JP5543908B2 - Piston for engine - Google Patents

Description

  The present invention relates to a head part comprising a ceiling part and a thick cylindrical part connected to the outer peripheral part of the ceiling part, and a pair of pin bosses protruding from the lower surface of the ceiling part and arranged coaxially with each other with a piston central axis therebetween And a pair of skirts extending from the lower end of the thick cylindrical portion and connecting between the pin boss portions and having a wall thickness smaller than that of the thick cylindrical portion. .

  Such a piston for an engine is already known as disclosed in, for example, Patent Document 1 below.

Special table 2009-531583 gazette

  In such a conventional piston, in order to ensure the durability against the thrust load from the cylinder inner wall of the engine, a reinforcing rib extending from the lower end portion of the skirt portion to the ceiling portion of the head portion is provided on the inner surface of the piston.

  However, in such a piston, if the skirt portion receives a strong thrust load from the cylinder inner wall during the expansion stroke of the engine, the load is transmitted to the head portion via the reinforcing rib, and the durability of the head portion is impaired. It might be. Further, when the head portion receives the combustion pressure of the engine, a load accompanying the pressure is transmitted to the skirt portion through the reinforcing rib, and the durability of the skirt portion may be impaired.

  The present invention has been made in view of such circumstances, and provides a piston for an engine that can effectively improve the durability against the thrust load of the skirt portion without affecting the durability of the head portion. The purpose is to do.

  In order to achieve the above-mentioned object, the present invention provides a head part composed of a ceiling part and a thick cylindrical part connected to the outer peripheral part of the ceiling part, and a lower surface of the ceiling part so as to sandwich a piston central axis. A pair of pin boss portions arranged coaxially with each other and a pair of skirt portions extending from the lower end of the thick cylindrical portion to connect the pin boss portions and having a wall thickness smaller than that of the thick cylindrical portion. In the engine piston, at least during the expansion stroke of the engine, at the center in the circumferential direction of the inner peripheral surface of the skirt portion on the side receiving the thrust load from the cylinder inner peripheral wall, from the lower end of the thick cylindrical portion to the lower end of the skirt portion A first feature is that a reinforcing rib extending along the piston central axis and having a lateral width increasing toward the thick cylindrical portion is formed.

  In addition to the first feature, the present invention has a second feature that the top surface of the reinforcing rib is retreated from the inner peripheral surface of the thick cylindrical portion.

  According to the first feature of the present invention, when the thrust side skirt portion of the piston receives a thrust load from the cylinder inner peripheral wall of the engine during the expansion stroke of the engine, the thrust side skirt portion is bent and deformed radially inward. At this time, since the central portion in the circumferential direction of the skirt portion is reinforced by the reinforcing rib extending along the piston center axis from the lower end of the thick cylindrical portion to the lower end portion of the skirt portion, the above-described bending deformation of the skirt portion is effective. Can be suppressed.

  In addition, since the reinforcing rib starts from the lower end of the thick cylindrical portion of the head portion, the thrust load acting on the skirt portion is transmitted to the head portion via the reinforcing rib, and the combustion pressure acting on the head portion is caused. It is possible to prevent the load from being transmitted to the skirt portion via the reinforcing rib, and the durability of the head portion and the skirt portion can be ensured.

  Furthermore, since the reinforcing rib is formed so that the lateral width increases toward the thick cylindrical portion, the reinforcement of the skirt portion is strengthened as it goes to the thick cylindrical portion side. Corresponding to the generated bending moment, the skirt can be effectively reinforced over its entire length. As a result, almost the entire outer peripheral surface of the skirt portion comes into sliding contact with the inner peripheral wall of the cylinder of the engine, which can prevent uneven wear of the skirt portion and contribute to improvement of the durability of the piston.

  Furthermore, since the reinforcing rib has a shape that can be easily released during casting or forging, the castability or forgeability of the piston can be improved and the service life of the mold can be extended.

  According to the second feature of the present invention, load transmission between the skirt portion and the thick cylindrical portion due to the reinforcing rib can be more effectively prevented, and the durability of the piston can be further improved.

1 is a longitudinal side view of a piston for an engine according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line 2-2 in FIG. 1. FIG. 3 is a sectional view taken along line 3-3 in FIG. 1. FIG. 4 is a view taken in the direction of arrow 4 in FIG. 1. The side view which shows the behavior of the piston in the expansion stroke of an engine. The diagram which compared the piston which concerns on this invention, and the comparative example piston (piston reflecting the shape disclosed by the said patent document 1) by the bending deformation characteristic of the skirt part. FIG. 4 is a diagram corresponding to FIG. 3, showing another embodiment.

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

  First, in FIGS. 1 to 3, an engine piston P is made of an Al alloy and includes a head portion 1, a pair of pin boss portions 2, 2, and a pair of skirt portions 3, 4. The head portion 1 is composed of a ceiling portion 1a facing the combustion chamber of the engine and a thick cylindrical portion 1b connected to the outer periphery thereof, and the thick cylindrical portion 1b slides on the cylinder inner peripheral wall 5 (see FIG. 5) of the engine. A plurality of ring grooves 7 for mounting a plurality of piston rings 6 in contact therewith are provided on the outer periphery thereof.

  The pair of pin bosses 2, 2 are integrally projected on the lower surface of the ceiling portion 1 a so as to support both ends of the piston pin 13. Therefore, both pin bosses 2 and 2 are arranged coaxially with each other with the piston center axis Y in between. A thinned concave portion 8 is provided between the pin boss portions 2 and 2 and the thick cylindrical portion 1b, and the weight of the piston P can be reduced without impairing the strength of the head portion 1. Thus, the pin bosses 2 and 2 are connected to the crankshaft 15 of the engine via the piston pin 13 and the connecting rod 14 as shown in FIG.

  1 to 3 again, the pair of skirt portions 3 and 4 are arranged with the pin boss portion central axis X interposed therebetween, and both extend from the lower end of the thick cylindrical portion 1b to form a pair of pin boss portions 2. , 2 extending in an arc shape in the direction of arrangement of the skirt 2 and slidably contacting the cylinder inner peripheral wall 5 of the engine, and extending from the lower end surface of the head portion 1, and both ends of the skirt portions 3, 4 are connected to the pair of skirt portions 3, 4. The pin bosses 2 and 2 are formed of a pair of side walls 11 and 11 integrally connected to one side of the pin bosses 2 and 2. In that case, a pair of side walls 11 and 11 are arrange | positioned so that the space | interval between them may decrease toward the pin boss | hub parts 2 and 2. FIG. Further, a thin extension 16 that is thinner and shorter and has an outer peripheral surface continuous to the skirt main body 10 is integrally connected to the lower end of the skirt main body 10. When the piston P is finished, the inner peripheral surface of the thin extension 16 is used for mounting the processing reference jig.

  The pin boss center axis X is offset from the piston center axis Y by a certain amount e on one side. This is because, as shown in FIG. 5, during the expansion stroke of the engine, the piston P is tilted in a certain direction so that the side opposite to the offset e direction is directed downward, thereby reducing piston slap caused by oscillation of the oscillation. At this time, the thrust load F acts on the skirt portion 3 on the offset e side from the cylinder inner peripheral wall 5 of the engine. Therefore, hereinafter, the skirt portion 3 on the offset e side is referred to as a thrust side skirt portion 3, and the skirt portion 4 opposite to the offset e is referred to as an anti-thrust side skirt portion 4.

  As shown in FIGS. 1 to 3, in both the skirt portions 3 and 4, the central portion in the circumferential direction of the inner peripheral surface of each skirt portion main body 10 is formed from the lower end of the thick cylindrical portion 1 b to the skirt portion main body 10. Reinforcing ribs 12 extending along the piston central axis Y are integrally formed up to the lower end (that is, before the thin extension 16).

  At this time, the protruding height H of the reinforcing rib 12 is substantially constant over the entire length along the piston center axis Y so that the protruding top surface occupies a position retracted from the inner peripheral surface of the thick cylindrical portion 1b. Set to In other words, the total thickness T3 obtained by adding the raised height H of the reinforcing rib 12 to the thickness T2 of the skirt portion main body 10 is set to be smaller than the thickness T1 of the thick cylindrical portion 1b.

  The reinforcing rib 12 has an inverted trapezoidal shape when viewed from the side. That is, the reinforcing rib 12 has a shape in which the lateral width W increases toward the thick cylindrical portion 1b. Further, the top surface of the reinforcing rib 12 is formed as a flat surface in FIG.

  Next, the operation of this embodiment will be described.

  When the thrust side skirt portion 3 of the piston P receives a thrust load F from the cylinder inner peripheral wall 5 (see FIG. 5) during the expansion stroke of the engine, the skirt portion main body 10 of the thrust side skirt portion 3 in particular is It is bent and deformed inward in the radial direction around the root connected to the thick cylindrical portion 1b. At this time, both ends in the circumferential direction of the skirt body 10 are reinforced by being integrally connected to one side of the pair of pin bosses 2, 2 via the pair of side walls 11, 11. Since the central portion in the direction is reinforced by the reinforcing rib 12 extending along the piston center axis Y from the lower end of the thick cylindrical portion 1b to the lower end portion of the skirt main body 10, the above-described bending deformation of the skirt main body 10 is effectively prevented. Can be suppressed. At that time, the pair of side walls 11, 11 that integrally connect both ends in the circumferential direction of the skirt body 10 to one side of the pair of pin bosses 2, 2 are reduced toward the pin bosses 2, 2. Thus, the thrust load F applied to the skirt body 10 can be efficiently transmitted to and supported by the pin bosses 2 and 2 through the pair of side walls 11, and the skirt body 10 is effective. Can be reinforced.

  On the other hand, since the reinforcing rib 12 starts from the lower end of the thick cylindrical portion 1 b of the head portion 1, the thrust load F acting on the skirt portion 3 is prevented from being transmitted to the head portion 1 through the reinforcing rib 12. The durability of the head unit 1 is not affected. At this time, the reinforcing rib 12 has its top surface retracted from the inner peripheral surface of the thick cylindrical portion 1b of the head portion 1. This is because the thrust from the skirt portion main body 10 to the thick cylindrical portion 1b is caused by the reinforcing rib 12. This is effective in effectively preventing the transmission of the load F. This prevents the load accompanying the combustion pressure from being transmitted to the skirt portion 3 via the reinforcing rib 12 when the combustion pressure of the engine acts on the head portion 1, thereby ensuring the durability of the skirt portion 3. Means that. In particular, when the reinforcing rib 12 is formed low so that the top surface thereof recedes from the inner peripheral surface of the thick cylindrical portion 1b of the head portion 1, the reinforcing rib 12 is formed between the skirt body 10 and the thick cylindrical portion 1b. Load transmission can be prevented more effectively.

  Further, the reinforcing rib 12 has an inverted trapezoidal shape when viewed from the side, despite the fact that the raised height H is substantially constant over its entire length, so that the reinforcement of the skirt body 10 is directed to the thick cylindrical portion 1b side. The skirt part body 10 can be reinforced over the entire length corresponding to the bending moment generated in each part of the skirt part body 10 as it goes. As a result, the substantially entire outer peripheral surface of the skirt portion main body 10 comes into sliding contact with the cylinder inner peripheral wall 5 of the engine, so that uneven wear of the skirt portion main body 10 can be prevented and the durability of the piston P can be improved.

  FIG. 6 shows a central portion of the skirt portion main body 10 of the thrust side skirt portion 3 during the expansion stroke of the engine for the piston P according to the present invention and the comparative example piston (piston reflecting the shape disclosed in Patent Document 1). The difference between the amount of bending deformation generated in A and the amount of bending deformation generated in the side B of the skirt body 10 that is a fixed distance away from the central portion A is determined for each part along the axial direction of the skirt body 10. It is calculated and graphed. As is clear from this, the difference in the amount of bending deformation is smaller in the piston P according to the present invention than in the comparative example piston. This result confirms that substantially the entire outer peripheral surface of the skirt body 10 is in sliding contact with the cylinder inner peripheral wall 5 of the engine.

  As shown in FIG. 4, the reinforcing rib 12 projects the skirt portion main body 10 and the reinforcing rib 12 onto a plane L (see FIG. 1) including the piston center axis Y and parallel to the pin boss portion center axis X. In some cases, it is desirable that the projected area S2 of the reinforcing rib 12 is 20 to 50% of the projected area S1 of the skirt body 10 between the side walls 11 and 11. If it is less than 20%, the reinforcing effect of the reinforcing rib 12 is lost, and if it exceeds 50%, the reinforcing effect is too strong for the reinforcing rib 12 and uneven wear tends to occur in the central portion of the skirt body 10.

  Further, as described above, the reinforcing rib 12 is formed so that the top surface thereof is so low as to recede from the inner peripheral surface of the thick cylindrical portion 1b of the head portion 1 and has an inverted trapezoidal shape in side view. When the piston P is cast or forged, it can be easily released from the reinforcing rib 12, which contributes to extending the service life of the mold.

  During the intake stroke of the engine, negative pressure is applied to the head portion 1 of the piston P from the combustion chamber side, so that the piston P tilts in the direction opposite to that during the expansion stroke, and the anti-thrust side skirt portion 4 is the inner peripheral wall of the cylinder. 5, the thrust load is much smaller than the thrust load during the expansion stroke. Therefore, the reinforcing rib 12 of the anti-thrust side skirt portion 4 may be omitted or the reinforcing rib 12 Can be made lower than that of the thrust side skirt portion 3.

  The present invention is not limited to the above embodiment, and various design changes can be made without departing from the scope of the invention. For example, the top surface of the reinforcing rib 12 can be formed into a convex curved surface or a concave curved surface as shown in FIG. In addition, the thin extension 16 connected to the lower end of the skirt body 10 can be deleted.

P ··· Piston Y ··· Piston center axis 1 ··· Head portion 1a ··· Ceiling portion 1b ··· Thick cylindrical portion 2 ··· Pin boss portion 3 ··· ····· Thrust side skirt 4 ··· Anti-thrust side skirt 5 · · · Cylinder inner peripheral wall 8 ··· Meat removal recess 10 ··· Skirt body 11 ··· ..Side wall 12 ... Reinforcing rib

Claims (2)

A head portion (1) composed of a ceiling portion (1a) and a thick cylindrical portion (1b) connected to the outer peripheral portion of the ceiling portion (1a), and a piston central axis projecting from the lower surface of the ceiling portion (1a) A pair of pin boss portions (2, 2) arranged coaxially with each other across (Y) and the lower end of the thick-walled cylindrical portion (1b) to connect the pin boss portions (2, 2); In a piston for an engine comprising a pair of skirt portions (3, 4) whose thickness is smaller than that of the thick cylindrical portion (1b),
At least during the expansion stroke of the engine, from the lower end of the thick cylindrical portion (1b) to the circumferential center of the inner peripheral surface of the skirt portion (3) on the side receiving the thrust load (F) from the cylinder inner peripheral wall (5) The reinforcing rib (12) extending along the piston central axis (Y) to the lower end of the skirt (3) and having a lateral width (W) increasing toward the thick cylindrical portion (1b) is formed. Characteristic piston for engines. The piston for an engine according to claim 1,
A piston for an engine, wherein the top surface of the reinforcing rib (12) is retracted from the inner peripheral surface of the thick cylindrical portion (1b).

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