JP2024061550A - A variable compression length four-stroke reciprocating engine with a pipe shutter valve whose rotation phase can be changed. - Google Patents

Abstract

[Problem] By adding a simple mechanism to a four-stroke reciprocating engine, variable compression length operation is possible at any stroke, thereby changing the amount of air compressed at the top dead center of the compression stroke. [Solution] A rotating pipe shutter valve that rotates at half the speed of the crankshaft and closes the opening angle of the air vent during the intake stroke is provided upstream of the intake poppet valve, and the opening angle at the top dead center is set to a required value by a mechanism that changes the rotational phase of the pipe that blocks the intake. When the crankshaft rotates to an angle twice the set opening angle, the shutter valve that rotates synchronously closes, blocking the flow of air into the cylinder. In this way, a four-stroke reciprocating engine can be made to perform variable compression length operation simply by changing the phase of the synchronously rotating pipe. [Selected Figure] Figure 2

Description

Detailed Description of the Invention

To realize variable compression length operation in a four-stroke reciprocating engine.
This controls the load instead of the throttle valve.

It is known that variable compression length operation can be achieved by closing the intake poppet valve while the piston is in the intake stroke, thereby blocking the intake air.
However, because the cam that opens and closes the poppet valve is made of metal, it was nearly impossible to freely change the timing at which the poppet valve opened and closed.

Other similar technologies

Some engines use a lost motion mechanism with a rocking cam to close the intake poppet valve midway through the intake process to control the load, but this is not widely used.

Patent Publication 2014-005756
Above is a diagram of a lost motion mechanism that uses an oscillating cam.

Problem to be solved by the invention

The present invention realizes variable compression length operation in a four-stroke reciprocating engine by cutting off the inflow of air midway through the intake process using as simple a mechanism as possible.

Means for solving the problem

In order to cut off the intake of air into the cylinder while the piston is performing its intake movement, a separate valve is provided upstream of the intake poppet valve, and the intake is cut off by opening and closing this valve.
By blocking the valves arranged in series, the supply of air to the cylinder is cut off even when the intake poppet valve is open.
By making it possible to change the timing of blocking, variable compression length operation is achieved.

Detailed Description of the Invention

The sum of twice the opening angle of the pipe's air window and the opening angle of the pipe holder does not exceed 360 degrees, in other words, each air window has an opening angle of close to 120 degrees, and it is a shutter valve made of a pipe that rotates synchronously with the crankshaft at half the rotational speed of the crankshaft.Air sucked in from the axial direction of the pipe passes through a composite air window created by the overlapping air windows of the pipe and pipe holder, and is sucked into the cylinder through the intake poppet valve.
The synchronously rotating shutter valve and the intake poppet valve are arranged in series, so if either one of the valves is closed, the intake is cut off.

Ventilation is possible only when the windows of the pipe and the pipe holder, which rotate synchronously, overlap. When they do not, ventilation is cut off.
The heat and pressure generated by combustion are borne by the intake poppet valve, so the synchronous rotating valve is not exposed to high temperatures and pressures.

In the following description, it is assumed that the opening angle of the window from the center of the pipe and the opening angle of the pipe holder are 120 degrees, and the geometric compression ratio of the piston is 10.
The pipe rotates at half the speed of the crankshaft through a mechanism that can change the phase of the rotating shaft, with the torque transmitted from the crankshaft by a chain or the like.
In other words, unless the phase is changed, when the crankshaft rotates twice and the piston reaches the top dead center of the intake, the ventilation hole in the synchronous rotating pipe will always be in the same position.
By changing the phase, it is possible to change the rotational position of the pipe ventilation hole when the crank reaches the top dead center.

This makes it possible to arbitrarily set the opening angle of the composite ventilation window formed by the ventilation window of the pipe and the ventilation window of the pipe holder at the top dead center.
During the intake stroke, the opening angle of the composite ventilation window closes at half the angular velocity of the crankshaft as the crankshaft rotates from the top dead center.
If the composite opening angle of the window created by the synchronous rotating pipe and pipe holder at top dead center is 45 degrees, then the crankshaft is 90 degrees, if it is 90 degrees it is 180 degrees, and if it is 120 degrees it is 240 degrees, and the intake is cut off at the point when the crankshaft rotates from top dead center and passes that angle.In other words, by simply changing the rotational phase of the synchronous rotating pipe and changing the composite opening angle when the piston is at top dead center of the intake, the intake can be cut off at any position, even if the intake poppet valve is open while the piston is in the middle of the intake, and the compression length can be controlled continuously.

The main purpose of the variable compression length structure of the present invention is to control the load of a gasoline engine in place of a throttle valve.
By simply removing the throttle valve and replacing it with a rotary shutter valve and redesigning the cooling of the cylinder head, there was no need to make any major changes to the engine itself, and there are no high-temperature, high-pressure parts or particularly precise parts.
Of course, a mechanism to control the rotation and rotation phase of the pipes is necessary, but no major changes are required to the spark plugs, exhaust valves, or fuel injection.

How it works

For example, when operating a spark ignition engine at half load using a throttle valve, the throttle opening is narrowed to reduce the amount of air (air-fuel mixture) flowing in so that the pressure inside the cylinder when the piston reaches bottom dead center on the intake stroke is 1/2 atmospheric pressure.
The air in the cylinder at 1/2 atmosphere at bottom dead center is compressed to 5 atmospheres at top dead center and ignited, thereby operating at 1/2 load.
However, when load control is performed using the throttle valve, the lower the engine speed, the more the throttle is closed, which has the disadvantage of increasing the area of negative pressure, which indicates loss, on the PV diagram, resulting in increased intake loss and a deterioration in the thermal efficiency of the engine.

Effect of the Invention

Reducing intake loss

When a variable compression length engine is operated at half load, the intake is blocked by closing the air vent in the synchronously rotating pipe when the piston has progressed halfway through its intake stroke (4/9 of the stroke).
At that point, the pressure inside the cylinder is approximately 1 atmosphere, and when the piston reaches bottom dead center, the volume inside the cylinder doubles and the pressure inside the cylinder becomes approximately 1/2 atmosphere.
During the compression stroke thereafter, until the piston returns to the point where the intake air was blocked by the synchronous rotating pipe, almost no loss other than that due to friction occurs, except for a small loss due to the pressure remaining in the space between the outer periphery of the pipe and the intake poppet valve.
Then, at top dead center, the air in the cylinder is compressed to approximately 5 atmospheres and ignited.
In other words, the earlier the intake is cut off and the lower the load is operated, the fewer the strokes that cause intake losses and the higher the thermal efficiency becomes, which is the opposite of load control using the throttle.
This results in better thermal efficiency compared to using the throttle.

Maximizing intake air volume

In engines that use a throttle, the intake poppet valve is designed to close when the piston has passed bottom dead center.
This is because when operating at high speed and full load, even if the throttle is fully open and the piston reaches bottom dead center, the pressure inside the cylinder is lower than 1 atmosphere due to resistance in the intake passage, and by keeping the intake valve open until the pressure inside the cylinder reaches 1 atmosphere even after the piston has passed bottom dead center and entered the compression stroke, air is allowed to flow into the cylinder, and by sucking in more air into the cylinder, the maximum output of the engine is improved.
However, on the other hand, at low revolution ranges, the piston pushes out the air that it has just sucked in during the compression stroke, reducing the amount of air compressed and resulting in a reduction in torque.
To prevent this, one method is to use a variable intake valve timing mechanism to change the phase of the intake poppet valve drive cam shaft, but this has the disadvantages of increasing cost and weight and changing the valve overlap.
When performing the engine load control of this invention, by changing the phase of the rotating shaft of the shutter pipe according to the engine speed, it is possible to optimize the closing position of the variable shutter valve, thereby always maximizing the intake volume at that speed.

No knocking occurs

Knocking is a big no-no in reciprocating engines. Especially in supercharged engines, the temperature of the mixture rises too high due to compression heating and high temperature in the cylinders during high-boost operation, making knocking more likely to occur.
To prevent this, the pistons are sometimes designed to have a lower compression ratio in advance, which means that supercharged engines tend to have a smaller expansion ratio and lower thermal efficiency than naturally aspirated engines.
In a variable compression length engine, if signs of knocking are detected by an intercooler outlet temperature sensor or a knock sensor, the compression length is shortened to reduce compression heating by the piston, thereby preventing knocking.
Shortening the compression length reduces power output, but it does not increase intake loss, so this is not a major problem compared to the occurrence of knocking.

Furthermore, by varying the compression length, it may be possible to freely control the ignition timing in HCCI engines, something that was previously impossible.

In addition, in diesel engines, if the compression superheat temperature becomes too high during high turbocharging, the combustion temperature will rise too much and increase the generation of NOx. However, by reducing the compression length of the piston, the combustion temperature can be lowered and the generation of NOx can be reduced.
Even in this case, the expansion ratio that deteriorates the thermal efficiency remains unchanged, so the thermal efficiency does not decrease.
Conversely, increasing the compression length of the piston also improves starting performance in low temperature environments.

Figure 1 is a cross-sectional view of the basic concept of an in-line three-cylinder engine. The rotary pipe valve and the cylinders are drawn separately for easy understanding. A differential gear that cancels the difference in the inner wheel of the car is used as a mechanism for changing the phase of the rotary shaft. The actuator is connected to the part that corresponds to the axis of the propeller shaft. When one shaft is rotated at half the speed of the crankshaft while the rotation of the actuator is fixed, the other shaft rotates in the opposite direction at the same rotation speed. The phase of the output rotary shaft can be changed by rotating the actuator on the propeller shaft. The shape of the pipe window is a cylindrical square or a square with rounded corners, and each window of the synchronous rotary pipe is arranged in the order of combustion of each cylinder, lagging the angle by half the angle with the crankshaft of the piston that will burn next.

Figure 2 is a cross-sectional view of the synchronous rotating pipe valve and cylinder. The opening angle and composite opening angle of the windows of the synchronous rotating pipe and pipe holder are drawn at 120 degrees, representing the state when the piston is at top dead center with the engine running at high speed and high load. As the piston descends, the synchronous rotating pipe rotates in the direction of the arrow, reducing the composite opening angle. When changing the load, the compression length can be reduced by advancing the phase of the synchronous rotating pipe to reduce the composite opening angle at the apex. The smaller the volume of the space created by the back of the synchronously rotating pipe and the poppet valve, the closer it is to the ideal variable compression length operation.

FIG. 3 shows that the synthetic opening angle at the top dead center of the intake stroke is 45 degrees and the engine is operated at 1/2 load.

Figure 4 shows the composite opening angles of 30, 60, 90, and 120 degrees when the piston is at top dead center, and the angle at which the crankshaft must rotate before the intake air is blocked. The angled lines represent the ventilation area of the poppet valve at each crank angle.

Figure 5 shows a rotating shaft phase change mechanism using the differential gear mechanism of claim 2. An actuator is used instead of a propeller shaft to control the rotation and stopping of the shaft. One of the two rotating shafts that correspond to the axle is rotated by the rotational force from the crankshaft, and the rotation of the other rotating shaft rotates a synchronous rotating pipe. As long as the actuator is in operation, the output shaft rotates in the opposite direction at the same speed as the input shaft. The rotation phase of the output shaft can be changed by rotating the actuator.

Figure 6 shows a rotating shaft phase change mechanism using a planetary gear mechanism according to claim 3. In this example, the rotating shaft of the planetary gear carrier is rotated by an actuator. The gear ratio between the sun gear and the ring gear is 1:2, and when the sun gear is rotated with the actuator stopped, the ring gear rotates at half the rotational speed. The rotational phase of the ring gear can be changed by rotating the actuator.

Claims (3)

This four-stroke reciprocating engine is characterized by the fact that a rotary pipe shutter valve, which rotates at half the speed of the crankshaft through a mechanism that changes the phase of the rotating output shaft by command from an ECU, is independently installed in front of the intake poppet valve of each cylinder. As a mechanism for changing the phase of the rotating output shaft in claim 1 by a command from an ECU, a differential gear mechanism having three rotating shafts is used, the rotational position of one shaft is changed by an actuator, the rotational force of the crankshaft is input to one of the other two shafts, and the rotational force of the output of the remaining shaft is used to rotate a pipe shutter valve. As a mechanism for changing the phase of the rotating output shaft in claim 1 by a command from an ECU, a planetary gear mechanism having three rotating shafts is used, the rotational position of one shaft is changed by an actuator, the rotational force of the crankshaft is input to one of the other two shafts, and the rotational force of the output of the remaining shaft is used to rotate a pipe shutter valve.

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