JPH0742862B2 - Exhaust system for 4-cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is an exhaust system applied to a four-cycle engine having a plurality of exhaust valves per cylinder and a plurality of branch pipes connected to the respective exhaust valves. It is about.

(Background of the Invention) In a 4-cycle engine, it is widely practiced to increase the opening period of intake / exhaust valves in order to achieve high output at high speed rotation. However, in this case, there is a problem that the output drop in the middle / low speed range becomes large and a so-called torque valley occurs.

(Object of the Invention) The present invention has been made in view of such circumstances, and makes it possible to increase the output in the medium and low speed ranges while suppressing the occurrence of torque valleys and the decrease in the torque in the medium and low speed ranges. An object is to provide an exhaust device for a cycle engine.

(Structure of the Invention) According to the present invention, a plurality of exhaust valves for one cylinder, a plurality of branch pipes respectively connected to the exhaust valves, and a plurality of branch pipes provided in some of the branch pipes are provided. An open / close valve and control means for opening / closing each open / close valve are provided, and all open / close valves are opened in the high speed region of the engine, and the exhaust valve side volume of the branch pipe increases in response to deceleration of the engine in the medium speed region. The exhaust system for a four-cycle engine is characterized in that the on-off valve is controlled so as to control the on-off valve, and the on-off valve on the most upstream side is closed at least in the low speed range.

(Operation) In the high speed region, all the branch pipes are opened and the exhaust gas passes through the branch pipes at a sufficiently high speed. In the low speed region, some of the branch pipes are closed, so that the exhaust gas flows through the remaining branch pipes at a sufficiently high speed. Therefore, the exhaust gas inertia is utilized to promote the exhaust gas, improve the suction efficiency, and increase the output in the high speed region and the low speed region.

Further, in the medium speed range, the exhaust valve side volume of some of the branch pipes increases as the engine decelerates. The exhaust valve side volume acts as a resonance chamber for the combustion chamber, and the resonance chamber increases in response to engine deceleration, that is, a reduction in the opening / closing frequency of the exhaust valve. The pressure wave that accompanies the opening and closing of the exhaust valve is transmitted through the exhaust at the speed of sound, and is repeatedly reflected in the resonance chamber. Since the volume of the resonance chamber increases with the deceleration of the engine, the resonance frequency also decreases with the deceleration. Therefore, in the medium speed range, the resonance chamber having a volume suitable for the engine speed can bring the vicinity of the exhaust valve to the optimum pressure immediately before the exhaust valve is closed, and the suction efficiency can be improved. Therefore, it is possible to prevent the occurrence of a torque valley in the medium speed range and increase the torque and the output.

(Embodiment) FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is an operation explanatory view thereof, FIG. 3 is a side view of an engine, and FIG. 4 shows torque characteristics and a control mode of an on-off valve. It is a figure.

In FIG. 3, reference numeral 10 is a crankcase, 12 is a cylinder, 14 is a cylinder head, 16 is a piston, 18 is a connecting rod, and 20 is a crankshaft. 2 on the cylinder head 14
Two intake valves 22 (22a, 2b) and two exhaust valves 24 (24a, 24)
b) and are provided, and these are opened and closed by the cam shaft 30 via the rocker arms 26 and 28. The cam shaft 30 is rotationally driven by the crank shaft 20 at half the speed of the crank shaft 20.

Each intake valve 22a. Intake pipes 32 (32a, 32b) are independently connected to 22b as shown in FIGS.
Vaporizers 34 (3a, 34b) are attached to 2a, 32b, respectively.

A branch pipe 36 (36a, 36b) is independently connected to each of the exhaust valves 24a, 24b. The downstream sides of the respective branch pipes 36a and 36b join and are connected to the exhaust pipe 38. 40 is a muffler connected to the exhaust pipe 38.

Two branch valves 42 (42a, 42b) are attached to one branch pipe 36a. One on-off valve 42b is arranged in proximity to the collecting portion at the rear end of the branch pipe 36a. These on-off valves 42
Motors 44 and 46 open and close a and 42b.

Reference numeral 48 denotes a control means, which reads the rotational speed N of the crankshaft 20 into the CPU 52 via the input interface 50, the CPU 52 performs a predetermined calculation according to a program stored in advance in the memory 54, and outputs the result to the output interface 56, D / A converter 58, 60 and driver 62, 64, each motor 44,
Control 46.

As shown in FIG. 4, the control means 48 controls the on-off valves 42a and 42b.
Open and close.

That is, in the low speed range of 5500 rpm or less, both valves 42a and 42b are closed as shown in FIG. 1, and the low speed side (5500 to 7500rp) in the middle speed range is closed.
m), as shown in FIG. 2A, only the valve 42a is opened to increase the volume A of the exhaust valve 24a of the branch pipe 36a, and at the high speed side (7500 to 9000 rpm) in the medium speed range, the same figure (B) is used. Valve 4 as shown
Only 2b is opened to reduce the volume B of the branch pipe 36a on the exhaust valve 24a side. Then, in the high speed range of 9000 rpm or more, both valves 42a and 42b are opened as shown in FIG.

Therefore, in the low speed range, as shown in FIG.
Exhaust gas flows only to the outside, increasing the flow velocity of the exhaust gas to increase the exhaust gas inertia and increase the torque in the low speed range. On the low speed side in the medium speed range, the volume A is large as shown in FIG. 2 (A), and the portion of this volume A acts as a resonance chamber for the combustion chamber to improve the suction efficiency and increase the torque. On the high speed side in the medium speed range, the volume B becomes small as shown in FIG. Therefore, the volume of the resonance chamber is changed to an appropriate volume in accordance with the change of the engine speed, and the torque is similarly increased. Further, in the high speed range, the branch pipe 36a is opened, so that the exhaust gas is discharged through the two branch pipes 36a and 36b. At this time, the exhaust inertia can be effectively used to increase the torque and the output.

In FIG. 4, T ₁ is T ₂ when both valves 42a and 42b are opened.
The when opening only valve 42a, T ₃ is when opening only valve 42b, T ₄ denotes 42a, when 42b was both closed, the respective torque characteristics. Therefore, according to the present embodiment, the maximum torque is always obtained in each of the low, medium and high speed regions, the torque valley in the medium speed region is shallow and small, and the engine torque and output are increased over the entire speed range. Can be made.

In this embodiment, as shown in FIG. 2 (B), since the valve 42b is opened on the high speed side in the medium speed range, the volume C of the branch pipe 36a on the downstream side of the valve 42a is set to the other branch pipe 36b and the exhaust pipe. It can be used as a resonance chamber for 38. Therefore, it becomes possible to further increase the output in this speed range.

FIG. 5 is a block diagram of another embodiment of the present invention. In this embodiment, one branch pipe 36a is provided with four on-off valves 42A to 42D. These on-off valves 42A to 42D control the valves 42A to 42C so as to close at least 42A in the low speed region and decrease the volume D on the exhaust valve 22a side as the engine speed increases in the medium speed region. At this time, the valve on the downstream side can be appropriately opened and used as the resonance chamber of the expansion chamber 40A. Further, in the high speed range, all valves 42A to 42D are controlled to open.

According to this embodiment, since there are four on-off valves 42A to 42D, it is possible to perform more delicate control in the medium speed range as compared with the one shown in FIGS.

Among the on-off valves in the present invention, the exhaust valve on the most upstream side can be used as a part of the exhaust valves. That is, opening and closing of a part of the exhaust valves can be stopped, and the exhaust valves are stopped in the low speed range and the high speed side of the medium speed range, whereby the same effect as each of the above-described embodiments can be obtained.

The present invention can also be applied to an engine having three exhaust valves and a branch pipe, and in this case, one or two branch pipes can be provided with a plurality of on-off valves. The present invention is also applicable to and includes engines having more than two exhaust valves and branch pipes.

(Effects of the Invention) As described above, according to the present invention, a plurality of exhaust valves for one cylinder are respectively connected with branch pipes, and some branch pipes are provided with a plurality of open / close valves to open all open / close valves in a high speed range. The opening / closing valve is controlled so that the opening / closing valve on the most upstream side is closed in the low speed range, and the volume on the exhaust valve side is increased with deceleration in the medium speed range. Therefore, in the high / low speed range, it is possible to increase torque and output by utilizing sufficient exhaust inertia. Further, in the medium speed range, the exhaust valve side volume of a part of the branch pipe that substantially acts as a resonance chamber for the combustion chamber is changed according to the speed, so that the suction efficiency in the middle speed range can be improved and The torque valley can be reduced to increase the torque and output.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is an operation explanatory diagram thereof, FIG. 3 is a side view of an engine, and FIG. 4 is a diagram showing a torque characteristic and an on-off valve control mode. FIG. 5 is a block diagram of another embodiment of the present invention. 24 ... Exhaust valve, 36 ... Branch pipe, 42, 42A to 42D ... Open / close valve, 48 ... Control means.

Claims (3)

[Claims] 1. A plurality of exhaust valves for one cylinder, a plurality of branch pipes respectively connected to the respective exhaust valves, a plurality of open / close valves provided in some of the branch pipes, and open / close of each open / close valve. A control means for controlling, opening and closing all the open / close valves in the high speed range of the engine, and controlling the open / close valves so that the exhaust valve side volume of the branch pipe increases in response to deceleration of the engine in the medium speed range, Furthermore, in the low speed range, the exhaust system for a 4-cycle engine is characterized in that it closes at least the open / close valve on the most upstream side. 2. An exhaust system for a four-cycle engine according to claim 1, wherein each cylinder has two exhaust valves and two branch pipes. 3. Two on-off valves are provided on one branch pipe, the upstream on-off valve is closed on the high speed side in the medium speed range and the downstream on-off valve is opened, while the upstream on-off valve is opened on the low speed side in the medium speed range. And opening the downstream side on-off valve.
The exhaust system for a four-cycle engine according to the item.