JP2011032989A - Atkinson cycle engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine enabling an Atkinson cycle without variably controlling the opening/closing timing of an intake valve. <P>SOLUTION: This Atkinson cycle engine includes two pistons reciprocating at different cycles in a single cylinder. The main piston which is one of the two pistons reciprocates so as to increase the volume of the inside of a cylinder in a suction stroke and an expansion stroke and reduce the volume of the inside of the cylinder in a compression stroke and an exhaust stroke. The sub piston which is the other of the two pistons reciprocates so that the volume of the inside of the cylinder at the time of completion of the expansion stroke is larger than the volume of the inside of the cylinder at the time of completion of the suction stroke. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an Atkinson cycle engine in which an expansion ratio is larger than a compression ratio.

  In order to increase the thermal efficiency of the engine and improve fuel efficiency, it is effective to expand the intake air mixture to a greater extent, but in conventional Otto cycle engines with an expansion ratio ≒ compression ratio, the expansion ratio is reduced due to the occurrence of knocking. Since the increase was limited, the expansion ratio could not be increased sufficiently. In view of this, an Atkinson cycle engine has been proposed in which the expansion ratio is set larger than the compression ratio of the engine, thereby achieving improvement in thermal efficiency while avoiding knocking. For example, one type of Atkinson cycle engine is a Miller cycle engine that suppresses the compression ratio by adjusting the closing timing of the intake valve to limit the intake amount.

  The Miller cycle engine is usually provided with a variable valve timing device that adjusts the opening and closing timing of the intake valve, so that the closing timing of the intake valve is greatly advanced from the bottom dead center. The intake amount is limited by so-called slow closing that is greatly retarded, thereby suppressing the compression ratio and increasing the apparent expansion ratio.

  On the other hand, a method for realizing an Atkinson cycle engine without performing variable control of the opening / closing timing of the intake valve has been developed. For example, a crank member is rotatably interposed at the pivotal support portion between the connecting rod and the piston or the pivotal support portion between the connecting rod and the crankshaft to form a double crank structure, and the relative position between the piston and the crankshaft is defined as the compression stroke and the expansion stroke. An engine configured differently is proposed (Patent Document 1).

JP 2008-240617 A

  However, the Miller cycle engine must be provided with a variable valve timing device, and it is necessary to accurately control the opening / closing timing of the intake valve, resulting in increased cost and complicated control. In addition, in an engine having a double crank structure as in Patent Document 1, the structure and movement of the entire piston are complicated, which may make it difficult to perform high-speed operation.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an engine capable of an Atkinson cycle without performing variable control of the opening / closing timing of the intake valve. .

  In order to achieve the above object, the invention of claim 1 includes a first piston and a second piston that reciprocate in one cylinder at different periods, and the first piston is used in an intake stroke and an expansion step. While the volume in the cylinder is increased, the second piston reciprocates so as to decrease the volume in the cylinder in the compression stroke and the exhaust process, and the second piston has a volume in the cylinder at the end of the expansion stroke at the end of the intake stroke. The reciprocating timing is set to be larger than the volume in the cylinder.

According to a second aspect of the present invention, the reciprocating period of the second piston is twice the reciprocating period of the first piston in the first aspect, and the volume in the cylinder is maximized at the end of the expansion process. It is set so that it becomes.
According to a third aspect of the present invention, there is provided a power transmission member for transmitting power between the crankshaft connected to the first piston and the crankshaft connected to the second piston. It is further provided with the feature.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, at least one of the intake valve or the exhaust valve of the engine and the second piston are disposed adjacent to each other above the cylinder. The crankshaft connected to the piston No. 2 and the camshaft for driving the intake valve or the exhaust valve are gear-connected.

  As described above, according to the Atkinson cycle engine of the first aspect of the invention, the volume in the cylinder at the end of the expansion stroke becomes larger than the volume in the cylinder at the end of the intake stroke due to the movement of the second piston. It is possible to increase the expansion ratio with respect to the compression ratio. Therefore, the Atkinson cycle can be performed without changing the opening / closing timing of the intake valve. In addition, since one piston is not different from a conventional engine and does not need to have a double crank structure, high-speed operation can be performed without complicating the movement of the entire piston.

  According to the Atkinson cycle engine of the invention of claim 2, since the volume in the cylinder becomes maximum at the end of the expansion process, the amount of volume change in the cylinder due to the reciprocating motion of the second piston is increased in the cylinder at the end of the expansion process. It appears as the difference between the volume and the volume in the cylinder at the end of the intake stroke. Therefore, the difference between the compression ratio and the expansion ratio is maximized by the reciprocation of the second piston, and the Atkinson cycle can be efficiently performed.

  According to the Atkinson cycle engine of the invention of claim 3, not only the first piston but also the second piston can be used during the expansion stroke, and energy loss for driving the second piston is reduced. Can be made.

  According to the Atkinson cycle engine of the fourth aspect of the invention, since the second piston reciprocates at a cycle twice that of the first piston, the speed is increased or decreased from the crankshaft driven to rotate by the second piston. Therefore, power can be transmitted to the camshaft of the intake valve or the exhaust valve. Therefore, the intake and exhaust valves can be driven with a simple structure by disposing the crankshaft and the camshaft of the second piston close to each other and transmitting power by the gear.

1 is a configuration diagram of an Atkinson cycle engine according to a first embodiment of the present invention. It is explanatory drawing which shows the motion of the piston at the time of each stroke. It is a block diagram of the Atkinson cycle engine which concerns on the 2nd Embodiment of this invention. It is a block diagram of the Atkinson cycle engine which concerns on the 3rd Embodiment of this invention. It is a block diagram of the Atkinson cycle engine which concerns on the 4th Embodiment of this invention. It is a block diagram of the Atkinson cycle engine which concerns on the 5th Embodiment of this invention.

Hereinafter, an embodiment of an Atkinson cycle engine of an engine embodying the present invention will be described.
FIG. 1 is an explanatory diagram showing a schematic configuration of an Atkinson cycle engine (hereinafter simply referred to as an engine) of the present embodiment.

  As shown in FIG. 1, the engine 1 of the present embodiment is a four-cycle engine having two pistons 2 and 3 in one cylinder. The cylinder 4 of the engine 1 is formed in a cylindrical shape having an axial center extending in the left-right direction in the drawing. The two pistons 2 and 3 are arranged in the cylinder 4 so as to be opposed to each other in the left-right direction at intervals. An intake port 6 and an exhaust port 7 communicating with the inside of the cylinder 4 are formed in the upper cylinder head 5 between the two pistons 2 and 3. The intake port 6 can be opened and closed by an intake valve 8, and the exhaust port 7 can be opened and closed by an exhaust valve 9. An intake camshaft 10 for driving the intake valve 8 is supported above the intake port 6, and an exhaust camshaft 11 for driving the exhaust valve 9 is rotatably supported by the cylinder head 5 above the exhaust port 7. This constitutes a so-called DOHC engine.

  Of the two pistons 2 and 3, one main piston 2 (first piston) shown on the right side in the drawing is rotatably connected to the main crankshaft 21 via the main connecting rod 20. The other sub-piston 3 (second piston) of the two pistons 2 and 3 is rotatably connected to a sub-crankshaft 23 via a sub-connecting rod 22. The main crankshaft 21 is disposed on the right side of the cylinder 4 and the sub crankshaft 23 is disposed on the left side of the cylinder 4.

  The two pistons 2 and 3 are configured to be movable in the left-right direction in the cylinder 4, and formed between the pistons 2 and 3 as the two pistons 2 and 3 move. The volume in the cylinder 4, that is, the volume of the combustion chamber changes. The sub piston 3 has substantially the same diameter as the main piston 2 and a stroke smaller than that of the main piston 2.

  A main sprocket 24 is fixed to the main crankshaft 21, and a subsprocket 25 is fixed to the sub crankshaft 23. Below the cylinder 4, an output shaft 27 that is rotatably supported by the cylinder block 26 is provided as an output shaft of the engine 1. An output sprocket 28 is fixed to the output shaft 27. A timing chain 31 (power transmission member) is wound around the main sprocket 24, the sub sprocket 25, the output sprocket 28, the intake sprocket 29 fixed to the intake camshaft 10, and the exhaust sprocket 30 fixed to the exhaust camshaft 11. Has been. Tensioners 32 and 33 for applying appropriate tension to the timing chain 31 are provided between the main sprocket 24 and the intake sprocket 29 and between the sub sprocket 25 and the exhaust sprocket 30, respectively. Therefore, the rotational driving force of the main crankshaft 21 and the sub crankshaft 23 is transmitted to the output shaft 27 via the timing chain 31. Further, the intake camshaft 10 and the exhaust camshaft 11 are rotationally driven with the rotation of the main crankshaft 21 and the sub crankshaft 23.

The number of teeth of the sub sprocket 25 is set to be twice the number of teeth of the main sprocket 24. Therefore, every time the main crankshaft 21 rotates twice, the sub crankshaft 23 rotates once.
FIG. 2 is an explanatory diagram showing the position of the piston during each stroke. The vertical direction in the figure corresponds to the horizontal direction in FIG.

  As shown in FIG. 2, in this embodiment, the main piston 2 reciprocates at the same timing as that of a conventional engine. Specifically, the main piston 2 is positioned at approximately bottom dead center when the intake stroke ends (compression stroke starts), approximately top dead center when the compression stroke ends (expansion stroke starts), and approximately bottom dead center when the expansion stroke ends. On the other hand, the sub-piston 3 reciprocates at a cycle twice that of the main piston 2. Specifically, the sub-piston 3 is positioned at approximately the bottom dead center at the end of the intake stroke (start of the compression stroke), at the intermediate point at the end of the compression step (start of the expansion stroke), and at approximately the top dead center at the end of the expansion step.

  With this configuration, in the engine 1 of the present embodiment, the main piston 2 is substantially at the bottom dead center at the end of the intake stroke and at the end of the expansion stroke, whereas there is no difference in piston position. The sub-piston 3 is substantially at the bottom dead center at the end of the intake process, while at the top dead center at the end of the expansion process. Therefore, the expansion volume Qe, which is the volume at the end of the expansion process, is larger by the movement of the sub-piston 3 than the intake volume Qi, which is the volume in the cylinder 4 at the end of the intake process. Thereby, in the engine 1 of this embodiment, the expansion ratio (expansion volume Qe / compression volume Qc) becomes larger than the compression ratio (intake volume Qi / compression volume Qc). The compression volume Qc is the volume in the cylinder 4 at the end of the compression stroke (at the start of the expansion stroke).

  As described above, in the engine 1 of the present embodiment, an Atkinson cycle with high thermal efficiency and excellent fuel efficiency can be realized without changing the opening / closing timing of the intake valve 8, that is, without requiring a variable valve timing device. it can. The structure of the entire main piston 2 that transmits power from the main piston 2 to the main crankshaft 21 is not different from the conventional structure, and it is not necessary to use a double crank structure as in Patent Document 1. High-speed operation can be performed without complicated movement.

In the present embodiment, since the driving force during the expansion stroke of the sub piston 3 is also transmitted to the output shaft 27 by the timing chain 31, energy loss for driving the sub piston 3 can be reduced.
Note that the piston diameter and stroke of the sub-piston 3 may be appropriately set as long as the volume change amount is smaller than that of the main piston 2.
Next, another embodiment of the present invention will be described with reference to FIGS.
FIG. 3 is a schematic configuration diagram of an engine 50 according to the second embodiment of the present invention. Hereinafter, differences from the first embodiment will be described.

  In the engine 50 of the second embodiment of the present invention, the cylinder 51 is installed so that the axis extends in the vertical direction in the figure, and the main piston 2 and the sub-piston 52 are relative to each other in the cylinder 51 in the vertical direction in the figure. Are arranged to be. The engine 50 does not have the output shaft 27 in the first embodiment, and the main crankshaft 21 is the output shaft of the engine 1 as in the conventional engine. The sub piston 52 has a smaller diameter than the main piston 2, and the sub piston 52 is arranged above the cylinder 51 together with the intake valve 8 and the exhaust valve 9. The engine 50 is a so-called SOHC engine in which the intake valve 8 and the exhaust valve 9 are driven by a single camshaft 53. The camshaft 53 is in gear connection with the subcrankshaft 23 connected to the subpiston 52 and transmits power from the subcrankshaft 23 to the camshaft 53 to drive the intake valve 8 and the exhaust valve 9. A timing chain 31 is wound around a sub sprocket 25 provided on the sub crankshaft 23 and a main sprocket 24 provided on the main crankshaft 21 to transmit power to each other.

In the present embodiment, since the sub-piston 52 has a smaller diameter than the main piston 2, the volume change due to the movement of the sub-piston 52 is less than that of the main piston 2, but, as in the first embodiment, the intake volume Qi. In contrast, the expansion volume Qe is increased, and the expansion ratio can be made larger than the compression ratio.
Incidentally, the intake valve 8 and the exhaust valve 9 need to be moved up and down at a cycle twice that of the main piston 2. In the present embodiment, the sub-crankshaft 23 disposed adjacent to the camshaft 53 is used to extract power from the sub-crankshaft 23 and drive the intake valve 8 and the exhaust valve 9 without shifting. Thereby, the length of a push rod can be shortened compared with an OHV engine, for example.

In the present embodiment, since the sub piston 52 is arranged side by side with the intake valve 8 and the exhaust valve 9 above the cylinder 51, an increase in the lateral dimension of the engine 50 can be suppressed.
The engine 60 of the third embodiment of the present invention shown in FIG. 4 is different from the second embodiment in the driving method of the camshaft 53.
In the engine 60 according to the third embodiment of the present invention, the camshaft 53 is driven by the timing chain 31 without being gear-connected to the sub crankshaft 23. Specifically, a sprocket 61 is provided on the camshaft 53, and the timing chain 31 wound around the main sprocket 24 and the sub sprocket 25 is hung on the sprocket 61 together.

Thereby, the freedom degree of arrangement | positioning of the cam shaft 53 can be increased, and the layout design can be facilitated.
The engine 70 of the fourth embodiment of the present invention shown in FIG. 5 and the engine 80 of the fifth embodiment of the present invention shown in FIG. 6 have two camshafts, an intake camshaft 71 and an exhaust camshaft 72. This is a so-called DOHC engine. As for other configurations, the fourth embodiment is the same as the second embodiment, and the fifth embodiment is the same as the third embodiment.
When the present invention is applied to a DOHC engine, as shown in FIGS. 5 and 6, the sub-piston 52 is disposed in the vicinity of the axis of the cylinder 71, and the intake valve 8 and the exhaust valve are arranged to the left and right so as to sandwich the sub-piston 52. 9 may be arranged.

In the engine 70 of the fourth embodiment shown in FIG. 5, the intake camshaft 71 and the exhaust camshaft 72 are in gear connection with the sub crankshaft 23, respectively. Therefore, also in the present embodiment, as in the second embodiment, the intake valve 8 and the exhaust valve 9 can be driven by obtaining power from the sub crankshaft 23.
In the engine 80 of the fifth embodiment shown in FIG. 6, the camshaft 53 is driven by winding the timing chain 31 around the intake sprocket 81 provided on the intake camshaft 71 and the sprocket 82 provided on the exhaust camshaft 72. Therefore, the freedom degree of arrangement | positioning of the cam shafts 71 and 72 can be increased similarly to 3rd Embodiment.

  In the above embodiment, the sub-pistons 3 and 52 are set so as to be positioned substantially at the top dead center at the end of the expansion process, but the present invention is not limited to this, and the sub-piston 3 is more than this. , 52 may be slightly retarded or advanced. Further, the arrangement of the main piston 2 and the sub pistons 3 and 52 is not limited to the above layout. In the present invention, where the main piston 2 alone has the same intake volume Qi and expansion volume Qe, the expansion volume Qe may be increased with respect to the intake volume Qi by the movement of the sub-pistons 3 and 52. Such a configuration enables the Atkinson cycle.

1, 50, 60, 70 Engine 2 Main piston 3, 52 Sub piston 4, 51, 71 Cylinder 23 Sub crankshaft 31 Timing chain 53 Camshaft

Claims (4)

A first piston and a second piston that reciprocate at different periods in one cylinder;
The first piston reciprocates so as to increase the volume in the cylinder in the intake stroke and the expansion process, while decreasing the volume in the cylinder in the compression stroke and the exhaust process,
The Atkinson cycle engine is characterized in that the second piston has a reciprocating timing set so that a volume in the cylinder at the end of the expansion stroke is larger than a volume in the cylinder at the end of the intake stroke. .   The reciprocating cycle of the second piston is twice the reciprocating cycle of the first piston and is set so that the volume in the cylinder is maximized at the end of the expansion step. The Atkinson cycle engine according to claim 1, wherein   The power transmission member according to claim 1, further comprising a power transmission member configured to transmit power between the crankshaft connected to the first piston and the crankshaft connected to the second piston. The described Atkinson cycle engine. At least one of the intake valve or the exhaust valve of the engine and the second piston are disposed adjacent to and above the cylinder;
The Atkinson cycle according to any one of claims 1 to 3, wherein a crankshaft coupled to the second piston and a camshaft for driving the intake valve or the exhaust valve are gear-connected. engine.

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