JP2007211730A - Reciprocating internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reciprocating internal combustion engine which provides intake air inertia effect appropriately according to an engine operation condition. <P>SOLUTION: This engine includes: a intake air compression piston 13 slidably fitted in an intake air compression cylinder 11 in which intake/compression stroke is performed; and an expansion exhaust piston 15 slidably fitted in an expansion exhaust cylinder 12 and driving and rotating a crankshaft 3. A linear motor 25 is driven and controlled by a control part 5, and intake stroke angle which is rotation angle of the crankshaft 3 until the intake compression piston 13 reaches bottom dead center from top dead center in intake stroke is variably controlled according to engine operation conditions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement of a reciprocating internal combustion engine.

In Patent Document 1, in order to increase the volumetric efficiency in a four-cycle reciprocating internal combustion engine, a pause period is provided at the bottom dead center of the piston when shifting from the intake stroke to the compression stroke. In Patent Document 2, in order to enhance the intake inertia effect when the internal combustion engine (engine) is operating at a low rotation speed, a descent time (intake air) is compared with a piston rise time (compression / exhaust stroke) using a link mechanism.・ Expansion stroke is shortened.
Japanese Patent Publication No. 8-6607 Japanese Patent Laid-Open No. 2003-083102

  However, just providing a pause period in which the piston is stopped at the intake bottom dead center as in the above-mentioned Patent Document 1, for example, when the engine is operating at a low speed, the piston motion is slow, so the air flow rate is low. Slow, volumetric efficiency cannot be improved sufficiently. If the piston motion in the intake stroke or the expansion stroke is constant regardless of the engine operation conditions such as the engine required torque and the engine speed, the optimum intake inertia effect cannot be realized depending on the operation conditions. For example, when setting is made such that an effect is obtained on the low rotation side as in Patent Document 2, the piston speed is too fast on the high rotation side, and the intake resistance at the intake valve increases, conversely the torque decreases. There is a concern to do.

  In order to solve the above-described problem, in the reciprocating internal combustion engine of the present invention, the intake stroke for changing the intake stroke angle, which is the rotation angle of the crankshaft until the piston reaches the bottom dead center from the top dead center in the intake stroke. An angle changing means is provided, and the intake stroke angle is changed according to the engine operating conditions so as to obtain the intake inertia effect.

  According to the present invention, it is possible to set an appropriate intake stroke angle in accordance with the engine operating conditions and effectively obtain the intake inertia effect in a form in accordance with the engine operating conditions.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a reciprocating internal combustion engine according to an embodiment of the present invention.

  The cylinder block 1 of the reciprocating internal combustion engine includes an intake / compression cylinder 11 that performs an intake / compression stroke among four strokes of intake / compression / expansion / exhaust, and an expansion / exhaust cylinder 12 that performs an expansion / exhaust stroke. Are provided adjacent to each other. An intake compression piston 13 is slidably fitted to the intake compression cylinder 11, and a compression chamber 14 is formed above the intake compression piston 13. An expansion exhaust piston 15 is slidably fitted to the expansion exhaust cylinder 12, and a combustion chamber 16 is formed above the expansion exhaust piston 15.

  The cylinder head 2 fixed to the upper side of the cylinder block 1 includes an intake passage 17 that supplies intake air to the compression chamber 14, an exhaust passage 18 that discharges exhaust from the combustion chamber 16, and the compression chamber 14 and the combustion chamber 16. A communication passage 19 that communicates and connects, and an intake valve 21 that opens and closes the intake passage 17, an exhaust valve 22 that opens and closes the exhaust passage 18, and a compression valve 23 that opens and closes the communication passage 19. It is installed. In addition, in the example of FIG. 1, although the compression valve 23 is provided in two places, the compression chamber 14 side and the combustion chamber 16 side, you may provide only in one place.

  The expansion / exhaust piston 15 is linked to a crankshaft 3 that is an engine output shaft by a connecting rod 4. The lower end of the connecting rod 4 is rotatably attached to the crankpin 3A of the crankshaft 3. The upper end of the connecting rod 4 is rotatably attached to a piston pin 15A of the expansion exhaust piston 15. Accordingly, the reciprocating motion of the expansion exhaust piston 15 due to the combustion pressure generated in the combustion chamber 16 is converted into the rotational motion of the crankshaft 3 via the connecting rod 4, and the crankshaft 3 is rotationally driven. In this embodiment, the intake compression piston 13 is connected to an output shaft 25A of a linear motor 25, and is directly reciprocated by the linear motor 25. As will be described later, the linear motor 25 changes the piston stroke of the intake compression piston 13 so that the intake stroke is the crank angle until the intake compression piston 13 reaches the bottom dead center from the top dead center in the intake stroke. The angle can be changed according to the engine operating state (intake stroke angle changing means).

  The cylinder block 1 includes a crank angle sensor 26 that detects the rotational position of the crankshaft 3 corresponding to the engine speed, and an intake piston position sensor that detects the piston position of the intake compression piston 13 (distance from the bottom dead center BDC). 27 are provided. Fuel is injected into the intake passage 17 in order from the upstream side, an air flow meter 28 for measuring the intake flow rate, an electric throttle (throttle valve) 29 for adjusting the opening of the intake passage 17, and an intake passage (intake port) 17. And a fuel injection valve 30 is disposed. In the case of the gasoline engine, as shown in FIG. In the case of a diesel engine, the ignition plug is omitted, and the fuel injection valve is disposed in the combustion chamber 16 (position of the ignition plug 31 in FIG. 1).

  As sensors for detecting engine operating conditions, in addition to the sensors 26 to 28, an accelerator opening sensor 32 for detecting an accelerator pedal opening corresponding to an accelerator operation amount of the driver is provided. The control unit (ECM) 5 has a function of storing and executing various control processes. Based on detection signals from the sensors 26 to 28, 32, etc., the electric control throttle 29, the fuel injection valve 30, the ignition A control signal is output to an actuator such as the plug 31 and the linear motor 25 to control its operation.

  In the present embodiment, the above-described valves 21 to 23 are electromagnetic valves and are driven and controlled according to the engine operating state based on a signal from the control unit 5. However, these valves 21 to 23 do not necessarily need to be electromagnetic valves as long as the closing timing of the intake valve 21 can be changed, and may be any one that can be synchronized with the rotation of the crankshaft 3. In other words, it may be a (variable) valve operating system that is operated by the rotational power of the crankshaft 3 that is well known.

  The intake stroke and the compression stroke are performed by one rotation of the crankshaft 3 in the intake compression cylinder 11. The compression valve 23 is opened near the end of compression, and the compressed air-fuel mixture is introduced from the compression chamber 14 to the combustion chamber 16 via the communication path 19. The expansion stroke and the exhaust stroke are performed by one rotation of the crankshaft 3 in the expansion exhaust cylinder 12. Since the end time of the compression stroke and the end time of the exhaust stroke are executed almost synchronously, four strokes of intake, compression, expansion, and exhaust can be performed by one rotation of the crankshaft 3.

  More specifically, the intake valve 21 is opened when the intake compression piston 13 is lowered, and is closed near the bottom dead center of the intake compression piston 13. Preferably, the opening / closing timing of the intake valve 21 is variably controlled according to the driver's required load, engine speed, and the like. When the intake compression piston 13 approaches top dead center, the compression valve 23 is opened, and the air-fuel mixture compressed in the compression chamber 14 is sent to the combustion chamber 16 via the communication path 19. When the intake compression piston 13 reaches top dead center, the compression valve 23 is closed to prevent the compressed air-fuel mixture from flowing backward from the combustion chamber 16 to the compression chamber 14. The compressed air-fuel mixture is ignited by the spark plug 31 and burned, and the expansion exhaust piston 15 is lowered. When the expansion exhaust piston 15 reaches bottom dead center, the exhaust valve 22 is opened and exhaust is performed.

  In this way, the compression stroke in which the intake compression piston 13 approaches the top dead center and the exhaust stroke in which the expansion exhaust piston 15 approaches the top dead center are performed synchronously at a relatively close timing. Further, the intake stroke in which the intake compression piston 13 approaches the bottom dead center and the expansion stroke in which the expansion exhaust piston 15 approaches the bottom dead center are performed in synchronization with each other at a relatively close timing. However, in this embodiment, as will be described later, the piston motion of the intake compression piston 13 is changed according to the engine operating state, so the timing is not always exactly the same.

  As described above, in the reciprocating internal combustion engine, the intake / compression cylinder 11 in which the intake / compression stroke is performed is separated from the expansion / exhaust cylinder 12 in which the expansion / exhaust stroke is performed, and the above four strokes are performed once per rotation of the crankshaft 3. Therefore, a large output can be obtained as compared with a general four-cycle type reciprocating internal combustion engine in which four strokes are performed every two rotations of the crankshaft 3. In addition, since the compression ratio and the expansion ratio can be set individually, the thermal efficiency can be increased without causing knocking by increasing the expansion ratio while lowering the compression ratio. Furthermore, since the intake / compression cylinder 11 and the expansion / exhaust cylinder 12 are configured separately, the intake / compression cylinder 11 can be cooled separately from the expansion / exhaust cylinder 12 where combustion is performed, and intake air can be easily cooled. In this embodiment, the operation of the intake compression piston 13 (piston motion) can be arbitrarily controlled with respect to the angle of the crankshaft 3 by the linear motor 25.

  FIGS. 2 and 3 are a block diagram and a flowchart showing the control contents of the present embodiment in a simplified manner. This routine is executed by the control unit 5 in a very short predetermined period Δt (for example, every 10 ms or every predetermined crank angle). ) Is repeatedly executed.

  In step S1, the accelerator opening detected by the accelerator opening sensor 32 is read. In step S2, the engine (engine) speed obtained by the crank angle sensor 26 (and cam angle sensor) or the like is read. In step S3 and block B1, an engine torque, that is, a required load is calculated based on the accelerator opening and the engine speed. FIG. 4 shows an example of a required load setting map. As shown in the figure, the required load is set according to the low, medium and high engine speed ranges, and is set higher as the accelerator opening is higher.

  In step S4 and block B1, a target intake stroke angle, which is a target value of the intake stroke angle, is calculated based on the engine speed and the required load. The intake stroke angle is a crank angle until the intake compression piston 13 reaches the bottom dead center from the top dead center in the intake stroke. The target intake stroke angle is set within a range of 0 to 180 degrees as a crank angle. FIG. 5 (A) shows the relationship between the (target) intake stroke angle and the maximum intake air amount at a constant engine speed, and FIG. 5 (B) shows the target intake stroke in the full speed range and the full required load range. An example of an angle setting map is shown. As shown in FIG. 5B, the larger the required load and the lower the engine speed, the smaller the target intake stroke angle, the faster the piston speed at the intake stroke angle, and the use of the inertial effect of air. Thus, it is possible to effectively secure a large amount of intake air exceeding the amount of air corresponding to the cylinder volume according to the engine speed and the engine load.

  2 and 3 again, in step S5 and block B2, the piston position (bottom dead center BDC) of the intake compression piston 13 is determined based on the crank angle detected by the crank angle sensor 26 and the target intake stroke angle. The target piston position, which is the target value of the distance from (see Fig. 9).

When the acceleration of the intake compression piston 13 becomes extremely large, the required motor torque of the linear motor 25 becomes excessive. Therefore, the target intake piston position tIP1 is, for example, a sin function so that the acceleration of the intake compression piston 13 does not become extremely large. Is obtained based on the crank angle θ by the following equation (1) using Note that min (a, b) is a function that selects the smaller of a and b.
Target intake piston position tIP1
= Stroke / 2 × (1-sin (min (θ / intake stroke angle × 180, 180) −90 °)): (0 ≦ θ <180)
= Stroke / 2 × (1-sin (θ−90 °)): (180 ≦ θ <360) (1)
Further, since the amount of air that can be sucked and the negative pressure in the intake compression cylinder 11 greatly depend on the opening area around the intake valve 21 (see FIG. 6), preferably, the opening area around the intake valve 21 is taken into consideration. To determine the target piston position tIP2. That is, the target intake piston position tIP2 is set by the following equation (2) in consideration of the allowable piston speed determined in advance in consideration of the opening area of the intake valve 21 so that the negative pressure in the cylinder 11 is not extremely generated. . Note that min (a, b) is a function that selects the smaller of a and b, and Δt is the calculation interval of this routine.
Target intake piston position tIP2
= Min (previous value of tIP1, tIP1 + allowable piston speed × Δt) (2)
In step S6 and block B3, a target intake valve closing timing (IVC) that is a target value of the closing timing of the intake valve 21 is calculated based on the target intake stroke angle and the engine speed (see FIG. 7). FIG. 7B shows an example of an IVC setting map. As shown in the figure, the IVC is basically set in a form corresponding to the (target) intake stroke angle. Further, the IVC is set to the retard side so as to ensure a longer intake valve opening period as the engine speed is higher. More specifically, as indicated by reference numeral (A) in FIG. 9, the intake stroke angle increases and the timing at which the piston 13 reaches the bottom dead center is delayed, that is, the piston 13 stops at the bottom dead center. The shorter the idle period, the longer the valve opening period of the intake valve is retarded by IVC. In addition, as shown in FIG. 9 (B), the intake stroke angle becomes smaller, and the time when the piston reaches the bottom dead center is advanced before the bottom dead center, that is, the piston stops at the bottom dead center. The longer the idle period is, the more the IVC is advanced to shorten the intake valve opening period.

  In a piston motion of a general single link type piston-crank mechanism in which a piston and a crank pin are connected by a single connecting rod, the intake stroke angle is always a fixed value (180 deg). On the other hand, in this embodiment, as shown in FIG. 5B, the target intake stroke angle is appropriately set according to the engine operating conditions (engine speed and required load), so as to meet the engine operating conditions. As a result, it is possible to improve the engine torque and output while suppressing the increase of friction and pump loss while effectively increasing the intake air amount by the inertia effect. However, as shown in FIG. 5A, if the intake stroke angle is set too small, the air sucked into the combustion chamber 16 side blows back to the compression chamber 14 side due to the inertia effect, and the desired inertia effect cannot be obtained. Since it is impossible to secure an intake air amount that exceeds the cylinder volume, it is prohibited to change the intake stroke angle in such a case.

  FIG. 6A shows an example of the relationship between the opening area around the intake valve and the crank angle. The opening area around the intake valve can be estimated by the following equation (3).

Opening area around the intake valve = 2 × π × intake valve radius × lift amount × number of valves (3)
As described above, by increasing the piston motion (decreasing the intake stroke angle), the intake inertia effect can be increased. However, if the piston motion is fast when the opening area is small, a large negative pressure is generated in the cylinder 11. It may occur and the loss may increase. Therefore, it is preferable to set a permissible change value of the piston 13 per unit time, that is, a permissible piston speed by using at least the opening area around the intake valve to restrict or prohibit the piston speed from becoming excessively high. An example is shown in FIG. As shown in the figure, the allowable piston speed is reduced as the opening area around the intake valve decreases. As a result, it is possible to effectively prevent a large negative pressure from being generated in the cylinder during the intake stroke.

  FIG. 7B shows a setting example of the closing timing (IVC) of the intake valve 21 as described above. Depending on the intake stroke angle, the IVC where the inertial effect is generated changes, but the IVC that secures the maximum intake amount also changes accordingly. This is mainly due to air returning to the intake passage (intake port) 17 by wiping back. Further, the higher the engine speed, the shorter the time per unit crank angle. Therefore, in order to secure a sufficient intake time, it is necessary to retard the IVC as compared to when the engine speed is low. In this embodiment, as shown in FIG. 7B, the IVC is advanced as the intake stroke angle is decreased from 180 degrees to prevent blowback.

  In an area where the intake stroke angle is a predetermined lower limit value α1 to α3 and the piston motion is likely to be excessively fast, IVC is fixed to the most advanced angle values β1 to β3, and IVC corresponding to the intake stroke angle is set. Change (advance) is prohibited. This is to prevent the intake air from becoming unable to be sufficiently sucked due to a flow delay although the flow velocity of the intake air increases due to the inertia effect. As shown in the figure, the lower limit values α1 to α3 and the most advanced angle values β1 to β3 of the intake stroke angle are individually set according to the engine speed.

  FIG. 8 shows the relationship between the throttle opening, the intake stroke angle, and the intake valve closing timing with respect to changes in the accelerator opening in the present embodiment. However, the engine speed is constant. As shown in the figure, in the low load area where the accelerator opening is smaller than the predetermined threshold value sAPO and the required load (torque) is small, the intake air amount is small. Therefore, only the throttle opening is changed according to the accelerator opening, specifically, the throttle opening is reduced according to the decrease in the accelerator opening, and the (target) intake stroke angle and Prohibit changes to IVC. Specifically, the intake stroke angle is fixed to the maximum value (180 deg), and IVC is fixed to the most retarded value near the bottom dead center.

  On the other hand, in the region on the high load side where the accelerator opening is greater than or equal to the threshold value sAPO, as the accelerator opening increases, the intake stroke angle is reduced in order to speed up the piston motion, and the intake stroke angle is reduced accordingly. To advance the intake valve closing timing. As a result, the intake inertia effect can be increased and a larger amount of intake air can be secured without causing blowback from the cylinder.

  The characteristic technical ideas of the present invention that can be understood from the above description will be listed with reference to the above-described embodiments. However, the present invention is not limited to the configuration of the embodiment given the reference numerals, and includes various modifications and changes. For example, the present invention can be similarly applied not only to the reciprocating internal combustion engine shown in FIG. 1 but also to an internal combustion engine that can change the intake piston speed according to the engine speed and the required load. Moreover, in the said Example, it is set as the structure which can change only IVC irrespective of the opening timing (IVO) of the intake valve 21 by making the engine valves 21-23 into solenoid valves, but it is not limited to this, For example, a known valve timing changing mechanism (VTC) that simultaneously changes the opening timing and closing timing of the intake valve may be used.

  (1) Intake stroke angle changing means (linear motor 25) for changing the intake stroke angle, which is the rotation angle of the crankshaft 3 until the piston 13 reaches the bottom dead center from the top dead center in the intake stroke, and engine operating conditions And a control unit 5 that variably controls the intake stroke angle according to the control.

  Therefore, by appropriately setting the intake stroke angle according to the engine operating conditions, the intake inertia effect can be obtained to the maximum in the form according to the operating conditions.

  (2) As shown in FIG. 5B, the larger the required torque, the smaller the intake stroke angle, thereby reducing the friction on the low load side where the required torque is small and the high load side where the required torque is large. Torque and output can be improved. In particular, by reducing the intake stroke angle on the high load side that requires a large amount of intake air and speeding up the piston motion, a large amount of intake air according to the required torque can be secured.

  (3) Since the amount of air required at low and medium loads is smaller than the maximum amount of air, it is not necessary to provide a region for increasing the piston speed even at low speeds. That is, a standard piston motion (for example, approximately sin wave) with respect to the crank angle that is the output shaft rotation angle may be used. Moreover, since friction generally increases in proportion to the piston speed, the lower the piston speed, the lower the friction. Accordingly, as shown in FIG. 5B, in the predetermined low load region F1 where the required torque is small, the change of the intake stroke angle is prohibited and the intake stroke angle is fixed to the maximum value.

  (4) As shown in FIG. 5B, the intake stroke angle is reduced as the engine speed is lower. As a result, on the low rotation side where an inertial effect cannot be expected so much, it is possible to secure a sufficient intake air amount by increasing the piston speed by reducing the intake stroke angle. On the other hand, since a sufficient inertial effect is originally obtained on the high rotation side, the piston speed can be reduced by increasing the intake stroke angle, and the friction can be reduced.

  (5) As shown in FIG. 5B, in a predetermined high engine speed F1 where the engine speed is high, the intake stroke angle is prohibited from being changed, and the intake stroke angle is fixed to the maximum value. It is possible to avoid an unnecessary increase in friction and an increase in pumping loss.

  (6) If the closing timing of the intake valve relative to the rotation angle of the crankshaft can be changed, the intake air amount can be secured more efficiently by operating the closing timing of the intake valve according to the change of the intake stroke angle. . Here, in the intake stroke, as the intake compression piston 13 descends, the pressure in the compression chamber 14 of the cylinder 11 becomes negative with respect to the intake pressure upstream of the intake passage 17, and then the air to the compression chamber 14 It becomes positive pressure due to inflow. If the intake valve can be closed at the timing when the pressure becomes positive, a larger amount of intake air can be secured, but if it is delayed, it will blow back to the intake passage 17. Therefore, it is desirable that the closing timing of the intake valve is close to the above timing. However, as the piston working distance with respect to the rotation angle of the crankshaft, that is, the intake stroke angle is changed, the timing at which the air flowing into the cylinder blows back also changes. Therefore, as shown in FIG. 8, when the intake stroke angle is decreased, the intake valve closing timing is advanced in accordance with the intake stroke angle, whereby the intake air amount can be effectively secured according to the intake stroke angle. . Note that, as shown in FIG. 9, the closing timing of the intake valve is set to be retarded from the end timing of the intake stroke.

  (7) When the intake stroke angle is small, the inertial effect is increased, but it takes time to sufficiently fill the cylinder with air due to the delay of the air flow. Therefore, as shown in FIG. 7B, when the intake stroke angle is smaller than the predetermined values α1 to α3, changing the intake valve closing timing to the advance side is prohibited and the intake valve closing timing is most advanced. By fixing the angle values to β1 to β3, it is possible to secure a sufficient intake air amount without being affected by the delay of the air flow while being simple control.

  (8) In the above embodiment, as shown in FIG. 1, the intake compression piston 13 slidably fitted to the intake compression cylinder 11 in which the intake stroke and the compression stroke are performed, and the expansion in which the expansion stroke and the exhaust stroke are performed. An expansion valve 15 that is slidably fitted to the exhaust cylinder 12 and rotationally drives the crankshaft 3 and an intake valve 21 that opens and closes an intake passage 17 connected to the compression chamber 14 formed on the intake and compression piston 13. An exhaust valve 22 that opens and closes an exhaust passage 18 connected to the combustion chamber 16 formed on the expansion exhaust piston 15, and a compression valve 23 that opens and closes a communication passage 19 that communicates the compression chamber 14 and the combustion chamber 16. And the intake stroke angle of the intake compression piston is changed by the linear motor 25 as the intake stroke angle changing means.

  In such a reciprocating internal combustion engine, as described above, four strokes of intake, compression, expansion, and exhaust can be performed by one rotation of the crankshaft 3, so that high output can be achieved, and the intake compression cylinder 11 And the expansion / exhaust cylinder 12 are configured separately, the intake air can be easily cooled, and the compression ratio and the expansion ratio can be set appropriately.

  Since the intake compression piston 13 is not connected to the crankshaft 3 and the combustion pressure does not act, the operation of the intake compression piston 13, that is, the piston motion and the intake stroke angle are controlled by a relatively small linear motor 25 or the like. The crank angle can be changed and controlled relatively easily, and is suitable for embodying the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows simply the reciprocating type internal combustion engine which concerns on one Example of this invention. The control block diagram which shows simply the control content of the said Example. The flowchart which shows the flow of control of the said Example. The characteristic view which shows the relationship between the accelerator opening and engine torque for every engine rotation area. (A) is a characteristic diagram showing the relationship between the intake stroke angle and the intake air amount, (B) is a characteristic diagram showing a setting example of the intake stroke angle according to the engine speed and the required load. (A) is a characteristic diagram showing the relationship between the crank angle and the intake valve opening area, (B) is a characteristic diagram showing the relationship between the intake valve opening area and the allowable piston speed. (A) is a characteristic diagram showing the relationship between the closing timing of the intake valve and the intake air amount, and (B) is a characteristic diagram showing a setting example of the intake valve closing timing according to the intake stroke angle for each engine rotation range. The time chart which shows one setting example of the throttle opening according to the accelerator opening which concerns on a present Example, an intake stroke angle, and an intake valve closing timing. Explanatory drawing for demonstrating operation | movement of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Crankshaft 5 ... Control part 11 ... Intake compression cylinder 12 ... Expansion exhaust cylinder 13 ... Intake compression piston 15 ... Expansion exhaust piston 25 ... Linear motor (intake stroke angle change means)

Claims (8)

An intake stroke angle changing means for changing an intake stroke angle which is a rotation angle of the crankshaft until the piston reaches the bottom dead center from the top dead center in the intake stroke;
A control unit that variably controls the intake stroke angle according to engine operating conditions;
And a reciprocating internal combustion engine controlled by the control unit so as to obtain an intake inertia effect.   The reciprocating internal combustion engine according to claim 1, wherein the control unit decreases the intake stroke angle as the required torque increases.   The reciprocating internal combustion engine according to claim 2, wherein the control unit fixes the intake stroke angle to a maximum value in a predetermined low load range where the required torque is small.   The reciprocating internal combustion engine according to any one of claims 1 to 3, wherein the control unit decreases the intake stroke angle as the engine speed decreases.   5. The reciprocating internal combustion engine according to claim 4, wherein the control unit fixes the intake stroke angle to a maximum value in a predetermined high engine speed range where the engine speed is high. The intake valve closing timing relative to the crankshaft rotation angle can be changed,
6. The reciprocating internal combustion engine according to claim 1, wherein the control unit advances the intake valve closing timing when the intake stroke angle is decreased.   The reciprocating internal combustion engine according to claim 6, wherein the control unit fixes the intake valve closing timing at a most advanced angle value when the intake stroke angle is smaller than a predetermined value. An intake compression piston slidably fitted to an intake compression cylinder in which an intake stroke and a compression stroke are performed;
An expansion exhaust piston that is slidably fitted to an expansion exhaust cylinder in which an expansion stroke and an exhaust stroke are performed, and rotationally drives the crankshaft;
An intake valve for opening and closing an intake passage connected to a compression chamber formed on the intake compression piston;
An exhaust valve for opening and closing an exhaust passage connected to a combustion chamber formed on the expansion exhaust piston;
A compression valve that opens and closes a communication passage communicating the compression chamber and the combustion chamber,
8. The reciprocating internal combustion engine according to claim 1, wherein the intake stroke angle changing means changes the intake stroke angle of the intake compression piston.

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