JPH0586824A - Four-cycle engine with decompressor - Google Patents

Abstract

PURPOSE:To disperse loads by the first decompressor and the second decompressor and improve durability of each part by disposing the first decompressor which decreases the compressed pressure in a cylinder when the engine starts, and the second decompressor which releases the compressed pressure in the cylinder when ignition is de-energized on an exhaust cam shaft rationally. CONSTITUTION:In a four-cycle engine which is provided with a pair of exhaust valves 81, 82 per cylinder and an exhaust cam shaft 16 opening and closing the exhaust valves, the first and second decompressors D1, D2 are formed at the exhaust cam shaft 16, adjoining to bearing parts 211, 213 which support both edges of the exhaust cam shaft 16 respectively. The first decompressor D1 opens one exhaust valve 81 during operating and the second decompressor D2 opens the other exhaust valve 82 during operating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a pair of first and second exhaust valves per cylinder, an exhaust cam shaft for opening and closing both exhaust valves, and exhaust cam shafts on both sides in the arrangement direction of both exhaust valves. The present invention relates to a four-cycle engine having a cylinder head and at least a pair of bearings that are rotatably supported, and particularly to a four-cycle engine having a decompression device.

[0002]

2. Description of the Related Art Conventionally, in a four-cycle engine, in particular, one equipped with a kick-type starter, in order to reduce the starting operation force, the engine speed is lower than a predetermined extremely low speed lower than the idling speed. It is known that a cam shaft is provided with a decompression device that opens the exhaust valve so as to reduce the compression pressure in the cylinder when the cam shaft is actuated (for example, see Japanese Patent Publication No. 25007/1990). Time,
In order to prevent the behavior of the engine due to the compression pressure in the cylinder, it is also known to provide a cam shaft with a decompression device that opens an exhaust valve so as to discharge the compression pressure.

[0003]

DISCLOSURE OF THE INVENTION According to the present invention, the above-mentioned two types of decompression devices having different functions are rationally arranged in the engine, the loads of these decompression devices are dispersed, and the durability of each part of the engine is improved. The purpose is to

[0004]

In order to achieve the above object, the present invention provides a first decompression device for opening a first exhaust valve to reduce a compression pressure in a cylinder when an engine is started, and an ignition extinguishing device. A second decompression device that opens the second exhaust valve to discharge the compression pressure in the cylinder when energized is provided on the exhaust cam shaft adjacent to the both bearing portions.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

First, referring to FIG. 1 to FIG.
The engine 1 is a four-valve, two-spark plug type. That is,
Upper surface of cylinder block 2 having a single cylinder 2a
The cylinder head 3 joined to the
A combustion chamber 5 facing the piston 4 and an air-fuel mixture in the combustion chamber 5.
Introducing a pair of intake ports 6₁, 6₂And eject from the same room 5.
A pair of exhaust ports 7 for discharging gas₁, 7₂And formed
And these ports 6₁, 6₂; 7₁, 7₂Open
Each pair of intake valves (not shown) and exhaust valve 8 to be closed₁, 8
₂And both exhaust valves 8₁, 8₂Combustion chambers 5 lined up in the arrangement direction of
Pair of spark plugs 9 facing the electrodes on both sides of the₁, 9₂And
It is installed. Both exhaust valves 8₁, 8 ₂Of which, Figure 2
The left one 8₁The first exhaust valve, the right one 8₂The second
Call it an exhaust valve.

Further, the cylinder head 3 has guide cylinders 10 ₁ , 1 for concentrically surrounding the upper portions of the intake valve and the exhaust valve.
0 ₂ ; 11 ₁ and 11 ₂ are integrally formed, and these guide cylinders have valve springs 12 ₁ and 12 ₂ (for intake valves not shown, which urge corresponding intake and exhaust valves in the closing direction). ) Is accommodated and abuts against the upper ends of the corresponding intake and exhaust valves. Bucket type cam followers 13 ₁ , 13 ₂ ; 14 ₁ , 14 ₂
Is slidably fitted.

Cam follower 13 on the intake valve side₁, 13₂of
Immediately above is a single intake camshaft that extends in the arrangement direction.
And a cam follower 14 on the exhaust valve side.₁，
14 ₂Immediately above the, there is also one
A book exhaust camshaft 16 is provided. The intake camshaft 15 is
Cam follower 13₁, 13₂Control the opening and closing of the intake valve via
Pair of intake cams 17₁, 17₂Equipped with exhaust cam
The shaft 16 is a cam follower 14.₁, 14₂Through the first,
Second exhaust valve 8₁, 8₂A pair of exhaust cams 18 that control the opening and closing of the
₁, 18₂Is equipped with.

Both cam shafts 15 and 16 are driven from a crank shaft (not shown) via a timing transmission device 19 connected to one end thereof.

[0010] the exhaust camshaft 16, the journal 2 to three at the both end portions and both exhaust cams 18 _1, 18 central portion between the _two
The cylinder head 3 is provided with bearings 21 _{1 to} 21 ₃ having 0 _{1 to} 20 ₃ and rotatably supporting them.

The bearings 21 _{1 to} 21 ₃ are formed integrally with the cylinder head 3 and correspond to the journals 20 _{1 to} 20.
₃ and bearing stand 22 _{1-22 3} for supporting the lower half surface of bolted thereto bearing stand 22 _{1-22 3} for supporting the upper half surface of the corresponding journal 20 ₁ to 20 ₃ cam holder 23 _1-23 Composed of ₃ and.

Since the structure for supporting the intake cam shaft 15 is substantially the same as that for the exhaust cam shaft 16, the description of the structure is omitted.

A head cover 24 is fixed to the cam holders 23 ₁ to 23 ₃ with bolts 25 so as to be in close contact with the upper peripheral edge of the cylinder head 3. The head cover 24 covers both the cam shafts 15 and 16 and the timing transmission device 19. ..

The exhaust camshaft 16 has a shaft when the engine is started.
In order to reduce the compression pressure in the binder 2a, the first exhaust valve 8₁To
First decompression device D for slightly opening the valve₁And ignition deenergization
At this time, the second exhaust valve for discharging the compression pressure in the cylinder 2a
8₂Second decompression device D that slightly opens the valve₂And provided
Be done. At that time, in FIG. 1, the first decompression device D₁To the left
Outer bearing portion 21₁And the exhaust cam 18 on the left side₁Between
The second decompression device D ₂To the right outer bearing portion 21₃And right
Side exhaust cam 18₂It was placed between the
Device D₁, D₂May be replaced with each other.

The structures of these decompression devices D ₁ and D ₂ will be described below.

First, as shown in FIGS. 2 and 3, the first decoration
Pump device D₁Is a cam follower 14 ₁Exhaust cam directly above
18₁Mounted on the exhaust camshaft 16 adjacent to the outside of the
A comp cam 26 is provided. This decompression cam 26
Qi cam 18₁A contour similar to but slightly smaller than
Has an exhaust cam 18₁Base circle part b₁Adjacent to
The portion 26a that constitutes the lift portion constitutes the lift portion, and the exhaust cam 18
₁Nose part n₁The portion 26b adjacent to the
Constitute.

The shaft hole 27 of the decompression cam 26 is formed to have a diameter slightly larger than the shaft diameter of the exhaust cam shaft 16 penetrating the decompression cam 26.
Inoperative position B to fall within ₁ of the contour (FIG. 3), it is possible to lift portion 26a is displaced between an operating position A projecting from the base circle portion b ₁ of exhaust cam 18 ₁ (Figure 4).

A support groove 28 in the axial direction is provided on the inner surface of the shaft hole 27 on the side of the weight portion 26b, and a fulcrum pin 29 projecting from the outer peripheral surface of the exhaust cam shaft 16 slides relative to the support groove 28. It is loosely fitted.

The support groove 28 is formed on the inner surface of the shaft hole 27.
An axial lock groove 30 is provided on the opposite side to the lock pin 31 that can be engaged with and disengaged from the lock groove 30.
Is projected on the outer peripheral surface of the.

Further, on the outer peripheral surface of the exhaust cam shaft 16, a spring holding hole 32 is opened close to the lock pin 31, and a return spring 33 for pressing the inner surface of the shaft hole 27 is provided in a contracted manner. The return spring 33 urges the decompression cam 26 toward the operating position A, and in the operating position A, the lock groove 30 is urged.
Is disengaged from the lock pin 31.

Decompression cam 26 and left outer bearing 21 ₁
A washer 34 that restricts the axial position of the cam 26 is inserted between and.

Next, as shown in FIGS. 2, 5 to 7,
The second decompression device D ₂ includes a decompression cam 36 fitted to the exhaust cam shaft 16 adjacent to the outside of the exhaust cam 18 ₂ .
A one-way clutch 37 interposed between the decompression cam 36 and the exhaust cam shaft 16 is provided.

The decompression cam 36 has a base circular portion 36a lower than the base circular portion b ₂ of the exhaust cam 18 ₂ and the exhaust cam 1
8 _{2 and} a lift portion 36 b which is slightly higher than the base circle portion b ₂ of the cam follower 14 _{2 and} are arranged to face the upper surface of the cam follower 14 ₂ .

The one-way clutch 37 is connected to the decompression cam 36.
A clutch outer ring 38 integrally connected to one end of the clutch outer ring 38 to surround the exhaust cam shaft 16, and a clutch roller 40 disposed in a wedge groove 39 on the inner peripheral surface of the clutch outer ring 38 and in contact with the outer peripheral surface of the exhaust cam shaft 16. A spring 41 for urging the clutch roller 40 toward the shallow side of the wedge groove 39 is provided.

The wedge groove 39 has a shallow groove bottom in the direction R opposite to the normal direction N of the exhaust cam shaft 16. Therefore, when the exhaust cam shaft 16 rotates in the forward direction, the clutch roller 40 rolls deeper in the wedge groove 39 to be in a free state, but when the exhaust cam shaft 16 rotates in the opposite direction R, the wedge groove 3 is formed.
9 and bite into the shallower side to put the clutch outer ring 38 on the exhaust camshaft 1
Connect to 6.

A protrusion 42 is formed on the outer peripheral surface of the clutch outer ring 38, and an end surface 42a of the protrusion 42 on the N side in the normal rotation direction stands upright from the outer peripheral surface of the clutch outer ring 38, but on the opposite side thereof. The end surface 42b of the is an inclined surface. On the other hand, a stopper pin 44 is provided in the guide hole 43 formed in the cylinder head 3 so as to be disengaged from the protrusion 42.
And a spring 45 for urging the pin 44 in the projecting direction are housed. Thus, by bringing the end surface 42a of the protrusion 42 into contact with the stopper pin 44,
The decompression cam 36 connects the lift portion 36b to the cam follower 1.
4 is held in _two inoperative position is retracted (see Fig. 5).

The clutch outer ring 38 and the right outer bearing portion 21 ₃
Between, and to prevent axial movement of the clutch outer ring 38,
And the washer 4 for preventing the clutch roller 40 from being pulled out.
6 is inserted.

Intake cams 17 ₁ and 17 ₂ and exhaust cam 1
8 _1, 18 ₂ and the first, shown in a second decompression device D _1, 8 a valve lift characteristic of the decompression cam 26, 36 of D _2.
As is clear from the figure, the decompression cam 26 of the first decompression device D ₁ exerts a valve lift in the compression stroke of the engine. On the other hand, the decompression cam 26 of the second decompression device D ₂ has a valve lift amount larger than that of the decompression cam 36 and a valve lift period longer than that of the decompression cam 26.

Next, the operation of this embodiment will be described.

When the crankshaft is cranked by the kick-type starter when the engine is started, the intake and exhaust camshafts 15 and 16 are driven via the timing transmission device 19. Indicates that the rotation speed of the exhaust camshaft 16 is lower than that during idling, and
The decompression device D ₁ is kept in the operating state shown in FIG.

That is, since the decompression cam 26 of the first decompression device D ₁ is held in the operating position A by the return spring 33 against the centrifugal force of the weight portion 26b, the lift portion 26
a is projected to the outside of the base circle b ₁ of the exhaust cam 18 ₁ . Therefore, as is clear from the valve lift curve of the decompression cam 26 in FIG. 8, the lift portion 26a pushes down the cam follower 14 ₁ during the compression stroke of the engine, and the first exhaust valve 8 ₁
Is slightly opened to appropriately reduce the compression pressure in the cylinder 2a, so that the engine can be cranked with a relatively light kick operation force, and the engine can be started easily.

When the engine is started and the exhaust camshaft 16 exceeds a predetermined extremely low rotational speed, the decompression cam 26 is inactivated by the centrifugal force of the weight portion 26b.
The lock pin 31 is engaged with the lock groove 30.
Therefore, since the entire decompression cam 26 falls within the contour of the exhaust cam 18 ₁ , the first exhaust valve 8 ₁ can be normally opened and closed by the exhaust cam 18 ₁ .

During this time, the second decompression device D ₂ is held in the inoperative state as shown in FIG. That is, the one-way clutch 37 is brought into a free state by the normal rotation of the exhaust cam shaft 16, and the clutch outer ring 38 makes the end surface 42a of the projection 42 abut against the stopper pin 44 to prevent the exhaust cam shaft 16 from rotating around. Therefore, the decompression cam 36 is held in the inoperative position, and the second exhaust valve 18 ₂ is not opened.

Next, when stopping the operation of the engine,
When the ignition device is deenergized, the compression pressure in the cylinder 2a may cause the engine to behave in an opposite manner to the normal behavior, and when the exhaust camshaft 16 rotates in the direction R opposite to the normal rotation direction N, The one-way clutch 37 is immediately engaged and the rotation of the exhaust camshaft 16 in the R direction is transmitted to the decompression cam 36, and the lift portion 36b of the cam 36 pushes down the cam follower 14 ₂ as shown in FIG. Valve 8 ₂
Open the valve. The valve opening amount and the valve opening period at this time are larger than those by the decompression cam 26 of the first decompression device D ₁ as shown in the valve lift curve of FIG. 8, and the compression pressure in the cylinder 2a is discharged to the exhaust port 7 ₂ . Is enough for As a result, said behavior of the engine will stop immediately.

By the way, such first and second deconvolution
Device D₁, D₂Supports both ends of the exhaust camshaft 16.
Left and right outer bearings 21₁, 21₃Adjacent to the exhaust
Since it is provided on the shaft 16, both decompression devices D₁, D₂
Load on both bearings 21₁, 21₃Is shared by the load
Since the inside was avoided, each bearing part 21₁, 21₂Of durability
Can contribute to improvement. Also, the first and second decompression devices
D₁, D₂Are the corresponding first and second exhaust valves 8
₁, 8₂Since each valve is opened, each valve 8₁, 8₂Burden of
However, it can contribute to the improvement of their durability. Furthermore the first
And the second decompression device D₁, D₂Separated as above
Placed on both exhaust cams 18₁, 18₂Each side facing each side of
Mufollower 14₁, 14₂To the narrow dead space above
It enables the installation of each decompression cam 26, 36
Yes, as a result, the bearing parts 21 on both outer sides ₁, 21₃Distance
Both to a single exhaust camshaft 16 without widening the
Pump device D₁, D₂Can be installed and the engine 1
It can contribute to compactness.

[0036]

As described above, according to the present invention, the first decompression device for opening the first exhaust valve in order to reduce the compression pressure in the cylinder when the engine is started, and the first decompression device in the cylinder when the ignition is deactivated. Since the second decompression device that opens the second exhaust valve to discharge the compression pressure is provided on the exhaust cam shaft adjacent to both the bearing portions, the reduction of the compression pressure in the cylinder at the time of engine start and the ignition. It is possible to satisfy both the discharge of compression pressure when deenergized, and the load of both decompression devices is shared by the bearings on both sides, so that the concentration of load does not occur and the durability of each bearing is improved. Further, since both decompression devices respectively open the corresponding first and second exhaust valves, the burden on each valve is reduced and the durability thereof can be improved.

[Brief description of drawings]

FIG. 1 is a plan view of a four-cycle engine with a decompression device according to an embodiment of the present invention with a head cover removed.

FIG. 2 is a sectional view taken along line 2-2 of FIG.

3 is a sectional view taken along line 3-3 of FIG.

FIG. 4 is an operation explanatory diagram corresponding to FIG.

5 is a sectional view taken along line 5-5 of FIG.

FIG. 6 is an operation explanatory diagram corresponding to FIG.

7 is a sectional view taken along line 7-7 of FIG.

FIG. 8: Valve lift characteristic diagram of each cam

[Explanation of symbols]

1 Engine 3 Cylinder Head 8 ₁ , 8 ₂ 1st, 2nd Exhaust Valve 16 Exhaust Cam Shaft 21 ₁ -21 ₃ Bearing Part b ₁ , b ₂ Base Circle Part D ₁ , D ₂ 1st, 2nd Decompression Device

Claims (1)

[Claims] 1. A pair of first and second cylinders per cylinder.
Exhaust valve (8₁, 8₂) And both exhaust valves (8₁, 8₂) Open
Exhaust cam shaft (16) to be closed and both exhaust valves (8 ₁, 8₂)
Exhaust cam shaft (16) is rotatably supported on both sides in the arrangement direction of
At least a pair of bearings (21₁, 21₃) And
A four-cycle engine smell for the Linda Head (3)
Reduce the compression pressure in the cylinder (2a) when starting the engine.
First exhaust valve (8 ₁) Open the first decompression device
Set (D₁) And compression in the cylinder (2a) when the ignition is deenergized
The second exhaust valve (8₂) To open the second
Decompression device (D₂) And the two bearing portions (21₁, 2
1₃) Is attached to the exhaust cam shaft (16) adjacent to
A four-cycle engine with a decompression device.