
0 is never pushed down.

As a result, the volume of the cavity 21 becomes smaller than that when the variable piston 30 is lowered, and the compression ratio becomes higher. Further, since the variable piston 30 is raised, the swirl ratio is also increased.

As the engine speed increases, B shown in FIG.
4 (a), the spool 61 of the relief valve (I) 60 generates an upward inertial force while the piston 20 is moving upward, and the spool 20 near the top dead center of the piston 20. , The spool 61 rises by overcoming the set load of the spring 64, and the ring groove 62 causes the spool 61 to discharge.
Open 5

Further, as shown in FIG. 4 (b), a downward inertial force is generated on the spool 61 of the relief valve (II) 65 while the piston 20 is descending, and the spring 64 near the bottom dead center of the piston 20. Spool 6 overcoming the set load of
1 descends and opens the discharge circuit 27 by the ring groove 62. The engine speed at which the low speed range A shifts to the high speed range B is predetermined based on the engine performance.

As a result, the relief valve (I) 60 is always
Either of the relief valves (II) 65 will open. Therefore, as shown in FIG. 4A, the pressure oil in the pressure chamber 34 flows out of the piston 20 through the discharge circuit 25 or 27, the hydraulic pressure in the pressure chamber decreases, and the variable piston 30 is moved by the spring 33. To descend.

Therefore, the volume of the cavity 21 becomes large, the compression ratio becomes low, and the swirl ratio also becomes low.

[0022]

As described above in detail, the present invention provides a direct injection diesel engine with a variable piston movable up and down in the central hill portion of the cavity on the upper surface of the piston, and a pressure oil discharge circuit for operating the variable piston. In addition, a relief valve that closes the circuit at low engine speeds and opens the circuit at high speeds is provided.Therefore, in the low engine speed range, the variable piston is raised to increase the compression ratio and improve low-temperature startability and whiteness in cold weather. It is possible to suppress smoke, increase the swirl ratio, improve smoke at low speeds, and secure low speed torque. Also, in the high engine speed range, the variable piston is lowered to lower the compression ratio and suppress P _MAX to further increase the output, and the swirl ratio is reduced to avoid the overswirl output, smoke and fuel. A variable compression ratio piston with improved consumption is obtained.

[Brief description of drawings]

FIG. 1 is a torque performance curve of an engine.

FIG. 2 is a sectional view of an engine.

FIG. 3 is a sectional view of the piston of the present invention when the engine rotates at a low speed.

FIG. 4 is a sectional view of the piston of the present invention when the engine rotates at high speed.

FIG. 5 is a sectional view of a conventional piston.

[Explanation of symbols]

 5 Connecting Rod 7 Piston Pin 20 Piston 21 Cavity 22 Ring Groove 25, 27 Exhaust Circuit 30 Variable Piston 31 Stem 32 Spring Seat 33 Spring 34 Pressure Chamber 44 Introducing Circuit 50 Check Valve 51 Valve Seat 52 Valve 53 Spring 60 Relief Valve (I ) 61 spool 64 spring 65 relief valve (II)

Claims (3)

[Claims] 1. A variable piston characterized by comprising a vertically movable variable piston for varying a compression ratio in a central hill portion in a cavity formed on an upper surface of a piston of a direct injection diesel engine. Compression ratio piston. 2. The variable compression ratio piston according to claim 1, wherein the variable piston is provided with a circuit for introducing and discharging pressure oil for operating the variable piston. 3. A circuit for introducing the pressure oil includes a check valve, and a circuit for discharging the pressure oil closes the circuit when the engine speed is equal to or lower than a predetermined engine speed, and the engine speed is The variable compression ratio piston according to claim 2, further comprising a relief valve that opens the circuit when a predetermined rotation speed is exceeded.