JPH0513955Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to the intake air of a two-stroke engine.

[Prior Art] Conventionally, the outer periphery of the webs disposed on both sides of the large end of the connecting rod on the crankshaft and the inner periphery of the crankcase are formed into circular shapes.
There is a two-stroke engine in which both are arranged close to each other (for example, see Japanese Utility Model Application No. 106717/1983).
By doing so, the crank chamber is made smaller and the preload in the crank chamber is increased.

[The problem that the idea aims to solve]

However, according to the above configuration, a reed valve having a V-shaped valve seat is disposed in the intake passage connected to the intake port, and this reed valve has an intake valve located closer to the center than in the tangential direction of the circular outer peripheral surface of the web. Because the flow is directed, the intake air flow collides with the outer peripheral surface of the web throughout the entire intake process, creating a turbulent flow.
This results in a decrease in intake efficiency.

Conventionally, a connecting rod has a pair of crank arms protruding from the crankshaft in the radial direction, a crank pin is installed between the two crank arms at an eccentric position of the crankshaft, and one end is pivotally supported by the piston. It is known that the other large end is pivotally supported on the crank pin (see Japanese Utility Model Publication No. 48-9441).

The crankcase in which the above-mentioned crank arm is housed has a circular inner peripheral surface, and an intake port is formed on the outer periphery of the crankcase. A reed valve with parallel valve seat surfaces is provided.

The crank arm is formed into a substantially triangular shape, and the bottom of the triangular shape is formed into a circular shape close to the circular inner peripheral surface of the crankcase.

However, according to the above configuration, the two sides of the crank arm extending from the apex to the bottom of the triangle are formed as flat surfaces in order to balance the crank. As disclosed in the above-mentioned Japanese Utility Model Application Publication No. 52-106717, it is possible to achieve the initial objective of making the crank chamber smaller and increasing the preload in the crank chamber. Can not.

Furthermore, according to the above configuration, since the reed valve having a valve seat surface substantially parallel to the axis of the crankshaft is disposed in the intake passage, in order to improve intake efficiency, the reed valve is disposed in the intake passage. Therefore, the valve seat of the reed valve on the side to which the large end of the conrod approaches first must be formed shorter than the other valve seat.

Moreover, even with such troublesome machining, the flow of intake air from the valve seat opening on the shorter side is directed almost orthogonally to the flat surface of the crank arm, resulting in a turbulent flow, which reduces intake efficiency. It cannot be improved much.

This means that instead of using the reed valve as described above, which has a valve seat surface that is almost parallel to the axis of the crankshaft,
Even when a reed valve (see Japanese Utility Model Publication No. 51-30493) having a V-shaped valve seat with an opening divided into three parts is used, almost the same problem occurs.

This invention was made to solve the above problems, and aims to provide a two-stroke engine that can reduce the size of the crank chamber, increase the prepressure in the crank chamber, and increase intake efficiency. .

[Means to solve the problem]

The two-stroke engine according to this invention has a pair of circular webs disposed close to the circular inner peripheral surface of the crankcase, and a crank pin installed between the two webs at an eccentric position of the crankshaft. A reed valve having a V-shaped valve seat with an opening divided into three parts, which pivotally supports the large end of the conrod and directs the flow of intake air in the tangential direction of the circular outer peripheral surface of the web, is disposed in the intake passage, A notch is formed in the outer circumferential surface of both webs near the large end of the connecting rod and on the opposite side in the diametrical direction, and the notch of the square web has a circular arc concentric with the crankshaft. The reed valve has a bottom surface and a side surface, and is opposed to the intake port formed on the outer periphery of the crankcase during the intake process, and is opposed to both end openings divided into three parts of the valve seat of the reed valve, and has a central opening of the reed valve. It is characterized in that it is configured to face the large end of the cooking stove.

[Effect]

In the above configuration, since a pair of circular webs are arranged close to the circular inner peripheral surface of the crankcase, the initial purpose of making the crank chamber smaller and increasing the preload in the crank chamber is achieved. be able to.

Further, a notch having an arc-shaped bottom and side surfaces concentric with the crankshaft is formed on the outer circumferential surface of both webs near the large end of the cooking rod and on the opposite side in the diametrical direction thereof, and Since the intake air flow is directed in the tangential direction of the circular outer circumferential surface of the crankcase, when the notch faces the intake port during the intake process, the intake air is also introduced into the crankcase from this notch, and The flow of intake air becomes smooth in a laminar flow state, and intake efficiency can be improved.

[Example] An example of this invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of this invention, and is a longitudinal sectional view of a two-stroke engine at the top dead center of the piston. In this figure, 1 is a piston, 2 is a connecting rod, 3 is a crankshaft, 4 is a cylinder block, 5 is a crankcase, 6 is a crank chamber, 7 is an intake port, 8 is a reed valve, 9 is an exhaust passage, 10
is the scavenging passage.

11 and 12 are webs, connecting rod 2 in Fig. 2.
located on both sides of the big end 13 of the crank pin 14
(Fig. 3, Fig. 4). As shown in FIG. 1, the webs 11 and 12 have circular outer circumferences 11a and 12a, and are close to the circular inner circumferential surface 5a of the crankcase 5. The outer periphery 11a of these webs 11, 12,
A part of the web 12a is connected to the web 11, as shown in FIG.
The side opposite to the connecting rod 2 in the axial direction A of 12 is partially cut out to form arcuate notches 11b and 12 in FIG.
b is formed.

FIG. 4 shows a longitudinal section in a state where intake is started. The above air intake is performed while the crank pin 14 rotates from the rotational position indicated by arrow B to the rotational position indicated by arrow C. In this intake stroke, the web 1
The cutout portions 11b and 12b of 1 and 12 face the intake port 7. Portions 11c and 12c of the webs 11 and 12 corresponding to the large end 13 of the connecting rod 2
is not cut out because the crank pin 14 is press-fitted therein. In addition, a portion 11 of the webs 11 and 12 that does not face the intake port 7 during the intake stroke
d and 12d are not cut out. In other words, these portions 11d and 12d face the intake port 7 only during the exhaust stroke. Note that the crankshaft 3 rotates clockwise.

The intake port 7 is provided on the outer periphery of the crankcase 5. That is, the intake port 7 is provided in a portion of the crankcase 5 that covers the webs 11 and 12 in the radial direction. 15 is an intake passage, and its axial direction D, that is, the direction of intake air flowing through this intake passage 15, is the outer periphery 11a of the webs 11, 12,
12a is set in the tangential direction.

Reed valve 8 provided in the intake passage 15
The valve body 21 is divided into three parts as shown in FIG. Therefore, the openings 23, 24, 2 of the valve seat 22
5 is also divided into three parts, as shown by the dashed line. These openings 23, 24, and 25 are the cutout portion 11b of the web 11, and
The large end 13 is disposed at a position A in the axial direction corresponding to the notch 12b of the web 12.

A slit 13a is formed on the outer periphery of the large end 13. This slit 13a is provided at a position corresponding to the central opening 24,
As shown in FIG. 1, a portion of the big end bearing 17 is visible from the radial direction, and intake air is introduced into the big end bearing 17.

Note that 16 in FIG. 2 is a bearing that rotatably supports the crankshaft 3 in the crankcase 5.

In the above configuration, the outer periphery 1 of the webs 11 and 12
Notches 11b and 12b formed in 1a and 12a
is opposed to the intake port 7 in the intake stroke of FIGS. 4 and 1. Therefore, the notch 11
Since the intake air is also introduced into the crank chamber 6 from b and 12b, the flow of intake air becomes smooth. In particular, the direction of the intake air flowing through the intake passage 15 (axial direction D) is
Since the cutouts 11b and 12b are set in the tangential direction of the outer peripheries 11a and 12a of the webs 11 and 12, the arcuate cutouts 11b and 12b form an intake passage in the crank chamber 6. Therefore, the flow of intake air becomes smoother.

Moreover, the webs 11, 12, their outer peripheries 11a, 1
Since a part of 2a in the axial direction A in FIG. 3 is cut out, that is, as shown in FIG.
Since a and 12a are kept circular, they are close to the inner surface 5a of the crankcase 5. Therefore, there is little risk that the crankcase 5 will become larger or that the preload in the crank chamber 6 will decrease.

By the way, the valve body of a reed valve is generally divided into multiple parts due to vibration characteristics, etc.
Along with this, the valve seat that comes into contact with the valve body is located where the intake air flows, and thus obstructs the flow of the intake air. Here, this invention divides the valve body 21 and the openings 23...25 of the valve seat 22 into three parts as shown in FIG. They are arranged corresponding to the notches 11b, 12b and the large end 13. Therefore, the intake air is guided to the valve seat 22 (Fig. 5), and the opening 23...
...25 to the notches 11b, 12b and the web 1
Since it goes toward the gap S between 1 and 12, it is smoothly introduced into the crank chamber 6.

Incidentally, the large end bearing 17 shown in FIG. 1 needs to be sufficiently lubricated and cooled. In this embodiment, a slit 13a is provided on the outer periphery of the large end 13 in FIG. 2, which corresponds to the central opening 24 in FIG. Therefore, the intake air from the opening 24 toward the big end 13 is introduced from the slit 13a to the big end bearing 17 shown in FIG. 3, so that the big end bearing 17 can be sufficiently lubricated and cooled with a simple structure. .

[Effects of the invention] As described in detail above, this invention can provide a two-stroke engine with a small crank chamber, high pre-pressure in the crank chamber, and high intake efficiency.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of a two-stroke engine showing an embodiment of this invention, Fig. 2 is a sectional view taken along the - line in Fig. 1, Fig. 3 is a sectional view taken along the - line in Fig. 1, and Fig. 4 is a sectional view taken along the - line in Fig. 1.
The figure is a longitudinal cross-sectional view of the state where the intake stroke is started.
The figure is a plan view of the valve body of the reed valve. 2...Conn rod, 3...Crankshaft, 5...
Crank case, 5a...Inner peripheral surface of crank case, 7...Intake port, 8...Reed valve, 11,
12... Web, 11a, 12a... Outer periphery of the web, 11b, 12b... Notch, 13... Big end, 15... Intake passage, 17... Bearing (big end bearing), 22... Valve seat , 23, 24, 25...
Opening, A...Axial direction.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A crankcase having a circular inner circumferential surface and an intake port formed on the outer circumference, and a circular outer circumferential surface close to the inner circumferential surface of the crankcase. and a pair of circular webs concentrically fixed to a crankshaft that is rotatably supported by the crankcase, and one end of which is pivotally supported by a piston, and both webs are arranged at an eccentric position of the crankshaft. A connecting rod having its other large end supported by a bearing on a crank pin installed between the connecting rods and a connecting rod disposed in an intake passage connected to the intake port and intake air in a tangential direction of the circular outer circumferential surface of the web. a reed valve having a V-shaped valve seat with an opening divided into three parts to direct the flow of the reed valve; and a notch having an arcuate bottom and side surfaces concentric with the crankshaft, the notch facing the intake port during the intake process and opening at both ends of the valve seat of the reed valve divided into three parts. faced by
A two-stroke engine characterized in that the central opening of the reed valve is configured to face the large end of the connecting rod. (2) The two-stroke engine according to claim 1, wherein a slit is formed on the outer periphery of the large end for introducing intake air into the bearing of the large end.