JPH021965B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust silencing device for a two-stroke internal combustion engine.

Conventionally, in two-stroke internal combustion engines, pressure pulsations in the exhaust pipe have been utilized to improve engine performance. This is generally done by constructing the exhaust pipe with a narrower pipe that can be thought of as a diffuser and a plurality of throttles or a continuous series of throttles. That is, the differential user part acts over its entire length as an open end for the positive pressure waves coming out of the exhaust port, and by reflecting the negative pressure waves that continue to the exhaust port, it promotes the scavenging action and supplies air. It acts to increase the ki ratio. In addition, the constricted part or tapered part reflects positive pressure waves and increases the pressure at the exhaust outlet after the scavenging port is closed until the exhaust port closes, thereby preventing fresh air from flowing out and improving air supply efficiency. do. The above-mentioned positive and negative pressure waves propagate in the exhaust pipe at a sound speed determined by the temperature of the exhaust gas at that time, regardless of the engine speed. Therefore, the reason why the positive and negative pressure waves propagating in the exhaust pipe, which is composed of a differential user and a constrictor or tapered pipe, reaches the exhaust port and acts as described above is due to the dimensions initially given to the exhaust pipe. The reflected pressure wave that propagates at the sound speed determined by the shape, the distance from the exhaust port to the differential user and the rear end throttle, and the shape of these, and the temperature of the exhaust gas at that time, increases the engine speed. However, the above-mentioned effect cannot be obtained over the entire operating range of the engine. As a way to achieve this goal, it has been proposed to change the length of the exhaust pipe to match the engine speed.
It has not yet been put into practical use due to problems such as gas sealing properties and malfunction due to carbon deposits. Therefore, in the past, the shape and length of the exhaust pipe (the distance from the exhaust port to the differential user, the distance between the throttles, and their shape) was determined according to the required engine rotation range even though it had the above-mentioned effect. In other words, the passage length and shape (which affects the duration of reflected waves) were given so that pressure waves propagating at the speed of sound would be reflected in synchronization with the opening and closing timing of the exhaust port, which is determined by the engine speed. It is.

This invention was created in view of the above circumstances, and focused on the fact that the propagation speed of pressure waves in the exhaust pipe changes depending on the temperature of the exhaust gas, and by constantly detecting the engine rotation speed, it is possible to know when to open and close the exhaust port. By controlling the speed of the pressure waves, that is, the temperature of the exhaust gas, so that the reflected pressure waves reach the exhaust port in sync with this, the length of the path for reflecting the pressure waves can be changed in accordance with the engine speed. This makes it possible to obtain the same effect as described above, and to improve the air supply ratio and air supply efficiency over the entire operating range of the engine, as mentioned at the beginning.

A first embodiment of the present invention will be described below based on FIG.

In the figure, 1 is a two-stroke internal combustion engine to which the present invention is applied, 2 is an exhaust silencing device, 3 is an exhaust port, and 4 is an exhaust passage provided in the cylinder block.
Reference numeral 2a denotes a differential user portion of the exhaust silencer 2, and the diameter thereof increases as it moves away from the exhaust outlet passage 4. 2b is an expansion part of the exhaust silencer 2 and has the same diameter. Similarly, 2c is a rear constriction portion of the exhaust noise muffling device 2 and is formed in a tapered shape. Similarly, 2d is a tail pipe. 5 is exhaust silencer 2
6 is a cooling water conduit wrapped around the outer periphery near the connection part from the expansion part 2b to the engine 1, and 6 is a jacket covering the outside of the cooling water conduit 5. 5a and 5b are the inlet and outlet of the cooling water of the cooling water conduit 5, respectively. 7 is a valve provided at the cooling water outlet 5a, 8 is a cooling water spray nozzle provided in the exhaust pipe immediately after the connection part of the exhaust silencer 2 to the engine 1, and 8a is a cooling water spray nozzle provided to the nozzle 8. It is an injection port. 9
1 is a cooling water storage tank, and 10 is a cooling water supply pump. 11 is an exhaust temperature sensor, 12 is an engine speed detection sensor, 13 and 14 are amplifiers, and 15 is a control device 16 is a mechanical/electrical valve drive device, and in this embodiment, cooling is performed by an electric signal output from the control device. Mechanically opens and closes the water control valve. 1
7 is a piston, and 18 is a suction reed valve device.
The dimensions and shape of the exhaust silencer 2 are set so as to improve performance in the high engine speed range.

Next, the operation of the first embodiment configured as above will be explained.

High-temperature burnt exhaust gas discharged from the exhaust port 3 of the engine 1 flows into the exhaust silencer 2 from the exhaust passage 4, passes through the differential user part 2a, the expansion part 2b, and the tapered part 2c as a throttle to the tail. It is discharged from pipe 2d. During this time, the positive pressure wave generated at the exhaust port 3 propagates inside the exhaust silencer 2 at a sound speed determined by the temperature of the exhaust gas, and is continuously reflected as a negative pressure wave from the wall surface of the differential user section 2a. This negative pressure wave reaches the exhaust port at the speed of sound, and furthermore, the positive pressure wave is reflected by the rear aperture taper portion 2c and returns to the exhaust port at the speed of sound as a positive pressure wave. In order to control these positive and negative reflected pressure waves so that they reach the exhaust port in synchronization with the opening and closing timing of the exhaust port, the control device 15 is programmed in advance with the engine speed and the corresponding optimum pressure wave propagation velocity, that is, the exhaust Memorize the gas temperature data. The actual engine speed and exhaust gas temperature during engine operation are detected by an engine speed sensor 12 and an exhaust gas temperature sensor 11, respectively, and are sequentially input to a control device 15 via amplifiers 13 and 14. Control device 1
5 The engine speed and optimal exhaust gas temperature stored in advance are compared with the actual data input from the sensor, and if the actual exhaust gas temperature is higher than the optimal exhaust gas temperature, the valve is activated by the control device 15. A command is output to the device 16 to open the valve 7 and increase the amount of water injected from the spray nozzle 8, and the exhaust gas temperature is lowered to a required temperature commensurate with the engine speed at that time. Of course, when the exhaust gas temperature is low, a reverse operation command is output from the control device. Cooling water is stored in a tank 9, and is fed into the cooling water conduit 5 from the inlet 5a by the feed pump 10, cooling the outer periphery of the exhaust pipe, and reaching the valve 7 from the outlet 5b, where the flow rate is controlled. Cooling water enters the spray nozzle 8 from the inlet 8a and is injected into the exhaust gas to control the exhaust gas temperature. As described above, negative reflected pressure waves for exhaust extraction and positive reflected pressure waves to prevent fresh air from flowing out reach the exhaust port in synchronization with the timing of opening and closing of the exhaust port, which changes according to the engine speed. This makes it possible to improve performance in the entire operating range of the engine.

FIG. 2 is a diagram showing a second embodiment of the invention. In the drawings, parts having the same or similar functions as those in the first embodiment are designated by the same reference numerals, and explanations thereof will be omitted. In the second embodiment, an engine 1 to which the present invention is applied is a water-cooled engine and includes a cooling water passage 19, a radiator 20, and a cooling water circulation pump 21. Thus, the outer circumference of the differential user part 2b of the exhaust silencer 2 is
A watertight space 22 is provided in the engine, and cooling water for the engine is passed through this space 22 to control the exhaust gas temperature. The cooling water is branched from the return port from the radiator 20 to the cooling water passage 19 of the engine 1,
It flows into the space 22 from an inlet 22a provided at one end of the front space 22 whose flow rate is controlled by the valve 7,
After the exhaust gas is cooled to the required temperature, the cooling water inlet 20 of the radiator 20 is passed from the outlet 22b at the other end.
It returns to the radiator 20 via a branch pipe 20c from a. The mechanism for controlling the valve 7 by detecting the exhaust gas temperature and engine speed is exactly the same as in the first embodiment. The second embodiment does not require a separate cooling water tank or the like compared to the first embodiment.

FIG. 3 is a diagram showing a third embodiment of the invention. In the drawings, parts having the same or similar functions as those in the first and second embodiments are given the same reference numerals, and explanations thereof will be omitted. In this third embodiment, the outer periphery of the exhaust pipe section is double-layered, and air is introduced into the space so that the exhaust gas temperature is controlled by controlling the amount of introduced air. In the figure, 22 is an airtight space provided by doubling the outer periphery of the exhaust pipe section as in the second embodiment, and 23
are a plurality of holes for introducing air into this space 22, and are provided directly behind the attachment portion of the exhaust silencer 2 to the cylinder block. Further, in this space 22, an air outflow pipe 24 is provided near the end of the outer periphery of the throttle 2c of the exhaust silencer 2. It is connected to an ejector 25 connected to the tail pipe 2d through a valve 7 that controls the amount of water. In the third embodiment configured in this way, the valve 7 is controlled to open or close depending on the exhaust gas temperature, and air is sucked through the air outflow pipe 25 by the ejector 25 operated by the exhaust flow depending on the throttle amount. The exhaust gas is cooled to a required temperature by flowing in from the upstream air inflow hole 23. This third embodiment does not require a water-cooled engine as in the second embodiment, and has the advantage that the invention can be carried out with a minimum of equipment since cooling air is sucked in by an ejector operated by the exhaust flow. There is.

Fig. 4 is a pressure diagram of the exhaust port section depending on the crank angle when the present invention is applied, EX.O and SC.O indicate the crank positions with the exhaust port open and the scavenging port open, respectively, and SC.C. , EX.C indicate the crank position of the scavenging port closed and scavenging port closed, respectively. In the figure, the negative pressure in the period between SC.O and BDC when the scavenging port is open is a negative pressure wave reflected from the differential user part, which promotes the suction of burned gas and increases the air supply ratio, and when the scavenging port is closed. The positive pressure between SC.C and EX.C with the exhaust port closed pushes back the fresh air flowing out of the still open exhaust port after the scavenging port is closed, increasing air supply efficiency.

As explained in detail above, the present invention, in a two-stroke internal combustion engine, arbitrarily changes the pulsation of pressure waves that propagate in the exhaust pipe at the speed of sound determined by the temperature of the exhaust gas by controlling the temperature of the exhaust gas. Since the engine is designed to constantly suck out burnt gas and suppress the outflow of fresh air throughout the entire rotational range of the engine, the air supply ratio increases and air supply efficiency is improved.
It is possible to improve the performance of the engine and reduce fuel consumption.

[Brief explanation of drawings]

Figures 1, 2, and 3 are diagrams showing the first, second, and third embodiments of the present invention, respectively, and Figure 4 shows the pressure at the exhaust port when the present invention is implemented. Figures 5 and 6 are diagrams qualitatively representing an example of the relationship between engine speed, average exhaust gas temperature, and average sound velocity in the exhaust pipe. DESCRIPTION OF SYMBOLS 1... 2-cycle internal combustion engine, 2... Exhaust silencer, 3... Exhaust port, 5... Cooling water conduit, 7... Valve, 8... Cooling water spray nozzle, 11... Exhaust temperature sensor, 12... ...Engine speed sensor, 1
3, 14...Amplifier, 15...Control device, 16...
...Valve drive device, 19...Cooling water passage, 20...
...radiator, 22 ... annular space, 23 ... air inlet, 24 ... air suction pipe, 25 ... ejector.

Claims (1)

[Claims] 1. In a two-stroke internal combustion engine, the exhaust silencer has a cooling device that cools at least the exhaust pipe section, a sensor that detects the exhaust gas temperature, and a sensor that detects the engine speed, and is activated by input from both sensors. An exhaust silencing device for a two-stroke internal combustion engine, comprising a control device that operates or stops the cooling device based on an output from the control device.