JPH085317Y2 - Engine decompression device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an engine decompression device for releasing compressed gas in a combustion chamber.

[Conventional technology]

In small two-cycle engines used for brush cutters, chainsaws, etc., a dencop device is provided to reduce the starting force required to start the engine.
2-2447 publication). On the other hand, in this type of small engine, the throttle opening is narrowed by a speed governor in order to suppress an overrun in which the engine speed unnecessarily increases. By setting a low overrun speed, the load on the engine is reduced and the engine can be made lighter.

[Problems to be solved by the device]

However, in the above-mentioned conventional technique, the speed governor is provided in addition to the decompression device, so that the structure is inevitably complicated. In addition, the engine becomes heavy and the cost becomes high.

This invention was made in view of the above conventional problems,
An object of the present invention is to provide an engine decompression device that can reduce the starting torque at the time of starting, suppress overrun, and have a simple structure and a lightweight engine.

[Means for solving the problem]

In order to achieve the above object, the present invention relates to a two-cycle engine in which a scavenging passage and an exhaust passage are provided in a peripheral wall of a cylinder. First, a valve body for opening and closing a decompression passage for releasing compressed gas in a combustion chamber to the scavenging passage. , And a detector for detecting the number of revolutions of the engine. Based on the rotation speed detected by the detector, the valve body is driven by the drive device to rotate in a starting rotation range of a first predetermined rotation speed or lower of the engine and a high rotation speed of a second predetermined rotation speed or higher that is higher than the first rotation speed range. It is held in the open position in the range and is moved to the closed position in the use range except the starting rotation range and the high speed rotation range. Here, the rotational speed means a rotational speed (rpm) as is generally used in the field of engines.

[Action]

According to this invention, since the valve element is held in the open position in the engine starting rotation range and the high-speed rotation range,
Compressed gas in the combustion chamber escapes from the decompression passage. Therefore, the starting torque becomes small in the starting rotation range and the output decreases in the high speed rotation range, so that overrun is suppressed. Therefore, with one decompression device, the starting torque at the time of starting can be reduced and overrun can be suppressed. Further, since the compressed gas is released to the scavenging passage in the exhaust stroke, the output in the high speed rotation range is reduced by the EGR (exhaust gas recirculation) effect, and the overrun is further suppressed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 show a first embodiment. The two-cycle engine of this embodiment is used as a driving machine such as a brush cutter.

In FIG. 1, a combustion chamber 12 is formed between the cylinder 10 and the piston 11. The combustion chamber 12 is provided with a decompression passage 13 that allows the compressed gas G in the combustion chamber 12 to escape to the scavenging passage 15.

The decompression passage 13 is formed in the cylinder 10 and the decompression body 14, and connects the combustion chamber 12 to the scavenging passage 15. The decompression passage 13 is provided with a valve element 16 that opens and closes the decompression passage 13. In addition,
A flame-extinguishing device 25 is provided in the decompression passage 13 of the decompression body 14.

The valve body 16 is held in the open position where the decompression passage 13 is opened by the compression coil spring 17 on the right side. On the other hand, the valve body 16 constitutes a part of the solenoid valve 18, and when the coil 19 of the solenoid valve 18 is energized, the valve body 16 moves to the right side and is held at the closed position where the decompression passage 13 is closed. It The solenoid valve 18 is controlled by the control means 20.

The control means 20 has a map that divides the engine speed into a starting rotation range shown in FIG. 2, a high-speed rotation range, and a used rotation range excluding the starting rotation range and the high-speed rotation range.
The rotation speed signal a from the detector 21 shown in FIG. 1 for detecting the rotation speed of the engine is input. The control means 20 is composed of, for example, a microcomputer, and originally controls the ignition timing of the engine.

The control means 20 controls the rotation speed signal a from the detector 21.
In response to this, a closing signal b is output to the drive circuit 22 in the use rotation range. The drive circuit 22 receiving the closing signal b is a coil
Energize 19 The electromagnetic valve 18, the drive circuit 22, and the control means 20 constitute a drive device 23.

In addition, 24 is an exhaust passage. The decompression body 14 is fixed to the cylinder 10 by a bolt (not shown).

 Next, the operation of the above configuration will be described.

In FIG. 2, the alternate long and short dash line shows the output characteristic of the engine that does not allow the compressed gas G (FIG. 1) to escape, and the alternate long and two short dashed line shows the output characteristic when the compressed gas G (FIG. 1) has always escaped. Shows the absorbed horsepower when no load is applied to the engine and the brush cutter, and the solid line shows the output characteristic of the engine of this embodiment.

First, the engine is started by a recoil starter (not shown). At this start, the engine speed is the first
The valve body 16 in FIG. 1 is held in the open position shown in the figure because it is in the starting rotation range below the predetermined rotation speed N11. Therefore, the compressed gas G in the combustion chamber 12 escapes from the decompression passage 13 to the scavenging passage 15, so that the starting torque becomes small.

Then, when the engine speed approaches the idling speed Nc (for example, 3000 rpm) in FIG. 2 and enters the operating speed range, a current flows through the coil 19 in FIG. It moves to the right against the spring force, and the decompression passage 13 is closed. As a result, the compressed gas G is confined in the combustion chamber 12, and the output becomes large as shown in FIG.

When the brush cutter is in the no-load state and the engine speed increases, the engine output falls into the high speed rotation range of the second predetermined rotation speed N12 or higher. In this high speed rotation range, the coil 19 of FIG. 1 is de-energized, and the force of the compression coil spring 17 holds the valve element 16 in the open position again. As a result, the compressed gas G in the combustion chamber 12 escapes from the decompression passage 13 to the scavenging passage 15, so that the output is reduced as shown in FIG. The engine rotates at N. Since this maximum rotation speed N is smaller than the maximum rotation speed N1 of the engine that does not allow the compressed gas G (Fig. 1) to escape, overrun is suppressed.

As described above, the present invention can reduce the starting torque at the time of starting and suppress the overrun by one decompression device. Therefore, the structure of the engine is simplified and the weight of the engine is reduced. Also, the cost will be low.

Further, in this invention, the compressed gas G in the combustion chamber 12 of FIG.
Is exhausted to the scavenging passage 15 in the exhaust stroke, exhaust gas flows through the scavenging passage 15 to the crankcase in the intake stroke in which the piston 11 rises, and the new air-fuel mixture in the crankcase is diluted with the exhaust gas. The air-fuel mixture diluted with the exhaust gas is guided from the scavenging passage 15 to the combustion chamber 12 and burned in the scavenging stroke. Due to such an EGR effect, the output in the high speed rotation range is further reduced, and the maximum rotation speed N in FIG. 2 is further reduced.
That is, overrun is further suppressed.

[Effect of device]

As described above, according to the present invention, in the engine starting rotation range and the high-speed rotation range, the valve body is held in the open position, and the compressed gas in the combustion chamber escapes from the decompression passage. And the suppression of overrun can be performed by one decompression device. Therefore, the engine has a simple structure and the weighing is performed. Further, since the compressed gas is released to the scavenging passage in the exhaust stroke, the output in the high speed rotation range is reduced by the EGR effect, and the overrun is further suppressed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a decompression device showing a first embodiment of the present invention, and FIG. 2 is a characteristic diagram showing output with respect to rotation speed. 12 ... Combustion chamber, 13 ... Decompression passage, 16 ... Valve body, 21 ... Detector, 23 ... Drive device, G ... Compressed gas.

Front page continuation (72) Inventor Hide Yamauchi, 1-1 Kawasaki-cho, Akashi-shi, Hyogo Kawasaki Heavy Industries, Ltd. Inside Akashi Plant (56) References: Kaihei 2-96011 (JP, U) Shokai: 57-28140 (JP, U)

Claims (1)

[Scope of utility model registration request] 1. In a two-cycle engine having a scavenging passage and an exhaust passage on a peripheral wall of a cylinder, a decompression passage for releasing compressed gas in a combustion chamber to the scavenging passage, a valve body for opening and closing the decompression passage, and an engine Based on the detector that detects the number of revolutions and the number of revolutions detected by this detector,
The valve body is held in the open position in the starting rotation range of the engine at or below the first predetermined rotation speed and in the high speed rotation range of at least the second predetermined rotation speed that is higher than the first rotation speed, and the start rotation range and the high speed rotation range are A decompression device for an engine, comprising: a drive device that moves the valve element to a closed position in a rotation range other than that used.