JPH08105310A - Engine valve driving device - Google Patents

Abstract

PURPOSE: To provide a diaphragm type engine valve driving device capable of ensuring the durability of the diaphragm. CONSTITUTION: A rocker arm 106 is disposed between a valve driving diaphragm 109 and valve, and small displacement is amplified to the displacement of the diaphragm to drive the valve. Also, the rocker arm 106 can pivot about a rocker arm pin 107 to engage the diaphragm 109 at a position spaced by L1 from the rocker arm pin 107 and the valve at a position spaced by L2 from the rocker arm pin 107 while L1 is set smaller than L2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crankcase compression type small two-stroke gasoline engine.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional compact crankcase compression type two-stroke gasoline engine. FIG. 2 shows a conventional example and is a sectional view taken along the center line of the cylinder. In FIG. 2, 1 is a cylinder, 2 is a piston, 3 is a crankshaft, 4 is a connecting rod, 5 is a crankcase, and 8
Is a cylinder head, 9 is a combustion chamber, and 12 is a spark plug. Reference numeral 21 denotes a scavenging valve mounted on the cylinder head 8, which is a mushroom valve opened toward the combustion chamber 9 side. A pressurizing chamber 33 and a valve chamber 32 of the diaphragm actuator 100 are formed above the scavenging valve 21, and both chambers are partitioned by the diaphragm 31. A scavenging valve spring 29 urges the scavenging valve 21 to be normally closed.

Reference numeral 24 is a scavenging hole formed in the lower portion of the cylinder 1, 23 is a scavenging passage whose lower end opens into the crankcase 5, and the upper end of the scavenging passage 23 is, as described later,
It is connected to the pressurizing chamber 33 and the scavenging port 22.
Reference numeral 27 is a valve guide, 28 is a spring bearing, and 35 is a hole for communicating the valve chamber 32 with the outside (atmosphere). 40 is cylinder 1
Is an exhaust port provided at the bottom of the. The scavenging passage 2
3 branches into two passages at the top of the cylinder,
One of them becomes the working air passage 23a, and the pressurizing chamber 33
Scavenging port 22 that is connected to
It is connected to the.

Next, the operation of the above embodiment will be described. When the piston 2 is displaced to a certain position in the expansion stroke of the engine, the exhaust port 40 opens and the exhaust port 40 opens the cylinder 1
The burnt gas inside is discharged. On the other hand, the lowering of the piston 2 compresses the air-fuel mixture introduced into the crankcase 5 from the suction passage (not shown). This air-fuel mixture is introduced into the scavenging port 22 through the scavenging passage 23, part of which is introduced into the pressurizing chamber 33 through the working air passage 23a. The pressure in the combustion chamber 9 decreases due to the further lowering of the piston 2 and the opening of the exhaust port 40, and the crankcase 5
When the internal pressure rises, the diaphragm 3 in the pressurizing chamber 33
The pressure of the air-fuel mixture acting on 1 overcomes the elasticity of the spring 29, and the air-fuel mixture pushes the scavenging valve 21 toward the combustion chamber 9 side.

As a result, the scavenging from the scavenging port 22
It is introduced into the combustion chamber 9 from the scavenging valve 21. The air-fuel mixture introduced from the scavenging valve 21 into the combustion chamber 9 flows from the upper part (in the scavenging valve 21 side) of the cylinder 1 toward the lower part where the exhaust port 40 is provided, and the burned gas is pushed out from the exhaust port 40. , The inside of the cylinder 1 is scavenged. On the other hand, the effect of introducing the air-fuel mixture into the crankcase 5 is that the pressure in the crankcase 5 decreases due to the rise of the piston 2 in the compression stroke of the previous cycle, and the suction passage (not shown) provided in the lower portion of the cylinder 1 ) Is opened. This is done by introducing the air-fuel mixture formed by a vaporizer (not shown). The flow pattern of the gas in the cylinder 1 in this embodiment is a simple one-way flow from the scavenging valve 21 on the upper part of the cylinder to the exhaust port 40 on the lower part of the cylinder, that is, a uniflow scavenging engine.

[0006]

The problem to be solved by the present invention is to improve the durability of the diaphragm 31, which is a drawback of the conventional engine. The reason why the diaphragm 31 lacks in durability is as follows. (1) The stroke of the scavenging valve 21 driven by the diaphragm 31 is determined by the scavenging amount required by the engine, but this stroke may be larger than the stroke of the diaphragm that allows the diaphragm 31 to exhibit sufficient durability.

(2) To increase the stroke of the diaphragm, a method of enlarging the outer diameter of the diaphragm is adopted.
In the diaphragm 31 of the present engine used to drive the scavenging valve 21 of the engine, there is a condition that the outer diameter cannot be increased because high responsiveness equal to the engine speed is required. In this example, the engine speed is 10,000
Since it is rpm, a response of 170 Hz is required.

An object of the present invention is to provide a diaphragm type engine valve drive device capable of ensuring the durability of the diaphragm.

[0009]

According to a first aspect of the present invention, there is provided an engine valve drive device, wherein an engine of a system in which various valves arranged in a cylinder head are driven by a diaphragm is provided with a rocker arm between the valve drive diaphragm and the various valves. Are arranged to drive the various valves by amplifying a small displacement of the diaphragm.

In the engine valve drive system of the second invention, the rocker arm is swingable about the rocker arm pin as a fulcrum, and the rocker arm engages with the diaphragm at the position L ₁ and various valves at the position L ₂ with respect to the rocker arm pin. In addition to that, it is characterized in that the first invention is set such that L ₁ <L ₂ .

[0011]

The lever ratio L _{2 of the} rocker arm 106 shown in FIG.
By selecting / L ₁ appropriately, the diaphragm 10
A large stroke of the scavenging valve 103 required by the engine can be obtained by the stroke of the diaphragm 109 corresponding to the outer diameter of 9.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the first embodiment of the present invention.
In the figure, a scavenging valve 103 mounted on the cylinder head 101 is a mushroom valve and is opened toward the combustion chamber 102 side.
Above the scavenging valve 103, the rocker arm 106 swinging around the rocker arm pin 107 and the diaphragm 10 are arranged.
9 is provided, the tip of the rocker arm 106 and the scavenging valve 1
03 upper end and the rocker arm 106 and the diaphragm 1
Pins attached to the center of 09 are each rocker arm 1
06 is configured so as to come into contact with one point on the tip side from the opposite side, and the contact positional relationship between them is the rocker arm pin 1
If L ₂ and L ₁ are compared with 07, respectively, L ₁ <L ₂ .

A large-diameter valve spring 104 and a small-diameter valve spring 105 are provided on the outer periphery of the scavenging valve 103 so as to close the valve and the valve seat 108, and a rocker arm pin 107.
On the other hand, a spring 112 is installed on the side opposite to the valve to prevent the rocker arm 106 from dancing. A pressurizing chamber 110 provided above the diaphragm 109 is connected to a crankcase (not shown).

The opening / closing operation of the scavenging valve 103, which is the main part of the above embodiment, will be described. Since the engine to which this valve drive device is attached is a two-cycle gasoline engine with crankcase scavenging, the internal pressure of the crankcase changes to positive and negative pressure in response to the vertical movement of a piston (not shown). The pressure of the pressurizing chamber 110 connected to this also changes in conjunction with this.

When the piston descends, the pressure in the pressurizing chamber 110 rises (positive pressure) and presses the diaphragm 109 downward. Since the pin provided in the center of the diaphragm 109 and the rocker arm 106 are in contact with each other at the position L ₁ from the rocker arm pin 107, the rocker arm 106 also moves downward. Further, since the rocker arm 106 is in contact with the upper end of the scavenging valve 103 at the position L ₂ from the rocker arm pin 107, the scavenging valve 103 is opened to the combustion chamber 102 side. The timing of opening the scavenging valve 103 depends on the valve opening force of the scavenging valve 103 caused by the pressure generated by the crankcase pressure, the pressure in the combustion chamber 102, and the spring force of (large diameter valve spring 104, small diameter valve spring 105). It is determined.

When the opening force of the scavenging valve 103 exceeds the valve opening force, the valve is opened, and the valve closing is performed by a completely opposite action to the valve opening.
The relationship between the stroke of the diaphragm 109 and the stroke of the scavenging valve 103 is expressed by the following equation. Scavenging valve stroke = diaphragm stroke × (L ₂ /
L ₁ ) For reference, the case of the example is as follows. (L ₂ / L ₁ ) = 2.5, diaphragm center stroke = 0.8 mm Scavenging valve stroke = 2.0 mm, diaphragm outer diameter = 2
4 mm.

[0017]

According to the diaphragm type engine valve drive device of the present invention, the stroke of the diaphragm can be made smaller than that of the conventional example, so that the durability of the diaphragm can be secured.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment according to the present invention.

FIG. 2 is a cross-sectional view of a conventional engine.

[Explanation of symbols]

101 ... Cylinder head, 102 ... Combustion chamber, 103 ... Scavenging valve, 104 ... Large diameter valve spring, 105 ... Small diameter valve spring, 10
6 ... Rocker arm, 107 ... Rocker arm pin, 108
... valve seat, 109 ... diaphragm, 110 ... pressurizing chamber, 111 ... cap, 112 ... spring.

Claims (2)

[Claims] 1. In an engine of a system in which various valves arranged on a cylinder head are driven by a diaphragm, a rocker arm is arranged between the valve driving diaphragm and the various valves to amplify a small displacement of the diaphragm. An engine valve drive device characterized by driving various valves. 2. The rocker arm is swingable around a rocker arm pin as a fulcrum, and engages with the diaphragm at a position L ₁ from the rocker arm pin and various valves at a position L ₂ , and L ₁ <L ₂ The engine valve drive device according to claim 1, wherein