JPH01300041A - Two-cycle engine - Google Patents

Abstract

PURPOSE:To level the fastening force applied to a cylinder liner from a cylinder barrel by forming a fastening force decreasing groove forming a gap to the cylinder liner outer circumferential face at the inner face of barrel near a crank case on the exhaust passage side of a cylinder block. CONSTITUTION:Inside each barrel 6 of cylinder block 1 made from aluminum alloy, a cast iron cylinder liner 5 is shrinkage fitted and fixed, while at each barrel 6, there is formed an excavation passage 10 arranged in opposition to an exhaust passage 7 (shown by dotted line) and side excavation passages 11 to 14 symmetrical around an axis of symmetry formed by a center line O1-O2 connecting the passages. In this kind of engine, at the passage 7 of barrel 6, fastening force reducing grooves 17, 18 extending to the side end of crank case are formed. The grooves serve to prevent fastening force to act on a liner similarly as the respective excavation passages 10-14 and to prevent the liner to act its fastening force in support parts 19... substantially distributed at an equal interval.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a two-stroke engine in which a cylinder liner is press-fitted into a cylinder block, and the present invention relates to a two-stroke engine in which a cylinder liner is press-fitted into a cylinder block. This is what I did.

(Prior art) A groove-shaped scavenging passage is provided on the inner surface of the cylinder barrel of a two-stroke engine near the crankcase, so that when the cylinder liner is fitted by means such as shrink fitting, The tightening force becomes uneven at various points on the circumference near the crankcase, and the bore surface of the liner is no longer a perfect circle, resulting in unevenness.

Conventionally, one method for solving this problem has been to fit the cylinder liner and then finish grind its inner circumferential surface. Another method is JP-A-61-2
52853, which makes the outer diameter of the lower half of the cylinder liner, from the vicinity of the exhaust port to the end on the crankcase side, slightly smaller to reduce the tightening margin than the upper half, thereby increasing the tightening force. By reducing , the effect of uneven tightening force is reduced.

(Problems to be Solved by the Invention) In the above-mentioned prior art, the former technique of finishing the bore surface after fitting the cylinder liner to the cylinder block is as follows:
Due to the difference in the materials of both parts, undesirable effects are likely to occur after the engine temperature rises.

If the coefficient of thermal expansion of the cylinder block is larger than that of the cylinder liner, the diameter of the support part of the barrel on which the tightening force is applied will expand, and the diameter of the part of the cylinder liner that is in contact with the support part will expand together with the support part. Since the diameter of other portions of the liner expands only according to their own coefficient of thermal expansion, there is a difference in the amount of diameter expansion, resulting in unevenness on the bore surface.

Fig. 6(a) conceptually shows the deformed state of the bore face of the cylinder liner after the engine temperature has risen. It has a total of three scavenging passages, one on each side, and an exhaust port on the 02 side.

Let p and q be the bore surfaces of the part of this cylinder liner that contacts the scavenging passage and the part that is tightened by the inner surface of the barrel.As the barrel expands as the engine temperature rises and the tightening force decreases, the bore surface of the liner , q portions have a large amount of expansion, and since no tightening force is originally applied to portion 9, the amount of expansion is small, and the entire portion deforms into an oval shape.

In two-stroke engines, this tendency is unavoidable because the scavenging passage is generally unevenly located on one side, and the clearance with the piston becomes uneven, creating a biased gap between the piston and the piston, which impedes airtightness. This also impairs the straightness of the piston.

In addition, in the latter of the above conventional techniques, precision machining must be performed to reduce the diameter of the lower half of the liner, which inevitably leads to high costs, and sufficient contact can be achieved by reducing the interference. It is considered that the heat conduction is likely to be insufficient. .

The present invention overcomes these difficulties of the conventional technology and averages out the amount of diameter expansion of the bore surface in each part when the temperature rises, as shown in Figure 6(t), without increasing costs. The challenge is to keep the clearance with the piston approximately constant.

(Means for Solving the Problems) The means for solving the above problems of the present invention includes a cylinder head, a cylinder block, a cylinder liner, and a crankcase, the cylinder block has an exhaust passage and a groove-shaped scavenging passage, and the cylinder liner has a cylinder block, a cylinder liner, and a crankcase. In a two-stroke engine that has an exhaust port and a scavenging port that communicate with these passages, a tightening force reduction method that creates a gap between the cylinder liner outer circumferential surface on the inside of the barrel near the crankcase on the exhaust passage side of the cylinder block. It is characterized in that the groove is provided in the direction of the generatrix.

(Function) By providing the four parts for reducing the tightening force on the exhaust port side, the recesses and the scavenging passage are arranged at approximately equal intervals on the barrel surface, and the support part contacts the cylinder liner in the barrel and exerts a pressurizing force. Since the heat is distributed almost evenly, the amount of thermal expansion in each part is uniform even after the engine temperature rises, and a shape close to a perfect circle is maintained.

(Example) An example will be described below with reference to the drawings. This embodiment is an example in which the present invention is applied to a three-cylinder outboard motor, and in FIGS. 1 and 2, l is an aluminum alloy cylinder block, and 2.8
．． 4 is a cylinder, 5 is a cast iron cylinder liner, B is the barrel of the cylinder block l, 8a is a small diameter part for forming a step, and the liner 5 is fitted into the barrel B from the cylinder head side by shrink fitting. After fixing, the inner surface is finished.

Each cylinder 2.3.4 is provided with an exhaust passage 7 shown by a dotted line, and a front scavenging passage 10 opposite to the exhaust passage is provided in the shape of a groove on the inner surface of the barrel, and a center line 0. −
02 is inclined with respect to the crankshaft center line 0-O.

Side scavenging passage 1 with the center line 01-02 as the axis of symmetry
1S12.13.14 is provided, and as shown in FIG.
A cylinder liner 5 with -14b is fixed within the barrel 6. In FIG. 2, 15 is a journal bearing seat, 1B is an upward recess that is a movement space for the balance weight of the crankshaft, and the scavenging passage 1O113, which is in the same phase as the upward recess 1B, has its starting end in the recess te. Another scavenging passage 11 that is open and located on the back side of the journal bearing seat 15
．． 12.14 opens inward in the middle of the barrel 6, as shown in FIG.

A tightening force reducing groove 17.18 is provided on the exhaust passage 7 side of the barrel 6 up to the end on the crankcase side, and the tightening force reducing groove 17.18 is connected to the liner 5 similarly to each of the scavenging passages IO to 14.
No clamping force can be applied to the liner 5, and the clamping force is exerted on the liner 5 by the support portions 19, 19, . . . formed between these.

What is shown in FIGS. 4 and 5 is a cross-sectional view of an engine using the above means, in which 15a is a journal bearing, 20 is a crankshaft, 21 is a balance weight thereof, 22 is an output shaft,
23 is a piston, 24 is a cylinder head, 25 is a crankcase, and 2B is an intake valve. Each cylinder 2.3.4
are arranged at extremely small intervals, and the scavenging passage 1 on the side thereof
1-14 are arranged so as to intertwine between adjacent cylinders, as shown in FIGS. 1 and 2, so that the space between the cylinders is effectively used for the scavenging passage. The tightening force reducing grooves 17 and 18 extend from the vicinity of the exhaust lower to the recess 1 on the crankcase 25 side, as one of them 17 is shown in FIG.
6, but it is a dead-end groove and does not communicate with the inside of the cylinder or the exhaust path.

With such a configuration, the support portion 19.1 of the barrel 6
9 have similar widths and are arranged at approximately equal intervals, so that the tightening force applied when fitting and fixing the cylinder liner 5 is applied evenly over the circumference.

As the temperature of the cylinder rises and expands due to engine operation, the expansion amount of the cylinder block 1 is larger than that of the cylinder liner 5. Therefore, the support portions 19, 19... expand in diameter and retreat, and the corresponding parts of the cylinder liner 5 are expanded. The bore surface of the portion supported by the support portion 19 is also forced to retreat as shown by q in FIG.
．． Since no tightening force is applied to the portion p inside the liner 18 from the beginning, the liner 6 expands based on the expansion coefficient of the liner 6 itself, and the amount of expansion is small, and the amount of deformation of the portion p is equal to the portion q.
less than.

The support portions 19, 19... are provided with the tightening force reducing grooves 17.
．． 18, they are arranged approximately evenly on the circumference, so the picture parts p and q are also formed alternately at approximately the same pitch, and the bore surface of the liner 5 is also circularly overlapped with wave-like irregularities. It becomes a shape. At this time, the piston 28 expands while maintaining its circular cross section, so there is no significant difference in the gap between the bore surface and the piston 23 at each part, and the gap is not unevenly distributed to one side. Thereby, the degree of reduction in airtightness can be suppressed to a low level, and the straightness of the piston 23 is not inhibited.

The example above has been explained in which five scavenging passages and two tightening force reducing grooves are provided, but the number of passages and grooves is not limited to this, and the scavenging passages and tightening force reducing grooves are They may be arranged so that they are distributed approximately symmetrically or approximately equally.

(Effects of the Invention) As described above, the present invention provides the cylinder barrel with the tightening force reducing groove in the exhaust passage band, thereby making it possible to provide the support portions of the liner so as to be approximately evenly distributed. It is possible to equalize the tightening force over the entire range. Therefore, even when the cylinder block expands due to temperature rise, the amount of expansion can be suppressed substantially uniformly, and the gap with the piston is not biased to one part. Therefore, the degree of decrease in airtightness can be suppressed to a low level, and since the piston can be guided in a concentric manner and the straightness of the piston can be maintained, the generation of vibration and noise is extremely small. In addition, all the supporting surfaces except for the scavenging passage and the tightening force reducing groove are in close contact with the cylinder liner with interference, so that heat conduction is good and the cylinder liner can be sufficiently cooled.

Furthermore, in order to form the tightening force reducing groove, it is sufficient to provide a protrusion for the groove on the core of the mold of the cylinder block, so there is no difficulty in machining the cylinder block, and there is little impact on production costs. It has the advantage of not occurring.

[Brief explanation of the drawing]

Figure 1 is a longitudinal sectional view of the cylinder block, Figure 2 is a front view, Figure 3 is a developed view of the cylinder liner, Figure 4 is a cross-sectional view of the engine, Figure 5 is a longitudinal sectional view, and Figure 6 is a longitudinal sectional view of the engine. The figures show examples of thermal deformation of cylinder bores, (a) is a conventional example, (b)
) indicates an example of the present invention. ■...Cylinder block 6...Cylinder bore...Exhaust passages 10-14...Scavenging passages 17.18...Tightening force reduction groove 19...Support part

Claims (1)

[Claims] In a two-stroke engine that includes a cylinder head, a cylinder block, a cylinder liner, and a crankcase, the cylinder block has an exhaust passage and a groove-shaped scavenging passage, and the cylinder liner has an exhaust port and a scavenging port that communicate with these passages. A two-stroke engine, characterized in that a tightening force reducing groove is provided in the inner surface of the barrel near the crankcase on the exhaust passage side of the cylinder block in the generatrix direction, forming a gap with respect to the outer circumferential surface of the cylinder liner.