JPH0143480Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a piston for an internal combustion engine, and more particularly to a technique for varying the clearance between a piston and a cylinder in order to reduce piston slap noise.

Prior Art and Problems In a reciprocating internal combustion engine, because there is a clearance between the piston and the cylinder, the piston collides with the cylinder near top dead center or bottom dead center, producing a piston slap sound. This piston slap noise is one of the major causes of engine noise.
In order to reduce the piston slap noise, it is effective to reduce the clearance between the piston and the cylinder, but there is a problem in that reducing the clearance increases the sliding resistance of the piston. Furthermore, since the piston expands thermally, there is a limit to how small the clearance can be made. Conventionally, in order to suppress the thermal expansion of the piston, ideas have been made to insert a ring or a thermal expansion insert into the piston, which has a coefficient of thermal expansion smaller than that of the piston material. . For example, JP-A-53-14218 discloses a light metal piston having a thermal expansion control insert made of a material with a low coefficient of thermal expansion. The present invention provides a piston in which the clearance between the piston and the cylinder is reduced only at the moment when the piston slap sound occurs, so that the sliding resistance does not become substantially large.

Means for Solving the Problems The piston of the internal combustion engine according to the present invention has a pressure-sensitive element that generates a voltage in response to pressure applied to the piston, and the pressure-sensitive element is arranged on the side circumference of the piston. electrically connected to the actuator. The pressure-sensitive element can generate a driving voltage for the actuator in response to a pressure equal to or higher than a predetermined value, and the actuator is actuated in response to an impact force when the piston is reversed due to an explosive load, and Instantly expand the area.

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

1 and 2, a hole 3 that opens into the lower cavity of the piston 1 is formed in the crown portion 2 of the piston 1, and a piezo element (pressure-sensitive element) 4 is formed in the enlarged portion of the hole 3. are inserted in close contact. The piezo element 4 receives a compressive load transmitted to the piston wall when an explosive load is applied to the top surface of the piston 1, and generates a voltage in response thereto.
The compressive load becomes maximum when the piston 1 reverses at the top dead center and the bottom dead center, and the piezo element 4
The voltage can be extracted as a voltage output when the applied pressure is greater than or equal to a predetermined value near the maximum value.

A ceramic actuator 5 is arranged around the side circumference of the piston 1. In the example shown in FIGS. 1 and 2, a pair of ceramic actuators 5
is inserted at a height near the pin boss portion and perpendicular to the piston pin (not shown). A position orthogonal to the piston pin is a position where piston slap is likely to occur as the connecting rod moves, and is called a position in the thrust or anti-thrust direction. As is known, the ceramic actuator is formed as a stack of ceramics and is displaced in the direction of the stack when a voltage is applied. In the example of FIGS. 1 and 2, the ceramic actuator 5 is arranged so that it can be displaced along the circumferential direction.

The piezo element 4 and the ceramic actuator 5 are electrically connected by a lead wire 6. Now, when the explosion load of the internal combustion engine is applied to the piston 1, a piezoelectric charge weight P is applied to the piezo element 2. When P is applied, a voltage is instantaneously generated, and the ceramic actuator 5 is energized via the lead wire 6. Therefore, the ceramic actuator 5 extends in the direction of the arrow Q, thereby increasing the diameter of the side circumferential portion of the piston 1 by a minute amount and reducing the clearance between the piston 1 and the cylinder. The voltage supplied from the piezoelectric piezoelectric element 4 can be cut below a predetermined value so that the energization time to the ceramic actuator 5 is extremely short, and the engine temperature can be sufficiently increased. After this, the ceramic actuator can be de-energized.

FIG. 3 shows an example in which the ceramic actuator 5 is arranged so as to be displaced in the radial direction. In this example as well, the ceramic actuator 5 is displaced by energizing the ceramic actuator 5 from the piezo element 4, thereby expanding the diameter of the piston 1 and appropriately reducing the clearance. Furthermore, although the piezo element 4 is preferably located near the top surface of the piston 1, it can also be mounted, for example, on a connecting rod to respond to impact forces when the piston is reversed. Furthermore, it is preferable to install the ceramic actuator 5 at a position in the thrust or anti-thrust direction. It can be attached to the lower end of the piston skirt as shown in FIG. 4, or near the top land of the piston as shown in FIG. In this way, the ceramic actuator can be installed in a desired position as needed, and can be appropriately applied to pistons with different clearances at the crown and skirt parts, or split pistons made of different materials, for example. I can do it.

Effects of the Invention As explained above, according to the present invention, slapping noise can be reduced without increasing sliding friction, and it is possible to cope with thermal expansion and the like.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the piston according to the present invention, Figure 2 is a sectional view of the piston according to the present invention;
The figure is a bottom view of the piston in Figure 1, Figure 3 is a variation of Figure 2, Figure 4 is a variation of Figure 1, and Figure 5 is a further variation of Figure 1. FIG. 1... Piston, 4... Piezo element, 5... Ceramic actuator.

Claims (1)

[Scope of utility model registration request] An internal combustion engine characterized in that it has a pressure-sensitive element that generates a voltage in response to pressure applied to the piston, and the pressure-sensitive element is electrically connected to an actuator disposed on the side circumference of the piston. engine piston.