JPH0364604A - Valve system on two-stroke engine - Google Patents

Abstract

PURPOSE:To reduce the thermal load of exhaust valves by constructing cams to open exhaust valves so as to have two cam noses in which the phase of the larger cam nose of at least one of the cams and that of the smaller cam nose of at least one of the other cams are nearly same. CONSTITUTION:Poppet exhaust valves 14a, 14b to open and close the two exhaust ports 15 provided in a cylinder head 14 are opened and closed by the rotation of a camshaft 20, arranged above the valve lifters (tappets) 6 inserted freely in the end portions of the shafts of valves 14a, 14b, through the 1st. and the 2nd cams 18, 19 respectively. In the above, the 1st. and the 2nd cams 18, 19 are provided with the 1st. cam noses 18a, 19a of larger profile and the 2nd cam noses 18b, 19b of smaller profile 180 deg. phase shifted to cam noses 18a, 19a in circumferential direction respectively, and the phases of the nose 18a and the nose 19a and those of the nose 18b and the nose 19b are made 180 deg. different to each other respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a valve control device for a two-stroke engine, and particularly to a device capable of reducing the thermal load on an exhaust valve.

[Conventional technology]

Two-stroke (cycle) engines are easy to increase output, have a simple structure, and can be made smaller and lighter. However, it is difficult to improve scavenging efficiency, especially in gasoline engines, which consumes a lot of fuel and has low exhaust emissions. It has drawbacks such as difficulty in dealing with gas.

To solve these problems, there is a two-stroke engine that combines a valve train with intake and exhaust valves, a fuel injection device, a scavenging pump (roots blower), etc. to achieve optimal performance. .

[Problem to be solved by the invention]

In a two-stroke engine equipped with the above-mentioned exhaust valve, the exhaust valve operates once for each rotation of the crankshaft, so the heat load is greater and the temperature tends to rise more easily than in a four-stroke engine.

As a result, a portion of the valve becomes a heat spot, causing abnormal combustion such as early ignition and knocking, resulting in a decrease in performance.

There is also a risk that the valve may burn out or break due to a decrease in strength.

The present invention has been made to solve the above problems, and provides a valve train for a two-stroke engine that improves the cooling performance of the exhaust valve and reduces the heat load, thereby providing a highly durable and reliable valve train for a two-stroke engine. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the invention of claim (1) provides the following.

A plurality of cams each having two types of large and small cam noses on the outer periphery for opening a plurality of exhaust valves independently of each other are arranged so that at least one of the cams has a larger cam nose and at least one other cam has a larger cam nose. By mounting the cam so that the phase with the smaller cam nose is almost the same, at least one exhaust valve is opened by the larger cam nose during blowdown exhaust immediately after the completion of the expansion stroke, and The present invention is characterized in that at least one exhaust valve corresponding to the smaller cam nose is closed, and in the subsequent scavenging stroke, at least two exhaust valves are opened by the larger and smaller cam noses, respectively.

The invention of claim (2) provides a plurality of cams each having two types of cam noses, large and small, on the outer circumferential edge for opening a plurality of exhaust valves independently of each other. By installing the cam nose of at least one other cam in such a phase that it slightly precedes the smaller cam nose of at least one other cam, at least one of the exhaust valves is mounted so that the larger cam nose is slightly ahead of the smaller cam nose of at least one other cam during blowdown exhaust immediately after the end of the expansion stroke. The valve is opened by the cam nose, and at least one exhaust valve corresponding to the smaller cam nose is closed, and in the subsequent scavenging stroke, at least two exhaust valves are opened by the larger and smaller cam noses. That's what I mean.

The invention according to claim (3) includes a plurality of cams each having a cam nose on an outer periphery that opens a plurality of exhaust valves independently of each other.
By mounting the cam nose with a slightly different phase with respect to the camshaft, at least one exhaust valve is closed during blowdown exhaust immediately after the completion of the expansion stroke, and the remaining at least l exhaust valves are closed. is opened, and in the subsequent scavenging stroke, at least two exhaust valves are each opened.

Further, the invention of claim (4) provides a plurality of cams each having a plurality of cam noses on an outer peripheral edge that open a plurality of exhaust valves independently of each other, the phase of the cam noses being adjusted by one rotation of the crankshaft with respect to the camshaft. The present invention is characterized in that when at least one exhaust valve is open, the remaining at least one exhaust valve is closed by mounting the exhaust valves with a shift of a cycle corresponding to .

[For production]

According to the invention of claims (1) to (3), at least one exhaust valve opens and at least one other exhaust valve opens during blowdown exhaust in which high-temperature combustion gas is discharged immediately after the completion of the expansion stroke. Since the closed exhaust valve is seated on the valve seat, the cooling performance of the closed exhaust valve is enhanced and the heat load is reduced.

Incidentally, it is preferable to appropriately determine the arrangement of the cam noses of each cam so that the exhaust valves that open during blowdown exhaust are sequentially alternated for each rotation of the crankshaft.

According to the invention of claim (4), one exhaust valve opens,
When the combustion gas is being exhausted, the other upper exhaust valve is closed and is seated on the valve seat, so the cooling time due to one seat is extended, the cooling performance is improved, and the heat load is significantly reduced.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

The second construction drawing shows a two-stroke engine equipped with an embodiment (first construction embodiment) of the invention according to claims (1) and (2),
(1) is a piston that moves up and down in the cylinder block (2), (3) is a poppet-type intake valve that opens and closes the intake boat (5) provided in the cylinder head (4), and (6) is
A valve lifter (tappet) (7) with an open lower end is slidably fitted into the cylinder head (4) and loosely fitted onto the shaft end of the intake valve (3) from above. 4) and a retainer (as shown) fixed to the shaft end of the intake valve (3), the valve spring (8) is an injector for injecting fuel into the combustion chamber. .

Compressed air is supplied to the intake boat (5) via an intake pipe (9) by a scavenging pump (10) such as a Roots blower.

Above the valve lifter (6) is an intake valve camshaft (12) equipped with a cam (11) for driving the intake valve (3).
is the timing gear linked to the crankshaft (13),
It is provided so as to be able to rotate in synchronization with the crankshaft (13) using a timing chain (all shown) or the like.

As a result, the intake valve (3) has a crankshaft (13) of 1
It is activated once every rotation.

Note that two intake valves (3) may be arranged in the front-rear direction so that they can operate in synchronization with each other.

(14a) and (14b), as shown in Fig. 2, are two poppets per cylinder arranged in the front-rear direction and inclined to form a V-shape with respect to the intake valve (3). The first and second exhaust valves of the mold can open and close each exhaust boat (15) provided in the cylinder head (4).

(16) and (17) are valve lifters and valve springs similar to those attached to the intake valve (3).

Above the valve lifter (16), as shown in the second figure,
Each 1st. A camshaft (20) for an exhaust valve is provided with first and second cams (18) (19) that independently drive the second exhaust valves (14a) (14b).1 Timing gear, timing chain, etc. (not shown) The first cam (18) and the second cam (19) each have a first cam nose with a large profile. (L8a) (1'
la) and a second cam nose (18b) with a slightly smaller profile that is 180° out of phase in the circumferential direction.
) (19b), and the I-th cam noses (18a) (19a) and the second cam nose (t
ab) (19b) The phases of (19b) are relatively different from each other by 180°.

In this way, as shown in FIG. 3(A), the first exhaust valve (14a) is operated greatly (with a high lift) by the first gum nose (18a) of the first cam (18). When the second exhaust valve (14b) is activated by the second cam nose (19b) by the second cam (19), the second exhaust valve (14b) is actuated in a small manner (with low lift).

Then, when the crankshaft (13) rotates once and the camshaft (20) rotates half a rotation, as shown in FIG. 18) is smaller by the second cam nose (18b),
And the second !11' air valve (14b) is connected to the second cam (19
) is largely actuated by the first cam nose (19a).

Note that the first cam nose (18a) of the first cam (18)
) and the second cam nose (19b) of the second cam (19)
and the first cam nose (19a) of the second cam (19) and the second cam nose (18) of the first cam (18).
The phase with the first cam nose (18a) (18b) may be the same, but the phase with the first cam nose (18a) (18b) with the larger profile may be the same.
It is preferable that the cam nose 9a) slightly precedes the second cam nose (19b) (18b).

Next, the operation of the above embodiment will be explained.

FIG. 4 shows the opening degree of the intake and exhaust valves relative to the piston displacement, that is, the valve timing, where (a) is the lift curve of the intake valve (3), (b) is the lift tube line of the first exhaust valve,
(C) is a lift curve of the second exhaust valve.

Immediately after the end of the expansion stroke (d), that is, 120a after top dead center
When the first exhaust valve (14a) starts to open by the first cam nose (18a) of the first cam (18) in the front and rear, blowdown exhaust (e) is performed, and part of the high temperature and high pressure combustion gas is is discharged. This blowdown exhaust (e
), the intake valve (3) and the second exhaust valve (14b)
is still closed.

Near bottom dead center, the intake valve (3) and the second exhaust valve (1
4b) are opened at almost the same time, compressed air is sent into the cylinder from the scavenging pump (10) and the scavenging air (f)
starts, and the combustion gas flows through the first and second ports, both of which are open. It is quickly exhausted through the second exhaust valves (14a) (14b).

When the scavenging stroke is completed and the gas exchange in the cylinder is completed,
The second exhaust valve (14b) is opened slightly earlier, then the intake valve (3)
and the first exhaust valve (14a) close almost simultaneously, and the compression stroke (g) begins.

In this compression stroke (g), when fuel is injected from the injector (8) at a predetermined timing, it explodes near top dead center due to spark ignition or compression ignition, and the crankshaft (
13) rotates once and enters the expansion stroke (d) again, starting the next cycle.

In this cycle, contrary to the above, the first exhaust valve (L4a
) is operated at a low lift, and the second exhaust valve (14b) is operated at a high lift, so the blowdown exhaust (e) and scavenging air (f) are mainly carried out by the second exhaust valve (14b), and the second exhaust valve (14b) is operated at a high lift. The valve (14a) has an auxiliary function.

As is clear from the above description, in the above embodiment, during blowdown exhaust where high-temperature, high-pressure combustion gas is discharged, one of the exhaust valves is closed, and during the scavenging stroke where compressed air is supplied, one of the exhaust valves is closed. Since the valve is opened occasionally, the cooling performance of the valve is improved, the heat load is reduced, and the scavenging and exhausting efficiency can be increased.

Further, the first and second exhaust valves <14a) (14b) are
Since the timing at which the valves are greatly opened is every one cycle, the time during which each exhaust valve (14a) (14b) is seated is substantially extended, leading to a reduction in heat load.

In addition, the phase of the first cam nose (18a) and the second cam nose (19b), and the first cam nose (19a)
When the phases of the and second cam nose (18b) are the same, the lift curves (b) and (c) of each exhaust valve are (b')
Although it is slightly changed like (C'), the action and effect are as follows.
Almost the same as above.

Next, an example (second example) of the invention described in claim (4)
will be explained with reference to FIGS. 5 and 6.

As shown in Figure 1, this embodiment includes first and second cams (2I) (22) provided on an exhaust valve camshaft (20).
), only the I-th nose (21a) (22a) with a large profile whose phase is different from each other by 180@,
The second nose with a small profile as in the above-mentioned first embodiment is eliminated.

In this way, as shown in FIG. 6(A), when the first exhaust valve (14a) is operated by the first cam (21), the second exhaust valve (14b) is closed. Become.

Next, when the camshaft (20) rotates half a turn (the crankshaft rotates once), as shown in Figure (B), the No. 1 exhaust valve (
14a) is closed and the second exhaust valve (14b) is opened by the second cam (22).

As a result, the first and second exhaust valves (14a) (14b
) are operated alternately every l cycle, that is, once every two revolutions of the crankshaft, and each exhaust valve (14a) (1
4b) Seating time is significantly increased.

As a result, the cooling performance of each exhaust valve (14a) (14b) is enhanced, and the heat load is halved.

FIG. 7 and FIG. 8 show an embodiment (third embodiment) of the invention described in claim (3).

In the third embodiment, the first cam nose (23a) and the second cam nose (23b) of the first cam (23)
), and the first cam nose (24a) and second cam nose (24b) of the second cam (24) all have the same shape and same size profile, and the first cam nose of the first cam (23) (23a) from the first cam nose (24a) of the second cam (24) and from the second cam (24).
)'s second cam nose (24b) is the first cam (23)
Each cam nose (23a) (23b) slightly precedes the second cam nose (23b) of the
) (24a) By shifting the phase of (z+b), the lift curve (h) (i) shown in FIG. Lift curve (i) is the lift curve of the second exhaust valve opened and closed by the second cam (24)), at the time of blowdown exhaust (e) immediately after the end of the engraving process (d). , the first exhaust valve opens, the second exhaust valve closes, during the subsequent scavenging (f), both the first exhaust valve and the second exhaust valve open, and during the next blowdown exhaust (e), the second exhaust valve closes. The valve opens, the first exhaust valve closes, and during the subsequent scavenging (f), both the first exhaust valve and the second exhaust valve open, and this relationship is repeated thereafter.

Other functions and effects are almost the same as those of the first embodiment.

In the above embodiments, in order to simplify the explanation, the number of exhaust valves is two, and the camshaft rotates once for every two revolutions of the crankshaft. The number of cam noses may be three or more, or the re-camshaft may rotate once when the crankshaft rotates three or more times, and the number of cam noses of each cam may be increased accordingly.

In other words, the number of exhaust valves is N, and the camshaft is 1/Nx (x is an integer greater than or equal to 1) relative to the mechanical rotation of the crankshaft.
If the cam is rotated, the number of cam noses on each cam is N.
x cams, and by mounting the cams on the camshaft with the mutual phase of each cam shifted by 360"/Nx, the above I.
The same operations and effects as those of the third embodiment can be obtained from the embodiment.

For example, as in the fourth embodiment shown in FIG.
= 2), the first cam (
25) and the second cam (26), two types of large and small cam noses (25a) (25b) (26a) (
26b), 2 pieces each, 4 pieces in total, 360"/2
2 = 90 @ intervals, and the first cam (25) and second cam (26) are rotated 1/2 x 2 = 1/4 rotation for one rotation of the crankshaft. The camshaft (27) has a mutual phase of 360°/2.
By shifting the position by X2=90' and installing the
Almost the same actions and effects as those of the embodiment can be brought about.

The fifth embodiment shown in FIG. 10 is a case where the number (N) of exhaust valves is two (N=2) and the multiple (x) is three (x=3). In this case, the first cam (28) and the second cam (29) each have two types of cam noses (large and small).
28a) (28b) (29a) (29b), 3 each, a total of 6, are provided at intervals of 360°/2 x 3 = 60@, and the first cam (28) and the second cam (28)
cam (29) and 1/2 for one revolution of the crankshaft.
X 3 = 1/6 camshaft (3
0), the mutual phase is 360°/2 x 3 = 60°
It is installed by shifting it only.

Even in this case, the same functions and effects as those of the first embodiment can be achieved.

The sixth embodiment shown in FIG. 11 is a case where the number (N) of exhaust valves is three (N=3) and the multiple (x) is one (x=1).

In this case, the first to third cams (31) (32)
(33), one large cam nose (31
a) (32a) (33a) and two small cam noses (31b) (32b) (33b), respectively.
The cams (31), (32, and 33) were set at intervals of 60°/3 x 1 = L20°, and each cam (31) (32) (33) rotated 1/3 x 1 = 1/3 of the working rotation number of the crankshaft. The camshaft (34) has a mutual phase of 360°/3.
They are installed with a difference of X 1 = 120''.

In this sixth embodiment, during blowdown exhaust, 1
One exhaust valve opens, two exhaust valves I close, and one exhaust valve opens only once during three blowdown exhausts, so the cooling performance is improved compared to that of the first embodiment. There are advantages that can be further improved.

It should be noted that the second embodiment and the third embodiment can also be modified as in the fourth to sixth embodiments with respect to the second embodiment.

Furthermore, the present invention is not limited to a two-stroke engine equipped with a direct-acting valve mechanism as described above,
The present invention can also be applied to engines equipped with a rocker arm type or bush rod type valve mechanism.

Further, the intake valve may be a piston valve that performs a valve action depending on the positional relationship between an intake hole provided in a cylinder side wall and a piston skirt, or a reed valve (check valve) using a spring plate.

〔Effect of the invention〕

According to the present invention, since the thermal load on the exhaust valve is reduced, there is no risk of accidents such as burnout or breakage of the valve, and a highly durable and reliable valve operating system can be provided. Since abnormal combustion such as early ignition and knocking is prevented, engine performance can be improved.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional front view of the main parts of a two-stroke engine equipped with the first embodiment, Fig. 2 is a perspective view showing the linked state of the exhaust valve and cam, and Fig. ) is an explanatory diagram similarly showing the operating state of the exhaust valve, FIG. 4 is an explanatory diagram similarly showing the relationship between piston displacement and valve timing of the intake valve and exhaust valve, and FIG.
FIGS. 6(A) and 6(B) are perspective views showing the state of cooperation between the exhaust valve and the cam in the embodiment; FIGS. 6(A) and 6(B) are explanatory views showing the operating state of the exhaust valve; FIG. 7 is a longitudinal sectional front view showing essential parts of the third embodiment, and FIG. 8 is an explanatory diagram showing a lift curve of the exhaust valve of the third embodiment. FIGS. 9(A) and 9(B) are longitudinal sectional front views respectively showing a first cam and a second cam of the fourth embodiment. FIGS. 10(A) and 10(B) are longitudinal sectional front views respectively showing a first cam and a second cam of the fifth embodiment. Figures U (A), (B), and (C) are longitudinal sectional front views showing the first cam, second cam, and third cam of the sixth embodiment, respectively. (1) Piston (2) Cylinder block (3) Intake valve (4) Cylinder head (5) Intake boat (6) (16) Valve lifter (7) (17) Valve spring (8) Injector (9) Intake pipe (10 )Scavenging pump (11) Cam (12) Camshaft for intake valve (13) Crankshaft
(14a) First exhaust valve (14b) Second exhaust valve (18) First cam (18a) (19a) First cam nose (20) Exhaust valve camshaft (22) Second cam (23) (25) (28) (31) First cam (
23a) (24a) First cam nose (27) (3
0) (34) To the camshaft (15> Exhaust port (19) Second cam (18b) (19b) Second cam nose (21) First
cam (21a) (22a) first cam nose (24) (
26) (29) (32) Second cam (23b) (
24b) Second cam nose (33) Third cam

Claims (4)

[Claims] (1) Large and small 2 that open multiple exhaust valves independently of each other
A plurality of cams each having different types of cam noses on the outer periphery are arranged such that the phase of the larger cam nose of at least one cam and the smaller cam nose of at least one other cam is approximately the same with respect to the camshaft. By mounting in this manner, at least one exhaust valve is opened by the larger cam nose and at least one exhaust valve corresponding to the smaller cam nose is opened during blowdown exhaust immediately after the expansion stroke ends. 1. A valve operating system for a two-stroke engine, characterized in that at least two exhaust valves are closed and then opened by large and small cam noses in a subsequent scavenging stroke. (2) Large and small 2 to open multiple exhaust valves independently of each other
A plurality of cams having different types of cam noses on their outer periphery are arranged in a phase relative to the camshaft such that the larger cam nose of at least one cam slightly precedes the smaller cam nose of at least one other cam. By mounting the exhaust valve as a blowdown exhaust valve immediately after the completion of the expansion stroke, at least one exhaust valve is opened by the larger cam nose, and at least one exhaust valve corresponding to the smaller cam nose is closed. A valve operating system for a two-stroke engine, characterized in that in a subsequent scavenging stroke, at least two exhaust valves are respectively opened by large and small cam noses. (3) The expansion stroke is completed by installing multiple cams with cam noses on the outer periphery that open multiple exhaust valves independently of each other, with the cam noses slightly different in phase from the camshaft. At least one exhaust valve is closed and at least one remaining exhaust valve is opened during blowdown exhaust immediately after, and at least two exhaust valves are each opened during the subsequent scavenging stroke. A valve train for a two-stroke engine characterized by: (4) A plurality of cams are provided with cam noses on the outer periphery that open the plurality of exhaust valves independently of each other, and the phase of the cam noses is shifted by a cycle corresponding to one revolution of the crankshaft with respect to the camshaft. 1. A valve train for a two-stroke engine, characterized in that when at least one exhaust valve is opened, the remaining at least one exhaust valve is closed by being installed therein.